Probe diagnostics of RF plasmas for material processing

Abstract

Summary form only given. Contemporary probe diagnostics of low pressure rf discharge plasmas implies the measurement of electron energy distribution function, EEDF and variety of plasma parameters found as the corresponding EEDF's integrals. Such task is quite doable for laboratory plasma experiments in noble gases at a moderate rf power. The attempts to implement probe diagnostics (proved in the laboratory plasma) for diagnostics of chemically active plasma reactors are in many cases frustrating. This problem is not recognized when one just measures the probe I/V characteristic, since distorted and undistorted probe characteristics look similarly. But the problem becomes apparent after double differentiation of the distorted probe characteristics to infer the EEDF. There are three major problems in implementing of meaningful probe diagnostics in rf plasma reactors. They are: a) large frequency spectrum with significant amplitudes of the plasma rf potential corresponding to source and bias fundamental frequencies and their harmonics; b) contamination of the probe surface with a low conductive layer of the reaction products; and c) too high impedance between the plasma and grounded chamber due to the chamber contamination or/and an artificial protective coating. The way to address these problems and examples of EEDF measurements in different rf plasma reactors where these problems are successfully resolved are discussed in this presentation.