| AVS 59th Annual International Symposium and Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuM |
| Session: | Surface Reactivity of Oxides |
| Presenter: | N.S. Faradzhev, University of Virginia |
| Authors: | N.S. Faradzhev, University of Virginia J.T. Yates, Jr., University of Virginia S.B. Hill, National Institute of Standards and Technology T.B. Lucatorto, National Institute of Standards and Technology |
| Correspondent: | Click to Email |
We report the photo oxidation of a carbonaceous layer originally grown by 92 eV radiation-induced chemistry. The C film is supported on a surface of a nm thick amorphous TiO2 film. Photo oxidation is achieved using various oxygen-containing molecules. The TiO2 film mimics one of the possible protective layers of EUV Lithography optics, and the C film mimics optics contamination produced by 92 eV photons in a EUVL stepper apparatus. The C layer (~4 nm) is deposited by photodecomposition of the linear hydrocarbon molecule, n-tetradecane, using the NIST synchrotron ultraviolet facility (SURF III) in an UHV cell. The kinetics of C growth and C removal are monitored in real time using in situ single wavelength ellipsometric measurements. After each set of experiments, ex-situ XPS is used to detect the residual thickness of the carbonaceous film and the changes in its chemical state. We found that exposure to a vapor beam of several O-containing molecules has little or no effect on the C film in the dark. In the presence of EUV photons, the ability of these molecules to volatilize carbon as either CO or CO2 increases significantly. The carbon removal rate increases with the partial pressure of the oxidizer. The substrate temperature has little effect on the carbon removal rate and this is in contrast to the rate of radiation-induced C growth that exhibits a very strong temperature dependence. The rate of removal of C depends upon the EUV irradiation and does not occur appreciably in the dark.
Although the studies are not finished yet, our results indicate that processes of C growth and C removal may proceed via different routes. In an earlier study, we found that during C growth, the hydrocarbon molecule arrives at the surface in its ground state and forms a weak bond to the bare or C- covered TiO2 surface. The molecule is not trapped permanently and will thermally desorb within a characteristic time. It can also be either photo-desorbed or photo-decomposed to produce the carbonaceous film via direct (photo excitation) or indirect (secondary electron excitation, e.g. DEA) processes. For photo oxidation, the first step requires the formation of a strong bond of the oxidizer molecule to the surface. An oxidizer molecule will either arrive at the surface in an electronically excited molecular state or arrive in its ground state and find an EUV-activated long-lived electronically excited state at the surface. In both cases, the oxidizer molecule will stay on the surface for a sufficiently long time to decompose and react to produce a volatile product (e.g. CO).
This study is being performed as a part of EUVL Contamination cooperative research at NIST and UVA.