The “world’s smallest trophy” is a silicon chip etched with a design consisting of nested football fields, with a helmet in the center of each field. The largest field, about 12 mm long, is visible with the naked eye; within that lies a 120 micrometer long football field that is visible with an ordinary optical microscope; and within that is a 2 micrometer long football field that requires an electron microscope to view. In the smallest football field, the yard lines are about 60 nanometers wide, 1000 times thinner than a human hair. The chip itself is about the size of a penny.
The trophy was designed and produced by Phil Waggoner, a graduate student in Harold Craighead’s research group at Cornell University. The group is known for producing the nanoguitar in 1997.
The football field design and the words “Physics Central Nano Bowl Champion 2008” were etched onto a silicon nitride film that had been deposited on a silicon wafer. The largest football field was created using standard photolithography, in which a light beam wears away a coating called photoresist in the pattern desired. The exposed areas are then etched out of the silicon chip, and the remaining photoresist is washed away. The smaller two football fields were patterned using electron beam lithography, which is similar to photolithography, but uses a beam of tightly focused electrons instead of light to create the pattern.
“The main challenge was working with the design and the electron beam lithography in order to optimize the exposure dose given to the electron-beam photoresist in defining the smallest field patterns,” said Waggoner.
While the photolithography process is standard and has been in use for some time, “Electron beam lithography is a newer technique and can produce extremely small feature sizes, much smaller than the wavelength of light used in standard photolithography,” said Waggoner. Electron beam lithography can be used for other things besides nanobowl trophies. “Common applications include NEMS, nanofluidics, and many other applications in nanotechnology,” he said.