EP3021351A1 - Secondary electron multiplier and method for producing same - Google Patents

Abstract

The present invention relates to a secondary electron multiplier (10) having an electrically insulating substrate (12, 12 ') on which a plurality of discrete dynodes (14) and optionally at least one focusing electrode (18) and optionally a detector (16) are arranged, wherein a line structure is also provided for applying defined different electrical potentials to the dynodes (14), and wherein at least one volume spatially positioned between the dynodes (14) and optionally a volume between at least one dynode (14) and the at least one focusing electrode (18 ) positioned volume and optionally a volume positioned between at least one dynode (14) and the detector (16) can be subjected to a vacuum, characterized in that at least the dynodes (14) and optionally also the detector (16) and optionally the at least one Focusing electrode (18) a spatial dimension have a range of greater than or equal to 50 µm to ‰ ¤ 1000 µm and are applied using a microsystem technology process. A secondary electron multiplier (10) described above allows a good amplification potential along with a simplified producibility.

Description

The present invention relates to a secondary electron multiplier especially for use in microsystems with improved manufacturability. The present invention further relates to a method of manufacturing a photomultiplier.

Secondary electron multipliers (SEVs) with discrete dynodes serve to multiply low photon, ion and electron currents. The multiplication of low primary electron currents by a photomultiplier is used in electron tubes, for example, in a photomultiplier for amplification.

Typically, a photomultiplier includes a plurality of dynodes, that is, a plurality of individual electrodes from an overall array of discrete electrodes, often in the millimeter range, such as in a range of 5mm or more. In addition, each end of a source for the photon, ion or electron flow or a detector for detecting the amplified photon, ion and electron flow may be provided, wherein the source and the detector are further connected to a per se known voltage divider to the individual dynodes can create a defined voltage. Furthermore, focusing devices can be provided in order to allow a suitable alignment of the electrodes, in particular the anode and the cathode, for the purpose of a desired focusing of the charge carrier beam.

In the operation of a secondary electron multiplier, an accelerator voltage is usually applied across the entire series of dynodes. As a result, the voltage can drop between the outermost dynodes and electrons, for example, can be accelerated from dynode to dynode. If an electron strikes the surface of a dynode, further electrons are emitted and the current is amplified.

The individual discrete dynodes thus form the amplifier stages of the secondary electron multiplier. The primary charge carriers strike the first discrete dynode and generate more secondary electrons than primary charge carriers are hit on this dynode. The prerequisite for this is that the surface of the dynodes has a secondary electron coefficient δ = secondary electrons / primary charge carrier> 1. Normally values of δ = 3 to 10 are achieved in the case of secondary electron multipliers, but the secondary electron coefficient here depends not only on the material of the dynodes used but also, for example, on the energy of the primary charge carrier and thus on the voltage between the dynodes. The gain of the photomultiplier is therefore δ ⁿ at n dynodes.

The production of secondary electron multipliers according to the prior art is complex in many respects. One requirement in the production of secondary electron multipliers is, for example, the exact and optimum geometry and alignment of all components to one another. In detail, all the components of the secondary electron multiplier must be adjusted and / or aligned as reproducibly and exactly as possible in a separate step of the method.

There has therefore been a need for a photomultiplier as well as a method for manufacturing a photomultiplier tube in which at least one disadvantage of the prior art can be circumvented. In particular, it is the object of the present invention to provide a photomultiplier tube and a method for producing a photomultiplier tube, which reduces the manufacturing requirements.

This object is achieved by a secondary electron multiplier having the features of claim 1. This object is further achieved by a method for producing a secondary electron multiplier having the features of claim 7. Further features are specified in the subclaims, the description and in the figures, wherein the further features individually or in any combination can form part of the invention, unless the context explicitly results in the opposite.

A secondary electron multiplier is proposed, comprising an electrically insulating substrate on which a plurality of discrete dynodes and optionally at least one focusing electrode and optionally a detector are arranged. Furthermore, a line structure for applying defined different electrical potentials to the dynodes is provided. A volume positioned spatially between the dynodes and, if appropriate, a volume positioned between at least one dynode and the at least one focusing electrode and optionally a volume positioned between at least one dynode and the detector can be subjected to a vacuum. The secondary electron multiplier is characterized in that at least the dynodes and, if appropriate, the detector and possibly the at least one focusing electrode have a spatial extent in a range of ≥ 50 μm to ≦ 1000 μm, in particular 100 μm to ≦ 750 μm.

In a previously described secondary electron multiplier, it is thus provided in particular not to produce the active structures, in particular the dynodes and, if appropriate, the detector and the focusing electrodes, as is customary in the prior art, in the millimeter range, but rather in a range of ≦ 1000 μm and thereby produced by microsystem technology. A prescribed In this way, secondary electron multipliers allow a significantly simplified manufacturability compared to the systems of the prior art, in particular without an additional adjustment step, accompanied by a large variability in shaping and a high amplification potential using microsystem processes for the production of microsystem components and thereby an improved integration into existing systems.

For the purposes of the present invention, a "plurality of dynodes" may mean that at least two and, in principle, any number greater than two may be present on dynodes.

Further, the term "discrete dynodes" may mean, in a manner understood by those skilled in the art, that the intended dynodes are spatially separated and thus do not touch, so that the discrete dynodes may have a different electrical potential.

For the purposes of the present invention, "microsystem components" may in particular be understood to mean components which have a maximum extent and thus a size in the length and / or the width and, if appropriate, the height which is in a range of micrometers, in particular 50 μm to less or equal to 1000μm, lies. In the context of the present invention, microsystem components may have a maximum extent or size in the above-described region, in particular in each of the provided planes or three-dimensionally. The length may mean the longest extent of the corresponding structure, whereas the width may be the corresponding transversely extending extent. Furthermore, the height may in particular mean the thickness of the structure, for instance on the substrate.

The size of the corresponding structures can be determined in a manner which is readily understood by the person skilled in the art by optical methods, for example by means of scanning electron microscopy.

