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Summary Objective This study evaluated the differences in the appearance of COVID-19 pneumonia on chest computed tomography (CT) images of outpatient and cases that developed during hospitalisation. Method Chest CT images of 66 patients (median age, 76 years; range, 29–94 years) who underwent the severe acute respiratory syndrome coronavirus-2 reverse-transcription polymerase chain reaction (RT-PCR) test were included in this retrospective study. The chest CT appearance was categorised as “typical,” “indeterminate,” “atypical,” or “negative” in accordance with the recommendations of the Radiological Society of North America for COVID-19 pneumonia and compared among the following four subgroups: PCR-positive outpatient (n = 14); PCR-positive hospitalised (n = 7); PCR-negative outpatient (n = 9); and PCR-negative hospitalised (n = 36). Findings The frequency of “typical” findings in the PCR-positive outpatient cases (13/14, 92.9%) was significantly higher than that of those in the PCR-positive hospitalised cases (2/7, 28.6%, P = 0.022). There was no significant difference between the frequency of the “typical” appearance in PCR-positive hospitalised cases and that of those in the PCR-negative hospitalised cases (1/36, 2.8%, P = 0.192). Conclusions When COVID-19 patients acquire infections while hospitalised, their chest CT images are less likely to show typical findings than those of outpatient cases. Comprehensive and careful assessments of CT findings and consideration of the possibility of concomitant infections with other pathogens and clinical information, such as underlying diseases, background lung structure, and time course of the infection, are required for the management of such cases.

Understanding of the dynamics of the bonding states of molecules with electrodes while the molecular conformation is changed is particularly important for elucidating the details of electrochemical devices as well as molecular devices in which the reaction dynamics of the electrodes and molecules plays an important role, such as in fuel cells, catalysis and bioelectrochemical devices. However, it has been difficult to make measurements when the distance between counter electrodes is short, namely, the molecule is raised from a lying form, almost parallel and close to the electrodes, toward a standing form and vice versa. We previously have developed a method called the three-dimensional (3D) dynamic probe method, which enables conductance measurement while the conformation of a single-molecule junction is precisely controlled by scanning tunneling microscopy (STM) techniques. Here, by combining this method with density functional theory (DFT) calculations, it has become possible to simultaneously consider the effects of the dynamics of molecular structures and the bonding states at the electrodes on the local transmission pathways, local-bond contributions to conductance. Here, by performing an analysis on 1,4-benzenediamine (BDA) and 1,4-benzenedithiol (BDT) single molecule junctions, we have observed, for the first time, the effect of a change in the molecular conformations and bonding states on the local transmission pathways for a short Au electrode distance condition.

We have applied our previously developed three-dimensional dynamic probe method to analyze the conductance in a Au-/1,4-benzenediamine (BDA)/Au single molecule junction. This structure is a typically used example to demonstrate the high performance of the break junction (BJ) method for measuring conductance with small variations, however, details of the interaction of the nitrogen (N) lone-pair in the amine group with a Au electrode, which is considered to have a fundamental role in determining the conductance of the single molecule junction with the amine, have not yet been clarified and still remain an important issue to be resolved. In this study, we have succeeded, for the first time, in observing the site-dependent change in conductance of this system while the molecular conformation was accurately controlled, and the results were well reproduced by a simulation taking account of the effect of the N lone-pair in an amine bonding with a Au electrode.

Single-molecule junctions have been extensively studied because of their high potential for future nanoscale device applications as well as their importance in basic studies for molecular science and technology. However, since the bonding sites at an electrode and the molecular tilt angles, for example, cannot be determined experimentally, analyses have been performed assuming the structures of such interactive key factors, with uncertainties and inconsistencies remaining in the proposed mechanisms. We have developed a methodology that enables the probing of conformational dynamics in single-molecule junctions simultaneously with the direct characterization of molecular bonding sites and tilt angles. This technique has revealed the elemental processes in single-molecule junctions, which have not been clarified using conventional methods. The mechanisms of the molecular dynamics in 1,4-benzenedithiol and 4,4'-bipyridine single-molecule junctions, which, for example, produce binary conductance switching of different types, were clearly discriminated and comprehensively explained.

