Hybrid simulation of radio frequency biased inductively coupled Ar/O₂/Cl₂ plasmas

Abstract

In the etching process, a bias source is usually applied to the substrate of the inductively coupled plasma (ICP) to realize independent modulation of the ion energy and ion flux. In this work, a hybrid model, i.e. a global model combined bi-directionally with a fluid sheath model, is employed to investigate the plasma properties and ion energy distribution function (IEDF) in biased inductively coupled Ar/O₂/Cl₂ plasmas. The results indicate that at a bias frequency of 2.26 MHz, the Cl^– ion density and ClO⁺ ion density first increase with bias voltage rising, and then they decrease, and finally they rise again, which is different from the densities of other charged species, such as O and Cl atoms. At the bias frequency of 13.56 MHz and 27.12 MHz, except Cl^– and <inline-formula><tex-math id="M3">\begin{document}$ {\text{Cl}}_2^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231369_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231369_M3.png"/></alternatives></inline-formula> ions, the evolutions of other species densities with bias voltage are similar to the results at lower bias frequency. The evolution of the species densities with bias frequency depends on the bias voltage. For instance, in the low bias voltage range (< 200 V), the densities of charges species, O and Cl atoms increase with bias frequency increasing due to a significant increase in the heating of the plasma by the bias source. However, when the bias voltage is high, say, higher than 300 V, except <inline-formula><tex-math id="M4">\begin{document}$ {\text{Cl}}_2^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231369_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231369_M4.png"/></alternatives></inline-formula> and Cl^– ions, the densities of other charged species, O and Cl atoms first decrease with bias frequency increasing and then they increase due to a decrease and then an increase in the heating of the plasma by the bias source. In addition, as the bias frequency increases, the peak separation of IEDF becomes narrow, the high energy peak and low energy peak approach each other and they almost merge into one peak at high bias frequency. The results obtained in this work are of significant importance in improving the etching process.