| abstract |
Using imaging techniques to determine if stacked wafers are in proper alignment. An infrared radiation source and an infrared camera are positioned on opposing sides of a stacked wafer. The infrared radiation source emits infrared radiation that penetrates and passes through the stacked wafer. The infrared radiation is then captured by the infrared camera. Fiducial marks that were previously patterned on each wafer of the stack are exposed in an image produced by the captured infrared radiation. The degree of alignment of the wafers can be measured using the fiducial marks exposed in the image. |