Accordingly, a "microsystem method" is understood to mean a method by which components in the above-described size range can be defined and reproducibly produced or produced.

A prescribed secondary electron multiplier thus initially comprises an electrically insulating substrate on which a plurality of discrete dynodes and optionally at least one focusing electrode and optionally a detector are arranged. In this case, an electrically insulating substrate can be understood as meaning a substrate whose electrical resistance is sufficiently high so as to allow a desired operation of the secondary electron multiplier and, in particular, to allow the presence of a respective different electrical potential of the dynodes separated from each other.

The intended dynodes serve in a conventional manner as the actual gain components of the secondary electron multiplier by these, when primary charge carriers or primary electrons meet in the first direction discrete in the gain direction dynode generate more secondary electrons are taken as primary charge carriers to this dynode, wherein the increased number of electrodes are accelerated toward the next dynode in the gain direction by the respective electric potential of the dynodes so as to cause a boosting effect. This amplification effect is fundamentally in accordance with the basically known operating principle of a secondary electron multiplier.

In this case, the invention will be described in particular below by amplifying an electron current or electron beam. However, it is understood by those skilled in the art and equally encompassed by the invention that in addition to electron currents, for example, photon or ion currents can be amplified, for example, if a fundamentally known conversion electrode or a substrate with a photoelectron emitter layer is provided at the entrance of the secondary electron multiplier. For example, a conversion electrode or conversion dynode can generate electrons from ions in a manner known per se. For example, the electrode may comprise an alkali metal or an alkali metal alloy as a coating, whereby electrons may be released upon the impact of an ion beam. Accordingly, a photoelectron emitter layer may be such a layer that releases electrons upon impact of photons or light. Such a layer may include, for example, sub-oxides of cesium, alkali metals or antimony. The conversion electrode as well as the photoelectron emitter layer can also be arranged approximately on the substrate and manufactured in terms of process technology uniformly with the dynodes, for example by the same methods, whereby a fully integrated photon electron multiplier can be realized.

Furthermore, optionally at least one, possibly a plurality, may be provided on so-called focusing electrodes. These electrodes are arranged in particular in the beam path of the electrons at the beginning of the photomultiplier. Thus, when entering the secondary electron multiplier, the electrons first strike or pass through the focusing electrodes as the charge carrier current or the charge carrier beam to be amplified. These electrodes serve to align the electron beam in a particularly defined manner and to direct it to the first dynode. As a result, a particularly defined electron flow and thus a particularly advantageous amplification can be realized.

Furthermore, the last dynode in the direction of amplification can be followed by a further electrode serving as a detector, to which the amplified electron current or Carrier current meets after continuous amplification. Furthermore, with regard to its positioning, the detector can also be arranged on the electrically insulating substrate and configured as a microsystem component in the above-described size range and be produced with the same method as the dynodes.

By way of example and not limitation, the dynodes are provided in a number from greater than or equal to 2 to less than or equal to 20, preferably greater than or equal to 5 to less than or equal to 15, greater than or equal to 5 to less than or equal to 10, the above values not being limiting are. Due to the above-described number of dynodes, however, a high gain can already be combined with a very compact design. In principle, the number of dynodes is to be selected, for example, as a function of the desired amplification factor and, for example, as a function of the pressure or vacuum that can be generated between the dynodes.

Thus, it may be preferred that at least one spatially between the dynodes and optionally between at least one dynode, so in particular the gain first direction dynode, and the at least one focusing electrode, or in the presence of a plurality of focusing electrodes preferably also between the respective focusing electrodes, and optionally between at least one dynode, so in particular the last in the direction of amplification dynode, and the detector positioned volume with a vacuum or a reduced pressure can be acted upon. For example, the dynodes can be arranged in a chamber which can be acted upon with a reduced pressure. For the purposes of the present invention, such a chamber can be understood to mean, in particular, a chamber which can be closed in a pressure-tight or vacuum-tight manner at least temporarily for using the secondary electron multiplier and which, in particular, can have a connection for connecting a vacuum pump. In this case, a vacuum may also be understood as meaning, in particular, a reduced pressure with respect to the ambient atmosphere (1 atm; 1.01325 bar), which, for example but not restricting, in a range of greater than or equal to 10 ^-3 mbar to less than or equal to 10 ^-2 mbar , or may be over it. In this case, a gain can be the more effective, the lower the pressure. However, the pressure can basically be selected application-related, for example, depending on the number of dynodes, the desired gain and the spacing of the dynodes.

The chamber which can be acted upon with a reduced pressure can be designed in such a way that at least the dynodes and optionally the at least one focusing electrode and optionally the detector are completely or at least partially and the space located between the dynodes and used as the electron radiation space is arranged completely in the chamber that at least the active surfaces of the dynodes and the intervening space can be acted upon by a vacuum. Correspondingly, a conversion electrode and / or a photoelectron emitter layer can also be arranged in the chamber, if present. For example, the substrate which serves as a support for the electrodes can be arranged completely in the chamber, or the substrate can form a part of the chamber wall.

A low pressure or a vacuum may therefore be advantageous because the gain is reduced by collisions of the charge carriers with neutral gas particles, which are located between the dynodes. Thus, accordingly, the gain decreases with increasing ambient pressure, so that operating under a vacuum can enable a particularly advantageous amplification potential. Furthermore, it can be prevented by the formation of a vacuum, or at least reduce the risk that, by forming plasmas to electrical breakdowns in the operation of the Sekundärelektonenvervielfachers.

The shape of the dynodes can furthermore basically be freely selectable. Practically, however, at least the active surface of the dynodes should be designed or formed and / or aligned such that the irradiated electrons can be reflected such that they strike the dynode following in the radiation direction or in the amplification direction. For example, it may be preferable for the dynodes to have a curved, somewhat banana-like shape. However, it will be understood by those skilled in the art that the electrons move through the photomultiplier, in particular through acceleration caused by the corresponding potential of the dynodes.

