Patent Publication Number: US-6908368-B2

Title: Advanced Bi-directional linear polishing system and method

Description:
REFERENCE TO RELATED APPLICATIONS 
     This is application is a continuation of U.S. patent Ser. No. 10/126,464 filed Apr. 18, 2002, now U.S. Pat. No. 6,589,105, and related to (U.S. Patent Application entitled “Drive System For a Bi-Directional Linear Chemical Mechanical Polishing Apparatus” Ser. No. 10/126,469 filed Apr. 18, 2002, all incorporated herein by reference. 
     This application is a continuation-in-part of and claims the benefit of priority under 35 USC 119/120 to the following: Ser. No. 10/252,149 filed Sep. 20, 2002, now U.S. Pat. No. 6,604,988, entitled “Polishing Apparatus and Method With Belt Drive System Adapted to Extend the Lifetime of a Refreshing Polishing Belt Provided Therein”, which is a continuation of Ser. No. 09/880,730 filed Jun. 12, 2001, now U.S. Pat. No. 6,464,571 Entitled “Polishing Apparatus and Method With Belt Drive System Adapted to Extend the Lifetime of a Refreshing Polishing Belt Provided Therein”, which is a continuation-in-part of Ser. No. 09/684,059 filed Oct. 6, 2000 now U.S. Pat. No. 6,468,139 entitled “Chemical Mechanical Polishing Apparatus and Method with Loadable Housing”, which is a continuation-in-part of Ser. No. 09/576,064 filed May 22, 2000 now U.S. Pat. No. 6,207,572 entitled “Reverse Linear Chemical Mechanical Polisher with Loadable Housing”, which is a continuation of Ser. No. 09/201,928 filed Dec. 1, 1998 now U.S. Pat. No. 6,103,628 entitled “Reverse Linear Polisher With Loadable Housing”, all incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to manufacture of semiconductor wafers and more particularly to a method and system of polishing pad tensioning in a chemical mechanical polishing apparatus. 
     DESCRIPTION OF THE RELATED ART 
     U.S. Pat. No. 6,103,628, assigned to the assignee of the present invention, describes a reverse linear chemical mechanical polisher, also referred to as bi-directional linear chemical mechanical polisher, that operates to use a bi-directional linear motion to perform chemical mechanical polishing. In use, a rotating wafer carrier within a polishing region holds the wafer being polished. 
     U.S. patent application Ser. No. 09/684,059, filed Oct. 6, 2000, which is a continuation-in-part of U.S. Pat. No. 6,103,628, describes various features of a reverse linear chemical mechanical polisher, including incrementally moving the polishing pad that is disposed between supply and receive spools. 
     While the inventions described in the above patent and application are advantageous, further novel refinements are described herein which provide for a more efficient drive system that creates the reverse linear (or bi-directional linear) motion. 
     SUMMARY OF THE INVENTION 
     The present invention offers many advantages, including the ability to efficiently produce reverse linear motion for a chemical mechanical polishing apparatus. 
     Another advantage of the present invention is to provide for the ability to efficiently produce bi-directional linear motion in a chemical mechanical polishing apparatus that also allows for the incremental movement of the polishing pad. 
     Another advantage of the present invention is the provision for a single casting that houses the polishing pad, including the supply spool, the receive spool, and pad path rollers. 
