Takashi Saitou

LPP-EUV light source development for high volume manufacturing lithography

Since 2002, we have been developing a CO2-Sn-LPP EUV light source, the most promising solution as the 13.5 nm high power (>200 W) light source for HVM EUV lithography. Because of its high efficiency, power scalability and spatial freedom around plasma, we believe that the CO2-Sn-LPP scheme is the most feasible candidate as the light source for EUVL. By now, our group has proposed several unique original technologies such as CO2 laser driven Sn plasma generation, double laser pulse shooting for higher Sn ionization rate and higher CE, Sn debris mitigation with a magnetic field, and a hybrid CO2 laser system that is a combination of a short pulse oscillator and commercial cw-CO2 amplifiers. The theoretical and experimental data have clearly demonstrated the advantage of combining a laser beam at a wavelength of the CO2 laser system with Sn plasma to achieve high CE from driver laser pulse energy to EUV in-band energy. Combination of CO2 laser power and droplet generator improvements on new EUV chamber (Proto-2) enables stable EUV emission. EUV burst operation data shows stable average 10.2W(clean power @ I/F) EUV emission and maximum 20.3W(clean power @ I/F) was demonstrated. For future HVM the maximum of 4.7% CE with a 20 μm droplet are demonstrated by ps pre-pulse LPP. Also reported 40kW CO2 laser development project cooperate with Mitsubishi electric.

Performance of one hundred watt HVM LPP-EUV source

We have been developing CO2-Sn-LPP EUV light source which is the most promising solution as the 13.5nm high power light source for HVM EUVL. Unique and original technologies such as: combination of pulsed CO2 laser and Sn droplets, dual wavelength laser pulses shooting, and mitigation with magnetic field, have been developed in Gigaphoton Inc. The theoretical and experimental data have clearly showed the advantage of our proposed strategy. Based on these data we are developing first practical source for HVM - “GL200E”. This data means 250W EUV power will be able to realize around 20kW level pulsed CO2 laser. We have reported engineering data from our recent test such around 43W average clean power, CE=2.0%, with 100kHz operation and other data 19). We have already finished preparation of higher average power CO2 laser more than 20kW at output power cooperate with Mitsubishi Electric Corporation 14). Recently we achieved 92W with 50kHz, 50% duty cycle operation 20). We have reported component technology progress of EUV light source system. We report promising experimental data and result of simulation of magnetic mitigation system in Proto #1 system. We demonstrated several data with Proto #2 system: (1) emission data of 140W in burst under 70kHz 50% duty cycle during 10 minutes. (2) emission data of 118W in burst under 60kHz 70% duty cycle during 10 minutes. (3) emission data of 42W in burst under 20kHz 50% duty cycle (10000pls/0.5ms OFF) during 3 hours (110Mpls). Also we report construction of Pilot #1 system. Final target is week level operation with 250W EUV power with CE=4%, more than 27kW CO2 laser power by the end of Q2 of 2015.

Changes in the spatial distribution of sclerostin in the osteocytic lacuno-canalicular system in alveolar bone due to orthodontic forces, as detected on multimodal confocal fluorescence imaging analyses.

OBJECTIVE Mechanical loading on the bone is sensed by osteocytes. Sclerostin is a molecule secreted by osteocytes that is downregulated by mechanical loading; therefore, its expression level is a potent sensor that indicates the spatial transduction of biomechanical properties in bone. This study applied macroconfocal microscopy to observe the spatial response of alveolar bone to orthodontic forces after immunofluorescence using anti-sclerostin antibodies. DESIGN Orthodontic tooth movement with the Ni-Ti closed-coil spring was applied between the upper bilateral incisors and the left first molar of mice. Four days after this application, the animals were subjected to multimodal confocal fluorescence imaging analyses. RESULTS Obvious downregulation of sclerotin in the osteocytic lacuna-canalicular system (LCS) was observed specifically in tensile sites of alveolar bone. Confocal-based three-dimensional fluorescence morphometry further quantitatively demonstrated that the distribution and expression of sclerostin in the tensile sites was significantly reduced compared to that observed in the corresponding control sites. Interestingly, the levels of sclerotin signals in the compression sites were significantly higher than those observed in the control sites, although the distribution of sclerotin was not significantly different. CONCLUSIONS Our observations suggest that spatial changes in the level and distribution of sclerostin in the alveolar LCS trigger successive bone remodelling due to orthodontic tooth movement. The multimodal confocal imaging analyses applied in this work will enhance comprehensive understanding regarding the spatial regulation of molecules of interest from the tissue to the cellular level.

