# Patent

## Title
Microfeature workpieces having interconnects and conductive backplanes, and associated systems and methods

## Abstract

Microfeature workpieces having interconnects and conductive backplanes and associated systems and methods are disclosed herein. One such device includes a semiconductor substrate having integrated circuitry and terminals electrically coupled to the integrated circuitry. The device also includes electrically conductive interconnects extending through at least a portion of the semiconductor substrate and electrically coupled to corresponding terminals. The device further includes a conductive backplane assembly having a conductive layer at a back side of the semiconductor substrate. One or more of the interconnects are electrically coupled to the conductive layer at the back side of the semiconductor substrate.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application is a divisional of U.S. application Ser. No. 11/514,568 filed Aug. 31, 2006, now U.S. Pat. No. 7,902,643, which is incorporated herein by reference in its entirety.


TECHNICAL FIELD
The present disclosure is directed generally toward microfeature workpieces having interconnects and conductive backplanes, and associated systems and methods.
BACKGROUND
Processors, memory devices, imagers and other types of microelectronic devices are often manufactured on semiconductor workpieces or other types of workpieces. In a typical application, several individual dies (e.g., devices) are fabricated on a single workpiece using sophisticated and expensive equipment and processes. Individual dies generally include an integrated circuit and a plurality of bond-pads coupled to the integrated circuit. The bond-pads provide external electrical contacts on the die through which supply voltage, signals, etc., are transmitted to and from the integrated circuit. The bond-pads are usually very small, and they are arranged in an array having a fine pitch between bond-pads. The dies can also be quite delicate. As a result, after fabrication, the dies are packaged to protect the dies and to connect the bond-pads to another array of larger terminals that is easier to connect to a printed circuit board. The dies can be packaged after cutting the workpiece to separate the dies (die-level packaging), or the dies can be packaged before cutting the workpiece (wafer-level packaging).
Conventional die-level packaged microelectronic devices include a microelectronic die, an interposer substrate or lead frame attached to the die, and a molded casing around the die. The bond-pads of the die are typically coupled to terminals on the interposer substrate or the lead frame. In addition to the terminals, the interposer substrate also includes ball-pads coupled to the terminals by conductive traces supported in a dielectric material. Solder balls can be attached to the ball-pads in one-to-one correspondence to form a “ball-grid array.” Packaged microelectronic devices with ball-grid arrays are generally higher-grade packages having lower profiles and higher pin counts than conventional packages using lead frames.
Packaged microelectronic devices such as those described above are used in cellphones, pagers, personal digital assistants, computers, and many other electronic products. To meet the demand for smaller electronic products, there is a continuing drive to increase the performance of packaged microelectronic devices, while at the same time reducing the height and the surface area or “footprint” of such devices on printed circuit boards. Reducing the size of high performance devices, however, is difficult because the sophisticated integrated circuitry requires more bond-pads, which results in larger ball-grid arrays and thus larger footprints. One technique for increasing the component density of microelectronic devices within a given footprint is to stack one device on top of another.
One concern with many high-density packaged microelectronic devices is electromagnetic emissions or radiation generated by the devices during operation. Such electromagnetic disturbances are often referred to as electromagnetic interference (“EMI”). EMI within a particular system or device generally occurs as a result of the generation and/or transmission of electromagnetic radiation by integrated circuits, power supplies, or other radiation sources. Left unchecked, EMI can produce a number of undesirable effects. For example, EMI can interfere with or impair the operation and integrity of unshielded equipment and/or systems proximate to the source of the emissions. Furthermore, EMI can significantly degrade or otherwise negatively affect the performance of unshielded devices.
One approach to addressing the problems with EMI is to shield or ground the integrated circuitry within packaged microelectronic devices. A conventional method for shielding lead frame devices, for example, includes forming a conductive backplane on a back side of the wafer. Portions of the lead frame can then be electrically coupled to the backplane, and one or more bond-pads can be electrically coupled to the backplane via the corresponding portions of the lead frame to ground the device. One significant drawback with this approach, however, is that it is not suitable for devices with small arrays of back side contacts (e.g., ball-grid arrays) because (a) many of the ball-pads or back side contacts should not be grounded or otherwise connected in common, and (b) the remaining ball-pads or back side contacts cannot be connected to the backplane using wire-bonding or other conventional techniques. Accordingly, there is a need to provide the methods for packaging microelectronic devices having small arrays of back side contacts and conductive backplanes.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a partially schematic illustration of a representative microfeature workpiece carrying microfeature dies configured in accordance with embodiments of the invention.
FIG. 1B is a schematic illustration of a microfeature die singulated from the workpiece shown in FIG. 1A.
FIG. 2 is a partially schematic, side cross-sectional view of a portion of a microfeature workpiece including one or more interconnects coupled to a conductive backplane structure in accordance with several embodiments of the invention.
FIGS. 3A-3F are schematic, side cross-sectional views illustrating various stages in a method for forming a conductive backplane in accordance with an embodiment of the invention.
FIGS. 4A-4C are schematic, side cross-sectional views illustrating various stages in a method for forming a conductive backplane in accordance with another embodiment of the invention.
FIGS. 5A-5D are schematic, side cross-sectional views illustrating various stages in a method for forming a conductive backplane in accordance with still another embodiment of the invention.
FIG. 6 is a schematic, side cross-sectional view of a packaged microelectronic device in accordance with one embodiment of the invention.
FIG. 7 is a schematic illustration of a system that can include one or more microelectronic devices configured in accordance with embodiments of the invention.



