Role of ions in electron cyclotron resonance plasma-enhanced chemical vapor deposition of silicon dioxide

Abstract

Silicon dioxide films were deposited in an electron cyclotron resonance plasma onto substrates at temperatures ranging from 65 to 200 °C. In order to determine the effect of ions on the deposition, both ion flux and ion energy were investigated. The ratio of ion flux to deposition flux was found to be a significant parameter and this ‘‘flux ratio’’ was varied between 8 and 100. Mean ion energy was investigated at 10, 50, and 75 eV. The silicon dioxide films were characterized by measurement of wet etch rate, density, composition, and stress, and by infrared spectroscopy. It was found that above a flux ratio of about 20, high-quality SiO2 was deposited whether or not the substrate was thermally floating or at 65–200 °C, indicating that the flux ratio was dominant over the temperature. Use of radio-frequency bias to increase the mean ion energy to 50 eV or above was effective in producing high-quality SiO2 when the flux ratio was below 20, but not as effective as using a high flux ratio. Thus high ion flux and low ion energy were found to be useful in producing SiO2 at temperatures as low as 65 °C with properties close to that of thermal silicon dioxide. The role of ions in the deposition process was found to be densification, removal of –OH (or hydrogen) and alteration of Si–O bonding.