Ceramic heater

Abstract

A ceramic heater is provided that can achieve both a reduction in power consumption through high resistance and temperature uniformity within the plane of the ceramic plate. The ceramic heater comprises a ceramic plate including a central portion within a radius of 60 mm from the center of the ceramic plate, an intermediate portion with a radius of 80 to 120 mm from the center, and an outer portion with a radius of 130 mm or more from the center, and a resistance heating element embedded in the central portion, intermediate portion, and outer portion within the ceramic plate. The resistance heating element is configured such that the volume resistivity of the resistance heating element gradually increases as it moves away from the center of the ceramic plate. When the volume resistivity of the resistance heating element at the outer edge of the central portion is set to 100%, the ratio of the volume resistivity of the resistance heating element at the intermediate portion is within the range of 102 to 120%, and the ratio of the volume resistivity of the resistance heating element at the outer portion is within the range of 108 to 139%.

Description

Technology Field

[0001] The present disclosure relates to a ceramic heater. Background Technology

[0002] In film deposition equipment for semiconductor manufacturing processes, ceramic heaters are used as support stages to uniformly control the temperature of wafers. As such ceramic heaters, those equipped with a ceramic plate on which a wafer is loaded and a cylindrical ceramic shaft installed on the ceramic plate are widely used. Additionally, multi-zone ceramic heaters having multiple heating zones are also known.

[0003] Patent Document 1 (Japanese Patent Publication No. Hei 11-339939) discloses a ceramic heater having a ceramic body with a resistance heating element embedded therein having a heating pattern that is approximately concentric or approximately spiral, and a ceramic tubular support bonded to the lower surface of the ceramic body. In this ceramic heater, when the area of ​​the region located inside the tubular support in the heating pattern is S1 and the resistance value of the resistance heating element in the region located inside the tubular support is R1, and the area of ​​the region located outside the tubular support in the heating pattern is S2 and the resistance value of the resistance heating element in the region located outside the tubular support is R2, the ratio of R1 / S1 is greater than the ratio of R2 / S2 in the range of 3 to 60%.

[0004] Patent Document 2 (Japanese Patent Publication No. Hei 8-274147) discloses a wafer holding support device in which first to nth heating resistors (n≥2) that are sequentially energized are embedded in a ceramic body forming a wafer holding support surface, and the ratio of the resistance value of the m-1st heating resistor to the m-th heating resistor (m=2 to n) is 1.5 to 4.

[0005] Patent Document 3 (Japanese Patent Publication No. 2019-194939) discloses a ceramic heater comprising a disc-shaped ceramic substrate, an electrode for electrostatic adsorption or an electrode for high-frequency generation embedded in the ceramic substrate, a first heating resistor embedded in the ceramic substrate below the electrode, and a second heating resistor embedded in the ceramic substrate below the first heating resistor. The first heating resistor has a planar first resistance part provided in the inner region of a virtual circle defined by the outermost contour line of the electrode, a linear or strip-shaped second resistance part provided within the inner region and extending along the circumferential direction of the ceramic substrate, extending outward in the diameter direction of the ceramic substrate from the first resistance part, and a connecting part connecting the first resistance part and the second resistance part. Additionally, the second heating resistor is disposed inward from the virtual circle defined by the innermost contour line of the second resistance part.

[0006] Patent document 4 (WO2020 / 153218) discloses a ceramic heater having a ceramic plate having a circular inner circumferential zone and an annular outer circumferential zone, an inner circumferential resistance heating element made of a high melting point metal provided in the inner circumferential zone, and an outer circumferential resistance heating element made of at least a metal carbide on the surface provided in the outer circumferential zone. Prior art literature

[0007] Japanese Patent Publication No. Hei 11-339939 Japanese Patent Publication No. Hei 8-274147 Japanese Patent Publication No. 2019-194939 WO2020 / 153218

[0008] Miniaturization and high stacking for semiconductor high integration are progressing at an accelerated pace, accompanied by increased temperatures and longer process times in semiconductor manufacturing processes. Consequently, the power consumption of manufacturing equipment is on the rise. Meanwhile, as compliance with the SDGs (Sustainable Development Goals) becomes inevitable, there is a demand for higher power voltages to enable the reduction of power loss throughout the entire semiconductor manufacturing plant. This is because higher power voltages allow for a reduction in current, thereby mitigating power loss. Furthermore, along with this increase in power voltage, each component constituting the manufacturing equipment is also required to handle high voltages. Additionally, the demand for temperature uniformity (resistance) in ceramic heaters is becoming increasingly stringent. Therefore, achieving both high-voltage capability and temperature uniformity in ceramic heaters is a critical challenge.

[0009] In fact, the high voltage of power supplies in semiconductor manufacturing plants has been 208V until now, but it is expected to exceed 440V in the future. As a countermeasure against this increase in voltage, a method is being considered to reduce the current flowing through the ceramic heater by increasing the resistance value of the resistance heating element embedded in the ceramic heater. This is because, when considering the entire semiconductor manufacturing plant, if the total current value can be reduced, power loss can also be reduced accordingly. In conventional ceramic heaters, resistance has been increased by thinning the wires or expanding the winding diameter for 3D coil-type resistance heating elements; by thinning the wires or expanding the amplitude for 2D resistance heating elements such as linear zigzag structures; and by thinning the film or reducing the printing width for printed pattern-type resistance heating elements. However, while the conventional method of increasing resistance values ​​can achieve high resistance, temperature uniformity of the ceramic heater has not been achieved due to deformation or degradation of the resistance heating element.

[0010] The inventors have discovered that, in a ceramic heater having a resistance heating element embedded in a central part, an intermediate part, and an outer periphery defined radially from the center of a ceramic plate, the volume resistivity of the resistance heating element is gradually increased as it moves away from the center of the ceramic plate, and furthermore, by adjusting the ratio of the volume resistivity of the resistance heating element in the intermediate part and the outer periphery to the volume resistivity of the resistance heating element in the outer edge of the central part to each within a predetermined range, it is possible to achieve both a reduction in power consumption due to increased resistance and temperature uniformity within the surface of the ceramic plate.

