JP5783866B2 - Hot cathode ionization gauge - Google Patents

Description

  The present invention relates to a hot cathode ionization vacuum gauge for measuring pressure (total pressure) in a test body such as a vacuum vessel.

In a vacuum process performed in a vacuum processing apparatus such as film formation by sputtering or vapor deposition, the pressure in the vacuum chamber of the vacuum processing apparatus may greatly affect, for example, product yield. A (triode tube type) hot cathode ionization vacuum gauge is generally known as one that accurately measures a wide pressure range of 1 Pa to 10 ⁻⁵ Pa among the pressures in the vacuum chamber during the vacuum process.

  A hot-cathode ionization vacuum gauge is a filament formed in a hairpin shape in a glass vacuum partition to be mounted on a specimen, a grid having a cylindrical outline disposed around the filament, and a periphery of the grid (See, for example, Patent Document 1). Then, the filament is energized to light the filament to emit thermoelectrons, a potential higher than that of the filament is applied to the grid, and gas atoms and molecular positive ions generated by colliding with the thermoelectrons around the grid are ionized. Collected by the collector, the pressure in the test body is detected from the ion current at this time.

  Here, there is a relationship of Ii = S · Ie · P (Equation 1) between the ion current and the pressure (In Equation 1, Ii is the ion current, Ie is the electron current, S is the sensitivity coefficient, and P is Pressure). And it is known that there is a soft X-ray effect as one factor for determining the measurement limit (measurement lower limit value) of the hot cathode ionization vacuum gauge. That is, soft X-rays are emitted when electrons emitted from the filament are collected by the ion collector. When this soft X-ray irradiates the ion collector, electrons are emitted from the ion collector by the photoelectric effect. As a result, a pseudo ion current flows to the ion collector. Therefore, the above equation 1 is expressed as Ii = lip + lix = S · Ie · P + lix (equation 2). In this case, Iip = S · Ie · P, lix is a pseudo ion current generated by a soft X-ray, and is expressed by lix = α · β · Ie (formula 3). α is the probability that soft X-rays are emitted from the grid surface by electron impact, and β is the probability that electrons are emitted from the ion collector surface by soft X-ray irradiation.

From the above formula 2, even if the pressure is sufficiently low, there is an ion current due to soft X-rays that does not depend on the pressure, so a value equal to or lower than the pressure corresponding to this ion current is not shown. Therefore, the hot cathode ionization vacuum gauge of the above conventional example has a large surface area of the ion collector and a large irradiation area of the soft X-ray, so that the pseudo ion current due to the soft X-ray increases, resulting in a high measurement lower limit value of 10 ^−5. It becomes about Pa.

By the way, a BA vacuum gauge is conventionally known as a vacuum gauge in which the pseudo ion current due to the soft X-ray is remarkably reduced (see, for example, Patent Document 2). The BA vacuum gauge is configured by arranging a filament outside the grid and an ion collector inside the grid. In this case, the irradiation area of the soft X-ray is reduced by making the ion collector a thin line or needle, and the pseudo ion current due to the soft X-ray is reduced. Thereby, a measurement lower limit of about 10 ⁻⁸ Pa is obtained.

  Therefore, in the hot cathode ionization vacuum gauge, it is necessary to make the ion collector thinner in order to lower the measurement lower limit value. However, if the surface area of the ion collector is reduced, the probability of collecting positive ions is lowered. In addition, when the hot cathode ionization gauge is used for a test body in which a gas atmosphere such as hydrocarbon gas or siloxane is formed, these are deposited as an insulating film or a high resistance film and are incident on an ion collector. Ions cannot be detected as an ion current, and sensitivity is lowered. When the area of the ion collector is small as described above, the deposition rate of the insulating layer or high resistance film deposited on the surface of the ion collector is increased, and the sensitivity is decreased. That is, the larger the surface area of the ion collector, the better the stability.

JP 2006-343305 A JP 2002-39902 A

  In view of the above points, the present invention has a sensitivity stability equivalent to that of the conventional triode-type hot cathode ionization gauge and has a lower measurement lower limit than that of the conventional example. The object is to provide a vacuum gauge.