We studied the impact of Yttrium and Lanthanum incorporation into HfO2 on reliability (TDDB, PBTI and 1/f noise). They introduce smaller Weibull β values and early failure in TDDB, with negative shift in PBTI. They are caused by the negatively charged interstitial oxygen defect generated by Yttrium and Lanthanum incorporation. The effect of Lanthanum is larger than that of Yttrium. It can be explained by the larger ion radius and molecular volume of La2O3 than Y2O3. On the other hand, they are effective in noise reduction, as an effect of interface state density reduction. The key point in fabricating low Vth and highly reliable MOSFETs is the technology for suppression of this interstitial oxygen defect generation.

We propose a novel approach to control the effective work function by taking advantage of crystal structures in metal gate electrodes. The crystal structures determine the predominant material elements at the metal/high-k interface. We have found that, in a Ru-Mo alloy system, a randomly-oriented Ru (fcc) structure promotes the segregation of Mo at the interface, enabling us to achieve a wide controllability of flatband voltage by the amount of 0.6-0.8 eV. In addition, the segregation of Mo within a Ru-rich electrode is a key to reducing Fermi level pinning at the metal/HfSiON interfaces.

Methods of improving Fermi-level pinning of pure metal gate electrodes on Hf-based high-k dielectrics have been investigated. The pinning phenomenon is a crucial problem, resulting in an unintentional threshold voltage increase in p-MOSFETs when applying pure metal gate electrodes such as Ru and TiN in Hf-based high-k CMOS. After systematic investigation of the relation between oxygen vacancies in Hf-based high-k dielectrics and electrical characteristics, we concluded that the Fermi-level pinning is unavoidable in principle with a thin EOT, but is a stable phenomenon that should be intentionally utilized. It is necessary to modulate the stable pinning energy position of Hf-based high-k dielectrics in p-MOSFETs in order to obtain thin EOTs in the gate-first process.

Structural changes of Y2O3 films and La2O3 films deposited on some oxidized silicon substrates were studied using X-ray photoelectron spectroscopy (XPS), Secondary ion mass spectrometry (SIMS), and Fourier transform infrared spectroscopy attenuated total reflection method (FT-IR ATR). Y2O3 and La2O3 films on chemical oxide and NH3 annealed oxy-nitride were prepared by the Low-pressure chemical vapor deposition (LPCVD) method using an lanthanide–dipivaloyl-methanate (Ln–DPM) complex. The Y2O3 film and the La2O3 film on the both kinds of substrate already contained a partly silicate structure at the interface side as a result of an interface reaction during the deposition process. During post deposition annealing, the whole film structure of the Y2O3 and the La2O3 on the chemical oxide changed to a silicate structure due to silicon diffusion with interface reaction. In the case of the Y2O3 film, this interface reaction can be suppressed using thermal oxy-nitride as the interfacial layer. In the case of the La2O3 film, the suppression effect using oxy-nitride was smaller than the case with the Y2O3 film. Also, it was found that there was a strong correlation between the structural change of the films and the change of flat-band-voltage of both Y2O3 and La2O3 MIS diodes during post-deposition-annealing.

Rare-earth oxides are promising high dielectric constant gate oxides to be used in metal-oxide-semiconductor devices in future. Properties of rare earth oxides are very different from those of the well-reported high dielectric constant materials such as HfO2. In this article, basic properties of rare-earth oxides are described comparing with La2O3 and Y2O3. These are typical rare earth oxides with a large and a middle ion radius, respectively. It is shown that interfacial silicate formation is an important character of rare-earth oxides on silicon substrates. To control silicate formation during thermal process, the addition of alumina into the rare-earth oxides is proposed. Physical and electrical properties of yttrium-aluminate films on silicon substrates are reported.

The social and professional isolation of physicians remains an important issue in rural areas. However, few studies have investigated the involvement of geographic factors in the isolation. This study investigates rural public clinics in inland and remote island locations and attempts to objectively compare the isolation of these physicians. A mailed questionnaire was sent to rural clinics where graduate physicians from Jichi Medical School were working in 1994 and 1995. Among the 198 clinics with one or more full-time physicians, 185 (93 percent) responded to the inquiry. Geographic and demographic factors of the communities were compared between 43 clinics located in remote islands and the other 142 rural inland clinics. Rural clinics in remote islands have smaller subject populations, fewer part-time physicians, a longer journey to the nearest city, and a longer distance and travel time to the base hospital than rural inland clinics. Physicians in remote island clinics had less medical training and are more isolated than other physicians. More than half of the clinic physicians in remote islands have no regular training schedule, in contrast to less than a quarter of the inland clinic physicians. Almost all clinics (97.7%) in remote islands do not have a part-time physician, whereas about 20 percent of the rural inland clinics do. Physicians in remote island clinics are more socially and professionally isolated than those in inland clinics. Strategies to reduce these problems should be given priority in rural health policy and measures tailored to rural clinics in remote islands. Asia Pac J Public Health 2000;12(1): 22-26

