Patent Publication Number: US-2022223537-A1

Title: Method for fabricating interconnection using graphene

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 15/602,699, filed on May 23, 2017, which claims priority to Chinese patent application No. 201610620762.0, filed with the State Intellectual Property Office of People&#39;s Republic of China on Aug. 1, 2016, the content of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to semiconductor technology, and more particularly to a semiconductor interconnect structure and the method of forming the same. 
     BACKGROUND 
     A gradual reduction in the dimension of interconnect structures may limit the speed of signal propagation in semiconductor devices. The use of copper and low-k dielectric materials may reduce the delay in signal propagation. However, the diffusion of copper into a dielectric material will affect the effective dielectric k constant value of the dielectric material, and that the diffusion effect becomes more significant with increasing diffusion severity that may cause the dielectric material to become conductive, thereby affecting the device reliability. 
     Further, after planarization, exposed copper is easily oxidized by air, resulting in a relatively short queue time (Q-time) of a chemical mechanical planarization (CMP) process, which is disadvantageous to the development of semiconductor manufacturing processes. 
     SUMMARY 
     Embodiments of the present disclosure provide a novel method of manufacturing a metal interconnect structure that can prevent the metal in the metal interconnection from diffusing into the dielectric layer. 
     Embodiments of the present disclosure also provide a novel interconnect structure. 
     According to some embodiments of the present invention, a method for manufacturing an interconnect structure may include providing a substrate structure comprising a substrate, a first dielectric layer on the substrate, and a metal interconnect line extending through the first dielectric layer; removing a portion of the first dielectric layer on the metal interconnect line to form a recess exposing a surface of the metal interconnect line; forming a graphene layer on the exposed surface of the metal interconnect line; and forming a second dielectric layer filling the recess and covering the graphene layer. 
     In one embodiment, the substrate structure may further include a first barrier layer between the substrate and the first dielectric layer, the metal interconnect line extending through the first dielectric layer and the first barrier layer. 
     In one embodiment, the first barrier layer is formed on the substrate prior to forming the first dielectric layer, and removing the portion of the first dielectric layer on the metal interconnect line also exposes a surface of the first barrier layer. The method further includes forming an amorphous carbon layer on the exposed surface of the first barrier layer. 
     In one embodiment, the substrate structure further includes a second barrier layer formed at a bottom and on a side surface of the metal interconnect line. 
     In one embodiment, removing the portion of the first dielectric layer on the metal interconnect line to form the recess includes exposing a portion of the second barrier layer on the side surface of the metal interconnect line; and removing the exposed portion of the second barrier layer on the side surface of the metal interconnect line to form the recess. 
     In one embodiment, providing the substrate structure may include providing the substrate; forming the first barrier layer on the substrate; forming the first dielectric layer on the first barrier layer; forming a patterned first hardmask on the first dielectric layer; sequentially etching the first dielectric layer and the first barrier layer using the patterned first hardmask as a mask to form a through-hole; forming the second barrier layer on a sidewall of the through-hole; forming a metal layer filling the through-hole; and performing a planarization process to remove the patterned first hardmask to expose a surface of the first dielectric layer. 
     In one embodiment, the through-hole is a through-hole having a damascene structure, and sequentially etching the first dielectric layer and the first barrier layer includes performing a first etching process on the first dielectric layer using the patterned first hardmask as a mask to form a first opening and a second opening; forming a patterned second hardmask on the first opening; performing a second etching process on the first dielectric layer using the patterned first hardmask and the patterned second hardmask as a mask to form a third opening; removing the patterned second hardmask; performing a third etching process on the first dielectric layer and the first barrier layer using the patterned first hardmask as a mask to form a first through-hole and a second through-hole extending to the substrate, the first through-hole including the first opening and the third opening, and the second through-hole including the second opening. 
     In one embodiment, the graphene layer includes a layer of fluorinated graphene. 
