Self-aligned protection layer for copper post structure

Abstract

A semiconductor device includes a copper-containing post overlying and electrically connected to a bond pad region. The semiconductor device further includes a protection layer on a surface of the copper-containing post, where the protection layer includes manganese.

Description

TECHNICAL FIELD

This disclosure relates to bump structures of semiconductor devices.

BACKGROUND

Modern integrated circuits are made up of literally millions of active devices such as transistors and capacitors. These devices are initially isolated from each other, but are later interconnected together to form functional circuits. Typical interconnect structures include lateral interconnections, such as metal lines (wirings), and vertical interconnections, such as vias and contacts. Interconnections are increasingly determining the limits of performance and the density of modern integrated circuits. On top of the interconnect structures, bond pads are formed and exposed on the surface of the respective chip. Electrical connections are made through bond pads to connect the chip to a package substrate or another die. Bond pads can be used for wire bonding or flip-chip bonding. Wafer level chip scale packaging (WLCSP) is currently widely used for its low cost and relatively simple processes. In a typical WLCSP, interconnect structures are formed on metallization layers, followed by the formation of under-bump metallurgy (UBM), and the mounting of solder balls.

Flip-chip packaging utilizes bumps to establish electrical contact between a chip's I/O pads and the substrate or lead frame of the package. Structurally, a bump actually contains the bump itself and a so-called under bump metallurgy (UBM) located between the bump and an I/O pad. An UBM generally contains an adhesion layer, a barrier layer and a wetting layer, arranged in this order on the I/O pad. The bumps themselves, based on the material used, are classified as solder bumps, gold bumps, copper pillar bumps and bumps with mixed metals. Recently, copper interconnect post technology is proposed. Instead of using solder bump, the electronic component is connected to a substrate by means of copper post. The copper interconnect post technology achieves finer pitch with minimum probability of bump bridging, reduces the capacitance load for the circuits and allows the electronic component to perform at higher frequencies. However, copper has a tendency to be oxidized during manufacturing processes. The oxidized copper post may lead to poor adhesion of the electronic component to a substrate. The poor adhesion causes serious reliability concerns due to high leakage currents. The oxidized copper post may also lead to underfill cracking along the interface of the underfill and the copper post. The cracks may propagate to low-k layers or the solder used to bonding the copper post to the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned objects, features and advantages of this disclosure will become apparent by referring to the following detailed description of the preferred embodiments with reference to the accompanying drawings, wherein:

FIGS. 1A to 1G are cross-sectional diagram depicting an exemplary embodiment of a Cu post process;

FIG. 2 is a cross-sectional diagram depicting an exemplary embodiment of a Cu post structure;

FIGS. 3A to 3C are cross-sectional diagram depicting an exemplary embodiment of a Cu post process;

FIG. 4 is a cross-sectional diagram depicting an exemplary embodiment of a Cu post structure;

FIGS. 5A to 5C are cross-sectional diagram depicting an exemplary embodiment of a Cu post process;

FIG. 6 is a cross-sectional diagram depicting an exemplary embodiment of a Cu post structure;

FIGS. 7A to 7C are cross-sectional diagram depicting an exemplary embodiment of a Cu post process; and

FIG. 8 is a cross-sectional diagram depicting an exemplary embodiment of a Cu post structure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following description, numerous specific details are set forth to provide a thorough understanding of the disclosure. However, one having an ordinary skill in the art will recognize that the disclosure can be practiced without these specific details. In some instances, well-known structures and processes have not been described in detail to avoid unnecessarily obscuring the disclosure.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be appreciated that the following figures are not drawn to scale; rather, these figures are merely intended for illustration.

This disclosure provides a novel integrated circuit structure formed in a copper interconnect post process and methods of forming the same. Throughout this disclosure, the term “copper (Cu) post” refers to a copper protrusion formed over a bond pad, and/or a copper-containing protrusion formed over an interconnection layer over the bond pad. As used throughout this disclosure, the term “copper” is intended to include substantially pure elemental copper, copper containing unavoidable impurities, and copper alloys containing minor amounts of elements such as tantalum, indium, tin, zinc, manganese, chromium, titanium, germanium, strontium, platinum, magnesium, aluminum or zirconium.

