Abstract:
Disclosed is a dressing apparatus wherein a polishing surface can be regenerated stably over a long period without any danger of an object to be polished being scratched. A dressing surface  50   a  of a dresser  48  is caused to slide on a polishing surface  30   a  of a polishing table  22  while the dressing surface is urged against the polishing surface. The dressing surface is formed from a grindstone  50.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dressing apparatus for use with a polishing apparatus for polishing a work object to be polished, such as a semiconductor wafer, which is used to regenerate a polishing surface of a polishing table. 
     2. Related Arts 
     With recent rapid progress in technology for fabricating high-integration semiconductor devices, circuit wiring patterns have been becoming increasingly fine and, as a result, spaces between wiring patterns have also been decreasing. As wiring spacing decreases to less than 0.5 microns, the depth of focus in circuit pattern formation in photolithography or the like becomes shallower. Accordingly, surfaces of semiconductor wafers on which circuit pattern images are to be formed by a stepper are required to be polished by a polishing apparatus to an exceptionally high degree of surface flatness, and a polishing process using a polishing apparatus is conducted as one method for obtaining such surface flatness. 
     A polishing apparatus of this kind generally comprises a polishing table on which a polishing cloth is provided to form a polishing surface, and a top ring for holding a substrate (object to be polished) with a surface thereof (to be polished) being orientated towards the polishing table. The substrate is urged against the polishing table under a predetermined pressure exerted by the top ring while rotating the top ring and the polishing table so that the surface of the substrate is polished to have a flat and mirror-finish surface while a polishing liquid is supplied. 
     A dressing apparatus is disposed aside the polishing table, and, by rotating the dressing apparatus and the polishing table while urging a flat dressing surface of the dressing apparatus against the polishing surface of the polishing table, any polishing liquid and abraded particles adhering to the polishing surface are removed and the polishing surface is normalized. 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     The dressing surface of the dressing apparatus comprises particles such as diamond particles which are adhered to the lower surface of a dresser by means of electrical deposition. However, during the dressing, some particles detach from the dressing surface and remain on the polishing surface of the polishing table, with the result that scratches are formed on the substrate. Further, in such a dresser, since diamond particles are usually adhered by electrical deposition in the form of a single layer, detachment and deterioration of the particles tends to occur, which necessitates the frequent exchange or replacement of the dresser itself. This is a time-consuming and costly operation. 
     The present invention aims to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a dressing apparatus in which a polishing surface can be regenerated for a long period without any danger of scratching an object to be polished. 
     Means for Solving the Problems 
     According to a first aspect of the present invention, there is provided a dressing apparatus in which a dressing surface of a dresser is urged in a sliding motion against a polishing surface, the dressing surface being formed from grindstone. 
     The grindstone is formed by binding abrasive particles having a particle diameter of 1 micrometer or less by means of a predetermined binder to obtain a layer having a predetermined thickness. Since the abrasive particles have a small diameter, even if the abrasive particles remain on the polishing surface of the polishing table, an object to be polished (substrate) can be prevented from being damaged by the abrasive particles. It is preferable that strength of the binder be selected so that the abrasive particles can be held in opposition subject to whatever force is applied during a dressing operation, and that such a binder strength be adjusted in accordance with the selection of a material and setting of a void ratio. 
     By setting the strength and property of the binder so that the binder is gradually denuded to form a new dressing surface as the dressing operations progress, a dresser having a long service life can be provided. As the dressing grindstone, a grindstone may have a so-called “abrasive particle self-generating function” formed by binding polishing particles by means of a binder having certain dissolving or destroying ability so that the abrasive particles are regenerated due to dissolution or destruction of the binder may be used. 
     According to a second aspect of the present invention, in the dressing apparatus according to the first aspect, a grindstone configuration correcting mechanism for maintaining a flat dressing surface is further provided, whereby the dressing surface of the grindstone is reoriented as necessary, to maintain a constant surface configuration. 
     According to a third aspect of the present invention, in the dressing apparatus according to the first or second aspect, the dressing surface is provided with a number of grooves or minute holes. By this arrangement, an abrasive particle removing function during dressing can be enhanced, a lubricating and cooling function of the dressing liquid for the dressing surface can also be enhanced, and, a surface tension force during the separation of the grindstone from the polishing table or the grindstone configuration correcting machine can be reduced to facilitate separation. 
