Patent Publication Number: US-2011057322-A1

Title: Carbon nanotube interconnect and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-209527, filed Sep. 10, 2009; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a carbon nanotube interconnect and a method of manufacturing the same. 
     BACKGROUND 
     A carbon nanotube (CNT) causes ballistic conduction parallel to the tube surface, and hence is expected to provide a low-resistance interconnect regardless of its length. Also, in a multi-walled carbon nanotube (MWCNT) having several layers of tube walls, electric currents equal in number to the walls flow. Letting R be the resistance of a single-walled carbon nanotube, therefore, the resistance value of the MWCNT is R/n (n is the number of walls). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are sectional views showing a carbon nanotube plug interconnect of a first embodiment; 
         FIGS. 2A to 3C  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the first embodiment; 
         FIGS. 4A and 4B  are sectional views showing a carbon nanotube plug interconnect of a second embodiment; 
         FIGS. 5A to 6B  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the second embodiment; 
         FIGS. 7A to 7C  are sectional views showing a method of manufacturing a carbon nanotube plug interconnect of a modification of the second embodiment; 
         FIGS. 8A to 8D  are sectional views showing the method of manufacturing the carbon nanotube plug interconnect of the modification of the second embodiment; 
         FIGS. 9A to 10C  are sectional views showing a method of manufacturing a carbon nanotube plug interconnect of a third embodiment; 
         FIGS. 11A to 12B  are sectional views showing a method of manufacturing a carbon nanotube plug interconnect of a modification of the third embodiment; 
         FIGS. 13A and 13B  are sectional views showing a carbon nanotube plug interconnect of a fourth embodiment; 
         FIGS. 14A to 15C  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the fourth embodiment; 
         FIGS. 16A and 16B  are sectional views showing a carbon nanotube plug interconnect of a fifth embodiment; 
         FIGS. 17A to 18B  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the fifth embodiment; 
         FIGS. 19A and 19B  are sectional views showing a carbon nanotube plug interconnect of a sixth embodiment; and 
         FIGS. 20A to 21B  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the sixth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will be explained below with reference to the accompanying drawing. In the following explanation, the same reference numerals denote the same parts throughout the drawing. 
     In embodiments, in a multilayered interconnection structure including first and second interconnection layers and an interlayer dielectric film formed between the first and second interconnection layers, a plug interconnect for electrically connecting the first and second interconnection layers is formed in the interlayer dielectric film. The plug interconnect has carbon nanotubes formed in a contact hole in the interlayer dielectric film. 
     In general, according to one embodiment, a carbon nanotube interconnect includes a first interconnection layer, an interlayer dielectric film, a second interconnection layer, a contact hole, a plurality of carbon nanotubes and a film. The interlayer dielectric film is formed on the first interconnection layer. The second interconnection layer is formed on the interlayer dielectric film. The contact hole is formed in the interlayer dielectric film between the first interconnection layer and the second interconnection layer. The carbon nanotubes are formed in the contact hole. The carbon nanotubes have a first end connected to the first interconnection layer and a second end connected to the second interconnection layer. The film is formed between the interlayer dielectric film and the second interconnection layer. The film has a portion filled between the second ends of the carbon nanotubes. 
     (1) Problems of End Opening 
     A carbon nanotube (CNT) causes ballistic conduction parallel to the tube surface, and hence is expected to provide a low-resistance interconnect regardless of its length. Also, in a multi-walled carbon nanotube (MWCNT) having several layers of tube walls, electric currents equal in number to the walls flow. Letting R be the resistance of a single-walled carbon nanotube, therefore, the resistance value of the MWCNT is R/n (n is the number of walls). 
     On the other hand, conduction from the wall to the wall of the carbon nanotube experiences a very high resistance. When growing the MWCNT, the terminal end of the growth is generally closed in the form of a dome. Even when the growth height of the MWCNT is ideally uniform and the upper surface of the MWCNT is in contact with an interconnection metal, an electric current crossing several layers of sidewalls need to be supplied in order to use parallel conduction paths inside the MWCNT. 
     In addition, the length of the MWCNT has variations in practice, and a portion extending from the opening of a via falls or inclines in the lateral direction. Consequently, an upper interconnection metal is in contact with the sidewalls of the MWCNT. 
     This poses the problem that it is impossible to fully utilize the merit of a low resistance of the MWCNT. This problem decreases the efficiency from the viewpoint of not only a low resistance but also a current density durability: the current density decreases because not all the walls in the MWCNT can be used in conduction. 
     To solve these problems, it is possible to destroy the crystal structure at the end of the MWCNT (an end-opening process), and form a connection by which an upper interconnect is in contact with multilayered wall surfaces inside the MWCTN. Examples of this end-opening process are a method of destroying the structure by irradiation with an energy line such as a plasma, UV light, or an ion beam, and a method of opening the end by a reaction with a chemical species or radical such as oxygen, hydrogen, or fluorine. 
     Unfortunately, there are spaces between individual carbon nanotubes. If any of these end-opening processes is performed on an actual carbon nanotube interconnection structure, therefore, the crystal structure is destroyed in portions other than the end of the carbon nanotube to be opened. Furthermore, the surface of a first interconnect as the root of the carbon nanotube sometimes changes. 
     (2) Excess Growth from Hole and Difficulty in Removal by Chemical Mechanical Polishing 
     When growing carbon nanotubes in a via hole or contact hole, the carbon nanotubes sometimes grow to protrude from the hole, and these excess carbon nanotubes are removed by using chemical mechanical polishing (CMP) or the like. Since the carbon nanotubes have a low CMP rate, however, an interlayer dielectric film is polished, and the carbon nanotubes remain as dust on the interlayer dielectric film. 
     Also, there is a method of coating the carbon nanotubes with spin-on-glass (SOG) and performing CMP in order to fix the carbon nanotubes (see, e.g., JP 2008-41954). Generally, however, the CMP rate of the SOG is high, and the carbon nanotubes are hard to polish. Therefore, the carbon nanotubes are dragged or pulled out from a hole. Alternatively, while the carbon nanotubes are not polished at all, only the SOG and the underlying interlayer dielectric film are polished, and the carbon nanotubes just fall. If a second interconnect is formed on the carbon nanotubes in this state, a pattern defect occurs or dust causes an electrical defect. 
     It is also possible to remove the excess portions of the carbon nanotubes by using plasma etching instead of CMP. As described in “(1) Problems of End Opening”, however, damage may be inflicted not only to the ends of the carbon nanotubes, but also to the side walls of the carbon nanotubes or an interconnect below the carbon nanotubes. 
