Abstract:
There is provided a polishing apparatus comprising an attitude controller for controlling an attitude or orientation of a turntable having a polishing surface and/or a carrier for holding an article to be polished in a sliding contact relation with the polishing surface. The turntable and carrier are connected to their drive shafts through universal joints. The attitude controllers control angles of tilting of the turntable and the carrier relative to their drive shafts.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a polishing apparatus for polishing an article such as a semiconductor wafer, and in particular, relates to a polishing apparatus provided with an attitude controller for controlling an attitude of a turntable which is provided with a polishing surface and/or a carrier for carrying an article to be polished and bringing it into contact with the polishing surface of the turntable. 
     With recent rapid progress in technology for fabricating high-integration semiconductor devices, circuit wiring patterns have been becoming increasingly fine, with spaces between wiring patterns also decreasing. As wiring spacing decreases to less than 0.5 microns, the depth of focus in circuit pattern formation in photolithography and 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 or planarization. As one method for effecting such planarization, for example, a chemical/mechanical polisher (CMP) has recently been used, in which polishing is carried out while a polishing solution having a predetermined chemical composition is supplied. 
     FIG. 26 shows such a conventional polisher for polishing a semiconductor wafer. The polisher includes a turntable  52  provided on its upper surface with a polishing cloth  51  and a wafer carrier  54  for holding a semiconductor wafer  53 . In a polishing operation, the turntable and the wafer carrier are independently rotated about their axes by motors (not shown) while the wafer  53  is engaged with the polishing cloth  51  and an abrasive liquid Q is supplied through a nozzle  57  provided above the turntable. However, during polishing, if the polishing cloth  51  does not engage with the wafer  53  under a uniform pressure across respective engaging surfaces, the wafer fails to be polished evenly. To solve this problem, the conventional polishing apparatus is provided with a universal joint comprising a ball bearing  56  between the wafer carrier  54  and a drive shaft  55  for pressing the wafer  53  against the polishing cloth  51  while drivingly rotating the wafer carrier  54 . The universal joint enables the wafer  54  to tilt about the ball bearing  56  in response to inclinations in the polishing surface of the polishing cloth  51 . Consequently, the polishing surface of the polishing cloth  51  and the polished surface of the wafer  53  held by the wafer carrier  54  are kept in a parallel relation with each other, whereby pressure between the wafer and the polishing cloth is kept even across the entire surface of the water. Japanese Patent Application 06198561 A discloses such a universal joint. 
     However, as stated above, since the drive shaft presses the wafer  53  against the polishing cloth  51  under a pressure F, a friction force μF, in which μ is a friction coefficient, is generated and this causes a rotational moment M=μFH, in which H is a height of the center of the ball bearing  56  relative to the upper surface of the polishing cloth  51 . The wafer  53  is thus inclined downward in a direction opposite to the direction D in which the polishing cloth  51  on the turntable  52  passes under the wafer  53 , with the result that the wafer  53  is subject to an uneven pressure imposed by the polishing cloth  51 . To make the rotational moment M zero, it is necessary to make the above-noted height H zero. There is proposed an apparatus in which the center of tilting is positioned at a level of engagement between a wafer and a polishing cloth. 
     In theory, if the center of tilting lies on a surface where the polishing cloth and the wafer engage with each other, the rotational moment M which tends to tilt the wafer carrier will become zero and thus the wafer carrier can be kept parallel to the turntable. However, in practice, the polishing surface or upper surface of the polishing cloth on the turntable is not exactly even across its entire area which gives rise to a change in inclination of the polishing surface which is in contact with the wafer when the turntable is rotated. As a consequence of such a change in inclination of the polishing surface, the wafer carrier tends to tilt excessively under its inertia moment resulting in unstable tilting. Consequently, the wafer is unable to be engaged with the polishing cloth under a uniform pressure. 
     JP 1058308A discloses a polishing apparatus which is provided with an electromagnetic bearing including an electromagnetic thrust bearing device and an electromagnetic radial bearing device for bearing a drive shaft of a wafer carrier with an electromagnetic force, and an attitude controller for controlling the attitude of the drive shaft to keep the wafer carrier parallel to a turntable. 
     However, since in the polishing apparatus in accordance with JP 1058308A, the drive shaft of the wafer carrier is designed to be supported only by the electromagnetic bearing under the influence of the electromagnetic force generated thereby, it involves the following problems: 
     1) It is necessary for the thrust bearing device to be capable of generating a large magnetic force to press a wafer against the polishing cloth. 
     2) In terms of design, a motor for actuating the wafer carrier is required to be accommodated in a housing which also houses the electromagnetic bearing, and thus the size of the housing becomes large. 
