Chamber for ionization vacuum gauge

Abstract

A chamber (11, 12, 13) for delimiting a plasma generation zone (42) in a vacuum pressure sensor (40), where the chamber comprises an electrically conductive housing element (1, 1 ', 1' ') located radially on the outside with respect to a central axis. The chamber comprises electrically conductive wall elements (2, 2 ', 2' ') arranged substantially perpendicular to the central axis and connected to the housing element, at least one of the wall elements having a first opening (3) through which the central axis extends, the housing element comprising at least a first region (B1) and a second region (B2), the first region is positioned closer to the central axis than the second region. The invention also relates to a vacuum pressure sensor comprising a chamber.

Description

Technical Field

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

[0002] Vacuum pressure sensors or vacuum gauges are known, by which pressures significantly lower than normal pressure can be determined. Among the known vacuum pressure sensors, the so-called ionization vacuum gauges have a particularly wide measuring range. In an ionization vacuum gauge, the residual gas is ionized and a plasma is generated. The electrons required to ionize the gas are generated by a hot cathode (hot cathode ionization vacuum gauge) or in a self-sustaining gas discharge between cold electrodes (cold cathode vacuum gauge). For example, the current from the anode to the cathode is measured as a parameter for determining the pressure. The anode and the cathode are in contact with the generated plasma. By appropriately combining the electric field and the magnetic field, the trajectory of the electrons in the vacuum pressure sensor can be extended, and the ion yield can therefore be increased. The generated plasma emits radiation, which can be analyzed in addition to the measured current and can be used to determine the pressure or also to determine the composition of the residual gas. For example, document WO2021 / 052599A1 discloses a method for determining the 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 which is transparent at least in the range of the electromagnetic spectrum to a detector which is arranged separately from the region in which the plasma is generated. Due to the plasma and possibly due to plasma-related sputtering effects on the cathode, it can happen that the plasma side of the window or lens becomes increasingly impermeable to radiation over a longer operating time, for example due to the accumulation of thin metal layers on the window or lens. Summary of the invention

[0004] The object of the present invention is to provide a component of an alternative device for generating plasma in a vacuum pressure sensor. In particular, the object of the present invention is to provide a device that minimizes the aforementioned side effects of generating plasma in a vacuum pressure sensor.

[0005] According to the invention, this object is achieved by a chamber according to claim 1 .

[0006] The chamber according to the invention is designed to define a plasma generation zone in a vacuum pressure sensor. The chamber comprises an electrically conductive housing element located radially on the outside relative to a central axis. The chamber further comprises an electrically conductive wall element, which is arranged substantially perpendicular to the central axis and is connected to the housing element. At least one of the wall elements has a first opening through which the central axis extends. The housing element comprises at least a first region and a second region, wherein the first region is located closer to the central axis than the second region.

[0007] Due to the opening in the wall element, the chamber is adapted to receive an anode rod of an ionization vacuum gauge along a central axis of the chamber.The chamber may function as a cathode.

[0008] Because the first region and the second region of the housing element are at different distances from the axis, the housing element is not cylindrical. For example, the first region and the second region may be located at different axial positions, or they may be located at different positions in the azimuthal direction relative to the axis. When a voltage is applied between the central anode and the housing element, a higher electric field is generated between the central axis and the first region of the housing element than between the second region of the housing element and the central anode. As the inventors have recognized, this difference may be advantageous for the service life of optical elements that are physically arranged close to the chamber.

[0009] The housing element may be formed in one piece, or it may consist of multiple parts.

[0010] The wall element may comprise, for example, a ferromagnetic material.The ferromagnetic wall element may, for example, interact with an arrangement of permanent magnets of an ionization gauge arranged outside the chamber to influence the magnetic field characteristics in the interior of the chamber.

[0011] Exemplary embodiments of the chamber according to the invention are apparent from the features of the dependent claims 2 to 7 .

