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SEMATECH cautious over novel materials to extend immersion lithography |
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Mar 09, 2007 at 02:21 PM |
 In the wake of disappointment over the slow progress of EUV lithography, renewed efforts to extend 193nm Arf immersion lithography below the 32nm half-pitch node, whether in single or double patterning mode, are heavily dependent on a host of novel materials, according to SEMATECH.
A new bottom lens material with a higher refractive index than fused silica's 1.56 is being sought with lutetium aluminum garnet (LuAG), a crystalline mineral seen by SEMATECH as the leading candidate. LuAG has a refractive index of 2.14.
However, significant work is required to produce and evaluate LuAG before the material could be made in the size and quantities required for hyper NA lens assemblies. A joint development program between Schott Lithotec and SEMATECH is currently underway, but projection-quality LuAG lens elements with a diameter of 80mm for beta testing are not expected to be ready until 2009, with tools ready the following year. LuAG lens elements of around 150mm in diameter will actually be required for high-volume manufacturing environments. A timetable for this has yet to be made public.
Fluids with an index greater than water (1.44) were first touted at SPIE several years ago but have disappointed lithography tool vendors with bottom lens contamination and viscosity issues, to name a few.
A wide range of fluids in the range of 1.6 to 1.7 have been evaluated but all appear to have significant drawbacks. SEMATECH, through support of research groups at MIT Lincoln Laboratory and at the University of Wisconsin, is pursuing approaches to ‘third generation' fluids - based on nanocomposites, carbon-ring organics and hetero-compounds - with refractive indexes above 1.8.
Separately, SEMATECH and the University of Queensland in Australia have recently developed a sulfur-based fluid with a resist index of 1.76. The challenge once again is not just the fact that there are technical hurdles, but that timing is of the essence.
"We need to make the technology for these future generations available in the next 10 ½ months—that's our mission," said Bryan Rice, manager of SEMATECH's 193i program. "We need to offer a choice of technologies to semiconductor manufacturers."
With the semiconductor industry remaining focused on optical extensions to 193nm ArF lithography - with EUV remaining a distant hope - alternative technologies such as multiple e-beam systems remain in the shadows for now!
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