JP4811341B2 - Method for adjusting voltage applied to correction electrode provided in helium leak detector and helium leak detector - Google Patents

Description

  The present invention relates to a leak detector used for airtightness inspection of a vacuum vessel.

A helium leak detector that separates helium ions from other ions having different orbital radii from helium ions by a slit provided in an intermediate partition wall of the analysis tube is known as a prior art (see, for example, Patent Document 1).
JP 2000-121484 A

  Among various ions traveling on the magnetic field deflection trajectory in the helium ion analysis tube, heavy ions such as hydrocarbon, which are caused by the oil of the oil rotary pump, easily adhere to the inner surface of the analysis tube and cause contamination. In the conventional helium leak detector as described in Patent Document 1, when hydrocarbon adheres to the inner surface of an analysis tube such as an intermediate partition wall, distortion occurs in the original magnetic field deflection trajectory of helium ions, resulting in a decrease in detection sensitivity. This causes a problem that the amount of leak cannot be measured accurately.

(1) The invention of claim 1 is a helium leak detector for detecting helium gas leaked from a subject by introducing it into an analysis tube, the analysis tube comprising an ion source unit and an ion beam generated by the ion source unit. A magnetic material that deflects the magnetic field, a slit member that selectively passes the helium ion beam deflected by the magnetic material, and a position where the ion beam heavier than the helium ion is irradiated are provided. A correction electrode to which a correction voltage to be corrected is applied, and an ion collector section that detects helium ions that have passed through the slit member as an ion current are provided.
(2) The invention of claim 2 is the helium leak detector according to claim 1, further comprising a power supply for variably applying a correction voltage to the correction electrode.
(3) The invention according to claim 3 is the helium leak detector according to claim 1 or 2, wherein the ion current detected by the ion collector when the acceleration voltage is applied to the ion source and the voltage is applied to the correction electrode. And a correction voltage adjusting means for determining a correction voltage based on the correction voltage.
(4) The invention according to claim 4 is the helium leak detector according to any one of claims 1 to 3, wherein the ions heavier than the helium ions are ions generated from a hydrocarbon.
(5) The invention of claim 5 is a method for adjusting the voltage applied to the correction electrode provided in the helium leak detector according to claim 1 or 2, wherein helium for leak amount calibration is led to the analysis tube. When the ion current is detected by the ion collector while changing the voltage applied to the correction electrode, a voltage that maximizes the ion current is applied to the correction electrode.
(6) A sixth aspect of the present invention is the method for adjusting a voltage applied to the correction electrode according to the third aspect, wherein the ion collector unit further changes the acceleration voltage of the ion source unit together with the voltage applied to the correction electrode. When the ion current is detected, the acceleration voltage of the ion source when the ion current becomes maximum is the acceleration voltage of the ion source, and the voltage applied to the correction electrode is the voltage applied to the correction electrode. To do.

  According to the present invention, since it is possible to suppress a decrease in detection sensitivity, it is possible to provide a helium leak detector with high measurement accuracy.

Hereinafter, a helium leak detector according to the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram schematically showing a helium leak detector according to an embodiment of the present invention. The helium leak detector 1 is connected via a test port 2 to a vacuum vessel 100 that is a subject for leak inspection.

  The helium leak detector 1 includes three exhaust pumps, an oil rotary pump 3, a mechanical dry pump 4, and a turbo molecular pump 5, four valves V1, V2, V3, and V4 that open and close an exhaust path, and a leak. A calibration unit 6 and an analysis tube 10 are provided. The analysis tube 10 is connected to the oil rotary pump 3 through a turbo molecular pump 5, a mechanical dry pump 4, and a valve V2. The vacuum vessel 100 is connected to the oil rotary pump 3 through a test port 2 and a valve V1. The vacuum vessel 100 is connected to the exhaust port 5a of the turbo molecular pump 5 through a test port 2 and a valve V4. The leak calibration unit 6 is connected to the exhaust port 5a of the turbo molecular pump 5 through a valve V3 and a valve V4.

