Faculty Profiles - HARADA Shunta

Papers - HARADA Shunta

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Machine learning for semiconductor process simulation described by coupled partial differential equations Reviewed

Rikuya Sato, Kentaro Kutsukake, Shunta Harada, Miho Tagawa, Toru Ujihara

Advanced theory and simulations Vol. 6 ( 9 ) 2023.9

Numerical Modeling of the Cellular Structure Formation Process in SiC Solution Growth for Suppression of Solvent Inclusions Reviewed

Huiqin Zhou, Hitoshi Miura, Yifan Dang, Yuma Fukami, Hisaki Takemoto, Shunta Harada, Miho Tagawa, Toru Ujihara

CRYSTAL GROWTH & DESIGN Vol. 23 ( 5 ) page： 3393 - 3401 2023.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

For the solution growth of silicon carbide, solvent inclusions are significant technological issues, and methods to suppress the formation of solvent inclusions are investigated in this study. Experimental observations show that solvent inclusions are formed behind the cellular structures. A phase field model is used to reproduce the formation process of cellular structures and solvent inclusions. Simulation results indicate that slight perturbations of the step front can convert into cellular structures in the case of insufficient supply of carbon, and the overdeveloped cellular structures consequently result in solvent inclusions. Accordingly, several schemes can be suggested by the simulation model to suppress the formation of cellular structures by enhancing the carbon supply. By increasing the carbon diffusion coefficient, cellular structures can be suppressed. Moreover, the step height and the solution flow direction also play an important role in suppressing the cellular structures. This study provides a comprehensive understanding of the formation process of cellular structures and solvent inclusions. A growth process with a high diffusion coefficient and opposite solution flow to the step flow direction was proposed to suppress the formation of cellular structures. The proposed numerical model could be applied in other solution crystal growth methods.

DOI： 10.1021/acs.cgd.2c01512

Web of Science

Scopus

Development of High-Resolution Nuclear Emulsion Plates for Synchrotron X-Ray Topography Observation of Large-Size Semiconductor Wafers Reviewed Open Access

Shunta Harada, Taketo Nishigaki, Nobuko Kitagawa, Kotaro Ishiji, Kenji Hanada, Atsushi Tanaka, Kunihiro Morishima

Journal of Electronic Materials Vol. 52 ( 5 ) page： 2951 - 2956 2023.5

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

Characterization of defects in semiconductor wafers is essential for the development and improvement of semiconductor devices, especially power devices. X-ray topography (XRT) using synchrotron radiation is a powerful methods used for defect characterization. To achieve detailed characterization of large-size semiconductor wafers by synchrotron XRT, we have developed nuclear emulsion plates reaching a high-resolution and wide dynamic range. We have shown that higher-resolution XRT images could be obtained using emulsions with smaller iodobromide crystals, and demonstrated clear observation of threading edge dislocations in a SiC epitaxial layer having small contrast. Furthermore, we demonstrated XRT image acquisition for almost all of a 150-mm SiC wafer with one plate. Our development will contribute to advances in electronic materials, especially in the field of power electronics, in which defect characterization is important for improving the performance and yield of devices.

DOI： 10.1007/s11664-023-10270-8

Open Access

Web of Science

Scopus

Thermal conduction in titanium-chromium oxide natural superlattices with an ordered arrangement of nearly pristine interfaces Reviewed

Shunya Sugimoto, Gareoung Kim, Tsunehiro Takeuchi, Miho Tagawa, Toru Ujihara, Shunta Harada

Journal of Alloys and Compounds Vol. 934 page： 167915 2023.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

Thermal conduction was investigated in titanium-chromium oxide natural superlattices with an ordered arrangement of crystallographic shear planes, which were nearly pristine interfaces for thermal phonons. Thermal conductivity exhibited a clear maximum value at around 50 K, which indicates interface roughness as small as 20 pm based on the calculation of thermal conductivity by a modified Debye-Callaway model. With an ordered arrangement of nearly pristine interfaces at nanoscale, the wave contribution to phonon transport was estimated to be predominant at lower temperatures (less than 100 K) and as much as 30 % even at room temperature. We found that the interface roughness greatly influences the thermal conduction in natural superlattice systems, which may lead to variations in the reported value of thermal conductivity. We have demonstrated that the wave contribution of thermal conductivity become apparent in bulk crystal having nano scale periodic structure with pristine interfaces.

