Ceramic heater

Abstract

The present invention provides a ceramic heater capable of achieving improved heat uniformity by suppressing the generation of cool spots even in a central region of a plate with four or more bottomed holes. This ceramic heater comprises: a disc-shaped ceramic plate with a diameter of 220 mm or more having a first surface on which a wafer is placed and a second surface opposite the first surface; at least one heater circuit embedded in the ceramic plate; four or more bottomed holes provided from the second surface in the direction of the thickness of the ceramic plate, within a central region within a radius of 25 mm from the center of the ceramic plate; and at least one pair of heater elements inserted into at least two of the bottomed holes and electrically connected to the heater circuit. The heater circuit includes a heater main section which is disposed so as to be capable of heating the region on the outside of the central region and which includes a resistance heating element in the form of a coil or the like, and a heater strand section which is disposed so as to be capable of heating the central region and which is formed from a resistance heating element in the form of a strand rather than a coil.

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 2022-120251 A) discloses a wafer support table including a ceramic base having a wafer mounting surface and multiple heaters embedded in the ceramic base. The ceramic base has a first heater-forming surface, a second heater-forming surface, and a third heater-forming surface, in this order, from the wafer mounting surface toward the surface opposite the wafer mounting surface. The multiple heaters include a first heater provided on the first heater-forming surface, a second heater provided on the second heater-forming surface, and a third heater provided on the third heater-forming surface. The first heater is provided so as to be located at the center of the ceramic base. The second heater is provided so as to be located on the outer periphery of the first heater. The third heater is provided so as to overlap the second heater, and is provided in each of the zones into which the third heater-forming surface is divided by radial line segments. In this wafer support table, a jumper extending linearly from the center of the ceramic base is connected to the coil portion of the heater.

[0004] Japanese Patent Application Laid-Open No. 2022-120251

[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 have 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 throughout the entire ceramic heater. However, in multi-zone heaters (e.g., with two or more zones), the number of holes for inserting heater terminals and the like increases structurally as the number of zones increases. For example, in ceramic heaters with a ceramic shaft disposed in the center of a ceramic plate, terminal holes, thermocouple holes, vacuum chuck holes, and the like are concentrated in the center of the plate, making it difficult to distribute the resistance heating element throughout the entire plate center. As a result, insufficient heating occurs in areas where a resistance heating element cannot be disposed, resulting in a problem of poor heater thermal uniformity.

[0006] The inventors have now discovered that by arranging an unwound wire-like resistance heating element as part of a heater circuit, rather than a conventional resistance heating element such as a coil, in a central region within a radius of 25 mm from the center of the ceramic plate, it is possible to suppress the occurrence of cool spots and improve thermal uniformity even in the central region of the plate where four or more bottomed holes are present.

[0007] Therefore, an object of the present invention is to provide a ceramic heater that can suppress the occurrence of cool spots and achieve improved temperature uniformity even in the central region of the plate where four or more bottomed holes are present.

