Hafnium alkylamides and alkoxide adsorption and reaction on hydrogen terminated silicon surfaces in a flow reactor
This work is a study of the gas phase and surface chemistry of three metalorganic Hf (IVB) precursors - tetrakis(dimethylamido)hafnium (TDMAH), tetrakis(ethylmethylamido)hafnium (TEMAH), and hafnium tert-butoxide (HTB) adsorption and reaction onto hydrogen terminated Si(100), Si(111) and Ge surfaces during low pressure chemical vapor deposition (CVD) in a temperature range of 25 ºC to 300 ºC in a flow reactor. The main methods used include in-situ attenuated total reflectance Fourier transforms infrared spectroscopy (ATR-FTIR), transmission IR, quadrupole mass spectrometer (Q-MS), ab inito density functional theory (DFT), photoelectron spectroscopy (XPS), finite element analysis (FEA), computational fluid dynamics (CFD), and atomic force microscopy (AFM). Possible gas phase decomposition and surface adsorption reactions were surveyed. Reaction energies, vibrational spectra and transition states were calculated for the three precursors and especially the two alkylamido hafnium precursors to support experimental observations. Interfacial bonding and surface catalyzed reaction processes initiated by the adsorption of precursors were detected. For TDMAH and TEMAH, β-hydride elimination and insertion reactions were calculated to be not favorable thermodynamically at these low experimental temperatures. Interfacial bonding during adsorption between the Si was through N-Si and/or C-Si. Decomposition products containing Hf-H species were observed on the surface at room temperature and 100 ºC and the peak assignment was confirmed by deuterated water experiments. The gas phase by-products were mostly dimethylamine (DMA) and a small amount of methylmethleneimine (MMI) or ethylmethylamine (EMA) and methylethyleneimine (MEI). A surface three-member cyclo species was tentatively identified. For HTB, interfacial bonding was Si-O or Ge-O. Another β-hydride elimination generated Hf-OH on the surface and t-butene in the gas phase. A monodentate and bidentate model was proposed for chemisorption of HTB with different concentration on two Si surface orientations at temperatures below 150 ºC. Carbonate was found to form in the film at higher temperatures. The effect of HTB buoyancy driven flow in the ATR flow through cell on thin film topography was observed using AFM of thin films deposited from HTB at 250 ºC. The images showed a wavy surface at the downstream end of the substrate due to roll-type flow predicted by CFD calculations.