Tetrakis(ethylmethylamido)hafnium and water are commonly used precursors for atomic layer deposition of HfO2. Using reflection absorption infrared spectroscopy with a buried-metal-layer substrate, we probe surface species present during typical deposition conditions. We observe evidence for thermal decomposition of alkylamido ligands at 320 degrees C. Additionally, we find that complete saturation of the SiO2 substrate occurs in the first cycle at approximate to 100 degrees C whereas incomplete coverage is apparent even after many cycles at higher temperatures. The use of this technique as an in situ diagnostic useful for process optimization is demonstrated. Published by Elsevier B.V.