Formation of TiO 2 Thin Films by Oxidation of TiN
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FORMATION OF TiO 2 THIN FILMS BY OXIDATION OF TiN J.K. TRUMAN*t, P.H. BALLENTINE*, E. TERZIOGLU**, and A.M. KADIN** * CVC Products, Inc., 525 Lee Road, Rochester, NY 14603 ** University of Rochester, Dept. of Electrical Engineering, Rochester, NY 14627 ABSTRACT TiN thin films were deposited by reactive sputtering onto Si substrates. TiO 2 films were formed by subsequent oxidation of the TiN films, using either conventional furnace heating or rapid thermal processing (RTP). The materials properties of the resulting films were characterized by x-ray diffraction and Rutherford backscattering, and indicate conversion of the TiN to fully-oxidized rutile TiO 2 by a diffusion-limited process. Electrical measurements of the insulating properties of the TiO 2 films indicated a relative dielectric constant greater than 100, although the leakage current was greater than optimum. A fully in-situ process for the fabrication of microcapacitors is proposed, which involves the sputter deposition of TiN, the formation of TiO 2 by RTP, and the deposition of a top TiN counterelectrode. This can be carried out under conditions that are compatible with Si microelectronic device processing. INTRODUCTION The basic element of computer memory chips (dynamic random-access memories or DRAMs) includes a thin-film capacitor. As the scale of the circuit decreases, it will be necessary to shrink the capacitors to submicron dimensions while maintaining values of capacitance C=eA/d, where e is the dielectric constant, A the capacitor area, and d the dielectric thickness [1]. One approach has been to make use of the vertical dimension through trench or stack geometries to maximize the area, but this is reaching practical limits. An alternative approach, which will be essential in developing 64 Mb DRAMs and beyond, is to make use of a dielectric material with a much higher dielectric constant than the Si0 2 /Si 3 N4 in use today. This dielectric must be deposited as a thin film by a process that is compatible with Si technology. No widely accepted technology for these microcapacitors has yet been developed. We propose to use TiO 2 as the high-dielectric material, since in its rutile crystalline form it exhibits a relative dielectric constant er = C/so greater than 100 [2]. We further propose to encapsulate this insulator between electrodes of TiN, a conductor that is compatible both with TiO 2 and with Si process technology. The rutile crystalline form of TiO 2 has the highest dielectric constant of any simple metallic oxide [3]. A number of attempts have been made over the years to exploit this by depositing thin films of TiO 2 for use as capacitors or MOS gate dielectrics [4-8]. Although acceptable values of capacitance have sometimes been achieved, this material has not been more generally adopted because there have been problems with excess dielectric conductance and loss, combined with relatively low breakdown voltages. These, in turn, have been correlated with oxygen depletion during processing or with the microcrystalline morphology. Improved
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