Design of ion energy distributions by a broad beam ion source

We characterize the performance of a built-in hot filament broad beam ion source by mass spectrometry, energy analysis, and beam profile measurements. In the ion energy; distribution we detect various peak structures which can be explained by the potential across the ion source and different charge transfer processes. Depending on the typical cross sections for these processes, differences between the energy distributions of the ion species are observed. The total ion current obtained with the source is determined by the ionization rate in the discharge and the current share directed toward the extraction grid system. The performance of the source is strongly dependent on the process gas used. We observe much broader energy distributions in oxygen and nitrogen than in argon. This broadening is explained by spatial inhomogeneities in the discharge region and can be reduced by a suitable setting of the source parameters. The main contribution to the ion flux is caused by species generated directly from the process gas, with important impurities from source materials appearing only with additional chemical reactions in oxygen. (C) 1996 American Institute of Physics.