Apr 23, 2010
Scanning probe etches tiniest patterns
IBM researchers have used a heated nanoscale tip to create patterns as small as 15 nm in an organic resist. This is half the size of structures that can be produced by conventional methods, such as electron-beam lithography. The technique could be ideal for fabricating nanoscale electronic devices in the future.
Today, computer chips and other microelectronic devices are made by optical and electron-beam lithography, which are used to pattern organic resists. However, the problem is that these techniques do not work very well for making structures smaller than 30 nm because of so-called "proximity effects". This is where the electron or optical beams begin to encroach on nearby, unwanted areas in the resist, which leads to certain areas being unintentionally exposed, and a larger final pattern.
Armin Knoll and colleagues at IBM in Zurich, Switzerland, and their colleagues in Almaden, California, and Yorktown Heights, New York, have now developed a new method that overcomes this problem. Their scanning probe lithography technique employs a heated nanotip to locally evaporate material from a thin film of organic glass (Sciencexpress 1187851). The nanopatterns produced can then be transferred to silicon – the most widely used electronic material – using standard nanofabrication techniques. "Being able to transfer patterns in this way opens up new prospects for fabricating nanosized electronics and objects in fields ranging from future chip technology and optoelectronics, to medicine and life sciences," say the researchers.
The tip is 500 nm long and a few nanometres wide at its apex. It is attached to a cantilever that scans the surface of the substrate with an accuracy of just 1 nm. By applying heat and force, the tip can remove substrate material based on predefined patterns, rather like a "nanomilling" machine, says Knoll.
The IBM team chose to use organic glass in its proof-of principle experiment because the bonds between the molecules in this material can be easily broken at the temperatures of the tip (300–500 °C).
The new technique is also cheaper than e-beam lithography because it uses less power and can sit happily on a bench top – as opposed to electron-beam machines, which are much bulkier devices. It can be used to make 2D patterns or 3D "sculptures" by successive rounds of etching. Indeed, the same team previously showed that they could fashion a 25 nm high 3D replica of the Matterhorn, the famous Swiss mountain that is 4478 m high, in molecular glass. This represents a scale of 1:5 billion (1 nm in the replica corresponds to 57 m).
The researchers have also made the tiniest 3D map of the world ever using a tip at higher temperatures of 700 °C. They were able to produce the map in just a couple of minutes (Advanced Materials upcoming).
The team now hopes to take its technology to market and make it widely available to university researchers too. "This will also help to develop the tech further and enlarge its potential applications," Knoll told nanotechweb.org. The researchers also plan to improve the technique so that it can etch even smaller and deeper patterns, while operating faster.
About the author
Belle Dumé is contributing editor at nanotechweb.org.