Structural member

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 Art

[0002] A structural member having a protective film on the surface of a base material is used in various fields such as semiconductor manufacturing equipment. For example, in a plasma etching apparatus, a protective film for protecting the base material from plasma is formed on the surface of the base material constituting the inner wall of the chamber. As such a protective film, for example, oxide ceramics such as yttria, fluoride ceramics such as yttrium fluoride, etc. are used. As described in Patent Document 1 below, the protective film is formed using various methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and aerosol deposition method.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the process of forming a protective film on the surface of a base material, bubbles may be contained in the protective film. For example, in order to fully exhibit the function of the protective film such as plasma resistance, it is considered desirable that there are no bubbles in the protective film. Therefore, when forming the protective film, it is common to set the film-forming conditions so that the bubbles in the protective film become as small as possible or less.

[0005] On the other hand, according to the experiments conducted by the inventors, if the entire protective film is formed too densely (i.e., without any bubbles), while the plasma resistance is sufficiently improved, a new problem has emerged that the deterioration of the protective film due to the thermal expansion difference during temperature changes is likely to occur.

[0006] The present invention has been made in view of such problems, and an object thereof is to provide a structural member capable of suppressing the deterioration of the protective film due to the thermal expansion difference while ensuring plasma resistance.

Means for Solving the Problems

[0007] In order to solve the above problems, the structural member according to the present invention includes a base material and a protective film covering the surface of the base material. When the cross-section obtained by cutting the protective film perpendicular to the surface is considered, and the porosity is defined as the ratio of the voids occupied per unit area, in this structural member, the porosity in the first part, which is a part of the cross-section, is smaller than the porosity in the second part, which is the part on the base material side of the cross-section compared to the first part.

[0008] In such a structural member, the porosity of the protective film is not uniform throughout, and the porosity varies depending on the position in the thickness direction. Specifically, the porosity of the first part, which is relatively on the surface side, is smaller than the porosity of the second part, which is on the base material side.

[0009] In such a configuration, in the part of the protective film on the surface side that is exposed to the plasma, since the porosity is relatively small, for example, plasma resistance comparable to the conventional level can be ensured. The "plasma resistance" mentioned here refers to, for example, the performance of suppressing the generation of dust associated with the deterioration of the protective film after exposing the protective film to the plasma under predetermined conditions.

[0010] In the part of the protective film on the substrate side, the porosity is relatively large, so the elastic modulus is smaller than that of other parts. That is, it is easier to absorb deformation. Therefore, when there is a thermal expansion difference between the substrate and the protective film during a temperature change of the structural member, the part of the protective film on the substrate side will deform following the substrate, but the stress generated in this part is relatively small. As a result, it is possible to suppress the deterioration of the protective film due to the thermal expansion difference as compared with the prior art.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a structural member that can suppress the deterioration of the protective film due to the thermal expansion difference while ensuring plasma resistance.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0013] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. For ease of understanding of the description, the same reference numerals are given to the same components in each drawing as much as possible, and duplicate descriptions are omitted.

[0014] 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 semiconductor manufacturing apparatuses. However, the structural member 10 is preferably used as a member for applications that require durability against plasma.

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

[0016] The base material 100 is a member that generally occupies the entire structural member 10. In this embodiment, the base material 100 is configured as a ceramic sintered body containing high-purity aluminum oxide (Al2O3). The base material 100 may be a ceramic sintered body made of a material different from the above, and depending on the use of the structural member 10, the base material 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 configured as a film containing polycrystalline yttria (Y2O3). 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 on the surface 110 of the base material 100 after firing by using the aerosol deposition method. As is well known, in the aerosol deposition method, fine particles that are the material of the protective film 200 are dispersed in a gas to form an "aerosol", and then this is sprayed toward the surface 110 and made to collide. On the surface 110, due to the impact of the collision, the fine particles are deformed and crushed, so while the fine particles are bonding to each other, they 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 or the like after the film formation. The protective film 200 may be formed by a method other than the aerosol deposition method (for example, PVD or the like).

