Patent Document

PRIORITY CLAIM  
       [0001]    This application claims the benefit of provisional application serial No. 60/357,025, filed Feb. 13, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to non-stick, durable performance coatings for use on equipment components, particularly including coatings for use in the semiconductor industry.  
         BACKGROUND OF THE INVENTION  
         [0003]    The semiconductor industry uses equipment known as Chemical Mechanical Polishing (CMP) equipment in the manufacture of wafers. CMP equipment flattens the silicon or other wafer surface to within 50-nanometer precision or better. CMP flattens the wafer by removing material from the uneven wafer surface until a flat, or “planarized” surface is created. By flattening the surface, photolithography can take place with greater accuracy, enabling film layers to be built up with minimal height variations. CMP is both a chemical and mechanical process, combining an acidic or basic fluid solution with an abrasive polishing material. The CMP system usually has a polishing head that presses the rotating wafer against a flexible pad. A wet chemical slurry containing a micro-abrasive is placed between the wafer and pad.  
           [0004]    CMP is especially critical to fabricating copper-based semiconductors, where it is used to define the copper wiring structures. This advanced smoothing capability enables chipmakers to continue shrinking circuits and extends the performance of lithographic tools. Accordingly, CMP is an important part of the semiconductor chip-making process.  
           [0005]    Unfortunately, the chemicals used in this smoothing process attack and degrade the CMP equipment and all related components. As a result, the CMP equipment wears out rapidly and must be replaced or refurbished frequently. In addition, the coating on the tooling degrades and sheds particulates, introducing foreign matter and hindering the process of smoothing the wafers.  
           [0006]    The industry presently relies exclusively on anodized aluminum and standard powder coating to protect the CMP equipment and to reduce particle contamination. While anodized aluminum is better than uncoated metals or certain other materials, it still suffers from degradation and particle contamination  
           [0007]    Accordingly, there is a need to provide better protection for tooling against the damaging effects from the slurry used in the industry. Aside from the CMP uses, there is a general need for improved coatings for equipment parts that are used in an environment of wear or foreign matter build-up.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a wear indicating coating for a variety of tools or other components, particularly including Chemical Mechanical Polishing equipment having a working surface configured to planarize a semiconductor material surface. The wear indicating coating includes a fluoropolymer based primer coating adjacent the working surface. Adjacent the primer coating is a fluoropolymer based coating. The coating may contain a pigment or colorant to visually contrast the coating from the particulates or foreign matter that may be deposited on the CMP equipment. Thus, the pigment allows CMP equipment users to see equipment wear and particle build-up as indicated by slurry build-up at early stages.  
           [0009]    The present invention further includes a unique method of forming a mechanical and chemical resistant coating upon a substrate, which, in the case of CMP parts, is typically a metallic substrate. The method starts by masking the areas of the substrate that are not to be coated. Subsequently, the surface to be coated is prepared by roughing the surface to improve the surface&#39;s bonding characteristics. The next step is preheating the substrate to a predetermined temperature followed by applying a primer coating. After applying the primer coating to the substrate, another heating step occurs followed by applying at least one intermediate coating over the primer coating and then again heating the part. Finally, the method includes applying an optional top coating to the at least one intermediate coating with its appropriate process. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings.  
         [0011]    [0011]FIG. 1 is an exploded side view of a coated CMP part according to the instant invention;  
         [0012]    [0012]FIG. 2 is a schematic of the coating process of the preferred embodiment of this invention;  
         [0013]    [0013]FIG. 3 is a representative illustration of CMP equipment having a coated CMP part in operation; and  
         [0014]    [0014]FIG. 4 is a representative illustration of a coated CMP part. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    The present invention provides a system and method for applying a protective coating on various components, including parts of CMP equipment. By way of overview and with reference to FIG. 1, one presently preferred embodiment of the invention includes a coated part  20  adaptable to CMP equipment, including a part surface or substrate  22  that is covered by a laminate coating  24 . The laminate coating  24  includes a base primer coating  26  used to facilitate an adequate bond between the substrate  22  and subsequent coatings; at least one intermediate colored coating  28 ; and, a top coating  30 . Together, the coating  24  protects the substrate  22  from mechanical and chemical harm. Specific details of the coated part  20  are described in more detail below.  
         [0016]    As used in this specification, the term “substrate” means the surface of any part, equipment component, or other object that can be coated. Likewise, the term “laminate” coating refers to the preferred coating embodiment having several layers as well as a coating comprising a single layer. Similarly, while the preferred embodiment includes a primer, intermediate layer, and top coat, the term “intermediate” layer also refers to a part coating comprised of a single layer, without a top coat or primer.  
