Amorphous boron nitride shows excellent insulating properties for next generation of electronics

By June 29, 2020July 6th, 2020ICN2

The Catalan Institute of Nanoscience and Nanotechnology (ICN2), a BIST centre, participates in a collaboration that published a report in Nature last week about the synthesis of a thin film of amorphous Boron Nitride (a-BN) which shows extremely low dielectric characteristics, high breakdown voltage, and likely superior metal barrier properties, all of which represent a significant achievement for future electronics.

The Ulsan National Institute of Science and Technology (UNIST, Republic of Korea) and the Samsung Advanced Institute of Technology (SAIT) lead a collaboration involving two Graphene Flagship partners: the Catalan Institute of Nanoscience and Nanotechnology (ICN2, a BIST centre) and the University of Cambridge (UK). The collaboration published a report in Nature last week, describing the synthesis of a thin film of amorphous Boron Nitride, which could have a significant impact for future electronics.

In the ongoing process of miniaturisation of logic and memory devices in electronic circuits, reducing the dimensions of interconnects — metal wires that link components on a chip — is crucial for guaranteeing fast response of the device and improving its performance. Research efforts have been focused on developing materials with excellent insulating properties to separate the interconnects from each other. A suitable material for this application is required to have a dielectric constant (parameter that defines its insulating properties) no higher than 2. Furthermore, it should serve as a diffusion barrier against migration of metals into semiconductors and be thermally, chemically, and mechanically stable.

The quest for such a heavily insulating material has driven the semiconductor industry for at least the past 20 years. However, while materials with the desirable characteristics have been reported over time (organic polymeric materials and others), and have created excitement in the industry, they have systematically failed to be successfully integrated into the interconnects due to poor mechanical properties or insufficient chemical stability upon integration, causing reliability failures.

In a paper published last week in Nature, led by researchers from UNIST and SAIT, with the participation of two teams from the Graphene Flagship (ICN2 and the University of Cambridge), the first large-scale synthesis of a thin film of amorphous Boron Nitride (a-BN) showing record low dielectric characteristics is described. This groundbreaking achievement suggests that a-BN is an excellent candidate for application in high-performance electronics. The first author of the article is Seokmo Hong and the last one is Prof. Hyeon Suk Shin, both from the Department of Chemistry at UNIST.

In particular, a-BN as thin as 3nm was synthesised on a silicon substrate (using low temperature inductively coupled plasma-chemical vapor deposition, ICP-CVD), which showed an exceptionally low dielectric constant of 1.78 at 100 kHz. Tests of the diffusion barrier properties of this amorphous material, conducted in very harsh conditions, have also demonstrated that it is able to prevent metal atom migration from the interconnects into the insulator. Together with a high breakdown voltage, these characteristics make a-BN very attractive for practical electronic applications.

State-of-the-art techniques such as HRTEM, XPS, Raman spectroscopy, FTIR, and PEY-NEXAFS, have been successfully employed to characterise the material. In contrast with other materials with a low dielectric constant, which are sometimes made porous to exploit the low dielectric constant of air at the expense of mechanical strength, a-BN film features the lowest dielectric constant at the highest density. Remarkably, measurements also indicate that the material has hardness and stiffness larger than bulk silicon.

To explain the correlation between the structural and morphological properties and the dielectric response of the a-BN film, Dr. Aleandro Antidormi from the ICN2 Theoretical and Computational Nanoscience Group, led by ICREA Prof. Stephan Roche, has performed atomistic calculations on samples of a-BN generated “in silico”. By means of classical molecular dynamics, the chemical vapor deposition (CVD) method employed experimentally was simulated to build an a-BN film on Si having similar dimensions as the fabricated one. Ultimately, the calculations helped to identify the key factors for the excellent performances of a-BN: the nonpolar character of the BN bonds and the lack of order preventing dipoles alignment. The results of this simulation have contributed to understanding the structural morphology of this amorphous material as well as explaining its superior dielectric performances.

More information can be found on the ICN2 website

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