대구경 선집속 초음파 탐촉자를 이용한 실리콘 판재의 결정방향 측정

Abstract

Lamb waves have numerous modes depending on the frequency of the waves, the thickness of the plate and the incident angle. In this experiment, the wave propagation in (100), (110) and (111) single-crystal silicon wafers were investigated. Lamb waves were generated using a line-focused ultrasonic transducer with a large aperture in the wafers, and these waves were detected using the same transducer. The frequency and phase velocity were determined from the incident angle at which a specific mode of Lamb waves were generated. However there are numerous incident angles with the transducer used in this experiment, received signal contains various waves of different frequencies. The V(z)curve for a specific frequency was obtained from V(f,z) which is the FFT (fast Fourier transform) of V(t,z). The phase velocity can be obtained from the V(z) curves by using a method similar to that used in acoustic microscopy. Finally, the phase velocity can be determined as a function of the propagation direction by rotating the silicon wafers. The angular dependences of the wavenumber and Lamb wave phase velocity were obtained, and they show good agreement with the crystalline orientation of the silicon wafers. In conclusion, a line-focused ultrasonic transducer with a large aperture is an epoch tool for evaluating anisotropic plates.