Washington, Sept 26 : Scientists at the University of California, Santa Barbara have created a new nanoscale process that will ultimately help make computers smaller, faster, and more efficient.
The scientists have for the first time devised a technology, called block co-polymer lithography, to make square, nanoscale, chemical patterns -- from the bottom up -- that may be used in the manufacture of integrated circuit chips as early as 2011.
Led by Craig Hawker, materials professor and director of the Materials Research Laboratory at UCSB, with professors Glenn Fredrickson and Edward J. Kramer, the researchers have developed a novel process for creating features on silicon wafers that are between five and 20 nanometers thick.
Hawker explained that for the future we need more powerful microprocessors that use less energy.
"If you can shrink all these things down, you get both. You get power and energy efficiency in one package. We've come up with this new blending approach, called block co-polymer lithography, or BCP," said Hawker.
He added: "It essentially relies on a natural self-assembly process. Just like proteins in the body, these molecules come together and self assemble into a pattern. And so we use that pattern as our lithographic tool, to make patterns on the silicon wafer."
By using this technique, the size of the features is about the same as that of the molecules. They are very small, between five and 20 nanometers.
"With this strategy, we can make many more features, and hence we can pack the transistors closer together and everything else closer together -- using this new form of lithography," said Hawker.
Hawker said that the new technology was designed to be compatible with current manufacturing techniques, giving it the potential to be a "slip-in" technology. The interesting feature about this work is that the scientists combined the repulsive force with another self-assembly force which is slightly attractive.
"What we do is take one BCP (made of two components that hate each other) another BCP (again made of two components that hate each other) and simply mix these together. When we mix them together, we've designed groups on one chain to be attracted to groups on a different chain, and so they actually start to blend and mix together. It is this combination of all these forces trying to get away from each other, and attract to each other that allows us to make the square arrays. Whereas what nature gives you is hexagonal, if you just use a single component system," said Hawker.
The scientists design the BCPs to have specific structures. And they use simulation to define the structures that are needed to prepare.
"We design the molecule by understanding what needs size." to happen during the self-assembly process. We need one block to be oil-like and one block to be water-like. So that's our first level of sophistication. We then design the molecular weight or the size of the molecule, to give us the desired feature," said Hawker.
In the next step, the scientists design into the oil block the sticky groups that will form this attractive interaction, and by controlling the number of sticky groups, different levels of phase separation and different structures are created.
Polystyrene is the oil-like block, and one of the water-soluble blocks is polyethylene glycol. By putting those together, the polyethylene glycol loves the water and the polystyrene loves the oil, and they hate each other. Polystyrene is found in disposable coffee cups, and according to the scientists is a fairly cheap commodity material that if designed in the right way, becomes a high value added application.
"The key to this work is that we put all the information into those molecules. From a molecular level, we've built all the information into them that will allow them to undergo controlled phase separation. And the key is then just simply blending of two specifically designed materials, and then all we do is spin that down into a thin film on a silicon wafer. And then we heat it, and all the information that is pre-built into the molecule does its thing, and gives us the structure. And so that's why it is a really cheap technique. Because all you have to do is heat things up and you get the structures that you desire," said Hawker.
The researchers have created a bottom-up approach to making these nanostructures, whereas the standard photolithographic technique, shining light onto the wafer -- is a top down engineering approach that requires multimillion dollar equipment.
The new process is described in Science Express, the online version of the journal Science.