Method of manufacturing charged particle detector

Abstract

To provide: a substrate-holding apparatus with a sensor device, the sensor device having a substrate layer and a sensitive layer; and a manufacturing method thereof.SOLUTION: A sensor device 120 at least comprises a substrate layer 180 and a sensitive layer 140. A manufacturing method comprises providing a mechanical supporting layer 160, and connecting the mechanical supporting layer 160 to the sensor device 120. After the connection, the sensitive layer 140 is situated between the substrate layer 180 and the mechanical supporting layer 160. By connecting the mechanical supporting layer 160, it is possible to thin the substrate layer 180 for forming a charged particle detector. The mechanical supporting layer 160 forms part of the manufactured detector. The detector can be used in a charged particle microscope, such as a transmission electron microscope for direct electron detection.SELECTED DRAWING: Figure 4b

Description

Technical Field

[0001] Description The present invention relates to a method for manufacturing a charged particle detector, which comprises a sensor device having a substrate layer and a sensitive layer.

Background Art

[0002] Charged particle microscopy is a well-known and increasingly important technique for imaging microscopic objects, particularly in the form of electron microscopes. So far, basic types of electron microscopes have evolved into several well-known devices such as transmission electron microscopes (TEMs), scanning electron microscopes (SEMs), and scanning transmission electron microscopes (STEMs), and further, for example, so-called "dual beam" devices (e.g., FIB-SEM) that additionally employ "machining" focused ion beams (FIBs) enabling assisting actions such as ion beam milling or ion beam induced deposition (IBID) have evolved into various auxiliary types. Those skilled in the art will be familiar with different types of charged particle microscopes.

[0003] In an SEM, irradiation of a sample with a scanning electron beam promotes the emission of "auxiliary" radiation in the form of secondary electrons, backscattered electrons, X-rays, and cathodoluminescence (infrared, visible light, and / or ultraviolet photons) from the sample. One or more components of this emitted radiation can be detected and used for sample analysis.

[0004] In a TEM, an electron beam passes through a sample, and due to the interaction between the sample and the electrons, the beam passes through the sample to form an image. Next, the image is magnified and focused on an imaging device such as a sensor, such as a fluorescent screen, a layer of photographic film, or a scintillator attached to a charge-coupled device (CCD). The scintillator converts primary electrons in the microscope into photons so that the CCD can detect them.

[0005] Recent developments in TEMs involve the use of direct electron detectors. These direct electron detectors can directly detect imaging electrons in the microscope without using a scintillator. Direct electron detectors are based on sensor technology, where electrons directly collide with a lightly doped silicon epi-layer supported on a more highly doped silicon substrate. A passivation layer is provided on top of the epi-layer and includes highly doped wells and readout electronics as well as interconnects. Using this type of direct electron detector, already improved resolution, signal-to-noise (SNR) ratio, and sensitivity can be obtained (McMullan, Faruqi, and Henderson, 2016). This favorable SNR ratio, combined with fast CMOS electronics, enables the counting of individual primary electrons. SUMMARY OF THE INVENTION

[0006] It is an object to provide an improved charged particle detector, particularly an improved direct electron detector, and a method of manufacturing such a detector.

[0007] For this purpose, a method of manufacturing a charged particle detector as defined in claim 1 is provided. The method as defined herein includes the step of providing a sensor device such as an active pixel sensor (APS), the sensor device including a substrate layer and a sensitive layer. The sensor device with the sensitive layer can detect incoming charged particles and is arranged particularly to detect incoming electrons. The substrate layer can be, for example, a highly doped silicon substrate. The sensitive layer can include an epi-layer. A sensor device such as an APS can also include a passivation layer on top of the sensitive layer. In that case, the sensitive layer may be sandwiched between the passivation layer and the substrate layer. The passivation layer can include highly doped wells and readout electronics as well as interconnects.

[0008] According to the method defined herein, the method includes providing a mechanical support layer and connecting the mechanical support layer to the sensor device such that the sensing layer is positioned between the substrate layer and the mechanical support layer. The mechanical support layer may be provided such that the sensing layer is directly adjacent to the mechanical support layer. In other embodiments where the sensor device, such as an APS, includes a passivation layer, the passivation layer is positioned between the sensing layer and the mechanical support layer.

