TW201908706A - Transistor type ionization vacuum gauge and pressure measuring method - Google Patents

Abstract

A triode type ionization vacuum gauge capable of accurately measuring the internal pressure of a measurement object is disclosed. The triode type ionization vacuum gauge of the present invention includes a filament, a grid, and an ion collector. The grid is disposed around the filament. The cylinder-shaped ion collector is disposed around the grid, and is made of a material having a thermal conductivity above 173 W/m DEG K under 300K.

Description

   Triode type ionization vacuum gauge and pressure measuring method   

The invention relates to a technology of a triode type ionization vacuum gauge and the like.

The vacuum processing apparatus includes a vacuum chamber capable of performing film formation by sputtering or evaporation. Because the pressure in the vacuum chamber will have a great impact on the yield of the product, it is necessary to accurately measure the pressure in the vacuum chamber. As a device for accurately measuring a pressure in a range of 1 Pa to 10 ^-6 Pa among pressures in a vacuum chamber, a triode type ionization vacuum gauge is known.

The triode ionization vacuum gauge generally includes a hairpin (inverted V) filament, a spiral grid arranged around the filament, and a grid arranged coaxially with the grid. A cylindrical ion collector around the pole. A higher voltage (positive voltage) is applied to the grid system than the filament, and a lower voltage is applied to the ion collector system than the grid.

When the filament is energized, thermionic electrons are emitted from the filament (near the top of the filament), and the thermionic electrons are accelerated toward the grid and captured by the grid. A part of the thermoelectron is near the grid and collides with the gas molecules scattered inside the triode-type ionization vacuum gauge, whereby the gas molecules are ionized.

The ionized gas molecules (positive ions) are attracted by the ion collector, collide with the ion collector, and receive electrons from the ion collector. The ionized gas molecules receive electrons from the ion collector, thereby generating an ion current in the ion collector. Since the value of the ion current is directly proportional to the amount of gas molecules scattered inside the triode ionization vacuum gauge, by measuring the value of the ion current, it is possible to measure a measurement object (such as a vacuum) equipped with the triode ionization vacuum gauge. Treatment device).

Here, as described in the following Patent Documents 1 and 2, when gas molecules (positive ions) collide against the surface of the ion collector, gas molecules are adsorbed (for example, physically and chemically) on the surface of the ion collector and formed In the case of a molecular layer (physical adsorption layer, chemisorption layer).

The area near the center in the axial direction of the ion collector is an area where the probability of positive ions colliding is high. When positive ions continue to hit the area, particles such as neutral fragment molecules, neutral atoms, or these ions are removed from the molecules. The layer is released as much as possible. Therefore, the area near the center in the axial direction of the ion collector is regarded as an area where the molecular layer is not easily deposited. On the other hand, the area near both ends in the axial direction of the ion collector is an area where the probability of collision of positive ions is low. Since positive ions do not continuously collide, they are regarded as areas where positive ions are easily deposited as molecular layers.

In addition, as a technology related to this case, the following patent documents 3 and 4 are mentioned.

[Prior technical literature]

[Patent Literature]

Patent Document 1: International Publication No. 2016/151997.

Patent Document 2: International Publication No. 2016/139894.

Patent Document 3: Japanese Patent Application Laid-Open No. 2006-343305.

Patent Document 4: Japanese Patent Application Laid-Open No. 5-66170.

Due to the influence of molecular layers and the like formed near both ends in the axial direction of the ion collector, there is a problem that the internal pressure of the measurement object cannot be accurately measured.

In view of the above, an object of the present invention is to provide a triode type ionization vacuum gauge which can accurately measure the pressure inside a measurement object.

In order to achieve the above object, the triode type ionization vacuum gauge of the present invention includes a filament, a grid, and an ion collector. The grid is arranged around the filament. The ion collector is cylindrical and is arranged around the grid. The ion collector is made of a material having a thermal conductivity of 173 W / (m˙K) or more at 300K.

In this triode-type ionization vacuum gauge, the ion collector is composed of a material having a thermal conductivity coefficient of 173 W / (m˙K) or more at 300K. In other words, the ion collector is made of a material with a high thermal conductivity. Thereby, the heat generated in the filament becomes easy to be transmitted to the entire ion collector, and the temperature of the ion collector can be increased even near the two ends in the axial direction of the ion collector. Thereby, it is possible to prevent a molecular layer from being formed near both ends of the ion collector in the axial direction. As a result, in this triode-type ionization vacuum gauge, the pressure inside the measurement object can be accurately measured.

In the above-mentioned triode type ionization vacuum gauge, the power supplied to the filament may be 4 W or less.

Here, in a small triode type ionization vacuum gauge in which the power supply to the filament can be set to 4W or less, since the heat generated by the filament is easily reduced, the temperature is likely to be in the axis direction of the ion collector. There is a problem that the vicinity of both ends becomes low. On the other hand, as described above, the triode-type ionization vacuum gauge of the present invention constitutes an ion collector with a material having a high thermal conductivity. Therefore, even in a small triode-type ionization vacuum gauge in which the power supply to the filament can be set to 4 W or less and the heat of the filament is easily reduced, the ion collector can be appropriately increased near the two ends in the axial direction of the ion collector The temperature of the ion collector.

