INTERDIFFUSION AND RESISTIVITY OF CU/AU, CU/CO, CO/AU, AND CU/CO/AU THIN-FILMS AT 25-550-DEGREES-C

The interdiffusion and resistivity of Cu/Au, Cu/Co, Co/Au, and Cu/Co/Au thin-film structures were studied, at temperatures ranging from 25 to 550 °C, using Rutherford backscattering spectroscopy, Auger analysis, and four-point probe resistance measurements. Intermetallic phase formation was studied by x-ray diffraction and changes in microstructure were analyzed by scanning electron microscopy. Interdiffusion of Cu and Au in the Cu/Au structure is observed at temperatures as low as 150 °C and is accompanied by an increase in resistivity. No significant reactions occur in the Cu/Co, Co/Au, and Cu/Co/Au thin-film structures up to 400 °C, after which the resistivity increases. The very rapid increase in resistivity observed at 250 °C for the Cu/Au system and at 450 °C for Cu/Co/Au, is associated with structural changes in the films which result in large grains and the formation of AuCu, Cu3Au, and Cu3Au2 compounds. The structural changes in the Cu/Co/Au system occur at a higher temperature because of the time needed for Cu and Au to diffuse through the Co barrier, which did not react significantly with either Au or Cu.