Low Stressed In-situ Boron doped Poly SiGe Layers for High-Q Resonators

In-situ boron doped LPCVD polycrystalline silicongermanium (poly SiGe) layers are deposited from SiH4 and GeH4 with 0.2% diborane (B2H6) in argon (Ar) as dopant precursor at 430 C and 0.2 mbar. The characterized layers show very low tensile stress (12 MPa) for the diborane mixture flow of 50 sccm for fixed SiH4 and GeH4 flow. However, an increase in diborane mixture flow to 100 sccm at the same SiH4 and GeH4 flow results in a transition from low tensile to low compressive stress (3 MPa) in the deposited layers. The sheet resistance of these in-situ doped layers is two orders of magnitude lower compared to undoped layers with the same Ge contents. However, we have not observed any appreciable difference in the sheet resistance of these in-situ doped layers due to the saturation limit of the active dopants in the deposited layers. Hence, the deposited layers are found to be suitable for post processing high-Q resonators on top of readily available CMOS circuitry not only due to low thermal budget requirements (< 450 C) but also because of their superior electrical and mechanical properties. Additionally, the analyzed samples through XRD reveal the preferential columnar grain growth on 100 nm SiO2 that can be exploited to have steep etch profiles with SF6 and O2 plasma at cryogenic temperatures.