Latent Image Formation Research Articles

Dark matter event in nuclear emulsions: Comparative analysis by time-resolved photoconductivity of silver halide grains

Dark matter (DM) detection by new nuclear emulsions composed of 40 nm AgBrI grains (Lindhard–Scharff theory) has been compared with minimum ionizing particle (MIP) detection and radiation therapy (RT) by conventional nuclear emulsions composed of 200 nm AgBrI grains (Bethe-Bloch theory), and with picture-taking by color films composed of 500–1000 nm AgBrI grains (band-to-band transition), and characterized by its uniqueness: latent image formation in the presence of electron–hole pairs with extremely high concentration (∼1000/grain) and insufficient space for chemical sensitization centers on a grain (∼10/grain). While AgBrI grains in nuclear emulsions for RT are also associated with electron–hole pairs with high concentration, they have space available for chemical sensitizations. Then, we have studied the effect of these characteristics on latent image formation by analyzing the behaviors of electrons and positive holes with variation of their concentrations in 200 nm AgBr grains by means of time-resolved microwave and radio-frequency photoconductivity methods. It has been predicted from the results of the above-stated experiments that DM detection and RT by nuclear emulsions are disturbed by direct recombination and by reaction between Agn and Br2 owing to high activity of positive holes on the contrary to MIP detection by nuclear emulsions and picture-taking by color films, both of which are solely disturbed by indirect recombination. On the basis of the obtained results, discussions are made on ideas to enhance the latent image formation in the presence of electron–hole pairs with high concentration.

Relationship between blurring factors and interfacial effects in chemically amplified resist processes in photomask fabrication

Chemically amplified resists are an indispensable technology for photomask fabrication. The formation of latent images near interfaces in resist films is strongly affected by low-energy electron dynamics at the interfaces. On the other hand, the latent images are blurred by low-energy electron migration and acid diffusion in latent image formation. In this study, the relationship between blurring factors and interfacial effects was investigated by simulating the latent image formation on the basis of the sensitization and reaction mechanisms of chemically amplified electron beam resists. For low-energy electron dynamics, the interfacial effects on the protected unit distribution was reduced and the chemical gradient slightly increased with decreasing thermalization distance. For acid diffusion, the decrease in exposure pattern width significantly reduced the interfacial effects on the protected unit distribution in the depth direction because the acid diffusion length can be increased without sacrificing resolution.

Theoretical study of interfacial effects on low-energy electron dynamics in chemically amplified resist processes of photomask fabrication

The resist thickness has decreased with the miniaturization of transistors. In chemically amplified electron beam resists used for photomask fabrication, thermalized electrons play an important role in acid generation. The interfacial effects of low-energy electrons strongly affect the latent image formation in thin resist films. In this study, we investigated the relationships between the boundary conditions of low-energy electrons at interfaces and the protected unit distribution in terms of resist thickness, concentrations of photoacid generators and photodecomposable quenchers (PDQs), and sensitivity. The dependences of chemical gradient and optimum PDQ concentration on the boundary conditions at the interfaces for low-energy electrons were clarified. It was found that the PDQ concentration should be optimized, depending on not only the boundary conditions but also the resist film thickness. That is, the resist depth profile can be controlled by the boundary conditions at the interfaces for low-energy electrons.

Latent image stabilization in nuclear emulsions for cosmic-ray imaging

Latent image stability is one of the most important characteristics of nuclear emulsions for cosmic-ray imaging. The emulsions studied are composed of AgBrI grains (about 200 nm in diameter) with a benzothiazolium compound (Additive Ⅰ) as a new latent-image stabilizer, and characterized by means of photoelectron yield spectroscopy in air (PYSA). The results thus observed are discussed in the light of the mechanism of latent image formation. A latent image center is composed of a small Ag cluster, and situated at a site with electric charge of +1/2, thus being expressed as Agn+1∕2. The growth processes for a latent image center are the trapping of an electron by Agn−1+1∕2 to form Agn−1−1∕2 (electronic process), and the attachment of an interstitial silver ion to Agn−1−1∕2 to form Agn+1∕2 (ionic process). It is thus considered that the first step of a latent image fading is its discharge of a silver ion to form Agn−1−1∕2, and that the second step is the oxidation of Agn−1−1∕2 to form Agn−1+1∕2. It is proposed and has been confirmed by means of PYSA that Additive Ⅰ opens its ring to disclose –SH and depresses the first step of latent image fading by forming on a latent image center barely soluble silver salt with tolerance to oxidation. Discussions have been made on latent image stabilization in nuclear emulsions for cosmic-ray imaging.