The leak inspection of the vacuum vessel 100 is performed according to the following procedure.
(1) The valves V1, V3, and V4 are closed and the valve V2 is opened, and the analysis tube 10 has a predetermined background value (vacuum) in a series configuration of the turbo molecular pump 5, the mechanical dry pump 4, and the oil rotary pump 3. Exhaust until
(2) After the inside of the analysis tube 10 is lowered to a predetermined background value, the valve V2 is closed and the valve V1 is opened, and the vacuum vessel 100 is evacuated (roughly evacuated) by the oil rotary pump 3. At this time, the turbo molecular pump 5 and the mechanical dry pump 4 are stopped.
(3) The valve V1 is closed and the valve V4 is opened, and leak gas detection by the analysis tube 10 is started. That is, helium (He) gas is sprayed on the leak test location of the vacuum vessel 100.
(4) When there is a leak at the leak test location of the vacuum vessel 100, He gas enters the vacuum vessel 100, and the amount corresponding to the partial pressure of the He gas is an open valve V4, turbo molecular pump 5 and arrives at the analysis tube 10. When the analysis tube 10 detects the He gas, the leak amount of the vacuum vessel 100 is measured.

  When the leak amount is calibrated, the test port 2 is closed, the valves V3 and V4 are opened, and He gas is guided from the leak calibration unit 6 to the analysis tube 10. He gas flows out from the leak component 6 at a predetermined flow rate. The detected value at this time becomes a reference value for the leak amount.

Next, the configuration and operation of the analysis tube of the helium leak detector will be described in more detail with reference to FIGS.
FIG. 2 is a perspective view schematically showing the configuration and operation of the analysis tube of the helium leak detector according to the embodiment of the present invention, and the direction is expressed by orthogonal coordinates. FIG. 3 is an operation principle diagram of the analysis tube of FIG. 3, the same components as those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted. FIG. 4 is a cross-sectional view of a conventional analysis tube corresponding to FIG. 3, and is used for comparison with FIG.

As shown in FIG. 2, the analysis tube 10 includes an ion source 11, an acceleration slit 12, an intermediate partition wall 13, a first earth slit 14, a dresser slit 15, a second earth slit 16, an ion collector 17, and a correction electrode. 18 A magnetic field is generated in the direction opposite to the Z direction inside the analysis tube 10 by a U-shaped (horse-shoe) permanent magnet (not shown). The He gas introduced into the analysis tube 10 is ionized by the action of the flow of thermal electrons (emission current) emitted from the filament 11a of the ion source 11. He ions enter the magnetic field space formed by the permanent magnet 13 from the opening 12 a of the acceleration slit 12 as an ion beam by the acceleration slit 12. The acceleration voltage is applied by the power source 110, and the voltage value of the acceleration voltage is 240 to 300V. This ion beam may contain not only He ions but also hydrogen (H) ions, hydrocarbon (C _m H _n ) ions, and the like.

The analysis tube 10 is configured such that the He ions are bent by the magnetic field space, pass through the deflection trajectory A, pass through the slit 13a of the intermediate partition wall 13, and then enter the opening 14a of the first earth slit 14. . On the other hand, H ions lighter than He ions are largely deflected by the magnetic field space and pass through the deflection trajectory B, and therefore do not pass through the slits 13a of the intermediate partition wall 13. C _m H _n ions heavier than He ions are less deflected by the magnetic field space and pass through the deflection trajectory C, and therefore do not pass through the slit 13a of the intermediate partition wall 13.

  Therefore, the beam of only He ions almost completely passes through the intermediate partition wall 13 and the first earth slit 14, and further passes through the dresser slit 15 and the second earth slit 16 to enter the ion collector 17. The deflection trajectories A, B, and C are actually three-dimensional arc trajectories. An ion current is detected by an ion ammeter 19 for He ions incident on the ion collector 17, and a measurement unit (not shown) measures the amount of leakage of the vacuum vessel 100 as a subject based on the ion current value.

Here, the problem of the conventional analysis tube will be described with reference to FIG. As shown in FIG. 4, the He ions exit from the opening 22 a of the acceleration slit 22 and pass through the deflection trajectory A that enters the opening 24 a of the earth slit 24. On the other hand, C _m H _n ions adhere to the surface S 1 facing the acceleration slit 22 and a part of the surface S 2 of the intermediate partition wall 23 as carbon while passing through the deflection trajectory C. The carbon adhering to the surfaces S1 and S2 is charged by the action of ions, and this electrostatic force causes distortion in the deflection trajectory A of He ions. He ions are surely no longer incident on the opening 24a of the first earth slit 24 (deflection orbit A ′). As a result, the detection value of the ion current of He ions by the ion ammeter 19 is lowered, that is, the sensitivity is lowered.