DETAILED DESCRIPTION
The following disclosure describes several embodiments of methods for forming conductive backplanes on microfeature workpieces having interconnects, and devices formed using such methods. As used herein, the terms “microfeature workpiece” and “workpiece” refer to substrates on and/or in which microfeature electronic devices are integrally formed. A microfeature workpiece can include a wafer and/or individual dies or combinations of dies that make up the wafer. Typical electronic devices formed on and/or in microfeature workpieces include processors, memory, imagers, thin-film recording heads, data storage elements, and other products with integrated circuits. Micromachines, microfluidic devices and other micromechanical devices are included within this definition because they are manufactured using much of the same technology that is used in the fabrication of integrated circuits. The substrates can be semi-conductive pieces (e.g., doped silicon wafers, gallium arsenide wafers, or other semiconductor wafers), non-conductive pieces (e.g., various ceramic substrates), or conductive pieces. In some cases, the workpieces are generally round, and in other cases the workpieces can have other shapes, including rectilinear shapes. Several embodiments of methods for forming conductive backplanes in connection with microfeature workpiece fabrication are described below. A person skilled in the relevant art will understand, however, that the invention has additional embodiments, and that the invention may be practiced without several of the details of the embodiments described below with reference to FIGS. 1A-7.
FIG. 1A is a microfeature workpiece 100 in the form of a semiconductor wafer 110 that includes multiple microfeature dies 120. At least some of the processes described below may be conducted on the microfeature workpiece 100 at the wafer level, and other processes may be conducted on the individual microfeature dies 120 of the microfeature workpiece 100 after the dies 120 have been singulated from the larger wafer 110. Accordingly, unless otherwise noted, structures and methods described below in the context of a microfeature workpiece can apply to the wafer 110, the dies 120 that are formed from the wafer 110, and/or an assembly of one or more dies 120 in a stacked-die configuration or attached to a support member. FIG. 1B is a schematic illustration of an individual die 120 after it has been singulated from the wafer 110 shown in FIG. 1A. The die 120 can include operable microelectronic structures, optionally encased within a protective encapsulant. The die 120 can be electrically connected to external structural devices by pins, bond pads, solder balls, redistribution structures, and/or other conductive structures.
FIG. 2 is a partially schematic, side cross-sectional view of a portion of a microfeature workpiece 200 configured in accordance with several embodiments of the invention. More specifically, FIG. 2 illustrates the workpiece 200 after a plurality of interconnects have been formed in the workpiece 200 and one or more of the interconnects have been selectively coupled to a conductive backplane structure 240 to provide EMI shielding and/or grounding for the various components of the workpiece 200. The microfeature workpiece 200 includes a semiconductor substrate 210 having a front or active side 212, a back side 214, and a plurality of microelectronic dies 220 formed on and/or in the substrate 210. The workpiece 200 can include several features generally similar to the workpiece 100 described above with reference to FIG. 1A. The substrate 210, for example, can be a semiconductor wafer with the dies 220 arranged in a die pattern on the wafer. Individual dies 220 can include integrated circuitry 222 and electrical connectors 230 electrically coupled to the integrated circuitry 222. Although the illustrated dies 220 have the same structure, in other embodiments the dies 220 can have different features to perform different functions.
The connectors 230 shown in FIG. 2 provide a small array of back side contacts within the footprint of each die 220. Individual connectors 230, for example, can include a terminal or bond site 232 (e.g., a bond-pad), a conductive coupler 234 (e.g., a solder ball or other external interconnect structure), and an interconnect 236 coupling the terminal 232 to the conductive coupler 234. In the embodiment illustrated in FIG. 2, the terminals 232 are at the front side 212 of the substrate 210, the conductive couplers 234 are at the back side 214 of the substrate 210, and the interconnects 236 are through-substrate or through-wafer interconnects that extend completely through the substrate 210 to couple the terminals 232 to corresponding conductive couplers 234. In other embodiments, however, the terminals 232 can be internal features that are embedded at an intermediate depth within the substrate 210 and coupled to corresponding conductive couplers 234 with interconnects 236 that extend through only a portion of the substrate 210. The conductive couplers 234 can be attached either before or after singulating the dies 220 from the workpiece 200.
The workpiece 200 further includes the backplane structure 240 at the back side 214 of the substrate 210. The backplane structure 240 can include, for example, a metal or conductive “shield” layer 242 on and/or in the substrate 210. In several embodiments, the backplane structure 240 can also include one or more dielectric layers (not shown) and/or other structures. Various embodiments of the backplane structure 240 are described in detail below. As mentioned previously, one or more of the interconnects 236 can be selectively coupled to the backplane structure 240 to provide EMI shielding and/or grounding. More specifically, the backplane structure 240 can be configured such that (a) the individual conductive couplers 234 contact both the corresponding interconnect 236 and the portion of the conductive layer 242 adjacent to the associated interconnect 236 to electrically connect the interconnect to the backplane structure 240, or (b) the individual conductive couplers 234 contact only the corresponding interconnect 236 and remain electrically isolated from the conductive layer 242. After coupling selected interconnects 236 to the backplane structure 240, the workpiece 200 can be cut along lines A-A to singulate the dies 220. Various embodiments of the backplane structure 240 and processes for selectively coupling one or more of the interconnects 236 to the backplane structure 240 are discussed in greater detail below.
