The hydrogen content of plasma-deposited silicon nitride

The hydrogen content of glow-discharge-deposited silicon nitride (SiN) films made at 330–350 °C has been determined. Preparation conditions were varied to produce a range of compositions of Si/N=0.7–1.4. Quantitative hydrogen profiling of the samples was carried out using the resonant nuclear reaction 15N+H→12C+4He+γ ray. Calibration factors for Si-H (2160 cm−1) and N-H (3350 cm−1) absorption-band areas or absorbances have also been determined, enabling infrared transmission spectra to be used for hydrogen analyses of these films. All samples were homogeneous in hydrogen content and were in the range (1.6–2.1) ×1022 H atoms/cm3, or about 20–25 at.% H. Roughly three-quarters of the H is bonded to Si, the remainder to N. One plasma SiO2 sample made at 300 °C from SiH4 and N2O was measured also, and contained 5.7 at.% H, all as OH. Although there was little variation in the H content of SiN, there is a correlation between the total H concentration and the buffered HF etch rate. Some observations on the effects of the 15N ion beam (6–8 MeV) on the SiN are reported. Many Si-H and N-H bonds are broken, but the liberated H atoms or ions are unable to diffuse out of the film.