Herein, cross-sectional diagrams of FIG. 1A to FIG. 1G illustrate an exemplary embodiment of a Cu post structure.

In FIG. 1A, an example of a substrate 10 used for Cu post interconnection fabrication may comprise a semiconductor substrate as employed in a semiconductor integrated circuit fabrication, and integrated circuits may be formed therein and/or thereupon. The semiconductor substrate is defined to mean any construction comprising semiconductor materials, including, but is not limited to, bulk silicon, a semiconductor wafer, a silicon-on-insulator (SOI) substrate, or a silicon germanium substrate. Other semiconductor materials including group III, group IV, and group V elements may also be used. The integrated circuits as used herein refer to electronic circuits having multiple individual circuit elements, such as transistors, diodes, resistors, capacitors, inductors, and other active and passive semiconductor devices.

The substrate 10 further includes inter-layer dielectric layers and a metallization structure overlying the integrated circuits. The inter-layer dielectric layers in the metallization structure include low-k dielectric materials, un-doped silicate glass (USG), silicon nitride, silicon oxynitride, or other commonly used materials. The dielectric constants (k value) of the low-k dielectric materials may be less than about 3.9, or less than about 2.8. Metal lines in the metallization structure may be formed of copper or copper alloys. One skilled in the art will realize the formation details of the metallization layers. A conductive region 12 is a top metallization layer formed in a top-level inter-layer dielectric layer, which is a portion of conductive routs and has an exposed surface treated by a planarization process, such as chemical mechanical polishing (CMP), if necessary. Suitable materials for the conductive region 12 may include, but are not limited to, for example copper, aluminum, copper alloy, or other mobile conductive materials. In one embodiment, the conductive region 12 is a bond pad region 12, which may be used in the bonding process to connect the integrated circuits in the respective chip to external features.

FIG. 1A also illustrates a passivation layer 14 formed on the substrate 10 and patterned to form an opening 15 exposing a portion of the conductive region 12. In one embodiment, the passivation layer 14 is formed of a non-organic material selected from un-doped silicate glass (USG), silicon nitride, silicon oxynitride, silicon oxide, and combinations thereof. In another embodiment, the passivation layer 14 is formed of a polymer layer, such as an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), and the like, although other relatively soft, often organic, dielectric materials can also be used.

Referring to FIG. 1B, an adhesion layer 16 and a seed layer 18 are formed and patterned on a portion of the passivation layer 14 and line the sidewalls and bottom of the opening 15. Also, a post-passivation interconnect (PPI) line 22 is formed and patterned on the layers 16 and 18 and fills the opening 15. The adhesion layer 16, also referred to as a glue layer, is blanket formed, covering the passivation layer 14 and the sidewalls and the bottom of opening 15. The adhesion layer 16 may include commonly used barrier materials such as titanium, titanium nitride, tantalum, tantalum nitride, and combinations thereof, and can be formed using physical vapor deposition, sputtering, and the like. The adhesion layer 16 helps to improve the adhesion of the subsequently formed copper lines onto passivation layer 14. The seed layer 18 is blanket formed on the adhesion layer 16. The materials of the seed layer 18 include copper or copper alloys, and metals such as silver, gold, aluminum, and combinations thereof may also be included. The seed layer 18 may also include aluminum or aluminum alloys. In an embodiment, the seed layer 18 is formed of sputtering. In other embodiments, other commonly used methods such as physical vapor deposition or electroless plating may be used. For clarity, the seed layer 18 and the adhesion layer 16 are shown as layers 20 in subsequent drawings.

