Low-temperature fabrication of high-quality (Ba, Sr)TiO 3 films using charged liquid cluster beam method
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Yi Yang,b) HoChul Kang,c) and Kyekyoon (Kevin) Kim Thin Film and Charged Particle Research Laboratory, Departments of Electrical and Computer Engineering and Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
M.Y. Sungd) and Ho G. Jange) Department of Electrical Engineering and Division of Chemistry and Molecular Engineering, Korea University, Seoul 136-701, Korea (Received 29 August 2001; accepted 20 May 2002)
Low-temperature deposition of high-quality (Ba,Sr)TiO3 (BST) thin films was achieved in air on Pt/Ti/SiO2/Si substrates using the charged liquid cluster beam (CLCB) method. The Ba, Sr, and Ti precursors were synthesized using alkoxy carboxylate ligands to tailor their physical properties to the CLCB process. The as-deposited BST films fabricated at substrate temperatures as low as 280 °C exhibited high purity. The leakage current density and dielectric constant of the film, deposited at 300 °C and subsequently annealed at 700 °C, were 2.5 × 10−9 A/cm2 at 1.5 V and 305, respectively.
High-permittivity perovskite thin films have been extensively studied for a wide range of applications from high-density dynamic random access memory (DRAM) devices to microwave tuning devices for wireless communication. Among these materials, BaxSr1−xTiO3 (BST) has attracted more attention because of its large dielectric constant, low leakage current (dc), low loss tangent, and stable operation at high temperatures.1,2 Chemical vapor deposition (CVD) has been known as the most promising method for fabricating high-quality BST thin films for DRAM devices where conformal coverage over challenging topography is required. An essential requirement for a successful CVD process is the availability of suitable precursors with sufficient volatility and stability. However, developing suitable CVD precursors for BST thin films has been challenging due to the low volatility of the barium and strontium compounds originating from their tendency for oligomerization. Although the liquid source delivery method 3
a)
Address all correspondence to this author. Current address: KLA-Tencor Corporation, M/S I-1216, 160 Rio Robles, San Jose, CA 95134. c) On leave from Korea University. d) Department of Electrical Engineering, Korea University. e) Division of Chemistry and Molecular Engineering, Korea University. b)
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http://journals.cambridge.org
J. Mater. Res., Vol. 17, No. 8, Aug 2002
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utilizing flash vaporization has demonstrated advantages over the conventional bubbler-type delivery for low vapor pressure solids and liquids, the control of stoichiometry for each component in the BST films is still problematic. The liquid delivery method utilizing aerosols generated by ultrasonic nebulizers may be considered attractive due to the fact that it does not require vaporization of the precursors. However, this method too would be inappropriate for fabricating films for DRAM devices because the aerosols are in the micrometer range. The charged liquid cluster beam (CLCB)
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