Abstract:
Methods of forming carbon nanotubes include forming a catalytic metal layer on a sidewall of an electrically conductive region, such as a metal or metal nitride pattern. A plurality of carbon nanotubes are grown from the catalytic metal layer. These carbon nanotubes can be grown from a sidewall of the catalytic metal layer. The plurality of carbon nanotubes are then exposed to an organic solvent. This step of exposing the carbon nanotubes to the organic solvent may be preceded by a step of applying centrifugal forces to the plurality of carbon nanotubes. Alternatively, the exposing step may include applying a centrifugal force to the plurality of carbon nanotubes while simultaneously exposing the plurality of carbon nanotubes to an organic solvent.

Description:
REFERENCE TO PRIORITY APPLICATION 
     This application claims priority to Korean Patent Application No. 10-2008-0120365, filed Dec. 1, 2008, the contents of which are hereby incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to integrated circuit devices and, more particularly, to methods of forming carbon nanotubes for integrated circuit devices. 
     BACKGROUND 
     As semiconductor devices are highly integrated and become smaller in size, new methods of forming semiconductor devices have been studied, and forming a CNT is one of the above methods. A CNT may substitute for a metal wiring of a semiconductor device, however, forming a CNT structure having reproducibility is not easy. 
     A CNT structure may be formed by vertically growing CNTs on a substrate on which catalyst patterns are formed. However, uniformly controlling lengths of and distances between the CNTs, and growing the CNTs only at specific portions of the substrate are not easy. Additionally, the CNTs vertically grown may not be adapted to all processes for manufacturing semiconductor devices. 
     SUMMARY 
     Methods of forming carbon nanotubes according to embodiments of the present invention include forming a catalytic metal layer on a sidewall of an electrically conductive region, such as a metal or metal nitride pattern. A plurality of carbon nanotubes are grown from the catalytic metal layer. In particular, these carbon nanotubes can be grown from a sidewall of the catalytic metal layer. The plurality of carbon nanotubes are then exposed to an organic solvent. This step of exposing the carbon nanotubes to the organic solvent may be preceded by a step of applying centrifugal forces to the plurality of carbon nanotubes. Alternatively, the exposing step may include applying a centrifugal force to the plurality of carbon nanotubes while simultaneously exposing the plurality of carbon nanotubes to an organic solvent. In these embodiments of the invention, the exposing step may include spin coating an organic solvent onto the plurality of carbon nanotubes. 
     According to additional embodiments of the invention, the step of forming a catalytic metal layer may be preceded by a step of forming the electrically conductive region on a surface of a substrate. The growing step may then include growing the plurality of carbon nanotubes from a sidewall of the catalytic metal layer and parallel to the surface. 
     Still further embodiments of the invention include forming carbon nanotubes by forming an electrically conductive layer on a substrate and then forming a catalytic metal layer on a sidewall of the electrically conductive layer. A plurality of carbon nanotubes are then grown from the catalytic metal layer. This plurality of carbon nanotubes may be exposed to an organic solvent. This application of the organic solvent may occur concurrently with applying a centrifugal force to the plurality of carbon nanotubes. For example, the exposing of the carbon nanotubes to the organic solvent and the application of the centrifugal force may be achieved by spin coating an organic solvent onto the plurality of carbon nanotubes. Moreover, in the event the substrate includes an electrically insulating layer thereon, then the growing may include growing the plurality of carbon nanotubes in a direction parallel to a surface on the electrically insulating layer. The application of the centrifugal force may also be achieved by rotating the substrate at a speed in a range from 3000 rpms and 5000 rpms. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.  FIGS. 1 to 14  represent non-limiting, example embodiments as described herein. 
         FIGS. 1 to 4  are cross-sectional views illustrating a method of forming a carbon nanotube (CNT) in accordance with example embodiments; 
         FIGS. 5 to 9  are cross-sectional views illustrating a method of forming a CNT in accordance with other example embodiments; 
         FIG. 10  is a block diagram illustrating a memory card including the horizontal CNTs in accordance with example embodiments; 
         FIG. 11  is a block diagram illustrating a portable device including the horizontal CNTs in accordance with example embodiments; and 
         FIG. 12  is a block diagram illustrating a computer including the horizontal CNTs in accordance with example embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Various example embodiments will be described more fully hereinafter with reference to the accompanying drawings, in which some example embodiments are shown. The present inventive concept may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Rather, these example embodiments are provided so that this description will be thorough and complete, and will fully convey the scope of the present inventive concept to those skilled in the art. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numerals refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present inventive concept. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present inventive concept. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized example embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the present inventive concept. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive concept belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Hereinafter, example embodiments will be explained in detail with reference to the accompanying drawings. 
