JP2934862B2 - Silica glass filter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silica glass filter used for filtering a gas such as a reaction gas and a liquid such as a chemical solution used in a semiconductor manufacturing process and the like.

[Prior art] Conventionally, as this type of filter, a resin filter made of a synthetic resin such as nitrocellulose, acetylcellulose, polytetrafluoroethylene, a ceramic filter made of ceramics such as alumina, silicon carbide, and mullite, or Vycor A glass filter of a system is known.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional resin filter, heat resistance and chemical resistance are limited, and the strength is low. The eyes are partially widened and the collected matter passes through the filter, making it impossible to perform complete filtration. In addition, there is a problem that it cannot be reproduced and used by baking or the like.

In the case of the ceramic filter, although the problems of the resin filter can be largely solved, since the constituent particles have a structure in which the particles are crystalline and intertwined with a polyhedron, the flow of the filtration fluid becomes complicated, the pressure loss increases, and the permeability increases. The rate drops. In addition, a clear grain boundary is formed at the boundary between the sintered particles, and impurities and the like in the particles gather at the grain boundary due to segregation of the grain boundary to easily form an intergranular phase. There is a problem that impurities are eluted due to the erosion and strength is reduced.

In the Vycor type glass filter,
There is a problem that impurities are mixed in due to elution of boron, alkali ions and the like contained therein.

Therefore, an object of the present invention is to provide a silica glass filter having high purity, excellent chemical resistance, high transmittance, and a large filtration area.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the silica glass filter of the present invention comprises a porous support made of a sintered body of an amorphous silica powder. It is composed by laminating a fine porous filtration layer consisting of a body, with a purity of 99.9% or more,
The total of Na, K, Li, Fe, Al, Ca, Mg, Cu and Ti is 150 ppm or less.

In the above silica glass filter, the porosity of the support is preferably 10% or more.

The support and the filtration layer are made of a sintered body of amorphous silica powder.

The thickness of the filtration layer is preferably 10 to 500 times the particle diameter constituting the filtration layer.

The particle size of the particles constituting 75% by weight or more of the powder constituting the support and / or the filtration layer is preferably within a range of ± 50% of the respective average particle sizes.

The particles of the powder constituting the support and / or the filtration layer are preferably substantially spherical.

[Action] In the above means, the support and the filter layer form a so-called asymmetric membrane structure, and since the constituent particles are amorphous, an intergranular phase is formed at the grain boundary like a crystalline one. This has no uniform continuous structure, and the adhered particles become nearly spherical, and the surface becomes smooth.
Also, the negative electrostatic charge becomes very large.

The upper limit of the porosity of the support is considered to be about 60%, but may be high if there is no problem in strength. Also, 10%
If it is less than 1, the pressure loss increases and the amount of permeation decreases.

If the thickness of the filtration layer is less than 10 times the particle diameter constituting the filtration layer, pinholes and the like are likely to occur, and if it exceeds 500 times, the pressure loss increases and the transmittance decreases.

By setting the particle size of the particles constituting 75% by weight or more of the powder constituting the support and / or the filtration layer to be within a range of ± 50% of the respective average particle sizes, a material having a high porosity can be obtained. Outside this is not preferable because the porosity decreases.

Further, by making the particles of the powder constituting the support and / or the filtration layer substantially spherical, the surface becomes smooth, the flow of the filtration fluid becomes smooth, the pressure loss becomes small, and the high permeability is obtained. Rate is obtained.

[Example] Hereinafter, an example of the present invention will be described in detail.

Example 1 A synthetic silica glass cullet synthesized by a flame method (a method of obtaining silica (SiO ₂ ) by pyrolyzing silicon tetrachloride (SiCl ₄ ) in an oxygen-hydrogen flame, the same applies hereinafter) in a silica glass ball mill. To obtain a silica powder having an average particle size of 15 μm. Table 1 shows the impurity concentration in this powder.

After classifying the above powder to 10 to 20 μm, water was added thereto, and the diameter was 15 mm and the thickness was 2 mm by slip casting.
Was formed. The compact was fired at a temperature of 1500 ° C. to produce a porous support made of a sintered body of amorphous silica powder.

On the other hand, a synthetic silica glass cullet synthesized by a flame method was wet-pulverized in a silica glass ball mill to obtain an average particle size of 3%.
A slurry containing μm silica powder was obtained. The slurry is flowed on the upper surface of the support, silica particles are adhered thereto, and the mixture is calcined at a temperature of 1200 ° C. to form a fine porous filtration layer made of a sintered body of amorphous silica powder on the support. They were laminated to obtain a silica glass filter having a so-called asymmetric membrane structure.

This silica glass filter has a silica purity of 99.9
%, The impurity concentrations were as shown in Table 2.

Example 2 A similar support was prepared in the same manner as in Example 1, and a slurry containing silica powder having an average particle diameter of 3 μm was obtained in the same manner as in Example 1.

The slurry was wet-classified to 1 to 5 μm, the classified slurry was flowed on the upper surface of the support, and silica particles were attached thereto, and then calcined at a temperature of 1200 ° C. to form a support of amorphous silica powder on the support. Were laminated to obtain a silica glass filter having a so-called asymmetric membrane structure.

