In situ transmission infrared spectroscopy of high-k oxide atomic layer deposition onto silicon surfaces

Ultra-thin aluminum oxide (Al2O3 ) and hafnium oxide (HfO2) layers have been grown by atomic layer deposition (ALD) using tri-methyl-aluminum (TMA) and tetrakis-ethyl-methyl-amino-hafnium (TEMAH) respectively with heavy water (D2O) as the oxidizing agent. Several different silicon surfaces were used as substrates such as hydrogen terminated silicon (H/Si), SC2 (or RCA 2) cleaned native silicon oxide (SiO2/Si), and silicon (oxy)nitride. In-situ transmission Fourier transform infrared spectroscopy (FTIR) has been adopted for the study of the growth mechanisms during ALD of these films.The vibrational spectra of gas phase TEMAH and its reaction byproducts with oxidants have also been investigated. Density functional theory (DFT) normal mode calculations show a good agreement with the experimental data when it is combined with linear wave-number scaling method and Fermi resonance mechanism. Ether (-C-O-C-) and tertiary alkylamine (N(R1R2R3)) compounds are the two most dominant products of TEMAH reacting with oxygen gas and water. When ozone is used as the oxidant, gas phase CH2O, CH3NO2, CH3-N=C=O and other compounds containing -(C=O)- and --C- O-C- (or --O-C-) segments are observed.With substrate temperatures less than 400oC and 300oC for TMA and TEMAH respectively, Al oxide and Hf oxide ALD can be appropriately performed on silicon surfaces. Thin silicon (oxy)nitride thermally grown in ammonia on silicon substrate can significantly reduce silicon oxide interlayer formation during ALD and post-deposition annealing. The crystallization temperature of amorphous ALD grown HfO2 on nitridized silicon is 600oC, which is 100oC higher than on the other silicon surfaces.When HfO2 is grown on H/Si(111) at 100oC deposition temperature, minimum 5 -- 10 ALD cycles are required for the full surface coverage. The steric effect can be seen by the evolution of the H-Si stretching mode at 2083 cm-1. The observed red shift of H-Si stretching to ~ 2060 cm-1 can be caused by Si-H...Hf interactions or by the dielectric screening effect of as-grown high-κ moiety. A summary of local bonding models with vibrational mode assignments of the adsorbed TMA and TEMAH on silicon surfaces is presented based on the analysis of the substructure of silicate interfacial band at 900 -- 1100 cm-1.