Structural members

Abstract

To provide a structural member capable of inhibiting deterioration of a protective film due to a difference in thermal expansion.SOLUTION: A structural member 10 includes a base material 100 and a protective film 200 that covers a surface 110 of the base material 100. In a cross section obtained by cutting the protective film 200 vertically with respect to the surface 110, a ratio occupied by a void per unit area is a void ratio. The void ratio in a first part 201 that is a part of the cross section is smaller than the void ratio in a second part 202 that is a part of the cross section which is closer to the base material 100 than the first part 201.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a structural member. [Background technology]

[0002] Structural members having a protective film on the surface of a substrate are used in various fields such as semiconductor manufacturing equipment. For example, in a plasma etching device, a protective film is formed on the surface of a substrate constituting the inner wall of a chamber to protect the substrate from plasma. For example, oxide ceramics such as yttria and fluoride ceramics such as yttrium fluoride are used as such protective films. As described in the following Patent Document 1, the protective film is formed using various methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and aerosol deposition. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 102075 Summary of the Invention [Problem to be solved by the invention]

[0004] In the process of forming a protective film on the surface of a substrate, air bubbles may be included in the protective film. In order to fully exert the functions of the protective film, such as plasma resistance, it is considered desirable that there are no air bubbles in the protective film. For this reason, when forming a protective film, it is common to set the film formation conditions so that the air bubbles in the protective film are as small or few as possible.

[0005] On the other hand, experiments conducted by the present inventors have revealed that if the entire protective film is formed too densely (i.e., so as to contain no air bubbles), while the plasma resistance is sufficiently improved, a new problem arises in that the protective film becomes more susceptible to deterioration due to differences in thermal expansion when the temperature changes.

[0006] The present invention has been made in consideration of such problems, and its object is to provide a structural member that can suppress deterioration of a protective film due to differences in thermal expansion while ensuring plasma resistance. [Means for solving the problem]

[0007] In order to solve the above problems, a structural member according to the present invention includes a substrate and a protective film covering a surface of the substrate. When the porosity is defined as the ratio of voids per unit area in a cross section of the protective film cut perpendicularly to the surface, the porosity of this structural member in a first portion that is a part of the cross section is smaller than the porosity of a second portion that is a portion of the cross section closer to the substrate than the first portion.

[0008] In such a structural member, the porosity of the protective film is not uniform throughout, but varies depending on the position in the thickness direction. Specifically, the porosity of a first portion located relatively closer to the surface is smaller than the porosity of a second portion located closer to the substrate.

[0009] In such a configuration, the porosity of the surface side of the protective film exposed to plasma is relatively small, so that it is possible to ensure, for example, plasma resistance at the same level as in the past. The "plasma resistance" here refers to, for example, the ability to reduce dust generation due to deterioration of the protective film after the protective film is exposed to plasma under specified conditions.

[0010] The portion of the protective film facing the substrate has a relatively large porosity, and therefore a smaller elastic modulus than the other portions. In other words, it is easier to absorb deformation. Therefore, when a difference in thermal expansion occurs between the substrate and the protective film during a temperature change in the structural member, the portion of the protective film facing the substrate deforms to follow the substrate, but the stress generated in this portion is relatively small. As a result, it is possible to suppress deterioration of the protective film due to the difference in thermal expansion compared to conventional methods. Effect of the Invention

[0011] According to the present invention, it is possible to provide a structural member capable of suppressing deterioration of a protective film caused by a difference in thermal expansion while ensuring plasma resistance. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic cross-sectional view of a structural member according to the present embodiment. [Diagram 2] 1 is an image obtained by observing a cross section of a structural member according to this embodiment using a scanning electron microscope. [Diagram 3] FIG. 2 is a schematic cross-sectional view of a structural member according to the present embodiment. [Figure 4] FIG. 2 is a schematic cross-sectional view of a structural member according to the present embodiment. [Diagram 5] 10 is a schematic cross-sectional view of a structural member according to a modified example of the present embodiment. FIG. [Figure 6] 10 is a schematic cross-sectional view of a structural member according to a modified example of the present embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicated description will be omitted.

[0014] The structural member 10 according to this embodiment is used as a member constituting the inner wall of a processing chamber in a semiconductor manufacturing apparatus (not shown) such as a plasma etching apparatus. Note that the use of such a structural member 10 is merely an example and is not limited to use in semiconductor manufacturing apparatuses, but the structural member 10 is preferably used as a member for applications requiring durability against plasma.

[0015] As shown in Fig. 1, the structural member 10 has a substrate 100 and a protective film 200 formed so as to cover a surface 110 of the substrate 100. In a plasma etching apparatus, a surface 210 of the protective film 200 is exposed to the space inside a chamber. The protective film 200 of this embodiment is provided for the purpose of protecting the substrate 100 from plasma. The cross section shown in Fig. 1 is a cross section of the structural member 10 cut perpendicularly to the surface 110.

