Electrical characterization and plasma impedance measurements of a RF plasma etch system

Abstract

A modified Tegal MCR-1 plasma etch system has been electrically characterized, and the plasma impedance has been measured at 13.56MHz. Important aspects of radio-frequency (RF) impedance measurements are addressed as they pertain to the measurement of the plasma impedance. These include: transmission line effects, magnitude and phase errors of the measurement probes, and the intrinsic impedance of the empty plasma chamber. Plasma harmonics are discussed, and a technique for measuring the plasma impedance at harmonic frequencies is presented. Transients in the plasma impedance are observed during the first 5 minutes after the plasma is initiated, and represent a decrease in the plasma impedance. Residual gas analysis (RGA) confirms the presence of H₂O in the plasma. The H₂O ion current measured by RGA shows a downward transient similar to the impedance transients, suggesting a possible relationship between H₂O and the impedance transients. A possible explanation for these impedance transients is presented.