Writing in the scientific journal Nature, three Bell Labs researchers report that they have created insulating films of zirconium, tin and titanium oxides that appear compatible with established semiconductor fabrication techniques but are seven times more effective than the standard silicon dioxide films used as insulators in today's chips. The researchers also describe their approach to creating the materials, which involves sophisticated materials fabrication and automated evaluation techniques.

"Silicon dioxide is bumping into performance limits as semiconductor feature sizes shrink below .10 microns, a size the Semiconductor Industry Association predicts the industry will be producing in about eight years," said Mark Pinto, chief technical officer for Lucent's Microelectronics Group. "Bell Labs scientists are working to develop materials that will meet the performance challenges posed by these future design rules while being compatible with established semiconductor industry fabrication techniques."

In their Nature article, researchers Bruce van Dover, Lynn Schneemeyer and Robert Fleming describe a novel materials exploration approach called continuous composition spread (CCS), which makes it practical to produce thousands of samples simultaneously - each varying slightly in composition from the next. Automated dielectric and leakage-current measurements enable the researchers to quickly pinpoint those samples that deliver optimum performance.

Over a three-month period, the researchers evaluated some 120,000 compositions using a variety of metallic elements. They found that even slight variations in chemical composition could deliver major improvements in insulating effectiveness. If they had to use conventional techniques capable of producing and evaluating one sample per day, it would have taken them more than 300 years to create and analyze this many samples. The researchers are continuing to use the technique to search for even better materials.

"Materials scientists are developing techniques related to those known as 'combinatorial chemistry,' which biological and pharmaceutical scientists have used to synthesize wide varieties of molecules and organic compounds," said van Dover. "Our continuous composition spread technique is particularly well-suited to forming amorphous and metastable insulators. It combines the elements simultaneously, makes many combinations with fine variations, and uses fully automated methods to rapidly characterize the materials' properties."

To produce their films, the researchers positioned three sputtering guns, one for each of the metallic elements to be deposited, along the edges of a rectangular silicon wafer measuring 63-by-66 millimeters. Oxygen was supplied during sputtering to form the insulating oxide films. The amount of each element deposited varied with the distance from its gun, thus delivering films with varying proportions of each element across the whole surface. Researchers evaluated the electrical properties of the films by scanning the wafer’s surface with a mercury-probe instrument small enough to measure some 4,000 discrete points.

The researchers' full report appears in the March 12 issue of Nature. They will also make a presentation at the American Physical Society meeting in Los Angeles on March 19.

Lucent Technologies, headquartered in Murray Hill, N.J., designs, builds and delivers a wide range of public and private networks, communications systems and software, data networking systems, business telephone systems and microelectronic components. Bell Labs is the research and development arm for the company. For more information on Lucent Technologies, visit our web site at http://www.lucent.com.

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