Gas purification filter unit

Abstract

This gas purification filter unit (10) is provided with: a first elimination unit (11) that eliminates gas component impurities among the impurities contained in ozone generated from an ozone generating device; and a second elimination unit (12) that is disposed at a later stage than the first elimination unit and that further eliminates solid particulate impurities from among the impurities from which the gas component has been eliminated. Ozone containing impurities are caused to flow in from the inflow end (10a) of such a gas purification filter unit (10) and is passed through the first elimination unit (11) and second elimination unit (12), and thus ozone from which impurities have been eliminated is discharged from an outflow end (10b).

Claims

1. A gas purification filter unit for removing impurities contained in ozone gas, comprising: a first removal section for removing a gas component from the impurities, and a second removal section which is disposed at a stage after the first removal section and removes solid fine particles from impurities from which the gas component has been removed, said gas purification filter unit comprises an accommodation section for detachably accommodating the second removal section, said accommodation section is formed at the end of the first removal section and includes a cylindrical space formed therein to enable the second removal section, which has a substantially cylindrical external shape, to be received therein.

2. The gas purification filter unit as claimed in claim 1, wherein the first removal section is provided with an adsorbent for adsorbing the gas component.

3. The gas purification filter unit as claimed in claim 2, wherein the adsorbent is silica gel.

4. The gas purification filter unit as claimed in claim 3, wherein the silica gel has a large number of pores, the diameter of the respective pores being no greater than 10 nm.

5. The gas purification filter unit as claimed in claim 3, wherein the silica gel is in the form of spheres having a diameter of between 0.5 mm and 3 mm.

6. The gas purification filter unit as claimed in claim 2, wherein the adsorbent includes silica and alumina.

7. The gas purification filter unit as claimed in claim 6, wherein the adsorbent comprises a high-silica zeolite in which the proportion of silica is at least 10 times that of alumina.

8. The gas purification filter unit as claimed in claim 1, wherein the second removal section is provided with an area for straining the solid fine particles.

9. The gas purification filter unit as claimed in claim 8, wherein the second removal section comprises a resin case which is resistant to ozone corrosion, and the area which is accommodated inside the resin case.

10. The gas purification filter unit as claimed in claim 9, wherein the area is a filtration material in the form of a sheet which is pleated for accommodation inside the resin case.

11. The gas purification filter unit as claimed in claim 10, wherein the filtration material has a nominal pore size ranging between 0.2 μm and 0.5 μm.

12. The gas purification filter unit as claimed in claim 9, wherein the resin case and the filtration material comprise a fluororesin.

13. The gas purification filter unit as claimed in claim 12, wherein the fluororesin comprises at least one from among: tetrafluoroethylene-hexafluoropropylene copolymer, polytetrafluoroethylene and perfluoroalkoxy fluororesin.

14. The gas purification filter unit as claimed in claim 9, wherein wherein the first removal section is provided with an external covering for accommodating the adsorbent, and an accommodation section which is formed on part of the external covering and can detachably accommodate the resin case forming part of the second removal section.

15. The gas purification filter unit as claimed in claim 14, wherein the accommodation section is provided with a mesh member made of stainless steel.

16. The gas purification unit according to claim 1, wherein said first and second removal portions for an integral construction in which both removal sections are continuously arranged so as to be adjacent to each other.

17. The gas purification filter unit as claimed in claim 1, wherein the first removal section is provided with an adsorbent for adsorbing the gas component, said adsorbent does not contain transition metal elements.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a view in cross section showing a gas purification filter unit according to a mode of embodiment of the present invention.

(2) FIG. 2A is a view in cross section showing the situation when the second removal section has been removed from the first removal section in the gas purification filter unit according to a mode of embodiment of the present invention.

(3) FIG. 2B is a schematic view in cross section of the second removal section in the gas purification filter unit according to a mode of embodiment of the present invention.

(4) FIG. 3 is a main-part oblique cutaway view showing the structure of the filtration material which is preferably used in the second removal section.

