Classifications

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  • H01L25/18—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof the devices being of types provided for in two or more different subgroups of the same main group of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N
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  • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
  • H01L24/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
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  • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L2224/10—Bump connectors; Manufacturing methods related thereto
  • H01L2224/15—Structure, shape, material or disposition of the bump connectors after the connecting process
  • H01L2224/16—Structure, shape, material or disposition of the bump connectors after the connecting process of an individual bump connector
  • H01L2224/161—Disposition
  • H01L2224/16135—Disposition the bump connector connecting between different semiconductor or solid-state bodies, i.e. chip-to-chip
  • H01L2224/16145—Disposition the bump connector connecting between different semiconductor or solid-state bodies, i.e. chip-to-chip the bodies being stacked
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  • H01L2224/10—Bump connectors; Manufacturing methods related thereto
  • H01L2224/15—Structure, shape, material or disposition of the bump connectors after the connecting process
  • H01L2224/16—Structure, shape, material or disposition of the bump connectors after the connecting process of an individual bump connector
  • H01L2224/161—Disposition
  • H01L2224/16151—Disposition the bump connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
  • H01L2224/16221—Disposition the bump connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
  • H01L2224/16225—Disposition the bump connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being non-metallic, e.g. insulating substrate with or without metallisation
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  • H01L2224/80001—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected by connecting a bonding area directly to another bonding area, i.e. connectorless bonding, e.g. bumpless bonding
  • H01L2224/808—Bonding techniques
  • H01L2224/80894—Direct bonding, i.e. joining surfaces by means of intermolecular attracting interactions at their interfaces, e.g. covalent bonds, van der Waals forces
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  • H01L24/10—Bump connectors ; Manufacturing methods related thereto
  • H01L24/15—Structure, shape, material or disposition of the bump connectors after the connecting process
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  • H01L24/81—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a bump connector
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  • H01L24/93—Batch processes
  • H01L24/94—Batch processes at wafer-level, i.e. with connecting carried out on a wafer comprising a plurality of undiced individual devices
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  • H01L25/03—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes
  • H01L25/04—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers
  • H01L25/065—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers the devices being of a type provided for in group H01L27/00
  • H01L25/0657—Stacked arrangements of devices
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  • H01L2924/0001—Technical content checked by a classifier
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  • H01L2924/11—Device type
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  • H01L2924/11—Device type
  • H01L2924/14—Integrated circuits
  • H01L2924/143—Digital devices
  • H01L2924/1434—Memory
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  • H01L2924/151—Die mounting substrate
  • H01L2924/153—Connection portion
  • H01L2924/1531—Connection portion the connection portion being formed only on the surface of the substrate opposite to the die mounting surface
  • H01L2924/15311—Connection portion the connection portion being formed only on the surface of the substrate opposite to the die mounting surface being a ball array, e.g. BGA

Definitions

• Some embodiments of the invention provide a three-dimensional (3D) circuit that is formed by vertically stacking two or more integrated circuit (IC) dies to at least partially overlap.
• 3D circuit in some embodiments can be any type of circuit such as a processor, like a CPU (central processing unit), a GPU (graphics processing unit), a TPU (tensor processing unit), etc., or other kind of circuits, like an FPGA (field programmable gate array), AI (artificial intelligence) neural network chip, encrypting/decrypting chips, etc.
• connections in some embodiments cross the bonding layer(s) in a direction normal to the bonded surface.
• the overlapping, connected circuit block pairs include pairs of computation blocks and pairs of computation and memory blocks.
• the connections that cross bonding layers to electrically connect circuit blocks on different dies are referred to below as z-axis wiring or connections. This is because these connections traverse completely or mostly in the z-axis of the 3D circuit, with the x-y axes of the 3D circuit defining the planar surface of the IC die substrate or interconnect layers. These connections are also referred to as vertical connections to differentiate them from the horizontal planar connections along the interconnect layers of the IC dies.
• Figure 1 illustrates a 3D circuit of some embodiments of the invention.
• Figure 2 illustrates an example of a high-performance 3D processor that has a multi-core processor on one die and an embedded memory on another die.
• FIG. 3 illustrates how multi-core processors are commonly used today in many devices.
• Figure 4 illustrates an example of a 3D processor that is formed by vertically stacking three dies.
• Figure 5 illustrates three vertically stacked dies with the backside of the second die thinned through a thinning process after face-to-face bonding the first and second dies but before face-to- back mounting the third die to the second die.
• FIGS 6-9 illustrate other 3D processors of some embodiments.
• Figure 10 illustrates that some embodiments place on different stacked dies two compute circuits that perform successive computations.
• Figure 11 illustrates an example of a high-performance 3D processor that has overlapping processor cores on different dies.
• Figure 12 illustrates another example of a high-performance 3D processor that has a processor core on one die overlap with a cache on another die.
• Figure 13 illustrates an example of a 3D processor that has different parts of a processor core on two face-to-face mounted dies.
• Figure 14 shows a compute circuit on a first die that overlaps a memory circuit on a second die, which is vertically stacked over the first die.
• Figure 15 shows two overlapping compute circuits on two vertically stacked dies.
• Figure 16 illustrates an array of compute circuits on a first die overlapping an array of memories on a second die that is face-to-face mounted with the first die through direct bonded interconnect (DBI) boding process.
• DBI direct bonded interconnect
• Figure 17 illustrates a traditional way of interlacing a memory array with a compute array.
• Figures 18 and 19 illustrates two examples that show how high density DBI connections can be used to reduce the size of an arrangement of compute circuit that is formed by several successive stages of circuits, each of which performs a computation that produces a result that is passed to another stage of circuits until a final stage of circuits is reached.
• Figure 20 presents a compute circuit that performs a computation (e.g., an addition or multiplication) on sixteen multi-bit input values on two face-to-face mounted dies.
• a computation e.g., an addition or multiplication
• Figure 21 illustrates a device that uses a 3D IC.
• Figure 22 provides an example of a 3D chip that is formed by two face-to-face mounted IC dies that are mounted on a ball grid array.
• Figure 23 illustrates a manufacturing process that some embodiments use to produce the 3D chip.
• Figures 24-27 show two wafers at different stages of the fabrication process of Figure 23.
• Figure 28 illustrates an example of a 3D chip with three stacked IC dies.
• Figure 29 illustrates an example of a 3D chip with four stacked IC dies.
• Figure 30 illustrates a 3D chip that is formed by face-to-face mounting three smaller dies on a larger die.
• Some embodiments of the invention provide a three-dimensional (3D) circuit that is formed by vertically stacking two or more integrated circuit (IC) dies to at least partially overlap.
• IC integrated circuit
• several circuit blocks defined on each die (1) overlap with other circuit blocks defined on one or more other dies, and (2) electrically connect to these other circuit blocks through connections that cross one or more bonding layers that bond one or more pairs of dies.
• the overlapping, connected circuit block pairs include pairs of computation blocks and pairs of computation and memory blocks.
• connections that cross bonding layers to electrically connect circuit blocks on different dies are referred to below as z-axis wiring or connections. This is because these connections traverse completely or mostly in the z-axis of the 3D circuit (e.g., because these connections in some embodiments cross the bonding layer(s) in a direction normal or nearly normal to the bonded surface), with the x-y axes of the 3D circuit defining the planar surface of the IC die substrate or interconnect layers. These connections are also referred to as vertical connections to differentiate them from the horizontal planar connections along the interconnect layers of the IC dies.
• Figure 1 illustrates an example of such a 3D circuit. Specifically, it illustrates a 3D circuit 100 that is formed by vertically stacking two IC dies 105 and 110 such that each of several circuit blocks on one die (1) overlaps at least one other circuit block on the other die, and (2) electrically connects to the overlapping die in part through z-axis connections 150 that cross a bonding layer that bonds the two IC dies.
• the two dies 105 and 110 are face-to-face mounted as further described below.
• the stacked first and second dies in some embodiments are encapsulated into one integrated circuit package by an encapsulating epoxy and/or a chip case.
• the first die 105 includes a first semiconductor substrate 120 and a first set of interconnect layers 125 defined above the first semiconductor substrate 120.
• the second IC die 110 includes a second semiconductor substrate 130 and a second set of interconnect layers 135 defined below the second semiconductor substrate 130.
• numerous electronic components e.g., active components, like transistors and diodes, or passive components, like resistors and capacitors) are defined on the first semiconductor substrate 120 and on the second semiconductor substrate 130.
