Ceramic heater

Abstract

Provided is a ceramic heater which comprises a ceramic plate assembly having a temperature measurement hole for measuring the temperature of an outer zone, and is suitable for more accurately measuring the temperature of the outer zone of the ceramic plate assembly. This ceramic heater comprises: a ceramic plate assembly including an upper ceramic plate and a lower ceramic plate; a ceramic shaft attached to one surface of the ceramic plate assembly; an inner zone heater circuit and an outer zone heater circuit embedded in the upper ceramic plate; and a first temperature measurement hole for measuring the temperature of the inner zone and a second temperature measurement hole for measuring the temperature of the outer zone, the temperature measurement holes being provided in the ceramic plate assembly. The second temperature measurement hole includes, in the ceramic plate assembly, a vertical hole that reaches a joining surface of the ceramic plate assembly, and a horizontal hole that extends in the horizontal direction from the vertical hole toward the outer periphery along the joining surface. The lower ceramic plate has a lower thermal conductivity than the upper ceramic plate.

Description

Ceramic heater

[0001] The present disclosure relates to ceramic heaters.

[0002] In film deposition equipment for semiconductor manufacturing processes, ceramic heaters are used as support stages for uniformly controlling the temperature of wafers. A widely used ceramic heater includes a ceramic plate on which the wafer is placed and a cylindrical ceramic shaft attached to the ceramic plate. Multi-zone ceramic heaters, which have multiple heating zones, are also known as ceramic heaters.

[0003] Patent Document 1 (JP 2012-80103 A) discloses a susceptor including a disc-shaped ceramic plate, a thermocouple storage space formed inside the ceramic plate, and a thermocouple stored in the thermocouple storage space. The ceramic plate is formed by bonding a pair of ceramic disks, and the thermocouple storage space is formed by a horizontal groove formed in the bonding surfaces of one or both of the pair of ceramic disks. A hollow shaft is bonded to the surface (back surface) of the ceramic plate opposite the wafer-mounting surface.

[0004] Patent Document 2 (JP 2010-109346 A) discloses a mounting table structure for mounting a workpiece such as a semiconductor wafer, the mounting table structure including a dielectric mounting table provided with a heating means, a plurality of dielectric protective support pipes whose upper ends are joined to the underside of the mounting table to support the mounting table, and functional rods inserted into the protective support pipes so that their upper ends reach the mounting table. This document describes that the mounting table includes a mounting table main body made of transparent quartz and a heat diffusion plate made of an opaque dielectric (e.g., a ceramic material such as aluminum nitride) provided on the mounting table main body.

[0005] JP 2012-80103 A JP 2010-109346 A

[0006] In recent years, attempts have been made to reduce the wasted space within the chamber in which the ceramic heater is placed in semiconductor manufacturing process film deposition equipment. In other words, the larger the wasted space within the chamber, the more film deposition gas must be introduced into the chamber. However, by reducing the wasted space within the chamber, film deposition can be performed with less gas, improving production efficiency. For example, as in the ceramic heater 11 shown in FIG. 2 , the wasted space within the chamber can be reduced by placing a lower member 32 directly below the ceramic plate 13 and surrounding the ceramic shaft 14. The lower member 32 can be a component of the chamber or a separate member such as a spacer. However, when the lower member 32 is placed directly below the ceramic plate 13 as shown in FIG. 2 , the amount of heat transfer from the ceramic plate 13 to the lower member 32 increases, making it difficult to accurately measure the temperature of the outer zone Z2 of the ceramic plate 13.

[0007] The present inventors have now found that in a ceramic plate assembly having a temperature measurement hole for measuring the temperature of the outer zone, by making the thermal conductivity of the lower ceramic plate lower than that of the upper ceramic plate, the amount of heat transferred to the lower member can be reduced, and the temperature of the outer zone of the ceramic plate assembly can be measured more accurately.

[0008] Therefore, an object of the present invention is to provide a ceramic heater that includes a ceramic plate assembly having a temperature measurement hole for measuring the temperature of the outer zone, and that is suitable for more accurately measuring the temperature of the outer zone of the ceramic plate assembly.