By way of non-limiting example, the dynodes may be positioned in an array that corresponds to one or more, particularly parallel, rows. Such an arrangement can be simple and very compact. Basically, the geometry of the dynodes and their arrangement with each other or each other, however, freely selectable, as far as a suitable radiation path of the electrons can be formed.

For the supply of the dynodes each having different electrical potentials for accelerating the electrons for the gain, as is advantageous and basically known for the mode of operation of the secondary electron multiplier, the secondary electron multiplier according to the invention may further comprise a line structure, which includes the dynodes and optionally the at least one focusing electrode supplied electrical voltage or brings them to a desired electrical potential. In order to be able to set the potential of the individual dynodes to one another differently, voltage dividers, for example in the form of, for example, thin-film resistors, electrical resistors may also be provided in the line structure, as is fundamentally known functionally for secondary electron multipliers. The line structure can be, for example, by approximately metallic Conductor tracks are formed, which are connected to the corresponding dynodes or connected to these. The shape and size of the line structure can be adapted to the corresponding microstructure components. The line structure may also be applied to the substrate, which may allow a particularly simple manufacturability. The conductor tracks of the line structure may, for example, have a thickness in a range of ≥ 0.1 to ≦ 2 μm, for example of 1 μm, and / or a width in a range of ≥ 1 μm to ≦ 100 μm. A corresponding voltage supply can advantageously take place via a discrete voltage supply system, as is basically known.

To avoid electrical breakdowns between the terminals of the power supply, shields can be provided which can be arranged between the line structures which can bring the dynodes to the corresponding electrical potential. Such shields may also be referred to as floating mechanical barriers made in the same way as and simultaneously with the dynodes. As a result, the free propagation of charge carriers, in particular by electron impact generated ions can be prevented.

The shields are preferably narrow, beyond the width of the leads "walls" that prevent electrical breakdown between the leads due to their mechanical barrier effect for ions and electrons. They are not electrically connected, so floating. The distance should be smaller than the free path between the dynodes depending on the ambient pressure.

In an operation of the photomultiplier further, a source for a photon, ion or electron flow may be provided, such as a mass spectrometer or other source for the above-described charge carrier beam to be amplified. In this case, the charge carrier beam to be amplified may be directed onto the secondary electrode multiplier such that it impinges on the first dynode in amplification direction or, if appropriate, on the first focusing electrode or photoelectron emitter layer or conversion electrode in the beam direction.

For accelerating and detecting the electrons, the above-described source for the photon, ion or electron current and the detector can likewise be connected to the line structure, so that a voltage applied between source and detector can be generated and a current flowing through the detector can be detected which can increase in accordance with the amplification factor of the photomultiplier.

In the above-described secondary electron multiplier, it is further provided that at least the dynodes and, if appropriate, the at least one focusing electrode, the line structure and in particular when the detector is applied to the substrate and the detector are designed as microsystem components and are applied to the substrate by a microsystem method. Thus, the secondary electron multiplier is at least partially produced by a microsystem method or by the methods of microsystem technology. These methods are particularly advantageous in the ability to produce discrete dynodes and other microstructures with distances of ≥ 10μm to ≤500μm, for example> 50μm to ≤500μm, such as in a range bis≤ 300μm, for example up to ≤ 250μm, such as 20μm in which the structures, that is to say in particular the dynodes and optionally the focusing electrodes and the detector itself, can easily have a spatial maximum extent in a range of ≥ 50 μm to ≦ 1000 μm, for example up to ≦ 750 μm, wherein an extension extends in the case of the focusing electrodes and the detector 100μm can be beneficial. Further, they may have a thickness in a range of ≥ 100μm to ≦ 500μm.

Exemplary and particularly preferred production methods of microsystem technology are for the production of the lithography process by geometry defining anisotropic reactive ion etching (DRIE etching) for silicon (Bosch process) and for the production of metallic microstructures the LIGA process, for coating and production of interconnects, for example, deposition methods, such as such as PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), sputtering and vapor deposition. Exemplary corresponding methods will be described in detail with reference to the method.

For example, a sandwich structure may be formed, which is composed of several layers, wherein the dynodes and optionally the other microsystem components, such as at least one of the focusing electrode or focusing electrodes, the detector and the line structure, for example, in the middle of the sandwich structure are arranged. By way of example, such a structure may in no limited way have the following layer sequences: glass-silicon-glass or about insulator-metal-glass. As a result, the dynodes can be surrounded, for example, at low pressure by a hermetically sealing ring of silicon or metal. In this case, for electrical connection of the dynodes, for example, an approximately anodic bonding carried out under vacuum, the contact can then be advantageously carried out by means of metallic feedthroughs through the insulating bottom or top substrates by here, for example, pressure-tight closed cable bushings are provided.

A prescribed photomultiplier has significant advantages over the conventional prior art multipliers.

Thus, a prescribed secondary electron multiplier can be used particularly advantageously in microsystem technology or in microsystems. In particular, yours such secondary electron multiplier be integrated directly into such systems. For example, integration in a micro-mass spectrometer, for example in a so-called PIMMS system (planar integrated miniaturized mass spectrometer), may be advantageous. In many cases, the entire system can be produced simultaneously or in a batch process, so that a cost-effective and simple production of such a microsystem can result. In addition, such a secondary electron multiplier can usually be easily incorporated into an existing or to be formed peripherals, such as resistors for a potential distribution and optics, or dynodes. With respect to the vacuum to be formed, the entire unit comprising secondary electron multipliers and further systems, for example mass spectrometers, can then be arranged preferably in a vacuum chamber. In this case, in particular, the measuring units can be arranged in the vacuum chamber, whereas evaluation units, for example, can be arranged outside the chamber.

The frequency of collisions between neutral particles located between the dynodes and charge carriers to be amplified is further determined, apart from the gas pressure, as described in detail above, by the ratio of the mean free path and the total travel distance of the charge carriers. Thus, in addition to the use of a vacuum, as described above, also due to the small dimensions of the secondary electron multiplier as microsystem component or in particular the dynodes and concomitantly due to the small distance between the dynodes, as described above in a range of ≥ 10μm to ≤ 500μm, For example, from ≥ 150μm to ≤ 300μm, for example, be of about 250μm or up to 20μm, a particularly high effectiveness of reinforcement may be possible. In this case, the above-described ranges may relate in particular to use in a pressure range from 10 ^-4 Pa to 1 Pa or from 10 ^-6 mbar to 0.01 mbar.

