Abstract:
A polishing apparatus has a polishing table having a polishing surface, a carrier for carrying a plate-like member and bringing the plate-like member into contact with the polishing surface, and a dresser including a dressing tool adapted to be brought into contact with the polishing surface to dress or normalize the polishing surface. The carrier is movable along a first path between a work position for bringing into contact the plate-like member with the polishing surface and a rest position. The dresser is movable along a second path between a work position for bringing the dressing tool into contact with the polishing surface and a rest position. The first and second paths have a common overlapping area. A contact prevention device is provided to prevent the carrier and the dresser from coming into contact with each other. An actuator is provided to bring the plate-like member into a condition that a predetermined area of the surface of the plate-like member extends beyond a peripheral edge of the polishing surface.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a polishing apparatus for polishing a plate-like article such as a semiconductor wafer. 
     With recent rapid progress in technology for fabricating high-integration semiconductor devices, circuit wiring patterns have been becoming increasingly fine and, as a result, spaces between wiring patterns have also been decreasing. As wiring spacing decreases to less than 0.5 microns, the depth of focus in circuit pattern formation in photolithography or the like becomes shallower. Accordingly, surfaces of semiconductor wafers on which circuit pattern images are to be formed by a stepper are required to be polished by a polishing apparatus to an exceptionally high degree of surface flatness. To accomplish such a high degree of surface flatness, it has become common to use a polishing apparatus known as “CMP” or “Chemical Mechanical Polisher”. 
     FIG. 12 shows a polishing apparatus of this type. The apparatus includes a polishing table  102  provided with a polishing cloth  100  on its upper surface, a wafer carrier  104  for carrying a semiconductor wafer W to be polished and an abrasive liquid supply nozzle  106  for supplying an abrasive liquid to the polishing cloth  100 . In a polishing operation, a wafer W is held on a lower surface of a wafer carrier  104  to be brought into contact with a surface (polishing surface) of the polishing cloth  100  which is provided on the polishing table  102 , with the wafer carrier  104  and the polishing table  102  being rotated about their respective axes. Simultaneously, the abrasive liquid nozzle  106  supplies the polishing cloth  100  with an abrasive liquid consisting of, for example, an alkaline slurry containing abrasive particles such as silica which effects polishing of the semiconductor wafer chemically and mechanically. 
     The polishing apparatus is also generally provided with a dresser tool  108  which is employed to normalize the polishing surface of the polishing cloth either during or after polishing of a semiconductor wafer. When brought into contact with the polishing surface of the polishing cloth  100 , the dresser tool  108  is rotated so as to remove any accumulated abrasive particles and debris and planarize the polishing surface. The wafer carrier  104  and the dressing tool  108  are pivotably supported on struts (not shown) positioned adjacent to and radially outside the polishing table  102 , so as to enable each unit to be moved between a work position shown in FIG. 11 and a rest position radially outside the polishing table  102 . 
     The polishing surface of the polishing table  102  is subject to a decrease in rotational movement the closer it is to the center of rotation. Accordingly, during polishing, a semiconductor wafer is brought into contact only with a polishing surface remote from the center axis, thus making it necessary for a diameter of a polishing table to be in excess of twice that of a wafer to be polished. Consequently, a large polishing apparatus must be employed whereby production and installation costs increase. 
     In an attempt to overcome this problem, there has been employed a polishing apparatus in which a polishing table having a polishing surface is driven in such a manner as to generate a circulatory translational motion thereof in which the polishing table is rotated about an axis spaced away from and parallel to the central axis of the polishing table without any change in orientation of the polishing table, whereby every point on the polishing surface is caused to describe a substantially identical locus, i.e., a circle. The motion of the polishing surface relative to a surface of a semiconductor wafer enables the polishing surface to polish the wafer surface uniformly at all the points of the polishing surface. Consequently, this enables a small diameter polishing surface of a polishing table to be employed having a diameter which is generally equal to that of a semiconductor wafer and is able to polish the semiconductor wafer appropriately. 
