Carbon nitride (CNx) thin films with high nitrogen content were deposited on Si (100) substrates by using electron cyclotron resonance nitrogen plasma assisted pulsed laser deposition (ECR-PLD), and their thermal stability were studied by examining their composition and bonding behaviors upon post-deposition heat annealing in vacuum and in nitrogen ambient. The as-deposited films contain nitrogen content varying around 50 at.% and are primarily amorphous containing several bonding configurations between carbon and nitrogen atoms with different bond components depending on bias voltage applied to the substrates. In addition to the D, G and L Raman bands reported for most CNx thin films, three prominent Raman peaks were observed at 170, 260 and 616 cm(-1) from our as-deposited films. Composition analysis by Rutherford backscattering spectroscopy measurement and chemical structure characterization by Fourier Transform infrared spectroscopy and Raman scattering measurements showed that the ECR-PLD deposited CNx thin films are quite stable upon annealing in vacuum up to 750 degrees C. The CNx films exhibit even higher thermal stability in nitrogen ambient. (c) 2008 Elsevier B.V. All rights reserved.