The great LEAP forward

Spanning fewer than a thousand atoms, the electronic devices on semiconductor chips have become so minuscule they defy most efforts to characterise them. Now for the first time, engineers have demonstrated a way to image these small devices by mapping them atom by atom.

In a study published in the August 1 issue of Applied Physics Letters, John Booske, a UW-Madison professor of electrical and computer engineering, and Keith Thompson, David Larson and Tom Kelly of the Madison-based company Imago Scientific Instruments, used Imago's local electrode atom probe (LEAP) microscope to pinpoint individual atoms of boron, a common additive, or dopant, in semiconductors, within a sea of silicon atoms.

The precise placement of dopants has long concerned engineers because these elements control the electrical properties of silicon transistors — the tiny, voltage-controlled switches found by the millions on semiconductor chips. But as manufacturers have relentlessly reduced the size of transistors in order to squeeze more of them on chips, locating dopants has become progressively difficult.