Atomic layer deposition of HfO2: Growth initiation study on metallic underlayers

The initial stages of HfO₂ film growth by atomic layer deposition (ALD) on Co, Ta, and Pt thin films have been compared by x-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy. The initial tetrakis-dimethylamido(IV) hafnium (TDMAH) adsorption rate was highest on Co and increased with substrate temperature between 150 °C and 250 °C. The initial adsorption rate of TDMAH on Ta was less than on Co or Pt at the same substrate temperatures. The Ta surface also proved to be more stable with regard to TDMAH decomposition as fluctuations of adsorbed Hf and decomposition products were not observed during ALD cycling. Larger amounts of carbon were observed on Pt after TDMAH exposure compared to Co or Ta, suggestive of decomposition products. The XPS Hf(4f) peak measured after initial exposure of TDMAH on Pt showed evidence of two Hf oxidation states at the surface. It is postulated that the reaction of TDMAH and decomposition by-products with available oxygen or hydroxyl molecules at the surface of the various metal underlayers affected the initial growth of HfO₂.