Therefore, in the helium leak detector 1 according to the embodiment, as shown in FIGS. 2 and 3, the correction electrode is provided at a position where the heavier ions such as C _m H _n ions are irradiated (positions of the surfaces S1 and S2). 18 is provided. The correction electrode 18 is insulated from the inside of the analysis tube 10 such as the intermediate partition wall 13. The correction electrode 18 is connected to the power source 111. The power supply 111 can vary the voltage value of the voltage applied to the correction electrode 18. The power source 111 applies a voltage (for example, −70 to 0 V) to the correction electrode 18 so as to cancel the electrostatic force exerted on the deflection trajectory A by the carbon adhered to the surfaces S1 and S2. Thereby, distortion of the deflection trajectory A of He ions can be suppressed.

The voltage value applied to the correction electrode 18 is adjusted as follows.
(1) Close the test port 2 and open the valves V3 and V4 to guide He gas from the leak calibration unit 6 to the analysis tube 10 and detect the ion current value of He ions, as in the case of leak amount calibration. To do.
(2) The voltage applied to the correction electrode 18 is adjusted so that the ion current value becomes maximum. The voltage value at the time when the ion current value becomes maximum becomes the voltage value of the voltage applied to the correction electrode 18.

According to the embodiment described above, the following operational effects can be obtained.
(1) A correction electrode 18 to which a correction voltage for correcting the deflection trajectory A of the He ion beam is applied is provided at a position irradiated with ions heavier than He ions such as C _m H _n ions. Thereby, distortion of the deflection trajectory A of He ions due to electrostatic force of charged carbon can be suppressed. As a result, the magnetic field strength in the magnetic field space is stabilized, the deflection trajectory A is stabilized, and the He detection sensitivity is improved. Therefore, the measurement system of the helium leak detector 1 can be stably maintained in a high state.

  In addition, the work frequency for removing the carbon adhering to the inner surface of the analysis tube 10 can be reduced, and the maintenance of the helium leak detector 1 is facilitated.

  If the internal pressure of the analysis tube 10 is high, ions that are heavier than He ions will increase, and the electrostatic force of the heavy ions may cause distortion in the deflection trajectory A of He ions. Even when a leak test is performed in a state where the pressure is high, by applying a voltage to the correction electrode 18, distortion of the deflection trajectory A of He ions can be suppressed, and the helium ion detection sensitivity of the analysis tube 10 can be increased. Can do.

  When there is a lot of residue such as dirt on the surface of the subject to be subjected to the leak test, the increase rate of the residue adhering to the inside of the analysis tube 10 increases, so that the helium ion detection sensitivity of the analysis tube 10 decreases in a short time. . Even when such a specimen is inspected for leaks, the helium ion detection sensitivity of the analysis tube 10 can be maintained high by inspecting while adjusting the voltage value applied to the correction electrode 18.

  If a subject is automatically inspected for leaks using a robot or the like, a large amount of subjects are inspected in a short time, and the rate of increase of carbon adhering to the inside of the analysis tube 10 is also increased. As a result, the helium ion detection sensitivity of the analysis tube 10 also decreases in a short time. Even when the leak inspection is automated, the helium ion detection sensitivity of the analysis tube 10 can be maintained high by adjusting the voltage value applied to the correction electrode 18.

(2) As in the case of calibrating the leak amount, He gas is guided from the leak calibrating unit 6 to the analysis tube 10 and the ion current value of He ions is detected. Then, the voltage applied to the correction electrode 18 is changed to detect the voltage value at which the ionic current value becomes maximum, and the voltage value is applied to the correction electrode 18 to perform a leak test. Therefore, a voltage value suitable for suppressing distortion of the deflection trajectory A of He ions can be easily determined.

