# Patent

## Title
Semiconductor stacked die devices and methods of forming semiconductor stacked die devices

## Abstract

Semiconductor devices and methods of forming semiconductor devices are described. In one embodiment, at least one conductive structure is formed within a plurality of semiconductor substrates. At least portions of one of the conductive structures have oppositely facing, exposed outer surfaces. Individual substrates are stacked together in a die stack such that individual conductive structures on each substrate are in electrical contact with the conductive structures on a next adjacent substrate. In a preferred embodiment, the conductive structures comprise multi-layered, conductive pad structures.

## Background
RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 10/706,897, filed on Nov. 13, 2003 now U.S. Pat. No. 6,902,953 which, in turn, is a divisional of Ser. No. 09/679,143 filed Oct. 3, 2000, now U.S. Pat. No. 6,674,161, both of which are incorporated by reference herein.


TECHNICAL FIELD
This invention relates to generally to semiconductor devices and, more particularly to semiconductor stacked die constructions and methods of forming the same.
BACKGROUND
Semiconductor devices are typically constructed from a silicon or gallium arsenide wafer through a process involving a number of deposition, masking, diffusion, etching, and implanting steps. Usually, many individual devices are constructed on the same wafer. After fabrication, the wafer is typically sawed or otherwise singulated into individual units, where each unit takes the form of an integrated circuit (IC) die.
It has become a practice in the industry to provided integrated circuit devices in the form of so-called “stacked die” arrangements. Stacked die arrangements typically involve two or more IC die that are fixed upon one another, typically through some type of adhesive arrangement. Interconnections can then be made between the individual die to provide an overall device with a desirable density and enhanced functionality.
Examples of stacked die arrangements are described in detail in the following U.S. patents, to which the reader is referred for additional detail: U.S. Pat. Nos. 5,291,061; 6,051,886; 5,397,916; 5,434,745; 6,093,939; and 5,864,177.
To date, interconnections between the individual die of stacked die arrangements have been made at or near the periphery of each die. U.S. Pat. Nos. 5,291,061, and 5,397,916 provide very good examples of this type of interconnection. As device processing speeds continue to increase, those involved in the design of semiconductor devices are necessarily forced to consider and reconsider traditionally accepted notions of circuit design. One particular area of interest in the industry concerns the design and fabrication of memory devices, and particularly those memory devices that employ stacked die arrangements.
Accordingly, this invention arose out of concerns associated with providing improved systems that employ stacked die arrangements, and methods of forming the same.
SUMMARY
Semiconductor devices and methods of forming semiconductor devices are described. In one embodiment, at least one conductive structure is formed within a plurality of semiconductor substrates. At least portions of one of the conductive structures has oppositely facing, exposed outer surfaces. Individual substrates are stacked together such that individual conductive structures on each substrate are in electrical contact with the conductive structure on a next adjacent substrate.
In another embodiment, at least one conductive structure is formed within each of a plurality of semiconductor substrates. The conductive structures have oppositely-facing surfaces. Portions of each oppositely-facing surface are exposed on at least one of the substrates. The substrates are processed sufficient to form electrical connections between the substrates by stacking the substrates on one another so that the conductive structures on adjacent substrates are electrically connected.
In yet another embodiment, at least one multi-layered, conductive pad structure is formed within each of a plurality of semiconductor substrates. Each conductive pad structure has oppositely-facing surfaces. Portions of each oppositely-facing surface are exposed on at least one of the substrates. At least one such surface is exposed by etching portions of the substrate. After the oppositely-facing surface portions are exposed, additional conductive material is formed over and in electrical contact with the exposed surface portions by plating at least one additional conductive material over the exposed portions.
In still a further embodiment, a semiconductor device comprises a first semiconductor die comprising IC devices. At least one conductive structure is disposed within and through the first die and in operative contact with the IC devices. A second semiconductor die comprises IC devices, and is mounted together with the first die in a stacked arrangement. The second semiconductor die has at least one conductive structure disposed therewithin and in electrical contact with both the IC devices of the second semiconductor die and the conductive structure of the first semiconductor die.
In yet another embodiment, a semiconductor device comprises multiple semiconductor die, each of which comprising IC devices. At least one conductive structure is disposed generally in the center of each die. The multiple die are joined together in a die stack such that electrical contact between adjacent die is made through the conductive structures associated with each of the die.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic side sectional view of a semiconductor wafer fragment, in process, in accordance with the described embodiment.
FIG. 2 is diagrammatic side sectional view of the FIG. 1 wafer fragment, in process, in accordance with the described embodiment.
FIG. 3 is a diagrammatic side sectional view of the FIG. 2 wafer fragment, in process, in accordance with the described embodiment.
FIG. 4 is a diagrammatic side sectional view of the FIG. 3 wafer fragment, in process, in accordance with the described embodiment.
FIG. 5 is a diagrammatic side sectional view of two exemplary substrates mounted in a stacked die arrangement in accordance with the described embodiment.
FIG. 6 is a diagrammatic side sectional view of four exemplary substrates mounted in a stacked die arrangement in accordance with the described embodiment.
FIG. 7 is a diagrammatic side sectional view of the FIG. 6 wafer fragment, in process, in accordance with the described embodiment.