• the electronic components on the first substrate 120 are connected to each other through interconnect wiring on the first set of interconnect layers 125 to form numerous microcircuits (e.g., Boolean gates, such as AND gates, OR gates, etc.) and/or larger circuit blocks (e.g., functional blocks, such as memories, decoders, logic units, multipliers, adders, etc.).
• the electronic components on the second substrate 130 are connected to each other through interconnect wiring on the second set of interconnect layers 135 to form additional microcircuits and/or larger circuit block.
• a portion of the interconnect wiring needed to define a circuit block on one die's substrate is provided by interconnect layer(s) (e.g., the second set interconnect layers 135) of the other die (e.g., the second die 110).
• interconnect layer(s) e.g., the second set interconnect layers 135) of the other die (e.g., the second die 110).
• the electronic components on one die's substrate e.g., the first substrate 120 of the first die 105 in some embodiments are also connected to other electronic components on the same substrate (e.g., substrate 120) through interconnect wiring on the other die's set of interconnect layers (e.g., the second set of interconnect layers 135 of the second die 110) to form a circuit block on the first die.
• the interconnect layers of one die can be shared by the electronic components and circuits of the other die in some embodiments.
• the interconnect layers of one die can also be used to carry power, clock and data signals for the electronic components and circuits of the other die, as described in United States Patent Application 15/976,815 filed May 10, 2018, which is incorporated herein by reference.
• the interconnect layers that are shared between two dies are referred to as the shared interconnect layers in the discussion below.
• Each interconnect layer of an IC die typically has a preferred wiring direction (also called routing direction). Also, in some embodiments, the preferred wiring directions of successive interconnect layers of an IC die are orthogonal to each other.
• the preferred wiring directions of an IC die typically alternate between horizontal and vertical preferred wiring directions, although several wiring architectures have been introduced that employ 45 degree and 60 degree offset between the preferred wiring directions of successive interconnect layers. Alternating the wiring directions between successive interconnect layers of an IC die has several advantages, such as providing better signal routing and avoiding capacitive coupling between long parallel segments on adjacent interconnect layers.
• the first and second dies are face-to-face stacked so that the first and second set of interconnect layers 125 and 135 are facing each other.
• the top interconnect layers 160 and 165 are bonded to each other through a direct bonding process that establishes direct-contact metal-to-metal bonding, oxide bonding, or fusion bonding between these two sets of interconnect layers.
• An example of such bonding is copper-to-copper (Cu-Cu) metallic bonding between two copper conductors in direct contact.
• the direct bonding is provided by a hybrid bonding technique such as DBI® (direct bond interconnect) technology, and other metal bonding techniques (such as those offered by Invensas Bonding Technologies, Inc., an Xperi Corporation company, San Jose, CA).
• DBI direct bond interconnect
• other metal bonding techniques such as those offered by Invensas Bonding Technologies, Inc., an Xperi Corporation company, San Jose, CA.
• DBI connects span across silicon oxide and silicon nitride surfaces.
• the DBI process is further described in United States Patent 6,962,835 and United States Patent 7,485,968, both of which are incorporated herein by reference. This process is also described in U.S. Patent Application 15/725,030, which is also incorporated herein by reference.
• the direct bonded connections between two face-to-face mounted IC dies are native interconnects that allow signals to span two different dies with no standard interfaces and no input/output protocols at the cross-die boundaries.
• the direct bonded interconnects allow native signals from one die to pass directly to the other die with no modification of the native signal or negligible modification of the native signal, thereby forgoing standard interfacing and consortium-imposed input/output protocols.
• Direct bonded interconnects allow circuits to be formed across and/or to be accessed through the cross-die boundary of two face-to-face mounted dies. Examples of such circuits are further described in U.S. Patent Application 15/725,030. The incorporated United States Patent 6,962,835, United States Patent 7,485,968, and U.S. Patent Application 15/725,030 also describe fabrication techniques for manufacturing two face-to-face mounted dies.
• a DBI connection between two dies terminates on electrical contacts (referred to as pads in this document) on each die's top interconnect layer.
• the DBI-connection pad on each die electrically connects the DBI connection with circuit nodes on the die that need to provide the signal to the DBI connection or to receive the signal from the DBI connection.
• a DBI-connection pad connects to an interconnect segment on the top interconnect layer of a die, which then carries the signal to a circuit block on the die's substrate through a series of vias and interconnect lines.
• Vias are z-axis structures on each die that carry signals between the interconnect layers of the die and between the IC die substrate and the interconnect layers of the die.
• the direct bonding techniques of some embodiments allow a large number of direct connections 150 to be established between the top interconnect layer 165 of the second die 110 and top interconnect layer 160 of the first die 105.
• the first die uses other IC structures (e.g., vias) to carry these signals from its top interconnect layer to these other layers and/or substrate.
• more than 1,000 connections/mm 2 , 10,000 connections/mm 2 , 100,000 connections/mm 2 , 1,000,000 connections/mm 2 or less, etc. can be established between the top interconnect layers 160 and 165 of the first and second dies 105 and 110 in order to allow signals to traverse between the first and second IC dies.
• the direct-bonded connections 150 between the first and second dies are very short in length.
• the direct-bonded connections can range from a fraction of a micron to a single-digit or low double-digit microns (e.g., 2-10 microns).
• the short length of these connections allows the signals traversing through these connections to reach their destinations quickly while experiencing no or minimal capacitive load from nearby planar wiring and nearby direct-bonded vertical connections.
• the planar wiring connections are referred to as x-y wiring or connections, as such wiring stays mostly within a plane defined by an x-y axis of the 3D circuit.
• the pitch (distance) between two neighboring direct-bonded connections 150 can be extremely small, e.g., the pitch for two neighboring connections is between 0.5 ⁇ to 15 ⁇ .
• This close proximity allows for the large number and high density of such connections between the top interconnect layers 160 and 165 of the first and second dies 105 and 110.
• the close proximity of these connections does not introduce much capacitive load between two neighboring z-axis connections because of their short length and small interconnect pad size.
• the direct bonded connections are less then 1 or 2 ⁇ in length (e.g., 0.1 to 0.5 ⁇ in length), and facilitate short z-axis connections (e.g., 1 to 10 ⁇ in length) between two different locations on the two dies even after accounting for the length of vias on each of the dies.
• the direct vertical connections between two dies offer short, fast paths between different locations on these dies.
• electrical nodes in overlapping portions of the circuit blocks on the first and second dies can be electrically connected.
• These electrical nodes can be on the IC die substrates (e.g., on the portions of the substrates that contain node of electronic components of the circuit blocks) or on the IC die interconnect layers (e.g., on the interconnect layer wiring that form the circuit block).
• vias are used to carry the signals to or from the z-axis connections to these nodes.
• vias are z- axis structures that carry signals between the interconnect layers and between the IC die substrate and the interconnect layers.
• Figure 1 illustrates numerous z-axis connections 150 between overlapping regions 181- 185 in the top interconnect layers 160 and 165. Each of these regions corresponds to a circuit block 171-175 that is defined on one of the IC die substrates 120 and 130. Also, each region on the top interconnect layer of one die connects to one or more overlapping regions in the top interconnect layer of the other die through numerous z-axis connections. Specifically, as shown, z-axis connections connect overlapping regions 181 and 184, regions 182 and 184, and regions 183 and 185. Vias are used to provide signals to these z-axis connections from the IC die substrates and interconnect layers. Also, vias are used to carry signals from the z-axis connections when the electrical nodes that need to receive these signals are on the die substrates or the interconnect layers below the top layer.
• the density of connections between overlapping connected regions can be in the range of 1,000 connections/mm 2 to 1,000,000 connections/mm 2 .
• the pitch between two neighboring direct-bonded connections 150 can be extremely small, e.g., the pitch for two neighboring connections is between 0.5 ⁇ to 15 ⁇ .
• these connections can be very short, e.g., in the range from a fraction of a micron to a low single-digit microns.
• each top interconnect-layer region 181-185 corresponds to a circuit block region 171-175 on an IC die substrate 120 or 130.
• a circuit block's corresponding top interconnect-layer region i.e., the region that is used to establish the z-axis connections for that circuit block
• all the z- axis connections that are used to connect two overlapping circuit blocks in two different dies do not connect one contiguous region in the top-interconnect layer of one die with another contiguous region in the top-interconnect layer of the other die.
• the z-axis connections connect circuits on the two dies that do not overlap (i.e., do not have any of their horizontal cross section vertically overlap).
• the number of connections that can be established between them is limited by the number of connections that can be made through their perimeters on one or more interconnect layers.
