Abstract:
A method including forming an interconnect of single-walled carbon nanotubes on a sacrificial substrate; transferring the interconnect from the sacrificial substrate to a circuit substrate; and coupling the interconnect to a contact point on the circuit substrate. A method including forming a nanotube bundle on a circuit substrate between a first contact point and a second contact point, the nanotube defining a lumen therethrough; filling a portion of a length of the lumen of the nanotube bundle with an electrically conductive material; and coupling the electrically conductive material to the second contact point. A system including a computing device comprising a microprocessor, the microprocessor coupled to a printed circuit board, the microprocessor including a substrate having a plurality of circuit devices with electrical connections made to the plurality of circuit devices through interconnect structures including carbon nanotube bundles.

Description:
BACKGROUND 
     1. Field 
     Nanotubes and integrated circuit processing 
     2. Description of Related Art 
     Modern integrated circuits use conductive interconnections to connect the individual devices on a chip or to send and/or receive signals external to the device(s). Common types of interconnections include copper and copper alloy interconnections (lines) coupled to individual devices, including other interconnections (lines) by interconnections through vias. 
     Nanotubes are generally seamless tubes of graphite sheets with full fullerene caps. Typically, the nanotubes are formed as multi-layer concentric tubes for multi-walled carbon nanotube bundles or as single-walled nanotube bundles. Nanotubes have shown promising applications in nano-scale electronic devices, high strength materials, and electron field emission tips for scanning probe microscopy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features, aspects, and advantages of the invention will become more thoroughly apparent from the following detailed description, appended claims, and accompanying drawings in which: 
         FIG. 1  shows two separate host substrates each having a dielectric material formed thereon. 
         FIG. 2  shows the two substrates of  FIG. 1  following the introduction of a catalyst of a substrate. 
         FIG. 3  shows the two substrates of  FIG. 2  following the formation of single-walled nanotube bundles on each substrate. 
         FIG. 4  shows the two substrates following the deposition of a conductive material at a contact point for a nanotube bundle on each substrate. 
         FIG. 5  shows the separation of the dielectric material and the nanotube bundle from each substrate and bonding of the conductive materials to connect the nanotubes from each substrate. 
         FIG. 6  shows the bonded dielectric layers including the nanotube bundles connected to a circuit substrate as interlayer dielectrics containing interconnects including the nanotubes. 
         FIG. 7  shows a cross-sectional side view of a circuit substrate in an xy direction having a nanotube bundle formed on a surface thereof. 
         FIG. 8  shows the structure of  FIG. 7  from a yz cross section. 
         FIG. 9  shows the structure of  FIG. 7  following the coating of a material on the nanotube bundle. 
         FIG. 10  shows the structure of  FIG. 9  in a yz direction. 
         FIG. 11  shows the structure of  FIG. 9  following the filling of a core of the nanotube bundle with a conductive material. 
         FIG. 12  shows the structure of  FIG. 11  in a yz plane. 
         FIG. 13  shows the structure of  FIG. 11  following the deposition of a conductive material on the nanotube to a contact point on the substrate. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows two hosts or sacrificial substrates that may serve as hosts for the formation of individual interconnection layers or levels disposed in dielectric material (e.g., interlayer dielectric material). As noted above, integrated circuits use conductive interconnections to connect individual devices on a chip or to send and/or receive signal external to the devices. A typical microprocessor chip may have a number of interconnection layers or levels stacked one on top of the other to accomplish the interconnections. Generally speaking, circuit devices and interconnections are formed at the wafer level. Accordingly, sacrificial substrate  110 A and sacrificial substrate  110 B may have a size suitable to accommodate a dielectric film that may be formed over a wafer as well as multiple interconnection lines that might be formed in individual layers on a wafer. 
     In one embodiment, substrate  110 A and substrate  110 B are each a material selected for a property such that a dielectric layer may be formed thereon and later separated from the sacrificial material. In one embodiment, sacrificial substrate is a silicon material, such as silicon formed into the shape of a wafer. 
