Chamber for ionization vacuum gauge

Abstract

To provide a device that generates plasma in a vacuum pressure sensor, and minimizes the above described adverse effect.SOLUTION: Provided is a chamber for bounding a plasma generation region in a vacuum pressure sensor, where the chamber is equipped with a conductive casing element (1) which is arranged outside in a radial direction to a center shaft, the chamber is arranged substantially perpendicular to the center shaft, and is equipped with conductive wall elements (2, 2', 2") connected to the casing element, at least one of the wall elements has a first opening (3) through which the center shaft extends, the casing element is equipped with at least a first region (B1) and a second region (B2), and the first region is positioned closer to the center shaft than the second region. Further, provided is a vacuum pressure sensor equipped with the chamber.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to the technical field of vacuum pressure sensors, in particular to a chamber for a vacuum pressure sensor in the form of an ionization gauge, and to a vacuum pressure sensor comprising a chamber according to the invention. [Background technology]

[0002] Vacuum pressure sensors or gauges capable of determining pressures significantly below atmospheric pressure are known. Among known vacuum pressure sensors, so-called ionization gauges have a particularly wide measurement range. In ionization gauges, residual gas is ionized to generate plasma. The electrons required to ionize the gas are generated either by a hot cathode (hot cathode ionization gauge) or by a self-sustaining gas discharge between cold electrodes (cold cathode gauge). For example, the current from the anode to the cathode is measured as a parameter for determining pressure. The anode and cathode are in contact with the generated plasma. By appropriately combining electric and magnetic fields, the electron trajectories within the vacuum pressure sensor can be extended, thus increasing the ion yield. The generated plasma emits radiation, which can be analyzed in addition to the measured current and used to determine pressure or the composition of the residual gas. For example, WO 2021 / 052599 discloses a method for determining pressure in a vacuum system and a vacuum pressure sensor designed to evaluate the radiation emitted by the plasma.

[0003] In such vacuum pressure sensors, the electromagnetic radiation to be analyzed passes through a window or lens that is transparent at least within the electromagnetic spectrum onto a detector located separately from the zone where the plasma is generated. Due to the plasma, and possibly due to plasma-related sputtering effects on the cathode, the plasma side of the window or lens can become less and less transparent to the radiation over longer periods of operation, for example due to a thin metal layer building up on the window or lens. Summary of the Invention [Problem to be solved by the invention]

[0004] It was an object of the present invention to provide components for an alternative device for generating a plasma in a vacuum pressure sensor. In particular, it was an object of the present invention to provide a device which minimizes the aforementioned side effects of generating a plasma in a vacuum pressure sensor. [Means for solving the problem]

[0005] This object is achieved according to the invention by a chamber as claimed in claim 1. The chamber according to the present invention is designed to bound a plasma generation region within a vacuum pressure sensor. The chamber includes a conductive casing element disposed radially outward relative to a central axis. The chamber further includes a conductive wall element disposed substantially perpendicular to the central axis and connected to the casing element. At least one of the wall elements has a first opening through which the central axis extends. The casing element includes at least first and second regions, the first region being closer to the central axis than the second region.

[0006] Due to the opening in the wall element, the chamber is suitable for receiving the anode rod of an ionization gauge along the central axis of the chamber, which can act as a cathode.

[0007] The first and second regions of the casing element are at different distances from the axis, so that the casing element The element is not cylindrical. By way of example, the first and second regions may be located at different axial positions or at different azimuthal positions relative to the axis. When a voltage is applied between the central anode and the casing element, a higher electric field is generated between the central axis of the casing element and the first region than between the second region of the casing element and the central anode. As recognized by the inventors, this difference can be advantageous for the service life of optical elements located physically close to the chamber.

[0008] The casing element may be integrally formed or may be constructed from multiple pieces.

[0009] The wall elements can include, for example, ferromagnetic material that can interact with, for example, a permanent magnet arrangement of an ionization gauge located outside the chamber to affect the magnetic field pattern inside the chamber.

[0010] Exemplary embodiments of the chamber according to the invention will become apparent from the features of the dependent claims 2-7.

