Effects of Hydrogen Bonding in Silicon Nitride/Polyimide Passivation Bilayer in SiC Power Devices

Abstract

Composition and morphology of two types of bilayers of plasma‐enhanced chemical vapor deposition hydrogened silicon nitride (SiNx:H) and polyimide (PI), as effcient barrier against moisture in SiC‐based power devices, are investigated. Two types of silicon nitrides are obtained by changing the flow ratios of the SiH4 and NH3 precursors. Rutherford Backscatterered analyses show that the Si/N ratio varies from 0.6 to 0.8. Elastic recoil detection analyses show that the sample with higher nitrogen content has a higher total bound hydrogen content of 7.8 × 1017 cm−2 with respect to the 7.1 × 1017 cm−2. Fourier‐transform infrared spectroscopy characterizations show Si–H group concentrations of 0.96 × 1017 and 6.86 × 1017 cm−2 and NH groups of 4.82 × 1017 and 2.28 × 1017 cm−2, respectively. Silicon nitride films with higher concentration of N–H groups show higher reactivity and permeability to water, making them less effective as a barrier layer. Atomic force microscopy analyses of a PI layer deposited on the nitride layer, SiNx:H/PI show for both type of samples a similar roughness, indicating planarization that can increase the adhesion of SiNx:H/PI and resistance to moisture. The delamination mechanism of the bilayer under pressure pot test conditions is proposed.