Patent Publication Number: US-9409277-B2

Title: Polishing apparatus and polishing method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This document claims priorities to Japanese Patent Application Number 2012-240394, filed Oct. 31, 2012 and Japanese Patent Application Number 2012-242951, filed Nov. 2, 2012, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a polishing apparatus and a polishing method, and more particularly to a polishing apparatus and a polishing method for polishing and planarizing a surface of a polishing object (substrate), such as a wafer, while preventing the formation of scratches on the surface of the polishing object, caused by a polishing liquid that has been scattered and dried. 
     The present invention also relates to a polishing apparatus, and more particularly to a polishing apparatus for polishing and planarizing a surface of a polishing object (substrate), such as a wafer, while preventing a polishing liquid from contaminating various covers and other parts disposed around a polishing table. 
     2. Description of the Related Art 
     A polishing apparatus for polishing a wafer surface generally includes a polishing table for supporting a polishing pad having a polishing surface, and a top ring (or a polishing head) for holding a wafer. While the polishing table and the top ring are moved relative to each other, the wafer, held by the top ring, is pressed against the polishing surface of the polishing pad at a predetermined pressure to come into sliding contact with the polishing surface. As a result, the wafer is polished to have a flat mirror surface. In the case of chemical mechanical polishing (CMP), a polishing liquid (or slurry) is supplied onto the polishing pad during polishing. 
     When the surface of the substrate, such as a wafer, is polished while the polishing liquid is supplied to the polishing pad, the polishing liquid is scattered around the polishing table. After the polishing of the substrate, a liquid (e.g., pure water) or a mixed fluid of a liquid (e.g., pure water) and a gas (e.g., nitrogen gas) is sprayed in a mist state from an atomizer to the polishing surface of the polishing pad to clean the polishing surface. During the cleaning of the polishing surface by means of the atomizer, the polishing liquid remaining on the polishing surface is also scattered around the polishing table. The scattered polishing liquid can be attached to and dried on various constituent parts disposed around the polishing table or on an inner surface of a chamber in which the polishing apparatus is housed. If the dried polishing liquid falls onto the polishing table, the fallen matters may cause a scratch on the substrate. 
     In general, various cleaning nozzles are disposed in predetermined positions in the polishing apparatus. A cleaning liquid is periodically emitted from the cleaning nozzles toward predetermined sites in the polishing apparatus in order to rinse off the polishing liquid that has been attached to the polishing table or the surfaces of constituent parts disposed around the polishing table. However, despite the rinsing with the cleaning liquid, some polishing liquid may remain and be dried on the surfaces of the constituent parts disposed around the polishing table. Once the polishing liquid is attached to and dried on the surfaces of the constituent parts, it is difficult to rinse off the dried polishing liquid with the cleaning liquid. Moreover, if the dried polishing liquid is deposited repeatedly, the dried polishing liquid may fall onto the polishing pad, thus causing a scratch on the substrate. 
     A top ring head cover that surrounds a top ring head having the top ring may be employed to protect the top ring head from the scattered polishing liquid. The polishing apparatus typically includes a dresser for dressing the polishing surface. A dressing head cover that surrounds a dressing head having the dresser may be employed to protect the dressing head from the scattered polishing liquid. Further, an atomizer cover that surrounds spray nozzle(s) of the atomizer may be employed to prevent dispersion of the mixed fluid or the polishing liquid that has bounced off the polishing pad. 
     The atomizer cover generally has a fairly complicated shape. As a result, a liquid containing the polishing liquid, which has bounced off the polishing pad, is likely to stay in the atomizer cover. In addition, since the atomizer cover has a number of corners where the liquid is likely to remain, it is generally difficult to clean an external surface of the atomizer cover with a cleaning liquid. If the liquid containing the polishing liquid is attached to and solidified on the atomizer cover, the solid matter may fall onto the polishing surface, thus contaminating the polishing surface. 
     It is difficult to completely prevent the scattered polishing liquid from flowing into the top ring head cover. Thus, the polishing liquid may enter the interior of the top ring head cover and stay there, thus contaminating the top ring head cover or the top ring head. Further, the polishing liquid may drop from the top ring head cover onto the polishing surface, thus contaminating the polishing surface. 
     SUMMARY OF THE INVENTION 
     It is a first object of the present invention to provide a polishing apparatus and a polishing method which can prevent a polishing liquid, scattered around a polishing table e.g., during polishing of a substrate, from being attached to and dried on surfaces of various constituent parts disposed around the polishing table to thereby prevent formation of scratches on a substrate surface. 
     It is a second object of the present invention to provide a polishing apparatus having an atomizer cover which can prevent a liquid, which has bounced off a polishing surface, from remaining on an inner surface of the atomizer cover, which is relatively easy to be cleaned with a cleaning liquid, and which can prevent a solid matter from falling onto and contaminating the polishing surface. 
     It is a third object of the present invention to provide a polishing apparatus having a top ring head cover which can prevent a polishing liquid from contaminating the top ring head cover or a top ring head even if the polishing liquid has entered the interior of the top ring head cover, and in addition can prevent the polishing liquid from dropping onto and contaminating a polishing surface. 
     An embodiment of the polishing apparatus includes: a rotatable polishing table for supporting a polishing pad having a polishing surface; a top ring head having a top ring configured to press a substrate against the polishing surface, the top ring being movable between a polishing position above the polishing table and a substrate transfer position beside the polishing table; a top ring head cover surrounding the top ring head; a dresser head having a dresser configured to dress the polishing surface, the dresser being movable between a dressing position above the polishing table and a retreated position beside the polishing table; a dresser head cover surrounding the dresser head; a spray nozzle configured to spray a cleaning liquid onto an upper surface of the top ring and an outer surface of the top ring head cover when the top ring is in the substrate transfer position; and a spray nozzle configured to spray a cleaning liquid onto an outer surface of the dresser head cover when the dresser is in the retreated position. 