In order to solve the above-mentioned problems, the present invention is a hot cathode ionization vacuum gauge that is mounted on a test body and detects the pressure inside the test body, and includes a filament and a cylindrical shape disposed so as to surround the filament. A grid having an outline and an ion collector are provided. The filament is energized to light the filament to emit thermoelectrons, and a potential higher than the filament is applied to the grid, colliding with the thermoelectrons around the grid. the resulting gas atoms, positive ions of the molecule are collected by the ion collector, the one that detects the pressure from the ion current at this time, ion-collector is a plate-like member, the predetermined on the extension of the generatrix direction of the grid disposed presence of intervals so as to cover at least one opening of the grid, 1.5 more than double the opening area of the grid surface area of the ion collector And then, and sets the interval in the range of 1 to 5 mm.

  According to the present invention, since the ion collector is composed of a plate-like member having an area that closes at least one opening of the grid, the surface area of the ion collector is larger than that of the BA vacuum gauge, and the probability of collecting positive ions is increased. While it is suppressed from lowering, it is possible to prevent a decrease in sensitivity even when used in a test specimen in which a gas atmosphere such as hydrocarbon gas or siloxane is formed, and is equivalent to the conventional hot cathode ionization vacuum gauge Sensitivity stability. In addition, compared to the cylindrical ion collector used in the conventional ionization vacuum gauge, because the surface area is small, the pseudo ion current due to soft X-rays can be reduced, and as a result, the measurement lower limit value than the conventional example Can be lowered. In the present invention, the predetermined interval is set in consideration of mechanical accuracy and the flight distance of ions generated in the grid, and is set in the range of 1 to 5 mm, for example. If this distance is smaller than 1 mm, there is a mechanical problem that the grid and the ion collector come into contact. On the other hand, if it exceeds 5 mm, the flight distance of ions becomes longer, and if the pressure increases, the ion-molecule collision occurs. When the pressure increases and the pressure increases, the linearity of the output signal versus pressure is lost.

  By the way, when the filament, the grid, and the ion collector are accommodated in a glass vacuum partition as in the above-described conventional example, the thermoelectrons are charged up on the glass surface and surrounded by the vacuum partition. The potential distribution in the space changes, causing problems such as a decrease in ionization rate. Therefore, by adopting a configuration in which the filament, the grid, and the ion collector are housed in a metal vacuum partition, the potential distribution in the space surrounded by the vacuum partition is prevented by preventing charge-up of thermoelectrons. Since the pressure is always kept constant, the pressure can be measured with a constant sensitivity over a long period of time.

  In the present invention, the filament is preferably composed of an alloy of tungsten and rhenium. According to this, it is possible to suppress thermal deformation and deformation due to its own weight, and it is possible to suppress fluctuations in the thermoelectron emission region. Good.

The figure which shows typically the structure of the hot cathode ionization vacuum gauge of embodiment of this invention. The model perspective view which expands and shows a sensor part. The graph of the experimental result which shows the effect of this invention. The graph of the other experimental result which shows the effect of this invention.

  Hereinafter, an embodiment of the present invention will be described by taking a triode-type hot cathode ionization vacuum gauge as an example with reference to the drawings. In the following description, the mounting direction of a sensor unit (described later) with respect to a test specimen (not shown) will be described as upward.

  1 and 2, the hot cathode ionization vacuum gauge IG includes a sensor unit S and a control unit C. The sensor unit S includes a sensor body 1 that is a bottomed cylindrical metal container (envelope), and a vacuum chamber (not shown) or the like through a flange 11 (and an O-ring) formed at the top end of the reduced diameter. Removably attached to the test body. The sensor body 1 is made of stainless steel, nickel, an alloy of nickel and iron, aluminum alloy, copper, copper alloy, titanium, titanium alloy, tungsten, molybdenum, tantalum or at least two kinds of alloys selected from these, A vacuum partition is formed. In this case, the metal sensor body 1 is preferably grounded.