     However, the reduced size of the polishing table gives rise to the following problems. Firstly, the work positions of a dresser tool and a wafer carrier, which units are located above the polishing surface of the polishing table, overlap with each other, whereby the possibility of accidental contact and damage increases. In addition, following completion of a polishing operation, the wafer carrier must be raised to separate a polished wafer from the polishing surface of the polishing table. However, the existence of an abrasive liquid between the polished wafer and the polishing surface generates surface tension, requiring a relatively large force to be applied in order to separate a polished wafer from the polishing surface. Thus, upon completion of a polishing operation, the wafer carrier is generally first pivoted about its holding strut positioned outside of the polishing table to move the wafer to a position where a potion of the wafer extends radially outwardly from the periphery of the polishing surface of the polishing table, whereby surface tension is decreased prior to raising of the wafer carrier and separation of the polished wafer from the polishing surface. However, the circulatory translational motion applied to the polishing table as stated above, results in a shifting effective center point in the polishing table, with the peripheral edge of the polishing table thus becoming indeterminate. Accordingly, if the wafer carrier is, as stated above, moved to a predetermined position before being lifted from the polishing surface, the actual area of the wafer which is in contact with the polishing surface is indefinite, as is the surface tension acting between the wafer and the polishing surface. As a result, it becomes difficult to effectively separate a polished wafer from a polishing surface, and the likelihood of inappropriate movement and consequential damage to the wafer increases. 
     SUMMARY OF THE INVENTION 
     The present invention aims to solve the problems stated above. 
     According to the present invention, a polishing apparatus comprises a polishing table having a polishing surface, a carrier for carrying a plate-like member such as a semiconductor wafer and bringing the plate-like member into contact with the polishing surface, and a dresser including a dressing tool adapted to be brought into contact with the polishing surface to dress or normalize the polishing surface. The carrier is movable along a first path between a work position for bringing the platelike member into contact with the polishing surface and a rest position located radially outside the polishing surface, and the dresser is movable along a second path between a work position and a rest position. The second path and the first path have a common overlapping area. 
     The polishing apparatus further comprises a contact prevention means for preventing the carrier and the dresser from coming into contact with each other during movement along the stated first and second paths. 
     The contact prevention means may be designed so as to prevent the carrier and the dresser from entering simultaneously any overlapping area. 
     The polishing apparatus may further comprise means for  25  sensing that a carrier and dresser have approached each other beyond a predetermined limit, whereby movement of either or both units is halted. 
     The carrier and the dresser may be mechanically connected to each other so as to be able to be moved simultaneously along the first and second path, respectively. 
     According to another aspect of the present invention, a polishing apparatus comprises a polishing table having a polishing surface, a carrier for carrying a plate-like member such as a semiconductor wafer and bringing the plate-like member into contact with the polishing surface to polish a surface of the plate-like member, a circulatory translational motion mechanism for generating a relative circulatory translational motion between the polishing table and the carrier while maintaining constant contact of the plate-like member with the polishing surface, and an actuator for moving the carrier relative to the polishing surface, to bring the plate-like member into a condition where a predetermined area of the surface of the plate-like member extends beyond a peripheral edge of the polishing surface. Incidentally, the term “circulatory translational motion” noted above is defined as “a motion wherein every point on an article moves along closed paths in parallel with each other. The closed path may be in the form of, for example, a circle, an ellipse and a polygon. Accordingly, it should be understood that the “relative circulatory translational motion” noted above causes every point on the polishing surface to describe a substantially identical locus with respect to the plate-like member. 
