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The ability to affordably fabricate complex 3D geometry on the nanoscale is critical to the development and commercialization of numerous emerging technologies.  For example, technologies such as chiral photonics for advanced communication and nanofluidics for Lab-on-a-Chip applications benefit from the fabrication and integration of 3D nanostructures.  Additionally, any nanofabrication technique suitable for commercial manufacturing must exhibit a high degree of within-wafer uniformity and wafer-to-wafer repeatability.

Unfortunately, nanofabrication techniques that scale economically for commercial applications are typically limited to fabricating either 1D or 2D structures with a high degree of geometric control and 3D structures with little geometric control.  These limitations restrict the impact of nanotechnology. Fabricating large arrays of 3D structures in an affordable, scalable manner are needed.

Metal-assisted Chemical Etching (MaCE) of silicon has recently immerged as a new technique capable of fabricating arrays of reasonably complex 3D geometry in a single lithograph/etch cycle.  Example structures include chiral 3D spiraling structures, spiraling nanopillars, vertically aligned thin-film metallic nanostructures, sub-surface curved nanohorns, and zig-zag nanowires.  The ability of MaCE to fabricate 3D structures results from a unique etching process in which the object that defines the etch profile travels with the etch front, enabling extremely tight feature resolution over the entire etch length.

Currently, a liquid-phase MaCE (LP MaCE) is being used; however, it faces a number of challenges that could block it from being commercially viable.  Specifically, fluid flow over the catalyst, which occurs when the etchant solution is introduced onto or removed from the substrate, can induce unwanted catalyst motion.  As a result, controlling the etching path with the consistency necessary for large volume manufacturing is challenging, especially when attempting to etch structures across an entire wafer. LP MaCE generates H2 gas bubbles under most catalyst/etchant, resulting in non-uniform etching across a sample due to lower etch rates under the bubble.  Additionally, LP MaCE relies on catalyst motion to define the etch path. For large wafers the flow of the etchant over the substrate can induce undesirable catalyst motion. 

Instead of using LP MaCE, this technology uses vapor phase MaCE (VP MaCE) as a way to bypass some of the processing challenges found LP MaCE.  VP MaCE has shown to improve the controllability and repeatability of MaCE while maintaining the high feature resolution and 3D nanofabrication capabilities of LP MaCE, but eliminating the problems associated with fluid flow and fluid-based processes.  Additionally, VP MaCE enables tighter control over etching path and length and reduces process stop-lag (time between when you remove the etchant to when the etching process actually stops).

The figure below shows a micrograph of an etch void in a substrate using VP MaCE. The motion of the catalyst during the vapor composition etching of the samples was studied.  Catalysts travelled through three-dimensional volumes during the etching process, as exemplified by the helical structure shown in the figure. Accordingly, the vapor composition etching of the samples showed that the vapor composition formed complex structures without action issues.



A process for etching includes disposing an activating catalyst on a substrate; providing a vapor composition that includes an etchant oxidizer, an activatable etchant, or a combination thereof; contacting the activating catalyst with the etchant oxidizer,; contacting the substrate with the activatable etchant; performing an oxidation-reduction reaction between the substrate, the activatable etchant, and the etchant exidizer in a presence of the activating catalyst and the vapor composition; forming an etchant product that includes a plorality of atoms from the substrate; and removing the etchant product from the substrate to etch the substrate.

Hildreth Owen
Patent Number: 
Technology Type(s): 
Advanced Manufacturing Processes, Analytical Chemistry, Manufacturing, Materials Physics and Chemistry, Biochemical Science, Chemical Sciences, Nanotechnology, Physical and Chemical Properties,
Internal Laboratory Ref #: 
Patent Issue Date: 
November 28, 2017
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