Faceting at the periphery of the shallow trench isolation during SiGe epitaxial base growth and its influence on SiGe HBT collector-base capacitance are investigated utilizing Technology Computer Aided Design techniques. The simulations suggest peripheral diffusion of boron from the extrinsic base into the intrinsic device may be attributed to depletion of germanium and carbon on the faceted plane that drives the boron diffusion and contributes to the collector-base capacitance, Ccb. Increases in the angle of the facet relative to the {110} plane are shown to reduce Ccb. Moreover, a significant reduction in Ccb was observed with no faceting, suggesting that moving the facet away from the active silicon region was desirable for reducing this key parasitic capacitance. These results serve to highlight the role that faceting plays in extrinsic device parasitic capacitances and identifies a focus area for scaling the device capacitance.

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