LPCVD SiO₂ Layers Prepared from SiH₄ and O₂ at 450 °C in a Rapid Thermal Processing Reactor

Abstract
In this paper experimental results of the silane oxidation kinetics in a rapid thermal low pressure chemical vapor deposition (RTLPCVD) cold wall reactor at 450 °C are presented. For a certain total pressure kept constant in the range of 0.6-4.5 mbar. it is always found a certain threshold silane partial pressure p(th)_SiH4 (decreasing from 0.15 mbar to 0.076 mbar when the total pressure increases) which determines a sharp transition from no film formation to high deposition rates of the SiO₂ layers. Critical partial pressures for lower limits of explosion at room temperature (0.223 mbar) and at deposition temperature (0.17 mbar) are noticed. The film deposition is very sensitive to the changes in the chemical state of the walls. These results may indicate that the silane oxidation process is controlled by the gas phase chain reactions. By keeping constant the total pressure (4.5 mbar), the SiH₄ partial pressure (0.079 mbar) and the total gas flow rate (570 sccm), with the nitrogen varied as a gas balance, an increase-maximum-decrease dependence of deposition rate as a function of O₂/SiH₄ mole ratio is found. Uniform SiO₂ layers (5% around the averaged value) were found for the above CVD conditions and an O₂/SiH₄ ratio equal to 11. Without further process and equipment improvements this process cannot be used in practice.