Mixed alkylamido-cyclopentadienyl compounds of zirconium, (RCp)Zr(NMe 2 ) 3 (R ¼ H, Me or Et) are introduced as precursors for atomic layer deposition (ALD) of high permittivity zirconium oxide thin films. Ozone was used as the oxygen source. Only slight differences were observed in the ALD growth characteristics between the three liquid precursors. The ALD-type growth mode was verified at 300 C with a growth rate of about 0.9 A ˚cycle À1 . Good film conformality was observed, as step coverages of 80-90% were measured for films deposited onto high aspect ratio (60 : 1) trenches. As compared to the commonly used Zr(NEtMe) 4 precursor, these novel precursors showed comparative volatility and growth rate but higher thermal stability, as well as lower impurity content in the deposited stoichiometric ZrO 2 films. The films deposited by the (RCp)Zr(NMe 2 ) 3 /O 3 processes tended to crystallize in the high temperature cubic form even when the film thickness exceeded 50 nm, while the Zr(NEtMe) 4 /O 3 process resulted in films with mixed phases. The cubic phase ensures high permittivity and thus the capacitance equivalent thickness remained extremely low, even below 0.8 nm, with low leakage current density of 10 À7 A cm À2 at 1 V when a 6.4 nm ZrO 2 film was deposited on TiN.

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The identification of appropriate ligand-metal combinations, which successfully present the features of : (i) having acceptable melting point, (ii) being more thermally stable than hafnium alkylamides, (iii) having sufficient volatility for vapor phase distribution and (iv) enabling the deposition by LI-MOCVD and ALD of hafnium containing thin films, should go through new generations of well-behaved molecular precursors. We report herein the chemical design and full characterizations of a portfolio of novel mono- and di- amidinate and guanidinate alkylamide hafnium complexes of N,N'-unsymmetrically substituted 1,3-amidinate and 1,3-guanidinate [R'-N=CX-NR"]xHf(NR2)4-x (R'≠ R" = Et, iPr, tBu ; R = Me or Et ; X = Me or NMe2 ; x = 1 or 2). We will exemplify the remarkable influence of the molecular structure on the melting point, the volatility and the thermal stability (see figure 1) and the nature (cubic, monoclinic) of HfO2 thin films by LI-MOCVD.

Topic: Advanced Processes and Materials AbstractAtomic Layer Deposition (ALD) of Hf and Zr oxide films is of considerable interest and promise for future generation Metal-Insulator-Metal (MIM) structures in memory applications. Hafnium and zirconium alkylamides such as tetrakis(ethylmethylamino) hafnium (TEMAH) and tetrakis(ethylmethylamino) zirconium (TEMAZ) are the most considered precursors. However, their relatively low thermal stability might become a drawback under heated distribution conditions that could result in vaporizer clogging or insufficient long-term stability. Moreover, these precursors may not be suitable if higher deposition temperature processes are sought.Alternative ALD precursors with improved thermal stability could be viable alternatives. Among the precursor families that could be considered (halides, alkoxides, β-diketonates, tetranitrates, etc.), metallocenes are particularly attractive. New hafnocenes -dimethyl bis(ethylcyclopentadienyl) hafnium, Hf(EtCp)2Me2, and dimethyl bis(methylcyclopentadienyl) hafnium, Hf(MeCp)2Me2 -with improved physical properties and thermal stability are studied here. The thermal behavior of these new precursors has been extensively characterized for vapor pressure, thermal stability, and evaporation kinetics.The ALD behavior of Hf(EtCp)2Me2 with O3 as coreactant was investigated at high temperature (350-400°C), an ALD deposition rate of 0.72Å/cycle was achieved. Hf(EtCp)2Me2 showed the best compromise between thermal stability, physical properties, and deposition behavior. Similar zirconocenes were als o studied: ZrCp2Me2, Zr(MeCp)2Me2, Zr(EtCp)2Me2 and Zr(EtCp)(NMe2)3.

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