Laser-driven micro-explosive bonding of aluminium films to copper and silicon

Abstract

Laser explosive microfabrication was used to bond micrometre-thick aluminium films to both copper and silicon substrates. Bonding was observed in both systems for laser intensities greater than about 1 × 10 9 W cm −2 and resulted in contiguous, uniform films when performed in a rough vacuum of 25 to 70 millitorr. At intensities greater than 9 × 109 W cm-2 the transferred films were generally black in colour due to oxidation in the aluminium-on-copper shots and due to substrate vaporization in the aluminium-on-silicon shots. SEM examination of the bond interfaces indicated mixing of film and substrate through wave formation and possibly through liquid-phase mixing due to thermal conduction of the laser pulse. Tape adhesion testing of the laser-bonded films showed a significant increase in adhesion over vapour-deposited films in both Al-Cu and Al-Si. Vapour-deposited films were easily removed in their entirety by a single tape pull while metallic portions of the laser-bonded films resisted removal by the tape in all but two tests. The enhanced adhesion evident in the laser-bonded films was a result of intermixing observed at the film-substrate interface.