[0009] According to the present disclosure, the following aspects are provided: [Aspect 1] A disc-shaped ceramic plate assembly including an upper ceramic plate and a lower ceramic plate joined together at their joining surfaces, the ceramic plate assembly having a first surface opposite to the joining surface of the upper ceramic plate and a second surface opposite to the joining surface of the lower ceramic plate, a cylindrical ceramic shaft attached to the second surface of the ceramic plate assembly and having an internal space, an inner zone heater circuit embedded in the upper ceramic plate and configured to be capable of heating an inner zone defined as a circular region within a predetermined distance from the center of the ceramic plate assembly, an outer zone heater circuit embedded in the upper ceramic plate and configured to be capable of heating an outer zone defined as an annular region outside the inner zone of the ceramic plate assembly, and a first temperature measurement hole for measuring the temperature of the inner zone, provided in the ceramic plate assembly from a position facing the internal space on the second surface to a depth position directly below the inner zone heater circuit. A ceramic heater comprising: in the ceramic plate assembly, a second temperature measurement hole for measuring an outer zone temperature, the second temperature measurement hole including a vertical hole reaching the joining surface from a position different from the first temperature measurement hole facing the internal space of the second surface, and a horizontal hole extending horizontally from the vertical hole along the joining surface toward the outer periphery, wherein the lower ceramic plate has a thermal conductivity lower than that of the upper ceramic plate. [Aspect 2] The ceramic heater according to Aspect 1, wherein the lower ceramic plate has a thermal conductivity of 60% or less of the thermal conductivity of the upper ceramic plate. [Aspect 3] The ceramic heater according to Aspect 1 or 2, wherein the upper ceramic plate has a thermal conductivity of 120 to 240 W / m·K at room temperature, and the lower ceramic plate has a thermal conductivity of 50 to 100 W / m·K at room temperature. [Aspect 4] The ceramic heater according to any one of Aspects 1 to 3, wherein the upper ceramic plate includes Y-doped aluminum nitride, and the lower ceramic plate includes Mg- and Ti-doped aluminum nitride.[Aspect 5] The ceramic heater according to any one of Aspects 1 to 4, further comprising: a first temperature measuring means which is a thermocouple or resistance temperature detector inserted into the first temperature measuring hole for measuring the temperature of the inner zone; and a second temperature measuring means which is a thermocouple or resistance temperature detector inserted into the second temperature measuring hole for measuring the temperature of the outer zone. [Aspect 6] The ceramic heater according to any one of Aspects 1 to 5, further comprising: a first terminal rod connected to the inner zone heater circuit and extending into the internal space; and a second terminal rod connected to the outer zone heater circuit and extending into the internal space. [Aspect 7] An apparatus comprising: a chamber; the ceramic heater according to any one of Aspects 1 to 6, disposed within the chamber; and a lower member disposed directly below the ceramic plate assembly and surrounding the periphery of the ceramic shaft, wherein the lower member is a component of the chamber, a member separate from the chamber, or a combination thereof.

[0010] 1 is a schematic cross-sectional view showing an example of a ceramic heater according to the present invention, and FIG. 2 is a schematic cross-sectional view showing an example of a conventional ceramic heater.

[0011] The ceramic heater according to the present invention is a ceramic platform for supporting a wafer in a semiconductor manufacturing device. Typically, the ceramic heater according to the present invention can be a ceramic heater for a semiconductor film deposition device. Typical examples of film deposition devices include CVD (chemical vapor deposition) devices (e.g., thermal CVD devices, plasma CVD devices, photo CVD devices, and MOCVD devices) and PVD (physical vapor deposition) devices.

