Wafer planarization apparatus and planarization method thereof

Abstract

Wafers are prevented from getting damaged on delivery thereof from a sucking and carrying device to a table. A wafer before planarization sucked and held by a sucking board is positioned above a table. Next, wafer is vacuum-attracted by the table, and the table is moved upward by that attraction power in a direction to suck the wafer so as to vacuum-suck it on the table. Subsequently, the wafer is sucked and held only by the table by releasing the sucking and holding thereof by the sucking board.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wafer planarization apparatus for, in a semiconductor wafer manufacturing process, grinding a backside on which no chip of a semiconductor wafer is formed and a planarization method thereof.

2. Description of the Related Art

The planarization apparatus for grinding a backside of a semiconductor wafer is generally comprised of a storing stage for storing the wafer and a grinding stage for grinding it, where the wafer is carried by a sucking and carrying apparatus between the storing stage and the grinding stage.

The sucking and carrying apparatus has a sucking board for sucking and holding the wafer with a suction pad and carries the wafer sucked and held by the suction pad to a wafer chuck table on the grinding stage. And the wafer is ground by a rotating grinding wheel in a state of being sucked and held by the chuck table.

There is a problem that, if the wafer forcefully contacts the chuck table on conveying the wafer from the sucking board to the chuck table, the wafer gets chipped or cracked or a chip gets damaged due to an impact thereof. As for this problem, while there is a method of exerting control by decelerating the wafer conveyance speed on delivering the wafer from the sucking board to the chuck table, this control is very difficult in terms of variations in board thickness of the wafer and assembly errors of the apparatus.

SUMMARY OF THE INVENTION

The present invention has been developed in view of the above-described circumstances, and an object thereof is to provide the planarization apparatus of the wafer capable of preventing the wafer from getting damaged on delivering the wafer from the sucking and carrying device to the table and a planarization method thereof.

In order to achieve the above described object, the present invention is directed to a wafer planarization apparatus, comprising: a body; a table which sucks and holds a first surface of a wafer; a sucking and carrying device including a sucking board which sucks and holds the wafer and carries the wafer to the table; and a working division which works on a second surface of the wafer of which the first surface is sucked and held with the table, wherein: the table is placed to be vertically mobile on the body; the wafer before planarization sucked and held with the sucking board is vacuum-attracted when positioned above the table, the table being moved upward by that attraction power in a direction to suck the wafer so as to vacuum-suck the wafer; and when the wafer is vacuum-sucked with the table, the sucking and carrying device releases the sucking and holding of the wafer with the sucking board.

The present invention is also directed to a wafer planarization method, comprising the steps of: sucking and holding, with a sucking board, a wafer before planarization; positioning the wafer sucked and held by the sucking board above a table which is capable of vacuum-attracting the wafer and is placed to be vertically mobile; vacuum-attracting the wafer with the table so that the table is moved upward by that attraction power in a direction to suck the wafer so as to vacuum-suck the wafer; and releasing the sucking and holding of the wafer with the sucking board so that the wafer is only sucked and held with the table.

According to the present invention, the wafer before planarization sucked and held by the sucking board is positioned above the table. Next, the table vacuum-attracts the wafer so that the table is moved upward by that attraction power in the direction to suck the wafer so as to vacuum-suck it. And then, the wafer is only sucked and held by the table by releasing the sucking and holding of the wafer by the sucking board. The conveyance of the wafer from the above described sucking and carrying device to the table is thereby finished. Thus, according to the present invention, the wafer is conveyed to the table not by moving the sucking board by a mechanical feeding apparatus but by moving the table upward by vacuum attraction, so that the wafer can be softly conveyed from the sucking and carrying device to the table without considering variations in board thickness of the wafer and assembly errors of the apparatus. Accordingly, it is possible to prevent the wafer from getting damaged on conveyance thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein:

FIG. 1 is an overall perspective view of a semiconductor wafer planarization apparatus according to an embodiment of the present invention;

FIG. 2 is a plan view of the planarization apparatus shown in FIG. 1 ;

FIG. 3 is a sectional view showing configuration of a sucking board;

FIG. 4 is a bottom view of the sucking board shown in FIG. 3 ;

FIG. 5 is a sectional view showing the configuration of the sucking board of another embodiment; and

FIG. 6 is a sectional view showing the configuration of a table of the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereunder, preferred embodiments will be described in detail for a wafer planarization apparatus and a planarization method thereof related to the present invention in accordance with the accompanied drawings.