     According to the above-described embodiment, when the top ring is in the substrate transfer position, the cleaning liquid is sprayed from the spray nozzle onto the upper surface of the top ring and the outer surface of the top ring head cover to keep these surfaces in a wet state. Further, when the dresser is in the retreated position, the cleaning liquid is sprayed from the spray nozzle onto the outer surface of the dresser head cover to keep this outer surface in a wet state. The polishing liquid can therefore be prevented from being attached to and dried on the upper surface of the top ring, the outer surface of the top ring head cover, and the outer surface of the dresser head cover. 
     In a preferred embodiment, the polishing apparatus may further include: an atomizer configured to spray a cleaning fluid onto the polishing surface to clean the polishing surface; and a spray nozzle configured to spray a cleaning liquid onto an outer surface of the atomizer. 
     According to this embodiment, the cleaning liquid is sprayed from the spray nozzle onto the outer surface of the atomizer when a substrate is not being polished, e.g., when the polishing surface is being cleaned with the cleaning fluid sprayed from the atomizer, or when the polishing surface is being dressed by the dresser. By thus keeping the outer surface of the atomizer in a wet state with the cleaning liquid, the polishing liquid can be prevented from being attached to and dried on the surface. 
     In a preferred embodiment, the polishing apparatus may further include a polishing liquid supply nozzle configured to supply a polishing liquid onto the polishing surface; and a spray nozzle configured to spray a cleaning liquid onto the polishing liquid supply nozzle. 
     According to this embodiment, the cleaning liquid is sprayed from the spray nozzle onto the polishing liquid supply nozzle when the substrate is not being polished, e.g., when the polishing surface is being cleaned with the cleaning fluid sprayed from the atomizer or when the polishing surface is being dressed by the dresser. By thus keeping the outer surface of the polishing liquid supply nozzle in a wet state with the cleaning liquid, the polishing liquid can be prevented from being attached to and dried on the surface. 
     In a preferred embodiment, the polishing apparatus may further include a spray nozzle configured to spray a cleaning liquid onto an inner surface of a chamber in which the polishing apparatus is housed. 
     According to this embodiment, the cleaning liquid is sprayed from the spray nozzle onto the inner surface of the chamber when the substrate is not being polished. By thus keeping the inner surface of the chamber in a wet state with the cleaning liquid, the polishing liquid can be prevented from being attached to and dried on the surface. 
     Another embodiment of the polishing method includes moving a top ring, holding a substrate, to a polishing position above a polishing table; rotating the polishing table; pressing the substrate against a polishing surface of a polishing pad on the polishing table by the top ring while supplying a polishing liquid from a polishing liquid supply nozzle onto the polishing surface to polish the substrate; moving the top ring, holding the polished substrate, from the polishing position to a substrate transfer position beside the polishing table; and spraying a cleaning liquid onto an upper surface of the top ring and an outer surface of a top ring head cover surrounding a top ring head having the top ring. 
     In a preferred embodiment, the polishing method may further include: moving a dresser to a dressing position above the polishing table when the top ring is in the substrate transfer position; pressing the dresser against the polishing surface to dress the polishing surface; moving the dresser from the dressing position to a retreated position beside the polishing table; and spraying a cleaning liquid onto an outer surface of a dresser head cover surrounding a dresser head having the dresser. 
     In a preferred embodiment, the polishing method may further include spraying a cleaning fluid from an atomizer onto the polishing surface to clean the polishing surface while spraying a cleaning liquid onto an outer surface of the atomizer when the substrate is not being polished. 
     In a preferred embodiment, the polishing method may further include spraying a cleaning liquid onto the polishing liquid supply nozzle when the substrate is not being polished. 
     Still another embodiment of the polishing apparatus includes: a rotatable polishing table for supporting a polishing pad having a polishing surface; an atomizer head configured to spray a cleaning fluid onto the polishing surface to clean the polishing surface; and an atomizer cover that covers an upper surface of the atomizer head. The atomizer cover includes a semicylindrical top plate having a semicylindrical shape, and a first side plate and a second side plate extending downward from both lower ends of the semicylindrical top plate. The semicylindrical top plate includes a first top plate having a vertical cross section in a shape of arc whose radius is constant over its entire length from a base end to a distal end of the atomizer cover, and a second top plate having a vertical cross section in a shape of arc whose radius decreases gradually from the base end toward the distal end of the atomizer cover. The first top plate and the second top plate are connected to each other at their top portions to constitute the semicylindrical top plate. 
     According to this embodiment, the atomizer cover has a smooth shape with no angular portion so that a liquid, which has come into contact with the inner or outer surface, will easily run down. Such a shape can prevent the contamination of the atomizer cover with a liquid containing the polishing liquid. Even if a liquid containing the polishing liquid has adhered to the atomizer cover, the liquid can be easily removed. It therefore becomes possible to prevent a liquid containing the polishing liquid from being solidified on the inner surface or the outer surface of the atomizer cover, thereby preventing a solid matter from falling onto and contaminating the polishing surface. 
     In a preferred embodiment, the semicylindrical top plate, the first side plate, and the second side plate are formed integrally from resin. 
     The atomizer cover, because of its smooth shape with no angular portion, can be produced by integral molding of a resin. 
     In a preferred embodiment, the semicylindrical top plate, the first side plate, and the second side plate are formed integrally from resin. 
     According to the embodiment, the atomizer cover can be designed so that a liquid, which has flowed down the semicylindrical top plate and one of the side plates, and reached the lower end surface of the side plate, is allowed to flow on the lower end surface in a direction from the distal end to the base end of the atomizer cover. 
     In a preferred embodiment, the second side plate is connected to the second top plate, and the second side plate is provided with a projecting portion projecting in a horizontal direction. 
