Front side copper post joint structure for temporary bond in TSV application

Abstract

An integrated circuit structure includes a semiconductor substrate; a conductive via (TSV) passing through the semiconductor substrate; and a copper-containing post overlying the semiconductor substrate and electrically connected to the conductive via.

Description

TECHNICAL FIELD

This disclosure relates generally to integrated circuit structures, and more particularly to interconnect structures in the integrated circuit structures.

BACKGROUND

Since the manufacturing of integrated circuits, the semiconductor industry has experienced continuous rapid growth due to constant improvements in the integration density of various electronic components (i.e., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from repeated reductions in minimum feature size, allowing more components to be integrated into a given chip area.

These integration improvements are essentially two-dimensional (2D) in nature, in that the volume occupied by the integrated components is essentially on the surface of the semiconductor wafer. Although dramatic improvements in lithography have resulted in considerable improvements in 2D integrated circuit formation, there are physical limitations to the density that can be achieved in two dimensions. One of these limitations is the minimum size needed to make these components. Also, when more devices are put into one chip, more complex designs are required.

An additional limitation comes from the significant increase in the number and lengths of interconnections between devices as the number of devices increases. When the number and the lengths of interconnections increase, both circuit RC delay and power consumption increase.

Among the efforts for resolving the above-discussed limitations, three-dimensional integrated circuits (3D ICs) and stacked dies are commonly used. Through-substrate vias (TSVs) are thus used in 3D ICs and stacked dies for connecting dies. In this case, TSVs are often used to connect the integrated circuits on a die to the backside of the die. In addition, TSVs are also used to provide short grounding paths for grounding the integrated circuits through the backside of the die, which may be covered by a grounded metallic film.

SUMMARY

In accordance with one aspect of the embodiment, an integrated circuit structure includes a semiconductor substrate; a conductive via (TSV) passing through the semiconductor substrate; and a copper-containing post overlying the semiconductor substrate and electrically connected to the conductive via.

Other embodiments are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIGS. 1 through 9 are cross-sectional views of intermediate stages in the manufacturing of a front side interconnect structure in accordance with an embodiment; and

FIGS. 10 through 19B are cross-sectional views of intermediate stages in the manufacturing of a front side interconnect structure in accordance with another embodiment, wherein a post-passivation interconnect (PPI) is formed.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the embodiments, and do not limit the scope of the embodiments.

A novel interconnect structure and the method of forming the same are presented in accordance with an embodiment. The intermediate stages of manufacturing the embodiment are illustrated. The variations of the embodiment are then discussed. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.

Referring to FIG. 1, wafer 2, which includes substrate 10, is provided. Wafer 2 has a front side (facing up) and a backside. Substrate 10 is a semiconductor substrate such as a bulk silicon substrate, although it may include other semiconductor materials such as group III, group IV, and/or group V elements. Semiconductor devices 14, such as transistors, may be formed at the front surface/side 10a (the surface 10a facing up in FIG. 1) of substrate 10. Interconnect structure 12, which includes metal lines and vias (not shown) formed therein, is formed under substrate 10 and may be connected to semiconductor devices 14. The metal lines and vias may be formed of copper or copper alloys, and may be formed using the well-known damascene processes. Interconnect structure 12 may include commonly known inter-layer dielectric (ILD) and inter-metal dielectrics (IMDs).

Through-substrate via (TSV) 20 extends from front surface 10a of substrate 10 into substrate 10. In a first embodiment, TSV 20 is formed using a via-first approach, and is formed before the formation of interconnect structure 12. Accordingly, TSV 20 only extends to the ILD that is used to cover the active devices, but not into the IMD layers in interconnect structure 12. In alternative embodiments, TSV 20 is formed using a via-last approach, and is formed after the formation of interconnect structure 12. Accordingly, TSV 20 penetrates into both substrate 10 and interconnect structure 12. Isolation layer 22 is formed on the sidewalls and bottom of TSV 20, and electrically insulates TSV 20 from substrate 10. Isolation layer 22 may be formed of commonly used dielectric materials such as silicon nitride, silicon oxide (for example, tetra-ethyl-ortho-silicate (TEOS) oxide), and the like.

