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A new method to improve the thickness uniformity of a silicon-on-insulator layer in a defined area by photoetching with N -fluoropyridinium salts using a projector was proposed. The method involved initial calculation of the red–green–blue tone distribution from the top silicon layer thickness distribution to be etched using the relationship between the etching depth and red–green–blue tone in a projector. Photoetching was then conducted by projection of an image with the required tone distribution onto a silicon layer surface coated with N -fluoropyridinium salts. The uniformity of silicon layers with a thickness of less than 10 nm was improved in an area of approximately 20 × 20 mm by photoetching after prior thinning by thermal oxidation and wet etching. The developed method enables the thickness uniformity in a defined area to be improved while avoiding exfoliation of the silicon layer or the formation of silicon islands in subsequent thermal treatment. In addition, this method has the potential to be cost-effective because it uses a projector.

Control of the microroughness of Ge surfaces is required to realize field-effect transistors with high performances. We propose a novel surface-flattening process for Ge that involves the preferential transformation of surface protrusions on Ge into soluble GeO2 with the help of a catalyst in water. To carry out this process, we developed a setup comprising a catalyst plate covered with a Pt film in contact with a Ge surface in saturated O2-dissolved water. The role of the metallic film is to enhance the oxygen reduction reaction in water that accompanies the oxidation of protrusions or microbumps on a Ge surface. After presenting the fundamental etching properties of a Ge surface treated with this metal-assisted chemical etching method, we demonstrate that our water-based process creates a flattened Ge surface that has few protrusions with a lateral size on the order of 10 nm.

The deposition of carbon is the key to yielding pit-free graphene terraces on SiC(0 0 0 1) surfaces. We present a novel technique to form a carbon overlayer at the monolayer scale on a SiC(0 0 0 1) Si-face substrate involving plasma oxidation at atmospheric pressure followed by HF etching, both of which are performed at near room temperature. We discuss the mechanism by which carbon atoms aggregate at the SiO2/SiC interface, which occurs in plasma oxidation but not in conventional thermal oxidation. We subsequently anneal the SiC surface with additional carbon atoms in vacuum to grow graphene. Its surface morphology exhibits few pits on terraces with widths of approximately 500 nm, in strong contrast to graphene grown on SiC after simple HF cleaning. This is probably due to carbon clusters deposited on SiC assisting the nucleation of more uniform buffer layers over the surface, which suppresses the vertical sublimation of Si prior to graphene growth.

Epitaxial graphene on silicon carbide (SiC) is promising for future electronic devices. A well-known scheme for the epitaxial growth of graphene is to heat a Si-face SiC(0001) surface to 1100-1300°C in ultrahigh vacuum (UHV), which results in the sublimation of Si. However, this simple process produces a SiC surface with a pitted morphology, which degrades the transport properties of graphene on it. The pitted morphology originates from the rapid and random sublimation of Si from the terraces that are not covered by a carbon-rich buffer layer. Thus, a strategy to avoid the pitted morphology is to form a homogeneous buffer layer on the entire SiC surface. For this purpose, a key technique is the deposition of carbon at the monolayer level on a SiC substrate in a controllable manner. Researchers have reported various methods to enrich carbon concentration on a SiC surface with a Si face. Some examples are the direct deposition of carbon onto SiC, the rapid annealing of SiC surfaces, and the enhanced removal of silicon atoms by atomic hydrogen, all of which are based on sophisticated UHV techniques. In this study, we demonstrate that carbon atoms are segregated at the SiO2/SiC interface at the monolayer level when a SiC surface, atomically flattened by a solution-based process[1-3], is oxidized by an atmospheric-pressure plasma (He-based plasma with a small amount of O and OH species) at near room temperature. The behavior of carbon atoms has been an object of study in thermal oxidation of SiC. We discuss the mechanism of carbon aggregation at the SiO2/SiC interface occurring in the plasma oxidation at room temperature. After the plasma oxidation, the sample was etched in HF solution to strip off the oxide layer, which leaves a carbon source for graphene growth on the SiC substrate. And we show the carbon-rich surface yields a surface morphology with reduced pits on graphene when it is treated at elevated temperatures in vacuum. We speculate this is achieved by the additional carbon atoms assisting the formation of the buffer layer more uniformly over the surface prior to graphene growth. [1] K. Arima, K. Endo, K. Yamauchi, K. Hirose, T. Ono, and Y. Sano, J. Phys.: Condens. Matter 23, 394202 (2011). [2] A.N. Hattori, T. Okamoto, S. Sadakuni, J. Murata, K. Arima, Y. Sano, K. Hattori, H. Daimon, K. Endo and K. Yamauchi, Surf. Sci. 605, 597 (2011). [3] K. Nishitani, H. Sakane, A.N. Hattori, T. Okamoto, K. Kawai, J. Uchikoshi, Y. Sano, K. Yamauchi, M. Morita and K. Arima, ECS Transactions, 41(6), 241 (2011).

