Aluminum nitride sintered compact

Abstract

[Problem] To provide an aluminum nitride sintered compact which is grain shedding-resistant and suitably applicable to an electrostatic chuck utilizing JR force. [Solution] An aluminum nitride sintered compact according to an embodiment of the present invention has a plurality of grains and grain boundaries. Each of the plurality of grains contains aluminum nitride. The grain boundaries are positioned between grains adjacent to each other among the plurality of grains. The average particle diameter of the plurality of grains is 1.5-3.0 μm. The grain boundaries include portions in which calcium-containing aluminum oxynitride is present in an isolated state. In the aluminum nitride sintered compact, the content of metal elements other than aluminum is more than 30 ppm and 300 ppm or less.

Description

Aluminum nitride sintered body

[0001] This invention relates to an aluminum nitride sintered body.

[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. As a material for such a susceptor, for example, an aluminum nitride sintered body has been proposed in which the content of all metal elements except aluminum is 100 ppm or less, and which exhibits a black color with a brightness of N4 or less as defined in JIS Z 8721 (see Patent Document 1).

[0003] Patent No. 2883207

[0004] In some cases, electrodes are provided on such susceptors to configure them as electrostatic chucks 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 electrostatic chucks utilizing the Coulomb force (hereinafter referred to as Coulomb-type electrostatic chucks), 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 electrostatic chucks utilizing the JR force (hereinafter referred to as JR-type electrostatic chucks), 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. However, since the volume resistivity of aluminum nitride sintered bodies decreases with increasing temperature, using a Coulomb-type electrostatic chuck in the temperature range above 250°C may result in unstable Coulomb force generation. Therefore, JR-type electrostatic chucks are typically used in the temperature range above 250°C. In addition, in the manufacturing of semiconductor devices, it is desirable to reduce the amount of particles adhering to the silicon wafer. One example of the cause of particles is the shedding of crystal grains from the aluminum nitride sintered body that constitutes the susceptor (hereinafter referred to as grain shedding). Therefore, reducing the grain size of the crystal grains in the aluminum nitride sintered body is being considered to suppress grain shedding. However, reducing the grain size increases the proportion of grain boundaries in the aluminum nitride sintered body, which may increase the volume resistivity of the aluminum nitride sintered body. When such an aluminum nitride sintered body is applied to a JR-type electrostatic chuck, it may become difficult to generate an appropriate leakage current between the silicon wafer and the electrode in certain temperature ranges, and there is a risk that the JR force may not be able to be generated stably. The main objective of the present invention is to provide an aluminum nitride sintered body that can suppress grain shedding and is suitably applicable to electrostatic chucks utilizing JR force.

[0005] [1] An aluminum nitride 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 aluminum nitride. The grain boundaries are located between adjacent crystal grains among the plurality of crystal grains. The average grain size of the plurality of crystal grains is 1.5 μm to 3.0 μm. The grain boundaries include portions in which aluminum oxynitride containing calcium exists in an isolated state. In the aluminum nitride sintered body, the content of metal elements other than aluminum is greater than 30 ppm and 300 ppm or less. [2] In the aluminum nitride sintered body described in [1] above, the content of metal elements other than aluminum may exceed 100 ppm. [3] In the aluminum nitride sintered body described in [1] or [2] above, the standard deviation of the average grain size of the plurality of crystal grains may be 1.0 μm or less. [4] In the aluminum nitride sintered body described in any of [1] to [3] above, the volume resistivity measured by applying a voltage of +500V at 300°C is 5.0 × 10 ９ Ω・cm~1.0×10 １０ It may be Ω·cm. [5] The bending strength of the aluminum nitride sintered body described in any of [1] to [4] above may be 300 MPa or more.

[0006] According to embodiments of the present invention, it is possible to realize an aluminum nitride sintered body that can suppress grain detachment and is suitably applicable to electrostatic chucks utilizing JR force.