[0011] In one embodiment, a cross section through the casing element has the shape of a polygon in a plane perpendicular to the central axis.

[0012] The polygon may be, for example, a hexagon or a dodecagon. Such a polygonal cross section fits well in a substantially cylindrical environment, but ensures the existence of regions located at smaller and larger distances from the central axis. Thus, the distance between the central axis and the casing element varies depending on the azimuthal direction.

[0013] In one embodiment, the casing element is at least partially conical. The casing element can have, for example, the shape of the side of a truncated cone, with the first region closer to the central axis being located at the end of the truncated cone with a smaller radius.

[0014] In one embodiment, the first region of the casing element is located in the center of the chamber relative to the axial direction of the central axis.

[0015] For example, the casing element may be formed from two parts, each part having the shape of a flank of a truncated cone, the flanks with the smaller radius abutting each other in the centre of the chamber or fixed to a central wall element.

[0016] In one embodiment, the chamber comprises three mutually parallel wall elements, all three wall elements having a central opening with a central axis extending therethrough.

[0017] This embodiment is suitable for receiving the anode rod of an ionization gauge, which protrudes through all wall elements.

[0018] In one embodiment, at least one of the wall elements has a second opening. The second or further opening can provide a better hydrodynamic connection to the volume in which pressure is measured. The second or further opening can also provide multiple continuous radiation paths for the electromagnetic radiation generated within the plasma. The second or further opening is an opening positioned radially offset from the central axis.

[0019] In a further embodiment, the first opening is defined by an inner edge of at least one wall element. The inner edge has at least a first section that protrudes toward the central axis, and a second section that is farther from the central axis than the first section.

[0020] The inventors have recognized that when a chamber is used to bound a plasma generation region within a vacuum pressure sensor, a change in the distance between the inner edge of the wall element and the central axis, resulting in a change in the distance between the inner edge of the wall element and the anode, can help to ignite the plasma under unfavorable conditions, such as pressures in the lower operating range of the vacuum pressure sensor.

[0021] Such ignition assistance can be achieved by smoothly varying the contour of the circular inner edge in the azimuthal direction, for example, by one or several small spikes protruding inward from the circular inner edge. When analyzing radiation emitted from the plasma, sections that are farther from the central axis block less radiation. This embodiment is particularly useful in vacuum pressure gauges equipped with spectrometers. Alternatively, or in combination with the above, the surface of the inner edge may be oriented obliquely relative to the central axis, so that sections protruding toward the central axis are at a different axial position than sections farther from the central axis. As an example, a tapered rim around the first opening can be formed by drilling the opening with a conical drill. In this way, a relatively sharp edge can be created around the first opening. In embodiments with wall elements containing ferromagnetic material, the change in distance between the inner edges of the first opening not only shapes the electric field, but also helps to concentrate the magnetic field in a specific region along the central axis or at a specific azimuthal position.

[0022] The present invention also relates to a vacuum pressure sensor according to claim 8. The vacuum pressure sensor according to the invention comprises a chamber according to the invention, the vacuum pressure sensor further comprising an anode arranged along a central axis of the chamber and means arranged radially outside the chamber for generating a magnetic field inside the chamber.

[0023] The chamber is suitable to function as a cathode or part of a cathode of a vacuum pressure sensor in the form of an ionization gauge, in particular the vacuum pressure sensor described above is an ionization gauge of the inverted magnetron type.

[0024] In an alternative form of the inverted magnetron type, the invention further relates to a vacuum pressure sensor as claimed in claim 9.

[0025] This vacuum pressure sensor according to the invention comprises a chamber according to the invention acting as an anode, a cathode arranged at least partially along the central axis of the chamber, and means arranged radially outside the chamber for generating a magnetic field inside the chamber.

[0026] The chamber is suitable to function as the anode or part of the anode of a vacuum pressure sensor in the form of an ionization vacuum gauge. Since the roles of the anode and cathode are reversed with respect to the previously described vacuum pressure sensor of the inverted magnetron type, this alternative vacuum pressure sensor is an ionization vacuum gauge of the magnetron type.

