Patent Publication Number: US-2006003267-A1

Title: Nano-structure and method of fabricating nano-structures

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application is a continuation-in-part of copending U.S. utility application entitled, “Fabrication and Use of Superlattice,” having Ser. No. 10/817,729, filed Apr. 2, 2004, which is entirely incorporated herein by reference. 
    
    
     BACKGROUND  
      Although fabrication of structures on a “nano” scale has been practiced for several years, there are still many challenges that are to be overcome to enable manufacture of desired structures.  
      For instance, problems can be encountered when a nano-structure is formed that includes a plurality layers of material that are to be planarized. Such problems may include, for example, fraying, delamination, erosion, dishing, and rounding.  
      Desired is a method for forming nano-structures that overcome or reduce such problems.  
     SUMMARY  
      In one embodiment, a nano-structure comprises a substrate, a feature formed on the substrate that extends upwardly from a surface of the substrate, layers of material that overlie the substrate surface and at least a portion of the feature, and an exposed surface comprising a top surface of the feature and edges of the layers of material, wherein portions of selected layers of material have been etched away to form trenches adjacent the top surface of the top surface of the feature.  
      In one embodiment, a method for fabricating a nano-structure comprises forming a feature on a substrate, depositing multiple layers of material over the substrate and feature to form a multi-layer stack, depositing a film over the multi-layer stack, removing a portion of the film and the multi-layer stack to expose edges of the layers of material, and removing portions of the layers of material to form trenches at a surface of the nano-structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The disclosed nano-structure and method can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale.  
       FIG. 1  is an end view of an embodiment of a nano-structure in an initial stage of fabrication.  
       FIG. 2  is a top perspective view of the nano-structure shown in  FIG. 1 .  
       FIG. 3  is an end view of the nano-structure of  FIG. 1  in a later stage of fabrication.  
       FIG. 4  is an end view of the nano-structure of  FIG. 1  in yet a later stage of fabrication.  
       FIG. 5  is an end view the nano-structure of  FIG. 1  in yet another later stage of fabrication.  
       FIG. 6  is an end view of an embodiment of a completed nano-structure.  
       FIG. 7  is a detail view of trenches formed in the nano-structure of  FIG. 6 .  
       FIG. 8  is a flow diagram of an embodiment of a method for fabricating a nano-structure. 
    
