Structural member

Abstract

To provide a structural member equipped with a protective film with excellent particle resistance.SOLUTION: A structural member 10 comprises a substrate 100, and a protective film 200 covering a surface S1 of the substrate 100. In the case where a cut surface in the case of cutting the substrate 100 perpendicularly to the surface S1 is a cross section, a shape of a line corresponding to the surface S1 of the substrate 100 on the cross section is a surface shape, Fourier transformation is applied to a function showing the surface shape, and a function after transformation is drawn as a graph in which a wavelength (μm) is on the axis of abscissa, an average inclination of the graph in the range of the wavelength of 30 μm or less is 0.0050 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to structural members. [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 apparatus, a protective film is formed on the surface of the substrate that constitutes the inner wall of the chamber to protect the substrate from plasma. For example, oxide ceramics such as yttrium oxide (yttria) are used as such a protective film.

[0003] When a protective film is exposed to plasma, some of the deteriorated protective film breaks down into large particles that fly away, which can have a detrimental effect on the semiconductor manufacturing process. A protective film that is less susceptible to this phenomenon will be referred to below as a "protective film with excellent particle resistance." For example, a protective film that is less susceptible to deterioration even when exposed to plasma, or a protective film that, even if it does deteriorate, breaks down into particles so small that they do not cause problems in the process (i.e., a protective film that is less likely to break down into large particles), would both be called a "protective film with excellent particle resistance."

[0004] Various film formation methods, such as PVD and CVD, can be used to form protective films on the surface of substrates. In recent years, aerosol deposition has also become popular. Using aerosol deposition and other film formation methods, it has become possible to form dense, particle-resistant protective films composed of fine crystalline particles. While forming dense, particle-resistant protective films requires a longer film formation time than conventional methods, such protective films can achieve a certain lifespan even when they are relatively thin. Therefore, efforts are being made to make the protective film relatively thin. When the film thickness is thin, the shape of the protective film surface is more strongly influenced by the shape of the substrate surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-160097 [Patent Document 2] Japanese Patent Publication No. 2020-050536 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to suppress particle generation, irregularities on the surface of the protective film are removed and the arithmetic mean roughness Ra is reduced. Also, in order to suppress peeling of the protective film and to obtain a dense protective film, it was thought that the surface of the substrate on which the protective film is formed needed to be a smooth surface with an arithmetic mean roughness Ra of about 0.1 μm or less.

[0007] The present inventors have discovered that a structural member with excellent particle resistance can be obtained by controlling the index in the planar direction, rather than the arithmetic mean roughness Ra, which is an index in the height direction, of the surface of a substrate on which a protective film is formed.An object of the present invention is to provide a structural member provided with a protective film with excellent particle resistance. [Means for solving the problem]

[0008] To achieve the above object, the present invention provides a structural member comprising a substrate and a protective film covering the surface of the substrate. When a cross section of the substrate cut perpendicularly to its surface is taken as the cut surface, the shape of the line on the cut surface corresponding to the surface of the substrate is taken as the surface shape, a function representing the surface shape is subjected to a Fourier transform, and the transformed function is plotted as a graph with wavelength (μm) as the horizontal axis, the average slope of the graph in the wavelength range of 30 μm or less is 0.0050 or less.

