JP4367724B2 - Dust-free air ionization apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dust-free air ionization apparatus and method for removing static electricity generated in a clean room by generating ions.
[0002]
[Prior art]
Conventionally, the generation of static electricity has been a problem in clean rooms of semiconductor or liquid crystal manufacturing. For example, in the case of a clean room for semiconductor manufacturing, the low humidity environment, the plastic container for transporting the wafer and the semiconductor element are easily charged, and the like cause the generation of static electricity. This static electricity causes dust to adhere to the wafer surface and destroys ICs and semiconductor elements on the wafer, thereby reducing the yield of products.
[0003]
Further, even in a production environment other than a clean room, various production failures are caused by adhesion of dust to products due to electrostatic charging, electrostatic breakdown due to electrostatic discharge, and electric shock, which is a problem.
[0004]
Therefore, conventionally, as a countermeasure for removing static electricity in such a production environment such as a clean room, an air ionizer that neutralizes the charge of a charged body with ions has been used. This air ionizer generates corona discharge by applying a positive or negative high voltage to a positive or negative needle-like electrode, respectively. Then, the air around the tip of the electrode is ionized into positive and negative, and the ions are conveyed by an air flow to neutralize the charge on the charged body with ions of opposite polarity.
[0005]
However, the air ionizer has a problem that a small amount of impurities contained in air such as in a clean room is deposited on the corona electrode, and these accumulated impurities are scattered again and generate dust. Therefore, in the air ionization apparatus, the periphery of the corona electrode is covered (sheathed) with a gas not containing impurities, thereby preventing impurities from being deposited on the tip of the corona electrode due to discharge energy. The gas used for the sheath is referred to as a sheath gas. As the sheath gas, high purity N ₂ gas used in a semiconductor factory or the like, air in a clean room, or the like is used.
[0006]
As an example of the type of air ionizer that covers the corona electrode with a gas or the like that does not contain impurities, FIG. 8 shows the configuration of the air ionizer described in Japanese Patent No. 1843114. In this apparatus, a fine particle deposition apparatus (ion generator 63) using a phenomenon in which a trace amount of impurities in air (mainly a substance containing Si element) is deposited on a corona electrode.
[0007]
That is, in the figure, a high-performance filter 52 of an air purifier is provided on the ceiling of a clean room 51, and an ion generator 53 is installed. A pair of positive and negative needle electrodes 54a and 54b are attached to the ion generator 53, and a corona discharge is generated by applying a positive and negative high voltage to these needle electrodes 54a and 54b. As a result, the air around the needle-shaped electrodes 54a and 54b is ionized, and the positive and negative ions 55 and 56 neutralize the charge on the charged body 57.
[0008]
On the other hand, an air supply path 58 is disposed inside the clean room 51 so that the air in the clean room 51 is sucked from the intake port 59 at one end by the air pump 60 and discharged from the supply port 61 at the other end. It is configured. The supply port 61 is disposed in the vicinity of the needle electrodes 54 a and 54 b of the ion generator 53.
[0009]
The air supply path 58 is provided with a membrane filter 62 and an ion generator 63 as a fine particle deposition device. The ion generator 63 is provided with a plurality of needle-like electrodes 64. When an alternating current or a direct current is passed from the power supply 65, the needle electrode 64 performs corona discharge. At this time, ultrafine particles of about 0.005 μm or less having a size of about 0.03 μm are generated by an electric suction force. Precipitate as fine particles. The fine particles re-scatter from the needle electrode 64. Further, the air that has passed through the ion generator 63 is sent to the membrane filter 62, and particulates are collected by the membrane filter 62. The air that has collected the particulates is discharged from the supply port 61 to the discharge electrode 54 a of the ion generator 53. , 54b.
[0010]
Since the air supplied in this manner has also removed ultrafine particles of about 0.005 μm or less by the ion generator 63 and the membrane filter 62, even if the ion generator 53 operates, the air remains on the needle-like electrode 54. Fine particles are not deposited.
[0011]
[Problems to be solved by the invention]
By the way, the above-mentioned conventional air ionization apparatus has the following problems. Conventionally, high purity N ₂ gas, which is frequently used in factories, has been used as a sheath gas for sheathing corona electrodes in semiconductor and liquid crystal manufacturing factories. However, there is a problem that this high purity N ₂ gas is expensive. In recent years, there is a demand for a dust-free air ionization apparatus in a factory where high-purity N ₂ gas is not used, or in a process in which oxygen deficiency is a concern due to the use of N ₂ gas in a semiconductor manufacturing process. Is growing.
