Tetrakis(ethylmethylamido) Hafnium Adsorption and Reaction on Hydrogen-Terminated Si(100) Surfaces

The surface chemistry of the hafnium-based atomic layer deposition precursor, tetrakis(ethylmethylamido) hafnium (TEMAH), on hydrogen-terminated Si(100) was studied for comparison with the previously reported tetrakis(dimethylamido) hafnium (TDMAH) results by in situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and in vacuo X-ray photoelectron spectroscopy (XPS). The adsorption and reaction experiments were investigated at substrate temperatures between 25 and 400 °C. Gas-phase products were detected by in situ transmission FTIR. Density functional theory (DFT) calculations were performed for gas-phase decomposition as well as the adsorption and reaction of TEMAH onto a hydrogen-terminated model of a Si(100) surface. The formation of cyclo species containing alkyl C on Hf formed by a intramolecular insertion reaction and Hf–H species formed by β-hydride elimination on the surface were identified by XPS at temperatures > 270 °C and a partial pressure of about 0.02 Torr for the former and ATR-FTIR at 100 °C and 0.1 Torr, for the latter. The latter was confirmed by a TEMAH/D 2 O reaction experiment, supporting the previous observations of Hf–H species for TDMAH. The observation of an alkyl C on Hf as a proposed cyclo species is sensitive to experimental conditions, such as residence time, pressure, and temperature. Decompositions at higher pressures had an increased reaction rate. Transmission FTIR detected the formation of the gas-phase products ethylmethylamine and methylethyleneimine or ethylmethyleneimine. DFT calculations predicted the interface between the adsorbed molecules and H-Si(100) to involve Hf–Si, Hf–N–Si, and/or Hf–N–C–Si bonds. The formation of bridged Si–N interfacial bonds provides a thermodynamically allowable way to generate these surface species and is supported by the observation of a N 1s XPS peak associated with Si–N.