Ceramic heater

Abstract

Provided is a ceramic heater capable of uniformizing an amount of gas ejected from a plurality of lateral holes. The ceramic heater includes: a ceramic plate having a first surface and a second surface and having a heater electrode embedded therein; a ceramic shaft attached to the second surface of the ceramic plate; a shaft hole provided so as to penetrate into a side wall constituting the ceramic shaft; a gas groove provided in an arc shape at the second surface of the ceramic plate to form a gas flow path communicating with the shaft hole; a plurality of gas introduction holes provided in the ceramic plate in the vertical direction and communicating with the section directly above the gas groove and arranged spaced apart from each other in the longitudinal direction of the gas groove; and a plurality of lateral holes provided in the ceramic plate in the lateral direction from the plurality of gas introduction holes and reaching the first surface or a side end surface of the ceramic plate. At least one of the gas introduction holes has a diameter different from the other gas introduction holes so that gas flow rates in the plurality of gas introduction holes are uniform.

Description

Technical Field

[0001] The present invention relates to a ceramic heater.

Background Art

[0002] In a film forming apparatus for a semiconductor manufacturing process, a ceramic heater is used as a support stage for uniformly controlling the temperature of a wafer. As such a ceramic heater, one including a ceramic plate on which a wafer is placed and a cylindrical ceramic shaft attached to the ceramic plate is widely used.

[0003] During the manufacturing process of a semiconductor device, process gas may enter the back surface of a wafer placed on a ceramic heater and deposits may occur. To prevent this, a technique of providing a purge function to a ceramic heater with a shaft is known. The purge function is a function of ejecting an inert gas from the outer peripheral portion of the ceramic plate to prevent the process gas from flowing into the back surface of the wafer.

[0004] Ceramic heaters with shafts having various structures with a purge function have been proposed. For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2022-147715) discloses an electrode-embedded member including a flat plate-shaped ceramic substrate having a placement surface and an electrode embedded in the substrate. This substrate has at least two gas grooves formed inside and parallel to the placement surface, communication holes for communicating the gas grooves of adjacent layers, a plurality of discharge holes for discharging gas from the first layer gas groove closest to the placement surface to the outside, and a supply hole for supplying gas from the outside to the second layer gas groove farthest from the placement surface. Further, Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2007-46141) discloses a heating device including a ceramic substrate in which a resistance heating element is embedded and a tubular member for supporting the substrate. This substrate includes a gas ejection port formed on the substrate heating surface, a gas supply port formed at the center of the back surface of the substrate, and a gas path formed inside the substrate so as to communicate from the gas supply port to the gas ejection port.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] As described above, a method of providing a purge function to a ceramic heater with a shaft is known. An example of such a conventional ceramic heater with a shaft is shown in FIGS. 4A to 4D. The ceramic heater 110 shown in FIG. 4A includes a ceramic plate 112 in which a heater electrode 124 is embedded, and a ceramic shaft 114 attached to the ceramic plate 112. A heater rod 126 connected to the heater electrode 124 extends through the internal space S of the ceramic shaft 114. A shaft hole 116 that penetrates from one end to the other end of the ceramic shaft 114 is provided in the side wall constituting the ceramic shaft 114. On the surface of the ceramic plate 112 on the side of the ceramic shaft 114, a gas groove 118 is provided in an arc shape, and together with the upper end surface of the ceramic shaft 114, a gas flow path communicating with the shaft hole 116 is formed. In the ceramic plate 112, a plurality of gas introduction holes 120 that communicate vertically directly above the gas groove 118 are arranged at intervals in the longitudinal direction of the gas groove 118. On the other hand, a lateral hole 122 is provided in the direction from each of these gas introduction holes 120 toward the outer periphery of the ceramic plate 112 and reaches the outer peripheral portion of the ceramic plate 112. In such a configuration, the gas supplied to the shaft hole 116 is ejected to the outer peripheral portion of the ceramic plate 112 through the shaft hole 116, the gas groove 118, the plurality of gas introduction holes 120, and the plurality of lateral holes 122 in order. However, as can be seen from FIG. 4D, since the distances from the shaft hole 116 to the plurality of gas introduction holes 120 are different from each other, the difference in the flow rate transmitted to each gas introduction hole 120 is large, and finally the difference in the amount of gas ejected from each lateral hole 122 also becomes large.

