JP2001189199A - Ion generator and charge removal equipment - Google Patents

Abstract

(57) [Problem] To provide an ion generator and a charge removal device capable of suppressing deterioration of a discharge electrode and suppressing generation of noise and ozone. SOLUTION: A needle-shaped discharge electrode 12 and a conductive counter electrode 13 are provided, and an AC high voltage is applied to the discharge electrode 12 to ionize air around the discharge electrode 12 by corona discharge. At least the tip 12 ″ of the discharge electrode 12 is made of silicon single crystal, and the shortest distance L between the tip 12 ″ of the discharge electrode 12 and the counter electrode 13.
Is 0.4 cm or more and 4 cm or less, the effective value V of the AC high voltage applied to the discharge electrode 12 is 8 kV or less, and 1.8 L (cm) +0.5 <V (kV) <2.8 L ( c
m) +1.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion generator for ionizing air by corona discharge, and further relates to a charge removing facility using the ion generator.

[0002]

2. Description of the Related Art For example, in a clean space such as a clean room used for manufacturing semiconductors, the degree of cleanliness of operators, robots, various types of manufacturing equipment and the like is class 100.
Level (the particle size contained in the space per 1 ft ³ is 0.
The cleanliness of particles having a particle size of 5 μm or more is 100 or less). However, class 1 (0.5μ
m standard) atmosphere, for example, 1 Gbit DRA
Estimating the number of particles of 0.06 μm or more corresponding to １ ／ of the minimum dimension of M on an 8-inch wafer is 1 to 2 / hr in a state where the wafer is not charged. 20 to 30 pieces /
hr. Therefore, in the recent gigabit era, especially in semiconductors and LCDs (Liquid Crystals).
tal Display), HDD (Hard Dis
2. Description of the Related Art In a clean room or the like for manufacturing k Drive) or the like, as one of measures for preventing the adhesion of fine particles on a product surface, removal of a charge on a product and its periphery is performed.

Conventionally, an ion generator for ionizing air by corona discharge has been used for the purpose of such charge removal, as disclosed, for example, in Japanese Patent Publication No. 2541857 by the present inventors. The positive and negative air ions generated by the various ion generators are supplied to products such as semiconductors to remove the charge. As disclosed in Japanese Patent No. 2541857, there are known ion generation methods including a method of applying a Pulsed-DC voltage to a discharge electrode, a method of applying a DC voltage, and a method of applying an AC voltage. I have.

On the other hand, in an ion generator utilizing corona discharge, metal particles are generated from the discharge electrode due to surface oxidation and sputtering phenomenon during corona discharge, causing metal contamination. Therefore, in the above-mentioned Patent Publication No. 2541857,
By covering the discharge electrode with quartz glass, such dust generation is prevented. Also, by constructing the discharge electrode itself with polycrystalline silicon of the same component as the semiconductor material,
There is also known a method for preventing chemical contamination even if the discharge electrode is deteriorated and scattered.

[0005]

However, when the discharge electrode is covered with quartz glass, the applied voltage needs to be 8 kV or more, and electromagnetic radiation noise is generated. In particular, electronic devices and electronic systems that have been highly integrated in recent years are vulnerable to external electromagnetic radiation noise, and the generated electromagnetic radiation noise causes electromagnetic noise disturbances such as electrostatic breakdown of electronic devices, deterioration of characteristics, and malfunction of electronic systems. . In addition, when the voltage applied to the discharge electrode increases, a problem such as generation of ozone also occurs. Ozone is not suitable for manufacturing semiconductors such as HDDs and LCDs because of its high reactivity.

On the other hand, when the discharge electrode itself is made of polycrystalline silicon, the discharge electrode deteriorates violently due to grain boundary sliding or grain boundary cracks occurring along crystal grain boundaries, causing dust generation.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ion generator and a charge removing device capable of suppressing deterioration of a discharge electrode and suppressing generation of electromagnetic radiation noise and ozone.

[0008]

In order to achieve this object, a first aspect of the present invention comprises a needle-shaped discharge electrode and a conductive counter electrode, and a high AC voltage is applied to the discharge electrode to perform corona discharge. An ion generator for ionizing the air around the discharge electrode by using a silicon single crystal at least at the tip of the discharge electrode, and the shortest distance L between the tip of the discharge electrode and the counter electrode is 0.4c.
m to 4 cm, the effective value V of the AC high voltage applied to the discharge electrode is 8 kV or less, and 1.8 L (c
m) +0.5 <V (kV) <2.8 L (cm) +1.0
It is characterized by being.

