WO2017052653A1

WO2017052653A1 - Selective die transfer using controlled de-bonding from a carrier wafer

Info

Publication number: WO2017052653A1
Application number: PCT/US2015/052478
Authority: WO
Inventors: Brennen Mueller; Paul Fischer; Kimin JUN; Lei Jiang
Original assignee: Intel Corporation
Priority date: 2015-09-25
Filing date: 2015-09-25
Publication date: 2017-03-30
Also published as: TW201721781A; TWI721002B

Abstract

Selective die transfer is described using controlled de-bonding from a carrier wafer. In one example, small dies are formed on a wafer and attached to a temporary carrier. Larger host dies are formed on a host wafer. Raised mesas are formed on the host dies at locations of the host dies that are to receive a small die. The small dies are aligned over the host dies using the temporary carrier and the small dies are applied to the host dies using the temporary carrier so that a subset of the small dies physically contact the raised mesas of the respective host dies while the small dies that are not of the subset do not contact the host dies. The temporary carrier and the remaining small dies are separated from the host dies. The host dies are singulated and packaged.

Description

SELECTIVE DIE TRANSFER USING CONTROLLED DE-BONDING FROM A CARRIER

WAFER

FIELD

The present disclosure relates to assembling semiconductor dies for a package and in particular to an assembly with dies of different sizes connected together.

BACKGROUND

In order to increase speed and power efficiency and to reduce the size of electronic equipment, integrated circuit dies are made ever smaller. These dies are mounted closer together so that the connections between these dies are also made shorter. The shortest connection is a connection that is made within an integrated circuit package. In some cases dies are mounted side by side on a package substrate and connected together through the package substrate or directly with wires. In other cases, dies are mounted one on the other for a direct connection without any intervening wire or package substrate. This is sometimes called a stacked die package. One die can be placed over another using a pick and place machine or a variety of other types of equipment. The combination can be packaged as if it is a single die with double the height.

Combining multiple dies into a single package allows for two or more different types of dies to be placed into a single package. This may be referred to as heterogeneous integration of die-to-die connections. As one example, the dies may be made using different materials such as Si, Ge, III-V, SiC, etc.. As another example the dies may be made using different technology nodes such as 22 nm, 14 nm, 10 nm, etc.. These differences may be combined and combined with other types of differences so that different types of dies from different processes and different fabricators may be placed into a single compact package.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements.

Figure 1 is a side cross-sectional view diagram of a portion of a donor wafer carrying multiple small dies according to an embodiment.

Figure 2 is a side cross-sectional view diagram of the donor wafer with a temporary carrier attached to the front side of the small dies using a temporary adhesive according to an embodiment. Figure 3 is a side cross-sectional view diagram of the donor wafer and temporary carrier after the donor wafer is thinned according to an embodiment.

Figure 4 is a side cross-sectional view diagram of the donor wafer and temporary carrier after the dies are singulated through the donor wafer on the back sides of the dies according to an embodiment.

Figure 5 is a side cross-sectional view diagram of the donor wafer and temporary carrier after the dies are singulated through the donor wafer on the back sides of the dies according to an embodiment.

Figure 6 is a side cross-sectional view diagram of a host wafer carrying a host die with a raised mesa at a location that is to receive one of the small dies according to an embodiment.

Figure 7 is a side cross-sectional view diagram of the donor wafer and temporary carrier aligned over a portion of a host wafer and applied to the raised mesa according to an

embodiment.

Figure 8 is a side cross-sectional view diagram of removing the temporary carrier and the other of the small dies that was not applied to a mesa of the host die away from the host wafer according to an embodiment.

Figure 9 is a side cross-sectional view diagram of adding dielectric and metal routing layers over the small die to finish a package according to an embodiment.

Figure 10 is a side cross-sectional view diagram of a portion of a donor wafer carrying multiple small dies aligned over a temporary carrier with an array of heating elements according to an embodiment.

Figure 11 is a side cross-sectional view diagram of the donor wafer with the temporary carrier attached to the front side of the small dies using a temporary adhesive according to an embodiment.

Figure 12 is a side cross-sectional view diagram of the donor wafer and temporary carrier after the donor wafer is thinned according to an embodiment.

Figure 13 is a side cross-sectional view diagram of the donor wafer and temporary carrier after the dies are singulated through the donor wafer on the back sides of the dies according to an embodiment.

Figure 14 is a side cross-sectional view diagram of the donor wafer and temporary carrier aligned over a portion of a host wafer and applied to the optional raised mesa according to an embodiment. Figure 15 is a side cross-sectional view diagram of the donor wafer and temporary carrier applied to the host wafer and of heating the adhesive for one of the small dies to debond the small die from the temporary carrier according to an embodiment.

Figure 16 is a side cross-sectional view diagram of removing the temporary carrier and the other of the small dies for which the adhesive was not heated for debonding away from the host wafer according to an embodiment.

Figure 17 is a side cross-sectional view diagram of adding dielectric and metal routing layers over the small die to finish a package according to an embodiment.

