Wafer Support

Abstract

To provide a novel wafer support which is excellent in corrosion resistance against plasma.SOLUTION: A wafer support 28 comprises: a base material 14 which is made of machinable ceramic; an intermediate layer 15 covering a surface of the base material; a protective layer 16 covering a surface of the intermediate layer; and a conductive member 18 at least part of which is included in the base material. The intermediate layer 15 is made of a metallic material or an alloy material whose melting point is 800°C or higher. The protective layer 16 is made of a material which is less corroded by plasma than the base material 14 is.SELECTED DRAWING: Figure 5

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] To solve the above problems, one embodiment of the present invention provides a wafer support comprising a base material made of machinable ceramics, an intermediate layer covering the surface of the base material, a protective layer covering the surface of the intermediate layer, and a conductive member at least partially contained in the base material. The intermediate layer is made of a metal or alloy material with a melting point of 800°C or higher, and 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, even if complex shapes are not realized at the stage of manufacturing the substrate, the substrate can be manufactured and then processed, making it possible to manufacture wafer support bodies with various shapes. In addition, according to this embodiment, the protective layer can reduce plasma corrosion of the substrate. Furthermore, even if the material constituting the substrate is prone to peeling, the protective layer can reduce peeling. Furthermore, by providing an intermediate layer made of a metal material or alloy material with a melting point of 800°C or higher between the substrate and the protective layer, the adhesion between the substrate and the protective layer can be improved.

[0008] The intermediate layer may be a metal material or an alloy material containing at least one element selected from the group consisting of titanium, chromium, beryllium, cobalt, nickel, tantalum, platinum, silicon, copper, vanadium, palladium, niobium, germanium, zirconium, silver, gold, hafnium, and yttrium.

[0009] The intermediate layer may have a thickness in the range of 0.1 to 10 μm. The protective layer may have a thickness in the range of 1.0 to 30 μm. The total thickness of the intermediate layer and the protective layer may be in the range of 2.0 to 31 μm. This allows for both the desired adsorptive power and corrosion resistance against plasma to be achieved. If the protective layer is preferably 2 μm or more, more preferably 5 μm or more, better corrosion resistance against 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. Furthermore, if the thickness of the intermediate layer is too thin, the stress relaxation effect may be weak and the desired durability may not be obtained. On the other hand, if the thickness of the intermediate layer is too thick, the desired adsorptive power may not be obtained.

[0010] 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.

[0011] The substrate may contain 15 to 55 mass% of boron nitride, 0 to 10 mass% of zirconium oxide, 25 to 65 mass% of silicon nitride, and 10 to 30 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 substrate may further contain 3 to 25 mass% of a sintering aid component, where the total of the ceramic components is taken as 100 mass%.

[0012] The substrate may contain 15 to 55 mass% of boron nitride, 25 to 65 mass% of zirconium oxide, 0 to 10 mass% of silicon nitride, and 10 to 30 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 substrate may further contain 3 to 25 mass% of a sintering aid component, where the total of the ceramic components is taken as 100 mass%.

[0013] The substrate may have a water absorption rate of 0.2% or less, which allows a dense intermediate layer to be obtained when the intermediate layer is formed on a dense substrate with low water absorption rate.

[0014] 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.

[0015] 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.

[0016] The protective layer may contain 99.0% or more AlN, which provides the inherent corrosion resistance of AlN to plasma.

[0017] 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.

[0018] 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]

[0019] According to the present invention, a new wafer supporter having excellent corrosion resistance against plasma can be realized. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view of a wafer support according to an embodiment of the present invention. [Figure 2] 1 is a photograph of a cross section of a wafer supporting member according to Reference Example 1 taken by a scanning electron microscope (SEM). [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 Reference Example 1. [Figure 4] 4(a) to 4(c) are schematic diagrams for explaining the plasma exposure test. [Figure 5] FIG. 2 is a schematic diagram showing a main part of a wafer supporting device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] 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.

[0022] (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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] (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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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%.

[0033] 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.

[0034] 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.

[0035] 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).

[0036] 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.

[0037] (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 Reference Examples and Reference Comparative Examples described below. This mixing can be performed, for example, using a wet ball mill or the like.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] (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.

[0044] 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.

[0045] (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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] [Reference example] Next, the characteristics of the wafer support body according to each Reference Example and Reference Comparative Example will be described. The contents of the ceramic components and sintering aid components in each Reference Example and Reference 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 Reference 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 Reference Example 1 is a dense film without voids. [Table 1]

[0053] Table 2 shows the surface characteristics of the wafer support samples according to Reference Examples 1 to 6 and Reference Comparative Examples 1 to 3 and the results of the plasma exposure test. [Table 2]

[0054] (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 Reference 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 Reference Examples 1 to 6, and the surface of the sintered base material was measured for Reference Comparative Examples 1 to 3.