[0027] Embodiments of the vacuum pressure sensor will become apparent from the features of claims 10 and 11.

[0028] One embodiment of the vacuum pressure sensor further comprises a housing having a flange surrounding an opening for establishing a fluid connection between a plasma generation region inside the vacuum pressure sensor and a measurement space outside the vacuum pressure sensor, the radiation transparent element preventing electromagnetic radiation emitted from the plasma generation region from reaching the outside of the housing through the radiation transparent element. The chamber according to the present invention is arranged inside the housing, with a first region of the casing element of the chamber arranged on a first side of the chamber, the first side facing the flange, and a second region of the casing element of the chamber arranged on a second side of the chamber, the second side facing the radiolucent element.

[0029] In a particular realization of this embodiment, the conductive casing element of the chamber has a frustoconical shape tapering towards said flange.

[0030] Surprisingly, a relatively slight taper, corresponding to an angle of about 3° between the central axis and the surface line on the conical casing element, results in an increase in the power of radiation emitted from the plasma in a low-pressure environment. This is surprising, as with this configuration, the plasma generation region is expected to be located farther from the radiation-transparent element, which at first glance might be expected to result in a lower radiation intensity experienced outside the housing.

[0031] In a further embodiment of the vacuum pressure sensor, an optical element, such as a lens or mirror, and a spectrometer are located outside the housing, the radiation-transparent element and the optical element cooperating to collect and focus electromagnetic radiation emitted from the area around the anode onto an optically sensitive element of the spectrometer.

[0032] This type of vacuum pressure sensor benefits from increased uptime as well as increased radiation intensity reaching the optically sensitive element of the spectrometer.

[0033] In a particular variant of the embodiment, the optical element can be adapted to compensate for the axial displacement of the radiation emission region. This variant may be particularly combined with the above-mentioned embodiment in which the conductive casing element of the chamber has a truncated conical shape tapering towards the flange. In this embodiment, the center and axial extension of the plasma region with the highest radiation emission can vary depending on the pressure. An adaptable optical element, for example a lens movable in the direction of the central axis, serves to adjust the focus of the overall arrangement formed by the spectrometer, the optical element and the radiation-transparent element in the housing wall. A control loop can be used to continuously adjust the position of the optical element for the maximum radiation intensity admitted to the spectrometer. In particular, the radiation-transparent element may itself be shaped in the form of a lens.

[0034] Exemplary embodiments of the invention are explained in more detail below with reference to the figures. [Brief explanation of the drawings]

[0035] [Figure 1]Different views of the first embodiment of the chamber are shown in subfigures 1.a) to 1.c). [Figure 2] Different views of the second embodiment of the chamber are shown in subfigures 2.a) to 2.d). [Figure 3] Different views of the third embodiment of the chamber are shown in subfigures 3.a) to 3.d). [Figure 4] 1 is a longitudinal cross-sectional view of a vacuum pressure sensor having a chamber shown schematically; [Figure 5] FIG. 1 is a longitudinal cross-sectional view of an embodiment of a vacuum pressure sensor. [Figure 6] In subfigures 6.a) to 6.c) axial cross-sections of variants of the first opening are shown, and in subfigure 6.d) longitudinal cross-sections of variants of the first opening are shown. [Figure 7] In sub-figures 7.a) to 7.e) variations of the contour of the first opening with specific dimensions are shown. [Figure 8] In sub-figures 8.a) to 8.d), wall elements with variants of the first opening are shown in perspective views. DETAILED DESCRIPTION OF THE INVENTION

[0036] Figures 1.a) and 1.b) show two perspective views from two viewing directions of a first embodiment of the chamber 11. In this embodiment, the chamber has a casing element 1 in the shape of the side of a prism with a dodecagonal base. Three wall elements 2, 2', and 2" form closures at both ends of the chamber (2, 2") and at the intermediate wall 2', respectively. Six protrusions on the periphery of the intermediate wall 2' protrude beyond the outer surface of the casing element through rectangular slots in the casing element. A first opening 3 is located in the center of wall 2", so that the central axis A of the chamber extends through this opening. Not visible here are the central openings of the two walls 2 and 2', whose central axes also extend through them so that the central anode rod of the ionization gauge can pass through all three central openings.

