New technique can help further shrink silicon chips

London, July 11 : US scientists have achieved a breakthrough that can cause silicon chips to become more densely packed with transistors than before.

Ralf Heilmann of the Massachusetts Institute of Technology's Space Nanotechnology Laboratory in Cambridge, Massachusetts, says that his team has devised a way to carve features in silicon that are many times smaller than the wavelength of the light used to make them.

The researcher says that the new technique can facilitate the production of grids of parallel lines just 25 nanometers wide, using light with a wavelength of 351 nm.

Though the grids thus made are not functional circuits, the researchers believe that they could be made into working chips by adding extra small features.

According to the researchers, the new approach could enable them to keep track with Moore's law, which states that the number of transistors we can fit on a chip will double every two years.

They say that reductions in the size of the structures on electronic chips from time to time may make it possible.

The smallest features on most computer chips these days are about 65 nm in size, but the first 45-nm chips have begun rolling off production lines, and 32-nm chips have been made in the laboratory.

The university experts say that such features are created with the aid of a technique called photolithography, in which light is used to imprint circuit patterns onto a chip.

The process, however, has limited applications because it is really very difficult to produce features that are smaller than the wavelength of light.

So far, this technique has relied on 193-nm ultraviolet light produced by argon-fluoride lasers.

The feature size can be reduced even further by using a number of tricks, such as double exposures and immersing chips in special liquids that sharply focus the light.

Heilmann and colleagues produced even smaller feature sizes by creating an interference pattern using light from a laser with a wavelength of 351 nm, which consisted of alternating light and dark zones repeating every 200 nm.

The researchers said that the pattern enabled them to etch 25-nm lines into a silicon wafer, each 175 nm apart.

The process was repeated thrice, each time shifting the interference pattern by 50 nm and etching another 25-nm groove.

Heilmann said that the resulting grid had alternating 25-nm stripes and grooves, reports New Scientist magazine.

The researcher believes that the grids may be used in chip making, where engineers build circuits by placing electronic elements on to an underlying grid or registration pattern.

Heilmann said that the fact that the technique uses a comparatively long-wavelength laser, the grid-writing stage would be relatively simple, and only the electronic elements would have to be written with more complex techniques.

An article on the research project has been reported in Optics Letters.

ANI