Ceramic heater and method for manufacturing ceramic heater

Abstract

To provide a ceramic heater capable of suppressing current consumption and a manufacturing method for the same.SOLUTION: A ceramic heater 100 includes a ceramic substrate 110 and a metallic electrode foil 120 embedded in the ceramic substrate 110. A plurality of through-holes is distributed on the electrode foil 120. The open-hole ratio of the plurality of through-holes distributed on the electrode 120 is 2.5% or more.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a ceramic heater and a method for manufacturing a ceramic heater. [Background technology]

[0002] Patent Document 1 discloses a ceramic heater including a ceramic substrate on which an object to be heated is placed, and a heating resistor embedded in the ceramic substrate. The heating resistor has an arc-shaped heating resistor element and a linear heating resistor element that extend in different directions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-5998 A Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses that the resistance per unit length of a connection where an arc-shaped heating resistance element and a linear heating resistance element overlap is smaller than the resistance per unit length of the arc-shaped heating resistance element and the linear heating resistance element, and that this causes a localized decrease in the amount of heat generated at the connection. Therefore, in the above-mentioned ceramic heater, a through hole is formed locally at the connection, thereby increasing the resistance per unit length of the connection and preventing a local decrease in the amount of heat generated at the connection.

[0005] In the ceramic heater described in Patent Document 1, a metal mesh is used as the heating resistor, but Patent Document 1 also discloses that a metal foil heating resistor may also be used. However, if the metal mesh heating resistor is simply replaced with a metal foil heating resistor, the resistance value of the metal foil heating resistor will be too small compared to the resistance value of the metal mesh heating resistor, resulting in increased current consumption and a risk of the power supply for the ceramic heater becoming larger.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a ceramic heater capable of suppressing current consumption, and a method for manufacturing the same. [Means for solving the problem]

[0007] According to an aspect of the present invention, a heating apparatus includes: a ceramic base on which an object to be heated is placed; A band-shaped metal electrode foil is embedded in the ceramic base material, The electrode foil has a plurality of through holes that are distributed throughout the electrode foil, The thickness of the electrode foil is 0.05 mm to 0.1 mm. The through holes have an average opening diameter of 1.0 mm to 3.0 mm, The aperture ratio is a ratio of the sum of the aperture areas of the plurality of through holes to the area of ​​the upper surface of the electrode foil when the plurality of through holes are not formed. 5.7 % or more Less than 10.1% and The plurality of through holes The above Opening The above There is provided a ceramic heater characterized in that the average diameter is 2% to 20% of the width of the belt-shaped electrode foil. Effect of the Invention

[0008] In the above embodiment, the aperture ratio of the multiple through holes distributed in the electrode foil is 2.5% or more. Since the electrode foil is formed using a metal foil instead of a metal mesh, no contact resistance occurs due to contact between the wires that make up the mesh. This makes it possible to suppress variations in the resistance value of the electrode foil, and to reduce variations in the temperature distribution of the ceramic heater. Furthermore, since the multiple through holes are distributed in the metal foil so that the aperture ratio is 2.5% or more, the resistance value of the metal foil can be made high (for example, 1 Ω or more). This makes it possible to suppress the current consumption of the power supply used in the ceramic heater, and to prevent the power supply from becoming larger. [Brief description of the drawings]

[0009] [Figure 1] 1A is a schematic diagram of the ceramic heater 100, and FIG. 1B is a schematic diagram of the ceramic heater 100 viewed from a different direction. [Diagram 2] FIG. 2 is a schematic explanatory diagram showing the shapes of the ceramic base 110 and the electrode foil 120. As shown in FIG. [Diagram 3] 1(a) to 1(e) are diagrams showing a flow of a method for producing the ceramic base 110. FIG. [Figure 4] 1(a) to 1(e) are diagrams showing the flow of another method for producing the ceramic base 110. FIG. [Diagram 5] FIG. 11 is a schematic diagram of an electrode foil 120 of Example 4. [Figure 6] 13 is a schematic diagram of a mesh electrode 220 of Comparative Example 2. FIG. [Figure 7] 1 is a table summarizing the results of Examples 1 to 4 and Comparative Examples 1 and 2. [Figure 8] 13 is a schematic diagram showing a modified example of the electrode foil 120. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Ceramic heater 100> A ceramic heater 100 according to an embodiment of the present invention will be described with reference to Figures 1(a) and 1(b). The ceramic heater 100 is used to heat semiconductor wafers such as silicon wafers (hereinafter simply referred to as wafer 10). In the following description, the up-down direction 5 is defined based on the state in which the ceramic heater 100 is installed so as to be usable (the state shown in Figure 1(a)). As shown in Figures 1(a) and 1(b), the ceramic heater 100 according to this embodiment comprises a ceramic base material 110, an electrode foil 120, a shaft 130, and a power supply line 140.