     3) The wafer carrier is required to be movable up and down so as to load and unload a semiconductor wafer. This means that the wafer carrier, the electromagnetic bearing and the motor noted above are required to be moved as a unit and thus a mechanism for moving the unit also becomes large. 
     The present invention aims to solve the problems 1)-3) outlined above and, specifically, to provide a polishing apparatus which includes an attitude controller for controlling an attitude of a wafer carrier and/or a turntable so that the wafer or an object to be polished can be engaged with a polishing cloth on a turntable with a uniform pressure being exerted across its entire area. 
     SUMMARY OF THE INVENTION 
     In view of the above-described circumstances, an object of the present invention is to provide a polishing apparatus with an attitude controller for controlling an attitude of a turntable and/or a carrier for carrying an article to be polished, whereby the article is engaged with a polishing surface on the turntable under a uniform pressure thereby being polished to a very high degree of flatness. 
     In accordance with one aspect of this invention, there is provided a polishing apparatus comprising a turntable having a polishing surface that comes into sliding contact with an object to be polished, a support for tiltably supporting the turntable, and, an attitude controller for controlling an attitude or orientation of the turntable. The attitude controller may control the attitude of the turntable by controlling an angle of tilting of the turntable relative to the support by virtue of an electromagnetic force. The polishing apparatus may include a stationary frame, and the attitude controller may comprise an electromagnetic device fixedly provided on the stationary frame of the polishing apparatus, and an armature fixedly provided on the turntable and adapted to be moved by virtue of an electromagnetic force generated by the electromagnetic device. The attitude controller may comprise a cylinder device provided under the turntable and fixed to a stationary frame of the polishing apparatus and engaged with a lower surface of the turntable so that the cylinder device controls the attitude of the turntable by extension and retraction thereof. 
     In accordance with another aspect of the present invention, there is provided a polishing apparatus comprising a turntable having a polishing surface, a carrier for holding an article to be polished in a sliding contact relation with the polishing surface, a pressing device connected to the carrier and adapted to press the carrier towards the turntable with the article engaged with the polishing surface, and an attitude controller for controlling an attitude or orientation of the carrier. The pressing device may be a drive shaft for drivingly rotating the wafer carrier and the polishing apparatus includes a universal joint connecting the drive shaft and the carrier in such a manner that the carrier can tilt relative to the drive shaft. The attitude controller may comprise an electromagnetic device fixedly provided on a frame for rotatably supporting the drive shaft and an armature fixedly provided on the carrier and adapted to be moved by virtue of an electromagnetic force generated by the electromagnetic device. The attitude controller includes a sensor for sensing the attitude or orientation of the carrier so that the attitude controller controls the attitude of the wafer in response to the sensed attitude or orientation. The polishing apparatus may further include a pressing member provided radially outside the carrier and movable up and down independently of the carrier, an urging device for urging the pressing member, and a bearing for supporting the pressing member on the carrier in such a manner that the pressing member is kept stationary while allowing the carrier to rotate. The carrier may include a mounting member connected to the pressing device and an article holding member with a gap interposed therebetween, and the article holding member has a lower surface for holding an article to be polished and is flexible so that it can be deformed in both a concave and convex manner in a vertical direction by controlling a pressure in the gap. The carrier may include a retainer ring provided on the outer periphery of the carrier to confine the article held on the lower surface of the holding member. The retainer ring is movable vertically relative to the holding member, and the carrier further includes a pressing device for pressing the retainer ring vertically against the polishing surface of the turntable. 
     In accordance with yet another aspect of this invention, there is provided a polishing apparatus including both the turntable attitude controller and the carrier attitude controller as noted above. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical sectional view showing the general arrangement of a first embodiment of the polishing apparatus according to the present invention. 
     FIG. 2 is a fragmentary sectional view showing an essential part of the polishing apparatus according to the first embodiment. 
     FIG. 3 is a sectional view taken along the line III—III in FIG.  2 . 
     FIG. 4 is a sectional view taken along the line IV—IV in FIG.  3 . 
     FIG. 5 is a block diagram showing the functional arrangement of a control part for controlling an attitude controller for a carrier. 
     FIG. 6 is a diagram illustrating the relationship between the tilt α of the carrier with respect to an X-axis and the tilt β of the carrier with respect to a Y-axis. 
     FIG. 7 is a vertical sectional view showing the general arrangement of a second embodiment of the polishing apparatus according to the present invention. 
     FIG. 8 is a fragmentary sectional view showing an essential part of the polishing apparatus of FIG.  7 . 
     FIG. 9 is a vertical sectional view showing the general arrangement of a third embodiment of the polishing apparatus according to the present invention. 
     FIG. 10 is a fragmentary sectional view showing an essential part of the polishing apparatus of FIG.  9 . 
     FIG. 11 is a sectional view taken along the line XI—XI in FIG.  10 . 
