Bump structure and manufacturing method thereof

A manufacturing method of a bump structure is provided. A substrate having at least one pad and a passivation layer is provided. The passivation layer has at least one first opening exposing the pad. An insulating layer is formed on the passivation layer. The insulating layer has at least one second opening located above the first opening. A metal layer is formed on the insulating layer. The metal layer electrically connects the pad through the first and second openings. A first bump is formed in the first and second openings. A second bump is formed on the first bump and a portion of the metal layer. The metal layer not covered by the second bump is partially removed by using the second bump as a mask, so as to form at least one UBM layer. The first bump is completely covered by the UBM layer and the second bump.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 99144947, filed on Dec. 21, 2010. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a semiconductor structure and a manufacturing method of the same. More particularly, the invention relates to a bump structure and a manufacturing method thereof.

2. Description of Related Art

In a fabricating process of a semiconductor, a conductive bump is required to be formed on each pad of the wafer structure that will serve as a flip-chip package, and the conductive bump that transmits electric signals includes a solder bump, a gold bump, a copper bump, a conductive polymer bump, a polymer bump, and so on. When an electric field is applied to the bumps, stress resulting from electro-migration is generated. Namely, when the bumps made of metal materials conduct electricity, metallic atoms of the bumps migrate along the grain boundary of the material and move toward the current-flow direction, which leads to the reduction of the sectional area of the bumps and finally causes an open circuit. Accordingly, it is necessary to form the so-called under bump metallurgic (UBM) layer between the bumps and pads, so as to enhance the bonding strength between the bumps and the pads and prevent the electro-migration phenomenon.

However, since the conventional UBM layer is merely configured below the bumps, an under cut effect is likely to be generated when there are cracks between the UBM layer and the bumps or between the UBM layer and the passivation layer that is located above the pads. Moreover, the bumps must have certain height, such that the bumps can be electrically connected to a circuit board or any other carrier. Hence, given the gold bumps are applied, the higher the gold bumps, the more the manufacturing costs. By contrast, when the gold bumps are replaced by the copper bumps, the manufacturing costs can be reduced. Nevertheless, copper is apt to be oxidized, which may give rise to the reduction of the bonding reliability between the bumps and the UBM layer.

SUMMARY OF THE INVENTION

The invention is directed to a bump and a manufacturing method thereof in order to prevent the under cut effect and ensure favorable bonding reliability.

In an embodiment of the invention, a manufacturing method of a bump structure is provided. First, a substrate is provided. The substrate has at least one pad and a passivation layer. The passivation layer has at least one first opening to expose the pad. An insulating layer is formed on the passivation layer. The insulating layer has at least one second opening that is located above the first opening. A metal layer is formed on the insulating layer. Here, the metal layer is electrically connected to the pad through the first opening and the second opening. A first bump is formed in the first and second openings. A second bump is formed on the first bump and a portion of the metal layer. A portion of the metal layer which is not covered by the second bump is removed with use of the second bump as a mask, so as to form at least one UBM layer. The first bump is completely covered by the UBM layer and the second bump.

According to an embodiment, the step of forming the first bump includes following steps. A first patterned photoresist layer is formed on the insulating layer. The first patterned photoresist layer has at least one third opening corresponding to the second opening. A diameter of the third opening is substantially equal to a diameter of the second opening, and the third opening exposes a portion of the metal layer located in the first opening and the second opening. The first bump is formed in the first opening and the second opening. Here, the first bump fills the first opening and the second opening, and a portion of the metal layer is located between the first bump and the insulating layer. The first patterned photoresist layer is removed to expose a portion of the metal layer located below the first patterned photoresist layer.

According to an embodiment of the invention, a nickel layer is formed on the first bump before the second bump is formed on the first bump.

According to an embodiment of the invention, the nickel layer is formed on the first bump before the first patterned photoresist layer is removed.

According to an embodiment of the invention, the nickel layer is formed on the first bump after the first patterned photoresist layer is removed.

According to an embodiment of the invention, the nickel layer extends and is configured between the second bump and a portion of the metal layer located on the insulating layer.

According to an embodiment of the invention, the step of forming the second bump includes following steps. A second patterned photoresist layer is formed on a portion of the metal layer located on the insulating layer. The second patterned photoresist layer has at least one fourth opening corresponding to the at least one second opening. The fourth opening exposes the first bump located in the first opening and the second opening and exposes a portion of the metal layer located on the insulating layer. The second bump is formed in the fourth opening. Here, the second bump is stacked on the first bump. The second patterned photoresist layer is removed to expose a portion of the metal layer located below the second patterned photoresist layer.

