JPS60259924A - Measurement of vacuum value of ion source - Google Patents

Abstract

PURPOSE:To enable a vacuum value measurement in an ion source without a vacuum meter for exclusive use, by installing an electric current shock type ion source repeller or detecting a current value of an electric current flowing in a correspond unit of the repeller. CONSTITUTION:Between a repeller 4 and a filament 8, an electric current detector 6 detecting a repeller current Ir and between a grid 14 and the filament 8 an electric current detector 18 detecting an emission current Ie are installed respectively. An electric current flow quantity of the filament 8 is so controlled that the current Ie becomes 10mA assuming a bombard voltage Vb as 200V and a repeller voltage Vr as 10V, then a distinctive dependability is brought to existence between the current Ir at the time when Ar gas is introduced and a vacuum value of an ionizing chamber. Accordingly, by obtaining preliminarily a relation between current Ir and vacuum value, measurement of the vacuum value of the ionizing chamber can be made after detection of the current Ir.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for measuring the degree of vacuum within an electron impact ion source used in an ion gun or the like.

Ion guns can be used for solid surface analysis methods such as AES (Auger electron spectroscopy), ESCA (X-ray electron spectroscopy), and S
TMS (Secondary Ion Mass Spectrometry), IS.

It is used for sputtering solid surfaces in S (ion scattering spectroscopy) and the like.

(Prior art) An ion gun is configured to generate ions in an ion source and guide them in a specific direction, but in order to control the amount of ions emitted, the pressure of the gas introduced into the ion source must be controlled. must be controlled. Therefore, conventionally, the ion source is provided with a vacuum gauge to control the introduced gas pressure so that the degree of vacuum within the ion source is constant.

Ionization vacuum gauges are generally used as vacuum gauges.

Among these, BA (Bayard-Alpert) type vacuum gauges are often used.

(Problems to be Solved by the Invention) In order to provide a vacuum gauge in the ion source, a space is required for installing the vacuum gauge measurement bulb, which complicates the configuration of the ion source. The cost will increase accordingly.

(Means for Solving the Problems) The present invention does not provide a dedicated vacuum gauge to measure the degree of vacuum of the ion source, but instead measures the degree of vacuum using the constituent members of the ion source. .

In the present invention, the degree of vacuum of the ion source is measured by measuring the current flowing through the repeller of the electron impact ion source or a member corresponding to the repeller (hereinafter referred to as repeller current).

That is, as shown in FIG. 1, the repeller 4 for pushing back the electrons emitted from the thermionic generation means 2 such as a filament is maintained at a lower potential than the thermionic generation means 2, and the repeller 4 and the thermionic generation A current detector 6 is inserted between the means 2 to detect the repeller current Ir. Thermionic generation means 2 and repeller 4 are constituent members of an ion source, and current detector 6 is added for the purpose of the present invention.

(Operation) When electrons are emitted from the thermoelectron generating means 2, the electrons collide with gas particles in the ionization chamber of the ion source and ionize the gas particles. Some of the generated ions are extracted from the ion source and used as ions ejected from the ion gun, but most of the ions collide with the bellows 4 and lose charge, producing a repeller current Ir. The amount of ions generated in the ionization chamber depends on the gas pressure (degree of vacuum) in the ionization chamber when the amount of electrons emitted from the thermionic generation means 2 is constant, so this repeller current Ir also depends on the degree of vacuum in the ionization chamber. Dependent.

Therefore, if you measure the relationship between the degree of vacuum in the ionization chamber (using a vacuum gauge at this time) and the repeller current Ir in advance, you can then measure the degree of vacuum by detecting the repeller current. .

(Example) FIG. 2 is a diagram showing an example of an ion source to which the present invention is applied. A repeller 4 is provided behind and on the side of the filament 8 as a thermoelectron generating means, and a voltage lower than the filament 8 by a repeller voltage Vr is applied to the repeller 4. In front of the filament 8 is an aperture surface 12 made of soft iron having an aperture 10 for extracting ions, and a grid 14 for accelerating electrons emitted from the filament 8 is provided between the filament 8 and the aperture surface 12. A voltage higher than that of the filament 8 by the bombardment voltage vb is applied to the filament 14.

A cylindrical permanent magnet 16 is provided so as to surround the grid 14, and the filament 8 is placed near the position of the permanent magnet 16 where the magnetic field becomes zero. This permanent magnet 16 collects the electrons emitted from the filament 8 around the central axis passing through the aperture 10, and increases the amount of ions extracted from the aperture 10 by making it easier to generate ions near the central axis. be.

The permanent magnet 16 is Alnico 5. The permanent magnet 16 and the aperture surface 12 are made of Alnico 8 or filament, and a voltage of the same potential as that of the lever 4 is applied to the permanent magnet 16 and the aperture surface 12. The space surrounded by the permanent magnets 16 becomes an ionization chamber, but the permanent magnet 16 and the aperture surface 10 also serve as a repeller that confines electrons in the ionization chamber.

The beam between the repeller 4 and the filament 8 is the propeller current I
A current detector 6 is provided to detect r, and a filament 8 is provided between the grid 14 and the filament 8.
A current detector 18 is provided for detecting an emission current Iθ due to electrons emitted from the grid 14 and captured by the grid 14.

In this example, the bombardment voltage vb is set to 200■, the repeller voltage Vr is set to IOV, the amount of current flowing through the filament 8 is controlled so that the emission current Ie becomes 10 mA, and when Ar gas is introduced, the repeller current Ir and ionization The relationship with the degree of vacuum in the chamber is shown in Figure 3. The degree of vacuum in the ionization chamber was measured using a BA type vacuum gauge.

