Three dimensional integrated circuit (3DIC) with support structures

Abstract

The present disclosure, in some embodiments, relates to an integrated chip structure. The integrated chip structure has a first conductive layer on a first substrate and a second conductive layer on a second substrate. A bonding structure is disposed between the first conductive layer and the second conductive layer. A support structure is disposed between the first substrate and the second substrate. A passivation layer covers a bottom surface of the first conductive layer and has a lower surface facing an uppermost surface of the support structure.

Claims

1. An integrated chip structure, comprising: a first conductive layer on a first substrate; a second conductive layer on a second substrate; a bonding structure disposed between the first conductive layer and the second conductive layer; a support structure disposed between the first substrate and the second substrate, wherein the support structure is a polymer material that is configured to soften and melt upon being heated; a passivation layer covering a bottom surface of the first conductive layer and having a lower surface facing an uppermost surface of the support structure; wherein the bonding structure comprises a copper post having an uppermost surface facing the first substrate; and wherein a horizontal plane that is parallel to and extending along the uppermost surface of the copper post is over a top of the support structure.

2. The integrated chip structure of claim 1, further comprising: a third conductive layer on a third substrate; a second bonding structure disposed between the third conductive layer and a fourth conductive layer on the first substrate, wherein the first conductive layer and the fourth conductive layer are electrically coupled by a through-substrate-via extending through the first substrate; and a second support structure disposed between the first substrate and the third substrate.

3. The integrated chip structure of claim 1, wherein the copper post is arranged between sidewalls of the passivation layer and extends from the uppermost surface contacting the first conductive layer to a bottom surface that is vertically between the top and a bottom of the support structure, the copper post having a height that is less than a height of the support structure.

4. The integrated chip structure of claim 1, wherein the passivation layer laterally contacts sidewalls of the copper post, the sidewalls of the copper post vertically extending past a bottommost surface of the passivation layer and the passivation layer vertically extending past the uppermost surface of the copper post.

5. The integrated chip structure of claim 1, wherein the lower surface of the passivation layer comprises a flat lower surface that continuously extends from directly over the support structure to directly below the first conductive layer.

6. The integrated chip structure of claim 1, wherein the polymer material of the support structure is configured to directly contact the lower surface of the passivation layer upon being heated to a temperature used to reflow the bonding structure.

7. The integrated chip structure of claim 1, wherein the lower surface of the passivation layer directly contacts the uppermost surface of the support structure.

8. The integrated chip structure of claim 1, wherein the lower surface of the passivation layer continuously extends from directly above the support structure to a sidewall of the bonding structure, the sidewall of the bonding structure vertically extending from above the lower surface of the passivation layer to below the lower surface of the passivation layer.

9. A multi-dimensional integrated chip structure, comprising: a first connecting structure disposed on a first substrate; a second connecting structure disposed on a second substrate and bonded to the first connecting structure by a solder layer disposed between outer surfaces of the first connecting structure and the second connecting structure facing one another, wherein the second connecting structure has a rounded outer surface facing the solder layer; a support structure disposed between the first substrate and the second substrate and laterally separated from the second connecting structure; and a passivation layer disposed on the first substrate and comprising an uppermost surface that faces away from the first substrate and that directly contacts a polymer material of the support structure.

10. The multi-dimensional integrated chip structure of claim 9, wherein the polymer material of the support structure has a topmost surface that is configured to directly contact a surface of the second substrate upon being heated to a temperature configured to reflow the solder layer.

11. The multi-dimensional integrated chip structure of claim 9, wherein the support structure has a topmost surface that is vertically separated from the first substrate by a non-zero distance.

12. The multi-dimensional integrated chip structure of claim 9, wherein the second connecting structure comprises: a nickel layer having a rounded surface facing the first substrate.

13. The multi-dimensional integrated chip structure of claim 12, wherein the second connecting structure further comprises a palladium layer disposed on the nickel layer and a gold layer disposed on the palladium layer.

14. The multi-dimensional integrated chip structure of claim 12, wherein the nickel layer is disposed over a through-substrate-via (TSV) extending through the second substrate and the passivation layer laterally surrounding the TSV.

