A low-cost cobalt-gold IC package bump and its production process

Abstract

The present invention discloses a low-cost cobalt-gold IC package bump and a production process. The package bump includes a silicon wafer carrier, an aluminum pad conductive layer arranged on the silicon wafer carrier, a sputtering layer arranged on the aluminum pad conductive layer, an electroplated cobalt layer formed by electroplating cobalt metal arranged on the sputtering layer, an electroplated gold layer arranged above the electroplated cobalt layer, and an insulating layer arranged between the sputtering layer and the aluminum pad conductive layer. By using the electroplated cobalt layer formed by electroplating cobalt metal to replace the traditional gold layer, and combining with the corresponding production process, a low-cost cobalt-gold IC package bump is obtained. When a large current passes through the bump, the electromigration phenomenon from the upper gold layer to the sputtering UBM gold layer is effectively prevented, so as to achieve the purpose of reducing costs, improving the wear resistance of the IC package bump, improving the high resistance to electron migration of the IC package bump, and improving the stability of the conduction of the IC package bump.

Description

Technical Field

[0001] The present invention relates to the field of IC packaging, and in particular to a low-cost cobalt-gold IC packaging bump and a production process thereof. Background Art

[0002] In the prior art, the core packaging process of DDIC (display driver chip) is bump manufacturing, which uses bumps instead of traditional leads as electrical connections for chip I / O ports. This process technology can make the packaging more precise and compact.

[0003] With the rapid development of technology, consumers have higher and higher demands on the visual experience of electronic products, and they pursue displays with lower latency and higher resolution. Therefore, DDIC needs to process more and more data, and its I / O ports will continue to increase, which puts higher requirements on packaging technology. Bump manufacturing technology is closely related to the transmission performance and resolution of the display.

[0004] Existing bump materials are generally pure gold, which has problems such as electromigration failure. How to effectively solve the above technology is a technical problem that needs to be solved urgently at the current stage.

[0005] Terminology explanation:

[0006] 1.DDIC: display driver integrated circuit, display driver chip.

[0007] 2. Sputtering: A physical vapor deposition process.

[0008] 2.UBM: under bump metallization, bump bottom metallization.

[0009] 3. Bump: (bump) The part that provides electrical interconnection for the chip.

[0010] 4. Electromigration: When a large current flows through a lead, electrons collide with metal atoms, causing the metal atoms to migrate along the direction of the current. This phenomenon may cause changes in the physical structure of the metal wire, such as the formation of voids or hillocks, which may eventually lead to short circuits, open circuits, performance degradation, or equipment failure.

[0011] 5. Resistance scaling characteristics: Resistance scaling characteristics refer to the changing characteristics in microelectronics technology whereby as the feature size of integrated circuits continues to decrease, the width and thickness of interconnect lines also decrease, resulting in an increase in resistance value.

[0012] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0013] In order to solve the above technical problems, the present invention proposes a low-cost cobalt-gold IC package bump and its production process, so as to achieve the purpose of reducing costs, improving the wear resistance of the IC package bump, improving the high resistance to electron migration of the IC package bump and improving the conductive stability of the IC package bump.

[0014] To achieve the above object, the technical solution of the present invention is as follows:

[0015] A low-cost cobalt-gold IC package bump comprises a silicon wafer carrier, an aluminum pad conductive layer arranged on the silicon wafer carrier, a sputtering layer arranged on the aluminum pad conductive layer, an electroplated cobalt layer formed by electroplating cobalt metal arranged on the sputtering layer, an electroplated gold layer arranged above the electroplated cobalt layer, and an insulating layer arranged between the sputtering layer and the aluminum pad conductive layer;

[0016] The sputtered coating is an inverted convex structure, the bottom of the sputtered coating is arranged closely to the aluminum pad conductive layer, the insulating layer is arranged in the gap between the sputtered coating and the aluminum pad conductive layer, and the insulating layer is tightly connected to the sputtered coating, the silicon wafer carrier and the aluminum pad conductive layer.

[0017] The present invention utilizes an electroplated cobalt layer formed by electroplating cobalt metal to replace the traditional gold layer, and combines it with a corresponding production process to obtain a low-cost cobalt-gold IC package bump. When a large current passes through the bump, the electromigration phenomenon from the upper gold layer to the sputtered UBM gold layer is effectively prevented, thereby achieving the purposes of reducing costs, improving the wear resistance of the IC package bump, improving the high resistance to electron migration of the IC package bump, and improving the conductive stability of the IC package bump.

