Photoacid Generator Research Articles

Effective Optimization Strategy for Electron Beam Lithography of Molecular Glass Negative Photoresist

AbstractAs the crucial dimension (CD) of logic circuits continues to shrink, the photoresist metrics, including resolution, line edge roughness, and sensitivity, are faced with significant challenges. Photoresists are indispensable in the integrated circuit manufacturing industry, and specifically in achieving smaller critical dimensions. In this study, the effects of two categories of photosensitive compounds on lithography performance are explored, through a series of sulfonium salt‐based photoacid generators (PAGs) with diverse reactivity and photodegradable nucleophiles (PDNs) with varying nucleophilicity. The detailed characterization and exposure experiments suggest that the reactive alterations of different PAGs are mostly associated with the amount of phenyl composed of cations in PAGs. The “PDN first, PAG second” strategy, which employs a combination of low reactivity PAG and high reactivity PDN and involves PDN decomposition first and PAG decomposition second in the electron beam lithography process, achieves high sensitivity (100–270 µC cm−2), high resolution (25 nm 1:1 line/space, L/S), and low line edge roughness (LER ≤ 3.3 nm) stripes. This approach outperforms conventional formulations and may provide a potentially effective and useful strategy to improve electron beam photoresists.

Latent and controllable doping of stimuli-activated molecular dopants for flexible and printable organic thermoelectric generators

Conjugated polymers (CPs) are a promising class of materials for organic thermoelectric generators (OTEGs); however, achieving high electrical conductivity through molecular doping while maintaining compatibility with thin-film printing processes remains a huge challenge. In this paper, we present a novel doping strategy using stimuli-activated molecular dopants (SAMDs) based on photoacid generators (PAGs) that can be activated by light of a specific wavelength. We demonstrate that this approach can effectively control the doping efficiency and optoelectronic properties of CP-PAG-blended thin films, resulting in a wide range of electrical conductivities. Our selected PAG molecules enabled efficient printing of the CP-PAG mixed solution and yielded a high thermoelectric figure of merit. To elucidate the mechanism behind this high thermoelectric performance, we systematically investigated the morphologies, microstructures, and energy structures of the PAG-doped CP thin films and performed various comparative tests. We also demonstrate the feasibility of using SAMDs to print flexible OTEG modules on thin polyimide substrates. We believe that our work represents a significant step toward the development of efficient, scalable, and sustainable thermoelectric devices for power generation and waste heat recovery, and highlights the advantages of PAG-based SAMDs for printable organic thermoelectrics.

Characterization of Photoacid Generator Bound Resist with X-ray Absorption Spectroscopy at NewSUBARU

Characterization of Photoacid Generator Bound Resist with X-ray Absorption Spectroscopy at NewSUBARU

Green deep‐UV photoresist based on chitosan for microelectronics

AbstractPhotolithography is a core part in microelectronic processes. This technological step implies the use of numerous hazardous carcinogenic compounds in the formulations, the use of solvents for processing synthetic polymers to obtain micro and nanostructures. We proposed the use of chitosan‐based biosourced water‐soluble resins to significantly reduce the environmental impact of the photolithography step, for 193 nm photolithography. We show in this report that chitosan‐based photoresist is suitable for microelectronic application, and in particular, we could significantly improve photosensitivity by adding a water‐soluble photoacid generator (PAG). UV–visible and Fourier transform infrared‐attenuated total reflectance characterizations reveal an increase of the macromolecular chain scission kinetics in the presence of PAG. Moreover, the local decrease of the pH favors the solubility of chitosan in irradiated areas. Finally, the photolithography tests demonstrate that the dose to clear and the optimal dose for photopatterning are divided by a factor of two. Moreover, the physical etching transfer tests show that the presence of PAG does not decrease the transfer performance, making these aqueous‐based formulated resins still more adapted for the fabrication of microelectronic devices.

Long-lived Photoacid-doped Conducting Composites Induce Photocurrent for Efficient Wound Healing.

