Ceramic heater

Abstract

Provided is a ceramic heater capable of improving heat uniformity in the central part of an inner zone. This ceramic heater comprises: a ceramic plate including an inner zone and an outer zone; a ceramic shaft; an inner zone heater circuit; an outer zone heater circuit; a pair of first power supply terminals provided to the central part of the inner zone; a pair of second power supply terminals provided to the central part of the inner zone; and at least a pair of jumpers embedded in the inner zone. The inner zone heater circuit is provided in a manner so as to start from one of the first power supply terminals and meanderingly reach the other of the first power terminals by one stroke. In the central part of the inner zone: the inner zone heater circuit, which starts from the one of the first power supply terminals, is provided in a manner so as to meander while circumventing a prescribed position; and the total of the opening angles formed by one or more pairs of tangential lines drawn from the center of the ceramic plate in a manner so as to define one or more openings in a circumvention part of the inner zone heater circuit is 60° or less.

Description

Ceramic heater

[0001] The present disclosure relates to ceramic heaters.

[0002] In film deposition apparatuses 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, such as two-zone ceramic heaters with two heating zones consisting of an inner zone and an outer zone, are also known.

[0003] For example, Patent Document 1 (WO2020 / 153071) discloses a ceramic heater including a ceramic plate having a circular inner zone and an annular outer zone, a two-dimensional inner resistance heating element provided in the inner zone, and a coil-shaped outer resistance heating element provided in the outer zone, and terminals of the inner resistance heating element and the outer resistance heating element are arranged in the inner zone.

[0004] WO2020 / 153071

[0005] In a multi-zone ceramic heater with a ceramic shaft, when the ceramic plate is viewed from the ceramic shaft side, there is a circular region defined by the outer periphery of the ceramic shaft. This region is referred to herein as the "center of the inner zone." Because the center of the inner zone generates relatively little heat from the embedded resistance heating element and receives a large amount of heat radiation from the shaft, the temperature tends to be lower than the outer regions during high-temperature operation of the heater. When the temperature at the center is lower than that of the entire heater circuit, differential thermal expansion can cause cracks, resulting in the heater breaking. Furthermore, a temperature gradient occurs throughout the heater circuit, resulting in poor thermal uniformity. Increasing the occupancy of the coil (resistance heating element) in the center of the inner zone can reduce the temperature difference and improve thermal uniformity. However, in the center of the inner zone, it is necessary to ensure insulation distances between the resistance heating elements while avoiding unnecessary contact with embedded objects such as terminals concentrated in the center. Therefore, there are many constraints on the placement of the coil in the center of the inner zone, making it difficult to achieve desirable thermal uniformity.

[0006] The present inventors have now discovered that by providing an inner zone heater circuit in a meandering manner around a predetermined position in the center of the inner zone to provide an opening with an opening angle of 60° or less, it is possible to reduce the temperature difference in the center of the inner zone and improve thermal uniformity.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a ceramic heater that can reduce the temperature difference in the center of the inner zone and achieve improved thermal uniformity.

[0008] According to the present disclosure, the following aspects are provided.[Aspect 1] A circular ceramic plate having a first surface on which a wafer is placed and a second surface opposite the first surface, the ceramic plate including, when viewed from above, 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; a cylindrical ceramic shaft attached to the second surface of the ceramic plate and having an internal space; 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; a pair of first power supply terminals provided in a center of the inner zone of the ceramic plate for supplying power to the inner zone heater circuit; and a pair of second power supply terminals provided in a center of the inner zone of the ceramic plate for supplying power to the outer zone heater circuit. at least one pair of jumpers embedded in the inner zone of the ceramic plate, one of the pair of jumpers electrically connecting one of the second power supply terminals to the outer zone heater circuit, and the other of the pair of jumpers electrically connecting the other of the second power supply terminals to the outer zone heater circuit, wherein the inner zone heater circuit is arranged to pass through the inner zone, starting from one of the pair of first power supply terminals and meandering while alternately progressing and turning back in a unicursal manner, until it reaches the other of the pair of first power supply terminals, a ceramic heater in which, in a central portion of the inner zone, the inner zone heater circuit starting from one of the pair of first power supply terminals is provided in a serpentine manner, detouring around the center of the ceramic plate, a singular point including the pair of first power supply terminals and the pair of second power supply terminals, and the pair of jumpers, and a sum of opening angles formed by at least one pair of tangents drawn from the center of the ceramic plate to the detouring portion of the inner zone heater circuit so as to identify at least one opening is 60° or less, and the central portion of the inner zone is defined as a circular region surrounded by the outer periphery of the ceramic shaft when the ceramic plate is viewed in a plan view from the ceramic shaft side.[Aspect 2] The ceramic heater according to Aspect 1, wherein the sum of the opening angles is 40° or less. [Aspect 3] The ceramic heater according to Aspect 1 or 2, wherein, when the ceramic plate is viewed in a plan view or a plan view perspective, the ratio of the area of ​​the region occupied by the inner zone heater circuit in the center of the inner zone to the area of ​​the center of the inner zone is 16 to 35%. [Aspect 4] The ceramic heater according to Aspect 3, wherein the ratio of the area occupied by the inner zone heater circuit is 20 to 35%. [Aspect 5] The ceramic heater according to any one of Aspects 1 to 4, wherein the inner zone heater circuit and the outer zone heater circuit comprise 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. [Aspect 6] The ceramic heater according to any one of Aspects 1 to 5, wherein the ceramic plate comprises aluminum nitride or aluminum oxide. [Aspect 7] The ceramic heater according to any one of Aspects 1 to 6, further comprising: an RF electrode and / or an ESC electrode embedded in the ceramic plate; and a third power supply terminal provided in a center of the inner zone of the ceramic plate for supplying power to the RF electrode and / or the ESC electrode, wherein the singular point includes the third power supply terminal. [Aspect 8] The ceramic heater according to any one of Aspects 1 to 7, wherein the ceramic plate has a thermocouple hole provided in a thickness direction of the ceramic plate, and the singular point includes the thermocouple hole. [Aspect 9] The ceramic heater according to any one of Aspects 1 to 8, wherein the ceramic plate has a gas hole provided in a thickness direction of the ceramic plate, and the singular point includes the gas hole.