     By providing the projecting portion integrally to the second side plate, the atomizer cover can be reinforced with the projecting portion. Furthermore, the projecting portion can prevent the disperse of the liquid. 
     In a preferred embodiment, the polishing apparatus may further include a top ring head having a top ring configured to press a substrate against the polishing surface while holding and rotating the substrate; and a top ring head cover surrounding the top ring head. The top ring head cover includes a side cover that surrounds the top ring head, and a lower cover that closes a bottom opening of the side cover. The lower cover includes a bottom plate inclined downwardly toward a radially outward direction of the polishing table when the top ring is in a polishing position above the polishing table. 
     According to this embodiment, the polishing liquid that has entered the interior of the top ring head cover reaches the bottom plate of the lower cover, flows on the inclined bottom plate, and is collected at a place lying beside the polishing table. This can prevent the polishing liquid from contaminating the top ring head cover and the top ring head, and dropping onto and contaminating the polishing surface. 
     In a preferred embodiment, the lower cover includes a side plate which extends upwardly from a peripheral portion of the bottom plate and which is in contact with or in proximity to a side plate of the side cover. 
     According to this embodiment, a coupling portion between the side cover and the lower cover can be located at a higher position than a corner between the side cover and the lower cover. This configuration can prevent the polishing liquid from remaining in the corner. 
     According to the above-described polishing apparatus, constituent parts disposed around the polishing table, such as the upper surface of the top ring, the outer surface of the top ring head cover, and the outer surface of the dresser head cover, can be kept in a wet state. Therefore, it is possible to prevent the polishing liquid from being attached to and dried on the constituent parts to thereby prevent the dried polishing liquid from falling onto the polishing table and causing a scratch on the substrate. 
     The above-described polishing apparatus can prevent the contamination of the atomizer cover with a liquid containing the polishing liquid. Even if a liquid containing the polishing liquid has adhered to the atomizer cover, the liquid can be easily removed. It therefore becomes possible to prevent a liquid containing the polishing liquid from being solidified on the inner surface or the outer surface of the atomizer cover to thereby prevent a solid matter from falling onto and contaminating the polishing surface. Further, even if the polishing liquid has entered the interior of the atomizer cover, the polishing liquid can be prevented from contaminating the top ring head cover or the top ring head and, in addition, can be prevented from dropping onto and contaminating the polishing surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a polishing apparatus according to an embodiment of the present invention when a top ring is in a polishing position above a polishing table and a dresser is in a dressing position above the polishing table; 
         FIG. 2  is a front view showing the polishing apparatus of  FIG. 1 , together with spray nozzles, when the top ring is in a substrate transfer position beside the polishing table and the dresser is in a retreated position beside the polishing table; 
         FIG. 3  is a plan view showing the polishing apparatus of  FIG. 1 , together with the spray nozzles, when the top ring is in the substrate transfer position beside the polishing table and the dresser is in the retreated position beside the polishing table; 
         FIG. 4  is a front view showing spray nozzles and an atomizer provided in the polishing apparatus shown in  FIG. 1 ; 
         FIG. 5  is a perspective view showing spray nozzles and a polishing liquid supply nozzle provided in the polishing apparatus shown in  FIG. 1 ; 
         FIG. 6  is a cross-sectional view showing a waterproof plate provided on a surrounding wall of a chamber; 
         FIG. 7  is a perspective view showing the polishing apparatus according to another embodiment of the present invention; 
         FIG. 8  is a front view of an atomizer cover, with an atomizer head depicted by imaginary line; 
         FIG. 9  is a bottom view of the atomizer cover; 
         FIG. 10  is a left side view of the atomizer cover of  FIG. 8 ; 
         FIG. 11  is a right side view of the atomizer cover of  FIG. 8 ; 
         FIG. 12  is an enlarged front view of a lower cover of a top ring head cover; 
         FIG. 13  is a cross-sectional view taken along line A-A in  FIG. 12 ; 
         FIG. 14  is a vertical cross-sectional view of a second dresser head cover; and 
         FIG. 15  is a perspective view showing details of the polishing liquid supply nozzle. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described with reference to the drawings.  FIG. 1  is a perspective view of a polishing apparatus according to an embodiment of the present invention.  FIG. 1  shows the polishing apparatus when a top ring  14  is in a polishing position above a polishing table  12  and a dresser  20  is in a dressing position above the polishing table  12 . Depiction of spray nozzles is omitted in  FIG. 1 . 
     As shown in  FIG. 1 , the polishing apparatus includes a polishing pad  10  whose upper surface serves as a polishing surface  10   a , a polishing table  12  with the polishing pad  10  attached to an upper surface thereof, a top ring head  16  having a top ring  14  for bringing a substrate (polishing object), such as a wafer, into sliding contact with the polishing surface (upper surface)  10   a  of the polishing pad  10  to polish the substrate, and a dresser head  22  having a dresser  20  for conditioning (or dressing) the polishing surface  10   a  of the polishing pad  10 . The polishing table  12  is coupled to a not-shown motor, so that the polishing table  12  and the polishing pad  10  are rotated in a direction shown by arrow by means of the motor. 
     Elements of the top ring head  16 , excepting the top ring  14 , are surrounded by a top ring head cover  24 . The top ring head  16  is coupled to an upper end of a rotatable top ring head pivot shaft  26 . This top ring head pivot shaft  26  extends upward through a bottom plate of the top ring head cover  24 . The top ring  14  is coupled to a lower end of a top ring drive shaft  28  that extends downward through the bottom plate of the top ring head cover  24 . The top ring  14  has a lower surface that constitutes a substrate holding surface for holding a substrate by e.g., vacuum suction. 