The triode-type ionization vacuum gauge may further include a supporting member. The supporting member supports the ion collector and is made of a material having a lower thermal conductivity than a material constituting the ion collector.

Thereby, the heat of the ion collector can be prevented from being dissipated to the supporting member, and the heat of the ion collector can be maintained at a high state.

The above-mentioned triode type ionization vacuum gauge may further include a receiving portion. The accommodating portion is made of a metal material, and the filament, the grid, and the ion collector are accommodated inside.

In this way, by arranging the receiving portion with a metal material, it is possible to prevent the charge up from occurring when the hot electrons collide with the receiving portion, and the potential distribution in the space in the receiving portion can be fixedly maintained. Thereby, the pressure can be measured with a fixed sensitivity for a long time.

The pressure measuring method of the present invention is to prepare a triode type ionization vacuum gauge, and measure the internal pressure of the measurement object by using the triode type ionization vacuum gauge. The triode type ionization vacuum gauge is provided with: a filament; a grid; The periphery of the filament; and the ion collector, which is cylindrical and is arranged around the grid, is made of a material having a thermal conductivity coefficient of 173 W / (m˙K) or more at 300K.

As described above, according to the present invention, it is possible to provide a triode type ionization vacuum gauge capable of accurately measuring the internal pressure of a measurement object.

1‧‧‧ positive ion

2‧‧‧ adsorption molecules

10‧‧‧ Sensor Unit

11‧‧‧ sensor body (containment section)

11a‧‧‧ flange

11b‧‧‧Groove section

11c‧‧‧ bottom

12‧‧‧ filament

13‧‧‧ grid

14‧‧‧ ion collector

15, 15a to 15e‧‧‧ terminals

16‧‧‧ grid support member

17‧‧‧ ion collector support member (support member)

20‧‧‧Control unit

21‧‧‧controller

22‧‧‧ ammeter

23a to 23c‧‧‧ Power

100‧‧‧ Triode type ionization vacuum gauge

Hf‧‧‧ Filament Height

Hg‧‧‧ grid height

Hi‧‧‧ height of ion collector

φg‧‧‧ diameter of grid

φi‧‧‧diameter of ion collector

FIG. 1 is a schematic view of a triode type ionization vacuum gauge according to an embodiment of the present invention as viewed from the side.

Fig. 2 is a schematic view of a triode type ionization vacuum gauge viewed from above.

FIG. 3 is a graph showing the pressure in the vacuum chamber measured by a triode-type ionization vacuum gauge with different materials of the ion collector.

FIG. 4 is a schematic diagram showing a moving state of positive ions impinging on the ion collector in a comparative example in which the ion collector is made of a material having a thermal conductivity coefficient of less than 173 W / (m˙K) at 300K.

FIG. 5 is a schematic diagram showing a moving state of positive ions impinging on the ion collector when the ion collector is composed of a material having a thermal conductivity coefficient of 173 W / (m˙K) or more at 300K.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

    <Overall structure of triode type ionization vacuum gauge and structure of each part>    

FIG. 1 is a schematic view of a triode-type ionization vacuum gauge 100 according to an embodiment of the present invention as viewed from the side. FIG. 2 is a schematic view of a triode-type ionization vacuum gauge 100 viewed from above.

As shown in these figures, the triode-type ionization vacuum gauge 100 includes a sensor unit 10 and a control unit 20. The sensor unit 10 is provided with a sensor body 11 (receiving portion), a filament 12, a grid 13, an ion collector 14, a plurality of terminals 15a to 15e, a grid support member 16, and an ion collector support member 17 (support member).

The sensor body 11 has a cylindrical shape having a bottom portion 11c, and a filament 12, a grid 13, an ion collector 14, a plurality of terminals 15a to 15e, and a grid are housed inside the sensor body 11. The support member 16 and the ion collector support member 17.

The sensor body 11 has a flange portion 11 a above the sensor body 11, and the flange portion 11 a is used to freely attach and detach the sensor unit 10 to and from a measurement object such as a vacuum chamber. installation. In the flange portion 11a, a groove portion 11b for forming a vacuum seal such as an O-ring is formed along the circumferential direction (θ direction) on the upper side and the inner peripheral side. The flange portion 11 a is fixed to a measurement target such as a vacuum chamber through a vacuum seal, and thereby the pressure inside the measurement target can be measured by the triode-type ionization vacuum gauge 100.

The sensor body 11 is made of stainless steel, nickel, nickel-iron alloy, aluminum alloy, copper, copper alloy, titanium, titanium alloy, tungsten (tungsten), molybdenum, Or it may consist of a metal material such as a combination of two or more of these. The sensor body 11 is grounded.

