# Patent

## Title
Graphene devices and silicon field effect transistors in 3D hybrid integrated circuits

## Abstract

A three dimensional integrated circuit includes a silicon substrate, a first source region disposed on the substrate, a first drain region disposed on the substrate, a first gate stack portion disposed on the substrate, a first dielectric layer disposed on the first source region, the first drain region, the first gate stack portion, and the substrate, a second dielectric layer formed on the first dielectric layer, a second source region disposed on the second dielectric layer, a second drain region disposed on the second dielectric layer, and a second gate stack portion disposed on the second dielectric layer, the second gate stack portion including a graphene layer.

## Background
FIELD OF INVENTION
The present invention relates to hybrid integration of heterogeneous field effect devices for integrated circuits, and more specifically, to 3-D hybrid integration of graphene field-effect transistors and silicon based devices.
DESCRIPTION OF RELATED ART
Graphene field effect transistor (FET) devices include a layer of graphene material that results in a device having high charge carrier mobility. These devices exhibit promise in high-frequency, e.g. radio-frequency, electronic applications.
The performance properties of graphene devices suggest that such devices may be useful when used in integrated circuits.
BRIEF SUMMARY
According to one embodiment of the present invention, a method for forming a three dimensional integrated circuit includes forming a first source region, a first drain region, and a first gate stack portion on a substrate, forming a first dielectric layer over the first source region, the first drain region, the first gate stack portion and the substrate, forming a first conductive interconnect portion in the first dielectric layer, forming a second dielectric layer on the first dielectric layer, forming a second conductive interconnect portion in the second dielectric layer, forming a graphene layer on the second dielectric layer, forming a second source region on the second dielectric layer and a second drain region on the second dielectric layer, forming a third dielectric layer on the graphene layer, and forming a metallic gate material on the third dielectric layer.
According to another embodiment of the present invention, a method for forming a three dimensional integrated circuit includes forming a first source region, a first drain region, and a first gate stack portion on a substrate, forming a first dielectric layer over the first source region, the first drain region, the first gate stack portion and the substrate, forming a first conductive interconnect portion in the first dielectric layer, forming a second dielectric layer on the first dielectric layer, forming a second conductive interconnect portion and the second metallic gate material in the second dielectric layer, forming a third dielectric layer on the second dielectric layer, forming a graphene layer on the third dielectric layer, forming a second source region and a second drain region on the third dielectric layer.
According to yet another embodiment of the present invention a three dimensional integrated circuit includes a silicon substrate, a first source region disposed on the substrate, a first drain region disposed on the substrate, a first gate stack portion disposed on the substrate, a first dielectric layer disposed on the first source region, the first drain region, the first gate stack portion, and the substrate, a second dielectric layer formed on the first dielectric layer, a second source region disposed on the second dielectric layer, a second drain region disposed on the second dielectric layer, and a second gate stack portion disposed on the second dielectric layer, the second gate stack portion including a graphene layer.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings.



BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 illustrates an exemplary embodiment of a portion of a 3-D hybrid integrated circuit including a top-gated graphene FET.
FIGS. 2-8 illustrate side views of an exemplary method for forming a circuit similar to the illustrated embodiment of FIG. 1, in this regard:
FIG. 2 illustrates the formation of a silicon FET device;
FIG. 3 illustrates the formation of a dielectric layer;
FIG. 4 illustrates the formation of interconnects;
FIG. 5 illustrates the formation of a graphene layer;
FIG. 6 illustrates the formation of source and drain regions;
FIG. 7 illustrates the formation of a dielectric layer; and
FIG. 8 illustrates the formation of a conductive gate material.
FIG. 9 illustrates an exemplary embodiment of a portion of an integrated circuit device including a bottom-gated graphene FET.
FIGS. 10-16 illustrate side views of an exemplary method for forming a circuit similar to the illustrated embodiment of FIG. 9, in this regard:
FIG. 10 illustrates the formation of a silicon FET device;
FIG. 11 illustrates the formation of a dielectric layer;
FIG. 12 illustrates the formation of interconnects;
FIG. 13 illustrates the formation of a dielectric layer;
FIG. 14 illustrates the formation of a graphene layer;
FIG. 15 illustrates the patterning of the graphene layer; and
FIG. 16 illustrates the formation of source and drain regions.
FIG. 17 illustrates an exemplary embodiment of a portion of an integrated circuit including a double-gated graphene FET.
FIGS. 18-19 illustrate side views of an exemplary method for forming a circuit similar to the illustrated embodiment of FIG. 17, in this regard:
FIG. 18 illustrates the formation of a dielectric layer; and
FIG. 19 illustrates the formation of a gate stack.
FIG. 20 illustrates an exemplary embodiment of a portion of a 3-D hybrid integrated circuit including multiple top-gated graphene FETs.