     [1] First Embodiment 
     In the first embodiment, an example in which an insulating film as a stopper film is formed on an interlayer dielectric film having a plug interconnect and a second interconnection layer is formed in an etching step will be explained. In a CMP step of polishing carbon nanotubes protruding from a contact hole, the insulating film on the interlayer dielectric film functions as a stopper film and fixes the carbon nanotubes. The carbon nanotubes are held by the stopper film. 
     [1-1] Carbon Nanotube Plug Interconnect 
       FIG. 1A  is a sectional view showing a carbon nanotube plug interconnect of the first embodiment. 
     As shown in  FIG. 1A , a first interconnection layer  12  is formed in an interlayer dielectric film  11 . The interlayer dielectric film  11  is made of, e.g., SiO 2  or SiOC, and formed on a semiconductor substrate (not shown). The first interconnection layer  12  is made of, e.g., Cu, and buried in the interlayer dielectric film  11 . The top surface of the first interconnection layer  12  is exposed from the interlayer dielectric film  11 . 
     A barrier metal (not shown) is formed between the first interconnection layer  12  and the interlayer dielectric film  11  as needed. The barrier metal is made of at least one of, e.g., Ta, TaN, Ti, and TiN, or a multilayered film of these metals. 
     An interlayer dielectric film  13  is formed on the interlayer dielectric film  11  and the first interconnection layer  12 . The interlayer dielectric film  13  is made of, e.g., SiO 2  or SiOC. 
     In the interlayer dielectric film  13  on the first interconnection layer  12 , a contact hole  15  for electrically connecting the first interconnection layer  12  and a second interconnection layer  14  to be formed on the interlayer dielectric film  13  is formed. Carbon nanotubes  16  are formed in the contact hole  15 . The carbon nanotubes  16  electrically connect the first interconnection layer  12  and the second interconnection layer  14 . The second interconnection layer  14  is made of, e.g., Al. 
     A stopper film  17  is formed on the interlayer dielectric film  13 . The stopper film  17  is filled in the ends of the carbon nanotubes  16  on the side of the second interconnection layer  14 , so as to fix the carbon nanotubes  16 . The stopper film  17  is made of an insulating film, e.g., SiN, SiC, or SiCN, and also has the effect of cutting ultraviolet (UV) radiation. The stopper film  17  can also be a multilayered film of SiN and SiO 2 , or a multilayered film of SiN and SiOC. 
     A barrier metal  18  is formed between the stopper film  17  and second interconnection layer  14 . The carbon nanotubes  16  each have one end in contact with the first interconnection layer  12 , and the other end in contact with the barrier metal  18 . The first interconnection layer  12  and second interconnection layer  14  are electrically connected via the carbon nanotubes  16 . The barrier metal  18  is made of at least one of, e.g., Ta, TaN, Ti, and TiN, or a multilayered film of these metals. 
     Note that  FIG. 1A  shows an example in which the stopper film  17  is formed at the ends of the carbon nanotubes  16  on the side of the second interconnection layer  14 , from the bottom surface of the barrier metal  18  to that of the stopper film  17 . However, as shown in  FIG. 1B , the stopper film  17  can also be formed from the bottom surface of the barrier metal  18  to a position deeper than the bottom surface of the stopper film  17 . That is, the stopper film  17  may be protruded to the contact hole  15  from the bottom surface of the barrier metal  18 . 
     [1-2] Method of Manufacturing Carbon Nanotube Plug Interconnect 
       FIGS. 2A to 3C  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the first embodiment. 
     After an interconnect trench is formed in an interlayer dielectric film  11 , a first interconnection layer  12  is formed in the interconnect trench, as shown in  FIG. 2A . After that, an interlayer dielectric film  13  is formed on the interlayer dielectric film  11  and first interconnection layer  12  by, e.g., chemical vapor deposition (CVD). In addition, a contact hole  15  is formed in the interlayer dielectric film  13  on the first interconnection layer  12  by lithography. 
     Subsequently, carbon nanotubes  16  are formed on the first interconnection layer  12  in the contact hole  15 . More specifically, the carbon nanotubes  16  are grown in the contact hole  15  from the surface of the first interconnection layer  12  by the ordinary method, until they protrude from the contact hole  15 . That is, the carbon nanotubes  16  having ends protruding from the contact hole  15  are formed. 
     Then, as shown in  FIG. 2B , a stopper film  17  is formed by CVD on the interlayer dielectric film  13  and between the carbon nanotubes  16  above the contact hole  15 . In this step, the stopper film  17  enters and fills the spaces between the carbon nanotubes  16  above the contact hole  15  and near the opening of the contact hole  15 . Thus, the stopper film  17  fixes the carbon nanotubes  16 . 
     After that, an interlayer dielectric film is formed on the stopper film  17  and carbon nanotubes  16 . For example, a spin-on-glass (SOG) film  19  is formed by spin coating. 
     As shown in  FIG. 2C , the SOG film  19  and carbon nanotubes  16  above the stopper film  17  are polished by CMP. More specifically, the SOG film  19  above the carbon nanotubes  16  is polished first. When the polished portion has reached the carbon nanotubes  16  after that, the carbon nanotubes  16  are polished together with the SOG film  19 , as shown in  FIG. 3A . Then, as shown in  FIG. 3B , the SOG film  19  on the stopper film  17  is polished, and the carbon nanotubes  16  protruding upward from the stopper film  17  over the contact hole  15  are polished. 
     Note that the stopper film  17  is made of an insulating film, e.g., SiN, SiC, or SiCN having selectivity to the SOG film  19  in the CMP step of polishing the SOG film  19  and carbon nanotubes  16 . In other words, a film whose polishing rate in the CMP step is lower than that of the SOG film  19  is used as the stopper film  17 . This facilitates stopping the polishing when the SOG film  19  and carbon nanotubes  16  above the stopper film  17  are polished. 
     In this step, the carbon nanotubes  16  are fixed by the stopper film  17  filled between them. In the polishing step (CMP step), therefore, it is possible to suppress a lateral force acting on the carbon nanotubes  16 , thereby preventing damage to the carbon nanotubes  16 . That is, it is possible to prevent the carbon nanotubes  16  from falling or being pulled out from the contact hole  15 , and form carbon nanotubes  16  having aligned upper surfaces. This makes it possible to reduce pattern defects of the carbon nanotubes  16  and electrical characteristic defects caused by dust. 
