Abstract:
A polishing apparatus includes a cleaning device for critical cleaning of a top ring or a dressing tool to obtain high quality polishing by minimizing surface damage caused by contaminants originating from the top ring and/or dressing tool. The polishing apparatus includes a polishing table; a workpiece holding member for pressing a workpiece onto the polishing table; a dressing tool for conditioning a work surface provided on the polishing table. A cleaning device is provided for cleaning the dressing tool and/or the workpiece holding member. The cleaning device is provided with a spray nozzle for directing a cleaning solution toward at least an upper surface of the workpiece holding member or the dressing tool.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a polishing apparatus that includes a dressing device to maintain the surface quality of a polishing tool while minimizing polishing defects on a workpiece such as a semiconductor wafer. 
     2. Description of the Related Art 
     As the density of circuit integration in semiconductor devices becomes ever higher, circuit patterns are becoming finer and interline spacing narrower. In this type of technology, the depth of focus becomes very shallow in photolithographic reproduction of circuit patterns, and it requires that the surface of the wafer placed at the focal plane of a stepper must be microscopically flat to produce the required degree of image sharpness. As illustrated in FIGS. 4 and 5, a method of obtaining a flat surface is to polish the workpiece in a polishing apparatus comprised by a turntable  12  having a polishing tool  10  such as a polishing cloth or a grinding stone thereon, and a top ring (wafer holding member)  14  known as chemical mechanical polishing (CMP). 
     In the conventional CMP apparatus, a wafer W is held on the bottom surface of the top ring  14 , and the wafer is pressed against the polishing cloth  10  mounted on the rotating polishing table  12  by means of a pressing cylinder. During the polishing process, a polishing solution Q is supplied from a nozzle  16  so that polishing action takes place while the polishing solution Q is retained between the wafer surface to be polished and the polishing cloth  10 . 
     The ability of the polishing cloth  10  to provide efficient surface material removal becomes degraded as polishing is continued, and to regenerate the polishing ability of the polishing cloth  10 , a dressing device  18  is used at suitable intervals, such as when exchanging wafers. The dressing device  18  is disposed opposite to the top ring  14  across the center of the turntable  12 . The dressing device  18 , similar to the top ring  14 , may be attached to a swing arm  20  so that it can be swung back and forth between the dressing position above the polishing cloth  10  on the turntable  12  and a standby position outside of the turntable  12 . Dressing tool  24  is attached to a shaft  22  at the bottom end of the arm  20 , so that it can be driven by an elevating device and a rotation device. A dressing operation is carried out by rotating the turntable  12  and the dressing tool  24  and pressing the dressing tool  24  onto the work surface of the polishing cloth  10 . 
     After dressing is finished, the dressing tool  24  returns to the standby position, but because the tool  24  has been contaminated with polishing debris and polishing solution adhering to the polishing cloth  10 , it is necessary that the tool  24  be cleaned before the next cycle of dressing. For this purpose, a cleaning device  28  having a container  26  filled with a cleaning solution L is placed in the standby location, and the dressing surface of the dressing tool  24  is immersed in the cleaning solution L, as shown in FIG. 6. A similar device has also been used to clean the top ring. 
     However, in such a conventional cleaning device, even if a fresh solution L is used each time, there is always a chance of contamination of the fresh solution L by spent polishing solution or polishing debris that were removed from the dressing tool  24  during the previous cleaning step and are adhering to the inner surface of the container  26 . Also, polishing debris adhering to the bottom surface of the dressing tool  24  float into the cleaning solution L, and when the dressing tool  24  is immersed in the cleaning solution L, the solution level rises, the debris will adhere to upper surfaces  24   a  or side surfaces  24   b  of the tool  24  (see FIG.  1 ). Furthermore, mist produced during the normal polishing operation of the polishing solution can sometimes adhere to the upper surfaces  24   a  or side surfaces  24   b  of the tool  24 , and such a contaminant cannot be removed simply by immersing the tool  24  in the cleaning solution L. such contaminants can sometimes fall on the polishing cloth  10  during the dressing operation. Such dried and solidified contaminants that have fallen on the polishing cloth  10  have been known to cause scratching on the polished surface of the wafer. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a polishing apparatus to include a cleaning device for critical cleaning of the top ring or the dressing tool to obtain high quality polishing by minimizing surface damage caused by contaminants originating from the top ring and/or dressing tool. 
