# Patent

## Title
Semiconductor device with copper wirebond sites and methods of making same

## Abstract

Semiconductor devices with external wirebond sites that include copper and methods for fabricating such semiconductor devices are disclosed. One embodiment of a method for fabricating a semiconductor device comprises forming a dielectric layer on an active side of a semiconductor substrate. The dielectric layer has openings aligned with corresponding wirebond sites at the active side of the substrate. The method further includes forming a plurality of wirebond sites located at the openings in the dielectric layer. The wirebond sites are electrically coupled to an integrated circuit in the semiconductor substrate and electrically isolated from each other. Individual wirebond sites are formed by electrolessly depositing nickel into the openings and forming a wirebond film on the nickel without forming a seam between the nickel and the dielectric layer.

## Background
TECHNICAL FIELD
The present invention relates to semiconductor devices and methods for making semiconductor devices with external wirebond sites that include copper.
BACKGROUND
Semiconductor devices are typically manufactured on semiconductor wafers or other types of workpieces using sophisticated equipment and processes that enable reliable, high-quality manufacturing. The individual dies (e.g., devices) generally include integrated circuits and a plurality of bond-pads coupled to the integrated circuits. The bond-pads provide external contacts through which supply voltage, electrical signals, and other input/output parameters are transmitted to/from the integrated circuits. Bond-pads are usually very small, and they are typically at an active side of a die in a dense array having a fine pitch. As a result, the bond-pads are typically electrically connected to a larger array of ball-pads or pins using wirebonds and/or redistribution structures.
Conventional bond-pads are typically formed by depositing an aluminum layer onto a semiconductor substrate using physical vapor deposition (PVD) techniques. The aluminum layer is then patterned and etched to form electrically isolated bond-pads. This process is relatively expensive because patterning and etching require expensive microlithography equipment and materials. Aluminum is also being replaced by copper to increase the speed of devices and enable smaller lines because of the higher conductivity of copper. Copper lines are often made by depositing a seed layer of copper into trenches using physical vapor deposition processes, electroplating copper into the trenches, and planarizing the copper to form copper damascene lines and copper bond pads coupled to the copper damascene lines. Copper, however, does not provide a suitable surface for wirebonding, so the copper bond pads must be coated with gold, silver, palladium, aluminum, or another suitable wirebonding film to which wirebonds can be attached.
One existing method for forming copper bond-pads is to form copper terminals at the active side of the substrate and then cover the copper terminals with suitable wirebonding materials. For example, after forming copper terminals at the active side of the substrate, a passivation layer with openings aligned with corresponding copper terminals is formed over the active side of the substrate. Nickel is then electrolessly plated onto the copper terminals, and a suitable wirebonding material, such as gold, silver, palladium, or aluminum, is subsequently deposited onto the nickel. Although this process is useful, copper bond-pads formed according to this process are subject to reliability concerns, such as the passivation layer delaminating from the copper when exposed to moisture for extended periods of time. This can cause shorting or other problems with a die, and bridging is more acute as the spacing between metal lines decreases.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view of a semiconductor wafer having a plurality of dies with wirebond sites in accordance with an embodiment of the invention.
FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1 that schematically illustrates semiconductor devices.
FIGS. 3A-F are schematic cross-sectional views illustrating a number of stages of a method for fabricating semiconductor devices in accordance with an embodiment of the invention.
FIGS. 4A-C are schematic cross-sectional views of another method for fabricating semiconductor devices.
FIGS. 5A and 5B are schematic cross-sectional views of an additional method for fabricating semiconductor devices.
FIG. 6 is a schematic view of a system incorporating one or more semiconductor devices.
FIGS. 7 and 8 are flow charts of embodiments of methods of fabricating semiconductor devices.