The sensor main body 1 has a filament 2, a grid 3 having a cylindrical outline disposed concentrically so as to surround the filament 2, and a generatrix direction of the grid 3 (vertical direction in FIG. 1). Disc-shaped (collecting plate-like) ion collectors 4 ₁ disposed so as to extend parallel to the upper and lower openings 31a and 31b of the grid and to cover the openings 31a and 31b, respectively. 4 equipped with a ₂ and. As the filament 2, the weight ratio of rhenium is 3 to 26% by weight so that the filament 2 has high mechanical strength in a temperature range of 2000 to 2500 ° C. when the filament 2 is turned on by being energized (red heat). It is made of an alloy of tungsten and rhenium and is formed by shaping a wire having a diameter of 0.1 to 0.2 mm into a hairpin shape. Then, both free ends of the filament 2 are positioned at predetermined positions in the sensor body 1 by support pins 21a and 21b projecting into the sensor body 1 by penetrating the bottom of the sensor body 1 through an insulator (not shown). Supported. In this case, the support pins 21a and 21b also serve as connection terminals (electrodes).

  The filament 2 is inserted into the lower opening 31b side of the grid 3 from the top 22 side turned back in the form of a hairpin at the front end of the filament 2 in the insertion direction, and the top 22 is in the vicinity of the middle point Mp in the generatrix direction of the grid 3 It is arranged to be located in the central region. The “central region” refers to a certain region in the height direction of the grid 3 including the midpoint Mp, where the length (height) in the generatrix direction of the grid is l, specifically, the grid 3 The top 22 should just be located in the range of 2/5 to 3/5 of the height. If it exceeds 3/5, the electric field for extracting the electrons does not concentrate on the top portion 22 of the filament 2 where the electrons are likely to be emitted, so that the electron emission efficiency decreases, that is, the power applied to the filament 2 increases, The region where electrons for ionization fly becomes narrow and the sensitivity is deteriorated, and further, deformation due to the length of the filament is likely to occur and the change in sensitivity becomes large. On the other hand, if it is smaller than 2/5, the flight distance of the electrons becomes long and the flight distance of the generated ions also becomes long, so that charged particles (here, electrons and ions) at high pressure versus neutral particles (gas molecules). ), The sensitivity is lowered due to the increased collision frequency.

  The grid 3 includes tungsten, molybdenum, molybdenum coated with platinum, tantalum, platinum, iridium, an alloy of platinum and iridium, an alloy of nickel, nickel and iron, stainless steel, or at least two alloys selected from these The product made from is used. And it is comprised by winding a 0.1 to 0.5 mm wire in a coil shape so as to have a cylindrical outline. In this case, the top portion 22 of the filament 2 is positioned on the hole axis Ha of the grid. In addition, the form of the grid 3 is not limited to this, The thing which assembled | attached the said wire rod in the grid | lattice shape, and shape | molded in the cylinder shape, and what shape | molded the punching metal or the photo-etching sheet | seat in the cylinder shape may be sufficient. The grid 3 is also positioned and supported at a predetermined position in the sensor main body 1 by support pins 31c and 31d projecting from the sensor main body 1 through an insulator (not shown) through the bottom of the sensor main body 1. In this case, the support pin 31c also serves as a connection terminal.

The ion collectors 4 ₁ , 4 ₂ are molybdenum, molybdenum coated with platinum, tantalum, platinum, iridium, an alloy of platinum and iridium, an alloy of nickel, nickel and iron, or at least two alloys selected from these It is made of a disc-shaped plate material made of steel. In this case, the thickness is set in the range of 50 to 300 μm. Further, the surface area of the surface of the ion collectors 4 ₁ , 4 ₂ facing the grid 3 is set to be equal to or greater than the opening area (area calculated from the winding diameter) in the vertical direction of the grid 3 to cover the opening of the grid 3. It is like that. The surface area of the ion collectors 4 ₁ and 4 ₂ is preferably 1.5 times or less the opening area of the grid 3. If it exceeds 1.5 times, the pseudo ion current due to soft X-rays becomes large, and the measurement lower limit cannot be lowered. The predetermined interval is set in consideration of mechanical accuracy and the flight distance of ions generated in the grid 3, and is set in the range of 1 to 5 mm, for example. If this distance is smaller than 1 mm, there is a mechanical problem that the grid 3 and the ion collector 4 come into contact. On the other hand, if the distance exceeds 5 mm, the flight distance of ions becomes longer, and if the pressure increases, If the probability of a collision increases and the pressure increases, a problem arises that the linearity of the output signal versus pressure is lost.