Lowering the surface reflectance of Si wafers by texturization is important for improving the efficiency of Si solar cells. For single crystalline Si solar cells, the anisotropic etching of an Si(100) plane with alkaline solutions is effective in formation of pyramid textures and has been widely applied in their production (1). Invertedpyramid textures with low reflectance have been formed by alkaline etching with an oxide mask (2). Photolithography is often used in the formation of etching masks. In photolithography and etching, a pattern is formed on an Si surface by the following processes: applying resist, exposure, developing and etching. A number of processes increases the cost of the production. It is necessary to reduce the number of processes in order to reduce the production cost. We have proposed a new photo-etching method (3) of an Si wafer involving fewer processes: applying N-fluoropyridinium salt (4) and light exposure. In this work, we have found that random inverted-pyramid textures are formed on an Si surface by this method of photo-etching.

We describe a novel method for generation of femtolitre-order monodisperse droplets using a multistage dividing microfluidic channel. A droplet is uniformly divided into 16 parts in a four-stage microfluidic channel without the need for external equipment. The droplets become smaller as the cross-junction part becomes narrower (range from 87.8 to 9.05 pL). Central micropillar structures at each bifurcation reduce the difference in the channel resistance throughout the microchannel between two side-channel that is divided by micropillar structures, which enables the equivalent division of femtolitre-order-volume droplets. After the fourth bifurcation, the minimum radius of a daughter droplet is 5 μm ( ca . 524 fL) and the coefficient variation is 0.51%. The generation rate is 3800 droplets/s in a single-droplet generation line.

The etching mechanism of Si by N-fluoropyridinium salt has been discussed. The etching rate increases with light intensity or temperature. Si is etched by the irradiation of light with an energy higher than the band gap of Si. The etching rate is almost independent of the carrier type or the dopant concentration. The back bond of Si weakens by exciting electrons in the back bond. The N–F bond in the salts is broken by receiving excited electrons and releases an active F species. The F species react with Si to produce SiF4 because of the weakened back bond. The SiF4 is released.

We demonstrate that pyramidal etch pits composed of (111) micro facets are formed on single-crystalline Ge(100) surfaces when the Ge samples with metallic particles are immersed into water. The mechanism behind this anisotropic etching is the enhanced oxidation of Ge around metallic particles by the catalytic activity of noble metals to reduce dissolved oxygen (O2) to water molecules, and the subsequent removal of the oxide in water due to the soluble nature of Ge oxides. This enhanced etching of Ge surfaces is observed not only with metallic particles but also with a metallic thin film. The results insist that remaining metallic contaminants can roughen Ge surfaces during a rinse process with water, which will be important to design wet cleaning processes for Ge wafers.

Germanium (Ge) is a promising substrate for semiconductor devices in the near future. However, wet-chemical preparations that enable the control of the structure of the Ge surface have not yet been developed. In this study, the surface structure of Ge(111) after HCl treatment is characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). XPS spectra revealed that purging with inert gas, such as nitrogen, is necessary to obtain a Ge surface free of oxide, probably because dissolved oxygen from air rapidly oxidizes the surface. Cl-terminated Ge surfaces are microscopically rough, but are composed of terraces and steps, as revealed by magnified STM images. Step edges run not along specific directions reflecting the crystallographic nature of the (111) surface but randomly. Many atomic-scale protrusions with the height of around 0.1 nm are dispersed on terraces. They are likely to be impurities such as carbon contaminants and water on Cl-terminated terraces attracted by Cl atoms with high electronegativity.

We investigate the selective adsorption of organosilane molecules (3-aminopropyltriethoxysilane (APTES) and octadecyltrichlorosilane (OTS)) at the step edges of a flattened Si(111) surface by atomic force microscopy. The flattened Si(111) surface is formed by dipping a vicinal Si(111) wafer into ultralow-dissolved-oxygen water after treatment with HF. The selective adsorption of these organosilanes is achieved only when the Si(111) sample is pretreated with a Cu-containing solution to form Cu wires along the step edges of the Si(111) surface. This is probably due to the simultaneous formation of one-dimensional Si oxide covered with hydroxyl (OH) groups underneath Cu wires during the electroless reduction of Cu ions in water. At the step edges, APTES and OTS molecules are adsorbed as disperse clusters and as rows of bumps, respectively. The reason for this difference is still unclear, but a key factor is probably the control of the moisture content in the environment. The step edges, which are functionalized by organosilane molecules with various terminations such as -NH2 and -CH3, are expected to be utilized in novel nanoscale devices and processes.

Electroluminescence characteristics of metal-oxide-semiconductor tunnel diodes with a silicon nano-layer on silicon-on-insulator substrates have been studied. Peaks in the spectrum from the diode have been observed at ~1030 nm (~1.20 eV), ~950 nm (~1.31 eV), ~910 nm (~1.36 eV) and ~620 nm (~2.00 eV). It is suggested that the electroluminescence at ~620 nm is due to transitions between ultrathin silicon subbands.

Silicon is etched by applying N-fluoropyridinium salts to its surface and exposing the surface to light. Etching depth increases with exposure time. The H-terminated hydrophobic Si is easier to be etched than the OH-terminated hydrophilic Si. SiF4 is produced by the photo-etching.

