Ceramic susceptor

Abstract

The present invention provides a ceramic susceptor comprising internal electrodes and a thermocouple hole in a ceramic plate while being capable of suppressing occurrence of cracks between the hole bottom and the internal electrodes. This ceramic susceptor is provided with: a disk-shaped ceramic plate having a first surface for mounting a wafer and a second surface opposite the first surface, with a first electrode being embedded at a position closer in depth to the first surface and a second electrode being embedded at a position closer in depth to the second surface; a cylindrical ceramic shaft attached to the second surface of the ceramic plate and having an internal space; and a thermocouple hole and ss formed in the ceramic plate from a position aligned with the internal space of the second surface to a depth position between the first electrode and the second electrode. The thermocouple hole has an R shape with a curvature radius of 0.10 mm or more on the bottom or outer periphery thereof when viewed in a cross-sectional direction perpendicular to the center axis of the thermocouple hole, and the thermocouple hole has a diameter of 0.20 mm or more.

Description

Technical Field

[0001] The present invention relates to a ceramic susceptor.

Background Art

[0002] In a film-forming apparatus for a semiconductor manufacturing process, a ceramic heater is used as a support stage for uniformly controlling the temperature of a wafer. As such a ceramic heater, one including a ceramic plate on which a wafer is placed and a cylindrical ceramic shaft attached to the ceramic plate is widely used. The ceramic plate generally has a configuration in which internal electrodes such as a heater electrode, an RF electrode, and an electrostatic chuck (ESC) electrode are embedded inside a ceramic substrate made of aluminum nitride (AlN) or the like having excellent heat resistance and corrosion resistance.

[0003] As a ceramic heater, one having a bottomed hole for temperature measurement provided in a ceramic plate is known. For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2010-42967) discloses a ceramic member in which a ceramic sintered body having a thermal expansion coefficient equivalent to that of yttria and a yttria sintered body are integrally sintered with a conductive member interposed therebetween. An opening for measuring the temperature of a substrate is formed in the ceramic sintered body by drilling, and it is proposed to measure the temperature of the substrate through this opening via the yttria sintered body with a temperature measuring device. According to this configuration, since the temperature measuring device is isolated from the process gas atmosphere by the yttria sintered body, it is said that deterioration of the temperature measuring device can be prevented. In addition, Patent Document 2 (Japanese Patent Application Laid-Open No. 2001-148371) discloses an electrostatic adsorption device including a dielectric in which an adsorption electrode and a heater are embedded, and having a temperature measuring device for measuring the temperature of an object to be processed on the dielectric and the temperature of the dielectric. This dielectric is provided with a bottomed hole in which the dielectric is exposed on the bottom surface, and the temperature of the dielectric can be measured by measuring the amount of infrared light emitted from the dielectric by an infrared light receiving portion attached to an optical path body inserted into the bottomed hole.

Prior Art Documents

Patent Document

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] As described above, a ceramic heater having a bottomed hole for temperature measurement (hereinafter referred to as a thermocouple hole) provided in a ceramic plate is known. However, when such a ceramic heater is used in a film forming apparatus, cracks may occur between the bottom of the hole and the internal electrode (for example, an RF electrode) during the film forming process. The formation of these cracks is due to the fact that during the film forming process, the surface of the ceramic plate is exposed to a high temperature (for example, 600 ° C in the case of plasma CVD) in the film forming chamber, resulting in a temperature distribution and a thermal expansion difference between the high temperature surface of the ceramic plate and the lower temperature back surface of the ceramic plate. As a result, it is considered that stress is excessively concentrated near the bottom of the hole.

[0006] The present inventors have now found that by configuring the thermocouple hole provided in the ceramic plate to have an R shape with a radius of curvature of 0.10 mm or more at the outer periphery or the bottom of the bottom and a diameter of 0.20 mm or more, the generation of cracks between the bottom of the hole and the internal electrode can be suppressed.

[0007] Therefore, an object of the present invention is to provide a ceramic susceptor that can suppress the generation of cracks between the bottom of the hole and the internal electrode while including an internal electrode and a thermocouple hole in the ceramic plate.