[0012] FIG. 1 shows one embodiment of a ceramic heater. The ceramic heater 10 shown in FIGS. 1 and 2 includes a ceramic plate assembly 12, a ceramic shaft 14, an inner zone heater circuit 16, an outer zone heater circuit 18, a first temperature measurement hole 20, and a second temperature measurement hole 22. The ceramic plate assembly 12 is disk-shaped and includes an upper ceramic plate 12a and a lower ceramic plate 12b joined to each other at a joining surface 12c. The ceramic plate assembly 12 has a first surface 12d opposite the joining surface 12c of the upper ceramic plate 12a and a second surface 12e opposite the joining surface 12c of the lower ceramic plate 12b. The ceramic shaft 14 is a cylindrical member attached to the second surface 12e of the ceramic plate assembly 12 and has an internal space S. The inner zone heater circuit 16 is embedded in the upper ceramic plate 12a and is configured to heat an inner zone Z1, which is defined as a circular region within a predetermined distance from the center of the ceramic plate assembly 12. The outer zone heater circuit 18 is embedded in the upper ceramic plate 12a and is configured to heat an outer zone Z2, which is defined as an annular region outside the inner zone Z1 of the ceramic plate assembly 12. The first temperature measurement hole 20 is a hole for measuring the temperature of the inner zone Z1 and is provided in the ceramic plate assembly 12 from a position facing the internal space S of the second surface 12e to a depth position directly below the inner zone heater circuit 16. The second temperature measurement hole 22 includes a vertical hole 22a that reaches the joining surface 12c from a position different from the first temperature measurement hole 20 that faces the internal space S of the second surface 12e of the ceramic plate assembly 12, and a horizontal hole 22b that extends horizontally from the vertical hole 22a along the joining surface 12c toward the outer periphery. The lower ceramic plate 12b has a thermal conductivity lower than that of the upper ceramic plate 12a. In the ceramic plate assembly 12 having the second temperature measuring hole 22 for measuring the temperature of the outer zone Z2, the thermal conductivity of the lower ceramic plate 12b is set lower than that of the upper ceramic plate 12a, thereby reducing the amount of heat transferred to the lower member 32 as described above, and enabling more accurate measurement of the temperature of the outer zone of the ceramic plate assembly 12.

[0013] As mentioned above, attempts have been made to reduce the wasted space within the chamber in which the ceramic heater is placed in a film deposition apparatus for semiconductor manufacturing processes. Specifically, the larger the wasted space within the chamber, the more film deposition gas must be introduced into the chamber. However, by reducing the wasted space within the chamber, film deposition can be performed with less gas, improving production efficiency. FIG. 2 shows an example of a conventional ceramic heater 11. This ceramic heater 11 has the same configuration as the ceramic heater 10 shown in FIG. 1, except that a single highly thermally conductive ceramic plate 13 is used instead of the ceramic plate assembly 12 (hence, similar components are designated by the same reference numerals as in FIG. 1). Furthermore, as shown in FIG. 2, by arranging a lower member 32 directly below the ceramic plate 13 and surrounding the ceramic shaft 14, the wasted space within the chamber can be reduced. However, when the lower member 32 is disposed directly below the ceramic plate 13 as shown in Fig. 2, the amount of heat transfer from the ceramic plate 13 to the lower member 32 increases, making it difficult to accurately measure the temperature of the outer zone Z2 of the ceramic plate 13 (particularly the temperature near the outer zone heater circuit 18). In this regard, in the present invention, the amount of heat transfer to the lower member 32 can be reduced by changing the material of the lower ceramic plate 12b constituting the ceramic plate assembly 12 to one having a lower thermal conductivity than that of the upper ceramic plate 12a. As a result, an unintended temperature decrease in the outer zone Z2 due to heat transfer from the second surface 12e of the ceramic plate assembly 12 to the lower member 32 is reduced, making it possible to more accurately measure the temperature of the outer zone of the ceramic plate assembly 12.

