TWI786129B - Triode type ionization vacuum gauge and pressure measurement 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°K under 300K.

Description

Triode ionization vacuum gauge and pressure measuring method

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

The vacuum processing apparatus has a vacuum chamber (vacuum chamber) capable of film formation by sputtering or evaporation. Since the pressure in the vacuum chamber greatly affects product yield, it is necessary to accurately measure the pressure in the vacuum chamber. A triode type ionization vacuum gauge is known as a device for accurately measuring the pressure in the range of 1 Pa to 10 ⁻⁶ Pa among the pressures in the vacuum chamber.

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

When the filament is energized, hot electrons are emitted from the filament (near the top of the filament), which are accelerated towards and captured by the grid. A part of the thermal electrons is near the grid and collides with the gas molecules scattered inside the triode 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 ionic current is 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 the measurement object (such as vacuum) on which the triode ionization vacuum gauge is installed. processing device) internal pressure.

Here, as described in the following patent documents 1 and 2, when gas molecules (positive ions) hit the surface of the ion collector, gas molecules will be adsorbed (such as physical adsorption, chemical adsorption) on the surface of the ion collector and form Molecular layer (physical adsorption layer, chemical adsorption layer) situation.

The area near the center of the central axis of the ion collector is an area with a high impact probability of positive ions. By continuously impacting positive ions on this area, the particles of neutral fragment molecules, neutral atoms, or such ions are separated from the molecules. Layers are released as much as possible. Therefore, the area near the center of the ion collector in the axial direction is regarded as the area where the molecular layer is not easy to be deposited. On the other hand, the regions near both ends in the central axis direction of the ion collector are regions where the collision probability of positive ions is low, and since positive ions do not continuously collide, they are regarded as regions where positive ions are easily deposited as a molecular layer.

In addition, the following patent document 3 and patent document 4 are mentioned as a technique related to this application.

[Prior Art Literature]

[Patent Document]

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

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

Patent Document 3: Japanese Unexamined Patent Publication No. 2006-343305.

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

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

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

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

In this triode type ionization vacuum gauge, the ion collector is made of a material whose thermal conductivity at 300K is 173W/(m˙K) or more. In other words, the ion collector is made of materials with high thermal conductivity. Thereby, the heat generated in the filament can be easily transmitted to the whole ion collector, and the temperature of the ion collector can be raised even in the vicinity of both ends of the ion collector in the axial direction. Thereby, it is possible to prevent molecular layers from being formed in the vicinity of both ends in the axial direction of the ion collector. As a result, in this triode type ionization vacuum gauge, the pressure inside the object to be measured can be accurately measured.

In the above-mentioned triode type ionization vacuum gauge, the electric power supplied to the above-mentioned filament may be 4W 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 in the filament tends to be low, the temperature tends to be in the axial direction of the ion collector. The problem that the vicinity of the two ends becomes lower. On the other hand, as mentioned above, in the triode ionization vacuum gauge of the present invention, the ion collector is formed of a material with 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 4W or less and the heat of the filament tends to be low, it is still possible to appropriately increase The temperature of the ion collector.

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

The above triode type ionization vacuum gauge may further include a housing portion. The aforesaid accommodating part is made of metal material, and accommodates the aforesaid filament, the aforesaid grid and the aforesaid ion collector inside.

In this way, by constituting the housing portion with a metal material, it is possible to prevent charge-up from occurring when thermal electrons collide with the housing portion, and to maintain a constant potential distribution in the space in the housing portion. Thereby, the pressure can be measured with a fixed sensitivity for a long time.

The pressure measuring method of the present invention prepares a triode type ionization vacuum gauge, and measures the internal pressure of the object to be measured by the aforementioned triode type ionization vacuum gauge. The triode type ionization vacuum gauge is equipped with: a filament; The periphery of the aforementioned filament; and the ion collector are cylindrical and arranged around the aforementioned grid, and are made of a material with a thermal conductivity 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 an object to be measured.

