Patent Publication Number: US-7901586-B2

Title: Method of manufacturing self-ordered nanochannel-array and method of manufacturing nanodot using the nanochannel-array

Description:
This application claims the priority of Korean Patent Application No. 2003-25082, filed Apr. 21, 2003, the contents of which are incorporated herein by reference in their entirety and U.S. application Ser. No. 10/819,143, now U.S. Pat. No. 7,282,446, issued Oct. 16, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of manufacturing an array of vertical nanochannels and a method of manufacturing a nanodot using the array, and more particularly, to a method of forming a self-ordered nanochannel-array by two-step anodizing and a method of fabricating a nanodot using the nanochannel-array. 
     2. Description of the Related Art 
     Recently, researches have been actively conducted to form nano-scale patterns or structures in memories, laser diodes (LDs), photo diodes (PDs), transistors, far-infrared detectors, solar cells, optical modulators, and the likes. For example, a nanodot associated with an electronic control changes the number of bound electrons in correspondence to its size. Since electronic devices using nanodots can be actuated with a smaller number of electrons compared to conventional electronic devices, a threshold current level is lowered to enable low voltage actuation. The devices using nanodots also have the advantage of offering a high throughput with low voltage. 
     A conventional nanodot fabrication method utilizes a traditional deposition process including low pressure chemical vapor deposition (LPCVD) to form Si/Si 3 N 4  nuclei or sprays nanoparticles onto a substrate. However, the conventional approach makes it difficult to control the sizes of nanoparticles. Furthermore, spraying nanoparticles of an equal size cannot guarantee uniform nanodot distribution. 
     Another conventional method is to use electron beam lithography or laser beam lithography. This approach not only makes it difficult to obtain a nanodot of the desired size due to process limitation but also suffers from restriction in reducing its size. Furthermore, it is well known that lithography is a complicated and expensive process. 
     Meanwhile, Stephen Y. Chou et al. have proposed a method of forming a metal nanodot on a silicon substrate. This method involves imprinting a PMMA layer formed on a silicon substrate with a mold, forming a channel array to a predetermined depth, removing the residual PMMA from the bottom of a channel and forming a metal layer on the resulting structure, and soaking the substrate in an etching solution and lifting off the PMMA layer and residual metal thereon (Appl. Phys. Lett., Vol. 67. No. 21. 20 Nov. 1995). According to this technique, the size or spacing of a nanodot is determined by the mold. That is, the nanodot size is limited by a microscale patterning of the mold such as photolithography. Thus, its size cannot be reduced to less than the limit allowed in a photolithography process. 
     Hideki Masuda et al. have proposed a method of manufacturing a nanochannel-array that can be usefully used for developing various nanoscale devices (Appl. Phys. Lett. 71(19), 10 Nov. 1997). This method involves performing compression molding on a shallow-concavity, carrying out an anodizing process, and forming a self-ordered channel-array. However, this method has a problem in that the size of each channel or array is limited by the mold. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for easily forming a smaller and highly ordered nanochannel-array using a self-alignment technique. 
     The present invention also provides a method of manufacturing a nanodot using the highly ordered nanochannel-array, which is designed to allow a simplified and faster process and low manufacturing cost. 
     According to an aspect of the present invention, there is provided a method of manufacturing a self-ordered nanochannel array which includes the steps of: performing first anodizing an aluminum substrate to form a first alumina layer having a channel array formed by a plurality of cavitie; etching away the first alumina layer to form a plurality of concave portions on the aluminum substrate, wherein each concave portion corresponds to the bottom of each channel of the first alumina layer; and performing second anodizing to form a second alumina layer having an array of a plurality of channels corresponding to the plurality of concave portions on the aluminum substrate. 
     According to another aspect of the present invention, there is provided a method of manufacturing a nanodot, including the steps of: performing a first anodizing to form a first alumina layer having an array of a plurality of channels on a template containing an aluminum layer; etching the first alumina layer to a predetermined depth and forming a plurality of concave portions, each of which corresponds to the bottom of each channel of the first alumina layer, on the aluminum layer; performing second anodizing to form a second alumina layer having an array of a plurality of channels corresponding to the plurality of concave portions on the aluminum layer; forming a mask layer that covers a processing object layer on a substrate where the processing object layer has been formed; performing compression molding on the mask layer using the second alumina layer in the template and transferring the profile of the channel array in the second alumina layer to the mask layer; and etching the mask layer and the underlying processing object layer and transferring the compression molded profile of the mask layer to the processing object layer. 
     In the nanodot manufacturing method, the mask layer may be made from photoresist or polymethylmethyacrylate (PMMA). The processing object layer may be made from silicon. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
         FIGS. 1A-1E  show steps of a method of manufacturing a self-ordered nanochannel-array using two-step anodizing according to exemplary embodiments of the present invention; 
         FIG. 2  shows a cross-section (left) and a top view (right) showing a nano-hole array of a nanochannel-array manufactured according to an embodiment of this invention; and 
         FIGS. 3A-3H  show steps of a method of manufacturing a nanodot using the nanochannel-array of  FIG. 2  as a template according to an embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a method of manufacturing a self-ordered nanochannel-array and a method of manufacturing a nanodot using the nanochannel-array as a template according to preferred embodiments of this invention will be described with reference to the accompanying drawings. 