     According to a fourth aspect of the present invention, there is provided a polishing apparatus comprising a polishing table having a polishing surface, a substrate holding member for holding a substrate and for urging the substrate against the polishing surface, and a dressing apparatus according to any one of the first to third aspects. 
     According to a fifth aspect of the present invention, in the polishing apparatus according to the fourth aspect, a fluid injecting mechanism for injecting fluid onto the polishing surface of the polishing table or the dressing surface of the dresser is further provided. By this arrangement, fluid is supplied between the grindstone and the polishing surface of the polishing table by the fluid injecting mechanism, thereby reducing the surface tension force between the grindstone and the polishing surface so as to facilitate separation of the grindstone from the polishing surface. 
     According to a sixth aspect of the present invention, in the polishing apparatus according to the fourth aspect, a residual abrasive particle cleaning nozzle for removing from the polishing table abrasive particles which have become detached from the grindstone is disposed in the vicinity of the polishing table. By this arrangement, any residual abrasive particles can be quickly removed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a polishing apparatus having a dressing apparatus  26  according to an embodiment of the present invention; 
     FIG. 2 is a sectional view showing a condition where a polishing operation is being performed in the apparatus of FIG. 1; 
     FIGS.  3 ( a ) and  3 ( b ) are perspective views showing a condition where a configuration of a dressing surface  50   a  is corrected by using the apparatus of FIG.  1 . FIG.  3 ( a ) shows the dresser  48  above the correcting table  54 , FIG.  3 ( b ) shows the dresser  48  urged against the correcting table  54 ; 
     FIG. 4 is a perspective view showing a condition where a dressing operation is being performed in the apparatus of FIG. 1; 
     FIG. 5 is a plan view of a dressing grindstone according to another embodiment; and 
     FIG. 6 is a plan view of a dressing grindstone according to a further embodiment. 
    
    
     REFERENCE SIGNS IN THE DRAWINGS 
       10 : polishing apparatus,  22 : polishing table,  24 : top ring,  26 : dressing apparatus,  30 : polishing cloth,  30   a : polishing surface,  32 : cleaning nozzle member,  36 ,  44 : head,  38 ,  46 : shaft,  40 : top ring,  48 : dresser,  50 : grindstone,  50   a : dressing surface,  52 : grindstone configuration correcting mechanism,  54 : configuration correcting table,  56   a ,  56   b : water supply nozzle member. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be explained in connection with embodiments thereof with reference to the accompanying drawings. 
     FIGS. 1 to  4  show a polishing apparatus including a dressing apparatus according to an embodiment of the present invention. The polishing apparatus is installed in a rectangular space on a floor, and a polishing apparatus  10  is disposed at one end of the space and a load/unload unit  14  on which a substrate containing cassettes  12   a ,  12   b  are rested is disposed at the other end of the space. Between the polishing apparatus  10  and the load/unload unit  14 , there are provided two conveying robots  16   a ,  16   b  and two cleaning devices  18   a ,  18   b  in opposing relation to each other, and a reversing mechanism  20  is located between the cleaning devices  18   a  and  18   b.    
     The polishing apparatus  10  includes a polishing table  22 , and a top ring device  24  and a dressing apparatus  26  with the interposition of the polishing table  22 . A pusher  28  for sending and receiving a substrate with respect to the conveying robot  16   b  is disposed aside the polishing table  22 . 
     As shown in FIG. 2, a polishing cloth (polishing member)  30  is adhered to an upper surface of the polishing table  22 , and a flat polishing surface  30   a  is formed on the polishing cloth  30 . The polishing table  22  is rotated by a drive motor (not shown) disposed below the polishing table. Above the polishing surface  30   a , there are provided a polishing liquid supplying nozzle  31  the opening of which is located above a center of the polishing table  22 , and a residual abraded particle cleaning nozzle member having a plurality of holes located above and opening along a radius of the polishing table  22 . The cleaning nozzle member  32  serves to remove detached abrasive particles remaining on the polishing surface  30   a , for example, by injecting a gas such as nitrogen gas or a liquid such as pure water or a chemical agent liquid onto the polishing surface  30   a . It should be noted that in place of the polishing cloth  30 , a grindstone (including fixed abrasive particles) may be used. 
