High-Tech PR Insights
A new study from the University of Wisconsin-Madison has provided some key insights into the field of hi-tech public relations.

The way a scientific breakthrough is presented can change how a technology is perceived among the general public, according to the study. Participants in the study were given one of three definitions regarding the same technical breakthrough.

One definition highlighted a technology’s applications. The second focused on the risks and benefits. And the third involved both applications and risks and benefits.

The results were mixed. If the definition was highlighted, the participants would support the technology, “but they weren’t motivated to gather more information,” according to the University of Wisconsin-Madison. Meanwhile, if the definition focused on risks and benefits, participates wanted to learn more, but were “less likely to support nanotechnology,” according to the researchers.

“Explaining nanotechnology in terms of applications promotes acceptance, but motivation to learn more is triggered by mentioning potential risks,” said Dietram Scheufele, UW-Madison professor of life sciences communication, on the university’s Web site.

On the site, Ashley Anderson, a research fellow in the Center for Climate Change Communication at George Mason University, added: “This has important implications for those interested in engaging members of the public in scientific issues.”

Molecular DSA For Mobile Apps
The National University of Singapore and the Tyndall National Institute at the University College Cork have developed a molecular and self-assembly technology that could boost the energy efficiency in smart phones and tablets.

Researchers have devised tiny devices using molecules, which do not overheat while showing good electrical properties. By altering just one carbon atom of an active molecular component, the devices provide a tenfold improvement in switching efficiency.

Redox active ferrocenealkanethiol molecules pack together and assemble into monolayer thin films on silver electrodes. Molecules standing tall instead of crouching form tighter assemblies, which dramatically improve the device properties. Source: NUS

For years, researchers have been looking to tap the potential of organic and molecular electronics. The challenge is that organic and molecular electronic devices are complex. They generally consist of at least two electrodes, an organic component and two different organic/inorganic interfaces, according to researchers.

Isolating each structure has also been a challenge. Researchers have considered the idea of using “strong π–π interactions” for organic electronic devices.

Using a different approach, the National University of Singapore and Tyndall showed that changes in the “intermolecular van der Waals interactions” in the active component of a molecular diode impacts the performance of the device. In chemistry, the van der Waals force is named after Dutch scientist Johannes Diderik van der Waals. The concept involves the sum of the attractive or repulsive forces between molecules.

Researchers discovered an odd–even effect as the number of alkyl units is varied in a ferrocene–alkanethiolate self-assembled monolayer. Consequently, junctions made from an odd number of alkyl units have a lower packing energy and rectify currents 10 times more efficiently, according to researchers.

This, in turn, gives a 10% higher yield in working devices. What’s more, the molecules can be made two to three times more often than junctions made from an even number of alkyl units, according to researchers.

Balloon Lithography
Helium-ion microscopes were once targeted to replace traditional scanning-electron microscopes (CD-SEMs) for semiconductor metrology applications. Helium-ion microscopy never lived up to those promises, but the technology has found a new application in nanofabrication.

Quadruple quantum dots patterned on bilayer graphene using He-ion-beam milling. Source: SPIE

The University of Southampton and the Japan Advanced Institute of Science and Technology have demonstrated that helium-ion microscopy can be used to sputter and pattern graphene structures. In turn, the technology can be used to create tiny nanoscale designs on graphene.

In the lab, researchers first used an traditional electron-beam tool to pattern metal contacts on graphene flakes. Then, in a milling process, they used a helium-ion microscope to pattern structures. The tool patterned structures like nanoribbons and quantum dots on graphene.

With the process, researchers patterned quadruple quantum dots on bilayer graphene at 5nm feature sizes. Researchers cla
im that the process could enable devices with an accuracy of 1nm with good yields.

—Mark LaPedus

Seeing In The Dark
The University of Wisconsin-Madison, the U.S. Air Force and the U.S. Department of Defense have developed curved night-vision goggles using germanium nanomembranes.

Using flexible semiconductors, the goggles supposedly will make night vision more accurate and easier for soldiers and pilots to use.

There are several major challenges with the technology. “Because of their higher dark current, the image often comes up much noisier on germanium-based imagers,” said Zhenqiang Ma, a professor of electrical and computer engineering at the University of Wisconsin-Madison, on the university’s Web site. “We solved that problem.”