[0007] Figure 1 is a schematic diagram of an aluminum nitride sintered body according to one embodiment of the present invention. Figure 2 is a schematic cross-sectional view of an electrostatic chuck including the aluminum nitride sintered body of Figure 1. Figure 3 is a mapping image of aluminum (Al) in the aluminum nitride sintered body of the example. Figure 4 is a mapping image of calcium (Ca) in the aluminum nitride sintered body of the example. Figure 5 is a mapping image of oxygen (O) in the aluminum nitride sintered body of the example. Figure 6 is a mapping image of nitrogen (N) in the aluminum nitride sintered body of the example. Figure 7 is a mapping image of aluminum (Al) in the aluminum nitride sintered body of the comparative example. Figure 8 is a mapping image of calcium (Ca) in the aluminum nitride sintered body of the comparative example. Figure 9 is a mapping image of oxygen (O) in the aluminum nitride sintered body of the comparative example. Figure 10 is a mapping image of nitrogen (N) in the aluminum nitride sintered body of the comparative 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 Figure 1 of the aluminum nitride sintered body is a schematic diagram of the aluminum nitride sintered body according to one embodiment of the present invention. In one embodiment, the aluminum nitride sintered body 1 comprises a plurality of crystal grains 11 and grain boundaries 12. Hereinafter, the aluminum nitride sintered body may be referred to as an AlN sintered body. The AlN sintered body 1 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 aluminum nitride (AlN). The average grain size of the plurality of crystal grains 11 is 1.5 μm to 3.0 μm. The grain boundaries 12 are located between adjacent crystal grains 11. The grain boundaries 12 are continuous in a three-dimensional network. In a temperature range of 250°C or higher, the volume resistivity of the grain boundaries 12 is typically smaller than the volume resistivity of the crystal grains 11. Therefore, the grain boundaries 12, which are continuous in a three-dimensional network, can function as conductive paths when a voltage is applied to the AlN sintered body 1. Calcium-containing aluminum oxynitride 13 exists in an isolated state within the grain boundaries 12. In other words, the grain boundaries 12 include portions where calcium-containing aluminum oxynitride 13 exists in an isolated state. The chemical formula for aluminum oxynitride is typically Al ５ O ６This is N. Hereafter, aluminum oxynitride containing calcium may be referred to as Ca-containing AlON. In such an AlN sintered body 1, the content of metal elements other than Al (aluminum) is greater than 30 ppm and less than or equal to 300 ppm by weight. The inventors have diligently studied how to appropriately control the volume resistivity in a temperature range of 250°C or higher in an AlN sintered body in which the average grain size of the crystal grains is 3.0 μm or less. As a result, they have found that in an AlN sintered body, if the average grain size of the crystal grains is set to a predetermined level or higher, metal elements other than Al are sufficiently included, and Ca-containing AlON is appropriately present at the grain boundaries, the volume resistivity of the AlN sintered body in a temperature range of 250°C or higher can be adjusted to a range suitable for a JR type electrostatic chuck. More specifically, in an AlN sintered body, since the average grain size of the crystal grains is 1.5 μm or more, a sufficient proportion of grain boundaries can be ensured. Furthermore, since Ca-containing AlON exists in an isolated state at the grain boundary, and the content of metal elements other than Al in the AlN sintered body exceeds 30 ppm, the volume resistivity of the crystal grains and grain boundaries can be adjusted in a balanced manner, allowing the grain boundaries to function as appropriate conductive paths for the JR-type electrostatic chuck. In addition, since the content of metal elements other than Al in the AlN sintered body is 300 ppm or less, excessive grain growth of the crystal grains can be suppressed, and the average grain size of the crystal grains can be stably adjusted to 3.0 μm or less. As a result, degrainization in the AlN sintered body can be sufficiently suppressed. Consequently, an AlN sintered body can be realized that suppresses degrainization and has a volume resistivity suitable for the JR-type electrostatic chuck.

[0010] In AlN sintered body 1, the volume resistivity measured by applying a voltage of +500V at 300°C (hereinafter sometimes referred to as the volume resistivity of AlN sintered body at 300°C) is, for example, 1.0 × 10⁻⁶. ９ Ω·cm or more, preferably 5.0 × 10 ９ Ω·cm or more, more preferably 6.0 × 10 ９is Ω·cm or more. When the volume resistivity of the AlN sintered body at 300°C is at or above such a lower limit, in the JR type electrostatic chuck to which the AlN sintered body is applied, generation of excessive leakage current can be suppressed, and damage to the silicon wafer due to the leakage current can be suppressed. On the other hand, the volume resistivity of the AlN sintered body at 300°C is, for example, 5.0×10 １１ Ω·cm or less, preferably 1.5×10 １０ Ω·cm or less, more preferably 9.6×10 ９ Ω·cm or less, still more preferably 8.0×10 ９ Ω·cm or less. When the volume resistivity of the AlN sintered body at 300°C is at or below such an upper limit, in the JR type electrostatic chuck to which the AlN sintered body is applied, an appropriate leakage current can be generated between the silicon wafer and the electrode, and the JR force can be stably expressed. In the AlN sintered body 1, the volume resistivity measured by applying a voltage of +500 V at room temperature (25°C) is, for example, 1.0×10 １４ Ω·cm to 9.0×10 １４ Ω·cm, preferably 2.0×10 １４ Ω·cm to 8.0×10 １４ Ω·cm. The volume resistivity of the aluminum nitride sintered body is measured, for example, in accordance with JIS-C2141-1992.