[0011] The ceramic base 110 is a member having a circular plate shape with a diameter of 12 inches (approximately 300 mm), and the wafer 10 to be heated is placed on its upper surface 111. Note that in FIGS. 1(a) and 1(b), the wafer 10 and the upper surface 111 of the ceramic base 110 are shown separated from each other to make the drawings easier to see. The ceramic base 110 can be formed of a ceramic sintered body such as aluminum nitride, alumina, silicon nitride, or the like.

[0012] The electrode foil 120 cut into a strip shape is embedded inside the ceramic base material 110. The electrode foil 120 is formed of a heat-resistant metal (high melting point metal) foil such as a tungsten (W) foil, a molybdenum (Mo) foil, or a foil of an alloy containing molybdenum and / or tungsten. The purity of the tungsten foil or molybdenum foil is preferably 99% or more. The thickness of the electrode foil 120 is 0.15 mm or less. From the viewpoint of increasing the resistance value of the electrode foil 120 and reducing the current consumption of the ceramic heater 100, the thickness of the electrode foil 120 is preferably 0.1 mm or less. The width of the electrode foil 120 cut into a strip shape is preferably 2.5 mm to 20 mm, and more preferably 5 mm to 15 mm. The electrode foil 120 is cut into a shape shown in FIG. 2. Details of the shape of the electrode foil 120 will be described later. In addition to the electrode foil 120, at least one of an electrostatic chuck electrode for attracting the wafer 10 to the upper surface 111 by the Johnsen-Rahbek force and a plasma electrode for generating plasma above the ceramic base material 110 may be embedded inside the ceramic base material 110.

[0013] A shaft 130 extending downward is disposed at approximately the center of the lower surface 112 of the ceramic base material 110. The shaft 130 has a hollow, approximately cylindrical cylindrical portion 131 and a large diameter portion 132 provided below the cylindrical portion 131. The large diameter portion 132 has a diameter larger than that of the cylindrical portion 131. The upper surface of the cylindrical portion 131 is fixed to approximately the center of the lower surface 112 of the ceramic base material 110 by a bonding agent such as ceramic or glass. The upper surface of the cylindrical portion 131 and the lower surface 112 of the base material 110 can be fixed by diffusion bonding. Alternatively, they can be fixed by screws, brazing, or the like. The shaft 130 may be formed of a ceramic sintered body such as alumina, aluminum nitride, or silicon nitride, like the ceramic base material 110. Alternatively, in order to improve thermal insulation, the shaft 130 may be formed of a material having a lower thermal conductivity than the ceramic base material 110.

[0014] As described above, shaft 130 has a hollow cylindrical shape, and a through hole extending in the vertical direction is formed inside shaft 130. A power supply line 140 for supplying power to electrode foil 120 is arranged in the hollow portion (through hole) of shaft 130. An upper end of power supply line 140 is electrically connected to terminal portion 121 (see FIG. 2 ) arranged in the center of electrode foil 120. A power supply terminal 141 is provided at a lower end of power supply line 140. Power supply terminal 141 is connected to a heater power supply (not shown). As a result, power is supplied to electrode foil 120 via power supply terminal 141.

