Surface-Anchored Metal–Organic Frameworks as Versatile Resists for Gas-Assisted E-Beam Lithography: Fabrication of Sub-10 Nanometer Structures

Abstract

We demonstrate that surface-anchored metal-organic frameworks (SURMOFs) are extraordinary well-suited as resists for high-resolution focused electron beam induced processing (FEBIP) techniques. The combination of such powerful lithographic protocols with the huge versatility of MOF materials are investigated in respect to their potential in nanostructures fabrication. The applied FEBIP methods rely on the local decomposition of Fe(CO) and Co(CO)NO as precursors, either by the direct impact of the focused electron beam (electron beam induced deposition, EBID) or through the interaction of the precursor molecules with preirradiated/activated SURMOF areas (electron beam induced surface activation, EBISA). We demonstrate the huge potential of the approach for two different types of MOFs (HKUST-1 and Zn-DPDCPP). Our "surface science" approach to FEBIP, yields well-defined deposits with each investigated precursor/SURMOF combination. Local Auger electron spectroscopy reveals clean iron deposits from Fe(CO); deposits from Co(CO)NO contain cobalt, nitrogen, and oxygen. EBISA experiments were successful with Fe(CO). Remarkably EBISA with Co(CO)NO does not result in deposit formation on both resists, making the process chemically selective. Most importantly we demonstrate the fabrication of "nested-L" test structures with Fe(CO) on HKUST-1 with extremely narrow line widths of partially less than 8 nm, due to reduced electron proximity effects within the MOF-based resists. Considering that the actual diameter of the electron beam was larger than 6 nm, we see a huge potential for significant reduction of the structure sizes. In addition, the role and high potential of loading and transport of the precursor molecules within the porous SURMOF materials is discussed.

Rapid Prototyping of a Dammann Grating in DMD-Based Maskless Lithography

“…The working stage has a travel range of 200 mm * 200 mm in the X-Y plane and 5 mm in the vertical direction with a resolution of 50 nm, which enables us to achieve a large exposure area over the substrate and a precise control of the focus. This lithography technique can generate features on the 2∼8 inch substrate and the maximum exposure area is 200 * 200 mm 2 . Fig.…”

“…The resin used in this fabrication process is photocurable resin, which can be identified from the relationship between the exposure dose and height, where the exposure threshold Eth and the contrast γ of the photoresist are 1.2 mJ/cm 2 and 0.2598, respectively, the maximum height of the development, H total , is 2.8 μm, and the required exposure dose is 61 mJ/cm 2 . Then, the exposure dose for the structure height can be calculated according to (1) and (2).…”

Additive Nano-Lithography with Focused Soft X-rays: Basics, Challenges, and Opportunities

“…On the one hand this is advantageous at the current status of the project, since deposits do not alter significantly during fabrication of further structures and several deposits can be analyzed in parallel after removal of the precursor gas. However, autocatalytic growth is an important mechanism towards clean deposits in FEBIP [1,15,100,101]. We propose that the current gas flow cell does not provide sufficiently clean conditions for proper autocatalytic growth and any catalytic effect is quenched by rapid contamination of deposited metal atoms.…”

Fabrication of Metal–Organic Framework Thin Films Using Programmed Layer‐by‐Layer Assembly Techniques

“…In an autocatalytic growth process, the initial deposits fabricated by either method grow in size as long as the precursor is supplied. Reproduced with permission . Copyright 2018, American Chemical Society.…”

“…Very recently, Drost et al demonstrated that SURMOFs can be loaded with metal–organic guest molecules and then used as resists for high‐resolution focused electron beam induced processing techniques, as shown in Figure B. Based on this technique, a deposit structure less than 8 nm has been achieved.…”