JP4196367B2 - Ionization gauge - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to pressure measurement, and more particularly to an ionization vacuum gauge that enables Pirani vacuum gauge operation for the purpose of providing a vacuum gauge with a wide operating pressure range from atmospheric pressure to high vacuum.
[0002]
[Prior art]
In various semiconductor manufacturing apparatuses and electronic device manufacturing apparatuses that use a high vacuum region, pressure measurement in a wide range from atmospheric pressure to high vacuum region is required depending on start-up, maintenance, and various process conditions.
[0003]
Generally, in a high pressure region (low vacuum region) of about 10 ⁵ Pa to 1 Pa, a vacuum gauge based on a gas transport phenomenon typified by a heat conduction vacuum gauge such as a Pirani vacuum gauge is used. On the other hand, in a low pressure region (high vacuum region) of 1 Pa or less, an ionization vacuum gauge represented by a Baird Alpert vacuum gauge (hereinafter referred to as a BA type vacuum gauge) is used.
[0004]
What is shown in FIG. 3 is a Pirani vacuum gauge widely used in the measurement of a high pressure region (low vacuum region) of about 10 ⁵ Pa to 1 Pa in the prior art. In this Pirani vacuum gauge, a filament 3 is arranged in a measuring sphere container 2 made of a metal such as SUS304, and a connection flange 2b is provided in a gas inlet 2a opened at the top of the measuring sphere container 2. , Connected to the vacuum vessel 1. The gas molecules 30 remaining in the vacuum container 1 can be introduced into the measurement sphere container 2.
[0005]
When the vacuum vessel 1 is evacuated, a large amount of gas molecules 30 remain in the measurement sphere vessel 2 in a high pressure region. Therefore, when the filament 3 is energized to generate heat at a constant temperature, the filament 3 is collided by the collision of the gas molecules 30. Heat is taken away from. The amount of heat taken away is proportional to the density of the gas molecules 30, that is, the pressure in the measurement sphere container 2, and thus the pressure in the measurement sphere container 2 can be measured by calculating the amount of heat from the change in the filament energization power. On the other hand, what is shown in FIG. 4 is a BA type vacuum gauge used for measurement in a low pressure region (high vacuum region) of 1 Pa or less in the prior art.
[0006]
In the BA type vacuum gauge shown in FIG. 4, three electrodes of an ion collector 6, a filament 3, and a grid 4 are arranged in a measurement sphere container 2 made of metal such as SUS304. The measurement sphere container 2 is connected to the vacuum container 1 by a connection flange 2b provided in a gas introduction port 2a that is open at the top, and is configured so that gas molecules remaining therein can be introduced into the measurement sphere container 2. Has been. When a positive grid voltage is applied to the grid 4 in the low pressure region (high vacuum region) and the filament 3 is energized and heated, thermoelectrons are emitted from the filament 3 toward the grid 4. The thermoelectrons are accumulated in the grid 4 while reciprocating near the grid 4 before reaching the grid 4, collide with gas molecules remaining in the measurement sphere container 2, and positively charged ions are generated by ionization. .
[0007]
When the thermoelectrons finally reach the grid 4, an emission current flows between the filament 3 and the grid 4, but if a negative voltage is applied to the ion collector 6 with respect to the filament potential, positively charged ions Is captured by the ion collector 6, and an ion current flows into the ion collector 6. If the applied voltage of each electrode is a constant voltage and the emission current is a constant current, the density of the thermoelectrons reciprocating in the vicinity of the grid 4 is constant, and the amount of ions generated is a gas molecule in the measuring sphere container 2. Therefore, by measuring the magnitude of the ion current flowing into the ion collector 6, the pressure in the measuring sphere container 2 can be measured.
[0008]
[Problems to be solved by the invention]
However, when the filament of such a BA type vacuum gauge is heated to a high temperature in a high pressure region (low vacuum region), particularly in an atmosphere containing a large amount of oxygen, moisture, etc., the filament 3 is broken due to thinning or burning. May cause deterioration. In the above-mentioned Pirani vacuum gauge, due to radiant heat from the inner wall of the vacuum vessel 1, thermal radiation of the filament 3 itself, heat loss due to heat conduction, etc., a temperature change factor that does not involve gas molecules in the low pressure region (high vacuum region). The effect will increase and the measurement accuracy will deteriorate.
