Direct copper wire bonding on nano twin copper structures

Abstract

Embodiments of the invention relate to direct copper wire bonding on nano-twin copper structures. A package (104) includes a semiconductor die (110) including a device side (111) with circuitry formed in the device side. The package includes: a metal member (114) coupled to the device side; and a nano-twin copper member (118) having a bottom surface coupled to the metal member, the nano-twin copper member including a twin boundary separating a first region having a first grain structure from a second region having a second grain structure. The package also includes a wire bond (120) directly coupled to a top surface of the nano-twin copper member, the wire bond contacting the plurality of regions of the nano-twin copper member. The package also includes a molding compound (126) covering the die, the metal member, the nano-twin copper member, and the wire bonds.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and more particularly to direct copper wire bonding on nanotwinned copper structures. Background Art

[0002] A semiconductor wafer is a circular piece of semiconductor material, such as silicon, used to make semiconductor chips. Typically, complex manufacturing processes are used to form many integrated circuits on a single wafer. Forming such circuits on a wafer is called fabrication. After wafer fabrication, the wafer is cut into multiple pieces, called semiconductor dies, where each die contains a circuit. Cutting or sawing the wafer into individual dies is called singulation. The dies are then coupled to a lead frame and covered with a molding compound, which is then sawn to produce a package. Summary of the invention

[0003] A package includes a semiconductor die, the semiconductor die including a device side, the device side having a circuit system formed therein. The package includes: a metal component coupled to the device side; and a nanotwinned copper component having a bottom surface coupled to the metal component, the nanotwinned copper component including a twin boundary separating a first region having a first grain structure from a second region having a second grain structure. The package also includes wire bonds directly coupled to the top surface of the nanotwinned copper component, the wire bonds contacting multiple regions of the nanotwinned copper component. The package also includes a molding compound covering the die, the metal component, the nanotwinned copper component, and the wire bonds.

[0004] A method for manufacturing a package includes: sputtering a seed layer over a metal component, the metal component coupled to a semiconductor die; and patterning a photoresist having a cavity over the metal component using photolithography. The method also includes forming a nanotwinned copper component in the cavity, the nanotwinned copper component including a twin boundary separating a first region having a first grain structure from a second region having a second grain structure. The method also includes forming a wire bond on a top surface of the nanotwinned copper component using a wire bonder. The method includes covering the semiconductor die and the nanotwinned copper component with a molding compound. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1A is a cutaway cross-sectional view of a package including direct copper wire bonding on a nanotwinned copper structure according to various examples.

[0006] Figure 1B is a top view of a package including direct copper wire bonding on a nanotwinned copper structure according to various examples.

[0007] Figure 1Cis a perspective view of a package including direct copper wire bonding on a nanotwinned copper structure according to various examples.

[0008] Figure 2 is a cutaway cross-sectional view of a nanotwinned copper structure coupled to a wire bond according to various examples.

[0009] Figure 3 is a flow chart of a method for fabricating a package including direct copper wire bonding on nanotwinned copper structures according to various examples.

[0010] Figures 4A1 to 4H3 A process flow for fabricating a package including direct copper wire bonding on nanotwinned copper structures according to various examples.

[0011] Figure 5A is a cutaway cross-sectional view of a wire bond coupled directly to a polycrystalline copper structure.

[0012] Figure 5B is a cutaway cross-sectional view of a wire bond directly coupled to a nanotwinned copper structure according to various examples.

[0013] Figure 6 is a block diagram of an electronic device including a package with wire bonds directly coupled to a nanotwinned copper structure according to various examples. DETAILED DESCRIPTION

[0014] The package typically includes bonding wires that connect metal components on the device side (i.e., the circuit system side) of the semiconductor die to various structures within the package, such as conductive terminals (e.g., package leads). In this way, the bonding wires provide power and / or data signals between the die and the conductive terminals of the package. When forming bonds on the metal components of the die, corrosion or pad oxidation and adhesion may pose challenges. Metal stacks of nickel and palladium deposited on the top surface of these metal components of the die can be used to mitigate electromigration and promote adhesion to wire bonds. However, palladium is expensive, and it is not practical to remove nickel and palladium because the underlying copper of the metal components of the die has a polycrystalline structure that cannot bond well to other copper structures such as wire bonds. This poor bonding between copper wire bonds and copper metal components is due to a variety of factors, such as corrosion and poor diffusion of copper in polycrystalline copper applications. In copper to polycrystalline copper bonding applications, the bonding area typically achieved is less than 60%.