• the connections between the two circuits are not limited to periphery connections that come through the perimeter of the circuits, but also include z-axis connections (e.g., DBI connections and via connections) that are available through the area of the overlapping region.
• circuit blocks 173 and 175 on dies 105 and 110 share a data bus 190 on the top interconnect layer of the second die 110. This data bus carries data signals to both of these circuits.
• Direct-bonded connections are used to carry signals from this data bus 190 to the circuit block 175 on the first die 105. These direct-bonded connections are much shorter than connections that would route data-bus signals on the first die about several functional blocks in order to reach the circuit block 175 from this block's periphery. The data signals that traverse the short direct- bonded connections reach this circuit 175 on the first die very quickly (e.g., within 1 or 2 clock cycles) as they do not need to be routed from the periphery of the destination block.
• a data-bus line can be positioned over or near a destination circuit on the first die to ensure that the data-bus signal on this line can be provided to the destination circuit through a short direct-bonded connection.
• Z-axis connection and the ability to share interconnect layers on multiple dies reduce the congestion and route limitations that may be more constrained on one die than another.
• Stacking IC dies also reduces the overall number of interconnect layers of the two dies because it allows the two dies to share some of the higher-level interconnect layers in order to distribute signals. Reducing the higher-level interconnect layers is beneficial as the wiring on these layers often consumes more space due to their thicker, wider and coarser arrangements.
• two dies are face-to-face mounted
• these two dies are face-to-back stacked (i.e., the set of interconnect layers of one die is mounted next to the backside of the semiconductor substrate of the other die), or back-to-back stacked (i.e., the backside of the semiconductor substrate of one die is mounted next to the backside of the semiconductor substrate of the other die).
• a third die (e.g., an interposer die) is placed between the first and second dies, which are face-to-face stacked, face-to-back stacked (with the third die between the backside of the substrate of one die and the set of interconnect layers of the other die), or back-to- back stacked (with the third die between the backsides of the substrates of the first and second dies).
• the vertical stack of dies in some embodiments includes three or more IC dies in a stack.
• While some embodiments use a direct bonding technique to establish connections between the top interconnect layers of two face-to-face stacked dies, other embodiments use alternative connection schemes (such as through silicon vias, TSVs, through-oxide vias, TOVs, or through-glass vias, TGVs) to establish connections between face-to-back dies and between back-to-back dies.
• alternative connection schemes such as through silicon vias, TSVs, through-oxide vias, TOVs, or through-glass vias, TGVs
• the overlapping circuit blocks 171-175 on the two dies 105 and 110 are different types of blocks in different embodiments. Examples of such blocks in some embodiments include memory blocks that store data, computational blocks that perform computations on the data, and I/O blocks that receive and output data from the 3D circuit 100.
• Figures 2, 4, and 6 illustrate several different overlapping memory blocks, computational blocks, and/or I/O blocks architectures of some embodiments. Some of these examples illustrate high performance 3D multi-core processors.
• Figures 10-11 then illustrate several examples of overlapping computation blocks, including different cores of a multi- core processor being placed on different IC dies.
• Figure 13 illustrates an example of overlapping functional blocks of a processor core.
• Figure 2 illustrates an example of a high-performance 3D processor 200 that has a multi- core processor 250 on one die 205 and an embedded memory 255 on another die 210.
• the horizontal cross section of the multi-core processor has a substantially vertical overlaps with the horizontal cross section of the embedded memory.
• the two dies 205 and 210 are face-to-face mounted through a direct bonding process, such as the DBI process. In other embodiments, these two dies can be face-to-back or back-to-back mounted.
• numerous z-axis connections 150 cross a direct bonding layer that bonds the two IC dies 205 and 210 in order to establish numerous signal paths between the multi- core processor 250 and the embedded memory 255.
• the z-axis connections can be in the range of 1,000 connections/mm 2 to 1,000,000 connections/mm 2 .
• the DBI z-axis connections allow a very large number of signal paths to be defined between the multi-core processor 250 and the embedded memory 255.
• the DBI z-axis connections 150 also support very fast signal paths as the DBI connections are typically very short (e.g., are 0.2 ⁇ to 2 ⁇ ).
• the overall length of the signal paths is also typically short because the signal paths are mostly vertical.
• the signal paths often rely on interconnect lines (on the interconnect layers) and vias (between the interconnect layers) to connect nodes of the processor 250 and the embedded memory 255. However, the signal paths are mostly vertical as they often connect nodes that are in the same proximate z-cross section.
• the length of a vertical signal path mostly accounts for the height of the interconnect layers of the dies 205 and 210, which is typically in the single digit to low- double digit microns (e.g., the vertical signal paths are typically in the range of 10-20 ⁇ long).
• z-axis connections provide short, fast and plentiful connections between the multi-core processor 250 and the embedded memory 255, they allow the embedded memory 255 to replace many of the external memories that are commonly used today in devices that employ multi-core processors.
• robust z-axis connections between vertically stacked IC dies enable next generation system on chip (SoC) architectures that combine the computational power of the fastest multi-core processors with large embedded memories that take the place of external memories.
• SoC system on chip
• Figure 3 illustrates how multi-core processors are commonly used today in many devices.
• a multi-core processor 350 in a device 305 typically communicates with multiple external memories 310 of the device 305 through an external I/O interface 355 (such as a double data rate (DDR) interface).
• the multi-core processor has multiple general processing cores 352 and one or more graphical processing cores 354 that form a graphical processing unit 356 of the processor 350.
• Each of the processing cores has its own level 1 (LI) cache 362 to store data. Also, multiple level 2 (L2) caches 364 are used to allow different processing cores to store their data for access by themselves and by other cores. One or more level 3 (L3) caches 366 are also used to store data retrieved from external memories 310 and to supply data to external memories 310. The different cores access the L2 and L3 caches through arbiters 368. As shown, I/O interfaces 355 are used to retrieve data for L3 cache 366 and the processing cores 352 and 354. LI caches typically have faster access times than L2 caches, which, in turn, have faster access times often than L3 caches.
• the I/O interfaces consume a lot of power and also have limited I/O capabilities. Often, I/O interfaces have to serialize and de-serialize the output data and the input data, which consumes power and also restricts the multi-core processors input/output. Also, the architecture illustrated in Figure 3 requires enough wiring to route the signals between the various components of the multi- core processor and the I/O interfaces.
• the power consumption, wiring and processor's I/O bottleneck is dramatically improved by replacing the external memories with one or more embedded memories 255 that are vertically stacked with the multi-core processor 250 in the same IC package.
• This arrangement dramatically reduces the length of the wires needed to carry signals between the multi-core processor 250 and its external memory (which in Figure 2 is the embedded memory 255). Instead of being millimeters in length, this wiring is now in the low microns. This is a 100-1000 times improvement in wirelength.
• the reduction in wirelength allows the 3D processor 200 of Figure 2 to have much lower power consumption than the present day design of Figure 3.
• the 3D processor's stacked design also consumes much less power as it foregoes the low throughput, high power consuming I/O interface between the external memories 310 and the multi-core processor 350 with plentiful, short z-axis connections between the embedded memory 255 and the multi-core processor 250.
• the 3D processor 200 still needs an I/O interface on one of its dies (e.g., the first die 205, the second die 210 or another stacked die, not shown), but this processor 200 does not need to rely on it as heavily to input data for consumption as a large amount of data (e.g., more than 200 MB, 500 MB, 1 GB, etc.) can be stored in the embedded memory 255.
• a large amount of data e.g., more than 200 MB, 500 MB, 1 GB, etc.
• the stacked design of the 3D processor 200, Figure 2 also reduces the size of the multi- core processor by requiring less I/O interface circuits and by placing the I/O interface circuits 257 on the second die 210.
• the I/O interface circuits 257 are on the first die 205, but are fewer and/or smaller circuits.
• the I/O interface circuits are placed on a third die stacked with the first and second dies, as further described below.
• the stacked design of the 3D processor 200 also frees up space in the device that uses the multi-core processor as it moves some of the external memories to be in the same IC chip housing as the multi-core processor.
• Examples of memories that can be embedded memories 255 stacked with the multi-core processor 250 include any type of memory, such as SRAM (static random access memory), DRAM (dynamic random access memory), MRAM (magnetoresi stive random access memory), TCAM (ternary content addressable random access memory), NAND Flash, NOR Flash, RRAM (resistive random access memory), PCRAM (phase change random access memory), etc.