[0011] The average grain size of the plurality of crystal grains 11 is preferably 1.8 μm or more, more preferably 2.0 μm or more. When the average grain size of the crystal grains is at or above such a lower limit, the crystal grains and grain boundaries in the AlN sintered body can be present in a well-balanced manner, and the volume resistivity of the AlN sintered body at 300°C can be stably adjusted within the above-described range. On the other hand, the average grain size of the plurality of crystal grains 11 is preferably 2.8 μm or less, more preferably 2.6 μm or less. When the average grain size of the crystal grains is at or below such an upper limit, grain detachment in the AlN sintered body can be stably suppressed, and generation of particles can be sufficiently suppressed.

[0012] 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 AlN sintered body at 300°C can be stably adjusted within the above range.

[0013] The content of metal elements other than Al in the AlN sintered body 1 is preferably greater than 100 ppm, more preferably 150 ppm or more, and even more preferably 200 ppm or more. When the content of metal elements other than Al is above this lower limit, the volume resistivity of the AlN sintered body at 300°C can be adjusted more stably within the above range. On the other hand, the content of metal elements other than Al in the AlN sintered body is preferably 280 ppm or less, more preferably 250 ppm or less. When the content of metal elements other than Al is below this upper limit, the average grain size of the crystal grains can be stably adjusted within the above range, and the formation of particles from metal atoms other than Al can be suitably suppressed. The content of the constituent elements in the aluminum nitride sintered body is measured, for example, by ICP-AES (inductively coupled plasma emission spectrometry) in accordance with JIS-K0116.

[0014] Examples of metallic elements other than Al include alkaline earth metals such as calcium (Ca) and magnesium (Mg); rare earth elements such as yttrium (Y), cerium (Ce), and samarium (Sm); transition metals such as zirconium (Zr), iron (Fe), and titanium (Ti); and metalloids such as silicon (Si). These metallic elements other than Al can be used individually or in combination.

[0015] In one embodiment, the metal elements other than Al include alkaline earth metals. Among the alkaline earth metals, Ca and Mg are preferred, and Ca is more preferred. With such a configuration, the crystal grains can be stably reduced in diameter, and Ca-containing AlON can be stably present at the grain boundaries.

[0016] The content of alkaline earth metals is, for example, 50% by weight or more, preferably 70% by weight or more, when the total amount of metal elements other than Al is taken as 100% by weight. On the other hand, the content of alkaline earth metals is, for example, 95% by weight or less, preferably 90% by weight or less, when the total amount of metal elements other than Al is taken as 100% by weight. Furthermore, the content of alkaline earth metals is, for example, 100 ppm or more, preferably 150 ppm or more, relative to the total amount of AlN sintered body 1. On the other hand, the content of alkaline earth metals is, for example, 280 ppm or less, preferably 250 ppm or less, more preferably 200 ppm or less, relative to the total amount of AlN sintered body 1. In one embodiment, the metal elements other than Al contain only Ca as an alkaline earth metal. If the content of Ca is within the above range, it is possible to suppress the formation of a continuous phase of Ca-containing AlON at grain boundaries, and Ca-containing AlON can exist in an isolated state.

[0017] In addition to alkaline earth metals, metal elements other than Al may also include transition metals that are not classified as rare earth elements. Among such transition metals, iron (Fe) and titanium (Ti) are preferred. The content ratio of alkaline earth metals is, for example, 2.0 to 8.0, and preferably 4.0 to 7.0, relative to the content ratio of transition metals. The content ratio of transition metals is, for example, 40 ppm or less, and for example, 30 ppm or less, relative to the total amount of AlN sintered body 1. On the other hand, the lower limit of the content ratio of transition metals is typically 0 ppm relative to the total amount of AlN sintered body 1.

[0018] Furthermore, the metal elements other than Al preferably do not contain substantially any rare earth elements. With such a configuration, the generation of particles can be suppressed. The content of rare earth elements is, for example, 10 ppm or less, preferably 5 ppm or less, and more preferably 3 ppm or less, relative to the total amount of AlN sintered body 1. On the other hand, the lower limit of the content of rare earth elements is typically 0 ppm relative to the total amount of AlN sintered body 1. If the content of rare earth elements is within this range, the crystal grains can be made smaller in a more stable manner.

[0019] B. Details of Aluminum Nitride Sintered Body Next, referring to FIG. 1, the details of the aluminum nitride sintered body 1 will be described. The AlN sintered body 1 contains AlN and Ca-containing AlON as described above. In other words, the AlN sintered body 1 contains an AlN crystal phase and a Ca-containing AlON crystal phase.