Figure 18 is a block diagram of a computing device incorporating a hybrid semiconductor die package according to an embodiment.

DETAILED DESCRIPTION

As described herein functional small dies or islands may be integrated into existing positions on a die that is constructed on a host wafer. Very small and thin dies may be handled in bulk by using wafer level handling. Instead of manipulating a single small die into a small location, a whole wafer may be handled at once but dies are only transferred to selected areas of the large dies on the host wafer.

Two or more different integrated circuit die fabrication technologies may be integrated onto the same die. The different technologies may include different process nodes, different cores or blocks, different areal dimensions, or different (heterogeneous) materials. As described herein small islands of one or more technologies may be transferred onto a die of another technology.

As described herein a device wafer is fabricated with a mesa that protrudes some thickness above the rest of the device wafer at the layer of the mesa. The carrier wafer and device wafer are aligned and brought into contact. This creates a bond between the island to be transferred and the mesa. The wafers are debonded, and the transferred islands debond from the carrier wafer at the weakened interface. The carrier wafer can then be aligned and bonded with the same or another device wafer, e.g. though offset from the original position, to transfer a different island. A material is used to bond two substrates together with a strong bond. The bond is then weakened to allow for layer transfer.

For island transfer processes, bonding, bond-strengthening, bond-weakening, or debonding can be improved with selective heating. A small region of a wafer can be heated as a bonding, bond-strengthening, bond-weakening, or debonding mechanism. The localized heating may be used for heating only a subset of islands in a field of islands so that only the subset of islands is transferred to the device wafer. As described a carrier wafer is fabricated with micro-heaters for bonding, bond- strengthening, bond-weakening, and debonding purposes. Some bonding mechanisms are strongly dependent on temperature, so locally heating one island may be used to provide a selective layer transfer. After a carrier wafer, with islands, and a device wafer are brought into physical contact with each other, the integrated heaters of one or more regions of the carrier is selectively activated to bond or debond only the islands that are to be transferred. After an island or set of islands are transferred, the carrier can be contacted to another device wafer to selectively transfer another set of islands. The described heater-integrated carrier wafer may be fabricated with each donor wafer, or it may be fabricated once and reused.

As described, the small dies are handled as a group on a wafer. When held on a carrier wafer, very small and thin dies can be transferred. The dies may be much smaller and thinner than can easily be manipulated by a die pick-and-place assembly. By forming interconnects on both the top and the bottom of the islands, more routing resources can be obtained.

Figures 1-9 show a an example process for placing a small island die in a location so that it may be a fully embedded small island die inside a host die. Figure 1 is a side cross-sectional diagram of a set of small dies 104, 105 formed on a donor wafer 102. The islands can have different areal dimensions than the dies 122 on the host device wafer 120 of Figure 6, and the carrier wafer 110 of Figure 2 can be reused to transfer islands onto many device wafers. The donor wafer of Figure 1 is the substrate on which the small dies or islands have been formed and securely carries the dies in an accurately aligned position. The dies may now or later be partially diced by sawing or scribing so that there is a scribe trench or saw kerf through the dies and into the wafer.

In this example, the dies are referred to as small meaning only that they are smaller than the host die to which they will be attached. The small dies may be half the size of the host die, one tenth the size or any other relative size. The donor wafer contains many small dies to be transferred to host dies that have been formed on a device wafer. The small dies may be functional materials which are beneficial to integrate with a host die. Examples of such functional materials may include silicon, germanium, silicon carbide, III-V and Ill-nitride compound semiconductors. Because the small dies are formed independently on a separate wafer, they may be formed using a different technology, different materials, or different process nodes than the host die. The small dies may be power, radio-frequency, optical, memory, or other types of devices that are best formed separate from the host wafer.

Figure 2 is a cross-sectional side view diagram of the donor wafer 102 of Figure 1 inverted and attached to a temporary carrier 110 using a temporary adhesive 108. This adhesive may be applied to the donor wafer, the carrier wafer, or both wafers before attaching the two wafers to each other. The front side of the dies 104, 105 is covered by the carrier and the back side of the wafer 102 side is exposed. This donor wafer is bonded to the temporary carrier wafer so that the wafer may be handled by the carrier. Examples of temporary carrier materials are silicon and glass. However, other suitable materials may be used. The temporary adhesive is selected to withstand any mechanical forces that may be caused during grinding the wafer and any thermal or mechanical overburden during wafer thinning. These forces may include shear forces, compressive forces, tensile forces, etc.

The temporary adhesive is also selected so that the dies may easily be debonded from the carrier when desired. One such class of adhesive is polymer adhesives. Polymer adhesives may include polymethacrylates, polyacrylates, polystyrenes, polysilsesquioxanes, polysiloxanes, polynorbornenes, polyimides, polybenzoxazoles, epoxies, novolac, benzocyclobutenes, polycarbonates. Inorganic adhesives may include H-implanted silicon (or silicon implanted with other volatile species), or amorphous Si:H.

