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Silicon dioxide films were deposited on crystalline silicon substrates by electron cyclotron resonant (ECR) microwave plasma-enhanced chemical vapor deposition (PECVD). Films were grown on Si〈100〉 substrates at temperatures of 140–600 °C, flow rates of 0.5–10 sccm SiH4, 10–30 sccm O2, and at a pressure of 10−3 Torr. Infrared absorption spectroscopy of the samples indicated no detectable SiH, OH, or SiOH groups. Neither an afterglow chemistry nor He dilution was required to eliminate H impurities as was previously reported for silicon oxide films deposited from rf plasmas. This suggests that significant differences exist between rf and ECR microwave plasma chemistries. We have found that the stoichiometry and index of refraction was not sensitive to oxidant ratio for a wide range of conditions in contrast to other studies. Stoichiometric SiO2 films, with good physical properties, were grown for a much wider range of oxidant ratios relative to those which are characteristic of the rf PECVD technique. In addition, films grown under optimal conditions had infrared absorption spectra nearly identical to those of thermally grown oxides and index of refraction of 1.456, as measured by ellipsometry. We concluded that by using an ECR microwave plasma, SiO2 films with optical and bonding properties comparable to oxides thermally grown at 1000 °C in dry oxygen can be deposited at a low temperature (350 °C) and a low pressure (10−3 Torr) in a O2/SiH4 reactant gas mixture without the need for a carrier gas.

The optical emission spectra of microwave oxygen plasmas under various gas pressures have been investigated. At the gas pressure of 0.01 Torr the plasma-generated particles are mainly excited atomic oxygen and ionic molecular oxygen species. As the gas pressure is increased to a value higher than 0.2 Torr, the plasma contains excited atomic oxygen with emission peaks at 777 and 844 nm and a new emission peak at 759 nm. When the gas pressure reaches 2.9 Torr, only a single emission peak at 759 nm appears. To the best of our knowledge, the optical emission spectra peak at 759 nm has not been reported before. This peak is thought to be due to the presence of excited molecular oxygen species. At low gas pressures, the concentrations of atomic oxygen and ionic molecular oxygen increase linearly with increasing input power to the plasma, while there is no such input power dependence for excited molecular oxygen. SiO2 films have also been fabricated by means of oxidation of silicon wafers in microwave oxygen plasmas at two gas pressures, 0.01 and 2.2 Torr. It is found that the SiO2 films grown at 0.01 and 2.2 Torr have properties similar to those of thermally grown oxide, and that the films grown at 0.01 Torr have a lower value of interface trap density (≊9×10−10 eV−1 cm−2) and a smaller leakage current. Atomic oxygen species are found to be the main species to contribute to the oxidation of silicon in microwave oxygen plasmas.

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An electron cyclotron resonance microwave plasma processing system consisting of a plasma chamber and a processing chamber as well as a new apparatus called the ‘‘species selector and energy controller (SSEC)’’ are described in detail. Silicon dioxide (SiO2) films fabricated using this system without and with the SSEC are used for various experiments to demonstrate that the SSEC can effectively suppress the damaging effects resulting from the bombardment on the substrates and the on-growing films by energetic particles and photons produced in the plasma during film deposition, as well as effectively reduce the upstream diffusion of the reactant gas from the processing chamber to the plasma chamber, thus suppressing the formation of microdust particles due to the heterogeneous gas phase reaction. The film growth for the films fabricated without the SSEC is due mainly to mass-limited reaction and that with the SSEC is due to surface rate-limited reaction. The electronic properties of the SiO2 films fabricated with the SSEC at temperatures higher than 250 °C approach those of high-quality thermally grown silicon oxides. The effects of the SSEC on the film properties and the film growth mechanism are also discussed.