[0014] Furthermore, in the ceramic heater 10 of the present invention, the second temperature measurement hole 22 is located below the inner zone heater circuit 16 and the outer zone heater circuit 18 located in the upper ceramic plate 12a, so that heat transfer from the inner zone heater circuit 16 and the outer zone heater circuit 18 near the first surface 12d to the first surface 12d is not hindered by the second temperature measurement hole 22. This is advantageous in that it is easy to control the first surface 12d and the wafer placed thereon to a desired temperature. That is, if a horizontal hole as a temperature measurement hole is located above the inner zone heater circuit 16 and the outer zone heater circuit 18, the portion of the first surface 12d where heat transfer from the inner zone heater circuit 16 and the outer zone heater circuit 18 is hindered by the horizontal hole can create a low-temperature region on the first surface 12d that has a shape corresponding to the shape of the horizontal hole. However, according to the present invention, such a low-temperature region does not occur, making it easy to achieve good temperature uniformity.

[0015] The ceramic plate assembly 12 includes an upper ceramic plate 12a and a lower ceramic plate 12b having a thermal conductivity lower than that of the upper ceramic plate 12a, which are joined together at a joining surface 12c. In this specification, the thermal conductivity can be measured by a laser flash method in accordance with the method described in JIS R 1611:2020, using a cylindrical sample machined from the ceramic plate to have a diameter of 10 mm and a thickness of 3 mm.

[0016] The upper ceramic plate 12a may be made of the same material as ceramic plates used in known ceramic heaters. The main portion of the upper ceramic plate 12a other than the inner zone heater circuit 16 and the outer zone heater circuit 18 (i.e., the ceramic substrate) preferably contains aluminum nitride or aluminum oxide, more preferably aluminum nitride, from the viewpoints of excellent thermal conductivity, high electrical insulation, and thermal expansion characteristics similar to those of silicon. The thermal conductivity of the upper ceramic plate 12a at room temperature (e.g., 25°C) is preferably 120 to 240 W / m·K, more preferably 140 to 180 W / m·K, and even more preferably 150 to 170 W / m·K. From the viewpoint of such high thermal conductivity, the upper ceramic plate 12a preferably contains Y-doped aluminum nitride. A preferred Y content in Y-doped aluminum nitride is an oxide (Y ２ O ３ ) is 1 to 5% by weight.

[0017] The lower ceramic plate 12b has a lower thermal conductivity than the upper ceramic plate 12a. The thermal conductivity of the lower ceramic plate 12b is preferably 60% or less, more preferably 50% or less, of the thermal conductivity of the upper ceramic plate. The thermal conductivity of the lower ceramic plate 12b is typically 20% or more, more typically 30% or more, of the thermal conductivity of the upper ceramic plate. The lower ceramic plate 12b may be made of the same material as the upper ceramic plate 12a, except for its low thermal conductivity. The main portion of the lower ceramic plate 12b (i.e., the ceramic substrate) preferably contains aluminum nitride or aluminum oxide, more preferably aluminum nitride, from the viewpoints of excellent thermal conductivity, high electrical insulation, and thermal expansion characteristics similar to those of silicon. The thermal conductivity of the lower ceramic plate 12b at room temperature (e.g., 25°C) is preferably 50 to 100 W / m·K, more preferably 60 to 90 W / m·K. From the viewpoint of having such low thermal conductivity, the lower ceramic plate 12b preferably contains Mg and Ti doped aluminum nitride. The preferred Mg content in the Mg and Ti doped aluminum nitride is 0.5 to 3 wt % in terms of oxide (MgO). The preferred Ti content in the Mg and Ti doped aluminum nitride is 0.5 to 3 wt % in terms of oxide (TiO ２ ) is 0.05 to 0.5% by weight.

[0018] The ceramic plate assembly 12 is disk-shaped. However, the planar shape of the disk-shaped ceramic plate assembly 12 does not need to be a perfect circle; for example, it may be an incomplete circle with a missing portion, such as an orientation flat. The size of the ceramic plate assembly 12 is not particularly limited and can be determined appropriately depending on the diameter of the wafer to be used. However, when the ceramic plate assembly 12 is circular, the diameter is typically 150 to 450 mm, and particularly for 300 mm silicon wafers, the diameter is typically 320 to 380 mm. The thickness of the ceramic plate assembly 12 is typically 10 to 25 mm.