In contrast with conventional unshielded BGA devices described previously, several embodiments of the interconnects 236 and the backplane structure 240 enable devices having small arrays of back side contacts (e.g., ball-grid arrays) to use conductive backplanes. Electrically coupling one or more of the interconnects 236 to the backplane 240 can accordingly provide EMI shielding and grounding for such devices. The back side arrays of electrical connectors also allow the dies 220 to be stacked on other dies or directly attached to an interposer substrate without peripheral wire-bonds. The individual dies 220 accordingly have a significantly smaller footprint and profile than conventional stacked devices including wire-bonds or other conventional devices with backplanes. Thus, the dies 220 can be used in smaller electronic devices and the problems associated with EMI or other electromagnetic radiation in such high density packaged devices can be mitigated.
In the embodiment illustrated in FIG. 2, formation of the interconnects 236 and the backplane structure 240 is complete. FIGS. 3A-5D described below illustrate various embodiments of conductive backplane structures and methods for forming such structures. Although the following description illustrates only two interconnects adjacent to a portion of the backplane structure, it will be appreciated that (a) a plurality of interconnects are constructed simultaneously through a plurality of dies on a wafer, and (b) the backplane structure is fabricated across all or a substantial portion of the workpiece.
FIGS. 3A-3F illustrate various stages of a method for forming one embodiment of the backplane structure 240 of FIG. 2. FIG. 3A, more specifically, is a schematic, side cross-sectional view of a portion of the workpiece 200 at an early stage of this process after constructing a substantial portion of an embodiment of the interconnect 236, but before forming the backplane structure. More specifically, the workpiece 200 has dielectric layers 302 and 304 over at least a portion of the front side 212 of the substrate 210 to protect the substrate 210 and the terminals 232. The dielectric layers 302 and 304 and/or one or more of the subsequent dielectric layers can be parylene, low temperature chemical vapor deposition (CVD) materials, such as tetraethylorthosilicate (TEOS), silicon nitride (Si3Ni4), silicon oxide (SiO2), and/or other suitable dielectric materials. The foregoing list of dielectric materials is not exhaustive. The dielectric layers 302 and 304 are not generally composed of the same material as each other, but these layers may be composed of the same material. In addition, one or both of the dielectric layers 302 and 304 may be omitted and/or additional layers may be included.
The workpiece 200 also includes a plurality of vias or apertures 310 formed through at least part of the substrate 210 using etching, laser drilling, or other suitable techniques. The illustrated vias 310 are blind vias that extend only partially through the substrate 210 or are otherwise closed at one end. In other embodiments, however, the vias 310 can extend entirely through the workpiece 200 and/or the substrate 210. Further details of representative methods for forming vias 310 are disclosed in pending U.S. patent application Ser. No. 11/027,443, filed Dec. 30, 2004, and incorporated herein by reference in its entirety.
The vias 310 are generally lined with another dielectric layer and one or more conductive layers (shown collectively as liner 320). The embodiment of the liner 320 is shown schematically as a single layer, but in many embodiments the liner 320 has a number of different dielectric and conductive materials. The dielectric layer(s) of the liner 320 electrically insulate the components in the substrate 210 from the interconnects that are subsequently formed in each via 310. The dielectric layer can include materials similar to those of the dielectric layers 302 and 304 described above. The conductive layer(s) of the liner 320 can include tantalum (Ta), tungsten (W), copper (Cu), nickel (Ni), and/or other suitable conductive materials.
After lining the vias 310, vent holes 325 are formed in the substrate 210 to extend from a bottom portion of each via 310 to the back side 214 of the substrate 210. After forming the vent holes 325, a conductive fill material 327 is deposited into each via 310 to form the interconnects 236. The fill material 327 can include Cu, Ni, silver (Ag), gold (Au), solder, conductive polymer, or other suitable materials or alloys of materials having the desired conductivity. The vent holes 325 allow trapped air, gases, or volatile solvents to escape from the larger vias 310 when filling the vias with the conductive fill material 327. The vent holes 325 are an optional structure that can be omitted in several embodiments.
Referring next to FIG. 3B, the substrate 210 is thinned to a desired thickness “T” by removing material from the back side 214 of the substrate 210. In the illustrated embodiment, a back side portion 237 of each interconnect 236 is at least partially exposed after removing material from the back side 214. In one embodiment, the initial thickness of the substrate 210 is approximately 750 μm, and the final thickness T is approximately 100-500 μm. The initial and final thicknesses can be different in other embodiments. The back side 214 of the substrate 210 can be thinned using chemical-mechanical planarization (CMP) processes, dry etching processes, chemical etching processes, chemical polishing, grinding procedures, or other suitable processes.
Referring to FIG. 3C, the back side 214 of the substrate 210 is etched back to further expose the back side portions 237 of each interconnect 236, thus forming conductive “posts” 238. In other embodiments, other suitable processes in addition to, or in lieu of, the etching process can be used to offset the back side 214 of the substrate 210 from the ends of the interconnects 236 to form the posts 238. After etching the back side 214, a first dielectric layer 330 is deposited onto the back side 214 of the substrate 210 and over the posts 238. The first dielectric layer 330 can be a low temperature CVD oxide or other suitable dielectric material, such as one of the materials described above with reference to FIG. 3A. A conductive or metal layer 332 is then deposited over the first dielectric layer 330. The conductive layer 332 is an embodiment of the metal or conductive layer 242 shown in FIG. 2. The conductive layer 332 can be composed of aluminum (Al), Cu, Ni, W, a conductive polymer, or another suitable conductive material.
