INITIAL-STAGES OF ALN THIN-FILM GROWTH ON ALUMINA USING TRIMETHYLAMINE ALANE AND AMMONIA PRECURSORS

A novel precursor combination, trimethylamine alane (TMAA) and ammonia (NH3), has been investigated for the low-temperature chemical vapor-deposition of AlN thin films. The initial stages of AlN growth on alumina powder substrates were studied by Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy. Upon exposure of TMAA to the alumina surface at 300 K, infrared data show the presence of molecular trimethylamine alane on the surface. NH3 reacts with the TMAA derivatized surface at 300 K, removing all of the trimethylamine, and leaving a four-coordinate -NH2- species bound to aluminum in extended networks. Concurrently, the population of alane on the surface is greatly reduced as a result of reaction with NH3 to form -NH2- and liberate H-2. Subsequent exposure of TMAA leads to reaction with the surface -NH2- species and the further adsorption of TMAA. These reactions continue to propagate following additional alternating exposures of NH3 and TMAA, although with decreasing efficiency. The efficiency is increased if the processing is carried out at 400 K. X-ray photoelectron spectroscopy results confirm the formation of AIN after repeated cyclic exposure/processing at substrate temperatures as low as 400 K but not at 300 K.