Reduction of beam dropout related defects in a hybrid scan implanter

Traditional raster scan systems were able to minimize the effect of beam dropouts by using fast beam scanning speeds combined with long minimum implant times. However, with 200 and 300 mm wafer sizes, most medium current implant systems have been developed using hybrid scanning techniques to minimize beam angles and these systems are inherently more susceptible to beam dropouts. Additionally the drive for increased productivity combined with wafer rotation capability has shortened minimum allowable implant times. This paper describes a method implemented on Axcelis medium current systems for actively correcting the effect of beam dropouts. Implant results are presented that demonstrate spec level wafer uniformity and dose repeatability with induced beam dropouts. This improvement is of particular relevance for very short implants, such as a single rotation of a quadrant implant