     This object is achieved in a polishing apparatus comprising: a polishing table; a workpiece holding member for pressing a workpiece onto the polishing table; a dressing tool for conditioning a work surface provided on the polishing table; and a cleaning device for cleaning the dressing tool and/or the workpiece holding member; wherein the cleaning device is provided with a spray nozzle for directing a cleaning solution toward at least an upper surface of the workpiece holding member or the dressing tool. 
     Accordingly, the present polishing apparatus enables cleaning the top ring or the dresser in a fresh cleaning solution free of residual contaminants originating from such areas as the solution container, and critically cleaning the upper surface of the workpiece holding device or the dressing tool, which has been difficult to do with conventional cleaning devices. Therefore, the workpiece holding member holding a wafer can now be made totally clean, and the dressing tool can be cleaned thoroughly so that dressing of the polishing cloth can be performed without the fear of contaminating the polishing cloth by particles detached from the dressing tool. The overall result is that superior polishing is achieved by the polishing apparatus of the present invention. 
     The cleaning device may be provided with a covering member to prevent splashing of cleaning solution. Accordingly, polishing scum and debris are prevented from flying out of the cleaning device so that high pressure sprays can be used to clean the dressing tool or the workpiece holding device. 
     The cleaning device may be provided with a solution storage section for immersing at least a lower surface of the workpiece holding device or the dressing tool. Accordingly, spray cleaning and immersion cleaning can be combined to provide an even more effective cleaning process. 
     The cleaning device should be made corrosion resistant in those regions of solution passages and/or solution contacting parts. Accordingly, reactive chemicals which might be needed for cleaning some polishing materials may be used. 
     The cleaning device may be provided with a control section for controlling operation of the spray nozzle. Accordingly, a most effective cleaning method can be chosen to suit each application. 
     Therefore, as explained above, the present cleaning device with the spray cleaning produces superior cleaning compared with using immersion cleaning only. Furthermore, an important advantage is the reliability of removing contamination from the upper surface of the workpiece holding device or the dressing tool, which has been a difficult task using the conventional cleaning devices. Therefore, probability of contamination by a dressing tool or a workpiece holding device is reduced significantly, to enable a high quality of polishing on workpieces required for advanced device production. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an embodiment of the dresser cleaning device in the polishing apparatus of the present invention; 
     FIG. 2 is a perspective view of an external appearance of a protective covering for the cleaning device shown in FIG. 1; 
     FIG. 3 is a plan view of the polishing apparatus having the dresser cleaning device shown in FIG. 1; 
     FIG. 4 is a schematic diagram of the polishing apparatus of the present invention; 
     FIG. 5 is a plan view of a conventional polishing apparatus; and 
     FIG. 6 is a cross-sectional view of the conventional polishing apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the dressing device will be presented with reference to FIGS. 1 to  3 . As shown in such Figures, the dressing device is positioned opposite to the top ring  14  across the center of the turntable  12 , and comprises a swing arm  20  swingable in a horizontal plane; a downward extending shaft  22  disposed at the tip end of the arm  20 ; a dressing tool  24  attached to the bottom end of the shaft  22 ; and a cleaning device  30 , in a standby position outside the turntable  12 . 
     Referring to FIG. 1, the dressing device further comprises a swing mechanism (arm moving mechanism) for swinging the arm  20 , and a pressing mechanism (shaft elevating mechanism) for pressing the dressing tool  24  onto the turntable  12 . FIG. 3 illustrates that the dressing tool  24  can be moved by the arm  20  to swing between the standby position and a dressing position above the turntable  12 . The top ring  14  is similarly provided with a top ring arm  13  and a top ring arm swing mechanism; a shaft  15  and a pressing mechanism; in such a way that the top ring  14  can be moved back and forth freely from a wafer loading position (for loading/unloading the wafer by means of a pusher  17 ), to the polishing position above the turntable  12 , and to waiting position  29 . 
     The dresser cleaning device  30  is housed in a cleaning container  32 , shown in FIG. 1, which is comprised by a container body  34  having a sufficient depth to hold a given quantity of liquid at the bottom section, and a detachable protective covering  36 . As shown in FIG. 2, the covering  36  is provided with an opening  38 , opening both on a side plate  36   a  and top plate  36   b , so as to enable the dresser tool  24  and the shaft  22  to enter into or exit from the covering  36 . The opening  38  comprises a wide section  38   a  for passing the dresser tool  24  or the top ring  14  and narrow sections  38   b ,  38   c  for passing the shaft  15  or  22 . The opening  38  may be provided with a flap door to prevent the cleaning solution L from splashing outside the covering  36 . 