     After that, as shown in  FIG. 3C , an end-opening process is performed on the exposed ends of the carbon nanotubes  16 . Examples of this end-opening process are a method of destroying the ends of the carbon nanotubes by irradiation with an energy line such as a plasma, UV light, or an ion beam, and a method of processing the ends of the carbon nanotubes by a reaction with a chemical species or radical such as oxygen, hydrogen, or fluorine. 
     Subsequently, a barrier metal  18  is formed on the end-opened carbon nanotubes  16  and stopper film  17  by, e.g., sputtering, CVD, or atomic layer deposition (ALD). In addition, an aluminum film serving as a second interconnection layer  14  is formed on the barrier metal  18 . The second interconnection layer  14  is formed by patterning the barrier metal  18  and aluminum film by lithography, as shown in  FIG. 1A . 
     When the dielectric constant of the stopper film is high, it is favorable to entirely remove the stopper film from the viewpoint of the dielectric constant. If there is no film fixing the upper ends of the carbon nanotubes, however, the sidewalls of the carbon nanotubes are damaged when performing the end-opening process or the like. 
     As described previously, therefore, a double structure such as a multilayered film of SiN and SiO 2  or a multilayered film of SiN and SiOC can also be used as the stopper film  17 . SiN is a high-k film, and SiO 2  or SiOC is a low-k film. When using the double structure as described above such that the upper layer (SiN) is removed after the CMP step and the lower layer (SiO 2  or SiOC) is left behind, it is possible to remove the high-k film and leave the film that fixes the upper ends of the carbon nanotubes behind. 
     Even when the stopper film is a single layer, the stopper film  17  can be deposited to enter the spaces between the carbon nanotubes  16  in the contact hole  15 , as shown in  FIG. 1B . In this case, even after the single-layered stopper film  17  is removed, the opening of the contact hole  15  can be closed with the stopper film. This makes it possible to prevent damage to the sidewalls of the carbon nanotubes when performing the end-opening process or the like. 
     [1-3] Effects of First Embodiment 
     In the first embodiment, the carbon nanotubes  16  are fixed by the stopper film  17  filled between them. Therefore, damage to the carbon nanotubes  16  can be prevented in the step of polishing the carbon nanotubes  16  protruding from the contact hole  15 . This makes it possible to reduce pattern defects of the carbon nanotubes  16  and electrical characteristic defects caused by dust, thereby improving the electrical connection between the first interconnection layer  12  and second interconnection layer  14 . 
     Furthermore, in the end-opening process of the carbon nanotubes  16 , the opening of the contact hole  15  is blocked with the stopper film  17 . During the end-opening process, therefore, the amount of energy line, chemical species, or radical entering the contact hole can be reduced. This makes it possible to prevent damage to the sidewalls of the carbon nanotubes  16  in the contact hole  15  and to the surface of the first interconnection layer  12  on the bottom of the contact hole. 
     [2] Second Embodiment 
     In the second embodiment, an example in which a metal film or the like as a stopper film is formed on an interlayer dielectric film having a plug interconnect and a second interconnection layer is formed in an etching step will be explained. In a CMP step of polishing carbon nanotubes protruding from a contact hole, the metal film or the like on the interlayer dielectric film functions as a stopper film and fixes the carbon nanotubes. 
     [2-1] Carbon Nanotube Plug Interconnect 
       FIG. 4A  is a sectional view showing a carbon nanotube plug interconnect of the second embodiment. 
     As shown in  FIG. 4A , a first interconnection layer  12  is formed in an interlayer dielectric film  11 . The interlayer dielectric film  11  is formed on a semiconductor substrate (not shown). The first interconnection layer  12  is buried in the interlayer dielectric film  11  so as to expose the surface. A barrier metal (not shown) is formed between the first interconnection layer  12  and the interlayer dielectric film  11  as needed. 
     An interlayer dielectric film  13  is formed on the interlayer dielectric film  11  and first interconnection layer  12 . In the interlayer dielectric film  13  on the first interconnection layer  12 , a contact hole  15  for electrically connecting a second interconnection layer  14  and the first interconnection layer  12  is formed. Carbon nanotubes  16  are formed in the contact hole  15 . The carbon nanotubes  16  electrically connect the first interconnection layer  12  and second interconnection layer  14 . 
     A barrier metal  18  is formed on the carbon nanotubes  16  and the interlayer dielectric film  13 . The second interconnection layer  14  is formed on the barrier metal  18 . The carbon nanotubes  16  each have one end in contact with the first interconnection layer  12 , and the other end in contact with the barrier metal  18 . The first interconnection layer  12  and second interconnection layer  14  are electrically connected via the carbon nanotubes  16 . 
     Note that  FIG. 4A  shows an example in which the metal film as a stopper film does not remain at the ends of the carbon nanotubes  16  on the side of the second interconnection layer  14 . However, as shown in  FIG. 4B , a stopper film  21  can also be formed at the ends of the carbon nanotubes  16  on the side of the second interconnection layer  14 . That is, the stopper film  21  may enter the contact hole from the bottom surface of the barrier metal  18 . The stopper film  21  is made of a metal film, metal compound, refractory metal, or refractory metal compound, e.g., Ta, TaN, TiN, or W. The stopper film  21  can also be made of amorphous silicon. 
     [2-2] Method of Manufacturing Carbon Nanotube Plug Interconnect 
       FIGS. 5A to 6B  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the second embodiment. 
     After an interconnect trench is formed in an interlayer dielectric film  11 , a first interconnection layer  12  is formed in the interconnect trench, as shown in  FIG. 5A . After that, an interlayer dielectric film  13  is formed on the interlayer dielectric film  11  and first interconnection layer  12  by, e.g., CVD. In addition, a contact hole  15  is formed in the interlayer dielectric film  13  on the first interconnection layer  12  by lithography. 
     Subsequently, carbon nanotubes  16  are formed on the first interconnection layer  12  in the contact hole  15 . More specifically, the carbon nanotubes  16  are grown from the surface of the first interconnection layer  12  by the ordinary method until they protrude from the contact hole  15 . 
     Then, as shown in  FIG. 5B , a stopper film  21 , e.g., a metal film is formed by sputtering on the interlayer dielectric film  13  and between the carbon nanotubes  16  above the contact hole  15 . In this step, the stopper film  21  enters and fills the spaces between the carbon nanotubes  16  above the contact hole  15  and near the opening of the contact hole  15 . Thus, the stopper film  21  fixes the carbon nanotubes  16 . After that, an SOG film  19  is formed on the stopper film  21  and carbon nanotubes  16  by spin coating. 