By complementary use of X-ray crystal truncation rod (CTR) scattering and difference X-ray reflectivity (DXR), structural properties on ultra-thin thermal oxides grown on Si(0 0 1) substrates were obtained. A thin film which contains SiO 2 crystallites concentrated at the SiO 2 /Si(0 0 1) interface revealed to have an interfacial thin layer characterized by high electron density, and vice versa. An effect of annealing in Ar gas has been understood consistently. The CTR scattering data indicated that probability of finding the crystallites in the oxide film remained, but the lattice constant of the crystallites increased along the direction perpendicular to the interface by the annealing. The decrease in the density calculated by this volumetric expansion agrees well with the decrease in average density of the interfacial thin layer observed by the DXR measurements.

We developed a low-resolution, high intensity monochromator composed of one multilayer mirror, two plane Pt mirrors, and a filter to investigate core-electron excitation effects induced by a photochemical reaction. We used a Mo/B4C multilayer mirror, which exhibits a high reflectivity at the L-shell absorption edge of Si (100 eV). We also examined the photoinduced fragmentation of SiH4 and Si2H6 molecules at the absorption edge using a synchrotron radiation beam. We confirmed that core–electron excitation initiated the fragmentation of these molecules into multiple ionization particles.

We have studied the removal of surface oxides from a partially oxidized Si(111) surface and the simultaneous hydrogenation of the new dangling bonds in hot water. The amount of remaining oxides decreased by lowering dissolved-oxygen concentration (DOC) from 4 to 0.004 ppm. After immersing in hot water with 0.004 ppm of DOC for 60 min, almost all of the surface was hydrogenated and only a tiny amount of silanol groups remained. We discuss the formation of the dihydride step-edges observed during the oxide removal.

We analyzed the density of thermally grownSiO 2 /Siby X-ray reflectivity measurements and local vibration properties by infrared spectroscopy. The macroscopic density varied with growth conditions. A lower growth temperature caused higher film density. We also found a thin (1 nm) and dense (2.35–2.4 g/cm 3 ) transient layer at theSiO 2 /Siinterface. The film density was constant to the thickness direction without the transient layer. On the other hand, IR properties showed characteristic film thickness dependencies. At a film thickness greater than 10 nm, the frequency of the transverse optic (TO) mode of Si-O stretching shifted to the red direction, decreasing with the film thickness; while the frequency of the longitudinal optic (LO) mode is unchanged. This red shift of TO mode has no relation to the film density. At a film thickness of less than 6 nm, we found that both the TO and LO mode shift to the red direction simultaneously. The red shifts gradually increased with decreasing film thickness. This indicates that the SiO 2 network was densified by compressive stress. We assumed that the macroscopic and microscopic fluctuation were related to the oxide growth and formation of a hetero-junction.

We observed stretching and bending vibrations of H on stepped Si(111) surfaces formed in hot water. These observations were explained by a simple surface model which included a monohydride on a terrace, a monohydride chain at the step edge of a (111) micro-facet, and a vertical dihydride at the step edge of a (001) micro-facet. We found that the dynamic polarization associated with the bending vibration modes were quite anisotropic and were along (110) for both step modes of the wagging modes of the vertical dihydride and the monohydride chain, and was two-dimensionally isotropic in the (111) plane for the monohydride on the (111) terrace.

We have developed a high‐precision difference‐x‐ray‐reflectivity technique using intense synchrotron radiation and applied this to evaluate native oxides and ultrathin thermal oxides on Si(100). We have successfully evaluated the density of native oxides. Native oxides formed by HCl and NH4OH solutions have a low density, in contrast to the oxides formed by H2SO4 solution and UV/O3 whose densities are close to those of thermal oxides. By carefully analyzing ultrathin thermally grown oxides with thicknesses of 40 and 70 A grown at 800–1000 °C, we have revealed the existence of a dense (∼2.4 g/cm3), thin (∼10 A) layer at the SiO2/Si interface. Oxides grown in O3 or HCl/O2 have a thinner interfacial layer compared to those grown in O2. We have evaluated the effects of ambient and temperature at oxidation on the interfacial layer and the SiO2 layer.