15. The multi-dimensional integrated chip structure of claim 9, wherein a first surface of the first substrate and a second surface of the second substrate continuously extend past opposing outermost sidewalls of the material of the support structure.

16. The multi-dimensional integrated chip structure of claim 9, wherein the passivation layer has a planar upper surface continuously extending between the first connecting structure and the support structure.

17. An integrated chip structure, comprising: a first conductive layer on a first substrate; a second conductive layer on a second substrate; a bonding structure disposed between the first conductive layer and the second conductive layer; a plurality of support structures disposed vertically between the first substrate and the second substrate and laterally along opposing sides of the bonding structure; and a passivation layer laterally contacting opposing sides of the second conductive layer, wherein the plurality of support structures comprise a first support structure that includes a polymer material that continuously extends from a top surface directly contacting the first substrate to a bottom surface directly contacting the passivation layer.

18. The integrated chip structure of claim 17, wherein the bonding structure comprises a first connecting structure and a second connecting structure that meet along an interface; and wherein the polymer material of the first support structure continuously extends from a top of the first support structure that is above the interface to a bottom of the first support structure that is below the interface.

19. The integrated chip structure of claim 17, wherein the bonding structure protrudes outward from an upper surface of the passivation layer and the first support structure vertically contacts the upper surface of the passivation layer, a height of the bonding structure above the upper surface being equal to a height of the first support structure.

20. The integrated chip structure of claim 17, wherein the plurality of support structures comprise polybenzoxazole or benzocyclobutene and are configured to soften and melt upon reflow of the bonding structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, and like reference numerals designate like structural elements.

(2) FIG. 1 is a cross-sectional view of a three-dimensional integrated circuit (3DIC) structure, in accordance with some embodiments.

(3) FIG. 2A is a cross-sectional view of a die, in accordance with some embodiments.

(4) FIG. 2B is a diagram the warpage of a die with temperatures of a thermal cycling of the die of FIG. 2A, in accordance with some embodiments.

(5) FIG. 3A is a cross-sectional view of a die, in accordance with some embodiments.

(6) FIG. 3B is a cross-sectional view of a connecting structure on a die of FIG. 3A, in accordance with some embodiments.

(7) FIG. 3C is a diagram the warpage of a die with temperatures of a thermal cycling of the die of FIG. 3A, in accordance with some embodiments.

(8) FIG. 4 is a cross-sectional view of dies stacked over a substrate, in accordance with some embodiments.

(9) FIG. 5A is a cross-sectional view of a die, in accordance with some embodiments.

(10) FIG. 5B is a top view of the die of FIG. 5A, in accordance with some embodiments.

(11) FIG. 5C is a top view of supporting structures and connecting structures on a die, in accordance with some other embodiments.

(12) FIG. 5D are top views of various shapes of a support structure, in accordance with some embodiments.

(13) FIG. 6A is cross-sectional view of 3 dies and a substrate for forming a three dimensional integrated circuit (3DIC) structure before a reflow process, in accordance with some embodiments.

(14) FIG. 6B is a cross-sectional view of a support structure of a die next to a connecting structure aligned with a connecting structure of another die, in accordance with some embodiments.

(15) FIG. 7A is a cross-sectional view of a 3DIC structure, in accordance with some embodiments.

(16) FIG. 7B is a cross-sectional view of a support structure next to a bonding structure between on two dies, in accordance with some embodiments.

(17) FIG. 8 is a cross-sectional view of a 3DIC structure, in accordance with some embodiments.