[0037] Figure 1.c) shows a plan view of the wall element 2. Apart from the centrally located first opening 3, the wall element has a total of six further openings 4 at larger radii. Located between the outwardly projecting protrusions on the periphery of the wall element are fastening areas 5, where the wall element is connected to the casing element, for example by spot welding.

[0038] Figures 2.a) and 2.b) show two perspective views from two viewing directions of a second embodiment of the chamber 12. In this embodiment, the casing element 1 has the shape of a truncated cone.

[0039] FIG. 2.c) shows the same second embodiment 12 in plan view. Figure 2.d) shows a side view of the same second embodiment 12. By way of example, the half-opening angle of the truncated cone may be 3°, as shown in this side view. By way of example, the length L of the chamber may be in the range of 20 mm to 30 mm. This embodiment of the chamber also has three wall elements 2, 2', 2".

[0040] Figures 3.a) and 3.b) show two perspective views from two viewing directions of a third embodiment of the chamber 13. In this embodiment, the casing element is formed from two parts, each part 1' and 1" of the casing element having the shape of a flank of a truncated cone, the flank of the truncated cone having the smaller radius in each case being fastened to an intermediate wall element 2'. In this way, the first region of the casing element is the region radially closer to the central axis and is located in the center of the chamber.

[0041] FIG. 3.c) shows the same third embodiment 13 in plan view. Figure 3.d) shows a side view of the same third embodiment 13. The two truncated cones, each with a cone half-opening angle of 3°, can be clearly seen in this view.

[0042] FIG. 4 shows a longitudinal section along the central axis A through a vacuum pressure sensor 40 in the form of an ionization vacuum gauge having an anode 41 and a chamber according to the invention as cathode. The chamber has wall elements 2, 2', 2". The shape and position of the casing element 1 is shown here diagrammatically by the area enclosed in dashed lines as a placeholder. Various shapes of the casing element 1 are conceivable here, i.e. any one of the casing elements of the above-mentioned embodiments 11, 12 and 13 of the chamber is a possible option here. In any of these embodiments of the chamber, the chamber is a kind of pressed chamber, which can be pressed from the flange side 45 of the vacuum pressure sensor into the position shown in the chamber. Radially outward of the chamber, a magnetic field is disposed within the chamber. A permanent magnet arrangement 44 is arranged, which serves as a means for generating a field. The permanent magnet arrangement extends annularly around the axis. According to one possible embodiment, this permanent magnet arrangement interacts with a wall element, advantageously made of a ferromagnetic material. During operation of the vacuum pressure sensor, i.e. when a high voltage is applied between the anode and the cathode and when there is a pressure in the chamber that is within the measurement range of the pressure sensor, a plasma is generated in a plasma generation region 42 around the anode. The plasma emits electromagnetic radiation 43, which is transmitted through a radiation-transparent element 46, e.g., a magnetic field, as indicated by the corresponding arrow. If necessary, the outside can be reached through a window or lens.

