Experimental Characterization of A Pulsed-Modulated RF Capacitively Coupled Argon Plasma Based on Multi-Parameter Diagnostics

The temporal evolution of the argon metastable density( n Ar * ), the electron density( n e ), the optical emission intensity (OEI), and the electrical parameters in a pulsed CCP was experimentally investigated under various operating conditions. The radially-averaged n Ar * was measured using tunable diode laser absorption spectroscopy (TDLAS), the n e at the discharge center was determined by a hairpin probe, and the spatiotemporal distribution of theOEI was obtained by time-resolved optical emission spectroscopy (OES). The temporal evolution of the RF voltage and current amplitudes and their phase difference was derived from the measured waveforms using fast Fourier transform (FFT) analysis. The results show that both n Ar * and theOEI exhibit pronounced transient overshoots during pulse ignition and saddle-shaped axial profiles under steady-state discharge at the pressures considered here. However, the overshoot of n Ar * at the discharge center is limited to about 50% of that near the electrodes due to spatial transport and loss processes. Increasing the pulse-off time weakens the contribution of residual electrons and metastable atoms to re-ignition, thereby delaying ignition while enhancing the metastable overshoot during the ignition phase. Higher gas pressure shortens the electron mean free path and reduces ionization efficiency, delaying ignition; however, reduced diffusion losses and increased neutral density result in higher overshoot and steady-state n Ar * . Increasing the RF voltage strengthens the electric field, elevates electron energy, and advances ignition, leading to a higher overshoot of n Ar * . Meanwhile, it shifts the electron energy distribution toward higher energies, reduces excitation efficiency, enhances ionization competition and electron-impact quenching, and ultimately lowers steady-state n Ar * .