Five terminals 15a to 15e are inserted into the bottom 11c of the sensor body 11 through an insulator (not shown). The five terminals 15a to 15e are cylindrical members that are long in the Z-axis direction. In addition, the shape of the terminal may also be a shape such as a triangular pillar shape or a quadrangular prism shape, and the shape of the terminal is not particularly limited. These terminals are made of a metal material such as iron, nickel, cobalt, or the like.

Among the five terminals 15a to 15e, two terminals 15a and 15b are terminals connected to the filament 12, one terminal 15c is a terminal connected to the grid 13, and the remaining two terminals 15d and 15e are connected to the ion collector 14. Terminal.

The filament 12 is arranged near the center position of the sensor body 11. The filament 12 has a hairpin shape (inverted V shape), and is formed by bending a linear member having a thickness of, for example, about φ0.1 mm to φ0.2 mm in the center. The filament 12 may have a linear shape, and the shape of the filament 12 is not particularly limited.

The height Hf of the filament 12 (the height of the filament 12 above the terminals 15a and 15b) is set to about 5 mm to 15 mm, for example.

In the filament 12, a thermoelectron is emitted from the curved top. The curved top portion of the filament 12 is located in the center of the grid 13 and the ion collector 14 in the axial direction (Z-axis direction) (see FIG. 1). Moreover, even in the horizontal direction, the top of the filament 12 is still located at the center of the grid 13 and the ion collector 14 (see FIG. 2).

The filament 12 is made of, for example, a metal material such as iridium or tungsten whose surface is covered with yttrium oxide.

One end of the filament 12 is electrically and mechanically connected to the terminal 15a, and the other end of the filament 12 is electrically and mechanically connected to the terminal 15b. In addition to the task of serving as the terminal of the filament 12, the terminal 15a and the terminal 15b also have the task of supporting the filament 12 from below. In this embodiment, the power supply to the filament 12 is set to 4 W or less.

The grid 13 is arranged around the filament 12 concentrically with the filament 12. The grid 13 has a spiral shape, and is formed, for example, by winding a linear member having a thickness of about φ0.1 mm to φ0.3 mm in a spiral shape. In addition, the gate electrode 13 may be formed into a cylindrical shape by a punching metal sheet or a photoetching sheet, and the shape of the gate electrode 13 is not particularly limited.

The height Hg (see FIG. 1) of the grid 13 is set to, for example, about 10 mm to 30 mm, and the diameter φg (see FIG. 2) is, for example, about 5 to 15 mm. The height Hg of the grid 13 is set to be twice the height Hf of the filament 12.

The gate 13 is, for example, tungsten, molybdenum, molybdenum covered with platinum, tantalum, platinum, iridium, an alloy of platinum and iridium, nickel, an alloy of nickel and iron, stainless steel, or the like. It consists of two or more metal materials.

The lower end portion of the gate 13 is electrically and mechanically connected to the terminal 15c. In addition to the task of serving as the terminal of the grid 13, the terminal 15 c also has the task of supporting the grid 13 from below. A gate support member 16 is erected above the terminal 15c. The gate supporting member 16 is a cylindrical member that is long in the axial direction (Z-axis direction), for example, abuts against the inner peripheral side of the gate 13 and can support the gate 13 from the inner peripheral side.

The ion collector 14 is arranged around the grid 13 concentrically with the grid 13. The ion collector 14 has a cylindrical shape and is formed into a cylindrical shape by a plate-like member having a thickness of about 0.05 mm to 0.3 mm. In addition, as long as the ion collector 14 has a cylindrical shape, it is not limited to a cylindrical shape, and may be configured by a shape such as a square tube.

The height Hi (see FIG. 1) of the ion collector 14 is set to, for example, about 10 mm to 30 mm, and the diameter φi (see FIG. 2) of the ion collector 14 is set to, for example, about 10 mm to 30 mm. In addition, the height Hi of the ion collector 14 is set to the same level as the height Hg of the grid 13 and is set to be twice the height Hf of the filament 12.

The ion collector 14 is composed of a metal material having a thermal conductivity coefficient of 173 W / (m˙K) or more at 300K. Although the material of the ion collector 14 may be any material as long as it has the above-mentioned characteristics, metal materials such as tungsten, copper, and graphite can be used as the material. The reason for using such a material as the material of the ion collector 14 will be described in detail later.

The ion collector 14 is electrically and mechanically connected to the terminal 15d and the terminal 15e through the ion collector support member 17. In addition to the task of serving as a terminal of the ion collector 14, the terminal 15d and the terminal 15e also have a task of supporting the ion collector 14 from below.

The ion collector support member 17 is electrically and mechanically connected to the terminals 15d and 15e and the ion collector 14 and supports the ion collector 14 from below while supporting the terminals 15d and 15e from below. One ion collector support member 17 is provided on each of the terminal 15d side and the terminal 15e side.

The ion collector support member 17 is formed such that a thin plate-shaped member is curved along the outer periphery of the ion collector 14. In this embodiment, although the ion collector support member 17 is formed in a short shape in the circumferential direction (θ direction), it may be provided over the entire circumference (360 °) of the ion collector 14.

