The surface groups created during plasma-assisted atomic layer deposition (ALD) of Al2O3 were studied by infrared spectroscopy. For temperatures in the range of 25–150°C, –CH3 and –OH were unveiled as dominant surface groups after the Al(CH3)3 precursor and O2 plasma half-cycles, respectively. At lower temperatures more –OH and C-related impurities were found to be incorporated in the Al2O3 film, but the impurity level could be reduced by prolonging the plasma exposure. The results demonstrate that –OH surface groups rule the surface chemistry of the Al2O3 process and likely that of plasma-assisted ALD of metal oxides from organometallic precursors in general.
Multiple in situ diagnostics have been employed to study the reaction mechanism of plasma-assisted ALD of Al 2 O 3 and the influence of the substrate temperature on the material properties obtained. The results demonstrate that the ALD mechanism is governed by the formation of -CH 3 surface groups and CH 4 byproducts upon Al(CH 3 ) 3 adsorption, while -OH surface groups and H 2 O, CO, and CO 2 by-products are formed during the remote O 2 plasma step. It has been observed that the amount of -OH involved in the ALD process increases with decreasing substrate temperatures which can account for the increase in growth per cycle at lower substrate temperatures. Moreover for substrate at 25 ºC, it has been found that a prolonged plasma exposure in the ALD cycle is effective in improving the film quality by a reduction of the impurity content and an increase in the mass density.
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