Using a mask and a photolithography process, a conductive material fills the opening of the mask followed by removing the mask and the exposed layers 20. The conductive material formed on the layer 20 and filling the opening 15 serves as the PPI line 22. The PPI line 22 may include, but not limited to, for example copper, aluminum, copper alloy, or other mobile conductive materials. The PPI line 22 may further include a nickel-containing layer (not shown) on the top a copper-containing layer. The PPI formation methods include plating, electroless plating, sputtering, chemical vapor deposition methods, and the like. The PPI line 22 connects the bond pad region 12 to bump features. The PPI line 22 may also function as power lines, re-distribution lines (RDL), inductors, capacitors or any passive components. The PPI line 22 may have a thickness less than about 30 μm, for example between about 2 μm and about 25 μm. Then the exposed portions of the layers 20 including the adhesion layer 16 and the seed layer 18 are removed. The removal step may include a wet etching process or a dry etching process. In one embodiment, the removal step includes an isotropic wet etching using an ammonia-based acid, which may be a flash etching with a short duration.

Next, in FIG. 1C, a dielectric layer 24, also referred to as an isolation layer or a passivation layer, is formed on the passivation layer 14 and the PPI line 22. The dielectric layer 24 may be formed of dielectric materials such as silicon nitride, silicon carbide, silicon oxynitride or other applicable materials. The formation methods include plasma enhance chemical vapor deposition (PECVD) or other commonly used CVD methods. Then a polymer layer 26 is formed on the dielectric layer 24 through the steps of coating, curing, descum and the like. Lithography technology and etching processes such as a dry etch and/or a wet etch process are then performed to pattern the polymer layer 26 and an opening 27 passing through the polymer layer 26 and the dielectric layer 24, thus exposing a portion of the underlying PPI line 22. The polymer layer 26, as the name suggests, is preferably formed of a polymer, such as an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), and the like, although other relatively soft, often organic, dielectric materials can also be used. In one embodiment, the polymer layer 26 is a polyimide layer. The polymer layer 26 is soft, and hence has the function of reducing inherent stresses on the substrate. In addition, the polymer layer 26 can easily be formed to thickness of tens of microns.

In FIG. 1D, the formation of an under-bump-metallurgy (UBM) layer 28 includes a diffusion barrier layer and a seed layer is performed on the resulted structure. The UBM layer 28 is formed on the polymer layer 26 and the exposed portion of the PPI line 22, and lines the sidewalls and bottom of the opening 27. The diffusion barrier layer, also referred to as a glue layer, is formed to cover the sidewalls and the bottom of the opening 27. The diffusion barrier layer may be formed of tantalum nitride, although it may also be formed of other materials such as titanium nitride, tantalum, titanium, or the like. The formation methods include physical vapor deposition (PVD) or sputtering. The seed layer may be a copper seed layer formed on the diffusion barrier layer. The seed layer may be formed of copper alloys that include silver, chromium, nickel, tin, gold, and combinations thereof. In one embodiment, the UBM layer 28 is a Cu/Ti layer.

Next, a mask layer 30 is provided on the UBM layer 28 and patterned with an opening 32 exposing a portion of the UBM layer 28 for bump formation. The opening 32 is over the opening 27. In one embodiment, the diameter of the opening 32 is greater or equal to the diameter of the opening 27. The mask layer 30 may be a dry film or a photoresist film.

Referring to FIG. 1E, the opening 32 is filled with a Cu alloy layer 34. The formation methods may include sputtering, printing, electro plating, electroless plating, and commonly used chemical vapor deposition (CVD) methods. For example, electro-chemical plating (ECP) is carried out to form the Cu alloy layer 34. In one embodiment, the Cu alloy layer 34 is a copper-manganese (CuMn) layer. The ratio of manganese (Mn) to copper contained in the CuMn layer is not limited. In other embodiments, Ti, Al, Nb, Cr, V, Y, Tc, Re, or the like can be utilized as an additive metal for forming the Cu alloy layer 34.

