silica glass porous material and method for manufacturing the same

Abstract

The purpose of the present invention is to provide a technology with which a shower plate that has a washing tolerance property is obtained without machining. The present invention relates to a silica glass porous body that has a plurality of air bubbles, wherein the plurality of air bubbles include non-communicating air bubbles and communicating air bubbles, and the average air bubble diameter of the air bubbles as calculated by mercury porosimetry is 10 μm to 150 μm.

Description

[Technical Field]

[0001] The present invention relates to a silica glass porous body and a method for producing the same. [Background technology]

[0002] The manufacturing process for semiconductor devices includes etching and CVD (Chemical Vapor Deposition) processes, and shower plates are typically used to supply the source gas in these processes.

[0003] Shower plates are manufactured, for example, by machining a plate-like member made of glass or ceramics to form numerous straight, tubular through-holes. The through-holes are formed to have a diameter of several hundred micrometers to several millimeters.

[0004] However, forming through holes by machining as described above has several problems: it is difficult to process, there is a high possibility of the shower plate being damaged during processing, and it tends to be costly.

[0005] Therefore, a shower plate with through holes formed without machining has been proposed, for example, as shown in Patent Document 1. Patent Document 1 discloses a shower plate made of a porous amorphous silica. By preparing a slurry containing silica particles with an average particle size of 20 to 100 μm and within ±50% of the average particle size, molding, and firing it, an imperfect sintered porous body is obtained in which the contact length between adjacent silica particles at at least one location is 1 / 15 to 3 / 4 of the particle size of the silica particle, and the porous body has communicating pores with an average pore diameter of 5 μm to 25 μm. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2013-147390 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Incidentally, in etching and CVD processes, reaction by-products generated by various chemical reactions can accumulate on the shower plate, becoming a source of particle dust. These generated particles can adhere to the substrate, potentially reducing yield.

[0008] Therefore, shower plates are regularly cleaned to suppress the generation of particles. Typically, cleaning solutions such as aqua regia, hydrofluoric acid, or a mixture of hydrofluoric acid and nitric acid are used.

[0009] However, when the shower plate described in Patent Document 1 is cleaned with a chemical solution, the bonding portions between adjacent silica particles are easily etched, causing the silica particles to easily peel off. At this time, the volume of the shower plate decreases significantly, due to the reduction in volume by the amount of the etched material plus the volume of the peeled-off silica particles themselves. Furthermore, the peeled-off silica particles may remain inside the shower plate, potentially hindering gas permeability. Therefore, the shower plate described in Patent Document 1 is unsuitable for repeated use after cleaning, as its properties can change significantly due to cleaning.

[0010] Therefore, it was difficult to obtain a shower plate with wash resistance without machining. The present invention aims to provide a technology for obtaining a shower plate with wash resistance without performing machining. [Means for solving the problem]

[0011] The present invention relates to the following [1] to [7]. [1] A porous silica glass material having multiple bubbles, the multiple bubbles including non-communicating bubbles and communicating bubbles, and the average bubble diameter of the bubbles determined by the mercury intrusion method being 10 μm to 150 μm. [2] The gas permeability coefficient determined using the palm parameter is 0.01 μm 2 ~10 μm 2 The silica glass porous body described in [1]. [3] The specific surface area determined by the BET method is 0.01 m 2 / g ~ 0.1 m 2 / g. The silica glass porous body described in [1] or [2]. [4] The bulk density is 0.3 g / cm 3 ~2 g / cm 3 The silica glass porous body described in any one of [1] to [3]. [5] The content of each metal impurity of lithium (Li), aluminum (Al), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), titanium (Ti), cobalt (Co), zinc (Zn), silver (Ag), cadmium (Cd), lead (Pb), sodium (Na), magnesium (Mg), potassium (K), calcium (Ca) and iron (Fe) is 0.5 mass ppm or less respectively. The silica glass porous body described in any one of [1] to [4]. [6] A shower plate made of the silica glass porous body described in any one of [1] to [5]. [7] A method for producing a silica glass porous body having a plurality of bubbles, the plurality of bubbles including non-connected bubbles and connected bubbles, and the average bubble diameter of the bubbles determined by the mercury intrusion method being 10 μm to 150 μm, the method comprising depositing silica particles generated by flame hydrolysis of a silicon compound to obtain a soot body, densifying the soot body in an inert gas atmosphere to obtain a silica glass dense body, and making the silica glass dense body porous under conditions of at least low pressure or high temperature from when the silica glass dense body is obtained. A method for producing a silica glass porous body.