[0019] The ceramic shaft 14 is a cylindrical shaft with an internal space S attached to the second surface 12e of the ceramic plate assembly 12 and may have a configuration similar to that of ceramic shafts used in known ceramic susceptors or ceramic heaters. The internal space S is configured to allow elongated members such as the first terminal rod 28, the second terminal rod 30, the first temperature measuring means 24, and the second temperature measuring means 26 to pass through it. The ceramic shaft 14 is preferably made of the same ceramic material as the ceramic plate assembly 12. Therefore, the ceramic shaft 14 preferably contains aluminum nitride or aluminum oxide, more preferably aluminum nitride. The upper end surface of the ceramic shaft 14 is preferably bonded to the second surface 12e of the ceramic plate assembly 12 by solid-state bonding or diffusion bonding. The outer diameter of the ceramic shaft 14 is not particularly limited, but is preferably 40 to 60 mm. The inner diameter of the ceramic shaft 14 (the diameter of the internal space S) is also not particularly limited, but is preferably 33 to 55 mm.

[0020] The ceramic heater 10 is a multi-zone heater (e.g., a two-zone heater). Therefore, when viewed from above, the ceramic plate assembly 12 has an inner zone Z1 defined as a circular region within a predetermined distance from the center of the ceramic plate assembly 12, and an outer zone Z2 defined as an annular region outside the inner zone Z1. The outer zone Z2 may be divided into multiple outer subzones (e.g., two to four). For example, the outer zone Z2 may be composed of multiple outer subzones defined in arc shapes (e.g., two to four). Alternatively, the outer zone Z2 may have two or more concentric annular regions of different sizes that do not overlap each other. In this case, the outer zone Z2 has at least a first outer zone adjacent to the inner zone Z1 and a second outer zone located outside the first outer zone. If necessary, a third or more outer zones may be present outside the second outer zone.

[0021] The inner zone heater circuit 16 and the outer zone heater circuit 18 preferably include a resistance heating element having at least one form selected from the group consisting of a coil, a linear zigzag structure, a printed pattern, a ribbon, and a mesh. A coil has a configuration in which a resistance heating wire is wound three-dimensionally, while a linear zigzag structure has a configuration in which a resistance heating wire is alternately folded two-dimensionally within a plane. The printed pattern is not particularly limited, but a typical pattern is a strip-shaped line of the resistance heating element layer that alternates between straight and bent (e.g., zigzag). It is preferable to use resistance heating elements of the same form for the inner zone heater circuit 16 and the outer zone heater circuit 18 because of ease of fabrication, but resistance heating elements of different forms may also be used. Each of the inner zone heater circuit 16 and the outer zone heater circuit 18 is preferably arranged in a single-stroke form when viewed in a plan view. The single-stroke form may be any of various known forms, such as an alternating forward and backward trajectory or a spiral.

[0022] The inner zone heater circuit 16 is embedded in the upper ceramic plate 12a and configured to heat the inner zone Z1. Preferably, the inner zone heater circuit 16 is embedded in the inner zone Z1 of the ceramic plate assembly 12 parallel to the first surface 12d. First terminal rods 28 extending into the internal space S of the ceramic shaft 14 are connected to the inner zone heater circuit 16, thereby enabling power to be supplied to the inner zone heater circuit 16. Preferably, the first terminal rods 28 are connected to both ends of the inner zone heater circuit 16, respectively. Two or more pairs of the first terminal rods 28 may be provided. Preferably, the inner zone heater circuit 16 is connected to a heater power supply (not shown) via the first terminal rods 28.