(5) FIG. 4 is a main-part oblique cutaway view showing the filtration material when it is accommodated.

MODE OF EMBODIMENT OF THE INVENTION

(6) A mode of embodiment of the gas purification filter unit according to the present invention will be described below with reference to the figures. It should be noted that this mode of embodiment is intended to provide a specific description in order to improve an understanding of the essential point of the invention and does not limit the present invention unless specifically stated otherwise. Furthermore, for the sake of convenience, the portions constituting the main parts in the figures used in the following description are sometimes enlarged in order to aid comprehension of the features of the present invention, and what is depicted may not necessarily be the same as the dimensional proportions etc. of the constituent elements.

(7) FIG. 1 is a view in cross section showing a gas purification filter unit according to this mode of embodiment.

(8) A gas purification filter unit 10 is used to purify ozone (ozone gas) which is used in a semiconductor device production process, and may be used as an in-line filter which is inserted partway along a pipe for supplying ozone between an ozone generator and the semiconductor device production process.

(9) The gas purification filter unit 10 is provided with a first removal section 11 for removing, from among impurities contained in ozone generated by means of an ozone generator, gas-component impurities, and a second removal section 12 which is disposed at a stage after the first removal section 11 and further removes impurities in the form of solid fine particles from the impurities from which the gas component has been removed. The ozone containing impurities is made to flow from an inflow end 10a of the gas purification filter unit 10 and is made to flow through the first removal section 11 and second removal section 12, and ozone from which impurities have been removed is discharged from an outflow end 10b as a result (see the dotted arrow in FIG. 1).

(10) One end of the first removal section 11 comprises the inflow end 10a for when ozone containing impurities generated by an ozone generator is introduced into the gas purification filter unit 10. The first removal section 11 is provided with an external covering 21 having a substantially cylindrical outer shape. The external covering 21 is formed from a material which is resistant to the oxidative power of ozone and is very strong, e.g. stainless steel. A connector 22 which narrows in such a way as to have a predetermined opening diameter is formed at one end of the external covering 21 in order to connect a pipe which is joined to the ozone generator.

(11) An accommodation section 23 for detachably accommodating the second removal section 12 is formed at the other end of the first removal section 11. A cylindrical space is formed in this accommodation section 23 in such a way as to enable the second removal section 12, which has a substantially cylindrical external shape, to be received therein. A mesh member 24 comprising stainless steel which is resistant to ozone is provided in the accommodation section 23. The mesh member 24 allows ozone that has passed through the first removal section 11 to flow into the post-stage second removal section 12.

(12) The inside of the external covering 21 which forms part of the first removal section 11 is filled with an adsorbent 25 for physically adsorbing or chemically adsorbing and removing gas-component impurities from the impurities contained in the ozone generated by the ozone generator. One end of the external covering 21 preferably has a structure which can be opened/closed in such a way that the adsorbent 25 can be easily replaced.

(13) A purification material for removing metal compounds from ozone gas is used as the adsorbent 25. When ozone containing impurities is brought into contact with the adsorbent 25, the gas-component impurities are reduced to a low level. As a result of ozone containing impurities passing through the first removal section 11, the total metal contamination of the gas component in the ozone is reduced to less than 100 ppt by volume, preferably less than 10 ppt by volume, and more preferably less than 1 ppt by volume.

(14) The purification material which is used as the adsorbent 25 is a high-surface-area inorganic oxide that does not contain any transition metal elements and has an ozone decomposition catalytic action, for example. A number of purification materials are understood to bring about metal removal in the method according to the present invention. An example of a purification material which is used as the adsorbent 25 that may be mentioned is a high-surface-area inorganic compound containing high-silica zeolite having a Si/Al ratio of about four or greater. High-silica zeolite having a SiO.sub.2/Al.sub.2O.sub.3 ratio of 10 or greater should preferably be used. Furthermore, it is also important that said compound contains very little in the way of heavy metals or does not contain heavy metals.