     In one embodiment, forming the graphene layer includes a chemical vapor deposition process including supplying a reaction gas comprising methane, hydrogen, and a carrier gas, the chemical vapor deposition process being carried out at a temperature in a range between 600.degree. C. and 1500.degree. C., a reaction time in a range between 5 minutes and 300 minutes, a flow rate of the carrier gas in a range between 50 sccm and 10,000 sccm, a ratio of a flow rate of the method to a flow rate of the carrier gas in a range between 0.05% and 50%, and a ratio of a flow rate of the hydrogen to the flow rate of the carrier gas in a range between 0.05% and 50%. 
     In one embodiment, the method further includes performing a planarization process on the second dielectric layer. 
     In one embodiment, the method further includes forming a third dielectric layer on the second dielectric layer for a second interconnect structure. 
     In one embodiment, the method further includes forming a third barrier layer on the second dielectric layer, wherein the third dielectric layer is formed on the third barrier layer. 
     In one embodiment, the metal interconnect line includes copper, and the first and second dielectric layers each comprise silicon oxide or a low-k dielectric material. 
     In one embodiment, the first barrier layer includes SiCN, and the second barrier layer includes Ta, TaN, or stacked layers of Ta and TaN. 
     In one embodiment, the graphene layer includes 1 to 30 layers of monoatomic graphene layers. 
     Embodiments of the present disclosure also provide an interconnect structure, which includes a substrate; a metal interconnect line including an upper surface and a side surface on the substrate and; a graphene layer on the upper surface and the side surface of the metal interconnect line; and a dielectric layer on the substrate covering a portion of the graphene layer on the side surface of the metal interconnect line. 
     In one embodiment, the dielectric layer does not cover a portion of the graphene layer on the upper surface of the metal interconnect line. 
     In one embodiment, the dielectric layer further covers a portion of the graphene layer on the upper surface of the metal interconnect line. 
     In one embodiment, the interconnect structure further includes a first barrier layer between the substrate and the dielectric layer, wherein the graphene layer is formed on the upper surface and the side surface of the metal interconnect line and on a side portion of the first barrier layer. 
     In one embodiment, the interconnect structure further includes an amorphous carbon layer between the first barrier layer and the dielectric layer. 
     In one embodiment, the interconnect structure further includes a second barrier layer having a portion between the metal interconnect layer and the substrate and a portion between the metal interconnect layer and the first barrier layer. 
     In one embodiment, the interconnect structure further includes a second dielectric layer on the graphene layer for forming a second interconnect structure. 
     In one embodiment, the interconnect structure further includes a third barrier layer on the on the upper surface of the metal interconnect line and on the dielectric layer; and a third dielectric layer on the third barrier layer for forming a new interconnect structure. 
     In one embodiment, the interconnect structure further includes a next dielectric layer on the dielectric layer for forming a next interconnect structure. In one embodiment, the interconnect structure also includes a next barrier layer on the between the dielectric layer and the next dielectric layer. 
     In one embodiment, the graphene layer includes a layer of fluorinated graphene. 
     In one embodiment, the metal interconnect line includes a damascene structure. 
     In one embodiment, the metal interconnect line includes copper, and the dielectric layer includes silicon oxide or a low-k dielectric material. 
     In one embodiment, the first barrier layer includes SiCN, and the second barrier layer includes Ta, TaN, or stacked layers of Ta and TaN. 
     In one embodiment, the graphene layer includes 1 to 30 layers of monoatomic graphene layers. 
     The following detailed description together with the accompanying drawings will provide a better understanding of the nature and advantages of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart illustrating a method for manufacturing an interconnect structure according to one embodiment of the present disclosure. 
         FIG. 2A  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to one embodiment of the present disclosure. 
         FIG. 2B  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to one embodiment of the present disclosure. 
         FIG. 2C  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to one embodiment of the present disclosure. 
         FIG. 2D  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to one embodiment of the present disclosure. 
