Vacuum assembly, electrode arrangement and device for generating a silent plasma discharge

Description

[0001] The present invention relates to a vacuum feedthrough, an electrode arrangement, and a device for generating a silent plasma discharge. Furthermore, the invention relates to a measuring device for characterizing a 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, the ionization and excitation of molecules and ions to generate plasma light, and further, the measurement and evaluation of information about the gas composition of the generated plasma. One possible type of plasma discharge is the so-called DBD plasma discharge. A DBD plasma discharge (also called silent electrical discharge or dielectric barrier discharge, abbreviated DBD) is an AC gas discharge in which at least one of the electrodes is electrically insulated from the gas space by galvanic separation using a dielectric. It is also referred to as a dielectric barrier discharge because the insulation prevents the formation of an arc discharge.

[0003] The measurement and evaluation of the light generated in a DBD plasma is fraught with numerous challenges. The lifetime and, if applicable, vacuum suitability of elements, the size and complexity of setups, and the achievable sensitivity pose major challenges.

[0004] The vacuum-tight electrical feedthrough described in WO 2021 / 052600 A1 comprises an electrically insulating insulator element with a through-opening, with a first boundary surface adjacent to the through-opening, and with a second boundary surface also adjacent to the through-opening and opposite the first boundary surface. The vacuum-tight electrical feedthrough further comprises an electrically conductive conductor element which extends through the through-opening and which is connected to the insulator element in a vacuum-tight manner along a circumferential line of the conductor element. The insulator element is permeable to electromagnetic radiation in an optical wavelength range. The first and / or second boundary surface is formed as a curved surface. The curved surface can in particular be formed as a convex or concave surface.

[0005] The object of the present invention was to mitigate at least one of the problems of the prior art. Specifically, one aim of the invention is to enable a compact sensor for pressure and / or gas composition based on a DBD plasma discharge and to provide suitable components for this purpose. This object is achieved according to the invention by a vacuum feedthrough according to claim 1. Embodiments emerge from the features of dependent claims 2 to 4.

[0006] The vacuum feedthrough includes the elements Lens element, first ring made of glass, first hollow cylinder made of a first dielectric material, first electrically conductive layer, second hollow cylinder made of glass, third hollow cylinder made of ceramic, second ring made of glass, frame made of metal, in the sequence mentioned radially from inside to outside.

[0007] The frame can, in particular, be ring-shaped. The frame can, in particular, be made of stainless steel.

[0008] There is at least one continuous radiation path for radiation from an optical wavelength range starting from a first point on a first side, through the lens element to a second point on a second side of the vacuum feedthrough.

[0009] The lens element is transparent for at least one wavelength range in the optical wavelength range and thus represents the optical part of the vacuum feedthrough. Insofar as the elements of the vacuum feedthrough are not transparent in the said wavelength range, they leave the passage along the at least one continuous radiation path unblocked. The optical wavelength range comprises electromagnetic radiation with wavelengths from 100 nm to 1 mm, i.e. in particular the ranges of visible light, UV radiation and infrared radiation. The lens element can, for example, have the shape of a plano-convex lens, with the convex side directed towards the first side of the sealing plane. The lens element can, for example, have a mushroom-head-like diameter enlargement on the first side, so that a radial overlap with the first ring occurs. In this way, radiation arriving from the first side can be bundled.For example, the lens element can be designed by the combination of lens radii and refractive index to concentrate parallel radiation paths arriving from the first side on the second side into a focal point, or at least into a focal volume.

[0010] The first side can, in particular, be provided as the vacuum side, and the second side can, in particular, be provided as the atmosphere side. In the context of the present invention, the term "vacuum feedthrough" should be understood to mean that the feedthrough is suitable for use in a situation with a significant pressure difference between the first and second sides, without any gas passing through the sealing surface to the other side. This requirement is typical for the use of a feedthrough in vacuum technology, but can also be useful in other applications where there is no pressure in the vacuum range on either side.