     As the top ring head  16  pivots by the rotation of the top ring head pivot shaft  26 , the top ring  14  moves between the polishing position just above the polishing table  12 , shown in  FIG. 1 , and a substrate transfer position beside the polishing table  12 , shown in  FIGS. 2 and 3 . 
     Elements of the dresser head  22 , excepting the dresser  20 , are surrounded by three dresser head covers: a first dresser head cover  30   a ; a second dresser head cover  30   b ; and a third dresser head cover  30   c . The dresser head  22  is coupled to an upper end of a rotatable dresser head pivot shaft  32  that extends upward through a bottom plate of the first dresser head cover  30   a . The dresser  20  is coupled to a lower end of a dresser drive shaft  38  that extends downward through a bottom plate of the second dresser head cover  30   b.    
     As the dresser head  22  pivots by the rotation of the dresser head pivot shaft  32 , the dresser  20  moves between the dressing position just above the polishing table  12 , shown in  FIG. 1 , and a retreated position beside the polishing table  12 , shown in  FIGS. 2 and 3 . 
     An atomizer  40  is disposed adjacent to the polishing table  12 . The atomizer  40  is configured to spray (or eject) a cleaning fluid, such as a liquid (e.g., pure water) or a mixed fluid of a liquid (e.g., pure water) and a gas (e.g., nitrogen gas), in a mist form onto the polishing surface  10   a  of the polishing pad  10  so as to clean the polishing surface  10   a . The atomizer  40  has its upper surface composed of an atomizer cover  42 . A large number of jet orifices (not shown) for emitting the cleaning fluid downward are provided in a lower surface of the atomizer  40  at predetermined intervals along a longitudinal direction of the atomizer  40 . The atomizer  40  is coupled to an upper end of an atomizer pivot shaft  44  so that, as the atomizer pivot shaft  44  rotates, the atomizer  40  pivots between a retreated position beside the polishing table  12 , shown by solid line in  FIG. 1 , and a cleaning position above the polishing table  12 , shown by imaginary line in  FIG. 1 . 
     A polishing liquid supply nozzle  46  is disposed adjacent to the polishing table  12 . The polishing liquid supply nozzle  46  is configured to supply a polishing liquid (or slurry) through a supply orifice  46   a , which is provided at a distal end thereof, onto the polishing surface  10   a  of the polishing pad  10 . The polishing liquid supply nozzle  46  is coupled to an upper end of a nozzle pivot shaft  48  so that, as the nozzle pivot shaft  48  rotates, the polishing liquid supply nozzle  46  pivots between a polishing liquid supply position, shown in  FIG. 1 , where the supply orifice  46   a  is located above the polishing table  12  and a retreated position (not shown) where the supply orifice  46   a  is located beside the polishing table  12 . In this embodiment the polishing liquid supply nozzle  46  is constituted by a single pipe  50  and a plurality of polishing liquid tubes housed in the pipe  50 . 
     The polishing table  12 , the top ring head  16 , the dresser head  22 , the atomizer  40 , and the polishing liquid supply nozzle  46  are coupled to an operation controller  5 , which is configured to control the operations of these elements. 
     As shown in  FIGS. 2 and 3 , the polishing apparatus is housed in a chamber  52 . Spray nozzles are disposed in the chamber  52  for spraying a cleaning liquid, such as pure water, onto an inner surface of the chamber  52 . More specifically, the spray nozzles include ceiling spray nozzles  54  for spraying a cleaning liquid onto a ceiling  52   a  and surrounding wall spray nozzles  56  for spraying a cleaning liquid onto a surrounding wall  52   b.    
     A top ring spray nozzle  58  is disposed in the chamber  52 . This top ring spray nozzle  58  is configured to spray a cleaning liquid onto the upper surface of the top ring  14  when the top ring  14  is in the substrate transfer position beside the polishing table  12 . The top ring spray nozzle  58  is disposed obliquely above the top ring  14  in the substrate transfer position. Further, spray nozzles for spraying a cleaning liquid onto the outer surface of the top ring head cover  24  are disposed in the chamber  52 . More specifically, an upper spray nozzle  60  is provided for spraying a cleaning liquid onto a polishing-table-side surface of the top ring head cover  24  from obliquely above, and a side spray nozzle  62  is provided for spraying a cleaning liquid horizontally toward the polishing-table-side surface of the top ring head cover  24 . The upper spray nozzle  60  has a large number of jet orifices  60   a  arranged horizontally along a longitudinal direction of the upper spray nozzle  60 . 
     Further, spray nozzles are disposed in the chamber  52  for spraying a cleaning liquid onto the outer surfaces of the dresser head covers  30   a ,  30   b ,  30   c  when the dresser  20  is in the retreated position beside the polishing table  12 . More specifically, an upper spray nozzle  64  is provided for spraying a cleaning liquid onto polishing-table-side surfaces of the dresser head covers  30   a ,  30   b ,  30   c  from obliquely above, and a side spray nozzle  66  is provided for spraying a cleaning liquid horizontally toward the polishing-table-side surfaces of the dresser head covers  30   a ,  30   b ,  30   c . The upper spray nozzle  64  has a large number of jet orifices  64   a  arranged horizontally along a longitudinal direction of the upper spray nozzle  64 . 
     As shown in  FIG. 4 , a bracket  70  is coupled to the upper end of the atomizer pivot shaft  44  so that the bracket  70  rotates together with the atomizer pivot shaft  44 . Spray nozzles  72  are mounted to the bracket  70 . These spray nozzles  72  are provided for spraying a cleaning liquid onto the atomizer cover  42  in its entirety both when the atomizer cover  42  is in the cleaning position and when the atomizer cover  42  is in the retreated position. Two spray nozzles  72  are provided in the illustrated embodiment. 
