Patent Publication Number: US-7223297-B2

Title: Planarizing solutions including abrasive elements, and methods for manufacturing and using such planarizing solutions

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 10/683,676, entitled “PLANARIZING SOLUTIONS INCLUDING ABRASIVE ELEMENTS, AND METHODS FOR MANUFACTURING AND USING SUCH PLANARIZING SOLUTIONS” filed Oct. 9, 2003, now U.S. Pat. No. 6,939,211 issued Sep. 6, 2005. which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to chemical-mechanical planarization of microfeature workpieces. Several aspects of the present invention are related to unique abrasive elements used in slurries for mechanical and/or chemical-mechanical polishing of microfeature workpieces on the planarizing surface of a polishing pad. 
     BACKGROUND 
     Mechanical and chemical-mechanical planarization (“CMP”) processes remove material from the surface of microfeature workpieces in the production of microelectronic devices and other products.  FIG. 1  schematically illustrates a rotary CMP machine  10  with a platen  20 , a carrier head  30 , and a planarizing pad  40 . The CMP machine  10  may also include an under-pad  50  between an upper surface  22  of the platen  20  and a lower surface of the planarizing pad  40 . The under-pad  50  provides a thermal and mechanical interface between the planarizing pad,  40  and the platen  20 . A drive assembly  26  rotates the platen  20  (indicated by arrow F) and/or reciprocates the platen  20  back and forth (indicated by arrow G). Since the planarizing pad  40  is attached to the under-pad  50 , the planarizing pad  40  moves with the platen  20  during planarization. 
     The carrier head  30  has a lower surface  32  to which a microfeature workpiece  12  may be attached, or the workpiece  12  may be attached to a resilient pad  34  or bladder system. The carrier head  30  may be a weighted, free-floating wafer carrier, or an actuator assembly  31  may be attached to the carrier head  30  to impart rotational motion to the microfeature workpiece  12  (indicated by arrow J) and/or reciprocate the workpiece  12  back and forth (indicated by arrow I). 
     The planarizing pad  40  and a planarizing solution  44  define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the microfeature workpiece  12 . The planarizing solution  44  may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the microfeature workpiece  12 . 
     To planarize the microfeature workpiece  12  with the CMP machine  10 , the carrier head  30  presses the workpiece  12  facedown against the planarizing pad  40 . More specifically, the carrier head  30  generally presses the microfeature workpiece  12  against the planarizing solution  44  on a planarizing surface  42  of the planarizing pad  40 , and the platen  20  and/or the carrier head  30  moves to rub the workpiece  12  against the planarizing surface  42 . As the microfeature workpiece  12  rubs against the planarizing surface  42 , the planarizing medium removes material from the face of the workpiece  12 . The force generated by friction between the microfeature workpiece  12  and the planarizing medium will, at any given instant, be exerted across the surface of the workpiece  12  primarily in the direction of the relative movement between the workpiece  12  and the planarizing pad  40 . The carrier head  30  can include a retaining ring  33  to counter this force and hold the microfeature workpiece  12  in position. 
     The CMP process must consistently and accurately produce a uniformly planar surface without defects on workpieces to enable precise fabrication of circuits and photo-patterns. A nonuniform surface can result, for example, when the removal rate of material is not uniform across the surface of the workpiece. 
     Defects in the form of voids, tear outs, indents, scratches or chatter marks can be caused by the interface between the workpiece, the planarizing solution, and the planarizing pad. The planarizing solution can greatly affect the nonuniformity in removal rates and the number of defects on a workpiece. For example, hard abrasive particles and/or large abrasive particles are a significant source of defects because they are more likely to cause scratches or other types of surface asperities on the workpiece. On the other hand, small particles have a very low polishing rate that is unacceptable in many applications, and small particles can also cause dishing because they are more likely to contact the inner portions of deep depressions on the workpiece. The problems associated with planarizing solutions are exacerbated as the feature sizes shrink because even slight defects and/or dishing can ruin such small features. 
