Etch characteristics of maskless Oxide/Nitride/Oxide/Nitride (ONON) stacked structure using C4H2F6-based gas

Etch characteristics of maskless Oxide/Nitride/Oxide/Nitride (ONON) stacked structure using C4H2F6-based gas | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Etch characteristics of maskless Oxide/Nitride/Oxide/Nitride (ONON) stacked structure using C4H2F6-based gas Nam Il Cho, Jong Woo Hong, Hee Jin Yoo, Hyeong Joon Eoh, Chan Ho Kim, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4678024/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 02 Oct, 2024 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract Oxide/Nitride/Oxide/Nitride (ONON; SiO 2 /SiN x /SiO 2 /SiN x ) stacked structure is widely used in the 3D vertical structure of semiconductor cells. Previously, to form a 3D cells, photoresist (PR) was patterned and repeatedly trimmed on the top of ONON after the etching of one ON layer. Due to the time-consuming process of etching layer-by-layer of ON layer, two-step etch processing using C 4 F 8 -based or C 4 F 6 -based gases composed of maskless ONON stack feature etching and followed one ON layer-by layer etching by PR trimming in the ONON stack feature are employed these days. However, the two-step etching method resulted in poor etch profiles of maskless ONON stack feature in addition to high global warming potential of C 4 F 8 and C 4 F 6 . In this study, we investigated the etching of maskless ONON stack feature using C 4 H 2 F 6 -based gas having a low global warming potential and the effects of C 4 H 2 F 6 -based gas on the etch characteristics of maskless ONON stack feature such as etch rate, etch profile, change in critical dimensional (CD), and etch selectivity between SiO 2 and SiN x have been investigated. C 4 H 2 F 6 -based gas showed the highest etch rates compared to C 4 F 6 and C 4 F 8 -based gases in addition to the etch selectivity of ~1:1 between SiO 2 and SiN x due to hydrogen included in the gas structure. In addition, the change in horizontal CD was lower in the order of C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases due to the more effective sidewall passivation in the order of C 4 F 8 , C 4 F 6 , and C 4 H 2 F 6 -based gases. The thicker carbon-based polymer layer on the sidewall also played an important role in maintaining the shape of the top edge shape of maskless ONON stack feature when etching a line feature in an environment without a mask. Physical sciences/Materials science Physical sciences/Nanoscience and technology ONON stack feature Maskless etching Oxide/Nitride C4F8 C4F6 C4H2F6 Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 I. Introduction Today, oxide/nitride/oxide/nitride (ONON) stacking structures are widely used in 3 dimensional (3D) vertical memory devices.[ 1 – 6 ] For 3D Not-and (NAND) devices, an essential process for controlling the stacked memory cell is the staircase etching process which etches one ON layer in the ONON stack repeatedly after recessing photoresist (PR) layer on the top of the ONON structure. In the past, for the staircase etch process, layer-by-layer etching of one ON layer while trimming of PR after one ON layer etching was used.[ 5 ] This method is highly selective and precise etch method in etching one ON layer-by-layer but has led to an increase in cost due to an increase in the number of process cycles as the number of layers increases. In order to solve this problem, methods of etching multiple ON layers at once by increasing the dimensions of the staircase, through the formation of maskless ONON stack feature in advance, have been studied (see supplementary information Figure S1 ).[ 1 , 7 ] These methods have more complex shapes than the existing process, so the maskless ONON stack feature etch profile through the passivation of the sidewall has become important, and, for this, fluorocarbon rich gases such as C 4 F 8 and C 4 F 6 -based gases have been actively studied.[ 8 – 12 ] In addition, many studies have been conducted on the selectivity etching of O/N or N/O for profile improvement and accurate etch stop.[ 13 – 17 ] However, there are remaining issues on these etch methods on the areas not protected by PR such as critical dimension (CD) reduction, degradation of etch profile, trench formation at the edge of maskless ONON stack feature, etc. Also, these days, as the reduction of carbon emission has become a hot issue around the world, reinforcement of regulations and reduction measures for carbon emitted in the semiconductor manufacturing process are required. Since the fluorocarbon-based gas such as C 4 F 8 , C 4 F 6 , CF 4 , etc. used in the etching process generally has a high global warming potential (GWP), research on alternative gas with the same or better etching properties is required.[ 18 ] Therefore, in this study, staircase etch characteristics of maskless ONON stack feature using C 4 H 2 F 6 -based gas, which is a low GWP gas, have been investigated using ~ 510 nm ONON stack feature without a mask (SiO 2 /SiN x composed of 30 nm in thickness and 9/8 layers, respectively). The staircase etch characteristics of C 4 H 2 F 6 -based gas were compared with the etch characteristics of C 4 F 8 -based and C 4 F 6 -based gases. As a result, C 4 H 2 F 6 -based gas showed the fastest ONON etch rate with the etch selectivity of SiO 2 /SiN x close to ~ 1:1 and highly anisotropic etch profiles without varying CD of maskless ONON stack feature. II. Experimental The ONON etching was conducted on a 300mm inductively coupled plasma (ICP) etcher system shown in Fig. 1 (a). The ICP source had an inner/outer configuration with a two-turn silver coated copper coil. Additionally, there was a 35 mm thick alumina window installed above the process window. The alumina window and antenna coil were separated by approximately 30 mm using a jig. The substrate was located ~ 150 mm below the dielectric window. The ICP source utilized a 13.56MHz RF power (Seren-R3001) and bias voltage was applied using a 2MHz RF power (Seren-R2001). The process gases were distributed using a gas ring located at the chamber's top edge. The process pressure was automatically controlled using a main valve (VAT-model PM. 7) installed between the turbopump and dry pump. A 1500 nm thick ONON stack was deposited on a silicon wafer, followed by patterning with a 480 nm PR on the top of ONON stack as shown in Fig. 1 (b). (the thickness of one monolayer SiO 2 or SiN x was 30 nm) To investigate the etch characteristics of ONON staircase etching in an environment without masks, the ONON stack was etched ~ 510 nm with the PR line pattern and the PR was removed as shown in Fig. 1 (c) to form a maskless ONON stack feature. To etch initial ~ 510 nm thick ONON stack feature with a PR mask, a gas mixture of C 4 F 6 /CF 4 /O 2 /Ar was used at 2mTorr of operating pressure with 2000W of RF source power and − 500V of DC bias voltage for 2.5 min. Subsequently, the residual PR layer was removed through the PR strip process using O 2 gas at 50 mTorr and with 2kW of ICP power only without biasing the substrate, and finally a ~ 510 nm thick ONON rectangular shaped stack feature on the remaining 1000 nm thick ONON stack shown in Fig. 1 (c) was obtained for maskless ONON stack feature etching. The etching of the ~ 510 nm thick maskless ONON stack feature shown in Fig. 1 (c) was processed using C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 mixed with CF 4 /O 2 /Ar while applying 2kW of ICP power and a -60V DC bias voltage. During the maskless ONON stack feature etching, the substrate temperature was maintained at 18°C and the process pressure was kept at 2mTorr. Detailed SEM images of Fig. 1 (b) and (c) are shown in the supplementary information, Figure S2. To determine the etch rates of SiO 2 and SiN x , etching was performed on respective blank wafers and the etch depths were measured using a step profilometer (Tencor, Alpha step 500). A field emission scanning electron microscope (FE-SEM; Hitachi, S-4700) was used to examine the etch profiles after etching maskless ONON stack feature. Hydrocarbon and fluorocarbon radicals were measured using optical emission spectroscopy (OES; ANDOR technology, SR-ASZ-0103), and the further analysis of dissociated radicals and ions was conducted through a quadrupole mass spectrometer (QMS; Hiden Analytical, PSM 500). Surface analysis was carried out using X-ray photoelectron spectroscopy (XPS; VG Microtech Inc., ESCA2000). III. Results and Discussion III-I. Etching of ONON stack using C 4 F 8 , C 4 F 6 , and C 4 H 2 F 6 -based gases Figure 2 (a) shows etch rates of blank SiO 2 , SiN x , and ONON stack, and Figure 2 (b) shows the etch selectivity between SiN x and SiO 2 using C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases. As the process conditions, 2000 W of source power, -60 V of DC bias voltage, and additive gases composed of CF 4 /O 2 /Ar were used. The process conditions were selected through the maskless ONON stack feature etching with C 4 H 2 F 6 -based gas (see supplementary information Figure S3). For C 4 F 8 and C 4 F 6 -based gases, which are the fluorocarbon gases generally used for staircase etching, the optimized etch conditions were similar to C 4 H 2 F 6 -based gas as functions of process variables except for C 4 F 8 and C 4 F 6 gas flow rates. As shown in Fig. 2(a), for blank sample etching with this process conditions, all three gases showed similar etch rates of 72 ~ 81 nm/min for ONON stack even though the ONON stack was the highest for C 4 H 2 F 6 -based gas. On the contrary, the SiO 2 etch rates were higher in the sequence of C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases by showing 72, 87, and 92 nm/min, respectively, and SiN x etch rates were higher in the reverse sequence of C 4 F 8 , C 4 F 6 , and C 4 H 2 F 6 -based gases, respectively. The highest SiN x etch rates and the lowest SiO 2 etch rates observed for C 4 H 2 F 6 -based gas compared to C4F8 and C 4 F 6 -based gases are believed to be related to existence of hydrogen in the gas chemical formula which assists SiN x etching by forming NH x but decreases SiO 2 etching by forming a thicker fluorocarbon layer on the SiO 2 surface. The etch selectivities of SiO 2 /SiN x estimated by the blank sample etching of SiO 2 and SiN x were 1.25, 0.62, and 0.56 for C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 , respectively, as shown in Fig. 2(b), therefore, the higher etch rate of ONON stack observed for C 4 H 2 F 6 -based gas compared to C 4 F 6 -based and C 4 F 8 -based gases in Figure 2(a) was related to the similar etch rates between SiO 2 and SiN x . The ONON stack having maskless ~510 nm thick ONON pre-etched feature shown in Figure 1 (c) was etched using the C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases with the process conditions in Figure 2. Figure 3 shows cross-sectional SEM images of maskless ONON stack feature etched about 300 nm, 600 nm, and 1000 nm with (a) C 4 H 2 F 6 , (b) C 4 F 6 , and (c) C 4 F 8 -based gases. The other etch conditions are the same as those in Figure 2. When comparing the shape differences between the reference (pre-etch) feature profile and etched ONON stack feature, the ONON stack feature etched with C 4 H 2 F 6 -based gas showed a square shaped feature without changing the feature shape significantly during the etching of 1000 nm thick ONON stack. On the contrary, C 4 F 8 -based gas exhibited gradual change in feature size with etch depth and finally showed a thin trapezoidal shaped feature after etching 1000 nm thick ONON stack while C 4 F 6 -based gas showed intermediate feature shape change. Additionally, the most significant trenching phenomenon was observed for C 4 F 6 -based gas. Using SEM images, the top/bottom CDs and sidewall angles of maskless ONON stack feature etched ~1000 nm with C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases were measured as shown in Fig.4 (a), and the results on sidewall angles, CD differences (ref top CD – top CD of etched structure), and (bottom CD – top CD)/2 of the etched features for C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases are shown in Figure 4(b). As shown in Fig. 4 (b), C 4 H 2 F 6 -based gas exhibited the smallest CD differences, with sidewall angles close to 90 degrees while C 4 F 8 -based gas showed the largest CD difference (reduction in top and bottom CDs) compared to the reference, and its sidewall angle was also observed to be the least favorable. For C 4 F 6 -based gas, intermediate CD differences and sidewall angles were observed compared to C 4 H 2 F 6 -based and C 4 F 8 -based gases. III-2. Plasma analysis for C 4 F 8 , C 4 F 6 , and C 4 H 2 F 6 -based gases For the etching conditions in Figure 2, dissociated gas species were investigated using QMS and the mass spectra of the positive ions directly extracted from the plasma for C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases are shown in Figure 5 (a). (Dissociated radicals in the plasmas observed using QMS for these gases are shown in supplementary information Figure S4.) As shown in Fig. 5 (a), various ions dissociated and recombined from the reactive gases can be seen. Among those reactive ions, ions such as F + , CF + , CF 2 + , CF 3 + , CHF + , and CHF 2 + can be more related to passivation or etching of SiO 2 and SiN x . Mass amount (intensity) of these ions detected by the QMS are shown in Figure 5 (b). Among these ions, CF + , CF 2 + , CHF + , and CHF 2 + are more related to the passivation on the materials surface while CF 3 + and F + are more related to etching. Therefore, the ratio of (CF + + CHF + + CF 2 + + CHF 2 + )/(CF 3 + + F + ) was taken to estimate the reactive ion flux ratios from plasma to the ONON stack sample surface between passivation flux and etchant flux, and the result is shown in Figure 5 (c). As shown in Figure 5 (c), the ratio was higher for C 4 H 2 F 6 -based gas compared to C 4 F 6 and C 4 F 8 -based gases. This indicates that among the three different fluorocarbon gases, C 4 H 2 F 6 provides the most polymeric radicals to the ONON stack sample surface during the etching, and which can provide the strongest sidewall protection condition. And, it is believed that the sidewall protection during the maskless ONON stack feature etching with C 4 H 2 F 6 -based gas is the related to maintaining a square shaped ONON stack feature until 1000 nm ONON thickness is etched. Using OES, the radical species formed in the plasma were also observed with C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases mixed with CF 4 /O 2 /Ar. The process conditions are the same as those in Fig. 2. From OES, species such as CF 2 at 251.9 nm, CH at 390 nm, F at 704 nm, Ar at 750 nm, O at 844.7 nm, etc. could be observed as shown in Figure 6 (a) [19–21]. The radical peak intensities such as CF 2 , CH, and F which are related to passivation and etching were normalized by Ar peak intensity to estimate the radical density in the plasma and the results are shown in Figure 6 (b). As shown in Fig. 6 (b), the F/Ar which is related to the etching was the highest for C 4 F 8 -based gas and the CF 2 /Ar + CH/Ar which is related to the passivation was the highest for C 4 H 2 F 6 -based gas. Figure 6 (c) shows the ratio of (CF 2 + CH)/F for three gases which could show the degree of sidewall protection or sidewall etching during the maskless ONON feature etching and, among the three gas compositions, the C 4 H 2 F 6 -based gas showed the highest while it is lowest for C 4 F 8 -based gas. The results were similar to the QMS results in Fig. 5 (c) but, in the case of QMS with the positive ion measurement mode, even though it can measure all the positive ions in the plasma as-is for the estimation of the radicals in the plasma, it is difficult to estimate the F density due to the difficulty in positive ionization of F in the plasma. Therefore, for the estimation of F radical density, OES shows more reliable data. Therefore, based on the results of OES and QMS shown in Figure 5 and 6, it can be confirmed that C 4 H 2 F 6 -based gas provides an environment with the highest abundance of hydrofluorocarbon polymer, which protects the sidewalls of the profile the most. Additionally, it was noted that C 4 F 8 provides an environment with the least amount of polymer. Under maskless conditions, it was observed that, to maintain the horizontal CD of the maskless ONON stack feature, the polymer layer on the sidewalls needs to be sufficiently thick, and a lesser amount of polymer layer can result in a reduction of the final CDs of the maskless ONON stack feature. To understand the differences in trenching of the etched maskless ONON stack feature for the gases used in the experiment, the total positive ions, the sum of light positive ions (< 40 amu, that is, lighter than Ar mass), and the sum of heavy positive ions (≥ 40 amu), and in the plasma were calculated from the QMS data in Figure 5 (a) and the results are shown in Figure 6. As shown in Fig. 7, not only the sum of total positive ions but also the sum of heavy positive ions was the highest for C 4 F 6 -based gas and C 4 H 2 F 6 -based gas showed the lowest total positive ions for both total positive ions and heavy positive ions. The positive ions incident to the sidewall of the maskless ONON stack feature can be reflected at the sidewall and can lead to trenching due to increased ion flux at the edge of the feature. The most significant trenching observed for the maskless ONON stack feature etched with C 4 F 6 -based gas and the least significant trenching for C 4 H 2 F 6 -based gas are believed to be related to the differences in the positive ion flux, especially in the heavy positive ion flux. III-3. ONON stack etch mechanism for C 4 F 8 , C 4 F 6 , and C 4 H 2 F 6 -based gases XPS surface analysis was conducted to investigate the residue remaining on the sidewall of the etched maskless ONON stack features. To observe the residues at the sidewall of the etched maskless ONON stack features, XPS analysis was performed after tilting the sample 50° as shown in Figure 8 (a). (XPS widescan data measured for the sidewall residues remaining on the etched maskless ONON stack features for C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases are shown in supplementary information Figure S5.) The atomic percentages of the elements etched with C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases were observed by the XPS and the results are shown in Figure 8 (b) and the ratios of C/(Si+O+N) and F/(Si+O+N), which are the ratio of fluorocarbon residue component/substrate components, are shown in Figure 8 (c). As shown in Figure 8 (b) and (c), the carbon and fluorine forming fluorocarbon residue at the sidewall of the ONON stack feature were the highest for C 4 H 2 F 6 -based gas and the lowest for C 4 F 8 -based gas. To investigate the bonding states of the fluorocarbon residue at the sidewall of the ONON stack features, XPS narrow data of C1s were also measured and Figure 8 (d), (e), and (f) are C1s narrow scan XPS data for C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases, respectively. As shown in Figure 8 (d), (e), and (f), carbon bonding related to C–C (~285 eV), C-CF (~287.5 eV), C-F (~289.5 eV), and C-CF 2 (~291.8 eV) were observed.