FIG. 1 is a perspective view of a planarization apparatus 10 for grinding a backside of a semiconductor wafer, and FIG. 2 is a plan view thereof.

A body 12 of the planarization apparatus 10 shown in FIG. 1 has a cassette storing stage 14 , an alignment stage 16 , a rough grinding stage 18 , a finish grinding stage 20 and a cleaning stage 22 provided in predetermined positions respectively.

The cassette storing stage 14 has two cassettes 24 , 24 removably set, and these cassettes store a large number of wafers 26 before backside grinding. These wafers 26 are held by a carrying robot 28 sheet by sheet to be sequentially carried to the alignment stage 16 that is a next step. The carrying robot 28 is supported by having it hung down from a beam 30 erected on the body 12 via an elevating apparatus 32 . In addition, the elevating apparatus 32 is coupled to a feed screw apparatus (not shown) built in the beam 30 , and if the feed screw apparatus feeds and moves the elevating apparatus 32 , the carrying robot 28 can move to and from in the directions of arrows A and B on FIGS. 1 and 2 along the installation direction of the beam 30 . The wafers 26 are sequentially carried according to a route predetermined in the planarization apparatus 10 by the above-described movement of the carrying robot 28 and its operation.

The carrying robot 28 is a general-purpose industrial robot, which is comprised of a U-shaped arm 34 for sucking and holding the wafers 26 , and three links 36 , 38 and 40 and so on. Suction pads 35 , 35 for sucking the wafers 26 are placed at the tips of the arm 34 . And suction power is generated to the suction pads 35 , 35 by sucking via these pads. In addition, the arm 34 has its end rotatably supported centering on its shaft center by the link 36 , and can be rotated centering on the shaft center by a driving force from a motor (not shown). The link 36 is rotatably coupled to the link 38 via a shaft 42 , and can be rotated centering on the shaft 42 by the driving force from the motor (not shown). In addition, the link 38 is rotatably coupled to the link 40 via a shaft 44 , and can be rotated centering on the shaft 44 by the driving force from the motor (not shown). Furthermore, as the link 40 is coupled via a shaft 46 to an output shaft of the motor (not shown), it can be rotated centering on the shaft 46 by driving the motor. In addition, the motor is coupled to an elevating rod (not shown) of the elevating apparatus 32 . Therefore, the robot 28 can control operations of the arm 34 and the three links 36 , 38 and 40 with the respective motors and also control a contraction operation of the elevating rod of the elevating apparatus 32 so as to take out the wafers 26 stored in the cassettes 24 by sucking and holding them on the suction pads 35 and carry them to the alignment stage 16 .

The alignment stage 16 is a stage for aligning the wafers 26 carried from the cassettes 24 in predetermined positions. The wafers 26 aligned at this alignment stage 16 are sucked and held by the suction pads 35 , 35 of the carrying robot 28 again, and then they are carried toward an empty chuck table 48 and sucked and held in predetermined positions of this chuck table 48 .

The chuck table 48 is mounted on a turntable 50 , and the chuck tables 52 and 54 having the same function are mounted with predetermined spacing on the turntable 50 . The chuck table 52 is located on the rough grinding stage 18 , where the sucked wafers 26 are roughly ground. In addition, the chuck table 54 is located on the finish grinding stage 20 , where the sucked wafers 26 are given finish grinding (fine refining, spark out). Moreover, although not shown in FIG. 1 and FIG. 2 , the chuck tables 48 , 52 and 54 have spindles of rotational motors coupled to their bottoms respectively, and are rotated by their driving power.

The wafers 26 sucked and held by the chuck table 48 have their thickness measured by a measurement gauge (not shown). The wafers 26 having their thickness measured are positioned on the rough grinding stage 18 by the rotation in the direction of an arrows C on FIG. 1 and FIG. 2 of the turntable 50 , and the backsides of the wafers 26 are roughly ground by a cup-shaped grinding wheel 56 of the rough grinding stage 18 . As shown in FIG. 1 , this cup-shaped grinding wheel 56 is coupled to the output shaft (not shown) of the motor 58 , and also mounted on a grinding wheel feeding apparatus 62 via a support casing 60 of the motor 58 . The grinding wheel feeding apparatus 62 elevates the cup-shaped grinding wheel 56 along with the motor 58 , where the cup-shaped grinding wheel 56 is pressed onto the backsides of the wafers 26 by this descending movement. The backsides of the wafers 26 are thereby roughly ground. The descending movement amount of the cup-shaped grinding wheel 56 , that is, an amount of grinding by the grinding wheel is set based on a reference position thereof registered in advance and the thickness of the wafers 26 .

The wafers 26 having their backsides roughly ground at the rough grinding stage 18 have their thickness measured by a measurement gauge (not shown) after the cup-shaped grinding wheel 56 receded therefrom. The wafers 26 having their thickness measured are positioned at the finish grinding stage 20 by the rotation of the turntable 50 in the same direction, and the fine refining and spark out are performed to them by a cup-shaped grinding wheel 64 shown in FIG. 2 of the finish grinding stage 20 . As the finish grinding stage 20 has almost the same configuration as the rough grinding stage 18 , the description thereof is omitted here.

The wafers 26 having been given the finish grinding at the finish grinding stage 20 are carried to the position of the empty chuck table 48 shown in FIG. 1 by the rotation of the turntable 50 in the same direction after the cup-shaped grinding wheel 56 receded from the wafers 26 . And the wafers are sucked by a sucking board 68 having a disc-like sucking surface 68 A formed by a porous element 73 of approximately the same diameter as the wafers 26 placed at the tip of a carrying arm 66 , and then they are carried to the cleaning stage 22 by the rotation of the carrying arm 66 in the direction of an arrow D on FIG. 1 .

FIG. 3 is a sectional view of the sucking board 68 placed at the tip of the carrying arm 66 , and FIG. 4 is a bottom view of the sucking board 68 .

As shown in these drawings, the sucking board 68 is formed to have the configuration wherein the disc-like porous element 73 of approximately the same diameter as the wafers 26 is put in a body frame 71 of a reverse-bowl shape having an attraction opening 69 formed. The attraction opening 69 is connected to an attraction apparatus (not shown) via an attraction route formed in the carrying arm 66 . Thus, if the attraction apparatus operates, the suction power is generated on the sucking surface 68 A of the sucking board 68 formed by the porous element 73 , and the entire surface of the wafer 26 is vacuum-sucked by the sucking surface 68 A. As for the porous element 73 forming the sucking surface 68 A, ceramic porous, sintered metal, porous resin wherein resin is foamed and so on may be used for instance.

Thus, as the planarization apparatus 10 has the wafer 26 that is in a thin-wall state due to rough and fine grinding sucked and held by the sucking board 68 having the sucking surface 68 A formed by the disc-like porous element 73 of approximately the same diameter as the wafer 26 , it can entirely suck the wafer surface on the sucking surface 68 A of the sucking board 68 . Accordingly, it is in a state where the entire wafer surface and the entire sucking surface 68 A of the sucking board 68 are bonded together, so that it becomes as if the wafer 26 and the sucking surface 68 A of the sucking board 68 are rendered one-piece. Thus, the sucking surface 68 A plays a role of a reinforcing plate, and so, in particular, marginal portions of the wafers 26 do not get chipped or cracked when sucking or carrying the wafers 26 in the thin-wall state.

The wafers 26 carried to the cleaning stage 22 are cleaned at the cleaning stage 22 and then stored on a predetermined shelf of the predetermined cassette 24 . The above is a flow of a wafer working step by the planarization apparatus 10 .

FIG. 5 is a sectional view showing another embodiment of a sucking board 80 , and any member that is the same as or similar to that of the sucking board 68 shown in FIG. 3 is numbered likewise and the description thereof will be omitted.

The sucking board 80 in FIG. 5 is coupled to the carrying arm 66 via an air cylinder apparatus 82 . The air cylinder apparatus 82 is comprised of a cylinder case 84 , a rod 86 , a suction pump 90 and so on.

The cylinder case 84 is fixed on the carrying arm 66 , and the rod 86 is supported to be vertically mobile by the cylinder case 84 , and the sucking board 80 is placed on the rod 86 via a globe 92 . The globe 92 is rotatably supported between the rod 86 and a supporting member 96 made of hard rubber fixed at the bottom of the rod 86 by a screw 94 . Accordingly, the sucking board 80 fixed on the globe 92 by a screw 98 can be freely fluctuated against the carrying arm 66 , and so it can be tilted according to the inclination of the surface of the wafer 26 held by the chuck table 48 . Thus, the entire surface of the wafer 26 is evenly sucked by the sucking board 80 . Moreover, a symbol 104 denotes a sleeve put in the cylinder case 84 , and a spring 102 is mounted between a sleeve 104 and an upper flange portion 87 of the rod 86 . The rod 86 is energized upward by energization power of the spring 102 .

On the other hand, if the suction pump 90 is driven, the air in a globe storage room 106 surrounded by the rod 86 and the supporting member 96 is attracted so that the supporting member 96 is elastically deformed by this negative pressure in a direction to reduce capacity of the globe storage room 106 . Thus, the globe 92 is supported between the rod 86 and the supporting member 96 and is fixed so as not to be rotated. Moreover, if a vacuum breaker 107 is opened, the pressure of the globe storage room 106 returns to atmospheric pressure so that the supporting member 96 returns to its original shape and the sucking board 80 is restored to the freely fluctuating state.

The sucking board 80 is coupled to a suction pump 110 via a vacuum breaker 108 . Accordingly, if the vacuum breaker 108 is closed and the suction pump 110 is driven, the sucking board 80 is vacuum-driven. Moreover, the sucking board 80 is connected to a vacuum sensor 112 that measures vacuum pressure thereof.

In addition, the chuck table 48 (same with chuck tables 52 and 54 ) is coupled to a suction pump 116 via a vacuum breaker 114 . Accordingly, if the vacuum breaker 114 is opened, the suction power of the wafers 26 by the chuck table 48 is released.

The sucking board 80 is thus configured in order to solve the problems mentioned below.

To be more specific, as for the conventional method of removing the wafers from the chuck table to suck and hold them by the sucking board, the method was adopted, wherein, after destroying the vacuum of the chuck table, liquid, gas or bubbles got spurted from the sucking surface of the chuck table so as to suck and hold the wafers having ascended due to momentum thereof by the sucking board.

However, the conventional method had a fault that, when blowing up the wafers, the very thin wafers get damaged due to the momentum or the wafers were sucked in a position deviated from the sucking board.

On the other hand, if the sucking board is fixed on the carrying arm in a state incapable of fluctuation, the sucking board has no degree of freedom, so that there are the cases where adhesion of the wafers to the sucking board is reduced and the wafers are left on the chuck table.

In addition, there are the cases where, if the arm is turned without lifting (receding) the wafer from the chuck table after sucking it by the sucking board, the underside (element forming surface) thereof is rubbed by the chuck table and so the underside gets damaged, and furthermore, there are the cases where, if the wafer is lifted from the chuck table without considering surface tension of the liquid involved between the chuck table and the wafer, the wafer is left on the chuck table due to that surface tension.

Therefore, the workings of the sucking board 80 to solve such problems will be described.

First, the sucking board 80 is positioned by the carrying arm 66 above the wafers 26 sucked and held by the chuck table 48 as shown in FIG. 5 . At this time, the vacuum breaker 107 is opened and so the globe 92 is in a free state so that the sucking board 80 can be freely fluctuated against the carrying arm 66 . In addition, a distance L between the sucking board 80 and the wafers 26 at this time is set at the distance capable of having the sucking board 80 descend on the wafer 26 side by its own attraction power, and it is also set at the distance not to interrupt the surface tension of the liquid involved between the chuck table 48 and the wafers 26 on having the wafers 26 removed from the chuck table 48 by the sucking board 80 .

Next, the vacuum breaker 108 is closed and the suction pump 110 is driven. Thus, the sucking board 80 descends toward the wafer 26 by its own attraction power and resisting the energization power of the spring 102 so as to suck the wafer 26 . At this time, the sucking board 80 can be freely fluctuated against the carrying arm 66 so that it tilts following the surface of the wafer 26 and sucks and holds the entire surface thereof.

Subsequently, once it is checked that the wafer 26 is securely sucked and held by the sucking board 80 by seeing that the vacuum pressure of the vacuum sensor 112 has reached an optimum value, the vacuum breaker 107 is closed and the suction pump 90 is driven. Thus, the globe 92 is supported between the rod 86 and the supporting member 96 and is fixed so as not to be rotated, and the sucking board 80 is fixed on the carrying arm 66 so as not to be fluctuated.

If the vacuum breaker 114 on the chuck table 48 side is opened in this state, the sucking and holding of the wafer 26 by the chuck table 48 are released. Thus, the rod 86 ascends due to the energization power of the spring 102 so that the sucking board 80 ascends and is restored to its original position.

As the position of the sucking board 80 at this time is one that does not interrupt the surface tension of the liquid involved between the chuck table and the wafers, the wafer 26 will not be left on the chuck table 48 .

Thereafter, the carrying arm 66 is driven horizontally to carry the wafers 26 sucked and held by the sucking board 80 toward the cleaning stage. At this time, as the wafer 26 has receded above the chuck table 48 in advance, the underside (element forming surface) thereof is not rubbed by the chuck table 48 . And so the underside thereof does not get damaged by the chuck table 48 .

Accordingly, it is possible to solve all of the aforementioned problems in the past by using the sucking board 80 .

Moreover, while an example of sucking and holding with the sucking board 80 the wafers sucked and held by the chuck table 48 was described in the above described embodiment, the following workings and effects arise by placing on the chuck table 48 side the air cylinder apparatus 82 placed on the sucking board 80 side as shown in FIG. 6 . To be more specific, it is possible, by placing the air cylinder apparatus 82 on the chuck table 48 side, to deliver to the chuck table 48 the wafers 26 before the workings vacuum-sucked and held by the sucking board 80 without damaged them.

FIG. 6 is a sectional view showing an example thereof, and any member that is the same as or similar to that of the air cylinder apparatus 82 shown in FIG. 5 is numbered likewise and the description thereof will be omitted.

The cylinder case 84 of the air cylinder apparatus 82 is placed on the turntable 50 side, and the rod 86 is supported to be vertically mobile by the cylinder case 84 . In addition, the chuck table 48 is coupled to the rod 86 via the globe 92 . The globe 92 is rotatably supported between the rod 86 and the supporting member 96 made of hard rubber fixed in the upper part of the rod 86 by the screw 94 . Accordingly, the chuck table 48 fixed on the globe 92 by the screw 98 can be freely fluctuated against the turntable 50 , and so it can be tilted according to the inclination of the surface of the wafer 26 held by the sucking board 80 . Thus, the entire surface of the wafer 26 is evenly sucked by the chuck table 48 .

In addition, the chuck table 48 is connected to the vacuum sensor 112 that measures the vacuum pressure thereof. Furthermore, the chuck table 48 (same with chuck tables 52 and 54 ) is coupled to the suction pump 116 via the vacuum breaker 114 . Accordingly, if the vacuum breaker 114 is opened, the suction power of the wafers 26 by the chuck table 48 is released. A sucking division of the chuck table 48 is also comprised of the porous element 73 just like the sucking board 80 .

Moreover, the spring 102 is mounted between the sleeve 104 and the lower flange portion 87 of the rod 86 . The rod 86 is energized downward by the energization power of the spring 102 .

Once the suction pump 90 is driven, the air in the globe storage room 106 surrounded by the rod 86 and the supporting member 96 is attracted, so that the supporting member 96 is elastically deformed by this negative pressure in the direction to reduce capacity of the globe storage room 106 . Thus, the globe 92 is supported between the rod 86 and the supporting member 96 and is fixed so as not to be rotated. Moreover, if a vacuum breaker 107 is opened, the pressure of the globe storage room 106 returns to the atmospheric pressure so that the supporting member 96 returns to its original shape and the sucking board 80 is restored to the freely fluctuating state.

The sucking board 80 is coupled to the suction pump 110 via the vacuum breaker 108 . Accordingly, if the vacuum breaker 108 is closed and the suction pump 110 is driven, the sucking board 80 is vacuum-driven, and if the vacuum breaker 108 is opened, the suction power of the wafers 26 by the sucking board 80 is released.

