Spring 2007 Meeting Scene -- Day 2

Symposium T: The Nature of Design--Utilizing Biology’s Portfolio

T2.10: Geckel: Nanostructured Wet/Dry Adhesive Inspired by the Gecko and the Mussel

What do you get by crossing the materials equivalent of a gecko with a mussel? A geckel. That is what Phillip Messersmith of Northwestern University called the feat (or feet) of creating a hybrid system mimicking the biological adhesives that enable geckos to walk on ceilings and mussels to grab on to the slippery ocean floor. Geckos have very finely structured and hierarchical hairs on the tips of their feet, splitting down to contact pads of just 100-200 nm dimensions. This structure helps geckos attach and detach their feet easily in dry conditions. Mussels, on the other hand, just need to get a grip so that they are not tossed around by the sea. They have a system of secreted protein threads terminated with adhesive pads specially adapted for attaching in wet environments. These proteins are 27% DOPA, which has a role in gelation and interfacial adhesion. Messersmith reported development of polymers that incorporate DOPA to achieve gripping strengths of mussels, along with the development of nanostructured pillar arrays mimicking the fine structure of gecko feet. The hybrid geckel exhibits attractive features of both, making temporary adhesion in wet and dry environments possible. While the synthesized gecko structure quickly loses strength in wet conditions, the hybrid design lasted for 1000s of cycles gripping and releasing in wet environments, with only a 15% decay over that time.

Symposium B: Materials, Processes, Integration, and Reliability in Advanced Interconnects for Micro- and Nano-Electronics

B1.1: ALD or CVD of Pore-Sealing Barrier, Adhesion, and Seed Layers for Interconnects

Roy G. Gordon of Harvard University spoke about alternatives to physical vapor deposition, specifically atom layer deposition (ALD) and chemical vapor deposition (CVD), to seal the surfaces of porous, low k dielectrics with SiO2 . Al2O3 is used as a catalyst, coated on the surface and extending slightly into the depth of a pore. Application of silanol by one ALD cycle results in a 6-nm-thick sealing layer of SiO2. To avoid deposition of SiO2 on copper at via bottoms, they protect the copper layer with a monolayer of alkythiol.

Next, tungsten nitride (WN) or tungsten carbide (WC) is added as a diffusion barrier to replace the commonly used TaN; both adhere strongly to oxides and metals. These are deposited using ALD or CVD. Specifically, CVD with NH 3 produces a layer of WN at a fast rate of 20 angstroms per minute, suitable for manufacturing purposes. Then, a layer of Ru or Co is added provide a adhesive layer for Cu seeds. Ru has been used successfully, creating 2-nm-thick layers that completely cover WN with no pinholes. Cu can be nucleated on this surface using Cu(I) N,N'-di- sec -butylacetamidinate as a precursor. "SEM shows that Cu is continuous," Gordon said. "We think this whole structure is suitable for electroplating."

But there is one problem: there is not very much Ru on Earth, and the price is going up with increasing demand. So, in an effort to find a suitable replacement, Gordon and coworkers looked at Co. Starting with Co amidinates, they showed that they could cover the WN surface completely and evenly with Co. Cu tends to agglomerate on WN, but distributes smoothly on the Co adhesion layer. This process results in a sealed SiO2/WN barrier/Co adhesion surface/Cu seed layered structure. Gordon says the process is extendable to the end of the semiconductor roadmap, and can be carried out using simplified CVD equipment because no plasma is needed.

B1.2: Interface Engineering for High Interfacial Strength between SiCOH Dielectrics and SiCHN Caps

"In order to make reliable interconnect structures, we need good adhesion between all layers," Alfred Grill of IBM said at the start of his invited presentation entitled "Interface Engineering for High Interfacial Strength between SiCOH Dielectrics and SiCHN Caps." Delamination between the dielectric and the caps has been a problem; analysis has shown that the failures are interfacial. Measured interfacial strain limits are 2.0 J/m2, while the bulk material can withstand 6.0 J/m2.

