Characterization of oxygen doped plasma-deposited silicon nitride.

The physical properties of amorphous plasma-deposited silicon nitride and silicon oxynitride films deposited in a load-locked, parallel plate reactor operation at 380kHz were determined. Nitrous oxide was added to a mixture of 2% silane in nitrogen to produce the oxynitride films deposited from 200C to 350C. The hydrogen content of these films is about half that of films deposited with ammonia as the source of nitrogen. The refractive index of the undoped silicon nitride is proportional to the Si-H/N-H ratio of the film while the refractive index of all films is proportional to Si-H content. Increasing the nitrous oxide flow at constant silane and nitrogen flow rates: (1) improves the thickness uniformity across a wafer; (2) increases the deposition rate; (3) increases the oxygen content and decreases the silicon content; (4) decreases the total H content; (5) reduces the compressive stress; and (6) increases the buffered HF etch rate of the film. Our results show that discrepancies in the literature about the properties of plasma nitride are because of unwanted oxygen in the films.