Chemical surface and interface structure of sulfur-passivated silicon with a SiNx capping layer

• Published in: 2022 IEEE 49th Photovoltaics Specialists Conference (PVSC) p. 0076
• Main Authors: Hua, Amandee, Jiang, Nan, Upadhyaya, Ajay, Lam, Issac, Mouri, Tasnim K, Hauschild, Dirk, Weinhardt, Lothar, Yang, Wanli, Rohatgi, Ajeet, Das, Ujjwal, Heske, Clemens
• Format: Conference Proceeding
• Language: English
• Published: IEEE 05.06.2022
• Subjects: Chemicals; Passivation; Silicon; Silicon compounds; Spectroscopy; Sulfur; Xenon
• DOI: 10.1109/PVSC48317.2022.9938794

SiO2 passivation is commonly used to improve the efficiency of silicon-based photovoltaics. However, SiO2 passivation requires high processing temperatures, potentially leading to a deterioration of the Si bulk quality. A novel sulfur-based passivation, requiring lower processing temperatures (~550 degree C), has been introduced, which, however, can suffer from degradation during the subsequent manufacturing process. Hence, a SiNx capping layer is required to protect the passivation layer. In this study, we have investigated sulfur-passivated n-n+ diffused silicon wafers with SiNx capping layers of varying thicknesses, as well as the impact of subsequent rapid thermal processing (RTP) on these layers, using x-ray photoelectron spectroscopy (XPS) and x-ray emission spectroscopy (XES). The surface-sensitive XPS data gives detailed insights into the local chemical bonding environments at the surface. In particular, it shows sulfur in a sulfite-like chemical environment and the presence of Si-O bonds on the sulfur-passivated silicon sample. The more bulk-sensitive XES S L2,3 spectra reveal the presence of S-Si bonds, which is maintained upon SiNx layer deposition. Subsequent RTP causes an increase in oxygen and sulfur content at the surface, accompanied with the formation of sulfates. A detailed description of the various chemical structure findings will be discussed in view of their ability to protect and passivate the Si surface.