Plasma characterization and technological application of a hollow cathode plasma source with an axial magnetic field

Abstract

An efficient plasma source has been established by arranging a hot hollow cathode electron emitter in a strong axial magnetic field, allowing for a reduction of working gas flow by one order of magnitude without loss of discharge stability. Moreover, with the reduction of gas flow not only an increase of the discharge impedance was observed, but also a multiplication of ion current density together with a highly expanded volume of the plasma plume. By means of spatially resolved Langmuir probe measurements, combined with the usage of an energy-resolved mass-spectrometer, plasma density profiles and energy distribution functions of electrons and ions have been measured. Generally, with an increase of the magnetic field and with the reduction of the working gas flow ion energy distribution functions shift from mean values of a few eV to 10 eV and more, while charge carrier densities increase from 10 9 cm − 3 to more than 10 12 cm − 3 . A strongly increased ability to dissociate and ionize reactive gases was observed. Two promising applications related to the coating of tools and components are discussed: the sputter etching with argon ions and the reactive pulse magnetron sputter deposition of wear-resistant chromium nitride layers. Whereas the first mentioned process provides pre-heating and etching rates higher than all actually used in tool coating industry, the second one offers advantages for film growth kinetics leading to significant improvements in composition, structure, surface morphology, and hardness of the deposited layers.