         FIG. 2E  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to one embodiment of the present disclosure. 
         FIG. 2F  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to one embodiment of the present disclosure. 
         FIG. 3A  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to another embodiment of the present disclosure. 
         FIG. 3B  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to another embodiment of the present disclosure. 
         FIG. 3C  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to another embodiment of the present disclosure. 
         FIG. 3D  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to another embodiment of the present disclosure. 
         FIG. 3E  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to another embodiment of the present disclosure. 
         FIG. 3F  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to another embodiment of the present disclosure. 
         FIG. 3G  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to another embodiment of the present disclosure. 
         FIG. 3H  is a cross-sectional view illustrating an intermediate stage of an interconnect structure according to another embodiment of the present disclosure. 
         FIG. 4A  is a cross-sectional view illustrating an intermediate stage of a substrate structure according to one embodiment of the present disclosure. 
         FIG. 4B  is a cross-sectional view illustrating an intermediate stage of a substrate structure according to one embodiment of the present disclosure. 
         FIG. 4C  is a cross-sectional view illustrating an intermediate stage of a substrate structure according to one embodiment of the present disclosure. 
         FIG. 4D  is a cross-sectional view illustrating an intermediate stage of a substrate structure according to one embodiment of the present disclosure. 
         FIG. 4E  is a cross-sectional view illustrating an intermediate stage of a substrate structure according to one embodiment of the present disclosure. 
         FIG. 4F  is a cross-sectional view illustrating an intermediate stage of a substrate structure according to one embodiment of the present disclosure. 
         FIG. 4G  is a cross-sectional view illustrating an intermediate stage of a substrate structure according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention now will be described more fully hereinafter with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The features may not be drawn to scale, some details may be exaggerated relative to other elements for clarity. Like numbers refer to like elements throughout. 
     It will be understood that when an element such as a layer, region or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “lateral” or “vertical” may be used herein to describe a relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. 
     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”, “comprising”, “includes”, and/or “including” when used herein, 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, elements, components, and/or groups thereof. 
     Embodiments of the invention are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments and intermediate structures) of the invention. The thickness of layers and regions in the drawings may be enlarged relative to other layers and regions for clarity. Additionally, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a discrete change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the invention. 
     Embodiments of the present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
       FIG. 1  is a flowchart illustrating a method for manufacturing an interconnect structure according to one embodiment of the present disclosure. The method may include the following steps: 
     Step  102 : providing a substrate structure including a substrate, a first dielectric layer on the substrate, and a metal interconnect line (wire) extending through the first dielectric layer. 
     Step  104 : removing a portion of the first dielectric layer on the metal interconnect line to form a recess and expose a surface of the metal interconnection line. 
     Step  106 : forming a graphene layer on the exposed surface of the metal interconnect line. 
     Step  108 : forming a second dielectric layer filling the recess and covering the graphene layer. 
     The present inventor has discovered that the graphene atomic layer can insulate the metal interconnect line from contacting external active medium, and even under heating, there is no significant oxidation in the graphene atomic layer, and the graphene has good anti-oxidation performance. 
     In the method of manufacturing the interconnect structure according to the present disclosure, the dielectric layer on the metal interconnect line is removed to expose a surface of the metal interconnect line, the graphene layer is formed on the exposed surface of the metal interconnect line, and a new (next) dielectric layer is formed. The graphene layer separates the metal interconnect line from the dielectric layer, so that metal atoms of the metal interconnect line can be prevented from diffusing into the dielectric layer. In addition, the high oxidation resistance of the graphene layer prevents the graphene layer from being oxidized even when the graphene layer is exposed to air, further preventing the metal interconnect line from being oxidized by the air, thereby improving the reliability of the device. 
       FIGS. 2A to 2F  are simplified cross-sectional views of intermediated stages of an interconnect structure according to an embodiment of the present disclosure. 
