Abstract
The emitter diffusion depth of wider emitters was found to be shallower than that of narrower emitters for transistors with a TiSi/sub 2/-formed in-situ phosphorus doped polysilicon (IDP) emitter. This dependence of emitter diffusion depth on emitter width W/sub E/ resulted in a large dependence of h/sub FE/ on W/sub E/. We found that the emitter diffusion in emitters with TiSi/sub 2/ formation was shallower than that in emitters without TiSi/sub 2/ formation. We conclude that the dependence of emitter diffusion depth on W/sub E/ is due to variation in phosphorus diffusivity caused by the TiSi/sub 2/ formation. We found by X-ray diffraction measurements that TiSi/sub 2/ 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 TiSi/sub 2/ 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/sub E/ is due to variations in the density of vacancies depending on W/sub E/.
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