Next-generation lithography
From Wikipedia, the free encyclopedia
Next-Generation Lithography (NGL) is a term used in integrated circuit manufacturing to describe the lithography technologies slated to replace photolithography. Currently the most advanced form of photolithography is immersion lithography, in which water is used as an immersion medium for the final lens.
Candidates for next-generation lithography include: extreme ultraviolet lithography (EUV-lithography), X-ray lithography, electron beam lithography, focused ion beam lithography, and nanoimprint lithography. Electron beam lithography was most popular during the 1970s, but was replaced in popularity by X-ray lithography during the 1980's and early 1990's, and then by EUV lithography from the mid-1990's to the mid-2000's. Focused ion beam lithography has carved a niche for itself in the area of defect repair. Nanoimprint's popularity is rising, and is positioned to succeed EUV as the most popular choice for next-generation lithography, due to its inherent simplicity and low cost of operation as well as its success in the LED, hard-disk and microfluidics sectors.
The rise and fall in popularity of each NGL candidate largely hinged on its throughput capability and its cost of operation and implementation. Electron beam and nanoimprint lithography are limited mainly by the throughput, while EUV and X-ray lithography are limited by implementation and operation costs. The projection of charged particles (ions or electrons) through stencil masks was also popularly considered in the early 2000's but eventually fell victim to both low throughput and implementation difficulties.
Ironically, each NGL candidate faced more competition from the extension of photolithography than from any other NGL candidate, as more and more methods of improving photolithography continued to be developed, including optical proximity correction, off-axis illumination, phase-shift masks, liquid immersion lithography, and double patterning. Even within the area of photolithography, there is a list of "next-generation" techniques, including two-photon lithography, 157 nm wavelength, and high-index immersion.
Regardless of whether NGL or photolithography is used, etching of polymer (resist) is the last step. Ultimately the quality (roughness) as well as resolution of this polymer etching limits the inherent resolution of the lithography technique.
