Effect of hydrogen dilution on the properties and bonding in plasma-deposited silicon nitride

The effects of hydrogen dilution on the properties and structure of silicon nitride films deposited by plasma-enhanced chemical vapor deposition from NH3/SiH4 mixtures were studied. The addition of relatively small amounts of hydrogen at a fixed NH3/SiH4 ratio increased the excess Si in the film with a corresponding increase in the Si—H/N—H bonding ratio. At higher dilution [H2/(NH3+SiH4)] the films became more stoichiometric with significant changes in the hydrogen bonding. Decreases in the etch rate and refractive index with increasing hydrogen flow are discussed in terms of the changes in bonding structure and were found to be well correlated to changes in the Si—N bond density.