Impact of auxiliary capacitively coupled plasma on the properties of ICP-CVD deposited a-SiNx:H thin films

In this study, we report on the properties of amorphous hydrogenated silicon nitride (a-SiNx:H) thin films synthesized by inductively coupled plasma enhanced chemical vapour deposition (ICP-CVD), combined with an auxiliary capacitively coupled plasma excitation. Physical properties, such as the deposition rate, refractive index and film stress, as well as the chemical composition, microstructure and etch resistance of the samples were investigated. Depending on the capacitively coupled plasma power P-RF, two regions can be distinguished which are dominated either by an increased generation of plasma radicals or by an enhanced ion bombardment. At P-RF = 35W, a maximum in the deposition rate is observed as well as an abrupt change in the chemical composition, resulting in an extremely high (>2.5 GPa) compressive stress, in comparison to the layers deposited with P-RF = 0. In addition, the wet etch rate in hydrofluoric acid (HF) decreases substantially. Above, up to P-RF = 150W, ion bombardment of the growing film surface is more pronounced due to an increased self-bias of the substrate decreasing the effective deposition rate. Fourier-transform infrared spectroscopy measurements indicate that this behaviour is in close relation to the N-H bond density in the samples. Additionally, the continuous increase of the refractive index and Si-H bond density, accompanied by the redshift of the Si-N infrared absorption peak show that with higher P-RF the Si content of the films increases. (C) 2015 Elsevier B.V. All rights reserved.