Ion Bombardment Effects on the Growth of Rutile Phase of Reactively Sputtered TiO 2 Thin Films
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ION BOMBARDMENT EFFECTS ON THE GROWTH OF RUTILE PHASE OF REACTIVELY SPUTTERED TiO2 THIN
FILMS D. Wicaksana, T. Tsujikawa, A. Kobayashi, K. Ono* and A. Kinbara Department of Applied Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113 *Engineering Research Institute, The University of Tokyo, Bunkyo-ku, Tokyo 113 JAPAN
ABSTRACT Titania thin films grown by reactive bias sputtering were characterized. In order to investigate the role of energetic ion on the growth of crystalline phases of TiC 2 thin films, we applied substrate biases during deposition. The structural properties were analyzed using X-ray diffractometry (XRD), and related to the optical properties of the films. The atomic composition was determined using Rutherford backscattening spectrometry (RBS). Negative substrate bias, Vb, showed a significant influence on the phase formed composition and microstructure: Vb in the range of 15 and 60 V enhanced the growth of crystalline phases and the rutile dominated the phase composition. However, the quantity of rutile decreased when Vb was raised to 100 V. The excess of oxygen was shown in the films by RBS.
I. INTRODUCTION TiO 2 thin films have been investigated intensively for practical applications [1]-[7]. It is well known that the obtained films are consisted of many phases including amorphous, anatase and rutile depending upon the growth condition [l][2]. The rutile is a stable phase obtained at higher temperature (Ž800"C) [81. We have previously shown that the growth of the amount of the rutile phase polycrystalline in the films can be controlled by the deposition conditions, e.g., total pressure, 02 flow rate and discharge current, when the films are grown on substrates kept at low temperature (•200"C), and an explanation on the growth process of the rutile phase polycrystalline in the films at low temperature has been made qualitatively [ 1]. In the present work, we have tried a reactive bias sputtering process for understanding the effect of energetic ions on the growth of the rutile phase in the films. The role of the energetic ions will be discussed.
II. EXPERIMENTAL All TiO 2 films were deposited using a conventional dc magnetron sputtering system ( Figure 1). The vacuum chamber has a diameter of 200 mm and a height of 150 mam. The water cooled target was a sintered titanium disc with 99.9% purity. The target was 80 mm in diameter, and 3 mm in thickness. The target to substrate distance was fixed at 40 mam. The substrates were Si(100) wafers and conductive NESA glasses with a size about 30 mm by 30 mam. To ignite the discharge plasma, dc voltage, Vs, was applied between the target and a mesh electrode which was located between the target and the substrates to serve as an anode. In the present work, the power supply was operated under the constant current of 180 mA
(current density = 3.6 mA/cm 2 ).
Discharge gases of Ar and 02 were introduced separately through a mass flow controller. The partial pressures of reactive gas were monitored using a quadrupole mass spectrometer. The flow rates of Ar
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