Composite sintered body and electrostatic chuck

Abstract

Provided is a composite sintered body which has excellent thermal conductivity and can be suitably applied to an electrostatic chuck using JR force. A composite sintered body according to one embodiment of the present invention comprises a plurality of crystal grains and grain boundaries. Each of the plurality of crystal grains contains an aluminum nitride crystal phase. The grain boundaries are each positioned between crystal grains adjacent to each other among the plurality of crystal grains. The grain boundaries each contain an yttrium aluminate crystal phase. The average particle diameter of the plurality of crystal grains is 3.0-8.0 μm. The c-axis length of the aluminum nitride crystal phase is at most 4.9815 Å.

Description

Composite sintered body and electrostatic chuck

[0001] This invention relates to a composite sintered body and an electrostatic chuck.

[0002] Conventionally, in the manufacturing of semiconductor devices such as integrated circuits, it is known that various processes are performed on silicon wafers supported by susceptors. Typically, susceptors comprise a ceramic substrate containing aluminum nitride. Adding rare earth element oxides to such ceramic substrates has been investigated to improve the thermal conductivity of the ceramic substrate. For example, an AlN ceramic substrate containing a yttrium aluminate phase as a crystalline phase has been proposed (see Patent Document 1).

[0003] Patent No. 6393006

[0004] In some cases, electrodes are provided on the ceramic substrate of such a susceptor to create an electrostatic chuck capable of adsorbing silicon wafers. Examples of adsorption principles for electrostatic chucks include the Coulomb force and the Johnson-Rabec force (hereinafter referred to as the JR force). In an electrostatic chuck utilizing the Coulomb force (hereinafter referred to as a Coulomb-type electrostatic chuck), a voltage is applied to the electrodes to charge them to either positive or negative, and the dielectric layer of the electrostatic chuck is polarized to adsorb the silicon wafer. In an electrostatic chuck utilizing the JR force (hereinafter referred to as a JR-type electrostatic chuck), when a voltage is applied to the electrodes, a minute leakage current is generated between the silicon wafer and the electrodes to adsorb the silicon wafer. In recent years, the miniaturization and / or high integration of semiconductor devices have progressed, and in the manufacturing of semiconductor devices, silicon wafers are processed in various temperature ranges. Electrostatic chucks are sometimes required to stably adsorb silicon wafers in temperature ranges of, for example, 250°C or higher. Since the volume resistivity of aluminum nitride decreases with increasing temperature, using a Coulomb-type electrostatic chuck in the temperature range above 250°C may result in the inability to stably generate the Coulomb force. Therefore, in the temperature range above 250°C, JR-type electrostatic chucks are typically used. However, when an AlN ceramic substrate as described in Patent Document 1 is provided with electrodes to form a JR-type electrostatic chuck, it may become difficult to generate an appropriate leakage current between the silicon wafer and the electrodes in certain temperature ranges, potentially resulting in the inability to stably generate the JR force. The main objective of the present invention is to provide a composite sintered body and an electrostatic chuck that have excellent thermal conductivity and are suitably applicable to electrostatic chucks utilizing the JR force.

[0005] [1] A composite sintered body according to one embodiment of the present invention comprises a plurality of crystal grains and grain boundaries. Each of the plurality of crystal grains contains an aluminum nitride crystal phase. The grain boundaries are located between adjacent crystal grains among the plurality of crystal grains. The grain boundaries contain a yttrium aluminate crystal phase. The average grain size of the plurality of crystal grains is 3.0 μm to 8.0 μm. [2] In the composite sintered body described in [1] above, the c-axis length of the aluminum nitride crystal phase may be 4.9815 Å or less. [3] In the composite sintered body described in [1] or [2] above, the volume resistivity measured by applying a voltage of +500 V at 300°C may be 0.5 to 2.0 relative to the volume resistivity measured by applying a voltage of -500 V at 300°C. [4] An electrostatic chuck according to another aspect of the present invention comprises a ceramic substrate and a conductor. The ceramic substrate contains the composite sintered body described in any of [1] to [3] above. The conductor is provided within the ceramic substrate. [5] In the electrostatic chuck described in [4] above, the conductor may have a mesh shape. In this case, the conductor comprises a plurality of linear portions. The plurality of linear portions are spaced apart from each other in a first direction intersecting the thickness direction of the ceramic substrate in a cross-section obtained by cutting the electrostatic chuck in the thickness direction of the ceramic substrate. When a first measurement line passing through the center of the linear portion in the first direction and a second measurement line extending in a second direction perpendicular to the first direction and passing through the center of the linear portion are line-analyzed by an electron beam microanalyzer in the cross-section of the electrostatic chuck, the average value of the Y intensity in the linear portion and the first adjacent portion adjacent in the first direction may be smaller than the average value of the Y intensity in the linear portion and the second adjacent portion adjacent in the second direction. [6] In the electrostatic chuck described in [5] above, the conductor may contain molybdenum.

[0006] According to embodiments of the present invention, a composite sintered body having excellent thermal conductivity and suitable for use in electrostatic chucks utilizing JR force can be realized.

