A 3-in-1 doping process for interdigitated back contact solar cells exploiting the understanding of co-diffused dopant profiles by use of PECVD borosilicate glass in a phosphorus diffusion

Abstract

Boron and phosphorus doping of crystalline silicon using a borosilicate glass (BSG) layer from plasma-enhanced chemical vapor deposition (PECVD) and phosphorus oxychloride diffusion, respectively, is investigated. More specifically, the simultaneous and interacting diffusion of both elements through the BSG layer into the silicon substrate is characterized in depth. We show that an overlying BSG layer does not prevent the formation of a phosphorus emitter in silicon substrates during phosphorus diffusion. In fact, a BSG layer can even enhance the uptake of phosphorus into a silicon substrate compared with a bare substrate.From the understanding of the joint diffusion of boron and phosphorus through a BSG layer into a silicon substrate, a model is developed to illustrate the correlation of the concentration-dependent diffusivities and the emerging diffusion profiles of boron and phosphorus. Here, the in-diffusion of the dopants during diverse doping processes is reproduced by the use of known concentration dependences of the diffusivities in an integrated model. The simulated processes include a BSG drive-in step in an inert and in a phosphorus-containing atmosphere.Based on these findings, a PECVD BSG/capping layer structure is developed, which forms three different n++−, n+− and p+−doped regions during one single high temperature process. Such engineered structure can be used to produce back contact solar cells.