Patent Publication Number: US-2007096616-A1

Title: Vertical interconnection structure including carbon nanotubes and method of fabricating the same

Description:
CLAIM OF PRIORITY  
      This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for VERTICAL INTERCONNECTION STRUCTURE USING CARBON NANOTUBE AND METHOD OF FABRICATING THE SAME earlier filed in the Korean Intellectual Property Office on 2 Nov. 2005 and there duly assigned Serial No.  10-2005-0104359.    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a vertical interconnection structure including carbon nanotubes and a method of fabricating the same.  
      2. Description of the Related Art  
      Normally, carbon nanotubes (CNTs) are cylindrical with a minute diameter of approximately a few nm (nanometers) and a very large aspect ratio of 10 to 1000. Carbon atoms in CNTs have a honeycomb arrangement, and each of the carbon atoms is coupled to three adjacent carbon atoms. CNTs can have conductor characteristics or semiconductor characteristics according to the structure thereof. Conductive CNTs have very high electrical conductivity.  
      CNTs have very high mechanical strength, a Young&#39;s modulus of tera digits, high thermal conductivity, etc. CNTs are applied to various technical fields such as field emission devices (FEDs), backlight units for liquid crystal display (LCD) devices, nanoelectronic devices, etc.  
      When conductive CNTs are used as vertical interconnections, a highly integrated circuit can be realized.  
      However, when the CNTs are used as vertical interconnections between an upper electrode and a lower electrode, the CNTs can cause a device failure because the carbon atoms diffuse in lateral directions during a growing process as illustrated in  FIG. 1 , and lift an insulating layer formed between the upper electrode and the lower electrode.  
     SUMMARY OF THE INVENTION  
      The present invention provides a vertical interconnection structure having a catalyst layer for growing carbon nanotube in a limited region and a method of fabricating the same.  
      According to an aspect of the present invention, there is provided a vertical interconnection structure including carbon nanotubes, including a substrate; a lower electrode formed on the substrate; a catalyst layer formed on the lower electrode; an inactivated catalyst layer covering the lower electrode and having a first hole exposing the catalyst layer; an insulating layer which is formed on the inactivated catalyst layer and has a second hole connected to the first hole; a plurality of carbon nanotubes grown from an exposed area of the catalyst layer by the first hole; an upper electrode on the insulating layer being electrically connected to the carbon nanotubes, wherein the inactivated catalyst layer is formed through a thermal reaction between the catalyst layer covering the lower electrode except for the catalyst layer in the first hole and a passivation layer having a third hole corresponding to the second hole.  
      The catalyst layer may be formed of at least one metal selected from the group including Fe, Ni, Co, Y, Mo, Pd, and Pt.  
      The passivation layer may be Si, and the inactivated catalyst layer may be metal silicide.  
      The passivation layer may be formed of a metal selected from the group including W, Al, In, Zn, and Pb, and a stack including the lower electrode, the catalyst layer, and the passivation layer is an island insulated by the insulating layer.  
      The catalyst layer can have a thickness of 1 to 100 nm (nanometers).  
      The passivation layer can have substantially the same thickness as the catalyst layer, and the inactivated catalyst layer twice thicker than the catalyst layer.  
      The passivation layer can be composed of an oxide, a fluoride, a chloride, or a nitride formed through a reaction between the catalyst layer and an element selected from the group including oxygen, nitrogen, fluorine, and chlorine.  
      According to another aspect of the present invention, there is provided a method of fabricating a vertical interconnection structure including carbon nanotubes, including: forming a lower electrode on a substrate; sequentially forming a catalyst layer and a passivation layer covering the lower electrode on the substrate; forming an island stack including the lower electrode, the catalyst layer and the passivation layer; forming an insulating layer covering the island stack on the substrate; forming a via hole that exposes the catalyst layer by etching the catalyst layer and the passivation layer on the lower electrode; forming an inactivated catalyst layer by annealing the substrate to cause a thermal reaction between the catalyst layer and the passivation layer in a region that is not exposed by the via hole; growing carbon nanotubes from the catalyst layer exposed by the via hole; and patterning upper electrodes on the via holes.  
