Patent Publication Number: US-2004058623-A1

Title: Polishing media for chemical mechanical planarization (CMP)

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     [0001] This application is a continuation-in-part of U.S. application Ser. No. 10/251,324, filed Sep. 20, 2002, the disclosure of which is incorporated herein by reference. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] The present invention relates generally to semiconductor fabrication and, more particularly, to polishing media for chemical mechanical planarization (CMP) and to methods for conducting a CMP operation.  
       [0003] In the fabrication of semiconductor devices, chemical mechanical planarization is used to planarize globally the surface of an entire semiconductor wafer. To planarize a wafer surface using CMP, a polishing surface, e.g., a pad, is contacted against the wafer surface in the presence of a slurry. Generally speaking, to obtain a uniformly high polishing rate, the polishing surface area should be maximized. Thus, from this perspective, the polishing surface should be free from grooves, scribes, imperfections, etc. To effectively deliver slurry to and remove slurry byproducts from the wafer surface, however, the polishing surface must have grooves or pores.  
       [0004] Current commercially available CMP pads are typically formed of porous polymeric materials. In these CMP pads, the pores are usually closed pores. Unfortunately, it is difficult to control the pore size distribution and the pore density of closed pores in polymeric materials. As pores may play a significant role in slurry delivery, it is difficult to produce consistent CMP pads having closed pores because of the variations in pore size distribution and pore density.  
       [0005] In view of the foregoing, there is a need for a polishing media for CMP that can be manufactured by a process that allows the porosity and pore size distribution of closed pores to be controlled more reliably.  
       SUMMARY OF THE INVENTION  
       [0006] Broadly speaking, the present invention fills this need by providing a polishing media for chemical mechanical planarization (CMP) that may be formed by blending cyclodextrin into a CMP pad material and subsequently removing the cyclodextrin. The present invention also provides methods for conducting a CMP operation.  
       [0007] In accordance with one aspect of the present invention, a polishing media for CMP is provided. The polishing media includes a layer comprised of a CMP pad material having a water-soluble material comprised of cyclodextrin dispersed therein. The layer may form part of a pad configured for rotary CMP or part of a belt pad configured for linear CMP. In one embodiment, the layer contains 1% by volume to 60% by volume of the water-soluble material comprised of cyclodextrin.  
       [0008] In one embodiment, the CMP pad material is comprised of a thermoplastic material such as, for example, polyurethane, polyurea, polyester, polyacrylate, and polyvinyl chloride. In one embodiment, the CMP pad material is a polyurethane-based CMP pad material. As used in connection with the description of this embodiment, the term “polyurethane-based CMP pad material” refers to any material suitable for use in a CMP pad that contains more than 50% by weight of polyurethane.  
       [0009] In accordance with another aspect of the present invention, a first method for conducting a CMP operation is provided. In this method, a polishing media having a layer comprised of a CMP pad material with a water-soluble material comprised of cyclodextrin dispersed therein is provided. The layer is contacted with at least one of a slurry, water, and an aqueous solution to remove the water-soluble material comprised of cyclodextrin from the CMP pad material. The contacting of the layer with the slurry, water, or the aqueous solution may occur in either a rotary CMP operation or a linear CMP operation.  
       [0010] In accordance with yet another aspect of the present invention, a second method for conducting a CMP operation is provided. In this method, a polishing media having a layer comprised of a CMP pad material with a water-soluble material comprised of cyclodextrin dispersed therein is provided. The water-soluble material comprised of cyclodextrin is removed from the layer. The layer is then contacted with a substrate in the presence of a slurry to planarize the substrate. The contacting of the layer with the substrate may occur in either a rotary CMP operation or a linear CMP operation.  
       [0011] One advantage of a CMP pad material containing cyclodextrin is that the cyclodextrin may complex with the CMIP byproducts and thereby provide an efficient and highly effective mechanism for removing such byproducts from the substrate being planarized during a CMP operation. To minimize variations in pore size distribution, the cyclodextrin can be processed to provide particles having a specific size distribution. To minimize variations in pore distribution, the cyclodextrin can be homogeneously blended with the CMP pad material, e.g., by mechanical mixing. Additional advantages of the polishing media of the present invention will be apparent to those skilled in the art upon consideration of the specification and practice of the invention.  
       [0012] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0013] The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the principles of the invention.  
     [0014]FIG. 1 is a simplified cross-sectional view of a polishing media for chemical mechanical planarization having a polishing layer with continuous pores in accordance with one embodiment of the invention.  
     [0015]FIG. 2 is a simplified cross-sectional view of a polishing media for chemical mechanical planarization having a polishing layer with closed pores in accordance with another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
     [0016] Several exemplary embodiments of the invention will now be described in detail with reference to the accompanying drawings.  