[0007] Figure 1 is a schematic diagram of a composite sintered body according to one embodiment of the present invention. Figure 2 is a schematic cross-sectional view of an electrostatic chuck including the composite sintered body of Figure 1. Figure 3 is a mapping image of aluminum (Al) in the composite sintered body of the example. Figure 4 is a mapping image of nitrogen (N) in the composite sintered body of the example. Figure 5 is a mapping image of oxygen (Y) in the composite sintered body of the example. Figure 6 is a mapping image of oxygen (O) in the composite sintered body of the example. Figure 7 is a graph showing the correlation between temperature and volume resistivity in the composite sintered bodies of the example and comparative example. Figure 8 is a graph showing the correlation between temperature and thermal conductivity in the composite sintered bodies of the example and comparative example. Figure 9 is the characteristic X-ray spectrum of Y on the first measurement line in the electrostatic chuck of the example. Figure 10 is the characteristic X-ray spectrum of Y on the second measurement line in the electrostatic chuck of the example.

[0008] The embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In addition, the drawings may be schematic in terms of the width, thickness, shape, etc. of each part compared to the embodiments in order to make the explanation clearer, but these are merely examples and do not limit the interpretation of the present invention.

[0009] A. Schematic diagram 1 of the composite sintered body is a schematic diagram of the composite sintered body according to one embodiment of the present invention. In one embodiment, the composite sintered body 10 comprises a plurality of crystal grains 11 and grain boundaries 12. The composite sintered body 10 typically has a polycrystalline structure containing a plurality of crystal grains 11. Among the plurality of crystal grains 11, adjacent crystal grains 11 are bonded to each other, and grain boundaries 12 are formed between them. Each of the plurality of crystal grains 11 contains an aluminum nitride (AlN) crystal phase. The average grain size of the plurality of crystal grains 11 is 3.0 μm to 8.0 μm. The grain boundaries 12 are located between adjacent crystal grains 11. The grain boundaries 12 are continuous in a three-dimensional network. The grain boundaries 12 contain a yttrium aluminate crystal phase 13. In the temperature range of 250°C to 350°C, the volume resistivity of the AlN crystal phase is smaller than that of the yttrium aluminate crystal phase, and the volume resistivity of the crystal grains 11 containing the AlN crystal phase is smaller than that of the grain boundaries 12 containing the yttrium aluminate crystal phase. Therefore, in the temperature range of 250°C to 350°C, multiple crystal grains 11 can function as conductive paths. The inventors diligently studied how to appropriately control the volume resistivity in the temperature range of 250°C to 350°C in a composite sintered body containing an AlN crystal phase and a yttrium aluminate crystal phase. As a result, they found that by adjusting the average grain size of the crystal grains within a predetermined range, the volume resistivity of the composite sintered body in the temperature range of 250°C to 350°C can be adjusted to a range suitable for a JR-type electrostatic chuck. More specifically, in a composite sintered body, if the average grain size of the crystal grains is 3.0 μm to 8.0 μm (especially 4.0 μm or more), the proportion of grain boundaries can be reduced, and the proportion of crystal grains can be improved. As a result, the crystal grains can function as appropriate conductive paths for a JR-type electrostatic chuck. Furthermore, since the composite sintered body contains a yttrium aluminate crystal phase, the thermal conductivity of the composite sintered body can be improved. As a result, a composite sintered body with excellent thermal conductivity that can be suitably applied to an electrostatic chuck utilizing JR force can be realized. In such a composite sintered body 10, the c-axis length of the AlN crystal phase is typically 4.9815 Å or less.When the c-axis length of the AlN crystal phase contained in the crystal grains is 4.9815 Å or less, the volume resistivity of the crystal grains can be stably reduced to be lower than the volume resistivity of the grain boundaries in the temperature range of 250°C to 350°C. As a result, the crystal grains can stably function as appropriate conductive paths in a JR-type electrostatic chuck. Furthermore, in a composite sintered body, when the c-axis length of the AlN crystal phase is 4.9815 Å or less, the volume resistivity of the composite sintered body can be sufficiently reduced, and the volume resistivity of the composite sintered body in the temperature range of 250°C to 350°C can be stably adjusted to a desired range.

[0010] In the composite sintered body 10, the volume resistivity measured by applying a voltage of +500V at 300°C (hereinafter sometimes referred to as the volume resistivity of the composite sintered body at 300°C (+500V)) is, for example, 1.0 × 10⁻¹⁰ ９ The density is Ω·cm or greater, preferably 1.0 × 10⁻⁶. １０ The density is Ω·cm or greater, and more preferably 1.0 × 10⁻⁶. １１ It is Ω·cm or greater. If the volume resistivity (+500V) of the composite sintered body at 300°C is above this lower limit, it is possible to suppress the generation of excessive leakage current in the JR type electrostatic chuck to which the composite sintered body is applied, and to suppress damage to the silicon wafer due to leakage current. On the other hand, the volume resistivity (+500V) of the composite sintered body at 300°C is, for example, 1.0 × 10⁻⁶. １２ It is less than or equal to Ω·cm, preferably 5.0 × 10⁻⁶. １１ It is less than or equal to Ω·cm. When the volume resistivity of the composite sintered body at 300°C is below this upper limit, an appropriate leakage current can be generated between the silicon wafer and the electrode in a JR-type electrostatic chuck to which the composite sintered body is applied, and the JR force can be stably expressed.

