Abstract:
In a chemical mechanical wafer processing apparatus, a platen for supporting a polishing pad, a manifold for delivering a chemical to the platen, a workpiece substantially in contact with a polishing pad supported by the platen, a light transmission medium for transmitting and receiving light to and from the workpiece, one end of the medium being substantially flush with the top of the polishing pad, the other end of the transmission medium having a hollow portion for receiving a light transmitting and receiving probe, thereby providing a light transmitting and receiving probe in close proximity to the workpiece. The platen and manifold of the apparatus are substantially of non-metallic material and may be joined by spaced clamps and latches.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/403,355, filed Aug. 14, 2002. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to an apparatus and method for polishing a surface of a workpiece. More particularly, the invention relates to improved methods and apparatus for utilizing chemical-mechanical planarization in the manufacture of semiconductors. 
     BACKGROUND 
     Chemical-mechanical polishing or planarization of the surface of an object may be desirable for several reasons. For example, a flat disk or wafer of single crystal silicon is the basic substrate material in the semiconductor industry for the manufacture of integrated circuits. Semiconductor wafers are typically created by growing an elongated cylinder or boule of single crystal silicon and then slicing individual wafers from the cylinder. The slicing causes both faces of the wafer to be extremely rough. The front face of the wafer on which integrated circuitry is to be constructed must be extremely flat in order to facilitate reliable semiconductor junctions with subsequent layers of material applied to the wafer. Also, the material layers (composite thin film layers usually made of metals for conductors or oxides for insulators) applied to the wafer must also be made of a uniform thickness. 
     Planarization is the process of removing projections and other imperfections to create a flat planar surface and/or a uniform thickness for a deposited thin film layer on a wafer. Semiconductor wafers are planarized or polished to achieve a smooth, flat finish before performing lithographic processing steps that create integrated circuitry or interconnects on the wafer. A considerable amount of effort in the manufacturing of modern complex, high-density multilevel interconnects is devoted to the planarization of the individual layers of the interconnect structure. Non-planar surfaces result in poor optical resolution of subsequent photolithographic processing steps which in turn prohibits the printing of high-density features. If a metallization step height is too large, there is a serious danger that open circuits will be created. Since planar interconnect surface layers are required for the fabrication of modern high density integrated circuits, chemical-mechanical polishing (CMP) tools have been developed to provide controlled planarization of both structured and unstructured wafers. 
     In a conventional CMP tool for planarizing a wafer, the wafer is secured in a carrier connected to a shaft. The shaft is typically connected to mechanical means for transporting the wafer between a load or unload station and a position adjacent to a polishing pad mounted to a rigid or a flexible platen. Pressure is exerted on the back surface of the wafer by the carrier in order to press the wafer against the polishing pad usually in the presence of a slurry. The wafer and/or polishing pad are then moved in relation to each other by means of, for example, motors connected to the shaft and/or platen, in order to remove material in a planar manner from the front surface of the wafer. 
     Existing solid platens and associated slurry delivery systems (manifolds) are typically made from stainless steel (for example, 300 series stainless steel) and titanium. In the CMP process these metals are exposed to chemical environments where the pH range is from 1.0 to 14.0. Under these conditions metallic corrosion will occur. Treatments such as passivation and electropolish reduce the corrosion rate but, inevitably, all metals will corrode. 
     The effects of corrosion on the CMP process are unacceptable. Corrosion adds destructive particles to the slurry and could potentially damage devices on a wafer being polished. Another effect of metallic corrosion is increased defectivity beyond acceptable limits, particularly in today&#39;s environment of increasing smaller tolerances and feature size of semiconductor wafer patterning. 
     Consequently it would be desirable to provide a platen and slurry delivery system that eliminates metallic corrosion in the platen and manifold of a CMP system. 
     In addition to metallic corrosion, adhesive wear, also known as Galling, contributes to particle generation within the slurry delivery system. Galling initiates at the platen/manifold interface, and is induced by pressure and slight relative movement. As with corrosion, particle generation from Galling contributes to an increase in defectivity. 
     It would, therefore, be desirable to provide an improved platen/manifold interface to reduce or eliminate Galling. 
     It is often desirable to monitor the front surface of a wafer during the planarization process. One known method involves the use of an optical system that interrogates the front surface of the wafer in situ by positioning an optical probe under the polishing surface and transmitting and receiving an optical signal through an opening in the polishing pad. In some systems, the opening in the polishing pad is filled with an optically transparent material, or “window”, in order to prevent polishing slurry or other contaminants from being deposited into the probe and obscuring the optical path to the wafer. It is possible to adjust the planarization process based upon these real-time measurements or to terminate the process when the front surface of the wafer has reached the desired condition. 