Electroluminescence characteristics of a metal-oxide-semiconductor tunneling diode on a silicon-on-insulator wafer have been studied. The spectrum from the diode is peaked at 1050 nm (1.18 eV) and at 1145 nm (1.08 eV). The spectrum from the diode on a silicon wafer is peaked at 1145 nm. The peak at 1145 nm can be assigned as phonon-assisted indirect transitions. It is indicated that the peak at 1050 nm is due to the quantum confinement in an ultra thin silicon layer.

We report on the use of sensing devices that have a metal-insulator-gap-insulator-semiconductor structure. We have used capacitance-voltage measurements from a metal-insulator-gap-insulator-semiconductor sensing device to characterize different pH solutions and deoxyribonucleic acid (DNA) solutions. Hysteresis in the capacitance-voltage curves results from mobile ionic charges in the solutions and the influence of changes on the sensing surface condition. As the pH decreases in the pH range of 2.7 to 7.0, the flatband voltage shift toward the negative voltage increases. The differences in the flatband voltage shift in capacitance-voltage curves are related to the mobile ionic charge density in solutions with different pH values or DNA molecules.

Absolute line profiles of three silicon plane mirrors were measured by the three-flat method using a near-infrared interferometer. The interferometer was constructed using a near-infrared laser diode with 1310 nm wavelength light, to which the silicon plane mirror is transparent. The maximum height difference in the absolute line profiles is less than 8.9 nm and the rms value of height difference is less than 2.0 nm for a measured line of 12.7 mm. The near-infrared interferometer is useful for measuring a set of line profiles at the height difference level to calculate the absolute flatness of silicon plane mirrors.

The tunneling currents through ultrathin silicon dioxide films from metal to silicon in the oxide thickness regime between 1.4 and 3.5 nm are characterized using different-metal gates. The energy barrier heights and the effective mass of the silicon dioxide films are determined by the curve fitting of the data calculated by the transfer matrix method with current density–oxide voltage characteristics of metal–oxide–semiconductor (MOS) diodes with aluminum or gold gates. As the oxide thickness decreases, the energy barrier height decreases and the effective mass of the silicon dioxide film increases. The difference in the energy barrier heights between aluminum–oxide and gold–oxide interfaces nearly corresponds to the flatband voltage difference multiplied by the electron charge in the capacitance–voltage curves between MOS diodes with aluminum and gold gates. This makes it possible to precisely characterize tunneling currents by a new different-metal gates method for individually determining the energy barrier heights and the effective mass using the height difference obtained from the flatband voltage difference.

Surface Hall potentiometry is a method of detecting the Hall effect occurring in a semiconductor material as the surface potentials change. An experimental setup to detect surface Hall potentials by the Kelvin method is introduced. After we reveal the basic characteristics of surface Hall potentials, a silicon sample is prepared to induce the variation of the drift velocity of carriers. Line-profile measurements of surface Hall potentials with this sample demonstrate that our method reveals the distribution of drift velocities of carriers in semiconductors, which reflects electronic or structural properties such as the carrier type (hole or electron), current density, and thickness.

A patterned oxide buried in bonded silicon-on-insulator (SOI) wafers before thinning has been characterized using a near-infrared scattering topography system. This system has been combined with transmission and reflection microscopy. The edge of the patterned oxide buried in the SOI wafer has been observed. Micron-scaled oxide disks formed by the focused ion beam technique in stacked SOI structures have been observed by near-infrared scattering topography. A particle has been identified to be located inside a silicon/air/silicon structure by both near-infrared and visible laser scattering topographies. The size of the particle inside the silicon/air/silicon structure has been estimated to be 0.2 µm from the intensity of scattered near-infrared light. This method has an advantage over semiconductor failure analysis in future scaled-down technologies.

A metal-insulator-gap-insulator-semiconductor sensing device has been characterized in different pH solutions and with different single strand DNA solutions by capacitance-voltage measurements. The capacitance-voltage curves show the difference from pH and the difference from DNA base by hysteresis and flat band voltage shift due to mobile ionic charge in the solution. As the pH decreases, the flat band voltage shift increases in the pH range of 2.7 to 7.0. The hysteresis in the capacitance-voltage curves shows the influence of ionic charge in the solutions and the change of the sensing surface condition. The difference of the flat band voltage shift in the capacitance-voltage curves is related to the mobile ionic charge in the solutions due to pH or DNA molecules.

We immerse flattened H-terminated Si(111) surfaces into Cu-containing ultralow-dissolved-oxygen water. We confirm, by atomic force microscopy (AFM) observations, that Cu wires with the width of about 10 nm are formed at atomic-step edges of the Si(111) surfaces. On the contrary, ex situ scanning tunneling microscopy (STM) images show grooves at step edges on this surface. Both XPS spectra of Cu signals and possible chemical reactions during the electroless deposition of Cu atoms at the step edges suggest that Si oxides underneath the Cu nanowires are the origin of the grooves in the STM images. Furthermore, we present the possibility of controlling the width of one-dimensional Si oxides along the Cu nanowires at step edges by subsequent processes using oxidants.

