Effects of surface topography on oxide deposition rates using TEOS/O2 chemistry

The effect of surface topography on ${\mathrm{TEOS/O}}_2$ oxide deposition rates is investigated. It is found that the oxide thickness is significantly less on the top layers of topography used in static random access memory device structures compared to flat wafers for fixed conditions of power, flow, and pressure. The total mass deposition increases, however, in the presence of topography. These effects can be understood from the perturbation on the precursor radical densities near the surface caused by the surface topography. A simple model based on the diffusion-reaction equation with an appropriate boundary condition is proposed to explain the effect. The boundary condition is developed as an effective macroscopic reflection coefficient that takes into account trapping effects of film precursors in the topography. The application of the model to the experimental data gives an estimate for the effective microscopic surface reflection coefficient of $\text{r≈0.87}$ for the oxide film precursors.