[0015] Next, the shape of the electrode foil 120 will be described with reference to FIG. 2. The electrode foil 120 is a metal foil cut into a strip shape and has a symmetrical shape. The outer diameter of the electrode foil 120 is approximately 300 mm. The electrode foil 120 has four pairs of arch portions 122-125 and three pairs of straight portions 126-128. The diameters of the four pairs of arch portions 122-125 increase in this order, and they are arranged at equal intervals from the center side to the outside in the radial direction of the substrate 110. The pair of arch portions 125 located on the outermost side in the radial direction are connected to each other, but the remaining three pairs of arch portions 122-124 are arranged separately on the left and right. The pair of straight portions 126 extend in the vertical direction of FIG. 2 so as to connect the arch portions 122 and 123. Similarly, a pair of straight portions 127 connect the arch portions 123 and 124, and a pair of straight portions 128 connect the two arch portions 124 and 125. A terminal portion 121 is formed on the lower surface of the end portion of the innermost arch portion 122, and the upper end of a power supply line 140 is connected from below.

[0016] As shown in the enlarged view of FIG. 2, a plurality of through holes are formed so as to be distributed over the entire electrode foil 120. The diameter of the through holes is preferably 2% to 20% of the width of the electrode foil 120, and more preferably 5% to 15%. The diameter of the through holes is, for example, φ0.05 mm to φ3.0 mm. In the following description, the ratio of the total opening area of ​​the through holes to the area of ​​the upper surface of the electrode foil 120 when no through holes are formed is called the opening ratio. A plurality of through holes are distributed in the electrode foil 120 so that the opening ratio is 2.5% or more. The resistance value of the electrode foil 120 can be adjusted by adjusting the opening ratio. From the viewpoint of increasing the resistance value of the electrode foil 120 and reducing the current consumption of the ceramic heater 100, the opening ratio is preferably 2.5% or more, and more preferably 20% or more. The multiple through holes can be formed, for example, by forming a mask of a predetermined shape on the upper surface of the molybdenum foil (or tungsten foil) using a photoresist or dry film, and etching with an etching solution of a mixture of phosphoric acid, nitric acid, acetic acid, and water. The multiple through holes can also be formed by mechanical processing or electric discharge processing.

[0017] Next, a method for manufacturing the ceramic heater 100 will be described. In the following, a case where the ceramic base 110 and the shaft 130 are made of aluminum nitride will be described as an example.

[0018] First, a method for manufacturing the ceramic base material 110 will be described. As shown in FIG. 3(a), granulated powder P mainly composed of sodium nitride (AlN) powder is put into a bed-type mold 501 made of carbon and pre-pressed with a punch 502. The granulated powder P preferably contains 5 wt% or less of a sintering aid (for example, Y2O3). Next, as shown in FIG. 3(b), an electrode foil 120 cut into a predetermined shape is placed on the pre-pressed granulated powder P. A plurality of through holes are formed in the electrode foil 120 by etching in advance. The electrode foil 120 is placed so as to be parallel to a surface (bottom surface of the bed-type mold 501) perpendicular to the pressing direction. At this time, a pellet of W or a pellet of Mo may be embedded at the position of the terminal 121 of the electrode foil 120.

[0019] As shown in FIG. 3(c), granulated powder P is further poured into bed mold 501 so as to cover electrode foil 120, and pressed and molded with punch 502. Next, as shown in FIG. 3(d), granulated powder P with electrode foil 120 embedded therein is fired in a pressed state. The pressure applied during firing is preferably 1 MPa or more. Also, firing is preferably performed at a temperature of 1800° C. or more. Next, as shown in FIG. 3(e), necessary processing is performed to form terminal 121, such as drilling a blind hole to electrode foil 120, and ceramic base material 110 is formed. When pellets are embedded, it is sufficient to drill a blind hole to the pellet.

[0020] The ceramic substrate 110 can also be manufactured by the following method. As shown in Fig. 4(a), a binder is added to aluminum nitride granulated powder P, which is then CIP molded and processed into a disk shape to produce an aluminum nitride molded body 510. Next, as shown in Fig. 4(b), the molded body 510 is degreased to remove the binder.

[0021] As shown in FIG. 4(c), a recess 511 for embedding electrode foil 120 is formed in degreased molded body 510. Electrode foil 120 is placed in recess 511 of molded body 510, and another molded body 510 is laminated. Next, as shown in FIG. 4(d), molded body 510 laminated with electrode foil 120 sandwiched therebetween is fired in a pressed state. The pressure applied during firing is preferably 1 MPa or more. In addition, firing is preferably performed at a temperature of 1800° C. or more. Next, as shown in FIG. 4(e), necessary processing such as drilling a blind hole to electrode foil 120 is performed to form terminal 121, and ceramic base material 110 is formed.

