A hydrogen atomic beam generated by microwave discharge was successfully used for dissociating trimethylaluminum (TMA) at the low substrate temperature of 300 °C. The results indicate that ‘‘H’’ atomic beam can stimulate the clean and complete dissociation of organometallics at substrate temperatures only slightly above the onset of thermal pyrolysis of the organometallics. The clean dissociation of TMA is dependent on both thermal as well as plasma stimulation. Residual oxygen present in our system resulted in growth of high quality Al2O3films. In a clean metalorganic chemical vapor deposition system H atomic beam can be used to dissociate organometallics at significantly lower temperatures (300–400 °C) relative to the presently used growth temperature of 700 °C.