DETAILED DESCRIPTION

(18) It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

(19) FIG. 1 is a cross-sectional view of a three-dimensional integrated circuit (3DIC) structure 200, in accordance with some embodiments. 3DIC structure 200 includes semiconductor dies A, B, C, and D stacked on top of one another on a substrate 100. Each of the semiconductor dies A, B, and C has one or more through silicon vias (TSVs) 40.sub.A, 40.sub.B, or 40.sub.C, for inter-die communications and heat dissipation. The TSVs 40.sub.A, 40.sub.B, and 40.sub.C are connected to other TSVs or substrate 100 through bonding structures 30.sub.A 30.sub.B, 30.sub.C, and 30.sub.D in semiconductor dies A, B, C, and D, respectively, which could be electrically connected to integrated circuits (not shown) in each die. In some embodiments, the bonding structures 30.sub.A 30.sub.B, 30.sub.C, and 30.sub.D include various types of metal, such as solder, gold, copper, etc. Substrate 100 also includes external connectors 110. The width of substrate 100 is wider than the widths of each of semiconductor dies A, B, C, and D.

(20) Each semiconductor die includes a semiconductor substrate as employed in a semiconductor integrated circuit fabrication, and integrated circuits may be formed therein and/or thereupon. The semiconductor substrate refers to any construction comprising semiconductor materials, including, but not limited to, bulk silicon, a semiconductor wafer, a silicon-on-insulator (SOI) substrate, or a silicon germanium substrate. Other semiconductor materials including group III, group IV, and group V elements may also be used. The semiconductor substrate may further comprise a plurality of isolation features (not shown), such as shallow trench isolation (STI) features or local oxidation of silicon (LOCOS) features. The isolation features may define and isolate the various microelectronic elements. Examples of the various microelectronic elements that may be formed in the semiconductor substrate include transistors (e.g., metal oxide semiconductor field effect transistors (MOSFET), complementary metal oxide semiconductor (CMOS) transistors, bipolar junction transistors (BJT), high voltage transistors, high frequency transistors, p-channel and/or n-channel field effect transistors (PFETs/NFETs), etc.); resistors; diodes; capacitors; inductors; fuses; and other suitable elements. Various processes are performed to form the various microelectronic elements including deposition, etching, implantation, photolithography, annealing, and/or other suitable processes. The microelectronic elements are interconnected to form the integrated circuit device, such as a logic device, memory device (e.g., SRAM), RF device, input/output (I/O) device, system-on-chip (SoC) device, combinations thereof, and other suitable types of devices. In some embodiments, each semiconductor die also includes passive devices such as resistors, capacitors, inductors and the like.

(21) Each semiconductor die may include interconnect structures or redistribution layer(s) (RDL) (not shown) to enable electrical connection between interconnect in each die and external connectors. RDLs are interconnect structures near a surface of die packages or on packaging structures to facilitate electrical connections. Dies, such as dies A, B, and C, between top die D and substrate 100 may further include through substrate vias (TSVs) and may be interposers.

(22) Substrate 100 may be made of a semiconductor wafer, or a portion of wafer. In some embodiments, substrate 100 includes silicon, gallium arsenide, silicon on insulator (“SOI”) or other similar materials. In some embodiments, substrate 100 also includes passive devices such as resistors, capacitors, inductors and the like, or active devices such as transistors. In some embodiments, substrate 100 includes additional integrated circuits. In addition, the substrate 100 may be made of other materials. For example, in some embodiments, substrate 100 is a multiple-layer circuit board. In some embodiments, substrate 100 also includes bismaleimide triazine (BT) resin, FR-4 (a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant), ceramic, glass, plastic, tape, film, or other supporting materials that may carry the conductive pads or lands needed to receive conductive terminals.

(23) To form the 3DIC structure 200 in FIG. 1, dies A, B, C, and D are stacked over substrate 100 and then undergo a reflow process to form the bonding structures 30.sub.A 30.sub.B, 30.sub.C, and 30.sub.D. In some embodiments, some or all of semiconductor dies A, B, C, and D bow before or after the reflow process used to form bonding structures 30.sub.A 30.sub.B, 30.sub.C, and 30.sub.D. The bowing of a die is caused by a mis-match of coefficients of thermal expansion (CTE) and stress of various layers in the die. During the formation of devices and structures of dies on a substrate, films with different CTE and stress are formed on the substrate. The substrate also undergoes different thermal processes during the formation of the devices and structure. After the formation of devices and structures are completed, dies formed on the substrate are separated into individual pieces, such as semiconductor dies A, B, C, and D. The separated and individual dies could bow due to mis-match of coefficients of thermal expansion (CTE) and stress of various layers in the die.

