Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

‘Stress Tests’ Probe Nanoscale Strains in Materials

27.11.2008
Researchers at the National Institute of Standards and Technology (NIST) have demonstrated their ability to measure relatively low levels of stress or strain in regions of a semiconductor device as small as 10 nanometers across.

Their recent results* not only will impact the design of future generations of integrated circuits but also lay to rest a long-standing disagreement in results between two different methods for measuring stress in semiconductors.

Mechanical stress and strain in semiconductors and other devices is caused by atoms in the crystal lattice being compressed or stretched out of their preferred positions, a complex—and not always harmful—phenomenon. Stress in the underlying structure of light-emitting diodes and lasers can shift output colors and lower the device’s lifetime. Stress in microelectromechanical systems can lead to fracture and buckling that also truncates their lifespan.

On the other hand, stress is deliberately built into state-of-the-art microcircuits because properly applied it can increase the speed of transistors without making any other changes to the design. “Stress engineering has allowed the semiconductor industry to increase the performance of devices well beyond what was expected with the current materials set,” said NIST research physicist Robert Cook, “thus avoiding the significant engineering problems and expense associated with changing materials.”

Both the good and the bad stresses need to be measured, however, if they’re to be controlled by device designers. As the component size of microcircuits has become smaller and smaller, this has become more difficult—particularly since two different and widely used methods of stress measurement have been returning disparate results. One, electron back scattered diffraction (EBSD), deduces underlying stress by observing the patterns of electrons scattered back from the crystal planes. The other, confocal Raman microscopy (CRM), measures minute shifts in the frequency of photons that interact with the atomic bonds in the crystal—shifts that change depending on the amount of stress on the bond. The NIST team used customized, highly sensitive versions of both instruments in a series of comparison measurements to resolve the discrepancies.

The key issue, they found, was depth of penetration of the two techniques. Electron beams sample only the top 20 or 30 nanometers of the material, Cook explained, while the laser-generated photons used in CRM might penetrate as deep as a micrometer or more. The NIST researchers found that by varying the wavelength of the Raman photons and positioning the focus of the microscope they could select the depth of the features measured by the Raman technique—and when the CRM was tuned for the topmost layers of the crystal, the results were in close agreement with EBSD measurements.

The NIST instruments also demonstrate the potential for using the two techniques in combination to make reliable, nanoscale measurements of stress in silicon, which enables device developers to optimize materials and processes. EBSD, although confined to near-surface stress, can make measurements with resolutions as small as 10 nanometers. CRM resolution is about 10 times coarser, but it can return depth profiles of stress.

* M.D. Vaudin, Y.B. Gerbig, S.J. Stranick and R.F. Cook. Comparison of nanoscale measurements of strain and stress using electron back scattered diffraction and confocal Raman microscopy. Applied Physics Letters 93, 193116. (2008)

Michael Baum | Newswise Science News
Further information:
http://www.nist.gov

More articles from Physics and Astronomy:

nachricht The moon is front and center during a total solar eclipse
24.07.2017 | NASA/Goddard Space Flight Center

nachricht Superluminous supernova marks the death of a star at cosmic high noon
24.07.2017 | Royal Astronomical Society

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: 3-D scanning with water

3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects

A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

Ultrathin device harvests electricity from human motion

24.07.2017 | Power and Electrical Engineering

Scientists announce the quest for high-index materials

24.07.2017 | Materials Sciences

ADIR Project: Lasers Recover Valuable Materials

24.07.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>