(15) The purification material which is used as the adsorbent 25 preferably has a surface area exceeding about 20 m.sup.2/g, and more preferably exceeding about 100 m.sup.2/g, but a larger surface area is still permissible. The surface area of the material must take account of the surface area of both the inside and the outside. The surface area of the purification material may normally be measured in accordance with industry standards using the Brunauer-Emmett-Teller method (BET method).

(16) In simple terms, the BET method involves measuring the amount of adsorption gas (e.g., nitrogen, krypton) or adsorbate required to cover the external surface and contactable internal pore surface of a solid with a complete single-molecule layer of adsorbate. The volume of the single-molecule layer can be calculated from the adsorption isotherm using the BET equation, and the surface area can then be calculated from the volume of the single-molecule layer using the dimensions of the molecules of adsorbate.

(17) The type of metal oxide employed for the purification material which can be used as the adsorbent 25 is not limited to what has been described above, and silicon oxide, aluminum oxide, aluminosilicate oxide (sometimes referred to as zeolite) and titanium oxide are included.

(18) In a preferred mode of embodiment, the purification material is provided in the external covering 21 which is resistant to chemical and physical deterioration caused by ozone. For example, high-purity stainless steel such as 316L having a minimum surface roughness of 0.2 ra or similar makes an especially preferable external covering 21 vessel. For certain modes of embodiment employing gases which are corrosive, oxidative or reactive in other states, the vessel is selected from materials which are stable under operating conditions.

(19) Silica gel is preferably cited as a purification material which can be used as the adsorbent 25 in addition to the abovementioned silica zeolite.

(20) Silica gel is a material in which an acid component obtained from an aqueous solution of sodium metasilicate (Na.sub.2SiO.sub.3) is hydrolyzed, and the resulting silicic acid gel is dewatered and dried.

(21) An example of the silica gel which fills the external covering 21 of the first removal section 11 that may be mentioned is silica gel in the form of spheres having a diameter of between 0.5 mm and 3 mm. Furthermore, the silica gel which is used preferably has a large number of pores, the diameter of the respective pores being no greater than 10 nm, from the point of view of adsorption power.

(22) The silica gel is a substance which absorbs moisture, as is known, but there are concerns regarding a reduction in the capacity to remove metal compounds when the moisture content of the silica gel increases. This is because moisture is adsorbed first by the pores in the silica gel which adsorbs metal compounds. The silica gel used as the adsorbent 25 is therefore preferably controlled beforehand in such a way that a suitable amount of moisture is not exceeded.

(23) When silica gel is used as the adsorbent 25, it is possible to efficiently remove metal compounds with respect to high-level ozone. With the abovementioned silica zeolite, there is a possibility of ozone decomposition progressing and of adsorbed metal compounds being released again due to heat generated by the heat of decomposition when high-level ozone of several tens of g/m.sup.3 or greater is passed through. However, ozone decomposition can be suppressed by using silica gel as the adsorbent 25 and metal compounds can be reliably adsorbed from low-level ozone of several g/m.sup.3 or less up to high-level ozone of several tens of g/m.sup.3 or greater.

(24) A Teflon®-based or lined material is preferably used as the external covering 21 in several modes of embodiment. In terms of the flow line for various normal gas flows, the external covering 21 normally handles a gas flow rate in the range of about 1-300 standard liters of gas/minute (slm) and has a required average lifespan of up to 24 months. The external covering 21 can preferably cope with an ozone temperature in the range of −80° C. to +100° C. The maximum inlet pressure to the external covering 21 at the inflow end 10a is normally in the range of about 0 psig to 3000 psig (20,700 kPa). For example, a cylindrical external covering 21 having a diameter in the range of about 3-12 inches (6-25 cm) and a length of 4-24 inches (8-60 cm) is preferred. The ozone must have a sufficient residence time within the adsorbent 25 in order to remove the metal contaminants down to a level below 100 ppt, so the dimensions of the external covering 21 are dependent on the flow rate and volume of ozone, the activity of the purified material, and the amount of impurity to be removed.

