Tungsten contamination in BF/sub 2/ implants

Evidence is presented showing that tungsten contamination can be detected in the range of 10-110 ppm of implanted dose for BF/sub 2//sup +/ implants. The contamination is absent in As/sup +/ implants. Analysis of isotopic ratios of the contaminant atoms, beam energy dependence of the contamination levels, and energy of the contaminant ions (based on SIMS analysis) is used to deduce the origin of the contamination. Direct analysis of W-bearing ions, molecular breakup reactions and charge change are evaluated as potential causes and we conclude that charge and or decomposition change of a molecular species is the only viable candidate as the root cause. Specific molecular decompositions are offered as potential causes. Possible methods of elimination and/or minimization of the contaminant are presented.