Antisticking Layer Research Articles

Impact of the resist properties on the antisticking layer degradation in UV nanoimprint lithography

In this work, the authors evaluate the impact of chemical and mechanical properties of UV nanoimprint lithography resists on the durability of antisticking treatments applied on the quartz mold surface. To do this, three acrylate-based resists were formulated and characterized. Fourier transform infrared spectroscopy was used to investigate the degree of conversion of each formulation as a function of the exposure dose and electron spin resonance was used to investigate the chemical reactivity of each formulation with respect to a fluorinated antisticking layer (Optool DSX from Daikin Chemicals). The impact of resist mechanical properties on the mold surface treatment degradation was also studied. Elastic modulus and hardness were measured by nanoindentation as a function of the polymerization degree. Then, these resists were imprinted with a dummy quartz template treated beforehand with the antisticking layer. The release properties of the molds were monitored by measuring their free surface energy as a function of the chemical and mechanical properties of the imprinted resists. A detailed comparative study has shown that release properties degradation is more governed by a mechanical than by a chemical interaction.

Characterization of adhesion property between fused silica and thermoplastic polymer film in thermal nanoimprint lithography using a novel pull-off test

A novel pull-off test that mimics the actual thermal NIL process was conducted to investigate the adhesion properties between a flat fused silica and thermoplastic polymer film used in thermal NIL process. The pull-off force was measured under various NIL conditions—such as use of various polymer materials, imprint pressures, and separation velocities—and the surfaces of the mold and polymer film were observed after the test. The anti-sticking layer (ASL) derived from (1H,1H,2H,2H-perfluorooctyl)trichlorosilane (F 13-OTS) was coated on the fused silica and its effects on the adhesion characteristics was also examined. In cases of the mold without ASL, the pull-off force varied significantly according to the process conditions and damage on the polymer film was observed in most of the tests. In cases of the mold coated with the ASL, on the other hands, the pull-off force was maintained at a lower level in the range of the imprint pressure from 2 to 10 MPa or separation velocity from 1 to 25 μm/s, and there was no damage to the polymer film due to adhesion.

Three-dimensional nanoimprint lithography using photocurable resins

Three-dimensional nanoimprint lithography was carried out using a photocurable resin. First, a fabricated nanoimprint lithography mould was coated with an antisticking layer. Then, an ultraviolet photocurable resin was dispensed onto cleaned glass slides or poly(ethylene terephthalate) films. The mould was pressed against the resin on the substrate, and the impressed photocurable resin was exposed to ultraviolet radiation. The mould was then removed, leaving a replica of its pattern. Using a three-dimensional mould with a very rough surface, it was possible to evaluate the photocurable resins, and it was found that the use of monomers with weaker intermolecular forces improved the transfer and release properties.

Characterization of Antisticking Layers for UV Nanoimprint Lithography Molds with Scanning Probe Microscopy

Antisticking layers (ASLs) on UV nanoimprint lithography (UV-NIL) molds were characterized by scanning probe microscopies (SPMs) in addition to macroscopic analyses of work of adhesion and separation force. Local physical properties of the ASLs were measured by atomic force microscopy (AFM) and friction force microscopy (FFM). The behavior of local adhesive forces measured with AFM on several surfaces was consistent with that of work of adhesion obtained from contact angle. The ASLs were coated by two different processes, i.e., one is a vapor-phase process and the other a spin-coating process. The homogeneity of the ASLs prepared by the vapor-phase process was better than that of those prepared by the spin-coating process. In addition, we measured the thicknesses of ASL patterns prepared by a lift-off method to investigate the effect of the ASL thicknesses on critical dimensions of the molds with ASLs and found that this effect is not negligible.

