Dependence of chemical structures of transition layer at SiO 2 /Si(100) interface on oxidation temperature, annealing in forming gas, and oxidizing species Tomoyuki Suwa 1 , Akinobu Teramoto 1 , Takayuki Muro 2 , Toyohiko Kinoshita 2 , Shigetoshi Sugawa 1,3 , Takeo Hattori 1 , Tadahiro Ohmi 1 1 New Industry Creation Hatchery Center, Tohoku University, 6-6-10, Aza-Aoba, Aramaki, Aoba-ku, Sendai, Japan Phone: +81-22-795-3977 E-mail: suwa@fff.niche.tohoku.ac.jp 2 Japan Synchrotron Radiation Research Institute 3 Graduate School of Engineering, Tohoku University Introduction The chemical structures of 0.5-nm-thick composi- tional transition layer (CTL) formed at SiO 2 /Si(100) inter- face [1] have been studied extensively [2,3] because of their significant influence on the performance of Si-based devices. However, the dependences of chemical structures of CTL stabilized by more than one monolayer of SiO 2 on oxidation temperature, annealing in forming gas, and oxi- dizing species were not clarified yet and is the subject of the present study using angle-resolved photoelectron spec- troscopy (ARPES) at photon energy of 1050 eV. Experimental Results and Discussion Figure 1(a) shows the Si 2p 3/2 spectra measured at photoelectron take-off angles at vacuum/oxide interface (TOAs) of 15 and 85 arising from the interface formed in dry O 2 at 900 C. Figure 1(b), in which the spectra arising from Si-O 4 (Si 4+ ), Si-Si-O 3 (Si 3+ ), Si + , Si 2 -Si-O 2 (Si 2+ ), Si + , Si 3 -Si-O (Si 1+ ), Si substrate (Si 0 ), α-Si, β-Si, and γ-Si are resolved, is obtained by taking difference between two spectra in Fig. 1(a), to eliminate the spectrum arising from the bulk Si after multiplying the spectrum measured at a TOA of 85 by an appropriate factor. Here, α-Si, β-Si were found to arise from Si substrate.[3] The α-Si are considered to be affected by its second nearest neighbor O atoms.[4] Because the binding energy (BE) of Si 2+ > BE of Si + > BE of Si 1+ can be explained by considering the influence of second nearest neighbor O atoms on Si 1+ , Si + is considered as Si 1+ in the analyses of the spectra. Also, because BE of Si 3+ > BE of Si + > BE of Si 2+ can be explained by consid- ering the influence of second nearest neighbor O atoms on Si 2+ , Si + is considered as Si 2+ in the analyses of the spectra. Figures 2(a) and 2(b) show TOA dependences of I 0 /I 1+ , I 1+ /I + , I + /I 2+ , I 2+ /I + , I + /I 3+ , I 0 /I 4+ , I  /I 1+ , I  /I 1+ , and I  /I 1+ measured for the interface formed in dry O 2 at 900 C and those measured for the interface formed using oxygen radicals at 400 C, respectively. Here, I 0 , I 1+ , I + , I 2+ , I + , I 3+ , I 4+ , I  , I  , and I  denote the integrated intensity of the Si 2p 3/2 spectrum arising from Si 0 , Si 1+ , Si + , Si 2+ , Si + , Si 3+ , Si 4+ , -Si, -Si, and -Si, respectively. Because I 1+ /I + and I + /I 2+ are almost independent on TOA in Fig. 2(a), Si 1+ , Si + , and Si 2+ must be localized in the same layer, and form the first CTL (FCTL) with Si 0 , a part of which forms dimer bonds [5]. Also because I + /I 3+ are almost independent on TOA in Fig. 2(a), Si + and Si 3+ must be localized in the same layer and form the second CTL (SCTL) with Si 4+ . Here, TOA dependence of I 2+ /I + , which suggests the spacing of 0.23 nm (> 0.136 nm) between the layer containing Si 2+ and that cotaining Si + , is considered. The same compositions of FCTL and SCTL are also obtained for interfaces formed in dry O 2 at 1000 and 1050 C, that formed in dry O 2 at 900 C followed by annealing in forming gas at 400 C (FGA). Thicknesses of SiO 2 layers denoted by d formed on SCTL in dry O 2 at 900, 1000, and 1050 C, and that formed in dry O 2 at 900 C followed by FGA are 0.58, 0.36, 0.44, and 0.61 nm, respectively. 0 1.0 2.0 3.0 4.0 -1.0 5.0 6.0 -2.0 Binding Energy (eV relative to bulk Si 2p 3/2 ) Intensity (Arb. Units) (a) TOA = 85 TOA = 15 h = 1050 eV Si 2p 3/2 Intensity (Arb. Units) (b) 0 1.0 2.0 3.0 4.0 -1.0 Binding Energy (eV relative to bulk Si 2p 3/2 ) A Si 2+ B Si 1+ γ-Si β-Si α-Si Si 3+ Si ν+ Si μ+ Si 0 Si 4+ FIG. 1. (a) Si 2p 3/2 spectra arising from interface formed in dry O 2 at 900 °C measured at photon energy of 1050 eV and photoelectron take-off angles (TOAs) of 15° and 85°, (b) spectrum obtained by taking difference between two spectra in (a) to eliminate spectrum arising from bulk Si. Figure 2 was analyzed by considering that one monolayer of Si 4+ , that of SCTL, that of FCTL, and that of Si 0 are continuosly connected with each other. For these analyses the volume of Si n+ denoted by 1/c n+ , the thickness of hypothetical monolayer consisting of Si n+ denoted by t mn+ , and the inelastic mean free path in hypothetical bulk Si n+ denoted by  n+ are defined as follows by considering that Si n+ (n = 1, 2, 3) can be expressed as Si {1 –(n/4)} (SiO 2 ) (n/4) . Firstly, 1/c n+ is defined by eq. (1) as follows using c 0 (den- sity of Si atoms in Si 0 ) = 5×10 28 m -3 and c 4+ (density of Si atoms in Si 4+ in structural transition layer) = 2.38×10 28 m -3 . Secondly, t mn+ is defined by D 100 /c n+ using c n+ . Here, D 100 denotes areal density of Si atoms on Si(100) and takes a value of 6.8×10 18 m -2 . Furthermore, if the oxidation- induced volume expansion occurs perpendicular to the in- terface by a factor of (1/c 4+ )/(1/c 0 ) = 2.10, t m4+ takes a value -28- Extended Abstracts of the 2012 International Conference on Solid State Devices and Materials, Kyoto, 2012, pp28-29 PS-1-11