     Composite Abrasive Slurries (CAS) show promising results in reducing defects and dishing.  FIG. 2  schematically illustrates an existing CAS  44  that has been developed for CMP processing. The slurry  44  includes a liquid solution  60  and composite abrasive particles  70 . The composite abrasive particles  70  have cores  72  with exterior surfaces  73  and a plurality of abrasive particles  74 . The abrasive particles  74  are held to the exterior surface  73  of a core  72  by interaction forces, such as chemical bonding and/or electrical attraction forces. The cores  72  can be soft cores made from polymeric materials or hard cores made from large abrasive particles. In a soft core application, the composite abrasive particles  70  are formed by (a) forming polymeric microspheres without abrasive particles and then curing the microspheres to make the cores  72 , (b) mixing the cores  72  and the abrasive particles  74  in a liquid solution such that the zeta potentials between the cores  72  and the abrasive particles  74  cause the particles  74  to be attracted to the exterior surfaces  73  of the cores  72 , and (c) optionally chemically reacting the particles and polymer to form a chemical bond. The known composite abrasive particles  70  accordingly have abrasive particles  74  only on the exterior surfaces  73  of the cores  72 . 
     Although the CAS  44  shown in  FIG. 2  produces some desirable results, it also raises several problems for CMP processing. First, the composite abrasive particles  70  require very small abrasive particles  74  that are not readily available. This results in high material costs and requires complex manufacturing techniques to handle such particles. Second, the small abrasive particles  74  can be detached from the cores  72  because the interaction forces may not be sufficient to withstand the forces exerted against the composite abrasive particles  70  during a planarizing cycle. This results in a relatively slow polishing rate and dishing because the CAS  44  begins to act like a conventional CMP slurry with very small particles as more abrasive particles  74  become detached from the cores  72 . Third, the liquid solution  60  and any cleaning solutions are limited to maintaining the zeta potentials between the cores  72  and the particles  74  so that the liquid solution  60  does not cause the cores  72  to repel the particles  74 . This limits the composition of the cores  72  and the particles  74 , and it also restricts the constituents of the planarizing solution. Therefore, existing CASs also have several problems and limitations. Similar limitations exist with mixed abrasive slurries in which different types of abrasive particles are mixed in a common solution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a planarizing system in accordance with a prior art. 
         FIG. 2  is a schematic cross-sectional view of a composite abrasive slurry in accordance with the prior art. 
         FIG. 3  is a schematic cross-sectional view of an abrasive element for a composite abrasive slurry in accordance with an embodiment of the invention. 
         FIG. 4  is a schematic cross-sectional view of an abrasive element for a composite abrasive slurry in accordance with another embodiment of the invention. 
         FIG. 5  is a schematic cross-sectional view of an abrasive element for a composite abrasive slurry in accordance with another embodiment of the invention. 
         FIG. 6  is a schematic cross-sectional view of an abrasive element for a composite abrasive slurry in accordance with another embodiment of the invention. 
         FIG. 7  is a schematic cross-sectional view of a planarizing system using a composite abrasive slurry in accordance with an embodiment of the invention. 
         FIG. 8  is a cross-sectional view showing a portion of the planarizing system of  FIG. 7  in greater detail. 
     
    
    
     DETAILED DESCRIPTION 
     A. Overview 
     The present invention is directed to slurries, planarizing systems, and methods for mechanical and/or chemical-mechanical planarization of microfeature workpieces. The term “microfeature workpiece” is used throughout to include substrates in or on which microelectronic devices, micro-mechanical devices, data storage elements, and other features are fabricated. For example, microfeature workpieces can be semiconductor wafers, glass substrates, insulated substrates, or many other types of substrates. Furthermore, the terms “planarization” and “planarizing” mean either forming a planar surface and/or forming a smooth surface (e.g., “polishing”). Several specific details of the invention are set forth in the following description and in  FIGS. 3–8  to provide a thorough understanding of certain embodiments of the invention. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that other embodiments of the invention may be practiced without several of the specific features explained in the following description. 
