Wafer Support

Abstract

To provide a new wafer support which has excellent corrosion resistance.SOLUTION: Provided is a wafer support 30 which comprises: a base material 14 made of machinable ceramic including boron nitride; a first layer for covering a surface of the base material; and conductive members 18, 20 in which at least a part is included in the base material. The first layer is composed of a ceramic sintered compact essentially consisting of aluminum nitride, and the ratio of the boron nitride included in the base material 14 is higher than that included in the first layer.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a support for supporting a wafer. [Background technology]

[0002] The ceramic materials used in conventional electrostatic chucks and the like are often fine ceramics such as silicon nitride and aluminum nitride, which are difficult to process, and complex processing is difficult from the standpoint of cutting speed and chipping. Therefore, a wafer support device has been devised that uses a machinable ceramic, which has excellent processability, as its base material (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-155571 Summary of the Invention [Problem to be solved by the invention]

[0004] When the wafer support is exposed to the corrosive gases and plasma atmospheres used in semiconductor manufacturing processes, particles are likely to be generated from its surface. If these particles adhere to the wafer, they can cause defects in subsequent semiconductor manufacturing processes. One solution is to cover the machinable ceramic substrate with a thin film of aluminum nitride, which is less susceptible to corrosion by plasma.

[0005] However, if corrosion originates from tiny defects such as pinholes in the aluminum nitride film and reaches the machinable ceramic substrate, it will corrode significantly, generating particles and resulting in defective products.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a new wafer supporter having excellent corrosion resistance. [Means for solving the problem]

[0007] To solve the above problems, one embodiment of the present invention provides a wafer support comprising a substrate made of a machinable ceramic containing boron nitride, a first layer covering the surface of the substrate, and a conductive member at least partially contained in the substrate. The first layer is made of a ceramic sintered body containing aluminum nitride as its main component, and the proportion of boron nitride contained in the substrate is higher than the proportion of boron nitride contained in the first layer.

[0008] Compared to general fine ceramics, machinable ceramics are easier to process and have excellent thermal shock resistance. On the other hand, machinable ceramics such as boron nitride are not necessarily the most suitable materials in terms of corrosion resistance. Therefore, according to this embodiment, the substrate can be manufactured and then machined, without the need to achieve a complex shape during the substrate manufacturing stage. This makes it possible to manufacture wafer supports with a variety of shapes. Additionally, according to this embodiment, the first layer can reduce corrosion of the substrate caused by processing gases and plasma.

[0009] The first layer may have a thickness of 0.3 to 3.0 mm, which makes it difficult for corrosion to reach the substrate even if the first layer has minute defects such as pinholes.

[0010] The first layer may contain 90 to 100 mass % of aluminum nitride and 0 to 10 mass % of boron nitride, thereby improving the corrosion resistance of the first layer.

[0011] The substrate may further include a second layer covering the first layer. The second layer may be made of at least one material selected from the group consisting of aluminum nitride, aluminum oxide, yttrium oxide, and magnesium oxide, and may have a thickness of 1.0 to 20 μm. This can further improve the corrosion resistance of the substrate compared to a substrate having only the first layer.

[0012] The thermal expansion coefficient of the substrate is Δ1 [1 × 10 -6 / °C], and the thermal expansion coefficient of the first layer is Δ2 [1 × 10 -6 / °C], |Δ2-Δ1|≦1.0 is satisfied. This allows the base material and the first layer to be produced by integral sintering.

[0013] The machinable ceramic may contain 15 to 40 mass% of boron nitride, 0 to 40 mass% of zirconium oxide, 0 to 55 mass% of silicon nitride, 0 to 20 mass% of silicon carbide, and 0 to 75 mass% of aluminum nitride, assuming the total ceramic components of boron nitride, zirconium oxide, silicon nitride, silicon carbide, and aluminum nitride to be 100 mass%. It may also contain 3 to 15 mass% of a sintering aid component, assuming the total ceramic components to be 100 mass%.

[0014] The conductive member may be made of a metallic material selected from the group consisting of molybdenum, tungsten, tantalum, and alloys containing any of these.

[0015] Any combination of the above components and any transformation of the present invention into a method, device, system, etc. are also valid aspects of the present invention. Appropriate combinations of the above elements may also be included in the scope of the invention for which patent protection is sought by this patent application. [Effects of the Invention]

