JP4060043B2 - Polishing equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the vibration of the rotating shaft of the polishing surface plate during polishing caused by the difference in the amount of wear between the bearing that receives the thrust load and the bearing that receives the radial load, which is incorporated in the polishing surface plate bearing. The present invention relates to a semiconductor wafer polishing apparatus for preventing.
[0002]
[Prior art]
After the chamfering, the etched silicon wafer is subjected to mechanical chemical polishing on the surface of the silicon wafer in the next polishing step. Here, the surface is finished to a smooth and undistorted mirror surface by the polishing apparatus.
2. Description of the Related Art Conventionally, as a polishing apparatus, a polishing surface plate having a polishing cloth stretched on its upper surface, and a polishing head that is disposed facing the upper surface of the polishing surface plate and one silicon wafer is held on a lower surface by a predetermined holding structure There is known a single wafer polishing apparatus that reciprocates the polishing head in the radial direction of the platen during polishing.
The polishing surface plate has a surface plate body on which the polishing cloth is stretched. A rotating shaft is suspended from the center of the lower surface of the surface plate body, and the polishing cloth rotates together with the surface plate body by rotating the rotating shaft by a rotation motor.
[0003]
During polishing, a silicon wafer is brought into sliding contact with the surface of the polishing cloth (polishing working surface) at a predetermined relative rotational speed and a predetermined polishing pressure while supplying an abrasive (slurry) containing abrasive grains to the polishing cloth. And polish. At this time, the polishing head is reciprocated in the radial direction of the surface plate, and a part of the outer peripheral portion of the silicon wafer is protruded outside the polishing cloth. As a result, the frictional heat is uniformized over the entire sliding surface of the polishing cloth with the silicon wafer, and the wafer flatness is increased.
[0004]
Here, with reference to the schematic sectional view of the polishing apparatus according to the conventional means of FIG. 5, the bearing structure of the rotating shaft of the conventional polishing surface plate will be specifically described.
That is, as shown in FIG. 5, in a conventional polishing apparatus 100, a polishing surface plate 102 having an upper surface with a polishing cloth 101 stretched thereon and an upper surface of the polishing surface plate 102 are opposed to each other. And a polishing head 103 on which a silicon wafer W is held.
The polishing surface plate 102 mainly includes a surface plate body 104 and a bearing 106 that pivotally supports the rotating shaft 105 of the surface plate body 104 in a vertical state.
[0005]
The bearing 106 supports the outer peripheral portion of the surface plate main body 104 from below, receives a thrust load on the rotating shaft 105, and is disposed at the upper portion in the axial direction of the rotating shaft 105. A radial bearing 108 for receiving a load is incorporated. Among these, the radial bearing 108 is disposed radially inward of the rotation shaft 105 with respect to the thrust bearing 107, and an inner ring of the bearing is in contact with the outer peripheral surface of the rotation shaft 105.
The thrust load is a polishing pressure mainly acting on the rotating shaft 105 from the polishing head 103 via the surface plate body 104, and the radial load is mainly when the polishing head 103 reciprocates on the polishing cloth 101. This is a force acting on the rotary shaft 105 via the surface plate body 104 that is dragged by this reciprocation.
[0006]
[Problems to be solved by the invention]
As described above, in the conventional polishing apparatus 100, the bearing (thrust bearing 107) that receives the thrust load and the bearing (radial bearing 108) that receives the radial load are provided inside the bearing 106 of the polishing surface plate 102. Each was incorporated alone.
Therefore, when polishing is performed for a long period of time, a difference occurs between the wear amount of the thrust bearing 107 and the wear amount of the radial bearing 108, and the rotating shaft 105 rattles during the polishing, causing vibration. As a result, the flatness of the silicon wafer W is lowered, and if this vibration becomes intense, the polished surface of the silicon wafer W may be damaged.
[0007]
Therefore, as a result of earnest research, the inventor has replaced the bearing structure of a pair of thrust bearings and radial bearings incorporated in the bearing of the conventional polishing surface plate, and is a cross that simultaneously receives thrust loads and radial loads. It has been found that if a roller bearing is used, such vibration of the rotating shaft can be suppressed, and the present invention has been completed.
In addition, in a polishing apparatus equipped with a pair of reciprocating polishing heads in particular, a cross roller bearing is disposed at a position overlapping with the reciprocal movement trajectory of each polishing head as viewed from the axial direction of the polishing surface plate, If polishing is performed while reciprocating the head, the polishing pressure acting on the polishing surface plate from the polishing head can be satisfactorily received by the cross roller bearing during this reciprocating polishing. As a result, during this reciprocating polishing, polishing is performed. The present invention was completed by discovering that the amount of inclination of the polishing surface plate inclined downward in the moving direction of the head can be reduced.
[0008]
OBJECT OF THE INVENTION
An object of the present invention is to provide a polishing apparatus that can prevent vibration of a rotating shaft of a polishing surface plate during polishing and reduce damage to a semiconductor wafer due to the vibration.
In addition, the present invention can reduce the amount of inclination of the polishing surface plate during reciprocating polishing, and as a result, a polishing apparatus capable of preventing a decrease in wafer flatness due to the inclination of the polishing surface plate. The purpose is to provide.
[0009]
[Means for Solving the Problems]
The invention according to claim 1 comprises: a polishing surface plate provided rotatably; and a polishing head disposed opposite to the polishing surface plate and holding a semiconductor wafer on a surface facing the polishing surface plate. In the polishing apparatus provided, the rotating shaft of the polishing platen is pivotally supported by a cross roller bearing , and the polishing head reciprocates as a pair, and the annular platen is viewed from the axial direction of the polishing platen. Cross roller bearings are arranged at positions that overlap with the reciprocation trajectories of the pair of polishing heads, respectively, and the reciprocation direction of the pair of polishing heads is a tangential direction of the cross roller bearings. The polishing apparatus is disposed on a pair of imaginary lines that are parallel to the rotation axis of the polishing surface plate and pass through an intermediate position of the reciprocation locus of the axis of the pair of polishing heads .
[0010]
This polishing apparatus may be a system that vacuum-sucks a semiconductor wafer to a polishing head or a wax mount system that wax-bonds a semiconductor wafer to a polishing head. Alternatively, a waxless mount method in which the semiconductor wafer is held on the polishing head by a back pad containing water may be used. In addition, the polishing head may be disposed above the polishing surface plate, or may be disposed upside down. Further, it may be a vertical polishing apparatus in which the axial directions of the polishing head and the polishing surface plate are horizontal.
The polishing cloth is usually spread on the surface of the polishing surface plate that faces the polishing head. Examples of the polishing cloth include a hard urethane pad and a CeO ₂ pad.
[0011]
As the semiconductor wafer, various wafers such as a gallium arsenide wafer can be adopted in addition to a typical silicon wafer.
The polishing head may be a single wafer type in which one semiconductor wafer is held on the surface facing the polishing surface plate, or a batch type in which a large number of semiconductor wafers are held together. The polishing head may be reciprocated along the surface of the polishing pad or may be non-reciprocal. When reciprocating, a part of the outer peripheral portion of the semiconductor wafer may be protruded outside the polishing cloth and may or may not be polished. The number of polishing heads used is not limited. There may be one or more.
[0012]
The material of the surface plate body is not limited. However, ceramics, low expansion metals (including alloys), cast iron, steel and the like are preferable.
One or a plurality of cross roller bearings that can simultaneously receive a thrust load and a radial load acting on the rotating shaft may be incorporated in the bearing. When there are a plurality of cross roller bearings, the cross roller bearings may be arranged close to each other or may be arranged apart from each other. In the case of two or more, each cross roller bearing may have the same diameter or different diameters.
[0013]
The structure of the cross roller bearing is not limited. For example, between the inner ring and the outer ring, it may have an annular holding plate that holds a large number of rollers in a rotatable manner, or may not have this holding plate. In short, it is only necessary that the rollers are arranged between the inner ring and the outer ring so that the axis lines of adjacent ones cross each other at a predetermined number in the circumferential direction.
Examples of means for driving and rotating the polishing surface plate include an electric motor and a hydraulic motor.
[0014]
The cross roller bearing only needs to partially overlap with the reciprocation locus of the pair of polishing heads when viewed from the axial direction of the polishing surface plate.
[0015]
However, the reciprocating direction of each polishing head is the tangential direction of the cross roller bearing, and the cross roller bearing is disposed on a virtual line passing through the center of reciprocation of each polishing head, parallel to the rotation axis of the polishing surface plate. Shall. As a result, when polishing a pair of polishing heads while reciprocating in the tangential direction of the cross roller bearing, in most of the reciprocating polishing, the polishing pressure acting on the polishing platen from the polishing heads in the pressure direction is increased. It can be received by the arranged cross roller bearing. As a result, it is possible to further reduce the amount of inclination of the polishing surface plate during the reciprocating polishing even when the cross roller bearings are arranged at positions overlapping with the reciprocating trajectories of the pair of polishing heads.
The structure of the reciprocating means for reciprocating the polishing head is not limited. In short, it is only necessary that the polishing head can be reciprocated with a predetermined reciprocating stroke while the semiconductor wafer is in contact with the polishing cloth.
[0016]
[Action]
According to the present invention, during polishing of the semiconductor wafer, the surface plate body and the polishing cloth are integrally rotated by supplying the polishing agent to the polishing cloth and rotating the rotating shaft by the rotating means. A semiconductor wafer held by a polishing head is brought into sliding contact with the polishing surface at a predetermined pressure to polish the semiconductor wafer. At that time, if necessary, the polishing head is reciprocated on the polishing surface.
A cross roller bearing is disposed in the bearing of the polishing surface plate. As a result, both the thrust load and the radial load acting on the rotating shaft during polishing are received by the cross roller bearing. As a result, even if grinding is performed for a long time, the amount of wear between the bearing that receives the thrust load and the bearing that receives the radial load is always different, for example, unlike a conventional bearing that combines a thrust bearing and a radial bearing. It becomes almost the same. As a result, it is possible to prevent the vibration of the rotating shaft during polishing, which has conventionally been caused by the difference in the amount of wear of both bearings, and to reduce damage to the semiconductor wafer due to this vibration.
[0017]
In addition, since the annular cross roller bearings are arranged at positions overlapping with the reciprocal movement trajectories of the pair of polishing heads as viewed from the axial direction of the polishing surface plate, the polishing head acts on the polishing surface plate during reciprocating polishing. The polishing pressure to be applied can be received by a part of the cross roller bearing arranged in the pressure direction. As a result, the amount of inclination of the polishing surface plate during the reciprocating polishing can be reduced. Therefore, it is possible to prevent the flatness of the semiconductor wafer from being lowered due to the inclination of the polishing surface plate.
Further, the reciprocating direction of both polishing heads is the tangential direction of the cross roller bearing, and the cross roller bearing is parallel to the rotation axis of the polishing surface plate and passes through the intermediate position of the reciprocating locus of the axis of both polishing heads. It is arranged on a pair of virtual lines. As a result, when polishing a pair of polishing heads while reciprocating in the tangential direction of the cross roller bearings, the polishing pressure acting on the polishing platen from the polishing heads in the reciprocating polishing is mostly in the pressure direction. It can be received by the arranged cross roller bearing. Thereby, even when the cross roller bearings are arranged at positions overlapping with the reciprocating trajectories of the pair of polishing heads, the amount of inclination of the polishing surface plate during the reciprocating polishing can be further reduced.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a longitudinal sectional view of an essential part of a polishing apparatus according to one embodiment of the present invention. FIG. 2 is a schematic plan view showing a reciprocating state of the polishing head of the polishing apparatus according to one embodiment of the present invention. FIG. 3 is a perspective view of a cross roller bearing incorporated in a polishing apparatus according to one embodiment of the present invention. FIG. 4 is an enlarged cross-sectional view of a main part of a cross roller bearing incorporated in a polishing apparatus according to an embodiment of the present invention.
In FIG. 1, reference numeral 10 denotes a polishing apparatus according to an embodiment of the present invention. The polishing apparatus 10 is disposed on the upper surface of the polishing surface plate 11 so as to face the polishing surface plate 11. A pair of polishing heads 12 and 12 are provided, on which each of the silicon wafers W is vacuum-sucked. On the upper surface of the polishing surface plate 11, a polyurethane polishing cloth 13 is stretched through a thick sponge rubber (not shown). In this polishing apparatus 10, each silicon wafer W of the pair of polishing heads 12, 12 is reciprocated while being in sliding contact with the polishing surface of the polishing pad 13, so that the surface of each silicon wafer W is mirror-finished one by one. Grind.
[0019]
As shown in FIGS. 1 and 2, the polishing heads 12 and 12 are respectively arranged at symmetrical positions around a rotation shaft 18 of a polishing surface plate 11 described later. These polishing heads 12 and 12 have circular head main bodies 14 and 14 in plan view, respectively. Work chucks 15, 15, on which a silicon wafer W is vacuum-sucked, are fixed to lower portions of the head bodies 14, 14, respectively, on a wafer holding surface (lower surface). In addition, rotary shafts 16 and 16 are provided upright at the center upper portions of the head main bodies 14 and 14, respectively.
[0020]
When the rods of a pair of air cylinders (not shown) are taken in and out, the polishing heads 12 and 12 are vertically moved up and down via the corresponding rotating shafts 16 and 16, respectively. Further, when the corresponding rotation shafts 16 and 16 are rotated by a pair of rotation motors (not shown), the pair of polishing heads 12 and 12 are rotated in predetermined directions, respectively. These polishing heads 12 and 12 are reciprocated in a predetermined direction by reciprocating means (not shown). The specific reciprocating direction is a tangential direction of a cross roller bearing 25 described later. During this reciprocation, the respective polishing heads 12 and 12 are controlled so that their moving directions are always the same. However, the moving directions of the polishing heads 12 and 12 may be controlled so as to always be opposite. In this way, the polishing pressure from each of the polishing heads 12 and 12 always acts at symmetrical positions around the rotation axis 18 of the polishing surface plate 11. As a result, the cross roller bearing 25 can receive the polishing pressure from these polishing heads 12 and 12 in a well-balanced manner, and the tilt amount of the polishing surface plate 11 during reciprocating polishing can be further reduced.
[0021]
Next, the configuration of the polishing surface plate 11 will be described with reference to FIGS.
As shown in FIGS. 1 and 2, the polishing surface plate 11 includes a surface plate main body 17, the polishing cloth 13 that is spread on the surface plate main body 17, and a lower surface central portion of the surface plate main body 17. The rotary motor 18 that rotates the rotary shaft 18 at a predetermined rotational speed via the rotary shaft 18 and the joint 19, and the rotary shaft 18, the air cylinder, and the rotary motor 20 are fixed at predetermined positions. And a bearing 22 attached between the upper frame portion 21a constituting a part of the surface plate base 21 and the surface plate body 17. Hereinafter, each component will be described in detail.
[0022]
The platen body 17 is a thick plate material that is circular in plan view. A short cylindrical inner ring housing 23 is suspended from the outer periphery of the lower surface of the surface plate body 17. A short cylindrical outer ring housing 24 with respect to the inner ring housing 23 is erected on the periphery of a portion where the rotary shaft insertion hole 21c formed in the upper frame portion 21a is formed. The large-diameter cross roller bearing 25 is incorporated between the inner ring housing 23 and the outer ring housing 24. The bearing 22 is mainly constituted by the inner ring housing 23, the outer ring housing 24 and the cross roller bearing 25.
The rotary motor 20 is suspended from an upper frame portion of a portal-type motor mounting frame 21 d that is erected on a lower frame portion 21 b that constitutes another part of the surface plate base 21. The output shaft 20a faces upward, and the upper end portion is accommodated in the rotation shaft insertion hole 21c with a space. Of course, the lower end portion of the rotary shaft 18 connected to the output shaft 20a is also housed in the rotary shaft insertion hole 21c. When the output shaft 20 a is rotated by the rotary motor 20, the rotary shaft 18 rotates through the joint 19. As a result, the surface plate main body 17 rotates horizontally in the predetermined direction together with the polishing pad 13 via the cross roller bearing 25.
[0023]
Next, the cross roller bearing 25 will be described in detail with reference to FIGS. 1 and 3.
The cross roller bearing 25 is a bearing having a special structure that simultaneously receives a thrust load acting on the rotating shaft 18 from the axial direction and a radial load acting on the rotating shaft 18 from a direction orthogonal to the axial direction. .
Specifically, it has an inner ring 25a, an outer ring 25b, a large number of rollers 25c arranged between them, and an annular spacer retainer 25d that holds these rollers 25c in a rotatable manner. Yes. The outer ring 25b is divided into two at an intermediate position in the axial direction. Further, the rollers 25c are arranged so that adjacent ones cross each other's axis. The spacer retainer 25d is a retaining ring that is thick and has a long effective contact length with each roller 25c.
[0024]
In this way, since the adjacent rollers 25c are arranged so as to cross each other's axes, the thrust load and the radial load acting on the inner ring 25a or the outer ring 25b are each in a state in which the respective axial directions are directed in a predetermined direction. The roller 25c receives it. Further, since each roller 25c is held by the spacer retainer 25d, the effective contact length of each roller 25c is increased and the load resistance performance is increased as compared with the conventional annular thin iron plate that pivotally supports each roller. An effect of preventing collapse of 25c is obtained. Moreover, even when the load on the cross roller bearing 25 is increased, there is little possibility that the smooth rotation of the roller 25c due to frictional resistance is hindered.
In this embodiment, the following positional relationship exists between the cross roller bearing 25 and the pair of polishing heads 12, 12. That is, the reciprocating directions of the polishing heads 12 and 12 are respectively tangential to the cross roller bearing 25 and parallel to the rotating shaft 18 of the polishing platen 11 and pass through the reciprocating centers of the polishing heads 12 and 12. A cross roller bearing 25 is disposed on the pair of virtual lines a and a. The center of reciprocation of each of the polishing heads 12 and 12 means an intermediate position of the reciprocation locus of the axis of each polishing head 12 and 12.
[0025]
Next, a method for polishing the silicon wafer W by the polishing apparatus 10 will be described.
As shown in FIG. 1, at the time of polishing, first, the silicon wafer W is vacuum-sucked to the wafer holding surfaces of the work chucks 15 and 15 of the polishing heads 12 and 12 by a negative pressure generated by a vacuum generator (not shown).
Thereafter, an abrasive is supplied at a rate of 5 liters / minute through a slurry nozzle (not shown) onto the center of the polishing pad 13 spread on the surface of the surface plate body 17. While maintaining the supply of the abrasive, the corresponding polishing heads 12 and 12 are respectively rotated at a predetermined rotational speed by a pair of rotation motors (not shown). Further, the polishing heads 12 and 12 are lowered by the protrusion of a predetermined amount of rod of an air cylinder (not shown), and a predetermined polishing pressure is applied to each silicon wafer W. These polishing pressures are maintained, and the polishing surface of each silicon wafer W is pressed against the polishing surface of the polishing pad 13. The specific pressing position at this time is on the pair of virtual lines a and a described above. Thereby, the cross roller bearing 25 exists just under each pressing position.
[0026]
Moreover, the polishing heads 12 and 12 reciprocate in the tangential direction of the opposing portions of the cross roller bearing 25 by a reciprocating mechanism (not shown) (see FIG. 2). At this time, a part of the outer periphery of each silicon wafer W protrudes outside the polishing pad 13.
As a result, the pair of polishing heads 12 and 12 rotate on the polishing platen 11, and the respective polishing heads 12 and 12 reciprocate in the above-described direction, while each silicon wafer W holds the polishing agent. The surface is polished by the polished polishing cloth 13.
[0027]
As described above, the cross roller bearing 25 is disposed at a position overlapping with the reciprocal movement trajectory of the pair of polishing heads 12 and 12, respectively. Therefore, the polishing pressure acting on the polishing platen 11 from the polishing heads 12 and 12 is changed to the pressure. It can be received by cross roller bearings 25 arranged in the direction. As a result, the amount of inclination of the polishing surface plate 11 during reciprocating polishing can be reduced. Therefore, it is possible to prevent the flatness of the silicon wafer W from being lowered due to the inclination of the polishing surface plate 11.
In addition, the reciprocating direction of each polishing head 12, 12 is set to the tangential direction of the cross roller bearing 25, and is parallel to the rotating shaft 18 of the polishing surface plate 11 and passes through the reciprocating center of each polishing head 12, 12. Since the cross roller bearing 25 is disposed on the pair of virtual lines a and a, when the pair of polishing heads 12 and 12 are polished while reciprocating in the tangential direction of the cross roller bearing 25, the reciprocating polishing is performed. In most cases, the polishing pressure acting on the polishing surface plate 11 from the polishing heads 12, 12 can be received by the cross roller bearing 25 arranged in the pressure direction. Thereby, even when the cross roller bearing 25 is arranged at a position overlapping with the reciprocal movement trajectory of the pair of polishing heads 12 and 12, the amount of inclination of the polishing surface plate 11 during the reciprocating polishing can be further reduced. it can.
[0028]
Further, during reciprocating polishing, a thrust load from the pair of polishing heads 12 and 12 and a radial load due to the reciprocating power of the pair of polishing heads 12 and 12 act simultaneously on the rotary shaft 18. Both the thrust load and the radial load are received by a single cross roller bearing 25 incorporated in the bearing 22. Specifically, the thrust load is received around the position Pa between the outer ring 25b and each roller 25c on the entire circumference of the cross roller bearing 25 (see FIG. 2). Further, the radial load accompanying the reciprocation of the pair of polishing heads 12 and 12 is received around the opposing positions Pb and Pb corresponding to both sides of the inner ring 25a in the head reciprocation direction.
As a result, even if polishing work is performed over a long period of time, the amount of wear between the bearing receiving the thrust load and the bearing receiving the radial load is different from, for example, a combination of a conventional thrust bearing and a radial bearing. Always the same. Therefore, the vibration of the rotating shaft 18 during polishing can be prevented, and the deterioration of the flatness of the silicon wafer W and the damage of the silicon wafer W due to the vibration can be reduced.
[0029]
【The invention's effect】
According to this invention, instead of the conventional thrust bearing and radial bearing pair structure, the cross roller bearing that receives both the thrust load and the radial load is incorporated in the bearing of the rotary shaft. The vibration of the rotating shaft of the polishing surface plate can be prevented, and damage to the semiconductor wafer due to the vibration can be reduced.
[0030]
In addition, since the annular cross roller bearing is disposed at a position overlapping with the reciprocal movement trajectory of the pair of polishing heads as viewed from the axial direction of the polishing surface plate, the polishing head is reciprocated on the polishing surface of the polishing cloth. While polishing, the cross roller bearing existing in the pressure direction receives the polishing pressure acting on the polishing platen from the polishing head. Thereby, the amount of inclination of the polishing surface plate during the reciprocating polishing can be reduced. Therefore, it is possible to prevent the flatness of the semiconductor wafer from being lowered due to this inclination.
Further, the reciprocating direction of both polishing heads is the tangential direction of the cross roller bearing, and the cross roller bearing is parallel to the rotation axis of the polishing surface plate and passes through the intermediate position of the reciprocating locus of the axis of both polishing heads. It is arranged on a pair of virtual lines. As a result, when polishing a pair of polishing heads while reciprocating in the tangential direction of the cross roller bearings, the polishing pressure acting on the polishing platen from the polishing heads in the reciprocating polishing is mostly in the pressure direction. It can be received by the arranged cross roller bearing. Thereby, even when the cross roller bearings are arranged at positions overlapping with the reciprocating trajectories of the pair of polishing heads, the amount of inclination of the polishing surface plate during the reciprocating polishing can be further reduced.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an essential part of a polishing apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic plan view showing a reciprocating state of a polishing head of a polishing apparatus according to an embodiment of the present invention.
FIG. 3 is a perspective view of a cross roller bearing incorporated in a polishing apparatus according to an embodiment of the present invention.
FIG. 4 is an enlarged cross-sectional view of a main part of a cross roller bearing incorporated in a polishing apparatus according to an embodiment of the present invention.
FIG. 5 is a schematic sectional view of a polishing apparatus according to conventional means.
[Explanation of symbols]
10 Polishing device,
11 Polishing surface plate,
12 polishing head,
18 rotation axis,
22 bearings,
25 Cross roller bearing,
W Silicon wafer.

Claims (1)

A polishing surface plate provided rotatably,
In a polishing apparatus provided with a polishing head disposed opposite to the polishing surface plate and holding a semiconductor wafer on the surface facing the polishing surface plate,
The rotating shaft of the polishing surface plate is supported by a cross roller bearing ,
These polishing heads reciprocate as a pair,
When viewed from the axial direction of the polishing surface plate, the annular cross roller bearings are arranged at positions that respectively overlap with the reciprocating movement trajectories of the pair of polishing heads,
The reciprocating direction of the pair of polishing heads is the tangential direction of the cross roller bearing,
The cross roller bearing is disposed on a pair of imaginary lines that are parallel to the rotation axis of the polishing surface plate and pass through an intermediate position of the reciprocation locus of the axis of the pair of polishing heads .

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