Copper interconnection structure and manufacturing method thereof

Abstract

The invention provides the copper interconnection structure for the integrated circuit chip, which is easy to form a welding spot with good electric connection performance with a large-size metal wire. The copper interconnection structure comprises a copper surface, a metal barrier layer and a weldable metal layer. The copper interconnection structure comprises a weldable metal layer formed on the metal barrier layer, wherein the thickness of the weldable metal layer ranges from 0.03 micrometer to 0.05 micrometer.

Description

Technical Field

[0001] This application relates to semiconductor structures, and more particularly to copper interconnect structures and methods for manufacturing the same. Background Technology

[0002] In the trend of miniaturization of modern integrated circuit (IC) chips, aluminum interconnect structures, which have relatively high resistivity and are used to provide electrical connections or couplings in IC chips, are gradually being replaced by copper interconnect structures, which have higher conductivity. Copper bonding pads and copper redistribution structures are common interconnect structures in modern ICs. In order to reliably solder metal wires to the soldering areas of these copper interconnect structures, engineers have developed mature structures and processes.

[0003] However, in some applications, larger aluminum wires are required to increase the current-carrying capacity of the wires. The significant cost advantage of large-size aluminum wires compared to copper or gold wires of the same size has strongly driven research into how to weld large-size aluminum wires to the soldering zones of conventional copper interconnect structures.

[0004] Studies have found that aluminum has good mechanical adhesion, making it suitable for pressure welding. In contrast, copper has poor pressure welding performance, and most mature processes are optimizations of fusion welding. Although a few technologies can achieve pressure welding of metal wires on copper interconnect structures, the cost is high and does not meet the application requirements of actual IC production and mass production. Summary of the Invention

[0005] This application provides a copper interconnect structure. The copper interconnect structure includes a copper surface, a metal barrier layer, and a solderable metal layer. The metal barrier layer is disposed on the copper surface. The solderable metal layer is disposed on the metal barrier layer, and the thickness of the solderable metal layer is between 0.03 micrometers and 0.05 micrometers.

[0006] This application also provides a method for manufacturing a copper interconnect structure. The method includes preparing a clean, oxide-free copper surface and depositing a metal barrier layer on the copper surface using electroless deposition. The method further includes depositing a solderable metal layer on the metal barrier layer using electroless deposition. The thickness of the finally formed solderable metal layer is between 0.03 micrometers and 0.05 micrometers. Attached Figure Description

[0007] Figure 1 This is a cross-sectional view of a copper interconnect structure 100 according to an embodiment of the present disclosure, and also shows a metal wire A bonded to the copper interconnect structure 100.

[0008] Figure 2 This is a cross-sectional view of a copper interconnect structure 200 according to an embodiment of the present disclosure, and also shows a metal wire A bonded to the copper interconnect structure 200.

[0009] Figure 3 For comparison, another copper interconnect structure 300 that does not employ the scheme of this disclosure is shown, along with the metal wire A bonded to it.

[0010] Figure 4 The method for forming copper interconnect structure 100 / 200 disclosed herein is shown.

[0011] Figure 5 The method of this disclosure for bonding copper interconnect structures 100 / 200 and wire A is shown.

[0012] Figure 6 SEM images of the comparative sample are shown.

[0013] Figure 7 SEM images of a sample of the copper interconnect structure described in this disclosure are shown. Detailed Implementation

[0014] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known processes and structures have not been specifically described to avoid obscuring the focus of the invention.

[0015] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "in an embodiment," "in a particular embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. When describing a layer disposed on top of another layer or on a surface, this can mean it is directly disposed on that layer or surface, or it may include cases where other material layers are disposed between them. Moreover, those skilled in the art will understand that the accompanying drawings provided herein are for illustrative purposes and are not necessarily drawn to scale. The same reference numerals indicate the same elements. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0016] Appendix Figure 1A copper interconnect structure 100 according to one embodiment of the present disclosure is shown, along with a metal wire A bonded thereto. In one embodiment, the copper interconnect structure 100 includes copper pads 101 disposed on a semiconductor substrate 103, the copper pads 101 including copper surfaces 102 for forming solder areas, the copper surfaces 102 being exposed in openings in a protective material 106. (See attached diagram) Figure 2 The illustration schematically shows another copper interconnect structure 200 according to this application, which includes a redistribution structure. Typically, the redistribution structure may include multiple metal layers disposed in the dielectric layer 107 and interconnect structures connecting the multiple metal layers. (See attached diagram) Figure 2 The copper redistribution layer 108 shown is the outermost / topmost layer of the redistribution structure. The copper redistribution layer 108 includes a copper surface 109 for forming the solder area.