[0016] According to the present invention, a new wafer support having excellent corrosion resistance can be realized. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 10 is a schematic cross-sectional view of a wafer support according to a reference example. [Figure 2] 1A and 1B are schematic diagrams for explaining corrosion that occurs when there is a defect in the protective layer. [Figure 3] FIG. 10 is a photograph taken by a scanning electron microscope (SEM) of a cross section of a wafer support having a defect in the AlN film. [Figure 4]1 is a schematic cross-sectional view of a wafer support according to an embodiment of the present invention. [Figure 5] 5(a) to 5(e) are diagrams showing an example of a method for manufacturing a wafer supporting member according to this embodiment. [Figure 6] Figure 6(a) is a photograph of the cross section of the protective layer of the aluminum nitride sintered body of Example 1 taken with a scanning electron microscope (SEM), Figure 6(b) is a photograph of the cross section of the protective layer of the aluminum nitride sintered body of Example 3 taken with a scanning electron microscope, and Figure 6(c) is a photograph of the cross section of the aluminum nitride thin film of the reference example taken with a scanning electron microscope. [Figure 7] Figure 7(a) is a photograph of the surface of the protective layer of the aluminum nitride sintered body of Example 1 taken with a scanning electron microscope (SEM); Figure 7(b) is a photograph of the surface of the protective layer of the aluminum nitride sintered body of Example 3 taken with a scanning electron microscope; Figure 7(c) is a photograph of the surface of the aluminum nitride thin film of a reference example taken with a scanning electron microscope; Figure 7(d) is an image converted from the photograph of Figure 7(a) using image analysis software; Figure 7(e) is an image converted from the photograph of Figure 7(b) using image analysis software; and Figure 7(f) is an image converted from the photograph of Figure 7(c) using image analysis software. [Figure 8] 8(a) to 8(c) are schematic diagrams for explaining the plasma exposure test. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and redundant description will be omitted where appropriate.

[0019] (Wafer support) First, a schematic configuration of a wafer support will be described as a reference example. The wafer support may be capable of supporting a semiconductor substrate such as a silicon wafer, and may include an adsorption mechanism and a heating mechanism. For example, the wafer support may simply be a susceptor on which a wafer is mounted. Alternatively, the wafer support may be an electrostatic chuck that generates an adsorption force for the mounted wafer, or a heater that heats the wafer. Furthermore, the object supported by the wafer support is primarily a wafer, but it may also support other members or components.

[0020] In the reference example, the case where the wafer supporter is an electrostatic chuck with a heater will be described as an example. Fig. 1 is a schematic cross-sectional view of the wafer supporter according to the reference example.

[0021] A wafer support 10 according to the reference example is used to support a wafer W in a chamber 12 of a semiconductor manufacturing apparatus such as plasma CVD. The wafer support 10 has a base 14 made of machinable ceramics, a protective layer 16 covering a surface 14a of the base 14, and conductive members 18, 20 at least partially embedded in the base 14. The wafer W is mounted on the surface of the protective layer 16, which is the mounting surface 16a.

[0022] The conductive member 18 functions as an electrostatic chuck electrode through which a current flows to generate an attraction force for fixing the wafer W to the mounting surface 16a. The conductive member 20 also functions as a resistance heater (heater) for heating the wafer W to a predetermined process temperature. In the wafer support 10 according to this embodiment, the conductive members 18 and 20 are embedded in the base material 14, which is a sintered body. Therefore, the conductive members 18 and 20 must be disposed inside the raw material powder during the firing process, and are preferably made of a high-melting-point metal that does not melt at the firing temperature. For example, the conductive members are preferably made of a high-melting-point metal such as molybdenum, tungsten, or tantalum, or an alloy containing two or more of these metals.

[0023] The wafer support 10 may also be formed with a gas inlet 22 that connects the mounting surface 16a exposed to the chamber side to an external gas supply source (not shown) through the inside of the base material 14. The gas inlet 22 is for supplying gas that cools the wafer W adsorbed on the mounting surface 16a from the backside.

[0024] (machinable ceramics) The present inventors have conducted extensive research to find a material suitable for the wafer support, and have found that a sintered body made of so-called machinable ceramics, which has good workability (free machinability), is preferable.

[0025] Compared to common fine ceramics such as aluminum oxide, silicon nitride, aluminum nitride, and silicon carbide, machinable ceramics are easier to machine. This means that chipping, a problem that occurs when machining ceramics, is less likely to occur with machinable ceramics, making complex machining possible. Furthermore, the amount of grinding required when machining machinable ceramics (machining rate) is several to several hundred times greater than the amount of grinding required when machining fine ceramics, allowing for efficient machining.

[0026] Machinable ceramics are composite materials made from a mixture of multiple raw materials that make up the ceramic components. For example, the volume resistivity can be adjusted by varying the proportion of silicon carbide. As a result, they are compatible with both Coulomb-type and Johnson-Rahbek-type electrostatic chucks. Furthermore, in the case of heaters, they can be used as an insulator by not adding silicon carbide. Machinable ceramics do not need to have a uniform composition throughout; the portion housing the conductive member 18 near the mounting surface 16a on which the wafer W is mounted and the portion housing the conductive member 20 may each have different compositions to optimize the functionality of each portion.

[0027] Furthermore, boron nitride is listed as one of the main components, which has superior thermal shock resistance compared to common aluminum oxide, silicon nitride, aluminum nitride, and silicon carbide, and when it is made into a finished wafer support, it can prevent damage due to cracking.

