Thermal stability and breakdown strength of carbon-doped SiO2:F films prepared by plasma-enhanced chemical vapor deposition method

Carbon-doped SiO2:F films were deposited by changing the CH4 flow rate, [CH4], using a plasma-enhanced chemical vapor deposition technique from SiH4/O-2/CF4/CH4 mixtures. The thermal stability for the films deposited with a fixed temperature of 300 degrees C was investigated through the changes in the dielectric constant (epsilon(S)), IR spectra and stress with annealing temperature, T-A, from 400 to 800 degrees C. The breakdown strength for films as-deposited were also measured. The addition of carbon to SiO2:F films resulted in the films with low epsilon(S) (up to 3.0) and high water resistivity. Addition of high [CH4] in the films resulted in stable epsilon(S) for T-A=500 degrees C or less. The CH4 addition initially decreased the breakdown strength but then increases again. Under the application of sum rule to the analysis of the vibrational absorption, it was suggested that the decrease in epsilon(S) with [CH4] results from the decrease in the effective dynamic charge of Si-O dipoles along with the direct contribution of Si-F bonds incorporated to SiO2. The decrease in Si-F and Si-O peak frequencies based on the analysis of the charge transfer model suggested an increase in the Si-F and Si-O bond length, in addition to a decrease in the Si-O-Si bond angle. (C) 2000 American Institute of Physics. [S0021-8979(00)04908-2].