JP7515583B2 - Breathable plug, substrate support assembly and shower plate - Google Patents

Description

The present disclosure relates to a breathable plug and a substrate support assembly comprising the breathable plug.

Conventionally, in semiconductor manufacturing equipment such as plasma etching equipment and plasma CVD (Chemical Vapor Deposition) equipment, as shown in Patent Document 1, a high-frequency voltage is applied between a substrate such as a semiconductor wafer placed on a substrate support assembly and a shower plate (gas distribution plate) for introducing a plasma generating gas and supplying it toward the substrate to create a plasma state, and a film is formed on the surface of the substrate or a thin film formed on the surface of the substrate is etched. This substrate support assembly has a flow path in its thickness direction, and a cooling gas is supplied to this flow path to suppress a temperature rise of the workpiece W.

When processing substrates in the processing chamber of a semiconductor manufacturing device, an arc discharge may occur from the top to the bottom of the substrate support assembly, and the flow path may become a discharge path. Therefore, in order to prevent the flow path from becoming a discharge path, Patent Document 2 proposes an electrostatic chuck (substrate support assembly) in which a ceramic plug made of a porous honeycomb is attached to the flow path.

JP 2018-162205 A JP 2019-165193 A

The breathable plug of the present disclosure comprises a honeycomb structure made of dense ceramics having multiple through holes in the axial direction.

The substrate support assembly of the present disclosure comprises a substrate made of a plate-shaped ceramic having an adsorption surface to which a workpiece is adsorbed and an opposing surface located opposite the adsorption surface, an electrostatic adsorption member having an internal electrode located within the substrate and a flow path located along the thickness direction of the substrate, and the above-mentioned breathable plug attached inside the flow path.

The shower plate of the present disclosure comprises a second substrate made of plate-shaped ceramic having a plurality of second flow paths in the thickness direction through which plasma generating gas passes, and the above-mentioned breathable plug attached inside the second flow paths.

1A is a cross-sectional view showing a part of a plasma processing apparatus equipped with a breathable plug according to the present disclosure, and FIG. 1B is an enlarged cross-sectional view of part A. FIG. 2 is an enlarged cross-sectional view of a substrate support assembly disposed inside the plasma processing apparatus shown in FIG. 1. FIG. 2 is a cross-sectional view showing an example of a cross section perpendicular to the axial direction of the breathable plug of the present disclosure. FIG. 11 is a cross-sectional view showing another example of a cross section perpendicular to the axial direction of the breathable plug of the present disclosure. FIG. 11 is a cross-sectional view showing yet another example of a cross section perpendicular to the axial direction of the breathable plug of the present disclosure. 1A is a partially cutaway perspective view showing a through-hole formed in a breathable plug of the present disclosure, and FIG. 1B is an enlarged explanatory view of region X shown in FIG.

An example of a breathable plug according to the present disclosure will be described in detail below with reference to the drawings. However, in all the drawings in this specification, the same parts will be given the same reference numerals, and their explanations will be omitted as appropriate, unless confusion arises.

1 is a cross-sectional view showing a portion of a plasma processing apparatus including a breathable plug according to the present disclosure. FIG. 2 is an enlarged cross-sectional view of a substrate support assembly disposed inside the plasma processing apparatus shown in FIG.

The plasma processing apparatus 20 shown in Figure 1 is, for example, a plasma etching apparatus, and has a chamber 1 inside which a workpiece W such as a semiconductor wafer is placed, with a shower plate 2 arranged on the upper side of the chamber 1 and a substrate support assembly 3 arranged on the lower side opposite each other.

The shower plate 2 is a second substrate made of plate-shaped ceramics and includes a diffusion section 2a, which is an internal space for diffusing plasma generation gas G, and a gas supply section 2b having a plurality of second flow paths 2c for supplying plasma generation gas G into the chamber 1.

Then, the plasma generating gas G discharged in a shower-like manner from the gas supply section 2b through the second flow path 2c becomes plasma by supplying high frequency power (RF) from the high frequency power source 15 to the substrate support assembly 3, thereby forming a plasma space P.

Here, examples of the plasma generating gas G include fluorine-based gases such as _SF6 , _CF4 , _CHF3 , _ClF3 , _NF3 , _C4F8 , and HF, _and chlorine-based gases such as _Cl2 , HCl, _BCl3 , and _CCl4 .

The substrate support assembly 3 is an electrostatic chuck comprising an attachment portion 4, an insulating portion 5, a support portion 6, a thermally conductive portion 7 and an electrostatic attraction portion 8, and the electrostatic attraction portion 8 is joined to the thermally conductive portion 7 via a bonding layer 9 made of a silicone adhesive, for example, as shown in Figure 2.

The electrostatic adsorption unit 8 has a substrate 8b made of a plate-shaped ceramic that adsorbs a workpiece W such as a silicon wafer to an adsorption surface 8a by electrostatic adsorption, a clamp electrode (internal electrode) 8c located within the substrate 8b, and a flow path 8d located along the thickness direction of the substrate 8b. The clamp electrode (internal electrode) 8c is electrically connected to a high-frequency power source via a matching circuit for maintaining the plasma generated from the plasma generation gas G in the chamber 1.

The coating film formed on the surface of the workpiece W is then etched by the ions and radicals contained in the plasma.

The O-ring 11 is attached around the bonding layer 9 to protect the bonding layer 9. The insulating part 5 is made of, for example, plastic, and is electrically insulated from the mounting part 4. The flow path 8d passes through the substrate support assembly 3 in the vertical direction to supply helium gas for cooling into the chamber 1. The breathable plugs 13 and 14 are attached to the flow path 8d. That is, the breathable plug 13 is installed in the flow path 8d in the electrostatic adsorption part 8, and the breathable plug 14 is installed in the flow path 8d in the insulating part 5.