[0020] The content ratio of AlN in the AlN sintered body 1 is, for example, 95.00% by weight or more, preferably 97.00% by weight or more. On the other hand, the content ratio of AlN in the AlN sintered body 1 is, for example, 99.90% by weight or less, also for example 99.50% by weight or less, also for example 99.05% by weight or less, and also for example 99.00% by weight or less. The content ratio of Ca-containing AlON in the AlN sintered body 1 is, for example, 0.10% by weight or more, preferably 0.50% by weight or more, more preferably 0.95% by weight or more, and even more preferably 1.00% by weight or more. On the other hand, the content ratio of Ca-containing AlON in the AlN sintered body 1 is, for example, 5.00% by weight or less, preferably 3.0% by weight or less. The content ratio of the crystal phase in the aluminum nitride sintered body is measured in accordance with JIS-Z2201 and JIS-K0114 by, for example, XRD (X-ray Diffraction).

[0021] 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 system). Oxygen may be dissolved in the AlN crystal phase or may not be dissolved. In one embodiment, oxygen is dissolved in the AlN crystal phase. When oxygen is dissolved in the AlN crystal phase, the crystal lattice of AlN can be suitably adjusted.

[0022] The a-axis length in the AlN crystal phase is, for example, 3.11190 Å or more, preferably 3.11200 Å or more. On the other hand, the a-axis length in the AlN crystal phase is, for example, 3.11250 Å or less, preferably 3.11220 Å or less. The c-axis length in the AlN crystal phase is, for example, 4.97900 Å or more, preferably 4.97910 Å or more. On the other hand, the c-axis length in the AlN crystal phase is, for example, 4.97940 Å or less, preferably 4.97920 Å or less.

[0023] The lattice volume in the AlN crystal phase is, for example, 41.7600 Å ３ to 41.7630 Å ３ and preferably 41.7610 Å ３ to 41.7620 Å ３ is.

[0024] In the AlN crystal phase, the ratio of the c-axis length to the a-axis length (c / a) is, for example, 1.60010 or less, preferably less than 1.60000. On the other hand, the lower limit of c / a in the AlN crystal phase is typically 1.59990. When the AlN crystal phase has such c / a, the volume resistivity of the AlN sintered body in the temperature range of 250°C or higher can be adjusted to a range suitable for the JR type electrostatic chuck. The crystal lattice is measured by, for example, XRD (X-ray diffraction).

[0025] B-2. Grain boundary At least a part of the Ca-containing AlON crystal phase exists in an isolated state at the grain boundary 12. At the grain boundary 12, all of the Ca-containing AlON crystal phases may be isolated, or a part of the Ca-containing AlON crystal phase may be isolated and the remainder of the Ca-containing AlON crystal phase may be continuous. That is, the grain boundary 12 includes a portion where the Ca-containing AlON crystal phase exists in an isolated state. In one embodiment, at least a part of the Ca-containing AlON crystal phase 13 exists isolated at the triple point of the grain boundary 12. According to such a configuration, the volume resistivity of the AlN sintered body can be adjusted more stably within the above-described range. The triple point of the grain boundary 12 means a portion of the grain boundary 12 surrounded by three or more grains 11.

[0026] In a cross-section of the AlN sintered body 1, the area ratio of the Ca-containing AlON crystal phase 13 is, for example, 20% to 70%, preferably 30% to 65%, when the total area of ​​the grain boundaries 12 is taken as 100%. Furthermore, in the cross-section of the AlN sintered body 1, the isolated Ca-containing AlON 13 accounts for, for example, 60% to 100% of the total area of ​​the Ca-containing AlON 13. When the area ratio of the Ca-containing AlON crystal phase is within this range, the volume resistivity of the grain boundaries can be stably adjusted to an appropriate range for the conductive path of the JR-type electrostatic chuck. The area ratio of calcium-containing aluminum oxynitride is calculated, for example, from an elemental mapping image obtained by analyzing the cross-section of the aluminum nitride sintered body using a field emission electron beam microanalyzer (FE-EPMA).

[0027] In the cross-section of the AlN sintered body 1, the isolated Ca-containing AlON crystal phase 13 has any suitable shape. Examples of cross-sectional shapes of the Ca-containing AlON crystal phase 13 include circular, elliptical, polygonal, and other irregular shapes. In the cross-section of the AlN sintered body 1, the average size (maximum dimension) of the domains of the Ca-containing AlON crystal phase 13 is, for example, 0.5 μm to 3.0 μm, preferably 0.8 μm to 2.0 μm. When the domain size of the Ca-containing AlON crystal phase is within this range, the volume resistivity of the grain boundaries can be stably adjusted to a range suitable for the conductive path of the JR-type electrostatic chuck.

