In this paper, results about tuning of electrical properties of a-SION:H thin film is presented. Issues related to structural and electrical characterization of these layers is investigated. Ellipsometry is used to determine accurately layer thickness and Kelvin Force Microscopy (KFM) permits to characterize local electrical properties. Results emphasize that tuning layer process parameter permit to modify surface and volume conduction. More particularly, increasing of Si-environment increases volume conduction and charges retention. So, local electrical properties of dielectric film can be engineered with this process