SPLTRAK Abstract Submission
Chemical surface and interface structure of sulfur-passivated silicon with a SiNx capping layer
Amandee Hua1, Nan Jiang1, Ajay Upadhyaya2, Issac Lam3, Tasnim K Mouri3, Dirk Hauschild1,4,5, Lothar Weinhardt1,4,5, Wanli Yang6, Ajeet Rohatgi2, Ujjwal Das3, Clemens Heske1,4,5
1Department of Chemistry and Biochemistry, University of Nevada Las Vegas (UNLV), Las Vegas, NV, United States
/2School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, United States
/3Institute of Energy Conversion, University of Delaware, Newark, DE, United States
/4Institute for Photon Science and Synchrotron Radiation (IPS), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
/5Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe, Germany
/6Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, CA, United States

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.