[0011] The vacuum feedthrough according to the invention is therefore an electrical-optical vacuum feedthrough. The first electrically conductive layer forms the electrical feedthrough, isolated from the frame. The lens element forms the optical feedthrough.

[0012] Optionally, a rod- or wire-shaped electrode can be inserted through the lens element along a central axis. This additional electrode can be enclosed by an additional glass ring. Such an additional electrode can keep the entire structure compact in case a power supply for additional elements is required.

[0013] In one embodiment of the vacuum feedthrough according to the invention, the adjacent elements (elements are the lens element and the other elements from the above list) are connected to one another in a vacuum-tight manner to form a sealing surface which separates a first side, in particular a vacuum side, and a second side, in particular an atmosphere side, of the vacuum feedthrough from one another.

[0014] The first electrically conductive layer is applied to the outer surface of the first hollow cylinder. This electrically conductive layer can be made of a metal, in particular platinum.

[0015] The first hollow cylinder and the first electrically conductive layer protrude beyond the second hollow cylinder on the atmospheric side to form an electrically conductive contact surface. At the contact surface, the first electrode can be connected, for example, to a high-voltage source, so that the first electrically conductive layer can serve as an electrode for the DBD plasma discharge. The first electrically conductive layer can have the shape of a hollow cylinder. The first electrically conductive layer can be segmented, i.e., for example, in the area in which it serves as an electrode for the DBD discharge and / or in the area of ​​the feedthrough under the glass ring, it can be formed as adjacent longitudinal strips.

[0016] The first, second and third hollow cylinders, as well as the first electrically conductive layer, protrude beyond the lens element on the first side.

[0017] The elements each form an essentially annular zone of the sealing surface. The first glass ring borders the lens element radially outwards and is connected to the lens element in a vacuum-tight manner. The first hollow cylinder borders the first ring radially outwards and is connected to it in a vacuum-tight manner, etc. In this arrangement, each layer has at least one adjacent layer of glass. The first and second glass rings, as well as the second hollow cylinder, can in particular consist of molten glass. The molten glass can in particular be a so-called solder glass, which is particularly suitable for producing a vacuum-tight connection to a metal or a ceramic. The metallic frame can be in the form of a ring. The metallic frame can, for example, have a flange which is designed to facilitate welding of the frame to other elements.The metallic frame can, for example, be made of a stainless austenitic steel, such as steel 1.4435 or steel 1.4404, which is characterized by high corrosion resistance.

[0018] The elements can each individually have the shape of a rotational body with a rotational axis. The elements can be arranged coaxially with each other with respect to their rotational axes.

[0019] On the first side, i.e., for example, the vacuum side, the electrically conductive layer can be completely enclosed between the first and second hollow cylinders. In this case, only a capacitive coupling to the electrode is possible on the vacuum side. Completely enclosing the electrically conductive layer in insulating material has the advantage of preventing the occurrence of an arc discharge.

[0020] The third hollow ceramic cylinder has the effect of suppressing electrical breakdown through the second hollow glass cylinder in the event that the glass is not sufficiently resistant to breakdown. For example, a discharge between a metal housing tube of a measuring device, which will be discussed below, is successfully prevented by the third hollow ceramic cylinder. The third hollow cylinder can, in particular, be made of an Al 2 O 3 ceramic.

[0021] In one embodiment of the vacuum feedthrough, the lens element is made of sapphire.

[0022] Sapphire has a high transmittance in the wavelength range from 200 nm to 5000 nm, making it particularly suitable for transmitting electromagnetic radiation from the optical range out of a vacuum with low loss. Its transmittance is particularly high in the ultraviolet range above 200 nm. Sapphire is also mechanically very robust.

[0023] In one embodiment of the vacuum feedthrough, the first hollow cylinder is made of sapphire.

[0024] Furthermore, the invention is directed to an electrode arrangement according to claim 5. An embodiment of the electrode arrangement results from the features of claim 6.

