Using a pulsed-plasma enhanced chemical vapor deposition system, silicon nitride films were deposited at room temperature. A refractive index was examined in the range of bias power and duty ratio, 200-800 W and 40-90%. respectively. Ion energy diagnostics was related to the refractive index. The refractive index decreased with decreasing the duty ratio at all powers but 800 W. For all the duty variations at all powers but 200 W. the refractive index was strongly correlated with the ion energy flux. The refractive index varied between 1.662 and 1.817. Using a neural network model, the refractive index was optimized. (C) 2010 Elsevier B.V. All rights reserved.