The pixellated Alpine scene below might look like a CGI render of a mountain, but it is in fact a real-life sculpture of Mount Matterhorn that measures just 20nm high. That’s a good 12nm less than the width of transistors used in Intel’s latest generation of CPUs, and it’s a fully detailed three dimensional structure.
The miniscule mountain showcases a new nanopatterning technique developed by IBM’s researchers in Zurich, which the scientists think could change the way we produce tomorrow’s silicon chips in many ways. Not only could we start to think about lithography patterns with three dimensions, but the technology could also enable the production of intricate lenses for nanoscale optical connections.
Science (requires subscription) has just published a paper detailing the research, in which the scientists demonstrate a half pitch pattern 15nm on organic molecular glass, and claim that the process doesn’t require any of the proximity corrections needed in traditional lithography techniques.
The idea began several years ago, when IBM developed Millipede; a way of using a probe to punch holes in a polymer sheet and create dense binary patterns for storage. Speaking to THINQ, one of the scientists who worked on the paper, Urs Dueirg, explained that after that “it was always sort of a dream that we could use this probe technology to actually write arbitrary patterns.”
“The key to doing that,” says Dueirg, “is to actually remove the material rather than displace it. So the major breakthrough for us was the eventual discovery of materials that served precisely that purpose. When you heat them locally with a probe tip, they disintegrate into molecular units that don’t interact with the tip and don’t redeposit on the substrate. Basically, they evaporate into the free air.”
According to Dueirg, this is a major breakthrough when it comes to manufacturing tiny transistors. When using standard electron beam lithography, as Dueirg explains: "When you write with an electron beam, you not only expose where the electron beam hits, but you also form a halo cloud of secondary electrons, which then partially expose the material adjacent to what you really want to write.
"As a result of that, if you want to place two lines close together, you have great difficulties, because these lines will non-linearly interact and merge into one large object."
Using IBM’s nanoscale patterning technique, you instead use a probe with a heated tip that Dueirg says "doesn’t propagate far into the polymer."
The nanopatterning tool at IBM's lab
This avoids what’s known as the proximity effect in electron beam lithography, and Dueirg says it means you can now "write pretty much arbitrary patterns without having to apply horrendous mathematics and corrections. So when you write a pixel, this is the pixel – you can go to the neighbouring pixel and it behaves in exactly the same way as the first one."
Nanoscale optical lenses
As well as potentially overhauling chip lithography technology, the scientists also reckon that it could speed up the move towards optical connections in silicon chips. Today, silicon chips still rely on electrical connections, and it’s becoming increasingly difficult to push ever-expanding amounts of data through much smaller connections. "The problem is that as the clock speed goes up, wires become lossy and you lose the signal integrity," explains Deurig.
He also points out that one of today’s average chips has a number of dedicated processors creating a wealth of data, which needs to be handled and transported between processors or other components. "The amount of data is exploding. All over the world, there are big research initiatives studying the technology that would eliminate the electrical connection, and do the data transfer optically because you could transfer a much higher amount of data than you can do with wires."
This is all well and good, but you also need a lens to guide the light into a fibre, and this is where nanoscale patterning could become really handy. "You can sculpt lenses which have a very defined shape," says Dueirg. "They could be aspheric, for example, and they could have any arbitrary pattern to shape the face of the light wave."
As well as eliminating the need for error corrections, and potentially enabling nanoscale optical lenses, nanopatterning could also completely change the way we look at the traditional silicon chip. Using the nanopatterning, you could create a three-dimensional master stamp for imprint lithography, which opens up a whole new world of possibilities.
"It would be very interesting if one could pattern the stamp in the third dimension in a reliable way," says Dueirg, "because then you could make room for material to be displaced, or if you’d like to write different levels into one pattern."
So when should we expect nanopattering to start making its way into new chips? "It doesn’t really change the way we build processors at this stage," says Dueirg, "but it enables the development community to rapidly make smaller transistors on a test bed.
"If you want to continue on the roadmap for CMOS technology, what’s built today was tinkered with five to ten years ago in the labs, where people have tried to figure out how to make the gates smaller. In order to be able to go to the next step, which means writing gate structures as small as 10 or 20nm, we need to have a tool that allows you to make these structures in the first place."
As well as the Mount Matterhorn sculpture, the scientists have also shown the capabilities of the technology by creating a nanoscale world map, which you can see below.