Manufacturing Bits: July 9

Fishy robots; MEMS lithography; EUV mask inspection.

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Fishy Robots
National University of Singapore (NUS) has developed a robotic fish that mimics the movements of a carp—a technology that could pave the way for more efficient autonomous underwater vehicles.

This robot is classified as an autonomous underwater vehicle (AUV). Applications include military, pipeline leakage detection, and the laying of communication cable. The robot could be used in underwater archaeology or exploring ship wreckages.

NUS constructed two fish robots. One prototype, which can dive to a depth of 1.8 meters, is about 1.5 meters in length and weighs about 10kg. The second robot is about 60 centimeters long and weighs 1.5kg. It can only swim on the surface of water.

The fins and tails need to be flexible. NUS used 1mm acrylic boards for the fins and tails. Buoyancy and balance is maintained by using plastic foam attached to both sides of the robot. An internal ballast system is used for the diving mechanism.

“We chose to study carps because most fish swim like them. There is no literature at all on designing a mathematical model on the locomotion of fish and so we had to start from scratch,” said Fan Lupeng, a research fellow, on NUS’s site.

On the site, Xu Jianxin, a professor at NUS, added: “Currently, robot fish capable of 2D movements are common, meaning that these models are not able to dive into the water. Our model is capable of 3D movements as it can dive and float, using its fins like a real fish. Compared to traditional AUVs, they are certainly more mobile, with greater maneuverability. If used for military purpose, fish robots would definitely be more difficult to detect by the enemy.”

MEMS Lithography
Boston University has developed what it calls atomic calligraphy. The technology enables resist-free patterning of nanostructures using tiny apertures fabricated on a microelectromechanical system (MEMS) structure.

The university reported its findings in the online edition of NANO Letters. The MEMS devices themselves are made using Memscap’s PolyMUMPs process. Using a focused ion beam (FIB), researchers fabricated apertures on the MEMS structure with features less than 50nm in diameter on a small central plate.

Researchers then constructed what it calls a MEMS writer. “The central plate is suspended over the substrate by four doubly folded flexure springs and tethers,” according to a paper from researchers at Boston University. “The springs and tethers can be combined into a single device that can move laterally >10μm in all four quadrants. The device is actuated by four electrostatic comb drives, each attached to a folded spring.”

The MEMS writer is able to deposit thermally evaporated gold atoms through the apertures on nanoscale metal patterns. Adding a shutter positioned above the aperture enables the deposition of materials at atomic levels.

In one experiment, researchers deposited a ring with a radius of 100nm and a line width of just under 90nm. One of the smallest dots imaged was about 42- x 57nm-square. Further optimizing the two step milling process using the FIB should result in apertures as small as 10- x 10nm-square.

“The ability to evaporate materials with high precision, and thereby fabricate circuits and structures in situ, enables new kinds of experiments based on the interactions of a small number of atoms and eventually even single atoms,” according to researchers.

EUV Mask Inspection
The U.S. Department of Energy’s Lawrence Berkeley National Laboratory will soon deploy its long-awaited microscope based on extreme ultraviolet (EUV) technology.

The microscope, dubbed the Sematech High-NA Actinic Reticle review Project (SHARP), has been in the works for some time. It was conceived and built by Berkeley Lab’s Center for X-ray Optics (CXRO).

SHARP is designed to inspect defects in EUV photomasks from 40nm to 10nm. Photomasks carry the circuit pattern that becomes printed on a wafer. For EUV, masks are made from six-inch glass plates coated with a reflective multilayer material, and a patterned absorbing layer on top.

Created by the Center for X-Ray Optics at Berkeley Lab, SHARP gives researchers from the world's leading semiconductor companies a window into the future of computer-chip fabrication.

Today’s mask inspection tools are based on optical techniques. Initially, current mask inspection tools will be used for EUV masks, but they could eventually run out of gas and may be unable to predict the impact of defects for EUV wavelengths. The ultimate goal is to develop a machine based on actinic technology. In simple terms, an EUV mask inspection tool would operate at the same wavelength as an EUV scanner, which is 13.5nm.

The development of the SHARP microscope is a step towards actinic mask inspection. Previously, Berkeley Lab has been using the so-called Sematech Berkeley Actinic Inspection Tool (AIT) for mask EUV inspection. The AIT is based on a Fresnel zoneplate technology.

SHARP replaces the older AIT tool, also located at the lab. Recently, the lab ran SHARP through a series of acceptance tests prior to taking it online for users. “It got all As and a couple of Bs,” said Kenneth Goldberg, a researcher in Berkeley Lab’s Materials Sciences Division, and deputy director of CXRO, on the agency’s Web site. “But we can improve it based on those tests. We’ll learn and get better over time.”

—Mark LaPedus