Dosimetry enhancements for Varian's high-energy ion implanters

Two of the most important aspects of ion implanters are dose accuracy and repeatability. Space limitation inside the MeV process chamber requires that a small disc Faraday cup be used. The old disc Faraday cup on these high-energy implanters exhibited dose inaccuracy at very low energies. A new effective disc faraday cup assembly was designed to correct the problem. One of the major issues associated with the old cup was the ability to capture larger beams at low energy implants. The new cup was designed to have a large enough opening to capture the whole beam in a wider working energy range. For higher energy implants, emphasis on the design had to be placed to prevent the escape of secondary and tertiary electrons. The edges for the cover and suppression aperture were designed to minimize the escape of the secondary/tertiary electrons. A strong magnetic field was added to help to suppress the secondary electrons and ions. Although the aspect ratio is less than 1:1, the data gathered from the tests on the new disc Faraday cup showed very good results. Since preventative maintenance must be performed periodically on the cup assembly, mechanical re-assembly can also be a factor in the repeatability process. Mechanical components were redesigned to minimize the repeatability issues.