Characterization of SiOxNy anti-reflective coatings using SIMS and RBS/HFS

Abstract

Silicon oxynitride films formed using low-temperature plasma-enhanced chemical vapor deposition (PECVD) are being investigated as anti-reflective coatings (ARC) for deep- ultraviolet (DUV) photolithography. SiOxNy films reduce undesirable substrate reflections by phase-shift cancellation that is dependent on the film refractive index, extinction coefficient, and film thickness. The accurate characterization of these films is necessary in order to maintain quality control over the process. The challenge presented to the process engineers and metrologists is to use a standardized protocol for a high degree of accuracy and reproducibility in composition while achieving optimal depth resolution. A protocol based on combining the strengths of multiple techniques was investigated. Specifically, the quantitative nature of Rutherford backscattering spectrometry (RBS) and hydrogen forward scattering (HFS) was desired while the depth resolution and detection limits of low energy, quadrupole secondary ion mass spectroscopy (SIMS) was necessary. Several SiOxNy films, 10–30 nm thick, were deposited on p-type 〈100〉 Si and analyzed using RBS, HFS, and SIMS. The average composition of the films from RBS and HFS were used to normalize the depth profiles of the SIMS analysis for a comprehensive analysis of the H, N, O and Si concentrations. This multiple technique approach overcomes the weaknesses of each technique and provides a higher level of quantification and reproducibility than either technique alone.