[0015] The present disclosure describes various examples of packages in which copper wire bonds are formed directly on a nanotwinned copper component of the package, such as a nanotwinned copper component formed on a semiconductor die within the package. The nanotwinned copper component includes horizontally oriented twin boundaries that separate multiple regions of the copper component from each other, wherein each of the multiple regions has a different grain structure. These nanotwinned copper components are significantly more suitable for direct copper to copper bonding relative to polycrystalline copper structures. Direct copper to nanotwinned copper bonding no longer requires nickel plating and palladium plating, while improving diffusivity. In copper to nanotwinned copper bonding applications, a bonding area greater than 80% is typically achieved. In an example, a package includes a semiconductor die, the semiconductor die including a device side, in which a circuit system is formed. The package includes a metal component coupled to the device side, wherein the metal component is vertically aligned with the circuit system on the device side. The package also includes a nanotwinned copper component having a bottom surface coupled to the metal component, wherein the nanotwinned copper component includes a twin boundary that separates a first region having a first grain structure from a second region having a second grain structure. The twin boundary is horizontally oriented and is substantially parallel to a horizontal plane in which the semiconductor die lies. The package also includes a wire bond coupled directly to a top surface of the nanotwinned copper member. The package also includes a molding compound covering the die, the metal member, the nanotwinned copper member, and the wire bond.

[0016] Figure 1A1 is a cross-sectional view of a package 104 including direct copper wire bonding on a nanotwinned copper structure according to various examples. Specifically, package 104 includes a die pad 106 and a conductive terminal 108. Although package 104 is depicted as a quad flat no-lead (QFN) package, package 104 can be any suitable type of package in which a copper bonding pad is coupled to other copper components, such as wire bonds. Package 104 includes a semiconductor die 110 coupled to die pad 106, for example using a die attach material. Semiconductor die 110 includes a device side 111 in which circuitry is formed. Metal member 114 is coupled to device side 111, for example, to a metallization on device side 111, the metallization being coupled to the circuitry of semiconductor die 110. A sputtered barrier layer 121 (e.g., titanium-tungsten, titanium) contacts metal member 114. A sputtered seed layer 116 contacts barrier layer 121. Copper member 118 contacts seed layer 116. As described in more detail below, copper member 118 is a nanotwinned copper member and does not include polycrystalline copper. Insulating layer 112, such as a passivation layer, contacts device side 111 and metal member 114. Insulating layer 124, such as a polyimide layer, can contact insulating layer 112 and copper member 118. Wire bond 120 (e.g., ball bond, such as copper ball bond) is bonded to copper member 118. Bond wire 122 is coupled to wire bond 120 and one of conductive terminals 108. Molding material 126 covers the various structures described above, as shown in the figure. Conductive terminal 108 is exposed to the outside of molding material 126, as shown in the figure. The stack including metal member 114, barrier layer 121, seed layer 116 and copper member 118 does not include nickel or palladium. Figure 1B Based on various examples Figure 1A Top view of the structure. Figure 1C Based on various examples Figure 1A perspective view of the structure.