[0009] 3A is a perspective cross-sectional view schematically showing an example of a ceramic heater according to the present invention. For convenience of explanation, the jumper 24 is drawn at a position slightly lower than its original position in order to clearly show the configurations of the inner zone heater circuit 16 and the jumper 24, which are originally located at the same height.

[0034] FIG. 3B is a top view diagram schematically showing the ceramic heater shown in FIG. 1.

[0035] FIG. 3C is a diagram showing an example of a heater circuit pattern (opening angle: 35°) within the scope of the present invention. The coils constituting the heater circuit are drawn in the form of a band with a width corresponding to the coil winding diameter.

[0036] FIG. 3D is an enlarged view of the center of the inner zone in the inner zone heater circuit shown in FIG. 3A.

[0037] FIG. 3E is a diagram showing an example of a heater circuit pattern (opening angle: 126°) outside the scope of the present invention. The coils constituting the heater circuit are drawn in the form of a band with a width corresponding to the coil winding diameter.

[0038] FIG. 4A is an enlarged view of the center of the inner zone in the inner zone heater circuit shown in FIG. 4A.

[0039] FIG. 4B is a diagram showing another example of a heater circuit pattern (opening angle: 188°) outside the scope of the present invention. The coils constituting the heater circuit are drawn in the form of a band with a width corresponding to the coil winding diameter. 5B is an enlarged view of the center of the inner zone in the inner zone heater circuit shown in FIG. 5A. FIG. 5C is a temperature distribution map measured in a region within a radius of 100 mm from the in-plane center of the heated ceramic plate in Example 1. FIG. 5D is a temperature distribution map measured in a region within a radius of 100 mm from the in-plane center of the heated ceramic plate in Example 2. FIG. 5E is a temperature distribution map measured in a region within a radius of 100 mm from the in-plane center of the heated ceramic plate in Example 3. FIG. 5F is a diagram showing the assignment of the X-axis and Y-axis to the temperature distribution map shown in FIG. 6. FIG. 5G is a diagram showing the temperature distribution profile on the X-axis in the temperature distribution map obtained in Examples 1 to 3. FIG. 5H is a graph showing the center-cooled temperature of the heated ceramic plate measured in Examples 1 to 3 in relation to the sum of the opening angles. FIG. 5I is a graph showing the maximum in-plane temperature difference in a region within a radius of 100 mm from the in-plane center of the heated ceramic plate measured in Examples 1 to 4 in relation to the heater circuit occupied area ratio in a region within a radius of 40 mm from the in-plane center of the ceramic plate.

[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, a ceramic shaft 14, an inner zone heater circuit 16, an outer zone heater circuit 18, a pair of first power supply terminals 20, a pair of second power supply terminals 22, and at least one pair of jumpers 24. The ceramic plate 12 is disk-shaped and has a first surface 12a on which a wafer W is placed and a second surface 12b opposite the first surface 12a. When viewed from above, the ceramic plate 12 includes an inner zone Z1 defined as a circular region within a predetermined distance from the center of the ceramic plate 12, and an outer zone Z2 defined as an annular region outside the inner zone Z1. The ceramic shaft 14 is cylindrical, attached to the second surface 12b of the ceramic plate 12, and has an internal space S. The inner zone heater circuit 16 is embedded in the inner zone Z1 of the ceramic plate 12. The outer zone heater circuit 18 is embedded in the outer zone Z2 of the ceramic plate 12. A pair of first power supply terminals 20 are terminals for supplying power to the inner zone heater circuit 16 and are provided in the center C of the inner zone Z1 of the ceramic plate 12. A pair of second power supply terminals 22 are terminals for supplying power to the outer zone heater circuit 18 and are provided in the center C of the inner zone Z1 of the ceramic plate 12. At least one pair of jumpers 24 are embedded in the inner zone Z1 of the ceramic plate 12. One of the pair of jumpers 24 electrically connects one of the second power supply terminals 22 to the outer zone heater circuit 18, while the other of the pair of jumpers 24 electrically connects the other of the second power supply terminals 22 to the outer zone heater circuit 18. The inner zone heater circuit 16 is provided so as to pass through the inner zone Z1, starting from one of the pair of first power supply terminals 20 and meandering while alternately progressing and turning back in a single stroke, until it reaches the other of the pair of first power supply terminals 20. In the central portion C of the inner zone Z1, the inner zone heater circuit 16 starts from one of the pair of first power supply terminals 20 and meanders while detouring the center of the ceramic plate 12, a singular point including the pair of first power supply terminals 20 and the pair of second power supply terminals 22, and a pair of jumpers 24.The sum of the opening angle θ formed by at least one pair of tangents drawn from the center of the ceramic plate 12 to the detour portion of the inner zone heater circuit 16 so as to identify at least one opening 16a is 60° or less. The central portion C of the inner zone Z1 is defined as a circular region surrounded by the outer periphery of the ceramic shaft 14 when the ceramic plate 12 is viewed in plan from the ceramic shaft 14 side. In this way, by providing the inner zone heater circuit 16 in the central portion C of the inner zone Z1 in a meandering manner while detouring around predetermined positions to provide openings 16a with an opening angle of 60° or less, the temperature difference in the central portion C of the inner zone Z1 can be reduced, thereby improving thermal uniformity.

