X-ray inspection may meet computer chip-making need

False color images of the molecular Bose-Einstein condensate forming. Left—A cloud of gaseous fermionic potassium cooled to 250 nanoKelvin and paired into bosonic molecules. Right—The same experiment starting at 90 nanoKelvin where the molecules collapse into a Bose-Einstein condensate. In both images higher areas indicate a greater density of atoms For a high resolution version of this image, contact mark.bello@nist.gov.

A decades-old, X-ray-based method for studying the atomic structure of materials may be the answer to a looming semiconductor industry need--a rugged, high-throughput technology for measuring dimensions of chip circuitry packed with devices approaching molecular proportions.

A team led by National Institute of Standards and Technology (NIST) scientists recently reported* their initial success in adapting small-angle X-ray scattering (SAXS) to rapidly characterize the size and shape of grid-like patterns with nanometer-scale linewidths. With better than one nanometer (billionth of a meter) precision, the team determined the average size of periodically repeating features arrayed on three chemically different samples much like the intricately patterned polymer masks used to print integrated-circuit designs.

With the size of on-chip devices soon to shrink to below 100 nanometers, current dimensional measurement tools are approaching their limits. The versatile SAXS method, the team suggests, could be an able substitute. It can be used on a wide range of materials to evaluate the quality of surface and subsurface patterns consisting of features considerably smaller than 100 nanometers.

In proof-of-concept experiments supported by the Defense Advanced Research Projects Agency, NIST, and the U.S. Department of Energy, essential data were gathered, within a second, over an area about 40 micrometers on a side--a large swath, nanotechnologically speaking. Images assembled from X-rays deflected by electrons in the samples yielded high-precision measurements of linewidths, spaces, line-edge roughness, and feature geometry.

Implementing the SAXS method actually should become easier as feature sizes decrease and near molecular dimensions, explains NIST's Ronald Jones.

In addition to NIST polymer scientists, the team included researchers from ExxonMobil Research Co., Argonne National Laboratory's Advanced Photon Source, and the Shipley Co. For more details, see www.nist.gov/public_affairs/newsfromnist_says.htm

*Ronald L. Jones, Tengijao Hu, Eric K. Lin, Wen-Li Wu, Rainer Kolb, Diego M. Casa, Patrick J. Bolton, and George G. Barclay, "Small angle X-ray scattering for sub-100 nm pattern characterization," Applied Physics Letters, Vol. 83, Issue 19, pp. 4059-4061.