Wafer Support

Abstract

To provide a new wafer support with excellent corrosion resistance to plasma.SOLUTION: A wafer support 10 includes a base material 14 made of machinable ceramics, a protective layer 16 that covers the surface of the base material, and conductive members 18 and 20 at least a part of which is included in the base material. The protection layer 16 is composed of a material that is less corroded by plasma than the base material 14.SELECTED DRAWING: Figure 1

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] However, when the wafer support is exposed to the corrosive gas or plasma atmosphere in the semiconductor manufacturing process, particles are likely to be generated from the surface. If these particles adhere to the wafer, they can cause defects in the subsequent semiconductor manufacturing process.

[0005] 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 against plasma. [Means for solving the problem]

[0006] In order to solve the above problems, a wafer support according to one embodiment of the present invention includes a base material made of machinable ceramics, a protective layer covering the surface of the base material, and a conductive member at least partially contained in the base material. The protective layer is made of a material that is less susceptible to corrosion by plasma than the base material.

[0007] Machinable ceramics are easier to process than general fine ceramics. Therefore, according to this embodiment, it is possible to manufacture wafer support bodies with various shapes, since the substrate can be manufactured and then machined, without having to achieve a complex shape at the stage of manufacturing the substrate. In addition, according to this embodiment, the protective layer can reduce corrosion of the substrate by plasma. Furthermore, even if the material constituting the substrate is prone to peeling, the protective layer can reduce peeling.

[0008] The protective layer is made of aluminum nitride (AlN), aluminum oxide (Al2O3), yttrium oxide (Y2O3), magnesium oxide (MgO), yttrium aluminum garnet (YAG: Y3O5Al 12 The substrate may be made of at least one material selected from the group consisting of yttrium aluminum monoclinic (YAM: Y4Al2O9), and yttrium aluminum monoclinic (YAM: Y4Al2O9). This can further reduce plasma corrosion of the substrate.

[0009] The protective layer may have a thickness in the range of 1 to 30 μm. This allows for both the desired adsorptive power and corrosion resistance to plasma to be achieved. If the protective layer is preferably 2 μm or more, more preferably 5 μm or more, better corrosion resistance to plasma can be obtained. Furthermore, if the protective layer is preferably 20 μm or less, more preferably 10 μm or less, more sufficient adsorptive power can be obtained.

[0010] The protective layer may have an arithmetic mean height Sa in the range of 0.07 to 0.20 μm, which allows for proper contact with the wafer it supports.

[0011] The protective layer may contain 99.0% or more AlN, which provides the inherent corrosion resistance of AlN to plasma.

[0012] Machinable ceramics may be sintered bodies made of at least two or more materials containing boron nitride as an essential component, selected from the group consisting of boron nitride (BN), zirconium oxide (ZrO2), silicon nitride (Si3N4), and silicon carbide (SiC). Boron nitride 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 wafer support structures containing a conductive member made of a different material 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 temperature differences between the outer periphery and center of the wafer support structure. However, boron nitride has excellent thermal shock resistance, making the substrate less susceptible to cracking.

[0013] The machinable ceramic may contain 10-80 mass% of boron nitride, 0-80 mass% of silicon nitride, 0-80 mass% of zirconium oxide, and 0-40 mass% of silicon carbide, where the total of the ceramic components, boron nitride, zirconium oxide, silicon nitride, and silicon carbide, is taken as 100 mass%. The machinable ceramic may further contain 3-25 mass% of a sintering aid component, where the total of the ceramic components is taken as 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 supporter having excellent corrosion resistance against plasma can be realized. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view of a wafer support according to an embodiment of the present invention. [Figure 2] 3 is a photograph of a cross section of the wafer support member according to Example 1 taken by a scanning electron microscope (SEM). FIG. [Figure 3] Figure 3(a) is a SEM photograph of the surface of an aluminum nitride substrate, Figure 3(b) is a SEM photograph of the surface of a machinable ceramic substrate, and Figure 3(c) is a SEM photograph of the surface of the protective layer of a wafer support body according to Example 1. [Figure 4] 4(a) to 4(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) The wafer support may be any device capable of supporting a semiconductor substrate such as a silicon wafer, and may include an adsorption mechanism or 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 this embodiment, the wafer support body is an electrostatic chuck with a heater, as an example, and Fig. 1 is a schematic cross-sectional view of the wafer support body according to this embodiment.

