JP3751650B2 - Static neutralizer - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an electrostatic neutralization device that generates positive and negative charges in a gas by the ionizing action of X-rays and neutralizes static electricity charged by a charged object such as a semiconductor device.
[0002]
[Prior art]
Conventionally, it is known that ions are generated by the ionizing action of X-rays. An example of the generation mechanism is helium atoms. As shown in FIG. 8, when the X-ray photon 101 collides with the helium atom 100, the energy is absorbed by the external electrons 102. When the external electrons 102 give energy of a certain value or more, they are emitted from the orbit to the free electrons 104. This is ionization, and when this atomization has many electrons, the amount of X-ray absorption increases and the amount of ionization also increases. A static electricity neutralizing device that utilizes such an ion generating action is disclosed in, for example, Japanese Patent Application No. 4-216807.
[0003]
[Problems to be solved by the invention]
The above-described neutralization apparatus is configured to irradiate soft X-rays by placing a charged object in a nitrogen gas or air atmosphere. For example, when the X-ray energy is 6 KeV, the neutralization apparatus 2 At a distance of × 10 ³ mm, 100% is absorbed, and gas ionization does not occur at positions further away (see FIG. 9).
[0004]
Further, since the irradiated X-ray is a point light source, the distance dependency of the irradiation intensity is also high, and the attenuation of the irradiation intensity is extremely large as the distance from the X-ray source increases. For this reason, in order to effectively neutralize (static charge) static electricity over a wide range, it is necessary to generate high-energy X-rays.
[0005]
The present invention has been made to solve such a problem, and its purpose is to irradiate X-rays over a wide range with low energy to efficiently neutralize static electricity. It is to provide a sum device.
[0006]
[Means for Solving the Problems]
Therefore, the static electricity neutralizing apparatus according to the present invention is an electrostatic charge neutralizing apparatus that irradiates a charged object placed in a predetermined atmospheric gas with X-rays and neutralizes static electricity charged with the charged object, An X-ray generating means for generating a ray and a thin film having X-ray permeability are formed in a bag shape, and a gas having a higher X-ray transmittance than that of the above atmospheric gas is sealed inside the X-ray. A film back accommodated in a case for fixing the generating means, and the film back is provided between the X-ray emitting portion of the X-ray generating means and the charged object in the case.
[0007]
The film back is filled with a gas having a higher X-ray transmittance than the ambient gas surrounding the charged object, and the X-ray emitted from the X-ray emitting portion is transmitted through the film back and charged. It is emitted to the object.
[0008]
Further, it is desirable that the gas enclosed in the film back is mainly an element gas having an atomic number smaller than that of nitrogen, for example, hydrogen gas, helium gas, and a mixed gas of hydrogen or helium. Preferably there is.
[0009]
[Action]
X-rays emitted from the X-ray emission part of the X-ray generation means are incident on the gas filled body and pass through the inside of the gas filled body. The gas filled body absorbs a gas having a high X-ray transmittance, that is, X-ray absorption. Gas with a low rate is enclosed. For this reason, attenuation of the X-rays emitted from the X-ray emission part can be sufficiently suppressed, and the X-rays can be guided to the vicinity of the charged object.
[0010]
Further, the vicinity of the charged object to which such X-rays reach is covered with a gas having a higher X-ray absorption rate than that of the gas enclosed in the gas enclosure, that is, a gas having a high ionization rate. For this reason, the amount of ionization of gas molecules is large in the vicinity of the charged object, and a large amount of ions used for neutralization can be generated.
[0011]
【Example】
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[0012]
FIG. 1 shows an electrostatic neutralizer according to the present embodiment. This neutralization device is configured by an X-ray generator 10 that generates soft X-rays, and a gas enclosure 20 that is disposed in an X-ray emitting portion of the X-ray generator 10.
[0013]
In the X-ray generator 10, an electron gun 12 that emits an electron beam is disposed in an envelope 11, and a target 15 made of tungsten is held by a flange 13. The target 15 is electrically connected to the focusing grid 14. Further, an emission window 16 for emitting the generated soft X-rays is provided below the target 15, and the emission window 16 is formed away by a rolling element such as beryllium or carbon.
[0014]
The gas enclosure 20 has a bag-like film back 21 formed of a polyethylene thin film having a thickness of 0.04 mm as a thin film having X-ray permeability. A cap 22 is screwed into the gas circulation port 25 of the film back 21, and the gas supply nozzle 23 and the exhaust nozzle 24 are fixed to the cap 22. Further, the film back 21 is filled with helium gas as a gas having a higher X-ray transmittance than the gas (here, air) surrounding the charged object 30 disposed below the film back 21.
[0015]
The function of the neutralizing device configured as described above will be described.
[0016]
First, an electron beam is emitted from the electron gun 12 of the X-ray generator 10, and the target 15 is irradiated with this beam to generate soft X-rays. The generated soft X-rays are emitted through the emission window 16 made of beryllium. The emitted soft X-rays pass through the gas enclosure 20 and irradiate the charged object 30.
