Observations on the Morphological Changes in Thin Copper Deposits during Annealing and Oxidation

Thin copper films were deposited in an ultrahigh vacuum on carbon and silicon monoxide substrates at room temperature. Their morphological changes after annealing and oxidation were investigated by electron microscopy and electron diffraction. The changes during annealing of very thin deposits (<50 Å mean thickness) are strongly influenced by the substrate. The copper on carbon substrates grows into large crystallites during heat treatment at 500°C whereas on silicon monoxide substrates very little recrystallization occurs. During the annealing of thicker deposits of copper, self-diffusion of the metal can take place and the change in structure of the heat-treated film is independent of the substrate. The structures of the cuprous oxide particles formed during exposure to different pressures of oxygen at 150° to 200°C indicate that different transport mechanisms are involved in the oxidation process at very low oxygen pressures from those at pressures above 10−2 Torr.