Abstract:
Chemical mechanical polishing (CMP) equipment for use in planarizing a semiconductor wafer prevents slurry from being deposited on the surfaces of respective components of the equipment. The CMP equipment includes a turntable, a polishing pad mounted to the table so as to rotate with the table, a slurry supply unit for dispensing slurry onto the polishing pad, a polishing head unit for pressing a wafer downward atop the polishing pad, a conditioning unit for scoring the pad to maintain the surface of the polishing pad uniform, and a cleaning fluid supply unit. The cleaning solution supply unit has at least one spray nozzle by which cleaning solution is sprayed onto the polishing pad and respective components of the CMP equipment.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the manufacturing of semiconductor wafers. More particularly, the present invention relates to chemical mechanical polishing (CMP) equipment for planarizing wafers during the manufacturing of semiconductor devices. 
     2. Description of the Related Art 
     Semiconductor devices are generally made by subjecting wafers to such selective and repetitive processes as photolithography, etching, diffusion, chemical vapor deposition, ion implantation and metal deposition processes. However, before being undergoing any of such processes, the wafers may be subjected to a chemical mechanical polishing (CMP) process that planarizes the wafers to make it easy to form circuit patterns on the surfaces of the wafers. 
     The CMP process involves uniformly distributing slurry onto a surface of a polishing pad that rotates at a high speed, and placing a surface of a wafer to be polished onto the surface of the polishing pad. As a result, the surface of the wafer chemically reacts with the slurry and is physically abraded by the slurry under the force of the high speed rotation of the polishing pad. 
       FIGS. 1 and 2  show conventional CMP equipment  10 . The CMP equipment  10  includes a table  12  capable of rotating at a high speed, a polishing pad  14  mounted to the table  12 , a slurry supply nozzle  16  disposed above the table  12  for supplying slurry onto the polishing pad  14  during the planarization process, and a cleaning solution supply nozzle  18  for supplying a cleaning solution onto the surface of the polishing pad  14  when the polishing process has been completed. The cleaning solution is used to remove slurry, etc., from the surface of the polishing pad  14 . 
     The slurry and the cleaning solution are supplied through the slurry supply nozzle  16  and the cleaning solution supply nozzle  18 , respectively, onto a central portion of the polishing pad  14 . At either of these times, the polishing pad  14  is rotated at a uniform speed. Accordingly, the slurry or the cleaning solution gradually flows from the central portion of the polishing pad  14  toward the outer peripheral edge of the polishing pad  14 , whereby the slurry or the cleaning solution is uniformly distributed over the surface of the polishing pad  14 . Eventually, the slurry and the cleaning solution flow over the outer peripheral edge of the polishing pad  14 . 
     Meanwhile, a surface of the wafer W to be planarized is placed against the surface of the polishing pad  14  by a polishing head unit  20  to which the wafer W is mounted. The polishing head unit  20  is situated to one side of the table. At this time, the wafer W is rotated at a high speed by a head  22  of the head unit  20  while the head  22  is moved over a region that is roughly shown by the dotted line  20   a  in FIG.  3 . Simultaneously, the head  22  is raised/lowered to hold the wafer W proximate the surface of the polishing pad  14  or press the wafer against the pad  14  whereupon the polishing process takes place. 
     A conditioning unit  24  is also disposed beside the table  12 . The conditioning unit  24  has a pad conditioner  26  for cutting the surface of the polishing pad  14  to maintain the surface uniform, i.e., so that the polishing pad  14  planarizes the surface of the wafer W uniformly. The pad conditioner  26  rotates at a high speed, opposite the polishing pad  14 , and receives a constant downward force. The pad conditioner  26  is moved over a conditioning region shown by the dotted line  24   a  in  FIG. 3  to condition the polishing pad  14  while the pad  14  rotates at a high speed. 
     The operation of the respective components will now be described. 
     First, the table  12  is rotated at a high speed under the command of a control signal applied thereto. At this time, the slurry supply nozzle  16  continuously supplies a constant amount of slurry onto the central portion of the rotating polishing pad  14  so as to be uniformly distributed across the entire surface of the polishing pad  14 . Also, the polishing head unit  20  moves the wafer W round-trip across the head region  20   a , with one entire surface of the wafer W proximate the surface of the polishing pad  14  or in contact therewith. Accordingly, the surface of the wafer W in contact with the slurry or the polishing pad  14  is polished by chemically reacting with and physically rubbing against the slurry. 
