Phosphorous emitter etch back and bulk hydrogenation by means of an ECR-hydrogen plasma applied to form a selective emitter structure on mc-Si

In this paper, we study the effect of hydrogen-electron cyclotron resonance plasma (ECR plasma) on the phosphorous-doped emitter of a solar cell based on multicrystalline silicon (POLIX®). The purpose of this experiment is to realise a selective emitter structure, using the front metal contacts as a mask. We show that hydrogen plasma etches the surface of the emitter away, and simultaneously diffuses into the silicon and increase the bulk lifetime. Both minority carrier lifetime and etch rate depend on the grain orientation. Hydrogen diffusion is hindered by the high phosphorous concentration of the emitter, as shown on the SIMS profiles. Besides, SIMS profiles are revealing an anomalous behaviour of phosphorous, which diffuses into the silicon at temperatures as low as 350°C on (1 0 0) oriented grains.