JPH06273307A - Method and equipment for evaluating concentration of particles - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide a particle concentration evaluation method and apparatus that can obtain information on small particles without being affected by ambient light. [Structure] The particle concentration evaluation device includes a pulsed X-ray source, electrostatic field generation electrodes 45 and 46, a drift tube 47, and a collector 48. The particles are charged by the pulsed X-rays 24, the charged particles 44 are caused to travel in the drift tube 47 and flow into the collector 48, and profile data of collector inflow current vs. running time is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the concentration of particles (suspended particles) using X-rays and a concentration evaluation device.

[0002]

2. Description of the Related Art Conventionally, as a method for detecting and measuring particles, as shown in FIG. 4, a laser beam 1 is projected in an enlarged manner, and scattered light 3 from particles 2 in a laser optical path is detected by a photoelectric converter 4. The method of transmitting the output electric signal to the pulse counter 5 and counting is known as a typical one (Applied Physics Vol. 54, No. 3 (1985), pages 260 to 268, "Laser Beam Scanning Dust Counter". )).

[0003]

In the above-mentioned measuring method, scattered light is affected by surrounding light in a bright environment, so that it is generally difficult to measure. Further, it was impossible to detect small particles having a particle size of about 0.5 μm or less. This is because the intensity of scattered light decreases as the particle size decreases, and the sensitivity of the photoelectric converter decreases.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a particle concentration evaluation method which is not affected by ambient light and which can obtain information on small particles, and The purpose is to provide a device.

According to the particle concentration evaluation method of the present invention which achieves the above object, the particles are irradiated with pulsed X-rays to be charged, the charged particles are attracted by an electrostatic field and run for a certain distance, and then flow into the collector. The profile data of the collector inflow current or the inflow value of the number of particles versus the transit time of the charged particles is obtained.

Further, the particle concentration evaluation apparatus of the present invention comprises a pulsed X-ray source, an electrostatic field generating electrode installed in the radiation space of the pulsed X-ray, and a drift tube disposed adjacent to the electrostatic field generating electrode. And a collector installed at one end of the drift tube.

The pulsed X-ray source may be composed of a pulsed laser beam source and a target or a pulsed electron beam source and a target.

Further, the X-ray source chamber constituting the pulsed X-ray source and the measurement chamber containing the electrostatic field generating electrode, the drift tube and the collector are separated by a partition plate having a thin plate serving as an X-ray window. It can be configured.

[0009]

According to the particle concentration evaluation method and apparatus of the present invention, particles can be detected with little influence of ambient light, and small particles of 0.5 μm or less can be detected.

When the particles are irradiated with X-rays, photoelectrons are emitted from the particles and the particles are positively charged. When an electrode having a potential lower than the space where these charged particles are generated is arranged near this space, the charged particles are pulled by the electrode. When the electrode is provided with an appropriate hole, the charged particle passes through the hole, so that the charged particle can be guided into the drift tube and run at a constant speed to flow into the collector.

The time required for the charged particles to travel inside the drift tube is shorter as the charged charge is larger,
Also, the larger the mass of the particles, the longer it becomes. That is,
This transit time changes according to the specific charge (e / m), which is the ratio of the charge to the mass of the particles.

Since gas molecules have a large specific charge, the traveling speed is fast and the traveling time is extremely short. The dust-like particles that impair the cleanliness of the room have a much smaller specific charge than gas molecules and require a long running time. The larger the particle size and the larger the mass, the longer the running time.

Therefore, the time-dependent change profile of the collector current value every minute time or the number of charged particles flowing into the collector per unit time from the time when the pulsed X-ray is generated corresponds to the value of the specific charge. Gives concentration information of gas molecules and particles. Gas molecules and particles can be separated by the difference in running time, and since there is a fixed relationship between the particle size and running time, it is possible to obtain information related to the concentration profile according to the particle size.

[0014]

Embodiments of the present invention will be described below.

