Modeling and analysis of SiO2 deposition during high-purity fused silica glass synthesis by SiCl4 chemical vapor deposition

Large-size and high-purity fused silica glass fabricated by chemical vapor deposition (CVD) has been widely applied to many advanced optical systems. The deposition process is critical during fused silica glass synthesis. In this study, SiO2 deposition at the substrate is modelled and analyzed. First, numerical simulations are performed with the computational fluid dynamics method to predict the flame feature. The gas temperature and velocity agree well with the experimental data. Then, the predicted distributions of gas temperature and concentrations are used as the input parameters to a two-dimensional soot dynamic model. The particle characteristics and particle deposition at the substrate are analyzed. It is found that the particle number density first increases and then decreases in the flame along the axial and radial directions. The predicted mean diameter of the particle is smaller than 50 nm near the substrate surface. The mechanism for SiO2 deposition is different along the substrate surface. In the central region of substrate, the particle deposition is dominant, while in the exterior region the surface chemical deposition is more important.