NO-driven etching behavior of SiO2 and Si3N4 in cryogenic NF3/NO plasmas

Gas composition and substrate temperature play key roles in governing surface reaction pathways and the etching behavior of dielectric films. In this study, the temperature- and composition-dependent etching characteristics of silicon dioxide and silicon nitride films were investigated in cryogenic NF3/NO plasmas, with the aim of clarifying how NO modulates material-dependent surface reactions. A range of observations revealed systematic variations in NO-, F-, and NOF-related species as functions of substrate temperature and gas composition. When the substrate temperature was reduced below 0 °C, the dominant reaction pathway of NO shifted from gas-phase reactions to processes dominated by surface reactions. Surface chemical analysis using x-ray photoelectron spectroscopy revealed distinct material-dependent responses under cryogenic conditions. For SiO2, lowering the substrate temperature promoted fluorine transfer reactions at the surface, consistent with enhanced chemical etching. In contrast, SiN exhibited increased surface trapping of NO- and NOF-related species, which suppressed the overall etching reaction under otherwise identical plasma conditions. These results demonstrate that NO acts as a reaction moderator whose influence depends on both the material type and the processing conditions. By correlating plasma diagnostics with surface chemical analysis, this work provides insight into non-polymer-based selective etching mechanisms in cryogenic NF3/NO plasmas and contributes to the understanding of process control strategies for high-aspect-ratio dielectric structures.