     The polishing apparatus may comprise means for halting the said relative circulatory translational motion in such a state that the plate-like member has a predetermined orientation at a predetermined position relative to the polishing surface. The circulatory translational motion means generates a circulatory translational motion of the polishing table while the carrier is positioned at a predetermined position to keep the plate-like member stationary. The polishing apparatus may include a sensor positioned adjacent to the polishing table for sensing that a predetermined reference point on the polishing table has passed the sensor whereby a signal is emitted, in response to which the circulatory translational motion of the the polishing table is halted by the halting means once the table reaches a predetermined position relative to the emission of the sensor signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a polishing apparatus in accordance with a first embodiment of the present invention. 
     FIG. 2 is a plan view of a polishing table of the polishing apparatus of FIG.  1 . 
     FIG. 3 is a side elevation view of the polishing table of FIG.  2 . 
     FIG. 4 is a perspective view of a wafer carrier and a dresser used in the polishing apparatus of FIG.  1 . 
     FIG. 5 is a plan view of the wafer carrier and the dresser of FIG. 4 showing their relationship in motion. 
     FIG. 6 is a perspective view of a wafer carrier and a dresser in accordance with another embodiment of the present invention. 
     FIG. 7 is a perspective view showing a variation of the wafer carrier and dresser of FIG.  6 . 
     FIG. 8 is a plan view of a polishing apparatus in accordance with a different embodiment of the present invention. 
     FIG. 9 is a plan view of a polishing apparatus in accordance with a further different embodiment of the present invention. 
     FIG. 10 is a side elevation view of a wafer carrier and a polishing table in accordance with another embodiment of the present invention. 
     FIG. 11 a  is a perspective view of the polishing table and the wafer carrier in a polishing operation. 
     FIG. 11 b  is a perspective view of the polishing table and the wafer carrier showing a state in which the wafer carrier has started to move laterally relative to the polishing table. 
     FIG. 11 c  is a perspective view of the polishing table and the wafer carrier showing a state in which the wafer carrier has been moved to a predetermined position relative to the polishing table from which the wafer carrier should be lifted. 
     FIG. 11 d  is a bottom view of the polishing table and the wafer carrier of FIG. 11 c.    
     FIG. 11 e  is a perspective view of the polishing table and the wafer carrier showing a state that the wafer carrier has lifted separating from the polishing table. 
     FIG. 12 is a side elevation view of a prior art polishing apparatus. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, there is shown a polishing apparatus in accordance with a first embodiment of this invention. 
     As shown, the polishing apparatus is, as a whole, rectangular in its plan view configuration and includes a polishing station  10  located at the left end thereof and a wafer loading and unloading station  14  at the other end, including wafer storage cases  12   a  and  12   b . Between the wafer loading and unloading station  14  and the polishing station  10 , there are positioned wafer transfer robots  16   a  and  16   b  and cleaning devices  18   a  and  18   b  in parallel, with a wafer reverser  20  interposed between the cleaning devices. 
     The polishing station  10  includes a polishing table  22  positioned at the center thereof, a wafer carrier  24  and a dresser  26  positioned opposite sides of the polishing table  22 . The arrangement of the wafer carrier  24  and the dresser  26  relative to the polishing table  22  enables the size of the polishing station  10  to be kept to a minimum. This arrangement also enables the dresser and the wafer carrier to operate with a low incidence of interference therebetween. Reference  28  designates a wafer transfer station to facilitate transfer of a wafer between the polishing station  10  and the transfer robot  16   b.    
