Extreme ultraviolet lithography: A review

Extreme ultraviolet lithography (EUVL) was thoroughly reviewed over a broad range of topics, including history, tools, source, metrology, condenser and projection optics, resists, and masks. Since 1988, many studies on EUVL have been conducted in North America, Europe, and Japan, through state sponsored programs and industrial consortiums. To date, no show stopper has been identified, but challenges are present in almost all aspects of EUVL technology. Commercial alpha lithography step-and-scan tools are installed with full-field capability; however, EUVL power at intermediate focus (IF) has not yet met volume manufacturing requirements. Compared with the target of 180 W IF power, current tools can supply only approximately 55-62 W. EUV IF power has been improved gradually from xenon- to tin-discharge-produced plasma or laser-produced plasma. EUVL resist has improved significantly in the last few years, with 25 nm 1:1 line/space resolution being produced with approximately 2.7 nm (3 sigma) line edge roughness. Actual adoption of EUVL will depend on the extension of current optical lithography, such as 193 nm immersion lithography, combined with double patterning techniques. Mask fabrication and application technologies may be the most substantial challenges. Creating a defect-free EUVL mask is currently an obstacle to its application, although a combination of removable pellicle and thermophoretic protection may overcome nonpellicle challenge. Cost of ownership is a critical consideration for EUVL; nevertheless, it has been predicted that EUVL may be in pilot production at 32 nm and in large-scale production at 22 nm with the capability to extend to the next technology node. (C) 2007 American Vacuum Society.