[0012] As mentioned above, multi-zone ceramic heaters with ceramic shafts have a circular region (the central portion of the inner zone) defined by the outer circumference of the ceramic shaft. Because the central portion of the inner zone generates relatively little heat from the embedded resistance heating element and receives a large amount of heat radiation from the shaft, the temperature tends to be lower than the outer regions when the heater is operating at high temperatures. When the temperature at the center of the inner zone is lower than that of the entire heater circuit, differential thermal expansion can cause cracks, potentially resulting in the heater breaking. Furthermore, a temperature gradient occurs throughout the heater circuit, resulting in poor thermal uniformity. Increasing the occupancy of the coil (resistance heating element) in the central portion of the inner zone can reduce the temperature difference and improve thermal uniformity. However, because it is necessary to ensure an insulating distance between the resistance heating elements constituting the heater circuit while avoiding unnecessary contact with embedded objects such as terminals concentrated in the central portion, there are many constraints on the placement of the coil in the central portion of the inner zone, making it difficult to achieve desirable thermal uniformity. Furthermore, because embedded objects such as terminals are concentrated in the center of the inner zone, residual stress concentrates in the heater circuit in the center, which is thought to be the cause of cracks in the center. One or more of these problems are successfully solved by the present invention. That is, as shown in Figures 3A and 3B, in the center C of the inner zone Z1, the inner zone heater circuit 16 is arranged in a serpentine manner, bypassing elements that should not come into contact with it, such as the center of the ceramic plate 12 (where, for example, a third power supply terminal 28 described below may be disposed), singular points including the pair of first power supply terminals 20 and the pair of second power supply terminals 22, and the pair of jumpers 24. As described above, by configuring the bypass portion of the inner zone heater circuit 16 to form at least one opening 16a and setting the sum of the opening angles θ to 60° or less, the area in the center C where the inner zone heater circuit 16 is sparse can be significantly reduced, thereby reducing the temperature difference in the center C of the inner zone Z1 and improving thermal uniformity. Furthermore, it is believed that the improvement in thermal uniformity can prevent damage such as cracks caused by differences in thermal expansion.

[0013] From this perspective, the sum of the opening angles θ formed by at least one pair of tangent lines drawn from the center of the ceramic plate 12 to the detour portion of the inner zone heater circuit 16 so as to identify at least one opening 16a is 60° or less, preferably 40° or less. An opening 16a is defined as a portion of a line drawn radially from the center of the ceramic plate 12 that does not intersect with the inner zone heater circuit 16 meandering closest to the center of the ceramic plate 12. The number of openings 16a is typically one, but may be two or more as shown in Figures 5A and 5B. In such cases, the number of openings 16a may be determined based on whether the sum of the opening angles of the two or more openings is within the above-mentioned range (although Figures 5A and 5B do not fall within the scope of the present invention, since the sum of the opening angles θ exceeds 60°). While there is no particular lower limit to the sum of the opening angles θ, from the viewpoint of ease of installation of the inner zone heater circuit 16, the lower limit is typically 10° or more, more typically 20° or more.

[0014] 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 inner zone heater circuit 16, the outer zone heater circuit 18, and the jumper 24, from the viewpoints of excellent thermal conductivity, high electrical insulation, and thermal expansion characteristics similar to those of silicon.

[0015] 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 size of the ceramic plate 12 is not particularly limited and can be determined appropriately depending on the diameter of the wafer to be used. However, when the ceramic plate 12 is circular, the diameter is typically 150 to 450 mm, and particularly for 300 mm silicon wafers, the diameter is typically 320 to 380 mm. The thickness of the ceramic plate 12 is typically 10 to 25 mm.

[0016] The ceramic plate 12 includes 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. 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 with 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.

