Optical Lithography Gets Another Challenger

Electronic News, May 8, 2000 by Jeff Chappell

An April 25 announcement heralding a next-generation lithography technology caused a ripple of speculation and skepticism throughout the industry, which spread, well, nearly as fast as a beam from a krypton fluoride laser.

The announcement about the technologyaknown as reference distribution aerial image formation (RIF)acame from analyst Robert Castellano at The Information Network and its client Mulith Inc. The news piqued the industry's interest, but many insiders, reluctant to comment on the record, said they remain skeptical, with some even dismissing the announcement altogether.

Mulith is a small intellectual property company that is looking to either get acquired by a larger company, license its technology, or partner with a larger technology or venture capital company, Castellano said. Mulith said its technique can produce feature sizes well below 0.1 micron using standard i-Line photoresist without the need for image-enhancement processes such as phase-shifting and optical proximity correction. The company also said its technology completely eliminates conventional optical lens systems.

"What we are trying to point out is that not only is the technology available, but it's at lower cost," Castellano said.

Greyson Gilson, Mulith president, said the new technology could challenge optical lithography tools as IC features shrink.

"With conventional lithographic tools on the market, the minimum feature size that can be printed is limited by the wavelength of light used," Gilson said. "No such fundamental resolution limit exists for the new RIF technology."

Apparently building on optical microscopy technology, Mulith's RIF involves taking the aerial image of an object after it has passed through an imaging system and combining it with a second optical signal. This second signal contains a reference image that is separated from the original aerial image and contains additional information and provides a more detailed image when combined with the aerial image. Similar technology is used in high-frequency optical telecommunications.

Castellano said the April 25 announcement did generate a lot of interest. He received calls from the likes of Conexant Systems Inc., Micronas Semiconductor Holding AG, DuPont Photomasks Inc., Photronics Inc., ASML, and Lam Research Corp.

Lithography Death Knell?

Whether or not Mulith's RIF technology can usurp conventional optical lithography is, of course, anyone's guess. But many who work inside the lithography industry are quick to point out that RIF joins other next-generation technologies waiting in the wings for an end to optical lithography that never seems to arrive.

"The field is littered with folks trying to break into this business. a[broken (vertical) bar] There are five next-generation lithography technologies; this would be number six. But over the last five years, no one has proven any of these technologies" for production, said Steve Carlson, senior vice president of technology for mask maker Photronics Inc., Jupiter, Fla.

Carlson and other lithography insiders pointed out that whatever next-generation lithography technology comes to the forefront, if any, it will have to prove economically advantageous. Optical lithography already has an advantage in that it is an entrenched technology athe tools are already in place and the technology proven.

Historically of course, the industry has consistently managed to stretch optical lithography technology further than anyone expected, and that trend seems to be continuing. Numerical Technologies Inc. executives recently noted that the industry has demonstrated that the manufacture of 0.1-micron devices is possible using today's technology and tools. At a lithography trade show earlier this year in Silicon Valley, participants displayed working structures of .055 micron made with a 248-nanometer Canon stepper and a conventional light source and photoresist.

"It's an indication of where things will go in the future," said Atul Sharan, vice president of marketing and business development for Numerical Technologies, San Jose.

Carlson suggested that Mulith has a long way to go before it can convince the entire industry, which is traditionally conservative. "Without having a little bit more information a[broken (vertical) bar] the consensus is cautiously pessimistic that (RIF) has enough substance to make it," he said.