Ceramic heater

Abstract

Provided is a ceramic heater that makes it possible to prevent the occurrence of cracks during use, while preventing the exposure of a heater coil portion to a heater terminal hole and the occurrence of local center cooling. The ceramic heater comprises: a ceramic plate that has a first surface and a second surface; a heater circuit and at least one pair of spherical terminals connected thereto, said heater circuit and terminals being buried in the ceramic plate; at least one pair of heater terminal holes; and at least one pair of heater rods that are inserted into the heater terminal holes, are electrically connected to the spherical terminals, and extend in a direction away from the first surface. The heater circuit includes: a heater coil portion that is disposed parallel to the first surface; and a heater strand portion that is composed of a strand-shaped resistance heating element, the heater strand portion extending from the heater coil portion, and the tip of the heater strand portion reaching the inside of the spherical terminal. When the ceramic plate is viewed in cross section, the heater strand portion is disposed at a depth position that is close to the second surface at the same depth or deeper than the lower end of the heater coil portion.

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 2022-48064 A) discloses a holding device including a plate-shaped member, an internal electrode (e.g., a heater electrode) disposed inside the plate-shaped member, a via disposed inside the plate-shaped member extending in a direction substantially perpendicular to the surface of the plate-shaped member and electrically connected to the internal electrode, a terminal member capable of conducting current through the internal electrode, and a conductive connecting member electrically connecting the via and the terminal member. The connecting member has a via-side connecting portion connected to the via and a terminal-side connecting portion connected to the terminal member, and the via-side connecting portion and the terminal-side connecting portion are disposed at different positions in a direction substantially parallel to the surface of the plate-shaped member.

[0004] JP 2022-48064 A

[0005] Ceramic heaters are required to minimize temperature differences across the wafer-mounted surface (i.e., thermal uniformity). In particular, with the recent trend toward finer process miniaturization and higher integration, ceramic heaters are required to provide even greater thermal uniformity. From this perspective, it is desirable to minimize the temperature difference between areas where a resistance heating element is present and areas where it is not. To achieve this, it is preferable to distribute the resistance heating element as a heater circuit throughout the entire ceramic heater. Furthermore, the ceramic plate in which the resistance heating element is embedded is provided with heater terminal holes for electrically connecting a power supply rod (heater rod) to the resistance heating element. From the perspective of improving thermal uniformity, smaller heater terminal holes are desirable, but the current flowing through the resistance heating element tends to increase as the process temperature increases, limiting the miniaturization of the heater terminal holes. Meanwhile, it is desirable to place the resistance heating element in a limited space around the heater terminal hole. However, attempting to place more resistance heating elements in a limited space poses a problem of the heater coil, which is a coil-shaped resistance heating element, becoming more easily exposed in the heater terminal hole. If the heater coil is placed away from the heater terminal hole to avoid this problem, then when used in the semiconductor manufacturing process, insufficient heat generation will result in localized cool spots with low temperatures.The localized center-cool temperature distribution accompanied by cool spots is caused by tensile thermal stress, which can lead to cracks.

[0006] The present inventors have now discovered that by employing a heater circuit including a heater coil portion made up of a coil-shaped resistance heating element and a heater wire portion made up of a wire-shaped resistance heating element, and by arranging the heater wire portion at a depth closer to the back surface of the plate than or equal to the lower end of the heater coil portion, it is possible to prevent exposure of the heater coil portion in the heater terminal hole and the occurrence of localized center cooling, while also preventing the occurrence of cracks during use.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a ceramic heater that can prevent the heater coil from being exposed in the heater terminal hole and the occurrence of localized center cooling, while also preventing the occurrence of cracks during use.

[0008] According to the present disclosure, the following aspects are provided: [Aspect 1] A ceramic plate having a first surface on which a wafer is placed and a second surface opposite the first surface, a heater circuit embedded in the ceramic plate, at least one pair of spherical terminals embedded in the ceramic plate and connected to the heater circuit, at least one pair of heater terminal holes formed in the second surface of the ceramic plate to reach each of the spherical terminals, and at least one pair of heater rods inserted into each of the heater terminal holes and electrically connected to each of the spherical terminals, extending in a direction away from the first surface for supplying power to the heater circuit, wherein the heater circuit includes: a heater coil portion arranged parallel to the first surface and composed of a coiled resistance heating element, and a heater wire portion extending from the heater coil portion and composed of a wire-like resistance heating element that is not wound into a coil, the tip of which reaches the inside of the spherical terminal. A ceramic heater in which, when the ceramic plate is viewed in cross section, the heater wire portion is disposed at a depth closer to the second surface than or deeper than a lower end of the heater coil portion. [Aspect 2] The ceramic heater according to Aspect 1, in which, when the ceramic plate is viewed in cross section, a line passing through the center of an imaginary circle specified by the cross-sectional arc of the spherical terminal and parallel to the first surface is defined as a terminal center line, and the heater wire portion is disposed along the terminal center line. [Aspect 3] The ceramic heater according to Aspect 1 or 2, in which the ceramic plate contains aluminum nitride or aluminum oxide. [Aspect 4] The ceramic heater according to any one of Aspects 1 to 3, in which the spherical terminal is formed by a resistance heating element having the same type of composition as the coil-shaped resistance heating element. [Aspect 5] The ceramic heater according to any one of Aspects 1 to 4, wherein the resistance heating element contains at least one selected from the group consisting of tungsten, molybdenum, a tungsten-molybdenum alloy, tungsten carbide, a tungsten carbide-titanium nitride composite material, a tungsten carbide-aluminum oxide composite material, and niobium.[Aspect 6] The ceramic heater according to any one of Aspects 1 to 5, wherein the heater coil portion is not present within an area defined by the heater terminal hole when the ceramic plate is seen through from above from the second surface. [Aspect 7] The ceramic heater according to any one of Aspects 1 to 6, further comprising a cylindrical ceramic shaft attached to the second surface of the ceramic plate and having an internal space. [Aspect 8] The ceramic heater according to any one of Aspects 1 to 7, wherein the heater wire portion does not extend through the spherical terminal to the outside thereof, and therefore the heater wire portion terminates within the spherical terminal. [Aspect 9] The ceramic heater according to any one of Aspects 1 to 8, wherein the ceramic plate includes, when viewed in a plane, an inner zone defined as a circular region within a predetermined distance from the center of the ceramic plate, and an outer zone defined as an annular region outside the inner zone, and the heater circuit includes: an inner zone heater circuit embedded in the inner zone of the ceramic plate and including the heater coil portion and the heater wire portion, and an outer zone heater circuit embedded in the outer zone of the ceramic plate and including the heater coil portion and the heater wire portion, wherein the pair of spherical terminals are connected to each of the inner zone heater circuit and the outer zone heater circuit, and the heater rod is connected to each of the pair of spherical terminals. [Aspect 10] The ceramic heater according to Aspect 9, wherein the inner zone heater circuit and the outer zone heater circuit are arranged on different planes when viewed in a cross section of the ceramic plate.[Aspect 11] When the ceramic plate is viewed from above, the ceramic plate includes an inner zone defined as a circular region within a predetermined distance from the center of the ceramic plate, and an outer zone defined as an annular region outside the inner zone, and the heater circuit comprises: an inner zone heater circuit embedded in the inner zone of the ceramic plate and including the heater coil portion and the heater wire portion; an outer zone heater circuit embedded in the outer zone of the ceramic plate and including the heater coil portion and the heater wire portion; and a pair of jumpers embedded in the inner zone of the ceramic plate so as not to come into contact with the inner zone heater circuit and composed of wire-shaped resistance heating elements extending from the heater wire portion of the outer zone heater circuit. The ceramic heater according to any one of Aspects 1 to 8, wherein the pair of spherical terminals are connected to the inner zone heater circuit and the jumper, respectively, and the heater rod is connected to each of the pair of spherical terminals (however, the jumper does not have to be disposed at a depth position closer to the second surface that is the same as or deeper than a lower end of the heater coil portion of the outer zone heater circuit). [Aspect 12] The ceramic heater according to Aspect 11, wherein the inner zone heater circuit and the outer zone heater circuit are arranged on the same plane when the ceramic plate is viewed in cross section. [Aspect 13] The ceramic heater according to Aspect 11, wherein the inner zone heater circuit and the outer zone heater circuit are arranged on different planes when the ceramic plate is viewed in cross section.

