Summary: The scaling down of the dimensions of Metal Oxide Semiconductor Field-Effect Transistors (MOSFET) in the microelectronics industry is approaching a fundamental limit due to direct electron tunneling through the silicon dioxide (SiO 2) gate dielectric. Consequently, a higher dielectric constant (κ) material must be engineered to replace SiO2 (κ = 3.9) so that the gate dielectric can be made physically thicker to prevent leakage current and enhance reliability. However, the solution is not as straightforward as simply replacing SiO2 with a higher-κ material. The high-κ dielectric must meet several stringent requirements in order to effectively replace SiO2. This is proving to be a difficult problem to solve, and therefore there is a need for a segue material to extend MOSFET scaling for the near term. Silicon oxynitride (SiOxN y, κ: 3.9–7.0) has received much attention as a segue material, due to its enhanced durability and diffusion barrier properties. Several methods have been investigated for producing SiOxNy, however much work needs to be done to develop a method, which allows control over the nitrogen composition and location to produce a film with a high enough electronic quality to replace SiO2. To this end, a combined electron cyclotron resonance (ECR) and radio frequency (RF) plasma process was employed to study SiOxNy films with the goal of preserving the high quality silicon-SiO2 interface and increasing the nitrogen content towards the surface of the film to increase κ. Specifically, the plasma nitridation of thermal SiO2 films, and the plasma oxynitridation of bare silicon substrates were studied. Plasma process parameters such as; plasma mode, chamber pressure, RF bias magnitude, ECR power, and gas feed composition were varied allowing the ability to tailor the film properties. Selection of the proper plasma parameters has afforded control over film thickness, nitrogen content, nitrogen location, density of interface trapped charge ( Dit), and density of fixed charge (Dfc). Spectroscopic ellipsometry (SE), Auger electron spectroscopy (AES), atomic force microscopy (AFM), capacitance-voltage (C-V) measurements, and thermal annealing studies were used to characterize the films and are presented throughout.