Plasma Deposition of a Amorphous Silicon Dopant Sources

The basic idea of a dry solar cell process is to minimize the application of wet chemical process steps. By using plasma-enhanced chemical processes, many steps can be converted from wet chemical to dry plasma processes. In previous studies it could be demonstrated, that it is possible to deposit a phosphorus silicate glass (PSG) via plasma-enhanced chemical vapor deposition (PECVD) processes and to use these layers for emitter diffusion in a high-temperature furnace. In order to enable the removal of the dopant source combined with an etch back of the highly phosphorus containing top layer of the emitter (so called "dead layer") within a single plasma etch step, the use of doped amorphous silicon as dopant source has been investigated throughout this study. To the knowledge of the authors, the application of a-Si as dopant source prior to high temperature diffusion is almost unexplored; therefore the paper investigates the suitability of this approach for industrial solar cell processing. As shown, doped a-Si layers offer a diffusion of phosphorus as well as boron, but an oxidation of the layer while the high temperature diffusion could not be avoided straightforwardly.