[0009] FIG. 1 is a perspective cross-sectional view schematically showing one example of a ceramic heater according to the present invention, corresponding to Example 1. FIG. 2 is a perspective top view schematically showing the ceramic heater shown in FIG. 1, corresponding to Examples 1 and 2. FIG. 3 is a schematic cross-sectional view conceptually showing the internal structure of the ceramic plate in the ceramic heater shown in FIG. 1, corresponding to Examples 1 to 3. FIG. 4 is a schematic cross-sectional view showing one example of the positional relationship between a spherical terminal and a heater wire portion. FIG. 5 is a schematic cross-sectional view showing another example of the positional relationship between a spherical terminal and a heater wire portion. FIG. 6 is a schematic cross-sectional view schematically showing another example of the positional relationship between a spherical terminal and a heater wire portion. FIG. 7 is a perspective cross-sectional view schematically showing another example of the positional relationship between a spherical terminal and a heater wire portion. FIG. 8 is a perspective cross-sectional view schematically showing another example of the ceramic heater according to the present invention, corresponding to Example 2. FIG. 9 is a perspective cross-sectional view schematically showing another example of the ceramic heater according to the present invention, corresponding to Example 3. For convenience of explanation, the jumper 14c is drawn slightly lower than its actual position in order to clearly show the configurations of the inner zone heater circuit 14a and the jumper 14c, which are actually located at the same height. 12 is a perspective top view schematically showing the ceramic heater shown in FIG. 8 , corresponding to Examples 3 and 4. FIG. 13 is a plan view schematically showing the arrangement of heater circuits in the central region of the ceramic plate shown in FIG. 8 , corresponding to Example 3. FIG. 14 is a schematic cross-sectional view conceptually showing the internal structure of the ceramic plate in the ceramic heater shown in FIG. 8 , corresponding to Example 3. FIG. 15 is a perspective cross-sectional view conceptually showing another example of the ceramic heater according to the present invention, corresponding to Example 4. FIG. 16 is a schematic cross-sectional view conceptually showing the internal structure of the ceramic plate in the ceramic heater shown in FIG. 12 , corresponding to Example 4. FIG. 17 is a schematic cross-sectional view conceptually showing the internal structure of the ceramic plate in an example of a ceramic heater not according to the present invention, corresponding to Example 5 (Comparative Example). FIG. 18 is a schematic cross-sectional view conceptually showing the internal structure of the ceramic plate in another example of a ceramic heater not according to the present invention, corresponding to Example 6 (Comparative Example).

[0010] 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.

[0011] 1 to 3 show one embodiment of a ceramic heater. The ceramic heater 10 shown in FIGS. 1 and 2 comprises a ceramic plate 12, a heater circuit 14, at least one pair of spherical terminals 20, at least one pair of heater terminal holes 22, and at least one pair of heater rods 24. The ceramic plate 12 has a first surface 12a on which a wafer W is placed and a second surface 12b opposite the first surface 12a. The heater circuit 14 is embedded in the ceramic plate 12. The spherical terminals 20 are embedded in the ceramic plate 12 and connected to the heater circuit 14. The heater terminal holes 22 are holes formed from the second surface 12b of the ceramic plate 12 to reach each of the spherical terminals 20. The heater rods 24 are rod-shaped electrode terminals for supplying power to the heater circuit 14. The heater rod 24 is inserted into each of at least one pair of heater terminal holes 22, electrically connected to each of at least one pair of spherical terminals 20, and extends in a direction away from the first surface 12a. The heater circuit 14 includes a heater coil portion 16 and a heater wire portion 18. The heater coil portion 16 is composed of a coiled resistance heating element and is arranged parallel to the first surface 12a. The heater wire portion 18 is composed of a wire-like resistance heating element that is not wound into a coil, and extends from the heater coil portion 16, with the tip of the heater wire portion 18 reaching the interior of the spherical terminal 20. When the ceramic plate 12 is viewed in cross section, the heater wire portion 18 is disposed at a depth closer to the second surface 12b than or deeper than the lower end of the heater coil portion 16. In this way, by employing the heater circuit 14 including the heater coil portion 16 composed of a coil-shaped resistance heating element and the heater wire portion 18 composed of a wire-shaped resistance heating element, and by arranging the heater wire portion 18 at a depth position closer to the second surface 12b that is the same as or deeper than the lower end of the heater coil portion 16, it is possible to prevent exposure of the heater coil portion 16 to the heater terminal hole 22 and the occurrence of local center cooling, while also preventing the occurrence of cracks during use.

[0012] As mentioned above, with the recent trend toward miniaturization and high integration of processes, ceramic heaters are required to have even greater thermal uniformity. To achieve this, it is preferable to arrange resistance heating elements as heater circuits throughout the entire area of ​​the ceramic heater. Furthermore, from the perspective of improving thermal uniformity, smaller heater terminal holes are desirable. However, as process temperatures increase, the current flowing through resistance heating elements also tends to increase, limiting the miniaturization of heater terminal holes. Meanwhile, it is desirable to arrange resistance heating elements in the limited space around the heater terminal holes. However, attempting to arrange more resistance heating elements in a limited space poses a problem: the heater coil, which is a coil-shaped resistance heating element, is more likely to be exposed in the heater terminal holes. In this regard, ceramic heaters should naturally be designed so that the heater coil is not exposed in the heater terminal holes; however, unintentional heater coil exposure can occur. Specifically, ceramic plates are fabricated by placing a heater circuit and other components on a ceramic powder compact, followed by press molding and firing. During this process, the heater circuit, particularly the heater coil, can become displaced or deformed. As a result, the heater coil can become exposed in the heater terminal hole when a heater terminal hole is drilled in the fired ceramic plate. If the heater coil is exposed in the heater terminal hole, the exposed portion of the heater coil's material (typically molybdenum or tungsten) can rapidly oxidize and disappear when exposed to high temperatures (e.g., 500°C) during use in a semiconductor manufacturing process, resulting in the loss of part of the heater circuit (i.e., the heater circuit can break). If the heater coil is positioned away from the heater terminal hole in an attempt to avoid this problem, a cool spot with a low temperature due to insufficient heat generation can result during use in a semiconductor manufacturing process. 14, in order to distance the heater terminal hole 22 (particularly the bottom of the hole) from the heater coil portion 16, the heater wire portion 18 must be lengthened, which results in a relative decrease in coil density in that portion, resulting in the formation of a cool spot. A localized center-cool temperature distribution accompanied by a cool spot is caused by tensile thermal stress, which can cause cracks.These problems are successfully solved by the present invention. Specifically, as shown in Figures 3 and 13, the present invention positions the heater wire portion 18 at a depth closer to the second surface 12b than the lower end of the heater coil portion 16, thereby positioning the heater coil portion 16 away from the heater terminal hole 22 (particularly the bottom of the hole) toward the first surface 12a. As a result, even if deformation occurs during manufacturing of the ceramic plate 12, the risk of the heater coil portion 16 being exposed in the heater terminal hole 22 is reduced. Since coil exposure can be prevented in this way, the heater coil portion 16 can be positioned horizontally closer to the spherical terminal 20, increasing coil density and preventing the occurrence of cool spots. In other words, exposure of the heater coil portion 16 in the heater terminal hole 22 and the occurrence of localized center cooling can be simultaneously prevented. Furthermore, preventing the occurrence of center cooling reduces tensile thermal stress, thereby preventing cracks caused by tensile thermal stress.

[0013] The ceramic plate 12 preferably contains aluminum nitride or aluminum oxide, more preferably aluminum nitride, in its main portion (i.e., the ceramic substrate) other than the embedded members such as the heater circuit 14, the spherical terminal 20, and the RF electrode 30, from the viewpoints of excellent thermal conductivity, high electrical insulation, and thermal expansion characteristics similar to those of silicon.

