Manufacturing Bits: June 16

Harmonic EUV; plasmonic metrology; European R&D effort.


Harmonic EUV
The U.S. Department of Energy’s Lawrence Berkeley National Laboratory has devised an efficient extreme ultraviolet (EUV) source. The technology could one day be used for a new class of metrology tools, based on angle-resolved photoemission spectroscopy (ARPES). This technique makes use of a photoelectric effect for studying materials.

To enable the source, Berkeley Labs developed a technology called high-harmonic generation. With the technology, researchers devised a source of femtosecond EUV pulses at 50-kHz repetition rates.

Light is used to efficiently generate EUV light at high repetition rates. (Source: Berkeley Lab)

Light is used to efficiently generate EUV light at high repetition rates. (Source: Berkeley Lab)

In the lab, the system converts infrared pulses from a femtosecond laser into the UV range. Then, the pulses gain back energy through high-harmonic conversion. The latter pulses must be focused into the thin column of Krypton gas. In this cascaded scheme, a photon flux is generated at 22.3eV.

The spectral isolation of a single 72-meV-wide harmonic renders a bright, 50-kHz EUV source. It could one day be used for fast photoemission, nanoscale imaging and other applications.

“It’s very difficult to generate XUV light in the first place. This is made possible by a process called high-harmonic generation, where you expose atoms to extremely strong laser fields with peak intensities of 100 Terawatts or more,” said He Wang, a researcher at Berkeley Lab, on the organization’s Web site. “An electron can then tunnel out of the atom and return having picked up a lot of energy that, subsequently, it can lose by emitting an XUV photon. An important result of our work is that we achieve very efficient high-harmonic conversion into the XUV, despite operating at high repetition rates where the driving laser power has to be divided among many pulses.”

Plasmonic metrology
Rice University has devised a way to make ultra-sensitive measurements at optical frequencies for chips.

Researchers linked pairs of puck-shaped metal nanodisks with metallic nanowires. The flow of current through the nanowires produced “charge transfer plasmons” with optical signatures.

The technology could be used to identify the conductance of nanowires or related technologies at optical frequencies. “To reduce the size of electronics even beyond today’s limits, scientists want to study electron transfer through a single molecule, particularly at extremely high, even optical frequencies,” said Fangfang Wen, a Rice graduate student, on the university’s Web site. “Such changes cannot be measured using standard electronic devices or instruments that operate at microwave frequencies. Our research provides a new platform for the measurement of nanoscale conductance at optical frequencies.”

Linked pairs of nanodisks as seen with a SEM. (Credit: Fangfang Wen/Rice University)

Linked pairs of nanodisks as seen with a CD-SEM. (Credit: Fangfang Wen/Rice University)

Some metallic nanoparticles convert light into plasmons. Plasmons are waves of electrons that flow across a surface. One type of interaction is plasmonic coupling, where two or more plasmonic particles are located near each other.

Researchers from Rice took a close look at plasmonic coupling. For example, they examined the properties two and separate bridged nanodisks. Researchers set up a series of experiments, where they varied the width and shape of the bridging nanowires. They also used two different metals–gold and aluminum.

“In the case where a conducting wire was present in the junction, we saw an optical signature that was very different from the case without a wire,” Wen said. “We also found that our platform gave a different optical signature in cases where the level of conductance was the same but the junction material was different,” Wen said. “If we had nanowires with the same conductance that were made of different materials, we saw a different optical signature. If we used the same material, with different geometries, we saw the same signature.”

European R&D effort
Tyndall National Institute, CEA-Leti and Imec have entered into a collaborative R&D effort in Europe. The project is called ASCENT or Access to European Nanoelectronics Network.

The €4.7 million project will share best practices, form a knowledge-innovation hub, and train new researchers. The three partners will provide researchers access to advanced device data, test chips and characterization equipment.

In recent times, Asian and European R&D organizations have expanded their efforts while the United States is taking a step back. Case in point: Sematech, a major R&D chip consortium in the U.S., is falling by the wayside, at least as a standalone organization.