Photoacoustic Elastic Bending Method: Characterization of Thin Films on Silicon Membranes

Photoacoustic (PA) elastic bending effects have been studied and used to develop the experimental non-contact and non-destructive method that make it possible to investigate the optical, thermal, and elastic properties of thin films. A theoretical model for optically excited thin films on a Si membrane, which includes plasmaelastic, thermoelastic, and thermodiffusion mechanisms, is given. Relations for the PA elastic bending signal in the optically excited two-layer Si membrane are derived. The method was verified by measuring the experimental amplitude and phase of the PA elastic bending of the thin film on Si square membranes and compared with the theoretically calculated spectra. The analysis shows that it is possible to obtain the optical, thermal, and elastic parameters of a film thinner than 1 mu m.