[0017] The ceramic shaft 14 is attached to the second surface 12b of the ceramic plate 12. The central axis of the ceramic shaft 14 preferably coincides with the center of the ceramic plate 12. The ceramic shaft 14 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 terminal rods such as the first power supply terminal 20, the second power supply terminal 22, and the third power supply terminal 28 to pass therethrough. The ceramic shaft 14 is preferably made of the same ceramic material as the ceramic plate 12. Therefore, the ceramic shaft 14 preferably contains aluminum nitride or aluminum oxide, more preferably aluminum nitride. The upper end surface of the ceramic shaft 14 is preferably bonded to the second surface 12b of the ceramic plate 12 by solid-state bonding or diffusion bonding. The outer diameter of the ceramic shaft 14 is not particularly limited, but is preferably 40 to 60 mm. The inner diameter of the ceramic shaft 14 (the diameter of the internal space S) is also not particularly limited, but is preferably 33 to 55 mm.

[0018] The inner zone heater circuit 16 and the outer zone heater circuit 18 preferably include a resistance heating element having at least one form selected from the group consisting of a coil, a linear zigzag structure, a printed pattern, a ribbon, and a mesh. A coil has a configuration in which a resistance heating wire is wound three-dimensionally, while a linear zigzag structure has a configuration in which a resistance heating wire is alternately folded two-dimensionally within a plane. The printed pattern is not particularly limited, but a typical pattern is a strip-shaped line of the resistance heating element layer that alternates between straight and bent (e.g., zigzag). It is preferable to use resistance heating elements of the same form for the inner zone heater circuit 16 and the outer zone heater circuit 18 because of ease of fabrication, but resistance heating elements of different forms may also be used. Each of the inner zone heater circuit 16 and the outer zone heater circuit 18 is preferably arranged in a single-stroke form when viewed in a plan view. The single-stroke form may be any of various known forms, such as an alternating forward and backward trajectory or a spiral.

[0019] The inner zone heater circuit 16 is embedded in the inner zone Z1 of the ceramic plate 12 parallel to the first surface 12a. A pair of first power supply terminals 20 for supplying power to the inner zone heater circuit 16 is provided in the center C of the inner zone Z1 of the ceramic plate 12. Preferably, the first power supply terminals 20 are connected to both ends of the inner zone heater circuit 16, respectively. There may be two or more pairs of first power supply terminals 20. The first power supply terminals 20 are rod-shaped, and the inner zone heater circuit 16 is connected to a heater power supply (not shown) via the rod-shaped first power supply terminals 20.

[0020] In a preferred embodiment of the present invention, the inner zone heater circuit 16 includes a resistance heating element in the form of a coil. In this case, the winding diameter of the coil is preferably 2.5 to 5.0 mm, more preferably 2.5 to 4.0 mm, and even more preferably 3.0 to 3.5 mm. The wire diameter of the coil is preferably 0.3 to 0.7 mm, more preferably 0.4 to 0.6 mm, and even more preferably 0.4 to 0.5 mm. In another preferred embodiment of the present invention, the inner zone heater circuit 16 includes a resistance heating element in the form of a linear zigzag structure. In this case, the maximum amplitude of the linear zigzag structure is preferably 5 to 15 mm, more preferably 5 to 10 mm, and even more preferably 6 to 8 mm. The maximum amplitude of the linear zigzag structure is defined as the distance between the line connecting the vertices on one side of the linear zigzag structure and the line connecting the vertices on the opposite side. The wire diameter of the linear zigzag structure is preferably 0.3 to 0.7 mm, more preferably 0.4 to 0.6 mm, and even more preferably 0.4 to 0.5 mm. In yet another preferred embodiment of the present invention, the inner zone heater circuit 16 includes a resistance heating element in the form of a printed pattern. In this case, the printing thickness of the printed pattern (thickness of the resistance heating element layer) is preferably 0.01 to 0.06 mm, more preferably 0.01 to 0.04 mm, and even more preferably 0.015 to 0.03 mm.

[0021] When the ceramic plate 12 is viewed from above or through a plan view, the ratio of the area of ​​the region occupied by the inner zone heater circuit 16 in the central portion C of the inner zone Z1 to the area of ​​the central portion C of the inner zone Z1 is preferably 16 to 35%, and more preferably 20 to 35%. Within this range, a center-cooled state in which the temperature is locally low in the central portion C of the inner zone Z1 can be effectively prevented, further improving thermal uniformity. Furthermore, the insulation distance between the resistance heating elements constituting the heater circuit can be easily ensured, facilitating the placement of the inner zone heater circuit 16. Here, in this specification, the "region occupied by the inner zone heater circuit 16 in the central portion C of the inner zone Z1" refers to the area occupied by the general shape of the inner zone heater circuit 16 and therefore includes the gaps between the wires constituting the inner zone heater circuit 16. Therefore, when the inner zone heater circuit 16 is a coil, the gaps between the wires caused by the coil winding are also included in the area occupied by the inner zone heater circuit when calculating the area ratio. That is, the coil winding diameter is regarded as the wire width, and the occupied area of ​​the coil can be calculated by multiplying that wire width by the length of the coil passing through the center C (i.e., the occupied area is calculated by regarding the coil constituting the inner zone heater circuit 16 as a strip with the above wire width). Similarly, when the inner zone heater circuit 16 has a linear zigzag structure, the occupied area is calculated by regarding the linear zigzag structure as a strip with the maximum swing width as the wire width.

