Organometallic chemical vapor deposition of copper oxide thin films

Copper oxide thin films were prepared by organometallic chemical vapor deposition (OMCVD or MOCVD) technique. This MOCVD process uses copper acetylacetonate (Cu(acac)[subscript]2) as the copper precursor. Spectroscopic (X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and infrared spectroscopy (IR)) and diffraction (X-ray diffraction (XRD)) methods were employed to analyze the chemical composition and oxidation state of copper in these films. According to spectroscopic results, the composition of these MOCVD film primarily depends on the deposition temperature and partial pressures of the reactants. As indicated by XPS and XRD results, Cu[subscript]2O films were prepared at 360°C, with an oxygen partial pressure of 150 torr and copper precursor partial pressure of 0.20 torr. CuO films were grown at temperatures above 420°C, with an oxygen pressure of 190 torr and precursor pressure of 0.20 torr. By using water vapor instead of oxygen as the co-reactant, Cu films were deposited at temperatures above 380°C, with a water vapor pressure of 15 torr and precursor pressure of 0.20 torr. To examine the specific mechanism of precursor decomposition, a molecular vibrational spectroscopic technique, Fourier Transform Infrared spectroscopy (FTIR), was employed to investigate the vapor phase product distribution in the MOCVD effluent stream. Based on FTIR results, a kinetic model was proposed. This model suggests that steric effect from chelating ligands and bond strength sequence in the precursor molecule are the principle factors determining the decomposition products of Cu(acac)[subscript]2 in the MOCVD reactor. Differential scanning calorimetry (DSC) was used to study the pyrolysis pattern of Cu(acac)[subscript]2. Particularly, the impacts of oxygen concentration, carrier gas molecular weight, and heating rate on the pyrolysis of this precursor were studied. From DSC results, it seems that Cu(acac)[subscript]2 undergoes a single-step, exothermic reaction in the ambient with oxygen gas present. In DSC pattern, the exothermic peak height also increased as oxygen concentration increased. The activation energy for the exothermic step was derived by Kissinger equation as 20 kcal/mol. Based on experimental results of deposition, FTIR, and DSC, it seems that a deposition temperature above a critical value is necessary to initiate the decomposition of Cu(acac)[subscript]2 and oxygen can assist this reaction by accelerating the reaction rate