[0014] The ceramic plate 12 is disk-shaped. However, the planar shape of the disk-shaped ceramic plate 12 does not need to be a perfect circle; for example, it may be an incomplete circle with a portion missing, such as an orientation flat. The diameter of the ceramic plate 12 is 220 mm or more, typically 220 to 450 mm, and particularly for 300 mm silicon wafers, typically 320 to 380 mm. The thickness of the ceramic plate 12 is typically 10 to 25 mm.

[0015] The heater circuit 14 is embedded in the ceramic plate 12 so as to be generally parallel to the first surface 12a. Here, the expression "generally parallel" means that as shown in Fig. 13, the heater coil portion 16, which constitutes the main portion of the heater circuit 14, is parallel to the first surface 12a, and at least a portion of the heater wire portion 18 may be parallel or non-parallel to the first surface 12a (see, for example, the heater wire portion 18 partially disposed at an angle in Fig. 13). Furthermore, "parallel to the first surface 12a" does not necessarily mean completely parallel to the first surface 12a but may mean approximately parallel. Specifically, even if the distance from the first surface 12a to the heater coil portion 16 varies within a range of ±20% of the average distance from the first surface 12a to the heater coil portion 16, it is still considered to be "parallel to the first surface 12a." The "distance from the first surface 12a to the heater coil portion 16" refers to the distance from the upper end of the heater coil portion 16 on the first surface 12a side (the highest point closest to the first surface 12a in a substantially circular cross section of the heater coil 16 when viewed in a cross section along the central axis of the coil) to the first surface 12a. Typically, the heater circuit 14 is formed by wiring a resistance heating element across the entire ceramic plate 12 in a single stroke. The single-stroke shape may be any of various known shapes, such as a repeated pattern of alternating forward and backward movements or a spiral shape. The ceramic plate 12 is formed with at least one pair of heater terminal holes 22 extending from the second surface 12b to each of the spherical terminals 20. A heater rod 24 for supplying power to the heater circuit 14 is inserted into each of the heater terminal holes 22 and electrically connected to each of the spherical terminals 20. The heater rod 24 and the spherical terminal 20 may be electrically connected directly or indirectly via another conductive member, such as a buffer material 26 or an eyelet 28, as shown in FIG. 3. The heater rod 24 extends in a direction away from the first surface 12a. For example, at both ends of the heater circuit 14, the heater rod 24 inserted into the heater terminal hole 22 is connected via the spherical terminal 20 (and, if desired, the buffer material 26 or the eyelet 28), and the heater rod 24 is electrically connected to a heater power source (not shown) (via the internal space S of the ceramic shaft 38, if present).When power is supplied from the heater power supply, the heater circuit 14 generates heat to heat the wafer W placed on the first surface 12a.

[0016] As shown in FIG. 3 , the heater circuit 14 includes a heater coil portion 16 and a heater wire portion 18. The heater coil portion 16 and the heater wire portion 18 are preferably a continuous, integrated resistance heating element. However, the heater coil portion 16 and the heater wire portion 18 may be separate resistance heating elements connected to each other via a connection terminal. The connection terminal allows connection of resistance heating elements with different wire diameters. The connection terminal is preferably a conductive member having two through holes with different diameters that can connect resistance heating elements with different wire diameters. In this configuration, the heater coil portion 16 and the heater wire portion 18 are inserted into the two through holes and crimped and / or fixed, respectively, to ensure electrical connection between the heater coil portion 16 and the heater wire portion 18. The shape of the connection terminal is not particularly limited, but may be, for example, spherical. Note that if the wire diameter of the heater coil portion 16 and the wire portion 18 is the same, the connection terminal is not necessary.

[0017] The heater coil portion 16 is composed of a coil-shaped resistance heating element and is arranged parallel to the first surface 12a. The coil-shaped resistance heating element has a configuration in which a resistance heating wire is wound three-dimensionally, and can be a heater coil commonly used in ceramic heaters, etc. The winding diameter of the coil is preferably 2.5 to 5.0 mm, more preferably 2.5 to 4.0 mm, and even more preferably 3.0 to 3.5 mm. The wire diameter of the coil is preferably 0.3 to 0.7 mm, more preferably 0.4 to 0.6 mm, and even more preferably 0.4 to 0.5 mm.

[0018] The heater wire portion 18 is a wire-like resistance heating element that is not wound into a coil. It extends from the heater coil portion 16, and its tip reaches the interior of the spherical terminal 20. When viewed cross-sectionally from the ceramic plate 12, the heater wire portion 18 is disposed at the same depth as the lower end of the heater coil portion 16 or at a deeper depth closer to the second surface 12b. In this specification, the term "same" in the above-mentioned depth position is defined as "same" if the difference in height is within ±10% of the diameter of the spherical terminal 20. The diameter of the spherical terminal 20 is defined as the diameter of an imaginary circle C defined by the cross-sectional arc of the spherical terminal 20. That is, although the spherical terminal 20 can be originally manufactured in a spherical shape, when the ceramic plate 12 is machined to form the heater terminal hole 22, a portion of the spherical terminal 20 is scraped or removed, resulting in an incomplete spherical shape with a flat portion (hereinafter referred to as a "nearly spherical shape") as shown in FIG. 3 . The imaginary circle C is an imaginary circle that is set to fit the cross-sectional arc of this substantially spherical portion. The diameter (wire diameter) of the wire-shaped resistance heating element is preferably 0.3 to 0.7 mm, more preferably 0.4 to 0.6 mm, and even more preferably 0.4 to 0.5 mm.

[0019] Length L of the portion of the heater wire portion 18 that is not buried in the spherical terminal 20 １ 3 and 13) is not particularly limited, but is preferably 2.0 to 3.5 mm, more preferably 2.0 to 3.0 mm, and even more preferably 2.0 to 2.5 mm. ２ (see FIGS. 3 and 13) is not particularly limited, but is preferably 1.0 to 1.5 mm, more preferably 1.0 to 1.3 mm, and even more preferably 1.0 to 1.2 mm.

[0020] In a preferred embodiment of the present invention, the heater wire portion 18 is arranged parallel to the coil center line Lc of the heater coil portion 16 when the ceramic plate 12 is viewed in cross section, as shown in Fig. 3. This configuration has the advantage of facilitating the formation of the heater circuit 14. It is particularly preferable that the heater wire portion 18 is arranged along the terminal center line Lt of the spherical terminal 20. The terminal center line Lt is defined as a line parallel to the first surface 12a and passing through the center of a circle defined by the cross-sectional arc of the spherical terminal 20 (i.e., the above-mentioned imaginary circle C) when the ceramic plate 12 is viewed in cross section.

[0021] In another preferred embodiment of the present invention, the heater wire portion 18 may be disposed in an oblique or arc-shaped configuration away from the coil center line Lc of the heater coil portion 16 when the ceramic plate 12 is viewed in cross section, as shown in FIG. 13 . This configuration allows the heater coil portion 16 to be located further away from the heater terminal hole 22 (particularly the bottom of the hole), further reducing the risk of the heater coil portion 16 being exposed in the heater terminal hole 22 due to deformation during manufacturing, etc. This allows the heater coil portion 16 to be positioned closer horizontally to the spherical terminal 20, further increasing coil density and more effectively preventing the occurrence of cool spots. The oblique or arc-shaped portion of the heater wire portion 18 is typically located outside the spherical terminal 20, but the portion located inside the spherical terminal 20 may also be disposed in an oblique or arc-shaped configuration.

[0022] The distance L between the center line Lc of the heater coil portion 16 and the center line Lt of the spherical terminal 20 ３ 3 and 13) is not particularly limited, but is preferably 1.2 to 4.5 mm, more preferably 1.5 to 3.5 mm, and even more preferably 1.8 to 2.8 mm. ４ (see FIGS. 3 and 13) is not particularly limited, but is preferably 1.5 to 4.0 mm, more preferably 1.5 to 3.5 mm, and even more preferably 1.5 to 3.0 mm. ４is defined as the length of the shortest straight line connecting the vertex or inflection point formed by the heater coil portion 16 and the heater wire portion 18 to the bottom of the heater terminal hole 22 when the ceramic plate 12 is viewed in cross section.