[0028] The machinable ceramics according to the reference examples and the embodiments described below are sintered bodies made of at least two or more materials, essentially containing boron nitride, selected from the group consisting of boron nitride, zirconium oxide, silicon nitride, silicon carbide, and aluminum nitride. Boron nitride also has excellent machinability, and the use of machinable ceramics containing boron nitride as an essential component can increase the processing rate. Furthermore, in the case of a wafer support in which a conductive member made of a different material is embedded within the substrate, internal stresses are generated in response to temperature changes due to differences in the physical properties of the substrate and the conductive member. Alternatively, thermal stresses are generated due to the temperature difference between the outer periphery and the center of the wafer support. However, boron nitride has excellent thermal shock resistance, making the substrate less susceptible to cracking.

[0029] The machinable ceramic of the reference example preferably contains 10 to 80 mass% of boron nitride, 0 to 80 mass% of silicon nitride, 0 to 80 mass% of zirconium oxide, and 0 to 40 mass% of silicon carbide, where the total of the ceramic components of boron nitride, zirconium oxide, silicon nitride, and silicon carbide is 100 mass%.

[0030] Furthermore, the machinable ceramics according to the reference examples and the embodiments described below contain a sintering aid component. The sintering aid can be selected from those used in sintering silicon nitride and boron nitride. Preferred sintering aids are one or more selected from aluminum oxide (alumina), magnesium oxide (magnesia), yttrium oxide (yttria), and oxides of lanthanoid metals. More preferred are mixtures of alumina and yttria, or mixtures to which magnesia has been added, or mixtures of yttria and magnesia.

[0031] The amount of sintering aid component blended is preferably in the range of 1 to 25 mass%, preferably 3 to 15 mass%, and more preferably 5 to 10 mass%, based on 100 mass% of the total ceramic components. If the amount of sintering aid component blended is 1 mass% or more, preferably 3 mass% or more, densification is facilitated, and insufficient density of the sintered body and deterioration of mechanical properties can be suppressed. On the other hand, if the amount of sintering aid component blended is 25 mass% or less, the grain boundary phase, which has low strength, is reduced, thereby suppressing deterioration of mechanical strength and deterioration of workability due to an increase in the grain boundary phase.

[0032] Although boron nitride has excellent machinability, it has poor strength characteristics. Therefore, if coarse boron nitride particles are present in a sintered compact, they can become fracture initiation sites, causing chipping and cracking during processing. To prevent the formation of such coarse boron nitride particles, it is effective to finely grind the raw material powder. It is desirable to use a main raw material powder, especially boron nitride raw material powder, with an average particle size of less than 2 μm. Boron nitride exists in various phases, such as the hexagonal (h-BN) low-pressure phase and the cubic (c-BN) high-pressure phase. From the perspective of machinability, hexagonal boron nitride is preferred. Furthermore, from the perspective of processability, the more boron nitride and the less silicon nitride (and zirconium oxide) present, the better. Furthermore, the mechanical strength and Young's modulus decrease with increasing boron nitride and decreasing silicon nitride (and zirconium oxide).

[0033] An example of a machinable ceramic is a BN-containing silicon nitride ceramic ("Photoveel II" and "Photoveel II-k70" manufactured by Ferrotec Material Technologies Corporation). The composition of Photoveel II-k70 is 38.5 mass% boron nitride, 54.1 mass% silicon nitride, 5.5 mass% yttria, and 1.9 mass% magnesia. This BN-containing silicon nitride ceramic has a bending strength of 600 MPa or less, a Young's modulus of 250 GPa or less, and a Vickers hardness of 5 GPa or less. Machinable ceramics with these characteristics have a large grinding amount per unit time (processing rate) during processing, allowing for the efficient production of wafer supports with complex shapes. Furthermore, by fabricating a substrate as a block of a simple shape and then cutting it into the desired shape, complex wafer supports can be manufactured in a single component.

[0034] (Method of manufacturing sintered body) First, a raw material powder is prepared by mixing a main raw material powder of ceramic components such as boron nitride, zirconium oxide, silicon nitride, silicon carbide, and aluminum nitride in a predetermined blending ratio with 1 to 25 mass% of sintering aid powder, assuming the total ceramic components to be 100 mass%. This mixing can be carried out, for example, by a wet ball mill.

[0035] Next, the raw material powder, the molded body, or both are molded under high temperature and pressure, followed by sintering to produce a sintered body. Note that a portion of the raw material powder or the molded body may be replaced with a sintered body. To provide a resistance heater for a heater or an electrode for an electrostatic chuck inside the sintered body, a component or material that will become a conductor after sintering (e.g., a metal plate, metal foil, conductive paste, coil, mesh, etc.) may be placed (embedded) in a predetermined position when the raw material powder, molded body, or sintered body is filled into a hot press apparatus. The shape of the conductor is not particularly limited. This sintering can be performed, for example, using a hot press apparatus. Hot pressing is performed in a non-oxidizing (inert) atmosphere, such as a nitrogen or argon atmosphere, but it can also be performed in pressurized nitrogen. The hot pressing temperature is, for example, in the range of 1300 to 1950°C. If the temperature is too low, sintering will be insufficient, while if it is too high, thermal decomposition of the main raw material will occur. A pressure of 20 to 50 MPa is appropriate. The duration of hot pressing depends on the temperature and dimensions, but is typically about 1 to 4 hours. High-temperature pressure sintering can also be performed by HIP (hot isostatic pressing). In this case, the sintering conditions can also be appropriately determined by a person skilled in the art.

