SiGe Heterojunction Bipolar Transistors on Bonded SOI Incorporating Buried Silicide Layers

A technology is described for fabricating SiGe Heterojunction Bipolar Transistors (HBTs) on wafer bonded 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 TEM, 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 characteristics. A resistivity of 50ohm.cm is obtained for the buried silicide layer for a bond anneal of 120mins at 1000C. Collector/base reverse diode characteristics show a voltage dependence of approximately V1/2, indicating that the leakage current is due to Shockley-Read-Hall generation in the depletion region. Fitting of the current/voltage characteristics gives a generation lifetime of 90ns, which is as expected for the collector doping of 7x1017cm-3. These results indicate that the buried tungsten silicide layer does not have a serious impact on junction leakage