DE102013008486A1 - Low-noise optical element for detecting radiation by measuring electrical signals - Google Patents

Abstract

The application describes a low-noise optical element for the detection of radiation by means of electrical signals, which comprise a substrate and to which at least two spaced-apart contacts are applied and at least one selectively reflecting component layer is applied to the substrate, the substrate being applied before the component layer is applied an implantation method was processed in order to generate radiation-sensitive areas for generating the electrical signals, which can be dissipated via the contacts.

Description

field of use

The invention relates to a particularly low-noise optical element for detecting radiation (electromagnetic and particle radiation), in particular X-ray radiation and EUV radiation, by means of measuring electrical signals.

PRIOR ART, DISADVANTAGES OF THE PRIOR ART Optical elements according to the principle of the invention are used for a wide range of the electromagnetic spectrum. Especially for the EUV (extreme ultraviolet radiation, wavelength range: about 50 nm to about 10 nm) and the X-ray range (about 10 nm to about 1 pm), these principles have a special meaning. In the case of X-rays, the refractive indices of air and matter are only slightly different, so that the radiation is only slightly deflected. In the case of EUV radiation, these have a very high absorption capacity in matter, so that large parts of the beam intensity are lost. Therefore, in both cases, compared to visible light, special beam optical concepts are required. For a compact presentation but without limitation of generality applications in these two areas are described.

X-ray radiation is used as a probe in the chemical, medical, scientific and technical fields. In addition to conventional x-ray tubes, more recently microfocus tubes or pyroelectric materials, electronic synchrotrons - all emitting a polychromatic X-ray spectrum with divergent radiation - are also used as sources.

For the vast majority of applications, in particular X-ray diffractometric and X-ray reflectometric methods, a focusing or parallelization of the radiation and in particular a narrowing of the spectral range and thereby mostly the constriction to quasi-monochromatic X-radiation is desired. For spectroscopic applications, i. H. Qualitative and quantitative elemental determination of substances by X-ray fluorescence (XRF) analysis requires energy-dispersive or wavelength-dispersive decomposition of the components of the characteristic radiation of the sample atoms.

In X-ray diffractometry or reflectometry mostly reflective materials for X-ray influencing / -assembling, ie monochromatization, alignment or bundling of the X-rays on the way from the X-ray source to the sample and further from the sample to the detector, are used. In particular, X-ray interferences that can occur on crystals or nanometer multilayer systems are utilized. Such so-called X-ray mirrors (also multilayer or Goebel mirror) are for example in DE 198 33 524 A1 or DE 44 07 278 called.

In energy dispersive X-ray spectroscopy, energy-resolving detectors are used which measure the electrical (elemental) charges released as a result of a photon absorbed in the detection medium and numbered in a certain ratio.

In X-ray spectroscopy with wavelength dispersive X-ray interference, which can occur on crystals or nanometer multilayer systems and divert the radiation energy-dependent in different spatial areas, used.

UV or EUV radiation is used, inter alia, for optical lithography (EUVL) in the semiconductor industry, which radiation z. Example, for imaging of the smallest circuit patterns of a mask on a substrate provided with a radiation-sensitive paint, which are then transferred by etching processes on the substrate. Due to the above-mentioned high absorption of this radiation in matter, similar beam-optical concepts as for X-radiation are necessary for the imaging process, so that also here reflection-based optics are used. In DE 10 2004 062 289 B4 such an appearance is described. This is composed of a periodic layer sequence of a plurality of thin-film pairs with generally two layers of different materials.

Using X-ray methods as well as methods based on EUV radiation, which can be treated analogously, diffractive, refractive, absorbing and reflective materials can be used for beam influencing / assembly. In particular, however, beam interferences, which can occur on periodic objects, such as nanometer multilayer systems, are used, since the X-ray and in particular the EUV radiation can be deflected comparatively strongly on the one hand and then only comparatively slightly weakened (absorbed) and thus high utility intensities are available.

For crystals, after the generally sufficiently accurate so-called kinematic approximation, the deflection angle 2θ of an X-ray incident on a crystal (θ measured with respect to the lattice plane (with atoms) is determined parallel crystal planes)) on fulfillment of the condition for an interference maximum with the interplanar spacing and the wavelength of the X-ray in simple mathematical form (Bragg equation) linked. Characteristic parameters of the interference maxima occurring (also called reflexes) are, when referring to a scale of the angle 2θ (0 ° for straight alignment), the half-width of the reflex profiles, the integral reflex intensity and the maximum intensity combined over the respectively assigned angular range - that is to the reflex background with respect to an angle 2θ. The half-width determines in spectroscopic applications, the energy resolution, ie the lower limit z. B. yet to be distinguished energy differences characteristic X-ray lines. The integral reflex intensity is followed by a specification for the measurement time required for a required statistical verification of the measurement results. The reflectance of a substance is given by the intensity maximum or the integral over a defined angular interval. When using nanometer multilayers as well as when using crystals, eg. B. as optical elements, these parameters can be optimized by appropriate measures (layer or crystal quality and by optical elements such as diaphragms, collimators, etc.).

In the case of the use of nanometer multilayers for X-ray radiation, because of the predominant use in grazing incidence, ie in the region just above the critical angle of total reflection, the deflection due to refraction when passing through the individual interfaces in the Bragg equation must additionally be taken into account. A closer connection is in DE 198 33 524 A1 specified.

In the case of EUV optics, angles of incidence near 90 ° are used.

In the diffraction at lattice planes of crystals and in the constructive interference of partial rays reflected at the interfaces of a nanometer multilayer system, Bragg maxima can be used to diffract different orders. For a corresponding optical element, it should be possible to set the Bragg condition or an assigned position without reference to an external radiation detector.

An accurate positioning or adjustment of such an optical element can be done so far only with an external radiation detector. Since up to four and especially in the area of EUV radiation up to 10 or more optical elements, arranged in series, can be used for the imaging process in the field of X-radiation, their precise and exact alignment is essential in order to provide high reflectivities (useful intensities) and thus to keep the accuracy and the speed of the analyzes as well as the component manufacturing (in EUV lithography) high.

