Nitrogen dilution effects on structural and electrical properties of hot wire deposited a-SiN:H films for deep sub-micron CMOS technologies

Abstract

Hot-wire chemical vapor-deposited silicon nitride is a potential dielectric material compared to glow-discharge-deposited material due to its lower hydrogen content. In several earlier publications we have demonstrated these aspects of the HWCVD nitride. However, to replace SiO₂ with a-SiN:H as the gate dielectric, this material needs further improvement. In this paper we report the results of our efforts to achieve this through nitrogen dilution of the SiH₄+NH₃ gas mixture used for deposition. To understand the electrical behavior of these nitride films, we characterized the films by high-frequency capacitance-voltage (HFCV) and DC J-E measurements. We attempted to evolve a correlation between the breakdown strength, as determined from the J-E curves, and aspects such as the bond density, etching rate, deposition rate and refractive index. From these correlations, we infer that nitrogen dilution of the source gas mixture has a beneficial effect on the physical and electrical properties of the hot-wire a-SiN:H films. For the highest dilution, we obtained a breakdown voltage of 12 MV cm⁻¹.