1‧‧‧positive ion

2‧‧‧adsorbed molecules

10‧‧‧Sensor unit

11‧‧‧Sensor body (containment part)

11a‧‧‧flange

11b‧‧‧groove

11c‧‧‧bottom

12‧‧‧Filament

13‧‧‧Gate

14‧‧‧ion collector

15, 15a to 15e‧‧‧terminal

16‧‧‧Grid support member

17‧‧‧Ion collector support member (support member)

20‧‧‧Control Unit

21‧‧‧Controller

22‧‧‧galvanometer

23a to 23c‧‧‧Power

100‧‧‧Triode Ionization Vacuum Gauge

Hf‧‧‧Filament height

Hg‧‧‧Gate height

Hi‧‧‧The height of the ion collector

φg‧‧‧Gate diameter

φi‧‧‧Ion collector diameter

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

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

Fig. 3 is a graph showing the pressure in the vacuum chamber measured by triode ionization vacuum gauges with different materials of ion collectors.

FIG. 4 is a schematic diagram showing the movement of positive ions striking the ion collector in a comparative example in which the ion collector is made of a material whose thermal conductivity at 300K is less than 173 W/(m˙K).

5 is a schematic diagram showing the movement of positive ions impacting on the ion collector when the ion collector is made of a material with a thermal conductivity of 173 W/(m˙K) or higher at 300K.

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

<The overall structure and the structure of each part of the triode ionization vacuum gauge>

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

As shown in the drawings, the triode 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 (accommodating 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 with a bottom 11c, and a filament 12, a grid 13, an ion collector 14, a plurality of terminals 15a to 15e, and a grid are accommodated inside the sensor body 11. Support member 16 and ion collector support member 17 .

The sensor body 11 has a flange portion 11a on the upper portion of the sensor body 11, and the flange portion 11a is used to attach and detach the sensor unit 10 to a measurement object such as a vacuum chamber. Install. In the flange portion 11a, a groove portion 11b for accommodating a vacuum seal such as an O-ring is formed along the circumferential direction (theta direction) at an upper and inner peripheral position. The flange portion 11 a is fixed to a measurement object such as a vacuum chamber through a vacuum seal, so that the pressure inside the measurement object can be measured by the triode ionization vacuum gauge 100 .

The sensor body 11 is made of stainless steel, nickel, alloy of nickel and iron, aluminum alloy, copper, copper alloy, titanium (titanium), titanium alloy, tungsten (tungsten), molybdenum (molybdenum), Or a combination of two or more of these metal materials. The sensor body 11 is grounded.

Five terminals 15a to 15e are inserted through 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. Furthermore, the shape of the relevant terminals may also be in the shape of a triangular prism or a square prism, and the shape of the relevant terminals is not particularly limited. These terminals are made of metal materials such as iron, nickel, cobalt, etc., for example.

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

The filament 12 is disposed near the center of the sensor body 11 . The filament 12 has a hairpin shape (inverted V shape), and is formed by bending a linear member with a thickness of, for example, 0.1 mm to 0.2 mm in the center. Furthermore, the filament 12 may also 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 portion of the filament 12 above the terminals 15a, 15b) is set, for example, to about 5 mm to 15 mm.

In the filament 12, hot electrons are emitted from the curved top. The curved top of the filament 12 is located at 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 (refer to FIG. 2 ).

The filament 12 is made of, for example, metal materials such as iridium and 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 having a role as a terminal of the filament 12, the terminal 15a and the terminal 15b also have a role as a support pin for supporting the filament 12 from below. In addition, in this embodiment, the electric power supplied to the filament 12 is made into 4W or less.

The grid 13 is arranged concentrically with the filament 12 around the filament 12 . The grid 13 has a helical shape, for example, is formed by winding a linear member with a thickness of about φ0.1 mm to φ0.3 mm in a helical shape. Furthermore, the grid 13 can also be formed into a cylindrical shape by punching metal sheets or photoetching sheets, and the shape of the grid 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 set to, for example, about 5 mm to 15 mm. Furthermore, the height Hg of the grid 13 is set to be twice the height Hf of the filament 12 .

The grid 13 is made of, for example, tungsten, molybdenum, molybdenum covered with platinum on the surface, tantalum (tantal), platinum, iridium, alloys of platinum and iridium, nickel, alloys of nickel and iron, stainless steel, or among these Composed of metal materials such as a combination of two or more.

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

The ion collector 14 is arranged concentrically with the grid 13 around the grid 13 . The ion collector 14 has a cylindrical shape, and is formed of a plate-shaped member with a thickness of about 0.05 mm to 0.3 mm to form a cylindrical shape. Furthermore, as long as the ion collector 14 is cylindrical, it is not limited to a cylindrical shape, and may be formed in a shape such as an angular cylinder.