Analyses and design of nuclear emulsions for dark matter detection

Studies were made on a nuclear emulsion system with 40-nm AgBrI grains for dark matter detection. This system is characterized by its efficient detection of a nuclear recoil to form a latent image center composed of several Ag atoms on the grain and by reduction of an AgBrI grain with the center to form an Ag grain by development, achieving a degree of magnification of ~106. Dark matter detection with this system has two problems: rapid recombination between electrons and positive holes with high concentrations (≥1000 per grain at its maximum) for short times (10–100 fs) in the first step and re-halogenation of once formed latent image centers by halogen molecules formed from positive holes, taking place for long times (up to several days) in the second step of dark matter events. In the framework of detective quantum efficiency (DQE) as a criterion for system evaluation, theoretical and experimental approaches were used to characterize and design emulsions for dark matter detection, in which low-velocity ion beams were used to simulate the behavior of nuclear recoil induced by dark matter events. Instead of chemical sensitization used in conventional photographic emulsions, the immersion of the emulsion layers in an aqueous solution of sodium sulfite (i.e. HA treatment) was most effective for latent image formation by ion beams. Ion beam experiments and photoelectron spectroscopy revealed that HA treatment could overcome both of the problems. Ideas for the reduction of fog in nuclear emulsions for dark matter detection considering DQE are proposed.

Connecting the Dots: Mott for Emulsions, Collapse Models, Colored Noise, Frame Dependence of Measurements, Evasion of the “Free Will Theorem”

We review the argument that latent image formation is a measurement in which the state vector collapses, requiring an enhanced noise parameter in objective reduction models. Tentative observation of a residual noise at this level, plus several experimental bounds, imply that the noise must be colored (i.e., non-white), and hence frame dependent and non-relativistic. Thus a relativistic objective reduction model, even if achievable in principle, would be incompatible with experiment, the best one can do is the non-relativistic CSL model. This negative conclusion has a positive aspect, in that the non-relativistic CSL reduction model evades the argument leading to the Conway--Kochen "Free Will Theorem".

High-resolution patterning of silver conductive lines by adhesion contrast planography

We developed printed electronics compatible planographic printing methods that enable single-micrometer-order patterning with high rectangularity and thickness uniformity. Instead of conventional planographic printing methods where selective wetting is used for pattern generation, an adhesive latent image produced on a silicone surface is exploited for patterning in the proposed printing methodologies. We further investigated the fundamental mechanisms of the proposed methods by focusing on adhesion contrasts between the blanket, printing area, and non-printing area of a printing plate (PP) and determined that printing is feasible when a simple magnitude relation of adhesions is satisfied for thin layers of size ranging from approximately 50 nm to 100 nm. Latent image formation can be carried out via a simple ultraviolet exposure of the silicone surface, thereby enabling the rapid prototyping of printed device fabrications. The easily preparable, single material-based flat PPs developed in this study have the advantages of flexibility in pattern designs, washing process, fabrication cost, and pattern-rewriting capability compared with the conventional printing methods in which raised surfaces such as stamps or clichés are required for patterning.

電離放射線に対するハロゲン化銀乳剤の潜像形成機構（II） 分光増感した乳剤への適用

電離放射線に対するハロゲン化銀乳剤の潜像形成機構（II） 分光増感した乳剤への適用

Effect of photodecomposable quencher on latent image quality in extreme ultraviolet lithography

A basic compound, called a quencher, plays an important role in the formation of latent images in chemically amplified resists. In this study, the effect of photodecomposable quenchers on latent image quality was investigated using a simulation on the basis of the reaction mechanisms of chemically amplified extreme ultraviolet (EUV) resists. When the concentration of photodecomposable quenchers was relatively low (∼10% of the acid generator concentration), the effect of photodecomposable quenchers was negligible because of the competition between acid generators and photodecomposable quenchers for thermalized electrons. When the concentration of photodecomposable quenchers was increased, latent image quality was improved, compared with that in the resist with non-photodecomposable quenchers. The concentration of photodecomposable quenchers relative to that of acid generators has to be increased to some degree for photodecomposable quenchers to enhance latent image quality.

Charge Trapping in Photovoltaically Active Perovskites and Related Halogenoplumbate Compounds.

Halogenoplumbate perovskites (MeNH3PbX3, where X is I and/or Br) have emerged as promising solar panel materials. Their limiting photovoltaic efficiency depends on charge localization and trapping processes that are presently insufficiently understood. We demonstrate that in halogenoplumbate materials the holes are trapped by organic cations (that deprotonate from their oxidized state) and Pb(2+) cations (as Pb(3+) centers), whereas the electrons are trapped by several Pb(2+) cations, forming diamagnetic lead clusters that also serve as color centers. In some cases, paramagnetic variants of these clusters can be observed. We suggest that charge separation in the halogenoplumbates resembles latent image formation in silver halide photography. Electron and hole trapping by lead clusters in extended dislocations in the bulk may be responsible for accumulation of trapped charge observed in this photovoltaic material.