Electrical stimulation is an effective strategy for facilitating wound healing. However, it is hindered by unwieldy electrical systems. In this study, we used a light-powered dressing based on long-lived photoacid generator (PAG)-doped polyaniline composites, which can generate a photocurrent under visible light irradiation to interact with the endogenous electric field and facilitate skin growth. Light-controlled proton binding and dissociation result in oxidation and reduction of the polyaniline backbone, inducing charge transfer to generate a photocurrent. Due to the rapid intramolecular photoreaction of PAG, a long-lived proton-induced localized acidic environment is formed, which protects the wound from microbial infection. In summary, we have introduced a simple and effective therapeutic strategy for light-powered and biocompatible wound dressings that show great potential for wound treatment. This article is protected by copyright. All rights reserved.

Optimal combination of UV‐induced cationic ring opening polymerization monomers for light‐weight automotive plastic coating

AbstractCROP reactivity of organic coatings composed of three structurally different monomers with epoxy or oxetane derivatives was investigated, focusing on rheological and surface mechanical properties. Real‐time crosslinking behavior of CROP monomers was monitored using a rotational rheometer. Results of differential scanning calorimetry with in situ UV irradiation revealed that the ring opening reactivity of CROP monomers protonated by a photoacid generator (PAG) was correlated with the heat released during the exothermic polymerization reaction. In addition, reaction conversions of monomers with epoxy and oxetane groups were compared using Fourier transform infrared spectroscopy (FT‐IR) under dark curing conditions. Surface and internal mechanical properties of coating films, including adhesion with polycarbonate substrate, were comprehensively evaluated by nano‐indentation, nano‐scratch, and surface and interfacial cutting analysis system (SAICAS) tests. By understanding the unique crosslinking characteristics of each CROP monomer, the ternary CROP monomer system, optimally containing with ECC of 53.6 wt%, DOX of 22.9 wt%, and DEO of 15.3 wt%, exhibited improved crosslinking density (G′ from 104 to 107 Pa) and exceptional mechanical (with scratch resistance increasing from 7.11 to 16.17 mN for Lc1), adhesion (with crosscut resistance increasing from 0 to 5B), and transparency properties, surpassing the performance of unitary ECC coating system.

New Chemically Amplified Positive Photoresist with Phenolic Resin Modified by GMA and BOC Protection.

In this paper, a chemically amplified (CA) i-line photoresist system is described including a phenolic resin modified with glycidyl methacrylate (GMA) addition and protected with di-tert-butyl dicarbonate (BOC group), here called JB resin. JB resin with different degrees of BOC protection was synthesized and characterized with ultraviolet spectrophotometry, Fourier transform infrared spectroscopy and gel permeation chromatography. These resins were also evaluated in CA resists by formulating the JB resin with a photoacid generator (PAG) and tested at 405 nm and 365 nm exposure wavelengths. The BOC protection ratio at approximately 25 mol% of the Novolak phenol group showed the best performance. The resist showed high sensitivity (approximately 190 mJ/cm2), high resolution and good alkali developer resistance with reliable repeatability, indicating the great practical potential of this JB resist system.

A Single-Component Molecular Glass Resist Based on Tetraphenylsilane Derivatives for Electron Beam Lithography.

A novel molecular glass (TPSiS) with photoacid generator (sulfonium salt group) binding to tetraphenylsilane derivatives was synthesized and characterized. The physical properties such as solubility, film-forming ability, and thermal stability of TPSiS were examined to assess the suitability for application as a candidate for photoresist materials. The sulfonium salt unit underwent photolysis to effectively generate photoacid on UV irradiation, which catalyzed the deprotection of the t-butyloxycarbonyl groups. It demonstrates that the TPSiS can be used as a 'single-component' molecular resist without any additives. The lithographic performance of the TPSiS resist was evaluated by electron beam lithography. The TPSiS resist can resolve 25 nm dense line/space patterns and 16 nm L/4S semidense line/space patterns at a dose of 45 and 85 μC/cm2 for negative-tone development (NTD). The etching selectivity of the TPSiS resist to Si substrate is 8.6 under SF6/O2 plasma, indicating a potential application. Contrast analysis suggests that the significant solubility switch within a narrow exposure dose range (18-47 μC/cm2) by NTD is favorable for high-resolution patterns. This study supplies useful guidelines for the optimization and development of single-component molecular glass resists with high lithographic performance.

