Too soon for deep-UV steppers
Because Perkin-Elmer Corp may be bought by Japanese interests, the situation for VLSI integrated circuit production technology in Japan and the US is becoming more interesting. Japanese manufacturers have bet on deep-UV technology for manufacturing VLSI integrated circuits, and have pursued development of deep-UV steppers, photoresists and lasers.
Meanwhile, US manufacturers’ gradual transition to I-line for submicron technology has proved unexpectedly successful. The Japanese had maintained that I-line was not practical to use. The key for US companies is to push I-line technology as far as possible before the Japanese make deep-UV equipment ready and available. Perkin-Elmer Corp, which may be bought by a Japanese firm, is a US company developing a deep-UV stepper.
Now that Perkin-Elmer Corp., Menomonee Falls, Wisc., is for sale and may be bought by Japanese interests, it makes for an interesting situation regarding VLSI IC production technology in the U.S. and Japan. While equipment manufacturers in both countries press on toward the next technology level, Japanese chip makers may have waited too long to pursue an interim step that many U.S. companies took. The result: U.S. chip makers may find themselves, for the meantime, with an unexpected technology edge.
As recently as 1985, 1-[micrometer] design rules were considered state of the art for advanced VLSI production. Optical equations predicted that 0.5 [micrometer] was the resolution limit. Today, however, manufacturing is shifting from G-line lithography, with its 436-nm exposure source, to I-line, which sports a 365-nm source.
These new frontiers in line widths for VLSI circuits are the result of polymer chemistry as well as the associated optics. Polymer chemists are now placing the limit at 0.25 [micrometer]. They’re making no promises, though, because theoretically, the line widths can’t go beyond the wavelength of the I-line exposure source, which is 365 nm, or 0.36 [micrometer]. The next level is a deep-UV exposure source, which is 254 nm. In theory, this could take lines and spaces down to about 0.25 [micrometer]. But it’s probably a year or two from viability.
Apparently, Japanese manufacturers of VLSI ICs are looking to 0.25 [micrometer] for next-generation VLSI devices, which is a factor-of-four density increase compared with 0.5-[micrometer] I-line. Those companies have bet heavily on deep-UV and have hotly pursued development of deep-UV steppers, lasers, and photoresists. Meanwhile, I-line has become unexpectedly successful and gained a new life. Essentially, it was written off too soon, especially by the Japanese chip makers who maintained that I-line was unpractical due to its 0.5-[micrometer] limit. Meanwhile, deep-UV became more difficult to develop than was believed.
Concurrent with their drive toward deep-UV, the Japanese tried holding their technology edge by pushing G-line lithography to its limit by improving the optics. Indeed, they took G-line farther than anyone thought possible and achieved much tighter production parameters than U.S. companies. But because U.S. companies weren’t able to push G-line as far as Japan, they promoted the more gradual transition to I-line as a viable strategy for submicron lithography. As a result, U.S. companies gained a small technology edge. The key, now, will be to get as far ahead as possible with I-line before deep-UV is ready and viable, and before the Japanese shift gears and catch up in I-line.
But Japanese manufacturers are already on the move. Nikon, San Bruno, Calif., is one Japanese-based company that got to market with an I-line stepper by recently introducing its NSR-1755i7 A. Moreover, Nikon claims to have the largest exposure area available in an I-line stepper (17.5 mm square) as well as a production resolution of 0.58 [micrometer]. European companies are also joining the I-line parade. ASM Lithography, based in Tempe, Ariz., but owned by Philips, the Netherlands, rolled out its PAS 5000/50 I-line stepper and claims 0.50-[micrometer] production resolution and 0.35-[micrometer] resolution for research work. ASM also has a deep-UV machine in progress.
Among U.S. manufacturers, Perkin-Elmer is developing a deep-UV stepper. GCA, Andover, Mass., is marketing its AutoStep 200 I-line stepper and is working on a deep-UV machine. Sematech, the Austin, Texas-based consortium, is concentrating on I-line lithography, but is committed to transferring a well-characterized 0.5-[micrometer] process to its member companies by 1991.
KTI Chemicals, Sunnyvale, Calif., (a Union Carbide subsidiary) already offers its 895i I-line photoresist product. It’s betting that I-line will be the way to go because deep-UV will require a massive equipment investment. But just in case, KTI has a deep-UV photoresist in the works.