     The top ring device  24  includes a support post  34 , and a top ring head  36  attached to a distal end of the support post  34  and rocked by a servo motor or the like. A top ring shaft  38  is attached to a free end of the top ring head  36  for rotational and vertical movements induced by a motor (not shown) and a cylinder for generating vertical movement (not shown), and a substantially disc-shaped top ring (substrate holding member)  40  is attached to a lower end of the top ring shaft  38 . 
     With the arrangement described above, by way of a horizontal swing movement of the top ring head  36 , the top ring  40  can be shifted between an upper position (polishing position) on the polishing surface  30   a , a substrate sending/receiving position on the pusher  28  and a standby position, and the top ring shaft  38  and the top ring  40  are together rotated and shifted in a vertical direction by driving the motor disposed within the top ring head  36  and by activating the cylinder for generating vertical movement. 
     Similarly, the dressing apparatus  26  includes a support post  42 , and a dresser head  44  attached to a distal end of the support post  42  and rocked by a servo motor or the like. A dresser shaft  46  is attached to a free end of the dresser head  44  for rotational and vertical movement generated by a motor (not shown) and a vertical movement applying cylinder (not shown), and a dresser  48  is attached to a lower end of the dresser shaft  46 . 
     The dresser  48  is a disc-shaped member in a taper form flaring in an outward direction downwardly. A thin circular plate-shaped grindstone (including fixed abrasive particles)  50  is fixed to a lower surface of the dresser, and a dressing surface  50   a  is defined on a lower surface of the grindstone  50 . The grindstone  50  is manufactured by binding dressing abrasive particles having a predetermined hardness and particle size by a binder having a predetermined strength and void ratio, and by dispersing the particles within the binder. A fine powder of cerium dioxide (CeO 2 ) and the like is used as the dressing abrasive particles, and a heat curing resin such as polyimide is used as the binder. 
     The abrasive particles should be sufficiently hard to be able to dress the polishing cloth (polishing member) and be of the smallest possible size. Preferably, the particle size of the dressing abrasive particles should be substantially the same as that of the polishing particles included in the polishing liquid. In the illustrated embodiment, the abrasive particles each mainly have a diameter of 1 micrometer or less. The abrasive particles may be formed from SiO 2 , Al 2 O 3 , ZrO 2 , MnO 2  or Mn 2 O 3 , as well as CeO 2 . 
     Further, the binder should be sufficiently strong so as to be able to hold the abrasive particles subject to a force applied to the dressing abrasive particles during a dressing operation which consists of a sliding motion on the polishing member. In order to maintain such a strength, an appropriate binder must be selected or a void ratio decreased. Further, the binder may be designed to gradually lose its function whereby abrasive particles become detached therefrom and a new dressing surface is revealed. In other words, while the dressing surface  50   a  of the grindstone  50  is urged against and slides along the polishing member, a portion of the binder is destroyed, whereby abrasive particles bound by this portion of the binder are released from the grindstone and additional abrasive particles bound by another portion of the binder are presented as the dressing surface. By this arrangement, since the grindstone is formed to have a predetermined thickness, a desired dressing performance can be maintained for a long term, thereby reducing the frequency with which the dresser is required to be replaced. 
     In consideration of the above, various materials can be selected for use as the binder. For example, phenol resin, urethane resin, epoxy resin or polyvinyl alcohol resin can be used, as well as the aforementioned polyimide resin. The dressing abrasive particles and the binder are appropriately selected in consideration of the kind of polishing member to be dressed and any affinity between the abrasive particles and the binder. 
     A number of grooves or fine holes may be formed in the dressing surface  50   a  of the dressing grindstone  50  to thereby enhance fluidity of the dressing liquid. Further, a fluid supplying mechanism for supplying fluid such as pure water or N 2  gas from the grindstone  50  onto the dressing surface  50   a  may be provided. In this case, a passage for such a fluid is formed within the dresser shaft and is connected to an external supply means via a universal joint. 