Next, as shown in FIG. 1F, the mask layer 30 is removed. In the case the mask layer 30 is a dry film, it may be removed using an alkaline solution. If the mask layer 30 is formed of photoresist, it may be removed using acetone, n-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), aminoethoxy ethanol, and the like. Then the exposed portion of the UBM layer 28 is etched to expose the underlying polymer layer 26 outside the Cu alloy layer 34. In an exemplary embodiment, the step of removing the UBM layer 28 is a dry etching or a wet etching. For example, an isotropic wet etching (often referred to as flash etching due to its short duration) using an ammonia-based acid is employed. Thus the Cu alloy layer 34 protrudes from the polymer layer 26.

Thereafter, in FIG. 1G, Using an annealing process 36, the Mn existed in the Cu alloy layer 34 diffuses out from the Cu alloy layer 34, and thus the Cu alloy layer 34 with less Mn refers to a Cu post 34a. The ratio of Mn to copper contained in the Cu post 34a is less than the ratio of Mn to copper contained in the Cu alloy layer 34. Also, the diffused-out Mn reacts with the annealing ambient to form a protection layer 38 in a self-aligned manner at the surface of the Cu post 34a. The protection layer 38 may be formed at the top surface 34t and the sidewall surface 34s of the Cu post 34a. In one embodiment, during an annealing process with NH₃ or N₂/H₂ ambient, the Mn will react with nitrogen to form a manganese nitride (MnN_x) layer as the protection layer 38 in a self-aligned manner at the surface of the Cu post 34a. Alternatively, during the annealing process 36, copper oxidation layer (CuO_x) at the surface of the Cu post 34a is reduced, forming a manganese oxide layer, such as MnO_x or MnO_xN_y as the protection layer 38 in a self-aligned manner at the surface of the Cu post 34a. The protection layer 38 can lower resistance and prevent copper diffusion to enhance back end of the line (BEOL) performance. Moreover, the protection layer can improve the adhesion between the Cu post 34a formed by ECP method and the underlying Cu layer formed by PVD method, and thus the Cu peeling issue can be suppressed. Further, the protection layer 38 formed in a self-aligned manner can prevent openings existed in the dielectric layer adjacent the bottom of the opening, thus solving the contact issue. These can improve package capabilities.

The substrate 10 may then be sawed and packaged onto a package substrate, or another die, with solder balls or Cu posts mounted on a pad on the package substrate or the other die.

FIG. 1F is a cross-sectional diagram illustrating an exemplary embodiment of a Cu post 34a with the surface protection layer 38 formed overlying the PPI line 22 that is electrically connected to the bond pad region 12. FIG. 2 is a cross-sectional diagram illustrating an exemplary embodiment of the Cu post 34a with a surface protection layer 38 overlying and electrically connecting the bond pad region 12, while explanation of the same or similar portions to the description in FIG. 1G will be omitted. As depicted in FIG. 2, the UBM layer 28 is formed on the sidewalls and bottom of the opening 15 in the passivation layer 14, and the Cu post 34a is formed on the UBM layer 28 to fill the opening 15 and protrude from the passivation layer 14. The protection layer 38 is formed in a self-aligned manner on the top surface and the sidewall surface of the Cu post 34a. Thus the Cu post 34a and the UBM layer 28 are formed directly on the bond pad region 12.

FIG. 3A to FIG. 3C are cross-sectional diagrams depicting an exemplary embodiment of a Cu post structure with a cap layer, while explanation of the same or similar portions to the description in FIG. 1A to FIG. 1G will be omitted.

Referring to FIG. 3A, after forming the Cu alloy layer 34 in the opening 32 of the mask layer 30, a cap layer 40 is deposited on the Cu alloy layer 34 within the opening 32. The cap layer 40 could act as a barrier layer to prevent copper in the Cu post 24a to diffuse into bonding material, such as solder ball, that is used to bond the substrate 10 to external features. The prevention of copper diffusion increases the reliability and bonding strength of the package. The cap layer 40 may include nickel, tin, tin-lead (SnPb), gold (Au), silver, palladium (Pd), In, nickel-palladium-gold (NiPdAu), nickel-gold (NiAu), other similar materials, or alloy. In one embodiment, the cap layer 40 is a lead-free pre-solder layer, for example, SnAg. In another embodiment, the cap layer 40 is a solder material including alloys of tin, lead, silver, copper, nickel, bismuth, or combinations thereof. In the other embodiment, the cap layer 40 is a nickel layer, an Au layer, or a NiAu layer. After removing the mask layer 30 and the UBM layer 28 no covered by the Cu alloy layer 34 as depicted in FIG. 3B, the annealing process 36 is performed to form the protection layer 38 in a self-aligned manner at the sidewall surface 34t of the Cu post 34a. The protection layer 38 may be a manganese nitride (MnN_x) layer, or a manganese oxide layer, such as MnO_x or MnO_xN_y.

