Real-time characteristic impedance monitoring for end-point and anomaly detection in the plasma etching process

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We propose a practical and highly sensitive characteristic impedance monitoring (CIM) system for detecting the etching end point and anomalies during the plasma etching process. The CIM system employs a directional coupler and a newly developed vector processing system. The etching end point was successfully detected when a SiO2/Si wafer was etched with CF4 plasma; the system also detected wafer fluttering occurring during SF6–N2 plasma etching. The reactance component of the characteristic impedance primarily changed with the transient response of the electric potential on the inner glass surface during SF6–N2 plasma etching.