Quencher Diffusion Research Articles

Quencher diffusion in chemically amplified poly(4-hydroxystyrene-co-t-butyl methacrylate) resist

Understanding of resist fundamentals is important for the efficient development of resist materials. In this study, we investigated the quencher diffusion in a chemically amplified resist consisting of poly(4-hydroxystyrene-co-t-butyl methacrylate), triphenylsulfonium nonafluorobutanesulfonate (an acid generator), and tri-n-octylamine (a quencher). The dose-pitch matrices of line width and line edge roughness were analyzed on the basis of the sensitization and reaction mechanisms of chemically amplified extreme ultraviolet resists. The ratio of the diffusion constant of tri-n-octylamine to that of nonafluorobutanesulfonic acid was estimated to be 1.2 ± 0.7.

Theoretical study of fabrication of line-and-space patterns with 7 nm quarter-pitch using electron beam lithography with chemically amplified resist process: III. Post exposure baking on quartz substrates

Electron beam (EB) lithography is a key technology for the fabrication of photomasks for ArF immersion and extreme ultraviolet (EUV) lithography and molds for nanoimprint lithography. In this study, the temporal change in the chemical gradient of line-and-space patterns with a 7 nm quarter-pitch (7 nm space width and 21 nm line width) was calculated until it became constant, independently of postexposure baking (PEB) time, to clarify the feasibility of single nano patterning on quartz substrates using EB lithography with chemically amplified resist processes. When the quencher diffusion constant is the same as the acid diffusion constant, the maximum chemical gradient of the line-and-space pattern with a 7 nm quarter-pitch did not differ much from that with a 14 nm half-pitch under the condition described above. Also, from the viewpoint of process control, a low quencher diffusion constant is considered to be preferable for the fabrication of line-and-space patterns with a 7 nm quarter-pitch on quartz substrates.

Effects of diffusion constant of photodecomposable quencher on chemical gradient of chemically amplified extreme-ultraviolet resists

The photodecomposable quencher is an important resist technology used for the high-volume production of semiconductor devices. In this study, the effects of the diffusion constant of photodecomposable quenchers on the chemical gradient were investigated by calculating the chemical gradient of line-and-space patterns with an 11 nm half-pitch on the basis of the sensitization and reaction mechanisms of chemically amplified extreme-ultraviolet resists. It was found that the concentration of photodecomposable quencher and the chemical gradient can be markedly increased by decreasing the quencher diffusion constant relative to the acid diffusion constant. Because of the resolution requirement, we should consider the exclusion volume effect of resist units in the future resist design. From this viewpoint, it is attractive that the quenchers have two functions (not only the termination of catalytic reactions but also the capture of thermalized electrons).

Relationships between quencher diffusion constant and exposure dose dependences of line width, line edge roughness, and stochastic defect generation in extreme ultraviolet lithography

Control of the acid catalytic chain reaction is essential in the pattern formation of chemically amplified resists used for the high-volume production of semiconductor devices. In this study, the relationships between the quencher diffusion constant and the exposure dose dependences of the line width, line edge roughness (LER), and stochastic defect generation were investigated assuming extreme ultraviolet (EUV) lithography. The dependence of the latent images of line-and-space patterns with 16 nm half-pitch on the quencher diffusion constant was calculated on the basis of sensitization and reaction mechanisms of chemically amplified EUV resists. The exposure latitude of the line width increased with the quencher diffusion constant. The dependences of LER and stochastic defect (bridges and pinching) generation on the deviation of the exposure dose became weak by increasing the quencher diffusion constant, similarly to the case for the dependence of the line width.

Theoretical relationship between quencher diffusion constant and effective reaction radius for neutralization in contact hole imaging using chemically amplified extreme ultraviolet resists

With extreme ultraviolet (EUV) lithography approaching its realization, the imaging characteristics of two-dimensional patterns such as contact holes have attracted much attention. In this study, the relationship between the quencher diffusion constant and the effective reaction radius for neutralization in contact hole imaging was investigated. Although the rate constant for neutralization is expressed by the product of both factors, their effects on the chemical gradient differed. The chemical gradient of 16 nm contact holes increased with the effective reaction radius for neutralization. The chemical gradient did not significantly depend on the quencher diffusion constant at an exposure dose of 20 mJ cm−2 and below. At a higher exposure dose, the chemical gradient increased with the quencher diffusion constant. On the other hand, both the quencher diffusion constant and the effective reaction radius for neutralization did not affect the protected unit fluctuation after postexposure baking.