[0009]
Therefore, the pressure measurement from the atmospheric pressure to the high vacuum region according to the prior art is performed by measuring a high pressure region (low vacuum region) from 10 ⁵ Pa to 1 Pa in one vacuum vessel 1 as shown in FIG. 31 and an ionization vacuum gauge ball 32 for measuring a low pressure region (high vacuum region) of 1 Pa or less, and a wide range of pressure measurement was performed by using two vacuum gauges according to the pressure range.
[0010]
However, in the above prior art, as shown in FIG. 5, two types of vacuum gauges must be provided in the vacuum vessel 1, and in this case, it is necessary to secure an installation space for two measurement balls, In some cases, it is difficult to compare the same pressure in the vacuum vessel because the measurement position differs depending on the mounting position.
[0011]
In the case of measuring a wide pressure range, the two types of vacuum gauges (Pirani vacuum gauge and ionization vacuum gauge) that use the action of a heated filament are one measuring object, for example, a production apparatus using a vacuum. As both types are installed together, periodic replacement or replacement work due to sudden filament breakage will surely increase, resulting in a problem of total cost increase due to a decrease in production efficiency. ing.
[0012]
The present invention solves the above-mentioned problems, enables a wide range of pressure measurement from atmospheric pressure to low pressure region (high vacuum region) with a single measuring sphere, and utilizes the operation of a heated filament. Compared to the case where two types of vacuum gauges (Pirani vacuum gauge and ionization vacuum gauge) are installed or used together, the filament breakage frequency is significantly reduced, durability is improved, and a long-life and highly reliable vacuum gauge is provided. There is.
[0013]
[Means for solving the problems]
The present invention uses a grid, which is a basic component of an ionization vacuum gauge, as a grid for ionization vacuum gauge operation and a filament for Pirani vacuum gauge operation, and a single vacuum gauge, ionization vacuum gauge operation and Pirani vacuum The present invention solves the above-mentioned problems by switching between metering operations.
[0014]
That is, the present invention provides a filament for supplying electrons necessary for ionizing gas molecules in a vacuum, a grid for forming a potential necessary for accelerating the thermal electrons supplied from the filament, and an ionized gas. In the ionization vacuum gauge constituted by an ion collector for collecting positive ions, the grid is configured so that the operation of the filament in the Pirani vacuum gauge can also be performed.
[0015]
In other words, in the high pressure region (low vacuum region) of about 10 ⁵ Pa to 1 Pa where ionization vacuum gauge operation cannot be performed, the grid, which is the basic component of the ionization vacuum gauge as described above, is energized to raise the temperature of the grid surface. The grid is operated as a Pirani vacuum gauge that measures pressure from the amount of heat deprived by gas molecules, that is, the grid, which is a basic component of the ionization vacuum gauge, operates the filament in the Pirani vacuum gauge.
[0016]
On the other hand, if the pressure measurement value when operating as a Pirani gauge as described above becomes a pressure at which the ionization gauge can operate, the grid for operating the grid as a filament in the Pirani gauge The voltage necessary for the operation of the ionization gauge is applied to each electrode, which is the basic component of the ionization gauge as described above, including the grid, and the filament is energized to supply thermionic electrons. Release and switch to ionization gauge operation.
[0017]
【Example】
Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an embodiment of the present invention, showing a part of a vacuum container to be measured and a configuration of a main part of a vacuum gauge attached thereto.
[0018]
In FIG. 1, 1 is a vacuum vessel to be measured. The measuring sphere container 2 is a cylindrical container made of metal such as SUS304, and has an inner diameter of approximately 24 mm in order to optimize the electron trajectory while maintaining an appropriate distance from the filament 3 and the grid 4, and a grounding cable. Alternatively, it is kept at the ground potential through the vacuum vessel 1 to which the measurement ball vessel 2 is attached.
[0019]
A gas introduction port 2 a is opened above the measurement bulb container 2, and a connection flange 2 b is provided for connection to the vacuum container 1. For this connection, the exhaust pipe 2c can be connected to the vacuum vessel 1 by an O-ring seal structure without providing the connection flange 2b. A plurality of pins insulated by an insulator 5 are introduced into the measurement ball container 2 from the bottom of the measurement ball container 2 to support each electrode of the vacuum gauge and to apply an operating voltage.
[0020]
An ion collector 6 made of tungsten having a thickness of about 0.2 mm is attached to the pin 7 so as to protrude from the substantially upper end surface of the coil of the grid 4 on substantially the central axis of the measurement sphere container 2. A grid 4 made of a molybdenum wire having a thickness of about 0.2 mm and a total length of about 180 mm, which surrounds the ion collector 6 and whose surface is coated with platinum, is supported by pins 8a and 8b.