     However, the upper surface of the polishing pad  14  eventually becomes irregular due to the contact with the wafer W. The conditioning unit  24  is used to obviate the problems that such an irregular surface of the polishing pad  14  would otherwise create. Specifically, the conditioning unit  24  rotates the pad conditioner  26  at a high speed, places the pad conditioner  26  in contact with the polishing pad  14 , and simultaneously moves the pad conditioner  26  back and forth across the conditioning region  24   a . As a result, the pad conditioner  26  cuts the entire surface of the polishing pad  14  to planarize it to a given thickness. 
     Once the polishing process for the wafer W or the conditioning process for the polishing pad  14  is completed, the formerly supplied slurry and particles from the conditioned (cut) polishing pad  14  remain on the surface of the polishing pad  14 . If allowed to stay there, the slurry and particles would scratch or negatively affect the uniformity of the next wafer W to be polished. 
     Therefore, a cleaning process is performed at the completion of the polishing process or at some other time at which the removal of various foreign substances from the surface of the polishing pad  14  is required. The cleaning process is executed by supplying a cleaning solution through the cleaning solution supply nozzle  18  onto a central portion of the polishing pad  14  while the pad rotates at a high speed. The cleaning solution thus gradually flows toward the outer peripheral edge of the pad  14  due to the centrifugal force created by the high speed rotation of the polishing pad  14 . At this time, the slurry and various foreign substances on the polishing pad  14  are slid an upper surface of the polishing pad  14 , and toward the outer peripheral edge thereof, by the flow of the cleaning solution. Finally, the slurry and various foreign substances entrained by the cleaning solution deviate are forced over the outer peripheral edge of the polishing pad  14 . 
     However, the slurry and the various foreign substances not only flow along the surface of the polishing pad  14  to the outer peripheral edge of the polishing pad  14 , but also are entrained in fumes that rise from the surface of the polishing pad  14 . The particulate matter of these fumes are deposited throughout the CMP chamber C including on the walls of the chamber C and on respective components of the CMP equipment  6 . The deposited slurry and various foreign substances accumulate and solidify over time. The solidified slurry and various foreign substances eventually flake off and fall onto the polishing pad  14  during a polishing process, whereby they scratch the wafer W being polished. 
     Furthermore, a sensor (not shown) is usually provided for checking whether a wafer W is present on an arm of a transfer device for loading/unloading the wafers W into and from the CMP equipment  10 . If such a sensor is covered with the slurry and various foreign substances from the fumes produced in the chamber C, the sensor outputs erroneous information to the controller of the CMP equipment  10 . The malfunction of the sensor in this way may result in a collision between the wafers W or between a wafer W and other components of the CMP equipment  10 . Such collisions will damage or otherwise break the wafers W. 
     The CMP equipment  10  is thus cleaned periodically to prevent these and other problems that would otherwise be caused by the deposited and solidified slurry and foreign substances. This cleaning process is laborious and thus, requires much time. Also, the slurry and various solidified foreign substances produce dust, which poses a danger to the health of workers and pollutes the respective components of the CMP equipment  10 . 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide chemical mechanical polishing (CMP) equipment that substantially overcomes one or more of the problems, limitations and disadvantages of the prior art. 
     Accordingly, one object of the present invention is to provide CMP equipment capable of preventing slurry and various foreign substances from remaining on the polishing pad of the CMP equipment following a polishing process and/or a conditioning process. 
     Another object of the present invention is to provide CMP equipment capable of preventing slurry and various foreign substances from depositing and solidifying on respective components of the CMP equipment. 
     It is still another object of the present invention to provide CMP equipment that requires less frequent cleaning that the prior art, and that provides a safer working environment by reducing the amount of dust that might otherwise be created by slurry and various foreign substances that are produced as the result of the CMP process. 
     According to one aspect of the present invention, the CMP equipment includes a turntable, a polishing pad mounted to the table so as to rotate with the table, a slurry supply unit for dispensing slurry onto the polishing pad, a polishing head unit for pressing a wafer downward atop the polishing pad, a conditioning unit for scoring the pad to maintain the surface of the polishing pad uniform, a cleaning fluid supply unit for spraying cleaning solution over a region in the CMP equipment encompassing at least a portion of the upper surface of the polishing pad, and a controller for controlling the operating components of the CMP equipment. 