The ion collector support member 17 is made of a material having a lower thermal conductivity than the ion collector 14. Although any material can be used as long as the material of the ion collector support member 17 is a material having a lower thermal conductivity than that of the ion collector 14, metal materials such as stainless steel (SUS304), iron, nickel, and cobalt can be used as the material.

The control unit 20 is provided with a housing, and a controller 21, an ammeter 22, three power sources 23a to 23c, and the like are built in the housing. The controller 21 includes a CPU (Central Processing Unit), a volatile and non-volatile memory, and the like.

The CPU is based on various programs stored in the memory, and integrally controls each part of the triode ionization vacuum gauge 100. For example, the CPU performs processing for controlling the operations of the respective power sources 23a to 23c, or processing for calculating the pressure based on the ion current value measured by the ammeter 22, and displays the calculated pressure on a display (not shown) Processing.

The ammeter 22 measures an ion current value flowing through the ion collector 14 and outputs the measured value to the controller 21. Among the three power sources 23a to 23c, the first power source 23a is a power source for applying a direct current to the filament 12 to make the filament 12 red, and the second power source 23b is used to impart a higher potential to the grid 13 than the filament 12 Power. The third power source 23c is a power source for increasing the potential of the filament 12 to be higher than the potential of the ion collector 14.

Furthermore, an output terminal (not shown) that is connected to each power source 23 is provided in the frame system, and the sensor unit 10 and the control unit 20 are connected by a cable with a connector. Moreover, the sensor unit 10 and the control unit 20 can also be embedded in the same frame.

    <Trial>    

Next, a test performed to investigate the relationship between the thermal conductivity of the ion collector 14 and the measured pressure will be described. In this test, seven types of materials are prepared as the materials of the ion collector 14, and the seven types of triode-type ionization vacuum gauges 100 are used to measure the vacuum exhaust chambers when the materials of the ion collector 14 are different. The pressure.

Table 1 shows the relationship between the seven types of metal materials used as the material of the ion collector 14 and the thermal conductivity at 300K among these metal materials. FIG. 3 is a schematic diagram showing the pressure in the vacuum chamber measured by the triode-type ionization vacuum gauge 100 with different materials of the ion collector 14.

In this test, iridium coated on the surface with yttrium oxide can be used as the material of the filament 12, and the thickness of the filament 12 is set to φ0.127 mm (before yttrium oxide coating). The height Hf of the filament 12 is set to 10 mm.

In addition, molybdenum coated with platinum may be used as the material of the gate electrode 13, and the thickness of the gate electrode 13 is set to φ0.25 mm. The height Hg of the grid 13 is set to 20 mm, and the diameter φg of the grid 13 is set to 10 mm.

As shown in Table 1, seven types of graphite, copper, tungsten, molybdenum, nickel, platinum, and stainless steel (SUS304) were used as the material of the ion collector 14. As shown in Table 1, the thermal conductivity (plane direction) at 300K of these seven types of materials is 700W / (m˙K), 401W / (m˙K), 173W / (m˙K), 138W / (m˙K), 90.9W / (m˙K), 71.6W / (m˙K), 16W / (m˙K).

The thickness of the ion collector 14 is set to 0.1 mm, the height of the ion collector 14 is set to 20 mm, and the diameter φi of the ion collector 14 is set to 17 mm.

In addition, stainless steel (SUS304) was used as a material of the ion collector support member 17.

The potential of the filament 12 is set to 25V, the potential of the grid 13 is set to 150V, and the potential of the ion collector 14 is set to 0V. The power supply to the filament 12 is set to 4 W or less, and the emission current between the filament 12 and the grid 13 is set to 1 mA.

The case where graphite, copper, and tungsten with a thermal conductivity of 173 W / (m˙K) or more at 300 K are used as the material of the ion collector 14 corresponds to an embodiment of the present invention. On the other hand, the case of using molybdenum, nickel, platinum, and stainless steel (SUS304) having a thermal conductivity of less than 173 W / (m˙K) at 300 K as the material of the ion collector 14 corresponds to a comparative example.

Referring to FIG. 3, the pressure in the vacuum chamber measured by the triode ionization vacuum gauge 100 with different materials of the ion collector 14 is shown in FIG. 3. In Fig. 3, the vertical axis shows the measured pressure, and the horizontal axis shows the time (12 hours overall). In addition, since molybdenum, nickel, and platinum have substantially the same curve, they are represented by the same curve.

In Figure 3, the result is that the graphite with the highest thermal conductivity has the lowest arrival pressure (2 × 10 ^-6 Pa), and the arrival pressure will gradually increase as the thermal conductivity becomes lower, and the stainless steel with the lowest thermal conductivity (SUS304) The arrival pressure (1 × 10 ^-4 Pa) is the highest. After reaching the pressure-based pressure and the vacuum evacuation, the pressure is stabilized and becomes a constant value.

