TWI626435B - Triode type ion vacuum gauge - Google Patents

Abstract

A triode-type ion vacuum gauge capable of reducing the influence of particles emitted from the surface of the ion collector without measuring a measurement error and measuring the pressure of the object to be measured is provided.

A triode-type ion vacuum gauge (IG) having a filament (2) and a grid-like grid (3) disposed around the filament; and concentrically arranged around the gate The cylindrical ion collector (4). Further, the power supply (E1) for filament lighting and the power supply (E2) for the gate for giving a higher potential to the gate than the filament, and the filament are further provided. The potential is set to a higher power supply (E3) than the potential of the ion collector. The power supply to the filament is set to 4 W or less, and the emission current between the filament and the gate is controlled to be in the range of 2 mA to 10 mA.

Description

Triode type ion vacuum gauge

The present invention relates to a triode-type ion vacuum gauge that is mounted on a measurement object such as a vacuum container and is used to detect the pressure inside.

In the vacuum process performed in a vacuum processing apparatus such as film formation by sputtering or vapor deposition, the pressure in the vacuum chamber as the object to be measured may have a large influence on the yield of the product, for example. Case. In the vacuum process, a triode type ion vacuum gauge is known as a wide range of pressures of 1 Pa to 10 ^-6 Pa in the pressure in the vacuum chamber (for example, refer to Patent Document 1) Non-patent document 1).

The triode-type ion vacuum gauge is provided with a filament in a glass vacuum partition (housing) that is attached to the object to be measured, and a cylindrical contoured grid disposed around the filament. a pole; and a cylindrical ion collector disposed around the gate. Moreover, the direct current is applied to the filament by the power source for the filament lighting, and the filament is heated red to emit hot electrons, and the gate is powered by the power source for the gate. Higher potential than the filament, and the potential of the filament is set higher than the potential of the ion collector by other power sources, and the ion collector is used to capture the periphery of the grid and collide with the hot electrons. The generated gas atoms, positive ions of the molecules, and the pressure in the test body are determined according to the ion current at this time.

As the ion collector, in general, in order to capture positive ions as much as possible, and the length in the bus direction using the same is equal to or higher than the length in the bus line direction of the gate, the gate and the ion collector are configured as Concentric. In the triode-type ion vacuum gauge disclosed in the above-mentioned non-patent document 1, if it is desired to obtain an emission current of about 2 mA, it is necessary to set the supply power to the filament to 9 W (in this case, it is estimated that The surface temperature of the ion collector is over 400 ° C).

In addition, in recent years, in order to achieve improvement in usability, there is a demand for miniaturization of such an ion vacuum gauge, and accordingly, the vacuum partition itself is reduced in size and assembled in the interior thereof. Filaments, gates, and ion collectors are also downsized. In this case, if the electric power of more than 9 W is supplied to the filament according to the above configuration, the vacuum partition wall made of glass is heated to a temperature exceeding 70 ° C, and the use of the triode type ion vacuum gauge is not ideal. Therefore, it is considered that the power supply to the filament is set to be one-half or less (for example, 4 W) of the above-described prior art, so that the vacuum partition wall is not heated to a specific temperature (for example, 50 ° C) or more, as long as As disclosed in the above Patent Document 1, for example, it is suitable for the material of the filament to be selected, and even at a lower temperature, the gauge can be obtained. The injection current is determined (that is, the pressure measurement can be performed with high sensitivity), and the vacuum partition wall can be prevented from being heated more than necessary.

However, it is known that if a vacuum pump is connected to the vacuum partition, the vacuum is pumped from the atmospheric pressure at a certain exhaust speed until it becomes a high vacuum region (pressure of 10 ^-5 Pa). For example, when the output current is controlled to 1 mA, the electric power of 4 W or less is supplied to the filament, and the pressure is measured by the above-described miniaturized triode type ion vacuum gauge, and the pressure indication value is continuously decreased. Until the pressure is 10 ^-5 Pa near the measurement limit (lower limit) value, the system will rise again to 10 ^-4 Pa and become balanced. When such a triode-type ion vacuum gauge is attached to the object to be measured and the pressure is measured, measurement errors are generated (that is, the pressure is higher than the actual object to be measured). The problem of stress).

