Abstract
Hexagonal boron nitride (hBN) has emerged as a promising protection layer for dielectric integration in the next-generation large-scale integrated electronics. Although numerous efforts have been devoted to growing single-crystal hBN film, wafer-scale ultraflat hBN has still not been achieved. Here, we report the epitaxial growth of 4 in. ultraflat single-crystal hBN on Cu0.8Ni0.2(111)/sapphire wafers. The strong coupling between hBN and Cu0.8Ni0.2(111) suppresses the formation of wrinkles and ensures the seamless stitching of parallelly aligned hBN domains, resulting in an ultraflat single-crystal hBN film on a wafer scale. Using the ultraflat hBN as a protective layer, we integrate the wafer-scale ultrathin high-κ dielectrics onto two-dimensional (2D) materials with a damage-free interface. The obtained hBN/HfO2 composite dielectric exhibits an ultralow current leakage (2.36 × 10−6 A cm−2) and an ultrathin equivalent oxide thickness of 0.52 nm, which meets the targets of the International Roadmap for Devices and Systems. Our findings pave the way to the synthesis of ultraflat 2D materials and integration of future 2D electronics.
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Data supporting the findings in this manuscript are available from the corresponding authors upon reasonable request.
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Acknowledgements
We thank J. Tang for help in fabrication of metal substrates, H. Liu for help in fabrication of devices and for discussions and J. Wang and C. Song for support in electrical measurements. We thank R. Shao and X. Chang of Analysis & Testing Center, Beijing Institute of Technology. We acknowledge the Molecular Materials and Nanofabrication Laboratory (MMNL) in the College of Chemistry at Peking University for use of instruments. This work was supported by the National Key R&D Program of China (grant no. 2022YFA1204900 to H.P.), the National Natural Science Foundation of China (52021006 to H.P., T2188101 to Z.L., 21920102004 to H.P.), Beijing National Laboratory for Molecular Sciences (BNLMS-CXTD-202001 to H.P.) and the Tencent Foundation (XPLORER PRIZE to H.P.).
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H.P. and Y.W. conceived the project. Y.W. performed the hBN growth and characterizations. F.D. and C.Z. performed the theoretical calculations. Y.W. and Xin Gao carried out the synthesis and transfer of hBN/HfO2 dielectrics and MIM measurements. L.Z. analysed the characterization data. J.Q. and C.T. were involved in the fabrication and measurement of devices. Xiaoyin Gao and L.Z. conducted the STEM characterizations. J.L., X.Z. and J.G. conducted the LEED measurements. J.T. conducted the SAED characterizations. J.W. and Z.L. carried out the fabrication of single-crystal CuNi(111) wafers. The manuscript was written by L.Z., Y.W., Xin Gao and H.P. with input from the other authors. The whole work was supervised by H.P. All authors contributed to the scientific planning and discussions.
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Y.W. and H.P. have filed the Chinese patent applications 2024108361139, 2024108364688, covering the growth of ultraflat hBN and fabrication of ultrathin hBN/HfO2 dielectrics. The other authors declare no competing interests.
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Extended data
Extended Data Fig. 1 Fabrication and characterizations of single-crystal CuNi(111) wafers.
a, Schematic of the fabrication method of CuNi(111) wafers. b, Typical XRD pattern of single-crystal Cu0.8Ni0.2(111)/sapphire. The Cu0.8Ni0.2(111) was alloyed by 400-nm-thick Cu and 100-nm-thick Ni. c, φ scan of Cu0.8Ni0.2(111)/sapphire. d, In-depth Ni distribution of Cu0.8Ni0.2(111) measured by XPS depth profile analysis with Ar+ ion beam etching. The Ni concentration on the surface is about 15%, while increases to about 35% from 5 nm to 20 nm depths in the bulk. The slightly lower concentration of Ni at surface might be caused by the smaller surface energy of Cu than Ni. e, EBSD images of Cu0.8Ni0.2(111) wafers. Upper, along the [001] direction. Lower, along [010] direction. f, AFM images of Cu0.8Ni0.2(111) wafers. The average roughness of Cu0.8Ni0.2(111) films is 0.36 nm.
Extended Data Fig. 2 SEM images of hBN domains grown on CuNi(111) substrates with Ni concentrations of 0%, 5%, 10%, 15%, 20% and 30%.
The hBN domains on Cu(111), Cu0.9Ni0.1(111), Cu0.85Ni0.15(111), Cu0.8Ni0.2(111) films with Ni concentration from 0% to 20% were grown by heating the precursors to 60–70 °C within 5 min. While for the hBN domains grown on Cu0.7Ni0.3(111) with Ni concentration of 30%, the precursors were heated up to 85 °C and the growth time was increased to 10 min to obtain hBN domains with a lateral size of several micrometers.
Extended Data Fig. 3 The distances between hBN and CuNi(111) substrates with different Ni concentrations.
a, Cross-section iDPC-STEM images of hBN grown on Cu(111), Cu0.95Ni0.05(111), Cu0.9Ni0.1(111), Cu0.85Ni0.15(111) and Cu0.8Ni0.2(111), respectively. b, The observed distances between hBN and substrates as a function of Ni content in substrates. In the plot, the red triangle shows the average and the error bar represents the standard deviation. The sample number of each statistic distance between hBN and substrates is 3.