The carrier wafer may be brought into physical contact with the dies on the donor wafer to bond them. The wafer with the dies may be annealed at an elevated temperature to increase the bond strength. Heating a polymer adhesive above its glass transition temperature would allow it to flow and form good contact with both substrates. Upon cooling, the polymer regains its rigidity and results in a strong, mechanically stable bond.

Figure 3 is a cross-sectional side view diagram of the carrier wafer 110 and dies 104, 105 of Figure 2 after the donor wafer is thinned. This may be done by grinding or in any other way. Bulk micromachining techniques such as grinding, wet etching, dry etching and chemical- mechanical polishing may be used, among others. The amount of thinning or the thinning target varies upon the integration level. If the dies are to be embedded into an interconnect stack as shown in Figure 8, then the die requires no structural stability and the wafer can made very thin, for example, less than 1 μιη thick. As another example, if the small die is to be embedded as a part of C4 (Controlled Collapse Chip Connection) or packaging as in Figure 18, then the die requires some mechanical reinforcement and stability but still may be only a few tens of a μιη thick.

Figure 4 is a side cross-sectional diagram of the wafer of Figure 3 with the island dies singulated. The singulation may be by masking and etching trenches 106 between the islands until the adhesive or carrier wafer is exposed. Other singulation techniques may be used depending on the island size, composition, and other process and structural features. Laser scribe etching may also be used if dimensions allow. Wet or dry etch methods may also be used for this singulation. Blade singulation may also be used.

The singulation may be performed before or after bonding to the temporary carrier. The islands may be mechanically singulated deep enough into the donor wafer using scribe trenches or another structure so that the separations between the dies are revealed during the grind. In other words, the grind may be performed to the depth of the trenches so that the donor wafer no longer extends between the dies. In this case only the carrier wafer is holding the dies in position. The result is similar to that shown in Figure 4 after singulation.

At this stage vias and other attachment features may be added if desired. "Through-die- vias" may be fabricated in a fashion similar to through-silicon-vias (TSV). These may be drilled, etched or bored through the back side substrate or wafer to make contact with the front end circuitry of the dies. The drilled holes are then filled with a metal such as Cu, Ti, Ta to make the connection. The holes may be overfilled so that the metallic surfaces at the tops of the vias are exposed. The through die vias may be formed before singulation or after the islands are transferred and bonded to the respective host die, depending on the implementation.

Figure 5 is a cross-sectional side view of the singulated dies and donor wafer of Figure 4 after the adhesive bond 108 has been weakened 109. After singulation, the temporary adhesive is weakened so that the interfacial bond strength decreases but so that the lateral positions of the islands do not change. For polymer adhesives, this can be done thermally. Heating the polymer above its decomposition temperature or ceiling temperature causes the polymer to decompose or depolymerize. This results in a loss of the entangled polymer structure and the strong bond. The islands 104, 105 remain bonded to the carrier wafer through weaker bonding forces. One example is van der Waals forces between the island and carrier or between polymer residues at both interfaces. The strong bond 108 of Figure 3 is no longer required after the donor wafer has been thinned.

Figure 6 is a cross-sectional side view diagram of a larger host die 122 formed on a host wafer 120. The host wafer also has an underlying stack. There are vertical conductive posts 114 to connect to pads or through-die- vias of the small die 105. The large die 122 has a conductive redistribution layer or other metal or conductive layer with conductive lines or traces 124 over the die.

A mesa 118 has been fabricated on the device wafer. The mesa protrudes some thickness above the last layer 116. The raised mesa is higher or farther from the die substrate than the surrounding surface or layer of the host die. The small die will connect through the raised mesa or will connect with pads on or in the raised mesa. The mesa can be made from a variety of materials. One example material is Si0₂. Another example is a carbon doped oxide (CDO). The mesa may be fabricated by vacuum deposition or spin coating of the mesa material, masking of the layer with a photoresist, and then wet or dry etch of the field. The mesa may be deposited over a finished last layer 116 or the last layer may be formed so that it is higher in some locations than in others.

Figure 7 is a cross-sectional side view diagram of the small dies and temporary carrier inverted again so that the back side of the dies is face down. As shown the two wafers, the host device wafer 120 and the carrier wafer 110 are aligned. A subset of the small dies 105 are brought into physical contact with the mesas 118 for example by moving the carrier wafer 110 and the two dies 104, 105. The elevated mesas allow contact only to the islands 105 which are to be transferred. For the other islands 104 there is a small gap corresponding to the height of the mesas 118 over the surrounding layer 116. The bond formed at the island-mesa interface is stronger than the weakened bond at the island-carrier interface.

The bond between an island and a mesa may optionally be strengthened in a variety of different ways. Heat, pressure, metallic bonding, or any other technique may be used. The conditions may be adjusted to form a stronger bond with the island. The rest of the area of the host wafer which, in this example is made primarily of ILD (Inter- Layer Dielectric) has little or no physical contact with the other islands so there is little or no bond. These areas will later separate.