[0022] The ceramic heater 100 is manufactured by fixing the shaft 130 to approximately the center of the lower surface 112 of the ceramic base 110 thus formed. The shaft 130 is formed by forming aluminum nitride granulated powder P to which several wt % of binder has been added under hydrostatic pressure (about 1 MPa), processing the formed body into a predetermined shape, and then firing it in a nitrogen atmosphere. EXAMPLES

[0023] The present invention will be further described below using examples and comparative examples, but the present invention is not limited to the examples and comparative examples described below.

[0024] [Example 1] In Example 1, a molybdenum foil having a thickness of 0.1 mm and a diameter of 350 mm was used as the electrode foil 120. A through hole having a diameter of 1.0 mm was formed at each vertex of a pattern of equilateral triangles with a side length of 4 mm laid out over the entire surface of the molybdenum foil. The molybdenum foil was then cut into a shape as shown in FIG. 2 to obtain the electrode foil 120. The opening ratio of the electrode foil 120 in Example 1 was about 5.7%.

[0025] In addition, an evaluation test of the temperature distribution of the ceramic heater 100 was performed in the following procedure. First, before the evaluation test, the resistance value between the terminals 121 was measured with a tester to obtain the resistance value of the electrode foil 120 at room temperature. In Example 1, the resistance value of the electrode foil 120 was 2.27 Ω. Next, a current was applied to the ceramic heater 100 from an external power source (not shown), and the temperature was controlled at a set temperature of 450° C. by a thermocouple (not shown). With the set temperature kept at 450° C., the temperature distribution of an area of ​​290 mm in diameter on the upper surface 111 (wafer mounting surface) of the substrate 110 was measured with an infrared camera. The maximum temperature minus the minimum temperature of the measured temperature distribution was obtained as the temperature difference Δ. The temperature difference Δ is an index of the variation in the temperature distribution of the upper surface 111 of the substrate 110. In Example 1, the temperature difference Δ for the set temperature of 450° C. was 3.3° C.

[0026] After the temperature distribution evaluation test, substrate 110 was cut in the radial direction, and the cross section was visually inspected using an optical microscope to check whether peeling of electrode foil 120 had occurred. In Example 1, peeling of electrode foil 120 was not observed.

[0027] [Example 2] The ceramic heater 100 of Example 2 is the same as the ceramic heater 100 of Example 1, except that the thickness of the molybdenum foil that serves as the electrode foil 120 is changed to 0.05 mm.

[0028] The resistance value of the electrode foil 120 at room temperature was found to be 4.55Ω in the same manner as in Example 1. The temperature difference Δ with respect to the set temperature of 450° C. was 3.2° C. Peeling of the electrode foil 120 was not observed.

[0029] [Example 3] Ceramic heater 100 of Example 3 is the same as ceramic heater 100 of Example 1, except for the size and arrangement of the through holes in electrode foil 120. In Example 3, through holes with a diameter of 3.0 mm are formed at positions corresponding to the vertices of equilateral triangles with sides of 9 mm laid out all over the surface of the molybdenum foil that constitutes electrode foil 120. The opening rate of electrode foil 120 of Example 3 is approximately 10.1%.

[0030] The resistance value of the electrode foil 120 at room temperature was found to be 2.46 Ω in the same manner as in Example 1. The temperature difference Δ with respect to the set temperature of 450° C. was 4.8° C. Peeling of the electrode foil 120 was not observed.

[0031] [Example 4] The ceramic heater 100 of Example 4 is the same as the ceramic heater 100 of Example 1, except for the size and arrangement of the through holes in the electrode foil 120. The electrode foil 120 of Example 4 is shown in FIG. 5. In the arch portion 122 and the arch portion 125, as in Example 1, through holes having a diameter of 1.0 mm are formed at positions corresponding to the vertices of a pattern in which equilateral triangles having a side length of 4 mm are laid out. The opening ratio of the electrode foil 120 in the arch portion 122 and the arch portion 125 is about 5.7%, as in Example 1. In the arch portion 123 and the arch portion 124, through holes having a diameter of 0.5 mm are formed at positions corresponding to the vertices of a pattern in which equilateral triangles having a side length of 2 mm are laid out. The opening ratio of the electrode foil 120 in the arch portion 123 and the arch portion 124 is also about 5.7%. In addition, no through holes are formed in the straight portions 126 to 128. The hole ratio of electrode foil 120 as a whole is slightly smaller than 5.7% since no through holes are formed in straight portions 126-128.