In the ion generator according to the first aspect,
The needle-shaped discharge electrode is made of a material such as a conductive metal, and has, for example, a needle-like shape in which a tip portion of a cylindrical discharge electrode is formed in a tapered conical shape.
The tip of the discharge electrode is a vertex of the needle-shaped discharge electrode. When the tip of the discharge electrode is formed in a conical shape, the tip of the discharge electrode is a vertex of a cone shape. Since corona discharge occurs at the tip of the needle-shaped discharge electrode, at least the tip of the discharge electrode is made of silicon single crystal. Single crystal silicon has a diamond structure in which silicon is covalently bonded and regularly arranged in a regular manner, and has extremely high hardness, toughness, and excellent mechanical strength as compared with amorphous silicon or polycrystalline silicon. For this reason, single-crystal silicon generates much less dust than amorphous silicon or polycrystalline silicon. The counter electrode has, for example, a configuration in which a hole having a circular or square shape is formed in a conductive metal plate or the like.
Further, the counter electrode may have a configuration such as a line, a grid, or a ring made of a conductive material.

The shortest distance L between the tip of the discharge electrode and the counter electrode is 0.
4 cm or more and 4 cm or less. When an AC voltage is applied to the discharge electrode to generate corona discharge, if the applied voltage to the discharge electrode is constant, the shorter the shortest distance L between the tip of the discharge electrode and the counter electrode, the greater the intensity of the corona discharge. . Shortest distance L
If it exceeds 4 cm, corona discharge of sufficient strength will not occur. On the other hand, when the shortest distance L is smaller than 0.4 cm, most of the air ions generated by the corona discharge at the tip of the discharge electrode become the counter electrode due to the action of the electric field formed between the tip of the discharge electrode and the counter electrode. It will be absorbed, making it impossible to carry it out by airflow. Minimum distance L is 0.4cm or more 4
cm or less, the amount of ions that can be carried out by an air current also increases, and charge removal of the charged body becomes possible.

The effective value V of the AC high voltage applied to the discharge electrode
Is 8 kV or less, and 1.8 L (cm) +0.5 <V (k
V) <2.8 L (cm) +1.0. The effective value V of the AC high voltage applied to the discharge electrode is 1.8 L (cm) +0.
If it is smaller than 5, no corona discharge occurs. on the other hand,
The effective value V (kV) of the AC voltage applied to the discharge electrode is 2.8.
If the value exceeds L (cm) +1.0, the strength of the corona discharge is too large, and the tip of the discharge electrode deteriorates due to surface oxidation caused by a small amount of ozone generated during the corona discharge and sputtering caused by air ions. And generate dust. If the effective value V (kV) of the AC high voltage is in the range of V <2.8 L + 1.0 and is 8 kV or less, ozone generation is almost 1
It can be suppressed to 0 volppb or less.

In the ion generator according to the first aspect,
As described in claim 2, the frequency of the AC high voltage is 20
It is preferable that the frequency be equal to or higher than 100 kHz. 10
At frequencies above 0 kHz, positive and negative ions combine.
The degree of neutralization and extinction is remarkable, and the charge elimination time of the charged material is much longer than that of 100 kHz or less. On the other hand, if the frequency is too low, the ratio of positive and negative ion bonds will decrease, but large clusters of positive and negative ions will alternately reach the charged surface. 20Hz
At frequencies below, even after the charged surface has been neutralized, its surface potential alternates between positive and negative tens of volts each time positive and negative ions arrive. Recent LSI, LCD,
Since the HDD may be destroyed by the fluctuation of the surface potential of several tens of volts, the frequency lower than 20 Hz may lower the product yield.

[0013] As described in the third aspect, the radius of curvature of the tip of the discharge electrode is preferably 0.1 mm to 0.4 mm. If the radius of curvature at the tip of the discharge electrode is smaller than 0.1 mm, the tip of the discharge electrode is significantly deteriorated and dusted. On the other hand, if the radius of curvature of the tip of the discharge electrode is larger than 0.4 mm, the deterioration of the tip of the discharge electrode is suppressed, but corona discharge itself is less likely to occur, and there is a concern that the function as an ion generator may be poor.

According to a fourth aspect, the ion generator according to the first or second aspect is arranged in a flow of clean air having a flow velocity of 0.2 m / s or more and 1.0 m / s or less, and the discharge electrode is provided. There is provided a static elimination device, wherein a plurality of the devices are arranged with a two-dimensional spread in a direction crossing the flow of the clean air.

According to a fifth aspect of the present invention, at least a tip of the discharge electrode of the ion generator according to the first or second aspect has a flow rate of 10 or less.
The present invention provides a static elimination facility characterized in that it is configured to supply a stream of clean air of m / s or more.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of an ion generator 1 according to an embodiment of the present invention, FIG. 2 is a plan view of an ion generator 10 of the ion generator 1, and FIG.
FIG. 2 is an enlarged cross-sectional view taken along line AA in FIG. 1.

In the ion generator 10 of the ion generator 1, a plurality of needle-shaped discharge electrodes 12 are attached to both sides of a rod-shaped electrode support member 11 at predetermined intervals. In the illustrated example, the discharge electrodes 12 are arranged on both side surfaces of the electrode support member 11 so as to project vertically. Each discharge electrode 12 has a cylindrical shape, and a tip portion 12 'is formed in a tapered conical shape. The discharge electrode 12 is made of a material such as a conductive metal, and at least the tip 12 ″ of the discharge electrode 12 (the apex of the tip portion 12 ′ formed in a conical shape).
Is made of silicon single crystal. The discharge electrode 12
May be made of silicon single crystal, but in order to make the discharge electrode 12 easy,
The tip portion 12 'of the discharge electrode 12 can be entirely made of silicon single crystal, or the discharge electrode 12 can be entirely made of silicon single crystal.

