We characterize the performance of a built-in hot filament broad beam
ion source by mass spectrometry, energy analysis, and beam profile mea
surements. In the ion energy; distribution we detect various peak stru
ctures which can be explained by the potential across the ion source a
nd different charge transfer processes. Depending on the typical cross
sections for these processes, differences between the energy distribu
tions 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 use
d. We observe much broader energy distributions in oxygen and nitrogen
than in argon. This broadening is explained by spatial inhomogeneitie
s 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 im
purities from source materials appearing only with additional chemical
reactions in oxygen. (C) 1996 American Institute of Physics.