M. Kondo et al., Variation in emitter diffusion depth by TiSi2 formation on polysilicon emitters of Si bipolar transistors, IEEE DEVICE, 48(9), 2001, pp. 2108-2117
The emitter diffusion depth of wider emitters was found to be shallower tha
n that of narrower emitters for transistors with a TiSi2-formed in-situ pho
sphorus doped polysilicon (IDP) emitter. This dependence of emitter diffusi
on depth on emitter width W-E resulted in a large dependence of h(FE) on W-
E. found that the emitter diffusion in emitters with TiSi2 formation was sh
allower than that in emitters without TiSi2 formation. We conclude that the
dependence of emitter diffusion depth on W-E is due to variation in phosph
orus diffusivity caused by the TiSi2 formation. We found by X-ray diffracti
on measurements that TiSi2 formation reduced the crystal lattice volume of
the EDP emitter layers by 0.2-0.3%. We attribute this reduction to a reduct
ion 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 emitte
r 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.