To verify experimentally the unified Si oxidation reaction model mediated by point defect generation due to the oxidation-induced strain [1], real-time photoelectron spectroscopy using synchrotron radiation (687 eV) at SPring-8 was employed to monitor the oxidation-induced strained Si atom at SiO2/Si interface, and the oxidation state simultaneously during oxidation on n-type Si(001) surfaces with O2 gas.
O 1s and Si 2p photoelectron spectra were alternately obtained with 24 and 65 s, respectively, during oxidation. After subtracting a Shirley-type background and a Si 2p1/2 spin-orbit splitting component, Si 2p3/2 photoelectron spectra were curve-fitted with nine components; Si1+, Si2+, Si3+, and Si4+ for the oxidation states, and Siβ and Siα for the first- and second-strained-layer Si atoms below the SiO2/Si(001) interface, respectively, as suggested experimentally [2] and theoretically [3], S and SS for the up- and down-dimer atoms, and SiB for the Si substrate.
Upon introducing O2 gas at 300°C, both Siβ and Siα increase with time and then Siβ decreases gradually at first oxide layer coverage above ~75%, where S and SS almost disappear, and during second oxide layer growth, while Siα continues to increase, but with a decreased rate. It is found that the amount of fist and second strained Si atom at the completion of first oxide layer growth decrease gradually with raising temperature from 300 to 600°C, where oxide grows in the Langmuir-type adsorption manner. This result indicates that the oxidation-induced strain decreases with temperature. We will discuss the reason for the oxide coverage and oxidation temperature dependences of interfacial strain from view point of the behavior of adsorbed oxygen during first oxide layer growth [1].
[1] S. Ogawa et al., JJAP 44 (2005) L1048 and 46 (2006) 7063.
[2] S. Dreiner et al., JESRP 144-147 (2005) 405.
[3] O. V. Yazyev et al., PRL 96 (2006) 157601. |