Therefore, the inventors of the present invention have repeatedly tried to carry out research and have obtained the following knowledge: that is, the above problem arises from the fact that although the power supplied to the ion collector is high (for example, 9 W) When the surface temperature of the ion collector exceeds 400 ° C, the above problem does not occur. However, due to the reduction of the supply power of the filament, both ends of the ion collector in the direction of the bus bar, positive ions The probability of collision is low, and it becomes a region where particles (gas molecules) may accumulate, and it may become a source of particles released by collision of positive ions. That is, at the initial stage of vacuum evacuation, atoms or molecules (components in the atmosphere) of the gas such as moisture attached to the gate or the ion collector are gradually released and exhausted (ie, Yes, the amount of adsorption decreases along the so-called adsorption isotherm), and the pressure indication value drops all the way to its measurement limit (for example, 10 ^-5 Pa). It can be inferred that at this point in time, the composition of the atoms or molecules attached to the ion collector (mainly the inner surface) is a composition ratio of the interconnection with the atmosphere.

The gas that has been released or the gas molecule that has become a positive ion collides with the ion collector again, and is chemically adsorbed or physically adsorbed as an oxide or the like on the surface of the ion collector (mainly the inner surface). In this case, in a region where the collision probability of positive ions is high, a positive ion having energy capable of being desorbed is a neutral molecule, a neutral fragment molecule, a neutral atom, or the like by continuously colliding. Some particles such as positive ions are released as much as possible (that is, it is difficult to accumulate as a molecular layer). On the other hand, in a region where the collision probability of positive ions is low, the positive ion system is caused by In the case of a continuous collision, for example, a molecular layer (oxidation layer or the like) which is a weak bond is easily deposited as compared with a region having a high collision probability of positive ions, and becomes a state in which the thickness of the molecular layer is easily maintained. .

If the time passes further, the gas system in the vacuum partition changes to a composition corresponding to the exhaust capability. Due to this compositional change, the composition of the atomic or molecular layer attached to the surface of the ion collector (mainly the inner surface) will also change. For example, it is changed to a composition in which water molecules and the like which are difficult to be exhausted are increased. Due to factors such as changes in the composition, in the region where the collision probability of positive ions is low, the adsorption system becomes more advantageous than the detachment, and is, for example, a molecular layer (oxidation layer or the like) of a weak bond. And pile up. In addition, it is presumed that after the pressure has been lowered to the vicinity of the measurement limit value, the particles released by the collision of the positive ions with the deposited molecular layer (including the further adsorbed water molecules, etc.) The amount of the system gradually increases, and along with this, the pressure indication value rises, and then, if the balance between the release of the particles and the re-adsorption or exhaust of the released particles is maintained, the pressure will be at a specific pressure (for example, 10 ^{- 4} Pa) becomes a balance. The amount of chemical adsorption or physical adsorption at the molecular layer and the amount of particles released from the molecular layer are dependent on the collision probability of positive ions or the like, so that the collision probability of ions is low. Both ends of the ion collector in the bus direction are the source of the particles, and the pressure indication value is increased.

[prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2013-72694

[Non-patent literature]

[Non-Patent Document 1] Vacuum No. 40, No. 11 (1997) "Development of Sub-standard Ion Vacuum Gauge Subsequent Ball (VS-1A)"

The present invention is based on the above knowledge and provides a means of reducing the amount of particles emitted from the surface of the ion collector. A triode-type ion vacuum gauge that measures the pressure of the object to be measured without causing measurement errors is a problem.

In order to solve the problem, the triode-type ion vacuum gauge of the present invention is a triode-type ion vacuum gauge that is attached to a measurement object and detects a pressure inside thereof, and is characterized in that: a filament is provided; a cylindrical electrode having a cylindrical profile disposed around the filament; and a cylindrical ion collector configured concentrically around the gate; and a power source for filament lighting for energizing the filament The current causes the filament to heat red; and the power source for the gate is to apply a higher potential to the gate for the gate; and the power supply is to set the potential of the filament to be higher than the potential of the ion collector Further, the power supply to the filament is set to be 4 W or less, and the control is performed such that the emission current between the filament and the gate is in the range of 2 mA to 10 mA.

