Abstract:
A method and apparatus for polishing a substrate with a polishing pad and slurry entails washing polishing-pollutants produced by the polishing operation off of the pad in such a way that the pollutants are not splashed onto components of the polishing apparatus. A washing solution for removing the pollutants is directed onto the polishing pad as at least one free-flowing vertical stream. because the washing solution flows freely and vertically as it impinges the polishing pad, the washing solution does not rebound from the pad and flows from the surface of the polishing pad without causing the pollutants on the pad to be splashed up from the surface of the pad.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method and an apparatus for polishing a substrate using a polishing pad and slurry. More particularly, the present invention relates to the washing of the polishing pad to remove slurry and other particles therefrom.  
         [0003]     2. Description of the Related Art  
         [0004]     Recently, the semiconductor industry has made great strides as the use of information media including computers has increased. As concerns its function, a semiconductor device must operate at a high speed and have a large data storage capacity. Accordingly, improvements in semiconductor manufacturing techniques have centered around increasing the degree of integration, reliance and response speed of semiconductor devices.  
         [0005]     Chemical mechanical polishing (CMP) was developed in the 1980s for increasing the degree of integration of semiconductor devices. CMP is a manufacturing technique for polishing a surface on a substrate to attain a high degree of surface flatness. Examples of CMP polishing technologies are disclosed in U.S. Pat. No. 5,709,593 issued to Guthrie et al., and in U.S. Pat. No. 6,051,499 issued to Tolles et al.  FIG. 1  illustrates the polishing of a surface on a substrate  10  using a conventional a polishing apparatus.  
         [0006]     Referring to  FIG. 1 , the substrate  10  is grasped by a carrier head  12  which can simultaneously rotate and oscillate. The substrate  10  is pressed by the carrier head  12  against a rotatable polishing pad  14  mounted on a platen  13 . In this state, the substrate  10  is polished by slurry  16  which is sprayed onto the polishing pad  14 . More specifically, the substrate  10  is polished mechanically by an abrasive component of the slurry  16  and the abrasive surface of polishing pad  14 , and the substrate  10  is polished chemically by a chemical component the slurry  16 .  
         [0007]     In this polishing process, particles generated by the polishing process and some of the slurry remain on the polishing pad  14 . If these particles and slurry were to remain on the polishing pad, they could cause a defect to occur on a substrate as it is being polished. Therefore, the particles and slurry are removed from the polishing pad  14  while the substrate  10  is being polished.  
         [0008]      FIG. 2  shows a washing device  20  for washing a polishing pad  14  of the conventional polishing apparatus. Referring to  FIG. 2 , the washing device  20  includes an arm, and nozzles  21 ,  22 ,  23 ,  24 ,  25  mounted to the arm to spray deionized water  30  onto the polishing pad  14 . A slurry dispenser  40 , which supplies slurry  32  onto the polishing pad  22 , is also mounted to the arm of the washing device  20 . The outlet  34  of the slurry dispenser  40  is located at the end of the arm of the washing device  20 .  
         [0009]     Other conventional slurry dispensers, similar to that described above, are known. For example, a slurry dispenser disclosed in U.S. Pat. No. 5,928,062, issued to Miller et al., includes several slurry outlets through which the slurry flows. The several slurry outlets each are in the form of a nozzle or a hole. The nozzles function to spray the slurry, whereas the holes function to drip the slurry. Another slurry dispenser, disclosed in Japanese Patent Laid-open No. Hei 5-343375, is mounted on the polishing pad itself.  
         [0010]     In any case, during the polishing operation, the washing device  20  sprays deionized water  30  through the nozzles  21 ,  22 ,  23 ,  24 ,  25  and onto the polishing pad  14  to remove particles and slurry from the polishing pad  14 . Specifically, the sprayed deionized water  30  flows from polishing pad  14  carrying the remaining particles and slurry with it and hence, the particles and slurry are removed. In addition to removing particles and slurry during the polishing operation, the washing device  20  serves to clean the polishing pad  14  by supplying deionized water  30  onto the polishing pad  14  after the polishing of substrate has been completed.  
         [0011]      FIG. 3  is a cross-sectional view of the washing device  20  shown in  FIG. 2 . Referring to  FIG. 3 , the deionized water  30  sprayed onto the polishing pad  14  rebounds from the surface of polishing pad  14  due to the pressure under which the deionized water  30  is sprayed. Moreover, the slurry  30   a  remaining on the polishing pad  14  also flies off of the polishing pad  14  together with the deionized water. The slurry  30   a  adheres to the washing device  20  itself and to other components of the polishing apparatus, whereupon the slurry  30   a  accumulates on the washing device  20  and on other components of the polishing apparatus. Such slurry  30   a  causes a defect to occur on a substrate during the polishing process. That is, it is difficult to clean the slurry, especially from the components of the polishing apparatus. Eventually, clumped particles of the slurry begin to continuously fall from the components of the polishing apparatus onto the surface of the polishing pad  14 . There, the slurry particles scratch the surface of the substrate during the polishing process.  