[0023] 4 and 5, the heater wire portion 18 does not extend through the spherical terminal 20 to the outside thereof, and therefore, it is preferable that the heater wire portion 18 terminates within the spherical terminal 20. If the heater wire portion 18 protrudes from the spherical terminal 20 as shown in Fig. 6, the protruding portion of the heater wire portion 18 could become a starting point for cracks, but such a risk can be reduced by configuring the heater wire portion 18 to terminate within the spherical terminal 20.

[0024] The spherical terminal 20 is embedded in the ceramic plate 12 and connected to the heater circuit 14. The spherical terminal 20 is preferably made of a resistance heating element having the same composition as the coil-shaped resistance heating element (i.e., the heater coil portion 16). As mentioned above, the spherical terminal 20 does not need to be a perfect sphere, but can be an incomplete sphere having a flat portion, i.e., a nearly spherical shape, as shown in FIG. 3. The diameter of the spherical terminal 20 (i.e., the diameter of the imaginary circle C) is preferably 3.0 to 5.0 mm, more preferably 3.5 to 4.5 mm, and even more preferably 3.5 to 4.0 mm.

[0025] As described above, the heater wire portion 18 is disposed at a depth closer to the second surface 12b than or equal to the lower end of the heater coil portion 16, and is preferably disposed along the terminal center line Lt of the spherical terminal 20. Therefore, it is preferable to appropriately set the depth position of the terminal center line Lt of the spherical terminal 20 in relation to the lower end of the heater coil portion 16. For example, as shown in Figures 3 and 13, the depth position D of the center line Lt of the spherical terminal 20 relative to the lower end of the heater coil portion 16 (the lower end closer to the second surface 12b) is preferably 0 to +2.0 mm, more preferably 0 to +1.5 mm, and even more preferably +0.2 to +1.0 mm, when the depth position closer to the second surface 12b than the lower end of the heater coil portion 16 is taken as plus (+).

[0026] When the ceramic plate 12 is viewed from the second surface 12b in plan view, it is preferable that the heater coil portion 16 does not exist within the area defined by the heater terminal hole 22. This effectively reduces the risk that the heater coil portion 16 will be exposed in the heater terminal hole 22 due to deformation during manufacturing, etc.

[0027] The resistance heating element that constitutes the heater circuit 14 (i.e., the heater coil portion 16, the heater wire portion 18, and the jumper 14c, if present) and the spherical terminal 20 preferably contains at least one material selected from the group consisting of tungsten, molybdenum, a tungsten-molybdenum alloy, tungsten carbide, a tungsten carbide-titanium nitride composite material, a tungsten carbide-aluminum oxide composite material, and niobium.

[0028] The ceramic heater 10 may be a one-zone heater or a multi-zone heater. In the case of a one-zone heater, the heater circuit 14 may be a single continuous heater circuit capable of heating the entire ceramic plate 12, as shown in FIGS. 1 and 7. On the other hand, in the case of a multi-zone heater (e.g., a two-zone heater), the ceramic plate 12 may include an inner zone Z1 and an outer zone Z2 when viewed from above, as shown in FIGS. 8, 9, and 12. The inner zone Z1 is defined as a circular region within a predetermined distance from the center of the ceramic plate 12. The outer zone Z2 is defined as an annular region outside the inner zone Z1. The outer zone Z2 may be divided into multiple outer subzones (e.g., 2 to 4). For example, the outer zone Z2 may be composed of multiple outer subzones divided into arcs (e.g., 2 to 4). 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, there may be a third or more outer zones outside the second outer zone.

[0029] In the case of a multi-zone heater (e.g., a two-zone heater), the heater circuit 14 may include an inner zone heater circuit 14a, an outer zone heater circuit 14b, and, optionally, a pair of jumpers 14c, as shown in FIGS. 8 to 12. That is, the heater circuit 14 may be configured without the jumper 14c, as shown in FIG. 12, or may be configured with the jumper 14c, as shown in FIGS. 8, 10, and 11. Like the heater circuit 14, both the inner zone heater circuit 14a and the outer zone heater circuit 14b include a heater coil portion 16 and a heater wire portion 18. The inner zone heater circuit 14a is embedded in the inner zone Z1 of the ceramic plate 12. However, as shown in FIG. 12, the inner zone heater circuit 14a may extend not only to the inner zone Z1 but also to the outer zone Z2. In this case, the inner zone heater circuit 14a may be configured to selectively or preferentially heat the inner zone Z1. The outer zone heater circuit 14b is embedded in the outer zone Z2 of the ceramic plate 12. However, as shown in FIG. 12 , the outer zone heater circuit 14b may extend not only to the outer zone Z2 but also to the inner zone Z1. In this case, the outer zone heater circuit 14b may be configured to selectively or preferentially heat the outer zone Z2. Therefore, the inner zone heater circuit 14a and the outer zone heater circuit 14b may overlap each other when viewed from above in a perspective view of the ceramic plate 12, as shown in FIG. 12 . In either embodiment, the inner zone heater circuit 14a and the outer zone heater circuit 14b are preferably arranged in a single-stroke pattern when viewed from above in a perspective view. The single-stroke pattern may be any of various known patterns, such as a pattern that alternates between forward and reverse directions or a spiral pattern.

[0030] In an embodiment in which the heater circuit 14 has a jumper 14c, the jumper 14c is embedded in the inner zone Z1 of the ceramic plate 12 so as not to come into contact with the inner zone heater circuit 14a, and is composed of a wire-shaped resistance heating element extending from the heater wire portion 18 of the outer zone heater circuit 14b, as shown in Figures 8, 10, and 11. The inner zone heater circuit 14a and the outer zone heater circuit 14b may be arranged on the same plane in a cross-sectional view, as shown in Figure 8. Alternatively, the inner zone heater circuit 14a and the outer zone heater circuit 14b may be arranged on different planes in a cross-sectional view. As shown in Figures 3 and 11, a pair of spherical terminals 20 are connected to each of the inner zone heater circuit 14a and the jumper 14c, and a heater rod 24 is connected to each of the pair of spherical terminals 20. However, the jumper 14c does not need to be disposed at a depth closer to the second surface 12b than the bottom end of the heater coil portion 16 of the outer zone heater circuit 14b. This is because the jumper 14c can keep the heater coil portion 16 of the outer zone heater circuit 14b sufficiently away from the heater terminal hole 22 (particularly the bottom of the hole), thereby reducing the risk of the heater coil portion 16 of the outer zone heater circuit 14b being exposed in the heater terminal hole 22. Note that while the jumper 14c and the terminal center line Lt of the spherical terminal 20 are generally aligned in a cross-sectional view in FIG. 11 , the jumper 14c may be tilted or partially curved in a cross-sectional view, thereby positioning the spherical terminal 20 so that the terminal center line Lt is closer to the second surface 12b. This allows the jumper 14c to be located away from the bottom of the heater terminal hole 22.

[0031] In an embodiment in which the heater circuit 14 does not have a jumper 14c, as shown in FIG. 12 , a pair of spherical terminals 20 can be connected to each of the inner zone heater circuit 14a and the outer zone heater circuit 14b, and a heater rod 24 can be connected to each of the pair of spherical terminals 20. That is, a first heater rod 24a is connected to each end of the inner zone heater circuit 14a, and a second heater rod 24b is connected to each end of the outer zone heater circuit 14b. The heater rods 24 (i.e., the first heater rod 24a and the second heater rod 24b) are rod-shaped electrode terminals, and the inner zone heater circuit 14a and the outer zone heater circuit 14b are connected to a heater power supply (not shown) via the first heater rod 24a and the second heater rod 24b, respectively. In this embodiment, the inner zone heater circuit 14a and the outer zone heater circuit 14b are preferably arranged on different planes when the ceramic plate 12 is viewed in cross section, as shown in FIG. 12 . In this case, it becomes easier to keep the heater coil portion 16 away from the bottom of the heater terminal hole 22 in each zone, preventing the heater coil portion 16 from being exposed and allowing more heater coil portions 16 to be placed, thereby more effectively eliminating cool spots.