However, if the size of the components used and their distances from each other decreases, the demands on the geometric tolerances in the dynode shape and on the adjustment of the individual components to one another increase in equal measure. However, because the secondary electron multiplier is configured by a method of micro-system technology, this problem does not occur in a prescribed secondary electron multiplier. Rather, the above-described photomultiplier can be formed directly by the manufacturing method, such as by an etching method or by a deposition method, in the desired shape and geometry and thus in a defined orientation of the components to each other, so that an adjustment need not be made. As a result, the method step of the adjustment, which is often complex in the prior art, can be achieved completely eliminated, which can make a manufacturing process particularly simple and inexpensive.

Furthermore, a particularly good adaptability can be made possible by a largely arbitrary arrangement of the dynodes due to the customizable manufacturability of the structures to be produced, in particular the dynodes and the power supply. In this case, it is possible to speak of a good adaptability of the electron or ion optics, since here a beam path of the charge carriers is guided in a defined manner.

For example, implementation of integrated multipliers, such as photon multipliers, can be carried out in the batch process, or integration with other microanalysis systems may be possible in a common manufacturing process.

Because of the short transit times due to the close spacing of the dynodes to each other can be compared to conventional systems from the prior art additionally increase the temporal response. The ability to realize even very complex dynode geometries in a simple and highly defined manner also significantly improves the focusing properties and propagation delays, such as pulse broadening. As a result, a very variable and likewise a very adaptable embodiment can be realized. The close spacing between the dynodes also allows the vacuum requirements to be significantly reduced, so that under comparable conditions, the vacuum may be sufficient to provide a comparatively lower vacuum compared to prior art secondary electron multipliers in the millimeter range. Thus, pressures in a range of 0.1 mbar, about 10 ^-3 mbar or even more, ie a comparatively low vacuum, may already be sufficient, whereas in the prior art pressures in a range of, for example, 10 ^-6 mbar are often required. In other words, according to the invention, a vacuum lower by powers of ten may be sufficient. As a result, the requirements for the photomultiplier as well as the vacuum pumps, for example, allow a more cost-effective manufacturability.

Thus, in contrast to corresponding prior art systems, a prior art secondary electron splitter, since conventional discrete-mode secondary photomultipliers, also called discrete SEVs, have dynodes several millimeters in size, also in the millimeter range, in a range of 3mm or greater have and thus have a corresponding high space required. In addition, the prior art photomultiplier tubes have relatively high vacuum requirements because of the high spacing between the individual dynodes. Further, the prior art discrete photomultipliers are not suitable for direct integration with other microsystem components, such as Micro mass spectrometers, suitable. This is true even if they do not allow a reduced space requirement while maintaining the reinforcing properties in the rule.

Furthermore, it can result from the very space-saving design that a small area and volume requirement results at the same time with low volume requirements, which still dead volumes and loss distances can be prevented.

The secondary electron multiplier also allows a manufacturing method with a particularly simple supply of dynodes, for example, with the different potentials by thin film resistors, since these resistors can be connected directly to the dynodes. Furthermore, the line structure can be produced in a method together with the other structures, so that a particularly simple manufacturability can be made possible.

In summary, the above-described secondary electron multiplier allows in a simple manner a particularly simple and cost-effective manufacturability with simultaneously high amplification power.

In a preferred embodiment, the dynodes and, if appropriate, the at least one focusing electrode and optionally the detector can have a maximum extent which lies in a range of ≥ 50 μm to ≦ 750 μm, for example ≥ 250 μm to ≦ 500 μm. In particular, in this embodiment, a particularly compact training can be realized along with a good reinforcement. In addition, optionally a particularly good adaptability to given microsystem components or a particularly good implementability in microsystems can take place and thus particularly compact components having such a secondary electron multiplier can be produced. In this case, however, the maximum extent should be chosen in particular in order to still ensure a sufficient boosting force.

In a further advantageous embodiment, the substrate may comprise a material which is selected from the group consisting of glass, ceramic, silicon oxide, in particular silicon dioxide, and sapphire. In particular, the aforementioned materials can be used in a simple way in microsystems technology. In addition, these materials furthermore have an insulation quality which allows advantageous operation of the secondary electron multiplier. In this case, the substrates may, for example, have a thickness which is in a range of ≥ 300 μm to ≦ 1000 μm, for example of ≥ 400 μm to ≦ 500 μm.

In a further preferred embodiment, at least the dynodes and optionally the at least one focusing electrode and optionally the detector may comprise a material, in particular be formed from this material, which is selected from the group consisting of doped silicon or metals, such as gold, copper, nickel or silver. As far as silicon is used and described with reference to the present invention as doped silicon, dopants for the silicon include in particular boron, nitrogen, phosphorus, aluminum, indium, arsenic and antimony. Suitable doping concentrations further include, but are not limited to, the range of 10 ¹⁶ to 10 ²¹ cm ^-3 . In this case, a doping with respect to the selection of the dopant or the doping concentration is carried out in particular such that the selection is adapted to the desired efficiency of the secondary electron multiplier, or that a sufficient electrical conductivity of the structures for a desired operation of the photomultiplier is given.

In this case, the material, in particular in so far as the dynodes are designed with this, may also be coated with a material which is not electrically conductive and which increases the secondary electron coefficient, such as aluminum oxide (Al ₂ O ₃ ) or silicon dioxide (SiO ₂ ), wherein the Coating, for example, can be carried out by methods known per se, such as deposition methods known per se, for example physical vapor deposition (PVD) or chemical vapor deposition (CVD). For example, a dynode may be particularly preferably made of silicon, wherein a coating of silicon dioxide can be configured by oxidation. In particular, by the aforementioned materials or combinations of materials can be advantageous to apply methods of microsystems technology, so as to be able to produce defined structures. Furthermore, a high secondary electron coefficient can be made possible in particular by the aforementioned coating of the dynodes, which enables a particularly effective amplification.