This object is achieved by the optical element, which is already described in the patent no. DE 10 2007 033 210 B4 has been described. According to the main claim of the patent DE 10 2007 033 210 B4, the substrate and the selectively reflecting component layers for the detection of X-radiation can be assembled. This can be made possible by the assumption of appropriate suitable electronic solid state properties by electrical contacting and the possible detection of the charge carriers formed by photoionization in these regions.

The basic idea of the patent DE 10 2007 033 210 B4 is based on the fact that the constructive interference, that is, the excitation of a reflex, is associated with the development of standing wave fields in the crystal or layer system and thus, the X-ray intensity absorbed in the selectively reflecting component layer is characteristically modulated angle dependent and thus via an additional active Element as in patent no. DE 10 2007 063 682 B3 described, due to the derived electrical signal, a feedback for adjusting the reflection condition or other characteristic settings is possible.

Disadvantages / shortcomings of the obvious solution (s)

The invention is based on the object of specifying a low-noise optical element in the sense of a radiation mirror based on nanometer layers, in particular for the field of application of X-ray analysis and EUV lithography, for highly efficient detection of radiation (X-ray and EUV radiation) by measuring current signals , Which is designed so that an automated - ie independent -, high-precision and above all fast - in the range of seconds and less - adjustment according to the Bragg reflection condition or a similar reflection condition is possible, so that the radiation to be reflected with specific properties and can be suitably brought about without major component expenditure.

The alignment of such an optical element / mirror, in particular an X-ray mirror, can take place relative to a radiation source or relative to another optical element. Even the smallest misadjustments in the range of micrometers and a few thousandths of an angle lead to significant reflectivity or useful intensity losses. Furthermore, the thermal expansion due to temperature changes and mechanical forces on the housing leads to misalignments and thus intensity losses. Deviations of the beam position due to the dynamics of the X-ray source (eg in the case of a microfocus tube) can also occur, which likewise lead to losses of the useful intensity which can not be recorded during the measurement / analysis procedure or can not be distinguished from a malposition of the X-ray mirror and require a dedicated mirror position adjustment.

Most of the X-ray mirrors offered by the industry usually use fine-thread screws to position the optical element according to the necessary adjustment rule.

The need for high-precision adjustment of X-ray mirrors means that even for experienced specialists the adjustment process is too complex and lengthy and the end user is often overwhelmed with the task. In addition, for reasons of occupational safety and health, operating personnel are required to avoid radiation exposure wherever possible. The adjustment process is therefore often carried out in a complex, iterative process, which makes the constant switching off and on of the X-ray radiation, the opening and closing of the X-ray machine protective housing or the use of an additional detector necessary.

For high-precision measurement, analysis and manufacturing results, it is necessary to use an extremely stable radiation source. Variations in the useful intensities, for example by day / night cycles, by changes in room temperature, by aging effects of the source or by electronic fluctuations, are recorded during operation, eg. B. of X-ray analysis, not or insufficiently recorded, so that in retrospect, no review of the operation is possible. A subsequent correction in case of errors is even completely excluded. Further, it is required that the above-mentioned problems of mirror alignment are solved.

The in the patent no. DE 10 2007 033 210 B4 described variants could solve the problems mentioned, but can not be used for the required task, since they have the great disadvantage that the electrical signals are very small and the electronic noise is relatively large and, due to the fact that the signal-to-noise Ratio is small. This leads on the one hand to large control times in the range of minutes, which make the setting process of the optics and thus the measurement process very time consuming and on the other hand inaccurate positioning, as a result of which the maximum possible radiation component is not reflected by the selectively reflecting component layer.

For fast adjustment operations (adjustment), it makes sense to arrange active areas, ie areas where a detectable electrical signal is generated, in a characteristic manner on the substrate, thus generating a spatial resolution. Different signal strengths of the individual active regions at different locations of the substrate then give the specific indication which degree of freedom must be readjusted for optimum adjustment of the X-ray mirror. This has the advantage that fast setting operations by selective control of the individual degrees of freedom are possible. With the in DE 10 2007 033 210 B4 it is not possible to realize a characteristic arrangement of active regions.

In the patent document no. DE 10 2007 033 210 B4 described embodiments, it is necessary to position a mechanical mask above the substrate to subsequently apply the selectively reflecting component layer. On the one hand, this mask can have manufacturing tolerances in the range of 100 μm. On the other hand, there is a gap between the mask and the substrate - the substrate may have a bend - so that during the application of the selectively reflecting component layer, material (atoms) may also get under the mask and so the component layer does not have a sharp boundary and consequently no exact arrangement is made. This can lead to additional electronic noise due to the fact that oversized space charge areas and contact areas must be present, which additionally generate leakage currents and noise and thus further increase the mentioned disadvantages [ G. Lutz, Semiconductor Radiation Detectors, Springer-Verlag Berlin / Heidelberg, 1999 ]. In addition, the introduction of another mechanical component during the coating process causes a deterioration of the vacuum conditions, so that the quality of the applied component layer may deteriorate.

Causes of these disadvantages / defects

The disadvantages mentioned in terms of signal strength and signal-to-noise ratio are due, inter alia, to the fact that the construction used of the optical element of patent no. DE 10 2007 033 210 B4 as well as the process used for packaging itself, high leakage currents and high electronic noise. Among other things, leakage currents in the optical elements produced in this way cause these occur due to lack of surface passivation - arcing and diffusion of the chemical elements from the electrically conductive layers, as well as manufacturing tolerances - the significant reduction in the electrical signal to be detected produced by photoionization of the X-ray / EUV photons and the significant increase in electronic noise. These leakage currents are due to the fact that no gradient structures can be generated by the method described and, in particular, edge structures can not be avoided, and therefore the exemplary embodiments mentioned, based on homogeneous layers, can not be suitably assembled.