In one embodiment, the temporary carrier presses the small dies against each respective mesa to bond the small die to the host die through metal compression. Heat may be used to further strengthen the bond. In such a case, the raised mesa includes pads, electrodes, or other connectors to electrically connect to and physically bond to contact pads on the small dies. Alternatively, the electrical connections may be made on the opposite side of the small die and the small dies may be made to attach to the host die in another way.

Figure 8 is a cross-sectional side view diagram of separating the carrier wafer from the host wafer. This causes the two dies 104, 105 to be separated. The bonding on the weakened temporary adhesive is weaker than the island-mesa bonding so the islands remain with the device wafer. In some embodiments, some external stimulation such as heat may be applied to weaken the bond between the island dies and the temporary carrier wafer. After the separation, the carrier wafer may be used to apply dies to another host wafer. As shown, the islands on the device wafers are face up. The device wafer can be further processed so as to make electrical contact to the island through, for example, a device wafer interconnect stack. Since the temporary adhesive remains with the other dies, the second die 104 is lifted away from the host die 122 by the temporary carrier 110. As noted above the dies have already been separated or singulated as shown by the scribe trenches 106. Accordingly, only the carrier holds the dies together.

Figure 9 is a diagram with the temporary carrier and other small dies removed. The one attached small die 105 remains bonded to the mesa of the host die. The host wafer is further processed to embed the transferred small die fully into the interconnect stack. In the illustrated example, the further processing include additional dielectric 134, additional conductive posts or vias 130 and conductive contact pads or lines 132 to connect to other components. As shown, the smaller die 105 is fully embedded within the ILD of the host die. This allows special functions and specialized dies to be incorporated into a larger die assembly without any change in packaging and other processing aspects of the host die.

In this example, only two small dies 104, 105 are shown on the donor wafer 102.

Typically there will be many more. These dies are formed on the donor wafer together, and then the functional dies are carried on the carrier wafer 110 and manipulated as a group. Similarly, the host wafer 120 is only shown as having part of a single die 122, however, there will be many more. The transfer operation may be performed using wafer handlers so that many small dies are transferred to many host dies in one operation. The temporary carrier may then be moved to transfer more small dies to the same host wafer at a different location on the host dies or it may be moved to transfer small dies to the dies of a different host wafer.

As described, the temporary bonding layer 108 is weakened 109 so that the islands are more easily transferred to the mesas of the device wafer. In order to further stimulate the transfer of the islands, the bonding layer may be selectively weakened under the islands so that the islands are more easily transferred to the device wafer. If the weakening is sufficiently selective, then the bonds for the islands to be transferred are weakened but the bonds for the other islands are not affected. This helps in at least two different ways. First, the lack of bond- weakening for some islands helps to ensure that the non-transferred islands remain in good contact to the carrier. Second, with sufficient bond weakening for the islands, the islands may be transferred without requiring mesas on the device wafer.

There are many different ways to selectively weaken the bond. Some process examples of achieving selective bond weakening include heating the bonded stack rapidly from the device wafer side. A conduction path through a mesa to a selected island would cause a temperature excursion at that island first before reaching other islands. Timing the thermal excursion causes the selected island bond to be weakened without affecting the other islands. In another example, the stack may be heated from the carrier wafer side selectively. This may be accomplished using of micro-heaters near the bonded interface as described in more detail below.

In another example compression is applied. A bonding material may be used that weakens under compression. In this example, the selected islands are pressed against mesas on the device wafer. A compressive force is applied against the device wafer, the carrier wafer or both that weakens the temporary carrier to island bond interface.

In another example, tensile strain may be used. A bonding material may be used that is weak to tensile strain. The carrier wafer is pressed against the mesas of the device wafer with a mesa. Debonding may be used to provide the tensile strain required to weaken and debond the temporary material.

In examples, a poly(methyl methacrylate) bonding layer may be used. The bonded wafers may be annealed at e.g. about 150°C. This adhesive may be debonded at 400°C.

Alternatively, oxide fusion bonding for the mesa-to-island permanent bond may also be used.

As described these types of bonding materials allow for heterogeneous integration of different technologies. Materials and fabrication processes that cannot otherwise be fabricated on the same wafer may accordingly be combined. In addition, circuit blocks may be separated onto different wafers so that fabrication costs are minimized. These different block may then be integrated onto the same die later in the process as shown in Figure 9.

Figure 9 is provided as an example for how to finish the device with an embedded island

105. There are a variety of different types of connections between the island and the larger host die 122. Different types of vias 130 in different configurations may be used to connect the island to the host die. There may be metallic pads 132 above the adjacent ILD 134. While Figure 9 shows the island die backside or wafer side connected to the host die. The dies may also be attached face-to-face.

The host die after all of the islands have been attached may be finished as shown in Figure 9. Additional vertical vias 130 and metal routing layers 132 may be added to provide connections from the host die to external components. The small die may be connected only to the host die, however, there may be additional vias and routing layers to provide a direct or indirect connection between the small die and external components.