[0012] In one embodiment, a cross section through the housing element has a polygonal shape in a plane perpendicular to the central axis.

[0013] The polygon may be, for example, a hexagon or a dodecagon. Such a polygonal cross section fits well into a substantially cylindrical environment, but ensures that there are regions at smaller and larger distances from the central axis. Thus, the distance between the central axis and the housing element varies depending on the azimuthal direction.

[0014] In one embodiment, the housing element is at least partially conical.

[0015] The housing element may have the shape of a side surface of a truncated cone, for example. In this case, the above-mentioned first region located closer to the central axis is located at the end of the truncated cone with a smaller radius.

[0016] In one embodiment, the first region of the housing element is located in the middle of the chamber in an axial direction relative to the centre axis.

[0017] For example, the housing element may be formed from two parts, wherein each part has a side surface of a frustoconical cone and a shape with a smaller radius but which abut against each other in the middle of the chamber or are fastened to the side of the intermediate wall element.

[0018] In one embodiment, the chamber comprises three mutually parallel wall elements, wherein all three wall elements have a central opening through which the central axis extends.

[0019] This embodiment is suitable for receiving an anode rod of an ionization vacuum gauge, which anode rod protrudes through all wall elements.

[0020] In one embodiment, at least one of the wall elements has a second opening.

[0021] The second or even further openings may be used for a better fluid dynamic connection to the space in which the pressure is to be measured. The second or even further openings may also provide a plurality of continuous radiation paths for the electromagnetic radiation generated in the plasma. The second or further openings are openings positioned radially offset from the central axis.

[0022] In a further embodiment, the first opening is surrounded by an inner edge of at least one wall element. The inner edge has at least a first section protruding toward the central axis. The inner edge has a second section further away from the central axis than the first section.

[0023] The inventors have recognized that, when the chamber is used to define a plasma generation region in a vacuum pressure sensor, such a variation in the distance between the inner edge of the wall element and the central axis will result in a variation in the distance between the inner edge of the wall element and the anode, facilitating ignition of the plasma under adverse conditions (such as at pressures at the lower operating range of the vacuum pressure sensor).

[0024] For example, such an ignition aid can be achieved by one or several small tips protruding inwardly from the circular inner edge, by the profile of the inner edge varying smoothly in the azimuthal direction. In the case where the radiation emitted from the plasma is to be analyzed, the section with a larger distance to the central axis blocks less radiation. This embodiment is particularly useful in a vacuum pressure gauge having a spectrometer attached thereto. Alternatively or in combination with the above, the surface of the inner edge can be oriented obliquely relative to the central axis so that the section protruding toward the central axis is in a different axial position than the section further away from the central axis. As an example, a tapered edge around the first opening can be formed by drilling the opening with the aid of a conical drill bit. In this way, a relatively sharp edge can be produced around the first opening. In an embodiment with a wall element comprising a ferromagnetic material, the variation of the distance between the inner edges of the first opening not only leads to the shaping of the electric field, but also helps to concentrate the magnetic field in certain areas along the central axis or in certain azimuthal positions.

[0025] The 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 comprises an anode arranged along the central axis of the chamber and means arranged radially outside the chamber for generating a magnetic field in the interior of the chamber.

[0026] The chamber is suitable for use as a cathode or part of a cathode of a vacuum pressure sensor in the form of an ionization vacuum gauge.More specifically, the vacuum pressure sensor described above is an ionization vacuum gauge of the inverted magnetron type.

[0027] In an alternative of the inverted magnetron type, the invention also relates to a vacuum pressure sensor according to claim 9 .

[0028] The vacuum pressure sensor according to the invention comprises a chamber according to the invention having the function of an anode. The vacuum pressure sensor further comprises 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 in the interior of the chamber.