DOI： 10.1016/j.jallcom.2022.167915

Web of Science

Scopus

Suppression of partial dislocation glide motion during contraction of stacking faults in SiC epitaxial layers by hydrogen ion implantation Reviewed Open Access

Shunta Harada, Hitoshi Sakane, Toshiki Mii, Masashi Kato

APPLIED PHYSICS EXPRESS Vol. 16 ( 2 ) page： 021001 2023.2

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：IOP Publishing Ltd

Bipolar degradation in SiC bipolar devices, in which stacking faults (SFs) expand to accommodate the movement of partial dislocations during forward bias application, is one of the critical problems impeding the widespread implementation of SiC power devices. Here we clearly demonstrate that the movement of partial dislocations can be suppressed by proton implantation, which has good compatibility with semiconductor processing, through investigation of the contraction behavior of SFs in SiC epitaxial layers subjected to proton implantation.

DOI： 10.35848/1882-0786/acb585

Web of Science

Scopus

Modeling-Based Design of the Control Pattern for Uniform Macrostep Morphology in Solution Growth of SiC Reviewed

Yifan Dang, Xinbo Liu, Can Zhu, Yuma Fukami, Shuyang Ma, Huiqin Zhou, Xin Liu, Kentaro Kutsukake, Shunta Harada, Toru Ujihara

Crystal Growth and Design Vol. 23 ( 2 ) page： 1023 - 1032 2023.1

Language：English Publishing type：Research paper (scientific journal)

In the solution growth of the SiC crystal, macrosteps with sufficient height on an off-axis substrate are required to reduce defects and achieve a high-quality grown layer. However, over-developed macrosteps can induce new defects and adversely affect the crystal quality. To better understand and control the behavior of macrosteps corresponding to the control parameters of the growth system, a simulation method that consists of a global two-dimensional computational fluid dynamic (CFD) model, a local three-dimensional CFD model near the growth front, and a kinetics model that describes the movement of macrosteps on the crystal surface is proposed. The simulation method is first applied to investigate the effect of the crystal rotation speed on macrostep morphology. Although the results indicate that a higher crystal rotation speed results in less step bunching, constantly rotating the crystal in one direction is demonstrated to be incapable of yielding a uniform macrostep distribution on the whole surface. Accordingly, a sophisticated control pattern is designed by periodically switching the flow direction underneath the crystal surface, where the proposed simulation method is critical to determine detailed control-parameter values. When the control pattern suggested by the simulation is used, a grown crystal with a uniform macrostep morphology and ideal step height on the whole surface is obtained in the practical experiment.

DOI： 10.1021/acs.cgd.2c01194

Web of Science

Scopus

Analysis of carrier lifetime in a drift layer of 1.2-kV class 4H–SiC devices toward complete suppression of bipolar degradation Reviewed

Toshiki Mii, Hitoshi Sakane, Shunta Harada, Masashi Kato

Materials Science in Semiconductor Processing Vol. 153 page： 107126 2023.1

Language：English Publishing type：Research paper (scientific journal)

We analyzed the carrier lifetime in a drift layer of 1.2 kV-class SiC p-n diodes to suppress bipolar degradation. According to the device simulation results, the required carrier lifetime in the drift layer was estimated to be shorter than 10 ns with a current density of 300 A/cm2 if the threshold hole density for the expansion of the stacking fault at the interface of the drift layer and substrate was 2 × 1016 cm−3. Numerical analysis revealed that to ensure a carrier lifetime shorter than 10 ns, the 1/e2 lifetime obtained by microwave photoconductivity decay (μ-PCD) measurements should be shorter than 7.2 ns. Experimental μ-PCD measurements showed that 1/e2 lifetimes obtained from the as-received epiwafer were much longer than 7.2 ns, and even after H+ implantation, high-temperature annealing, or electron irradiation, 1/e2 lifetimes were still long. Therefore, carrier lifetime control in the drift layer is not sufficient to suppress bipolar degradation, and a combination of carrier lifetime control with other methods is necessary for the fabrication of 1.2 kV-class SiC p-n diodes for the complete suppression of bipolar degradation at a current capacity of 300 A/cm2.

