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Daisetsu Toh, Pho Van Bui, Kazuto Yamauchi, and Yasuhisa Sano, “Photoelectrochemical Oxidation Assisted Catalyst-Referred Etching for SiC (0001) Surface,” Int. J. Automation Technol., Vol.15, No.1, pp. 74-79, 2021., In a previous study, we developed an abrasive-free polishing method named catalyst-referred etching (CARE) and used it for the planarization of silicon carbide (SiC) (0001). In this method, Si atoms at step edges are preferentially removed through a catalytically assisted hydrolysis reaction to obtain an atomically smooth and crystallographically well-ordered surface. However, the removal rate is low (

Yasuhisa Sano, Ken Nishida, Ryohei Asada, Shinya Okayama, Daisetsu Toh, Satoshi Matsuyama, and Kazuto Yamauchi, "High-throughput deterministic plasma etching using array-type plasma generator system", Review of Scientific Instruments 92, 125107 (2021), https://doi.org/10.1063/5.0071623., A deterministic processing method is a high-precision finishing method, where the to-be-removed amount of material at each point of the work surface is calculated based on an accurately measured present surface shape and is removed precisely using a numerically controlled (NC) processing system. Although this method has achieved nanometer-scale accuracy, the method requires considerable time to scan the work surface, leading to low productivity. Therefore, using an individual on-off controllable array-type plasma generator covering the entire work surface, enabling simultaneous NC plasma processing is proposed herein. A novel intermittent gas flow system was constructed using cyclic on-off control of the gas supply and exhaust valves instead of the commonly used continuous gas flow to achieve uniform in-plane plasma etching. It was found that uniform removal could be achieved by combining it with a pulse-modulated high-frequency power supply and setting the plasma generation time in one cycle to be sufficiently short. Furthermore, a power control approach was developed for maintaining a constant plasma state, even while varying the plasma-generating array elements, which resulted in a demonstration experiment of NC plasma etching that successfully reduced the thickness variation of a silicon substrate.

Daisetsu Toh, Pho Van Bui, Ai Isohashi, Satoshi Matsuyama, Kazuto Yamauchi, and Yasuhisa Sano, "An abrasive-free chemical polishing method assisted by nickel catalyst generated by in situ electrochemical plating", Review of Scientific Instruments 91, 045108 (2020), https://doi.org/10.1063/1.5141381., An abrasive-free polishing method using water and a Pt catalyst, called catalyst-referred etching (CARE), has been developed for the finishing of optical and semiconductor surfaces. This method realizes well-ordered surfaces with a smoothness of several tens of picometers without crystallographic disturbance. In this study, we propose a new CARE method using a Ni catalyst with in situ electrochemical plating and dissolution, which enable enhancing the catalytic capability of Ni. This method has advantages to realize more than ten times higher removal rate and better stability compared with the conventional CARE method.

Daisetsu Toh, Pho Van Bui, Ai Isohashi, Naotaka Kidani, Satoshi Matsuyama, Yasuhisa Sano, Yoshitada Morikawa, and Kazuto Yamauchi, "Catalyzed chemical polishing of SiO2 glasses in pure water", Review of Scientific Instruments 90, 045115 (2019), https://doi.org/10.1063/1.5090320., A catalytically assisted etching system was developed for the ultra-precision fabrication of optical components, such as X-ray mirrors and extreme-ultraviolet mask blanks. This study demonstrates that an atomically smooth surface with a sub-Angstrom root-mean-square roughness could be achieved on a SiO2 glass substrate using pure water and Pt as the etching solution and catalyst, respectively. Density functional theory calculations confirmed that the mechanistic pathway was involved in catalyzed hydrolysis. The significant roles of the catalyst were clarified to be the dissociation of water molecules and the stabilization of a meta-stable state, in which a hypervalent silicate state is induced, and the Si-O backbond is elongated and loosened. To confirm the role of the catalyst, the Pt metal was replaced by Au, and the observed drastic difference in the removal rate was attributed to the degree of stabilization of the metastable state.

