Local valence electronic states of silicon (sub)oxides on HfO2/Si-(sub)oxide/Si(110) and HfSi2/Si-(sub)oxide/Si(110) Islands

• Published in: Surface science Vol. 681; pp. 9 - 17
• Main Authors: Kakiuchi, Takuhiro, Ikeda, Kyouhei, Mase, Kazuhiko, Nagaoka, Shin-ichi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2019; Elsevier BV
• Subjects: Annealing; Auger photoelectron coincidence spectroscopy; Chemical bonds; Diffusion layers; Electron states; Hafnium oxide; High-dielectric-constant material; Islands; Local valence electronic states at surface and interface; Metal-insulator-semiconductor structure; Organic chemistry; Oxidation; Oxygen; Photoelectrons; Silicides; Silicon dioxide; Silicon substrates; Spectrum analysis; Synchrotron radiation; Valence band; X-ray photoelectron spectroscopy; Auger photoelectron coincidence spectroscopy; Metal-insulator-semiconductor structure; High-dielectric-constant material; Local valence electronic states at surface and interface; X-ray photoelectron spectroscopy; Synchrotron radiation
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2018.10.024

•Hafnium-covered Si(110) is immediately oxidized up to HfO2 and SiO2.•Ultrathin hafnium deposition film acts as effective catalysis for Si oxidation.•Local valence electronic states are revealed by coincidence spectroscopy.•Local valence states at Si(sub)oxides are affected by the first neighbor atoms.•Local valence states at Si(sub)oxides are affected by the second neighbor atoms. The effect on the local valence electronic states of Sin+ suboxide components (n = 2, 3, and 4) of hafnium deposited on a low-index Si(110) substrate is investigated by Si-L23VV Auger electron Sin+-2p photoelectron coincidence spectroscopy (Si-L23VV-Sin+-2p APECS), and the chemical states and stabilities are discussed. Hafnium-covered Si(110) is immediately oxidized to HfO2 and SiO2 because hafnium serves as an effective catalyst for Si oxidation. Therefore, a HfO2/Sin+-(sub)oxide/Si(110) [HfO2/Sin+/Si(110)] structure is easily formed (n = 1, 2, 3, and 4). Oxygen diffusion from HfO2 layers toward the Si(110) substrate is promoted by annealing at 923 K. Oxygen atom desorption from the HfO2/Sin+/Si(110) surface occurs after annealing at 1073 K, and HfSi2 islands (i-HfSi2) are formed with a partly exposed Si(110)-16 × 2 double domain (DD) surface. i-HfSi2 shows low reactivity toward O2 molecules, whereas the exposed Si(110)-16 × 2 DD surface is immediately oxidized. Here, a i-HfSi2/Sin+-(sub)oxide/Si(110) (i-HfSi2/Sin+/Si(110)) structure is formed. Furthermore, we measure the Si-L23VV-Sin+-2p APECS spectra of Sin+ in the HfO2/Sin+/Si(110) and the i-HfSi2/Sin+/Si(110) structures (n = 2, 3, and 4) to evaluate the local valence electronic states of the Sin+ (sub)oxide components. The binding energy at the valence band maximum (BEVBM) of Sin+ in the i-HfSi2/Sin+/Si(110) structure is lower than 1.5 ± 0.7 eV as compared to that in the HfO2/Sin+/Si(110) structure (n = 2, 3, and 4). The local valence electric states of the nearest neighbors and the second neighbors through oxygen of Sin+ are determined to affect those of the Sin+ atom (n = 2, 3, and 4). The Sin+ atoms in the i-HfSi2/Sin+/Si(110) structure can directly bond to hafnium atoms as the nearest neighbors and most commonly have Sim+ atoms in lower ionic valence states as second neighbors (m < 4), whereas the Sin+ atoms in the HfO2/Sin+/Si(110) structure cannot form this bond. In addition, the existence of Hf silicide and Si in lower ionic valence states can reduce the band gap of the HfO2/Si(110) structure. [Display omitted]