Chemical "Defect" Engineering

At next week's symposium of the AVS Science & Technology Society in Anaheim, University of Illinois researchers (Edmund Seebauer, eseebaue@uiuc.edu) will report an approach to reliably make small-scale versions of a pn junction, the crucial region of a semiconductor that changes from electron-rich (the "n" zone) to electron-poor (the "p" zone).

Today, pn junctions are only 25 nanometers (100 atoms) deep. But to make increasingly smaller (and faster) silicon chips, the International Technology Roadmap for Semiconductors dictates that by 2010 the pn junctions must have depths of 10 nanometers, or just 40 atoms.

The conventional method for making the junctions is called "ion implantation," in which charged versions of a foreign atom ("dopant") are accelerated into a silicon wafer to create electrically active regions that are either electron-rich or electron-poor. Unfortunately, current ion-implantation methods cannot make 10-nm-deep pn junctions without inadvertently moving silicon atoms into some of the spots intended for dopants.

But the Illinois researchers are using surface chemistry to come to the rescue of this conventional technology. In computer simulations, they showed how removing surface layers such as silicon dioxide frees up dangling bonds. Silicon atoms then preferentially rise to the surface while tending to leave the dopant atoms in place.

Verified in subsequent experiments, this idea for "defect engineering" has been shown to be a feasible solution for using traditional ion-implantation technology to make smaller-scale silicon-based electronic devices. (Meeting Paper EM-TuA7; see also UIUC news release and meeting lay-language paper.)