[0008] According to the present invention, the following aspects are provided. [Aspect 1] A disc-shaped ceramic plate having a first surface for mounting a wafer and a second surface facing the first surface, with a first electrode embedded at a depth position near the first surface and a second electrode embedded at a depth position near the second surface, A cylindrical ceramic shaft attached to the second surface of the ceramic plate and having an internal space, In the ceramic plate, a thermocouple hole formed from a position on the second surface facing the internal space to a depth position between the first electrode and the second electrode, A ceramic susceptor comprising: The ceramic susceptor, wherein the thermocouple hole has an R shape with a curvature radius of 0.10 mm or more at the outer periphery or bottom of the bottom when viewed in cross section in a direction perpendicular to the central axis of the thermocouple hole, and the diameter of the thermocouple hole is 0.20 mm or more. [Aspect 2] The ceramic susceptor according to Aspect 1, wherein a distance B from the bottom of the thermocouple hole to the first electrode is longer than a distance A from the first surface to the first electrode. [Aspect 3] The ceramic susceptor according to Aspect 1 or 2, wherein a distance C from the bottom of the thermocouple hole to the second electrode is longer than a distance A from the first surface to the first electrode. [Aspect 4] The ceramic susceptor according to any one of Aspects 1 to 3, wherein the distance B is longer than the distance A and the distance C is longer than the distance A. [Aspect 5] The ceramic susceptor according to any one of Aspects 1 to 4, wherein the first electrode includes an RF electrode and the second electrode includes a heater electrode. [Aspect 6] The ceramic susceptor according to any one of Aspects 1 to 5, further comprising a thermocouple inserted into the thermocouple hole. [Aspect 7] The ceramic susceptor according to any one of Aspects 1 to 6, further comprising a first rod connected to the first electrode and extending into the internal space, and a second rod connected to the second electrode and extending into the internal space.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0010] The ceramic susceptor according to the present invention is a ceramic table for supporting a wafer in a semiconductor manufacturing apparatus. Preferably, the ceramic susceptor according to the present invention is a ceramic heater for a semiconductor film forming apparatus. Typical examples of the film forming apparatus include CVD (chemical vapor deposition) apparatuses (for example, thermal CVD apparatuses, plasma CVD apparatuses, photo CVD apparatuses, and MOCVD apparatuses) and PVD (physical vapor deposition) apparatuses, and particularly preferably a plasma CVD apparatus.

[0011] Fig. 1 shows an embodiment of a ceramic susceptor. The ceramic susceptor 10 shown in Fig. 1 includes a disc-shaped ceramic plate 12, a cylindrical ceramic shaft 14, and a thermocouple hole 16. The ceramic plate 12 has a first surface 12a for placing a wafer (not shown) and a second surface 12b facing the first surface 12a. A first electrode 18 (e.g., an RF electrode) is embedded at a depth position near the first surface 12a of the ceramic plate 12, while a second electrode 20 (e.g., a heater electrode) is embedded at a depth position near the second surface 12b of the ceramic plate 12. A ceramic shaft 14 is attached to the second surface 12b of the ceramic plate 12, and the ceramic shaft 14 has an internal space S. The thermocouple hole 16 is a bottomed hole formed in the ceramic plate 12 from a position facing the internal space S of the second surface 12b to a depth position between the first electrode 18 and the second electrode 20. As partially shown in Figs. 2 and 3 with an upside-down view, the thermocouple hole 16 has an R shape with a radius of curvature of 0.10 mm or more at the outer periphery 16a of the bottom (see Fig. 2) or the bottom 16b (see Fig. 3) when viewed in cross-section in a direction perpendicular to the central axis of the thermocouple hole 16, and the diameter of the thermocouple hole 16 is 0.20 mm or more. By configuring the thermocouple hole 16 provided in the ceramic plate 12 to have the above R shape and diameter, the generation of cracks between the hole bottom (i.e., the outer periphery 16a of the bottom and the bottom 16b, particularly the outer periphery 16a of the bottom) and the internal electrodes (i.e., the first electrode 18 and the second electrode 20, particularly the first electrode 18) can be suppressed.