     With reference to FIGS. 2 and 3, the polishing table  22  is provided on its upper surface with a circular polishing member  30  such as a grindstone disc and a polishing cloth having a polishing surface  30   a  on the upper side thereof Below the polishing table  22 , there is provided a motor  31  which drives the polishing table  22  by means of a drive train as explained below. The motor  31  includes a vertical output shaft  32  having a central axis O 1 . The drive output shaft  32  is provided on its upper end face with an eccentric vertical drive pin  32   a  having a center axis O 2  which is offset from the center axis  0   1  by a distance “e”. The top end of the drive pin  32   a  is rotatably received in a center hole of a radial bearing  34  which is, in turn, rotatably received in a recess  22   a  formed in the center of the bottom surface of the polishing table  22 . Upon rotation of the output shaft  32  of the motor, the drive pin  32   a  is rotated about the central axis O 1  of the output shaft  32  and the radial bearing  34  is also rotated about the central axis O 1  of the output shaft  32  accordingly. The polishing table  22  is designed to be permitted to move in a horizontal plane normal to the axis O 1 , but is prohibited from rotating about its central axis or the central axis O 2 . As a consequence, due to the turning motion of the drive pin  32   a  as noted above, the polishing table  22  is subjected to a circulatory translational motion. In other words, the polishing table  22  is driven by the motor to turn about the central axis O 1  of the output shaft  32  of the motor  31  without any change in its orientation, i.e., without rotating about its own axis O 2 . 
     The wafer carrier  24  includes a vertical strut  36 , a carrier head  38  pivotably mounted on the top end of the strut  36  at a proximal end thereof and adapted to be pivoted about a vertical axis of the strut by means of an actuator such as a servomotor (not shown), a wafer carrying member  42  in the form of a disc, and a carrying member drive shaft  40  extending downwards from a distal end of the carrier head and connected at its lower end to the center of the carrying member  42 . The drive shaft  40  is connected to a motor and a lift (not shown), both of which are mounted on the carrier head  38  so that the drive shaft  40  can be rotated about its axis and moved up and down while carrying or holding a wafer on the bottom surface of the carrying member  42 . A polishing operation is conducted by lowering the carrying member  42  to bring the wafer W into contact with the polishing surface of the polishing member  30  while rotating the carrying member. The carrier head  38  is, as stated above, pivotable, so that the carrying member can be moved between a work position over the polishing table  22 , a retracted position radially outside the polishing table  22  and a wafer transfer position over the wafer transfer station  28  in the polishing station  10 . Reference  38   a  designates a cover covering the complete carrier head  38 . 
     The dresser  26  likewise includes a vertical strut  44 , a dresser head  46  pivotably mounted on the top end of the strut at its proximal end and adapted to be pivoted about a vertical axis of the strut  44  by means of an actuator such as a servomotor (not shown), a dressing tool  50  in the form of a disc, and a dressing tool drive shaft  48  extending downwards from a distal end of the dresser head  46  and connected to the center of the dresser tool  50  at its lower end. The drive shaft  48  is connected to a motor and a lift (not shown) both of which are mounted on the dresser head  46  so that the dresser tool  50  can be rotated about its axis and moved up and down. A dressing operation is conducted by bringing the dressing tool  50  into contact with the polishing surface of the polishing member  30  while rotating the dressing tool. The dresser head  46  is, as stated above, pivotable, so that the dressing tool can be moved between a work position over the polishing table  22  and a retracted position radially outside the polishing table  22 . Reference  46   a  designates a cover covering the complete  15  dresser head  46 . 
     In this embodiment, there is provided a controller C (FIG. 1) for controlling the motors of the carrier head  38  and the dresser head  46  in such a manner that the carrier head  38  and the dresser head  46  are pivoted about the axes of the struts  36  and  44 , respectively, without interfering with each other For example, sensors are provided to sense pivotal angles of the carrier head  38  and the dresser head  46  around the axes of the struts  36  and  44 , respectively, and the controller C is adapted to control the pivotal motions of the carrier head  38  and the dresser head  46  on the basis of signals emitted from the sensors indicating the pivotal positions of the carrier head  38  and the dresser head  46 . FIG. 5 shows an example of a positional relationship between the carrier head  38  and the dresser head  46  controlled by the controller C. In this example, the controller C commands the motor of the carrier head  38  to turn the carrier head  38  in a counterclockwise direction so that the carrier head  38  comes into the work position over the polishing table  22  only when the controller C has confirmed that the dresser head  46  is at its rest position located within an angular range a shown in FIG. 5, whereby the carrier head  38  can turn without any interference from the dresser head  46 . Likewise, the controller C commands the motor of the dresser head  46  to turn the dresser head in a clockwise direction as viewed in FIG. 5 so that the dressing tool  50  comes into its work position over the polishing table only when it has been confirmed that the carrier head  38  is at its rest position located within an angular range  13 , or at a position closer to the wafer transfer station than the rest position. 