[0011] Accordingly, the objective of the present invention is to provide a ceramic heater capable of achieving both reduced power consumption through high resistance and in-plane temperature uniformity of the ceramic plate.

[0012] According to the present disclosure, the following embodiments are provided.

[0013] [Mode 1]

[0014] A ceramic plate having a first surface for loading a wafer and a second surface facing the first surface, wherein, when the ceramic plate is viewed in a planar view, the ceramic plate comprises a central portion defined as a circular area within a radius of 60 mm from the center of the ceramic plate, an intermediate portion defined as an annular area with a radius of 80 to 120 mm from the center, and an outer periphery portion defined as an annular area with a radius of 130 mm or more from the center.

[0015] Resistance heating elements embedded in the central part, the middle part, and the outer periphery within the ceramic plate

[0016] It is a ceramic heater equipped with,

[0017] The above resistance heating element is configured such that the volume resistivity of the resistance heating element gradually increases as it moves away from the center of the ceramic plate, and

[0018] A ceramic heater in which, when the volume resistivity of the resistance heating element at the outer edge of the central portion is set to 100%, the ratio of the volume resistivity of the resistance heating element at the middle portion is within the range of 102 to 120%, and the ratio of the volume resistivity of the resistance heating element at the outer periphery is within the range of 108 to 139%.

[0019] [Mode 2]

[0020] A ceramic heater described in Embodiment 1, wherein the resistance heating element is in at least one form selected from the group consisting of a coil, a linear zigzag structure, a printed pattern, a foil, and a mesh.

[0021] [Mode 3]

[0022] Each of the resistance heating element embedded in the central part, the resistance heating element embedded in the middle part, and the resistance heating element embedded in the outer periphery is arranged in a form that is continuously connected without interruption when viewed in a planar view, and also,

[0023] A ceramic heater described in embodiment 1 or 2, wherein the resistance heating element embedded in the central portion, the resistance heating element embedded in the middle portion, and the resistance heating element embedded in the outer periphery portion are composed of the same material.

[0024] [Mode 4]

[0025] The ceramic heater comprises at least two resistance heating elements,

[0026] One side of the resistance heating element embedded in the central part, the middle part, and the outer periphery forms an outer zone control heater circuit as a continuous single resistance heating element.

[0027] A ceramic heater described in Embodiment 3, wherein the other side of the resistance heating element, which is buried at a depth different from that of the outer zone control heater circuit of the central part, the middle part, and the outer periphery part, is a continuous single resistance heating element and forms an inner zone control heater circuit independent from the outer zone control heater circuit.

[0028] [Mode 5]

[0029] The ceramic heater comprises at least two resistance heating elements,

[0030] The resistance heating element embedded in the outer periphery or the outer periphery and the intermediate part forms an outer zone control heater circuit as a single continuous resistance heating element,

[0031] A ceramic heater described in Embodiment 3, wherein the resistance heating element embedded in the central part or the central part and the intermediate part is a continuous single resistance heating element and forms an inner zone control heater circuit independent from the outer zone control heater circuit.

[0032] [Mode 6]

[0033] A ceramic heater described in any one of embodiments 1 to 5, wherein the ceramic plate comprises aluminum nitride or aluminum oxide.

[0034] [Mode 7]

[0035] The ceramic plate comprises aluminum nitride, and furthermore, the ceramic plate has an upper ceramic plate providing the first surface and a lower ceramic plate providing the second surface, and the aluminum nitride constituting the upper ceramic plate has 1.0 × 10⁻⁶ at 550°C 8 A ceramic heater described in Embodiment 6 having a volume resistivity exceeding Ω·cm.

[0036] [Mode 8]

[0037] A ceramic heater described in any one of embodiments 1 to 7, further comprising an internal electrode, which is an RF electrode and / or an ESC electrode, within the ceramic plate.

[0038] [Mode 9]

[0039] A ceramic heater described in any one of embodiments 1 to 8, further comprising a cylindrical ceramic shaft having an internal space and installed concentrically on the second surface of the ceramic plate. Brief explanation of the drawing

[0040] FIG. 1 is a top view schematically illustrating an example of a ceramic heater according to the present invention. FIG. 2 is a perspective cross-sectional view schematically illustrating the cross-sectional structure of the ceramic heater shown in FIG. 1. FIG. 3 is a top view schematically illustrating another example of a ceramic heater according to the present invention. FIG. 4 is a schematic perspective cross-sectional view of the cross-sectional structure of the ceramic heater shown in FIG. 3. Additionally, for the sake of explanation, in order to make it easier to understand the respective configurations of the inner zone control heater circuit (14a) and the jumper (22) which are originally located at the same height, the jumper (22) is shown at a position slightly lower than its original position. FIG. 5 is a schematic diagram conceptually illustrating the pattern and heating density of the inner zone control heater circuits adopted in Examples 1 to 5. In this figure, the thickness of the line indicates the heating density. FIG. 6 is a schematic diagram conceptually illustrating the pattern and heating density of the outer zone control heater circuits adopted in Examples 1 to 5. In this figure, the thickness of the line indicates the heating density. Figure 7 is a graph showing the distribution of volume resistivity ratios with respect to the radial positions of heating resistors measured in Examples 1 to 5. Specific details for implementing the invention

[0041] The ceramic heater according to the present invention is a ceramic die for supporting a wafer within a semiconductor manufacturing apparatus. Typically, the ceramic heater according to the present invention may be a ceramic heater for a semiconductor film deposition apparatus. Typical examples of a film deposition apparatus include a CVD (Chemical Vapor Deposition) apparatus (e.g., a thermal CVD apparatus, a plasma CVD apparatus, a photoCVD apparatus, and an MOCVD apparatus) and a PVD (Physical Vapor Deposition) apparatus.

