Low-frequency dependence of plasma characteristics in dual-frequency capacitively coupled plasma sources

Author:

Zhou Yang1ORCID,Zhao Kai1ORCID,Ma Fang-Fang1ORCID,Liu Yong-Xin1ORCID,Gao Fei1ORCID,Schulze Julian2ORCID,Wang You-Nian1ORCID

Affiliation:

1. Key Laboratory of Materials Modification by Laser, Ion, and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology 1 , Dalian 116024, China

2. Chair of Applied Electrodynamics and Plasma Technology, Department of Electrical Engineering and Information Science, Ruhr-University Bochum 2 , D-44780 Bochum, Germany

Abstract

It is commonly recognized that in radio frequency capacitive discharges, a higher excitation frequency can yield an enhanced electron heating rate and ion flux. Here, we reveal the low-frequency dependence of the plasma density and ion energy/angular distribution in a low-pressure (2 Pa), dual-frequency (DF) capacitively coupled argon plasma based on a combination of experiments and kinetic particle simulations. As the low frequency (LF, fL) is decreased from 6.8 MHz to 40 kHz, the plasma density undergoes a moderate decline initially, followed by an increase, reaching a maximum at fL=400 kHz. The enhanced plasma density is attributed to a combined effect of (i) an attenuated modulation effect of the LF source on the high-frequency electron heating and (ii) enhanced emission of electron-induced secondary electrons. At a lower fL, the ion transit time across the sheath, τion, gets comparable to or shorter than the LF period, τLF, resulting in a higher ion energy with a narrower angular spread. The enhanced ion flux and ion energy in DF discharges operated at low frequencies in the range of hundreds of kHz are beneficial for the high-aspect-ratio plasma etching extensively used in the semiconductor industry.

Funder

National Natural Science Foundation of China

Fundamental Research Funds for the Central Universities

German Research Foundation

Publisher

AIP Publishing

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