Enhanced Durability of Antisticking Layers by Recoating a Silica Surface with Fluorinated Alkylsilane Derivatives by Chemical Vapor Surface Modification

Adsorbed monolayers from (3,3,3-trifluoropropyl)trimethoxysilane (FAS3), (tridecafluoro-1,1,2,2-tetrahydrooctyl)trimethoxysilane (FAS13), (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane (FAS17), and (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane (FAS17-Cl) were formed by chemical vapor surface modification (CVSM) on silica lens surfaces cleaned by exposure to vacuum ultraviolet (VUV) light at 172 nm. Changes in monolayer-modified lens surfaces concomitant with repeating a cycle of curing to induce the radical polymerization of a UV-curable resin and detaching the UV-cured resin were monitored by contact angle measurement with water and atomic force microscopy to investigate the property of the adsorbed monolayers as antisticking layers in UV nanoimprint lithography. A decrease of the contact angle for water with increasing the number of repeated cycles was mainly responsible for the removal of surface impurities in the form of nanoparticles on detaching the cured resin repeatedly. It was found that recoating the silica lens surface with monolayers from FAS13, FAS17, and FAS17-Cl after cleaning by VUV-light exposure resulted in the suppression of the decrease in the contact angle. These results indicate that the durability of an antisticking layer in UV nanoimprint lithography is markedly improved by the recoating.

Growth Behavior of an Adsorbed Monolayer from a Benzophenone-Containing Trimethoxysilane Derivative on a Fused Silica Surface for Nanoimprint Molds by Chemical Vapor Surface Modification

The formation of a monolayer from a benzophenone-containing trimethoxysilane derivative was studied to understand the growth behavior of an antisticking layer from a trimethoxysilane derivative with an alkyl long tail often used as an antisticking layer in nanoimprint lithography. An adsorbed monolayer was formed from 4-{[(3-trimethoxysilyl)propyl]oxy}benzophenone on a fused silica surface by chemical vapor surface modification (CVSM). The growth behavior of the adsorbed monolayer was monitored by UV–visible spectroscopy, and the results were compared with those obtained by contact angle measurement for water and atomic force microscopy. The monolayer formation was confirmed with absorption spectra showing a characteristic absorption band derived from a benzophenone moiety. Changes in contact angle and absorbance with an increase in CVSM period suggested that the monolayer formation was completed in 2 h. The period of 2 h suitable for CVSM was also supported by atomic force microscopy topographic images. These results suggested that the monolayer growth comprises the following three steps: the surface adsorption, condensation and packing, and excess adsorption steps.

Scanning probe nanoimprint lithography

The present paper reports on a novel lithographic approach at the nanoscale level, which isbased on scanning probe microscopy (SPM) and nanoimprint lithography (NIL). Theexperimental set-up consists of an atomic force microscope (AFM) operated via softwarespecifically developed for the purpose. In particular, this software allows one to apply apredefined external load for a given lapse of time while monitoring in real-time therelative distance between the tip and the sample as well as the normal and lateralforce during the embossing process. Additionally, we have employed AFM tipssculptured by means of focused ion beam in order to create indenting tools of thedesired shape. Anti-sticking layers can also be used to functionalize the tips if oneneeds to investigate the effects of different treatments on the indentation andde-molding processes. The lithographic capabilities of this set-up are demonstrated on apolystyrene NIL-patterned sample, where imprinted features have been obtainedupon using different normal load values for increasing time intervals, and on athermoplastic polymer film, where the imprint process has been monitored in real-time.

Formation of an Adsorbed Monolayer from Pentafluorophenyltriethoxysilane and its Antisticking Property to a UV-curable Resin studied by High-sensitive UV-visible Spectroscopy

Surface modification of a fused silica substrate was carried out by chemical vapor surface modification (CVSM) with (pentafluorophenyl)triethoxylsilane (F5Ph). The adsorption behavior of F5Ph was studied by high-sensitive UV-visible spectroscopy, contact angle measurement, and atomic force microscopy. The F5Ph adsorption on a silica substrate reached to the saturation by CVSM at 150 °C for 2 h. As a result, the adsorbed monolayer without aggregates was formed. The antisticking property of the F5Ph-adsorbed silica substrate to UV-curable resin causing radical photopolymerization was investigated. After curing and detaching a droplet of the resin, some organic components derived from the resin remained. The amount of remaining resin components on the F5Ph-adsorbed silica substrate was almost the same as that measured on silica substrates modified with (3,3,3-tri- fluoropropyl)trimethoxysilane (FAS3) and Optool-DSX forming antisticking layers. These results indicate that the F5Ph adsorbed monolayer is available as an antisticking layer in UV nanoimprint lithography. It was clear that high-sensitive UV-visible spectroscopy was a powerful tool to quantify adsorbed molecules on a silica mold surface and detect the adhesion of resin components after detachment.