[0036] The sintered body is then machined into the desired shape to produce a wafer support. The machinable ceramics according to the reference examples and embodiments have high strength and high machinability (free-cutting properties), making complex micromachining possible in an industrially practical timeframe. Furthermore, the conditions for manufacturing the sintered body are preferably selected so that the average crystal grain size of the machinable ceramic is 0.5 μm or less, taking into account the corrosion resistance to plasma described below. This allows for reduced defects in the semiconductor manufacturing process, even if part of the polycrystal is peeled off as particles due to corrosion in the plasma atmosphere, because the particles themselves are small. Furthermore, the average crystal grain size of the machinable ceramic is more preferably 0.1 μm or less.

[0037] As described above, the machinable ceramics used for the substrate 14 according to the reference example are easier to process than general fine ceramics. Therefore, according to this embodiment, even if a complex shape is not realized at the stage of manufacturing the substrate 14, the substrate can be manufactured and then machined, making it possible to manufacture wafer support bodies of various shapes.

[0038] On the other hand, depending on the application, the wafer support 10 is exposed to a corrosive gas or plasma atmosphere during the semiconductor manufacturing process. Examples of corrosive plasma include fluorine-based gases such as CF4, C4F8, SF8, NF3, and CHF3, and gases such as Ar, O2, and CO2 may also be mixed in. Because silicon components are highly reactive with fluorine-based plasma, substrates containing silicon have low resistance to these plasmas. Furthermore, boron nitride is highly reactive with O2 plasma.

[0039] As mentioned above, the machinable ceramics according to the reference example may contain silicon nitride, silicon carbide, or boron nitride as their main components, and the inventors of the present application have realized that machinable ceramics containing silicon or boron nitride may have low corrosion resistance in a corrosive plasma atmosphere. Therefore, in order to improve the corrosion resistance of the wafer support against plasma and process gases, a protective layer 16 is provided on the surface of the substrate 14 of the wafer support 10 according to this embodiment.

[0040] (protective layer) The protective layer 16 according to the reference example is made of a material that is less corroded by plasma than the substrate 14. This allows the protective layer 16 to reduce plasma corrosion of the substrate 14. Furthermore, even if the material constituting the substrate 14 is prone to peeling, the protective layer 16 can reduce peeling. The protective layer 16 according to the present embodiment is made of a material such as aluminum nitride, aluminum oxide, yttrium oxide, magnesium oxide, or yttrium aluminum garnet (YAG: Y3O5Al 12The electrostatic chuck is made of at least one material selected from the group consisting of aluminum nitride (AlN), yttrium aluminum monoclinic (YAM), and yttrium aluminum monoclinic (YAlO). Aluminum nitride, in particular, has excellent thermal shock resistance, making it an ideal material for processes in which high thermal shock is applied to the electrostatic chuck.

[0041] As shown in FIG. 1 , the thickness t of the dielectric layer is the distance between the mounting surface 16a, which is the surface of the protective layer 16, and the conductive member 18. Therefore, if the protective layer 16 is too thick, the thickness t of the dielectric layer increases, and sufficient chucking force cannot be obtained. Furthermore, if the thickness t is too large, cracks are likely to occur in the protective layer 16 when subjected to a high thermal shock. On the other hand, if the thickness t of the protective layer 16 is too small, sufficient corrosion resistance against plasma cannot be obtained. Therefore, the protective layer 16 according to the reference example has a thickness in the range of 1 to 30 μm. This allows for both the desired chucking force and corrosion resistance against plasma. If the thickness of the protective layer 16 is preferably 2 μm or more, more preferably 5 μm or more, better corrosion resistance against plasma can be obtained. Furthermore, if the thickness of the protective layer 16 is preferably 20 μm or less, more preferably 10 μm or less, more sufficient chucking force can be obtained.

[0042] (Method for forming protective layer) The protective layer is formed by methods such as CVD, PVD (sputtering or ion plating), aerosol deposition, etc. These methods are excellent at controlling the film thickness, and therefore can form a film with high precision in the range of 1 to 30 μm, such as the thickness of the protective layer mentioned above.

[0043] Sputtering is performed by placing the substrate and the target (material that will become the film) facing each other. -1 In an Ar gas atmosphere of around a few Pa, a negative high voltage is applied to the target to cause discharge, causing Ar ions to collide with the target. When the Ar ions collide, atoms are ejected from the target in a sputtering phenomenon. The ejected atoms are deposited on the substrate, forming a protective layer.

[0044] Reactive sputtering is suitable for forming the protective layer 16 of the reference example. It is known that when compounds such as aluminum oxide or aluminum nitride are used as targets, the sputtering rate drops significantly, resulting in an extremely slow coating speed. Furthermore, the sputtering rate differs for each element, resulting in a film that deviates from the target composition. Therefore, when the protective layer of the reference example is made of aluminum nitride, a reactive sputtering method is suitable, in which a single metal aluminum target is used and reacted with N2, a reactive gas.

