IMEC (Interuniversity Microelectronics Center) reports having used ASML’s EUV (extreme-ultraviolet) Alpha lithography tool to print the contact and metal patterns for a 22-nm-node SRAM cell—apparently, the first application of the tool for multiple layers at this density. The SRAM cell is both tiny—at 0.099 micron²—and based on a complex FinFET structure. The exercise emphasizes both the image fidelity and the overlay accuracy of the lithography system.

The FinFET structure, which IMEC developed, employs a hafnium-dioxide dielectric with a titanium-nitrogen-metal gate, draped over a nickel-platinum-silicide source-to-drain fin. IMEC printed the contact and metal layers using the EUV tool and all other patterns using conventional 193-nm immersion lithography. The researchers report that the lithography system achieved acceptable overlay accuracy in this application.

Perhaps the most significant aspect of this result, according to IMEC Chief Operating Officer Luc Van den hove, is that the team was able to print all the patterns for the cell without resorting to multiple-patterning techniques. This advantage could give EUV—notably slow, expensive, and not yet ready for prime time—just the edge it needs for consideration as at least a follow-on to process nodes in the 22-nm region.