Dose control accuracy in pressure compensation

NV-GSD series ion implanters utilize pressure compensation systems to suppress dose shifts resulting from charge exchange between the ions and residual gas in the beam line such as from plasma shower systems or photoresist outgassing. Here we report on the following improvements in the pressure compensation system, which increase both its accuracy and availability : (i) a consideration of charge exchange in the analyzer magnet region, referred to as the beam line effect (ii) tabulation of pressure compensation factors to aid the automation of the pressure compensation system, and (iii) adoption of a new type of ion gauge which shows less variation between individual units as well as more stable behavior over time. As a result, the deviation in sheet resistance of implanted photoresist-containing wafers from implanted bare wafers is reduced to less than 1% (1σ). The improved pressure compensation system described here is currently available on the NV-GSDIII series high current implanters