FIG. 4 is a cross-sectional diagram illustrating an exemplary embodiment of the Cu post 34a with a surface protection layer 38 and a cap layer 40 overlying and electrically connecting the bond pad region 12. The UBM layer 28 is formed on the sidewalls and bottom of the opening 15 in the passivation layer 14, and the Cu post 34a is formed on the UBM layer 28 to fill the opening 15 and protrude from the passivation layer 14. The protection layer 38 is formed in a self-aligned manner on the sidewall surface of the Cu post 34a. The cap layer 40 is formed on the top surface of the Cu post 34a. Thus the Cu post 34a and the UBM layer 28 are formed directly on the bond pad region 12.

FIG. 5A to FIG. 5C are cross-sectional diagrams depicting an exemplary embodiment of a Cu post structure, while explanation of the same or similar portions to the description in FIG. 1A to FIG. 1G will be omitted.

Referring to FIG. 5A, after the formation of the opening 27 in the polymer layer 26 as depicted in FIG. 1C, an under-bump-metallurgy (UBM) layer 28a including a diffusion barrier layer is formed on the resulted structure. The UBM layer 28a is formed on the polymer layer 26 and the exposed portion of the PPI line 22, and lines the sidewalls and bottom of the opening 27. The diffusion barrier layer, also referred to as a glue layer, may be formed of tantalum nitride, although it may also be formed of other materials such as titanium nitride, tantalum, titanium, or the like. In one embodiment, the UBM layer 28a is a Ti layer.

Next, a Cu ally film 29 is deposited on the UBM layer 28a, lining the sidewalls and bottom of the opening 27. The formation methods may include sputtering, printing, electro plating, electroless plating, and commonly used chemical vapor deposition (CVD) methods. In one embodiment, the Cu alloy film 29 is a copper-manganese (CuMn) layer. The ratio of manganese (Mn) to copper contained in the CuMn layer is not limited. In other embodiments, Ti, Al, Nb, Cr, V, Y, Tc, Re, or the like can be utilized as an additive metal for forming the Cu alloy film 29. For example, forming the Cu alloy film 29 with the concentration gradient of the Mn as described above by a physical method, such as sputtering like a PVD (physical vapor deposition), may be considered.

Thereafter, the mask layer 30 with the opening 32 is provided on the Cu alloy film 29, and then a copper deposition process, for example electro-chemical plating (ECP) is carried out to form a Cu layer 42 on the Cu alloy film 29 and fill the opening 32. Thus the underlying bond pad region 12 can be electrically connected to the Cu layer 42. The Cu layer 42 includes substantially pure elemental copper, copper containing unavoidable impurities, and copper alloys containing minor amounts of elements such as tantalum, indium, tin, zinc, manganese, chromium, titanium, germanium, strontium, platinum, magnesium, aluminum or zirconium. In FIG. 5B, the mask layer 30 is removed to make the Cu layer 42 protrude from the polymer layer 26 to become a Cu post 42a. Then the exposed portion of the Cu alloy film 29 and the UBM layer 28a is etched to expose the underlying polymer layer 26.