      The patterning of the upper electrodes may further include planarizing the insulating layer and the carbon nanotubes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
       FIG. 1  is a SEM image of carbon film diffused in a lateral direction on a catalyst layer during a growing process when the carbon nanotubes are used as a vertical interconnection between an upper electrode and a lower electrode;  
       FIG. 2  is a cross-sectional view of a vertical interconnection structure including carbon nanotubes according to an embodiment of the present invention;  
       FIGS. 3A through 3F  are cross-sectional views illustrating a method of manufacturing a vertical interconnection structure including carbon nanotubes according to another embodiment of the present invention; and  
       FIG. 4  is a SEM image of carbon nanotubes vertically grown from a catalyst layer in a via hole of an insulating layer according to a method of growing according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention will now be described more fully with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals refer to like elements throughout the drawings.  
       FIG. 2  is cross-sectional view of a vertical interconnection structure including carbon nanotubes according to an embodiment of the present invention.  
      Referring to  FIG. 2 , an insulating layer  112 , for example, a silicon oxide (SiO 2 ) layer, having a thickness of 2000 Å (Angstrom) is formed on a silicon substrate  110 . A lower electrode  120  is patterned on the insulating layer  112 . The lower electrode  120  can be patterned into dots. A catalyst layer  130  is formed on the central part of the lower electrode  120 . The catalyst layer  130  can be formed to a thickness of approximately 1 to 100 nm using a metal such as Fe, Co, Y, Mo, Pd, or Pt. The catalyst layer  130  is a catalyst layer for growing carbon nanotubes.  
      An inactivated catalyst layer  180  that surrounds the catalyst layer  130  is formed on the lower electrode  120 . The inactivated catalyst layer  180  has a first hole  182  exposing the catalyst layer  130 . The inactivated catalyst layer  180  is formed through a thermal reaction between the catalyst layer  130  covering the lower electrode  120  except the first hole  182  and a passivation layer (not shown) and covering the catalyst layer  130  except the first hole  182 . The inactivated catalyst layer  180  will be described in more detail later.  
      An insulating layer  150 , for example, a SiO 2  layer, having a second hole  152  connected to the first hole  182  and covering the inactivated catalyst layer  180 , is formed on the silicon substrate  110 . The first hole  182  and the second hole  152  form a via or through hole. Carbon nanotubes  160  grown from the catalyst layer  130  are formed in the via (through) hole. An upper electrode  170  electrically connected to the carbon nanotubes  160  is patterned on the insulating layer  150 . The carbon nanotubes  160  are vertical electrical interconnections between the lower electrode  120  and the upper electrode  170 .  
      The passivation layer  140  (see  FIG. 3 ) is formed to substantially the same thickness as the catalyst layer  130 , and the inactivated catalyst layer  180  is formed to double the thickness of the catalyst layer  130 . The passivation layer  140  forms the inactivated catalyst layer  180  through a thermal reaction with the catalyst layer  130  at a high temperature of, for example, 450° C. (celsius). The inactivated catalyst layer  180  prevents the carbon nanotubes  160  from growing underneath the insulating layer  150  during a carbon nanotube growing process.  
      The passivation layer  140  can be composed of silicon, in which case the inactivated catalyst layer  180  becomes metal silicide.  
      The passivation layer  140  can be a metal layer formed of a metal such as W, Al, In, Zn, or Pb. The lower electrode  120 , the catalyst layer  130 , and the passivation layer  140  may form islands insulated by the insulating layer  150 .  
      The passivation layer  140  can be composed of an oxide, a fluoride, a chloride, or a nitride formed through a reaction between the catalyst layer  130  and an element selected from the group including oxygen, nitrogen, fluorine, and chlorine.  
       FIGS. 3A through 3F  are cross-sectional views illustrating a method of fabricating a vertical interconnection structure including carbon nanotubes according to another embodiment of the present invention.  