Here, FIGS. 4A to 4C show discharge electrodes 1.
It is an enlarged view of the shape of 2 front-end | tip parts 12 '. FIG. 4 (a)
Is an example in which the tip 12 ″ of the tapered surface 120 formed in a conical shape is formed into a spherical surface. The tip 12 of the discharge electrode 12 shown in FIG. In the shape of ', the tapered surface 121 is constituted by a two-step inclined surface composed of a gentle inclined surface 122 near the tip 12 "and a steep inclined surface 123 away from the tip 12". 12 "is configured as a spherical surface. FIG.
The shape of the distal end portion 12 'of the discharge electrode 12 shown in (c) is such that the tapered surface 125 is
6 and a steeply inclined surface 127 on the side away from the tip 12 ″, and an intermediate inclined surface 128 between the gentlely inclined surface 126 and the steeply inclined surface 127. "Is a spherical surface. In either case,
Curvature radius R of tip 12 "of discharge electrode 12 formed in a spherical surface
Is set in the range of 0.1 mm to 0.4 mm.
The tip 12 "of the discharge electrode 12 has four or more inclined surfaces,
It may be constituted by a curved surface whose inclination angle changes continuously.

The method of manufacturing the discharge electrode 12 and the tip portion 12 'of the discharge electrode 12 is arbitrary. However, when the entire discharge electrode 12 and the whole tip portion 12' of the discharge electrode 12 are made of single crystal silicon, For example, an appropriate silicon single crystal piece is cut out from a silicon single crystal ingot or a wafer, and the silicon single crystal piece is formed into a discharge electrode 1 having a predetermined shape using a lathe or the like.
2 or, similarly, a method of manufacturing the tip portion 12 ′ of the discharge electrode 12. In addition, the discharge electrode 12
Is formed of silicon single crystal, the portion other than the tip portion 12 '(the portion other than the tip portion 12' of the discharge electrode 12) does not necessarily need to be formed of silicon single crystal. A portion other than the tip portion 12 'may be formed by a conductive member. In this case, for example, in a tube-shaped holder made of ceramics or plastic, a conductive member such as tungsten and a tip portion 12 'made of silicon single crystal processed into a predetermined shape are connected via a conductive coil spring or the like. An example of such a configuration is shown in FIG.

Further, as shown in FIG.
A plate-like counter electrode 13 is arranged at a position away from the front and rear sides. By providing the plate-shaped counter electrodes 13 on both front and rear sides of the electrode support member 11 as described above, the upper and lower surfaces of the ion generator 10 are open. The counter electrodes 13 are supported by insulating support members 14 provided at both ends of the electrode support member 11, so that both sides of the electrode support member 11 are parallel to the electrode support member 11 and are parallel to the electrode support member 11. 11 is provided in an insulated state. The counter electrode 13 is made of a material such as a conductive metal. The counter electrode 13 is provided with a plurality of circular holes 15 at predetermined intervals. The holes 15 corresponding to the discharge electrodes 12 are formed in the counter electrode 13 such that the centers of the holes 15 coincide with the central axes of the discharge electrodes 12.

The tip 12 "of the discharge electrode 12 and the counter electrode 1
The shortest distance L with respect to 3 is set to 0.4 cm or more and 4 cm or less. In the illustrated example, the tip 12 ″ of each discharge electrode 12
And the shortest distance L indicated by the distance from the inner peripheral surface of the circular hole 15 formed in the counter electrode 13 is set to 0.4 cm or more and 4 cm or less.

The ion generator 10 is supplied with a predetermined voltage from a power supply 20. Power supply unit 20
Is a controller 23 for adjusting the frequency of the AC voltage supplied from the power supply via the plug 21 and the cable 22.
And a DC transformer 25 which extracts a part of the AC voltage supplied from the cable 22, transforms the AC voltage into a desired DC voltage, and supplies power to each counter electrode 13 via the DC-side cable 24.
And an AC transformer 27 that transforms the AC voltage supplied from the cable 22 into a desired AC voltage and supplies power to each discharge electrode 12 via the AC-side cable 26.

The controller 23 is set so as to adjust the frequency of the AC voltage supplied from the power supply to 20 Hz or more and 100 kHz or less. And AC transformer 27
, An effective value V for each discharge electrode 12 is obtained.
Is set to apply an AC high voltage having a frequency of 20 kHz or more and 100 kHz or less. Also,
Relationship between the shortest distance L between the tip 12 "of the discharge electrode 12 and the counter electrode 13 (that is, the distance between the tip 12" of each discharge electrode 12 and the inner peripheral surface of the circular hole 15 formed in the counter electrode 13). But, 1.
8L (cm) +0.5 <V (kV) <2.8L (cm)
It is set to be +1.0.