[0042] FIGS. 1 and 2 illustrate an example of a two-zone ceramic heater as an embodiment of a ceramic heater. The ceramic heater (10) illustrated in FIGS. 1 and 2 comprises a ceramic plate (12) and a resistance heating element (14). The ceramic plate (12) is disc-shaped and has a first surface (12a) for loading a wafer (W) and a second surface (12b) facing the first surface (12a). When the ceramic plate (12) is viewed in a planar view, the ceramic plate (12) includes a central portion (12c), an intermediate portion (12d), and an outer portion (12e). The central portion (12c) is defined as a circular area within a radius of 60 mm from the center of the ceramic plate (12). The intermediate portion (12d) is defined as an annular area with a radius of 80 to 120 mm from the center of the ceramic plate (12). The outer periphery (12e) is defined as an annular region with a radius of 130 mm or more from the center of the ceramic plate (12). The resistance heating element (14) is embedded in the central part (12c), the middle part (12d), and the outer periphery (12e) within the ceramic plate (12). The resistance heating element (14) is configured such that the volume resistivity of the resistance heating element (14) gradually increases as it moves away from the center of the ceramic plate (12). When the volume resistivity of the resistance heating element (14) at the outer edge of the central part (12c) is set to 100%, the ratio of the volume resistivity of the resistance heating element (14) at the middle part (12d) is within the range of 102 to 120%, and the ratio of the volume resistivity of the resistance heating element (14) at the outer periphery (12e) is within the range of 108 to 139%.In this way, in a ceramic heater (10) having a resistance heating element (14) embedded in a central part (12c), an intermediate part (12d), and an outer part (12e) defined radially from the center of a ceramic plate (12), the volume resistivity of the resistance heating element (14) is gradually increased as it moves away from the center of the ceramic plate (12), and by adjusting the ratio of the volume resistivity of the resistance heating element (14) in the intermediate part (12d) and the outer part (12e) to the volume resistivity of the resistance heating element (14) in the outer edge of the central part (12c) to each within a predetermined range, it is possible to achieve both a reduction in power consumption due to high resistance and temperature uniformity within the surface of the ceramic plate (12).

[0043] As mentioned above, achieving both high voltage handling and temperature uniformity in ceramic heaters is a critical challenge. For example, the high voltage of power supplies in semiconductor manufacturing plants has been 208V until now, but it is expected to exceed 440V in the future. As a countermeasure against this increase in voltage, a method is considered to reduce the current flowing through the ceramic heater by increasing the resistance value of the resistance heating element embedded in the ceramic heater. In conventional ceramic heaters, the resistance of the resistance heating element has been increased by finer wires or increased winding diameter in 3D coil-type resistance heating elements; by finer wires or increased amplitude in 2D resistance heating elements such as linear zigzag structures; and by thinning the film or reducing the printing width in printed pattern-type resistance heating elements. However, in the case of 3D coil-type resistance heating elements, while finer wires or increased winding diameter double the resistance value, the difficulty of achieving temperature uniformity increases because the coil shape or pattern becomes prone to deformation during manufacturing. In the case of two-dimensional resistance heating elements such as linear zigzag structures, the resistance value is doubled when the lines are thinned or the amplitude is increased, but as mentioned above, the temperature uniformity deteriorates due to deformation during manufacturing. In the case of printed pattern type resistance heating elements, the resistance value is doubled when the printing width is reduced or the thinning is thinned, but in addition to the resistance heating element becoming prone to deterioration during manufacturing, the difficulty of achieving temperature uniformity increases as mentioned above. Thus, although high resistance can be achieved with conventional methods of increasing resistance values, temperature uniformity of the ceramic heater is not obtained due to deformation or deterioration of the resistance heating element.

[0044] Accordingly, by re-examining the firing method when manufacturing the ceramic plate (12) and significantly changing the series of firing processes from the rising temperature through the highest temperature to the falling temperature, it was successful to suppress deformation of the resistance heating element (14) and increase the volume resistivity of the entire resistance heating element (14) to a desirable profile. Temperature uniformity was also improved through these attempts. As a result, it became possible to make the volume resistivity of the resistance heating element (14) relatively large so that it gradually increases as it moves away from the center of the ceramic plate (12) (i.e., as it approaches the outer periphery). Consequently, the resistance value of the resistance heating element (14) could be significantly higher than before, and the resistance value of the resistance heating element (14) placed in the area close to the outer periphery became relatively higher than the resistance value of the resistance heating element (14) placed in the area close to the center of the ceramic plate (12). As a result, a reduction in the current value, which tends to flow heavily in the area close to the outer periphery of the ceramic plate (12) due to device configuration and process conditions, was also achieved. In this way, it was possible to improve both the reduction of the current value due to increased resistance (which leads to a reduction in power consumption) and the temperature uniformity within the surface of the ceramic plate (12). Furthermore, it can be said that increasing the volume resistivity of the entire resistance heating element (14) is more effective in reducing the current value. However, if this is to be realized, there is a problem that the firing time is doubled and the power consumption during firing is also doubled, which is counterproductive. In addition, the deformation of the resistance heating element may increase along with the doubling of the firing time. Therefore, it was concluded that the method of increasing the volume resistivity of the resistance heating element (14) placed in the area close to the outer periphery is optimal for achieving both power consumption reduction and temperature uniformity, and thus the present invention was completed.