FIG. 1 shows an apparatus for evaluating particle concentration in a vacuum chamber according to an embodiment, in which an opening / closing valve 14 is provided between a container wall 12 (only part of which is shown) of a vacuum chamber 11 and an isolation chamber 13. The isolation chamber 13 is provided with a section 15, and the isolation chamber 13 is further provided with a partition plate 17 having an X-ray window 16 for passing X-rays in a required wavelength range.
8 and an X-ray source room 19. A pulsed laser beam 21 emitted from a laser transmitter 20 placed outside the isolation chamber 13 enters the X-ray source chamber 19 through a laser window 22 and strikes a metal target 23 in the chamber 19 to locally It is designed to generate plasma. This laser plasma instantaneously generates a strong X-ray 24, and a part of it is transmitted through the X-ray window 16 and introduced into the adjacent measurement chamber 18. Vacuum piping 25 connected to the isolation chamber 13
The opening / closing valve 26 can open and close the flow path between the measurement chamber 18 and the X-ray source chamber 19, and the opening / closing valve 27 connects the vacuum pump (not shown) to the X-ray source chamber 19 and the measurement chamber 18. The exhaust passage between them can be opened and closed. In the X-ray source chamber 19, a window support member 28 that hermetically holds the laser window 22,
Rollers 29, 30 for winding and unwinding the metal target 23, and a vapor shield 31 for preventing vaporized substances such as metal emitted from the laser beam 21 irradiation portion of the metal target 23 from entering the pipe 25. And so on. The partition plate 17 provided with the X-ray window 16 also acts to prevent the inflow of metal vapor or the like into the measurement chamber 18 side.

When the particle concentration in the vacuum chamber 11 is evaluated, the measurement chamber 18 and the X-ray source chamber 19 are placed in a vacuum state in advance, and the on-off valve 14 is opened when the particle concentration in the vacuum chamber 11 is evaluated. . The X-rays 24 pass through the X-ray window 16 and are applied to a part of particles or the like existing in the measurement chamber 18, and emit photoelectrons to be charged particles. The charged particles are pulled and run for a certain distance to flow into the collector, but this measuring unit is not shown in FIG. 1, and details are shown in FIG.

FIG. 2 is an explanatory view showing an example of the structure of the measuring section installed in the measuring chamber 18, in which particles emitted by the X-rays 24 passing through the openings 43 of the X-ray shields 41, 42 and emitting photoelectrons. The positively charged particles 44 composed of
The electron collector 45 (for example, about +1 kv) and the electron collector 4
5 is pulled toward the accelerating electrode 46 by the electrostatic field formed between the electrostatic field generating electrodes composed of the reticulated accelerating electrode 46 having a potential lower than 5 (for example, about −1 kv), and most of them are connected to the accelerating electrode 46 network. After passing through, the constant potential space in the drift tube 47 is moved at a constant speed and flows into the collector 48 (eg, about −1 kv) having a lower potential than the generation portion of the positively charged particles 44. If a collector having a secondary electron amplifying action is used as the collector 48, for example, a microchannel plate is used, the current value flowing into the collector 48 can be multiplied and taken out to the output stage. Apply the voltage generated across the resistor to the vertical signal input terminal of the oscilloscope.

On the other hand, since photoelectrons 49 emitted from particles are collected in the electron collector 45, the voltage generated at this output stage is used as a sweep start trigger of the oscilloscope, or the output voltage at the output stage of the collector 48 is compared. The waveform of collector current vs. transit time is drawn and recorded on the oscilloscope by setting it as a reference voltage. The electron collector 45 may also be a microchannel plate having a multiplication effect. Further, one or more X-ray reflection mirrors 50 and the like are arranged around the incident space of the X-rays 24, and at least a part of the incident X-rays 24 are reflected several times so as to increase the generation probability of the positively charged particles 44. May be re-projected. The above-mentioned "collector current" may be expressed by a count value of the number of charged particles flowing into the collector per unit time.

The measuring unit shown in FIG. 2 is housed in the measuring chamber 18 shown in FIG. 1. Before the opening / closing valve 14 shown in FIG. 1 is opened, the measuring unit draws a waveform of collector current vs. transit time. By recording, the cleanliness of the measuring chamber 18 alone can be evaluated, and so-called background measurement can be performed.

The laser plasma X-ray source composed of the laser oscillator 20 and the metal target 23 may be a pulsed electron beam excitation X-ray source in which the electron gun and the metal target are opposed to each other.

FIG. 3 is an example of a particle concentration profile drawn on an oscilloscope.

The abscissa represents the elapsed time after the pulsed X-ray irradiation, which corresponds to the transit time of the particles, and corresponds to the size of the particles. The vertical axis represents the collector current, which corresponds to the particle concentration.

The relationship between the number of particles and the particle concentration with respect to the particle size in a vacuum chamber or a clean room usually tends to increase as the size decreases. However, as the particle size becomes smaller, the cross-sectional area where X-rays collide decreases, so that the profile generally becomes a profile that decreases at a place where the size and running time are large and a place where the running time is small as shown by the curve a in FIG.

