Evidence for the occurrence of subcutaneous oxidation during low temperature remote plasma enhanced deposition of silicon dioxide films

Chemical vapor deposition of SiO2 is often thought of as an innocuous process by which an insulating layer can be formed without affecting the underlying substrate. Here evidence is presented which indicates that a subcutaneous oxidation process takes place during remote plasma enhanced chemical vapor deposition of SiO2 which oxidizes a few monolayers of the underlying substrate. This oxidation process is evidenced most directly by electrical measurements on metal–insulator semiconductor (MIS) structures fabricated on Ge and GaAs materials. These MIS structures utilize a thin Si interlayer between the semiconductor and the SiO2 to form relatively low interface state density structures. Electrical measurements indicate that depositing SiO2 60 nm in thickness results in consumption of the 1 to 2 nm Si layer through oxidation. The performance of Si metal–oxide semiconductor structures fabricated using deposited oxides degrades as the thickness of the oxide is increased. The presence of a poor quality, highly strained, subcutaneous oxide formed at low temperature could lead to degraded device performance. Work has been carried out in a separate set of experiments to characterize the nature of oxides formed by direct exposure of Si, Ge, GaAs, and CdTe to remote plasma excited oxygen species.