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Ultralow-dielectric-constant amorphous boron nitride

Matters Arising to this article was published on 03 February 2021

Abstract

Decrease in processing speed due to increased resistance and capacitance delay is a major obstacle for the down-scaling of electronics1,2,3. Minimizing the dimensions of interconnects (metal wires that connect different electronic components on a chip) is crucial for the miniaturization of devices. Interconnects are isolated from each other by non-conducting (dielectric) layers. So far, research has mostly focused on decreasing the resistance of scaled interconnects because integration of dielectrics using low-temperature deposition processes compatible with complementary metal–oxide–semiconductors is technically challenging. Interconnect isolation materials must have low relative dielectric constants (κ values), serve as diffusion barriers against the migration of metal into semiconductors, and be thermally, chemically and mechanically stable. Specifically, the International Roadmap for Devices and Systems recommends4 the development of dielectrics with κ values of less than 2 by 2028. Existing low-κ materials (such as silicon oxide derivatives, organic compounds and aerogels) have κ values greater than 2 and poor thermo-mechanical properties5. Here we report three-nanometre-thick amorphous boron nitride films with ultralow κ values of 1.78 and 1.16 (close to that of air, κ = 1) at operation frequencies of 100 kilohertz and 1 megahertz, respectively. The films are mechanically and electrically robust, with a breakdown strength of 7.3 megavolts per centimetre, which exceeds requirements. Cross-sectional imaging reveals that amorphous boron nitride prevents the diffusion of cobalt atoms into silicon under very harsh conditions, in contrast to reference barriers. Our results demonstrate that amorphous boron nitride has excellent low-κ dielectric characteristics for high-performance electronics.

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Fig. 1: Atomic structure of a-BN.
Fig. 2: Chemical structure of a-BN.
Fig. 3: Dielectric properties of a-BN.

Data availability

The datasets generated and/or analysed during the current study are available from the corresponding authors on reasonable request.

Code availability

The code used to generate the figures is available from the corresponding authors on reasonable request.

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Acknowledgements

We thank UNIST Central Research Facilities (UCRF) and Y. K. Kim for the cross-sectional high-resolution TEM images. This work was supported by Samsung Electronics (Samsung-SKKU Graphene/2D Center), the research fund (NRF-2017R1E1A1A01074493 and NRF-2019R1A4A1027934), the IBS (IBS-R-019-D1) and a grant (CASE-2013M3A6A5073173) from the Centre for Advanced Soft Electronics under the Global Frontier Research Program via the National Research Foundation of the Ministry of Science and ICT, South Korea. The NEXAFS experiments performed at the 4D, 6D and 10A2 beamlines of the Pohang Accelerator Laboratory (PAL) were supported in part by the Ministry of Science and ICT, POSTECH and UNIST. M.C. acknowledges support from Leverhulme Trust Research Grant RPG-2019-227. S.R., A.A. and M.C. acknowledge the European Union Horizon 2020 research and innovation programme for grant number 785219 and 881603 (Graphene Flagship). A.A. is supported by Project MECHANIC (PCI2018-093120) funded by Ministerio de Ciencia, Innovación y Universidades. The Catalan Institute of Nanoscience and Nanotechnology is funded by the CERCA Programme/Generalitat de Catalunya and supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (grant number SEV-2017-0706).

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Contributions

H.S.S. and H.-J.S. planned and supervised this project. S.H., K.Y.M., G.K, S.I.Y. and H.S.S. performed the growth and characterization experiments. C.-S.L., M.-H.L. and H.-J.S. fabricated the electrical devices. S.W.K. performed and analysed the ellipsometry measurements. H.-I.L. obtained and analysed the RBS data. Y.L. and Z.L. obtained the TEM data. K.I., K.-J.K. and T.J.S. measured the NEXAFS data. E.-c.J., H.J. and J.-Y.K measured the mechanical properties and adhesion. A.A. and S.R. performed the molecular dynamics simulations. M.C. suggested key experiments and measurements and helped with the interpretation of results. M.C. wrote and edited the manuscript with H.S.S. All authors contributed to the writing of the manuscript and agreed on the contents of the paper.

Corresponding authors

Correspondence to Manish Chhowalla or Hyeon-Jin Shin or Hyeon Suk Shin.

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The authors declare no competing interests.

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Peer review information Nature thanks Francesca Iacopi, Lain-Jong Li and Junhao Lin for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Growth of a-BN on Cu and SiO2 substrates.

ac, Raman (a), XPS (b) and EDS mapping (c) images of a-BN grown on copper foils (plasma power 30 W, growth temperature 300 °C) and transferred onto SiO2 substrates for Raman measurements. The typical Raman spectrum of the a-BN film is similar to that of bare amorphous SiO2. df, Raman (d), XPS (e) and EDS mapping (f) images of an a-BN film grown directly on SiO2 (plasma power 10 W, growth temperature 200 °C). The spectra are largely the same for all substrates. The dielectric properties obtained from spectroscopic ellipsometry reveal no influence of the substrate. Scale bar, 40 nm.