[0055] 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 Reference 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, regardless of whether a protective layer is present, compared to when the substrate is aluminum nitride. 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.

[0056] (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)).

[0057] As shown in Table 2, the wafer support bodies according to Reference 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 Reference 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 Reference Examples 1 to 6 all had a smaller increase in the value of arithmetic mean height Sa, which indicates surface roughness after the plasma exposure test, compared to the wafer support bodies according to Reference 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.

[0058] (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.

[0059] 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) and converted to Vickers hardness (GPa). For example, the wafer support bodies according to Reference 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, suggests that they have even higher corrosion resistance to plasma. On the other hand, if the Vickers hardness is low, as in the case of the wafer support body according to Reference Comparative Example 2, scratches may occur during packaging or assembly into the device, which may result in particles.

[0060] (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.

[0061] 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.

[0062] 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 Reference Examples 1 and 3, the protective layer may be made of high-purity aluminum nitride. 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.

[0063] (protective layer thickness) Electrostatic chucks used in film deposition, particularly electrostatic chucks with heaters for CVD, have high processing temperatures (heater temperatures) of up to 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 around 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.

[0064] 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.

[0065] [Example] As described above, the wafer support according to the reference example includes a substrate made of a machinable ceramic containing at least boron nitride, a protective layer covering the surface of the substrate, and a conductive member at least partially embedded in the substrate. The protective layer is made of a material that is less susceptible to corrosion by plasma than the substrate. This allows for the realization of a new wafer support with excellent corrosion resistance against plasma.

[0066] When the wafer support is used as an electrostatic chuck with a heater, the temperature distribution of the heater is preferably as small as possible, since it directly affects the quality and yield of the device. Boron nitride has high thermal conductivity and good machinability among machinable ceramics, so a substrate containing boron nitride is preferable from the perspective of heater temperature distribution. On the other hand, boron nitride has an extremely low thermal expansion coefficient among machinable ceramics, and as the proportion of boron nitride contained in the substrate increases, the thermal expansion coefficient of the entire substrate decreases. Therefore, if the thermal expansion coefficient of the material constituting the protective layer of the wafer support according to the reference example is higher than that of the substrate, the greater the difference in the thermal expansion coefficients between the protective layer and the substrate, the greater the stress generated during heating and cooling, which may be a factor in the protective layer cracking or peeling off from the substrate over long-term use.

[0067] Therefore, the present inventors have conceived of a method for improving the adhesion between the substrate and the protective layer by adhering the substrate and the protective layer with an intermediate layer made of a metal or alloy material with a melting point of 800°C or higher. In the following examples, components that overlap with those in the reference example are given the same reference numerals and names, and descriptions thereof will be omitted as appropriate. FIG. 5 is a schematic diagram showing the main parts of a wafer support device according to the example. The wafer support device 28 according to the example includes a substrate 14 containing at least boron nitride as a machinable ceramic, an intermediate layer 15 covering the surface of the substrate, a protective layer 16 covering the surface of the intermediate layer 15, and a conductive member 18 at least partially embedded in the substrate 14.

[0068] The contents of the ceramic components and sintering aid components in each example and comparative example are as shown in Table 3.

[0069] [Table 3]

[0070] As shown in Table 3, Comparative Examples 1 to 6 are cases where no intermediate layer is present, and Examples 1 to 6 are cases where an intermediate layer is disposed on a substrate having the same composition as Comparative Examples 1 to 6. The manufacturing method of the wafer support body according to each Example and Comparative Example is almost the same as that of the Reference Example, but differs slightly in that an intermediate layer is provided between the substrate and the protective layer.

[0071] Specifically, the substrate is obtained by packing powder having the composition shown in Table 3 into a hot press mold, uniaxially pressing the molded body, and then hot-press firing the molded body. The substrate is then coated with a thin film to form the intermediate layer. Specifically, methods for obtaining a dense coating include vacuum deposition, ion plating, sputtering, and plating. In the case of a film formation method such as plating that results in a relatively large surface roughness, the surface may be polished after film formation to reduce the surface roughness. This allows the surface roughness Ra of the protective layer 16 formed on the intermediate layer 15 to be kept within a certain level.

[0072] In the wafer support member 28 according to this embodiment, as exemplified in Examples 1 to 6, an intermediate layer 15 made of a metal material or an alloy material is provided between the substrate 14 and the protective layer 16. By providing the intermediate layer 15 containing a metal that is easily plastically deformed, when thermal stress is applied, the intermediate layer 15 deforms and relieves the stress, thereby suppressing peeling of the protective layer 16.