     Referring to  FIG. 2A , a substrate structure is provided. The substrate structure includes a substrate  201 , a first dielectric layer  202  on substrate  201 , and a metal interconnect line  203  extending through first dielectric layer  202 . 
     It is to be understood that substrate  201  may include a semiconductor substrate, and a semiconductor device and a shallow trench isolation region (not shown) formed on the semiconductor substrate. In one embodiment, the metal interconnect line may be a damascene interconnect structure, i.e., metal interconnect line  203  may include a wide upper portion and a narrow lower portion, as shown in the left portion of metal interconnect line  203  in  FIG. 2A . In one embodiment, the metal interconnect line may include, but not limited to, copper, and the first dielectric layer may include silicon oxide, a low-k dielectric material, or an ultra-low-k dielectric material. 
     Next, referring to  FIG. 2B , a portion of first dielectric layer  202  on metal interconnect line  203  is removed to form a recess  204  such that a surface of metal interconnect line  203  is exposed. As shown in  FIG. 2B , the portion of the first dielectric layer on opposite sides of the metal interconnect line is removed, and recess  204  is formed adjacent to the opposite sides of the metal interconnect line to expose a surface of the metal interconnect line. 
     Wet or dry etching may be used to remove the portion of first dielectric layer  202  on the opposite sides of the metal interconnect line in accordance with the material of first dielectric layer  202 . For example, in the case where the material of first dielectric layer  202  is a polyethylene oxide (PEOX), the PEOX may be removed using a dilute hydrofluoric acid. For example, in the case where the material of first dielectric layer  202  is a low-k or ultra-low-k silicon carbide (SiOCH), the SiOCH may be removed using a hydrogen-containing plasma. 
     Next, referring to  FIG. 2C , a graphene layer  205  is formed on the exposed surface of metal interconnect line  203 . In one embodiment, while graphene layer  205  is formed on the exposed surface of metal interconnect line  203 , an amorphous carbon layer  206  may also be formed on the exposed surface of substrate  201 , which may serve as an insulating layer between the substrate and a subsequently formed dielectric layer. 
     In one embodiment, graphene layer  205  may be formed using a chemical vapor deposition (CVD) process. The CVD process conditions may include supplying a reaction gas including methane, hydrogen, and a carrier gas, which may be, for example, nitrogen or argon; at a reaction temperature in the range between 600 .degree. C. and 1500 .degree. C.; and a reaction time in the range between 5 minutes and 300 minutes. The flow rate of the carrier gas is in the range between 50 sccm and 10,000 sccm, the ratio of the flow rate of methane to the flow rate of the carrier gas is in the range between 0.05% and 50%, and the ratio of the flow rate of the hydrogen gas to the flow rate of the carrier gas is in the range between 0.05% and 50%. In one embodiment, graphene layer  205  may include 1 to 30 layers of monoatomic graphene layers, e.g., 5 layers, 10 layers, 25 layers, etc. In addition, graphene layer  205  may include a layer of fluorinated graphene, which is thermally stable and chemically more stable to allow a better insulation of the metal interconnect line from the dielectric layer. 
     Next, referring to  FIG. 2D , a second dielectric layer  207  is formed filling recess  204  and covering graphene layer  205 . Second dielectric layer  207  may be of the same material or a different material than first dielectric layer  202 . For example, second dielectric layer  207  and first dielectric layer  201  may include a low-k or ultra-low-k dielectric material, or one of second dielectric layer  207  and first dielectric layer  202  may include silicon oxide, and the other one may include a low-k dielectric material. 
     Next, referring to  FIG. 2E  and  FIG. 2F , a planarization (e.g., chemical mechanical polishing) process is performed on second dielectric layer  207 . In one embodiment, as shown in  FIG. 2E , after the planarization, the planarized second dielectric layer  207  has an upper surface that is substantially flush with the surface portion of graphene layer  205  on metal interconnect line  203 . In another embodiment, as shown in  FIG. 2F , after the planarization, the planarized second dielectric layer  207  may still cover graphene layer  205 . As used herein, the term “substantially flush” means flushness between two surfaces within some tolerance under normal process variation. 
