Solution Reactions of a Bis(pyrrolylaldiminate)copper(II) Complex with Peralkyl Zinc, Aluminum, and Boron Reagents: Investigation of the Pathways Responsible for Copper Metal Deposition

Abstract

The solution reactions of bis(N-isopropylpyrrolylaldiminate)copper(II) (CuL 2 ) with AlMe 3 , BEt 3 , and ZnEt 2 have been studied. In all cases, reduction occurs in two stages via a stable copper(I) pyrrolylaldiminate complex (Cu 2 L 2 ), with each stage initiated by copper alkyl complex formation. Reduction from "LCuR" (R=Me or Et) occurs with release of R 2 or L-R, consistent with bimolecular C-C or C-N bond-forming reductive elimination. At room temperature or below, copper deposition from "CuMe" occurs exclusively via reductive elimination of ethane, whereas decomposition of "CuEt" yields ethylene, ethane, and hydrogen, indicative of both β-hydride elimination and reductive elimination. The reaction byproducts [Cu 2 L 2 ], [LAlMe 2 ], [L 2 AlMe], [AlL 3 ], [LBEt 2 ], [LZnEt], [ZnL 2 ], L-Me, and L-Et were synthesized independently and isolated as pure compounds. All compounds are thermally stable, with the exception of LZnEt, which undergoes ligand redistribution to form ZnL 2 and ZnEt 2 in solution and as a solid at elevated temperatures. With the exception of [LZnEt] and [Cu 2 L 2 ], these complexes are also volatile; monoligated [LAlMe 2 ] and [LBEt 2 ] are particularly volatile, and therefore more desirable as byproducts in ALD or pulsed-CVD.

Mechanism for the Atomic Layer Deposition of Copper Using Diethylzinc as the Reducing Agent: A Density Functional Theory Study Using Gas-Phase Molecules as a Model

“…The formation of LEt and LZnEt as by-products is observed by Vidjayacoumar et al [11][12] in solution phase, but these by-products have not been reported by Lee et . The Perdew-Burke-Ernzerhof (PBE) functional 16 with the resolution-of-the-identity approximation (RI) 17,18 and valence double-zeta with polarization def-SV(P) basis set 19 The entropy of selected precursors and the corresponding by-products has been calculated at 120°C using vibrational analysis in TURBOMOLE 20 .…”

“…The intermediates found during the course of analogous reactions in solution [11][12] give a first picture for the reaction pathway. However, an improved understanding of the mechanism at its atomic level will help us to find a better precursor and identify the problems related to existing organometallic reagents as the reducing agent.…”

Copper(I) carbene hydride complexes acting both as reducing agent and precursor for Cu ALD: a study through density functional theory

“…In 2009, Lee et al [8] proposed the use of an organometallic reagent ZnEt 2 as the reducing agent. But a subsequent study by Vidjayacoumar et al [9,10] showed that there is Zn contamination in the system. We have studied this transmetallation reaction mechanism using Density Functional Theory (DFT) [11].…”

Kinetics and Coverage Dependent Reaction Mechanisms of the Copper Atomic Layer Deposition from Copper Dimethylamino-2-propoxide and Diethylzinc

“…22 Vidjayacoumar et al investigated ALD reactions of eight different copper (II) complexes separately with AlMe 3 , BEt 3 and Et 2 Zn in order to identify the most promising combination of the copper precursor and co-reagent. 20,23 The reductive properties of various metallocenes along with different copper precursors were investigated with density functional theory (DFT) and solution phase chemistry to evaluate the use of metallocene compounds as reducing agents for Cu ALD. 24 Cu(dmap) 2 has been a popular choice for other Cu ALD processes.…”