Mirror surfaces with nary an atom exposed?

May 04, 1998

How close can one come to perfection? In the case of Melissa Hines, an assistant professor of chemistry at Cornell University, it could be only an atom away. Her goal: a mirror surface above which not even a single atom protrudes. About five years ago, Bell Labs researchers found that by changing the acidity and composition of a chemical solution, they could produce small areas on a silicon chip that were totally flat, even at the atomic level. Surface roughness was equal to only one protruding atom out of every 30,000 surface atoms. Even on the atomic scale, however, such roughness can greatly decrease the performance of a transistor. The problem: such surface perfection is only reproducible on one type of silicon surface, silicon (111). This is a different plane from silicon (100), used for integrated circuits. Hines wants to find chemical solutions that produce perfection on different surfaces. To do this, she needs to know how a basic hydrofluoric acid solution used in her research etches away protruding atoms. To date, the most perfect surface appears through the electron tunneling microscope as a series of steps, with every step only a single atom high. The steps are the result of almost imperceptible errors in cutting a silicon wafer. If perfected, Hines sees the etching technique useful for integrated circuit technology, micromachining of very small parts, and for producing thin films. That feat, says Hines, is about five years away. E-mail deb27@cornell.edu.

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