[0017] Figure 2 is a cross-sectional view of a nanotwinned copper structure coupled to a wire bond according to various embodiments. More specifically, Figure 2 A close-up of a copper component 118 coupled to a wire bond 120 is shown. The copper component 118 is a nanotwinned copper structure (i.e., nanocrystalline copper with nanotwins). The nanotwinned copper structure contains nanoscale twin boundaries that separate the copper grains of the structure. Twin boundaries are planar defects that separate two regions of a crystal that are very similar or mirror images of each other. In nanotwinned copper, these twin boundaries are highly dense and closely spaced. Figure 2 , the copper member 118 includes regions 200 separated by respective twin boundaries 212. The twin boundaries 212 are horizontally oriented, as shown, and are generally parallel to the semiconductor die 110 ( Figure 1A) in a horizontal plane. As used herein, substantially parallel means parallel or within plus or minus 10 degrees of parallel. Each region 200 has a different grain structure, wherein a twin boundary 212 separates a corresponding pair of regions 200 having a mirror image grain structure.

[0018] The wire bonds 120 are bonded to the surface 214 of the copper member 118. The wire bonds 120 are bonded to two or more regions 200 of the copper member 118. The nanotwinned copper of the copper member 118 forms an excellent direct bond with other copper structures (e.g., copper ball bonds) by improving the diffusivity between the copper member 118 and the wire bonds 120 relative to polycrystalline copper. This excellent diffusivity is possible because the nanotwinned copper has a (111) plane orientation, which has the highest diffusivity of all crystal orientations. Direct copper to nanotwinned copper bonding eliminates the need for nickel and palladium plating while improving diffusivity.

[0019] The thickness of the copper member 118 is in the range of 5 microns to 13 microns. A thickness below this range is disadvantageous because damage to the metal member 114 may occur during the wire bonding process, resulting in cracking, and a thickness above this range is disadvantageous because it increases the electroplating cycle time and creates high stress due to its weight on top of the metal member 114.

[0020] Figure 3 is a flow chart of a method for fabricating a package including direct copper wire bonding on nanotwinned copper structures according to various examples. Figures 4A1 to 4H3 is a process flow for manufacturing a package including direct copper wire bonding on a nanotwinned copper structure according to various examples. Figure 3 and Figures 4A1 to 4H3 .

[0021] The method 300 begins by providing a semiconductor wafer having a metal feature positioned on a device side of the wafer ( 302 ). Fig.4A1 1 is a cutaway cross-sectional view of a semiconductor wafer 110 having metal features 114 positioned on a device side 111 of the wafer 110. The device side 111 is the side of the wafer 110 on which circuitry is formed. Although reference numeral 110 is used herein to refer to a semiconductor die, for ease of explanation, reference numeral 110 may also be used to refer to a semiconductor wafer that is subsequently singulated to produce semiconductor die 110. Figure 4A2 Based on various examples Fig.4A1 Top view of the structure. Figure 4A3 Based on various examples Fig.4A1 perspective view of the structure.

[0022] The method 300 includes applying and patterning a passivating overcoat (304). Figure 4B1 yes Fig.4A1 1, except that an insulating layer 112 (eg, a passivation overcoat) is added. The insulating layer 112 contacts the metal member 114 and the device side 111, as shown. Figure 4B2 Based on various examples Figure 4B1 Top view of the structure. Figure 4B3 Based on various examples Figure 4B1 perspective view of the structure. Fig.4C1 Shows Figure 4B1 The structure of FIG. 1 is different in that an opening 115 is formed in the insulating layer 112 above the metal member 114 (eg, using photolithography techniques). Figure 4C2 Based on various examples Fig.4C1 Top view of the structure. Figure 4C3 Based on various examples Figure 4C2 perspective view of the structure.

[0023] The method 300 includes sputtering a barrier layer on the metal component and sputtering a seed layer on the barrier layer (306). Fig.4D1 Shows Fig.4C1 The structure of FIG. 1 is different in that a barrier layer 121 is applied to the insulating layer 112 and the metal member 114, and a seed layer 116 is applied to the barrier layer 121. The barrier layer 121 includes titanium or a titanium-tungsten alloy, and the seed layer 116 is a copper seed layer. Figure 4D2 Based on various examples Fig.4D1 Top view of the structure. Figure 4D3 Based on various examples Fig.4D1 perspective view of the structure.