This technique and structures described herein may be used not only on backend-level integration, but also on C4 (Controlled Collapse Chip Connection) or far-backend-level integration. Rather than direct metal compression or heat bonding, a small or micro C4 bump may be placed on each of the pads of either the island or the host die. When the small die is brought into contact with the host die, the contact layers do not directly contact the host die but contact the host die through the micro C4 bumps. The assembly may then be reflowed so that the C4 bumps provide a connection between the two dies. The assembly may be finished using a standard C4 or solder bump attachment to a package substrate.

A small die with a thinned wafer is able to be attached within an array of C4 or solder bumps. As a result, the additional small dies do not affect the size of the overall package. By forming the small dies in a separate process, the small dies may contain very different components than may be formed on the host die. Heterogeneously integrated devices are enabled such as silicon processing dies with a gallium nitride voltage regulator, a gallium arsenide optical waveguide, a various passive devices, or RF modulators.

Figures 10-17 show an alternative process for attaching smaller dies to a larger host die. Figure 10 is a side cross-sectional diagram of a set of small dies 204, 205 formed on a donor wafer 202. The small dies are formed on the donor wafer as a substrate. The donor wafer contains many small dies to be transferred to dies that have been formed on a host wafer as described above. An adhesive 208 has been applied over the front sides of the small dies.

A carrier wafer 210 is fabricated from an inert and stable material such as glass or silicon. The carrier wafer has an array of resistive heater elements 240 on the side facing the islands, the heater elements are arranged to have a same or similar size as the islands. The heater elements are coupled to an external power source through vias 242 through the carrier wafer. This is provided as an example of how to power resistive heater elements. The heater elements may be powered in any other desired way. The top of the carrier wafer is covered in a dielectric layer 244 to cover and protect the heater elements. The dielectric may be a rigid material such as a Si0₂ or additional deposited glass.

In the examples described herein, the carrier wafer may alternatively be formed of silicon with resistive metal wires patterned on one side. The wires may be connected to an external power source using through-silicon vias (TSVs) to the back-side of the carrier.

Electrical connections to the resistive heaters 240 may be made through one or more routing layers on the heater side of the temporary carrier 210 instead of using the vias 242. This would allow the power supply to be connected at the edge of the carrier on the front side of the temporary carrier. Alternatively, metal routing layers may be fabricated on either the heater side or backside of the carrier 210 with or without TSVs 242 so that fewer contacts to the wafer are required to power all of the heater elements.

The metal wires may alternatively be separated from each other by a dielectric material. The dielectric may allow the top surface of the carrier wafer to be more planar by leveling out any imperfections. Many dielectrics may also be polished to provide an even more planar surface. Planarity allows for a stronger bond to be formed with the adhesive 208 to the islands.

The metal wires of the resistive heating elements may be coated with a thin protective layer. The protective layer provides a physical separation of the heater wires from the bonding material 208. This will protect the wires from corrosion that may be caused by the bonding material against the metal wires.

The heat flow near the heater elements may be mitigated and controlled in a variety of different ways. The carrier, as mentioned, may be formed of a dielectric or thermally non- conductive material. This will reduce heat flow between heater elements from those near one island to those near another island. The heater elements may be seated in an additional dielectric layer 244 at the top of the carrier wafer between the carrier and the islands. This dielectric layer may serve as a heat insulating layer between the heaters and the main body of the carrier. An additional heat-mitigating layer may also be fabricated between the heater and carrier wafer as a heat buffer..

Figure 11 is a cross-sectional side view diagram of the device wafer 202 of Figure 10 attached to the temporary carrier 210 using a temporary adhesive 208. The front side of the dies is covered by the carrier so that the wafer may be handled by the carrier. The donor wafer is aligned and bonded to the heater-integrated carrier wafer with a temporary adhesive that provides a strong bond. The temporary adhesive can be coated on the donor wafer, carrier wafer, or both wafers. Polymers or any other suitable adhesive may be used. The wafers are brought into contact to bond them. The wafers may then be annealed at an elevated temperature to increase the bond strength for the thinning of Figure 12.

Figure 12 is a cross-section side view diagram of the device wafer and dies of Figure 11 after the device is thinned. The donor wafer may be grinded, etched, and polished. The carrier wafer provides mechanical stability during this process. The final donor wafer is thin, possibly tens of micrometers or less than 10 micrometers thick.

Figure 13 is a side cross-sectional diagram of the dies of Figure 12 after singulating the individual dies with etching, sawing, or any other desired way. In this example there are scribe trenches 206 between the singulated dies. The dies may be further processed by the addition of vias, pads, metal layers, etc. In one example, islands are singulated by masking and etching trenches between the islands until the adhesive or carrier wafer is exposed

Figure 14 is a cross-sectional side view diagram of the dies and temporary carrier inverted so that the back sides of the dies are face down. A larger host die 222 is formed on a host wafer 220. The host wafer also has an underlying stack. There are vertical conductive posts 214 to connect to pads or through-die-vias of the small die 205. The larger host die has a conductive redistribution layer or other metal or conductive layer with conductive lines or traces 224 over the die.