[0011] The volume resistivity (+500V) of the composite sintered body at 300°C is, for example, 0.5 to 2.0 compared to the volume resistivity measured by applying a voltage of -500V at 300°C (hereinafter sometimes referred to as the volume resistivity (-500V) of the composite sintered body at 300°C). When the polarity difference of the volume resistivity of the composite sintered body (volume resistivity (+500V) of the composite sintered body at 300°C / volume resistivity (-500V) of the composite sintered body at 300°C) is within this range, the JR type electrostatic chuck to which the composite sintered body is applied can stably exhibit JR force regardless of the polarity of the applied voltage. The range of the volume resistivity (-500V) of the composite sintered body at 300°C is, for example, the same as the volume resistivity (+500V) of the composite sintered body at 300°C described above.

[0012] The thermal conductivity of the composite sintered body 10 at 300°C is, for example, 50 W / m·K or higher, preferably 60 W / m·K or higher. On the other hand, the thermal conductivity of the composite sintered body 10 at 300°C is, for example, 100 W / m·K or lower, preferably 80 W / m·K or lower. The thermal conductivity of the composite sintered body is measured, for example, in accordance with the flash method specified in JIS-R1611:2010.

[0013] The average grain size of the multiple crystal grains 11 is preferably 4.0 μm to 7.0 μm. When the average grain size of the crystal grains is within this range, the crystal grains and grain boundaries can be balanced in the composite sintered body, and the volume resistivity of the composite sintered body at 300°C can be stably adjusted to the above range.

[0014] The standard deviation of the average grain size of the multiple crystal grains 11 is, for example, 1.0 μm or less, preferably 0.5 μm or less, and more preferably 0.3 μm or less. On the other hand, the lower limit of the standard deviation of the average grain size of the multiple crystal grains 11 is typically 0 μm. When the standard deviation of the average grain size of the crystal grains is within this range, the volume resistivity of the composite sintered body at 300°C can be stably adjusted within the above range.

[0015] The c-axis length of the AlN crystal phase contained in the crystal grain 11 is preferably 4.9810 Å or less, and more preferably 4.98080 Å or less. When the c-axis length of the AlN crystal phase is below this upper limit, the crystal grain can function as a suitable conductive path for the JR type electrostatic chuck in the temperature range of 250°C to 350°C. On the other hand, the c-axis length of the AlN crystal phase contained in the crystal grain 11 is, for example, 4.97900 Å or more, and preferably 4.98000 Å or more. The crystal lattice is measured, for example, by XRD (X-ray diffraction).

[0016] B. Details of the composite sintered body Next, the details of the composite sintered body 10 will be described with reference to Figure 1. As described above, the composite sintered body 10 contains an AlN crystalline phase and a yttrium aluminate crystalline phase.

[0017] The content of the AlN phase in the composite sintered body 10 is, for example, 90.0% by weight or more, preferably 93.0% by weight or more. On the other hand, the content of the AlN phase in the composite sintered body 10 is, for example, 99.0% by weight or less, preferably 97.0% by weight or less, and more preferably 96.0% by weight or less. The content of the yttrium aluminate phase in the composite sintered body 10 is, for example, 1.0% by weight or more, preferably 3.0% by weight or more, and more preferably 4.0% by weight or more. On the other hand, the content of the yttrium aluminate phase in the composite sintered body 10 is, for example, 10% by weight or less, and preferably 7.0% by weight or less. The content of the crystalline phase in the composite sintered body is measured, for example, by XRD (X-ray diffraction) in accordance with JIS-Z2201 and JIS-K0114.

[0018] In one embodiment, the composite sintered body 10 substantially contains no other crystalline phases other than the AlN crystalline phase and the yttrium aluminate crystalline phase. With such a configuration, the volume resistivity of the composite sintered body at 300°C can be stably adjusted within the above range. The content of other crystalline phases in the composite sintered body 10 is, for example, 0.3% by weight or less, preferably 0.2% by weight or less, and more preferably 0.1% by weight or less. On the other hand, the lower limit of the content of other crystalline phases in the composite sintered body 10 is typically 0% by weight.

[0019] B-1. Crystal grains The AlN crystal phase is located within the crystal grains 11. The AlN crystal phase typically has a wurtzite structure (hexagonal crystal system). The AlN crystal phase may or may not contain dissolved oxygen. In one embodiment, the AlN crystal phase contains dissolved oxygen. When oxygen is dissolved in the AlN crystal phase, the AlN crystal lattice can be suitably adjusted.

[0020] The a-axis length in the AlN crystal phase is, for example, between 3.11190 Å and 3.11220 Å. The lattice volume in the AlN crystal phase is, for example, 41.7650 Å. ３ ~41.7750 Å ３ That is the case.

[0021] In the AlN crystalline phase, the ratio of the c-axis length to the a-axis length (c / a) is, for example, 1.59980 to 1.60080. When the AlN crystalline phase has such a c / a ratio, the volume resistivity of the composite sintered body in the temperature range of 250°C to 350°C can be adjusted to a range suitable for JR-type electrostatic chucks.