     The present invention provides the above advantages with a method and apparatus for producing bi-directional linear polishing that uses a flexible pad. In one aspect, a portion of the polishing pad is disposed under tension between a supply spool and a receive spool, with a motor providing the tension to either the supply spool or the receive spool and the other spool being locked during processing. If a new section of the polishing pad is needed, the same motor that provided the tension, if connected to the receive spool, is used to advance the polishing pad a determined amount. Further, during processing, a feedback mechanism is used to ensure that the tension of the polishing pad is consistently maintained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objectives, features, and advantages of the present invention are further described in the detailed description which follows, with reference to the drawings by way of non-limiting exemplary embodiments of the present invention, wherein like reference numerals represent similar parts of the present invention throughout several views and wherein: 
         FIG. 1  illustrates a bi-directional linear polisher according to the present invention; 
         FIG. 2  illustrates a perspective view of a pad drive system that includes a horizontal slide member that is horizontally moveable over a stationary casting using drive components according to the present invention; 
         FIG. 3  illustrates a polishing pad path through components of the casting that provide for a processing area in which bi-directional linear motion of the polishing pad results; 
         FIG. 4  illustrates a side view of a horizontal slide member and the drive system according to the present invention; 
         FIGS. 5A and 5B  illustrate a tensioning and incrementing mechanism according to the present invention; 
         FIG. 6  illustrates the controller used to control the tensioning and incrementing mechanism according to the present invention; and 
         FIG. 7  illustrates a flowchart of preferred operation using the tensioning and incrementing mechanism according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     U.S. Pat. No. 6,103,628 and U.S. patent application Ser. No. 09/684,059, both of which are hereby expressly incorporated by reference, together describe, in one aspect, a reverse linear polisher that can use a polishing pad to polish a wafer.  FIG. 1  illustrates a processing area  20  as described in the above references. A portion of the bi-directional linearly moving pad  30  for polishing a front wafer surface  12  of a wafer  10  within a processing area is driven by a drive mechanism. The wafer  10  is held in place by a wafer carrier  40  and can also rotate during a polishing operation as described herein. 
     Below the pad  30  is a platen support  50 . During operation, due to a combination of tensioning of the pad  30  and the emission of a fluid, such as air, water, or a combination of different fluids from openings  54  disposed in the top surface  52  of the platen support  50 , the bi-linearly moving portion of the pad  30  is supported above the platen support  50  in the processing area, such that a frontside  32  of the pad  30  contacts the front surface  12  of the wafer  10 , and the backside  34  of the pad  30  levitates over the top surface  52  of the platen support  50 . While the portion of the pad  30  within the processing area moves in a bi-linear manner, the two ends of the pad  30  are preferably connected to source and target spools  60  and  62  illustrated in  FIGS. 2 and 3 , respectively, allowing for incremental portions of the pad  30  to be placed into and then taken out of the processing area, as described in U.S. patent application Ser. No. 09/684,059 referenced above, as well as further hereinafter. 
     Further, during operation, various polishing agents without abrasive particles or slurries with abrasive particles can be introduced, depending upon the type of pad  30  and the desired type of polishing, using nozzles  80 . For example, the polishing pad  30  can contain abrasives embedded in the frontside  32 , and can be used with polishing agents but not a slurry being introduced, or with a polishing pad  30  that does not contain such embedded abrasives instead used with a slurry, or can use some other combination of pad, slurry and/or polishing agents. The polishing agent or slurry may include a chemical that oxidizes the material that is then mechanically removed from the wafer. A polishing agent or slurry that contains colloidal silica, fumed silica, alumina particles etc., is generally used with an abrasive or non-abrasive pad. As a result, high profiles on the wafer surface are removed until an extremely flat surface is achieved. 
     While the polishing pad can have differences in terms of whether it contains abrasives or not, any polishing pad  30  according to the present invention needs to be sufficiently flexible and light so that a variable fluid flow from various openings  54  on the platen support can affect the polishing profile at various locations on the wafer. Further, it is preferable that the pad  30  is made from a single body material, which may or may not have abrasives impregnated therein. By single body material is meant a single layer of material, or, if more than one layer is introduced, maintains flexibility such as obtained by a thin polymeric material as described herein. An example of a polishing pad that contains these characteristics is the fixed abrasive pad such as MWR66 marketed by 3M company that is 6.7 mils (0.0067 inches) thick and has a density of 1.18 g/cm 3 . Such polishing pads are made of a flexible material, such as a polymer, that are typically within the range of only 4-15 mils thick. Therefore, fluid that is ejected from the openings  54  on the platen support  50  can vary by less than 1 psi and significantly impact the amount of polishing that will occur on the front face  12  of the wafer  10  that is being polished, as explained further hereinafter. With respect to the pad  30 , the environment that the pad  30  is used in, such as whether a linear, bi-linear, or non-constant velocity environment will allow other pads to be used, although not necessarily with the same effectiveness. It has been determined, further, that pads having a construction that has a low weight per cm 2  of the pad, such as less than 0.5 g/cm 2 , coupled with the type of flexibility that a polymeric pad achieves, also can be acceptable. 
