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

Ceramic Susceptor

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

[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. The ceramic plate typically has a ceramic base made of aluminum nitride (AlN) or other material with excellent heat and corrosion resistance, with internal electrodes embedded therein, such as a heater electrode, an RF electrode, and an electrostatic chuck (ESC) electrode.

[0003] Known ceramic heaters include ceramic heaters with a ceramic plate provided with a bottomed hole for temperature measurement. For example, Patent Document 1 (JP 2010-42967 A) discloses a ceramic member in which a ceramic sintered body having a thermal expansion coefficient similar to that of yttria and the yttria sintered body are sintered together with a conductive member sandwiched therebetween. It proposes drilling an opening for measuring the temperature of a substrate in the ceramic sintered body, and measuring the temperature of the substrate through the opening with a temperature measuring device via the yttria sintered body. This configuration is said to prevent deterioration of the temperature measuring device because the temperature measuring device is isolated from the process gas atmosphere by the yttria sintered body. Furthermore, Patent Document 2 (JP 2001-148371 A) discloses an electrostatic chucking device including a dielectric body in which a chucking electrode and a heater are embedded, and a temperature measuring device for measuring the temperature of a processing object on the dielectric body and the temperature of the dielectric body. This dielectric has a bottomed hole that exposes the dielectric at its bottom, and the temperature of the dielectric can be measured by measuring the amount of infrared light emitted from the dielectric using an infrared receiving unit attached to an optical path inserted into the bottomed hole.

[0004] JP 2010-42967 A JP 2001-148371 A

[0005] As mentioned above, ceramic heaters are known that have bottomed holes (hereinafter referred to as thermocouple holes) in the ceramic plate for temperature measurement. However, when such ceramic heaters are used in film deposition equipment, cracks can occur between the bottom of the holes and the internal electrode (e.g., RF electrode) during the film deposition process. The formation of these cracks is thought to be due to the fact that the surface of the ceramic plate is exposed to high temperatures (e.g., 600°C in the case of plasma CVD) in the film deposition chamber during the film deposition process, which creates 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, resulting in excessive stress concentration near the bottom of the holes.

[0006] The inventors have now discovered that by configuring a thermocouple hole in a ceramic plate to have an R-shape with a curvature radius of 0.10 mm or more on the bottom periphery or at the bottom, and to have a diameter of 0.20 mm or more, it is possible to suppress the occurrence of cracks between the bottom of the hole and the internal electrode.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a ceramic susceptor that has an internal electrode and a thermocouple hole in a ceramic plate, yet is capable of suppressing the occurrence of cracks between the hole bottom and the internal electrode.

[0008] The present invention provides the following aspects: [Aspect 1] A ceramic susceptor comprising: a disc-shaped ceramic plate having a first surface for mounting a wafer and a second surface opposite the first surface, with a first electrode embedded at a depth closer to the first surface and a second electrode embedded at a depth closer 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 formed in the ceramic plate from a position facing the internal space on the second surface to a depth between the first and second electrodes, wherein the thermocouple hole has an R-shape on its bottom periphery or bottom portion with a curvature radius of 0.10 mm or more when viewed in cross section perpendicular to the central axis of the thermocouple hole, and the thermocouple hole has a diameter of 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 a 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 comprises an RF electrode and the second electrode comprises a heater electrode. [Aspect 6] The ceramic susceptor according to any one of Aspects 1 to 5, further comprising a thermocouple inserted in 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.

[0009] Fig. 1 is a schematic cross-sectional view showing an example of a ceramic susceptor according to the present invention. Fig. 2 is a schematic cross-sectional view showing an example of a thermocouple hole in a ceramic susceptor according to the present invention. Fig. 3 is a schematic cross-sectional view showing another example of a thermocouple hole in a ceramic susceptor according to the present invention. Fig. 4 is a process diagram showing the procedure of a thermal shock test. Fig. 5 is an X-ray CT image of a thermocouple hole in a test piece produced in Example 1. Fig. 6 is an X-ray CT image of a thermocouple hole in a test piece produced in Example 2 (comparison).

[0010] The ceramic susceptor according to the present invention is a ceramic platform 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 formation apparatus. Typical examples of film formation apparatuses include CVD (chemical vapor deposition) apparatuses (e.g., thermal CVD apparatuses, plasma CVD apparatuses, photo CVD apparatuses, and MOCVD apparatuses) and PVD (physical vapor deposition) apparatuses, with plasma CVD apparatuses being particularly preferred.

