Seeing The Light...

Drawing illustrates how tiny changes in wavy images scattered from lines in a grid-like array can be reconstructed when paired with advanced optical and computational techniques. Lines are 15 nanometers wide, 30 times smaller than the wavelength used to “see” them. The pattern depicts estimated uncertainties in the experimental data. Coloring corresponds to the magnitude of the variance for specific data points.

Topics: Carbon Nanotubes, Consumer Electronics, Nanotechnology, Semiconductor Technology

National Institute of Standards and Technology (NIST) researchers are seeing the light, but in an altogether different way. And how they are doing it just might be the semiconductor industry's ticket for extending its use of optical microscopes to measure computer chip features that are approaching 10 nanometers, tiny fractions of the wavelength of light.

Using a novel microscope that combines standard through-the-lens viewing with a technique called scatterfield imaging, the NIST team accurately measured patterned features on a silicon wafer that were 30 times smaller than the wavelength of light (450 nanometers) used to examine them. They report* that measurements of the etched lines—as thin as 16 nanometers wide—on the SEMATECH-fabricated wafer were accurate to one nanometer. With the technique, they spotted variations in feature dimensions amounting to differences of a few atoms.

"Historically, we would ignore this scattered light because it did not yield sufficient resolution," explains Richard Silver, the physicist who initiated NIST's scatterfield imaging effort. "Now we know it contains helpful information that provides signatures telling us something about where the light came from."

With scatterfield imaging, Silver and colleagues methodically illuminate a sample with polarized light from different angles. From this collection of scattered light—nothing more than a sea of wiggly lines to the untrained eye—the NIST team can extract characteristics of the bounced lightwaves that, together, reveal the geometry of features on the specimen.

NIST: Measuring Nanoscale Features with Fractions of Light, Mark Bello