         [0017]    The coating used in the present invention includes a non-stick coating applied to the surface of the CMP tooling. Preferably, the non-stick coating is a fluoropolymer such as PFA, FEP, ETFE, ECTFE, or other type of fluoropolymer. In an actual embodiment, the coating is an ECTFE fluoropolymer commercially available under the trademark Halar® and sold by Ausimont USA, Inc., 10 Leonards Lane Thorofare, N.J. 08086, USA. Fluoropolymers are also available from Dupont, under the brand names Tefzel® and Teflon®, or other sources.  
         [0018]    Generally one coat, preferably the intermediate coat  28 , of the laminate coating  24  is blended with a colorant or other additive to give it a distinctive color that provides contrast with the slurry, abrasive matter, or other particles expected to build up on the equipment. Accordingly, it is possible to readily see when the coated part  20  accumulates a build-up of foreign particles.  
         [0019]    In the preferred embodiment, the colorant is a blue pigment available from Ferro Corporation, 1000 Lakeside Avenue, Cleveland, Ohio 44114-7000. In an actual embodiment, the colorant is Ferro&#39;s product code F.6279. Other colorants and additives or different colors are also possible, consistent with this invention. Preferably, the fluoropolymer is blended with the pigment at a ratio of 50 grams of pigment to 5 pounds of fluoropolymer.  
         [0020]    In an alternate embodiment, multiple layers of the coating contain different colored pigments. Thus, for example, a layer close to the substrate (such as the primer layer or an intermediate layer) can be colored gray, while an adjacent layer is colored blue. When the blue layer begins to wear, the gray layer will become visible, signaling that it is time to replace or recoat the part. Any number of colors and layers may be used to accomplish the wear-indicating result, although the two colors preferably contrast with one another so that when the top layer begins to wear the lower layer is readily visible. For example, contrasting layers of black and white or blue and gray may be used. The same contrasting effect may also be possible by using a primer and an intermediate coating with naturally-contrasting colors, so that adding pigments are unnecessary. Depending on the application and the materials chosen, a sufficient contrast may be achieved. In this regard, “clear” is considered to be a color that may be desirable for a coating layer. For example, a clear base coat applied to a metallic surface will give the appearance of a metallic-colored layer. In the preferred embodiment, however, pigments are added to improve upon the contrast and to provide a final color that contrasts with contaminants expected to be deposited on the equipment.  
         [0021]    [0021]FIG. 2 illustrates a preferred embodiment of the coating process  40  beginning at block  42 . The parts to be coated, for example, substrate  22 , are first masked at block  44  to cover any surface areas intended not to be coated. Then, as indicated by block  46 , the parts are blasted with 80-grit aluminum oxide to rough up the surface to improve adhesion of the coating. While a grit-blast with 80-grit aluminum oxide is preferred, the surface may be roughed up in other manners, or using a different materials other than 80-grit aluminum oxide.  
         [0022]    Once the surface is prepared by roughing up surfaces to be coated, the masking is removed at block  48  and replaced with a heat-resistant tape, block  50 . In this case, the heat-resistant tape masks the same areas that are intended not to be coated, but does so with a tape or other material that can withstand high temperatures. The masked article is then pre-baked at 560° F. for about 15 minutes to remove impurities, improve the bonding ability, and prevent out-gassing under the coating, at block  52 .  
         [0023]    Next, as indicated by block  54 , the article is coated with a chemical resistant fluorpolymer primer at a thickness of about 0.005 inches or 5 mils. While a variety of materials would be suitable as a primer, in an actual embodiment it is Ausimont fluoropolymer  6814 , chosen because it has exceptional bonding and acid resistance qualities. After covering the component part with primer, at block  56  the article is put into the oven, which is still at 560° F., and immediately turned down to 500 deg F. It is left in for about 5 minutes.  
         [0024]    Once the primer coat is flowed out, a first coat of the coating mixed with pigment is applied to a thickness of 3 mils, block  58 , and baked at 500° F. for 15 minutes, at a block  60 . Additional coats of the colored fluoropolymer are added at block  62 , and heated at block  63  in the same manner as with block  60 , to achieve a preferred thickness of 11 mils. While this is the preferred thickness for a CMP application, the coating may be applied to produce a greater or lesser thickness, consistent with this invention. Likewise, the final thickness of 11 mils is preferably achieved by applying a total of four coats of fluoropolymer material. This thickness may alternatively be produced by a greater or lesser number of coatings, depending on the thickness of the coats applied.  
         [0025]    A top coating  30  of fluoropolymer is applied at a block  64 . The top coating  30  is preferably a clear fluoropolymer, having no added pigment. Alternatively, there need be no additional top coating or the top coating can include a colorant. The top coating is preferably a thin coat, less than 3 mils. Once applied, the article is baked at 490° F. for about 10-15 minutes at block  66 .  
         [0026]    While the temperatures and baking times described above have been found to be suitable for applying a colored fluoropolymer such as ECTFE, both the temperature and baking times may be varied, consistent with this invention.  