DETAILED DESCRIPTION
Specific details of several embodiments are described below with reference to semiconductor devices with external wirebond sites that include copper and methods for fabricating such semiconductor devices. The semiconductor components are manufactured on semiconductor wafers that can include substrates upon which and/or in which microelectronic devices, micromechanical devices, data storage elements, optics, read/write components, and other features are fabricated. For example, SRAM, DRAM (e.g., DDR/SDRAM), flash memory (e.g., NAND flash-memory), processors, imagers, and other types of devices can be constructed on semiconductor wafers. Although many of the embodiments are described below with respect to semiconductor devices that have integrated circuits, other types of devices manufactured on other types of substrates may be within the scope of the invention. Moreover, several other embodiments of the invention can have different configurations, components, or procedures than those described in this section. A person of ordinary skill in the art, therefore, will accordingly understand that the invention may have other embodiments with additional elements, or the invention may have other embodiments without several of the features shown and described below with reference to FIGS. 1-8.
FIG. 1 is a top plan view of a semiconductor wafer 100 having a plurality of dies 110, and FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1 that schematically illustrates two of the dies 110. The dies 110 include a plurality of wirebond sites 120 that are suitable for wirebonding. The wirebond sites 120 are arranged in arrays at each die and formed, at least in part, of copper. However, unlike the conventional wirebond site with copper, the structure of the wirebond sites 120 eliminates or at least mitigates associated reliability and delamination problems.
Referring to FIG. 2, the wafer 100 includes a semiconductor substrate 102 having a first side 104 and a second side 106. The first side 104 of the semiconductor substrate 102 can be an active side. The semiconductor substrate 102 can be composed of silicon, gallium arsenide, or other suitable semiconductor materials. Individual dies 110 can include one or more integrated circuits 108 formed on and/or in the semiconductor substrate 102 using known methods. The integrated circuits 108 are electrically coupled to individual arrays of wirebond sites 120. The arrays of wirebond sites 120 can be configured as illustrated in FIG. 1, or the arrays can have other configurations at the first side 104 and/or the second side 106 of the semiconductor substrate 102.
The wafer 100 can further include a dielectric layer 130 over the first side 104 of the semiconductor substrate 102. In this embodiment, the dielectric layer 130 has a plurality of openings 132, and individual openings 132 are at least partially aligned with corresponding wirebond sites 120. The dielectric layer 130 can be a polyimide or other suitable material for protecting the first side 104 of the substrate 102 and electrically isolating the wirebond sites 120 from each other. The dielectric layer 130, for example, can be a photoimageable polymer, such as a photoimageable polyimide, that can be patterned to form the openings 132 using microlithography techniques.
The wirebond sites 120 define external electrical connectors to which wirebonds or other suitable conductive elements may be attached. Individual wirebond sites 120 include a copper terminal 140 at the first side 104 of the substrate 102. The copper terminals 140 can be bases of the wirebond sites 120, and the copper terminals 140 are electrically connected to one of the integrated circuits 108 via interconnects or other conductive lines within the substrate 102. The copper terminals 140 can be formed by electrolessly plating copper or electroplating copper onto the substrate 102 before depositing the dielectric layer 130 onto the substrate 102. The wirebond sites 120 further include wirebond interfaces 141 on corresponding copper terminals 140. Individual wirebond interfaces 141 include an adhesion element 142 and a conductive wirebond element 144. The adhesion elements 142 can be conductive and include one or more layers on the copper terminals 140 and along the openings 132 of the dielectric layer 130. For example, the embodiment of the adhesion element 142 illustrated in FIG. 2 includes a liner 145 and a copper deposit 146 on the liner 145. The liner 145 can be a conductive layer formed from tantalum, tantalum nitride, titanium, titanium nitride, or another suitable material that is conductive and adheres well to the sidewalls of the openings 132. The wirebond elements 144 can include a nickel layer 147 and a wirebond film 148. The nickel layer 147 can be electrolessly deposited onto the copper deposit 146, and the wirebond film 148 can be gold, palladium, silver, aluminum, or another material suitable for attaching wirebonds to the dies 110.
Several embodiments of the semiconductor devices or dies 110 illustrated in FIG. 2 include copper wirebond sites that do not require an aluminum layer to be patterned and etched. The specific embodiments of the wirebond sites 120 illustrated in FIG. 2 are robust and do not suffer from the delamination problems to the same extent as the existing copper bond-pads described above in the Background section. More specifically, the present inventors discovered that the delamination, which can lead to dielectric breakdown and subsequent copper migration and bridging, was caused by the formation of a seam between the nickel layer and the sidewalls of the openings in the passivation layer. Without being bound by theory, the present inventors believe that seams form in such conventional devices because the tensile stress in the palladium or gold film deposited onto the nickel pulls the nickel away from the passivation layer. As a result, moisture can get into the seam and corrode the copper and/or delaminate the passivation layer during high temperature testing. It is this corrosion that can cause dielectric cracking and subsequent copper migration, which can cause bridging and line failures in the prior art devices, and particularly so with fine pitch bond-pad arrays. The adhesion elements 142 of the wirebond sites 120 overcome this problem. For example, the adhesion elements are formed such that the adhesion force between the adhesion elements 142 and the dielectric layer 130 is greater than the tensile stresses in the wirebond elements 144. As such, the tensile stresses in the wirebond elements 144 do not separate the adhesion elements 142 from the dielectric layer 130. The wirebond sites 120 can accordingly prevent, or at least inhibit, seams or gaps from forming between the metal and the dielectric layer.
