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Graduate Seminar Oct. 18th, 2021: Gregory Nielson:

Beyond the Constraints of Lithography: Direct 3D Microfabrication in Semiconductor Materials

Lithography and the various associated lithography-based microfabrication processes are remarkable capabilities that have driven Moore's Law for integrated circuits for five decades and enabled the development of MEMS, microfluidics, integrated optics, and other microdevices. However, lithography-based micro processing has handicaps. Lithography is a 2D process that creates extruded 2.5D structures by various follow-on processes. This limitation forces design compromises by microdevice designers working on applications that are fundamentally 3D such as MEMS, microfluidics, silicon photonics, and others. In addition, lithography-based processing is slow. It can require hundreds of individual process steps on different tools, often requiring a month or more for a device to be fabricated. Lithography-based processing also requires significant setup costs which make it uneconomical for small-lot production.

To address these challenges, we have developed a direct-write three-dimensional microfabrication technique for semiconductor materials. This capability can directly create complex, full 3D structures in single-crystal semiconductors from a 3D CAD file in a single tool, conceptually similar to a macro-scale 3D printer. With this new capability, a microdevice designer would be able to design, fabricate, and test a prototype device within a week. This technique combines electrochemical semiconductor etching with two-photon absorption to provide highly selective etching without the need for line-of-sight access to the etch location. Although still in the development stage, examples of 3D structures directly fabricated with this capability will be shown, many of which cannot be created with any other processing technology.

Greg Nielson has more than 20 years of experience in semiconductor and microsystem R&D through his time at Nielson Scientific, Vivint Solar, Sandia National Laboratories, and MIT. He has received ~$25M in competitively bid R&D grants and won many national awards including Sandia National Laboratories’ Truman Fellowship, an R&D 100 award, and was named one of Popular Science magazine’s “Brilliant Ten” in 2012. He has authored approximately 80 peer-reviewed technical publications and is an inventor on approximately 50 patents/patent applications. He received PhD and MS degrees from MIT and a BS degree from Utah State University and is a member of IEEE, OSA, and ASME.