After alignment, the two wafers are brought together for example by moving the carrier wafer 210 toward the device wafer. The back sides of the islands 204, 205 are pressed against the host wafer, so that at least the selected island 205 physically contacts the mesa. Heat or pressure or both are applied to form some sort of bonding. The rest of the area of the host wafer which, in this example is made primarily of ILD (Inter-Layer Dielectric) has little or no contact and only a very weak bond if any so that these areas will later separate.

A mesa 218 of the type described above has optionally been fabricated on the device wafer. The mesa protrudes some thickness above the last layer 216 of the metal wiring layers of the ILD. After singulation, the carrier/donor wafer is aligned and bonded to the device wafer using the annealed adhesive 208. When mesas 218 are used, they protrude from the device wafer surface so that contact is only made to select islands.

Figure 15 is a side view diagram of the connected wafers of Figure 14 with an external power supply 250 coupled to the resistive heater elements using the vias through the temporary carrier. This is to indicate that the heaters are activated to heat the carrier in the area of the selected island. The actual electrical connection may be permanent but at this time in the process, power is applied only to the desired heaters.

The carrier wafer is selectively heated to weaken the adhesive bond 208 in the area of the selected island 205. The weakened adhesive 209 will more easily transfer the selected island 205 from the carrier wafer to the device wafer. The heat can be used to anneal the fusion bond at the device-island interface. The heat can be used to weaken or debond the carrier-island interface. The heat can also be used to perform some combination of these two processes.

For both organic (polymer) and inorganic adhesives, the heat may be used to drive a chemical reaction. The rate of that reaction is exponentially dependent on the temperature. For many adhesives, the reaction rate is slow at low temperatures. At room temperatures, there is no significant change over many minutes. The reaction is much more rapid at elevated

temperatures. The rate of change may be one thousand times faster with an increase in temperatures of 100°C. The rate of change may be one million times faster for an increase of

200°C. With a safe operating range from room temperature to about 400°C, the adhesive may be heated enough to degrade the bond in a short amount of time.

The particular reaction depends on the precise nature of the adhesive. In most cases, the reaction breaks chemical bonds. For polymers, large molecules break down to small molecules which do not hold together well. A solid adhesive may liquefy given enough time. For inorganic materials, gases are released by breaking chemical bonds within the adhesive. The pressure of the released gases from inside a solid adhesive material cause the adhesive to fracture, reducing its strength.

Figure 16 is a diagram of separating the carrier wafer 210 from the host wafer 220. This causes the two dies to be separated. The weakened bonding 209 on the temporary adhesive is weaker than the bonding to the host device. The applied heat has weakened the bond between the island dies 205 and the temporary carrier wafer. The other dies 204 have the stronger bond 208 and stay with the carrier wafer 210 after separation. After the separation, the carrier wafer may be used to apply dies to another host wafer. For that process different heater elements will be activated.

Figure 17 is a diagram with the temporary carrier and other small dies removed. The one attached small die 205 remains bonded to the host die 222. The host wafer is further processed to embed the transferred small die fully into the interconnect stack. In the illustrated example, the further processing include additional dielectric 234, additional conductive posts or vias 230 and conductive contact pads or lines 232 to connect to other components. The smaller die 205 is then fully embedded within the ILD of the host die. The host die 222 may be finished in a variety of other ways. In this example, the islands on the device wafers are face up. The device wafer may be further processed so as to make electrical contact to the island through the device wafer interconnect stack or in any of a variety of other ways.

As described specific islands may be selectively transferred by controlling the adhesive layer. Several different dies that may have different technologies and heterogeneous substrates may then be integrated into the same die. The selective heating provides control over the island transfer process for batch, full-wafer methods. This same or a similar technique may also be used to select known good dies for transfer and to not transfer known failed dies. This improves control and allows bad dies to be rejected while still using a full- wafer method. This allows even smaller dies with poor yield rates to be used by selecting only known good dies. The selective heating approach is not subject to the same geometrical constraints as full-wafer methods. In other words, the islands do not need to be in the same wafer configuration as the locations that receive the islands. The carrier wafer may be aligned and islands selectively released. The wafer may then be moved again before one or more additional islands are released.

Figure 19 illustrates a computing device 11 in accordance with one implementation of the invention. The computing device 11 houses a board 2. The board 2 may include a number of components, including but not limited to a processor 4 and at least one communication chip 6. The processor 4 is physically and electrically coupled to the board 2. In some implementations the at least one communication chip 6 is also physically and electrically coupled to the board 2. In further implementations, the communication chip 6 is part of the processor 4.

