Purity of low energy beams in R.F. linear accelerator based implanters

Nearly monoenergetic beams of ions in the 10-200 keV range are critical in many implants for semiconductor fabrication. In this study, possible contamination scenarios leading to beam components significantly different in energy from the intended beam are examined in the context of a specialized use of an R.F. linear accelerator. In this specialized use, only the electrostatic quadrupole focusing elements of the linear accelerator are powered, and all R.F. components are unpowered. The beam is simply transported through the accelerator at extraction energy. Experiments have been performed to artificially create conditions which might lead to energy contamination. The susceptibility of the system to the transport of a contaminated beam was measured by direct observation of beam currents. For example, the transmitted current of the two partners in phosphorus dimer contamination are compared, showing large suppression factors. In these cases, it was found that the implanter system provides protection against contamination.