Critical thickness of Si0.7Ge0.3 layers in the fabrication of hf SiGe HBTs

The critical thickness of Si_0.7-Ge_0.3 films grown at 700°C by APCVD has been evaluated using photoluminescence spectroscopy and Nomarski microscopy after Schimmel etching. Correlations are also made to HF SiGe HBT device characteristics. The critical thickness is located around 300 Å, but the precise determination of a critical thickness is complicated by formation of dislocations at the wafer edge at much lower thicknesses. The growth of Si cap layers up to 1800 Å thick, affects the further development and severity of the resulting defects but does not initiate their formation