Ultrasonic Scholte wave dispersive properties and parameters characterization of films in water immersion layered thin film-substrate structure

The structure of multilayer films deposited on a substrate is widely used in many fields, such as microelectronic devices, but the ultrasonic measurement of the film material parameters, especially the shear velocity, is a difficult problem. The theoretical analysis for dispersion properties of liquid-solid interface Scholte wave and acoustic pressure response generated by a pulse excitation shows that the Scholte interface wave dispersion is associated significantly with the velocity distribution of multilayer films. The thickness and shear wave velocity of each layer of thin film materials significantly affect the interface wave dispersive characteristics. A multi-parameter inversion method for layered films is proposed based on the dispersive properties of Scholte wave at the interface between liquid and layered film-substrate structure. The proposed method is first processed and verified by theoretical synthetic signals, and further experiment is conducted to excite and acquire liquid-solid interface waves for different types of multilayer film material samples. The inversion results of layered film parameters for experimental signals confirm the feasibility, effectiveness and convenience of this method.