Experimental and numerical study of the ionization-attachment instability in an O₂ capacitively coupled radio frequency plasma

Abstract This study examines the emergence of an ionization-attachment plasma instability in a geometrically symmetric capacitively coupled plasma reactor with stainless steel electrodes operated in oxygen. Periodic fluctuations in optical emission intensity were observed under varying conditions of pressure and voltage. To interpret the experimental data, a kinetic (PIC/MCC) simulation approach was employed, with a particular focus on the influence of external parameters, including the voltage amplitude and the O <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mrow/> <mml:mn>2</mml:mn> <mml:mo>+</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> ion induced secondary electron emission coefficient (SEEC, γ ). By varying the γ coefficient at fixed pressure and voltage amplitude, the aim was to achieve the best possible agreement between the measured and computed oscillation frequencies. The experimentally observed oscillation frequency of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>f</mml:mi> <mml:mtext>in</mml:mtext> </mml:msub> </mml:mrow> </mml:math> = 0.25 kHz at φ 0 = 655 V voltage amplitude (with 13.56 MHz RF excitation) was reproduced in the simulation with γ = 0.0042 at φ 0 = 600 V. The results highlight the critical role of these parameters in the onset and characteristics of plasma instability and correspond to a computationally assisted diagnostic to determine ion induced secondary electron emission coefficients.