[0045] In the ceramic plate (12), the main part (i.e., the ceramic body) other than the embedded member such as the resistance heating element (14) preferably comprises aluminum nitride or aluminum oxide, and more preferably aluminum nitride, in terms of excellent thermal conductivity, high electrical insulation, and thermal expansion characteristics similar to silicon. In a preferred embodiment, the ceramic plate (12) comprises aluminum nitride, and the ceramic plate (12) also has an upper ceramic plate that provides a first surface (12a) and a lower ceramic plate that provides a second surface (12b). In this embodiment, the aluminum nitride constituting the upper ceramic plate is 1.0 × 10⁻⁶ at 550°C. 8 It is desirable to have a volume resistivity exceeding Ω·cm, and more preferably 1.0×10⁻⁶ 9 Up to 1.0×10 11 It is Ω·cm.

[0046] The ceramic plate (12) is disc-shaped. However, the shape of the disc-shaped ceramic plate (12) as seen in a flat plane does not need to be a perfect circle, and may be an incomplete circle with a portion cut out, such as an orientation flat. The diameter of the ceramic plate (12) is typically 320 to 380 mm for a 300 mm silicon wafer, for example, about 340 mm. In addition, the thickness of the ceramic plate (12) is typically 10 to 25 mm, for example, about 20 mm.

[0047] A resistance heating element (14) is embedded in the central part (12c), the middle part (12d), and the outer part (12e) within the ceramic plate (12). As described above, the central part (12c) is defined as a circular area within a radius of 60 mm from the center of the ceramic plate (12). The middle part (12d) is defined as an annular area with a radius of 80 to 120 mm from the center of the ceramic plate (12). The outer part (12e) is defined as an annular area with a radius of 130 mm or more from the center of the ceramic plate (12). Accordingly, an annular area with a width of 20 mm exists between the central part (12c) and the middle part (12d), while an annular area with a width of 10 mm exists between the middle part (12d) and the outer part (12e). An annular region that does not belong to any of these central part (12c), middle part (12d) and outer periphery part (12e) merely means that it is not considered when calculating the ratio of the volume resistivity of the resistance heating element (14), and the resistance heating element (14) may also exist in said annular region. That is, the resistance heating element (14) may be continuously embedded across the central part (12c), middle part (12d), and outer periphery part (12e) within the ceramic plate (12) (including the annular region between them), as shown in FIGS. 1 and 2. Alternatively, as illustrated in FIGS. 3 and 4, the resistance heating element (14) may be a combination of a resistance heating element (14) (inner zone control heater circuit (14a)) that is continuously embedded across the central part (12c) and the middle part (12d) within the ceramic plate (12) (including the annular region between them) and another resistance heating element (14) (outer zone control heater circuit (14b)) that is embedded in the outer part (12e) within the ceramic plate (12).

[0048] The resistance heating element (14) is configured such that the volume resistivity of the resistance heating element (14) gradually increases as it moves away from the center of the ceramic plate (12). Specifically, when the volume resistivity of the resistance heating element (14) at the outer edge of the central part (12c) is set to 100%, the ratio of the volume resistivity of the resistance heating element (14) at the middle part (12d) is within the range of 102 to 120%, preferably 103 to 118%, and more preferably 105 to 115%. In addition, the ratio of the volume resistivity of the resistance heating element (14) at the outer edge (12e) is within the range of 108 to 139%, preferably 112 to 135%, and more preferably 116 to 130%. Within these ranges, the reduction in power consumption due to high resistance and the uniformity of the temperature within the surface of the ceramic plate (12) can be achieved more effectively.

[0049] The resistance heating element (14) is preferably at least one type selected from the group consisting of a coil, a linear zigzag structure, a printed pattern, a foil, and a mesh.

[0050] It is preferable that each of the resistance heating element (14) embedded in the central part (12c), the resistance heating element (14) embedded in the middle part (12d), and the resistance heating element (14) embedded in the outer part (12e) be arranged in a continuous, uninterrupted manner when viewed in a planar view. The continuous, uninterrupted manner can be various known forms, such as a spiral shape. The resistance heating element (14) embedded in the central part (12c), the resistance heating element (14) embedded in the middle part (12d), and / or the resistance heating element (14) embedded in the outer part (12e) may be continuous with each other or separated. Accordingly, the resistance heating element (14) may be a single-zone heater circuit arranged continuously across the central part (12c), the middle part (12d), and the outer part (12e), or a multi-zone heater circuit divided into two or more zones. For example, as shown in FIGS. 1 and 2, they may be arranged continuously in a continuous, uninterrupted manner across the central part (12c), the middle part (12d), and the outer part (12e), or as shown in FIGS. 3 and 4, they may be arranged in a continuous, uninterrupted manner in the inner zone Z1 to form an inner zone control heater circuit (14a), and arranged in a continuous, uninterrupted manner in the outer zone Z2 to form an outer zone control heater circuit (14b). In any case, in the ceramic heater (10), it is preferable that the resistance heating element (14) embedded in the central part (12c), the resistance heating element (14) embedded in the middle part (12d), and the resistance heating element (14) embedded in the outer part (12e) are made of the same material. This is because, by re-examining the firing method when manufacturing the ceramic plate (12), the resistance and volume resistivity of the resistance heating element (14), which is composed of the same material, can be preferably controlled.In that sense, since the volume resistivity of the same material changes depending on the location, such as the central part (12c), middle part (12d), and outer part (12e), even if the material undergoes firing (e.g., depending on the degree of carbonization), the term “same material” in this specification means that the original material before firing is the same, without considering the alteration (e.g., carbonization) or change in volume resistivity caused by firing (it may also be referred to as “essentially the same material”).

