Measurement of electronegativity during the E to H mode transition in a radio frequency inductively coupled Ar/O_2 plasma |
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| Authors: | Peng-Cheng Du Fei Gao Xiao-Kun Wang Yong-Xin Liu You-Nian Wang |
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| Affiliation: | (Key Laboratory of Materials Modification by Laser,Ion,and Electron Beams(Ministry of Education),School of Physics,Dalian University of Technology,Dalian 116024,China) |
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| 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 O_2. 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 O_2 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 O_2 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. |
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