• Figure 2 illustrates one embedded memory on the second die 210
• multiple embedded memories are defined on the second die 210 in some embodiments, while multiple embedded memories are defined on two or more dies that are vertically stacked with the first die 205 that contains the multi-core processor 250.
• the different embedded memories all are of the same type, while in other embodiments, the different embedded memories are different types (e.g., some are SRAMs while others are NA D/NOR Flash memories).
• the different embedded memories are defined on the same IC die, while in other embodiments, different embedded memories are defined on different IC dies.
• FIG. 2 illustrates that in some embodiments the multi-core processor 250 has the similar components (e.g., multiple general processing cores 270, LI, L2, and L3 caches 272, 274, and 276, cache arbiters 278 and 280, graphical processing core 282, etc.) like other multi-processor cores.
• the I/O interface circuits 257 for the multi-core processor 250 are placed on the second die 205, as mentioned above.
• the I/O circuits 257 write data to the embedded memory 255 from external devices and memories, and reads data from the embedded memory 255 for the external devices and memories.
• the I/O circuit 255 can also retrieve data from external devices and memories for the L3 cache, or receive data from the L3 cache for external devices and memories, without the data first going through the embedded memory 255.
• Some of these embodiments have a direct vertical (z-axis) bus between the L3 cache and the I/O circuit 257.
• the first die 205 also includes I/O circuits as interfaces between the I/O circuit 255 and the L3 cache 276, or as interfaces between the L3 cache 276 and the external devices/memories.
• FIG. 4 illustrates an example of a 3D processor 400 that is formed by vertically stacking three dies 405, 410 and 415, with the first die 405 including multiple processor cores 422 and 424 of a multi-core processor, the second die 410 including L1-L3 caches 426, 428 and 430 for the processing cores, and the third die 415 including I/O circuits 435.
• the first and second dies 405 and 410 are face-to-face mounted (e.g., through a direct bonding process, such as a DBI process), while the second and third dies 410 and 415 are back-to-face mounted.
• the processor cores are in two sets of four cores 432 and 434. As shown, each core on the first die 405 overlaps (1) with that core's LI cache 426 on the second die 410, (2) with one L2 cache 428 on the second die 410 that is shared by the three other cores in the same four-core set 432 or 434, and (3) with the L3 cache 430 on the second die 410.
• numerous z-axis connections e.g., DBI connections
• some or all of the cache memories are multi -ported memories that can be simultaneously accessed by different cores.
• One or more of the cache memories include cache arbiter circuits that arbitrate (e.g., control and regulate) simultaneous and at time conflicting access to the memories by different processing cores.
• the 3D processor 400 also includes one L2 cache memory 436 on the first die 405 between the two four-core sets 432 and 434 in order to allow data to be shared between these sets of processor cores.
• the L2 cache memory 436 includes a cache arbiter circuit (not shown).
• the 3D processor 400 does not include the L2 cache memory 436.
• the different processor core sets 432 and 434 share data through the L3 cache 430.
• the L3 cache 430 stores data for all processing cores 422 and 424 to access. Some of this data is retrieved from external memories (i.e., memories outside of the 3D processor 400) by the I/O circuit 435 that is defined on the third die 415.
• the third die 415 in some embodiments is face- to-back mounted with the second die.
• TSVs 460 are defined through the second die's substrate, and these TSVs electrically connect (either directly or through interconnect segments defined on the back side of the second die) to direct bonded connections that connect the backside of the second die to the front side of the third die (i.e., to the top interconnect layer on the front side of the third die).
• the backside of the second die is thinned through a thinning process after face-to-face bonding the first and second dies but before face-to-back mounting the third die to the second die.
• This thinning allows the TSVs through the second die's substrate to be shorter.
• the shorter length of the TSVs allows the TSVs to have smaller cross sections and smaller pitch (i.e., smaller center-to-center distance to neighboring TSVs), which thereby improves their density.
• Most of the signal paths between the second and third dies 410 and 415 are very short (e.g., typically in the range of 10-20 ⁇ long) as they mostly traverse in the vertical direction through the thinned second die's substrate and third die's interconnect layers, which have relatively short heights.
• a large number of short, vertical signal paths are defined between the L3 cache 430 on the second die 410 and the I/O circuit 435 on the third die 415. These signal paths use (1) direct-bonded connections between the top interconnect layer of the third die 415 and the backside of the second die 410, (2) TSVs 460 through the second die's substrate, and (3) vias between the interconnect layers, and interconnect segments on the interconnect layers, of the second and third die. The number and short length of these signal paths allow the I/O circuit to rapidly write to and read from the L3 cache.
• the signal paths between the first and second dies 405 and 410 use (1) direct-bonded connections between the top interconnect layers of the first and second dies 405 and 410, and (2) vias between the interconnect layers, and interconnect segments on the interconnect layers, of the first and second dies 405 and 410. Most of these signal paths between the first and second dies 405 and 410 are also very short (e.g., typically in the range of 10-20 ⁇ long) as they mostly traverse in the vertical direction through the first and second dies' interconnect layers, which have relatively short heights. In some embodiments, a large number of short, vertical signal paths are defined between the processing cores on the first die 405 and their associated L1-L3 caches.
• the processor cores use these fast and plentiful signal paths to perform very fast writes and reads of large data bit sets to and from the L1-L3 cache memories.
• the processor cores then perform their operations (e.g., their instruction fetch, instruction decode, arithmetic logic, and data write back operations) based on these larger data sets, which in turn allows them to perform more complex instruction sets and/or to perform smaller instruction sets more quickly.
• FIG. 6 illustrates another 3D processor 600 of some embodiments.
• This processor 600 combines features of the 3D processor 200 of Figure 2 with features of the 3D processor 400 of Figure 4. Specifically, like the processor 400, the processor 600 places multiple processor cores 422 and 424 on a first die 605, L1-L3 caches 426, 428 and 430 on a second die 610, and I/O circuits 435 on a third die 615. However, like the processor 200, the processor 600 also has one die with an embedded memory 622. This embedded memory is defined on a fourth die 620 that is placed between the second and third dies 610 and 615.
• the first and second dies 605 and 610 are face-to-face mounted (e.g., through a direct bonding process, such as a DBI process), the fourth and second dies 620 and 610 are face- to-back mounted, and the third and fourth dies 615 and 620 are face-to-back mounted.
• TSVs 460 are defined through the substrates of the second die and third dies.
• the TSVs through the second die 610 electrically connect (either directly or through interconnect segments defined on the back side of the second die) to direct bonded connections that connect the backside of the second die 610 to the front side of the fourth die 620, while the TSVs through the fourth die 620 electrically connect (either directly or through interconnect segments defined on the back side of the second die) to direct bonded connections that connect the backside of the fourth die 620 to the front side of the third die 615.
• the backside of the second die is thinned through a thinning process after face-to-face bonding the first and second dies but before face-to-back mounting the fourth die 620 to the second die 610.
• the backside of the fourth die 620 is thinned through a thinning process after face-to-back mounting the fourth and second dies 620 and 610 but before face-to-back mounting the third die 615 to the fourth die 620.
• the shorter length of the TSVs allows the TSVs to have smaller cross sections and smaller pitch (i.e., smaller center-to-center distance to neighboring TSVs), which thereby improves their density.
• the L3 cache 430 in Figure 6 stores data for all processing cores 422 and 424 to access.
• the L3 cache does not connect to the I/O circuits 435 but rather connects to the embedded memory 622 on the fourth die through vertical signal paths.
• the embedded memory 622 connects to the I/O circuits 435 on the third die 615 through vertical signal paths.
• the vertical signal paths between the second and fourth dies 610 and 620 and between the fourth and third dies 620 and 615 are established by z-axis direct bonded connections and TSVs, as well as interconnect segments on the interconnect layers and vias between the interconnect layers. Most of these signal paths are very short (e.g., typically in the range of 10-20 ⁇ long) as they are mostly vertical and the height of the thinned substrates and their associated interconnect layers is relatively short.
• the embedded memory 622 is a large memory (e.g., is larger than 200 MB, 500 MB, 1 GB, etc.) in some embodiments. As such, the embedded memory in some embodiments can replace one or more external memories that are commonly used today in devices that employ multi-core processors. Examples of the embedded memory 622 include SRAM, DRAM, MRAM, NAND Flash, NOR Flash, RRAM, PCRAM, etc. In some embodiments, two or more different types of embedded memories are defined on one die or multiple dies in the stack of dies that includes one or more dies on which a multi-core processor is defined.
• the embedded memory 622 receives data from, and supplies data to, the I/O circuit 435.
