Numerical investigation of ion energy distribution and ion angle distribution in a dual-frequency capacitively coupled plasma with a hybrid model

Abstract

A one-dimensional hybrid model is developed to study the characteristics of energy and angular distributions of the ions and fast neutrals impinging on the rf-biased electrode in a dual-frequency capacitively coupled Ar discharge. The hybrid model consists of a fluid model that determines the spatiotemporal evolution of the discharge, and a Monte-Carlo model that, including the electron-neutral, ion-neutral, and fast neutral-neutral collisions, predicts the energy and angular distributions of the ions and fast neutrals on the rf-biased electrode. The influence of pressure, voltage amplitude, and frequencies of the two rf sources on the energy and angular distributions is discussed. The ion energy distributions (IEDs) appear to have multiple peaks in the dual-frequency capacitively coupled rf discharge rather than bimodal shape in a conventional single-frequency rf discharge. The ion angle distributions (IADs) have a significant peak at a small angle, and most ions strike to the process surface with the angle less than 4°. With the increase of the pressure, the maximum energy of IEDs and the peaks of IADs decrease. The structures of IEDs are controlled mainly by the voltage and frequency applied to the two rf sources. By decreasing the frequency or adding the voltage applied to the low-frequency (LF) source, the width of IEDs and the maximum energy increase. More ions strike to the electrode with a small angle by increasing either the voltage of LF source or the frequency of high-frequency source. The energy and angular distributions of the fast neutrals are correlative with those of the ions. Compared with the ions, the fast neutrals have a much lower energy and the scattering effect becomes more prominent.

The electrical asymmetry effect in multi-frequency capacitively coupled radio frequency discharges

“…2 and 27 MHz [3][4][5][6][7]. The quality of the separate control of ion energy and flux in these discharges is, however, limited due to the coupling of both frequencies [8][9][10][11][12][13][14][15][16][17][18] and the effect of secondary electrons [14,19,20]. In order to obtain better control of the ion energy distribution function at the substrate surface, triplefrequency CCRF discharges operated at substantially different frequencies [21,22] and hybrid discharges [23][24][25][26][27][28][29] have also been studied.…”

Field reversals in electrically asymmetric capacitively coupled radio-frequency discharges in hydrogen

“…Dual-frequency discharges with two substantially different frequencies are frequently used to achieve this independent control [1][2][3][4][5]. In these discharges, the independent control of ion energy and ion flux is limited by frequency coupling [6][7][8][9][10][11][12][13][14][15] and secondary electrons [16], however.…”

Control of plasma properties in capacitively coupled oxygen discharges via the electrical asymmetry effect

“…The concept of dual frequency discharges, i.e., driving the plasma with two substantially different radio frequencies, had, therefore, been introduced as a promising way to achieve this separate control [2][3][4][5][6][7][8]. However, it is known that the coupling of both frequencies [9][10][11][12][13][14][15][16][17][18][19] and the effect of secondary electrons [8,[20][21][22] places a strong limitation to realize this goal. A rather new approach was recently proposed to control the ion properties via the Electrical Asymmetry Effect (EAE) [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]: By applying a voltage waveform, that contains a fundamental frequency and (at least) one even harmonic, the symmetry of the discharge can be changed by tuning the phase angle between the driving harmonics.…”