       FIGS. 1 to 4  are cross-sectional views illustrating methods of forming carbon nanotubes (CNT) in accordance with example embodiments. 
     Referring to  FIG. 1 , a substrate  100  may be provided. The substrate  100  may include a semiconductor substrate such as a silicon substrate, a germanium substrate, a silicon-germanium substrate, etc., an epitaxial substrate, or an insulating substrate such as a glass substrate. The substrate  100  may include various devices thereon, e.g., transistors, contact plugs, bitlines, capacitors, metal wirings, etc. 
     An insulation layer  110  may be formed on the substrate  100 . The insulation layer  110  may be formed using silicon oxide, silicon nitride, silicon oxynitride, indium tin oxide (ITO), aluminum oxide, etc. The silicon oxide may include borophosphor silicate glass (BPSG), phosphor silicate glass (PSG), undoped silicate glass (USG), spin on glass (SOG), plasma-enhanced tetraethyl-orthosilicate (PE-TEOS), etc. 
     A metal structure  120  may be formed on the insulation layer  110 . The metal structure  120  may include a metal layer pattern or a metal nitride layer pattern of which a surface the CNT may grow from. The metal (nitride) layer pattern may include nickel, cobalt, iron, titanium, titanium nitride, etc. These may be used alone or in combination thereof. The metal (nitride) layer pattern may be formed by a deposition process using the above material. A capping layer (not shown) may be further formed on the metal (nitride) layer pattern. 
     Referring to  FIG. 2 , a catalytic metal layer may be formed on the insulation layer  110  to cover the metal structure  120 . The catalytic metal layer may include a catalyst material such as nickel, cobalt, iron, etc. The catalyst material layer may be annealed to have nano-particles such as nano-dots. The catalytic metal layer may be etched until a top surface of the metal structure  120  may be exposed, thereby forming a catalyst spacer  140  on sidewalls of the metal structure  120 . 
     Referring to  FIG. 3 , a plurality of CNTs  150  may be formed on sidewall surfaces of the catalyst spacer  140 . The CNTs  150  may be formed using a source gas including hydrocarbon. The source gas may be formed by vaporizing, e.g., methane, acetylene, carbon monoxide, benzene, ethylene, etc. The CNTs  150  may be formed by a catalytic thermal reduction process, a chemical vapor deposition (CVD) process, a thermal chemical vapor deposition process, a plasma-enhanced chemical vapor deposition (PE-CVD) process, a hot filament vapor deposition process, etc. The CNTs  150  may be grown by catalyst, and the performance of the catalyst material included in the catalyst spacer  140  may depend on the characteristics of a layer contacting the catalyst spacer  140 . Thus, the catalyst spacer  140  may selectively grow the CNTs  150 . 
     The CNTs  150  may grow on the sidewall surfaces of the catalyst spacer  140 , and the grown CNTs  150  shown may not extend in a direction parallel to a top surface of the insulation layer  110  or the substrate  100 , but an end portion of each CNT  150  may be bent upward, as shown in  FIG. 3 . 
     Referring to  FIG. 4 , the substrate  100  having the bent CNTs  150  thereover may be rotated. Thus, a tensile force and a compressive force may be applied to the CNTs  150 . The tensile force may be generated by a turning force of the substrate  100 , and the compressive force, which compresses the CNTs  150  downward, may be generated by a structure over the substrate  100 , e.g., the metal structure  120  when the substrate  100  is rotated. In an example embodiment, the substrate  100  may be rotated at a speed of about 3,000 to about 5,000 rpm, preferably, about 3,500 to about 4,500 rpm. 
     A volatile organic solvent may be provided on the top surface of the insulation layer  110 . The volatile organic solvent may include acetone, xylene, a volatile alcohol such as isopropyl alcohol, etc. The volatile organic solvent may be provided onto a central top surface of the insulation layer  110  and may be spin coated on the whole surface thereof by a centrifugal force. Thus, the CNTs  150  may be wet by the volatile organic solvent, and be adsorbed onto the top surface of the insulation layer  110 . The volatile organic solvent may apply an adhesion force to the CNTs  150 . 
     The bent CNTs  150  may be changed into a horizontal CNTs  151 , which extends in the direction parallel to the top surface of the insulation layer  110  or the substrate  100 , by the above three forces. The horizontal CNTs  151  may be close to the top surface of the insulation layer  110 , and extend in the direction parallel to the top surface of the insulation layer  110  or the substrate  100 . 
       FIGS. 5 to 9  are cross-sectional views illustrating methods of forming a CNT in accordance with other example embodiments. 
     Referring to  FIG. 5 , a substrate  200  may be provided. The substrate  200  may include a semiconductor substrate such as a silicon substrate, a germanium substrate, a silicon-germanium substrate, etc., an epitaxial substrate, or an insulating substrate such as a glass substrate. The substrate  200  may include various devices thereon, e.g., transistors, contact plugs, bitlines, capacitors, metal wirings, etc. 