    
     DETAILED DESCRIPTION  
      Disclosed is a nano-structure and a method for fabricating nano-structures. According to at least one embodiment of the method, multiple layers of material that overlie a feature that is formed on the surface of a substrate are covered by a sacrificial film that enables planarization of the multiple layers while reducing or preventing one or more of fraying, delamination, erosion, dishing, and rounding.  
      Referring now in more detail to the drawings, in which like numerals indicate corresponding parts throughout the several views,  FIG. 1  illustrates an embodiment of a nano-structure  100  in an initial stage of fabrication. As is indicated in  FIG. 1 , the nano-structure  100  includes a substrate  102  that, for example, comprises a silicon wafer. Formed on a surface  104  of the substrate  102  is a feature  106  that, in the embodiment shown in  FIG. 1 , comprises a dielectric bump. The bump  106  can be composed of silicon oxide and can be formed using any one of various fabrication methods. For example, the bump  106  can be formed by depositing a layer of silicon oxide (not shown), and etching the silicon oxide away to leave a bump having the general shape and configuration illustrated in  FIG. 1 .  
      In this embodiment, the bump  106  has a trapezoidal cross-section that is defined by a base  108 , opposed sides  110 , and a top  112 . As is apparent from  FIG. 1 , the base  108  is larger than the top  112 , and the opposed sides  110  extend diagonally or obliquely toward each other from the base to the top. As is shown in  FIG. 2 , the bump  106  is elongated (as compared to the sides  110  and top  112 ) so as to extend a relatively long distance across the surface  104  of the substrate  102 . Although the feature  106  formed on the substrate  102  is described and illustrated as comprising a bump having a trapezoidal cross-section, other configurations and shapes are possible.  
      As is described above, the nano-structure  100  is constructed on a nano-scale. By way of example, the bump  106  has a height dimension, h, that ranges from approximately 200 nanometers (nm) to approximately 5000 nm, and a width dimension, w, that ranges from approximately 250 nm to 100 microns (μm). In one embodiment, the bump  106  has a height of approximately 2500 nm and a width of approximately 5000 nm.  
      It is noted that, although the feature has been illustrated and described as a bump, the feature could take substantially any other form including, for example, a step. Moreover, although specific example dimensions have been described, those dimensions are only examples, and the feature could have other dimensions, which may only be limited by the size of the substrate.  
      Referring next to  FIGS. 3-6 , various other steps of the fabrication of the nano-structure  100  will be described. Beginning with  FIG. 3 , multiple overlapping layers  114  of material (e.g., metal) are deposited over the substrate  102  and the bump  106  to form a multi-layered stack  116  of material having opposed comers  118 . When more than one type of material is used to form the layers  114 , such as two types of material, the layers can alternate between the types of material. For instance, a first layer of gold can be deposited, followed by a layer of tantalum, followed by a further layer of gold, followed by a further layer of tantalum, etc., until a desired number of alternating layers  114  of material have been deposited. Depending on the material, such deposition can be achieved using chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), or another process. Notably, other types of materials can be used to form the layers  114 . Example alternative materials include titanium nitride, silicon, silicon oxide, and metal oxides.  
      In the embodiment shown in the figures, nine layers  114  of material have been deposited. By way of example, each layer  114  is approximately 10 Angstoms (Å) to approximately 1000 Å thick. For instance, in one embodiment, each layer  114  can be approximately 500 Å thick.  
      With the structure illustrated in  FIG. 3 , multiple trenches, which are useful for nano-imprinting (for example), can be formed by planarizing the layers  114  above the bump  106  to yield a bump that has multiple layers of material along both sides of its length. Assuming an alternating arrangement of materials such as that described above, multiple trenches can be formed by etching away one of the materials (i.e., multiple layers of that material), leaving trenches defined by the layers of material that were not etched away. Unfortunately, such planarization often results in one or more of fraying, delamination, erosion, dishing, and rounding using known techniques.  
      To avoid such problems, a sacrificial or planarizing film  120  of material is deposited over the multiple layers  114  prior to planarization, as is shown in  FIG. 4 . By way of example, the planarizing film  120  comprises a thick layer of silicon oxide. Examples of other materials that can be used for the planarizing film.  120  include amorphous silicon and spin-on-glass. Regardless of the particular material that is used, the planarizing film  120  has a thickness that will result in a film height that equals or exceeds the height of the multi-layered stack  116  (see  FIG. 4 ). With such a configuration, the low-topography points of the structure  100  are brought above the bump  106  and the multi-layered stack  116  that has been deposited thereon. This enables a non-zero removal rate of the low points to be above the height of the multi-layered stack  116 . In some embodiments, the planarizing film  120  has a thickness of approximately 200 nm to approximately 10 μm. For example, the film  120  can be approximately 2.5 micons (μm) thick.  
      At this point, the planarizing film  120  and the top of the multi-layered stack  116  can be removed. Specifically, as is indicated in  FIG. 5 , the film  120  and top of the stack  116  are removed, for example using a chemical-mechanical planarization (CMP) process, such that the top portion of the bump  106  is exposed. Alternatively, mechanical or chemical-mechanical polishing can be used to achieve this result. As is indicated in  FIG. 5 , little or no fraying, delamination, erosion, or dishing has occurred. In addition, the comers  118  of the multi-layered stack  116  are minimized due to the provision of the planarizing film  120 .  
      At this point, multiple trenches can be formed in the new surface  122 , and the exposed edges of the stacked layers  114 , that results from the planarization process. Referring to  FIG. 6 , trenches  124  can be formed by etching one or more of the layers  114  of material of the multi-layer stack  116 . For instance, in cases in which the stack  116  is composed of alternating materials, one of the materials (and therefore multiple layers  114 ) can be selectively etched away to produce trenches  124  that are defined by the remaining layers. To cite a specific example, when alternating layers of tantalum and gold are deposited, a portion of the gold layers can be etched away to define the trenches  124 .  FIG. 7  illustrates such an embodiment in detail. As is shown in that figure, the tantalum layers (Ta) remain intact and extend to the surface  122 , while the gold layers (Au) have been etched away to define the trenches  124 . As is further shown in the figure, the trenches  124  are defined by side walls  126  (e.g., of tantalum) and bases  128  (e.g., of gold). The trenches  124  have widths equal to the thickness of the layers (in this example gold layers) that have been etched away.  
      The structure that results from the above-described fabrication is a comb-like structure in which diagonal or oblique trenches  124  are formed in the surface of the nano-structure  100 . In particular, multiple parallel, oblique trenches  124  are formed on both sides of the bump  106  such that the trenches are angled toward each other as they are traversed upward from the bases  126  to the surface  122 . By way of example, each trench  124  forms an angle, α, of approximately 30 to approximately 90 degrees relative to the surface  122  (see  FIG. 7 ). As is mentioned above, the structure  100  can, for example, be used for nano-imprinting. In such a case, the nano-structure  100  may be considered to be a nano-imprinting structure.  
      An embodiment of a method for fabricating a nano-structure can be summarized as provided in  FIG. 8 . Beginning with block  800 , a feature, such as a dielectric bump, is formed on a substrate. The feature can be formed by, for instance, depositing a layer of material on top of the substrate, and etching away a portion of the deposited layer. Next, multiple layers of material are deposited over the substrate and feature to form a multi-layer stack, as indicated in block  802 . By way of example, two or more different types of materials are deposited in an alternating fashion.  
      Referring next to block  804 , a sacrificial film is deposited over the multi-layer stack such that the height of the film equals or exceeds the height of the multi-layer stack, including the portion of the stack that overlies the feature. Once the film has been deposited, a portion of the film and the stack is removed, as indicated in block  806 , for example using a planarization process.  
      Finally, as is indicated in block  808 , portions of various layers of the multi-layer stack are removed to form trenches in a surface that results when the portion of the film and stack are removed (in block  806 ). By way of example, the portions of the layers can be removed using a selective etching process.