Manufacturing Bits: Dec. 2

Storage ring EUV source
Needless to say, extreme ultraviolet (EUV) lithography is delayed. Chipmakers hope to insert EUV at the 7nm node, but that’s not a given. As before, the big problem is the EUV light source. So far, the source can’t generate enough power to enable the required throughput for EUV in mass production.

Researchers at the SLAC National Accelerator Laboratory have one possible solution to the problem. The group is exploring the development of a high-power EUV source based on a storage ring technology. This technology is still in the R&D stage and it would require backing from the IC industry to make it commercially viable.

Researchers are exploring the concept using an existing storage ring. In this case, they would use the SPEAR3 at SLAC as a test case. In 1972, SLAC completed the Stanford Positron Electron Accelerating Ring (SPEAR), a colliding-beam storage ring for use in particle physics research. SPEAR consists of a single ring, which is about 80 meters in diameter.

In 2004, the facility was upgraded. That facility, dubbed the SPEAR3, is a 3-GeV, third-generation storage ring. With limitations imposed by the existing parameters, researchers aim for a target of 1 kW of EUV power.

To enable the EUV storage ring source, researchers have devised a technique called steady-state microbunching (SSMB). “The basic idea is to manipulate the beam’s dynamics in a storage ring so that its distribution is not the conventional Gaussian, but microbunched,” said Alex Chao, a professor of physics at SLAC at Stanford University. “The whole concept of SSMB lies in the invention of a way to make the beam microbunched and tstay microbunched in the turn-by-turn environment of a storage ring.”

In the EUV source, the ring consists of one modulator and one radiator. The modulator (300nm undulator) and the radiator (13.5nm undulator) are installed in a storage ring of low momentum-compaction. A weak 300nm seed laser is applied at the modulator. Mirrors are optional depending on available laser power. In operation, a beam is microbunched and focused at 300nm. This, in turn, could enable power at 13.5nm wavelengths due to the high repetition rate of the technology.

The technology does not consist of free electron lasers (FEL). “FEL, as suggested by some, disrupts the beam too much. Therefore, it destroys the microbunching structure,” Chao said. “SSMB intentionally avoids an FEL mechanism. The key to SSMB is that it is microbunched and steady-state. That is why is has the potential of high-power EUV.”

Initially, Chao and his team will make use of the SPEAR3 facility, but eventually, the technology may require the development a dedicated storage ring. A dedicated storage ring would be half the size of the SPEAR3 facility. In theory, each fab would require one storage ring. “However, a dedicated storage ring can have multiple insertions. Each storage ring can serve several 1-kW tools within each fab,” he said.

This technology is different than the ill-fated X-ray lithography sources in the 1980s. In those days, IBM and several Japanese companies were separately developing X-ray lithography based on giant synchrotron storage rings. “The SSMB makes the electron beam microbunched in steady-state,” Chao said. “The usual synchrotron beam is not microbunched, and the radiation power is therefore lower by a factor of N, where N is the number of electrons in an electron bunch. In practice, N is about 10^9. SSMB source is potentially nine orders of magnitude stronger than a synchrotron source, although in practice it is somewhat less.”

Lift-off for flexible chips
Flexible electronics is a promising technology that could be used in consumer electronics, displays, medical devices and other products. But the technology also has some challenges. Insufficient performance of the organic materials presents an issue. And high temperature processes have restricted the development of flexible electronics because of the fundamental thermal instabilities of polymer materials.

To help solve the issues, Korea Advanced Institute of Science and Technology (KAIST) has developed a new methodology to realize flexible electronics by using what the research organization calls Inorganic-based Laser Lift-off (ILLO) technology.

In the lab, researchers devised a crossbar-structured memory comprising of 32 × 32 arrays with one selector–one resistor (1S-1R) components. The device was initially fabricated on a rigid substrate. It was transferred to a plastic substrate via a ILLO process.

This schematic picture shows the flexible crossbar memory developed via the ILLO process. (Source: KAIST)

The ILLO process involves depositing a laser-reactive exfoliation layer on rigid substrates, and then fabricating inorganic electronic devices on top of the exfoliation layer. “By laser irradiation through the back of the substrate, only the ultrathin inorganic device layers are exfoliated from the substrate as a result of the reaction between laser and exfoliation layer, and then subsequently transferred onto any kind of receiver substrate such as plastic, paper, and even fabric,” according to KAIST.

On the organization’s Web site, Keon Jae Lee, a professor of the Department of Materials Science and Engineering at KAIST, said: “By selecting an optimized set of inorganic exfoliation layer and substrate, a nanoscale process at a high temperature of over 1000 °C can be utilized for high performance flexible electronics. The ILLO process can be applied to diverse flexible electronics, such as driving circuits for displays and inorganic-based energy devices such as battery, solar cell, and self-powered devices that require high temperature processes.”

T-shirt lithography
Nanyang Technological University (NTU) has printed complex electronic circuits using a common t-shirt printer. With the technology, researchers have printed a 4-bit digital-to-analog converter and radio-frequency identification (RFID) tags.

The circuits are printed using materials in layers on top of flexible materials, such as plastic, aluminum foil and paper. Resistors, transistors and capacitors can be printed using non-toxic organic materials like silver nanoparticles, carbon and plastics.

The key difference between Nanyang’s method and the other types of printed electronics is that it is a fully additive technology. The circuits are printed entirely without the use of any toxic chemicals or oxidizing agents.
A new startup company is being established to commercialize the technology. A multinational biomedical company has also expressed interest to adopt the technology for biomedical devices.

“This means we can have smarter products, such as a carton that tells you exactly when the milk expires, a bandage that prompts you when it is time for a redressing, and smart patches that can monitor life signals like your heart rate,” said NTU Associate Professor Joseph Chang, on the university’s Web site.

“We are not competing with high-end processors like those found in smartphones and electronic devices. Instead we complement them with cheaply printed circuits that cost mere cents instead of a few dollars, making disposable electronics a reality,” he said. “Our innovative process is green, using non-corrosive chemicals. It can be printed on demand when needed within minutes. It is also scalable, as you can print large circuits on many types of materials and most importantly, it is low cost, as print technology has been available for decades.”

Nanyang Technological University has printed complex electronic circuits using a common t-shirt printer. (Source: NTU)