[0008] According to the present disclosure, the following aspects are provided: [Aspect 1] A circular ceramic plate having a diameter of 220 mm or more and having a first surface on which a wafer is placed and a second surface opposite the first surface, at least one heater circuit embedded in the ceramic plate, four or more blind holes provided from the second surface in a thickness direction of the ceramic plate so that at least a portion of each blind hole is located within a central region within a radius of 25 mm from the center of the ceramic plate, and at least one pair of heater terminals inserted into at least two of the blind holes and electrically connected to the heater circuit, wherein the heater circuit comprises: a heater main portion arranged to be able to heat a region outside the central region, and including a resistance heating element in at least one form selected from the group consisting of a coil, a linear zigzag structure, a printed pattern, a ribbon, and a mesh; and a heater wire portion arranged to be able to heat the central region and composed of a wire-like resistance heating element that is not in a coil shape, the heater wire portion being arranged so as to start from one of the heater terminals and reach one end of the heater main portion while avoiding or detouring all of the blind holes in the central region except for the blind hole in which one of the heater terminals is located, when viewed from above. [Aspect 2] The ceramic heater according to Aspect 1, wherein the wire-like resistance heating element has a diameter of 0.3 to 0.8 mm.[Aspect 3] The ceramic heater according to Aspect 1 or 2, wherein the ceramic plate includes, in a plan view of the ceramic plate, 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, an outer zone heater circuit embedded in the outer zone of the ceramic plate, and a pair of jumpers embedded in the inner zone of the ceramic plate so as not to contact the inner zone heater circuit and electrically connected to the outer zone heater circuit, wherein the inner zone heater circuit includes the heater main portion and the heater wire portion, and the outer zone heater circuit includes the heater main portion, and the heater wire portion is arranged so as not to intersect with the pair of jumpers in a plan view. [Aspect 4] The ceramic heater according to any one of Aspects 1 to 3, wherein the ceramic plate includes aluminum nitride or aluminum oxide. [Aspect 5] The ceramic heater according to any one of Aspects 1 to 4, further comprising a cylindrical ceramic shaft attached to the second surface of the ceramic plate and having an internal space. [Aspect 6] The ceramic heater according to any one of Aspects 1 to 5, wherein the resistance heating element comprises 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 7] The ceramic heater according to any one of Aspects 1 to 6, wherein the heater main portion and the heater wire portion are a continuous, integrated resistance heating element. [Aspect 8] The ceramic heater according to any one of Aspects 1 to 7, wherein the heater main portion and the heater wire portion are separate resistance heating elements and connected to each other via connection terminals. [Aspect 9] The ceramic heater according to Aspect 8, wherein the connection terminals are arranged within the central region of the ceramic plate.[Aspect 10] The ceramic heater according to any one of Aspects 1 to 9, wherein the connection terminal is a conductive member having two through holes of different diameters to which resistance heating elements of different wire diameters can be connected. [Aspect 11] The ceramic heater according to any one of Aspects 1 to 10, further comprising an internal electrode that is an RF electrode and / or an ESC electrode within the ceramic plate, and an RF terminal and / or an ESC terminal is inserted into at least one of the blind holes other than the blind holes into which the pair of heater terminals is inserted. [Aspect 12] The ceramic heater according to any one of Aspects 1 to 11, wherein a thermocouple is inserted into one of the blind holes other than the blind holes into which the pair of heater terminals is inserted. [Aspect 13] The ceramic heater according to any one of Aspects 3 to 12, wherein the inner zone heater circuit and the outer zone heater circuit are arranged on the same plane in a cross-sectional view. [Aspect 14] The ceramic heater according to any one of Aspects 3 to 12, wherein the inner zone heater circuit and the outer zone heater circuit are arranged on different planes in a cross-sectional view.