According to the present invention, the amount of positive ions generated is increased by 2 mA or more in a state where the electric power supplied to the filament is 4 W or less in order to prevent the heating of the vacuum partition wall, and the amount of positive ions is increased. At low emission currents, positive ions are continuously collided at both ends of the ion collector where the collision probability of positive ions is low, and positive ions are accumulated as molecular layers (oxidation layers, etc.) of weak bonds. The situation is suppressed. As a result, when it is attached to the object to be measured and the pressure is measured, it is possible to suppress the influence of the particles emitted from the surface of the ion collector in the high vacuum region as much as possible, and it is possible to correctly The pressure of the object to be measured is measured. Further, if the injection current is set to a value exceeding 10 mA, the power supply to the filament exceeds 4 W, and the temperature of the vacuum partition wall exceeds 50 °C.

Further, in the invention, it is preferable that the filament, the gate electrode, and the ion collector are housed in a vacuum partition wall made of metal. According to this, the charging of the vacuum electrons to the vacuum partition wall is prevented, and the potential distribution in the space surrounded by the vacuum partition wall is constantly maintained constant. As a result, it is possible to measure the pressure with a certain degree of sensitivity over a long period of time.

IG‧‧‧ triode type ion vacuum gauge

S‧‧‧Sensor Department

C‧‧‧Control Department

1‧‧‧Metal shell (vacuum partition)

2‧‧‧filament

3‧‧‧Gate

4‧‧‧Ion collector

A ₁ , A ₂ ‧‧‧ galvanometer

Fig. 1 is a schematic view showing the configuration of a triode type ion vacuum gauge according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of the sensor portion.

[Fig. 3] is a graph showing changes in pressure with respect to time when vacuum pumping of a triode type ion vacuum gauge is performed.

[Fig. 4] is a graph showing the pressure in the test body with respect to the passage of time when the injection current is changed.

[Fig. 5] is a graph showing the surface temperature of the ion collector when the emission current is changed.

Hereinafter, with reference to the drawings, the triode type of the present invention is The embodiment of the sub-vacuum meter will be described. In the following description, the direction in which the sensor portion to be described later, which is an object to be measured, which is not shown, is attached upward is described.

Referring to Fig. 1 and Fig. 2, a triode type ion vacuum gauge IG is composed of a sensor unit S and a control unit C. The sensor unit S is provided with a case 1 made of a metal having a bottomed cylindrical shape as a vacuum partition wall, and is detachably attachable via a flange 11 (and a vacuum seal portion) provided at an upper portion thereof. It is installed in a measurement object such as a vacuum chamber outside the drawing. The casing 1 is made of stainless steel, nickel, an alloy of nickel and iron, an aluminum alloy, copper, a copper alloy, titanium, a titanium alloy, tungsten, molybdenum, niobium or an alloy of at least two selected from the above. And constitute it. In this case, the metal case 1 is preferably grounded.

The casing 1 is internally provided with a filament 2, and a grid 3 having a cylindrical contour concentrically arranged to surround the periphery of the filament 2; and surrounding the grid 3 A cylindrical ion collector 4 that is concentrically arranged in a surrounding manner. As the filament 2, a crucible coated with enamel or a metal such as tungsten is used, and The wire of 0.1~0.2mm is formed into a hairpin. Further, the two free ends of the filament 2 are positioned and supported by the housing 1 by the support pins 21a and 21b which are inserted through the bottom of the casing 1 and protruded from the casing 1 via an insulator (not shown). At a specific location within. In this case, the support pins 21a and 21b also function as connection terminals (electrodes). The filament 2 is inserted at one end of the grid 3 (the lower end in Fig. 1) from the side of the tip end 22a of the filament 2 which is folded back to the hairpin shape. In this case, the top portion 22a is disposed, for example, in such a manner as to be located near the midpoint Mp of the length of the gate line 3 in the bus line direction.

As the gate electrode 3, an alloy of molybdenum, niobium, platinum, rhodium, platinum, and rhodium, nickel, an alloy of nickel and iron, stainless steel, or the like, which is coated with platinum or platinum, is coated with platinum. At least two of the alloys selected in the alloy. Again, The wire of 0.1 to 0.5 mm is wound into a coil shape so as to have a cylindrical shape. In this case, the top portion 22a of the filament 2 is positioned on the hole axis Ha of the grid 3. Further, the form of the gate electrode 3 is not limited thereto, and the wire member may be formed into a lattice shape and formed into a cylindrical shape, or may be formed by molding a punched metal or a photo-etched sheet into a cylindrical shape. Further, the gate electrode 3 is also positioned and supported in the casing 1 by passing through the bottom of the casing 1 and protruding from the support pins 31a and 31b provided in the casing 1 via an insulator (not shown). At a specific location. In this case, the support pins 31a and 31b also function as connection terminals.

