SiGe HBTs on bonded SOI incorporating buried silicide layers

A technology is described for fabricating SiGe heterojunction bipolar transistors (HBTs) on wafer-bonded silicon-on-insulator (SOI) substrates that incorporate buried tungsten silicide layers for collector resistance reduction or buried groundplanes for crosstalk suppression. The physical structure of the devices is characterized using cross section transmission electron microscopy, and the electrical properties of the buried tungsten silicide layer are characterized using sheet resistance measurements as a function of bond temperature. Possible contamination issues associated with the buried tungsten silicide layer are investigated by measuring the collector/base reverse diode tics. A resistivity of 50 /spl mu//spl Omega/cm is obtained for the buried silicide layer for a bond anneal of 120 min at 1000/spl deg/C. Collector/base reverse diode tics show a voltage dependence of approximately V/sup 1/2/, indicating that the leakage current is due to Shockley-Read-Hall generation in the depletion region. Fitting of the current-voltage tics gives a generation lifetime of 90 ns, which is as expected for the collector doping of 7 /spl times/ 10/sup 17/ cm/sup -3/. These results indicate that the buried tungsten silicide layer does not have a serious impact on junction leakage.