(24) FIG. 2A is a cross-sectional view of a die D′, in accordance with some embodiments. Die D′ is similar to semiconductor die D and includes a substrate 20.sub.D′ with devices (not shown) and interconnect structures (not shown) formed therein. Die D′ has connecting structures 25.sub.D′. Each connecting structure 25.sub.D′ includes a copper post 22.sub.D′ and a solder layer 23.sub.D′ formed over the copper post 22.sub.D′. The copper post 222.sub.D′ comes in contact with a metal pad 24.sub.D′, which is connected to interconnect structures (not shown) and devices (not shown) in die D′. In some embodiments, an under bump metallurgy (UBM) layer (not shown) is between copper post 22.sub.D′ and the metal pad 24.sub.D′. The structure of a connecting structure 25.sub.D′ described above is merely an example. Other connecting structures may also be used.

(25) A passivation structure 21.sub.D′ is formed over substrate 20.sub.D′ to protect substrate 20.sub.D′. The passivation structure 21.sub.D′ may include one or more passivation layers. The passivation layer(s) is made of silicon nitride, silicon oxynitride, polymers, or combinations thereof, in some embodiments. Die D′ may or may not have has TSVs. In some embodiments where die D′ is a top die, die D′ does not have TSVs. In some embodiments where die D′ is a die between a top die and a substrate, die D′ has TSVs.

(26) As shown in FIG. 2A, die D′ bows upward at the edges. As a result, die D′ has a crescent cross-sectional shape. For a lead-free bump scheme, the reflow process for forming bonding structures is performed at a peak temperature in a range from about 230° C. to about 250° C., in accordance with some embodiments. To understand the effect of a thermal process, such as reflow, on the planarity (or flatness) of dies, in a non-limiting example, die D′ undergoes a thermal cycling with temperature rising from room temperature (25° C.) to 240° C. and back to room temperature (25° C.). FIG. 2B is a diagram of the warpage of die D′ with temperatures of the thermal cycling, in accordance with some embodiments. The die warpage □H is defined as a difference of heights between a top surface at a center of die and a top surface at an edge of die. For example, a warpage of −20 □m for a die means the edges of the die are higher than the center of the die by 20 □m. FIG. 2B indicates that the die warpages for die D′ stay consistently at about −20 □m during the thermal cycling. The data in FIG. 2B indicate that die D′ bows upward at the edges under various temperatures of the thermal cycling. The shape of die D′ with edges higher than center of die resembles a crescent shape, as in FIG. 2A.

(27) FIG. 3A is a cross-sectional view of die A′, in accordance with some embodiments. Die A′ is similar to die A (FIG. 1), and includes a substrate 20.sub.A′ with devices (not shown) and interconnect structures (not shown) formed therein. Die A′ also has TSVs 40.sub.A′ and also connecting structures 25.sub.A′. Each connecting structure 25.sub.A′ includes a copper post 22.sub.A′ and a solder layer 23.sub.A′ formed over the copper post 22.sub.A′. The copper post 22.sub.A′ comes in contact with a metal pad 24.sub.A′, which is connected to TSV 40.sub.A′. In some embodiments, an under bump metallurgy (UBM) layer (not shown) is between copper post 22.sub.A′ and metal pad 24.sub.A′. A passivation structure 21.sub.A′ is formed over substrate 20.sub.A′ to protect substrate 20.sub.A′. The passivation structure 21.sub.A′ is similar to passivation structure 21.sub.D′ and may include one or more passivation layers. The other end of TSV 40.sub.A′ is connected to another connecting structure 26.sub.A′. In some embodiments, a passivation structure 29.sub.A′ is formed over a backside of substrate 20.sub.A′ opposite passivation layer 21.sub.A′, as in FIG. 3A. The passivation structure 29.sub.A′ may include one or more passivation layers. The passivation layer(s) is made of silicon nitride, silicon oxynitride, polymers, or combinations thereof, in some embodiments.