Extended Data Fig. 4 The DFT calculation of the adhesion energies and the friction forces of hBN on Cu(1-x)Nix(111), where 0.0 < x < 0.5, surfaces.
a, Atomic models of monolayer hBN atop four-layer slabs of Cu(1-x)Nix(111) surfaces with varying fractions of Ni from 0% to 50%. b, c The adhesion energy of hBN on Cu(1-x)Nix(111) substrate (b) and the separation distance between hBN and Cu(1-x)Nix(111) substrate (c) as a function of Ni fraction. Compared with hBN on pure Cu(111) surface, at 18.75% Ni fraction, the adhesion energy is increased by ~ 90 meV/BN and the separation distance between hBN and CuNi(111) is decreased by ~ 0.8 Å. In the plot, the blue circle shows the average and the error bar represents the standard deviation. The sample number of hBN-metal distance is 32. d, Frictional force of hBN sliding on the Cu(1-x)Nix(111) substrate as a function of Ni fractions.
Extended Data Fig. 5 Mechanism of strong-coupling growth of hBN on Cu0.8Ni0.2(111).
a, Two local minimum configurations (BfNt and BhNt) of hBN clusters on Cu(111), Cu0.8Ni0.2(111) (consists of ~18% Ni in top layer and ~38% Ni in the bottom layers) and Ni(111) surfaces, respectively. BfNt indicates that B atoms (light red) are on the fcc sites and N atoms (blue) are on the top sites, while BhNt refers to B on hcp sites and N on the top sites. b, The adhesion energy of BfNt and BhNt on Cu(111), Cu0.8Ni0.2(111) and Ni(111), revealing that introducing Ni atoms can increase the coupling of hBN and substrates. c, The energy differences (EBhNt – EBfNt) between BhNt and BfNt on Cu(111), Cu0.8Ni0.2(111) and Ni(111) substrates.
Extended Data Fig. 6 Large-area surface flatness of hBN/Cu foils, hBN/Cu(111) wafer and hBN/Cu0.8Ni0.2(111) wafer.
a, Representative OM image of hBN/Cu foil, where plenty of rolling lines were observed. b, OM image of hBN/Cu(111) film. c, OM image of hBN/Cu0.8Ni0.2(111) film. d-f, White light interferometer images of hBN/Cu foil (d), hBN/Cu(111) (e) and hBN/Cu0.8Ni0.2(111) (f). The Ra values are 116.5 nm, 1.19 nm and 0.95 nm for hBN/Cu foil, hBN/Cu(111) and hBN/Cu0.8Ni0.2(111), respectively. g, Height profiles of hBN/Cu foil (red curve), hBN/Cu(111) film (blue curve) and hBN/Cu0.8Ni0.2(111) film (black curve), respectively.
Extended Data Fig. 7 The ultraflat hBN monolayer transferred onto SiO2/Si.
a, Photograph of 2-inch ultraflat single-crystal hBN monolayer transferred onto 4-inch 90 nm SiO2/Si wafer. b, Optical microscope image of ultraflat hBN on SiO2/Si. c, AFM image of ultraflat hBN on SiO2/Si.
Extended Data Fig. 8 The growth mechanism of uniform HfO2 on hBN/CuNi.
a, Water contact angle of CuNi(111) substrate before (upper) and after (bottom) hBN growth. b, DFT calculations of the adhesion energy between H2O molecular and hBN with different layer numbers on Cu0.8Ni0.2(111) substrates. c-f, AFM images of HfO2 deposited on bare Cu0.8Ni0.2(111), monolayer hBN/Cu0.8Ni0.2(111), bilayer hBN/Cu0.8Ni0.2(111) and wrinkle of hBN/Cu0.8Ni0.2(111).
Extended Data Fig. 9 The relationship between EOT and thickness of HfO2.
a-d, AFM images of hBN and different composite dielectric transferred onto SiO2/Si. e, The function between EOT and thickness of HfO2. In the plot, the red circle shows the average and the error bar represents the standard deviation. The sample number of the thickness of 1.4 nm HfO2 is 3 and the others are 5. We plotted the EOT of hBN/HfO2 composite dielectrics as a function of HfO2 thickness of the MIM devices. The extrapolated EOT of hBN at the zero HfO2 thickness is ~0.21 nm, and the linear slope of the plot is ~0.23, corresponding a dielectric constant for HfO2 of ~17.0. Considering the distance of hBN-Cu0.8Ni0.2 is about 0.27 nm (Fig. 1d) and the dielectric constant of hBN is about 5, the calculated ~0.21 nm EOT of hBN is reasonable. Thus, the trend between EOT and thickness of HfO2 is reasonable after calibrating the thickness of HfO2.
Extended Data Fig. 10 The 2D Bi2O2Se FET devices with hBN/HfO2 as top gate.
a, Schematic structure of Bi2O2Se top-gate FET. b, c, Output (b) and transfer (c) characteristics of Bi2O2Se device.
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Supplementary Figs. 1–20, Tables 1–3 and References.
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Wang, Y., Zhao, C., Gao, X. et al. Ultraflat single-crystal hexagonal boron nitride for wafer-scale integration of a 2D-compatible high-κ metal gate. Nat. Mater. (2024). https://doi.org/10.1038/s41563-024-01968-z
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DOI: https://doi.org/10.1038/s41563-024-01968-z
