Pressure dependence on spatio-temporal distribution of excitation rates of Ar 2p₁ and Ne 2p₁ in Ar and Ar/Ne capacitively coupled plasmas

Plasma processing is used in a lot of semiconductor manufacturing steps today. For ultra-precision nano-fabrication, spatio-temporal structures of plasma must be clarified and controlled. High-energy electrons have important roles of the dissociation and ionization of gas molecules [1]. In this study, We have investigated the spatio-temporal distribution of excitation rates of some ions in a capacitively coupled plasma using Phase Resolved Optical Emission Spectroscopy (PROES) measurement. The input rf frequency was 13.56 MHz and the power was 25 W, respectively. The ICCD camera had a gate width of 3 ns. The excitation rate was a relative evaluation. Spatio-temporal distributions of excitation rates of Ar 2p₁ and Ne 2p₁ were measured by PROES from gas pressure p = 37.5 mTorr to 900 mTorr. These measurement results showed as follows; as gas pressure increased,1) the excitation rates of Ar 2p1 and Ne 2p1 decreased, 2) the spatio-temporal region of high excitation rate became small, and 3) the sheath expansion width became narrow and the beam velocity of the high energy electron decreased, respectively. These three results considered to affect electron energy distribution function and electron density. Details will be shown at the conference.

[1] B Horváth et. al, Plasma Sources Sci. Technol. 29, 055002 (2020).