Structural members

Abstract

To provide a structural member with sufficient durability against plasma. [Solution] The structural member 10 comprises a base material 100 and a protective film 200 covering the surface 110 of the base material 100. The protective film 200 mainly contains ytterbium oxide. When the protective film 200 is analyzed using X-ray diffraction and the diffraction pattern obtained is determined, the maximum intensity of the peak attributed to the (401) plane of the monoclinic crystal is denoted as PM, and the maximum intensity of the peak attributed to the (222) plane of the cubic crystal is denoted as PC, then in the structural member 10, PM / PC > 0.38 holds true.

Description

Technical Field

[0001] The present invention relates to structural members.

Background Art

[0002] Members constituting semiconductor manufacturing equipment, such as members of the inner wall of a chamber, etc., are required to have durability against plasma. For this reason, as such members, it has generally become common to use structural members in which a protective film is formed on the surface of a base material, as described in Patent Document 1 below, for example. As the protective film, materials such as yttria are often used.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present inventors have been studying the use of ytterbium oxide as a material for the protective film and further enhancing the durability of the protective film against plasma.

[0005] The present invention has been made in view of such problems, and an object thereof is to provide a structural member having sufficient durability against plasma.

Means for Solving the Problems

[0006] To solve the above problems, the structural member according to the present invention comprises a base material and a protective film covering the surface of the base material. The protective film mainly contains ytterbium oxide. When the protective film is analyzed using X-ray diffraction and the diffraction pattern obtained is determined, the maximum intensity of the peak attributed to the (401) plane of the monoclinic crystal is denoted as PM, and the maximum intensity of the peak attributed to the (222) plane of the cubic crystal is denoted as PC, then in this structural member, PM / PC > 0.38 holds true.

[0007] Experiments conducted by the inventors confirmed that the durability of the protective film against plasma can be sufficiently increased by increasing the proportion of monoclinic crystals in the protective film to such an extent that PM / PC > 0.38 holds true. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a structural member that has sufficient durability against plasma. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing a cross-section of a structural member. [Figure 2] This figure shows the relationship between the monoclinic ratio of the protective film and the durability of the protective film against plasma. [Figure 3] This figure shows the relationship between the monoclinic ratio of the protective film and the durability of the protective film against plasma. [Figure 4] This is a diagram illustrating an analytical method using X-ray diffraction. [Figure 5] This is a diagram illustrating an analytical method using X-ray diffraction. [Figure 6] This table shows a list of film formation conditions and other factors used when forming a protective film. [Figure 7] This is a diagram illustrating the surface shape of the protective film. [Figure 8] This is a diagram illustrating the porosity of the protective film. [Modes for carrying out the invention]

[0010] This embodiment will now be described with reference to the attached drawings. To facilitate understanding of the explanation, the same reference numerals are used for identical components in each drawing whenever possible, and redundant explanations are omitted.

[0011] The structural member 10 according to this embodiment is configured as a component for semiconductor manufacturing equipment, such as a plasma etching apparatus. Specifically, the structural member 10 is a component used as the inner wall of a processing chamber in semiconductor manufacturing equipment. However, this application of the structural member 10 is merely an example. The structural member 10 may also be a component placed inside the processing chamber of semiconductor manufacturing equipment, such as a focus ring.

[0012] As shown in Figure 1, the structural member 10 comprises a base material 100 and a protective film 200. In a plasma etching apparatus, the surface 210 of the protective film 200 is exposed to the space inside the processing chamber. The protective film 200 is provided for the purpose of protecting the surface 110 of the base material 100 from plasma.

[0013] The base material 100 is a component that occupies approximately the entirety of the structural member 10. In this embodiment, the base material 100 is a ceramic sintered body containing high-purity aluminum oxide (Al2O3), but it may be a different type of ceramic, or a component other than ceramic (for example, a metal component). Also, in this embodiment, the surface 110 of the base material 100 is a flat surface, but it may be a curved surface or the like. Furthermore, a slope may be provided on a part of the surface 110.

