Using CHARM-2 wafers to increase reliability in ion implant processing

This paper describes the use of CHARM-2 charge monitor wafers as a BIR (building-in-reliability) tool to identify, monitor and ultimately reduce implanter charging levels, resulting in increased die yields and enhanced product and equipment reliability. An ion implant engineering group at National Semiconductor Corporation has actively used CHARM-2 wafers to quantify charge potential levels existing in high current ion implanters, to baseline and monitor their set of four high current implanters, and to correlate die-level charging patterns on CHARM-2 wafers to product wafer yield patterns. CHARM-2 wafers have been successfully used to determine the effects of implanter equipment modifications and process changes on wafer charging. These equipment modifications have resulted in reduced wafer charging levels, and have therefore, helped to resolve charging-related product yield and reliability issues. The equipment and process modifications implemented with the aid of CHARM-2 wafers have also resulted in significantly improved equipment reliability and increased process robustness. Because of the consistently high degree of correlation of CHARM-2 charging patterns to product wafer yield patterns, CHARM-2 wafers serve as an effective in-line, implant charge monitor in a manufacturing environment.