[0009] According to experiments conducted by the present inventors, a new finding was obtained that a structural member has high particle resistance when the substrate surface has relatively few small irregularities and the average slope of the above graph is 0.0050 or less. In other words, when the average slope of the above graph is 0.0050 or less, it is possible to obtain a structural member having a protective film with excellent particle resistance, even if the substrate surface has an arithmetic mean roughness Ra exceeding 0.15 μm. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a structural member provided with a protective film that has excellent particle resistance. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram schematically illustrating a cross section of a structural member according to the present embodiment. [Figure 2] FIG. 2 is a diagram for explaining the surface shape of a substrate. [Figure 3] FIG. 10 is a diagram showing the results of a film formation test. [Figure 4] This is an image of the surface of the substrate photographed using a laser microscope. [Figure 5] 5 is a graph of a Fourier transform function calculated for the surface of FIG. 4. [Figure 6] This is an image of the surface of the substrate photographed using a laser microscope. [Figure 7] 6 is a graph of a function calculated for the surface of FIG. 5 after a Fourier transform. [Figure 8] This is an image of the surface of the substrate photographed using a laser microscope. [Figure 9] 9 is a graph of the Fourier transform function calculated for the surface of FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. To facilitate understanding of the description, the same components in the drawings will be denoted by the same reference numerals as much as possible, and duplicated descriptions will be omitted.

[0013] The structural member 10 according to this embodiment is used as a member that constitutes 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.

[0014] 1, the structural member 10 includes a substrate 100 and a protective film 200. In a plasma etching apparatus or the like, a surface S2 of the protective film 200 is exposed to the space within the chamber. The protective film 200 is provided to protect the surface S1 of the substrate 100 from the plasma.

[0015] The substrate 100 is a member that occupies substantially the entire structural member 10. In this embodiment, the substrate 100 is a ceramic sintered body containing high-purity aluminum oxide (Al2O3), but it may be made of a different type of ceramic. The substrate 100 may also be made of a material other than ceramic. In this embodiment, the surface S1 of the substrate 100 is flat, but the surface S1 may have through holes, an inclined surface, or the like.

[0016] As described above, the protective film 200 is a film formed to protect the substrate 100 from plasma. The protective film 200 is formed so as to cover the entire surface S1 of the substrate 100. In this embodiment, the protective film 200 is configured as a film containing polycrystalline yttrium oxide (yttria: Y2O3), but it may also be a ceramic film made of a different material. The thickness of the protective film 200 is set appropriately depending on the length of time over which durability is required to be maintained, etc. In this embodiment, the thickness of the protective film 200 is, for example, about 10 μm, but it may be thinner.

[0017] The protective film 200 of this embodiment is formed on the surface S1 of the base material 100 after firing by using a PVD method or an aerosol deposition method.

[0018] It is known that if the arithmetic surface roughness Ra of the surface S1 of the substrate 100 is too large, the protective film 200 cannot be formed or the protective film peels off. For this reason, it is considered necessary to smooth the surface S1 before film formation. Conventionally, the surface S1 has been polished or otherwise processed to achieve a smooth surface with an arithmetic mean roughness Ra of 0.1 μm or less. Polishing or otherwise processing the surface S1 to achieve such a smooth surface often requires time and effort. Particularly when the thickness of the protective film is relatively thin, the surface shape of the protective film is strongly affected by the surface shape of the substrate, and therefore, it has been considered necessary to strictly control the surface shape of the substrate.

[0019] The inventors have conducted numerous experiments and studies to determine what conditions the shape of the surface S1 must satisfy in order to form the protective film 200. As a result, they have gained new knowledge that a structural member with excellent particle resistance can be obtained by controlling the index in the planar direction, rather than the arithmetic mean roughness Ra, which is an index in the height direction of the surface S1 of the substrate 100.

[0020] FIG. 2 shows a schematic cross section of the substrate 100 before film formation. The "cross section" here refers to a cross section of the substrate 100 cut along a plane perpendicular to the surface S1. In the cross section shown in FIG. 2, the shape of the surface S1 of the substrate 100 appears as a line shape corresponding to the surface S1. This shape will also be referred to as the "surface shape" hereinafter.

[0021] The roughness of the surfaces S1 shown in Figures 2(A) and 2(B) is approximately the same in terms of arithmetic mean roughness Ra, specifically, Ra 0.40 μm. However, the surface S1 in Figure 2(B) has fewer fine irregularities than the example in Figure 2(A). This difference in shape does not appear as a difference in the arithmetic mean roughness Ra, which is an index in the height direction. Therefore, although the two surfaces S1 shown in Figure 2 are different in shape, as described above, both have a Ra of 0.40 μm. However, the surface shapes in Figures 2(A) and 2(B) can be distinguished using indexes in the planar direction.

