Deep UV Exposure Research Articles

N-Acyl Dibenzazepine Chemistry as Versatile Approach for Photoreversible Thiol-Ene Networks.

It is herein reported that a facile application of N-acyl dibenzazepine (ADBA) photochemistry for preparing photoreversible ADBA based thiol-ene networks. Crosslinking of the ADBA thiol-ene networks is successfully achieved by UV induced dimerization of ADBA groups at wavelengths above 300nm while a subsequent deep UV exposure (λ= 250nm) results in a well-defined cleavage of the crosslinks. The photochemical bonding and cleavage of the process has been determined and studied in detail by spectroscopic measurements.

Electric heating performance of carbon thin films prepared from SU-8 photoresist by deep UV exposure and carbonization

We report the structural characterization and electric heating performance of carbon thin films (CTFs), which were prepared from negative-type SU-8 photoresist by deep UV exposure and following carbonization. The prepared CTFs were found to have pseudo-graphitic carbon structures containing partially graphite domains in the amorphous carbon matrix. The CTFs showed a very smooth surface morphology with a roughness of 0.42 nm. The 107 nm-thick CTFs exhibited an excellent electric heating performance by attaining a high maximal temperature of 207 °C and a rapid heating rate of 13.2 °C/s at an applied voltage of 30 V. Therefore, the CTFs prepared in this study can be applied as electrode materials for high-performance electric heaters.

55‐3: Distinguished Paper: Development of G6 Exposure Tool for 1.2 µm Resolution

We have proposed exposure method using Deep UV (DUV) exposure light to realize high resolution and high productivity in FPD lithography. [1] Here we show development concepts for our new G6 exposure tools with DUV light sources, and exposure test results with a test exposure tool.

Development of G6 exposure tool for 1.2 μm resolution

AbstractWe have proposed exposure method using Deep UV (DUV) exposure light to realize high resolution and high productivity in FPD lithography. Here, we show development concepts for our new G6 exposure tools with DUV light sources and exposure test results with a test exposure tool.

Localized and cascading secondary electron generation as causes of stochastic defects in extreme ultraviolet projection lithography

Projection lithography using extreme ultraviolet (EUV) light at 13-nm wavelength is expected to achieve production of integrated circuits below 10 nm design-rules. In pursuit of further miniaturization, however, stochastic pattern defect problems have arisen. Here, we discuss the possible impact of spatially inhomogeneous secondary electron (SE) generation on stochastic defects. Two mechanisms are investigated: (1) accidental connections of photon shot noises enhanced by densely localized SE generation and (2) cascading SE generation along photoelectron trajectory traveling from pattern edge into a dark region. Since such defect probabilities are extremely low (typically 10 − 4 to ∼10 − 12), results of Monte Carlo simulation based on classical optical image and electron scattering simulations are converted into probability functions for densities of physical/chemical events such as photon absorption, SE generation, and elementary reaction in chemically amplified resists. Probabilities of pattern formation and of defect generation are modeled using these functions. Results of performance optimization using a multiobjective genetic algorithm show higher stochastic defects probability in EUV than in conventional deep-UV exposure due to larger spatial inhomogeneity in reaction density and existence of SE generation strings. Defect probabilities are strongly dependent on absolute pattern sizes in the two mechanisms, regardless of the resolution capability of imaging systems. Guidelines for suppressing stochastic defects are suggested, such as homogenization of reaction density, material composition for increasing scattering cross-section, and suppression of pattern edge fluctuation.

Thermal effects and photoluminescence of zirconium doped hybrid sol gel waveguide

Multifactor lithographic process conditions have been achieved in order to fabricate 3-D single mode waveguide. One of the key factors is the heating (preheating and post-baking) process. Good waveguides were formed with 30 min of pre-heating at 100 °C. Sol gel waveguides have low light loss (0.16 dB/cm), which was achieved with an aged sol gel slab waveguide. By carefully controlling the index difference between cladding and core, light was easily launched into 4-inch lengths of single mode 3-D ridge waveguides. As the heating time increases, the luminescence intensities increase until 65 h and ceased further post-baking process at 110 °C. The thermally produced chromophore luminescence intensity was reduced about 10% after deep UV exposure for 12 min and no further reduction was observed.

