The Era of High-NA EUV Lithography Has Arrived!

With full-field high-NA EUV exposure tools now in operation at multiple sites, the move towards this latest generation of lithographic technology is well under way.Fittingly, the current issue JM 3 includes a Special Section on High Numerical Aperture Exposure Tools and Lithography, with papers addressing several aspects of this leading-edge lithographic technology.One paper, with authors from ASML and Carl Zeiss, describes the high-NA exposure tools in considerable detail, allowing readers to appreciate what extraordinary pieces of engineering these tools are.Also included in the special section are papers on aspects of computational lithography, resolution enhancement techniques, and novel processes for making ample use of the exposure tools' capabilities.Additionally, there are papers on facets of a very important component of EUV technology: masks.Two papers look even further ahead and cover topics relevant to further extension of EUV lithography and its ultimate limits.The realization of high-NA EUV lithography is a testament to the optimism and confidence of engineers.Even before the first 0.33 NA exposure tool had been shipped to a customer, workshops were held and papers published on high-NA EUV lithography.Development of high-NA EUV lithography continued even during the years when people struggled to bring 0.33 NA EUV lithography to a level of maturity sufficient for its use in high volume manufacturing.It is remarkable that resources were invested in next-generation EUV lithography during a time when a number of people were voicing their opinions that EUV lithography could never be useful at any numerical aperture for high volume manufacturing.Through persistence and determination, EUV lithography was enabled and the skeptics proven wrong.It has been a long journey to get to this point with high-NA EUV lithography.Some of the earliest studies were on EUV resists.Similar to what had been done when developing patterning materials for prior generations of lithographic technology, the capabilities of resists for high-NA EUV lithography were first investigated using microexposure tools.These tools were later supplemented with interferometric lithography systems.These small-field imaging tools were used by resist chemists, who extended the capabilities of chemically amplified resists, long the workhorse resist platform for leading-edge lithography.The research tools also provided capability for exploring and developing entirely new concepts for EUV resists, some of which are now being used in high volume manufacturing.Small field systems continue to be used in parallel with the full-field high-NA tools that have recently become available.Calculations and simulation were also leveraged to gain insight into the issues relevant to high-NA EUV lithography.One early learning was the need to increase lens reduction, at least in the scan direction, in order to enable imaging at high NA.This led to the first change in lens reduction for exposure tools used for leading-edge lithography since the early 1990s, and addressing the issues resulting from this change is an ongoing effort.Computational lithography remains important for fully enabling high-NA EUV lithography (particularly because of mask 3D effects).Earlier generations of EUV lithography have contributed to the development of computational solutions for high-NA lithography, by providing the patterning capability used in the fabrication of the integrated circuits utilized for high-performance computing.