         [0012]     In a short, the slurry entrained by the deionized water rebounding from the polishing pad is a constant source of defects during the polishing process. These defects, which occur on the substrates, decrease the reliability of the semiconductor devices manufactured therefrom.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention has been developed in view of the above-mentioned problems of the prior art. Accordingly it is a first object of present invention to provide a method of polishing a substrate which can minimize the rebounding of washing liquid from the polishing pad. Likewise, it is a second object of the present invention to provide an apparatus for polishing a substrate which can dispense a washing solution onto a polishing pad during the polishing operation in such a way as to minimize the rebounding of the washing liquid from the polishing pad.  
         [0014]     To achieve the first object of the present invention, the method of polishing a substrate comprises steps of rotating a substrate, rotating a polishing pad, polishing a surface of the substrate by placing the substrate in contact with the polishing pad and supplying slurry onto the polishing pad, and eliminating polishing-pollutants produced as a result of the polishing of the substrate by directing washing solution onto the polishing pad in the form of at least one free-flowing vertical stream to prevent the washing liquid from rebounding from the polishing pad.  
         [0015]     Preferably, the washing liquid is deionized water, and is directed onto the upper surface of the polishing pad as a number of free-flowing vertical streams, spaced at equal intervals from one another.  
         [0016]     To achieve the second object of the present invention, the polishing apparatus comprises a polishing station, a polishing pad mounted to the polishing station for contacting a substrate to polish the substrate, and a washing device located at one side of the polishing pad and having at least one feed hole through washing liquid flows freely onto the polishing pad as a vertically stream to eliminate polishing-pollutants from the polishing pad.  
         [0017]     According to the present invention, because the washing liquid flows vertically and freely onto the polishing pad, the washing liquid is prevented from rebounding. Therefore, the splashing of the slurry due to the rebounding of the washing liquid is also be minimized. As a result, slurry is prevented from accumulating on components of the polishing apparatus including on the washing device. Hence, defects in the polishing process, which are otherwise caused by agglomerations of slurry falling off of components of the polishing apparatus and onto the polishing pad during the polishing operation, are prevented.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The above and other objects and advantages of the present invention will become readily apparent from the following detailed description thereof made with reference to the accompanying drawings wherein:  
         [0019]      FIG. 1  is a schematic diagram of a conventional CMP apparatus, showing a state wherein the surface of a substrate is polished;  
         [0020]      FIG. 2  is a vertical sectional view of a washing device of the conventional polishing apparatus;  
         [0021]      FIG. 3  is a cross-sectional view of the washing device shown in  FIG. 2 ;  
         [0022]      FIG. 4  is a perspective view of an apparatus for polishing a substrate according to the present invention;  
         [0023]      FIG. 5  is a perspective view of a polishing pad of the apparatus shown in  FIG. 4 ;  
         [0024]      FIG. 6  is a vertical sectional view of a washing device of the apparatus for polishing a substrate according to the present invention;  
         [0025]      FIG. 7  is a horizontal sectional view of part of the washing device shown in  FIG. 6 ;  
         [0026]      FIG. 8  is another vertical sectional view of a washing device according to the present invention; and  
         [0027]      FIG. 9  is a schematic cross-sectional view of the washing device, illustrating the spraying of washing liquid according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.  
         [0029]     Referring to  FIG. 4 , an apparatus  40  for polishing a substrate includes a polishing station  400  at which a plurality of polishing pads  410  are disposed, and a carrier supporting a plurality of carrier heads  420 . Each carrier head  420  presses a substrate  430  against a polishing pad  410  whereupon a surface of the substrate  430  is polished.  
         [0030]     More specifically, referring to  FIG. 5 , the polishing pad  410  is mounted on platen  460  connected to a rotary member  450 . The rotary member  450  comprises a motor for rotating the polishing pad  410 . That is, the polishing pad  410  is rotated while the surface of the substrate  430  is polished.  
         [0031]     The carrier head  420  includes a vacuum chuck that grasps the substrate  430  by creating a vacuum at a side of the substrate opposite that which is to be polished. While the substrate  430  is so grasped, the carrier head  420  is moved downwardly to lower the substrate  430  into contact with the polishing pad  410 . As the surface of the substrate  430  is being polished, the carrier head  420  rotates and oscillates to the left and right. To this end, the carrier head  420  is connected to a rotary member  440 .  