[0012]
Further, in the air ionization apparatus as shown in FIG. 8, the ion generator 63, which is a fine particle deposition apparatus, uses the needle electrode 64 and the high-voltage power supply 65, and there is a problem that the apparatus is large and expensive. It was.
[0013]
The present invention has been proposed to solve the problems of the prior art as described above, and its purpose is to prevent dust generation from the ion generating electrode without using high-purity N ₂ gas, The object is to provide a compact and inexpensive dust-free air ionizer.
[0014]
[Means for Solving the Problems]
Conventionally, it was thought that the particles deposited on the corona electrode were coarsened because ultrafine particles contained in the air in the clean room were deposited on the corona electrode by electrostatic force. It has been found that a trace gas component in the air is formed into particles by the chemical reaction action of corona discharge and deposited on the corona electrode by electrostatic force. The trace gas component is mainly a gas containing Si element and is considered to be siloxane degassed from the silicon sealant.
[0015]
Thus, as a result of intensive studies on a method for efficiently removing trace gas components in the air in the clean room, the present inventors have completed the present invention.
[0016]
That is, the dust-free air ionization apparatus according to the first aspect of the present invention includes a corona electrode, an ion generator that generates positive or negative ions by corona discharge, and a gas adsorbent that removes a trace gas component in the air. Alternatively, it is characterized by comprising gas removing means comprising a gas separation membrane and sheath gas supply means for supplying air from which trace gas components have been removed by the gas removing means as sheath gas around the corona electrode.
[0017]
The invention according to claim 2 captures the invention according to claim 1 from the viewpoint of the method, and the trace gas component in the air is removed by a gas adsorbent or a gas separation membrane, and the trace gas component is removed. The air is supplied around the corona electrode as a sheath gas, and positive or negative ions are generated in the corona electrode by corona discharge.
[0018]
According to the first and second aspects of the present invention, a trace gas component such as siloxane contained in the air or compressed air in the clean room is removed, and the processed air is supplied as a sheath gas around the corona electrode. . For this reason, the corona electrode is covered with the sheath gas, and ions are generated in the sheath gas.
[0019]
As described above, since the trace gas component is removed from the sheath gas, the trace gas component is prevented from becoming particles and depositing on the corona electrode. Therefore, air in a clean room, compressed air, or the like can be used as the sheath gas without using expensive high-purity N ₂ gas as in the prior art. Therefore, the apparatus or method according to the present invention can be used even in a factory that does not use high-purity N ₂ gas or in a process that may be deficient in oxygen. Further, since it is not necessary to provide an ionization apparatus as a fine particle precipitation apparatus as in the prior art, an inexpensive apparatus can be provided with a simple configuration.
[0020]
In addition, by configuring the gas removal means with a gas adsorbent or a gas separation membrane, a simple structure and easy maintenance can be achieved, and a small and inexpensive apparatus can be obtained.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.
[0022]
[1. Constitution]
FIG. 1 is a schematic configuration diagram showing an air ionization apparatus according to an embodiment of the present invention. In the figure, a ULPA filter 1 that is a high-performance filter for sending clean air and an ion generator 2 are installed on the ceiling of the clean room. The ion generator 2 is provided with positive and negative corona electrodes 3a and 3b, similarly to the ion generator 53 shown in FIG. DC pulse power supplies 4a and 4b are connected to the corona electrodes 3a and 3b, respectively.
[0023]
In addition, the ion generator 2 is provided with sheath gas nozzles 5a and 5b downward, and the corona electrodes 3a and 3b are disposed in the sheath gas nozzles 5a and 5b. The sheath gas nozzles 5 a and 5 b are supplied with a sheath gas from a sheath gas supply unit 7 via a valve 6.
[0024]
On the other hand, the sheath gas supply unit 7 is provided with an air pump 8 and is configured to take in air in the clean room by a blowing force. When compressed air is used instead of the air in the clean room, the pressure is reduced to a constant pressure by the pressure reducing valve 9 and is taken in.
[0025]
A gas adsorbing material 10 carrying activated carbon or an oxidation catalyst is removed by adsorbing a trace gas component in the air. Reference numeral 11 denotes a valve, and reference numeral 12 denotes a flow meter. The flow rate of air in the sheath gas supply unit 7 is adjusted by these. A membrane filter 13 collects dust in the air supplied as a sheath gas.