Figure 3 is a cross-sectional view showing an example of a cross section perpendicular to the axial direction of the breathable plug of the present disclosure. Figures 4 and 5 are cross-sectional views showing other examples of cross sections perpendicular to the axial direction of the breathable plug of the present disclosure.

As shown in Figures 3 to 5, the breathable plug 13 is a straight cylindrical body made of a honeycomb structure 16 made of dense ceramics with multiple through holes 16a, 16b in the axial direction. The breathable plug 14 is a cylindrical body having a shaft made of the honeycomb structure 16 and a flange portion (not shown) at one end of the shaft portion that is larger in diameter than the shaft portion. The flange portion is also made of dense ceramics.

The breathable plugs 13 and 14 in this disclosure are disposed in a flow path for flowing a fluid such as gas, and block the flow path. The fluid can be allowed to flow through a through hole provided in a part of the breathable plug. The flow path in which the breathable plug is disposed is a narrow flow path having an inner diameter of, for example, 1 mm to 10 mm, and the maximum inner dimension of the through hole provided in the breathable plug is narrow, for example, about 5 μm to 20 μm.

The honeycomb structure in this disclosure refers to a structure in which multiple (e.g., 10 or more) through holes 16a, 16b are arranged along the axial direction. The arrangement of the multiple through holes is not particularly limited, and for example, when they are arranged in a honeycomb shape, the through holes can be arranged densely while maintaining high strength of the breathable plug. The cross section perpendicular to the axial direction of the through holes is not particularly limited, and is, for example, circular, triangular, rectangular, or hexagonal. The through hole 16a in Figures 3 and 4 is an example in which the cross section perpendicular to the axial direction of the honeycomb structure 16 is circular, and the through hole 16b in Figure 5 is an example in which the cross section perpendicular to the axial direction of the honeycomb structure 16 is hexagonal. For example, the diameter of the through hole 16a is 5 μm to 20 μm, and the diagonal length of the through hole 16b is 5 μm to 20 μm.

The breathable plugs 13, 14 can suppress the generation of secondary plasma in the flow path 8d. If the breathable plugs 13, 14 are made of a dense ceramic honeycomb structure 16, shedding is unlikely to occur, and even if particles floating in the chamber 1 enter the through holes 16a, 16b, the particles are unlikely to adhere to the inner surface 16f, and the mechanical strength is also high.

Dense ceramics are mainly composed of aluminum oxide ( _Al2O3 ), yttrium aluminum composite oxide (YAG, YAM, or YAP ₎ , aluminum nitride (AlN), silicon oxide ( _SiO2 ), silicon carbide ( _SiC ), silicon nitride ( _Si3N4 ), yttrium oxide ( _Y2O3 ), or yttrium zirconate. Yttrium zirconate has a composition formula of, for example, _YZrOx (3≦x≦ _3.5 ), YZr2O7 _{, Y2ZrO5 , Y2Zr2O3 , Zr0.92Y0.08O1.96 ,} or _{the like} .

Dense ceramics refers to ceramics with a relative density of 96% or more, and preferably 97% or more and 99.8% or less. This relative density is the percentage of the apparent density of the honeycomb structure 16 relative to the theoretical density of the ceramics.

In addition, the theoretical density of the ceramics is determined by crushing a portion of each of the breathable plugs 13 and 14, dissolving the resulting powder in a solution such as hydrochloric acid, and then determining the content of metal components using an ICP (Inductively Coupled Plasma) optical emission spectrometer (for example, Shimadzu Corporation's ICPS-8100).

Each component constituting the honeycomb structure 16 is identified by an X-ray diffraction apparatus using CuKα radiation. If the identified component is Al ₂ O ₃ , it is converted to Al ₂ O ₃ using the content of Al determined by an ICP (Inductively Coupled Plasma) emission spectroscopic analyzer. If the identified components are MgO and Na ₂ O, they may be converted to MgO and Na ₂ O, respectively, by the same method. The apparent density of the honeycomb structure 16 may be determined in accordance with JIS R 1634-1998.

When the main component constituting the ceramic is aluminum oxide and the other component is magnesium oxide, assuming that the contents are a% by mass and b% by mass, respectively, the theoretical density (T.D.) of the ceramic can be calculated by the following formula (1) using the theoretical density values of aluminum oxide and magnesium oxide (aluminum oxide = 3.99 g/ ^cm3 , magnesium oxide = 3.58 g/ ^cm3 ).
T. D = 1 / (0.01 × (a / 3.99 + b / 3.58)) ... (1)
For example, when the content of the components constituting the ceramic is 99 mass % aluminum oxide and 1 mass % magnesium oxide, the theoretical density (T.D.) of the ceramic is 3.96 g/ ^cm3 according to the calculation using formula (1), and the relative density can be obtained by dividing the apparent density of the ceramic obtained in accordance with JIS R 1634-1998 by this theoretical density (T.D.) of 3.96 g/ ^cm3 .

The honeycomb structure 16 shown in Figures 4 and 5 has an outer peripheral region 16c including an outer peripheral surface 16e along the axial direction, and an inner peripheral region 16d excluding the outer peripheral region 16c.

The outer peripheral region 16c including the outer peripheral surface 16e of the honeycomb structure 16 may have a smaller open porosity than the inner peripheral region 16d excluding the outer peripheral region 16c. With this configuration, the length of the contour forming the open pores increases, and the length of the outer peripheral surface 16e from one end face to the other end face is substantially longer than that of the inner peripheral surface 16f, thereby enhancing the effect of suppressing arc discharge.