[0022] The outer zone heater circuit 18 is embedded in the outer zone Z2 of the ceramic plate 12 parallel to the first surface 12a at the same or a different depth as the inner zone heater circuit 16. As shown in Figures 1 and 2, the outer zone heater circuit 18 may be embedded in the outer zone Z2 of the ceramic plate 12 parallel to the first surface 12a at the same depth as the inner zone heater circuit 16. Alternatively, the outer zone heater circuit 18 may be embedded in the outer zone Z2 of the ceramic plate 12 parallel to the first surface 12a at a different depth than the inner zone heater circuit 16. In this case, the inner zone heater circuit 16 may be embedded higher than the outer zone heater circuit 18 (i.e., at a depth closer to the first surface 12a), or the inner zone heater circuit 16 may be embedded lower than the outer zone heater circuit 18 (i.e., at a depth closer to the second surface 12b). In either embodiment, a pair of second power supply terminals 22 for supplying power to the outer zone heater circuit 18 via a jumper 24 is provided in the center C of the inner zone Z1 of the ceramic plate 12 (but at a position different from the first power supply terminals 20). That is, the pair of second power supply terminals 22 is located at a position away from the outer zone heater circuit 18, and therefore the pair of second power supply terminals 22 is electrically connected to the outer zone heater circuit 18 via the pair of jumpers 24. Two or more pairs of second power supply terminals 22 may be provided. The second power supply terminals 22 are rod-shaped, and the outer zone heater circuit 18 is connected to a heater power source (not shown) via the jumper 24 and the rod-shaped second power supply terminals 22.

[0023] In a preferred embodiment of the present invention, the outer zone heater circuit 18 includes a resistance heating element in the form of a coil. In this case, the winding diameter of the coil is preferably 2.5 to 5.0 mm, more preferably 2.5 to 4.0 mm, and even more preferably 3.0 to 3.5 mm. The wire diameter of the coil is preferably 0.3 to 0.7 mm, more preferably 0.4 to 0.6 mm, and even more preferably 0.4 to 0.5 mm. In another preferred embodiment of the present invention, the outer zone heater circuit 18 includes a resistance heating element in the form of a linear zigzag structure. In this case, the maximum amplitude of the linear zigzag structure is preferably 5 to 15 mm, more preferably 5 to 10 mm, and even more preferably 6 to 8 mm. The wire diameter of the linear zigzag structure is preferably 0.3 to 0.7 mm, more preferably 0.4 to 0.6 mm, and even more preferably 0.4 to 0.5 mm. In yet another preferred embodiment of the present invention, the outer zone heater circuit 18 includes a resistance heating element in the form of a printed pattern. In this case, the printing thickness of the print pattern (thickness of the resistance heating layer) is preferably 0.01 to 0.06 mm, and more preferably 0.03 to 0.06 mm.

[0024] The outer zone heater circuit 18 may be either a series circuit or a parallel circuit. That is, the outer zone heater circuit 18 may be provided so as to start in one direction from one of the pair of jumpers 24 and reach the other of the pair of jumpers 24 in a single stroke, forming a series circuit. Alternatively, the outer zone heater circuit 18 may be provided so as to start in two directions from one of the pair of jumpers 24 and reach the other of the pair of jumpers 24 in a single stroke, forming a parallel circuit. The outer zone heater circuit 18 shown in Figures 3A and 3B corresponds to this series circuit.

[0025] A pair of jumpers 24 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 16, and are electrically connected to the outer zone heater circuit 18. They may be embedded parallel to the first surface 12a at the same or a different depth as the outer zone heater circuit 18. The pair of jumpers 24 are separated from each other, with one jumper 24 electrically connecting one of the second power supply terminals 22 to one end of the outer zone heater circuit 18, and the other jumper 24 electrically connecting the other of the second power supply terminals 22 to the other end of the outer zone heater circuit 18. Two or more pairs of jumpers 24 may be present.

[0026] The jumper 24 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 curve (e.g., an arc), and a combination of a straight line and a curve (e.g., a straight line bent with a partial curvature). In a preferred embodiment of the present invention, the jumper 24 is a linear resistance heating element (i.e., a resistance heating element wire). In this case, the wire diameter of the resistance heating element wire is preferably 0.3 to 0.8 mm, more preferably 0.4 to 0.8 mm, and even more preferably 0.5 to 0.8 mm. In another preferred embodiment of the present invention, the jumper 24 is a printed pattern. In this case, the printing thickness of the printed pattern (thickness of the resistance heating element layer) is preferably 0.01 to 0.06 mm, more preferably 0.03 to 0.06 mm.

[0027] When the ceramic plate 12 is viewed from above, the pair of jumpers 24 and the pair of second power supply terminals 22 are preferably arranged symmetrically with respect to the perpendicular bisector of the line segment connecting the pair of second power supply terminals 22. With this configuration, the lengths of the power supply paths from the pair of second power supply terminals 22 through the pair of jumpers 24 to the outer zone heater circuit 18 can be made equal, making it easier to achieve good temperature uniformity.

