Effect of N2 Gas Flow Ratio in Plasma-Enhanced Chemical Vapor Deposition with SiH4–NH3–N2–He Gas Mixture on Stress Relaxation of Silicon Nitride

Abstract

The effects of N2 gas flow ratios in silicon nitride deposition with SiH4–NH3–N2–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 N2 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 N2 flow ratio, resulting in a higher composition ratio of N/Si. At a higher N2 gas flow ratio, excess N2 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 N2 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.