Abstract:
A carrier comprising a disk-shaped body portion having fluid circulation holes, a ring-shaped diaphragm portion expanding outward from the outer peripheral surface of the body portion and having pliability, a ring-shaped edge portion projecting at least downward from an outer edge portion of the diaphragm portion and having an inner diameter of at least an outer diameter of a work piece, a pliable sheet having an outer peripheral portion affixed air tightly to a bottom end portion of said edge portion, the back surface of the sheet defining a single pressure chamber communicating with the fluid circulation holes, and a ring-shaped member surrounding the work piece affixed to the bottom surface of the sheet.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a carrier and a chemical mechanical polishing (CMP) apparatus for uniformly polishing the surface of a rotating wafer or other workpiece while pressing the workpiece against a polishing pad of a platen. 
     2. Description of the Related Art 
     FIG. 15 is a sectional view of a carrier of a general CMP apparatus. 
     As shown in FIG. 15, a CMP apparatus is provided with a carrier  100  and with a platen  110  to which a polishing pad  111  is attached. By making the carrier  100  and the platen  110  rotate by a rotating mechanism while supplying a polishing solution in a state with the wafer W pressed against the platen  110  side by a carrier base  101  of the carrier  100 , the surface of the wafer W is polished by the polishing pad  111 . 
     Further, this CMP apparatus polishes the wafer W by the back side reference polishing system. Thus, a backing pad  102  is attached to the carrier base  101  and the surface of the wafer W is polished with the backing pad  102  in contact with the back surface of the wafer W. 
     Even if the sectional shapes of the backing pad  102  and the polishing pad  111  are uniform, there is sometimes warping or undulations in the wafer W itself. As opposed to this, the CMP apparatus shown in FIG. 15 is not structured to deal with such warping or undulations in the wafer W, so it is not possible to uniformly press the surface of the wafer W as a whole. 
     Therefore, the carrier of the CMP apparatus of the air pressurizing system shown in FIG. 16 has been devised. 
     A carrier  300 , as shown in the figure, provides a ring-shaped projecting portion  302  at the outer peripheral portion of the bottom surface of a carrier base  301 . By using a double-sided adhesive tape  304  to attach a backing pad  307  to the bottom surface of the projecting portion  302 , a pressure chamber  306  is defined. 
     In this configuration, air arriving through air holes in the carrier base  301  is introduced into the pressure chamber  306  to uniformly press the wafer W through the backing pad  307  by the air pressure in the pressure chamber  306 . 
     The above CMP apparatus of the related art, however, suffered from the following problems. 
     In the carrier  300  of the CMP apparatus according to the above related art, it is possible to press the entire surface of the wafer W by a uniform air pressure, but there was a large range of over polishing at the outer peripheral portion of the wafer W and the yield was remarkably poor. 
     FIG. 17 is an enlarged sectional view of the state of over polishing. 
     As shown in FIG. 17, this carrier  300  is structured with the wafer W covered by the backing pad  307  adhered to the projecting portion  302  of the carrier base  301 , so if a downward pressing force is applied to the carrier  300  during the polishing work, the outer peripheral portion of the backing pad  307  will be pulled downward by the projecting portion  302 . 
     Therefore, a tension T occurs at the outer peripheral portion of the backing pad  307  and a pressure of the vertical component T 1  of the tension T is applied to the outer peripheral portion of the wafer W in addition to the air pressure P. 
     As a result, the polishing rate of the outer peripheral portion of the wafer W becomes remarkably larger than the polishing rate of the other portions, the range of over polishing L becomes as larger as 10 mm to 20 mm, and the yield of the wafer W ends up becoming remarkably poor. 
     SUMMARY OF THE INVENTION 
     The present invention was made so as to solve the above problems and has as its object to provide a carrier and CMP apparatus which make uniform the distribution of pressure applied to the surface of the workpiece, including the outer peripheral portion, and improve the uniformity of polish of the entire surface of the workpiece. 
     Therefore, and according to a preferred embodiment of the presnt invention, there is provided a carrier comprising: a disk-shaped body portion having fluid circulation holes; a ring-shaped diaphragm portion expanding outward from the outer peripheral surface of the body portion and having pliability; a ring-shaped edge portion projecting at least downward from an outer edge portion of the diaphragm portion and having an inner diameter of at least an outer diameter of a workpiece; a pliable sheet having an outer peripheral portion affixed air-tightly to a bottom end portion of the edge portion and defining a pressure chamber communicating with the fluid circulation holes; and a ring-shaped member surrounding the workpiece affixed to the bottom surface of the sheet. 