[0029] The chamber is suitable for use as an anode or part of an anode of a vacuum pressure sensor in the form of an ionization vacuum gauge.Since the roles of anode and cathode are interchanged relative to the previously described inverted magnetron type vacuum pressure sensor, the alternative vacuum pressure sensor is an ionization vacuum gauge of the magnetron type.

[0030] Embodiments of the vacuum pressure sensor will become apparent from the features of claims 10 and 11 .

[0031] An embodiment of the vacuum pressure sensor further comprises a housing. The housing has a flange surrounding an orifice for establishing a fluid connection between a plasma generation zone inside the vacuum pressure sensor and a measuring space outside the vacuum pressure sensor. A radiation-permeable element is arranged in the wall of the housing in such a way that electromagnetic radiation emitted from the plasma generation zone can reach the outside of the housing through the radiation-permeable element. A chamber according to the present invention is located inside the housing. A first region of a housing element of the chamber is located on a first side of the chamber, the first side being oriented toward the flange. A second region of the housing element of the chamber is located on a second side of the chamber, the second side being oriented toward the radiation-permeable element.

[0032] In a particular implementation of this embodiment, the electrically conductive housing element of the chamber has a frustoconical shape tapering towards the flange.

[0033] Surprisingly, a relatively slight taper corresponding to an angle of about 3° between the central axis and a surface line on the conical housing element results in an increased output of radiation emitted from the plasma in a low pressure environment. This is surprising because with this configuration, the plasma generation region is expected to be located further away from the radiation transparent element, which at first glance might be expected to result in a lower radiation intensity received on the exterior of the enclosure.

[0034] In a further embodiment of the vacuum pressure sensor, an optical element (such as, for example, a lens or a reflector) and a spectrometer are arranged on the outside of the housing. The radiation permeable element and the optical element cooperate to collect and focus electromagnetic radiation emitted from the area around the anode to the optically sensitive element of the spectrometer.

[0035] This type of vacuum pressure sensor benefits from increased use time and increased radiation intensity reaching the optical sensitive element of the spectrometer.

[0036] In a particular variant of the embodiment, the optical element is adapted to compensate for the axial displacement of the radiation emission region. This variant can be combined in particular with the embodiment discussed above, in which the conductive housing element of the chamber has a frustoconical shape that tapers 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 (e.g. a lens movable in the direction of the central axis) helps to adjust the focus of the entire construction formed by the spectrometer, the optical element and the radiation-permeable element in the wall of the housing. A control loop can be used to continuously adjust the position of the optical element to maximize the radiation intensity received in the spectrometer. In particular, the radiation-permeable element itself can be shaped in the form of a lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Exemplary embodiments of the present invention will be explained in more detail below with reference to the accompanying drawings, in which:

[0038] Figure 1 Figures 1.a) to 1.c) ] Different views of a first embodiment of a chamber are shown;

[0039] Figure 2 Figures 2.a) to 2.d) ] Different views of a second embodiment of the chamber are shown;

[0040] Figure 3 Figures 3.a) to 3.d) ] Different views of a third embodiment of a chamber are shown;

[0041] Figure 4 shows a longitudinal section through a vacuum pressure sensor having a schematically illustrated chamber;

[0042] Figure 5 shows a longitudinal section through an embodiment of a vacuum pressure sensor;

[0043] Figure 6 Figure 6.a) to 6.c) A cross-sectional view of a variant of the first opening in the axial direction is shown in FIG. Figure 6.d ) shows a longitudinal section through a variant of the first opening;

[0044] Figure 7 Figures 7.a) to 7.e) A variation of the profile of the first opening having a specific size is shown in FIG.