The in the patent no. DE 10 2007 033 210 B4 two variants described in more detail relate to the construction in the sense of a Schottky diode and in the sense of a metal (oxide) semiconductor contact, wherein high reverse currents are characteristic for both variants, which result in high noise, in the small signal changes in the case of the optical element, are not significantly detectable. Furthermore, the trained space charge zone has only small dimensions. The consequence of this is that not all photons (radiation quanta) on the way through this area generate an electron-hole pair (same electrical signal) due to a finite interaction cross-section of photon and electron, but partly pass through "unused". In addition to minimizing the electrical signal to be measured, this also means that the smallest signals generated by individual X-ray photons can not be detected.

In the patent no. DE 10 2007 033 210 B4 mentioned substrates was not discussed their defect densities. It is known that structural defects in substrates also lead to increased leakage currents and are therefore unsuitable for the detection of very small signals.

An advantageous arrangement of active areas on the substrate is for the in DE 10 2007 033 210 B4 described embodiment of the optical element based on a Schottky or MOS structure not possible. This is due to the fact that they must be provided with an additional metal layer in close contact with the substrate for the generation of active areas. Consequently, one would have to create a characteristic array of areal areas. Subsequently, the coating would have to take place with the selectively reflecting component layer, which would be applied over a large area over all active regions. The finite thickness of the active regions due to the metal layers - this is in the range of about 50 nm - would cause the surface of the substrate to have large roughnesses. For the selectively reflecting component layer, however, it is a mandatory prerequisite that the substrate surface is characterized by the lowest possible roughness values. These should be in the range of 1 nm and below, so that maximum reflectivity values for the X-ray mirrors and high-quality beam conditioning can be achieved.

Object of the invention

Due to the described problems, it is the object of the invention to provide an optical element which automates the adjustment processes, continuously indicates the quality of the adjustment and thereby significantly increases the precision of the measurement and exposure processes.

Solution of the task

The problem solution according to the invention is achieved by generating a surface-passivated, leakage current-reducing p-n junction (semiconductor-semiconductor junction) within a substrate, by using photolithographic processing and ion implantation and by using a special high-resistance substrate material. The processed substrate material then represents a radiation-sensitive PIN diode, which consists of a weakly n- or p-doped base material with a more heavily n- or p-doped layer on the back, which forms the one contact. The radiation-sensitive side is defined by a region with a thin n- or p-doped layer on the front side. This layer is thin enough for the radiation to reach the active area, the p-n junction and the underlying space charge zone as unhindered as possible. An electronic contact structure is provided on the front and back sides of the semiconductor substrate.

In principle, all materials and combinations (for example CdTe, Ge, InGaAs, Si) which are used for the detection of radiation (electromagnetic and particle radiation, in particular X-ray and EUV radiation) based on solids are used as substrates for an optical element according to the invention are suitable, in particular high-resistance silicon wafers, grown according to the "floating zone" (FZ) method in question. In particular, these substrates must be of high quality, highly crystalline and virtually defect-free, and have a comparatively high specific resistance (low substrate doping). The substrate may have a doping (n- or p-type).

The substrate may be subjected to mechanical bending and fixation. The surface on which the nanometer layer system is applied may then have permanent different shapes, depending on the nature of its Task. The surface shape can be one-dimensional concave, convex, or planar, or it can follow a complex mathematical function (parabolic, elliptical).

For the production of a substrate (substrate) suitable for the selectively reflecting component layer, it is possible to use lithographic structuring according to the state of the art in the semiconductor industry. In this case, the structures to be produced, which are imprinted in a mask, are imaged by optical exposure on a substrate coated with a photosensitive lacquer. Subsequent wet-chemical processing of the substrate and subsequent ion implantation enables the targeted, precise generation of structures with high dimensional stability, including gradient and edge-reduced structures, on the substrate. The lithographic process can be repeated several times.

To create a p-n junction, depleted regions are doped by implantation (eg, ion implantation) on both sides of the substrate. For p-type regions, elements from the third main group are used, such as, for example, aluminum, boron, gallium or indium and for n-type regions the elements from the fifth main group, such as, for example, antimony, arsenic or phosphorus. The diffusion as an implantation method is also suitable, but has the disadvantage that the delimited areas can not be placed accurately, and thus higher leakage currents and no optimal noise suppression is achieved.

For electrical contacting at the top and bottom of the substrate are conductive materials such as the chemical elements Al, Ag, Au, Cu, Ga, Pd or element compounds or conductive oxides or polymers used. These electrical contacts may have any shapes (eg, points, lines, rings, surfaces) and may be located at different positions on the substrate.

A further conductive or insulating layer (metal, semiconductor or oxide) may be arranged between substrate and selectively reflecting component layer.

The processed substrate or the optical element can have a surface passivation, which can be realized for example by an SiO ₂ layer.

Various embodiments are in 4 and 5 shown. In addition to spaced electrically conductive structures ( 40 . 41 ) generates on the surface of the substrate by means of ion implantation electrically active regions in the interior of the substrate ( 5 . 6 . 10 In which the radiation transmitted parasitically through the selectively reflecting component layer generates an electrical signal (current) as a result of photoionization, which can then be measured.

In a final step of the lithographic process, to further improve the signal-to-noise ratio, a further resist layer may be applied, exposed and selectively stripped, such that the selectively reflective component layer without a mechanical mask is nanometer-accurate and technically easily supported on the substrate by physical (e.g. B. by means of magnetron sputtering or laser beam evaporation) or chemical deposition methods (eg., By sol-gel method) can be positioned. This allows an uncomplicated and exact coating of the substrate in that the component layer is first applied over the entire surface and later targeted, by detachment of the paint layer, with the receipt of a specific geometry can be replaced (lift-off method). This allows for an additional (mechanical) mask during application of the. are selectively omitted reflective component layer. This has the advantage that the vacuum in the coating system for applying the selectively reflecting component layer does not deteriorate, which would result in a lower quality (eg increase of the surface roughnesses due to defects, non-exact layer thickness variations) of the component layer. Instead, the coating quality can be obtained and nanometer-accurate positioning is possible.

