Effect of N 2 Gas Flow Ratio in Plasma-Enhanced Chemical Vapor Deposition with SiH 4 –NH 3 –N 2 –He Gas Mixture on Stress Relaxation of Silicon Nitride

The effects of N 2 gas flow ratios in silicon nitride deposition with SiH 4 –NH 3 –N 2 –He gas mixtures at a temperature of 275 °C on stress relaxation have been investigated. We have demonstrated that film stress can be controlled in the range from -692 MPa (compression) to 170 MPa (tension) by increasing N 2 gas flow ratio. From the evaluation of the composition ratio of N/Si, film density, and bonding structure, the relationships between film stress and these properties are investigated. The amount of nitrogen incorporated into the film as N–H bonds increased with increasing N 2 flow ratio, resulting in a higher composition ratio of N/Si. At a higher N 2 gas flow ratio, excess N 2 gas in the plasma may disturb the ion bombardment of ionized species on the film surface, resulting in a decrease in the film density. The higher N 2 gas flow ratio leads to the generation of a Si–N bonding structure with a larger bond angle at the nitrogen atom site due to bond-strain relaxation, leading to a higher frequency of Si–N stretching vibration. Therefore, a nitrogen-richer SiN film with many N–H bonds and a lower film density exhibits bonding structures with a lower bond strain, leading to the relief of film stress.