Fluorine atom induced decreases to the contribution of infrared vibrations to the static dielectric constant of Si-O-F alloy films

Si-O-F alloy films deposited by chemical vapor deposition have static dielectric constants, epsilon(s), significantly reduced with respect to those of similarly prepared SiO2, similar to 3.2 to 3.4 as compared to 4.0 to 4.2. Infrared absorption spectra provide a basis modeling the molecular structure of these alloys, as well as helping to identify microscopic mechanisms responsible for static dielectric constant reductions. Contributions of electronic and vibrational transitions to epsilon(s) are discussed in terms of an empirical chemical bonding model. Ab initio calculations are then used to identify inductive effects of Si-F bonds on the properties of Si-O-Si groups that are back-bonded to the Si atom of that Si-F group. The ab initio calculations provide a theoretical framework for understanding why relatively low concentrations of F atoms; similar to 10-12 at. %, produce significant decreases in epsilon(s), similar to 22%, as reported for the Si-O-F alloys. (C) 1997 American Vacuum Society.