Conversely, the outer peripheral region 16c including the outer peripheral surface 16e of the honeycomb structure 16 may have a larger open porosity than the inner peripheral region 16d excluding the outer peripheral region 16c. With this configuration, when the breathable plugs 13, 14 are fixed in the flow passage 8d of the substrate support assembly 3 with an adhesive, a high anchor effect is obtained, improving reliability over a long period of time.

In the case of a breathable plug 14, the outer peripheral region 16c refers to the region extending radially from the outer peripheral surface 16e to, for example, within 4.5% of the diameter of the honeycomb structure 16 in a cross section perpendicular to the axial direction.

The open porosity of each of the outer peripheral region 16c and the inner peripheral region 16d may be determined in accordance with JIS R 1634-1998. In either case, the difference in open porosity should be 0.8% or more.

In this disclosure, the term "main component" refers to the component that is present in the greatest amount out of a total of 100% by mass of the components that make up the dense ceramic.

The root-mean-square slope (RΔq) of the roughness curve of the inner surface 16f forming the through holes 16a, 16b may be smaller than the root-mean-square slope (RΔq) of the roughness curve of the outer surface 16e of the honeycomb structure 16.

The root mean square slope (RΔq) of a roughness curve is the root mean square of the local slope dZ/dx at the reference length l of the roughness curve, measured in accordance with JIS B 0601:2001, and is defined by the following formula:

If the root mean square slope (RΔq) value is large, the surface irregularities will be steep, and if the root mean square slope (RΔq) value is small, the surface irregularities will be gentle.

If the root mean square slope (RΔq) of the roughness curve of the inner circumferential surface 16f is smaller than the root mean square slope (RΔq) of the roughness curve of the outer circumferential surface 16e, particles floating in the chamber 1 will be more difficult to adsorb to the inner circumferential surface 16f. On the other hand, since the unevenness of the outer circumferential surface 16e becomes steep, when the honeycomb structure 16 is fixed to the electrostatic adsorption section 8, the insulating section 5, etc. with an adhesive, the adhesive penetrates deep from the outer circumferential surface 16e toward the inside along the slope of the uneven shape, so that the honeycomb structure 16 can obtain a high adhesive strength and maintain high reliability over a long period of time.

The root-mean-square slope (RΔq) of the roughness curve of the outer peripheral surface 16e of the honeycomb structure 16 may be smaller than the root-mean-square slope (RΔq) of the roughness curve of the inner peripheral surface 16f forming the through holes 16a, 16b.

With this configuration, the inner peripheral surface 16f from one end face to the other end face has an increased local inclination or a steep inclination, and its length is substantially longer than the outer peripheral surface 16e, so that the effect of suppressing arc discharge is further enhanced. When the honeycomb structure 16 is attached to the electrostatic adsorption section 8, the insulating section 5, etc., even if the honeycomb structure 16 comes into contact with the inner peripheral surfaces of these members in a manner that damages them, fewer particles are detached from the honeycomb structure 16, and fewer particles are floating in the space within the chamber 1. In addition, stress concentration on the outer peripheral surface 16e is also mitigated.

The root mean square slope (RΔq) can be measured in accordance with JIS B 0601:2001 using a shape analysis laser microscope (Keyence Corporation, VK-X1100 or its successor). The measurement conditions are as follows: first, the illumination method is a coaxial epi-illumination method, the magnification is 240x, there is no cutoff value λs, the cutoff value λc is 0.08 mm, there is no cutoff value λf, there is correction for end effect, and the measurement range per point from the outer peripheral surface 16e and the inner peripheral surface 16f to be measured is set to, for example, 1420 μm x 1070 μm, and for each measurement range, a line to be measured is drawn along the longitudinal direction of the measurement range, and line roughness measurement is performed. The length to be measured is, for example, 1320 μm.

Figure 6(A) is a partially cutaway perspective view showing a through hole formed in a breathable plug of the present disclosure, and Figure 6(B) is an enlarged explanatory view of region X shown in Figure 6(A). Figures 6(A) and (B) show the state in which the honeycomb structure has been polished from the outer peripheral surface toward the axis C of the through hole in a direction parallel to the axis C.

The number of recesses 19 having a depth d of 10 μm to 20 μm, starting from the ridge 18 between the inner circumferential surface 16f and the observation surface 17 obtained by polishing from the outer circumferential surface 16e toward the axis of the through holes 16a and 16b, may be 2 or less, preferably 1 or less, per 1 mm of the length of the ridge 18. The recesses 19 are, for example, sunken. Polishing from the outer circumferential surface 16e of the honeycomb structure 16 toward the axis C is to make it easier to measure the depth d of the recesses 19. The direction of the depth d is the direction from the ridge 18 toward the outer circumferential surface 16e within the observation surface 17.

Here, the arithmetic mean roughness (Ra) of the observation surface 17 is, for example, 0.01 μm or more and 0.1 μm or less, and the arithmetic mean roughness (Ra) may be determined in accordance with JIS B 0601:2013. In addition, to obtain the observation surface 17, the abrasive may be WA (white alundum) with an average particle size (D50) of 1 μm, and the polishing disc may be a polisher made of pitch.

In addition, in the case of a honeycomb structure 16 having an outer diameter of 3 mm or more, the honeycomb structure 16 may be ground from the outer surface 16e toward the axis C, leaving a grinding allowance of 0.1 mm to 0.2 mm, and then polished.

