CN100367464C - Method for manufacturing metal bump - Google Patents

Abstract

The invention provides a method for manufacturing a metal bump, which comprises the following steps: providing a substrate with a surface comprising a protective layer, exposing at least one bonding pad metal surface, forming a photoresist layer to cover the substrate surface, performing a photoetching process to pattern the photoresist layer to expose part of the protective layer and the bonding pad metal, removing part of the protective layer, and finally removing the photoresist layer and performing a metal bump processing process. The invention can make the thickness of the protective layer covering the metal surface of the bonding pad smaller than the thickness of the protective layer covering the surface of the substrate.

Description

Method of making metal bumps

technical field

The invention relates to a method for manufacturing a metal bump, in particular to a method which can improve the step height of the metal bump periphery and increase the packaging quality.

Background technique

With the development of portable electronic devices, various light, thin, and short packages are continuously developed, and the flip-chip ball grid array (BGA) package is one example. In a flip-chip BGA package, the die (die) is no longer connected to the package substrate by bonding the pad metal (bonding pad) via wire bonding, but is reversed through gold bumps or conductive polymer bumps, etc. Connected to the package substrate, so the flip-chip BGA package can increase circuit density and improve electrical characteristics.

Flip-chip bonding belongs to area array bonding, so it can be applied to extremely high-density packaging. To put it simply, the concept of flip-chip bonding is to first grow metal bumps on the bonding pad metal of the die, and then use such as anisotropic conductive film (ACF) or silver glue to adhere the metal bumps to the chip. on the packaging substrate, and then complete the bonding of the die and the packaging substrate. This method not only breaks through the limitation of the number of traditional wire bonding technology, but also is suitable for multi-pin component packaging, and the electrical performance is also greatly improved due to the shorter connection path.

Referring to FIG. 1 , FIG. 1 is a schematic diagram of a conventional metal bump 20 bonded to a packaging substrate 22 . As shown in FIG. 1 , the surface of a die 10 includes at least one pad metal 12 , an oxide layer 14 , and a silicon nitride 16 . Wherein, the oxide layer 14 and the silicon nitride 16 are a protective layer 18 which are sequentially stacked on the surface of the die 10 and cover part of the surface of the bonding pad metal 12 . In addition, there is a metal bump 20 above the die 10, because the protective layer 18 has a step height above the periphery of the bonding pad metal 12, so after the metal bump 20 is formed, its periphery will also have a corresponding step. jump height. In this way, when the metal bump 20 is bonded to a packaging substrate 22, because of the step height of the periphery of the metal bump 20, it is very easy to partially coat the surface between the metal bump 20 and the packaging substrate 22 interface. The anisotropic conductive adhesive film 24 cannot reliably bond the metal bump 20 to the packaging substrate 22 .

It can be seen from the above that if the step height of the metal bump 20 is too large, the quality of the package will be seriously affected. However, if there is no step height of the metal bump 20, the anisotropic conductive adhesive film 24 cannot be properly sealed Gather on the surface of the metal bump 20 . The known technology generally utilizes two methods to improve this problem. The first method is to reduce the deposited thickness of the protective layer 18, but this method will greatly reduce the reliability of the product. The second method is to reduce the bonding pad metal 12 , however, this method will reduce the bonding area and cause the anisotropic conductive adhesive film 24 to be uneven.

Contents of the invention

Therefore, the main objective of the present invention is to provide a method for manufacturing metal bumps to solve the above-mentioned problems.

In order to achieve the above object, according to a preferred embodiment of the present invention, the present invention firstly provides a substrate, the surface of the substrate includes a patterned protective layer exposing a part of the surface of at least one bonding pad metal, and then a photoresist layer is formed to cover the surface of the substrate, Then use a photomask to perform a photolithography process to pattern the photoresist layer to expose part of the protective layer and the bonding pad metal, and then remove part of the protective layer so that the thickness of the protective layer covering the surface of the bonding pad metal is less than The thickness of the protective layer covering the surface of the substrate is finally removed and a metal bumping process is performed using a photomask.

Since the present invention can effectively improve the step height of the periphery of the metal bump, the reduction of the step height of the periphery of the metal bump through the present invention will be more conducive to improving the bonding effect between the metal bump and the packaging substrate, thereby greatly improving the The quality of the package. In addition, the present invention does not need to add an additional photomask during the manufacturing process, and therefore does not need to increase the cost of the photomask.

In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are specifically cited below and described in detail with accompanying drawings. However, the drawings are only for reference and auxiliary description, and are not used to limit the present invention.

Description of drawings

FIG. 1 is a schematic diagram of a conventional metal bump bonded to a package substrate;

2 to 7 are schematic diagrams of a method for manufacturing a metal bump according to a first embodiment of the present invention;

8 to 10 are schematic diagrams of a method for manufacturing a metal bump according to a second embodiment of the present invention.