• the I/O circuit 435 writes data to the embedded memory 622 from external devices and memories, and reads data from the embedded memory 622 for the external devices and memories.
• the I/O circuit 435 can also retrieve data from external devices and memories for the L3 cache, or receive data from the L3 cache for external devices and memories, without the data first going through the embedded memory 622.
• Some of these embodiments have a direct vertical (z-axis) bus between the L3 cache and the I/O circuit 435.
• the second die 610 and/or fourth die 620 also include I/O circuits as interfaces between the I/O circuit 435 and the L3 cache 430, or as interfaces between the L3 cache 430 and the external devices/memories.
• FIG. 7 illustrates yet another 3D processor 700 of some embodiments.
• This processor 700 is identical to the processor 600 of Figure 6, except that it only has two layers of caches, LI and L2, on a second die 710 that is face-to-face mounted on a first die 705 that has eight processor cores 722.
• each LI cache 726 overlaps just one core 722.
• the L2 cache 728 is shared among all the cores 722 and overlaps each of the cores 722.
• each core connects to each LI or L2 cache that it overlaps through (1) numerous z- axis DBI connections that connect the top interconnect layers of the dies 705 and 721, and (2) the interconnects and vias that carry the signals from these DBI connections to other metal and substrate layers of the dies 705 and 710.
• the DBI connections in some embodiments allow the data buses between the caches and the cores to be much wider and faster than traditional data buses between the caches and the cores.
• LI caches are formed by memories that can be accessed faster (i.e., have faster read or write times) than the memories that are used to form L2 caches.
• Each LI cache 726 in some embodiments is composed of just one bank of memories, while in other embodiments it is composed of several banks of memories.
• the L2 cache 728 in some embodiments is composed of just one bank of memories, while in other embodiments it is composed of several banks of memories.
• the LI caches 726 and/or L2 cache 728 are denser than traditional LI and L2 caches as they use z-axis DBI connections to provide and receive their signals to and from the overlapping cores 722.
• the LI and L2 caches 726 and 728 are much larger than traditional LI and L2 caches as they are defined on another die than the die on which the cores are defined, and hence face less space restrictions on their placement and the amount of space that they consume on the chip.
• FIG. 8 illustrates another 3D processor 800 of some embodiments.
• This processor 800 is identical to the processor 700 of Figure 7, except that it does not have the L2 cache 728.
• the processor 900 has a network on chip (NOC) 8028 on the die 810, which is face-to-face mounted to the die 705 through a DBI bonding process.
• NOC network on chip
• the NOC 828 is an interface through which the cores 722 communicate. This interface includes one or more buses and associated bus circuitry.
• the NOC 828 in some embodiments also communicatively connects each core to the LI caches that overlap the other cores. Through this NOC, a first core can access data stored by a second core in the LI cache that overlap the second core. Also, through this NOC, a first core in some embodiments can store data in the LI cache that overlaps a second core.
• an LI and L2 cache overlaps each core 722, and the NOC 828 connects the cores to L2 caches of other cores, but not to the LI caches of these cores. In other embodiments, the NOC 828 connects the cores to both LI and L2 caches that overlap other cores, as well as to the other cores.
• FIG. 9 illustrates yet another 3D processor 900 of some embodiments.
• This processor 900 is identical to the processor 400 of Figure 4, except that it only has one LI cache 932 on a die 910 for each of six CPU (central processing unit) cores 922 and one LI cache 934 for each of two GPU (graphical processing unit) cores 924 that are defined on a die 905 that is face-to-face mounted to the die 910 through a DBI bonding process.
• the processor 900 does not use layers 2 and 3 caches as it uses large LI caches for its CPU and GPU cores.
• the LI caches can be larger than traditional LI caches as they are defined on another die than the die on which the cores are defined, and hence face less space restrictions on their placement and the amount of space that they consume on the chip.
• the processor 900 has its I/O interface defined on a third die 415 that is face- to-back mounted on the die 910. In other embodiments, the processor 900 does not include the third die 415, but just includes the first and second dies 905 and 910. In some of these embodiments, the I/O interface of the processor 900 is defined on the first and/or second dies 905 and 910. Also, in other embodiments, one LI cache 932 is shared across multiple CPU cores 922 and/or multiple GPU cores 924.
• Figure 10 illustrates that some embodiments place on different stacked dies two compute circuits that perform successive computations.
• a compute circuit is a circuit that receives a multi- bit value as input and computes a multi-bit value as output based on the received input.
• one compute circuit 1015 is defined on a first die 1005 while the other compute circuit 1020 is defined on a second die 1010.
• the first and second dies are face-to-face mounted through a direct bonding process (e.g., a DBI process).
• This mounting defines numerous z-axis connections between the two dies 1005 and 1010.
• the z-axis connections define numerous vertical signal paths between the two compute circuits 1015 and 1020. These vertical signal paths are short as they mostly traverse in the vertical direction through the die interconnect layers, which are relatively short. As they are very short, these vertical signal paths are very fast parallel paths that connect the two compute circuit 1015 and 1020.
• the first compute circuit 1015 receives a multi-bit input value 1030 and computes a multi-bit output value 1040 based on this input value.
• the multi- bit input value 1030 and/or output value 1040 are large bit values, e.g., 32 bits, 64 bits, 128 bits, 256 bits, 512 bits, 1024 bits, etc.
• the first compute circuit 1015 provides its multi-bit output value 1040 as the input value to the compute circuit 1020. Based on this value, the compute circuit 1020 computes another multi- bit output value 1045.
• the two overlapping computation circuits on the two dies 1005 and 1010 are different cores of a multi-core processor.
• Figure 11 illustrates an example of a high- performance 3D processor 1 100 that has overlapping processor cores on different dies.
• two dies 1 105 and 1 1 10 are face-to-face mounted through a direct bonding process (e.g., the DBI process).
• the first die 1 105 includes a first processor core 1 1 12, while the second die 1 1 10 includes a second processor core 1 1 14.
• the first die 1 105 also includes an LI cache 1 1 16 for the second core 1 1 14 on the second die 1 1 10, and L2 and L3 caches 1 122 and 1 126 for both cores 1 1 12 and 1 1 14.
• the second die 1 1 10 also includes an LI cache 1 1 18 for the first core 1 1 12 on the first die 1 105, and L2 and L3 caches 1 124 and 1 128 for both cores 1 1 12 and 1 1 14.
• each core completely overlaps its corresponding LI cache, and connects to its LI cache through numerous vertical signal paths that are partially defined by z-axis connections between the top two interconnect layers of the dies 1 105 and 1 1 10. As mentioned above, such vertical signal paths are also defined by (1) vias between interconnect layers of each die, and/or (3) interconnect segments on interconnect layers of each die.
• Each core on one die also overlaps with one L2 cache and one L3 cache on the other die and is positioned near another L2 cache and another L3 cache on its own die.
• Each L2 and L3 cache 1 122-826 can be accessed by each core 1 1 12 or 1 1 14.
• Each core accesses an overlapping L2 or L3 cache through numerous vertical signal paths that are partially defined by z-axis connections between the top two interconnect layers of the dies 1 105 and 1 1 10 and by (1) vias between interconnect layers of each die, and/or (3) interconnect segments on interconnect layers of each die.
• Each core can also access an L2 or L3 cache on its own die through signal paths that are defined by visa between interconnect layers, and interconnect segments on interconnect layers, of its own die.
• each core when additional signal paths are needed between each core and an L2 or L3 cache on its own die, each core also connects to such L2 or L3 cache through signal paths that are not only defined by vias between interconnect layers, and interconnect segments on interconnect layers, of its own die, but by vias between interconnect layers and interconnect segments on interconnect layers of the other die.
• each core 1112 or 1114 retrieves much larger sets of data bits and performs more complex operations faster with such larger sets of data bits.
• each core uses wider instruction and data buses in its pipelines as it can retrieve wider instructions and data from overlapping memories.
• each core has more pipelines that perform more operations in parallel as the core can retrieve more instruction and data bits from the overlapping memories.
• each core on one die only uses the L2 cache or L3 cache on the other die (i.e., only uses the L2 or L3 cache that vertically overlaps the core) in order to take advantage of the large number of vertical signal paths between it and the overlapping L2 cache.
• Each core in some of these embodiments stores a redundant copy of each data, which it stores in its own overlapping cache (e.g., its own overlapping L2 cache) in the corresponding cache (e.g., in the other L2 cache) that is defined on the core's own die, so that the data is also available for the other core.
