Development of stable extreme-ultraviolet sources for use in lithography exposure systems

Laser-produced plasma sources offer the best option for scalability to support high-throughput lithography. Challenges associated with the complexity of such a source are being addressed in a pilot program where sources have been built and integrated with extreme-ultraviolet (EUV) scanners. Up to now, five pilot sources have been installed at R&D facilities of chip manufacturers. Two pilot sources are dedicated to product development at our facility, where good dose stability has been demonstrated up to levels of 32 W of average EUV power. Experimental tests on a separate experimental system using a laser prepulse to optimize the plasma conditions or EUV conversion show power levels equivalent to approximately 160 W within a low duty-cycle burst, before dose control is applied. The overall stability of the source relies on the generation of Sn droplet targets and large EUV collector mirrors. Stability of the Sn droplet stream is well below 1 mu m root mean square during 100 + h of testing. The lifetime of the collector is significantly enhanced with improved coatings, supporting uninterrupted operation for several weeks. (c) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JMM.11.2.021110]