[0009] 1 is a perspective cross-sectional view schematically showing one example of a ceramic heater according to the present invention (corresponding to Example 1). For convenience of explanation, the jumper 14c is drawn at a position 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 originally located at the same height. FIG. 1 is a top view schematically showing the ceramic heater shown in FIG. 1. FIG. 2 is a plan view schematically showing the arrangement of heater circuits in the central region of the ceramic plate shown in FIG. 1 and its vicinity. FIG. 3 is a plan view schematically showing the configuration of the heater circuit shown in FIG. 4. FIG. 4 is a plan view schematically showing the connection terminals shown in FIG. 5. FIG. 5 is a perspective cross-sectional view schematically showing another example of a ceramic heater according to the present invention. FIG. 6 is a perspective cross-sectional view schematically showing an example of a ceramic heater not according to the present invention (corresponding to Example 2 (Comparative Example)). FIG. 7 is a plan view schematically showing the arrangement of heater circuits in the central region of the ceramic heater shown in FIG. 7 and its vicinity. FIG. 8 is a temperature distribution map of the ceramic plate measured in Example 1. FIG. 9 is a temperature distribution map of the ceramic plate measured in Example 2 (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 and 2 show one embodiment of a ceramic heater. The ceramic heater 10 shown in FIGS. 1 and 2 includes a ceramic plate 12, at least one heater circuit 14, four or more blind holes 22, and at least one pair of heater terminals 24. The ceramic plate 12 is disk-shaped with a diameter of 220 mm or more and 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 and may be, for example, a multi-zone heater (e.g., a two-zone heater) including an inner zone heater circuit 14a and an outer zone heater circuit 14b. The blind holes 22 are provided from the second surface 12b in the thickness direction of the ceramic plate 12 so that at least a portion of each blind hole 22 is located within a central region C within a radius of 25 mm from the center of the ceramic plate 12. At least one pair of heater terminals 24 (i.e., at least two heater terminals 24) are inserted into at least two of the blind holes 22 and electrically connected to the heater circuit 14. The heater circuit 14 includes a heater main portion 16 and a heater wire portion 18. The heater main portion 16 includes a resistance heating element in at least one form selected from the group consisting of a coil, a linear zigzag structure, a printed pattern, a ribbon, and a mesh, and is arranged to be able to heat an area outside the central region C. On the other hand, the heater wire portion 18 is composed of a wire-like resistance heating element that is not coil-shaped, and is arranged to be able to heat the central region C. When viewed from above and perspectively through the ceramic plate 12, the heater wire portion 18 is arranged so as to start from one of the heater terminals 24 and reach one end of the heater main portion 16 within the central region C, avoiding or bypassing all of the blind holes 22 other than the blind hole 22 in which one of the heater terminals 24 is located. In this way, by arranging an unwound wire-like resistance heating element as part of the heater circuit rather than a normal resistance heating element such as a coil within the central region C within a radius of 25 mm from the center of the ceramic plate 12, it is possible to suppress the occurrence of cool spots and improve thermal uniformity even in the central region C of the plate where four or more bottomed holes 22 are present.

[0012] As mentioned above, with the recent trend toward finer process miniaturization and higher integration, ceramic heaters are required to have even greater thermal uniformity. To achieve this, it is preferable to distribute resistance heating elements throughout the entire ceramic heater. On the other hand, in multi-zone heaters (e.g., two or more zones), the number of holes for inserting heater terminals and the like increases structurally as the number of zones increases. For example, in a ceramic heater with a ceramic shaft disposed in the center of the ceramic plate, terminal holes, thermocouple holes, vacuum chuck holes, etc. are concentrated in the center of the plate, making it difficult to distribute resistance heating elements throughout the center of the plate. As a result, as shown in Figure 8, insufficient heating occurs in areas where resistance heating elements cannot be placed, resulting in a problem of poor heater thermal uniformity. Furthermore, the cool spot in the center of the ceramic plate results in a center-cooled temperature distribution profile in which the temperature is locally lowered in the center of the plate, causing thermal stress concentration in the area where the terminal holes are concentrated, which can lead to heater damage. The present invention successfully solves or alleviates these problems. That is, in the present invention, a simple wire-shaped resistance heating element (heater wire portion 18) is employed as part of the heater circuit 14 in the central region C of the ceramic plate 12, which may be considered an area densely packed with terminals and where it has previously been difficult to place a resistance heating element. In this way, the heater circuit 14 (particularly the heater wire portion 18) can be arranged so that it reaches one end of the heater main portion 16 while avoiding or detouring all of the blind holes 22 other than the blind hole 22 that is the starting point, thereby achieving desired heating while suppressing the occurrence of cool spots even in the central region C. As a result, the heating uniformity of the ceramic plate 12 can be improved.

[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, 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] As shown in FIGS. 3 and 4 , the heater circuit 14 includes a heater main portion 16 arranged to be able to heat an area outside the central area C of the ceramic plate 12, and a heater wire portion 18 arranged to be able to heat the central area C of the ceramic plate 12.

[0016] The heater main portion 16 includes 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 back two-dimensionally within a plane. The printed pattern is not particularly limited, but typically has a pattern in which strip-shaped lines of the resistance heating element layer alternate between straight and bent (e.g., zigzag).

