DIFFUSION OF BORON INTO SILICON FROM BOROSILICATE GLASS USING RAPID THERMAL-PROCESSING

Diffusion of boron into Si from borosilicate glass (BSG) using rapid thermal processing (RTP) is studied. Sheet resistance of diffused layers in RTP doping decreases more steeply with diffusion time t than t-1/2 for short diffusion times and low diffusion temperature. This corresponds to a rapid increase in surface boron concentration at the initial stage of diffusion. This is attributed to the presence of thin native oxide between BSG and Si. The time required for surface boron concentration to be saturated is shorter for higher boron-concentration BSG. Boron diffusion in Si is enhanced for diffusion from BSG in which the boron concentration is larger than 18 atom percent (a/o). Enhanced diffusion is also observed for furnace diffusion from BSG where the boron concentration is larger than 18%, but not for 7% BSG. Enhanced diffusion is not observed during RTP if BSG is not present. From these results, it is clarified that the origin of enhanced diffusion is not in RTP but inherent in the BSG/Si system itself, and it occurs for diffusion from high boron-concentration BSG.