The DC transformer 25 is set to apply a DC voltage of, for example, about several hundred volts to each counter electrode 13, and generates positive and negative ions generated by corona discharge near each discharge electrode 12. The ratio can be changed freely.

The ion generator 1 configured as described above
As shown in FIG. 1, the ion generator 10 is disposed in a flow of clean air. In this case, the flow velocity of the flow of the clean air is preferably 0.2 m / s or more and 1.0 m / s or less. As shown in FIG. 1, by disposing the clean air flow through the open upper and lower surfaces of the ion generator 10, the discharge electrodes 12 disposed on both side surfaces of the electrode support member 11 and the discharge electrodes 12. It is configured such that clean air flows along the surface of the counter electrode 13.

FIG. 5 is a schematic explanatory view of the charge removing equipment 2 according to the first embodiment of the present invention, which is configured by using the ion generator 1. As shown in FIG. The clean air, which has passed through the high-performance filter 40 disposed above and has been cleaned, is 0.2 m
It is supplied downward at a flow rate of not less than 1.0 m / s and not more than 1.0 m / s in the figure. In the illustrated example, the high-performance filter 4
Below 0, the ion generators 10 of the ion generator 1 described above are arranged at two places (however, the power supply unit 20 is omitted in FIG. 5). High-performance filter 40
For example, a filter capable of collecting submicron particles with a removal performance of 99.7% or more with respect to 0.3 μm particles is used.
(High Efficiency Particul
ateAir) filter and ULPA (Ultra Lo)
w PenetrationAir) filter.

The two ion generators 10 are arranged in parallel at the same height. As in the case described above with reference to FIG. 1, the two ion generators 10 are arranged so that the flow of clean air can flow through the upper and lower surfaces of the ion generator 10, so that the two ion generators 10 are provided. Each of the discharge electrodes 12 has the same height, and the discharge electrodes 12 are arranged with a two-dimensional spread in a direction crossing the flow of the clean air supplied through the high-performance filter 40. I have.

High-performance filter 40 and ion generator 10
A work table 41 is disposed below the work table. On the upper surface of the work table 41, a product 42 such as a semiconductor or an HDD head is placed. Note that FIG. 5 is a schematic diagram, and does not correctly show the size of the charge removal equipment 2 and the work table 41 and the intervals between them.

Now, in the static electricity removal equipment 2 configured as described above, clean air is passed through the high-performance filter 40,
The air is supplied downward at a flow rate of 0.2 m / s or more and 1.0 m / s or less, and clean air flows through the ion generating unit 10 through the open upper and lower surfaces of the ion generating unit 10. Then, the discharge electrode 1 is supplied by the power supply unit 20 (not shown in FIG. 5).
An AC high voltage having an effective value V of 8 kV or less and a frequency of 20 Hz or more and 100 kHz or less is applied to
For example, a DC voltage of about several hundred volts is applied.
As a result, when flowing through the ion generator 10, the clean air flowing along the surfaces of the discharge electrode 12 and the counter electrode 13 is ionized by corona discharge near the tip 12 ″ of the discharge electrode 12. The positive and negative air ions flow further downward due to the flow of the clean air, and are supplied to the upper surface of the work table 41 arranged below.

Therefore, according to the charge removing device 2 configured as described above, the charge of the product 42 such as a semiconductor or an HDD head placed on the upper surface of the work table 41 is supplied in a flow of clean air. It can be removed by the positive and negative air ions.

Next, FIG. 6 is a sectional view of the charge removing equipment 3 for explaining the charge removing equipment 3 according to the second embodiment of the present invention. In this embodiment, a plurality of cylindrical guide walls 31 are provided at predetermined intervals on the lower surface of a casing 30 made of a hard vinyl chloride material, and the lower ends of the respective guide walls 31 are open. Further, a clean air introduction hole 32 is formed on a side surface of the casing 30. Except for the lower end of the guide wall 31 and the introduction hole 32, the casing 30
Is sealed so that clean air introduced into the casing 30 from the introduction hole 32 is ejected downward from the guide wall 31.

The support member 3 is provided on the inner upper surface of the casing 30.
The support member 33 is provided with a plurality of needle-like discharge electrodes 34 at predetermined intervals. In the illustrated example, the discharge electrode 34 is disposed so as to project vertically downward from the lower surface of the support member 33, and the central axis of each cylindrical guide wall 31 and the central axis of each discharge electrode 34 coincide with each other. ing. Thereby, the guide wall 31 is introduced into the casing 30 from the introduction hole 32 as described above.
The clean air spouting downward from the discharge electrodes 34
It flows along the surface of the. Then, by adjusting the flow rate of the clean air introduced into the casing 30 from the introduction hole 32, a setting is made such that the clean air flow having a flow velocity of 10 m / s or more is supplied to at least the tip 34 ″ of the discharge electrode 34. Each discharge electrode 34 has a columnar shape, and a tip portion 34 'of each discharge electrode 34 is formed in a tapered conical shape, similarly to the ion generator 1 described above with reference to FIG. The discharge electrode 34 is made of a material such as a conductive metal.
4 ″ (the apex of the tip portion 34 ′ formed in a conical shape) is made of silicon single crystal. Further, as in the case described above with reference to FIG. The radius of curvature of the tip 34 "is 0.1 mm to 0.1 mm.
It is set in a range of 4 mm.