[0017] The heater wire portion 18 is composed of a wire-like resistance heating element that is not coiled (i.e., not wound). In a planar perspective view, as shown in Fig. 3, the heater wire portion 18 is arranged so as to start from one of the heater terminals 24 and reach one end of the heater main portion 16 while avoiding or detouring all of the blind holes 22 in the central region C except for the blind hole 22 in which that one of the heater terminals 24 is located. The heater wire portion 18 typically has a meandering shape (with curves) as shown in Fig. 3 in a planar view, but may also have a combination of curved and straight portions, or a combination of a plurality of straight portions. 3, in order to uniformly heat the central region C, it is preferable to draw an inscribed circle I that is tangent to all of the blind holes 22 (five blind holes 22 in the figure) located outside the center of the central region C, and to provide the heater wire portion 18 in a shape that makes a substantial circle (preferably in a serpentine manner) around the annular region between the inscribed circle I and the blind hole 22 located at the center of the central region C. Examples of blind holes 22 other than the blind hole 22 in which one of the heater terminals 24 is located include the blind hole 22 in which the other heater terminal 24 is located, the blind hole 22 in which the RF terminal 28 is located, and the blind hole 22 in which the thermocouple 30 is located. The diameter of the wire-shaped resistance heating element is preferably 0.3 to 0.8 mm, and more preferably 0.3 to 0.5 mm.

[0018] The heater main portion 16 and the heater wire portion 18 may be a continuous, integrated resistance heating element. Alternatively, the heater main portion 16 and the heater wire portion 18 may be separate resistance heating elements connected to each other via a connection terminal 20, as shown in FIGS. 3 and 4 . In this case, the connection terminal 20 is preferably disposed within the central region C of the ceramic plate 12. Therefore, by using the connection terminal 20, resistance heating elements with different wire diameters can be connected. That is, this embodiment is advantageous when the wire diameter of the heater main portion 16 and the wire diameter of the heater wire portion 18 are different. As shown in FIG. 5 , the connection terminal 20 is preferably a conductive member having two through holes 20 a with different diameters that can connect resistance heating elements with different wire diameters. In this configuration, the heater main portion 16 and the heater wire portion 18 can be electrically connected to each other by inserting the heater main portion 16 and the heater wire portion 18 into the two through holes 20 a and crimping and / or fixing them, respectively. The shape of the connection terminal 20 is not particularly limited, but may be, for example, spherical. Note that if the wire diameter of the heater main portion 16 (e.g., coil) and the wire diameter of the heater element portion 18 are the same, the connection terminal 20 is not necessary.

[0019] The resistance heating element constituting the heater circuit 14 (i.e., the heater main portion 16, the heater wire portion 18, and the connection 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.

[0020] 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. The inner zone Z1 is defined as a circular region within a predetermined distance from the center of the ceramic plate 12. A central region C is located at the center of the inner zone Z1. 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., 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. However, the ceramic heater 10 of the present invention may be a one-zone heater.

[0021] In the case of a multi-zone heater (e.g., a two-zone heater), the heater circuit 14 preferably includes an inner zone heater circuit 14a, an outer zone heater circuit 14b, and a pair of jumpers 14c, as shown in Figures 1 and 2. The inner zone heater circuit 14a is embedded in the inner zone Z1 of the ceramic plate 12. However, the inner zone heater circuit 14a may extend not only to the inner zone Z1 but also to the outer zone Z2. The outer zone heater circuit 14b is embedded in the outer zone Z2 of the ceramic plate 12. However, the outer zone heater circuit 14b may extend not only to the outer zone Z2 but also to the inner zone Z1. 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. A pair of jumpers 14c are embedded in the inner zone Z1 of the ceramic plate 12 so as not to contact the inner zone heater circuit 14a and are electrically connected to the outer zone heater circuit 14b. The inner zone heater circuit 14a includes a heater main portion 16 and a heater wire portion 18, while the outer zone heater circuit 14b includes the heater main portion 16. The heater wire portion 18 is arranged so as not to intersect with the pair of jumpers 14c when the ceramic plate 12 is viewed from above. As shown in FIG. 1, the inner zone heater circuit 14a and the outer zone heater circuit 14b may be arranged on the same plane when viewed from above. Alternatively, as shown in FIG. 6, the inner zone heater circuit 14a and the outer zone heater circuit 14b may be arranged on different planes when viewed from above. Preferably, the inner zone heater circuit 14a and the outer zone heater circuit 14b are arranged in a single stroke when viewed from above. The shape of the single stroke may be any of various known shapes such as a repeating pattern of alternating forward and backward strokes, or a spiral shape.