We investigate the cross-sectional profile of microscratches remaining on a Si(001) wafer surface by a combination of laser light scattering and atomic force microscopy (AFM). AFM observations reveal that most microscratches detected by laser light scattering are very shallow trenches with widths and depths of 80-200 nm and 0.10-0.20 nm, respectively. A ridge- shaped structure with a height of 0.10 nm is also found. These results demonstrate that the combined method of laser light scattering with AFM enables us to not only detect atomic- scale defects on a Si wafer, but to also speculate when microscratches are formed during chemical mechanical polishing (CMP) processes.

The photodetective characteristics of aluminum grid gate–ultrathin silicon dioxide–silicon structures have been studied. The on–off ratio calculated from the photo and dark current densities rapidly changes at the threshold optical-power density. The threshold optical-power density is controlled by the silicon dioxide film thickness and increases with decreasing silicon dioxide film thickness. The difference between the surface potential with and without light irradiation rapidly changes at the same optical-power density. Holes do not significantly accumulate under optical-power densities lower than the threshold.

A nanohot embossing using a curved stage is proposed to improve the replication ratio of nanostructures at near the edge of a thick (sub-mm-order thickness) polymer substrate. The lower replication ratio at near the edge resulting from a conventional hot embossing is due to lower compressive stress, which is simulated by the finite-element method (FEM). The height of the proposed curved stage is gradually increased from the center to the edge to bring the levels of compressive stress at the center and at the edge closer. Here, we demonstrate replications of antireflection nanostructures, which have both pitch and height of 200 nm, onto the 0.75-mm-thick light guide for the light emitting diode (LED) frontlight systems used in mobile phones. It was found that a cutting depth of 14 μm on the curved stage is necessary to achieve a high uniformity of the replication ratio at near the edge. The replication ratio at near the edge is improved from 65% to 94%. The reflectance of the antireflection structures is 0.6%, which is a high enough quality for use in LED frontlight systems.

Allelic imbalance (AI), which represents certain chromosomal gains or losses, has been described in hepatocellular carcinoma (HCC), but the significance of AI analysis in focal nodular hyperplasia (FNH) has not been fully clarified. We hypothesized, therefore, that comprehensive allelotyping of FNH could be a useful tool for differentiating FNH from HCC. A 27-year-old man was admitted to the hospital because of general fatigue. A computed tomography (CT) scan disclosed a hepatic nodule 8 cm in diameter. No definite diagnosis was made after imaging or by biopsy before surgery. Macroscopically and microscopically, the surgical specimen showed typical features of FNH. Comprehensive microsatellite analysis was carried out with 382 microsatellite markers distributed throughout all chromosomes. To detect AI effectively, the cutoff value of the AI index was set at 0.70. Among the 382 microsatellite markers, 212 loci were informative, but no AI was detected. The absence of gross chromosomal alterations strongly suggested that the large nodule was FNH rather than HCC, in terms of its genetic background. The patient's subsequent clinical course revealed the nodule to be benign. The results suggest that this genome-wide microsatellite analysis is a useful tool for the differential diagnosis of non-neoplastic liver nodules from HCC.

Electrical properties of metal/SiC/p-Si(100) structures have been examined under conditions with and without light exposure. SiC films are formed by thermal chemical vapor deposition using a monomethylsilane gas, and are amorphous. The dark current density of the metal/SiC/p-Si structure at positive voltages is lower than that at negative voltages. The difference between the photo and dark current of metal/SiC/p-Si structures is relatively large at positive voltages. A SnO2/SiC/p-Si structure has high sensitivity compared with an Al/SiC/p-Si structure. Metal/SiC/p-Si structures can be used as photodetectors at positive voltages.

Surface photovoltage measurements of intrinsic hydrogenated amorphous Si (a-Si:H) films are performed by scanning tunneling microscopy/spectroscopy (STM/STS). The intrinsic a-Si:H film is formed on a Si substrate, and its surface is H-terminated by wet treatments before surface photovoltage measurements. A current–sample bias ( I – V ) curve shows a rectifying behavior in the dark, and an increase in tunneling current is detected only in the reverse direction under light irradiation. As a result, a large surface photovoltage appears in the reverse direction. The corrugation pattern of a surface photovoltaic image is different from that of a topographic image. Because surface states are eliminated by the passivation of the a-Si:H surface with H atoms, it is likely that the variation in surface photovoltage originates from the subsurface structures of the a-Si:H film, such as dangling bonds and grain boundaries, or surface impurities. This method can be useful for the nanometer-scale evaluation of an active layer for solar cells.

The reaction of hydrogen-terminated Si(100) surfaces with water during heating is analyzed using a combination of heating and cooling in thermal desorption spectroscopy. The reaction of the Si surface with water after hydrogen desorption is observed even at about 400°C at a low concentration of water molecules. An estimation method of surface hydrogen coverage by the combined measurement is proposed and the surface coverage as a function of temperature is estimated for quantitative understanding of hydrogen desorption and the subsequent reaction during heating. The combined measurement in thermal desorption spectroscopy is useful for revealing the reaction after hydrogen desorption during heating and for estimating the surface coverage.