DETAILED DESCRIPTION
Exemplary Embodiment
FIG. 1 shows a semiconductor wafer, in process, generally at 10 and includes a semiconductor substrate 12. In the context of this document, the term “semiconductor substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon) and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure including, but not limited, to the semiconductive substrates described above.
Substrate 12 includes regions 14 that are fabricated to contain or comprise integrated circuit (IC) devices. In a preferred implementation, the integrated circuit devices comprise memory devices. One type of exemplary memory device is a dynamic random access memory (DRAM) device, such as DRAM devices designed by the assignee of this document. It is to be understood, however, that this constitutes but one exemplary type of integrated circuit device that can be provided. Other types of integrated circuit devices (and not necessarily memory devices) can be provided without departing from the spirit and scope of the claimed subject matter.
A pair of regions 16 are shown and comprise interface regions that are designed to provide an interface between the integrated circuit devices within regions 14 and other circuitry that is external of the substrate 12.
A conductive structure 18 is formed within and supported by substrate 12. The exemplary structure 18 can comprise any suitable type of conductive structure and is positioned to make electrical contact with regions 16, and other conductive structures that will ultimately electrically connect the integrated circuit devices to the outside world, as will become apparent below. In a preferred implementation, conductive structure 18 comprises a multi-layered pad structure that is fabricated during processing of the devices in regions 14. The pad structure preferably comprises aluminum and can be formed through successive deposition/etching (or removal) steps.
The conductive structure can be formed at any suitable location within the substrate. It is desirable, however, to have the conductive structure formed at a substrate location that is not at the periphery of the substrate. This is because the conductive structure is going to be used to form electrical connections with other similar conductive structures on other substrates. These substrates will be mounted together in a stacked arrangement so that adjacent substrates are electrically connected through the conductive structures. The manner in which these electrical connections is to be made desirably eliminates the need to make such electrical connections between the substrates at the periphery of, and external to the substrates, as will become apparent below. In the illustrated example, the conductive structure is disposed within the center of the substrate.
An insulative layer 20 is formed over substrate 12 and patterned to expose a front side 18a of conductive structure 18 as shown.
Referring to FIG. 2, wafer 10 is processed to remove a portion of the back side of the wafer, thus thinning the wafer. The wafer can be thinned through the use of any suitable techniques. For example, the wafer can be mechanically (or chemically-mechanical) abraded or polished to achieve the desired thinned wafer.
Referring to FIG. 3, portions of the wafer are removed, as by any suitable processing technique, sufficient to expose at least a portion of backside 18b of conductive structure 18. In the illustrated example, material of the wafer can be selectively etched, relative to the material from which the conductive structure 18 is formed, so that the back side 18b of the conductive structure is exposed. Thus, at this point in the processing of wafer 12, conductive structure 18 has portions of both of its oppositely-facing surfaces exposed.
Referring to FIG. 4, additional conductive material 22, 24 is formed respectively, over and in electrical contact with the oppositely-facing surfaces (i.e. front side 18a and back side 18b) of conductive structure 18. In the illustrated and described embodiment, the conductive material is formed through known plating techniques. In this specific example, more than one conductive material is plated over the conductive structure 18. Specifically, a first conductive material 26, such as nickel, is first formed over the exposed surfaces of the conductive structure 18. Any suitable plating technique, e.g. electroless plating, can be used. After the first conductive material 26 is plated over the exposed surfaces of the conductive structure 18, a second conductive material 28 is formed over and in electrical contact with first conductive material 26. Any suitable techniques can be used such as sputtering, evaporating, or plating to name a few. In the illustrated and described embodiment, second conductive material 28 comprises gold. The second conductive material can, however, comprise any suitable conductive material. For example, an alloy of tin and gold can be used. For purposes of further discussion, conductive material 22 will be referred to as the “top most” conductive material, and conductive material 24 will be referred to as the bottommost” conductive material.
