Delaminations and Voids
Bonded Wafer Delaminations and Voids - Application Note 419
Sample & Method
A pair of fusion-bonded silicon wafers was imaged using a high frequency 230 MHz transducer on C-SAM®. The ultrasonic echoes were gated narrowly on the interface between the two bonded wafers. The purpose was to detect voiding and delamination in the bond between the wafers.
- Grey areas in the acoustic image are well bonded and free from voids. Colored areas show two types of voiding.
- Finely mottled red-yellow areas contain very numerous microvoids separated horizontally by very small regions of bonding. Magnification of small areas of this high-resolution image (~4,000 x 4,000 pixels) permitted viewing of these microvoids in detail (inset).
- More solidly red areas are much more extensive delaminations. These areas tend to be arranged peripherally.
Repeated experiments at Sonoscan have used SEM imaging to demonstrate that gap-type defects such as voids reflect all of the ultrasound even if the z-dimension of the defect is <0.1 micron. More recent work at Sonoscan suggests that reflection is total even if the z-dimension is as little as 100 Angstroms.