[0007] The inventors of the present invention have now found that by providing at least one of the gas introduction holes with a diameter different from that of the other gas introduction holes, the gas amounts ejected from a plurality of lateral holes can be made uniform.

[0008] Accordingly, an object of the present invention is to provide a shafted ceramic heater having a purge function capable of making uniform the gas amounts ejected from a plurality of lateral holes.

[0009] According to the present invention, the following aspects are provided. [Aspect 1] A disk-shaped ceramic plate having a first surface for mounting a wafer and a second surface facing the first surface, and having heater electrodes embedded therein; A cylindrical ceramic shaft attached to the second surface of the ceramic plate; A shaft hole provided to penetrate from one end to the other end of the ceramic shaft within a side wall constituting the ceramic shaft; A gas groove provided in an arc shape on the second surface of the ceramic plate, and forming a gas flow path communicating with the shaft hole together with an upper end surface of the ceramic shaft; A plurality of gas introduction holes provided vertically and communicating directly above the gas groove within the ceramic plate, and arranged at intervals from each other in a longitudinal direction of the gas groove; A plurality of lateral holes provided within the ceramic plate in a direction from the plurality of gas introduction holes toward an outer periphery of the ceramic plate, and reaching a first surface or a side end surface of the ceramic plate; A ceramic heater comprising: When gas is supplied to the shaft hole, the ceramic heater is configured to be able to purge gas from a first surface or a side end surface of the ceramic plate through the shaft hole, the gas groove, the gas introduction holes, and the lateral holes in this order; A ceramic heater in which at least one of the gas introduction holes has a diameter different from that of the other gas introduction holes so that gas flow rates in the plurality of gas introduction holes are made uniform. [Aspect 2] The ceramic heater according to Embodiment 1, wherein the gas groove is provided in an arc shape with a central angle of 270 to 330 degrees. [Embodiment 3] The ceramic heater according to Embodiment 1 or 2, wherein the shaft hole is located at the longitudinal center of the gas groove. [Embodiment 4] The ceramic heater according to any one of Embodiments 1 to 3, wherein at least one gas introduction hole located in a region not belonging to the vicinity of the shaft hole and the vicinity of both ends of the gas groove has a diameter larger than the diameters of the gas introduction holes located in the vicinity of the shaft hole and the gas introduction holes located in the vicinity of both ends of the gas groove. [Embodiment 5] The ceramic heater according to any one of Embodiments 1 to 4, wherein at least one gas introduction hole located in a region not belonging to the vicinity of the shaft hole and the vicinity of both ends of the gas groove has a diameter 10% or more larger than the diameters of the gas introduction holes located in the vicinity of the shaft hole and the gas introduction holes located in the vicinity of both ends of the gas groove. [Embodiment 6] The ceramic heater according to Embodiment 4 or 5, wherein the number of gas introduction holes having the larger diameter is two. [Embodiment 7] The number of the plurality of gas introduction holes is six, the shaft hole is located between the third and fourth gas introduction holes counted from one end of the gas flow path, The ceramic heater according to any one of Embodiments 1 to 6, wherein the second and fifth gas introduction holes counted from one end of the gas flow path have a diameter 10% or more larger than the diameters of the other gas introduction holes. [Embodiment 8] The ceramic heater according to any one of Embodiments 1 to 7, wherein the lateral hole reaches the first surface of the ceramic plate. [Embodiment 9] The ceramic heater according to any one of Embodiments 1 to 7, wherein the lateral hole reaches the side end surface of the ceramic plate. [Embodiment 10] The ceramic heater according to any one of Aspects 1 to 9, wherein the lateral holes are provided obliquely with respect to the first surface so as to approach or reach the first surface as they approach the outer periphery of the ceramic plate. [Aspect 11] The ceramic heater according to any one of Aspects 1 to 10, wherein a part of the lateral holes is configured in the vertical direction so as to reach the first surface. [Brief Description of the Drawings]

