The effect of phosphorus contamination on an antimony collector implant has been studied by SRP, SIMS, and SUPREM modeling. The results indicate that this is one of the most serious cases of cross-contamination; where P levels in excess of 0.07% of the implant can modify the resulting junction depth and therefore all subsequent electrical parameters. The SRP curves resulting from phosphorus contamination may be recognized by a characteristic stepped curve which is reminiscent of P-push in As. SIMS data indicates that the antimony profile is marginally modified by the presence of phosphorus while the increase in junction depth is due not only to the larger diffusion constant of the phosphorus but also to an interaction that increases that constant. Methods of eliminating this contamination are discussed.