[0024] The method 300 includes patterning a photoresist having a cavity over a metal feature using photolithography ( 308 ). Fig.4E1 yes Fig.4D1 1 is a cross-sectional view of a structure of , except that a photoresist layer 117 is applied to the seed layer 116, and a cavity 119 is formed over the metal member 114 using photolithography techniques, as shown. Figure 4E2 Based on various examples Fig.4E1 Top view of the structure. Figure 4E3 Based on various examples Fig.4E1 perspective view of the structure.

[0025] The method 300 includes forming a nanotwinned copper component in a cavity using pulsed electrodeposition, wherein the nanotwinned copper component includes a twin boundary separating a first region having a first grain structure from a second region having a second grain structure ( 310 ). Figure 4F1 yes Fig.4E1, except that copper member 118 (i.e., nanotwinned copper member) is formed by pulse electrodeposition in cavity 119. Copper member 118 has physical features attributed herein to nanotwinned copper structures, such as reference Figure 2 Those physical characteristics described. Figure 4F2 Based on various examples Figure 4F1 Top view of the structure. Figure 4F3 Based on various examples Figure 4F2 . In some instances, techniques other than electrodeposition may be useful, such as a nanotwinned copper electroplating bath. In addition, the aforementioned titanium barrier layer 121 orients the sputtered copper seed layer 116 to a (111) plane orientation, and during electroplating, this (111) plane orientation serves as a precursor material for forming nanotwinned copper, and pulsed electrodeposition is no longer required.

[0026] Method 300 includes removing the photoresist and portions of the barrier and seed layers and optionally applying a polyimide layer (312). Method 300 also includes attaching the die attach material to the substrate. Figure 4F1 After the structure is coupled to the die pad, wire bonds (314) are formed on the top surface of the nanotwinned copper member. Figure 4G1 yes Figure 4F1 , except that the photoresist layer 117 is stripped, the portion of the seed layer 116 that is not directly below the copper member 118 is etched away, and an insulating layer 124 (e.g., a polyimide layer) is coated to contact the insulating layer 112 and the copper member 118, as shown. Figure 4G1 Also depicted is a wire bond 120 bonded to a top surface of the copper member 118 (ie, a nanotwinned copper member), with a bond wire 122 bonded to one of the conductive terminals 108, such as by stitch bonding. Figure 4G2 Based on various examples Figure 4G1 Top view of the structure. Figure 4G3 Based on various examples Figure 4G1 perspective view of the structure.

[0027] Forming the wire bonds 120 includes using a wire bonding temperature in a range between 90° C. and 120° C., wherein temperatures below this range are disadvantageous because a bond cannot be formed because low temperature bonding is still driven by diffusion, which is accelerated by temperature, and wherein temperatures above this range are disadvantageous because pad oxidation may occur during the wire bonding process and prevent good bond formation. During a first wire bonding time period, a first force is applied to a top surface of the copper member 118 using a wire bonder for a first length of time, wherein the first force ranges between 15 grams and 25 grams, and the first length of time ranges between 1 millisecond and 5 milliseconds. During a second wire bonding time period after the first wire bonding time period, a second force is applied to a top surface of the copper member 118 using a wire bonder while scrubbing the top surface of the copper member 118, wherein the second force ranges between 15 grams and 25 grams. During a third wire bonding time period after the second wire bonding time period, a third force is applied to the top surface of the copper member 118 using the wire bonder for a second time length, wherein the third force ranges between 45 grams and 55 grams, and wherein the second time length ranges between 15 milliseconds and 25 milliseconds. The ultrasonic energy applied during the third wire bonding time period is greater than the ultrasonic energy applied during the second wire bonding time period. The ultrasonic energy applied during the second wire bonding time period is greater than the ultrasonic energy applied during the first wire bonding time period.

