Dust phenomena in processing plasmas

Abstract

Dust phenomena in processing plasmas are reviewed from the new viewpoint of birth of material in the plasma. The gas-phase growth of particles has been extensively studied for Si4 RF plasmas. The Si particles usually grow through three distinctive stages: an initial growth phase up to about 10 nm, whose size is between size ranges dominated by plasma properties and their electron affinity; a rapid growth phase and a growth saturation phase. In the first phase, particles are localized around the plasma/sheath boundary in spite of a large fraction of neutral particles. In the second phase, extremely fast coagulations between particles appear, which can be explained by the generation of positively charged particles due to high-energy electrons. In the third phase, most of the particles are charged negatively and hence repel each other. Experiments on the formation of Coulomb solids in carbon RF plasmas and production of K-C60 plasmas are attractive since they indicate great potential for dusty plasmas. In the former experiments, almost perfectly spherical and monodisperse particles are successfully formed and transitions from liquid to solid phases and between body-centred cubic and hexagonal structures are clearly observed. In the latter experiments, plasmas composed of K+ and C60- ions are almost realized. Film properties change by controlling the energies of charged particles impinging on substrates and, under the specified plasma conditions, C60 with the K atom in its cage is successfully formed.