[0014] As described above, the protective film 200 is a film formed to protect the base material 100 from plasma. The protective film 200 is formed to cover the entire surface 110 of the base material 100. The protective film 200 is formed of a material containing ytterbium oxide (Yb2O3) as a main component. The ratio of the number of ytterbium (Yb) atoms and the number of oxygen (O) atoms contained in the protective film 200 may be different from the above. The protective film 200 of the present embodiment is a film formed by using the aerosol deposition method, but may be a film formed by using other film formation methods.

[0015] In this specification, the "main component" refers to the compound most contained in the object (here, the protective film 200). Specifically, the "main component" refers to a compound that is confirmed to be relatively more contained in terms of volume ratio or mass ratio than any other compound contained in the object when quantitative analysis or semi-quantitative analysis using X-ray diffraction (XRD) is performed on the object.

[0016] In the protective film 200 of the present embodiment, the ratio occupied by the main component (ytterbium oxide) is greater than 50% in terms of volume ratio or mass ratio. The ratio may be greater than 70%, may be greater than 90%, or may be 100%.

[0017] The thickness of the protective film 200 is appropriately set according to the length of the period for which durability is required, etc. In the present embodiment, the thickness of the protective film 200 is 15 μm or less. The thickness of the protective film 200 may be 1 μm or more.

[0018] The inventors decided to use ytterbium oxide as the material for the protective film 200 as in the present embodiment, and have been further studying how to enhance the durability of the material against plasma. As a result, it was confirmed that when the protective film 200 is formed using a material containing ytterbium oxide as a main component, the durability of the protective film 200 against plasma changes according to the crystal structure of the protective film 200. Specifically, it was confirmed that the greater the proportion of the monoclinic crystal structure in the protective film 200, the higher the durability of the protective film 200 against plasma.

[0019] The inventors created a plurality of samples of the structural member 10 that are different from each other in the crystal structure of the protective film 200, and for each protective film 200, evaluated the durability against plasma and the like. In evaluating the durability of the protective film 200 against plasma, the surface 210 of each protective film 200 was exposed to a plasma atmosphere using an inductively coupled reactive ion etching (ICP-RIE) apparatus (not shown). As conditions for exposing the surface 210 to the plasma atmosphere, the following two conditions were used.

[0020] Under the first condition, a 4-inch silicon wafer was held by electrostatic chuck within the chamber of an inductively coupled reactive ion etching apparatus. A sample of the structural member 10 to be evaluated was placed on the silicon wafer. Subsequently, plasma was generated in the chamber to expose the surface 210 of the protective film 200 to a plasma atmosphere. SF6 was used as the process gas and supplied to the chamber at a flow rate of 100 sccm. The pressure inside the chamber was adjusted to 0.5 Pa. The exposure time was 30 minutes. The power output was set to 1500W for the ICP coil output and 750W for the bias output. The test in which the surface 210 of the protective film 200 is exposed to a plasma atmosphere under the first condition described above will also be referred to as the "first standard plasma test" below. In the first standard plasma test, as described above, the bias output was set to 750W, causing the plasma to be drawn towards the protective film 200 and subjected to etching of the protective film 200.

[0021] Under the second condition, a 4-inch silicon wafer was held by electrostatic chuck within the chamber of an inductively coupled reactive ion etching apparatus. A sample of the structural component 10 to be evaluated was placed on the silicon wafer. Subsequently, plasma was generated in the chamber to expose the surface 210 of the protective film 200 to a plasma atmosphere. SF6 was used as the process gas and supplied to the chamber at a flow rate of 100 sccm. The pressure inside the chamber was adjusted to 0.5 Pa. The exposure time was 60 minutes. The power output was set to 1500W for the ICP coil output and the bias output was turned OFF (i.e., 0W). The test in which the surface 210 of the protective film 200 is exposed to a plasma atmosphere under the second condition described above will also be referred to as the "second standard plasma test" below. In the second standard plasma test, as described above, the bias output was turned OFF, so the plasma was not drawn towards the protective film 200 and was hardly used for etching the protective film 200. The surface 210 of the protective film 200 is simply exposed to a non-directional plasma.