In an embodiment of the invention, a bump structure is adapted to be configured on a substrate. The substrate has at least one pad and a passivation layer that has at least one opening exposing a portion of the pad. The bump structure includes an insulating layer, an UBM layer, a first bump, and a second bump. The insulating layer is configured on the passivation layer and has at least one second opening. The second opening exposes a portion of the passivation layer and a portion of the pad. The UBM layer is configured on a portion of the insulating layer, in the first opening, and in the second opening. Here, the UBM layer covers an inner wall of the first opening, an inner wall of the second opening, and a portion of the passivation layer exposed by the second opening. The first bump fills the first opening and the second opening. A portion of the UBM layer is located between the first bump and the insulating layer. The second bump is stacked on the first bump and covers the first bump. A portion of the second bump extends to a portion of the UBM layer that is located on the insulating layer.

According to an embodiment of the invention, the first bump is a copper bump, and the second bump is a gold bump.

According to an embodiment of the invention, the bump structure further includes a nickel layer configured between the first bump and the second bump.

According to an embodiment of the invention, a bottom area of the nickel layer is greater than or substantially equal to an area of a diameter of the second opening.

According to an embodiment of the invention, a top surface of the first bump is a planar surface.

According to an embodiment of the invention, a bottom area of the second bump is greater than or substantially equal to an area of a diameter of the second opening.

Based on the above, the first bump of the invention is completely covered by the UBM layer and the second bump, the UBM layer is covered by the insulating layer, and a portion of the UBM layer located on the insulating layer is covered by the second bump. Hence, the under cut effect on the bump structure of the invention is rather unlikely to occur. Moreover, the bonding reliability of the bumps and the UBM layer is favorable.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a schematic cross-sectional view illustrating a bump structure according to an embodiment of the invention. With reference toFIG. 1, in this embodiment, the bump structure100ais adapted to be configured on a substrate10, and the substrate10has at least one pad12and a passivation layer14. InFIG. 1, two pads12are schematically depicted. Specifically, the passivation layer14has at least one first opening16. InFIG. 1, two first openings16are schematically depicted. The first openings16expose a portion of the pads12. The substrate10is a circuit board or a wafer, for instance. The pads12are made of aluminum, copper, or any other appropriate metal, for instance.

The bump structure100aof this embodiment includes an insulating layer110, an UBM layer120, a first bump130, and a second bump140. Two bump structures100aare schematically illustrated inFIG. 1. More specifically, the insulating layer110is configured on the passivation layer14and has at least one second opening112. InFIG. 1, two second openings112are schematically depicted. In each bump structure100a, the second opening112exposes a portion of the passivation layer14and a portion of the pad12, and a diameter of the second opening112is greater than a diameter of the first opening16. The UBM layer120is configured on a portion of the insulating layer110, in the first opening16, and in the second opening112. Here, the UBM layer120covers an inner wall of the first opening16, a portion of the pad12which is exposed by the first opening16, an inner wall of the second opening112, and a portion of the passivation layer14which is exposed by the second opening112.

The first bump130fills the first and second openings16and112. The UBM layer120covers the inner wall of the first opening16and the inner wall of the second opening112, such that a portion of the UBM layer120is located between the first bump130and the insulating layer110. More particularly, the height of the first bump130in this embodiment is less than the depth of the second opening112, and the first bump130is a copper bump, for instance. It should be mentioned that the first bump130has a first width W1and a second width W2. The first width W1is slightly less than the diameter of the first opening16, and the second width W2is slightly less than the diameter of the second opening112. Here, the second width W2is greater than the first width W1. The second bump140is stacked on the first bump130and covers the top surface of the first bump130. A portion of the second bump140extends to a portion of the UBM layer120located on the insulating layer110, and another portion of the second bump140is located in the second opening112and connected to the first bump130. Besides, the second bump140of this embodiment is a gold bump, for instance. It should be mentioned that the first bump130and the second bump140can be made of other appropriate metallic materials in other embodiments of the invention, which should not be construed as a limitation to the invention. For instance, the first bump130can be made of palladium, and the second bump140can be made of gold, for instance.

In the bump structure100a, the first bump130is completely covered by the UBM layer120and the second bump140, and thus the under cut effect on the bump structure100ais less likely to occur. Besides, the first bump130made of the copper material is completely covered by the UBM layer120and the second bump140which is made of the gold material, the UBM layer120is covered by the insulating layer110, and a portion of the UBM layer120located on the insulating layer110is covered by the second bump140. As such, metal oxidization can be effectively prevented, and the bonding reliability between the first and second bumps130and140and the UBM layer120can be enhanced. In comparison with the conventional bump structure, the bump structure100ais not entirely made of the gold bump. Instead, the bump structure100ahas the first bump130made of the copper material and the second bump140made of the gold material, and the first and second bumps130and140are stacked. Thereby, the manufacturing costs can be effectively lowered down.