The ion collectors 4 ₁ , 4 ₂ are also positioned at predetermined positions in the sensor body 1 by support pins 41 a to 41 d protruding from the sensor body 1 through the bottom of the sensor body 1 through an insulator (not shown). Supported. In this case, the support pins 41a and 41c also serve as connection terminals. The form of the ion collectors 4 ₁ , 4 ₂ is not limited to the above, and can be configured by a rectangular plate material, and is arranged in at least one of the upper and lower openings 31 a, 31 b of the grid 3. You can also.

On the other hand, the control unit C includes a housing F (indicated by a one-dot chain line in FIG. 1), and a control means C1 including a computer, a memory, a sequencer, and the like is built in the housing F. The control unit C1 performs various controls such as the operation of each power source described later and the ion current value measured by the ammeter A described later to display pressure on a display (not shown), for example. Further, in the housing F, a filament lighting power source E1 for supplying a direct current to the filament 2 to red heat (light) the filament 2 and a grid power source for applying a higher potential to the grid 3 than the filament 2 are provided. and E2, the potential of the filament 2 and the power source E3 to higher than the potential of the ion collector 4 _1, 4 _2, and a current meter a for measuring the ion collector 4 _1, 4 ₂ respectively flowing ion current is built.

  In the present embodiment, although not shown and described in particular, the housing F is provided with output terminals that are conducted to the respective power sources, and the sensor unit S and the control unit C are connected by a cable with a connector. Further, the sensor unit S and the control unit C can be incorporated in the same housing.

Next, a usage example of the hot cathode ionization vacuum gauge will be described. After the sensor unit S is attached to the test port of the test body (not shown) via the flange part 11 and an O-ring (not shown), the test body is evacuated by a vacuum pump, and when a predetermined vacuum pressure is reached, pressure measurement is performed. Start. First, a direct current is applied to the filament 2 by the power source E1 to light the filament 2 and emit thermoelectrons. Then, thermoelectrons are drawn to the grid 3 side by an ionization voltage corresponding to the potential difference between the grid 3 and the filament 2 by the power source E2. At this time, positive ions are generated from gas atoms and molecules around the grid 3 colliding with the thermal electrons. The generated gas atoms and molecular positive ions are collected by the ion collectors 4 ₁ and 4 ₂ , respectively. At this time, the pressure in the test body is detected from the ion current measured by the ammeter A. In addition, since the well-known thing can be utilized about the control method of a hot cathode ionization vacuum gauge, the calculation method of the pressure from an ionic current, etc., detailed description is abbreviate | omitted here.

As described above, according to the embodiment of the present invention, the ion collectors 4 ₁ and 4 ₂ are configured by the plate-like members having an area that covers at least one of the openings 31a and 31b of the grid 3, so that the ion collector 4 is compared with the BA vacuum gauge. _While the surface area of ₁ , 4 and ₂ is increased and the probability of collecting positive ions is suppressed, it is used for a test body in which a gas atmosphere such as a hydrocarbon-based gas or siloxane is formed. Even in this case, the sensitivity can be prevented from decreasing, and the sensitivity stability is equivalent to that of the conventional hot cathode ionization vacuum gauge. In addition, compared to the cylindrical ion collector used in the conventional ionization vacuum gauge, because the surface area is small, the pseudo ion current due to soft X-rays can be reduced, and as a result, the measurement lower limit value than the conventional example Can be lowered.

