KR20180134288A - Polishing device - Google Patents

Abstract

Provided is a polishing apparatus capable of preferentially and efficiently controlling the temperature of an area, which is considered as an important temperature control target, on a polishing surface without complicating a structure, and suppressing that the temperature of the polishing surface is changed with polishing of a work, or a polishing condition is partially unmatched thereby. According to the present invention, a temperature control structure (40) formed on the rear side of a polishing surface of a lower polishing plate (2) comprises: an inlet (41) to supply a temperature control fluid; an outlet (42) to discharge the temperature control fluid; a flow path (43) extended along a plurality of concentric circles arranged in the diametric direction of the lower polishing plate (2); and a partition wall (44) extended in the diametric direction of the lower polishing plate (2) to partition the concentric circle. The temperature control fluid flows from the inlet (41) in a third flow path (43c) following a third concentric circle (R3) in a first direction to be U-turned along the partition wall (44) so as to flow in a fourth flow path (43d) following a fourth concentric circle (R4) and flows in the fourth flow path (43d) in an opposite direction to the first direction to be discharged through the outlet (42).

Description

[0001] POLISHING DEVICE [0002]

The present invention relates to a polishing apparatus having a temperature control structure in which a fluid for temperature control flows on the rear side of a polishing surface.

BACKGROUND ART Conventionally, a polishing apparatus having a temperature control structure in which a fluid for temperature control flows on the rear side of a polishing surface in contact with a work, in order to proceed with temperature control such as cooling of a base plate for polishing a work such as a silicon wafer It is known. As a temperature control structure in this polishing apparatus, for example, there is a structure in which a water outlet is formed in the vicinity of an outer peripheral portion (outer peripheral portion) from a water supply port provided in the vicinity of an inner peripheral portion of a base, (See, for example, Patent Document 1) or a plurality of flow paths extending in the main direction of the surface plate and having a temperature control fluid flow path extending in a spiral shape toward the flow path (See, for example, Patent Documents 2 and 3) that can individually control the temperature of the fluid and the like.

[Patent Document 1] Japanese Utility Model Utility Model Publication No. 59-151655 [Patent Document 2] JP-A-2002-373875 [Patent Document 3] JP-A-2002-233948

However, in the temperature control structure having the fluid flow path extended in the spiral shape, the temperature control efficiency of the polishing surface gradually decreases from the center of the surface to the outer peripheral portion. Therefore, it is not possible to preferentially and efficiently control the temperature of a region, which is regarded as a main temperature control target, such as a region having a high contact ratio with the work during polishing of the work. Therefore, there arises a problem that the temperature of the polished surface partially rises due to the influence of the polishing heat caused by the polishing of the work, or the polished condition partially deviates from the temperature.

On the other hand, in the temperature control structure capable of individually controlling the temperature of the temperature controlling fluid flowing through the plurality of flow paths, it is necessary to make the fluid supply / drainage path a plurality of systems, And the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problem, and it is an object of the present invention to provide a polishing apparatus and a polishing apparatus which are capable of preferentially and efficiently controlling a temperature of a polishing surface, , Or a polishing apparatus capable of inhibiting the polishing conditions from being partly deviated from the polishing conditions in relation thereto.

Means for Solving the Problems In order to achieve the above object, the present invention is a polishing apparatus comprising a base having a temperature control structure formed on a rear side of a polishing surface for polishing a work, through which a temperature controlling fluid flows.

The temperature control structure may include a water supply port for supplying the temperature control fluid, a drain port through which the temperature control fluid is discharged, and a plurality of concentric circles extending in the radial direction of the base plate and communicating with the water supply port and the drain port. And a partition wall extending in the radial direction of the base and partitioning the concentric circles.

The temperature regulating fluid supplied from the water supply port flows in the flow path along the first concentric circle in the first direction and then flows in the flow path along the second concentric circle by the U-turn along the partition wall, Flows in a direction opposite to the first direction within the flow path along the concentric circle of the outlet, and is discharged from the drain port.

As a result, it is possible to preferentially and efficiently adjust the temperature of a region regarded as a main object of temperature control of the polishing surface without complicating the structure, and the temperature of the polishing surface accompanying the polishing of the work part is partially changed or related It is possible to prevent the polishing conditions from being partly deviated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view schematically showing the entire configuration of a polishing apparatus according to a first embodiment. FIG.
Fig. 2 is a plan view showing the cooling structure of the polishing apparatus of the first embodiment. Fig.
Fig. 3 is an explanatory view for explaining the area when the polishing surface of the surface plate is divided.
4 is a plan view showing the cooling structure of the polishing apparatus of the comparative example.
Fig. 5 is an explanatory view showing the cooling state of the polishing surface by the cooling structure of the comparative example. Fig.
6 is an explanatory diagram showing the flow direction of the cooling water in the cooling structure according to the first embodiment.
7 is an explanatory view showing a cooling state of the polishing surface by the cooling structure of the first embodiment.
8 is a plan view showing a first modification of the cooling structure of the first embodiment.
9 is a plan view showing a second modification of the cooling structure of the first embodiment.

Hereinafter, an embodiment for carrying out the polishing apparatus of the present invention will be described based on Embodiment 1 shown in the drawings. In the following embodiments, the temperature control structure of the present invention is described as a cooling structure.

(Example 1)

First, the configuration will be described.

The polishing apparatus 1 according to the first embodiment grinds both surfaces of a thin workpiece W such as a semiconductor wafer, a quartz wafer, a sapphire wafer, a glass wafer or a ceramic wafer, It is a double-sided polishing machine. Hereinafter, the configuration of the polishing apparatus 1 according to the first embodiment will be described by dividing it into "the whole configuration", "the detailed configuration of the surface plate" and "the detailed configuration of the cooling structure".

[Overall configuration]

1 is a cross-sectional view schematically showing the overall configuration of a polishing apparatus according to a first embodiment. Hereinafter, the entire configuration of the polishing apparatus of the first embodiment will be described based on Fig.

As shown in Fig. 1, the polishing apparatus 1 according to the first embodiment comprises a lower polishing table 2 and an upper polishing table 3 arranged concentrically with respect to an axis L1, a lower polishing table 2, An internal gear 5 disposed on the outer peripheral side of the lower half 2 and the upper half 3 and a sun gear 4 rotatably disposed in the center of the upper half 3, And a carrier plate 6 which is disposed between the lower stage 2 and the upper stage 3 and in which a workpiece holding hole (not shown) is formed. A polishing pad 2a is attached to the upper surface of the lower polishing table 2 and a polishing pad 3a is attached to the lower surface of the upper polishing table 3. The surface of each of the polishing pads 2a and 3a serves as a polishing surface for polishing the work W.

The lower half 2, sun gear 4 and internal gear 5 are connected to drive devices (not shown) via drive shafts 7a, 7b and 7c, respectively, and are rotationally driven.

Further, the carrier plate 6 is engaged with the sun gear 4 and the internal gear 5. The carrier plate 6 revolves about the axis L1 while rotating by the sun gear 4 and the internal gear 5. The rotation of the carrier plate 6 and the rotation of the lower and upper polishing plates 2 and 3 allow both surfaces of the workpiece W disposed in the workpiece holding holes to be polished by the polishing pads 2a and 3a Is polished.

The assumed column 3 is supported by the rod 8b of the elevating actuator 8 via a table suspender 8a mounted on the upper surface of the column 3. [ Here, a centering bearing 8c is interposed at the leading end of the rod 8b. As a result, the supporter 3 is supported by the lifting actuator 8 so as to be swingable and rotatable.

On the other hand, a drive shaft 9 for a drive mechanism, which is rotated by a drive device (not shown), is inserted and inserted into a drive shaft 7b to which the sun gear 4 is fixed, and the upper end 9a of the drive shaft 9 for the drive mechanism, (An opening, 7d) of the upper surface 7b. A driving mechanism 10 is fixed to the upper end 9a of the driving mechanism 10, and the driving mechanism 10 rotates integrally with the driving shaft 9 for the driving mechanism. A groove portion (not shown) is formed in the outer circumferential surface of the drive mechanism 10 to engage with a hook 3b provided in the supporter 3. When the rod 8b is extended and the supporter 3 moves downward and the hook 3b is engaged with the groove of the drive mechanism 10, (3) are integrally rotated.

That is, the imaginary plane 3 is moved up and down by the expansion and contraction operation of the rod 8b, and is rotated by the rotation of the drive shaft 9 for the drive mechanism. Further, a feed hole (not shown) for feeding a polishing slurry is provided in the supposition plate 3.

[Detailed Configuration of Plate]

The lower half 2 of the polishing apparatus 1 according to the first embodiment is used for suppressing partial temperature changes of the polished surface (the surface of the polishing pad 2a) caused by frictional heat generated during polishing of the work W, A cooling structure 40 (temperature control structure) is formed on the rear side of the polishing surface. The lower flat plate 2 has a lower flat plate member 21, a lower jacket member 22 and a lower side plate receiving member 23 as shown in Fig.

The lower flat plate member 21 is a plate member having a flat surface on which the polishing pad 2a is adhered and is located on the uppermost surface of the lower polishing plate 2. The lower flat plate member 21 is formed of a low thermal expansion material (a material having a small thermal expansion) that is low in coefficient of linear expansion and hardly thermally deformed.

The lower jacket member 22 is a plate member fixed to the rear side (lower surface) of the lower side plate member 21 and a cooling structure 40 is formed on the side opposite to the lower side plate member 21. The tip of the partition wall 46 (see Fig. 2) for partitioning the flow path 43 of the cooling structure 40 is fixed to the lower flat plate member 21. The lower jacket member 22 is formed of stainless steel having a higher linear expansion coefficient and higher rigidity than the lower side plate member 21 and the lower side plate receiving member 23. [

The lower side plate receiving member 23 is a plate member fixed to the rear (lower surface) of the lower jacket member 22 and fixed to the drive shaft 7a.

In order to suppress the partial temperature change of the polishing surface (the surface of the polishing pad 3a) caused by the frictional heat generated in the polishing process of the work W, the preliminary polishing layer 3 of the polishing apparatus 1 of the embodiment 1, A cooling structure 40 (temperature control structure) is formed on the rear side of the polishing surface. As shown in Fig. 1, this supposing plate 3 has an upper flat plate member 31 and an upper jacket member 32. As shown in Fig.

The upper side plate member 31 is a plate member having a flat surface to which the polishing pad 3a is attached and is located on the lowermost side of the upper side support plate 3. The upper flat plate member 31 is formed of a low thermal expansion material which is low in coefficient of linear expansion and hardly thermally deformed.

The upper jacket member 32 is a plate member which is fixed to the rear side (upper surface) of the upper side plate member 31 and is suspended by the side plate suspender 8a. In the upper jacket member 32, a cooling structure 40 is formed on a surface facing the upper side plate member 31. The leading end of the partition wall 46 for partitioning the flow path 43 of the cooling structure 40 is fixed to the upper flat plate member 31. The upper jacket member 32 is formed of stainless steel having a higher coefficient of linear expansion and higher rigidity than the upper flat plate member 31.

[Detailed configuration of cooling structure]

2 is a plan view showing the cooling structure of the polishing apparatus of the first embodiment. Hereinafter, the detailed structure of the cooling structure of the first embodiment will be described based on Fig.

The lower jacket member 22 and the upper jacket member 32 of the first embodiment all have a cooling structure 40 formed thereon. The cooling structure 40 circulates cooling water (a fluid for controlling temperature) supplied from a cooling water circulating device (not shown) and performs heat exchange between the cooling water and the lower flat plate member 21 or the upper flat plate member 31 The lower flat plate member 21 and the upper flat plate member 31 are cooled. Since the cooling structure 40 formed on the lower jacket member 22 and the cooling structure 40 formed on the upper jacket member 32 have the same configuration, (40) will be described.

2, the cooling structure 40 of the first embodiment includes a water supply port 41 for supplying cooling water, a water discharge port 42 for discharging cooling water, a water supply port 41 and a water discharge port 42, And a partition wall 44 extending along the radial direction of the lower half 2.

The water supply port 41 is an opening of a vertical hole penetrating the lower jacket member 22 in the direction of the axis L1 and connected to the water supply port of the cooling water circulation device (Not shown). The water supply passage has a vertical hole extending axially in the drive shaft 7a and a horizontal hole extending horizontally in the lower side plate receiving member 23. [

The drain hole 42 is an opening of the vertical hole penetrating the lower jacket member 22 in the direction of the axis L1 and communicates with a drainage path (not shown) connected to an absorption port (water intake port) of the cooling water circulation device. The opening area of the drain hole (42) is set to a size equivalent to that of the water supply hole (41). The drainage passage has a vertical hole extending axially in the drive shaft 7a and a horizontal hole extending horizontally in the lower side plate receiving member 23. [

The flow path 43 is a trough through which the cooling water flows from the water supply port 41 toward the drain port 42. The flow path 43 is partitioned by a partition wall 46 formed in the lower jacket member 22 and extends along a plurality of concentric circles arranged in the radial direction of the lower half 2. [ The flow path 43 of the first embodiment has a structure in which a plurality of concentric circles (here, five concentric circles, the first concentric circles R1 to the first concentric circles R1, ...) arranged in order from the inner peripheral portion? A second flow path 43b, a third flow path 43c, a fourth flow path 43d and a fifth flow path 43e, respectively, each of which has a plurality of concentric circles R5.

The first flow path 43a formed at the closest position to the inner peripheral portion a along the first concentric circle R1 located on the innermost periphery is provided with an extension of the first flow path 43a (Two in this case) drain openings 42 are formed in the direction of the arrows. A plurality of second flow paths 43b arranged in the extending direction of the second flow paths 43b are provided in the second flow paths 43b adjacent to the first flow paths 43a along the second concentric circle R2 located second from the innermost row (In this case, two) water supply ports 41 are formed. That is, in this first embodiment, a drain port 42 is formed inside the lower half 2 rather than the water supply port 41.

The flow path 43 extends in the main direction of the lower half 2 along a plurality of concentric circles (the first concentric circle R1 to the fifth concentric circle R5), but extends along the partition wall 44 It is turning (U-turn).

That is, among the oil passage 43, the second oil passage 43b and the third oil passage 43c communicate with each other at the first U-turn portion 45a, and the third oil passage 43c and the fourth oil passage 43d communicate with each other at the second U- And the fourth flow path 43d and the fifth flow path 43e communicate with each other at the third U-turn portion 45c. The fifth flow path 43e and the first flow path 43a communicate with each other at the fourth U- And communicates with each other at the portion 45d. The first to fifth flow paths 43a to 43e are formed so as to form a single cooling water route connected as a whole by a midway position along the main direction of the lower half 2, .

The partition wall 44 is a wall surface extending in the radial direction of the lower half 2. The partitioning wall 44 divides the positions of the plurality of concentric circles (the first concentric circle R1 to the fifth concentric circle R5) along which the flow path 43 follows. The partition wall 44 of the first embodiment has a first partition wall 44a partitioning all of the first concentric circles R1 to the fifth concentric circles R5 and a second partition wall 44b partitioning all of the first concentric circles R1 to the fifth concentric circles R5, R2, R3, and R4 of the first partition wall 44a.

That is, the first U-turn part 45a and the third U-turn part 45c are formed along the first partition wall 44a, and the second U-turn part 45b is formed along the second partition wall 44b . In addition, a fourth U-turn portion 45d is formed between the first partition wall 44a and the second partition wall 44b to communicate the fifth flow path 43e and the first flow path 43a.

Next, the operation will be described.

First, the structure and the problem of the surface plate having the cooling structure of the comparative example will be described, and then the action of the polishing apparatus of the first embodiment will be described as " And the characteristic positional action of the position of the drain port ", and" other characteristic action ".

[Configuration and Tasks of Plate with Cooling Structure of Comparative Example]

Fig. 4 is a plan view showing a cooling structure of the polishing apparatus of the comparative example, Fig. 5 is a graph showing the surface temperature of the polishing surface by the cooling structure of the comparative example, Fig. Hereinafter, the configuration and problems of the surface plate having the cooling structure of the comparative example will be described with reference to Figs. 3 to 5.

Generally, in a polishing apparatus for polishing a work such as a silicon wafer, a carrier plate is sandwiched between a lower stage and an upper stage, and a work is disposed inside a work holding hole formed in the carrier plate. Therefore, the movement range of the work is limited by the carrier plate. On the other hand, the carrier plate is engaged with the sun gear and the internal gear. Therefore, the workpiece holding hole needs to be formed at a predetermined distance from the inner periphery of the carrier plate and the outer periphery thereof.

3, the polishing surface K of the table is divided into a central region A located at the central portion of the table, an outer peripheral region C along the outer peripheral portion of the table, The intermediate region B having the highest ratio of contact with the workpiece due to the polishing of the workpiece is divided into an intermediate region B located between the outer peripheral regions C, Quot; process heat "), the temperature becomes higher than the central area A and the outer peripheral area C.

On the contrary, in the cooling structure 100 (temperature control structure) of the comparative example, as shown in Fig. 4, the entirety of the table is divided into 15 parts by the partition wall surface 101 extending in the radial direction, A water supply port 102 and a drain port 103 and a flow path forming wall 104 extending from the inner peripheral portion? Toward the outer peripheral portion? Are formed. Here, the water supply port 102 and the drain port 103 are located at positions sandwiching the flow path forming wall 104, all in the vicinity of the inner peripheral portion? Of the surface plate.

In the cooling structure 100 of this comparative example, the cooling water (temperature controlling fluid) flowing from the water supply port 102 flows along the flow path forming wall 104 as shown by arrows in Fig. 4, (?). The cooling water passes through the gap 106 between the flow path forming wall 104 and the outer peripheral wall 105 formed along the outer peripheral portion beta and then flows along the flow path forming wall 104 along the inner peripheral portion a) and flows into the drain hole 103.

That is, in the cooling structure 100 of this comparative example, the cooling water flows radially in the radially divided sub-areas in the radial direction, and turns around along the outer periphery (?). Therefore, the polishing surface of the table X having the cooling structure 100 is cooled substantially uniformly over the entire surface. As a result, the polishing surface of the surface plate X is deformed by the influence of the machining heat generated during the polishing of the workpiece so that the intermediate region B having a high probability of contact with the workpiece is in the range of about 23 to 24 Deg. C, and becomes higher than the central region A or the peripheral region C, which is suppressed to 23 deg. C or lower. That is, in the surface plate X having the cooling structure 100 of this comparative example, the temperature of the polishing surface partially rises with polishing of the workpiece, and a part of the polishing surface is thermally deformed, distorted, Or a fine polishing condition in which a change within a certain ratio is desirable deviates locally. In addition, there is a possibility that the surface of the polishing pad is locally deteriorated. The surface of the work can not be uniformly polished by the action of one of these phenomena or a composite action, and the polishing precision is lowered.

In the cooling structure 100 of the comparative example, the partition wall surface 101 and the flow path forming wall 104 extend in the radial direction of the surface plate in order to form a flow path along the radial direction of the surface plate. Therefore, when the base X is suspended at the time of conveyance, a bending moment force is imparted to the dividing wall surface 101 and the flow path forming wall 104. Here, when the divided wall surface 101 and the flow path forming wall 104 are formed concentrically, the bending moment force flows in a concentric circle, so that the force can be dispersed. However, in the case of the cooling structure 100 of the comparative example, the drag on the bending moment force depends on the rigidity of the dividing wall surface 101 and the flow path forming wall 104. Therefore, unless the stiffness of the divided wall surface 101 and the flow path forming wall 104 is made large, there is a tendency that bending deformation of the surface plate is likely to occur.

For this reason, for example, it is required to insert a ball into a fixing method at the time of a rough machining of a base, to shorten a conveyance time (hang time) during the production of a base, to achieve a predetermined hardening ) Time is required, there is a problem that the quality of the base X is affected unevenly, or the delivery time delay occurs.

In addition, in the cooling structure 100 of this comparative example, the dividing wall surface 101 and the flow path forming wall 104 extend in the radial direction of the surface plate, The cutting surface is continuous in the radial direction of the surface plate X. In this case, As a result, there arises a problem such that the bending of the base X in the radial direction due to the influence of the residual stress generated by the cutting process becomes large.

[Polishing operation of cooling the surface of the air]

Fig. 6 is an explanatory view showing the flow direction of cooling water in the cooling structure of the first embodiment, and Fig. 7 is an explanatory diagram showing the surface temperature of the polishing surface by the cooling structure of the first embodiment. Hereinafter, the polishing of the polishing apparatus 1 according to the first embodiment will be described based on Figs. The cooling structure 40 in the lower half 2 and the cooling structure 40 in the upper half 3 have the same function. Therefore, only the cooling structure 40 formed in the lower half 2 will be described below.

In the cooling structure 40 of the lower half 2 of the polishing apparatus 1 according to the first embodiment, when cooling water is supplied from a cooling water circulating device (not shown), the cooling water is supplied to the lower jacket member 22 and the lower- (Not shown) formed in the water supply port 23 and flows out from the water supply port 41. At this time, although a plurality of (two) water supply ports 41 are provided along the extending direction of the second flow path 43b, the same amount of cooling water flows from all of the water supply ports 41 at the same time.

The cooling water flowing from the water supply port 41 is first filled in the second flow path 43b of the flow path 43 in which the water supply port 41 is formed and then as shown by the arrow in FIG. And flows to the third flow path 43c through the U-turn section 45a. The cooling water flowing into the third flow path 43c flows in the third flow path 43c in the direction of the half-clock shown in FIG. 6 and flows into the fourth flow path 43d through the second U-turn part 45b. The cooling water flowing into the fourth flow path 43d flows in the fourth flow path 43d in the hour hand direction shown in FIG. 6 and flows into the fifth flow path 43e through the third U-turn part 45c. In addition, the cooling water flowing into the fifth flow path 43e flows in the fifth flow path 43e in the counterclockwise direction shown in Fig. 6 and flows into the first flow path 43a through the fourth U-turn portion 45d .

The cooling water flowing into the first flow path 43a is discharged from the drain port 42 formed in the first flow path 43a. At this time, although a plurality of (two) drain holes 42 are provided along the extending direction of the first flow path 43a, the same amount of cooling water is discharged from the drain holes 42 of all of them.

Heat exchange between the cooling water flowing in the flow path 43 and the lower flat plate member 21 provided with the polishing pad 2a proceeds as described above to cool the surface (polishing surface) of the polishing pad 2a.

Here, in the cooling structure 40 of the first embodiment, the cooling water flows from the water supply port 41 to the second flow path 43b, the third flow path 43c, the fourth flow path 43d, the fifth flow path 43e, Flows into the first flow path 43a → the drain port 42. [ Therefore, the flow path 43 cools the entire surface of the polished surface by a single cooling route. As a result, the water supply and drainage path can be made simple, and the structure can be prevented from being complicated.

Further, since the flow path 43 is a single root, the flow rate of the cooling water flowing through the flow path 43 can be improved. Therefore, the heat transfer coefficient by the cooling water is increased, and the temperature control efficiency can be improved.

In addition, the third flow path 43c is formed along the third concentric circle R3 positioned third from the innermost perimeter. The fourth flow path 43d is formed along the fourth concentric circle R4 located fourth from the innermost periphery. Here, the third flow path 43c and the fourth flow path 43d are flow paths formed at positions opposed to the middle region B (see FIG. 3) where the ratio of contact with the work W during the work polishing is highest .

On the other hand, in the cooling structure 40, the cooling water flowing from the second flow path 43b in which the water supply port 41 is formed flows into the third flow path 43c and then sequentially flows into the fourth flow path 43d Flow structure. Therefore, in the cooling structure 40 of the first embodiment, the cooling water having a relatively low temperature is supplied to the flow paths (the third flow path 43c and the fourth flow path 43d ). That is, the third flow path 43c and the fourth flow path 43d, in which the temperature control efficiency is high, can be opposed to the intermediate region B of the grinding surface that needs to be efficiently cooled, It can be cooled first.

Although the cooling water temperature is the lowest in the second flow path 43b formed with the water supply port 41, cooling water is simultaneously supplied from the plurality of water supply ports 41 arranged along the extending direction of the second flow path 43b Therefore, the flow velocity is lowered compared with the third flow path 43c and the fourth flow path 43d. That is, the plate temperature control efficiency of the second flow path 43b is lower than that of the third flow path 43c and the fourth flow path 43d. However, since the second flow path 43b having a low temperature control efficiency is opposed to the central region A of the lower polishing table 2, it is possible to prevent the second flow path 43b from greatly influencing the cooling state of the polishing surface.

In the cooling structure 40 of the first embodiment, the flow path 43 is turned on by the partition wall 44 partitioning the plurality of concentric circles (the first concentric circle R1 to the fifth concentric circle R5) , The cooling water flows along the partition wall 44 in a U-turn. That is, the flow direction of the cooling water is reversed every time the flow of the cooling water flows in the main direction of the surface plate. Therefore, unlike the case where the flow path is formed in a spiral shape, for example, the distribution of the cooling water temperature in an arbitrary region in the main direction can be made uniform.

As a result, in the lower half 2 of the grinding apparatus 1 of the first embodiment, the region (middle region B) having a high cooling demand among the polished surfaces can be efficiently and preferentially cooled, As described above, even when the processing heat is generated during the polishing of the workpiece, the entire surface of the polishing pad 2a can be adjusted to an approximately uniform temperature of 23 DEG C or less. The temperature of the surface (polishing surface) of the polishing pad 2a can be restrained from being partially changed (raised in this case), thereby suppressing the thermal deformation of the lower polishing pad 2 and / It is possible to maintain fine polishing conditions on the entire surface (polishing surface) of the polishing pad 2a in the apparatus. As a result, it is possible to prevent bad influences on the workpiece W during polishing, such as lowering of the polishing accuracy.

[Combination of different materials]

Generally, the surface of a polishing apparatus such as a lower surface polishing plate or an upper surface polishing plate causes a change with time after a long time in units of years (years), and there is a case where the polishing surface is distorted. In this case, it is necessary to remove the lower half and the upper half from the drive shaft for rotating the lower half and the rod supporting the upper half, and to perform lapping and the like of the polishing surface again to correct the shape.

On the other hand, the lower polishing plate 2 of the polishing apparatus 1 of the first embodiment has the lower flat plate member 21, the lower jacket member 22, and the lower plate receiving member 23. The lower flat plate member 21 and the lower side plate receiving member 23 are formed of a low thermal expansion material having a coefficient of linear expansion smaller than that of the lower side jacket member 22 and the lower side jacket member 22 has a linear expansion coefficient of And is formed of a large, high-rigidity stainless steel.

The lower flat plate member 21 is fixed to the rear side of the lower flat plate member 21 and the cooling structure 40 is fixed to the lower flat plate member 21, The formed lower jacket member 22 is formed of a material having a different linear expansion coefficient.

Therefore, the entire bottom plate 2 has a structure similar to a bimetal in which two sheets of metal plates having different coefficients of thermal expansion are stuck together. Thus, by controlling the temperature of the cooling water flowing through the cooling structure 40, the bending amount of the lower half 2 can be controlled.

The upper plate 3 of the polishing apparatus 1 of the first embodiment has the upper flat plate member 31 and the upper jacket member 32 and the upper flat plate member 31 has the upper jacket member 32, And the upper jacket member 32 is formed of stainless steel having a higher coefficient of linear expansion and higher rigidity than that of the upper jacket member 32.

The upper plate 3 is fixed to the rear side of the upper plate 31 and the cooling structure 40 is fixed to the lower plate 31. [ The formed upper jacket member 32 is formed of a material having a different linear expansion coefficient.

Therefore, the entirety of the imaginary perforated plate 3 becomes a bimetal-like structure in which two sheets of metal plates having different coefficients of thermal expansion are attached together. Thus, by controlling the temperature of the cooling water flowing through the cooling structure 40, the amount of bending of the supporter 3 can be controlled.

Since the control of the amount of bending of the base can be performed by controlling the temperature of the cooling water in both of the lower stage 2 and the upper stage 3, the distortion of the polishing surface due to a change over time If the temperature of the cooling water is adjusted, the distortion can be alleviated. Therefore, it is possible to eliminate the necessity of correcting the polishing surface by lapping or the like.

In the first embodiment, the coefficient of linear expansion of the lower flat plate member 21 is smaller than that of the lower jacket member 22, and the coefficient of linear expansion of the upper flat plate member 31 is smaller than that of the upper jacket member 32. That is, the lower flat plate member 21 and the upper flat plate member 31, which are in contact with the work W and are directly transmitted frictional heat, are formed of a material having a small coefficient of linear expansion which is hard to be thermally deformed. Therefore, it is possible to prevent the lower flat plate member 21 and the upper flat plate member 31 from being thermally deformed by the processing heat generated during the work polishing, suppress deformation of the lower and upper flat plates 2 and 3, It is possible to control the front bending.

In addition, stainless steels are generally inexpensive compared to low thermal expansion materials. Therefore, as in the case of the polishing apparatus 1 of the first embodiment, the lower jacket member 22 and the upper jacket member 32 are replaced by stainless steel in comparison with the case where the entirety of the surface plate is formed of a low thermal expansion material , And the manufacturing cost can be reduced.

Further, in the pretensioner 3 of the first embodiment, the upper side plate member 31 to which the processing heat is directly transferred during the work polishing is formed by the low thermal expansion material which is less likely to be thermally deformed due to the small linear expansion coefficient, (32) is made of inexpensive stainless steel. This makes it possible to suppress the thermal deformation of the upper flat plate member 31 and reduce the manufacturing cost in the supposition plate 3.

In addition, the stainless steel forming the lower jacket member 22 and the upper jacket member 32 is a material having relatively high rigidity. Therefore, the rigidity of the lower half 2 and the upper half 3 can be improved as compared with the case where the lower side jacket member 22 and the upper side jacket member 32 are formed of a low thermal expansion material. Therefore, even if the lower half 2 and the upper half 3 are stuck in the middle of manufacturing, for example, the bending can be suppressed and the ease of manufacturing can be improved.

[Characteristic action by formation position of water supply port and drainage port]

In the first embodiment, the water channel connected to the cooling water circulating unit (not shown) includes a vertical hole formed in the vertical direction inside the drive shaft 7a and a horizontal hole formed in the horizontal direction I have a hole. The drainage channel has a vertical hole formed in the vertical direction inside the drive shaft 7a and a horizontal hole extending horizontally in the lower side plate receiving member 23.

2, the drain port 42 is located closest to the inner peripheral portion? Of the lower half 2, that is, the lower half 2 The water supply port 41 is formed in the first flow path 43a along the first concentric circle R1 located at the innermost periphery of the first flow path 41. The water supply port 41 follows the second concentric circle R2, Is formed in the second flow path (43b) adjacent to the second flow path (43a). That is, both the water supply port 41 and the drain port 42 are formed in the vicinity of the drive shaft 7a.

Therefore, as compared with the case where the water supply port 41 and the water discharge port 42 are formed in the vicinity of the outer peripheral portion? Of the lower half 2, the inside of the lower side surface receiving member 23 among the water supply lines and the drain water is horizontally It is possible to shorten the length of the horizontal hole portion extending to the rear side. In other words, the complexity of the cooling structure 40 can be further suppressed, and the ease of manufacture of the base can be improved.

Particularly, when the water supply port 41 and the drain port 42 are formed in the vicinity of the outer peripheral portion beta of the lower half 2 in the large lower half 2 having a diameter exceeding 2 m, A long transverse hole extending in the horizontal direction is required in the inside of the plate receiving member 23. However, it is very difficult to form the long hole, and even if it can be realized, the cost of the machining can not be increased. However, in the polishing apparatus 1 of the first embodiment, the water supply port 41 and the drain port 42 are formed in the vicinity of the inner peripheral portion?, So that the inside of the lower tray receiving member 23 is moved in the horizontal direction It is possible to suppress the increase in the processing cost by eliminating the need for elongated long holes.

In addition, in the first embodiment, a plurality of (two) water supply ports 41 and a plurality of discharge ports 42 are formed. The same amount of cooling water flows out from the entire water supply ports 41 at the same time, and the same amount of cooling water is discharged from the entire drain ports 42 almost simultaneously. This is nothing but the design of a water channel (water channel design) inside the machine up to the water feed opening in the counter or the design of the water channel inside the machine from the drain hole. Therefore, the number is not necessarily limited to this number. In other words, the number of the water supply port 41 and the number of the water discharge ports 42 is required to be a design for obtaining a desired flow rate and a flow velocity within an allowable withstand pressure.

In the first embodiment, a plurality of water supply ports 41 are formed and arranged in the extending direction of the second flow path 43b in which the water supply port 41 is formed. Therefore, the interference of the cooling water flowing out of the plurality of water supply ports (41) can be suppressed, so that the smooth flow of the cooling water can be prevented from being disturbed. By flowing the cooling water smoothly, the flow rate can be ensured and the efficiency of controlling the temperature of the plate surface can be improved.

In addition, the plurality of drain holes 42 are also arranged in the extending direction of the first flow path 43a in which the drain holes 42 are formed, so that it is possible to quickly discharge the flow of the cooling water without disruption. As a result, there is no obstruction to the smooth flow of the cooling water, and the flow rate of the cooling water can be ensured, and the efficiency of regulating the plate temperature can be further improved.

[Other characteristic features]

In the cooling structure 40 of the first embodiment, the flow paths 43 are formed along a plurality of concentric circles (the first concentric circle R1 to the fifth concentric circle R5) arranged in the radial direction of the lower half 2 . Therefore, the partition wall 46 dividing the first flow path 43a to the fifth flow path 43e extends in the main direction of the lower half 2.

The partitioning wall 46 extends in the main direction of the lower half 2 and the suspended position when the lower half 2 is suspended at the time of conveyance and the inner periphery of the lower half 2, And the outer peripheral portion? Are not continuous. As a result, it is possible to suppress the bending deformation in the radial direction of the base plate when the lower half 2 is conveyed. In other words, the deformation of the lower half 2 during manufacturing can be reduced, and the manufacturing time of the lower half 2 can be shortened, and the ease of manufacture can be improved.

In addition, in the cooling structure 40 of the first embodiment, the flow path 43 follows a plurality of concentric circles (the first concentric circle R1 to the fifth concentric circle R5) arranged in the radial direction of the lower half 2 Therefore, the tips of the partition walls 46 partitioning the first to fourth flow paths 43a to 43e are discontinuous in the radial direction of the table. Therefore, the influence of the residual stress generated when the cutting edge is formed at the tip end of the partition wall 46 can be reduced, and the bending in the radial direction of the lower half 2 can be further suppressed.

Next, the effect will be described.

In the polishing apparatus 1 of the first embodiment, the following effects can be obtained.

(1) A polishing table (2) having a cooling structure (40) through which cooling water flows is formed on the rear side of the polishing surface (the surface of the polishing pads (2a, 3a) ), Characterized in that the polishing apparatus (1)

The cooling structure 40 includes a water supply port 41 for supplying the cooling water, a drain port 42 through which the cooling water is discharged, a water supply port 41 communicating with the drain port 42, A flow path 43 extending along a plurality of concentric circles (first concentric circle R1 to fifth concentric circle R5) arranged in the radial direction of the lower surface (lower surface level 2 and the upper surface level 3) (The first concentric circle R1 to the fifth concentric circle R5) extending in the diametrical direction of the first and second concentric circles 2, 3,

The cooling water supplied from the water supply port 41 flows in the first direction (half-clockwise direction) through the flow path (third flow path 43c) along the first concentric circle (third concentric circle R3) Flows along the wall 44 and flows to the flow path (the fourth flow path 43d) along the second concentric circle (the fourth concentric circle R4), and flows along the second concentric circle (the fourth concentric circle R4) (The hour hand direction) opposite to the first direction (the half-clockwise direction) and discharged from the drain port 42 in the flow path (fourth flow path 43d).

This makes it possible to preferentially and efficiently control the temperature (middle region B), which is regarded as the main temperature control object of the polishing surface, without complicating the structure, and the temperature of the polishing surface, Or to inhibit the polishing conditions from being partially deviated in relation thereto.

(2) The water supply port 41 is provided with a second flow path 43b along a concentric circle (second concentric circle R2) positioned second from the innermost circumference of the base (bottom half 2, Respectively,

When the water supply port 41 is formed in the second flow path 43b, the drain hole 42 is formed in a concentric circle (the first concentric circle) located at the innermost periphery of the table (lower table 2, Is formed in the first flow path 43a along the concentric circle R1.

Thus, in addition to the effect (1), it is possible to further reduce the complexity of the cooling structure 40 by shortening the lengths of the water supply passages and drainage passages in the horizontal direction formed inside the table.

(3) The water supply ports 41 are arranged in a plurality of directions in the extending direction of the flow path (second flow path 43b) along a predetermined concentric circle (second concentric circle R2).

Therefore, in addition to the effects (1) and (2), the load caused by the pressure of the cooling water can be reduced and the cooling water can flow smoothly.

(4) The drain holes 42 are formed in a plurality of rows arranged in the extending direction of the flow paths (the first flow paths 43a) along the predetermined concentric circles (the first concentric circles R1).

Therefore, in addition to any of the effects (1) to (3), the load caused by the pressure of the cooling water can be further reduced, and the flow of the cooling water can be further smoothly performed.

(The lower flat plate member 21 and the upper flat plate member 31) in which the polishing surface is formed and the flat plate member (the lower flat plate member 21) (The lower jacket member 22 and the upper jacket member 32) which are fixed to the upper surface side plate member 21 and the upper side plate member 31 and in which the cooling structure 40 is formed,

The flat plate members (the lower flat plate member 21 and the upper flat plate member 31) and the jacket members (the lower jacket member 22 and the upper jacket member 32) are formed of materials having different coefficients of linear expansion Respectively.

Thus, in addition to any of the effects (1) to (4), the temperature of the cooling water flowing in the cooling structure 40 can be controlled to control the amount of bending of the base, It is possible to eliminate the distortion of the surface plate.

(6) The flat plate members (the lower flat plate member 21 and the upper flat plate member 31) are formed by a material having a coefficient of linear expansion smaller than that of the jacket members (the lower jacket member 22 and the upper jacket member 32) .

Thus, in addition to the effect of (5), it is possible to suppress the thermal deformation of the flat plate member in contact with the work W and to directly transfer the frictional heat, thereby further preventing the deformation of the platen.

(7) The surface plate (lower surface plate 2) is designed so as to have the above-described jacket member (lower jacket member 22) and a surface-receiving member (lower surface-receiving member 23) It is also possible.

In this case, depending on the design of the coefficient of linear expansion of the plate receiving member (lower plate receiving member 23), the unit amount of the change control may be arbitrarily set. Thus, in addition to the effect of (5), it is possible to appropriately adjust the degree of suppression of thermal deformation of the surface plate.

The polishing apparatus according to the present invention has been described above based on the first embodiment. However, the present invention is not limited to this embodiment, and various modifications and changes may be made without departing from the gist of the invention, Changes or additions to the design are permitted.

In the first embodiment, a drain port 42 is formed in the first flow path 43a located at the innermost periphery of the surface plate and a water supply port 41 is provided in the second flow path 43b adjacent to the first flow path 43a An example formed is presented. However, the present invention is not limited to this. For example, the water supply port 41 may be formed in the first flow path 43a and the drain port 42 may be formed in the second flow path 43b. In this case, the cooling water filled in the first flow path 43a sequentially flows from the fifth flow path 43e to the fourth flow path 43d to the third flow path 43c and finally flows to the second flow path 43b It flows. In this manner, by changing the water supply port 41 and the discharge port 42 in the opposite direction without changing the cooling structure 40, it is possible to change the region where the temperature control is to be preferentially performed.

At this time, the water supply port 41 and the drain hole 42 are formed in the vicinity of the drive shaft 7a, and the length of the horizontal hole extending in the horizontal direction of the lower side plate receiving member 23 is shortened Thus, complication of the cooling structure 40 can be further suppressed.

In the cooling structure 40 of the first embodiment, the cooling water is supplied from the water supply port 41 to the second flow path 43b (coolant full) to the third flow path 43c (counter clockwise direction) 43d (the hour hand direction) → the fifth flow path 43e (the half-clockwise direction) → the first flow path 43a (cooling water discharge) → the drain port 42. [ However, the present invention is not limited to this. For example, the cooling structure shown in Fig. 6 may be a left-right reversed cooling structure in which the flow of cooling water is reversed (water supply port 41 → second flow path 43b ) → the third flow path 43c (the hour hand direction) → the fourth flow path 43d (the half hour direction) → the fifth flow path 43e (the hour hand direction) → the first flow path 43a )). As a result, the water supply and drainage path can be made simple, and the structure can be prevented from being complicated. Further, since the flow path 43 is a single root, the flow rate of the cooling water flowing through the flow path 43 can be improved. Therefore, the heat transfer coefficient by the cooling water is increased, and the temperature control efficiency can be improved. In addition, since the direction of the flow path can be reversed without changing the structure, it is possible to change the region where the temperature control is desired to proceed first.

The water supply port 41 and the water discharge port 42 may be formed in the fifth flow path 43e located at the outermost periphery of the surface plate. In the case where the water supply port 41 or the drain hole 42 is formed at the outermost circumferential position of the table or the like, it is possible to form a tube or the like The cooling water may be supplied and drained.

In the first embodiment, two water supply ports 41 and two water discharge ports 42 are provided, but the present invention is not limited thereto. The number of the water supply port 41 and the water discharge port 42 may be one or two or more. The number of the water supply ports 41 and the number of the water discharge ports 42 may be different. In addition, the opening area of the water supply port 41 may be different from the opening area of the drain port 42, or the opening areas of the plurality of water supply ports 41 may be different from each other, Or may be different.

The flow path 43 extends along a plurality of concentric circles (the first concentric circle R1 to the fifth concentric circle R5) arranged in the diametrical direction of the surface plate (the lower plate 2 and the upper plate 3) (The first concentric circles R1 to the fifth concentric circles R5) may be partitioned by the partition wall 44. In this case, Therefore, the shape of the flow path is not limited to that shown in the first embodiment. For example, the cooling structure 40A of the first modification shown in Fig. 8 and the cooling structure 40A of the second modification shown in Fig. (40B).

That is, in the cooling structure 40A of the first modification, the water supply port 41 and the water discharge port 42 are formed in the first flow path 43a located at the innermost periphery of the surface plate. The first partition wall 47a partitioning all of the first to fifth concentric circles R1 to R5 and the first concentric circle R1 to the fourth concentric circle R4 are provided as the partition wall 47, A third partition wall 47c partitioning the second and third concentric circles R2 and R3 and a fourth partition wall 47b partitioning the first and second concentric circles R1 and R2 Thereby forming a partition wall 47d.

A first U-turn portion 48a communicating the first flow path 43a and the third flow path 43c is formed between the first partition wall 47a and the fourth partition wall 47d, A second U-turn portion 48b communicating with the second flow path 43b and the third flow path 43c along the wall 47c is formed and the first flow path 43a and the second flow path portion 43b are formed along the fourth partition wall 47d. And the third and fourth flow paths 43b and 43c are formed between the second partition wall 47b and the third partition wall 47c. And a fifth U-turn portion 48e communicating with the fourth flow path 43d and the fifth flow path 43e is formed along the first partition wall 47a, A sixth U-turn portion 48f is formed between the first partition wall 47a and the second partition wall 47b to communicate the first flow path 43a and the fifth flow path 43e. At this time, the water supply port 41 is formed in the first U-turn portion 48a and the water discharge port 42 is formed in the sixth U-turn portion 48f.

Therefore, in the cooling structure 40A of the first modification, the cooling water flowing from the water supply port 41 flows through the water supply port 41 → the first U-turn part 48a → the third flow path 43c → the second U- The second U-turn portion 48b, the second U-turn portion 43b, the third U-turn portion 48c, the first flow path 43a, the fourth U-turn portion 48d, the fourth flow path 43d, Flows through the fifth flow path 43e, the sixth U-turn portion 48f, and the drain port 42, respectively.

In the cooling structure 40B of the second modification, the water supply port 41 is formed in the first flow path 43a located at the innermost periphery of the surface plate, and the water supply port 41 is formed in the fifth flow path 43e located at the outermost periphery of the surface plate Thereby forming a drain hole 42. Further, the partition wall 49 only divides all of the first concentric circle R1 to the fifth concentric circle R5.

The first U-turn portion 50a, the second U-turn portion 50b, the third U-turn portion 50c, and the fourth U-turn portion 50d are formed alternately with the partition wall 49 interposed therebetween . The first and second flow paths 43a and 43b communicate with each other through the first U-turn portion 50a and the second and third flow paths 43b and 43c communicate with each other through the second U-turn portion 50b, The third and fourth flow paths 43c and 43d communicate with each other via the third U-turn portion 50c and the fourth and fifth flow paths 43d and 43e communicate with each other through the fourth U-turn portion 50d.

Therefore, in the cooling structure 40B of the second modification, the cooling water flowing out from the water supply port 41 flows through the water supply port 41, the first flow path 43a, the first U-turn part 50a, The second U-turn part 50b, the third flow path 43c, the third U-turn part 50c, the fourth flow path 43d, the fourth U-turn part 50d, the fifth flow path 43e, (42).

In Example 1, the lower flat plate member 21 of the lower half 2 is formed of a low thermal expansion material having a small linear expansion coefficient, and the lower jacket member 22 is formed of stainless steel having a large linear expansion coefficient Respectively. However, the present invention is not limited to this. For example, when the lower flat plate member 21, the lower jacket member 22 and the like are selected from a material having a large coefficient of linear expansion, Select it. When a material having a small coefficient of linear expansion is selected, it may be arbitrarily selected from ceramics, granite, carbon fiber reinforcing material, silicon carbide fiber reinforcing material, invar alloy material, and the like. Further, according to the combination, it is possible to set and control the unit distortion amount in accordance with the adjustment accuracy of the temperature of the cooling water in accordance with the difference in coefficient of linear expansion between the lower flat plate member 21 and the lower jacket member 22. [ That is, it is possible to select and combine them in consideration of the deformation control characteristic and the rigidity preferable on the constitution of the device (equipment). The same holds true for the assumed unit 3.

The lower side jacket member 23 is provided below the lower jacket member 22 and the material thereof is made different from that of the lower jacket member 22 as in the example shown in Embodiment 1, It can also be adjusted appropriately.

Although the cooling structure is exemplified as the temperature control structure in the first embodiment, the present invention can also be applied to a heating structure in which a heating fluid for raising the temperature of the polishing surface flows.

In the first embodiment, a double-side polishing apparatus capable of grinding both surfaces of the work W simultaneously with the lower and upper polishing planes 2 and 3 is proposed. However, in the case of the single-sided polishing apparatus in which only one surface of the work W is polished The present invention can be applied to a single-surface polishing apparatus.

In the first embodiment, the number of concentric circles along the flow path 43 is five, but the number of concentric circles is not limited to five, and an arbitrary number of concentric circles can be set.

1: Polishing apparatus
2: Lower half
2a: Polishing pad
3: Introductory class
3a: Polishing pad
3b: Hook
4: Sunfish
5: Internal gear
6: carrier plate
21: Lower flat plate member
22: Lower jacket member
23: Lower side plate receiving member
31: upper flat plate member
32: Upper jacket member
40: cooling structure (temperature control structure)
41: Water supply
42: Sewer
43: Euro
43a:
43b:
43c: Third Euro
43d: the fourth channel
43e: the fifth euro
44: partition wall
45a: first U-
45b: the second U-
45c: the third U-
45d: the fourth U-

Claims (10)

1. A polishing apparatus comprising a polishing table having a temperature adjusting structure in which a temperature controlling fluid is formed on a rear side of a polishing surface for polishing a work,
The temperature control structure may include a water supply port for supplying the temperature control fluid, a drain port through which the temperature control fluid is discharged, and a plurality of concentric circles extending in the radial direction of the base plate and communicating with the water supply port and the drain port. And a partition wall extending in the radial direction of the base and partitioning the concentric circles,
Wherein the temperature controlling fluid supplied from the water supply port flows in the flow path along the first concentric circle in the first direction and then flows in the flow path along the second concentric circle after turning on the partition wall, And flows out in the flow path in the direction opposite to the first direction, and is discharged from the drain port. The method according to claim 1,
Wherein the water supply port is formed in a first flow path along a concentric circle located at the innermost circumference of the plate or a second flow path along a concentric circle located second from the innermost circumference of the plate,
Wherein the drain port is formed in the second flow path when the water supply port is formed in the first flow path and is formed in the first flow path when the water supply port is formed in the second flow path. . The method according to claim 1,
Wherein a plurality of the water supply ports are arranged in the extending direction of the flow path along a predetermined concentric circle. 3. The method of claim 2,
Wherein a plurality of the water supply ports are arranged in the extending direction of the flow path along a predetermined concentric circle. The method according to claim 1,
Wherein a plurality of the drain holes are arranged in the extending direction of the flow path along a predetermined concentric circle. 3. The method of claim 2,
Wherein a plurality of the drain holes are arranged in the extending direction of the flow path along a predetermined concentric circle. The method of claim 3,
Wherein a plurality of the drain holes are arranged in the extending direction of the flow path along a predetermined concentric circle. 5. The method of claim 4,
Wherein a plurality of the drain holes are arranged in the extending direction of the flow path along a predetermined concentric circle. 9. A compound according to any one of claims 1 to 8,
Wherein the surface plate has a flat plate member on which the polishing surface is formed, a jacket member which is fixed to the flat plate member and in which the temperature control structure is formed,
Wherein the flat plate member and the jacket member are formed of a material having a different linear expansion coefficient. 10. The method of claim 9,
Wherein the flat plate member is formed of a material having a coefficient of linear expansion smaller than that of the jacket member.

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