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論文

Self-accelerating oxidation on Si(111)7$$times$$7 surfaces studied by real-time photoelectron spectroscopy

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

Surface and Interface Analysis, 46(12-13), p.1147 - 1150, 2014/12

 被引用回数:1 パーセンタイル:1.7(Chemistry, Physical)

Long-time oxidation on Si(111)7$$times$$7 surfaces at room temperature has been investigated by real-time photoelectron spectroscopy to clarify the mechanism of the interface oxidation. It is found that the oxidation mode gradually transformed from oxygen adsorption on the Si(111)7$$times$$7 surface in the initial stage to SiO$$_{2}$$ amorphous-like oxidation on the Si(001)2$$times$$1 surface in the interface oxidation. The self-accelerating oxidation with a significant increase of oxidation rate occurred during the interface oxidation on the Si(111)7$$times$$7 surface, where the strained Si atoms were obviously generated at the SiO$$_{2}$$/Si interface. The strains generated at interface layers induce the emission of Si atoms from the interface when strain is over a critical value, which contributes to the interface oxidation due to the reaction activities of both the vacancy sites and emitted Si atoms.

論文

SiO desorption kinetics of Si(111) surface oxidation studied by real-time photoelectron spectroscopy

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

e-Journal of Surface Science and Nanotechnology (Internet), 11, p.116 - 121, 2013/11

The kinetics of the initial oxide growth on the Si(111) surface have been investigated using real-time photoelectron spectroscopy and density functional theory calculations. Including SiO desorption into the description of the transition from Langmuir-type adsorption to two-dimensional oxide island growth reveals that oxidation at high temperature and low oxygen pressure is not governed by 2D oxide island growth despite sigmoidal oxygen uptake curves. Because SiO desorption during the initial oxide growth depends strongly on temperature and oxide coverage in the transition region, an initial oxidation model for the transition region is proposed. According to O$$_{2}$$-pressure dependent experimental results and theoretical calculations, the SiO desorption is due to the formation of the transition state tri-ins$$times$$2 species, SiO desorption during the initial oxidation is suppressed by the most thermally stable oxygen adsorption species tri-ins$$times$$3 formed on Si(111)7$$times$$7.

論文

Nonlinear O$$_{2}$$ pressure dependence of the initial oxide growth kinetics on Si(111) surfaces; Photoelectron spectroscopy observation and molecular orbital calculation of oxidation states

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

第18回ゲートスタック研究会予稿集, p.191 - 194, 2013/01

Oxygen pressure dependence of the initial oxide growth kinetics on Si(111)- 7$$times$$7 surfaces has been investigated by real-time photoelectron spectroscopy and molecular orbital (MO) calculations. A nonlinear relationship between initial oxidation rate and oxygen pressure $$P$$$$_{rm O2}$$ was found, which is quite different from the linear results on Si(001)-27$$times$$71 surfaces. It was also observed that a larger amount of oxygen adsorption species ${it tri-ins}$ $$times$$3 were formed in the Si(111)-7$$times$$7 subsurface at higher $$P$$$$_{rm O2}$$ leading to an obstacle for the diffusion of O atoms into Si bulk due to its high potential energy barrier. Further a reaction path of oxygen adsorption states on Si(111)- 7$$times$$7 surfaces at room temperature was proposed based on the experimental and theoretical calculation results.

口頭

Si(111)表面酸化状態のO$$_{2}$$圧力依存

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

Lifetime of metastable oxygen molecule (O$$_{2}$$$$^{*}$$) is so long on a Si(111)-7$$times$$7 surface that the reaction kinetics is significantly affected with respect to the saturated oxide thickness. In this study, $$P$$$$_{rm O_2}$$ dependence of oxygen adsorption states on the Si(111)-7$$times$$7 surface was investigated by photoelectron spectroscopy with changing surface sensitivity: work function, O 1s level, and O 2p bands to clarify the initial oxide growth kinetics. This is because the DAS structural model of Si(111)-7$$times$$7 is composed of three Si layers (about 1 nm) in depth, so that adsorbed oxygen is likely distributed down to 1 nm. Based on the $$P$$$$_{rm O_2}$$ dependence of oxygen adsorption states obtained from the curve fitting analysis of O 1s, we propose a reaction model of O$$_{2}$$ adsorption on Si(111) by taking account of O$$_{2}$$$$^{*}$$.