[0022] Figure 2 shows the results of the first standard plasma test performed on each of the multiple structural members 10. The horizontal axis of the graph in Figure 2, "monoclinic ratio," is an index that indicates the proportion of the protective film 200 that is monoclinic crystal structure. The larger the proportion of monoclinic crystal structure in the protective film 200, the larger the value of the monoclinic ratio. The specific definition and calculation method of the monoclinic ratio will be explained later.

[0023] The vertical axis of the graph in Figure 2 represents the etching rate in the first standard plasma test, i.e., the depth to which the protective film 200 is etched per unit time, expressed in units of "μm / h". The higher the durability of the protective film 200 against the plasma, the lower its etching rate. The etching rate can be used as one indicator of the durability of the protective film 200 against the plasma.

[0024] Figure 2 shows the etching rate values, along with the error range, for four samples of protective film 200 that differ in their monoclinic ratio, measured after the first standard plasma test.

[0025] As is clear from Figure 2, the larger the monoclinic ratio of the protective film 200, the smaller the etching rate of the protective film 200 generally becomes. For protective films 200 to the right of the dotted line shown in Figure 2, i.e., with a monoclinic ratio greater than 0.38, the etching rate is sufficiently small, confirming that they have sufficient durability against plasma. The monoclinic ratio of the protective film 200 may be 3 or less.

[0026] Figure 3 shows the results of the second standard plasma test performed on each of the multiple structural members 10. The horizontal axis of the graph in Figure 3 is the same monoclinic ratio as the horizontal axis in Figure 2. Each sample prepared for the second standard plasma test was prepared using the same method as each sample prepared for the first standard plasma test. Therefore, the monoclinic ratio values ​​for each sample shown in Figure 3 are the same as the monoclinic ratio values ​​for each sample shown in Figure 2.

[0027] The vertical axis of the graph in Figure 3 represents the fluorination amount of protective film 200 after the second standard plasma test. "Fluorination amount" is an indicator of how much fluorine atoms, which are part of the plasma, have penetrated into the protective film 200. The specific method for calculating the fluorination amount is as follows.

[0028] First, the surface 210 of the protective film 200, which had undergone the second standard plasma test, was sputtered with argon, and the amount of fluorine atoms present on the surface 210 was continuously measured using X-ray photoelectron spectroscopy (XPS). The measurement was performed over 145 seconds. At each time point, the percentage (in units: %) of the argon measurement was calculated, and the cumulative value of the obtained values ​​was calculated as the "fluorination amount" of the sample. The higher the durability of the protective film 200 against plasma, the smaller the fluorination amount calculated as described above. The fluorination amount, like the etching rate mentioned earlier, can be used as one of the indicators of the durability of the protective film 200 against plasma.

[0029] As is clear from Figure 3, the amount of fluoride in the protective film 200 generally decreases as the monoclinic ratio of the protective film 200 increases. For protective films 200 to the right of the dotted line shown in Figure 3, i.e., with a monoclinic ratio greater than 0.38, the amount of fluoride is sufficiently small, and it was confirmed that they have sufficient durability against plasma. The monoclinic ratio of the protective film 200 may be 3 or less.

[0030] The method for calculating the monoclinic ratio is explained below. The monoclinic ratio is calculated based on the results of analyzing the crystal structure of protective film 200 using X-ray diffraction.

[0031] The monoclinic ratio of the protective film 200 was measured using the following method. First, X-ray diffraction (XRD) was performed on the protective film 200 formed on the substrate 100 using an out-of-plane θ-2θ scan.

[0032] Line L10 in Figure 4 is an example of a diffraction pattern obtained by analyzing the protective film 200 using X-ray diffraction. This diffraction pattern will also be referred to as the "measured diffraction pattern L10" below. Multiple peaks appear in the measured diffraction pattern L10, and each peak is unique to the material of the protective film 200 and its crystal structure. For example, the diffraction angle 2θ corresponding to the maximum value of each peak corresponds to the crystal structure of the protective film 200. Furthermore, the height of each peak corresponds to the proportion of the crystal structure corresponding to the diffraction angle 2θ that occupies in the protective film 200.

[0033] The maximum intensity value for each peak can be directly used as the maximum intensity value represented on the vertical axis in Figure 4. However, in order to determine with higher accuracy the proportion of monoclinic crystal structure in the protective film 200, in this embodiment, the maximum intensity value of each peak is obtained using the following method.

