MIM Capacitors Using ALD Al 2 O 3 for RF IC and DRAM Applications
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MIM Capacitors Using ALD Al2O3 for RF IC and DRAM Applications Sung Yong Ko, Jung Ik Oh, Joung Cheul Choi, Kang Hee Lee, Young Ho Bae1, Young Chul Jung2, Yong Hyun Lee School of Electrical Engineering and Computer Science, Kyungpook National University, Deagu, Korea 1 Division of Information and Communication Engineering, Uiduk University, Gyeongju, Korea 2 School of Computer and Electronic Engineering, Gyongju University, Gyeongju, Korea ABSTRACT Metal-insulator-metal (MIM) capacitors were fabricated in a coplanar waveguide type using the Al2O3 thin film. The Al2O3 film was grown by atomic layer deposition(ALD) using MethylPyrolidine-Tri-Methyl-Aluminum (MPTMA) and H2O on Ti. The capacitance per unit area of the fabricated MIM capacitor was 0.229 µF/cm2. And it had lower voltage coefficient of capacitance (VCC) and lower leakage current than that of Al2O3 MIM capacitor prepared by Al oxidation and Si3N4 MIM capacitor prepared by PECVD respectively. The fabricated Al2O3 MIM capacitors prepared by ALD exhibited low VCC, low leakage current, small frequencydependent capacitance reduction, low temperature coefficient of capacitance (TCC) and good reliability. The characteristics of the device were suitable for RF ICs and DRAM. INTRODUCTION A MIM capacitor is widely used for the Si RF and analog circuits because its resistance and stray capacitance are smaller than that of MOS capacitor. The conventional materials used for MIM capacitor such as SiO2 (κ ~ 3.9) or Si3N4 (κ ~ 7) are not suitable for Si RF and analog circuits due to low circuit density because of their low dielectric constant. Therefore, the choice of high-κ and low loss dielectric material is an important issue to increase the capacitance density for high circuit density [1-3]. In a conventional method, the dielectric materials of MIM capacitors were fabricated by PVD [4] or CVD [5, 6] method. In that case, bottom electrode was degraded by oxidation or capacitance values were not uniform because of high process temperature, low uniformity, and poor step-coverage and so on. In this paper, MIM capacitors were fabricated using Al2O3 deposited by atomic layer deposition (ALD) method. Al2O3 is a relatively high-κ material with the merit of low leakage current, good thermal and chemical stability, etc. The coplanar waveguide type MIM capacitors
Mater. Res. Soc. Symp. Proc. Vol. 833 © 2005 Materials Research Society
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were fabricated for investigation of RF characteristics. Through I-V and C-V measurements, its leakage current, capacitance density, VCC, TCC and frequency-dependent capacitance reduction were investigated. EXPERIMENTAL Figure 1 is a photo-micrograph of fabricated GSG type MIM capacitor and a cross-sectional view. Corning 1737 glass was used for the substrate to reduce the RF loss. The tri-layer metal Ti(100 Å)/Au(2000 Å)/Ti(300 Å) was e-beam evaporated and patterned for the bottom electrode. 300 Å-Al2O3 was deposited by ALD using precursors of methyl-pyrolodine-tri-methyl-aluminum (MPTMA) for Al and H2O for O at 200 °C. The depos
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