     The cleaning solution supply unit can also be used to spray the cleaning solution over respective ones of the operating components of the CMP equipment, such as the polishing head unit and the pad conditioning unit. 
     The cleaning solution supply unit includes at least one cleaning solution supply line extending alongside the polishing the polishing pad (and the respective operating components), a spray nozzle installed at an end of the cleaning solution supply line and oriented to spray the cleaning solution over a predetermined region in the CMP equipment, and a regulator installed in the cleaning solution supply line for controlling the pressure of the cleaning solution issuing from the spray nozzle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention will become more fully understood from the detailed description that follows, and the accompanying drawings in which: 
         FIG. 1  is a perspective view of conventional CMP equipment; 
         FIG. 2  is a side view of the conventional CMP equipment shown in  FIG. 1 ; 
         FIG. 3  is a plan view of the polishing pad of the conventional CMP equipment, illustrating regions over which a pad conditioner and a polishing head are moved; 
         FIG. 4  is a perspective view of CMP equipment according to the present invention; and 
         FIG. 5  is a side view of the CMP equipment according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     CMP equipment for use in planarizing a semiconductor wafer according to the present invention will now be described with reference to  FIGS. 4 and 5 . It should be noted that the same reference characters designate like elements throughout the drawings. 
     Referring first to  FIG. 4 , the CMP equipment  30  includes a rotary table  12 , a polishing pad  14  disposed on the rotary table so as to rotate therewith, and a slurry supply unit. The slurry supply unit comprises a slurry supply nozzle  16  disposed above the table  12  and positioned to supply slurry onto a central portion of the polishing pad  14  that includes the center of rotation of the pad  14 . 
     The slurry that is supplied onto the central portion of the polishing pad  14  flows gradually from the central portion of the polishing pad  14  toward the outer peripheral edge thereof due to the centrifugal force created by the high speed rotation of the table  12 . The slurry eventually begins to flow from the rim of the polishing pad  14 . At this time, the slurry is supplied at a constant rate, whereby a uniform level of slurry is maintained across the entire upper surface of the polishing pad  14 . 
     The CMP equipment  30  also includes a polishing head unit  20  disposed beside the table  12 . The wafer W is mounted to a polishing head  22  of the unit  20 . The polishing head  22  may be moved up and/or down to position the wafer W proximate or against the upper surface of the polishing pad  14 . The polishing head  22  is also rotatable to rotate the wafer W while the wafer W is proximate or against the upper surface of the polishing pad  14 . Finally, the polishing head unit is swung about an axis of rotation to also move the wafer W across a region similar to the region  20   a  of FIG.  3 . 
     Likewise, a conditioning unit  24  is also disposed beside the table  12 . The conditioning unit  24  has a pad conditioner  26  for cutting the surface of the polishing pad  14  to maintain the surface uniform, i.e., so that the polishing pad  14  planarizes the surface of the wafer W uniformly. The pad conditioner  26  rotates at a high speed, opposite the polishing pad  14 , and receives a constant downward force. The pad conditioner  26  is moved over a conditioning region shown by the dotted line  24   a  in  FIG. 3  to condition the polishing pad  14  while the pad  14  rotates at a high speed. 
     The continuous supplying of slurry onto the polishing pad  14  rotating at a high speed, and the conditioning (scoring) of the polishing pad  14  by the pad conditioning unit  24  create fumes in the chamber C of the CMP equipment  30 . Slurry and the various foreign substances that make up these fumes are deposited on the polishing pad  14  and the peripheral components of the CMP equipment  30 . 
     The CMP equipment  30  also includes a cleaning solution supply unit. The unit includes one or more cleaning solution supply lines  32  disposed beside the table  12 . The cleaning solution supply line  32  is equipped with a spray nozzle  34 . The spray nozzle  34  is oriented to spray cleaning solution flowing through the line  32  onto the polishing pad  14  and/or onto the components of the CMP equipment described above. The cleaning solution supply unit also includes a flow regulator  36  and a control valve (not shown) disposed on the cleaning solution supply line  32  to control the pressure of the cleaning solution fed to the spray nozzle  34 , and hence, the pressure of the spray, in response to a control signal applied from a controller (not shown). 