     In this configuration, if the body portion is pressed in a state where the workpiece on the platen is held by the ring-shaped member of the carrier, the sheet contacts substantially the entire surface, essentially molding itself to the warping etc. of the workpiece. If fluid of a predetermined pressure is supplied from the fluid circulation holes of the body portion in this state, the fluid will pass through the fluid circulation holes of the body portion and fill the pressure chamber and substantially the entire surface of the workpiece will receive a uniform fluid pressure through the sheet. 
     If the body portion of the carrier is pressed, however, the downward pressing force will be transmitted to the edge portion as well and the edge portion will act to pull the outer peripheral portion of the sheet downward. Since the edge portion is connected to the body portion through the pliable diaphragm portion, however, the pliable diaphragm portion will flex and the pressing force applied to the edge portion will be relieved. Therefore, no downward tension will occur at the outer peripheral portion of the sheet and the distribution of pressure of the fluid acting on the entire surface of the workpiece will become uniform. 
     Further, since the workpiece is surrounded by the ring-shaped member, the workpiece will not jump outside when the carrier is rotating. 
     For a sheet, it is possible to use various types of pliable sheets. According to a preferred embodiment of the invention, the sheet is formed by a single hard or soft sheet and the outer peripheral portion of the upper surface of the hard or soft sheet is affixed air-tightly to the bottom surface of the edge portion by an insoluble adhesive or soluble adhesive. 
     Further, according to another embodiment of the invention, a soft sheet is adhered to the bottom surface of a hard sheet. 
     Further, according to yet another embodiment of the invention, the hard and the soft sheets are adhered through an intermediate sheet having an adhesive on its upper and lower surfaces. 
     If a fluid is supplied inside the rotating air-tight pressure chamber, however, the fluid pressure at the outer peripheral portion of the pressure chamber may differ from the fluid pressure at other portions. Therefore, according to another embodiment of the invention, the edge portion is provided with through holes communicating the pressure chamber and the outer portion. 
     In this configuration, the fluid flowing from the fluid circulation holes into the pressure chamber flows out from the through holes to the outside, the flow of the fluid in the pressure chamber is stabilized, and the uniformity of distribution of pressure is further improved. 
     Further, according to another embodiment of the invention, the diaphragm portion at locations near the edge portion is provided with holes communicating the pressure chamber and an outer portion. 
     CMP apparatuses using the carrier also stand as aspects of the invention in their own right. Therefore, according to another embodiment of the invention, there is provided a CMP apparatus provided with a platen to the surface of which a polishing pad is attached, a carrier capable of rotating in a state where the workpiece on the polishing pad of the platen is held, a fluid supply means capable of supplying fluid of a desired pressure to the carrier, and a rotary drive means for rotating the carrier while pressing against it, wherein the carrier is comprised of a disk-shaped body portion having fluid circulation holes through which a fluid supplied from the fluid supply means can enter and exit; a ring-shaped diaphragm portion expanding outward from the outer peripheral surface of the body portion and having pliability; a ring-shaped edge portion projecting at least downward from an outer edge portion of the diaphragm portion and having an inner diameter of at least an outer diameter of a workpiece; a pliable sheet having an outer peripheral portion affixed air-tightly to a bottom end portion of the edge portion and defining a pressure chamber communicating with the fluid circulation holes; and a ring-shaped member surrounding the workpiece affixed to the bottom surface of the sheet. 
     Further, according to another embodiment of the invention, the edge portion of the carrier is provided with through holes communicating the pressure chamber and the outer portion. 