[0045] Ion plating, another method for forming a protective layer, is performed by placing the substrate and the evaporation source (the material that will become the film) face to face. -2 ~10 -4 This method involves dissolving and evaporating film raw materials from an evaporation source in a vacuum of about 100 Pa and depositing them on a substrate. Films of various materials can be produced by varying the type of evaporated material and the introduction of reactive gases. Among vacuum deposition-based coating technologies, ion plating generally refers to methods that use ions. Specifically, there are various techniques, such as radio-frequency ion plating, reactive ion plating, and ion-assisted deposition, and any of these can be used. In the reference example, when the protective layer is made of yttrium oxide, metal yttrium is used as the evaporation source, and O2 is introduced as the reactive gas, allowing film formation in a plasma atmosphere. Furthermore, in the case of ion-assisted deposition, a protective layer made of yttrium oxide can be formed by using yttrium oxide as the evaporation source and O2 ions as the assist ions. In addition, protective layers made of magnesium oxide or aluminum oxide can also be formed by radio-frequency ion plating, reactive ion plating, and ion-assisted deposition.

[0046] In the case of film deposition methods that use ions, such as the aforementioned sputtering and ion plating, the surface can be cleaned with Ar ions before deposition (removing surface deposits and oxide films through ion bombardment), resulting in a film with high adhesion. N2 and H2 ions are particularly effective for cleaning organic materials (a process commonly known as ion bombardment). The bombardment process can remove extremely fine particles (which cannot be completely removed by ultrasonic cleaning, etc.) from the surface of the machinable ceramic substrate, so substrates with a protective film can generate fewer initial particles than substrates without a protective film. These methods can also increase the purity of aluminum nitride compared to bulk ceramics made by sintering powder, reducing concerns about wafer contamination and contributing to reduced defects.

[0047] Furthermore, electrostatic chucks using a machinable ceramic substrate can achieve point contact with the wafer when the substrate has a surface roughness within a predetermined range (e.g., an arithmetic mean roughness Ra in the range of 0.02 μm≦Ra≦0.2 μm), resulting in minimal rubbing between the wafer and the substrate during dechucking. However, due to the cleavage properties of boron nitride, physical forces can easily cause particle peeling (cracks), which can easily generate particles. However, coating the surface of the substrate 14 with a protective layer 16 such as the aforementioned aluminum nitride reduces particle peeling and particle generation. Additionally, the protective layer 16 fabricated using the film-forming method of the reference example conforms to the surface roughness of the substrate 14 and has a surface with an arithmetic mean roughness Ra in the range of 0.02 μm≦Ra≦0.2 μm. In other words, the wafer support 10 of the reference example is extremely effective at reducing particles because it has a protective layer 16 that is resistant to plasma corrosion and yet can itself be in point contact with the wafer.

[0048] Furthermore, in the case of a multilayer member in which each layer is made of a hard material (a combination of materials with a high Young's modulus), cracks are likely to occur due to thermal stress because each layer is difficult to deform. However, by using a substrate 14 containing boron nitride as a main component, as in the wafer support 10 according to the reference example, stress can be absorbed (mitigated). Furthermore, because the machinable ceramic according to the reference example is a composite material, it is possible to match the thermal expansion coefficient of the substrate 14 to that of the protective layer 16. As a result, thermal stress due to differences in the thermal expansion coefficients of the layers can be reduced, and the occurrence of cracks, i.e., particle generation, is suppressed.

[0049] The wafer support body according to the above-described reference example has the excellent thermal shock resistance of machinable ceramics, while the protective layer 16 improves corrosion resistance against plasma and process gases. However, the inventors have realized that the following problems can occur if there are minute defects such as pinholes (small holes) in the AlN film that serves as the protective layer. Figure 2 is a schematic diagram illustrating the corrosion that occurs when there is a defect in the protective layer. Figure 3 is a photograph taken with a scanning electron microscope (SEM) of a cross section of a wafer support body with a defect in the AlN film.

[0050] As shown in Figures 2 and 3, when corrosion originates from a defect, it becomes significantly corroded when it reaches the machinable ceramic substrate. This results in the generation of particles, which leads to the production of defective products. Furthermore, it is extremely difficult to eliminate micro-defects such as pinholes using conventional film formation techniques. Furthermore, if the AlN film is completely corroded, the machinable ceramic substrate, which has low corrosion resistance, is exposed on the front, generating a large number of particles that not only result in defective products but also contaminate the equipment. This results in equipment failure and increased downtime.

[0051] Therefore, in the wafer support body according to this embodiment, a sintered body containing aluminum nitride as a main component is provided between the protective layer 16 and the substrate 14. Fig. 4 is a schematic cross-sectional view of the wafer support body according to this embodiment. Note that components similar to those of the wafer support body 10 according to the reference example shown in Fig. 1 (conductive members 18, 20, gas inlet 22, etc.) are not shown.

[0052] Wafer support member 30 according to this embodiment includes substrate 14 made of machinable ceramics containing boron nitride, protective layer 15 covering surface 14a of substrate 14, and conductive members 18, 20 at least partially embedded in substrate 14. Protective layer 15 is made of a ceramic sintered body containing aluminum nitride as its main component, and the proportion of boron nitride contained in substrate 14 is higher than that of protective layer 15. An intermediate layer containing machinable ceramics as its main component may be provided between protective layer 15 and substrate 14.