The height Hi (see FIG. 1 ) of the ion collector 14 is set to about 10 mm to 30 mm, and the diameter φi (see FIG. 2 ) of the ion collector 14 is set to about 10 mm to 30 mm, for example. Furthermore, the height Hi of the ion collector 14 is set to be approximately the same 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 made of a metal material whose thermal conductivity at 300K is above 173W/(m˙K). Any material can be used as the material of the ion collector 14 as long as it has the above-mentioned characteristics, but for example, a metal material such as tungsten, copper, graphite (graphite) can be used as the material. Furthermore, 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 having a role as a terminal of the ion collector 14, the terminal 15d and the terminal 15e also have a role as a support pin for 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 being supported by the terminals 15d and 15e from below. The ion collector supporting member 17 is arrange|positioned one each on the side of the terminal 15d and the side of the terminal 15e.

The ion collector support member 17 is formed as a thin plate-like member bent along the outer periphery of the ion collector 14 . In this embodiment, the ion collector supporting member 17 is formed in a short shape in the circumferential direction (theta direction), but 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 with a lower thermal conductivity than the ion collector 14 . Any material can be used for the ion collector supporting member 17 as long as it has a lower thermal conductivity than that of the ion collector 14, but for example, metal materials such as stainless steel (SUS304), iron, nickel, cobalt, etc. can be used as the material.

The control unit 20 is equipped 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; central processing unit), or a volatile or non-volatile memory (memory) and the like.

The CPU integrally controls each part of the triode ionization vacuum gauge 100 based on various programs stored in the memory. For example, the CPU executes a process of controlling the operation of each power supply 23a to 23c, or a process of 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 etc.

The ammeter 22 measures the value of ion current flowing in 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 used to energize the filament 12 with direct current to make the filament 12 red hot, and the second power source 23b is used to give the grid 13 a higher potential than the filament 12. power supply. Also, the third power source 23c is used to raise the potential of the filament 12 to a power source higher than the potential of the ion collector 14 .

Furthermore, output terminals (not shown) leading to the power sources 23 are provided in the frame system, and the sensor unit 10 and the control unit 20 are connected by cables with connectors. Furthermore, the sensor unit 10 and the control unit 20 can also be embedded in the same frame.

<test>

Next, an experiment conducted to investigate the relationship between the thermal conductivity of the ion collector 14 and the measured pressure will be described. In this test, seven kinds of materials were prepared as the materials of the ion collector 14, and the triode ionization vacuum gauge 100 of the seven kinds of different materials of the ion collector 14 measured the vacuum chamber during vacuum exhaust. pressure.

Table 1 shows the relationship between 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 ionization vacuum gauge 100 with different materials of the ion collector 14 .

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

In addition, molybdenum whose surface is covered with platinum can be used as the material of the grid 13, and the thickness of the grid 13 is set to φ0.25 mm. Also, the height Hg of the grid 13 was set to 20 mm, and the diameter φg of the grid 13 was set to 10 mm.

Also, as shown in Table 1, seven kinds 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) of these seven kinds of materials at 300K is 700W/(m˙K), 401W/(m˙K), 173W/(m˙K), 138W/(m˙K), 90.9W/(m˙K), 71.6W/(m˙K), 16W/(m˙K).

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

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

Also, the potential of the filament 12 was set to 25V, the potential of the grid 13 was set to 150V, and the potential of the ion collector 14 was set to 0V. In addition, the power supplied to the filament 12 was set to 4W or less, and the emission current between the filament 12 and the grid 13 was set to 1mA.

Furthermore, the use of graphite, copper, and tungsten whose thermal conductivity at 300K is 173 W/(m˙K) or higher 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) whose thermal conductivity at 300K is less than 173 W/(m˙K) as the material of the ion collector 14 corresponds to the comparative example.

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

In Figure 3, the result is that graphite with the highest thermal conductivity has the lowest reaching pressure (2×10 ^-6 Pa), and the reaching pressure will gradually increase as the thermal conductivity decreases, and stainless steel with the lowest thermal conductivity (SUS304) The reaching pressure (1×10 ^-4 Pa) is the highest. It should be noted that the attained pressure is a value when the pressure is stabilized and becomes a constant value after the pressure is lowered together with the evacuation.