The invention makes it possible, not only in the field of X-radiation, but also in the field of EUV radiation, by a highly efficient detection property, and thus a dramatically improved signal-to-noise ratio, the adjustment operations of the optical element of the patents DE 10 2007 033 210 B4 and DE 10 2007 063 682 B3 to accelerate strongly (by at least a factor of 90) with respect to the incident radiation and at the same time to significantly (at least a factor of 10) improve the positioning accuracy of the optical element.

Description of the pictures

In 1 are the diode characteristic of the inventive structure of the optical element for the detection of. Radiation (a) compared to the execution of patent DE 10 2007 033 210 B4 (b) shown. It can be seen at a reverse voltage U _S = 0 V reduced by a factor of 69 dark current (leakage current). The factor assumes considerable values when a blocking voltage U _{S is} applied. Here, the structure according to the invention already shows a factor of 100 reduced by U _S = -2 V. Dark current. If U _{S is} further increased, the factor can continue to increase significantly. This can be concluded from the linear-like course of the measurement curve shown in (c) (extended range of the measurement curve (a)) compared to the non-linear-like course of the measurement curve in (b). Thus, it becomes possible to detect minute changes of the electric signal and to surely recognize them.

2 shows measured results of the characteristic current profile (a) of the optical element according to the invention as a function of the angle of incidence (Omega, ω) of the X-radiation (b). In the region of the maximum reflection of the X-radiation (ω = 1.3 °, (b)) increasingly more and more X-ray photons are reflected away, so that fewer total charge carriers are generated by the remaining, absorbed X-ray photons. The current signal decreases and finally has a minimum in the Bragg maximum. After passing through the optimum Bragg angle, more X-ray photons enter the substrate and the current signal increases.

3 shows a cross section of the low-noise optical element for detecting radiation by measuring electrical signals (U _S = blocking voltage).

4 shows various embodiments for the front-side contacting ( 40 ) of the low-noise optical element for detecting radiation.

5 shows exemplary embodiments (cross sections) for the low-noise optical element for detecting radiation, wherein between the selectively reflecting component layer (FIG. 1 ) and the substrate ( 2 ) an oxide layer ( 3 ) may be present (variant B) or not (variant A).

6 shows a possible embodiment of the low-noise optical element for detecting radiation ( 20 ) in combination with Peltier elements ( 30 and or 31 and or 32 ) for constant cooling to increase (improve) the signal-to-noise ratio.

7 shows an embodiment of the low-noise optical element for detecting radiation (rear view) with Peltier elements ( 30 . 31 . 32 ) and printed circuit board ( 50 ).

8th shows an embodiment of a printed circuit board ( 50 , Front view), consisting of an electrically non-conductive ( 49 ) and a conductive material ( 51 ), for contacting the substrate or the bottom of the low-noise optical element for the detection of radiation.

9 shows the possible embodiment with a control circuit consisting of a low-noise optical element for the detection of radiation ( 20 ), whereby an ammeter ( 16 ) and the electrical signal is amplified ( 9 ) and digitized ( 14 ), and where a controller ( 17 ) processes the signals and sends them to a control element ( 18 ) for controlling the positioning unit ( 11 ).

10 shows various embodiments of lithographically processed substrates ( 2 ) for the low-noise optical element for detecting radiation, in which the active regions ( 10 ), these include the space charge zone generated by a pn junction ( 10 ), are arranged in a characteristic manner (dot or strip). The contact structures ( 40 ) should at least (in the plane) on one side of the respective active areas ( 10 ) and may be point, line or planar.

11 shows a nanometer multilayer system ( 1 ), consisting of two individual layers ( 12 . 13 ) of different elements (eg W ( 13 ) and Si ( 12 )) or element compounds of different density. Both monolayers repeat n times, where n can assume typical values of 40, 60 or 80.

12 shows an embodiment of the characteristic arrangement of active areas ( 10 ) and corresponding contact structures ( 40 ) on a substrate ( 2 ) for the specific regulation of the optimal settings of the optical element for the detection of radiation. While in the case of correct positioning of the optical element relative to the incident X-ray ( 70 ) all four active areas ( 1' . 2 ' . 3 ' . 4 ' ) provide comparable electrical signals (a), a misalignment (b) leads to significantly different electrical signals of the active regions: only on ( 1' ) and ( 4 ' ) such as ( 2 ' ) and ( 3 ' ) comparable electrical signals would be measurable.

Presentation of the invention

The invention relates to a low-noise optical element for the detection of radiation by measuring electrical signals with the inventive structure in 3 , A selectively reflective component ( 1 ) of the optical element reflects incident radiation ( 70 . 71 ), one part ( 8th ) by an underlying modified substrate or additional metal, semiconductor or oxide layer ( 2 . 3 . 5 . 6 . 10 ) in a back contacted ( 41 ) Substrate ( 2 ) is transmitted. In the photosensitive layer ( 5 . 6 . 10 ) free charge carriers are generated by the electrode structures on the upper side ( 40 ) and at the bottom ( 41 ) flow away and with an ammeter ( 16 ) are measured.

In principle, all materials and combinations (for example CdTe, Ge, InGaAs, Si) which are suitable for the detection of radiation (in particular X-ray and EUV radiation) based on solids are used as substrates for a low-noise optical element according to the invention. in particular high-resistance silicon wafers, grown according to the "floating zone" (FZ) method, in question. In particular, these substrates must be of high quality, highly crystalline and virtually defect-free, and have a comparatively high specific resistance (low substrate doping). The substrate may have a doping (n- or p-type).

The modified / processed substrate may be subjected to mechanical bending and fixation, wherein the fixation z. On an Invar block ( 21 ) by gluing. The surface on which the nanometer layer system is applied may then have permanent different shapes, depending on the nature of its task. The surface shape can be one-dimensional concave, convex, or planar, or it can follow a complex mathematical function (parabolic, elliptical).

The substrate may be p-type or n-type. As dopants, elements of the third main group, for. As aluminum, boron or indium (p-type) or the fifth main group, z. As antimony, arsenic or phosphorus (n-type) may be used.