As an empirical fact, there is a relationship that if the number of particles of a certain size decreases in a vacuum chamber or a clean room, the number of particles of a different size also decreases, so from the profile shown in FIG. If the density information of particles having a size smaller than about 0.5 μm is obtained, the situation of the particle density of particles having a size larger than that can be almost determined. If the change in the particle concentration information is monitored at a small size, it is possible to detect a change in the overall image of particle concentration regardless of the size.

Since the evaluation method according to the present invention is based on the principle of ionizing a substance by X-rays, in principle, even if the particle size is small, no matter how small the particle size is, it becomes ionized. , By the action of the electric field,
It can be detected as a current. That is, the smaller particle size makes it possible to easily obtain the information on the particle concentration and its increase / decrease even at a local minimum close to the gas molecule size. In the production of semiconductor devices, clean spaces are becoming more and more necessary in recent years. For example, the number of particles with a size of 0.5 μm or more is less than 10 particles per cubic foot, or less than 1 particle. Space is being demanded. The particle concentration information when the number of particles having a size of about 0.5 μm or more in such an ultra-clean space is small can be relatively easily and stably known as qualitatively shown by the curve b in FIG.

Not only the floating particles can be directly measured and evaluated, but also the concentration information of the particles adhered on the substrate or wafer can be obtained by charging the adhered particles with X-rays and pulling them out with an electric field. Further, since this method utilizes the photoelectron emission effect by X-rays, light from the surroundings hardly interferes with the evaluation function, and it suffices to take care so that strong ultraviolet rays do not enter.

In order to obtain a quantitative value of the number of particles from the profile data, sensitivity calibration is performed using standard particles such as polystyrene latex.

[0028]

As described above, according to the present invention, the influence of ambient light is eliminated and the diameter of 0.
It is designed to measure even small particles of 5 μm or less, and is effective in providing a useful means especially for evaluating an ultraclean space.

Not only the particle concentration in the vacuum chamber can be evaluated, but also the particle concentration information in the air can be obtained by placing the substrate in the air and accommodating the substrate having the particles accumulated on the surface in the measuring chamber. It is also possible to directly inject air into the measurement chamber and then to evacuate it to a vacuum, and to charge the remaining particles by X-ray irradiation for measurement and evaluation.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a measuring unit of the embodiment as well.

FIG. 3 is an example of profile data of collector current vs. transit time similarly obtained in the example.

FIG. 4 is a principle diagram of a conventional method that uses scattered light of a laser beam.

[Explanation of symbols]

 11 vacuum chamber 13 isolation chamber 14 on-off valve 16 X-ray window 18 measurement chamber 19 X-ray source chamber 20 laser transmitter 21 laser beam 23 thin metal plate target 24 X-ray 25 vacuum piping 44 positively charged particles 45 electron collector 46 acceleration electrode 47 Drift tube 48 collector

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] April 23, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

The relationship between the number of particles and the particle concentration with respect to the particle size in a vacuum chamber or a clean room usually tends to increase as the size decreases. However, since the cross-sectional area of the particle size decreases X-rays impinge is reduced, the profile will be generally profile decreases at where large size and the running time and small, such as curve a in FIG.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction content]

[0024] As empirical facts, in a vacuum chamber or a clean room, there is a number of particles is also reduced relation size to differ from this as the number of particles of a certain size Helle, from the profile shown in FIG. 3, for example, the size corresponding value If the density information of particles having a size smaller than about 0.5 μm is obtained, the situation of the particle density of particles having a size larger than that can be almost determined. If the change in the particle concentration information is monitored at a small size, it is possible to detect a change in the overall image of particle concentration regardless of the size.

Claims (5)

[Claims] 1. A profile of a particle inflow value vs. a traveling time of a charged particle, which is obtained by irradiating a particle with pulsed X-rays to charge the particle, attracting the charged particle with an electrostatic field and causing the particle to travel for a predetermined distance before flowing into a collector. A particle concentration evaluation method characterized by obtaining data. 2. The particle concentration evaluation method according to claim 1, wherein the collector inflow value is a collector inflow current or the number of collector inflow particles. 3. A pulsed X-ray source, an electrostatic field generation electrode installed in a pulsed X-ray radiation space, a drift tube disposed adjacent to the electrostatic field generation electrode, and installed at one end of the drift tube. A particle concentration evaluation device comprising a collector. 4. The particle concentration evaluation apparatus according to claim 3, wherein the pulsed X-ray source comprises a pulsed laser beam source or a pulsed electron beam source and a target. 5. An X-ray source chamber comprising a pulsed X-ray source,
The particle concentration evaluation device according to claim 3, wherein the measurement chamber containing the electrostatic field generating electrode, the drift tube, and the collector is separated by a partition plate having a thin plate serving as an X-ray window.