[0053] Machinable ceramics are easier to process than general fine ceramics and have excellent thermal shock resistance. Therefore, the wafer support body 30 according to this embodiment can be machined after the base material 14 is fabricated, without the need to achieve a complex shape at the stage of fabricating the base material 14, making it possible to manufacture wafer support bodies in a variety of shapes.

[0054] On the other hand, machinable ceramics such as boron nitride are not necessarily the most suitable material in terms of corrosion resistance. Therefore, by providing a protective layer 15 made of a ceramic sintered body primarily composed of highly corrosion-resistant aluminum nitride on the substrate 14, even if micro-defects or wear occur in the protective layer 16 made of a thin film of aluminum nitride, the substrate 14 is less likely to be directly exposed to a corrosive atmosphere, and corrosion of the substrate 14 by the process gas or plasma can be suppressed. As a result, the amount of particles is suppressed, reducing the occurrence of defects in the manufacturing process and protecting the semiconductor manufacturing equipment.

[0055] The thickness of protective layer 15 may be in the range of 0.3 to 3.0 mm, more preferably 0.5 to 2.0 mm. This makes it difficult for corrosion to reach the substrate even if micro-defects such as pinholes are present in protective layer 15. If the thickness of protective layer 15 is too thin (for example, less than 0.3 mm), it becomes difficult to manufacture it as a sintered body, and if micro-defects are present, holes will easily penetrate to the substrate. On the other hand, if the thickness of protective layer 15 is too thick (for example, greater than 3.0 mm), the effect of improving thermal shock resistance by stacking machinable ceramic substrate 14 and protective layer 15 with a gradient structure will be lost.

[0056] The protective layer 15 may contain 70 to 100 mass % aluminum nitride and 0 to 30 mass % boron nitride, or may contain 80 to 100 mass % aluminum nitride and 0 to 20 mass % boron nitride, and preferably contains 90 to 100 mass % aluminum nitride and 0 to 10 mass % boron nitride. This improves the corrosion resistance of the protective layer 15. From the viewpoint of thermal shock resistance, the more boron nitride the protective layer 15 contains, the better. The smaller the particle size of the aluminum nitride or boron nitride contained in the protective layer 15, the better the corrosion resistance, and the average particle size is preferably 5 μm or less, and more preferably 2 μm or less. The fine particle size reduces the size of particles generated, thereby reducing defects in semiconductors manufactured in an apparatus using the wafer support.

[0057] The wafer support 30 according to this embodiment further includes a protective layer 16 that covers the protective layer 15. The protective layer 16 according to this embodiment is made of at least one material selected from the group consisting of aluminum nitride, aluminum oxide, yttrium oxide, and magnesium oxide, and has a thickness of 1.0 to 20 μm. The thickness of the protective layer 16 is more preferably 1.0 to 10 mm. This further improves the corrosion resistance of the substrate 14 compared to the case where only the protective layer 15 is provided. Note that if the protective layer 15 is too thin, the corrosion resistance will be reduced (reducing the component life), and if the protective layer 15 is too thick, cracks will be more likely to occur due to internal stress during film formation.

[0058] Furthermore, by forming a thin film of aluminum nitride such as protective layer 16 on the relatively thick protective layer 15 of the ceramic sintered body, even if protective layer 16 corrodes and exposes the protective layer 15 of the ceramic sintered body underneath, the wafer support can be reused by fabricating a new protective layer 16. As a result, the life of the wafer support can be extended.

[0059] In the wafer support 30 according to this embodiment, the thermal expansion coefficient of the base material 14 is set to Δ1 [1×10 -6 / °C], and the thermal expansion coefficient of the first protective layer 15 is Δ2 [1 × 10 -6 / °C], |Δ2 - Δ1| ≦ 1.0 is satisfied. This allows the substrate 14 and protective layer 15 to be fabricated by co-sintering. Note that a large value of |Δ2 - Δ1| increases the likelihood of cracks occurring in either the substrate 14 or the protective layer 15 due to thermal stress during sintering, resulting in a poorly sintered product. Boron nitride, in particular, has a low Young's modulus, which relieves thermal stress and suppresses cracking, making it an effective gradient material for mitigating mismatches between the properties of each layer. Furthermore, the co-sintering method allows for the formation of a layer made of a high-thermal conductivity material on or near the wafer contact surface, which is not possible with conventional machinable ceramics. This improves wafer thermal uniformity during semiconductor manufacturing. Specifically, while conventional machinable ceramics could only achieve a thermal conductivity of approximately 70 W / m·K, providing protective layer 15 (a sintered ceramic body primarily composed of aluminum nitride) on substrate 14 can achieve a thermal conductivity of 90 W / m·K or higher.