(28) In some embodiments, each connecting structure 26.sub.A′ includes a nickel (Ni) layer 27.sub.A′, a palladium (Pd) layer 27.sub.B′, and a gold (Au) layer 27.sub.C′, as in FIG. 3B. In some embodiments, the connecting structure 26.sub.A′ are made of electroless Ni, electroless Pd, and immersion Au (or electroless-Ni/electroless-Pd/immersion-Au, or ENEPIG). Connecting structures using ENEPIG layers are used for bonding and are lead-free (Pb-free).

(29) To understand the effect of a thermal process on the planarity (or flatness) of dies, in a non-liming example, die A′ undergoes a thermal cycling with temperature rising from room temperature (25° C.) to 260° C. and back to room temperature (25° C.). FIG. 3C is a diagram of the warpage (□H) of die A′ with temperatures of the thermal cycling, in accordance with some embodiments. FIG. 3C indicates that the die warpage stay consistently at about 50 □m at room temperature and decrease to about 17 □m at 260° C. The warpage recovers to about 50 □m when the temperature cycles back to room temperature. The data in FIG. 3C indicate that die A′ bows downward at the edges during the various temperatures of thermal cycling. The shape of die A′ with edges lower than a center of the die resembles a downward facing crescent shape.

(30) FIG. 4 is a cross-sectional view of dies A′, B′, C′, and D′ stacked over substrate 100′ after reflow and at room temperature, in accordance with some embodiments. Dies B′ and C′ are similar to die A′ and also bow downward at the edges. Substrate 100′ is similar to substrate 100. In some embodiments, substrate 100′ is a wafer and is substantially planar. Due to the bowing of dies A′, B′, C′, and D′, bonding structures in region M and regions N are likely to have cold joints (open joints). Region M is near a center of substrate 100′. The center portion of die A′ is pulled away from the connectors 26.sub.S on substrate 100′. As a result, region M could have open or cracked bonding structures between substrate 100′ and die A′ after reflow due to bowing of die A′. Regions N are near the edges of dies D′ and C′. Due to the upward bowing of die D′ and the downward bowing of die C′ at edges, the bonding structures between dies D′ and C′ near regions N are likely to have opens or cracks. Bonding structures with opens or cracks would cause yield reduction.

(31) In order to reduce the effect of bowing, thermal compression bonding process may be used. Thermal compression bonding involves applying external pressure on the stacked dies and substrate during a thermal process. The pressure reduces the effect of bowing. However, the processing is costly and bonding structures near high stress regions, such as regions M and N, still have a risk of cracking. Therefore, finding a mechanism for bonding multiples dies on a substrate that reduces the effect of bowing of dies is desirable.

(32) FIG. 5A is a cross-sectional view of die A″ with support structures 50.sub.A″ formed on a side of die A″ with connecting structures 25.sub.A″, in accordance with some embodiments. The supportive structures 50.sub.A″ are formed on a surface 31.sub.A″ of die A″ not occupied by connecting structures 25.sub.A″. The support structures 50.sub.A″ are formed next to or near the connecting structures 25.sub.A″. A height H.sub.1 of support structure 50.sub.A″ is about the same as a height H.sub.2 of connecting structures 25.sub.A″ above surface 31.sub.A″ (or surface of passivation structure 21.sub.A″), in some embodiments. In some embodiments, H.sub.1 is greater than H.sub.2. The support structures 50.sub.A″ include polymers and adhere to the surface 31.sub.A″ of passivation structure 21.sub.A″. In some embodiments, a width W.sub.1 of a support structure 50.sub.A″ is in a range from about 20 □m to about 500 □m.

