Optimization of LPCVD phosphorous-doped SiGe thin films for CMOS-compatible thermoelectric applications

The incessant downscaling of building blocks for memory and logic in computer chips requires energy-efficient devices. Thermoelectric-based temperature sensing, cooling as well as energy harvesting could be useful methods to reach reliable device performance with stable operating temperatures. For these applications, complementary metal-oxide-semiconductor (CMOS)-compatible and application ready thin films are needed and have to be optimized. In this work, we investigate the power factor of different phosphorous-doped silicon germanium (SiGe) films fabricated in a 300 mm CMOS-compatible cleanroom. For the thermoelectric characterization, we used a custom-built setup to determine the Seebeck coefficient and sheet resistance. For sample preparation, we used low pressure chemical vapor deposition with in situ doping and subsequent rapid thermal annealing on 300 mm wafers. Thin film properties, such as film thickness (12-250 nm), elemental composition, crystallinity, and microstructure, are studied via spectroscopic ellipsometry, x-ray photoelectron spectroscopy, x-ray diffraction, atomic force microscopy, and TEM. The SiGe-based thin films vary in the ratio of Si to Ge to P and doping concentrations. A power factor of 0.52 mW/m K2 could be reached by doping variation. Our results show that SiGe is a very attractive CMOS-compatible material on the 300 mm wafer level and is immediately ready for production of thermoelectric embedded applications.