[0022] The inner zone heater circuit 14a may be embedded in at least the inner zone Z1 of the ceramic plate 12, parallel to the first surface 12a. A pair of first heater terminals 24a for supplying power to the inner zone heater circuit 14a may be provided in the inner zone Z1 (particularly the central region C) of the ceramic plate 12. Preferably, the first heater terminals 24a are connected to both ends of the inner zone heater circuit 14a, respectively. Two or more pairs of first heater terminals 24a may be provided. The first heater terminals 24a are rod-shaped, and the inner zone heater circuit 14a is connected to a heater power supply (not shown) via the rod-shaped first heater terminals 24a.

[0023] The outer zone heater circuit 14b may be embedded in the outer zone Z2 of the ceramic plate 12 at the same or a different depth as the inner zone heater circuit 14a and parallel to the first surface 12a. In a preferred embodiment of the present invention, as shown in FIG. 1, 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 parallel to the first surface 12a. In another preferred embodiment of the present invention, as shown in FIG. 6, 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 parallel to the first surface 12a. In FIG. 6, the inner zone heater circuit 14a is embedded higher than the outer zone heater circuit 14b (i.e., at a depth closer to the first surface 12a), but this is not limiting. Therefore, the inner zone heater circuit 14a may be buried lower than the outer zone heater circuit 14b (i.e., at a depth closer to the second surface 12b). In either embodiment, a pair of second heater terminals 24b for supplying power to the outer zone heater circuit 14b via jumpers 14c is provided in the inner zone Z1 of the ceramic plate 12 (particularly at a position different from the first heater terminals 24a in the central region C). That is, the pair of second heater terminals 24b are located away from the outer zone heater circuit 14b, and are electrically connected to the outer zone heater circuit 14b via the pair of jumpers 14c. Two or more pairs of second heater terminals 24b may be provided. The second heater terminals 24b are rod-shaped, and the outer zone heater circuit 14b is connected to a heater power supply (not shown) via the jumpers 14c and the rod-shaped second heater terminals 24b.

[0024] 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.

[0025] 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 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 terminals 24b to one end of the outer zone heater circuit 14b, and the other jumper 14c electrically connecting the other of the second heater terminals 24b to the other end of the outer zone heater circuit 14b. Two or more pairs of jumpers 14c may be present.

[0026] The jumper 14c preferably includes a resistance heating element in at least one form selected from the group consisting of a line, a printed pattern, and a ribbon. The specific form of the line is not particularly limited, but typical examples include a straight line, a curved line (e.g., an arc), and a combination of a straight line and a curved line (e.g., a straight line that is partially bent with a curvature). In a preferred embodiment of the present invention, the jumper 14c is a linear resistance heating element (i.e., a resistance heating element wire).

[0027] The pair of jumpers 14c and the pair of second heater terminals 24b are preferably arranged symmetrically with respect to the perpendicular bisector of the line segment connecting the pair of second heater terminals 24b when viewed in a plan view of the ceramic plate 12. With this configuration, the lengths of the power supply paths from the pair of second heater terminals 24b to the outer zone heater circuit 14b via the pair of jumpers 14c can be made equal, making it easier to achieve good temperature uniformity.