[0023] The outer zone heater circuit 18 is embedded in the upper ceramic plate 12a and is configured to heat the outer zone Z2. In a preferred embodiment of the present invention, as shown in FIG. 1, the outer zone heater circuit 18 may be embedded in the outer zone Z2 of the ceramic plate assembly 12 at the same depth as the inner zone heater circuit 16 and parallel to the first surface 12d. In another preferred embodiment of the present invention, the outer zone heater circuit 18 may be embedded in the outer zone Z2 of the ceramic plate assembly 12 at a different depth than the inner zone heater circuit 16 and parallel to the first surface 12d. In either embodiment, a second terminal rod 30 extending into the interior space is connected to the outer zone heater circuit 18, thereby enabling power to be supplied to the inner zone heater circuit 16. In this case, a pair of second terminal rods 30 are preferably provided in the outer zone heater circuit 18 via a jumper in the inner zone Z1 of the ceramic plate assembly 12. That is, since the pair of second terminal rods 30 are located at a position remote from the outer zone heater circuit 18, the pair of second terminal rods 30 are preferably electrically connected to the outer zone heater circuit 18 via a pair of jumpers. Two or more pairs of second terminal rods 30 may be present. The second terminal rods 30 are preferably connected to a heater power supply (not shown) via the jumpers and the second terminal rods 30.

[0024] The first temperature measurement hole 20 is a hole for measuring the temperature of the inner zone Z1, and is provided in the ceramic plate assembly 12 from a position facing the internal space S on the second surface 12e to a depth position directly below the inner zone heater circuit 16. The first temperature measurement hole 20 may be a thermocouple hole for measuring the temperature of the inner zone Z1, which is commonly used in ceramic heaters. Therefore, by inserting a thermocouple or a resistance thermometer as a first temperature measuring means 24 into the first temperature measurement hole 20, the temperature of the inner zone Z1 of the ceramic plate assembly 12 (particularly the upper ceramic plate 12a) can be measured.

[0025] The second temperature measurement hole 22 is a hole for measuring the temperature of the outer zone Z2 and includes a vertical hole 22a and a horizontal hole 22b. The vertical hole 22a is a hole that reaches the joining surface 12c from a position on the ceramic plate assembly 12 different from that of the first temperature measurement hole 20, which faces the internal space S of the second surface 12e. The horizontal hole 22b is a hole that extends horizontally from the vertical hole 22a along the joining surface 12c toward the outer periphery of the ceramic plate assembly 12. The horizontal hole 22b may be formed in either the upper ceramic plate 12a or the lower ceramic plate 12b. That is, although the horizontal hole 22b is formed on the lower ceramic plate 12b in FIG. 1, the horizontal hole 22b may also be formed on the upper ceramic plate 12a. In either case, the second temperature measurement hole 22 may also be a thermocouple hole for measuring the temperature of the outer zone Z2, which is commonly used in ceramic heaters. Therefore, by inserting a thermocouple or a resistance thermometer as a second temperature measuring means 26 into the second temperature measuring hole 22, the temperature of the outer zone Z2 of the ceramic plate assembly 12 (particularly the upper ceramic plate 12a) can be measured.

[0026] The ceramic plate assembly 12 may further include an RF electrode and / or an ESC electrode. In this case, the RF electrode and / or the ESC electrode are preferably embedded in the ceramic plate assembly 12 at a depth closer to the first surface 12d than the inner zone heater circuit 16 and the outer zone heater circuit 18, but may also be embedded at a depth farther from the first surface 12d than the inner zone heater circuit 16 and the outer zone heater circuit 18. The RF electrode enables film formation by a plasma CVD process when high frequency is applied. The ESC electrode is an abbreviation for an electrostatic chuck (ESC) electrode and is also called an electrostatic electrode. When a voltage is applied from an external power source, the ESC electrode chucks a wafer placed on the surface of the ceramic plate assembly 12 by the Johnsen-Rahbek force. The ESC electrode is preferably a circular thin-layer electrode with a diameter slightly smaller than that of the ceramic plate assembly 12. For example, it may be a mesh electrode formed by weaving thin metal wires into a net shape. The ESC electrode may also 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 an RF electrode, and film formation can be performed by a plasma CVD process. An RF terminal or ESC terminal for power supply is connected to the RF electrode or ESC electrode. The RF terminal or ESC terminal is rod-shaped, and the RF electrode or ESC electrode can be connected to an external power supply via the rod-shaped RF terminal or ESC terminal.