Tunneling current through ultrathin silicon dioxide films with a thickness of approximately 3.1 nm, formed on n-Si (100) by controlling preoxide growth during heating, is examined using Al/oxide/n-Si structures. Electron tunneling current through the oxide from n-Si to Al is decreased and the dielectric breakdown voltage is increased by the preoxide growth control. Electron tunneling current from Al to n-Si is increased by light exposure. The increase in electron tunneling current can be explained by the increase in oxide voltage with an inversion layer formed by photoexcitation.

Continuous visible light irradiation is used to observe intrinsic hydrogenated amorphous silicon (a-Si:H) surfaces by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). A deposited a-Si:H surface is wet-cleaned in order to terminate the a-Si:H surface with H atoms. A current-sample bias ( I – V ) curve shows a rectifying behavior in the dark, and the tunneling current increases dramatically only under the reverse-bias condition with light irradiation. This is attributed to the photoexcited minority carriers that lead to the appearance of a higher voltage across the vacuum than that in the dark. Experiments with both p-type and n-type substrates justify the suggested model. High tunneling current under irradiation enables us to obtain highly resolved STM images. Current imaging tunneling spectroscopy observations show that the detected tunneling current in the reverse direction is increased over the entire surface with irradiation, and the increment of the tunneling current is different at each surface site.

Malignant fibrous histiocytoma (MFH) arising from the renal capsule is a rare tumor. We report a case of 55-year-old man with this tumor. Radiological imaging, including magnetic resonance (MR) imaging, was helpful in the differential diagnosis between MFH of the renal capsule and other renal tumors. In particular, a hypo-intense area identified on T(2)-weighted images reflecting the fibrous component was identified as an important characteristic of renal MFH.

This article presents an extremely rare case of solitary metastasis in the choroid plexus of the inferior horn of the right lateral ventricle three years after a colectomy for colon cancer. We discuss the current literature on this tumor together with the magnetic resonance (MR) imaging and computed tomography (CT) findings.

Metal-assisted chemical etching is a simple and low-cost etching process for semiconductor surfaces. There have been many reports on Si surfaces loaded with noble metals in HF solutions with oxidants such as H2O2.[1,2] Noble metals catalyze the reduction of the oxidant (H2O2), resulting in enhanced oxidation of the Si surface around the loaded metals. Because the oxide is immediately dissolved in the HF solution, selective etching of the Si surface occurs. This etching mode is used to form a variety of three-dimensional nanostructures not only on Si but also on other semiconductor surfaces. We have applied this etching mode to the machining of a Ge surface in O2-containing water. So far, we revealed fundamental etching properties such as pore formation and patterning in this system with noble metals (Pt and Ag),[3] and recently, we demonstrated Pt-assisted chemical flattening.[4,5] In this scheme, a catalyst plate comprising a soft elastomer coated with a sputtered Pt film, and a Ge wafer were brought into contact and rotated independently in the same plane in water. The processed Ge surface includes few protrusions with a lateral size on the order of 10 nm, which is probably caused by the selective removal of protrusions from the Ge surface by the catalytic activity of Pt. However, a problem in this system is the use of noble metals as catalysts. After metal-assisted chemical etching, residual metals on a semiconductor surface have to be removed. For example, aqua regia is effective for dissolving Pt. However, such a strong oxidative solution causes severe damage to a Ge surface. To solve this issue, graphene can be used as a substitute for noble metals to achieve catalyst-assisted chemical etching.[6] In this talk, we discuss the etching properties of a p-type Ge(100) surface loaded with reduced graphene oxide (RGO) in O2-containing water. In order to obtain the RGO, a graphene oxide (GO) ink, used as a starting material, was either heated at 900°C in Ar ambient for 10 min or immersed in a solution comprising the GO ink, hydrazine and N,N-dimethylformamide.[7] Then we deposited the obtained RGO on a Ge surface in the form of aggregated particles or dispersed flakes. After immersing the samples into water exposed to air, we found that the Ge surface was preferentially etched around the loaded RGO. The etching rate as well as the etched morphology was revealed by atomic force microscopy observations, and the etching mechanism is proposed. These findings show the possibility of using RGO as a catalyst to enhance the chemical etching of a Ge surface in water. [1] Z. Huang, N. Geyer, P. Werner, J. de Boor and J. Gösele, Adv. Mat., vol. 23, no. 2, pp. 285-308 (2011). [2] X. Li, Current Opinion in Solid State and Materials Science, vol. 16, pp. 71-81 (2012). [3] T. Kawase, A. Mura, K. Nishitani, Y. Kawai, K. Kawai, J. Uchikoshi, M. Morita and K. Arima, J. Appl. Phys., vol. 111, no. 12, pp. 126102 1-3 (2012). [4] T. Kawase, Y. Saito, A. Mura, T. Okamoto, K. Kawai, Y. Sano, M. Morita, K. Yamauchi, and K. Arima, ChemElectroChem, vol. 2, no. 11, pp. 1656-1659 (2015). [5] T. Kawase, A. Mura, Y. Saito, T. Okamoto, K. Kawai, Y. Sano, K. Yamauchi, M. Morita, and K. Arima, ECS Transactions, vol. 75, no. 1, pp. 107-112 (2016). [6] J. Kim, D.H. Lee, J.H. Kim and S.-H. Choi, ACS Appl. Mat. and Inter., vol. 7, no. 43, pp. 24242-24246 (2015). [7] S. Park, J. An, I. Jung, R.D. Piner, S.J. An, X. Li, A. Velamakanni and R.S. Ruoff, Nano Lett., vol. 9, no. 4, pp. 1593-1597 (2009).