• each core reaches the cache on its own die through signal paths that are not only defined through the interconnect lines and vias on the core's die, but also defined through interconnect lines and vias of the other die.
• Figure 12 illustrates another example of a high-performance 3D processor 1200 that has a processor core on one die overlap with a cache on another die.
• two dies 1205 and 1210 are face-to-face mounted through a direct bonding process (e.g., the DBI process).
• the first die 1205 includes a first processor core 1212
• the second die 1210 includes a second processor core 1214.
• the first die 1205 includes an LI cache 1216 for the second processor core 1214 defined on the second die 1210
• the second die 1210 includes an LI cache 1218 for the first processor core 1212 defined on the first die 1205.
• each LI cache on one die completely overlaps the cross-section of the corresponding core on the other die.
• This ensures the largest region for defining z-axis connections (e.g., DBI connections) in the overlapping regions of each core and its corresponding LI cache.
• z-axis connections are very short and hence can be used to define a very fast bus between each core and its corresponding LI cache.
• this z-axis bus can be wide and it can be defined wholly within the x-y cross-section of the core and its LI cache, as further described below.
• the z-axis bus would not consume routing resources around the core and its LI cache. Also, the speed and width of this bus allows the bus to have a very high throughput bandwidth, which perfectly complements the high speed of the LI cache.
• the 3D processor 1200 defines an L2 cache for each core on the same die on which the core is defined.
• each core can access the other core's L2 cache through z-axis connections established through the face-to-face bonding of the two IC dies.
• the 3D process 1200 in some embodiments does not use an L3 cache.
• FIG. 13 illustrates an example of a 3D processor 1300 that has different parts of a processor core on two face-to-face mounted dies 1305 and 1310.
• the first die 1305 includes multiple pipeline 1390, with each pipeline having an instruction fetch (IF) unit 1312, an instruction decode unit 1314, an execution unit 1316 and a write-back unit 1318.
• the second die includes the instruction memory 1322 and data registers and memories 1324.
• the instruction memory 1322 on the second die overlaps with the IF units 1312 on the first die 1305.
• the data registers and memories 1324 on the second die overlap with the execution units 1316 and the write-back units.
• Numerous vertical signal paths are defined between overlapping core components by the z-axis connections between the top two interconnect layers of the dies 1305 and 1310, and by (1) vias between interconnect layers of each die 1305 or 1310, and/or (2) interconnect segments on interconnect layers of each die.
• each IF unit 1312 retrieves instructions from the instruction memory and provides the retrieved instructions to its instruction decode unit 1314.
• This decode unit decodes each instruction that it receives and supplies the decoded instruction to its execution unit to execute.
• each execution unit receives, from the data registers and memories 1324, operands that it needs to execute a received instruction, and provides the result of its execution to its write-back unit 1318.
• each writeback unit 1318 stores the execution results in the data registers and memories 1324.
• Other embodiments use other architectures to split a processor core between two different dies. For instance, some embodiments place the instruction decode and execution units 1314 and 1316 on different layers than the instruction fetch and write back units 1312 and 1318.
• Still other embodiments use other arrangements to split a processor core between different dies. These or other embodiments put different ALUs, or different portions of the same ALU, of a processor core on different vertically stacked dies (e.g., on two dies that are face-to-face mounted through a DBI bonding process).
• FIG. 14 presents an example that illustrates this.
• This figure shows a compute circuit 1415 on a first die 1405 that overlaps a memory circuit 1420 on a second die 1410, which is vertically stacked over the first die 1405.
• the compute circuit can be any type of compute circuit (e.g., processor cores, processor pipeline compute units, neural network neurons, logic gates, adders, multipliers, etc.) and the memory circuit can be any type of memory circuit (e.g., SRAMs, DRAMs, non-volatile memories, caches, etc.).
• both circuits 1415 and 1420 occupy a square region of 250 by 250 microns on their respective dies 1405 and 1410 (only the substrate surfaces of which are shown in Figure 14).
• a 100-bit z-axis bus 1425 is defined between these circuits, with the term bus in this example referring to the data and control signals exchanged between these two circuits 1415 and 1420 (in other examples, a bus might only include data signals).
• Figure 14 illustrates that when TSVs are used to define this z-axis bus 1425, this bus will consume on each die a region 1435 that is at least 2.5 times as large as the size of either circuit on that die. This is because TSVs have a 40 micron pitch. For the TSV connections, the two dies 1405 and 1410 will be front-to-back mounted with the TSVs going through the substrate of one of the two dies.
• the cross-section 1430 of the DBI bus can be contained within the footprint (i.e., the substrate region) of both circuits 1415 and 1420 on their respective dies.
• the 100 DBI connections can be fit in as little as 20-by-20 micron square, as the 100 connections can be defined as a 10-by-lO array with each connection having a minimum center-to-center spacing of 2 microns with its neighboring connections.
• DBI connections By being contained within the footprint of the circuits 1415 and 1420, the DBI connections would typically not consume any precious routing space on the dies 1405 and 1410 beyond the portion already consumed by the circuits.
• DBI connections can have a pitch ranging from less than 1 micron (e.g., 0.2 or 0.5 microns) to 5 microns.
• the difference between the amount of space consumed by the TSV connections and the space consumed by DBI connections becomes even more pronounced.
• a 60-by-60 TSV array would require a minimum 2400-by-2400 micron region (at a 40- micron DBI pitch), while a 60-by-60 DBI array would require a minimum 120-by-120 region (at a 2-micron DBI pitch).
• the TSVs would have a footprint that is at least 400 times greater than the footprint of the DBI connections.
• DBI connections allow for very large bandwidth (e.g., in the high gigabytes or in the terabytes range) between overlapping compute and memory circuits.
• the density of DBI connection is also advantageous in connecting overlapping circuit regions on two dies that are vertically stacked.
• Figure 15 presents an example that illustrates this.
• This figure shows two overlapping compute circuits 1515 and 1520 on two vertically stacked dies 1505 and 1510.
• Each of the circuits occupies a 250-by-250 micron square on its corresponding die's substrate, and can be any type of compute circuit (e.g., processor cores, processor pipeline compute units, neural network neurons, logic gates, adders, multipliers, etc.).
• the example in Figure 15 shows that when DBI connections are used (i.e., when the two dies 1505 and 1510 are face-to-face mounted through DBI), and the DBI connections have a 2-micron pitch, a 100-bit bus 1525 between the two circuits 1515 and 1520 can be contained in a region 1530 that is 20-by-20 micron square that can be wholly contained within the footprints of the circuits.
• TSV connections e.g., when the two dies are face-to-back mounted and connected using TSVs
• the 100-bit bus 1525 would consume at a minimum a 400-by-400 micron square region 1535, which is larger than the footprint of the compute circuits 1515 and 1520. This larger footprint would consume additional routing space and would not be as beneficial as the smaller footprint that could be achieved by the DBI connections.
• High density DBI connections can also be used to reduce the size of a circuit formed by numerous compute circuits and their associated memories.
• the DBI connections can also provide this smaller circuit with very high bandwidth between the compute circuits and their associated memories.
• Figure 16 presents an example that illustrates these benefits. Specifically, it illustrates the reduction in the size of an array 1600 of compute circuits 1615 on a first die, by moving the memories 1620 for these circuits to a second die 1610 that is face-to-face mounted with the first die 1605 through DBI boding process.
• a 6-by-10 array of compute circuits is illustrated, but in other examples, the array can have larger number of circuits (e.g., more than 100 circuits, more than 1000 circuits).
• the compute circuits and their associated memory circuits can be organized in an arrangement other than an array.
• the compute circuits 1615 and the memory circuits 1620 can be any type of computational processing circuits and memory circuits.
• the circuit array 1600 is part of an FPGA that has an array of logic circuits (e.g., logic gates and/or look-up tables, LUTs) and an array of memory circuits, with each memory in the memory array corresponding to one logic circuit in the circuit array.
• the compute circuits 1615 are neurons of a neural network or multiplier-accumulator (MAC) circuits of neurons.
• the memory circuits 1620 in these embodiments store the weights and/or the input/output data for the neurons or the MAC circuits.
• the compute circuits 1615 are processing circuits of a GPU, and the memory circuits store the input/output data from these processing circuits.
• a memory array is typically interlaced with the circuit array in most single die implementations today.
• the combined length of the two interlaced arrays is X microns in the example in Figure 17.
• the wiring would have to be at least X microns. But by moving the memory circuits onto the second die 1610, as shown in Figure 16, two circuits in the same column can be connected with a minimum wiring length of X/2 microns.