[0018] It is further worth noting that the sputtered coating includes a sputtered UBM titanium-tungsten layer and a sputtered UBM gold layer disposed above the sputtered UBM titanium-tungsten layer, the sputtered UBM titanium-tungsten layer and the sputtered UBM gold layer are both inverted convex structures, and the convex portion of the sputtered UBM gold layer matches the concave portion of the sputtered UBM titanium-tungsten layer;

[0019] The raised portion of the sputtered UBM titanium-tungsten layer is arranged on the aluminum pad conductive layer, and the insulating layer is filled in the gap formed between the two sides of the sputtered UBM titanium-tungsten layer and the aluminum pad conductive layer, the head end of the insulating layer is arranged between the sputtered UBM titanium-tungsten layer and the aluminum pad conductive layer, and the bottom front part of the insulating layer is arranged on the aluminum pad conductive layer, and the bottom rear part of the insulating layer is arranged on the silicon wafer carrier.

[0020] It is further worth noting that a groove is provided on the silicon wafer carrier for accommodating the aluminum pad conductive layer.

[0021] It is further worth noting that the electroplated cobalt layer also presents an inverted convex structure, and the bottom end of the electroplated cobalt layer matches the groove opened on the top of the sputtered UBM gold layer.

[0022] It is further worth noting that a concave structure is formed above the electroplated gold layer through continuous deposition.

[0023] A low-cost cobalt-gold IC package bump production process, the specific steps are as follows:

[0024] (1) Clean the incoming wafers with two fluids to make the surfaces of the insulating layer and the aluminum pad conductive layer clean and dust-free;

[0025] (2) performing a process of removing oxide from the surfaces of the insulating layer and the aluminum pad conductive layer;

[0026] (3) forming a film layer on the surface of the wafer by physical vapor deposition technology;

[0027] (4) Process the product through gluing, exposure and development;

[0028] (5) using a soluble cobalt salt buffer, a complexing agent, a conductive additive and other solvents as an electroplating solution to perform an electroplating process to form an electroplated cobalt layer;

[0029] (6) A gold layer is electroplated on the surface of the electroplated cobalt layer to complete the production of the entire package bump.

[0030] It is further worth noting that step (3) is as follows:

[0031] (3-1) forming a dense and highly adhesive TiW film on the surface of the wafer by physical vapor deposition (PVD) technology to form a sputtered UBM titanium-tungsten layer, and using the sputtered UBM titanium-tungsten layer as a barrier layer and a stress layer;

[0032] (3-2) A dense and highly adhesive Au film is formed on the sputtered UBM titanium-tungsten layer through physical vapor deposition (PVD) technology to form a sputtered UBM gold layer; the sputtered UBM gold layer is used as a seed layer to ensure that the bump and the substrate have good adhesion and conductivity.

[0033] It is further worth noting that step (4) is specifically as follows: liquid photoresist is evenly coated on the Au film on the surface of the wafer using a coating machine through high-precision spin coating technology, and then patterned through exposure and development steps to obtain the area to be electroplated in the next step.

[0034] It is further worth noting that in step (5), the optimal deposition rate is achieved by controlling the concentration of the cobalt salt, the stability of the pH of the electroplating environment is controlled by the concentration of the buffer, and the current density of the electroplating is controlled to ensure the optimal electroplating rate, avoid the occurrence of voids and bubbles in the electroplating layer, and complete the electroplating of pure cobalt.

[0035] It is further worth noting that step (6) is specifically as follows: on the electroplated cobalt layer, a variety of additives are added to the electroplating solution. Due to the synergistic effect of the additives, the deposition rate of the metal at the top is lower than that at the bottom, and the holes are evenly filled. At the same time, auxiliary salts are added to control the current density so that atoms are continuously deposited to form a "concave" shaped gold plating layer, and then an annealing process is performed to release stress and achieve the set hardness requirement.

[0036] The present invention has the following advantages:

[0037] 1. The present invention utilizes an electroplated cobalt layer formed by electroplating cobalt metal to replace the traditional gold layer, and combines it with a corresponding production process to obtain a low-cost cobalt-gold IC package bump. When a large current passes through the bump, the electromigration phenomenon from the upper gold layer to the sputtered UBM gold layer is effectively prevented, thereby achieving the purpose of reducing costs, improving the wear resistance of the IC package bump, improving the high resistance to electron migration of the IC package bump, and improving the conductive stability of the IC package bump. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0039] Figure 1 A schematic diagram of the structure of a low-cost cobalt-gold IC package bump disclosed in an embodiment of the present invention;

[0040] The numbers and letters in the figure represent the corresponding component names:

[0041] 1. Silicon wafer carrier 2. Aluminum pad conductive layer 31. Sputtered UBM titanium tungsten layer 32. Sputtered UBM gold layer

[0042] 4. Electroplated cobalt layer 5. Electroplated gold layer 6. Insulation layer. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0044] The present invention provides a low-cost cobalt-gold IC package bump and a production process thereof. The working principle is to replace a traditional gold layer with an electroplated cobalt layer formed by electroplating cobalt metal, and to obtain a low-cost cobalt-gold IC package bump in combination with a corresponding production process. When a large current passes through the bump, the electromigration phenomenon from the upper gold layer to the sputtered UBM gold layer is effectively prevented, thereby achieving the purposes of reducing costs, improving the wear resistance of the IC package bump, improving the high resistance to electron migration of the IC package bump, and improving the conductive stability of the IC package bump.

[0045] The present invention is further described in detail below with reference to examples and specific implementation modes.

[0046] like Figure 1 As shown, a low-cost cobalt-gold IC package bump includes a silicon wafer carrier 1, an aluminum pad conductive layer 2 arranged on the silicon wafer carrier, a sputtered layer arranged on the aluminum pad conductive layer, an electroplated cobalt layer 4 formed by electroplating cobalt metal on the sputtered layer, an electroplated gold layer 5 arranged above the electroplated cobalt layer, and an insulating layer 6 arranged between the sputtered layer and the aluminum pad conductive layer.

[0047] The silicon wafer carrier is provided with a groove for accommodating the aluminum pad conductive layer, and the side wall of the aluminum pad conductive layer is closely attached to the side walls at both ends of the groove provided on the silicon wafer carrier.

[0048] The sputtered coating is an inverted convex structure, and includes a sputtered UBM titanium-tungsten layer 31 and a sputtered UBM gold layer 32 disposed above the sputtered UBM titanium-tungsten layer. The sputtered UBM titanium-tungsten layer and the sputtered UBM gold layer are both inverted convex structures, and the convex portion of the sputtered UBM gold layer matches the concave portion of the sputtered UBM titanium-tungsten layer; the convex portion of the sputtered UBM titanium-tungsten layer is disposed on the aluminum pad conductive layer, and the gap formed between the two sides of the sputtered UBM titanium-tungsten layer and the aluminum pad conductive layer is filled with the insulating layer, and the head end of the insulating layer is disposed between the sputtered UBM titanium-tungsten layer and the aluminum pad conductive layer. The bottom front portion of the insulating layer is disposed on the aluminum pad conductive layer, and the bottom rear portion of the insulating layer is disposed on the silicon wafer carrier. The sputtered UBM gold layer 32 plays an important role in improving film quality, enhancing adhesion, preventing diffusion and reaction, improving electrical properties, promoting grain growth, and controlling stress.

[0049] The electroplated cobalt layer also presents an inverted convex structure, and the bottom end of the electroplated cobalt layer matches the groove opened on the top of the sputtered UBM gold layer.

[0050] The upper part of the electroplated gold layer is continuously deposited to form a concave structure [in actual application, the upper part of the electroplated gold layer is continuously deposited to form a downward concave semicircular arc]. Since the electroplated gold layer adopts a "concave" structure design, the IC package bump can fully lock the conductive particles during the later bonding process, preventing the edge conductive particles in contact with the IC package bump from escaping after experiencing severe vibration, thermal expansion and contraction, providing more stable conductive performance and improving product reliability.

[0051] Among them, the five metal layers of electroplated gold layer, electroplated cobalt layer, sputtered UBM gold layer, sputtered UBM titanium tungsten layer and aluminum pad conductive layer are vertically distributed concentrically; the thickness ratio of the electroplated cobalt layer and the electroplated gold layer can be adjusted, and the thickness of the electroplated cobalt layer can be less than or equal to the thickness of the electroplated gold layer.

[0052] In summary, cobalt can play the biggest cost advantage as the main material of IC package bumps. Pure gold with a relatively thin thickness as the surface layer of IC package bumps can maintain the good physical properties of the IC package bump surface, is not prone to chemical reactions, and is easy to bond in the later stage. As a hard metal material, cobalt can adapt to higher hardness range requirements in future high-density I / O interface chip applications. At the same time, due to its good anti-electromigration ability, cobalt can solve the electromigration problem that occurs in the future package bump manufacturing nodes with smaller pitches.