[0051] As described above, the ceramic plate (12) may include an inner zone Z1 and an outer zone Z2 when viewed in a planar view. The inner zone Z1 is defined as a circular area within a predetermined distance from the center of the ceramic plate (12) and typically includes part or all of the central portion (12c) and, if desired, the middle portion (12d). The outer zone Z2 is defined as an annular area outside the inner zone Z1 and typically includes part or all of the outer periphery (12e) and, if desired, the middle portion (12d). Accordingly, the inner zone Z1 and the central portion (12c) (or the combined area of ​​the central portion (12c) and the middle portion (12d)) do not necessarily coincide, and the outer zone Z2 does not necessarily coincide with the outer periphery (12e) (or the combined area of ​​the outer periphery (12e) and the middle portion (12d). The outer zone Z2 may be composed of a plurality of outer sub-zones partitioned in an arc shape. The outer zone Z2 may have two or more non-overlapping annular regions of different sizes concentrically. 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 exist outside the second outer zone.

[0052] In a preferred embodiment of the present invention, as illustrated in FIGS. 1 and 2, the ceramic heater (10) may comprise at least two resistance heating elements (14) in an overlapping area. In this embodiment, it is preferable that one of the resistance heating elements (14) embedded in the central part (12c), the middle part (12d), and the outer periphery part (12e) forms an outer zone control heater circuit (14b) for selectively or preferentially heating the outer zone Z2 as a continuous single resistance heating element, and the other of the resistance heating element (14) embedded at a depth position different from the outer zone control heater circuit (14b) of the central part (12c), the middle part (12d), and the outer periphery part (12e) forms an inner zone control heater circuit (14a) for selectively or preferentially heating the inner zone Z1, which is independent from the outer zone control heater circuit (14b) as a continuous single resistance heating element. In this embodiment, the inner zone control heater circuit (14a) and the outer zone control heater circuit (14b) are both arranged at different depths in overlapping areas including a central part (12c), an intermediate part (12d), and an outer periphery part (12e). However, the inner zone control heater circuit (14a) can be configured to selectively heat the inner zone Z1 by arranging it so that the resistance in the inner zone Z1 is high and the resistance in the outer zone Z2 is low (for example, by changing the coil pitch in the case of a coil). Similarly, the outer zone control heater circuit (14b) can be configured to selectively heat the outer zone Z2 by arranging it so that the resistance in the inner zone Z1 is low and the resistance in the outer zone Z2 is high (for example, by changing the coil pitch in the case of a coil).

[0053] In another preferred embodiment of the present invention, as illustrated in FIGS. 3 and 4, the ceramic heater (10) may comprise at least two resistance heating elements (14) in different regions. In this embodiment, it is preferable that a resistance heating element (14) embedded in an outer zone Z2 (typically an outer periphery (12e) or an outer periphery (12e) and a middle section (12d)) forms an outer zone control heater circuit (14b) for selectively or preferentially heating the outer zone Z2 as a single continuous resistance heating element (14), and a resistance heating element embedded in an inner zone Z1 (typically a central section (12c) or a central section (12c) and a middle section (12d)) forms an inner zone control heater circuit (14a) for selectively or preferentially heating the inner zone Z1 as a single continuous resistance heating element (14) independent of the outer zone control heater circuit (14b).

[0054] In any embodiment of FIGS. 1 to 4, the inner zone control heater circuit (14a) is embedded in the inner zone Z1 (and, if present, the outer zone Z2) of the ceramic plate (12) parallel to the first surface (12a). A pair of first power supply terminals (18) for supplying power to the inner zone control heater circuit (14a) is provided in the central part of the inner zone Z1 of the ceramic plate (12). Preferably, the first power supply terminals (18) are each connected to both ends of the inner zone control heater circuit (14a). Two or more first power supply terminals (18) may exist. The first power supply terminals (18) are rod-shaped, and the inner zone control heater circuit (14a) is connected to a heater power source (not shown) via the first power supply terminals (18) on the rod.

[0055] In any embodiment of FIGS. 1 to 4, the outer zone control heater circuit (14b) is embedded in the outer zone Z2 (and, if present, the inner zone Z1) of the ceramic plate (12) parallel to the first surface (12a). In the central part of the inner zone Z1 of the ceramic plate (12) (at a location different from the first power supply terminal (18)), a pair of second power supply terminals (20) for supplying power to the outer zone control heater circuit (14b) is provided. The pair of second power supply terminals (20) may be directly connected to the outer zone control heater circuit (14b) as shown in FIG. 2, or may be electrically connected to the outer zone control heater circuit (14b) through a pair of jumpers (22) as shown in FIG. 4. There may be two or more pairs of second power supply terminals (20). The second power supply terminal (20) is on the load, and the outer zone control heater circuit (14b) is connected to the heater power supply (not shown) via the second power supply terminal (20) on the load (via a jumper (22) as needed).

[0056] The ceramic plate (12) may further be provided with an RF electrode (30) and / or an ESC electrode as internal electrodes. In this case, it is preferable that the RF electrode (30) and / or the ESC electrode be embedded at a depth closer to the first surface (12a) than the resistive heating element (14) and (if present, the jumper (22)) of the ceramic plate (12). The RF electrode enables film formation by a plasma CVD process by applying a high frequency. The ESC electrode is an abbreviation for electrostatic chuck (ESC) electrode and is also referred to as an electrostatic electrode. When voltage is applied by an external power source, the ESC electrode chucks the wafer loaded on the surface of the ceramic plate (12) by the Johnson-Rabek force. The ESC electrode is preferably a circular thin-layer electrode with a diameter slightly smaller than that of the ceramic plate (12), and may be, for example, a mesh-shaped electrode formed by weaving thin metal wires into a mesh. The ESC electrode may be used as a plasma electrode. That is, by applying a high frequency to the ESC electrode, the ESC electrode can also be used as an RF electrode, and a film can be formed by a plasma CVD process. An RF terminal (32) or an ESC terminal for power supply is connected to the RF electrode (30) or the ESC electrode. The RF terminal (32) or the ESC terminal is on a load, and the RF electrode (30) or the ESC electrode is connected to an external power source (not shown) via the RF terminal (32) or the ESC terminal on the load.

