These micrographs show a cross-section of a two-wafer stack. Each wafer has five metal
circuitry layers and a series of copper bondpoints on its face. The wafers are joined face-to-face. Each
photo shows one tungsten Super-Contact™ in the top wafer.
The bright horizontal features across the center of most of the pictures are the copper
bondpoints,
joined face-to-face. Note the precise alignment of the two wafers! Finer horizontal features are the
aluminum in the metal layers. The one bright vertical feature in each picture is a Super-Contact.
Some photos also also show the tiny vertical connections between the metal layers.
If a third wafer were to be added to this stack, copper bondpoints would be added to the top of the
two-wafer stack. One of those bondpoints would cover the end of the Super-Contact shown here. Adding a
third wafer, face-down, would connect the two sets of copper bondpoints, providing vertical electrical
connectivity throughout the stack. This could be repeated for additional wafers.
Click on any picture to see a larger image
(All pictures taken in February, 2005)
| Ten pairs of connected copper bondpoints mark the boundary between the two wafers.
Five layers of aluminum are visible on each wafer. Vertical interconnects between the aluminum
layers can be seen at the lower left, upper right, and upper middle. The Super-Contact is at
center top. |
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| At lower left, vertical interconnects provide electrical paths from the metal
layers to the copper bondpoint. At upper right, the Super-Contact touches the last metal layer and
runs through to the backside of the wafer (the surface of the stack). |
|
| The Super-Contact provides electrical connectivity between the metal layers and
the top of the stack, where an aluminum pad has been added for wire bonding and final packaging. |
|
| Only the top wafer is visible here, except for one copper
bondpoint on the face of the
lower wafer. Note the smaller interconnects between the metal layers at center right. |
|
| This extreme magnification shows just the Super-Contact, the metal layer to
which it connects (bottom), and the aluminum on the backside of the wafer (top). |
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