The role of etching gas purity in C4F8/Ar plasma to optimize SiO2 etching process

Abstract

The relentless miniaturization of critical feature sizes in integrated circuits has set increasingly stringent demands on the precision of via etching processes. Current research predominantly focuses on the development of gases and optimization of processes. However, the role of etching gas purity and the impact of gas impurities have not yet been the subject of dedicated studies. Here, the etching behavior of silicon dioxide using two different purities of etching gases is investigated, examining the etching rate and morphology of SiO₂ films under identical etching parameters. Compared to 99.999 % purity, the 99.99999 % purity C₄F₈ gas achieves a more stable and uniform etching rate with sidewall angles of 86.6° (closer to a 90° angle). This is primarily attributed to the reduction of etch-active impurities in the C₄F₈ gas, which decreases etching variability and minimizes damage to the sidewall fluorocarbon protective layer. Our research provides theoretical and experimental support for the advancement of subsequent etching simulation studies and the application of high-purity etching gases.