Abstract:
Methods and apparatus are provided for performing a chemical-mechanical process on a workpiece surface. The apparatus includes a platen having a top surface and at least one inlet configured to receive a polishing fluid, a plurality of holes formed in the top surface, a manifold system in fluid communication with the at least one inlet and each of the holes, a controller adapted to supply valve command signals, and a plurality of valves, each valve being disposed in one of the holes and coupled to the controller to receive the valve command signals and being operable, in response thereto, to selectively move between an open and a closed position. The method includes the steps of supplying the valve command signals, and selectively opening and closing the valves in response to the valve command signals.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to chemical-mechanical polishing devices. More particularly, the present invention relates to wafer planarization enhancement through improved polishing fluid distribution on a polishing pad.  
       BACKGROUND OF THE INVENTION  
       [0002]     Chemical-mechanical polishing (CMP) is the process of removing projections and other imperfections from a semiconductor wafer to create a smooth planar surface. The wafer is the basic substrate material in the semiconductor industry for the manufacture of integrated circuits. Wafers are typically created by growing an elongated cylinder or boule of single crystal silicon and then slicing individual wafers from the cylinder. Slicing causes both faces of the wafer to be somewhat rough. Planarization is desirable because the front face of the wafer on which integrated circuitry is to be constructed must be substantially flat in order to facilitate reliable semiconductor junctions with subsequent layers of material applied to the wafer. Composite thin film layers comprising metals for conductors or oxides for insulators must also be made of a uniform thickness if they are to be joined to the semiconductor wafers or to other composite thin film layers.  
         [0003]     Planarization is typically completed before performing lithographic processing steps that create integrated circuitry or interconnects on the wafer. Non-planar surfaces result in poor optical resolution of subsequent photolithographic processing steps which in turn hinders high-density features from being adequately printed. If a metallization step height is too large, open circuits will likely be created. Consequently, CMP tools are continually being improved upon with an aim toward controlling wafer planarization.  
         [0004]     In a conventional CMP assembly the wafer is secured in a carrier connected to a shaft. The shaft is typically connected to a transporter that moves the carrier between a load or unload station and a position adjacent to a polishing pad. One side of the polishing pad has a polishing surface thereon, and an opposite side is mounted to a rigid platen. Pressure is exerted on a wafer back surface by the carrier in order to press a wafer front surface against the polishing pad. Polishing fluid is introduced onto the polishing surface while the wafer and/or polishing pad are moved in relation to each other by means of motors connected to the shaft and/or platen. The above combination of chemical and mechanical stress results in removal of material from the wafer front surface. One requisite for removing wafer material at a high rate (“removal rate”) and for forming a wafer with high surface uniformity is a uniform distribution of polishing fluid about the polishing surface.  
         [0005]     In the case of CMP tools that use a rotating polishing platen and pad, one way that the polishing fluid is supplied to the polishing surface is through one or more delivery outlets that deposit the polishing fluid onto the polishing pad near the wafer leading edge. However, polishing fluid is not efficiently utilized with this type of delivery system. Due to the centrifugal force from the rotating platen the polishing fluid is quickly evacuated from the pad surface and the wasted polishing fluid must be continuously replaced. Visual examination of the polishing pad also reveals that the polishing fluid accumulates at the pad outer edge during polishing. As mentioned above, non-uniform polishing fluid distribution causes poor wafer planarization, and this problem alone necessitates an improved polishing fluid supply mechanism.  
         [0006]     Another way that the polishing fluid is supplied to the polishing surface is through a plurality of through-holes distributed about the polishing pad. The polishing pad through-holes are in communication with a supply source via holes or passageways extending through the platen. This “through-the-pad” polishing fluid delivery system is known to provide improved polishing fluid uniformity during polishing. Through-the-pad polishing fluid delivery systems have been successfully used on “non-rotational” type CMP tools having a polishing surface not much larger than the wafer, and which moves in an orbital or reciprocating motion. However through-the-pad fluid delivery has not been shown to provide improved polishing fluid uniformity when used in conjunction with the type of CMP tool incorporating a rotating polishing pad. This is due at least in part to the relative mismatch in wafer and platen diameter. Because the polishing surface is necessarily substantially larger than the wafer in a rotating polishing pad CMP tool, usually more than twice the wafer diameter, some polishing pad through-holes are covered by the wafer that is being polished, while others are left uncovered. The uncovered holes are naturally passages of lesser resistance, and consequently, little if any polishing fluid is delivered directly to the wafer-pad interface during polishing, while large amounts of slurry is wasted through the uncovered holes.  
