Energy contamination from multiple-charged ion implantation in conventional implanter

We studied the energy contamination (EC) in multiple-charged ion implantation with conventional implanters. The presence of the EC of low energy ions caused by the charge exchange with the outgassing molecules from photoresist is a serious problem. We evaluated the dose and energy of the EC using the SIMS analysis. The dose of EC reaches 12% of the P/sup ++/ dose for a beam current of 400 p/spl mu/A. When the beamline pressure is improved by reducing the beam current to 200 p/spl mu/A the amount of EC decreases to 5%. The ratio of EC to P/sup ++/ dose has a good linearity with the beamline pressure. We examined the influence of EC on the device characteristic for several type of structures when a retrograded n-well is formed by P/sup ++/ implantation. In the case of 0.25 /spl mu/m PMOS surface channel transistors, a shift in the threshold voltage is suppressed to less than 1% when R/sub EC/ is 5%.