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

[0020] The first portion 201 is a portion near the surface 210 of the protective film 200, but may also be a portion including the surface 210. Further, the second portion 202 is a portion near the surface (interface with the base material 100) on the base material 100 side of the protective film 200, but may also be a portion including the said surface. Incidentally, such definitions of the first portion 201 and the second portion 202 are merely examples. The first portion 201 may be a portion at a position different from the above as long as it is a portion of the protective film 200 on the surface 210 side of the second portion 202. Similarly, the second portion 202 may be a portion at a position different from the above as long as it is a portion of the protective film 200 on the base material 100 side of the first portion 201.

[0021] FIG. 2 shows an example of an image obtained by observing the cross-section of the protective film 200 with a scanning electron microscope. The image shown in FIG. 2(A) is an image of the first portion 201, and the image shown in FIG. 2(B) is an image of the second portion 202. The magnifications of the respective images are the same as each other, and the areas are also the same as each other.

[0022] As shown in FIG. 2, in each cross-section, cross-sections of a plurality of voids P included in the protective film 200 appear. The voids P are formed, for example, inside the protective film 200 in the process of forming the protective film 200.

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

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

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

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

[0027] In the example of FIG. 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. On the other hand, 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. Thus, 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 such a configuration will be described. Among the protective film 200, the portion on the surface 210 side including the first portion 201, that is, the portion on the surface 210 side exposed to the plasma, is a dense film with a relatively small porosity. Therefore, deterioration of the surface 210 when exposed to the plasma is unlikely to occur, and shedding of particles from the surface 210 (which can also be said to be dust generation) is also unlikely to occur. That is, at least in the portion of the protective film 200 on the surface 210, at least the same high plasma resistance as in the conventional case is ensured, and deterioration of the protective film 200 due to particle shedding is unlikely to occur.

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

[0030] However, according to the experiments conducted by the inventors of the present invention, if the entire protective film 200 is formed too densely (i.e., without any bubbles), while the plasma resistance is sufficiently improved, the protective film 200 is likely to deteriorate due to the thermal expansion difference during temperature change. The "thermal expansion difference during temperature change" refers to the thermal expansion difference between the base material 100 and the protective film 200 when the temperature of the entire structural member 10 changes.

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

[0032] In the configuration of this embodiment, in the part of the protective film 200 on the side of the base material 100, the porosity is relatively large, so the elastic modulus is smaller than that of other parts. That is, it is easier to absorb deformation. Therefore, when the temperature of the structural member 10 changes and a thermal expansion difference occurs between the base material 100 and the protective film 200, the part of the protective film 200 on the side of the base material 100 deforms following the base material 100, but the stress generated in this part is suppressed to be relatively small. As a result, the deterioration of the protective film 200 due to the thermal expansion difference can be suppressed compared to the conventional case. That is, in the structural member 10 according to this embodiment, it is possible to 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 in the conventional case.

[0033] FIG. 4 schematically shows the distribution of the voids P in the entire range from the surface 210 to the surface 110 of the protective film 200. Note that since FIG. 4 is only a schematic diagram, the size of the voids P relative to the thickness of the protective film 200 is different from the actual one.

[0034] As shown in FIG. 4, in the protective film 200 of the present embodiment, the cross-sectional area per void P gradually decreases as it moves away from the base material 100 throughout the range from the surface 210 to the surface 110. As a result, the porosity values in each part of the protective film 200 also gradually (i.e., continuously) decrease as it moves away from the base material 100, and as a result, the porosities in the first part 201 and the second part 202 are different from each other.

[0035] The porosity values in each part of the protective film 200 may change continuously as in the present embodiment according to the position in the depth direction (vertical direction in FIG. 3) perpendicular to the surface 110, or may change stepwise.

[0036] In addition, the porosity in each of the first part 201 and the second part 202 may be adjusted in a manner different from that of the present 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 void P included in the first part 201 and the average value of the cross-sectional area per void P included in the second part 202 are substantially equal to each other. On the other hand, the number of voids P per unit area in the first part 201 is less than the number of voids P per unit area in the second part 202. As in this modified example, instead of the cross-sectional area per void P, the porosity in each of the first part 201 and the second part 202 may be adjusted by the arrangement density of the voids P.

[0037] FIG. 6 schematically depicts the distribution of the voids P in the protective film 200 according to the modified example of FIG. 5, similar to FIG. 4. As shown in FIG. 6, in the protective film 200 of this modified example, the number of voids P per unit area gradually decreases as it moves away from the base material 100 throughout the range from the surface 210 to the surface 110. As a result, the porosity values in each part of the protective film 200 also gradually (i.e., continuously) decrease as it moves away from the base material 100, and as a result, the porosities in the first part 201 and the second part 202 are different from each other.