     [0017]FIG. 1 is a simplified cross-sectional view of polishing media  100  for chemical mechanical planarization (CMP) in accordance with one embodiment of the invention. As shown therein, polishing media  100  includes substrate  102  and polishing layer  104 , which is disposed over substrate  102 . Substrate  102  may be any underlayer or combination of underlayers such as, for example, those found in conventional pads for rotary CMP or conventional belt pads for linear CMP. Polishing layer  104  is comprised of a CMP pad material and has continuous pores therein, as will be described in more detail later. As used in connection with the description of the invention, the term “CMP pad material” means any material suitable for polishing a substrate, e.g., a semiconductor wafer, in a CMP operation. Exemplary CMP pad materials include, but are not limited to, polyurethane, polyurea, polyester, polyacrylate, and polyvinyl chloride. It will be apparent to those skilled in the art that polishing media  100  can be configured either as a pad for use in a rotary CMP operation or as a belt pad for use in a linear CMP operation.  
     [0018] As mentioned above, polishing layer  104  has continuous pores therein. The continuous pores may be formed by dispersing a water-soluble material appropriately in the CMP pad material, as will be described in more detail later. After the polishing media has been fabricated, the water-soluble material may be removed before a CMP operation by placing the polishing media in water (or an aqueous solution) to dissolve the water-soluble material. Alternatively, the polishing media can be used directly in a CMP operation without removing the water-soluble material. In this case, the water-soluble material will be removed during the CMP operation either when the water-soluble material comes into contact with the slurry during polishing or when the water-soluble material comes into contact with water or an aqueous solution, e.g., during cleaning, conditioning, or wet cycling of the polishing media.  
     [0019] For polishing media intended for use in the semiconductor industry, the water-soluble material should be compatible with the cleanliness requirements of the semiconductor industry. Suitable water-soluble materials include both natural and synthetic water-soluble materials. Exemplary natural water-soluble materials compatible with the cleanliness requirements of the semiconductor industry include, but are not limited to, starch, urea, and guar gum. Exemplary synthetic water-soluble materials compatible with such requirements include, but are not limited to, polyvinyl alcohol, polyacrylic acid, polyacrylimide, polyaspartate, and polysaccharide.  
     [0020] An exemplary method for forming the polishing media will now be described. A CMP pad material and a water-soluble material (both in powder form) are first blended together. The blended powder mixture is then spray coated onto a suitable substrate. By way of example, to form a belt pad for a linear CMP operation, the substrate may be a belt formed of a suitable fabric, e.g., Kevlar™. Next, the substrate is heated to an operating temperature with a heat source, e.g., an infrared (IR) lamp, to melt the blended powder mixture. To obtain continuous pores, both the CMP pad material and the water-soluble material are required to melt but not to decompose at the operating temperature, which is typically below 250° C. for CMP pad materials. Thorough mixing of the water-soluble material in the CMP pad material is obtained by melting the water-soluble material. If the water-soluble material does not melt, then the resulting polishing media will have closed pores.  
     [0021] After the heating operation, a cooling operation is performed to cool the melted mixture of the CMP pad material and the water-soluble material. In one embodiment, the cooling operation is carried out with a cooling drum. Once the melted mixture has been cooled, the substrate may be subjected to any desired machining operations. By way of example, to form pads for use in rotary CMP operations, the substrate may be cut into circular shapes. Other machining operations that may be performed include grinding, grooving, or embossing. In the event it is desired to remove the water-soluble material from the polishing media at this point, the substrate may be placed in water (or an aqueous solution) to dissolve the water-soluble material. Alternatively, as described above, the water-soluble material may be left intact for subsequent removal either just before a CMP operation or during the CMP operation. Thereafter, any other needed operations may be performed, e.g., applying an adhesive.  
     [0022] The overall porosity of the polishing media may be controlled by varying the amount of the water-soluble material dispersed in the CMP pad material. In one embodiment, the amount of the water-soluble material is in the range from 1 volume % to 60 volume %. Thus, in this embodiment, when the water-soluble material is removed, the overall porosity of the polishing media will be in the range from 1% to 60%. In some applications, it may be desirable to have the overall porosity of the polishing media in a narrower range, e.g., from 10% to 40%. One advantage of polishing media having continuous pore structures is that, particularly at higher porosity levels, it may be possible to eliminate the grooving normally provided to facilitate slurry distribution.  
     [0023] The pore size distribution of the continuous pores within the CMP pad material can be controlled by adjusting the cooling rate used to cool the melted mixture of the CMP pad material and the water-soluble material. Thus, by controlling the amount of the water-soluble material and the cooling rate, polishing media having desirable continuous pore structures can be fabricated consistently. This is technically significant because it enables consistent polishing performance to be obtained in CMP operations conducted using such polishing media.  
