By Griff Resor, Resor Associates, Solid State Technology Editor Advisory Board Member
We are entering a new era, in which nano-fabrication is moving beyond IC fabrication. Chasing Moore’s Law is still an important challenge, but there are now other interesting challenges. Making electronics ubiquitous, particularly in the medical field, has attracted many researchers. Harnessing Nature’s self-assembly methods has attracted many other researchers.
These were among the paths followed at the Electron, Ion, & Photon Beam Technology & Nanofabrication (EIPBN) held May 29 to June 2 in Baltimore, MD. The conference included people from university and government research labs around the world, whose focus was on new ways to make very small things for many markets. In the true spirit of a research conference, some of the tiny objects shown were just made for fun, to show it could be done. (See figure below: CNF “nanobugs” created using e-beam lithography.)
At the first meeting of EIPBN in Boston in 1956, the focus was on electron beams used to melt or convert materials. For example, the plastic covering on many phone cables is “cured” by an e-beam process. Over time, the conference focus shifted to alternative ways to make integrated circuits using electron, ion and then X-ray (photon) beams. Recently, nanofabrication has been added to the conference agenda. This year’s meeting attracted people who represented the full gamut of interests.
Lord Alec Broers from the Royal Academy of Engineering and a pioneer of scanning electron microscope technology while at IBM, provided the lead-off keynote talk, reviewing some successes (e.g., e-beam writing of masks) and some failures of technology presented at this conference. He suggested that keeping new technology in the lab longer might have been a wiser use of research funds, although most attendees privately disagreed with this view. Commercializing technology requires getting it into the market — some win and some fail. How to find the right balance is always a timely topic, and renewing that debate was really Broers’ goal.
George Bourianoff from Intel presented the likely future for Moore’s Law, suggesting that the doubling of transistors in a chip every 18 months will go on for a long time. “Moore’s Law will outlive CMOS,” he predicted, reminding the audience that bipolar technology was the mainstream choice when Gordon Moore made his initial prediction. CMOS should scale through 2012, which will be the 22nm node on Intel’s roadmap. Beyond that, Bourianoff said, we need to look at new ways to store information, beyond electrons. Examples include using electron spin states to store information. He presented Intel’s research pipeline, invited people in the audience to join any or all of the major paths in this pipeline, and also provided a map of consortia worldwide working to sustain IC industry momentum. This is an impressive worldwide research effort.
Tom Jackson from the Center for Thin Film Devices and Materials Research Institute at Penn State U. provided an alternative view. “If we continue along Moore’s Law, we will soon have a transistor for every cell in every person, even allowing for population growth,” he observed. Of course, this question was asked when Gordon Moore first made his forecast. Jackson suggested that the researchers in the audience look for alternatives, to apply electronics in new ways, suggesting flat-panel displays as an example of a major new use of electronics that does not require pushing Moore’s Law to the limit. In another example, he presented a case for smart bandages. One hundred years ago operations were nearly all fatal; if you survived the operation, a nurse would peel back the bandage to check for infection. Operating technology has improved, and today nearly everyone survives — but the bandage is still being checked the same way. By building many sensors into a bandage, temperature can be monitored and infection can be detected.
Erik Winfree from the California Institute of Technology championed another career path. Like many others at the conference, he is exploring the use of biological self assembly to build small structures, utilizing small fragments of DNA that operate like software code. Winfree demonstrated that his team now understands how this code can be used to control self-assembly of organic building blocks. At the moment they are building biological equivalents of binary formulas to verify the technology, but it is clear that bits of DNA can be used to control self-assembly of larger structures. It is only a matter of time before this technology is applied to making biological structures with more commercial utility and value.
The power of self assembly
What makes EIPBN so interesting is that far out ideas for nanomanufacturing are presented long before the research is perfected and used in industry. There are interesting research challenges in nano-fabrication, such as biological self-assembly methods, beyond chasing Moore’s Law.
