10 March 2015

Patent for off-axis SiC substrate process to reduce epi defects

Jim Edgar, a professor of chemical engineering at Kansas State University, together with researchers at the State University of New York at Stony Brook and the UK's University of Bristol, have been assigned a US patent (number 8,823,014, 'Off-axis silicon carbide substrates') for research that may help to improve electronic devices and could benefit the power electronics industry and manufacturers of semiconductor devices, it is reckoned.

Several years ago, when Yi Zhang, a 2011 doctoral graduate in chemical engineering, was working in the laboratory, she found a substrate sample that was very smooth. The research has subsequently developed a better method for fabricating substrates that minimizes potential defects in epitaxial layers.

The patent hence relates to a method of epitaxial growth of a material on a crystalline substrate that includes selecting a substrate with a crystal plane including a multiple terraces with step risers that join adjacent terraces. Each terrace presents a lattice constant that substantially matches a lattice constant of the material, and each step riser presents a step height and offset that is consistent with portions of the material nucleating on adjacent terraces being in substantial crystalline match at the step riser. The method also includes preparing a substrate by exposing the crystal plane, and epitaxially growing material on the substrate such that the portions of the material nucleating on adjacent terraces merge into a single crystal lattice without defects at the step risers.

Collaborative researchers at the State University of New York at Stony Brook and the UK's University of Bristol later proved that the epilayer had fewer defects than on the standard substrate.

"We have applied this process to other systems," says Edgar. "We are working on verifying that it is not just these specific materials we started with, but that it can be applied to a lot of different materials," he adds. Some of Edgar's latest research focuses on two different boron compounds: boron phosphide and icosahedral phosphide.

The researchers received support from the US National Science Foundation (NSF).

Tags: SiC substrates SiC epitaxy

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