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

In FIG. 3 , focus is placed on two curves of the following comparative example: the curve corresponding to molybdenum, nickel, and platinum whose thermal conductivity at 300K is less than 173W/(m˙K); and the curve corresponding to stainless steel. The pressure shown in these curves decreases slowly as the pressure in the vacuum chamber decreases due to vacuum exhaust, and then rises slowly to reach about 2×10 ^-5 Pa (measurement limit value) About 8×10 ^-5 Pa, and then in a stable state.

In this way, when a material with a low thermal conductivity is used as the material of the ion collector 14, the measured pressure temporarily drops, then rises to a constant value and becomes a steady state.

<The reason why pressure becomes unstable movement>

Hereinafter, in a comparative example in which the ion collector 14 is made of a material whose thermal conductivity at 300K is less than 173 W/(m˙K), the reason why the pressure acts as such will be described. 4 is a schematic diagram showing the movement of positive ions 1 that hit the ion collector 14 in a comparative example in which the ion collector 14 is made of a material whose thermal conductivity at 300K is less than 173 W/(m˙K). . In addition, for the sake of convenience, in FIG. 4 , the grid 13 is omitted from the illustration.

When the filament 12 is energized, hot electrons are emitted from near the top of the filament 12, which are accelerated towards the grid 13 to be captured by the grid 13. A part of the hot electrons collides with the gas molecules scattered inside the triode ionization vacuum device 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 and collide with the ion collector 14 , and receive electrons from the ion collector 14 .

When the positive ions 1 receive 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 the focus is on two curves: the curve for stainless steel and the curves for molybdenum, nickel and platinum. In these curves, when the pressure decreases slowly corresponding to the vacuum exhaust of the vacuum chamber, the gas molecules (positive ions 1) will hit the surface of the ion collector, and the gas molecules hitting the surface will form part of the gas The remaining part becomes the equilibrium state of the molecular layer (for example, the physical adsorption layer or chemical adsorption layer caused by the adsorption of molecules 2).

Furthermore, since platinum is very stable chemically, when the ion collector 14 is made of platinum, compared with other examples, a molecular layer due to chemical adsorption 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. The resulting molecular layer system can be considered to be dominated by physisorption.

Relative to the probability of forming a molecular layer caused by adsorption on the surface of the ion collector 14, the area near the center of the central axis of the ion collector 14 is regarded as a region with a high probability of positive ions 1 impacting, and is in equilibrium The region where the molecular layer is not easy to deposit under the state. In this area, since the molecular layer is not easy to deposit, even if the positive ions 1 hit the area, it is still difficult to release particles such as neutral molecules, neutral fragment molecules, neutral atoms or these ions.

On the other hand, the regions near both ends in the central axis direction of the ion collector 14 are regions where the impact probability of positive ions 1 is lower than that near the center, so they are regarded as regions where the molecular layer is easily deposited over time. When positive ions 1 collide with the deposited molecular layer, neutral molecules, neutral fragment molecules, neutral atoms or ions of these will be released.

The energy of a molecule detaching from a surface can also be considered from the temperature as a molecular motion. When the ion collector 14 is viewed from this point of view, the vicinity of the center in the axial direction is a region close to the top of the filament 12 that generates heat, so it becomes a region with a high temperature (see FIG. 4 ). Therefore, the molecular layer near the center in the axial direction of the ion collector 14 holds higher energy than that at both ends. In other words, compared with the two ends, the equilibrium state near the center can be considered to be dominated by detachment, and the two ends can be considered to be dominated by adsorption. Therefore, from the viewpoint of the temperature of the ion collector 14, the region 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 regions near both ends in the axial direction are regarded as the molecular layer. Areas prone to deposition.

As time elapses further from the start of evacuation of the vacuum chamber, the composition of gas molecules in the sensor body 11 changes to a composition corresponding to the evacuation capability of the vacuum chamber. Generally speaking, the gas molecules with more advantages in detachment than adsorption will be preferentially exhausted, and as a result, the gas molecules with 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 inside the sensor body 11 is changed to a composition in which 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 corresponding to the change of the composition in the vacuum chamber as the measurement object.

Due to the fact that the composition of gas molecules in the sensor body 11 is not easy to change, etc., in the entire surface area of the ion collector 14, it will change to an equilibrium state where adsorption is more advantageous than detachment. 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/9 hours in FIG. The change. In other words, the final equilibrium state can be considered to have passed the 12h time point. This can be considered to indicate that the composition in the vacuum chamber has changed from the normal atmospheric composition ratio to a gas composition that is predominant in adsorption around the time point of 12h/9 hours.