Then, for an image (e.g., 2.3 mm horizontally and 1.7 mm vertically) of the observation surface 17 taken with a scanning electron microscope, the depth d of the recesses is measured using, for example, free software called "Pinch Ruler," and the number of recesses 19 with a depth d of 10 μm or more and 20 μm or less is counted.

Here, the depth of the recess 19 is set to 10 μm or more because a depth of 10 μm is the minimum value, i.e., the threshold value, at which shed and floating particles have a significant adverse effect on the plasma space P.

In this way, since there are almost no recesses 19 on the inner peripheral surface 16f, the occurrence of chipping originating from the inner peripheral surface 16f is suppressed. Therefore, even if a fluid such as gas passes through the through holes 16a and 16b, it is possible to reduce the occurrence of detached particles becoming new particles and floating in the plasma space P.

Here, the recess 19 is, in other words, a depression that opens onto the inner circumferential surface 16f.

The straightness of the ridgeline 18 on the observation surface 17 may be, for example, 20 μm or less. Straightness refers to the degree of deviation of the ridgeline 18 from a geometrically correct straight line. The straightness of the ridgeline 18 can be measured, for example, using free software called "Pinch Ruler" on an image (for example, 1.2 mm horizontally and 1.4 mm vertically) of the observation surface 17 taken with an optical microscope. The axial direction of the through holes 16a and 16b is aligned with the vertical direction of the image, and at least one of the left and right ridgelines 18 sandwiching the inner circumferential surface 16f is included in the image, and the length of the geometrically correct straight line is set to 1.4 mm.

If the straightness of the ridge line 18 is 20 μm or less, large depressions 19 are almost absent from the inner surface 16f, reducing the risk of new particles floating in the plasma space P even if the gas flow is turbulent.

The dense ceramics may be mainly composed of aluminum oxide and contain sodium, the sodium content of which may be 20 ppm by mass or less. Since sodium is an element that increases dielectric loss, if the sodium content is 20 ppm by mass or less, the dielectric loss can be reduced and high electromagnetic wave transparency can be obtained.

The through holes 16a, 16b may be bent as they penetrate from one end face to the other end face. Since the effective flow path in the axial direction of the through holes 16a, 16b is longer than when the through holes 16a, 16b are highly straight, it is easier to suppress the occurrence of arc discharge.

The cylindricity of the through holes 16a and 16b may be, for example, 0.05 mm or more and 0.2 mm or less. If the cylindricity of the through holes 16a and 16b is 0.05 mm or more, the distance through which the current flows can be increased, making it difficult for electrons to be accelerated and making it even more difficult for arc discharge to occur. If the cylindricity of the through holes 16a and 16b is 0.2 mm or less, the increase in the ventilation resistance of the cooling gas can be suppressed, the cooling efficiency can be maintained, and distortion is unlikely to occur even when exposed to repeated temperature increases and decreases, so that it can be used for a long period of time.

The dense ceramics may be primarily composed of aluminum oxide and contain magnesium aluminate, and the value obtained by subtracting the average value of the circle equivalent diameter of the magnesium aluminate crystal particles from the average value of the distance between the centers of gravity of adjacent magnesium aluminate crystal particles may be greater in the outer peripheral region 16c than in the inner peripheral region 16d.

With this configuration, magnesium aluminate has a greater linear expansion coefficient than aluminum oxide, and therefore in the outer peripheral region 16c, the crystal particles of magnesium aluminate move to rise higher on the outer peripheral surface than the crystal particles of aluminum oxide during the temperature drop process in sintering. Therefore, even if the honeycomb structure 16 is placed on a powder bed after sintering and heat-treated to reduce warping or remove distortion, adhesion of the powder bed to the outer peripheral surface, which is the surface on which the honeycomb structure 16 is placed, can be suppressed.

On the other hand, in the inner peripheral region 16d, the spacing between the magnesium aluminate crystal particles is small, i.e., the dispersion is advanced, and even when a tensile load is applied at high temperatures, crack-like cavities are less likely to occur, thereby improving high-temperature ductility.

The spacing between crystal particles of magnesium aluminate can be determined by the following method: The cut surfaces of the inner peripheral region 16d and the outer peripheral region 16c of the dense ceramic are each observed at a magnification of 100 times, and an average range is selected, for example, an area of 1.044 ^mm2 (horizontal length 1.18 mm, vertical length 0.885 mm) is photographed with a scanning electron microscope to obtain a backscattered electron image.

Using this backscattered electron image as the subject, the image analysis software "A-zo-kun (ver. 2.52)" (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.; hereafter, when the image analysis software "A-zo-kun" is mentioned, it refers to the image analysis software manufactured by Asahi Kasei Engineering Co., Ltd.) can be used to determine the distance between the centers of gravity of the magnesium aluminate crystal particles using the distance between the centers of gravity method of dispersion measurement.

The setting conditions for this method may be, for example, a threshold value, which is an index showing the brightness of an image, of 180, a brightness value of bright, a small figure removal area of 10 ^μm2 , and no noise removal filter. Note that in the above measurement, the threshold value was set to 180, but the threshold value may be adjusted according to the brightness of the observed image, and the brightness may be set to bright, the binarization method may be set to manual, the small figure removal area may be set to 10 ^μm2 , and no noise removal filter may be set, and the threshold value may be adjusted so that the markers appearing in the observed image match the shape of the crystal grains of magnesium aluminate.