[0057] Depending on the preference, the ceramic shaft (28) may be installed concentrically on the second surface (12b) of the ceramic plate (12). The ceramic shaft (28) is a cylindrical member having an internal space S and may have a configuration similar to that of a ceramic shaft employed in a known ceramic susceptor or ceramic heater. The internal space S is configured so that terminal rods such as a first power supply terminal (18), a second power supply terminal (20), and an RF terminal (32) pass through it. It is preferable that the ceramic shaft (28) be composed of a ceramic material similar to that of the ceramic plate (12). Accordingly, it is preferable that the ceramic shaft (28) include aluminum nitride or aluminum oxide, and more preferably, aluminum nitride. It is preferable that the upper surface of the ceramic shaft (28) be bonded to the second surface (12b) of the ceramic plate (12) by solid bonding or diffusion bonding. The outer diameter of the ceramic shaft (28) is preferably 40 to 60 mm, for example, about 55 mm. The inner diameter of the ceramic shaft (28) (diameter of the internal space S) is preferably 33 to 55 mm, for example, about 50 mm.

[0058] The ceramic plate (12) may be provided with a thermocouple insertion hole (34). The thermocouple insertion hole (34) may be a vertical hole formed from the second surface (12b) toward the first surface (12a). By inserting a thermocouple (36) into this thermocouple insertion hole (34), the temperature of the internal electrode, such as the ceramic plate (12) or the RF electrode (30), can be measured. In this case, it is preferable that the thermocouple insertion hole (34) extends to the internal electrode, such as the RF electrode (30), or to the vicinity thereof.

[0059] A ceramic plate (12) having a unique volume resistivity ratio profile according to the present invention can be preferably manufactured, for example, as follows. First, a first aluminum nitride compact is obtained by press-molding aluminum nitride powder. By placing aluminum nitride powder and an inner zone control heater circuit (14a) on the obtained first aluminum nitride compact and press-molding, a second aluminum nitride compact is obtained in which an inner zone control heater circuit (14a) is embedded inside. By placing aluminum nitride powder and an outer zone control heater circuit (14b) on the obtained second aluminum nitride compact and press-molding, a third aluminum nitride compact is obtained in which an outer zone control heater circuit (14b) is further embedded inside. By placing aluminum nitride powder and an RF electrode (30) on the obtained third aluminum nitride compact and press-molding them, a fourth aluminum nitride compact with an RF electrode (30) further embedded inside is obtained. In this way, as shown in FIG. 2, a press-molded body consisting of an aluminum nitride compact with an inner zone control heater circuit (14a), an outer zone control heater circuit (14b), and an RF electrode (30) embedded therein is obtained. The process up to this point is conventional and can be carried out according to known manufacturing methods. Furthermore, to obtain the ceramic plate (12) of the present invention, it is preferable to fire the obtained press-molded body (laminated body) under a nitrogen atmosphere under the following specific firing conditions.

[0060] · Maximum temperature: 1760 to 1870℃

[0061] · Holding time at maximum temperature: 5 to 13 hours

[0062] · Number of changes in heating rate to maximum temperature: 2 to 7 times

[0063] · Heating rate: Change within the range of 40 to 60℃ / min

[0064] · Firing pressure: 60 to 120 kg / ㎠

[0065] By undergoing such firing, the degree of carbonization of the resistance heating element (14) can be varied according to the radial position, and thereby, the volume resistivity of a desirable profile according to the radial position, such as the central part (12c), the middle part (12d), and the outer part (12e), can be realized.

[0066] Examples

[0067] The present invention will be explained in more detail by the following examples. However, the present invention is not limited to the following examples.

[0068] Examples 1 to 5

[0069] (1) Fabrication of a 2-zone ceramic heater

[0070] Using the components shown below, a two-zone ceramic heater (10) having a structure as shown in FIGS. 1 and FIGS. 2 was manufactured in a known procedure, except for the firing conditions.

[0071] <Components and Specifications>

[0072] · Ceramic plate (12): Disc-shaped aluminum nitride sintered body (diameter: 330 mm, thickness: 20 mm, volume resistivity at 550°C: 1.0 × 10⁻⁶ 10 Ω·cm (measured at 550°C by cutting out a coupon (test specimen)) (inner zone control heater circuit (14a), outer zone control heater circuit (14b), and RF electrode (30) embedded inside)

[0073] · Ceramic shaft (28): Cylindrical aluminum nitride sintered body (height: 170 mm, outer diameter: 45 mm, inner diameter: 36 mm)

[0074] · Inner zone control heater circuit (14a): A coil embedded according to the circuit pattern shown in FIG. 5 at a position where the depth from the first surface (12a) of the inner zone Z1 and outer zone Z2 (area with a diameter of 320 mm) in the ceramic plate (12) is 11.5 mm (material: molybdenum, wire diameter: 500 μm, outer diameter: 3.5 mm, arranged so that the coil pitch becomes shorter (coil becomes denser) as it approaches the center of the ceramic plate (12), as conceptually represented by the thickness of the wire in the circuit pattern of FIG. 5).

[0075] · Outer zone control heater circuit (14b): A coil embedded according to the circuit pattern shown in FIG. 6 at a position where the depth from the first surface (12a) of the inner zone Z1 and outer zone Z2 (area with a diameter of 320 mm) in the ceramic plate (12) is 6.5 mm (material: molybdenum, wire diameter: 500 μm, outer diameter: 3.5 mm, arranged so that the coil pitch becomes shorter (coil becomes denser) as it approaches the outer circumference of the ceramic plate (12), as conceptually represented by the thickness of the wire in the circuit pattern of FIG. 6).

[0076] ·RF electrode (30): A molybdenum electrode layer embedded at a depth of 1.0 mm from the first surface (12a) of the ceramic plate (12).