[0017]
Here, FIG. 2 schematically shows a state where the charged object 30 is irradiated with soft X-rays. In the figure, white circles indicate gas molecules, and white circles with + and − indicate positive and negative ions generated by ionization.
[0018]
In the figure, soft X-rays emitted from the X-ray generator 10 in the state of a point light source proceed while gradually spreading, pass through a polyethylene thin film, and enter the film back 21. The film back 21 is filled with helium gas, which has a property of high X-ray transmittance. Therefore, in the film back 21, the soft X-ray absorption rate is low, and the amount of gas ionization is small. As a result, the soft X-rays travel through the film back 21 without being attenuated so much. The soft X-rays that have traveled in the helium gas in this manner are transmitted downward through the polyethylene thin film below the film back 21.
[0019]
Soft X-rays that have passed through the film back 21 travel in the air atmosphere where the charged object 30 is disposed. However, air has a higher X-ray absorption rate than the helium gas in the film back 21, and gas molecules The amount of ionization is large. For this reason, a large amount of ions used for neutralization (static elimination) are generated in the vicinity of the charged object 30. In addition, by interposing the film back 21, the X-ray generator 10 and the charged object 30 can be sufficiently separated from each other, and the area where the soft X-rays are irradiated extends over a wide range.
[0020]
The neutralizing apparatus having the above-described features can also be configured as shown in FIGS. In the figure, the same components as those in the neutralizing device in FIG.
[0021]
The neutralization device of FIG. 3 has a cylindrical metal case 18 fixed to the X-ray generator 10, and a film back 21 is arranged in a state of being accommodated inside the metal case 40. Yes. Further, the cap 22 of the film back 21 protrudes outside through the through hole 40a provided on the side surface of the metal case 40, and the gas supply nozzle 23 provided with the opening / closing lever 26 is fixed to the cap 22. Yes. By comprising in this way, the X-ray generator 10 and the gas enclosure 20 can also be comprised integrally.
[0022]
On the other hand, the neutralizing apparatus of FIG. 4 houses the X-ray generator 10 in a cylindrical case 41, and the gap between the X-ray generator 10 and the case 41 is filled with fixing silicon rubber. ing. In addition, a high voltage cable 44 for voltage supply extends outside through the bushing 45 via the inside of the case 41.
[0023]
A cylindrical metal case 42 having a diameter larger than that of the case 41 is fixed to the lower end portion of the case 41, and a polyethylene film 46 having a thickness of 0.04 mm is provided in the opening at the lower end of the metal case 42. It is stretched. Further, a plurality of support columns 47 are provided at the lower end opening of the metal case 42 to prevent the polyethylene film 46 from being bent. Thus, the above-mentioned gas enclosure 20 is constituted by the space 20 ′ surrounded by the metal case 42 and the polyethylene film 46, and the inside thereof is filled with a desired gas such as helium gas. A gas supply nozzle 23 provided with an opening / closing lever 26 is provided on the side surface of the metal case 42, and the space 20 ′ is filled with gas through the nozzle 23.
[0024]
Here, the effect when the gas enclosure 20 was provided was investigated using the neutralization apparatus shown in FIG. In this measurement, as shown in FIG. 2, a gas enclosure 20 having a length of 15 cm at the time of gas filling is arranged at the X-ray emission part of the X-ray generator 10, and the position 30 cm from the X-ray generator 10. The dose of X-rays was measured with a dosimeter (reference number 50) placed in the box. In addition, helium gas or nitrogen gas was individually enclosed in the gas enclosure 20 for measurement, and the gas enclosure 20 was compared with a state where the gas enclosure 20 was removed.
[0025]
The results are shown in the graph of FIG. From this graph, the dose rate increases when the gas enclosure 20 filled with each gas is provided in the X-ray emission part of the X-ray generator 10 compared to the case where soft X-rays are irradiated in a normal air atmosphere. I found out.
[0026]
Further, the time until a charged object charged to 3 kV was discharged to 300 V was measured. In this case, a charged object is disposed at the position of the dosimeter described above, the separation distance between the X-ray generator 10 and the charged object is kept constant by 30 cm, and the gas enclosure 20 disposed therebetween is filled with helium gas, and the filling is performed. The length of time was changed to 15 cm, 10 cm, and 5 cm. As a comparative example, the gas enclosure 20 was removed, and the same measurement was performed even in an air atmosphere.
[0027]
The result is shown in FIG. From this graph, it can be seen that the static elimination time is shortened when the gas enclosure 20 is provided and the thickness of the gas enclosure 20 is increased compared to the case where soft X-rays are irradiated in a normal air atmosphere. It turns out that time is shortened more. For example, when the X-ray tube voltage is 6 kV, the static elimination time when performed in an air atmosphere is about 3.5 seconds, whereas when the gas enclosure 20 having a thickness of 15 cm is arranged, the static elimination time is about It has been shortened to 1.5 seconds.
