Measurement of electronegativity during the E to H mode transition in a radio frequency inductively coupled Ar/O₂ plasma*

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.

Numerical simulation of inductively coupled Ar/O₂ plasma

“…Hsu 等人 [9] 研究了气压在 10-80 mTorr 范围内等离子体参数(如电子密度、中性粒 子组分等)的变化. Du 等人 [10] 重点关注了 Ar/O2 ICP 中气压在 22.5-82.5 mTorr 范 围内，O2 含量在 0-80%范围内的模式转换问题. Han 等人 [11] 则研究了不同气压下 (气压最高达到 1 Torr) ，电子密度和温度随 O2 含量(0-100%)的变化.…”