From this result, it is understood that the higher the thermal conductivity becomes, the lower the reaching pressure becomes. In other words, it can be understood that there is an inverse relationship between the thermal conductivity of the ion collector 14 and the arrival pressure.

In FIG. 3, two curves of the following comparative example are looked at: a curve corresponding to molybdenum, nickel, and platinum having a thermal conductivity coefficient of less than 173 W / (m˙K) at 300 K; and a curve corresponding to stainless steel. The pressure shown in these curves gradually decreases as the pressure in the vacuum chamber decreases due to the lowering of the vacuum exhaust. After falling to about 2 × 10 ^-5 Pa (measurement limit value), it gradually rises and reaches It was about 8 × 10 ^-5 Pa, and then it was stable.

In this way, when a material with a lower thermal conductivity is used as the material of the ion collector 14, the measured pressure will drop temporarily, and then rise to a fixed value and a stable state.

    <The reason why pressure becomes unstable action>    

Hereinafter, in a comparative example in which the ion collector 14 is made of a material having a thermal conductivity coefficient of less than 173 W / (m˙K) at 300 K, the reason why the pressure becomes such an operation will be described. FIG. 4 is a schematic diagram showing a movement state of the positive ion 1 colliding with the ion collector 14 in a comparative example composed of a material having a thermal conductivity coefficient of less than 173 W / (m˙K) at 300 K. FIG. . Note that, for convenience, the gate electrode 13 is omitted and shown in FIG. 4.

When the filament 12 is energized, thermionic electrons are emitted from the vicinity of the top of the filament 12. The thermionic electrons are accelerated toward the grid 13 and captured by the grid 13. Part of the hot electrons collide with the gas molecules scattered inside the triode-type ionization vacuum 100 near the grid 13, whereby the gas molecules are ionized to generate positive ions 1.

The positive ions 1 are attracted by the ion collector 14, collide with the ion collector 14, and receive electrons from the ion collector 14.

The positive ion 1 receives electrons from the ion collector 14, an ion current is generated in the ion collector 14, and the value of the ion current can be measured by the ammeter 22. Thereby, the pressure inside the vacuum chamber is measured.

In FIG. 3, two curves are focused on: the curve corresponding to stainless steel and the curve corresponding to molybdenum, nickel, and platinum. In these curves, when the pressure slowly decreases in accordance with the vacuum exhaust of the vacuum chamber, gas molecules (positive ions 1) will hit the surface of the ion collector, and the gas molecules that hit the surface will form part of the gas. The mode is detached, and the remaining part becomes an equilibrium state of a molecular layer (for example, a physical adsorption layer or a chemisorption layer caused by adsorbing molecules 2).

Moreover, since platinum is chemically very stable, when the ion collector 14 is composed of platinum, compared with other examples, a molecular layer due to chemisorption is hardly formed. In other words, although the schematic diagram of the gas molecules existing on the surface of the ion collector 14 in FIG. 4 shows the equilibrium state at a certain time point, the gas molecules (such as water molecules) hit the surface of the ion collector 14 here. The molecular layer system formed as a result can be considered to be dominated by physical adsorption.

With respect to the probability that a molecular layer due to adsorption is formed on the surface of the ion collector 14, the area near the center in the axial direction of the ion collector 14 is a region with a high probability of being hit by positive ions 1 and is in equilibrium Areas where it is not easy to deposit molecular layers. In this region, since the molecular layer is not easy to be deposited, even if the positive ion 1 collides with the region, it is difficult to release particles such as neutral molecules, neutral fragment molecules, neutral atoms, or these ions.

On the other hand, the region near both ends in the axial direction of the ion collector 14 is a region where the probability of collision of the positive ions 1 is lower than that in the vicinity of the center, and therefore it is used as a region where the molecular layer is easily deposited over time. When the positive ion 1 hits the deposited molecular layer, it will release neutral molecules, neutral fragment molecules, neutral atoms or these ions.

The energy from which molecules detach from the surface can also be examined from the temperature at which the molecules move. When the ion collector 14 is viewed from this point of view, since the vicinity of the center in the axial direction is a region near the top of the filament 12 that generates heat, it becomes a region having a high temperature (see FIG. 4). Therefore, the molecular layer system near the center in the axial direction of the ion collector 14 retains a higher energy than both ends. In other words, compared with the two ends, the equilibrium state near the center can be considered to be dominating, and the two ends can be considered to be dominating. Therefore, from the viewpoint of the temperature of the ion collector 14, the area near the center in the axial direction of the ion collector 14 is regarded as a region where the molecular layer is not easily deposited, and the area near the two ends in the axial direction is regarded as the molecular layer. Areas easy to deposit.

