Spectroscopic study of AlN film formation by the sequential reaction of ammonia and trimethylaluminum on alumina

Aluminum nitride is grown on an alumina substrate by several sequential exposures to trimethyl aluminum and ammonia. Broad similarities are evident between the chemistry in this case and that found for the reaction between trimethylaluminum and water except that temperatures of in excess of 500 K are required to form AlN layers whereas alumina is formed at room temperature. It is found, using infrared spectroscopy to examine the surface species formed during repeated sequential adsorption of trimethylaluminum and ammonia, that trimethylaluminum initially reacts to form an adsorbed dimethylaluminum species. This reacts with ammonia to initially form a Lewis acid-base adduct which subsequently reacts to form bridging and terminal NH2 species. The first methyl group in the adsorbed species is found to be more reactive than the second, an effect that was also noted for reactions with water. The ultimate formation of AlN films by several sequential exposures to trimethylaluminum and ammonia is confirmed using X-ray photoelectron spectroscopy and gravimetrically by weighing the samples after several trimethylaluminum and ammonia exposure cycles.