Example 3 A silica powder having an average particle size of 15 μm was obtained in the same manner as in Example 1, water was added to the powder without classification, and a diameter of 15 mm was obtained by slip casting in the same manner as in Example 1.
A 2 mm thick disk was formed. The compact was fired at a temperature of 1500 ° C. to produce a porous support made of a sintered body of amorphous silica powder.

A fine filtration layer made of a sintered body of amorphous silica powder was laminated on the support in the same manner as in Example 1 to obtain a silica glass filter having a so-called asymmetric membrane structure.

Here, when the pores of the supports prepared in Example 2 and Example 3 were measured, the relationship between the pore diameter and the pore volume was 1st.
In the figure, curves A and B are shown.

Therefore, it can be seen that the use of the classified powder and the classified slurry provides a larger pore volume and a uniform pore size.

When the nitrogen gas permeation amount was measured, the pressure loss was 0.5k.
When gf · cm ^-2 , 100 m ³ · hr ^-1 · m ^-2 in Example ² ;
It was 30 m ³ · hr ^-1 · m ^{-2 in} Example 3.

Therefore, it is understood that the permeation amount can be increased by using the classified powder and the classified slurry.

Example 4 Silica powder particles having an average particle diameter of 15 μm obtained in the same manner as in Example 1 were spheroidized in a fire, and then classified into 10 to 20 μm and 1 to 5 μm.

Water is added to the spherical powder having a particle size of 10 to 20 μm, and the diameter is 15 mm and the thickness is 2 m by slip casting in the same manner as in Example 1.
m disks. Firing the molded body at a temperature of 1500 ° C,
A support made of a sintered body of amorphous silica powder was prepared.

On the other hand, water is added to the 1 to 5 μm spherical classified powder to form a slurry. The slurry is flowed on the upper surface of the support, silica particles are adhered to the slurry, and baked at a temperature of 1200 ° C. A fine porous filtration layer made of a sintered body of crystalline silica powder was laminated to obtain a silica glass filter having a so-called asymmetric membrane structure.

Example 5 A similar support was prepared in the same manner as in Example 4, while water was added to a 1 to 5 μm crushed classified powder of amorphous silica to form a slurry, and the slurry was poured on the upper surface of the support. After adhering silica particles, it is fired at a temperature of 1200 ° C. to form a fine porous filtration layer composed of a sintered body of amorphous silica powder on a support, having a so-called asymmetric membrane structure. A silica glass filter was obtained.

Here, when the nitrogen gas permeation amount of the silica glass filters of Examples 4 and 5 was measured, the pressure loss was 0.5 k.
When gf · cm ^-2 , 600 m ³ · hr ^-1 · m ^-2 in Example 4;
It was 400 m ³ · hr ^-1 · m ^{-2 in the} case of Example 5.

Therefore, it is understood that the permeation amount can be further increased by using the classified powder and the classified slurry composed of the spherical particles.

Example 6 A similar support was produced in the same manner as in Example 4.

On the other hand, 1500 ml of ethanol and 200 ml of 29% aqueous ammonia were added to a silica glass reaction vessel equipped with a stirrer and mixed to obtain a reaction solution. Also, 1000 ml of ethanol and 250 ml of tetraethoxysilane were mixed to prepare a raw material solution, and
The mixture was dropped into the reaction solution adjusted to a temperature of ° C., and stirred for 8 hours to obtain a slurry containing spherical monodispersed silica powder having a particle diameter of 0.4 μm.

This slurry is flowed on the upper surface of the support to adhere spherical monodisperse silica particles, and then calcined at a temperature of 1150 ° C. to form a fine porous silica powder comprising a sintered body of amorphous silica powder on the support. The filtration layer was laminated to obtain a silica glass filter having a so-called asymmetric membrane structure.

The pore size of the filtration layer of this silica glass filter is 0.
It was 2 μm.

As shown in FIG. 2, the silica glass filter 1 is mounted in a casing 2 made of silica glass to form a size separation unit.
A 6-inch silicon wafer (not shown) was placed downstream of the filter and nitrogen gas was filtered. The number of particles (0.1 μm dust) attached to the silicon wafer from the filtered nitrogen gas was measured by a surface dust counter. Table 3 shows the alumina ceramic filter and the pore size of the filtration layer together.

 In FIG. 2, reference numerals 3 and 4 are a supply port and a discharge port.

Therefore, it can be seen that the silica glass filter exhibits a higher collection rate than the alumina ceramic filter.

Example 7 A slurry containing a spherical monodisperse silica powder having a particle diameter of 0.4 μm obtained by a method similar to that of Example 6 was flowed on the upper surface of the filtration layer of a silica glass filter obtained by a method similar to that of Example 6, and a spherical shape was obtained. After attaching the monodisperse silica particles, 11
The process of baking at a temperature of 50 ° C. was repeated, and the permeation amount of nitrogen gas through the silica glass filter (pressure loss 0.5 kgf · cm ⁻² ) in which the thickness of the filtration layer was gradually increased as shown in Table 4
Was as shown in Table 4.