If the contrast between the magnesium aluminate crystal grains and other parts is difficult to distinguish, the crystal grains may be blackened before the distance between the centers of gravity of the crystal grains is determined by setting, for example, the threshold value to 85, the brightness to dark, the small figure removal area to 10 μm ² , and no noise removal filter.

The equivalent circle diameter of magnesium aluminate crystal grains can be determined by particle analysis using the backscattered electron image and the image analysis software "A-image-kun". The settings for this method should be the same as those used for the centroid distance method for measuring dispersion.

Here, magnesium aluminate is identified using an X-ray diffraction apparatus, and to determine whether the crystal particles observed in the backscattered electron image are magnesium aluminate, an electron probe microanalyzer (EPMA) is used. If aluminum and magnesium are detected, the crystal particles can be deemed to be made of magnesium aluminate.

The dense ceramics may contain silicon carbide as the main component and metallic silicon. In this case, for example, the silicon carbide content is 70% by mass or more and 92% by mass or less, and the metallic silicon content is 8% by mass or more and 30% by mass or less. Silicon carbide is superior to metallic silicon in mechanical properties such as Young's modulus (dynamic elastic modulus) and three-point bending strength. Therefore, when the silicon carbide content is 70% by mass or more, the mechanical properties of the dense ceramics are improved. On the other hand, metallic silicon has a higher thermal conductivity than silicon carbide. Therefore, when the silicon carbide content is 92% by mass or less, the thermal conductivity of the dense ceramics is improved. Therefore, when the silicon carbide content is 70% by mass or more and 92% by mass or less, both mechanical properties and thermal conductivity can be achieved.

The components contained in dense ceramics can be identified using an X-ray diffraction device, and the silicon carbide and silicon contents can be determined using the Rietveld method.

The difference between the average distance between the centers of gravity of the metallic silicon and the average circle equivalent diameter of the metallic silicon is not limited, and may be, for example, 8 μm or more and 20 μm or less. If this difference is 8 μm or more, the distribution density of the silicon carbide increases. As a result, the rigidity of the dense ceramic is improved and the bias in rigidity is reduced. On the other hand, if this difference is 20 μm or less, the thermal conductivity of the dense ceramic is improved and the bias in thermal conductivity is reduced.

The distance between the centers of gravity of metallic silicon in dense ceramics can be determined by the following method.

First, a portion of the dense ceramic is cut out, and the cross section is polished with diamond abrasive grains to obtain a mirror surface. An average area is selected from the mirror surface, and an image of the area of 0.191 ^mm2 (horizontal length 351 μm, vertical length 545 μm) is photographed with a scanning electron microscope to obtain an observation image.

Using this observation image as the subject, the image analysis software "A-zo-kun (ver. 2.52)" (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.; in the following explanation, when the image analysis software "A-zo-kun" is mentioned, it refers to the image analysis software manufactured by Asahi Kasei Engineering Co., Ltd.) is used to determine the distance between the centers of gravity of silicon using a method known as the distance between the centers of gravity method for measuring dispersion.

The conditions set for this method are a threshold value, which is an index showing the brightness of an image, of 190 to 195, brightness of bright, a small figure removal area of 1 μm ² , and a noise removal filter.

The circular equivalent diameter of silicon is determined using a technique called particle analysis on the above observed image.

The setting conditions for this method are the same as those used in the centroid distance method. In addition, at least the outer peripheral surface of the honeycomb structure 16 may be provided with a first conductive portion made of a conductive layer or film.

Recently, the radio frequency (RF) power applied to the electrostatic attraction unit 8 has been increasing. When this high frequency power increases, abnormal discharges such as arc discharges may occur inside or near the flow path 8d. That is, when radio frequency (RF) power is applied to the substrate support assembly 3, a potential difference occurs between the workpiece W and the rear surface of the electrostatic attraction unit 8 due to the capacitance of the electrostatic attraction unit 8. This potential difference creates an RF potential difference inside the flow path 8d, and when this potential difference exceeds the limit value at which discharge occurs, abnormal discharge occurs.

When the outer peripheral surface is provided with the first conductive portion, static electricity can be easily removed along the outer peripheral surface, making it easier to suppress abnormal discharge within the flow path 8d.

At least one of the end faces of the honeycomb structure 16 may have a second conductive portion made of a conductive layer or film. When the end face has the second conductive portion, static electricity can be easily removed along the end face having the second conductive portion, so that abnormal discharge in the flow path 8d can be further suppressed.

The inner peripheral surface of the honeycomb structure 16 may have a third conductive portion made of a conductive layer or film. When the inner peripheral surface has a third conductive portion, it becomes easier to remove static electricity along the inner peripheral surface, so that abnormal discharge in the flow path 8d can be further suppressed.

Here, having electrical conductivity means that the surface resistance is 10 ⁴ Ω or less. The surface resistance can be determined by using a two-needle electrical resistance meter (PROSTAT, PRS-802) with an applied voltage of 100 V.
The first conductive portion, the second conductive portion, and the third conductive portion are made of at least one of graphite, graphene, carbon nanotubes, fullerene, amorphous carbon, and DLC (diamond-like carbon), for example.

In addition, after immersion in hydrochloric acid having a concentration of 35% by mass for 72 hours from the start of immersion, it is preferable that the mass change C per unit area, as expressed by the following formula (2), is 0.3 g/ ^cm2 or less.
C = (W ₀ -W ₁ ) / A ... (2)
(W ₀ : mass (g) of the test piece before immersion, W ₁ : mass (g) of the test piece 72 hours after the start of immersion, A: surface area (cm ² ) of the test piece before immersion)
When the mass change C per unit area is 0.3 g/ ^cm2 or less, the particles constituting the first conductive part, the second conductive part, and the third conductive part are less likely to peel off, and therefore the parts can be immersed in hydrochloric acid for a long period of time, thereby improving the effect of removing dirt.