Extended Data Fig. 2 Analysis of the reduced radial distribution function obtained from the electron diffraction data and cross-sectional chemical mapping of the a-BN film.

a, Azimuthally averaged experimental electron diffraction intensity of a-BN. b, Reduced radial distribution function, G(r), of a-BN obtained from the electron diffraction data. The peak position r = 1.44 Å corresponds to the nearest-neighbour distance of B–N. The G(r) curve was calculated using eRDF Analyser (an open-source interactive GUI for electron reduced density function analysis). c, High-angle annular dark-field (HAADF) scanning TEM image (left) overlaid with EDS maps of carbon (red), nitrogen (green) and silicon (blue). An image with overlaid EDS maps for all elements is shown on the right. Scale bars, 20 nm.

Extended Data Fig. 3 Molecular dynamics simulation.

a, b, Side view (a) and top view (b) of a-BN grown on Si substrates at 673 K, calculated using molecular dynamics simulations. Different atomic species are shown in different colours: yellow (Si), blue (N) and pink (B). c, Mass density profile along the transverse direction (z), obtained from the results shown in a and b. Coloured solid lines denote the densities of different chemical species. The simulated density of a-BN is consistent with the experimental result. The black dashed line corresponds to the measured BN mass density.

Extended Data Fig. 4 FTIR, HR-RBS, HR-ERDA and NEXAFS analyses of a-BN films.

a, FTIR spectra of a-BN, showing the absence of B–H and N–H bonds. Abs, absorption. b, c, HR-RBS (b) and HR-ERDA (c) spectra of an a-BN film in the energy range 240–400 keV and 52–68 keV, respectively. d, Elemental composition calculated using the HR-RBS and HR-ERDA spectra. e, PEY-NEXAFS spectra for the N K edge of a-BN, measured at incident angles of 30°, 55° and 70°, demonstrating a small angular dependence of the N K edge.

Extended Data Fig. 5 Comparison of a-BN and nc-BN films.

a, Structure of nc-BN film deposited at 700 °C. b, Low-magnification TEM images of nc-BN. The selected-area electron diffraction pattern in the inset shows a typical polycrystalline ring pattern. c, High-resolution TEM images of nc-BN, clearly showing small crystallites of hBN. The cross-sectional TEM image in the inset indicates a layered structure. d, Magnification of the area indicated by the blue box in c. e, Fast Fourier transform image showing the hexagonal superstructure of multilayer hBN. f, g, XPS profiles of the B 1s (f) and N 1s (g) peaks observed in 3-nm-thick a-BN and nc-BN samples. h, Raman spectra of a-BN, nc-BN and epitaxially grown trilayer hBN (tri-hBN; 1.2 nm thick; used as reference) samples transferred onto SiO2/Si substrates. i, FTIR spectra for a-BN (red) and nc-BN (blue) measured using s-polarized radiation at an incident angle of 60°. The E1u longitudinal optical (LO) mode is related to the amorphous phase of BN; see ref. 19.

Extended Data Fig. 6 Nanoindentation and nanoscratch test results.

a, b, Nanoindentation results showing that the deposition of a-BN on Si substrates leads to an enhancement in surface hardness and stiffness. The average and standard deviation values for the hardness in b are 11.31 ± 0.13 for a-BN on Si and 10.93 ± 0.09 for bare Si. c, Nanoscratch test results revealing that a scratch depth of 40 nm (more than 10 times the film thickness) is required to delaminate the film, which suggests excellent adhesion with the Si substrate. Scanning electron microscopy observations show that the scratch regions are clean, with no evidence of delamination of a-BN for a scratch depth smaller than 40 nm. The datasets 1–4 in the bottom panel represent scratch test data obtained at four different positions under the same experimental conditions.

Extended Data Fig. 7 Cross-sectional TEM images of Co(80 nm)/TiN(3 nm)/Si films after thermal diffusion tests at different temperatures.

ac, Images obtained after thermal diffusion at 600 °C for 60 min (a), 600 °C for 30 min (b) and 400 °C for 30 min (c). d, Magnified cross-sectional TEM image (right) and EDS line profile (left) of the film shown in a.

Extended Data Fig. 8 Large-area cross-sectional TEM images, EDS line profiles and maps of a Co/a-BN(3 nm)/Si film after thermal diffusion at 600 °C for 60 min.

a, Large-area cross-sectional TEM image and EDS line profiles. b, EDS maps of Co and Si showing that Co is isolated above the a-BN film and does not diffuse into the Si. c, EDS maps of a magnified area in b.

Extended Data Fig. 9

Breakdown bias at different temperatures for a-BN and TiN barriers.

Extended Data Table 1 Comparison of dielectric constants of various dielectric materials

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Hong, S., Lee, CS., Lee, MH. et al. Ultralow-dielectric-constant amorphous boron nitride. Nature 582, 511–514 (2020). https://doi.org/10.1038/s41586-020-2375-9

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