Abstract:
A method for treating an edge portion of a wafer with a plasma or select chemical formulation in order to enhance adhesion characteristics and inhibit delamination of a layer of material from the wafer surface only on the edge portion that is being treated. Alternatively, the method may be utilized to effectuate a cleaning of an edge portion of a wafer.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates generally to processing wafers, and more particularly relates to a method for treating an edge portion of a wafer with a plasma or select chemical formulation in order to enhance adhesion characteristics and inhibit delamination of a layer of material from the wafer surface or to clean the wafer surface only on the edge portion that is being treated. 
         [0003]    2. Related Art 
         [0004]    Delamination is a major problem for the integration of interconnect structures for integrated circuits. Delamination occurs during chemical-mechanical polishing (CMP) of layered stacks of films, and is due to the inherently poor mechanical qualities of the materials used. The problem is especially prevalent in the edge region of the wafer since the induced stress during CMP is highest in regions of great surface topology. 
         [0005]    Prior art treatments to prevent delamination treat the entire wafer area. These treatments cause the surface of the treated material to densify, thus hardening the surface, and are accompanied by compositional changes of material. While addressing the issue of delamination, these whole-wafer treatments cause unacceptable new problems, including: uncontrolled change in the composition chemistry of the treated material, moisture uptake after the treatment, increases in the relative permeability of the dielectric materials, and the introduction of a new interface inside the treated material between the densified surface and the untreated bulk. 
         [0006]    U.S. Pat. No. 6,642,128, “Method for High Temperature Oxidations to Prevent Oxide Edge Peeling,” issued to Lu et al. on Nov. 4, 2003, which is hereby incorporated by reference, teaches a method for preventing oxide peeling by applying a silicon nitride layer to a backside of a wafer prior to carrying out high temperature annealing. Unfortunately, the teachings are limited to, inter alia, batch processing, require the presence of a silicon nitride film, and the processing according to the teaching impacts the entire wafer surface. 
         [0007]    Accordingly, a need exists for an improved method for preventing delamination that occurs during CMP. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention addresses the above-mentioned problems, as well as others, by providing a method for treating an edge portion of a wafer with a plasma or select chemical formulation in order to enhance adhesion characteristics and inhibit delamination of a stack of material from the wafer surface only on the edge portion that is being treated, or to clean a wafer surface on the edge portion only. 
         [0009]    In a first aspect, the invention provides a method for treating an outside edge region of a wafer comprising: applying a protective film over a central region of the wafer such that only an outer edge region of both the wafer and stack of material on the wafer surface are exposed; and applying a plasma treatment to the wafer, wherein the protective film protects a central portion of the stack of material and limits treatment to the outer edge region of both the wafer and stack of material on the wafer surface. 
         [0010]    In a second aspect, the invention provides a method for treating an outside edge region of a wafer comprising: providing a plasma delivery system that limits a plasma exposure to an outer edge region of both the wafer and stack of material; and applying a plasma treatment to the outer edge region of both the wafer and stack of material, wherein a central portion of the stack of material situated on the wafer is not exposed to the plasma treatment. 
         [0011]    In a third aspect, the invention provides a method for treating an outside edge region of a wafer, comprising: dispensing a wet chemical solution by means of, e.g., a nozzle, a chemical bath or a brush, only to an outer edge region of both the wafer and stack of material situated on a wafer surface; and rotating the wafer so that the wet chemical solution treats an entire outer perimeter of the wafer and stack of material situated on a wafer surface, wherein a central portion of the wafer and stack of material situated on the wafer is not exposed to the wet chemical solution. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein: 
           [0013]      FIG. 1A  depicts a partial side view of a wafer in which a portion of the stack has been removed. 
           [0014]      FIG. 1B  depicts a partial side view of a wafer in which the stack extends to the beveled edge portion of the wafer. 
           [0015]      FIG. 2  depicts a partial side view of a wafer receiving a plasma treatment in accordance with an embodiment of the present invention. 
           [0016]      FIG. 3  depicts a partial side view of a wafer receiving a localized plasma treatment in accordance with an embodiment of the present invention. 
           [0017]      FIG. 4  depicts a top view of a system for generating a localized plasma treatment in accordance with embodiment of  FIG. 3 . 
           [0018]      FIG. 5  depicts a top view of an alternative system for generating a localized plasma treatment in accordance with embodiment of  FIG. 3 . 
           [0019]      FIG. 6  depicts a side view of a wafer receiving a localized bath in accordance with an embodiment of the present invention. 
           [0020]      FIG. 7  depicts a side view of a wafer receiving a brush treatment in accordance with an embodiment of the present invention. 
       
    
    
       [0021]    The drawings are not necessarily to scale. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Referring now to the Figures,  FIGS. 1A and 1B  depict side views of a substrate  10  having a thin film or thin film stack (hereinafter “stack” or “stack of material”)  12  on a surface of the substrate  10 . In  FIG. 1A , a portion of the stack  12  on the outer edge  15  of the wafer has been removed, e.g., with edge bead removal (EBR), as is typical for films applied from wet solution by spinning. In  FIG. 1B , stack  12  extends to the beveled edge region  16  of the substrate, as is typical for chemical-vapor-deposited (CVD) films. Stack  12  may comprise, e.g., silicon dioxide, silicon nitride, silicon carbide, organo-silicate glasses (OSG), organic polymer-based materials, methyl-silsesquioxane (MSQ) based materials, all of which can be dense or porous, or metallic films. Moreover, stack  12  may include any number of layers/films (i.e., one or more), comprising one or more materials. Substrate  10  may comprise, e.g., a silicon wafer, a stack of thin films, etc. As noted above, during CMP, significant stress occurs at edge bead  14  of the stack  12  ( FIG. 1A ), as well as at a beveled edge region  16  ( FIG. 1B ). In either case, this causes the stack  12  to delaminate. Furthermore, certain processing steps, especially dry etching, tend to leave residue at the edge region of the substrate  10 . 