As described above, the substrate support assembly 3 of the present disclosure comprises a substrate 8b made of a plate-shaped ceramic having an adsorption surface 8a to which the workpiece W is adsorbed, an electrostatic adsorption section 8 having an internal electrode 10 located within the substrate 8b and a flow path 8d located along the thickness direction of the substrate 8b, and breathable plugs 13, 14 of the present disclosure mounted inside the flow path 8d.

The breathable plugs 13 and 14 are less susceptible to shedding, and even if particles floating within the chamber 1 enter the through holes 16a and 16b, the particles are less likely to adhere to the inner surface 16f, and furthermore, have high mechanical strength, so that they can be used for a long period of time.

In addition, the base material 8b and the breathable plugs 13, 14 are made of ceramics mainly composed of aluminum oxide, and the purity (content) of the aluminum oxide may be higher in the breathable plugs 13, 14 than in the base material 8b. When the purity of the aluminum oxide is high, the corrosion resistance to plasma is improved and the voltage resistance is also high, so that the occurrence of arc discharge can be suppressed.

In particular, the purity of the aluminum oxide in the breathable plugs 13, 14 is preferably 99.6% by mass or more. The calcium content is preferably 0.01% by mass or less. If the calcium content is 0.01% by mass or less, even if the breathable plugs 13, 14 are washed with citric acid, there is little calcium, which has low corrosion resistance to citric acid, so the risk of the calcium source turning into particles and contaminating the inside of the chamber 1 is reduced.

1(b), the shower plate 2 may have the breathable plug 2d of the present disclosure attached inside the second flow path 2c. With this configuration, it is possible to suppress backflow of plasma and particles from the plasma space P toward the shower plate 2 and to suppress abnormal discharge occurring in the second flow path 2c, and it is possible to prevent fires that may be caused by abnormal discharge.

Next, an example of a manufacturing method for the breathable plug of the present disclosure will be described.

To obtain a breathable plug made of dense ceramics whose main component is aluminum oxide, first mix aluminum oxide powder having a purity of 99.6% by mass or more and an average particle size (D50) of 1 μm or more and 3 μm or less, a binder, a lubricant, and a solvent.

The aluminum oxide powder may contain magnesium oxide and sodium. The magnesium oxide content in 100% by mass of the aluminum oxide powder is, for example, 0.1% by mass or more and 0.3% by mass or less. The sodium content in 100% by mass of the aluminum oxide powder is, for example, 20 ppm by mass or less. Here, the average particle size (D50) can be determined by a laser diffraction particle size distribution measurement method.

When obtaining a gas-permeable plug made of dense ceramics whose main component is silicon carbide, first prepare coarse and fine powders as silicon carbide powder, and grind and mix them with ion-exchanged water and a dispersant in a ball mill or bead mill for 40 to 60 hours to make a slurry. Here, the particle sizes of the fine and coarse powders after grinding and mixing are in the range of 0.4 μm to 4 μm and 11 μm to 34 μm, respectively.

Next, a sintering aid consisting of boron carbide powder and amorphous carbon powder or phenolic resin, and a binder are added to the resulting slurry and mixed.

The mass ratio of the fine powder to the coarse powder may be, for example, 6% by mass or more and 15% by mass or less of the fine powder, and 85% by mass or more and 94% by mass or less of the coarse powder.

Examples of binders include methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), etc. The total amount of binder may be 2 to 8 parts by mass in solid content per 100 parts by mass of aluminum oxide or silicon carbide powder. When the solid content of the binder is within this range, it is possible to improve the fluidity during extrusion molding and the shape retention of the molded body.

The lubricant may be wax, glycerin, stearic acid, etc. The total amount of lubricant may be 1 part by mass or more and 8 parts by mass or less in terms of solid content per 100 parts by mass of aluminum oxide or silicon carbide powder.

The solvent is, for example, water, and ion-exchanged water is particularly preferable because it has a small amount of impurities. The solvent is, for example, 10 parts by weight to 20 parts by weight per 100 parts by weight of aluminum oxide powder so that the viscosity of the clay in the kneading process is 15,000 Pa·s to 22,000 Pa·s.

After mixing aluminum oxide or silicon carbide powder, binder, lubricant and solvent in the above-mentioned ratio, knead using a universal mixer or a three-roll mill to obtain a clay with a viscosity of, for example, 15,000 Pa·s or more and 22,000 Pa·s or less. The viscosity can be measured by a flow characteristic evaluation method using a constant-load extrusion rheometer (Shimadzu Flow Tester CFT-500C, manufactured by Shimadzu Corporation).

This clay is molded using an extrusion molding machine equipped with a die for forming through holes in the molded body, to obtain a honeycomb-shaped molded body with multiple through holes in the axial direction.

Here, the root mean square slope (RΔq) of the roughness curve of the inner surface forming the through holes of the honeycomb structure and the outer surface of the honeycomb structure is affected by the transfer surface of the die, so the transfer surface of the die can be adjusted appropriately.

The molded body is cut, for example, to a length of 20 mm or more and 80 mm or less, and then dried to remove moisture from within the molded body. The drying temperature is, for example, 40 to 70°C. When the main component of the dried molded body is aluminum oxide, the molded body can be fired in an air atmosphere at a holding temperature of 1550°C to 1650°C for 0.5 hours to 5 hours to obtain the breathable plug of the present disclosure.

