Laser enhanced adhesion of copper films to sapphire substrates

Abstract

Strongly adherent films of copper on sapphire can be grown by discrete and sequential sputter depositions alternating with pulsed laser treatment (PLT). In this work the influence of various processing parameters on the film adhesion and morphology are analyzed. Ultraviolet excimer lasers produce less damage to metallic films than do other visible or infrared pulsed lasers. However, the laser energy density must be carefully controlled in order to prevent excessive evaporation or film damage. Film damage and separation from the substrate are likely to occur during PLT if the initial copper films are thicker than 80 nm. Transmission electron microscopy reveals the formation of an intermediate copper/alumina compound in a 30‐nm‐thick film grown in two steps (10 nm+PLT+20 nm+PLT). The regions of strong copper–sapphire bonding and good thermal contact that are established in the early stages of the sequential deposition process, and that are maintained during the subsequent process of building up a thick, adherent copper film, most probably consist of this intermediate compound.