We investigated the initial stage of the oxidation of H-terminated Si (100) and (111) surfaces in oxidation solution. A specially designed spectrochemical cell in attenuated-total-reflection geometry was used for observing infrared absorption feature attributed to these surfaces in a contact with the solution. After removing surface oxide and making an H-terminated surface by HF solution, we introduced the oxidation solution into the cell and recorded infrared spectra as a function of time, after exchanging the solution to deionized water to pose the oxidation. We used 3% of H2O2 and 2 ppm of ozonized water as the oxidation solutions. We found that the time evolution of the surface hydride structures, which were observed from 2000 to 2300 cm-1, appeared differently, depending on both the surface orientation and the oxidation solution. With either H2O2 solution or ozonized water, we observed one of the oxide structures of -O3SiH but the other oxide structures such as - (O2Si) SiH and - (OSi2) SiH were not observed on Si (100) as oxide intermediates. On the other hand, all the intermediate structures were observed on (111). When we continued the oxidation for 10 min in ozonized water, all hydride structures were disappeared on both (100) and (111), while a part of the hydride structures were still observable in H2O2 solution. We discussed these features on a basis of our in-situ experiment.

Vacuum-ultraviolet (VUV) light induced etching of thermally grown silicon dioxide films was investigated near room temperature. We used synchrotron radiation as a VUV light source and anhydrous-hydrogen-fluoride as an etching gas. The silicon dioxide is etched only in the VUV light irradiated area, and etched selectively with respect to (100) oriented singlecrystalline silicon, which is not etched even under the irradiation. Moreover, we have found anisotropic etching with the patterned polycrystalline silicon etching mask. The ratio of the etch rate of SiO2 in the vertical direction compared to the horizontal direction of the substrate surface is about 30. From these results, the etching process is due to the photo-induced surface reaction. The excitation of the adsorbed AHF molecules or SiO2 surface would be a dominant process.

Using polarized infrared spectroscopy, stretching and bending vibration modes of H chemisorbed on 4° and −9° misoriented Si(111) surfaces were investigated. Both the stretching and bending modes and their polarization responses were explained by surface structures such as monohydrides on a terrace, monohydride chains at the step edge of a (11 1 ) micro-facet and vertical dihydrides at the step edge of a (00 1 ) micro-facet. The dynamic polarizations for these bending vibration modes were anisotropic, i.e. the polarizations for the two step modes were along 〈 1 10〉, while that of the terrace mode was in the (111) plane.

Evidence of the removal of surface oxides from a partially oxidized Si(111) surface, and the simultaneous termination of the new dangling bonds by hydrogen in hot water, has been obtained. The amount of remaining oxides decreased by lowering the dissolved-oxygen concentration (DOC) from 4 to 0.004 ppm. After immersing in hot water with a DOC of 0.004 ppm for 60 min, almost all of the surface was hydrogen-terminated and only a tiny amount of silanol groups remained. The appearance of vertical dihydrides at step edges showed that the oxidation process on the hydrogen-terminated surface continues, even in water with a DOC of 0.004 ppm.

The hydrophobic process of the Si(111) surface was investigated by FT-IR attenuated total reflection (ATR) method using a Si prism. By changing the immersion time in hydrofluoric solution, thermally grown silicon-dioxides and some chemically grown oxides on the Si(111) surface were removed. The variations in the ATR spectra of Si-H and O-H were compared with those in the contact angle (CA) of water on the surfaces. After the removal of the silicon-dioxide film, a hydrophobic surface is formed and Si-H and Si-OH structures appear. The surface structures having low CA (10∼40°) depend on the way to form the oxides. The degree of hydrophobia represented by CA does not directly relate to the quantity of Si-OH. At higher CA (more than 40°) surfaces, the main surface reaction is etching of Si. The growth of terraces and reduction of step-edge structures create a smooth surface and Si-OH structures are gradually removed at the same time. The re-oxidation and the etching process in hydrofluoric solution seem to occur on these surfaces.

We implanted B ions in a 110-nm-thick HfO/sub 2/ layer, subjected the substrates to various thermal processes, and evaluated the diffusion coefficient by comparing experimental and numerical data. We found that the diffusion coefficient of B in HfO/sub 2/ is higher than that in SiO/sub 2/ by about four orders and almost the same as that in Si. Therefore, the penetration of B through this layer can be expected to be significant, making the use of a cover layer indispensable for p/sup +/ polycrystalline silicon gate devices.