Using Grazing-Incidence Small-Angle Neutron Scattering to Study the Orientation of Block Copolymer Morphologies in Thin Films

We used grazing-incidence small-angle neutron scattering (GISANS) to probe the depth-dependent orientation of self-assembled morphologies of block copolymers. A hydrophobic–hydrophobic block copolymer, poly(solketal methacrylate)-block-polystyrene (PSM-b-PS), was synthesized and spin-coated into films tens of nanometers in thickness where the polymers adopted a disordered state. PSM-b-PS was then hydrolyzed by exposing the polymer thin film to trifluoroacetic acid vapor or embedding a photoacid generator in the film during spin coating, followed by exposure to UV light. The hydrolysis converted the block copolymer into a hydrophilic–hydrophobic block copolymer, poly(glycerol monomethacrylate)-block-polystyrene (PGM-b-PS), significantly increasing the segmental interaction parameter (χ) and causing microphase separation of the copolymers. GISANS was used to study the depth-dependent structure of the films and revealed that the orientation of the microphase-separated structure differed at the polymer–air and polymer–substrate interfaces. In the regions where the lamellae were parallel to the interfaces, the orientation propagated into the film from the interfaces. However, in the areas where the lamellae were perpendicular to the interfaces, the orientation did not persist with increasing distance from the interfaces.

Near-infrared light triggered degradation of metal−organic frameworks for spatiotemporally-controlled protein release

Metal−organic frameworks (MOFs) have emerged as a promising platform for protein delivery due to their high loading capacity and tunable functionality. However, spatiotemporally-controlled release of loaded proteins from MOFs-based nanocarriers remains an outstanding challenge. Herein, we report a MOFs-based protein delivery system that is capable of precisely controlling protein release with deep tissue penetrable near-infrared (NIR) light. The responsive system was constructed by encapsulating a protein of interest and upconversion nanoparticles (UCNPs) within zeolitic imidazolate framework-8 (ZIF-8) MOFs and further trapping a photoacid generator (PAG) in the pores of ZIF-8. Upon NIR light irradiation, UCNPs emit ultraviolet light that activates PAG to produce protons, which enables local pH acidification and thus degradation of ZIF-8 for spatiotemporally-controlled protein release. By employing insulin as a model protein, we demonstrate that the system allows for on-demand control over its therapeutic efficacy against diabetes with NIR light. This work illustrates a general strategy to regulate MOFs-based nanocarriers for controlled drug delivery.

Extreme UV Resist Exhibiting Synergism between Chemical and Physical Crosslinking Mechanisms.

Carbon-fluorine bonds in fluorinated molecules can undergo homolytic cleavage reactions when electrons are injected, and the resulting radicals combine to form network structures characterized by reduced solubility. This crosslinking chemistry suggests a new category of patterning materials that function under electron beam (e-beam) and extreme ultraviolet (EUV) lithographic conditions. Although this chemistry enables the production of 50 nm or smaller-sized features of simple fluoroalkylated polymers, it is limited by the need for relatively large amounts of irradiation energy to achieve required solubility changes. Therefore, this study was undertaken to devise a sensitivity-enhancing strategy based on a synergistic combination of radical crosslinking and hydrogen-bonding interactions between highly fluoroalkylated copolymers. An alternating copolymer was synthesized using tert-butoxystyrene and a fluoroalkylated maleimide, the former of which produces active hydrogens through catalytic acidolysis reactions. When the polymer was blended with a catalytic amount of a photoacid generator and subjected to lithographic patterning tests under e-beam and EUV irradiation, the deprotection reactions of tert-butoxy moieties proceeded at room temperature and led to a solubility decrease. We presume the small number of hydroxyl moieties produced formed an intermolecular hydrogen-bonding network, which acted synergistically with the covalent crosslinks generated by C-F bonds. When 30 nm features of copolymer thin films were fabricated by EUV lithography, sensitivity was improved by 25-34% without significant deterioration of pattern quality, especially line-edge roughness. These results demonstrate that EUV resists with improved patterning capabilities can be achieved by combining catalytic acidolysis reactions and noncatalytic crosslinking chemistry.

