Chemical composition and spatial distribution of plasma species in inductively coupled N2–O2 plasmas: Insights from a 2D fluid model

Abstract

The investigation of N2–O2 discharges is critically important for optimizing photoresist ashing efficiency and controlling plasma-induced damage in advanced semiconductor manufacturing. This study employs a two-dimensional fluid model to investigate the plasma characteristics of N2–O2 radio frequency inductively coupled discharges, with particular focus on the effects of N2 fraction, discharge power, and gas pressure on particle spatial distribution and chemical composition. Our results demonstrate that the plasma's chemical composition is determined by the N2 fraction. Specifically, N2+ and O2+ are the major ion species within the N2 fraction range of 50%–70%, whereas N2+ become predominant at 90% N2 fraction. This change in composition can be attributed to the competition between electron-impact ionization and charge exchange reactions. At elevated N2 ratios, the balance between ion transport and ionization source terms results in a spatial distribution of NO+ ions characterized by two high-density regions. Furthermore, when the nitrogen fraction is fixed at 50%, the discharge power has little effect on the relative proportion of chemical components, but it significantly increases the particle density. In contrast, the pressure not only affects the particle density but also significantly influences the relative proportion of the plasma's chemical components. Moreover, the results demonstrate that the surface loss coefficient predominantly governs the density of the corresponding species, exerting minimal influence on other species. The findings of this work enhance the understanding of the physical processes in RF inductively coupled N2–O2 discharges and provide essential insights for optimizing N2–O2 mixed-gas plasma processes in semiconductor manufacturing.