[0011] FIG. 1 shows one embodiment of a ceramic susceptor. The ceramic susceptor 10 shown in FIG. 1 includes a disk-shaped ceramic plate 12, a cylindrical ceramic shaft 14, and a thermocouple hole 16. The ceramic plate 12 has a first surface 12a on which a wafer (not shown) is placed and a second surface 12b opposite the first surface 12a. A first electrode 18 (e.g., an RF electrode) is embedded in the ceramic plate 12 at a depth closer to the first surface 12a, while a second electrode 20 (e.g., a heater electrode) is embedded in the ceramic plate 12 at a depth closer to the second surface 12b. 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 blind hole formed in the ceramic plate 12 from a position facing the internal space S on the second surface 12b to a depth between the first electrode 18 and the second electrode 20. 2 and 3, the thermocouple hole 16 has an R-shaped shape on the bottom periphery 16a (see FIG. 2) or the bottom 16b (see FIG. 3) with a radius of curvature of 0.10 mm or more when viewed in cross section 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-shaped shape and diameter, it is possible to suppress the occurrence of cracks between the hole bottom (i.e., the bottom periphery 16a and the bottom 16b, particularly the bottom periphery 16a) and the internal electrode (i.e., the first electrode 18 and the second electrode 20, particularly the first electrode 18).

[0012] As mentioned above, when a ceramic heater with thermocouple holes in a ceramic plate is used in a film deposition apparatus, cracks may occur between the bottom of the holes and an internal electrode (e.g., an RF electrode) during the film deposition process. The formation of these cracks is believed to be due to the temperature distribution and resulting thermal expansion difference between the high-temperature ceramic plate surface and the lower-temperature ceramic plate back surface, which occurs when the surface of the ceramic plate is exposed to high temperatures (e.g., 600°C in the case of plasma CVD) in the film deposition chamber during the film deposition process. This leads to excessive stress concentration near the bottom of the holes. In this regard, the inventors have found that, as shown in FIG. 4 , if the bottom periphery 116a and bottom 116b of the thermocouple holes 116 in the ceramic plate 112 are angular and not rounded (when viewed in cross section perpendicular to the central axis of the thermocouple holes 116), excessive stress concentration at the angular portions of the hole bottoms is likely to cause cracks. Therefore, by forming the thermocouple hole 16 to have the above-mentioned R-shape (i.e., rounded shape) and diameter, it is possible to suppress excessive concentration of stress at a local position at the bottom of the hole (i.e., to distribute the stress), thereby suppressing 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 holes 16, and may have the same configuration as ceramic plates used in known ceramic heaters. The main portion of the ceramic plate 12 other than the first electrode 18 and the second electrode 20 (i.e., the ceramic substrate) is preferably made of aluminum nitride from the viewpoints of excellent thermal conductivity, high electrical insulation, and thermal expansion characteristics similar to those of silicon.

[0014] The ceramic plate 12 is preferably disk-shaped. However, the planar shape of the disk-shaped ceramic plate 12 does not need to be a perfect circle, and may be an incomplete circle with a portion missing, such as an orientation flat. The size of the ceramic plate 12 may be determined appropriately depending on the diameter of the wafer 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] The first surface 12a of the ceramic plate 12 may be provided with protrusions (not shown). The protrusions are preferably arranged at equal intervals on the first surface 12a of the ceramic plate 12. The shape of each protrusion is not particularly limited, but is preferably cylindrical. The diameter of each protrusion is not particularly limited, but is preferably 0.1 to 8 mm, more preferably 0.5 to 5 mm, even 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, even 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, even more preferably 7 to 26 mm, and particularly preferably 7 to 15 mm.

[0016] A first electrode 18 is embedded in the ceramic plate 12 at a depth near the first surface 12a. The first electrode 18 can be any electrode depending on the function required of the ceramic susceptor 10, but preferably includes an RF electrode. The RF electrode enables film deposition using a plasma CVD process when high frequency is applied. In particular, conventional ceramic plates with thermocouple holes tend to be prone to cracking when using an RF electrode to deposit films using a plasma CVD process. Therefore, the advantages of the crack suppression effect of the present invention can be maximized when the first electrode 18 is an RF electrode. 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. An ESC electrode is an abbreviation for an electrostatic chuck (ESC) electrode, also known as an electrostatic electrode. Furthermore, the ESC electrode may be used as an RF electrode by applying high frequency to the ESC electrode.