[0034] The dashed-dotted line L0 shown in Figure 4 represents the background intensity when no peaks appear. The waveform of the dashed-dotted line L0 can be estimated and obtained, for example, from the overall waveform of the diffraction pattern.

[0035] Line L11 in Figure 5 represents a hypothetical diffraction pattern when only the peaks that are maximum at a diffraction angle of 2θ of 20.55 degrees are added to the background shown by the dashed line L0 in Figure 4. The same applies to lines L12 to L18 in Figure 5, each representing a hypothetical diffraction pattern when only the peaks that are maximum at a specific diffraction angle of 2θ are added to the background.

[0036] The diffraction angle 2θ corresponding to the peak of line L12 is 25.52 degrees, the diffraction angle 2θ corresponding to the peak of line L13 is 28.33 degrees, the diffraction angle 2θ corresponding to the peak of line L14 is 29.38 degrees, the diffraction angle 2θ corresponding to the peak of line L15 is 30.24 degrees, the diffraction angle 2θ corresponding to the peak of line L16 is 32.34 degrees, the diffraction angle 2θ corresponding to the peak of line L17 is 33.45 degrees, and the diffraction angle 2θ corresponding to the peak of line L18 is 35.09 degrees.

[0037] The dashed line L30 shown in Figure 5 is the diffraction pattern obtained by superimposing all the provisional diffraction patterns shown by lines L11 to L18. This diffraction pattern will also be referred to as the "approximate diffraction pattern L30" below. When superimposing multiple provisional diffraction patterns, the overlapping background is not added.

[0038] Each of the provisional diffraction patterns shown by lines L11 to L18 is individually adjusted so that the waveform of the approximate diffraction pattern L30 obtained by summing them up roughly matches the measured diffraction pattern L10 shown in Figure 4. In other words, for each of lines L11, etc., the value of the diffraction angle 2θ at which the peak is maximized, the height of the peak relative to the background, etc. are individually adjusted to bring the waveform of the approximate diffraction pattern L30 closer to the measured diffraction pattern L10. When the waveforms of the two roughly match as a result of this work, each of the provisional diffraction patterns shown by lines L11 to L18 corresponds to the waveform obtained by decomposing the measured diffraction pattern L10 into waveforms for each diffraction angle of 2θ. This processing may be performed manually while observing the waveform of the approximate diffraction pattern L30, etc., but it may also be performed automatically using the functions of software.

[0039] It is known that when the protective film 200 is made of ytterbium oxide, the diffraction angle 2θ of the peak attributed to the (401) plane of the monoclinic crystal is approximately 30.2 degrees. Therefore, in the example shown in Figure 5, it can be inferred that the peak attributed to the (401) plane of the monoclinic crystal is the peak of line L15. The maximum intensity of this peak, specifically the maximum intensity of this peak relative to the background, will also be referred to as "maximum intensity PM" below.

[0040] When the material of the protective film 200 is ytterbium oxide, it is known that the diffraction angle 2θ of the peak attributed to the (222) plane of the cubic crystal is approximately 29.4 degrees. Therefore, in the example shown in Figure 5, it can be inferred that the peak attributed to the (222) plane of the cubic crystal is the peak of line L14. The maximum intensity of this peak, specifically the maximum intensity of this peak relative to the background, will also be referred to as "maximum intensity PC" below.

[0041] Using the maximum intensity PM and PC values ​​calculated by the method described above, the monoclinic ratio is defined and calculated as shown in equation (1) below. Monoclinic ratio = PM / PC····(1)

[0042] As mentioned earlier, the maximum intensity PM is the maximum intensity of the peak attributed to the (401) plane of the monoclinic crystal. Similarly, the maximum intensity PC is the maximum intensity of the peak attributed to the (222) plane of the cubic crystal. Therefore, the monoclinic ratio defined in equation (1) above can be used as an indicator of the proportion of the protective film 200 occupied by the monoclinic crystal structure. As described with reference to Figures 2 and 3, if the monoclinic ratio = PM / PC > 0.38 holds true for the protective film 200, then sufficient durability against plasma is ensured for the protective film 200. More preferably, it has been confirmed that if the protective film 200 is formed such that PM / PC > 0.50 holds true, the etching rate of the protective film 200 becomes even smaller.

