Strong variation of average ion energy in oscillation frequency of sheath potential

Abstract

In a modern plasma etching device, the plasma sheath potential is usually superposed by an externally driven oscillating voltage to enhance and control the bombarding ion energy. A collisionless particle simulation is used to study the variation of average kinetic energy 〈K〉(νrf) of bombarding ions as a function of a wide range of sheath oscillation frequency νrf (0.1νpi⩽νrf⩽10νpi, where νpi is the ion plasma frequency). It is found that a resonance phenomenon between the ion transit motion and the sheath oscillation can yield a strongly peaked enhancement of 〈K〉(νrf) near νrf≃0.5νpi. Ion species with different mass show the peaks at different νrf. The relative importance of different ion molecules in an ion-enhanced etching process will be sensitive to νrf. This phenomenon may allow a reduction of the undesirable capacitive coupling by optimizing νrf to yield an enhanced 〈K〉 of desired ion species at low applied voltages.

Electron density and ion energy dependence on driving frequency in capacitively coupled argon plasmas

“…There is an increasing interest for high frequency (ω 13.56 MHz) CCP discharges, aimed at higher electron density and lower ion bombardment energy on the powered electrode, or controlling both the electron density and ion bombardment energy by dual-frequency discharges [2][3][4]. In fact, there are many theoretical and experimental works in this area and the variation of electron density and ion energy versus the rf driving frequency has been obtained under various conditions [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. In general, at constant rf power, the electron density increases and the ion bombardment energy decreases with the driving frequency.…”