UV-laser photolysis of trimethylaluminum for Al film growth

Abstract

The photodissociation of dimerized trimethylaluminum, Al2(CH3)6, (TMA) by KrF laser irradiation (248 nm, 5 eV) has been investigated. Optical spectroscopy was used to measure the emission intensities I of excited photofragments as a function of TMA pressure P. The intensities of neutral Al atoms and CH radicals were observed to have quite different pressure dependencies indicating that they were formed by different mechanisms. IAl and ICH initially increased linearly with increasing pressure, however IAl saturated at P≂0.6 Torr (80 Pa) while ICH reached a maximum at P≂0.01 Torr (1.33 Pa) and then decreased with further increases in pressure. Based upon the experimental results and molecular orbital calculations, a model was proposed for the photolysis of TMA. The primary conclusions were that Al atoms were formed directly by a cascade process initiated by a single-photon absorption while CH radicals were generated through a chemical reaction between photofragments. An analysis of the steps involved in the cascade process suggests that it should be possible to grow high-purity, essentially C-free, Al films by photodecomposition of TMA in ultrahigh vacuum in agreement with preliminary experiments.