FIG. 3D illustrates the workpiece 200 after the portions of the conductive layer 332 and the first dielectric layer 330 on the ends of the posts 238 (FIG. 3C) have been removed to expose the back side portions 237 of each interconnect 236. In this embodiment, for example, the overburden portions of the conductive layer 332 and the first dielectric layer 330 are removed from the workpiece 200 by pressing the workpiece 200 against a planarizing medium and moving the workpiece and/or the planarizing medium relative to each other in a CMP process. As a result, the conductive layer 332 has a planarized surface and the first dielectric layer 330 has a planarized portion proximate to and at least generally surrounding each interconnect 236 to electrically insulate the conductive layer 332 from the interconnects 236. In other embodiments, the overburden portions of the conductive layer 332 and the first dielectric layer 330 can be removed using an etching process in lieu of, or in addition to, the CMP process.
Referring next to FIG. 3E, a second dielectric layer or “cap” layer 334 is applied to the back side 214 of the substrate 210 over the remaining portions of the first dielectric layer 330, the conductive layer 332, and the exposed back side portions 237 of the interconnects 236. The second dielectric layer 334 can include a low temperature CVD oxide (e.g., SiO2), a photosensitive polyimide, or another suitable dielectric material. After depositing the second dielectric layer 334, a plurality of openings 340 including a first opening 340a and a second opening 340b are formed in the second dielectric layer 334 to expose the back side portions 237 of the interconnects 236 and, in some cases, a portion of the conductive layer 332. If the second dielectric layer 334 is a low temperature CVD oxide, the first and second openings 340a and 340b can be formed by patterning and etching the second dielectric layer 334 to form the openings. For example, the first and second openings 340a and 340b can be etched using one or more etching steps that selectively remove the material from the second dielectric layer 334 compared to the interconnects 236 and the conductive layer 332. Alternatively, if the second dielectric layer 334 is a photosensitive polyimide material, a photolithographic procedure is used to selectively expose portions of the second dielectric layer 334, and the exposed portions of the second dielectric layer 334 are developed to form the first and second openings 340a and 340b. In other embodiments, other suitable techniques and/or processes can be used to form the first and second openings 340a and 340b. 
The dimensions and/or alignment of the first and second openings 340a and 340b can be used to selectively control which interconnects 236 will be electrically coupled to the conductive layer 332. For example, the first opening 340a has a first diameter or cross-sectional dimension D1 and the second opening 340b has a second diameter or cross-sectional dimension D2 less than the first diameter D1. The first diameter D1 of the first opening 340a is sized such that both the back side portion 237 of the corresponding interconnect 236 and at least a portion of the conductive layer 332 adjacent to the interconnect 236 is exposed. Conversely, the second diameter D2 of the second opening 340b is sized such that the portions of the conductive layer 332 adjacent to the second opening 340b are covered by the second dielectric layer 334 to ensure electrical isolation between the corresponding interconnect 236 and the conductive layer 332. In one embodiment, the second opening 340b is configured so that only the backside portion 237 of the associated interconnect 236 is exposed.
Referring to FIG. 3F, the conductive couplers 234 are attached to the back side portions 237 of each interconnect 236 to (a) selectively couple particular interconnects 236 to the conductive layer 332 of the backplane structure 240, and (b) provide an external connection to other electronic devices at the back side 214 of the workpiece 200. More specifically, the conductive coupler 234 in the first opening 340a is in electrical contact with both the interconnect 236 and the conductive layer 332 to electrically couple the corresponding interconnect 236 to the backplane 240. In contrast, the conductive coupler 234 in the second opening 340b is electrically coupled to the corresponding interconnect 236, but the size and/or alignment of the second opening 340b prevent the conductive coupler 234 from contacting the conductive layer 332. This interconnect 236 accordingly remains electrically isolated from the backplane 240. Any number of interconnects 236 within a particular die 220 (FIG. 2) can be selectively coupled to the backplane 240 based on the particular specifications or operational requirements of the resulting device.
As discussed previously, electrically coupling one or more of the interconnects 236 to the backplane 240 can provide EMI shielding and/or grounding for devices having small arrays of back side contacts, such as the dies 220 (FIG. 2) and the resulting packaged devices. Embodiments of the method described above with reference to FIGS. 3A-3F are also expected to mitigate the problems associated with “floating” backplanes in which a conductive backplane is present in a particular device but is not electrically coupled to the circuitry in the device. As discussed above, for example, electrically and physically coupling one or more interconnects 236 to the backplane 240 with the conductive couplers 234 can provide a robust connection between the device's circuitry and the backplane 240.
In one embodiment, a microfeature device comprises a semiconductor substrate having a front side, a back side, integrated circuitry and terminals electrically coupled to the integrated circuitry. The device also includes electrically conductive interconnects, electrically coupled to the terminals. The interconnects extend through at least a portion of the semiconductor substrate and have back side portions at the back side of the substrate. The device further includes a conductive backplane at the back side of the semiconductor substrate, and one or more of the interconnects are electrically coupled to the conductive layer at the back side of the semiconductor substrate.
