New Photoresist Shrinks Features

Kathleen G. Tatterson

SAN FRANCISCO -- Integrated circuit manufacturers are taking a very close look at a single-layer photoresist that scientists say will support component design smaller than 0.18 µm, with the promise of 0.13-µm design capability within a year.
At the American Chemical Society meeting in San Francisco in April, researchers from Bell Laboratories of Murray Hill, N.J., announced the development of a 193-nm, etch-resistant, aqueous-base photoresist material that they believe will fulfill the next phase of Moore's Law of the semiconductor industry. According to this popular standard, in order to stay competitive, integrated circuit manufacturers must be able to double the number of components on a chip every two years.
The report said that this design is compatible with existing technologies used in manufacturers' quest for ever-smaller design rules, leading to faster, more powerful devices.
"The semiconductor industry is moving toward 193-nm resists by the turn of the century," said Elsa Reichmanis, head of Bell Labs' Polymer and Organic Materials Research Department. "Key players would like to see it as a standard in semiconductor lithography before the year 2000."
Conventional photoresists are based on an aromatic polymer containing benzene rings that provide a means of resisting the etching process. However, at 193 nm, such materials absorb too much light, so uniform image definition is impossible. Bell's material consists of a class of matrix resins based on cyclo-olefin-maleic anhydride alternating copolymers, containing large quantities of alicyclic structures directly in the polymer backbone. Not only do these materials result in lower light absorption, but the decreased oxygen content provides higher etching resistance.

Smaller and smaller
Traditionally, photoresists using 248-nm (KrF) lithography are employed to resolve features between 0.25 and 0.18 µm. In Bell Labs' view, 193-nm photoresists (using ArF lasers) will be the standard for component design down to 0.13 µm; however, chip makers will need an alternate technology for devices smaller than that. The lab is working on a proprietary electron-beam exposure technology for sub-0.13-µm imaging.
Although Lucent Technologies, the lab's parent company, will apply the technology in its semiconductor manufacturing arm, the lab is also interested in the bigger picture. "We're developing advanced material processes with the intent of gaining the expertise within Lucent, but we are also interested in licensing and working with resist suppliers who will be making the materials technology available," Reichmanis said.