Studies on some aspects of plasma surface interaction in DC and RF discharges

Abstract

Introduction: The aim of the thesis is to investigate the plasma surface interactions in some DC and RF discharge plasmas. There has been widespread use of DC and RF discharges in basic plasma studies as well as material processing applications. The surface plasma interaction at the plasma boundary is a unique problem in plasma physics and has been receiving importance for its outstanding applications in plasma processing and fusion research. When a material surface is in contact with plasma, a space charge layer i.e. a sheath is formed adjacent to the surface that separates it from the bulk plasma. The explicit formulation and clear interpretation of the sheath formation in plasmas is due to Bohm, who introduced the idea of pre-sheath which accelerates ions to sufficient velocity for the ion density to exceed the electron density everywhere within the sheath. Main objectives of the research work: (a) To study the effect of negative ions in Ar/SF6 DC discharge plasma on its different parameters and sheath formed in front of a negatively biased metal plate. A theoretical model to be developed to relate the experimental findings quantitatively. (b) To study the pre-sheath and the drift velocity of the positive ions at the sheath-presheath edge in presence of negative ions in Ar/SF6 DC discharge plasma. (c) To study the effects of discharge voltages and the working gas pressure on the plasma parameters and the sheath of the powered electrode in a cylindrical capacitive RF plasma. Negative ion plasmas are involved and widely used in industrial applications of plasma-assisted techniques, such as surface coating with reactive sputtering, chemical vapour deposition process, plasma etching process etc. In plasma processing, a good understanding of the characteristic properties of plasma sheath formed near a physical boundary is required to have a proper control over the parameters governing the surface processes. The study of negative ion plasma is essential to acquire proper knowledge about these physical processes....