[0073] Furthermore, since wafer support bodies are often used at temperatures up to 800°C, it is preferable that the melting point of the metal contained in the intermediate layer is high. If the melting point is low, the intermediate layer 15 will melt during use, causing the protective layer 16 to peel off from the substrate 14. Furthermore, there is a possibility that the metal will flow into the device in which the wafer support body is installed and contaminate the device and the wafer. Therefore, the intermediate layer 15 in this embodiment is preferably made of a metal or alloy material with a melting point of 800°C or higher. Preferably, the intermediate layer 15 contains a metal with a melting point of 900°C or higher.

[0074] The intermediate layer 15 according to this embodiment is preferably a metal material or alloy material containing at least one element selected from the group consisting of titanium, chromium, beryllium, cobalt, nickel, tantalum, platinum, silicon, copper, vanadium, palladium, niobium, germanium, zirconium, silver, gold, hafnium, and yttrium. Titanium, chromium, or an alloy containing titanium or chromium is preferred. Titanium and chromium have high affinity with a wide range of materials and tend to provide high adhesion.

[0075] The adhesion strength of the protective film was measured in accordance with a scratch test (ISO20502) for the wafer support bodies shown in Examples 1 to 6 and Comparative Examples 1 to 6. Specifically, the load (N) was read at the point where the substrate 14 was exposed. The read value was divided by the value for the reference comparative example, and the ratio was calculated as a percentage. As shown in Table 3, the adhesion strength of the wafer support body according to each Example was 120 to 210% of the adhesion strength of the wafer support body according to the reference comparative example, indicating that the provision of an intermediate layer improves adhesion.

[0076] The thickness of the intermediate layer 15 is preferably in the range of 0.1 to 10 μm, more preferably in the range of 0.2 to 8 μm, and even more preferably in the range of 1.0 to 5 μm. If the thickness of the intermediate layer is too thin, the stress relaxation effect may be weak, and the desired durability may not be obtained. On the other hand, if the thickness of the intermediate layer is too thick, not only will the surface roughness of the intermediate layer increase, but the surface roughness of the protective layer 16 thereon also tends to increase, making it difficult to achieve the desired surface roughness range. Furthermore, if the thickness of the intermediate layer is too thick, the desired chucking force may not be obtained in the wafer support. The suitable thickness of the protective layer 16 is the same as in the reference example. Furthermore, the total thickness of the intermediate layer and the protective layer is preferably in the range of 2.0 to 31 μm, more preferably in the range of 5 to 20 μm, and even more preferably in the range of 6 to 13 μm.

[0077] In this way, the metal contained in intermediate layer 15 not only improves the adhesive strength with protective layer 16, but also plastically deforms to relieve stress when a load is applied, such as when contacting a wafer. As a result, the durability of the wafer support body is improved. Therefore, it is preferable that intermediate layer 15 has a lower Young's modulus than protective layer 16 and substrate 14. Since the Young's modulus of a machinable ceramic substrate is 150 to 300 GPa, the Young's modulus of intermediate layer 15 is preferably 300 GPa or less, and more preferably 250 GPa or less.

[0078] Furthermore, it is preferable that the metal of intermediate layer 15 has a thermal expansion coefficient close to that of protective layer 16 and substrate 14. If the difference in thermal expansion coefficient is large, thermal stress will be applied during thermal cycling, reducing durability. Since the thermal expansion coefficient of substrate 14 is about 2 to 10 ppm and the thermal expansion coefficient of protective layer 16 is about 4 to 10 ppm, it is preferable that the thermal expansion coefficient of intermediate layer 15 be 12 ppm or less.

[0079] Furthermore, because a substrate made of machinable ceramics is a composite material made from a mixture of various raw materials, its surface appearance is more likely to be uneven than that of a single-substrate material. If the protective layer 16 is thin and transparent, the underlying substrate can be seen through, making the uneven appearance more apparent, and this appearance leaves room for improvement from an aesthetic standpoint. However, by providing an intermediate layer with a uniform appearance, the wafer support can have a uniform surface appearance, improving its commercial value.

[0080] In the wafer supporting body according to this embodiment, as exemplified in Examples 1 to 3, the substrate 14 preferably contains 15 to 55 mass% of boron nitride, 0 to 10 mass% of zirconium oxide, 25 to 65 mass% of silicon nitride, and 10 to 30 mass% of silicon carbide, where the total of the ceramic components of boron nitride, zirconium oxide, silicon nitride, and silicon carbide is taken as 100 mass%, and further preferably contains 3 to 25 mass% of a sintering aid component, where the total of the ceramic components is taken as 100 mass%.

