Comparative life cycle assessment of silicon and silicon carbide substrates for RF applications

This thesis presents a comparative cradle-to-gate life cycle assessment of silicon and silicon carbide substrates intended for gallium nitride high-electron-mobility transistor devices. The results indicate that silicon carbide substrates have environmental impacts between six and twenty times greater than silicon, depending on the indicator. The global warming potential was shown to be 15 times greater. The primary driver is the energy-intensive physical vapor transport process used to grow silicon carbide, with over 100 times higher climate change, ecotoxicity, and energy use impacts compared to the Czochralski process used for silicon. The study aims to fill a knowledge gap due to a lack of recent, accessible, high-quality process data in the semiconductor industry. The results, as well as the limitations, highlight the need for greater data transparency in semiconductor manufacturing. Further life cycle assessments and research into potential lower impact technologies, such as high-temperature chemical vapor deposition silicon carbide growth and substrate liftoff methods, are recommended to continue moving the industry in a sustainable direction.