[0022] B-2. The grain boundary yttrium aluminate crystal phase 13 is located at the grain boundary 12. In one embodiment, at least a part of the yttrium aluminate crystal phase 13 exists in an isolated state at the grain boundary 12. At the grain boundary 12, all of the yttrium aluminate crystal phases 13 may be isolated, or a part of the yttrium aluminate crystal phase 13 may be isolated and the remainder of the yttrium aluminate crystal phase 13 may be continuous. In one embodiment, at least a part of the yttrium aluminate crystal phase 13 exists isolated at the triple point of the grain boundary 12. According to such a configuration, the thermal conductivity of the composite sintered body can be stably adjusted within the above-described range. Note that the triple point of the grain boundary 12 means a portion of the grain boundary 12 surrounded by three or more crystal grains 11.

[0023] In the cross section of the composite sintered body 10, the isolated yttrium aluminate crystal phase 13 has an arbitrary appropriate shape. Examples of the cross-sectional shape of the yttrium aluminate crystal phase 13 include a circular shape, an elliptical shape, a polygonal shape, and other irregular shapes. In the cross section of the composite sintered body 10, the average size (maximum dimension) of the domain of the yttrium aluminate crystal phase 13 is, for example, 0.1 μm to 10 μm. When the average size (maximum dimension) of the domain of the yttrium aluminate crystal phase is within such a range, the thermal conductivity of the composite sintered body can be adjusted more stably within the above-described range.

[0024] In one embodiment, the yttrium aluminate crystal phase contains Y ４ Al ２ O ４ (hereinafter sometimes referred to as YAM), and / or YAlO ３ (hereinafter sometimes referred to as YAL).

[0025] YAM typically has a monoclinic system. The length of the a-axis in YAM is, for example, 7.3800 Å or more and 7.3900 Å or less. The length of the b-axis in YAM is, for example, 10.460 Å or more and 10.480 Å or less. The length of the c-axis in YAM is, for example, 11.100 Å or more and 11.130 Å or less. The β angle in YAM is, for example, 108.50° or more and 108.70° or less.

[0026] The lattice volume in YAM is, for example, 813.00 Å ３ to 815.00 Å ３ is.

[0027] The weight ratio of YAM to YAL (YAM / YAL) is, for example, 3.0 to 50, preferably 7.0 to 20, and more preferably 14.0 to 16.0.

[0028] In one embodiment, the portion other than the yttrium aluminate crystal phase 13 in the grain boundary 12 (hereinafter referred to as the matrix portion of the grain boundary 12) contains elements (Al, N) derived from AlN as the main components.

[0029] B-3. Physical properties of the composite sintered body The open porosity of such a composite sintered body 10 is, for example, 1.0% or less. The open porosity of the composite sintered body is measured, for example, in accordance with JIS-R1634.

[0030] The density of the composite sintered body 10 is, for example, 3.1 g / cm ３ or more, preferably 3.2 g / cm ３ or more. On the other hand, the upper limit of the density of the composite sintered body 10 is typically 3.4 g / cm ３ is. The density of the composite sintered body is measured, for example, in accordance with JIS-R1634.

[0031] The flexural strength of the composite sintered body 10 is, for example, 260 MPa or more, preferably 300 MPa or more. On the other hand, the upper limit of the flexural strength of the composite sintered body 10 is typically 420 MPa. The flexural strength of the composite sintered body is measured, for example, in accordance with JIS-R1601.

[0032] The dielectric constant ε' of the composite sintered body 10 in the range of 1 MHz to 13.56 MHz is, for example, 8.0 to 9.0. Also, the dielectric loss tanδ of the composite sintered body 10 in the range of 1 MHz to 13.56 MHz is, for example, 1.0×10 －３ is as follows. On the other hand, the lower limit of the dielectric loss tanδ of the composite sintered body 10 is typically 0. Note that the dielectric constant and dielectric loss of the composite sintered body are measured, for example, by the two-terminal short-circuit resonance method in accordance with JIS-R1627.

[0033] C. Manufacturing method of composite sintered body Next, a manufacturing method of a composite sintered body according to one embodiment will be described. In one embodiment, the manufacturing method of the composite sintered body 10 includes a mixing step of mixing raw materials of the composite sintered body, a molding step of preparing a molded body from the raw material mixture obtained in the mixing step, and a firing step of firing the molded body.

[0034] C-1. Mixing step In the mixing step, an aluminum nitride raw material (hereinafter, AlN raw material) and a Y-containing raw material are mixed to prepare a mixed powder.

[0035] The AlN raw material typically has a powdery form. The average particle size D50 of the AlN raw material powder is, for example, 1.0 μm to 1.5 μm. Such an AlN raw material may be granulated by any suitable granulation method. Also, the oxygen content ratio contained in the AlN raw material may be adjusted. For example, by adjusting the oxygen content ratio in the AlN raw material to 0.7 wt% to 1.0 wt%, the c-axis length of AlN in the manufactured composite sintered body can be appropriately controlled. The AlN crystal phase typically has a wurtzite structure (hexagonal system). When oxygen is dissolved in such an AlN crystal phase and substitutes for nitrogen, the c-axis length of AlN becomes shorter. Therefore, by increasing the oxygen content ratio contained in the AlN raw material and increasing the amount of oxygen dissolved in the AlN crystal phase, the c-axis length of AlN in the composite sintered body can be shortened.