Detailed ways

Referring to FIG. 2 to FIG. 7 , FIG. 2 to FIG. 7 are schematic diagrams of a method for manufacturing the metal bump 48 according to the first embodiment of the present invention. As shown in FIG. 2 , a substrate 30 is firstly provided. The substrate 30 can be a chip with internal components and circuits fabricated or a multilayer printed circuit board with internal circuit layout completed. The surface of the substrate 30 includes at least one pad metal 32 , an oxide layer 34 and a silicon nitride 36 . The bonding pad metal 32 is made of aluminum, and the oxide layer 34 and silicon nitride 36 combine to form a patterned protective layer 38 , the protective layer 38 covers part of the surface of the bonding pad metal 32 and exposes part of the surface of the bonding pad metal 32 . The oxide layer 34 and the silicon nitride 36 are respectively formed on the surface of the substrate 30 and the pad metal 32 through a deposition process. In this embodiment, the protection layer 38 formed by the oxide layer 34 and the silicon nitride 36 has approximately the same thickness on the surface of the base 30 and the bonding pad metal 32 .

As shown in Figure 3, then utilize the method for spin-coating to coat a first photoresist layer 40 on the surface of the substrate 30, and use a photomask (not shown in the figure), through photolithography processes such as exposure and development. The first photoresist layer 40 is patterned to expose part of the surface of the passivation layer 38 and the surface of the bonding pad metal 32 .

Subsequently, as shown in FIG. 4, an etching process is performed using the first photoresist layer 40 as an etching barrier, such as a wet etching process or a dry etching process, etc., to remove part of the protective layer 38, such as removing part of the nitrogen vertically. silicon 36 , so that the thickness of a portion of the passivation layer 38 covering the surface of the bonding pad metal 32 is smaller than the thickness of the passivation layer 38 covering the surface of the substrate 30 . Then the first photoresist layer 40 is removed.

As shown in FIG. 5 , an under bump metallurgy (UBM) process is performed to form a titanium-tungsten alloy metal layer 42 and a gold metal layer 44 on the surface of the passivation layer 38 and the bonding pad metal 32 . However, the UBM layer of the present invention is not limited to the above-mentioned combination, and it can also be replaced by other materials, which is a technology known to those skilled in the art, and will not be repeated here. Then, a second photoresist layer 46 is coated on the surface of the substrate 30, and the second photoresist layer 46 is patterned by using the same photomask (not shown in the figure) described above to carry out photolithography processes such as exposure and development. , so as to expose part of the surface of the gold metal layer 44 .

Then as shown in Figure 6, utilize the second photoresist layer 46 to do shielding to carry out an electroplating treatment process, so that a metal bump made of gold is formed on the gold metal layer 44 surface that is not covered by the second photoresist layer 46 Block 48 , so that metal bumps 48 are positioned corresponding to the pad metal 32 , and then the second photoresist layer 46 is removed. It should be noted that, since the present invention has removed part of the protective layer 38 earlier, the step height of the periphery of the metal bump 48 is smaller than the step height of the periphery of the metal bump made by known methods, which is more conducive to improving the metal The bonding effect between the bump 48 and the package substrate (not shown).

As shown in FIG. 7 , the titanium-tungsten alloy metal layer 42 and the gold metal layer 44 that are not covered by the metal bump 48 are removed sequentially through an etching process, followed by a thermal annealing process. In this way, the method for manufacturing the metal bump 48 according to the first embodiment of the present invention is completed.

Referring to FIG. 8 to FIG. 10 , FIG. 8 to FIG. 10 are schematic diagrams of a method for manufacturing metal bumps according to a second embodiment of the present invention. The main difference between the second embodiment of the present invention and the above-mentioned first embodiment is that in the second embodiment of the present invention, the photomask used to remove part of the protective layer is different from the photomask used in the metal bumping process. . This difference is because if the process of removing part of the protective layer in the present invention is carried out in a general chip factory, the chip factory needs to prepare the photomask by itself, but the photomask only needs a relatively simple pattern, unlike the metal bumping process The photomask used in the process needs to be prepared corresponding to the position of each metal bump, so the cost is relatively low. Compared with the effect of improving the step height of the metal bump periphery, it is still worth the investment.

As shown in FIG. 8 , a substrate 50 is firstly provided. The substrate 50 can be a chip with internal components and circuits fabricated or a multilayer printed circuit board with internal circuit layout completed. The surface of the substrate 50 includes a plurality of bonding pad metals 52 , 54 and 56 , an oxide layer 58 and a silicon nitride 60 . Wherein, the pad metals 52, 54, and 56 are made of aluminum, and the oxide layer 58 and silicon nitride 60 combine to form a patterned protection layer 62, and the protection layer 62 covers part of the pad metals 52, 54, and 56 to form protrusions. The passivation layer 62 and parts of the surfaces of the bonding pad metals 52 , 54 and 56 are exposed. Oxide layer 58 and silicon nitride 60 are formed on substrate 50 and pad metals 52 , 54 and 56 simultaneously through a deposition process. In this embodiment, the protection layer 62 formed by the oxide layer 58 and the silicon nitride 60 has approximately the same thickness on the substrate 50 and the surfaces of the bonding pad metals 52 , 54 and 56 .