• each memory circuit can have a higher density of storage cells as less space is consumed for defining shared peripheral channels for outputting signals to the circuits, as these output signals can now traverse in the z-axis.
• more routing space is available in the open channels 1650 (on the substrate and metal layers) between the compute circuits in the compute array 1600 on the first die 1605, and between the memory circuits in the memory array 1602 on the second die 1610.
• This additional routing space makes it easier to connect the outputs of the compute circuits. In many instances, this extra routing space allows these interconnects to have shorter wire lengths. It also makes it easier for compute circuits in some embodiments to read or write data from the memory circuits of other compute circuits.
• the DBI connections are also used in some embodiments to route signals through the metal layers of the second die 1610 in order to define the signal paths (i.e., the routes) for connecting the compute circuits 1615 that are defined on the first die 1605.
• the higher density of DBI connections also allow a higher number of z-axis connections to be defined between corresponding memory and compute circuits that are wholly contained within the footprints (i.e., within the substrate regions occupied by) of a pair of corresponding memory and compute circuits.
• these DBI connections connect the top interconnect layer of one die with the top interconnect layer of the other die, while the rest of the connection between a pair of memory and compute circuits is established with interconnects and vias on these dies.
• the compute circuits need wide buses (e.g., 128 bit buses, 256 bit buses, 512 bit buses, 1000 bit buses, 4000 bit buses, etc.) to their corresponding memory circuits.
• One such example would be when the array of compute circuits are arrays of neurons that need to access a large amount of data from their corresponding memory circuits.
• Figures 18 and 19 illustrates two examples that show how high density DBI connections can be used to reduce the size of an arrangement of compute circuit that is formed by several successive stages of circuits, each of which performs a computation that produces a result that is passed to another stage of circuits until a final stage of circuits is reached.
• an arrangement of compute circuits can be an adder tree, with each compute circuit in the tree being an adder.
• the circuits in the arrangement are multiply accumulate (MAC) circuits, such as those used in neural networks to compute dot products.
• MAC multiply accumulate
• each input value is a multi-bit value (e.g., a thirty-two bit value).
• the circuit 1800 has three stages with the first stage 1802 having four compute circuits A-D, the second stage 1804 having two compute circuits E and F, and the third stage 1806 having a compute circuit G.
• Each compute circuit in the first stage 1802 performs an operation based on two input values.
• the compute circuit E performs a computation based on the outputs of compute circuits A and B
• the compute circuit F performs a computation based on the outputs of compute circuits C and D.
• the compute circuit G in the third stage 1806 performs a computation based on the outputs of compute circuits E and F.
• Figure 18 illustrates a prior art implementation of the circuit 1800 on one IC die 1805.
• the compute circuits A-G are arranged in one row in the following order: A, E, B, G, C, F and D.
• the first stage compute circuits A-D (1) receive their inputs from circuits (e.g., memory circuits or other circuits) that are above and below in the planar y-axis direction, and (2) provide their results to the compute circuit E or F.
• the compute circuits E and F provide the result of their computations to compute circuit G in the middle of the row.
• the signal path from the compute circuits E and F is relatively long and consumes nearby routing resources.
• the length and congestion of interconnects become worse as the size of the circuit arrangement (e.g., the adder or multiplication tree) grows. For instance, to implement an adder tree that adds 100 or 1000 input values, numerous adders are needed in numerous stages, which quickly results in long, big data buses to transport computation results between successive stages of adders.
• Figure 19 illustrates a novel implementation of the circuit 1800 that drastically reduces the size of the connections needed to supply the output of compute circuits E and F to the compute circuit G.
• this implementation defines the compute circuits A, B, E and G on a first die 1910, while defining the compute circuits C, D and F on a second die 1905 that is face-to-face mounted on the first die 1905 through a DBI boding process.
• the compute circuits A, B, E, and G are defined in a region on the first die 1910 that overlaps with a region on the second die 1905 in which the compute circuits C, D and F are defined.
• the compute circuit G is placed below the compute circuit E in the planar y-direction.
• the compute circuit G receives the output of the compute circuit E through a short data bus defined on the die 1910, while receiving the output of the compute circuit F through (1) z-axis DBI connections that connect overlapping locations 1950 and 1952 on the top interconnect layers of the dies 1905 and 1910, and (2) interconnects and vias on these dies that take the output of circuit F to the input of circuit G.
• the interconnects that provide the inputs to the compute circuit G are very short.
• the computation circuits E and G are next to each other and hence the signal path just includes a short length of the interconnect and vias between the circuit E and G. Also, the length of interconnects, vias, and z-axis DBI connections needed to provide the output of the compute circuit F to the compute circuit G is very small.
• Compute circuit arrangements can have more than three stages.
• large adder or MAC trees can have many more stages (e.g., 8 stages, 10 stages, 12 stages, etc.).
• some embodiments (1) divide up the compute circuits into two or more groups that are then defined on two or more vertically stacked dies, and (2) arrange the different groups of circuits on these dies to minimize the length of interconnects needed to connect compute circuits in successive stages.
• Figure 20 presents an example to illustrate this point.
• This example shows one implementation of a compute circuit 2000 that performs a computation (e.g., an addition or multiplication) on sixteen multi-bit input values.
• This circuit includes two versions 2012 and 2014 of the compute circuit 1800 of Figures 18 and 19.
• the compute circuits in the second version are labeled as circuits H-N.
• Each of these versions has three stages.
• the outputs of these two versions are provided to a fourth stage compute circuit O that performs a computation based on these outputs, as shown.
• the two versions 2012 and 2014 have an inverted layout.
• the compute circuits A, B, and E that operate on the first four inputs of the first version 2012
• the compute circuits H, I and L that operate on the first four inputs of the second version
• the compute circuits C, D, and F that operate on the second four inputs of the first version 2012
• the compute circuits J, K, and M that operate on the second four inputs of the second version
• the third stage circuit G of the first version is defined on the IC die 2010, while the third stage circuit N is defined on the IC die 2005.
• the fourth stage aggregating circuit O is also defined on IC die 2010.
• the second version 2014 is placed to the right of the first version in the x-axis direction.
• This overall inverted arrangement of the second version 2014 with respect to the first version ensures that the length of the interconnect needed to provide the output of the third stage compute circuits G and N to the fourth stage compute circuit O is short.
• the compute circuits L, M, and N are placed in nearby and/or overlapping locations, which allows these three circuits L, M and N to be connected through short DBI connections, and mostly vertical signal paths facilitated by small planar interconnects plus several via connections.
• This arrangement also places compute circuits G, N and O in nearby and/or overlapping locations, which again allows them to be connected through short DBI connections, and mostly vertical signal paths facilitated by small planar interconnects plus several via connections.
• Figure 21 illustrates a device 2102 that uses a 3D IC 2100 (like any of the 3D IC 210, 200, 400, 600-900).
• the 3D IC 2100 is formed by two face-to-face mounted IC dies 2105 and 2110 that have numerous direct bonded connections 2115 between them.
• the 3D IC 2100 includes three or more vertically stacked IC dies.
• the 3D IC die 2100 includes a cap 2150 that encapsulates the dies of this IC in a secure housing 2125.
• the die 2110 On the back side of the die 2110 one or more TSVs and/or interconnect layers 2106 are defined to connect the 3D IC to a ball grid array 2120 (e.g., a micro bump array) that allows this to be mounted on a printed circuit board 2130 of the device 2102.
• the device 2102 includes other components (not shown). In some embodiments, examples of such components include one or more memory storages (e.g., semiconductor or disk storages), input/output interface circuit(s), one or more processors, etc.
• the first and second dies 2105 and 2110 are the first and second dies shown in any of the Figures 1-2, 4, 6-16, and 19-20.
• the second die 2110 receives data signals through the ball grid array, and routes the received signals to I/O circuits on the first and second dies through interconnect lines on the interconnect layer and vias between the interconnect layers.
• data signals need to traverse to the first die, these signals traverse through z-axis connections crossing the face-to-face bonding layer.
• Figure 22 provides another example of a 3D chip 2200 that is formed by two face-to-face mounted IC dies 2205 and 2210 that are mounted on a ball grid array 2240.
• the first and second dies 2205 and 2210 are face-to-face connected through direct bonded connections (e.g., DBI connections).
• direct bonded connections e.g., DBI connections
• several TSVs 2222 are defined through the second die 2210. These TSVs electrically connect to interconnects/pads on the backside of the second die 2210, on which multiple levels of interconnects are defined.
