Patent Publication Number: US-2015087212-A1

Title: Cmp conditioner pads with superabrasive grit enhancement

Description:
This application claims priority to U.S. Provisional Application No. 61/642,874 filed May 4, 2012. Said application is incorporated herein by reference including the Appendix thereto. 
    
    
     FIELD OF THE INVENTION 
     The disclosure is directed generally to semiconductor manufacturing equipment. More specifically, the disclosure is directed to conditioning devices for the cleaning of polishing pads used in the manufacture of semiconductors. 
     BACKGROUND 
     Chemical mechanical planarization (CMP) is used extensively in the manufacture of semiconductor chips and memory devices. During a CMP process, material is removed from a wafer substrate by the action of a polishing pad, a polishing slurry, and optionally chemical reagents. Over time, the polishing pad becomes matted and filled with debris from the CMP process. Periodically the polishing pad is reconditioned using a pad conditioner that abrades the polishing pad surface and opens pores and creates asperities on the surfaces of the polishing pad. The function of the pad conditioner is to maintain the removal rate in the CMP process. 
     CMP represents a major production cost in the manufacture of semiconductor and memory devices. These CMP costs include those associated with polishing pads, polishing slurries, pad conditioning disks and a variety of CMP parts that become worn during the planarizing and polishing operations. Additional cost for the CMP process includes tool downtime in order to replace the polishing pad and the cost of the test wafers to recalibrate the CMP polishing pad. 
     A typical polishing pad comprises closed-cell polyurethane foam with a thickness in the range of approximately 0.15 to 0.20 centimeters thick. During pad conditioning, the pads are subjected to mechanical abrasion in order to physically cut through the cellular layers of the pad surface. The exposed surface of the pad contains open cells, which can be used during the CMP process to trap abrasive slurry consisting of the spent polishing slurry and material removed from the wafer. The pad conditioner removes the outer layer of cells containing the embedded materials and minimizes removal of layers below the outer layer. Over-texturing of the polishing pad results in a shortened life, while under-texturing results in insufficient material removal rate and lack of wafer uniformity during the CMP step. 
     Certain pad conditioners utilize superabrasive particles such as diamond that are adhered to a substrate. See, e.g., U.S. Pat. No. 7,201,645 to Sung (Sung) (disclosing a contoured CMP pad dresser that has a plurality of superabrasive particles attached to the substrate); U.S. Patent Application Publication No. 2006/0128288 to An et al. (An) (disclosing a layer of metal binder fixing the abrasive particles to a metal substrate, with a diameter difference between smaller and bigger abrasive particles ranging from 10% to 40%). A problem with prior art pad conditioners is that the forces generated on the proudest features of the pad conditioners can result in the particles that experience the higher forces to become dislodged from the pad conditioner. Dislodged particles can be captured by the polishing pad which can lead to scratching of the wafers during the polishing operation. 
     There is a continuing need for CMP pad dressers that reduce or eliminate abrasive particles becoming dislodged and CMP pad dressers that have varying surface heights for dressing CMP polishing pads. 
     SUMMARY OF THE INVENTION 
     In various embodiments of the invention, a pad conditioner machined from a substrate to have a desired distribution of feature heights and roughness characteristics is provided. The protrusions on the shaped substrate act as geometric features that provide force concentrations on the pad surface. In embodiments first a substrate is produced having roughened or textured repeating protrusions, diamond grains are dispersed over the surface area and a layer of a polycrystalline CVD diamond coating that is grown over the surface protrusions and diamond grains. The roughness of the substrate facilitating securement of the diamond seed grains within the diamond coating to minimize or prevent dislodging. 
     In embodiments, the diamond grains being of a size that is less than the average thickness of the CVD coating measured in a direction extending away from the pad. 
     Features and advantages of embodiments of the invention are enhanced performance of the pad conditioner. In embodiments conditioner to conditioner cut rate repeatability is provided and consistent cut rate over the life of the conditioner, and reduced defects followed by the addition of diamond grit crystals onto the roughened surfaces and the addition of a CVD diamond layer wherein the diamond grit seed crystals are part of the matrix and the thickness of the CVD 
     In embodiments, silicon carbide segments having a roughened substrate with roughened protrusions formed thereon are first provided with small diamond seed grains (for example, diamond grit in the 1 nm to 30 nm diameter size range). Larger diamond grit seed crystals (for example, in the range from about 1 micrometer (μm) to about 12 μm range) can then be applied to the substrate and protrusions. A few milligrams of the large diamond grit can be applied to each segment. The large diamond grit adheres to the silicon carbide substrate and protrusions, with the roughened surface (for example, about 2 μm to about 5 μm RMS roughness) helps retain the larger diamond particles. 