Depending on its applications, computing device 11 may include other components that may or may not be physically and electrically coupled to the board 2. These other components include, but are not limited to, volatile memory (e.g., DRAM) 8, non- volatile memory (e.g., ROM) 9, flash memory (not shown), a graphics processor 12, a digital signal processor (not shown), a crypto processor (not shown), a chipset 14, an antenna 16, a display 18 such as a touchscreen display, a touchscreen controller 20, a battery 22, an audio codec (not shown), a video codec (not shown), a power amplifier 24, a global positioning system (GPS) device 26, a compass 28, an accelerometer (not shown), a gyroscope (not shown), a speaker 30, a camera 32, and a mass storage device (such as hard disk drive) 10, compact disk (CD) (not shown), digital versatile disk (DVD) (not shown), and so forth). These components may be connected to the system board 2, mounted to the system board, or combined with any of the other components.

The communication chip 6 enables wireless and/or wired communications for the transfer of data to and from the computing device 11. The term "wireless" and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. The communication chip 6 may implement any of a number of wireless or wired standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, Ethernet derivatives thereof, as well as any other wireless and wired protocols that are designated as 3G, 4G, 5G, and beyond. The computing device 11 may include a plurality of communication chips 6. For instance, a first communication chip 6 may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth and a second

communication chip 6 may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others.

The processor 4 of the computing device 11 includes an integrated circuit die packaged within the processor 4. In some implementations of the invention, the integrated circuit die of the processor, memory devices, communication devices, or other components include or are packaged together and bonded on a host die as described herein. The term "processor" may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory.

In various implementations, the computing device 11 may be a laptop, a netbook, a notebook, an ultrabook, a smartphone, a tablet, a personal digital assistant (PDA), an ultra mobile PC, a mobile phone, a desktop computer, a server, a printer, a scanner, a monitor, a set- top box, an entertainment control unit, a digital camera, a portable music player, or a digital video recorder. In further implementations, the computing device 11 may be any other electronic device that processes data including a wearable device.

Embodiments may be implemented as a part of one or more memory chips, controllers, CPUs (Central Processing Unit), microchips or integrated circuits interconnected using a motherboard, an application specific integrated circuit (ASIC), and/or a field programmable gate array (FPGA).

References to "one embodiment", "an embodiment", "example embodiment", "various embodiments", etc., indicate that the embodiment(s) of the invention so described may include particular features, structures, or characteristics, but not every embodiment necessarily includes the particular features, structures, or characteristics. Further, some embodiments may have some, all, or none of the features described for other embodiments.

In the following description and claims, the term "coupled" along with its derivatives, may be used. "Coupled" is used to indicate that two or more elements co-operate or interact with each other, but they may or may not have intervening physical or electrical components between them.

As used in the claims, unless otherwise specified, the use of the ordinal adjectives "first", "second", "third", etc., to describe a common element, merely indicate that different instances of like elements are being referred to, and are not intended to imply that the elements so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

The following examples pertain to further embodiments. The various features of the different embodiments may be variously combined with some features included and others excluded to suit a variety of different applications. Some embodiments pertain to a method that includes forming a plurality of small dies on a wafer, attaching the dies to a temporary carrier, forming a plurality of larger host dies on a host wafer, forming raised mesas on the host dies at locations of the host dies that are to receive a small die, aligning the small dies over the plurality of host dies using the temporary carrier, applying the small dies to the host dies using the temporary carrier so that a subset of the small dies physically contact the raised mesas of the respective host dies while the small dies that are not of the subset do not contact the host dies, and separating the temporary carrier so that the subset of small dies stays with the respective host die in contact with the raised mesas and the remaining small dies are separated from the host dies and stay with the temporary carrier.

Further embodiments include bonding the subset of small dies to the respective host die raised mesa.

In further embodiments the subset of small dies are attached to a respective host die raised mesa after bonding and the remaining small dies are attached to the temporary carrier;

In further embodiments bonding comprises pressing the subset of small dies against the respective host die raised mesa while the small dies that are not of the subset do not contact the host die.

In further embodiments each raised mesa comprises an added layer of oxide over an area of the host die that is to receive a small die, the raised mesa protruding some thickness above the surface of the host die.

Some embodiments pertain to an apparatus that includes a host die having a plurality of raised mesas, the raised mesas protruding higher than the surrounding layer of the host die, a plurality of small dies, each over a respective raised mesa, physically contacting the respective raised mesa, and electrically connected through the respective raised mesa to the host die, and a package to cover the host die and the small dies together.

In further embodiments the small dies are bonded to the host die by metal compression.

In further embodiments each raised mesa comprises an added layer of oxide over an area of the host die that is attached to a small die, the raised mesa protruding some thickness above the surrounding layer of the host die. Some embodiments pertain to a method that includes forming a plurality of small dies on a wafer, attaching the dies to temporary carrier using an adhesive, aligning the dies over a plurality of larger host dies on a host wafer using the temporary carrier, applying the small dies to the host dies using the temporary carrier so that a subset of the small dies physically contact respective host dies, weakening the adhesive between a subset of the small dies and the temporary carrier, and separating the temporary carrier so that the subset of small dies are stays with the respective host die and the remaining small dies are separated from the host dies with the temporary carrier.