     FIG. 12 is a vertical sectional view showing the general arrangement of a fourth embodiment of the polishing apparatus according to the present invention. 
     FIG. 13 is a sectional view taken along the line XIII—XIII in FIG.  12 . 
     FIG. 14 is a vertical sectional view showing the general arrangement of a fifth embodiment of the polishing apparatus according to the present invention. 
     FIG. 15 is a fragmentary sectional view showing an essential part of the polishing apparatus of FIG.  14 . 
     FIG. 16 is a sectional view taken along the line XVI—XVI In FIG.  15 . 
     FIG. 17 is a sectional view taken along the line XVII—XVII in FIG.  16 . 
     FIG. 18 is a block diagram showing the functional arrangement of a control part for controlling an attitude controller for a turntable. 
     FIG. 19 is a view similar to FIG. 16 but showing an electromagnetic device including eight electromagnetic coils. 
     FIG. 20 is a sectional view taken along the line XX—XX in FIG.  19 . 
     FIG. 21 is a vertical sectional view showing the general arrangement of a sixth embodiment of the polishing apparatus according to the present invention. 
     FIG. 22 is a side elevation view of a cylinder device employed in the polishing apparatus of FIG.  21 . 
     FIG. 23 is a vertical sectional view showing the general arrangement of a seventh embodiment of the polishing apparatus according to the present invention. 
     FIG. 24 is a fragmentary sectional view showing an essential part of a polishing apparatus according to a eighth embodiment of the present invention. 
     FIG. 25 is a block diagram showing the functional arrangement of control parts for controlling attitude controllers for a turntable and a wafer carrier. 
     FIG. 26 is a schematical side elevation view of a conventional polishing apparatus. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the polishing apparatus according to the present invention will be described below in detail with reference to FIGS. 1 to  25 . 
     FIG. 1 is a vertical sectional view showing the general arrangement of a first embodiment of the polishing apparatus according to the present invention, and FIG. 2 is a fragmentary sectional view showing an essential part of the polishing apparatus. 
     As shown in FIGS. 1 and 2, the polishing apparatus includes a turntable  1  having a polishing cloth  2  bonded to the upper surface thereof, and a carrier apparatus  5 . The carrier apparatus  5  includes a wafer carrier  6  for holding a semiconductor wafer  3 , and a drive shaft  7  for supporting the wafer carrier  6  and applying a pressing force and rotational driving force to the wafer carrier  6 . The carrier apparatus  5  further includes a universal coupling  8  for transmitting a pressing force from the drive shaft  7  to the wafer carrier  6  while allowing the wafer carrier to tilt relative to the drive shaft  7 , and an attitude or orientation controller  11  for controlling the attitude of the wafer carrier  6 . An abrasive liquid supply nozzle  60  is provided above the turntable  1  to supply an abrasive liquid onto the polishing cloth  2  on the turntable  1 . The upper surface of the polishing cloth  2  constitutes a polishing surface that comes into contact with a surface of a semiconductor wafer to be polished. 
     As shown in FIG. 2, the wafer carrier  6  includes a carrier body  9  comprising a wafer holding plate  9 A and a mounting plate  9 B and a retainer ring  10  fixed to the outer periphery of the carrier body  9 . The wafer carrier  6  is adapted to hold a semiconductor wafer  3  on the lower surface of the holding plate  9 A in such a manner that the wafer  3  is prevented from being displaced from the lower surface of the holding plate  9 A by the retaining ring  10 . The holding plate  9 A is fixedly provided on its lower surface with a resilient mat  61 . 
     Further, as shown in FIG. 2, there is provided a gap G between the holding plate  9 A and the mounting plate  9 B which is adapted to be subject to a fluid pressure including a vacuum. The holding plate  9 A includes a plurality of through holes (not shown) connecting the gap G to the lower surface thereof. The resilient mat also includes a plurality of through holes (not shown) corresponding to the through holes of the holding plate  9 A. This enables the fluid pressure to be applied to the upper surface of a wafer on the lower surface of the resilient mat  61 . 
     As shown in FIG. 1, the carrier drive shaft  7  is coupled to a carrier air cylinder  22  secured to a carrier head  21 . The carrier air cylinder  22  vertically moves the carrier drive shaft  7  thereby enabling the wafer  3  held by the carrier to be pressed against the turntable  1 . 
     The carrier drive shaft  7  is coupled to a rotating cylinder  23  through a key (not shown). The rotating cylinder  23  has a timing pulley  24  on an outer peripheral portion thereof. The timing pulley  24  is connected through a timing belt  25  to a timing pulley  27  provided on a carrier motor  26  secured to the carrier head  21 . Accordingly, the carrier motor  26  drivingly rotates the rotating cylinder  23  and the carrier drive shaft  7  through the timing pulley  27 , the timing belt  25  and the timing pulley  24 , thereby drivingly rotating the carrier  6 . The carrier head  21  is supported by a carrier head shaft  29  fixedly supported on a frame. 
