Ion beam induced modification of energy of adhesion for copper films on Al₂O₃ substrates

Abstract

Thin films deposited on inert substrates can break up into an array of beads or islands after prolonged heating at temperatures well below the melting point. The energy of adhesion can be readily determined from the shape of equilibrated beads. We have established the feasibility of using this beading technique for direct and quantitative determination of the changes in the energy of adhesion produced by ion bombardment of Cu/ Al2O3 system. Copper films 10 and 20 nm thick were e-beam deposited on prepared substrates of alumina, a and c axis sapphire. After bombardment with 200 keV He or Ne ions, samples were heat treated at 450°C, up to 100 h or at 850°C for 30 h. Beading was studied using scanning electron microscopy. He bombardment had a minor effect on the beading while Ne ions suppressed it dramatically at 450°C, showing complete wetting. The morphology of beads depended on substrate orientation and at higher temperature, it approached the shape of a sessile liquid drop, except for α-axis substrates. The Ne induced adhesion enhancement was reduced at 850°C. © 1987 Elsevier Science Publishers B.V.