Vacuum feedthrough, electrode assembly, and apparatus for generating silent plasma discharge

Abstract

The radially stacked vacuum feedthrough (10) includes the following elements (from inside to outside): a lens element (11), a first ring of glass (12), a first hollow cylinder of a first dielectric material (13), a first conductive layer (18), a second hollow cylinder of glass (14), a third hollow cylinder of ceramic (15), a second ring of glass (16), and a metal frame (17). The invention also relates to an electrode assembly based on the vacuum feedthrough, an apparatus for generating a DBD plasma discharge, a measurement apparatus for characterizing pressure and / or gas composition, and a method for operating the measurement apparatus.

Description

Technical Field

[0001] The present invention relates to a vacuum feedthrough, an electrode assembly, and an apparatus for generating a silent plasma discharge. The present invention also relates to a measuring device for characterizing pressure and / or gas composition, and a method for operating the measuring device.

[0002] The present invention belongs to the technical field of plasma generation, generation of plasma light by ionization and excitation of molecules and ions, and measurement and evaluation of information on the gas composition of the generated plasma. One possible type of plasma discharge is the so-called DBD plasma discharge. (Also called silent discharge or dielectric barrier discharge (DBD)) The DBD plasma discharge is an alternating current gas discharge in which at least one electrode is electrically insulated from the gas space by galvanic separation using a dielectric. Since the insulator prevents the occurrence of arc discharge, the DBD plasma discharge is also called a dielectric suppressed discharge.

[0003] Measurement and evaluation of light generated by DBD plasma involve many difficulties. The lifetime of the element, in some cases vacuum suitability, the size and complexity of the device, and the achievable sensitivity are major issues.

[0004] An object of the present invention was to solve at least one problem of the prior art. That is, one object of the present invention is to enable a small sensor for measuring pressure and / or gas composition based on DBD plasma discharge and to provide components suitable for this purpose.

[0005] According to the present invention, this object is solved by the vacuum feedthrough according to claim 1. Embodiments result from the features of dependent claims 2 to 4.

[0006] The vacuum feedthrough comprises the following elements, arranged radially from the inside outwards in the following order: a lens element, a first glass ring, a first hollow cylinder made of a first dielectric material, a first conductive layer, a second glass hollow cylinder, a third ceramic hollow cylinder, a second glass ring, and a metal frame. The frame may be particularly annular. The frame can be made of stainless steel in particular.

[0007] There is at least one continuous radiation path for radiation from the optical wavelength range, starting from a first point on the first side of the vacuum feedthrough and passing through the lens element to a second point on the second side of the vacuum feedthrough.

[0008] The lens element is transparent to at least one wavelength range within the optical wavelength range and thus constitutes the optical portion of the vacuum feedthrough. The elements of the vacuum feedthrough are not obstructed when traveling along the path along at least one continuous radiation path, unless they are transparent in the aforementioned wavelength range. The optical wavelength range includes electromagnetic radiation having wavelengths from 100 nm to 1 mm, particularly visible light, ultraviolet, and infrared. The lens element may, for example, have the shape of a plano-convex lens, with the convex surface facing the first side of the sealing surface. The lens element may have, for example, a truss-head-shaped diameter-enlarging portion on the first side such that it radially overlaps with the first ring. In this way, radiation from the first side can be focused. For example, the lens element may be designed, by a combination of lens radius and refractive index, to focus parallel radiation from the first side to the second side focal point or at least the focal volume.

[0009] In particular, the first side may be provided as the vacuum side, and the second side may be provided as the atmospheric side. In the context of this invention, the term vacuum feedthrough should be understood to mean that feedthrough is suitable for use in situations where there is a substantial pressure difference between the first and second sides, and gas cannot pass through the sealing surface to the other side. This requirement is typical of the use of feedthrough in vacuum technology, but is also useful for other applications where vacuum-range pressure is not present on either side.

[0010] Therefore, the vacuum feedthrough of the present invention is an electro-optical vacuum feedthrough. A first conductive layer, insulated from the frame, forms an electrical feedthrough. A lens element forms an optical feedthrough.