Evaluation of Heat Durability of Fluorinated Antisticking Layers

Evaluation of Heat Durability of Fluorinated Antisticking Layers

Degradation and surfactant-aided regeneration of fluorinated anti-sticking mold treatments in UV nanoimprint lithography

In nanoimprint lithography, the most common approach to prevent resist to adhere to the mold is to graft a fluorinated anti-sticking layer on the mold’s surface. But it is known that these layers suffer from degradation after a certain number of imprints. In this work, we study the influence of the presence, type and quantity of fluorinated surfactant additives in the resist formulation on the degradation of the mold’s treatment. It is found that the presence of a fluorinated surfactant drastically increases the possible maximal number of imprints before retreatment. Also, we observed that fluorinated surfactants with a silane end-group are able to be adsorbed at the surface of the mold after repeated imprints to progressively replace the initial mold’s treatment. Nevertheless, a balance has still to be found between quantity, reactivity and type of surfactant to maintain a smooth and extremely thin fluorinated layer at the surface of the mold.

172 nm pre-treatment for PDMS/PDMS replication

Preparation of a micro-zipper for component assembly requires an efficient anti-sticking layer between the two counterparts during preparation by moulding and during operation as well. In order to deposit a fluorinated silane on the PDMS-type materials used for zipper preparation, a UV-ozone pre-treatment at 172 nm was investigated in detail. It was found that already at 2 min of irradiation the surface features a sufficient amount of OH-groups for silane binding. Longer irradiation times were found to result in a surface layer of increasing brittleness that would prevent successful zipper operation.

Ultrathin fluorinated diamondlike carbon coating for nanoimprint lithography imprinters

Nanoimprint lithography (NIL) has proven to be an exceptional lithographic technique for achieving arbitrary, nanoscale features, over large areas without the use of costly step-and-repeat UV lithography tools. One requirement for NIL is to eliminate adhesion of the imprinted polymer to the imprinter upon withdrawal of the imprinter. Previous work on thick (>100nm) diamondlike carbon (DLC) layers indicates that fluorinated DLC (F-DLC) provides a durable antiwear, antistick layer. In this work, a process for depositing an ultrathin layer of F-DLC is shown for SiO2 based imprinters.

Cross-sectional observation of nanoimprint resins filled in SiO 2/Si mold pattern using scanning electron microscopy

Nanoimprint lithography (NIL) is a simple process for fabricating nanostructure devices. There are many factors in nanoimprinting such as nanoimprint pressure, an antisticking layer, temperature, and the viscosity of resin. Although these factors affect the imprinted pattern, the nanoimprint mechanism has not been resolved. The flow behavior during nanoimprinting is important for investigating the nanoimprint mechanism. We propose a cross-sectional observation method for filling a nm-scale pattern with nanoimprint resins after nanoimprinting using scanning electron microscopy (SEM). A polyvinyl alcohol (PVA), which is soluble in water, was used in this observation. We demonstrated the cross-sectional observation of UV-, thermal-, and room temperature-nanoimprint resins using the proposed method.

XPS study of the degradation mechanism of fluorinated anti-sticking treatments used in UV nanoimprint lithography

Thanks to their low surface energy, fluorinated anti-sticking layers are widely used in UV nanoimprint lithography (UV-NIL) to treat the mold and facilitate its separation from the imprinted resist. However, it has been reported that release properties of the stamp deteriorate with repeated imprint operations. In this paper, X-ray photoelectron spectroscopy is used to study the mechanism of the fluorinated treatment degradation. A specific experimental protocol is used in order to avoid further degradation under X-ray exposure. It has been observed that a large amount of fluorinated molecules are removed in the first imprint steps and deposited on the surface of the imprinted resist. After this first stage, we observed that fluorinated molecules are progressively degraded along their chain during the NIL process.