As the ion collector 4, an alloy of molybdenum, rhenium, platinum, rhodium, platinum, and rhodium, nickel, nickel, and iron alloy coated with stainless steel, molybdenum, and the surface thereof by platinum or the like is used. At least two alloys of choice are selected. Further, a rectangular plate material having a thickness of 50 to 300 μm is formed into a cylindrical shape. In this case, in order to capture positive ions as much as possible, the length of the ion collector 4 in the bus line direction is set to be equal to the length of the gate 3 in the bus line direction. Further, the ion collector 4 is also positioned and supported by the support member 41a, 41b which penetrates the bottom of the casing 1 and protrudes from the inside of the casing 1 via an insulator (not shown). At a specific location within body 1. In this case, the support pins 41a and 41b also function as connection terminals. In addition, the form of the ion collector 4 is not limited thereto, and the strip-shaped wire may be assembled into a lattice shape and formed into a cylindrical shape, or the punched metal or the photo-etched sheet may be formed into a cylinder. Shape.

On the other hand, the control unit C includes a frame F (indicated by a one-dot chain line in FIG. 1), and a control unit Cu is housed in the frame F, and the control unit Cu is provided with a computer. , memory and sequencer, etc. The control unit Cu, such an operation for the system to raise the power of each of the later processing, or the current value of the ion current meter A is described by measured after ₁ and the pressure in the illustrated example, the display of the display or the like is omitted variety of control. Further, in the casing F, a power supply E1 for filament lighting for supplying a direct current to the filament 2 and heating the filament 2 (lighting) is included, and for the grid 3, the filament 2 is higher. The power source E2 for the gate to which the gate 3 is applied, and the power source E3 having the potential of the filament 2 higher than the potential of the ion collector 4, and the ions flowing at the ion collector 4 Current is measured by ammeter A ₁ . Further, in the present embodiment, although not particularly illustrated, an output terminal that is electrically connected to each of the power sources E1 to 3E is provided in the housing F, and the sensor unit S and the control unit are provided. C is connected by a cable with a connector attached thereto. Further, the sensor unit S and the control unit C may be incorporated in the same casing.

Here, the triode type ion vacuum gauge IG is configured so that the predetermined output current can be obtained even if the electric power supplied to the filament 2 is 4 W or less, and the filament 2 is used as the filament 2 The 0.127mm long wire with a length of 20mm is formed into a hairpin shape and is covered with a enamel. 0.25mm white gold coated molybdenum wire is formed into a diameter 10mm, the length L1 of the busbar direction is 20mm, and as the ion collector 4, a plate made of SUS304 having a thickness of 0.1 mm is formed into a diameter. In the case of a cylindrical shape of 17 mm and a height of 20 mm, the filament 2, the grid 3, and the ion collector 4 are assembled to have an inner diameter according to the above embodiment. A test piece was prepared by a cylindrical metal case of 25 mm.

Next, the inside of the casing 1 was vacuum-extracted by a vacuum pump at a constant exhaust speed, and the injection current was set to 1 mA and operated, and the pressure in the test body was measured. In this case, the gate voltage is 150 V, the filament voltage is 25 V, and the ion collector voltage is 0 V. During the measurement of the pressure, the emission current is kept at 1 mA. In the range where the supply voltage to the filament 2 exceeds 4 W, the filament current and voltage from the power source E1 are appropriately controlled. Figure 3 is a graph showing the change in pressure within the test body over time. According to this, as shown by the dotted line in Fig. 3, it is confirmed that the pressure indication value in the casing 1 is again increased to 10 ^-4 Pa after continuously decreasing to 10 ^-5 Pa. The degree of Pa is up to the balance. In this state, if only the gate voltage is changed from 150V to 800V, although a lower pressure is indicated, the pressure immediately rises to the original pressure. From this, it can be inferred that the cause of the pressure rise is not caused by the gate 3.

Next, while controlling the filament current and voltage from the power source E1, the injection current is changed to 0.01 mA, 1 mA, 2 mA, 3 mA, and 0.5 mA at a specific time, respectively, for the passage of time. The pressure in the test body was measured separately, and the results are shown in Fig. 4. According to this, it can be known that as the injection current becomes larger, the indicated pressure gradually decreases. Further, when the injection current is set to 2 mA, if the change in the pressure in the test body with respect to the passage of time is measured, as shown by the solid line in FIG. 3, it is confirmed that the inside of the casing 1 is The pressure indication value continues to drop continuously to around 10 ^-5 Pa and directly becomes equilibrium.

