Hydrogenated amorphous silicon nitride (a-SiN:H) and silicon carbonitride (a-SiCN:H) films grown byplasma enhanced chemical vapor deposition (PECVD) are widely investigated for their interesting opticaland electrical properties [1]. In this work, we discuss the effect of the deposition power on SiN-based filmsduring plasma deposition. The influence on the optical and mechanical properties of the films wasinvestigated. In order to study this issue on a broader basis, two types of plasmas were applied to deposit0.5 to 1.5 μm a-SiN:H and a-SiCN:H films. First, a-SiN:H and a-SiCN:H films were deposited by electroncyclotron resonance (ECR) PECVD using the same deposition parameters for all films. During thedeposition process, the carbon content in the a-SiCN:H thin films was introduced into the chamber througha pure CH4 gas source to avoid any perturbation on the deposition pressure. Second, a-SiN:H films were deposited by a capacitively coupled plasma reactor CCP-PECVD using a SiH4/NH3/N2/Ar precursor mixture. In both deposition processes, the ion bombardment energy was tuned only by the depositionpower. The mechanical properties of the films were determined ex-situ by profilometry to evaluate theresidual stress using the wafer curvature method and by nanoindentation to determine Young’s modulusand hardness of the films. The thickness and the refractive index were measured by variable anglespectroscopic ellipsometry (VASE). It was observed that the evolution of the residual stress according tothe deposition power in the ECR PECVD was different from the CCP PECVD. Besides, we notice a slightincrease in the refractive index when the residual stress becomes more compressive as illustrated infigure 1 for a-SiN:H and a-SiCN:H films. Through this discussion, we try to have a better understanding ofthe different interactions taking place when the deposition power increases in terms of ion bombardmentenergy. Then, we will study the effect of ion bombardment on the film structure based on the compositionand structure of the films and the hydrogen bond concentration measured by Fourier transmission infraredspectroscopy (FTIR). In addition, we have also investigated the influence of carbon incorporation on a-SiN:H thin film properties. We notice a decrease in the refractive index and an increase in thecompressive residual stress caused by the carbon incorporation.