In FIG. 5C, using an annealing process 36, the Mn existed in the Cu alloy film 29 diffuses out to decrease the Mn ratio to Cu in the Cu alloy film 29. Also, the out-diffused Mn reacts with the annealing ambient to form a protection layer 38 in a self-aligned manner at the surface of the Cu post 42a. In one embodiment, the UBM layer underlying the Cu post 42a becomes an UBM layer 28b including the diffusion barrier layer 28a and a copper layer after the self-aligned protection formation. In other embodiments, Mn may remain in the UBM layer 28b.

The protection layer 38 may be formed at the top surface 42t and the sidewall surface 42s of the Cu post 42a. In one embodiment, during an annealing process with NH₃ or N₂/H₂ ambient, the Mn will react with nitrogen to form a manganese nitride (MnN_x) layer as the protection layer 38 in a self-aligned manner at the surface of the Cu post 42a. Alternatively, during the annealing process 36, copper oxidation layer (CuO_x) at the surface of the Cu post 42a is reduced, forming a manganese oxide layer, such as MnO_x or MnO_xN_y as the protection layer 38 in a self-aligned manner at the surface of the Cu post 42a. The protection layer 38 can lower resistance and prevent copper diffusion to enhance BEOL SPICE performance. Moreover, the protection layer can improve the adhesion between the Cu post 42a formed by ECP method and the underlying Cu layer formed by PVD method, and thus the Cu peeling issue can be suppressed. Further, the protection layer 38 formed in a self-aligned manner can prevent openings existed in the dielectric layer adjacent the bottom of the opening, thus solving the contact issue. These can improve package capabilities.

FIG. 6 is a cross-sectional diagram illustrating an exemplary embodiment of the Cu post 42a with a surface protection layer 38 overlying and electrically connecting the bond pad region 12, while explanation of the same or similar portions to the description in FIG. 5A to FIG. 5C will be omitted.

FIG. 7A to FIG. 7C are cross-sectional diagrams depicting an exemplary embodiment of a Cu post structure with a cap layer, while explanation of the same or similar portions to the description in FIG. 5A to FIG. 5C will be omitted.

Referring to FIG. 7A, after forming the Cu layer 42 in the opening 32 of the mask layer 30, a cap layer 40 is deposited on the Cu layer 42 within the opening 32. The cap layer 40 could act as a barrier layer to prevent copper in the Cu post 42a to diffuse into bonding material, such as solder ball, that is used to bond the substrate 10 to external features. The prevention of copper diffusion increases the reliability and bonding strength of the package. The cap layer 40 may include nickel, tin, tin-lead (SnPb), gold (Au), silver, palladium (Pd), indium (In), nickel-palladium-gold (NiPdAu), nickel-gold (NiAu) or other similar materials or alloy. In one embodiment, the cap layer 40 is a lead-free pre-solder layer, for example, SnAg. In another embodiment, the cap layer 40 is a solder material including alloys of tin, lead, silver, copper, nickel, bismuth, or combinations thereof. In the other embodiment, the cap layer 40 is a nickel layer, an Au layer, or a NiAu layer. After removing the mask layer 30 and the exposed UBM layer 28a and the Cu alloy film 29 as depicted in FIG. 7B, the annealing process 36 is performed to form the protection layer 38 in a self-aligned manner at the sidewall surface 42t of the Cu post 42a. The protection layer 38 may be a manganese nitride (MnN_x) layer, or a manganese oxide layer, such as MnO_x or MnO_xN_y.

FIG. 8 is a cross-sectional diagram illustrating an exemplary embodiment of the Cu post 42a with a surface protection layer 38 and a cap layer 40 overlying and electrically connecting the bond pad region 12.

One aspect of this description relates to a semiconductor device. A semiconductor device includes a copper-containing post overlying and electrically connected to a bond pad region. The semiconductor device further includes a protection layer on a surface of the copper-containing post, where the protection layer includes manganese.

Another aspect of this description relates to another semiconductor device. A semiconductor device includes a copper-containing post overlying and electrically connected to a bond pad region. The semiconductor device further includes a cap layer on a top surface of the copper-containing post, where the cap layer includes at least one of tin, silver, nickel, gold or combinations thereof.

