Etch Rate Modeling of SiO₂ Using Impedance Monitoring and Optical Emission Spectroscopy

Impedance analysis with an equivalent circuit model (ECM) was combined with optical emission spectroscopy (OES) signals. ECM was applied to monitor plasma density and etch rate in an oxide etching process. Parasitic impedance was extracted using a VI sensor and the ECM was constructed for the bias path of plasma reactor. The model was verified with SiO₂ etching conducted in an inductively coupled plasma (ICP) reactor using CF₄, O₂, and Ar gases. Plasma density and sheath capacitance were used as circuit-derived parameters to analyze the physical mechanism of plasma. OES signals were used for analyzing the chemical mechanism of plasma. Line ratios, such as 703.3 nm / 750.3 nm and 251.4 nm / 750.3 nm, were measured for estimation of F and CF radical density. Under increasing source power, a 173% increase in CF radical density was observed, and the etch rate was reduced.. An etching model was constructed using ECM derived parameter and F, CF intensity ratio. The model achieved an R² value of 0.996 for predicting the etch rate. These results demonstrate that combining plasma diagnostics with ECM enables accurate prediction of etch behavior under varying plasma conditions.