Two precursor model for low-pressure chemical vapor deposition of silicon dioxide from tetraethylorthosilicate

The low-pressure deposition of SiO2 from tetraethylorthosilicate (TEOS) is studied. Experiments have been done to get the profile evolution in trenches of different aspect ratios and at various time steps until closure. A fast analytical simulator, using an adsorption/reemission model, which can handle multiple species, has been developed to simulate the profile evolution. The deposition profiles were simulated using a single or a two rate limiting precursor model. It has been previously shown that low-pressure chemical vapor deposition (LPCVD) of SiO2 from other sources, such as silane, can be modeled accurately using only one rate limiting precursor. Comparison of simulation results and experimental profiles of LPCVD of SiO2 from TEOS indicates that a deposition model which includes two rate limiting precursors is consistent with experiments. It is suggested that an intermediate species, having a very high reaction sticking coefficient (Sc∼1), is likely to be formed by gas phase reactions. This along with another species of low reaction sticking coefficient, thought to be from the source gas, react separately with the surface to deposit SiO2. Although a one precursor model gives approximate results for early stages of deposition or for thin coverages, it fails to predict the entire profile evolution, from the initial profile until closure. The two precursor model gives more accurate results for all profiles from the initial until closure. The pressure dependence of the step coverage and deposition rate is due to the change in the ratio of the partial pressures of the two rate limiting precursors with deposition pressure.