Conformal ion implantation

Using a 40–50 kV system we have made measurements of how small the sheath can be in plasma implantation with the objective of finding the limits of the process. We have made measurements of sheath size in plasma implantation using the probe technique developed at the University of Wisconsin [M.M. Shamim et al., J. Appl. Phys. 70 (1991)]. We also developed a tritium tracer technique for rapidly measuring the relative implanted dose. The tritium tracer technique is particularly attractive because the amount of tritium required is extremely small (below the activity level which requires regulatory approval) and it can be obtained from a source such as a display tube. In the measurements, we find that implantation with sheaths of distance 1.5–3 cm at voltages of 40–50 kV is similar to operation in other parameter regimes. The only limits occur in the range (100 kV/cm) where vacuum breakdown of the substrate is anticipated in any case.