[0036] The Y-containing raw material typically has a powdery form. In one embodiment, the Y-containing raw material is Y ２ O ３ is.

[0037] The amount of Y-containing raw material added is, for example, 0.5 parts by weight or more, preferably 1.0 part by weight or more, and more preferably 3.0 parts by weight or more, per 100 parts by weight of AlN raw material. On the other hand, the amount of Y-containing raw material added is, for example, 10 parts by weight or less, preferably 8.0 parts by weight or less, and more preferably 6.0 parts by weight or less, per 100 parts by weight of AlN raw material.

[0038] Any suitable mixing apparatus can be used in the mixing process. Examples of mixing apparatus that can be used in the mixing process include ball mills, bead mills, and vibratory mills, with ball mills being preferred.

[0039] Furthermore, the mixing method in the mixing process may be dry mixing or wet mixing. In one embodiment, dry mixing is performed in the mixing process.

[0040] The environmental conditions during the mixing process are not particularly limited. Typically, the mixing process is carried out at room temperature (25°C) and atmospheric pressure (0.1 MPa). The duration of the mixing process is set arbitrarily and appropriately. For example, the duration of the mixing process is between 1 and 30 hours.

[0041] Based on the above, AlN raw material and Y-containing raw material (typically Y) ２ O ３ A raw material mixture containing ) is prepared. If the mixing process is dry mixing, the raw material mixture will be in powder form; if the mixing process is wet mixing, the raw material mixture will be in slurry form.

[0042] The raw material mixture is granulated as needed. One example of a granulation method is a spray dryer. This prepares granules (raw material granules) of the raw material mixture.

[0043] C-2. Molding Process In the molding process, the above-mentioned raw material mixture is molded into the desired shape using any appropriate molding method to prepare a molded body.

[0044] Examples of forming methods include press forming, sheet forming, cold isostatic pressing (CIP) forming, and doctor blade forming, with press forming being preferred. The pressure in press forming is, for example, 10 kgf / cm². ２~500kgf / cm ２ The pressure is preferably 100 kgf / cm². ２ ~300kgf / cm ２ That is the case.

[0045] This allows for the preparation of a molded body having the desired shape.

[0046] C-3. Firing Process Next, in the firing process, the molded body is typically fired in a vacuum or non-oxidizing atmosphere. More specifically, the temperature is raised from room temperature (23°C) to a predetermined firing temperature, and then the firing temperature is maintained for a predetermined firing time.

[0047] The firing temperature is, for example, 1750°C to 1850°C. The firing time is, for example, 8 hours to 15 hours. When the firing temperature and / or firing time are within this range, the amount of oxygen dissolved in AlN can be appropriately adjusted, and the average grain size of the crystal grains and the c-axis length of the AlN crystal phase contained in the crystal grains can be stably adjusted to the above range. In particular, the average grain size of the crystal grains can be sufficiently adjusted by adjusting the firing time. Specifically, the average grain size of the crystal grains can be increased by increasing the firing time, and the average grain size of the crystal grains can be decreased by decreasing the firing time. The environmental pressure during the firing process is, for example, 100 kPa to 900 kPa.

[0048] Examples of firing methods include hot pressing and hot isostatic pressing (HIP), with hot pressing being preferred. In hot pressing, typically, the molded body is placed in a hot pressing die (e.g., a carbon jig), heated to the firing temperature as described above, and then pressurized at a predetermined pressure. The pressure in hot pressing is, for example, 5 MPa or more and less than 15 MPa. When the pressure in hot pressing is within this range, the average grain size of the crystal grains and the c-axis length of the AlN crystal phase contained in the crystal grains can be stably adjusted within the above range.

[0049] In this firing process, the AlN contained in the molded body is sintered, forming multiple crystal grains and grain boundaries located between the crystal grains. At this time, AlN and Y-containing raw materials (typically Y) ２ O ３) reacts with the yttrium aluminate crystal phase, which is formed at the grain boundaries. Thus, the composite sintered body 10 is manufactured.

[0050] D. Applications of the composite sintered body The composite sintered body 10 is typically applied to components of semiconductor manufacturing equipment (semiconductor manufacturing components) for manufacturing semiconductor devices. Semiconductor manufacturing components are devices that can be distributed individually and are industrially usable. Examples of semiconductor manufacturing components include susceptors, heaters, electrostatic chucks, ceramic conductors, input terminals, and shower heads.

[0051] As shown in Figure 2, in one embodiment, the composite sintered body 10 is suitably applied to an electrostatic chuck 100. The electrostatic chuck 100 typically comprises a ceramic substrate 1 including the composite sintered body 10 described above, and a conductor 2.

[0052] The ceramic substrate 1 functions as a wafer mounting plate. In the illustrated example, the ceramic substrate 1 has a mounting surface 1a on which a silicon wafer 8 can be mounted. The mounting surface 1a is one side of the ceramic substrate 1 in the thickness direction. The ceramic substrate 1 has any suitable shape. In the illustrated example, the ceramic substrate 1 has a disc shape (see Figure 1). The thickness of the ceramic substrate 1 is, for example, 10 mm to 50 mm.