Theoretical Relationship between Quencher Diffusion Constant and Image Quality in Chemically Amplified Resists Used for Extreme Ultraviolet Lithography

Quenchers play an important role in the control of the acid catalytic chain reaction in chemically amplified resists, which is an indispensable technology in the high-volume production of semiconductor devices. In this study, the effects of quencher diffusion constants on the chemical gradient of latent images formed in chemically amplified resists were investigated assuming 16 nm line-and-space patterns. Although it has been reported that the chemical gradient of 22 nm line-and-space patterns was increased with quencher diffusion constant, it was found that the chemical gradient of 16 nm line-and-space patterns was increased with the decrease of quencher diffusion constant.

3D Photonic Nanostructures via Diffusion-Assisted Direct fs Laser Writing

We present our research into the fabrication of fully three-dimensional metallic nanostructures using diffusion-assisted direct laser writing, a technique which employs quencher diffusion to fabricate structures with resolution beyond the diffraction limit. We have made dielectric 3D nanostructures by multiphoton polymerization using a metal-binding organic-inorganic hybrid material, and we covered them with silver using selective electroless plating. We have used this method to make spirals and woodpiles with 600 nm intralayer periodicity. The resulting photonic nanostructures have a smooth metallic surface and exhibit well-defined diffraction spectra, indicating good fabrication quality and internal periodicity. In addition, we have made dielectric woodpile structures decorated with gold nanoparticles. Our results show that diffusion-assisted direct laser writing and selective electroless plating can be combined to form a viable route for the fabrication of 3D dielectric and metallic photonic nanostructures.

Diffusion-Assisted High-Resolution Direct Femtosecond Laser Writing

We present a new method for increasing the resolution of direct femtosecond laser writing by multiphoton polymerization, based on quencher diffusion. This method relies on the combination of a mobile quenching molecule with a slow laser scanning speed, allowing the diffusion of the quencher in the scanned area and the depletion of the multiphoton-generated radicals. The material we use is an organic-inorganic hybrid, while the quencher is a photopolymerizable amine-based monomer which is bound on the polymer backbone upon fabrication of the structures. We use this method to fabricate woodpile structures with a 400 nm intralayer period. This is comparable to the results produced by direct laser writing based on stimulated-emission-depletion microscopy, the method considered today as state-of-the-art in 3D structure fabrication. We optically characterize these woodpiles to show that they exhibit well-ordered diffraction patterns and stopgaps down to near-infrared wavelengths. Finally, we model the quencher diffusion, and we show that radical inhibition is responsible for the increased resolution.

A Direct Probe of the Interplay between Bilayer Morphology and Surface Reactivity in Polymersomes

Bilayer vesicles self-assembled from amphiphilic poly(ethylene oxide)-b-polybutadiene (PEO-b-PBd) copolymers are cell-like structures whose high stability and tunable membrane properties make them ideal for use as potential drug carriers and cell mimicry templates. Understanding how the surface interactions (reaction, binding, etc.) are governed by the bilayer structure is critical to enable construction of polymersomes with tailored colloidal behavior. Here, we adapt a previously established chemical labeling method by incorporating coumarin functionalized copolymer into the vesicular structure. This allows us to probe the effect of poly(ethylene glycol) (PEG) brush and surface architecture on the bimolecular quenching reaction occurring at the polymersome surface. Using these measurements, we have tracked quenching in free solution, on bare particles, and on two types of vesicle surfaces: one where the functionalized copolymer groups are longer than the surrounding unfunctionalized copolymer, and one where both functionalized and unfunctionalized groups are the same length. We find that quenching in the presence of the PEG brush proceeds at less than half the free solution rate in both vesicle architectures. However, the quenching rate is further reduced when the functionalized and unfunctionalized groups are the same length. The surface reaction appears to be dominated by quencher diffusion, a conclusion supported by conductivity measurements and ion partition studies indicating that these effects arise as a consequence of retarded ion mobility in the presence of the PEG brush rather than ion exclusion effects. These studies reveal the interplay between the vesicle bilayer architecture (copolymer composition, chain length, local concentration surrounding the active site) and the surface reaction rate, thereby providing useful insights that can help guide the design of polymersomes with desired functional properties.

