# Patent

## Title
Wafer backside interconnect structure connected to TSVs

## Abstract

An integrated circuit structure includes a semiconductor substrate having a front surface and a back surface; a conductive via passing through the semiconductor substrate; and a metal feature on the back surface of the semiconductor substrate. The metal feature includes a metal pad overlying and contacting the conductive via, and a metal line over the conductive via. The metal line includes a dual damascene structure. The integrated circuit structure further includes a bump overlying the metal line.

## Background
This application is a continuation of U.S. Ser. No. 12/832,019, filed Jul. 7, 2010 which claims the benefit of U.S. Provisional Application No. 61/244,773 filed on Sep. 22, 2009, entitled “Wafer Backside Interconnect Structure Connected to TSVs,” which applications are hereby incorporated herein by reference.


TECHNICAL FIELD
This disclosure relates generally to integrated circuit structures, and more particularly to interconnect structures formed on the backside of wafers and connected to through-substrate vias.
BACKGROUND
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 circuit (3D IC) 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.
Since the bonding of chips comprising TSVs requires relatively large pitch between TSVs, the location of the TSVs is restricted and the distance between the TSVs needs to be big enough to allow room for, for example, solder balls. In addition, with the existing methods for forming wafer backside structures, it is impossible to route the electrical connection of TSVs to locations far away from the respective TSVs.
SUMMARY
In accordance with one aspect of the embodiment, an integrated circuit structure includes a semiconductor substrate having a front surface and a back surface; a conductive via passing through the semiconductor substrate; and a metal feature on the back surface of the semiconductor substrate. The metal feature includes a metal pad overlying and contacting the conductive via, and a metal line over the conductive via. The metal line includes a dual damascene structure. The integrated circuit structure further includes a bump overlying the metal line.
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 12B illustrate cross-sectional views of intermediate stages in the manufacturing of a backside interconnect structure in accordance with an embodiment, in which the back surface of a substrate and a through-substrate via (TSV) are recessed;
FIGS. 13 through 23B illustrate cross-sectional views of intermediate stages in the manufacturing of a backside interconnect structure in accordance with another embodiment, in which the back surface of a substrate is recessed; and
FIGS. 24 through 29B illustrate cross-sectional views of intermediate stages in the manufacturing of a backside interconnect structure in accordance with yet another embodiment, in which the backside interconnect are formed on the back surface of a substrate.



DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The making and using of the embodiments of the disclosure 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 invention, and do not limit the scope of the invention.
A novel backside connection structure connected to through-substrate vias (TSVs) and the method of forming the same are provided. The intermediate stages of manufacturing an embodiment are illustrated. The variations of the embodiment are discussed. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.
Referring to FIG. 1, chip 2, which includes substrate 10 and integrated circuits (not shown) therein, is provided. Chip 2 may be a portion of a wafer. Substrate 10 may be 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. Active semiconductor devices such as transistors (symbolized by block 15) may be formed on front side 10f of substrate 10. Throughout the description, the term “backside” refers to the side of substrate 10 opposite the side having the active semiconductor devices. Interconnect structure 12, which includes metal lines and vias (not shown) formed therein, is formed on front side 10f of substrate 10 and connected to the active semiconductor devices. 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). Bond pad 14 is formed on the front side 10f of substrate 10.
TSV 20 is formed in substrate 10, and extends from the front side 10f into substrate 10. In an embodiment, as shown in FIG. 1, 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 through both substrate 10 and interconnect structure 12. Isolation layer 22 is formed on the sidewalls and an end 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. Chip 2 and the corresponding wafer is adhered to carrier 25.
Referring to FIG. 2, a backside grinding is performed so that TSV 20 is exposed through the back surface 10b of substrate 10. The backside grinding may be performed using TSV 20 as a stop layer. Next, as shown in FIG. 3, TSV 20 is recessed, so that it's top surface is lower than the back surface 10b of substrate 10. The recess depth D1 may be greater than about 0.5 μm, and may be 3 μm in an exemplary embodiment. As a result of the recessing, opening 24 is formed.
FIG. 4 illustrates the recessing of substrate 10, which is performed using photo resist 26 as a mask. As a result of the recessing, the horizontal dimension of opening 24 is increased to greater than that of TSV 20. Although, FIG. 3 illustrates that in opening 24 lower portion 28 of back surface 10b is level with the exposed end of TSV 20. Alternatively, lower portion 28 may also be higher than or lower than the exposed end of TSV 20, as also illustrated by dotted lines. At the same time opening 24 is formed, (trench) openings 27 are also formed.
Referring to FIG. 5, dielectric isolation layer 30 is deposited. The deposition methods include low-temperature chemical vapor deposition (LTCVD), although other commonly used methods may also be used. In an exemplary embodiment, dielectric isolation layer 30 comprises silicon nitride (SiNx), and may have a thickness of a several hundred angstroms. Next, as shown in FIG. 6, a portion of the dielectric isolation layer 30 overlying the end of the TSV 20 is exposed in a via opening 33 by applying photo resist 31 and performing photolithography processes, so that the subsequently formed bump may be electrically connected to TSV 20.
FIGS. 7 through 9 illustrate the formation of redistribution lines and pads. Referring to FIG. 7, conductive barrier layer 32, which may comprise titanium, titanium nitride, tantalum, tantalum nitride, or the like, is formed, for example, by sputtering. Copper 34 is then plated, as shown in FIG. 8. The thickness of copper 34 depends on depth D1 (FIG. 3). A chemical mechanical polish (CMP) is then performed to form metal features 36 (denoted as 36-1 and 36-2), and the resulting structure is shown in FIG. 9. Metal features 36 may include metal lines 36-1, which may actually be connected to other TSVs (not shown). Accordingly, metal lines 36-1 are used as redistribution lines. Metal feature 36-2 may be a metal pad or a metal line. The metal pad may have dimensions (viewed from top) greater than that of TSV 20, and the metal pad may extend beyond the edges of TSV 20 in all horizontal directions. Accordingly, metal pad 36-2 and TSV 20 have a reliable connection with a large interface area, and hence a small contact resistance. Further, the accuracy requirement for aligning metal pad 36-2 to TSV 20 is relaxed.
FIGS. 10-12A illustrate the formation of bump 42. Referring to FIG. 10, dielectric layer 38 is blanket deposited. In an exemplary embodiment, dielectric layer 38 comprises silicon nitride (SiNx), and may have a thickness, for example, of about 0.2 μm. Next, as shown in FIG. 11, with photo resist 40, an opening is formed in dielectric layer 38 so that metal pad 36-2 is exposed. FIG. 12A illustrates the formation of bump 42, which is also referred to as a micro-bump (U-bump) since is may have a horizontal dimension (length or width) of less than about 30 μm. The formation methods of bump 42 include electrical chemical plating (ECP), electroless plating, and immersion. The resulting bump 42 may have an electroless nickel immersion gold (ENIG) structure, a nickel electroless palladium immersion gold (ENEPIG) structure, or a nick palladium structure. It is realized that although FIG. 12A illustrates that bump 42 is directly over metal pad 36-2, bump 42 may also be not directly over metal pad 36-2, and may actually be connected to metal pad 36-2 through a redistribution line similar to metal lines 36-1, which redistribution lines are formed simultaneously with the formation of metal features 36.
FIG. 12B illustrates an alternative embodiment. Instead of forming bump 42 directly on metal pad 36-2, additional layers of redistribution lines may be formed. For example, an additional layer 60 including etch stop layer 46, dielectric layer 48, via 50, and metal line 52 may be inserted between metal pad 36-2 and bump 42. If needed, more layers similar to layer 60 may be stacked on layer 60 to increase the routability of the backside interconnect structure. The formation details of layer 60 may be essentially the same as shown in FIGS. 18-21, as will be discussed in subsequent paragraphs.
