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Donor-functionalized alkoxide precursor as reactive alternative for Ce β-diketonate Complexes

Thin films of cerium dioxide (CeO₂) have a variety of applications including optical waveguides, anodes in solid oxide fuel cells, gas sensors, buffer layers for the superconductor YBCO (YBa₂Cu₃O_7-x), and as a high-κ dielectric layer for complementary metal-oxide-semiconductor (CMOS) logic and memory devices. Moreover, the addition of CeO₂ to hafnium oxide stabilizes the high-κ cubic and tetragonal phases improving the functional properties of the common monoclinic phase [1-3]. In this regard, the tertiary oxide CeAlO₃ is another attractive candidate due to its high bulk permittivity (κ) of ~3000 [4]. Additionally, CeO₂ is employed as a catalyst for reactions like NO reduction and CO oxidation [5]. In combination with Pt (e.g. 1% Pt/CeO₂) the catalytic activity of Pt particles can be improved [6].

In pursuit of a highly volatile and reactive precursor for the growth of Cerium dioxide (CeO₂) thin films using chemical vapor deposition (CVD) and atomic layer deposition (ALD) methods, the monomeric Ce^IV complex Tetrakis[1-(methoxy)-2-methyl-2-propanolato] cerium, [Ce(mmp)₄] was synthesized and evaluated in 2009 as an alternative to the thermally more stable β-diketonate compounds such as [Ce(thd)₄]. It was found to be more volatile evaporating with essentially no residue as revealed by thermogravimetric analysis. Additionally, [Ce(mmp)₄] provides a high reactivity towards water, enabling atomic layer deposition at temperatures as low as 150 °C and avoiding the need for a stronger oxidizer like ozone [1].

The high solubility of [Ce(mmp)₄] enables trouble-free liquid injection delivery for both CVD and ALD processes using cyclohexane and toluene as possible solvents [1-6]. For CVD, oxygen is used as a co-reagent yielding CeO₂ thin films at temperatures of 250-600 °C with low carbon content and an enhanced growth rate with respect to [Ce(thd)₄] [1-6]. The ALD processes use water to serve as oxidant and has a broad ALD window from 150-350 °C [2, 3].  Attributed to the high thermal stability of [Ce(mmp)₄]   (~275 °C under CVD conditions) in contrast to other homoleptic mmp compounds such as [La(mmp)₃] and [Gd(mmp)₃] [1].

Figure 8 in reference 2 (Inorg. Chem. 2011, 50, 11644)

Fig. 1. Thermogravimetric analysis of a series of Ce complexes.

References:

1. Chem. Vap. Deposition 2009, 15, 259.
2. Inorg. Chem. 2011, 50, 11644.
3. Nanoscale Res. Lett. 2013, 8, 456.
4. Thin Solid Films 2013, 536, 68.
5. Thin Solid Films 2015, 589, 246.
6. Surf. Coat. Tech. 2015, 280, 148.

FEATURED PRODUCT:

58-5500: Tetrakis[1-(methoxy)-2-methyl-2-propanolato] cerium, [Ce(mmp)4], 98% (1262520-82-0)

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High Purity Chemicals for Materials R&D
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