Polyvinyl-alcohol-based color resist for low-temperature color-filter production

A color resist comprising partially hydrolyzed polyvinyl alcohol, a crosslinker, a photoacid generator, and dyes was designed for color-filter production. The resist was photoexposed, followed by post-exposure baking, development, and curing at 150 °C to yield a solvent-resistant film. The degree of hydrolysis of polyvinyl alcohol affected the preparation of the homogeneous resist solution and the solvent resistance of the cured film. The cured film was insoluble in the resist solvent when the degree of hydrolysis was high, whereas the film displayed insufficient solvent resistance when degree of hydrolysis was low. Nanoindentation experiments of the polyvinyl alcohol film revealed good mechanical properties that were comparable to those of poly(methyl methacrylate). The crosslinking reaction of the polyvinyl alcohol film was analyzed by monitoring the amount of methanol, a volatile compound emitted during the curing of the film; the results suggest that the reaction was likely completed below the process temperature.

Post-Polymerization Modification of Fluoropolymers via UV Irradiation in the Presence of a Photoacid Generator.

Fluorinated polymers have unique wettability and protein adsorption properties. The site-specific alteration of these properties could expand their application to different research areas. In this work, a fluorinated homopolymer and two of its copolymers with 4-vinylbenzyl glycidyl ether (VBGE) are synthesized by free radical polymerization. The produced polymers are then used to develop resist formulations by the addition of a photoacid generator. Films of these formulations are exposed to ultraviolet radiation through a binary mask and heated to create the pattern. It is found that the water contact angle values of the exposed films areas are reduced compared to those of the unexposed ones, with the exception of pentafluorophenyl methacrylate (PFMA) homopolymer film. This is attributed to the reaction of the epoxy groups creating x-links and producing hydroxyl groups and the cleavage of the pentafluorophenyl group from the ester group leading to carboxylic acid groups. Both modifications on the exposed areas are verified by FTIR spectroscopy and ToF-SIMS analysis. In addition, the biomolecules adsorption ability of the exposed area is increasing 10-15 times compared to the unexposed one for the PFMA homopolymer and the PFMA/VBGE 1:1 copolymer. Thus, the proposed polymers and patterning procedure could find application to spatially directed immobilization of biomolecules and/or cells onto a surface for both biosensing and tissue engineering purposes.

Friedel-Crafts arylation of aldehydes with indoles utilizing arylazo sulfones as the photoacid generator.

A versatile, inexpensive and sustainable protocol for the preparation of valuable bis-indolyl methanes via visible light-mediated, metal-free Friedel-Crafts arylation has been developed. The procedure, that exploits the peculiar behavior of arylazo sulfones as non-ionic photoacid generators (PAGs), was applied to the conversion of a variety of aliphatic and aromatic aldehydes into diarylmethanes in good to highly satisfactory yields, employing a low-catalyst loading (0.5 mol%) and irradiation at 456 nm.

Recent developments in the UV-visible light-intervened ring-opening polymerization of cyclic esters

Synthesis of biodegradable polyesters using the photoinduced ring-opening polymerization (photoROP) technique in the presence of photoacid generators (PAGs) and photobase generators (PBGs) as catalysts.

Surface property control for 193 nm immersion resist by addition of Si compound

In ArF immersion lithography, the presence of immersion liquid between the resist surface and the lens causes problems, such as the leaching of the photoacid generator into the liquid and the presence of residual liquid on the resist surface, which can result in watermarks and other defects. One method to address such issues is adding an F-based compound with low dry-etch resistance to the resist. In the present study, we developed a novel resist for ArF immersion exposure that replaces the F compound with an Si (dimethylpolysiloxane)-based additive to enhance dry-etch resistance. We experimentally evaluated contact angles with respect to water and developer solution, depth concentration of the additives (segregation), agent dissolution (leaching), dry-etch resistance, and spectral transmittance of the comparative resists. Simulation studies were performed to evaluate pattern profiles. The developed resist with the Si-based additive showed improved properties compared with that with the F-based additive.