     As shown in  FIGS. 5C and 6A , the SOG film  19 , stopper film  21 , and carbon nanotubes  16  are polished by CMP. More specifically, the SOG film  19  on the carbon nanotubes  16  and stopper film  21  is polished first. When the polished portion has reached the carbon nanotubes  16  after that, the carbon nanotubes  16  are polished together with the stopper film  21 . As shown in  FIG. 6B , the polishing of the stopper film  21  and carbon nanotubes  16  is further advanced, thereby removing the SOG film  19  and carbon nanotubes  16  on the interlayer dielectric film  13  and above the contact hole  15 . 
     In this step, since the carbon nanotubes  16  are fixed by the stopper film  21  filled between them, they are intensively polished at the stopper film  21 . In the polishing step (CMP step), therefore, it is possible to suppress a lateral force acting on the carbon nanotubes  16 , thereby preventing damage to the carbon nanotubes  16 . That is, it is possible to prevent the carbon nanotubes  16  from falling or being pulled out from the contact hole  15 . This makes it possible to reduce pattern defects of the carbon nanotubes  16  and electrical characteristic defects caused by dust. 
     After that, an end-opening process is performed on the exposed ends of the carbon nanotubes  16  above the contact hole. This end-opening process is preferably performed immediately before the next sputtering step, and can also be performed as pre-processing of the sputtering step. 
     Subsequently, a barrier metal  18  is formed on the carbon nanotubes  16  and the interlayer dielectric film  13  by, e.g., sputtering. In addition, an aluminum film serving as a second interconnection layer  14  is formed on the barrier metal  18 . The second interconnection layer  14  is formed by patterning the barrier metal  18  and aluminum film by lithography, as shown in  FIG. 4A . 
     Note that if there is no film fixing the upper ends of the carbon nanotubes, the sidewalls of the carbon nanotubes are damaged when performing the end-opening process or the like. Therefore, the double structure of a multilayered film including a metal film or the like and an insulating film can also be used. When using the double structure as described above such that the upper layer (metal film or the like) is removed after the CMP step and the lower layer (insulating film) is left behind, it is possible to prevent damage to the sidewalls of the carbon nanotubes when performing the end-opening process or the like. Note that the rest of the arrangement such as the materials to be used are the same as those of the first embodiment. 
     [2-3] Effects of Second Embodiment 
     In the second embodiment as has been explained above, the carbon nanotubes  16  are fixed by the stopper film  21  filled between them. Therefore, damage to the carbon nanotubes  16  can be prevented in the step of polishing the carbon nanotubes  16  protruding from the contact hole  15 . This makes it possible to reduce pattern defects of the carbon nanotubes  16  and electrical characteristic defects caused by dust, thereby improving the electrical connection between the first interconnection layer  12  and second interconnection layer  14 . 
     [2-4] Carbon Nanotube Plug Interconnect and Method of Manufacturing the Same of Modification 
     In this modification, a metal film or the like as a stopper film  21  is not entirely removed but left behind in a CMP step of polishing carbon nanotubes  16  protruding from a contact hole  15 . 
     Steps shown in  FIGS. 7A to 8A  are the same as those shown in  FIGS. 5A to 6A  described previously, so a repetitive explanation will be omitted. 
     As shown in  FIG. 8A , the stopper film  21  and carbon nanotubes  16  are polished and left behind by a predetermined thickness on an interlayer dielectric film  13  and over a contact hole  15 . 
     Then, as shown in  FIG. 8B , an end-opening process is performed on the exposed ends of the carbon nanotubes  16 . This end-opening process is preferably performed immediately before the next sputtering step, and can also be performed as pre-processing of the sputtering step. 
     Subsequently, as shown in  FIG. 8C , a barrier metal  18  is formed on the end-opened carbon nanotubes  16  and stopper film  21  by, e.g., sputtering. In addition, an aluminum film serving as a second interconnection layer  14  is formed on the barrier metal  18 . The second interconnection layer  14  is formed by patterning the barrier metal  18 , aluminum film, and stopper film  21  by lithography, as shown in  FIG. 8D . 
     [2-5] Effects of Modification of Second Embodiment 
     In the modification of the second embodiment, as in the second embodiment, damage to the carbon nanotubes  16  can be prevented in the step of polishing the carbon nanotubes  16 , because the carbon nanotubes  16  are fixed by the stopper film  21 . 
     In addition, during the end-opening process of the carbon nanotubes  16 , it is possible to reduce the amount of energy line, chemical species, or radical entering the contact hole  15 , because the opening of the contact hole  15  is blocked with the stopper film  21 . This makes it possible to prevent damage to the sidewalls of the carbon nanotubes  16  in the contact hole  15  and to the surface of a first interconnection layer  12  on the bottom of the contact hole. 
     [3] Third Embodiment 
     In the third embodiment, an example in which an insulating film as a stopper film is formed on an interlayer dielectric film having a plug interconnect and a second interconnection layer is formed by the single damascene method will be explained. In a CMP step of polishing carbon nanotubes protruding from a contact hole, the insulating film on the interlayer dielectric film functions as a stopper film and fixes the carbon nanotubes. 
     [3-1] Carbon Nanotube Plug Interconnect 
       FIG. 9A  is a sectional view showing a carbon nanotube plug interconnect of the third embodiment. 
     As shown in  FIG. 9A , a first interconnection layer  12  is formed in an interlayer dielectric film  11 . The interlayer dielectric film  11  is formed on a semiconductor substrate (not shown). The first interconnection layer  12  is buried in the interlayer dielectric film  11  so as to expose the surface. A barrier metal (not shown) is formed between the first interconnection layer  12  and the interlayer dielectric film  11  as needed. 
     An interlayer dielectric film  13  is formed on the interlayer dielectric film  11  and first interconnection layer  12 . In the interlayer dielectric film  13  on the first interconnection layer  12 , a contact hole  15  for electrically connecting a second interconnection layer  33  and the first interconnection layer  12  is formed. Carbon nanotubes  16  are formed in the contact hole  15 . The carbon nanotubes  16  electrically connect the first interconnection layer  12  and second interconnection layer  33 . The second interconnection layer  33  is made of, e.g., Cu. 
     A stopper film  31  is formed on the interlayer dielectric film  13 . The stopper film  31  is filled in the ends of the carbon nanotubes  16  on the side of the second interconnection layer  33  so as to fix the carbon nanotubes  16 . The stopper film  31  is made of an insulating film, e.g., SiN or SiO 2 . 
