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. Credit: IBM
This is a second article on the new IBM 3D nanotip based patterning system.
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.
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.”
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.
The new instrument uses an extremely small silicon tip that is rapidly scanned across the surface of the substrate. The tip is cantilevered like those used in atomic force microscopy (or AFM: an offshoot of STM that was invented in 1986), enabling it to apply nanonewtons of force to the surface. But unlike AFM, the tip is heated.
Where it touches the substrate, the thermal energy at the tip is sufficient to break weak bonds within the material. “We provide enough thermal energy so these molecules become mobile, crawl along the hot tip and evaporate,” says Urs Duerig, a scientist IBM’s Zurich Research Laboratory, in Switzerland. Together with colleague Armin Knoll and others, Duerig developed the new technique. What’s remarkable about this, he says, is that it removes exactly the same amount of the material each time.