Manufacturing Bits: Oct. 27

CD-SAXS makes progress
For years, chipmakers have used metrology tools based on various optical techniques, such as scatterometry.

But optical-based scatterometry may one day run out of steam, prompting the need for a possible replacement. One long-awaited candidate is called X-ray scattering. There are various flavors of X-ray scattering, including CD small-angle X-ray scattering (CD-SAXS).
 
CD-SAXS is promising, but it still suffers from the same problem—the light source. CD-SAXS uses an X-ray source and they are low in power. As a result, the throughput for CD-SAXS is slow.

The technology is making progress, however. Intel and the National Institute of Standards and Technology (NIST) recently used CD-SAXS to measure features on a chip to within fractions of a nanometer.

In the lab, researchers devised 12nm lines on a device. The space between lines varied by less than 0.5nm from a pitch of 32nm. CD-SAXS measurements of periodic pitch errors were accurate to within 0.1nm, and measurements of line shapes were accurate to about 0.2nm.

An example CD-SAXS scattering pattern (left) shows the interference patterns created by the shape of the nanostructure, which ultimately yield a “best fit” shape model (top, right). The corresponding cross-sectional image (bottom), obtained with a TEM shows the nanostructure measured by NIST and Intel. (Source: R.J. Kline/NIST)

So is CD-SAXS ready for prime time? Not quite yet.

“The results show there are no inherent resolution limitations for CD-SAXS in measuring next-generation devices when you have a lot of X-rays,” said Joseph Kline, a materials engineer at NIST. “Throughput is still the primary limitation. There are several companies and research groups working on new compact X-ray sources that would make CD-SAXS viable if the sources work as proposed.”

Today’s CD-SAXS systems are based on a rotating anode source, which is limited in terms of power. Another source technology, liquid-metal-jet, is promising but it is not ready yet.

Measuring van Gogh’s paintings
Using X-ray diffraction measurement techniques, a group of researchers determined that Vincent van Gogh’s famous Sunflowers painting is changing over time. What this means is that the painting may have originally looked different from what we see today.

Completed by van Gogh in 1889, the painting shows a colorful bouquet of sunflowers in a vase. In this painting, the Dutch artist made use of colors based on chrome yellows. This is a class of compounds based on lead, chromium and oxygen, according to the Deutsches Elektronen-Synchrotron (DESY), a research center of the Helmholtz Association.

Sunflowers, 1889, Vincent van Gogh (1853-1890). (Credit: Van Gogh Museum, Amsterdam–Vincent van Gogh Foundation)

The Institute of Molecular Science and Technology (CNR-ISTM), the University of Perugia and the University of Antwerp determined that the chrome yellow in the painting is becoming darker.

Researchers took two small samples from the painting, which measured less than 1mm. Both were examined within DESY’s PETRA III facility, which consists of a 300-meter long storage ring based on an X-ray source. The experiments were conducted on the Hard X-ray Micro/Nano-Probe beamline P06 within the PETRA III facility. The beamline provides various measurements using different X-ray techniques.

Micrograph of a paint sample taken from the table area of the Sunflowers painting (Source: Letizia Monico)

In this case, researchers used X-ray diffraction to study the painting. “There are different shades of the pigment, and not all of them are photochemically stable over time,” said Letizia Monico of CNR-ISTM. “Lighter chrome yellow has sulphur mixed into it, and is susceptible to chemical degradation when exposed to light, which leads to a darkening of the pigment.”

Koen Janssens from the University of Antwerp, added: “Since chrome yellow pigments were widely used by late 19th-century painters, this study also has broader implications for assessing the colors of other works of art.”

Imaging cancer and aging enzymes
Using cryo-electron microscopes and other measurement technologies, researchers from both the University of California at Los Angeles and Berkeley have produced the highest resolution images ever produced of telomerase, an enzyme that plays a major role in aging and most cancers.

The ability to produce high-resolution images could provide a path towards treating cancer and preventing premature aging

Telomerase is an enzyme comprised of protein and RNA subunits. It is found in fetal tissues, adult germ cells and tumor cells.

Originally, researchers believed that telomerase contains eight sub-units–seven proteins and an RNA. But researchers found two additional proteins, dubbed Teb2 and Teb3. This, in turn, increases telomerase’s activity.

Researchers also made other breakthroughs. Among the technologies the researchers used to produce the images were cryo-electron microscopes. Researchers also used nuclear magnetic resonance spectroscopy, X-ray crystallography, mass spectrometry and biochemical methods.

“Many details we could only guess at before, we can now see unambiguously, and we now have an understanding of where the different components of telomerase interact,” said Juli Feigon, a professor of chemistry and biochemistry at UCLA. “If telomerase were a cat, before we could see its general outline and the location of the limbs, but now we can see the eyes, the whiskers, the tail and the toes.”

A rendering of telomerase, showing the enzyme’s various subunits. (Source: UCLA)