     First, a method of manufacturing a nanochannel-array on an aluminum substrate will be described. 
     The nanochannel-array manufacturing method according to this exemplary embodiment of the invention includes a two-step anodizing process. 
     As shown in  FIG. 1A , an aluminum substrate  11  is prepared. Here, the aluminum substrate  11  may be constructed from a pure aluminum plate or a structure in which an aluminum layer has been formed on a separate supporting substrate. 
     Referring to  FIG. 1B , the aluminum substrate  11  is oxidized to a predetermined depth by first anodizing to form a porous alumina layer  13 . During the extending of the alumina layer  13  from the surface of the original aluminum surface  11  by the first anodizing, the first anodizing, the vertical shape of a channel  13   a  is irregularly distorted due to nonuniformity in morphology of the aluminum substrate  11  that begins to be oxidized. 
     In  FIG. 1C , the alumina layer  13  is cleaned off with an etching solution. In this case, equally nano-sized concave portions  11   a  remain to form an array on the aluminum substrate  11  that has been exposed after etching. 
     Referring to  FIG. 1D , second anodizing is performed under the same condition as was given for the first anodizing to form a porous alumina layer  14  having a plurality of channels  14   a  to a predetermined depth. 
     As shown in  FIG. 1E , the channel  14   a  is widened by appropriately adjusting the temperature and concentration of a solution and a value of an applied voltage only when necessary. 
       FIG. 2  shows a cross-section (left) of the nanochannel-array formed by the two-step anodizing process, a top view (right) of the nanochannel-array presenting an arrangement of the nanochannels. 
     The nanochannel-array described above can be used as a template in a method of forming a nanodot according to this invention. 
     Referring to  FIG. 3A , a substrate  5  on which a processing object layer  4  on which crystalline or amorphous silicon have been formed is prepared. Here, the substrate  5  may be a silicon substrate, and silicon oxide  5   a  is sandwiched between the processing object layer  4  and silicon substrate  5 . Since the silicon oxide is only an example of material that can reside beneath the processing object layer  4 , a material other than silicon oxide may be used. Furthermore, the processing object layer  4  may be constructed of a material other than silicon. That is, a nanodot manufacturing method according to this invention is not limited by the material forming the processing object layer  4 , and a method of adopting this material provides another embodiment of this invention. 
     Referring to  FIG. 3B , a mask layer  6  made of photoresist or polymethylmethyacrylate (PMMA) is formed on the processing object layer  4  to a predetermined thickness. Here, the thickness of the mask layer  6  is set considering compressing molding. 
     As shown in  FIG. 3C , compression molding is performed on the mask layer  6  using a template  10  where the alumina layer  14  having an array of a plurality of channels has been formed on the aluminum substrate  11 . At that time, the alumina layer  14  faces the mask layer  6  so that the profile of the channel array in the alumina layer  14  can be transferred to the mask layer  6 . 
     In  FIG. 3D , the template  10  is separated from the mask layer  6 , and as shown in  FIG. 3G , etching is performed on the entire surface of the mask layer  6 . In this case, RIE or ion milling is performed to etch the mask layer  6  by a uniform thickness. Sufficient etching proceeds under these conditions so that the template profile transferred to the mask layer  6  can be transferred to the processing object layer  4 . After the transfer process, the processing object layer  4  remains in the form of nanodots. 
     If residue  6 ′ of the mask layer  6  remains as shown in  FIG. 3E  after having processed the processing object layer  4  in the form of nanodots, the residue  6 ′ is removed as shown in  FIG. 3F . This step can be skipped to the next one if no residue remains. 
     As shown in  FIG. 3H , if the processing object layer  4  is made of amorphous silicon, the processing object layer  4  is annealed by applying heat. The annealing process is carried out as needed and in particular when making amorphous silicon into crystalline silicon. 
     The above steps for forming nanodots with the processing object layer  4  have been generally described herein. That is, the steps are only a part of the process of manufacturing an electric device so this invention is not limited by a method of fabricating a specific electric device. 
     The nanochannel-array fabricating method according to this invention involves forming self-ordered concave portions by first anodizing and etching and then self-ordered channels by second anodizing. This invention allows a channel-array obtained in this way to be used as a template in place of a mold formed by lithography, thus eliminating the need to perform an expensive lithography process while providing a faster process that can be applied to a large area. Furthermore, this invention makes it possible to easily adjust channel spacing and size of a nanochannel-array through an anodizing process and then the size and spacing of a nanodot array fabricated using the nanochannel-array. 
     The channel-array manufacturing method and a method of fabricating nanodots using the channel-array according to this invention can be applied to the manufacturing of various types of electronic devices including memories, laser diodes (LDs), photo diodes (PDs), transistors, far-infrared detectors, solar cells, and optical modulators. 
     While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.