(33) In some embodiments, support structures 50.sub.A″ are made of polymers with fillers, such as silica and/or rubber. The fillers are used to provide (or enhance) strength to the support structures 50.sub.A″, which are placed between two dies. The examples of polymer(s) used for the support structures 50.sub.A″ include, but are not limited to, materials such as polyimide, polybenzoxazole (PBO), or benzocyclobutene (BCB). The polymer used for support structures 50.sub.A″ soften and melt under reflow of bonding structures and adhere to a substrate bonded to die A″. In some embodiments, a glass transition temperature of support structures 50.sub.A″ is in a range from about 40° C. to about 150° C. After the thermal reflow process with die A″ and substrate 100″ returning to room temperature, the support structures 50.sub.A″ maintain sufficient strength to maintain the height between die A″ and the substrate. In some embodiments, a Young's modulus of support structures 50.sub.A″ is in a range from about 1 GPa to about 10 GPa.

(34) FIG. 5B is a top view of die A″ with support structures 50.sub.A″ formed over surface 31.sub.A″, in accordance with some embodiments. The support structures 50.sub.A″ are distributed across surface 31.sub.A″ of die A″ and are formed on surface 31.sub.A″ not occupied by connecting structures 25.sub.A″. Since there is limited surface space near the center of die A″, support structures 50.sub.A″ are arranged mostly surrounding connecting structures 25.sub.A″ which are congregated near the center of die A″. If the connecting structures are arranged differently, the support structures 50.sub.A″ are re-arranged accordingly. FIG. 5C is a top view of die A″ with supporting structures 50.sub.A″ and connecting structures 25.sub.A″ on surface 31.sub.A″, in accordance with some embodiments. The connecting structures 25.sub.A″ are arranged around an outer portion of surface 31.sub.A″. Some support structures 50.sub.A″ are placed near the center of die A″ and others are place near outer edges of die A″.

(35) The support structures 50.sub.A″ are placed at various locations across the surface (31.sub.A″) of die A″ to counter the effect of bowing. In some embodiments, the placement of the support structures 50.sub.A″ is based on the bowing of the two dies or substrates that the support structures are sandwiched between.

(36) The support structures 50.sub.A″ in FIGS. 5B and 5C have cross sections in the shapes of squares. However, the support structures 50.sub.A″ are in other shapes, in some embodiments. FIG. 5D are top views of a support structure 50.sub.A″ having oval, circle, triangle, rectangle, and hexagon shapes. Other shapes are also possible.

(37) Support structures 50.sub.A″ may be formed on the surface 31.sub.A″ of substrate 20.sub.A″ by various methods. In some embodiments, passivation layer 21.sub.A″ is over substrate 20.sub.A″ and support structures 50.sub.A″ are formed on surface 31.sub.A″ on top of the passivation layer. For example, structures 50.sub.A″ may be formed by printing (or screening) with a stencil. During the printing (or screening) process, the support structures 50.sub.A″ or substrate 20.sub.A″ are heated to allowed the support structures 50.sub.A″ to adhere to surface 31.sub.A″ of substrate 20.sub.A″.

(38) Alternatively, a layer for material for the support structures 50.sub.A″ may be deposited on surface 31.sub.A″ of substrate 20.sub.A″ prior to forming support structures. After the layer of material is deposited, the layer is than patterned by lithography and etched. Other applicable methods may also be used to form support structures 50.sub.A″.

(39) FIG. 6A is cross-sectional view of 3 dies and a substrate for forming a three dimensional integrated circuit (3DIC) structure before a reflow process, in accordance with some embodiments. Support structures similar to support structures 50.sub.A″ may also formed on dies B″, C″, and D″ by similar mechanisms described above. Dies A″, B″, C″, and D″ are similar to dies A′, B′, C′, and D′, respectively. After support structures 50.sub.A″, 50.sub.B″, 50.sub.C″, and 50.sub.D″ are on formed on dies A″, B′, C′, and D′, these dies are stacked on top of each other over substrate 100″, as in FIG. 6A in accordance with some embodiments. The connecting structures 25.sub.A″ are aligned with and connecting structures 26.sub.S of substrate 100″. Support structures 50.sub.A″ on die A″ are between die A″ and substrate 100″. Similarly, connecting structures 25.sub.B″ of substrate B″ are aligned connecting structures 26.sub.A″ on the opposite side of substrate A″ from connecting structures 25.sub.A″. Support structures 50.sub.B″ formed on die B″ are between die B″ and die A″.