         [0027]    The part is allowed to cool to room temperature, at block  68 . Once it is cool, it is unmasked and inspected at block  70  to determine whether the desired thickness, smoothness, and any other desired attributes have been achieved. An R.A. test is then performed. The preferred end product is specified at 15-25 mils thick, with R.A. less than 16. Some parts may have either a higher or lower thickness requirement, depending upon the final environment and the end use to which the user subjects the part. A determination is made regarding the acceptability of the laminate coating thickness at block  72 . If it is not thick enough, the process returns to block  62  to add further coating layers, as desired.  
         [0028]    If the thickness is acceptable, the process proceeds to block  74  to evaluate overall quality. If it is unacceptable, it is possible to either reheat and reflow the product, to add further coatings (returning to blocks  60  or  62 ) or to strip the coating at block  78  and start again. Upon meeting the established criteria for uniform and complete coverage, showing no delaminations or release of coating, no pinholes, and the part has uniform color, thickness and surface texture, the part is then passed through quality control testing, the part thus accepted, and the process finished, block  76 .  
         [0029]    The resulting application produces a nonstick surface that is chemical-resistant and abrasion-resistant. When used with a pigment, the pigment allows users to see the CMP slurry when it is starting to build up at the earliest stages, providing a forewarning that slurry is starting to build up and parts may have to be removed, cleaned, re-coated, or replaced. Because the coating is non-stick, the slurry can be usually be wiped clean and will only need to be recoated or replaced after an extended period of use.  
         [0030]    Although the process has been described above with reference to CMP parts in particular, it is also valuable for other tools, equipment parts, and other components. In such applications, the addition of pigments allows operators to see the buildup of oil, debris, or other contaminants that can then be easily cleaned from the non-stick surface.  
         [0031]    [0031]FIG. 3 shows a generic CMP system in operation, including a rotating base  102  having a top-mounted polishing pad  104 . A wafer  106  is mounted to a rotating polishing head  108  to polish the wafer by abrasion. Slurry particles  110  used in the polishing process and worn away from the wafer  106  are sprayed from the working surface. As discussed above, some of the slurry  110  will splatter and deposit onto the rotating polishing head  108  or other components. For that reason, the polishing head  108  is coated as discussed above, preferably in a color that contrasts with the color of the slurry  110  or other materials that may build-up on the equipment. The inside of the polishing head  108  to which the wafer  106  is mounted need not be coated, and is preferably masked and not coated during the coating process. Because the polishing head is coated, it allows the slurry to be wiped away, avoiding any significant build-up. Likewise, the abrasive nature of the slurry will eventually cause the coating to wear away (though it will take longer than with other coatings). By using color contrasting layers, it will be easy to readily see when the coating is beginning to wear away, indicating at an early stage when the part must be re-coated or replaced.  
         [0032]    Another example of a coated CMP part is a clamp as illustrated in FIG. 4. The clamp  120  may be used, for example, to hold a silicon wafer for polishing. The clamp  120  includes a right semi-circular retainer  122  and a mating left semi-circular retainer  124  joined by a pin  126 . The pin  126 , which may be a rivet, bolt, or other connector, forms a pivot point allowing the two retainers  122 ,  124  to open and close about a wafer. Each retainer includes an internal channel  128 ,  130  to receive the wafer.  
         [0033]    At an end of the retainers opposite the pin  126 , each retainer  122 ,  124  includes a descending prong  132 ,  134 . The right prong  132  descends perpendicularly from the right retainer  122 , and includes upper and lower tabs that form the prong. Likewise, the left prong  134  includes upper and lower tabs to form the left prong  134 . Another pin  136  extends through the right prong  132  to pivotally retain a bolt  138 . The bolt is allowed to freely pivot downward to allow the clamp to open, or upward to lock the clamp in a closed position. A hemispherical washer (not shown) slides over the bolt  138 , followed by an internally threaded nut (not shown). The hemispherical washer mates with a concave section  140  within the left prong  134  so that the clamp is held firmly closed when the nut is tightened on the bolt  138 . The left retainer  124  and right retainer  122  are each coated with the coating of the preferred embodiment, as described above, so that they are covered with a blue-pigmented fluoropolymer coating. Accordingly, slurry or other materials deposited onto the clamp are easily wiped away.  
         [0034]    While the coating invention has been described primarily in association with a CMP process, aspects of the invention are equally applicable to other environments. For example, parts used in aircraft or automotive industries that are in abrasive or high wear environments can be coated as described above. Depending on the amount of wear encountered by the particular component, a thicker or thinner layer of coating may be applied. By using multiple color-contrasting layers, users can quickly see when a part is beginning to wear and must be replaced. Likewise, the non-stick aspect allows oil, grease, tar, dirt, or other contaminants to be wiped clean before they build-up and damage the system.  
         [0035]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be limited only by the claims that follow.

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