Control of ion energy distribution in low-pressure and triple-frequency capacitive discharge

Abstract

One-dimensional particle-in-cell Monte Carlo collision (PIC-MCC) simulations of low-pressure (10 mTorr) argon plasmas sustained by a triple-frequency (1, 30 and 120 MHz) source in symmetrical current-driven and voltage-driven capacitively coupled plasma reactors are carried out. We concluded that the effective current, the effective voltage and the effective frequency are helpful in explaining the physics of triple-frequency capacitively coupled plasma sources (CCPs) alike single-frequency CCPs. The rf discharge parameters such as the ion energy distribution function (IEDF), the sheath length, the plasma potential and the powers dissipated by electrons and ions can be expressed as the effective frequency and the effective current density (or effective voltage). The analytical model of the IEDF for triple-frequency CCPs in the high-frequency regime is developed. The analytical calculations of the IEDF in the high-frequency regime through the effective frequency visualized in this paper are compared with the simulation results of the IEDF calculated from the 1D PIC-MCC model. The ion energy width and the average ion energy of the IEDF are controlled by the effective frequency, which is expressed as a function of the current density (or voltage) and frequency ratios of the triple-frequency source. The evolution of the effective frequency with the current density or voltage ratio of three frequency sources is different depending on the mode of operating source, which is either voltage or current. The effective frequency in voltage-driven CCPs is 2-10 times higher than that of current-driven CCPs at the same ratio of current density and voltage. As a result, the current-driven CCPs is more desirable than the voltage-driven CCPs from the aspect of independent control of ion flux and ion bombardment energy because the ion energy width increases with decreasing effective frequency.

Power supply and impedance matching to drive technological radio-frequency plasmas with customized voltage waveforms

“…11 Dual-frequency plasmas operated at two substantially different frequencies (e.g., 2 MHz and 27 MHz) provide an improved control. [11][12][13][14][15][16] This approach is based on the idea that the charged particle generation, density, and fluxes mainly depend on the amplitude of the high-frequency component, whereas the energy gain of ions in the plasma-substrate sheath mainly depends on the amplitude of the low-frequency component. However, the control of the ion FEDF is again limited due to the effects of frequency coupling and secondary electrons 11,[16][17][18][19] as well as the limited control of the voltage drop across the sheaths as a function of time.…”

Negative resistance phenomenon in dual-frequency capacitively coupled plasma-enhanced chemical vapor deposition system for photovoltaic manufacturing process

“…These IEDFs on the driven electrode are affected by the ratio of the ion transit time (s ion ¼ 3 sðM=2e V s Þ 1=2 ) to the rf period (s rf ¼ 2p=x eff ). 6,19 This ratio can be expressed as a function of effective frequency, sheath length, and average potential difference between driven electrode and the bulk plasma and is given by…”

“…5,[18][19][20] It means that a DF CCP discharge can be treated as a SF CCP discharge with effective parameters such as effective frequency and effective current density. When one of the two power sources in a DF CCP discharge is much stronger than the other, then DF CCP discharge behaves as a SF CCP discharge operated with the stronger power source of the two and in this case one can say that the effective frequency simply corresponds to the driving frequency of the stronger power source in terms of the effective frequency concept.…”

Analytical modeling of collisionless triple frequency capacitive sheath

“…al. [11] introduced an effective frequency for a dual frequency and triple frequency CCP, respectively, based on homogenous sheath and ion energy distribution. But they ignored the inhomogeneity in the sheath.…”