Process control enhancements in a medium current implanter: (1) 2× improvement in dose repeatability (2) maximum dose sensitivity at 70 keV

A medium current implanter at National Semiconductor was upgraded to obtain better dose repeatability and uniformity. Major enhancements were made in the cup calibration, scanning, beam profiling, and dose digital interface systems. Sets of SIMS monitor wafers were implanted with a low energy, medium dose B implant before and after the upgrade. Depth profiles were measured and integrated to get the implanted SIMS dose. For the pre-upgrade set and post-upgrade sets, the SIMS dose sigmas were 2.54% and 1.06% of their averages, respectively, an improvement of 2.4×. Sets of B, As, and P sheet resistance (Rs) monitor wafers were implanted, annealed, and four-point probed before and after the upgrade. Sigmas in Rs for before and after the upgrade showed improvements of 1.81×, 1.87×, and 1.86×, respectively. To find the maximum dose sensitivity at 70 keV, implants of As, BF₂, and B at 70 keV were done at doses of 5E13-1E15 cm^-2. The Therma Wave sensitivity peaked near 1E14 cm^-2 for As and BF₂, but was fairly flat over the measured range for B. The sheet resistance sensitivity was relatively flat over the 5E13-1E15 cm^-2 range for all 3 species, with a slight increase at the higher doses for As and B