[0021]
On the outside of the grid 4, a filament 3 obtained by processing a triaco-coated lithium wire having a thickness of about 0.1 mm into a hairpin shape having a height of about 12 mm is provided with pins 9 a at a distance of 2.5 mm from the grid 4. It is supported and attached to 9b.
[0022]
An electric circuit portion is provided for the structure. This electric circuit includes an ionization vacuum gauge circuit 10 used when an ionization vacuum gauge operates in the above structure, an ionization vacuum gauge pressure display unit 11 in the ionization vacuum gauge operation, and a Pirani vacuum gauge operation in the above structure. It consists of a Pirani vacuum gauge operating circuit 12 and a Pirani vacuum gauge pressure display unit 13 used for the above.
[0023]
Between the pin 8a and the pin 8b connected to the grid 4, an operation changeover switch 14 for switching between the ionization vacuum gauge operating circuit 10 and the Pirani vacuum gauge operating circuit 12 is provided.
[0024]
The ionization vacuum gauge operating circuit 10 includes a filament operating power source 16 for generating thermoelectrons from the filament 3, a grid potential power source 17 for accumulating the thermoelectrons emitted from the filament 3, and a power supply for heating the grid 4. A gas power source 18, an emission control circuit 19 for controlling electrons flowing into the grid 4 to a constant amount, and an emission ammeter 21 connected between the ion collector 6 and the ground.
[0025]
The degassing of the grid 4 functions only when the ionization vacuum gauge is operated by the degassing switch 22. The emission control circuit 19 feeds back the filament operating power source 15 based on the collector current Ii measured by the ion collector ammeter 20 and the emission current Ie measured by the emission ammeter 21. The Pirani gauge operation circuit 12 functions when connected to the grid 4 by the operation changeover switch 14.
[0026]
In the vacuum gauge having the above-described configuration, the grid 4 is connected to the Pirani vacuum gauge operation circuit 12 using the operation changeover switch 14 in the high pressure range (low vacuum range) from atmospheric pressure to about 1 Pa, and the upper part of the measurement bulb container 2 is connected. Gas molecules remaining in the vacuum vessel 1 introduced from the gas inlet 2a opened in the cylinder collide with the grid 4 heated by the Pirani vacuum gauge operation circuit 12, and take heat away from the grid 4. Since the amount of heat taken is proportional to the density of gas molecules, that is, the pressure in the measuring sphere container 2, the pressure is measured from the power supplied to the grid by controlling the temperature of the grid 4 to a constant temperature by the Pirani vacuum gauge operation circuit 12. it can. At this time, the surface temperature of the grid 4 is energized and heated in a temperature range in which the grid 4 does not cause deterioration due to burning or oxidation, disconnection or thinning due to burning in an atmospheric pressure atmosphere. For example, the surface temperature of the grid 4 is controlled at a constant temperature between 40 ° C. and 50 ° C.
[0027]
Next, when the display pressure of the Pirani vacuum gauge pressure display unit 13 reaches a pressure at which the ionization vacuum gauge can be operated, the operation changeover switch 14 is switched to connect the grid 4 to the ionization vacuum gauge operation circuit 10. Here, since the vacuum gauge having the above configuration is switched to the operation of the ionization vacuum gauge, the grid 4 that previously functioned as the filament of the Pirani vacuum gauge functions as the grid of the ionization vacuum gauge, and the other electrodes have an ionization vacuum. Application and energization of a voltage necessary for meter operation are started.
[0028]
Thermal electrons are emitted from the filament 3 by power supply from the filament operating power supply 15. The thermoelectrons are accumulated in the measurement sphere container 2 by the grid. At this time, the electrons collide with gas molecules in the measurement sphere container 2 and flow into the grid 4 while generating positive ions by ionization. Positive ions are captured by the ion collector 6, and an ion current flows into the ion collector 6. The pressure at this time is obtained from the equation of vacuum pressure P = 1 / S · Ii / Ie using the ion current Ii measured by the ion ammeter 20 and the emission current Ie measured by the emission ammeter 21. Here, S is the sensitivity of the measurement sphere.