[0027] When the ceramic heater 10 is placed in a chamber, a lower member 32 is preferably placed directly below the ceramic plate assembly 12 and surrounding the periphery of the ceramic shaft 14. The presence of the lower member 32 can reduce wasted space in the chamber, resulting in film formation using less gas and improving production efficiency. Therefore, according to a preferred embodiment of the present invention, there is provided an apparatus including a chamber, the ceramic heater 10 placed in the chamber, and a lower member 32 placed directly below the ceramic plate assembly 12 and surrounding the periphery of the ceramic shaft 14. The lower member 32 can be a component of the chamber (e.g., an inner wall of the chamber), a component separate from the chamber (e.g., a spacer), or a combination thereof.

[0028] REFERENCE SIGNS LIST 10, 11 Ceramic heater 12 Ceramic plate assembly 13 Ceramic plate 12a Upper ceramic plate 12b Lower ceramic plate 12c Joining surface 12d First surface 12e Second surface 14 Ceramic shaft 16 Inner zone heater circuit 18 Outer zone heater circuit 20 First temperature measurement hole 22 Second temperature measurement hole 22a Vertical hole 22b Horizontal hole 24 First temperature measurement means 26 Second temperature measurement means 28 First terminal rod 30 Second terminal rod 32 Lower member S Internal space Z1 Inner zone Z2 Outer zone

Claims

1. A disc-shaped ceramic plate assembly including an upper ceramic plate and a lower ceramic plate joined together at their joining surfaces, the upper ceramic plate having a first surface opposite the joining surface of the upper ceramic plate and a second surface opposite the joining surface of the lower ceramic plate; a cylindrical ceramic shaft attached to the second surface of the ceramic plate assembly and having an internal space; an inner zone heater circuit embedded in the upper ceramic plate and configured to heat an inner zone defined as a circular region within a predetermined distance from the center of the ceramic plate assembly; an outer zone heater circuit embedded in the upper ceramic plate and configured to heat an outer zone defined as an annular region outside the inner zone of the ceramic plate assembly; and a first temperature measurement hole for measuring the temperature of the inner zone, provided in the ceramic plate assembly from a position facing the internal space on the second surface to a depth position directly below the inner zone heater circuit. a second temperature measuring hole for measuring the temperature of an outer zone in the ceramic plate assembly, the second temperature measuring hole including a vertical hole reaching the joining surface from a position different from the first temperature measuring hole facing the internal space of the second surface, and a horizontal hole extending horizontally from the vertical hole along the joining surface toward the outer periphery, wherein the lower ceramic plate has a thermal conductivity lower than that of the upper ceramic plate.

2. The ceramic heater according to claim 1, wherein the lower ceramic plate has a thermal conductivity that is 60% or less of the thermal conductivity of the upper ceramic plate.

3. A ceramic heater according to claim 1 or 2, wherein the upper ceramic plate has a thermal conductivity of 120 to 240 W / m·K at room temperature, and the lower ceramic plate has a thermal conductivity of 50 to 100 W / m·K at room temperature.

4. The ceramic heater according to claim 1 or 2, wherein the upper ceramic plate comprises Y-doped aluminum nitride and the lower ceramic plate comprises Mg- and Ti-doped aluminum nitride.

5. A ceramic heater as described in claim 1 or 2, further comprising: a first temperature measuring means which is a thermocouple or resistance thermometer inserted into the first temperature measuring hole for measuring the temperature of the inner zone; and a second temperature measuring means which is a thermocouple or resistance thermometer inserted into the second temperature measuring hole for measuring the temperature of the outer zone.

6. The ceramic heater according to claim 1 or 2, further comprising: a first terminal rod connected to said inner zone heater circuit and extending into said interior space; and a second terminal rod connected to said outer zone heater circuit and extending into said interior space.

7. An apparatus comprising: a chamber; a ceramic heater according to any one of claims 1 to 6, which is placed in the chamber; and a lower member which is placed directly below the ceramic plate assembly and so as to surround the periphery of the ceramic shaft, wherein the lower member is a component of the chamber, a member separate from the chamber, or a combination thereof.

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