[0081] As illustrated in Examples 4 to 6, the substrate 14 preferably contains 15 to 55 mass% of boron nitride, 25 to 65 mass% of zirconium oxide, 0 to 10 mass% of silicon nitride, and 10 to 30 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%. Furthermore, where the total of the ceramic components is taken as 100 mass%, the substrate 14 preferably further contains 3 to 25 mass% of a sintering aid component.

[0082] Furthermore, the substrate 14 in each example has a water absorption rate of 0.2% or less. As a result, when an intermediate layer 15 is formed on a dense substrate 14 with low water absorption rate, a dense intermediate layer 15 is obtained. The water absorption rate was measured in accordance with JIS C 2141. Furthermore, the intermediate layer 15 may be more than one layer.

[0083] If the boron nitride particles are large, they have low strength characteristics and can become the starting point of cracks, so the average particle size of the boron nitride contained in the substrate 14 is preferably 2.0 μm or less.

[0084] 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]

[0085] 10 wafer support, 12 chamber, 14 substrate, 15 intermediate layer, 16 protective layer, 16a mounting surface, 18 conductive member, 20 conductive member, 22 gas inlet, 24 sample, 26 mask, 28 wafer support, W wafer.

Claims

1. The device comprises a substrate made of machinable ceramics, an intermediate layer covering a surface of the substrate, a protective layer covering a surface of the intermediate layer, and a conductive member at least a portion of which is enclosed within the substrate, the intermediate layer is made of a metal material or an alloy material having a melting point of 800°C or higher, The wafer support body is characterized in that the protective layer is made of a material that is less corroded by plasma than the base material.

2. 2. The wafer support of claim 1, wherein the intermediate layer is a metal material or an alloy material containing at least one element selected from the group consisting of titanium, chromium, beryllium, cobalt, nickel, tantalum, platinum, silicon, copper, vanadium, palladium, niobium, germanium, zirconium, silver, gold, hafnium, and yttrium.

3. A substrate made of machinable ceramics, an intermediate layer covering the surface of the substrate, a protective layer covering the surface of the intermediate layer, and a conductive member at least partially contained in the substrate, the intermediate layer is made of a metal material or an alloy material having a melting point of 800°C or higher, the protective layer is made of a material that is less corroded by plasma than the base material, the intermediate layer has a thickness in the range of 0.1 to 10 μm; the protective layer has a thickness in the range of 1.0 to 30 μm; A wafer support body characterized in that the total thickness of the intermediate layer and the protective layer is in the range of 2.0 to 31 μm.

4. 2. The wafer support according to claim 1, wherein 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.

5. the substrate contains 15 to 55 mass% of boron nitride, 0 to 10 mass% of zirconium oxide, 25 to 65 mass% of silicon nitride, and 10 to 30 mass% of silicon carbide, where the total of the ceramic components of boron nitride, zirconium oxide, silicon nitride, and silicon carbide is 100 mass%, 5. The wafer supporting body according to claim 4, 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 %.

6. the substrate contains 15 to 55 mass% of boron nitride, 25 to 65 mass% of zirconium oxide, 0 to 10 mass% of silicon nitride, and 10 to 30 mass% of silicon carbide, where the total of the ceramic components of boron nitride, zirconium oxide, silicon nitride, and silicon carbide is 100 mass%, 5. The wafer supporting body according to claim 4, 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 %.

7. 7. The wafer support device according to claim 1, wherein the base material has a water absorption rate of 0.2% or less.

8. 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 7. The wafer support according to claim 1, wherein the wafer support is made of at least one material selected from the group consisting of:

9. A substrate made of machinable ceramics, an intermediate layer covering the surface of the substrate, a protective layer covering the surface of the intermediate layer, and a conductive member at least partially contained in the substrate, the intermediate layer is made of a metal material or an alloy material having a melting point of 800°C or higher, the protective layer is made of a material that is less corroded by plasma than the base material, The protective layer has an arithmetic mean height Sa in the range of 0.07 to 0.20 μm. A wafer support.

10. A substrate made of machinable ceramics, an intermediate layer covering the surface of the substrate, a protective layer covering the surface of the intermediate layer, and a conductive member at least partially contained in the substrate, the intermediate layer is made of a metal material or an alloy material having a melting point of 800°C or higher, the protective layer is made of a material that is less corroded by plasma than the base material, The wafer support body is characterized in that the protective layer contains 99.0% or more aluminum nitride.

11. 7. 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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