Nanofabrication in the Clean Room

The Nanofabrication Research Laboratory, housed in a wing of the ORNL nanocenter, occupies a room that is clean to the extreme.

The "clean room," which occupies almost 10,000 sq. ft of the 80,000-sq.-ft nanocenter, is designed to have extremely low levels of airborne particles, acoustic noise, vibrations, and electromagnetic interference. The clean room's air is highly filtered to remove a large fraction of the particles present in ambient air.

The Clean Room.

The clean room air is 10 times cleaner than the cleanest hospital air and 1,000 times cleaner than the air people normally breathe.

A clean room is needed at the ORNL nanocenter so that "the sensitive tools used to fabricate nanostructures can achieve the best performance," says Richard Kasica, a research engineer in ORNL's Engineering Science and Technology Division. Too many airborne particles and vibrations, for example, could undermine the nanocenter's extensive, novel synthesis capabilities.

The most impressive tools in the clean room for science-based synthesis of nanoscale materials and structures are a unique, state-of-the-art electron beam (e-beam) lithography system and a dual-beam scanning electron microscope/focused ion beam (SEM/FIB) system. Kasica, who has considerable experience in e-beam lithography, is training researchers from ORNL and elsewhere in the use of the clean room's various tools. The tools also include optical lithography, plasma etching, and techniques for depositing and etching away electrically conductive metals and insulators. Scanning probe microscopies are also used in nanofabrication, but they are located elsewhere in the nanocenter.

According to Kasica, this particular e-beam lithography tool will have a few more features than those found on the other 17 systems currently installed across the world. The system at ORNL is the world's fastest writing tool for creating nanosized features over an area as large as 200 millimeters in diameter. For basic research purposes at CNMS, this tool will probably be used on substrates as small as 50 mm².

"This e-beam lithography tool can quickly scan a substrate, put down square pixels, and connect them, with less error in alignment," Kasica says. "It's like stitching together patches to make a quilt."

The dual-beam SEM/FIB system, which produces electrons and ions from a tank of liquid gallium, will be used to deposit material, etch it away, and make patterns on a substrate. Rarely are patterning, depositing, and etching—the elements of nanofabrication—made available in one tool. The microscope in this system, which is rapidly gaining popularity for sample preparation and analytical work, produces images to ensure precision in researchers' nanofabrication projects, which will include nanoelectronic devices, nanoscale sensors, and drug delivery devices.

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