         [0023]    The present invention addresses these problems by restricting a treatment to only an outer edge area of the substrate  10 . In particular, the treatment may result in a modification, e.g., densification, of only the stack  12  around the outer edge region. Thus, any detrimental effects of the treatment are limited to an extreme edge area of the wafer, thereby not impacting the performance of the final fabricated chip devices on a central portion of the substrate  10 . Described below are several embodiments for implementing the invention. Note that while the embodiments discussed below are described for the case shown in  FIG. 1A  in which a portion of the stack  12  on the outer edge  15  of the wafer has been removed, the invention may be applied to, inter alia, the case described in  FIG. 1B  in which stack  12  extends to the beveled edge region  16 . 
         [0024]      FIG. 2  depicts a first embodiment for implementing the invention. Namely, as shown in  FIG. 2 , a protective film  18  is first placed onto the stack  12  in order to protect the central portion of the substrate  10  and stack  12 , so that only the outer edge region of the substrate  10  and stack  12  are exposed. Protective film  18  may comprise, e.g., a photoresist layer such as those applied in commercial 356 nm (I-line) implant resist systems, or another protective layer. A portion of the protective film  18  is then removed, either by edge bead removal (EBR) or other techniques, such as conventional lithographic patterning. The removed portion of the protective film  18  is large enough to expose an outside edge region of the stack  12  and the substrate  10 . For example, for a spin-on film with an EBR distance of 2 mm, the EBR distance for the protective layer  18  will be greater than 2 mm, e.g., 3 mm, exposing a 1 mm ring of film at the outer substrate edge. Next a plasma  20  (or effluent of the plasma) is delivered by a plasma device  22  onto the substrate  10  and stack  12  (shown by downward arrows). Protective film  18  restricts exposure of the plasma  20  to only the outer edge region of the substrate  10  and the outer edge of thin film  12 . Thus, the central portion of both the substrate  10  and stack  12  are not treated. Subsequently, protective film  18  can be removed using any known methodology. 
         [0025]    Note that the treatment of the outer edge region may simply comprise a cleaning operation. A cleaning of the substrate  10  can be effectuated using the techniques described herein, e.g., if the removed portion of the protective layer  18  is not large enough to expose the stack  12 , thus allowing, e.g., cleaning of the substrate edge without impacting the stack  12 . 
         [0026]      FIG. 3  depicts a second embodiment in which a small area plasma device  24  is provided for delivering plasma  26  to a localized area along an outer edge region (shown by downward arrows) of substrate  10  and stack  12 .  FIGS. 4 and 5  depict illustrative alternatives for implementing this embodiment, both being shown as top views. In  FIG. 4 , small area plasma device  24  sits above a portion of an outer edge region of substrate  10 . When the substrate  10  is rotated, as shown by directional arrows, the entire outer circumferential region of both substrate  10  and stack  12  is treated. The central portion of both substrate  10  and stack  12  remain untreated.  FIG. 5  depicts an alternative embodiment in which a plasma generating ring  26  is placed above the substrate  10  such that it covers the entire outer regions of both substrate  10  and stack  12 . Again, the central portion of the substrate  10  remains untreated. Note that depending on the specific requirements, plasma device  24  or plasma ring  26  may extend over the beveled edge  16 . 
         [0027]    Any type of plasma and/or plasma device that will cause a reaction that leads to the desired surface modifications, such as densification and hardening of the treated surface, changes in the chemical composition of the surfaces, e.g., oxidation or nitridation, removal of some exposed material, or cleaning, may be utilized. For instance, an RF plasma may be generated with a metallic electrode, and gases typically used in the field, such as Argon, Oxygen or Nitrogen. 
         [0028]      FIG. 6  depicts a further embodiment of a system for treating an outer edge region of both a substrate  10  and stack  12  using a wet chemistry solution. In this case, a chemical bath  28  is provided that receives an outside edge of both the wafer  10  and film  12 . A rotating device  30  is then used to rotate wafer  10  such that the entire outer perimeter of wafer  10  and stack  12  pass through the bath  28 . Alternatively, the chemical solution could be dispensed through a nozzle over the outer edge region of substrate  10  as the substrate  10  rotates. An additional protective layer (e.g., photoresist) may be utilized, such as that described above with respect to  FIG. 2 , to protect the central region of the substrate  10 . 
         [0029]      FIG. 7  depicts an alternative embodiment in which a brush  40  have a dispensing channel  42  is utilized to process, i.e., treat or clean, an edge portion of the wafer. In this embodiment, either the wafer or the brush  40  may be rotated to effectuate processing along the edge. As shown, the brush may extend around of the edge of the wafer to process the top, side and bottom. Alternatively, the brush may be configured to just process part (e.g., a top surface) of the edge portion. A protective layer  18  may or may not be utilized. A treatment fluid (i.e., chemicals) may be dispensed via channel  42  (or via any other type of dispensing system) as part of the process. 
         [0030]    Suitable chemicals for the above operations may include, e.g., an oxidizing agent such as H 2 O 2 , HMDS (Hexamethyldisilazane), an acid, a base, an organic solvent, an inorganic solvent, or commercial chemicals, such as AP6000. Moreover, the chemical solution can be dispensed in any manner (in addition to that described above) such that only an outer edge region of both the wafer  10  and film  12  are affected. Furthermore, the chemical solution may be applied under supercritical conditions. 
         [0031]    The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of this invention as defined by the accompanying claims.