Controlling line-edge roughness in EUV resist with sturdy, small molecules

by Dr. Paula Doe, Contributing Editor, Solid State Technology

Tokyo Ohka and Hitachi have demonstrated patterns with 28nm half-pitch resolution, with EUV resist made using small molecules that eliminate much line-edge roughness.

The very size of the large individual polymer molecules in conventional resist creates a problematic uneven edge in very small features at 32nm and beyond, though these polymers also provide the high mechanical strength that allows the resist to withstand etching and developing.

In work supported by the New Energy and Industrial Technology Development Organization (NEDO) and the Association of Super-Advanced Electronics Technologies (ASET), the companies designed a molecule with molecular weight an order of magnitude less than those used in current resists, but which still maintained etch resistance and developing characteristics similar to existing polymer-based products, reports SST partner Nikkei Microdevices.

The resist uses a new small-molecule polyphenol with molecular weight of around 1000, while the typical polymer weight is around 10,000. With resist sensitivity of 12.2mJ/cm2, the LER of printed 45nm features was 3.6nm, matching that of the best polymer resists. Features at 28nm half-pitch were also comparable those made with leading-edge conventional resists. These initial results were at exposures on the edge of the capability of the EUV lithography tool used, suggesting the approach may have considerable potential to be extended to smaller geometries.

Tokyo Ohka plans to start supplying samples of the resist for EUV and e-beam exposure this spring, targeting commercial sales in 2010. — Dr. Paula Doe, Contributing Editor

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