[0032] The inner zone heater circuit 14a may be embedded in at least the inner zone Z1 of the ceramic plate 12, generally parallel to the first surface 12a. The inner zone heater circuit 14a includes a heater coil portion 16 and a heater wire portion 18. A pair of first heater rods 24a for supplying power to the inner zone heater circuit 14a may be provided in the inner zone Z1 of the ceramic plate 12. Preferably, the first heater rods 24a are connected to both ends of the inner zone heater circuit 14a. Two or more pairs of first heater rods 24a may be provided. The first heater rods 24a may be the same as the heater rods 24 used in a single-zone heater, and the inner zone heater circuit 14a is connected to a heater power supply (not shown) via the first heater rods 24a.

[0033] The outer zone heater circuit 14b may be embedded in at least the outer zone Z2 of the ceramic plate 12 at the same or a different depth as the inner zone heater circuit 14a and generally parallel to the first surface 12a. In a preferred embodiment of the present invention, as shown in FIG. 8, the outer zone heater circuit 14b may be embedded in the outer zone Z2 of the ceramic plate 12 at the same depth as the inner zone heater circuit 14a and generally parallel to the first surface 12a. In this case, it is preferable that the coil center lines Lc of the heater coil portions 16 of the inner zone heater circuit 14a, the heater coil center lines Lc of the heater coil portions 16 of the outer zone heater circuit 14b, and the jumpers 14c, if any, are arranged on generally the same plane. In another preferred embodiment of the present invention, as shown in FIG. 12, the outer zone heater circuit 14b may be embedded in the outer zone Z2 of the ceramic plate 12 at a different depth than the inner zone heater circuit 14a and generally parallel to the first surface 12a. 12, the outer zone heater circuit 14b is embedded higher than the inner zone heater circuit 14a (i.e., at a depth closer to the first surface 12a), but this is not limiting. Therefore, the outer zone heater circuit 14b may be embedded lower than the inner zone heater circuit 14a (i.e., at a depth closer to the second surface 12b).

[0034] In an embodiment in which the heater circuit 14 includes a jumper 14c, a pair of second heater rods 24b are provided in the inner zone Z1 of the ceramic plate 12 (particularly, in a position different from the first heater rods 24a within the inner region of the ceramic shaft 38 in a plan view) to supply power to the outer zone heater circuit 14b via the jumper 14c. That is, because the pair of second heater rods 24b are positioned away from the outer zone heater circuit 14b, the pair of second heater rods 24b are electrically connected to the outer zone heater circuit 14b via the pair of jumpers 14c. Two or more pairs of second heater rods 24b may be provided. The second heater rods 24b are rod-shaped electrode terminals, and the outer zone heater circuit 14b is connected to a heater power supply (not shown) via the jumper 14c and the second heater rods 24b.

[0035] The outer zone heater circuit 14b may be either a series circuit or a parallel circuit. That is, the outer zone heater circuit 14b may be provided so as to start in one direction from one of the pair of jumpers 14c and reach the other of the pair of jumpers 14c in a single stroke, so as to form a series circuit. Alternatively, the outer zone heater circuit 14b may be provided so as to start in two directions from one of the pair of jumpers 14c and reach the other of the pair of jumpers 14c in a single stroke, so as to form a parallel circuit.

[0036] A pair of jumpers 14c are embedded in the inner zone Z1 of the ceramic plate 12 so as not to come into contact with the inner zone heater circuit 14a and are electrically connected to the outer zone heater circuit 14b. The pair of jumpers 14c may be embedded generally parallel to the first surface 12a at the same or a different depth as the outer zone heater circuit 14b. The pair of jumpers 14c are separated from each other, with one jumper 14c electrically connecting one of the second heater rods 24b to one end of the outer zone heater circuit 14b, and the other jumper 14c electrically connecting the other of the second heater rods 24b to the other end of the outer zone heater circuit 14b. Two or more pairs of jumpers 14c may be present.

[0037] The jumper 14c is made of a wire-shaped resistance heating element. The specific shape of the wire is not particularly limited, but typical examples include a straight line, a curve (e.g., an arc), and a combination of a straight line and a curve (e.g., a straight line that is bent partially with a curvature).

[0038] 10, the pair of jumpers 14c and the pair of second heater rods 24b are preferably arranged symmetrically with respect to the perpendicular bisector of the line segment connecting the pair of second heater rods 24b when the ceramic plate 12 is viewed from above. With this configuration, the lengths of the power supply paths from the pair of second heater rods 24b through the pair of jumpers 14c to the outer zone heater circuit 14b can be made equal, making it easier to achieve good temperature uniformity.

[0039] A cushioning material 26 may be provided at the bottom of the heater terminal hole 22. The cushioning material 26 is a metal member provided as a buffer to alleviate the difference in thermal expansion between the spherical terminal 20 and the heater rod 24, and is provided between the spherical terminal 20 and the heater rod 24. A preferred example of the metal constituting the cushioning material 26 is an alloy such as Kovar (registered trademark) (an Fe—Ni—Co alloy).

[0040] The eyelet 28 is a metallic cylindrical member that is housed in or fitted into the heater terminal hole 22. The eyelet 28 serves to guide the heater rod 24 for smooth insertion into the heater terminal hole 22. The eyelet 28 may be threaded. In this case, the heater rod 24 may also be threaded so that the heater rod 24 can be inserted while threaded into the eyelet 28. The metal constituting the eyelet 28 is not particularly limited, but preferred examples include Ni, W, Mo, and W-Mo alloys, with Ni being preferred. The eyelet 28 may also have a male thread on its outer periphery. Providing a threaded portion allows the heater rod 24 and eyelet 28 to be threaded together.

[0041] When the buffer material 26 and / or the eyelet 28 are used, the spherical terminal 20, the heater rod 24, the buffer material 26 and / or the eyelet 28 are preferably brazed together.

[0042] The ceramic plate 12 may further include an RF electrode 30 and / or an ESC electrode. In this case, the RF electrode 30 and / or the ESC electrode are preferably embedded in the ceramic plate 12 at a depth closer to the first surface 12a than the heater circuit 14. The RF electrode 30 enables film formation by a plasma CVD process when high frequency is applied to it. The ESC electrode is an abbreviation for electrostatic chuck (ESC) electrode and is also called an electrostatic electrode. When a voltage is applied to the ESC electrode from an external power source, it chucks a wafer placed on the surface of the ceramic plate 12 by the Johnsen-Rahbek force. The ESC electrode is preferably a circular thin electrode with a diameter slightly smaller than that of the ceramic plate 12. For example, it may be a mesh electrode formed by weaving thin metal wires into a net shape into a sheet. The ESC electrode may also be used as a plasma electrode. That is, by applying high frequency to the ESC electrode, the ESC electrode can also be used as an RF electrode, and film formation by a plasma CVD process can also be performed. An RF rod 32 or an ESC rod for power supply is connected to the RF electrode 30 or the ESC electrode. The RF rod 32 or the ESC rod is a rod-shaped electrode terminal, and the RF electrode 30 or the ESC electrode is connected to an external power source (not shown) via the RF rod 32 or the ESC rod.

[0043] The second surface 12b of the ceramic plate 12 may have a temperature measurement hole 34. The temperature measurement hole 34 may be a thermocouple hole for temperature measurement, which is commonly used in ceramic heaters. Therefore, by inserting a thermocouple 36 or a resistance thermometer into the temperature measurement hole 34, the temperature of the ceramic plate 12 can be measured. The temperature measurement hole 34 may be a vertical hole, a horizontal hole, or a combination thereof, and may be formed to fit the area whose temperature is to be measured.