     Further, according to yet another embodiment of the invention, the diaphragm portion at a location near the edge portion is provided with holes communicating the pressure chamber and an outer portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, and advantages of the present invention will become more readily apparent from the following description of presently preferred embodiments of the invention taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a partial cutaway front view of a CMP apparatus according to a first embodiment of the present invention; 
     FIG. 2 is a sectional view of the structure of a rotary drive mechanism; 
     FIG. 3 is a sectional view of the structure of a carrier; 
     FIG. 4 is a disassembled perspective view of the carrier; 
     FIG. 5 is a front view of the state of wafer suction; 
     FIG. 6 is a sectional view of the state of the hard sheet and soft backing sheet molding against the unevenness of the wafer; 
     FIG. 7 is a partial enlarged sectional view of the state of flexing of the diaphragm; 
     FIG. 8 is a partial enlarged sectional view of the state of flexing of the diaphragm when the carrier is inclined; 
     FIG. 9 is a sectional view of a carrier of a CMP apparatus according to a second embodiment of the present invention; 
     FIG. 10 is a partial enlarged sectional view of the waist portion of the carrier shown in FIG. 9; 
     FIG. 11 is a sectional view of a first modification of the embodiment; 
     FIG. 12 is a sectional view of a second modification of the embodiment; 
     FIG. 13 is a sectional view of a third modification of the embodiment; 
     FIG. 14 is a sectional view of a fourth modification of the embodiment; 
     FIG. 15 is a sectional view of the carrier of a general CMP apparatus; 
     FIG. 16 is a sectional view of a carrier of an air-pressurizing type CMP apparatus of the related art; and 
     FIG. 17 is an enlarged sectional view of the state of over polishing. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be explained below with reference to the drawings. 
     (First Embodiment) 
     FIG. 1 is a partially cutaway front view of a CMP apparatus according to a first embodiment of the present invention. 
     As shown in FIG. 1, this CMP apparatus is provided with a platen  110  having a polishing pad  111  attached to its surface, a carrier  1 , a rotary drive mechanism  8  serving as the rotary drive means, and an air pump  9  serving as a fluid supply means. 
     The platen  110  is designed to be driven to rotate by a main motor  112  inside the apparatus housing. 
     That is, a belt  118  is wound around a pulley  114  attached to the main motor  112  and a pulley  117  attached to an input shaft  116  of a transmission  115 . The platen  110  is attached to an output shaft  119  of the transmission  115 . 
     Due to this, the rotation of the main motor  112  is transmitted to the pulley  117 , the rotation of the pulley  117  is converted in speed by the transmission  115  and transmitted to the output shaft  119 , and the platen  110  is rotated at a predetermined speed. 
     The rotary drive mechanism  8  is a mechanism for making the carrier  1  rotate while pressing against it and is provided with a cylinder  80  and a motor  84 . 
     FIG. 2 is a sectional view of the rotary drive mechanism  8 . 
     As shown in FIG. 2, the cylinder  80  is comprised of a piston rod  82  passing through a cylinder body  81  and a piston  83  air-tightly fitting in the cylinder body  81  in a state affixed to the outer side of the piston rod  82 . 
     Due to this, by adjusting the air pressure in the cylinder body  81 , it is possible to make the piston rod  82  move up and down integrally with the piston  83  and adjust the pressing force on the carrier  1 . 
     On the other hand, the motor  84  is linked with the piston rod  82  of the cylinder  80 . That is, a gear  85  of the shaft of the motor  84  is engaged with a gear  87  attached through a bearing  86  at the upper portion of the piston rod  82 . The upper end of the cylindrical inner rod  89  is affixed to a support member  88  affixed to the upper surface of the gear  87 . 
     Due to this, when the motor  84  is driven, the rotation is transmitted to the inner rod  89  through the gears  85  and  87  and the support member  88  and the inner rod  89  rotates at a predetermined speed in the piston rod  82 . 
     The carrier  1  is structured to be able to rotate in a state where the wafer W on the polishing pad  111  of the platen  110  is held and is attached to the lower end portion of the piston rod  82 . 
     FIG. 3 is a sectional view of the structure of the carrier  1 , while FIG. 4 is a disassembled perspective view of the same. 
     As shown in FIG.  3  and FIG. 4, the carrier  1  is provided with a housing  10 , a carrier base  11 , a sheet supporter  13 , a hard sheet  18 , a soft backing sheet  19 , and a collar  20  as a ring-shaped member. 
     The housing  10 , as shown in FIG. 3, has a rotatable connecting member  10   a  at its center portion. The lower end portion of the piston rod  82  is connected to this connecting member  10   a.  Further, this housing  10  has an internal gear  10   b  at the bottom side of the connecting member  10   a . The internal gear  10   b  engages with an external gear  89   a  formed at the lower end side of the inner rod  89  passing through a center hole of the connecting member  10   a.    
     Due to this, when the inner rod  89  rotates by being driven by the motor  84 , the rotational force of the motor  84  is transmitted to the housing  10  by the engagement of the internal gear  10   b  and the external gear  89   a.    
