Trimethylaluminum (TMA) is often used as a source gas for composite semiconductor or gate insulator films containing aluminum. However, TMA readily reacts with O-2 and this reaction causes film performance to degrade. Film formation is affected by the decomposition properties of the source gas, so it is important to investigate the influence of O-2 on the decomposition behavior of TMA. The starting decomposition temperature of TMA was 332 degrees C in an Al2O3 tube filled with Ar gas, and the decomposition rate increased rapidly above 380 degrees C. However, when TMA was heated in an atmosphere containing more than 1 ppm O-2, the temperature at which TMA began to decompose increased. It is assumed that this phenomenon resulted from the formation of methoxy groups through reaction between TMA and O-2. Thus, the presence of O-2 in TMA not only caused the films to be contaminated with oxygen atoms but also altered the decomposition behavior of TMA. This means that fluctuations in the deposition rate and film performance are caused by the presence of O-2 in TMA when deposition conditions are otherwise kept constant. As a result, it is desirable that the O-2 concentration present in TMA is maintained below 0.1 ppm during deposition. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3517080] All rights reserved.