[0028] The blind holes 22 are blind holes formed from the second surface 12b in the thickness direction of the ceramic plate 12 so that at least a portion of each blind hole 22 is located within the central region C of the ceramic plate 12. Therefore, the entire blind holes 22 may be located within the central region C of the ceramic plate 12, or only a portion of each blind hole 22 may be located within the central region C, with the remaining portion of each blind hole 22 extending beyond the central region C. The number of blind holes 22 is four or more. Examples of blind holes 22 include terminal holes for heater terminals 24, terminal holes for RF terminals 28, thermocouple holes for inserting thermocouples 30, and vacuum chuck holes for fixing the wafer W toward the first surface 12a by vacuum suction. At least two of the four or more blind holes 22 are holes for heater terminals 24. That is, at least one pair of heater terminals 24 is inserted into at least two of the blind holes 22 and electrically connected to the heater circuit 14. 1 and 6, it is preferable for accurately measuring and controlling the temperature of the ceramic plate 12 that a thermocouple 30 be inserted into one of the blind holes 22 other than the blind holes 22 into which a pair of heater terminals 24 are inserted. Therefore, the diameter of the blind hole 22 may be determined appropriately depending on the diameter of the terminals, thermocouple, or other components to be inserted. In any case, when four or more blind holes 22 are present in the central region C, the holes are concentrated in the central region C, making it difficult to arrange a resistance heating element throughout the central region C in a conventional heater circuit. In this regard, the present invention effectively solves this problem by arranging the heater wire portion 18 in the central region C.

[0029] The ceramic plate 12 may further include an RF electrode 26 and / or an ESC electrode therein. In this case, the RF electrode 26 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 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 referred to as 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-layer 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 terminal 28 or an ESC terminal for power supply is connected to the RF electrode 26 or the ESC electrode. The RF terminal 28 or the ESC terminal is rod-shaped, and the RF electrode 26 or the ESC electrode is connected to an external power supply (not shown) via the rod-shaped RF terminal 28 or ESC terminal. The RF terminal 28 and / or the ESC terminal is preferably inserted into at least one of the bottomed holes 22 other than the bottomed holes 22 into which the pair of heater terminals 24 are inserted.

[0030] Optionally, a ceramic shaft 32 may be attached to the second surface 12b of the ceramic plate 12. The ceramic shaft 32 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 terminal 24, RF terminal 28, thermocouple 30, etc. to pass therethrough. The ceramic shaft 32 is preferably made of the same ceramic material as the ceramic plate 12. Therefore, the ceramic shaft 32 preferably contains aluminum nitride or aluminum oxide, more preferably aluminum nitride. The upper end surface of the ceramic shaft 32 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 32 is not particularly limited, but is preferably 40 to 60 mm. The inner diameter of the ceramic shaft 32 (the diameter of the internal space S) is also not particularly limited, but is preferably 33 to 55 mm. The central region C is defined as the region within a radius of 25 mm (i.e., within a diameter of 50 mm) from the center of the ceramic plate 12, but if the inner diameter of the ceramic shaft 32 (referred to as inner diameter D) is smaller than 50 mm, the central region C is defined as the region within a radius of D / 2 from the center of the ceramic plate 12.

[0031] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0032] 1 to 4 was produced using the following components according to a known procedure, except for the firing conditions. <Components and their specifications> Ceramic plate 12: Disc-shaped sintered aluminum nitride body (diameter: 330 mm, thickness: 20 mm) (with inner zone heater circuit 14a, outer zone heater circuit 14b, jumper 14c, and RF electrode 26 embedded inside) Ceramic shaft 32: Cylindrical sintered aluminum nitride body (height: 172 mm, outer diameter: 42 mm, inner diameter: 36 mm) Inner zone Z1: Circular region with a diameter of 216 mm located at the center of ceramic plate 12 Outer zone Z2: Annular region on ceramic plate 12 outside inner zone Z1 Inner zone heater circuit 14a: A circuit in which a heater main portion 16 (material: molybdenum, winding diameter: 3.5 mm, and wire diameter: 0.5 mm) consisting of a three-dimensional coil-shaped resistance heating element buried according to a predetermined circuit pattern at a depth of 6.5 mm from the first surface 12a of the inner zone Z1 and a heater wire portion 18 consisting of a simple resistance heating wire (material: molybdenum, wire diameter: 0.4 mm, disposed in the central region C of the ceramic plate 12) that is not in a coil shape are connected by connection terminals 20. Outer zone heater circuit 14b: A heater main portion 16 (material: molybdenum, winding diameter: 3.5 mm, and wire diameter: 0.5 mm) consisting of a three-dimensional coil-shaped resistance heating element buried according to a predetermined circuit pattern at a depth of 6.5 mm from the first surface 12a of the outer zone Z2. Jumper 14c: A pair of substantially linear, symmetrical resistance heating wires (material: molybdenum, wire diameter: 0.7 mm) buried at a depth of 6.5 mm from the first surface 12a in the inner zone Z1 according to the circuit pattern shown in FIG. 3 (the wires are substantially linear with some curved portions as shown in FIG. 3). Connection terminal 20: A spherical member made of molybdenum having the shape shown in FIG. 5 (diameter 3 mm, diameter of large through hole 20a: 0.55 mm (maximum 0.05 mm larger than the wire diameter of the heater main portion 16), diameter of small through hole 20a: 0.42 mm (0.02 mm larger than the wire diameter of the heater wire portion 18)Bottomed holes 22: six holes in the central region C of the ceramic plate 12 (four bottomed holes 22 for the heater terminals 24, one bottomed hole 22 for the RF terminal 28, and one bottomed hole 22 for the thermocouple 30) First heater terminal 24a: two terminal rods made of nickel Second heater terminal 24b: two terminal rods made of nickel RF electrode 26: a molybdenum electrode layer buried at a depth of 1.0 mm from the first surface 12a of the ceramic plate 12 RF terminal 28: one terminal rod made of nickel