The manufacturing method of the aforesaid bump structure100ais elaborated in the following embodiment with reference toFIG. 2AtoFIG. 2I.

FIG. 2AtoFIG. 2Iare schematic cross-sectional views illustrating a manufacturing method of a bump structure according to an embodiment of the invention. With reference toFIG. 2A, the bump structure in the embodiment includes following steps. First, a substrate10is provided. The substrate10has at least one pad12and a passivation layer14. The passivation layer14has at least one first opening16to expose the pad12. InFIG. 2A, two first openings16are depicted. The substrate10is a circuit board or a wafer, for instance. The pad12is made of aluminum, copper, or any other appropriate metal, for instance.

With reference toFIG. 2B, an insulating layer110is formed on the passivation layer14. Here, the insulating layer110has at least one second opening112located above the first opening16. InFIG. 2A, two second openings112are schematically depicted. In this embodiment, the diameter of the second opening112is substantially greater than the diameter of the first opening16.

As indicated inFIG. 2C, a metal layer125is formed on the insulating layer110. Here, the metal layer125is electrically connected to the pad12through the first and second openings16and112. The metal layer125can be formed by performing a sputtering process, a physical vapor deposition (PVD) process, or a chemical vapor deposition (CVD) process.

With reference toFIG. 2D, a first patterned photoresist layer160is formed on the insulating layer110. The first patterned photoresist layer160has at least one third opening162corresponding to the second opening112. InFIG. 2D, two third openings162are schematically depicted. A diameter of the third opening162is substantially equal to the diameter of the second opening112, and the third opening162exposes a portion of the metal layer125located in the first and second openings16and112.

As indicated inFIG. 2E, a first bump130is formed in the first and second openings16and112. Here, the first bump130fills the first and second openings16and112, and a portion of the metal layer125is located between the first bump130and the insulating layer110. In this embodiment, the height of the first bump130is less than the depth of the second opening112, and the first bump130is a copper bump, for instance. Besides, the first bump130is formed by performing an electroplating process, for instance.

With reference toFIG. 2F, the first patterned photoresist layer160is removed to expose a portion of the metal layer125located below the first patterned photoresist layer160.

As shown inFIG. 2F, a second patterned photoresist layer170is formed on a portion of the metal layer125located on the insulating layer110. The second patterned photoresist layer170has at least one fourth opening172corresponding to the second opening112. InFIG. 2F, two fourth openings172are schematically depicted. Here, each of the fourth openings172exposes the first bump130located in the first and second openings16and112and exposes a portion of the metal layer125located on the insulating layer110.

With reference toFIG. 2F, the second bump140is formed in the fourth opening172, and the second bump140is stacked on the first bump130. The bottom area of the second bump140is greater than the area of the diameter of the second opening112. In detail, a portion of the second bump140is located in the second opening112and covers the first bump130, and a portion of the second bump140located outside the second opening112covers a portion of the metal layer125located on the insulating layer110. In this embodiment, the second bump140has a third width W3and a fourth width W4. The third width W3is slightly less than the diameter of the second opening112, and the fourth width W4is greater than the diameter of the second opening112. Here, the bottom area of the second bump140is defined based on the fourth width W4of the second bump140. In addition, the second bump140of this embodiment is a gold bump, for instance, and the second bump140is formed by performing an electroplating process, for instance.

With reference toFIG. 2G, the second patterned photoresist layer170is removed to expose a portion of the metal layer125located below the second patterned photoresist layer170.

With reference toFIG. 2H, a portion of the metal layer125which is not covered by the second bump140is removed with use of the second bump140as a mask, so as to form at least one UBM layer120. InFIG. 2H, two UBM layers120are schematically depicted. The first bump130is completely covered by the UBM layer120and the second bump140. So far, the bump structure100ais completely formed.

There is an insulating layer110located between the bump structures100a. The insulating layer110surrounds the bump structures100aand can prevent electro-migration of the adjacent bump structures and the oxidization of the UBM layers120located at the bottom of the bump structures. Moreover, when the bump structures are bonded to external devices, the insulating layer110can act as a buffer.

In this embodiment, a portion of the insulating layer110which is not covered by the second bump140and the UBM layer120can be further removed with use of the second bump140as a mask, such that an individual insulating layer110′ is formed around each of the bump structures100a′. InFIG. 2I, two bump structures100a′ are schematically depicted. Here, the insulating layer110′ is a hollow insulating tube.

