Dec 15, 2011
Step-and-repeat nanoimprint lithography delivers single digit nanostructures
Researchers at aBeam Technologies and the Molecular Foundry have developed a novel strategy for fabricating imprint templates with sub-10 nm patterns by combining electron beam lithography and atomic layer deposition. The nanostructures are replicated by step-and-repeat nanoimprint lithography and successfully transferred into a functional material with high fidelity. This process demonstrates for the first time the ability of step-and-repeat nanoimprint lithography as a single digit nanofabrication method.
Step-and-repeat nanoimprint lithography (NIL) is a promising technique to replicate nanoscale patterns at low cost across a large area. Last year, researchers Christophe Peroz and Scott Dhuey and coworkers demonstrated a simplified imprint process to replicate patterns with minimum size down to 14 nm across six inch wafers. To test the ultimate resolution of this process, a novel and robust strategy to fabricate NIL templates with sub-10 nm patterns was explored.
Feature sizes down to 4 nm
This strategy for fabricating very high-resolution molds combines the advantages of electron beam lithography (EBL) and atomic layer deposition (ALD). The first step consists of patterning hydrogen silsesquioxane gratings on a quartz template using EBL. Next, ALD is used to deposit highly conformal alumina films and reduce the final sizes of the trench patterns on the template. Atomic level control over thickness deposited by ALD allows the fabrication of molds with features sizes down to 4 nm. At such a small scale, the deposition rate is highly dependent on the size of the trench and is dramatically reduced for trenches smaller than 8.5 nm.
The step-and-repeat process is performed at room temperature and at low pressure (force <30 N) with an Imprio 55 press (Molecular Imprints). Low viscous resist films are pre-spin coated on six-inch wafers and are imprinted with ultraviolet light. Patterns down to 7 nm can be successfully imprinted with a variation of less than 1 nm between the mold and the final structures. Thanks to a high control over the residual layer underneath the imprinted features, the patterns are easily transferred with high aspect ratio into silicon.
"We believe that our nanoimprint process has not yet reached its limit in terms of resolution, especially for reducing the pitch of gratings," commented Peroz and Dhuey.
Full details can be found in the journal Nanotechnology.
About the author
The work was led by Dr Christophe Peroz and Scott Dhuey at the Molecular Foundry, Lawrence Berkeley National Laboratory, in Berkeley, California. The Molecular Foundry is one of five United States Department of Energy (DOE) Nanoscale Science Research Centers – national user facilities for interdisciplinary research at the nanoscale, supported by the DOE Office of Science. The nanoimprint technology was developed by Christophe Peroz, Senior Scientist at aBeam Technologies Inc. and Scott Dhuey, Senior Scientific Engineer. Dr Deirdre Olynick, staff scientist, and Marion Cornet, master student, at the Molecular Foundry, helped to develop this process. Resist materials was provided by Dr Marko Volger, manager at Micro Resist Technologies, Germany. This work was supported by Dr Stefano Cabrini, director of the Nanofabrication Facility at the Molecular Foundry. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under contract no. DE-AC02- 05CH11231.