         [0032]     Once the surface of polishing pad  410  becomes worn, the polishing pad  410  can damage the substrate  430  because the polishing pad  410  contacts the substrate  430 . Therefore, the apparatus  40  for polishing a substrate also includes a pad conditioning (not shown) unit that can dress the surface of the polishing pad  410  during the polishing process.  
         [0033]     The apparatus  40  for polishing a substrate also includes a washing device  500  for washing the polishing pad  410  with washing liquid while the substrate  430  is being polished. Referring to  FIG. 6  and  FIG. 7 , the washing device  500  includes an arm  505  defining a cavity therein, and a plate  508  mounted in the cavity of the arm  505  so as to define a chamber  507  therewith. Deionized water can be supplied into the chamber  507  via a washing liquid supply line. The plate  508  has several feeding holes  510  therethrough to supply deionized water  515  onto the polishing pad  410 . In the preferred embodiment, the washing device  500  has more than six feeding holes  510  and preferably, has more than ten feeding holes  510  to ensure that the deionized water  515  is supplied onto the polishing pad  410  uniformly. The diameter of each of the feeding holes  510  is about 2 mm. A washing liquid outlet tube  510   a  is also provided as extending from one of the holes  510  to supply deionized water  515  onto the polishing pad  410  at a distal end of the washing device  500 . Therefore, the deionized water  515  will flow to the center of the polishing pad  410 .  
         [0034]     In addition, the arm  505  of the washing device  500  is fixed to a post of the polishing station  400  by a screw  520 . Accordingly, the washing device  500  can be easily attached to and detached from the polishing station  400 , and the height of the washing device  500  is adjustable. The screw  520  makes repairing the washing device  500  easy because it can be detached with ease from the polishing station  400 . In an actual case, the time it took to repair the washing device was less than 30 minutes, compared to a repair time of more than 1 hour for repairing the washing device of the prior art.  
         [0035]     As was described earlier, particles generated by the polishing process and slurry used during the polishing process have to be removed. The washing device  500  supplies deionized water  515  onto the polishing pad  410  through the feeding holes  510  during the polishing process to remove the particles and slurry. That is, the deionized water  515  flows from the polishing pad  410  carrying the particles and slurry along with it. The deionized water  515  can also flow readily from the points on the polishing pad  410  where the deionized water  515  is supplied because the washing device  500  is positioned more than 20 mm above the surface of the polishing pad  410 .  
         [0036]     The apparatus  40  for polishing a substrate also includes a slurry dispenser  530  which supplies the slurry  538  onto the polishing pad  410 . The slurry dispenser  530  is installed in the arm  505  of the washing device  500 . A slurry outlet  535  of the slurry dispenser  530  is located at the distal end of the washing device  500 . The slurry dispenser  530  can include several slurry outlets  538 . Referring to  FIG. 8 , a slurry outlet  535  can be located closer to the outer edge of the platen  460  so that the slurry is supplied to various points on the surface of the polishing pad  410 . By positioning the outlet of the slurry dispenser away from the center of the polishing pad  410 , the washing efficiency is improved and as a result, the polishing efficiency is improved as well.  
         [0037]     A method of polishing a substrate using the apparatus  40  will now be described.  
         [0038]     First, the carrier head  420  carrying the substrate  430  is rotated and then the polishing pad  410  is rotated. Subsequently, the substrate  430  is brought into contact with the polishing pad  410  by lowering the carrier head  420 . Accordingly, the surface of the substrate  430  is polished on the polishing pad  410 . At this time, the slurry  538  is supplied onto the polishing pad  410 . Therefore, the substrate  430  is polished mechanically by the abrasive component (particles) of the slurry  538  and the abrasive surface of polishing pad  410 , and is polished chemically by the chemical component of the slurry  538 . And, while the slurry  538  is being supplied onto the polishing pad  410 , several streams of washing liquid are supplied through the feeding holes  510  of the washing device  500  and onto the surface of the polishing pad  410 . The feeding holes  510  are spaced from one another by equal intervals and so, the water streams are also spaced from one another by the same intervals.  
         [0039]     In the preferred embodiment, deionized water  515  is used as the washing liquid. The deionized water is fed into the chamber  507  of the washing device and is allowed to drain through the feed holes  510  in the plate  508 . The deionized water  515  thus forms several streams that flow to the polishing pad vertically and freely to prevent the deionized water  515  from rebounding from the polishing pad  410 . As a result, the deionized water  515  removes particles and slurry from the polishing pad  410 . Preferably, the washing device  500  is positioned to supply deionized water  515  from a height of more than 20 mm, and more preferably, 20-40 mm, above the surface of the polishing pad  410 .  