[0032] The resistance value of the electrode foil 120 at room temperature was found to be 1.99 Ω in the same manner as in Example 1. The temperature difference Δ with respect to the set temperature of 450° C. was 2.8° C. Peeling of the electrode foil 120 was not observed.

[0033] [Comparative Example 1] In Comparative Example 1, electrode foil 120 is similar to electrode foil 120 in Example 1, except that no through holes are formed.

[0034] As in Example 1, the resistance value of the electrode foil 120 at room temperature was found to be 0.68 Ω. The temperature difference Δ with respect to the set temperature of 450° C. was 12° C. It was also confirmed that the electrode foil 120 had peeled off from the ceramic base 110 in some places.

[0035] [Comparative Example 2] Mesh electrode 220 of Comparative Example 2 (see FIG. 6) is not formed from molybdenum foil, but is formed by cutting a molybdenum mesh into the same shape as electrode foil 120 of Example 1. The wire diameter of the molybdenum mesh is 0.1 mm, and the mesh size (number of wires per inch) is 50. The opening ratio of mesh electrode 220 of Comparative Example 2 is approximately 80.3%.

[0036] The resistance value of mesh electrode 220 at room temperature was found to be 3.41 Ω in the same manner as in Example 1. The temperature difference Δ with respect to the set temperature of 450° C. was 5.5° C. Peeling of mesh electrode 220 was not observed.

[0037] <Summary of Examples and Comparative Examples> FIG. 7 shows a table summarizing the results of Examples 1 to 4 and Comparative Examples 1 and 2 described above.

[0038] It is believed that in Examples 1 and 2, the variation in the resistance value of electrode foil 120 after cutting could be suppressed by distributing a plurality of through holes over the entire area of ​​electrode foil 120. As a result, in both Examples 1 and 2, the temperature difference Δ with respect to the set temperature of 450° C. could be suppressed to less than 5° C. (3.2° C. in Example 1, and 3.3° C. in Example 2).

[0039] In Example 1, a plurality of through holes are distributed over the entire area of ​​electrode foil 120 so that the aperture ratio is 5% or more. Therefore, the resistance value of electrode foil 120 can be made 1 Ω or more (2.27 Ω). This makes it possible to keep the current consumption of ceramic heater 100 low. Furthermore, in Example 2, by changing the thickness of the molybdenum foil that becomes electrode foil 120 from 0.1 mm to 0.05 mm, the resistance value of electrode foil 120 can be increased to 4.55 Ω. This makes it possible to further keep the current consumption of ceramic heater 100 low.

[0040] In Example 3, through holes with a larger diameter than those in Examples 1 and 2 are formed so that the hole ratio of electrode foil 120 is increased to approximately 10.1%. Even in such a case, by distributing a plurality of through holes in electrode foil 120, the resistance value of electrode foil 120 can be made 1 Ω or more (2.46 Ω). This makes it possible to keep the current consumption of ceramic heater 100 low. Furthermore, by distributing a plurality of through holes in electrode foil 120, it is possible to reduce the variation in the resistance value of electrode foil 120 after cutting. As a result, in Example 3, the temperature difference Δ with respect to the set temperature of 450° C. can be kept below 5° C. (4.8° C.).

[0041] In Example 4 as well, by distributing a plurality of through holes in the electrode foil 120, the resistance value of the electrode foil 120 could be made 1 Ω or more (1.99 Ω). This made it possible to keep the current consumption of the ceramic heater 100 low. The electrode foil 120 of Example 4 does not have the through holes evenly distributed over the entire surface of the electrode foil 120, but the distribution of the through holes is adjusted to increase or decrease locally. This made it possible to prevent the pattern of the electrode foil 120 from causing heat spots and cold spots. As a result, in Example 4, the temperature difference Δ with respect to the set temperature of 450°C could be kept below 5°C (2.8°C).

