Stacked IC structure with system level wiring on multiple sides of the IC die
Some embodiments of the invention provide a three-dimensional (3D) circuit that is formed by stacking two or more integrated circuit (IC) dies to at least partially overlap and to share one or more interconnect layers that distribute power, clock and/or data-bus signals. The shared interconnect layers include interconnect segments that carry power, clock and/or data-bus signals. In some embodiments, the shared interconnect layers are higher level interconnect layers (e.g., the top interconnect layer of each IC die). In some embodiments, the stacked IC dies of the 3D circuit include first and second IC dies. The first die includes a first semiconductor substrate and a first set of interconnect layers defined above the first semiconductor substrate. Similarly, the second IC die includes a second semiconductor substrate and a second set of interconnect layers defined above the second semiconductor substrate. As further described below, the first and second dies in some embodiments are placed in a face-to-face arrangement (e.g., a vertically stacked arrangement) that has the first and second set of interconnect layers facing each other. In some embodiments, a subset of one or more interconnect layers of the second set interconnect layers of the second die has interconnect wiring that carries power, clock and/or data-bus signals that are supplied to the first IC die.
1. A method of fabricating a three-dimensional (3D) circuit comprising:
face-to-face mounting a first integrated circuit (IC) die and a second IC die, the first IC die comprising a first semiconductor substrate and a first set of interconnect layers defined on a front side the first semiconductor substrate, the second IC die comprising a second semiconductor substrate and a second set of interconnect layers defined on a front side of the second semiconductor substrate, the first and second sets of interconnect layers abutting each other after the face-to-face mounting of the first and second IC dies; and
defining a third set of interconnect layers on a back side of the second semiconductor substrate.
2. The method of claim 1 , wherein the third set of interconnect layers provides system level signals to a set of interconnect segments of the first and second interconnect layers.
3. The method of claim 2 , wherein the system level signals are further provided to circuits defined on the first and second substrates of the first and second dies through the set of interconnect segments of the first and second interconnect layers.
4. The method of claim 2 , wherein the set of interconnect segments includes a plurality of interconnect segments in each of the first and second sets of interconnect layers.
5. The method of claim 2 , wherein the system level signals comprise power signals.
6. The method of claim 5 , wherein
at least one of the first and second sets of interconnect layers comprises power interconnect segments, and
the third set of interconnect layers comprise power interconnect segments that are wider than power interconnect segments of the first and second sets of interconnect layers.
7. The method of claim 6 further comprising defining a plurality of through silicon vias (TSVs) to carry power signals from the wider power interconnect segments of the third set of interconnect layers to core circuits in the interior of the first or second die.
8. The method of claim 7 , wherein at least a set of TSVs connect to power interconnect segments of the third set of interconnect layers to power interconnect segments of the first or second set of interconnect layers.
9. The method of claim 7 , wherein at least a set of TSVs connect to power interconnect segments of the third set of interconnect layers to circuits defined on the first or second substrate of the first or second IC die.
10. The method of claim 7 , wherein at least a set of TSVs supply power signals to core circuits that are closer to the center of the first or second die than to peripheral sides of the first or second die.
11. The method of claim 5 , wherein the third set of interconnect layers comprise a power mesh formed by overlapping power/ground interconnect segments on different interconnect layers of the third set of interconnect layers.
12. The method of claim 2 , wherein the system level signals comprise clock signals.
13. The method of claim 12 , wherein the third set of interconnect layers comprise a clock distribution interconnect structure.
14. The method of claim 13 , wherein the clock distribution interconnect structure comprises interconnected clock interconnect segments on different interconnect layers of the third set of interconnect layers.
15. The method of claim 2 , wherein the system level signals comprise data signals from a data bus formed by a plurality of topologically, parallel data lines.
16. The method of claim 1 , wherein the face-to-face mounting comprises using a direct bonded connections to face-to-face mount the first and second IC dies.
17. The method of claim 1 further comprising defining a plurality of through silicon vias to establish electrical connections between the face-to-face mounted first and second dies, said electrical connections allowing signals to be exchanged between the first and second dies.
18. The method of claim 1 further comprising performing a thinning operation to thin the back side of the second semiconductor substrate die before defining the third set of interconnect layers on the back side of the second semiconductor substrate.
19. The method of claim 1 further comprising mounting a third IC die on the back side of the second IC die, the third IC die comprising a third semiconductor substrate and the third set of interconnect layers on a front side of the third semiconductor substrate, wherein the second and third IC dies are back-to-front mounted.