1 Key Laboratory of Materials Modification by Laser, Ion, and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology, Dalian 116024, China
Abstract This paper presents the evolution of the electronegativity with the applied power during the E to H mode transition in a radio frequency (rf) inductively coupled plasma (ICP) in a mixture of Ar and O2. The densities of the negative ion and the electron, as well as their ratio, i.e., the electronegativity, are measured as a function of the applied power by laser photo-detachment combined with a microwave resonance probe, under different pressures and O2 contents. Meanwhile, the optical emission intensities at Ar 750.4 nm and O 844.6 nm are monitored via a spectrograph. It was found that by increasing the applied power, the electron density and the optical emission intensity show a similar trench, i.e., they increase abruptly at a threshold power, suggesting that the E to H mode transition occurs. With the increase of the pressure, the negative ion density presents opposite trends in the E-mode and the H-mode, which is related to the difference of the electron density and energy for the two modes. The emission intensities of Ar 750.4 nm and O 844.6 nm monotonously decrease with increasing the pressure or the O2 content, indicating that the density of high-energy electrons, which can excite atoms, is monotonically decreased. This leads to an increase of the negative ion density in the H-mode with increasing the pressure. Besides, as the applied power is increased, the electronegativity shows an abrupt drop during the E-to H-mode transition.
(Plasma diagnostic techniques and instrumentation)
Fund: Project supported by the National Natural Science Foundation of China (Grant Nos. 11675039, 11875101, and 11935005) and the Fundamental Research Founds for the Central Universities, China (Grant Nos. DUT18TD06 and DUT20LAB201).
Peng-Cheng Du(杜鹏程), Fei Gao(高飞, Xiao-Kun Wang(王晓坤), Yong-Xin Liu(刘永新), and You-Nian Wang(王友年) Measurement of electronegativity during the E to H mode transition in a radio frequency inductively coupled Ar/O2 plasma 2021 Chin. Phys. B 30 035202
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