[0045] Figure 8 Figures 8.a) to 8.d) A variant wall element with a first opening is shown in a perspective view. DETAILED DESCRIPTION

[0046] Figure 1.a )and Figure 1.b ) shows two perspective views of a first embodiment 11 of a chamber from two viewing directions. In this embodiment, the chamber has a housing element 1 in the shape of the side surface of a prism with a dodecagonal base. Three wall elements 2, 2', 2" form closures at the two ends (2, 2") and the middle wall 2' of the chamber, respectively. Six protrusions on the outer periphery of the middle wall 2' extend out of the outer surface of the housing element through rectangular slots in the housing element. The first opening 3 is centrally located in the wall 2", so that the center axis A of the chamber extends through the opening. Not visible here are the central openings in the two walls 2 and 2', through which the center axis also extends, so that the center anode rod of the ionization vacuum gauge can pass through all three center openings.

[0047] Figure 1.c ) shows a plan view of a wall element 2. In addition to the centrally arranged first opening 3, the wall element has a total of six further openings 4 on a larger radius. Located between the outwardly projecting projections on the outer circumference of the wall element is a fastening area 5 at which the wall element is connected to the housing element, for example by spot welding.

[0048] Figure 2.a )and Figure 2.b ) shows two perspective views of a second embodiment of a chamber 12 from two viewing directions. In this embodiment, the housing element 1 has the shape of a frustoconical cone.

[0049] Figure 2.c ) shows a plan view of the same second embodiment 12.

[0050] Figure 2.d ) shows a side view of the same second embodiment 12. By way of example, the half angle of the truncated cone can be 3°, as shown in this side view. By way of example, the length L of the chamber can be in the range from 20 mm to 30 mm. This embodiment of the chamber also has three wall elements 2, 2', 2".

[0051] Figure 3.a )and Figure 3.b ) shows two perspective views of a third embodiment 13 of a chamber from two viewing directions. In this embodiment, the housing element is formed from two parts, wherein each part 1' and 1" of the housing element has the shape of the side surface of a frustum of a cone and wherein, in each case, the side of the frustum of a cone with the smaller radius is fastened to an intermediate wall element 2'. In this way, the first region of the housing element, which is the region located radially closer to the center axis, is located in the middle of the chamber.

[0052] Figure 3.c ) shows a plan view of the same third embodiment 13.

[0053] Figure 3.d ) shows a side view of the same third embodiment 13. In this view, two truncated cones can be clearly seen, each of which has a cone half angle of 3°.

[0054] Figure 4A longitudinal section is shown extending along a center 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 a cathode. The chamber has wall elements 2, 2', 2". The shape and position of the housing element 1 are schematically indicated here by the area outlined in dashed lines as a position marker. Various geometries of the housing element 1 are conceivable here, i.e. any of the housing elements of the above-mentioned embodiments 11, 12 and 13 of the chamber are possible options here. For any of these embodiments of the chamber, the chamber is a push-in chamber, which can be pushed into the illustrated position of the chamber from the flange side 45 of the vacuum pressure sensor. Radially outside the chamber is a permanent magnet arrangement 44, which serves to generate a magnetic field in the chamber. The device. The permanent magnet arrangement extends annularly around the axis. According to one possible embodiment, the permanent magnet arrangement advantageously interacts with a wall element made of 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 a pressure within the measuring range of the pressure sensor is present in the chamber, a plasma is generated in a plasma generation region 42 around the anode. The plasma emits electromagnetic radiation 43, which can reach the outside through a radiation transparent element 46, such as a window or a lens, as illustrated by corresponding arrows.