[0028] Preferably, an RF electrode 26 and / or an ESC electrode are further embedded in the ceramic plate 12. 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 inner zone heater circuit 16, the outer zone heater circuit 18, and the jumper 24. 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 called an electrostatic electrode. When a voltage is applied from an external power source, the ESC electrode chucks a wafer placed on the surface of the ceramic plate 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 a high frequency to the ESC electrode, the ESC electrode can also be used as an RF electrode, and film formation can also be performed by a plasma CVD process.

[0029] A third power supply terminal 28 for supplying power is connected to the RF electrode 26 or the ESC electrode. The third power supply terminal 28 is a terminal for supplying power to the RF electrode 26 and / or the ESC electrode, and is provided in the center C of the inner zone Z1 of the ceramic plate 12. Because contact between the inner zone heater circuit 16 and the third power supply terminal 28 should be avoided, the third power supply terminal 28 is also included in the singular points that the inner zone heater circuit 16 should bypass. The third power supply terminal 28 is preferably rod-shaped, and the RF electrode 26 or the ESC electrode is connected to an external power supply (not shown) via the rod-shaped third power supply terminal 28.

[0030] The ceramic plate 12 may have a thermocouple hole (not shown) provided in the thickness direction of the ceramic plate 12. Because contact between the inner zone heater circuit 16 and the thermocouple hole should be avoided, the thermocouple hole is also included in the singular points that the inner zone heater circuit 16 should bypass. The thermocouple hole is a blind hole formed in the ceramic plate 12 from a position facing the internal space S of the second surface 12b to an arbitrary depth position. The ceramic heater 10 may further include a thermocouple in the thermocouple hole.

[0031] The ceramic plate 12 may have gas holes (not shown) formed in the thickness direction of the ceramic plate 12. Contact between the inner zone heater circuit 16 and the gas holes should be avoided, so the gas holes are also included in the singular points that the inner zone heater circuit 16 should bypass. The gas holes may be, for example, through-holes configured to penetrate the ceramic plate 12 and the ceramic shaft 14 from the first surface 12a of the ceramic plate 12 through the second surface 12b to the distal end of the ceramic shaft 14. The gas holes allow gas to be supplied to the first surface 12a of the ceramic plate 12. With this configuration, since the wafer W is placed on the first surface 12a, supplying gas to the backside of the wafer W allows heat generated in the ceramic plate 12 (particularly the inner zone heater circuit 16 and the outer zone heater circuit 18) to be efficiently transferred to the wafer W. Therefore, the gas supplied to the gas holes is preferably an inert gas with excellent heat conductivity, and He gas is particularly preferred.

[0032] As described above, the central portion C of the inner zone Z1 has multiple singular points through which the inner zone heater circuit 16 must bypass. Examples of these singular points include the center of the ceramic plate 12, the pair of first power feed terminals 20, the pair of second power feed terminals 22, the third power feed terminal 28, the thermocouple holes, and the gas holes. It is preferable that these singular points be as evenly spaced as possible (e.g., with respect to the center of the ceramic plate 12) from the standpoints of facilitating the installation of the inner zone heater circuit 16 and improving thermal uniformity.

[0033] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0034] Examples 1 to 3 (1) Fabrication of Ceramic Heater Using the components shown below, ceramic heaters 10 having the basic structure shown in FIGS. 1 and 2 and the circuit patterns shown in FIGS. 3A and 3B (opening angle θ=35°) in Example 1, FIGS. 4A and 4B (opening angle θ=126°) in Example 2, and FIGS. 5A and 5B (total opening angles θ1+θ2=188°) in Example 3 were fabricated in the following manner.

[0035] <Constituent members and their specifications> Ceramic plate 12: a disc-shaped sintered aluminum nitride body (diameter: 350 mm, thickness: 20 mm) (with the inner zone heater circuit 16, outer zone heater circuit 18, jumper 24, and RF electrode 26 embedded inside) Ceramic shaft 14: a cylindrical sintered aluminum nitride body (height: 150 mm, outer diameter: 50 mm, inner diameter: 40 mm) Inner zone Z1: a circular region with a diameter of 150 mm located in the center of the ceramic plate 12 Outer zone Z2: an annular region on the ceramic plate 12 outside the inner zone Z1 Inner zone heater circuit 16: a three-dimensional coil-shaped resistance heating element (material: molybdenum, winding diameter: 4 mm, and wire diameter: 0.5 mm) embedded at a position 10 mm deep from the first surface 12 a of the inner zone Z1 according to the circuit pattern shown in Figures 3A and 3B (Example 1), 4A and 4B (Example 2), or 5A and 5B (Example 3) (a common coil pitch is used in Examples 1 to 3, and the heat generation amount per unit length is also common). Outer zone heater circuit 18: a three-dimensional coil-shaped resistance heating element (material: molybdenum, winding diameter: 4 mm, and wire diameter: 0.5 mm) embedded at a position 10 mm deep from the first surface 12 a of the outer zone Z2 according to a common circuit pattern shown in Figures 3A and 3B (Example 1), 4A and 4B (Example 2), or 5A and 5B (Example 3) (a common coil pitch is used in Examples 1 to 3, and the heat generation amount per unit length is also common). Jumper 24: A pair of substantially linear, bilaterally symmetrical resistance heating wires (material: molybdenum, wire diameter: 0.7 mm) buried at a depth of 10 mm from the first surface 12 a of the inner zone Z1 according to the circuit pattern shown in FIGS. 3A and 3B (Example 1), 4A and 4B (Example 2), or 5A and 5B (Example 3). RF electrode 26: An electrode layer made of molybdenum buried at a depth of 1.0 mm from the first surface 12 a of the ceramic plate 12. First power supply terminal 20: Two terminal rods made of nickel. Second power supply terminal 22: Two terminal rods made of nickel. Third power supply terminal 28 (RF terminal): One terminal rod made of nickel.