[0016] The substrate 100 is a member that occupies almost the entirety of the structural member 10. In this embodiment, the substrate 100 is made of high-purity aluminum oxide (Al 2 O 3 The substrate 100 may be a ceramic sintered body made of a material different from the above, and depending on the application of the structural member 10, the substrate 100 may be a metal.

[0017] The protective film 200 is a film formed so as to cover the surface 110 of the base material 100 as described above. In this embodiment, the protective film 200 is made of polycrystalline yttria (Y 2 O 3 The protective film 200 may be a ceramic film made of a material different from the above.

[0018] The protective film 200 of this embodiment is formed by using an aerosol deposition method on the surface 110 of the base material 100 after firing. As is well known, in the aerosol deposition method, microparticles, which are the material of the protective film 200, are dispersed in a gas to form an "aerosol," which is then sprayed toward the surface 110 and collided with it. On the surface 110, the microparticles are deformed or crushed by the impact of the collision, so that the microparticles bond to each other and gradually accumulate as the protective film 200. The surface 210 of the protective film 200 may be the surface itself when the film formation is completed, or may be a surface that has been polished after the film formation. The protective film 200 may be formed by a method other than the aerosol deposition method (for example, PVD, etc.).

[0019] The portion surrounded by the dotted line DL1 in Fig. 1 is a part of the cross section shown in Fig. 1 of the protective film 200. This part will also be referred to as "first portion 201" below. In the figure, the portion surrounded by the dotted line DL2 is a part of the cross section of the protective film 200 shown in Fig. 1, and is a portion that is closer to the base material 100 than the first portion 201. This portion will hereinafter also be referred to as the "second portion 202."

[0020] The first portion 201 is a portion of the protective film 200 near the surface 210, but may be a portion including the surface 210. The second portion 202 is a portion of the protective film 200 near the surface on the substrate 100 side (the interface with the substrate 100), but may be a portion including the surface. The definitions of the first portion 201 and the second portion 202 are merely examples. The first portion 201 may be a portion of the protective film 200 located at a different position from the above, so long as it is a portion of the protective film 200 closer to the surface 210 than the second portion 202. Similarly, the second portion 202 may be a portion of the protective film 200 located at a different position from the above, so long as it is a portion of the protective film 200 closer to the substrate 100 than the first portion 201.

[0021] Fig. 2 shows examples of images obtained by observing a cross section of protective film 200 with a scanning electron microscope. Fig. 2(A) shows an image of first portion 201, and Fig. 2(B) shows an image of second portion 202. The magnifications of the respective images are the same, and the areas are also the same.

[0022] 2, each cross section shows a cross section of a plurality of voids P contained in protective film 200. Voids P are formed inside protective film 200, for example, in the process of forming protective film 200.

[0023] 2(A) and 2(B), the shape and distribution of each void P are not uniform across the entire cross section of the protective film 200, but vary depending on the position. For example, each void P included in the first portion 201 in FIG. 2(A) is larger than each void P included in the second portion 202 in FIG. 2(B). small .

[0024] Hereinafter, the ratio of voids per unit area in a cross section of protective film 200 cut perpendicularly to surface 110 is defined as "void ratio." The void ratio is an index calculated individually for each part of the cross section of protective film 200, including first portion 201 and second portion 202. The above "unit area" may be set arbitrarily as long as it is an area that can include a plurality of voids P. For example, the above "unit area" may be set to the same area as each of first portion 201 and second portion 202 shown in FIG. 2.

[0025] In this embodiment, the shape and distribution of the voids P in the cross section of the protective film 200 are adjusted so that the porosity in the first portion 201 is smaller than the porosity in the second portion 202.

[0026] 3, cross sections corresponding to the respective images in FIG. 2 are depicted as schematic cross-sectional views showing the shape and distribution of voids P. Fig. 3(A) shows the shape and distribution of voids P in first portion 201, and Fig. 3(B) shows the shape and distribution of voids P in second portion 202.

[0027] 3, the number of voids P per unit area in the first portion 201 and the number of voids P per unit area in the second portion 202 are approximately equal to each other. Meanwhile, the average value of the cross-sectional area per void P included in the first portion 201 is smaller than the average value of the cross-sectional area per void P included in the second portion 202. In this manner, in this embodiment, as a result of making the cross-sectional area per void P different, the porosity in the first portion 201 is smaller than the porosity in the second portion 202.

