The world-class clean room in the NIST Boulder Microfabrication Facility (BMF) has just gotten a bit more crowded – in a good way. Staff members have recently acquired a new system: a high-end electron beam (“e-beam”) lithography machine, which will boost NIST researchers’ efforts to develop tools for a range of applications including quantum information processing, energy-efficient lighting, advanced computing, medical imaging, high-resolution sensors, and cancer treatment.
The e-beam system was “a long time coming,” says BMF clean room manager John Nibarger. A relatively large amount of clean room real estate was set aside for the acquisition of a device like this inside the BMF’s state-of-the-art facility, completed in 2012.* The new machine uses a beam of electrons to pattern or “write” features that can be smaller than 10 nanometers onto the surface of a silicon wafer. These features might serve as channels for light to flow through, or miniscule magnets for data storage, or even patterns on which forests of nanowires can be grown.
The e-beam machine itself isn’t novel; there are a few dozen systems of this caliber worldwide. But its acquisition by the Boulder clean room significantly increases the control researchers will have over the structures they can create – nanoscale structures that can be used to fabricate “innovative devices for advanced technology and precision measurement,” Nibarger says.
Previously, NIST Boulder researchers often used a scanning electron microscope (SEM) for their nanoscale etching applications. SEMs also use a beam of electrons directed onto a surface. But write times were relatively slow, since the system was optimized for imaging. Also, the SEM did not have the ability to track the position of the wafer if it was moved, which effectively prevented scientists from etching over surfaces larger than about 100 micrometers (millionths of a meter).
With the e-beam lithography machine, the scientists are now able to write features five times smaller than they could before. Not only is the beam denser – which gives them a thousand times faster write speed – but it’s built so that users can move the wafer around and still identify a point on its surface to within 10 nm. That’s a factor of 1000 more precision than they had with the SEM, and it allows them to cover an entire wafer’s surface with nanofeatures.
Immediate uses for the new tool include building tiny devices to be used in spintronics, a burgeoning field with computing applications that offers the possibility of significant energy reduction compared to conventional electronics. Other applications include making comparatively large arrays – of a thousand or even a million pixels each – of superconducting nanowire single-photon detectors (SNSPDs), which are capable of measuring individual photons, with potential applications in quantum computing. With the new system, they can write a 16-kilopixel SNSPD in just two hours.
“They couldn’t even dream of doing that before,” Nibarger says. And it will just get quicker, he adds, as they optimize the process. “We’re only just starting to scratch the surface with what we’re going to see out of it.”
-- Reported and written by Jennifer Lauren Lee
*The 18,000-square-foot BMF is a “class 100” clean room, which means for every cubic foot of air there are fewer than 100 particles half a micrometer in size or larger. The room dedicated to the e-beam machine is about 500 square feet.