口頭

高温Si(111)表面酸化における相転移のリアルタイム光電子分光観察

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

The dynamics of oxidation on Si(001) surfaces has been elucidated by DOS model, in which the SiO desorbed from the surface just as 2D island growth started and no desorption was reported during the Langmuir type adsorption, and a thermal activation of SiO desorption was found during the phase transition. However, the mechanism of SiO desorption during the phase transition on Si(111)-7$$times$$7 surfaces is still far from understanding. In this study, SiO desorption process depends on the temperature and oxygen pressure and the relation between oxygen adsorption and SiO desorption during the phase transition have been investigated by real-time photoelectron spectroscopy. It is suggested that SiO desorption occurs during the high temperature Langmuir-type adsorption. It is proposed to be affected by the substable oxygen adsorption states on the surface in the initial oxidation, which is strongly depends on the temperature and oxygen pressure.

口頭

Si(111)表面酸化における準安定吸着酸素分子の解離反応キネティクス

西本 究*; Tang, J.*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

Si(111)7$$times$$7表面酸化では準安定吸着酸素分子が長い寿命をもち、Si(001)2$$times$$1表面酸化とは顕著に異なる酸化反応様式を示す。本研究ではSi(111)7$$times$$7表面室温酸化過程におけるO$$_{2}$$$$^{*}$$の挙動を解明するために、酸素吸着曲線,仕事関数,バンドベンディング,酸素原子とSi原子の化学結合状態を光電子分光によりリアルタイム観察した。それらの観察結果の相関から、初期酸化途中でO$$_{2}$$供給停止後のSi(111)表面酸化状態変化について詳しく検討した。Si表面のアドアトムに吸着したO$$_{2}$$$$^{*}$$は解離して内部に潜り込み、酸素吸着状態がpaul構造からins/tri構造に変化したと考えられる。

口頭

O$$_{2}$$供給停止後のSi(111)表面酸化状態変化のリアルタイム光電子分光観察

西本 究*; Tang, J.*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

Si(111)-7$$times$$7表面の酸化では準安定吸着酸素分子(O$$_{2}$$$$^{*}$$)が長い寿命をもち、Si(001)-2$$times$$1表面の酸化とは顕著に異なる酸化反応様式を示す。本研究ではSi(111)-7$$times$$7表面の室温での酸化過程におけるO$$_{2}$$$$^{*}$$の挙動を解明するために、酸素吸着曲線,仕事関数,バンドベンディング,酸素原子とSi原子の化学結合状態を光電子分光によりリアルタイム観察した。それらの観察結果から、初期酸化途中でO$$_{2}$$供給停止後のSi(111)表面の酸化状態の変化について詳しく検討した。O$$_{2}$$$$^{*}$$が解離して内部に潜り込み、酸化状態がpaulからins/triに変化したことがわかった。

口頭

統合Si酸化反応モデルの実験的検証,6; Si(111)における準安定吸着酸素分子の挙動

西本 究*; Tang, J.*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

Si(111)-7$$times$$7表面酸化では準安定吸着酸素分子(O$$_{2}$$$$^{*}$$)が長い寿命を持ち、Si(001)-2$$times$$1表面酸化とは異なる酸化反応様式を示すことがわかっている。本研究ではSi(111)-7$$times$$7表面室温酸化過程におけるO$$_{2}$$$$^{*}$$分子の挙動を解明するため、酸素吸着曲線、仕事関数、バンドベンディング、OとSi原子の化学結合状態を光電子分光によりリアルタイム観察した。O$$_{2}$$ガスの供給停止後に酸素吸着状態が顕著に変化することがO2pとO1s光電子スペクトルから観察され、また、仕事関数も変化することから、O$$_{2}$$$$^{*}$$分子が解離してシリコン表面内部に潜り込み、酸化状態が分子状吸着からバックボンド酸化状態に変化することがわかった。

口頭

Dissociation reaction kinetics of metastable oxygen molecule on partially oxidized Si(111) surfaces by real-time photoelectron spectroscopy

西本 究*; Tang, J.*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

Metastable oxygen molecule has long lifetime of dissociation on Si(111) surface. We reported that the number of adsorbed oxygen atoms at the completion of Langmuir-type adsorption on Si(111) surface increases about three times with increasing temperature from room temperature to 873 K. In this study to clarify the role of metastable oxygen molecules in the initial oxide growth, real-time photoelectron spectroscopy techniques were used to measure time evolutions of oxygen uptake on partially oxidized Si(111) surface after oxygen supply was stopped. We concluded that the decrease of work function is ascribed to dissociation of metastable oxygen molecules, suggesting metastable oxygen molecules are concerned with the oxide growth until Langmuir-type adsorption is completed.

