Variation in emitter diffusion depth by TiSi2 formation on polysilicon emitters of Si bipolar transistors

The emitter diffusion depth of wider emitters was found to be shallower than that of narrower emitters for transistors with a TiSi₂-formed in-situ phosphorus doped polysilicon (IDP) emitter. This dependence of emitter diffusion depth on emitter width W _E resulted in a large dependence of h_FE on W_E . We found that the emitter diffusion in emitters with TiSi₂ formation was shallower than that in emitters without TiSi₂ formation. We conclude that the dependence of emitter diffusion depth on W_E is due to variation in phosphorus diffusivity caused by the TiSi₂ formation. We found by X-ray diffraction measurements that TiSi₂ formation reduced the crystal lattice volume of the IDP emitter layers by 0.2-0.30%. We attribute this reduction to a reduction in packing density due to a supersaturation of vacancies caused by the TiSi₂ formation. We believe that the vacancy supersaturation decreases the density of interstitials in the emitter regions, which decreases the emitter diffusion depth, and that the dependence of emitter diffusion depth on W_E is due to variations in the density of vacancies depending on W_E