[0042] In Comparative Example 1, the electrode foil 120 is formed using a molybdenum foil of the same thickness as in Examples 1, 3, and 4, but no through holes are formed in the electrode foil 120. As a result, the resistance value of the electrode foil 120 is 1 Ω or less (0.68 Ω), and the current consumption of the ceramic heater 100 cannot be kept low. In addition, it is believed that the electrode foil 120 peels off because the electrode foil 120 is not directly bonded to the ceramic sintered body. This causes localized heat spots, and the temperature of the upper surface 111 of the ceramic base 110 of the ceramic heater 100 varies greatly. As a result, in Comparative Example 1, the temperature difference Δ with respect to the set temperature of 450°C rises to 5°C or more (12°C).

[0043] In Comparative Example 2, mesh electrode 220 is formed using a molybdenum mesh instead of molybdenum foil. As shown in Fig. 6, when a mesh is used, there are locations where wires come into contact with each other and cross each other, and contact resistance occurs at these contact locations. It is believed that the magnitude of such contact resistance is not necessarily uniform, and therefore the variation in resistance value of mesh electrode 220 is larger than when electrode foil 120 is formed using molybdenum foil. As a result, in Comparative Example 2, the temperature difference Δ with respect to the set temperature of 450°C increased to 5°C or more (5.5°C).

[0044] <Effects of the embodiment> In the above embodiment, the ceramic heater 100 includes a ceramic base 110 and a metal electrode foil 120 embedded in the ceramic base 110. A plurality of through holes are distributed in the electrode foil 120. The aperture ratio of the plurality of through holes distributed in the electrode foil is 2.5% or more. Since the electrode foil is formed using a metal foil instead of a metal mesh, no contact resistance occurs due to contact between wires constituting the mesh. Therefore, it is possible to suppress the variation in the resistance value of the electrode foil 120, and to reduce the variation in the temperature distribution of the ceramic heater 100. In addition, since a plurality of through holes are distributed in the electrode foil 120 so that the aperture ratio is 2.5% or more, the resistance value of the electrode foil 120 can be made high (for example, 1 Ω or more). This makes it possible to suppress the current consumption of the power supply used in the ceramic heater 100, and to prevent the power supply from becoming large.

[0045] In addition, since a plurality of through holes are dispersed in electrode foil 120 embedded inside ceramic base 110, regions of ceramic base 110 positioned above and below electrode foil 120 are in contact with each other via the through holes. This provides strong bonding between electrode foil 120 and ceramic base 110, thereby preventing electrode foil 120 from peeling off from ceramic base 110.

[0046] In the above embodiment, tungsten (W) foil, molybdenum (Mo) foil, and alloy foil containing molybdenum and / or tungsten are used as the electrode foil 120. All of these have high melting points, making them suitable as electrode materials for heaters. However, since these metal foils (alloy foils) have relatively low volume resistivities, it was necessary to increase the resistance value of the electrode foil by adopting a thin and long pattern or the like in order to use them as the electrode foil 120. However, in this case, the risk of breakage of the electrode foil increases. In this embodiment, the resistance value of the electrode foil is increased by dispersing through holes in the electrode foil 120, so that the risk of breakage of the electrode foil associated with the adoption of such a thin and long pattern can be avoided.

[0047] <Modification form> The above-described embodiment is merely an example and may be modified as appropriate. For example, the shape, size, and thickness of the electrode foil 120 are not limited to those of the above-described embodiment and may be modified as appropriate. In addition, in the above-described embodiment, molybdenum foil, tungsten foil, and foil of an alloy containing molybdenum and / or tungsten are used as the electrode foil, but the present invention is not limited to such an embodiment. For example, foil of a metal other than molybdenum or tungsten, or foil of an alloy may be used.