口頭

Si(111)表面上準安定吸着酸素分子の酸化膜被覆率依存

西本 究*; Tang, J.*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

本研究ではSi(111)7$$times$$7表面室温酸化過程におけるO$$_{2}^{*}$$の挙動を解明するために、酸素吸着曲線,仕事関数,バンドベンディング,酸素原子とSi原子の化学結合状態を光電子分光によりリアルタイム観察した。酸化実験は東北大学の紫外線光電子分光とSPring-8/BL23SUのX線光電子分光装置を用いて行った。p型Si(111)7$$times$$7表面を純度99.99%の乾燥酸素を用いて酸化させた。基板温度は室温で、酸素圧力は1.5$$times$$10$$^{-6}$$Paである。O2p光電子強度から求めた酸化膜被覆率が20%のときO$$_{2}$$供給を停止した。O$$_{2}$$供給停止後、酸素被覆率はわずかな増加にもかかわらず、急激な0.6eVの仕事関数の変化が見られた。Si2p光電子スペクトルから求めたバンドベンディングは0.04eVであるので、仕事関数の変化は表面電気二重層の変化によりもたらされたことが示唆された。また、O$$_{2}$$供給停止後に酸素吸着状態が顕著に変化することが、O1s光電子スペクトルから観察された。光電子スペクトル解析と仕事関数の変化から、O$$_{2}^{*}$$が解離して内部に潜り込み、酸化状態がpaulからins/triに変化したことがわかった。

口頭

Phase transition of oxide growth on Si(111)7$$times$$7 studied by real-time photoelectron spectroscopy and theoretical calculations

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

To clarify the influence of adsorbed oxygen molecules; O$$_{2}^{*}$$ in the oxidation of Si(111)7$$times$$7 surface, the initial oxidation kinetics were investigated by real-time photoelectron spectroscopy using He resonance line and synchrotron radiation at SPring-8, and theoretical calculations. The O2p uptakes indicate that Langmuir-type adsorption is in progress. When the supply of O$$_{2}$$ gas was stopped at the oxide coverage of 50%, however, the O2p uptakes has almost no decrease and slightly decreased at 863 K and 883 K, respectively, while it steeply decreased at 913 K and eventually no oxide remained on Si(111) after 5000 s. O2p intensities decrease at slower rate when O$$_{2}$$ supply was stopped at the larger oxide coverage. The observed changes of decomposition rate are ascribed to those of oxygen adsorption states. A surface reaction model is proposed to make clear the phase transition taking into account the role of O$$_{2}^{*}$$.

口頭

Nonlinear O$$_{2}$$ pressure dependence of initial oxide growth on Si(111)7$$times$$7 and Si(001)2$$times$$1 surfaces studied by real-time photoelectron spectroscopy and first-principles calculations

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

The real-time photoelectron spectroscopy using He-I resonance line at Tohoku University and synchrotron radiation at BL23SU, SPring-8 have been carried out to investigate the initial oxide growth kinetics on Si(001)2$$times$$1 and Si(111)7$$times$$7 at room temperature and 873 K. The oxygen uptake curves obtained by UPS showed that the initial oxide growth rate does not increase with increasing O$$_{2}$$ pressure on both Si(001) and Si(111) surfaces, implying that the oxide growth is not limited by the number of O$$_{2}$$ molecules impinging on the surface but governed by the surface reaction of O$$_{2}$$ molecule. Assuming the O$$_{2}$$ pressure dependences is represented by a power-low function of P$$^{n}$$, n is obtained to be 0.42 for Si(111) and 0.54 for Si(001) at room temperature. Based on the XPS and UPS observations, a surface reaction model for the nonlinear O$$_{2}$$ pressure dependence is proposed.

