The development of extreme ultraviolet lithography (EUVL) continues at an accelerating pace. Today, industry is looking at EUVL for the 16-nm node and below. Optics, sources, masks, and resist materials are all objects of intense research. Photoresists are a gating component of EUVL, because of the conflicting requirements of high sensitivity, high resolution, and low line-edge roughness. This development of advanced imaging materials is hampered by the scarcity of EUVL exposure systems and by limited access to these tools. There is a need for alternative exposure systems where novel materials can be tested and characterized quickly, economically, and without fear of contamination of the optics. Interferometric lithography (IL) is such a technique: in its simplest form, two coherent beams interfere to form a high-density fringe pattern that exposes the resist material. The uniformity, large area, and simplicity of operation make this fringe pattern ideal for the study of resist materials; in fact, several systems have been built for ArF lithography, including immersion. The extension of interferometric lithography to the EUV region is a natural technology evolution and makes high-resolution, simple, and fast-exposure systems available to the general research community. These exposure tools, based on the use of diffractive optics in various mounts, have shown patterning ability to the 10-nm region. Systems using two, three, and four beams have been demonstrated. Holographic lithography at EUV wavelengths has been proposed and demonstrated. Finally, we would like to point out that EUV-IL's freedom from cumbersome reflective optics makes it easily extensible to wavelengths shorter than the canonical 13.4 nm of EUVL. Thus, using synchrotrons or novel plasma sources in combination with 4× demagnification setups, EUV-IL will provide patterning ability in the 4- to 5-nm range, and even below.
© 2009 Society of Photo-Optical Instrumentation Engineers
"Guest Editorial: Extreme Ultraviolet Interference Lithography", J. Micro/Nanolith. MEMS MOEMS. 8(2), 021201 (June 15, 2009). ; http://dx.doi.org/10.1117/1.3156651