[0048] In the above embodiment and Examples 1 to 4, the electrode foil 120 having an aperture ratio of 5% or more has been described as an example, but the present invention is not limited to such an embodiment. For example, a through hole having a diameter of 1 mm may be formed at each vertex of the electrode foil 120 when equilateral triangles with a side length of 6 mm are laid out. In this case, the aperture ratio of the electrode foil 120 is about 2.52%. In the above embodiment and Examples 1 to 4, the electrode foil 120 having an aperture ratio of 10.1% or less has been described as an example, but the present invention is not limited to such an embodiment, and the aperture ratio can be further increased. For example, a through hole having a diameter of 0.05 mm may be formed at each vertex of the electrode foil 120 when equilateral triangles with a side length of 0.1 mm are laid out. In this case, the aperture ratio of the electrode foil 120 is about 22.26%. Alternatively, a through hole having a diameter of 3 mm may be formed at each vertex of the electrode foil 120 when equilateral triangles with a side length of 5 mm are laid out. In this case, the aperture ratio of electrode foil 120 is about 32.63%. These cases are preferable because the resistance value of electrode foil 120 can be further increased.

[0049] In the above description, the through holes are formed at positions corresponding to the vertices of equilateral triangles evenly arranged so that the through holes are arranged at equal intervals. However, the present invention is not limited to such an embodiment, and a plurality of through holes can be distributed at any position. For example, as shown in FIG. 8, a plurality of through holes can be randomly arranged. In addition, in the above Examples 1 to 4, an embodiment in which through holes of the same shape with a diameter of 0.5 mm to 3.0 mm are distributed is given as an example, but the present invention is not limited to such an embodiment. The through holes arranged in a distributed manner are not limited to having the same shape, and may have an average diameter within a range of 0.05 mm to 3.0 mm. Here, the diameter refers to the longest diameter of the opening of the through hole (for example, the length of the diagonal in the case of a square).

[0050] Although the present invention has been described above using the embodiment and its modified form, the technical scope of the present invention is not limited to the above description. It is obvious to those skilled in the art that various modifications or improvements can be made to the above embodiment. It is also clear from the claims that such modifications or improvements can be included in the technical scope of the present invention.

[0051] The order of execution of each process in the manufacturing method shown in the specification and drawings is not particularly specified, and may be any order unless the output of a previous process is used in a subsequent process. For convenience, even if the description uses "first," "next," etc., it does not mean that the process must be performed in that order. [Explanation of symbols]

[0052] 100 Ceramic heater 110 Ceramic substrate 120 Electrode foil 130 Shaft 140 Feed line

Claims

1. A ceramic base material on which an object to be heated is placed on an upper surface; A band-shaped metal electrode foil is embedded in the ceramic base material, The electrode foil has a plurality of through holes arranged to be distributed throughout the electrode foil, The thickness of the electrode foil is 0.05 mm to 0.1 mm, The average diameter of the through holes is 1.0 mm to 3.0 mm; an aperture ratio, which is a ratio of a sum of an aperture area of ​​the plurality of through holes to an area of ​​the upper surface of the electrode foil when the plurality of through holes are not formed, of 5.7% or more and 10.1% or less; a ceramic heater, wherein the average diameter of the openings of the plurality of through holes is 2% to 20% of the width of the band-shaped electrode foil;

2. A ceramic heater as described in claim 1, wherein the electrode foil is a foil of at least one metal selected from the group consisting of molybdenum, tungsten, molybdenum alloys, and tungsten alloys.

3. A ceramic heater as described in claim 1 or 2, wherein the width of the band-shaped electrode foil is 5 mm to 15 mm.

4. A method of manufacturing a ceramic material by laminating a ceramic material on the upper and lower sides of a strip-shaped metal electrode foil having a plurality of through holes arranged so as to be dispersed on a surface of the electrode foil such that the ceramic material is embedded in the electrode foil; and firing the laminated ceramic material and the electrode foil. The thickness of the electrode foil is 0.05 mm to 0.1 mm, The average diameter of the through holes is 1.0 mm to 3.0 mm; an aperture ratio, which is a ratio of the sum of the aperture areas of the plurality of through holes to the area of ​​the surface of the electrode foil when the plurality of through holes are not formed, of 5.7% or more and 10.1% or less; a plurality of through holes each having an average opening diameter that is 2% to 20% of a width of the strip-shaped electrode foil;

5. A method for manufacturing a ceramic heater as described in claim 4, wherein the electrode foil contains at least one metal selected from the group consisting of molybdenum, tungsten, molybdenum alloys, and tungsten alloys.

6. A method for manufacturing a ceramic heater as described in claim 4 or 5, wherein the width of the band-shaped electrode foil is 5 mm to 15 mm.

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