When the time elapses further from the start of the vacuum exhaust of the vacuum chamber, the composition of the gas molecules in the sensor body 11 changes to a composition corresponding to the exhaust capability of the vacuum chamber. Generally speaking, the gas molecules that have more advantages in detachment than the adsorption will be preferentially exhausted. As a result, the gas molecules that have more advantages in adsorption in the vacuum chamber will change to the dominant composition. For example, it can be considered that the composition of the gas in the sensor body 11 changes to a composition in which the water molecules that are not easily exhausted from the vacuum chamber have increased. Of course, the composition of the molecular layer on the surface of the ion collector 14 will also change according to the composition change in the vacuum chamber as the measurement object.

Since the composition of the gas molecules in the sensor body 11 is difficult to change, etc., the entire surface area of the ion collector 14 changes to an equilibrium state in which the adsorption ratio is more advantageous. However, the process of this change is slow, and it can be said that it cannot be clearly confirmed at the time point of 12h / nine hours in FIG. 3 as an experimental example, and it can be confirmed during the period of 12h / nine hours to 12h. The change. In other words, it can be considered that the final equilibrium state has passed the time point of 12 hours. This can be considered to indicate that the composition in the vacuum chamber was changed from a general atmospheric composition ratio to a gas composition having an adsorption advantage near the time point of 12 h / elapsed 9 hours.

Although the environment with a vacuum exhaust system is shown in FIG. 3, the vacuum exhaust system is an environment where the gas with an adsorption advantage is found below 1.0 × 10 ^-3 Pa, but the gas from the opening time of the atmosphere to the beginning of the vacuum exhaust The composition system is not significantly different from the atmospheric composition in the initial state. In other words, the entire surface area of the ion collector 14 is in a state of equilibrium in which detachment is dominant, and is not in a state of being adsorbed. In other words, when the tangents of the time-varying curves of the various materials in FIG. 3 are used as the values of the slopes of the first-order functions in the original situation, it can be confirmed from all cases where the values are negative.

However, below 1.0 × 10 ^-4 Pa, a change in the composition on the surface of the ion collector 14 with a change in the gas composition can be confirmed from the change in FIG. 3. Although the description of the vacuum degree measured by other vacuum degree measuring devices is omitted in FIG. 3, since the value of graphite is close to the true vacuum degree in the vacuum chamber, the same vacuum degree as graphite should be displayed . However, the vacuum of other materials will gradually deteriorate, that is, although the slope is negative, it still shows a tendency to approach zero.

This is because the composition of the surface of the ion collector 14 was changed from the composition of the atmosphere to the composition of the gas with the advantage of adsorption, thereby changing the thickness of the molecular layer on the surface of the ion collector 14. No difference will occur until this vacuum is reached.

Since this phenomenon is the gas composition that has become the advantage of adsorption, compared to the previous case, the temperature conditions of the surface being adsorbed will become dominant. In other words, in the comparison of the materials in FIG. 3, it can be considered that the material having a lower temperature surface easily adsorbs gas molecules and increases the adsorption amount, in other words, increases the thickness of the molecular layer.

Here, when the positive ion 1 hits (incident) the molecular layer having the increased thickness, the molecules of the molecular layer given the incident energy are detached. Although detailed physical phenomena need to be studied in the future, according to FIG. 3 and the like, it can be considered that the amount of molecules separated from the incidence of positive ions on the surface of the ion collector of the triode ionization vacuum gauge in the vacuum degree is related to the number of molecules The thickness of the layers is proportional.

In other words, because there is a relationship that molecules released (detached) increase by increasing the thickness of the molecular layer, the detached molecules also increase as the equilibrium state below 1.0 × 10 ^-4 Pa becomes an adsorption advantage. It is large and the detached molecule can be measured by a vacuum meter again. As a result, the slope of the measured value of the vacuum degree will shift to the zero side.

Generally, adsorption / desorption is stabilized at a stage where it has migrated to an equilibrium state. In other words, it can be considered that at the time point when the slope of the measured value of the vacuum degree has become zero, the adsorption / desorption is in an equilibrium state. Although the user of the vacuum gauge regards the point of time when the equilibrium state has been reached as the measurement limit and regards the vacuum gauge as having a poor ability, when the measurement limit changes with time, it is difficult to match the original vacuum level. The situation of deterioration is different, and the change itself as a measuring device will bring distrust to the user. According to this, it can be said that it is problematic to be a product.

In other words, although it is necessary to avoid the situation in which the slope is changed from zero to a positive degree of vacuum for measurement, this problem occurs with the material containing platinum. This is because the temperature on the surface of the ion collector 14 is low. In other words, compared with other materials, the equilibrium state of the detachment and adsorption relative to the incidence frequency of positive ions is the adsorption side, so the molecular layer will be further deposited. As the thickness is increased, as a result, the amount of detachment of molecules caused by the incidence of positive ions is increased.

The reason why the above-mentioned slope becomes positive in the period from 12 hours / nine hours to 12 hours has elapsed is that the molecular layers have been deposited near the two ends (low temperature portions) of the ion collector 14 in the axial direction. The molecular layer will be the source of the release of the molecules. In other words, when the ion collector 14 is composed of various materials including platinum, the pressure in the sensor body 11 becomes locally high due to the influence of molecules released by the release source. It is a problem that the pressure is different from the pressure in the vacuum chamber as the measurement target. Therefore, there is a problem that the pressure in the vacuum chamber cannot be accurately measured.