(40) Similarly, connecting structures 25.sub.C″ of substrate C″ are aligned with connecting structures 26.sub.B″ and support structures 50.sub.C″ are between die C″ and die B″. Connecting structures 25.sub.D″ of substrate D″ are aligned with connecting structures 26.sub.C″ and support structures 50.sub.D″ are between die D″ and die C″.

(41) FIG. 6B is an enlarged cross-sectional view of a support structure 50.sub.C″ on die C″ next to a connecting structure 25.sub.C″ aligned with and in contact with a connecting structure 26.sub.B″ of die B″, in accordance with some embodiments. FIG. 6B includes a gap with a distance D.sub.1 between support structure 50.sub.C″ and a surface 32.sub.B″ of die B″. In some embodiments, the support structure 50.sub.C″ touches surface 32.sub.B″. To provide support for the 3DIC with dies A″, B″, C″, D″, over substrate 100″, the support structure 50.sub.C″ adheres to surface 32.sub.B″ after reflow. D.sub.1 is in a range from about 0 nm to about 2000 nm, in accordance with some embodiments. D.sub.1 can be greater than zero, because solder layer 23.sub.C″ of die C″ softens and melts to cover at least a portion of connecting structure 26.sub.B″. In some embodiments, connecting structure 26.sub.B″ is formed over a metal pad 36.sub.B″. Due to the softening and melting of solder layer 23.sub.C″, a height of solder layer 23.sub.C″ between copper post 22.sub.C″ and connecting structure 26.sub.B″ is shortened from a pre-reflow height, which allows support structure 50.sub.C″ to touch surface 32.sub.B″ and become adhered to surface 32.sub.B″.

(42) FIG. 7A is a cross-sectional view of a 3DIC structure, in accordance with some embodiments. After dies A″, B″, C″ and D″ are stacked over substrate 100″, the stacked structure undergoes a reflow process. The reflow process enables the solder layers 23.sub.A″, 23.sub.B″, 23.sub.C″ and 23.sub.D″ to bond to connecting structure 26.sub.S, 26.sub.A″, 26.sub.B″, and 26.sub.C″ respectively to form bonding structures 28.sub.A″, 28.sub.B″, 28.sub.C″ and 28.sub.D″, as in FIG. 7A, in accordance with some embodiments. The bonded dies A″, B″, C″, D″ and substrate 100′ form a 3DIC structure 200″. The reflow process also bonds support structures 50.sub.D″ to the back surface 32.sub.C″ of die C″, support structures 50.sub.C″ to the back surface 32.sub.B″ of die B″, support structures 50.sub.B″ to the back surface 32.sub.A″ of die A″, and support structures 50.sub.A″ to the back surface 32.sub.S of substrate 100″.

(43) The reflow process is conducted at a peak temperature in a range from about 230° C. to about 250° C., in accordance with some embodiments. For example under the reflow process, the polymer material of the support structures 50.sub.D″ softens and adheres to surface 32.sub.C″. One end of each of support structures 50.sub.D″ adheres to surface 31.sub.C″ of die D″ and the other end of the same support structure 50.sub.D″ adheres to surface 32.sub.C″ of die C″. As mentioned above, the support structures 50.sub.D″ include fillers used to increase strength of the support structures. Heights of the support structures 50.sub.D″ are maintained during the reflow process to keep the distance between dies D″ and C″.

(44) FIG. 7B is an enlarged cross-sectional view of a support structure 50.sub.C″ next to a bonding structure 28.sub.C″ between on dies C″ and B″, in accordance with some embodiments. A height D.sub.2 of support structures 50.sub.C″ is in a range from about 10 □m to about 50 □m.

(45) The support structures 50.sub.C″ also relieve stress exerted on bonding structures 28.sub.C″ between dies C″ and B″ and reduces the risk of cracking of bonding structures. The Young's Modulus of the support structures 50.sub.C″ helps to relieve stress exerted on bonding structures 28.sub.C″ by absorbing forces associated with bowing of dies B″ and C″ during formation of the dies. As a result, support structures 50.sub.C″ improve the yield of the 3DIC structure 200″ of bonded dies A″, B″, C″, D″ and substrate 100″, in comparison with a 3DIC which does not include support structures 50.sub.C″. Support structures 50.sub.D″, 50.sub.B″ and 50.sub.A″ provide similar function as structures 50.sub.C″.

