Editorial

Reflection on the Last 17 Years

J. Micro/Nanolith. MEMS MOEMS. 3(3), 373-374 (Jul 01, 2004). doi:10.1117/1.1778174
History: Online July 19, 2004
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On February 23, at the 2004 SPIE Microlithography Symposium in Santa Clara, this editor was awarded the first Frits Zernike Award for Microlithography for fundamental achievements in the theory, practice, and extension of optical lithography. This is definitely a cherished recognition. It also prompted a nostalgic trip in lithography for me. In 1987 I published the resolution and depth of focus (DOF) scaling coefficients k1 and k2. Subsequently, I also laid out an extensive roadmap showing k1 must be reduced by resolution enhancement techniques such as phase-shifting masks, optimized NA and illumination, proximity correction, managing reflections on the wafer and in the mask, and reducing mask-to-wafer vibration. I pointed out that a large field size can be realized by step and scanning a slot area taken from the circular field of a stepper projection lens. I also pointed out the advantages and challenges in immersion lithography. The exposure-defocus (E-D) tree methodology to construct a common processing window was my tool to quantify the advancement of optical lithography. With wavelength reduced to 193 nm, NA to 0.65, and k1 to 0.35, I pointed out that the ultimate resolution of optical lithography was 0.15-μm half pitch to support a 0.7-μm DOF. The common E-D window I used was from the windows of closely packed lines and spaces, isolated lines, and isolated spaces. At that time the majority of experts considered that optical lithography would peak out at 0.12 μm using VUV free-electron laser and all-reflective projection optics. The year it went to manufacturing was supposed to be 1999. The 157-nm wavelength would come two years earlier. In my predictions, I failed to anticipate that the NA could be raised to above 0.9 while maintaining the field size. I also failed to foresee the practicality of chemical mechanical polishing to reduce the DOF requirement. Now, by factoring 193-nm immersion in water and a much lower DOF requirement, the ultimate resolution in optical lithography becomes 45-nm half pitch as reported in my article in this issue. We have carefully included the multimedia, high NA, and polarization effects in our calculation to reflect as close to reality as possible.

© 2004 Society of Photo-Optical Instrumentation Engineers

Citation

Burn J. Lin
"Reflection on the Last 17 Years", J. Micro/Nanolith. MEMS MOEMS. 3(3), 373-374 (Jul 01, 2004). ; http://dx.doi.org/10.1117/1.1778174


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