     The addition of the larger diamond grit seed also allows the cut rate of the pad conditioner to be “tailored” over a wide range depending upon the size of the larger diamond grit seed crystals. “Larger” grit crystal sizes that are typically much less than the prior art utilization of grit that actually provided the cutting features. In embodiments, the grit is generally within the average thickness in the z-direction of the CVD coating. The textured surface helps retain the seed crystals, thereby abating the problem of particle dislodgement experienced with prior art pad conditioners. The seeded surfaces can then be coated with, for example, polycrystalline diamond. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  is a pictorial view of a wafer polishing apparatus with a pad conditioner. 
         FIG. 2  is a perspective view of a pad conditioner assembly in accord with the inventions. 
         FIG. 3  is a perspective view of a pad conditioner assembly in accord with the inventions. 
         FIG. 4  is a photo image of a conditioner pad in accord with the inventions. 
         FIG. 5  is a perspective image showing projections on a surface in accord with the inventions. 
         FIG. 6   a  is a plan view of a projection array on a pad in accord with the inventions herein. 
         FIG. 6   b  is a plan view of a projection array on a pad in accord with the inventions herein  FIG. 7  is a plan view of a projection array on a pad in accord with the inventions herein. 
         FIG. 8  is a cross sectional view of a protrusion on a substrate with coatings in accord with the inventions herein. 
         FIG. 9  is a chart showing experimental cut rates utilizing the inventions herein. 
         FIG. 10  is a micrograph. 
         FIG. 11  is a micrograph. 
         FIG. 12  is a micrograph. 
         FIG. 13  is a micrograph. 
         FIG. 14  is a cross sectional view of a protrusion on a substrate with coatings in accord with the inventions herein. 
         FIG. 15  is a cross sectional view of a protrusion on a substrate with coatings in accord with the inventions herein. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , a wafer polishing apparatus  30  with a pad conditioner  32  in a chemical mechanical planarization (CMP) process is depicted in an embodiment of the invention. The depicted wafer polishing apparatus  30  includes a rotation table  34  having an upper face  36  with a CMP pad  38  (such as a polymeric pad) mounted thereon. A wafer head  42  having a wafer substrate  44  mounted thereon is arranged so that the wafer substrate  44  is in contact with the CMP pad  38 . In one embodiment, a slurry feed device  46  provides an abrasive slurry  48  to the CMP pad  38 . 
     In operation, the rotation table  34  is rotated so that the CMP pad  38  is rotated beneath the wafer head  42 , pad conditioner  32  and slurry feed device  46 . The wafer head  42  contacts the CMP pad  38  with a downward force F. The wafer head  42  can also be rotated and/or oscillated in a linear back-and-forth action to augment the polishing of the wafer substrate  44  mounted thereon. The pad conditioner  32  is also in contact with the CMP pad  38 , and is translated back and forth across the surface of the CMP pad  38 . The pad conditioner  32  can also be rotated. 
     Functionally, the CMP pad  38  removes material from the wafer substrate  44  in a controlled manner to give the wafer substrate  44  a polished finish. The function of the pad conditioner  32  is to remove debris from the polishing operation that fills the debris from the CMP process and to open the pores of the CMP pad  38 , thereby maintaining the removal rate in the CMP process. 
     Referring to  FIGS. 2 and 3 , pad conditioner assemblies  50 A, and  50   b  are depicted in embodiments of the invention. The pad assemblies (collectively referred to as pad assemblies  50 ) include conditioning segments  52   a,    52   b  respectively (collectively referred to as conditioning segments  52 ), affixed to an underlying substrate or backing plate  54 . The conditioning segments  52  can have protrusions of two or more different average heights, as discussed for various embodiments as discussed in WO 2012/1221186 A2, also PCT Patent Application No. PCT/US2012/027916 (“Smith”), assigned to the owner of the instant invention and application, is incorporated herein by reference. In one embodiment, the segments are bonded to the backing plate  54  using an adhesive such as an epoxy.  FIG. 4  illustrates an individual segments.  FIG. 5  illustrates an enlarged perspective view of a substrate surface  64  with protrusions  66  in a spaced pattern thereon formed by suitable machining in accord with the invention herein.  FIGS. 6A ,  6 B, and  7  illustrate various densities of matrixical patterns  70 A,  70 B, and  70 C suitable for the invention herein. “Matrix” when used herein may refer to a matrix with rows and columns or a circular matrix with circular rows expanding outwardly or portions thereof. 