Here we propose a texturing method for crystal Silicon solar cells, which enables a low reflecting surface of random double inverted pyramids easily. The surfaces of the reported crystal Silicon solar cells that have world-record efficiency were inverted pyramids, whereas the widely-used conventional texturing surface is a random pyramid surface by alkaline solution. Our method can realize a random double inverted pyramid surface of nanometer-sized inverted pyramids on micrometer-sized inverted pyramids without photo-lithography. This random double inverted pyramid surface is obtained by a kind of fluorinating agent of N-fluoropyridinium salt, under optical illuminating and heating condition. Using reflectance measurement with integrating sphere, we realized a black surface of 6.3% reflectance, whereas the as-slice surface is 23% and random pyramid surface is 11.9%

In this work we propose a standard practice covering temperature calibration of a Si substrate, ranging from 400 to 1000 °C, for temperature programmed desorption (TPD) analysis. The practice consists of heating silicon calibration materials at a controlled rate in a TPD instrument, measuring characteristic desorption peak temperatures, and quadratic calibration fitting the measured temperatures to standard temperatures. The calibration materials are (1) a CaC2O4⋅H2O pellet on Si, (2) Ar, and (3) H ion implanted into Si wafers. The standard temperatures of the characteristic desorption, associated with decomposition, structural transformation, and lamination of Si, were determined by a special TPD instrument with the highest isothermal space around the specimen in several laboratories, which was confirmed to be accurate for practical application. The precision of this practice was determined in an interlaboratory test in which four to five laboratories participated using two different instrumental models. This proved that the correction practice provided interlaboratory precision of 5.7 °C between 400 and 1000 °C for ramping rates of 10, 30, and 60 °C/min.

The effects of ion species/ion bombardment energy in sputtering deposition process on gate oxide reliability have been experimentally investigated. The use of xenon (Xe) plasma instead of argon (Ar) plasma in tantalum (Ta) film sputtering deposition for gate electrode formation makes it possible to minimize the plasma-induced gate oxide damage. The Xe plasma process exhibits 1.5 times higher breakdown field and five times higher 50%-charge-to-breakdown ( Q BD ). In the gate-metal sputtering deposition process, the physical bombardment of energetic ion causes to generate hole traps in gate oxide, resulting in the lower gate oxide reliability. The simplified model providing a better understanding of the empirical relation between the gate oxide damage and the ion-bombardment energy to gate oxide in gate-metal sputtering deposition process is also presented.

We have proposed a metal-gap-semiconductor (MGS) sensing device. Different concentrations of λDNA solutions have been characterized by capacitance–voltage measurements of the sensing device. Hysteresis due to electron traps and flatband voltage shift due to negative charge are observed in capacitance–voltage curves. As the λDNA concentration increases, the flatband voltage shift toward the positive voltage increases in the concentration between 0.01 and 0.3 µg/µl. It is suggested that the hysteresis in capacitance–voltage curves arises from the capture and emission of electrons through the states of the λDNA solution, and the flatband voltage shift is attributed to the charge of the λDNA solution. Copyright © 2008 John Wiley & Sons, Ltd.

A void in bonded silicon-on-insulator wafers before thinning has been characterized using a near-IR microscope with an interference filter for controlling the coherence length of the light source. The visibility of interference fringes is improved by controlling the coherence length of the light. The cause of the void formation is discussed by comparing the void shape obtained from an observation image with deflection curve models of discs under a uniformly distributed load of gas molecules or under a concentrated load of a particle. It is suggested that the void is formed by gas molecules trapped in the bonded interface.

Absolute flatness of three silicon plane mirrors have been measured by a three-intersection method based on the three-flat method using a near-infrared interferometer. The interferometer was constructed using a near-infrared laser diode with a 1,310-nm wavelength light where the silicon plane mirror is transparent. The height differences at the coordinate values between the absolute line profiles by the three-intersection method have been evaluated. The height differences of the three flats were 4.5 nm or less. The three-intersection method using the near-infrared interferometer was useful for measuring the absolute flatness of the silicon plane mirrors.

Air-operated actuators have its merits that are safety, lightweight, high torque, robustness, and low cost comparing to electrical or magnetic actuators. However, the pneumatic actuator requires own control valve for introducing and releasing compressed air to drive the actuators. We designed and fabricated an integrated microvalve system for pneumatic actuators, which uses normally closed valve. Miniaturizing pneumatic control system enables robotics drive system that is combined lightweight and high power. Employing normally closed valves low power consumption. The system can control (m*n) outputs with (m+n) solenoid valves. The prototype device that is regulated by 8 solenoid valves controls independent 16 outputs.