DOI： 10.1016/j.mssp.2022.107126

Web of Science

Scopus

Prediction of operating dynamics in floating-zone crystal growth using Gaussian mixture model Reviewed

R. Omae, S. Sumitani, Y. Tosa, S. Harada

Science and Technology of Advanced Materials: Methods Vol. 2 ( 1 ) page： 294 - 301 2022.12

Analysis of Phonon Dispersion of Rutile-type Titanium Oxides Reviewed

Harada Shunta, Kosaka Naoki, Tsutsui Satoshi, Tanaka Katsushi, Tagawa Miho, Ujihara Toru

SPring-8/SACLA Research Report Vol. 10 ( 6 ) page： 521 - 523 2022.12

Suppression of stacking-fault expansion in 4H-SiC PiN diodes using proton implantation to solve bipolar degradation Reviewed Open Access

Masashi Kato, Ohga Watanabe, Toshiki Mii, Hitoshi Sakane, Shunta Harada

Scientific Reports Vol. 12 ( 1 ) page： 18790 2022.11

Authorship：Last author Language：English Publishing type：Research paper (scientific journal)

4H-SiC has been commercialized as a material for power semiconductor devices. However, the long-term reliability of 4H-SiC devices is a barrier to their widespread application, and the most important reliability issue in 4H-SiC devices is bipolar degradation. This degradation is caused by the expansion of single Shockley stacking-faults (1SSFs) from basal plane dislocations in the 4H-SiC crystal. Here, we present a method for suppressing the 1SSF expansion by proton implantation on a 4H-SiC epitaxial wafer. PiN diodes fabricated on a proton-implanted wafer show current–voltage characteristics similar to those of PiN diodes without proton implantation. In contrast, the expansion of 1SSFs is effectively suppressed in PiN diodes with proton implantation. Therefore, proton implantation into 4H-SiC epitaxial wafers is an effective method for suppressing bipolar degradation in 4H-SiC power-semiconductor devices while maintaining device performance. This result contributes to the development of highly reliable 4H-SiC devices.

DOI： 10.1038/s41598-022-23691-y

Optimization of Flow Distribution by Topological Description and Machine Learning in Solution Growth of SiC Reviewed

Masaru Isono, Shunta Harada, Kentaro Kutsukake, Tomoo Yokoyama, Miho Tagawa, Toru Ujihara

Advanced Theory and Simulations Vol. 5 ( 9 ) page： 2200302 2022.9

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal)

The macroscopic distribution of fluid flows, which affect the quality of final products for various kinds of materials, is often difficult to describe in mathematical formulae and hinders the implementation of empirical knowledge in scaling up. In the present study, the characteristics of the flow distribution in silicon carbide (SiC) solution growth are described by using the position of the saddle point and the solution growth conditions are optimized by computational fluid dynamics simulation, machine learning, and a genetic algorithm. As a result, the candidates of the optimal condition for the solution growth of 6-in. SiC crystals are successfully obtained from the empirical knowledge gained from 3-in. crystal growth, by adding the topological description to the objective function. The present design of the objective function using the topological description can possibly be applied to other crystal growth or materials processing problems and to overcome scale-up difficulties, which can facilitate the rapid development of functional materials such as SiC wafers for power device applications.