In a separate project, the U.S. Department of Defense also has provided Ma with $750,000 in support of development of imagers for military surveillance. The imagers span multiple spectra, combining infrared (IR) and visible light into a single image.

The current approach involves a sensor for IR images and a sensor for visible light. This combines the two images in post-processing. This, however, requires greater computing power and hardware complexity.

To enable the next-generation imager, researchers will implement a heterogeneous semiconductor nanomembrane technology. They will stack two incompatible materials on each pixel of the new imager in order to create a single image. The result will be imagers that can seamlessly shift between IR and visible images. The DoD is interested in IR, “because visible light can be blocked by clouds, dust, smoke,” Ma said.

It’s A Material World
Researchers led by the CSIRO and RMIT University have devised the layers of crystal known as molybdenum oxide, a new 2D material that enables the free flow of electrons at high speeds.

Researchers adapted graphene to create this new material. Monash University, the University of California at Los Angeles (UCLA) and the Massachusetts Institute of Technology (MIT) also participated in the work. The Commonwealth Scientific and Industrial Research Organization (CSIRO) is Australia’s national science agency.

Artist impression of high carrier mobility through layered molybdenum oxide crystal lattice. Credit: Dr Daniel J White, ScienceFX

Graphene itself consists of one-atom-thick planar sheets, which are packed in honeycomb crystal lattice structures. The technology is expensive and difficult to put into manufacturing. And it doesn’t have a band gap, meaning it can’t be turned off in a system.

Researchers were able to overcome graphene’s apparent limitations. They demonstrate that the energy bandgap of layered, high-dielectric α-MoO3 can be reduced to values viable for the fabrication of 2D electronic devices.

This is achieved through embedding Coulomb charges within the high dielectric media, thereby limiting charge scattering. Devices with α-MoO3 of ∼11 nm thickness were obtained. It also resulted in electron mobility values of >1,100 cm2/Vs, according to researchers.

“Within these layers, electrons are able to zip through at high speeds with minimal scattering,” said Serge Zhuiykov, a scientist from CSIRO on the research organization’s Web site. “The importance of our breakthrough is how quickly and fluently electrons–which conduct electricity – are able to flow through the new material.”

RMIT’s Professor Kourosh Kalantar-zadeh added: “Quite simply, if electrons can pass through a structure quicker, we can build devices that are smaller and transfer data at much higher speeds. While more work needs to be done before we can develop actual gadgets using this new 2D nano-material, this breakthrough lays the foundation for a new electronics revolution and we look forward to exploring its potential.”

Sensing A Breakthrough
The A*STAR Institute of Microelectronics in Singapore and others have devised a MEMS-based miniaturized pressure sensor that combines a stable diaphragm with sensitive silicon nanowires. With the technology, researchers are looking to develop tiny and implantable medical devices.

The idea was to create a pressure-deformable diaphragm and then embed a piezoresistor made from a material in which pressure causes a change in electrical resistance, such as a silicon nanowire.

Researchers devised a pressure sensor with a 200µm diaphragm using silicon nanowires. The silicon nanowires are embedded in a multilayered diaphragm structure comprising silicon nitride (SiNx) and silicon oxide (SiO2).

Optimizations were performed on both silicon nanowires and the diaphragm structure. The diaphragm with a 1.2µm SiNx layer is considered to be an optimized design in terms of small initial central deflection (0.1µm), relatively high sensitivity (0.6% psi−1) and good linearity within a given measurement range.

SiO2 was used because of its pressure sensitivity. But the material tended to buckle and twist even without pressure. Researchers, in turn, used a double layer of SiO2, with piezoresistive silicon nanowires embedded in between, topped by a stabilizing layer of SiNx.

By etching down the silicon nitride and varying the thickness and treatment of the silicon nanowires, the team found an optimum combination. “The high internal stress of silicon nitride improves the diaphragm structure with good flatness, a large measurement range and waterproof properties,” said Liang Lou, a researcher at the A*STAR Institute of Microelectronics, on the research organization’s Web site. “Our work provides a pioneering demonstration that integrating silicon nanowires into a multi-layer diaphragm allows us to scale down the sensor without losing high sensitivity.”