Grill and coworkers considered three potential solutions: (1) modifying the cap surface, (2) introducing a transition layer, and (3) a combination of steps (1) and (2). Step 1 involved treatment of the surface with inert or reactive plasmas; Step 2 consisted of insertion of amorphous Si or a layer of SiCOH with a reduced C content and an elevated O content. While some improvements were achieved using these approaches, ultimately they still resulted in interfacial adhesive failure. Improved interfacial strength was finally achieved by first precleaning the SiCHN cap and then adding a porous poly-SiCOH dielectric layer. With this structure, failure no longer occurred at the interface, but was instead transferred to the bulk phase. The research improved the interface strength from 2.0 J/m2 to 3–4 J/m2 due to SiCHN treatment, and up to 5 J/m2 with the optimized pSiCOH transition layer.

Symposium G: Extending Moore’s Law with Advanced Channel Materials

G1.1: Future Direction of Strained Si/Channel MOSFETs for Advanced 90 to 22 nm Logic Technologies

Symposium G has the rather unique title of "Extending Moore’s Law with Advanced Channel Devices." To kick off this symposium, Scott Thompson of the University of Florida stated unequivocally that "Uniaxial stress is and will continue to be the dominant performance enhancer for all 90 and 22 nm logic technology nodes." Uniaxial stress is used in all markets, he said, including consumer, computer, and wireless markets. There is a large barrier to moving off the path described by the technology roadmap: a new fabrication facility in the 45 nm node will cost about $3 billion dollars to open.

Carrier mobility is enhanced either through scattering or through hole effective mass change. A uniaxial compressive stress can reduce the mass in the channel direction, thereby increasing mobility. This applies not only to Si but to Ge, SiGe, and GeAs. The initial mobility in SiGe is higher than that of Si, and this difference increases with increasing stress. Ge and GeAs both show a larger mobility enhancement under stress than Si.

Strained Si defects are key in the continuing use of stress to enhance mobility along the technology roadmap. The 65 nm node contains about 400 million transistors per chip, and "you need them all to work," Thompson said. Research has shown that the dominant defect that leads to "killed" devices is a source-to-drain short dislocation. So it is important to build structures that minimize these dislocations. This means putting strain-producing processing steps toward the end of the manufacturing cycle.

Symposium J: Nanoscale Magnetics and Device Applications

J1.4: Particle Size, Structure, and Magnetic Characteristics of Cobalt Nanoparticles

Abhishek Singh of San Jose State University and his coworkers investigated the magnetic properties of cobalt nanoparticles synthesized by thermal oxidation/reduction of CoCl2 in a nitrogen atmosphere. By adding organophosphine surfactants that differed in size and concentration, they were able to produce unique cobalt nanoparticles with an organic cap layer. When a bulky tri-octylphosphine surfactant was used with a high surfactant/reactant (S/R) ratio, they formed 7-nm Co particles in a 2D hexagonal network. A smaller surfactant, tri-butyl phosphine, under the same S/R conditions, yielded particle sizes of 12.5 nm. When the surfactant type was held constant and the S/R ratio varied, lower S/R values led to larger particle sizes. Magnetically, the particles showed ferromagnetic behavior, with the larger particle sizes resulting in squarer hysteresis loops than the smaller particles.

Symposium P: Materials and Strategies for Lab-on-a Chip

P2.1: Electrohydrodynamic Jet Printing for Digital Micro/Nanofabrication

The trend toward macroelectronics—mainly large area, thin film devices used for display screens that form the core of a $70 billion industry today—suggests that alternatives to photolithographic processes traditionally used for small area wafers be examined. John Rogers of the University of Illinois, Urbana, and his coworkers have been investigating electrohydrodynamic, hi-resolution ink jet printing as one possible avenue. The advantages of inkjet technology are that it is scalable to very large substrates, and it uses material efficiently (requiring no coating, patterning, or developing steps).

