Investigation of an Additional Oxidation in-situ Step During Boron Diffusion Processes on P+ Emitter Properties

Diffusion of boron in n-type silicon from preform source when using one step high temperature as drive-in temperature during the diffusion process was found to produce p+ emitter with relatively high surface concentration up to 1020 atoms /cm3, leading to high surface recombination, and resulting, therefore, in the formation of an undesirable boron rich layer (BRL) which is found to be responsible for the degradation of the bulk lifetime. One way to reduce the emitter boron surface concentration and to avoid the formation of the BRL is to add an additional step during the diffusion process which is the oxidation in-situ. The main purpose of the present work is to investigate the effect of a combination between an oxidation at 800°C for 30 min in oxygen ambient following a drive-in step at 910°C for 20 min in nitrogen ambient and a variable boron dose on the properties of the produced emitters.