PROPERTIES OF PLASMA-DEPOSITED SILICON-NITRIDE

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-to-silane 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°C) and 900°C 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 SiH centers from Si-rich films. The annealing effects are analogous to those for hydrogenated amorphous Si. © 1979, The Electrochemical Society, Inc. All rights reserved.