     One aspect of the invention is directed to a planarizing slurry for mechanical and/or chemical-mechanical planarization of microfeature workpieces. In one embodiment, the planarizing slurry comprises a liquid solution and a plurality of abrasive elements mixed in the liquid solution. The abrasive elements comprise a matrix material having a first hardness and a plurality of abrasive particles at least partially within the matrix material. The matrix material can be formed into a core having an exterior surface and an interior. The abrasive particles can have a second hardness independent of the first hardness of the matrix material. The first and second hardnesses, for example, can be different from each other such that the first hardness is either greater or less than the second hardness. In several embodiments, the abrasive particles are at least partially surrounded by the matrix material such that the abrasive particles are at least partially embedded into the interior of the core. 
     Another aspect of the invention is a planarizing system for chemical-mechanical planarization of microfeature workpieces. In one embodiment, the planarizing system includes a support member, a planarizing pad on the support member, and a workpiece holder configured to releasably retain a microfeature workpiece relative to the planarizing pad. The planarizing system further includes a planarizing slurry disposed on a planarizing surface of the planarizing pad. The planarizing slurry can comprise a liquid solution and a plurality of abrasive elements mixed in the liquid solution. The abrasive elements can comprise a matrix material and a plurality of abrasive particles at least partially within and bonded to the matrix material. As explained above, the matrix material can have a first hardness, and the abrasive particles can have a second hardness independent of the first hardness of the matrix material. 
     Another aspect of the present invention is a method of processing a microfeature workpiece. In one embodiment, the method includes disposing a planarizing slurry on a planarizing surface. The planarizing slurry can comprise any of the foregoing embodiments of planarizing slurries. For example, the planarizing slurry can comprise a liquid solution and a plurality of abrasive elements including a matrix material having a first hardness and a plurality of abrasive particles at least partially within and bonded to the matrix material. The method further includes removing material from the workpiece with the abrasive elements. 
     Still another aspect of the present invention is a method of manufacturing a slurry for chemical-mechanical planarization of microfeature workpieces. In one embodiment, the method includes making a plurality of abrasive elements by (a) mixing a plurality of abrasive particles and a matrix material when the matrix material is in a flowable state, and (b) atomizing the mixture of the matrix material and the abrasive particles into microspheres or other shapes with embedded abrasive particles. The abrasive elements accordingly have a volume of the matrix material and a number of the abrasive particles at least partially embedded into the matrix material. The method further includes mixing the abrasive elements with a liquid solution to form the planarizing slurry. In another embodiment, the method of making the abrasive elements further includes curing the matrix material to harden the matrix material and further retain the abrasive particles. 
     B. Embodiments of Abrasive Elements and Planarizing Slurries 
       FIG. 3  is a schematic cross-sectional view illustrating an abrasive element  300  in accordance with one embodiment of the invention. In this embodiment, the abrasive element  300  includes a matrix material  310  and a plurality of abrasive particles  320 . The matrix material  310  defines a core or binder with an exterior surface  312 , and the abrasive particles  320  are at least partially embedded into the interior of the matrix material  310 . The abrasive particles  320  are not merely attached to the exterior surface  312  of the matrix material  310 , but rather the abrasive particles  320  are at least partially surrounded by the matrix material  310 . Several of the abrasive particles  320 , for example, are at least partially contained within and bonded to the interior of the matrix material  310 . Some of the abrasive particles  320  have bearing surfaces  322  projecting beyond the exterior surface  312  of the matrix material  310 . The bearing surfaces  322  of these abrasive particles  320  provide the mechanical elements that abrade the workpieces. As shown in  FIG. 3 , several other abrasive particles  320  can be completely surrounded by the matrix material  310  such that these abrasive particles  320  do not have an exposed bearing surface. 
