Method of forming one or more nanopores for aligning molecules for molecular electronics

Abstract

A technique is provided for forming a molecule or an array of molecules having a defined orientation relative to the substrate or for forming a mold for deposition of a material therein. The array of molecules is formed by dispersing them in an array of small, aligned holes (nanopores), or mold, in a substrate. Typically, the material in which the nanopores are formed is insulating. The underlying substrate may be either conducting or insulating. For electronic device applications, the substrate is, in general, electrically conducting and may be exposed at the bottom of the pores so that one end of the molecule in the nanopore makes electrical contact to the substrate. A substrate such as a single-crystal silicon wafer is especially convenient because many of the process steps to form the molecular array can use techniques well developed for semiconductor device and integrated-circuit fabrication.

What is claimed is:  
     
         1 . A method for forming at least one nanopore for aligning at least one molecule for molecular electronic devices or for forming a mold for deposition of a material, comprising: 
 (a) providing a substrate having a first major surface and a second major surface, substantially parallel to said first major surface;    (b) forming an etch mask on said first major surface, said etch mask comprising at least one nanoparticle;    (c) directionally etching said substrate from said first major surface toward said second major surface, using said etch mask to protect underlying portions of said substrate against said etching, thereby forming at least one pillar underneath said etch mask;    (d) forming a layer of insulating material on said etched substrate, including around said at least one pillar and at least partially covering said at least one pillar; and    (e) removing said at least one pillar to leave at least one said nanopore in said insulating layer.    
     
     
         2 . The method of  claim 1  for forming a nanopore array for either aligning or spacing molecules for electronic devices or for forming said mold, wherein: in step (b), said etch mask comprises a plurality of said nanoparticles; in step (c), a plurality of said pillars is formed by said directional etching; in step (d) said layer of insulating material is formed between said pillars and at least partially covering said pillars; and in step (e), said plurality of pillars is removed to leave said array of nanopores.  
     
     
         3 . The method of  claim 1  wherein said at least one nanoparticle has an average particle size within a range of about 1 to 10 nm.  
     
     
         4 . The method of  claim 1  wherein said at least one nanoparticle comprises an inorganic crystalline core covered with an organic layer.  
     
     
         5 . The method of  claim 1  wherein said at least one nanoparticle is formed by depositing a material of a first lattice constant on said substrate wherein said substrate has a second and different lattice constant to create a lattice mismatch and using forces from said lattice mismatch to form at least one nanoparticulate island of said deposited material.  
     
     
         6 . The method of  claim 1  wherein said directional etching is carried out using reactive ion etching.  
     
     
         7 . The method of  claim 1  wherein said insulating material is selected from the group consisting of oxides, nitrides, oxynitrides, diamond-like carbon, and insulating polymers.  
     
     
         8 . The method of  claim 7  wherein said insulating material is selected from the group consisting of silicon dioxide, aluminum oxide, silicon nitride, and silicon oxynitride.  
     
     
         9 . The method of  claim 7  wherein said insulating material is formed by chemical vapor deposition or by liquid-phase techniques.  
     
     
         10 . The method of  claim 1  wherein said etch mask comprising said at least one nanoparticle is removed prior to forming said insulating material.  
     
     
         11 . The method of  claim 1  wherein in step (d), said layer of said insulating material is formed to completely cover said at least one pillar and following step (d), said layer of insulating material is reduced in thickness to expose a top of said at least one pillar.  
     
     
         12 . The method of  claim 1  wherein said layer of insulating material is reduced in thickness by chemical-mechanical polishing or by an unmasked single-step or multi-step plasma/reactive-ion etch technique.  
     
     
         13 . The method of  claim 1  wherein said at least one pillar is removed by selective etching.  
     
     
         14 . The method of  claim 1  further comprising filling said at least one nanopore with said material.  
     
     
         15 . The method of  claim 14  wherein said material comprises a molecular species.  
     
     
         16 . The method of  claim 14  wherein the bottom of said at least one nanopore is electrically conducting.  
     
     
         17 . The method of  claim 16  wherein said bottom of said at least one nanopore is made electrically conducting by using as said substrate a material that is electrically conducting.  
     
     
         18 . The method of  claim 17  wherein said substrate comprises doped single crystal silicon or a doped polycrystalline silicon layer on said substrate.  
     
     
         19 . The method of  claim 14  wherein prior to filling said nanopores, the bottom of said nanopores is covered with a thin tunnel barrier.  
     
     
         20 . The method of  claim 14  wherein said material comprises a material selected from the group consisting of semiconductor and magnetic materials.  
     
     
         21 . The method of  claim 1  wherein said at least one nanopore has a length of about 5 to 100 nm and a diameter of about 1 to 10 nm.  
     
