New method demonstrated for etching smooth surfaces on semiconductors with X-rays

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, including 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 to radar to microwave detectors.

Using X-rays keeps 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 ionize, allowing scientists to etch one 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. By placing a gold template to "mask" the wafer, like a stencil, they controlled exactly where the X-rays hit the sample.

"We have concentrated on understanding the etching of gallium arsenide," said researcher Richard Rosenberg, "but 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." A nanometer is one-billionth of a meter.

Shining X-rays on a semiconductor ionizes atoms by ejecting electrons, leaving behind vacancies. What follows is a complex cascade of electron processes that results in the formation of "holes" that oxidize the semiconductor’s surface atoms, which then dissolve in the acid. The X-rays carve out smooth patterns on the semiconductor surface.

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