Notice that bottommost conductive material 24 is received entirely within an opening that is defined by a via that exposes the surface of the backside 18b of conductive structure 18. The reason for this will become apparent below.
It should be understood that while only one exemplary substrate is shown as being processed as described, in the preferred embodiment, multiple substrates are typically processed at one time so that they can be eventually joined or bonded together in a die stack.
Referring to FIG. 5, two exemplary substrates 12, 12a are shown. It will be appreciated that substrate 12a can be identical to or different from substrate 12. Substrates 12 and 12a are first moved into engagement with one another and then processed sufficiently such that a conductive bond forms between the bottommost conductive material of substrate 12 and the top most conductive material of substrate 12a. In one exemplary implementation, the conductive bond can be formed by stacking the substrates, either in wafer form or singulated die form, and then joining the conductive material on each of the substrates through ultrasonic thermal compression. This is a good technique to use when the top- and bottommost conductive materials comprise gold. Other techniques can, of course, be used, e.g. thermal compression.
The FIG. 5 construction can thus comprise a first die 12 having IC devices thereon and a second die 12a also having IC devices thereon. Die 12, 12a are mounted together in a stacked arrangement such that the conductive structures of each die are in electrical contact with one another. Thus, the necessity for any such electrical contact to be made external of the substrates or die can be eliminated.
The above technique can be used to form any suitable number of individual dies into a stacked die arrangement. For example, FIG. 6 shows an arrangement of multiple stacked die that consists of four separate substrates (12–12c) that are joined together as described above. Notice that substrate 12c does not have both faces of its conductive structure 18 exposed.
Hence, the inventive techniques described above enable multiple substrates or die to be formed into a stacked arrangement, with operative electrical connections between the die being made by virtue of conductive structures that are disposed entirely within internal regions of the die. In one preferred embodiment, the conductive structures are formed so that they are generally disposed in the center of each die. It is to be appreciated, however, that the conductive structures can be formed at any suitable location on or within the individual die. In the illustrated and described embodiment, the collection of conductive structures for each die are disposed along a common line A.
Once the die have been formed into a stacked arrangement as described above, they can further processed into individual packages. For example, FIG. 7 shows the FIG. 6 die stack where an insulative layer 30 has been formed over the die stack. A conductive line 32 is provided and makes contact with conductive material 22 of the uppermost die 12. Multiple conductive pads 34 are provided over layer 30, with exemplary solder balls 36 being received over each of the pads 34. Processing the die stack can now continue using conventional techniques to form an IC package, as will be appreciated and understood by those of skill in the art.
The various stacked die arrangements that can be formed through the inventive techniques described above are advantageous in that the connective distances as between the individual die can be drastically reduced over other constructions where connections are typically made at the periphery of the die. This is particularly advantageous in the field of memory devices, e.g. SDRAMs and the like, where, for performance purposes, it is highly desirable to reduce stub lengths to the shortest possible distances. In addition, the inventive techniques can enable increased package capacity while providing constructions that more easily dissipate heat. These constructions can more easily dissipate heat because the conductive material joining the individual die can act as a funneling mechanism for heat. Additionally, other material layers, e.g. non-conductive joining material can be formed on the die surfaces to provide not only mechanical support, but further assist in heat dissipation. In addition, the constructions that are provided by the inventive techniques can reduce the number of I/O connections per die. Other advantages will be apparent to those of skill in the art.
Although the invention has been described in language specific to structural features and/or methodological steps, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or steps described. Rather, the specific features and steps are disclosed as preferred forms of implementing the claimed invention.

