Nondestructive inspection of through silicon via depth using scanning acoustic microscopy

In this paper, an innovative application of an existing nondestructive inspection, i.e, time-of-flight mode of scanning acoustic microscopy (SAM), was proposed for the measurement of through silicon via (TSV) depth. A feasibility study was performed on a dummy wafer with various sizes of TSVs to evaluate this method. From the image reconstruction of B-scan SAM, the depth of TSVs can be clearly identified. In addition, cross-section inspections were performed to verify this nondestructive inspection method. It was found that, for TSV sizes larger than φ30 μm, the depth measured by the ultrasonic scanning method could be very close to the results of cross-section inspection (less than 5% error). The current results are considered very encouraging and the proposed nondestructive inspection method should have very good potential for the high throughput and low cost in-line measurement of TSV depth during the TSV forming process.