     The carrier base  11  is affixed by screws  1   a  to the bottom surface of the housing  10 . A plurality of grooves  11   a  are formed in its bottom surface. At the intersections of these grooves  11   a  are formed air exits/inlets  11   b  allowing the exit and entry of air from the previously mentioned air pump  9 . Further, a guard  11   h  is formed at the outer periphery of the bottom surface of the carrier base  11 . 
     The sheet supporter  13  is formed from a material such as polyvinyl chloride (PVC) and, as shown in FIG. 3, is affixed to the bottom surface of the carrier base  11  by screws  1   c.    
     The sheet supporter  13  is formed by a supporter body  14  (body portion), diaphragm  15  (diaphragm portion), and edge ring  16  (edge portion). 
     Specifically, the supporter body  14  forms a disk shape and is directly affixed to the bottom surface of the carrier base  11  by screws  1   c . Further, a plurality of holes  14   a  (fluid circulation holes) formed in the supporter body  14  are communicated through the grooves  11   a  with the air exit/inlets  11   b . Further, an O-ring  11   e  is fitted to the outside of the grooves  11   a . Due to this O-ring lie, the air-tightness between the carrier base  11  and the supporter body  14  is held and the air inside the grooves  11   a  is prevented from leaking outside. 
     The diaphragm  15  extends outward substantially horizontally from the lower end of the outer peripheral surface-of the supporter body  14  and forms a ring shape overall. The thickness of this diaphragm  15  is set to a value in the range of for example 0.5 mm to 2.0 mm. The diaphragm  15  can flex up and down. 
     The edge ring  16  is formed in a ring shape along the outer edge portion of the diaphragm  15  and is comprised of an upper projecting portion  16   b  and a lower projecting portion  16   a  projecting in the upward and downward directions. The lower projecting portion  16   a  is positioned at the outside of the wafer W. That is, the inner diameter of the lower projecting portion  16   a  is set to be larger than the outer diameter of the wafer W. As opposed to this, the inner diameter of the upper projecting portion  16   b  is set substantially equal to the outer diameter of the wafer W. Further, the upper surface of the upper projecting portion  16   b  is positioned exactly a predetermined distance down from the bottom, surface of the carrier base  11  in the initial state and forms a gap A between the upper surface of the upper projecting portion  16   b  and the bottom surface of the carrier base  11 . The outer diameter of the edge ring  16  is set smaller than the inner diameter of the guard  11   h  of the carrier base  11 . A gap B is formed between the outer peripheral surface of the edge ring  16  and the inner peripheral surface of the guard  11   h.    
     The hard sheet  18  is formed by a fusible material such as polyvinyl chloride, polyethylene, polyacrylate, and polycarbonate. The soft backing sheet  19  is formed by a soft material such as a silicone rubber, polyurethane foam, fluororubber, and nitrile rubber. 
     The hard sheet  18  and the soft backing sheet  19  are bonded together in the state with the hard sheet  18  at the top. They form a circular shape with a diameter substantially equal to that of the lower projecting portion  16   a  of the edge ring  16 . 
     Further, the outer peripheral portion of the upper hard sheet  18  is affixed air-tightly by a nonsoluble adhesive or soluble adhesive to the bottom surface of the lower projecting portion  16   a  of the edge ring  16 . 
     Due to this, a pressure chamber R communicating with the through holes  14   a  of the supporter body  14  is defined between the hard sheet  18  and the sheet supporter  13 . When the soft backing sheet  19  contacts the wafer W, the hard sheet  18  and the soft backing sheet  19  flex molding against the warping, undulation, etc. of the wafer W. 
     Note that reference numeral  17  indicates wafer suction holes passing through the hard sheet  18  and the soft backing sheet  19 . 
     The collar  20  is a member for holding the wafer W. The outer diameter of the collar  20  is set substantially equal to the inner diameter of the lower projecting portion  16   a  of the edge ring  16 , while the inner diameter of the collar  20  is set substantially equal to the outer diameter of the wafer W. Further, the outer peripheral surface of the collar  20  is bonded to the lower surface of the soft backing sheet  19  so as to substantially match the inner peripheral surface of the lower projecting portion  16   a .The thickness of the collar  20  is set to not more than ½ of the thickness of the wafer W and holds the upper portion of the outer peripheral surface of the wafer W. 
     On the other hand, the air pump  9  shown in FIG.  1  and FIG. 2 supplies air of a desired pressure into the above pressure chamber R of the carrier  1  to make the inside of the pressure chamber R a positive pressure or sucks air inside of the pressure chamber R out to make the inside of the pressure chamber R a negative pressure. Specifically, an air hose  90  is inserted through the inner rod  89  and, as shown in FIG. 3, has a front end portion fit into the air exit/inlet  11   b  of the carrier base  11 . 