[0022] The inventors have devised a new index relating to the planar direction to define a surface S1 having a surface shape with few fine irregularities, as shown in Figure 2(B), as an alternative to the conventional index of "arithmetic mean roughness Ra of surface S1 ≦ 0.1 μm."

[0023] The index will now be explained. First, a function representing the surface shape of the surface S1 of the substrate that appears on a cut surface of a structural member on which a protective film is formed is set. For example, the function is expressed in the form y=f(x), where x (μm) represents the position in the left-right direction in FIG. 2, and y (μm) represents the position in the up-down direction in the same figure.

[0024] Next, this function is transformed into the form Y = F(λ) by applying a Fourier transform. In this formula, "λ" is a parameter that represents the wavelength of each wave in units of [μm] when the surface shape shown in Figure 2 is considered to be the superposition of multiple waves with different wavelengths.

[0025] In the above conversion, x (μm) in the formula y = f(x) can be treated as a "time" parameter and then subjected to a Fourier transform to convert it into the form Y1 = F1(ω), which indicates the frequency characteristics. "ω" indicates frequency. After that, by converting each frequency into a wavelength, it can be converted into the form Y = F(λ).

[0026] After converting the function representing the surface shape of surface S1 into the form Y=F(λ) as described above, the converted function can be plotted on a graph, as shown in, for example, Figure 5G. The horizontal axis of the graph is the above-mentioned "λ," i.e., wavelength (unit: μm), and the vertical axis is the above-mentioned "Y," i.e., a parameter representing the intensity of each wavelength component. Note that in Figure 5G, the graph of Y=F(λ) is plotted as a scatter plot, but the graph may also be plotted as a continuous curve.

[0027] L shown in Figure 5 is an approximation line of G in the wavelength range of 30 μm or less. The slope of this L can be said to be the average slope of the graph showing Y=F(λ) in the wavelength range of 30 μm or less. In the example of Figure 5, the slope of L is 0.0046.

[0028] As in the example of FIG. 2(A), when the surface shape of the substrate surface S1 of a structural member has many small irregularities, the slope of L is calculated to be a large value. As in the example of FIG. 2(B), when the surface shape of surface S1 has few small irregularities, the slope of L is calculated to be a small value. Therefore, the present inventors have investigated the use of the slope of L as a new index for evaluating particle resistance. As a result, they have discovered that a structural member with high particle resistance can be obtained if the surface S1 has a slope of L of 0.0050 or less.

[0029] The inventors created three samples of substrate 100 with different shapes of the surface S1, and prepared a structural member with a protective film 200 formed on each surface S1. The substrate 100 was an alumina substrate, and the protective film was an yttria film. In this example, the protective film was formed by aerosol deposition. The slope of L was calculated for each surface S1 on the fracture surface of the structural member. The slope of L was also calculated for each surface S1 before film formation, but in this test, the surface shape (slope of L) of the substrate in the structural member (after protective film formation) was approximately the same as the surface shape (slope of L) of the substrate before film formation.

[0030] The slope of L for the surface S1 of the substrate in a structural member was calculated using the following method. First, a predetermined area of ​​the surface S1 of the substrate to be measured was photographed using a laser microscope. The laser microscope used was a VK-X3000 manufactured by KEYENCE. A 50x objective lens was used, and images were obtained at 1000x magnification.

[0031] Next, profile data (data showing the surface shape of surface S1) was extracted from the image, and the surface shape within a certain length range was obtained by sampling. The "certain length" was set to 0.2826 mm, and 1,024 locations within this range were sampled at regular intervals. As described above, the shape obtained by sampling was then converted into the form Y = F(λ) by performing a Fourier transform on the function (y = f(x)) representing the shape, and the converted function was plotted as a graph with λ as the horizontal axis. The average slope of the graph within a wavelength range of 30 μm or less was then calculated.

