Face-to-face mounted IC dies with orthogonal top interconnect layers
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, the method comprising:
selecting (i) a first integrated circuit (IC) die comprising a first semiconductor substrate and a first set of interconnect layers defined on top of the first semiconductor substrate, and (ii) a second IC die comprising a second semiconductor substrate and a second set of interconnect layers defined on top of the second semiconductor substrate, said first and second sets of interconnect layers having similar sets of alternating preferred wiring directions;
rotating the second IC die by 90 degrees; and
face-to-face mounting the first and second IC dies so that an outermost interconnect layer of the first IC die has a preferred wiring direction that is orthogonal to the preferred wiring direction of an outermost interconnect layer of the second IC die.
2. The method of claim 1 , wherein said rotation ensures that the preferred wiring directions of the outermost layers of the two IC dies are orthogonal with respect to each other.
3. The method of claim 1 , wherein
each of the first and second sets of interconnect layers has N interconnect layers,
the preferred wiring direction of each layer M in the first set of interconnect layers matches the preferred wiring direction of a corresponding layer M in the second set of interconnect layers, and
N and M are integers.
4. The method of claim 1 further comprising establishing a plurality of connections between the outermost layers of the first and second sets of interconnect layers.
5. The method of claim 4 , wherein the plurality of connections between the first and second sets of interconnect layers comprise a plurality of direct bonded connections.
6. The method of claim 5 , wherein the first and second IC dies are bonded to each other across silicon oxide or silicon nitride surfaces.
7. The method of claim 1 , wherein the plurality of connections between the first and second sets of interconnect layers comprise a plurality of vias, each via bonding a conductive pad on an interconnect layer of the first IC die with a conductive pad on an interconnect layer of the second IC die.
8. The method of claim 1 , wherein the first and second IC dies are fabricated with a common or partially common set of masks as the first and second IC dies implement one IC design.
9. The method of claim 1 , wherein the first and second IC dies have orthogonal crystalline directions after the first and second IC dies have been face-to-face mounted.
10. The method of claim 1 , wherein the second IC die is a passive interposer.
11. The method of claim 1 , wherein the preferred wiring directions are horizontal and vertical wiring directions.
12. A method of fabricating a three-dimensional (3D) circuit, the method comprising:
selecting a first integrated circuit (IC) die comprising a first semiconductor substrate and a first set of interconnect layers defined on top of the first semiconductor substrate;
selecting a second IC die comprising a second semiconductor substrate and a second set of interconnect layers defined on top of the second semiconductor substrate
face-to-face mounting the first and second IC dies so that an outermost interconnect layer of the first IC die has a preferred wiring direction that is orthogonal to the preferred wiring direction of an outermost interconnect layer of the second IC die.
13. The method of claim 12 , wherein
the first set of interconnect layers has N interconnect layers while the second set of interconnect layers has N+1 interconnect layers,
N is an integer, and
each Mth layer in the first N layers of the first set of interconnect layers has the same preferred wiring direction as the Mth layer in the first N layers of the second set of interconnect layers.
14. The method of claim 12 , wherein the first set of interconnect layers has N interconnect layers and the second set of interconnect layers has N interconnect layers, wherein N is an integer.
15. The method of claim 12 further comprising establishing a plurality of connections between the outermost layers of the first and second sets of interconnect layers.
16. The method of claim 15 , wherein the plurality of connections between the first and second sets of interconnect layers comprise a plurality of direct bonded connections.
17. The method of claim 16 , wherein the first and second IC dies are bonded to each other across silicon oxide or silicon nitride surfaces.
18. The method of claim 12 , wherein the plurality of connections between the first and second sets of interconnect layers comprise a plurality of vias, each via bonding a conductive pad on an interconnect layer of the first IC die with a conductive pad on an interconnect layer of the second IC die.
19. The method of claim 12 , wherein the first and second IC dies are fabricated with a common or partially common set of masks as the first and second IC dies implement one IC design.
20. The method of claim 12 , wherein the first and second IC dies have orthogonal crystalline directions after the first and second IC dies have been face-to-face mounted.
21. The method of claim 12 , wherein the second IC die is a passive interposer.
22. The method of claim 12 , wherein the preferred wiring directions are horizontal and vertical wiring directions.