[0021] The wafer support 10 according to this embodiment is used to support a wafer W in a chamber 12 of a semiconductor manufacturing device 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 ceramic according to this embodiment is a sintered body made of at least two or more materials, each containing boron nitride selected from the group consisting of boron nitride, zirconium oxide, silicon nitride, and silicon carbide. 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 stress is generated in response to temperature changes due to differences in the physical properties of the substrate and the conductive member. Alternatively, thermal stress is 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 this embodiment 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] The machinable ceramic according to this embodiment also contains a sintering aid component. The sintering aid can be selected from those used in sintering silicon nitride or 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 of alumina and yttria with magnesia added thereto, or mixtures of yttria and magnesia, etc.

[0031] The amount of sintering aid component blended is preferably in the range of 1 to 25 mass%, particularly 3 to 25 mass%, when the total ceramic components are taken as 100 mass%. 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, and deterioration of mechanical strength and deterioration of workability due to an increase in the grain boundary phase can be suppressed.

[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 main raw material powders that will become ceramic components such as boron nitride, zirconium oxide, silicon nitride, and silicon carbide, etc., with 3 to 25 mass% of sintering aid powder, assuming the total ceramic components to be 100 mass%, according to the blending amounts in each of the examples and comparative examples described below. This mixing can be carried out, for example, using a wet ball mill or the like.

[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 of this embodiment have high strength and high machinability (free cutting), making complex micromachining possible in an industrially practical time frame. 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, since 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 this embodiment 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 this embodiment may contain silicon nitride, silicon carbide, or boron nitride as a main component, and the inventors of the present application have recognized the possibility 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, 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 this embodiment is made of a material that is less corroded by plasma than the substrate 14. This allows the protective layer 16 to reduce corrosion of the substrate 14 by plasma. 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 this 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 this embodiment 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 (the material that will become the film) opposite 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 according to this embodiment. It is known that using compounds such as aluminum oxide or aluminum nitride as targets significantly reduces the sputtering yield, resulting in an extremely slow coating speed, and that different sputtering yields for different elements result in the formation of a film that deviates from the target composition. Therefore, when the protective layer according to this embodiment is made of aluminum nitride, reactive sputtering is suitable, using a single metal aluminum target and reacting it 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 material evaporated and the introduction of a reactive gas. Among coating technologies based on vacuum deposition, the general term for methods using ions is ion plating. Specifically, there are various techniques, such as radio-frequency ion plating, reactive ion plating, and ion-assisted deposition, and any of these can be employed. In the case of the present embodiment, 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, when the protective layer is made of magnesium oxide or aluminum oxide, it can also be formed by radio-frequency ion plating, reactive ion plating, or 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 surface roughness is within a predetermined range (e.g., 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, particles are prone to peeling (cracks) due to physical forces, 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 according to this embodiment 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 protective layer 16 is resistant to plasma corrosion, yet the protective layer 16 itself can make point contact with the wafer, making the wafer support 10 according to this embodiment extremely effective at reducing particles.

[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, etc., 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 this embodiment, stress can be absorbed (mitigated). Furthermore, because the machinable ceramic according to this embodiment 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] [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 as shown in Table 1. The film thickness was measured from a cross-sectional photograph taken with a scanning electron microscope. FIG. 2 is a photograph of the cross section of the wafer support body according to Example 1 taken with a scanning electron microscope (SEM). The protective layer 16 shown in FIG. 2 is an aluminum nitride film with a thickness of 5 μm formed by reactive sputtering. As shown in FIG. 2, the protective layer 16 according to Example 1 is a dense film without voids. [Table 1]