     As shown in  FIG. 5 , a bracket  74  is coupled to the upper end of the nozzle pivot shaft  48  so that the bracket  74  rotates together with the nozzle pivot shaft  48 . Spray nozzles  76  are mounted to the bracket  74 . These spray nozzles  76  are provided for spraying a cleaning liquid onto the polishing liquid supply nozzle  46  in its entirety, i.e., the outer surface of the pipe  50 , when the supply orifice  46   a  of the polishing liquid supply nozzle  46  is in the retreated position beside the polishing table  12 . Two spray nozzles  76  are provided in the illustrated embodiment. 
     The operations of the above-described spray nozzles  54 ,  56 ,  58 ,  60 ,  62 ,  64 ,  66 ,  72 ,  76 , including the start and stop of spraying of the cleaning liquid, are controlled by the operation controller  5 . 
     An operational sequence of the above-described polishing apparatus will now be described. The operational sequence is controlled by the operation controller  5  according to an operation recipe that is preset in the operation controller  5 . When the top ring  14  is in the substrate transfer position, the top ring  14  receives a substrate. The top ring  14  is then moved to the polishing position above the polishing table  12 . While the top ring  14  is rotating the substrate, the top ring  14  lowers the substrate and brings the substrate into contact with the polishing surface  10   a  of the rotating polishing pad  10 , so that the substrate is polished. During the polishing of the substrate, the polishing liquid is supplied onto the polishing surface  10   a  from the polishing liquid supply nozzle  46  that has been moved from the retreated position to the polishing liquid supply position. 
     After the polishing of the substrate is terminated, the top ring  14  is raised and then moved to the substrate transfer position beside the polishing table  12 . The polished substrate is transferred for the next process step. Simultaneously, the polishing liquid supply nozzle  46  is moved from the polishing liquid supply position to the retreated position. 
     After the polishing of the substrate is terminated, the dresser  20  is moved from the retreated position to the dressing position. While the dresser  20  is rotated, the dresser  20  is lowered to bring its lower surface into contact with the polishing surface  10   a  of the rotating polishing pad  10 , thereby rubbing and dressing the polishing surface  10   a . After the dressing of the polishing surface  10   a  is terminated, the dresser  20  is moved from the dressing position to the retreated position. 
     Further, the atomizer  40  is moved from the retreated position to the cleaning position. The cleaning fluid is then ejected from the atomizer  40  onto the polishing surface  10   a  of the polishing pad  10 , thereby cleaning the polishing surface  10   a . After the cleaning of the polishing surface  10   a  is terminated, the atomizer  40  is moved from the cleaning position to the retreated position. Although the atomizer  40  in this embodiment is configured to be movable from the cleaning position to the retreated position, the atomizer  40  may be fixed at the cleaning position. 
     When the top ring  14  is in the substrate transfer position, the cleaning liquid is sprayed onto the upper surface of the top ring  14  from the top ring spray nozzle  58  disposed obliquely above the top ring  14  and, at the same time, the cleaning liquid is sprayed onto the outer surface of the top ring head cover  24  from the upper spray nozzle  60  and the side spray nozzle  62 , which are disposed around the top ring head cover  24 , thereby keeping the upper surface of the top ring  14  and the outer surface of the top ring head cover  24  in a wet state with the cleaning liquid. Since these surfaces are kept in a wet state with the cleaning liquid, the polishing liquid, when it comes into contact with the wet surfaces, can be prevented from being attached to and dried on these surfaces. Further, since the cleaning liquid is sprayed from the top ring spray nozzle  58 , the upper spray nozzle  60 , and the side spray nozzle  62  when the top ring  14  is in the substrate transfer position, the cleaning liquid that has been once sprayed does not fall onto the polishing pad  10 , and therefore does not affect the polishing performance of the polishing pad  10 . 
     The spraying of the cleaning liquid from the top ring spray nozzle  58 , the upper spray nozzle  60 , and the side spray nozzle  62  is stopped before the top ring  14  moves from the substrate transfer position to the polishing position. In this manner, the operation controller  5  controls the start and stop of spraying the cleaning liquid from the spray nozzles  58 ,  60 ,  62  based on the position of the top ring  14 . 
     When the dresser  20  is in the retreated position beside the polishing table  12 , the cleaning liquid is sprayed onto the outer surfaces of the dresser head covers  30   a ,  30   b ,  30   c  from the upper spray nozzle  64  and the side spray nozzle  66  disposed around the dresser head covers  30   a ,  30   b ,  30   c , thereby keeping the outer surfaces of the dresser head covers  30   a ,  30   b ,  30   c  in a wet state. By thus keeping the surfaces in a wet state with the cleaning liquid, the polishing liquid, when it comes into contact with the wet surfaces, can be prevented from being attached to and dried on the surfaces. 
     The spraying of the cleaning liquid from the upper spray nozzle  64  and the side spray nozzle  66  is stopped before the dresser  20  moves from the retreated position to the dressing position. The operation controller  5  thus controls the start and stop of spraying the cleaning liquid from the upper spray nozzle  64  and the side spray nozzle  66  based on the position of the dresser  20 . 
     The cleaning liquid is sprayed from the spray nozzles  72  onto the outer surface of the atomizer cover  42  when a substrate is not being polished, e.g., when the polishing surface  10   a  is being cleaned with the cleaning fluid, such as the mixed fluid or the liquid, sprayed from the atomizer  40  in the cleaning position, or when the polishing surface  10   a  is being dressed by the dresser  20  while the atomizer  40  is in the retreated position. By thus keeping the outer surface of the atomizer cover  42  in a wet state with the cleaning liquid, the polishing liquid, when it comes into contact with the wet surface, can be prevented from being attached to and dried on the surface. 
     In particular, since the cleaning liquid is sprayed from the spray nozzles  72  onto the outer surface of the atomizer cover  42  when the polishing surface  10   a  is being cleaned with the cleaning fluid sprayed from the atomizer  40 , the cleaning fluid that has bounced off the polishing surface  10   a  can be prevented from attaching to the atomizer cover  42 . 