A new etching method of semiconductor materials using ionization of CF4 gas by synchrotron radiation (SR) and acceleration of SR-generated ions by external electric field is proposed. The SR is irradiated parallel to the substrate and the electric filed is applied perpendicular to the substrate. The dominant quasi-stable gas-phase ion is CF3+ which is measured by photoionization mass analysis. This method is applied to etch silicon substrate having resist mask and fine pattern of 0.1μm line and space is successfully fabricated.

We studied the impact of Yttrium and Lanthanum incorporation into HfO 2 on reliability (TDDB, PBTI and 1/f noise). They introduce smaller Weibull β values and early failure in TDDB, with negative shift in PBTI. They are caused by the negatively charged interstitial oxygen defect generated by Yttrium and Lanthanum incorporation. The effect of Lanthanum is larger than that of Yttrium. It can be explained by the larger ion radius and molecular volume of La 2 O 3 than Y 2 O 3 . On the other hand, they are effective in noise reduction, as an effect of interface state density reduction. The key point in fabricating low V th and highly reliable MOSFETs is the technology for suppression of this interstitial oxygen defect generation.

We have clarified that, in a metal/high-k gate stack, as well as the variability introduced by random dopant fluctuations (RDF), the threshold voltage variability (TVV) is attributable to the crystal structure and grain size in the metal gate. We have successfully eliminated this additional factor by reducing the grain size in the metal gate. We demonstrated that the incorporation of C into TiN metal gates transforms the crystalline film into an amorphous one, effecting a reduction in the TVV in HfSiON pFET devices. We observed that the TVV of C-incorporated TiN devices was dominated by RDF, indicating that the additional factor due to the metal gate had been diminished.

We have clarified the difference in NBTI and 1/f noise of high-k/metal gate pMOSFETs between (110) and (100) oriented surfaces. Although the initial interface state density on (110) is higher than that on (100), the NBTI is better on the (110) surface. That is due to the different interface defect nature of interface defect states on (110) surface compared to (100). This difference has a strong impact on 1/f noise.

We propose here cost-effective gate-first dual-metal/dual-high-k CMOS technology in which Fermi-level pinning is "positively" utilized to reduce threshold voltages for the first time. After systematic investigation on the relation between oxygen vacancies in Hf-based high-k film and electrical characteristics, we concluded that the Fermi-level pinning is unavoidable in principle with a thin EOT, but is a stable phenomenon that should be intentionally utilized. In our proposed method, source of oxygen interstitials (Al) is contained in metal gate material for p-FET, and consequently the flatband voltage is properly modulated by "opposite" Fermi-level pinning due to the oxygen interstitials incorporated into the underlying high-k film after high temperature annealing. It is also noteworthy that this method is simple and cost-effective because the initial high-k films are identical for n-and p-FET but they are automatically converted into dual high-k after the annealing process.

We propose a novel approach to control the effective workfunction (WF) by taking advantage of crystal structures in metal gate electrodes. The crystal structures determine the predominant material elements at the metal/high-k interface. We have found that, in a Ru-Mo alloy system, a randomly-oriented Ru (fcc) structure promotes the segregation of Mo at the interface, enabling us to achieve a wide controllability of flatband voltage (Vfb) from 0.6-0.8 eV In addition, the segregation of Mo within a Ru-rich electrode is a key to reducing Fermi level pinning at metal/HfSiON interfaces. Further tunability in Vfb has been examined by employing C-incorporation in the RuMo alloy, thus reducing the crystal grain size and facilitating the control of Vfb for a HfSiON (2 nm)/SiO2(0.7 nm)/Si capacitor. These results demonstrate that the crystal structure control in metal gates is essential for realizing the MIS-FET devices with a short gate length in the 32-22 nm node and beyond.

The x-ray interference technique has been applied to evaluate the structural changes of high temperature grown chemical vapor deposited (CVD) SiO2 film under several post annealing conditions. In annealing above 800 °C in O2 ambient, a thermal oxide growth has been found at the CVD SiO2/Si interface, and its precise thicknesses have been determined. The estimated diffusion coefficient of the oxidant in CVD film was about three times larger compared to that of thermal oxide. A threshold voltage shift in the oxide was found to strongly correlate to the thickness of the thermal oxide rather than to thermal modifications of the CVD SiO2 itself.