[0077] · First power supply terminal (18): Two terminal rods made of nickel

[0078] · Second power supply terminal (20): Two nickel terminal rods

[0079] ·RF terminal (32): One terminal rod made of nickel

[0080] The ceramic plate (12) having the aforementioned inner zone control heater circuit (14a), outer zone control heater circuit (14b), and RF electrode (30) embedded inside is manufactured in the following steps. First, a first aluminum nitride compact was obtained by press-molding aluminum nitride powder. By placing the aluminum nitride powder and the inner zone control heater circuit (14a) on the obtained first aluminum nitride compact and press-molding, a second aluminum nitride compact was obtained with the inner zone control heater circuit (14a) with a pattern as shown in FIG. 5 embedded inside. By placing the aluminum nitride powder and the outer zone control heater circuit (14b) on the obtained second aluminum nitride compact and press-molding, a third aluminum nitride compact was obtained with the outer zone control heater circuit (14b) with a pattern as shown in FIG. 6 further embedded inside. By placing aluminum nitride powder and RF electrode (30) on the obtained third aluminum nitride compact and press-molding them, a fourth aluminum nitride compact with an RF electrode (30) further embedded inside was obtained. In this way, as shown in FIG. 2, a press-molded body consisting of an aluminum nitride compact with an inner zone control heater circuit (14a), an outer zone control heater circuit (14b), and an RF electrode (30) embedded therein was obtained. By firing the obtained press-molded body (laminated body) under a nitrogen atmosphere under the firing conditions shown in Table 1, a ceramic plate (12) with an inner zone control heater circuit (14a), an outer zone control heater circuit (14b), and an RF electrode (30) embedded inside was obtained.

[0081] (2) Evaluation

[0082] Various evaluations were performed on the obtained 2-zone ceramic heater.

[0083] Distribution of Volume Resistivity Ratio

[0084] With respect to the resistance heating elements constituting the inner zone control heater circuit (14a) and the outer zone control heater circuit (14b) embedded in the 2-zone ceramic heater, the volume resistivity at various positions in the radial direction from the center of the ceramic plate (12) was measured as follows. The distribution of the volume resistivity ratio was investigated by determining the relative value (%) of the volume resistivity at each position with respect to the volume resistivity at a position 60 mm from the center of the ceramic plate (12) (outer edge of the central part) (set to 100%). The results were as shown in FIG. 7.

[0085] (Measurement of volume resistivity)

[0086] In the same manner as (1) above, a ceramic heater for measuring the volume resistivity of a resistance heating element was manufactured and divided into six equal parts to obtain six test specimens having a fan-shaped planar shape. A terminal with a diameter of 2 mm was installed on the cross-section of each resistance heating element exposed on the cut surface of each test specimen, and the resistance value of each resistance heating element was measured at room temperature using a 4-terminal tester. The length of each resistance heating element on an arc was determined from the radius at each measurement position, and the volume resistivity of each resistance heating element was calculated from the measured resistance value, the length of the resistance heating element, and the cross-sectional area of ​​the resistance heating element (calculated from the wire diameter of 0.5 mm). In the ceramic heater of this example, since the inner zone control heater circuit (14a) and the outer zone control heater circuit (14b) coexist in two layers at the same radial position, two volume resistivity values ​​were obtained at each radial position. In this way, 12 volume resistivity values ​​(= 6 × 2 layers) based on 6 test specimens for each radial position were obtained, and the average value of these values ​​was calculated to be the volume resistivity of the ceramic heater at each radial position.

[0087] <Resistance Value>

[0088] At each evaluation temperature of room temperature and 650°C, the resistance value of the inner zone control heater circuit (14a) and the resistance value of the outer zone control heater circuit (14b) were measured. The resistance value of the inner zone control heater circuit (14a) at room temperature was measured by connecting a 4-terminal tester to a pair of first power supply terminals (18). Likewise, the resistance value of the outer zone control heater circuit (14b) at room temperature was measured by connecting a 4-terminal tester to a pair of second power supply terminals (20). The resistance value of the inner zone control heater circuit (14a) at 650°C was obtained by calculating from the current and voltage values ​​applied to the inner zone control heater circuit (14a). Likewise, the resistance value of the outer zone control heater circuit (14b) at 650°C was obtained by calculating from the current and voltage values ​​applied to the outer zone control heater circuit (14b). The results were as shown in Table 1.

[0089] <Cracking>

[0090] A 2-zone ceramic heater (10) was installed inside the chamber of the film-forming device. The chamber was evacuated to introduce N2 gas, and the N2 gas pressure inside the chamber was set to 5 Torr. By supplying power to the inner zone control heater circuit (14a) and the outer zone control heater circuit (14b) through the first power supply terminal (18) and the second power supply terminal (20), the 2-zone ceramic heater (10) was heated to a set temperature of 650°C. 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 highest and lowest temperatures within the surface (i.e., the maximum temperature difference within the surface) was determined as an indicator of cracking potential, and the following criteria:

[0091] - Assessment A: Maximum temperature difference within the plane is less than 5.0℃

[0092] - Assessment B: Maximum temperature difference within the plane is 5.0℃ or higher and less than 7.0℃

[0093] - Evaluation C: Maximum temperature difference within the plane is 7.0℃ or more

[0094] A grading evaluation was conducted. The results are as shown in Table 1.

[0095] <Total Current Value and Current Value Reduction Effect>

[0096] In the same manner as the above cracking method, power was supplied from a power source (power voltage: 208V) to the inner zone control heater circuit (14a) and the outer zone control heater circuit (14b) through the first power supply terminal (18) and the second power supply terminal (20), thereby heating the 2-zone ceramic heater (10) to a set temperature of 650°C. At this time, the value of the current flowing through each of the inner zone control heater circuit (14a) and the outer zone control heater circuit (14b) was measured, and the measured current values ​​were summed to calculate the total current value. The result was as shown in Table 1. In addition, the total current value in Example 1 (Comparative Example) was set as a reference value, and the amount of reduction in the total current of Examples 2 to 5 relative to this reference value was shown in Table 1 as the effect of reducing the total current value.

