| AVS 64th International Symposium & Exhibition | |
| Applied Surface Science Division | Thursday Sessions |
| Session AS+BI+SA+SS-ThM |
| Session: | Spectroscopy of the Changing Surface |
| Presenter: | Yuki Sekihata, Tohoku University, Japan |
| Authors: | Y. Sekihata, Tohoku University, Japan S. Ogawa, Tohoku University, Japan A. Yoshigoe, JAEA, Japan R. Taga, Tohoku University, Japan S. Ishidzuka, National Institute of Technology, Akita College, Japan Y. Takakuwa, Tohoku University, Japan |
| Correspondent: | Click to Email |
An oxidation reaction is the “trade” of electrons between oxygen and other materials, therefore it is thought that there is a difference in the oxidation kinetics on between p-type and n-type Si substrates. In the previous researches about the kinetics of the thermal oxidation of Si, the oxidation rate have not taken account of the difference of conduction type because the thermal oxidation was performed in high temperature region above 600℃ named intrinsic region where the intrinsic carrier concentration becomes comparable to the donor or acceptor concentration. On the other hand, oxidation temperature becomes lower to form thin oxide films below 1nm. Therefore, we believe that the difference of conductivity affects an oxidation kinetics on the Si(001) surfaces, but there is no oxidation reaction models that takes into account the difference of conductivity. In this study, we investigated the oxidation reaction kinetics on p- and n-type Si surfaces using real-time ultraviolet photoelectron spectroscopy.
The samples for oxidation were p-Si(001) and n-Si(001) surfaces. The dopants were Boron and arsenic for p- and n-type substrates, respectively. Their density of dopants were approximately 1018 atoms/cm3 so extrinsic region can be kept in the high temperature region even below 700℃. These samples were oxidized using O2 gas at the pressure of 1.0×10-5 Pa. During the oxidation reaction, the photoelectron spectra were measured repeatedly, therefore time evolution of the amount of oxygen adsorption, work function, and band bending can be investigated.
In the room temperature oxidation, it is found that oxidation reaction coefficient on n-Si(001) is larger than that on p-Si(001). To clarify the reasons, we focus to the changes of work function due to the formation of dipole layer. The work function of the n-Si(001) surface shows negative value but p-Si(001) is positive value. From this result, we can estimate the adsorption positions of O atoms. O atoms have a negative charge in the bond of Si-O, so it can be assumed that oxygen is placed on the n-Si(001) surfaces, but it is subsurface in case of the p-Si(001) surface. In case of n-Si(001) substrates, the doped electrons spill out into the surface because many electrons exist in the substrate. As the result, oxidation reaction is promoted in the n-Si(001) surface. From these results, we found that there is a difference of oxidation kinetics depending on the conductivity. In the presentation, we will show also the difference of oxide states between them.