Searching for the Flaws That Make Silicon Sing
We normally think of defects as bad. however, in silicon chips, they're essential. Why? Pure silicon is useless for circuits. Only when certain impurities are embedded in silicon does it become a semiconductor. Implanting these defects, a process called doping, must be precisely controlled. But that precision is getting tougher as circuit pathways on chips keep shrinking.
So tough, in fact, that materials physicist Yimei Zhu and his colleagues at the Energy Dept.'s Brookhaven National Laboratory have created a groundbreaking electron microscope to help scientists work with materials in submicron dimensions. Zhu's instrument can find defects a trillionth of a meter wide. That's the smallest flaw ever measured, analogous to singling out a speck of dust in an area the size of the U.S. The scope works by sending a beam of electrons through a tiny slice of material. As the electrons pass through the sample, they're scattered and form a diffraction pattern unique to each structure, giving the exact location of each atom.
With this sort of atomic-level mapping ability, Zhu points out that the technology holds promise beyond silicon. "Now we can measure any deviations from perfect crystals. We can make useful materials that we couldn't before."By Petti Fong