—Mark LaPedus

Carbon Nanotube Uniforms
Using a carbon nanotube fabric, Lawrence Livermore National Laboratory (LLNL) is developing a new military uniform material that repels chemical and biological agents.

The material can move from a breathable to a protective state. In theory, if a chemical warfare agent hits the carbon nanotube fabric then the functional groups on the carbon nanotube membrane will sense and block the threat. Then, a second response scheme also will be developed. “Similar to how a living skin peels off when challenged with dangerous external factors, the fabric will exfoliate upon reaction with the chemical agent,” according to researchers. In turn, the fabric will be able to block chemical agents such as sulfur mustard, GD and VX nerve agents, toxins such as staphylococcal enterotoxin, and biological spores such as anthrax.

The highly breathable membranes have pores made of a few nanometer-wide vertically aligned carbon nanotubes that are surface modified with a chemical warfare agent-responsive functional layer.

“The uniform will be like a smart second skin that responds to the environment,” said Francesco Fornasiero, LLNL’s principal investigator for the Defense Threat Reduction Agency (DTRA)-funded project, on LLNL’s Web site. “Without the need of an external control system, the fabric will be able to switch reversibly from a highly breathable state to a protective one in response to the presence of the environmental threat. In the protective state, the uniform will block the chemical threat while maintaining a good breathability level.”

The new uniforms could be deployed in the field in less than 10 years.

Chicken Wire Chips
Ferromagnetism in non-magnetic materials, such as the edge states in graphene nano-ribbons and defects in graphite, have attracted attention in R&D circles.

The Department of Energy’s Oak Ridge National Laboratory and others have made a surprising discovery: Nano-ribbons of silicon configured so the atoms resemble chicken wire could hold the key to data storage. Researchers investigated electron spins arising from intrinsic broken bonds at the step edges. They used scanning tunneling spectroscopy (STS).

In the lab, the step edges on the silicon-gold surface underwent a 1 × 3 reconstruction at low temperature. Oak Ridge, Argonne National Laboratory, the University of Wisconsin and Naval Research Laboratory showed that the electron spins are ordered anti-ferromagnetically. The up and down spin-polarized atoms serve as effective substitutes for conventional “0s” and “1s” common to electrons.

“By exploiting the electron spins arising from intrinsic broken bonds at gold-stabilized silicon surfaces, we were able to replace conventional electronically charged zeros and ones with spins pointing up and down,” said Paul Snijders of the Department of Energy’s Oak Ridge National Laboratory. “For the first time we were able to clearly establish that the edges of nano-ribbons feature magnetic silicon atoms.”

This confirms the prediction of spin-polarization in silicon. It also provides an avenue for studying low-dimensional magnetism. Most importantly, silicon–gold surfaces provide a precise template for single-spin devices at the ultimate limit of high-density data storage and processing.

Vortex Devices
Researchers from the Universities of Bristol, the University of Glasgow, Sun Yat-sen University and Fudan University have demonstrated integrated arrays of emitters of “optical vortex beams” in silicon chips. The quantum mechanical properties of optical vortices can be applied in quantum communications and computation.

The research contradicts the conception that light moves in straight rays. Instead, researchers demonstrated that the energy travels in a spiral fashion in a conical beam shape.

The research is related to the orbital angular momentum (OAM) of photons, in which photons orbit around a beam axis. Researchers demonstrated silicon-integrated optical vortex emitters using angular gratings with high OAM. The smallest device has a radius of 3.9 micrometers.

Siyuan Yu, professor of photonics information systems in the Photonics Research Group at the University of Bristol, said: “Our microscopic optical vortex devices are so small and compact that a silicon micro-chip containing thousands of emitters could be fabricated at a very low cost and in high volume. Such integrated devices and systems could open up entirely new applications of optical vortex beams previously unattainable using bulk optics.”

Mark Thompson, deputy director of the Centre for Quantum Photonics at the University of Bristol, added: “Perhaps one of the most exciting applications is the control of twisted light at the single photon level, enabling us to exploit the quantum mechanical properties of optical vortices for future applications in quantum communications and quantum computation.”

