JP2863652B2 - Ultra high vacuum gauge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum gauge for an ultra-high vacuum which generates ions by electron bombardment of gas molecules and measures pressure from the value of the generated ion current.

[0002]

2. Description of the Related Art Various ionization gauges are known as this kind of high vacuum gauge. The measurement limit on the low pressure side of an ionization gauge is generally a soft X-ray generated by an electron impact from a collector electrode. It is also known that the residual current is determined by the residual current due to photoelectrons emitted from the ion collector by the irradiation of the ion collector and the residual current due to the electron-excited desorbed ions generated by the electron impact from the collector electrode. In other words, when measuring pressure with an ionization gauge, electrons bombard gas molecules not only to generate gas molecule ions, excited neutral particles, and light, but also to collide with the collector electrode to emit soft X-rays. Then, electrons excited desorbed ions are released from the molecules adsorbed on the electrode. Other than the ions of the gas molecules, an error occurs in the measurement of the pressure, which is a factor that determines the measurement limit on the low pressure side.

[0003] As a vacuum gauge capable of measuring an ultra-high vacuum region by reducing the influence of soft X-rays, there is a Baird-Alpert vacuum gauge, which is used for measuring an ultra-high vacuum up to about 10 ^-8 Pa. . In the ultra-high vacuum measurement, the electron-excited desorbed ions from the surface of the collector electrode are superimposed on the ions of gas molecules generated in space, which also hinders the measurement when measuring a higher vacuum. Therefore, in order to measure a pressure of 10 ⁻⁹ Pa or less, it is necessary to further reduce the residual current due to the influence of soft X-rays and to remove the influence of the ions excited and desorbed.

[0004] From such a viewpoint, as a vacuum gauge for ultra-high vacuum, a Helmer gauge or other other device incorporating a means for removing an electron-excited desorbed ion by performing energy analysis while avoiding the collector electrode from directly looking at the collector electrode, is used. Deflected beam vacuum gauges, extractor gauges, etc., have been proposed, which have made it possible to reduce the influence of soft X-rays and electronically excited desorbed ions to reduce the measurable pressure range. The extractor gauge separates an ion generation unit such as a grid from an ion detection unit such as a collector, reduces the incidence of soft X-rays on the ion collector by means of a shielding plate, and reduces the number of electrons excited and desorbed ions (number (with eV energy) so that only the ions of the gas molecules reach the ion collector.
The Helmer gauge is configured to deflect the flow of ions drawn from the holes in the shield plate by an electric field, so that only gaseous molecular ions are incident on the ion collector and straight X-rays are reduced to enter the ion collector. I have.

[0005]

Meanwhile, Helmer gauges, other deflection beam vacuum gauges, and extractor gauges for performing energy analysis to remove electronically excited desorbed ions are all soft X-rays or electronically excited ones. It helps reduce the pressure range that can be measured by reducing the influence of desorbed ions, but reflected in the deflector because Helmer gauges and other deflection beam vacuum gauges use a 90-degree deflector as a deflector. Soft X-rays and electronically excited desorbed ions have not yet been completely removed. In the case of an extractor gauge, the angle at which the source of soft X-rays and electron-excited desorbed ions can see the collector can be reduced, but it cannot be reduced to zero. Not done.

In order to achieve complete removal of electronically excited desorbed ions, it has recently been proposed to use an astigmatic deflector as a deflector. However, even in this proposal, the deflector is reflected by the electrode of the deflector and reflected on the collector. The effects of arriving soft X-rays and light cannot be eliminated. Light, especially vacuum ultraviolet light, causes residual current when a secondary electron multiplier is used for the detector.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ultrahigh vacuum gauge capable of measuring only gas molecules by eliminating the influence of light, electron-excited desorbed ions, and soft X-rays caused by electron impact. It is an object.