[0011] If necessary, additional rod-shaped or wire-shaped electrodes can be passed through the lens element along its central axis. These additional electrodes can be fitted using a further glass ring. When power supply to additional elements is required, these additional electrodes allow the overall structure to remain compact.

[0012] In one embodiment of the vacuum feedthrough of the present invention, adjacent elements (lens elements and further elements from the above list) are vacuum-tightly connected to each other so as to form a sealing surface that separates the first side of the vacuum feedthrough, particularly the vacuum side, from the second side, particularly the atmospheric side.

[0013] The first conductive layer is applied to the outer surface of the first hollow cylinder. This conductive layer can be made of a metal, particularly platinum.

[0014] The first hollow cylinder and the first conductive layer protrude beyond the second hollow cylinder on the atmospheric side to form a conductive contact surface. The first electrode may be connected at the contact surface, for example, to a high-voltage source, so that the first conductive layer functions as an electrode for a DBD plasma discharge. The first conductive layer may have the shape of a hollow cylinder. The first conductive layer can be segmented; that is, the first conductive layer may be formed as adjacent longitudinal strips in the region that functions as an electrode for a DBD discharge and / or in the feedthrough region below the glass ring.

[0015] The first hollow cylinder, the second hollow cylinder, the third hollow cylinder, and the first conductive layer extend beyond the lens element on the first side.

[0016] Each element forms a substantially annular zone of the sealing surface. A first glass ring is adjacent to the lens element on its radially outer side and is vacuum-sealed to the lens element. A first hollow cylinder is adjacent to the first ring on its radially outer side and is vacuum-sealed. In this configuration, each layer is adjacent to at least one glass layer. The first glass ring, the second glass ring, and the second hollow cylinder can be made of molten glass in particular. In particular, the molten glass may be so-called solder glass, which is especially suitable for vacuum-sealed connections with metals or ceramics. The metal frame may be ring-shaped. The metal frame may have flanges designed to facilitate welding the frame to further elements, for example. The metal frame can be made of stainless austenitic steel, for example, steel 1.4435 or steel 1.4404, which are characterized by high corrosion resistance.

[0017] Each element may have the shape of a body of revolution with an axis of rotation. These elements can be arranged coaxially with respect to the axis of rotation.

[0018] On the first side, for example, the vacuum side, the conductive layer can be completely sealed between the first hollow cylinder and the second hollow cylinder. In this case, only capacitive coupling with the electrodes is possible on the vacuum side. Completely sealing the conductive layer in the insulating material has the advantage of preventing the occurrence of arc discharge.

[0019] The third hollow cylinder made of ceramic has the effect of suppressing dielectric breakdown through the second hollow cylinder made of glass when the second hollow cylinder made of glass does not have sufficient dielectric breakdown resistance. For example, discharge between the metal housing tubes of the measuring device described later is well prevented by the third hollow cylinder made of ceramic. In particular, the third hollow cylinder may be made of Al2O3 ceramic.

[0020] In one embodiment of a vacuum feedthrough, the lens element is made of sapphire. Sapphire has high transmittance in the wavelength range of 200 nm to 5000 nm, exhibits almost no loss from the vacuum region, and is particularly suitable for guiding electromagnetic waves outside the optical range. It exhibits especially high transmittance in the ultraviolet region above 200 nm. Furthermore, sapphire is mechanically very robust.

[0021] In one embodiment of the vacuum feedthrough, the first hollow cylinder is made of sapphire. The present invention further relates to the electrode assembly described in claim 5. Embodiments of the electrode assembly arise from the features of claim 6.

[0022] The electrode assembly of the present invention is an electrode assembly for generating DBD plasma discharge. The electrode assembly includes the vacuum feedthrough of the present invention as described above. The electrode assembly further comprises a fourth hollow cylinder made of ceramic, on which a second conductive layer is supported on its outer surface. The second conductive layer may be made of molybdenum in particular.

[0023] The fourth hollow cylinder is arranged on the first side (vacuum side) of the vacuum feedthrough so as to be coaxial with the first hollow cylinder. The fourth hollow cylinder is at least partially located within the first hollow cylinder. The first conductive layer and the second conductive layer partially overlap along the axial direction.

