Two silicon wafers, bonded together. Echoes were gated at the depth of the bond between the two wafers.
There are two types of defects at this depth. First, the large white area at center is a large delamination – a region where the wafers are not bonded and are separated by a gap, which may be as thin as 100Å-1000Å.
Second, the darker “clouds” around the white area are composed of thousands of tiny voids, perhaps caused by very tiny particles of silicon dioxide. Magnification of a portion of the image shows more detail. Small voids in bonded wafers are not unusual, but this quantity of voids suggests extensive contamination of the wafer surfaces. |