DOI： 10.1002/adts.202200302

Web of Science

Scopus

A Transfer Learning-Based Method for Facilitating the Prediction of Unsteady Crystal Growth Reviewed

Yifan Dang, Kentaro Kutsukake, Xin Liu, Yoshiki Inoue, Xinbo Liu, Shota Seki, Can Zhu, Shunta Harada, Miho Tagawa, Toru Ujihara

Advanced Theory and Simulations Vol. 5 ( 9 ) page： 2200204 2022.9

Language：English Publishing type：Research paper (scientific journal)

Real-time prediction and dynamic control systems that can adapt to an unsteady environment are necessary for material fabrication processes, especially crystal growth. Recent studies have demonstrated the effectiveness of machine learning in predicting an unsteady crystal growth process, but its wider application is hindered by the large amount of training data required for sufficient accuracy. To address this problem, this study investigates the capability of transfer learning to predict geometric evolution in an unsteady silicon carbide (SiC) solution growth system based on a small amount of data. The performance of transferred models is discussed regarding the effect of the transfer learning method, training data amount, and time step length. The transfer learning strategy yields the same accuracy as that of training from scratch but requires only 20% of the training data. The accuracy is stably inherited through successive time steps, which demonstrates the effectiveness of transfer learning in reducing the required amount of training data for predicting evolution in an unsteady crystal growth process. Moreover, the transferred models trained with relatively more data (no more than 100%) further improve the accuracy inherited from the source model through multiple time steps, which broadens the application scope of transfer learning.

DOI： 10.1002/adts.202200204

Web of Science

Scopus

Suppression of stacking fault expansion in a 4H-SiC epitaxial layer by proton irradiation Reviewed Open Access

Shunta Harada, Toshiki Mii, Hitoshi Sakane, Masashi Kato

Scientific Reports Vol. 12 ( 1 ) page： 13542 2022.8

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

SiC bipolar degradation, which is caused by stacking fault expansion from basal plane dislocations in a SiC epitaxial layer or near the interface between the epitaxial layer and the substrate, is one of the critical problems inhibiting widespread usage of high-voltage SiC bipolar devices. In the present study, we investigated the stacking fault expansion behavior under UV illumination in a 4H-SiC epitaxial layer subjected to proton irradiation. X-ray topography observations revealed that proton irradiation suppressed stacking fault expansion. Excess carrier lifetime measurements showed that stacking fault expansion was suppressed in 4H-SiC epitaxial layers with proton irradiation at a fluence of 1 × 1011 cm−2 without evident reduction of the excess carrier lifetime. Furthermore, stacking fault expansion was also suppressed even after high-temperature annealing to recover the excess carrier lifetime. These results implied that passivation of dislocation cores by protons hinders recombination-enhanced dislocation glide motion under UV illumination.

DOI： 10.1038/s41598-022-17060-y

Observation of in-plane shear stress fields in off-axis SiC wafers by birefringence imaging Reviewed Open Access

Shunta Harada, Kenta Murayama

Journal of Applied Crystallography Vol. 55 page： 1029 - 1032 2022.8

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

For the nondestructive characterization of SiC wafers for power device application, birefringence imaging is one of the promising methods. In the present study, it is demonstrated that birefringence image contrast variation in off-axis SiC wafers corresponds to the in-plane shear stress under conditions slightly deviating from crossed Nicols according to both theoretical consideration and experimental observation. The current results indicate that the characterization of defects in SiC wafers is possible to achieve by birefringence imaging.

DOI： 10.1107/S1600576722006483

Designing a High-Crystallinity Nano-Gapped Particle Superlattice via DNA-Guided Colloidal Crystallization and Dehydration Reviewed

Hayato Sumi, Noboru Ohta, Hiroshi Sekiguchi, Shunta Harada, Toru Ujihara, Katsuo Tsukamoto, Miho Tagawa

Crystal Growth & Design Vol. 22 ( 6 ) page： 3708 - 3718 2022.6

Language：English Publishing type：Research paper (scientific journal)

For the emergence of quantum effects such as plasmonic enhancement, we successfully assembled high-crystallinity nano-gapped particle superlattices composed of sub-10 nm nanoparticles into the solid state through the self-assembly of DNA-programmed nanoparticles (DNA-NPs) in solution followed by dynamic isotropic contraction during dehydration. By this method of isotropic contraction, the crystal symmetry of the self-assembled DNA-NP superlattice in solution was inherited into a dehydrated and contracted one. The optimal isotropic contraction during dehydration was achieved by minimizing the g-factor, which is the index value of the degree of crystallinity. The g-factor was calculated using small-angle X-ray scattering and scanning electron microscopy data for self-assembled DNA-NP superlattices before and after dehydration. The experimental success was driven by our theoretical prediction based on the geometrical calculation regarding the spatial restriction of the nearest-neighbor particle arrangement in a three-dimensional crystal lattice, which was quantified as the particle volume fraction in the lattice, φ. By reducing the nanogap to less than 4 nm through DNA-programmed sub-10 nm nanoparticle crystallization, nanofabrication on a scale exhibiting quantum effects in a bottom-up manner would be feasible.