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

[0018] A second electrode 20 is embedded in the ceramic plate 12 at a depth closer to the second surface 12b. The second electrode 20 may be any electrode depending on the function required of the ceramic susceptor 10, but preferably includes a heater electrode. The heater electrode is not particularly limited, but may be, for example, a conductive coil wired in a single stroke across the entire surface of the ceramic plate 12. The heater electrode is not limited to a coil, and may be, for example, a ribbon (a long, 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. The second rod 26 is connected to an external power source (not shown) such as a heater power source through the internal space S of the ceramic shaft 14, thereby enabling power to be supplied to the second electrode 20. When the second electrode 20 is a heater electrode, the second rods 26 are connected as heater rods to both ends of the heater electrode for power supply, and when power is supplied from the heater power source, the heater electrode generates heat to heat the wafer placed on the first surface 12 a.

[0020] The ceramic shaft 14 is a cylindrical shaft attached to the second surface 12b of the ceramic plate 12 and may have a configuration similar to that of ceramic shafts used in known ceramic heaters. The ceramic shaft 14 has 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-state bonding or diffusion bonding. The outer diameter of the ceramic shaft 14 is not particularly limited and may be, for example, approximately 40 mm. The inner diameter of the ceramic shaft 14 (the diameter of the internal space S) is also not particularly limited and may be, for example, approximately 36 mm.

[0021] The thermocouple hole 16 is a blind hole formed in the ceramic plate 12 from a position facing the internal space S on the second surface 12b to a depth position between the first electrode 18 and the second electrode 20. When viewed in cross section perpendicular to its central axis, the thermocouple hole 16 has an R-shaped bottom periphery 16a (see FIG. 2) or bottom 16b (see FIG. 3). That is, the thermocouple hole 16 may have an R-shaped portion formed on the periphery of the flat bottom 16b (i.e., bottom periphery 16a) as shown in FIG. 2, or the bottom 16b itself may have an R-shaped portion as shown in FIG. 3. In either case, it is desirable that the bottom 16b and bottom 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 present on 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, and more preferably 0.20 to 1.00 mm, which can suppress the occurrence of cracks between the hole bottom and the internal electrode.

[0022] The diameter of the thermocouple hole 16 is 0.20 mm or more, preferably 0.30 to 3.00 mm, and more preferably 0.40 to 2.00 mm. Within this range, the size necessary for inserting the thermocouple 22 is ensured, and in combination with the radius of curvature of the R-shape, the occurrence of cracks can be further suppressed.

[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 a depth between the first electrode 18 and the second electrode 20, but is preferably 10.0 to 14.0 mm, and more preferably 11.2 to 13.5 mm. In this case, the depth of the thermocouple hole 16 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 be longer than the distance A from the first surface 12a to the first electrode 18 (i.e., 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 (in the thickness direction of the ceramic plate 12) between the bottom 16b and the first electrode 18. This positional relationship ensures a sufficient distance between the first electrode 18 and the bottom periphery 16a or the bottom 16b. As a result, a sufficient insulation distance can be ensured, preventing arcing. This also suppresses cracks caused by arcing. In other words, even if a 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 (e.g., an RF electrode), ensuring that the insulation distance B exceeds the distance A can more effectively prevent breakdown between the hole bottom and the internal electrode.

[0025] It is preferable that the distance C from the bottom 16b of the thermocouple hole 16 to the second electrode 20 be longer than the distance A from the first surface 12a to the first electrode 18 (i.e., 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 (in the thickness direction of the ceramic plate 12) between the bottom 16b and the second electrode 20. This positional relationship ensures a sufficient distance between the second electrode 20 and the bottom periphery 16a or the bottom 16b. As a result, a sufficient insulation distance can be ensured, preventing arcing. This also suppresses cracks caused by arcing. In other words, even if a 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 (e.g., an RF electrode), ensuring that the insulation distance C exceeds the distance A can more effectively prevent breakdown between the hole bottom and the internal electrode.

[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 adopting such a positional relationship, it is possible to further suppress the occurrence of cracks between first electrode 18 and bottom periphery 16a or bottom 16b, and between second electrode 20 and bottom periphery 16a or bottom 16b.

[0027] The ceramic susceptor 10 may further include a thermocouple 22 inserted into the thermocouple hole 16. In this case, a temperature measuring device (not shown) is connected to the other end of the thermocouple 22. In this way, 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.

[0028] The present invention is further illustrated by the following examples.