Misbehaving MEMS
Researchers can calculate the movement of tiny MEMS devices. The impression is that MEMS devices move in uniform increments. However, the National Institute of Standards and Technology (NIST) made a new and surprising finding: MEMS do not march in uniform steps.

To track a MEMS device, NIST has devised a super-resolution fluorescence microscopy technology. This technology is said to measure a MEMS device in motion across a surface. More specifically, NIST tracked a MEMS device called a “scratch drive actuator.” This device is said to drag itself over a surface by repeatedly flexing and relaxing a hooked arm.

A micromachine called a scratch drive actuator, labeled with fluorescent dots, (top) rests atop a platform underlain by an electric circuit that initiates the device’s step-by-step movements. Under a fluorescence microscope, the nanoparticles appear as points of light in a starlike constellation (bottom), making it possible to measure small changes in the position and orientation of the device at each step. Credit: NIST

The device is imaged by widefield epi-fluorescence microscopy. The image is then placed into a Gaussian distribution model to calculate its position. NIST calculated the size of each movement to within 1.85nm. This technique is also used to measure the stepwise motion of a scratch drive actuator across each of 500 duty cycles with a 130nm localization precision.

“Our method revealed very irregular step sizes, which had neither been observed previously nor predicted by established models of MEMS behavior,” said Craig McGray of NIST on the organization’s Web site. Super-resolution fluorescence microscopy can be used in MEMS R&D and other applications.

—Mark LaPedus

By Mark LaPedus
Directed self-assembly (DSA) is making progress for potential use in semiconductor production, but the industry must make some major advances in a sometimes forgotten and unsung segment—materials.

DSA is a complementary patterning technology that makes use of block copolymer materials to enable fine pitches in chip designs. But today’s block copolymers based on poly (MMA-co-styrene), or better known as PS-b-PMMA materials, do not scale beyond 11nm.

To bring DSA from the lab to the fab, Arkema, AZ, Dow, IBM, JSR, SEH, TOK and others are separately developing next-generation DSA copolymers that promise to scale beyond 11nm. But for the most part, the commercial vendors are keeping their R&D work close to the vest.

To date, most of the research in the public domain has originated at universities. Given that the universities provide a clue of what’s coming down the pike, there are several DSA materials candidates on the table, including high chi copolymers, blended compounds, and even one based on simple sugar.

Each approach, which is still in R&D, consists of complex chemical compounds that resemble a mix of letters in a bowl of alphabet soup. The candidates have various trade-offs, but there is no clear leader in the next-generation copolymer race right now.

“The field is much more wide open than it was for the first generation PS-b-PMMA materials,” said Ralph Dammel, chief technology officer for AZ Electronic Materials, a supplier of materials for DSA and other applications. “There certainly are a number of possible high chi materials. It may be that one single high chi polymer technology will evolve, or several ones may co-exist, possibly for different applications. It is too early to say.”

DSA to the rescue?
DSA is one of several lithographic options for chip production. In the current lithography landscape, chipmakers are expected to use 193nm immersion and double patterning at 20nm. Then, at 14nm and 10nm, the industry would like to insert extreme ultraviolet (EUV) lithography. If EUV misses those windows, the industry will extend 193nm immersion and move to a more complex multi-patterning scheme.

The wild card is DSA, which is still in R&D. Technically, DSA is a complementary scheme. When used in conjunction with a pre-pattern that directs the orientation for patterning, DSA is said to reduce the pitch of the final printed structure. Used in conjunction with 193nm immersion, DSA could extend 193nm lithography beyond 10nm, eliminate expensive multi-patterning steps and push out EUV.

In the lab, DSA has demonstrated the ability to devise features down to 5nm. The likely insertion point for DSA is the 10nm node, said Moshe Preil, manager of emerging lithography and tools at GlobalFoundries. “If it was only about the chemistry, we would know how to implement DSA at 14nm,” Preil said. “We still don’t know how to design a chip using DSA.”

Design enablement and defectivity are among the challenges with DSA. And to put DSA in a production fab, chipmakers must make some complex choices. First, there are two main types of DSA methods: graphoepitaxy and chemical epitaxy. In chemical epitaxy, self-assembly is guided by a sparse chemical pre-pattern. Graphoepitaxy is based on a topographical pre-pattern.

