Multi-module photon detector and use thereof

Abstract

The invention relates to a photon detector (10), in particular an x-ray detector, in the form of a measurement finger, which extends along a detector axis (23) and has a detector head (11) at a first end of the measurement finger, wherein the detector head (11) comprises a plurality of at least two detector modules (22), each comprising a sensor chip (12) sensitive to photon radiation (14), in particular x-radiation, said sensor chip having an exposed end face (13) and a face facing away from the end face (13), wherein the detector modules (22) are arranged around the detector axis (23) in a plane (24) extending orthogonally to the detector axis (23).

Claims

1. A photon detector (10), having the form of a column-like measurement finger which extends longitudinally along a detector axis (23), the photon detector comprising: a detector head (11) provided at a first end of the measurement finger, wherein the detector head (11) comprises a plurality of at least two detector modules (22), each comprising a sensor chip (12) sensitive to photon radiation (14), said sensor chip having an exposed end face (13), wherein the detector modules (22) are arranged around the detector axis (23) in a plane (24) extending orthogonally to the detector axis (23), at least a part of the sensor chips (12) being inclined relative to the plane (24) extending orthogonally to the detector axis (23), such that said sensor chips (12) have an angle of inclination of within a range from 10 degrees (10°) to less than 90 degrees (90°) between the end face (13) of the sensor chip (12) and the detector axis (23) in the viewing direction of the X-ray detector (10), and a housing (20) having the form of a column extending longitudinally along the detector axis (23), wherein the housing (20) accommodates the detector head (11) including the at least two detector modules (22).

2. The photon detector (10) according to claim 1, wherein the detector modules (22) have an axially symmetric arrangement relative to the detector axis (23).

3. The photon detector (10) according to claim 1, wherein the angle of inclination of the sensor chips (12) relative to the detector axis (23) is within a range from 20 degrees (20°) to less than 80 degrees (80°).

4. The photon detector (10) of claim 1, wherein the number of detector modules (22) is 2 to 12.

5. The photon detector (10) of claim 1, wherein each of the detector modules (22) further comprises a printed circuit board (15) which is arranged on the face of the sensor chip (12) facing away from the end face (13) and connected in a signal-conducting manner to the sensor chip (12).

6. The photon detector (10) of claim 1, wherein each of the detector modules (22) further comprises an active cooling element (16), in particular a thermoelectric cooling element.

7. The photon detector (10) of claim 1, wherein each of the detector modules (22) further comprises a heat-conducting base, said heat-conducting bases of the detector modules (22) being in thermal contact with a common means for heat removal of the detector (10) or with a common active cooling element of the detector (10).

8. The photon detector (10) of claim 1, further comprising at least one collimator (19) arranged upstream of the individual sensor chips (12) or arranged upstream of all said sensor chips.

9. The photon detector (10) of claim 1, further comprising at least one window (21) arranged upstream of the individual detector modules (22) or arranged upstream of all said detector modules, said window being permeable to the photon radiation (14).

10. The photon detector (10) of claim 1, wherein the sensor chips (12) are formed as silicon drift detectors (SDD).

11. The photon detector (10) of claim 1, wherein the end faces (13) of the sensor chips (12) independently of each other have a surface area within a range from 2 mm.sup.2 to 100 mm.sup.2.

12. A use of a photon detector (10) according to claim 1 for energy-dispersive X-ray detection (EDX) within an electron microscope (25, 32).

13. The use according to claim 12, wherein the electron microscope is a transmission electron microscope (32) and the X-ray detector (10) is arranged with its detector axis (23) substantially in a sample plane.

Description

(1) In the following, the invention will be explained in detail using some embodiments and the accompanying drawings. The figures show:

(2) FIG. 1 an X-ray detector in accordance with the state of the art in a sectional view;

(3) FIG. 2 an X-ray detector in accordance with the present invention in a first embodiment in a sectional view;

(4) FIG. 3 an arrangement of an X-ray detector according to FIG. 2 within a scanning electron microscope (SEM);

(5) FIG. 4 an X-ray detector in accordance with the present invention in a second embodiment in a sectional view;

(6) FIG. 5 an arrangement of an X-ray detector according to FIG. 4 within a transmission electron microscope (TEM) and

(7) FIG. 6 an example of a photon spectrum recorded using an arrangement according to FIG. 5.

(8) The following description relates to an X-ray detector, specifically an energy-dispersive X-ray detector (EDX detector). It is to be understood, however, that all explications also apply to detectors sensitive to other spectral ranges.

(9) The fundamental design of an X-ray detector 10′ in accordance with the state of the art according to FIG. 1 has already been presented in the introduction.

(10) FIG. 2 shows an X-ray detector 10 according to a first embodiment of the present invention.