[0028] The reason for adopting such a configuration will be described. In the protective film 200, the portion on the surface 210 side including the first portion 201, i.e., the portion on the surface 210 side exposed to plasma, is a dense film with a relatively small porosity. Therefore, the surface 210 is unlikely to deteriorate when exposed to plasma, and particles are unlikely to fall off (which can also be said to be dust generation) from the surface 210. In other words, at least the surface 210 portion of the protective film 200 has high plasma resistance at least as high as that of the conventional one, and the protective film 200 is unlikely to deteriorate due to particles falling off.

[0029] From the viewpoint of ensuring the plasma resistance of protective film 200, it is preferable that the porosity of protective film 200 is small. For this reason, it seems better to make the porosity as small as possible not only in first portion 201 but also in the entire cross section of protective film 200 including second portion 202.

[0030] However, according to an experiment conducted by the present inventors, it has been found that if the entire protective film 200 is formed too densely (i.e., without any air bubbles), while the plasma resistance is sufficiently improved, the protective film 200 becomes more susceptible to deterioration due to the difference in thermal expansion when the temperature changes. The "difference in thermal expansion when the temperature changes" refers to the difference in thermal expansion between the base material 100 and the protective film 200 when the temperature of the entire structural member 10 changes.

[0031] In this embodiment, as a countermeasure to this problem, the distribution and size of the voids P in each portion of the protective film 200 are adjusted so that the porosity in the first portion 201 is smaller than the porosity in the second portion 202.

[0032] In the configuration of this embodiment, the porosity of the portion of the protective film 200 on the substrate 100 side is relatively large, and the elastic modulus is smaller than that of other portions. In other words, it is easy to absorb deformation. Therefore, when a thermal expansion difference occurs between the substrate 100 and the protective film 200 during a temperature change of the structural member 10, the portion of the protective film 200 on the substrate 100 side deforms following the substrate 100, but the stress generated in the portion is kept relatively small. As a result, it is possible to suppress the deterioration of the protective film 200 due to the thermal expansion difference compared to the conventional case. In other words, the structural member 10 according to this embodiment can suppress the deterioration of the protective film 200 due to the thermal expansion difference while ensuring at least the same level of plasma resistance as the conventional case.

[0033] 4 is a schematic diagram showing the distribution of voids P in the entire area of ​​protective film 200 from surface 210 to surface 110. Note that, since FIG. 4 is merely a schematic diagram, the size of voids P relative to the thickness of protective film 200 and the like differ from the actual size.

[0034] 4, in the protective film 200 of this embodiment, the cross-sectional area of ​​each void P gradually decreases with increasing distance from the substrate 100 over the entire range from the surface 210 to the surface 110. As a result, the porosity value in each portion of the protective film 200 also gradually (i.e., continuously) decreases with increasing distance from the substrate 100, and as a result, the porosity in the first portion 201 and the second portion 202 are different from each other.

[0035] The porosity value in each portion of the protective film 200 may change continuously as in this embodiment depending on the position in the depth direction (the vertical direction in Figure 3) perpendicular to the surface 110, or it may change in stages.

[0036] The porosity in each of the first portion 201 and the second portion 202 may be adjusted in a manner different from that of this embodiment (FIGS. 3 and 4). For example, in the configuration of the modified example shown in FIG. 5, the average value of the cross-sectional area per each of the voids P included in the first portion 201 and the average value of the cross-sectional area per each of the voids P included in the second portion 202 are approximately equal to each other. Meanwhile, the number of the voids P per unit area in the first portion 201 is smaller than the number of the voids P per unit area in the second portion 202. As in this modified example, the porosity in each of the first portion 201 and the second portion 202 may be adjusted by the arrangement density of the voids P, rather than the cross-sectional area per each of the voids P.

[0037] Fig. 6 is a schematic diagram of the distribution of voids P in protective film 200 according to the modified example of Fig. 5, similar to Fig. 4. As shown in Fig. 6, in protective film 200 of this modified example, the number of voids P per unit area gradually decreases with increasing distance from substrate 100 over the entire range from surface 210 to surface 110. As a result, the porosity value in each portion of protective film 200 also gradually (i.e., continuously) decreases with increasing distance from substrate 100, and as a result, the porosity in first portion 201 and second portion 202 are different from each other.

[0038] The protective film 200 with the porosity value adjusted as described above may be formed by stacking a plurality of types of films with different chemical compositions, but in that case, there is a possibility that a defect occurs at the boundary between the different types of films due to, for example, a difference in thermal expansion. Therefore, as in this embodiment, it is preferable that the protective film 200 is formed so that the chemical composition of the material is the same throughout the entire protective film 200. In other words, it is preferable that the chemical composition of the protective film 200 in the first portion 201 and the chemical composition of the protective film 200 in the second portion 202 are the same. The chemical composition being "same" means that the ratio of the elements constituting the protective film 200 is the same in each portion. The "elements constituting the protective film 200" may include elements that are mixed into the protective film 200 as impurities, but the identity of the "chemical composition" may be evaluated after excluding the elements.