     An interlayer dielectric film, e.g., an SOG film  19  is formed on the stopper film  31 . An interconnect trench is formed in the SOG film  19  over the contact hole  15 . A barrier metal  32  is formed in this interconnect trench, and the second interconnection layer  33  is formed on the barrier metal  32 . The carbon nanotubes  16  each have one end in contact with the first interconnection layer  12 , and the other end in contact with the barrier metal  32 . The first interconnection layer  12  and second interconnection layer  33  are electrically connected via the carbon nanotubes  16 . The barrier metal  32  is made of at least one of, e.g., Ta, TaN, Ti, and TiN, or a multilayered film of these metals. The second interconnection layer  33  is made of, e.g., Cu. 
     Note that  FIG. 9A  shows an example in which the stopper film  31  is formed at the ends of the carbon nanotubes  16  on the side of the second interconnection layer  33 , from the bottom surface of the barrier metal  32  to that of the stopper film  31 . However, the stopper film  31  can also be formed from the bottom surface of the barrier metal  32  to a position deeper than the bottom surface of the stopper film  31 . That is, the stopper film  31  may enter the contact hole from the bottom surface of the barrier metal  32 . 
     [3-2] Method of Manufacturing Carbon Nanotube Plug Interconnect 
       FIGS. 9B to 10C  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the third embodiment. 
     After an interconnect trench is formed in an interlayer dielectric film  11 , a first interconnection layer  12  is formed in the interconnect trench, as shown in  FIG. 9B . After that, an interlayer dielectric film  13  is formed on the interlayer dielectric film  11  and first interconnection layer  12  by, e.g., CVD. In addition, a contact hole  15  is formed in the interlayer dielectric film  13  on the first interconnection layer  12  by lithography. 
     Subsequently, carbon nanotubes  16  are formed on the first interconnection layer  12  in the contact hole  15 . More specifically, the carbon nanotubes  16  are grown from the surface of the first interconnection layer  12  by the ordinary method until they protrude from the contact hole  15 . 
     Then, as shown in  FIG. 10A , a stopper film  31  is formed by CVD on the interlayer dielectric film  13  and between the carbon nanotubes  16  above the contact hole  15 . In this step, the stopper film  31  enters and fills the spaces between the carbon nanotubes  16  above the contact hole  15  and near the opening of the contact hole  15 . Thus, the stopper film  31  fixes the carbon nanotubes  16 . 
     After that, an interlayer dielectric film is formed on the stopper film  31  and carbon nanotubes  16 . For example, an SOG film  19  is formed by spin coating. As the stopper film  31 , a film having etching selectivity much higher than that of the SOG film  19  is used. 
     As shown in  FIG. 10B , an interconnect trench  34  is formed in the SOG film  19  over the contact hole  15  by reactive ion etching (RIE) using lithography. Subsequently, as shown in  FIG. 10C , plasma processing, e.g., RIE is performed on the carbon nanotubes  16  protruding from the stopper film  31  in the interconnect trench  34 , thereby removing the carbon nanotubes  16  protruding from the stopper film  31 , and performing an end-opening process of opening the ends of the carbon nanotubes  16 . This end-opening process is preferably performed immediately before the next sputtering step, and can also be performed as pre-processing of the sputtering step. 
     Since the stopper film  31  is filled between the carbon nanotubes  16  above the contact hole  15 , it is possible to reduce the amount of energy line, chemical species, or radical entering the contact hole in the above-mentioned plasma processing. This makes it possible to prevent damage to the sidewalls of the carbon nanotubes  16  in the contact hole  15  and to the surface of the first interconnection layer  12  on the bottom of the contact hole. 
     Then, a barrier metal is formed in the interconnect trench  34  by, e.g., sputtering, and a Cu film is formed on the barrier metal. The Cu film and barrier metal on the SOG film  19  are polished by CMP, thereby forming a barrier metal  32  and second interconnection layer  33  in the interconnect trench  34 , as shown in  FIG. 9A . 
     [3-3] Effects of Third Embodiment 
     In the third embodiment as has been explained above, the stopper film  31  is filled between the carbon nanotubes  16  above the contact hole  15 . Therefore, the amount of energy line, chemical species, or radical entering the contact hole can be reduced during the etching process and end-opening process of the carbon nanotubes  16 . This makes it possible to prevent damage to the sidewalls of the carbon nanotubes  16  in the contact hole  15  and to the surface of the first interconnection layer  12  on the bottom of the contact hole. Consequently, it is possible to prevent electrical defects of the plug interconnect having the carbon nanotubes  16 , thereby improving the electrical connection between the first interconnection layer  12  and second interconnection layer  33 . 
     [3-4] Method of Manufacturing Carbon Nanotube Plug Interconnect of Modification 
       FIGS. 11A to 12B  are sectional views showing a method of manufacturing a carbon nanotube plug interconnect of a modification of the third embodiment. 
     In this modification, when a stopper film  31  is formed on an interlayer dielectric film  13  and over a contact hole  15  by CVD, as shown in  FIG. 11B , the stopper film  31  enters the spaces between carbon nanotubes  16 , and is formed on the carbon nanotubes  16 . 
     A step shown in  FIG. 11A  is the same as that shown in  FIG. 9B  described previously, so a repetitive explanation will be omitted. After that, as shown in  FIG. 11B , the stopper film  31  is formed by CVD on the interlayer dielectric film  13 , and formed on and between the carbon nanotubes  16  above the contact hole  15 . In this step, the stopper film  31  is formed on the carbon nanotubes  16  under predetermined deposition conditions, and enters and fills the spaces between the carbon nanotubes  16  above the contact hole  15  and near the opening of the contact hole  15 . Thus, the stopper film  31  fixes the carbon nanotubes  16 . 
     After that, interlayer dielectric film is formed on the stopper film  31  and carbon nanotubes  16 . For example, an SOG film  19  is formed by spin coating. 
     Then, as shown in  FIG. 11C , an interconnect trench  34  is formed in the SOG film  19  over the contact hole  15  by lithography. Subsequently, as shown in  FIG. 12A , the stopper film  31  on the carbon nanotubes  16  in the interconnect trench  34  is etched by, e.g., RIE. In addition, plasma processing, e.g., RIE is performed on the carbon nanotubes  16  protruding from the stopper film  31 , thereby removing the carbon nanotubes  16  protruding from the stopper film  31 , and performing an end-opening process of opening the ends of the carbon nanotubes  16 . This end-opening process is preferably performed immediately before the next sputtering step, and can also be performed as pre-processing of the sputtering step. 
     Since the stopper film  31  is filled between the carbon nanotubes  16  above the contact hole  15 , it is possible, in the above-mentioned plasma processing, to prevent damage to the sidewalls of the carbon nanotubes  16  in the contact hole  15  and to the surface of the first interconnection layer  12  on the bottom of the contact hole. 