In another embodiment, a microfeature workpiece comprises a semiconductor substrate having a front side, a back side, and a plurality of microelectronic dies on and/or in the substrate. The individual dies include integrated circuitry and bond-pads electrically coupled to the integrated circuitry. The workpiece also includes a plurality of electrically conductive through-substrate interconnects electrically coupled to corresponding bond-pads. The workpiece further includes a shield layer at the back side of the semiconductor substrate. First interconnects of individual dies are electrically coupled to the shield layer, and second interconnects of individual dies are electrically isolated from the shield layer.
In still another embodiment, a microelectronic device includes a semiconductor substrate having integrated circuitry and bond-pads electrically coupled to the integrated circuitry. The device also includes electrically conductive through-substrate interconnects in contact with corresponding bond-pads and having back side portions. The device further includes an EMI shield at a back side of the semiconductor substrate for EMI shielding. The back side portion of at least one interconnect is electrically coupled to the EMI shielding, and the back side portion of at least one other interconnect is electrically isolated from the EMI shield.
In yet another embodiment, a microfeature workpiece includes a semiconductor substrate having a front side, a back side, and a plurality of microelectronic dies on and/or in the semiconductor substrate. The individual dies include integrated circuitry, an array of bond-pads electrically coupled to the integrated circuitry, and a plurality of electrically conductive through-substrate interconnects electrically coupled to corresponding bond-pads. The dies also include a back side metal layer. One or more of the interconnects are electrically coupled to the metal layer. The workpiece further includes a plurality of scribe lines spacing apart the individual dies.
In still another embodiment, a microelectronic device includes a semiconductor substrate having a front side, a back side opposite the front side, integrated circuitry, and an array of bond-pads at the front side of the substrate electrically coupled to the integrated circuitry. The device also includes a plurality of electrically conductive interconnects extending through the substrate. The interconnects have front side portions electrically coupled with corresponding bond-pads and back side post portions at the back side of the substrate. The device further includes a conductive layer at the back side of the substrate. The conductive layer has an array of openings aligned with corresponding interconnects such that the back side post portions of the interconnects extend through the openings in the conductive layer. The device also includes dielectric spacers in the openings between the conductive layer and the back side post portions of the corresponding interconnects. The back side post portions of first interconnects are electrically coupled to the conductive layer, and the back side post portions of second interconnects are electrically isolated from the conductive layer.
Another embodiment is directed toward a method of processing a semiconductor substrate. The semiconductor substrate includes integrated circuitry and a plurality of terminals electrically coupled to the integrated circuitry. The method includes forming a plurality of electrically conductive interconnects extending at least partially through the substrate and in contact with corresponding terminals. The interconnects have back side portions at a back side of the semiconductor substrate. The method also includes constructing a conductive backplane at a back side of the semiconductor substrate. The method further includes electrically coupling at least one of the back side portions of the interconnects to the backplane, and electrically isolating at least one other interconnect from the backplane.
Another embodiment is directed toward yet another method of processing a semiconductor substrate having a plurality of microelectronic dies. The individual dies include an integrated circuit and bond-pads electrically coupled to the integrated circuit. The method includes constructing a plurality of electrically conductive through-substrate interconnects extending at least partially through the semiconductor substrate and in contact with corresponding bond-pads. The method also includes forming a metal layer at a back side of the semiconductor substrate. The method further includes selectively coupling a back side portion of first interconnects of individual dies to the metal layer, while keeping second interconnects of individual dies electrically isolated from the metal layer.
Still another embodiment is directed toward a method of fabricating a semiconductor substrate. The semiconductor substrate has integrated circuitry, a plurality of bond-pads electrically coupled to the integrated circuitry, and a plurality of electrically conductive through-substrate interconnects in contact with corresponding bond-pads. The method includes forming an EMI shield at a back side of the semiconductor substrate that does not directly contact the interconnects. The method further includes coupling an interconnect to the shield with a solder ball in direct physical contact with a back side portion of the interconnect and a corresponding portion of the shield.
FIGS. 4A-4C are schematic, side cross-sectional views illustrating various stages of a method for forming another embodiment of the backplane structure 240 shown in FIG. 2. The initial stages of this method are at least generally similar to the steps described above with reference to FIGS. 3A-3C, and as such FIG. 4A shows a workpiece configuration similar to that illustrated in FIG. 3C. The subsequent stages of this method, however, differ from that described above with reference to FIGS. 3A-3F in that a dielectric layer is not deposited over the back side 214 of the substrate 210. Instead, a conductive or metal layer 402 is deposited directly onto the back side 214 and over the exposed back portions 237 of the interconnects 236. The conductive layer 402 can include an argon (Ar) pre-sputter with TiAl, Ti-silicide, or another suitable conductive material that can bond directly to the silicon material of the substrate 210.