Passivation layers 24 and 26 are formed over interconnect structure 12. Passivation layers 24 and 26 are commonly referred to in the art as being passivation-1 and passivation-2, respectively, and may be formed of materials such as silicon oxide, silicon nitride, un-doped silicate glass (USG), polyimide, and/or multi-layers thereof. Metal pad 28 is formed over passivation layer 24. Metal pad 28 may be formed of aluminum, and hence may also be referred to as aluminum pad 28, although it may also be formed of, or include, other materials such as copper, silver, gold, nickel, tungsten, alloys thereof, and/or multi-layers thereof. Metal pad 28 may be electrically connected to semiconductor devices 14, for example, through underlying interconnection structure 12. Opening 32 is formed in passivation layer 26, with metal pad 28 exposed through opening 32.

Referring to FIG. 2, dielectric buffer layer 30, which may be formed of polyimide, is formed. Dielectric buffer layer 30 is patterned to form an additional opening in opening 32, so that metal pad 28 is exposed through opening 32 and the additional opening in dielectric buffer layer 30.

Referring to FIG. 3, an under-bump metallurgy (UBM) 34, is formed. The usable materials of UBM 34 include a diffusion barrier layer, a seed layer, or a combination thereof. The diffusion barrier layer may include Ti, TiN, Ta, TaN, or combinations thereof. The seed layer may include copper or copper alloys. However, other metals, such as nickel, palladium, silver, gold, aluminum, combinations thereof, and multi-layers thereof, may also be included. In an embodiment, UBM 34 is formed using sputtering. In other embodiments, electro plating may be used.

FIG. 4 illustrates the formation of mask 38. In an embodiment, mask 38 is a dry film, which may include an organic material such as Ajinimoto buildup film (ABF). Alternatively, mask 38 is formed of photo resist. Mask 38 is then patterned to form opening 40, wherein metal pad 28 is under opening 40.

In FIG. 5, opening 40 is filled selectively with a metallic material, forming metal post 44 in opening 40. In an embodiment, the filling material includes copper or copper alloys, and hence metal post 44 is also referred to as copper post 44, although other metals, such as aluminum, silver, gold, and combinations thereof, may also be used. Copper post 44 may have a thickness less than about 60 μm, or even between about 30 μm and about 50 μm. The edge of the copper post may be vertical, or in other words, perpendicular to the top surface of semiconductor substrate 10. Next, conductive barrier layer 46, which may be formed of a nickel-containing layer, a copper-containing layer, or a tin-containing layer, is formed. Solder 48, which may comprise a lead-free solder or a eutectic solder, is then formed. Solder 48 may have a thickness less than about 15 μm. The formation methods of copper post 44, conductive barrier layer 46, and solder 48 include electro-chemical plating (ECP), electroless plating, or other commonly used deposition methods such as sputtering, printing, and chemical vapor deposition (CVD) methods. The top surface of solder 48 may be lower than the top surface of mask 38, so that the edges of copper post 44, conductive barrier layer 46, and solder 48 are vertically aligned, and the edges of solder 48 do not extend beyond the edges of copper post 44.

Next, as shown in FIG. 6, mask 38 is removed. As a result, the portions of UBM 34 underlying mask 38 are exposed. Referring to FIG. 7, the exposed portions of UBM 34 are removed by a flash etching. A re-flow is then performed, as shown in FIG. 8A, so that solder 48 forms a rounded top surface. In an embodiment, as shown in FIG. 8C, an intermetallic compound (IMC) layer 49 is formed between the copper post 44 and the reflowed solder 48. The IMC layer 49 may be formed between the conductive barrier layer 46 and the reflowed solder 48, in which the conductive barrier layer 46 may be partially or entirely consumed.

Conductive barrier layer 46 and solder 48 as shown in FIG. 8A may also be replaced with a metal finish. Referring to FIG. 8B, after the formation of copper post 44, mask 38 is formed. After the removal of mask 38, metal finish 60 is formed. The formation methods of metal finish 60 include electro-chemical plating (ECP), electroless plating, and the like. In an embodiment, metal finish 60 includes tin formed of immersion. In other embodiments, metal finish 60 includes electroless nickel immersion gold (ENIG). In yet other embodiments, metal finish 60 include nickel palladium. In yet other embodiments, metal finish 60 includes electroless palladium immersion gold (ENEPIG).

