Chemical vapour deposition of zeolitic imidazolate framework thin films

Journal name:
Nature Materials
Volume:
15,
Pages:
304–310
Year published:
DOI:
doi:10.1038/nmat4509
Received
Accepted
Published online

Abstract

Integrating metal–organic frameworks (MOFs) in microelectronics has disruptive potential because of the unique properties of these microporous crystalline materials. Suitable film deposition methods are crucial to leverage MOFs in this field. Conventional solvent-based procedures, typically adapted from powder preparation routes, are incompatible with nanofabrication because of corrosion and contamination risks. We demonstrate a chemical vapour deposition process (MOF-CVD) that enables high-quality films of ZIF-8, a prototypical MOF material, with a uniform and controlled thickness, even on high-aspect-ratio features. Furthermore, we demonstrate how MOF-CVD enables previously inaccessible routes such as lift-off patterning and depositing MOF films on fragile features. The compatibility of MOF-CVD with existing infrastructure, both in research and production facilities, will greatly facilitate MOF integration in microelectronics. MOF-CVD is the first vapour-phase deposition method for any type of microporous crystalline network solid and marks a milestone in processing such materials.

At a glance

Figures

  1. Chemical vapour deposition of ZIF-8 thin films.
    Figure 1: Chemical vapour deposition of ZIF-8 thin films.

    The procedure consists of a metal oxide vapour deposition (Step 1) and a consecutive vapour–solid reaction (Step 2). Metal, oxygen and ligand sources are labelled as M, O and L, respectively. Metal oxide deposition can be achieved by atomic layer deposition (M, diethylzinc; O, oxygen/water) or by reactive sputtering (M, zinc; O, oxygen plasma). Atom colours: zinc (grey) oxygen (red), nitrogen (light blue) and carbon (dark blue); hydrogen atoms are omitted for clarity.

  2. Characterization of chemical vapour deposited ZIF-8 thin films.
    Figure 2: Characterization of chemical vapour deposited ZIF-8 thin films.

    a, X-ray diffraction pattern of a ZIF-8 CVD film and simulated pattern for ZIF-8. b, Scanning electron microscopy top view. c, 3D rendered AFM topograph. d, Focused-ion beam TEM cross section. Inset: high-resolution magnification of the interface between ZIF-8 and the titanium oxide substrate. e, HAADF and EDS cross-section maps of a completely transformed film. f, HAADF and EDS cross-section maps of a partially transformed film. The completely transformed film (ae) was obtained by vapour–solid reaction of a 6-nm-thick ALD zinc oxide film. The partially transformed film (f) was obtained by vapour–solid reaction of a 15-nm-thick ALD zinc oxide film. Scale bars, 2μm for bd, 20nm for inset in d, 100nm for ef.

  3. Conformal ZIF-8 thin films deposition on high-aspect-ratio pillar arrays.
    Figure 3: Conformal ZIF-8 thin films deposition on high-aspect-ratio pillar arrays.

    a,b, Scanning electron microscopy images showing the ZIF-8-coated silicon pillar array. c,d, High-magnification scanning electron microscopy images showing the homogeneous coverage at the base of the pillars. e, Kr adsorption isotherms for the zinc-oxide-coated pillar array (grey circles) and after 15min (red crosses), 30min (blue diamonds) and 45min (yellow squares) vapour–solid reaction. f, Single-pulse Kr adsorption kinetics experiment for a 85-nm-thick high-aspect-ratio ZIF-8 film (green) and a 2,500-nm-thick flat film (dashed, grey). Scale bars, 50μm for a, 5μm for b,c and 1μm for d.

  4. Vapour-solid reaction of zinc oxide and HmIM studied by in situ powder X-ray diffraction (PXRD).
    Figure 4: Vapour–solid reaction of zinc oxide and HmIM studied by in situ powder X-ray diffraction (PXRD).

    a, Schematic overview of the transformation mechanism. b, Plot of the time-resolved diffraction patterns viewed down the intensity axis, showing the transformation of crystalline phases in a 1:2 mixture of crystalline zinc oxide and HmIM powder at 130°C. Colour scale from blue (low intensity) to red (high intensity). Simulated pure-phase diffraction patterns are plotted at the top for reference and peaks corresponding to ZIF-8 are highlighted by the blue arrows. c, ZIF-8 phase quantification for in situ reaction experiments at 115°C (blue) and 130°C (red). d, ZIF-8 phase quantification for in situ reaction experiments at 115°C under a continuous dry nitrogen flow (purple) and a nitrogen flow humidified to 33% relative humidity at room temperature (green).

  5. MOF integration routes enabled by the MOF-CVD process: lift-off patterning and coating of fragile features.
    Figure 5: MOF integration routes enabled by the MOF-CVD process: lift-off patterning and coating of fragile features.

    a, Schematic diagram of MOF pattern deposition by MOF-CVD and subsequent lift-off of a patterned photoresist. b,c, Scanning electron microscopy images of the manufactured ZIF-8 patterns. d, Schematic diagram of the production of ZIF-8-coated polydimethylsiloxane pillars by soft lithography and MOF-CVD. e, Scanning electron microscopy image of MOF-CVD-coated PDMS pillars. f, Scanning electron microscopy image of identical PDMS pillars after conventional solution processing of ZIF-8. The MOF-CVD processing steps are indicated with a dashed line in a and d. Oxide and MOF films are represented in red and blue, respectively. Scale bars, 100μm for b, 10μm for c, 20μm for e,f, 1μm for insets.

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Author information

Affiliations

  1. Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis, KU Leuven–University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium

    • Ivo Stassen,
    • Dirk De Vos,
    • Philippe Vereecken &
    • Rob Ameloot
  2. imec, Kapeldreef 75, B-3001 Leuven, Belgium

    • Ivo Stassen &
    • Philippe Vereecken
  3. CSIRO Manufacturing Flagship, Clayton, Victoria 3168, Australia

    • Mark Styles &
    • Paolo Falcaro
  4. MBI, National University of Singapore T-Lab, 5A Engineering Drive 1, Singapore 117411, Singapore

    • Gianluca Grenci
  5. Department of Chemistry, KU Leuven–University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium

    • Hans Van Gorp,
    • Willem Vanderlinden &
    • Steven De Feyter

Contributions

I.S. and R.A. conceived and designed the experiments. I.S. carried out and analysed all film deposition and characterization experiments. M.S., P.F. and R.A. designed and conducted the X-ray diffraction measurements. M.S. and I.S. analysed the X-ray diffraction data. H.V.G. and W.V. conducted the atomic force microscopy experiments. G.G. and P.F. designed and manufactured the photolithography and soft lithography patterned substrates. The manuscript was primarily written by I.S. and R.A., with the input of all authors.

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The authors declare no competing financial interests.

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