The substrate may have at least one electrically conductive contact structure and a doped substrate surface (front side), wherein the selectively reflecting component layer (FIG. 1 ) is applied at least above the doped substrate surface and possibly a metal, semiconductor or insulator layer therebetween ( 3 ) and finally (on the back of the substrate) with an electrically conductive back contact ( 41 ), wherein at the contact structure and the back contact the connections for the current measuring device ( 16 ) available.

Current measuring devices for measuring a current signal generated by the radiation absorbed in the selectively reflecting component layer and / or the substrate may be connected to predetermined electrically conductive layers of the selectively reflecting component layer and / or predetermined contact structures of the substrate.

At least one active region in the substrate with corresponding contact structures is present, active regions in the substrate representing at least one p-n junction. If there is more than one active area, then all active areas can be contacted separately and / or contacted together.

To further reduce the diode leakage current and to protect against electrostatic discharge (ESD), one or more so-called guard rings can be used, which surround the active region and are short-circuited to the cathode.

The incident radiation ( 70 ), a first part as reflected radiation may be applied to the selectively reflecting component layer and / or to the substrate under an angle of incidence ω predetermined by the position of an associated radiation source or another optical element and / or rotational position of the optical element. 71 ) and a second part as transmitted radiation ( 8th ) occur, wherein a third part of the incident radiation is absorbed and the absorbed radiation is electrically registerable due to forming charge carrier movements at least by the connected current measuring device.

The selectively reflective component layer may be a nanometer layer of a solid or a nanometer multilayer system of solids. Such a layer system can be produced reproducibly by means of physical vapor deposition (predominantly laser ablation, magnetron sputtering and ion sputtering) or by wet-chemical synthesis (for example with the sol-gel method).

The nanometer multilayer system ( 11 ) can consist of two individual layers ( 12 . 13 ) of different elements or element compounds, at least consist of materials of different density, for. B. from a silicon layer (or carbon layer, 12 ) in contact with a tungsten layer (or molybdenum or nickel layer, 13 ), wherein either the silicon layer (carbon layer) or the tungsten layer (molybdenum, nickel layer) with the substrate ( 2 ) or a layer additionally present on the substrate (preferably in the nanometer range). Both monolayers repeat n times, where n can assume typical values of 40, 60 or 80. Typical lengths for such X-ray mirrors are, for example, 60 mm, 80 mm, 100 mm, 120 mm and 150 mm, whereby significantly larger mirrors up to 1 m are possible.

The selectively reflecting component layer may be covered with an applied electrically conductive layer whose layer thickness is preferably in the nanometer range and which has a connection to the current measuring device.

The electrically conductive contact structures may consist of metal, metal alloys and / or conductive oxides or polymers.

The use of the optical element can be provided as a monochromator or as the X-ray assembling unit for X-ray analysis devices or as deflecting / imaging mirrors in devices of EUV lithography. It is also possible for two optical elements according to the invention to be arranged at an angle of 90 ° to one another and fixed to one another in the manner of a Kirkpatrick-Baez optical system ( US 6041099A ).

By means of the low-noise optical element according to the invention for the detection of radiation, on the one hand, a crystal or the nanometer multilayer system for the detection of radiation can be assembled. This can be made possible by the assumption of associated electronic solid state properties by electrical contacting and the thus possible detection of the charge carriers formed by photoionization in active regions. On the other hand, and this does not make any demands on the electronic properties of crystal and nanometer multilayer systems, substrates underlying these component layers, which carry the reflective crystal layer or nanometer multilayer, and at the same time the derivation of an electrical signal by suitable lithographic structuring, the reflected by these components transmits part of the radiation, allow to be used.

The basic idea of the invention is based on the circumstance that the constructive interference, that is to say the excitation of a reflex, is associated with the formation of standing wave fields in the substrate, crystal or layer system and thus absorbed in the substrate, crystal or the nanometer multilayer as well as by this transmitted radiation is characteristically modulated angle-dependent and due to the derived signal, a feedback for adjusting the reflection condition or characteristic settings is possible.

The photosensitive layer ( 5 ) may be doped with a pentavalent (n-dopant, eg antimony, arsenic or phosphorus) or trivalent element (p-type doping, eg aluminum, boron or indium) and is produced by a lithographic process using the Ion implantation generated.

The crystal or the nanometer multilayer system ( 1 ) is applied by chemical or physical deposition methods, wherein the nanometer-accurate positioning is carried out by an additional lithographic process step after the lift-off process, in which the processed substrate provided in a final step with a photosensitive coating, this suitably exposed and finally is partially removed. After the deposition of the selectively reflecting component layer, in a last step the remaining photoresist is removed and, at the same time, the excess material of the selectively reflecting component layer is removed.

The optical element according to the invention may have additionally attached Peltier elements, which cause a further signal amplification and a noise reduction by constant cooling of the optical element according to the invention.

It can, as in 3 respectively. 5 is shown, the selectively reflecting component layer ( 1 ) on a substrate ( 2 ) and are in close contact with the substrate or, as in 5 shown to have an intermediate layer that does not belong to the selectively reflective component layer.

At the predetermined layers of the selectively reflecting component layer ( 1 ), as in 3 is shown, there are two spaced apart terminals on which at least a current measuring device ( 15 respectively. 15 . 16 ) for measuring one of the in the selectively reflecting component layer ( 1 ) and / or the substrate ( 2 ) can be connected to the absorbed X-ray intensity, the substrate ( 2 ) with the selectively reflecting component layer ( 1 ) dependent on the angle to the incident radiation (X-ray or EUV radiation) ( 70 ) is arranged relatively movable.

The incident radiation ( 70 ) can be applied to the selectively reflecting component layer under an angle of incidence ω predetermined by the position of an associated radiation source (not shown) and / or the rotational position of the optical element ( 1 ), whereby the incident radiation ( 70 ) after appropriate interaction with the selectively reflecting component layer ( 1 ) and / or the substrate ( 2 ) a first part as reflected radiation ( 71 ) and a second part as transmitted radiation ( 8th ), wherein a third part of the incident radiation ( 8th ) is absorbed and the absorbed radiation due to a forming charge carrier movement at least by the connected current measuring device ( 16 ) is electrically recordable.

