Time-resolved two-photon photoemission study of silicon surface at initial stage of oxidation (original) (raw)
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Applied Surface Science, 2003
The initial oxidation on a Si(110)-16 Â 2 surface at room temperature and 540 C has been investigated by real-time X-ray photoemission spectroscopy (O 1s) using 687 eV photons. At both temperatures, the initial oxidation of Si(110) is characterized by its unique rapid oxidation regime immediately after the introduction of oxygen molecules. O 1s spectra are shown to consist of at least four oxidation states. It is likely that oxidation at or around the adatoms of pentagon pairs, reportedly present on the Si(110)-16 Â 2 reconstructed surface, is the predominant process in the very early stage of oxidation.
Photoemission study of the effect of bulk doping and oxygen exposure on silicon surface states
Physical Review B, 1974
The energy distribution of electrons photoemitted from the surface of ultrahigh-vacuum-cleaved silicon has been studied as a function of bulk doping and controlled oxygen exposure. The high sensitivity of surface states to oxygen has been utilized to observe the saturation of dangling bonds, identify the formation of the first monolayer of oxide, and to monitor the growth of the first few silicon dioxide layers. Comparison is made with the electron-spin-resonance signal. Recently we have reported the observation, ' using ultraviolet-photoemission and ultrahighvacuum techniques, of a band of surface states containing about one electron per surface atom on the cleaved (111)face of silicon. ' Eastman and Qrob
Japanese Journal of Applied Physics, 2003
The real-time photoemission measurements of the initial thermal oxidation on the Si(001) surface with O 2 gas (1 Â 10 À4 Pa) at the surface temperatures of 860, 895, 945 and 1000 K have been performed by using synchrotron radiation. In order to study the oxide-layer growth mode depending on the surface temperature, the time evolution of integrated peak area intensity of O-1s photoemission spectra was analyzed on the basis of the Langmuir-type and the auto-catalytic reaction kinetics models. It was found that the oxidation at 860, 895 and 945 K has progressed with the Langmuir-type adsorption. On the other hand, the oxidation at 1000 K has shown the characteristic of the auto-catalytic growth. We have succeeded in analyzing the reaction kinetics of thermal Si(001) oxidation by using the real-time in-situ O-1s photoemission measurements.
Japanese Journal of Applied Physics, 2007
High-resolution O 1s and Si 2p photoelectron spectroscopy using synchrotron radiation was employed to clarify a layer-bylayer oxidation reaction mechanism on a Si(001) surface from the viewpoint of point defect generation due to an oxidationinduced strain at a SiO 2 /Si interface. The Si and Si components in Si 2p 3=2 spectra, which are assigned to the first and second strained Si layers, respectively, below the transition layer composed of suboxides, Si 1þ , Si 2þ , and Si 3þ , significantly decrease during the step-by-step temperature increase-enhanced growth of the second oxide layer. Because of the corresponding band bending changes measured using the O 1s peak position, which are caused by defect-related band gap states, the observed decreases in Si and Si components, indicating a decrease in interfacial strain, are induced not only by the structural relaxation of a SiO 2 network due to a thermal annealing effect, but also due to the generation of point defects at the SiO 2 /Si interface. Continuous band bending changes with the growth of the third oxide layer also suggest that the point defects are generated during oxide growth, whereas the Si and Si components are maintained almost constant. On the basis of the observed interfacial strain and point defect generation changes, the layer-by-layer growth kinetics of the first, second and third oxide layers is discussed using a unified Si oxidation reaction model mediated by point defect generation at the SiO 2 /Si interface [S.