In Fig. 3, it is an environment with a vacuum exhaust system, and the vacuum exhaust system is a gas composition environment where an adsorption advantage is found below 1.0×10 ^-3 Pa, but the gas from the time when the atmosphere was opened to the start of vacuum exhaust There is no big difference between the composition system and the atmospheric composition of the initial state. In other words, the entire surface area of the ion collector 14 is in an equilibrium state out of favor, and it is a state in which adsorption is not performed. In other words, when the tangent to the time-varying curves of various materials in FIG. 3 is taken as the value of the slope of the linear function in this initial situation, it can be confirmed from the fact that all of them are negative values.

However, below 1.0×10 ⁻⁴ Pa, the composition on the surface of the ion collector 14 starts to change with the change of the gas composition, as 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, the value of graphite is close to the true vacuum degree in the vacuum chamber, so it should show the same vacuum degree as graphite . However, the vacuum degree of other materials will gradually deteriorate, that is to say, although the slope is negative, it still shows a tendency to approach zero.

This is because the original composition of the surface of the ion collector 14 is changed from the atmospheric composition to the gas composition with adsorption advantages, whereby the thickness of the molecular layer on the surface of the ion collector 14 will change. The difference does not occur until this vacuum level is reached.

Since this phenomenon is due to the gas composition that has become dominant in adsorption, it appears that the temperature condition of the surface to be adsorbed becomes more dominant than before. In other words, in the comparison of the materials in FIG. 3 , it can be considered that the material with a lower temperature surface is easier to adsorb gas molecules, and the amount of adsorption is increased, in other words, the thickness of the molecular layer is increased.

Here, when the positive ions 1 collide (incident) with the molecular layer whose thickness has been increased, the molecules of the molecular layer to which the incident energy has been given are detached. Although the detailed physical phenomena need to be studied in the future, according to Fig. 3, etc., it can be considered that the amount of molecules detached with respect to the incident positive ions on the surface of the ion collector of the triode ionization vacuum gauge in the vacuum degree depends on the number of molecules There is a proportional relationship between the thickness of the layer.

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

In general, the adsorption/desorption system stabilizes at a stage that has shifted to an equilibrium state. In other words, it can be considered that the adsorption/desorption is in an equilibrium state at the point in time when the slope of the measured value of the degree of vacuum has become zero. Although users who use vacuum gauges recognize the point in time when the equilibrium state has been reached as the measurement limit, and consider the vacuum gauge to be poor in capability, when the measurement limit changes with time, it is difficult to compare with the original vacuum degree. The situation of deterioration is different, and the change itself as a measuring device will bring distrust to users. From this, it can be said that it is problematic to use it as a product.

In other words, although it is necessary to avoid the measurement of the vacuum degree whose slope changes from zero to positive, this problematic phenomenon occurs with respect to the material containing platinum. This is because the temperature of the surface of the ion collector 14 is low. In other words, compared with other materials, since the equilibrium state of detachment and adsorption relative to the incident frequency of positive ions is on the adsorption side, the molecular layer will be further deposited. And increasing the thickness, as a result, will increase the amount of detachment of molecules caused by the incident positive ions.

In the period from 12h/after 9 hours to 12h, the reason why the above-mentioned slope becomes positive is that in the molecular layer that has been deposited near both ends of the ion collector 14 in the axial direction (low temperature position), the The molecular layer will be the source of release of molecules. In other words, when the ion collector 14 is made of various materials including platinum, the pressure in the sensor body 11 may locally become high due to the influence of molecules released from the release source. , and there is a problem of a pressure different from the pressure in the vacuum chamber which is the object to be measured. Therefore, there is a problem that the pressure in the vacuum chamber cannot be accurately measured.

<adsorbed molecules>

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

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

This shows that the amount of water molecules scattered in the sensor body 11 when the filament 12 is turned on is far more than the amount of water molecules scattered in the sensor body 11 when the filament 12 is turned off. This result shows that the adsorbed molecules 2 are mainly water molecules.

In other words, when the filament 12 is disconnected, since the water molecules will not become positive ions 1, the water molecules will not be attracted by the ion collector 14, so the water molecules will be adsorbed on the ion collector 14 as adsorbed molecules 2. few. Therefore, when the filament 12 is disconnected, since there is no release source of water molecules, the amount of water molecules scattered in the sensor body 11 is approximately the same as the amount of water molecules in the vacuum chamber, and the amount of water molecules few.