     Referring to  FIG. 8 , a substrate  80 , such as from one of the segments above, comprises a protrusion  80  having large diamond seed crystals  82  and small diamond seed crystals  84  seeded thereon and a polycrystalline diamond coating  86  thereover is depicted in an embodiment of the invention. The sectional view depicts the height h of the protrusions, the thickness t of the polycrystalline layer, and the roughness R of the substrate/protrusion material. The protrusion is characterized as having a height referenced from a floor level F of the substrate. To the extent the floor f is not uniform, the floor level may be considered the average of the lowest level between each adjacent protrusion, the height of the protrusions may be measured from this average datum level. 
     In various embodiments, the thickness of the polycrystalline diamond layer can be about the diameter of the large diamond grit particles, as depicted in  FIG. 8 , or it can be larger in embodiments and in embodiment smaller. In various embodiments, the thickness of the polycrystalline diamond overlying the diamond grit seed and the surfaces ranges from about 50% to about 100% of the diameter of the large diamond grit size, the latter case of 100% of the grit size being depicted. 
     Functionally, the large diamond grit seed crystals add another dimension of roughness to the substrate and protrusion surfaces. The cut rate of the pad conditioner can advantageously be varied by choosing narrow size ranges for the large diamond grit seed crystals; narrow size ranges can be 1 μm, 2 μm, 4 μm, and up to about 6 μm. 
     Referring to  FIG. 9 , performance metrics for a pad conditioner for varying large sized grit diameters is depicted in an embodiment of the invention. The data presented in  FIG. 2  was for a conditioning pad having a 4 inch diameter with 5 segments coupled thereto. The features on the segments have a base dimension of 125 μm at a density of 10 features per square millimeter. The height of the features was nominally 20 μm. The pad cut rate using this conditioner was determined using a Buehler Ecomet 4 Benchtop Polisher. The pad used was an IC 1000™ pad (Rohm and Haas) rotated at 50 rpm. The IC 1000 pad was contacted with the prototype pad conditioner with 7 lbs force and the rotation of the prototype pad conditioner was 35 rpm. Deionized water at a flow of 80 milliliters per minute was dispensed onto the pad during the cut rate experiment. The experiment was repeated with a new polishing pad having the large seed crystals, with diameters corresponding to the seeding process on the x-axis for  FIG. 2 . 
     The cut rate for a pad with large seed crystals in the range of 1 μm to 2 μm, (x-axis label 1) is about 23 μm per hour; for the 2 μm to 4 μm seed crystals (x-axis label 2) the cut rate is about 28 μm per hour; for the 4 μm to 8 μm seed crystals (x-axis label 3), the cut rate is about 32 μm per hour; and for 6-12 μm seed crystals the cut rate is about 50 μm per hour. The cut rate can also vary depending upon the type of pad conditioner. The point at “0 seeding” process in the graph corresponds to the case where only nanometer sized small diamond grit seed crystals are used (about 10 μm per hour cut rate). 
       FIG. 10  is a photograph of a protrusion without polycrystalline diamond (not the roughness).  FIG. 11  is a photograph of a protrusion coated with polycrystalline diamond (with small nanometer sized seed crystals).  FIG. 12  is a photograph of large diamond grit seed crystals on a protrusion and surfaces of a silicon carbide substrate having roughened surfaces.  FIG. 13  is a photograph of polycrystalline diamond coating with larger diamond grit seed crystals, 6 to 12 microns, on a protrusion. 
     Example an non-limiting dimensions for the various aspects of  FIG. 1  include: protrusion heights in the range of 10 to 150 μm; the polycrystalline diamond layer of about 7 to 15 μm average thickness with approximately 2 μm variation; the RMS roughness of the polycrystalline diamond coating can be from about 0.1 μm to about 2 μm; the roughness of the substrate, which can be silicon carbide, can be about 2 μm to about 5 μm. The protrusion features and their fabrication can be as described in Smith. 