The above embodiment can be modified as follows.
(1) The helium leak detector 1 is such that He ions are bent by the magnetic field space, pass through the deflection track A, pass through the slit 13a of the intermediate partition wall 13, and then enter the opening 14a of the first earth slit 14. , And a function of automatically correcting the acceleration voltage for accelerating He ions. With this acceleration voltage automatic correction function, the acceleration voltage is corrected so that the ion current value becomes maximum. At this time, the voltage value of the correction electrode 18 may be adjusted.

  For example, when calibrating the first leak amount after cleaning the inside of the analysis tube 10, there is no deposit due to hydrocarbons inside the analysis tube 10, so acceleration without applying a voltage to the correction electrode 18 is performed. Adjust the voltage. From the next time, the accelerating voltage is not changed, and the voltage applied to the correction voltage 18 is adjusted so that the ion current value becomes maximum. Further, both the voltage value of the acceleration voltage and the voltage value of the correction electrode 18 may be adjusted so that the ion current value becomes maximum.

  By examining the voltage value of the acceleration voltage together with the voltage value applied to the correction electrode 18, more He ions can be incident on the opening 14 a of the first earth slit 14.

(2) The position where the correction electrode 18 is provided is not limited to the position where the C _m H _n ions are irradiated as long as the position is irradiated with ions generated from the hydrocarbon. Further, the position is not limited to the position irradiated with ions generated from the hydrocarbon as long as the position is irradiated with ions heavier than He ions. This is because a compound generated at a position irradiated with such ions may be charged and affect the deflection trajectory A of He ions.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

1 is an overall configuration diagram schematically showing a helium leak detector according to an embodiment of the present invention. It is a perspective view showing typically composition and operation of an analysis tube of a helium leak detector concerning an embodiment of the invention. FIG. 3 is an operation principle diagram of the analysis tube of FIG. 2. It is an operation principle diagram of a conventional analysis tube and is a diagram corresponding to FIG.

Explanation of symbols

1: Helium leak detector 2: Test port 3: Oil rotary pump 4: Mechanical dry pump 5: Turbo molecular pump 10: Analytical tube 11: Ion source 12: Acceleration slit 13: Intermediate partition 14: First earth slit 15: Sublesser slit 16: second earth slit 17: ion collector 18: correction electrode 100: vacuum vessel (subject for leak inspection)
110, 111 Power supply A, B, C: deflection trajectory

Claims (6)

In the helium leak detector that detects helium gas leaked from the analyte by guiding it to the analysis tube.
The analysis tube is
An ion source,
A magnetic body for deflecting a magnetic field of an ion beam generated by the ion source unit;
A slit member that selectively passes a helium ion beam that is orbitally deflected by the magnetic material;
A correction electrode provided at a position where an ion beam of ions heavier than helium ions is irradiated, and a correction voltage applied to correct the trajectory of the helium ion beam;
A helium leak detector, comprising: an ion collector that detects helium ions that have passed through the slit member as an ion current. The helium leak detector according to claim 1,
A helium leak detector, comprising: a power source that variably applies a correction voltage to the correction electrode. The helium leak detector according to claim 1 or 2,
And a correction voltage adjusting unit configured to determine the correction voltage based on an ion current detected by the ion collector when an acceleration voltage is applied to the ion source and a voltage is applied to the correction electrode. Helium leak detector. The helium leak detector according to any one of claims 1 to 3,
The helium leak detector according to claim 1, wherein the heavier ions than the helium ions are ions generated from hydrocarbon. A method for adjusting a voltage applied to a correction electrode provided in the helium leak detector according to claim 1 or 2,
Helium for leak amount calibration is introduced to the analysis tube, and when the ion current is detected by the ion collector while changing the voltage applied to the correction electrode, the voltage that maximizes the ion current is applied to the correction electrode. A method for adjusting a voltage applied to a correction electrode. In the adjustment method of the voltage applied to the correction electrode according to claim 3,
In addition to the voltage applied to the correction electrode, when the ion current is detected by the ion collector while changing the acceleration voltage of the ion source, the acceleration voltage of the ion source when the ion current becomes maximum A method for adjusting a voltage applied to a correction electrode, characterized in that the acceleration voltage of the ion source unit is used, and the voltage applied to the correction electrode is a voltage applied to the correction electrode.

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