Ellipsometry Study on thickness gradient silicon nitride (SiNx) film by plasma-enhanced chemical vapor deposition

Abstract As passivation layer and anti-reflection layer, silicon nitride (SiNx) thin film has been widely used in photovoltaic devices such as solar cells. The structure of SiNx film with thickness gradient can make full use of different wavelengths of sunlight. In this paper, we have studied this structure for the first time. While introducing a quartz layer by plasma-enhanced chemical vapor deposition (PECVD), we obtained a thin SiNx film in the center and gradually thicker toward the edge. The effects of PECVD process parameters, including deposition time, RF power, dielectric layer thickness, etc. on the thickness gradient of SiNx thin film are systematically studied. The film composition changing in the radial direction is also analyzed by ellipsometry. This study provides an instructive method for controlling the thickness gradient of SiNx films and plays an important role in using this structure to the solar cell application.