| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF-MoM |
| Session: | ALD Precursors and Surface Reactions |
| Presenter: | Vincent Vandalon, Eindhoven University of Technology, Netherlands |
| Authors: | V. Vandalon, Eindhoven University of Technology, Netherlands W.M.M. Kessels, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
The surface chemistry during atomic layer deposition (ALD) of Al2O3 and Pt were investigated with vibrational broadband sum-frequency generation (BB-SFG) spectroscopy. These two processes represent examples of two different material classes for ALD: For metal oxides, ALD of Al2O3 with Al(CH3)3 and H2O as reactants is the prototypical ALD process. Whereas for noble metals, ALD of Pt using MeCpPtMe3 and O2 as reactants can be considered as prototypical.
Vibrational BB-SFG spectroscopy is excellently suited for in-situ studies of the surface chemistry governing ALD because of its inherent interface selectivity, submonolayer sensitivity, and short acquisition times. It is a nonlinear optical technique which uses the mixing of picosecond visible and femtosecond mid-IR pulses to probe the vibrational response of surface groups. The unique nature of BB-SFG allows the in-situ investigation of the surface chemistry on both reflective and transparent substrate without any modifications to the setup.
For ALD of Al2O3, both the -CH3 and -OH surface groups ruling the growth mechanism were monitored in-situ with BB-SFG. This study resulted in several new insights into the surface chemistry of this ALD process: Persistent -CH3 groups were observed after the H2O half-cycle at low temperatures and these significantly influence the growth [Vandalon and Kessels, Appl. Phys. Lett., 2016, Vol. 108] Moreover, the reaction kinetics were studied as a function of temperature and reaction cross sections for both half-cycles were quantified. At low temperatures it was found that the reaction kinetics in the H2O half-cycle showed a strong dependence on surface coverage. Furthermore, the initial growth of Al2O3 on H-terminated silicon was investigated.
ALD of Pt was studied with BB-SFG by probing the C-H stretch region around 3000 cm-1. After precursor exposure, the signature of the C-H stretch mode of the -CH3 groups was clearly observed. Moreover, a spectrally broad feature was observed in the BB-SFG spectra. This contribution was assigned to unsaturated C chains such as present in the Cp ring. Dosing gas phase MeCp on a Pt and SiO2 surfaces showed a similar broad feature, supporting this assignment. After O2 exposure both the -CH3 and Cp related signals disappeared. These results suggest that after precursor adsorption both -CH3 and Cp rings (or parts of it) are present at the surface and these groups are removed in the O2 half-cycle.