     [0024] It will be apparent to those skilled in the art that methods other than the exemplary spray coating method described above can be used to form polishing media having continuous pores. By way of example, polishing media having continuous pores also can be formed by extrusion, molding, or casting. As mentioned above, continuous pores will be obtained so long as the water-soluble material melts (but does not decompose) during the fabrication process. It will be further apparent to those skilled in the art that suitable water-soluble materials are not limited to those specifically named herein. Rather, in the case of polishing media for the semiconductor industry, any water-soluble material that 1) melts but does not decompose at the melting temperature required for fabrication of the polishing media, and 2) meets the cleanliness requirements of the semiconductor industry is suitable for use in forming polishing media having continuous pores.  
     [0025] In the case of polyurethane-based CMP pad materials, the temperature required for fabrication of the polishing media is typically in the range of 180° C. and 200° C. Consequently, any water-soluble material to be dispersed in a polyurethane-based CMP pad material must be stable up to at least 200° C. Thus, certain water-soluble materials, e.g., urea, which decomposes at a temperature of about 120° C., are not suitable for use in the fabrication of polyurethane-based CMP pads.  
     [0026]FIG. 2 is a simplified cross-sectional view of polishing media  100 ′ for chemical mechanical planarization (CMP) in accordance with another embodiment of the invention. As shown therein, polishing media  100 ′ includes substrate  102  and polishing layer  104 ′, which is disposed over substrate  102 . As set forth above, substrate  102  may be any underlayer or combination of underlayers such as, for example, those found in conventional pads for rotary CMP or conventional belt pads for linear CMP. Polishing layer  104 ′ is comprised of a CMN pad material and has closed pores therein, as will be described in more detail later. It will be apparent to those skilled in the art that polishing media  100 ′ can be configured either as a pad for use in a rotary CMP operation or as a belt pad for use in a linear CMP operation.  
     [0027] The closed pores in polishing layer  104 ′ may be formed by dispersing a water-soluble material comprised of cyclodextrin appropriately in the CMP pad material, e.g., in the manner described above in connection with the description of polishing media  100 , which includes a polishing layer having continuous pores. After the polishing media  100 ′ has been fabricated, the cyclodextrin may be removed before a CMP operation by placing the polishing media in water (or an aqueous solution) to dissolve the cyclodextrin. Alternatively, the polishing media can be used directly in a CMP operation without removing the cyclodextrin. In this case, the cyclodextrin will be removed during the CMP operation either when the cyclodextrin comes into contact with the slurry during polishing or when the cyclodextrin comes into contact with water or an aqueous solution, e.g., during cleaning, conditioning, or wet cycling of the polishing media.  
     [0028] Generally speaking, cyclodextrins are bucket-shaped molecules formed of glucose units. As used in connection with the description of the invention, the term “cyclodextrin” includes the three known forms of cyclodextrin, i.e., alpha-cyclodextrin, beta-cyclodextrin, and gamma-cyclodextrin. Cyclodextrin is soluble in water, has a high temperature stability (it is stable up to 300° C.), and does not melt before it starts to decompose. By virtue of its high temperature stability, cyclodextrin is suitable for use in the fabrication of polyurethane-based CMP pads. The incorporation of cyclodextrin in a CMP pad material and the subsequent removal thereof will not result in the formation of continuous pores. Instead, closed pores will be formed in the CMP pad material because cyclodextrin does not melt before it starts to decompose.  
     [0029] One of the unique aspects of cyclodextrin is that the internal cavity of cyclodextrin can complex with other molecules. Thus, when a CMP pad material containing cyclodextrin is used in a CMP operation, the cyclodextrin may complex with the CMP byproducts and thereby provide an efficient and effective mechanism for removing such byproducts from the substrate being planarized. In addition, to minimize variations in pore size distribution, the cyclodextrin can be processed to provide particles having a specific size distribution. To minimize variations in pore distribution, the cyclodextrin can be homogeneously blended with the CMP pad material, e.g., by mechanical mixing.  
     [0030] As noted above, the polishing media of the invention can be configured either as a pad for use in a rotary CMP operation or as a belt pad for use in a linear CMP operation. As is well known to those skilled in the art, the rotary or linear CMP system in which the polishing media of the invention is implemented may form part of a cluster tool, which includes other processing modules, e.g., clean, etch, etc.  
     [0031] In summary, the present invention provides a polishing media for CMP and methods for conducting a CMP operation. The invention has been described herein in terms of several exemplary embodiments. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention. The embodiments and preferred features described above should be considered exemplary, with the invention being defined by the appended claims and equivalents thereof.