     Then, a barrier metal is formed in the interconnect trench  34  by, e.g., sputtering, and a Cu film is formed on the barrier metal. The Cu film and barrier metal on the SOG film  19  are polished by CMP, thereby forming a barrier metal  32  and second interconnection layer  33  in the interconnect trench  34 , as shown in  FIG. 12B . The rest of the arrangement and effects are the same as those of the third embodiment described above. 
     [4] Fourth Embodiment 
     In the fourth embodiment, an example in which a metal film or the like as a stopper film is formed on an interlayer dielectric film having a plug interconnect and a second interconnection layer is formed by the single damascene method will be explained. In a CMP step of polishing carbon nanotubes protruding from a contact hole, the metal film or the like on the interlayer dielectric film functions as a stopper film and fixes the carbon nanotubes. 
     [4-1] Carbon Nanotube Plug Interconnect 
       FIG. 13A  is a sectional view showing a carbon nanotube plug interconnect of the fourth embodiment. 
     As shown in  FIG. 13A , a first interconnection layer  12  is formed in an interlayer dielectric film  11 . The interlayer dielectric film  11  is formed on a semiconductor substrate (not shown). The first interconnection layer  12  is buried in the interlayer dielectric film  11  so as to expose the surface. A barrier metal (not shown) is formed between the first interconnection layer  12  and the interlayer dielectric film  11  as needed. 
     An interlayer dielectric film  13  is formed on the interlayer dielectric film  11  and first interconnection layer  12 . In the interlayer dielectric film  13  on the first interconnection layer  12 , a contact hole  15  for electrically connecting a second interconnection layer  33  and the first interconnection layer  12  is formed. Carbon nanotubes  16  are formed in the contact hole  15 . The carbon nanotubes  16  electrically connect the first interconnection layer  12  and second interconnection layer  33 . The second interconnection layer  33  is made of, e.g., Cu. 
     An interlayer dielectric film, e.g., an SOG film  42  is formed on the interlayer dielectric film  13 . An interconnect trench is formed in the SOG film  42  over the contact hole  15 . A barrier metal  32  is formed in this interconnect trench, and the second interconnection layer  33  is formed on the barrier metal  32 . The carbon nanotubes  16  each have one end in contact with the first interconnection layer  12 , and the other end in contact with the barrier metal  32 . The first interconnection layer  12  and second interconnection layer  33  are electrically connected via the carbon nanotubes  16 . 
     Note that  FIG. 13A  shows an example in which the metal film as a stopper film does not remain at the ends of the carbon nanotubes  16  on the side of the second interconnection layer  33 . As shown in  FIG. 13B , however, a stopper film  41  can also be formed at the ends of the carbon nanotubes  16  on the side of the second interconnection layer  33 . That is, the stopper film  41  may enter the contact hole from the bottom surface of the barrier metal  32 . The stopper film  41  is made of a metal film, metal compound, refractory metal, or refractory metal compound, e.g., Ta, TaN, TiN, or W. The stopper film  41  can also be made of amorphous silicon. 
     [4-2] Method of Manufacturing Carbon Nanotube Plug Interconnect 
       FIGS. 14A to 15C  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the fourth embodiment. 
     After an interconnect trench is formed in an interlayer dielectric film  11 , a first interconnection layer  12  is formed in the interconnect trench, as shown in  FIG. 14A . After that, an interlayer dielectric film  13  is formed on the interlayer dielectric film  11  and first interconnection layer  12  by, e.g., CVD. In addition, a contact hole  15  is formed in the interlayer dielectric film  13  on the first interconnection layer  12  by lithography. 
     Subsequently, carbon nanotubes  16  are formed on the first interconnection layer  12  in the contact hole  15 . More specifically, the carbon nanotubes  16  are grown from the surface of the first interconnection layer  12  by the ordinary method until they protrude from the contact hole  15 . 
     Then, as shown in  FIG. 14B , a stopper film  41 , e.g., a metal film is formed by sputtering on the interlayer dielectric film  13  and between the carbon nanotubes  16  above the contact hole  15 . In this step, the stopper film  41  enters and fills the spaces between the carbon nanotubes  16  above the contact hole  15  and near the opening of the contact hole  15 . Thus, the stopper film  41  fixes the carbon nanotubes  16 . After that, an SOG film  19  is formed on the stopper film  41  and carbon nanotubes  16  by spin coating. 
     As shown in  FIGS. 14C and 14D , the SOG film  19 , stopper film  41 , and carbon nanotubes  16  are polished by CMP. More specifically, the SOG film  19  on the carbon nanotubes  16  and stopper film  41  is polished first. When the polished portion has reached the carbon nanotubes  16  after that, the carbon nanotubes  16  are polished together with the stopper film  41 . As shown in  FIG. 15A , the polishing of the stopper film  41  and carbon nanotubes  16  is further advanced, thereby removing the stopper film  41  and carbon nanotubes  16  on the interlayer dielectric film  13  and above the contact hole  15 . 
     In this step, the carbon nanotubes  16  are fixed by the stopper film  41  filled between them. In the above-described polishing step (CMP step), therefore, it is possible to suppress a lateral force acting on the carbon nanotubes  16 , thereby preventing damage to the carbon nanotubes  16 . That is, it is possible to prevent the carbon nanotubes  16  from falling or being pulled out from the contact hole  15 . This makes it possible to reduce pattern defects of the carbon nanotubes  16  and electrical characteristic defects caused by dust. 
     After that, as shown in  FIG. 15B , an SOG film  42  is formed on the interlayer dielectric film  13  and over the contact hole  15 . In addition, as shown in  FIG. 15C , an interconnect trench  43  is formed in the SOG film  42  over the contact hole  15  by RIE using lithography. Subsequently, an end-opening process is performed on the exposed ends of the carbon nanotubes  16  in the interconnect trench  43  as needed. This end-opening process is preferably performed immediately before the next sputtering step, and can also be performed as pre-processing of the sputtering step. 
     Then, a barrier metal is formed in the interconnect trench  43  by, e.g., sputtering, and a Cu film is formed on the barrier metal. The Cu film and barrier metal on the SOG film  42  are polished by CMP, thereby forming a barrier metal  32  and second interconnection layer  33  in the interconnect trench  43 , as shown in  FIG. 13A . 
     [4-3] Effects of Fourth Embodiment 
     In the fourth embodiment as has been explained above, the carbon nanotubes  16  are fixed by the stopper film  41  filled between them. Therefore, damage to the carbon nanotubes  16  can be prevented in the step of polishing the carbon nanotubes  16  protruding from the contact hole  15 . This makes it possible to reduce pattern defects of the carbon nanotubes  16  and electrical characteristic defects caused by dust, thereby improving the electrical connection between the first interconnection layer  12  and second interconnection layer  33 . 