     The universal coupling  8 , which transmits a pressing force from the carrier drive shaft  7  to the carrier  6  while allowing these members to tilt relative to each other, has a spherical bearing mechanism  40  that allows the carrier  6  and the carrier drive shaft  7  to tilt relative to each other. The universal coupling  8  further has a rotation transmitting mechanism  45  for transmitting the rotation of the carrier drive shaft  7  to the carrier body  9 . The spherical bearing mechanism  40  includes a spherical recess  41   a  formed in the center of the lower surface of a driving flange  41  secured to the lower end of the carrier drive shaft  7 . The spherical bearing mechanism  40  further includes a spherical recess  9   a  formed in the center of the upper surface of the mounting plate  9 B, and a ball bearing  42  interposed between the two recesses  41   a  and  9   a.  The ball bearing  42  is made of a material of high hardness, such as a ceramic. 
     The rotation transmitting mechanism  45  includes a driving pin (not shown) secured to the driving flange  41  and a driven pin (not shown) secured to the mounting plate  9 B. The driven pin and the driving pin are vertically movable relative to each other. Therefore, even when the carrier body  9  tilts, the driven pin and the driving pin are kept in engagement with each other, with a point of contact shifting between them. Thus, the rotation transmitting mechanism  45  transmits the rotational torque of the carrier driving shaft  7  to the carrier body  9  in a reliable and stable fashion. 
     Next, the attitude controller  11  for controlling the attitude or orientation of the carrier  6  will be described with reference to FIGS. 2 to  6 . FIG. 2 is a fragmentary sectional view showing an essential part of the polishing apparatus, as stated above. FIG. 3 is a view as seen from the arrow III—III in FIG. 2, and FIG. 4 is a sectional view taken along the line IV—IV in FIG.  3 . 
     As shown in FIGS. 2 and 3, the attitude controller  11  includes an electromagnetic core  12  secured to the carrier head  21 . Four magnetic poles  12   a,    12   b,    12   c  and  12   d  project radially outward from the electromagnetic core  12 . Four electromagnetic coils  13   a,    13   b,    13   c  and  13   d  are wound on the magnetic poles  12   a  to  12   d,  respectively. The attitude controller  11  further includes a cylindrical armature  14  facing the magnetic poles  12   a  to  12   d  across a gap. The armature  14  is secured to the carrier body  9 . 
     According to FIG. 4, the magnetic poles  12   a  to  12   d  (only magnetic pole  12   b  is illustrated) each have a U-shaped sectional configuration having a 90-degree rotation. The upper horizontally projecting portions of the magnetic poles  12   a  to  12   d  are wound with the electromagnetic coils  13   a  to  13   d,  respectively. The magnetic poles  12   a  to  12   d  and the armature  14  are formed from a magnetic material, e.g. a permalloy. As shown in FIG. 3, the electromagnetic coil  13   a  is placed at a position in positive alignment with the X- axis. The electromagnetic coil  13   b  is placed at a position in negative alignment with the X-axis. The electromagnetic coil  13   c  is placed at a position in negative alignment with the Y-axis. The electromagnetic coil  13   d  is placed at a position in negative alignment with the Y-axis. Four pairs of displacement sensors  15   a   1 ,  15   a   2 ;  15   b   1 ,  15   b   2 ;  15   c   1 ,  15   c   2 ; and  15   d   1 ,  15   d   2  are placed on two axes P and Q tilted at an angle of 45 degrees with respect to the X- and Y-axes. Each pair of displacement sensors consists of upper and lower displacement sensors. Each displacement sensor pair is held by a sensor holder  17 . 
     FIG. 5 is a block diagram showing the functional arrangement of a control part for controlling the attitude controller  11 . As shown in the figure, the control part has a subtracter  30  and a controller  31 . The subtracter  30  is supplied with desired values for the attitude of the carrier  6 , and values α and β of displacement of a controlled system (carrier  6 ) that are detected by sensors  15  (displacement sensors  15   a   1 .  15   a   2 ;  15   b   1 ,  15   b   2 ;  15   c   1 ,  15   c   2 ; and  15   d   1 ,  15   d   2 ) and converted in a coordinate converter  35 . Differences between the desired values and the displacement values a α and β derived from the subtracter  30  are input to the controller  31  as error signals eα and eβ. As shown in FIG. 6, α and β indicate a tilt with respect to an X-axis and a tilt with respect to a Y-axis, respectively. The X-axis and the Y-axis lie along a horizontal plane. In this case, the carrier  6  performs a combined motion consisting of tilting with respect to the X-axis and tilting with respect to the Y-axis about the bearing ball  42  acting as the center of rotation. 
