Simplified CVD route to near-zero thickness silicon nitride films

Abstract

Silicon nitride (SiNx, x ∼ 1) thin films were deposited by chemical vapor deposition on silicon oxide (SiO2) substrates by combining controlled pulses of the precursor 1,3,5-tri(isopropyl)cyclotrisilazane (TICZ, C9H27N3Si3) with a continuous ammonia (NH3) plasma. This plasma-assisted pulsed CVD (PPCVD) process enables the integration of the nanoscale thickness and uniformity control achieved in atomic layer deposition with the efficiency of plasma-enhanced CVD (PE-CVD). TICZ was selected because it is a nonpyrophoric stable liquid with a high vapor pressure (∼133 Pa at 70 °C) and could act as a single source for SiNx with both high Si and N contents. An optimized PPCVD process window was identified consisting of a substrate temperature of 350 °C, a TICZ pulse of ≤0.2 s, and a TICZ purge pulse ≥10 s in a continuous direct NH3 plasma at a NH3 flow rate and a power of 40 SCCM and 3000 W, respectively. The as-deposited films were analyzed by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. XPS analysis confirmed the absence of any C inclusion and demonstrated the existence of the 1:1 Si:N ratio. In situ, real-time ellipsometry measurements indicated that SiNx growth occurred in a typical PE-CVD regime. They also yielded an as-grown SiNx average refractive index of ∼1.75.