These micrographs show a cross-section of a two-wafer
stack. Each wafer has five metal circuitry layers and a series of copper
pads 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 pads, 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 pads
would be added to the top of the two-wafer stack. One of those pads would cover
the end of the Super-Contact shown here. Adding a third wafer, face-down, would
connect the two sets of copper pads, 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)
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Ten pairs of connected copper pads 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 pad. 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). |
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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. |
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Only
the top wafer is visible here, except for one copper pad on the face of
the lower wafer. Note the smaller interconnects between the metal layers
at center right. |
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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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