[0028] The Ca-containing AlON crystalline phase typically has a cubic crystal system. In one embodiment, Ca is dissolved in AlON.

[0029] The a-axis length in Ca-containing AlON is, for example, 7.9570 Å or more, preferably 7.9580 Å or more. On the other hand, the a-axis length in Ca-containing AlON is, for example, 7.9650 Å or less, preferably 7.9640 Å or less.

[0030] The lattice volume in Ca-containing AlON is, for example, 503.70 Å. ３ ~505.00 Å ３ Preferably 504.00 Å ３ ~504.70 Å ３ That is the case.

[0031] In one embodiment, the portion of the grain boundary 12 other than the Ca-containing AlON crystal phase 13 (hereinafter referred to as the matrix portion of the grain boundary 12) mainly contains elements derived from AlN (Al, N). The matrix portion of the grain boundary 12 may further contain metal elements other than Al as described above. In one embodiment, the matrix portion of the grain boundary 12 further contains Ca as a metal element other than Al. When the matrix portion of the grain boundary 12 contains Ca, the volume resistivity of the AlN sintered body in a temperature range of 250°C or higher can be adjusted to a range suitable for a JR type electrostatic chuck.

[0032] B-3. ​​Physical Properties of Aluminum Nitride Sintered Body The open porosity of such AlN sintered body 1 is, for example, 1.0% or less. The open porosity of the aluminum nitride sintered body is measured, for example, in accordance with JIS-R1634.

[0033] The density of the AlN sintered body 1 is, for example, 3.0 g / cm³. ３ Preferably, the above is 3.2 g / cm³. ３ That concludes the explanation. On the other hand, the upper limit of the density of aluminum nitride sintered body 1 is typically 3.4 g / cm³. ３ The density of the aluminum nitride sintered body is measured, for example, in accordance with JIS-R1634.

[0034] The bending strength of the AlN sintered body 1 is, for example, 280 MPa or more, preferably 300 MPa or more, and more preferably 310 MPa or more. On the other hand, the upper limit of the bending strength of the AlN sintered body 1 is typically 450 MPa. The bending strength of the aluminum nitride sintered body is measured, for example, in accordance with JIS-R1601.

[0035] The dielectric constant ε' of the AlN sintered body 1 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 AlN sintered body 1 in the range of 1 MHz to 13.56 MHz is, for example, 1.0 × 10⁻⁶. －３The following applies. On the other hand, the lower limit of the dielectric loss tanδ of the AlN sintered body 1 is typically 0. The dielectric constant and dielectric loss of the aluminum nitride sintered body are measured, for example, by the short-circuit type resonance method in accordance with JIS-R1627.

[0036] The thermal conductivity of the AlN sintered body 1 at 300°C is, for example, 50 W / m·K to 100 W / m·K, preferably 60 W / m·K to 80 W / m·K. The thermal conductivity of the aluminum nitride sintered body is measured, for example, in accordance with the flash method specified in JIS-R1611:2010.

[0037] C. Method for Manufacturing an Aluminum Nitride Sintered Body Next, a method for manufacturing an aluminum nitride sintered body according to one embodiment will be described. In one embodiment, the method for manufacturing the AlN sintered body 1 includes a molding step of preparing a molded body from an aluminum nitride raw material (hereinafter referred to as the AlN raw material) and a firing step of firing the molded body.

[0038] C-1. Molding Process In the molding process, the AlN raw material is molded into the desired shape using any appropriate molding method to prepare a molded body.

[0039] AlN raw materials contain AlN as their main component. Typically, AlN raw materials also contain metal elements other than Al, as mentioned above.

[0040] In one embodiment, the AlN raw material contains Ca as a metal element other than Al. The AlN raw material may also further contain oxygen. When the AlN raw material contains Ca and / or oxygen, Ca-containing AlON can be stably formed at the grain boundaries.

[0041] The AlN raw material is typically in powder form. The average particle size D50 of the AlN raw material is, for example, 1.0 μm to 1.5 μm. Such AlN raw material may be granulated by any suitable granulation method.

[0042] 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.

[0043] This allows for the preparation of a molded body having the desired shape.

[0044] C-2. 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.

[0045] The firing temperature is, for example, 1900°C or lower, preferably 1800°C or lower, and more preferably 1780°C or lower. On the other hand, the firing temperature is, for example, 1600°C or higher, preferably 1650°C or higher, and more preferably 1700°C or higher. The firing time is, for example, 10 hours or less, preferably 5 hours or less, and more preferably 2 hours or less. On the other hand, the lower limit of the firing time is typically 0.5 hours. When the firing temperature and / or firing time are within this range, the average grain size of the crystal grains can be adjusted to the above range, and Ca-containing AlON can be present in an isolated state at the grain boundaries. The environmental pressure during the firing process is, for example, 100 kPa to 900 kPa.