[0044] Optionally, a ceramic shaft 38 may be attached to the second surface 12b of the ceramic plate 12. The ceramic shaft 38 is a cylindrical member with an internal space S 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 the heater rod 24, RF rod 32, thermocouple 36, etc. to pass therethrough. The ceramic shaft 38 is preferably made of the same ceramic material as the ceramic plate 12. Therefore, the ceramic shaft 38 preferably contains aluminum nitride or aluminum oxide, more preferably aluminum nitride. The upper end surface of the ceramic shaft 38 is preferably joined to the second surface 12b of the ceramic plate 12 by solid-state bonding or diffusion bonding. The outer diameter of the ceramic shaft 38 is not particularly limited, but is preferably 40 to 60 mm. The inner diameter of the ceramic shaft 38 (the diameter of the internal space S) is also not particularly limited, but is preferably 33 to 55 mm.

[0045] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0046] Example 1 (1) Fabrication of Ceramic Heater Using the components shown below, a ceramic heater 10 having a one-zone heater structure as shown in FIGS. 1 and 2 and a terminal connection structure as shown in FIG. 3, and satisfying the conditions shown in Tables 1 and 2, was fabricated by a known procedure except for the firing conditions.

[0047] <Constituent members and their specifications> Ceramic plate 12: a disc-shaped aluminum nitride sintered body (diameter: 330 mm, thickness: 20 mm) (with heater circuit 14, spherical terminal 20, and RF electrode 30 embedded inside) Heater circuit 14: a circuit composed of a heater coil portion 16 (material: molybdenum, winding diameter: 3.5 mm, wire diameter: 0.5 mm) made of a three-dimensional coil-shaped resistance heating element and a heater wire portion 18 made of a wire-shaped resistance heating element (material: molybdenum, wire diameter: 0.5 mm) that is not wound into a coil, both embedded in a predetermined circuit pattern at a depth of 10 mm from the first surface 12a Spherical terminal 20: a molybdenum spherical member (diameter: 4.0 mm) with a through hole formed along the terminal center line Lt for inserting and connecting the heater wire portion 18 RF terminal hole: nominal diameter 7 mm ( Heater terminal hole 22: a bottomed hole with a nominal diameter of 7 mm (M7); Heater rod 24: two nickel terminal rods; Buffer material 26: a metal part made of Kovar (registered trademark) (Fe-Ni-Co alloy); Eyelet 28: a cylindrical nickel member; RF electrode 30: a disc-shaped molybdenum electrode with a diameter of 320 mm embedded at a depth of 1.0 mm from first surface 12 a of ceramic plate 12; RF rod 32: a nickel terminal rod; Ceramic shaft 38: a cylindrical aluminum nitride sintered body (height: 172 mm, outer diameter: 42 mm, inner diameter: 36 mm).

[0048] The ceramic plate 12 having the heater circuit 14, spherical terminal 20, and RF electrode 30 embedded therein was fabricated by the following procedure. First, aluminum nitride powder was press-molded to obtain a first aluminum nitride compact. The aluminum nitride powder, heater circuit 14, and spherical terminal 20 were arranged on the obtained first aluminum nitride compact according to a predetermined circuit pattern, and then press-molded to obtain a second aluminum nitride compact having the heater circuit 14 and spherical terminal 20 embedded therein. The heater circuit 14 and spherical terminal 20 were arranged in advance by inserting and connecting the ends of the heater wire portions 18 into the through-holes of the spherical terminal 20 to form a wiring assembly composed of the heater circuit 14 and the spherical terminal 20, and then this wiring assembly was placed on the first aluminum nitride compact. The aluminum nitride powder and RF electrode 30 were then arranged on the obtained second aluminum nitride compact, and then press-molded to obtain a third aluminum nitride compact having the RF electrode 30 further embedded therein. In this way, a press-molded body was obtained consisting of an aluminum nitride powder compact in which a heater circuit 14, a spherical terminal 20, and an RF electrode 30 were embedded, as shown in Figure 1. The obtained press-molded body (laminate) was fired in a nitrogen atmosphere under the following conditions: Maximum temperature: 1810°C; Holding time at maximum temperature: 5 hours; Heating rate: Vary within the range of 10 to 120°C / min (temperature range including each heating rate in multiple heating steps); Firing pressure: 90 kg / cm ２ By firing at this temperature, a ceramic plate 12 was obtained in which the heater circuit 14, the spherical terminal 20, and the RF electrode 30 were embedded.

[0049] (2) Evaluation Various evaluations were carried out on the obtained ceramic heater.

[0050] <Maximum In-Plane Temperature Difference> The ceramic heater 10 was installed in the chamber of a film forming apparatus. The chamber was evacuated and N ２ Introduce N gas into the chamber. ２The gas pressure was set to 5 Torr. The ceramic heater 10 was heated to a set temperature of 550°C by supplying power to the heater circuit 14 via the heater rod 24. At this set temperature, the temperature distribution on the first surface 12a of the ceramic plate 12 was measured using an infrared camera. Based on the obtained temperature distribution map, the difference between the maximum and minimum temperatures (i.e., the maximum in-plane temperature difference) was calculated as an index of thermal uniformity. The results are shown in Table 2.

[0051] <Cool Spots> Based on the temperature distribution map obtained above, the presence or absence of cool spots where the temperature locally drops was confirmed in the central region within a radius of 30 mm (i.e., a diameter of 60 mm) from the center of the ceramic plate 12. As a result, as shown in Table 2, no cool spots were observed in this example.

[0052] <Crack Generation During Operation> The ceramic heater 10 was installed in the chamber of a film forming apparatus. The chamber was evacuated and N ２ Introduce N gas into the chamber. ２ The gas pressure was 5 Torr. By supplying power to the heater circuit 14 via the heater rod 24, the ceramic heater 10 was heated from room temperature (20°C) to a set temperature of 550°C at a temperature increase rate of 20°C / min. The temperature was maintained at 550°C for 10 minutes, after which the power supply was stopped and the ceramic heater 10 was allowed to cool to room temperature (20°C). This cycle of increasing the temperature from 20°C to 550°C and then cooling to 20°C was repeated a total of 100 times. The presence or absence of cracks in the ceramic plate 12 was then examined using an ultrasonic flaw detector. As shown in Table 2, it was confirmed that no cracks had occurred in this example.

[0053] <Coil Exposure During Manufacture> When the heater terminal hole 22 was opened by grinding in the ceramic plate 12, in which the heater circuit 14, the spherical terminal 20, and the RF electrode 30 were embedded, so as to reach a part of the spherical terminal 20 from the second surface 12b, it was investigated whether or not there were any cases in which the heater coil portion 16 was exposed in the heater terminal hole 22. As a result, as shown in Table 2, in this example, no cases in which the heater coil portion 16 was exposed in the heater terminal hole 22 occurred.

[0054] Example 2 A ceramic heater 10 was fabricated in the same manner as in Example 1, except that the ceramic heater 10 had a structure without a ceramic shaft 38 as shown in Figure 7 and satisfied the conditions shown in Tables 1 and 2. Therefore, the ceramic heater 10 of this example has a structure corresponding to Figures 2, 3 and 7. The results are as shown in Table 2.

[0055] Example 3 (1) Fabrication of Ceramic Heater Using the components shown below, a ceramic heater 10 having the planar two-zone heater structure shown in FIGS. 8 and 9 and the terminal connection structure shown in FIGS. 3, 10, and 11, and satisfying the conditions shown in Tables 1 and 2, was fabricated by a method similar to that of Example 1 with appropriate modifications.