     An inclined solution discharge path  40  to a exterior drainage by way of a valve is provided on one side of the bottom surface of the container body  34 , and serves to operate the container body  34  either in a solution storage mode or in a discharge mode. The container body  34  has at least one first nozzle  42  for spraying the cleaning solution L over the upper surfaces  24   a  of the dressing tool  24  and at least one second nozzle  44  for spraying the cleaning solution L toward the lower surface of the dressing tool  24 . FIG. 1 shows only one nozzle each for the first and second nozzles  42 ,  44 , but more than two nozzles may be placed suitably. The cleaning solution L is delivered to the nozzles  42 ,  44  under pressure by a solution delivery device and a control device to control the operation of the cleaning device  30 , which are not shown in the drawings. The side surface of the tool  24  can be cleaned by sprays from either one or both of the nozzles  42 ,  44 . 
     The operation of the dressing device  30  will be explained. As shown in FIG. 4, at the same time as the polishing operation or after the polishing operation is finished, the swing arm  20  is turned to position the dressing tool  24  at a desired spot above the turntable  12 , and the shaft  22  is revolved and lowered to press the dressing tool  24  against the polishing cloth  10  to condition the polishing cloth  10 . 
     When the dressing operation is finished, the dressing tool  24  is raised, and the swing arm  20  is swung back to the standby position. When the arm  20  is moved to the standby position, the dressing tool  24  naturally enters into the cleaning device  30  through the opening  38  provided on the covering  36 . A given volume of a cleaning solution L such as deionized water is stored beforehand in the container body  34  so that the tool  24  can be immersed in the cleaning solution to perform rough cleaning especially of its lower surface  24   c . At this stage, the tool  24  may be rotated or vertically moved in the cleaning solution, as necessary. 
     Next, the tool  24  is raised to come out of the cleaning solution, and spray cleaning is performed by jetting the cleaning solution from the nozzles  42 ,  44  at a pressure of about 1 kgf/cm 2 , as illustrated in FIG.  1 . Spray parameters, such as the spray volume, pressure, duration and number of spray nozzles, should be selected appropriately. The tool  24  may be rotated to wash the entire surfaces in accordance with the number or location of the nozzles provided. Polishing scum and debris can be removed with the cleaning solution L by a centrifugal force generated by spinning the tool  24 . 
     The use of spray nozzles  42 ,  44  for cleaning the tool  24  enables removal of the polishing scum and debris by using a fresh and clean cleaning solution, but it also allows cleaning of the upper surfaces  24   a  of the tool  24 , which has been a difficult task for the conventional cleaning devices. The present dressing device enables the polishing cloth  10  to be dressed with a critically cleaned dressing tool  24 , thereby avoiding contamination of the polishing cloth  10  during the dressing operation and enabling achieving high quality polishing. Furthermore, a combination of immersion cleaning and shower spray cleaning by spray nozzles reduces overall cleaning time and the amount of cleaning solution used, and improves the degree of cleanliness of the dressing tool  24 . 
     It is obvious that shower spray cleaning only may be sufficient in some cases. In such a case, a combination of primary cleaning at a high pressure and secondary cleaning at a low pressure may be used. Spray nozzles may be oriented at different angles and used selectively or combined in some suitable manner. Other possibilities include computer control of the cleaning process so that procedures using different nozzles may be programmed in a control application and selected by judging according to sensors or visual observation. 
     Further, a combined application of different cleaning solutions L may be preferable in some cases, such that primary cleaning is a chemical cleaning process and secondary cleaning employs deionized water for rinsing. If the cleaning solution is corrosive, it is necessary that the liquid passages and the container body  34  should be made corrosion resistant. 
     When the cleaning process is completed, the dressing tool  24  is returned to the dressing position by swinging the arm  20 . 
     It should be noted that, while the dressing tool is standing-by for the next dressing operation, it is preferable that the dressing tool  24  be kept inside the cleaning container  32  to avoid being splashed by the polishing solution and the like. In such a case, to prevent drying of the dressing tool  24 , low-volume sprays from the nozzles  42 ,  44  may be applied continually or periodically on the dressing tool  24 . 
     Although the above embodiment explained cleaning of a dressing tool, a similar device may be provided for the top ring  14  in the waiting position  29  to remove polishing debris and solution mist adhering to the upper surface of the top ring  14 .