The feasibility of aluminum nitride thin‐film deposition from chemical reactions of trimethyl aluminum (TMA) with active nitrogen downstream from a N2microwave plasma has been investigated. Chemiluminescence spectra of the downstream reaction showed the presence of CN and Al and the luminescence has been proposed to result from reactions between atomic nitrogen and methyl groups of the TMA. From nitrous oxide titration measurements of the atomic nitrogen concentration, the reaction rate constant has been estimated to bek=3×10−12cm3 s−1. Auger and infrared absorption spectroscopy measurements of a typical film indicated that AlN with carbon contamination in the form of CN had formed.