Advantages of the Invention

[0012] According to the present invention, a shower plate having washing resistance can be obtained without performing machining.

Brief Description of the Drawings

[0013] [Figure 1] Figure 1 is a diagram schematically showing a cross-section of an arbitrary part of a silica glass porous body according to an embodiment. [Figure 2] Figure 2 is a diagram showing a member obtained by cutting out an arbitrary part of a silica glass porous body according to an embodiment in a rectangular parallelepiped shape. (A) of Figure 2 is a perspective view of the member, and (B) of Figure 2 is a cross-sectional view taken along the X-X' arrow of (A). [Figure 3] Figure 3 is a flowchart showing a method for manufacturing a silica glass porous body according to an embodiment. [Figure 4] Figure 4 is an optical microscope image obtained by photographing the cross-section of the silica glass porous body according to Example 1 after optical polishing. [Figure 5] Figure 5 is a SEM image of the soot body according to Example 8. [Figure 6] Figure 6 is a SEM image of the calcined body according to Example 9.

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention (hereinafter, simply referred to as "the present embodiment") will be described in detail with reference to the drawings. In the drawings, the positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Note that the dimensional ratios in the drawings are not limited to the illustrated ratios. Also, in the specification, "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value. The lower limit value and the upper limit value include the range of rounding.

[0015] First, referring to FIGS. 1 and 2, the structure of the silica glass porous body 1 according to the present embodiment will be described. FIG. 1 shows a diagram schematically showing a cross-section of an arbitrary part of the silica glass porous body 1. The silica glass porous body 1 has a silica glass part 10 and air bubbles 12. The silica glass part 10 has amorphous silicon oxide (SiO2) as a main component and is transparent. Also, its density is about 2.2 g / cm 3In addition to SiO2, the silica glass portion 10 may also contain other elements for the purpose of controlling the properties of the silica glass portion 10. The bubbles 12 include non-communicating bubbles 14 and communicating bubbles 16. The non-communicating bubbles 14 are dispersed almost uniformly in the silica glass porous body 1 and contain gas inside. The shape of the non-communicating bubbles 14 is approximately spherical. Communicated bubbles 16 are formed when adjacent non-communicated bubbles 14 communicate with each other. Figure 1 depicts the communication in two dimensions, but three-dimensional communication also occurs. At least some of the bubbles 12 in the silica glass porous body 1 form communicated bubbles 16.

[0016] Figure 2(A) is a perspective view of member 2 obtained by cutting out an arbitrary portion of silica glass porous material 1 into a rectangular parallelepiped shape, and Figure 2(B) is a cross-sectional view taken along the line X-X' in (A). Member 2, which is made of silica glass porous material 1, has a silica glass portion 10, non-through holes 22a, 22b, and through holes 24. Non-through holes are formed by bubbles that do not penetrate from one surface of the member to another. Here, bubbles may be interconnected but not penetrate. Therefore, non-through holes are formed by interconnected or non-connected bubbles that do not penetrate from one surface of the member to another. As shown in Figure 2(B), non-through hole 22a is formed by non-connected bubbles that do not penetrate, and non-through hole 22b is formed by interconnected bubbles that do not penetrate. The appearance of non-through holes 22a and 22b on the surface of member 2 is approximately circular or a shape consisting of a series of approximately circular shapes. The through-holes 24 are formed by interconnected bubbles that penetrate from one surface of the member 2 to another. The appearance of the through-holes 24 on the surface of the member 2 is substantially circular or consists of a series of substantially circular shapes. Since liquids or gases can pass through the through-holes 24, the member 2 can be suitably used as a shower plate for semiconductor manufacturing equipment. However, the application of the member 2 is not limited to a shower plate, and it can be applied to various applications within the range in which the properties of the silica glass porous body 1 described herein are advantageous.

