CoSi2 and TiSi2 for Si/SiGe heterodevices

Novel Si/SiGe heterodevices with enhanced performance demand low thermal budget contact formation. CoSi2 and TiSi2 can meet this requirement. The investigation of self-aligned rapid thermal processes for the formation 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 device 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 implanted layers below 6 mu Omega cm(2) have been derived from TLM structures. The silicide formation is severely affected by SiGe. Therefore the 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 measurements on SiGe layers confirmed the formation of a mixture of CoSi and Co germanides with higher resistivity due to the interfacial reaction and the accumulation of Ge at the interface, which may act as a diffusion barrier. The choice of a Si cap above SiGe, whose thickness was properly adjusted to the material consumption correlated with the resulting silicide thickness, is proposed. The process and the performance 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 advantage of using TiSi2.