         [0007]     Accordingly, it is desirable to provide a CMP polishing fluid supply mechanism that enables substantially uniform polishing fluid distribution about a pad-wafer interface during polishing on a rotating platen type polishing apparatus. In addition, it is desirable to provide a CMP polishing fluid supply mechanism that efficiently utilizes the polishing fluid. 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.  
       BRIEF SUMMARY  
       [0008]     An apparatus is provided for performing a chemical-mechanical process on a workpiece surface. The apparatus comprises a platen having a top surface and at least one inlet configured to receive a polishing fluid, a plurality of holes formed in the top surface, a manifold system in fluid communication with the at least one inlet and each of the holes, a controller adapted to supply valve command signals, and a plurality of valves, each valve being disposed in one of the holes and coupled to the controller to receive the valve command signals and being operable, in response thereto, to selectively move between an open and a closed position.  
         [0009]     A platen is also provided for performing a chemical-mechanical polishing process on a workpiece surface. The platen comprises a top surface having a plurality of holes formed therein, at least one inlet configured to receive a polishing fluid, a manifold system in fluid communication with the at least one inlet and each of the holes, and a plurality of valves, each valve being disposed in one of said holes and being adapted to receive the valve command signals and operable, in response thereto, to selectively move between an open and a closed position.  
         [0010]     A method is also provided for distributing a polishing fluid to a workpiece surface using a chemical-mechanical polishing platen having a top surface, a plurality of holes formed in the top surface, and a plurality of valves, each valve being disposed in one of said holes. The method comprises the steps of supplying valve command signals from a controller to the valves, and selectively opening and closing the valves in response to the valve command signals to control fluid distribution to the workpiece surface. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and  
         [0012]      FIG. 1  is a top cutaway view of a polishing system in accordance with an embodiment of the present invention;  
         [0013]      FIG. 2  is a top cutaway view of a portion of a polishing apparatus in accordance with an embodiment of the present invention;  
         [0014]      FIG. 3  is a bottom cutaway view of a carousel for use with the apparatus depicted in  FIG. 2 ;  
         [0015]      FIG. 4  is a top plan view of a typical workpiece carrier for use in conjunction with a polishing apparatus;  
         [0016]      FIG. 5  is a top cutaway view of apportion of a polishing apparatus in accordance with still another embodiment of the present invention;  
         [0017]      FIG. 6  is a top view of a platen for use in a chemical-mechanical polishing apparatus according to an embodiment of the present invention;  
         [0018]      FIG. 7  is a diagram showing a control system and valves responsive to command signals from the control system according to an embodiment of the present invention; and  
         [0019]      FIG. 8  is a cross sectional view of the platen depicted in  FIG. 6 . 
     
    
     DETAILED DESCRIPTION  
       [0020]     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.  
         [0021]      FIG. 1  illustrates a top cutaway view of a CMP polishing apparatus  100 . The apparatus  100  depicted is suitable for polishing or planarizing material from the surface of a workpiece and can incorporate the fluid distribution system of the present invention. The apparatus  100  includes a multi-station polishing system  102 , a clean system  104 , and a wafer load/unload station  106 . In addition, the apparatus  100  includes a cover (not shown) that surrounds the apparatus  100  to isolate the apparatus  100  from the surrounding environment. The apparatus  100  may be any machine capable of removing material from a workpiece surface.  
         [0022]     Although the present invention may be used to remove or polish material from the 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 the surface of a wafer. In the context of the present invention, the term “wafer” shall mean semiconductor substrates, which may include layers of insulating, semiconductor, and conducting layers or features formed thereon and used to manufacture microelectronic devices.  
