In situ mass spectrometry is implemented in AlGaN/GaN/AIN metalorganic chemical vapor deposition processes on SiC substrates as a real-time process- and wafer-state metrology tool. Dynamic chemical sensing through the process cycle, carried out downstream from the wafer, revealed generation of methane and ethane reaction by-products as well as other residual gas species. The methane and ethane by-products are believed to reflect the two parallel chemical reaction pathways leading to GaN-based materials growth, namely the gas phase adduct formation route and the direct surface decomposition of the metalorganic precursor, respectively. Having detected both types of by-products as evidence for the presence of both paths, we monitored and integrated the methane and ethane signals to derive a real-time film thickness metric. Integrating the sum of the two by-product signals in this manner through the AlGaN growth period (similar to 1 min or less) enabled us to predict the AlGaN cap layer thickness (similar to 20 nm) to within similar to 1% or similar to 0.2 min precision. This was verified by postprocess x-ray reflectance measurement, which produced a thickness map over the 2 in. wafer and yielded an average thickness for the AlGaN cap layer for comparison to the real-time mass spectrometry. These results demonstrate an opportunity for advanced process control based on real-time in situ chemical sensing, with the promise of major benefit in reproducibility and cost reduction in AlGaN/GaN-based semiconductor manufacturing. (c) 2005 American Vacuum Society.