In a further preferred embodiment, the secondary electron multiplier may have a layer structure in which two substrates are provided, between which at least the dynodes and optionally the detector and optionally the at least one focusing electrode and optionally at least partially the line structure are arranged. Such a structure can thus form, in particular, a so-called sandwich structure, in which the microsystem components, in particular the dynodes and optionally the at least one focusing electrode and optionally the detector are arranged. In this case, such a structure may comprise, for example, two glass substrates, between which the microsystem components, in particular the dynodes and, if appropriate, the at least one focusing electrode and optionally the detector, are formed approximately from doped silicon. A realization of such systems, in particular with regard to the direct integration into other microsystems, such as micromass spectrometers, for example in so-called PIMMS systems, is particularly advantageous. Because in this structure, channels can be formed, through which a gas escaping from a mass spectrometer can be directed. In addition, uniform or the same manufacturing processes can be used for the entire system. Such a structure can be realized, for example, by the DRIE etching method already mentioned above and described in detail below, in which all components that are critical with respect to geometry and that are electrically conductive can be realized by highly accurate anisotropic etching in silicon.

In a further preferred embodiment, the dynodes can be arranged in two concentrically arranged arcs. The arches can form, for example, circular arcs. The dynodes are expediently arranged such that the electrons are respectively directed from the inner arc to the outer arc and back to the inner arc and so on. This in turn allows a very compact design to be combined with a high amplification power. In this way, e.g. reduce the space requirement of the arrangement and so the manufacturing costs even further. In the context of the present invention, the formation in two concentric arcs should mean, in particular, that all dynodes would be touched by two imaginary concentric arcs, for example circular arcs. In other words, the concentric arcs are defined by at least a portion of the dynodes thus arranged.

With regard to further technical features and advantages of the above-described secondary electron multiplier, reference is hereby made explicitly to the statements concerning the method for producing a secondary electron multiplier and to the figures or the description of the figures.

1. a) Bereitstellen eines elektrisch isolierenden Substrats;
2. b) Aufbringen zumindest einer Mehrzahl von Dynoden und gegebenenfalls wenigstens einer Fokussierungselektrode und gegebenenfalls eines Detektors auf das elektrisch isolierende Substrat unter Ausbildung von Strukturen mit einer maximalen räumlichen Ausdehnung von jeweils > 50µm bis ≤ 1000µm, wobei
3. c) die Dynoden zum Sekundärelektronenvervielfachen angeordnet werden, und
4. d) Aufbringen einer Leitungsstruktur auf das Substrat zum Anlegen eines jeweils unterschiedlichen elektrischen Potentials an die Dynoden.

The present invention furthermore relates to a method for producing a secondary electron multiplier configured as described above, comprising the method steps:

1. a) providing an electrically insulating substrate;
2. b) applying at least a plurality of dynodes and optionally at least one focusing electrode and optionally a detector on the electrically insulating substrate to form structures having a maximum spatial extent of> 50μm to ≤ 1000μm, wherein
3. c) the dynodes are arranged for secondary electron multiplication, and
4. d) applying a conduction structure to the substrate for applying a respective different electrical potential to the dynodes.

It is obvious to the person skilled in the art that the method can not be carried out in the above-described order but also in an at least partially deviating order or at least partially simultaneously.

Thus, according to method step a), the provision of an electrically insulating substrate takes place first, reference being made to the above statements with regard to the secondary electron multiplier with reference to the precise configuration of the substrate. In summary, for example, a substrate having a thickness in a range of ≥ 300 μm to less than 1000 μm, for example made of glass, sapphire, oxidized silicon or silicon oxide, or a ceramic, can be provided.

In accordance with method step b), at least a plurality of dynodes and optionally a detector and optionally at least one focusing electrode are then applied to the electrically insulating substrate to form structures with a maximum spatial extent of the respective individual structure of .gtoreq.50 .mu.m to 1000 .mu.m in each case Extension for a dynode, a focusing electrode and the detector applies. Thus, this process step is carried out with a method of microsystem technology to form microsystem components. In this case, the dynodes for secondary electron multiplication are arranged according to method step c) as structures, in particular as functional structures, which can be done for example by defined etching, as described in detail below. With regard to the exact configuration of the dynodes, reference is again made to the above statements concerning the secondary electron multiplier.

Arranging the dynodes for secondary electron multiplication is further intended to mean that the dynodes have a shape and orientation that allows a carrier current, such as an electron current, to be reflected or accelerated from dynode to dynode, thus permitting amplification.

In this case, it is further provided that, in accordance with method step d), a line structure for connecting the dynodes to the substrate is additionally applied, in particular wherein the line structure has approximately metallic interconnects, shields optionally arranged therebetween, and optionally resistors, so that the be able to supply different dynodes, each with different electrical potential. In particular, the conductive structures may be deposited by deposition techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), vapor deposition, or sputtering, as described in detail below. By a method described above, a particularly simple and cost-effective production of a secondary electron multiplier can be made possible, wherein in particular a separate adjustment step of the individual components can be dispensed with each other. In this case, the shape and position of the dynodes can be generated to less than 1 .mu.m and with each other in the plane of any geometry and arrangement to each other, which allows the production of a particularly defined structure.

As a result, a high gain can furthermore be realized, since this requires that the electron-optical components, that is to say the dynodes, of a secondary electron multiplier are optimally adjusted or aligned with one another. If the size of the components used, as well as their distances from one another, also reduces the requirements on the geometric tolerances in the dynode shape and adjustment. The components of a secondary electron multiplier as described above meet these requirements due to the exact manufacturability problem-free, since a subsequent adjustment due to the production-related exact, immediately in the production taking place alignment is not necessary. This also allows any arrangement of the dynodes to each other.