[0046] 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, 10 kgf / cm². ２ ~500kgf / cm ２ The pressure is preferably 100 kgf / cm². ２ ~300kgf / cm ２ More preferably, 150 kgf / cm² ２ ~250kgf / cm ２ And more preferably 180 kgf / cm² ２ ~220kgf / cm ２Therefore, when the pressure in the hot press is within this range, the average grain size of the crystal grains can be stably adjusted to the above range, and Ca-containing AlON can be sufficiently present in an isolated state at the grain boundaries.

[0047] 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, Ca-containing AlON is formed in isolation at the grain boundaries. In one embodiment, Ca and oxygen contained in the molded body react with AlN to form Ca-containing AlON. Through this process, an AlN sintered body 1 is manufactured.

[0048] D. Applications of Aluminum Nitride Sintered Bodies AlN sintered bodies 1 are typically applied to components of semiconductor manufacturing equipment (semiconductor manufacturing materials) for manufacturing semiconductor devices. Semiconductor manufacturing materials are devices that can be distributed individually and are industrially usable. Examples of semiconductor manufacturing materials include susceptors, heaters, electrostatic chucks, ceramic conductors, input terminals, and shower heads.

[0049] As shown in Figure 2, in one embodiment, the AlN sintered body 1 is suitably applied to an electrostatic chuck 100. The electrostatic chuck 100 typically comprises a ceramic substrate 1a made of the AlN sintered body 1 and an ESC electrode 2.

[0050] The ceramic substrate 1a functions as a wafer mounting plate. In the illustrated example, the ceramic substrate 1a has a mounting surface 15 on which a silicon wafer 8 can be mounted. The mounting surface 15 is one side of the ceramic substrate 1a in the thickness direction. The ceramic substrate 1a has any suitable shape. In the illustrated example, the ceramic substrate 1a has a disc shape (see Figure 1). The thickness of the ceramic substrate 1a is, for example, 10 mm to 50 mm.

[0051] The ESC electrode 2 is provided inside the ceramic substrate 1a. In other words, the ESC electrode 2 is embedded in the ceramic substrate 1a. The ESC electrode 2 is typically made of a conductive material with a lower volume resistivity than the AlN sintered body 1. 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.

[0052] The ESC electrode 2 has any suitable shape. Typically, the ESC electrode 2 has a plate shape. In one embodiment, the ESC electrode 2 has a shape similar to the outer shape of the ceramic substrate 1a when viewed from the thickness direction of the ceramic substrate 1. In the illustrated example, the center of the ESC electrode 2 and the center of the ceramic substrate 1a substantially coincide when viewed from the thickness direction of the ceramic substrate 1a.

[0053] The thickness of the ESC electrode 2 (the dimension in the thickness direction of the ceramic substrate 1a) is, for example, 10 μm to 50 μm, and preferably 20 μm to 30 μm.

[0054] In the illustrated example, the electrostatic chuck 100 is equipped with one ESC electrode 2. The number of ESC electrodes 2 is not particularly limited. The electrostatic chuck 100 may be equipped with multiple ESC electrodes 2.

[0055] A ceramic substrate 1a in which the ESC electrode 2 is embedded is manufactured, for example, by embedding the ESC electrode 2 (or a precursor of the ESC electrode) at a desired position in a molded body made of AlN raw material in the molding process described above, and then firing them in the firing process described above.

[0056] The electrostatic chuck 100 may further include a resistive heating element 3. The resistive heating element 3 is configured to generate heat when a voltage is applied.

[0057] The resistive heating element 3 is located inside the ceramic substrate 1a. In other words, the resistive heating element 3 is embedded in the ceramic substrate 1a. In the illustrated example, the resistive heating element 3 is located on the opposite side of the mounting surface 15 of the ceramic substrate 1a from the ESC electrode 2.

[0058] The resistive heating element 3 is made of the conductive material described above. The resistive heating element 3 has any suitable shape. Examples of shapes for the resistive heating element 3 include a coil shape, a zigzag shape, and a mesh shape.

[0059] In such an electrostatic chuck 100, the AlN sintered body 1 constituting the ceramic substrate 1a has a suitable volume resistivity. Therefore, when a DC voltage is applied to the ESC electrode 2 with the silicon wafer 8 placed on the mounting surface 15 at a temperature of 250°C or higher, 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 2. As a result, a JR force can be generated between the silicon wafer 8 and the ESC electrode 2, and the silicon wafer 8 can be stably chucking the ceramic substrate 1a. Consequently, various processes can be performed on the silicon wafer 8 with high precision, and the manufacturing of semiconductor devices can be miniaturized.