[0026]
[2. Effect]
Next, the effect of this Embodiment which has the structure mentioned above is demonstrated. That is, in the sheath gas supply unit 7, the air in the clean room is taken in by the air pump 8, or the compressed air is taken in by being reduced to a constant pressure by the pressure reducing valve 9. The taken-in air passes through the gas adsorbent 10 to remove trace gas components. Thereafter, dust is collected by passing through the membrane filter 13.
[0027]
In this way, the air from which the trace gas component has been removed in the sheath gas supply unit 7, that is, the sheath gas, is supplied to the vicinity of the corona electrodes 3 a and 3 b via the valve 6. On the other hand, when a high voltage is applied to the corona electrodes 3a and 3b by the positive and negative DC pulse power supplies 4a and 4b, corona discharge is generated. As a result, in the sheath gas nozzles 5a and 5b, the air around the corona electrodes 3a and 3b is ionized positively and negatively, respectively. The positive ions 14 and the negative ions 15 are carried out of the sheath gas nozzles 5a and 5b by the sheath gas, and are conveyed below the clean room by vertical one-way rectification from the ULPA filter 1.
[0028]
As described above, according to the present embodiment, the following effects can be obtained. That is, in order to remove trace gas components in the air in the clean room or compressed air by the gas adsorbent 10 and supply the processed air around the corona electrodes 3a and 3b, and generate ions in this air, A trace gas component in the air is not particulated and deposited on the corona electrodes 3a and 3b. For this reason, the air in the clean room can be used as the sheath gas without using high-purity N ₂ gas. Further, since it is configured to remove a trace gas component by the gas adsorbent, the structure is simple and easy to maintain, and it is small and inexpensive compared to a fine particle deposition apparatus such as the ion generator 63 shown in FIG. Device.
[0029]
[3. Experiments for measuring siloxane removal efficiency using gas adsorbents]
Here, FIGS. 2 to 4 show a measurement experiment of the removal performance of siloxane (cyclic low-molecular siloxane) with a gas adsorbent. FIG. 2 is a schematic diagram of an experimental apparatus for this measurement experiment.
[0030]
In FIG. 2, the adsorbent 21 has a configuration in which a Cu—Mn oxidation catalyst is supported by a ceramic support and is formed in a honeycomb shape (for example, AKHLLLE manufactured by Kobe Steel). This adsorbent 21 is ₂₀ to 65% by weight of Al ₂ O ₃ , 5 to 55% by weight of SiO ₂ , 5 to 50% by weight of manganese oxide in terms of MnO, and copper oxide in terms of CuO. A material containing 2 to 50% by weight is supported on a ceramic support.
[0031]
In this experiment, a silicon sealant is introduced into the desiccator 22 to generate siloxane. The generated siloxane was transported to the adsorbent 21 supported by the holder 34 together with the transport air of 3.1 liter / min supplied by the air pump 23, and the siloxane was removed. At this time, the carrier air is sampled at a flow rate of 0.1 liter / min by the collection pipes 24 and 25, the air pumps 26 and 27 and the flow meters 28 and 29 filled with Tenax-GR before and after the adsorbent 21, Microanalysis of siloxane was performed using a chromatographic method. Reference numerals 30, 31, and 32 are valves, and 33 is a flow meter.
[0032]
FIG. 3 shows the structures of three types of cyclic low-molecular siloxanes (D3, D4, D5) to be analyzed in a trace amount. FIG. 4 shows the results measured as described above. That is, as shown in the table of FIG. 4, siloxane removal efficiency was determined from the total amount of each siloxane sampled at the inlet of the adsorbent 21 and the total amount of each siloxane sampled at the outlet of the adsorbent 21. . As shown in this table, it is understood that any siloxane is removed by the adsorbent 21 with an efficiency of 90% or more.
[0033]
[4. Other Embodiments]
In addition, this invention is not limited to embodiment mentioned above, The various aspects as shown below are also possible. That is, the specific shape of each member, the mounting position, and the method can be changed as appropriate. For example, the means for removing trace gas components in the air is not limited to the gas adsorbent, and a gas separation membrane may be used.