[0017] Next, the characteristics of the silica glass porous body 1 according to the present embodiment will be described. The lower limit value of the average bubble diameter of the bubbles 12 is 10 μm, preferably 25 μm, and the upper limit value is 150 μm, preferably 125 μm. If the average bubble diameter is 10 μm or more, when used as a shower plate, the pressure loss when the gas passes through the through-hole 24 formed by the bubbles 12 is reduced, and uniform gas supply becomes possible. Further, if the average bubble diameter is 150 μm or less, when used as a shower plate, the occurrence of abnormal discharge can be sufficiently suppressed. The average bubble diameter of the bubbles 12 is determined by the mercury intrusion method.

[0018] The lower limit value of the gas permeability coefficient of the silica glass porous body 1 is 0.01 μm 2 , preferably 0.1 μm 2 , more preferably 0.2 μm 2 and the upper limit value is 10 μm 2 , preferably 5 μm 2 , more preferably 4 μm 2 . If the gas permeability coefficient is within this range, it can be suitably used as a shower plate. The gas permeability coefficient of the silica glass porous body 1 is determined using a palm porometer.

[0019] The lower limit value of the specific surface area of the silica glass porous body 1 is 0.01 m 2 / g, preferably 0.03 m 2 / g and the upper limit value is 0.1 m 2 / g. If the specific surface area is within this range, when used as a shower plate, it can be suitably used for washing. The specific surface area of the silica glass porous body 1 is determined by the BET method.

[0020] The lower limit value of the bulk density of the silica glass porous body 1 is 0.3 g / cm 3 , preferably 0.6 g / cm 3 and the upper limit value is 2 g / cm 3 , preferably 1.6 g / cm 3 is. If the bulk density is 0.3 g / cm 3If the above conditions are met, sufficient strength can be obtained for the silica glass porous body 1. Furthermore, the bulk density is 2 g / cm³. 3 If the following conditions are met, the silica glass porous body 1 will contain sufficient air bubbles 12 and can be suitably used as a shower plate.

[0021] The silica glass portion 10 contains 0.5 ppm by mass or less, preferably 0.1 ppm by mass or less, of each of the following metal impurities: lithium (Li), sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), calcium (Ca), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), titanium (Ti), cobalt (Co), zinc (Zn), silver (Ag), cadmium (Cd), and lead (Pb). If the content of each metal impurity is 0.5 ppm by mass or less, it can be suitably used as a component in semiconductor manufacturing equipment. In this specification, ppm represents parts per million and ppb represents parts per billion.

[0022] Next, with reference to Figure 3, a method for manufacturing the silica glass porous body 1 according to this embodiment will be described. In this embodiment, the VAD (Vapor-phase Axial Deposition) method is used as the synthesis method for silica glass, but the manufacturing method may be changed as appropriate, as long as the effects of the present invention are achieved. As shown in Figure 3, the method for manufacturing the silica glass porous body 1 includes steps S31 to S34.

[0023] In step S31, the raw materials for the synthesis of silica glass are selected. The raw materials for the synthesis of silica glass are not particularly limited as long as they are silicon-containing raw materials that can be gasified, but typically include silicon compounds containing halogens such as silicon chlorides (e.g., SiCl4, SiHCl3, SiH2Cl2, SiCH3Cl3) and silicon fluorides (e.g., SiF4, SiHF3, SiH2F2), or RnSi(OR) 4-nExamples include alkoxysilanes represented by (R: alkyl group with 1 to 4 carbon atoms, n: integer from 0 to 3) and halogen-free silicon compounds such as (CH3)3Si-O-Si(CH3)3.