The orientation of the components relative to each other can be carried out depending on the specific manufacturing process and thereby for example by a photomaskierte alignment of the dynodes by the arrangement of these directly during manufacture, so that an additional adjustment step or an additional alignment can be prevented or may be superfluous. Thus, the adjustment takes place directly in the production of the corresponding structures by a defined orientation or arrangement. In addition, a miniaturized precise and in the lateral geometry arbitrarily selectable electrode / dynode geometry or shape can allow due to the manufacturing process, which can allow a particularly good adaptability.

Due to the microsystem technology used in manufacturing in 2 ½ - dimensional geometry, ie in a geometry in which, in addition to the position geometry, the height is defined, not only the structures of the secondary electron multiplier can be produced in an integrated manner. Further processing of the corresponding structures, such as coating of coatings on dynodes, can be made possible in an integrated manufacturing process.

In addition, the conductor structure, as well as the shields, can also be produced in an integrated manner by deposition and patterning of printed conductors, for example by depositing layers of titanium (Ti), nickel (Ni), chromium (Cr), gold (Au ), Copper (Cu), silver (Ag), platinum (Pt) or palladium (Pd), preferably by direct contacting of the Electrodes and dynodes are integrated into the process. The production of the voltage divider required for the supply of the dynodes with ascending potentials can also be implemented integrated in terms of circuitry between the dynodes. This is possible, for example, in the form of photolithographically etched thin-film resistors, preferably of materials with a high specific resistance, but preferably still a positive temperature coefficient. Non-limiting examples of the design of the resistors include, for example, titanium oxynitride (TiON), nickel-chromium alloys (NiCr) or copper-nickel-manganese alloys (CuNiMn), for example, constantan.

By virtue of their production processes compatible with other analysis systems in microsystem technology, in particular of micromass spectrometers (PIMMS), these secondary electron multipliers can also be integrated directly into these systems. They not only allow a simplified simultaneous production, they can also be integrated without losses of charge carriers to be amplified because of the thus avoidable dead volumes and highly accurate assignment, for example by using photomask-based geometries.

Thus, the choice of materials which are not readily producible in thermodynamic equilibrium, such as, for example, silicon dioxide (SiO ₂ ), (Al ₂ O ₃ ), zinc oxide (ZnO) or amorphous diamond, for example for coating the dynodes, can be applied without problems. Such materials can be integrated into the process for coating the dynodes, for example by thin-film processes, such as PVD processes, sputtering and vapor deposition, or by chemical vapor deposition (CVD).

In a preferred embodiment, at least one process step may be performed using a photolithography process. Such a method step may serve in particular for defining the structures, in particular the dynodes, the line structure, shields, the detector and the at least one focusing electrode. For example, the production of all structures arranged on a substrate may be based on a photolithography step.

In such a step, a surface of a base body, such as a silicon wafer, for example of doped silicon or glass, is provided in a conventional manner with a layer of a photoresist. In this case, a negative varnish is to be understood in a manner known per se as meaning a varnish whose solubility decreases as a result of exposure, whereas a positive varnish is to be understood as meaning a varnish whose solubility increases as a result of exposure.

Depending on whether a positive or a negative resist is used, can be done by a partially UV-transparent mask exposing the paint layer, which changes the solubility and the corresponding areas can be removed or remain stable, such as by the action of a solvent, such as acetone, or a plasma. The structure of the mask is then transferred directly or as a negative into the lacquer layer, so that it can serve as the basis for generating the corresponding structures.

Such a processed basic body can then be the basis for further process steps for generating the desired structures.

With regard to the application of the line structure, for example, a photoresist may be applied by masking us structured removal by photolithography on the positions where no material of the line structure is to be present. Subsequently, a layer of the material of the line structure can be applied, for example by means of physical vapor deposition, chemical vapor deposition, sputtering or vapor deposition, whereupon the photoresist is removed again. This can be done for example by introduced channels or a lateral treatment. As a result, the material on the photoresist also dissolves. Alternatively, a photoresist can be applied, which has only a reduced adhesion of the material to be applied. The applied material then only adheres to the positions next to the photoresist, whereupon it can be removed again.

In particular with respect to the dynodes, optionally the detector and optionally the at least one focusing electrode, in one embodiment at least one process step can be carried out using a reactive ion etching. A reactive ion deposition, also known as the DRIE process (deep reactive ion etching), is known in a manner known per se, in which structures are realized by highly anisotropic etching in a base body, in this case in particular in doped silicon. In this case, a reactive ion deep etching in particular proceed as follows. First of all, the base body can be masked, for example with a photoresist, as explained above, or with a hard mask, such as silicon dioxide, covering the regions which are not to be etched. Subsequently, the exposed regions are etched, for example, using reactive hexane based on sulfur hexafluoride (SF ₆ ) in argon (Ar), which may be generated by, for example, forming a sulfur hexafluoride based plasma and argon based plasma. In order to produce a high anisotropy, an etching substep may alternate with a substep of the passivation. For this purpose, for example, the etched surface can be protected with a passivation layer, such as formed by the application of Teflon or by bringing the etched surface into contact with octafluorocyclobutane (C ₄ F ₈ ). By an alternating application of the aforementioned partial steps, a highly accurate structure can be etched. The method described above is also known as the Bosch process. This method is thus particularly suitable if the structures, such as the dynodes, the detector and / or the at least one conversion electrode are to be formed from doped silicon.

