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October 22, 2008

Plasmonic lithography : potential for 5 nanometer features



Engineers at the University of California, Berkeley, are reporting a new way of creating computer chips that could enable commercial speed 5 nanometer optical lithography. It can also mean higher density hard drives and optical disks with 20 times the density of Blu-ray.

The 5 page research paper: Flying plasmonic lens in the near field for high-speed nanolithography, Published online: 12 October 2008; doi:10.1038/nnano.2008.303.

This lowcost nanofabrication scheme has the potential to achieve throughputs that are two to five orders of magnitude higher than other maskless techniques.


By combining metal lenses that focus light through the excitation of electrons - or plasmons - on the lens' surface with a "flying head" that resembles the stylus on the arm of an old-fashioned LP turntable and is similar to those used in hard disk drives, the researchers were able to create line patterns only 80 nanometers wide at speeds up to 12 meters per second, with the potential for higher resolution [maybe 5 nanometers] detail in the near future.

Currently, the minimum feature size with conventional photolithography is about 35 nanometers, but our technique is capable of a much higher resolution at a relatively low cost.

This technology could also lead to ultra-high density disks that can hold 10 to 100 times more data than disks today.

The engineers designed a silver plasmonic lens with concentric rings that concentrate the light to a hole in the center where it exits on the other side. In the experiment, the hole was less than 100 nanometers in diameter, but it can theoretically be as small as 5 to 10 nanometers. The researchers packed the lenses into a flying plasmonic head, so-called because it would "fly" above the photoresist surface during the lithography process.

The researchers said the flying head design could potentially hold as many as 100,000 lenses, enabling parallel writing for even faster production.

"I expect in three to five years we could see industrial implementation of this technology," said Zhang. "This could be used in microelectronics manufacturing or for optical data storage and provide resolution that is 10 to 20 times higher than current blu-ray technology."








The researchers designed an air bearing that uses the aerodynamic lift force created by the spinning to help keep the two surfaces a mere 20 nanometers apart.

Air bearings are used to create magnetic tapes and disk drives, but this is the first application for a plasmonic lens.

With this innovative setup, the engineers demonstrated scanning speeds of 4 to 12 meters per second.

"The speed and distances we're talking about here are equivalent to a Boeing 747 flying 2 millimeters above the ground," added Zhang. "Moreover, this distance is kept constant, even when the surface is not perfectly flat."

The researchers pointed out that a typical photolithography tool used for chip manufacturing costs $20 million, and a set of lithography masks can run $1 million. One of the reasons for the great expense is the use of shorter light wavelengths to create higher resolution circuitry. Shorter wavelengths require nontraditional and costly mirrors and lenses.

The system described by the UC Berkeley engineers uses surface plasmons that have much shorter wavelengths than light, yet are excitable by typical ultraviolet light sources with much longer wavelengths. The researchers estimate that a lithography tool based upon their design could be developed at a small fraction of the cost of current lithography tools.


FURTHER READING
Xiang Zhang's lab website Xiang Zhang has been a leader with metamaterials and nanophotonics.

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