[0056] <Constituent members and their specifications> Ceramic plate 12: a disk-shaped aluminum nitride sintered body (diameter: 330 mm, thickness: 20 mm) (with inner zone heater circuit 14a, outer zone heater circuit 14b, jumper 14c, spherical terminal 20, and RF electrode 30 embedded inside) Inner zone Z1: a circular region with a diameter of 216 mm located at the center of the ceramic plate 12 Outer zone Z2: an annular region on the ceramic plate 12 outside the inner zone Z1 Inner zone heater circuit 14a: a circuit composed of a heater coil portion 16 (material: molybdenum, winding diameter: 3.5 mm, wire diameter: 0.5 mm) made of a three-dimensional coiled resistance heating element and a heater wire portion 18 made of a wire-shaped resistance heating element (material: molybdenum, wire diameter: 0.5 mm) that is not wound into a coil, both embedded at a depth of 6.5 mm from the first surface 12a of the inner zone Z1 according to a predetermined circuit pattern Outer zone heater circuit 14b: a circuit composed of a heater coil portion 16 (material: molybdenum, winding diameter: 3.5 mm, wire diameter: 0.5 mm) made of a three-dimensional coiled resistance heating element and a heater wire portion 18 made of a wire-shaped resistance heating element (material: molybdenum, wire diameter: 0.5 mm) that is not wound into a coil Outer zone heater circuit 1 4b: A heater coil portion 16 (material: molybdenum, winding diameter: 3.5 mm, wire diameter: 0.5 mm) made of a three-dimensional coil-shaped resistance heating element buried according to a predetermined circuit pattern at a position 6.5 mm deep from the first surface 12a of the outer zone Z2, and a heater wire portion 18 made of a wire-shaped resistance heating element (material: molybdenum, wire diameter: 0.5 mm) that is not wound into a coil. Circuit / jumper 14c: A pair of substantially linear, symmetrical resistance heating wires (material: molybdenum, wire diameter: 0.5 mm) buried according to the circuit pattern shown in FIG. 10 at a position 6.5 mm deep from the first surface 12a of the inner zone Z1.Spherical terminal 20: A spherical member (diameter: 4.0 mm) made of molybdenum, with a through hole formed along the terminal center line Lt for inserting and connecting the heater wire portion 18; RF terminal hole: A blind hole with a nominal diameter of 7 mm (M7); Heater terminal hole 22: A blind hole with a nominal diameter of 7 mm (M7); First heater rod 24a: Two nickel terminal rods; Second heater rod 24b: Two nickel terminal rods; Buffer material 26: A metal part made of Kovar (registered trademark) (Fe—Ni—Co alloy); Eyelet 28: A cylindrical member made of nickel; RF electrode 30: A disc-shaped molybdenum electrode with a diameter of 320 mm, embedded at a depth of 1.0 mm from the first surface 12a of the ceramic plate 12; RF rod 32: A nickel terminal rod; Ceramic shaft 38: A cylindrical aluminum nitride sintered body (height: 172 mm, outer diameter: 42 mm, inner diameter: 36 mm).

[0057] (2) Evaluation The obtained ceramic heater was subjected to various evaluations in the same manner as in Example 1. The results are shown in Table 2.

[0058] Example 4 (1) Fabrication of Ceramic Heater Using the components shown below, a ceramic heater 10 having the stacked two-zone heater structure shown in FIGS. 9 and 12 and the terminal connection structure shown in FIG. 13, and satisfying the conditions shown in Tables 1 and 2, was fabricated by a method similar to that of Example 1 with appropriate modifications.

[0059] <Constituent members and their specifications> Ceramic plate 12: a disc-shaped sintered aluminum nitride body (diameter: 330 mm, thickness: 20 mm) (with the inner zone heater circuit 14a, outer zone heater circuit 14b, jumper 14c, spherical terminal 20, and RF electrode 30 embedded inside) Inner zone Z1: a circular region having a diameter of 216 mm located at the center of the ceramic plate 12. Outer zone Z2: an annular region on the ceramic plate 12 outside the inner zone Z1. Inner zone heater circuit 14a: a circuit including a heater coil portion 16 (material: molybdenum, winding diameter: 3.5 mm, wire diameter: 0.5 mm) made of a three-dimensional coil-shaped resistance heating element and a heater wire portion 18 made of a wire-shaped resistance heating element (material: molybdenum, wire diameter: 0.5 mm) that is not wound into a coil and that is embedded according to a predetermined circuit pattern at a depth of 11.5 mm from the first surface 12a in the inner zone Z1 and the outer zone Z2 (regions having a diameter of 320 mm) of the ceramic plate 12 (however, the heater coil portion 16 is arranged so that the coil pitch becomes shorter (the coils become denser) as it approaches the center of the ceramic plate 12, thereby enabling selective or preferential heating of the inner zone Z1. Outer zone heater circuit 14b: A circuit composed of a heater coil portion 16 (material: molybdenum, winding diameter: 3.5 mm, wire diameter: 0.5 mm) made of a three-dimensional coil-shaped resistance heating element and a heater wire portion 18 made of a wire-shaped resistance heating element (material: molybdenum, wire diameter: 0.5 mm) that is not wound into a coil and is embedded according to a predetermined circuit pattern at a depth of 6.5 mm from the first surface 12a in the inner zone Z1 and outer zone Z2 (area with a diameter of 320 mm) of the ceramic plate 12 (however, the heater coil portion 16 is arranged so that the coil pitch becomes shorter (the coils become denser) as it approaches the outer periphery of the ceramic plate 12, thereby enabling the outer zone Z2 to be heated selectively or preferentially.) - Spherical terminal 20: A spherical member (diameter: 4.5 mm) made of molybdenum, having a through hole formed along the terminal center line Lt for inserting and connecting the heater wire portion 18; - RF terminal hole: A bottomed hole with a nominal diameter of 7 mm (M7); - Heater terminal hole 22: A bottomed hole with a nominal diameter of 7 mm (M7); - First heater rod 24 a: Two nickel terminal rods; - Second heater rod 24 b: Two nickel terminal rods; - Buffer material 26: A metal part made of Kovar (registered trademark) (An Fe-Ni-Co alloy); - Eyelet 28: A cylindrical member made of nickel; - RF electrode 30: A disk-shaped molybdenum electrode with a diameter of 320 mm, embedded at a depth of 1.0 mm from the first surface 12 a of the ceramic plate 12; - RF rod 32: A nickel terminal rod; - Ceramic shaft 38: A cylindrical aluminum nitride sintered body (height: 172 mm, outer diameter: 42 mm, inner diameter: 36 mm).

[0060] The ceramic plate 12 having the inner zone heater circuit 14a, outer zone heater circuit 14b, spherical terminal 20, and RF electrode 30 embedded therein was fabricated by the following procedure. First, aluminum nitride powder was press-molded to obtain a first aluminum nitride compact. Then, aluminum nitride powder, the inner zone heater circuit 14a, and the spherical terminal 20 were arranged on the obtained first aluminum nitride compact according to a predetermined circuit pattern, followed by press-molding to obtain a second aluminum nitride compact having the inner zone heater circuit 14a and the spherical terminal 20 embedded therein. The inner zone heater circuit 14a and the spherical terminal 20 were arranged in advance by inserting and connecting the end of the heater wire portion 18 into the through-hole of the spherical terminal 20 to form a wiring assembly composed of the inner zone heater circuit 14a and the spherical terminal 20, and then the wiring assembly was placed on the first aluminum nitride compact. The aluminum nitride powder, the outer zone heater circuit 14b, and the spherical terminal 20 were arranged on the obtained second aluminum nitride compact and press-molded to obtain a third aluminum nitride compact having the outer zone heater circuit 14b further embedded therein. The arrangement of the outer zone heater circuit 14b and the spherical terminal 20 was performed by first preparing a wiring assembly consisting of the outer zone heater circuit 14b and the spherical terminal 20 by inserting and connecting the ends of the heater wire portions 18 into the through-holes of the spherical terminal 20, and then placing this wiring assembly on the second aluminum nitride compact. The aluminum nitride powder and the RF electrode 30 were arranged on the obtained third aluminum nitride compact and press-molded to obtain a fourth aluminum nitride compact having the RF electrode 30 further embedded therein. In this way, a press-molded body was obtained consisting of an aluminum nitride compact having the inner zone heater circuit 14a, the outer zone heater circuit 14b, the spherical terminal 20, and the RF electrode 30 embedded therein, as shown in FIG. 12 . The obtained press-molded body (laminate) was fired under a nitrogen atmosphere under the following conditions: Maximum temperature: 1810°C; Holding time at maximum temperature: 5 hours; Heating rate: Vary within the range of 10 to 120°C / min (temperature range including the individual heating rates in multiple heating steps); Firing pressure: 100 kg / cm ２By firing at this temperature, a ceramic plate 12 was obtained in which the heater circuit 14, the spherical terminal 20, and the RF electrode 30 were embedded.