     In view of the foregoing, it should be appreciated that it would be desirable to provide an improved polishing pad/platen window or lens for use in a chemical-mechanical polishing apparatus that exhibits good optical properties through which in situ monitoring of the wafer may be accomplished during the chemical-mechanical polishing process. It would further be desirable that the polishing pad/platen window or lens be easy to manufacture, easily to deploy in the polishing pad/platen, and easy to remove and replace. 
     Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     SUMMARY 
     In a chemical mechanical wafer processing apparatus, a platen for supporting a polishing pad, a manifold for delivering a chemical to the platen, a workpiece substantially in contact with a polishing pad supported by the platen, a light transmission medium for transmitting and receiving light to and from the workpiece, one end of the medium being substantially flush with the top of the polishing pad, the other end of the transmission medium having a hollow portion for receiving a light transmitting and receiving probe, thereby providing a light transmitting and receiving probe in close proximity to the workpiece. The platen and manifold of the apparatus are substantially of non-metallic material and may be joined by spaced clamps and latches. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  illustrates a top cutaway view of a prior art polishing apparatus suitable for removing material from a surface of a workpiece in accordance with the present invention; 
         FIG. 2  illustrates a cross-sectional view of a polishing apparatus in accordance with one embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of a lower portion of the lower polishing module as shown schematically in  FIG. 2 ; 
         FIG. 4  shows a platen and a manifold in exploded view; 
         FIG. 5  shows in some detail a side view of a portion of the lower polish head assembly; 
         FIG. 6  shows an exploded illustration of a light pin and end point probe; 
         FIG. 7  illustrates a method and apparatus for clamping a manifold and platen; 
         FIG. 8  illustrates a platen retaining latch that latches the platen-manifold combination to the polishing bell; 
         FIG. 9  illustrates the latch of  FIG. 8  in a latched position; and 
         FIG. 10  illustrates a method for releasing a pad from a platen. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
       FIG. 1  illustrates a top cutaway view of a polishing apparatus suitable for removing material from a surface of a workpiece in accordance with the present invention. The apparatus may include a multi-platen polishing system  102 , a cleaning system  104 , and a wafer load and unload station  106 , or may be a single platen polishing system in which the polishing, cleaning and wafer load and unload systems are separated. In addition, the apparatus includes a cover (not illustrated) that surrounds the apparatus to isolate it from the surrounding environment. An example of such an apparatus is a Momentum machine available from SpeedFam-IPEC Corporation of Chandler, Ariz.; however, it may be any machine capable of removing material from a workpiece surface. Such a machine is also described in U.S. Pat. No. 6,586,337, dated Jul. 1, 2003, and assigned to the assignee of the present invention. U.S. Pat. No. 6,586,337 is incorporated herein by reference. 
     Although the present invention may be used to remove material from a surface of a variety of workpieces such as magnetic disks, optical disks, and the like, the invention is conveniently described below in connection with removing material from a surface of a semiconductor wafer. In the context of the present invention, the term “wafer” shall mean semiconductor substrates, that may or may not include layers of insulating, semiconducting, and conducting layers or features formed thereon and used in the manufacture of microelectronic devices. 
       FIG. 2  is a schematic cross-sectional view of a polishing apparatus suitable for use in the apparatus shown in  FIG. 1  for polishing a surface of a wafer in accordance with the present invention. The apparatus includes a lower polishing module  144  that in turn includes a platen  166  and a polishing surface or pad  148 . An upper polishing module  150  includes a body  152  and a retaining ring  154  which retains wafer  156  during polishing. 
     Upper polishing module or carrier  150  is generally configured to receive a wafer for polishing and urge the wafer against the polishing surface during the polishing process. Carrier  150  applies a vacuum force to the back side of wafer  156 , retains the wafer, moves in the direction of the polishing surface to place the wafer in contact with polishing surface  148 , releases the vacuum, and applies a force (e.g., about 3 PSI) in the direction of the polishing surface. In addition, carrier  150  is configured to cause the wafer to move. For example, carrier  150  may be configured to cause the wafer to move in a rotational, orbital, or translational direction. Carrier  150  may be configured to rotate at a rate between two RPM and twenty RPM about an axis  158 . 