     An insulation layer  210  may be formed on the substrate  200 . The insulation layer  210  may be formed using silicon oxide, silicon nitride, silicon oxynitride, indium tin oxide (ITO), aluminum oxide, etc. The silicon oxide may include borophosphor silicate glass (BPSG), phosphor silicate glass (PSG), undoped silicate glass (USG), spin on glass (SOG), plasma-enhanced tetraethyl-orthosilicate (PE-TEOS), etc. 
     A first metal layer pattern  220  may be formed on the insulation layer  210 . The first metal layer pattern  220  may include a first metal such as nickel, cobalt, iron, titanium, etc. These may be used alone or in combination thereof. Alternatively, the first metal layer pattern  220  may include a metal nitride such as titanium nitride. The first metal layer pattern may be formed by performing a deposition process using the above material to form a first metal layer and patterning the first metal layer. 
     Referring to  FIG. 6 , a second metal layer may be formed on the insulation layer  210  to cover the first metal layer pattern  220 . The second metal layer may include a second metal preventing a CNT from growing from a surface of the second metal layer. The second metal may include palladium, platinum, tungsten, niobium, vanadium, molybdenum, etc. These may be used alone or in combination thereof. The second metal layer may be formed by a deposition process. 
     The second metal layer may be patterned by a photolithography process so that a lateral surface A of the first metal layer pattern  220  may be exposed. Thus, a second metal layer pattern  230  surrounding the first metal layer pattern  220  except for the lateral surface A thereof may be formed. 
     The first and second metal layer patterns  220  and  230  may be called as a metal structure  235 . 
     Referring to  FIG. 7 , a catalytic metal layer may be formed on the insulation layer  210  to cover the metal structure  235 . The catalytic metal layer may include a catalyst material such as nickel, cobalt, iron, etc. The catalyst material layer may be annealed to have nano-particles such as nano-dots. The catalytic metal layer may be etched until a top surface of the metal structure  235  may be exposed, thereby forming first and second catalyst spacers  242  and  244  on sidewalls of the metal structure  235 . The first catalyst spacer  242  may be formed on the sidewall of the metal structure  235  to contact the lateral surface A of the first metal layer pattern  220 , and the second catalyst spacer  244  may be formed on the sidewall of the metal structure  235  to be spaced apart from the first metal layer pattern  220 . 
     Referring to  FIG. 8 , a plurality of CNTs  250  may be formed on a lateral surface of the first catalyst spacer  242 , and may not be formed on a lateral surface of the second catalyst spacer  244 . The CNTs  250  may be grown by catalyst, and the performance of the catalyst material included in the catalyst spacers  242  and  244  may depend on the characteristics of the first and second metal layer patterns  220  and  230  contacting the catalyst spacers  242  and  244 , respectively. Thus, only the first catalyst spacer  242  may grow the CNTs  250 . The CNTs  250  may be formed using a source gas including hydrocarbon. The source gas may be formed by vaporizing, e.g., methane, acetylene, carbon monoxide, benzene, ethylene, etc. The CNTs  250  may be formed by a catalytic thermal reduction process, a CVD process, a thermal chemical vapor deposition process, a PE-CVD process, a hot filament vapor deposition process, etc. 
     The CNTs  250  may grow only on the lateral surface of the first catalyst spacer  242 , and the grown CNTs  250  shown may not extend in a direction parallel to a top surface of the insulation layer  210 , but an end portion of each CNT  250  may be bent upward, as shown in  FIG. 8 . 
     Referring to  FIG. 9 , the substrate  200  including the bent CNTs  250  thereover may be rotated. Thus, a tensile force and a compressive force may be applied to the CNTs  250 . The tensile force may be generated by a turning force of the substrate  200 , and the compressive force, which compresses the CNTs  250  downward, may be generated by a structure over the substrate  100 , e.g., the metal structure  235  when the substrate  200  is rotated. In an example embodiment, the substrate  200  may be rotated at a speed of about 3,000 to about 5,000 rpm, preferably, about 3,500 to about 4,500 rpm. 
     A volatile organic solvent may be provided on the top surface of the insulation layer  210 . The volatile organic solvent may include acetone, xylene, a volatile alcohol such as isopropyl alcohol, etc. The volatile organic solvent may be provided onto a central top surface of the insulation layer  210  and may be spin coated on the whole surface thereof by a centrifugal force. Thus, the CNTs  250  may be wet by the volatile organic solvent, and be adsorbed onto the top surface of the insulation layer  210 . The volatile organic solvent may apply an adhesion force to the CNTs  250 . 
