Mechanistic feature-scale profile simulation of SiO2 low-pressure chemical vapor deposition by tetraethoxysilane pyrolysis

Abstract

Simulation of chemical vapor deposition in submicron features typical of semiconductor devices has been facilitated by extending the EVOLVE [T. S. Cale, T. H. Gandy, and G. B. Raupp, J. Vac. Sci. Technol. A 9, 524 (1991)] thin film etch and deposition simulation code to use thermal reaction mechanisms expressed in the Chemkin format. This allows consistent coupling between EVOLVE and reactor simulation codes that use Chemkin. In an application of a reactor-scale simulation code providing surface fluxes to a feature-scale simulation code, a proposed reaction mechanism for tetraethoxysilane [Si(OC2H5)4] pyrolysis to deposit SiO2, which had been applied successfully to reactor-scale simulation, does not correctly predict the low step coverage over trenches observed under short reactor residence time conditions. One apparent discrepancy between the mechanism and profile-evolution observations is a reduced degree of sensitivity of the deposition rate to the presence of reaction products, i.e., the by-product inhibition effect is underpredicted. The cause of the proposed mechanism’s insensitivity to by-product inhibition is investigated with the combined reactor and topography simulators. This is done first by manipulating the surface-to-volume ratio of a simulated reactor and second by adjusting parameters in the proposed mechanism such as the calculated free energies of proposed surface species. The conclusion is that simply calibrating mechanism parameters to enhance the by-product inhibition can improve the fit to profile evolution data; however, the agreement between with reactor-scale data and simulations decreases. Additional surface reaction channels seem to be required to simultaneously reproduce experimental reactor-scale growth rates and feature-scale step coverages.