[0055] Figure 5 A longitudinal section through an embodiment of a vacuum pressure sensor is shown, which is partially compared to Figure 4 The embodiment shown in is more general, partly with specific details. The vacuum pressure sensor 50 shown here has a housing 51 with a flange 45 to be connected to the measurement space. At its opposite end, a radiation-transmissive element 46 formed as a lens in this case allows the electromagnetic radiation emitted from the radiation emission area 55 to be transmitted to the outside of the housing. The radiation path can, for example, pass into a spectrometer 54 across an optional optical element 53. The radiation emission area 55 indicating the radiation path, the optical element 53 in the form of a lens, and the spectrometer 54 indicated by the symbol are shown in dotted lines to indicate that these features are not part of the vacuum pressure sensor 50, but are useful for understanding its function and further illustrating specific embodiments. The chamber located inside the housing has a housing element 1 in the shape of a truncated cone that tapers toward the flange 45. In this way, the first area B1, which is closer to the central axis than the second area B2, is on the side closer to the flange, while the second area B2 is closer to the side of the radiation-transmissive element 46. The anode rod 41 is arranged on the common central axis of the housing and the chamber. The electrical contacts denoted as "+" and "-" indicate the manner in which the vacuum pressure sensor operates. The variant shown here has a central anode rod 41 electrically connected to the "+" contact, so that an inverted magnetron vacuum pressure gauge is produced. As discussed above, in the case where the roles of anode and cathode are switched, i.e., primarily by interchanging the "+" and "-", the vacuum pressure sensor can be switched by only switching the "+" and "-" contacts. Figure 5 The pressure sensor shown in is slightly modified to implement a magnetron type gauge. The housing 51 and the inserted chamber together form the cathode of the sensor. Means 52 for generating a magnetic field in the interior of the housing are arranged radially outside the housing. The chamber has three wall elements denoted by 2, 2' and 2", each of which has an opening across which the central axis extends. The optical element 53 can optionally be movable in the axial direction, as indicated by the double-sided arrow, in order to adjust the focus in the case of a displacement of the radiation emission area 55 along the anode or when the radiation emission area 55 extends or contracts in its axial extension depending on the pressure.

[0056] FIG. 6 shows variants of the shape of the first opening in the center of the wall element. Only a small part of the respective wall element is shown. All variants shown here have in common that the first opening 3 is surrounded by an inner edge of the wall element, wherein the inner edge has at least a first section S1 (at the center of the wall element) protruding toward the center axis A. Figure 6.a) to Figure 6.c) A plurality of protruding segments S1 are possible, for example, Figure 6.a )and Figure 6.b ) there are three first sections S1, and Figure 6.c ) there are six first segments S1. Figure 6.d ) shows a protruding area S1 formed by the conical surface of the inner edge. All the variants shown here can be used as ignition aids, i.e., to help the plasma to be ignited and maintained at a relatively low pressure relative to the measuring range of the vacuum pressure gauge. The protruding section can be formed as a sharp tip, as in Figure 6.b )and Figure 6.d ), or they may be formed to have a large radius ( Figure 6.a ) or even flat in the case where a corresponding recess of the segment S2 is formed in its vicinity ( Figure 6.d ).

[0057] Figure 7.a) to Figure 7.e) Variants of the profile of the first opening in the wall element are shown, all based on an approximate diameter of the opening of 5 mm. The protruding section (S1) and the recessed section (S2) are each repeated three times along the circumference of the opening ( Figure 7.a and Figure 7.b ), six times( Figure 7.c) , Four Second-rate( Figure 7.d ) or eight times ( Figure 7.e The protruding section may be limited to a small portion of the perimeter ( Figure 7.a ) or covers a large part of the perimeter ( Figure 7.b , Figure 7.c , Figure 7.d ), separated by a more confined concave portion therebetween.

[0058] Figure 8.a) to Figure 8.d) A perspective view of a complete wall element is shown, which wall element can have the function of one of the wall elements 2, 2' or 2" in one of the above figures and has a first opening 3 having a profile as shown in the corresponding sub-figure of FIG. 7. That is, as an example, Figure 8.a ) has a profile of the first opening having Figure 7.a ). The thickness of the wall elements shown in FIG8 may be about 1.5 mm to match the dimensions indicated in the corresponding sub-figure of FIG7. These wall elements may be made of ferromagnetic material, for example. In addition to the first opening 3 shown here, the wall elements may be further modified to have additional openings at other radial positions, such as for example Figure 1.c The form of the first opening of all wall elements shown in FIG. 8 can be used as an ignition aid so that the plasma is ignited at a relatively low pressure.

