Swiss study shows photons aren’t the problem for hyper-NA EUV

Researchers at the Paul Scherrer Institute (PSI) have created 5 nm half-pitch line/space patterns with 13.5 nm EUV light. For comparison, the theoretical maximum resolution of ASML’s high-NA EUV tool is 8 nm half-pitch. The Swiss approach isn’t interesting for high-volume manufacturing, because it’s slow and can produce only simple and periodic structures rather than a complex chip design. It’s very useful, however, for early development purposes ahead of a new generation of EUV tools, which in this case would be the hyper-NA system ASML has hinted at.

The technique employed by PSI is called EUV interference lithography (EUV-IL), in which two EUV beams are made to interfere with one another to create periodic images. Previously, the Swiss researchers used diffraction gratings to generate patterns down to 6 nm half-pitch. This EUV-IL sub-variety has been extensively used in the development and evaluation of photoresist materials for EUV lithography.

Because of their low diffraction efficiency, EUV-IL gratings require relatively high exposure times, even when using a very bright synchrotron light source. This encourages thermal and mechanical drift, resulting in lower imaging quality.