[0010]

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 4C

Figure 4D

Mode for Carrying Out the Invention

[0011] The ceramic heater according to the present invention is a ceramic table for supporting a wafer while controlling its temperature inside a semiconductor manufacturing apparatus. Typically, the ceramic heater according to the present invention can be a ceramic heater for a semiconductor film forming apparatus. Typical examples of the film forming apparatus include CVD (Chemical Vapor Deposition) apparatuses (for example, thermal CVD apparatuses, plasma CVD apparatuses, photo CVD apparatuses, and MOCVD apparatuses) and PVD (Physical Vapor Deposition) apparatuses.

[0012] An aspect of the ceramic heater is shown in FIGS. 1A to 1D. FIG. 1 A to 1D The ceramic heater 10 shown in FIGS. 1 and 2 includes a disc-shaped ceramic plate 12, a cylindrical ceramic shaft 14, a shaft hole 16, a gas groove 18, a plurality of gas introduction holes 20, and a plurality of lateral holes 22. A heater electrode 24 is embedded in the ceramic plate 12. The ceramic plate 1 2It has a first surface 12a for placing a wafer (not shown) and a second surface 12b facing the first surface 12a. A ceramic shaft 14 is attached to the second surface 12b. A shaft hole 16 is provided through the side wall constituting the ceramic shaft 14 from one end to the other end of the ceramic shaft 14. A gas groove 18 is provided in an arc shape on the second surface 12b of the ceramic plate 12, and together with the upper end surface of the ceramic shaft 14, it forms a gas flow path communicating with the shaft hole 16. A plurality of gas introduction holes 20 are provided vertically in the ceramic plate 12 in communication directly above the gas groove 18. These gas introduction holes 20 are arranged at intervals from each other in the longitudinal direction of the gas groove 18. A plurality of lateral holes 22 are provided in the ceramic plate 12 in a direction from the plurality of gas introduction holes 20 toward the outer periphery of the ceramic plate 12, and these lateral holes 22 reach the first surface 12a or the side end surface 12c of the ceramic plate 12. Thus, when gas is supplied to the shaft hole 16, the ceramic heater 10 is configured to be able to purge the gas through the shaft hole 16, the gas groove 18, the gas introduction holes 20, and the lateral holes 22 in sequence from the first surface 12a or the side end surface 12c of the ceramic plate 12. And at least one of the gas introduction holes 20 has a diameter different from that of the other gas introduction holes 20 so that the gas flow rates in the plurality of gas introduction holes 20 are equalized. In this way, by making at least one of the gas introduction holes 20 have a diameter different from that of the other gas introduction holes 20, the amount of gas ejected from the plurality of lateral holes 22 can be equalized.

[0013] As described above, in the conventional ceramic heater 110 having a gas purge function, as can be seen from FIG. 4D, since the distances from the shaft hole 116 to the plurality of gas introduction holes 120 are different from each other, the difference in the flow rate transmitted to each gas introduction hole 120 is large, and finally the difference in the gas amount ejected from each lateral hole 122 also becomes large. That is, the gas amounts ejected from the plurality of lateral holes 122 become non-uniform. However, in order to sufficiently exert the purge function of preventing the process gas from flowing into the back surface of the wafer, it is desirable to make the gas amounts ejected from the outer peripheral portion of the ceramic plate as uniform as possible. In this regard, according to the present invention, by providing at least one of the gas introduction holes 20 with a diameter different from that of the other gas introduction holes 20, the gas amounts ejected from the plurality of lateral holes 22 can be made uniform.

[0014] The ceramic plate 12 is not particularly limited except for the configuration of the gas groove 18, the gas introduction hole 20, and the lateral hole 22, and may have the same configuration as the ceramic plate employed in a known ceramic heater.