     The cleaning liquid is not sprayed onto the atomizer cover  42  when a substrate is being polished on the polishing pad  10 . In this manner, the operation controller  5  controls the start and stop of spraying of the cleaning liquid from the spray nozzles  72  based on whether a substrate is being polished or not. 
     As described above, the atomizer  40  may be fixed at the cleaning position and the spray nozzles  72  may spray the cleaning liquid onto the outer surface of the atomizer cover  42  when a substrate is not being polished. The cleaning liquid that covers the atomizer cover  42  can prevent a liquid, which has been scattered from the polishing pad  10  during dressing, from contacting the atomizer  40 . Although the cleaning liquid that has been sprayed from the spray nozzles  72  falls onto the polishing pad  10 , the fallen cleaning liquid is removed by the cleaning fluid that is being supplied simultaneously from the atomizer  40  to the polishing surface  10   a  and therefore does not remain on the polishing pad  10 . 
     The cleaning liquid is sprayed from the spray nozzles  76  onto the polishing liquid supply nozzle  46 , i.e., the pipe  50 , when the polishing liquid supply nozzle  46  is in the retreated position and a substrate is not being polished, e.g., when the polishing surface  10   a  is being cleaned with the cleaning fluid, such as the mixed fluid or the liquid, sprayed from the atomizer  40 , or when the polishing surface  10   a  is being dressed by the dresser  20 . By thus keeping the outer surface of the polishing liquid supply nozzle  46 , i.e., the pipe  50 , in a wet state with the cleaning liquid, the polishing liquid, when it comes into contact with the wet surface, can be prevented from being attached to and dried on the surface. 
     The spraying of the cleaning liquid from the spray nozzles  76  is stopped before the polishing liquid supply nozzle  46  moves from the retreated position to the polishing liquid supply position. In this manner, the operation controller  5  controls the start and stop of spraying the cleaning liquid from the spray nozzles  76  based on the position of the polishing liquid supply nozzle  46 . 
     In this embodiment the polishing liquid supply nozzle  46  is configured to be movable between the polishing liquid supply position and the retreated position. However, as with the above-described atomizer  40 , the polishing liquid supply nozzle  46  may be fixed at the polishing liquid supply position. In this case, the cleaning liquid may be sprayed onto the polishing liquid supply nozzle  46  in the polishing liquid supply position to keep it in a wet state e.g., when the polishing surface  10   a  is being cleaned with the cleaning fluid sprayed from the atomizer  40  or when the polishing surface  10   a  is being dressed by the dresser  20 . 
     When a substrate is not being polished, the cleaning liquid is sprayed from the ceiling spray nozzles  54  onto the ceiling  52   a  of the chamber  52 , and sprayed from the surrounding wall spray nozzles  56  onto the surrounding wall  52   b  of the chamber  52 , thereby keeping the ceiling  52   a  and the surrounding wall  52   b , constituting the inner surface of the chamber  52 , in a wet state. By thus keeping the inner surface in a wet state, the polishing liquid, when it comes into contact with the wet surface, can be prevented from being attached to and dried on the surface. 
     The cleaning liquid is not sprayed onto the ceiling  52   a  and the surrounding wall  52   b  of the chamber  52  when a substrate is being polished on the polishing pad  10 . The operation controller  5  thus controls the start and stop of spraying the cleaning liquid from the ceiling spray nozzles  54  and the surrounding wall spray nozzles  56  based on whether a substrate is being polished or not. 
     As shown in  FIG. 6 , a waterproof plate  84  may be provided at a predetermined position on the surrounding wall  52   b  of the chamber  52 . The waterproof plate  84  includes a flat support plate  80  and a plurality of return plates  82  mounted to the support plate  80  at predetermined intervals along the vertical direction. Each return plate  82  is inclined downward. The thus-constructed waterproof plate  84  can prevent bouncing of air flow coming from the polishing pad  10 . 
     According to the polishing apparatus of this embodiment, the constituent parts disposed around the polishing table  12 , such as the upper surface of the top ring  14 , the outer surface of the top ring head cover  24 , and the outer surfaces of the dresser head covers  30   a ,  30   b ,  30   c , can be kept in a wet state without any influence on processing, including polishing of the substrate. This structure can prevent the polishing liquid from being attached to and dried on the constituent parts disposed around the polishing table  12 , thus preventing the dried polishing liquid from falling onto the polishing table  12  and causing a scratch on the substrate. 
     Operations of the start and stop of spraying of the cleaning liquid from all of the above-described cleaning nozzles are carried out according to the operation recipe that is set in the operation controller  5 . The cleaning liquid, supplied from any of the spray nozzles onto a constituent part, can keep the constituent part in a wet state even when the polishing apparatus is in an idling operation (or a standby operation). The “idling operation” herein refers to a standby operation performed when polishing of a substrate is not carried out for a relatively long period of time. One example of the idling operation is a standby operation performed during a period of time from the completion of polishing of one lot of substrates to the start of polishing of the next lot of substrates. 
     In order to more effectively prevent the attachment of the polishing liquid, a water-repellent coating material may be applied to some or all of the constituent parts disposed around the polishing table  12 . 
       FIG. 7  is a perspective view showing the polishing apparatus according to another embodiment of the present invention. With reference to the construction and the operation of this embodiment which are the same as those of the above-described embodiment shown in  FIG. 1 , a duplicate description thereof will be omitted. Depiction of the operation controller  5  is omitted in  FIG. 7 . 