    <Adsorption molecule>    

Next, the measurement performed to determine what kind of molecule the adsorbed molecule 2 is mainly described will be described. In this measurement, as described above, a triode-type ionization vacuum gauge of seven kinds of ion collectors 14 (graphite, copper, tungsten, molybdenum, nickel, platinum, stainless steel (SUS304)) was prepared. Then, after the vacuum evacuation of the vacuum chamber, the sensor body was measured by a quadruple mass spectrometer when the filament 12 was turned OFF and when the filament 12 was turned ON. Mass spectrum of gas molecules in 11.

As a result, in a triode-type ionization vacuum gauge (comparative example) corresponding to four materials of molybdenum, nickel, platinum, and stainless steel having a low thermal conductivity (comparative example), the peak of water in the mass spectrum when the filament 12 is turned on is higher than that when the filament 12 is turned off. The water peak of the mass spectrum becomes more significant.

This is a case where the amount of water molecules scattered in the sensor body 11 when the filament 12 is on is shown to be much larger than the amount of water molecules scattered in the sensor body 11 when the filament 12 is off. This result shows that the adsorption molecules 2 are mainly water molecules.

In other words, when the filament 12 is turned off, since the water molecules do not become positive ions 1, the water molecules are not attracted by the ion collector 14, so the amount of water molecules adsorbed on the ion collector 14 as the adsorption molecules 2 less. Therefore, when the filament 12 is turned off, there is no source of water molecules release, so the amount of water molecules scattered in the sensor body 11 is substantially the same as the amount of water molecules in the vacuum chamber, and the amount of water molecules is less.

When the filament 12 is turned on, water molecules become positive ions 1 and the water molecules are attracted by the ion collector 14. Since the ion collector 14 is made of a material having a low thermal conductivity, water molecules are deposited on the ion collector 14 as the adsorption molecules 2. Then, since the deposited water molecules will become the release source of the water molecules, when the filament 12 is turned on, the amount of water molecules scattered in the sensor body 11 becomes far more than when the filament 12 is turned off.

This shows that the peak of water in the mass spectrum when the filament 12 is turned on is significantly larger than the peak of water in the mass spectrum when the filament 12 is turned off. Therefore, it can be understood that the adsorption molecule 2 is mainly a water molecule.

In this measurement, even with regard to platinum that is chemically very stable, the peak of water in the mass spectrum when the filament 12 is on is still significantly larger than the peak of water in the mass spectrum when the filament 12 is off. In other words, this shows the case where, for the reason that the pressure becomes unstable in the comparative example, the formation of the molecular layer caused by chemical adsorption is not the main reason, and the molecular layer caused by the adsorption of water molecules is not the main reason. Formation is the main reason (because platinum does not easily form a molecular layer caused by chemisorption).

Furthermore, even in the triode-type ionization vacuum gauge 100 (this embodiment) corresponding to three materials with high thermal conductivity, such as graphite, copper, and tungsten, the peak of water in the mass spectrum when the filament 12 is turned on is still smaller than the filament. The water peak of the mass spectrum at the time of the 12 disconnection is larger, but the difference is small. This shows that when the filament 12 is turned on in this embodiment, the amount of water molecules adsorbed becomes much smaller than that in the comparative example.

    <Function, etc.>    

As described above, in the comparative example in which the ion collector 14 is composed of a material having a thermal conductivity coefficient of less than 173 W / (m˙K) at 300 K, the measured pressure becomes less than the adsorption of water molecules to the ion collector 14 The main reason for being correct.

Therefore, in this embodiment, in order to prevent the occurrence of the adsorption molecules 2 (especially water molecules), the material is made of a material (for example, graphite, copper, tungsten) having a thermal conductivity of 173 W / m˙K at 300K or more. Ion collector 14.

FIG. 5 is a schematic diagram showing the movement of the positive ion 1 colliding with the ion collector 14 when the ion collector 14 is made of a material having a thermal conductivity coefficient of 173 W / (m˙K) or more at 300K. The gate 13 is omitted in FIG. 5 for the sake of convenience.

As shown in FIG. 5, in this embodiment, since the ion collector 14 is formed of a material having a high thermal conductivity coefficient, the heat generated in the filament 12 can be efficiently transmitted to the entire ion collector 14. Therefore, in the ion collector 14, the temperature can be increased not only at the center portion in the axial direction (Z-axis direction) but also near both ends in the axial direction, and the temperature of the entire ion collector 14 can be increased.

Therefore, in FIG. 5, which is different from FIG. 4 of the comparative example, in the vicinity of both end portions in the axial direction of the ion collector 14, gas molecules that collide with the ion collector 14 as positive ions 1 are separated from the ion collector 14. The energy will get higher. Thereby, occurrence of the adsorption molecules 2 (especially water molecules) can be prevented.