  Further, since the sensor unit S is housed in the metal vacuum partition 1, the charge distribution of the thermoelectrons is prevented, and the potential distribution in the space surrounded by the vacuum partition 1 is always kept constant. The pressure can be measured with a constant sensitivity over a period of time. Moreover, since the filament 2 is made of an alloy of tungsten and rhenium, thermal deformation and deformation due to its own weight can be further suppressed. That is, the alloy of tungsten and rhenium in the above weight ratio has high rigidity and ductility in the temperature range of 2000 to 2500 ° C. when the filament 2 is lit, and is relatively chemically stable. Therefore, it is more suitable as a hot cathode material in the above temperature range. That is, structural changes due to thermal history, changes in shape due to vibration and impact (including disconnection) are small, and there is no need to coat oxide at the same time. For this reason, there is little sensitivity change at the time of using as a filament 2 material of a hot cathode ionization vacuum gauge IG.

Next, in order to confirm the effect of the present invention, the following experiment was performed using the hot cathode ionization vacuum gauge IG. In this case, a grid 3 made of a molybdenum net member having a diameter of 10 mm and a height of 24 mm was used as the grid 3. The filament 2 is made of a tungsten-rhenium alloy with a rhenium weight ratio of 3% by weight so that the top portion 22 of the filament 2 formed into a hairpin shape is positioned at the center of the grid 3. Inserted in the grid 3. The material of the ion collectors 4 ₁ , 4 ₂ is SUS304, and a plate material of φ10 mm is used.

  The potential of the power source E1 with respect to the ground potential is + 25V, the potential of the power source E2 is + 150V, the potential of the power source E3 is 0V, and the electron current for ionization is controlled to 1 mA. And what measured the measurement lower limit of the hot cathode ionization vacuum gauge IG is shown in FIG. In FIG. 3, the-□-line is for the hot cathode ionization vacuum gauge IG (invention). Also, FIG. 3 shows a conventional hot cathode ionization vacuum gauge (conventional product: indicated by -O- in FIG. 3) and a BA vacuum gauge (comparative product: indicated by-[Delta]-in FIG. 3). It also shows the measurement of the measurement lower limit value. According to this, it was confirmed that the product according to the invention has a lower pressure measurement lower limit than the BA vacuum gauge, but the pressure measurement lower limit is lower than that of the conventional product.

  Next, another experiment was performed using the same hot cathode ionization vacuum gauge IG as described above. That is, in order to show the stability of the ionization vacuum gauge, it was operated while exposed to siloxane, and then calibrated against nitrogen to measure the change in sensitivity. FIG. 4 shows the measurement results. In FIG. 4, the-□-line indicates the invention product,-○-indicates the conventional product, and-△-indicates the comparison product. Thus, it can be seen that exposure to siloxane for about 1.5 hours reduces the sensitivity to about two digits. On the other hand, it was confirmed that the inventive product has little change in sensitivity and has the same stability as the conventional product.

  As mentioned above, although embodiment of this invention was described, this invention is not limited above. In the above embodiment, the sensor body 1 has been described as an example. However, the present invention can also be applied to the case where the sensor unit is directly attached to the test body.

IG ... Hot cathode ionization vacuum gauge, S ... Sensor part, C ... Control part, 1 ... Metal container (vacuum partition), 2 ... Filament, 3 ... Grid, 4 ₁ , 4 ₂ ... Ion collector, A ... Ammeter , Ha... Hole axis, Mp.

Claims (3)

A hot cathode ionization vacuum gauge that is mounted on a test body and detects the internal pressure of the test body,
A filament, a grid having a cylindrical outline disposed so as to surround the filament, and an ion collector are provided. The filament is energized to light the filament to emit thermoelectrons, and has a higher potential than the filament. Is applied to the grid, and the positive ions of the gas atoms and molecules generated by colliding with the thermoelectrons around the grid are collected by the ion collector, and the pressure is detected from the ion current at this time.
Ion-collector is a plate-like member, at a predetermined interval on the extension of the generatrix direction of the grid are arranged so as to cover at least one opening of the grid, the open area of the grid surface area of the ion collector A hot-cathode ionization vacuum gauge characterized by being 1.5 times or less and setting the interval in a range of 1 to 5 mm .
  The hot cathode ionization vacuum gauge according to claim 1, wherein the filament, the grid, and the ion collector are housed in a metal vacuum partition.   3. The hot cathode ionization vacuum gauge according to claim 1, wherein the filament is made of an alloy of tungsten and rhenium.

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