[0029] Examples 1 and 2 (1) Preparation of ceramic plates AlN raw material powder was mixed with Y as a sintering aid. ２ O ３ The powder was added and mixed in a ball mill to obtain a mixed powder slurry. ２ O ３was added to the total mixed powder at 5 mass%. The resulting mixed powder slurry was granulated by spray drying. Subsequently, a disk-shaped compact was produced using the mixed powder granules. At this time, a first electrode 18 (RF electrode) and a second electrode 20 (heater electrode) were embedded in the mixed powder and mechanically pressed to obtain a compact with these electrodes embedded. This compact was then hot-press fired to produce an AlN sintered body. The hot-press firing was performed under the following conditions: maximum firing temperature (firing temperature): 1850-1890°C, holding time at the firing temperature: 2 hours, pressing pressure: 20 MPa, and atmosphere: nitrogen atmosphere. The resulting AlN sintered body was processed by rotary surface grinding to produce a ceramic plate. Rectangular parallelepiped test pieces (14 mm long, 14 mm wide, 18 mm thick) were cut out from the obtained ceramic plates and drilled to form thermocouple holes 16, 116 having a rounded bottom periphery 16a with a radius of curvature of approximately 0.5 mm as shown in Figure 2 (Example 1), or a rectangular bottom 116b and bottom periphery 116a (θ = 166°) as shown in Figure 4 (Example 2). In this way, three test pieces of aluminum nitride ceramic plates 12 with embedded first electrodes 18 and second electrodes 20 were prepared for each example (hereinafter referred to as Test Pieces No. 1, 2, and 3).

[0030] The distances A, B, and C in the prepared ceramic plate 12 test piece 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, the ceramic plate 12 test specimen was placed on a heater 30 maintained at 550°C and heated. The first surface 12a of the ceramic plate 12, which was the side without the thermocouple holes 16, was placed in contact with the heater 30. The test specimen, heated to approximately 440°C, was then immersed from the first surface 12a into water (room temperature) in a water tank 32, creating a temperature difference across the thickness of the test specimen. The temperature of the test specimen immediately before immersion was approximately 440°C, and the difference between the water temperature and the test specimen temperature was approximately 410°C. The thermally shocked test specimens were then inspected with an X-ray CT scanner to obtain X-ray CT images and confirm the presence or absence of cracks. Figure 6 shows an X-ray CT image of Test Specimen No. 1 of Example 1, and Figure 7 shows an X-ray CT image of Test Specimen No. 1 of Example 2 (comparison). In addition, for Example 1, the X-ray CT image was analyzed to determine the R shape of the bottom periphery, and the R on the left side of the cross section. Ｌ and cross section right side R Ｒ The curvature radius of each of the surfaces (see FIG. 6) was measured. The results are shown in Table 1.

[0032]

[0033] As shown in Table 1, the crack occurrence rate was 33% in Example 2 (Comparative Example) which did not have an R shape, and as shown in Figure 7, in Test Piece No. 1 of Example 2, cracks occurred between the outer periphery of the bottom of the thermocouple hole (see "Corner" in the figure) and the internal electrode. In contrast, in Example 1 (Example) which had an R shape with a curvature radius of 0.10 mm or more on the outer periphery of the bottom and in which a thermocouple hole with a diameter of 0.20 mm or more was formed, the crack occurrence rate was 0%, and the occurrence of cracks between the bottom of the hole and the internal electrode was suppressed when a thermal shock was applied.

Claims

1. a circular ceramic plate having a first surface on which a wafer is placed and a second surface opposite to the first surface, a first electrode embedded in a depth position near the first surface and a second electrode embedded in a depth position near the second surface; a cylindrical ceramic shaft attached to a second surface of the ceramic plate and having an internal space; a thermocouple hole formed in the ceramic plate from a position facing the internal space on the second surface to a depth position between the first electrode and the second electrode; A ceramic susceptor comprising: The thermocouple hole has an R shape with a curvature radius of 0.10 mm or more on the bottom outer periphery or 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, a distance B from a bottom of the thermocouple hole to the first electrode is longer than a distance A from the first surface to the first electrode, and a distance C from the bottom of the thermocouple hole to the second electrode is longer than the distance A; The ceramic susceptor, wherein the first electrode comprises an RF electrode and the second electrode comprises a heater electrode.

2. The ceramic susceptor of claim 1 further comprising a thermocouple inserted into said thermocouple hole.

3. 3. The ceramic susceptor of claim 1, further comprising a first rod connected to the first electrode and extending into the interior space, and a second rod connected to the second electrode and extending into the interior space.