Surface Chemistry of Copper(I) Acetamidinates in Connection with Atomic Layer Deposition (ALD) Processes

Qiang Ma,Hansheng Guo,Roy G Gordon,Francisco Zaera

doi:10.1021/cm200432t

Abstract

The thermal chemistry of copper(I)-N,N′-di-sec-butylacetamidinate on Ni(110) single-crystal and cobalt polycrystalline surfaces was characterized under ultrahigh vacuum (UHV) conditions by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). A complex network of reactions were identified, starting with the dissociative adsorption of the precursor, from its dimeric form in its free state to a monomer once bonded to the nickel surface. The dissociation of a C–N bond in the acetamidinate ligand at ∼200 K leads to the formation of adsorbed 2-butene and N-sec-butylacetamidinate. Some of the latter intermediates hydrogenate around 300 K to release N-sec-butylacetamidine into the gas phase, while the remaining adsorbed species dissociate further around 400 K, as the copper atoms become reduced to a metallic state, possibly to form acetonitrile and a sec-butylamido surface species that reacts further at 485 K to release 2-butene. By 800 K, only copper and a small amount of carbon can be seen on the surface by XPS. The implications of this chemistry to the growth of metal films by atomic layer deposition (ALD) are discussed.

Highlights

Given the high stability of amidines, they have long been considered good choices as bidentate ligands in organometallic compounds
The thermal chemistry of copper(I)-N,N'-di-sec-butylacetamidinate on the Ni(110) single-crystal surface was first explored by using X-ray photoelectron spectroscopy (XPS)
The first type is clear in the spectra obtained after annealing at temperatures below 300 K, with the Cu 2p3/2 XPS peak centered at 934.1 eV and the Cu L3VV AES signal at 913.8 eV, which amounts to an Auger parameter (BE(Cu 2p3/2) + KE(Cu L3VV) - hν) of 361.3

Summary

Introduction

Given the high stability of amidines, they have long been considered good choices as bidentate ligands in organometallic compounds. Most organometallic precursors used in ALD do show some secondary thermal chemistry involving the conversion of the ligands during adsorption into new surface species. This is often undesirable, because the new adsorbates may bind strongly to the surface and remain there even after exposures to the second reactant. Such side reactions are the most common source of impurities in the films grown by chemical means, and the reason why stable ligands are sought for these applications. In the case of amidinates ligands, for instance, the hope is that those moieties survive the first half of the cycle so they can be hydrogenated to the corresponding amidine in the second half

Results

Discussion

Conclusion