JPS5815051B2 - Hot cathode ionization vacuum gauge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot cathode ionization vacuum gauge that is small, highly sensitive, and reduces the amount of soft X-rays that the ion collector is exposed to.

Conventionally, the vacuum gauge used to measure pressure in the ultra-high vacuum region has been exclusively the Beanie type ionization vacuum gauge (developed by Messrs. Payand and Alpert, and usually referred to as the B-A type ionization vacuum gauge).

Hereinafter referred to as the B-A type ionization vacuum gauge.

) was used. This B-A type ionization vacuum gauge has an ion collector placed on the central axis of the anode, which is made of a spiral wire molded or a mesh material molded into a cylinder. It has a so-called three-pole structure with a hot cathode placed on the outside, and by passing an electron current between the hot cathode and anode, electrons are oscillated between the hot cathode and the ion collector with the anode as the center. The residual gas in the vacuum is ionized, the generated ions are captured in an ion collector, and the pressure is determined from this ion current.

When using the above measurement method, electrons emitted from the hot cathode collide with the anode while repeating the vibration, and this corresponds to the electron current.

), soft X-rays are constantly emitted from the anode due to this impact.

When the ion collector is exposed to the soft X-rays, it emits photoelectrons, producing a photocurrent in the same direction as the ion current.

Therefore, there is a limit to pressure measurement using a B-A type ionization vacuum gauge due to this photocurrent.

That is, in the case of a measurement bulb in which the electrode is housed in a glass tube, 1O
-18 Torr level, and IQ-11 Torr level for the nude type measurement bulb with electrodes exposed directly in the vacuum chamber.

In order to improve this pressure measurement limit to the lower pressure side, the photocurrent must be reduced.

One possible way to reduce the photocurrent is to reduce the wire diameter and length of the ion collector to reduce the surface area exposed to soft There was a problem that the sensitivity of the meter was reduced.

On the other hand, in the vacuum chamber where the vacuum gauge is attached, for example, vacuum evaporation and various measurements are performed, and it is desirable to be able to use the space inside the vacuum chamber effectively, so as a vacuum gauge,
Something as small as possible is required.

However, if the B-A type ionization vacuum gauge is miniaturized, the effective ionization space is reduced and the ion collector must also be made smaller, so the sensitivity decreases for the same reason as mentioned above, making miniaturization difficult.

However, the present invention provides an ionization vacuum gauge with a three-electrode structure in which the anode is formed to approximate a spherical surface, a hot cathode is disposed outside of the anode, and an ion collector is disposed on the central axis of the anode. , the orbit of the electrons that contribute to the ionization of the residual gas is directed toward the center of the spherical space surrounded by the anode, and the electron density and ion density at the center of the spherical space are increased, resulting in increased sensitivity and, as a result, the vacuum In addition, as the ion collector became smaller, the pressure measurement limit was improved by reducing the amount of soft X-ray exposure, and all of the conventional problems were solved.

That is, the present invention will be described in the embodiment shown in FIGS. 1 and 2 (hereinafter referred to as "Embodiment I").

), a plurality of wire rods 1, 1 (for example, molybdenum wire, wire diameter 0.15 imf) are strung together via rings 2, 2 along the meridian of the sphere while maintaining a predetermined interval. Anode 3 (diameter approximately 20 mm) formed to approximate a spherical surface
mm).

By fixing one annular body 2 of this anode 3 to a stem 5 installed through the bottom of the glass tube 4, the anode 3 is installed at the center of the glass tube 4, and the anode 3
Against, its outside.

Maintaining a gap of approximately 5 mm at the center height, stem 5a
, 5a, 5b, and 5b (a support rod may be provided in some cases).

) Cathode 6 made of tungsten wire (wire diameter 0.2 mmf)
, 6a are stretched in an arc shape, and through the other annular body 2 of the anode 3, from the tip of the stem 7 provided at the top of the glass bulb 4 to the center of the inner space 8 of the anode 3, the anode 3 A needle-shaped ion collector 9 made of a tungsten wire (wire diameter 10 μf) is suspended along the central axis of the hot cathode ionization vacuum gauge of the present invention.

In the figure, numeral 10 denotes this hot cathode ionization vacuum gauge in a vacuum chamber (not shown).

) is a connecting pipe that connects with

Note that either one of the cathodes 6 and 6a is used for measurement,
The other is reserved.

Next, the example shown in FIGS. 3 and 4 (referred to as Example 2).

) was constructed using a mesh material (transmittance 60
%) molded into a bowl shape and put them together to form a circular tsuba.
1 to form an anode 12 that approximates a spherical surface.
Similarly, various components are arranged inside the glass tube 13.

Incidentally, the ion collector 14 is also introduced from the bottom of the tube 13.

Further, the embodiment shown in FIGS. 5 and 6 (hereinafter referred to as "Embodiment 2").

), the cathodes 6, 6a are located below the anode 12, whereas the cathode 6.6a in the embodiment (2) was placed at the center height of the anode 12.

