Electron diagnostics of magnetron discharges

Abstract

The magnetron is a weakly magnetised plasma source used for physical vapour deposition to produce high-quality thin films and coatings for technological applications. In this research, electron plasma property measurements were performed in conventional DC magnetron discharges and in high power impulse magnetron sputtering (HiPIMS) discharges. The two main topics of this thesis are: (i) a comparison of electron plasma property measurements made by Langmuir probe and incoherent laser Thomson scattering, and (ii) an investigation of electron dynamics in HiPIMS discharges using a combination of incoherent laser Thomson scattering and optical emission spectroscopy. Electrons are responsible for driving many important processes in low temperature discharge plasmas, such as, plasma heating, ionisation and plasma chemistry. The Langmuir probe is commonly employed to measure electron plasma properties, but its data can be difficult to interpret, especially from magnetised plasma. The aim of the first part of the research was to assess the accuracy of electron plasma property measurements made by Langmuir probes in weakly magnetised plasma, by comparing the results from the probe measurements with reliable results obtained via laser Thomson scattering. Standard unmagnetised theories were used to interpret the probe data. The range of magnetic field strength, electron temperature and electron density in the study were 1 10^{19} m^{-3}), metal-rich plasma propagating along the axial direction from the magnetic trap region to a typical substrate position. The main outcomes from this research were experimental confirmation of the expected features of HiPIMS discharges using the reliable laser Thomson scattering technique, and validation of trends identified in previous Langmuir probe studies at a typical substrate position. Therefore, the results provide a solid foundation for the understanding of electron dynamics in HiPIMS.