[22–25] Among the bonding peaks, C-CF, C-F, and C-CF 2 are related to the fluorocarbon layer [26,27] and C 4 H 2 F 6 -based gas showed also highest intensities of these bonding peaks and the C 4 F 8 -based gas showed the lowest intensities. Through XPS surface analysis, it can be understood that C 4 H 2 F 6 -based gas provided the most carbon-rich polymer at the sidewall of the etched ONON feature while C 4 F 8 -based gas formed the least polymer. From the results of plasma analysis in Fig. 5~7 and surface analysis in Fig. 8 in addition to cross-sectional images of etched maskless ONON stack features in Fig. 3~4, the etch mechanism for the etching of maskless ONON stack features can be shown schematically as Figure 9. Etch profiles and CDs of the maskless ONON stack feature are influenced by the thickness of the C x H y F z hydrofluorocarbon or fluorocarbon polymer layer that provides protection of the sidewall, preventing the reduction of the subsequent pattern's mask line. In addition, heavy ion bombardment from the plasma to the substrate can form trenching at the edge of the maskless ONON stack feature by reflecting heavy ions at the sidewall of the maskless ONON stack feature during the etching. In the case of C 4 H 2 F 6 -based gas, despite ion bombardment, it is evident that the vertical sidewall is maintained and trenching phenomenon is protected by a thick polymer layer formed on the sidewall area as shown in Fig. 8(a). However, in the case of C 4 F 6 -based gas, due to a thinner polymer layer compared to C 4 H 2 F 6 -based gas, the CD and etch profile of the maskless ONON stack feature were slightly degraded and trenching was prominent due to heavy ion bombardment effect as shown in Fig. 8(b). Especially for C 4 F 8 -based gas, due to the thinnest polymer layer at the sidewall of the maskless ONON stack feature, sidewall etching was dominant during the etching even though the trenching was not significant due to the lower ion bombardment. For the staircase etching for 3D NAND device, it is important to maintain pattern CD width and to keep vertical etch profile without trenching during etching maskless ONON stack features because, if the CD is decreased and slanted etch profile is formed, during the following additional ON layer-by-layer etching with PR trimming, the metal contact area for each ON layer can be significantly reduced. (for more details, see supplementary information Figure S1.) Therefore, under maskless etching conditions, maintaining the etched CD is crucial because the current feature pattern serves as a mask for the etching of the next layer, necessitating the formation of a sufficiently thick passivation layer to prevent etching of the sidewall. Furthermore, it can be observed that adequate polymer layer on the sidewall in addition to low ion bombardment is also required to suppress trenching phenomena in addition to preventing the reduction of the CD. IV. Conclusions Maskless ONON stack feature pattern was etched using inductively coupled plasma with C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 -based gases mixed with O 2 /Ar and its etching characteristics were investigated. C 4 H 2 F 6 -based gas showed the highest ONON stack etch rate and also showed ~ 1:1 etch selectivity between SiO 2 and SiN x layers in the ONON stacked layers while C 4 F 6 and C 4 F 8 -based gases exhibited similar etch rates which are lower than that by C 4 H 2 F 6 -based gas, with the etch selectivity of SiN x /SiO 2 lower than 1.0. The etch selectivity of SiN x /SiO 2 close to ~ 1.0 and the higher ONON stack etch rate for C 4 H 2 F 6 -based gas were related to H radicals dissociated from C 4 H 2 F 6 which increased the etch rate of Si 3 N 4 layer in the ONON stack. When maskless ONON stack features were etched, it was found that, among the three gases investigated, C 4 H 2 F 6 -based gas showed no significant CD change from the reference and vertical sidewall with the lowest trenching phenomenon due to a thick polymer layer formed on the sidewall of the etched maskless ONON stack feature caused by the highest ratio of passivation flux/etchant flux to the sample. In the case of C 4 F 6 -based gas, due to a thinner polymer layer compared to C 4 H 2 F 6 -based gas, the CD and etch profile of the maskless ONON stack feature were slightly degraded while trenching was prominent due to heavy ion bombardment effect. Especially, in the case of C 4 F 8 -based gas, due to the thinnest polymer layer at the sidewall of the maskless ONON stack feature caused by the lowest ratio of passivation flux/etchant flux to the sample, the sidewall etching was significant during the etching even though the trenching was not significant due to the lower ion bombardment from the plasma. These results are believed to be related to the generation of polymer forming radicals versus etchant radicals in the plasma as observed by OES and QMS, the relative amount of heavy positive ions as observed by QMS, and the formation of fluorocarbon layer on the sidewall of the etched maskless ONON feature as observed by XPS, depending on fluorocarbon gases such as C 4 H 2 F 6 , C 4 F 6 , and C 4 F 8 used in the etching. In conclusion, the ONON stacked staircase structure will continue to be adopted in next-generation 3D vertical cell memory semiconductors, and the importance of profile quality in a maskless environment will continue to increase with the increasing complexity. Through this research, it has been confirmed that ratio of passivation radical flux to etchant radical flux, heavy ion flux, and finally the fluorocarbon layer thickness on the sidewall of the maskless ONON stack feature are important in determining the etched maskless ONON stack feature shapes. And, with C 4 H 2 F 6 -based gas having low global warming potential (even though the additive CF 4 gas having a high global warming potential also needs to be replaced), a more stable etch profile and higher etch rate compared to the conventional C 4 F 6 -based and C 4 F 8 -based gases having high global warming potential could be achieved. Declarations Data Availability All data generated or analyzed during this study are included in the article and supporting information. Acknowledgments This work was supported by the Technology Innovation Program Development Program-Development of core technology in Carbon Neutrality (RS-2023-00265858, Development of alternative PFC gas with low GWP value under 150 for OLED display oxide TFT insulator patterning) funded By the Ministry of Trade, Industry & Energy(MOTIE, Korea) and supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20224000000360) Supplementary materials Supplementary material associated with this article can be found, in the online version. Author contributions N.I.C and J.W.H contributed to the experimental design. H.J.Y contributed to the experimental setup. H.J.E, C.H.K, J.W.J and K.L.K contributed to the data analysis. 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Cardinaud, Selective and deep plasma etching of SiO 2 : Comparison between different fluorocarbon gases (CF 4 , C 2 F 6 , CHF 3 ) mixed with CH 4 or H 2 and influence of the residence time, Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena 20 (2002) 1514–1521. https://doi.org/10.1116/1.1495502. H.J. Lee, H.W. Tak, S.B. Kim, S.K. Kim, T.H. Park, J.Y. Kim, D. Sung, W. Lee, S.B. Lee, K. Kim, B.O. Cho, Y.L. Kim, K.C. Lee, D.W. Kim, G.Y. Yeom, Characteristics of high aspect ratio SiO 2 etching using C 4 H 2 F 6 isomers, Appl Surf Sci 639 (2023). https://doi.org/10.1016/j.apsusc.2023.158190. J.W. Hong, Y.H. Kim, H.J. Kim, H.W. Tak, K.D. Bae, J.Y. Lee, H.S. Bae, Y.S. Kim, G.Y. Yeom, Effect of various pulse plasma techniques on TiO 2 etching for metalens formation, Vacuum (2023) 111978. https://doi.org/10.1016/j.vacuum.2023.111978. J.W. Hong, Y.H. Kim, H.J. Kim, H.W. Tak, S.N. Goong, S.B. Kim, K.D. Bae, J.Y. Lee, H.S. Bae, G.Y. Yeom, D.W. Kim, Etched characteristics of nanoscale TiO 2 using C 4 F 8 -based and BCl3-based gases, Mater Sci Semicond Process 164 (2023). https://doi.org/10.1016/j.mssp.2023.107617. J.W. Hong, H.W. Tak, Y.H. Choi, H.J. Kim, D.W. Kim, G.Y. Yeom, Etch Characteristics of Low-K Materials Using CF 3 I/C 4 F 8 /Ar/O 2 Inductively Coupled Plasmas , Sci Adv Mater 14 (2022) 1258–1264. https://doi.org/10.1166/sam.2022.4312. G. Greczynski, L. Hultman, Reliable determination of chemical state in x-ray photoelectron spectroscopy based on sample-work-function referencing to adventitious carbon: Resolving the myth of apparent constant binding energy of the C 1s peak, Appl Surf Sci 451 (2018) 99–103. https://doi.org/10.1016/j.apsusc.2018.04.226. G. Greczynski, L. Hultman, A step-by-step guide to perform x-ray photoelectron spectroscopy, J Appl Phys 132 (2022). https://doi.org/10.1063/5.0086359. G. Greczynski, L. Hultman, The same chemical state of carbon gives rise to two peaks in X-ray photoelectron spectroscopy, Sci Rep 11 (2021). https://doi.org/10.1038/s41598-021-90780-9. G. Greczynski, L. Hultman, X-ray photoelectron spectroscopy: Towards reliable binding energy referencing, Prog Mater Sci 107 (2020). https://doi.org/10.1016/j.pmatsci.2019.100591. D. Fang, F. He, J. Xie, L. Xue, Calibration of Binding Energy Positions with C1s for XPS Results, Journal Wuhan University of Technology, Materials Science Edition 35 (2020) 711–718. https://doi.org/10.1007/s11595-020-2312-7. G. Greczynski, L. Hultman, X-ray photoelectron spectroscopy: Towards reliable binding energy referencing, Prog Mater Sci 107 (2020). https://doi.org/10.1016/j.pmatsci.2019.100591. Additional Declarations No competing interests reported. Supplementary Files 01stairononsupplymentary202406151.docx Cite Share