         [0023]     An exemplary polishing system  102  includes four polishing stations,  108 ,  110 ,  112 , and  114 , that operate independently; a buff station  116 ; a stage  118 ; a robot  120 ; and optionally, a metrology station  122 . Polishing stations  108 - 114  may be configured as desired to perform specific functions.  
         [0024]     The polishing system  102  also includes polishing surface conditioners  140  and  142 . The configuration of the conditioners  140  and  142  generally depends on the type of polishing surface to be conditioned. For example, when the polishing surface comprises a polyurethane polishing pad, conditioners  140  and  142  may include a rigid substrate coated with diamond material. Various other surface conditioners may also be used in accordance with the present invention.  
         [0025]     The clean system  104  is generally configured to remove debris such as polishing fluid residue and material from the wafer surface during polishing. In accordance with the illustrated embodiment, the system  104  includes clean stations  124  and  126 , a spin rinse dryer  128 , and a robot  130  configured to transport the wafer between the clean stations  124  and  126  and the spin rinse dryer  128 . Alternatively, the clean station  104  may be separate from the remainder of the planarization apparatus. In this case, the load station  106  is configured to receive dry wafers for processing, but the wafers may remain in a wet (e.g., deionized water) environment until the wafers are transferred to the clean station. In operation, cassettes  132 , including one or more wafers, are loaded onto apparatus  100  at station  106 . The wafers are then individually transported to a stage  134  using a dry robot  136 . A wet robot  138  retrieves a wafer at the stage  134  and transports the wafer to metrology station  122  for film characterization or to the stage  118  within the polishing system  102 . The robot  120  picks up the wafer from the metrology station  122  or the stage  118  and transports the wafer to one of the polishing stations  108 - 114  for wafer surface planarization. After a desired amount of material has been removed, the wafer may be transported to another polishing station.  
         [0026]     After material has been removed from the wafer surface, the wafer is transferred to the buff station  116  to further polish the surface of the wafer. After the polishing and/or buff process, the wafer is transferred to the stage  118  which is configured to maintain one or more wafers in a wet (e.g. deionized water) environment.  
         [0027]     After the wafer is placed on the stage  118 , the robot  138  picks up the wafer and transports it to the clean system  104 . In particular, the robot  138  transports the wafer to the robot  130 , which in turn places the wafer in one of the clean stations  124 ,  126 . The wafer is there cleaned and then transported to the spin rinse dryer  128  to rinse and dry the wafer prior to transporting it to the load/unload station  106  using the robot  136 .  
         [0028]      FIG. 2  illustrates a top cut away view of another exemplary polishing apparatus  200 , configured to planarize a wafer. The apparatus  200  is suitably coupled to a carousel  300  illustrated in  FIG. 3  to form an automated polishing system. The system in accordance with this embodiment may also include a removable cover (not shown) overlying the apparatus  200  and the carousel  300 .  
         [0029]     The apparatus  200  includes three polishing stations,  202 ,  204 , and  206 , a wafer transfer station  208 , a center rotational post  210  that is coupled to carousel  300  and which operatively engages carousel  300  to cause carousel  300  to rotate, a load and unload station  212 , and a robot  214  configured to transport wafers between stations  212  and  208 . Furthermore, the apparatus  200  may include one or more rinse washing stations  216  to rinse and/or wash a surface of a wafer before or after a polishing, process. Although illustrated with three polishing stations, the apparatus  200  may include any desired number of polishing stations, and one or more such polishing stations may be used to buff a surface of a wafer. Furthermore, the apparatus  200  may include an integrated wafer clean and dry system similar to the system  104  described above. The wafer station  208  is generally configured to stage wafers before or between polishing and/or buff operations and may be further configured to wash and/or maintain the wafers in a wet environment.  
         [0030]     The carousel  300  includes polishing heads, or carriers,  302 ,  304 ,  306 , and  308 , each configured to hold a single wafer and urge the wafer against the polishing surface (e.g., a polishing surface associated with one of stations  202 - 206 ). Each carrier  302 - 308  is suitably spaced from post the  210  such that each carrier aligns with a polishing station or the wafer station  208 . In accordance with one embodiment of the invention, each carrier  302 - 308  is attached to a rotatable drive mechanism that allows the carriers  302 - 308  to cause a wafer to rotate (e.g., during a polishing process). In addition, the carriers may be attached to a carrier motor assembly that is configured to cause the carriers to translate as, for example, along tracks  310 . Furthermore, each carrier  302 - 308  may rotate and translate independently of the other carriers.  