(25) FIG. 2A is a view in cross section showing the situation when the second removal section has been removed from the first removal section forming part of the gas purification filter unit, and FIG. 2B is a schematic view in cross section of the second removal section along the line A-A in FIG. 2A.

(26) The second removal section 12 which is accommodated in such a way as to be detachable from the post-stage side of the first removal section 11, i.e. the accommodation section 23 of the first removal section 11, comprises: a substantially cylindrical resin case 31 which is resistant to ozone corrosion; and a filtration material (area) 32 for straining solid fine particles, from the impurities contained in the ozone.

(27) The filtration material (area) 32 comprises a sheet-like filter material which should be folded into a flower-shaped or pleated form in order to increase the exposed surface area, and then accommodated inside the resin case 31. Furthermore, the resin case 31 comprises a material which is very resistant to corrosion by ozone which has strong oxidative power, e.g. a fluororesin. Particularly preferred fluororesins which may be cited include: tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polytetrafluoroethylene (PTFE) and perfluoroalkoxy fluororesin (PFA).

(28) One end of the second removal section 12, that is, the portion facing the mesh member 24 formed in the accommodation section 23 of the first removal section 11, constitutes an inflow side which receives as inflow ozone from which gas-component impurities have been removed by means of the first removal section 11. Furthermore, the other end thereof forms an outflow end 10b which allows an outflow of high-purity ozone gas from which solid fine particles have been strained by means of the second removal section 12, toward a semiconductor device production process or the like.

(29) Examples of the filtration material 32 for straining the solid fine-particle impurities which may be cited include a woven fabric, a nonwoven fabric, a molded article and a mesh. A woven fabric filter may be formed by weaving fibers, or it may be formed by intertwining fibers to produce twisted yarns which are then woven. In addition, particles which adsorb heavy metals that affect the semiconductor device production process are also preferably woven into the twisted yarns.

(30) A nonwoven fabric filter may be formed by using a known method to entwine fibers cut to a length of between several mm and several cm, for example. It is also possible to entwine multiple types of fibers. A molded-article filter may be obtained by using a known molding method to mold, into any form, fibers cut to a length of between several mm and several cm, for example. A mesh filter may be formed by knitting fibers into a mesh. It should be noted that particles which adsorb heavy metals that affect the semiconductor device production process are also preferably bonded to these fibers.

(31) The size between open portions of the fibers in the material used as the filtration material 32 affects the trapping performance, but the nominal pore size for this performance preferably ranges between 0.2 μm and 0.5 μm. If the nominal pore size of the filtration material 32 is less than 0.2 μm, the difference in pressure between the inflow side and the outflow side of the filtration material 32 is excessively large and there are concerns regarding ozone decomposition. On the other hand, if the nominal pore size of the filtration material 32 is larger than 0.5 μm, this risks affecting the likelihood of particles of heavy metals, which affect the semiconductor device production process, being strained.

(32) An example of a method for producing a porous PTFE film (filtration membrane) which can be suitably used as the filtration material 32 will be described below. As shown in FIG. 3, a non-porous edge film 51 made of a thermoplastic fluororesin is thermo-compression bonded using a heat roll heated to 200° C. or more on both edges 40b of a hydrophobic porous PTFE film 40, after which the assembly is sandwiched between support nets 52, 53 comprising a thermoplastic fluororesin forming fluid passages for supply liquid and filtrate. The support nets have the role of supporting the porous PTFE film which is very soft and sags easily.

(33) It should be noted that in this case the “thermoplastic fluororesin” is a thermoplastic fluororesin or the like selected from the following compounds which melt as a result of heating: tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer-hexafluoropropylene copolymer (EPE). When PTFE is used as the hydrophobic porous film and this is thermally bonded to a fluororesin member, it is necessary to use a thermoplastic fluororesin as the edge film. The edge film need not be used when a film other than PTFE is used as the hydrophobic porous resin film. A filtration material 32 which is suitable for the second removal section 12 can be obtained by means of the abovementioned process.

