SILICON chip makers are taking a lesson from farmers on how to create patterns over large areas. Researchers in France have built a 鈥渕icroplough鈥� capable of carving furrows only a few tens of nanometres wide-but stretching across a microchip鈥檚 surface. The plough could be used to make high-quality light polarisers, diffraction gratings and high-density data storage devices that are larger and cheaper than those available today.
The features of microchips are etched using optical lithography. But creating patterns over large areas is expensive, as it requires big masks in the shape of the required pattern and optics that can focus light over a large area.
For several years, researchers have used the tips of atomic force microscopes to gouge small features into the surface of chips. But this technique is too slow and expensive to make larger patterns: what was needed was a way to create many features in parallel. So Chen Yong and his colleagues at the Laboratory of Microstructures and Microelectronics in Bagneux, France, turned their thoughts towards the plough.
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Chen built a row of several dozen microploughs, each with blades only 30 nanometres across at their tips. He then coated a silicon wafer with a protective layer or 鈥渞esist鈥� and dragged the microploughs across it. The furrows revealed the silicon beneath, allowing him to deposit a layer of cobalt on the strands. This resulted in several dozen closely spaced wires, each only 50 nanometres across. Such a pattern could be used as a diffraction grating or a polariser.
鈥淭he technique is much cheaper than conventional lithography. In fact, it doesn鈥檛 get cheaper than this. You can drag the microploughs by hand if you wish,鈥� says Chen. By pulling the microplough back across the wires at 90掳 to the original pattern, Chen can create a pattern of square nanodots out of cobalt, which could be used, for instance, in a high-density magnetic data storage device.