     As shown in  FIG. 7 , atomizer  40  includes an atomizer head  89  (see  FIG. 8 ) for spraying (or ejecting) a cleaning fluid, such as a liquid (e.g., pure water) or a mixed fluid of a liquid (e.g., pure water) and a gas (e.g., nitrogen gas), in a mist form onto the polishing surface  10   a  of the polishing pad  10  to clean the polishing surface  10   a , and atomizer cover  42  that covers an upper surface of the atomizer head  89 . A large number of spray nozzles  89   a  (see  FIG. 8 ) for emitting the cleaning fluid downward are provided in a lower surface of the atomizer head  89  at predetermined intervals in the longitudinal direction of the atomizer head  89 . The atomizer  40  is coupled to the upper end of the atomizer pivot shaft  44  so that, as the atomizer pivot shaft  44  rotates, the atomizer  40  pivots between the retreated position beside the polishing table  12 , shown by the solid line in  FIG. 7 , and the cleaning position above the polishing table  12 , shown by the imaginary line in  FIG. 7 . 
       FIGS. 8 through 11  show the atomizer cover  42 . In  FIGS. 8 and 9 , the left side of the atomizer cover  42  is a base end of the atomizer cover  42 , and the right side of the atomizer cover  42  is a distal end of the atomizer cover  42 . As shown in  FIGS. 8 through 11 , the atomizer cover  42  has a first top plate  90   a  having a vertical cross section in a shape of ¼ circle whose radius R 1  is constant, and a second top plate  90   b  having a vertical cross section in a shape of ¼ circle whose radius decreases gradually from the base end toward the distal end, i.e., a radius R 2  at the base end is larger than a radius R 3  at the distal end (R 2 &gt;R 3 ). A top portion of the first top plate  90   a  and a top portion of the second top plate  90   b  are connected to each other to constitute a semicylindrical top plate  90  having a semicylindrical shape. The semicylindrical top plate  90  has a semicircular vertical cross section. The atomizer cover  42  has two side plates, i.e., a first side plate  92  and a second side plate  94 , continuously extending vertically downward from both lower ends of the semicylindrical top plate  90 . An upper end of the first side plate  92  is integrally connected to the lower end of the first top plate  90   a , and an upper end of the second side plate  94  is integrally connected to the lower end of the second top plate  90   b.    
     The first top plate  90   a , the second top plate  90   b , and the side plates  92 ,  94  form an open-bottom space  96  inside the atomizer cover  42 . A vertical plane Y-Y represents an imaginary vertical plane that vertically passes through the top portions of the first top plate  90   a  and the second top plate  90   b  (i.e., the top portion of the semicylindrical top plate  90 ). In the interior space  96  of the atomizer cover  42 , a distance “a” from the vertical plane Y-Y to the first side plate  92  is constant, whereas a distance “b” from the vertical plane Y-Y to the second side plate  94  decreases gradually from the base end toward the distal end. The interior space  96  of the atomizer cover  42  is asymmetric with respect to the vertical plane Y-Y. As shown in  FIG. 8 , the atomizer head  89  is housed in the space  96  in such a state that the upper surface of the atomizer head  89  is covered with the atomizer cover  42 . The atomizer head  89  has the spray nozzles  89   a  for spraying the cleaning fluid, such as the liquid (e.g., pure water) or the mixed fluid of a liquid (e.g., pure water) and the gas (e.g., nitrogen gas), in a mist form onto the polishing surface  10   a  of the polishing pad  10  to clean the polishing surface  10   a.    
     While in this embodiment the first top plate  90   a  and the second top plate  90   b , each having the vertical cross section of ¼ circle, are connected together at their top portions to form the semicylindrical top plate  90 , a first top plate and a second top plate, each having a vertical cross section in a shape of arc, may be connected to each other at their top portions to form a semicylindrical top plate. 
     A projecting portion  98 , whose amount of outward projection decreases gradually from the base end toward the distal end, is formed integrally on the second side plate  94  that is connected to the second top plate  90   b . The projecting portion  98  functions to prevent the cleaning fluid, which has been sprayed from the spray nozzles  89   a  onto the polishing pad  10  and bounced off the polishing pad  10 , from diffusing in the chamber  52  (see  FIG. 2 ). The lower end surface  94   a  of the second side plate  94 , in its portion where the projecting portion  98  is not formed, and a lower end surface  98   a  of the projecting portion  98  are connected continuously. Although in this embodiment the projecting portion  98  is provided only on the second side plate  94  connected to the second top plate  90   b , it is possible to additionally provide a projecting portion on the first side plate  92  connected to the first top plate  90   a.    
     As shown in  FIG. 8 , the lower end surface  92   a  of the first side plate  92  is inclined downward with respect to a horizontal plane X-X in a direction from the distal end toward the base end of the atomizer cover  42 . Similarly, the lower end surface  94   a  of the second side plate  94  and the lower end surface  98   a  of the projecting portion  98 , connected to each other, are inclined downward in a direction from the distal end toward the base end of the atomizer cover  42 . 
     The atomizer cover  42  can be produced by integral molding of a resin, such as polyvinyl chloride. A draft angle in integral molding of the resin is, for example, 1.5°. Thus, in  FIG. 10 , a vertical portion  92 A of the first side plate  92  connected to the first top plate  90   a  and a vertical portion  92 B of the second side plate  94  connected to the second top plate  90   b  are not parallel to each other, and a distance between the vertical portion  92 A and the vertical portion  92 B gradually increases along a downward direction. The atomizer cover  42  thus has a shape that can be formed by integral molding of a resin. 
     A rectangular “Norseal”  100  is mounted to a distal-end-side back surface of the top plate  90  of the atomizer cover  42 , and a bolt mount  102  is mounted in a cutout which is formed in the base end. An elongated hole  102   a , extending in the longitudinal direction of the atomizer cover  42 , is formed in the bolt mount  102 . 