     In this embodiment, the dresser head  46  is provided on its cover  46   a  with a contact type sensor  56 . Specifically, the contact type sensor  56  is in the form of a character “U” and is separated from and supported around the lower portion of the dresser head cover  46   a  by means of a plurality of support members  54 . The sensor  56  may include a pair of elongated electrical conductors which are arranged in parallel with each other in a U-form and held together at their opposite ends by insulating members such as insulation film members. The conductor may be prepared by plating a tape-like member made of a spring material with copper. If the carrier head  38  engages with the conductors, the conductors are electrically connected and close a circuit in the sensor  56  so as to activate the controller C to halt the pivotal movement of the carrier head  38  and/or the dresser head  46 , and avoid damage being caused to the carrier head and/or the dresser head. 
     A contact type sensor of this type is highly resistant to atmospheric conditions, e.g., water and chemical proof. Further, a sensor of this type is inexpensive and easy to maintain, does not require complicated adjustment, and is readily replaceable and relatively freely configured. Although the contact type sensor is required to be brought into contact with the carrier head and the dresser head to be actuated, direct contact between the carrier head and the dresser head can be avoided by arranging the sensor so as to kept separate from the dresser head as shown in the above-noted embodiment. 
     Although in this embodiment, the sensor  56  is provided on the dresser head  46  taking into consideration a fact that the carrier head is often removed from the polishing apparatus for maintenance, the sensor may be mounted on the carrier head  38 . 
     In operation, a wafer to be polished is removed from the wafer case  12   a  or  12   b  by the first wafer transfer robot  16   a , and is then reversed by the reverser  20 , and placed on the wafer transfer station  28  by the second wafer transfer robot  16   b . Next, the controller C confirms that the dresser head  46  is positioned in its rest position located with the angular range a and then moves the carrier head  38  to a position over the wafer transfer station, where the wafer has been placed by the second transfer robot  16   b , from its rest position located in the angular range. The wafer is then lifted towards the carrier head  38  and the carrier head in turn holds the wafer by its lower surface under a vacuum. The controller C further confirms that the dresser head is kept in the angular range a and then pivots the carrier head  38  to bring the carrying member  42  carrying the wafer W to its work position over the polishing surface  30   a  of the polishing table  22 . 
     The carrying member  42  is then rotated about its axis and lowered to be brought into contact with the polishing surface  30   a  of the polishing member  30  on the polishing table  22  which is subject to the circulatory translational motion as stated above. After polishing of the wafer W, the carrying member  42  is lifted and moved towards the wafer transfer station  28  to bring the carrying member  42  to a position over the wafer transfer station  28  after the control confirms that the dresser head  46  is at its rest position. 
     The controller C then confirms that the carrying member  42  resides at its position over the wafer transfer station  28  and, thereafter, pivots the dresser head  46 , which was positioned at its rest position, to bring the dressing tool  50  to its position over the polishing surface  30   a  on the polishing table  22 . The dressing tool is then rotated at low speed and lowered to be brought into contact with the polishing surface  30   a  on the polishing table which is subject to a circulatory translational motion, whereby a dressing operation is conducted on the polishing surface  30   a.    
     After completion of the dressing operation, the dressing tool  50  is lifted and then moved to its rest position upon confirmation by the controller C that the carrier head is at its designated position over the wafer transfer station  28 . At the rest position of the dressing tool  50  there is provided a cleaning device for the dressing tool. 
