Electron trapping and chemical composition in radio frequency glow discharge a‐SiN:H

The electron trapping phenomenon in a‐SiN:H films deposited by radio frequency (rf) glow discharge has been studied as a function of rf power and gas feed ratio. The chemical composition of the films was determined with Fourier transform infrared spectroscopy. The nitrogen content of the films increased with rf power level if the feed ratio of silane to ammonia was sufficient, 1:10. A gas ratio of 1:5 lacked sufficient ammonia fraction to yield nitrogen rich films despite an increase in rf power level. The electrical resistivity increased and in general electron trapping decreased with increasing nitrogen content in the a‐SiN:H films. There is weak experimental evidence that an electron trapping minimum is obtained at a film composition similar to stoichiometric silicon nitride. The measured coordination number of 2.4 for films at this stoichiometric ratio corresponded to the optimum coordination number for a random covalent network. This conceivably should yield the lowest trap density material. At this time, however, it is safer to conclude that electron trapping decreases with increasing nitrogen content in the material.