[0015] The main part (i.e., the ceramic substrate) of the ceramic plate 12 other than the gas groove 18, the gas introduction hole 20, the lateral hole 22, and the heater electrode 24 is preferably made of aluminum nitride from the viewpoints of excellent thermal conductivity, high electrical insulation, and thermal expansion characteristics close to those of silicon.

[0016] The preferred shape of the ceramic plate 12 is a disc shape. However, the planar shape of the disc-shaped ceramic plate 12 does not need to be a perfect circle, and may be an incomplete circle lacking a part, such as an orientation flat, for example. The size of the ceramic plate 12 may be appropriately determined according to the diameter of the wafer assumed to be used and is not particularly limited. In the case of a circle, the diameter is typically 150 to 450 mm, for example, about 300 mm.

[0017] Protrusions (not shown) may be provided on the first surface 12a of the ceramic plate 12. The protrusions are preferably arranged at equal intervals from each other on the first surface 12a of the ceramic plate 12. The shape of each protrusion is not particularly limited, but a cylindrical shape is preferred. The diameter of each protrusion is not particularly limited, but is preferably 0.1 to 8 mm, more preferably 0.5 to 5 mm, still more preferably 0.5 to 4 mm, and particularly preferably 0.70 to 2.54 mm. The protrusions are preferably integrally formed with the ceramic plate 12 by embossing or the like. Therefore, the protrusions are also preferably made of aluminum nitride, like the ceramic plate 12. The height of the protrusions is not particularly limited, but is preferably 0.001 to 0.1 mm, more preferably 0.005 to 0.08 mm, still more preferably 0.01 to 0.05 mm, and particularly preferably 0.01 to 0.03 mm. The distance between the central axes of adjacent protrusions is preferably 4 to 30 mm, more preferably 5 to 26 mm, still more preferably 7 to 26 mm, and particularly preferably 7 to 15 mm.

[0018] As shown in FIGS. 1B and 1C, a heater electrode 24 is embedded in the ceramic plate 12. The heater electrode 24 is not particularly limited, and for example, it can be a conductive coil wired in one stroke over the entire surface of the ceramic plate 12. Heater rods 26 are connected to both ends of the heater electrode 24 for power supply, and the heater rods 26 are connected to a heater power source (not shown) through the internal space S of the ceramic shaft 14. When power is supplied from the heater power source, the heater electrode 24 generates heat and heats the wafer placed on the first surface 12a. The heater electrode 24 is not limited to a coil, and may be, for example, a ribbon (elongated thin plate) or a mesh.

[0019] The ceramic plate 12 may have internal electrodes other than the heater electrode 24 embedded therein. Examples of such internal electrodes include ESC electrodes and RF electrodes. The ESC electrode is an abbreviation for an electrostatic chuck (ESC) electrode and is also referred to as an electrostatic electrode. The ESC electrode is preferably a circular thin-film electrode having a slightly smaller diameter than the ceramic plate 12 and may be, for example, a mesh-shaped electrode formed by weaving thin metal wires into a net and forming a sheet. The ESC electrode may be used as a plasma electrode. That is, by applying a high frequency to the ESC electrode, the ESC electrode can also be used as a plasma electrode, and film formation by a plasma CVD process can also be performed. An ESC rod is preferably connected to the ESC electrode for power supply, and the ESC rod is preferably connected to an external power source (not shown) through the internal space S of the ceramic shaft 14. When a voltage is applied by an external power source, the ESC electrode chucks the wafer placed on the first surface 12a. The chucking force at this time is the Johnson-Rahbek force because the volume resistivity of aluminum nitride, which may constitute the main part of the ceramic plate 12, is 1×10 8 ~1×10 13 Ω·cm.