     The matrix material  310  is generally selected to be chemically compatible with a liquid solution with which the abrasive elements  300  are mixed to make a slurry. The matrix material  310  is also selected for its hardness or other physical properties for controlling the removal rate, mitigating defects, inhibiting dishing, or meeting other performance criteria. In one embodiment, the matrix material  310  is a polymer microsphere core in which the abrasive particles  320  are embedded. The matrix material  310 , however, can be formed into cores having configurations other than microspheres and being composed of materials other than polymers. In general, the matrix material  310  should be formed into cores that are discrete particle-like elements with a size not greater than 50 μm and, more particularly, from approximately 0.1 μm to 10.0 μm. The discrete cores formed from the matrix material  310  are accordingly sized to be suspended or otherwise mixed in the liquid solution of the planarizing slurry. Suitable materials for the matrix material  310  include latex, such as an emulsion polymerization of dienes or dienes with styrene. Other suitable materials include styrene, urethane, butyl rubber, silicones, and polyethylene. Urethane, for example, may be beneficial because the hardness of the urethane microspheres can be controlled by controlling the degree of cross linking and the amount of abrasives or other solids in the urethane. Because butyl rubber is relatively soft, butyl rubber may be beneficial in applications where it is desirable for the matrix material to erode and expose interior abrasive particles. 
     The abrasive particles  320  are selected to have a hardness independent of the hardness of the matrix material  310 . For example, the matrix material  310  can have a first hardness and the abrasive particles  320  can have a second hardness greater than the first hardness of the matrix material  310 . In other embodiments, however, the second hardness can be less than or equal to the first hardness. Suitable materials for the abrasive particles  320  include aluminum oxide, cerium oxide, silica, alumina, coated silicon oxides, zirconium compounds, titanium compounds, and other abrasive materials suitable for planarizing microfeature workpieces. The abrasive particles can have a median size of approximately 1 nm to approximately 0.5 μm. In several embodiments, the abrasive particles have a median size of approximately 25 nm to 250 nm, and in certain embodiments from approximately  50 nm to approximately 100 nm. 
     The abrasive elements  300  can be configured to provide a desired polishing rate, inhibit dishing, and reduce defects. The polishing rate of the abrasive elements  300  can be controlled by the compositions of the matrix material and the abrasive particles, the percentage of abrasive particles by volume or by weight in the elements, and the size of the matrix material and/or the abrasive particles. In general, the abrasive elements  300  should be sufficiently hard to have a reasonable polishing rate without being so hard that they produce defects. The abrasive elements  300  can inhibit defects by having sufficiently small bearing surfaces  322  projecting from the matrix material  310  and/or a sufficiently elastic or deformable matrix material  310  to avoid scratching or producing other surface asperities on the workpiece. The size of the bearing surfaces  322  can be controlled by the size of the abrasive particles  320  and the extent that the outer abrasive particles  320  project beyond the matrix material  310 . Additionally, dishing can be inhibited by having a sufficiently large overall size for the abrasive elements  300  and by embedding the abrasive particles  320  into the matrix material  310  so that they are not easily detached. The aspect of having a composite abrasive element  300  with embedded abrasive particles  320  enables a wide range of options to achieve a sufficiently high polishing rate without creating unacceptable defects and dishing. Thus, several embodiments of the abrasive elements  300  provide significant advantages over existing composite abrasive slurries and other types of slurries, as explained below. 
     One advantage of several embodiments of the abrasive element  300  shown in  FIG. 3  is that the embedded abrasive particles  320  are not as likely to be detached from the matrix material  310  compared to the composite abrasive particles shown in  FIG. 2 . Embedding the abrasive particles  320  within the matrix material  310  provides a strong bond between the abrasive particles  320  and the matrix material  310 . This allows the abrasive elements  300  to be used in a wider range of solutions because the pH of the solution is not limited by the zeta potentials of the abrasive particles  320  and the matrix material  310 . As such, a broad range of matrix materials can be used in a broad range of planarizing solutions and cleaning solutions to provide very good results for both planarizing and cleaning workpieces. Also, because only the bearing surfaces  322  of the abrasive particles  320  are exposed to the workpieces, the abrasive elements  300  can have larger abrasive particles  320  than existing CAS slurries that have particles only on the exterior surface of the core. This allows the abrasive elements to use less expensive, larger particles to reduce the costs of the slurry without producing defects normally associated with larger particles. Moreover, embedding the abrasive particles  320  into the matrix material  310  is expected to provide a more consistent polishing rate throughout a planarizing cycle because the abrasive particles  320  stay attached to the matrix material  310  during a planarizing cycle. The aggregate surface area of abrasive particles  320  exposed to the workpiece is expected to remain reasonably consistent throughout a planarizing cycle. 