In further embodiments weakening the adhesive comprises heating the adhesive.

In further embodiments heating the adhesive comprises activating an array of heating elements attached to the temporary carrier.

In further embodiments the array of heating elements is embedded in a dielectric layer formed over the temporary carrier.

In further embodiments the heating elements are connected to external power through vias through the temporary carrier.

In further embodiments heating the adhesive comprises applying heat to the temporary carrier on a side of the temporary carrier opposite the islands.

Further embodiments include singulating the small dies after attaching the dies to the temporary carrier.

Further embodiments include packaging a host die by covering the small dies in a dielectric and forming metal routing layers in the dielectric to connect the host die to external components.

Further embodiments include packaging a host die by attaching a solder ball array to the host die around the small die and attaching the solder ball array to a package substrate.

Some embodiments pertain to a carrier wafer that includes a dielectric substrate, a surface for attaching a plurality of dies formed on and attached to a common substrate, and an array of heating elements attached to the temporary carrier to heat an area of the temporary carrier corresponding to particular ones of the dies.

In further embodiments the array of heating elements are embedded in the dielectric layer.

Claims

1. A method comprising:

forming a plurality of small dies on a wafer;

attaching the dies to a temporary carrier;

forming a plurality of larger host dies on a host wafer;

forming raised mesas on the host dies at locations of the host dies that are to receive a small die;

aligning the small dies over the plurality of host dies using the temporary carrier;

applying the small dies to the host dies using the temporary carrier so that a subset of the small dies physically contact the raised mesas of the respective host dies while the small dies that are not of the subset do not contact the host dies; and

separating the temporary carrier so that the subset of small dies stays with the respective host die in contact with the raised mesas and the remaining small dies are separated from the host dies and stay with the temporary carrier.

2. The method of Claim 1 , further comprising bonding the subset of small dies to the respective host die raised mesa.

3. The method of Claim 2, wherein the subset of small dies are attached to a respective host die raised mesa after bonding and the remaining small dies are attached to the temporary carrier;

4. The method of Claim 2 or 3, wherein bonding comprises pressing the subset of small dies against the respective host die raised mesa while the small dies that are not of the subset do not contact the host die.

5. The method of any one or more of Claims 1-4, wherein each raised mesa comprises an added layer of oxide over an area of the host die that is to receive a small die, the raised mesa protruding some thickness above the surface of the host die.

6. An apparatus comprising:

a host die having a plurality of raised mesas, the raised mesas protruding higher than the surrounding layer of the host die;

a plurality of small dies, each over a respective raised mesa, physically contacting the respective raised mesa, and electrically connected through the respective raised mesa to the host die; and

a package to cover the host die and the small dies together.

7. The apparatus of Claim 6, wherein the small dies are bonded to the host die by metal compression.

8. The apparatus of Claim 6 or 7, wherein each raised mesa comprises an added layer of oxide over an area of the host die that is attached to a small die, the raised mesa protruding some thickness above the surrounding layer of the host die.

9. A method comprising:

forming a plurality of small dies on a wafer;

attaching the dies to temporary carrier using an adhesive;

aligning the dies over a plurality of larger host dies on a host wafer using the temporary carrier;

applying the small dies to the host dies using the temporary carrier so that a subset of the small dies physically contact respective host dies;

weakening the adhesive between a subset of the small dies and the temporary carrier; and separating the temporary carrier so that the subset of small dies are stays with the respective host die and the remaining small dies are separated from the host dies with the temporary carrier.

10. The method of Claim 9, wherein weakening the adhesive comprises heating the adhesive.

11. The method of Claim 10, wherein heating the adhesive comprises activating an array of heating elements attached to the temporary carrier.

12. The method of Claim 11, wherein the array of heating elements is embedded in a dielectric layer formed over the temporary carrier.

13. The method of Claiml2, wherein the heating elements are connected to external power through vias through the temporary carrier.

14. The method of any one or more of claims 9-13, wherein heating the adhesive comprises applying heat to the temporary carrier on a side of the temporary carrier opposite the islands.

15. The method of any one or more of claims 9-14, further comprising singulating the small dies after attaching the dies to the temporary carrier.

16. The method of any one or more of claims 9-15, further comprising packaging a host die by covering the small dies in a dielectric and forming metal routing layers in the dielectric to connect the host die to external components.

17. The method of any one or more of claims 9-16, further comprising packaging a host die by attaching a solder ball array to the host die around the small die and attaching the solder ball array to a package substrate.

18. A carrier wafer comprising: a dielectric substrate;

a surface for attaching a plurality of dies formed on and attached to a common substrate; and

an array of heating elements attached to the temporary carrier to heat an area of the temporary carrier corresponding to particular ones of the dies.

19. The carrier wafer of Claim 18, wherein the array of heating elements are embedded in the dielectric layer.

20. The carrier wafer of Claim 18 or 19, wherein the heating elements are connected to external power through vias through the temporary carrier.