[0028] The method 300 includes covering the semiconductor die and the nanotwinned copper features with a molding compound ( 316 ). Figure 4H1 yes Figure 4G1 The structure of FIG. 1 is a cross-sectional view, except that the molding compound 126 is applied to cover Figure 4G1 The conductive terminals 108 are exposed outside the molding compound 126 . Figure 4H2 Based on various examples Figure 4H1 Top view of the structure. Figure 4H3 Based on various examples Figure 4H1 perspective view of the structure.

[0029] Figure 5A is a cutaway cross-sectional view of a wire bond 120 directly coupled to a polycrystalline copper structure 500. As explained, polycrystalline copper is inferior to nanotwinned copper in terms of diffusivity, and therefore bondability to copper structures such as wire bonds. As a result, the bond area 502 of the bond formed by the wire bond 120 to the polycrystalline copper structure 500 is only 56%. This means that of the surface area of ​​the wire bond 120 that could be bonded to the polycrystalline copper structure 500, only 56% of the surface area is successfully bonded to the polycrystalline copper structure 500. In contrast, Figure 5Bis a cutaway cross-sectional view of a wire bond 120 directly coupled to a copper member 118 (ie, a nanotwinned copper structure) according to various examples. The bond area 504 of the wire bond 120 to the copper member 118 is 83% because the copper member 118 is a nanotwinned copper structure.

[0030] Figure 6 6 is a block diagram of an electronic device 600 including a package having wire bonds directly coupled to a nanotwinned copper structure according to various examples. The electronic device 600 includes a printed circuit board (PCB) 602. The package 104 can be coupled to the PCB 602. The electronic device 600 can include, for example, a personal computer, a laptop computer, a desktop computer, a notebook computer, a tablet computer, a smart phone, an appliance (e.g., a refrigerator, a television, an audio player, a video player, a video recorder, a lighting device, etc.), an automobile, an airplane, a spacecraft, etc.

[0031] In this specification, the term "coupled" may encompass connections, communications, or signal paths that achieve a functional relationship consistent with this specification. For example, if device A generates a signal to control device B to perform an action, then: (a) in a first instance, device A is coupled to device B through a direct connection; or (b) in a second instance, device A is coupled to device B through an intermediate component C, provided that the intermediate component C does not change the functional relationship between device A and device B, so that device B is controlled by device A via the control signal generated by device A.

[0032] A device "configured to" perform a task or function may be configured (e.g., programmed and / or hardwired) to perform the function when manufactured by a manufacturer, and / or may be configured (or reconfigurable) by a user after manufacture to perform the function and / or other additional or alternative functions. Configuration may be achieved through firmware and / or software programming of the device, through the construction and / or layout of the device's hardware components and interconnects, or a combination thereof.

[0033] In this specification, unless otherwise stated, "about," "approximately," or "substantially" preceding a parameter means within a + / - 10% range of the parameter. Modifications may be made in the described examples, and other examples are possible within the scope of the claims.

Claims

1. A package comprising: a semiconductor die including a device side having circuitry formed therein; a metal member coupled to the device side; a nanotwinned copper member having a bottom surface coupled to the metal member, the nanotwinned copper member including a twin boundary separating a first region having a first grain structure from a second region having a second grain structure; a wire bond coupled directly to a top surface of the nanotwinned copper member, the wire bond contacting a plurality of regions of the nanotwinned copper member; as well as A molding compound covers the die, the metal component, the nano-twinned copper component, and the wire bonds. 2 . The package of claim 1 , wherein the package does not include a nickel layer in the same metal stack as the nanotwinned copper member. 3 . The package of claim 1 , wherein the package does not include a palladium layer in the same metal stack as the nanotwinned copper member. The package of claim 1 , wherein the nanotwinned copper member does not comprise polycrystalline copper. 5 . The package of claim 1 , wherein at least 80% of a bottom surface of the wire bond is bonded to the nanotwinned copper member, the bottom surface of the wire bond facing the nanotwinned copper member. 6 . The package of claim 1 , wherein the twin boundary is oriented substantially parallel to a horizontal plane in which the semiconductor die lies. 7 . The package of claim 1 , wherein the nanotwinned copper member has a minimum thickness of 5 microns and a maximum thickness of 13 microns.