[0008]

In order to achieve the above object, an ultrahigh vacuum gauge according to the present invention comprises an ion generator for bombarding gas molecules with electrons from an electron beam source to generate ions. An energy analyzer that removes and separates electronically excited desorbed ions and excited neutral particles other than gas molecule ions generated together with gas molecule ions in the ion generator,
An ion detector that detects ions of gas molecules separated by the energy analysis unit; the electron beam source is composed of a pulsed electron beam source that generates a pulsed electron beam; It is characterized in that only ions of gas molecules can be detected by an ion detector based on a time difference of flight from light and soft X-rays. Preferably, the energy analyzer has at both ends an inlet side cap having an opening through which products containing ions of gas molecules from the ion generator and an outlet side cap having an opening through which only ions of gas molecules pass. A circle having a diameter substantially equal to the inner diameter of the opening across the axis passing through the openings of the two caps and capturing linear products other than ions of gas molecules entering through the opening of the inlet side cap. It may consist of a vessel box type energy analyzer having a cylindrical body with a plate member provided inside. Also, the ion detector may comprise a dynode or continuous dynode secondary electron multiplier, and the pulsed electron beam source may comprise a low temperature emitter such as a field emission electron source.

[0009]

In the vacuum gauge of the present invention thus configured, the electron-excited desorbed ions entering together with the ions of the gas molecules generated by the electron bombardment in the ion generating section have an energy several eV higher than the ions of the gas molecules. Therefore, they are removed and separated in the energy analyzer. On the other hand, part of the light and soft X-rays generated by the electron impact in the ion generation unit is removed by the disk member in the energy analyzer.
The components reflected from the surface are also distinguished by the difference in the flight time between the ions of gas molecules entering the ion detector, light and soft X-rays by using a pulsed electron beam source as an electron source for electron impact. Thus, it is possible to detect only ions of gas molecules while substantially eliminating the influence of light and soft X-rays.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 schematically shows the configuration of an ultrahigh vacuum gauge according to an embodiment of the present invention.
Reference numeral 1 denotes an ion generator, which is a pulsed electron beam source 2 for generating a pulsed electron beam, 150 to 200 eV.
It consists of a collector electrode 3 connected to a potential Vg of the order and an ion extraction electrode 4 connected to a variable extraction potential Ve.
Pulsed electron beam source 2 may comprise a low temperature emitter such as a field emission electron source. The electrons generated by the pulsed electron beam source 2 collide with gas molecules before being collected by the current collecting electrode 3 to generate ions, excited neutral particles, and light. In addition, when the electrons from the pulsed electron beam source 2 bombard the collector electrode 3, soft X-rays and electron excited desorbed ions are generated. Numeral 5 is a vessel box type energy analyzer constituting an energy analysis unit. This energy analyzer 5 has an inlet side cap 6, an outlet side cap 7, and a cylindrical shape extending between both caps as shown in the figure. It comprises a main body 8 and a disk member 9 arranged in the cylindrical main body 8. Further, the outlet-side cap 7 of the energy analyzer 5
A shield electrode 10 is provided adjacent to the shield electrode 10, and an ion detector 11 is arranged at a stage subsequent to the shield electrode 10. The ion detector 11 may be a dynode type or a secondary electron multiplier marketed under the trade name of Channeltron or Ceratron.

The inlet side cap 6 and the outlet side cap 7 of the energy analyzer 5 have a central opening through which ions of gas molecules pass, and have a potential about 10 eV lower than the potential Vg.
The disk members 9 connected to Vc and arranged in the central opening and the cylindrical body 8 are respectively positioned on the same axis, and the inner diameter of each central opening and the diameter of the disk member 9 are set substantially equal. As a result, products having rectilinear properties other than ions of gas molecules entering through the central opening of the inlet side cap 6 collide with the disk member 9 and are collected or reflected. That is, the energy analyzer 5 can prevent light and soft X-rays from directly entering the ion detector 11 due to its geometric shape, and can also remove excited neutral particles. The vessel box type energy analyzer 5 has a simple structure and the resolution as an analyzer is not very good, but it is necessary to separate the energy difference (several eV) between ions of gas molecules and ions excited by electron excitation. In addition, it has a sufficient resolution and the transmittance is large due to the poor resolution, thereby facilitating the measurement in the low pressure region. By properly setting the potential Vg and the potential Vc, the energy analyzer 5 obliquely enters ions having specific energies (gas molecule ions) as indicated by dotted lines.
It is configured to only pass through. In this case, the resolution of the energy analyzer 5 is actually determined by the inner diameters of the openings of the caps 6 and 7, the length of the cylindrical body 8, and the size of the disk member 9 disposed therein. If it is set to 10 eV, it can be set to have a resolution of 0.5 eV or less.

