Effect of hyperthermal annealing on LPCVD silicon nitride

The objective of this paper is to understand the effects of 1100°C annealing on film thickness, refractive index and especially residual stress of low-pressure chemical vapor deposition (LPCVD) silicon nitride films. The annealing effect on Young's modulus of silicon nitride films is also discussed. For these purposes, a number of 1100°C furnace annealing processes in N2 atmosphere were carried out. With the increase of annealing time, film thickness decreases exponentially and correspondingly the refractive index increases. Both film thickness and refractive index reach a stable value after several times annealing. Due to the film densification and viscous flow, residual stress of Si–Si3N4 system increases in the first 10min annealing treatment and then decreases in the following annealing processes. Based on the Maxwell viscoelastic model, an improved model which considers film densification and viscous flow simultaneously is built to explain the effect of annealing process on residual stress.