Rapid photo-oxidation of silicon at room temperature using 126 nm vacuum ultraviolet radiation
Applied Surface Science, 2002
Over the years, photo-oxidation of silicon has been found to proceed fastest when the progressively lower wavelength radiation has been used. Here, we use the shortest UV lamp radiation yet applied to Si oxidation, by employing 126 nm radiation from an Ar excimer lamp source. Oxidation rates as high as 5 nm/min were readily achievable at room temperature, which are more than two orders of magnitude higher than those for UV-induced oxidation of silicon using a low pressure mercury lamp at a temperature of 350 8C, and immeasurably higher than for thermal oxidation at room temperature. This enhancement is believed to arise from two effects: ozone produced by 126 nm light and more ef®cient photochemical reaction at lower wavelengths. Furthermore, thicknesses up to 9 nm have been obtained, which are not possible in reasonable times with conventional dry thermal oxidation processes at temperatures less than even 500 8C. The ®lms are found by XPS and FTIR to be stoichiometric in nature. Current±voltage measurements from metal oxide±semiconductor (MOS) devices fabricated using a 9 nm SiO 2 layer showed that leakage current densities as low as 10 À6 A/cm 2 at an electric ®eld of 1 MV/cm can be obtained in the as-grown ®lms. Further properties of these ®lms will be reported. #
Accounting for anomalous oxidation states of silicon at the Si/SiO2 interface
Surface and Interface Analysis, 2002
The early oxidation stages of hydrogen-terminated single-crystalline Si(100) exposed to a diluted N 2 /N 2 O atmosphere at 850 • C for different durations have been studied by XPS, following the evolution of the Si 2p signal. Evidence is given that the usual analysis, in terms of five pairs of peaks attributed to silicon in oxidation states from 0 to +4, does not account for the observed Si 2p signal. The spectrum is accurately reproduced only by assuming the existence of silicon in bonding configurations different from those usually assumed to occur at the Si/SiO 2 interface.
Kinetics of Initial Layer-by-Layer Oxidation of Si(001) Surfaces
Physical Review Letters, 1998
Layer-by-layer oxidation of Si(001) surfaces has been studied by scanning reflection electron microscopy (SREM). The oxidation kinetics of the top and second layers were independently investigated from the change in oxygen Auger peak intensity calibrated from the SREM observation. A barrierless oxidation of the first subsurface layer, as well as oxygen chemisorption onto the top layer, occurs at room temperature. The energy barrier of the second-layer oxidation was found to be 0.3 eV. The initial oxidation kinetics are discussed based on first-principles calculations. [S0031-9007(97)04959-4]
Japanese Journal of Applied Physics, 2003
The state-selective dissociation dynamics for anionic and excited neutral fragments of gaseous SiCl 4 following Cl 2p and Si 2p core-level excitations were characterized by combining measurements of the photoninduced anionic dissociation, x-ray absorption and UV/visible dispersed fluorescence. The transitions of core electrons to high Rydberg states/doubly excited states in the vicinity of both Si 2p and Cl 2p ionization thresholds of gaseous SiCl 4 lead to a remarkably enhanced production of anionic, Si − and Cl − , fragments and excited neutral atomic, Si * , fragments. This enhancement via core-level excitation near the ionization threshold of gaseous SiCl 4 is explained in terms of the contributions from the Auger decay of doubly excited states, shake-modified resonant Auger decay, or/and post-collision interaction. These complementary results provide insight into the state-selective anionic and excited neutral fragmentation of gaseous molecules via core-level excitation.
Layer-By-Layer Oxidation of Silicon Surfaces
MRS Proceedings, 1999
ABSTRACTLayer-by-layer oxidation of Si(111) and (001) surfaces has been studied by using scanning reflection electron microscopy (SREM). We found that SREM images reveal interfacial structures of the SiO2/Si system. Our results showed that the initial step structure of Si substrates was preserved at SiO2/Si interfaces and that interfacial steps did not move laterally during oxidation. We also observed a periodic reversal of terrace contrast in SREM images during the initial oxidation of Si(001) surfaces. These results indicate layer-by-layer oxidation of Si surfaces, which is promoted by the nucleation of nanometer-scale oxide islands at SiO2/Si interfaces. In addition, we investigated the kinetics of initial layer-by-layer oxidation of Si(001) surfaces. We found that a barrierless oxidation of the first subsurface layer, as well as oxygen chemisorption onto the top layer, occur at room temperature. The energy barrier of the second-layer oxidation was found to be 0.3 eV. The initial...
All-optical determination of initial oxidation of Si(100) and its kinetics
The European Physical Journal B, 2008
By comparison of measured and ab initio calculated surface optical spectra we demonstrate that two main oxidation processes initially occur after dissociation of oxygen molecules, forming in both cases Si-O-Si entities: (i) breaking of Si dimers by incorporation of oxygen atoms; (ii) incorporation into the silicon backbonds. The kinetics up to half-monolayer coverage is determined, and explained in terms of Langmuir-like adsorption mechanisms with different probabilities.