FIG. 4B illustrates the workpiece 200 after the overburden portions of the conductive layer 402 have been removed to expose the back side portions 237 of each interconnect 236. The overburden portions of the conductive layer 402 can be removed from the workpiece 300 using a CMP process or etching process similar to those described above with reference to FIG. 3D. In other embodiments, however, another suitable technique can be used to remove the desired portions of the conductive layer 402.
Referring next to FIG. 4C, a first dielectric layer 404 is applied to the back side 214 of the substrate 210 over the conductive layer 402 and the exposed back side portions 237 of the interconnects 236. The first dielectric layer 404 can include a low temperature CVD oxide, a photosensitive polyimide, or another suitable dielectric material similar to those described previously. After depositing the first dielectric layer 404, a plurality of openings 406 (two are shown as a first opening 406a and a second opening 406b) are formed in the first dielectric layer 404 to expose the back side portions 237 of the interconnects 236 and, in some cases, a portion of the conductive layer 402 adjacent to the interconnects 236. The first and second openings 406a and 406b can be formed using processes or techniques similar to those described above with reference to FIG. 3E. As discussed previously, the chosen technique depends largely on the composition of the first dielectric layer 404.
Similar to the first and second openings 340a and 340b described above with reference to FIG. 3E, the dimensions and/or alignment of the first and second openings 406a and 406b shown in FIG. 4C can be used to selectively control which interconnects 236 will be electrically coupled to the conductive layer 402. For example, the first opening 406a has a third diameter or cross-sectional dimension D3 and the second opening 406b has a fourth diameter or cross-sectional dimension D4 less than the third diameter D3. The third diameter D3 is sized such that both the interconnect 236 and a portion of the conductive layer 402 adjacent to the interconnect 236 are exposed. The fourth diameter D4, however, is sized such that the conductive layer 402 covers the dielectric portions of the liner 320 at the second opening 406b. A conductive coupler 410 (e.g., a solder ball or other external interconnect structure) in the first opening 406a accordingly electrically couples the associated interconnect 236 to the conductive layer 402 of the backplane structure, but another conductive coupler 410 in the second opening 406b is electrically coupled only to the corresponding interconnect 236 and remains electrically isolated from the backplane structure.
The methods for forming the backplane structure described above with reference to FIGS. 3A-4D include (a) a single CMP step to remove the overburden portions of the conductive layer and/or the dielectric layer, and (b) a single masking step to selectively form openings over the interconnects having the desired dimensions and alignment. Using only a single CMP step and a single masking step provides an efficient process to fabricate the backplane structure. Furthermore, reducing the amount of processing also mitigates the potential for damage to and/or contamination of the workpiece 200 that can result from CMP or other rigorous processes.
FIGS. 5A-5D are schematic, side cross-sectional views illustrating various stages of a method for forming still another embodiment of the backplane structure 240 shown in FIG. 2. Referring first to FIG. 5A, the initial stages of this method are at least generally similar to the steps described above with reference to FIGS. 3A and 3B, but the back side 214 of the substrate 210 is not etched or otherwise recessed back to form the conductive posts 238 (FIG. 3C). Instead, after thinning the substrate 210 to the desired thickness, a conductive layer 502 is deposited over the back side 214 of the substrate 210 and the exposed back side portions 237 of each interconnect 236 to provide the material for the conductive backplane. The conductive layer 502 can include conductive materials generally similar to those described above with reference to FIG. 3C and FIG. 4A.
After depositing the conductive layer 502, a first mask 504 is applied over the conductive layer 502. The first mask 504 can be a layer of resist that is patterned according to the arrangement of the interconnects 236 and the desired configuration of the resulting backplane structure. In the embodiment shown in FIG. 5A, for example, the first mask 504 has an opening 505 over one of the interconnects 236, and then an opening 506 is formed through the conductive layer 502 to expose the corresponding interconnect 236 and at least a portion of the back side 214 of the substrate 210. The opening 506 can be formed using etching or another suitable process. The first mask 504 can be removed.
Referring to FIG. 5B, a first dielectric layer 508 is deposited onto the workpiece 300 over the conductive layer 502 and into the opening 506 such that the first dielectric layer 508 covers the exposed back side portions of the interconnects 236 and the substrate 210. The first dielectric layer 508 can include a low temperature CVD oxide or another suitable dielectric material. A second mask 510 is subsequently applied over the first dielectric layer 508 and patterned to form openings over the interconnects 236.
Referring next to FIG. 5C, a plurality of openings 512 (two are shown as a first opening 512a and a second opening 512b) are formed in the first dielectric layer 508 using an etching process or another suitable technique. The first opening 512a exposes the back side portion 237 of the corresponding interconnect 236, and the second opening 512b exposes the conductive layer 508. In one embodiment, the etching process selectively removes the material of the dielectric layer 508 faster than the material of the conductive layer 502 or the interconnect 236. FIG. 5D illustrates the workpiece 200 after conductive couplers 520 have been deposited into the respective first and second openings 512a and 512b. The conductive coupler 520 in the first opening 512a is electrically coupled to the corresponding interconnect 236, but is electrically isolated from the conductive layer 502. On the other hand, the conductive coupler 520 in the second opening 512b is directly electrically coupled to the conductive layer 502, thus electrically coupling the corresponding interconnect 236 to the backplane structure.