[0029]
Next, when the pressure shifts from the low pressure region (high vacuum region) to the high pressure region (low vacuum region), the pressure display of the ionization vacuum gauge pressure display unit 11 reaches the measurement upper limit pressure of the ionization vacuum gauge. At that time, energization and voltage application to each electrode are stopped, and the operation changeover switch 14 is switched to the Pirani gauge operation circuit 12.
[0030]
FIG. 2 is data obtained by measuring a change in power applied to the grid 4 with respect to a pressure change when the Pirani vacuum gauge operation is performed in the vacuum gauge having the configuration shown in FIG. From the measurement data, it can be seen that the change in pressure from atmospheric pressure to 1 Pa can be measured because the power supplied to the grid changes by about 200 mW. In the above data, the power supplied to the grid 4 becomes constant at 1 Pa or less, which is due to the heat conduction loss from the end of the grid 4 and the heat release loss from the surface of the grid 4. In the measurement, the surface temperature of the grid 4 was controlled at a constant temperature of about 50 ° C. (grid resistance value: about 0.6Ω). That is, in the present invention, switching from the operation as the Pirani gauge to the operation as the ionization gauge can be performed by detecting the grid energization power when the grid temperature is a constant temperature. In addition, switching from the operation as the Pirani gauge to the operation as the ionization gauge can be configured to obtain the pressure by detecting the grid voltage with the grid energization current as constant current control, Moreover, it can also comprise so that a grid voltage may be made into constant voltage control and a pressure may be calculated | required also by detecting a grid conduction current.
[0031]
On the contrary, in the present invention, when switching from the operation as the ionization vacuum gauge to the operation as the Pirani vacuum gauge, the ion current flowing into the collector of the ionization vacuum gauge can be detected and performed.
[0032]
In this embodiment, the ionization vacuum gauge is a B-A type vacuum gauge. However, in the present invention, other ionization vacuum gauges such as an extractor type ionization vacuum gauge or a hot filament may be used as long as the grid can be heated by energization. The same can be applied to a cold cathode gauge that is not used.
[0033]
【The invention's effect】
In the ionization vacuum gauge of the present invention, the grid, which is a basic component of the ionization vacuum gauge, is commonly used as a grid for operating the ionization vacuum gauge and a filament for operating the Pirani vacuum gauge, and can be switched. In addition to being able to perform measurement over a wide pressure range from atmospheric pressure to high vacuum with a single measurement sphere, the single measurement sphere improves installation workability in the vacuum vessel and the installation space and cost of the measurement sphere There are effects such as minimizing.
[0034]
In particular, in the high pressure region (low vacuum region), the Pirani vacuum gauge operation is performed with a grid that is more durable than the filament and has a function that can be heated and energized, thereby significantly reducing the frequency of disconnection and extending the service life. In addition, the problem of the pressure difference caused by the difference in the mounting position with respect to the measurement object is also eliminated because a wide pressure range can be measured with a single measurement ball, and the reliability is remarkably improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of an ionization vacuum gauge according to the present invention.
FIG. 2 is a graph showing changes in the power supplied to the grid with respect to pressure changes, showing the operation of the Pirani gauge in the same ionization gauge.
FIG. 3 is a schematic configuration diagram of a conventional Pirani gauge.
FIG. 4 is a schematic configuration diagram of a conventional ionization vacuum gauge.
FIG. 5 is a configuration diagram of a vacuum gauge in the case of measuring a wide pressure range from a conventional atmospheric pressure to a high vacuum.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Measuring ball container 2a Gas inlet 2b Connection flange 2c Exhaust pipe 3 Filament 4 Grid 5 Insulator 6 Ion collector 7, 8a, 8b, 9a, 9b pin 10 Ionization gauge operation circuit 11 Ionization gauge pressure display part 12 Pirani vacuum gauge operation circuit 13 Pirani vacuum gauge pressure display section 14 Operation changeover switch 15 Filament operation power supply 16 Filament potential power supply 17 Grid potential power supply 18 Degassing power supply 19 Emission control circuit 20 Ion collector ammeter 21 Emission ammeter 22 Desorption Gas switch 30 Gas molecule 31 Pirani vacuum gauge 32 Ionization gauge

Claims (1)

Collects filaments for supplying electrons necessary for ionizing gas molecules in vacuum, grids for forming potentials necessary for accelerating the thermal electrons supplied from the filaments, and positive ions of the ionized gas An ionization vacuum gauge comprising an ion collector, wherein the grid is configured so as to be able to operate a filament in the Pirani vacuum gauge.

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