Yasuhisa Sano, Ken Nishida, Ryohei Asada, Shinya Okayama, Daisetsu Toh, Satoshi Matsuyama, and Kazuto Yamauchi, "High-throughput deterministic plasma etching using array-type plasma generator system", Review of Scientific Instruments 92, 125107 (2021), https://doi.org/10.1063/5.0071623., A deterministic processing method is a high-precision finishing method, where the to-be-removed amount of material at each point of the work surface is calculated based on an accurately measured present surface shape and is removed precisely using a numerically controlled (NC) processing system. Although this method has achieved nanometer-scale accuracy, the method requires considerable time to scan the work surface, leading to low productivity. Therefore, using an individual on-off controllable array-type plasma generator covering the entire work surface, enabling simultaneous NC plasma processing is proposed herein. A novel intermittent gas flow system was constructed using cyclic on-off control of the gas supply and exhaust valves instead of the commonly used continuous gas flow to achieve uniform in-plane plasma etching. It was found that uniform removal could be achieved by combining it with a pulse-modulated high-frequency power supply and setting the plasma generation time in one cycle to be sufficiently short. Furthermore, a power control approach was developed for maintaining a constant plasma state, even while varying the plasma-generating array elements, which resulted in a demonstration experiment of NC plasma etching that successfully reduced the thickness variation of a silicon substrate.

Daisetsu Toh, Pho Van Bui, Kazuto Yamauchi, and Yasuhisa Sano, “Photoelectrochemical Oxidation Assisted Catalyst-Referred Etching for SiC (0001) Surface,” Int. J. Automation Technol., Vol.15, No.1, pp. 74-79, 2021., In a previous study, we developed an abrasive-free polishing method named catalyst-referred etching (CARE) and used it for the planarization of silicon carbide (SiC) (0001). In this method, Si atoms at step edges are preferentially removed through a catalytically assisted hydrolysis reaction to obtain an atomically smooth and crystallographically well-ordered surface. However, the removal rate is low (

Daisetsu Toh, Pho Van Bui, Ai Isohashi, Satoshi Matsuyama, Kazuto Yamauchi, and Yasuhisa Sano, "An abrasive-free chemical polishing method assisted by nickel catalyst generated by in situ electrochemical plating", Review of Scientific Instruments 91, 045108 (2020), https://doi.org/10.1063/1.5141381., An abrasive-free polishing method using water and a Pt catalyst, called catalyst-referred etching (CARE), has been developed for the finishing of optical and semiconductor surfaces. This method realizes well-ordered surfaces with a smoothness of several tens of picometers without crystallographic disturbance. In this study, we propose a new CARE method using a Ni catalyst with in situ electrochemical plating and dissolution, which enable enhancing the catalytic capability of Ni. This method has advantages to realize more than ten times higher removal rate and better stability compared with the conventional CARE method.

Daisetsu Toh, Pho Van Bui, Ai Isohashi, Naotaka Kidani, Satoshi Matsuyama, Yasuhisa Sano, Yoshitada Morikawa, and Kazuto Yamauchi, "Catalyzed chemical polishing of SiO2 glasses in pure water", Review of Scientific Instruments 90, 045115 (2019), https://doi.org/10.1063/1.5090320., A catalytically assisted etching system was developed for the ultra-precision fabrication of optical components, such as X-ray mirrors and extreme-ultraviolet mask blanks. This study demonstrates that an atomically smooth surface with a sub-Angstrom root-mean-square roughness could be achieved on a SiO2 glass substrate using pure water and Pt as the etching solution and catalyst, respectively. Density functional theory calculations confirmed that the mechanistic pathway was involved in catalyzed hydrolysis. The significant roles of the catalyst were clarified to be the dissociation of water molecules and the stabilization of a meta-stable state, in which a hypervalent silicate state is induced, and the Si-O backbond is elongated and loosened. To confirm the role of the catalyst, the Pt metal was replaced by Au, and the observed drastic difference in the removal rate was attributed to the degree of stabilization of the metastable state.