[0043] Note that the waveform examples shown in Figures 4 and 5 are examples used to explain the definition and calculation method of the monoclinic ratio, and do not correspond to the protective film 200 according to this embodiment.

[0044] The manufacturing methods for each sample used to obtain the data in Figures 2 and 3 will be explained with reference to Figure 6. In the same figure, the sample shown as "No. 1" is a sample prepared under conditions where the monoclinic ratio of the protective film 200 is 0.00. "No. 2" is a sample prepared under conditions where the monoclinic ratio of the protective film 200 is 0.51, "No. 3" is a sample prepared under conditions where the monoclinic ratio of the protective film 200 is 1.05, and "No. 4" is a sample prepared under conditions where the monoclinic ratio of the protective film 200 is 1.34.

[0045] The protective films 200 for samples No. 1 to 4 were all deposited using the aerosol deposition method. As is well known, in the aerosol deposition method, fine particles, which are the material for the protective film 200, are dispersed in a gas to form an "aerosol," which is then sprayed from a nozzle onto the surface 110 and collided with it. On the surface 110, the impact of the collision causes deformation and fragmentation of the fine particles, and as the fine particles bond together, they gradually accumulate to form the protective film 200. Figure 6 shows the type of "gas" used during the deposition of each sample, and the flow rate at which the gas was sprayed from the nozzle.

[0046] The "fine particles" used in the above study were Yb2O3 powder. The average particle size of this powder was 3.0 μm, and the median diameter was 2.4 μm.

[0047] As shown in Figure 6, each of the samples from No. 1 to 4 differs from the others in terms of the deposition conditions (specifically, the gas flow rate) for the protective film 200, and as a result, the monoclinic ratio of the protective film 200 also differs from one another.

[0048] Samples No. 1 through 4 were each prepared in pairs. One sample underwent the first standard plasma test, yielding the results shown in Figure 2. The other sample underwent the second standard plasma test, yielding the results shown in Figure 3.

[0049] The inventors measured the arithmetic mean height (Sa) of surface 210 for each sample No. 1 to 4 before and after performing the first standard plasma test. In the table in Figure 6, the "Before Etching" column shows the arithmetic mean height of surface 210 measured before the first standard plasma test, in units of μm. The "After Etching" column shows the arithmetic mean height of surface 210 measured after the first standard plasma test, in units of μm. The "ΔSa" column shows the difference between the two arithmetic mean heights. That is, it shows the change in the arithmetic mean height of surface 210 due to the first standard plasma test, in units of μm. The method for measuring the arithmetic mean height was the method specified in ISO 25178.

[0050] In sample No. 1, i.e., the sample in which the monoclinic ratio of protective film 200 is 0.38 or less, the arithmetic mean height of the surface 210 of protective film 200 after the first standard plasma test is greater than 0.1 μm. On the other hand, in samples No. 2 to 4, i.e., the samples in which the monoclinic ratio of protective film 200 is greater than 0.38, the arithmetic mean height of the surface 210 of protective film 200 after the first standard plasma test is all less than 0.1 μm. The monoclinic ratio of protective film 200 may be 3 or less. The arithmetic mean height of the surface 210 of protective film 200 after the first standard plasma test may be 0.005 μm or more.

[0051] The inventors observed the surface 210 of each sample No. 1 to 4 using a scanning electron microscope (SEM) before and after performing the first standard plasma test. Figure 7 shows the images obtained from this observation. Each image is a so-called "secondary electron image" and was taken under an accelerating voltage of 3 kV. The magnification of the image was 5000x. The "Before Etching" column in Figure 7 shows the image obtained from observation before the first standard plasma test. The "After Etching" column shows the image obtained from observation after the first standard plasma test.

[0052] The inventors also measured the porosity of the protective film 200. Here, "porosity" refers to the percentage of the cross-section of the protective film 200 when it is cut along a plane perpendicular to the surface 210, where the cross-section is occupied by voids.