[0024] Next, in step S32, the above-mentioned synthetic raw materials are subjected to flame hydrolysis at a temperature of 1000°C to 1500°C to produce silica particles, which are then sprayed and deposited onto a rotating substrate to obtain a soot body. In the soot body, the silica particles are partially sintered with each other.

[0025] Furthermore, although not shown in the figures, the soot body may be dehydrated by heat treatment under a vacuum atmosphere to control its electrical properties and reduce the concentration of OH groups. In this case, the heat treatment temperature is preferably 1000°C to 1300°C and the treatment time is preferably 1 hour to 240 hours.

[0026] Next, in step S33, the soot body is subjected to high temperature and high pressure treatment in an inert gas atmosphere, causing sintering of silica particles within the soot body to progress and densification to obtain a silica glass dense body. The silica glass dense body is either transparent silica glass with virtually no air bubbles, or opaque silica glass containing minute air bubbles. In this case, the temperature during the high temperature and high pressure treatment is preferably 1200°C to 1700°C, the pressure is preferably 0.01 MPa to 200 MPa, and the treatment time is preferably 10 to 100 hours. In step S33, the inert gas dissolves into the silica glass. The inert gas is typically helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), nitrogen (N2), or a mixed gas containing at least two of these. Details will be described later, but Ar is preferred. Generally, it is known that the solubility of an inert gas in silica glass tends to decrease as the partial pressure of the inert gas in the atmosphere decreases, or as the temperature of the silica glass increases.

[0027] Next, in step S34, the silica glass dense body is subjected to high-temperature and low-pressure treatment, causing the inert gas dissolved in the silica glass to foam and the bubbles contained in the silica glass dense body to expand due to thermal expansion, resulting in porous silica glass porous body 1 having bubbles 12. At this time, the temperature during the high-temperature and low-pressure treatment is preferably 1300°C to 1800°C, the pressure is preferably 0 Pa to 0.1 MPa, and the treatment time is preferably 1 minute to 20 hours. If the treatment time is 20 hours or less, there is no risk of the bubbles 12 becoming blocked due to excessive heating.

[0028] Now, let's explain the mechanism of foaming. As mentioned earlier, the solubility of an inert gas in silica glass tends to decrease as the partial pressure of the inert gas in the atmosphere decreases, or as the temperature of the silica glass increases. Therefore, in step S34, processing at a lower pressure or higher temperature than in step S33 may cause the amount of dissolved inert gas to become supersaturated, and at this time, foaming occurs in the silica glass.

[0029] Considering the above mechanism, foaming can occur even if the temperature during the high-temperature, low-pressure treatment in step S34 is lower than the temperature during the high-temperature, high-pressure treatment in step S33. However, foaming is promoted and porosity is more likely to progress if the temperature is higher than that during the high-temperature, high-pressure treatment in step S33. Of the inert gas options mentioned above, Ar is preferred because it is relatively inexpensive, and its solubility in silica glass is highly temperature-dependent, making it easy to control the porosity.

[0030] By appropriately adjusting the temperature, pressure, and processing time in the high-temperature, high-pressure treatment in step S33 and the high-temperature, low-pressure treatment in step S34 above, the amount of foaming and the degree of bubble expansion can be changed, thereby controlling the number of bubbles 12 contained in the silica glass porous body 1, the bubble diameter, etc. [Examples]

[0031] Next, the experimental data will be explained with reference to Table 1 and Figures 4-6. In Table 1, Examples 1-7 are examples, and Examples 8-9 are comparative examples.

[0032] The physical properties shown in Table 1 were determined by the following method. The average bubble diameter was determined by the mercury intrusion method according to JIS-R1655:2003. Specifically, the sample to be evaluated was cut into a cylindrical shape with a diameter of 10 mm and a thickness of 5 mm, and the pore size distribution was measured using a mercury porosimeter (Micromeristics: AutoPore V9620). The pore size at which the cumulative pore volume reached 50% of the total pore volume was defined as the average bubble diameter.

[0033] The gas permeability coefficient was determined using a palm porometer. Specifically, the object to be evaluated was cut into a disc shape with a diameter of 25 mm and a thickness of 2 mm, set in the holder of a palm porometer (PMI Corporation: CFP-1200AEXL), and gas was passed through it at a flow rate of 1 to 200 L / min. At this time, the gas permeability coefficient (K) when ΔP = 10 kPa was determined from the following equation (1). Air was used as the gas.

[0034]

number

[0035] In the above formula (1), K is the gas permeability coefficient (unit: m 2 μ is gas viscosity (unit: Pa·s), L is sample thickness (unit: m), and Q is gas flow rate (m 3 ( / s), ΔP is the pressure difference between the gas inlet and gas outlet in the sample (unit: Pa), A is the cross-sectional area of ​​the sample (m²). 2 )

[0036] The specific surface area was determined by the BET method according to JIS-Z8830:2013. Specifically, a small piece of approximately 1 g was cut from the material to be evaluated, and as a pretreatment, it underwent degassing under reduced pressure at 200°C for approximately 5 hours. Then, the adsorption of krypton (Kr) gas was measured using a specific surface area measuring device (BELSORP-max, manufactured by Nippon Bell Co., Ltd.), and the specific surface area was calculated from the BET formula.

[0037] The bulk density was determined by cutting the sample into a cylindrical shape with a diameter of 10 mm and a thickness of 5 mm, and dividing the sample mass, measured using an electronic balance, by the apparent volume of the sample.

[0038] The weight change rate due to hydrofluoric acid was determined by cutting the object to be evaluated into a plate measuring 15 mm in width, 15 mm in depth, and 3 mm in thickness, immersing it in 5% by mass hydrofluoric acid at room temperature for 1 hour, and calculating the percentage change in the sample weight before and after immersion.

[0039] (Examples 1-7) As a raw material for the synthesis of silica glass, silicon tetrachloride (SiCl4) was selected. Silica particles were generated by flame hydrolysis of this material and deposited onto a rotating substrate by spraying, thereby obtaining a soot body. Next, this soot body was placed in a heating furnace, filled with Ar gas, and subjected to high-temperature, high-pressure treatment at a predetermined temperature, pressure, and processing time to densify the soot body. After that, it was returned to atmospheric pressure and allowed to cool. The resulting dense silica glass was an opaque silica glass containing minute bubbles. Next, the furnace was evacuated, and high-temperature, low-pressure treatment was performed at a predetermined temperature and processing time to porousize the dense silica glass. After that, it was returned to atmospheric pressure and allowed to cool, and the resulting porous silica glass 1 was removed. By arbitrarily combining the temperature, pressure, and processing time in the above high-temperature, high-pressure treatment and the above high-temperature, low-pressure treatment, porous silica glass 1 with the physical properties shown in Examples 1 to 7 of Table 1 were obtained. Figure 4 shows an optical microscope image of a cross-section of the silica glass porous material 1 of Example 1, which was optically polished and photographed. As is clear from Figure 4, the silica glass porous material 1 of Example 1 contains bubbles 12 dispersed almost uniformly, some of which exist as interconnected bubbles 16. Furthermore, the content of metal impurities in the silica glass porous body 1 of Example 1 was measured, and the results showed that Li, Al, Cr, Mn, Ni, Cu, Ti, Co, Zn, Ag, Cd, and Pb were all less than 3 ppb, Na was 41 ppb, Mg was 8 ppb, K was 70 ppb, Ca was 21 ppb, and Fe was 14 ppb. The content of metal impurities was determined by cutting the silica glass porous body 1 obtained above into an appropriate size and then using the ICP-MS (Inductively Coupled Plasma-Mass Spectrometer) method. The volume change rate due to hydrofluoric acid in the silica glass porous bodies of Examples 1 to 7 was all 10% or less. Therefore, it can be said that they have high cleaning resistance when used as shower plates for cleaning.