The bump structure and a manufacturing method thereof are described in the following embodiments. Note that the same reference numbers and some of the descriptions provided in the previous embodiments are also used in the following embodiments. The same reference numbers denote the same or like components, and descriptions of the same technical contents are omitted. The aforementioned embodiments can be referred for the descriptions of the omitted parts, and thus the omitted parts are not further described in the following embodiments.

FIG. 3is a schematic cross-sectional view illustrating another bump structure according to an embodiment of the invention. With reference toFIG. 3, the bump structure100bdepicted therein is similar to the bump structure100adepicted inFIG. 1, while the difference therebetween lies in that the bump structure100bfurther includes a nickel layer150bconfigured between the first and second bumps130band140b. Specifically, in this embodiment, the height of the first bump130bis greater than the depth of the second opening112. Namely, the first bump130bprotrudes from the second opening112. The nickel layer150bcovers the top surface132of the first bump130band connects the UBM layer120. The first bump130bis completely covered by the UBM layer120and the nickel layer150b.

The bump structure100bof this embodiment as depicted inFIG. 3can be formed by performing similar steps for manufacturing the bump structure100adepicted inFIG. 2AtoFIG. 2H. In the step shown inFIG. 2D, the first bump130bprotrudes from the second opening112. In the step shown inFIG. 2E, i.e., after the first patterned photoresist layer160is removed, the nickel layer150bis formed on the first bump130bto connect the UBM layer120. The step of forming the second patterned photoresist layer170and the second bump140bas shown inFIG. 2Fand the steps shown inFIG. 2GtoFIG. 2Hare then performed, so as to completely form the bump structure100b.

FIG. 4is a schematic cross-sectional view illustrating another bump structure according to an embodiment of the invention. The bump structure100cdepicted inFIG. 4is similar to the bump structure100bdepicted inFIG. 3, while the difference therebetween lies in where the nickel layer150cof the bump structure100cis configured. To be more specific, the nickel layer150ccovers the top surface132cof the first bump130c, and the nickel layer150cis located in the second opening112. The surface of the nickel layer150caway from the first bump130cis substantially lower than or aligned to the surface of the insulating layer110which is not in contact with the passivation layer14. The bottom area of the nickel layer150cis substantially equal to the area of the diameter of the second opening112.

The bump structure100cof this embodiment as depicted inFIG. 4can be formed by performing similar steps for manufacturing the bump structure100adepicted inFIG. 2AtoFIG. 2H. In the step shown inFIG. 2E, i.e., after the first bump130cis formed and before the first patterned photoresist layer160is removed, the nickel layer150cis formed on the first bump130c. The step of forming the second patterned photoresist layer170and the second bump140cas shown inFIG. 2Fand the steps shown inFIG. 2GtoFIG. 2Hare then performed, so as to completely form the bump structure100c.

FIG. 5is a schematic cross-sectional view illustrating still another bump structure according to an embodiment of the invention. The bump structure100ddepicted inFIG. 5is similar to the bump structure100bdepicted inFIG. 3, while the difference therebetween lies in where the nickel layer150dof the bump structure100dis configured. In particular, the nickel layer150dcovers the top surface132dof the first bump130d. Besides, the nickel layer150dextends and is configured between the second bump140dand a portion of the UBM layer120located on the insulating layer110. The bottom area of the nickel layer150dis greater than the area of the diameter of the second opening112.

The bump structure100dof this embodiment as depicted inFIG. 5can be formed by performing similar steps for manufacturing the bump structure100adepicted inFIG. 2AtoFIG. 2H. In the step shown inFIG. 2F, i.e., after the second patterned photoresist layer170is removed, the nickel layer150dis formed on the first bump130d. The step of forming the second patterned photoresist layer170and the second bump140das shown inFIG. 2Fand the steps shown inFIG. 2GtoFIG. 2Hare then performed, so as to completely form the bump structure100d.

In light of the foregoing, the first bump of the bump structure is completely covered by the UBM layer and the second bump, the UBM layer is covered by the insulating layer, and a portion of the UBM layer located on the insulating layer is covered by the second bump. Therefore, the under cut effect on the bump structure of the invention is rather unlikely to occur, metal oxidization can be effectively prevented, and the bonding reliability between the bumps and the UBM layer can be enhanced. Besides, in comparison with the conventional bump structure, the bump structure of this invention is not entirely made of the gold material, and thus the manufacturing costs can be effectively lowered down.