FIG. 6 is a schematic, side cross-sectional view of a packaged microelectronic device 600 configured in accordance with an embodiment of the invention. The microelectronic device 600 includes a plurality of microelectronic dies 620 (individually identified as a first microelectronic die 620a and a second microelectronic die 620b) interconnected in a stacked-die arrangement. The first and second microelectronic dies 620a and 620b can have many components at least generally similar to the microelectronic dies 220 discussed above and illustrated in FIG. 2. For example, the first and second dies 620a and 620b can each include integrated circuitry 622 and connectors 630 electrically coupled to the integrated circuitry 622. Each connector 630 can include a terminal 632 (e.g., a bond-pad), a conductive coupler 634 (e.g., a solder ball or other external interconnect structure), and an interconnect 636 extending through the respective die coupling the terminal 632 to the conductive coupler 634. The first and second dies 620a and 620b also include a conductive backplane structure 640 at a back side of the individual dies. The backplane structure 640 can include, for example, a conductive or metal layer 642 on the respective dies. The backplane structure 640 can be constructed using any of the methods described above with respect to FIGS. 3A-5D.
In the illustrated embodiment, the conductive couplers 634 of the first upper die 620a are coupled to corresponding terminals 632 of the second lower die 620b to electrically connect the first die 620a to the second die 620b. A suitable underfill material 690 or other compound can optionally be used to structurally attach the first and second dies 620a and 620b together in the illustrated stacked-die configuration. Additionally, the conductive couplers 634 at the back side of the second die 620b can in turn be used to electrically connect the microelectronic device 600 to another external device or board.
In one embodiment, for example, a microelectronic assembly includes a first microelectronic device and a second microelectronic device coupled to the first device in a stacked configuration. The first device has a first microelectronic die with a first integrated circuit and an array of first bond-pads electrically coupled to the first integrated circuit. The first die also includes first electrically conductive interconnects extending at least partially through the first die and in contact with corresponding first bond-pads. The first die further includes a first conductive backplane assembly having a first conductive layer at a back side of the first die, with at least one first interconnect electrically coupled to the first conductive layer. The second device has a second microelectronic die with a second integrated circuit and an array of second bond-pads electrically coupled to the second integrated circuit. The second die also includes second electrically conductive interconnects extending at least partially through the second die and in contact with corresponding second bond-pads. The second die further includes a second conductive backplane assembly having a second conductive layer at a back side of the second die, with at least one second interconnect electrically coupled to the second conductive layer.
The stacked microelectronic device 600 or any one of the microelectronic devices formed using the methods described above with reference to FIGS. 1A-6 can be incorporated into any of a myriad of larger and/or more complex systems 700, a representative one of which is shown schematically in FIG. 7. The system 700 can include a processor 702, a memory 704 (e.g., SRAM, DRAM, DDR-SDRAM, flash memory, such as NAND flash memory or other types of flash memory, and/or other suitable memory devices), input/output devices 706, and/or other subsystems or components 708. Microelectronic devices and/or microfeature workpieces (e.g., in the form of microfeature dies and/or combinations of microfeature dies) may be included in any of the components shown in FIG. 7. The resulting system 700 can perform any of a wide variety of computing, processing, storage, sensor, imagers, and/or other functions. Accordingly, representative systems 700 include, without limitation, computers and/or other data processors, for example, desktop computers, laptop computers, Internet appliances, hand-held devices (e.g., palm-top computers, wearable computers, cellular or mobile phones, personal digital assistants), multi-processor systems, processor-based or programmable consumer electronics, network computers, and mini-computers. Other representative systems 700 include cameras, light or other radiation sensors, servers and associated server subsystems, display devices, and/or memory devices. In such systems, individual dies can include imager arrays, such as a CMOS imager. Components of the system 700 may be housed in a single unit or distributed over multiple, interconnected units, e.g., through a communications network. Components can accordingly include local and/or remote memory storage devices and any of a wide variety of computer-readable media.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the invention. For example, structures and/or processes described in the context of particular embodiments may be combined or eliminated in other embodiments. In particular, the conductive backplane structures described above with reference to particular embodiments can include one or more additional dielectric or conductive layers, or one or more of the layers described above can be omitted. Further, the connections between the interconnects, backplane structures, and other devices (e.g., bond pads, conductive couplers, and/or external devices) can have arrangements different than those described above. In several embodiments, for example, the electrical connectors can include ball-pads at the back side of the dies and electrically coupled to corresponding interconnects and conductive couplers. Accordingly, the invention is not limited except as by the appended claims.

## Claims

1. A method of processing a semiconductor substrate, the semiconductor substrate having integrated circuitry and a plurality of terminals electrically coupled to the integrated circuitry, the method comprising:
forming a plurality of electrically conductive interconnects extending at least partially through the substrate and in contact with corresponding terminals, the interconnects having back side portions at a back side of the semiconductor substrate;
constructing a conductive backplane at the back side of the semiconductor substrate, wherein constructing a conductive backplane at the back side of the semiconductor substrate comprises depositing a conductive layer onto the back side of the substrate, the conductive layer having openings around the interconnects and dielectric spacers in the openings between the conductive layer and the interconnects; and
electrically coupling at least one of the back side portions of the interconnects to the backplane via a conductive coupler in one of the openings and in direct contact with the corresponding interconnect and the conductive layer, and electrically isolating at least one of the plurality of other interconnects from the backplane.

2. The method of claim 1 wherein electrically isolating at least one of the plurality of other interconnects comprises placing another conductive coupler in contact with the back side portion of the other particular interconnect and electrically isolated from the backplane.

3. The method of claim 1 wherein electrically coupling at least one of the back side portions of the interconnects to the backplane comprises electrically coupling at least one of the back side portions of the interconnects to the backplane within the footprint of the semiconductor substrate.

4. The method of claim 1 wherein:
constructing a conductive backplane at the back side of the semiconductor substrate comprises (a) depositing a metal layer onto the back side of the substrate and electrically isolated from the interconnects, (b) depositing a dielectric layer over the metal layer, and (c) forming the openings in the dielectric layer to at least partially expose the back side portions of the individual interconnects; and
electrically coupling at least one of the back side portions of the interconnects to the backplane comprises placing a solder ball in a particular opening sized to expose the corresponding interconnect and an adjacent portion of the metal layer, the solder ball being in direct contact with the respective interconnect and the metal layer.

5. The method of claim 1 wherein the plurality of electrically conductive interconnects comprises a first interconnect and a second interconnect, and wherein:
constructing a conductive backplane at the back side of the semiconductor substrate comprises—
depositing a first dielectric layer onto the back side of the substrate and in contact with the first and second interconnects;
depositing the conductive layer over the first dielectric layer;
planarizing the substrate by placing the back side of the substrate against a planarizing medium and moving the substrate and/or the planarizing medium relative to each other in a manner that removes portions of the first dielectric layer and conductive layer from the substrate to leave the remaining portions of the conductive layer out of direct contact with the first and second interconnects;
depositing a second dielectric layer over the first dielectric layer and the conductive layer; and
creating a first opening in the second dielectric layer to expose the first interconnect and a portion of the conductive layer, and creating a second opening the second dielectric layer to expose the second interconnect without exposing the conductive layer; and

electrically coupling at least one of the back side portions of the interconnects to the backplane comprises—
depositing a first conductive coupler into the first opening and in contact with the first interconnect and the conductive layer; and
depositing a second conductive coupler into the second opening and in contact with the second interconnect, wherein the second conductive coupler is out of contact with the conductive layer.

6. The method of claim 5 wherein:
depositing a first dielectric layer comprises depositing a low temperature CVD oxide;
depositing the conductive layer over the first dielectric layer comprises depositing Al, Cu, Ni, W, and/or a conductive polymer; and
depositing a second dielectric layer over the first dielectric layer and the conductive layer comprises depositing a low temperature CVD oxide and/or a photosensitive polyimide.

7. The method of claim 5 wherein the second dielectric layer comprises a low temperature CVD oxide, and wherein creating the first opening and the second opening in the second dielectric layer comprises etching the first and second openings in the second dielectric layer.

8. The method of claim 5 wherein the second dielectric layer comprises a photosensitive polyimide, and wherein creating the first opening and the second opening in the second dielectric layer comprises developing the photosensitive second dielectric layer to have the first and second openings aligned with the first and second interconnects, respectively.

9. A method of processing a semiconductor substrate having a plurality of microelectronic dies, the individual dies including an integrated circuit and bond-pads electrically coupled to the integrated circuit, the method comprising:
constructing a plurality of electrically conductive through-substrate interconnects extending at least partially through the semiconductor substrate and in contact with corresponding bond-pads, wherein the plurality of electrically conductive interconnects comprises first interconnects and second interconnects;
forming a metal layer at a back side of the semiconductor substrate; and
selectively coupling back side portions of the first interconnects of individual dies to the metal layer while keeping the second interconnects of individual dies electrically isolated from the metal layer,
wherein selectively coupling the back side portions of the first interconnects to the metal layer comprises placing solder balls in contact with the back side portions of the first interconnects and portions of the metal layer adjacent to the first interconnects.

10. The method of claim 9 wherein selectively coupling back side portions of the first interconnects of individual dies to the metal layer comprises coupling the back side portions of the first interconnects to the metal layer within the footprint of the respective dies.

11. The method of claim 9, further comprising:
depositing a dielectric layer onto the back side of the substrate and over the metal layer; and
forming first openings in the dielectric layer to expose the back side portions of the first interconnects and adjacent portions of the metal layer, and forming second openings in the dielectric layer to expose a back side portion of the individual second interconnects, wherein the metal layer is isolated from the second openings, and
selectively coupling a back side portion of first interconnects of individual dies to the metal layer while keeping second interconnects of individual dies electrically isolated from the metal layer comprises (a) placing the solder balls in the first openings in direct contact with the corresponding first interconnects and adjacent portions of the metal layer, and (b) placing the solder balls in the second openings in contact with the corresponding second interconnects and electrically isolated from the metal layer.