     The dressing apparatus  26  is provided with a grindstone configuration correcting mechanism  52  disposed alongside the polishing table  22 . As shown in FIGS.  3 ( a ) and  3 ( b ), the grindstone configuration correcting mechanism  52  comprises a configuration correcting table  54  formed from a porcelain-type material such as a ceramic, a metal material having electrically deposited diamond particles thereon, or a grindstone having a hardness greater than that of the dressing grindstone  50 . An upper surface of the configuration correcting table  54  is finished to form a flat surface having a flatness of about 0.20 to 0.01, for example. Further, around the table, there are provided a pure water supply nozzle member  56   a  for supplying pure water to prevent drying of the grindstone, and a pure water supply nozzle member  56   b  for supplying pure water to clean the configuration correcting mechanism. By intermittently supplying pure water from the pure water supply nozzle member  56   a  disposed at the standby position of the dresser  48  to the dressing grindstone  50  during a non-dressing operation, drying of the grindstone  50  is avoided so as to prevent deformation thereof. 
     In this way, the dresser  48  is shifted between the dressing position above the polishing surface  30   a  and a configuration correcting position above the configuration correcting table  54  by the horizontal rocking movement of the dresser head  44 , and the dresser shaft  46  and the dresser  48  are together rotated and shifted in a vertical direction by driving the motor disposed within the dresser head  44  and by activating the vertical movement applying cylinder. 
     Next, an operation of the polishing apparatus having the above-mentioned arrangement will be explained. First of all, a substrate W is picked up from the cassette  12   a  or  12   b  by the first conveying robot  16   a  and is reversed by the reversing device  20  and is then placed on the pusher  28  by the second conveying robot  16   b . The top ring  40  is then shifted above the pusher  28  by rocking the top ring head  36  of the top ring device  24  which was formerly in a standby position, and then, the pusher  28  is lifted, so that the substrate W is absorbed and held by the top ring  40 . Then, the top ring  40  is shifted above the polishing surface  30   a  by rocking the top ring head  36  of the top ring device  24  in a horizontal direction. And, as shown in FIG. 2, the top ring  40  is lowered while being rotated, thereby urging the top ring against the polishing surface  30   a  of the polishing table  22  which is being rotated by the drive motor. At the same time, a polishing liquid is supplied from the polishing liquid supply nozzle member  31 . In this way, the substrate W is polished. 
     After the polishing operation is complete, the top ring  40  is translated above the polishing surface  30   a  by the top ring head  36  while rotating the top ring  40 , and then, the top ring head  36  is stopped at an overhanging position where an area of about 50% of the substrate W protrudes outwardly from the polishing surface  30   a  and the center of the substrate W is located above the polishing surface  30   a . The top ring  40  is lifted to separate the top ring  40  and the substrate W from the polishing cloth  30  in this state whereby a surface tension acting between the substrate W and the polishing cloth  30  is reduced so as to facilitate accurate lifting and prevent any accidental movement. 
     In the top ring device  24 , the top ring  40  is shifted above the pusher  28  by rocking the top ring head  36 , and the polished substrate W is received by the pusher  28 , and the substrate W and the top ring  40  are cleaned, if necessary, by supplying pure water or a cleaning liquid. Thereafter, the top ring receives a new substrate W from the pusher  28  and is returned to the polishing table  22 , and a fresh polishing operation commences. 
     While the substrates W are being exchanged by the top ring, dressing for the polishing cloth is performed. Namely, the dresser  48  is located at the dressing position above the polishing surface  30   a , and the dresser  48  is lowered while being rotated, with the result that the dresser is urged against the polishing surface  30   a  of the polishing table  22 , thereby regenerating the polishing surface  30   a . As shown in FIG. 4, a cleaning fluid is ejected from the residual abraded particle cleaning nozzle member  32  having openings arranged along a radius of the polishing table, thereby removing any detached polishing particles from the polishing surface  30   a . As a cleaning fluid, pure water is normally used, and the water may be ejected under high pressure (water jet). 
     Since the dressing grindstone  50  is mainly formed from abrasive particles having a diameter of 1 micrometer or less, even if abrasive particles detached from the binder of the grindstone  50  during dressing remain on the polishing surface  30   a  of the polishing table  22 , the particles are buried in the polishing cloth  30 , and the substrate W will not be scratched. It should be noted, as shown in FIG. 2, that dressing may be performed while a polishing operation is being conducted by the top ring on the polishing table. In this case, damage resulting from abrasive particles detached from the grindstone  50  can also be prevented. 
     Further, since the dressing grindstone  50  has a predetermined thickness, a new dressing surface is created as the binder denudes, revealing a new surface, whereby the need for frequent replacement of the grindstone is obviated. 