[0025] The electrode assembly according to the invention is an electrode assembly for generating a DBD plasma discharge. The electrode assembly comprises the vacuum feedthrough according to the invention discussed above. It further comprises a fourth hollow cylinder made of ceramic, which bears a second, electrically conductive layer on its outer surface. The second electrically conductive layer can be made, in particular, of molybdenum.

[0026] The fourth hollow cylinder is arranged on the first side (the vacuum side) of the vacuum feedthrough coaxially with the first hollow cylinder. It is located at least partially within the first hollow cylinder. The first and second electrically conductive layers partially overlap in the axial direction.

[0027] A gap with a radial extension remains open between the second electrically conductive layer and the inner surface of the first hollow cylinder.

[0028] The first and second electrically conductive layers form the two electrodes of the electrode array. During operation, a plasma discharge zone forms in the gap, in the axial direction in the area where the two electrodes overlap.

[0029] The fourth hollow cylinder acts as a sputter shield, increasing the service life of the electrode assembly. The fourth hollow cylinder can be made of an Al 2 O 3 ceramic, for example. Another measure that provides sputter shielding is the dimension selection of the feedthrough. A large distance between the lens element and the plasma discharge region reduces the sputter effect on the lens element.

[0030] In particular, a large distance in relation to the diameter of the lens element is effective for this purpose.

[0031] In one embodiment of the electrode arrangement, the radial extent of the gap is less than 1 mm. The radial extent of the gap can, in particular, be between 0.05 mm and 0.5 mm. The inventors have recognized that with this gap extension, the DBD plasma discharge can be ignited with a high-frequency voltage in the kilovolt range (1-10 kV, 1-10 kHz) over a wide pressure range. Operation in a pressure range of approximately 0.047-199.98 kPa (0.35-1500 Torr) is possible.

[0032] Furthermore, the invention relates to a device according to claim 7.

[0033] The device according to the invention is a device for generating a DBD plasma discharge. The device comprises the electrode arrangement according to the invention discussed above. The gap between the second electrically conductive layer and the inner surface of the first hollow cylinder is in fluid-dynamic communication with the interior of the vacuum chamber.

[0034] The first electrically conductive layer is electrically conductively connected to an AC high-voltage source at the electrically conductive contact surface and the second electrically conductive layer is electrically conductively connected to ground.

[0035] The electrode assembly can, for example, be installed in a metallic wall of a vacuum chamber, with the frame being welded to the wall of the vacuum chamber at its periphery in a vacuum-tight manner. Due to the wide pressure range in which a DBD discharge is possible with the device according to the invention, the device can also be operated at ambient pressure, for example, i.e., without a chamber that fluid-dynamically separates the first from the second side.

[0036] The invention is further directed to a measuring device according to claim 8.

[0037] The measuring device according to the invention is a measuring device for characterizing a pressure and / or a gas composition. The measuring device comprises the above-discussed device according to the invention for generating a DBD plasma discharge. Additionally, an optical sensor is arranged on the atmosphere side of the lens element.

[0038] The optical sensor is sensitive to the wavelength range that can be transmitted through the lens element. The optical sensor can be a simple radiation sensor, such as a light sensor, or it can be a more complex optical sensor, such as a spectrometer. A photodiode with a wavelength-selective filter, for example, can serve as an optical sensor.

[0039] The measuring device according to the invention is suitable, for example, for characterizing a pressure and / or gas composition within a vacuum chamber. The optimal use of the invention is in the pressure range of 0.35–1500 Torr (-2000 mbar), i.e., also in the pressure range at and above atmospheric pressure, and is therefore broadly applicable. The specific choice of materials used can be specifically adapted to vacuum requirements according to the aforementioned embodiments. In particular, the use of sapphire as a dielectric, platinum and molybdenum as electrode material, and stainless steel for the frame contribute to the vacuum suitability of the measuring device. Furthermore, the aforementioned materials are compatible with the typical requirements of a vacuum processing system in the semiconductor industry.

