COSI2 AND TISI2 FOR SI SIGE HETERODEVICES

Novel Si/SiGe heterodevices with enhanced performance demand low therm al budget contact formation. CoSi2 and TiSi2 can meet this requirement . The investigation of self-aligned rapid thermal processes for the fo rmation of CoSi2 (at 600-650 degrees C) and TiSi2 (at 650-750 degrees C) and their application to n-channel hetero field effect transistors and heterobipolar transistors (HBTs) is described and effects on the d evice performance are presented. Specific resistances of around 20 mu Omega cm for CoSi2 and 17 mu Omega cm for TiSi2 could be confirmed for the Si/SiGe heterosystem. Contact resistances on n(+)-phosphorous imp lanted layers below 6 mu Omega cm(2) have been derived from TLM struct ures. The silicide formation is severely affected by SiGe. Therefore t he compound formation of CoSi2 in the Co/Si and the Co/Si1-xGex system has been investigated and compared as a function of annealing time in a temperature range from 400 to 600 degrees C. X-ray diffraction meas urements on SiGe layers confirmed the formation of a mixture of CoSi a nd Co germanides with higher resistivity due to the interfacial reacti on and the accumulation of Ge at the interface, which may act as a dif fusion barrier. The choice of a Si cap above SiGe, whose thickness was properly adjusted to the material consumption correlated with the res ulting silicide thickness, is proposed. The process and the performanc e of SiGe HBTs could be improved by the introduction of a Ti salicide process: base resistances yield values around 20 Omega (for an emitter area of 0.8 X 5 mu m(2)). Nearly ideal Gummel plots confirm the advan tage of using TiSi2.