In this case, the entire structural parts to be removed can be removed by etching, or only trenches can be etched. In the event that below the areas to be removed, such as on a substrate and below a layer of doped silicon, for example, also a photoresist or other releasable connection is applied, this can be removed, so that the areas to be removed no longer stop own on the substrate and so can fall out. It may be provided that the corresponding structure etched from the bottom or the corresponding edges are etched, so that not the entire structure to be removed needs to be etched out, but only the edges can be traversed, so that the corresponding structures can be separated out ,

Thus, in step b), all components which are critical with respect to geometry and electrically conductive can preferably be realized by highly accurate anisotropic etching in silicon, which are in particular hermetically connected to insulating substrates provided with electrical conductors, for example by anodic bonding or anodic bonding. Thus, in principle, in the production of the secondary electron multiplier, a connection of the silicon with a substrate, for example with a glass substrate, by a so-called anodic bonding, wherein under the action of pressure and electrical voltage, the substrate, such as the glass, and the doped silicon are connected ,

In such a bonding process, a particular alkali ion-containing glass substrate can be brought into close contact with the doped silicon and a voltage introduced from the outside into the glass or into the silicon such that the glass substrate negative and the silicon structure are positively charged. For this purpose, for example, electrodes connected to a voltage source can be used or a heating plate can serve as an electrode. Using pressure, chemical compounds can form between the silicon and glass, such as the oxygen from the silica of the glass, creating a stable bond.

In particular with regard to the dynodes, optionally the detector and optionally the at least one focusing electrode, in a further embodiment at least one method step can be carried out using a galvanic material structure. In this case, for example, a so-called LIGA method can be carried out or the method can be based thereon. In such a method, substantially the following steps are taken. The substrate, which in turn may be a glass substrate or a ceramic substrate, is provided with a metallic layer, such as by sputter deposition or vapor deposition. A photoresist may subsequently be applied to this layer, as described in detail above with reference to photolithography. After a structured development and removal of the paint, a negative mold of the structure to be applied may remain as a metallic pattern next to the remaining paint. In a galvanic process Subsequently, a metal can be deposited on the substrate in the areas in which the photoresist was removed during the development, that is, the metallic pattern has been exposed. After removing the remaining paint, the substrate, the metallic layer and the electrodeposited metal first remain behind. The electrodeposited metal can form the desired structures in this case. Thereafter, the metallic layer which is located directly on the substrate is then removed by an etching step, for example, between the galvanized structures. This method is therefore particularly suitable when the structures, such as the dynodes, the detector and / or the at least one conversion electrode should be formed from a metal.

With regard to further technical features and advantages of the method for producing a secondary electron multiplier, reference is hereby explicitly made to the statements concerning the secondary electron multiplier and the figures or the description of the figures.

• Fig. 1. eine schematische Darstellung einer Vorstufe einer Ausgestaltung eines Sekundärelektronenvervielfachers,
• Fig. 2 eine schematische Darstellung eines Sekundärelektronenvervielfachers basierend auf der Vorstufe aus Figur 1 während eines Betriebs;
• Fig. 3 eine schematische Darstellung einer weiteren Ausgestaltung eines Sekundärelektronenvervielfachers; und
• Fig. 4 eine Schnittansicht durch den Schnitt A-A' aus der Fig. 3 während eines Betriebs.

The invention will now be described by way of example with reference to the accompanying drawings with reference to preferred embodiments, wherein the features shown below, both individually and in combination may represent an aspect of the invention. Show it:

• Fig. 1 , 1 is a schematic representation of a preliminary stage of an embodiment of a photomultiplier tube,
• Fig. 2 a schematic representation of a secondary electron multiplier based on the precursor FIG. 1 during a business;
• Fig. 3 a schematic representation of another embodiment of a secondary electron multiplier; and
• Fig. 4 a sectional view through the section AA 'from the Fig. 3 during a business.

In the FIG. 1 is a schematic representation of a preliminary stage of an embodiment of a photomultiplier 10 shown. In this case, a substrate 12 is shown, which may be formed, for example, from glass, sapphire, silicon oxide or ceramic. By way of example, the substrate 12 may have a thickness which lies in a range of less than 1000 μm, for example greater than 300 μm, for example at 500 μm. Further, it may have a width or length which may be adapted to the number of components applied.

On the substrate 12, a plurality of discrete dynodes 14 are applied, wherein the individual dynodes 14 may have dimensions in a range of ≥ 50μm to ≤ 500μm. Purely By way of example, the dynodes 14 may each have a width in a range of ≥ 50 μm to ≦ 200 μm and / or a length of ≥ 50 μm to 400 μm and / or a thickness of ≥ 100 μm to ≦ 500 μm. In FIG. 1 It is shown that the dynodes 14 are arranged in two parallel rows with six dynodes 14 each. The distance between the dynodes 14 to each other may be in a range of ≥ 10μm to ≤ 500μm. The spacing of the dynodes in one row may be, for example, in a range of ≥ 10 μm to ≦ 40 μm, approximately 20 μm, and / or the spacing of the dynodes 14 to dynodes 14 arranged in the parallel row may be in a range of ≥ 10 μm to ≦ 150 μm. about 100μm, lie. In this case, the aforementioned values can relate in particular to use at a pressure of ≥ 10 ^-4 Pa to ≦ 1 Pa. Furthermore, the dynodes 14 may be configured, for example, with a thickness in a range of ≥ 100 μm to ≦ 500 μm, approximately to ≦ 400 μm, for example 300 μm.

In the FIG. 1 Furthermore, a detector 16 and focusing electrodes 18 are shown which may have a thickness comparable to the dynodes 14. Furthermore, the detector 16 and the focusing electrodes 18 may be in a comparable maximum size range as the dynodes 14. Furthermore, the dynodes 14, as well as the detector 16 and the focusing electrodes 18 may be made of doped silicon or of a metal such as gold or silver. The dynodes 14 may have a coating for effective reinforcement, such as alumina or silica. The dynodes 14, the detector 16 and the focusing electrodes 18 are manufactured by a microsystem method.

FIG. 1 further shows that on the dynodes 14, the focusing electrodes 18 and, not shown, on the detector 16, tracks 20 are arranged which may be part of a line structure to bring the dynodes 14 to a desired and mutually different electrical potential , In order that the electrical potential of the individual dynodes 14 can be set in a defined manner and, in particular, different from one another, are in the FIG. 2 further thin-film resistors 26 are shown, which may be arranged between the dynodes 14. Furthermore, shields 15 are shown, which may be arranged between the tracks 20 so as to prevent electrical flashovers. The shields 15 can be produced analogously to the electrodes or the line structures, such as the conductor tracks 20, but an electrical connection of the shields does not take place.