[0040] The invention is further directed to a method according to claim 9. This is a method for operating a measuring device according to the invention. In the method according to the invention, an alternating voltage with a voltage amplitude of 1 to 10 kilovolts and a frequency in the range 1 to 10 kilohertz is applied between the first electrically conductive layer and the second electrically conductive layer. For example, the voltage curve can change from -5 kV to +5 kV and back again over one period of the alternating voltage, i.e. a voltage of 10 kVpp can be applied. The voltage curve can, for example, correspond to a sine wave. A rectangular voltage is also possible. It is advantageous to vary the voltage from positive to negative relative to ground potential. In this way, a significantly more stable plasma is obtained than, for example, by varying between 0 and positive voltage or between 0 and negative voltage.

[0041] Applying the voltage ignites a plasma in the gap between the second electrically conductive layer and the dielectric, in the area of ​​axial overlap between the two electrically conductive layers. This plasma has a short lifetime due to the charge accumulation on the dielectric. By changing the sign of the applied alternating voltage, the accumulated charge carriers are moved away from the dielectric, thus maintaining a continuously glowing plasma. The radiation emitted by the plasma is detected by the optical sensor.

[0042] Embodiments of the present invention are explained in more detail below with reference to figures. Fig. 1schematically and partly in cross section a vacuum feedthrough according to the invention in connection with an embodiment of the electrode arrangement, an embodiment of the device and an embodiment of the measuring device; Fig. 2 a cross-section through the vacuum feedthrough according to the invention along the sealing surface; Fig. 3 a cross-section through an embodiment of the vacuum feedthrough along the sealing surface; Fig. 4 a cross-section through another embodiment of the vacuum feedthrough along the sealing surface.

[0043] In Figure 1 The central element of the invention, namely the vacuum feedthrough, is shown in a longitudinal section. The electro-optical vacuum feedthrough 10, constructed in radial layers, comprises a centrally arranged lens element 11 and the following additional elements arranged around the lens element, listed in the radial direction from the inside to the outside: a first ring 12 made of glass, 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 ring 16 made of glass, a frame 17 made of metal.

[0044] Furthermore, a first electrically conductive layer 18 is applied to the outer surface of the first hollow cylinder, which layer can in particular be made of platinum.

[0045] A sealing surface 1 separates a first side 2, in this case the vacuum side, which lies inside the vacuum chamber 31, from a second side 3, which in this case is the atmosphere side. In the longitudinal section shown, the sealing surface 1 is cut along a line represented as a dashed line. An optical sensor 41 and a high-voltage source 32 are housed on the atmosphere side of a vacuum chamber 31. A fourth hollow cylinder 21 and the second electrically conductive layer 22 applied to its outer surface complement the vacuum feedthrough to form an electrode arrangement 20. In the embodiment shown, the elements of the electrode arrangement all have the shape of rotational bodies with the common axis of rotation 4 (dash-dotted line).

[0046] A first electrically conductive layer 18 is connected to the high-voltage source 32 at a contact surface 19. The second electrically conductive layer is connected to ground, so that the first and second electrically conductive layers form the two electrodes of the electrode arrangement. The two electrodes overlap in an axial overlap region 23. In this overlap region and radially between the second electrically conductive layer 22 and the hollow cylinder 13, which can in particular be made of sapphire, a discharge region 25 forms during operation (shown in dotted lines). Electromagnetic radiation, e.g. from the visible range, the UV range or the IR range, is emitted from this discharge region. This radiation can in particular be radiated in the direction of the lens element (shown by wavy arrows).It is this radiation which passes through the lens element 11 to the optical sensor 41, where it is detected.

