Takahiro Kozawa

Raman spectra of n-type gallium nitride with different carrier concentrations have been measured. The LO phonon band shifted towards the high-frequency side and broadened with an increase in carrier concentration. Results showed that the LO phonon was coupled to the overdamped plasmon in gallium nitride. The carrier concentrations and damping constants were determined by line-shape fitting of the coupled modes and compared to values obtained from Hall measurements. The carrier concentrations obt

Historically, in the mass production of semiconductor devices, exposure tools have been repeatedly replaced with those with a shorter wavelength to meet the resolution requirements projected in the International Technology Roadmap for Semiconductors issued by the Semiconductor Industry Association. After ArF immersion lithography, extreme ultraviolet (EUV; 92.5 eV) radiation is expected to be used as an exposure tool for the mass production at or below the 22 nm technology node. If realized, 92.

Thermal stress in GaN epitaxial layers with different thicknesses grown on sapphire substrates by metalorganic vapor phase epitaxy using an AlN buffer layer was investigated. Biaxial compressive stress in the GaN layer, due to the difference in the thermal expansion coefficients between GaN and sapphire, was obtained by measuring the curvature of wafer bending, and the observed stress agreed with the calculated stress. In Raman measurements, the E2 phonon peak of GaN was found to shift and broad

The radiation-induced reactions of onium salts in some kinds of solutions and model compound solutions of chemically amplified electron beam (EB) and X-ray resists have been studied by means of picosecond and nanosecond pulse radiolysis. The following reaction mechanisms of the chemically amplified EB and X-ray resists have been elucidated. The radiation-induced reaction mechanisms are complicated due to the presence of several proton donors. The onium salts directly produce small amounts of Brø

Acid generators are sensitized by secondary electrons in chemically amplified resists for ionizing radiation. As acid generators react with low-energy electrons (as low as thermal energy), this sensitization mechanism generates a significant blur and an inhomogeneous acid distribution at the image boundary, which results in line edge roughness (LER) formation. The evaluation of resolution blur intrinsic to the reaction mechanisms is important in the optimization of resist processes for extreme u

With the shrinkage of feature sizes, ever precise accuracy has been required for process simulators because of the importance of nanoscale resist topography such as line edge roughness. Formation processes of latent images in chemically amplified electron beam (EB), x-ray, and EUV resists are different from both chemically amplified photoresists used in optical lithography and conventional, nonchemically amplified EB resists. A new simulation scheme precisely based on reaction mechanisms is nece

A highly sensitive extreme ultraviolet (EUV) resist is strongly needed to reduce the development costs of high power EUV sources. Although highly sensitive chemically amplified resists based on acid-catalyzed reactions have been used in mass production lines, the chain length of acid catalytic reactions must be suppressed within several nanometers to meet the resolution requirement below the 32nm technology node. Under such circumstances, the initial acid yield produced by EUV exposure is critic

We investigated the relationship between line edge roughness (LER) and the concentration gradient of chemical compounds that determines the solubility of the resist (chemical gradient). Two-dimensional (half-pitch and exposure dose) matrices of resist line width and LER were analyzed on the basis of the sensitization mechanisms of chemically amplified resists for extreme ultraviolet (EUV) lithography. The latent images of resist patterns were successfully reproduced by assuming that LER is inver

Radiation-induced reactions in chemically amplified resists based on deprotection of t-butoxycarbonyl groups have been investigated by both time-resolved (the pulse radiolysis methods) and steady-state optical absorption spectroscopy. Upon exposure of a partially tBOC-protected novolak by electron and synchrotron radiation beams, the yields of the intermediates contributing to the acid generation (phenoxyl radical and proton adducts of base resin) decreased with increasing the protection ratio o

Acid-related matters are a critical issue in a chemically amplified resist, in which photo- or radiation (ionizing radiation)-generated acids drive pattern formation reactions in exposed areas. The photosensitization of resist materials has been formulated by Dill et al. [IEEE Trans. Electron. Dev. 22, 445 (1975)]. The applicability of the formulation by Dill et al. to acid generation in chemically amplified photoresists has been proven by many researchers. The acid yields in photoresists are pr

The development of extreme ultraviolet (EUV) lithography has progressed owing to worldwide effort. As the development status of EUV lithography approaches the requirements for the high-volume production of semiconductor devices with a minimum line width of 22 nm, the extraction of resist parameters becomes increasingly important from the viewpoints of the accurate evaluation of resist materials for resist screening and the accurate process simulation for process and mask designs. In this study,

The line width and line edge roughness (LER) of resist patterns are related to the concentration and its gradient of chemical compounds that determine the solubility of the resist, respectively. Therefore, latent images can be obtained from the line width and LER of resist patterns. In this study, two-dimensional (exposure dose and half-pitch) matrices of resist line width and LER were analyzed on the basis of the sensitization mechanisms of chemically amplified resists used for extreme ultravio

Extreme ultraviolet (EUV) lithography is promising for the high-volume production of semiconductor devices for the 16 nm node and below. However, the stochastic effect is a significant concern in lithography using high-energy (92.5 eV) photons and highly sensitive resists. In this study, we report a technique for evaluating the stochastic effect on line edge roughness (LER). Resist patterns were analyzed using a Monte Carlo simulation on the basis of the sensitization and reaction mechanisms of

The resist materials are evaluated using their resolution, line edge roughness (LER), and sensitivity. However, the evaluation of chemically amplified resists is tricky because of the trade-off relationships between resolution, LER, and sensitivity. In this study, we investigated a chemically amplified resist with a fullerene matrix by analyzing the dose-pitch matrices of line width and LER. The effective quencher concentration of the fullerene resist obtained by the analysis was higher than tho

It is known that the chemical yield generated upon exposure to an ionizing radiation strongly depends on the thermalization distance of the electrons ejected through ionization. In this study, the acid yield upon exposure to extreme ultraviolet (EUV) radiation, the wavelength of which is 13.5 nm, was analyzed using a Monte Calro simulation of radiation-induced reactions. The thermalization distance in poly(4-hydroxystyrene), which is a typical backbone polymer of chemically amplified resists use