DETAILED DESCRIPTION
Integrated circuits may be formed on a silicon wafer using a variety of complimentary metal oxide semiconductor (CMOS) fabrication methods that form silicon based FET devices. Recently, a number of methods have been developed for fabricating graphene FET devices. Forming both silicon FET devices and graphene devices on a wafer in an integrated circuit offers increased performance benefits.
FIG. 1 illustrates an exemplary embodiment of a portion of an integrated circuit 100 including a top-gated graphene FET device 103. The circuit portion 100 includes a silicon wafer substrate 102. A silicon FET device 101, such as, for example, a metal oxide semiconductor FET (MOSFET) or other type of silicon FET device, is disposed on the substrate 102. The device 101 includes a source region 104 and a drain region 106 that may include, for example, ion doped silicon material. A gate stack 108 is disposed between the source region 104 and the drain region 106. The gate stack 108 may include a metallic or polysilicon type gate material. A dielectric layer 110 is formed over the source region 104, the drain region 106, the gate stack 108 and the exposed substrate 102. Conductive vias 112 are formed in cavities in the dielectric layer 110 that are filled with a conductive material such as, for example, copper or tungsten. The vias 112 may connect the source region 104, the drain region 106, and the gate stack 108 to wide conductive interconnects 114 that are formed in a second dielectric layer 111. The conductive interconnects and inductors (interconnects) 114 are connected to a graphene FET device (graphene device) 103 that is disposed on the dielectric layer 111. In the illustrated embodiment, the graphene device 103 includes a conductive source region 116 and a conductive drain region 118, and a gate stack 120 that includes a graphene layer 122 disposed on the dielectric layer 111 and a dielectric layer 124 such as a high-K dielectric layer disposed on the graphene layer 122 between the source and drain regions 116 and 118. A conductive gate material 126 forms the gate stack 120.
FIGS. 2-8 illustrate side views of an exemplary method for forming a device similar to the illustrated embodiment of FIG. 1 described above. Referring to FIG. 2, a silicon FET device 101 is fabricated by forming a source region 104 and drain region 106 in the substrate 102. The source and drain regions 104 and 106 may be formed by methods that include, for example, ion implantation or in-situ doping methods. The gate stack 108 is formed on a channel region of the substrate 102 partially defined by the source and drain regions 104 and 106. The gate stack 108 may include a variety of materials selected according to the specifications of the device 101. In the illustrated embodiment a CMOS device includes an oxide material layer 202 and a polysilicon material layer 204. Other embodiments of the device 101 may include, for example, a high-K/metallic gate or other type of FET gate stack structure.
FIG. 3 illustrates the formation of a dielectric layer 110 over the device 101 and the exposed substrate 102 using for example, a chemical vapor deposition process. The dielectric layer 110 may include thick silicon oxide, for example. Once the dielectric layer 110 is formed, via cavities are formed in the dielectric layer 110 to expose portions of the source region 104, the drain region 106, and the gate stack 108. The via cavities are filled with a conductive material such as, for example, copper or tungsten resulting in the formation of the vias 112.
FIG. 4 illustrates the formation of wide conductive interconnects and inductors (interconnects) 114 that are electrically connected to the vias 112. The interconnects 114 may be formed from a metallic material such as, for example, copper or aluminum and are surrounded by the second dielectric layer 111.
FIG. 5 illustrates the formation of second dielectric layer 111 over the dielectric layer 110 and a graphene layer 122 over the exposed interconnects 114 and portions of a second dielectric layer 111. The graphene layer 122 may be formed by any suitable method, for example, transferring the graphene material from a CVD grown graphene film on a copper foil or another graphene formation process.
FIG. 6 illustrates the resultant structure following the patterning and etching of the graphene layer 122 using, for example an oxygen plasma process, or other suitable process that removes portions of the graphene layer 122 and defines the graphene layer 122 over the channel region of the device. Following the patterning of the graphene layer 122, a source region 116 and drain region 118 are formed onto the graphene layer 122. The source region 116 and the drain region 118 may electrically contact the corresponding interconnects 114. The source and drain regions 116 and 118 may be formed by, for example, photolithographic patterning and metallic material deposition processes.