FIGS. 13 through 23B illustrate an alternative embodiment. The initial steps of this embodiment are the same as illustrated in FIGS. 1 and 2. Next. Referring to FIG. 13, substrate 10 is etched back from the backside, so that TSV 20 protrudes out of the back surface of substrate 10. In an exemplary embodiment, the etch back depth D2 is greater than about 0.5 μm, and may be about 1 μm. Isolation layer 22 may also be etched back from the top surface of TSV 20, for example, to about 0.5 μm lower than the top surface of TSV 20. Accordingly, portions of sidewalls of TSV 20 are exposed.
Referring to FIG. 14, dielectric layer 124 is formed on the back surface of substrate 10 and covers TSV 20. In an embodiment, dielectric layer 124 is formed of polyimide, and may have a thickness greater than about 2 μm, with an exemplary thickness equal to about 3 μm. In alternative embodiments, other dielectric materials may be used.
FIGS. 15 through 17 illustrate the formation of metal lines. Referring to FIG. 15, openings 126 are formed by etching dielectric layer 124, for example, with the help of a photo resist (not shown). In an embodiment, the opening formation process is controlled, for example, using a time mode, so that TSV 20 is exposed through one of openings 126, while a bottom portion of dielectric layer 124 (denoted as layer 124′) remains to separate openings 126 from substrate 10.
Referring to FIG. 16, a pre-clean is performed, and conductive barrier layer 128 is deposited, for example, by sputtering. Conductive barrier layer 128 may comprise titanium, tantalum, or the like. Metallic material 130 is then plated to a level higher than the top surface of dielectric layer 124. Metallic material 130 may include copper, although other metals such as aluminum, tungsten, or the like, may also be used. A CMP is then performed, as shown in FIG. 17, and hence metal lines/pads 132 (denoted as 132-1 and 132-2) are formed. Metal line 132-2 may be electrically connected to one of the TSVs in the chip. Accordingly, metal line 132-2 may be used as a redistribution line. Metal feature 132-1 may be a metal pad or a metal trace. The metal pad may have dimensions (viewed from top) greater than that of TSV 20, wherein in the top view, metal pad 132-1 may extend beyond the edges of TSV 20 in all lateral directions.
FIGS. 18 through 21 illustrate the formation of an additional layer of interconnect. Referring to FIG. 18, dielectric layer 125 is formed. In an embodiment, dielectric layer 125 is formed of polyimide, which may have a thickness of several microns such as about 2.5 μm. Photo resist 134 is then applied and patterned. Via openings 136 are then formed by etching dielectric layer 125 through patterned photo resist 134, until metal line 132-2 is exposed.
Referring to FIG. 19, photo resist 134 is removed, and an additional photo resist 140 is formed and patterned. Trench openings 138 are then formed by further etching dielectric layer 125 through patterned photo resist 140, as illustrated in FIG. 20. The etching may be performed using a time mode, so that the etching is stopped at an intermediate level of dielectric layer 125. Photo resist 140 is then removed, for example, by ashing. It is realized that the steps shown in FIGS. 18 through 20 are a via-first approach, in which via openings 136 are formed before the formation of trench openings 138. One skilled in the art will realize that the structure shown in FIG. 20 may be formed using a trench-first approach, in which the steps shown in FIGS. 19 and 20 may be performed before the step shown in FIG. 18.
FIG. 21 illustrates the formation of damascene structures including metal lines 144 and vias 146, which may include depositing conductive barrier layer 148 (for example, a Ti layer), plating copper, and performing a CMP to remove excess copper. FIGS. 22 through 23A illustrate the formation of dielectric layer 40 and bump 42. The formation processes may be essentially the same as described in the preceding embodiment, and hence are not repeated herein. FIG. 23B illustrates an alternative embodiment, wherein metal lines 144 and vias 146 are formed in dielectric layer 124.
FIGS. 24 through 29B illustrate yet another embodiment. The initial steps of this embodiment are the same as shown in FIGS. 1 and 2. Next, as shown in FIG. 24, etch stop layer 220 is formed. In an embodiment, etch stop layer 220 is formed of silicon nitride, and may have a thickness, for example, of about 750 Å. Dielectric layer 222 is then formed on etch stop layer 220. In an embodiment, dielectric layer 222 is formed using one of various chemical vapor deposition (CVD) methods, and may comprise, for example, an oxide. The thickness of the CVD dielectric layer 222 may be, for example, about 8 K Å. In alternative embodiments, dielectric layer 222 may be formed of polyimide, and hence may have a significantly greater thickness than what is formed using CVD. The thickness of dielectric layer 222 formed of polyimide may be greater than about 2 μm, and may be about 5 μm in an exemplary embodiment.
FIGS. 25 through 27 illustrate the formation of via opening 226 and trench openings 228. The formation details are essentially the same as illustrated in FIGS. 18 through 20, and hence are not repeated herein. Next, as shown in FIG. 28, a dual damascene structure including vias 232 and overlying metal lines 234, which may be formed of copper, are formed. Conductive barrier layers 236 are also formed.
FIG. 29A illustrates the formation of dielectric layer 40 and bump 42. The materials and the formation processes of dielectric layer 40 and bump 42 may be essentially the same as illustrated in FIGS. 10-12A. FIG. 29B illustrates an alternative embodiment with an additional layer of interconnection (60), which includes additional dual damascene structures. If necessary, more interconnection layers may be inserted.
The embodiments have several advantageous features. By forming backside interconnect structures using dual damascene processes, multiple interconnect layers may be stacked to provide a great routing ability. By recessing substrates to form metal pads (36-2 in FIGS. 10 and 132-1 in FIG. 17) to contact TSVs, the metal pads may have great sizes, so that the accuracy requirement in the alignment of the metal pads to TSVs is relaxed. Further, the metal pads and the underlying TSVs have large contact areas, and hence the contact resistances are reduced.
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 invention 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 of the present invention, 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 present invention. 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 invention.

