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The development of high-numerical aperture exposure tools for EUV lithography is in progress. The development process (the dissolution of resist films) is the key to fine patterning. The dissolution dynamics of acidic polymers (the backbone polymers of chemically amplified resists) depend on various parameters related to molecular structures. In this study, the dissolution dynamics in tetraalkylammonium hydroxide (TAAH) aqueous solutions were classified into six classes on the basis of the frequency and impedance changes observed during the development process by a quartz crystal microbalance method. The relationship between class and physical parameters of materials was analyzed by decision tree and support vector machine methods. The feature values used were the alkyl chain length, molecular weight, and concentration of TAAH; the viscosity of the developer; and the protection ratio, molecular weight, contact angle, surface free energies of polymers, and film thickness. The classification accuracy was 0.80 for the validation data. [ABSTRACT FROM AUTHOR]

With the improvement of lithography resolution in the horizontal direction, the thickness of resist films becomes thin to avoid pattern collapse. The thinning of resist films is an important issue in the development of the next-generation lithography process. In this study, the interfacial effects on the sensitization of chemically amplified extreme ultraviolet (EUV) resists were investigated using a Monte Carlo method on the basis of their sensitization mechanism. The chemically amplified resist is a standard resist used for the fabrication of semiconductor devices. In chemically amplified resists, thermalized electrons reduce sensitizer molecules upon exposure to EUV radiation. The low-energy secondary electron dynamics at the vacuum-resist and resist-underlayer interfaces strongly affected the distribution of decomposed sensitizers. In particular, the resist bulk layer almost disappeared at 20 nm pitch in the specific cases. The control of interfaces becomes important in the development of the next-generation lithography process. [ABSTRACT FROM AUTHOR]

The effects of pH and ionic strength on the dissolution behavior of poly(4-hydroxystyrene) (PHS) in an alkaline solution were studied to gain a fundamental understanding of the dissolution of chemically amplified resists (CARs). Tetramethylammonium hydroxide, which is a standard developer in recent lithography, and its corresponding salts were used. Dynamic light scattering (DLS) and quartz crystal microbalance (QCM) methods were used to study the state of PHS chains in solution and the dissolution behavior of PHS films, respectively. In DLS, a higher pH and ionic strength caused PHS chains to become more dispersed owing to an increase in the number of dissociated acidic groups and the resulting increase in repulsive force. The results of the QCM method showed that the diffusion of the polymer into the liquid phase from the film corresponds to an increase in the number of dissociated acidic groups, but did not correspond to the magnitude of transient swelling. [ABSTRACT FROM AUTHOR]

The dissolution behavior of a simple combination of poly(4-hydroxystyrene) films and tetramethylammonium hydroxide aqueous solution was analyzed to gain a fundamental understanding of the effects of film thickness and alkaline concentration on the dissolution kinetics of chemically amplified resists. Films of four different thicknesses, from thick (approximately 900 nm) to thin (approximately 50 nm), were developed in 22 different developers of different concentrations. The dissolution behavior of each combination was observed using a quartz crystal microbalance. Differences in dissolution kinetics due to film thickness were observed even between relatively thick films such as 900 and 500 nm thick films in dilute developers. These differences were considered to be caused by the diffusion of the solution into the films. Thin films also showed characteristic behavior with dilution. This behavior was due to the interaction between the substrate and the films, unlike in the case of thick films. [ABSTRACT FROM AUTHOR]

The demand for improved performance of chemically amplified resists (CARs) is continually increasing with the development of extreme ultraviolet lithography. Acid-generation promoters (AGPs) increase the sensitivity of CARs by increasing the initial acid yield immediately after the exposure process. However, the detailed mechanism of acid-yield enhancement has not been clarified yet. Deprotonation from the ionized polymer (i.e. radical cations) is an important reaction to assess acid generation. In this study, we investigated the dynamics of the radical cations of methacrylate polymers and the effect of an AGP on deprotonation from the radical cations formed by ionizing radiation. We clarified that the promotion of deprotonation by the AGP is more effective for the polymer with lower deprotonation efficiency. In addition, a molecular-level approach using density functional theory and molecular dynamics calculations were carried out. [ABSTRACT FROM AUTHOR]