[0036] The ceramic plate 12 having the inner zone heater circuit 16, the outer zone heater circuit 18, the jumper 24, 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. Then, aluminum nitride powder, the inner zone heater circuit 16, the outer zone heater circuit 18, and the jumper 24 were arranged on the obtained first aluminum nitride compact according to the circuit pattern shown in FIGS. 3A and 3B (Example 1), 4A and 4B (Example 2), or 5A and 5B (Example 3), and press-molded to obtain a second aluminum nitride compact having the inner zone heater circuit 16, the outer zone heater circuit 18, and the jumper 24 embedded therein. Then, aluminum nitride powder and the RF electrode 26 were arranged on the obtained second aluminum nitride compact, and press-molded to obtain a third aluminum nitride compact having the RF electrode 26 further embedded therein. In this way, a press-molded body was obtained consisting of an aluminum nitride powder compact in which the inner zone heater circuit 16, the outer zone heater circuit 18, the jumper 24, and the RF electrode 26 were embedded, as shown in Figure 2. 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 16, the outer zone heater circuit 18, the jumper 24, and the RF electrode 26 were embedded.

[0037] (2) Evaluation Various evaluations were carried out on the obtained ceramic heater.

[0038] <Relationship between Opening Angle and 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. ２The gas pressure was set to 5 Torr. Power was supplied to the inner zone heater circuit 16 and the outer zone heater circuit 18 via the first power supply terminal 20, the second power supply terminal 22, and the jumper 24, thereby heating the ceramic heater 10 to a set temperature of 550°C. The ratio of the power supplied to the outer zone heater circuit 18 to the power supplied to the inner zone heater circuit 16 was finely adjusted to achieve the most uniform temperature distribution, based on a standard of 1:1. At this set temperature, the temperature distribution was measured using an infrared camera in a region within a radius of 100 mm from the center of the first surface 12a of the ceramic plate 12 (a region corresponding to the inner zone Z1 (hereinafter referred to as the R100 area)). As a result, the temperature distribution maps shown in Figure 6 (Example 1), Figure 7 (Example 2), and Figure 8 (Example 3) were obtained. The obtained temperature distribution map was assigned an X-axis and a Y-axis as shown in FIG. 9, and the temperature distribution profile on the X-axis (hereinafter referred to as the X-profile) and the temperature distribution profile on the Y-axis (hereinafter referred to as the Y-profile) were obtained. The X-profile and Y-profile obtained in this way were as shown in FIGS. 10 and 11, respectively. For each of the X-profile and Y-profile, the difference between the maximum and minimum temperatures in the R100 area (i.e., the maximum temperature difference) was calculated as an index of thermal uniformity. The results are shown in Table 1.

[0039] 6 to 11, it can be seen that Example 1, an example of the present invention, has excellent thermal uniformity in the inner zone. In particular, the central portion of the inner zone Z1 is identified in Figures 10 and 11, and when the X and Y profiles within this identified central portion are examined, it can be seen that Example 1, an example of the present invention, exhibits significantly superior thermal uniformity compared to Examples 2 and 3, which are comparative examples.

[0040] As is clear from the temperature distribution maps shown in Figures 6 to 8 (particularly Figures 7 and 8), a state in which the temperature is locally low in the center C of the inner zone Z1 (hereinafter referred to as a center-cooled state) can occur. Therefore, the center-cooled temperature was defined as the temperature obtained by subtracting the central temperature Tc at the center of the R100 area from the average in-plane temperature Ta of the R100 area (i.e., Ta - Tc), and the calculated values ​​were as shown in Table 2. The relationship between the center-cooled temperature and the aperture angle was as shown in Figure 12.

[0041] From the results shown in Table 2 and Fig. 12, it can be seen that the temperature uniformity deteriorates as the total opening angle increases and the coil density in the center of the inner zone Z1 decreases. In particular, from the approximation line shown in Fig. 12, it can be understood that by setting the total opening angle to 60° or less, the center-cooled temperature becomes 0° or less (i.e., it becomes equal to or higher than the average in-plane temperature of the R100 area), and the center-cooled state can be eliminated.

