Swiss Develop Novel High-Resolution Lithography

-- Semiconductor International, 8/1/1999

Researchers at the IBM Laboratory in Zürich, Switzerland, have developed a fairly simple optical technique that can print features with a size less than half that of the wavelength of the light used. No complex or costly focusing optics are required. A 'light stamp'containing the pattern to be printed is placed directly on the wafer. Instead of the traditional contact lithography using chrome on glass masks, the IBM method uses a rubber-like mask that makes uniform contact with the wafer.

When light strikes the mask, it is guided into the substrate by the protrusions and is blocked or reflected in the recessed regions. Light scatter is minimized by the focusing effect of the protrusions and through the close contact between the stamp and the resist, which have matched refractive indices. Workers have printed lines down to widths of 100 nm (0.1 µm) using a 248 nm KrF excimer laser light source, but the stamp material now in use has too high an absorption at 193 nm and 157 nm for these wavelengths to be tried. They believe it is more important to increase the refractive index of the stamp material to reduce feature size than to reduce the wavelength of the light.

This system does not seem to produce defects or contamination of the wafer, but standing waves in the stamp protrusions can result in interference patterns during exposure. The group claims this contact lithography system has the potential to compete with optical lithography and next-generation techniques, so it might help avoid large investments in the quest for ever finer resolution. IBM is more likely to use it initially for niche applications than high-volume device production. It is said to be much less complex than any of the new lithography techniques.