Removal of surface oxides from a partially oxidized Si(111) surface, and simultaneous termination of the new dangling bonds by hydrogen in hot water with a 0.004 ppm concentration of dissolved oxygen, was observed. During removal for up to 60 min, vertical dihydrides at step edges appeared on the hydrogen‐terminated surface. From observing selective removal of vertical dihydrides from an oxygen‐free hydrogen‐terminated surface, the appearance of vertical dihydrides at step edges shows the existence of the dihydride creation reaction, while the oxides are dissolved in water.

Demonstrated the high-performance and high-reliability of ultra-thin poly-Si-gated SiN/HfO/sub 2//SiON high-k stack dielectrics. A SiN layer deposited on HfO/sub 2/ is shown to be indispensable to the suppression of the reaction of poly-Si and HfO/sub 2/, resulting in high thermal stability (1050/spl deg/C). This thermally stable SiN/HfO/sub 2//SiON structure can achieve an ultrathin oxide thickness of T/sub eff//sup inv/ (effective oxide thickness measured in strong inversion region) for 1.7 nm, which is less than 1 nm for EOT. A low leakage current of 5 to 6 orders of magnitude lower than that of SiO/sub 2/ was observed. In addition, this thermal stability can lead to high reliability, which includes TDDB and hot electron integrity.

We have fabricated 55-nm poly-Si gated n- and p-MOSFETs with HfO/sub 2/ gate dielectric of 3-nm physical thickness deposited by atomic layer deposition (ALD). A conventional CMOS process was used with high-temperature S/D anneal of /spl ges/1000/spl deg/C, cobalt-silicide and pocket implants. The devices showed very promising characteristics for low standby power applications due to drastic reduction of gate leakage current.

A significant improvement in ultra-thin (4 nm) gate oxide quality has been carried out using UV/O/sub 3/ pre-treatment of native oxide before thermal oxidation. UV/O/sub 3/ pre-treatment makes native oxide dense and close-packed without leaving any residue species. Ultra-thin gate oxide formed by UV/O/sub 3/ pre-treatment and O/sub 3/ oxidation has been found to have excellent behavior, low leakage current, low surface state density, and superior dielectric breakdown characteristics. UV/O/sub 3/ pre-treatment looks promising for using in ultra-thin gate oxidation necessary for 0.1 /spl mu/m ULSI fabrication.

We report on the nMISFETs (n-type metal-insulator-semiconductor field effect transistors) characteristics for the atomic layer chemical vapor deposition (ALCVD) HfO/sub 2/ gate stack and the behavior of the HfO/sub 2/ layer during annealing on various oxides.

Epitaxial silicon film is deposited on a Si(100) substrate by synchrotron radiation irradiation. Reflection high‐energy electron diffraction and high‐resolution transmittance electron microscopy observation reveal that epitaxial growth can be realized at temperatures as low as 100 °C. At substrate temperatures above 300 °C, the films show a clear 2×1 reconstructed surface, indicating a fairly good crystal quality. Below 500 °C, the growth rate increases as the substrate temperature is lowered, meaning that the surface adsorption of source gas and/or photogenerated radicals plays an important role in the epitaxial growth reaction.

The reaction between the H-terminated Si surfaces and H2SiF6 solution, which is a reaction product of the dissolving SiO2 in the HF solution, was examined. The H2SiF6 solution selectively oxidized the mono-hydride on Si and degraded the hydrophobicity of the surface, while the di-hydride on Si remained stable in the solution. These results explained the crystal orientation dependence of the oxide removal from the Si surface.

Fourier transform infrared attenuated total reflection method was employed to observe Si surfaces during wet chemical treatments. We observed the time evolution of the surface chemical structure during the oxidizing of hydrogenated Si surfaces in such oxidants as ozonized water and hydrogen peroxide using (100) and (111) surfaces. We also examined the adsorption of surfactants which were introduced in an HF solution. The interaction of adsorbates at the interface and with molecules in a liquid phase was discussed based on our in situ observations.

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In order to grow silicon films with good crystal quality, it is important to remove oxygen and carbon contaminants on the surface and to obtain clean substrate surface immediately before growth. In conventional surface cleaning process, silicon substrate is heated up to about 1000°C and the surface contaminants are evaporated or gas-etched from the substrate surface. However, such high temperature treatment causes the redistribution of impurity atoms in the substrates and it makes difficult to fabricate fine structures. Recently, synchrotron radiation (SR) stimulated evaporation of SiO2 film and its application to surface cleaning at 650°C have been reported1), and the usefulness of SR induced reactions for low-temperature process is being recognized.