(46) FIG. 8 is a cross-sectional view of a 3DIC structure, in accordance with some embodiments. After the 3DIC structure 200″ has been formed, an underfill 210 can be applied on the surface of substrate 100″ to fill the space between substrate 100″ and dies A″, B″, C″, and D″, as in FIG. 8 in accordance with some embodiments. The 3DIC structure 200″ with the underfill is bonded to another substrate 300 via external connectors 110″, as in FIG. 8.

(47) Substrate 300 may be made of a semiconductor wafer, or a portion of wafer. In some embodiments, substrate 100 includes silicon, gallium arsenide, silicon on insulator (“SOI”) or other similar materials. In some embodiments, substrate 300 also includes passive devices such as resistors, capacitors, inductors and the like, or active devices such as transistors. In some embodiments, substrate 300 includes additional integrated circuits. In addition, the substrate 300 may be made of other materials. For example, in some embodiments, substrate 300 is a multiple-layer circuit board. In some embodiments, substrate 300 also includes bismaleimide triazine (BT) resin, FR-4 (a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant), ceramic, glass, plastic, tape, film, or other supporting materials that may carry the conductive pads or lands needed to receive conductive terminals.

(48) In 3DIC structure, such as structure 200″, the numbers of support structures between different dies and/or between a die and a substrate could be the same or different. The layouts and designs of the support structures are based on the shapes and severity of bowing of the dies and substrate(s). The bowing shapes of dies A, B, C, and D described above are merely examples. Support structures 50.sub.A″, 50.sub.B″, 50.sub.C″, and 50.sub.D″ described above may be used to relieve stress and to help maintaining height between two neighboring dies with different bowing shapes from those described above.

(49) The embodiments described above provide methods and structures for forming support structures between dies and substrate(s) of a 3DIC structures. Each support structure adheres to surfaces of two neighboring dies or die and substrate to relieve stress caused by bowing of the die(s) and/or substrate on the bonding structures formed between the dies or die and substrate. A cost of the support structures is much lower than other processes, such as thermal compression bonding, to reduce the effect of bowing of dies and substrates on 3DIC formation. The support structures improves yield of 3DIC structures.

(50) In some embodiments, the present disclosure relates to a three dimensional integrated chip (3DIC) structure. The 3DIC structure comprises a first die and a second die that is bonded to the first die by one or more bonding structures. The one or more bonding structures respectively comprise a first metal pad arranged on the first die and a second metal pad arranged on the second die. A first plurality of support structures are disposed between the first die and the second die. The first plurality of support structures comprise polymers laterally spaced apart from a closest one of the one or more bonding structures. The first plurality of support structures extend below an upper surface of the second metal pad.

(51) In some other embodiments, the present disclosure relates to a three dimensional integrated chip (3DIC) structure. The 3DIC structure comprises a first die and a second die that is bonded to the first die by a plurality of bonding structures. The plurality of bonding structures respectively comprise a copper post. A first plurality of support structures are disposed between the first die and the second die. The first plurality of support structures comprise polymers that are laterally spaced apart from a closest one of the plurality of bonding structures. The copper post extends vertically past top surfaces of the first plurality of support structures facing the first die.

(52) In yet some other embodiments, the present disclosure relates to a three dimensional integrated chip (3DIC) structure. The 3DIC structure comprises a first die and a second die that is bonded to the first die by one or more bonding structures. A first plurality of support structures are disposed between the first die and the second die. The first plurality of support structures are comprise polymers laterally spaced apart from a closest one of the one or more bonding structures. The first plurality of support structures directly contact a surface of the second die that comprises a semiconductor material.

(53) Various modifications, changes, and variations apparent to those of skill in the art may be made in the arrangement, operation, and details of the methods and systems disclosed. Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.