Influence of Deposition Temperature, Gas Pressure, Gas Phase Composition, and RF Frequency on Composition and Mechanical Stress of Plasma Silicon Nitride Layers

TLDR

The study aims to explain experimental observations of silicon‑nitride layers by developing a simplified reaction model. Silicon‑nitride layers were deposited over a range of temperatures, pressures, and RF frequencies, and their composition and hydrogen content were characterized by RBS and IR spectroscopy, followed by a simplified reaction model. The study shows that hydrogen content, density, and mechanical stress of plasma‑deposited silicon‑nitride layers vary strongly with deposition temperature, pressure, and RF frequency, and the simplified model attributes these variations to cross‑linking reactions and ion bombardment.

Abstract

We have studied the influence of different process parameters on the composition and mechanical properties of silicon‐nitride layers deposited in a plasma. The layers were deposited at temperatures between 300° and 600°C, at total pressures between 65 and 195 Pa and RF frequencies between 0.1 and 20 MHz. The Si/N ratio and the density of the as‐deposited layers were determined by means of RBS. IR spectroscopy was used to measure the hydrogen content and Si‐H/N‐H ratio of the plasma nitride layers. It is shown that hydrogen content, density, and mechanical stress of plasma silicon‐nitride layers strongly depend on deposition conditions. To explain the experimental data, a simplified reaction model is given. With this model, differences in densities, hydrogen content, and stress can be related to cross‐linking reactions and to the extent of ion bombardment which takes place at different excitation frequencies.