When the filament 12 is turned on, the water molecules become positive ions 1 , and the water molecules are attracted by the ion collector 14 . Moreover, since the ion collector 14 is made of a material with a low thermal conductivity, water molecules will be deposited on the ion collector 14 as adsorbed molecules 2 . Then, since the deposited water molecules will become the release source of water molecules, when the filament 12 is turned on, the amount of water molecules scattered in the sensor body 11 becomes much 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, so it can be seen that the adsorbed molecules 2 are mainly water molecules.

In this measurement, even for platinum which is chemically very stable, it turned out that the peak of water in the mass spectrum when the filament 12 was turned on was significantly larger than the peak of water in the mass spectrum when the filament 12 was turned off. In other words, this shows that the formation of the molecular layer by chemical adsorption is not the main reason for the reason why the pressure becomes unstable in the comparative example, and the formation of the molecular layer by the adsorption of water molecules Formation is the main reason (since platinum does not easily form molecular layers caused by chemisorption).

Furthermore, even in the triode type ionization vacuum gauge 100 (present embodiment) corresponding to three materials of graphite, copper, and tungsten with high thermal conductivity, although the peak value of water in the mass spectrum when the filament 12 is turned on is still higher than that of the filament The mass spectrum with 12 off has a larger water peak, but the difference is small. This shows that in this embodiment, when the filament 12 is turned on, the amount of water molecules adsorbed becomes far less than that of the comparative example.

<function etc.>

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

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

FIG. 5 is a schematic diagram showing the movement of positive ions 1 striking the ion collector 14 when the ion collector 14 is made of a material with a thermal conductivity of 173 W/(m˙K) or more at 300K. In addition, in FIG. 5, illustration of the gate electrode 13 is abbreviate|omitted for convenience.

As shown in FIG. 5 , in this embodiment, since the ion collector 14 is made of a material with high thermal conductivity, the heat generated in the filament 12 can be efficiently transferred to the entire ion collector 14 . Therefore, in the ion collector 14, the temperature can be raised not only in the central part 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 raised.

Therefore, in Fig. 5, it is different from Fig. 4 of the comparative example, near both ends of the axial direction of the ion collector 14, the gas molecules that hit the ion collector 14 as positive ions 1 are separated from the ion collector 14. Energy will be high. Thereby, the occurrence of adsorbed molecules 2 (especially water molecules) can be prevented.

Furthermore, in the above test, the temperature of the ion collector 14 made of graphite, copper, and tungsten was actually measured, and the result was a temperature exceeding 210 degrees. Here, it is known that the adsorption of water molecules and the like can be prevented if the temperature of the ion collector 14 is 200 degrees or higher, and it is also clear from this that the generation of the adsorbed molecules 2 can be appropriately prevented in this embodiment. Furthermore, in the above test, the temperature of the ion collector 14 (comparative example) made of molybdenum, nickel, platinum, and stainless steel (SUS304) was actually measured, and the temperature was 160° to 180°.

As described above, in this embodiment, since the generation of adsorbed molecules 2 can be prevented, it is possible to prevent the measured pressure from becoming incorrect as in the comparative example, and it is possible to accurately measure the inside of the object to be measured such as a vacuum chamber. pressure.

This situation is shown in the curves corresponding to graphite, copper, tungsten in FIG. 3 . That is, as shown by such curves, in the present embodiment, the measured pressure gradually decreases as the pressure in the vacuum chamber becomes lower due to vacuum exhaust, and drops to a predetermined value (measured After that, it stabilizes in this state and takes a fixed value.

Here, in this embodiment, the electric power supplied to the filament 12 is 4W or less. In the small triode type ionization vacuum gauge 100 in which the electric power supplied to the filament 12 can be set to 4W or less, since the heat generated in the filament 12 tends to be low, there is a temperature that tends to collect ions when no countermeasures are taken. The vicinity of both ends in the axial direction of the device 14 becomes lower.

On the other hand, as described above, in the triode ionization vacuum gauge 100 of the present embodiment, the ion collector 14 is formed of a material with a high thermal conductivity. Therefore, even in the small-sized triode type ionization vacuum gauge 100 in which the power supply to the filament 12 can be set to 4W or less and the heat of the filament 12 tends to be low, the ion collector 14 can be positioned at both ends in the axial direction. Properly increase the temperature of the ion collector 14 near the portion.

