During the metal-organic chemical vapor deposition using bis-hexafluoroacetylacetonato-copper (Cu(HFA) 2 ) diluted with hydrogen gas, a gas-phase measurement was carried out using in-situ Fourier-transform infrared spectroscopy. The desorbates were investigated on titanium nitride (TiN), tungsten (W) and thermally oxidized silicon (SiO 2 ) substrates. At the initial stage of the deposition, the enol-form H-HFA was detected as desorbates on all substrate. As the deposition proceeded, different desorbates were observed on different substrates. In the case of W, the keto-form H-HFA was produced. When TiN was used, the substituted keto-form H-HFA desorbed due to reduction of the substituted Cu(HFA) on the surface by hydrogen, where the substituted structure means the replacement of the CF 3 group by the CF 2 H group. When SiO 2 was used, CF 3 COOH was observed due to the thermally decomposed keto-form HFA, which was one of the dissociatively adsorbed species of Cu(HFA) 2 . These differences in the gas-phase byproducts are explained based on the surface conditions.