(34) The filtration material 32 comprising a laminated body having a structure such as that shown in FIG. 3 is alternately folded in opposite directions to form pleats, and both edges are placed one over the other and thermally bonded to form an endless structure which can be used in this mode of embodiment. As shown in FIG. 4, for example, the filtration material 32 is inserted between a porous outside sleeve 64 having pores 63 and a porous inside core 62 made of a thermoplastic fluororesin having pores 61, the upper and lower edges of the edge film and support nets are sealed by an end cap 65 made of a thermoplastic fluororesin, and a filter element (second removal section) 66 can be obtained as a result.

(35) As described above in detail, the gas purification filter unit 10 according to this mode of embodiment comprises a first removal section 11 for removing, from among impurities contained in ozone generated by means of an ozone generator, gas-component impurities, and a second removal section 12 which is disposed at a stage after the first removal section 11 and further removes impurities in the form of solid fine particles from the impurities from which the gas component has been removed; as a result it is possible to efficiently remove both gaseous impurities and impurities in the form of solid fine particles which are contained in ozone generated by an ozone generator.

(36) If the gas purification filter unit 10 having the structure described above is inserted as an in-line filter between an ozone generator and a semiconductor device production process, for example, it is possible to supply high-purity ozone with very few metal impurities to an ozone treatment process in the production of a semiconductor device and it is possible to reduce concerns around contamination of the semiconductor device with heavy metals etc.

Exemplary Embodiment

(37) The capacity for adsorbing metal components using the gas purification filter unit according to the present invention was measured in order to confirm the advantage of the present invention.

(38) In order to make the abovementioned confirmation, an apparatus configuration was adopted in which a filter unit was connected to a high-level ozone generator by way of a stainless steel pipe and metal components contained in outflow gas from the filter unit were measured.

(39) As an example of the present invention, use was made of the gas purification filter unit 10 shown in FIG. 1, which was provided with the first removal section 11 and second removal section 12, and the first removal section 11 was filled with silica gel as the adsorbent 25. The silica gel which was used was in the form of spheres having a diameter of 1-3 mm, the pore diameter was 1-10 nm, and the silica gel was preheated and dried.

(40) Meanwhile, as a comparative example, the first removal section 11 was excluded from the abovementioned gas purification filter unit 10 so that it comprised only the second removal section 12.

(41) The gas introduced was high-level ozone gas of several tens of g/m.sup.3 or greater, and stainless steel was used for the pipe. Fe, Cr and Mn were included as metal components in the stainless steel pipe which would be a source of contamination.

(42) Atomic absorption spectroscopy was used as the method for measuring the concentration of metal components. Outflow gases from the inventive example and the comparative example were released by bubbling into pure water and the resulting test solutions were compared, whereby the metal components (Fe, Cr, Mn) contained in the outflow gases of the inventive example and the comparative example were measured.

(43) The results of this confirmation are shown in table 1. It should be noted that the concentration on the gas supply side in the table denotes the metal concentration on the supply side of ozone gas generated by an ozone generator, in other words the metal concentration in ozone gas before passage through the stainless steel pipe.

(44) TABLE-US-00001 TABLE 1 Fe Cr Mn Inventive Example 0.03 0.01 0.03 Comparative Example 0.05 2.68 0.69 Concentration on gas supply side 0.01 0.18 0.04 (ppb)

(45) According to the results of the confirmation, the concentration of metal components in ozone gas that had passed through a gas purification filter unit employing silica gel as the adsorbent for the first removal section 11 showed that 99% or more Cr and 95% or more Mn had been removed, compared with the comparative example using only the second removal section 12 without the first removal section 11. It was confirmed that by using the gas purification filter unit according to the present invention which can remove Cr and Mn with high precision, it is possible to reliably prevent metal contamination even when ozone is used in a semiconductor device production process.

KEY TO SYMBOLS

(46) 10 . . . Gas purification filter unit, 11 . . . First removal section, 12 . . . Second removal section, 23 . . . Accommodation section, 25 . . . Adsorbent, 31 . . . Resin case, 32 . . . Filtration material.