     Next, an explanation will be given of the operation of the CMP apparatus of this embodiment. 
     The wafer W is held by the carrier  1  and conveyed on the polishing pad  111  of the platen  110 , as shown in FIG. 5, by driving the air pump  9  to suck air in a state with the wafer W brought into contact against the bottom surface of the soft backing sheet  19  (see FIG.  3 ). 
     This being so, the air in the pressure chamber R and the suction holes  17  of the carrier  1  shown in FIG. 3 is sucked out through the air hose  90 . The inside of the pressure chamber R becomes a negative pressure and the wafer W is sucked against the soft backing sheet  19  through the suction holes  17 . 
     In this state, the cylinder  80  is driven and the piston rod  82  is made to descend until the wafer W contacts the polishing pad  111 , then the wafer W is pressed against the polishing pad  111  by a predetermined pressing force F. 
     Suitably thereafter, the air pump  9  is driven to supply air, air is sent from the air hose  90  to the inside of the pressure chamber R, and the inside of the pressure chamber R is made a positive pressure. 
     This being done, as shown in FIG. 6, the hard sheet  18 , soft sheet  19 , and polishing pad  111  deform molding against the unevenness etc. of the wafer W, a uniform air pressure P is applied over substantially the entire upper surface of the wafer W, and the polishing pad  111  molds against the unevenness etc. of the lower surface of the wafer W. 
     In this state, if the motors  84  and  112  shown in FIG. 1 are driven and the carrier  1  and platen  110  are made to rotate in mutually opposite directions while supplying a not shown polishing solution, the bottom surface of the wafer W is polished by the rotating polishing pad  111 . 
     At the time of this polishing, the pressing force F applied to the carrier  1  by the cylinder  80  is applied to the sheet supporter  13  and is applied through the air in the pressure chamber R to the hard sheet  18  and the soft backing sheet  19 . 
     Therefore, if the edge ring  16  is directly connected to the supporter body  14  like the conventional carrier  300  shown in FIG. 16, as shown in FIG. 17, the edge ring  16  pulls the outer peripheral portion of the hard sheet  18  downward and the polishing rate of the outer peripheral portion of the wafer W ends up becoming higher. 
     In the carrier  1  of the CMP apparatus of this embodiment, however, since the edge ring  16  is connected through the pliable diaphragm  15  to the supporter body  14 , as shown in FIG. 7, at the time of pressing of the carrier  1 , the upward resistance from the hard sheet  18  is applied to the edge ring  16  and at the same time the diaphragm  15  flexes upward. Accordingly, the outer peripheral portion of the hard sheet  18  will never be pulled downward, though it might be pulled upward. Therefore, no downward tension occurs at the outer peripheral portion of the hard sheet  18  and uniform air pressure P and component force f of the pressing force F act on the outer peripheral portion of the wafer W in the same way as at the center portion. As a result, uniform polishing of the entire surface of the wafer W, including the outer peripheral portion of the wafer W, becomes possible. 
     When there is unevenness in the surface of the polishing pad ill of the platen  110 , however, the carrier  1  will sometimes incline somewhat in accordance with that unevenness. 
     At this time, as shown in FIG. 8, the large resistance F 1  will act at the lowered portion of the edge ring  16 , but in this case as well, the diaphragm  15  will flex and the resistance F 1  will be relieved, so the polishing rate of the outer peripheral portion of the wafer W will not become higher. 
     Further, even if the carrier inclines somewhat, since the wafer is held by the collar  20  from the outside, it will not jump out to the outside of the carrier  1 . 
     Further, since the diaphragm  15  and the hard sheet  18  are pliable, if the pressure P in the pressure chamber R rises, the diaphragm  15  and the hard sheet  18  will both warp upward and the force applied to the outer peripheral portion of the wafer W will become smaller. 
     Accordingly, it is possible to adjust the polishing rate of the outer peripheral portion of the wafer W by controlling the air pressure P in the pressure chamber R. 
     (Second Embodiment) 
     FIG. 9 is a sectional view of a carrier of a CMP apparatus according to a second embodiment of the present invention and is a partial enlarged sectional view of the essential portions. 
     This embodiment differs from the above first embodiment in the point that holes  15   a  are made in the diaphragm  15  of the sheet supporter  13 . 