## Claims

1. A semiconductor device comprising:
a first semiconductor die having opposing first and second sides, the first semiconductor die comprising:
at least two first integrated circuit devices;
a first conductive structure electrically coupled between the at least two first integrated circuit devices, where the first conductive structure is disposed at least partially through the first semiconductor die and exposed at the first side of the first semiconductor die;

a second semiconductor die having opposing first and second sides, the second semiconductor die comprising:
at least two second integrated circuit devices;
a second conductive structure electrically coupled between the at least two second integrated circuit devices, where the second conductive structure is disposed at least partially through the second semiconductor die and exposed at the second side of the second semiconductor die,

wherein the first semiconductor die is stacked on top of the second semiconductor die such that the first conductive structure at the first side of the first integrated circuit die is aligned with, and electrically coupled to, the second conductive structure at the second side of the second semiconductor die.

2. The semiconductor device of claim 1, wherein the first conductive structure is disposed at the first side of the first semiconductor die at a location other than near a periphery of the first semiconductor die.

3. The semiconductor device of claim 1, wherein the second conductive structure is disposed at the second side of the second semiconductor die at a location other than near a periphery of the second semiconductor die.

4. The semiconductor device of claim 1, wherein the first conductive structure is disposed through the first semiconductor die from the first side to the second side of the first semiconductor die.

5. The semiconductor device of claim 4, wherein the first conductive structure is exposed at the second side of the first semiconductor die at a location other than near a periphery of the first semiconductor die.

6. The semiconductor device of claim 1, wherein the second conductive structure is disposed through the second semiconductor die from the second side to the first side of the second semiconductor die.

7. The semiconductor device of claim 6, wherein the second conductive structure is exposed at the first side of the second semiconductor die at a location other than near a periphery of the second semiconductor die.

8. The semiconductor device of claim 1, wherein the first conductive structure is disposed through a center of the first semiconductor die, and the second conductive structure is disposed through a center of the second semiconductor die.

9. The semiconductor device of claim 1, wherein the first conductive structure and the second conductive structure are aligned along a common line perpendicular to the first and second sides of the first semiconductor die and the second semiconductor die.

10. The semiconductor device of claim 1, wherein at least one of the first and second conductive structures comprises aluminum.

11. The semiconductor device of claim 1, wherein at least one of the first and second conductive structures comprises a multi-layered pad structure.

12. The semiconductor device of claim 1, wherein at least one of the first and second conductive structures comprises a multi-layered aluminum pad structure.

13. The semiconductor device of claim 1, wherein at least one of the first integrated circuit devices and the second integrated circuit devices is a memory device.

14. The semiconductor device of claim 1, wherein at least one of the first integrated circuit devices and the second integrated circuit devices is a DRAM device.

15. The semiconductor device of claim 1, further comprising an additional conductive material layered over at least one of the exposed first and second conductive structures.

16. The semiconductor device of claim 15, wherein the additional conductive material is a gold material or a gold and tin alloy.

17. The semiconductor device of claim 1, further comprising:
a insulative layer disposed on the second side of the first semiconductor die;
at least one conductive pad disposed on the insulative layer opposite the first semiconductor die; and
a conductive line disposed through the insulative layer to electrically couple the first conductive structure with the at least one conductive pad.

18. The semiconductor device of claim 7, further comprising a solder ball coupled to the at least one conductive pad.

19. The semiconductor device of claim 1, further comprising a separate insulative layer at each of the second side of the first semiconductor die and the second side of the second semiconductor die.

20. The semiconductor device of claim 1, wherein the first conductive structure is coupled to the second conductive structure using a thermal compression technique.

21. The semiconductor device of claim 1, wherein the first conductive structure is coupled to the second conductive structure using an ultrasonic thermal compression technique.

22. A semiconductor device comprising:
multiple semiconductor dies each comprising:
at least two integrated circuit devices;
a conductive structure electrically coupled to the at least two integrated circuit devices, where the conductive structure is disposed at least partially through the semiconductor die and exposed at one side of the semiconductor die at a location other than near a periphery of the semiconductor die,

wherein the multiple semiconductor dies are stacked on top of each other such that their respective conductive structures are aligned with, and are electrically coupled to, each other.

23. A method of forming a semiconductor device comprising:
forming a first semiconductor die having opposing first and second sides, the first semiconductor die comprising:
at least two first integrated circuit devices;
a first conductive structure electrically coupled between the at least two first integrated circuit devices, where the first conductive structure is disposed at least partially through the first semiconductor die and exposed at the first side of the first semiconductor die;

forming a second semiconductor die having opposing first and second sides, the second semiconductor die comprising:
at least two second integrated circuit devices;
a second conductive structure electrically coupled between the at least two second integrated circuit devices, where the second conductive structure is disposed at least partially through the second semiconductor die and exposed at the second side of the second semiconductor die;

stacking the first semiconductor die on the second semiconductor die such that the first conductive structure at the first side of the first integrated circuit die is aligned with the second conductive structure at the second side of the second semiconductor die; and
electrically coupling the first conductive structure to the second conductive structure.

24. The method of claim 23, wherein the first conductive structure is formed at the first side of the first semiconductor die at a location other than near a periphery of the first semiconductor die, and the second conductive structure is formed at the second side of the second semiconductor die at a location other than near a periphery of the second semiconductor die.