Noninvasive method of detecting blistering in thin-film specimens

With our newly created noninvasive technique of detecting blistering in thin-film systems, we analyzed platinum-silicon specimens. These thin-film specimens were configured as an end-mirror of the Michelson interferometer with the film surface facing the beam splitter and oscillated with an acoustic transducer from the rear in driving frequency of 3 kHz- 10 kHz. The reference arm was slightly tilted horizontally so that the interference image had carrier fringes. The fringe pattern was monitored with a digital camera. Since the digital camera’s frame rate was significantly lower than the acoustic frequency, the fringe contrast reduced as the oscillation amplitude increased. The film-surface oscillation amplitude was evaluated from the reduction in the fringe contrast. We hypothesized that blistered area had weaker adhesion, hence resonance frequency of oscillation is lower than well-adhered region. Our experimental results indicate that at some driving frequencies, the fringe contrast of certain regions is clearly lower. These results support our hypothesis.