       FIG. 1  shows sacrificial substrate  110 A and sacrificial substrate  110 B each having a layer of dielectric material formed on a surface thereof (a top surface as viewed). Dielectric layer  120 A and dielectric layer  120 B are each, for example, silicon dioxide (SiO 2 ) formed, for example, by a tetraethyl orthosilicate (TEOS) or a plasma enhanced chemical vapor deposition (PECVD) source. Carbon-doped silicon dioxide (CDO) may serve as another dielectric layer material. A material for dielectric layer  120 A and/or dielectric layer  120 B may also be a material having, for example, a dielectric constant less than the dielectric constant of SiO 2  (e.g., a “low k” material), including polymers as known in the art. 
     In the embodiment shown in  FIG. 1 , dielectric layer  120 A has a thickness, t A , less than a thickness, t B , of dielectric layer  120 B. In this representative example, a thickness of dielectric layer  120 B is selected to accommodate a conductive via between a device layer and an interconnect line or between interconnect lines. In one embodiment, a suitable thickness is on the order of 35-200 nm. Dielectric layer  120 A may have a thickness suitable to space an interconnect line from sacrificial substrate  110 A but, in this example, no other criteria may be necessary. A representative thickness is on the order of 25-200 nm. 
     Referring to the structure shown in  FIG. 1 , in one embodiment, dielectric layer  120 B has an opening or via formed through the dielectric layer to sacrificial substrate  110 B. The opening may be formed using photolithographic and etch techniques to be suitable for the formation of a conductive via therein. 
       FIG. 2  shows the structures of  FIG. 1  following the deposition of a catalyst on each structure. Referring to structure  100 A,  FIG. 1  shows catalyst  130 A formed on an exposed surface (an upper surface as shown) of dielectric layer  120 A. Structure  100 B shows catalyst  130 B formed in the via through dielectric layer  120 B. In one embodiment, catalyst  130 A and catalyst  130 B are each a catalyst suitable for the formation of a single-walled nanotube bundle thereon (e.g., a single-walled carbon nanotube bundle). A material suitable as a catalyst for forming single-walled nanotubes are, for example, metals that can be supersaturated with carbon such as, but not necessarily limited to, iron, iron oxide, iron cobalt alloys, iron molybdenum alloys, iron and iron alloys that form composites or are supported on dielectrics such as silicon dioxide, magnesium oxide or aluminum oxide. A single-walled nanotube typically differs from a multi-walled nanotube in that a single-walled nanotube is composed of a single graphite sheet while a multi-walled nanotube may be composed of concentric cylinders formed around a common central hollow with spacing between layers close to the inner layer spacing of graphite. Single-walled carbon nanotubes generally require high temperature formation processing (e.g., 900° C. to 1100° C.) making such tube challenging for use as interconnects formed directly on circuit structures where high temperature processing might damage the underlying circuit structure. 
     In one embodiment, catalyst  130 A and catalyst  130 B determine a position of a subsequent interconnect structure and a gas flow determines the growth direction of the nanotube bundle. Referring to  FIG. 2 , a nanotube bundle formed on structure  100 A, in one embodiment, will be grown in a lateral direction (to the right in the figure) while a nanotube bundle will be grown in the via on structure  100 B. A suitable process gas for growing nanotube bundles from catalysts such as, iron or alloys of iron both with or without dielectric material support is: methane, ethylene, mixtures of methane and ethylene, carbon monoxide. Hydrogen and water and oxygen may serve as co-reactants. 
       FIG. 3  shows the structures of  FIG. 2  following the growth of a nanotube bundle on each structure.  FIG. 3  shows nanotube bundle  140 A grown from catalyst  130 A in a lateral direction and nanotube bundle  140 B grown from catalyst  130 B in a via in dielectric layer  120 B. Nanotube bundle  140 A is a bundle of nanotubes (for example a tightly packed bundle of single-walled carbon nanotubes) in that it consists of a number of nanotubes defining its circumference as well as its length. A representative diameter for a nanotube in the bundle that forms nanotube bundle  140 A in  FIG. 3  is one nanometer. A representative diameter of the nanotube bundle  140 A as an interconnect is 20 to 100 nanometers. A representative length of the nanotube bundle  140 A is on the order of one micrometer to one millimeter. A suitable diameter for nanotube bundle  140 B is somewhat smaller but on the same order of magnitude. In one example, a length (measured in terms of depth of a via) of nanotube bundle  140 B is 1.75 its diameter. 