     Simultaneously with or following the dressing operation, the polished wafer W is transferred from the carrying member  42  to the wafer transfer station  28 , while being washed with pure water or rinsing liquid as required. 
     In this embodiment, in the event of an impending approach of the carrier head  38  and the dresser head in spite of the operation of the controller C as stated above, the contact type sensor  56  is able to sense such an approach whereby any pivotal movements of the carrier head  38  and the dresser head  46  are caused to instantaneously cease, so as to avoid collision therebetween. Such a protection function is of use when the polishing apparatus is being controlled manually, for example, during adjustment of the polishing apparatus subsequent to installation. 
     The polished wafer W placed on the wafer transfer station is then transferred by the second transfer robot  16   b  to the first cleaning device  18   a  where opposite side surfaces of the wafer are cleaned using, for example, sponge rolls and, thereafter, is transferred to and reversed by means of the reverser  20 . The reversed wafer is then picked up by the first wafer transfer robot  16   a  and placed on the second cleaning device  18   b , which is designed to conduct a cleaning operation, for example, by means of a pen-type sponge cleaning member and a spin dry operation with respect to the upper surface of the wafer, and is finally transferred to the loading and unloading station including the wafer cases  12   a  and  12   b.    
     In the first embodiment stated above, the dresser is of a contact type. However, this invention can also be applied to a polishing apparatus including a non-contact type dresser in the form of, for example, a fluid jet adapted to direct a jet of air, nitrogen gas, water or other fluids. 
     FIG. 6 shows a second embodiment of the present invention in which, instead of the contact type sensor in the first embodiment, a plurality of proximity switches  60  are provided on an area on the lower surface of the dresser cover  46   a , which area may be engaged with the carrier cover  38   a . As shown, the proximity switches  60  are separated from each other by predetermined distances. 
     FIG. 7 shows a third embodiment of the present invention which employs, in place of the proximity switches  60  in the second embodiment, photoswitches  66  each including light emitters  62  and light receivers  64 . 
     In the second and third embodiments, an inappropriate approach between the carrier head  38  and the dresser head  46  is sensed by the proximity switches  60  and photoswitches  66 , respectively, without any direct contact between the carrier head  38  and the dresser head  46 . It should be noted that, in order to sense an inappropriate approach between the carrier head and the dresser head, a single switch may be appropriately employed in place of a plurality of switches as disclosed in the second and third embodiments. 
     FIG. 8 shows a polishing apparatus in accordance with a fourth embodiment of the present invention. The apparatus includes a pair of polishing stations  10 ,  10 . For each of the polishing stations, there is provided two cleaning devices  18   a  and  18   b  and a single reverser  20  which are arranged in a line. The apparatus further includes first and second wafer transfer robots  16   a  and  16   b  arranged in a line between and in parallel with the lines of the cleaning devices  18   a  and  18   b  and the single reverser  20  and a single loading and unloading station  14  positioned at an end of the apparatus opposite the end where the polishing stations  10  and  10  are provided. The polishing apparatus of this embodiment makes it possible for one of the polishing stations to conduct a polishing operation of a wafer, while the other polishing station is conducting a dressing operation. In accordance with this embodiment, a pair of the first and second wafer transfer robots  16   a  and  16   b  is adapted to be used for both of the polishing stations  10  and  10  thereby enabling the polishing apparatus to polish a great number of wafers per unit area of an installation as compared with the polishing apparatus in accordance with the first embodiment where a pair of the wafer transfer robots  16   a  and  16   b  is used only for the single polishing station  10 . 
     FIG. 9 shows a polishing apparatus in accordance with a fifth embodiment of the present invention which includes in the polishing station  10 , a single bell-crank type head  70  provided at its opposite ends with the carrying member  42  and the dressing tool  50 , respectively. The head  70  is pivotably supported by a vertical strut  68  laterally spaced from the polishing table  22 . In this apparatus, the carrying member  42  and the dressing tool  50  are simultaneously moved between their work and rest positions in opposite directions relative to each other by pivotal movement of the head  70  about the strut  68 , in order to avoid any contact therebetween. The apparatus therefore needs no collision prevention means, such as is described with reference to FIGS. 4-7. 