Quencher Effects at 22 nm Pattern Formation in Chemically Amplified Resists

The trade-off between line edge roughness (LER), sensitivity, and resolution is the most challenging issue associated with the development of resist processes for extreme ultraviolet (EUV) lithography. It has been reported that quenchers (basic compounds) affect the sensitivity, resolution, and extent of LER. However, the details are still unclear. In this study, the effects of quencher diffusion constants in 22 nm pattern formation were investigated by a simulation based on the reaction mechanism of chemically amplified EUV resists. For the suppression of line width expansion due to acid diffusion, mobile quenchers are effective. The quality of a latent image is also improved with the increase in diffusion constant. However, the high mobility of quenchers increases the pattern dependence of line width. The same order of diffusion constants for acids and quenchers are preferable for 22 nm fabrication.

Estimation of diffusion lengths of acid and quencher in chemically amplified resist on the basis of extreme ultraviolet exposure results

Line- and space-type patterns with a half pitch (hp) of 32–65nm were printed with the extreme ultraviolet microexposure tool at the Lawrence Berkeley National Laboratory using the positive-tone chemically amplified resist MET-1K, and the diffusion lengths of the acid and quencher in the resist were estimated by fitting the calculated shapes of resist patterns to the experimental results. Simulations of the resist process employed an acid/quencher mutual-diffusion model. It was found that not only acid diffusion but also quencher diffusion had a considerable effect on the fidelity of hp 32–45nm patterns. When the diffusion lengths were assumed to be 40nm for the acid and 30nm for the quencher, the calculated shapes of resist patterns agreed well with the experimental results for both line- and space-type patterns. If quencher diffusion were not considered, the acid diffusion length would be underestimated, which would make it difficult to explain the shapes of various types of resist patterns using the same acid diffusion length. In order to fabricate various types of hp 32nm patterns, the diffusion lengths of both the acid and the quencher should be less than 10nm.

Identifiability of Models for Intramolecular Two-State Excited-State Processes with Added Quencher and Coupled Species-Dependent Rotational Diffusion

The parameters describing the kinetics of excited-state processes can possibly be recovered by analysis of the fluorescence decay surface measured as a function of the experimental variables. The identifiability analysis of a photophysical model assuming errorless time-resolved fluorescence data can verify whether the model parameters can be determined and may lead to the minimal experimental conditions under which this is possible. In this work, we used the method of similarity transformation to investigate the identifiability of three kinetic models utilized to describe the time-resolved fluorescence of reversible intramolecular two-state excited-state processes in isotropic environments: (1) model without added quencher, (2) model with added quencher, (3) model with added quencher coupled with species-dependent rotational diffusion described by Brownian reorientation. Without a priori information, model 1 is not identifiable. For model 2, two sets of quenching rate constants and combinations of excited-state deactivation/exchange rate constants are possible, but they cannot be allocated to a specific excited-state species. For both sets, upper and lower limits on the excited-state deactivation/exchange rate constants can be obtained. For model 3, both spherically and cylindrically symmetric rotors, with no change in the principal axes of rotation in the latter, are considered. The fluorescence delta-response functions I(parallel)(t) and I(perpendicular)(t), for fluorescence polarized parallel and perpendicular, respectively, to the electric vector of linearly polarized excitation, are used to define the sum S(t) identically equal to I(parallel)(t) + 2 I(perpendicular)(t) and the difference D(t) identically equal to I(parallel)(t) - I(perpendicular)(t). The identifiability analysis is performed using the S(t) and D(t) functions. Also for model 3, two sets of kinetic parameters (i.e., quenching rate constants, combinations of deactivation/exchange rate constants, and rotational diffusion coefficients) exist, but these parameters cannot be assigned unequivocally to a specific species. For the three models, an infinite number of alternative spectroscopic parameters associated with excitation and emission are found.

Stern−Volmer Law in Competing Theories and Approximations

The numerous theories of contact energy quenching are compared between themselves and with the theories of remote electron transfer. The Stern−Volmer constant used as a criterion is studied in the full range of quencher concentrations and diffusion. When any one of these parameters is increased, diffusion-controlled quenching gives way to kinetic control, although differently in the theories of contact and remote transfer.

Analysis of Quencher Diffusion in Chemically Amplified Resists and Its Effect on Imaging Characteristics.

Diffusion of quencher contained in most chemically amplified resists today can cause proximity effects such as dependence of pattern feature size on pattern density or iso-dense bias. Diffusion coefficients were measured for several quencher compounds, and significantly large diffusion coefficients (e.g. 0.003μm2/sec at 100°C) were observed compared with those observed for acid. To evaluate the influence of quencher diffusion on macroscopic imaging behavior of resists, a new resist model for mutual diffusion of acid and quencher was introduced and was implemented to our in-house lithography simulator. Simulation results based on the model explained various proximity effects observed on real wafers, assuming quencher diffusion length as large as 0.2μm. This is significantly long compared with acid diffusion lengths reported and agrees with the results of direct measurement. Our results suggest that very small amount of quencher can have a strong influence on imaging characteristics of chemically amplified resists.