When the main component of the dried molded body is silicon carbide, the degreased body is obtained by degreasing in a nitrogen atmosphere at a temperature of 450°C to 650°C for a holding time of 2 hours to 10 hours. Next, this degreased body is fired in a reduced pressure atmosphere of an inert gas such as argon at a holding temperature of 1800°C to 2200°C for 0.5 hours to 5 hours to obtain the breathable plug of the present disclosure.

Another example of the method for producing the breathable plug of the present disclosure will now be described.
The method for producing the breathable plug includes the following steps (a) to (e).

Step (a): A step of placing a powder mainly composed of aluminum oxide, having a cumulative 95% by volume particle size of 6.5 μm or less in a cumulative distribution curve, wax, a dispersant and a plasticizer in a container and stirring to obtain a slurry.

Step (b): Preheating the slurry.

Step (c): Degassing the preheated slurry.

Step (d): The slurry is poured into a mold whose outer periphery is surrounded by a heating means to obtain a molded body.

Step (e): Sintering the molded body.

Step (a) is a step of placing the raw materials in a container and stirring them to obtain a slurry. The raw materials are a powder mainly composed of aluminum oxide, wax, a dispersant, and a plasticizer.

The powder mainly composed of aluminum oxide has a cumulative 95% by volume particle size of 6.5 μm or less in the cumulative distribution curve. By using such a powder, for example, a dense ceramic having a relative density of 96% or more is obtained, and the formation of recesses 19 on the inner peripheral surface 16f is reduced. In particular, the recesses 19 can be further reduced by reducing the average particle size of the powder used. The purity of the powder of the main component is not limited, and for example, a powder having a purity of 99.5% by mass or more may be used.

A cumulative distribution curve is a curve that shows the cumulative distribution of particle sizes in a two-dimensional graph with particle size on the horizontal axis and cumulative percentage of particle size on the vertical axis. The cumulative distribution curve can be determined by the laser diffraction scattering method using, for example, a particle size distribution measuring device manufactured by Microtrac-Bell (MT3300 or its successor model).

For 100 parts by mass of the powder, the wax is used in an amount of 13 parts by mass to 14 parts by mass, the dispersant is used in an amount of 0.4 parts by mass to 0.5 parts by mass, and the plasticizer is used in an amount of 1.4 parts by mass to 1.5 parts by mass. Examples of the wax include paraffin wax and beeswax. Examples of the dispersant include higher fatty acids and higher fatty acid esters. Examples of the plasticizer include higher fatty acids and phthalate esters.

The powder, wax, dispersant and plasticizer are placed in a container that has been heated to, for example, 90°C or higher and 140°C or lower. At this time, the wax, dispersant and plasticizer are in liquid form. The container is made of, for example, resin. The container is set in a stirrer and rotated for three minutes (rotational kneading process), stirring the powder, wax, dispersant and plasticizer to obtain a slurry.

In step (b), the slurry obtained in step (a) is preheated. Preheating increases the fluidity of the slurry, and the effect obtained in step (c) can be further enhanced. Preheating is performed at a temperature of, for example, 120°C or higher and 180°C or lower.

In step (c), the slurry preheated in step (b) is subjected to a degassing treatment. By performing the degassing treatment, the number of bubbles contained in the slurry is reduced, so that dense ceramics with a higher relative density can be obtained. The degassing treatment is performed, for example, by filling the obtained slurry into a syringe and rotating the syringe on its axis for one minute using a degassing tool.

In step (d), the slurry degassed in step (c) is poured into a mold to obtain a molded body. As the mold, a mold whose outer periphery is surrounded by a heating means is used. By using a mold whose outer periphery is surrounded by a heating means in this manner, a honeycomb structure as shown in Figures 3 to 5 is obtained. The heating means is not limited, and examples thereof include a heater. It is preferable that the slurry is heated by the heating means so that the difference in temperature between the slurry and the slurry when it is poured into the mold is within 50°C. The shape of the molded body is not limited, and it may be cylindrical as shown in Figures 3 to 5, or may have other shapes such as a rectangular column.

In step (e), the molded body obtained in step (c) is fired. For example, firing may be performed in an air atmosphere at 1400°C to 1700°C for 1 hour to 3 hours. In this manner, the breathable plug of the present disclosure is obtained, which is provided with a honeycomb structure of dense ceramics having a plurality of through holes in the axial direction. In the breathable plugs 13 and 14 obtained in this manner, the number of recesses 19 having a depth d of 10 μm to 20 μm, starting from the ridge 18 between the inner circumferential surface 16f forming the through holes 16a and 16b and the observation surface 17 obtained by polishing from the outer circumferential surface 16e of the honeycomb structure toward the axial center C of the through holes 16a and 16b, is 2 or less per 1 mm of the length of the ridge 18.

To obtain a breathable plug in which at least the outer peripheral surface of the honeycomb structure is provided with a first conductive portion, a 2-propanol (IPA) solution containing carbon such as graphite, graphene, carbon nanotubes, fullerene, amorphous carbon, etc. may be applied or sprayed onto the outer peripheral surface of the dried molded body, and then the above-mentioned firing may be performed.

To obtain a breathable plug in which at least one end face of a honeycomb structure has a second conductive portion, the above-mentioned 2-propanol (IPA) solution is applied or sprayed onto the end face of a dried molded body, and then the above-mentioned firing is performed.

To obtain a breathable plug in which the inner surface of the honeycomb structure is provided with a third conductive portion, the above-mentioned 2-propanol (IPA) solution is applied or sprayed onto the inner surface of the dried molded body, and then the above-mentioned firing is carried out.