Chemical Gradient of Contact Hole Latent Image Created in Chemically Amplified Extreme Ultraviolet Resists

A contact hole pattern as well as a line-and-space pattern is a basic element for the fabrication of semiconductor devices. The critical dimension uniformity and edge roughness of contact hole patterns are critical issues for extreme ultraviolet (EUV) lithography. In this study, the quality of the latent images of contact hole patterns was investigated in terms of the chemical gradient using a simulation on the basis of the reaction mechanisms of chemically amplified EUV resists. The latent image formation of contact hole patterns was compared with that of line-and-space patterns. The latent image quality of contact hole patterns was significantly lower than that of line-and-space patterns. To obtain the same latent image quality as line-and-space patterns, the exposure dose should be increased 1.4±0.1 times. Similarly to the line-and-space patterns, the increase of acid generator concentration and effective reaction radius is effective for the enhancement of latent image quality. For the enhancement of latent image quality of contact hole patterns, the enhancement of the effective reaction radius is more effective in a low exposure dose region than a high exposure dose region.

Semi-Analytical Model of Charge Image Formation in Electrophotography

High resolution latent image formation is an important step in electrophotography to achieve high quality prints. Presently, analytical models exist for the other important steps: photoconductor charging, development (both single and dual component), and transfer. We present here an analytical model of charge image generation on the surface of an organic photoconductor due to laser exposure. The inputs to the model include laser intensity profile as a function of time, quantum efficiency of the charge generation layer, hole mobility of the charge transport layer, and initial charge density on the surface of the PC. The output of the model is the PC surface charge map as it evolves in time, which is a key input to the toner development process in electrophotography.

Architectural Effects on Acid Reaction-Diffusion Kinetics in Molecular Glass Photoresists

Understanding acid reaction-diffusion kinetics is crucial for controlling the lithographic performance of chemically amplified photoresists. In this work, we study how the molecular architectures of positive-tone chemically amplified molecular glass resists affect the acid reaction-diffusion kinetics during the post-expose bake (PEB) or annealing step. We compare the acid reaction-diffusion kinetics of a common photoacid generator in molecular glass resists with chemical similarity to poly(4-hydroxystyrene), and that are designed with branched and ring architectures. In situ Fourier transform infrared (FTIR) spectroscopy methods are used to measure reaction rate, acid trapping behavior, and acid diffusivity as a function of PEB temperature. We find that the acid reaction-diffusion kinetics in molecular glass resists is correlated to the film molar density that in turn depends on the architecture of the molecular glass molecules. These results allow modeling of the latent image formation in molecular glass...

Characterization of nuclear emulsions in overview of photographic emulsions

Nuclear emulsions for OPERA and WIMPs detection are characterized in the overview of photographic emulsions with respect to the grain size dependence of their sensitivities. The emulsions are classified into three groups. The grains in Class I, which are larger than 0.5 μm in diameter, are highly sensitive owing to their large light absorbance, and used for color films. The grains in Class II, which are 0.1 ∼ 0.5 μm in diameter and include those for OPERA films, are principally defect-free and therefore afford efficient latent image formation. The grains in Class III, which are smaller than 0.1 eV and expected to be available for WIMPs detection, are still poorly understood and interesting to study from the viewpoints of the formation and characterization of quantum-sized grains. Discussions are also made on the mechanism of the reset function brought about by the “refresh” treatment for OPERA films and its applicability to those for WIMPs detection.

Effects of Flare on Latent Image Formation in Chemically Amplified Extreme Ultraviolet Resists

Scattered light, referred to as flare hereafter, is a concern in extreme ultraviolet (EUV) lithography. The major problem related to flare is critical dimension (CD) variation. Flare compensation technologies have been investigated for the realization of EUV lithography. For effective compensation, basic understanding of the effects of flare on image formation is important. In this study, the effects of flare on latent image formation was investigated on the basis of the reaction mechanisms of chemically amplified EUV resists. The effects of flare on chemical gradients depended on the neutralization mechanism of chemically amplified resists. Also, the flare affected not only horizontal profiles but also vertical profiles.