     The error signals eα and eβ are subjected to a tilt control and attenuation processing in a PID+local phase-lead processing section  31 - 1  and are further passed through a notch filter  31 - 2  to remove vibrational components, and converted into voltage command signals Vα and Vβ. Then, in a coordinate converter  31 - 3 , the voltage command signals Vα and Vβ are converted into control signals V xu  and V yu  output by the attitude controller for supply to a driver section  32 . 
     The driver section  32  includes the electromagnetic coils  13   a ,  13   b ,  13   c  and  13   d  and drive circuits  24  for exciting these coils. The control signals V xu  and V yu  are supplied to the respective drive circuits  24 , in which they are converted into excitation currents I xu +, I xu −, I yu + and I yu − for displacing the armature  14  in any of the positive and negative directions of the X- and Y-axes shown in FIG.  3 . The excitation currents I xu +, I xu −, I yu − and I yu — are supplied to the electromagnetic coils  13   a ,  13   b ,  13   c  and  13   d  to control the attitude of the controlled system (carrier  6 ). In this case, the center of rotation (bearing ball  42 ) of the carrier  6  and the X- and Y-axes of the armature  14  shown in FIG. 3 are apart from each other by a predetermined height (L). Therefore, when the armature  14  is displaced in the positive or negative direction of the X- or Y-axis shown in FIG. 3, the carrier body  9 , that is, the carrier  6 , can be tilted in the desired direction with respect to the horizontal plane about the bearing ball  42  as the center of rotation. 
     In a polishing operation, the semiconductor wafer  3  carried by the wafer carrier  6  is pressed by the air cylinder  22  against the polishing cloth  2  which is being rotated by the motor, while an abrasive liquid Q is supplied onto the polishing cloth  2 . The force for pressing the wafer  3  is transferred through the drive shaft  7  and the universal coupling  8  to the wafer carrier body  9  holding the wafer  3 . The abrasive liquid Q supplied from the nozzle  60  flows between the wafer  3  and the polishing cloth  2  to facilitate polishing of the wafer. 
     During the polishing operation, the attitude of the carrier body  9  is controlled by the attitude controller  11 . In this case, as has been stated above, the tilt of the carrier body  9  is detected by processing the outputs of the displacement sensors  15  ( 15   a,   1 ,  15   a   2 ;  15   b   1 ,  15   b   2 ;  15   c   1 ,  15   c   2 ; and  15   d   1 ,  15   d   2 ) so that the carrier body  9  is controllably oriented relative to a horizontal plane in accordance with any inclination in the polishing surface of the polishing cloth  2  which is in contact with the wafer, in order to maintain the surface of the wafer to be polished strictly parallel with the polishing surface, with the pressure applied to the surface of the wafer to be polished being controlled to be kept uniform across the entire area thereof. However, in some cases, such parallelism between the surface of the wafer  3  to be polished and the polishing surface of the turntable may not be required and, instead, the pressure supplied to the surface of the wafer to be polished may be controlled to be uniform by maintaining the surface of the wafer at a slight angle relative to the polishing surface. 
     According to this embodiment, a force for pressing the carrier body  9  against the polishing surface of the turntable  1  is obtained by transmitting the pressing force of the air cylinder  22  directly to the carrier  6 . In contrast to the afore-mentioned prior art polishing apparatus which uses an electromagnetic bearing device to control an attitude of a wafer carrier, in accordance with this embodiment, the attitude controller  11  is used only to the control the tilt of the carrier. Consequently, the attitude controller  11  is able to be compact in size and simple in structure. To control the attitude of the carrier  6 , the state of the polishing surface on the upper side of the turntable  1 , including undulations or the like, are previously measured and input to the controller so that an optimum attitude or orientation of the carrier  6  is obtained on the basis of the data input in advance. Thus, optimum attitude of the carrier  6  is effected by the attitude controller  11  on the basis of the detection of the attitude by virtue of the displacement sensors  15 . 
     With reference to FIGS. 7 and 8, there is shown a second embodiment of a polishing apparatus with the attitude controller  11  as described above for controlling the attitude of the wafer carrier  6 . 
     In this polishing apparatus, the holding plate  9 A of the carrier body  9  is made of a flexible member and the gap G between the holding plate  9 A and the mounting plate  9 B is adapted to be supplied with a fluid pressure. Further, the retainer ring  10  is movable in a vertical direction relative to the wafer carrier  6 . The retainer ring  10  is provided on its upper portion with a fluid bag  88  so that the retainer ring  10  is pressed against the polishing cloth  2  independently of the wafer carrier by introducing a fluid pressure into the bag  88 . 
