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New study unveils ultrathin boron nitride films for next-generation electronics

Posted By Graphene Council, Friday, June 26, 2020
An international team of researchers, affiliated with UNIST has unveiled a novel material that could enable major leaps in the miniaturization of electronic devices. Published in the prestigious journal Nature, this study represent a significant achievement for future electronics.

This breakthrough comes from a research, conducted by Professor Hyeon Suk Shin (School of Natual Sciences, UNIST) and Principal Researcher Dr. Hyeon-Jin Shin from Samsung Advanced Institute of Technology (SAIT), in collaboration with Graphene Flagship researchers from University of Cambridge (UK) and Catalan Institute of Nanoscience and Nanotechnology (ICN2, Spain).

In this study, the team successfully demonstrated the synthesis of thin film of amorphous boron nitride (a-BN) with extremely low dielectric constant as well as high breakdown voltage and superior metal barrier properties. The research team noted that this newly fabricated material has great potential as interconnect insulators in the next-generation of electronic circuits.

In the ongoing process of miniaturization of logic and memory devices in electronic circuits, minimizing the dimensions of interconencts - metal wires that link the different device components on the chip - is crucial to guarantee improved performance and faster response of the device. Extensive research efforts have been devoted to decreasing the resistance of scaled interconnects because integration of dielectrics using complementary metal oxide semiconductor (CMOS) compatible processes has proven to be exceptionally challenging. According to the research team, the required interconnect isolation materials should not only possess low relative dielectric constants (referred to as k-values), but should also be thermally, chemically, and mechanically stable.

There has been an ongoing quest to obtain materials with ultra-low-k (relative permittivity around or below 2) avoiding the artificial addition of pores in the thin film in the semiconductor industry for at least the past 20 years. Several attempts had been made to develop materials with desired characteristics, yet those materials have failed to be successfully integrated in interconnects due to poor mechanical properties or poor chemical stability upon integration, causing reliability failures.

In this study, the joint research has succeeded in demonstrating a Back-End-ofthe-Line (BEOL) compatible approach to grow amorphous boron nitride (a-BN) with extremely low-k dielectrics. In particular, they synthesized approximately 3 nm thin a-BN on a Si substrate, using low temperature remote inductively coupled plasma-chemical vapour deposition (ICP-CVD). The resulting material showed an extremely low dielectric constant in the range of 1.78, which is 30% lower than the dielectric constant of currently available insulators.

In this study, the joint research has succeeded in demonstrating a Back-End-ofthe-Line (BEOL) compatible approach to grow amorphous boron nitride (a-BN) with extremely low-k dielectrics. In particular, they synthesized approximately 3 nm thin a-BN on a Si substrate, using low temperature remote inductively coupled plasma-chemical vapour deposition (ICP-CVD). The resulting material showed an extremely low dielectric constant in the range of 1.78, which is 30% lower than the dielectric constant of currently available insulators.

"We found that temperature was the most important parameter with ideal a-BN film deposition occurring at 400° C," says Seokmo Hong in the Doctoral program of Natural Sciences, the first author of the study. "This material with ultra-low-k also manifests a high breakdown voltage and likely superior metal barrier properties, making the film very attractive for practical electronic applications."

Angle-dependent near-edge X-ray absorption fine structure (NEXAFS) measured in partial electron-yield (PEY) mode at Pohang Light Source-II 4D beam line was also used to investigate the chemical and electronic structures of a-BN. Their findings indicated that the irregular, random atomic arrangement causes the dielectric constant value to drop.

The new material also manifests excellent mechanical properties of high strength. Moreover, when researchers tested the diffusion barrier properties of a-BN in very harsh conditions, they found it can prevent metal atom migration from the interconnects into the insulator. This result will help resolves a long-standing issue of interconnects in CMOS integrated circuit fabrication, enabling further miniaturaization of electronic devices.

"Development of electrically, mechanically and thermally robust low-k materials (k < 2) has long been technically challenging," says Dr. Hyeon-Jin Shin from Samsung Advanced Institute of Technology (SAIT). "Our research is also a great example that shows companies and academic institutions working together to create greater synergy."

"Our results demonstrate that the amorphous counterpart of two-dimensional hexagonal BN possesses the ideal low-k dielectric characteristics for high-performance electronics," says Professor Shin. "If they are commercialized, it will be a great help in overcoming the crisis looming over the semiconductor industry."

Tags:  boron nitride  Electronics  Graphene  hexagonal boron nitride  Hyeon Suk Shin  Hyeon-Jin Shin  Samsung Advanced Institute of Technology  UNIST 

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Crystal with a Twist: Researchers Grow Spiraling New Material

Posted By Graphene Council, Monday, February 17, 2020

With a simple twist of the fingers, one can create a beautiful spiral from a deck of cards. In the same way, scientists have created new inorganic crystals made of stacks of atomically thin sheets. These stacks unexpectedly spiral like a nanoscale card deck. Their surprising structures may yield unique optical, electronic and thermal properties. These properties may even include superconductivity, the ability to conduct electricity without loss. These crystals in the shape of a helix are made of stacked layers of germanium sulfide. This is a semiconductor material that, like graphene, readily forms sheets that are only a few atoms thick. Such “nanosheets” are also called “2D materials.”

This is the first time that scientists have made 2D materials that form a continuously twisting shape in a structure that is thousands layers thick. The spiral structures could hold unique properties that aren’t observed in regularly stacked materials. Scientists could likely use this technique to grow layers of other materials that form atomically thin layers.

Summary

To create the twisted structures, the team took advantage of a crystal defect called a screw dislocation, a “mistake” in the orderly crystal structure that gives it a bit of a twisting force. This “Eshelby Twist”, named after scientist John D. Eshelby, has been used by others to create nanowires that spiral like pine trees. But this study is the first time the Eshelby Twist has been used to make crystals built of stacked 2D layers of an atomically thin semiconductor.

In a major discovery last year, scientists reported that graphene becomes superconductive when two atomically thin sheets of the material are stacked and twisted at what’s called a “magic angle.” While other researchers have since succeeded at stacking two layers at a time, this new work provides a recipe for synthesizing stacked structures that are hundreds of thousands or even millions of layers thick in a continuously twisting fashion.

By adjusting the material synthesis conditions and length, the researchers could change the angle between the layers, creating a twisted structure that is tight, like a spring, or loose, like an uncoiled Slinky.

Scientists performed X-ray analyses for the study at the Advanced Light Source and measured the crystal’s twist angles at the Molecular Foundry, both DOE Office of Science user facilities.

Funding
Y.L. and J.Y. are supported by the Samsung Advanced Institute of Technology. Work at the Molecular Foundry and the Advanced Light Source was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy. H.S. and D.C.C. are supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering. within the Electronic Materials Program (KC1201). This work was performed, in part, at the Center for Nanoscale Materials, a US Department of Energy Office of Science User Facility. We thank C. So, C. Song, X. Wang, S. Yan, K. Bustillo and C. V. Stan for help with the experiments.

Tags:  2D materials  Electronics  Graphene  Samsung Advanced Institute of Technology  Semiconductor 

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