Nonlocal electron kinetics and spatial transport in radio-frequency two-chamber inductively coupled plasmas with argon discharges.

A two-chamber inductively coupled plasma (ICP) system, in which an expansion region with large volume is attached to a main ICP (driver region with a small vessel), is investigated. In order to give a comprehensive knowledge of this kind of plasma source, the axially and radially resolved measurements of the electron density, effective electron temperature, and electron energy probability function (EEPF) for an argon discharge are systematically conducted by means of Langmuir probe for various powers and gas pressures. Moreover, a hybrid model within COMSOL Multiphysics is employed to validate the experimental results. It is found that the diffusion combined with the nonlocal electron kinetics plays a predominant role in two-chamber ICPs. Along the axial direction, both the electron density and the electron temperature peak at the center of the driver region and they decline towards both sides. The depletion of high-energy tails of EEPFs with axial distance demonstrates the cooling mechanism for energetic electrons in the expansion region. Along the radial direction, the spatial distribution of the electron density exhibits a bell shape for various powers and pressures. However, the radial distribution of the effective electron temperature varies gradually from a convex shape to a concave shape with increasing gas pressure, indicating the transition from nonlocal to local electron kinetics. [ABSTRACT FROM AUTHOR]