The optical element ( 20 ) can, as in 3 shown with a device ( 11 ) for adjusting a position of a reflection condition of the component layer ( 1 ) for a particular wavelength or band of wavelengths (the fixation can be done, for example, mechanically or magnetically), which the selectively reflecting component layer ( 1 ) or the substrate ( 2 ) with the selectively reflecting component layer ( 1 ) and with which the angle-dependent reflection condition position of the component layer ( 1 ) to the incident radiation ( 70 ) is adjustable for a particular wavelength or a wavelength band.

It may be an edition ( 21 ), on which the selectively reflecting component layer ( 1 ) and / or the substrate ( 2 ) and with which the adjustment of the reflection condition of the selectively reflecting component layer ( 1 ) due to the current measuring device ( 16 ) measured electrical signal by a controlled rotation and / or tilting about horizontal and / or horizontal axes of the support ( 21 ) by means of an intended device ( 11 ) can be made to change at least the angle of incidence ω.

The optical element ( 20 ) associated current measuring device ( 16 ) can optionally be an interconnection, as in patent no. DE 10 2007 033 210 B4 described, done or as in 9 shown, wherein an amplifier may be connected downstream, which amplifies the electrical signal ( 9 ) and digitized ( 14 ), and where a controller ( 17 ) processes the signals and sends them to a control element ( 18 ) for controlling (rotation and / or tilting) the positioning unit ( 11 ), to change the angle of incidence ω or other degrees of freedom.

Alternatively, the adjustment for correct positioning of the optical element can also be done manually by a mechanical positioning unit. The regulator ( 17 ) and the control member ( 18 ) could then be replaced by an optical or acoustic signal display after the optimal setting could be carried out.

The with the optical element ( 20 ) related device ( 11 ) for changing at least the selectively reflecting component layer ( 1 ) associated with the angle of incidence ω may have a controlled by piezo elements piezo tilting table for rotation or tilting about horizontal and / or horizontal axes. Additional degrees of freedom can be set by additional piezo actuators.

The optical element for the detection of radiation ( 20 ) can also be in a housing, as in DE 10 2006 015 933 B3 described, which allows a multi-axis adjustment of optical elements by an eccentric device.

The selectively reflecting component layer ( 1 ) may be formed as a nanometer layer of a solid or as a nanometer multilayer system of solids.

The selectively reflecting component layer ( 1 ) but can also be or contain a crystalline layer.

The selectively reflecting component layer ( 1 ) can also be covered with an applied electrically conductive layer, the layer thickness is preferably in the nanometer range and with the current measuring device ( 15 . 16 ) is contacted.

The electrically conductive contact structures ( 40 . 41 ) may consist of metal, metal alloys and / or conductive oxides / polymers.

The substrate ( 2 ) can, as in 3 is shown to be a semiconductor structure having at least one pn junction region.

In the area between the edition ( 21 ) and the positioning unit ( 11 ) ( 3 . 6 ) as well as circulating ( 7 ) can be used to reduce thermally generated charge carriers, a selectively reflecting component layer ( 1 ) and / or the substrate ( 2 ) and / or the edition ( 21 ) cooling component-like device ( 30 . 31 . 32 ) can be arranged.

The cooling component device ( 30 . 31 . 32 ) may consist of Peltier elements.

The use of the optical element ( 20 ) may be provided in arrangements, in particular as monochromators for X-ray analysis devices or as imaging mirrors for EUV lithography.

In the following, in addition to further individual embodiments, the mode of operation of the optical element according to the invention ( 20 ) explained with reference to other figures.

In the case shown ( 3 ) can from the, with the involvement of the back contact ( 41 ) of the substrate ( 2 ), by predetermined electronic circuitry derived signals (eg, current or resistance) to the through the layer system ( 1 ) transmitted ( 8th ) - and thus not reflected by constructive interference forward ( 71 ) - radiation intensity are closed. There is a particular advantage of the invention is that even in the case of polychromatic primary radiation excitation of constructive interference for a narrow wavelength band leads to a measurable reduction in the transmitted integral intensity and thus z. B. a nanometer multilayer system ( 1 ), which as Monochromator operates on the basis of this signal, to the Bragg condition (or other characteristic situations related to it) can be adjusted.

This in 3 illustrated embodiment describes a tungsten-silicon nanometer multilayer system ( 1 ), which on the substrate ( 2 ), which acts as a PIN diode, is deposited. For the realization of a PIN diode, as in 3 is shown, a doping layer ( 5 . 6 ) structured by means of lithography, advantageously arranged directly in a silicon substrate (high-resistance FZ-Si wafer, n-doping), as well as also conductive contact structures ( 40 . 41 ) applied. For the back contact also a conductive material (eg metal) is used. Already when measuring with the sockets ( 40 . 41 ) connected ammeter ( 16 ) can be closed without additional electrical voltage on charge carriers formed in the conduction band of the PIN diode due to photoabsorption. To improve the signal-to-noise ratio, a voltage source between the terminals ( 40 . 41 ), which generates an additional voltage, which increases the detection efficiency of the generated charge carriers by the current measuring device (FIG. 16 ) causes.

The mode of operation of the PIN diode-like construction according to the invention can be illustrated by means of a simple band model. In this case, an incident photon lifts electrons from the semiconductor valence band into unoccupied states of the conduction band and / or leaves an atom ionized due to the photoelectric effect. Free charge carriers (electron-hole pairs) are generated. These electron-hole pairs are separated and flow in the space charge zone which is formed between the p and n regions and can be increased by an additional blocking voltage applied to the diode, when the contact is electrically connected between the contact structures (FIG. 40 ) and the back contact ( 41 ) is closed, off.

For the X-ray, the absorption is in the total thickness of the substrate ( 2 ) relevant. Due to the use of grazing incidence and thus long beam paths, standard wafers ( 2 ) of 0.3 mm or 0.5 mm thickness usually already "infinitely thick" substrates.