[0047] The first 18 and second 22 electrically conductive layers can overlap by, for example, 2-3 mm in the axial direction. The fourth hollow cylinder 21 can, for example, protrude approximately 5 mm beyond the second electrically conductive layer 22 in the direction of the lens element. The shortest distance from the second electrical layer 22 to the lens element 11 can, for example, be approximately 10 mm. These dimensions correspond to a discharge region with a radial extent of 0.05 to 0.5 mm, according to an embodiment described above. With these spacing ratios, the sputter protection effect mentioned above is created. In this arrangement, particles knocked out of the electrode material by the discharge will, with a high probability, adhere to the protruding ceramic surface of the fourth hollow cylinder and thus not contaminate the lens element.Radiation from the discharge region 25 can reach the lens element approximately parallel to the axial direction, even if the fourth hollow cylinder itself is not transparent to the radiation or is already contaminated by electrode material.

[0048] Shown is an embodiment of the measuring device or device in which the electrode arrangement is installed in a metallic wall of a vacuum chamber 31, the frame being welded vacuum-tight to the wall of the vacuum chamber at its periphery.

[0049] In particular, the vacuum chamber 31 and the wall, as well as the high-voltage source 32 and the optical sensor 41, are shown very schematically and their dimensions are not adapted to the dimensions of the electrode arrangement. In particular, the vacuum chamber can be many times larger than shown in relation to the vacuum feedthrough. Also shown schematically and incompletely is the end of the fourth hollow cylinder and the second electrically conductive layer further away from the lens element. The axial ends of these two elements are shown offset from one another so that the two layers are clearly visible. However, the two elements can extend further in the axial direction than shown and the second electrically conductive layer can rest on the fourth hollow cylinder, in particular over its entire length. A mechanical fastening device (not shown) holds the fourth hollow cylinder in its position.

[0050] In Figure 2A cross-section through the vacuum feedthrough 10 is shown. In a preferred embodiment, the sequence of materials from inside to outside is: sapphire (vertically hatched), glass (diagonally cross-hatched), sapphire, platinum (black), glass, ceramic (horizontally hatched), glass, metal (diagonally hatched). The first electrically conductive layer 18 is electrically insulated from the metallic frame 17. The elements of the shell-shaped feedthrough are each connected to the adjacent elements in a vacuum-tight manner.

[0051] In Figure 3A cross-section through an embodiment of the vacuum feedthrough 10 is shown, which has an additional central electrode 26 extending through the lens element. The additional electrode is glazed into the lens element by means of an additional ring 27. The additional electrode can be rod-shaped or wire-shaped and can protrude beyond the feedthrough on both sides, ie, the vacuum side and the atmosphere side.

[0052] In Figure 4A cross section through an embodiment of the vacuum feedthrough 10 is shown, which has further electrodes 28, 29 arranged radially in the region of the second ring 16 made of glass. Two further electrodes are shown here as an example, but a plurality of such electrodes in the form of azimuthally spaced strips with a longitudinal direction parallel to the axis of the hollow cylinders can be arranged on this radius. One of these further electrodes can, for example, be the central electrode 26 from the embodiment according to Fig. 3 In a further embodiment, the central electrode can be made of Fig. 3 also with further electrodes arranged radially further outwards according to Fig. 4The further electrodes 28, 29 can, for example, be applied as thin metallizations to the hollow cylinder 15 made of ceramic and can be vacuum-tightly encased by the second ring 16 made of glass on the side facing away from the ceramic cylinder. Various metals can be used as materials for the further electrodes, in particular platinum, molybdenum and titanium. Via the further electrodes, for example, further plasma chambers and / or sensors on the vacuum side can be electrically contacted, for example a cold cathode vacuum manometer or a Pirani pressure sensor. In order to enable electrical contact to such further electrodes on the outside, for example and deviating from the illustration in Fig. 1, the ceramic cylinder 15 also protrudes beyond the ring 16 on the side of the vacuum feedthrough facing away from the vacuum side, thus forming a support surface for the additional electrodes on this side as well and enabling electrical contact on the radially outer side. Such additional electrodes can, for example, be covered over their entire length with an insulating layer. This has the advantage that, in electron / ion optics, often undesirable exposed potentials that could influence charged particles are avoided. For this purpose, for example, a glass ring lying over the electrodes can be extended further axially, or individual conductor tracks can be implemented with a thin glass layer that overlaps the respective conductor track.