     An interconnect structure can thus be obtained according to the manufacturing method shown and described according to  FIGS. 2A to 2F . 
     An interconnect structure according to an embodiment of the present disclosure will be described with reference to  FIG. 2E . 
     Referring to  FIG. 2E , the interconnect structure may include a substrate  201 ; a metal interconnect line  203  on substrate  201 ; a graphene layer  205  on the upper surface and sidewalls (side surface) of metal interconnect line  203 ; and a dielectric layer (corresponding to second dielectric layer  207 ) on a portion of graphene layer  205  on the sidewalls of metal interconnect line  203 . Second dielectric layer  207  does not cover the upper surface of metal interconnect line  203 . In one embodiment, the upper surface of second dielectric layer  207  is substantially flush with the surface portion of graphene layer  205  on the upper surface of metal interconnect line  203 . 
     An interconnect structure according to another embodiment of the present disclosure will be described with reference to  FIG. 2F . 
     Referring to  FIG. 2F , the interconnect structure may include a substrate  201 ; a metal interconnect line  203  on substrate  201 ; a graphene layer  205  on the upper surface and sidewalls of metal interconnect line  203 ; and a dielectric layer (corresponding to second dielectric layer  207 ) on graphene layer  205  on the upper surface and sidewalls of metal interconnect line  203 . 
       FIGS. 3A to 3H  are simplified cross-sectional views of intermediated stages of an interconnect structure according to another embodiment of the present disclosure. It is noted that the manufacturing method of an interconnect structure has been described in detail above with reference to  FIGS. 2A to 2F , only the differences from the above-described method associated with  FIGS. 2A to 2F  will the described in detail below. 
     Referring to  FIG. 3A , a substrate structure is provided, which includes a substrate  201 , a first barrier layer  301  on substrate  201 , a first dielectric layer  202  on first barrier layer  301 , and a metal interconnect line  203  extending through first dielectric layer  202  and first barrier layer  301 . Comparing with the substrate structure in  FIG. 2A , the substrate structure further includes first barrier layer  301  disposed between substrate  201  and first dielectric layer  202 . First barrier layer  301  may include, but not limited to, SiCN. In addition, the substrate structure may further include a second barrier layer  302  disposed around metal interconnect line  203 , i.e., metal interconnect line  203  is disposed on second barrier layer  302 . In one embodiment, second barrier layer  302  may include Ta, TaN or stacked layers of Ta and TaN. However, embodiments of the present disclosure are not limited thereto. 
     Next, referring to  FIG. 3B , a portion of first dielectric layer  202  on opposite sides of metal interconnect line  203  is removed to form a recess  204 , such that the side surface of metal interconnect line  203  is exposed. In one embodiment, a portion of first dielectric layer  202  on opposite sides of metal interconnect line  203  may be removed to expose a portion of second barrier layer  302  on the opposite sides of metal interconnect line  203 , the exposed portion of second barrier layer  302  is then removed to form recess  204 . 
     Next, referring to  FIG. 3C , a graphene layer  205  is formed on the exposed surface of metal interconnect line  203 . In one embodiment, while graphene layer  205  is formed on the exposed surface of metal interconnect line  203 , an amorphous carbon layer  206  may also be formed on the exposed first barrier layer  301 , which may serve as an insulating layer between a subsequently formed dielectric layer and the substrate. The steps of forming graphene layer  205  can be referred to the above described sections, and will not be repeated herein. 
     Next, referring to  FIG. 3D , a second dielectric layer  207  is formed filling recess  204  and covering graphene layer  205 . 