[0009] According to the method defined herein, the method includes a subsequent step of thinning the substrate layer for forming the charged particle detector.

[0010] By providing the mechanical support layer and connecting it to the sensor device, easy thinning of the substrate layer becomes possible. The mechanical support layer provides mechanical support during the thinning process. Due to the use of the mechanical support layer, the vulnerability of the charged particle detector during the thinning process is reduced. In addition, the mechanical support layer enables removal of a significant portion of the substrate layer. In one embodiment, it becomes possible to completely remove the substrate layer. In other words, the mechanical support layer enables the charged particle detector to be back-thinned to the epi layer. Having such a back-thinned detector reduces the contribution of noise from scattered electrons.

[0011] In an advantageous embodiment, the mechanical support layer remains on the charged particle detector after manufacturing. In other words, the mechanical support layer is permanently connected to the sensor device and is not removed to complete the manufacturing process. The connection between the mechanical support layer and the sensor device may be designed such that a permanent connection is maintained or strengthened. By making the mechanical support layer part of the final charged particle detector, the speed of the manufacturing process is improved, and the strength and durability of the charged particle detector are similarly improved.

[0012] As a general rule, the use of a thinner sensor is advantageous, and thus it should be noted that adding a mechanically supportive layer that remains attached - and thereby making the charged particle sensor thicker - seems intuitively contrary. However, the inventors have found that by attaching a mechanically supportive layer to the sensor device and thinning the substrate layer down to the sensing layer, it becomes possible to use the manufactured charged particle detector in a so-called back-illumination mode. In back-illumination, the sensing layer is the outermost layer of the charged particle detector. The sensing layer can be arranged to face the expected incoming flux of charged particles, and the mechanically supportive layer is positioned behind the sensing layer and already reduces the effects of scattering. Thus, the application of the mechanically supportive layer and the maintenance of this layer in the final charged particle detector are not actually disadvantageous because the adverse effects are small enough to compensate for the advantages it provides.

[0013] The maintenance of the mechanically supportive layer is also advantageous when the sensor device includes a sensing layer, a passivation layer including highly doped wells, and electronics and interconnections for readout. In this case, the epi-layer of the sensing layer faces the (expected) incoming flux of charged particles such as electrons. The mechanically supportive layer is oriented away from the incoming flux of charged particles, and the passivation layer is sandwiched between the mechanically supportive layer and the sensing layer. The passivation layer is mechanically protected by the two surrounding layers. Since the passivation layer is not the first layer that incoming charged particles hit and can cause scattering and other undesirable effects, the detection of charged particles can also be performed in a more direct way.

[0014] To prevent the mechanical support layer from affecting the signals detected by the charged particle detector, for example, since backscattered electrons generated from the mechanical support layer may cause issues, in one embodiment, the mechanical support layer comprises a low-Z material. Such low-Z materials may include materials containing, for example, carbon, beryllium, and / or boron. The low-Z material may also include other materials. For example, the low-Z material may also include polymers such as polyethylene (PE), polystyrene (PS), polypropylene (PP), and polycarbonate (PC). Other low-Z materials are also conceivable.

[0015] In an advantageous embodiment, the mechanical support layer comprises a thermally conductive material. Direct electron detectors used in charged particle microscopes typically operate in a vacuum and need to dissipate a thermal output of about 0.2 - 20 W. Heat transfer in a vacuum is known to be a challenge. As the frame rate increases, typically the power consumption also increases. In one embodiment, the sensor device can be back-thinned to a thickness of about 20 - 40 μm. When the sensor device is back-thinned to these dimensions, the cross-sectional area is reduced, and thus the heat flux due to thermal conduction also decreases. In fact, cooling is a major challenge for these back-thinned detectors. For this purpose, in one embodiment, the mechanical support layer can comprise or be made of a thermally conductive material and is arranged to transfer the aforementioned thermal output of 0.2 - 20 W (e.g., by conduction), for example, to a heat sink or at least distribute the thermal output uniformly to prevent hot spots. The thermally conductive material can have a thermal conductivity of at least 500 W / mK, particularly at least 1000 W / mK. The thickness of the mechanical support layer can be, for example, in the range of 10 - 50 μm, particularly similar to the thickness of a back-thinned layer such as about 25 μm. The connection to the sensor device and the properties of the mechanical support layer are such that the mechanical support layer can transfer the aforementioned thermal output through conduction. The charged particle detector can include a heat sink connected to the mechanical support layer and arranged to actively cool, for example, using water cooling and / or Peltier cooling.