Photocrosslinking of low band-gap conjugated polymers using alkyl chloride sidechains: Toward high-efficiency, thermally stable polymer solar cells

Abstract

Switching "on" and "off" the adhesion in stimuli-responsive elastomers.

The present work aims at the preparation of dry adhesives with switchable bonding properties by using the reversible nature of the [4πs+4πs] cycloaddition of anthracenes. Photo-responsive hydrogenated carboxylated nitrile butadiene rubber with photo-responsive pendant anthracene groups is prepared by one-pot synthesis. The formation of 3D networks relies on the photodimerization of the anthracene moieties upon UV exposure (λ > 300 nm). Controlled cleavage of the crosslink sites is achieved by either deep UV exposure (λ = 254 nm) or thermal dissociation at 70 °C. The kinetics of the optical and thermal cleavage routes are compared in thin films using UV-vis spectroscopy and their influence on the reversibility of the network is detailed. Going from thin films to free standing samples the modulation of the network structure and thermo-mechanical properties over repeated crosslinking and cleavage cycles are characterized by low-field NMR spectroscopy and dynamic mechanical analysis. The applicability of the stimuli-responsive networks as adhesives with reversible bonding properties is demonstrated. The results evidence that the reversibility of the crosslinking reaction enables a controlled switching "on" and "off" of adhesion properties. The recovery of the adhesion force amounts to 75 and 80% for photo- and thermal dissociation, respectively. Spatial control of adhesion properties is evidenced by adhesion force mapping experiments of photo-patterned films.

Reduction of polymer residue on wet–transferred CVD graphene surface by deep UV exposure

Polymer residue from Polymethyl methacrylate (PMMA) on transferred graphene is a common issue for graphene devices. This residue affects the properties of graphene. Herein, we have introduced an improved technique to reduce the effect of this residue by deep UV (DUV) exposure of PMMA coated graphene samples within the wet transfer process. This technique has systematically been evaluated by optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and electrical measurements. The results show that this residue is effectively reduced on the graphene surface after DUV treatment. In addition, the electrical characteristics of transferred graphene confirm that the sheet resistance and contact resistance are reduced by about 60 and 80%, respectively, after the DUV exposure. Electrical current transport characteristics also show that minimizing this residue on the graphene surface gives less hysteresis of electronic transport in back-gate graphene field-effect transistors. Furthermore, repeating electrical tests and aging shift the neutral point voltage of graphene. We attribute these improvements to cleaving of the chemical bonds in PMMA by DUV exposure and hence increasing the solubility of PMMA in acetone for subsequent processing steps. This work provides a unique route to enhance the electrical properties of transferred graphene after the fabrication process.

Light triggered formation of photo-responsive epoxy based networks

Taking advantage of versatile o-nitrobenzyl chemistry, the present study highlights the design of photocurable epoxy networks that undergo spatially controlled bond cleavage in response to UV irradiation. The synthetic strategy involves the preparation of epoxy monomers with photolabile o-nitrobenzyl ester (o-NBE) links that are cured via photoinduced cationic ring opening reaction. Two different photoinitiation systems are employed which do not interfere with the absorbance of the o-NBE groups. The first initiation mechanism exploits the direct photolysis of N-hydroxynaphthalimide triflate upon deep UV exposure and the second mechanism follows a free radical promoted cationic polymerization upon visible light illumination. The crosslinking and cleavage kinetics of the photodegradable epoxy networks are characterized by spectroscopic techniques. In thin films, the UV induced increase in solubility is confirmed by sol-gel analysis and used for the fabrication of positive tone photoresists. Patterned films are obtained by photolithographic processes and microscopic analyses reveal that the resists provide a resolution of 4 μm and a good contrast behavior.

