Atomic-Layer Deposition of ZrO 2 Thin Films Using New Alkoxide Precursors
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Atomic-Layer Deposition of ZrO2 Thin Films Using New Alkoxide Precursors Anthony C. Jones1,2, Paul A. Williams,1,2 John L. Roberts,1 Timothy J. Leedham,2 Hywel O. Davies,2 Raija Matero,3 Mikko Ritala3 and Markku Leskelä3 1 Department of Chemistry, University of Liverpool, Liverpool, L69 7ZD, UK 2 Inorgtech Limited, 25 James Carter Road, Mildenhall, Suffolk, IP28 7DE, UK 3 Department of Chemistry, PO Box 55, FIN-00014, University of Helsinki, Finland
ABSTRACT Atomic layer deposition is a promising technique for the deposition of ZrO2 thin films for high-k gate dielectric applications. However, there are a number of problems associated with existing Zr precursors such as ZrCl4 and [Zr(OBut)4]. In this paper, we examine the ALD of ZrO2 using the new alkoxide complexes, [Zr(OBut)2(dmae)2], [Zr(OPri)2(dmae)2] and [Zr(dmae)4] (dmae = [OCH2CH2NMe2]), and compare the results with data obtained using [Zr(OBut)4].
INTRODUCTION Zirconium dioxide (ZrO2) has a high permittivity and is relatively stable in contact with silicon, making it a promising candidate to replace SiO2 as the gate dielectric material for sub-0.1 µm complementary metal-oxide-semiconductor (CMOS) technology [1]. Atomic layer deposition (ALD) [2] is a promising technique for the deposition of ZrO2 thin films, as it allows the deposition of highly conformal and uniform films at low substrate temperatures with precise control of layer thickness to the monolayer level. A number of precursors have been investigated for the ALD of ZrO2, but there are various drawbacks associated with their use. Crystalline ZrO2 films have been grown by ALD using ZrCl4 [3,4] and ZrI4 [5], but these are high melting point solid sources with a very fine particle size, leading to the risk of particle transport to the substrate. Films grown from ZrCl4 on hydrogen-terminated Si have shown poor morphologies [6], and the possibility of halide contamination is a serious concern in microelectronics applications. Recently the ALD of ZrO2 was reported using [Zr(thd)4], [Cp2Zr(CH3)2] and [Cp2ZrCl2] as zirconium precursors and ozone as the oxygen source [7]. However, these processes are likely to be unsuited to gate dielectric applications as the use of ozone causes extensive oxidation of silicon [8]. The use of high purity metal alkoxides offers significant process advantages over other precursors, and [Zr(OBut)4] has recently been used for the ALD of ZrO2 using H2O as the oxygen source[9]. The films obtained had permittivities as high as 32, which compares favourably with the permittivities of 18 - 24 obtained using halide precursors. However, films deposited from [Zr(OBut)4] had relatively low refractive indices compared to the Zr-halide deposited films, and films deposited at 250oC contained residual carbon (2 at. %) carbon and hydrogen (8 at.%). The presence of relatively stable metal-alkoxide species on the growth surface is a key requirement in achieving surface saturation and self-limiting growth [2], and a major concern of the [Zr(OBut)4] - based ALD process was that fully self-limiti
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