FIGS. 3A-F illustrate sequential stages of an embodiment of a method for forming wirebond sites, such as the embodiments of the wirebond sites 120 illustrated in FIG. 2. Although FIGS. 3A-F illustrate a single wirebond site, in practice a plurality of wirebond sites are constructed across the wafer simultaneously. FIG. 3A, more specifically, is a schematic cross-sectional view at an initial stage in which the copper terminals 140 have been formed at the first side 104 of the substrate 102. The copper terminals 140 can be formed by electrolessly depositing copper onto the substrate 102. FIG. 3B illustrates a subsequent stage in which the dielectric layer 130 has been deposited onto the first side 104 of the substrate 102 and the openings 132 have been formed in the dielectric layer 130. The dielectric layer 130 can be deposited using CVD, spin-on, or other suitable techniques for covering the first surface 104 with the dielectric layer 130. The openings 132 can be formed by patterning and etching the dielectric layer 130. The dielectric layer 130, for example, can be made from a photoimageable material, and the openings 132 can be formed by exposing areas of the dielectric layer to radiation such that the areas of the dielectric layer 130 aligned with the copper terminals 140 have a higher solubility in a developing fluid than the other areas of the dielectric layer 130. The portions of the dielectric layer 130 aligned with the copper terminals 140 are then removed using the developing solution to form the openings 132. The openings 132 accordingly expose at least a portion of the copper terminals 140.
FIGS. 3C and 3D illustrate subsequent stages of forming an embodiment of the adhesion element 142 (FIG. 3D). Referring to FIG. 3C, one embodiment of the adhesion element 142 is formed by (a) depositing a liner 145 onto the dielectric layer 130 and the exposed portions of the copper terminals 140 and (b) depositing a copper deposit 146 onto the liner 145. The liner 145 can be a conductive material that bonds or otherwise adheres to the material of the dielectric layer 130 with an adhesion force greater than the adhesion force between nickel and the dielectric layer 130 without the liner 145. The liner 145, for example, can be tantalum deposited using a physical vapor deposition (PVD) process or other suitable types of vapor deposition processes. The copper deposit 146 can be deposited using PVD processes or other suitable deposition processes. The liner 145 and copper deposit 146 have an overburden portion 149 on top of the dielectric layer 130 in areas outside of the openings 132. FIG. 3D illustrates a subsequent stage after the overburdened portion 149 has been removed to expose the top of the dielectric layer 130. The overburden portion 149 (shown in FIG. 3C) can be removed using chemical-mechanical planarization processes, grinding, or other suitable processes such that discrete portions of the liner 145 and copper deposit 146 remain in the openings 132 and on corresponding copper terminals 140. In this embodiment, individual adhesion elements 142 are defined by the discrete portions of the liner 145 and copper deposit 146 in corresponding openings 132.
FIGS. 3E and 3F illustrate stages of the method for forming an embodiment of the wirebond elements 144 (FIG. 3F) on the adhesion elements 142. Referring to FIG. 3E, the first stage of forming the wirebond elements includes depositing a nickel layer 147 or other suitable layer onto the copper deposit 146. The nickel layer 147, for example, can be electrolessly plated onto the copper deposit 146 using known techniques. The wirebond element 144 can be completed as shown in FIG. 3F by depositing a wirebond film 148 onto the nickel layer 147. The wirebond film 148 can be deposited using electroless plating processes, flash processes, other suitable immersion processes, or vapor deposition processes. The wirebond film 148, for example, can be gold and/or palladium deposited onto the nickel layer 147 using electroless plating processes. The wirebond site 120 is accordingly completed with the formation of the wirebond film 148. A wirebond 150 (shown in broken lines) can then be attached to the wirebond film 148 using wirebonding tools and techniques.
FIGS. 4A-4C illustrate stages of a method for forming a wirebond site 220 (FIG. 4C) in accordance with another embodiment. Referring to FIG. 4A, the die 110 is at a stage similar to the stage illustrated in FIG. 3D, but an aperture 210 is formed in the adhesion element 142. The aperture 210 can be formed by patterning and etching the aperture 210 through the copper deposit 146 and the liner 145. The liner 145 in this embodiment can be a conductive material or a dielectric material because the electrical connection to the copper terminal 140 can be made through the aperture 210. FIG. 4B illustrates forming the wirebond element 144 by depositing the nickel layer 147 into the aperture 210 and onto the copper deposit 146. The nickel layer 147 accordingly directly contacts the copper terminal 140. FIG. 4C illustrates a subsequent stage of forming the wirebond element 144 that includes depositing the wirebond film 148 onto the nickel layer 147 in a manner similar to the stage illustrated in FIG. 3F. The wirebond site 220 may provide many of the same advantages as the wirebond site 120 described above. In other embodiments, the wirebond film 148 can be deposited directly onto the copper deposit 146. The wirebond site 220 may provide a higher conductivity because the nickel layer 147 directly contacts the copper terminal 140. The conductivity of the liner 145, therefore, may not influence the electrical properties of the wirebond site 220 shown in FIG. 4B.