[0050] Table 2 shows the surface characteristics of the wafer support samples according to Examples 1 to 6 and Comparative Examples 1 to 3 and the results of the plasma exposure test. [Table 2]

[0051] (Sample surface characteristics) FIG. 3(a) is a SEM photograph of the surface of an aluminum nitride substrate, FIG. 3(b) is a SEM photograph of the surface of a machinable ceramic substrate, and FIG. 3(c) is a SEM photograph of the surface of the protective layer of the wafer support body according to Example 1. The arithmetic mean roughness Ra specified in JIS B 0601 was measured to assess the state of the sample surface. Furthermore, the arithmetic mean height Sa specified in ISO 25178 was measured using a confocal microscope VK-X1050 manufactured by Keyence Corporation to assess the state of another sample surface. The surface of the protective layer was measured for Examples 1 to 6, and the surface of the sintered base material was measured for Comparative Examples 1 to 3.

[0052] The aluminum nitride substrate surface shown in FIG. 3(a) has an Ra of 0.05 μm and an Sa of 0.061 μm. In contrast, the boron nitride-containing machinable ceramic substrate surface shown in FIG. 3(b) has an Ra of 0.05 μm and an Sa of 0.116 μm, while the protective layer surface of the wafer support according to Example 1 shown in FIG. 3(c) has an Ra of 0.08 μm and an Sa of 0.082 μm. That is, at least when the substrate is machinable ceramic, the arithmetic mean height Sa is larger and the contact area with the wafer is smaller compared to when the substrate is aluminum nitride, regardless of whether a protective layer is present. As a result, as described above, particles generated from the wafer support can be reduced. The protective layer according to this embodiment preferably has an arithmetic mean height Sa in the range of 0.07 to 0.20 μm. This ensures proper contact with the supported wafer.

[0053] (Plasma exposure test) 4(a) to 4(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. 4(a), a mask 26 such as Kapton tape was attached to a portion of the test sample 24, which simulates a wafer support, and plasma treatment was performed as shown in FIG. 4(b). After the specified treatment time, the mask 26 was removed, and the difference in level d between the area not covered by the mask 26 and the area covered by the mask 26 was measured as the amount of corrosion (see FIG. 4(c)).

[0054] As shown in Table 2, the wafer support bodies according to Examples 1 to 6 had a step d of 0 μm, and no corrosion was observed. On the other hand, the wafer support bodies according to Comparative Examples 1 to 3, which did not have a protective film, all had a step d of 4 μm or more. Furthermore, the wafer support bodies according to Examples 1 to 6 all had a smaller increase in the value of the arithmetic mean height Sa, which indicates the surface roughness after the plasma exposure test, compared to the wafer support bodies according to Comparative Examples 1 to 3. In other words, the smaller the amount of corrosion (step) and the smaller the surface roughness (arithmetic mean height), the higher the plasma resistance, and this demonstrates the usefulness of the protective layer in the wafer support body according to this embodiment.

[0055] (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.

[0056] Therefore, the inventors of the present application focused on the film hardness of the protective layer. The film hardness was measured using a nanoindentation method to determine the nanoindentation hardness H_IT, which was converted to Vickers hardness (GPa). For example, the wafer support members according to Examples 1, 3, and 4 have a Vickers hardness of 10 GPa or more, which, combined with the results of the corrosion amount in the plasma exposure test, is expected to have even higher corrosion resistance against plasma. On the other hand, if the Vickers hardness is low, as in the case of the wafer support member according to Comparative Example 2, scratches may occur during packaging or assembly into the device, which may result in particles.

[0057] (Purity of the material that makes up the protective layer) In the Johnsen-Rahbek (JR) type electrostatic chuck, the volume resistivity of the ceramics in the wafer support is set to 10 9 It is necessary to control the resistivity to about Ωcm. Electrostatic chucks for film formation (PVD, CVD) have a high operating temperature range of up to 500°C, but the resistivity of ordinary insulating ceramics decreases as the temperature rises. For this reason, ceramics with different resistivities are used for each operating temperature range.