[0012] As described above, when a ceramic heater having a thermocouple hole provided in a ceramic plate is used in a film forming apparatus, cracks may occur between the bottom of the hole and an internal electrode (for example, an RF electrode) during the film forming process. The formation of these cracks is considered to be due to the fact that during the film forming process, the surface of the ceramic plate is exposed to a high temperature (for example, 600°C in the case of plasma CVD) in the film forming chamber, resulting in a temperature distribution and a resulting thermal expansion difference between the high-temperature surface of the ceramic plate and the lower-temperature back surface of the ceramic plate. As a result, stress is excessively concentrated near the bottom of the hole. In this regard, according to the findings of the present inventors, as shown in FIG. 4, when the outer periphery 116a and the bottom 116b of the thermocouple hole 116 in the ceramic plate 112 are angular (when viewed in cross-section in a direction perpendicular to the central axis of the thermocouple hole 116) and have no roundness, it is considered that cracks are likely to be formed due to excessive stress concentration at the angular portion of the bottom of the hole. Therefore, by forming the thermocouple hole 16 to have the above R shape (that is, a rounded shape) and the above diameter, it is possible to suppress excessive stress concentration at a local position of the bottom of the hole (that is, to disperse the stress), and to suppress the occurrence of cracks between the bottom of the hole and the internal electrode.

[0013] The ceramic plate 12 is not particularly limited except for the configuration of the thermocouple hole 16, and may have the same configuration as the ceramic plate employed in a known ceramic heater. The main portion (that is, the ceramic substrate) other than the first electrode 18 and the second electrode 20 of the ceramic plate 12 is preferably made of aluminum nitride from the viewpoints of excellent thermal conductivity, high electrical insulation, and thermal expansion characteristics close to those of silicon.

[0014] The preferred shape of the ceramic plate 12 is a disc shape. However, the planar shape of the disc-shaped ceramic plate 12 does not have to be a perfect circle, and it may be an incomplete circle lacking a part, such as an orientation flat, for example. The size of the ceramic plate 12 may be appropriately determined according to the diameter of the wafer assumed to be used and is not particularly limited. In the case of a circle, the diameter is typically 150 to 450 mm, for example, about 300 mm.

[0015] Protrusions (not shown) may be provided on the first surface 12a of the ceramic plate 12. The protrusions are preferably arranged at equal intervals from each other on the first surface 12a of the ceramic plate 12. The shape of each protrusion is not particularly limited, but a columnar shape is preferred. The diameter of each protrusion is not particularly limited, but is preferably 0.1 to 8 mm, more preferably 0.5 to 5 mm, still more preferably 0.5 to 4 mm, and particularly preferably 0.70 to 2.54 mm. The protrusions are preferably integrally formed with the ceramic plate 12 by embossing or the like. Therefore, like the ceramic plate 12, the protrusions are preferably made of aluminum nitride. The height of the protrusions is not particularly limited, but is preferably 0.001 to 0.1 mm, more preferably 0.005 to 0.08 mm, still more preferably 0.01 to 0.05 mm, and particularly preferably 0.01 to 0.03 mm. The distance between the central axes of adjacent protrusions is preferably 4 to 30 mm, more preferably 5 to 26 mm, still more preferably 7 to 26 mm, and particularly preferably 7 to 15 mm.

[0016] The first electrode 18 is embedded at a depth position near the first surface 12a of the ceramic plate 12. The first electrode 18 can be any electrode according to the function required for the ceramic susceptor 10, but preferably includes an RF electrode. When a high frequency is applied to the RF electrode, film formation by a plasma CVD process becomes possible. In particular, when film formation by a plasma CVD process is performed using an RF electrode in a conventional ceramic plate having a thermocouple hole, cracks tend to occur easily. For this reason, when the first electrode 18 is an RF electrode, the advantages due to the crack suppression effect according to the present invention can be most enjoyed. However, the first electrode 18 is not limited to an RF electrode, and may be other electrodes such as a DC electrode or an ESC electrode. The ESC electrode is an abbreviation for an electrostatic chuck (ESC) electrode and is also referred to as an electrostatic electrode. Further, by applying a high frequency to the ESC electrode, the ESC electrode may be used as an RF electrode.