         [0040]     Furthermore, the several streams of the deionized water  515  are allowed to continuously flow onto the polishing pad  410  for 1 to 5 seconds after the substrate has been polished to eliminate remaining slurry and polishing pollutants.  
         [0041]      FIG. 9  illustrates the flow of a stream of the deionized water  515  according to the present invention. The deionized water is fed from a deionized water source  509  into the chamber  507  of the washing device  500 . From there, the deionized water  515  is allowed to drain through a feed hole(s) in the plate  508  so as to form a free flowing vertical stream. From  FIG. 9  it is clear how such a stream of deionized water  515  by virtue of its verticality and free flow from a predetermined height can and will not rebound from the surface of the polishing pad  410 . As a result, the amount of slurry that would otherwise fly up from the surface of the polishing pad  410  with the deionized water  515  is minimized which, in turn, prevents defects caused by the adherence of the slurry to components of the polishing apparatus.  
         [0042]     In fact, more than 80% fewer particles remain inside the polishing apparatus and on the washing device when the present invention, in which the deionized water flows through the feeding holes  510  freely and vertically, is practiced compared to the case in which deionized water is forcibly sprayed through nozzles. This fact has been verified by actual measurements, the results of which are shown in Table 1 and Table 2. Table 1 shows the number of particles of various sizes remaining inside the polishing apparatus, and Table 2 shows the number of particles of various sizes remaining on washing devices whose nozzles and holes, respectively, are located 20 mm above the surface of the polishing pad.  
                                                                           TABLE 1                                       Spraying through nozzles   Free flow through holes            Size of the   First   Second   First   Second       particles(μm)   measurement   measurement   measurement   measurement                        0.1   283,377   327,019   50,163   58,240           0.2   139,920   225,494   17,080   25,637           0.3   10,112   53,411   7,129   9,162           0.5   2,902   22,530   2,017   2,450           0.7   1,708   14,174   1,257   1,336           1.0   685   6,564   664   660                      
 
         [0043]     The particles inside the polishing apparatus were measured and counted for one minute with a laser particle counter. Referring to Table 1, the present invention allows 84% fewer particles to remain in comparison with the prior art in which the washing liquid is sprayed by nozzles onto the polishing pad.  
                                                                       TABLE 2                                       Spraying through nozzles   Free flow through holes            Size of the   First   Second   First   Second       particles(μm)   measurement   measurement   measurement   measurement                    0.1   377,199   354,827   88,358   93,578       0.2   252,043   217,593   25,308   18,207       0.3   55,610   46,617   10,784   7,894       0.5   26,560   20,016   3,352   1,855       0.7   17,606   12,856   2,002   1,302       1.0   8,250   6,132   1,038   759                  
 
         [0044]     The particles on the washing devices were measured and counted for one minute with a laser particle counter. Referring to Table 2, the present invention allows 82% fewer particles to remain on the washing device in comparison with the prior art in which the washing liquid is sprayed by nozzles onto the polishing pad.  
         [0045]     The improvements offered by the present invention in washing efficiency lead to increased uniformity in the polished surface of the substrate. An actual study has shown that when the washing device of the present invention is used during a polishing operation, the surface deviation of the polished substrate is about 173.5Δ less than that which is present in a polished substrate when the conventional washing device having spray nozzles is used. In this study, the measured surface deviation of a substrate polished by an apparatus comprising a washing device having conventional spray nozzles was 652.6Δ, whereas the measured surface deviation was 479Δ in the case of the present invention.  
         [0046]     In summary then, according to the present invention, during the polishing process, the deionized water for removing the particles and slurry remaining on the polishing pad flows onto the polishing pad freely and vertically. Therefore, the amount of deionized water rebounding from the polishing pad is minimal and the amount of slurry flung with the deionized water off of the polishing pad is also minimal. The area at which any of the deionized water might rebound from the polishing pad is also minimal. Accordingly, polishing defects due to excess slurry can be minimized so that the reliability of semiconductor devices can be improved. And, the efficiency of the polishing process is improved due to the ability of the washing device to be readily detached from the apparatus for repair.  
         [0047]     Finally, although the present invention has been described with respect to the preferred embodiment thereof, the present invention is not so limited. Rather, various changes and modifications can be made to the preferred embodiment within the true spirit and scope of the present invention as hereinafter claimed.