Ti-Si-Ge formation on the extrinsic base of SiGe heterojunction bipolar transistors

This work reports our investigation of a microstructure of self-aligned Ti germanosilicide made on polycrystalline Si/SiGe/Si multi-layers under identical process conditions where SiGe heterojunction bipolar transistors were fabricated The existence of the SiGe layer restricted the growth of the Ti germanosilicide layer and produced protrusions penetrating the underlying polycrystalline layer, whereas these conditions do not exist with TiSi/sub 2/ formation on Si substrates. Each protrusion corresponded to a stacking-faulted single grain of the C49 phase. The microstructure of the thin Ti germanosilicide layer and the deep protrusions caused degradation of the sheet resistance and the contact resistivity of the extrinsic base.