We propose the metal-assisted chemical etching of Ge surfaces in water mediated by dissolved oxygen molecules (O2). First, we demonstrate that Ge surfaces around deposited metallic particles (Ag and Pt) are preferentially etched in water. When a Ge(100) surface is used, most etch pits are in the shape of inverted pyramids. The mechanism of this anisotropic etching is proposed to be the enhanced formation of soluble oxide (GeO2) around metals by the catalytic activity of metallic particles, reducing dissolved O2 in water to H2O molecules. Secondly, we apply this metal-assisted chemical etching to the nanoscale patterning of Ge in water using a cantilever probe in an atomic force microscopy setup. We investigate the dependences of probe material, dissolved oxygen concentration, and pressing force in water on the etched depth of Ge(100) surfaces. We find that the enhanced etching of Ge surfaces occurs only when both a metal-coated probe and saturated-dissolved-oxygen water are used. In this study, we present the possibility of a novel lithography method for Ge in which neither chemical solutions nor resist resins are needed.

The effect of Cr, Mn, Fe, Ni, Cu, Zn, Pd, Ag, Pt, or Au metal particles on the rate of Si etching using N-fluoropyridinium salts was examined. The average etching depth increased when N-fluoropyridinium salts were mixed with Cu particles. The activation energy determined from the temperature dependence of the average etching rate for the Cu particles is lower than that without a metal. The Cu particles greatly improve the etching of Si with the salts compared with the other metals. The magnitude of the effect of the Cu particles on the rate of Si etching with the salts is larger than that of the Mn, Fe, Ni, or Zn particles. This can be explained by the order of the relative stabilities of the complexes formed by bivalent ions of transition metals. The etching method involves the application of easy-to-handle salts containing Cu particles as etchants on the Si surface and has the potential to be a simple and less expensive form of Si etching.

Mori D., Oka H., Hosoi T., et al. Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy. Journal of Applied Physics, 120, 9, 095306. https://doi.org/10.1063/1.4962202., The energy difference between the oxide and bulk peaks in X-ray photoelectron spectroscopy (XPS) spectra was investigated for both GeO2/Ge and SiO2/Si structures with thickness-controlled water films. This was achieved by obtaining XPS spectra at various values of relative humidity (RH) of up to ∼15%. The increase in the energy shift is more significant for thermal GeO2 on Ge than for thermal SiO2 on Si above ∼10-4% RH, which is due to the larger amount of water molecules that infiltrate into the GeO2 film to form hydroxyls. Analyzing the origins of this energy shift, we propose that the positive charging of a partially hydroxylated GeO2 film, which is unrelated to X-ray irradiation, causes the larger energy shift for GeO2/Ge than for SiO2/Si. A possible microscopic mechanism of this intrinsic positive charging is the emission of electrons from adsorbed water species in the suboxide layer of the GeO2 film to the Ge bulk, leaving immobile cations or positively charged states in the oxide. This may be related to the reported negative shift of flat band voltages in metal-oxide-semiconductor diodes with an air-exposed GeO2 layer.

Si sublimation from a silicon carbide (SiC) surface at elevated temperatures is a convenient and simple method of forming graphene [1]. The increase in carbon concentration at the monolayer scale on SiC prior to graphene growth is the key to obtaining graphene with reduced pit density. There have been some attempts to achieve this, one example of which is the use of vacuum evaporation from a solid carbon source [2, 3]. We have proposed a novel chemical route to enrich the carbon concentration on SiC. Namely, we have found that aggregated carbon compounds with a few monolayers are formed when an initial hexagonal SiC surface is treated by plasma oxidation at near room temperature and then the oxide layer (SiO2) with a thickness of ~10 nm is stripped off by HF etching [4, 5]. No additional carbon clusters were formed in the conventional thermal oxidation of SiC at 1000°C. Neither the composition of the aggregated compounds nor the mechanism of the generation of such carbon species by the plasma-assisted procedure is clear, however. In this study, we reveal that, after the plasma oxidation followed by wet etching, the SiC surface is more hydrophobic than the initial SiC surface terminated by hydroxyls. Taking the electronegativities of Si, C and O atoms into account, this result indicates the formation of C-O and C-C, which is confirmed by the chemical-shift analyses of O1s and C1s spectra taken by X-ray photoelectron spectroscopy. In thermal oxidation, it is widely accepted that the reaction (2SiC+3O2 -> 2SiO2+2CO) forms a SiO2 layer whereas CO molecules diffuse into the oxide and are finally emitted in the gas phase. However, it has also been reported that CO molecules can diffuse a high-quality SiO2 film at temperatures higher than 900°C [6]. It is reasonable to suppose that, in the case of plasma oxidation at near room temperature, CO molecules reside at the SiO2/SiC interface and form carbon compounds. In addition, a consideration based on thermodynamics implies the direct formation of solid carbon clusters during oxidation at low temperatures by the reaction SiC+O2 -> SiO2+C(s) [7]. These growth kinetics of SiO2 on SiC well explain the obtained results described in the previous paragraph. Such a carbon residue at the SiO2/SiC interface can degrade the performance of metal-oxide-semiconductor (SiC) devices. But it may serve as an additional carbon source for epitaxial graphene growth on SiC. [1] C. Berger et al., J. Phys. Chem. B, 108, 19912 (2004). [2] A. Al-Temimy et al., Appl. Phys. Lett., 95, 231907 (2009). [3] J. Park et al., Adv. Mater., 22, 4140 (2010). [4] N. Saito, K. Arima et al., Carbon, 80, 440-445 (2014). [5] N. Saito, K. Arima et al., ECS Transactions, 64, 17, 23 (2014). [6] O.H. Krafcsik et al., Jpn. J. Appl. Phys. 40, 2197 (2001). [7] K. Kita et al., ECS Transactions, 64, 8, 23 (2014).