[0042] <Relationship Between Heater Circuit Occupied Area Proportion and Heat Uniformity> We also investigated how the heat uniformity would change when the ratio of the area occupied by the inner zone heater circuit 16 to the area of ​​the center C of the inner zone Z1 (hereinafter referred to as the heater circuit occupied area ratio) was changed instead of the opening angle. The heater circuit occupied area ratio P was calculated using the following formula: P = (A / B) × 100 (where A is the area of ​​the area occupied by the inner zone heater circuit 16 in the center C of the inner zone Z1 when the ceramic plate 12 is viewed in plan or perspective, and B is the area of ​​the center C of the inner zone Z1). More specifically, A was calculated by considering the coil winding diameter of 5 mm as the wire width and multiplying this wire width by the length of the coil passing through the center C, so that gaps between the wires generated by the coil winding are included in the area occupied by the inner zone heater circuit (i.e., the occupied area was calculated by considering the coil of the inner zone heater circuit as a strip with a width of 5 mm). Furthermore, B was calculated as the area of ​​the region within a radius of 40 mm from the in-plane center on the first surface 12a of the ceramic plate 12 (hereinafter referred to as the R40 area). The heater circuit occupied area ratios P ​​in the R40 area for the ceramic heaters of Examples 1 to 3 calculated in this manner are shown in Table 3. The maximum in-plane temperature difference in the R100 area was determined as an index of thermal uniformity based on the above-mentioned measurement results (temperature distribution map), and the results shown in Table 3 were obtained. For reference, Example 4 was also fabricated in the same manner as Examples 1 to 3 (except for changing the circuit pattern of the inner zone heater circuit 16), with a heater circuit occupied area ratio P of 18.4% in the R40 area. The maximum in-plane temperature difference in the R100 area is also shown in Table 3. The relationship between the heater circuit occupied area ratio P in the R40 area and thermal uniformity (maximum in-plane temperature difference) was as shown in FIG. 13.

[0043] The results shown in Table 3 and FIG. 13 show that by setting the heater circuit occupied area ratio P to 16% or more in the central portion (R40 area) of the inner zone Z1, good thermal uniformity with a maximum in-plane temperature difference of 6°C or less can be achieved.

Claims

1. A disc-shaped ceramic plate having a first surface on which a wafer is placed and a second surface facing the first surface, wherein when the ceramic plate is viewed from above, it includes an inner zone defined as a circular region within a predetermined distance from the center of the ceramic plate and an outer zone defined as an annular region outside the inner zone, A cylindrical ceramic shaft having an internal space is attached to the second surface of the ceramic plate, An inner zone heater circuit is embedded in the inner zone of the ceramic plate, An outer zone heater circuit is embedded in the outer zone of the ceramic plate, A pair of first power supply terminals are provided in the center of the inner zone of the ceramic plate for supplying power to the inner zone heater circuit, A pair of second power supply terminals are provided in the center of the inner zone of the ceramic plate for supplying power to the outer zone heater circuit, At least one pair of jumpers embedded in the inner zone of the ceramic plate, wherein one of the jumpers electrically connects one of the second power supply terminals to the outer zone heater circuit, and the other of the jumpers electrically connects the other of the second power supply terminal to the outer zone heater circuit, Equipped with, The inner zone heater circuit is provided such that it passes through the inner zone, starting from one of the pair of first power supply terminals, and meandering through the circuit, alternating between moving forward and turning back in a single continuous line, until it reaches the other of the pair of first power supply terminals. In the central part of the inner zone, the inner zone heater circuit, starting from one of the pair of first power supply terminals, is provided in a meandering manner, bypassing the center of the ceramic plate, a singularity including the pair of first power supply terminals and the pair of second power supply terminals, and the pair of jumpers, and the sum of the opening angles formed by at least one pair of tangents drawn from the center of the ceramic plate to identify at least one opening in the bypass portion of the inner zone heater circuit is 60° or less. The central part of the inner zone is defined as a circular region surrounded by the outer circumference of the ceramic shaft when the ceramic plate is viewed from the ceramic shaft side in a plan view. A ceramic heater in which, when the ceramic plate is viewed from above or through a plane, the ratio of the area occupied by the inner zone heater circuit in the central part of the inner zone to the area of ​​the central part of the inner zone is 16 to 35%.

2. The ceramic heater according to claim 1, wherein the sum of the aforementioned opening angles is 40° or less.

3. The ceramic heater according to claim 1 or 2, wherein the proportion of the area occupied by the inner zone heater circuit is 20 to 35%.

4. The ceramic heater according to claim 1 or 2, wherein the inner zone heater circuit and the outer zone heater circuit include at least one form of resistive heating element selected from the group consisting of coils, linear zigzag structures, printed patterns, ribbons, and meshes.

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

6. The RF electrode and / or ESC electrode embedded in the ceramic plate, A third power supply terminal is provided in the center of the inner zone of the ceramic plate for supplying power to the RF electrode and / or the ESC electrode, The ceramic heater according to claim 1 or 2, further comprising the singularity including the third power supply terminal.

7. The ceramic heater according to claim 1 or 2, wherein the ceramic plate has thermocouple holes provided in the thickness direction of the ceramic plate, and the singularity includes the thermocouple holes.

8. The ceramic heater according to claim 1 or 2, wherein the ceramic plate has gas holes provided in the thickness direction of the ceramic plate, and the singularity includes the gas holes.