The reaction processes occurring during the formation of silicon nitride films were investigated in this study. Films were deposited by pulsed laser ablation (PLA) of a silicon target in nitrogen gas. To reveal reaction processes during the film deposition, both the nitrogen gas pressure and the applied laser fluence were varied. The size of the plume fluorescence and the properties of the resulting film were measured as functions of gas pressure and laser fluence. It was found that the reaction between nitrogen gas and silicon clusters in the plume region effectively takes place under limited conditions. The decomposition of the background gas and multiple collisions of the silicon species in the plume region are essential for the reactive PLA method. Confinement of the species in the plume is one of the key factors to determine the composition and morphology of the film. 0 2003 American Vacuum Society.