Open volumes in SiN films for strained Si transistors probed using monoenergetic positron beams

Open volumes in strained SiN films deposited on Si substrates by microwave plasma enhanced chemical vapor deposition were probed using monoenergetic positron beams. Positrons were found to annihilate from the trapped state by open volumes which exist intrinsically in amorphous structures of SiN. The formation of positronium atoms in large open volumes was observed. From their lifetimes, the estimated mean size of such volumes was 0.02–0.5nm3. A clear correlation between the size distribution of open volumes and the stress in the substrate was obtained. The relationship between the open volumes and impurities in the films is also discussed.