     The gap G is fluidly communicated with a fluid pressure source  85  through a tube  89  having a regulator R 1 . The holding plate  9 A is made thin as a whole so that, when the gap G is pressurized or depressurized by the fluid pressure introduced therein, the lower surface of the holding plate  9 A is uniformly deformed as a whole. 
     As shown in FIG. 8, the retainer ring  10  includes a first retainer ring element  10   a  and a second retainer ring element  10   b  having a cross-section in the form of a reversed “L” and fixed on the first retainer element  10   a.  The second retainer ring element  10   b  is fixedly connected by a plurality of pins  99  to the mounting plate  9 B of the wafer carrier body  9  at its upper end to enable the retainer ring  10  to rotate together with the wafer carrier  6 . Further, the fluid bag  88  is annular and located between the retainer ring  10  and the wafer carrier  6  and fixed to the holding plate  9 A. The bag  88  is fluidly connected to the fluid pressure source  85  through a tube  90  having a regulator R 2 . As shown in FIG. 7, the wafer carrier actuating cylinder  22  is connected to the fluid pressure source  85  through a tube having a regulator R 3 . The lower surface (wafer holding surface) of the holding plate  9 A is controllably deformed in both a concave and convex manner in a vertical direction by controlling a pressure In the gap G. 
     The regulators R 1 , R 2 , R 3 , are connected to a controller  124  to effect control thereof, whereby the pressures applied to the wafer  3  and the retainer ring  10  can be appropriately controlled. It is possible for the pressures under which the retainer ring  10  and the wafer  3  are pressed against the polishing cloth to be controlled independently from each other. 
     As shown in FIG. 8, the wafer carrier  6  is provided with an additional fluid line system including a through hole  2   h  formed in the mounting plate  98 , a through hole  3   h  formed In the holding plate  9 A, a connecting tube  126  connecting the through holes  2   h  and  3   h , and a fitting  127  which is fluidly connected to a pressure source (not shown). The fluid line system enables the lower surface of the holding plate  9 A to securely hold the wafer  3  under the influence of a vacuum applied to the upper surf ace of the wafer  3  through the fluid line system; for example, when the wafer is brought into contact with the polishing cloth  2  from the outside of the turntable. In a condition that the wafer held on the lower surface of the holding plate  9 A is engaged with the polishing cloth  2  as shown in FIG. 7, if a positive pressure is applied to the upper surface of the wafer in place of the vacuum which was applied, a deformation in the wafer which may result from the influence of the vacuum can be rectified by the application of a positive pressure. Further, it is also possible for the fluid line system to remove the wafer from the holding plate  9 A by applying a positive pressure to the upper surface of the wafer, for example, after polishing of the wafer. 
     The attitude controller  11  is substantially the same as that employed in the afore-mentioned embodiment in that the attitude controller  11  includes the annular armature  14  fixed to the mounting plate  9 B and the electromagnetic core  12  fixed to the carrier head  21  and provided with the electromagnetic coils  13   a - 13   d . The controller  11  controls the attitude of the wafer carrier  6  in the same manner as that described in connection with the first embodiment. 
     FIGS. 9,  10  and  11  show a third embodiment of a polishing apparatus of the present invention with the wafer carrier attitude controller  11  as described above. 
     This embodiment is distinguishable from the other embodiments in that the polishing apparatus of this embodiment additionally includes a pressing ring  133  provided radially outside the retainer ring  10 . The pressing ring  133  includes a first ring element  133   a  made from alumina-ceramic and second and third ring elements  133   b  and  133   c  made from stainless steel. The first and second ring elements  133   a  and  133   b  are bonded to each other with an adhesive and the second and third ring elements  133   b  and  133   c  are connected by bolts (not shown). The lower surface of the first ring element  133   a  constitutes a pressing surface  133   f  for pressing the polishing cloth  2 . The pressing element  133  is supported by an annular bearing  137  provided between the third ring element  133   c  and a cylindrical bearing raceway member  136  fixedly connected to the mounting plate  9 B of the wafer carrier  6 . The annular bearing  137  includes an annular bearing case  137   a  and a number of ball bearings  137   b  which are supported by a ball bearing retainer (not shown) in such a manner that the ball bearings  137   b  are, as shown in FIGS. 10 and 11, arranged along horizontal upper and lower circles in the bearing case  137   a . The bearing case  137   a  is fastened to the third ring element  133   c  by a fastener  150  provided on the top end of the third ring element  133   c . Between the pressing ring  133  and the carrier wafer head  21 , there is provided three air cylinder devices  122  (FIG.  11 ). The bearing  137  makes it possible for the pressing ring  133  to be stationary while the wafer carrier  6  rotates inside the pressing ring  133 . Accordingly, the pressing ring  133  is pressed by the air cylinder devices  122  against the polishing cloth  2  around the retainer ring  10  during polishing of the wafer  3  to optimize the polishing surface condition radially outside and adjacent to the periphery of the wafer  3 . 
