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

Abstract The effect on the local valence electronic states of Si n + suboxide components ( n  = 2, 3, and 4) of hafnium deposited on a low-index Si(110) substrate is investigated by Si- L 23 VV Auger electron Si n + -2 p photoelectron coincidence spectroscopy (Si- L 23 VV -Si n + -2 p APECS), and the chemical states and stabilities are discussed. Hafnium-covered Si(110) is immediately oxidized to HfO 2 and SiO 2 because hafnium serves as an effective catalyst for Si oxidation. Therefore, a HfO 2 /Si n + -(sub)oxide/Si(110) [HfO 2 /Si n + /Si(110)] structure is easily formed ( n  = 1, 2, 3, and 4). Oxygen diffusion from HfO 2 layers toward the Si(110) substrate is promoted by annealing at 923 K. Oxygen atom desorption from the HfO 2 /Si n + /Si(110) surface occurs after annealing at 1073 K, and HfSi 2 islands ( i -HfSi 2 ) are formed with a partly exposed Si(110)-16 × 2 double domain (DD) surface. i -HfSi 2 shows low reactivity toward O 2 molecules, whereas the exposed Si(110)-16 × 2 DD surface is immediately oxidized. Here, a i -HfSi 2 /Si n + -(sub)oxide/Si(110) ( i -HfSi 2 /Si n + /Si(110)) structure is formed. Furthermore, we measure the Si- L 23 VV -Si n + -2 p APECS spectra of Si n + in the HfO 2 /Si n + /Si(110) and the i -HfSi 2 /Si n + /Si(110) structures ( n  = 2, 3, and 4) to evaluate the local valence electronic states of the Si n + (sub)oxide components. The binding energy at the valence band maximum ( BE VBM ) of Si n + in the i -HfSi 2 /Si n + /Si(110) structure is lower than 1.5 ± 0.7 eV as compared to that in the HfO 2 /Si n + /Si(110) structure ( n  = 2, 3, and 4). The local valence electric states of the nearest neighbors and the second neighbors through oxygen of Si n + are determined to affect those of the Si n + atom ( n  = 2, 3, and 4). The Si n + atoms in the i -HfSi 2 /Si n + /Si(110) structure can directly bond to hafnium atoms as the nearest neighbors and most commonly have Si m + atoms in lower ionic valence states as second neighbors ( m n + atoms in the HfO 2 /Si n + /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 HfO 2 /Si(110) structure.