Indeed, to understand the power of this new way of controlling processes, consider for a moment how a tree would be built by today’s manufacturing methods. We’d start with a reinforced concrete core. Plastic tubes to carry fluids up and down would be glued to the core. Bark would be made from plastic using large rolling mills. The bark would be glued over the tubes. Some kind of electronic devices would be connected at the base to extract nutrients from the soil. Leaf like structures would be made in IC factories using multilayer processes. These would have to be attached to the plastic tubes at the top, at the end of steel branches. We would have separate companies make the concrete core, the nutrient extraction devices, the tubes, the bark, the steel branches and the IC like leaves. Assembly would be done in China to take advantage of low labor costs. Each assembly would be tested for compliance with fire and radiation standards. Each “tree” would be shipped by container to ports around the world. It would then be trucked to its final destination. Two large cranes would hoist the tree into place while a backhoe dumps soil over the base of the tree. A computer would be connected to control the tree. Sunlight falling on the leaf like structures would generate enough power to run and sustain the whole assembly, and provide some shade to those who chose to sit beneath its structure.
Or, we can plant a seed and watch it grow. This is biological self-assembly.
This conference has swung dramatically towards nanofabrication of novel items that are not IC’s. Many are using the established lithographic methods developed for IC manufacturing. An increasing number are exploring natural systems to build interesting structures.
Emerging applications
Still a significant number of research results presented at this year’s EIBPN apply directly to the IC world. Andrew Grenville of SEMATECH expects immersion technology will take 193nm lithography to the 45nm node, but the 32nm node looks challenging. High index glass for lenses and higher index fluids are needed.
Obducat has developed a novel e-beam direct write tool that it uses to generate CD masters for imprint lithography. Their e-beam tool may find other uses; its resolution and pattern placement rival far more complex systems now on the market.
Ted Fedynyshyn from MIT Lincoln Laboratory says the line-edge roughness (LER) in chemically amplified resists can be attributed to the PAG residue left after acid generation. This finding should lead to new PAG formulations that reduce LER and enable smaller transistor geometries.
Dr. Li from the U. of Michigan presented data for organic thin-film transistors. They looked quite good, comparable to the amorphous silicon TFTs used in today’s flat-panel displays. The material might be printable, moving electronics off silicon and glass and onto flexible substrates.
Axel Scherer from Caltech presented fluidic chips that can do blood analysis in minutes compared to several days needed now. Using this technology, blood tests can be run while the patient is still in the doctor’s office. Expect to see these chips move out of the lab as fast as FDA regulations permit.
C.L. Soles of NIST demonstrated that pressure used with some nanoimprint methods builds in stress that may relax later. This finding could drive nanoimprint technology toward UV cured methods that do not use pressure.
Molecular Imprints Inc. is working with Nano Geometry Research Inc. in Japan to develop a 20nm die-to-data base tool for inspecting imprint templates. This tool uses an electron beam to find very small defects. Doug Resnick presented early results which look promising — 20nm defects were detected — but false defects may be a limiting problem.
K.A. Goldberg of Lawrence Berkeley National Laboratory has built a high-resolution particle detector using 13.5nm radiation from their synchrotron. The experimental setup has been used to look for extreme-ultraviolet (EUV) mask particles and small phase defects on EUV masks. The tool has been used to benchmark optically based multibeam laser confocal EUV mask inspection tools. They found that optically based inspection tools have serious limitations, missing many defects. A particle detector that uses 13.5nm radiation is needed to reliably inspect EUV masks.
Both Rajesh Menon of MIT and Stephan Hell from the Max Planck Institute in Gottingen, Germany, presented methods for using bi-stable materials, two-wavelength imaging systems, and double exposure to compress the point-spread function in an optical system. Isolated structure resolution of 1/25th of a wave was predicted by Rajesh. If his technique, absorbance optical modulation lithography, can be controlled, and the bi-stable materials can be created, this might be the next technique that carries optical lithography to the 22nm node and beyond.
EIPBN is a research conference; the ideas and results presented may or may not find practical use in industry. The challenge is to see which ideas will be adopted. Tomorrow’s winners can be found at EIPBN. Immersion lithography is the most recent example for the IC industry. As Lord Broers said on the opening day, the challenge is to decide how to spend the development money needed to move these ideas to market. For many in the audience, this is the next challenge.
Photo courtesy of Dr. Michael Guillorn, IBM. The work was performed while Dr. Guillorn was a research staff member at the Cornell Nanoscale Facility at Cornell U. in Ithaca, New York.