Product-wafer focus-exposure monitor for advanced flash memory

Focus-exposure control in lithography is a key challenge for CD control at the 130nm technology node and below. Focus error alone can account for more than 50% of the critical dimension variation seen in new processes and devices. Unseen focus and exposure excursions degrade first-pass yield, cause unnecessary rework, and reduce scanner productivity. For low-runner flash memory in early production, focus-related yield losses can be several percent. At FASL LLC´s Fab 25, we have determined that the most serious deficiency in focus-exposure control is a monitor that can work directly on product wafers.