Still another aspect of this description relates to another semiconductor device. A semiconductor device includes a copper-containing post overlying and electrically connected to a substrate. The semiconductor device further includes a protection layer on a surface of the copper-containing post. Additionally, the semiconductor device includes a cap layer on a top surface of the copper-containing post.

In the preceding detailed description, the disclosure is described with reference to specifically exemplary embodiments thereof. It will, however, be evident that various modifications, structures, processes, and changes may be made thereto without departing from the broader spirit and scope of the disclosure, as set forth in the claims. The specification and drawings are, accordingly, to be regarded as illustrative and not restrictive. It is understood that the disclosure is capable of using various other combinations and environments and is capable of changes or modifications within the scope of the inventive concepts as expressed herein.

Claims

1. A semiconductor device, comprising: a copper-containing post overlying and electrically connected to a bond pad region;a protection layer on a surface of the copper-containing post, wherein the protection layer comprises manganese; anda cap layer on a top surface of the copper-containing post, wherein the cap layer is in physical contact with the copper-containing post.

2. The semiconductor device of claim 1, wherein the copper-containing post comprises a top surface and a sidewall surface, wherein the protection layer is on the sidewall surface of the copper-containing post.

3. The semiconductor device of claim 1, wherein the cap layer comprises at least one of tin, silver, nickel, gold or combinations thereof.

4. A semiconductor device, comprising: a copper-containing post overlying and electrically connected to a bond pad region;a cap layer on a top surface of the copper-containing post, wherein the cap layer comprises at least one of tin, silver, or combinations thereof;a protection layer on a sidewall surface of the copper-containing post; andan under bump metallurgy (UBM) layer between the copper-containing post and a semiconductor substrate, wherein an entirety of a top surface of the UBM layer is covered by the copper-containing post.

5. The semiconductor device of claim 4, further comprising an alloy layer between the copper-containing post and a semiconductor substrate, wherein an entirety of a top surface of the alloy layer is covered by the copper-containing post.

6. The semiconductor device of claim 4, wherein the protection layer comprises manganese.

7. The semiconductor device of claim 4, wherein the cap layer comprises lead-free solder.

8. The semiconductor device of claim 4, wherein the cap layer directly contacts a top surface of the copper-containing post.

9. A semiconductor device, comprising: a copper-containing post overlying and electrically connected to a substrate;a protection layer on a surface of the copper-containing post, wherein the protection layer comprises manganese; anda cap layer on a top surface of the copper-containing post, wherein the cap layer is in physical contact with the copper-containing post.

10. The semiconductor device of claim 9, further comprising a bond pad region in the substrate configured to electrically connect the substrate to the copper-containing post.

11. The semiconductor device of claim 10, further comprising a post-passivation interconnect line configured to electrically connect the bond pad region and the copper-containing post.

12. The semiconductor device of claim 9, further comprising an under bump metallurgy (UBM) layer between the substrate and the copper-containing post.

13. The semiconductor device of claim 12, wherein the protection layer covers sidewalls of the copper-containing post and sidewalls of the UBM layer.

14. The semiconductor device of claim 9, wherein the cap layer comprises at least one of nickel, tin, tin-lead, gold, bismuth, silver, palladium, indium, nickel-palladium-gold, or nickel-gold.

15. The semiconductor device of claim 1, wherein the cap layer comprises lead-free solder.

16. The semiconductor device of claim 9, wherein the cap layer comprises lead-free solder.

17. The semiconductor device of claim 1, further comprising a post-passivation interconnect line configured to electrically connect the bond pad region and the copper-containing post.

18. The semiconductor device of claim 1, further comprising a post-passivation interconnect line configured to electrically connect the bond pad region and the copper-containing post.

19. The semiconductor device of claim 1, further comprising an under bump metallurgy (UBM) layer between the copper-containing post and a substrate, wherein an entirety of a top surface of the UBM layer is covered by the copper-containing post.

20. The semiconductor device of claim 4, wherein the protection layer covers sidewalls of the copper-containing post.