Download PDF Status: Published Journal Publication published 02 Oct, 2024 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 25 Jul, 2024 Reviews received at journal 24 Jul, 2024 Reviews received at journal 23 Jul, 2024 Reviewers agreed at journal 16 Jul, 2024 Reviewers agreed at journal 16 Jul, 2024 Reviewers invited by journal 15 Jul, 2024 Editor assigned by journal 07 Jul, 2024 Editor invited by journal 07 Jul, 2024 Submission checks completed at journal 04 Jul, 2024 First submitted to journal 03 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4678024","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":331532068,"identity":"c87bcb73-0e9a-4a57-abe0-d30f612f8086","order_by":0,"name":"Nam Il Cho","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Nam","middleName":"Il","lastName":"Cho","suffix":""},{"id":331532071,"identity":"4f14bc76-6232-48bf-b258-8307d39dc6fa","order_by":1,"name":"Jong Woo Hong","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Jong","middleName":"Woo","lastName":"Hong","suffix":""},{"id":331532074,"identity":"de62c6f0-2042-4787-8b9a-d5b341b9e2a6","order_by":2,"name":"Hee Jin Yoo","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Hee","middleName":"Jin","lastName":"Yoo","suffix":""},{"id":331532077,"identity":"94b618d6-8fa3-492a-8fd7-eaa06d233e81","order_by":3,"name":"Hyeong Joon Eoh","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Hyeong","middleName":"Joon","lastName":"Eoh","suffix":""},{"id":331532080,"identity":"eb69d3d3-d069-48f5-9729-33065f79df7c","order_by":4,"name":"Chan Ho Kim","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Chan","middleName":"Ho","lastName":"Kim","suffix":""},{"id":331532083,"identity":"a26aa8ad-2c45-467a-9c2e-c2a532964825","order_by":5,"name":"Jun Won Jeong","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Jun","middleName":"Won","lastName":"Jeong","suffix":""},{"id":331532085,"identity":"fc35c73b-e20b-4549-9ec0-d9a8d22c8793","order_by":6,"name":"Kyung Lim Kim","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Kyung","middleName":"Lim","lastName":"Kim","suffix":""},{"id":331532086,"identity":"809aad7a-1b02-4b32-98e9-1a72734d9f7d","order_by":7,"name":"Jung Hun Kwak","email":"","orcid":"","institution":"Sk speicalty","correspondingAuthor":false,"prefix":"","firstName":"Jung","middleName":"Hun","lastName":"Kwak","suffix":""},{"id":331532090,"identity":"c1cc5a6f-4a14-4f8d-b685-54de67ea8cb2","order_by":8,"name":"Yong Jun Cho","email":"","orcid":"","institution":"Sk speicalty","correspondingAuthor":false,"prefix":"","firstName":"Yong","middleName":"Jun","lastName":"Cho","suffix":""},{"id":331532092,"identity":"6c961709-1255-4464-a8f8-89c700c7350d","order_by":9,"name":"Dong Woo Kim","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Dong","middleName":"Woo","lastName":"Kim","suffix":""},{"id":331532094,"identity":"48060a37-312a-4e0e-a024-d676f173c806","order_by":10,"name":"Geun Young Yeom","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtElEQVRIiWNgGAWjYPACGwYJHhDNRryWNNK1HCZBi3xEjuGDjznn7SV7zhgwfCg7TFiL4Y0cY8OZ224nzubtMWCccY4YLTNyzKR5t91OkOPnMWDmbSNOi/lv3m3n7MFa/hKjRV4ix4yZd9sBRpDDmBmJ0WLA86xYcua25MSZPccKDvacSyfClvbkjR8+brOzlziTvPHBjzJrImy5kGEA5xwgrB5kS//xB0QpHAWjYBSMghEMAMCsOdlqCXNWAAAAAElFTkSuQmCC","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":true,"prefix":"","firstName":"Geun","middleName":"Young","lastName":"Yeom","suffix":""}],"badges":[],"createdAt":"2024-07-03 06:22:34","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4678024/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4678024/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-024-74107-y","type":"published","date":"2024-10-02T15:58:16+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":61283212,"identity":"c2ead845-6e6e-4625-a9bc-04eea09a93cf","added_by":"auto","created_at":"2024-07-29 05:43:45","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":44373,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic diagram of the 300 mm planar type ICP equipment used in the experiment. (b) Vertical view by SEM image and schematic diagram of the basic sample, consisting of a 480 nm photoresist line-shaped pattern mask over 1500 nm of oxide/nitride pair layers on a silicon substrate. (c) To make maskless condition, ~510 nm thick ON layers were etched from (b) and remaining PR was stripped off using an O\u003csub\u003e2\u003c/sub\u003e plasma.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/a2229f22d5281c753a4095d3.png"},{"id":61281978,"identity":"5c707c80-b708-4203-81a7-54bc446d744a","added_by":"auto","created_at":"2024-07-29 05:19:45","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":17939,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Etch rates of SiO\u003csub\u003e2\u003c/sub\u003e, and SiN\u003csub\u003ex\u003c/sub\u003e, and SiO\u003csub\u003e2\u003c/sub\u003e/SiN\u003csub\u003ex \u003c/sub\u003estack with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases. (b) Etch selectivity between SiO\u003csub\u003e2\u003c/sub\u003e and SiN\u003csub\u003ex\u003c/sub\u003e for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases. 2000 W of source power, -60 V of DC bias voltage, and additive gases composed of CF\u003csub\u003e4\u003c/sub\u003e/O\u003csub\u003e2\u003c/sub\u003e/Ar were used.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/a7765063561b0dfd210c6d11.png"},{"id":61281977,"identity":"b1bc2325-1b24-4c86-94ad-874aa696ea69","added_by":"auto","created_at":"2024-07-29 05:19:44","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":98012,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of maskless ONON stack feature etched about 300 nm, 600 nm, and with (a) C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, (b) C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and (c) C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases. The other etch conditions are the same as those in Figure 2.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/2dedf216ab59bdbcd9cb2b9e.png"},{"id":61281979,"identity":"3802ba4d-cbad-4744-b0b6-53c6624558c1","added_by":"auto","created_at":"2024-07-29 05:19:45","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":44078,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Measurement of sidewall angles of 1000 nm etched maskless ONON stack feature and (b) measured sidewall angles, top CD differences (ref top CD – top CD of etched structure), and (bottom CD – top CD)/2 of the etched feature for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/b79c68b4cddba653c1305c27.png"},{"id":61282569,"identity":"4740f2a1-037a-46ec-bcf4-37057bc9cb80","added_by":"auto","created_at":"2024-07-29 05:27:45","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":62077,"visible":true,"origin":"","legend":"\u003cp\u003e(a) QMS spectra for the plasmas generated with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases mixed with Ar/O\u003csub\u003e2\u003c/sub\u003e/CF\u003csub\u003e4\u003c/sub\u003e. (b) Intensities of F+, CF\u003csup\u003e+\u003c/sup\u003e, CF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, CF\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, CHF\u003csup\u003e+\u003c/sup\u003e, and CHF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e extracted from (a). (c) Intensity ratios of (CF\u003csup\u003e+\u003c/sup\u003e+CF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e+CHF\u003csup\u003e+\u003c/sup\u003e+CHF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e) over (CF\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e+F\u003csup\u003e+\u003c/sup\u003e). The process conditions were the same as those in Figure 2.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/47d0335355379df7efb52590.png"},{"id":61282567,"identity":"b9636004-4d79-42f8-90a3-fe3b3df871bf","added_by":"auto","created_at":"2024-07-29 05:27:45","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":50449,"visible":true,"origin":"","legend":"\u003cp\u003e(a) OES spectra for (a) the plasmas generated with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases mixed with CF\u003csub\u003e4\u003c/sub\u003e/O\u003csub\u003e2\u003c/sub\u003e/Ar. (b) Intensities of F, CF\u003csub\u003e2\u003c/sub\u003e, and CH normalized by Ar intensity and (c) intensity ratios of (CF\u003csub\u003e2 \u003c/sub\u003e+ CH)/F.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/47ffecec7240bd9c010a06cd.png"},{"id":61283213,"identity":"0c7939a4-8e7d-49d4-a4f3-ce27a0249e62","added_by":"auto","created_at":"2024-07-29 05:43:45","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":12778,"visible":true,"origin":"","legend":"\u003cp\u003eTotal positive ion intensity, total light positive ion intensity (\u0026lt; 40 amu, that is, lighter than Ar mass), and total heavy positive ion intensity (≥ 40 amu) for the plasma generated with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases measured from QMS in Fig. 5 (a). \u0026nbsp;\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/249f7ce280c4360e74fc47f8.png"},{"id":61281982,"identity":"279cf2b0-81da-4e5c-8fb1-a8656fb86432","added_by":"auto","created_at":"2024-07-29 05:19:45","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":64116,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic diagram on 50° tilting of samples for the XPS study of sidewall residues remaining on the etched maskless ONON stack features. (b) Atomic composition measured by XPS for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases. (c) The ratio of carbon and fluorine relative to substrate material composed of Si, O, and N at the sidewall of the etched ONON feature. (d), (e), and (f) are C 1s narrow scan XPS data at the sidewall of the maskless ONON features etched with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases, respectively.