     The wafer carrier attitude controller  11  is substantially the same as that employed in the aforementioned embodiments. The annular armature  14  is fixed to the pressing ring  133  and the electromagnetic core  12  is fixed to the carrier head  21  and provided with the electromagnetic coils  13   a - 13   d . The controller  11  controls the attitude of the pressing ring  133  (and thus the wafer carrier  6 ) In the same manner as that described in connection with the other embodiments. 
     Incidentally, the holding plate  9 A of the wafer carrier  6  is formed with a plurality of through holes  135  connecting the gap G to the lower surface of the holding plate  9 A. On the lower surface of the holding plate  9 A, there is bonded a resilient pad  132  which includes a plurality of through holes corresponding to the through holes  135  formed in the holding plate  9 A. As such, the fluid pressure in the gap G can be applied to the upper surface of a wafer placed on the lower surface of the resilient pad  132 . Further, as shown in FIG. 10, the lower end portion of the retainer ring  10  is made thin in its radial direction so as to make it possible for the pressing ring  133  or the first ring element  133   a  thereof to be placed closer to the periphery of the wafer  3  held by the wafer carrier. 
     With reference to FIGS. 12 and 13, there is shown a fourth embodiment of a polishing apparatus with the attitude controller  11  as described above in connection with the other embodiments. 
     This polishing apparatus is substantially the same as that shown in FIGS. 9,  10  and  11  except for the bearing supporting the pressing ring  133  on the wafer carrier  6 . In this polishing apparatus, the bearing consists of two kinds of bearings  138  and  139 . The bearing  138  is a conventional radial bearing for allowing the wafer carrier to rotate relative to the pressing ring  133  which is kept stationary, while maintaining the positional relationship in the vertical direction between the wafer carrier  6  and the pressing ring  133 . The bearings  139  are, as shown in FIG. 13, provided around the wafer carrier  6  at an angular interval of 120° and allow relative movement between the pressing ring  133  and the wafer carrier  6  in a vertical direction. The bearing  139  includes an outside raceway member  139   a , cylindrical bearings  139   b  which are arranged in two rows and two columns and an inside raceway member  139   c . The bearing  138  is provided between the inside raceway member  139   c  and the mounting plate  9 B of the wafer carrier  6 . The above-described bearing construction enables the bearings to be used for a longer period than that employed in the embodiment shown in FIGS. 9-11. It should be noted that in this embodiment, labyrinth seals  175 ,  176 ,  177  are employed for the bearings  138  and  139  to prevent foreign particles from entering into the bearings. 
     With reference to FIGS. 14-18, there is shown a polishing apparatus in accordance with a fifth embodiment of the present invention. 
     This embodiment differs from the other embodiments in that the wafer carrier  6  is not provided with an attitude controller as explained above in connection with the other embodiments and, instead, a similar attitude controller  111  is provided for the turntable  1 . 
     As shown in FIGS. 14 and 15, the turntable  1  is connected to a rotating shaft  102  of a motor (not shown) through a universal joint including upper and lower coupling members  103  and  104 . The lower coupling member  104  is secured to the upper end of the rotating shaft  102  of the motor. The upper coupling member  103  is secured to the lower surface of the turntable  1 . A self-aligning roller bearing  105  is disposed between the lower coupling member  104  and the upper coupling member  103  to allow the turntable  1  and the upper coupling member  103  to tilt in any direction desired with respect to the lower coupling member  104  about the self-aligning roller bearing  105  as the center of rotation. The universal joint further includes a short column-shaped pin  106  which is fixed to the coupling member  104  and is engaged with an engagement hole  103   a  formed in the upper coupling member  103  to transmit rotation from the shaft  102  to the turntable  1 . It should be noted that a predetermined clearance is formed between the engagement hole  103   a  and the pin  106  so that tilting of the turntable  1  is allowed. 
     In this embodiment, the turntable attitude controller  111  for controlling the attitude of the turntable  1  includes an electromagnetic core  112  secured to a frame  128 . The electromagnetic core  112  is provided with four magnetic poles  112   a ,  112   b ,  112   c  and  112   d . Four electromagnetic coils  113   a ,  113   b ,  113   c  and  113   d  are wound on the magnetic poles  112   a  to  112   d , respectively. The attitude controller  111  further includes an annular disk-shaped armature  114  facing the magnetic poles  112   a  to  112   d  across a gap. The armature  114  is secured to the turntable  1 . 