[0053] The conductor 2 is provided within the ceramic substrate 1. In other words, the conductor 2 is embedded in the ceramic substrate 1. Examples of the conductor 2 include ESC electrodes, RF electrodes, resistance heating elements, and terminals. The electrostatic chuck 100 includes at least an ESC electrode 2a as the conductor 2. The electrostatic chuck 100 may further include another conductor 2 in addition to the ESC electrode 2a.

[0054] The conductor 2 is typically composed of a conductive material with a lower volume resistivity than the composite sintered body 10. Examples of such conductive materials include metal carbide compounds such as tungsten carbide (WC); metal nitride compounds such as titanium nitride (TiN); and transition metals such as molybdenum (Mo), tantalum (Ta), tungsten (W), platinum (Pt), rhenium (Re), and hafnium (Hf). The conductive materials can be used individually or in combination. In one embodiment, the conductor 2 contains molybdenum (Mo). With such a configuration, the volume resistivity of the conductor can be made sufficiently small.

[0055] The conductor 2 has any suitable shape. Examples of conductor shapes include mesh shape, plate shape, coil shape, and zigzag shape. In one embodiment, the conductor 2 (typically the ESC electrode 2a) has a mesh shape. In this case, the conductor 2 includes a plurality of linear portions 21. The plurality of linear portions 21 are spaced apart from each other in a first direction that intersects (preferably perpendicular to) the thickness direction of the ceramic substrate 1 in a cross-section obtained by cutting the electrostatic chuck 100 in the thickness direction of the ceramic substrate 1. The linear portions 21 have any suitable cross-sectional shape. Examples of cross-sectional shapes of the linear portions 21 include circular shape, elliptical shape, polygonal shape, and other irregular shapes. In the illustrated example, the cross-sectional shape of the linear portion 21 is circular.

[0056] Furthermore, in one embodiment, when line analysis is performed using an electron beam microanalyzer on the cross-section of the electrostatic chuck 100, with a first measurement line L1 passing through the center of one of the multiple linear portions 21 in a first direction and a second measurement line L2 passing through a second direction perpendicular to the first direction, the average value of the Y intensity in the first adjacent portion adjacent to the linear portion 21 in the first direction is smaller than the average value of the Y intensity in the second adjacent portion adjacent to the linear portion 21 in the second direction. In one embodiment, when line analysis is performed using an electron beam microanalyzer on the cross-section of the electrostatic chuck 100, with a first measurement line L1 and a second measurement line L2, the maximum value of the Y intensity in the first adjacent portion is smaller than the maximum value of the Y intensity in the second adjacent portion. In this specification, "adjacent portion of a linear portion" is defined as follows: In the cross-section of the electrostatic chuck 100, the reference point is the point on the periphery of the linear portion 21 closest to the center of the linear portion 21. Next, a first virtual circle is determined that shares its center with the linear portion 21 and passes through the reference point. Subsequently, a second virtual circle is determined that shares its center with the linear portion 21 and has a radius four times that of the first virtual circle. After that, in the cross-section of the electrostatic chuck 100, the region between the periphery of the linear portion 21 and the second virtual circle is defined as the "adjacent portion". That is, the first adjacent portion is the region between the periphery of the linear portion 21 and the second virtual circle that overlaps with the first measurement line L1, and the second adjacent portion is the region between the periphery of the linear portion 21 and the second virtual circle that overlaps with the second measurement line L2.

[0057] The dimensions of the conductor 2 in the thickness direction of the ceramic substrate 1 are arbitrarily and appropriately adjusted according to the application. The dimensions of the ESC electrode 2a in the thickness direction of the ceramic substrate 1 are, for example, 10 μm to 50 μm, preferably 20 μm to 30 μm. Also, if the linear portion 21 has a circular cross-sectional shape, the range of the outer diameter of the linear portion 21 is, for example, within that range.

[0058] In the illustrated example, the conductor 2 further includes a resistive heating element 2b. The resistive heating element 2b is configured to generate heat when a voltage is applied. In the illustrated example, the resistive heating element 2b is located on the opposite side of the mounting surface 1a of the ceramic substrate 1 from the ESC electrode 2a.

[0059] A ceramic substrate 1 in which a conductor 2 is embedded is manufactured, for example, by embedding the conductor 2 (or a precursor of the conductor) at a desired position in a molded body composed of a raw material mixture in the molding process described above, and then firing them in the firing process described above.

[0060] In such an electrostatic chuck 100, the composite sintered body 10 constituting the ceramic substrate 1 has a suitable volume resistivity. Therefore, when a DC voltage is applied to the ESC electrode 2a with the silicon wafer 8 placed on the mounting surface 1a in a temperature range of 250°C to 350°C, a suitable leakage current (for example, 0.5 mA to 1.5 mA) can be generated between the silicon wafer 8 and the ESC electrode 2a. As a result, a JR force can be generated between the silicon wafer 8 and the ESC electrode 2a, and the silicon wafer 8 can be stably chucking the ceramic substrate 1. Consequently, various processes can be performed on the silicon wafer 8 with high precision, and the manufacturing of semiconductor devices can be miniaturized.

[0061] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. The measurement methods for each characteristic are as follows.