       FIG. 4  shows the structures of  FIG. 3  following the introduction or formation of a conductive material on each respective nanotube bundle. Referring to structure  100 A, conductive material  150 A is formed on nanotube bundle  140 A at an end of the nanotube opposite catalyst  130 A. Similarly, in structure  100 B, conductive material  150 B is formed on nanotube bundle  140 B at an end opposite catalyst  130 B. In one embodiment, a conductive material for conductive material  150 A and conductive material  150 B is selected as a suitable interconnect material (e.g., low resistance, etc.) that will allow a metal to metal bond between conductive material  150 A and conductive material  150 B. In one embodiment, a suitable material for conductive material  150 A and conductive material  150 B includes, but is not limited to, platinum, palladium, and copper. Representatively, an electroless palladium seed material may be formed on the nanotube followed by copper plating to form conductive material  150 A and conductive material  150 B. 
     In one embodiment, to form conductive material  150 A on an end of nanotube bundle  140 A, a seed material may be placed only at the end of the nanotube and subsequent plating of a material such as copper will be limited to the area where the area of the nanotube bundle includes the seed material. One way this may be accomplished is by depositing an additional layer of dielectric material conformally over a surface of dielectric layer  120 A including the nanotube bundle. Following a conformal deposition, the dielectric material may be planarized.  FIG. 4  shows dielectric material  160  of, for example, a material similar to the material for dielectric layer  120 A formed over a surface of dielectric layer  120 A including over nanotube bundle  140 A. In one embodiment, a thickness of a layer of dielectric material  160  is suitable to encapsulate nanotube bundle  140 A after planarization. Following planarization, an opening may be made using photolithographic and etching techniques at a position where it is desired to form conductive material on the nanotube. This may be followed by deposition of a seed material and plating of a conductive material. 
     In one embodiment, to form dielectric material  150 B on nanotube bundle  140 B, a seed layer may be deposited on nanotube bundle  140 B followed by the electro-deposition of a material such as copper. The seed layer may be blanket deposited over a surface of dielectric layer  120 B then polished from the surface to confine the seed material to the via. 
     Following the formation of conductive material  150 A and conductive material  150 B, the dielectric material containing the nanotube structures may be separated from sacrificial substrate  110 A and sacrificial substrate  110 B. One way to separate the dielectric material and interconnect structures from sacrificial substrate  110 A and sacrificial substrate  110 B is a “smart cut” delamination utilizing ion bombardment techniques, such as ion bombardment with hydrogen or argon and heating. 
     Following separation of the dielectric material and interconnect structures from sacrificial substrate  110 A and sacrificial substrate  110 B, the interconnect structures may be connected through bonding conductive material  150 A to conductive material  150 B (e.g., a metal-metal bond). The conductive materials may be bonded through a thermal technique.  FIG. 5  shows the combined interconnect structure formed in joined dielectric layer  120 A (including dielectric material for dielectric layer  120 A and dielectric material  160 ) and dielectric layer  120 B.  FIG. 5  also shows the interconnect structures that were formed on/in the dielectric layers joined through a connection between conductive material  150 A and conductive material  150 B. As shown in this cross-sectional side view, nanotube bundle  140 A may serve as an interconnect line with nanotube bundle  140 B and conductive material  150 A and conductive material  150 B serving as a conductive via to the interconnect line.  FIG. 5  representatively shows the combined dielectric layers including the interconnect structures over a substrate such as a circuit substrate (e.g., a portion of a wafer). The interconnect structures may be patterned to be coupled to a contact point on device  170 .  FIG. 5  shows contact point  180  that may be a portion of a circuit device (e.g., a transistor) or an interconnect (e.g., an underlying interconnect line or contact). 
       FIG. 6  shows the structure of  FIG. 5  following the connection of the combined dielectric layers including the interconnect structures to substrate  170 , particularly connecting the combined interconnect structures to contact point  180  on substrate  170 .  FIG. 6  also illustrates the process described above with reference to  FIGS. 1-5  may be repeated, where desired, for subsequent interconnect structures (e.g., conductive vias and/or line). 
