MOCVD of HfO 2 from Alkoxide and Alkylamide Precursors
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MOCVD of HfO2 from Alkoxide and Alkylamide Precursors John L. Roberts,1 Paul A. Williams,2 Anthony C. Jones,1, 2 Paul Marshall,3 Paul R. Chalker,3 Jamie F. Bickley,1 Hywel O. Davies,2 and Lesley M. Smith2 1
Department of Chemistry, University of Liverpool, Liverpool, L69 3ZD, UK Epichem Limited, Power Road, Bromborough, Wirral, Merseyside, CH62 3QF, UK 3 Department of Materials Science and Engineering, University of Liverpool, Liverpool, L69 3BX, UK 2
ABSTRACT The alkoxide and alkylamide complexes [Hf(mmp)4] and [Hf(NMe2)4]2 are both promising precursors for the MOCVD of HfO2. A comparison has shown that [Hf(NMe2)4]2 deposits oxide at lower temperatures and over a wider temperature range then [Hf(mmp)4]. INTRODUCTION Thin films of hafnium dioxide (HfO2) have high permittivities and are stable in contact with silicon, making it a promising candidate for the replacement of SiO2 as the gate dielectric material for sub-0.1µm complementary metal-oxide-semiconductor (CMOS) technology [1]. Metalorganic chemical vapour deposition (MOCVD) is an attractive technique for the deposition of these films [2], offering the potential for good composition control and film uniformity, large area growth and good conformal step coverage. An important requirement for the growth of thin films by MOCVD is the availability of precursors with appropriate physical properties and decomposition characteristics. For instance, the precursors must be suitable volatile to efficiently transport in the vapour phase, and should undergo clean decomposition to deposit high purity films. There must also be a suitable temperature window between precursor evaporation and decomposition, and generally oxide deposition in the region of 500 °C is required for many electronics applications to prevent degradation of the underlying device structure.. There are a number of problems associated with existing Hf oxide precursors. For example, HfCl4 [3] is a low volatility solid which needs substrate temperatures of 800 °C and above for oxide deposition. The β-diketonate complex [Hf(acac)4] (acac = acetylacetone) will decompose to give HfO2 [4], but requires high evaporation temperatures (~ 200 °C) for sufficient evaporation [2], and the oxide films are often heavily contaminated with carbon [4]. The fluorinated complex [Hf(tfac)4] (tfac = trifluoroacetylacetonate) is more volatile [5], but the presence of fluorine is often undesirable in microelectronics applications. Metal alkoxides are attractive MOCVD precursors as they allow the use of lower deposition temperatures and, under optimised growth conditions, allow the deposition of carbon-free films [6]. Although metal alkoxide complexes have been successfully applied in a wide range of MOCVD applications [7], their use in the deposition of HfO2 thin films has been limited. This is because the majority of [Hf(OR)4] complexes are oligomeric with limited volatility, due to the tendency of Hf(IV) atoms to expand their coordination sphere to six, seven or eight [8]. In order
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REFERENCES 1. G.W. Wilk, R
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