[0062] (1) Measurement of the content ratio of crystalline phases in composite sintered bodies Samples were obtained by crushing the ceramic substrates of the electrostatic chucks manufactured in the examples and comparative examples. Next, silicon (Si) powder, which is an internal standard sample, was added to the samples and mixed. Subsequently, the resulting mixed powder was analyzed using an X-ray diffraction (XRD) apparatus to identify the crystalline phases in the composite sintered body and to calculate the content ratio of each crystalline phase. The results are shown in Table 1. The measurement conditions were CuKα, 40kV, 40mA, 2θ = 20 to 80°, and a sealed tube type X-ray diffractometer (Bruker AXS, D8-ADVANCE) was used. The step size for measurement was 0.02°.

[0063] (2) Calculation of lattice constants of AlN and YAM Test specimens were cut from the ceramic substrates provided in the electrostatic chucks manufactured in the examples and comparative examples. Next, the lattice constants of AlN and YAM were calculated in the test specimens using the WPPD method (powder pattern fitting method) with software (TOPAS, manufactured by Bruker AXS). The a-axis length of AlN, the c-axis length of AlN, the lattice volume of AlN, the a-axis length of YAM, the b-axis length of YAM, the c-axis length of YAM, the β-angle of YAM, and the lattice volume of YAM are shown in Table 1.

[0064] (3) Calculation of average grain size and standard deviation of multiple crystal grains Test specimens were prepared in the same manner as in "(2) Calculation of lattice constants of AlN and YAM" described above. Next, the average grain size and standard deviation of multiple crystal grains in the test specimens were calculated by acquiring backscattered electron images at a 3000x magnification field using a scanning electron microscope, and measuring the diameters of N=40 particles corresponding to AlN in the backscattered electron images. The results are shown in Table 1.

[0065] (4) Identification of elemental composition of conductors by FE-EPMA Test specimens were cut from the electrostatic chucks manufactured in the examples and comparative examples. The cross section of the test specimen along the thickness direction was polished to a mirror finish by lapping to serve as the measurement surface. This measurement surface included multiple linear portions of the ESC electrode. On this measurement surface, the multiple linear portions were spaced apart from each other in a direction perpendicular to the thickness direction of the ceramic substrate. Next, the polished surface was analyzed by FE-EPMA to obtain an elemental mapping image. This allowed for the identification of the elemental composition of the linear portions and adjacent portions in the composite sintered body. The results are shown in Table 1. Figure 3 shows the mapping image of aluminum (Al) in the test specimen of Example 1, Figure 4 shows the mapping image of nitrogen (N) in the test specimen of Example 1, Figure 5 shows the mapping image of yttrium (Y) in the test specimen of Example 1, and Figure 6 shows the mapping image of oxygen (O) in the test specimen of Example 1.

[0066] (5) Measurement of Y strength by EPMA A test specimen was prepared having a measurement surface polished by lapping, in the same manner as in "(4) Identification of elemental composition of conductor by FE-EPMA" described above. Next, a first measurement line and a second measurement line passing through the center of one linear portion were determined on the measurement surface of the test specimen. The first measurement line extended in a first direction perpendicular to the thickness direction of the ceramic substrate, and the distance between the end of the first measurement line and the center of the linear portion was 800 μm. The second measurement line extended in the thickness direction (second direction) of the ceramic substrate, and the distance between the end of the second measurement line and the center of the linear portion was 580 μm.

[0067] Subsequently, line analysis of the first and second measurement lines was performed using EPMA under the following conditions, and the intensity of the Y characteristic X-rays in each measurement line was measured. <Measurement conditions> Equipment: JEOL Ltd., JXA-8530FPlus Acceleration voltage: 15kV Irradiation current: 1 × 10⁻¹⁶ －７A. Magnification: 2000x Figure 9 shows the Y characteristic X-ray spectrum of the first measurement line in the test specimen of Example 1. In Figure 9, the center position of the linear portion is the midpoint of the horizontal axis. Figure 10 shows the Y characteristic X-ray spectrum of the second measurement line in the test specimen of Example 1. In Figure 10, the center position of the linear portion is the midpoint of the horizontal axis.

[0068] (6) Measurement of volume resistivity of composite sintered body Test specimens were prepared in the same manner as in "(2) Calculation of lattice constants of AlN and YAM" described above. The volume resistivity of the test specimens was then measured in accordance with JIS-C2141 at room temperature (25°C), 100°C, 200°C, 300°C, 400°C, 500°C, and 600°C. The applied voltage was +500V. The results are shown in Figure 7. In addition, the volume resistivity of the test specimens according to Example 1 was measured in accordance with JIS-C2141 at 300°C with an applied voltage of +500V or -500V. The volume resistivity of the test specimens was measured when the voltage was applied for 1 min, 30 min, and 60 min. The measurement of volume resistivity was repeated three times. The results are shown in Table 2. Furthermore, the volume resistivity of the test specimens according to Examples 2-4 and Comparative Examples 1-3 was measured in the same manner as described above, except that the timing of the volume resistivity measurement was changed to only when the voltage application time was 1 min and 60 min. The results are shown in Table 3.

