The dependence of silicon nitride film composition and properties on the flow rates of ammonia and silane gases during deposition and on subsequent thermal annealing has been investigated for films deposited from a reactive plasma in a commercially available reactor. Ammonia-to-silane flow ratios were varied between 1.3:1 and 4.4: 1, and determinations were made of the refractive index, etch rate, charge transport, absorption edge, Si/N ratio, Si-N bonds, and of chemically bound hydrogen. Increasing the ammonia-tosilane ratio during deposition has the following effects upon the films: decreases excess Si concentration, Si-H bond concentration, refractive index, and charge transport; and increases the concentrations of N-H and Si-N bonds, the energy of the absorption edge, and the etch rate. Isochronal annealing between the deposition temperature (300~ and 900~ causes a loss of chemically bound hydrogen, decreases the film thickness, etch rate, and the energy of the absorption edge, and increases the refractive index and the charge transport. Excess Si in the film composition is a major factor in determining the properties of plasma-deposited silicon nitride films, but the 20 to 25 atomic percent chemically bound hydrogen also plays a role. The importance of hydrogen is particularly apparent in the parallel behavior between an annealing induced shift of the absorption edge and the loss of Sill centers from Si-rich films. The annealing effects are analogous to those for hydrogenated amorphous Si.

Quantitative data are presented on the infrared (IR) absorption of interstitial oxygen in oxygen-rich silicon using Fourier transform spectroscopy. Besides the well-known 515 and 1106 cm-' room temperature IR bands, due to the symmetric and antisymmetric vibrations of the Si20 entity, respectively, three other bands at 1227, 1720, and 1013 cm-' are reported, whose intensities are scaled with those of the 515 and 1106 cm-' bands. The band at 1227 cm -1 has often been confused with an oxygen precipitate band observed at 1225 cm-' in annealed silicon. Evidence is given that the 1227 cm -~ band is related to interstitial oxygen. It is also shown that another band at 1720 cm -1 is a combination of the antisymmetric mode of Si20 with a phonon combination of the silicon lattice. A weak band at 1013 cm-' is reported for the first time, and it is attributed to an overtone of the 515 cm-' mode.