A method is provided for in-situ formation of a thin oxidized AlN film on a substrate. The method includes providing the substrate in a process chamber, depositing an AlN film on the substrate, and post-treating the AlN film with exposure to a nitrogen and oxygen-containing gas. The post-treating increases the dielectric constant of the AlN film with substantially no increase in the AlN film thickness. The method can also include pre-treating the substrate prior to AlN deposition, post-annealing the AlN film before or after the post-treatment, or both.