FIG. 7 illustrates the formation of a dielectric layer 124 that may include, for example, a high-K dielectric material. The dielectric layer 124 is formed over the exposed graphene layer 122 and the source and drain regions 116 and 118 using, for example, a chemical vapor deposition process or atomic layer deposition process.
FIG. 8 illustrates the formation of a metallic gate material 126 that is patterned such that the metallic gate material 126 is formed over the dielectric layer 124 in the gate stack region 120 partially defined by the graphene layer 122 of the FET device 103.
FIG. 9 illustrates an exemplary embodiment of a portion of an integrated circuit 900 including a bottom gated FET device 903. The circuit portion 900 includes a silicon wafer substrate 102. A silicon FET device 101, such as, for example, a metal oxide semiconductor FET (MOSFET) or other type of silicon FET device, is disposed on the substrate 102. The device 101 includes a source region 104 and a drain region 106 that may include, for example, ion doped silicon material. A gate stack 108 is disposed between the source region 104 and the drain region 106. The gate stack 108 may include a metallic or polysilicon type gate material. A dielectric layer 110 is formed over the source region 104, the drain region 106, the gate stack 108 and the exposed substrate 102. Conductive vias 112 are formed in cavities in the dielectric layer 110 that are filled with a conductive material such as, for example, copper or tungsten. The vias 112 may connect the source region 104, the drain region 106, and the gate stack 108 to conductive interconnects 114 that are formed in a second dielectric layer 111. The conductive interconnects and inductors (interconnects) 114 are connected to a graphene FET device (graphene device) 903 that is disposed on the dielectric layer 111. In the illustrated embodiment, the graphene device 903 includes a conductive source region 916 and a conductive drain region 918, and a gate stack 920 that includes a metallic gate material 926 formed in the dielectric layer 111, a dielectric layer 924 such as a high-K dielectric layer disposed on the metallic gate material 926 and the dielectric layer 111 and a graphene layer 922 formed on the dielectric layer 924. The source region 916 and the drain region 918 are electrically connected to the respective interconnects 114 with conductive vias 912 that pass through the dielectric layer 924.
FIGS. 10-16 illustrate side views of an exemplary method for forming a device similar to the illustrated embodiment of FIG. 9 described above. Referring to FIG. 10, a silicon FET device 101 is fabricated by forming a source region 104 and drain region 106 in the substrate 102. The source and drain regions 104 and 106 may be formed by methods that include, for example, ion implantation or in-situ doping methods. The gate stack 108 is formed on a channel region of the substrate 102 partially defined by the source and drain regions 104 and 106. The gate stack 108 may include a variety of materials selected according to the specifications of the device 101. In the illustrated embodiment a CMOS device includes an oxide material layer 202 and a polysilicon material layer 204. Other embodiments of the device 101 may include, for example, a metallic gate or other type of FET gate stack structure.
FIG. 11 illustrates the formation of a dielectric layer 110 over the device 101 and the exposed substrate 102 using for example, a chemical vapor deposition process. Once the dielectric layer 110 is formed, via cavities are formed in the dielectric layer 110 to expose portions of the source region 104, the drain region 106, and the gate stack 108. The via cavities are filled with a conductive material such as, for example, copper or aluminum resulting in the formation of the vias 112.
FIG. 12 illustrates the formation of a second dielectric layer 111 and conductive interconnects and inductors (interconnects) 114 that are electrically connected to the vias 112. The interconnects 114 may be formed from a metallic material such as, for example, copper or aluminum and are surrounded by the dielectric layer 111. A metallic gate material 926 is formed in the dielectric layer 111 using a similar method for forming the interconnects 114.
FIG. 13 illustrates the formation of a dielectric layer 924 such as, for example, a high-K layer over the exposed dielectric layer 111, the interconnects 114 and the metallic gate material 926.
FIG. 14 illustrates the formation of a graphene layer 922 over the dielectric layer 924. The graphene layer 922 may be formed by any suitable method, for example, transferring the graphene material from a CVD grown graphene film on a copper foil or another graphene formation process.