(11) The core element of the detector 10 is a sensor head 11 arranged at a front end of the detector. The sensor head 11 according to the present invention has a plurality of detector modules 22. In the given example there are four detector modules 22, of which only two are visible in the selected representation. Each individual detector module 22 comprises a sensor chip 12, which is a semiconductor element sensitive to X-radiation that is preferably designed as a silicon drift detector (SDD). The end faces 13 (also referred to as active surfaces) of the sensor chips 12 are exposed such that they can be exposed to photon radiation, in particular X-radiation, indicated as 14. Each of the detector modules 22 further comprises a printed circuit board 15 which is arranged on a face of the sensor chip 12 facing away from the end face 13, said printed circuit board having a signal-conducting connection to the respective sensor chip 12. The printed circuit board has bonding islands connected via bonding wires to contact connections for the purpose of transmitting the recorded signals (bonding islands, bonding wires and contact connections not shown here). To achieve a miniaturization of the X-ray detector, the printed circuit boards and the so-called bonding can be designed advantageously in accordance with DE 10 2008 028 487 A. The bonding is preferably applied only on two opposite sides of the printed circuit board.

(12) According to the example shown, each detector module 22 further comprises a cooling element 16 for individual active cooling of the sensor chips 12, said cooling element being arranged on the side of the printed circuit board 15 facing away from the sensor chip 12. The cooling elements 16 are preferably designed as thermoelectric cooling elements (Peltier elements).

(13) The sensor chip 12, the printed circuit board 15 and the cooling element 16 can further be mounted on a bottom plate that is not shown.

(14) The modules 22 forming the sensor head 11 are tightly bolted, plugged in or soldered via a solder connection 18 to the means for heat removal 17, in particular via the base of said modules which is not shown. The means for heat removal 17 comprises a heat-conducting material such as copper or is built as a so-called heat pipe and serves substantially to remove heat (passive cooling element).

(15) A collimator 19 can be optionally arranged in front of the sensor chip 12, said collimator shielding the sensor chip 12 from secondary photons. In addition, a magnetic electron trap can be optionally arranged in front of the sensor head 11, said magnetic electron trap shielding from stray electrons of the electron microscope. The magnetic electron trap can be advantageously designed in accordance with DE 10 2008 014 578 A.

(16) If the X-ray detector 10 is not designed as an open system but—as illustrated—as a closed system, the aforementioned components can be enclosed by a housing 20 which has a window 21 permeable to X-radiation located at its front end. Alternatively, the individual modules could also be protected by individual windows.

(17) In a preferred embodiment of the present invention, the detector 10 can be made of materials selected from low-interference materials in accordance with DE 10 2009 026 946 A, in particular from materials with a magnetic permeability value μ.sub.r that is smaller than 1.5. This could apply in particular to the materials used for the contact pins, the bottom plate, the housing 20, the window 21, any adhesive and barrier layers used and the solder connection 18. Suitable materials are designated in the aforementioned publication.

(18) It is furthermore possible to have the detector designed such that it not only detects photon radiation, in particular X-radiation, but also electrons. Such a detector is described in DE 10 2009 024 928 A.

(19) The detector 10 has the shape of a measurement finger which extends longitudinally along a detector axis 23. The detector modules 22 are arranged in a plane 24 on which the detector axis 23 is positioned orthogonally. According to the representation selected in FIG. 2, the plane 24 extends perpendicular to the paper plane. The detector modules 22 preferably have an axially symmetric arrangement relative to the detector axis 23. Therefore they have at least one mirror plane in which the axis 23 is located such that the detector modules 22 are mapped onto themselves if mirrored about the mirror plane.

(20) In the example shown, four sensor chips 12, each with a circular outline (in the view of the photon beam 14), are arranged in a square. However, other outlines can also be used in the context of the present invention.

(21) For further signal processing the detector 10 is equipped with or connected to an amplifier unit that is not shown, said amplifier unit typically having a field-effect transistor (FET) and a preamplifier. The signals recorded with such a detector are used in a spectrometer for further processing into photon spectra. The photon spectra can be measured location-dependently using electron beam scanning in an electron microscope. This is facilitated by imaging, meaning location-dependent, element analysis.

(22) FIG. 3 shows an exemplary arrangement of a detector as illustrated in FIG. 2 within a scanning electron microscope (SEM) 25. The SEM 25 comprises a pole shoe 26 from which a focused electron beam 27 emanates. The electron beam 27 hits the sample to be examined, said sample being held on a sample holder 28 which is arranged on a sample bench 29. The electron beam 27 excites the sample material, resulting in X-radiation 14 being emitted by the sample into all spatial directions. A part of the X-radiation 14 hits the X-ray detector 10 which is installed in a port 30 of a microscope wall 31 of the SEM 25. Here the X-ray detector 10 is arranged such that all sensor chips 12 of the detector modules 22 are facing the front side of the sample irradiated by the electron beam 27.

(23) It must be taken into account that the size of the detector 10 in FIG. 3 is not to scale relative to the electron microscope 25. Instead, the size of the detector 10 is shown exaggerated. Furthermore, the optional housing 20 and the optional window 21 are omitted in FIG. 3.

