Argonne X-rays on the cutting edge

Scientists at Argonne National Laboratory are using X-rays from the Advanced Photon Source (APS) to cut tiny patterns in semiconductor material.

Argonne scientists are using X-rays from the Advanced Photon Source (APS) to cut tiny patterns in semiconductor material, creating a new way to construct smooth, high-resolution electronic devices.

The APS is known as a tool for revealing the three-dimensional structure of proteins and other materials with unprecedented detail and efficiency. But the APS is being used for research in other areas, inducing photolithography.

Argonne scientists used APS X-rays to etch patterns into the semiconductor gallium arsenide and demonstrated that the technique produces smooth surfaces etched only in the irradiated regions.

Researchers use either a ‘mask’ or a focused X-ray beam to etch the semiconductor surfaces in selected areas to produce patterns.

In the future, this etching technique could have applications in devices that use semiconductors, from cell phones microwave detectors.

Using X-rays is said to keep the process simple, allowing it to be performed at room temperature and atmospheric pressure.

In addition, by tuning the X-ray energy, the process can select atoms of one type to ionise; allowing scientists to etch on material while an adjacent, different material stays unchanged.

The researchers trained their X-ray beam on a small gallium-arsenide wafer in contact with a weak acid solution. The scientists controlled exactly where the X-rays hit the sample by placing a gold template to ‘mask’ the wafer

‘So far, we have concentrated primarily on understanding the etching of gallium arsenide,’ said researcher Richard Rosenberg, ‘We have also shown that this type of processing can be used to etch other semiconductors, as well as to deposit metal films and particles in the size range of 10 to 100 nanometers.’

X-rays shined onto a semiconductor ionised atoms by ejecting electrons, leaving behind vacancies.

What followed is a complex cascade of electron processes, resulting in the formation of ‘holes,’ which are used to oxidise the semiconductor’s surface atoms, which then dissolve in the acid. The X-rays then carved out smooth patterns in the semiconductor surface.