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/a531af3683e4255f5525a5f3.png"},{"id":61282571,"identity":"6e997547-6dbc-427c-b883-01ae443bf746","added_by":"auto","created_at":"2024-07-29 05:27:45","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":37121,"visible":true,"origin":"","legend":"\u003cp\u003ePotential mechanism of maskless ONON stack feature etching. (a) when a suitably thick polymer layer is formed on the sidewall of the ONON stack feature during etching. (b) high and heavy ion bombardment to the ONON stack feature in addition to a thinner polymer layer on the sidewall of the ONON stack feature during etching. (c) when a thinnest polymer layer is formed on the sidewall of ONON stack feature during etching.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/8a7c3a92dd8deff40733bf9c.png"},{"id":66097462,"identity":"9e7f0353-ac32-4eaf-a817-460db1aed204","added_by":"auto","created_at":"2024-10-07 16:14:12","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1010814,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/c075e930-905c-40d0-bade-3ba4a3b1d2f4.pdf"},{"id":61281984,"identity":"04b2edb7-a1d1-4b6b-a5ec-4dd588b4a272","added_by":"auto","created_at":"2024-07-29 05:19:45","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1720093,"visible":true,"origin":"","legend":"","description":"","filename":"01stairononsupplymentary202406151.docx","url":"https://assets-eu.researchsquare.com/files/rs-4678024/v1/0eb0deacc5442a3016b3e49e.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Etch characteristics of maskless Oxide/Nitride/Oxide/Nitride (ONON) stacked structure using C4H2F6-based gas","fulltext":[{"header":"I. Introduction","content":"\u003cp\u003eToday, oxide/nitride/oxide/nitride (ONON) stacking structures are widely used in 3 dimensional (3D) vertical memory devices.[\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] For 3D Not-and (NAND) devices, an essential process for controlling the stacked memory cell is the staircase etching process which etches one ON layer in the ONON stack repeatedly after recessing photoresist (PR) layer on the top of the ONON structure. In the past, for the staircase etch process, layer-by-layer etching of one ON layer while trimming of PR after one ON layer etching was used.[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] This method is highly selective and precise etch method in etching one ON layer-by-layer but has led to an increase in cost due to an increase in the number of process cycles as the number of layers increases.\u003c/p\u003e \u003cp\u003eIn order to solve this problem, methods of etching multiple ON layers at once by increasing the dimensions of the staircase, through the formation of maskless ONON stack feature in advance, have been studied (see supplementary information Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] These methods have more complex shapes than the existing process, so the maskless ONON stack feature etch profile through the passivation of the sidewall has become important, and, for this, fluorocarbon rich gases such as C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gases have been actively studied.[\u003cspan additionalcitationids=\"CR9 CR10 CR11\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] In addition, many studies have been conducted on the selectivity etching of O/N or N/O for profile improvement and accurate etch stop.[\u003cspan additionalcitationids=\"CR14 CR15 CR16\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eHowever, there are remaining issues on these etch methods on the areas not protected by PR such as critical dimension (CD) reduction, degradation of etch profile, trench formation at the edge of maskless ONON stack feature, etc. Also, these days, as the reduction of carbon emission has become a hot issue around the world, reinforcement of regulations and reduction measures for carbon emitted in the semiconductor manufacturing process are required. Since the fluorocarbon-based gas such as C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, CF\u003csub\u003e4\u003c/sub\u003e, etc. used in the etching process generally has a high global warming potential (GWP), research on alternative gas with the same or better etching properties is required.[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eTherefore, in this study, staircase etch characteristics of maskless ONON stack feature using C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas, which is a low GWP gas, have been investigated using\u0026thinsp;~\u0026thinsp;510 nm ONON stack feature without a mask (SiO\u003csub\u003e2\u003c/sub\u003e/SiN\u003csub\u003ex\u003c/sub\u003e composed of 30 nm in thickness and 9/8 layers, respectively). The staircase etch characteristics of C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas were compared with the etch characteristics of C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gases. As a result, C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas showed the fastest ONON etch rate with the etch selectivity of SiO\u003csub\u003e2\u003c/sub\u003e/SiN\u003csub\u003ex\u003c/sub\u003e close to ~\u0026thinsp;1:1 and highly anisotropic etch profiles without varying CD of maskless ONON stack feature.\u003c/p\u003e"},{"header":"II. Experimental","content":"\u003cp\u003eThe ONON etching was conducted on a 300mm inductively coupled plasma (ICP) etcher system shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e1\u003c/span\u003e (a). The ICP source had an inner/outer configuration with a two-turn silver coated copper coil. Additionally, there was a 35 mm thick alumina window installed above the process window. The alumina window and antenna coil were separated by approximately 30 mm using a jig. The substrate was located\u0026thinsp;~\u0026thinsp;150 mm below the dielectric window. The ICP source utilized a 13.56MHz RF power (Seren-R3001) and bias voltage was applied using a 2MHz RF power (Seren-R2001). The process gases were distributed using a gas ring located at the chamber's top edge. The process pressure was automatically controlled using a main valve (VAT-model PM. 7) installed between the turbopump and dry pump.\u003c/p\u003e \u003cp\u003eA 1500 nm thick ONON stack was deposited on a silicon wafer, followed by patterning with a 480 nm PR on the top of ONON stack as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e1\u003c/span\u003e (b). (the thickness of one monolayer SiO\u003csub\u003e2\u003c/sub\u003e or SiN\u003csub\u003ex\u003c/sub\u003e was 30 nm) To investigate the etch characteristics of ONON staircase etching in an environment without masks, the ONON stack was etched\u0026thinsp;~\u0026thinsp;510 nm with the PR line pattern and the PR was removed as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e1\u003c/span\u003e (c) to form a maskless ONON stack feature. To etch initial\u0026thinsp;~\u0026thinsp;510 nm thick ONON stack feature with a PR mask, a gas mixture of C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e/CF\u003csub\u003e4\u003c/sub\u003e/O\u003csub\u003e2\u003c/sub\u003e/Ar was used at 2mTorr of operating pressure with 2000W of RF source power and \u0026minus;\u0026thinsp;500V of DC bias voltage for 2.5 min. Subsequently, the residual PR layer was removed through the PR strip process using O\u003csub\u003e2\u003c/sub\u003e gas at 50 mTorr and with 2kW of ICP power only without biasing the substrate, and finally a\u0026thinsp;~\u0026thinsp;510 nm thick ONON rectangular shaped stack feature on the remaining 1000 nm thick ONON stack shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c) was obtained for maskless ONON stack feature etching. The etching of the ~\u0026thinsp;510 nm thick maskless ONON stack feature shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e1\u003c/span\u003e (c) was processed using C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e mixed with CF\u003csub\u003e4\u003c/sub\u003e/O\u003csub\u003e2\u003c/sub\u003e/Ar while applying 2kW of ICP power and a -60V DC bias voltage. During the maskless ONON stack feature etching, the substrate temperature was maintained at 18\u0026deg;C and the process pressure was kept at 2mTorr. Detailed SEM images of Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b) and (c) are shown in the supplementary information, Figure S2.\u003c/p\u003e \u003cp\u003eTo determine the etch rates of SiO\u003csub\u003e2\u003c/sub\u003e and SiN\u003csub\u003ex\u003c/sub\u003e, etching was performed on respective blank wafers and the etch depths were measured using a step profilometer (Tencor, Alpha step 500). A field emission scanning electron microscope (FE-SEM; Hitachi, S-4700) was used to examine the etch profiles after etching maskless ONON stack feature. Hydrocarbon and fluorocarbon radicals were measured using optical emission spectroscopy (OES; ANDOR technology, SR-ASZ-0103), and the further analysis of dissociated radicals and ions was conducted through a quadrupole mass spectrometer (QMS; Hiden Analytical, PSM 500). Surface analysis was carried out using X-ray photoelectron spectroscopy (XPS; VG Microtech Inc., ESCA2000).\u003c/p\u003e"},{"header":"III. Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIII-I.