[0017] The copper surfaces 102 and 109 are highly susceptible to oxidation, forming a copper oxide film. Even a thin copper oxide film can affect soldering and consequently impact IC reliability. Therefore, a metal barrier layer 104 is needed to isolate the copper surfaces 102 and 109. It is called a "metal barrier layer" because it prevents copper atoms from diffusing to the surface of the metal barrier layer 104 and oxidizing there to form copper oxide, thus compromising soldering stability. To achieve this, the material and thickness of the metal barrier layer 104 must be considered. Materials for the metal barrier layer 104 include nickel, cobalt, chromium, molybdenum, tungsten, and their alloys. Typically, the thickness of the barrier layer ranges from 0.5 micrometers to 1.5 micrometers.

[0018] In the appendix Figure 1 and appendix Figure 2 In one embodiment, the metal barrier layer 104 is directly disposed on the copper surface 102 / copper surface 109. However, in other embodiments, a seed metal layer may be disposed between the copper surface 102 / copper surface 109 and the metal barrier layer 104. It should be clarified that when the metal barrier layer 104 is described as being disposed on the copper surface 102 / copper surface 109 in this application, it includes both the case where it is directly disposed on the copper surface 102 / copper surface 109 and the case where a seed metal layer is also disposed between the two.

[0019] The materials of these metal barrier layers 104 have poor solderability; therefore, a solderable metal layer 105 needs to be further disposed on top of them. The material of the solderable metal layer 105 can be gold, platinum, palladium, or silver. In the technical solution of this application, the thickness of the solderable metal layer 105 is set between 0.03 micrometers and 0.05 micrometers.

[0020] In some embodiments, such as Figure 1 and appendix Figure 2As shown, aluminum wires A with a diameter of 125 micrometers or more are bonded to the solderable metal layer 105 of the copper interconnect structure 100 / 200. In other embodiments, aluminum wires with diameters of 170 micrometers or more, 190 micrometers or more, 210 micrometers or more, 230 micrometers or more, 250 micrometers or more, 270 micrometers or more, and 300 micrometers or more are bonded to the solderable metal layer 105 of the copper interconnect structure 100 / 200, respectively. Good solder joints can be formed between the aluminum wires and the copper interconnect structure 100 / 200, and no delamination phenomenon occurs between the aluminum wires and the copper surface. The solder joints all exhibit good electrical connection performance. The above experimental results show that the copper interconnect structure provided in this application is suitable for bonding with metal wires larger than those of ordinary metal wires. Although large-size aluminum wires are bonded in the above embodiments, large-size copper wires, large-size gold wires, and other metal wires can also be bonded in other embodiments. Although the copper interconnect structure provided in this application has the characteristic of good bonding with large-size metal wires, this does not limit its application to bonding with conventional-size metal wires. In fact, in some embodiments, welding metal wires with a diameter of less than 125 micrometers onto the solderable metal layer 105 of the copper interconnect structure 100 can also yield solder joints with good electrical connection performance.

[0021] Appendix Figure 3 As a comparative example, another copper interconnect structure 300 that does not employ the scheme of this disclosure is shown. The copper interconnect structures 100 / 200 disclosed in this application have many of the same configurations as the copper interconnect structure 300 shown in the comparative example, attached... Figure 3 Use and Appendix Figure 1 The same reference numerals denote these same features. The difference lies in that the copper interconnect structure 300 includes a solderable metal layer 305 disposed on the barrier metal layer 104. The material of the solderable metal layer 305 can be gold, platinum, palladium, and silver, and in some comparative examples, the thickness of the solderable metal layer 305 is set between 0.4 micrometers and 1.5 micrometers. Attempts were made to pressure bond aluminum wires A with a diameter of 125 micrometers or more to the copper interconnect structure 300 of these comparative examples, and conductivity tests were performed on the solder joints. The results showed poor electrical connection performance between the copper interconnect structure 300 and the aluminum wire A, with a 100% failure rate in resistance testing.