In FIG. 9, wafer 2 is mounted onto carrier wafer 50 through adhesive 52. Carrier wafer 50 may be a glass wafer. It is observed that the combined thickness of copper post 44, conductive barrier layer 46, and solder 48 may be only between about 25 μm and about 60 μm. This combined thickness is within the achievable range of the thickness of adhesive 52. Adhesive 52 may thus fully fill in the gap between carrier wafer 50 and wafer 2 without generating voids. As a result, in subsequent backside grinding and interconnect formation processes, adhesive 52 may provide maximum protection to the structure inside wafer 2.

In subsequent process steps, the backside 10b of substrate 10 is grinded, and a backside interconnect structure is formed. For an example, the details of the backside grinding and the interconnect structure formation are provided in the co-pending U.S. patent applications: application Ser. No. 12/332,934, filed Dec. 11, 2008, and entitled “Backside Connection to TSVs Having Redistribution Lines;” and application Ser. No. 12/347,742, and entitled “Bond Pad Connection to Redistribution Lines Having Tapered Profiles,” which applications are hereby incorporated herein by reference. The details are thus not repeated herein. After the formation of the backside interconnect structure, and possibly after the bonding of wafer 2 to another wafer, carrier wafer 50 may be demounted from wafer 2, followed by the removal of adhesive 52.

FIGS. 10 through 19B illustrate an alternative embodiment, in which post-passivation interconnect (PPI) is formed. Referring to FIG. 10, the metal lines and vias in interconnect structure 12 are illustrated. Interconnect structure 12 may include top via 61, which is exposed through the respective dielectric layer. Top via 61 may be formed in a passivation layer, which may be essentially the same as passivation layers 24 and 26 as shown in FIG. 9. Next, as shown in FIG. 11, seed layer 62 is formed. Seed layer 62 may be formed of essentially the same material as UBM 34 as shown in FIG. 3.

Referring to FIG. 12, mask 64 is formed, for example, using a dry film or a photo resist. In FIG. 13, PPIs 66 and 68 are formed. PPI 66 may include a metal pad, while PPI 68 may be a metal line used for routing signals. PPI 66 is connected to metal finish 60. Again, PPI 66 may be formed of copper, although other metals such as aluminum, silver, tungsten, and the like, may be used or added. The formation methods include electro or electroless plating.

In FIG. 14, mask 64 is removed, followed by the removal of exposed portion of UBM 34. Since UBM 34 may be formed of essentially the same material as that of PPIs 66 and 68, UBM 34 appears to be merged into PPIs 66 and 68, and hence the remaining portions of UBM 34 are not shown hereinafter.

In subsequent process steps, as shown in FIGS. 15 through 19B, copper post 44, conductive barrier layer 46, and solder 48 are formed. The brief process is discussed herein, while the details may be essentially the same as in the process steps shown in FIGS. 3 through 8A. Unless specified otherwise, like elements in FIGS. 15 through 19B and in FIGS. 3 through 8A are denoted using like reference numerals. As shown in FIG. 15, dielectric buffer layer 30, which may be formed of polyimide, is formed. Opening 32 is formed in dielectric buffer layer 30 and exposing PPI 66. In FIG. 16, UBM 34 is formed. In FIG. 17, mask 38 is formed. Copper post 44, conductive barrier layer 46, and solder 48 are then formed, as shown in FIG. 18. FIG. 19A illustrates the removal of mask 38 and the exposed portion of UBM 34. FIG. 19B illustrates an alternative embodiment, in which metal finish 60 replaces conductive barrier layer 46 and solder 48.

The embodiments have several advantageous features. By forming copper posts instead of solder bumps, the thickness of the copper post may be well controlled, and can be lower than the feasible thickness of the adhesive for bonding the wafer to a carrier wafer. As a result, the internal structure in the wafer may be better protected. Further, since the copper post, the overlying solder, and the metal finish do not extend significantly sideways, it is easier to control the pitch between neighboring copper posts to less than about 150 μm. As a comparison, in existing integrated circuit structures, since solder bumps are used, the bump pitch needs to be greater than about 150 μm to avoid the shorting between neighboring solder bumps.