     Another consideration with respect to the pad  30  is its width with respect to the diameter of the wafer  10  being polished, which width can substantially correspond to the width of the wafer  10 , or be greater or less than the width of the wafer  10 . 
     As will also be noted hereinafter, the pad  30  is preferably substantially optically transparent at some wavelength, so that a continuous pad  30 , without any cut-out windows, can allow for detection of the removal of a material layer (end point detection) from the front surface  12  of the wafer  10  that is being polished, and the implementation of a feedback loop based upon the detected signals in order to ensure that the polishing that is performed results in a wafer  10  that has all of its various regions polished to the desired extent. 
     The platen support  50  is made of a hard and machineable material, such as titanium, stainless steel or hard polymeric material. The machineable material allows formation of the openings  54 , as well as channels that allow the fluid to be transmitted through the platen support  50  to the openings  54 . With the fluid that is ejected from the openings  54 , the platen support  50  is capable of levitating the pad. In operation, the platen support  50  will provide for the ejection of a fluid medium, preferably air, but water or some other fluid can also be used. This ejected fluid will thus cause the bi-linearly moving pad  30  to levitate above the platen support  50  and pushed against the wafer surface when chemical mechanical polishing is being performed. 
     A pad drive system  100  that is preferably used to cause the bi-linear reciprocating movement of the portion of the polishing pad within the processing area will now be described. 
     As an initial overview, as illustrated by  FIG. 3 , a path  36  that the polishing pad  30  travels within the pad drive system  100  between the supply spool  60  and the receive spool  62  is illustrated. As shown, from the supply spool  60  and alignment roller  114 B the path  36  includes passing through top  128 C and then bottom  128 D right slide rollers of the slide member  120 , and then over each of rollers  112 A,  112 B,  112 C and  112 D in a rectangularly shaped path and then around each of the bottom  128 B and then top  128 A left slide rollers of the slide member  120 , and then to the alignment roller  114 A and receive spool  62 . As is apparent from  FIG. 3 , and with reference to the points “A 1 , A 2 , B 1 , B 2 , and C, with the polishing pad  30  properly locked in position, preferably being attached between a supply spool  60  and the receive spool  62 , horizontal bi-directional linear movement of the horizontal slide member  120  creates a corresponding horizontal bi-directional linear movement of a portion of the polishing pad. Specifically, for example, as the horizontal slide member  120  moves from right to left from position P 1  to position P 2 , the point A 1  on the pad  30  will remain in the same position relative to the receive spool  62 , but the point A 2  will have moved through the left side rollers  128 A and  128 B of the horizontal slide member  120 . Similarly, the point B 1  on the pad  30  will remain in the same position relative to the supply spool  60 , and the point B 2  will have moved through the right side rollers  128 D and  128 C of the horizontal slide member  120 . As is apparent, by this movement, the point C will have moved linearly through the processing area. It is noted that the point C will move twice as far horizontally as compared to the horizontal movement of the horizontal slide member  120 . Movement of the horizontal slide member  120  in the opposite direction will cause the point C of the polishing pad  30  to also move in the opposite direction. Thus, the portion of the polishing pad disposed within a polishing area (point C) of the chemical mechanical polishing apparatus can polish a top front surface of a wafer using the bi-directional linear movement of the portion of the polishing pad  30 . 
     With the path  36  and the bi-linear pad movement mechanism having been described, a further description of the components within the path  36 , and the horizontal movement drive assembly  150  associated therewith, will now be provided. 
