Infrared study of the structure of silicon oxynitride films produced by plasma enhanced chemical vapor deposition

The structure of thin (∼300nm) SiOxNy (0.23≤x≤1.95, 0.01≤y≤0.32) films produced by plasma enhanced chemical vapor deposition is studied by infrared (IR) spectroscopy. The dependence of the shape of the main IR absorption band in the range of 700–1400 cm–1 upon film composition is analyzed. The IR spectra exhibit strong overlapping of the bands corresponding to absorption on Si–O and Si–N bonds. A problem of separating these components is solved. Analysis of their relative intensities provides an insight into the film structure. The films with high oxygen content are found to have a homogeneous structure similar to that of nonstoichiometric Si oxide that can be described by the random bonding model. Increase of relative Si concentration and simultaneous decrease of oxygen and nitrogen content changes the film structure to the two-phase one obeying the random mixture model. Such material may be represented as a uniform mixture of interconnecting silicon–oxygen tetrahedra (Si–OaSi4-a, a=0..4) and silicon–nitrogen pyramids (Si3N). Relative Si concentration in the Si oxynitride films and their deposition temperature are hypothesized to play a decisive role on their structure, which is supported by thermodynamic modeling.