Correlation of stress behavior with hydrogen-related impurities in plasma-enhanced chemical vapor deposited silicon dioxide films

The presence of undesirable hydrogen-related impurities and the resulting stress instability in chemical vapor deposited silicon dioxide films are important issues. In this work, the bonding nature and stress behavior of relatively low-temperature deposited silicon dioxide films deposited at high rates were investigated. Films were deposited at 1000 Å/min and at a substrate temperature in the 250–350 °C range. A considerable change in stress was observed in these films upon annealing in the 250–400 °C temperature range. Both as-deposited and annealed films were then stored in a cleanroom environment for long periods of time, and their stress was monitored intermittently. In parallel, Fourier transform infrared studies were performed on an identical set of as-deposited and annealed films to investigate changes in the bonding nature of the films during aging. Thus, film stress and their bonding nature were studied concurrently over an extended period of time. Si–H and silanol (Si–OH) were identified as impurities responsible for the observed stress instability of the deposited films. Initial concentrations of these impurities have been observed to vary depending on the deposition conditions. Also, depending on the concentrations of these impurities, both reversible and irreversible bond reconstruction were observed in the films upon annealing. Concomittantly, reversible and irreversible changes in stress were observed in annealed films, the amount of change depending on the impurity type and content. Impurities responsible for reversible and irreversible bond reconstruction were identified. Good correlation between film stress and bonding was observed.