FIG. 15 illustrates the resultant structure following the formation of conductive vias 912 that pass through the dielectric layer 924 and contact the interconnects 114. The illustrated embodiment includes patterning and etching of the graphene layer 922 using, for example, an oxygen plasma process, or other suitable process that removes portions of the graphene layer 922 and defines the graphene layer 922 over the channel region of the device.
FIG. 16 illustrates the resultant structure following the formation of a source region 916 and drain region 918 that are formed proximate to the graphene layer 922. The source region 916 and the drain region 918 electrically contact the corresponding interconnects 114. The source and drain regions 916 and 918 may be formed by, for example, photolithographic patterning and metallic material deposition processes. The gate stack 920 of the resultant device 903 includes the metallic gate material 926, the dielectric layer 924, and the graphene layer 922.
FIG. 17 illustrates an exemplary embodiment of a portion of an integrated circuit device 1700 including a double gated FET device 1703. The device 1700 includes a silicon wafer substrate 102. A silicon FET device 101, such as, for example, a metal oxide semiconductor FET (MOSFET) or other type of silicon FET device, is disposed on the substrate 102. The device 101 includes a source region 104 and a drain region 106 that may include, for example, ion doped silicon material. A gate stack 108 is disposed between the source region 104 and the drain region 106. The gate stack 108 may include a metallic or polysilicon type gate material. A dielectric layer 110 is formed over the source region 104, the drain region 106, the gate stack 108 and the exposed substrate 102. Conductive vias 112 are formed in cavities in the dielectric layer 110 that are filled with a conductive material such as, for example, copper or tungsten. The vias 112 connect the source region 104, the drain region 106, and the gate stack 108 to conductive interconnects 114 that are formed in the dielectric layer 110. The conductive interconnects and inductors (interconnects) 114 are connected to a graphene FET device (graphene device) 1703 that is disposed on the dielectric layer 111. In the illustrated embodiment, the graphene device 1703 includes a conductive source region 916 and a conductive drain region 918, and a gate stack 1720 that includes a metallic gate material 926 formed in the dielectric layer 111, a dielectric layer 924 such as a high-K dielectric layer disposed on the metallic gate material 926, the dielectric layer 111 and a graphene layer 922 formed on the dielectric layer 924. The source region 916 and the drain region 918 are electrically connected to the respective interconnects 114 with conductive vias 912 that pass through the dielectric layer 924. A dielectric layer 1724 is formed over the exposed portions of the dielectric layer 924, the source and drain regions 916 and 918 and the graphene layer 922. A metallic gate material 1726 is formed over the dielectric layer 1724 in the gate stack region 1720 forming a double gate stack.
FIGS. 18 and 19 illustrate side views of an exemplary method for forming a device similar to the illustrated embodiment of FIG. 17 described above. In this regard the fabrication methods are similar to the methods described above in FIGS. 10 through 16. Referring to FIG. 17, following the formation of the source and drain regions 916 and 918, a dielectric layer 1724 such as, for example, a high-K layer is formed over the dielectric layer 924, the source and drain regions 916 and 918, and the graphene layer 922.
FIG. 19 illustrates the resultant structure following the formation of a metallic gate material 1726 on the dielectric layer 1724. The metallic gate material 1726 may be formed by, for example, a lithographic patterning and lift-off process.
FIG. 20 illustrates an exemplary embodiment of a multilayer circuit arrangement 2000. In this regard, the integrated circuit 100 including a top-gated graphene FET device 103 is formed in a similar manner as discussed above. Following the formation of the circuit 100, a dielectric layer 2010 is formed over the circuit 100. Connective vias 112 are formed in the dielectric layer 2010, and another dielectric layer 2011 is formed over the dielectric layer 2010. Conductive interconnects 2014 are formed in the dielectric layer 2011. A second top-gated graphene FET device 103 is formed on the dielectric layer 2011 in a similar manner as discussed above. The illustrated embodiment is but one example of a multilayer circuit arrangement. Alternative embodiments may include any type of arrangement of graphene devices and silicon devices.
The 3-D hybrid integrated circuit structure as described above can be further extended to multi-chip stacking by the Through-Silicon Via (TSV) methods.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
The diagrams depicted herein are just one example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention.
While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.