[0069] (7) Measurement of the thermal conductivity of the composite sintered body Test specimens were prepared in the same manner as in "(2) Calculation of lattice constants of AlN and YAM" described above. The volume resistivity of the test specimens was then measured in accordance with JIS R1611 at room temperature (25°C), 100°C, 200°C, 300°C, 400°C, 500°C, and 600°C. The results are shown in Figure 8.

[0070] <<Example 1>> 95 parts by weight of AlN raw material powder and Y ２ O ３Five parts by weight of the powder were placed in a ball mill and dry-mixed for 10 hours. This yielded a mixed powder (raw material mixture). The mixed powder was then granulated by spray drying. At this time, the oxygen content in the AlN raw material was 0.8 wt%. An ESC electrode (conductor) with a mesh shape was also prepared. The ESC electrode contained molybdenum. Next, the granules of the mixed powder were filled into a predetermined mold, and the ESC electrode was embedded in the desired position. Then, the granules of the mixed powder filled into the mold were uniaxially pressed to obtain a disc-shaped molded body. The pressure during uniaxial pressing was 10 MPa. Next, the molded body was fired by the hot-press method. More specifically, first, the molded body was placed in a hot-press die made of graphite and set in a hot-press furnace. Then, the atmosphere inside the hot-press furnace was replaced with a nitrogen atmosphere and the pressure was increased to 0.1 MPa, and the molded body was pressed in the thickness direction at a pressure of less than 15 MPa. In this state, the molded body was fired at 1830°C for 10 hours. This produced an electrostatic chuck comprising a ceramic substrate and an ESC electrode (conductor). The ceramic substrate had a disc shape. The diameter of the ceramic substrate was 340 mm, and the thickness of the composite sintered body was 25 mm. The ceramic substrate contained the composite sintered body, which had multiple crystal grains containing an AlN crystal phase and grain boundaries containing a yttrium aluminate crystal phase.

[0071] <<Example 2>> An electrostatic chuck was manufactured in the same manner as in Example 1, except that the oxygen content in the AlN raw material was changed to 0.7 wt%.

[0072] <<Example 3>> An electrostatic chuck was manufactured in the same manner as in Example 1, except that the firing time of the molded body was changed to 15 hours.

[0073] <<Example 4>> An electrostatic chuck was manufactured in the same manner as in Example 1, except that the firing time of the molded body was changed to 8 hours and the oxygen content in the AlN raw material was changed to 0.85 wt%.

[0074] <<Comparative Example 1>> An electrostatic chuck was manufactured in the same manner as in Example 1, except that the firing temperature was changed to 1850°C, the firing time was changed to 2 hours, and the pressing pressure was changed to 20 MPa using the hot pressing method.

[0075] <<Comparative Example 2>> An electrostatic chuck was manufactured in the same manner as in Comparative Example 1, except that the firing time of the molded body was changed to 1 hour.

[0076] <<Comparative Example 3>> An electrostatic chuck was manufactured in the same manner as in Comparative Example 1, except that the firing time of the molded body was changed to 24 hours.

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[0079]

[0080] <Evaluation> As shown in Tables 1 to 3, it can be seen that in a composite sintered body, if the average grain size of multiple crystal grains is 5.0 μm to 6.0 μm, and the c-axis length of AlN is 4.9815 Å or less, the volume resistivity of the AlN sintered body at 300°C can be stably adjusted to a range suitable for a JR type electrostatic chuck.

[0081] The composite sintered body according to the embodiment of the present invention is typically used in semiconductor manufacturing equipment, and is particularly suitable for use in electrostatic chucks utilizing JR force.

[0082] 1 Ceramic substrate 10 Composite sintered body 11 Crystal grains 12 Grain boundaries 13 Yttrium aluminate crystal phase 2 Conductor 2a ESC electrode 100 Electrostatic chuck

Claims

1. A composite sintered body comprising: a plurality of crystal grains containing an aluminum nitride crystal phase; and grain boundaries located between adjacent crystal grains among the plurality of crystal grains, wherein the grain boundaries contain a yttrium aluminate crystal phase; the average grain size of the plurality of crystal grains is 3.0 μm to 8.0 μm; and the c-axis length of the aluminum nitride crystal phase is 4.9815 Å or less.

2. The composite sintered body according to claim 1, wherein the volume resistivity measured by applying a voltage of +500V at 300°C is 0.5 to 2.0 compared to the volume resistivity measured by applying a voltage of -500V at 300°C.

3. An electrostatic chuck comprising a ceramic substrate containing a composite sintered body according to claim 1 or 2, and a conductor provided within the ceramic substrate.

4. The electrostatic chuck according to claim 3, wherein the conductor has a mesh shape, and in a cross-section obtained by cutting the electrostatic chuck in the thickness direction of the ceramic substrate, it comprises a plurality of linear portions arranged at intervals from each other in a first direction intersecting the thickness direction of the ceramic substrate, and when line analysis is performed by electron beam microanalyzer on a first measurement line passing through the center of the linear portion in the first direction and a second measurement line extending in a second direction perpendicular to the first direction and passing through the center of the linear portion, the average value of the Y intensity in the first adjacent portion adjacent to the linear portion in the first direction is smaller than the average value of the Y intensity in the second adjacent portion adjacent to the linear portion in the second direction.

5. The electrostatic chuck according to claim 4, wherein the conductor comprises molybdenum.

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