Quantitative SHG imaging in osteoarthritis model mice, implying a diagnostic application

Osteoarthritis (OA) restricts the daily activities of patients and significantly decreases their quality of life. The development of non-invasive quantitative methods for properly diagnosing and evaluating the process of degeneration of articular cartilage due to OA is essential. Second harmonic generation (SHG) imaging enables the observation of collagen fibrils in live tissues or organs without staining. In the present study, we employed SHG imaging of the articular cartilage in OA model mice ex vivo. Consequently, three-dimensional SHG imaging with successive image processing and statistical analyses allowed us to successfully characterize histopathological changes in the articular cartilage consistently confirmed on histological analyses. The quantitative SHG imaging technique presented in this study constitutes a diagnostic application of this technology in the setting of OA.

Live Imaging-Based Model Selection Reveals Periodic Regulation of the Stochastic G1/S Phase Transition in Vertebrate Axial Development

In multicellular organism development, a stochastic cellular response is observed, even when a population of cells is exposed to the same environmental conditions. Retrieving the spatiotemporal regulatory mode hidden in the heterogeneous cellular behavior is a challenging task. The G1/S transition observed in cell cycle progression is a highly stochastic process. By taking advantage of a fluorescence cell cycle indicator, Fucci technology, we aimed to unveil a hidden regulatory mode of cell cycle progression in developing zebrafish. Fluorescence live imaging of Cecyil, a zebrafish line genetically expressing Fucci, demonstrated that newly formed notochordal cells from the posterior tip of the embryonic mesoderm exhibited the red (G1) fluorescence signal in the developing notochord. Prior to their initial vacuolation, these cells showed a fluorescence color switch from red to green, indicating G1/S transitions. This G1/S transition did not occur in a synchronous manner, but rather exhibited a stochastic process, since a mixed population of red and green cells was always inserted between newly formed red (G1) notochordal cells and vacuolating green cells. We termed this mixed population of notochordal cells, the G1/S transition window. We first performed quantitative analyses of live imaging data and a numerical estimation of the probability of the G1/S transition, which demonstrated the existence of a posteriorly traveling regulatory wave of the G1/S transition window. To obtain a better understanding of this regulatory mode, we constructed a mathematical model and performed a model selection by comparing the results obtained from the models with those from the experimental data. Our analyses demonstrated that the stochastic G1/S transition window in the notochord travels posteriorly in a periodic fashion, with doubled the periodicity of the neighboring paraxial mesoderm segmentation. This approach may have implications for the characterization of the pathophysiological tissue growth mode.

Performance of new high-power HVM LPP-EUV source

We have been developing CO2-Sn-LPP EUV light source which is the most promising solution as the 13.5nm high power light source for HVM EUVL since 2003. Unique original technologies such as; combination of pulsed CO2 laser and Sn droplets, dual wavelength laser pulse shooting and mitigation with magnetic field have been developed in Gigaphoton Inc.. The theoretical and experimental data have clearly showed the advantage of our proposed strategy. We demonstrated 108W EUV power (I/F clean in burst), 80 kHz, 24 hours stable operation at Proto#2 device. Based on these experimental data we are now constructing first practical source for HVM; “GL200E-Pilot#1”. Target of this device is 250 W EUV power by 27 kW pulsed CO2 driver laser system.

Mathematical modeling of invadopodia formation

In invasive cancer cells, specialized sub-cellular membrane structures which carry out a pivotal process in cancer invasion, termed invadopodia, are observed. Invadopodia appear irregularly within the cytoplasm and their general shape is small punctuated finger-like protrusions with dimension up to several μm long. They may exist and persist on a timescale between several tens of minutes to one hour. The formation of invadopodia requires the integration of several processes that include actin reorganization, extracellular matrix (ECM) degradation, signaling processes through receptors such as the epidermal growth factor receptor (EGFR) and matrix metalloproteinase (MMP) synthesis and delivery to the location of the invading front. In this paper, we consider a mathematical model investigating the coupling of these fundamental processes, and we investigate how invadopodia appear in this model. We investigate the spatio-temporal dynamics of the model in two spatial dimensions by using numerical computational simulations. We show that in a special parameter region of the model, random fluctuations of ECM degradation and a positive feedback loop regarding the up-regulation of MMPs allow us to reproduce finger-like protrusions which have similar size and lifetime as invadopodia. This study provides a new insight into how invadopodia appear in cancer cells and why space and time scales exist for invadopodia.

