Non-invasive real-time sheath diagnostics using RF wall sensor: application to transformer coupled plasma-reactive ion etch system

Abstract This study investigates plasma sheath dynamics in electronegative oxygen plasmas using a non-invasive plasma sheath monitoring sensor (PSMS). The PSMS detects radio-frequency (RF) magnetic field variations induced by sheath displacement currents, enabling real-time monitoring of sheath dynamics without perturbing the plasma. Variations in the PSMS signal are primarily attributed to changes in sheath capacitance caused by plasma density evolution and ion species transitions. Experiments on power and pressure-dependency in O2 plasma reveal continuous E–H mode transitions and shifts in electron heating mechanisms from collisionless to ohmic heating. Experiment on Ar and O2 gas mixing ratio demonstrates that the PSMS is sensitive to gas composition, and it successfully captured sheath stabilization and saturation behavior arising from increased electronegativity. These results indicate that the PSMS provides a potential of a non-invasive plasma process diagnostics for monitoring complex sheath dynamics, offering significant potential for optimizing high-aspect-ratio etching processes.