Electron Beam Lithography on Irregular Surface Using Grafted PMMA Monolayer as Resist

Abstract

An electron beam resist is usually coated by conventional coating methods such as spin‐coating, which cannot be reliably applied on irregular surfaces. Here, it is demonstrated that a monolayer resist can be grafted on nonflat surface to enable nanofabrication on it. As a proof‐of‐concept of patterning on irregular surfaces, poly(methyl methacrylate) (contains 1.6% methacrylic acid that has the carboxyl group needed for grafting) is chosen and is grafted on irregular surfaces by thermal treatment which induces a chemical reaction of the carboxyl group with the hydroxyl group on substrate. Subsequently, nanostructures are patterned by electron beam lithography on this monolayer resist grafted on nonflat surface such as atomic force mocroscopy (AFM) cantilevers, and then the patterns are transferred to the layer underneath. A high resolution of 30 nm line width is achieved using this monolayer resist. Nanofabrication on irregular surfaces may have applications in the fields of tip‐enhanced Raman spectroscopy for chemical analysis and lab‐on‐fiber technology for sensor applications.

Effect of the Al2O3 Deposition Method on Parylene C: Highlights on a Nanopillar-Shaped Surface

“…7 As for electronics, PC is broadly employed not only as a dielectric 8,9 but also as a flexible substrate 10,11 in electronics and, in particular, in organic electronics where the deposition process is compatible with organic materials 12 and nanomaterial-based electronics such as carbon nanotubes, 8,13,14 graphene, 15−18 and transition metal dichalcogenides 11,19 where the influence of water molecules is strongly diminished. 20−22 In order to obtain sub-100 nm electronic devices on top of flexible and biocompatible substrates, electron beam lithography (EBL) becomes mandatory with delicate requirements in terms of flatness of the substrate 23 as well as its resistance to basic solvents and chemicals. PC represents the perfect candidate due to its pinhole and stress-free nature arising from the CVD process as well as its chemical and biological inertness, making it almost completely unaffected by solvents and some basic chemicals.…”

“…In order to obtain sub-100 nm electronic devices on top of flexible and biocompatible substrates, electron beam lithography (EBL) becomes mandatory with delicate requirements in terms of flatness of the substrate as well as its resistance to basic solvents and chemicals. PC represents the perfect candidate due to its pinhole and stress-free nature arising from the CVD process as well as its chemical and biological inertness, making it almost completely unaffected by solvents and some basic chemicals .…”

Single Layer Surface-Grafted PMMA as a Negative-Tone e-Beam Resist

“…Figure shows a schematic diagram of the process used to fabricate protruding structures on a substrate by using single-layer surface-grafted PMMA as a negative e-beam resist. The PMMA is grafted onto a substrate in the same way as in previous work . First, a sacrificial metal layer (8–10 nm Al layer) for pattern transfer is coated onto the substrate because a single layer of PMMA is too thin for directly transferring the pattern onto the substrate.…”

“…The PMMA is grafted onto a substrate in the same way as in previous work. 16 First, a sacrificial metal layer (8−10 nm Al layer) for pattern transfer is coated onto the substrate because a single layer of PMMA is too thin for directly transferring the pattern onto the substrate. Then, PMMA containing 1.6% methacrylic acid (PMMA-co-PMAA, M w = 34 kg/mol, M n = 15 kg/mol) is spin coated on the substrate.…”

“…Therefore, there is still a huge demand for a versatile process that is applicable to nonflat and irregular surfaces that requires only a cheap resist and resist coating technique. As a new resist coating method that is applicable to nonflat surfaces, a monolayer polymer brush has recently been developed as an e-beam resist. , Nanofabrication on AFM tips was demonstrated using single-layer surface-grafted PMMA as a positive e-beam resist. Although it is well known that PMMA can work as a negative e-beam resist when it is exposed to a very high dose electron beam, , single-layer surface-grafted PMMA has been used only as a positive resist.…”