     Next, referring to  FIG. 3E  and  FIG. 3F , a planarization (e.g., chemical mechanical polishing) process is performed on second dielectric layer  207 . In one embodiment, as shown in  FIG. 3E , after the planarization, the planarized second dielectric layer  207  has an upper surface that is substantially flush with the surface portion of graphene layer  205  on metal interconnect line  203 . In another embodiment, as shown in  FIG. 3F , after the planarization, the planarized second dielectric layer  207  may still cover graphene layer  205 . 
     An interconnect structure can thus be obtained according to the manufacturing method shown and described in  FIGS. 3A to 3F . 
     An interconnect structure according to an embodiment of the present disclosure will be described with reference to  FIG. 3E . 
     Referring to  FIG. 3E , the interconnect structure may include a substrate  201 ; a metal interconnect line  203  on substrate  201 ; a graphene layer  205  on the upper surface and sidewalls (side surface) of metal interconnect line  203 ; a dielectric layer (corresponding to second dielectric layer  207 ) on a portion of graphene layer  205  on the sidewalls of metal interconnect line  203 ; and a barrier layer (corresponding to first barrier layer  301 ) disposed between the dielectric layer and substrate  201 . Graphene layer  205  is formed on the upper surface of metal interconnect line  203  and on side surface of metal interconnect line  203  above first barrier layer  301 ; and the dielectric layer (corresponding to second dielectric layer  207 ) does not cover the portion of graphene layer  205  on the upper surface of metal interconnect line  203 . Further, the interconnect structure may further include an amorphous carbon layer  206  between first barrier layer  301  and the dielectric layer (corresponding to second dielectric layer  207 ). 
     An interconnect structure according to another embodiment of the present disclosure will be described with reference to  FIG. 3F . Comparing with the interconnect structure in  FIG. 3E , the dielectric layer (corresponding to second dielectric layer  207 ) of the interconnect structure in  FIG. 3F  not only covers a portion of graphene layer  205  on the sidewalls of metal interconnect line  203 , but also a portion of graphene layer  205  on the upper surface of metal interconnect line  203 . 
     Further, the interconnect structures in  FIGS. 3E and 3F  may also include second barrier layer  302  disposed between metal interconnect layer  203  and substrate  201  and between metal interconnect layer  203  and first barrier layer  301 . 
     Thereafter, a third barrier layer  208  may be formed on the interconnect structures in  FIGS. 3E and 3F  to form another interconnect structures. A third dielectric layer  209  is formed on third barrier layer  208  of the interconnect structures, as shown in  FIGS. 3G and 3H . In one embodiment, third dielectric layer  209  may be formed directly on the interconnect structures in  FIGS. 3E and 3F . 
     Comparing with the interconnect structure in  FIG. 3E , the interconnect structure in  FIG. 3G  may further include a third barrier layer  208  on a portion of graphene layer  205  on the upper surface of metal interconnect line  203  and the dielectric layer (corresponding to second dielectric layer  207 ), and a third dielectric layer  209  on third barrier layer  208 . 
     Comparing with the interconnect structure in  FIG. 3F , the interconnect structure in  FIG. 3H  may further include a dielectric layer (corresponding to third dielectric layer  209 ) on the dielectric layer (corresponding to second dielectric layer  207 ). Preferably, the interconnect structure in  FIG. 3H  may further include a third barrier layer  208  between the second dielectric layer ( 207 ) and the third dielectric layer ( 209 ). 
       FIGS. 4A-4F  are simplified cross-sectional views illustrating the intermediate stages of forming the interconnect structure shown in  FIG. 3A . 
     Referring to  FIG. 4A , a substrate  201  is provided. A first barrier layer  301  is formed on substrate  201 ; and a first dielectric layer  202  is formed on first barrier layer  301 . 
     Next, referring to  FIG. 4B , a patterned first hardmask  401  is formed on first dielectric layer  202 . Hardmask  401  may include, for example, one or more of the following materials: titanium nitride (TiN), tetraethoxysilane (TEOS), and SiOCH. 
     Thereafter, first dielectric layer  202  and first barrier layer  301  are sequentially etched using patterned first hardmask  401  as a mask to form a through-hole extending to substrate  201 . 