     Referring to  FIG. 14 , a protrusion  90  having roughened or textured surfaces  91  on a rough base material  92  of a pad conditioner is depicted in an embodiment of the invention. The large diamond grit seed crystals  94  are interspersed on the roughened surface and in some cases the large diamond grit seed crystal in are substantially captured by the indentations or depressions that characterize the roughened surface. The large diamond seed crystals are shown on the “top” surface  95  of the protrusions, on the sides  96  of the protrusion, and in the channel  97  between protrusions. Advantageously the roughened surfaces of the protrusions helps to secure the large diamond grit seed crystals to part or all of the side surfaces, at least prior to the coating process. The roughness of the protrusions and substrate and the polycrystalline diamond coating atop the larger diamond grit seed also help to secure the diamond to the pad surface and reduces or eliminates loosening and loss of diamond crystals from the pad. The sides are typically form an obtuse angle measured between the channel region and incline. In embodiments the protrusion is rounded as illustrated. In embodiments the protrusion has a mesa or plateau, a flattened region rather than a rounded apex or peak. 
     Referring to  FIG. 15 , a portion of a pad conditioner, a substrate  100 , having post shaped protrusions  104 ,  106  of differing heights, larger diamond grit seed crystals  110  on the surfaces of the substrate and protrusions of the pad conditioner, and a layer  114  of polycrystalline diamond that has a thickness that covers the large diameter sized diamond grit and surfaces of the conditioner. In one embodiment, the diameters of the larger grit seed crystals is in a range of diameters that is less than 6 μm. The polycrystalline diamond can be between 50% and 100% of the diameter of the larger diamond grit seed crystals. In embodiments, greater than 100%. 
     Smith, assigned to the assignee of the present application, discloses the use of pad conditioners having protrusions with surfaces that are roughened or textured and coated with CVD diamond material. The application of small diamond grit to surfaces for nucleating polycrystalline diamond films is disclosed by Malshe et al., Electrochemical Society Proceedings, Vol. 97-32 (1998), pp. 399-421 (ISBN 1-56677-185-4), disclosing the use of 4 nm sized diamond crystals as seeds. See also in U.S. Pat. No. 4,925,701 to Jansen et al. (disclosing the implementation of 100 nm diamond seed) and U.S. Pat. No. 5,474,808 to Aslam (disclosing the use of 25 nm seed). The above-referenced publications are hereby incorporated by reference herein in their entirety except for express definitions contained therein. 
     As provided in the illustration, the pad cut rate and pad surface roughness are relatively steady for the pad conditioner of an embodiment of the invention compared to the commercial pad conditioners. The surface finish of an embodiment of the invention was also typically smoother than with the commercially available pad conditioner. As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to a “protrusion” is a reference to one or more protrusions and equivalents thereof known to those skilled in the art, and so forth. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. Methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention. All publications mentioned herein are incorporated by reference in their entirety, except for express definitions contained therein. Nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosure by virtue of prior invention. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. All numeric values herein can be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In some embodiments the term “about” refers to ±10% of the stated value, in other embodiments the term “about” refers to ±2% of the stated value. While compositions and methods are described in terms of “comprising” various components or steps (interpreted as meaning “including, but not limited to”), the compositions and methods can also “consist essentially of or “consist of the various components and steps, such terminology should be interpreted as defining essentially closed-member groups. Although the invention has been shown and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art based upon a reading and understanding of this specification and the drawings. The invention includes all such modifications and alterations and is limited only by the scope of the following claims. In addition, while a particular feature or aspect of the invention may have been disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features or aspects of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” Also, the term “exemplary” is merely meant to mean an example, rather than the best. It is also to be appreciated that features, layers and/or elements depicted herein are illustrated with particular dimensions and/or orientations relative to one another for purposes of simplicity and ease of understanding, and that the actual dimensions and/or orientations may differ substantially from that illustrated herein. 
     Although the invention has been described in considerable detail with reference to certain embodiments thereof, other versions are possible. Therefore the spirit and scope of the appended claims should not be limited to the description and the versions contain within this specification. While various compositions and methods are described, it is to be understood that this invention is not limited to the particular molecules, compositions, designs, methodologies or protocols described, as these may vary. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims.