Use of accelerator mass spectrometry for trace element detection

Reduction of metallic contamination during ion implantation is becoming increasingly critical for device performance. Modern implanters are therefore, being developed with novel beamline coating materials and optics to keep sputtered contamination to a minimum. The ever-shrinking devices require analytical techniques that can detect impurities down to trace levels. The most commonly used methods to characterize implanted wafers include SIMS, TXRF, AAS, and ICP-MS. The use of trace element accelerator mass spectrometry (TEAMS) for this application is investigated in this study. TEAMS offers a lower detection limit since it uses a charge exchange chamber to dissociate the molecular ions. Studies have shown that TEAMS can detect concentrations down to the ppb level for some elements by virtue of the elimination of molecular interference. A collaboration among Varian IIS, University of North Texas and Texas Instruments Inc. has been established to investigate the possibility of employing TEAMS for detection of contamination during ion implantation. Results of silicon wafers analyzed by TEAMS are presented. Future development of this collaboration is under way to understand the technique better.