     By utilizing sacrificial substrates to form interconnect structures, single-walled carbon nanotubes may be utilized as the interconnect structures. Experimental results indicate that a resistance of singled-walled carbon nanotubes compare favorably with predicted resistance of copper interconnects according to current technologies, with the resistance of the nanotubes being an order of magnitude better than the resistance of copper interconnects for technologically relevant interconnect links. 
       FIGS. 7-13  describe another technique of forming an interconnect structure using carbon nanotubes. In this technique, a multi-walled carbon nanotube is used as a portion of an interconnect. In one aspect the nanotubes are exploited for their atomically flat surface to define an interface for a metal conductor. The nanotube/metal interface will tend to produce less interface scattering compared to that produced with a typical dielectric/metal interface. The nanotube also serves as a highly defined barrier material around the metal interconnect and may decrease oxidation of the metal. 
       FIG. 7  shows a cross-sectional side view of a portion of a circuit substrate, such as a portion of a wafer having circuit devices formed thereon/therein.  FIG. 7  shows structure  200  including substrate  210  and contact point  220  on a surface of substrate  210  (a top surface as viewed). Contact point  220  may be a conductive contact to a device on substrate  210  (e.g., a transistor device) or a via formed to an underlying interconnect. 
     Overlying a surface of substrate  210  (a top surface as viewed) is carbon nanotube bundle  230 . In one embodiment, nanotube bundle  230  is a multi-walled carbon nanotube formed of a dimension suitable to define a volume for an interconnect line on a circuit substrate. Multi-walled carbon nanotubes such as nanotube bundle  230  can be deposited using various methods. One method involves catalytic conversion of gaseous hydrocarbon precursors (e.g., xylene) in the presence of a gaseous iron pre-catalyst (ferrocene) at silicone dioxide (SiO 2 ) nodules.  FIG. 7  shows nodule or a catalyst  240  from which nanotube bundle  230  is formed. As shown in  FIG. 7 , nanotube bundle  230  is formed in a lateral (x direction). One technique to control the directionality of the formation of nanotube bundle  230  is to render undesirable formation directions catalytically inactive with a metal (e.g., gold) or other material positioned next to the module. A size of nodule  240  may be selected to predetermine a dimension (e.g., diameter) of nanotube bundle  230 .  FIG. 8  shows a cross-sectional view of structure  200 , including nanotube bundle  230 , in a yz direction. 
       FIG. 9  shows structure  200  following the coating of nanotube bundle  230  with a barrier material. In one embodiment, nanotube bundle  230  is coated with a non-conductive material that will have a tendency to limit a subsequent deposition of a conductive material onto the nanotube periphery.  FIG. 9  shows barrier material  250  of, for example, non-conductive materials such as tantalum nitride, tungsten nitride, or aluminum oxide coating nanotube bundle  230 . The outer surface of the nanotube bundle  230  can also be plasma treated (for example, in a plasma containing hydrogen) to avoid subsequent nucleation of a conductive material.  FIG. 10  shows structure  200  in a yz direction and further illustrates barrier material  250  coating a periphery of nanotube bundle  230 . 
       FIG. 11  shows structure  200  following the filling of a portion of an interior of nanotube bundle  230  (e.g., an entire portion) with an electrically conductive material such as a metal material to incorporate an electrical conductor into the core of nanotube bundle  230 .  FIG. 11  shows conductive material  260  filling a portion, including an entire portion of conductive material  260 .  FIG. 12  shows a cross section of structure  200  in a yz direction and shows conductive material  260  filling a core of nanotube bundle  230  on substrate  210 . 