By appropriately selecting the geometrical shape of the energy analyzer and the applied potential of each part, excited neutral particles and electronically excited desorbed ions that hinder pressure measurement can be sufficiently removed. Soft X-rays can only be partially removed. Since light and soft X-rays reach the ion detector 11 almost at the same time as the electron impact, and then ions of gas molecules arrive, according to the present invention, it is necessary to pulse the electrons used to ionize the gas molecules. As a result, it is possible to use the difference in time of flight, whereby the ions of gas molecules can be detected without being affected by light or soft X-rays.

The illustrated embodiment conceptually shows the vacuum gauge of the present invention, and the configuration, shape, dimensions, etc. of each part can be arbitrarily designed. It is possible to set variously.

[0014]

As described above, according to the present invention, electron-excited desorption ions, which substantially affect a pressure measurement generated by an electron bombardment for ionizing gas molecules, and light and Part of the soft X-rays is removed by the energy analyzer, and the electrons used for electron bombardment are pulsed to make use of the time-of-flight difference between the ions of the gas molecules and light and soft X-rays, and the energy of the gas molecules together with the ions of the gas molecules. Since it is configured to remove the effects of the remaining light and soft X-rays that have passed through the analysis unit, electron-excited desorbed ions and light and soft X-rays, which have conventionally been a factor in the measurement limit on the low pressure side, Can be solved, so that the pressure in the ultrahigh vacuum region of 10 ⁻¹⁰ Pa or less can be accurately measured.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration of an ultrahigh vacuum gauge according to an embodiment of the present invention.

[Explanation of symbols]

 1: Ion generator 2: Pulsed electron beam source 5: Energy analyzer 11: Ion detector

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-18842 (JP, A) JP-A-48-17389 (JP, A) JP-B-51-13675 (JP, B2) JP-B-51- 13434 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01L 21/30

Claims (4)

(57) [Claims] An ion generator for bombarding gas molecules with electrons from an electron beam source to generate ions, and an electron-excited desorbed ion other than gas molecule ions generated together with gas molecule ions in the ion generator. An electron beam source comprising a pulsed electron beam source for generating a pulsed electron beam, comprising an energy analyzer for removing and separating ions, and an ion detector for detecting ions of gas molecules separated by the energy analyzer. An ultra-high vacuum gauge characterized in that only ions of gas molecules can be detected by an ion detector based on a time-of-flight difference between ions of gas molecules generated in step (1) and light and soft X-rays. 2. An energy analyzer comprising: an inlet cap having an opening through which a product containing ions of gas molecules from the ion generator is provided; and an outlet cap having an opening through which only ions of gas molecules are passed. It is provided at both ends, has a diameter substantially equal to the inner diameter of the opening across the axis passing through the openings of these two caps, and emits light, X-rays, and excitation other than ions of gas molecules that have entered through the opening of the inlet side cap. The vacuum gauge for ultra-high vacuum according to claim 1, comprising a Vessel box type energy analyzer having a cylindrical body provided therein with a disk member for capturing a linear product such as conductive particles. 3. The vacuum gauge according to claim 1, wherein the ion detector comprises a dynode type or continuous dynode type secondary electron multiplier. 4. The ultrahigh vacuum gauge according to claim 1, wherein the pulsed electron beam source comprises a low temperature emitter such as a field emission electron source.