[0061] (2) Evaluation The obtained ceramic heater was subjected to various evaluations in the same manner as in Example 1. The results are shown in Table 2.

[0062] Example 5 (Comparison) A ceramic heater 10 was fabricated in the same manner as in Example 1, except that the depth position of the heater wire portion 18 was changed to coincide with the center line Lc of the heater coil portion 16 so as to satisfy the conditions shown in Fig. 14 and shown in Tables 1 and 2. Therefore, the ceramic heater 10 of this example has a structure corresponding to Figs. 1, 2 and 14. As a result, as shown in Table 2, the temperature uniformity was poor, and cool spots and resulting cracks occurred.

[0063] Example 6 (Comparison) A ceramic heater 10 was fabricated in the same manner as in Example 1, except that the depth position of the heater wire portion 18 was changed to be above the lower end of the heater coil portion 16 and below the center line Lc of the heater coil portion 16 so as to satisfy the conditions shown in Fig. 15 and shown in Tables 1 and 2. Therefore, the ceramic heater 10 of this example has a structure corresponding to Figs. 1, 2, and 15. As a result, as shown in Table 2, poor temperature uniformity occurred, resulting in the occurrence of cool spots, and there were also cases where the heater coil portion 16 was exposed to the heater terminal hole 22 during fabrication.

[0064]

[0065]

[0066] 10: ceramic heater, 12: ceramic plate, 12a: first surface, 12b: second surface, 14: heater circuit, 14a: inner zone heater circuit, 14b: outer zone heater circuit, 14c: jumper, 16: heater coil portion, 18: heater wire portion, 20: spherical terminal, 22: heater terminal hole, 24: heater rod, 24a: first heater rod, 24b: second heater rod, 26: cushioning material, 28: eyelet, 30: RF electrode, 32: RF rod, 34: temperature measurement hole, 36: thermocouple, 38: ceramic shaft, W: wafer, D: depth position, C: imaginary circle, Lt: terminal center line, Lc: coil center line, Z1: inner zone, Z2: outer zone, S: internal space

Claims

1. A ceramic plate having a first surface on which a wafer is placed and a second surface facing the first surface, A heater circuit embedded in the ceramic plate, At least one pair of spherical terminals embedded in the ceramic plate and connected to the heater circuit, The ceramic plate has at least one pair of heater terminal holes formed on its second surface so as to reach each of the spherical terminals, At least one pair of heater rods for supplying power to the heater circuit, which are inserted into each of the heater terminal holes and electrically connected to each of the spherical terminals, and which extend in a direction away from the first surface, Equipped with, The heater circuit described above, A heater coil section, which is arranged parallel to the first surface and is composed of a coil-shaped resistance heating element, A heater wire portion is composed of a non-coiled, strand-shaped resistance heating element that extends from the heater coil portion and whose tip reaches the inside of the spherical terminal, Includes, When the ceramic plate is viewed in cross-section, the heater wire portion is positioned at a depth closer to the second surface, at the same depth as or deeper than the lower end of the heater coil portion. A ceramic heater in which the length L1 of the portion of the heater wire that is not embedded in the spherical terminal is 2.0 to 3.5 mm.

2. A ceramic plate having a first surface on which a wafer is placed and a second surface facing the first surface, A heater circuit embedded in the ceramic plate, At least one pair of spherical terminals embedded in the ceramic plate and connected to the heater circuit, The ceramic plate has at least one pair of heater terminal holes formed on its second surface so as to reach each of the spherical terminals, At least one pair of heater rods for supplying power to the heater circuit, which are inserted into each of the heater terminal holes and electrically connected to each of the spherical terminals, and which extend in a direction away from the first surface, Equipped with, The heater circuit described above, A heater coil section, which is arranged parallel to the first surface and is composed of a coil-shaped resistance heating element, A heater wire portion is composed of a non-coiled, strand-shaped resistance heating element that extends from the heater coil portion and whose tip reaches the inside of the spherical terminal, Includes, When the ceramic plate is viewed in cross-section, the heater wire portion is positioned at a depth closer to the second surface, at the same depth as or deeper than the lower end of the heater coil portion. A ceramic heater in which the shortest distance L4 between the bottom of the heater terminal hole and the heater coil portion is 1.5 to 4.0 mm, and the shortest distance L4 is defined as the length of the shortest straight line connecting the vertex or inflection point formed by the heater coil portion and the heater wire portion to the bottom of the heater terminal hole when the ceramic plate is viewed in cross-section.

3. The ceramic heater according to claim 1 or 2, wherein, when the ceramic plate is viewed in cross-section, a line parallel to the first surface passing through the center of a virtual circle identified by the cross-sectional arc of the spherical terminal is defined as the terminal centerline, and the heater wire portion is arranged along the terminal centerline.

4. The ceramic heater according to claim 1 or 2, wherein the ceramic plate comprises aluminum nitride or aluminum oxide.

5. The ceramic heater according to claim 1 or 2, wherein the spherical terminal is composed of a resistance heating element having the same composition as the coil-shaped resistance heating element.

6. The ceramic heater according to claim 1 or 2, wherein the resistive heating element includes at least one selected from the group consisting of tungsten, molybdenum, tungsten-molybdenum alloy, tungsten carbide, tungsten carbide-titanium nitride composite material, tungsten carbide-aluminum oxide composite material, and niobium.

7. The ceramic heater according to claim 1 or 2, wherein when the ceramic plate is viewed from the second surface in plan view, the heater coil portion is not located within the region defined by the heater terminal hole.

8. The ceramic heater according to claim 1 or 2, further comprising a cylindrical ceramic shaft attached to the second surface of the ceramic plate and having an internal space.

9. The ceramic heater according to claim 1 or 2, wherein the heater wire portion does not penetrate the spherical terminal and extend to the outside thereof, and therefore the heater wire portion terminates within the spherical terminal.

10. The ceramic plate includes an inner zone defined as a circular region within a predetermined distance from the center of the ceramic plate when viewed from above, and an outer zone defined as an annular region outside the inner zone. The heater circuit described above, An inner zone heater circuit, which includes the heater coil portion and the heater wire portion, is embedded in the inner zone of the ceramic plate. An outer zone heater circuit, which includes the heater coil portion and the heater wire portion, is embedded in the outer zone of the ceramic plate. Includes, The ceramic heater according to claim 1 or 2, wherein the pair of spherical terminals are connected to each of the inner zone heater circuit and the outer zone heater circuit, and the heater rod is connected to each of the pair of spherical terminals.

11. The ceramic heater according to claim 10, wherein the inner zone heater circuit and the outer zone heater circuit are arranged on different planes when the ceramic plate is viewed in cross-section.

12. The ceramic plate includes an inner zone defined as a circular region within a predetermined distance from the center of the ceramic plate when viewed from above, and an outer zone defined as an annular region outside the inner zone. The heater circuit described above, An inner zone heater circuit, which includes the heater coil portion and the heater wire portion, is embedded in the inner zone of the ceramic plate. An outer zone heater circuit, which includes the heater coil portion and the heater wire portion, is embedded in the outer zone of the ceramic plate. A pair of jumpers are embedded in the inner zone of the ceramic plate so as not to contact the inner zone heater circuit, and each jumper is composed of a strand-shaped resistive heating element extending from the heater strand portion of the outer zone heater circuit. A ceramic heater according to claim 1 or 2, comprising the inner zone heater circuit and the jumper, each of which is connected to the pair of spherical terminals, and each of the pair of spherical terminals is connected to the heater rod (however, the jumper does not have to be located at the same depth as or deeper than the lower end of the heater coil portion of the outer zone heater circuit, closer to the second surface).

13. The ceramic heater according to claim 12, wherein the inner zone heater circuit and the outer zone heater circuit are arranged on the same plane when the ceramic plate is viewed in cross-section.

14. The ceramic heater according to claim 12, wherein the inner zone heater circuit and the outer zone heater circuit are arranged on different planes when the ceramic plate is viewed in cross-section.