S. Iida

Ti thin-film reaction on SiO2/Si

Abstract This paper discusses 500 A thick SiO 2 layers formed on Si substrates having a crystal surface of (100), (110) or (111), and their reactions with Ti films which are deposited on the layers at room temperature (RT) in UHV. In situ inspections were carried out, from RT to 800°C, on the reacted film composition and film structure with AES and LEED, respectively. RBS, XRD and XPS were also used to analyze the interface, reacted components and formation energies. Results showed that Ti films do indeed react with SiO 2 layers at RT, and when annealed at 800°C, their reacted components show different characteristics depending on the crystal surface of the substrate. The dependency on the crystal surface is explained using a simple calculation method of obtaining the minimum number of bonds of surface atoms.

Auger electron spectroscopy of super-doped Si:Mn thin films

Abstract Thin films of Si heavily doped with Mn impurities at nonequilibrium doping levels have been successfully prepared by Laser-Ablation MBE. The electronic structure of Mn-doped Si thin films have been investigated by Auger Valence Electron Spectroscopy (AVES). The peak positions of Mn[3p,V,V] (V=3d) Auger spectra of Si:Mn thin films were located at the higher energy region than those of pure Mn and Mn 5 Si 3 compound. For the Si:Mn thin film grown on SiO 2 /Si(001) substrate, the new Auger peak was observed around 50 eV. The changes of the line shape were observed in Mn[L,M,M] (L=2s,2p; M=3s,3p,3d) Auger spectra of Si:Mn thin films compared with those of pure Mn and Mn 5 Si 3 compounds. In the Mn[2s,M,V] (M=3s,3p,V=3d) spectra for Si:Mn thin films, the new peaks were appeared around 700 eV. These new peaks were considered to arise from the new split of the 3d electron states due to the formation of the Mn–Si bonds in Si:Mn thin films.

Resistance Change in Thin Ag Film on Si (100)

We have been involved in studying the resistance change of thin Ag film formed on Si substrate at room temperature and at 473 K in UHV. In those studies, using a four terminal method, we measured the periodic resistance change in Ag thin film while film thickness was increased up to 2 nm. Recently, we have been studying film resistance in more detail, namely, how it changes in relation to increase in Ag film thickness at room (300 K) and low (50 K) temperatures. In the former case it was found that film resistance maintained a constant value for Ag thicknesses up to 20 nm and that thereafter resistance decreased monotonously with increase in film thickness. This suggests that electron conduction is mainly limited to Si substrate and is not caused by an increase in the size of Ag islands, consequently, a Schottky barrier which is electrically separated appears between the Ag islands and Si surface. After enough film thickness the islands become connected with each other and make electrical paths. In the case of low temperature, film resistance could not measured until the film thickness reached 2 nm because Si substrate showed too high resistance. When film thickness was greater than 2 nm, resistance was found to decrease monotonously with increase in film thickness. It is suggested that the Ag particles tend to stay where they initially precipitated. After a large amount of Ag particles have precipitated on to the Si surface, they form a lot of very small islands and, consequently, electrical conduction appears in very thin film.

Valence states analysis of Ca and Si in CaSi 2 during CaSi 2 –H 2 O reaction

The changes in the valence electron states of CaSi 2 during the chemical reaction with H 2 O have been investigated by Auger Valence Electron Spectroscopy (AVES). In order to study the reaction process, the reaction was precisely controlled by applying dc voltage between Pt electrode and CaSi 2 specimen. The Si[2 s , 2 p ,V] Auger spectra of CaSi 2 specimen remain unchanged under the applied voltage lower than −15 V relative to the Pt electrode in H 2 O. At higher applied voltage, 3 p components of Si[2 s , 2 p , V] (V = 3 s , 3 p ) Auger spectra get weak while the 3 s components increase drastically. The peak position due to Ca[2 p , 3 p , 3 p ] transitions gradually shifted toward the lower energy side by raising the applied voltage. The peak shift is due to the formation of Ca–O bonds in CaSi 2 . A new peak, which arises from the split of the valence electron states in Ca atoms due to the Ca–O bonds, appeared in Ca[2 p , 3 p ,V] Auger spectra for CaSi 2 after the reaction with H 2 O.

Thin Ag film formation onto Si/SiO2 substrate

A thin Ag film, which was formed on an insulator substrate using the ion beam deposition method, has an insufficient structure by the electro-migration effect caused by the electric charge left in the film. In contrast to the ion beam deposition method, the result was satisfactory when direct current flows were applied to the film during its forming. The results of an SiO 2 substrate were better than those for a Pyrex glass (PG) substrate. Using the direct current method, we formed a thin Ag film onto an SiO 2 substrate of 55 nm thickness and 1.0 nm native oxide. Experiments were carried out with a base pressure of 1.5 x 10 7 Pa at room temperature (RT). and film was examined using X-ray diffraction (XRD). Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM).

