Using a pulsed-plasma-enhanced chemical vapor deposition system, silicon nitride films were deposited at room temperature in SiH4-NH3-N-2 plasma. The impact of radio frequency bias power and duty ratio on a refractive index is detailed by using an ion energy analysis system. A decrease in the duty ratio resulted in a decrease in the refractive index at all powers but 60 W. As duty ratio is varied at lower powers, the refractive index strongly depended on E-h/E-l. Another strong, but negative correlation was noted at high powers. An increase in the bias power in the range of 60-100W led to a decrease in the refractive index at all duty ratios. For the variations in the bias power, no correlation was observed. For all the variations in the power and duty ratio, the refractive index varied from 1.60 to 2.21. Very high refractive index could be achieved by controlling duty ratio at 60 W. A neural network model was constructed using the experimental data. The model demonstrated a R-2 of 86.4%. It was used not only to investigate the effect of the diagnostic variables, but to optimize the refractive index. (C) 2010 Elsevier B. V. All rights reserved.