Characterization of Pyrene-Labeled Arborescent Polystyrenes Using Fluorescence Quenching Techniques

The chain segmental density and diffusional properties of arborescent (highly branched) polystyrenes were investigated by labeling the polymers with pyrene and observing their quenching behavior. A series of arborescent polymers with short (5000 g·mol-1) branches and a linear polymer were investigated. Nitrobenzene and nitrated linear polystyrene were used as quenchers for the pyrene fluorescence. For the nitrobenzene quenching experiments, quencher diffusion coefficients were calculated using the Smoluchowski equation. Comparison of the diffusion coefficients indicates a reduced diffusion rate for small molecules inside arborescent polystyrenes relative to the linear polymer and a decreasing trend with increasing generation number. Quenching experiments with linear nitrated polystyrene led to downward curvature in the Stern−Volmer plots, suggesting that a portion of the chromophores were not accessible to the quencher groups. The fractional Stern−Volmer model was applied, and the quenching rate constants and fraction of accessible chromophores were obtained. The arborescent samples had reduced quenching rate constants, and the fraction of accessible chromophores decreased for higher generation polymers.

Structural determinants of the intrinsic fluorescence emission in notexin and phospholipase A2 enzymes

Fluorescence measurements of the homologous proteins, notexin and PLA2 enzymes from Naja naja atra, Naja nigricollis, and Hemachatus haemachatus venoms, showed that the wave-length of maximum emission and the quantum yield of their intrinsic fluorescence emission spectra were different. To verify the factors which affected their fluorescence characteristics, the dynamics of tryptophan residues in those homologous proteins were studied by quenching with acrylamide, iodide, and cesium. The degrees of exposure of tryptophanyl groups in notexin and PLA2 enzymes assessed by acrylamide quenching were found to be the major factor that determined their fluorescence characteristics. However, the positively charged groups surrounding tryptophan residues of PLA2 enzymes from N. naja atra and N. nigricollis venoms might affect the quantum yield of their fluorophores. Tryptophan residues of notexin were in an environment with less fluctuation, which did not allow free diffusion of ionic quencher. This might render its tryptophan residues to fluoresce at a shorter wavelength. These results suggested that the structural determinants affecting the intrinsic fluorescence emission of homologous proteins can be easily assessed by quenching studies.

Effects of glucose and magnesium ion on the quenching of yeast hexokinase fluorescence by acrylamide

To probe the effects of the substrate, glucose, and the cofactor, Mg 2+, on the structure of hexokinase (ATP: d-hexose 6-phosphotransferase, EC 2.7.1.1), titrations of the tryptophan fluorescence of yeast hexokinase isozyme P-II(B) were performed. Acrylamide was used as a quenching titrant in the absence and in the presence of glucose and Mg 2+ singly and together at pH 5.5 and 8.3 at 20°C. The four tryptophan residues of the monomeric subunit of yeast hexokinase may be classified as two surface residues, one being highly accessible to dissolved I − and one with restricted accessibility to I −, one glucose-quenchable residue in the cleft, and one buried (Kramp, D.C. and Feldman, I. (1978) Biochim. Biophys. Acta 537, 406–416). The acrylamide data were analyzed by least-squares computer analysis for quenching constants and fractional fluorescence values of the tryptophan residues. The quenching constants measure the accessibilities of the residues to the quencher, while the fractional fluorescences are related to the microenvironments of the fluorophores. At each pH value, glucose altered the quenching constants, but not the fractional fluorescence, of the tryptophan residues. Mg 2+ greatly accentuated this glucose effect, especially for the surface residue near the cleft opening. Comparison of acrylamide- and I −-quenching data shows that this particular residue has a positively charged microenvironment. A pH change from 5.5 to 8.3 increased the acrylamide-accessibility of the cleft tryptophan but did not seem to influence accessibility of the surface residues or the buried residue significantly, thus strengthening our previous conclusion that the cleft opening is small enough at pH 5.5 to partially restrict entrance of organic molecules and negative ions. However, with saturating glucose present there was a pH effect on the surface residue accessibility. Titrations in 55 vol.% glycerol suggest the presence of transient channels (not just holes) in the hexokinase structure, which allows penetration of the protein by the solution. Consequently, the buried tryptophan residue is quenched more strongly by dissolved acrylamide than is attributable to diffusion of quencher through the protein matrix.