Furthermore, in the above test, the temperature of the ion collector 14 composed of graphite, copper, and tungsten was actually measured. As a result, the temperature exceeded 210 degrees. It can be understood here that as long as the temperature of the ion collector 14 becomes 200 ° C or more, the adsorption of water molecules and the like can be prevented, and it can be understood from this that the occurrence of the adsorption molecules 2 can be appropriately prevented in this embodiment. In the above test, the temperature of the ion collector 14 (comparative example) composed of molybdenum, nickel, platinum, and stainless steel (SUS304) was actually measured. As a result, it was 160 ° to 180 °.

As described above, in this embodiment, since the occurrence of the adsorption molecules 2 can be prevented, it is possible to prevent a situation where the pressure measured as in the comparative example becomes incorrect, and it is possible to accurately measure the inside of a measurement object such as a vacuum chamber. pressure.

This situation is shown in the graph corresponding to graphite, copper, and tungsten in FIG. 3. That is, as shown by such a curve, in this embodiment, the measured pressure is gradually decreased as the pressure in the vacuum chamber is lowered due to the decrease in vacuum exhaust, and it is reduced to a predetermined value (measurement After the limit value), it is stable and takes a fixed value in this state.

Here, in this embodiment, the power supply to the filament 12 is set to 4 W or less. In the small triode type ionization vacuum gauge 100 in which the power supply to the filament 12 can be set to 4W or less, the heat generated in the filament 12 is easily reduced. Therefore, when no measures are taken, the temperature is easy to collect in ions. There is a problem that the vicinity of both ends of the device 14 in the axial direction becomes low.

On the other hand, as described above, the triode-type ionization vacuum gauge 100 according to the present embodiment is composed of a material having a high thermal conductivity coefficient to constitute the ion collector 14. Therefore, even in a small triode-type ionization vacuum gauge 100 in which the power supplied to the filament 12 can be set to 4 W or less, the heat of the filament 12 can be reduced, the ion collector 14 can still be at both ends in the axial direction in the ion collector 14 The temperature of the ion collector 14 is appropriately increased near the portion.

In this embodiment, the ion collector support member 17 is made of a material having a lower thermal conductivity than a material constituting the ion collector 14. Therefore, it is possible to prevent the heat of the ion collector 14 from being dissipated toward the ion collector supporting member 17 and to maintain the heat of the ion collector 14 in a high state.

In this embodiment, the sensor body 11 is made of a metal material. In this way, by constructing the sensor body 11 with a metal material, it is possible to prevent the hot electrons from the filament 12 from charging when the sensor body 11 hits the sensor body 11, and the potential distribution in the space in the sensor body 11 can be fixed. To maintain. Thereby, the pressure can be measured with a fixed sensitivity for a long time.

Here, in order to prevent the occurrence of the adsorption molecules 2 on the ion collector 14, both ends of the ion collector 14 in the axial direction (Z-axis direction) may be cut to reduce the height Hi of the ion collector 14. However, when the height Hi of the ion collector 14 is lowered as described above, there is a possibility that the capture efficiency of the positive ions 1 in the ion collector 14 may be reduced.

On the other hand, in this embodiment, the ion collector 14 is formed of a material having a high thermal conductivity coefficient, thereby preventing the occurrence of the adsorption molecules 2. Therefore, it is not necessary to reduce the height Hi of the ion collector 14. Therefore, in this embodiment, it is possible to appropriately prevent the occurrence of the adsorption molecules 2 without reducing the trapping efficiency of the positive ions 1 in the ion collector 14. In addition, as described above, in the present embodiment, the height Hi of the ion collector 14 is about twice the height Hf of the filament 12 and is set to the same height as the height Hg of the grid 13.

Moreover, this interesting purpose does not necessarily increase the height Hi of the ion collector 14. For example, the height Hi of the ion collector 14 may be set to a lower height than the height Hg of the grid 13.

Claims (5)

    A triode type ionization vacuum gauge includes: a filament; a grid arranged around the aforementioned filament; and an ion collector, which is cylindrical and arranged around the aforementioned grid, and has a thermal conductivity of 173W / at 300K (m˙K) or more.         The triode type ionization vacuum gauge according to claim 1, wherein the power supplied to the filament is 4 W or less.         The triode-type ionization vacuum gauge according to claim 1 or 2, further comprising: a supporting member for supporting the ion collector, and composed of a material having a lower thermal conductivity than a material constituting the ion collector.         The triode-type ionization vacuum gauge according to claim 1 or 2, further comprising: a containing part, which is made of a metal material, and contains the filament, the grid, and the ion collector inside.         A pressure measuring method is to prepare a triode-type ionization vacuum gauge and measure the internal pressure of an object to be measured by the triode-type ionization vacuum gauge. The triode-type ionization vacuum gauge is provided with: a filament; a grid, which is arranged in the foregoing. The periphery of the filament; and the ion collector, which is cylindrical and disposed around the grid, is made of a material having a thermal conductivity coefficient of 173 W / (m˙K) or more at 300K.