Synthesis, Characterization, and Thermal Properties of Homoleptic Rare-Earth Guanidinates: Promising Precursors for MOCVD and ALD of Rare-Earth Oxide Thin Films

Abstract

Eight novel homoleptic tris-guanidinato complexes M[(N(i)Pr)(2)CNR(2)](3) [M = Y (a), Gd (b), Dy (c) and R = Me (1), Et (2), (i)Pr (3)] have been synthesized and characterized by NMR, CHN-analysis, mass spectrometry and infrared spectroscopy. Single crystal structure analysis revealed that all the compounds are monomers with the rare-earth metal center coordinated to six nitrogen atoms of the three chelating guanidinato ligands in a distorted trigonal prism geometry. With the use of TGA/DTA and isothermal TGA analysis, the thermal characteristics of all the complexes were studied in detail to evaluate their suitability as precursors for thin film deposition by MOCVD and ALD. The (i)Pr-Me(2)N-guanidinates of Y, Gd and Dy (1a-c) showed excellent thermal characteristics in terms of thermal stability and volatility. Additionally, the thermal stability of the (i)Pr-Me(2)N-guanidinates of Y and Dy (1a, c) in solution was investigated by carrying out NMR decomposition experiments and both the compounds were found to be remarkably stable. All these studies indicate that (i)Pr-Me(2)N-guanidinates of Y, Gd and Dy (1a-c) have the prerequisites for MOCVD and ALD applications which were confirmed by the successful deposition of Gd(2)O(3) and Dy(2)O(3) thin films on Si(100) substrates. The MOCVD grown films of Gd(2)O(3) and Dy(2)O(3) were highly oriented in the cubic phase, while the ALD grown films were amorphous.

Atomic Layer Deposition of Gd2O3 and Dy2O3: A Study of the ALD Characteristics and Structural and Electrical Properties

“…270°C) of compound 1, according to the TG experiment. 27 The rapid decrease in GPC beyond 300°C is probably due to either re-evaporation of the chemisorbed precursor species, dehydroxylation of the film surface, or reduction of the precursor flux owing to self-decomposition before it reaches the substrate surface. 30−32 Similar growth behavior has been previously observed for ALD of RE oxide (e.g., Sc 2 O 3 growth utilizing [Sc(Cp) 3 ]/H 2 O).…”

“…25,26 It has also been shown that these ligands offer necessary reactivity, volatility, and good thermal stability, which are essential for an ALD precursor. 27 H 2 O assisted ALD of Gd 2 O 3 thin films using tris(N,N′-diisopropyl-2-dimethylamido-guanidinato) gadolinium(III) [Gd(DPDMG) 3 ] with preliminary results on the characterization of the ALD grown films were published as a communication earlier. 28 The current work demonstrates that the thin films of Gd 2 O 3 and Dy 2 O 3 can be grown efficiently by ALD using guanidinate based complexes.…”

“…28 The current work demonstrates that the thin films of Gd 2 O 3 and Dy 2 O 3 can be grown efficiently by ALD using guanidinate based complexes. The homoleptic RE−guanidinate complexes tris(N,N′-diisopropyl-2-dimethylamido-guanidinato) gadolinium(III) [Gd(DPDMG) 3 ] (1) and tris(N,N′-diisopropyl-2-dimethylamido-guanidinato)dysprosium(III) [Dy-(DPDMG) 3 ] (2) 27 were used as ALD precursors in combination with water. The ALD grown Gd 2 O 3 and Dy 2 O 3 thin films were analyzed using a series of characterization techniques to study the structure, morphology, composition, interface quality, and electrical properties relevant for high-k applications.…”

“…be attributed to the similar chemical environment of both metal centers involved with similar chemical reactivity and thermal properties 27. In the case of Dy 2 O 3 ALD, unlike in the Gd 2 O 3 case, films could be grown at 150°C.…”

Atomic Layer Deposition of HfO2 Thin Films Employing a Heteroleptic Hafnium Precursor

“…[31] The overlapping ALD window for HfO 2 and Gd 2 O 3 should enable the development of a truly waterbased ALD process for rare-earth (e.g., Gd, Dy) doped HfO 2 using the similar class of precursors. [32] This could be an added advantage for the optimization of the ALD process to grow high dielectric constant HfO 2 thin films in the cubic or tetragonal phase. Research efforts in this direction are currently underway.…”