Then as shown in Figure 9, utilize the method for spin-coating to coat a photoresist layer 64 on the surface of the substrate 50, and use a first photomask (not shown in the figure), through photolithography processes such as exposure and development The photoresist layer 64 is patterned to expose portions of the raised surface of the passivation layer 62 and the surfaces of the bond pad metals 52 , 54 and 56 .

As shown in FIG. 10 , use the photoresist layer 64 as an etching barrier to perform an etching process, such as a wet etching process or a dry etching process, to remove part of the protective layer 62, such as removing part of the silicon nitride vertically. 60, so as to reduce the thickness of the protective layer 62 covering the surfaces of the bonding pad metals 52, 54 and 56 and therebetween. The photoresist layer 64 is then removed. The following process is similar to the first embodiment except that the second photomask used in the metal bumping process is different from the first photomask, so details are not repeated here.

Compared with the known technology, the present invention can effectively improve the step height of the periphery of the metal bump, and the step height of the periphery of the metal bump can be reduced through the present invention, which will be more conducive to improving the bonding effect between the metal bump and the package substrate , thereby greatly improving the quality of the package. In addition, the present invention does not need to add an additional photomask in the process of processing, so it does not need to increase the cost of the photomask, or use a simple and low-cost photomask to remove part of the protective layer, so The added photomask is also less costly.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the claims of the present invention shall fall within the protection scope of the present invention.

Claims (17)

1. A method of manufacturing a metal bump, the method comprising the following steps: A substrate is provided, the surface of the substrate includes a patterned protection layer and at least one pad metal, the protection layer covers the surface of the substrate and exposes a part of the surface of the pad metal; forming a first photoresist layer covering the surface of the substrate; patterning the first photoresist layer by performing a photolithography process using a photomask to expose a portion of the protection layer and the bonding pad metal; removing a portion of the protective layer such that the thickness of the protective layer covering the metal surface of the bonding pad is less than the thickness of the protective layer covering the surface of the substrate; removing the first photoresist layer; and A metal bumping process is performed using the photomask. 2. The method of claim 1, wherein the protection layer is composed of an oxide layer and a silicon nitride layer overlying the oxide layer. 3. The method of claim 1, wherein before removing part of the protective layer, the thickness of the protective layer covering the surface of the substrate is equal to the thickness of the protective layer covering the metal surface of the bonding pad. 4. The method of claim 1, wherein the bond pad metal is aluminum. 5. The method of claim 1, wherein the step of removing a portion of the protective layer utilizes a wet etching process. 6. The method of claim 1, wherein the step of removing a portion of the protective layer utilizes a dry etching process. 7. The method according to claim 1, wherein the metal bumping process further comprises the following sub-steps: performing an under bump metallization process to form a metal layer on the surface of the substrate; forming a second photoresist layer covering the surface of the substrate; performing a photolithography process using a photomask to pattern the second photoresist layer; Using the patterned second photoresist layer as a shield to form at least one metal bump on the surface of the substrate, and the metal bump is correspondingly arranged on the bonding pad metal; removing the second photoresist layer; removing the metal layer not covered by the metal bump; and A thermal annealing process is performed. 8. The method of claim 7, wherein the metal layer consists of a titanium-tungsten alloy metal layer and a gold metal layer. 9. The method of claim 7, wherein the metal bumps are composed of gold. 10. A method of manufacturing metal bumps, the method comprising the steps of: A substrate is provided, the surface of the substrate includes a plurality of bonding pad metals and a patterned protective layer, the protective layer covers the substrate and the plurality of bonding pad metal surfaces and exposes a part of the surface of each bonding pad metal, and A raised protective layer covering the bonding pad metal; forming a first photoresist layer covering the surface of the substrate; performing a photolithography process to pattern the first photoresist layer by using a first photomask, so as to expose part of the raised protection layer and the pad metal; Removing part of the protective layer to reduce the thickness of the protective layer covering the bond pad metal surface; removing the first photoresist layer; and A metal bumping process is performed using a second photomask. 11. The method of claim 10, wherein the protection layer is composed of an oxide layer and a silicon nitride layer overlying the oxide layer. 12. The method of claim 10, wherein the bond pad metal is aluminum. 13. The method of claim 10, wherein the step of removing a portion of the protective layer utilizes a wet etch process. 14. The method of claim 10, wherein the step of removing a portion of the protective layer utilizes a dry etching process. 15. The method of claim 10, wherein the metal bumping process further comprises the following sub-steps: performing an under bump metallization process to form a metal layer on the surface of the substrate; forming a second photoresist layer covering the surface of the substrate; performing a photolithography process using a second photomask to pattern the second photoresist layer; Using the patterned second photoresist layer as a shield, so as to form a plurality of metal bumps on the surface of the substrate, and the metal bumps are correspondingly arranged on the bonding pad metal; removing the second photoresist layer; removing the metal layer not covered by the metal bump; and A thermal annealing process is performed. 16. The method of claim 15, wherein the metal layer consists of a titanium-tungsten alloy metal layer and a gold metal layer. 17. The method of claim 15, wherein the metal bumps are composed of gold.

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