     Carrier  150  also includes a resilient film  160  interposed between wafer  156  and body  152  to provide a cushion during the polishing process and may also include an air bladder  162  configured to provide a desired, controllable pressure to a backside of the wafer during the polishing process. In this case, the bladder may be divided into zones such that various amounts of pressure may be independently applied to each zone. 
     Lower polishing module  144  is generally configured to cause the polishing surface to move. By way of example, lower module  144  may cause the polishing surface to rotate, translate, orbit, or any combination thereof. For example, lower module  144  may be configured such that platen  166  orbits at a radius of approximately one-eighth inch to one inch about an axis  164  at, for example, 30 to 2000 orbits per minute while simultaneously causing platen  166  to dither or partially rotate. In This case, material is removed primarily from the orbital motion of platen  166 . This allows a relatively constant speed between the wafer surface and the polishing surface to be maintained during a polishing process, and thus material removal rates are maintained relatively constant across the wafer surface. 
     Polishing machines including orbiting lower modules  144  are additionally advantageous because they require relatively little space when compared to rotational polishing modules. In particular, because a relatively constant velocity between the wafer surface and the polishing surface can be maintained across the wafer surface by moving the polishing surface in an orbital motion, the polishing surface can be about the same size as the surface to be polished. For example, a diameter of a polishing surface may be only 0.5 inches greater than the diameter of the wafer. 
       FIG. 3  is a cross-sectional view of a lower portion of the lower polishing module as shown schematically in  FIG. 2 . It includes the platen  166  and a polishing surface  148  suitable for use in conjunction with the polishing apparatus shown in  FIG. 2 . It should be noted that, although reference is made to polishing, the invention herein is equally applicable to buffing. For ease of description, however, we will continue to primarily reference polishing. Platen  166  and polishing surface or pad  148  include channels or conduits  170  formed therein to allow polishing fluid such as slurry to flow through platen  166  and surface  148  towards a surface of the wafer during the polishing process. Flowing slurry toward the surface of the wafer during the polishing process is advantageous because the slurry acts as a lubricant and thus reduces friction between the wafer surface and the polishing surface  148 . In addition, providing slurry through the platen and toward the wafer facilitates uniform distribution of the slurry across the surface of the wafer which in turn facilitates uniform material removal from the wafer surface. Slurry flow rates may be selected for a particular application, however, the slurry flow rates are generally less than 200 ml/minute and preferably about 120 ml/minute. 
     As illustrated in  FIG. 3 , the polishing pad  148  may consist of a single pad or may have multiple layers, usually bonded together to achieve a particular surface quality. Under the platen  166  is a slurry delivery system or manifold  174  that may be a single layer or have multiple layers depending upon the requirements for slurry distribution, volume, and the number of paths for slurry delivery that are required. A polish bell  180  supports the manifold  174 , platen  166  and polishing pad  148 . The polish bell  180  is driven in a preferred motion about an axis  164  as previously described. The bell may be manufactured of any suitable material having the requisite stiffness to support the manifold  174 , platen  166  and pad  148  in an extremely flat condition such that the polishing of the wafer removes material equally across the expanse of the wafer. 
     As previously noted, existing solid platens and associated slurry delivery systems (manifolds) are typically made from stainless steel (for example, 300 series stainless steel) and titanium. In the CMP process these metals are exposed to chemical environments where the pH range is from 1.0 to 14.0. Under these conditions metallic corrosion will occur. Treatments such as passivation and electropolish reduce the corrosion rate but, inevitably, all metals will corrode. 
     The effects of corrosion on the CMP process are unacceptable. Corrosion adds destructive particles to the slurry and could potentially damage devices on a wafer being polished. Another effect of metallic corrosion is increased defectivity beyond acceptable limits, particularly in today&#39;s environment of increasing smaller tolerances and feature size of semiconductor wafer patterning. 
     In addition, adhesive wear, or Galling, contributes to particle generation within the slurry delivery system. Galling initiates at the platen/manifold interface, and is induced by pressure and slight relative movement. As with corrosion, particle generation from Galling contributes to an increase in defectivity. 
     In order to reduce or eliminate the problems relating to metal corrosion and Galling, the platen and manifold of the present invention are constructed of non-metallic material such as plastic or ceramic materials, or of metallic materials coated with plastic or ceramic materials such that the metals do not contact the slurry and contribute to particle generation to contaminate the slurry. In addition, plastics and a number of ceramics have superior pH handling characteristics. 
