Study of Boron Precipitates Formed during Front Side Emitter Formation with Boron Spin on Dopant (BSOD) Diffusion in n- type c- Si Solar Cells

Boron precipitates formed during boron source diffusion is an unwanted phenomenon during front side emitter formation in n- type crystalline silicon solar cells. Boron spin on dopant (BSOD) is one of the mostly preferred alternative dopant sources to conventional liquid BBr3, used for p- type emitter formation, but has problems of forming boron precipitates during its diffusion. In this work, we have studied boron precipitates formed by BSOD diffusion and characterized borosilicate glass layer (BSG) and boron rich layer (BRL) at different process parameters. We have tried different process controlled steps to get very less amount of boron precipitates on the surface during diffusion of BSOD source and were successful in reducing boron precipitates from 56% atomic and 36% weight percentages to 0% values for optimized sheet resistance value of 50±5 Ω/ sq for the front side emitter.