     In one embodiment, the through-hole is formed as a through-hole having a damascene structure. The formation of the through-hole will be described with reference to  FIGS. 4C through 4E . 
     Referring to  FIG. 4C , first dielectric layer  202  is etched using patterned first hardmask  401  as a mask to form a first opening  412  and second opening  422 . 
     Referring to  FIG. 4D , a patterned second hardmask  403  is formed on first opening  412 , and first dielectric layer  202  is etched using patterned first hardmask  401  and patterned second hardmask  403  as a mask to form a third opening  432 . At the same time, the bottom surface of second opening  422  also continues to extend downwardly. 
     Referring to  FIG. 4E , patterned second hardmask  403  is removed, and the remaining first dielectric layer  202  and first barrier layer  301  are etched using patterned first hardmask  401  as a mask to form a first through-hole  402  and a second through-hole  422 . First though-hole  402  includes a wider first opening  412  at the upper portion and a narrower third opening  432  at the lower portion. At the same time, the bottom of second opening  422  extends to substrate  201  to form second through-hole  422 . It should be noted that, after the remaining first dielectric layer  202  and first barrier layer  301  are etched with patterned first hardmask  401 , a portion of first dielectric layer  202  between two third openings  432  includes two slopes as shown in  FIG. 4E , but it is merely illustrative and should not be construed as limiting the present disclosure. 
     Next, referring to  FIG. 4F , after forming the through-holes ( 402 ,  422 ), a second barrier layer  302  is formed on sidewalls of the through-holes (including first through-hole  402  and second through-hole  422 ). Herein, second barrier layer  302  is also formed on first hardmask  401 . 
     Next, referring to  FIG. 4G , a metal layer  203 ′ is formed in the through-holes (including first through-hole  402  and second through-hole  422 ). In an exemplary embodiment, copper may be deposited as metal layer  203 ′ using an electrochemical deposition (ECP) process. Preferably, a copper seed layer may also be formed on the surface of the through-holes prior to depositing copper by the ECP process. 
     Thereafter, a planarization process is performed to remove patterned first hardmask  401  and expose a surface of the remaining first dielectric layer  202 , thereby forming the substrate structure shown in  FIG. 3A . For example, a portion of the metal layer on first dielectric layer  202 , a portion of second barrier layer  302 , and first hardmask layer  401  may be removed through a planarization process. For example, metal layer  203 ′ may be planarized using a planarization (e.g., chemical mechanical polishing) process to expose a portion of second barrier layer  302  on first hardmask  401 , followed by an additional process to remove the portion of second barrier layer  302  on first hardmask  401  and first hardmask  401  to expose a surface of first dielectric layer  202 . A specific implementation of the substrate structure shown in  FIG. 3A  is thus described. However, the present disclosure is not limited thereto, and the substrate structure may be formed by other conventional means. After forming the substrate structure shown in  FIG. 3A , the subsequent steps may be continued according to the process flow shown and described with reference to  FIGS. 3A through 3H . 
     In summary, embodiments of the present disclosure provide detailed description of a semiconductor device and method of manufacturing the same. In order not to obscure the concept of the present disclosure, some of the details known in the art are not described. 
     As used herein, the term “substrate” may include, but is not limited to, a substrate of a semiconductor material (e.g., a silicon substrate). In an example embodiment, the term “substrate” may also include a semiconductor device formed on a substrate of a semiconductor material. In another example embodiment, the term “substrate” may also include a metal contact formed on a substrate of a semiconductor material. 
     As used herein, the term “flush” may include, but is not limited to, a substantially flat surface instead of absolute flat, that allows for some errors within the process tolerance and coplanar with another flat surface. In other words, the term “flush” is defined to include surfaces that are substantially disposed on the same plane, but may include minor differences with the process tolerance. 
     References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, “some embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     It is to be understood that the above described embodiments are intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.