[0022] Appendix Figure 4 A method for forming a copper interconnect structure according to an embodiment of the present disclosure is illustrated. The method includes a preparation step of providing a clean, oxide-free copper surface. In some processes, it may be necessary to protect the copper surface in non-soldering areas, for example, by applying a protective layer to the copper surface in the non-soldering areas. The protective layer has openings that expose the copper surface 102. The wafer comprising the copper interconnect structure is cleaned with a solution to obtain a clean, oxide-free copper surface.

[0023] The method also includes depositing a metal barrier layer on the copper surface by electroless deposition. The metal barrier layer is selected from nickel, cobalt, chromium, molybdenum, tungsten, and alloys thereof. In one embodiment, a 0.4-micrometer-thick layer of nickel can be electroless plated, and in another embodiment, a 0.6-micrometer-thick layer of a nickel-tungsten alloy can be electroless plated.

[0024] In some embodiments, a seed metal layer may be disposed between the copper surface and the metal barrier layer. It should be noted that the description of depositing a metal barrier layer on a copper surface in this application includes both the case of depositing the metal barrier layer directly on the copper surface and the case of first disposing of a seed metal layer and then depositing the metal barrier layer on the seed metal layer.

[0025] The method further includes depositing a solderable metal layer on the metal barrier layer by electroless deposition. The solderable metal layer is selected from gold, palladium, silver, and platinum. The thickness of the solderable metal layer is between 0.03 micrometers and 0.05 micrometers. In one embodiment, a 0.05-micrometer-thick layer of gold is deposited on the metal barrier layer; in another embodiment, a 0.03-micrometer-thick layer of a gold-palladium alloy is deposited on the metal barrier layer.

[0026] The above steps are the core steps for forming the copper interconnect structure described in this application. The copper interconnect structure formed according to the method has the characteristic of forming good bonds with large-size metal wires, but this does not limit its application in bonding with conventional-size metal wires.

[0027] In some embodiments, this copper interconnect structure is used for bonding with large-size metal wires. See attached... Figure 5 As shown, the method for forming such a bonding structure further includes bonding a metal wire with a diameter of 125 micrometers or more onto the weldable metal layer. For example, in one embodiment, an aluminum wire with a diameter of 170 micrometers or more can be bonded onto the weldable metal layer, and in another embodiment, an aluminum alloy wire with a diameter of 190 micrometers or more can be bonded onto the weldable metal layer.

[0028] This application provides a copper interconnect structure that facilitates good solder joint formation with large-size metal wires. The copper interconnect structure is obtained by forming a metal barrier layer on the copper surface and then depositing a solderable metal layer with a thickness between 0.03 and 0.05 micrometers on the metal barrier layer. The thickness of the solderable metal layer 105 in this application is less than 1 / 8 of the typical thickness of the solderable metal layer 305 in the comparative example, significantly reducing the amount of metal used in the solderable metal layer and resulting in a significant cost advantage. The wire-copper surface interface formed according to this application has a completely different microstructure from the wire-copper surface interface described in the comparative example. (Appendix) Figure 6These are scanning electron microscope (SEM) images of the copper interconnect structure 300 sample as described. The upper and lower images have different magnifications, and the arrows in the images point to the magnified interface morphology. This can be seen from... Figure 6 It can be seen that significant delamination occurs at the interface between the aluminum wire and the weldable metal layer. Such significant delamination is highly detrimental to the formation of low-resistance solder joints. Test results for the corresponding sample also show that the actual resistance value of the sample far exceeds the estimated resistance value from simulation experiments by several times, failing to meet mass production requirements.

