Reliable wafer level plasma diagnostics under various rf bias power

Accurate plasma diagnostics at the wafer level are essential for monitoring plasma processes and ensuring reproducibility. Various techniques have been developed for these purposes. One such technique is the Floating Harmonic Probe (FHP), which applies a small-amplitude AC voltage to a probe and analyzes the current collected by the probe. We develop an asymmetric double probe that enables plasma diagnostics at the wafer level by modifying FHP. Typically, when RF bias power is applied, the plasma potential oscillates at the RF bias frequency, leading to inaccurate measurements. To address this issue, the proposed probe features a highly asymmetric tip area to reduce the probe sheath impedance, thereby mitigating the distortion of plasma potential oscillations and improving measurement accuracy. In this study, Electron temperature is measured using double probe with area ratio of 1:300. The double probe with a 1:300 area ratio provides accurate and consistent electron temperature measurement under RF bias. These results demonstrate that the proposed highly asymmetric double probe is effective for accurate wafer level plasma diagnostics under RF-biased conditions in semiconductor processes.