Ion Implanter Cross Contamination And Maintenance Safety Considerations With High Dose Phosphorus

The contamination on previously implanted Phosphorus into other species, known as “implant memory” has been previously reported with emphasis on diffusivity of the P in As (or Sb). This study continues some of the investigations done earlier but with some additional focus on some safety considerations. The residual Phosphorus or Arsenic in beamlines, target chambers and on implant disks has resulted in emissions of PH₃ or ASH₃ exceeding the TLV locally for extended periods during maintenance. Measurements taken during the cleaning of P contaminated ion source chambers in situ or on a bench top show that the maintenance technician can be exposed to PH₃ levels in excess of several hundred ppb or more. Freshly created PH₃ is available during maintenance due to the reaction of water vapor and Al???P and Al???As in quantities that need attention. Certainly self‐contained breathing apparatus is used for gas bottle changes but that use is not always dictated for cleaning of major subassemblies whether in place (on the implanter) or under a designated, remote work area — and it should be in these circumstances.