[0028]
Next, the relationship between the thickness of an organic film that can be used as a thin film having X-ray permeability and the X-ray transmittance was examined. A plastic film as an organic film has a specific gravity of about 0.83 to 2.0. However, when considering the conditions of an applicable film, the thickness of the film that can be used in the lightest specific gravity is determined.
[0029]
Taking helium gas as the gas having a high X-ray transmittance as an example, the ratio of the dose rate at the X-ray tube voltage is obtained based on the graph of FIG.
4kV Dose rate (He) / Dose rate (Air) = 4.87 (times)
5 kV Dose rate (He) / Dose rate (Air) = 2.79 (times)
6 kV Dose rate (He) / Dose rate (Air) = 2.14 (times)
7 kV Dose rate (He) / Dose rate (Air) = 1.78 (times)
8 kV Dose rate (He) / Dose rate (Air) = 1.61 (times)
9 kV Dose rate (He) / Dose rate (Air) = 1.47 (times)
Based on this result, an X-ray transmittance greater than the reciprocal of the obtained magnification is required. Based on this value, the X transmittance required for the organic film at each X-ray tube voltage is determined.
[0030]
4kV 1 / 4.87 = 0.20
5kV 1 / 2.79 = 0.36
6kV 1 / 2.14 = 0.47
7kV 1 / 1.78 = 0.56
8 kV 1 / 1.61 = 0.62
9kV 1 / 1.47 = 0.68
The X-ray transmittance as described above is required for the organic film. As an example, FIG. 7 shows the relationship between the thickness of polyethylene having a specific gravity of 0.9 and the X-ray transmittance. From this graph, it is preferable that the film has a thickness of about 1000 μm or less in order to satisfy the above-described X-ray transmittance. In addition, since the specific gravity of other plastics is greater than 0.9, the X-ray transmittance is considered to be lower than that of polyethylene. Therefore, the thickness of the organic film is about 1000 μm even when it is the thickest, and may be appropriately selected according to the type of gas to be sealed and the material of the organic film. For example, in the example of FIG. 4, in addition to the organic film, a metal thin plate such as Be or a glassy carbon plate can also be used.
[0031]
In each of the embodiments described above, an example in which helium gas is used as a gas having a high X-ray transmittance is shown. However, other than this, hydrogen or the like can be applied, and an element gas having an atomic number smaller than that of nitrogen gas. If so, it is suitable for use. A plurality of gases may be mixed and filled in the gas enclosure. Further, the atmosphere in which the charged object is disposed is not limited to the air illustrated, and the atmosphere may be formed by nitrogen gas, argon gas, or a mixed gas thereof.
[0032]
【The invention's effect】
As described above, according to the static electricity neutralization apparatus according to the present invention, the gas sealing in which the X-ray emitting part of the X-ray generating means is filled with a gas having a higher X-ray transmittance than the atmospheric gas in which the charged object is disposed. Since the body is disposed, the emitted X-rays can be guided to the vicinity of the charged object in a state where attenuation of the X-rays emitted from the X-ray emitting unit is sufficiently suppressed. Thereby, the distance between the X-ray generation means and the charged object can be set long, and X-rays can be irradiated over a wide range, and the static electricity of the charged object can be neutralized efficiently with a small amount of energy.
[Brief description of the drawings]
FIG. 1 is a diagram showing an electrostatic neutralization apparatus according to an embodiment.
FIG. 2 is an explanatory view schematically showing a state in which gas molecules are ionized by X-ray irradiation.
FIG. 3 is a diagram showing another embodiment of the static electricity neutralizing apparatus.
FIG. 4 is a diagram showing another embodiment of the static electricity neutralizing apparatus.
FIG. 5 is a graph showing the relationship between X-ray tube voltage and dose rate.
FIG. 6 is a graph showing the relationship between X-ray tube voltage and static elimination time.
FIG. 7 is a graph showing the relationship between the film thickness of a polyethylene film and the X-ray transmittance.
FIG. 8 is an explanatory diagram showing a state where ion irradiation occurs when helium atoms are irradiated with X-rays.
FIG. 9 is a graph showing air absorptivity characteristics in soft X-rays.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... X-ray generator, 16 ... Output window, 20 ... Gas enclosure, 21 ... Film back, 30 ... Charged object

Claims (2)

An electrostatic neutralization device that irradiates a charged object placed in a predetermined atmospheric gas with X-rays and neutralizes static electricity on the charged object,
X-ray generation means for generating X-rays;
A thin film having X-ray permeability is formed in a bag shape, and the inside thereof is filled with a gas having a higher X-ray transmittance than the atmospheric gas, and is accommodated in a case for fixing the X-ray generation means. And a film back
The film back is provided between the X-ray emitting part of the X-ray generation means and the charged object in the case, and the electrostatic neutralizer.   The static electricity neutralization apparatus according to claim 1, wherein the gas sealed in the film back is any one of hydrogen gas, helium gas, and a mixed gas of hydrogen or helium.

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