Nondestructive Measurement by One-Port Surface Acoustic Wave Resonator for Accurate Evaluation of Film Thickness

Abstract

In this paper, a new method for nondestructive testing of SiO2 film thickness using a portable one-port surface acoustic wave (SAW) resonator based on lithium niobate (LiNbO3) is proposed. Firstly, the finite element method (FEM) is used to simulate and analyze the relationship between the resonant frequency of SAW resonator and film thickness. Subsequently, the vector network analyzer (VNA) is used to nondestructively characterize the thickness of SiO2 film by SAW resonator. The relationship between the thickness and the corresponding resonant frequency in a certain range is obtained and given by a second order polynomial. The results show that the resonant frequency is negatively correlated with film thickness, where the resonant frequency changes from 339.27 MHz to 318.40 MHz in the film thickness range of 100 nm to 2000 nm. To validate the prediction formula, when the film thicknesses are 201.20 nm, 504.60 nm, 842.10 nm and 1497.70 nm, the resonant frequency is used to verify the experimental fitting polynomial. The relative errors between the predicted thickness by SAW resonator and the actual film thickness are 1.60%, 0.34%, 0.67% and 0.96%. The results show that SAW resonator has great potential in detecting thin film thickness with high sensitivity and accuracy.