Chipmakers must come up with the right DSA materials, which is also a challenge. “The design of high chi block copolymers has a number of pitfalls. It is not easy, but there has already been a lot of progress, enough that we can say there will not be a technical issue with availability of high chi materials for <10nm patterning,” said AZ’s Dammel.

A polymer is a molecule that consists of repeating structural units. A copolymer is a polymer compound derived from two or more structural units. Block copolymers consist of dissimilar structural units or chains linked by covalent bonds.

In DSA, the dissimilar units are able to phase separate into distinct domains and then self-assemble into controllable dimensions. The trouble is today’s block copolymers based on PS-b-PMMA materials have a chi factor of about 0.04. If the chi N factor is less than 10.5 in certain mixes, the blocks will not phase separate. N denotes the degree of polymerization, while chi represents the interaction parameter.

So, the industry must find a suitable material that scales. In this area, there are two basic approaches: organic-organic versus organic-inorganic. Academia has focused on organic-organic compounds, while commercial vendors are narrowing their options down to organic-inorganic materials, said Mark Slezak, vice president of sales and technology at JSR Micro, the U.S. sales arm for JSR.

IBM and JSR have been co-developing a technology that blends a copolymer and organosilicate material. This blended approach can scale and consists of fewer process steps using sidewall image transfer technology, according to JSR and IBM. “This has opened Pandora’s Box,” said Yoshi Hishiro, director of R&D at JSR Micro. “The blended approach enables several possibilities. The chi for the blended system can be defined.”

IBM also is working on other solutions, including non-blended copolymers with AZ Electronic Materials. “Both polymer blends and block copolymers phase separate on annealing. Polymer blends are very easy to make, and they also are easier to process. Usually, they require lower annealing temperatures and it is easier to achieve short annealing times,” AZ’s Dammel said. “But the blended approaches are restricted to 2x frequency duplication. For 3x or more, one has to use the longer range self-assembly capability of block copolymers.”

Frequency duplication is key for DSA. “Let’s say we have 20nm lines with 160nm pitch. Let’s say we also use a copolymer with a natural period L0 of 40nm. After the process, we have 20nm equal lines and spaces, or 4x the lines that were there before. That’s what is called 4x frequency multiplication,” Dammel explained.

Today’s block copolymers have scaling limitations. “So, one needs to make block copolymers with higher chi factors. One problem is that some types of block copolymers with high chis are difficult to phase separate by thermal annealing. The blocks repel each other so strongly that they have a hard time moving past each other. One has to use solvent vapor to soften them enough to get them to phase separate.” Dammel explained.

The problem is that solvent annealing may not be the right solution, because the technology is incompatible with today’s semiconductor manufacturing processes, he added.

The contenders
At present, there are several promising next-generation, high chi copolymer candidates on the table. “All of them have their strong attributes. They also have their shortcomings,” said Christopher Ober, professor in the Department of Materials Science and Engineering at Cornell University.

For years, Cornell has been developing block copolymers. The other pioneers in the DSA materials field include the University of Massachusetts Amherst (UMASS) and the University of Wisconsin.

In a more recent effort, Intel and the University of Queensland in Australia described a diblock copolymer, based on poly(styrene)-b-poly(DL-lactide) or PS-b-PDLA materials. Using a graphoepitaxy process flow with 4x frequency multiplication, the entities demonstrated 8nm lines and spaces with PS-b-PDLA materials.

“The new high chi systems such as p(S-b-DLA) have even better selectivity than p(S-b-MMA),” Dammel said. “The p(S-b-DLA) system also has much lower annealing temperatures than the p(S-b-MMA) system.”

In another effort, the Massachusetts Institute of Technology (MIT) recently disclosed that self-assembly can form 3D structures. MIT used a poly (styreneb-dimethylsiloxane) or PS-b-PDMS block copolymer. PS-b-PDMS has a chi factor of 0.27. MIT also HAS devised higher chi materials based on poly(2-vinylpyridine-b-dimethylsiloxane) or P2VP-PDMS.

“I would not treat the chi parameter as the only figure of merit,” said Caroline Ross, professor in the Department of Materials Science and Engineering at MIT. “Chi is one consideration, but there are others that are relevant to microphase separation, such as the molecular weight, volume fraction, surface energy of the blocks and relative etch resistance.”