[0024] A gap having a radial extension is open between the second conductive layer and the inner surface of the first hollow cylinder.

[0025] The first conductive layer and the second conductive layer form two electrodes of the electrode assembly. During operation, a plasma discharge zone is formed within the gap, that is, within the axial region where the two electrodes overlap.

[0026] The fourth hollow cylinder has a sputtering protection effect. The fourth hollow cylinder extends the life of the electrode assembly. The fourth hollow cylinder can be made of, for example, Al2O3 ceramic. Another means to achieve the sputtering protection effect is the selection of the dimensions of the feedthrough. When the distance between the lens element and the plasma discharge region increases, the sputtering effect on the lens element decreases. In particular, a large distance relative to the diameter of the lens element is effective for this purpose.

[0027] In one embodiment of the electrode assembly, the radial extension of the gap is less than 1 mm. In particular, the radial extension of the gap may be 0.05 mm to 0.5 mm. The inventors have recognized that with this extension of the gap, DBD plasma discharge can be ignited with a high-frequency voltage (1 - 10 kV, 1 - 10 kHz) in the kilovolt range over a wide pressure range. It can operate in a pressure range of about 0.35 - 1500 torr.

[0028] Furthermore, the present invention relates to the device according to claim 7. [[ID=2l]] The device of the present invention is a device for generating DBD plasma discharge. The device includes the electrode assembly of the present invention described above.The gap between the second conductive layer and the inner surface of the first hollow cylinder is in hydrodynamic communication with the interior of the vacuum chamber.

[0029] The first conductive layer is conductively connected to a high-voltage AC power source at the conductive contact surface, and the second conductive layer is conductively connected to the ground.

[0030] The electrode assembly can be attached, for example, to the metal wall of a vacuum chamber, and the peripheral portion of the frame is welded to the wall of the vacuum chamber in a vacuum-tight manner. Since the device of the present invention has a large pressure range in which DBD discharge can be performed, the device can also operate, for example, at ambient pressure, i.e., without a chamber that hydraulically separates the first side from the second side.

[0031] Furthermore, the present invention relates to the measuring device according to claim 8. The measuring device of the present invention is a measuring device for characterizing pressure and / or gas composition. The measuring device includes the device of the present invention for generating the DBD plasma discharge described above. Also, an optical sensor is disposed on the atmosphere side of the lens element.

[0032] The optical sensor functions in a wavelength range that can pass through the lens element. The optical sensor may be a simple radiation sensor, such as an optical sensor, or may be a more complex optical sensor, such as a spectrometer. For example, a photodiode equipped with a wavelength selection filter can function as an optical sensor.

[0033] The measuring device of the present invention is suitable for characterizing, for example, the pressure and / or gas composition in a vacuum chamber. The present invention is optimally used in a pressure range of 0.35 to 1500 Torr (~2000 mbar) and can also be used in a pressure range above atmospheric pressure, so it is widely applicable. The specific selection of the materials used can be specifically adapted to the vacuum requirements according to the above embodiments. In particular, using sapphire as the dielectric, using platinum and molybdenum as the electrode materials, and using stainless steel as the frame contribute to the vacuum compatibility of the measuring device. Furthermore, the materials mentioned are compatible with the typical requirements of a vacuum process plant in the semiconductor industry.

[0034] Furthermore, the present invention relates to the method according to claim 9. This relates to a method for operating the measuring device of the present invention. In the method of the present invention, an AC voltage having a voltage amplitude of 1 to 10 kV and a frequency of 1 to 10 kH is applied between a first conductive layer and a second conductive layer. The voltage waveform may, for example, change from -5 kV to +5 kV over one period of the AC voltage, and then repeat. That is, a voltage of 10 kV pp may be applied. For example, the voltage waveform may be a sine wave. A square wave voltage is also possible. It is advantageous to change the voltage from positive to negative with respect to the ground potential. In this way, a much more stable plasma can be obtained than, for example, changing the voltage between 0 and positive or between 0 and negative.