[0097]

[0098] From the distribution of the volume resistivity ratio in the radial direction of the ceramic plate (12) shown in Fig. 7, the following can be seen for each example.

[0099] Example 1 (Comparison) is an example corresponding to the prior art, and the volume resistivity ratio within the resistance heating element was constant. This implies that there is a limit to increasing the resistance value further. In Example 2 (Comparison), the volume resistivity ratio increased as it approached the outer periphery due to an improvement in the firing method. However, since the volume resistivity ratio increased rapidly only near the outer periphery, it was not a desirable profile for the volume resistivity ratio. As a result, the crack resistance dropped to evaluation C.

[0100] In contrast, Example 3 is an example that employs optimal firing conditions and achieved a desirable volume resistivity profile having a linear gradient in which the volume resistivity ratio increases as it approaches the outer periphery. Furthermore, in the outer zone control heater circuit (14b), it was possible to realize a 22% increase in volume resistivity with respect to the volume resistivity at a position 60 mm from the center of the ceramic plate (12) (outer edge of the central part). Example 4 exhibited a profile in which the volume resistivity ratio increases as it approaches the outer periphery, but the volume resistivity ratio is smaller than that of Example 3. In this example, a current value reduction effect of about 1 A and good crack resistance (Evaluation A) were demonstrated. Example 5 is the highest volume resistivity among the examples showing a profile with a linear gradient in which the volume resistivity ratio increases as it approaches the outer periphery. In this example, acceptable crack resistance (Evaluation B) was demonstrated, and the current value reduction effect was high at about 3 A.

[0101] The volume resistivity profiles of Examples 1 to 5 were produced solely by the differences in firing conditions shown in Table 1. In other words, conventionally, it was necessary to employ methods that impede cracking, such as making the diameter of the heating element wire thinner to increase the resistance value or increasing the heating density (i.e., packing more resistance heating elements into the same area), but according to the method of the present disclosure, such factors that impede cracking can be avoided. As a result, a desirable profile in which the volume resistivity of the resistance heating element increases linearly toward the outer circumference can be realized, and the temperature difference within the plane can be reduced to a minimum of about 3°C ​​(Example 3) (i.e., cracking can be improved). In addition, the total current value can be reduced to a maximum of about 3A (Example 5). This is equivalent to 18A when converted to a system equipped with six times the number of heaters.

Claims

Claim 1 A ceramic plate having a first surface for loading a wafer and a second surface facing the first surface, wherein, when the ceramic plate is viewed in a planar view, the ceramic plate comprises a central portion defined as a circular area within a radius of 60 mm from the center of the ceramic plate, an intermediate portion defined as an annular area with a radius of 80 to 120 mm from the center, and an outer periphery portion defined as an annular area with a radius of 130 mm or more from the center; and a ceramic heater having a resistance heating element embedded in the central portion, the intermediate portion, and the outer periphery portion within the ceramic plate, wherein the resistance heating element is configured such that the volume resistivity of the resistance heating element gradually increases as it moves away from the center of the ceramic plate, and when the volume resistivity of the resistance heating element at the outer edge of the central portion is set to 100%, the ratio of the volume resistivity of the resistance heating element at the intermediate portion is within the range of 102 to 120%, and furthermore, the ratio of the volume resistivity of the resistance heating element at the outer periphery portion A ceramic heater within the range of 108 to 139%. Claim 2 A ceramic heater according to claim 1, wherein the resistance heating element is in at least one form selected from the group consisting of a coil, a linear zigzag structure, a printed pattern, a foil, and a mesh. Claim 3 A ceramic heater according to claim 1 or 2, wherein each of the resistance heating element embedded in the central part, the resistance heating element embedded in the middle part, and the resistance heating element embedded in the outer periphery is arranged in a form that is continuously connected without interruption when viewed in a planar view, and furthermore, the resistance heating element embedded in the central part, the resistance heating element embedded in the middle part, and the resistance heating element embedded in the outer periphery are composed of the same material. Claim 4 In paragraph 3, the ceramic heater comprises at least two resistance heating elements, wherein one of the resistance heating elements embedded in the central part, the middle part, and the outer periphery forms an outer zone control heater circuit as a continuous single resistance heating element, and the other of the resistance heating element embedded at a depth position different from the outer zone control heater circuit of the central part, the middle part, and the outer periphery forms an inner zone control heater circuit independent from the outer zone control heater circuit as a continuous single resistance heating element. Claim 5 In paragraph 3, the ceramic heater comprises at least two resistance heating elements, wherein the resistance heating element embedded in the outer periphery or the outer periphery and the middle portion forms an outer zone control heater circuit as a single continuous resistance heating element, and the resistance heating element embedded in the central portion or the central portion and the middle portion forms an inner zone control heater circuit independent from the outer zone control heater circuit as a single continuous resistance heating element. Claim 6 A ceramic heater according to claim 1 or 2, wherein the ceramic plate comprises aluminum nitride or aluminum oxide. Claim 7 In claim 6, the ceramic plate comprises aluminum nitride, and furthermore, the ceramic plate has an upper ceramic plate providing the first surface and a lower ceramic plate providing the second surface, and the aluminum nitride constituting the upper ceramic plate is 1.0 × 10⁻⁶ at 550°C 8 A ceramic heater having a volume resistivity exceeding Ω·cm. Claim 8 A ceramic heater according to claim 1 or 2, further comprising an internal electrode, which is an RF electrode and / or an ESC electrode, within the ceramic plate. Claim 9 A ceramic heater according to claim 1 or 2, further comprising a cylindrical ceramic shaft installed concentrically on the second surface of the ceramic plate and having an internal space.

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