Synthesis of Calcium(II) Amidinate Precursors for Atomic Layer Deposition through a Redox Reaction between Calcium and Amidines

• Published in: Angewandte Chemie 2016-08, Vol.128 (35), p.10384-10389
• Main Authors: Kim, Sang Bok, Yang, Chuanxi, Powers, Tamara, Davis, Luke M., Lou, Xiabing, Gordon, Roy G.
• Format: Article
• Language: English
• Subjects: Amidine; Ammonia; Asymmetry; Atomic layer deposition; Atomic layer epitaxy; Atomic structure; Atomlagenabscheidung; Bridging; Calcium; Chemistry; Crystallography; Deposition; Dünne Filme; Hydrogen sulfide; Ligands; Metals; Precursors; Redoxchemie; Solid state; Temperature effects; Thermal stability; Volatility; X-ray crystallography; X-rays
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201602406

We have prepared two new CaII amidinates, which comprise a new class of ALD precursors. The syntheses proceed by a direct reaction between Ca metal and the amidine ligands in the presence of ammonia. Bis(N,N′‐diisopropylformamidinato)calcium(II) (1) and bis(N,N′‐diisopropylacetamidinato)calcium(II) (2) adopt dimeric structures in solution and in the solid state. X‐ray crystallography revealed asymmetry in one of the bridging ligands to afford the structure [(η2‐L)Ca(μ‐η2:η2‐L)(μ‐η2:η1‐L)Ca(η2‐L)]. These amidinate complexes showed unprecedentedly high volatility as compared to the widely employed and commercially available CaII precursor, [Ca3(tmhd)6]. In CaS ALD with 1 and H2S, the ALD window was approximately two times wider and lower in temperature by about 150 °C than previously reported with [Ca3(tmhd)6] and H2S. Complexes 1 and 2, with their excellent volatility and thermal stability (up to at least 350 °C), are the first homoleptic CaII amidinates suitable for use as ALD precursors. Dimere Amidinat‐Komplexe 1 wurden als unbeständige weiße Kristalle aus der Redoxreaktion zwischen Ca‐Metall und Amidinliganden erhalten (siehe Schema). Der Dampf des Formamidinat‐Komplexes wurde für die Synthese von konformen und einheitlichen polykristallinen CaS‐Filmen durch ALD genutzt. Mit diesem Komplex war das Temperaturfenster des ALD‐Prozesses (150–280 °C) breiter und niedriger als mit der bekanntesten ALD‐Vorstufe.