## Claims

1. A method for forming an integrated circuit structure, the method comprising:
providing a semiconductor substrate having an active semiconductor device formed on a first side of the semiconductor substrate;
forming a conductive via passing through the semiconductor substrate; and
forming a metal feature on a second side of the semiconductor substrate opposing the first side of the semiconductor substrate, the metal feature comprising:
a metal pad overlying the conductive via in a first dielectric layer, wherein the metal pad contacts the conductive via, and wherein the conductive via is at least partially disposed in the first dielectric layer; and
a metal line higher than the conductive via, relative the second side of the semiconductor substrate, wherein the metal line comprises a dual damascene structure.

2. The method of claim 1 further comprising forming a metal bump overlying the metal line relative the second side of the semiconductor substrate.

3. The method of claim 1, wherein forming the metal feature comprises forming the metal line in the first dielectric layer.

4. The method of claim 1, wherein forming the metal feature comprises:
forming the first dielectric layer over the semiconductor substrate relative the second side of the semiconductor substrate;
forming the metal pad in the first dielectric layer;
forming a second dielectric layer over the first dielectric layer relative the second side of the semiconductor substrate; and
forming the metal line in the second dielectric layer.

5. The method of claim 1, wherein forming the metal feature comprises forming a conductive barrier layer on sidewalls and a bottom surface of the metal pad relative the second side of the semiconductor substrate.

6. The method of claim 1, wherein forming the metal feature comprises:
patterning a via opening extending through in a dielectric layer;
patterning a trench opening in the dielectric layer, wherein the trench opening is connected to and has a greater horizontal dimension than the via opening, and wherein the trench opening does not extend through the dielectric layer; and
filling the via opening and the trench opening with a metal to form the metal line.

7. A method for forming an integrated circuit structure, the method comprising:
providing a semiconductor substrate having a front surface and a back surface opposite the front surface;
forming an active device at the front surface of the semiconductor substrate;
forming a conductive via extending at least partially through the semiconductor substrate;
etching back the back surface of the semiconductor substrate to expose a sidewall of the conductive via;
forming a dielectric layer over the back surface of the semiconductor substrate and along a sidewall of the conductive via;
forming a first metal feature in the dielectric layer and electrically connected to the conductive via, wherein the first metal feature extends past edges of the conductive via in all horizontal directions; and
forming a second metal feature over the semiconductor substrate relative the back surface, wherein the second metal feature comprises a dual damascene structure.

8. The method of claim 7, wherein the first metal feature is disposed in a dielectric layer, and wherein the method further comprises forming an etch stop layer between the dielectric layer and the semiconductor substrate.

9. The method of claim 7, wherein forming the second metal feature comprises forming the second metal feature in a same dielectric layer as the first metal feature.

10. The method of claim 7, wherein forming the second metal feature comprises forming the second metal feature in a different dielectric layer as the first metal feature.

11. The method of claim 1, further comprising:
etching back the second side of the semiconductor substrate to expose sidewalls of a portion of the conductive via; and
forming the first dielectric layer over the second side of the semiconductor substrate, wherein the first dielectric layer extends along the sidewalls of the portion of the conductive via.

12. The method of claim 11, wherein forming the metal feature comprises:
patterning a pad opening in the first dielectric layer to expose the portion of the conductive via; and
forming the metal pad in the pad opening.

13. The method of claim 11 further comprising an isolation layer on a sidewall of the conductive via below a top surface of the portion of the conductive via.

14. The method of claim 1, wherein a bottom surface of a via portion of the metal line is substantially level with a bottom surface of the metal pad.

15. A method comprising:
forming a conductive via extending through a semiconductor substrate;
etching the semiconductor substrate so that the conductive via extends above a first surface of the semiconductor substrate;
depositing a dielectric layer over the first surface of the semiconductor substrate, wherein the dielectric layer extends along a sidewall of the conductive via;
patterning the dielectric layer to define a pad opening extending through the dielectric layer and exposing the conductive via, wherein the pad opening is wider than the conductive via; and
forming a conductive pad in the pad opening.

16. The method of claim 15, wherein patterning the pad opening comprises exposing the sidewall of the conductive via, and wherein the conductive pad extends partially along the sidewall of the conductive via.

17. The method of claim 15 further comprising forming a conductive feature in the dielectric layer adjacent the conductive pad, wherein the conductive feature comprises a dual damascene structure.

18. The method of claim 15 further comprising a conductive feature in a second dielectric layer over the dielectric layer, wherein the conductive feature comprises a dual damascene structure.

19. The method of claim 15 further comprising:
forming an isolation layer on sidewalls of the conductive via; and
recessing the isolation layer below a top surface of the conductive via.