[0060] If the difference in thermal expansion coefficients Δ=|Δ2-Δ1| between the substrate 14 and the protective layer 15 is greater than 1.0, an intermediate layer having a thermal expansion coefficient Δ3 (Δ1<Δ3<Δ2 or Δ2<Δ3<Δ1) between the thermal expansion coefficients Δ1 and Δ2 may be formed between the substrate 14 and the protective layer 15. In this case, the thermal expansion coefficient differences |Δ1-Δ3| and |Δ2-Δ3| are both 1.0×10 -6 / ℃ or less.

[0061] The machinable ceramic substrate according to this embodiment may contain 15 to 40 mass% of boron nitride, 0 to 40 mass% of zirconium oxide, 0 to 50 mass% of silicon nitride, 0 to 20 mass% of silicon carbide, and 0 to 75 mass% of aluminum nitride, assuming the total ceramic components of boron nitride, zirconium oxide, silicon nitride, silicon carbide, and aluminum nitride to be 100 mass%. It may also contain 3 to 15 mass% of a sintering aid component, assuming the total ceramic components to be 100 mass%.

[0062] 5(a) to 5(e) are diagrams illustrating an example of a method for manufacturing a wafer support according to this embodiment. First, as shown in FIG. 5(a), powder 32 adjusted to the composition of the base material 14 is packed into a hot press mold 34 and uniaxially pressed to form a first pressurized body 36 (FIG. 5(b)). Then, powder 38 adjusted to the composition of the protective layer 15 is packed onto the first pressurized body 36 and uniaxially pressed to form a second pressurized body 40 on the first pressurized body 36 (FIG. 5(c)). The resulting two-layered compact is placed in a firing furnace 42 and hot-press fired (FIG. 5(d)). This results in the base material 14 and the protective layer 15 being integrally formed. Furthermore, a protective layer 16 is formed on the protective layer 15 by CVD or PVD (FIG. 5(e)).

[0063] Alternatively, powder 32 may be packed into mold 34, and then powder 38 may be packed into mold 34 from above, and simultaneously uniaxially pressed. As another manufacturing method, a compact obtained by CIP (Cold Isostatic Pressing) of powder 32 may be placed on top of a compact obtained by CIP of powder 38, and the resulting mixture may be integrally molded by hot press firing.

[0064] [Example] Next, the characteristics of the wafer support body according to each example and comparative example will be described. The contents of the ceramic components and sintering aid components in each example and comparative example are shown in Table 1. The film thickness was measured from cross-sectional photographs taken with a scanning electron microscope. [Table 1]

[0065] (Cross-sectional structure) Figure 6(a) is a photograph of the cross section of the protective layer of the aluminum nitride sintered body of Example 1 taken with a scanning electron microscope (SEM), Figure 6(b) is a photograph of the cross section of the protective layer of the aluminum nitride sintered body of Example 3 taken with a scanning electron microscope, and Figure 6(c) is a photograph of the cross section of the aluminum nitride thin film of the reference example taken with a scanning electron microscope.

[0066] The protective layer 15 of the aluminum nitride sintered body shown in Figures 6(a) and 6(b) has a structure in which particles with a particle size of about 1 to 5 μm are packed together. On the other hand, the aluminum nitride film shown in Figure 6(c) is formed by sputtering, and has a structure in which columnar particles less than 1 μm are packed together. As such, it can be seen that there is a clear difference in structure between the sintered body and the thin film. Furthermore, by using the aluminum nitride sintered body as a gradient material, it is possible to form a protective layer 15 (corrosion-resistant layer) with a thickness that is difficult to achieve by the method of forming an aluminum nitride thin film. This improves the durability (longer life) of the wafer support body according to this embodiment.

[0067] The sample surface characteristics and plasma exposure test results of the wafer supporters according to Examples 1 to 5 and Comparative Examples 1 to 3 are shown in Table 2. The presence or absence of cracks was confirmed visually or with a stereo microscope (×20 magnification). [Table 2]

[0068] (Sample surface characteristics) Figure 7(a) is a photograph of the surface of the protective layer of the aluminum nitride sintered body of Example 1 taken with a scanning electron microscope (SEM); Figure 7(b) is a photograph of the surface of the protective layer of the aluminum nitride sintered body of Example 3 taken with a scanning electron microscope; Figure 7(c) is a photograph of the surface of the aluminum nitride thin film of a reference example taken with a scanning electron microscope; Figure 7(d) is an image converted from the photograph of Figure 7(a) using image analysis software; Figure 7(e) is an image converted from the photograph of Figure 7(b) using image analysis software; and Figure 7(f) is an image converted from the photograph of Figure 7(c) using image analysis software.

[0069] The magnification of the SEM photographs shown in Figures 7(a) to 7(c) is 1000 times. Image analysis was performed using image analysis software (WIN ROOF) to extract the recessed portions and calculate the area ratio of the recessed portions. In order to clearly extract the area ratio of the recessed portions, the image analysis software was used to extract the recessed portion area ratio. 2 The following recesses are excluded from the calculation.

