Microstructure study of the oxidation of TiN layers during sputtering process
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1195-B08-23
Microstructure study of the oxidation of TiN layers during sputtering process Chun Wang Department of Electrical and Computer Engineering, Data Storage Systems Center, Carnegie Mellon University, Pittsburgh, Pennsylvania, 15213
ABSTRACT TiN provides a good template layer for the epitaxial SrTiO3 (001) growth on Si(001) single crystal substrates by RF sputtering. However, TiN template layer was oxidized into TiO2 during the subsequent sputtering process of electrodes of SrRuO3. The effect of Ru ion catalyzed oxidation and delamination of the TiN layer has been studied using transmission electron microscopy (TEM) and high-resolution transmission electron microscope (HRTEM). The epitaxial orientation relationship of the SrRuO3 and SrTiO3 was reserved to be cube on cube with respect to Si and the crystal quality of the SrRuO3/SrTiO3 film remained even when the TiN template layer was oxidized. The stress in the thin film of SrRuO3/SrTiO3/TiN structure could be determined from the buckle shape in both plan view and cross sectional TEM images. INTRODUCTION Heteroepitaxial growth of perovskite oxides on Si substrate is very important for the ferroelectric memory applications.1 To achieve the epitaxial growth of perovskite oxides, a template layer has to be used between the Si substrate and the oxide. TiN turns out to be a good template layer between Si and the perovskite oxide because of the good lattice matching between TiN and most perovskite oxides (~4 Å) and the similar thermal expansion coefficient (~9x10-6 K-1). It also works well as a diffusion barrier to prevent the reaction and interdiffusion between oxide and Si due to its good chemical stability.2, 3 We have achieved epitaxial SrTiO3 films on Si using TiN templates.4 However, TiN layers were found to form anatase phase titanium oxide during the deposition of SrRuO3 due to the active oxygen plasma and Ru ions as a oxidation catalyst. In this paper, we studied the oxidation characteristics of the TiN template layer and the formation of anatase TiO2 by transmission electron microscopy and calculated the compressive stress, which causes the plastic deformation of the heterostructure.
EXPERIMENTAL DETAILS Sputtering was used to deposit these epitaxial films on Si substrates in this work. The base pressure was about 5x10-7 Torr. Compound targets of TiN, SrTiO3 and SrRuO3 were used in this experiment. TiN and SrTiO3 thin films were deposited at 400 °C and 500 °C sequentially by RF diode sputtering. The Ar sputtering gas pressure was fixed at 5 mTorr and the sputtering power density was about 2.5 W/cm2. Then SrRuO3 film was deposited at 700 °C in Ar/O2 mixture with ratio of 4:1. The microstructure and orientation of the samples were determined by a Philip x-ray diffractormeter with a Cu Kα radiation, a JEM 2000 EX II transmission electron microscope and high resolution transmission electron microscope.
RESULTS AND DISCUSSION
The x-ray diffraction (XRD) θ-2θ scan for the sample SrTiO3/TiN/Si was shown in Figure 1(a). Only strong (002) diffraction peaks a
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