     The atomizer cover  42  is fixed with one bolt (not shown) at a predetermined position by inserting a shank of the bolt into the elongated hole  102   a  of the bolt mount  102 , and fastening the bolt to bring a head of the bolt into contact with the bolt mount  102 . The mounting position of the atomizer cover  42  in its longitudinal direction can be finely adjusted through the elongated hole  102   a.    
     The atomizer cover  42  has a smooth shape with no angular portion so that a liquid, which has come into contact with the inner or outer surface, can easily run down. Such a shape can prevent contamination of the atomizer cover  42  with a liquid including the polishing liquid. Moreover, even if the liquid including the polishing liquid has adhered to the atomizer cover  42 , the liquid can be easily removed. Furthermore, the atomizer cover  42 , because of its smooth shape with no angular portion, can be produced by integral molding of a resin. 
     As described above, the lower end surface  92   a  of the first side plate  92  connected to the first top plate  90   a  is inclined with respect to the horizontal plane X-X downwardly from the distal end toward the base end of the atomizer cover  42 . Similarly, the lower end surface  94   a  of the second side plate  94  connected to the second top plate  90   b  and the lower end surface  98   a  of the projecting portion  98  are inclined downward from the distal end toward the base end of the atomizer cover  42 . A liquid flows down from the semicylindrical top plate  90  to the side plates  92 ,  94  and also flows down the projecting portion  98  to reach the lower end surfaces  92   a ,  94   a  of the side plates  92 ,  94  and the lower end surface  98   a  of the projecting portion  98 . Because the lower end surfaces  92   a ,  94   a ,  98   a  are inclined with respect to the horizontal plane X-X, the liquid flows on the lower end surfaces  92   a ,  94   a ,  98   a  in the direction from the distal end to the base end of the atomizer cover  42 . 
     By providing the projecting portion  98  integrally on the second side plate  94  connected to the second top plate  90   b , the atomizer cover  42  can be reinforced with the projecting portion  98 . 
     As shown in  FIG. 7 , the top ring head cover  24  has a side cover  112  including a side plate  110 , and a lower cover  114  that closes a bottom opening of the side cover  112 .  FIG. 12  shows the details of the lower cover  114 . As shown in  FIG. 12 , the lower cover  114  includes a bottom plate  116  and a side plate  118 . The side plate  118  extends upwardly from a peripheral portion of the bottom plate  116  and surrounds, together with the side plate  110  of the side cover  112 , the top ring head  16 . The top ring  14  is coupled to the lower end of the top ring drive shaft  28  that extends downward through the bottom plate  116  of the lower cover  114 . 
     The bottom plate  116  of the lower cover  114  has such an inclination that, when the top ring  14  is in the polishing position above the polishing surface  10   a , the bottom plate  116  is inclined downwardly toward a radially outward direction of the polishing table  12 . Specifically, the bottom plate  116  of the lower cover  114  is inclined downward in a direction toward the top ring head pivot shaft  26 . 
     The polishing liquid that has entered the interior of the top ring head cover  24  reaches the bottom plate  116  of the lower cover  114 , flows on the inclined bottom plate  116 , and is collected in a place beside the polishing table  12 . The polishing liquid can thus be prevented from contaminating the top ring head cover  24  and the top ring head  16 , and dropping onto and contaminating the polishing surface  10   a.    
       FIG. 13  shows an enlarged cross-sectional view taken along line A-A in  FIG. 12 . As shown in  FIG. 13 , the upper end surface of the side plate  118  of the lower cover  114  is in contact with or in proximity to the lower end surface of the side plate  110  of the side cover  112 , and a “Norseal”  120  is attached to back surfaces of the side plate  118  and the side plate  110 . A gap between these side plates  110 ,  78  is sealed by the Norseal  120 . Such a structure makes it possible to locate a coupling portion between the side cover  112  and the lower cover  114  at a higher position than a corner between the side cover  112  and the lower cover  114 . If the coupling portion between the side cover  112  and the lower cover  114  exists in the corner, the polishing liquid is likely to remain on the corner. The construction shown in  FIG. 13  can solve such a drawback. Furthermore, the Norseal  120  can prevent intrusion of the polishing liquid into the top ring head cover  24 . 
       FIG. 14  shows a vertical cross-sectional view of the second dresser head cover  30   b . As shown in  FIG. 14 , the second dresser head cover  30   b  includes an upper side plate  122  and a lower side plate  124  each having approximately a cylindrical shape. A lower end surface of the upper side plate  122  is in contact with or in proximity to an upper end surface of the lower side plate  124 , and a tape  126  is attached to outer circumferential surfaces of the upper side plate  122  and the lower side plate  124 . A gap between the upper side plate  122  and the lower side plate  124  is sealed by the tape  126 . A buffer material  132  is disposed between a protrusion  128 , mounted to an inner circumferential surface of the upper side plate  122 , and a protrusion  130  mounted to an inner circumferential surface of the lower side plate  124 . With such a structure, a coupling portion between the upper side plate  122  and the lower side plate  124  can be located at a higher position and, in addition, a liquid can be prevented from intruding into the second dresser head cover  30   b.    
     A curved-surface portion  120   a , which smoothly connects a vertical portion to a horizontal portion of the upper side plate  122 , is formed at an upper portion of the upper side plate  122 . The curved-surface portion  120   a  allows liquid droplets to flow smoothly on the outer surface of the upper side plate  122 . 
     The first dresser head cover  30   a  may have the same construction as the second dresser head cover  30   b.    
       FIG. 15  shows the details of the polishing liquid supply nozzle  46 . As shown in  FIG. 15 , the polishing liquid supply nozzle  46  includes the pipe  50  and a plurality of polishing liquid tubes  134  housed in the pipe  50 . Such a structure can prevent intrusion of the polishing liquid into gaps between the polishing liquid tubes  134  and can enhance the cleaning efficiency of the polishing liquid supply nozzle  46 . 
     The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims.