Polishing device

Abstract

To provide a polishing device which polishes a chuck with excellent reproducibility.SOLUTION: A CMP device 1 includes: a porous chuck 16 which includes a chuck table 17 provided at a lower end of a polishing head 10 and a chuck 18 received in a lower surface of the chuck table 17 so that a workpiece W can be held by a holding surface 16a; and a base member 13 which is fastened to the chuck table 17 and transmits rotational driving force input into the polishing head 10 to the chuck table 17. The chuck table 17 and the base member 13 are made of a material indicating a linear expansion coefficient in which flatness of the holding surface 16a changing according to a temperature of the chuck 18 caused by a difference between a linear expansion coefficient of the chuck table 17 and a linear expansion coefficient of the base member 13 is substantially linearly changed over a use temperature range of the CMP device 1. The difference between the linear expansion coefficient of the base member 13 and the linear expansion coefficient of the chuck table 17 is set to be 2.2 ppm / °C or less.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a polishing apparatus for polishing a workpiece. [Background technology]

[0002] 2. Description of the Related Art In the field of semiconductor manufacturing, CMP apparatuses are known that polish and flatten silicon wafers and the like (hereinafter referred to as "workpieces").

[0003] The polishing apparatus described in Patent Document 1 is a polishing apparatus that applies chemical mechanical polishing, or so-called CMP (Chemical Mechanical Polishing) technology. This CMP apparatus polishes a workpiece by pressing the workpiece, which is attached to a polishing head, against a polishing pad. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-159385 A Summary of the Invention [Problem to be solved by the invention]

[0005] In back-surface reference polishing, in which the back surface of the workpiece is held in the chuck of the polishing head and the front surface of the workpiece is pressed against a polishing pad to polish it, it is known that the flatness of the chuck holding the workpiece is transferred as a pressure distribution acting on the workpiece, and affects the shape of the workpiece after polishing.

[0006] In conventional polishing heads, the flatness of the chuck is set to 1 μm or less by lapping the chucking surface of the chuck. However, even when a workpiece is held on such a flat chucking surface and polished under the same polishing conditions, the workpiece shape is not stable, meaning that there are problems in which high reproducibility cannot be obtained.

[0007] Therefore, a technical problem arises that must be solved in order to polish a workpiece with good reproducibility, and an object of the present invention is to solve this problem. [Means for solving the problem]

[0008] As a result of extensive research, the inventors have discovered that in conventional polishing apparatuses, the difference in linear expansion coefficient between the alumina chuck table that houses the chuck and the linear expansion coefficient of a metal base member that is fastened to the chuck table and transmits the rotational driving force input to the polishing head to the chuck table causes nonlinear responsive distortion in the chuck in response to temperature changes during polishing.

[0009] The inventors have also discovered that by setting the difference between the linear expansion coefficient of the chuck table and the linear expansion coefficient of the base member within a predetermined range, the flatness of the chuck changes in a substantially linear manner.

[0010] In order to achieve the above-mentioned object, a polishing apparatus according to the present invention is a polishing apparatus that polishes a workpiece held by a polishing head by pressing it against a polishing pad on a platen, and is equipped with a holding mechanism including a chuck table provided at the lower end of the polishing head and a chuck that is accommodated on the underside of the chuck table and can hold the workpiece on its holding surface, and a base member that is fastened and pressed to the chuck table and transmits a rotational driving force input to the polishing head to the chuck table, wherein the chuck table and the base member are made of materials that exhibit a linear expansion coefficient such that the flatness of the holding surface, which changes according to the temperature of the chuck due to the difference between the linear expansion coefficient of the chuck table and the linear expansion coefficient of the base member, changes approximately linearly over the operating temperature range of the polishing apparatus, and the difference between the linear expansion coefficient of the base member and the linear expansion coefficient of the chuck table is set to 2.2 ppm / °C or less.

[0011] In the polishing apparatus according to the present invention, when the chuck table has a linear expansion coefficient of 7.2 ppm / °C, the base member preferably has a linear expansion coefficient of 5.0 to 9.4 ppm / °C.

[0012] In the polishing apparatus according to the present invention, it is preferable that the base member is made of a low thermal expansion alloy having a linear expansion coefficient lower than that of the chuck table. Effect of the Invention

[0013] The present invention can polish a workpiece to flatness with good reproducibility. [Brief description of the drawings]

[0014] [Figure 1] 1 is a perspective view illustrating a CMP apparatus according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a vertical cross-sectional view showing a schematic view of a main part of a polishing head. [Diagram 3] 13 is a graph showing the temperature dependence of the flatness of a holding surface in a CMP apparatus to which a base member according to a comparative example of the present invention is applied. [Figure 4] 5 is a schematic diagram showing how a holding surface is deformed due to a temperature change. [Diagram 5] 5A and 5B are schematic diagrams showing expansion of a base member and a chuck table due to an increase in temperature. [Figure 6] 5 is a graph showing the relationship between the temperature of a chuck and the flatness of a holding surface when a workpiece is polished by the CMP apparatus according to the first and second embodiments of the present invention. [Figure 7] 13 is a graph showing the finished shape of a workpiece for each polishing temperature when the workpiece is polished using a CMP apparatus according to a comparative example. [Figure 8] 4 is a graph showing the finished shape of a workpiece for each polishing temperature when the workpiece is polished using the CMP apparatus according to Example 1. [Figure 9] 11 is a graph showing the finished shape of a workpiece for each polishing temperature when the workpiece is polished using the CMP apparatus according to Example 2. [Figure 10] 13 is a graph showing the temperature dependence of the flatness of the holding surface in the CMP apparatus according to the comparative example, in which the slope of the flatness of the holding surface is added. [Figure 11]13 is a schematic diagram showing the state in which the holding surface is deformed into a convex shape in order to accommodate a polishing pad with a depressed center. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of the present invention will be described with reference to the drawings. In the following, when the number, numerical value, amount, range, etc. of components are mentioned, the number is not limited to the specific number, and may be more or less than the specific number, unless otherwise specified or when it is clearly limited to a specific number in principle.

[0016] In addition, when referring to the shape or positional relationship of components, etc., this includes things that are substantially similar or approximate to those shapes, etc., unless otherwise specified or considered to be clearly different in principle.

[0017] In addition, the drawings may exaggerate characteristic parts to make the features easier to understand, and the dimensional ratios of the components may not be the same as the actual ones. In addition, in cross-sectional views, hatching of some components may be omitted to make the cross-sectional structure of the components easier to understand.

[0018] 1 is a perspective view showing a schematic diagram of a CMP apparatus 1 according to one embodiment of the present invention. The CMP apparatus 1 polishes one surface of a workpiece W flat. The CMP apparatus 1 includes a platen 2 and a polishing head 10. The workpiece W is, for example, a silicon wafer, but is not limited to this.

[0019] The platen 2 is formed in a disk shape and is connected to a rotating shaft 3 arranged below the platen 2. The rotating shaft 3 is rotated by the drive of a motor 4, causing the platen 2 to rotate in the direction of arrow D1 in Fig. 1. A polishing pad 5 is attached to the upper surface of the platen 2, and CMP slurry, which is a mixture of an abrasive and a chemical agent, is supplied onto the polishing pad 5 from a nozzle (not shown).

[0020] In addition, a circulating cooling device 6 is connected to the platen 2, and temperature-controlled chilled water supplied from the circulating cooling device 6 is passed through the platen 2, thereby making it possible to adjust the temperature of the platen 2 according to the temperature and flow rate of the chilled water during polishing processing.

[0021] The polishing head 10 is formed with a smaller diameter than the platen 2, and is connected to a rotating shaft 10a disposed above the polishing head 10. The rotating shaft 10a is rotated by driving a motor (not shown), causing the polishing head 10 to rotate in the direction of arrow D2 in FIG. 1. The polishing head 10 is configured to be movable vertically and horizontally by a head moving mechanism (not shown). When polishing the workpiece W, the polishing head 10 descends to press the workpiece W against the polishing pad 5.

[0022] The operation of the CMP apparatus 1 is controlled by a control device (not shown). The control device controls each of the components that make up the CMP apparatus 1. The control device is, for example, a computer, and is composed of a CPU, memory, etc. The functions of the control device may be realized by control using software, or may be realized by something that operates using hardware.

[0023] Next, a description will be given of the structure of the polishing head 10. FIG 2 is a vertical cross-sectional view showing a schematic view of the main part of the polishing head 10.

[0024] The polishing head 10 includes a head body 11 connected to a rotating shaft 10a. The head body 11 is connected to a base member 13 via a rotation transmission unit 12, and the head body 11, the rotation transmission unit 12, and the base member 13 rotate together with the rotating shaft 10a.

[0025] A plate holder 14 made of PPS is fastened via a bolt B1 to the upper part of the base member 13. This allows the rotational driving force input to the polishing head 10 to be transmitted to the plate holder 14 via the base member 13.

[0026] An air bag 15 is interposed between the plate holder 14 and the head body 11. The air bag 15 can be inflated and contracted by air supplied from a compressed air source (not shown) via a vacuum line 15a. The pressure of the air supplied from the compressed air source is adjusted by a regulator (not shown). The air bag 15 pressurizes the plate holder 14 according to the pressure of the supplied air, thereby adjusting the polishing pressure with which the workpiece W is pressed against the polishing pad 5.

[0027] A porous chuck 16 is provided below the base member 13. The porous chuck 16 includes a chuck table 17 made of alumina and a chuck 18 made of porous alumina.

[0028] The chuck table 17 is fastened to the base member 13 via the bolts B2. As a result, the rotational driving force input to the polishing head 10 is transmitted to the porous chuck 16 via the base member 13.

[0029] The chuck 18 is embedded in the underside of the chuck table 17. The chuck 18 is connected to a vacuum source and a cooling water source (not shown) via a line 18a. By activating the vacuum source, the workpiece W is adsorbed and held on the holding surface 16a of the porous chuck 16. The cooling water supplied from the cooling water source is adjusted to be approximately equal to room temperature, and the chuck 18 is cooled by passing the water through it after polishing.

[0030] In this manner, the polishing head 10 presses the front surface of the workpiece W against the polishing pad 5 while the back surface of the workpiece W is held by suction on the chuck 18, and a load is transmitted to the workpiece W as the airbag 15 inflates, so that the workpiece W is polished so that the shape of the holding surface 16a is transferred to it (back surface reference polishing). The holding surface 16a is set to a flatness of approximately 1 μm or less by lapping, and in such back surface reference polishing, the flatness of the holding surface 16a of the chuck table 17 affects the finished shape of the workpiece W.

[0031] Moreover, the base member 13 is made of a material exhibiting a linear expansion coefficient close to that (7.2 ppm / °C) of alumina constituting the chuck table 17. The base member 13 is, for example, a low thermal expansion alloy (Invar alloy) prepared so as to have a linear expansion coefficient close to that of alumina.

[0032] The linear expansion coefficient of the base member 13 and the linear expansion coefficient of the chuck table 17 being close to each other means that the linear expansion coefficients of the base member 13 and the chuck table 17 are set so that when the base member 13 and the porous chuck 16 expand and contract while fastened to each other by the bolts B2 over the operating temperature range of the CMP apparatus 1 (for example, about 10 to 40° C.), the flatness of the holding surface 16a, which changes in response to the temperature change of the chuck 19 due to the difference between the linear expansion coefficient of the base member 13 and the linear expansion coefficient of the chuck table 17, changes in an approximately linear manner (responds linearly). The operating temperature range of the CMP apparatus 1 varies depending on the pressure pressing the workpiece W, the rotation speed of the polishing head 10, the rotation speed of the platen 2, the slurry flow rate, the temperature and flow rate of the chiller water, etc. EXAMPLES

[0033] Next, evaluation data comparing the change in flatness of the holding surface 16a over the operating temperature range for a CMP apparatus 1 (Example 1) employing a base member 13 using an Invar alloy with a linear expansion coefficient of 5.0 ppm / °C, a CMP apparatus 1 (Example 2) employing a base member 13 using an Invar alloy with a linear expansion coefficient of 7.0 ppm / °C, and a CMP apparatus 1 (Comparative Example) employing a conventional base member 13 made of SUS316 will be described.

[0034] [Evaluation method] First, FIG. 3 shows the relationship between the temperature of the chuck 18 and the flatness of the holding surface 16a when the temperature of the polishing head 10 of the CMP apparatus 1 according to the comparative example is changed by an external factor.

[0035] FIG. 3 is a graph showing the temperature dependence of the flatness of the holding surface 16a in the polishing head 10 of the CMP apparatus 1 according to the comparative example. In the graph of FIG. 3, the vertical axis indicates the flatness of the holding surface 16a, and the horizontal axis indicates the temperature of the chuck 18. Note that a positive flatness corresponds to a state in which the center of the porous chuck 16 is convex compared to the outer periphery, and a negative flatness corresponds to a state in which the center of the porous chuck 16 is concave compared to the outer periphery. The flatness of the holding surface 16a was measured using a Flat Master 200XRA-Indstrial manufactured by Corning Tropel. The temperature of the chuck 18 was measured using a digital thermometer HA-202K manufactured by Anritsu Keiki Co., Ltd.

[0036] 3 corresponds to a state in which the polishing head 10 of the CMP apparatus 1 according to the comparative example is on standby at room temperature (approximately 22 to 24° C.), and shows the change in flatness of the holding surface 16a when the temperature of the chuck 18 is changed at room temperature (approximately 22 to 24° C.) It can be seen that within this range, the flatness of the holding surface 16a responds linearly, becoming negative (concave) as the temperature increases.

[0037] The range indicated by the symbol b in FIG. 3 corresponds to a state in which the chuck 18 is heated due to frictional heat during polishing, and shows the change in the flatness of the holding surface 16a when the chuck 18 is heated to about 37°C, which is the temperature during polishing, using a hot plate set at 40°C. The range indicated by the symbol c in FIG. 3 corresponds to a state in which cooling water is passed through the polishing head 10 after polishing to cool it, and shows the change in the flatness of the holding surface 16a when it is left at room temperature after heating with a hot plate and cooled to about room temperature. It can be seen that the range indicated by the symbol b and the range indicated by the symbol c do not match, and the flatness of the holding surface 16a deviates from a linear response and changes in a hysteretic manner. It can also be seen that the flatness of the holding surface 16a cooled to room temperature (23°C) after heating is positively (about 5 μm) deformed into a convex shape.

[0038] The range indicated by the symbol d in FIG. 3 corresponds to a state in which the polishing head 10 is placed in an environment below room temperature due to transportation or other reasons, and shows the change in flatness of the holding surface 16a when the polishing head 10 is cooled to near the lower limit of the operating temperature range (about 11°C) with chiller water at 10°C. The range indicated by the symbol e in FIG. 3 shows the change in flatness of the holding surface 16a when the polishing head 10 after cooling with chiller water at 10°C is left at room temperature and warmed up to approximately room temperature. It can be seen that the range indicated by the symbol d and the range indicated by the symbol e do not match, and the flatness of the holding surface 16a deviates from a linear response and changes to hysteresis. It can also be seen that the flatness of the holding surface 16a warmed up to room temperature (23°C) after cooling is negative (about -4 μm) and deformed into a concave shape.

[0039] In this way, it can be seen that the flatness of the holding surface 16a waiting at approximately room temperature differs greatly from the flatness of the holding surface 16a that has reached approximately room temperature after being heated during polishing and cooled by the outside air in cold weather. Furthermore, since the flatness of the holding surface 16a changes with hysteresis, it has been very difficult to manage the flatness of the holding surface 16a.

[0040] Furthermore, considering that the flatness of the holding surface 16a after lapping is approximately 1 μm, while the flatness of the holding surface 16a that has reached approximately room temperature after heating and cooling is approximately 5 μm, it is clear that the workpiece W cannot be polished stably and that it is necessary to reduce the fluctuation in flatness that occurs due to temperature changes in the porous chuck 16.

[0041] Such temperature dependence of the porous chuck 16 is believed to be due to the following reason: That is, it is presumed that, due to the bimetal effect caused by the difference in linear expansion coefficient between the SUS316 base member 13 (linear expansion coefficient: 16.0 ppm / °C) and the alumina chuck table 17 (linear expansion coefficient: 7.2 ppm / °C), when heated, the base member 13 expands relatively more, causing the holding surface 16a to deform into a concave shape, as shown in Fig. 4, and when cooled, the base member 13 contracts relatively more, causing the holding surface 16a to deform into a convex shape.

[0042] Furthermore, when the base member 13 and the porous chuck 16 warm up, as shown in FIG. 5(a), the chuck table 17 is fastened to the base member 13 with bolt B2, and as shown in FIG. 5(b), in the initial stage of thermal expansion, the fastening force of bolt B2 and the surface friction force acting on the contact surface between bolt B2 and the base member 13 and the contact surface between the base member 13 and the chuck table 17 (dashed line portion in FIG. 5(b)) cause the base member 13 and the chuck table 17 to expand uniformly as the temperature rises (linear response).

[0043] 5(c), when the base member 13 expands to an extent that it cannot be supported by the fastening force of the bolt B2 and the surface friction between the base member 13 and the chuck table 17, the base member 13 reaches its holding limit and slides sideways relative to the chuck table 17, so that the base member 13 and the chuck table 17 do not expand uniformly and the flatness of the holding surface 16a tends to saturate with respect to changes in temperature. It is considered that the same tendency occurs when the base member 13 and the porous chuck 16 cool down.

[0044] It should be noted that the temperature range in which the linear response occurs can be expanded by increasing the fastening torque of bolt B2. However, since the chuck table 17 is fastened by bolt B2 via a helical insert tap (not shown), there is a risk that the chuck table 17 will chip or crack if the bolt is fastened with a torque greater than a specified value.

[0045] Next, Fig. 6 shows the relationship between the temperature of the chuck 18 and the flatness of the holding surface 16a when the workpiece W was polished by the CMP apparatus 1 according to Example 1 and Example 2 under the polishing conditions shown in Table 1. In the graph of Fig. 6, the flatness of the holding surface 16a is set on the vertical axis, and the temperature of the chuck 18 is set on the horizontal axis. The measurement of the flatness of the holding surface 16a and the temperature of the chuck 18 are performed in the same manner as in the comparative example described above. [Table 1]

[0046] 6, it can be seen that the variation in flatness of the porous chuck 16 due to the temperature change is smaller than that in FIG. 3. That is, the variation width of the flatness of the holding surface 16a in the operating temperature range is −4 to 4 μm around the flatness (0 μm) at room temperature in Example 1, and is 2 to 2.5 μm around the flatness (2.2 μm) at room temperature in Example 2. Therefore, it can be seen that the flatness of the holding surface 16a in a standby state at room temperature does not deviate from the flatness of the holding surface 16a after heating associated with polishing and cooling by a chiller, and the workpiece W can be stably polished with high reproducibility.

[0047] Furthermore, when the base member 13 is made of a material having a linear expansion coefficient close to that of the alumina chuck table 17, the flatness of the holding surface 16a responds linearly, and therefore it is found that the flatness of the holding surface 16a can be easily controlled by controlling the temperature of the chuck 18.

[0048] Next, Figures 7 to 9 show the finished shape of the workpiece W at each polishing temperature (adjusted by changing the temperature of the chiller water passing through the platen 2) when the workpiece W is polished using each CMP apparatus 1 of Example 1, Example 2, or the comparative example.

[0049] In the graphs of Figures 7 to 9, the vertical axis indicates the finished thickness of the workpiece W, and the horizontal axis indicates the radial coordinate. In Figures 7 to 9, the finished thickness at a point 70 mm away from the center in the radial direction R is set as the standard, and the finished thickness at each measurement point (R = 0 mm, approximately 17 mm, approximately 35 mm, approximately 53 mm) is plotted as a relative height to the standard, thereby representing the finished shape of the workpiece W for each polishing temperature. Note that multiple measurement points on the workpiece W are set at the same radial coordinate, and the finished thickness is indicated by the average value of multiple measurement points on concentric circles.

[0050] In the back surface reference polishing in which the holding surface 16a is transferred to the finished shape of the workpiece W, if the holding surface 16a is deformed into a convex shape with a convex center, the finished shape of the workpiece W will be a concave shape with a concave center, and if the holding surface 16a is deformed into a concave shape with a concave center, the finished shape of the workpiece W will be a convex shape with a convex center. In other words, the finished shape of the workpiece W and the shape of the holding surface 16a are reversed.

[0051] FIG. 7 shows the finished shape of the workpiece W at each polishing temperature when the workpiece W is polished by the CMP apparatus 1 according to the comparative example.

[0052] According to Figure 7, when the polishing temperature is below room temperature (approximately 23°C), the finished shape of the workpiece W is a curved surface that is convex in the middle and the slope gradually decreases toward the outer periphery, and when the polishing temperature is above room temperature (approximately 23°C), the finished shape of the workpiece W is a curved surface that is concave in the middle and the slope gradually increases toward the outer periphery.

[0053] FIG. 8 shows the finished thickness of the workpiece W for each polishing temperature when the workpiece W is polished by the CMP apparatus 1 according to the first embodiment.

[0054] According to Figure 8, compared to Figure 7, when the polishing temperature is below room temperature (approximately 23°C), the finished shape of the workpiece W is the same in that it is convex in the middle, but the height at the center is lower and the entire surface of the workpiece W is formed to be approximately flat, and when the polishing temperature is above room temperature (approximately 23°C), the finished shape of the workpiece W is the same in that it is concave in the middle, but the height at the center is higher and the entire surface of the workpiece W is formed to be approximately flat.

