Selective MOCVD of titanium oxide and zirconium oxide thin films ...

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ARTICLE IN PRESSB.-C. Kang et al. / Journal of Physics and Chemistry of Solids 69 (2008) 128–132 131OTS SAMs area and ZrO 2 deposited area is clear.However, as the deposition time was increased up to 4 h,the boundary became very unclear. It means the ZrO 2 wasable to deposit both hydrophilic area and hydrophobicarea. We can suggest that the terminal group of OTS wasoxidized and changed its character from hydrophobic tohydrophilic or removed from the substrate surface becausethe high deposition temperature and long deposition time[25]. The morphology of ZrO 2 thin film grown on Si(1 0 0)substrate was denser and smoother than that of ZrO 2 thinfilm grown on OTS SAMs surface.XPS survey spectrum analysis was carried out of the asdepositedZrO 2 film grown on Si(1 0 0) substrate at 450 1C(not shown here). The strong Zr 3d and O 1s peaks wereclearly indicated. However, C 1s peak clearly appearedaround 300 eV binding energy, we can guess that thecarbon comes from the precursor during depositions and/or surface contamination from the air. Also, the O 1s andZr 3d high-resolution XPS spectra were performed(not shown here). In the case of O 1s , there are twooxidation states attributed to O 2 and OH species at thebinding energy of about 532 and 530 eV. We can ensurethat the OH peak is just a surface contamination peakprobably originated from H 2 O in the air. The Zr 3d5/2 peakobserved as a single peak at binding energy of 182.2 eV,which is a good agreement to Zr 4+ .Fig. 7 shows the 3D AFM image of selectively grownZrO 2 thin film on OTS SAMs patterned Si(1 0 0) substrateat 450 1C for 2 h. The selectivity of thin film and the sharpboundary between ZrO 2 thin film area and OTS SAMs areclearly distinguished. The thickness of deposited ZrO 2 thinfilm was approximately 30–40 nm. The growth rate of ZrO 2thin films using Zr(O i Pr) 2 (tbaoac) 2 was much slower thanthat of TiO 2 thin films.OTS SAMs have been demonstrated as a promisingcandidate for a MOCVD resist layer which can block thesurface functional groups that are necessary for nucleationFig. 5. OM images of a ZrO 2 thin film deposited on the OTS patternedSi(1 0 0) substrate.Fig. 7. 3D and 2D AFM images of selective growth of a ZrO 2 thin film onSi(1 0 0) substrate.Fig. 6. SEM image of a ZrO 2 thin film deposited on the OTS patterned Si(1 0 0) substrate at (a) 450 1C for 2 h and (b) 450 1C for 4 h.
132ARTICLE IN PRESSB.-C. Kang et al. / Journal of Physics and Chemistry of Solids 69 (2008) 128–132and growth during the deposition [23]. In this experiment,OTS can prevent nucleation for TiO 2 and ZrO 2 thin film onthe SAMs surfaces because it has hydrophobic terminalgroup (–CH 3 ), i.e., there are no reaction factors forchemisorption between the metal-organic (MO) precursorsand –CH 3 groups. But the MO precursors can obtainelectrons from the ‘‘base’’ originated from native oxidelayers on the Si(1 0 0) surface and they can makechemisorptions with substrate very strongly. After all, thinfilm is able to be formed on it. However, OTS SAMs areweak in respect of thermal stability over 450 1C [25], theyshould change their identities or make some defects on theOTS SAMs area. Therefore, it is difficult to make thin filmsselectively on substrates by combination of mCP andMOCVD methods at high temperatures. Thomas et al.showed that Ti(O i Pr) 2 (tbaoac) 2 precursor showed slightlysuperior properties in terms of evaporation behavior,deposition temperature, and smaller amount of residuematerial than those of Zr(O i Pr) 2 (tbaoac) 2 precursor [24].And Zr(O i Pr) 2 (tbaoac) 2 precursor could induce high vander Waals force with OTS SAMs surface and lowmolecular mobility on the OTS SAMs area owing to itshigh molecular weight compared to Ti(O i Pr) 2 (tbaoac) 2 .These disadvantage factors should require a long nucleationtime on the Si(1 0 0) substrate and cause less siteselectivedeposition than that of TiO 2 in our experiment.4. ConclusionsWe successfully deposited patterned TiO 2 and ZrO 2 thinfilms directly using a combination method of mCP andMOCVD methods. New developed precursors of[M(O i Pr) 2 (tbaoac) 2 ,M¼ Ti, Zr] were used as precursorsfor TiO 2 and ZrO 2 thin films. In the case of TiO 2deposition, it showed a good selectivity growth on thepatterned Si(1 0 0) substrate. The boundaries between theOTS SAMs area and TiO 2 deposited area were very cleancut and sharp without any breaks. The micro-Ramanspectroscopy and the EDX data showed that the depositedTiO 2 thin films were stoichiometric with anatase phase. Inthe case of ZrO 2 thin films, they showed a selectivedeposition on the substrate as deposition time below 2 h;however, the selectivity disappeared above 2 h. It meansthat OTS should change or lose its identity due to hightemperature and/or long deposition time. Even though thecombination of MOCVD and mCP is a very convenienttechnique to make micro-size structures without involvingphotolithographic-type procedures, there are some limitationssuch as deposition temperature and deposition time.However, it is expected that the combination of mCPof SAMs and MOCVD is a better method for fabricatingmicro-size, various functional thin films at lowtemperatures.AcknowledgmentsThe authors gratefully acknowledge the support by theBK21 project of Ministry of Education, Korea.References[1] K.S. Goto, Solid State Electrochemistry and its Applications toSensors and Electronics Devices, Elsevier, New York, 1988.[2] L.A. Ryabova, Current Topics in Materials Science, vol. 7, North-Holland, Amsterdam, 1981 (Chapter 5).[3] M.F. Yan, W.W. Rhodes, Grain Boundaries in Semiconductors,North-Holland, New York, 1981.[4] J. Reintjes, M.B. Schultz, J. Appl. Phys. 39 (1968) 5254.[5] S.J. Tauster, S.C. Fung, R.L. Garten, J. Am. Chem. Soc. 100 (1978)170.[6] D.J. Dwyer, S.D. 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