[0035] When a voltage is applied, plasma is ignited in the gap between the second conductive layer and the dielectric in the region where the two conductive layers overlap axially; however, the lifetime of this plasma is short due to the accumulation of charge on the dielectric. By changing the sign of the applied AC voltage, the accumulated charge carriers move away from the dielectric again, and as a result, a continuously appearing plasma can be maintained. The radiation emitted by the plasma is detected by an optical sensor.

[0036] Illustrative embodiments of the present invention will be described in further detail below with reference to the drawings. [Brief explanation of the drawing]

[0037] [Figure 1] This is a schematic and partial cross-sectional view illustrating the vacuum feedthrough of the present invention in relation to one embodiment of an electrode assembly, one embodiment of a device, and one embodiment of a measuring device. [Figure 2] This is a cross-sectional view showing the vacuum feedthrough of the present invention along the sealing surface. [Figure 3] This is a cross-sectional view showing one embodiment of vacuum feedthrough along the sealing surface. [Figure 4] This is a cross-sectional view showing another embodiment of vacuum feedthrough along the sealing surface. [Modes for carrying out the invention]

[0038] Figure 1 is a longitudinal section showing the central element of the present invention, i.e., the vacuum feedthrough. The radially stacked electro-optic vacuum feedthrough 10 comprises a centrally located lens element 11, and the following further elements arranged around the lens element and listed radially from inside to outside: a first glass ring 12, a first hollow cylinder 13 made of a first dielectric material, a second hollow cylinder 14 made of glass, a third hollow cylinder 15 made of ceramic, a second glass ring 16, and a metal frame 17.

[0039] Furthermore, a first conductive layer 18, which may be made of platinum in particular, is applied to the outer surface of the first hollow cylinder.

[0040] The sealing surface 1 separates the first side 2, in this case the vacuum side, located inside the vacuum chamber 31, from the second side 3, in this case the atmospheric side. In the illustrated longitudinal section, the sealing surface 1 traverses along the dashed line. An optical sensor 41 and a high-voltage source 32 are located on the atmospheric side of the vacuum chamber 31. The fourth hollow cylinder 21 and the second conductive layer 22 attached to its outer surface complete the vacuum feedthrough and form the electrode assembly 20. In the illustrated embodiment, all elements of the electrode assembly have the form of a rotating body with a common axis of rotation 4 (dashed line).

[0041] The first conductive layer 18 is connected to the high-voltage source 32 at a contact surface 19. The second conductive layer is connected to ground. The first and second conductive layers form two electrodes of the electrode assembly. The two electrodes overlap in an axial overlapping region 23. In this overlapping region, a discharge region 25 (indicated by a dotted line) is formed radially between the second conductive layer 22 and the hollow cylinder 13, which may be made of sapphire in particular, during operation. Electromagnetic radiation in the visible, ultraviolet, or infrared regions is emitted from this discharge region. In particular, this radiation is emitted in the direction of the lens element (indicated by a dashed arrow). This radiation passes through the lens element 11 to the optical sensor 41, where it is detected.

[0042] The first conductive layer 18 and the second conductive layer 22 may overlap by, for example, 2 to 3 mm along the axial direction. The fourth hollow cylinder 21 may protrude, for example, about 5 mm beyond the second conductive layer 22 toward the lens element. The shortest distance from the second conductive layer 22 to the lens element 11 may be, for example, about 10 mm. According to the embodiments described above, these dimensions are suitable for a discharge region having a radial extension of 0.05 to 0.5 mm. The above-described spacing ratio produces the sputter protection effect described above. In this assembly, particles knocked out from the electrode material by the discharge adhere to the protruding ceramic surface of the fourth hollow cylinder with a high probability and therefore do not contaminate the lens element. Radiation from the discharge region 25 can reach the lens element substantially parallel to the axial direction even if the fourth hollow cylinder itself is not transparent to radiation or is already contaminated by the electrode material.

[0043] In the illustrated measuring apparatus or one embodiment of the apparatus, the electrode assembly is mounted on the metal wall of the vacuum chamber 31, and the periphery of the frame is vacuum-sealed and welded to the wall of the vacuum chamber.