In order to achieve a particularly effective reinforcement, the above-described arrangement is furthermore preferably arranged in a chamber 22 bounded by a wall 23 approximately made of a plastic, in which a vacuum 24 can be formed, as shown purely schematically in the figures. It may also be provided that in the chamber 22, a further chamber is provided, in which the arrangement comprising the substrate 12 is arranged with the components applied thereto. This chamber may in turn have a window or an opening for introducing a beam to be amplified, wherein in the not Chamber shown also the vacuum 24 can be introduced. The further chamber may again have a wall made of a plastic.

In the FIG. 2 Further, a charged particle beam 11 is shown, which is passed through the focusing electrodes 18, which may also have a suitable electrical potential, to the dynodes 14, wherein the charged particle beam 11 amplifies in the direction of the detector 16. In this case, the chamber 22 or the wall 23 in front of the first dynode 14 or in front of the first focusing electrode 18, for example, a window, not shown, such as glass, to direct a photon beam into the chamber 22. Then, it first encounters a photosensitive layer or photoelectron emitter layer, for example, upstream of the focusing electrodes 18 and / or, for example, on the substrate 12 in order to generate the charged-particle beam 11. Alternatively, the beam source of the charged particle beam 11 may be located directly in the chamber 22.

In the Figures 3 and 4 Furthermore, a further embodiment of a secondary electron multiplier 10 is shown. In this embodiment, the secondary electron multiplier 10 has a layer structure in which two substrates 12, 12 'are provided, between which at least the dynodes 14 and according to FIGS Figures 3 and 4 Furthermore, the detector 16 are arranged. Further, a made of a plastic wall 25 is shown, which closes a chamber 27, the chamber 27 corresponding to FIG. 1 can be arranged in a chamber 22, not shown, for forming a vacuum 24 In this case, the vacuum 24 is also in the chamber 27 before. The wall 25 may be configured circular and together with the substrates 12, 12 ', the chamber 27 form. In a preferred embodiment, it may be provided that the substrates 12, 12 'are formed of glass and the dynodes 14 are formed of doped silicon and are thereby anodically bonded to the glass substrate, as described in detail above. The interconnects 20 may be metal interconnects made of a nickel-gold multilayer system and may be connected approximately eutectically to the dynodes 14. Through these tracks 20 contacting can be done to the outside, for example, to a board.

Furthermore, the design of the dynodes 14 in two concentric arcs in the FIG. 4 shown.

In the FIG. 4 in turn, the gain beam 11 is shown, which is passed to the dynodes 14, wherein the gain beam 14 amplifies in the direction of the detector 16. For example, in the event that a photon amplification takes place, the in FIG. 4 not shown chamber 22 and the wall 23, not shown, also have a transparent or transparent area. In this case, in turn, a photoelectron emitter layer is provided, which may be arranged approximately on the substrate 12. Alternatively, the source of the amplification beam 11 in the chamber 22, not shown or be arranged inside or outside the chamber 27. Furthermore, the chamber 27 may be opened if an electron beam is to be amplified and the beam source is outside the chamber 27. Furthermore, focussing electrodes, not shown, may be provided, which may be arranged or aligned in accordance with the formation of the amplifying beam 11.

In the FIG. 4 Furthermore, an interconnection of the individual electrodes is not shown. However, this can be done in a manner understandable to the skilled person described above and for a secondary electron multiplier basically known manner.

Claims (11)

A photomultiplier having an electrically insulating substrate (12, 12 ') on which a plurality of discrete dynodes (14) and optionally at least one focusing electrode (18) and optionally a detector (16) are arranged, further comprising a line structure for applying defined and at least one volume positioned spatially between the dynodes (14) and optionally a volume positioned between at least one dynode (14) and the at least one focussing electrode (18) and optionally one between at least A volume which is positioned in a dynode (14) and the detector (16) can be subjected to a vacuum, characterized in that at least the dynodes (14) and optionally also the detector (16) and optionally the at least one focussing electrode (18) have a spatial extent in a range of greater or greater oak have 50μm to ≤ 1000μm. A photomultiplier according to claim 1, characterized in that the substrate (12, 12 ') comprises a material selected from the group consisting of glass ceramic, silicon oxide and sapphire. Secondary electron multiplier according to one of claims 1 or 2, characterized in that at least the dynodes (14) and optionally the detector (16) and optionally the at least one focusing electrode (18) comprise a material which is selected from the group consisting of doped silicon and metals. Secondary electron multiplier according to one of claims 1 to 3, characterized in that the secondary electron multiplier (10) has a layer structure in which two substrates (12, 12 ') are provided, between which at least the dynodes (14) and optionally the detector (16) and optionally the at least one focusing electrode (18) are arranged. A photomultiplier according to claim 4, characterized in that the two substrates (12, 12 ') are formed of glass and that at least the dynodes (14) and optionally the detector (16) and optionally the at least one focussing electrode (18) are formed of doped silicon are. Secondary electron multiplier according to one of claims 1 to 5, characterized in that the dynodes (14) are arranged in two concentrically arranged arcs. Secondary electron multiplier according to one of claims 1 to 6, characterized in that the dynodes (14) to each other have a distance which is in a range of> 100μm to ≤ 500μm. Method for producing a secondary electron multiplier (10) according to one of Claims 1 to 7, comprising the method steps: a) providing an electrically insulating substrate (12); b) applying at least a plurality of dynodes (14) and optionally a detector (16) and optionally at least one focusing electrode (18) to the electrically insulating substrate (12) to form structures with a maximum spatial extent of each 1000μm; in which c) the dynodes (14) for secondary electron multiplication are arranged; d) applying a conduction structure to the substrate for applying a respective different electrical potential to the dynodes (14). A method according to claim 8, characterized in that at least one method step is carried out using a photolithography method. A method according to claim 8 or 9, characterized in that at least one method step is carried out using a reactive ion etching. Method according to one of claims 8 to 10, characterized in that at least one method step is carried out using a galvanic material structure.

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