     As illustrated in  FIGS. 2 and 4 , the horizontal slide member  120  is horizontally moveable over rails  140 . The rails  140  are attached to a casting  110 , made of a metal such as coated aluminum, which casting also has all of the other pad path generating components attached thereto as well. Thus, various openings within the casting  110  exist for the inclusion of these pad path components, including the supply spool  60  and the receive spool  62  (which are each attached to a spool pin associated therewith), as well as each of rollers  112 A,  112 B,  112 C,  112 D,  114 A and  114 B, as well as a large opening for a roller housing  121  and pin connection piece  122 A that connect together the sidepieces  122 B 1  and  122 B 2  of the horizontal slide member  120 . The rails  140 , one on each side of the casting  110 , provide a surface for mounting rails  140  on which the horizontal slide member  120  will move. As illustrated in  FIG. 4 , the horizontal slide member  120  is mounted on the rails  140  using carriage members  126 . The carriage members  126  moveably hold the wafer in positions above and below the rail and can be used to reduce friction between the rails  140  and the horizontal slide member  120 . The carriage members  126  may include sliding elements such as metal balls or cylinders (not shown) to facilitate sliding action of the horizontal sliding member  120 . 
     With respect to the horizontal slide member  120 , as illustrated in  FIGS. 2 and 4 , a support structure  122  is shaped with side-walls  122 B 1  and  122 B 2  with connecting piece  122 A attached between them. The carrier members  126  are attached to the inner sides of the side-walls  122 B 1 ,  122 B 2 . Further, the roller housing  121  is shaped with sidepieces  121 A 1  and  121 A 2 , with a connecting piece  121 B between them. The roller housing  121  is supported by the support structure  122 . In this respect, side pieces  121 A 1  and  121 A 2  of the roller housing are attached to the side walls  122 B 1 ,  122 B 2  of the support structure  122 , using support pieces  123 . Attached between the two side pieces  121 A 1  and  121 A 2 , in the vicinity of the connecting piece  121 B, are four rollers  128 A-D, with left side rollers  128 A-B on one side of the connecting piece  121 B and right side rollers  128 C-D on the other side of the connecting piece  121 B. 
     Furthermore, a pin  130  is downwardly disposed from the pin connection piece  122 A as shown in  FIG. 4 , which pin  130  will connect to a link  164  associated with the horizontal drive assembly  150 , described hereinafter. The horizontal drive assembly  150  will cause horizontal bid-directional linear movement of the pin  130 , and therefore the horizontal bid-directional linear movement of entire horizontal slide member  120  along the rails  140 . 
     The horizontal drive assembly  150 , as shown in  FIG. 3 , is comprised of a motor  152  that will rotate shaft  154 . Shaft  154  is connected to transmission assembly  156  that translates the rotational movement of the shaft  154  into the horizontal bi-directional linear movement of the horizontal slide member  120 . In a preferred embodiment the transmission assembly  156  contains a gearbox  158  that translates the horizontal rotational movement of shaft  154  into a vertical rotational movement of shaft  160 . Attached to shaft  160  is a crank  162  to which one end  164 A of the link  164  is attached, with the other end  164 B of the link  164  being attached to the pin  130 , thereby allowing relative rotational movement of the pin  130  within the other end  164 B of the link  164 , which when occurring will also result in the horizontal bi-linear movement of the pin  130 . 
     Thus, operation of the horizontal drive assembly  150  will result in the bi-directional linear movement of the horizontal slide member  120 , and the corresponding horizontal bi-directional linear movement of a portion of the polishing pad  30  within the processing area. 
     As described in U.S. application entitled “Drive System For A Bi-Directional Linear Chemical Mechanical Polishing Apparatus” attorney reference 042496/0293224 mentioned above, during processing the polishing pad can be locked in position between the supply spool  60  and the receive spool  62 . As such, while a portion of the pad  30  within the processing area moves in the horizontal bi-directional linear manner, the pad can also be unlocked so that another portion of the polishing pad will move within the processing area, allowing incremental portions of the pad to be placed into and then taken out of the processing area, as describe in U.S. patent application Ser. No. 09/684,059 referenced above. 