[0055] FIG. 9 shows the finished thickness of the workpiece W for each polishing temperature when the workpiece W is polished by the CMP apparatus 1 according to the second embodiment.

[0056] 9, compared with FIGS. 7 and 8, it can be seen that the entire surface of the workpiece W is formed most flat, regardless of the temperature during polishing.

[0057] In this way, by constructing the base member 13 from a material whose linear expansion coefficient differs little from that of the chuck table 17, the finished shape of the workpiece W can be easily formed to be flat without strict control of the polishing temperature.

[0058] In order to easily control the flatness of the holding surface 16a in this way, when the linear expansion coefficient of the alumina constituting the chuck table 17 is 7.2 ppm / ° C., it is preferable that the material of the base member 13 has a linear expansion coefficient of 5.0 to 9.4 ppm / ° C. The reason for this will be explained below.

[0059] First, the difference between the linear expansion coefficient of the base member 13 made of SUS316 and the linear expansion coefficient of the porous chuck 16 made of alumina is approximately 8.8 ppm / ° C. Then, as shown in Fig. 10 (Fig. 3 with the gradient of the flatness of the holding surface 16a added), the gradient of the flatness of the holding surface 16a when the change is large (part shown by the dashed line in the figure) is -1.8 μm / ° C., and the gradient of the flatness of the holding surface 16a when the change is small (part shown by the broken line in the figure) is -0.45 μm / ° C., so the gradient of the flatness when the flatness of the holding surface 16a has changed the most is four times the gradient of the flatness when the change is small. Therefore, by constructing the base member 13 from a material whose difference in linear expansion coefficient with the porous chuck 16 is 2.2 ppm / °C or less (approximately 8.8 ppm / °C divided by 4), it is believed that the flatness of the holding surface 16a will respond linearly to temperature changes over the operating temperature range (e.g., approximately 10 to 40°C).

[0060] Furthermore, when the workpiece W is pressed into the polishing pad 5 during polishing, the polishing pad 5 may sag slightly, causing the finished shape of the workpiece W to have a concave center, as shown in Fig. 11. In that case, by forming the base member 13 from a material with a lower linear expansion coefficient than the alumina chuck table 17, the holding surface 16a deforms into a convex shape as the temperature rises, and the workpiece W can be polished in such a way that the sagging of the polishing pad 5 is cancelled out.

[0061] Furthermore, the present invention can be modified in various ways other than those described above without departing from the spirit of the present invention, and it goes without saying that the present invention extends to such modifications. [Explanation of symbols]

[0062] 1:CMP equipment 2: Platen 3: (Platen) rotation axis 4: Motor 5: Polishing pad 6: Circulating cooling device 10: Polishing head 10a: Rotating shaft (of polishing head) 11: Head body 12: Rotation transmission section 13: Base material 14: Plate holder 15: Airbag 16: Porous chuck (holding mechanism) 16a: Holding surface 17: Chuck table 18: Zipper W: Work

Claims

1. A polishing apparatus that polishes a workpiece held by a polishing head by pressing the workpiece against a polishing pad on a platen, a holding mechanism including a chuck table provided at a lower end of the polishing head and a chuck accommodated on a lower surface of the chuck table and capable of holding the workpiece on a holding surface; a base member that is fastened to the chuck table by pressure and transmits a rotational driving force input to the polishing head to the chuck table; Equipped with the chuck table and the base member are made of materials exhibiting a linear expansion coefficient such that the flatness of the holding surface, which changes in response to the temperature of the chuck due to a difference between the linear expansion coefficient of the chuck table and the linear expansion coefficient of the base member, changes in a substantially linear manner over the operating temperature range of the polishing apparatus; a difference between the linear expansion coefficient of said base member and the linear expansion coefficient of said chuck table being set to 2.2 ppm / ° C. or less;

2. 2. A polishing apparatus according to claim 1, wherein when the linear expansion coefficient of said chuck table is 7.2 ppm / .degree. C., the linear expansion coefficient of said base member is 5.0 to 9.4 ppm / .degree. C.

3. 2. A polishing apparatus according to claim 1, wherein the base member is made of a low thermal expansion alloy having a linear expansion coefficient lower than that of the chuck table.

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