[0020] As shown in FIGS. 1B and 1C, the ceramic shaft 14 is a cylindrical shaft attached to the second surface 12b of the ceramic plate 12 and may have the same configuration as the ceramic shaft employed in a known ceramic heater. The ceramic shaft 14 has an internal space S for accommodating the heater rod 26. The ceramic shaft 14 is preferably made of the same ceramic material as the ceramic plate 12. Therefore, the ceramic shaft 14 is preferably made of aluminum nitride. The upper end surface of the ceramic shaft 14 is preferably joined to the second surface 12b of the ceramic plate 12 by solid-phase bonding or diffusion bonding. The outer diameter of the ceramic shaft 14 is not particularly limited and is, for example, about 40 mm. The inner diameter of the ceramic shaft 14 (the diameter of the internal space S) is also not particularly limited and is, for example, about 36 mm.

[0021] As shown in FIGS. 1B and 1C, the shaft hole 16 is provided to penetrate from one end (e.g., the lower end face 14a) to the other end (e.g., the upper end face 14b) of the ceramic shaft 14 within the side wall constituting the ceramic shaft 14. Typically, the shaft hole 16 is provided parallel to the central axis of the ceramic shaft 14. The diameter of the shaft hole 16 is not particularly limited, but is preferably 4.5 to 5.5 mm, more preferably 4.8 to 5.2 mm. The shape of the shaft hole 16 in plan view may be any shape such as circular or polygonal, but is preferably circular. The number of shaft holes 16 provided in the ceramic shaft 14 may be two or more, but is preferably one. This is because the gas supplied from one shaft hole 16 can be distributed to the respective lateral holes 22 through the gas groove 18 and the gas introduction holes 20. From this perspective, the shaft hole 16 is preferably located at the center in the longitudinal direction of the gas groove 18 (i.e., the direction along the arc). Thereby, it becomes possible to distribute and supply the gas evenly from the shaft hole 16 toward both ends of the gas groove 18.

[0022] As shown in FIG. 1D, the gas groove 18 is provided in an arc shape on the second surface 12b of the ceramic plate 12, and forms a gas flow path communicating with the shaft hole 16 together with the upper end face 14b of the ceramic shaft 14 as shown in FIGS. 1B and 1C. That is, the gas groove 18 functions as a gas flow path for supplying the gas supplied from the shaft hole 16 to the plurality of gas introduction holes 20. The gas groove 18 can be provided in an arc shape with a central angle preferably of 270 to 330 degrees, more preferably 280 to 320 degrees, still more preferably 290 to 310 degrees, for example 300 degrees. This central angle means the angle formed by the side connecting one end of the arc and the center of the circle including the arc and the side connecting the other end of the arc and the center of the circle (i.e., the central angle of the sector including the arc) when the gas groove 18 is regarded as an arc in plan view. The cross-sectional shape of the gas groove 18 is typically rectangular, but may be any other shape and is not particularly limited.

[0023] As shown in FIGS. 1B to 1D, the gas introduction holes 20 are a plurality of holes provided vertically in the ceramic plate 12 in communication directly above the gas grooves 18, and are arranged at intervals in the longitudinal direction of the gas grooves 18 (i.e., the direction along the arc). The diameter of the gas introduction holes 20 is not particularly limited, but is preferably 0.5 to 5.0 mm, more preferably 1.0 to 3.0 mm. And, as shown in FIG. 1D, at least one (preferably two, such as holes 20b and 20e) of the gas introduction holes 20 has a different diameter from the other gas introduction holes 20 (for example, holes 20a, 20c, 20d, and 20f) so that the gas flow rates in the plurality of gas introduction holes 20 are equalized. That is, as shown in FIG. 4D, when the diameters of all the gas introduction holes 120 are the same, the gas flow rates supplied to the respective gas introduction holes 120 vary according to the distance from the shaft hole 1 16, and do not become uniform. For example, in the conventional example shown in FIG. 4D, a large amount of gas flows into the holes 120c and 120d located near the shaft hole 116 where gas is supplied, but less gas flows into the holes 120b and 120e away from the shaft hole 116. However, a large amount of gas flows into the holes 120a and 120 f located near both ends of the gas groove 118 because the gas flow is blocked at both ends of the gas groove 118. Therefore, as shown in FIG. 1D, by making at least one (preferably two, such as holes 20b and 20e) of the gas introduction holes 20 have a different diameter from the other gas introduction holes 20 (for example, holes 20a, 20c, 20d, and 20f), the gas flow rates in the plurality of gas introduction holes 20 (for example, holes 20a, 20b, 20c, 20d, 20e, and 20f) can be equalized. Note that "equalizing the gas flow rate" in this specification does not mean making the gas flow rates exactly the same, but means reducing the difference in the gas flow rates in the plurality of gas introduction holes 20 to make them closer to being uniform (i.e., correcting the non-uniformity).

[0024] Therefore, it is preferable that the diameter D1 of at least one of the gas introduction holes 20 (for example, holes 20b and 20e) located in a region that does not belong to either the vicinity of the shaft hole 16 or the vicinity of both ends of the gas groove 18 is larger than the diameter D2 of the gas introduction holes 20 (for example, holes 20c and 20d) located in the vicinity of the shaft hole 16 and the gas introduction holes 20 (for example, holes 20a and 20f) located in the vicinity of both ends of the gas groove. Specifically, it is preferable that the diameter D1 is 10% or more larger than the diameter D2, more preferably 10 - 20% larger, and still more preferably 10 - 15% larger. The number of gas introduction holes 20 having a larger diameter D1 (for example, holes 20b and 20e) is preferably two. In this case, as shown in FIG. 1D, if they are arranged symmetrically with respect to the shaft hole 16 located at the center in the longitudinal direction of the gas groove 18, it is easy to achieve uniform flow rate. Further, the diameter of the gas introduction holes 20 is not limited to two types as shown in FIG. 1D, and may be three or more types. The diameter of the gas introduction holes 20 may be individually set according to the number and position of the gas introduction holes 20 in order to further equalize the gas flow rate.

[0025] The number of the gas introduction holes 20 is not particularly limited, but is preferably 6 - 10, more preferably 6 - 8, and most preferably 6 as shown in FIG. 1D. In this case, the shaft hole 16 is located between the third and fourth gas introduction holes 20 (that is, holes 20c and 20d) counted from one end of the gas flow path, and the second and fifth gas introduction holes 20 (that is, holes 20b and 20e) counted from one end of the gas flow path are preferably 10% or more larger than the diameters of the other gas introduction holes (that is, holes 20a, 20c, 20d, and 20f). According to this configuration, although the number of the gas introduction holes 20 is relatively small, the gas can be fed into the six lateral holes 22 with a uniform flow rate, so that the uniformity of the gas amount ejected to the outer peripheral portion of the ceramic plate 12 can be efficiently achieved.

[0026] The horizontal hole 22 is provided in the ceramic plate 12 in a direction from the gas introduction hole 20 toward the outer periphery of the ceramic plate 12, and reaches the first surface 12a or the side end surface 12c of the ceramic plate 12. The horizontal hole 22 may be configured to reach the side end surface 12c of the ceramic plate 12, or may be configured to reach the first surface 12a of the ceramic plate 12. Further, as shown in FIG. 2, the horizontal hole 22 may be provided obliquely with respect to the first surface 12a so as to approach or reach the first surface 12a as it approaches the outer periphery of the ceramic plate 12. Alternatively, as shown in FIG. 3, a part of the horizontal hole 22 may be configured in the vertical direction so as to reach the first surface 12a.

[0027] If desired, an annular member (not shown) for gas purge is provided along the outer periphery of the ceramic plate 12. This annular member has a number of ejection holes so that the gas supplied from the outlet of the horizontal hole 22 can be evenly ejected toward a desired position on the outer peripheral portion of the ceramic plate 12. In practice, it is assumed that the user of the ceramic heater 10 disposes and uses a desired annular member on the outer periphery of the ceramic plate 12.