     While have the pad  30  locked in position at both the supply spool  60  and the receive spool  62  will work, it has been found that more effective results can be achieved using a tensioning mechanism at one end of the portion of pad  30  in cooperation with the drive system described in the Drive System application referenced above. In particular, as illustrated in  FIGS. 5A and 5B , a processing system is shown with only those parts needed for the present discussion, which includes a horizontal slide member  220  that includes rollers  228 A and  228 B that are connected together using an connector piece  222 . The polishing pad  30  travels in a pad path  36  that is similar to that described previously with reference to  FIG. 3 , from the supply spool  60  and alignment roller  214 B, through the horizontal slide member roller  228 B, and then around both rollers  212 B and  212 A, to the horizontal slide member roller  228 A, and then to the receive spool  62  via the alignment roller  214 A. It should be noted, however, that this simplified version is not preferred, since a portion of the frontside of the pad  30  will touch the rollers  228 A and  228 B. 
     Further, as shown in  FIGS. 5A and 5B , a belt  272  is connected between a tensioning and incrementing motor  270 , which will be referred as the motor  270  hereinafter, and the receive spool  62 . Further, a lock mechanism  280 , such as a clamp mechanism, is illustrated. In this embodiment, tensioning of the pad may be obtained by locking the supply spool  60  using the lock mechanism  280  and activating the motor  270  with a predetermined torque value to rotate the receive spool  62  which is connected to the motor  270  through the belt  272 . Further, incrementing of the pad is obtained by unlocking the lock mechanism to release the supply spool  60 , and rotating the motor  270 , preferably at a low rpm, until for example a used section of the pad is taken up by the receive spool  62 , and a new pad section is brought over the processing area. 
     The control system for controlling the tensioning and incrementing motor  270  and the lock mechanism  280  is illustrated in further detail in FIG.  6 . As shown, power for the motor  270  and a controller  320  is provided by power source  310 , which provides appropriate power along line  314  to a driver  324  and likely a different appropriate power along line  312  to controller  320 . Controller  320  includes a computer or microcontroller of some type, as is known. Further, line  322  from the controller inputs the predetermined torque value to the motor control unit  304  as a TORQUE signal, specifically to torque control unit  326 . The predetermined torque value for the motor  270  may be a torque value that is about 10% less than the rated torque value of the lock mechanism  280 . The line  323  from the torque control unit inputs the TORQUE signal to the driver  324 . Line  316  returns the TORQUE signal that is received from the driver  324  to the controller for feed-back or self-check purposes. If self-check is not desired, the line  316  is removed. As will be described hereinafter, the TORQUE signal is used to maintain the tension on the receive spool  62  at a desired level during processing. The driver  324 , through the line  328   a , applies this torque value to the motor  270  as electrical current. 
     If the pad needs to be incremented, however, with an appropriate signal from the controller, the motor  270  is rotated, preferably at a low rpm, and the pad is advanced. As the motor rotates, it generates predetermined number of encoder pulses per revolution. The encoder pulses generated by the motor  270  are fed back to the driver  324  through the line  328   b  and then from the driver  324  to the controller  320  through the line  328   c . By counting the pulses, the controller  320  tracks the position of the pad, as it is advanced by the motor  270 . In one example, a single revolution of the motor  270  advances the pad 280 millimeters. An exemplary motor may be Model no. SG255SA-GA05ACC which is available from Yaskawa Electric Co., Tokyo, Japan. In this particular example, the motor  270  generates 8192 pulses per revolution. These pulses are sent to the driver serially. However, encoder pulses are ignored by the controller when performing tensioning, because the motor  270  will try to rotate at a certain speed, but of course it will not be able to move since pad is constrained by the lock mechanism  280  on the supply spool. 