In addition, in the present embodiment, the ion collector support member 17 is made of a material having a lower thermal conductivity than the material constituting the ion collector 14 . Therefore, the heat of the ion collector 14 can be prevented from dissipating to the ion collector supporting member 17, and the heat of the ion collector 14 can be maintained in a high state.

Moreover, in this embodiment, the sensor body 11 is made of a metal material. In this way, by forming the sensor body 11 with a metal material, charging can be prevented when thermal electrons from the filament 12 collide with the sensor body 11, and the potential distribution in the space in the sensor body 11 can be fixed. maintained. Thereby, the pressure can be measured with a fixed sensitivity for a long time.

Here, in order to prevent the generation of adsorbed molecules 2 on the ion collector 14 , it may be considered to cut both ends of the ion collector 14 in the axial direction (Z-axis direction) to reduce the height Hi of the ion collector 14 . However, when the height Hi of the ion collector 14 is reduced in this way, the capture efficiency of the positive ions 1 in the ion collector 14 may be lowered.

On the other hand, in this embodiment, the ion collector 14 is made of a material with high thermal conductivity, thereby preventing the generation of adsorbed molecules 2, so it is not necessary to reduce the height Hi of the ion collector 14. Therefore, in the present embodiment, the generation of adsorbed molecules 2 can be appropriately prevented without reducing the capture efficiency of positive ions 1 in ion collector 14 . Furthermore, as described above, in the present embodiment, the height Hi of the ion collector 14 is approximately twice the height Hf of the filament 12 and is set to be equal to the height Hg of the grid 13 .

Furthermore, the purpose is not necessarily to increase the height Hi of the ion collector 14 , for example, the height Hi of the ion collector 14 may be set to be lower than the height Hg of the grid 13 .

10‧‧‧Sensor unit

11‧‧‧Sensor body (containment part)

11a‧‧‧flange

11b‧‧‧groove

11c‧‧‧bottom

12‧‧‧Filament

13‧‧‧Gate

14‧‧‧ion collector

15a to 15e‧‧‧terminal

16‧‧‧Grid support member

17‧‧‧Ion collector support member (support member)

20‧‧‧Control Unit

21‧‧‧Controller

22‧‧‧galvanometer

23a to 23c‧‧‧Power

100‧‧‧Triode Ionization Vacuum Gauge

Hf‧‧‧Filament height

Hg‧‧‧Gate height

Hi‧‧‧The height of the ion collector

Claims (6)

A triode-type ionization vacuum gauge is equipped with: a filament; a grid is arranged around the aforementioned filament; an ion collector is cylindrical and arranged around the aforementioned grid, and the thermal conductivity at 300K is 173W/( m˙K) or more; and a supporting member that supports the aforementioned ion collector and is made of a material that has a lower thermal conductivity than the material that constitutes the aforementioned ion collector, so as to maintain the aforementioned ion collector to prevent water The temperature at which molecules are adsorbed. The triode ionization vacuum gauge as described in claim 1, wherein the electric power supplied to the filament is 4W or less. The triode ionization vacuum gauge as described in claim 1 or 2 further includes: a housing part made of a metal material, and housing the aforementioned filament, the aforementioned grid and the aforementioned ion collector inside. The triode type ionization vacuum gauge as described in claim 1, wherein the ratio of the detachment rate of gas molecules striking the regions at both ends in the axial direction of the ion collector to the region striking the central region in the axial direction of the ion collector The rate of detachment of gas molecules is the same. A method for measuring pressure, which is to prepare a triode type ionization vacuum gauge, and the aforementioned triode type ionization vacuum gauge is equipped with: a filament; The grid is arranged around the aforementioned filament; the ion collector is cylindrical and arranged around the aforementioned grid, and is made of a material with a thermal conductivity of 173W/(m˙K) or more at 300K; and a support A member that supports the ion collector and is made of a material having a lower thermal conductivity than the material constituting the ion collector; heating the filament so that the temperature of the ion collector becomes a temperature that prevents the adsorption of water molecules; and The internal pressure of the object to be measured is measured by the aforementioned triode type ionization vacuum gauge. The pressure measuring method as described in claim 5, wherein the metal housing part is grounded, and the potential distribution in the space in the housing part is maintained fixedly, and the housing part accommodates the filament, the grid, and the ion collector in the interior.

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