Structural and electrical properties of silicon nitride films prepared by multipolar plasma-enhanced deposition

Abstract

A new system of dielectric deposition using a multipolar plasma enhanced by a hot filament has been used to deposit multipolar plasma chemical vapor deposition silicon nitride films on various substrates (GaAs, Si, GaInAs, etc.). Using in situ kinetic ellipsometry during the depositions, the flow ratio SiH4/N2 has been optimized to form as dense silicon nitride as possible. The density variation has been attributed to a variable amount of oxygen in the films certainly in the form of silicon dioxide. Using Rutherford backscattering and spectroscopic ellipsometry, the amounts of oxygen have been measured precisely. Using infrared absorption, we have demonstrated the low hydrogen concentration of our films compared to plasma-enhanced chemical vapor deposition ones. At constant flow ratio, we have demonstrated the effect of the deposition rate on the stoichiometry of the films. Films deposited at very low deposition rates (<10 Å/min) are quasistoichiometric and produce important reductions of GaInAs/Si3N4 interface densities of states compared to higher deposition rate films (>24 Å/min). The conduction mechanism appears ionic in oxygen-rich silicon nitride films and controlled by a Poole–Frenkel effect in the case of moderate deposition rates.