     Upon receipt of process sequence commands and external signals, such as the TORQUE signal discussed above, controller  320  will generate control signals along line  322  that are used by the motor control unit  304  to control the motor  270 . In particular, the signals generated include an ON/OFF signal, as well as a TENSION signal that is used to supply the motor control unit  304  with an indication of the proper amount of power to supply to the motor  270  in order to achieve the desired tension on the receive spool  62  during processing. Controller  320  will also generate a BRAKE signal along line  330 , which preferably passes through relay  332  to the lock mechanism  280 , which is preferably implemented as an electromagnetic clamp brake that is used to lock the supply spool  60  in position. A monitor  340  and a user-input device  350  such as a keyboard are also preferably connected to the controller  320 . 
     The motor control unit  304  includes a driver  324  and a torque adjustment unit  326 . Power supplied to the driver  324  is varied in dependence upon a signal that is generated by the torque adjustment unit  326 . 
     Operation of the tensioning and incrementing of the portion of the pad  30  according to the present invention will now be further described with reference to the flowchart illustrated in  FIG. 7 , with reference to the other Figures discussed above. 
     As illustrated, during processing, initially in step  410 , the controller  320  provides an OFF signal to both the motor control unit  304  and the lock mechanism  280 . This causes both the supply spool  60  and the receive spool  62  to rotate freely, thereby allowing the initial threading of the pad  30  through the pad path  36  as described above with reference to FIG.  5 A. Once threaded and processing is to occur, step  420  follows, at which time controller  320  provides an ON signal to the lock mechanism  280 , followed by a TENSION signal to the motor control unit  304 , which TENSION signal turns on the motor  270  and applies tension to the receive spool  62 . Thus, the supply spool  60  becomes locked, and the receive spool  62  is held under tension, thereby appropriately tensioning the entire portion of the pad  30  therebetween, including that portion of the pad  30  that is in the processing area  20  illustrated in FIG.  1 . 
     Thereafter, step  430  is begun and processing will occur. During processing, the controller  320  will initiate the bi-directional linear movement of the pad  30  using the pad drive system  100  discussed above with reference to  FIG. 3  for example. During processing using a specific portion of the pad  30 , typically some number of wafers  10  can be processed, which may result in the turning on and off of the pad drive system  100 . 
     At some point, however, the portion of the pad  30  used for polishing will need to be replaced, and another portion of pad  30  provided. While an entirely new portion of pad  30  will be described as being provided, it will be understood that incremental portions can also be provided. When any new portion of pad  30  is needed from the supply spool  60 , the same operation will apply. In particular, the controller  320  will first provide in step  430  an OFF signal to the motor control unit to signal that the motor  270  should be turned off. Thereafter follows step  440 , in which an OFF signal will also be provided to the lock mechanism  280 , thereby turning off the brake and unlocking the supply spool  60 . Step  460  then follows, in which the controller  320  signals to the motor control unit  304  to increment the pad  30  some specified amount, which amount will correspond to the linear distance the pad  30  is desired to move. Upon this signal, the motor control unit  304  turns on the motor  270  and advances the pad by rotating the receive spool  62 . As previously mentioned this specific amount that the pad is incremented may be determined through the encoder pulses generated by the rotating motor  270 . Once the pad advancement occurs, step  420  is then initiated again, so that the supply spool  60  can be locked and the receive spool tensioned as described above. 
     The above provided description illustrates a preferred manner of providing tension during processing for the portion of the pad  30  that is in the processing area, as well as the incrementing of the pad  30 , using the same motor  270 . It is understood that although described as tensioning the receive spool  62  and locking the supply spool  60  during processing, that tensioning the supply spool  60  and locking the receive spool  62  during processing is another manner of implementing the present invention. 
     While the tensioning and incrementing is preferably accomplished using the single motor  270 , it is understood that if two motors, one attached to the receive spool and the other to the supply spool, that a variety of arrangements for tensioning and incrementing would also exist. 
     Further, although various preferred embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications of the exemplary embodiment are possible without materially departing from the novel teachings and advantages of this invention.