口頭

Temperature dependence of O$$_{2}$$ adsorption reaction path on Si(001) and Si(111); Photoelectron spectroscopy observations and DVX$$alpha$$ calculations

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

In this study, the uptake curve and adsorption state of adsorbed oxygen on Si(111)7$$times$$7 and Si(001)2$$times$$1 surfaces was investigated as a function of temperature by real-time photoelectron spectroscopy using He-I resonance line at Tohoku University and synchrotron radiation at BL23SU, SPring-8 to clarify the initial reaction path of O$$_{2}$$ on Si. When increasing temperature from 300 K to 873 K in the Langmuir-type adsorption region, the saturation amount of oxygen was increased 2.9 times on Si(111) whereas such an increase was only 1.3 times on Si(001). On the other hand, the initial sticking coefficient on the Si(111) surface decreased down to 21% although it remained almost unchanged on Si(001). To reveal the reason for the significant difference of the initial oxide growth kinetics between Si(001) and Si(111), curve-fitting analysis of O1s spectra was performed and the adsorbed oxygen configurations were determined in comparison with the DVX$$alpha$$ calculations.

口頭

Real-time photoelectron spectroscopy and first-principle calculations study of very thin oxide formation on Si(111)7$$times$$7 surfaces

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

The surface electronic properties corresponding to real-time photoelectron spectroscopy have been analyzed by density functional theory and molecular orbital calculations to clarify the reaction path of the oxygen adsorption on Si(111)7$$times$$7. The change of work function was observed during the oxidation at room temperature and 873 K. It can be seen that the net charge of atom present at the surface is negative in the oxygen configurations of ad-insx2, ad-insx3, tri-insx3 and the surface electron negativity turns high with increasing oxidation state, implying the change of work function increases drastically at ad-insx3 and tri-insx3. However, the surface is electron positive for insx2 and insx3, leading to the decrease of change of work function. With combining the O1s binding energy calculated by DVXa, potential energy surface calculations and the XPS measurements, a reaction path of the oxygen adsorption on Si(111) is suggested.

口頭

Temperature dependence of strained Si atoms at SiO$$_{2}$$/Si(111) interface studied by real-time X-ray photoelectron spectroscopy

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

In the present study, the temperature dependence of strained Si atoms at SiO$$_{2}$$/Si(111) interface was investigated by real-time Si 2p and O 1s X-ray photoelectron spectroscopy (710 eV) at BL23SU, SPring-8 to clarify the influence of the point defect generation on the interface oxidation. The first and second strainer Si layer at SiO$$_{2}$$/Si(111) interface increases in accordance with the changes of the suboxides, Si$$^{2+}$$(Si$$^{3+}$$) and Si$$^{1+}$$, respectively. The temperature dependence of the interface oxide growth rate is concidered in terms of the O diffusion as well as the interface strain and furthermore is compared with that on SiO$$_{2}$$/Si(001) interface. The point defect generation caused by the oxidation-induced strain at SiO$$_{2}$$/Si(001) interface was reported to affect the interface oxide growth rate.

口頭

Self-accelerating oxidation at oxide/Si(111) interfaces studied by real-time photoelectron spectroscopy

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 渡辺 大輝*; 寺岡 有殿; 高桑 雄二*

no journal, , 

The self-limiting oxidation has been observed in the initial oxidation stage of a few nanometers oxide thickness. We have recently found that the oxidation rate on Si(111)7$$times$$7 surfaces at room temperature is accelerated with an incubation time. In this study, oxidation states, oxide thickness, and strained Si atoms were observed by real-time synchrotron X-ray photoelectron spectroscopy. Oxide thickness increased with increasing O$$_{2}$$ dosage but showed an increase at the dosage of 3.1$$times$$10$$^{5}$$ L. An additional oxide thickness change was noticed at 4.8$$times$$10$$^{5}$$ L. It is clear that Si$$^{4+}$$ oxidation state starts to increase together with the Si$$^{3+}$$ and Si$$beta$$ state. Consequently, the good coincidence between the growth of chemical states of Si and oxide thickness suggests that the self-accelerating oxidation is associated with the oxidation-induced strains.