      Referring to  FIG. 3A , an insulating layer  112 , for example, a SiO 2  layer, is formed to a thickness of 2000 Å (Angstroms) on a silicon substrate  110 . After depositing a conductive layer (not shown), a lower electrode  120  is formed by patterning the conductive layer. The lower electrode  120  can be patterned into dots. Next, a catalyst layer  130  covering the lower electrode  120  is formed on the insulating layer  112 . The catalyst layer  130  can be formed to a thickness of 1 to 100 nm (nanometers) using a metal such as Fe, Ni, Co, Y, Mo, Pd, or Pt. The catalyst layer  130  is a layer for growing carbon nanotubes.  
      Next, a passivation layer  140  is formed on the catalyst layer  130 .  
      Referring to  FIG. 3B , a stack “S” including the lower electrode  120 , the catalyst layer  130 , and the passivation layer  140  is formed by patterning the passivation layer  140  and the catalyst layer  130 . The stack “S” is formed in islands to prevent an electrical short between the lower electrodes  120  via the catalyst layer  130  or the passivation layer  140 .  
      Referring to  FIG. 3C , an insulating layer  150 , for example, a SiO 2  layer, covering the island stacks “S” is formed on the insulating layer  112 .  
      Referring to  FIG. 3D , via or through holes  154  are formed by etching the insulating layer  150  and the passivation layer  140  on the lower electrodes  120 .  
      Referring to  FIG. 3E , an inert catalyst layer  180  is formed by causing a reaction between the passivation layer  140  and the catalyst layer  130  contacting the passivation layer  140  through a thermal process of the silicon substrate  110 .  
      The passivation layer  140  can be composed of silicon, in which case, the inactivated catalyst layer  180  becomes metal silicide. When the catalyst layer  130  is formed of Fe (iron), the inactivated catalyst layer  180  can be formed by annealing the silicon substrate  110  at a temperature of 450° C. (celsius) for one hour. The annealing condition can vary according to the materials composing and the thicknesses of the catalyst layer  130  and the passivation layer  140 .  
      The passivation layer  140  can be a metal layer formed of W, Al, In, Zn, or Pb.  
      The passivation layer  140  can be composed of an oxide, a fluoride, a chloride, or a nitride formed through a reaction between the catalyst layer  130  and an element selected from the group including oxygen, nitrogen, fluorine, and chlorine.  
      Next, carbon nanotubes  160  are grown from the catalyst layer  130  exposed through the via or through hole  154  by injecting a carbon containing gas into a chamber where the silicon substrate  110  is placed. After the carbon nanotubes  160  are grown higher than the height of the via hole  154 , the carbon nanotubes  160  can be formed to have the same height as the insulating layer  150  by planarizing the carbon nanotubes  160  using a chemical mechanical polishing (CMP) process.  
      Referring to  FIG. 3F , after depositing a conductive layer (not shown) on the insulating layer  150 , upper electrodes  170  covering the via holes  154  are formed by patterning the conductive layer.  
       FIG. 4  is a SEM (scanning electron microscope) image of carbon nanotubes vertically grown from a catalyst layer in a via hole of an insulating layer according to the method of growing according to an embodiment of the present invention. Referring to  FIG. 4 , the catalyst layer that is not exposed through the via hole is an inactivated catalyst layer. Therefore, the carbon nanotubes  160  are not grown underneath the insulating layer.  
      The vertical interconnection structure according to the present invention provides favourable electrical characteristics since the vertical interconnection structure uses superior current transfer capabilities of the carbon nanotubes. Also, the vertical interconnection structure can be used for highly integrated circuits since the vertical interconnection is formed by a patterning technique.  
      In the method of fabricating the vertical interconnection structure including the carbon nanotubes according to the present invention, a catalyst layer can be aligned with a via or through hole, and a device yield can be increased by preventing the growing of the carbon nanotubes in regions other than the via hole since an inert catalyst layer is formed around the catalyst layer.  
      While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.