         [0031]     In operation, wafers are processed using the apparatus  200  and carousel  300  by loading a wafer onto the station  208  from the station  212  using the robot  214 . When a desired number of wafers are loaded onto the carriers, at least one of the wafers is placed in contact with the polishing surface. The wafer may be positioned by lowering a carrier to place the wafer surface in contact with the polishing surface, or a portion of the carrier (e.g., a wafer holding surface) may be lowered to position the wafer in contact with the polishing surface. After polishing is complete, one or more conditioners  218  may be employed to condition the polishing surfaces.  
         [0032]     During a polishing process, a wafer may be held in place by a carrier  400 , illustrated in  FIG. 4 . The carrier  400  comprises a retaining ring  406  and a receiving plate  402  including one or more apertures  404 . The apertures  404  are designed to assist retention of a wafer by the carrier  400  by, for example, allowing a vacuum pressure to be applied to the backside of the wafer or by creating enough surface tension to retain the wafer. The retaining ring  406  limits the movement of the wafer during the polishing process.  
         [0033]      FIG. 5  illustrates another polishing system  500  in accordance with the present invention. It is suitably configured to receive a wafer from a cassette  502  and return the wafer to the same or to a predetermined different location within the cassette in a clean common dry state. The system  500  includes polishing stations  504  and  506 , a buff station  508 , a head loading station  510 , a transfer station  512 , a wet robot  514 , a dry robot  516 , a rotatable index table  518 , and a clean station  520 . The dry robot  516  unloads a wafer from the cassette  502  and places the wafer on the transfer station  512 . The wafer then travels to the polishing stations  504 - 508  for polishing and returns to the station  510  for unloading by the wet robot  514  and the transfer station  512 . The wafer is then transferred to the clean system  520  to clean, rinse, and dry the wafer before the wafer is returned to the load and unload station  502  using the dry robot  516 .  
         [0034]     Turning now to the polishing fluid delivery system of the present invention,  FIG. 6  illustrates a rotatable platen  10  having a pattern of polishing fluid delivery holes therein. Although not shown, a CMP pad is provided on top of the platen  10  during use. It should be noted that the term “CMP pad” is used here purely for convenience, and is intended to more broadly cover any type of polishing, electropolishing, buffing, or cleaning pad disposed on a platen and used in conjunction with a suitable polishing, buffing, or cleaning fluid or slurry. The CMP pad includes a polishing surface for polishing a wafer or other workpiece, hereinafter generally referred to as a “wafer.” The CMP pad also includes through holes that are arranged in a pattern that matches the platen hole pattern so that the platen polishing fluid delivery holes are in fluid communication with the CMP through holes.  
         [0035]      FIG. 6  illustrates with shading an area  13  that is covered by the wafer at some time as the wafer is being polished. When the area  13  is covered, polishing fluid delivery holes  11  within the area  13  are open and deliver polishing fluid to the CMP pad top surface. All holes  12  that are not disposed within the area  13  are closed and consequently do not deliver polishing fluid to the CMP pad top surface. Consequently, the open holes  11  covered by the wafer form the only polishing fluid pathways to the CMP pad top surface.  
         [0036]     The selectively opening and closing polishing fluid delivery holes  11 ,  12  function to create an even polishing fluid distribution along the CMP pad/wafer interface during wafer polishing. The even polishing fluid distribution is a result of the polishing fluid pathways through each of the open holes  11  having substantially equal amounts of flow resistance since the wafer covering the holes  11  is essentially flat. Also, because the platen  10  rotates, all of the holes  11 ,  12  are covered by the wafer at some time during a single rotation of the platen, thereby utilizing the entire polishing surface of the CMP pad.  