## Claims

1. A method for forming a three dimensional integrated circuit, the method including:
forming a first source region, a first drain region, and a first gate stack portion on a substrate;
forming a first dielectric layer over the first source region, the first drain region, the first gate stack portion and the substrate;
forming a first conductive interconnect portion in the first dielectric layer the first conductive interconnect portion including vias;
forming a second dielectric layer on the first dielectric layer;
forming a second conductive interconnect portion in the second dielectric layer;
forming a graphene layer on the second dielectric layer;
removing portions of the graphene layer to expose portions of the second dielectric layer;
forming a second source region on the second dielectric layer and a second drain region on the second dielectric layer;
forming a third dielectric layer on the graphene layer; and
forming a metallic gate material on the third dielectric layer.

2. The method of claim 1, wherein the method includes forming conductive vias in the first dielectric layer by:
forming cavities in the first dielectric layer prior to forming the first conductive interconnect portion, the cavities exposing a portion of the first source region, the first drain region, and the first gate stack portion; and
filling the cavities with a conductive material.

3. The method of claim 1, wherein the first conductive interconnect portion and the second conductive interconnect portion are formed by:
forming cavities in the second dielectric layer; and
filling the cavities with a conductive material.

4. The method of claim 1, wherein the third dielectric layer includes a high-K material.

5. The method of claim 1, wherein the first source region and the first drain region include a doped silicon material.

6. The method of claim 1, wherein the second source region and the second drain region include a metallic material.

7. A method for forming a three dimensional integrated circuit, the method including:
forming a first source region, a first drain region, and a first gate stack portion on a substrate;
forming a first dielectric layer over the first source region, the first drain region, the first gate stack portion and the substrate;
forming a first conductive interconnect portion in the first dielectric layer;
forming a second dielectric layer on the first dielectric layer;
forming a second conductive interconnect portion and a second metallic gate material in the second dielectric layer;
forming a third dielectric layer on the second dielectric layer;
forming a graphene layer on the third dielectric layer;
forming a second source region and a second drain region on the third dielectric layer.

8. The method of claim 7, wherein the method includes forming conductive vias in the first dielectric layer by:
forming cavities in the first dielectric layer prior to forming the first conductive interconnect portion, the cavities exposing a portion of the first source region, the first drain region, and the first gate stack portion; and
filling the cavities with a conductive material.

9. The method of claim 7, wherein the first conductive interconnect portion and the second conductive interconnect portion are formed by:
forming cavities in the second dielectric layer; and
filling the cavities with a conductive material.

10. The method of claim 7, wherein the metallic gate material is formed by:
forming cavities in the second dielectric layer; and
filling the cavities with the metallic gate material.

11. The method of claim 7, wherein the third dielectric layer includes a high-K material.

12. The method of claim 7, wherein the first source region and the first drain region include a doped silicon material.

13. The method of claim 7, wherein the second source region and the second drain region include a metallic material.

14. The method of claim 7, wherein the method further includes:
forming a fourth dielectric layer on the graphene layer; and
forming a metallic gate material on the fourth dielectric layer.

15. A method for forming a three dimensional integrated circuit, the method including:
forming a first source region, a first drain region, and a first gate stack portion on a substrate;
forming a first dielectric layer over the first source region, the first drain region, the first gate stack portion and the substrate;
forming a first conductive interconnect portion in the first dielectric layer;
forming a second dielectric layer on the first dielectric layer;
forming a second conductive interconnect portion and a second metallic gate material in the second dielectric layer;
forming a third dielectric layer on and in contact with the second dielectric layer;
forming a graphene layer on and in contact with the third dielectric layer;
forming a second source region and a second drain region on the third dielectric layer.

16. The method of claim 15, wherein the method includes forming conductive vias in the first dielectric layer by:
forming cavities in the first dielectric layer prior to forming the first conductive interconnect portion, the cavities exposing a portion of the first source region, the first drain region, and the first gate stack portion; and
filling the cavities with a conductive material.

17. The method of claim 15, wherein the first conductive interconnect portion and the second conductive interconnect portion are formed by:
forming cavities in the second dielectric layer; and
filling the cavities with a conductive material.

18. The method of claim 15, wherein the metallic gate material is formed by:
forming cavities in the second dielectric layer; and
filling the cavities with the metallic gate material.

19. The method of claim 15, wherein the third dielectric layer includes a high-K material.

20. The method of claim 15, wherein the first source region and the first drain region include a doped silicon material.