[0029] Appendix Figure 7 The image shown is a scanning electron microscope (SEM) image of a sample of the copper interconnect structure 200. The SEM image of a sample of the copper interconnect structure 100 also has this morphology, so it is not shown. Figure 7 This includes two SEM screenshots at different magnifications, with arrows pointing to the magnified interface shape. (The text then abruptly shifts to a seemingly unrelated topic: "From...") Figure 7 It can be observed that there is no delamination at the interface between the aluminum wire and the weldable metal layer and the bond is tight, which helps to form a solder joint with low resistance and high bonding strength.

[0030] Although the invention has been described with reference to several exemplary embodiments, it should be understood that the terminology used is descriptive and exemplary, and not restrictive. Since the invention can be embodied in many forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims. Therefore, all variations and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A copper interconnect structure for use in an integrated circuit chip, comprising: Copper surface; A metal barrier layer is disposed on the copper surface; as well as A weldable metal layer is disposed on the metal barrier layer, the thickness of the weldable metal layer being between 0.03 micrometers and 0.05 micrometers.

2. The copper interconnect structure as described in claim 1, characterized in that... The metal barrier layer is selected from nickel, cobalt, chromium, molybdenum, tungsten, and alloys thereof.

3. The copper interconnect structure as described in claim 1, characterized in that... The weldable metal layer is selected from gold, palladium, silver and platinum.

4. The copper interconnect structure as described in claim 1, wherein a seed metal layer is disposed between the copper surface and the metal barrier layer.

5. A bonding structure including a copper interconnect structure for use in an integrated circuit chip, comprising: Copper surface; A metal barrier layer is disposed on the copper surface; A weldable metal layer is disposed on the metal barrier layer; as well as The metal wire bonded to the weldable metal layer has a diameter of 125 micrometers or more.

6. The bonding structure as described in claim 5, characterized in that... The metal barrier layer is selected from nickel, cobalt, chromium, molybdenum, tungsten, and alloys thereof.

7. The bonding structure as described in claim 5, characterized in that... The weldable metal layer is selected from gold, palladium, silver and platinum.

8. The bonding structure as described in claim 5, characterized in that... The metal wire material contains aluminum.

9. The bonding structure as described in claim 4, characterized in that... The metal wire material is aluminum or an aluminum alloy.

10. A method for forming a copper interconnect structure in an integrated circuit chip, comprising: Prepare a clean copper surface free of copper oxide; A metal barrier layer is deposited on the copper surface by electroless deposition. A weldable metal layer is deposited on the metal barrier layer by electroless deposition, the thickness of which is between 0.03 micrometers and 0.05 micrometers.

11. The method for forming a copper interconnect structure as described in claim 9, characterized in that... The metal barrier layer is selected from nickel, cobalt, chromium, molybdenum, tungsten, and alloys thereof.

12. The method for forming a copper interconnect structure as described in claim 9, characterized in that... The weldable metal layer is selected from gold, palladium, silver and platinum.

13. A method for bonding copper interconnect structures and metal wires in an integrated circuit chip, comprising: Prepare a clean copper surface free of copper oxide; A metal barrier layer is deposited on the copper surface by electroless deposition. A weldable metal layer is deposited on the metal barrier layer by electroless deposition, the thickness of which is between 0.03 micrometers and 0.05 micrometers. A metal wire with a diameter of 125 micrometers or more is press-welded onto the weldable metal layer.

14. The method for bonding copper interconnect structures and wires as described in claim 12, characterized in that... The metal barrier layer is selected from nickel, cobalt, chromium, molybdenum, tungsten, and alloys thereof.

15. The method for bonding copper interconnect structures and wires as described in claim 12, characterized in that... The weldable metal layer is selected from gold, palladium, silver and platinum.

16. The method for bonding copper interconnect structures and metal wires as described in claim 12, characterized in that... The metal wire material contains aluminum.

17. The method for bonding copper interconnect structures and metal wires as described in claim 12, characterized in that... The metal wire material is aluminum or an aluminum alloy.

18. A copper interconnect structure for use in an integrated circuit chip, comprising: Copper pads or copper redistribution layer; A metal barrier layer is disposed on the copper pad or copper redistribution layer; as well as A weldable metal layer is disposed on the metal barrier layer, the thickness of the weldable metal layer being between 0.03 micrometers and 0.05 micrometers.

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