\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;Etching of\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eONON\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003estack\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eusing C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eC\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gases\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 2 (a) shows etch rates of blank SiO\u003csub\u003e2\u003c/sub\u003e, SiN\u003csub\u003ex\u003c/sub\u003e, and ONON stack, and Figure 2 (b) shows the etch selectivity between SiN\u003csub\u003ex\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e using C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases. As the process conditions, 2000 W of source power, -60 V of DC bias voltage, and additive gases composed of CF\u003csub\u003e4\u003c/sub\u003e/O\u003csub\u003e2\u003c/sub\u003e/Ar were used. The process conditions were selected through the maskless ONON stack feature etching with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas (see supplementary information Figure S3). For C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gases, which are the fluorocarbon gases generally used for staircase etching, the optimized etch conditions were similar to C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas as functions of process variables except for C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e gas flow rates. As shown in Fig. 2(a), for blank sample etching with this process conditions, all three gases showed similar etch rates of 72 ~ 81 nm/min for ONON stack even though the ONON stack was the highest for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas. On the contrary, the SiO\u003csub\u003e2\u003c/sub\u003e etch rates were higher in the sequence of C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases by showing 72, 87, and 92 nm/min, respectively, and SiN\u003csub\u003ex\u003c/sub\u003e etch rates were higher in the reverse sequence of C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gases, respectively. The highest SiN\u003csub\u003ex\u003c/sub\u003e etch rates and the lowest SiO\u003csub\u003e2\u003c/sub\u003e etch rates observed for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas compared to C4F8 and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gases are believed to be related to existence of hydrogen in the gas chemical formula which assists SiN\u003csub\u003ex\u003c/sub\u003e etching by forming NH\u003csub\u003ex\u003c/sub\u003e but decreases SiO\u003csub\u003e2\u003c/sub\u003e etching by forming a thicker fluorocarbon layer on the SiO\u003csub\u003e2\u003c/sub\u003e surface. The etch selectivities of SiO\u003csub\u003e2\u003c/sub\u003e/SiN\u003csub\u003ex\u003c/sub\u003e estimated by the blank sample etching of SiO\u003csub\u003e2\u003c/sub\u003e and SiN\u003csub\u003ex\u003c/sub\u003e were 1.25, 0.62, and 0.56 for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e, respectively, as shown in Fig. 2(b), therefore, the higher etch rate of ONON stack observed for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas compared to C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases in Figure 2(a) was related to the similar etch rates between SiO\u003csub\u003e2\u003c/sub\u003e and SiN\u003csub\u003ex\u003c/sub\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe ONON stack having maskless ~510 nm thick ONON pre-etched feature shown in Figure 1 (c) was etched using the C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases with the process conditions in Figure 2. Figure 3 shows cross-sectional SEM images of maskless ONON stack feature etched about 300 nm, 600 nm, and 1000 nm with (a)\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, (b) C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and (c) C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases. The other etch conditions are the same as those in Figure 2. When comparing the shape differences between the reference (pre-etch) feature profile and etched ONON stack feature, the ONON stack feature etched with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas showed a square shaped feature without changing the feature shape significantly during the etching of 1000 nm thick ONON stack. On the contrary, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gas exhibited gradual change in feature size with etch depth and finally showed a thin trapezoidal shaped feature after etching 1000 nm thick ONON stack while C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas showed intermediate feature shape change. Additionally, the most significant trenching phenomenon was observed for C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUsing SEM images, the top/bottom CDs and sidewall angles of maskless ONON stack feature etched ~1000 nm with\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases were measured as shown in Fig.4 (a), and the results on sidewall angles, CD differences (ref top CD – top CD of etched structure), and (bottom CD – top CD)/2 of the etched features for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases are shown in Figure 4(b).\u0026nbsp;As shown in Fig. 4 (b), C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas exhibited the smallest CD differences, with sidewall angles close to 90 degrees while C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gas showed the largest CD difference (reduction in top and bottom CDs) compared to the reference, and its sidewall angle was also observed to be the least favorable. For C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas, intermediate CD differences and sidewall angles were observed compared to C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e\u003cbr\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIII-2.\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003ePlasma analysis for\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gases\u003c/em\u003e\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor the etching conditions in Figure 2, dissociated gas species were investigated using QMS and the mass spectra of the positive ions directly extracted from the plasma for\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e,\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e,\u0026nbsp;and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based\u0026nbsp;gases\u0026nbsp;are shown in Figure 5 (a). (Dissociated radicals in the plasmas observed using QMS for these gases are shown in supplementary information Figure S4.) As shown in Fig. 5 (a), various ions dissociated and recombined from the reactive gases can be seen. Among those reactive ions, ions such as F\u003csup\u003e+\u003c/sup\u003e,\u0026nbsp;CF\u003csup\u003e+\u003c/sup\u003e, CF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, CF\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, CHF\u003csup\u003e+\u003c/sup\u003e, and CHF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e can be more related to passivation or etching of SiO\u003csub\u003e2\u003c/sub\u003e and SiN\u003csub\u003ex\u003c/sub\u003e.\u0026nbsp;Mass amount (intensity) of these ions detected by the QMS are shown in Figure 5 (b). Among these ions,\u0026nbsp;CF\u003csup\u003e+\u003c/sup\u003e, CF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, CHF\u003csup\u003e+\u003c/sup\u003e, and CHF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e are more related to the passivation on the materials surface while CF\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e and F\u003csup\u003e+\u003c/sup\u003e are more related to etching. Therefore,\u0026nbsp;the ratio\u0026nbsp;of (CF\u003csup\u003e+\u003c/sup\u003e + CHF\u003csup\u003e+\u003c/sup\u003e + CF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e + CHF\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e)/(CF\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e+ F\u003csup\u003e+\u003c/sup\u003e) was taken to estimate the reactive ion flux ratios from plasma to the ONON stack sample surface between passivation flux and etchant flux, and the result is shown in Figure 5 (c). As shown in Figure 5 (c),\u0026nbsp;the ratio\u0026nbsp;was\u0026nbsp;higher\u0026nbsp;for\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas\u0026nbsp;compared to C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e and\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases.\u0026nbsp;This indicates that among the three\u0026nbsp;different fluorocarbon\u0026nbsp;gases, C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e provides\u0026nbsp;the most polymeric\u0026nbsp;radicals to the ONON stack sample surface during the etching, and which can\u0026nbsp;provide the strongest sidewall protection\u0026nbsp;condition. And, it is believed that the sidewall protection during the maskless ONON stack feature etching with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas is the related to maintaining a square shaped ONON stack feature until 1000 nm ONON thickness is etched.