Daisetsu Toh, Pho Van Bui, Ai Isohashi, Satoshi Matsuyama, Kazuto Yamauchi, and Yasuhisa Sano, "An abrasive-free chemical polishing method assisted by nickel catalyst generated by in situ electrochemical plating", Review of Scientific Instruments 91, 045108 (2020), https://doi.org/10.1063/1.5141381., An abrasive-free polishing method using water and a Pt catalyst, called catalyst-referred etching (CARE), has been developed for the finishing of optical and semiconductor surfaces. This method realizes well-ordered surfaces with a smoothness of several tens of picometers without crystallographic disturbance. In this study, we propose a new CARE method using a Ni catalyst with in situ electrochemical plating and dissolution, which enable enhancing the catalytic capability of Ni. This method has advantages to realize more than ten times higher removal rate and better stability compared with the conventional CARE method.

Yasuhisa Sano, Ken Nishida, Ryohei Asada, Shinya Okayama, Daisetsu Toh, Satoshi Matsuyama, and Kazuto Yamauchi, "High-throughput deterministic plasma etching using array-type plasma generator system", Review of Scientific Instruments 92, 125107 (2021), https://doi.org/10.1063/5.0071623., A deterministic processing method is a high-precision finishing method, where the to-be-removed amount of material at each point of the work surface is calculated based on an accurately measured present surface shape and is removed precisely using a numerically controlled (NC) processing system. Although this method has achieved nanometer-scale accuracy, the method requires considerable time to scan the work surface, leading to low productivity. Therefore, using an individual on-off controllable array-type plasma generator covering the entire work surface, enabling simultaneous NC plasma processing is proposed herein. A novel intermittent gas flow system was constructed using cyclic on-off control of the gas supply and exhaust valves instead of the commonly used continuous gas flow to achieve uniform in-plane plasma etching. It was found that uniform removal could be achieved by combining it with a pulse-modulated high-frequency power supply and setting the plasma generation time in one cycle to be sufficiently short. Furthermore, a power control approach was developed for maintaining a constant plasma state, even while varying the plasma-generating array elements, which resulted in a demonstration experiment of NC plasma etching that successfully reduced the thickness variation of a silicon substrate.

Daisetsu Toh, Pho Van Bui, Kazuto Yamauchi, and Yasuhisa Sano, “Photoelectrochemical Oxidation Assisted Catalyst-Referred Etching for SiC (0001) Surface,” Int. J. Automation Technol., Vol.15, No.1, pp. 74-79, 2021., In a previous study, we developed an abrasive-free polishing method named catalyst-referred etching (CARE) and used it for the planarization of silicon carbide (SiC) (0001). In this method, Si atoms at step edges are preferentially removed through a catalytically assisted hydrolysis reaction to obtain an atomically smooth and crystallographically well-ordered surface. However, the removal rate is low (

Daisetsu Toh, Pho Van Bui, Ai Isohashi, Naotaka Kidani, Satoshi Matsuyama, Yasuhisa Sano, Yoshitada Morikawa, and Kazuto Yamauchi, "Catalyzed chemical polishing of SiO2 glasses in pure water", Review of Scientific Instruments 90, 045115 (2019), https://doi.org/10.1063/1.5090320., A catalytically assisted etching system was developed for the ultra-precision fabrication of optical components, such as X-ray mirrors and extreme-ultraviolet mask blanks. This study demonstrates that an atomically smooth surface with a sub-Angstrom root-mean-square roughness could be achieved on a SiO2 glass substrate using pure water and Pt as the etching solution and catalyst, respectively. Density functional theory calculations confirmed that the mechanistic pathway was involved in catalyzed hydrolysis. The significant roles of the catalyst were clarified to be the dissociation of water molecules and the stabilization of a meta-stable state, in which a hypervalent silicate state is induced, and the Si-O backbond is elongated and loosened. To confirm the role of the catalyst, the Pt metal was replaced by Au, and the observed drastic difference in the removal rate was attributed to the degree of stabilization of the metastable state.