• the interconnects on the backside of the second die 2210 create the signal paths for defining one or more system level circuits for the 3D chip 2200 (i.e., for the circuits of the first and second dies 2205 and 2210).
• system level circuits are power circuits, clock circuits, data I/O signals, test circuits, etc.
• the circuit components that are part of the system level circuits are defined on the front side of the second die 2210.
• the circuit components can include active components (e.g., transistors, diodes, etc.), or passive/analog components (e.g., resistors, capacitors (e.g., decoupling capacitors), inductors, filters, etc.
• some or all of the wiring for interconnecting these circuit components to form the system level circuits are defined on interconnect layers on the backside of the second die 2210.
• Using these backside interconnect layers to implement the system level circuits of the 3D chip 2200 frees up one or more interconnect layers on the front side of the second die 2210 to share other types of interconnect lines with the first die 2205.
• the backside interconnect layers are also used to define some of the circuit components (e.g., decoupling capacitors, etc.) in some embodiments.
• the backside of the second die 2210 in some embodiments can also connect to the front or back side of a third die.
• one or more of the layers on the backside of the second die 2210 are also used to mount this die to the ball grid array 2240, which allows the 3D chip 2100 to mount on a printed circuit board.
• the system circuitry receives some or all of the system level signals (e.g., power signals, clock signals, data I/O signals, test signals, etc.) through the ball grid array 2240 connected to the backside of the third die.
• Figure 23 illustrates a manufacturing process 2300 that some embodiments use to produce the 3D chip 2200 of Figure 22. This figure will be explained by reference to Figures 24-27, which show two wafers 2405 and 2410 at different stages of the process. Once cut, the two wafers produce two stacked dies, such as dies 2205 and 2210. Even though the process 2300 of Figure 23 cuts the wafers into dies after the wafers have been mounted and processed, the manufacturing process of other embodiments performs the cutting operation at a different stage at least for one of the wafers. Specifically, some embodiments cut the first wafer 2405 into several first dies that are each mounted on the second wafer before the second wafer is cut into individual second dies.
• the process 2300 starts (at 2305) by defining components (e.g., transistors) on the substrates of the first and second wafers 2405 and 2410, and defining multiple interconnect layers above each substrate to define interconnections that form micro-circuits (e.g., gates) on each die.
• the process 2300 performs multiple IC fabrication operations (e.g., film deposition, patterning, doping, etc.) for each wafer in some embodiments.
• Figure 24 illustrates the first and second wafers 2405 and 2410 after several fabrication operations that have defined components and interconnects on these wafers.
• the fabrication operations for the second wafer 2410 defines several TSVs 2412 that traverse the interconnect layers of the second wafer 2410 and penetrate a portion of this wafer's substrate 2416.
• the process 2300 face-to-face mounts (at 2310) the first and second wafers 2205 and 2210 through a direct bonding process, such as a DBI process.
• Figure 25 illustrates the first and second wafers 2405 and 2410 after they have been face-to-face mounted through a DBI process. As shown, this DBI process creates a number of direct bonded connections 2426 between the first and second wafers 2405 and 2410.
• the process 2300 performs a thinning operation on the backside of the second wafer 2410 to remove a portion of this wafer's substrate layer. As shown in Figure 26, this thinning operation exposes the TSVs 2412 on the backside of the second wafer 2410.
• the process 2300 defines (at 2320) one or more interconnect layers 2430 the second wafer's backside.
• Figure 27 illustrates the first and second wafers 2405 and 2410 after interconnect layers have been defined on the second wafer's backside.
• These interconnect layers 2430 include one or more layers that allow the 3D chip stack to electrically connect to the ball grid array.
• the interconnect lines/pads on the backside of the third wafer also produce one or more redistribution layers (RDL layers) that allow signals to be redistributed to different locations on the backside.
• RDL layers redistribution layers
• the interconnect layers 2430 on the backside of the second die in some embodiments also create the signal paths for defining one or more system level circuits (e.g., power circuits, clock circuits, data I/O signals, test circuits, etc.) for the circuits of the first and second dies.
• the system level circuits are defined by circuit components (e.g., transistors, etc.) that are defined on the front side of the second die.
• the process 2300 in some embodiments does not define interconnect layers on the backside of the second wafer to create the signal paths for the system level circuits, as it uses only the first and second dies' interconnect layers between their two faces for establishing the system level signal paths.
• the process cuts (at 2325) the stacked wafers into individual chip stacks, with each chip stack include two stacked IC dies 2205 and 2210.
• the process mounts (at 2330) each chip stack on a ball grid array and encapsulates the chip stack within one chip housing (e.g., by using a chip case). The process then ends.
• Figure 28 illustrates an example of a 3D chip 2800 with three stacked IC dies 2805, 2810 and 2815.
• the first and second dies 2805 and 2810 are face-to-face connected through direct bonded connections (e.g., DBI connections), while the third and second dies 2815 and 2810 are face-to- back connected (e.g., the face of the third die 2815 is mounted on the back of the second die 2810).
• the first and second dies 2805 and 2810 are the first and second dies shown in any of the Figures 1-2, 4, 6-16, and 19-20.
• TSVs 2822 are defined through the second die 2810. These TSVs electrically connect to interconnects/pads on the backside of the second die 2810, which connect to interconnects/pads on the top interconnect layer of the third die 2815.
• the third die 2815 also has a number of TSVs that connect signals on the front side of this die to interconnects/pads on this die's backside. Through interconnects/pads, the third die's backside connects to a ball grid array 2840 that allows the 3D chip 2800 to mount on a printed circuit board.
• the third die 2815 includes system circuitry, such as power circuits, clock circuits, data I/O circuits, test circuits, etc.
• the system circuitry of the third die 2815 in some embodiments supplies system level signals (e.g., power signals, clock signals, data I/O signals, test signals, etc.) to the circuits of the first and second dies 2805 and 2810. In some embodiments, the system circuitry receives some or all of the system level signals through the ball grid array 2840 connected to the backside of the third die.
• system level signals e.g., power signals, clock signals, data I/O signals, test signals, etc.
• Figure 29 illustrates another example of a 3D chip 2900 with more than two stacked IC dies.
• the 3D chip 2900 has four IC dies 2905, 2910, 2915 and 2920.
• the first and second dies 2905 and 2910 are face-to-face connected through direct bonded connections (e.g., DBI connections), while the third and second dies 2915 and 2910 are face-to- back connected (e.g., the face of the third die 2915 is mounted on the back of the second die 2910) and the fourth and third dies 2920 and 2915 are face-to-back connected (e.g., the face of the fourth die 2920 is mounted on the back of the third die 2915).
• the first and second dies 2905 and 2910 are the first and second dies shown in any of the Figures 1-2, 4, 6-16, and 19- 20.
• TSVs 2922 are defined through the second, third and fourth die 2910, 2915 and 2920. These TSVs electrically connect to interconnects/pads on the backside of these dies, which connect to interconnects/pads on the top interconnect layer of the die below or the interconnect layer below. Through interconnects/pads and TSVs, the signals from outside of the chip are received from the ball grid array 2940.
• 3D chip stacking architectures instead of face- to-back mounting the fourth and third dies 2920 and 2915 in Figure 29, the 3D chip stack of another embodiment has these two dies face-to-face mounted, and the second and third dies 2910 and 2915 back-to-back mounted. This arrangement would have the third and fourth dies 2915 and 2920 share a more tightly arranged set of interconnect layers on their front sides.
• a first IC die is shown to be face-to-face mounted with a second IC die.
• the first IC die is face-to-face mounted with a passive interposer that electrically connects the die to circuits outside of the 3D chip or to other dies that are face-to- face mounted or back-to-face mounted on the interposer.
• Some embodiments place a passive interposer between two faces of two dies.
• Some embodiments use an interposer to allow a smaller die to connect to a bigger die.
• the 3D circuits and ICs of some embodiments have been described by reference to several 3D structures with vertically aligned IC dies. However, other embodiments are implemented with a myriad of other 3D structures.
• the 3D circuits are formed with multiple smaller dies placed on a larger die or wafer.
• Figure 30 illustrates one such example. Specifically, it illustrates a 3D chip 3000 that is formed by face-to-face mounting three smaller dies 3010a-c on a larger die 3005. All four dies are housed in one chip 3000 by having one side of this chip encapsulated by a cap 3020, and the other side mounted on a micro-bump array 3025, which connects to a board 3030 of a device 1935.
• Some embodiments are implemented in a 3D structure that is formed by vertically stacking two sets of vertically stacked multi-die structures.

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