FIGS. 5A and 5B illustrate stages of a method for forming a wirebond site 320 (FIG. 5B) in accordance with another embodiment. The stage illustrated in FIG. 5A is similar to the stage illustrated in FIG. 3D, but the adhesion element 142 in FIGS. 5A and 5B has a single layer. In one embodiment, the adhesion layer 142 has the liner 145, but not the separate copper deposit 146. The liner 145 can be a copper deposit or another material that provides a surface for depositing nickel or other suitable materials for the wirebond element. The liner 145 can be deposited on the dielectric layer 130 and the exposed portions of the copper terminals 140 using vapor deposition processes or other suitable process. The overburdened portion (not shown) of the liner 145 can then be removed using a planarizing process to electrically isolate the liners 145 on corresponding copper terminals 140. The nickel layer 147 can then be electrolessly deposited onto corresponding liners 145 as shown in FIG. 5A. FIG. 5B illustrates a subsequent stage in which the wirebond element 144 is formed by depositing the wirebond film 148 onto the nickel layer 147 as described above. The embodiment of the wirebond site 320 illustrated in FIG. 5B can include different configurations. For example, the single-layer adhesion element 142 may be formed from a material other than copper.
Any one of the semiconductor components described above with reference to FIGS. 1-5B can be incorporated into any of a myriad of larger and/or more complex systems, a representative example of which is system 600 shown schematically in FIG. 6. The system 600 can include a processor 601, a memory 602 (e.g., SRAM, DRAM, flash, and/or other memory device), input/output devices 603, and/or other subsystems or components 604. The foregoing semiconductor devices described above with reference to FIGS. 1-5B may be included in any of the components shown in FIG. 6. The resulting system 600 can perform any of a wide variety of computing, processing, storage, sensing, imaging, and/or other functions. Accordingly, representative systems 600 include, without limitation, computers and/or other data processors, for example, desktop computers, laptop computers, Internet appliances, hand-held devices (e.g., palm-top computers, wearable computers, cellular or mobile phones, personal digital assistants, etc.), multiprocessor systems, processor-based or programmable consumer electronics, network computers, and minicomputers. Other representative systems 600 include cameras, light or other radiation sensors, servers and associated server subsystems, display devices, and/or memory devices. In such systems, individual dies can include imager arrays, such as CMOS imagers. Components of the system 600 may be housed in a single unit or distributed over multiple, interconnected units (e.g., through a communications network). The components of the system 600 can accordingly include local and/or remote memory storage devices, and any of a wide variety of computer readable media.
FIG. 7 is a flow chart of a method 700 for fabricating semiconductor devices in accordance with an embodiment. The method 700 can include forming a dielectric layer on an active side of a semiconductor substrate (block 710). The dielectric layer may have openings aligned with corresponding wirebond sites at the active side of the substrate. The method 700 further includes forming a plurality of wirebond sites located at the openings in the dielectric layer (block 720). The wirebond sites are electrically coupled to an integrated circuit in the semiconductor substrate and electrically isolated from each other. The wirebond sites, for example, can be formed by electrolessly depositing nickel into the openings and forming a wirebond film on the nickel without forming a seam between the nickel and the dielectric layer.
FIG. 8 is a flow chart illustrating a method 800 in accordance with another embodiment. The method 800 can include forming a dielectric layer on an active side of a semiconductor substrate (block 810). The dielectric layer, for example, can have openings aligned with corresponding copper terminals at the active side of the substrate, and the copper terminals can be electrically coupled to an integrated circuit in the substrate. The method 800 further includes depositing a liner on the dielectric layer and the copper terminals (block 820), and depositing a copper layer on the liner (block 830). The method 800 continues by removing portions of the liner and the copper layer until the dielectric layer is exposed in areas between the openings (block 840). The process of removing portions of the liner and the copper layer produces adhesion elements having discrete portions of the liner and copper deposits remaining in individual openings of the dielectric layer. The method 800 also includes forming individual wirebond films over corresponding copper deposits (block 850) and attaching wirebonds to corresponding wirebond films (block 860).
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but well-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the invention. Where the context permits, singular or plural terms may also include the plural or singular term, respectively. Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the term “comprising” is used throughout to mean including at least the recited feature(s) such that any greater number of the same feature and/or additional types of other features are not precluded. It will also be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the inventions. For example, many of the elements of one of embodiment can be combined with other embodiments in addition to, or in lieu of, the elements of the other embodiments. Additionally, other embodiments can deposit a wirebond film or other wirebondable metal directly on an adhesion layer, or a layer of the wirebond elements can be cobalt, a cobalt alloy, or other suitable alloys. Accordingly, the invention is not limited except as by the appended claims.