     Another advantage of several embodiments of the abrasive elements  300  is that they do not produce dishing. The overall size of the abrasive elements  300  is sufficiently large to prevent removal of material from deep within depressions on the workpiece. Also, because the abrasive particles  320  are securely bonded to the matrix material  310 , the abrasive particles  320  do not become detached from the matrix material  310 . Therefore, the abrasive elements  300  are also expected to reduce dishing in CMP processes. 
     Yet other advantages of several embodiments of the abrasive elements  300  are that they produce a high polishing rate with abrasive surfaces that do not produce defects. Several embodiments of the abrasive elements  300  thus provide the benefits of a high polishing rate with low defects while mitigating dishing. 
       FIG. 4  is a schematic cross-sectional view illustrating an abrasive element  400  in accordance with another embodiment of the invention. In this embodiment, the abrasive element  400  includes a matrix material  410  defining a core, a plurality of first abrasive particles  420 , and a plurality of second particles  430 . The first abrasive particles  420  are at least partially embedded into the matrix material  410  such that they are at least partially within the matrix material  410 . The second particles  430  can also be embedded into the matrix material  410 , but in some embodiments the second particles  430  can be surface particles  440  that are merely attached to the exterior surface of the matrix material  410 . 
     The first abrasive particles  420  can be composed of a first material and the second particles  430  can be composed of second material different from the first material. In another embodiment, the first abrasive particles  420  can have a first size and the second particles  430  can have a second size different from the first size. The first abrasive particles  420  and the second particles  430 , for example, are not limited to being composed of different materials; rather, they may have different median sizes but be composed of the same material. It will be appreciated that at least one property of the first abrasive particles  420 , such as the size, composition, shape, hardness, etc., is different from a property of the second particles  430 . 
     Several embodiments of the abrasive elements  400  may provide desirable planarizing characteristics to the planarizing slurry. For example, the first abrasive particles  420  can be one type of an abrasive and the second particles  430  can be another type of an abrasive. The abrasive elements  400  can provide such results because embedding the particles  420  and  430  into the matrix material  410  enables much more flexibility in selecting materials for the abrasive elements compared to existing composite abrasive particles that are limited to materials and liquid solutions which provide the correct zeta potentials. 
       FIG. 5  is a schematic cross-sectional view illustrating an abrasive element  500  in accordance with yet another embodiment of the invention. In this embodiment, the abrasive element  500  includes a matrix material  510  and relatively large abrasive particles  520  at least partially embedded within the matrix material  510 . The abrasive element  500  accordingly illustrates that the overall size of the abrasive element  500  can remain substantially the same as abrasive elements  300  and  400 , but that the abrasive particles can be much larger to reduce dishing on the surface of a workpiece and avoid using costly small particles. 
       FIG. 6  is a schematic cross-sectional view illustrating an abrasive element  600  in accordance with another embodiment of the invention. In this embodiment, the abrasive element  600  includes an inner part  602 , a matrix material  610  surrounding the inner part  602 , and a plurality of abrasive particles  620  at least partially embedded into the matrix material  610 . The inner part  602  can be a relatively inexpensive material, or it can be selected to provide a desired hardness or size to the abrasive element  600 . The abrasive element  600  may be particularly useful for producing large abrasive elements because the inner element  602  can be sized to increase the overall element size. The abrasive element  600  can also be particularly useful to reduce the amount of matrix material  610  and/or abrasive particles  620  that are used to form the abrasive element  600  for reducing material costs. 