A ring-shaped counter electrode 35 is disposed outside the guide wall 31. Each counter electrode 35 is arranged such that the center thereof coincides with the central axis of each discharge electrode 34. Although not shown, the effective value V is applied to each discharge electrode 34 as in the ion generator 1 described above with reference to FIG.
By applying an AC high voltage having a frequency of 20 kHz or more and 100 kHz or less and applying a DC voltage of, for example, about several hundred volts to each counter electrode 35, thereby generating corona discharge in the vicinity of each discharge electrode 34. It is configured so that the positive and negative ion generation ratio can be freely changed.

The shortest distance L between the tip 34 "of each discharge electrode 34 and each counter electrode 35 is set to 0.4 cm or more and 4 cm or less. In the illustrated example, the tip 34" of each discharge electrode 34 is
The shortest distance L indicated by the distance from the ring-shaped counter electrode 35 is set to 0.4 cm or more and 4 cm or less. The relationship between the effective value V of the AC high voltage applied to each discharge electrode 34 and the shortest distance L is 1.8 L (cm) +0.5 <
It is set so that V (kV) <2.8 L (cm) +1.0.

A work table 3 is provided below the casing 30.
6 are arranged. On the upper surface of the work table 36, a product 37 such as a semiconductor or an HDD head is placed. FIG. 6 is a schematic diagram, and does not correctly show the size of the charge removal equipment 3 or the work table 36, the interval between them, and the like.

Now, in the charge removing equipment 3 configured as described above, the casing 3 is inserted through the introduction hole 32 as described above.
By supplying clean air with a blower into 0,
Flow velocity 10 m at least at tip 34 ″ of discharge electrode 34
/ S or more is formed, and is blown downward from the guide wall 31 by forming an air flow of the clean air. Then, an effective value V is set to 8 k for each discharge electrode 34 by a power supply unit (not shown).
An AC high voltage having a frequency of not more than V and a frequency of not less than 20 Hz and not more than 100 kHz is applied, and a DC voltage of, for example, about several hundred volts is applied to each counter electrode 35. As a result, the clean air flowing along the surface of the discharge electrode 34
It is ionized by corona discharge in the vicinity of 4 ".
The positive and negative air ions generated in this manner flow downward from the guide wall 31 by the flow of the clean air, and are supplied to the upper surface of the worktable 36 disposed below.

Accordingly, the charge of the product 37 placed on the upper surface of the work table 36 is similarly transferred to the positive and negative charges supplied on the flow of clean air by the charge removing device 3 configured as described above. It can be removed by air ions.
In addition, according to the charge removing device 3 of this embodiment, it is possible to prevent the fine particles generated by the gas-particle conversion from adhering and accumulating on the discharge electrode 34, and the particles adhering and accumulating on the discharge electrode 34 are desorbed. There is a feature that the problem that the product 37 is contaminated can be solved. In the case of the charge removing device 3 of the present embodiment, it is desirable that the clean air supplied into the casing 30 be air that does not change the humidity of the clean room.

In the above embodiment, the vertical flow type clean room has been described as an example. However, the present invention is also applied to a facility for blowing clean air from a horizontal or oblique direction to an object to be neutralized. It is possible. FIG.
Is installed at a clean air outlet (0.2 m / s to 1.0 m / s) of a HEPA / ULPA filter in a clean room, a clean bench, or a clean booth to remove static electricity from the entire surrounding environment including products. It is suitably used in such cases. On the other hand, the charge removal equipment 3 of FIG.
When the surface potential of a wafer or glass that is installed above the cleaning tank and pulled up from ultrapure water is instantaneously attenuated by ionized air that blows out from the nozzle, or an air current that contains air ions blows out from the nozzle to cover the entire surface of the large liquid crystal substrate It is suitable for use in a case where the charge is spread uniformly so as to completely cover the entire substrate in a short time without unevenness.

[0039]

EXAMPLE Next, the operation and effect of the present invention were confirmed by an example. First, Table 1 compares the dust generation characteristics from the tip of the discharge electrode when the tip of the discharge electrode is composed of single crystal silicon, polycrystalline silicon, and tungsten. In the ion generator 1 described with reference to FIGS. 1 to 3, a CNC (condensed nucleus particle measuring device) is provided below the ion generator 10.
The number concentration of particles having a size of 0.05 μm or more was measured by the CNC 30. The shortest distance L between the tip of the discharge electrode and the counter electrode was set to 2.5 cm. The curvature of the tip of each discharge electrode is 0.2 mm. Effective value V is 6k for each discharge electrode
V, an AC high voltage having a frequency of 50 Hz was applied. The airflow velocity of the clean air represented by the white arrow in FIG.
The distance from the discharge electrode to the entrance of the sampling tube of the CNC 30 was 3 mm / s, and the distance was 400 mm. The tip of the discharge electrode was observed with an electron microscope, and the range of surface roughness due to oxidation and sputtering was also shown. The range of the surface roughness is defined as the size of the region where the surface roughness is measured measured from the tip of the discharge electrode. The discharge electrode made of single-crystal silicon has extremely little dust generation and surface roughness as compared with discharge electrodes made of other two kinds of materials.