[0017] The ceramic susceptor 10 preferably further includes a first rod 24 that is connected to the first electrode 18 and extends into the internal space S. By connecting the first rod 24 to an external power source (not shown) such as an RF power source through the internal space S of the ceramic shaft 14, power can be supplied to the first electrode 18.

[0018] The second electrode 20 is embedded at a depth position near the second surface 12b of the ceramic plate 12. The second electrode 20 can also be any electrode according to the function required for the ceramic susceptor 10, but preferably includes a heater electrode. The heater electrode is not particularly limited, and for example, it can be a conductive coil wired in one stroke over the entire surface of the ceramic plate 12. The heater electrode is not limited to a coil, and may be, for example, a ribbon (long and thin thin plate) or a mesh.

[0019] The ceramic susceptor 10 preferably further includes a second rod 26 connected to the second electrode 20 and extending into the internal space S. By connecting the second rod 26 to an external power source (not shown) such as a heater power source through the internal space S of the ceramic shaft 14, power can be supplied to the second electrode 20. When the second electrode 20 is a heater electrode, the second rod 26 is connected as a heater rod to both ends of the heater electrode for power supply. When power is supplied from the heater power source, the heater electrode generates heat and heats the wafer placed on the first surface 12a.

[0020] The ceramic shaft 14 is a cylindrical shaft attached to the second surface 12b of the ceramic plate 12 and may have the same configuration as the ceramic shaft employed in known ceramic heaters. The ceramic shaft 14 includes an internal space S for accommodating the first rod 24 and the second rod 26. The ceramic shaft 14 is preferably made of the same ceramic material as the ceramic plate 12. Therefore, the ceramic shaft 14 is preferably made of aluminum nitride. The upper end surface of the ceramic shaft 14 is preferably joined to the second surface 12b of the ceramic plate 12 by solid-phase bonding or diffusion bonding. The outer diameter of the ceramic shaft 14 is not particularly limited and is, for example, about 40 mm. The inner diameter of the ceramic shaft 14 (the diameter of the internal space S) is also not particularly limited and is, for example, about 36 mm.

[0021] The thermocouple hole 16 is a bottomed hole formed in the ceramic plate 12 from a position facing the internal space S of the second surface 12b to a depth position between the first electrode 18 and the second electrode 20. When the thermocouple hole 16 is viewed in cross section in a direction perpendicular to its central axis, it has an R shape at the outer periphery 16a of the bottom (see FIG. 2) or at the bottom 16b (see FIG. 3). That is, the thermocouple hole 16 may have an R shape formed at the outer periphery of the flat bottom 16b (i.e., the bottom outer periphery 16a) as shown in FIG. 2, or the bottom 16b itself may form an R shape as shown in FIG. 3. In any case, it is desirable that the bottom 16b and the bottom outer periphery 16a of the thermocouple hole 16 do not have an angular shape as shown in FIG. 4. The radius of curvature of the R shape existing at the bottom outer periphery 16a or the bottom 16b of the thermocouple hole 16 is 0.10 mm or more, preferably 0.15 mm to 1.50 mm, more preferably 0.20 to 1.00 mm. By doing so, the generation of cracks between the hole bottom and the internal electrode can be suppressed.

[0022] The diameter of the thermocouple hole 16 is 0.20 mm or more, preferably 0.30 to 3.00 mm, more preferably 0.40 to 2.00 mm. When it is within such a range, while ensuring the size required for the insertion of the thermocouple 22, the generation of cracks can be further suppressed in combination with the radius of curvature of the above R shape.

[0023] The depth of the thermocouple hole 16 is not particularly limited as long as the bottom 16b of the thermocouple hole 16 is located at the depth between the first electrode 18 and the second electrode 20, but is preferably 10.0 to 14.0 mm, more preferably 11.2 to 13.5 mm. The depth of the thermocouple hole 16 at this time is the distance from the second surface 12b to the bottom 16b.

