Tailoring precursors for deposition: synthesis structure and thermal studies of cyclopentadienyl copper(I) isocyanide complexes

We report here the synthesis and characterization of a family of copper(I) metal precursors based around cyclopentadienyl and isocyanide ligands. The molecular structure of the several complexes cyclopentadienyl-copper(I) isocyanide complexes have been unambiguously determined by single crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted the isopropyl isocyanide complex [(η⁵-C₅H₅)Cu(CNⁱPr)] (2a) and the tert-butyl isocyanide complex [(η⁵-C₅H₅)Cu(CN^tBu)] (2b) as possible copper metal CVD precursors. Further modification of the precursors with variation of the substituents on the cyclopentadienyl ligand system (varying between H, Me, Et and iPr) have allowed the affect these changes would have on features such as stability, volatility and decomposition to be investigated. As part of this study the vapor pressures of the complexes [(η⁵-C₅H₅)Cu(CN^tBu)] (2b), [(η⁵-MeC₅H₄)Cu(CN^tBu)] (3b), [(η⁵-EtC₅H₄)Cu(CN^tBu)] (4b) and [(η⁵-iPrC₅H₄)Cu(CN^tBu)] (5b) over a 40-65 ºC temperature range have been determined. Low pressure chemical vapor deposition (LP-CVD) was employed using precursors 2a and 2b, to synthesize thin films of metallic copper on silicon, gold and platinum substrates, under an atmosphere of hydrogen (H₂). Analysis of the thin films deposited onto both silicon and gold substrates at substrate temperatures of 180 °C and 300 ^oC, by SEM and AFM reveal temperature dependent growth features: Films grown at 300 oC are continuous and pin hole free, whereas those films grown at 180 ^oC consist of highly crystalline nanoparticles. In contrast, deposition onto platinum substrates at 180 ^oC show a high degree of surface coverage with the formation of high density, continuous pin hole free thin films. Powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) all show the films to be high purity metallic copper.