[0032] In performing the Fourier transform, it is not necessary to explicitly calculate the function (y = f(x)) representing the surface shape or the transformed function (Y = F(λ)). In other words, the average slope of the graph after the Fourier transform may be calculated by directly performing software arithmetic processing on the data acquired by sampling.

[0033] In the above test, the arithmetic mean roughness Ra of the fracture surface S1 of each sample was also measured. The arithmetic mean roughness Ra was calculated using the profile data of the above image taken with a laser microscope. The "reference length" indicating the measurement range was set to 250 μm. The cutoff λs was set to 0.8 μm, and calculations were performed using stylus mode. The stylus tip radius was set to 2 μm, and the stylus tip angle was set to 60°. Measurements were performed at 20 different positions on the surface S1, and the arithmetic mean roughness Ra was calculated by averaging the obtained values.

[0034] Figure 3 shows the evaluation results. For sample No. 1, the surface S1 before film formation was subjected to surface grinding and then further polished by lapping. Figure 4 shows an image of the surface S1 of sample No. 1 photographed with a laser microscope. Figure 5 shows a graph (G) of the function after Fourier transformation calculated for the surface S1 of sample No. 1 and the approximation line (L) of the graph in the wavelength range of 30 μm or less. The "average slope" calculated for the surface S1 of sample No. 1, i.e., the slope of the approximation line (L) shown in Figure 5, was 0.0046. The arithmetic mean roughness Ra of the same surface was 0.10 μm.

[0035] For sample No. 2, the surface S1 before deposition was subjected to surface grinding, followed by free-abrasive processing using finer abrasive grains that did not remove the grinding waviness. Figure 6 shows an image of the surface S1 of sample No. 2 taken with a laser microscope. Figure 7 shows a graph (G) of the Fourier transform function calculated for the surface S1 of sample No. 2 and the approximation line (L) of the graph for wavelengths of 30 μm or less. The "average slope" calculated for the surface S1 of sample No. 2, i.e., the slope of the approximation line (L) shown in Figure 7, was 0.0042. The arithmetic mean roughness Ra of the same surface was 0.44 μm.

[0036] For sample No. 3, only surface grinding was performed on the surface S1 before film formation. Figure 8 shows an image of the surface S1 of the substrate of sample No. 3 taken with a laser microscope. Figure 9 shows a graph (G) of the function after Fourier transform calculated for surface S1 of sample No. 3 and an approximation line (L) of the graph in the wavelength range of 30 μm or less. The "average slope" calculated for surface S1 of sample No. 3, i.e., the slope of the approximation line (L) shown in Figure 9, was 0.0087. The arithmetic mean roughness Ra of the same surface was 0.57 μm.

[0037] As shown in FIG. 3, both Samples No. 2 and 3 have a roughness exceeding 0.1 μm in terms of the arithmetic mean roughness Ra, which is an index of the height direction of the surface S1.

[0038] In sample No. 2, the slope of L calculated for surface S1 was small, at 0.0050 or less, and there were fewer fine irregularities like those in the example in Figure 2(A). In contrast, in sample No. 3, the slope of L calculated for surface S1 was large, exceeding 0.0050, and there were many fine irregularities like those in the example in Figure 2(A). As a result, the particle resistance of structural member No. 3 was inferior to that of Nos. 1 and 2. On the other hand, there was no significant difference in particle resistance between sample No. 1, which had an arithmetic mean height Ra of only about 0.1 μm, and sample No. 2, which had an arithmetic mean height Ra of more than 0.1 μm.

[0039] Thus, it was confirmed that even for a sample whose surface S1 has an arithmetic mean roughness Ra exceeding 0.1 μm, high particle resistance can be achieved in the structural member if the slope of L calculated for the surface S1 is sufficiently small. According to experiments separately conducted by the present inventors, it was confirmed that good particle resistance is achieved when the slope of L calculated for the surface S1 is 0.0050 or less.