[0028] When gas is supplied to the shaft hole 16, the ceramic heater 10 is configured to be able to purge the gas from the first surface 12a or the side end surface 12c of the ceramic plate 12 through the shaft hole 16, the gas groove 18, the gas introduction hole 20, and the horizontal hole 22 in this order. According to this configuration, since the wafer is placed on the first surface 12a, by supplying gas to the back surface of the wafer, an inert gas can be ejected to the outer peripheral portion of the ceramic plate, preventing the process gas from flowing into the back surface of the wafer. In this way, during the manufacturing process of the semiconductor device (particularly the film forming process), it is possible to prevent the process gas from entering the back surface of the wafer placed on the ceramic heater and causing deposits. The gas supplied to the shaft hole 16 is preferably an inert gas having excellent heat conductivity, and particularly preferably He gas.

Claims

1. A disc-shaped ceramic plate having a first surface for placing a wafer and a second surface facing the first surface, and having heater electrodes embedded therein; A cylindrical ceramic shaft attached to the second surface of the ceramic plate; A shaft hole provided to penetrate from one end to the other end of the ceramic shaft within the side wall constituting the ceramic shaft; A gas groove provided in an arc shape on the second surface of the ceramic plate, and forming a gas flow path that communicates with the shaft hole together with the upper end surface of the ceramic shaft; A plurality of gas introduction holes provided vertically in communication directly above the gas groove within the ceramic plate, and arranged at intervals from each other in the longitudinal direction of the gas groove; A plurality of horizontal holes provided within the ceramic plate in a direction from the plurality of gas introduction holes toward the outer periphery of the ceramic plate, and reaching the first surface or the side end surface of the ceramic plate; A ceramic heater comprising: When gas is supplied to the shaft hole, the ceramic heater is configured to purge gas in sequence through the shaft hole, the gas groove, the gas introduction holes, and the horizontal holes from the first surface or the side end surface of the ceramic plate; At least one of the gas introduction holes has a diameter different from that of the other gas introduction holes so that the gas flow rates in the plurality of gas introduction holes are equalized; A ceramic heater, wherein at least one of the gas introduction holes located in a region that does not belong to either the vicinity of the shaft hole or the vicinity of both ends of the gas groove has a diameter larger than the diameters of the gas introduction holes located in the vicinity of the shaft hole and the gas introduction holes located in the vicinity of both ends of the gas groove.

2. The ceramic heater according to claim 1, wherein the gas groove is provided in an arc shape with a central angle of 270 to 330 degrees.

3. The ceramic heater according to claim 1 or 2, wherein the shaft hole is located at the longitudinal center of the gas groove.

4. The ceramic heater according to claim 1 or 2, wherein at least one of the gas introduction holes located in a region that does not belong to either the vicinity of the shaft hole or the vicinity of both ends of the gas groove has a diameter 10% or more larger than the diameters of the gas introduction holes located in the vicinity of the shaft hole and the gas introduction holes located in the vicinity of both ends of the gas groove.

5. The ceramic heater according to claim 1 or 2, wherein the number of the gas introduction holes having the larger diameter is two.

6. The number of the plurality of gas introduction holes is six, the shaft hole is located between the third and fourth gas introduction holes counted from one end of the gas flow path, and the second and fifth gas introduction holes counted from one end of the gas flow path are 10% or more larger in diameter than the other gas introduction holes. The ceramic heater according to claim 1 or 2.

7. The ceramic heater according to claim 1 or 2, wherein the horizontal hole reaches the first surface of the ceramic plate.

8. The ceramic heater according to claim 1 or 2, wherein the horizontal hole reaches the side end surface of the ceramic plate.

9. The ceramic heater according to claim 1 or 2, wherein the horizontal hole is provided obliquely with respect to the first surface so as to approach or reach the first surface as it approaches the outer periphery of the ceramic plate.

10. The ceramic heater according to claim 1 or 2, wherein a part of the horizontal hole is configured in a vertical direction so as to reach the first surface.

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