Effect of adding O2 on plasma characteristics of inductively coupled CF4/Ar plasma

Abstract

High aspect ratio etching is crucial in semiconductor manufacturing, and its improvement relies on the stability and controllability of the plasma. In this study, we combine Langmuir probe diagnostics with a global model to investigate how O2 addition affects plasma characteristics in CF4/Ar radio frequency (RF) inductively coupled discharges. The key operational parameters include the CF4 mixing ratio (binary: 30%–90%, ternary: 10%–40%), working pressure (1–8 Pa), and RF power (200–500 W). The results show that in CF4/Ar discharge, the electron density decreases, whereas the effective electron temperature increases as the CF4 content is raised from 30% to 90%. When O2 is added to the CF4/Ar discharge with the Ar fraction fixed at 50%, the effective electron temperature also increases with the CF4 content in the range 10%–40%, while the electron density remains nearly constant. Analysis of the electron energy probability functions reveals that O2 addition results in low-energy electrons remaining constant with varying CF4 content. Global model calculations further indicate that O2 diversifies the plasma chemical composition and enhances the formation of F and F2 through reactions with CFx. The resulting high density of F2, combined with its large dissociative attachment cross section, makes dissociative attachment to F2 the dominant electron-loss pathway. Furthermore, as the pressure increases from 1 to 8 Pa, the electron density in CF4/Ar discharge exhibits a non-monotonic behavior characterized by an initial increase followed by a decrease. In contrast, it decreases monotonically in O2/CF4/Ar discharge. This work systematically reveals the influence of O2 addition on fluorocarbon plasma characteristics, offering guidance for optimizing plasma etching processes with improved stability and controllability.