     The bent CNTs  250  may be changed into a horizontal CNTs  251 , which extends in the direction parallel to the top surface of the insulation layer  210  or the substrate  200 , by the above three forces. The horizontal CNTs  251  may be very close to the top surface of the insulation layer  210 , and extend in the direction parallel to the top surface of the insulation layer  210  or the substrate  200 , as shown in  FIG. 9 . The CNTs  251  may substitute for metal wirings in dynamic random access memory (DRAM) devices, flash memory devices, phase-change memory (PRAM) devices, etc. 
       FIG. 10  is a block diagram illustrating a memory card including the horizontal CNTs in accordance with example embodiments. 
     Referring to  FIG. 10 , a memory card  500  may include a memory controller  520  connected to a memory  510 . The memory  510  may be a DRAM or a flash memory (an NAND flash memory or an NOR flash memory) having the horizontal CNTs in accordance with example embodiments. The horizontal CNTs may also serve as wirings in a logic circuit of the memory controller  520 . The memory controller  520  may provide the memory  510  with input signals to control operations of the memory  510 . For example, in the memory card  500 , the memory controller  520  may transfer commands of a host to the memory  510  to control input/output data and/or may control various data of a memory based on an applied control signal. In addition to a simple memory card, the present invention may be applied to other digital devices which include a similar operative association between a memory and a memory controller. 
       FIG. 11  is a block diagram illustrating a portable device including the horizontal CNTs in accordance with example embodiments. 
     Referring to  FIG. 11 , a portable device  600  may include an MP3 player, a video player, or a portable multi-media player (PMP). The portable device  600  may include a memory  510  having the horizontal CNTs according to example embodiments, and a memory controller  620  as described above. The memory  510  may be a DRAM or flash memory including the horizontal CNTs. 
     The portable device  600  may include an encoder/decoder (EDC)  610 , a display element  620  and an interface  630 . As illustrated by the dashed lines of  FIG. 11 , data may be directly input from the EDC  610  to the memory  510 , or directly output from the memory  510  to the EDC  610 . 
     The EDC  610  may encode data to be stored in the memory  510 . For example, the EDC  610  may execute encoding for storing audio data and/or video data in the memory  510  of an MP3 player or a PMP player. Furthermore, the EDC  610  may execute MPEG encoding for storing video data in the memory  510 . The EDC  610  may include multiple encoders to encode different types of data depending on their formats. For example, the EDC  610  may include an MP3 encoder for encoding audio data and an MPEG encoder for encoding video data. 
     The EDC  610  may also decode data being output from in the memory  510 . For example, the EDC  610  may decode MP3 audio data from the memory  510 . Furthermore, the EDC  610  may decode MPEG video data from the memory  510 . The EDC  610  may include multiple decoders to decode different types of data depending on their formats. For example, the EDC  610  may include an MP3 decoder for audio data and an MPEG decoder for video data. 
     The EDC  610  may include only a decoder. For example, encoded data may be input to the EDC  610 , and then the EDC  610  may decode the input data and transfer the decoded data to the memory controller  520  or the memory  510 . 
     The EDC  610  may receive data to be encoded or data being encoded by way of the interface  630 . The interface  630  may be compliant with standard input devices, e.g. FireWire, or a USB. That is, the interface  630  may include a FireWire interface, an USB interface or the like. Data is output from the memory  510  by way of the interface  630 . 
     The display element  620  may display to an end user data output from the memory  510  and decoded by the EDC  610 . For example, the display element  620  may be an audio speaker or a display screen. 
       FIG. 12  is a block diagram illustrating a computer including the horizontal CNTs in accordance with example embodiments. 
     Referring to  FIG. 12 , a computer  700  may include a memory  510  and a central processing unit (CPU)  710  connected to the memory  510 . The memory  510  may be a DRAM or a flash memory having the horizontal CNTs in accordance with example embodiments. An example of such a computer  700  may be a laptop computer including a flash memory as its main memory. The memory  510  may be directly connected to the CPU  710 , or indirectly connected to the CPU  710  by buses. The computer  700  may have other conventional auxiliary devices (not illustrated in  FIG. 12 ). 
     According to example embodiments, a plurality of CNTs may be grown from a catalyst spacer on sidewalls of a metal structure on a substrate, and a volatile organic solvent may be provided onto the substrate to give the CNTs an adhesion force. Thus, the CNTs may extend in a direction parallel to a top surface of the substrate. 
     The foregoing is illustrative of example embodiments and is not to be construed as limiting thereof. Although a few example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of the present inventive concept. Accordingly, all such modifications are intended to be included within the scope of the present inventive concept as defined in the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of various example embodiments and is not to be construed as limited to the specific example embodiments disclosed, and that modifications to the disclosed example embodiments, as well as other example embodiments, are intended to be included within the scope of the appended claims.