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUsing OES, the radical species formed in the plasma were also observed\u0026nbsp;with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases mixed with CF\u003csub\u003e4\u003c/sub\u003e/O\u003csub\u003e2\u003c/sub\u003e/Ar. The process conditions are the same as those in Fig. 2. From OES, species such as CF\u003csub\u003e2\u003c/sub\u003e at 251.9 nm, CH at 390 nm, F at 704 nm, Ar at 750 nm, O at 844.7 nm, etc. could be observed as shown in Figure 6 (a)\u0026nbsp;[19–21]. The radical peak intensities such as CF\u003csub\u003e2\u003c/sub\u003e, CH, and F which are related to passivation and etching were normalized by Ar peak intensity to estimate the radical density in the plasma and the results are shown in Figure 6 (b). As shown in Fig. 6 (b), the F/Ar which is related to the etching was the highest for C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gas and the CF\u003csub\u003e2\u003c/sub\u003e/Ar + CH/Ar which is related to the passivation was the highest for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas. Figure 6 (c) shows the ratio of (CF\u003csub\u003e2\u003c/sub\u003e + CH)/F for three gases which could show the degree of sidewall protection or sidewall etching during the maskless ONON feature etching and,\u0026nbsp;among the three gas compositions,\u0026nbsp;the C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas showed the highest while it is lowest for\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gas. The results were similar to the QMS results in Fig. 5 (c) but, in the case of QMS with the positive ion measurement mode, even though it can measure all the positive ions in the plasma as-is for the estimation of the radicals in the plasma, it is difficult to estimate the F density due to the difficulty in positive ionization of F in the plasma. Therefore, for the estimation of F radical density, OES shows more reliable data. Therefore, based on the results of OES and QMS shown in Figure 5 and 6, it can be confirmed that\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas\u0026nbsp;provides an environment with the highest abundance of hydrofluorocarbon polymer, which protects\u0026nbsp;the sidewalls of the profile the most. Additionally, it was noted that\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e provides an environment with the least amount of polymer. Under\u0026nbsp;maskless\u0026nbsp;conditions, it was observed that,\u0026nbsp;to maintain the horizontal CD of the\u0026nbsp;maskless ONON stack feature, the polymer layer on the sidewalls needs to be sufficiently thick, and a lesser amount\u0026nbsp;of polymer layer can\u0026nbsp;result in a reduction\u0026nbsp;of\u0026nbsp;the final\u0026nbsp;CDs\u0026nbsp;of the maskless ONON stack feature.\u003c/p\u003e\n\u003cp\u003eTo understand the\u0026nbsp;differences in\u0026nbsp;trenching\u0026nbsp;of the etched maskless ONON stack feature for the gases used in the experiment,\u0026nbsp;the\u0026nbsp;total positive\u0026nbsp;ions,\u0026nbsp;the sum of light positive ions\u0026nbsp;(\u0026lt; 40 amu, that is, lighter than Ar mass), and\u0026nbsp;the sum of heavy positive ions\u0026nbsp;(≥\u0026nbsp;40 amu), and in the plasma were calculated from the QMS data in Figure 5 (a) and the results are shown in Figure 6. \u0026nbsp;As shown in Fig. 7, not only the sum of total positive ions but also the sum of heavy positive ions was the highest for C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas and C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas showed the lowest total positive ions for both total positive ions and heavy positive ions. The positive ions incident to the sidewall of the maskless ONON stack feature can be reflected at the sidewall and can lead to trenching due to increased ion flux at the edge of the feature. The most significant trenching observed for the maskless ONON stack feature etched with C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas and the least significant trenching for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas are believed to be related to the differences in the positive ion flux, especially in the heavy positive ion flux. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIII-3.\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eONON stack etch mechanism for\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gases\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eXPS surface analysis was conducted to investigate the residue remaining on the sidewall of the etched maskless ONON stack features. To observe the residues at the sidewall of the etched maskless ONON stack features, XPS analysis was\u0026nbsp;performed\u0026nbsp;after tilting\u0026nbsp;the sample\u0026nbsp;50°\u0026nbsp;as shown in Figure 8 (a).\u0026nbsp;(XPS\u0026nbsp;widescan data measured for the sidewall residues remaining on the etched maskless ONON stack features for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases are shown in supplementary information Figure\u0026nbsp;S5.)\u0026nbsp;The atomic percentages of the elements etched with\u0026nbsp;C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases\u0026nbsp;were observed by the XPS and the results are shown in Figure 8 (b) and the ratios of C/(Si+O+N) and F/(Si+O+N), which are the ratio of fluorocarbon residue component/substrate components, are shown in Figure 8 (c). As shown in Figure 8 (b) and (c), the carbon and fluorine forming fluorocarbon residue at the sidewall of the ONON stack feature were the highest for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas and the lowest for C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gas.\u0026nbsp;To investigate the bonding states of the fluorocarbon residue at the sidewall of the ONON stack features, XPS narrow data of C1s were also measured and Figure 8 (d), (e), and (f) are C1s narrow scan XPS data for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases, respectively. As shown in Figure 8 (d), (e), and (f), carbon bonding related to C–C (~285 eV), C-CF (~287.5 eV), C-F (~289.5 eV), and C-CF\u003csub\u003e2\u003c/sub\u003e (~291.8 eV) were observed.[22–25] Among the bonding peaks,\u0026nbsp;C-CF, C-F, and C-CF\u003csub\u003e2\u003c/sub\u003e are related to the fluorocarbon layer\u0026nbsp;[26,27] and C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas showed also highest intensities of these bonding peaks and the C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gas showed the lowest intensities. Through XPS surface analysis, it can be understood that C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas provided the most carbon-rich polymer at the sidewall of the etched ONON feature while C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gas formed the least polymer.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFrom the results of plasma analysis in Fig. 5~7 and surface analysis in Fig. 8 in addition to cross-sectional images of etched maskless ONON stack features in Fig. 3~4, the etch mechanism for the etching of maskless ONON stack features can be shown schematically as Figure 9. \u0026nbsp;Etch profiles and CDs of the maskless ONON stack feature are influenced by the thickness of the C\u003csub\u003ex\u003c/sub\u003eH\u003csub\u003ey\u003c/sub\u003eF\u003csub\u003ez\u003c/sub\u003e hydrofluorocarbon or fluorocarbon polymer layer that provides protection of the sidewall, preventing the reduction\u0026nbsp;of the subsequent pattern's mask line. In addition, heavy ion bombardment from the plasma to the substrate can form trenching at the edge of the maskless ONON stack feature by reflecting heavy ions at the sidewall of the maskless ONON stack feature during the etching. In the case of C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas, despite ion bombardment, it is evident that the vertical sidewall is maintained and trenching phenomenon is protected by a thick polymer layer formed on the sidewall area as shown in Fig. 8(a). However, in the case of C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas, due to a thinner polymer layer compared to C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas, the CD and etch profile of the maskless ONON stack feature were slightly degraded and trenching was prominent due to heavy ion bombardment effect as shown in Fig. 8(b). Especially for C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gas, due to the thinnest polymer layer at the sidewall of the maskless ONON stack feature, sidewall etching was dominant during the etching even though the trenching was not significant due to the lower ion bombardment.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor the staircase etching for 3D NAND device, it is important to maintain pattern CD width and to keep vertical etch profile without trenching during etching maskless ONON stack features because, if the CD is decreased and slanted etch profile is formed, during the following additional ON layer-by-layer etching with PR trimming, the metal contact area for each ON layer can be significantly reduced. (for more details, see supplementary information Figure S1.) \u0026nbsp; \u0026nbsp; \u0026nbsp;Therefore, under maskless etching conditions, maintaining the etched CD is crucial because the current feature pattern serves as a mask for the etching of the next layer, necessitating the formation of a sufficiently thick passivation layer to prevent etching of the sidewall. Furthermore, it can be observed that adequate polymer layer on the sidewall in addition to low ion bombardment is also required to suppress trenching phenomena in addition to preventing the reduction of the CD.