[0039] The protective film 200 of this embodiment also has a substantially uniform crystallite size throughout. The "crystallite size" refers to the average value of the diameters of a plurality of crystallites that appear in a cross section when the protective film 200 is cut perpendicular to the surface 110.

[0040] The crystallite size can be calculated, for example, by taking a transmission electron microscope (TEM) image at a magnification of 400,000 times or more and calculating the average diameter of 15 crystallites in this image by circular approximation. In this case, if the sample thickness during focused ion beam (FIB) processing is sufficiently thinned to about 30 nm, the crystallites can be more clearly identified. The magnification for photography can be appropriately selected within the range of 400,000 times or more.

[0041] In the protective film 200 of this embodiment, the crystallite size measured by the above method is generally uniform throughout the protective film 200, specifically, 50 nm or less. That is, the crystallite size of the protective film 200 in the first portion 201 and the crystallite size of the protective film 200 in the second portion 202 are both 50 nm or less. By making the crystallite size of the protective film 200 generally uniform, the durability of the protective film 200 can be improved.

[0042] As a method for adjusting the porosity of each portion of the protective film 200, various methods can be adopted.

[0043] For example, when forming the protective film 200 using the aerosol deposition method, the porosity of each part can be adjusted by changing the film formation conditions each time. Those skilled in the art who form films using the aerosol deposition method have accumulated know-how on film formation conditions for suppressing the formation of bubbles. In other words, the film formation conditions that increase the cross-sectional area of ​​the bubbles and the film formation conditions that increase the arrangement density of the bubbles have also been accumulated as know-how. Therefore, by forming the film using this knowledge, the protective film 200 having the porosity distribution as shown in the examples of FIG. 4 and FIG. 6 can be easily formed.

[0044] When forming the protective film 200, the porosity can be adjusted, for example, by forming the portion on the substrate 100 side using a porous raw material until halfway through the film formation.

[0045] When forming the protective film 200, the porosity can be adjusted, for example, by forming the film on the substrate 100 side using a raw material containing a pore-forming material until the middle of the film formation. The pore-forming material may be a material that disappears when heated, such as resin beads. If the entire structural member 10 is heated after the film formation is completed, the protective film 200 with the adjusted porosity can be obtained.

[0046] When forming the protective film 200, for example, a material having a different thermal expansion coefficient from the main material may be mixed in to form the film on the substrate 100 side until the middle of the film formation. After the film formation is completed, the entire structural member 10 is heated to generate voids at the interface between the different materials, thereby obtaining the protective film 200 with an adjusted porosity.

[0047] After forming the protective film 200 by the conventional method, the entire structural member 10 may be heated. If heating is performed under predetermined conditions, grain growth occurs in the protective film 200, and local voids can be generated during the process.

[0048] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Any design modifications made by a person skilled in the art to these specific examples are also included within the scope of the present disclosure as long as they have the features of the present disclosure. The elements of each of the above-mentioned specific examples and their arrangements, conditions, shapes, etc. are not limited to those exemplified and can be changed as appropriate. The combination of each of the elements of each of the above-mentioned specific examples can be changed as appropriate as long as no technical contradiction occurs. [Explanation of symbols]

[0049] 10: Structural members 100: Base material 110: Surface 200: Protective film 201: Part 1 202:Second part P: void

Claims

1. A substrate; a protective film covering a surface of the base material and having a thermal expansion coefficient different from that of the base material; When the cross section of the protective film is cut perpendicularly to the surface, the ratio of voids per unit area is defined as the porosity, The porosity in a first portion that is a part of the cross section is the porosity is smaller than the porosity in a second portion, which is a portion of the cross section closer to the substrate than the first portion, The average cross-sectional area of ​​each of the voids included in the first portion is A structural member, characterized in that the cross-sectional area of ​​each of the voids included in the second portion is smaller than the average cross-sectional area of ​​each of the voids.

2. 2. The structural member according to claim 1, wherein the porosity in the cross section gradually decreases with increasing distance from the substrate.

3. A chemical composition of the protective film in the first portion; 2. The structural member according to claim 1, wherein the chemical composition of the protective film in the second portion is the same as that of the protective film in the first portion.

4. The crystallite size of the protective film in the first portion, and 2. The structural member according to claim 1, wherein the crystallite size of the protective film in the second portion is 50 nm or less.

5. 2. The structural member according to claim 1, wherein the protective film is a film formed by an aerosol deposition method.

6. The substrate is a ceramic or a metal, The structure of claim 1 wherein said protective coating is ceramic.

7. The substrate is a ceramic sintered body containing aluminum oxide, 7. The structural member according to claim 6, wherein the protective film is a film containing yttria.

Images