[0040] (Example 8) Silicon tetrachloride (SiCl4) was selected as the raw material for the synthesis of silica glass. Silica particles were generated by flame hydrolysis of this material, and a soot was obtained by spraying and depositing these particles onto a rotating substrate. Figure 5 shows an SEM image of the soot body of Example 8. As is clear from Figure 5, the soot body of Example 8 had a structure in which adjacent silica particles were partially sintered together, similar to the porous body of Patent Document 1.

[0041] (Example 9) After obtaining a soot body using the same method as in Example 8, a calcined body was obtained by further sintering of silica particles within the soot body under a vacuum atmosphere at 1250°C for 50 hours. Figure 6 shows an SEM image of the calcined body of Example 9. As is clear from Figure 6, the calcined body of Example 9 has a structure in which adjacent silica particles are sintered together, similar to the porous body of Patent Document 1, and the sintering was more advanced than that of the soot body of Example 8.

[0042] The soot or calcined materials in Examples 8-9 showed a volume change of 30% or more due to hydrofluoric acid. Therefore, when used as a shower plate for cleaning, the volume decreases significantly due to the flaking of silica particles, and the properties change drastically, making them clearly unsuitable as shower plates.

[0043] [Table 1]

[0044] Although the silica glass porous body and its manufacturing method according to the present invention have been described above, the present invention is not limited to the embodiments described above. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope described in the claims. These also naturally fall within the technical scope of the present invention.

[0045] This application is based on Japanese Patent Application No. 2021-065433 filed on April 7, 2021, the contents of which are incorporated herein by reference. [Explanation of Symbols]

[0046] 1. Porous silica glass material 10 Silica glass part 12 bubbles 14 Non-communicating bubbles 16 interconnected bubbles 2 components 22a Non-through hole 22b Non-through hole 24 Through holes

Claims

1. It has multiple bubbles, The aforementioned plurality of bubbles include non-communicating bubbles and communicating bubbles. The average bubble diameter of the bubbles determined by the mercury intrusion method is 10 μm to 150 μm. The specific surface area determined by the BET method is between 0.035 m² / g and 0.1 m² / g. A porous silica glass material having a content of 0.5 ppm by mass or less of each of the following metal impurities: lithium (Li), aluminum (Al), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), titanium (Ti), cobalt (Co), zinc (Zn), silver (Ag), cadmium (Cd), lead (Pb), sodium (Na), magnesium (Mg), potassium (K), calcium (Ca), and iron (Fe).

2. The gas permeability coefficient determined using a palm porometer is 0.01 μm. ２ ~10 μm ２ The silica glass porous body according to claim 1.

3. The specific surface area calculated by the BET method is 0.01 m². ２ / g to 0.1m ２ A silica glass porous body according to claim 1 or 2, wherein the weight is / g.

4. Bulk density is 0.3 g / cm³ ３ ~2g / cm³ ３ A silica glass porous body according to any one of claims 1 to 3.

5. A shower plate made of a silica glass porous body according to any one of claims 1 to 4.

6. It has multiple bubbles, the multiple bubbles including non-communicating bubbles and communicating bubbles, and the average bubble diameter of the bubbles, as determined by the mercury intrusion method, is 10 μm to 150 μm. The specific surface area determined by the BET method is between 0.035 m² / g and 0.1 m² / g. A method for producing a silica glass porous body in which the content of each of the following metal impurities is 0.5 ppm by mass or less: lithium (Li), aluminum (Al), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), titanium (Ti), cobalt (Co), zinc (Zn), silver (Ag), cadmium (Cd), lead (Pb), sodium (Na), magnesium (Mg), potassium (K), calcium (Ca), and iron (Fe), The process involves depositing silica particles produced by flame hydrolysis of silicon compounds to obtain a soot material, The aforementioned soot body is densified under an inert gas atmosphere to obtain a silica glass dense body. A method for producing a silica glass porous body, comprising making the silica glass dense body porous under conditions at least lower pressure or higher temperature than when the silica glass dense body was obtained.

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