[0044] In particular, the vacuum chamber 31 and its walls, as well as the high-voltage source 32 and optical sensor 41, are shown very schematically and do not conform to the dimensions of the electrode assembly. Specifically, the vacuum chamber can be many times larger than shown relative to the vacuum feedthrough. Also, the ends of the fourth hollow cylinder and the second conductive layer, further away from the lens element, are shown schematically and incompletely. The axial ends of these two elements are shown offset from each other so that the two layers are clearly visible. However, the two elements may extend further axially than shown, and the second conductive layer may, in particular, be located on the fourth hollow cylinder along its entire length. A mechanical fixing device (not shown) holds the fourth hollow cylinder in place.

[0045] Figure 2 shows a cross-sectional view of the vacuum feedthrough 10. In a preferred embodiment, the order of materials from inside to outside is sapphire (vertical cross-hatching), glass (diagonal cross-hatching), sapphire, platinum (black), glass, ceramic (horizontal cross-hatching), glass, and metal (diagonal cross-hatching). The first conductive layer 18 is electrically insulated from the metal frame 17. Each element of the shell-structured feedthrough is vacuum-tightly connected to adjacent elements.

[0046] Figure 3 shows a cross-sectional view of one embodiment of a vacuum feedthrough 10 having an additional central electrode 26 that penetrates the lens element. The additional electrode is fitted into the lens element by an additional ring 27. The additional electrode may be rod-shaped or wire-shaped and may protrude beyond the feedthrough on both sides, i.e., the vacuum side and the atmospheric side.

[0047] Figure 4 shows a cross-sectional view of one embodiment of a vacuum feedthrough 10 having additional electrodes 28, 29 radially arranged in the region of a second glass ring 16. Exemplarily, two additional electrodes are shown in the figure, but multiple such electrodes may be arranged in the form of strips spaced azimuthally apart along the longitudinal direction parallel to the axis of the hollow cylinder of this radius. For example, one of these additional electrodes can replace the central electrode 26 in the exemplary embodiment shown in Figure 3. In a further embodiment, the central electrode in Figure 3 may be combined with additional electrodes further spaced radially apart, as shown in Figure 4. The additional electrodes 28, 29 may, for example, be applied to the hollow ceramic cylinder 15 as a thin metallization and may be vacuum-sealed by the second glass ring 16 on the side facing away from the ceramic cylinder. Various metals, particularly platinum, molybdenum, and titanium, can be used as the material for the additional electrodes. Through the additional electrodes, for example, an additional plasma chamber and / or sensor can be electrically contacted with, for example, a cold cathode vacuum pressure gauge or Pirani pressure sensor on the vacuum side. To enable electrical contact to such additional electrodes on the outside, the ceramic cylinder 15 can, for example, protrude beyond the ring 16 on the side away from the vacuum side of the vacuum feedthrough, unlike in the illustration in Figure 1, and thus form a contact surface for additional electrodes on this side as well, enabling radially outward electrical contact. Such additional electrodes can, for example, be covered with an insulating layer along their entire length. This has the advantage of avoiding undesirable open-circuit potentials that could affect charged particles in the electron / ion optical system. For this purpose, for example, the glass ring positioned on the electrodes can be further extended axially, or individual conductor tracks can be realized with thin glass layers overlapping each conductor track.

[0048] In summary, the present invention enables pressure measurement or gas analysis in the range of 0.35 Torre to 1500 Torre, i.e., the overpressure range, using, for example, a cylindrical sapphire high-voltage feedthrough with an integrated lens system. The DBD plasma can be ignited by applying an AC voltage in the range of 1 to 10 kV at a frequency in the range of 1 to 10 kHz. The present invention provides a highly sensitive, compact, energy-efficient, and flexible gas analyzer for use in a wide variety of applications.