     After the dressing operation, the dresser  48  is translated above the polishing surface  30   a  by the dresser head  44  while rotating the dresser  48 , and then, the dresser head  44  is brought to a halt at an overhanging position where an area of about 50% of the grindstone  50  protrudes outwardly from the polishing surface  30   a , and the center of the grindstone  50  is located above the polishing surface  30   a . In this overhanging condition, the dressing grindstone  50  is lifted to separate it from the polishing surface  30   a . Thereafter, the dresser head  44  of the dressing apparatus  26  is rocked to shift the grindstone  50  above the configuration correcting table  54 . 
     By providing a number of grooves or minute holes in the dressing surface  50   a  of the grindstone  50 , a contact area between the grindstone  50  and the polishing table  22  is reduced, thereby a reduction of surface tension is achieved. Further, a fluid injecting mechanism for injecting fluid from the dressing surface  50   a  of the grindstone  50  may be provided. And, by injecting the fluid from the fluid injecting mechanism, any surface tension acting between the dressing grindstone  50  and the polishing surface  30   a  via liquid can be removed, thereby facilitating separation. 
     The polished substrate W on the pusher  28  is conveyed, by the second conveying robot  16   b , to the first cleaning device  18   a  having a dual-surface cleaning function effected by a roll sponge, for example. After both surfaces of the substrate W are cleaned by the cleaning device  18   a , the substrate is conveyed, by the second conveying-robot  16   b , to the reversing device  20 , where the substrate is reversed. Thereafter, the substrate on the reversing device  20  is picked up by the first conveying robot  16   a , and the substrate is conveyed to the second cleaning device  18   b  having an upper surface cleaning function (effected by a pin sponge) and a spin dry function, where the substrate is cleaned and dried. Then, the substrate is returned to the cassette  12   a  or  12   b  by the first conveying robot  16   a.    
     On the other hand, in the dressing apparatus  26 , as shown in FIGS.  3 ( a ) and  3 ( b ), if necessary or periodically, the dresser  48  is lowered while being rotated (FIG.  3 ( a )), and the dresser is urged against the configuration correcting table  54  (FIG.  3 ( b )), thereby correcting (flattening) the configuration of the dressing surface  50   a . After the configuration of the dressing surface  50   a  has been corrected, the dresser  48  is moved to an overhanging position relative to the configuration correcting table  54  to facilitate separation form the latter. As described above, since a number of grooves or minute holes are formed in the dressing surface  50   a  of the dressing grindstone  50  and a fluid is injected from the dressing surface  50   a  of the dressing grindstone  50  by the fluid injecting mechanism, separation is made easy. 
     It should be noted that since the dressing grindstone  50 , a grindstone having a so-called “polishing particle self-generating function” is constituted by binding polishing particles by means of a binder that denudes over time thereby revealing a fresh layer of polishing particles operability of the polishing apparatus is greatly enhanced. 
     It should also be noted that, in the above-mentioned embodiments, while an example is given where a flat plate-shaped grindstone is used as explained, as shown in FIGS. 5 and 6, arcuate or pellet-shaped grindstone segments  62   a  or  62   b  may be adhered to an attachment plate  60  in a predetermined pattern such as a ring pattern, or adhered to the entire attachment plate to form a dressing grindstone  64   a  or  64   b . By such arrangements, since manufacture of a large grindstone is not required, costs can be reduced, and a desired grindstone pattern can easily be achieved. 
     In the above-mentioned embodiments, while an example is given that a turn table having a circle motion is used as the polishing table, and a polishing cloth is used as the polishing member, a table having a scroll-type movement (revolution movement describing a circular trace or translational circulative motion) or a reciprocal movement may be used, and a grindstone may be used as the polishing member. In this case, the dressing grindstone should be harder than the grindstone used as the polishing table. Further, when the void ratio of the dressing grindstone is less than that of the grindstone used as the polishing member, the service life of the dressing grindstone will be extended. However, in consideration of a ‘self-generation’ function, it is preferable that the diameters of particles of the grindstones are the same. 
     As mentioned above, according to the dressing apparatus of the present invention, by employing a grindstone as a dressing surface, the object to be polished is not damaged by residual dressing abrasive particles, and the service life of the dresser can be lengthened, and regeneration of the polishing surface can be effected for a long period.