[0043] FIG. 5 shows a longitudinal cross section of a vacuum pressure sensor embodiment, partially generalized compared to the embodiment shown in FIG. 4, with some specific details. The vacuum pressure sensor 50 shown here has a housing 51 with a flange 45 connected to the measurement space. At its opposite end, a radiation-transparent element 46, in this case formed as a lens, allows electromagnetic radiation emitted from a radiation-emitting region 55 to be transmitted outside the housing. The radiation path can, for example, lead to a spectrometer 54 across an optional optical element 53. The radiation-emitting region 55, the radiation path, the optical element 53 in the form of a lens, and the symbolic spectrometer 54 are shown in dashed lines to indicate that these features are not part of the vacuum pressure sensor 50 but are useful for understanding its function and illustrating the specific embodiment. The chamber located inside the housing has a casing element 1 with a truncated cone shape that tapers toward the flange 45. Thus, a first region B1, which is closer to the central axis than a second region B2, is located closer to the flange, while the second region B2 is located closer to the radiation-transparent element 46. The anode rod 41 is positioned on the common central axis of the housing and the chamber. The electrical contacts, designated "+" and "-", indicate the operating method of the vacuum pressure sensor. The variation shown here has the central anode rod 41 conductively connected to the "+" contact, resulting in an inverted magnetron vacuum pressure gauge. As mentioned above, by switching the roles of the anode and cathode, i.e., mainly by exchanging the "+" and "-", a magnetron-type instrument can be implemented with only minor modifications to the pressure sensor, as shown in Figure 5. The housing 51 and the inserted chamber together form the cathode of the sensor. Radially outside the housing is located a means 52 for generating a magnetic field inside the housing. The chamber has three wall elements, designated 2, 2', and 2", each with an opening through which the central axis extends. The optical element 53 may optionally be axially movable, as indicated by the double arrow, to adjust the focus when the radiation-emitting area 55 moves along the anode or when it expands or contracts in its axial extension depending on the pressure.

[0044] Figure 6 shows variations in the shape of the central first opening of the wall element. Only a small portion of each wall element is shown. All of the variations shown here have in common that the first opening 3 is surrounded by the inner edge of the wall element, which has at least a first section S1 (not shown in Figures 6a-6c) protruding toward the central axis A' and a second section S2 further away from the central axis than the first section. Multiple protruding sections S1 are possible; for example, Figures 6a-6b show three first sections S1, while Figure 6c shows six first sections S1. Figure 6d shows a protruding region S1 formed by a conical surface on the inner edge. All of the variations shown here can act as an ignition aid, i.e., to help the plasma be ignited and maintained at pressures relatively low relative to the measurement range of the vacuum manometer. The protruding sections may be formed as sharp spikes as in Figures 6.b) and 6.d), or they may be formed with a large radius (Figure 6.a) or flat, if corresponding recesses in section S2 are formed nearby them (Figure 6.d).

[0045] Figures 7a-e show variations in the contour of the first opening in the wall element; all variations are based on an approximate opening diameter of 5 mm. The protruding section (S1) and the recessed section (S2) are repeated three (Figures 7a and 7b), six (Figure 7c), four (Figure 7d), or eight (Figure 7e) times around the circumference of the opening. The protruding sections may be limited to a small portion of the circumference (Figure 7a) or cover most of the circumference (Figures 7b, 7c, and 7d), separated by more limited recesses between them.

[0046] Figure 8.a) to Figure 8.d) show wall elements 2, 2' or 2" of one of the above figures. 8.a) shows a perspective view of a complete wall element having a first opening 3 that can serve a specific purpose and has a contour as shown in the corresponding subfigure of FIG. 7. That is, the contour of the first opening in FIG. 8.a) has the shape shown in FIG. 7.a) as an example. The thickness of the wall element shown in FIG. 8 may be approximately 1.5 mm to match the dimensions shown in the corresponding subfigure of FIG. 7. These wall elements may be made of, for example, a ferromagnetic material. In addition to the first opening 3 shown here, the wall element can be further modified to have additional openings at other radial locations, as shown in FIG. 1.c). The first opening configuration of all wall elements shown in FIG. 8 can be used as an ignition aid so that the plasma can be ignited at relatively low pressures.

[0047] Returning to the technical effect of all embodiments of the present invention, the inventors have recognized that the present invention allows for geometrical changes in field strength, instead of setting the voltage between the electrodes to an appropriate value. Instead, it becomes possible to search for an appropriate spatial position. As an example, in an embodiment having a polygonal cross section along a circle around the anode, the position with the maximum light can be searched for and used for optical evaluation. This geometric position can be tracked as process conditions change.