[0024] It is preferable that the distance B from the bottom 16b of the thermocouple hole 16 to the first electrode 18 is longer than the distance A from the first surface 12a to the first electrode 18 (that is, A < B). As shown in FIG. 1, the distance B from the bottom 16b of the thermocouple hole 16 to the first electrode 18 is defined as the separation distance between the bottom 16b and the first electrode 18 (in the thickness direction of the ceramic plate 12). By setting such a positional relationship, the distance between the first electrode 18 and the bottom outer periphery 16a or the bottom 16b is sufficiently separated. As a result, a sufficient insulation distance can be ensured, and arcing can be prevented. Thereby, cracks caused by arcing can be suppressed. That is, even if dielectric breakdown due to arcing occurs between the first electrode 18 and the first surface 12a as a result of applying a voltage to the first electrode 18 (for example, an RF electrode), if an insulation distance exceeding the distance A is ensured as the distance B, the occurrence of dielectric breakdown between the hole bottom and the internal electrode can be more effectively prevented.

[0025] It is preferable that the distance C from the bottom 16b of the thermocouple hole 16 to the second electrode 20 is longer than the distance A from the first surface 12a to the first electrode 18 (that is, A < C). As shown in FIG. 1, the distance C from the bottom 16b of the thermocouple hole 16 to the second electrode 20 is defined as the separation distance between the bottom 16b and the second electrode 20 (in the thickness direction of the ceramic plate 12). By setting such a positional relationship, the distance between the second electrode 20 and the bottom outer periphery 16a or the bottom 16b is sufficiently separated. As a result, a sufficient insulation distance can be ensured, and arcing can be prevented. Thereby, cracks caused by arcing can be suppressed. That is, even if dielectric breakdown due to arcing occurs between the first electrode 18 and the first surface 12a as a result of applying a voltage to the first electrode 18 (for example, an RF electrode), if an insulation distance exceeding the distance A is ensured as the distance C, the occurrence of dielectric breakdown between the hole bottom and the internal electrode can be more effectively prevented.

[0026] It is particularly preferable that distance B is longer than distance A (i.e., A < B), and distance C is longer than distance A (i.e., A < C). By setting such a positional relationship, the generation of cracks between the first electrode 18 and the bottom outer periphery 16a or the bottom 16b, and between the second electrode 20 and the bottom outer periphery 16a or the bottom 16b can be more effectively suppressed.

[0027] The ceramic susceptor 10 may further include a thermocouple 22 inserted into the thermocouple hole 16. In this case, a thermometer (not shown) is connected to the other end of the thermocouple 22. By doing so, the temperature of the bottom 16b of the thermocouple hole 16 can be measured, and thereby the temperature of the wafer placed on the first surface 12a of the ceramic plate 12 can be indirectly measured or estimated.

Example

[0028] The present invention will be further specifically described by the following examples.

[0029] Examples 1 and 2 (1) Fabrication of ceramic plate Y2O3 powder was added to the AlN raw material powder as a sintering aid and mixed by a ball mill to obtain a mixed powder slurry. At this time, Y2O3 was added so as to be 5% by mass based on the whole mixed powder. The obtained mixed powder slurry was granulated by spray drying. Subsequently, a disk-shaped compact was fabricated using the granules of the mixed powder. At this time, the first electrode 18 (RF electrode) and the second electrode 20 (heater electrode) were embedded in the mixed powder and subjected to mechanical pressing to obtain a compact in which these electrodes were embedded. An AlN sintered body was fabricated by hot press sintering this compact. The hot press sintering was carried out under the conditions of the maximum temperature during sintering (sintering temperature): 1850 - 1890 °C, the holding time at the sintering temperature: 2 hours, the press pressure: 20 MPa, and the atmosphere: nitrogen atmosphere. The obtained AlN sintered body was processed by rotary surface grinding to obtain a ceramic plate. A rectangular parallelepiped test piece (length 14 mm, width: 14 mm, thickness: 18 mm) was cut out from the obtained ceramic plate, and drilling was performed to form a thermocouple hole 16, 116 having an R shape (Example 1) with a radius of curvature of about 0.5 mm as shown in FIG. 2 for the outer periphery 16a of the bottom, or an angular shape (Example 2) as shown in FIG. 4 (θ = 166°) for the bottom 116b and the outer periphery 116a of the bottom. Thus, three test pieces of the aluminum nitride ceramic plate 12 in which the first electrode 18 and the second electrode 20 were embedded were fabricated for each example (hereinafter referred to as test pieces No. 1, 2, and 3).

