Duty ratio-controlled reflective property of silicon nitride films deposited at room temperature using a pulsed-PECVD at SiH₄-NH ₃ plasma

Using pulsed, plasma-enhanced chemical vapor deposition system, silicon nitride films were deposited from SiH₄ and NH₃ at room temperature. Duty ratio was controlled in a range of 20-100% incrementally by 20% at radio frequency bias powers of 50, 70, and 90 W. Reflectance was studied as a function of the process parameters mentioned earlier. The impact of duty ratio on the reflectance was prominent at 70 W and this was strongly correlated with a ratio of high ion energy to low ion energy. Interestingly, the reflectance at other powers yielded a strong correlation with high ion energy flux. A comparison study with other film properties revealed that the reflectance decreased with a decrease in film thickness. A neural network model was constructed to predict various effects of diagnostic variables on the reflectance.