[0048] The conical and conical polygonal embodiments allow for varying the plasma density along the axis, which has the advantage that it is possible to define the emission volume and combine this with finding the sputtering minimum, i.e., a long service life of the radiation-transparent element. [Explanation of symbols]

[0049] List of Reference Numbers 1. Casing element 1',1" Part of multi-part casing element 2,2',2" wall elements 3 First opening (in wall element) 4 Second / further opening (in wall element) 5 Fastening area on wall element 6 Markings on wall elements 11, 12, 13 Chamber embodiments 40 Vacuum pressure sensor 41 anode, e.g., anode rod 42 Plasma generation region 43 Radiation 44 Permanent Magnet Device 45 flange 46 Radiolucent elements 50 Vacuum pressure sensor 51 Housing 52 Means for generating a magnetic field 53 Optical elements 54 Spectrometer 55 Radiation Emitting Region A center axis B1 First region (near the central axis) B2 Second region (farther from the central axis) L (chamber length) S1 First section of the inner edge of the wall element S2 Second section of the inner edge of the wall element

Claims

1. 1. A chamber (11, 12, 13) for bounding a plasma generation region (42) in a vacuum pressure sensor (40), the chamber comprising electrically conductive casing elements (1, 1', 1") arranged radially outward with respect to a central axis (A), the chamber comprising electrically conductive wall elements (2, 2', 2") arranged substantially perpendicular to the central axis and connected to the casing elements, at least one of the wall elements having a first opening (3) through which the central axis (A) extends, the casing element comprising at least a first region (B1) and a second region (B2), the first region being located closer to the central axis than the second region.

2. 2. The chamber (11) according to claim 1, wherein a cross section through the casing element has the shape of a polygon in a plane perpendicular to the central axis.

3. 3. A chamber (12, 13) according to claim 1 or 2, wherein the casing element is at least partly conical.

4. The chamber (13) according to any one of claims 1 to 3, wherein the first region of the casing element is located in the center of the chamber axially relative to the central axis.

5. A chamber (11, 12, 13) according to any one of claims 1 to 4, wherein the chamber comprises three mutually parallel wall elements, all three wall elements having a central opening through which the central axis extends.

6. A chamber (11, 12, 13) according to any one of claims 1 to 5, wherein at least one of the wall elements has a second opening.

7. The chamber (11, 12, 13) according to any one of claims 1 to 6, wherein the first opening (3) is surrounded by an inner edge of the at least one wall element, the inner edge having at least a first section (S1) protruding towards the central axis (A) and a second section (S2) remoter from the central axis than the first section.

8. A vacuum pressure sensor (40) comprising a chamber (11, 12, 13) according to any one of claims 1 to 7 as a cathode, an anode (41) arranged along the central axis of the chamber, and means (44) arranged radially outside the chamber for generating a magnetic field inside the chamber.

9. A vacuum pressure sensor comprising a chamber (11, 12, 13) according to any one of claims 1 to 7 as an anode or part of an anode, a cathode arranged at least partially along the central axis of the chamber, and means arranged radially outside the chamber for generating a magnetic field inside the chamber.

10. The vacuum pressure sensor further comprises a housing having a flange (45) surrounding an opening for establishing a fluid connection between the plasma generation region (42) inside the vacuum pressure sensor and a measurement space outside the vacuum pressure sensor, the radiation-transparent element being arranged in a wall of the housing so that electromagnetic radiation emitted from the plasma generation region can reach the outside of the housing through the radiation-transparent element, the chamber being arranged inside the housing, the first region (B1) being arranged on a first side of the chamber oriented towards the flange (45) and the second region (B2) being arranged on a second side of the chamber oriented towards the radiation-transparent element (46), in particular in front of the chamber.

10. A vacuum pressure sensor (40) according to claim 8 or 9, wherein the conductive casing element has a frusto-conical shape tapering towards the flange.

11. 11. A vacuum pressure sensor (40) as described in claim 10, wherein an optical element (53) and a spectrometer (54) are arranged outside the housing, and the radiation-transparent element (46) and the optical element (53) cooperate to collect and focus electromagnetic radiation emitted from a region (55) around the anode onto an optically sensitive element of the spectrometer, and in particular, the optical element (53) is adaptable to compensate for axial displacement of the radiation-emitting region (55).

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