This paper assesses the capabilities of scanning acoustic tomography (SAT) for the analysis of bonded silicon wafers. In order to quantitatively evaluate detectability and resolution, the authors acquired images from samples prepared with artificial voids. The samples consisted of two wafers, a cap wafer and a base wafer with dry-etched pits on a silicon-oxide layer. Cap wafers of different thicknesses were used along with transducers of appropriate focal length. The paper describes the experimental setup and test procedures in detail as well as the results.

This paper describes a method for obtaining high-resolution ultrasonic inspection images of semiconductor packages. We evaluated the effect of the incident ultrasonic frequency on the resolution and defect detection. When the incident frequency of the ultrasonic transducers is changed from 300 MHz to 400 MHz, the capability to detect package defect improves from 2.5 µm to 1.0 µm. The observed images of semiconductor packages proves that a 400 MHz transducer can be applied to inspect sophisticated LSIs.