     The abrasive elements  300 ,  400  and  500  illustrated in  FIGS. 3–5 , respectively, can be formed by mixing the abrasive particles with the matrix material while the matrix material is in a flowable state. In the case of polymeric matrix materials, for example, the abrasive particles can be mixed with a polymer melt. In general, the mixture of the matrix material and the abrasive particles is approximately 10%–99% matrix material by volume with approximately 1%–90% abrasive particles by volume. In other embodiments, the composition can have approximately 60%–90% matrix material by volume and approximately 10%–40% abrasive particles by volume. The individual abrasive elements can then be formed by emulsion polymerization, spray drying, or heterogeneous polymerization techniques. After the individual abrasive elements are formed, the polymeric matrix material can be cured or otherwise hardened in an optional process to securely bind the abrasive particles to the matrix material. In another optional process, part of the cured matrix material can then be dissolved to expose more of the bearing surfaces of the outer abrasive particles. Such erosion of the matrix material can accordingly optimize the abrasiveness of the abrasive elements. 
     Another advantage of several embodiments of the abrasive elements illustrated above with respect to  FIGS. 3–5  is that they are relatively simple to manufacture. Because the solid abrasive particles can be mixed with the polymer melt before forming the abrasive elements, it is possible to precisely control the distribution of the abrasive particles within the abrasive elements. This is also expected to provide good control of the hardness and abrasiveness of the abrasive elements. 
     The abrasive element  600  shown in  FIG. 6  can be made by mixing the abrasive particles  620  with the matrix material  610  while the matrix material  610  is in a flowable state. The inner part  602  can then be coated with the flowable mixture of matrix material  610  and abrasive particles  620 . The matrix material  610  can be cured in an optional procedure after coating the inner part  602 . 
     C. Embodiments of Planarizing Systems and Methods of Processing Workpieces 
       FIG. 7  is a schematic cross-sectional view illustrating a planarizing system  700  for planarizing a microfeature workpiece W using planarizing slurries with abrasive elements in accordance with an embodiment of the invention. The planarizing system  700  can include a support member  702 , such as a platen, and a drive assembly  704  coupled to the support member  702  to rotate and/or translate the support member  702 . The planarizing system  700  further includes a subpad  706  on the support member  702  and a planarizing pad  708  on the subpad  706 . The planarizing pad  708  has a planarizing surface  709  configured to engage the workpiece W. The planarizing system  700  further includes a carrier assembly  710  having a workpiece holder  712  and an actuator  714  coupled to the workpiece holder  712 . The actuator  714  moves the workpiece holder  712  to (a) raise and lower the workpiece W relative to the planarizing pad  708 , and (b) rotate and/or translate the workpiece holder  712  relative to the planarizing surface  709 . 
     The planarizing system  700  further includes a slurry supply  720  containing a planarizing slurry  730  in accordance with an embodiment of the invention. For example, the planarizing slurry  730  can include a liquid solution  732  and a plurality of abrasive elements  734  suspended or otherwise mixed in the liquid solution  732 . The abrasive elements  734  can be any of the embodiments of abrasive elements  300 ,  400 ,  500 , and  600  described above. The slurry supply  720  dispenses the planarizing slurry  730  onto the planarizing surface  709  of the planarizing pad  708  (shown schematically). 
       FIG. 8  is a cross-sectional view illustrating a portion of the planarizing system  700  of  FIG. 7  in greater detail. Referring to  FIG. 8 , the planarizing slurry  730  typically covers the planarizing surface  709  of the planarizing pad  708 . In operation, a method of planarizing a microfeature workpiece accordingly comprises disposing the planarizing slurry  730  onto the planarizing surface  709  such that a plurality of the abrasive elements  734  and the liquid solution  732  contact the workpiece Was the support member  702  and/or the workpiece holder  712  move relative to each other. The abrasive elements  734  accordingly remove material from the surface of the workpiece W. 
     From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.