[0033] The ceramic plate 12 having the inner zone heater circuit 14a, the outer zone heater circuit 14b, the jumper 14c, and the RF electrode 26 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, the inner zone heater circuit 14a, the outer zone heater circuit 14b, and the jumper 14c were arranged on the obtained first aluminum nitride compact according to a predetermined circuit pattern, and the resulting compact was press-molded to obtain a second aluminum nitride compact having the inner zone heater circuit 14a, the outer zone heater circuit 14b, and the jumper 14c embedded therein. The aluminum nitride powder and the RF electrode 26 were then arranged on the obtained second aluminum nitride compact, and the resulting compact was press-molded to obtain a third aluminum nitride compact having the RF electrode 26 further embedded therein. 1, a press-molded body was obtained, which was made of an aluminum nitride powder compact having embedded therein inner zone heater circuit 14a, outer zone heater circuit 14b, jumper 14c, and RF electrode 26. 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), and Firing pressure: 90 kg / cm. ２ By firing at this temperature, a ceramic plate 12 was obtained in which the inner zone heater circuit 14a, the outer zone heater circuit 14b, the jumper 14c, and the RF electrode 26 were embedded.

[0034] (2) Evaluation The obtained ceramic heaters were evaluated as follows.

[0035] <Heat Uniformity> 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 set to 5 Torr. The ceramic heater 10 was heated to a set temperature of 650°C by supplying power to the inner zone heater circuit 14a and the outer zone heater circuit 14b via the first heater terminal 24a, the second heater terminal 24b, and the jumper 14c. The ratio of power supplied to the outer zone heater circuit 14b to the inner zone heater circuit 14a was finely adjusted to achieve the most uniform temperature distribution, based on a 1:1 ratio. At this set temperature, the temperature distribution on the first surface 12a of the ceramic plate 12 was measured using an infrared camera. Figure 9 shows a temperature distribution map for a 300 mm diameter region including the central region C corresponding to Figure 3 . Based on the obtained temperature distribution map, the difference between the maximum and minimum temperatures within the 300 mm diameter region (i.e., the maximum in-plane temperature difference) was calculated as an index of thermal uniformity. The results are shown in Table 1. In this example, by arranging the heater wire portion 18 in the central region C where the six blind holes 22 constituting the heater wire portion 18 are concentrated, sufficient heating can be achieved in the central region C, and a cool spot (which can occur in the central region without the present invention) can be eliminated, as shown in Fig. 9. This is because the non-coil resistance heating wire serving as the heater wire portion 18 has a width of 1 mm or less, and therefore the heater wire portion 18 can be arranged in a serpentine manner to reach one end of the heater main portion 16 while avoiding or detouring all of the blind holes 22 other than the blind hole 22 that is the starting point, as shown in Fig. 3.

