Noninvasive method for monitoring plasma parameters and dielectric thickness applicable to plasma processing

Maintaining process uniformity is critical in high-aspect-ratio etching, where local plasma and surface conditions strongly influence etch performance. Among the hardware components affecting uniformity, the focus ring, a dielectric structure surrounding the wafer, plays a key role in shaping the edge plasma and maintaining uniform ion flux. However, its gradual erosion during operation causes nonuniform etch profiles, particle generation, and yield degradation, making real-time wear monitoring essential for stable, high-yield semiconductor processing. Here, we present an electrical sensing method for real-time, in situ monitoring of thick dielectric components under plasma operation. The plasma–dielectric system is modeled as an equivalent circuit, and dielectric thickness is extracted from capacitance using a dual-frequency method that decouples plasma effects. Fringing effects are incorporated into the ideal parallel-plate capacitor model using a Padé approximant, and the model is further refined by weighted least-squares fitting. The proposed method enables accurate thickness measurement despite plasma variations and provides a practical, noninvasive approach for monitoring both plasma parameters and focus ring wear during plasma processing.