     As shown in FIGS. 15 and 17, the magnetic poles  112   a  to  112   d  each have an inverted U-shaped sectional configuration. The inner portions of the inverted U-shaped magnetic poles  112   a  to  112   d  are wound with the electromagnetic coils  113   a  to  113   d , respectively. The magnetic poles  112   a  to  112   d  and the armature  114  are formed from a magnetic material, e.g. a permalloy. As shown in FIG. 16, the electromagnetic coil  113   a  is placed at a position in positive alignment with the X-axis. The electromagnetic coil  113   b  is placed at a position in negative alignment with the X-axis. The electromagnetic coil  113   c  is placed at a position in positive alignment with the Y-axis. The electromagnetic coil  113   d  is placed at a position in negative alignment with the Y-axis. Four displacement sensors  115   a ,  115   b ,  115   c  and  115   d  are placed on two axes R and S tilted at 45 degrees with respect to the X- and Y-axes. 
     FIG. 18 is a block diagram showing the functional arrangement of a control part for controlling the attitude controller  111 . As shown in the figure, the control part is substantially the same as that of the control part shown in FIG. 5 in both arrangement and function. 
     FIGS. 19 and 20 show another embodiment of the electromagnetic core  112  which is provided with eight electromagnetic coils  112   a - 112   h  arranged at an equal angular interval of  45 ° and gap sensors  115   a - 115   d  at an equal angular interval of 90°. 
     FIGS. 21 and 22 show a sixth embodiment or a variation of the fifth embodiment shown in FIGS. 14 and 15. In this embodiment, in place of the magnetic attitude controller  111 , another type of an attitude controller  111  is used. The controller includes a plurality of air cylinder devices  220  (only one is shown) arranged around the turntable drive shaft  102  at an equal angular interval under the periphery of the turntable  1 . The cylinder device  220  includes a cylinder body fixed to the stationary frame  222  and a rod extending from the cylinder body upward. The rod is provided on its upper end with a roller  230  which rotatably engages with the lower surface of the turntable  1 . The controller further includes a gap sensor  234  adapted to sense a gap between the sensor  234  and the lower surface of the turntable  1 . On the basis of values of the gaps sensed by the sensors  234 , the rods of the cylinder devices are extended or retracted as to control the attitude of the turntable. For the sake of simplicity, explanation of the control part of the controller is omitted, as it is substantially the same as that of the controllers for the wafer carrier and turntable explained in connection with the other embodiments. In FIG. 21, reference numeral  238  designates a universal joint for connecting the drive shaft  102  and the turntable  1 . 
     FIG. 23 shows a seventh embodiment or a variation of the fifth embodiment. In this embodiment, the turntable drive shaft  102  has a disc  250  fixed thereto and a plurality of cylinder devices  252  are fixedly provided between the disc  250  and the turntable  1 . Gap sensors (not shown) similar to those  234  employed in the sixth embodiment are mounted on the disc  250 . The attitude of the turntable  1  is effected in the same manner as that in the sixth embodiment. 
     FIGS. 24 and 25 show a eighth embodiment of the present invention or a combination of the embodiment shown in FIGS. 1-6 and the embodiment shown in FIGS. 14-18. For the purpose of simplicity, detailed explanation thereabout is omitted. FIG. 25 is a block diagram showing the functional arrangement of a combination of a control part for controlling the turntable attitude controller  111  and a control part for controlling the wafer carrier attitude controller  11 . As shown in the figure, the turntable control part and the wafer carrier control part each have an arrangement similar to that of the control part shown in FIGS. 5 and 18. Elements of the wafer carrier control part which are the same as those in FIG. 5 are designated by the same reference numerals as those of the latter and elements of the turntable control part which are the same as those in FIG. 18 are designated by the same reference numerals with primes “′” as those of the latter. The arrangement shown in FIG. 25 is additionally provided with a computing device  36  for precisely detecting relative positions of the carrier and the turntable on the basis of signals input thereto from the carrier control part and the turntable control part Specifically, the computing device  36  computes relative errors from information concerning the tilt of the carrier and information concerning the tilt of the turntable to generate rectified displacement values α, β, α′ and β′, thereby allowing control to be effected with a high degree of accuracy. Normally, the degree of accuracy can be increased by correcting the desired position of the carrier with reference to the tilt of the turntable. Thus, the feedback R 2  to the turntable may be omitted. Further, the computing device may be omitted. 
     As has been stated above, according to the present invention, the attitude of the wafer carrier and/or the turntable is controlled so that a polishing operation can be carried out while maintaining a distribution of pressure under which a wafer is pressed against the polishing cloth uniform across the entire wafer surface engaged with the polishing cloth. Accordingly, it is possible to obtain a polished surface having a high degree of flatness. 
     It should be noted that the present invention is not necessarily limited to the foregoing embodiments but can be modified in a variety of ways without departing from the gist of the present Invention.