[0053] The method for measuring the porosity is as follows. First, the above cross-section was observed using a scanning electron microscope (SEM) and a secondary electron image was obtained. The acceleration voltage was set to 3kV and the magnification was set to 30,000x. Figure 8(A) shows an example of an image obtained using the above procedure. The sample used for measurement is sample No. 2 in the table in Figure 6.

[0054] Next, the porosity of the protective film 200 was calculated by analyzing the images obtained as described above. The image analysis was performed using the OpenCV module for the Python language. First, the captured images were cropped to include only the cross-section of the protective film 200. Specifically, the part of the image in Figure 8(A) outside the dotted line DL was cropped and excluded.

[0055] Figure 8(B) shows the image after the above cropping process has been performed. The entire image is a cross-section of the protective film 200. The multiple black dots visible in the image of Figure 8(B) (one of which is indicated by arrow AR) are cross-sections of voids contained in the protective film 200.

[0056] After cropping, the image in Figure 8(B) was binarized so that the cross-sections of the voids were black and the other cross-sections were white. The binarization was performed using the "Variable Threshold Binarization Method" described in the Journal of the Institute of Image Electronics Engineers of Japan, Vol. 36 (2007), No. 3 (pp. 204-209). Subsequently, noisy areas were removed by dilation processing, etc., to obtain the binary image shown in Figure 8(C). In this figure, the black dots labeled "250" correspond to the cross-sections of the voids contained in the protective film 200.

[0057] The ratio of black pixels to the total number of pixels in the image in Figure 8(C) was calculated as the porosity of the protective film 200. In the example shown in Figure 8(C), the total number of pixels in the image was 1,100,800, and the number of black pixels was 35,180. Therefore, the porosity was calculated to be approximately 3.19%. The inventors have confirmed that the durability of the protective film 200 against plasma is further increased if the monoclinic ratio of the protective film 200 is greater than 0.38 and the porosity of the protective film 200 is 3.2% or less. The monoclinic ratio of the protective film 200 may be 3 or less. The porosity of the protective film 200 may be 0.01% or more.

[0058] Furthermore, the inventors have confirmed that forming the protective film 200 such that the average crystallite size is 50 nm or less further increases the durability of the protective film 200 against plasma. "Average crystallite size" refers to a value obtained, for example, by performing a circular approximation on each of the multiple (at least 15) crystallites appearing on the surface 210 of the protective film 200 and taking the average value of the diameter of each circle. To calculate the average crystallite size of the protective film 200, the surface 210 of the protective film 200 is photographed using a transmission electron microscope (TEM), and the average crystallite size is calculated based on the obtained image. In this case, it is preferable to use a magnification of 400,000 times or more. The average crystallite size of the protective film 200 may be 5 nm or more.

[0059] The durability of the protective film 200 can be further improved by setting the average crystallite size of the protective film 200 to more preferably 30 nm or less, and even more preferably 15 nm or less.

[0060] The embodiments have been described above with reference to specific examples. However, this disclosure is not limited to these specific examples. Modifications made to these specific examples by those skilled in the art are also included within the scope of this disclosure, as long as they retain the features of this disclosure. The elements, their arrangement, conditions, shapes, etc., of each of the aforementioned specific examples are not limited to those illustrated and can be modified as appropriate. The elements of each of the aforementioned specific examples can be combined in different ways as appropriate, as long as no technical inconsistencies arise. [Explanation of Symbols]

[0061] 10: Structural members 100: Base material 110: Surface 200: Protective film

Claims

1. Substrate and The substrate comprises a protective film covering the surface of the substrate, The protective film contains ytterbium oxide as its main component, In the diffraction pattern obtained by analyzing the protective film using X-ray diffraction, Let PM be the maximum intensity of the peak attributed to the (401) plane of the monoclinic crystal. When the maximum intensity of the peak attributed to the (222) plane of the cubic crystal is denoted as PC, A structural member characterized by the condition PM / PC > 0.

38.

2. The structural member according to claim 1, characterized in that the protective film is a film formed using the aerosol deposition method.

3. The structural member according to claim 1, characterized in that PM / PC > 0.50 holds true.

Images