[0049] List of reference symbols 1 Sealing surface, 2 First side (vacuum side), 3 Second side (atmospheric side), 4 Common axis, 5 Vacuum feedthrough, 11 Lens element, 12 First ring (glass), 13 First hollow cylinder (first dielectric material), 14 Second hollow cylinder (glass), 15 Third hollow cylinder (ceramic), 16 Second ring (glass), 17 Frame (metal), 18 First conductive layer, 19 Contact surface, 20 Electrode assembly, 21 Fourth hollow cylinder (ceramic), 22 Second conductive layer, 23 Axial overlap region, 24 Gap, 25 Discharge zone within the gap, 26 Additional (center) electrode, 27 Additional ring (glass), 28, 29 Other electrodes, 30 Apparatus, 31 Vacuum chamber, 32 High voltage AC power supply, 40 Measuring device, 41 Optical sensor.

Claims

1. A vacuum feedthrough (10) for an electrode assembly (20) for generating a DBD plasma discharge, wherein the following order is applied from the radial inside out: Lens element (11) and A first ring (12) made of glass, A first hollow cylinder (13) made of a first dielectric material, A first conductive layer (18) and A second hollow cylinder (14) made of glass, A third hollow cylinder (15) made of ceramic, A second glass ring (16), It comprises a metal frame (17), A vacuum feedthrough (10) having at least one continuous radiation path for radiation from an optical wavelength range, starting from a first point on the first side (2) of the vacuum feedthrough, passing through the lens element, to a second point on the second side (3) of the vacuum feedthrough.

2. Adjacent elements (11, 12, 13, 14, 15, 16, 17) are vacuum-tightly connected to each other to form a sealing surface (1) for separating the first side (2) and the second side (3) of the vacuum feedthrough from each other. In particular, the first conductive layer (18) made of platinum is applied to the outer surface of the first hollow cylinder. The first hollow cylinder and the first conductive layer protrude beyond the second hollow cylinder on the second side to form a conductive contact surface (19). The vacuum feedthrough (10) according to claim 1, wherein the first hollow cylinder, the second hollow cylinder, the third hollow cylinder, and the first conductive layer protrude beyond the lens element on the first side.

3. The vacuum feedthrough (10) according to claim 1 or 2, wherein the lens element (11) is made of sapphire.

4. The vacuum feedthrough (10) according to any one of claims 1 to 3, wherein the first hollow cylinder (13) is made of sapphire.

5. An electrode assembly (20) for generating DBD plasma discharge, The electrode assembly comprises the vacuum feedthrough (10) according to any one of claims 1 to 4, and further comprises a fourth hollow ceramic cylinder (21) on its outer surface bearing a second conductive layer (22) particularly made of molybdenum, The fourth hollow cylinder (21) is positioned on the first side (2) of the vacuum feedthrough so as to be coaxial with the first hollow cylinder (13), and is at least partially located within the first hollow cylinder. The first conductive layer and the second conductive layer partially overlap along the axial direction. An electrode assembly (20) having a radially extending gap (24) open between the second conductive layer and the inner surface of the first hollow cylinder.

6. The electrode assembly (20) according to claim 5, wherein the radial extension of the gap (24) is less than 1 mm, and in particular, the radial extension of the gap is 0.05 mm to 0.5 mm.

7. A device (30) for generating DBD plasma discharge, The apparatus comprises the electrode assembly (20) according to any one of claims 5 or 6, The gap between the second conductive layer and the inner surface of the first hollow cylinder is hydrodynamically connected to the inside of the vacuum chamber. The first hollow cylinder and the first conductive layer protrude beyond the second hollow cylinder on the second side to form a conductive contact surface (19). The first conductive layer is electrically connected to the high-voltage AC power supply (32) at the conductive contact surface. The apparatus wherein the second conductive layer is electrically connected to earth.

8. A measuring device (40) for characterizing pressure and / or gas composition, The measuring device comprises the device described in claim 7, A measuring device in which an optical sensor (41) is positioned on the atmospheric side (3) of the lens element (11).

9. A method for operating the measuring device (40) according to claim 8, wherein an alternating voltage having a voltage amplitude of 1 to 10 kV and a frequency of 1 to 10 kHz is applied between the first conductive layer (18) and the second conductive layer (22).

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