     The operation of these respective components of the CMP equipment  30  will now be described. 
     First, the table  12  is rotated at a high speed under the command of a control signal applied thereto. At this time, the slurry supply nozzle  16  continuously supplies a constant amount of slurry onto the central portion of the rotating polishing pad  14  so as to be uniformly distributed across the entire surface of the polishing pad  14 . In addition, a wafer W is adhered to the polishing head  22  of the polishing unit  20  by suction (a vacuum) or surface tension. The polishing head unit  20  moves the wafer W round-trip across a head region, with one entire surface of the wafer W proximate the surface of the polishing pad  14  or in contact therewith. Accordingly, the surface of the wafer W in contact with the slurry or the polishing pad  14  is polished by chemically reacting with and physically rubbing against the slurry. 
     The upper surface of the polishing pad  14  eventually becomes irregular due to the contact with the wafer W. Therefore, after the wafer W has been polished, the polishing head  22  is raised to move the wafer W above the pad  14  and the slurry on the pad. Subsequently, the conditioning unit  24  rotates the pad conditioner  26  at a high speed, places the pad conditioner  26  in contact with the polishing pad  14 , and simultaneously moves the pad conditioner  26  back and forth across a conditioning region. As a result, the pad conditioner  26  cuts the entire surface of the polishing pad  14  to planarize it to a given thickness. 
     Once the polishing process for the wafer W or the conditioning process for the polishing pad  14  is completed, the formerly supplied slurry and particles from the conditioned (cut) polishing pad  14  remain on the surface of the polishing pad  14 . Deposits of the slurry and the foreign substances are also formed above the pad  14  on respective parts of the CMP equipment  30 , such as on the walls of the chamber C. If allowed to stay on the pad  14 , or if allowed to fall onto the pad  14  and remain there, the slurry and particles would scratch or negatively affect the uniformity of the next wafer W to be polished. 
     Therefore, a cleaning process is performed using the cleaning solution supply unit to remove the various kinds of foreign substances from the surface of the polishing pad  14  at the completion of the polishing or conditioning process. The cleaning process entails spraying a cleaning solution onto the entire surface of the polishing pad  14  while the pad  14  is rotated at a high speed and over an entire region encompassing the polishing head unit  20  and the pad conditioning unit  24 . 
     Such a spraying of the cleaning solution prevents the slurry and the various foreign substances from solidifying on the polishing pad  14 , and also increases the mobility of the foreign substances so that the slurry and foreign substances move more readily along the surface of the pad  14 , i.e., by the cumulative effect of the force of the spray and the centrifugal force created by the rotation of the pad  14 . In addition, the spraying of the cleaning solution prevents the slurry and the various foreign substances deposited on the respective components of the polishing head unit  20  and the pad conditioning unit  24  from solidifying. Even though such foreign substances are sprayed off of the respective components and fall onto the surface of the polishing pad  14 , the foreign substances are entrained in a great deal of liquid. Therefore, the liquid condition at the surface of the polishing pad  14  is not likely to damage a wafer W during the next polishing process. 
     Further, the spray nozzle  34  can be oriented/designed to spray the cleaning solution onto a sensor (not shown) for checking for presence of a wafer W at a loading/unloading position. Therefore, even if fumes envelop the sensor and leave slurry or foreign substances deposited on the sensor; the deposits are diluted with the cleaning solution and are thereby removed before they thicken and solidify. Thus, the cleaning solution supply unit ensures the correct operation of the sensor and thus prevents associated operating errors from occurring. 
     In addition, the dust in the CMP equipment is minimized because the spray of the cleaning solution prevents the slurry and the various foreign substances deposited on the polishing pad  14  and the respective components from solidifying in the first place. Accordingly, a safer working environment is provided. Moreover, a comparatively longer period of time is required between the periodic cleanings typically required for the overall maintenance of the equipment. Thus, the present invention can reduce the labor associated with maintaining the equipment, and reduce the downtime of the equipment, thereby increasing the operating efficiency of the CMP equipment. 
     Finally, various changes to and modifications of the present invention will become apparent to those skilled in the art. Thus, all such changes and modifications that fall within the scope of the appended claims are seen to be within the true spirit of the present invention.