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Kakiuchi, Takuhiro*; Matoba, Tomoki*; Koyama, Daisuke*; Yamamoto, Yuki*; Yoshigoe, Akitaka
Langmuir, 38(8), p.2642 - 2650, 2022/03
Times Cited Count：1 Percentile：13.58(Chemistry, Multidisciplinary)0xidation processes at the interface and the surface of Si(111) substrate with thin Hf films were studied using photoelectron spectroscopy in conjunction with supersonic oxygen molecular beams (SOMB). The oxidation starts at the outermost Hf layers and produces stoichiometric HfO
. Hf silicates (Hf-O-Si configuration) were generated in the vicinity of the HfO/Si interface in the case of the irradiation of 2.2 eV SOMB. The oxidation of the Si substrate takes place to generate SiO compounds. Si atoms were emitted from the SiO/Si interface region underneath the HfO overlayers to release the stress generated within the strained Si layers. The emitted Si atoms can pass through the HfO overlayers and react with the impinging O gas.
7 surface using high-resolution core-level photoelectron spectroscopyKakiuchi, Takuhiro*; Matoba, Tomoki*; Koyama, Daisuke*; Yamamoto, Yuki*; Kato, Daiki*; Yoshigoe, Akitaka
Surface Science, 701, p.121691_1 - 121691_8, 2020/11
Times Cited Count：1 Percentile：5.82(Chemistry, Physical)Ultrathin hafnium films on Si(111)-77 were studied using synchrotron radiation photoelectron spectroscopies to reveal the chemical states at interface and surface. Ultrathin Hf layers grow on clean Si(111)-77 surface by lever rule. Surface and interface of Hf/Si(111) contain three components (metallic Hf layers, Hf monosilicide (HfSi) and Si-rich Hf silicide). Ultrathin Hf layers changes HfSi islands on bared Si(111)-77 surface after annealing at 1073 K. It was found that the long axes of the rectangle islands expand the direction connecting the corner holes in DAS model of clean Si(111)-77 surface.
1 surfaces studied using core-level X-ray photoelectron spectroscopyKakiuchi, Takuhiro*; Yamasaki, Hideki*; Tsukada, Chie*; Yoshigoe, Akitaka
Surface Science, 693, p.121551_1 - 121551_8, 2020/03
Times Cited Count：3 Percentile：19.14(Chemistry, Physical)We investigated the initial oxidation of ultrathin hafnium (Hf) film on Si(100)-21 using photoelectron spectroscopy. Metallic Hf rapidly oxidized, transforming into hafnium dioxide (HfO) and its suboxides. The other HfSi component at the interface was nearly unreactive with O molecules. These facts suggest that the metallic Hf component plays a vital role in the initial oxidation of the ultrathin Hf/Si(100) film. After annealing from 873 K to 973 K, the Hf suboxides in low ionic valences progressed into fully oxidized HfO. Once the annealing temperature reached c.a.1073 K, oxygen atoms were entirely removed from the ultrathin HfO/Si(100) film containing SiO at the interface. Simultaneously, ultrathin HfO layers changed into islands of Hf disilicide (
-HfSi) on a bare Si(100)-21 surface. The -HfSi component showed slight reactivity with O molecules at 298 K. In contrast to the initial oxidation of clean Si(100)-21 surface, the dangling bonds on bare Si(100)-21 surface among -HfSi oxidized preferentially.
Nagaoka, Shinichi*; Fukuzawa, Hironobu*; Pr
mper, G.*; Takemoto, Mai*; Takahashi, Osamu*; Yamaguchi, Takuhiro*; Kakiuchi, Takuhiro*; Tabayashi, Kiyohiko*; Suzuki, Isao*; Harries, J.; et al.
Journal of Physical Chemistry A, 115(32), p.8822 - 8831, 2011/07
Times Cited Count：29 Percentile：70.92(Chemistry, Physical)2 single domain surface studied by low energy electron diffraction and electron spectroscopyKakiuchi, Takuhiro*; Katsuragi, Takuma*; Nakano, Yuji*; Yoshigoe, Akitaka; Nagaoka, Shinichi*; Mase, Kazuhiko*
no journal, ,
HfO has been becoming important as a future dielectric material for future metal-oxide-semiconductor devices. In this study, surface structure, surface chemical state, and valence electronic structure after oxidation of single domain Si(110)-162 surface have precisely measured by using low-energy-electron diffraction and synchrotron radiation photroemission spectroscopy. It was found that five possible adsorption sites (SC1-SC5) of the single domain Si(110)-162 surface are uniformely reacted with Hf atoms with increasing its exposure, indicating that random Hf adsorption takes place on the surface.
Kakiuchi, Takuhiro*; Anai, Ryota*; Saiki, Taiju*; Tsuda, Yasutaka; Yoshigoe, Akitaka
no journal, ,
Initial oxidation mechanism of hafnium adsorbed Si(111)-77 [Hf-Si(111), the thickness of Hf:0.5 monolayer] was studied by synchrotron radiation X-ray photoelectron spectroscopy. The individual Hf atoms were associated with the back bonds of Si rest atoms or Si adatoms on Si(111)-77, and the Hf monosilicide HfSi) unit was formed on the outermost surface. Following the HfSi units immediately reacted with the thermal O molecules [translational energy (Et=0.03eV], Hf silicates (Hf-O-Si) were produced. In addition, some dissociated O atoms were inserted between the adsorbed Hf atoms. As a result, Hf sub-oxides/silicates up to 3+ states were formed. When a non-equilibrium condition was induced by irradiation of the supersonic O molecular beam of Et = 0.39 eV, the Hf4+ state was confirmed along with and the oxidation of Si bulk. This indicates that there is an activation energy to oxidize the Hf-Si bonds of the bulk side.
Kakiuchi, Takuhiro*; Tsuda, Yasutaka; Yoshigoe, Akitaka
no journal, ,
HfO has attracted much attention as a high-k gate dielectric material for Si semiconductor devices. In this study, oxidation by O gas exposure (Et: 0.03 eV) and supersonic O molecular beams (Et: 0.39, 2.2 eV) on Si(111) with different amounts of Hf adsorbed at about 0.5 and 2.0 ML were observed and analyzed by Hf4f, Si2p and O1s photoelectron spectroscopy. At low coverage of 0.5 ML, Hf adsorbs on rest-atoms and adatoms on Si(111)-77 to form a peculiar local structure (hexagonal structure), around which oxidation proceeds only to Hf
silicate. At 2.0 ML, on the other hand, the oxidation reaction proceeds rapidly over the entire surface metal Hf layer and is considered to produce up to Hf
silicate.
