Langmuir probe characterisation of ion source plasmas.

The precise conditions under which ions are generated in the ion source can have a major impact on how well the source performs, and how much of the extracted beam current can be transported. Because of the commercial focus on the repeatability and reliability of the overall ion implantation process, this vital aspect of the machine has received little scientific attention. hi order to address this issue, detailed studies of both the source and beam plasmas have been initiated. The research described in this thesis, was concerned with the former, and the characterisation of boron trifluoride (BF3) and argon plasmas created in a commercial indirectly heated cathode high current ion source, is described. Boron is still the main p-type dopant in the ion implantation industry but little information is available to date on the basic plasma parameters and the way in which they depend on the source operating conditions. Of major interest in the BF3 plasma is the cracking efficiency (gas and surface-phase phenomena may also be important), since the desired ion species is the singly charged atomic boron ion. Plasma parameters such as the density, electron and ion temperature, and the related plasma potential, dictate the nature of the processes occurring, and their rates. Detailed information on how the plasma parameters are affected by the source operating conditions (discharge "arc" voltage, discharge current, gas flow rate and confining magnetic field strength) was obtained from Langmuir probe measurements. In conjunction with the known performance of the source in field machines, the data have enabled the plasma parameters to be related to the overall system performance. Two electron temperatures were observed and significant spatial non-uniformities were apparent. The dependence of electron temperature on different operating conditions was found to be different, and source geometry and arc chamber material were also found to have an effect on the electron temperature