     [5] Fifth Embodiment 
     In the fifth embodiment, an example in which an insulating film is formed over a contact hole as a protective film to be used when etching carbon nanotubes protruding from the contact hole and a second interconnection layer is formed by the dual damascene method will be explained. 
     [5-1] Carbon Nanotube Plug Interconnect 
       FIG. 16A  is a sectional view showing a carbon nanotube plug interconnect of the fifth embodiment. 
     As shown in  FIG. 16A , a first interconnection layer  12  is formed in an interlayer dielectric film  11 . The interlayer dielectric film  11  is formed on a semiconductor substrate (not shown). The first interconnection layer  12  is buried in the interlayer dielectric film  11  so as to expose the surface. A barrier metal (not shown) is formed between the first interconnection layer  12  and the interlayer dielectric film  11  as needed. 
     An interlayer dielectric film  13  is formed on the interlayer dielectric film  11  and first interconnection layer  12 . In the interlayer dielectric film  13  on the first interconnection layer  12 , a contact hole  15  for electrically connecting a second interconnection layer  51  and the first interconnection layer  12  is formed. Carbon nanotubes  16  are formed in the contact hole  15 . The carbon nanotubes  16  electrically connect the first interconnection layer  12  and second interconnection layer  51 . The second interconnection layer  51  is made of, e.g., Cu. 
     An interlayer dielectric film  52 , e.g., SiO 2  is formed on the interlayer dielectric film  13 . An interconnect trench is formed in the interlayer dielectric film  52  over the contact hole  15 . A protective film  53  is formed in this interconnect trench so as to cover it. The protective film  53  is filled between the carbon nanotubes  16  protruding from the contact hole  15 . The protective film  53  is made of an insulating film, e.g., SiO 2 , SiN, or SiCN. 
     A barrier metal  54  is formed on the protective film  53  in the interconnect trench so as to cover the protective film  53 . In addition, the second interconnection layer  51  is formed on the barrier metal  54  in the interconnect trench. The barrier metal  54  is positioned between the second interconnection layer  51  and protective film  53 , and prevents the diffusion of the material of the second interconnection layer  51  to the protective film  53  and the interlayer dielectric film  52 . 
     Note that  FIG. 16A  shows an example in which the protective film  53  is not formed on the interlayer dielectric film  52 , i.e., the protective film  53  does not remain on the interlayer dielectric film  52 . As shown in  FIG. 16B , however, the protective film  53  can also be formed on the interlayer dielectric film  52 . 
     [5-2] Method of Manufacturing Carbon Nanotube Plug Interconnect 
       FIGS. 17A to 18B  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the fifth embodiment. 
     As shown in  FIG. 17A , an interconnect trench is formed in an interlayer dielectric film  11 , and a first interconnection layer  12  is formed in the interconnect trench. After that, interlayer dielectric films  13  and  52  are formed on the interlayer dielectric film  11  and first interconnection layer  12  by, e.g., CVD. A contact hole  15  and interconnect trench  55  are formed in the interlayer dielectric films  13  and  52  by lithography. 
     Then, carbon nanotubes  16  are formed on the first interconnection layer  12  in the contact hole  15 . More specifically, the carbon nanotubes  16  are grown from the surface of the first interconnection layer  12  by the ordinary method until they protrude from the contact hole  15 . 
     After that, as shown in  FIG. 17B , a protective film  53  is formed by CVD on and between the carbon nanotubes  16  above the contact hole  15 , and on the interlayer dielectric film  52 . In this step, the protective film  53  enters and fills the spaces between the carbon nanotubes  16  above the contact hole  15  and near the opening of the contact hole  15 . Thus, the protective film  53  and carbon nanotubes  16  protect the interior of the contact hole  15 . 
     Subsequently, as shown in  FIG. 17C , the ends of the carbon nanotubes  16  above the contact hole  15  are exposed by etching the protective film  53  by dry etching, e.g., RIE, such that the protective film  53  remains over the contact hole  15 . 
     After that, as shown in  FIG. 18A , plasma processing, e.g., RIE is performed on the carbon nanotubes  16  protruding from the protective film  53  in the interconnect trench  55 , thereby removing the carbon nanotubes  16  protruding from the protective film  53 , and performing an end-opening process of opening the ends of the carbon nanotubes  16 . This end-opening process is preferably performed immediately before the next sputtering step, and can also be performed as pre-processing of the sputtering step. 
     Since the protective film  53  is filled between the carbon nanotubes  16  above the contact hole  15 , it is possible to reduce the amount of energy line, chemical species, or radical entering the contact hole in the above-mentioned plasma processing. This makes it possible to prevent damage to the sidewalls of the carbon nanotubes  16  in the contact hole  15  and to the surface of the first interconnection layer  12  on the bottom of the contact hole. 
     Then, as shown in  FIG. 18B , a barrier metal  54  is formed in the interconnect trench  55  and on the interlayer dielectric film  52  by, e.g., sputtering, and a Cu film  51  is formed on the barrier metal  54 . The Cu film  51 , barrier metal  54 , and protective film  53  on the interlayer dielectric film  52  are polished by CMP, thereby forming the barrier metal  54  and second interconnection layer  51  in the interconnect trench  55 , as shown in  FIG. 16A . The protective film  53  may remain on the interlayer dielectric film  52 , as shown in  FIG. 16B . 
     [5-3] Effects of Fifth Embodiment 
     In the manufacturing method of the fifth embodiment as has been explained above, the protective film  53  is filled between the carbon nanotubes  16  above the contact hole  15 . Therefore, the amount of energy line, chemical species, or radical entering the contact hole can be reduced during the etching process and end-opening process of the carbon nanotubes  16 . This makes it possible to prevent damage to the sidewalls of the carbon nanotubes  16  in the contact hole  15  and to the surface of the first interconnection layer  12  on the bottom of the contact hole. Consequently, it is possible to prevent electrical defects of the plug interconnect having the carbon nanotubes  16 , thereby improving the electrical connection between the first interconnection layer  12  and second interconnection layer  51 . 
     [6] Sixth Embodiment 
     In the sixth embodiment, an example in which an insulating film as a stopper film is formed on an interlayer dielectric film having a plug interconnect, another insulating film is formed as a protective film to be used when etching carbon nanotubes protruding from a contact hole, and a second interconnection layer is formed by the dual damascene method will be explained. 