Hitachi and CNRS-CEA/LETI also are pursuing PS-b-PDMS. In a separate effort, CNRS and the University of Texas at Austin have recently described the synthesis and self-assembly of block copolymers “composed of naturally derived oligosaccharides” or sugar.

These block copolymers enable 5nm feature sizes. “However, that system can never be annealed thermally,” said C. Grant Willson, professor of chemical engineering at the University of Texas at Austin. “It has to be annealed with a solvent. I personally do not think that long solvent annealing processes are compatible with semiconductor manufacturing.”

Willson and his associates are working on other materials. “We have designed a new block copolymer that has all of the attributes of the sugar polymer, but can be annealed thermally with a top coat. This new material looks very promising,” he added.

Meanwhile, UMASS and others are developing copolymers based on polystyrene-block-poly(ethylene oxide) or PS-b-PEO materials. UMASS is also exploring tri-block copolymers based on poly(ethylene oxide) or PEO-b-PPO-b-PEO materials.

In another effort, Pohang University of Science and Technology, Tokyo Institute of Technology, and the University of Wisconsin-Madison, Wisconsin recently described an organic-inorganic diblock copolymer, dubbed poly(styrene-b-methacrylate) or PS-b-PMAPOSS.

Cornell has been developing the concept of orthogonal processing of block copolymers. By using a semi-flourinated photoresist/solvent system, researchers are able to selectively pattern or lift-off and then recover the block copolymer film intact. This relates to “orthogonal lithography,” a new patterning process for organic semiconductors. The process is based on a novel photoresist that is compatible with sensitive organic systems. The specially designed photoresist is composed of polymeric or molecular glass that enables the use of fluorous solvents, thus not damaging the organic material while enabling pattern formation.

By Mark LaPedus
Directed self-assembly (DSA) has been billed by some as a potential paradigm shift in semiconductor manufacturing, but it may not turn out to be quite the panacea its proponents suggest—or at least not yet.

There are many questions surrounding DSA, an alternative lithography technology that makes use of block copolymers to enable fine pitches. Key among those questions are when will DSA move into semiconductor production, what are the challenges for the technology, and what it will actually cost.

In theory, a university or research center could set up a DSA line for R&D for a mere $2,000, said Christopher Bencher, a member of the technical staff at Applied Materials, at a recent event. It’s unlikely that a university will produce complex multicore processors using DSA, but for years researchers have been conducting R&D and developed devices with DSA for a small cost.

It’s a different story to bring DSA from the lab to the fab, however. To insert DSA into production, a chipmaker would still need to own a leading-edge fab and 193nm immersion scanners, said Moshe Preil, manager of emerging lithography and tools at GlobalFoundries.

A new, leading-edge fab is projected to cost from $4.85 billion to $6.7 billion. But generally, a chipmaker could utilize an existing leading-edge fab and tools, and make relatively few new equipment purchases, to put DSA into production, Preil said. “I don’t think the cost to put DSA in production is going to be that outrageous,” he said.

The most obvious cost savings is lithography. With DSA, chipmakers could use existing 193nm tools—and push out the need for extreme ultraviolet (EUV) lithography. A 193nm immersion tool runs about $40 million. In contrast, a EUV scanner is projected to sell for $125 million per unit.

There are bigger hurdles to bring DSA into chip production. Current block copolymers based on today’s poly (MMA-co-styrene) materials could run out of steam at 11nm. There are still defect issues with DSA. And arguably the biggest hurdle is to develop a new design methodology around DSA.

Litho roadmap
For some time, leading-edge chipmakers have been evaluating several lithographic options for 14nm. There is a glimmer of hope that EUV will be ready at 14nm, but there are signs the technology is running into more delays due to inadequate power sources.

If EUV is late, the only option is to use 193nm immersion and a multi-patterning scheme at 14nm. Then, at 10nm, the IC industry is looking at several options: DSA, EUV, maskless, multi-patterning and nano-imprint.

Some believe that DSA could get inserted as early as the 14nm node. GlobalFoundries’ Preil said that a more realistic insertion point for DSA is 10nm. “It’s really too late to insert DSA at 14nm,” he said. “Progress continues to be made at the sort of rate that we need it for the 10nm node.”