[0040] Various known methods can be used to process the surface S1 to a roughness of 0.0050 or less in terms of the slope of L. Examples include grinding stone polishing, lapping polishing, buffing, barrel polishing, electrolytic polishing, and sandblasting. By appropriately selecting the type and size of the abrasive used in polishing and adjusting the polishing time, the calculated slope of L can be reduced to 0.0050 or less before the arithmetic mean roughness Ra of surface S1 reaches 0.1 μm or less. This simplifies the surface treatment of the substrate 100 before film formation, and improves productivity, compared to processing the surface S1 until the arithmetic mean roughness Ra reaches 0.1 μm or less.

[0041] More preferably, the surface S1 is set so that the calculated slope of L is 0.0046 or less. Still more preferably, the surface S1 is set so that the calculated slope of L is 0.0042 or less.

[0042] Even if the surface S1 of the substrate 100 is not flat but is, for example, a curved or other non-flat surface, it is possible to convert the function representing the surface shape of the surface S1 into the form Y=F(λ) and calculate the slope of the graph after conversion. When the surface S1 is a non-flat surface, the slope of L can be calculated using, for example, the following method.

[0043] First, a portion of the substrate 100 is cut out to create a plate-shaped sample including a surface S1 that is a non-flat surface. The sample may be prepared, for example, so that the entire main surface is surface S1 and has a shape of 20 mm x 20 mm. By cutting out a portion of the substrate 100 as such a small sample, the surface S1 to be measured can be made closer to a flat surface, making it easier to observe the surface using a laser microscope, etc.

[0044] As long as the cut surface S1 can be considered to be a generally flat surface, the size of the sample may be different from the above. For example, if the surface S1 of the substrate 100 is curved and has a relatively large radius of curvature, the substrate 100 may be cut out to produce a sample of a relatively large size. On the other hand, if the radius of curvature of a portion of the surface S1 is relatively small, the sample may be created by cutting the substrate 100 so as to avoid that portion.

[0045] After preparing the small sample piece as described above, the shape of the surface S1 may be measured and the slope of L may be calculated using the same methods as those described above.

[0046] If the sample vibrates during measurement, it becomes difficult to accurately measure the shape of surface S1. Therefore, the contact surface of the sample, i.e., the surface opposite surface S1, can be processed to have a shape (e.g., a flat surface) that allows stable placement. This suppresses sample vibration, making it possible to measure the shape of surface S1 with high accuracy.

[0047] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art as appropriate are also included within the scope of the present disclosure as long as they comprise the features of the present disclosure. The elements of the above-described specific examples, as well as their arrangement, conditions, shape, etc., are not limited to those exemplified and can be modified as appropriate. The elements of the above-described specific examples can be combined in various ways as appropriate, as long as no technical contradictions arise. [Explanation of symbols]

[0048] 10: Structural members 100: Base material 200: Protective film S1,S2:Surface

Claims

1. A substrate; a protective film covering the surface of the substrate; A cross section of the substrate cut perpendicularly to its surface is defined as a cut surface, a line shape corresponding to the surface of the base material on the cut surface is defined as a surface shape; When the function representing the surface shape is subjected to a Fourier transform and the transformed function is plotted as a graph with wavelength (μm) as the horizontal axis, A structural member characterized in that the average slope of the graph in the wavelength range of 30 μm or less is 0.0050 or less.

2. 2. The structural member according to claim 1, wherein the surface roughness of the substrate is greater than 0.15 [mu]m in terms of arithmetic mean roughness Ra.

3. 2. The structural member according to claim 1, wherein the substrate is formed from a material containing aluminum oxide.

4. 2. The structural member according to claim 1, wherein said protective film is formed of a material containing yttrium oxide.

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

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