(24) FIG. 4 shows an X-ray detector 10 according to a further embodiment of the present invention. Matching elements have the same reference symbols and—unless indicated otherwise—the same properties as in FIG. 2.

(25) While the sensor chips 12 of the X-ray detector shown in FIG. 2 are arranged orthogonally to the detector axis 23, the sensor chips 12 of the X-ray detector 10 according to FIG. 4 have an inclined arrangement relative to the detector axis 23 or the plane 24. In the example shown, the angle of inclination between the end face 13 of the sensor chip 12 and the detector axis 23 is uniformly 45°. However, deviations are possible where the angles of inclination of the individual sensor chips 12 differ from each other or where one part of the sensor chips is arranged orthogonally according to FIG. 2 and another part of the sensor chips is in an inclined arrangement according to FIG. 4.

(26) Preferably, the sensor chips 12 are inclined and aligned symmetrically about the detector axis 23 or the X-radiation 14 such that the totality of their individual end faces 13 approximates a spheroid or paraboloid.

(27) FIG. 4 shows no collimators; however, such collimators can be optionally present, either in the form of one individual collimator for each of the detector modules 22 or as a single common collimator or as one or more collimators for one or several of the modules.

(28) FIG. 5 shows the arrangement of the sensor according to FIG. 4 in a transmission electron microscope (TEM) 32 (the relative sizes are again not to scale). Here, unlike in FIG. 4, the housing 20 and the window 21 of the detector 10 are not shown; shown, however, are two collimators 19 for the individual modules.

(29) Apart from its upper pole shoe 26, the TEM 32 also has a lower pole shoe 33, with the sample holder 28 being arranged between the two pole shoes 26 and 33. The electron beam 27 traverses through the sample and exits through the lower pole shoe 33 for further electron microscopic analysis.

(30) According to FIG. 5, the X-ray detector 10 is arranged within the TEM 32 such that its detector axis 23 is substantially in the plane of the sample held on the sample holder 28. In this manner not only the X-radiation originating from the front side of the sample irradiated by the electron beam 27 but also the X-radiation originating from the back side of the sample can be recorded. A further advantage of this arrangement is that no active sensor surface is present in the plane of the sample where the X-radiation that has been altered only by the sample holder and the bulk portions of the sample and interferes with the measurement is emitted. Instead, the detector 10 has a gap between the detector modules 22 in this plane. Since the unwanted radiation components can be kept away from the active sensor chip surfaces in this manner, an improved signal-to-noise ratio results.

(31) Deviating from the arrangement illustrated in FIG. 5, the X-ray detector 10 according to the present invention can also be arranged within a transmission electron microscope such that it is exclusively located on the side of the sample facing the electron beam 27 or exclusively located on the side of the sample facing away from the electron beam 27.

(32) The embodiment of the X-ray detector according to the present invention with at least two detector modules 22 facilitates different approaches to reading out and further processing of the signals recorded. According to a first option, the signals recorded by all modules 22 can be read out jointly in the form of mixed signals. Alternatively it is possible to read out the signals recorded by each module individually, which can be done either at the same time (in parallel) or one after the other (sequentially). In the case of more than two detector modules 22, the signals recorded by any combination of two or more modules 22 can be read out jointly in aggregate form, which again can be done either at the same time (in parallel) or one after the other (serialised).

(33) The detector according to FIG. 4 has been tested in a transmission electron microscope using an arrangement according to FIG. 5. During the test, the signals recorded by the detector module 22 arranged on the side of the sample facing the electron beam 27 were evaluated separately from the signals recorded by the module 22 arranged on the side of the sample facing away from the electron beam 27. FIG. 6 shows the energy-dispersive X-ray photon spectra obtained in this manner. There the X-ray spectrum recorded at the front side of the sample appears in black and the spectrum recorded at the back side of the sample in grey.

(34) It can be seen that in particular the background radiation recorded in the low-energy range at the back side of the sample (grey) forms a larger part of the spectrum, as was to be expected, than at the front side of the sample (black). When measuring at the side of the sample facing the electron beam, the element sensitivity, meaning the peak-to-background ratio, is better than at the back side of the sample, in particular in the low-energy range. It can also be seen that more scattered radiation due to backscattered electrons hitting the upper pole shoe of the microscope is recorded at the side of the sample facing the electron beam, leading to the occurrence of peaks of the materials iron (Fe) and cobalt (Co) of the pole shoe.

REFERENCE SYMBOL LIST

(35) 10′ X-ray detector in accordance with the state of the art 10 X-ray detector in accordance with the invention 11 sensor head 12 sensor chip 13 end face 14 photon beam/X-ray beam 10 15 printed circuit board 16 cooling element 17 means for heat removal 18 solder connection 19 collimator 15 20 housing 21 window 22 detector module 23 detector axis 24 plane 25 scanning electron microscope 26 pole shoe 27 electron beam 28 sample holder 29 sample bench 30 port 31 microscope wall 32 transmission electron microscope 33 pole shoe