Initial stages of delamination of the aluminum film from silicon wafer

Aluminum films of thickness 0.5 µm were deposited on silicon substrates by pulsed laser physical vapor deposition. The substrate with the film was subjected to laser pulses from the backside of the wafer to initiate delamination of the film. Subsequently, the front side of the film was examined by atomic force, and optical and scanning electron microscopy, and found to contain blisters of different sizes. In addition, larger regions of the film debonded but did not spall. Transient thermo-reflectance was used to study the acoustic oscillations generated in the larger regions of the debonded film using the incidence of a pulsed laser beam with wave length of 532 nm and pulse repetition frequency 10 Hz. The periodicity of the acoustic oscillations was used to determine the size of the film that oscillated. The periods varied from 0.088 to 1.900 µs and the corresponding radii of the oscillating film from 296 to 6384 µm. The work of adhesion was found to reach a maximum value at blister radius close to 25 µm. There were no acoustic oscillations from the delaminated film in the blisters. Acoustic beats were also generated from larger debonded film by superposition of two acoustic oscillations. These results were used to investigate the initial stages of delamination of the films from the substrates.