         [0037]      FIG. 8  depicts the coordinated elements within a polishing station designated  108 , although the illustrated polishing station  108  may be representative of any of the above mentioned polishing stations  110 ,  112 ,  114 ,  202 ,  204 ,  206  or other conventional polishing stations to the extent that the polishing station features are commonly known in the art. As discussed above, a wafer  20  is secured in a carrier  400  that rotates during a polishing process as designated by arrow  16  and also oscillates in a radial direction relative to the platen as designated by arrow  15 . The platen  10  also rotates during a polishing process as designated by arrow  14 . The platen  10  is disposed on top of a rotary union  25  and houses a manifold distribution system  30 . Polishing fluid is introduced to the manifold system  30  via a supply port  17  that extends through the rotary union  25  that rotatably supports the platen  10 . The manifold system  30  distributes the polishing fluid about the platen interior. The manifold system  30  includes the platen holes  11 ,  12  through which the polishing fluid flows from the platen interior to the platen top surface  18 . A CMP pad  40  is disposed on top of the platen top surface  18 , and includes through-holes  42  that are contiguous with the platen holes  11 ,  12  and extend to a CMP pad top surface  41 .  
         [0038]     As illustrated in  FIG. 8 , only the platen holes  11  that are covered by the wafer  20  are open. Valves (not shown) are disposed proximate to or inside of each of the holes  11 ,  12  to regulate polishing fluid passage to the platen top surface  18 . Electronic components automatically control valve openings and closings.  FIG. 7  is a schematic of a valve control system  50  and the valves  19  it controls according to one embodiment of the invention. In an exemplary embodiment, valves  19  open as soon as it is determined that the wafer  20  entirely covers holes in which the valves  19  are disposed. The wafer  20  only momentarily covers any given hole due to the constant motion of the platen  10  and carrier  400 , so it is preferred that polishing fluid be quickly distributed to the CMP pad/wafer interface by disposing the valves  19  as close as possible to the platen top surface  18 . Valve opening and closing commands may be delayed or progressed as needed in order to allow the polishing fluid to always exist at the pad-wafer interface. For example, if polishing fluid will not reach the pad-wafer interface approximately at the instant that the wafer covers a hole  11 ,  12 , the valves  19  may be commanded to open momentarily before the wafer  20  covers the hole  11 ,  12 .  
         [0039]     The valve control system  50  depicted in  FIG. 7  produces control signals  53  that regulate valve openings and closings. The valve control system  50  can be placed in any convenient location for communication with the valves  11 ,  12 , but is preferably disposed within the platen  10 . The command signals  53  can be based on such factors as the hole configuration data  52  for the platen, and feedback data regarding the platen&#39;s angular position relative to the wafer  20 . In some cases it may be necessary to also base the command signals on data regarding the time required for polishing fluid to travel from the valves  19  to the wafer surface during polishing. The data regarding the polishing fluid travel time is a function of such determinants as the polishing fluid consistency, the depth at which the valves  19  are disposed in the platen  10 , the CMP pad thickness, and the pressure exerted on the polishing fluid. The angular position and wafer position can be provided for example by a rotary encoder  51  or other conventional clocking device.  
         [0040]     A rotary encoder  51  is positioned on an external surface or inside a cavity of the rotary union  25  in an exemplary embodiment of the invention. In another exemplary embodiment of the invention the rotary encoder  51  is positioned on an external surface or inside a cavity of the platen  10 . Conventionally known optical, magnetic, or capacitive techniques can be employed to produce an electrical signal that is converted to rotary position data, and to input the data into the control system  50 . The inputted data from the encoder and pertaining to the platen hole configuration and, if necessary, the distance between the valves  19  and the CMP pad top surface  41  enables the control system  50  to select a specific configuration of holes to be opened and closed at any moment and to thereby provide a uniform distribution of polishing fluid across the surface of the wafer  20  that is being polished during a polishing process.  
         [0041]     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. For example, in addition to a CMP polishing process, the present invention is equally applicable to an electro-polishing process for electrochemically polishing a metal layer such as copper on a substrate using a suitable pad and electro-active chemistry, to a wafer buffing process for buffing scratches from a polished wafer using a buffing pad and suitable buffing fluid, or to a wafer cleaning process using a suitable cleaning pad in the presence of a cleaning, etching, or rinsing solution. 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.