Full Paper Light-Induced CVD of Titanium Dioxide Thin Films II: Thin Film Crystallinity** By Estelle Halary-Wagner, Frank R. Wagner, Arnaud Brioude, Jacques Mugnier, and Patrik Hoffmann* Titanium dioxide thin films are obtained by CVD on low temperature (60±210C) substrates using perpendicular irradiation from a long pulse XeCl excimer laser (308 nm). The precursor, tetra-isopropoxide titanium, is used in an oxygen-containing atmosphere with a total pressure of 10 mbar in the chamber. X-ray photoelectron spectroscopy (XPS) analyses show that the chemical composition of the film, independent of the deposition parameters, is TiO 2 with some additional surface carbon contamination. Depending on deposition parameters, the film crystallinity varies between amorphous, anatase, and rutile. Numericaltemperaturesimulationsandsamplecharacterizationshowthatthecrystallinestateofthedepositedmaterialevolves from amorphous to anatase to rutile with an increase in the laser-induced temperature. Additionally, substrate temperature and laser repetition rate strongly influence the phase-transition behavior. Keywords: Anatase, Excimer laser, Rutile, Titanium dioxide 1. Introduction Light-induced (LI) CVD uses photon irradiation to promote or activate a CVD reaction. The use of excimer lasers (powerful UV pulsed-light sources) perpendicularly irradiating the substrate was shown to be a promising technique for growing a large number of oxides at low substrate temperature (see references in E. Halary-Wagner et al. [1] ). The UV photons can activate the deposition reaction in various ways: [2,3] d Photolytically, when light absorption by the precursor induces an electronic transition excitation leading to the precursor dissociation by internal energy relaxation. d Pyrolytically,whenlightabsorptioninthesubstrate(orin the film) activates a thermal decomposition of the precursor. d Photocatalytically,whenlightabsorptioninthesubstrate (or in the film) induces electronic transitions generating electrons and holes responsible for redox reactions of adsorbed precursor molecules on the surface. We focus here on TiO 2 deposition from titanium tetra- isopropoxide (TTIP) in an oxygen-containing atmosphere induced by irradiation using a long pulse (250 ns) XeCl excimer laser (308 nm). In this system, the deposition was shown to be induced photolytically with an Arrhenius dependence on the substrate temperature. [1] In addition to the activation of the chemical reaction leading to the deposition, the excimer laser photons interact photo- chemically or thermally with the substrate or the already deposited oxide film. Other processes, such as TiO 2 crystal- lization under irradiation (sol±gel, [4,5] or amorphous gas phase deposited films [6] )oroxideablation(forinstance,ITO electrode structuration [7] ), benefit from these interactions. Although LICVD is usually considered as a low temper- ature technique, due to the low substrate temperature, excimer laser irradiation of oxide films (which normally absorb light at excimer wavelengths) induces a temperature rise during very short time periods, as shown by laser- induced temperature rise simulations. [8] In the present work, a numerical approach was used to estimate the laser-induced temperature rise of the film in the experimental deposition conditions used, and laser-induced temperatures up to 1400 C were found. Titanium dioxide, which has been studied in this work, is a widely used material. Using CVD methods, amorphous material is usually deposited at low substrate temperature, while crystalline phases, mainly anatase and rutile, are successively obtained with increasing substrate tempera- ture. [9] Depending on the target application, one crystalline form may be preferable for instance, amorphous films are required for optical coatings, [10] while anatase layers are preferred for photochemically active layers, [11] and rutile ones are investigated for micro-electronic coatings, [12] soitis advantageous to be able to selectively deposit each phase. Chem. Vap. Deposition 2005, 11, No. 1 DOI: 10.1002/cvde.200306304  2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 29 ± [*] Dr. P. Hoffmann, Dr. E. Halary-Wagner,Dr. F. R. Wagner, Dr. A. Brioude Advanced Photonics Laboratory Ecole Polytechnique FØdØrale de Lausanne (EPFL) CH-1015 Lausanne-EPFL (Switzerland) E-mail: patrik.hoffmann@epfl.ch Prof. J. Mugnier Laboratoire de Physico-chimie des MatØriaux Luminescents UniversitØ Claude Bernard, Lyon 1 Domaine Scientifique de la Dona 10 rue A.M. Ampre, F-69622 Villeurbanne Cedex (France) [**] We thank N. Xanthopulos (LMC/DMX/EPFL) for XPS measurements and T. Lippert (PSI, Villigen) for access to Raman microscopy. The authorsalsogratefullyacknowledgeJamesA.DeRoseforproofreading the manuscript. This research was supported by grants from the Swiss National Science Foundation (project No. 20-59404.99).