Strained silicon is a new, rapidly developing material for building enhanced-performance silicon-based transistors. Introducing a slight tensile strain in the lattice of the silicon crystal dramatically improves the mobility of charges in the crystal, enabling faster, higher-performance devices. The strain is achieved by first growing a relatively thick crystalline layer of silicon-germanium (SiGe) on the normal silicon substrate wafer, and then growing a thin film of pure silicon on top. The difference in lattice spacing between pure silicon and SiGe creates the desired strain, but also creates occasional defects in the crystal that degrade performance. The problem is particularly bad when the defects cluster together in so-called "pile-ups."
X-ray topographs of three different strata of a strained-silicon wafer show close correspondence in defects from the base silicon layer (top) through the final strained-silicon layer (bottom). Color has been added for contrast, one particular defect area is highlighted. Credit: Courtesy National Institute of Standards and Technology
One of the best methods for studying crystal defects is to observe the image of X-rays diffracted from the crystal planes, a technique called X-ray topography. Until now, however, it's been impossible to study the interaction of defects in the multiple layers of these complex Si – SiGe – Si wafers. In a recent paper in Applied Physics Letters,* researchers from NIST and AmberWave Systems Corporation (Salem, N.H.) detail a high-resolution form of X-ray topography that can distinguish individual crystal defects layer by layer. The technique combines an extremely low-angle incident X-ray beam ("glancing incidence") to increase the signal from one layer over another and the use of highly monochromatic X-rays tuned to separate the contributions from each layer based on their different lattice spacings.
Their results show that crystal defects initially created at the interface between the silicon wafer and the SiGe layer become "templates" that propagate through that layer and create matching defects in the strained-silicon top layer. These defects, in turn, are notably persistent, remaining in the strained-silicon even through later processing that includes stripping the layer off, bonding it to an oxidized silicon wafer, and annealing it to create strained-silicon-on-insulator (SSOI) substrates.
Michael Baum | EurekAlert!
Enhancing the quantum sensing capabilities of diamond
23.11.2017 | The Hebrew University of Jerusalem
Quantum optics allows us to abandon expensive lasers in spectroscopy
22.11.2017 | Lomonosov Moscow State University
Heat from the friction of rocks caused by tidal forces could be the “engine” for the hydrothermal activity on Saturn's moon Enceladus. This presupposes that...
The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.
Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
23.11.2017 | Information Technology
23.11.2017 | Physics and Astronomy
23.11.2017 | Life Sciences