[0059] Returning to the technical effects of all embodiments of the present invention, the inventors have realized that the present invention also makes it possible to implement field strength variations in a geometrical manner, rather than setting the voltage between the electrodes to an appropriate value. Instead, it is now possible to find a suitable spatial position. For example, in an embodiment with a polygonal cross section along a circle around the anode, the position with the maximum light can be found and used for optical evaluation. If process conditions change, this geometric position can be tracked.

[0060] Embodiments of the conical and conical-polygonal type make it possible to vary the plasma density along the axis. This has the advantage that it is possible to locate the luminous volume and combine this with finding a sputtering minimum, ie a long service life of the radiation transparent element is possible.

[0061] Reference numerals list 1 Shell element 1',1" Sections of Multi-Part Housing Elements 2,2',2" wall elements 3 First opening (in the wall element) 4 Second / additional opening (in the wall element) 5 Fastening area on wall element 6 Marking on wall elements 11,12,13 Chamber Examples 40 Vacuum pressure sensor 41 Anode, such as anode rod 42 Plasma generation area 43 Radiation 44 Permanent magnet arrangement 45 flange 46Radiation transparent element 50 Vacuum pressure sensor 51 Shell 52 Means for generating a magnetic field 53 Optical elements 54 Spectrometer 55 Radiation emission area ACentral axis B1 first area (closer to the central axis) B2 Second area (further away from the central axis) L (chamber) length S1 First section of the inner edge of the wall element S2 A second section of the inner edge of the wall element.

Claims

1. A chamber (11, 12, 13) for defining a plasma generation region (42) in a vacuum pressure sensor (40), wherein: The chamber comprises a conductive shell element (1, 1', 1") located radially on the outside relative to a central axis (A), wherein the chamber comprises conductive wall elements (2, 2', 2") arranged substantially perpendicular to the central axis and connected to the shell element, wherein at least one of the wall elements has a first opening (3) through which the central axis (A) extends, wherein the shell element comprises at least a first area (B1) and a second area (B2), wherein the first area is located closer to the central axis than the second area.

2. The chamber (11) according to claim 1, wherein: A cross section through the housing element has a polygonal shape in a plane perpendicular to the central axis.

3. The chamber (12, 13) according to claim 1 or 2, wherein: The housing element is at least partially conical.

4. The chamber (13) according to any one of claims 1 to 3, wherein: The first region of the housing element is located in the middle of the chamber relative to the axial direction of the center axis.

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

6. The 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, wherein the inner edge has at least a first section (S1) protruding toward the center axis (A) and a second section (S2) further away from the center 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 a device (44) arranged radially outside the chamber for generating a magnetic field in the interior of 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 for generating a magnetic field in the interior of the chamber arranged radially outside the chamber.

10. The vacuum pressure sensor (40) according to claim 8 or 9, further comprising a housing having a flange (45) surrounding an orifice 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, wherein: A radiation-permeable element is arranged in the wall of the housing in such a way that electromagnetic radiation emitted from the plasma generation zone can reach the outside of the housing through the radiation-permeable element, wherein the chamber is located inside the housing, wherein the first area (B1) is located on a first side of the chamber oriented toward the flange (45), and wherein the second area (B2) is located on a second side of the chamber oriented toward the radiation-permeable element (46), in particular, wherein the conductive housing element of the chamber has a truncated conical shape tapering toward the flange.

11. The vacuum pressure sensor (40) according to claim 10, wherein: An optical element (53) and a spectrometer (54) are arranged on the outside of the housing, wherein the radiation permeable element (46) and the optical element (53) cooperate to collect and focus electromagnetic radiation emitted from the area (55) around the anode to an optically sensitive element of the spectrometer, in particular, wherein the optical element (53) is adapted to compensate for axial displacements of the radiation emission area (55).

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