A method and system are described for increasing the tensile stress in thin films formed on a substrate, such as silicon nitride films. The thin film may be a planar film, or a non-planar film, such as a nitride film formed over a NMOS gate. The thin film is exposed to electro-magnetic (EM) radiation, such as EM radiation having a wavelength component less than about 500 nm. The EM source can include a multi-frequency source of radiation. Additionally, the source of radiation is collimated in order to selectively treat regions of a non-planar film.