Modeling of polysilicon dopant diffusion for shallow-junction bipolar technology

The diffusion of boron and arsenic from polycrystaline silicon layers into bulk silicon is characterized. Diffusion coefficients are extracted and compared with bulk values used in the SUPREM III process simulator. Results show that for concentrations below nithere is enhanced diffusivity and diffusion "tails" are observed. Arsenic profiles show a dose dependence of the tail region. Under conditions of co-diffusion of boron and arsenic in poly, the boron diffusion is dramatically retarded and no tail region is observed in the bulk. Implications of diffusion in and from polysilicon will be discussed for bipolar technology.