The 2 shows the reflected beam intensity and the photocurrent for the optical element according to the invention ( 20 ) to 3 with a substrate ( 2 ) obtained using monochromatic characteristic radiation of an X-ray tube (not shown) with Cu anode. By comparing both curves, the reflection of the reflectivity situation of the characteristic radiation (Cu-Kα radiation, total reflection at the substrate ( 2 )) in the substrate ( 2 ) and in the current measuring device ( 16 ) received electrical signal recognizable. Thus, the possibility of obtaining a criterion for the adjustment of the reflection condition of the optical element according to the invention ( 20 ) detected from the current signal and thus detected a charge carrier movement. If this signal for the control of a - the current measuring device ( 16 ) supplementary device ( 11 ) used to change the angle of incidence ω, z. B. a piezo tilting table as in 9 illustrated, wherein the principle example of a dynamic control to the maximum intensity of reflection intensity, as in the patents DE 10 2007 033 210 B4 and DE 10 2007 063 682 B3 can be applied, so can a closed loop by means of the device in 9 be realized, which z. B. the tracking of the reflection condition for vibrations, etc. is possible.

The continuous measurement of the electrical signal allows the constant qualitative and quantitative characterization of the radiation source or the recording of the time course of the intensity of the radiation used and the verification of the setting of the optics.

For the selectively reflecting component layer ( 1 ) of the optical element ( 20 ), as in 3 in two connection examples ( 15 . 16 ), a detection of incident radiation and adjustment to the reflection condition are performed.

The optical element according to the invention ( 20 ) can be assigned beyond the simple electronic circuits, as described in the exemplary embodiments, also more expensive amplifier circuits, with a mode of operation with additional applied external electrical voltage (in the reverse direction) can be used. The latter can improve (increase) the signal-to-noise ratio. Instead of the nanometer multilayers ( 1 ), alternatively crystalline layers (Bragg reflection at the lattice planes) with sufficient transmittance can be provided as X-ray optical elements.

The optical element according to the invention can be accommodated in a housing which is protected against external influences, in particular atmospheric humidity, atmospheric oxygen, ozone. It may be designed vacuum-tight and / or light-tight.

Advantages over the prior art

For high-precision measurement, analysis and manufacturing results, it is necessary to have a very stable radiation source. use or their Fluctuations in the useful intensities, for example by day / night cycles, by room temperature changes, by aging effects of the source or by electronic (mains) fluctuations during operation, eg. B. of X-ray analysis equipment to record with, so in retrospect control of the operation and even a subsequent correction in case of deviations / errors is possible.

The invention makes it possible, not only in the field of X-radiation, but also in the field of EUV radiation, by a highly efficient detection property and thus a dramatically improved signal-to-noise ratio, the adjustment operations of the optical element of the patents DE 10 2007 033 210 B4 and DE 10 2007 063 682 B3 with respect to the incident radiation to accelerate significantly (by at least a factor of 90) and at the same time to improve the positioning accuracy significantly (by at least a factor of 10) or automated, high-precision setting operations of, for example DE 10 2004 062 289 B4 EUV level.

By means of the invention, on the one hand, the signal strength is increased by at least a factor of 90 compared with existing systems and the electronic noise, dark current and leakage currents are drastically reduced by a factor of at least 69.

Possible further advantageous features over representation of the invention

The optical element according to the invention can be cooled by means of combination with Peltier elements to increase the signal-to-noise ratio.

The positioning unit can consist of a combination of subunits of different degrees of freedom: a rotation unit (rotation about normal of the optical element), a tilting unit (tilting by angle ω, angle with respect to the surface of the optical element and incident radiation), a tilting unit (tilting by angle χ , Angle for tilting about the direction of the incident / reflected beam), a translating unit (translation perpendicular to the beam direction, vertical and horizontal). The rotation and translation units can be piezoactuators or micrometer screws (also motorized).

The optical element according to the invention can be accommodated in a housing.

Furthermore, bonded wires and / or printed circuit boards can be used.

The optical element can be used as a scanner, for. As X-ray or EUV scanners are used. Here, the positioning can perform a specific, even programmable sequence of movements, which can position the X-ray or EUV beam targeted to an object, eg. As for the observation of dynamic or in-line processes, with the requirement of rapid Einstrahlwinkeländerungen over relatively large distances. The advantage of this arrangement with a deflectable for X-ray and EUV radiation mirror is the low inertia of the system and its small size, which is interesting, for example, for portable devices.

The optical element for detecting radiation can also be used for interferometric applications in which semi-transmissive radiation mirrors are used, which must be positioned with high precision and constantly monitored. The advantage here lies in the simple expediency of an interferometer without additional, the exact positioning of the mirror-controlling detector and the constant verifiability of the settings or their correctability.

Embodiment (s)

The invention will be explained in more detail below in various embodiments with reference to exemplary embodiments.

3 shows the optical element according to the invention for the detection of incident EUV or X-radiation ( 70 ), by measuring current signals ( 16 ) in cross section. This consists at least of a high-impedance substrate ( 2 ) with an adhesive, passivating oxide layer ( 3 ) and a selectively reflecting component layer ( 1 ) and has at a predetermined distance connections ( 40 . 41 ) on which at least one current measuring device ( 16 ) for measuring one in the doped regions ( 5 . 6 ) as well as in the field ( 10 ) absorbed beam intensity ( 8th ) is connected and wherein the selectively reflecting component layer ( 1 ) for setting the reflection condition ( 70 . 71 ) of the component layer ( 1 ) for a particular wavelength relatively movable by a positioning unit ( 11 ) is arranged.

In the 4 are possible execution of the surface contacts ( 40 ) of the substrate ( 2 ) for measuring electrical signals. These can include area, ring, line and point structures.

5 shows two embodiments for the optical element according to the invention in cross section. Variant A does not have, variant B against it an additional oxide layer ( 3 ) between substrate ( 2 ) and component layer ( 1 ) on.

The optical element according to the invention may have additionally attached Peltier elements, which cause a further signal amplification and a noise reduction by constant cooling of the optical element according to the invention ( 6 . 7 ).

A possible back contact ( 41 ) on the substrate ( 2 ) is in 8th shown, with a correspondingly structured printed circuit board z. B. can be attached to the substrate with a conductive adhesive and the electrical lines are fastened to it.