Latent image formation in chemically amplified extreme ultraviolet resists with low activation energy for deprotection reaction

The trade-off relationships between resolution, sensitivity, and line edge roughness have become a serious problem in device manufacturing as the minimum feature size is reduced. To solve this problem, the improvement of pattern formation efficiency is necessary. The efficiency of pattern formation is mainly determined by the efficiencies of incident radiation absorption, acid generation, and deprotection. The deprotection efficiency is the number of times an acid can induce catalytic reactions during the diffusion of a unit distance. The highest expected deprotection efficiency is achieved by a diffusion-controlled reaction. In this study, the authors investigated the feasibility of low-Ea resists for 22nm fabrication. It was found that their efficiency is inadequate for 22nm fine patterning even when a diffusion-controlled rate is assumed. For 22nm fabrication with 5–10mJcm−2 exposure dose, increases in acid generation efficiency and polymer absorption are essential.

Effects of Rate Constant for Deprotection on Latent Image Formation in Chemically Amplified Extreme Ultraviolet Resists

The resolution of chemically amplified extreme ultraviolet (EUV) resists has reached sub-30 nm. However, the sensitivity and the reduction in the line edge roughness of such resists is still inadequate for the realization of EUV lithography. The pattern formation of chemically amplified resists is based on chemical reactions, which start with energy deposition from exposure tools and are terminated by quenchers or by cutting the heat supply for chemical reactions. In this study, the effects of rate constant for deprotection on latent image formation in chemically amplified EUV resists were investigated from the viewpoint of the difference between high- and low-activation-energy (Ea)-type resists. In chemically amplified resists, neutralization and deprotection competitively proceed. In high-Ea-type resists, in which neutralization proceeds before deprotection, the contrast of pattern edges is improved by suppressing deprotection in the low-dose region. In low-Ea-type resists, in which a fast deprotection is expected, the difference in the extent of deprotection between the high- and low-dose regions can be enhanced by promoting deprotection over neutralization. For the improvement in high- or low-Ea-resist performance, it is effective to enhance or balance all advantages of chemical reactions.

Photocatalytic lithography based on thin films of amorphous hydrated titanium dioxide

The mechanism of photoactivation of amorphous hydrated titanium dioxide thin films containing palladium ions toward the reaction of electroless deposition of nickel was studied. It was shown that the photocatalytic reduction of palladium ions during UV irradiation results in the formation of intermediate Pd(I) states that subsequently disproportionate, yielding a Pd nanophase. The palladium nanoparticle-catalyzed electroless deposition of nickel on exposed areas of the titanium dioxide photolayer makes it possible to fabricate metal patterns having a 5-μm resolution, with the fast and irreversible capture of photoelectrons at the latent image formation step preventing the image from blurring, including the process on conducting substrates.

Irradiation-induced Ag nanocluster nucleation in silicate glasses: Analogy with photography

The synthesis of Ag nanoclusters in soda lime silicate glasses and silica was studied by optical absorption and electron spin resonance experiments under both low (gamma ray) and high (MeV ion) deposited energy density irradiation conditions. Both types of irradiation create electrons and holes whose density and thermal evolution---notably via their interaction with defects---are shown to determine the clustering and growth rates of Ag nanocrystals. We thus establish the influence of redox interactions of defects and silver (poly)ions. The mechanisms are similar to the latent image formation in photography: Irradiation-induced photoelectrons are trapped within the glass matrix, notably on dissolved noble metal ions and defects, which are thus neutralized (reverse oxidation reactions are also shown to exist). Annealing promotes metal atom diffusion, which, in turn, leads to cluster nuclei formation. The cluster density depends not only on the irradiation fluence but also---and primarily---on the density of deposited energy and the redox properties of the glass. Ion irradiation (i.e., large deposited energy density) is far more effective in cluster formation, despite its lower neutralization efficiency (from ${\mathrm{Ag}}^{+}$ to ${\mathrm{Ag}}^{0}$) as compared to gamma photon irradiation.

Lower and upper bounds on CSL parameters from latent image formation and IGM heating

We study lower and upper bounds on the parameters for stochastic state vector reduction, focusing on the mass-proportional continuous spontaneous localization (CSL) model. We show that the assumption that the state vector is reduced when a latent image is formed, in photography or etched track detection, requires a CSL reduction rate parameter λ that is larger than conventionally assumed by a factor of roughly 2 × 109±2, for a correlation length rC of 10−5cm. We reanalyse existing upper bounds on the reduction rate and conclude that all are compatible with such an increase in λ. The best bounds that we have obtained come from a consideration of heating of the intergalactic medium (IGM), which shows that λ can be at most ∼108±1 times as large as the standard CSL value, again for rC = 10−5cm. (For both the lower and upper bounds, quoted errors are not purely statistical errors, but rather are estimates reflecting modelling uncertainties.) We discuss modifications in our analysis corresponding to a larger value of rC. With a substantially enlarged rate parameter, CSL effects may be within range of experimental detection (or refutation) with current technologies.