[0036] Example 2 (Comparison) A ceramic heater was fabricated and evaluated in the same manner as in Example 1, except that, as shown in Figures 7 and 8, no heater wire portion 18 was provided in the central region C of the ceramic plate 12 (i.e., the inner zone heater circuit 14a was composed only of the heater main portion 16). Figure 10 shows a temperature distribution map in a 300 mm diameter region including the central region C corresponding to Figure 8. Based on the obtained temperature distribution map, the difference between the maximum and minimum temperatures in the 300 mm diameter region (i.e., the maximum in-plane temperature difference) was calculated as an index of thermal uniformity. The results are shown in Table 1. In this example, since no heater circuit 14 was present in the central region C (i.e., there was no space to place the coil-shaped heater main portion 16), sufficient heating was not possible in the central region C, and a cool spot CS occurred in the center, as shown in Figure 10.

[0037]

Claims

1. A ceramic heater comprising: a disc-shaped ceramic plate having a first surface for placing a wafer and a second surface facing the first surface, the diameter of the ceramic plate being 220 mm or more; at least one heater circuit embedded in the ceramic plate; four or more bottomed holes provided in the thickness direction of the ceramic plate from the second surface such that at least a part of each bottomed hole is located within a central region within a radius of 25 mm from the center of the ceramic plate; and at least one pair of heater terminals inserted into at least two of the bottomed holes and electrically connected to the heater circuit, wherein the heater circuit includes: a heater main part disposed so as to be able to heat a region outside the central region and including a resistive heating element in at least one form selected from the group consisting of a coil, a linear zigzag structure, a printed pattern, a ribbon, and a mesh; and a heater wire part disposed so as to be able to heat the central region and composed of a wire-shaped resistive heating element that is not coiled, and when viewed in a plane perspective, starting from one of the heater terminals, in the central region, it is disposed so as to reach one end of the heater main part while avoiding or bypassing all of the bottomed holes other than the bottomed hole in which one of the heater terminals is located.

2. The ceramic heater according to claim 1, wherein the diameter of the wire-shaped resistive heating element is 0.3 to 0.8 mm.

3. 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 in plan, and an outer zone defined as an annular region outside the inner zone. The heater circuit includes an inner zone heater circuit embedded in the inner zone of the ceramic plate, an outer zone heater circuit embedded in the outer zone of the ceramic plate, and a pair of jumpers embedded in the inner zone of the ceramic plate so as not to contact the inner zone heater circuit and electrically connected to the outer zone heater circuit. The inner zone heater circuit includes the heater main part and the heater wire part, the outer zone heater circuit includes the heater main part, and the heater wire part is arranged so as not to intersect the pair of jumpers when viewed in plan. The ceramic heater according to claim 1 or 2.

4. The ceramic plate contains aluminum nitride or aluminum oxide. The ceramic heater according to claim 1 or 2.

5. 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.

6. The resistance 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. The ceramic heater according to claim 1 or 2.

7. The heater main part and the heater wire part are a continuous integral resistance heating element. The ceramic heater according to claim 1 or 2.

8. The heater main part and the heater wire part are separate resistance heating elements and are connected to each other via connection terminals. The ceramic heater according to claim 1 or 2.

9. The connection terminal is arranged within the central region of the ceramic plate. The ceramic heater according to claim 8.

10. The connection terminal is a conductive member having two through holes with different diameters capable of connecting resistance heating elements with different wire diameters. The ceramic heater according to claim 1 or 2.

11. The ceramic plate further includes internal electrodes that are RF electrodes and / or ESC electrodes, and RF terminals and / or ESC terminals are inserted into at least one of the bottomed holes other than the bottomed hole into which the pair of heater terminals are inserted. The ceramic heater according to claim 1 or 2.

12. A thermocouple is inserted into one of the bottomed holes other than the bottomed hole into which the pair of heater terminals are inserted. The ceramic heater according to claim 1 or 2.

13. The ceramic heater according to claim 3, wherein the inner zone heater circuit and the outer zone heater circuit are arranged on the same plane in a cross-sectional view.

14. The ceramic heater according to claim 3, wherein the inner zone heater circuit and the outer zone heater circuit are arranged on different planes in a cross-sectional view.

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