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

Abstract

We have studied the influence of different process parameters on the composition and mechanical properties of silicon-nitride layers deposited in a SiH4-NH3-N~ plasma. The layers were deposited at temperatures between 300 ~ and 600~ 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.Plasma silicon-nitride layers are widely used in the IC technology for passivation of devices. The layers act as barriers against the diffusion of impurity ions such as sodium, and they are also used for scratch protection during mounting operations. The electrical and mechanical properties of plasma silicon-nitride layers depend strongly on composition, density, and mechanical stress and, therefore, on the deposition conditions. Composition and stress measurements of plasma silicon-nitride layers have been reported (1-4), but attempts to make a more systematic study and quantitative evaluation of the results are relatively, scarce. Therefore, a systematic experimental approach was applied to study composition, density, and stress of plasma silicon-nitride layers prepared under various deposition conditions.In this paper, we report on the influence of deposition temperature, gas pressure, gas phase composition, and RF frequency on the composition, density, and stress of plasma silicon-nitride layers. The experimental data will be described by a simplified reaction model.

Two Layer Surface Exfoliation on Si3N4/Si by Sequential Implantation of He and H Ions

“…Actually, strain production at the Si 3 N 4 /Si interface has been well revealed by several authors. 19,20 Therefore, such strain may play an important role in the formation of a crack along the interface during deformation of the implanted layer. Thirdly, although the implanted depth is relatively far from the Si 3 N 4 /Si interface, a certain residual dose of He or H ions could remain near the interface, according to the TRIM simulations.…”

Thin Film Encapsulation for RF MEMS in 5G and Modern Telecommunication Systems

“…The stress measurement for the trilayer is greater than the expected value, which is the weighted volumetric average of the single layers. A possible reason for this result is that the first nitride layer undergoes an increase of the residual stress during the depositions of the amorphous silicon and the second nitride layers, due to the heating and subsequent H outgassing [44]. Three profiles were measured for each sample along its diameter; the resulting stress data show a standard deviation better than 5%.…”

PECVD silicon nitride diaphragms for condenser microphones

“…It has been found that by varying the substrate temperature, the stress can be varied from compressive, at lower substrate temperatures, to tensile, at higher temperatures [7- temperature at which zero film stress is obtained has been found to vary from 70 "C [9] to 580 "C [7], depending on the other experimental conditions, like reactor geometry, composition of reactive gases, gas pressure, plasma frequency, etc. In general, CVD silicon nitride films contain a certain amount of hydrogen, which decreases with increasing substrate temperature [7,8, lo].…”

“…It has been found that the use of low plasma frequencies ( ~4 MHz) results in films with compressive stress, and the use of high plasma frequencies in films with tensile stress [7]. This is ascribed to the fact that at low frequencies, ions in the plasma are accelerated by the alternating electric field and will 81 reach the substrate surface with high velocity.…”

“…The effect of the total gas pressure in the reactor on the film stress in silicon nitride has been described for low-frequency deposition only [7]. It has been found that the film stress was always compressive, but that its magnitude decreased as the total gas pressure increased.…”