[0053] In summary, the present invention enables pressure measurement or gas analysis in the range 0.047 - 199.98 kPa (0.35 - 1500 Torr), i.e., up to the overpressure range, for example, using a cylindrical sapphire high-voltage feedthrough with an integrated lens system. A DBD plasma can be ignited by applying an alternating voltage in the range 1-10 kilovolts and a frequency in the range 1-10 kilohertz. The invention enables a small, energy-efficient, and flexible gas analyzer with high sensitivity and for a wide variety of applications. List of reference symbols

[0054] 1 Sealing surface 2 First side (vacuum side) 3 Second side (atmosphere side) 4 Common axis 10 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 electrically conductive layer 19 Contact surface 20 Electrode arrangement 21 Fourth hollow cylinder (ceramic) 22 Second electrically conductive layer 23 Axial overlap area 24 Gap 25 Discharge zone in the gap 26 Additional (central) electrode 27 Additional ring (glass) 28, 29 Additional electrodes 30 Device 31 Vacuum chamber 32 AC high-voltage source 40 Measuring device 41 Optical sensor

Claims

1. Vacuum feedthrough (10) comprising the elements - lens element (11), - first ring (12) made of glass, - first hollow cylinder (13) made of a first dielectric material, - first electrically conductive layer (18), - second hollow cylinder (14) made of glass, - third hollow cylinder (15) made of ceramic, - second ring of glass (16), - frame (17) made of metal, in the above sequence radially from inside to outside, wherein at least one continuous radiation path exists for radiation from an optical wavelength range starting from a first point on a first side (2) of the vacuum feedthrough, through the lens element to a second point on a second side (3) of the vacuum feedthrough.

2. Vacuum feedthrough (10) according to claim 1, wherein adjoining elements (11, 12, 13, 14, 15, 16, 17) are connected to one another in a vacuum-tight manner to form a sealing surface (1) which separates the first side (2) and the second side (3) of the vacuum feedthrough from one another, wherein a first electrically conductive layer (18), in particular of platinum, is applied to the outer surface of the first hollow cylinder, wherein the first hollow cylinder and the first electrically conductive layer on the second side protrude beyond the second hollow cylinder to form an electrically conductive contact surface (19), wherein the first, second and third hollow cylinders and the first electrically conductive layer on the first side protrude beyond the lens element.

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

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

5. Electrode assembly (20) for generating a DBD plasma discharge, wherein the electrode assembly comprises the vacuum feedthrough (10) according to one of claims 1 to 4, and further comprises a fourth hollow cylinder (21) made of ceramic which carries on its outer surface a second electrically conductive layer (22), in particular of molybdenum, wherein the fourth hollow cylinder (21) is arranged on the first side (2) of the vacuum feedthrough coaxially with the first hollow cylinder (13) and lies at least partially inside the first hollow cylinder, wherein the first and the second electrically conductive layer partially overlap in the axial direction, and wherein a gap (24) with a radial extension remains open between the second electrically conductive layer and the inner surface of the first hollow cylinder.

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

7. Device (30) for generating a DBD plasma discharge, wherein the device comprises the electrode assembly (20) according to one of claims 5 or 6, wherein the gap between the second electrically conductive layer and the inner surface of the first hollow cylinder is in fluid dynamic communication with the interior of the vacuum chamber, wherein the first electrically conductive layer is electrically conductively connected to an AC high voltage source (32) at the electrically conductive contact surface, and wherein the second electrically conductive layer is electrically conductively connected to ground.

8. Measuring device (40) for characterizing a pressure and / or a gas composition, wherein the measuring device comprises the device according to claim 7 and wherein an optical sensor (41) is arranged on the atmosphere side (3) of the lens element (11).

9. Method for operating a measuring device (40) according to claim 8, wherein an AC voltage having a voltage amplitude of 1 to 10 kilovolts and a frequency in the range of 1 to 10 kilohertz is applied between the first electrically conductive layer (18) and the second electrically conductive layer (22).