[0058] To change the resistivity, additives are often added, for example, silicon carbide, carbon (C), titanium oxide (TiO2), etc. are mixed into aluminum nitride at several percent to several tens of percent. However, these additives can weaken the corrosion resistance to plasma or cause uneven etching (corrosion), which can generate particles.

[0059] Therefore, the wafer support according to this embodiment controls the volume resistivity of the base material while using a highly pure material for the protective layer covering its surface, thereby reducing the influence of additives in the protective layer. For example, as in the wafer support according to Examples 1 and 3, high-purity aluminum nitride may be provided as the protective layer. The protective layer preferably contains 99.0% or more, more preferably 99.5% or more, of aluminum nitride. This ensures the inherent corrosion resistance of aluminum nitride to plasma. When high-purity aluminum nitride is produced by sputtering, it can be achieved by using high-purity aluminum metal and high-purity N2 gas and depositing the film in a vacuum atmosphere with little impurity contamination.

[0060] (protective layer thickness) Electrostatic chucks used in film deposition, particularly electrostatic chucks with built-in heaters for CVD, have a high processing temperature (heater temperature) of approximately 500°C. For example, if a wafer at room temperature (25°C) is transported to such a high-temperature electrostatic chuck, it will be subjected to a thermal shock of Δ475°C. In contrast, the thermal shock resistance of aluminum nitride ceramics is approximately Δ400°C, so in the case of an electrostatic chuck made solely of a substrate primarily composed of aluminum nitride, there is concern that the ceramic may be damaged.

[0061] In contrast, when a substrate made of machinable ceramics is used, as in the wafer support device according to this embodiment, the thermal shock resistance is excellent. Furthermore, even if the protective layer covering the substrate surface is made of a material such as aluminum nitride, aluminum oxide, yttrium oxide, or YAG, which does not have as high thermal shock resistance as machinable ceramics, the thermal shock resistance is not impaired as long as the protective layer is a thin film of about 1 to 30 μm. Furthermore, while electrostatic chucks with a substrate made of machinable ceramics have anisotropy in thermal conductivity, the anisotropy obtained by the substrate is not impaired if the protective layer is a thin film.

[0062] 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]

[0063] 10 wafer support, 12 chamber, 14 substrate, 14a surface, 16 protective layer, 16a mounting surface, 18 conductive member, 20 conductive member, 22 gas inlet, 24 sample, 26 mask, W wafer.

Claims

1. The device comprises a substrate made of machinable ceramics, a protective layer covering the surface of the substrate, and a conductive member at least partially contained in the substrate, the protective layer is made of a material that is less corroded by plasma than the base material, The protective layer may be made of aluminum nitride, aluminum oxide, yttrium oxide, magnesium oxide, yttrium aluminum garnet (YAG). ３ O ５ Al １２ ) and yttrium aluminum monoclinic (YAM:Y ４ Al ２ O ９ a layer made of at least one material selected from the group consisting of: The machinable ceramic is a sintered body made of at least two or more materials essentially containing boron nitride selected from the group consisting of boron nitride, zirconium oxide, silicon nitride, and silicon carbide, The wafer support body is characterized in that the protective layer has an arithmetic mean height Sa, as defined by ISO 25178, in the range of 0.07 to 0.20 μm.

2. 2. The wafer support device according to claim 1, wherein the protective layer has a thickness in the range of 1 to 30 μm.

3. 3. The wafer support device according to claim 1, wherein the protective layer contains 99.0% or more aluminum nitride.

4. The machinable ceramics are When the total of ceramic components of boron nitride, zirconium oxide, silicon nitride, and silicon carbide is taken as 100% by mass, the ceramic material contains 10 to 80% by mass of boron nitride, 0 to 80% by mass of silicon nitride, 0 to 80% by mass of zirconium oxide, and 0 to 40% by mass of silicon carbide; 4. The wafer supporting body according to claim 1, further comprising a sintering aid component in an amount of 3 to 25 mass % when the total amount of said ceramic components is taken as 100 mass %.

5. 5. 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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