Technically, DSA is not a next-generation lithography (NGL) tool. It’s a complementary and double-patterning scheme. DSA enables frequency multiplication through the use of block copolymers. When used in conjunction with a pre-pattern that directs the orientation for patterning, DSA can reduce the pitch of the final printed structure.

Using 193nm immersion, DSA has demonstrated the ability to print images down to 12.5nm—without the need for multi-patterning. DSA could extend 193nm lithography beyond 10nm, eliminate expensive multi-patterning steps and push out EUV. On some roadmaps, there is a path to use EUV and DSA simultaneously to scale devices beyond 14nm.

There are two types of DSA methods: graphoepitaxy and chemical epitaxy. In chemical epitaxy, self-assembly is guided by chemical patterns. In graphoepitaxy, self-assembly is guided by pre-patterned templates.

Stanford University has been developing a DSA design methodology using individual guiding templates. Using 66nm templates, Stanford has demonstrated 25nm contact holes for 22nm SRAM cells. The end goal is to develop a “full character alphabet set of templates,” said H.S. Phillip Wong, professor of electrical engineering at Stanford University. “The templates would allow designers to compose any arbitrary feature.”

Even so, there are design challenges. Regarding the DSA templates, “the list of what you can do is still very limited,” said David Abercrombie, advanced physical verification methodology program manager at Mentor Graphics. “You would also be tied to very restrictive design rules or proscribed design rules.”

Design-for-manufacturing techniques like pattern matching aren’t exactly straightforward in DSA. With DSA, a design-rule-checker (DRC) may have to implement a “reverse pattern matching” technique, Abercrombie said.

DSA’s cost of ownership
Today, the DSA process flow is ahead of the design infrastructure. AZ Electronic, IBM and the University of Wisconsin have separately developed process flows, each aimed at moving DSA from the lab to the fab.

Unlike today’s chip production, which is dependent on lithography, DSA revolves around conventional wafer track systems, etchers and inspection gear. “For basic DSA, you need a coater and a bake plate, plus a way of generating the guide structures. Since the guides need to be fairly small, you need at least 193nm dry lithography, or for a university, more likely an e-beam tool” to pattern the individual guides, said Ralph Dammel, chief technology officer for AZ Electronic Materials, a supplier of materials for DSA and other applications.

“Then, you need to etch or at least decorate the structures, and a scanning electron microscope (SEM) or an atomic force microscope (AFM) to observe them. Wet development is also possible, at least for contact holes. ,” Dammel said. “For our customers, they already have all of the needed tools in-house. So, for R&D, no new equipment is needed. For production, it becomes a matter of track capacity. But, of course, the cost of track equipment is far cheaper than that of an EUV tool.”

The cost of ownership depends on several factors. “Assuming a university has standard tooling, their cost would be near zero,” he said. “For thermal annealing, a university could cobble something together for a few dollars.”

On the other hand, a chipmaker would still need to invest in new and more advanced materials, such as higher k films and metal gates, said GlobalFoundries’ Preil. The cost of the DSA materials themselves are expected to be similar to today’s photoresists, he added.

Another challenge is how to scale the DSA materials. AZ Electronic, Dow, JSR, SEH, TOK and others are developing next-generation DSA materials. Recently, CEA-Leti, Arkema and the Laboratoire de Chimie des Polymères Organiques devised a DSA development platform that enables a 20nm pitch and contacts down to 7nm.

Block copolymers consist of different polymer chains that are joined. Copolymers can be separated into ordered nanostructures. The inherit properties enable them to frequency double or quadruple into regular patterns. And a range of phase morphologies can be accessed depending on the block lengths.

“For 10 nm, p(MMA-co-styrene) block copolymer is no longer a suitable material. Its low chi factor implies that a high molecular weight (MW) is needed to obtain phase separation,” AZ’s Dammel said. “Since MW is related to domain size, the lowest line-space structures that can reliably be made are approximately 11nm.”

The goal is to develop higher chi materials for 10nm node and below. The University of Queensland in Australia is developing a promising class of diblock copolymers called PS-b-PDLA. Though in the R&D stage, these materials will make it “possible to extend DSA to the 8nm node, using guide structures made by immersion lithography,” he said.