Electrohydrodynamic technology relies on a difference in voltage between the inkjet nozzle and a conducting plate beneath the substrate to essentially suck fluids out of the nozzle and onto the substrate. This differs from the spraying technology of current inkjets. Using gold-coated, pulled-glass capillaries with a 2-nm opening as nozzles, Rogers and his colleagues were able to produce sub-micron dot diameters on a substrate. A low voltage difference between the nozzle and the conducting plate causes the jet to operate in pulse mode, while a higher voltage difference causes a stable jet to produce a single, continuous filament of fluid. By moving the substrate under the nozzle, the researchers can write patterns as desired.

To date they have used this method successfully with a variety of "inks," including PEDOT/PSS conducting polymers, UV-curable polyurethane, Si nanoparticles, and single-stranded DNA. They can digitize arbitrary patterns, such as a drawing of Mickey Mouse, and print them using any one of these inks. Rogers showed a portrait of Hypatia, an ancient philosopher from Alexandria, produced using 100-nm-diameter drops of UV-curable polyurethane. They have also developed individually-addressable nozzle arrays, with each nozzle capable of holding a different type of ink. Active devices such as TFTs have been made using this electrohydrodynamic ink jet process. Future goals include improving the resolution to less than 100 nm.

The National Research Council Town Hall Meeting
New Materials Synthesis and Crystal Growth (MSAC)

Paul Peercy of the University of Wisconsin at Madison led the National Research Council Town Hall Meeting on the topic of "New Materials Synthesis and Crystal Growth." The meeting was the second in a series funded by the National Science Foundation and the Department of Energy. A small group of 13 people showed up to discuss what some perceive as a crisis in the lack of bulk crystal growth facilities in the United States. While Japan and Europe forge ahead in this area, the U.S. continues to fall behind.

Peercy set the context of the meeting by stating "The basic research effort of U.S. industry is waning, and with it the domestic capacity for creating new materials and growing them in crystalline form." In contrast, the U.S. seems to be strong in characterizing these materials, even if they were not invented here. He then asked the audience to consider a series of eight formal questions, including "How do we increase the number of people and facilities who grow crystals?" and "What keeps us from having adequate crystal growth capabilities?"

In the discussion, various points of view were expressed. There is a perception by some that bulk crystal growth is not cutting edge science, and that new faculty avoid the field because it is not seen as a way to gain tenure. One person wondered whether manufacturing processes are more regulated than characterization processes in this country, leading to the preponderance of characterization facilities here. Another questioned whether crystal growers were viewed more as skilled technicians than research scientists. The advances in amorphous materials in the solar cell industry prompted one audience member to speculate that perhaps more research efforts are going in that direction because amorphous materials are easier and less costly to synthesize than pure crystalline materials. Another suggested that perhaps something that is considered mundane, like bulk crystal growth, is losing its share of funding to what are perceived as more exciting and exotic fields like biomaterials and nanoscale materials. Questions arose as to whether it would be beneficial to have a national center for crystal growth, or a network of separate labs that collaborate on bulk crystal growth. One participant thought it was a case of "real world materials competing with fantasy materials," among which he included carbon nanotubes.

The lively discussion was aided by representatives of the National Science Foundation and the Department of Energy, who were able to correct misperceptions about what they do and do not fund, and who also explained what response they would have to see from industry and academia to consider funding a center or network of laboratories. The small turnout at this Town Meeting was seen by some as evidence that perhaps there is not a groundswell of opinion in the materials community that there is, indeed, a crisis in bulk crystal technology and capacity in the U.S.

Though no answers emerged from this meeting, future ones are scheduled to be held at other scientific conferences, with a report due out later this year.

