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 complexand not always harmfulphenomenon. Stress in the underlying structure of light-emitting diodes and lasers can shift output colors and lower the devices 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 theyre to be controlled by device designers. As the component size of microcircuits has become smaller and smaller, this has become more difficultparticularly 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 frequenc
|Contact: Michael Baum|
National Institute of Standards and Technology (NIST)