     [6-1] Carbon Nanotube Plug Interconnect 
       FIG. 19A  is a sectional view showing a carbon nanotube plug interconnect of the sixth embodiment. 
     As shown in  FIG. 19A , a first interconnection layer  12  is formed in an interlayer dielectric film  11 . The interlayer dielectric film  11  is formed on a semiconductor substrate (not shown). The first interconnection layer  12  is buried in the interlayer dielectric film  11  so as to expose the surface. A barrier metal (not shown) is formed between the first interconnection layer  12  and the interlayer dielectric film  11  as needed. 
     An interlayer dielectric film  13  is formed on the interlayer dielectric film  11  and first interconnection layer  12 . In the interlayer dielectric film  13  on the first interconnection layer  12 , a contact hole  15  for electrically connecting a second interconnection layer  51  and the first interconnection layer  12  is formed. Carbon nanotubes  16  are formed in the contact hole  15 . The carbon nanotubes  16  electrically connect the first interconnection layer  12  and second interconnection layer  51 . 
     A stopper film  31  is formed on the interlayer dielectric film  13 . The stopper film  31  is filled in the ends of the carbon nanotubes  16  on the side of the second interconnection layer  51 , so as to fix the carbon nanotubes  16 . 
     An interlayer dielectric film  52 , e.g., SiO 2  is formed on the stopper film  31 . An interconnect trench is formed in the interlayer dielectric film  52  over the contact hole  15 . A protective film  53  is formed in this interconnect trench so as to cover it. The protective film  53  is filled between the carbon nanotubes  16  protruding from the contact hole  15 . 
     A barrier metal  54  is formed on the protective film  53  in the interconnect trench so as to cover the protective film  53 . In addition, the second interconnection layer  51  is formed on the barrier metal  54  in the interconnect trench. The barrier metal  54  is positioned between the second interconnection layer  51  and protective film  53 , and prevents the diffusion of the material of the second interconnection layer  51  to the protective film  53  and the interlayer dielectric film  52 . 
     Note that  FIG. 19A  shows an example in which the protective film  53  is not formed on the interlayer dielectric film  52 , i.e., the protective film  53  does not remain on the interlayer dielectric film  52 . As shown in  FIG. 19B , however, the protective film  53  can also be formed on the interlayer dielectric film  52 . Also, the stopper film  31  can also be formed to a position deeper than the bottom surface of the stopper film  31  existing between the interlayer dielectric film  13  and second interconnection layer  51 . That is, the stopper film  31  may enter the contact hole  15 . 
     [6-2] Method of Manufacturing Carbon Nanotube Plug Interconnect 
       FIGS. 20A to 21B  are sectional views showing a method of manufacturing the carbon nanotube plug interconnect of the sixth embodiment. 
     As shown in  FIG. 20A , carbon nanotubes  16  are formed on a first interconnection layer  12  in a contact hole  15 . A stopper film  31  is formed on an interlayer dielectric film  13  and between the carbon nanotubes  16  above the contact hole  15 . An interlayer dielectric film  52  is formed on the stopper film  31  and carbon nanotubes  16  by CVD. In addition, an interconnect trench  61  is formed in the interlayer dielectric film  52  over the contact hole  15 . 
     Then, as shown in  FIG. 20B , a protective film  53  is formed by CVD on and between the carbon nanotubes  16  above the contact hole  15 , on the stopper film  31 , and on the interlayer dielectric film  52 . In this step, the protective film  53  enters and fills the spaces between the carbon nanotubes  16  on the stopper film  31 . Thus, the protective film  53  and stopper film  31  protect the interior of the contact hole  15 . 
     Subsequently, as shown in  FIG. 20C , the ends of the carbon nanotubes  16  above the contact hole  15  are exposed by etching the protective film  53  by dry etching, e.g., RIE, such that the protective film  53  remains on the stopper film  31 . 
     After that, as shown in  FIG. 21A , plasma processing, e.g., RIE is performed on the carbon nanotubes  16  protruding from the protective film  53  in the interconnect trench  61 , thereby removing the carbon nanotubes  16  protruding from the protective film  53 , and performing an end-opening process of opening the ends of the carbon nanotubes  16 . This end-opening process is preferably performed immediately before the next sputtering step, and can also be performed as pre-processing of the sputtering step. 
     Since the protective film  53  and stopper film  31  are filled between the carbon nanotubes  16  above the contact hole  15 , it is possible to reduce the amount of energy line, chemical species, or radical entering the contact hole in the above-mentioned plasma processing. This makes it possible to prevent damage to the sidewalls of the carbon nanotubes  16  in the contact hole  15  and to the surface of the first interconnection layer  12  on the bottom of the contact hole. 
     Then, as shown in  FIG. 21B , a barrier metal  54  is formed in the interconnect trench  61  and on the interlayer dielectric film  52  by, e.g., sputtering, and a Cu film  51  is formed on the barrier metal  54 . The Cu film  51 , barrier metal  54 , and protective film  53  on the interlayer dielectric film  52  are polished by CMP, thereby forming the barrier metal  54  and second interconnection layer  51  in the interconnect trench  61 , as shown in  FIG. 19A . The protective film  53  may remain on the interlayer dielectric film  52 , as shown in  FIG. 19B . 
     [6-3] Effects of Sixth Embodiment 
     In the sixth embodiment as has been explained above, the protective film  53  and stopper film  31  are filled between the carbon nanotubes  16  above the contact hole  15 . Therefore, the amount of energy line, chemical species, or radical entering the contact hole can be reduced during the etching process and end-opening process of the carbon nanotubes  16 . This makes it possible to prevent damage to the sidewalls of the carbon nanotubes  16  in the contact hole  15  and to the surface of the first interconnection layer  12  on the bottom of the contact hole. Consequently, it is possible to prevent electrical defects of the plug interconnect having the carbon nanotubes  16 , thereby improving the electrical connection between the first interconnection layer  12  and second interconnection layer  51 . 
     In the embodiments, in a plug interconnect obtained by forming carbon nanotubes in a via hole or contact hole, those portions of the carbon nanotubes which have grown to protrude from the hole are surrounded by an insulating film, metal film, or the like, and the opening and its vicinity of the hole are protected as they are covered. This makes it possible to prevent the breakage of the carbon nanotubes themselves, the oxidation of an interconnect on the hole bottom, structural defects, and other damage, in later CMP, plasma processing, etching, and asking. 
     Each embodiment provides a carbon nanotube interconnect capable of obtaining a favorable electrical connection in a plug interconnect having carbon nanotubes, and a method of manufacturing the same. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.