Kumi Motai

Scanning tunneling microscopy observation of copper-phthalocyanine molecules on Si(100) and Si(111) surfaces

Abstract Molecules of Cu-phthalocyanine (CuPc) deposited on Si(100) and Si(111) surfaces have been observed by an ultra high vacuum field ion scanning tunneling microscope (FI-STM). On a Si(100) surface, STM images with four-fold symmetry are observed, which reflect the shape of the CuPc molecule. The STM pictures show that CuPc molecules are deposited with the molecular plane parallel to the substrate surface and have three kinds of adsorption configurations on the dimer-row of Si(100). The images of the CuPc are modified by the electronic state of the Si(100) surface. This behavior suggests strong interaction between the molecule and the substrate. The molecular images on the Si(111) surface have a unique bias-voltage dependence. At a sample bias of 1.6 V, the molecule looks transparent by STM, and becomes dark like a vacancy at 1.2 V. From the bias dependence, the electronic interaction between the CuPc molecule and the Si surface is discussed.

Scanning tunneling microscopy of oxygen adsorption on the Ag(110) surface

Our high-performance UHV-mode FI-STM/STS (field ion-scanning tunneling microscopy/spectroscopy) was used for the analysis of oxygen adsorption on the Ag(110) clean surface. When the surface was exposed to oxygen, one-dimensional linear chains with various separation widths were observed, corresponding to the (n × 1) LEED patterns. It was concluded that these linear chains consist of AgOAg components, similar to the case of the Cu(110)O system.

Field ion-scanning tunneling microscopy study of the Ag(110)-O system

Atomic-resolution scanning tunneling microscope (STM) images of the Ag(110) clean surface were obtained successfully using a high-performance UHV-mode FI-STM. When the surface was exposured to oxygen, one dimensional linear chains with various separation widths were observed, corresponding to the (n×1) LEED patterns. It was concluded that those linear chains consist of Ag O Ag components, similar to the case of the Cu(110)-O system.

C60 grown on the Cu(111)1×1 surface

C60 molecules adsorbed on the Cu(111)1×1 surface have been investigated by the field ion-scanning tunneling microscope (FI-STM). C60 molecules initially segregate to the terrace edges and grow, with increasing coverages, into a monolayer film with the close-packing fcc(111) configuration which results in a 4×4 overlayer phase. Highly featured STM images of C60 adsorbate have been observed and interpreted for the first time based on the local density of the states of C60 adsorbed on the surface. Based on various STM images as a function of the bias voltage, four possible C60 adsorption geometries are determined.

STM of the Cu(111)1×1 surface and its exposure to chlorine and sulfur

Abstract Surface reconstructions of the Cu(111)1 × 1 surface induced by chlorine and sulfur adsorption have been studied by field ion-scanning tunneling microscopy. Atomically resolved high-quality STM images were obtained and structural analysis was carried out for various phases as a function of coverage. The differences between the chlorine and the sulfur adsorption system are discussed.

Atomic hydrogen cleaning of surface Ru oxide formed by extreme ultraviolet irradiation of Ru-capped multilayer mirrors in H2O ambience

Atomic hydrogen generated by a heated catalyzer was used to clean Ru-capped extreme ultraviolet (EUV) multilayer mirrors, the surface of which was oxidized by EUV irradiation in an H2O ambience. An analysis of the change in surface composition by X-ray photoelectron spectroscopy (XPS) revealed that atomic hydrogen deoxidized the Ru oxide to metal. The EUV reflectivity of a multilayer mirror degraded by EUV-induced oxidation was almost restored, with only a marginal change in centroid wavelength within the measurement error. This indicates that the atomic hydrogen cleaning is a promising method of prolonging the lifetime of the multilayer optics of EUV lithography.

Homo-epitaxial growth on the Si(111) 7 × 7 surface

Abstract The initial stage of silicon growth on the Si(111)7 × 7 surface is investigated by a field ion scanning tunneling microscope (FI-STM) as a function of substrate temperature. It is found that structures of growth nuclei depend on the substrate temperature and most of the nucleations occur randomly at a faulted half of the unit cell of the dimer-adatom-stacking-fault (DAS) structure. It appears that coalescence between growth nuclei occurs rarely at low temperatures. At the substrate temperature of 300°C, characteristic figures of a cluster structure are found on the surface at submonolayer deposition. Most of the clusters are grown symmetrically with respect to the dimer rows of the DAS structure. The half segment of the symmetric cluster is also formed on the surface. Since crystal nuclei smaller than this cluster are scarcely observed in the STM images, it is concluded that the cluster is the smallest unit of the nuclei of homo-epitaxial growth at about 300°C. From the STM image analysis it is concluded that the structure of the cluster is not made of DAS-type structure, but a structure including dimers and/or pyramidal clusters. Structure analysis of the cluster is underway. At and above 300°C, small islands of 5 × 5 DAS structure are frequently observed on nucleation clusters. In large islands, however, a 5 × 5 structure is rarely observed, and a regular 7 × 7 is observed. This suggests that the transition from 5 × 5 to 7 × 7 structure occurs during the island growth. At temperatures higher than 500°C, step flow growth with 7 x 7 structure is observed as well as a few parts of island growth including 5 × 5 structure.

The Effect of Isopropyl Alcohol Adsorption on the Electrical Characteristics of Thin Oxide.

The effect of isopropyl alcohol (IPA) adsorption on the electrical characteristics of thin oxide has been investigated. Metal-oxide-semiconductor (MOS) capacitors were fabricated on Si substrates after IPA was intentionally adsorbed on the substrate surfaces. The leakage current was raised in the low electric field region for the 5-nm-thick thin oxide due to increased IPA adsorption, but the leakage current was not affected in the 8- and 10-nm-thick oxides. Using X-ray photoelectron spectroscopy, we found that the heat treatment creates C-Si bonds in the oxide due to organic adsorbates including IPA. These bonds appear likely to cause weak points or prevent uniform oxidation. A pre-annealing treatment was found to be effective in suppressing the formation of the C-Si bonds.

Analysis of printability of scratch defect on reflective mask in extreme ultraviolet lithography

The aim of this study was to investigate the printability of a scratch defect on the surface of a glass substrate. Simulations revealed that smoothing deposition made a scratch more printable than non-smoothing deposition did. Smoothing deposition changes the topography of a scratch by making it shallower and wider as it propagates from the bottom to the top of a Mo/Si multilayer on a reflective mask blank. This change in topography shifts the phase, thereby reducing the energy of light reflected from the mask. In contrast, non-smoothing deposition preserves the topography of a scratch from the bottom to the top of a multilayer. As a result, non-smoothing deposition changes the phase less than smoothing deposition does, which makes a scratch less printable. An analysis of the intensity of diffracted rays clarified how much of the energy used to create a printed image was lost at the pupil due to a defect: The energy loss was approximately 10 times larger for smoothing than for non-smoothing deposition; and thus, the change in the critical dimension of a printed image on wafer was also much larger for smoothing deposition.

Surface structure of selenium‐treated GaAs (001) studied by field ion scanning tunneling microscopy

For a selenium‐treated GaAs (001) surface followed by heat treatment at ∼530 °C, we have observed using field ion scanning tunneling microscopy ordered arrays with regular intervals of 4×periodicity in the [110] direction (1.6 nm) to line up in the [110] direction. These ordered arrays are in good agreement with the 4×1 structure previously observed by other methods. In a closer view, the 4×structure was found to be formed by closely placed double rows.