Microscope Shows Faults In Smallest, Most Advanced Circuits - New Technology

Researchers at Brown University have developed a scanning microscope that can uncover defects in the smallest and most complex integrated circuits at a resolution 1,000 times greater than current technology.

Such a scanner removes a barrier to further shrinking of integrated circuits: As circuits get smaller, non-visual defects become harder to find.

"This microscope will allow manufacturers to find defects in each embedded wire in ever-tinier circuits," said Brown University professor Gang Xiao. Xiao developed the instrument's hardware and software with Ben Schrag, who will soon receive his Ph.D. at Brown.

The microscope's magnetic-scanning technology suggests a new small, non-invasive form of remote detection, according to the researchers, who envision a "pass-over and detect" magnetic-sensor-tipped pen, for use in finding internal cracks within aircraft, sensing biological agents in the environment or body, or recognizing counterfeit bills or other objects.

Although magnetic sensing is used extensively, it is not applied widely for imaging electrical current flow, said Schrag. The only method that uses magnetic imaging to see current flow is restricted to extremely low temperatures, employing cryogenic aids such as liquid nitrogen. However, the Brown device works at room temperature. This design opens the way to greater use of magnetic sensing technology, he said.

Xiao and Schrag are using the technology to pinpoint how electrical current can form pinholes in magnetic tunnel junctions. The researchers have imaged current flow in electrical components as small as 50 nanometers, the smallest commercially available components, half the size of conventional chips.

Until now, little or no technology existed for actually watching electrical current flow, said Schrag. Whenever current runs through wires, such as those embedded within the semiconducting material of an integrated circuit, it creates a magnetic field. By measuring spatial changes in that magnetic field, the microscope visualizes electrical current, even within wires buried under layers of advanced materials, he said.

A scanner does not touch what it reads. Instead, a magnetic sensor the size of a small pea moves quickly back and forth over a circuit through which current flows. The sensor collects information, which is then converted by algorithms into a color picture of electron flow. Color changes in the image reflect the intensity of electron flow as well as the presence of defects.

Xiao and Schrag have filed patents on several aspects of the technology, which has been transferred to Micro Magnetics, a Fall River, Mass., company that makes scanning devices for manufacturers of integrated circuits.

The microscope is described in a paper in the May 12, 2003, issue of Applied Physics Letters. The National Science Foundation funded the research.

Posted 7th May 2003

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