Next, the surface temperature of the ion collector 4 when the filament current and voltage from the power source E1 are appropriately controlled and the injection current is changed is measured, and the result is shown in FIG. According to this, it is known that even if the injection current is set to 10 mA, the temperature of the ion collector 4 is 250 ° C or lower, and the temperature of the casing 1 at this time is about 40 ° C. In addition, when the injection current was set to exceed 10 mA, the supply power of the filament was 3.2 W.

From the above results, it can be inferred that since the filament 2 is further heated due to an increase in the emission current, the grid 3 and the ion collector 4 are heated, the temperature rises, and the surface is discharged. The influence of the particles may be less, but the temperature of the rising ion collector 4 at this time is only about +100 ° C, and the temperature of the casing 1 is only about +20 ° C, and Did not find that immediately after the injection The pressure change after the change of flow. As a result, it is estimated that if the injection current is 2 mA or more, the amount of positive ions generated increases, and even at a lower injection current, the collision probability of positive ions is low. The positive ions at the ends are also continuously collided, and the positive ions are deposited as a molecular layer (oxidation layer or the like) of weak bonds.

Therefore, in the present embodiment, based on the above knowledge, the triode type ion vacuum gauge IG (that is, the filament 2) is configured so that the predetermined output current can be obtained even if the supplied electric power of the filament 2 is 4 W or less. And the gate 3), and is configured to provide another galvanometer A ₂ for measuring the emission current flowing between the filament 2 and the gate 3 at the negative output side of the power source E2, and performing pressure measurement In the middle of the period, the power supply E1 is controlled by the control unit Cu so that the supplied electric power of the filament 2 is 4 W or less and the emission current measured by the ammeter A ₂ is in the range of 2 mA to 10 mA.

According to the above embodiment, the amount of positive ions generated is increased, and even at a lower injection current, positive ions are continued at both ends of the ion collector 4 having a low collision probability of positive ions. Collision is performed, and the case where positive ions are deposited as a molecular layer (oxidation layer or the like) of a weak bond is suppressed. As a result, when it is attached to the object to be measured and the pressure is measured, it is possible to suppress the influence of the particles emitted from the surface of the ion collector 4 in the high vacuum region as much as possible, and it is possible to accurately measure The pressure of the object is measured. In addition, if the injection current is set to a value exceeding 10 mA, the power is supplied to the filament. The system will exceed 4W, and the temperature of the vacuum partition will exceed 50 °C. Further, since the filament 2, the grid 3, and the ion collector 4 are housed in the metal casing 1, the charging of the casing 1 by the hot electrons is prevented, and the space surrounded by the casing 1 is The potential distribution is always kept constant. As a result, it is possible to measure the pressure with a certain degree of sensitivity over a long period of time.

Although the above description has been made on the embodiments of the present invention, the present invention is not limited to the above-described constituents. In the above embodiment, the vicinity of the point Mp in the length of the bus bar direction of the top portion 22a of the filament 2 and the ion collector 4 is taken as an example. The arrangement is not limited thereto, and the electron emission efficiency when the filament 2 is energized and the hot electrons are emitted does not fall within a range exceeding a certain value, but will be relative to the gate. The position of the filament 2 of 3 is preferably shifted upward or downward. Further, as the filament 2, for example, a linear shape or a coiled shape may be used. In this case, the region where the electron emission efficiency is high is located at the length of the gate line 3 in the bus line direction. The way to the midpoint of the midpoint Mp is configured.

Claims (2)

A triode-type ion vacuum gauge is a triode-type ion vacuum gauge that is attached to an object to be measured and detects a pressure inside thereof, and is characterized in that it is provided with a filament; and is disposed around the filament. a grid having a cylindrical profile; and a cylindrical ion collector configured concentrically around the gate; and a power source for filament lighting, which energizes the filament with a direct current and heats the filament And the power supply for the gate, for the gate, the higher potential than the filament is given to the gate; and the power supply, the potential of the filament is set higher than the potential of the ion collector, and the filament is The power supply is set to be 4 W or less, and is controlled so that the emission current between the filament and the gate is in the range of 2 mA to 10 mA. The triode-type ion vacuum gauge according to claim 1, wherein the filament, the gate electrode, and the ion collector are housed in a vacuum partition wall made of metal.