[0053] More importantly, cobalt, as a key connection layer, has finer line widths inside the chip and narrower interconnection spacing in the packaging field. The same metal is used as a conductor for interconnection, and the conductive properties are consistent. When current passes through, the current output can be kept stable, and no transient current will be generated to affect the function of the chip, making the bump have more stable current characteristics.

[0054] In actual processes, the material of the sputtered UBM titanium-tungsten layer 31 may also be Ti or TaN; the material of the sputtered UBM gold layer 32 may also be Cu.

[0055] The following figure shows the data comparison when gold, copper and cobalt are used as the main materials of the bump connection layer:

[0056]

[0057] It can be clearly seen from the above experimental data that the use of cobalt can greatly improve the performance of the entire IC package bump.

[0058] A low-cost cobalt-gold IC package bump production process, the specific steps are as follows:

[0059] (1) The incoming wafer is cleaned by two fluids to make the surface of the insulating layer and the aluminum pad conductive layer clean and dust-free.

[0060] (2) Perform an oxide removal process on the surfaces of the insulating layer and the aluminum pad conductive layer to ensure that there are no impurities on the surfaces of the insulating layer and the aluminum pad conductive layer.

[0061] (3) Forming a film layer on the surface of the wafer by physical vapor deposition technology, as follows:

[0062] (3-1) A dense and highly adhesive TiW film is formed on the surface of the wafer by physical vapor deposition (PVD) technology to form a sputtered UBM titanium-tungsten layer, and the sputtered UBM titanium-tungsten layer is used as a barrier layer and a stress layer.

[0063] (3-2) A dense and highly adhesive Au film is formed on the sputtered UBM titanium-tungsten layer through physical vapor deposition (PVD) technology to form a sputtered UBM gold layer; the sputtered UBM gold layer is used as a seed layer to ensure that the bump and the substrate have good adhesion and conductivity.

[0064] (4) The product is processed through coating, exposure, and development. Specifically, a coating machine is used to evenly coat the liquid photoresist on the Au film on the surface of the wafer through high-precision spin coating technology, and then patterning is performed through exposure and development steps to obtain the area to be electroplated in the next step.

[0065] (5) Use a soluble cobalt salt buffer, a complexing agent [which may be citrate or disodium hydroxyethylidene diphosphonate], a conductive additive and other solvents as the electroplating solution to carry out the electroplating process. The concentration of the cobalt salt is controlled to achieve the optimal deposition rate. The concentration of the buffer [in this embodiment, the buffer is boric acid, pH 4-3] is used to control the pH stability of the electroplating environment. The current density of the electroplating is controlled to ensure the optimal electroplating rate, avoid the occurrence of voids and bubbles in the electroplated layer, and complete the electroplating of pure cobalt.

[0066] (6) A gold layer is electroplated on the surface of the electroplated cobalt layer. Specifically, a variety of additives are added to the electroplating solution [in this embodiment, the additives include a hydroxylated acetylenic compound as an inhibitor and a nitrogen-containing derivative as a leveling agent]. Under the synergistic effect of the additives, the deposition rate of the metal at the top is lower than that at the bottom, and the holes are evenly filled. At the same time, auxiliary salts are added to control the current density so that atoms are continuously deposited to form a "concave"-shaped gold plating layer. Then, an annealing process is performed to release stress and achieve the set hardness requirement, thereby completing the production of the entire package bump.

[0067] The present invention replaces the pure gold bumps in the traditional process with cobalt-gold composite bumps, which greatly reduces the consumption of pure gold and effectively reduces the cost of product packaging. At the same time, the hardness of cobalt is higher than that of gold, so that the bump connection layer has stronger wear resistance, meeting the current demand for product development and application with smaller volume and higher reliability. In addition, the structure of cobalt itself has a low atomic diffusion rate and very high grain boundary stability, and has a strong ability to resist stress voids, which can prevent structural voids caused by electromigration and open circuit defects caused by fractures. Compared with gold, cobalt can work in thinner and narrower bump connection applications, and its vertical resistance is lower, which can give full play to its advantages in future manufacturing nodes with smaller pitches of package bumps.

[0068] The above is only a preferred implementation of a low-cost cobalt-gold IC package bump and its production process disclosed in the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the creative concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A low-cost cobalt-gold IC package bump, characterized in that: The invention comprises a silicon wafer carrier, an aluminum pad conductive layer arranged on the silicon wafer carrier, a sputtering layer arranged on the aluminum pad conductive layer, an electroplated cobalt layer formed by electroplating cobalt metal arranged on the sputtering layer, an electroplated gold layer arranged above the electroplated cobalt layer, and an insulating layer arranged between the sputtering layer and the aluminum pad conductive layer; The sputtered coating is an inverted convex structure, the bottom of the sputtered coating is arranged closely to the aluminum pad conductive layer, the insulating layer is arranged in the gap between the sputtered coating and the aluminum pad conductive layer, and the insulating layer is tightly connected to the sputtered coating, the silicon wafer carrier and the aluminum pad conductive layer.