[0040]

[Table 1]

FIG. 7 shows the shortest distance L between the discharge electrode tip 12 ″ made of single crystal silicon and the counter electrode 15 (that is, each discharge electrode tip 12 ″ and the inner peripheral surface of the circular hole 15 formed in the counter electrode 13). 4 is a graph showing a correlation between the distance between the ion generating section 10 and a positive or negative ion concentration measured below the ion generating section 10. The ion concentration was measured by changing the CNC 30 in FIG. 1 to an ion concentration meter. The curvature of the tip of each discharge electrode is 0.2 mm.
According to the shortest distance L (cm) between the discharge electrode tip 12 ″ and the inner peripheral surface of the circular hole 15 formed in the counter electrode 13, the effective value V ₀ of the corona discharge starting voltage (V ₀ = 1.8 L + 0. 5 (k
V)) of 1.1 times the effective value V (V = 1.1V ₀ (k
V)) AC voltage of 50 Hz was applied to the discharge electrode 12.
A direct current voltage of -10 V to -250 V was applied to the counter electrode 13 so that the positive and negative ion concentrations were balanced. If the shortest distance L is smaller than 0.4 cm, the discharge electrode tip 12 ″
Air ions generated by the corona discharge at the discharge electrode tip 1
Due to the action of the electric field formed between the 2 "and the counter electrode 13, most of it is absorbed by the counter electrode 13, making it impossible to carry out by air current. If the shortest distance L is 0.4 cm or more, In addition, the amount of ions that can be carried out by the air current increases, and the charge can be removed from the charged body, provided that the shortest distance L exceeds 4 cm.
Either the corona discharge of sufficient intensity will not occur, or it will be necessary to increase the applied voltage to increase the corona discharge. However, when the applied voltage is too high, there is a concern that electromagnetic noise is generated.

However, when the effective value V (kV) of the AC voltage applied to the discharge electrode 12 exceeds the value of (2.8 L + 1.0), the intensity of the corona discharge is too large, and the corona discharge occurs at the time of the corona discharge. The generation of dust due to the deterioration of the tip 12 "of the discharge electrode 12 was measured by the surface oxidation caused by the trace amount of ozone and the sputtering phenomenon caused by air ions. The dust generation was CN shown in FIG.
C30 was measured, and when the particle number concentration of 0.05 μm or more exceeded 10 particles / ft ³ after one month of operation, it was determined that dust was emitted from the discharge electrode 12. The effective value (2.8 L + 1.0) of the applied AC voltage at which dust generation starts as a result of the experiment and the effective value (1.8 L + 0.5) of the applied AC voltage at which corona discharge starts are determined by the shortest distance L
(Cm) is shown in FIG.

The ozone concentration was measured by replacing the CNC 30 in FIG. 1 with an ozone concentration meter. The results are also shown in FIG. Effective value V (kV) of AC high voltage is V <2.8L +
When it was in the range of 1.0 and 8 kV or less, the generation of ozone could be suppressed to about 10 volppb or less.

Next, a desirable range of the flow rate of the clean air was measured in the case where the head of the hard disk drive (HDD) was neutralized by the charge removal equipment 2 described with reference to FIG. 5, the shortest distance L between the tip of the discharge electrode and the counter electrode was set to L = 2.5 cm. The radius of curvature at the tip of the discharge electrode is 0.2 mm. An AC high voltage having an effective value V of 6 kV and a frequency of 50 Hz was applied to each discharge electrode. The cleanliness of the clean room provided with the static elimination equipment 2 is class 1000 (dust of 0.3 μm is 1f
in in the air t ³ is about 1,000 exist). Table 2 shows the relationship between the flow rate of the clean air and the number of dust particles having a size of 0.3 μm or more attached to the head. Clean air flow rate is 0.2
The range of m / s to 1.0 m / s is desirable. If the flow velocity is too slow, dust particles from an operator in the clean room cannot be kept sufficiently far from the head.
On the other hand, if the flow velocity is too high, the air flow will raise dust on the workbench around the head and the yield will be reduced.

[0045]

[Table 2]

Next, the dust generated from the tip 34 ″ of the discharge electrode 34 after the continuous operation for three months by the charge removal equipment 3 described with reference to FIG. The particle number concentration of
It was determined by measuring with C. An AC high voltage having an effective value V of 6 kV and a frequency of 50 Hz is applied to the discharge electrode 34, and the shortest distance L between the tip 34 "of the discharge electrode 34 and the counter electrode 35 is 2.0 cm. Has a radius of curvature of 0.2 mm. At this time, the tip 3 of the discharge electrode 34
The flow rate (m / s) of the clean air around 4 "was varied.
FIG. 9 shows the result.