[0038] The protective film 200 with the void fraction value adjusted as described above may be formed by laminating a plurality of types of films having different chemical compositions. However, in that case, at the boundary between different films, for example, problems associated with differences in thermal expansion may occur. Therefore, as in this embodiment, it is preferable that the protective film 200 is formed such that the chemical composition of the material is the same throughout. That is, it is preferable that the chemical composition of the protective film 200 in the first portion 201 is the same as the chemical composition of the protective film 200 in the second portion 202. "The same" chemical composition means that the ratio of the elements constituting the protective film 200 is the same in each part. The "elements constituting the protective film 200" may include elements mixed into the protective film 200 as impurities, but the identity of the "chemical composition" may also be evaluated after excluding such elements.

[0039] The protective film 200 of this embodiment is also substantially uniform throughout with respect to the crystallite size. The "crystallite size" is the average value of the diameters of a plurality of crystallites appearing in the 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 value of the diameters of 15 circular approximations of the crystallites in this image. At this time, if the sample thickness during focused ion beam (FIB) processing is made sufficiently thin to about 30 nm, the crystallites can be discriminated more clearly. The imaging magnification 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 substantially uniform throughout the protective film 200, and specifically, it is 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 substantially uniform throughout, the durability of the protective film 200 can be improved.

[0042] As a method for adjusting the porosity of each part 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-forming conditions each time. In those skilled in the art of forming a film by the aerosol deposition method, the film-forming conditions for suppressing the formation of bubbles have been accumulated as know-how. In other words, the film-forming conditions under which the cross-sectional area of the bubbles becomes large and the film-forming conditions under which the arrangement density of the bubbles becomes high have also been accumulated as know-how. Therefore, by utilizing these findings to form a film, the protective film 200 having a porosity distribution as in the examples of FIGS. 4 and 6 can be easily formed.

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

[0045] When forming the protective film 200, for example, the porosity can also be adjusted by forming a film on the part on the substrate 100 side using a raw material containing a pore-forming agent until halfway through the film formation. As the pore-forming agent, for example, a material that disappears by heating such as resin beads may be used. After the film formation is completed, if the entire structural member 10 is heated, a protective film 200 with adjusted porosity can be obtained.

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

[0047] After forming the protective film 200 in the same manner as in the prior art, 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] As described above, the present embodiment has been described with reference to specific examples. However, the present disclosure is not limited to these specific examples. Those obtained by appropriately modifying the design by those skilled in the art for these specific examples are also included in the scope of the present disclosure as long as they have the features of the present disclosure. Each element, its arrangement, conditions, shape, etc. included in each of the above-described specific examples are not limited to those illustrated and can be appropriately changed. Each element included in each of the above-described specific examples can be appropriately combined as long as no technical contradiction occurs.

Explanation of Reference Numerals

[0049] 10: Structural member 100: Substrate 110: Surface 200: Protective film 201: First portion 202: Second portion P: Void

Claims

1. A base material, and a protective film covering the surface of the base material, and when the cross-section obtained by cutting the protective film perpendicular to the surface is considered, the ratio of the voids per unit area is defined as the porosity, wherein the porosity in a first portion which is a part of the cross-section is smaller than the porosity in a second portion which is the portion on the base material side of the cross-section relative to the first portion. A structural member characterized by this.

2. The average value of the cross-sectional area per void in the first portion is smaller than the average value of the cross-sectional area per void in the second portion. The structural member according to Claim 1, characterized by this.

3. The number of voids per unit area in the first portion is smaller than the number of voids per unit area in the second portion. The structural member according to Claim 1, characterized by this.

4. In the cross-section, the porosity gradually decreases as the distance from the base material increases. The structural member according to Claim 1, characterized by this.

5. The chemical composition of the protective film in the first portion is the same as the chemical composition of the protective film in the second portion. The structural member according to Claim 1, characterized by this.

6. The crystallite size of the protective film in the first portion, and the crystallite size of the protective film in the second portion are both 50 nm or less. The structural member according to Claim 1, characterized by this.

7. The protective film is a film formed by an aerosol deposition method. The structural member according to Claim 1, characterized by this. ​ ​ ​

Images