2. A low-cost cobalt-gold IC package bump according to claim 1, characterized in that: The sputtered coating includes a sputtered UBM titanium-tungsten layer and a sputtered UBM gold layer disposed above the sputtered UBM titanium-tungsten layer, the sputtered UBM titanium-tungsten layer and the sputtered UBM gold layer are both inverted convex structures, and the convex portion of the sputtered UBM gold layer matches the concave portion of the sputtered UBM titanium-tungsten layer; The raised portion of the sputtered UBM titanium-tungsten layer is arranged on the aluminum pad conductive layer, and the insulating layer is filled in the gap formed between the two sides of the sputtered UBM titanium-tungsten layer and the aluminum pad conductive layer, the head end of the insulating layer is arranged between the sputtered UBM titanium-tungsten layer and the aluminum pad conductive layer, and the bottom front part of the insulating layer is arranged on the aluminum pad conductive layer, and the bottom rear part of the insulating layer is arranged on the silicon wafer carrier.

3. A low-cost cobalt-gold IC package bump according to claim 2, characterized in that: The silicon wafer carrier is provided with a groove for accommodating the aluminum pad conductive layer.

4. A low-cost cobalt-gold IC package bump according to claim 2, characterized in that: The electroplated cobalt layer also presents an inverted convex structure, and the bottom end of the electroplated cobalt layer matches the groove opened on the top of the sputtered UBM gold layer.

5. A low-cost cobalt-gold IC package bump according to claim 1, characterized in that: A concave structure is formed above the electroplated gold layer through continuous deposition.

6. A production process for preparing the low-cost cobalt-gold IC package bump according to claim 1, characterized in that: The specific steps are as follows: (1) Clean the incoming wafers with two fluids to make the surfaces of the insulating layer and the aluminum pad conductive layer clean and dust-free; (2) performing a process of removing oxide from the surfaces of the insulating layer and the aluminum pad conductive layer; (3) forming a film layer on the surface of the wafer by physical vapor deposition technology; (4) Process the product through gluing, exposure and development; (5) using a soluble cobalt salt buffer, a complexing agent, a conductive additive and other solvents as an electroplating solution to perform an electroplating process to form an electroplated cobalt layer; (6) A gold layer is electroplated on the surface of the electroplated cobalt layer to complete the production of the entire package bump.

7. A low-cost cobalt-gold IC package bump production process according to claim 6, characterized in that: Step (3) is as follows: (3-1) forming a dense and highly adhesive TiW film on the surface of the wafer by physical vapor deposition (PVD) technology to form a sputtered UBM titanium-tungsten layer, and using the sputtered UBM titanium-tungsten layer as a barrier layer and a stress layer; (3-2) A dense and highly adhesive Au film is formed on the sputtered UBM titanium-tungsten layer through physical vapor deposition (PVD) technology to form a sputtered UBM gold layer; the sputtered UBM gold layer is used as a seed layer to ensure that the bump and the substrate have good adhesion and conductivity.

8. A low-cost cobalt-gold IC package bump production process according to claim 7, characterized in that: Step (4) is specifically as follows: Use a coating machine to evenly coat the liquid photoresist on the Au film on the wafer surface through high-precision spin coating technology, and then pattern it through exposure and development steps to obtain the area to be electroplated in the next step.

9. A low-cost cobalt-gold IC package bump production process according to claim 6, characterized in that: In step (5), the optimal deposition rate is achieved by controlling the concentration of the cobalt salt, the stability of the pH of the electroplating environment is controlled by the concentration of the buffer, the current density of the electroplating is controlled, the optimal electroplating rate is ensured, the defects of cavities and bubbles in the electroplating layer are avoided, and the electroplating of pure cobalt is completed.

10. The low-cost cobalt-gold IC package bump production process according to claim 6, characterized in that: Step (6) is specifically as follows: on the electroplated cobalt layer, a variety of additives are added to the electroplating solution. Under the synergistic effect of the additives, the deposition rate of the metal on the top is lower than that on the bottom, and the holes are evenly filled. At the same time, auxiliary salts are added to control the current density so that atoms are continuously deposited to form a "concave"-shaped gold plating layer, and then an annealing process is performed to release stress and achieve the set hardness requirement.

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