\u003c/p\u003e"},{"header":"IV. Conclusions","content":"\u003cp\u003eMaskless ONON stack feature pattern was etched using inductively coupled plasma with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases mixed with O\u003csub\u003e2\u003c/sub\u003e/Ar and its etching characteristics were investigated. C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas showed the highest ONON stack etch rate and also showed\u0026thinsp;~\u0026thinsp;1:1 etch selectivity between SiO\u003csub\u003e2\u003c/sub\u003e and SiN\u003csub\u003ex\u003c/sub\u003e layers in the ONON stacked layers while C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases exhibited similar etch rates which are lower than that by C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas, with the etch selectivity of SiN\u003csub\u003ex\u003c/sub\u003e/SiO\u003csub\u003e2\u003c/sub\u003e lower than 1.0. The etch selectivity of SiN\u003csub\u003ex\u003c/sub\u003e/SiO\u003csub\u003e2\u003c/sub\u003e close to ~\u0026thinsp;1.0 and the higher ONON stack etch rate for C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas were related to H radicals dissociated from C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e which increased the etch rate of Si\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e layer in the ONON stack. When maskless ONON stack features were etched, it was found that, among the three gases investigated, C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas showed no significant CD change from the reference and vertical sidewall with the lowest trenching phenomenon due to a thick polymer layer formed on the sidewall of the etched maskless ONON stack feature caused by the highest ratio of passivation flux/etchant flux to the sample. In the case of C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas, due to a thinner polymer layer compared to C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas, the CD and etch profile of the maskless ONON stack feature were slightly degraded while trenching was prominent due to heavy ion bombardment effect. Especially, in the case of C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gas, due to the thinnest polymer layer at the sidewall of the maskless ONON stack feature caused by the lowest ratio of passivation flux/etchant flux to the sample, the sidewall etching was significant during the etching even though the trenching was not significant due to the lower ion bombardment from the plasma. These results are believed to be related to the generation of polymer forming radicals versus etchant radicals in the plasma as observed by OES and QMS, the relative amount of heavy positive ions as observed by QMS, and the formation of fluorocarbon layer on the sidewall of the etched maskless ONON feature as observed by XPS, depending on fluorocarbon gases such as C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e used in the etching.\u003c/p\u003e \u003cp\u003eIn conclusion, the ONON stacked staircase structure will continue to be adopted in next-generation 3D vertical cell memory semiconductors, and the importance of profile quality in a maskless environment will continue to increase with the increasing complexity. Through this research, it has been confirmed that ratio of passivation radical flux to etchant radical flux, heavy ion flux, and finally the fluorocarbon layer thickness on the sidewall of the maskless ONON stack feature are important in determining the etched maskless ONON stack feature shapes. And, with C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas having low global warming potential (even though the additive CF\u003csub\u003e4\u003c/sub\u003e gas having a high global warming potential also needs to be replaced), a more stable etch profile and higher etch rate compared to the conventional C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases having high global warming potential could be achieved.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data generated or analyzed during this study are included in the article and supporting information.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Technology Innovation Program Development Program-Development of core technology in Carbon Neutrality (RS-2023-00265858, Development of alternative PFC gas with low GWP value under 150 for OLED display oxide TFT insulator patterning) funded By the Ministry of Trade, Industry \u0026amp; Energy(MOTIE, Korea) and supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry \u0026amp; Energy (MOTIE) of the Republic of Korea (No. 20224000000360)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupplementary material associated with this article can be found, in the online version.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eN.I.C and J.W.H contributed to the experimental design. H.J.Y contributed to the experimental setup.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eH.J.E, C.H.K, J.W.J and K.L.K contributed to the data analysis. J.H.K and Y.J.C initiated the project.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eG.Y.Y and D.W.K\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eparticipated in writing the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence and requests for materials should be addressed to G.Y.Y and D.W.K\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eY. Kim, J.G. Yun, S.H. Park, W. Kim, J.Y. Seo, M. Kang, K.C. Ryoo, J.H. Oh, J.H. Lee, H. Shin, B.G. 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Xue, Calibration of Binding Energy Positions with C1s for XPS Results, Journal Wuhan University of Technology, Materials Science Edition 35 (2020) 711\u0026ndash;718. https://doi.org/10.1007/s11595-020-2312-7.\u003c/li\u003e\n \u003cli\u003eG. Greczynski, L. Hultman, X-ray photoelectron spectroscopy: Towards reliable binding energy referencing, Prog Mater Sci 107 (2020). https://doi.org/10.1016/j.pmatsci.2019.100591.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"ONON stack feature, Maskless etching, Oxide/Nitride, C4F8, C4F6, C4H2F6","lastPublishedDoi":"10.21203/rs.3.rs-4678024/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4678024/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eOxide/Nitride/Oxide/Nitride (ONON; SiO\u003csub\u003e2\u003c/sub\u003e/SiN\u003csub\u003ex\u003c/sub\u003e/SiO\u003csub\u003e2\u003c/sub\u003e/SiN\u003csub\u003ex\u003c/sub\u003e) stacked structure is widely used in the 3D vertical structure of semiconductor cells. Previously, to form a 3D cells, photoresist (PR) was patterned and repeatedly trimmed on the top of ONON after the etching of one ON layer. Due to the time-consuming process of etching layer-by-layer of ON layer, two-step etch processing using C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based or C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gases composed of maskless ONON stack feature etching and followed one ON layer-by layer etching by PR trimming in the ONON stack feature are employed these days. However, the two-step etching method resulted in poor etch profiles of maskless ONON stack feature in addition to high global warming potential of C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e. In this study, we investigated the etching of maskless ONON stack feature using C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas having a low global warming potential and the effects of C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas on the etch characteristics of maskless ONON stack feature such as etch rate, etch profile, change in critical dimensional (CD), and etch selectivity between SiO\u003csub\u003e2\u003c/sub\u003e and SiN\u003csub\u003ex\u003c/sub\u003e have been investigated. C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gas showed the highest etch rates compared to C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases in addition to the etch selectivity of ~1:1 between SiO\u003csub\u003e2\u003c/sub\u003e and SiN\u003csub\u003ex\u003c/sub\u003e due to hydrogen included in the gas structure. In addition, the change in horizontal CD was lower in the order of C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e-based gases due to the more effective sidewall passivation in the order of C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e8\u003c/sub\u003e, C\u003csub\u003e4\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e, and C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e6\u003c/sub\u003e-based gases. The thicker carbon-based polymer layer on the sidewall also played an important role in maintaining the shape of the top edge shape of maskless ONON stack feature when etching a line feature in an environment without a mask.\u003c/p\u003e","manuscriptTitle":"Etch characteristics of maskless Oxide/Nitride/Oxide/Nitride (ONON) stacked structure using C4H2F6-based gas","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-29 05:19:40","doi":"10.21203/rs.3.rs-4678024/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-07-25T06:16:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-24T23:35:12+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-23T06:30:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"172122157202680049267649732624641618504","date":"2024-07-17T03:16:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"317038721478541583252099753520531087289","date":"2024-07-16T10:08:49+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-07-15T18:36:44+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-07T08:04:39+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-07-07T07:14:41+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-04T07:50:15+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-07-03T06:21:22+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7ed57eaf-5889-46d4-8c3b-62075c678e0f","owner":[],"postedDate":"July 29th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":35100876,"name":"Physical sciences/Materials science"},{"id":35100886,"name":"Physical sciences/Nanoscience and technology"}],"tags":[],"updatedAt":"2024-10-07T16:09:06+00:00","versionOfRecord":{"articleIdentity":"rs-4678024","link":"https://doi.org/10.1038/s41598-024-74107-y","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2024-10-02 15:58:16","publishedOnDateReadable":"October 2nd, 2024"},"versionCreatedAt":"2024-07-29 05:19:40","video":"","vorDoi":"10.1038/s41598-024-74107-y","vorDoiUrl":"https://doi.org/10.1038/s41598-024-74107-y","workflowStages":[]},"version":"v1","identity":"rs-4678024","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4678024","identity":"rs-4678024","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}