Characteristics of Antisticking Layer Formed by CHF3 Plasma Irradiation for Nanoimprint Molds

Nanoimprint lithography (NIL) is very useful for mass-producing nanostructure devices at a low cost and a high throughput. To avoid the adhesion of replication materials, NIL molds are usually coated with an antisticking fluorinated self-assembled monolayer. In this study, we used a fluorinated plasma chemical vapor deposition film as the antisticking layer. First, we formed a CHF3 plasma chemical vapor deposition (CVD) film on SiO2/Si and quartz molds and carried out thermal and UV nanoimprint using these molds. However, the film was removed from these molds. We found that the proposed method can solve this problem. We irradiated plasma using a gas mixture of CHF3 and O2 as the source gas onto SiO2/Si and quartz molds. As imprinting results, the patterns were successfully imprinted onto the resins without the removal of the plasma CVD film. In addition, we were able to carry out 100 times of repeated nanoimprinting using the plasma-CVD-film-coated SiO2/Si mold.

Effect of surface treatments on interfacial adhesion energy between UV-curable resist and glass wafer

The interfacial adhesion energy between the resist and the substrate is very important in nanoimprinting because of problems with the resist sticking or pulling off during separation of the mold from the substrate. Substrate surface treatments with a self-assembled monolayer or oxygen plasma provide good adhesion between a resist coating and a silica substrate. In this paper, we describe the adhesion properties of a resist and a glass wafer measured using the four-point bending test. The interfacial adhesion energy between the resist and the glass wafer was evaluated for various substrate surface treatments of adhesion promoters and anti-sticking layers. The interfacial fracture energy without treatment was 1.23 J/m 2, and was in the range 0.49–2.57 J/m 2 for the other treatments tested. The interfacial fracture surfaces were also investigated by field emission scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy to determine the fracture mode at the interfaces.

Mold cleaning and fluorinated anti-sticking treatments in nanoimprint lithography

Fluorinated anti-sticking layers (F-ASLs) are generally used to prevent adhesion between molds and resists in nanoimprint lithography (NIL). Nevertheless, these layers are degraded after a certain number of imprints and the mold needs to be cleaned and re-treated. We have observed that the cleaning procedures before re-treatment impacts on the grafting of the fluorinated molecules and on the longevity of the ASL. We propose an efficient cleaning procedure of the damaged anti-sticking layers on both silicon and fused silica molds allowing a reproducible re-deposition. Surface chemistry analyses were conducted using a specific procedure based on X-ray photoelectron spectroscopy (XPS) experiments. This procedure was proven to be suitable for ultra thin organic layer composition analysis.

Chemical degradation of fluorinated antisticking treatments in UV nanoimprint lithography

In general, fluorinated antisticking layers (F-ASL) are deposited on the imprint stamps to ease their separation from the imprinted resist in UV nanoimprint lithography. However, these layers are found to degrade with repeated imprint operations. A drastic decrease in fluorinated species is observed on the mold surface. Yet, there is still a debate on the nature of the exact mechanisms involved in this degradation. In this paper, electron spin resonance (ESR) is used to investigate the chemical reaction occurring between the fluorinated molecules and the UV curable resist. Free radicals of the resist, generated under UV illumination, have been observed by ESR. The decrease in their corresponding signal in the presence of fluorinated ASL species shows evidence of the chemical reactivity of the resist toward the F-ASL.

Nanoimprinting using release-agent-coated resins

A fluorinated self-assembled monolayer (F-SAM) is mainly used as the antisticking layer. To prevent the F-SAM coated on the nanoimprint lithography (NIL) mold from deteriorating, we propose a new form of nanoimprinting using a release-agent-coated resin. The results from measuring the surface free energy and observations by scanning probe microscopy (SPM) confirmed that the surface free energy, frictional force, and adhesion force of the release-agent spray-coated polymethylmethacrylate (PMMA) were lower than those of PMMA. To prove the release-agent spray-coated PMMA had a releasing effect, we tried to undertake thermal nanoimprinting on it using a mold without F-SAM. The pattern was clearly imprinted on the resin without any signs of adhesion.

Characterization of Nanoimprint Resin and Antisticking Layer by Scanning Probe Microscopy

Characterization of Nanoimprint Resin and Antisticking Layer by Scanning Probe Microscopy