In 10 are various embodiments of lithographically processed substrates ( 2 ) for the low-noise optical element for detecting electrical signals in which the active regions ( 10 ), these include the space charge zone generated by a pn junction ( 10 ), are arranged in a characteristic manner (dot or strip). Suitable combinations of the examples shown as well as asymmetric arrangements (relative to the substrate or to the selectively reflecting component layer) may also be useful. The contact structures ( 40 ) should at least (in the plane) on one side of the respective active areas ( 10 ) and may be point, line or planar. Due to the spatial sensitivity thus generated conclusions about the misalignment regarding the individual degrees of freedom can be drawn and the correction of the optimal settings can be carried out specifically and thus quickly.

12 shows an embodiment of the characteristic arrangement of active areas ( 10 ) and corresponding contact structures ( 40 . 1' . 2 ' . 3 ' . 4 ' ) on a substrate ( 2 ) for the specific regulation of the optimal settings of the optical element for the detection of radiation. While in the case of correct positioning of the optical element relative to the incident x-ray beam ( 70 ) all four active areas ( 1' . 2 ' . 3 ' . 4 ' ) provide comparable electrical signals (a), a misalignment (b) leads to significantly different electrical signals of the active regions: only on ( 1' ) and ( 4 ' ) such as ( 2 ' ) and ( 3 ' ) comparable electrical signals would be measurable.

What should be protected?

Specifically, the following should be protected:
On the basis of (lithographically) processed implant-processed and surface-passivated substrates produced low-noise optical element for the detection of radiation, in particular X-ray or EUV radiation, by means of electrical signals,
consisting of at least one on a substrate ( 2 . 3 . 40 . 5 . 6 . 10 . 41 ), radiation, in particular X-ray or EUV radiation, selectively reflecting layer ( 1 ) containing at least two nanolayers ( 1 ) contains different density and in which the selective reflection of the radiation takes place at least after the Bragg reflection condition, and
having spaced apart, with electrically conductive structures ( 40 . 41 ) in associated connections to which at least one current measuring device ( 16 ) for measuring at least the selectively reflected component layer ( 1 ) transmitted radiation ( 8th ) in the radiation-sensitive substrate regions ( 5 . 6 . 10 ) is connected and the radiation-sensitive areas represent a pn junction,
wherein the selectively reflecting component layer ( 1 ) in conjunction with the substrate ( 2 . 3 . 40 . 41 . 5 . 6 . 10 ) for adjusting the component layer ( 1 ) given Bragg reflection condition for a particular wavelength or a wavelength band angle-dependent to the incident radiation ( 70 ) is movably arranged and
wherein, due to the measured current signal, feedback is possible for setting reflection conditions.

LIST OF REFERENCE NUMBERS

1

Selective reflective component layer

2

substratum

3

oxide

40

Front contact for the derivation of the electrical signals

41

Rear contact for the derivation of the electrical signals

5

p / n-doped substrate region

6

n / p-doped substrate region

70

Incident radiation

71

Reflected radiation

8th

Transmitted radiation

9

amplifier

10

Space charge region

11

positioning

12

Nanometer layer of low density, e.g. As silicon or carbon

13

Nanometer layer of high density, z. As molybdenum, tungsten or nickel

14

Analog to digital converter

15

Current measurement device

16

Current measuring device (*)

17

Controller (eg computer + control software)

18

Control element (eg motor driver)

19

voltage source

20

Low-noise optical element for the detection of radiation

21

metal back

30, 31, 32

Peltier element

49

Non-conductive areas

50

PCB for contacting (front / back)

51

Conductive areas for contacting

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19833524 A1 [0005, 0011]
• DE 4407278 [0005]
• DE 102004062289 B4 [0008, 0100]
• DE 102007033210 B4 [0015, 0016, 0022, 0023, 0024, 0025, 0026, 0027, 0028, 0040, 0041, 0077, 0094, 0100]
• DE 102007063682 B3 [0016, 0040, 0094, 0100]
• US 6041099 A [0066]
• DE 102006015933 B3 [0080]

Cited non-patent literature

• G. Lutz, Semiconductor Radiation Detectors, Springer-Verlag Berlin / Heidelberg, 1999 [0024]

Claims (12)

Low-noise optical element for detecting radiation by means of electrical signals, comprising a substrate ( 2 ), on which at least two spaced-apart contacts are applied and on the substrate at least one selectively reflecting component layer is applied, characterized in that the substrate ( 2 ) was processed prior to applying the component layer with an implantation method to produce radiation sensitive areas for generating the electrical signals that are dissipated through the contacts. Low-noise optical element according to claim 1, characterized in that the substrate ( 2 ) is high impedance. Low-noise optical element according to claim 1, characterized in that the processed substrate ( 2 ) has a characteristic bend. Low-noise optical element according to claim 1, characterized in that the substrate ( 2 ) on a fastener ( 21 ) is applied, wherein the fastener ( 21 ) is preferably designed as a metal backing. Low-noise optical element according to claim 1, characterized in that the processing implantation method, the ion implantation, is preferably the implantation of Ga, P, B ions. Low-noise optical element according to claim 1, characterized in that the selectively reflecting component layer for X-ray or EUV radiation has at least two layers of different density, which repeat n times, preferably n is 40 or 60 or 80. Low-noise optical element according to claim 1, characterized in that the surface or individual regions of the surface of the low-noise optical element are structured, preferably lithographically structured, particularly preferably in the sense of a pn junction. Low-noise optical element according to claim 1, characterized in that individual contacts can be locally structured differently, the preparation is preferably carried out lithographically. Low-noise optical element according to claim 7, characterized in that measuring devices of the electrical signals can be attached to the contacts. Low-noise optical element according to claim 1, supplemented by a positioning element in order to be able to mechanically adjust the spatial position. Low-noise optical element according to claim 1, characterized in that Peltier elements are mounted on the low-noise electrical element for cooling. Use of the low-noise optical element, wherein the electrical signals discharged via the contacts can be used to set the reflection conditions.

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