Fabrication of rutile TiO 2 thin films by low-temperature, bias-assisted cathodic arc deposition and their dielectric pr
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L. Wang, W.Y. Cheung, J.B. Xu, and S.P. Wong Solid State Laboratory of Electronic Engineering Department, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong (Received 21 April 2005; accepted 21 October 2005)
The use of rutile-type titanium dioxide (TiO2) thin films as advanced gate dielectrics has been hampered by thermodynamic instability during the high deposition or annealing temperature of 800 °C. In this work, we demonstrate that rutile-type TiO2 thin films can be produced on p-type Si (100) at lower substrate temperature by means of bias-assisted cathodic arc deposition. The influence of the substrate bias on the microstructural and dielectric characteristics of the TiO2 thin films is investigated in detail. Our results show that by applying a suitable bias to the Si substrate, as-deposited rutile-type TiO2 thin films can be obtained at 450 °C. The permittivity of the materials increases significantly from 21 up to 76. The interfacial and electrical properties of TiO2/Si (100) are also improved. The effects and mechanism of the bias on the microstructural and dielectric characteristics are described.
I. INTRODUCTION
The high integrated circuit density and performance demanded by the microelectronics industry requires thin gate dielectric layers. The use of SiO2-based thin films as the gate oxide dielectric is quickly reaching a limitation due to the rapid increase in the tunneling current causing unsustainably large energy consumption and worsened device reliability.1–3 One solution being extensively explored is to increase the capacitance by replacing SiO2based dielectrics with higher permittivity ones.4 Among various high-k materials, titanium dioxide (TiO2) is a possible substitute for silicon dioxide as storage capacitors in dynamic random-access memory (DRAM) and gate oxides in field effect transistors (FET) because its rutile phase has a high-dielectric constant of approximately 80 and good thermal stability on Si.5,6 Another polymorph of TiO2 is the anatase phase which is a metastable state at temperatures below 600 °C and whose dielectric constant is about 30, smaller than that of the rutile phase. It can be transformed to the rutile phase during deposition or postannealing at temperatures higher than 800 °C.7 However, it is difficult to control the interfacial layer between TiO2 and Si as an interfacial a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0119 844
J. Mater. Res., Vol. 21, No. 4, Apr 2006 http://journals.cambridge.org Downloaded: 14 Mar 2015
layer can easily be formed during high-temperature deposition or postannealing, thereby canceling the benefits of the high-dielectric constant.8 This issue is also one of the serious challenges in the use of metal-oxide films as high-k gate dielectrics because even a very thin interlayer of low-k material can decrease the capacitance of the stack so much that the electrical property of the device degrades.9 Therefore, it is necessary to control the crystallization temperature
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