     
         22 . The method of  claim 21  wherein said at least one nanopore has a length of about 10 nm and a diameter of about 1 nm.  
     
     
         23 . The method of  claim 1  wherein said substrate is selected from the group consisting of oxides, nitrides, oxynitrides, and carbides.  
     
     
         24 . A method for forming at least one molecule in a pre-selected orientation relative to a substrate, said method comprising: 
 (a) forming at least one nanopore by: 
 (1) providing said substrate having a first major surface and a second major surface, substantially parallel to said first major surface,  
 (2) forming an etch mask on said first major surface, said etch mask comprising at least one nanoparticle,  
 (3) directionally etching said substrate from said first major surface toward said second major surface, using said etch mask to protect underlying portions of said substrate against said etching, thereby forming at least one pillar underneath said etch mask,  
 (4) forming a layer of insulating material on said etched substrate, including around said at least one pillar and at least partially covering said at least one pillar, and  
 (5) removing said at least one pillar to leave at least one said nanopore in said insulating layer; and  
   (b) dispersing said at least one molecule in said at least one nanopore.    
     
     
         25 . The method of  claim 24  for forming a molecular array, wherein: in step (2), said etch mask comprises a plurality of said nanoparticles; in step (3), a plurality of said pillars is formed by said directional etching; in step (4) said layer of insulating material is formed between said pillars and at least partially covering said pillars; and in step (5), said plurality of pillars is removed to leave said array of nanopores and further wherein in step (b), a plurality of said molecules is dispersed, one in each said nanopore.  
     
     
         26 . The method of  claim 24  wherein said at least one nanoparticle has an average particle size within a range of about 1 to 10 nm.  
     
     
         27 . The method of  claim 24  wherein said at least one nanoparticle comprises an inorganic crystalline core covered with an organic layer.  
     
     
         28 . The method of  claim 24  wherein said at least one nanoparticle is formed by depositing a material of a first lattice constant on said substrate wherein said substrate has a second and different lattice constant to create a lattice mismatch and using forces from said lattice mismatch to form at least one nanoparticulate island of said deposited material.  
     
     
         29 . The method of  claim 24  wherein said directional etching is carried out using reactive ion etching.  
     
     
         30 . The method of  claim 24  wherein said insulating material is selected from the group consisting of oxides, nitrides, oxynitrides, diamond-like carbon, and insulating polymers.  
     
     
         31 . The method of  claim 30  wherein said insulating material is selected from the group consisting of silicon dioxide, aluminum oxide, silicon nitride, and silicon oxynitride.  
     
     
         32 . The method of  claim 30  wherein said insulating material is formed by chemical vapor deposition or by liquid-phase techniques.  
     
     
         33 . The method of  claim 24  wherein said etch mask comprising said at least one nanoparticle is removed prior to forming said insulating material.  
     
     
         34 . The method of  claim 24  wherein in step (4), said layer of said insulating material is formed to completely cover said at least one pillar and following step (4), said layer of insulating material is reduced in thickness to expose a top of said at least one pillar.  
     
     
         35 . The method of  claim 24  wherein said layer of insulating material is reduced in thickness by chemical-mechanical polishing or by an unmasked single-step or multi-step plasma/reactive-ion etch technique.  
     
     
         36 . The method of  claim 24  wherein said at least one pillar is removed by selective etching.  
     
     
         37 . The method of  claim 24  further comprising filling said at least one nanopore with said material.  
     
     
         38 . The method of  claim 37  wherein said material comprises a molecular species.  
     
     
         39 . The method of  claim 37  wherein the bottom of said at least one nanopore is electrically conducting.  
     
     
         40 . The method of  claim 39  wherein said bottom of said at least one nanopore is made electrically conducting by using as said substrate a material that is electrically conducting.  
     
     
         41 . The method of  claim 40  wherein said substrate comprises doped single crystal silicon or a doped polycrystalline silicon layer on said substrate.  
     
     
         42 . The method of  claim 37  wherein prior to filling said nanopores, the bottom of said nanopores is covered with a thin tunnel barrier.  
     
     
         43 . The method of  claim 37  wherein said material comprises a material selected from the group consisting of semiconductor and magnetic materials.  
     
     
         44 . The method of  claim 24  wherein said at least one nanopore has a length of about 5 to 100 nm and a diameter of about 1 to 10 nm.  
     
     
         45 . The method of  claim 44  wherein said at least one nanopore has a length of about 10 nm and a diameter of about 1 nm.  
     
     
         46 . The method of  claim 24  wherein said substrate is selected from the group consisting of oxides, nitrides, oxynitrides, and carbides.