Evaluation of Pb Precursors for Liquid Injection Atomic Layer Deposition of Pb(Zr x Ti 1-x )O 3 Thin Films
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0902-T04-07.1
Evaluation of Pb Precursors for Liquid Injection Atomic Layer Deposition of Pb(ZrxTi1-x)O3 Thin Films Takayuki Watanabe, Susanne Hoffmann-Eifert, Cheol Seong Hwang1, and Rainer Waser Institute of Solid State Research and CNI—Center of Nanoelectronic Systems for Information Technology, Research Center Juelich, Juelich, D-52428, Germany 1 School of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Korea ABSTRACT Pb(DPM)2 and Pb(TMOD)2 dissolved in ethylcyclohexane were evaluated as precursors for future atomic layer deposition (ALD) of Pb(Zr,Ti)O3 films. PbO films were deposited by a liquid injection atomic layer deposition on Pt-covered Si substrates at different deposition temperature and precursor volume per cycle. Pb(DPM)2 and Pb(TMOD)2 started thermal decomposition at deposition temperature of around 270ºC and 320ºC, respectively. Against increasing Pb(DPM)2 injection at 240ºC, the deposition rate of PbO films saturated at around 1 Å/cycle, but kept increasing at 300ºC, which is above the thermal decomposition temperature. The deposition rate of PbO films at 240ºC dropped to a constant value with enough purge time after precursor injection and reactant supply. A saturated deposition rate of PbO films was also observed for Pb(TMOD)2 below the thermal decomposition temperature. However, the saturation behavior observed for Pb(TMOD)2 was slower and the saturated growth rate was higher comparing to Pb(DPM)2. In addition, the film thickness of the PbO films had an apparent gradient over the substrates. These results indicate that Pb(DPM)2 shows more reactive and stable chemisorption comparing to Pb(TMOD)2 for the self-limiting growth rate.
INTRODUCTION One major challenge in the integration of ferroelectric thin films like Pb(Zr,Ti)O3 [PZT] into high-density non-volatile memory devices is the reduction of the film thickness below 50 nm combined with the necessity for homogeneous, stoichiometric films on complex 3D structures. Metalorganic chemical vapor deposition (MOCVD) was used for covering 3D nano-structures with ferroelectric thin films because of the high ability to achieve good step coverage [1,2]. However, recent studies indicated that the films deposited over 3D structures by MOCVD have a gradient in the cation composition, even if the film thickness appeared to be uniform over the complex structure [3]. This is because of the different sticking coefficients of original precursors and products given by a gas phase reaction of precursors. The switching charge and coercive field of PZT thin films will vary with local changes in the cation composition. Therefore, another approach that achieves uniform coverage of multi-component oxide films over 3D structures both in cation composition and in film thickness is necessary. Atomic layer deposition (ALD) is a surface reaction controlled process and by this gives the possibility to achieve homogeneity on complex structures. ALD is widely used for depositing binary high-k gate oxide thin films such as HfOx and AlOx on hydrog
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