口頭

Quick-cooling induced acceleration of oxidation on Si(001) studied by real-time photoelectron spectroscopy

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 寺岡 有殿; 高桑 雄二*

no journal, , 

Real-time photoelectron spectroscopy using a He-I resonance line and synchrotron radiation have been carried out to measure oxide thickness, oxidation states and strained Si atoms near the SiO$$_{2}$$/Si(001) interface during oxidation with varying temperature to clarify the mechanism of interface oxidation. A slight acceleration of oxidation rate also occurred even when substrate temperature was cooled down from 550$$^{circ}$$C to 90$$^{circ}$$C. In this case, the thermal activation effect is ruled out. It was found that the significant increase of Si$$_{beta}$$ occurred at the same time of the increase of Si$$^{4+}$$ only during cooling. After cooling down to about 90$$^{circ}$$C, both of Si$$_{beta}$$ and Si$$^{4+}$$ increase very slowly. This good accordance suggests that the increase of interface strain is associated with the increase of active site of O$$_{2}$$ dissociative adsorption at interface as expected in our Si oxidation model.

口頭

Reaction kinetics of oxygen molecule at SiO$$_{2}$$/Si(111) interface monitored in real time by X-ray photoelectron spectroscopy

Tang, J.*; 小川 修一*; 吉越 章隆; 西本 究*; 石塚 眞治*; 寺岡 有殿; 高桑 雄二*

no journal, , 

The oxidation kinetics at an SiO$$_{2}$$/Si(111) interface was monitored by O 1s and Si 2p photoelectron spectroscopy using synchrotron radiation to clarify the oxygen pressure dependence of oxidation rate. The initial oxygen uptake at the O$$_{2}$$ pressure of 4.6$$times$$10$$^{-5}$$ Pa and the substrate temperature of 500$$^{circ}$$C slowed down at about 0.4 nm, suggesting that the surface is covered with oxides. When the oxygen pressure was increased from 4.6$$times$$10$$^{-5}$$ Pa after saturation, the oxidation rate showed the increase depending on oxygen pressure difference. In addition to Si$$^{1+}$$, Si$$^{2+}$$, Si$$^{3+}$$, and Si$$^{4+}$$ components, Si$$_{alpha}$$ and Si$$_{beta}$$ components, which are associated with the interface strain, were examined carefully. To explain the observed correlation between the oxidation induced strain and the oxidation rate comprehensively, the vacancy and the emitted Si atoms from the interface are taken into account as oxygen adsorption sites.

口頭

Thermal decomposition reaction mechanism of ultrathin oxide on Si(111)

Tang, J.*; 小川 修一*; 吉越 章隆; 西本 究*; 石塚 眞治*; 寺岡 有殿; 高桑 雄二*

no journal, , 

The decomposition kinetics of ultrathin oxide on Si(111) have been investigated by real-time photoelectron spectroscopy using He-I resonance line and synchrotron radiation to clarify the void nucleation and its 2D enlargement mechanism. The oxidized Si(111) surface prepared by exposing O$$_{2}$$ at 773 K under P$$_{O2}$$=4.6$$times$$10$$^{-5}$$ Pa was decomposed by increasing T. The O2p photoelectron intensity I$$_{O2p}$$ shows a sigmoid-type function. The activation energies are almost the same as 2.8-2.9 eV, suggesting that the rate-limiting step is SiO desorption. The correlation between changes of work function and I$$_{O2p}$$ was measured to consider the surface migrating species. The $$theta$$ dependences of the oxidation state and oxidation-induced strain were monitored during the decomposition. Based on the observed results, the oxide decomposition mechanism is discussed in terms of Si atoms supplied from atomic steps within voids and due to point defect generation at oxide/Si(111) interface.

口頭

Temperature dependence of oxidation reaction paths on Si(111)7$$times$$7 studied by real-time photoelectron spectroscopy and theoretical calculations

Tang, J.*; 西本 究*; 小川 修一*; 吉越 章隆; 石塚 眞治*; 寺岡 有殿; 高桑 雄二*

no journal, , 

Temperature dependence of oxygen adsorption states at Si(111)-7$$times$$7 surface was observed by real-time photoelectron spectroscopy. Moreover, the reaction path of O$$_{2}$$ at the surface was obtained by molecular dynamics simulations and density functional theoretical calculations. The temperature dependent increase of saturated oxygen indicates that more oxygen atoms adsorb at the surface at higher tempetarures. Work function increases initially at low temperatures and then significantly decreases. It is known that work function is due to the surface dipole layer and the band bending effects. The band bending is found to be small during the initial oxidation, which implies that the surface dipole layer mainly affects work function.

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