Thermal reactions of thin Ti films with sapphire substrates

The interaction of Ti with a sapphire substrate under UHV conditions was investigated using AES, LEED, XRD and STM. Ti was deposited under UHV conditions onto a sapphire crystal plate substrate at room temperature, with the last deposition being followed by in situ annealing. It was subsequently observed that Ti interacted with the sapphire at room temperature and formed TiO2 at the interface. Additionally, it was found that when Ti was annealed at a temperature of 800°C, crystallization of TiO proceeded at the Ti/TiO2/Al2O3 interface.

Valence-electron spectral change and charge transfer mechanism of CaSi2 during CaSi2H2O reaction

Abstract The changes in the valence electron states of CaSi 2 during the chemical reaction with H 2 O have been investigated by Auger valence electron spectroscopy (AVES). The drastic changes in the valence electron spectra of 3s and 3p states, which are caused by the oxidization of the Si atoms in CaSi 2 , were observed in Si[2s, 2p, V] spectra for CaSi 2 after the reaction. In particular, the Si[2s, 2p, V] spectra of CaSi 2 samples reacted with H 2 O at 60 or 80°C for 3 h were almost similar to that of SiO 2 . The peak shift of Ca[2p, 3p, 3p] Auger transition toward the lower energy side has been observed, suggesting the formation of bonds between Ca 3p and O orbitals. New peaks due to CaO or CaOH bonds also appeared in the valence electron region of Ca[2p, 3p, V] Auger transition. The charge transfer and the chemical-bond formation can be well demonstrated by AVES during the CaSi 2 H 2 O reaction.

Structural evolution and valence electron-state change during ultra thin silicon-oxide growth

Abstract We have studied valence electron-state changes of Si during initial oxidation of Si(111) clean surface, HF-treated Si(001) and Si(111) surfaces by Auger valence electron spectroscopy (AVES). The results showed that the valence electron-state changes during initial oxidation were sensitively reflected in Si[2s,2p,V] (V=3s,3p) AVES spectra and that they depended on both initial surface treatment and surface orientation. The local valence electron-states, local density of states in other words, showed the characteristic-structure evolution depending on the initial surface treatment and surface orientation.

Effects of Ag Thickness and Deposition Temperature on Prevention of Cu Diffusion in Cu/Ag/Si System

The introduction of copper (Cu) wiring or electrodes for LSI is advanced by using a buffer layer of a material such as SiO2, TiN or TiSiN to prevent the formation of copper silicide on a silicon (Si) substrate. When metal silver (Ag) serves as a buffer between Cu and a Si substrate, the Cu might remain stable on the Ag film. A fundamental study was performed on the necessary Ag thickness for preventing Cu diffusion into the Si substrate at room temperature and 300°C; the effect of lapse time after deposition was also studied. When Ag was deposited on the Si substrate with a thickness of less than 22 nm at room temperature, Ag islands with nearly round shapes were formed and many gaps were observed between them. Cu deposited on the Ag film reached the Si surface through these gaps and diffused into the Si substrate. When the Ag film was more than 30 nm thick, the Ag islands increased in size, the Ag film became thicker, and they came into contact with each other. The gaps between the Ag islands also narrowed, preventing the diffusion of Cu. The depth profile of the Cu deposited six months prior showed no change. When the deposition was carried out at a temperature of 300°C, Ag islands grew into tall three-dimensional (3D) islands, and the gaps between them broadened. Cu diffused deeply into the Si substrate.

A study of surface resistance of Si(100)

Although a Si(100) surface forms dimers to produce a stable structure, it contains defects such as steps which are thought to affect surface resistance. We measured the surface resistance of step-containing Si manufactured by an ordinary process, and discovered that Si exhibits angular characteristics (anisotropy). After performing measurements at 10° intervals over two revolutions of 360°, we found that the results are reproducible between the first and second turns, that the resistance is periodic with periods of 180° and 360°, and that the sheet resistances measured by the four-point-probe method are 7–13-fold greater than those calculated from the bulk resistance and thickness of the samples. Similar measurements were performed on step-free Si surfaces, which were found to exhibit almost no periodicity and had a sheet resistance is of 4–10-fold the bulk value. It was suggested that the periodicity of resistance is caused by the presence of many steps on the Si surface.