## Claims

1. A semiconductor device, comprising:
a semiconductor substrate having a first side and a second side;
an integrated circuit in the semiconductor substrate;
a plurality of copper terminals at the first side of the substrate, wherein the copper terminals are electrically connected to the integrated circuit;
a dielectric layer on the first side of the substrate, wherein the dielectric layer has a plurality of openings at least partially aligned with corresponding terminals, and wherein individual openings have sidewalls;
a plurality of wirebond interfaces on corresponding copper terminals, wherein individual wirebond interfaces have an adhesion element attached to a corresponding copper terminal and a wirebond element on the adhesion element, the adhesion element having a depression at least partially extending into the opening, the wirebond element comprises nickel that at least substantially fills the depression in the adhesion element and a wirebond film on the nickel, at least a portion of the wirebond film being in the depression, and the nickel having a volume in the depression greater than a volume of the wirebond film in the depression; and wherein the adhesion elements comprise liners along the sidewalls of the openings in the dielectric layer and copper deposits on the liners.

2. The semiconductor device of claim 1 wherein the liners comprise at least one of tantalum, tantalum nitride, titanium, and titanium nitride.

3. The semiconductor device of claim 1 wherein the wirebond elements comprise nickel electrolessly plated onto the copper deposit and a wirebond film on the nickel.

4. The semiconductor device of claim 1 wherein the wirebond film comprises at least one of gold, silver, palladium, and aluminum.

5. The semiconductor device of claim 1 wherein the wherein the comprise a vapor deposited copper attached to the sidewalls of the openings and the wirebond film comprise at least one of gold, palladium, silver, or aluminum on the nickel.

