A method is provided for forming a thin film layer on a substrate. The method includes the steps of doping a thin surface layer on the substrate with low energy ions of a dopant material, and heating the thin surface layer sufficiently to produce a reaction between the dopant material and the surface layer. The heating step is performed simultaneously with at least part of the doping step. The doping step may utilize plasma doping of the thin surface layer. In one embodiment, the doping step includes plasma doping of a silicon oxide layer with nitrogen ions. The heating step may utilize thermal conduction or heating with radiation, such as heating with optical energy. The process may be used for forming dielectric layers having a thickness of 50 angstroms or less.