Metal-Organic Chemical Vapor Deposition of Copper and Copper(I) Oxide from Copper(I) Tert-Butoxide

Metal-organic chemical vapor deposition (MOCVD) from the tetrameric precursor copper(I) tert-butoxide, [Cu(O-t-Bu)]₄, results in the deposition of pure copper(I) oxide whiskers at 510 K and of copper metal films with ~2% oxygen contamination at 670 K. Both deposits are polycrystalline as judged by X-ray powder diffraction. Quantitative analyses of the gaseous byproducts generated during the deposition of copper(I) oxide show that 1.66 ± 0.08 equiv of tert-butyl alcohol, 2.14 ± 0.08 equiv of isobutylene, and 0.32 ± 0.16 equiv of water are formed for every mole of [Cu(O-t-Bu)]₄ consumed; essentially identical product distributions are obtained for the deposition of copper metal. The mechanisms by which copper(I) oxide and copper metal are produced from copper(I) tert-butoxide have been established from these product distribution studies combined with the results of high-resolution electron energy loss spectroscopy and temperature-programmed desorption studies of Cu(111) single crystals dosed with copper(I) tert-butoxide in ultra high vacuum. Copper (I) oxide is formed by elimination of isobutylene from surface-bound tert-butoxide groups to yield surface hydroxide intermediates, which subsequently engage in proton transfer processes to produce tert-butyl alcohol and water. The deposition of copper at 670 K evidently occurs by loss of oxygen from an initially deposited copper(I) oxide phase. This latter mechanism is supported by the observation that MOCVD deposits of high surface area copper(I) oxide deoxygenate under vacuum at 670 K to give copper metal. Thus, these studies show that MOCVD-grown films of pure metals can sometimes be produced via intermediate oxide phases whose bulk form is ldnetically stable under the same experimental conditions.