Design and application of photo-reversible elastomer networks by using the [4πs+4πs] cycloaddition reaction of pendant anthracene groups

Abstract In this work, the photo-reversible [4πs+4πs] cycloaddition reaction of anthracene moieties is employed to impart wavelength dependent properties into carboxylated nitrile butadiene rubber networks. Crosslinking of the side chain functionalized rubber is achieved by UV induced dimerization of pendant anthracene groups at wavelengths above 300 nm whilst a subsequent deep UV exposure (λ = 254 nm) results in a well-defined cleavage of the crosslinks. Crosslink kinetics and photo-reversibility of the dimerization reaction are determined by spectroscopic measurements. The changes in network structure and chain dynamics over multiple crosslinking and cleavage cycles are studied in detail by low field NMR. In thin films, the wavelength dependent changes in solubility are employed for the preparation of reversible photoresists enabling the preparation of 2D microstructures and a switching between negative- and positive-type patterns. Along with thin films, the wavelength dependent modulation of thermo-mechanical properties is also demonstrated for macroscopic samples, which shows the versatility of these optically stimuli-responsive networks.

Deep-UV biological imaging by lanthanide ion molecular protection.

Deep-UV (DUV) light is a sensitive probe for biological molecules such as nucleobases and aromatic amino acids due to specific absorption. However, the use of DUV light for imaging is limited because DUV can destroy or denature target molecules in a sample. Here we show that trivalent ions in the lanthanide group can suppress molecular photodegradation under DUV exposure, enabling a high signal-to-noise ratio and repetitive DUV imaging of nucleobases in cells. Underlying mechanisms of the photodegradation suppression can be excitation relaxation of the DUV-absorptive molecules due to energy transfer to the lanthanide ions, and/or avoiding ionization and reactions with surrounding molecules, including generation of reactive oxygen species, which can modify molecules that are otherwise transparent to DUV light. This approach, directly removing excited energy at the fundamental origin of cellular photodegradation, indicates an important first step towards the practical use of DUV imaging in a variety of biological applications.

High‐resolution technology for FPD manufacturing

AbstractUsing shorter wavelength for exposure light is one way to achieve high resolution while keeping sufficient depth of focus.We show exposure results for high resolution to confirm the effect of deep UV exposure light. With deep UV light, 1.2‐µm line and space pattern and 1.8‐µm contact hole pattern are resolved while keeping sufficient depth of focus.

Delineating fibronectin bioadhesive micropatterns by photochemical immobilization of polystyrene and poly(vinylpyrrolidone).

Bioadhesive micropatterns, capable of laterally confining cells to a 2D lattice, have proven effective in simulating the in vivo tissue environment. They reveal fundamental aspects of the role of adhesion in cell mechanics, proliferation, and differentiation. Here we present an approach based on photochemistry for the fabrication of synthetic polymer micropatterns. Perfluorophenyl azide (PFPA), upon deep-UV exposure, forms a reactive nitrene capable of covalently linking to a molecule that is in close proximity. PFPA has been grafted onto a backbone of poly(allyl amine), which readily forms a self-assembled monolayer on silicon wafers or glass. A film of polystyrene was applied by spin-coating, and by laterally confining the UV exposure through a chromium-on-quartz photomask, monolayers of polymers could be immobilized in circular microdomains. Poly(vinylpyrrolidone) (PVP) was attached to the background to form a barrier to nonspecific protein adsorption and cell adhesion. Micropatterns were characterized with high-lateral-resolution time-of-flight secondary ion mass spectrometry (TOF-SIMS), which confirmed the formation of polystyrene domains within a PVP background. Fluorescence-microscopy adsorption assays with rhodamine-labeled bovine serum albumin demonstrated the nonfouling efficiency of PVP and, combined with TOF-SIMS, allowed for a comprehensive characterization of the pattern geometry. The applicability of the micropatterned platform in single-cell assays was tested by culturing two cell types, WM 239 melanoma cells and SaOs-2 osteoblasts, on micropatterned glass, either with or without backfilling of the patterns with fibronectin. It was demonstrated that the platform was efficient in confining cells to the fibronectin-backfilled micropatterns for at least 48 h. PVP is thus proposed as a viable, highly stable alternative to poly(ethylene glycol) for nonfouling applications. Due to the versatility of the nitrene-insertion reaction, the platform could be extended to other polymer pairs or proteins and the surface chemistry adapted to specific applications.