In order to measure the vacuum pressure with the hot cathode ionization vacuum gauge of the above embodiment, a cathode power source (a heating power source that flows current through the tungsten wire) is connected to one of the cathodes 6 or 6a, and
An electronic current control circuit is connected between the cathode 6 and the anode 2 so that a predetermined thermionic current flows.

In this case, the potentials of the anodes 3, 12 and the cathode 6 are, for example, 150 volts for the anodes 3, 12 relative to the cathode, and 20 volts for the cathode 6 relative to the ion collector.

On the other hand, the ion collector 9°14 lowers its potential to zero volts (
(ground potential), connect a DC amplifier.

Under the above operating conditions, thermionic electrons emitted from the cathode 6 flow to the anodes 3 and 12, as described above.

In this case, some of the thermoelectrons behave so as to vibrate between the inner and outer spaces of the anodes 3 and 12, which are formed to approximate spherical surfaces.

Ions are generated in the inner space 8 surrounded by the anodes 3 and 12 by the collision of the thermoelectrons and the residual gas, and these ions are collected in the ion collectors 9 and 14.

The DC amplifier amplifies this ion current, indicates its value, and calculates the pressure from this value.

In the embodiment, the tips of the ion collectors 9 and 14 were formed to approximate spherical surfaces, and the anodes 3 and 12 were positioned at the center.

As shown in FIG. 7, the ion collectors 9a and 9 are placed on the central axis of the anode 3, which is formed to approximate a spherical surface.
B are placed facing each other with a tip gap of 0.3 mm, and the tip gap G is moved on the central axis to determine the proportion of ions incident on the ion collector.

The ion yield distribution curve obtained above is shown in FIG.

That is, it was found that the ion distribution density in the center of the inner space 8 surrounded by the anode 3 was particularly high. It was located at

(The ions are energized toward the ion collector by the electric field of the ion collectors 9 and 14 acting on the ions, so the tips of the ion collectors 9 and 14 are connected to the anode 3.
, 12 is not a limitation.

) This means that the flight trajectory of the electrons forming the electron current is
This is thought to be because the electron density is centripetal (towards the center of the anode, which is formed to approximate a spherical surface), and the electron density at the center is high.

Therefore, as in the embodiment, the ion collector can provide sufficient sensitivity even when the length of the anodes 3 and 12, which are formed to approximate spherical surfaces, is such that the tip is located in the center of the anodes.

On the other hand, the ion collector potential EC and ion current (collector current) are the conditions that should be more satisfied as an ion collector.
There is a relationship with 1c.

In other words, it is required that the ion current Ic does not vary with respect to variations in the potential Ec of the ion collector.

In the structure of the present invention, as mentioned above, the ion collectors -9 and 14 are reliably arranged at locations with high ion density, so as shown in FIG. 9, the ion current Ic is It saturates at a low value of EC and satisfies this condition.

In this respect, in the conventional B-A type ionization vacuum gauge, the flight trajectory of the electrons forming the electron current is not concentrated at one point as in the present invention, but is concentrated on one axis (uniformly aligned along the central axis of the cylindrical space surrounded by the anode). Concentrate on.

)it is conceivable that.

This can be seen from the fact that the ion collectors are arranged over the entire range on the central axis of the cylindrical space surrounded by the anode 5.

If the length of this conventional ion collector is halved, for example, the ion yield will be lowered, the sensitivity will be lowered, and the relationship 4 between the ion collector voltage Ec and the ion currents 1c and 5 will not be satisfied.

The more sensitivity can be improved, the more compact the structure can be.

Incidentally, in order to find the sensitivity ratio between the ionization vacuum gauge according to this invention and the conventional B-A type ionization vacuum gauge in the same volume,
When we calculated S/■ by dividing the sensitivity by the volume of the space occupied by the anode, it was 3.3 for the ionization vacuum gauge of the present invention, compared to 1 for the conventional B-A type ionization vacuum gauge.

High sensitivity means that the diameter of the tungsten wire that constitutes the ion collector 914 can also be made thinner.

In the above embodiment, the wire diameter is 10 .mu.f, which is about 1/15 of the wire diameter of 150 .mu.f in the conventional B-A type ionization vacuum gauge.

The fact that the wire diameter can be made smaller means that the surface area of the ion collector becomes smaller in proportion to it, and the amount of soft X-rays exposed to it can be reduced accordingly.

In the above embodiment, the length of the ion collectors 9 and 14 is approximately 1/6 to 1/10 of the length of the ion collector of the conventional B-A type ionization vacuum gauge, and as a result, the surface area is Then it will be about 1/100.

Therefore, since the photocurrent is also 1/100 of that of the conventional type, the limit of pressure measurement can be theoretically lowered by two orders of magnitude.

The embodiment shown in FIG. 10 (referred to as embodiment ①).

) is the same as Example I except that a reflector electrode is further provided.

That is, the cathode 6 is placed inside the cylindrical reflector electrode 15.
．． 6a, position the anode 3 and the ion collector 9;

Similarly to the other electrodes, the reflector electrode 15 also has a stem 16,
16 (sometimes via a support rod).

), and the distance between the reflector electrode 15 and the cathode 6.6a is maintained at about 2 mttt.

Further, the embodiment shown in FIG. 11 (referred to as embodiment ①).