Recently, metal-assisted chemical etching has attracted a great deal of attention because it is a simple and low-cost process for the fabrication of nanostructures on a semiconductor surface, mainly Si [1, 2]. This electroless etching is made possible by using noble metals, such as Pt and Ag, to catalyze the reduction of a chemical oxidant, such as H2O2, in the presence of HF. Namely, the reduction is accompanied by the selective oxidation around the loaded metals followed by the dissolution of oxide (SiO2) in HF solution. By controlling the etching conditions, a vast variety of nanostructures from porous structures to nanowire arrays can be fabricated in a chemical lab without the need for expensive equipment. Ge is regarded as a promising channel material in future electronics. It is necessary to develop and/or optimize wet processes, such as lithography, planarization and cleaning, for Ge. Ge oxide (GeO2) is soluble in water, unlike SiO2. Also, O2 molecules dissolved in water are oxidants. These chemical properties enable us to develop a novel process for a Ge surface using metal-assisted chemical etching in water. In this study, we immersed a Ge(100) surface loaded with Pt or Ag particles with the size of 10 nm order into O2-containing water and observed the formation of inverted pyramidal etch pits around the particles. This is caused by the catalytic effect of metals whereby O2 molecules in water are reduced, resulting in an enhanced oxidation of a Ge surface to form soluble GeO2. We confirmed that the O2 concentration in water is a key in etch rate [3, 4]. Then, we tested nanoscale patterning of a Ge surface by metal-assisted etching in O2-containing water. This was achieved by scanning a metal-coated cantilever on a Ge surface in the contact mode in an atomic force microscopy setup. We found that the Ge surface scanned by the cantilever was selectively removed, and the etched depths depended on experimental conditions such as the O2 concentration in water, the pressing force of the cantilever to the Ge surface, and the conduction type (n-type or p-type) of Ge. These findings indicate that the mechanism of inducing enhanced etching along the trajectory of the cantilever probe is a catalytic chemical effect rather than a mechanical one [4]. Finally, we used this metal-assisted chemical etching to improve the microroughness of a Ge surface. In this scheme, a thin film of noble metal (Pt) was deposited on a soft elastomer pad. This Pt surface was brought into contact with a Ge wafer surface by applying 0.01 MPa in O2-containing water. Both the pad coated with the metal and the Ge wafer were rotated independently in the same plane. Consequently, the Ge surface was flattened. The flattening mechanism is as follows. First, protrusions on the Ge surface have a higher probability of coming into contact with the metal surface than do grooves. These protrusions were selectively oxidized by the catalytic effect of the metallic film in water. After the oxidized protrusions were dissolved in water promptly, a flattened surface was created [5]. [1] X. Li et al., Appl. Phys. Lett. 77, 2572 (2000). [2] Z.P. Huang et al., Adv. Mater. 23, 285 (2011). [3] T. Kawase et al., J. Appl. Phys., 111, 126102 (2012). [4] T. Kawase et al., Nanoscale Res. Lett., 8, 151 (2013). [5] T. Kawase et al., ChemElectroChem, 2, 1656 (2015).

A chemical vapor deposition method for tungsten films using a chamber with a cold susceptor is proposed for attaining excellent selectivity and a cleaning-free process. High-rate selective deposition above 1.0 [mu]m/min using the reduction of tungsten hexafluoride by silane is achieved at a substrate temperature of 210 C by using a cold susceptor chilled by water at room temperature. No deposition of tungsten or by-products on the susceptor surface and the inner surface of the chamber is observed, indicating that the newly developed system is free from cleaning. The deposited tungsten film has the alpha-type structure. The lattice constant of the tungsten is changed by the deposition temperature and the flow ratio of silane to tungsten hexafluoride.

Gas molecular-flow preshowering treatment onto the silicon (Si) substrate surface during the temperature ramp prior to epitaxial Si film formation has been proposed in order to lower the epitaxy process temperature in chemical vapor deposition (CVD). High-quality phosphorus-doped Si films have been obtained at 550 o C by using Si 2 H 6 molecular-flow preshowering. The optimum starting temperature of the Si 2 H 6 preshowering has been found to be 520 o C. This is nearly equal to the temperature at which thermal desorption causes the coverage of hydrogen terminating the Si surface to drastically decrease