DOI： 10.1021/acs.cgd.2c00075

Web of Science

Scopus

「スペクトル超解像」による分光分析の高精度化 Invited

原田俊太

OplusE Vol. 44 ( 3 ) page： 217 - 217 2022.5

品質管理へのAI活用の現状と展望—外観検査・棚卸しの自動化を例に Invited Reviewed

炭谷翔悟、西田陽良、原田俊太

システム／制御／情報 Vol. 66 ( 5 ) page： 161 - 167 2022.5

Identification of a novel large duplication (exon2_6dup): copy number variation in the <i>LDLR</i> gene in a large family with familial hypercholesterolemia by whole-genome sequencing

Hori, M; Takahashi, A; Hosoda, K; Harada-Shiba, M

JOURNAL OF CLINICAL LIPIDOLOGY Vol. 16 ( 2 ) page： 167 - 172 2022.3

Crossover from incoherent to coherent thermal conduction in bulk titanium oxide natural superlattices Reviewed

Shunta Harada, Naoki Kosaka, Takashi Yagi, Shunya Sugimoto, Miho Tagawa, Toru Ujihara

Scripta Materialia Vol. 208 2022.2

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

We have investigated thermal conduction in bulk titanium oxide natural superlattices with crystallographic shear (CS) structures, in which dense planar faults are introduced with different periodicities, prepared by reductive annealing of rutile TiO2 and crystal growth by the floating zone method. High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) revealed that (132)rutile and (121)rutile CS planes with interspacings of 2.7 and 1.0 nm were introduced in the mother rutile structure. Time-domain thermoreflectance (TDTR) revealed that the thermal conductivity decreased by the introduction of CS planes, but that the decrease is not monotonic with increasing density of CS planes. Calculation of the thermal conductivity and the mean free path for phonons revealed that a crossover from incoherent to coherent thermal conduction took place, and coherent interfaces with nanoscale periodicity were formed as thermodynamically stable phases in bulk titanium oxide natural superlattices.

DOI： 10.1016/j.scriptamat.2021.114326

Web of Science

Scopus

Numerical investigation of solute evaporation in crystal growth from solution: A case study of SiC growth by TSSG method Reviewed

Yifan Dang, Can Zhu, Xin Liu, Wancheng Yu, Xinbo Liu, Koki Suzuki, Tomoaki Furusho, Shunta Harada, Miho Tagawa, Toru Ujihara

Journal of Crystal Growth Vol. 579 page： 126448 2022.2

Language：English Publishing type：Research paper (scientific journal)

Evaporation of the volatile solute from the liquid phase is a common problem for the crystal grown from solution, especially for the growth under high temperature. In the present study, a numerical model was constructed to quantitatively investigate the evaporation process in crystal growth. This model was applied in top-seeded solution growth (TSSG) of SiC crystal to simulate the transport of aluminum (Al), which is important for crystal surface morphology but easy to vaporize. The transport path of Al in the growth system was determined by analyzing the possible reactions on different boundaries. Accordingly, an improved structure was proposed to suppress the evaporation loss of Al during long-term growth, and was compared with the original case both numerically and experimentally. The simulation results showed that the improved structure could effectively decrease the Al loss by over 70%, and meanwhile had almost no influence on the thermal and flow environment in the solution. For the experimental results, the improved case presented much lower spontaneous nucleation possibilities and higher step height on the crystal surface, which matched well with the features of high Al addition in literatures. Therefore, the improved structure proposed in the present study was proven to be effective to enhance the composition stability of solution during long-term SiC solution growth, and this numerical method could be applied in the growth of other crystals facing the similar problem.

DOI： 10.1016/j.jcrysgro.2021.126448

Scopus

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Papers - HARADA Shunta