Evaluation of the surface damage of brittle materials based on the attenuation of laser-induced surface acoustic wave

Abstract

In this paper, the surface damage of machined surface of brittle material is evaluated by using the attenuation of laser-induced surface acoustic wave (SAW) in propagation. Taking the typical brittle material single crystal silicon as an example, the feasibility of evaluating surface layer damage based on the attenuation of SAW is demonstrated theoretically and experimentally. Theoretical analysis shows that the micro-cracks produced in the processing of brittle materials can cause significant changes in the attenuation coefficient of SAW. After the lapped silicon wafer is etched, the surface roughness Ra is almost unchanged, while the attenuation coefficient of SAW decreases from 4.3 dB/cm to 2.0 dB/cm, which indicates that the surface layer damage of the silicon can still significantly change the attenuation coefficient after removing the influence of the surface roughness. After measuring the attenuation coefficients of SAW of silicon wafers in different processing steps, it is found that with the improvement of processing accuracy, the attenuation coefficient of SAW decreases, and the attenuation coefficient of SAW reflects the changes in surface damage. Experiments show that surface scratches can also significantly change the attenuation coefficient of SAW. Therefore, the wave attenuation coefficient of the laser-induced SAW can be used to evaluate the surface damage of the brittle material machined surface.