When the flow rate of the clean air around the tip 34 "of the discharge electrode 34 is 10 m / s or less, the concentration of particles having a size of 0.05 μm or more exceeds 10 particles / ft ³ . -Particles due to particle conversion adhere to the discharge electrode 34
After being deposited, it was desorbed again. When the tip of the discharge electrode 34 at a flow rate of 2 m / s was observed with a microscope, a white dendrite having a size of about 0.5 mm, which was considered to be an aggregate of fine particles by gas-particle conversion, was observed. However, when the flow rate of the clean air around the tip 34 "of the discharge electrode 34 exceeds 10 m / s, the concentration of the number of particles having a size of 0.05 μm or more becomes 10 particles / ft ³ or less.
When the tip 34 ″ of the discharge electrode 34 at m / s was observed with a microscope, almost no deposits were observed.
It is considered that the fine particles generated by the gas-particle conversion were blown off by the high-speed airflow and did not adhere to or accumulate on the discharge electrode 34. The size of the fine particles is 0.05 μm or more but 0.1 μm or less, and does not affect the product process. Rather, the effect of avoiding detachment due to attachment / growth to the discharge electrode is large.

Further, in the charge removal equipment 3 described with reference to FIG.
A silicon wafer having a diameter of 300 mm and charged with V was placed, and static electricity was removed by supplying clean air ejected from the guide wall 31. Effective value V for discharge electrode 34
Applies an AC high voltage of 6 kV, and the tip 3 of the discharge electrode 34
The shortest distance L between 4 "and the counter electrode 35 is 2.5 cm, and the discharge electrode 3
In the case where the flow rate of the clean air around the tip 34 ″ of the No. 4 is 20 m / s, the frequency of the AC high voltage is set to 20 Hz or more and 500 kHz.
It was changed within the range of z or less. The charged potential of the silicon wafer is 1
FIG. 10 shows the relationship between time and frequency until the voltage is attenuated from 0 kV to 1/10 of 1 kV.

In the charge removal equipment using an AC voltage as in the present invention, positive and negative ions are transported by clean air to neutralize the charged material, but the ions reach the charged material while being mixed in the airflow during the transport. Therefore, the positive and negative ions are likely to recombine at a certain ratio before reaching. At a frequency exceeding 100 kHz, the degree to which the positive and negative ions are combined and neutralized and disappears is remarkable, and the charge elimination time of the charged material is much longer than at 100 kHz or less. On the other hand, at a frequency of less than 20 Hz, even after the charged surface is neutralized, the surface potential thereof alternates between positive and negative tens of volts each time positive and negative ions arrive, thereby lowering the product yield. It could be. Therefore, the discharge electrode 34
The frequency of the AC high voltage to be applied is 20Hz or more and 100k
Hz or less is desirable.

Also, by arranging a charged body such as a silicon wafer as close as possible to the discharge electrode 34 and shortening the ion arrival time, the charge elimination time of the charged body can be shortened. However, when the charged body is sensitive to electromagnetic radiation noise such as semiconductors, LCDs, and HDDs, it is necessary to take care not to be affected by the electromagnetic radiation noise generated at the tip 34 "of the discharge electrode 34. A monopole antenna having a length of 25 mm was placed at a distance of 15 cm from the tip of the discharge electrode, and a high-speed oscilloscope was connected to the antenna to measure electromagnetic radiation noise distributed in a band of 1 MHz to 120 MHz. High voltage effective value V is 8
kV or less, and the effective value V and the shortest distance L are 1.8L +
If it is in the range of 0.5 <V <2.8L + 1.0, the magnitude of the electromagnetic radiation noise is 5 to 10 mV, and the background noise (also called white noise) level is 2 to 5 mV.
This is slightly higher than the above, and it is possible to prevent the product from being affected by electromagnetic radiation noise.

Next, the dust generation characteristics were examined by changing the radius of curvature of the tip of the discharge electrode in various ways. In the ion generator 1 described with reference to FIGS.
An NC (condensed nucleus type particle measuring device) 30 is installed, and a CNC 30
Was used to measure the particle concentration of particles having a size of 0.05 μm or more. The shortest distance between the tip of the discharge electrode and the counter electrode L = 2.5 cm
And Each of them is made of single crystal silicon and has a radius of curvature of 0.05 mm, 0.08 mm, 0.1 mm,
0.2mm, 0.3mm, 0.4mm, 0.5mm,
When the ion generator 1 shown in FIGS. 1 to 3 was continuously operated for one year using each 0.6 mm discharge electrode, dust generation characteristics from the discharge electrode tip were examined with time. Table 3 shows the measured particle number concentrations. Effective value V is 6k for each discharge electrode
V, an AC high voltage having a frequency of 50 Hz was applied. The airflow velocity of the clean air represented by the white arrow in FIG.
The distance from the discharge electrode to the entrance of the sampling tube of the CNC 30 was 3 mm / s, and the distance was 400 mm. The tip of the discharge electrode was observed with an electron microscope, and the range of surface roughness due to oxidation and sputtering was also shown. The range of the surface roughness is defined as the size of the region where the surface roughness is measured measured from the tip of the discharge electrode.