) Beam flaper electrode 17 is in the form of a flat plate, and also serves as a collector shield, approximately 2 mm below the cathodes 6, 6a.
They are placed with a certain distance between them.

In the above examples (■) and (2), the cathode, anode, and ion collector were operated under the same conditions as in the previous example, and
The reflector electrodes 15 and 17 are operated by applying a negative potential (-50 to 100 V) lower than the potential of the cathode.

By using the reflector electrodes 15, 17, it is possible to prevent thermionic electrons emitted from the cathode from dissipating and to promote centripetal movement (movement concentrating on one point) of the oscillating electrons.

This can be expected to further increase sensitivity.

In addition, the ionization vacuum gauge was operated at 10' T by operating the glue flap electrode 15 of the embodiment shown in FIG. 10 as an anode and using the anode 3 formed to approximate a spherical surface as an ion collector.
It can also be used as a low vacuum ionization vacuum gauge with a measurement range of orr-I Torr.

However, with one vacuum gauge, I O'''T from I Torr stand.
It is also possible to measure pressure over a wide range of orr tables.

In order to use it as an ionization vacuum gauge to measure pressure, in addition to the amount of sensitive soft (3) Under constant pressure conditions, the relationship between electron acceleration voltage and ion current is similar to the ionization collision cross-sectional area curve due to electron energy.
4) Necessary characteristics include small fluctuations in ion current due to fluctuations in ion collector potential.

These characteristics are shown in FIG. 9 and FIGS. 12 to 18.

As for the symbols attached to the curves in the figure, I corresponds to the vacuum gauge of the embodiment shown in FIG. 1, ■ corresponds to the vacuum gauge of the embodiment shown in FIG. 3, ■ corresponds to the vacuum gauge of FIG.

From these measurement results, it can be said that the hot cathode ionization vacuum gauge of the present invention is a vacuum gauge having the necessary characteristics.

That is, according to the present invention, a cathode is placed outside an anode formed to approximate a spherical surface.

In both cases, the hot cathode ionization vacuum gauge is constructed by arranging the ion collector on the inner central axis of the anode, which has the effect of providing a vacuum gauge that is small, highly sensitive, and has improved measurement limits using soft X-rays.

Note that the anode formed to approximate a spherical surface is limited to the shape of the embodiment.

Instead, multiple rings made of wire are arranged along the latitudes of the sphere (therefore, rings with different diameters are prepared).

), or one in which the anode is formed by winding a wire into a spiral and gradually changing its curvature to approximate a spherical surface. It is possible to obtain effects.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of Embodiment I of the present invention;
FIG. 2 is a diagram of the arrangement of the electrodes, FIG. 3 is a partially cutaway perspective view of the embodiment (2) of the present invention, FIG. 4 is a diagram of the arrangement of the electrodes, and FIG. 5 is a diagram of the embodiment (2) of the invention. Figure 6 is a partially cutaway perspective view, Figure 6 is a diagram of the electrode arrangement, Figure 7 is a diagram of the electrode arrangement of the vacuum gauge used to determine the ion yield distribution, and Figure 8 is the ion yield distribution. The curves, Figures 9 and 18 are diagrams showing the relationship between ion collector potential and ion current, Figure 1.
0 is a partially cutaway perspective view of Embodiment 1 of the present invention;
Figure 1 is a partially cutaway perspective view of Example V of the present invention, Figures 12 and 15 are diagrams showing the relationship between pressure and ionic current, and Figures 13 and 16 are diagrams showing the relationship between electron current and ionic current. 14 and 17 are diagrams showing the relationship between electron acceleration voltage and ion current. 1... Wire rod, 2... Ring body, 3, 12...
...Anode, 4, 13--Glass tube, 5
．． 5a, 5b,? . 16...Stem, 6,6a...Cathode,
8...Inner space, 9.14...Ion collector, 10...Connecting pipe, 11...
- Annular collar, 15, 17...Reflector electrode.

Claims (1)

[Claims] 1. In an ionization vacuum gauge having a three-pole structure of a hot cathode, an anode, and an ion collector, a hot cathode is disposed outside an anode formed to approximate a spherical surface, and a hot cathode is placed on the central axis of the anode. A hot cathode ionization vacuum gauge featuring an ion collector. 2. The hot cathode ionization vacuum gauge according to claim 1, wherein the anode formed to approximate a spherical surface is constructed by stretching a plurality of wires along the meridian or latitude of the sphere. 3. The hot cathode ionization vacuum gauge according to claim 1, wherein the anode formed to approximate a spherical surface is a hollow sphere made of mesh material. 4. The hot cathode ionization vacuum gauge according to claim 1, wherein the ion collector has its tip located at the center of the inner space of the anode formed to approximate a spherical surface. 5. The hot cathode ionization vacuum gauge according to claim 1, characterized in that a reflector electrode is disposed close to the outside of the hot cathode. 6. The hot cathode ionization vacuum gauge according to claim 5, wherein the reflector electrode is cylindrical. 7. The hot cathode ionization vacuum gauge according to claim 5, wherein the reflector electrode is a flat plate.