     In a preferred embodiment a plastic such as PPS-techron may be used as it has low water absorption, good compressive strength, a wide pH range and a relatively low expansion coefficient. And although ceramics and coated materials offer some advantages over the metallic solutions now in use, plastic offers the additional advantages of lower relative cost, excellent chemical resistance, light weight for easy handling and lower bearing wear in use, and they are easy to machine. 
     The easy machineability allows both platens and manifolds to be inexpensively fabricated and allows easier production of, for example, multi-layer manifolds.  FIG. 4  shows a platen  166  and a manifold  174  in exploded view, it being understood that in use the platen and manifold are tightly coupled. Platen  166  has a plurality of holes  180  through which slurry from manifold  174  is carried. The polishing pad (not shown in this illustration) likewise has corresponding holes or sufficient porosity to allow the slurry to reach the workpiece or wafer  156  which may be mounted on the upper module  154  as shown in  FIG. 2 . The manifold  174  has a series of grooves or conduits  170  to carry slurry from the slurry supply mechanism (not shown) to the platen  166 . The conduits  170  communicate with holes  180  in the platen  166 . A second manifold  174 A is also shown, manifold  174 A having its own pattern of conduits  170  that communicate with conduits  170  in manifold  174 . Likewise, a third manifold  174 B is shown with its own conduits  170  that communicate with conduits  170  of manifold  174 A. 
     It can be seen that, as an example of the utility of multiple manifolds, beginning with four outlets in conduits  170  of manifold  174 B, the pattern in manifold  174 A increases the number of outlets to sixteen in manifold  174 A, and then to sixty-four in manifold  174 . This allows a pattern of 256 holes  180  in the platen  166  to be used to apply chemicals or slurry to the pad (not shown in this FIG. The easy machinability of the plastic material eases the manufacture of systems with multiple manifolds which allow for a greater number of fluid paths, the use of multiple chemicals simultaneously or serially, and separate inputs and outputs for different chemicals. If a plastic material is used, manifolds may be molded and then fuse bonded together to form a unitary manifold with multiple manifold characteristics thus avoiding problems usually associated with coupling various components of a system rigidly together. 
     The platen  166  and the manifolds  174 ,  174 A, and  174 B have another set of holes  182  through which a light pin or an end point probe is applied (depending upon whether reference is to the holes in the platen or the manifold) to sense the progress of the polishing and when the polishing process is complete. While four holes  182  are shown in each element here, the number of holes can be any number suitable for a particular process. End point detection will be addressed later. There is yet another set of holes  184  both in the platen  166  and the manifolds  174 ,  174 A, and  174 B. The function of these holes  184  will also be discussed later in conjunction with another figure. It is apparent that it is advantageous to easily machine both the platen and the manifold to provide the holes and conduits for the application of slurry and for the endpoint detection mechanism. 
       FIG. 5  shows in some detail a side view of a portion of the lower polish head assembly  144 . The polish pad  148  is atop the platen  166  that, in turn, is atop the slurry manifold  174  and the polish bell  180 . Conduits  170  in the manifold  174  are also shown. An end point probe  190  is shown extending through the polish bell  180 , the manifold  174 , and into the platen  166 . A light pin  192  is shown affixed to the platen  166  by a retaining screw  194 , although the pin could alternatively be press fit into the platen. The light pin  192  is of a plastic, epoxy, or urethane material and extends through the platen, through holes  182  as shown in  FIG. 4  and also through the polishing pad  148  when the pad is in place. Because the light pin initially extends through the polishing pad  148 , the pin can be used as a registration guide for providing proper position of the pad  148  on the platen  166 . As explained more fully below, the top portion of light pin  192  is subsequently trimmed off flush with the top surface of polishing pad  148 . Accordingly the top portion of light pin  192 , the portion that is subsequently removed, is shown in phantom in  FIG. 5 . 
     An end point probe  190  is inserted through a hole in the manifold that is in registration with hole  182  in the platen. The end point probe  190  has a larger diameter at the bottom for strength, but has a smaller diameter at its top portion. The light pin  192  is hollow at its bottom portion and the smaller diameter portion of the end point probe  190  is inserted into the hollow portion of the light pin. The end point probe itself is mounted on the polishing bell. 