Solvent induced nanostructure formation in polymer thin films: The impact of oxidation and solvent

Polystyrene (PS) films, upon deep UV exposure, readily formed nanostructures when soaking in a solvent. In this study, we provide compelling evidence confirming the critical roles of oxidation and solvent for the nanostructure formation. When the irradiation was carried out in argon, no structure could be generated on the films. Solvent is another critical parameter. Ordered concentric circular structures formed when the UV-irradiated PS films were soaked in an aromatic solvent such as toluene, benzene, and xylene. Addition of n-heptane to toluene reduced the size of the circles. The concentric circular structures disappeared when 0.1% methanol was added to the soaking solvent toluene. X-ray photoelectron spectroscopy (XPS) showed that the percentage of O-containing products decreased with increasing amount of added methanol, indicating that the polar solvent prevented the structure formation by removing the oxidation products from the films.

Laser micromachined wax-covered plastic paper as both sputter deposition shadow masks and deep-ultraviolet patterning masks for polymethylmethacrylate-based microfluidic systems

We report a technically innovative method of fabricating masks for both deep-ultraviolet (UV) patterning and metal sputtering on polymethylmethacrylate (PMMA) for microfluidic systems. We used a CO 2 laser system to cut the required patterns on wax-covered plastic paper; the laser-patterned wax paper will either work as a mask for deep-UV patterning or as a mask for metal sputtering. A microfluidic device was also fabricated to demonstrate the feasibility of this method. The device has two layers: the first layer is a 1-mm thick PMMA substrate that was patterned by deep-UV exposure to create microchannels. The mask used in this process was the laser-cut wax paper. The second layer, also a 1-mm thick PMMA layer, was gold sputtered with patterned wax paper as the shadow mask. These two pieces of PMMA were then bonded to form microchannels with exposed electrodes. This process is a simple and rapid method for creating integrated microfluidic systems that do not require cleanroom facilities.

Synthesis of dual‐functional copolymer with orthogonally photosensitive groups

AbstractA dual‐functional copolymer, poly(4‐styrenesulfonyl azide‐co‐t‐butyl‐methacrylate), with built‐in photoacid labile and photocrosslinkable components was designed and synthesized by radical copolymerization. The mixture of copolymer and photoacid generators was spin coated on aminosilane treated Si wafers and polycarbonate (PC). When exposed to 365 nm UV light, photoacids were generated, which decomposed the acid labile groups, t‐butyl‐ester, to carboxylic acid in the exposed region, leading to drastic change of wettability from hydrophobic to hydrophilic after developing the film in an aqueous base solution. The patterned polymer film could be subsequently photoimmobilized on the substrate under 254 nm deep UV exposure through CH insertion via exited azide groups. 1H‐NMR and Fourier transform infrared spectra confirmed the synthesis of the copolymer, and the photodecomposition and photografting reactions occurred orthogonally at 365 and 254 nm, respectively, without interfering each other. On the patterned surfaces, including a hexagonal dot array and a gradient line array, we demonstrated selective wetting in the 365 nm exposed regions. On the gradient line array, we showed an interesting ratchet wetting pattern. Finally, we showed that the copolymer could be used to modify the wettability of PC while maintaining its high optical quality. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Printed wax masks for 254 nm deep-UV pattering of PMMA-based microfluidics

