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 (SiO2) substrates. At the initial stage of the deposition, the enol-form H-HFA was detected as desorbates on all substrates. 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 CF3 group by the CF2H group. When SiO2 was used, CF3COOH 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.