Materials Research Support at the National Science Foundation

NSF Further Broadens Funding for Materials Research

W. Lance Haworth, Acting Director of the Division of Materials Research (DMR) at the National Science Foundation (NSF), provided an overview of NSF support for materials research and education, and laid out specific opportunities for funding. New opportunities include funding for research on nanoscale science and engineering, a new program for research on biologically related materials, support for international collaboration in materials research, support for research on "cyberscience," and computational materials.

NSF is broadening funding for materials research in terms of new focus areas. In the area of biology, DMR is interested in research projects addressing how to explore and develop the frontier between materials and biology. In terms of "cyberscience," DMR is interested in both how the cyberinfrastructure will have an enormous impact on the way materials research is done as well as how materials research enables the cyber infrastructure.

DMR is also interested in broadening participation in materials research by increasing the number of grants given to researchers who are women and ethnic minorities. The 2006 numbers show that 16% of the awards went to women and 9% went to ethnic minorities. To improve these percentages, DMR is looking into hosting "Gender Equity Workshops" for materials science and engineering similar to workshops done in the past for other science groups. DMR has also implemented a program called Partnerships for Research and Education in Materials (PREM), which supports funding for long-term collaborative partnerships between minority-serving institutions and DMR-supported centers and facilities.

Outreach to Asian and developing countries is another initiative of NSF through the Materials World Network. The purpose of the network is to enhance international collaborations in materials research, education, and technology.

A key component of NSF is education. In terms of materials research, DMR is dedicated to educating the next generation of materials researchers. Therefore, proposals to DMR need to integrate education into the research project. Proposals are particularly reviewed based on whether the project is most likely to produce new knowledge and on how it impacts the community beyond research, such as in terms of education, a benefit to society, or its impact on science and technology.

Upcoming proposal deadlines include the Fall of 2007 for the Materials World Network and the DMR instrumentation program for mid-scale instruments. The best window of time to send in unsolicited research proposals is September 17 to November 2, 2007. Haworth suggested that proposals be sent in early in order to leave time for revisions and resubmissions. Open competition for funding for Materials Research Science and Education Centers (MRSECs) occurs every three years, with an upcoming deadline of September 2007. MRSECs are funded for six years. More than half of the current Centers are due for renewal this Fall and will compete with proposals for new Centers.

More information on materials-supported research can be accessed at their Web-site www.nsf.gov/materials.

Spring Meeting Attendees Touch the Nanoworld

MRS Spring Meeting attendees touched the nanoworld with the help of interactive immersive activities developed through the Nanoscale Informal Science Education Network (NISENet) today in the lobby of the 2nd level of the Moscone West Center. After nucleating larger than life hexagonal ice cystals on his hand, crystal growth expert and MRS NISENet subcommittee chair, Jim DeYoreo, exclaimed "that was fun!" Others used their hands to play with water surface tension and to ask questions about the multi-story nanoscape and carbon nanotube balloon models.

      

In partnership with MRS and its volunteers, NISENet is developing new tools and techniques to engage the public in understanding the importance of our work and to inspire questions. Please stop by the MRS Public Outreach booth to take advantage of the opportunity to volunteer your expertise and passion as a NISENet advisor.

 