     FIG. 10 shows another embodiment of the present invention which employs a controller C 1  for halting the polishing table  22  at a fixed or predetermined position relative to the central axis O 1  of the output shaft of the motor  31  when a polishing operation is completed. As shown, the controller C 1  is connected to an encoder  60  provided on the motor  31  and generates pulse signals representing rotational movement of the output shaft  32  of the motor and a detector  61 , which is positioned under the polishing table  22  to detect a particular reference point provided on the lower surface of the polishing table  22  and passing thereover. 
     The controller C 1  operates as follows. At such a time as it has been determined that a wafer polishing operation is complete, the detector  61  detects the reference point on the lower surface of the polishing table  22  passing over the detector  61  at that time and delivers a signal representing the detection of the reference point to the controller C 1 . The controller then starts counting the pulses delivered from the encoder  60 . When the number of the pluses counted by the controller C 1  reaches a predetermined value which is stored in the controller C 1  in advance, the controller C 1  stops the operation of the motor  31 . As a result, the polishing table  22  is halted at a predetermined position relative to the central axis O 1 . Accordingly, in this embodiment, it is possible for the wafer carrying member  42  to place the wafer W carried by the carrying member  42  at a fixed position relative to the polishing surface  30   a  where a predetermined area of the wafer W facing the polishing surface  30   a  extends radially outwardly beyond the peripheral edge of the polishing surface  30   a , merely by pivoting the carrier head  38  about its strut  36  by a predetermined angle after movement of the polishing table  22  is halted following completion of a polishing operation. Specifically, as shown in FIG. 11 a , during a wafer polishing operation, the carrying member  42  carrying a wafer W is rotated about its axis while the polishing table  22  provided with the polishing member  30  is subjected to a circulatory translational motion. Following completion of a wafer polishing operation, the translation motion of the polishing table is halted as stated above so that the polishing surface  30   a  is positioned at a predetermined position relative to the axis O 1 , of the output shaft of the motor. Then, the wafer carrier head  38  is pivoted about its strut  36  through a predetermined angle with the carrying member  42 , as shown in FIG. 11 b , continuing to be rotated and kept in contact with the polishing surface  30   a . It is desirable that, when the carrier head has been turned through a predetermined angle, the surface of the wafer W is placed in such a manner that it extends radially outwardly from the peripheral edge of the polishing surface by around twenty to fifty percent of its overall surface area, for example, as shown in FIGS. 11 c  and  11   d . Although as the range of extension increases, the surface tension decreases thereby facilitating separation of a polished wafer from the polishing surface  30   a , as the center of the surface of the wafer approaches the peripheral edge of the polishing surface, it becomes increasingly difficult for the wafer carrying member  42  to maintain its attitude. It is therefore preferable for the range of extension noted above not to exceed around fifty percent of the overall surface area of the wafer. Then, the wafer W can be separated from the polishing surface  30   a , as shown in FIG. 11 e.    
     According to a variation of the embodiment of FIG. 10, a polishing apparatus may include a controller which is adapted to sense a position of the polishing table  22  which has been halted after a wafer polishing operation and to then command the motor for the carrier head to turn the carrier head through an angle which is determined on the basis of the sensed position of the polishing table relative to the center axis O 1 , so that the wafer is brought to a position where the surface of the wafer extends beyond the peripheral edge of the polishing surface by a desired percentage of the overall surface area of the wafer. Further, the position control of the carrier head relative to the polishing table as explained with reference to FIG. 10 can be applied to relative positions between the polishing table and the dresser head. 
     It should be noted that the present invention is not necessarily limited to the foregoing embodiments, and can be modified in a variety of ways without departing from the gist of the present invention.