[0060] 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.

[0061] (1) Measurement of the content ratio of constituent elements in aluminum nitride sintered bodies The central portion of the AlN sintered bodies produced in Example 1 and Comparative Example 1 was crushed to obtain the first sample. The portion of the AlN sintered body with a pitch circle diameter (PCD) of 285 mm to 335 mm was also crushed to obtain the second sample. Furthermore, the central portion of the AlN sintered bodies produced in Examples 2, 3 and Comparative Example 2 was crushed to obtain the first sample. Next, the content ratio of constituent elements in each of the first and second samples was measured by ICP-AES (inductively coupled plasma emission spectrometry) in accordance with JIS-K0116. The results are shown in Tables 1 and 2.

[0062] (2) Identification of the elemental composition of aluminum nitride sintered bodies by FE-EPMA A first test specimen was cut from the central portion of the AlN sintered bodies produced in Example 1 and Comparative Example 1. A second test specimen was cut from the portion of the AlN sintered body with a pitch circle diameter (PCD) of 285 mm to 335 mm. Furthermore, a first test specimen was cut from the central portion of the AlN sintered bodies produced in Examples 2, 3 and Comparative Example 2. The cross-section along the thickness direction of each of the first and second test specimens was polished to a mirror finish by lapping to serve as the measurement surface. The polished surface was then analyzed by FE-EPMA to obtain an elemental mapping image. The elemental composition of the AlN sintered bodies was identified using this method. The results are shown in Table 1. Furthermore, Figure 3 shows the mapping image of aluminum (Al) in the first test specimen of Example 1, Figure 4 shows the mapping image of calcium (Ca) in the first test specimen of Example 1, Figure 5 shows the mapping image of oxygen (O) in the first test specimen of Example 1, and Figure 6 shows the mapping image of nitrogen (N) in the first test specimen of Example 1. In addition, Figure 7 shows the mapping image of aluminum (Al) in the first test specimen of Comparative Example 1, Figure 8 shows the mapping image of calcium (Ca) in the first test specimen of Comparative Example 1, Figure 9 shows the mapping image of oxygen (O) in the first test specimen of Comparative Example 1, and Figure 10 shows the mapping image of nitrogen (N) in the first test specimen of Comparative Example 1. These mapping images confirmed that in the example, aluminum oxynitride (Ca-solid-solution ALON), in which calcium is solid-dissolved, exists in an isolated state at the grain boundaries. On the other hand, Ca-solid-solution ALON was not confirmed in the comparative example.

[0063] (3) Calculation of the average grain size and standard deviation of multiple crystal grains First and second test pieces were cut from the AlN sintered bodies produced in Example 1 and Comparative Example 1 in the same manner as in "(2) Identification of the elemental composition of aluminum nitride sintered bodies by FE-EPMA" described above. Furthermore, first test pieces were cut from the AlN sintered bodies produced in Examples 2, 3 and Comparative Example 2 in the same manner as described above. Next, the average grain size and standard deviation of multiple crystal grains in each of the first and second test pieces were calculated by acquiring backscattered electron images with a scanning electron microscope at a field of view of 3000x, and measuring the diameter of N=40 particles corresponding to AlN in the backscattered electron images. The results are shown in Tables 1 and 2.

[0064] (4) Calculation of the lattice constant of AlN First and second test pieces were cut from the AlN sintered bodies produced in Example 1 and Comparative Example 1 in the same manner as in "(2) Identification of the elemental composition of aluminum nitride sintered bodies by FE-EPMA" described above. Next, the lattice constant of AlN in each of the first and second test pieces was calculated 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 c-axis length relative to the a-axis length (c / a), and the lattice volume of AlN are shown in Table 1.

[0065] (5) Measurement of the density of the AlN sintered body First and second test pieces were cut from the AlN sintered bodies produced in Example 1 and Comparative Example 1 in the same manner as in "(2) Identification of the elemental composition of aluminum nitride sintered body by FE-EPMA" described above. The density of the first and second test pieces was then calculated using the Archimedes method in accordance with JIS-R1634:1998. The results are shown in Table 1.

[0066] (6) Calculation of bending strength and standard deviation of AlN sintered body First and second test specimens were cut from the AlN sintered bodies produced in Example 1 and Comparative Example 1 in the same manner as in "(2) Identification of elemental composition of aluminum nitride sintered body by FE-EPMA" described above. Then, the bending strength and standard deviation of the first and second test specimens were measured and calculated for N=10 specimens in accordance with JIS R1601. The results are shown in Table 1.

