Study on Structural and Thermal Characteristics of Heteroleptic Yttrium Complexes as Potential Precursors for Vapor Phase Deposition

Abstract

Yttrium oxide (Y2O3) thin films are implemented as a functional component in a broad field of applications such as optics, electronics or thermal barrier coatings. Atomic layer deposition (ALD) is a promising technique to fabricate high-quality thin films with atomic level precision in which the precursor choice plays a crucial role in process development. The limited number of suitable yttrium precursors available for ALD of Y2O3 has triggered increasing research activity seeking new or modified precursors. In this study, heteroleptic compounds of yttrium bearing the cyclopentadienyl (Cp) ligand in combination with the chelating amidinate or guanidinate ligands were targeted as potential precursors for ALD. In this context, a systematic and comparative study of the structure and thermal characteristics of (bis-cyclopentadienyl-(N,N'-diisopropyl-2-methyl-amidinato)yttrium) [YCp2(dpamd)] 1 and (bis-cyclopentadienyl-(N,N'-diisopropyl-2-dimethylamido-guanidinato)yttrium) [YCp2(dpdmg)] 2 was performed. Complementary characterization tools such as 1H-NMR, elemental analysis, electron-impact mass spectrometry (EI-MS) and single-crystal X-ray diffraction (XRD) confirmed the spectroscopic purity and the monomeric nature of the metalorganic compounds. Hirshfeld surface analysis revealed influence of the ligand choice on the intermolecular interactions of the compounds. The important figures of merit for a precursor, namely the thermal properties were investigated via thermogravimetric analysis. Thus, the volatility, transport behavior and thermal stability were examined and compared to their homoleptic counterparts [YCp3], [Y(dpamd)3] or [Y(dpdmg)3].