Therefore, the thickness of the filtration layer is preferably 10 to 500 times the constituent particle diameter, and if it is less than 10 times, pinholes are likely to occur,
It can be seen that when it exceeds 0 times, the transmission amount decreases.

Example 8 A silica powder having various average particle diameters was obtained by the same method as in Example 1, water was added to each powder, and a disk having a diameter of 15 mm and a thickness of 2 mm was formed by slip casting as in Example 1. did. Each molded body was fired at a temperature of 1500 ° C. to form a sintered body of amorphous silica powder, and as shown in Table 5, porous supports having different porosity were produced.

A slurry containing a spherical monodisperse silica powder having a particle diameter of 0.4 μm obtained by the same method as in Example 6 was flowed on the upper surface of each support, and the spherical monodisperse silica particles were attached.
, And a fine porous filtration layer made of a sintered body of amorphous silica powder was laminated on the support to obtain each silica glass filter.

Table 5 shows the nitrogen gas permeation amount (pressure loss 0.5 kgf · cm ⁻² ) of each silica glass filter.

Therefore, it is understood that the porosity of the support should be 10% or more.

Example 9 A similar support was produced in the same manner as in Example 4.

On the other hand, 1500 ml of ethanol and 100 ml of 29% aqueous ammonia were added to a silica glass reaction vessel equipped with a stirrer and mixed to obtain a reaction solution. Also, 1000 ml of ethanol and 200 ml of tetraethoxysilane were mixed to prepare a raw material solution, and
The solution was dropped into the reaction solution adjusted at a temperature of ° C. and stirred for 8 hours to obtain a slurry containing a spherical monodispersed silica powder having a particle size of 0.2 μm.

This slurry is allowed to flow on the upper surface of the support to adhere spherical monodisperse silica particles, and then calcined at a temperature of 1050 ° C. to form a fine porous material comprising a sintered body of amorphous silica powder on the support. The filtration layer was laminated to obtain a silica glass filter having a so-called asymmetric membrane structure.

The pore size of the filtration layer of this silica glass filter is 0.
It was 1 μm.

In addition, the gas permeation amount when filtering nitrogen gas by the silica glass filter, the liquid permeation amount when filtering pure water, and the porosity are those of alumina ceramic filters and those of the Vycor type glass filter and the filtration layer. The results are shown in Tables 6, 7 and 8, which also show the pore diameter.

Note that the glass filter is a porous filter manufactured by Vycor method.

Therefore, it can be seen that the silica glass filter of Example 9 can make the gas permeation amount, the fluid permeation amount and the porosity equal to or more than the alumina ceramic filter or the like.

Further, the size separation unit shown in FIG. 2 was constructed using the silica glass filter of Example 9, and various gases,
The liquid was filtered and the chemical resistance was examined. The results were as shown in Table 9 together with those of the alumina ceramic filter.

 In the table, ○ means good, Δ means good, × means bad.

Therefore, it is understood that the silica glass filter is stable against acids other than hydrofluoric acid.

Furthermore, using the silica glass filter of Example 9
20% H ₂ SO ₄ was filtered, and the impurity concentration in the 20% H ₂ SO ₄ after the filtration was measured. The results were as shown in Table 10 together with those of the alumina ceramic filter.

Therefore, it can be seen that the silica glass filter keeps the purity of the filtrate extremely high.

[Effects of the Invention] As described above, according to the present invention, since a so-called asymmetric membrane structure is formed by the support and the filtration layer, the filtration area can be increased.

In addition, the silica glass filter is high purity containing only a specific amount of a specific impurity, and the constituent particles are amorphous, and an intergranular phase containing segregated impurities is formed at a grain boundary like a ceramic filter. And a uniform continuous structure, so that the chemical resistance can be improved, and the support and the filter layer are formed of a sintered body of amorphous silica powder. Strength can be improved.

Furthermore, since the adhered particles become nearly spherical and the surface becomes smooth, the flow of the filtration fluid becomes smooth, the pressure loss can be reduced, and the transmittance can be increased.

Furthermore, when filtering the gas, the negative electrostatic charge of the filter becomes very large, so that small dust, especially positively charged particles, can be captured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the relationship between the pore diameter and the pore volume of the silica glass filters according to Embodiments 2 and 3 of the present invention,
FIG. 2 is a conceptual diagram of a size separation unit using a silica glass filter according to Embodiment 6. 1. Silica glass filter 2. Casing 3. Supply port 4. Discharge port

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junzo Shimai 30 Soya, Hadano-shi, Kanagawa Prefecture, Central Research Laboratory, Toshiba Ceramics Co., Ltd. Field (Int.Cl. ⁶ , DB name) B01D 39/20

Claims (1)

(57) [Claims] A fine porous filtration layer made of a sintered body of amorphous silica powder is laminated on a porous support made of a sintered body of amorphous silica powder, and has a purity of 99.9%. %, The total of Na, K, Li, Fe, Al, Ca, Mg, Cu and Ti is 150p
A silica glass filter characterized by being at most pm.