Dopants are chemical elements such as boron or phosphorus that are introduced into silicon and other semiconducting materials to selectively change their electrical characteristics. As circuitry has shrunk in size, the need for precise positioning and measurement of dopants has grown proportionately. It also shows promise for allowing manufacturers to check the alignment of overlaid metal circuit layers. Based on pioneering work at IBM, the new instrument was built by adapting electrically conducting probe tips to a commercial atomic-force microscope. By varying voltage applied to the tip, different semiconductor layers can be probed.
Higher voltages provide a signal from dopant concentrations in deeper layers than lower voltages.
They now are creating a database of experimental measurements and modeling predictions to help instrument makers ensure the reliability of quantitative measurements. The new method offers the promise of one day manufacturing integrated circuits or other microfabricated objects about 10 times smaller than is possible with light-based lithography methods. The scientists' results are reported in the Sept. 1 issue of the journal Science . The smallest circuit linewidths possible with light-based lithography are on the order of 100 to several hundred nanometers. The metastable atoms carry stored energy in the form of excited electrons.