Experimental Characterization of Plasma Instabilities in Moderate-Pressure Capacitively Coupled Plasmas Using Laser-Collision Induced Fluorescence

Self-organization in radiofrequency plasmas remains a persistent challenge for achieving spatially uniform processing in semiconductor manufacturing. This work presents an experimental investigation of spatiotemporal instabilities in symmetric, planar capacitively coupled plasmas (CCPs) operated at moderate pressures (0.1–10 Torr) in electropositive gases (He, Ar, N₂). Using laser-collision induced fluorescence (LCIF) and phase-resolved optical emission spectroscopy (PROES), we measure the electron density and temporal growth rates of emergent unstable modes. The diagnostics provide complementary views into the electron dynamics that lead to pattern formation. We compare our measurements to recent theoretical predictions based on a fluid electron model incorporating thermoelectric energy transport, with a focus on assessing the stability boundary and dynamics as a function of discharge gap, gas pressure, and chemistry. The results reveal trends consistent with the predicted dependence of instability on transport coefficients and support ongoing efforts to determine the dominant mechanisms responsible for self-organization in CCPs and inductively coupled plasmas (ICPs). These measurements also provide important validation data for modeling efforts aimed at predictive control of plasma uniformity in industrial systems.