The Low-Pressure, Chemical Vapor Deposition of SiO2 Layers Using CO2 as the Oxygen Source

Hill Aerospace Museum

Silicon Dioxide (SiO₂), useful in microelectronics and microfabrication, is often deposited via low pressure CVD (LPCVD). One method is to use dichlorosilane (DCS) and an oxidizer such as N₂O:SiH₂Cl₂+2N₂O->SiO₂+2N₂+2HCl. Carbon dioxide (CO₂) is isoelectric and should be able to replace N₂O as an oxidizer. Little work has been done with CO₂ and DCS at low pressure. We deposited rich SiO₂ on silicon wafers using CO₂ and DCS over the ranges of .6 to 5 Torr and 800 to 950ºC. We used ellipsometry and SEM-EDX to measure the thickness, refractive index, and chemical composition of each sample. We found that most of the films were hazy, i.e. light scattering off the surface was obvious to the eye. So little SiO₂ formed at .6 Torr and 800ºC that we concluded substrate oxidation rather than deposition occurred. It was the least silicon rich and least hazy. Around 5 Torr we achieved SiO₂ deposition with a refractive index of 1.6, atomic ratio of Si to O of 40:60, and the haziest surface.