Analyses of bone modeling and remodeling using in vitro reconstitution system with two-photon microscopy.

Bone modeling and remodeling are cellular events during which osteoblast lineage cells and osteoclasts interact. During these events, cells undergo drastic changes with time as they become differentiated. Their morphology, topology, and activity are affected by other cells and the extracellular matrices. Since the mechanisms underlying the cellular events of bone metabolism have not been elucidated, there is a need for systems to analyze these cellular networks and their microenvironments spatiotemporally at the cellular level. Here we report a novel in vitro system for reconstituting the bone cell network of osteoclasts, osteoblasts, and osteocytes in the mineralized nodule, allowing for observation of bone modeling and remodeling phenomena by 2-photon microscopy. Using this system, the change in morphology of osteoblasts from cuboidal to flat cells was observed and measured during the formation of mineralized nodules. Furthermore, the recruitment of osteoblasts to resorption pits and their replenishment by newly formed matrices were successfully observed, providing strong evidence for the coupling of bone resorption and bone formation at cellular level. During such remodeling cycle, flat osteoblasts that survived more than 7 weeks were recruited to resorption pits, where they became cuboidal osteoblasts that express osteocalcin. This novel system permitted the elucidation of cellular behavior during bone modeling and remodeling, and can be used to analyze cellular events involved in bone metabolism.

Sub-hundred Watt operation demonstration of HVM LPP-EUV source

Since 2002, we have been developing a CO2-Sn-LPP EUV light source, the most promising solution as the 13.5 nm high power (>200 W) light source for HVM EUV lithography. Because of its high efficiency, power scalability and spatial freedom around plasma. Our group has proposed several unique original technologies; 1) CO2 laser driven Sn plasma generation, 2) Double laser pulse shooting for higher Sn ionization rate and higher CE. 3) Sn debris mitigation with a magnetic field, 4) Hybrid CO2 laser system that is scalable with a combination of a short pulse oscillator and commercial cw-CO2 amplifiers. 5) High efficient out of band light reduction with grating structured C1 mirror. In past paper we demonstrated in small size (2Hz) experimental device, this experiment shoed the advantage of combining a laser beam at a wavelength of the CO2 laser system with Sn plasma to achieve high CE>4.7% (in maximum) from driver laser pulse energy to EUV in-band energy 1). In this paper we report the further updated results from last paper. (1) 20um droplets at 100kHz operation was successfully ejected by downsized nozzle and demonstrated dramatical improvement of debris on the collector mirror. We have been developing extension of high CE operation condition at 20kHz range, We have reported component technology progress of EUV light source system. (2)New generation collector mirror with IR reduction technology is equipped in mirror maker. (3)20kW CO2 laser amplifier system is demonstrated cooperate with Mitsubishi electric. (4) We develop new Proto #2 EUV LPP source system and demonstrated 200W EUV plasma power (43W EUV clean power at I/F ) at 100kHz operation was confirmed. (5) High conversion efficiency (CE) of 3.9% at 20kHz operation was confirmed in using pico-second pre-pulse laser. (6)Improvement of CO2 laser power from 8kW to 12kW is now on going by installation of new pre-amplifier. (7)Power-up scenario of HVM source is reported, target shipment of first customer beta LPP light source unit is 2015.

Quantitative imaging with Fucci and mathematics to uncover temporal dynamics of cell cycle progression

Cell cycle progression is strictly coordinated to ensure proper tissue growth, development, and regeneration of multicellular organisms. Spatiotemporal visualization of cell cycle phases directly helps us to obtain a deeper understanding of controlled, multicellular, cell cycle progression. The fluorescent ubiquitination‐based cell cycle indicator (Fucci) system allows us to monitor, in living cells, the G1 and the S/G2/M phases of the cell cycle in red and green fluorescent colors, respectively. Since the discovery of Fucci technology, it has found numerous applications in the characterization of the timing of cell cycle phase transitions under diverse conditions and various biological processes. However, due to the complexity of cell cycle dynamics, understanding of specific patterns of cell cycle progression is still far from complete. In order to tackle this issue, quantitative approaches combined with mathematical modeling seem to be essential. Here, we review several studies that attempted to integrate Fucci technology and mathematical models to obtain quantitative information regarding cell cycle regulatory patterns. Focusing on the technological development of utilizing mathematics to retrieve meaningful information from the Fucci producing data, we discuss how the combined methods advance a quantitative understanding of cell cycle regulation.