[0052]

[Table 3]

Further, in the ion generator 1 shown in FIG. 1, an ion concentration meter was installed at the position of the sampling tube entrance of the CNC 30 located 400 mm below the discharge electrode, and the air ion concentration was measured. Table 4 shows the results. The air ion concentration was defined as the average of the positive ion concentration and the negative ion concentration measured by an ion densitometer. For example, a positive ion concentration of 1.8 × 10 ⁵ / cm
³ , when the negative ion concentration is 2.2 × 10 ⁵ ions / cm ³ , the ion concentration shown in Table 4 is an average value of both, 2.0 × 10 ⁵ ions / cm ³ .

[0054]

[Table 4]

When the radius of curvature at the tip of the discharge electrode is smaller than 0.1 mm, significant dust is generated. For example, electric field concentration occurs at the tip having a small curvature radius of 0.05 mm, and the air ions are violently bombarded on the silicon single crystal surface at the tip. Due to this sputtering action, deterioration due to oxidation proceeds in the depth direction of the silicon single crystal surface.
The surface roughness of the tip of the discharge electrode having a radius of curvature of 0.05 mm is at most 6 μm at most, but the depth of the deterioration is 0.1 mm when the degree of electric field concentration at the tip is relatively small.
mm or more.

On the other hand, the radius of curvature at the tip of the discharge electrode is 0.5 mm.
, The tip of the discharge electrode deteriorates when the radius of curvature is 0.4 mm
It is considerably suppressed as compared with the following cases. The cause is that the corona discharge itself is less likely to occur and the generation of air ions is reduced. However, if the corona discharge is less likely to occur, there is a concern that the function as an ion generator is substantially deteriorated.

[0057]

According to the first to fifth aspects of the present invention, there is provided an ion generator and a charge removing device capable of suppressing deterioration of the discharge electrode and suppressing generation of electromagnetic radiation noise and ozone. In particular, according to the fourth aspect, it is possible to prevent dust and the like from adhering to the product surface. Further, according to the fifth aspect, it is possible to prevent the deposition of the deposit on the tip portion of the discharge electrode.

[Brief description of the drawings]

FIG. 1 is a perspective view of an ion generator according to an embodiment of the present invention.

FIG. 2 is a plan view of an ion generator.

FIG. 3 is an enlarged cross-sectional view taken along the line AA in FIG. 1;

FIG. 4 is an enlarged view of a shape of a discharge electrode tip portion.

FIG. 5 is a schematic explanatory view of a charge removal facility according to the first embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view of a charge removal facility according to a second embodiment of the present invention.

FIG. 7 is a graph showing a correlation between a shortest distance L and an ion concentration.

FIG. 8 shows the relationship between the effective value of the AC voltage for starting corona discharge and the shortest distance L, the relationship between the effective value of the applied AC voltage at which dust generation starts and the shortest distance L, and ozone generation of approximately 10 vo.
It is the graph which showed the range which can be controlled below lppb.

FIG. 9 is a graph showing the correlation between the flow rate of clean air at the tip of the discharge electrode and the particle number concentration.

FIG. 10 is a graph showing the relationship between the time until the charging potential of the silicon wafer attenuates to 1/10 and the frequency of the AC high voltage.

[Explanation of symbols]

 L Shortest distance 1 Ion generator 2, 3 Charge removal equipment 10 Ion generator 12 Discharge electrode 12 'Tip 12 "Tip 13 Counter electrode 15 Circular hole 20 Feeder 25 DC transformer 27 AC transformer 30 Casing 31 Guide wall 34 Discharge electrode 35 Counter electrode 36,41 Work table 37,42 Product 40 High performance filter

Claims (5)

[Claims] 1. An ion generator comprising a needle-shaped discharge electrode and a conductive counter electrode, wherein an AC high voltage is applied to the discharge electrode to ionize air around the discharge electrode by corona discharge. The tip is made of silicon single crystal, and the shortest distance L between the tip of the discharge electrode and the counter electrode is 0.4 cm or more and 4 c
m, the effective value V of the AC high voltage applied to the discharge electrode is 8 kV or less, and 1.8 L (cm) +0.5
<V (kV) <2.8 L (cm) +1.0. An ion generator. 2. The frequency of an AC high voltage is 20 Hz or more and 10 or more.
2. The ion generator according to claim 1, wherein the frequency is 0 kHz or less. 3. The curvature radius of the tip of the discharge electrode is 0.1 mm.
3. The method according to claim 1, wherein the distance is about 0.4 mm.
Ion generator. 4. The ion generator according to claim 1, 2 or 3 is disposed in a flow of clean air having a flow velocity of 0.2 m / s or more and 1.0 m / s or less, and a discharge electrode. A plurality of static eliminators are arranged with a two-dimensional spread in a direction crossing the flow of the clean air. 5. A flow rate of 10 m / s at least at a tip of the discharge electrode of the ion generator according to claim 1, 2 or 3.
A static elimination facility, characterized in that it is configured to supply the above-described clean air stream.