the Exhibit Experience

Lake Shore introduces the Model EMTTP4 horizontal (in-plane) field electromagnet-based probe station. Providing field strengths in excess of 0.4 T and operating over a temperature range from 10 K to 450 K, it can be configured with up to four ultra-stable micro-manipulated probe arms and can accommodate up to a 1-inch diameter wafer. Electro-magnet fields can be swept quickly from an external source, providing fast field cycling. Stop by Booth 317, e-mail us at info@lakeshore.com or visit us online at www.lakeshore.com/emps.html.
The NanoSight nanoparticle size analyzer from NanoAndMore tracks every particle that is in focus in its optics and gives a complete distribution of particle sizes from 7nm to 1µm. The Lyncee tec Digital Holographic Microscope technology will obsolete laser and white light interferometers. It is the only instrument that can capture 3D data on biological material, including live cells, in real time at up to 50,000 frames/second. For additional information, visit Booth 425 or contact us at usa@nanoandmore.com or www.nanoandmore.com.
The Nano-DST from Pacific Nanotechnology provides a radical new approach to the world of atomic force microscopy (AFM). Rather than having a single scanner restricted to scan area and resolution limitations, the Nano-DST incorporates two scanners. The Nano-DST uses the latest controller technology. It is the first SPM controller to use two x,y,z scanning control cards backed with 24 bit electronics using industry standard National Instrument cards. These advanced components enable fast scanning where collection of a 300 line image is made in one second. To learn more, visit PNI’s web site at www.pacificnano.com or stop by Booth 202.
New from Physical Electronics (PHI): The PHI 5000 VersaProbe XPS Microprobe is a multi-technique surface analysis instrument based on PHI’s highly successful scanning x-ray microprobe technology. This technology provides high performance XPS micro-area spectroscopy, chemical imaging, and secondary electron imaging with a raster scanned 10 µm diameter x-ray beam. PHI’s innovative and patented dual beam charge neutralization method provides turn-key analysis of insulating samples using a combination of low energy ions and electrons. Visit Booth 526 for additional information or contact us at sales@phi.com or http://www.phi.com.
PSIA Inc./Park Systems adds the XE-70, an economical version of the XE-100, to its XE Series Atomic Force Microscopes (AFM). Designed for general small sample measurement using manual optics, the XE-70 can support the same modes, options and electronics of conventional AFMs. Fully upgradeable, its compact mechanical design and affordability make it perfect for customers with limited budgets. Visit Park Systems at Booth 333 for demonstrations, or contact Brad Rangell at 408-986-1110.
The SonoPlot GIX Microplotter Desktop is a bench top picoliter fluid dispensing system capable of drawing spots, lines, or arcs as narrow as 5 microns. The patented ultrasonic fluid ejection enables the deposition of a wide range of fluids, including high-viscosity solutions, while minimizing dead volume. Integrated digital video and precise positioning allow for targeted dispensing on MEMS or other complex surfaces.  Visit SonoPlot at Booth 121 or contact us at info@sonoplot.com to find out more.
The new hemispherical analyzer PHOIBOS 225 (HV) by SPECS is an ultra high resolution, high energy analyzer, designed for studying bulk properties of solids in an electron energy range of up to 15 KeV. The analyzer is equipped with low dark-count detector units and works at high retarding ratios to provide <15meV resolution in Hard X-ray Photoelectron Spectroscopy (HAXPES). It also shows an ultimate performance of <1meV in Ultraviolet Photoelectron Spectroscopy (UPS). 2D CCD, 3D Delayline, Spin Detectors and combinations thereof are available. Contact sales@specsus.com or visit us at Booth 323. For more information, call SPECS in the US at 415-397-7327, or +49 30 467824-0 for requests from outside the US.
TMS (The Minerals, Metals & Materials Society) recently unveiled a web-based interface where materials science and engineering professionals can gather in communities to exchange knowledge, discuss technical issues, share resources, and network with peers. Communities include: Education, Integrated Computational Materials Engineering, Lead-Free Solders, Magnesium, Materials for Nuclear Power, and Superalloys. Any member of the materials community can contribute to the site.  Visit www.materialstechnology.org or stop by Booth 105 today to learn more.
For research and pilot-production, there’s no better system than the Veeco GEN20™. Incorporating industry–leading attributes from the GEN II™ and the GEN200®, this all-new model, in a proven platform, manufactures wafers up to 4" with multi-chamber processing capabilities. It seamlessly integrates application-specific design features for both existing and emerging materials, including nitrides and oxides. The GEN20 is available with either automatic or manual transfer. For more information, visit Booth 305 or http://www.veeco.com/gen20.

• Compiled and edited by Gopal Rao, MRS Web Science Editor with contributions from Betsy Fleischer, Judy Meiksin, Mike Driver and Tim Palucka.
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