Correlation between electron temperature and plasma power in inductively coupled plasma

It is generally recognized that the electron temperature T$_{\mathrm{e}}$ either remains constant or decreases slightly with plasma power (plasma density). This trend can be simply verified using a single-step or multi-step fluid global model. In this work, however, we observed the abnormal behavior of T$_{\mathrm{e}}$ in ICP. In the low RF power or plasma density region, T$_{\mathrm{e}}$ decreased, while it increased in the high RF power region. It was also demonstrated from the laser Rayleigh scattering measurement that gas temperature slightly increased with low RF powers, and it significantly increased in the high RF power region. The kinetic model, which considers stepwise ionization and gas heating, was developed to analyze the change in T$_{\mathrm{e}}$. From the kinetic model analysis, the apparently abnormal trend in Te can be understood by the contrasting effects of stepwise ionization and gas heating. It should be noted that the original notion was that Te is decoupled (or weakly coupled) to the plasma power or plasma density, and thus, Te must remain constant (or slightly decrease) with plasma density in the conventional global model. However, our experiments and improved modeling show that Te has a much stronger relationship with plasma power than we initially expected, and the gas heating effect should be considered [1]. [1] Lee et al., Appl. Phys. Lett. 110, 014106 (2017).