Ce(IV) Complexes with Donor-Functionalized Alkoxide Ligands: Improved Precursors for Chemical Vapor Deposition of CeO2

Abstract

Thin films of ceria (CeO₂) have many applications, and their synthesis by liquid-injection MOCVD (metal–organic chemical vapor deposition) or ALD (atomic layer deposition) requires volatile precursor compounds. Here we report the synthesis of a series of homoleptic and heteroleptic Ce(IV) complexes with donor-functionalized alkoxide ligands mmp (1-methoxy-2-methylpropan-2-olate), dmap (1-(dimethylamino)propan-2-olate), and dmop (2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)propan-2-olate) and their potential as precursors for MOCVD and ALD of CeO₂. New complexes were synthesized by alcohol exchange reactions with [Ce(OBu^t)₄]. [Ce(mmp)₄] and [Ce(dmap)₄] were both found to be excellent precursors for liquid-injection MOCVD of CeO₂, depositing high purity thin films with very low carbon contamination, and both have a large temperature window for diffusion controlled growth (350–600 °C for [Ce(mmp)₄]; 300–600 °C for [Ce(dmap)₄]). [Ce(mmp)₄] is also an excellent precursor for liquid-injection ALD of CeO₂ using H₂O as oxygen source and demonstrates self-limiting growth from 150 to 350 °C. [Ce(dmap)₄] has lower thermal stability than [Ce(mmp)₄] and does not show self-limiting growth in ALD. Heteroleptic complexes show a tendency to undergo ligand redistribution reactions to form mixtures in solution and are unsuitable as precursors for liquid-injection CVD.