Tantalum silicon nitride films have good potential to be used as hard coatings and diffusion barriers. In this work, films with different composition were deposited using a magnetron sputter under varying nitrogen flow rates. The composition, microstructure, thermal stability and electrical resistivity have been investigated. In the as-deposited state. all films consist of amorphous TaSi(x)O(y,) Ta(x)O(y), Ta(x)N(y) and TaSi(x) compounds. The composition of films is affected by N(2) flow rate. The resistivity of the as-deposited films increases with N concentrations. At elevated temperatures, all films show good thermal stability to at least 800 degrees C, while film with high Si concentration is largely amorphous at 900 degrees C because of highly stable TaSi(x)O(y) compounds. This study suggests that the TaSi(x)O(y) compounds could be the key factor in enhancing thermal stability of Ta-Si-N-O films. (C) 2009 Elsevier B.V. All rights reserved.