     A core of a carbon nanotube, such as nanotube bundle  230 , may be filled with a variety of transition metals including, though not limited to, palladium (Pu), platinum (Pt), copper (Cu), rhodium (Rh), ruthenium (Ru), gold (Au), osmium (Os), silver (Ag), iridium (Ir), molybdenum (Mo), tungsten (W), manganese (Mn), rhenium (Re), cobalt (Co), nickel (Ni) and other refractory metal compounds from D-block elements including groups 3-11 in the Period Table of the Elements. Tertiary and quaternary alloys including, but not limited, cobalt boron phosphorous (CoBP), cobalt phosphorous (CoP), cobalt tungsten phosphorus (CoWP), cobalt rhenium phosphorous (CoReP), nickel boron phosphorous (NiBP), nickel phosphorus (NiP), nickel boron (NiB), nickel tungsten phosphorus (NiWP), nickel rhenium phosphorous (NiReP), nickel rhenium boron phosphorus (NiReBP), cobalt nickel boron phosphorous (CoNiBP), cobalt nickel tungsten phosphorous (CoNiWP) and cobalt nickel rhenium phosphorus (CoNiReP) may also be employed. 
     A variety of techniques may be employed to fill a core of nanotube bundle  230  including electroless deposition, electroplating, atomic layer deposition (ALD) or chemical vapor deposition (CVD). Complete surface conformality and coverage is expected with ALD as it is a surface-limited deposition method. To minimize any diffusion limited non-coverage of nanotube bundle  230 , the nanotube bundle can be aligned nearly perpendicular to a reactant flow, the flow of precursor and co-reactants can be from different directions, and/or the nanotubes may be held freely (e.g., over an edge of sample). With respect to fill techniques employing CVD or ALD of a material such as platinum metal, precursor chemistries such as, though not limited to, beta-diketonates, cyclopentadienyl, arynes, allyls, or carbonyls may be used with an appropriate co-reactant such as oxygen or hydrogen. Metal CVD and ALD precursors may include, but are not limited to, inorganic and organometalic compounds such as 1,1,1,5,55-hexafluro-2,4-pentanedionato)Pd; bis(2,4-dimethylpentadienyl)Ru; M(acac) 2 , where M is Cu, Ni, Pd, Pt; M(diisopropylacetamidinato, where M is Ni, Cu, Co, Ag, lanthanum (La); MeCpptMe 3 , where Me is methyl and Cp is cyclopentadienyl; Ru(octandionate) 2 ; Pd(hfac) 2 ; Cp 2 Ru, where Cp is cyclopentadienyl; Cp 2 Os, where Cp is cyclopendienyl; silver chloride (AgCl); silver carbonate (Ag 2 CO 3 ); silver acetate (AgCOOCH 3 ); silvercyclohexanebutyrate (Ag[OOC(CH 2 ) 3 C 6 H 11 ]); nickel carbonyl (Ni(CO) 4 ); hydrogen tetrabromoaurate (HAuBr 4 ); gold cyanide (AuCN); and gold chloride (AuCl). Materials derived from these compounds may also be suitable (e.g., process-dependent transformations). 
     Nanotube bundle  230  may also be filled using electro/electroless plating methods of metals such as, though not limited to, ruthenium (Ru), cobalt (Co) and nickel (Ni). Another technique for filling nanotube bundle  230  that may be employed a polymeric immobilized palladium (PIP) process. 
       FIG. 13  shows structure  200  following the deposition of a conductive material to connect metal material  260  in a core of nanotube bundle  230  with contact point  220 . In this embodiment, a suitable metal is, for example, a transition metal such as might be used to fill nanotube bundle  230 . In this embodiment, conductive material  260  within nanotube bundle  230  may be described as an interconnect line connected to contact point  220  through conductive material  270 . Subsequent vias and/or interconnects of similar filled nanotube structures may be formed to the interconnect line defined by carbon nanotube bundle  230  and conductive material  260  or to other devices on/in substrate  210 . 
     In the embodiment described with reference to  FIGS. 7-13 , a multi-walled carbon nanotube bundle was utilized as a template for forming an interconnect. Multi-walled nanotubes may be formed according to techniques suitable for back side processing on circuit substrates, because such nanotubes may be formed at temperatures below, for example, 500° C. In an alternative embodiment, a single-walled nanotube bundle may be employed as the conduit for an interconnect structure. One technique to utilize a single-walled nanotube bundle to use the sacrificial substrate technique described above with reference to  FIGS. 1-6  and then filling the nanotube bundle as described, for example, with reference to  FIGS. 11-12 . 
     In the preceding detailed description, reference is made to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.