The dissolution (including the formation of a transient swelling layer) of a resist polymer is key to realizing ultrafine patterning. However, the details of the dissolution of resist polymers remain unclarified. In this study, the swelling and dissolution kinetics of poly(4-hydroxystyrene) (PHS) films in tetramethylammonium hydroxide (TMAH) and tetrabutylammonium hydroxide (TBAH) aqueous solutions were investigated by a quartz crystal microbalance method. PHS is a typical backbone polymer (a dissolution agent) of chemically amplified resists. The swelling and dissolution kinetics of PHS were observed by changing the protection ratio of the hydroxyl groups of PHS and the alkaline concentration in developers. Not only the dissolution rate but also the mode of dissolution depended on the molecular structure of tetraalkylammonium cations. For polymer matrices with strong hydrogen bond networks such as PHS, the penetration of tetrabutylammonium cations is considered to be strongly suppressed by their long alkyl chains. [ABSTRACT FROM AUTHOR]

The modeling of electron beam (EB) lithography processes from exposure to development is important for resist pattern prediction and material design. The effective reaction radius for deprotection indicates the capability of chemically amplified resists. However, this parameter cannot be directly measured by experiments. On the other hand, the concentration of protected units determines the resist pattern after development. To simulate the lithography processes, these two parameters must be estimated. In this study, we developed a strategy to determine these two parameters at the same time by Bayesian optimization to reduce the computational time. The simulation results were compared with the scanning electron microscopy images of resist patterns obtained by EB lithography. As a typical Bayesian inference method, Gaussian process regression with the Matérn kernel was applied to the analysis, which reduced the iterative calculation from 140 to 35. The probable effective reaction radius was found. [ABSTRACT FROM AUTHOR]

The requirements for the next generation resist materials are so challenging that it is indispensable for feasibility of EUV lithography to grasp basic chemistry of resist matrices in all stage. Under such circumstances, it is very important to know dissolution behavior of the resist film into alkaline developer though the dissolution of exposed area of resist films in alkaline developer to form a pattern is a complex reactive process. Therefore, the aqueous base development process is one of the most critical processes in EUV lithography. In this study, the influence of EUV and KrF exposure on the dissolution behavior of polymer-bound PAG and polymer-blended PAG was studied in detail using quartz crystal microbalance (QCM) methods. The difference in swelling formation between KrF and EUV exposure was observed. It is likely that difference of reaction mechanism induces the difference of these swelling. Also, it was observed that the swelling of polymer-bound PAG is less than that of polymer-blended PAG in both KrF and EUV exposure. This indicates that polymer-bound PAG suppresses swelling very well and showed an excellent performance. Actually, the developed polymer bound-PAG resist showed an excellent performance (half pitch 50 nm line and space pattern). Thus, polymer-bound PAG is one of the promising candidate for 16 nm EUV resist. [ABSTRACT FROM AUTHOR]

Novel resist materials are required for lithographic processing with ionization radiation such as extreme ultraviolet (EUV) and electron beam (EB) exposure tools. In this study, we synthesized positive-tone chemically amplified molecular resist materials with pendant adamantyl ester (AD) and cyclohexyl 2-propyl ether moieties based on cyclic oligomers such as noria, calixarene dimer, cyclodextrin, and pillar[5]arene, and we examined the lithographic performances of sensitivity, etching durability, and patterning under EUV and EB exposure. We clarified that the sensitivity of the resist materials was consistent with the structure of the cyclic oligomers, i.e., the hole size of the molecular structure might be an important factor relevant to high-resolution resist materials. We found that chemically amplified molecular resists based on cyclic oligomers such as noria, calixarene dimer, cyclodextrin, and pillar[5]arene are promising candidates for higher-resolution resist materials. [ABSTRACT FROM AUTHOR]