6. The semiconductor device of claim 1 wherein the liners have apertures at the copper terminals and the wirebond elements have a portion in the apertures in contact with corresponding copper terminals.

7. A semiconductor device, comprising:
a semiconductor substrate having an active side, an integrated circuit, and a dielectric layer on the active side, wherein the dielectric layer has a plurality of openings with sidewalls; and
a plurality of electrical connectors located at the openings in the dielectric layer and electrically connected to the integrated circuit, wherein individual connectors have a copper base at the active side of the substrate below the dielectric layer, a conductive liner attached to the copper base, a copper deposit on the liner and aligned with the copper base, and a wirebond element aligned with and electrically coupled to the copper deposit, wherein the conductive liner and the copper deposit are conformal layers that have a depression extending at least partially into the opening, wherein the wirebond element includes a nickel layer at least substantially filling the depression and a wirebond film on the nickel layer, and the nickel layer in the depression, and wherein at least a portion of the wirebond film is in the depression having a volume greater than a volume of the wirebond film in the depression.

8. The semiconductor device of claim 7 wherein the electrical connectors comprise wirebond interfaces, and wherein the semiconductor device further comprises wirebonds connected to corresponding wirebond interfaces.

9. The semiconductor device of claim 8, wherein the nickel layer is electrolessly plated on the copper deposit and under the wirebond film.

10. The semiconductor device of claim 8, wherein the conductive liner is configured to have a greater adhesion force with the dielectric layer than an adhesion force between nickel and the dielectric layer.

11. The semiconductor device of claim 8, wherein the conductive liner is adhered to the sidewalls of the openings such that the wirebond film does not separate underlying layers from the sidewalls of the dielectric layer.

12. The semiconductor device of claim 11, wherein the conductive liner comprises tantalum.

13. A semiconductor device, comprising:
a semiconductor substrate having an active side, an integrated circuit, a plurality of copper terminals at the active side of the substrate, wherein individual copper terminals are electrically connected to the integrated circuit, and a dielectric layer on the active side, wherein the dielectric layer has a plurality of openings with sidewalls; and
a plurality of wirebond sites located at the openings in the dielectric layer and electrically connected to the copper terminals, wherein individual wirebond sites have a copper deposit electrically coupled to the individual copper terminals, a nickel element, and a wirebond film on the nickel element, and wherein the copper deposit has a depression that extends at least partially into the opening and the nickel element at least substantially fills the depression and has a volume in the depression greater than a volume of the wirebond film in the depression such that the nickel is sufficiently adhered to the sidewall of a corresponding opening of the dielectric layer so that the wirebond film does not separate the nickel element from the sidewall of the dielectric layer; and wherein the copper deposits have apertures at copper terminals and the wirebond elements have a portion in the apertures in contact with corresponding copper terminals.

14. The semiconductor device of claim 13, wherein the wirebond sites further comprise a liner that adheres to the sidewall of a corresponding opening of the dielectric layer such that the wirebond film does not separate the nickel element from the sidewall of the dielectric layer.

15. The semiconductor device of claim 14, wherein the liner comprises tantalum.

16. A system, comprising:
at least one of a processor and memory device, and wherein at least one of the processor and memory device includes a semiconductor device comprising
a semiconductor substrate having a first side and a second side;
an integrated circuit in the semiconductor substrate;
a plurality of copper terminals at the first side of the substrate, wherein the copper terminals are electrically connected to the integrated circuit;
a dielectric layer on the first side of the substrate, wherein the dielectric layer has a plurality of openings aligned with corresponding terminals, and wherein individual openings have sidewalls;
a plurality of wirebond interfaces on corresponding copper terminals, wherein individual wirebond interfaces have an adhesion element attached to a corresponding copper terminal, the adhesion element having a depression extending at least partially into the opening, and a wirebond element comprising nickel that at least substantially fills the depression in the adhesion element and a wirebond film on the nickel, wherein there is more nickel than wirebond film in the depression; and wherein the adhesion elements have apertures at the copper terminals and the wirebond elements have a portion in the apertures in contact with corresponding terminals.