Nano-patterning: At the heart of the new tool is a tiny silicon tip. It is able to carve out features as small as 15 nanometers through heating and the application of nanonewtons of pressure.
This ability to create 3-D structures is intriguing, says Zahid Durrani at Imperial College London. “It’s completely novel,” he says. “I’ve never seen anything like this before.” However, as with other probe technologies, extending the process to large numbers of tips operating in parallel is likely to prove challenging, says Durrani.
Karl Berggren, co-director of MIT’s Nanostructures Laboratory, says IBM’s instrument is an incredibly “clever and elegant” solution. “They’ve done something quite creative here,” he says. Researchers have long struggled with thermal methods of probe lithography, but it was slow and resolutions were mediocre, says Berggren. “IBM has changed that,” he says. “So making sub-20-nanometer-scale lithography available to labs that need it at reasonable cost may be the long-term legacy of this work. And it is a very important one.”
In contrast, e-beam lithography requires several steps and tends to be very expensive, with systems costing up to $5 million, says Berggren. The IBM instrument is small enough to sit on a desktop and should cost around $100,000.
It is also relatively fast, says Duerig. Because the tip can write each “pixel” in microseconds, it can be scanned across the substrate very rapidly. The world map, for example, which consists of 500,000 pixels, took just two minutes to draw.
A crucial step in developing this technique involved finding suitable organic substrates. To this end, colleagues at IBM’s Research-Almaden, in California, were brought in to help find hard organic substrates that could be used as so-called “resists,” a sort of mask used in chip fabrication.
The challenge was to find materials that were tough enough to be used as substrates, but which could be thermally decomposed easily, evaporating into nonreactive chunks when brought into contact with the hot tip. In the case of the world map, a polymer called polyphthalaldehyde was found suitable, and for the Matterhorn, the IBM scientists used a form of molecular glass.