[0034]
Here, FIGS. 5 to 7 show a measurement experiment of the removal performance of siloxane (cyclic low molecular siloxane) by the gas separation membrane. FIG. 5 is a schematic diagram of an experimental apparatus for this measurement experiment.
[0035]
In FIG. 5, the gas separation membrane module 41 is comprised from the polyimide hollow fiber membrane (thin tube-like membrane) (for example, gas separation membrane module NM-B05 made from Ube Industries). This membrane selectively permeates only oxygen O ₂ , nitrogen N _2, and water vapor, and separates trace impurity gases such as siloxane. FIG. 6 conceptually shows a state in which siloxane Si (this symbol typically represents siloxane molecules) is removed by the tube-shaped gas separation membrane 41a. That is, when air containing siloxane molecules is supplied from the inlet A of the tubular gas separation membrane 41a, oxygen molecules O ₂ and nitrogen molecules N ₂ pass through the gas separation membrane 41a (outlet B side), but siloxane The trace impurity gas such as is passed through the gas separation membrane 41a without passing through it, and is discharged from the outlet C. Thereby, trace impurity gas such as siloxane is removed from the air.
[0036]
In this experiment, as shown in FIG. 5, 20.1 liter / min of compressed air was supplied to the inlet A of the gas separation membrane module 41 through the compressor 42, the air dryer 43 and the membrane filter 44. Then, between the inlet A and the outlet B of the separation membrane module 41, the collecting pipe 45 and the flow meter 46, or the collecting pipe 47, the air pump 48 and the flow meter 49, respectively, at a flow rate of 0.1 liter / min ( Compressed) air was sampled and siloxane microanalysis was performed using gas chromatography. 50 and 51 are flow meters, and 52 is a valve.
[0037]
FIG. 7 shows the results measured as described above. As shown in this table, it can be seen that each siloxane is removed by the gas separation membrane 41 with an efficiency of 70 to 90% or more. That is, it was found that siloxane can be removed with high efficiency even when the gas separation membrane 41 is used.
[0038]
【The invention's effect】
As described above, according to the present invention, the trace gas component contained in the air is removed, and the treated air is supplied as the sheath gas around the corona electrode. It is no longer formed into particles by the chemical reaction action and deposited on the corona electrode. Therefore, air in a clean room, compressed air, or the like can be used as the sheath gas without using expensive high-purity N ₂ gas as in the prior art. Therefore, the air ionizer can be used even in a factory that does not use high-purity N ₂ gas or in a process that may be deficient in oxygen. Moreover, since it is not necessary to provide an ion generator as a fine particle precipitation apparatus as in the prior art, an inexpensive apparatus with a simple configuration can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of a dust-free air ionization apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic diagram showing the configuration of an experimental apparatus that measures the removal performance of a trace gas component by a gas adsorbent.
FIG. 3 is a diagram showing the structure of a cyclic molecular siloxane that is microanalyzed in the experimental apparatus shown in FIG.
4 is a chart showing measurement results obtained by the experimental apparatus shown in FIG.
FIG. 5 is a schematic diagram showing the configuration of an experimental apparatus that measures the removal performance of a trace gas component by a gas separation membrane.
FIG. 6 is a conceptual diagram illustrating how siloxane is removed by a gas separation membrane.
7 is a chart showing measurement results obtained by the experimental apparatus shown in FIG.
FIG. 8 is a schematic view showing a configuration of a conventional dust-free air ionization apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... ULPA filter 2 ... Ion generator 3a, 3b ... Corona electrode 4a, 4b ... DC pulse power supply 5a, 5b ... Sheath gas nozzle 7 ... Sheath gas supply part 8 ... Air pump 9 ... Pressure reducing valve 10 ... Gas adsorbent 13 ... Membrane filter 14 ... positive ions 15 ... negative ions

Claims (2)

An ion generator that includes a corona electrode and generates positive or negative ions by corona discharge;
A gas removal means comprising a gas adsorbent or a gas separation membrane for removing trace gas components in the air;
A dust-free air ionization apparatus comprising: a sheath gas supply unit configured to supply air, from which trace gas components have been removed by the gas removal unit, to the periphery of the corona electrode as a sheath gas. A trace gas component in the air is removed by a gas adsorbent or a gas separation membrane, and the air from which the trace gas component has been removed is supplied around the corona electrode as a sheath gas, and positive or negative to the corona electrode by corona discharge. A dustless air ionization method characterized by generating ions.

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