       FIG. 6  shows an exploded illustration of the light pin  192  and end point probe  190  that more clearly shows the relationship among the polish bell  180 , manifold  174 , platen  166 , the pin  192  and the probe  190 . The shoulder  196  of The end point probe  190  is clearly shown, as is the hollow portion  197  of the light pin  192 . The hollow portion  197  of the light pin  192  allows the narrowed top of the end point probe  190  to be seated flush with the top of the platen as can be seen in  FIG. 5 . The flush mounting of The end of The end point probe provides an improvement in the ability of The end point detector (not shown) to detect the completion of the polishing process as earlier discussed. An O-ring seal  198  is shown that prevents fluid from getting past the top of the polishing bell  180 . Another seal  200 , seals the end point probe from the manifold  174  and platen  166 . 
     The portion of the light pin  192  extending through the polishing pad  148  is removed flush with the top of the polishing pad  148  prior to use, by severing the top of the pin  192  and utilizing a pad conditioner (which typically is a steel platform with an abrasive diamond surface that is used to condition or level the pad prior to wafer processing) to level the light pin to be flush with the pad. 
     The foregoing arrangement of light pin and probe offers several advantages. Since the end point probe  190  is accessible from the bottom of the polishing bell, it is not necessary to disassemble the bell, manifold and platen to replace the probe. Additionally, the light pin can be accessed for replacement in two ways; the manifold can be removed from the platen and the light pin  192  released from the platen by removing the retaining screw  194 , or The manifold can remain in place and the probe seal is removed from the manifold. The end point probe  190 , being mounted on the bell, remains in place. This arrangement is advantageous in requiring little or no disassembly to change pins or probes. 
     Typically the platen is held to the manifold by means of a v-band clamp that attaches over a rim of the platen and under a ridge of the manifold. This arrangement has become somewhat unsatisfactory as requirements for elimination of particles has become more critical. This is due to the propensity of v-band fasteners to allow very small relative movement between the platen and manifold thus causing Galling as previously discussed. 
       FIG. 7  illustrates a method and apparatus for clamping a manifold  174  and a platen  166  such that the micro relative motion between the manifold and platen is removed. Motion between the manifold  174  and the platen  166  would generate undesirable production of particles in the slurry delivery system due to Galling. The platen  166  is clamped to the manifold  174  by plastic (such as PEEK) or metal bolts and nuts. A slot  202  is machined into the edge of platen  166  and a bolt is inserted through a hole in the manifold and a hole in the platen at the location of slot  202 . A bolt  204  is inserted from the bottom of the manifold  174  to the hole in the platen  166 . A preferably plastic or Erdalite nut retainer biscuit  208  containing the nut  206  is placed in the slot  202  over the hole in the platen  166 . The center of nut  206  is offset from the center of biscuit  208  such that the biscuit will be held in place while bolt  204  is torqued to a specified value. When it is desired to disassemble the platen from the manifold, once the bolt is removed the biscuit  208  can be removed by pushing on one end of the off center biscuit which rotates the biscuit out of the slot  202 . A number of these clamping positions are provided around the perimeters of the platen and manifold to assure adequate clamping pressure. 
       FIG. 8  illustrates a platen retaining latch that latches the platen-manifold combination to the polishing bell  180 . A latch  210  is bolted by a bolt  212  that is inserted through a hole  230  in a recess  216  machined into the periphery of the manifold  174 . Bolt  212  is subsequently secured into the platen  166 . A torque pin  214  is mounted on The polishing bell  180  such that when the manifold is brought into contact with bell  180  the torque pin protrudes through a hole  218  in the recess  216 . In  FIG. 9  it can be seen that The latch  210  captures the platen/manifold assembly in the vertical axis. The torque pins capture the bell  180  in The XY plane as they cooperate with corresponding holes in the periphery of the manifold. The use of the clamping and manifold assembly techniques eliminates The need for the v-band clamps and provide a method for quickly disassembling the platen away from the bell assembly. 
     In prior art polishing systems, it was relatively difficult to remove the polishing pad  148  from the platen, the operator frequently having to resort to scraping the edge of the pad with a knife to loosen the pad from the platen. In  FIG. 4  there was described a platen/manifold combination having a series of holes therethrough. One or more of the holes  184  are provided for the purpose of allowing a Last and easy mechanism for removing pads from platens. As can be seen in  FIG. 10  holes  184  have been provided through the platen  166  and the manifold  174  near the periphery of the polishing pad  148 . A key or punch  224  may be inserted through one of the holes  184  in order to lift an edge of the pad  148  from the platen  166  thereby easing the task of securing the pad for removal. The ability to easily work the plastic platen and manifold material or alternatively ceramic or coated materials allows additional holes to be drilled and recesses to be machined more easily than do prior platen and manifold materials. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.