When at least one of the first conductive part, the second conductive part and the third conductive part is formed from DLC, a film made of DLC is formed on the sintered body obtained by the above-mentioned firing using a plasma ion implantation method, and then the temperature is set to 200°C or higher and 1000°C or lower, and heat treatment is performed for 1 hour or more.

The breathable plug of the present disclosure obtained by the above-mentioned manufacturing method is less susceptible to shedding, and even if particles floating within the chamber enter the through holes 16a, 16b, the particles are less likely to adhere to the inner surface 16f, and furthermore, has high mechanical strength, so that it can be used for a long period of time.

REFERENCE SIGNS LIST 1 Chamber 2 Shower plate 2a Diffusion section 2b Gas supply section 2c Second flow path 2d Breathable plug 3 Substrate support assembly support section 4 Mounting section 5 Insulation section 6 Support section 7 Thermal conduction section 8 Electrostatic adsorption section 8a Adsorption surface 8b Substrate 8c Clamp electrode (inner electrode)
Reference Signs: 8d flow path 9 bonding layer 11 O-ring 13 breathable plug 14 breathable plug 15 high frequency power source 16 honeycomb structure 16a, 16b through hole 16c outer periphery region 16d inner periphery region 16e outer periphery surface 16f inner periphery surface 17 observation target surface 18 ridge line 19 recess 20 plasma processing apparatus

Claims (16)

A honeycomb structure made of dense ceramics having a plurality of through holes in an axial direction is provided .
The dense ceramic is a breathable plug containing aluminum oxide as a main component and magnesium aluminate, and a value obtained by subtracting the average value of the circle equivalent diameter of the magnesium aluminate crystal particles from the average value of the distance between the centers of gravity of adjacent magnesium aluminate crystal particles is larger in an outer peripheral region including the outer peripheral surface of the honeycomb structure than in an inner peripheral region including the inner peripheral surface that forms the through holes . A honeycomb structure made of dense ceramics having a plurality of through holes in an axial direction is provided.
The dense ceramics is mainly composed of silicon carbide and contains metallic silicon,
A breathable plug, wherein the difference between the average distance between the centers of gravity of the metallic silicon and the average circle equivalent diameter of the metallic silicon is 8 μm or more and 20 μm or less. 3. The breathable plug according to claim 1, wherein an outer circumferential region including an outer circumferential surface of the honeycomb structure has a smaller open porosity than an inner circumferential region excluding the outer circumferential region. 3. The breathable plug according to claim 1 , wherein an outer periphery side region including an outer periphery surface of the honeycomb structure has a larger open porosity than an inner periphery side region excluding the outer periphery side region. The breathable plug according to any one of claims 1 to 4, wherein a root mean square slope (RΔq) of a roughness curve of an inner peripheral surface forming the through hole is smaller than a root mean square slope (RΔq) of a roughness curve of an outer peripheral surface of the honeycomb structure. The breathable plug according to any one of claims 1 to 4, wherein a root mean square slope (RΔq) of a roughness curve of an outer peripheral surface of the honeycomb structure is smaller than a root mean square slope (RΔq) of a roughness curve of an inner peripheral surface forming the through hole . 7. The breathable plug according to claim 1, wherein the number of recesses having a depth of 10 μm or more and 20 μm or less, starting from a ridge line between an inner circumferential surface forming the through hole and an observation surface obtained by polishing from the outer circumferential surface of the honeycomb structure toward the axis of the through hole, is 2 or less per 1 mm of the length of the ridge line. The breathable plug according to claim 7 , wherein the straightness of the ridge line on the observation surface is 20 μm or less. The breathable plug according to any one of claims 1 to 8 , wherein the dense ceramic contains sodium in an amount of 20 ppm by mass or less. The breathable plug according to any one of claims 1 to 9 , wherein at least an outer peripheral surface of the honeycomb structure is provided with a first conductive portion made of a conductive layer or film. The breathable plug according to any one of claims 1 to 10 , wherein at least one end face of the honeycomb structure is provided with a second conductive portion made of a conductive layer or film. The breathable plug according to claim 10 or 11 , wherein an inner peripheral surface of the honeycomb structure is provided with a third conductive portion made of a conductive layer or film. 13. The breathable plug according to any one of claims 1 to 12, wherein when the plug is immersed in hydrochloric acid having a concentration of 35% by mass for 72 hours from the start of the immersion, a mass change C per unit area, as represented by the following formula (2), is 0.3 g/ ^cm2 or less.
C=(W ₀ −W ₁ )/A (2)
(W ₀ : mass of the test piece before immersion, W ₁ : mass of the test piece 72 hours after the start of immersion, A : surface area (cm ² ) of the test piece before immersion) 14. A substrate support assembly comprising: a substrate made of a plate-shaped ceramic having an adsorption surface to which a workpiece is adsorbed and an opposing surface located opposite the adsorption surface; an electrostatic adsorption member having an internal electrode located within the substrate and a flow path located along the thickness direction of the substrate; and the breathable plug according to any one of claims 1 to 13 attached inside the flow path. The substrate support assembly of claim 14, wherein the substrate is made of a ceramic mainly composed of aluminum oxide, and among the gas permeable plugs of any one of claims 1 and 3 to 13, when the dense ceramic is mainly composed of aluminum oxide, the purity of the aluminum oxide is higher in the gas permeable plug than in the substrate. A shower plate comprising: a second substrate made of a plate-shaped ceramic having a plurality of second flow paths in a thickness direction through which a plasma generation gas passes; and the breathable plug according to any one of claims 1 to 13 , attached inside the second flow paths.

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