This paper reports a new technique for masking deep-UV exposure of poly(methyl methacrylate) (PMMA) using a printed wax mask. This technique provides an inexpensive and bulk fabrication method for PMMA structures. The technique involves the direct printing of the mask onto a polymer sheet using a commercial wax printer. The wax layer was then transferred to a PMMA substrate using a thermal laminator, exposed using deep-UV (with a wavelength of 254 nm), developed in an IPA:water solution, and completed by bonding on a PMMA cap layer. A sample microfluidic device fabricated with this method is also presented, with the microchannel as narrow as 50 µm. The whole process is easy to perform without the requirement for any microfabrication facilities.

Deep UV patterning of 3-amino-propyl-triethoxy-silane self-assembled molecular layers on alumina

Organosilane molecular layers are widely used to modify surface functionality and for the immobilization and assembly of more complex nanostructures. Unlike alkanethiol layers, simple organosilanes have not been directly photopatterened with easily accessible optical wavelengths. In particular, 3-amino-propyl-triethoxy-silane (APTES) is commonly used for such purposes, and a direct means of patterning molecular layers of APTES would be of interest for a variety of applications. However, previous efforts to photopattern aminosilanes have been limited to vacuum ultraviolet (VUV) radiation at 172 nm. Here APTES layers were photopatterned on partially oxidized aluminum using 266 nm laser irradiation. APTES layers were grown on both oxidized Al and Si surfaces for patterning and reflection absorption infrared spectroscopy purposes. APTES on aluminum oxide, in contrast to silicon, retains ethoxy groups. These groups are eliminated by 266 nm laser irradiation providing insight into the photopatterning mechanism. Unlike 172 nm irradiation, the 266 nm wavelength retains the APTES backbone. Microscale patterning of APTES has been performed and the exposed samples were processed in a second organosilane, n-butyltrichlorosilane (BTS) or n-octadecyltrimethoxysilane (ODS), that enhances secondary-electron contrast compared to a patterned APTES sample. The authors found that BTS/APTES patterns exhibited contrast reversal compared to ODS/APTES structures. Direct patterning of organosilane films using deep-UV (rather than VUV or e-beam) exposure allows the use of coherent and continuous-wave sources and also prevents exposure of underlying resist layers when using the organosilane pattern as an in situ metrology standard for electron-beam lithography.

UV initiated formation of polymer monoliths in glass and polymer microreactors

Polymer monoliths with good flow-through properties were prepared by UV initiated polymerisation to form a support for heterogeneous palladium catalysis in glass and polymer microchips. Preparation of homogeneous polymer monoliths required investigation of different light source/photoinitiator combinations and manipulation of the polymerisation mixture to accommodate different channel dimensions. A deep UV (DUV) flood exposure lamp, UV tubes with respective outputs at 255 and 365 nm and a UV LED array with output at 365 nm were used to initiate the polymerisation. The spectra of light source and initiator were matched; 2,2-dimethoxy-2-phenylacetophenone (DMPAP) was selected for polymerisation in the DUV and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) was used for polymerisation in the near UV (NUV). This is the first report of the use of a BAPO-type photoinitiator for the formation of organic polymer monoliths. Only the DUV lamp and 365 nm UV LED array resulted in the formation of homogenous and continuous monoliths which were subsequently used to create continuous-flow microreactors in fused silica capillaries, borosilicate chips and in cyclic olefin copolymer (COC) capillaries and chips. All microreactors gave high to quantitative yields for the Suzuki–Miyaura's coupling of iodobenzene with 4-tolyl boronic acid. In addition to demonstrating the first polymer chip for heterogeneous Suzuki–Miyaura's catalysis, the UV LED array in combination with BAPO was found to be a suitable budget alternative to a DUV exposure source for monolith formation in devices with internal diameter of up to 2 mm.