This result shows that there is a clear dependence between the repeller current 1r and the vacuum degree of the ionization chamber. Therefore, based on this result, the degree of vacuum in the ionization chamber can be measured by detecting the repeller current Ir.

Further, the bombardment voltage vb, the repeller voltage Vr, and the emission current Ie can be set to other values, and in that case, the correspondence relationship between the repeller current Ir and the degree of vacuum will also change.

To measure the degree of vacuum in the ionization chamber from the repeller current Ir, the current detector 6 is used as an ammeter to measure the repeller current Ir.
The degree of vacuum can be read from the data shown in Figure 3.

In addition, a degree of vacuum calculation display device 19 as shown in FIG.
are connected to the current detector 6, and Vb, Vr.

Repeller current 1 as shown in Figure 3 with Ie as a parameter
The data on the correspondence between r and the degree of vacuum is stored in the memory, and the degree of vacuum is recalled from the memory based on the current detector 6 or the propeller current Ir, and the value of the degree of vacuum is displayed appropriately. It can also be displayed by means.

FIG. 4 is a diagram showing another ion source to which the present invention is applied.

In this ion source, an aperture 10 is arranged so that ions are taken out in a direction perpendicular to the direction in which electrons emitted from a filament 8 as a thermoelectron generating means are accelerated by a grid 14, and the aperture 10 surrounds an ionization chamber. It is provided like this or opened in the bellows 20.

In this embodiment as well, if the bombardment voltage vb, repeller voltage Vr, and emission current Ie are kept constant, a correspondence relationship can be obtained between the degree of vacuum in the ionization chamber and the propeller current Ir, and by detecting the repeller current Ir, the ionization chamber The degree of vacuum can be measured.

FIG. 5 is a diagram showing an ion gun equipped with an example of an ion source to which the present invention is applied.

This ion gun is composed of an ion source section 30 that generates ions, an intermediate section 40 that extracts ions from the ion source section 30 and guides them in a predetermined direction, and an objective lens section 5o that is inserted into an ultra-high vacuum apparatus such as an analysis room. has been done.

The ion source section 30 has a structure similar to that of the ion source shown in FIG. 2, but differs in that a lanthanumolide (LaB6) cathode, which has no risk of breakage, is used as the thermoelectron generating means.

A gas to be ionized, such as argon gas, is introduced from a gas cylinder into the ionization chamber of the ion source section 30 via a pressure reduction valve 34 and a leak valve 36. 37 is a gas inlet. The exhaust port 38 is adapted to be evacuated by a vacuum pump such as a turbo-molecular pump.

In the intermediate portion 40, an ion extraction electrode 42 is provided near the aperture 10, and in front of it is provided a lens system 44 that focuses and deflects the extracted ions.

The permanent magnet 16 and aperture surface 12 of the ion source section 3o are kept at a potential higher than the ground potential by Va (for example, 2 KV), and the ion extraction electrode 42 is grounded, so that ions pass through the aperture 10 and reach the intermediate section 4o. It's brought out.

An exhaust port 46 is also provided in the intermediate portion 40, and differential exhaust is performed between the intermediate portion 40 and the ion source portion 3o through an aperture of 1°, and the intermediate portion 4o is approximately two orders of magnitude higher than the ion source portion 30. It's a vacuum.

The objective lens unit 50 is provided with an objective lens system 52, which allows ions to be emitted from an ion exit port 54 to the ultra-high vacuum apparatus. The objective lens section 5o and the intermediate section 40 are connected via an aperture 56 through which ions pass, and differential pumping is performed here as well, so that the objective lens section 50 is
The vacuum is about an order of magnitude higher.

In this ion gun, in order to keep the amount of ions emitted from the ion exit port 54 constant, V a is required.

With Vb and Vr being constant, the pressure of gas introduced into the ionization chamber is adjusted by the pressure reducing valve 34 and the leak valve 36 so that the repeller current Ir becomes a predetermined value, and the degree of vacuum in the ionization chamber is set to a predetermined pressure. Then, the ion current emitted from the ion exit port 54 may be detected and the ion current may be made constant by adjusting the emission current Ie.

To keep the repeller current Ir constant, the pressure reducing valve 34 or the leak valve 36 may be manually adjusted when the repeller current Ir fluctuates, or the valve drive mechanism 60 may be used as shown in FIG. Repeller current detector 6
It is also possible to automatically adjust the pressure reducing valve 34 or the leak valve 36 so that the output signal of the repeller current detector 6 becomes constant.

Furthermore, since the aperture surface 12 and the permanent magnet 16 also serve as a repeller, a repeller current detector 6 may be provided between them and the cathode 32.

(Effects of the Invention) According to the present invention, the degree of vacuum in the ionization chamber of the ion source can be measured by detecting the repeller current. No need to equip. Therefore, devices such as an ion gun can be simplified and made cheaper.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for explaining the present invention in detail, FIG. 2 is a schematic sectional view showing an example of an ion source to which the present invention is applied, and FIG. 3 is a diagram showing the vacuum degree of the ionization chamber in the ion source. FIG. 4 is a schematic sectional view showing another example of an ion source to which the present invention is applied, and FIG. 5 is a sectional view showing an example of an ion gun to which the present invention is applied. be. 2...Thermion generating means, 4,20...
・Repeller, 6...Repeller current detector, 8・
... Filament, 12 ... Aperture surface, 16 ... Permanent magnet, 32 ... Lanthanum poride cathode. Agent Patent Attorney Shigeo Noguchi

Claims (1)

[Claims] (1) A method for measuring the degree of vacuum, characterized in that the degree of vacuum within the ion source is determined by detecting the value of current flowing through the repeller of the electron impact ion source or a member corresponding to the repeller.