Although the embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. In addition, each claim constitutes a separate embodiment, and the combination of various claims and embodiments are within the scope of the embodiments.

Claims

1. An integrated circuit structure comprising: a semiconductor substrate;a conductive via (TSV) passing through the semiconductor substrate;an interconnect structure overlying the semiconductor substrate;a metal pad directly overlying the interconnect structure;a first polyimide layer overlying the metal pad;a second polyimide layer comprising a portion level with the interconnect structure, wherein the metal pad extends into the second polyimide layer and contacts the interconnect structure;an under-bump-metallurgy (UBM) directly coupled to the metal pad;a dielectric buffer layer between the first polyimide layer and the UBM, wherein the dielectric buffer layer comprises a first portion contacting the metal pad and a second portion over and separated from the metal pad; anda copper-containing post overlying the UBM layer, wherein the copper post is electrically connected to the conductive via.

2. The integrated circuit structure of claim 1 further comprising: a conductive barrier over the copper-containing post; anda solder over the conductive barrier.

3. The integrated circuit structure of claim 1 further comprising a metallic layer on the copper-containing post, wherein the metallic layer comprises a first portion directly over the copper-containing post, and a second portion on a sidewall of the copper-containing post.

4. The integrated circuit structure of claim 1, wherein the metal pad is connected to the UBM through a conductive feature in the dielectric buffer layer.

5. The integrated circuit structure of claim 1, wherein the copper-containing post has a thickness less than about 60 μm.

6. An integrated circuit structure comprising: a semiconductor substrate;a conductive via extending from a front surface to a back surface of the semiconductor substrate;an interconnect structure overlying the front surface of the semiconductor substrate, wherein the interconnect structure comprises copper;an aluminum-containing pad overlying the semiconductor substrate;a first polyimide layer over the aluminum-containing pad;a second polyimide layer overlying the interconnect structure, the second polyimide layer having an upper surface coplanar with an upper surface of the aluminum-containing pad;an under-bump-metallurgy (UBM) over and connected to the aluminum-containing pad;a dielectric buffer layer between the first polyimide layer and the UBM, wherein the dielectric buffer layer comprises a first portion contacting the aluminum-containing pad and a second portion over and separated from the aluminum-containing pad; anda copper-containing post overlying the front surface of the semiconductor substrate and electrically connected to the conductive via and the interconnect structure.

7. The integrated circuit structure of claim 6, wherein a thickness of the copper-containing post is between about 55 μm and about 30 μm.

8. The integrated circuit structure of claim 6, wherein the UBM comprises an extension extending into the first polyimide layer and electrically connected to the aluminum-containing pad.

9. The integrated circuit structure of claim 6 further comprising: a conductive barrier over the copper-containing post; anda solder over the conductive barrier.

10. The integrated circuit structure of claim 6 further comprising a metal finish on the copper-containing post, wherein the metal finish comprises a first portion directly over the copper-containing post, and a second portion on a sidewall of the copper-containing post.

11. The integrated circuit structure of claim 10, wherein the metal finish comprises a metal selected from the group consisting essentially of tin, nickel, palladium, gold, and combinations thereof.

12. An integrated circuit structure comprising: a semiconductor substrate;a conductive via extending from a front surface to a back surface of the semiconductor substrate;an interconnect structure overlying the semiconductor substrate;a metal pad directly overlying the interconnect structure;an under-bump-metallurgy (UBM) directly coupled to the metal pad;a pair of polyimide layers overlying the interconnect structure;a dielectric buffer layer between the UBM and an uppermost layer of the pair of polyimide layers, wherein the dielectric buffer layer comprises a first portion contacting the metal pad and a second portion over the metal pad;a copper-containing post over the UBM layer, wherein the copper post is electrically connected to the conductive via; anda conductive barrier over the copper-containing post, wherein the conductive barrier, the copper-containing post, and the conductive via are electrically connected.

13. The integrated circuit structure of claim 12, wherein the UBM comprising a first portion coupled to the metal pad, and a second portion over the second portion of the dielectric buffer layer.

14. The integrated circuit structure of claim 12 further comprising a solder over the conductive barrier.