[0067] (7) Measurement of volume resistivity of aluminum nitride sintered bodies First and second test pieces were cut from the AlN sintered bodies produced in Example 1 and Comparative Example 1 in the same manner as in "(2) Identification of elemental composition of aluminum nitride sintered bodies by FE-EPMA" described above. Furthermore, first test pieces were cut from the AlN sintered bodies produced in Examples 2, 3 and Comparative Example 2 in the same manner as described above. Next, the volume resistivity of the first and second test pieces was measured at 300°C or room temperature (25°C) in accordance with JIS-C2141. The applied voltage was +500V. The results are shown in Tables 1 and 2.

[0068] (8) Measurement of dielectric constant ε' and dielectric loss tanδ of aluminum nitride sintered bodies First and second test pieces were cut from the AlN sintered bodies produced in Example 1 and Comparative Example 1 in the same manner as in "(2) Identification of elemental composition of aluminum nitride sintered bodies by FE-EPMA" described above. The dielectric constant and dielectric loss of the first and second test pieces were then measured using the capacitance method (two-terminal method). The frequency was 1 MHz or 13.65 MHz. The results are shown in Table 1.

[0069] <<Example 1>> AlN raw material powder was filled into a predetermined mold and uniaxially pressed to obtain a molded body having a disc shape. The pressure during uniaxial pressing was 200 kgf / cm ２ Next, the molded body was fired using 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 pressure inside the hot press furnace was increased to 0.25 MPa, and the molded body was subjected to a pressure of 200 kgf / cm in the thickness direction. ２ The molded body was pressed with pressure. In this state, the molded body was fired at 1770°C for 2 hours. This produced an AlN sintered body having multiple crystal grains containing AlN and grain boundaries located between adjacent crystal grains. The AlN sintered body had a disc shape. The diameter of the AlN sintered body was 340 mm and the thickness of the AlN sintered body was 25 mm.

[0070] <<Examples 2 and 3>> AlN sintered bodies were manufactured in the same manner as in Example 1, except that the composition of the AlN raw material powder was adjusted so that the AlN sintered body to be manufactured had the composition shown in Table 2.

[0071] <<Comparative Example 1>> An AlN sintered body was manufactured in the same manner as in Example 1, except that the firing temperature for the molded body was changed to 1850°C and the firing time to 4 hours.

[0072] <<Comparative Example 2>> An AlN sintered body was manufactured in the same manner as in Comparative Example 1, except that the composition of the AlN raw material powder was adjusted so that the AlN sintered body to be manufactured had the composition shown in Table 2.

[0073]

[0074]

[0075] <Evaluation> As shown in Tables 1 and 2, in an AlN sintered body, even if the average grain size of the crystal grains is in the range of 1.5 μm to 3.0 μm, if the content of metal elements other than Al exceeds 30 ppm and is 300 ppm or less, and Ca solid-solution ALON exists in an isolated state at the grain boundaries, the volume resistivity of the AlN sintered body at 300°C is in a range suitable for JR type electrostatic chucks (typically 1.0 × 10⁻⁶). ９ Ωcm ~ 5.0 × 10 １１ Ωcm, preferably 1.0 × 10 ９ Ωcm ~ 1.5 × 10 １０ It can be seen that it can be stably adjusted to Ωcm.

[0076] The aluminum nitride 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.

[0077] 1. Aluminum nitride sintered body 1a. Ceramic substrate 11. Crystal grains 12. Grain boundaries 13. Ca-containing AlON 2. ESC electrode 3. Resistive heating element 100. Electrostatic chuck

Claims

1. An aluminum nitride sintered body comprising: a plurality of crystal grains containing aluminum nitride; grain boundaries located between adjacent crystal grains among the plurality of crystal grains, wherein the average grain size of the plurality of crystal grains is 1.5 μm to 3.0 μm; the grain boundaries include portions in which aluminum oxynitride containing calcium exists in an isolated state; and the content of metal elements other than aluminum is greater than 30 ppm and 300 ppm or less.

2. The aluminum nitride sintered body according to claim 1, wherein the content of metal elements other than aluminum exceeds 100 ppm.

3. The aluminum nitride sintered body according to claim 1 or 2, wherein the standard deviation of the average grain size of the plurality of crystal grains is 1.0 μm or less.

4. The volume resistivity measured by applying a voltage of +500V at 300℃ is 5.0 × 10⁻⁶. ９ Ω・cm~1.0×10 １０ The aluminum nitride sintered body according to claim 1 or 2, having an impedance of Ω·cm.

5. The aluminum nitride sintered body according to claim 1 or 2, wherein the bending strength is 300 MPa or more.

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