[0030] In addition, the distances A, B, and C in the fabricated test pieces of the ceramic plate 12 were as follows. · Distance A from the first surface 12a to the first electrode 18: 0.9 mm · Distance B from the bottom 16b of the thermocouple hole 16 to the first electrode 18: 2.1 mm · Distance C from the bottom 16b of the thermocouple hole 16 to the second electrode 20: 6.4 mm

[0031] (2) Thermal shock test As shown schematically in FIG. 5, a test piece of the ceramic plate 12 was placed on a heater 30 maintained at 550° C. and heated. At this time, the first surface 12a, which is the side where the thermocouple hole 16 of the ceramic plate 12 is not formed, was arranged to be in contact with the heater 30. By immersing the thus heated test piece at about 440° C. into the water (room temperature) in the water tank 32 from the first surface 12a, a temperature difference was generated in the thickness direction of the test piece. At this time, the temperature of the test piece just before being put into the water was about 440° C., and the difference between the water temperature and the test piece temperature was about 410° C. The test piece thus subjected to the thermal shock was inspected with an X-ray CT apparatus to obtain an X-ray CT image, and the presence or absence of crack generation was confirmed. FIG. 6 shows the X-ray CT image of the test piece No. 1 of Example 1, and FIG. 7 shows the X-ray CT image of the test piece No. 1 of Example 2 (comparison). Also, for Example 1, the X-ray CT image was subjected to image analysis, and as the R shape of the outer periphery of the bottom, the R on the left side of the cross section L and the R on the right side of the cross section R (see FIG. 6) were measured for the radius of curvature respectively. The results were as shown in Table 1.

[0032]

Table 1

[0033] As shown in Table 1, in Example 2 (comparative example) having no R shape, the crack generation rate was 33%, and in the test piece No. 1 of Example 2 as shown in FIG. 7, a crack occurred between the outer periphery of the bottom of the thermocouple hole (see “Corner” in the figure) and the internal electrode. On the other hand, in Example 1 (example) having an R shape with a radius of curvature of 0.10 mm or more on the outer periphery of the bottom and forming a thermocouple hole having a diameter of 0.20 mm or more, the crack generation rate was 0%, and the generation of cracks between the hole bottom and the internal electrode was suppressed when subjected to thermal shock.

Claims

1. A disc-shaped ceramic plate having a first surface for placing a wafer and a second surface facing the first surface, with a first electrode embedded at a depth position near the first surface and a second electrode embedded at a depth position near the second surface, A cylindrical ceramic shaft attached to the second surface of the ceramic plate and having an internal space, In the ceramic plate, a thermocouple hole formed from a position facing the internal space of the second surface to a depth position between the first electrode and the second electrode, A ceramic susceptor comprising: When the thermocouple hole is viewed in cross-section in a direction perpendicular to the central axis of the thermocouple hole, it has an R shape with a radius of curvature of 0.10 mm or more at the outer periphery or the bottom of the bottom, and the diameter of the thermocouple hole is 0.20 mm or more, The distance B from the bottom of the thermocouple hole to the first electrode is longer than the distance A from the first surface to the first electrode, and the distance C from the bottom of the thermocouple hole to the second electrode is longer than the distance A, A ceramic susceptor, wherein the first electrode includes an RF electrode and the second electrode includes a heater electrode.

2. The ceramic susceptor according to claim 1, further comprising a thermocouple inserted into the thermocouple hole.

3. The ceramic susceptor according to claim 1 or 2, further comprising a first rod connected to the first electrode and extending into the internal space, and a second rod connected to the second electrode and extending into the internal space.

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