Development of Selenonium PAGs in EUV Lithography toward High Sensitivity Achievement

Extreme ultraviolet (EUV) lithography at 13.5 nm has become an essential technology for the mass production of state-of-the-art semiconductor integrated circuits for use in devices such as smartphones. Chemically amplified resists (CARs) are primarily used for their production, and several performance requirements have to be met to achieve fine patterning. The requirements are known for simultaneous achievement of resolution, low line edge roughness (LER), high sensitivity, and low outgassing. As photoacid generators (PAGs) are ingredients for determine CARs sensitivity, high absorption of EUV light, acceptability of the secondary electron from matrix polymer, and high decomposability (high acid generation efficiency) are required in EUV lithography. Most onium-salt structures that have been proposed for use as EUV PAGs possess a sulfur atom at its center of cation. In this study, we focus on selenonium salts possessing selenium atoms at its center of cation, which exhibit strong absorption of EUV light, and evaluate their utility in EUV lithography.

Visible-Light Sensitive Reworkable Resins for Dental Application: Improved Stability

A reworkable resin, which is degradable after use, was developed for application as a dental resin with an enhanced stability. A dimethacrylate monomer containing a ketal linkage in the molecule was used as a reworkable monomer. The reworkable monomer was successfully cured by blue light irradiation (470-nm light) using the camphorquinone/amine photoinitiating system. The cured reworkable resins were degraded in the presence of a UV- and violet-light sensitive photoacid generator by subsequent irradiation of UV light (365-nm light) at room temperature. The degradation was due to the acid-catalyzed decomposition of the ketal linkages in the cured reworkable monomers. Selection of the evaluated photoacid generators is very important in order to improve the stability of the cured resin. The result suggested the possibility of application of the reworkable monomer as a dental resin.

A General Metal-Free Protocol for the Visible-Light-Driven Protection of Carbonyls.

The protection of a carbonyl is a standard procedure to mask the reactivity of this group towards nucleophiles and reductants. The present work pointed out the potentialities of arylazo sulfones as non-ionic photoacid generators (PAGs) to promote the efficient conversion of aldehydes and ketones into acetals, ketals, and 1,3-oxazolidines upon visible-light irradiation. This approach employed mild conditions and exhibited an easy scalability and a broad scope (80 examples included).

Encapsulation of zero valent iron nanoparticles in biodegradable amphiphilic janus particles for groundwater remediation

Reactive Zero Valent Iron (ZVI) nanoparticles have been widely explored for in situ ground water remediation to degrade both non-aqueous phase liquid (NAPL) and water-soluble contaminants. However, they usually suffer from rapid oxidation and severe agglomerations restricting their delivery at NAPL/water interface. Aim of this study was to encapsulate the ZVI nanoparticles (50 nm) in amphiphilic bicompartmental Janus particles (711 ± 11 nm) fabricated by EHDC (electrohydrodynamic co-jetting). The dual compartments were composed of PLA (polylactic acid) and a blend of PLA, PE (poly (hexamethylene 2,3-O-isopropylidenetartarate) and PAG (photo acid generator). Upon UV irradiation, PAG releases acid to unmask hydroxyl groups present in PE to make only PE compartment hydrophilic. The entrapped ZVI nanoparticles (20 w/w%; ∼99 % encapsulation efficiency) were observed to degrade both hydrophilic (methyl orange dye) and hydrophobic (trichloro ethylene) contaminants. UV treated Janus particles provided stable dispersion (dispersed up to 3 weeks in water), prolonged reactivity (∼24 days in contaminated water), and recyclability (recyclable up to 9 times) as compared to non-treated ones. In addition, the amphiphilic Janus particles demonstrated high transportability (>95%) through porous media (sand column) with very low attachment efficiency (0.07), making them a promising candidate to target contaminants at NAPL/water interface prevailed in groundwater.