8. A package comprising: a semiconductor die including a device side having circuitry formed therein; a metal member coupled to the device side, the metal member being vertically aligned with the circuitry; a nanotwinned copper member coupled to the metal member, the nanotwinned copper member having a minimum thickness of 5 microns and a maximum thickness of 13 microns, the nanotwinned copper member including twin boundaries oriented substantially parallel to a horizontal plane in which the semiconductor die lies; a wire bond directly coupled to a surface of the nanotwinned copper member; as well as A molding compound covers the die, the metal component, the nano-twinned copper component, and the wire bonds. 9 . The package of claim 8 , wherein the twin boundary separates a first region having a first grain structure from a second region having a second grain structure.

10. The package of claim 9, wherein the wire bonds contact a plurality of regions of the nanotwinned copper member, each of the plurality of regions having a different grain structure.

11. The package of claim 8, wherein the package does not include a nickel layer in the same metal stack as the nanotwinned copper member.

12. The package of claim 8, wherein the package does not include a palladium layer in the same metal stack as the nanotwinned copper member.

13. The package of claim 8, wherein the nanotwinned copper member does not comprise polycrystalline copper.

14. The package of claim 8, wherein at least 80% of a bottom surface of the wire bond is bonded to the nanotwinned copper member, the bottom surface of the wire bond facing the nanotwinned copper member.

15. A method for manufacturing a package, comprising: sputtering a seed layer over a metal feature coupled to the semiconductor die; patterning a photoresist having a cavity over the metal member using photolithography; forming a nanotwinned copper member in the cavity, the nanotwinned copper member comprising a twin boundary separating a first region having a first grain structure from a second region having a second grain structure; forming wire bonds on a top surface of the nanotwinned copper member using a wire bonder; as well as The semiconductor die and the nano-twinned copper member are covered with a molding compound.

16. The method of claim 15, wherein the package does not include a nickel layer in the same metal stack as the nanotwinned copper component.

17. The method of claim 15, wherein the package does not include a palladium layer in the same metal stack as the nanotwinned copper component.

18. The method of claim 15, wherein the nanotwinned copper component does not comprise polycrystalline copper.

19. The method of claim 15, wherein at least 80% of a bottom surface of the wire bond is bonded to the nanotwinned copper member, the bottom surface of the wire bond facing the nanotwinned copper member.

20. The method of claim 15, wherein the twin boundary is oriented substantially parallel to a horizontal plane in which the semiconductor die lies.

21. The method of claim 15, wherein the nanotwinned copper member has a minimum thickness of 5 microns and a maximum thickness of 13 microns.

22. The method of claim 15, wherein forming the wire bonds comprises using a wire bonding temperature ranging between 90°C and 120°C.

23. The method of claim 15, wherein forming the wire bonds comprises: applying a first force to the top surface of the nanotwinned copper member using a wire bonder for a first length of time during a first wire bonding period, the first force ranging between 15 grams and 25 grams, and the first length of time ranging between 1 millisecond and 5 milliseconds; applying a second force to the top surface of the nanotwinned copper member using the wire bonder while scrubbing the top surface of the nanotwinned copper member during a second wire bonding period after the first wire bonding period, the second force ranging between 15 grams and 25 grams; as well as During a third wire bonding time period after the second wire bonding time period, a third force is applied to the top surface of the nanotwinned copper component for a second time length using the wire bonder, the third force ranges between 45 grams and 55 grams, and the second time length ranges between 15 milliseconds and 25 milliseconds, wherein ultrasonic energy applied during the third wire bonding time period is greater than the ultrasonic energy applied during the second wire bonding time period, and the ultrasonic energy applied during the second wire bonding time period is greater than the ultrasonic energy applied during the first wire bonding time period.

24. The method of claim 15, wherein forming the nanotwinned copper member in the cavity comprises using pulsed electrodeposition.

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