[0070] The surface of the aluminum nitride sintered body shown in Figure 7(a) and Figure 7(b) differs from the surface of the aluminum nitride thin film shown in Figure 7(c) in terms of the shape, size, and area ratio of the irregularities. For example, the depressions (pores) on the surface of the aluminum nitride sintered body have sharp edges, while the depressions (pores) on the surface of the aluminum nitride thin film do not have sharp edges. Furthermore, the area ratio of the depressions on the surface of the aluminum nitride thin film (0.6%) is smaller than that of the aluminum nitride sintered body. Note that if there are many pores or sharp edges, the surface area increases, increasing the area exposed to corrosive gases, which is detrimental to corrosion resistance. Therefore, a smaller area ratio is preferable.

[0071] Furthermore, the state of the sample surface was measured by arithmetic mean roughness Ra as defined in JIS B 0601. In Examples 1 to 5, the surface of the thin film corresponding to the protective layer 16 was measured.

[0072] (Plasma exposure test) 8(a) to 8(c) are schematic diagrams illustrating the plasma exposure test. The plasma generator used in the test was a Samco RIE-10N. The plasma output was 100 W, and the gas species was a mixture of 40 sccm of CF4 and 10 sccm of O2. The pressure was 40 Pa, and the treatment time was 240 minutes (30 minutes x 8 times). As shown in FIG. 8(a), a mask 46 such as Kapton tape was attached to a portion of a test sample 44 simulating a wafer support, and plasma treatment was performed as shown in FIG. 8(b). After a predetermined treatment time, the mask 46 was removed, and the difference in level d between the area not covered by the mask 46 and the area covered by the mask 46 was measured as the amount of corrosion (see FIG. 8(c)). As shown in Table 2, the wafer support according to Examples 1 to 5 had a difference in level d of 0 μm, and no corrosion was observed.

[0073] (Vickers hardness) In addition to the etching caused by the chemical reaction mentioned above, physical etching can also affect corrosion resistance to plasma. For example, corrosion resistance to chemical reactions can be improved by using a protective layer made of a material containing a substance (such as aluminum or yttrium) that is resistant to sublimation when reacting with plasma using fluorine-based (CF4) gas. In addition, a highly hard protective layer that is resistant to physical impacts can be expected to provide even greater corrosion resistance to plasma.

[0074] Therefore, the inventors of the present application focused on the film hardness of the protective layer. The film hardness was measured by nanoindentation hardness H_IT and converted into Vickers hardness (GPa). For example, the wafer supporters according to Examples 1, 3, and 4 have a Vickers hardness of 10 GPa or more, and this, combined with the results of the corrosion amount in the plasma exposure test, suggests that they will have even higher corrosion resistance to plasma.

[0075] Although the present invention has been described above with reference to the above-mentioned embodiments and examples, the present invention is not limited to the above-mentioned embodiments, and suitable combinations and substitutions of the configurations of the embodiments are also included in the present invention. Furthermore, it is possible to suitably rearrange the combinations and order of steps in the embodiments based on the knowledge of a person skilled in the art, and to make modifications to the embodiments such as various design changes, and such modified embodiments are also included in the scope of the present invention. [Explanation of symbols]

[0076] 10 wafer support, 12 chamber, 14 substrate, 14a surface, 15 protective layer, 16 protective layer, 16a mounting surface, 18 conductive member, 20 conductive member, 22 gas inlet, W wafer.

Claims

1. The device comprises a substrate made of a machinable ceramic containing boron nitride, a first layer covering a surface of the substrate, and a conductive member at least a portion of which is contained within the substrate, the first layer is made of a ceramic sintered body containing aluminum nitride as a main component, a proportion of boron nitride contained in the substrate is higher than a proportion of boron nitride contained in the first layer; The wafer support member is characterized in that the first layer has a thickness of 0.3 to 3.0 mm.

2. 2. The wafer support according to claim 1, wherein the first layer contains 90 to 100 mass % of aluminum nitride and 0 to 10 mass % of boron nitride.

3. further comprising a second layer covering the first layer; 3. The wafer support according to claim 1, wherein the second layer is made of at least one material selected from the group consisting of aluminum nitride, aluminum oxide, yttrium oxide, and magnesium oxide, and has a thickness of 1.0 to 20 μm.

4. The thermal expansion coefficient of the substrate is Δ1 [1 × 10 －６ / °C], and the thermal expansion coefficient of the first layer is Δ2 [1 × 10 －６ / ° C.], the wafer supporting body satisfies |Δ2−Δ1|≦1.

0.

5. The machinable ceramics are When the total of ceramic components of boron nitride, zirconium oxide, silicon nitride, silicon carbide, and aluminum nitride is taken as 100% by mass, the ceramic material contains 15 to 40% by mass of boron nitride, 0 to 40% by mass of zirconium oxide, 0 to 55% by mass of silicon nitride, 0 to 20% by mass of silicon carbide, and 0 to 75% by mass of aluminum nitride, 3. The wafer supporting body according to claim 1, further comprising a sintering aid component in an amount of 3 to 15 mass % when the total amount of said ceramic components is taken as 100 mass %.

6. 3. The wafer support according to claim 1, wherein the conductive member is made of a metal material selected from the group consisting of molybdenum, tungsten, tantalum, and alloys containing these.

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