Studies of electron heating and transport in a low pressure Inductively coupled plasma

Abstract

Electron heating and transport are investigated in a low pressure inductively coupled plasma (ICP) and these subjects are essential to understand ICP as well as others plasma. In a finite size planar ICP at low pressure, plasma parameters from the measured electron energy distribution function (EEDF) are obtained with changing the chamber height at low pressure 2 mTorr. It is observed that electron density has a local peak at a certain chamber height while electron temperature decreases monotonously with increasing chamber height. The chamber height with the maximum electron density is shifted according to the bounce resonance condition when the driving frequency is changed. The electron kinetic model well agrees with the experiment. This shows that the electron density peak against the plasma size is due to the electron bounce resonance that has been theoretically discussed. In a solenoidal ICP, rf power with driving frequency 4MHz is applied at low pressure 1 mTorr. The EEDFs are measured by an rf compensated Langmuir probe at different rf powers. As the rf power increases, a Maxwellian EEDF evolves into a bi-Maxwellian EEDF with a low energy peak. This means that the electron heating in the plasma greatly changes. This EEDF transition can be understood by considering the rf magnetic field effect which is strong at low frequency. To investigate the nonlocal nonlocal and local property of the EEDF in a solenoidal ICP, The EEDFs at different radial positions are measured by an rf compensated Langmuir probe in a low pressure. It is found that the measured EEDFs for trapped electrons with total energy $∈ ＜ eφ_w$ (wall potential) are a function of only total energy while the EEDFs for free electrons that can escape plasma are functions of radial position and total energy. The depletion energy of the EEDFs in free electron range is determined not only the wall potential but also the electron canonical momentum $p_θ$. These results are consistent with the nonlocal e...