A Laser Technique Could Improve Electronics

This novel process might lead to purer silicon -- and faster chips.

A new process using lasers instead of high temperatures to remove hydrogen from silicon during the chip-manufacturing process could lead to faster semiconductors, by replacing the current technique, which often causes damage to silicon that inhibits chip speed.

Vanderbilt’s powerful free-electron laser is able to selectively remove hydrogen atoms from the surface of silicon, which could lead to an improved chip-making process. Light from the laser was directed into the semi-conductor processing chamber (on the left), where the experiment took place. (Credit: Neil Brake/Vanderbilt University)

Today, semiconductors are manufactured by layering silicon on a wafer, one "sheet" at a time. During this process, oxygen, which is a byproduct, can collect between the silicon layers -- which ruins the chip. To prevent that from happening, hydrogen is added to the silicon as a protective coating. While it solves the oxygen issue, the step has its own, albeit lesser, drawback: before the next layer of silicon can be added, the hydrogen must be removed, in a process that currently requires heating the chip to around 800 degrees Celsius. This heating creates defects in the silicon that keep chips from performing at their optimal speeds.

This new laser process, which can target and selectively remove molecules without heating the silicon, could replace the heating step, says Norman Tolk, physics professor at Vanderbilt University, and one of the researchers on the project. "The more you heat [silicon], the more you put it in a hostile environment," he says. Ideally, the chip-making process should be done with temperatures that are as low as possible, he says.

In a hydrogen-silicon bond, the energy required to break the bond corresponds to infrared light with a wavelength of 4.8 micrometers. The researchers adjusted their extremely powerful laser (called a "free electron laser") to emit a beam at this wavelength, and bathed the silicon-hydrogen bonds with the light. The laser's energy caused the bonded atoms to bounce back and forth, as if on a spring, until the vibrations grew large enough to break the bonds.