     In the carrier  1  shown in FIG. 3, if air continues to be supplied inside the air-tight pressure chamber R, since the carrier  1  is rotating at a high speed, the air in the pressure chamber R will move to the outer peripheral portion side of the pressure chamber R due to the centrifugal force and the air density at the outer peripheral portion of the pressure chamber R may become higher or turbulence will occur in the outer peripheral portion and the air pressure P applied to the outer peripheral portion of the hard sheet  18  may become higher than the other portions. 
     Therefore, in this embodiment, as shown in FIG. 10, holes  15   a  are made in diaphragm  15  at locations near the edge ring  16 . 
     Due to this, the air supplied inside the pressure chamber R, as shown by the arrows in FIG. 9, flows toward the outer peripheral portion side of the pressure chamber R and flows out from the holes  15   a  through the gaps A and B to the outside of the carrier  1 . Therefore, the air density in the pressure chamber R becomes uniform because a stable air circulation route of a substantially laminar state air is formed in the pressure chamber R. As a result, the air pressure P is applied uniformly over the entire surface of the hard sheet  18 . 
     Therefore, according to this embodiment, it is possible to make the distribution of the air pressure P in the pressure chamber R reliably uniform and possible to further improve the uniformity of polish of the wafer W. 
     The rest of the configuration and the mode of operation and advantageous effects are similar to those of the first embodiment explained above, so explanations thereof will be omitted. 
     Note that the present invention is not limited to the above embodiments and include various modifications and changes within the scope of the gist of the invention. 
     For example, in the above embodiments, air was used as the fluid, but it is also possible to use a liquid such as oil and press uniformly against the wafer W by oil pressure etc. 
     Further, in the above embodiments, as the pliable sheet, a double-layer structure sheet comprised of the hard sheet  18  and the soft backing sheet  19  was used, but as shown in FIG. 11, it is also possible to arrange either of the hard sheet  18  or soft backing sheet  19  at the bottom surface of the edge ring  16  and affix the outer peripheral portion of the upper surface of the sheet air-tightly to the edge ring  16  by a nonsoluble adhesive or soluble adhesive. 
     Further, as shown in FIG. 12, the hard sheet  18  and the soft backing sheet  19  are adhered together by an intermediate sheet  89  such as a double-sided adhesive tape and the outer peripheral portion of the upper surface of the hard sheet  18  is affixed air-tightly to the edge ring  16  by a nonsoluble adhesive or soluble adhesive. 
     Further, in the above embodiments, the inner diameter of the lower projecting portion  16   a  of the edge ring  16  was set larger than the outer diameter of the wafer W, but it may be set to be substantially equal as well. 
     Further, in the above embodiments, the width of the collar  20  was set to be substantially equal to the distance between the inner peripheral surface of the lower projecting portion  16   a  of the edge ring  16  and the outer peripheral surface of the wafer W, but as shown in FIG. 13, it is also possible to affix the wide width collar  21  extending from the outer peripheral surface of the wafer W to the outer peripheral surface of the edge ring  16  to the bottom surface of the soft backing sheet  19 . Note that in this case, as shown in the figure, it is preferable to form notches  21   a  at corresponding locations at the inner peripheral surface of the lower projecting portion  16   a  so that the diaphragm  15  can easily flex. 
     Further, in the above second embodiment, air relief holes  15   a  were formed in the diaphragm  15 , but as shown in FIG. 14, substantially the same advantageous effects can be obtained by making through holes  16   d  communicating the pressure chamber R and the outside of the carrier  1  at the bottom portion of the lower projecting portion  16   a  of the edge ring  16 . 
     As explained above in detail, according to the aspects of the invention, since the pliable diaphragm portion flexes and the pressing force applied to the edge portion is relieved when pressing the carrier, it is possible to prevent occurrence of downward tension on the outer peripheral portion of the sheet. As a result, it is possible to apply fluid pressure uniformly across the entire surface of the workpiece, including the outer peripheral portion, so there is the advantageous effect that it is possible to improve the uniformity of polish of the workpiece. Further, since the workpiece is surrounded by a ring-shaped member, it is possible to prevent the workpiece from jumping out when the carrier is rotating. 
     Further, according to the aspects of the invention, since it is possible to stabilize the flow of fluid in the pressure chamber, it is possible to further improve the uniformity of the distribution of pressure and as a result to further improve the uniformity of polish of the workpiece.