Effects of energy, dose, and beam current on particle counts in medium-current phosphorus implants

Abstract

The effects of energy, beam current, and implant time (dose) on particle counts on implanted wafers were investigated for phosphorus implants on an Eaton 6200AV implanter, before and after a thorough clean of the implanter's source, analyzer, and beamline. Before the system clean: 1) ion energy significantly affected the number of particles added to the wafer; 2) implant time (dose) had a significant effect at higher energy but not at lower energy; and 3) beam current had a minor effect. After the system clean, all particle counts were greatly reduced, and the energy- and time-dependence of particle counts was absent in the range of parameters studied. To explain these results qualitatively, it is hypothesized that, at higher beam energies, particles are sputtered off surfaces in the implanter, are trapped by the beam, and are transported by the beam to the wafer [1,2]. Lower beam energies may be insufficient to sputter and/or trap particles, so the implant's duration has little effect. At higher energies, as material is sputtered off, the number of particles deposited on the wafer would increase with implant time. The energy dependence of particle counts was studied in detail from 150 to 175 keV. Before the system clean, a smooth increase in particle counts with energy was seen.