Next, the workings of the chuck table 48 on which the air cylinder apparatus 82 is placed will be described.

First, as shown in FIG. 6 , the wafer 26 sucked and held by the sucking board 80 is positioned above the empty chuck table 48 by using the carrying arm 66 . At this time, as the vacuum breaker 107 is opened, the globe 92 is in a free state so that the chuck table 48 can be freely fluctuated against the turntable 50 . In addition, the distance L between the chuck table 48 and the wafer 26 at this time is set at the distance capable of having the chuck table 48 ascend on the wafer 26 side by its own attraction power, and it is also set at the distance not to interrupt the surface tension of the liquid involved between the sucking board 80 and the wafer 26 on having the wafer 26 removed from the sucking board 80 on the chuck table 48 .

Next, the vacuum breaker 114 is closed and the suction pump 116 is driven. Thus, the chuck table 48 ascends toward the wafer 26 by its own attraction power and resisting the energization power of the spring 102 so as to suck the wafer 26 . At this time, the chuck table 48 can be freely fluctuated against the turntable 50 so that it tilts following the surface of the wafer 26 and sucks and holds the entire surface thereof.

Subsequently, once it is checked that the wafer 26 is securely sucked and held by the chuck table 48 by seeing that the vacuum pressure of the vacuum sensor 112 has reached the optimum value, the vacuum breaker 107 is closed and the suction pump 90 is driven. Thus, the globe 92 is supported between the rod 86 and the supporting member 96 so as not to be rotated, and the chuck table 48 is fixed on the turntable 50 so as not to be fluctuated.

If the vacuum breaker 108 on the sucking board 80 side is opened in this state, the sucking and holding of the wafers 26 by the sucking board 80 are released. Thus, the rod 86 descends due to the energization power of the spring 102 so that the chuck table 48 descends and is restored to its original position.

As the position of the chuck table 48 at this time is one that does not interrupt the surface tension of the liquid involved between the sucking board 80 and the wafer 26 , the wafer 26 will not be left on the chuck table 48 .

Accordingly, it is possible, by placing the air cylinder apparatus 82 on the chuck table 48 side, to securely deliver to the chuck table 48 the wafer 26 before the workings vacuum-sucked and held by the sucking board 80 .

Thus, according to the embodiment, the wafer 26 is conveyed to the table not by moving the sucking board by a mechanical feeding apparatus but by moving the chuck table 48 upward by vacuum attraction, so that the wafer 26 can be softly conveyed from the sucking board 80 to the chuck table 48 without considering variations in the board thickness of the wafer 26 and assembly errors of the apparatus. Accordingly it is possible to prevent the wafer 26 from getting damaged on conveyance thereof.

As described above, according to the wafer planarization apparatus and the planarization method thereof involved in the present invention, the wafer is conveyed to the table by moving the table upward by vacuum attraction, so that the wafer can be softly conveyed from the sucking and carrying device to the table without considering the variations in board thickness of the wafer and the assembly errors of the apparatus, and so it is possible to prevent the wafer from getting damaged on conveyance thereof.

It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.

Claims

1. A wafer planarization apparatus, comprising:a body; a table which sucks and holds a first surface of a wafer; a sucking and carrying device including a sucking board which sucks and holds the wafer and carries the wafer to the table; and a working division which works on a second surface of the wafer of which the first surface is sucked and held with the table, wherein: the table is placed to be vertically mobile on the body; the wafer before planarization sucked and held with the sucking board is vacuum-attracted when positioned above the table, the table being moved upward by that attraction power in a direction to suck the wafer so as to vacuum-suck the wafer; and when the wafer is vacuum-sucked with the table, the sucking and carrying device releases the sucking and holding of the wafer with the sucking board.

2. A method of transferring a wafer within a wafer planarization apparatus, comprising the steps of:sucking and holding, with a sucking board, a wafer before planarization; positioning the wafer sucked and held by the sucking board above a table which is capable of vacuum-attracting the wafer and is placed to be vertically mobile; vacuum-attracting the wafer with the table so that the table is moved upward by that attraction power in a direction to suck the wafer so as to vacuum-suck the wafer; and releasing the sucking and holding of the wafer with the sucking board so that the wafer is only sucked and held with the table.