[0016] In an advantageous embodiment, the mechanical support layer comprises a low-Z thermal conductive material. In one embodiment, carbon materials such as graphite and carbon fiber composites are used. In one embodiment, pyrolytic carbon is used. In addition to providing support, it offers excellent thermal conductivity (~1950 W / mK) and a very low mass (low-Z). This enables excellent heat transfer from the detector towards the heat sink and minimizes the amount of (undesirable) electron scattering. In this regard, it should be noted that pyrolytic carbon also provides an improvement in thermal conductivity compared to currently used materials. Additionally, since pyrolytic carbon is also a vacuum-compatible material, the resulting charged particle detector can be used in a charged particle microscope. The thickness of the mechanical support layer may be in the range of about 10 - 50 μm, such as about 25 μm.

[0017] To enable the mechanical support layer to function as a thermal conductive material, it is advantageous when the mechanical support layer is in good thermal contact with the sensor device. For this purpose, the method can include the step of connecting the mechanical support layer to the sensor device by an adhesive. The adhesive can in principle be of any type, such as non-reactive (e.g., solvent-based adhesives, permanent or non-permanent pressure-sensitive adhesives, contact adhesives, high-temperature adhesives) or reactive (anaerobic adhesives, multi-part adhesives, premixed adhesives and freeze adhesives, one-component adhesives). In an advantageous embodiment, a liquid or flowable adhesive is used. By using such an adhesive, it is possible to ensure good thermal contact to be established between the sensor device and the mechanical support layer. Using an adhesive that can conform to non-flat surfaces (e.g., as generated in APS) results in good thermal contact and also improves the structural strength of the final direct electron detector.

[0018] In one embodiment, the mechanical support layer is directly connected to at least a portion of the sensitive layer. In other embodiments, when the sensor device includes a passivation layer, the mechanical support layer is directly connected to the passivation layer. The direct connection includes a direct connection where an adhesive is used. The adhesive can have a specific thickness and is present between the mechanical support layer and the layer to which the mechanical layer is directly connected. The direct connection to the relevant layers keeps the sensor relatively compact but also helps with heat dissipation.

[0019] According to one aspect, a sensor device such as an APS having a sensitive layer and a passivation layer, and a mechanical support layer connected to the sensor device such that the passivation layer is positioned between the sensitive layer and the mechanical support layer, a charged particle detector is provided.

[0020] The sensor device of the charged particle detector can consist of a sensitive layer and a passivation layer. The sensitive layer may include or consist of a lightly doped silicon epi-layer. The passivation layer may be connected to the epi-layer. The passivation layer can include highly doped wells and readout electronics as well as interconnections. The sensor device may not include any substrate layer, and in particular, may not include a more highly doped silicon substrate. The sensor device may be based on active pixel sensor (APS) technology such as monolithic active pixel sensor (MAPS) technology. The sensitive layer, particularly the epi-layer, can form the outermost layer of the charged particle detector. By fabricating the sensitive layer, for example, the epi-layer which is the outermost layer of the charged particle detector, a detector with improved noise characteristics can be obtained. The mechanical support layer helps with the robustness of the charged particle detector and, as previously explained, serves to provide or at least uniformly distribute sufficient heat transfer from the charged particle detector to the surroundings throughout the sensor device.

[0021] This type of charged particle detector exhibits improved resolution, signal-to-noise ratio, and sensitivity, and is particularly useful as a direct electron detector for TEM or general charged particle microscopes, and even more useful in the case of electron counting.

[0022] The charged particle detector can have a total thickness in the range of about 30 - 100 μm, more specifically in the range of (especially) 40 - 60 μm. The mechanical support layer can have a thickness similar to that of the sensor device. The mechanical support layer can have a thickness of about 10 - 50 μm, such as about 25 μm for example.

[0023] As described above, in one embodiment, the mechanical support layer may be made of a low-Z material with low thermal conductivity. The mechanical support layer can include carbon, especially pyrolytic carbon. In one embodiment, the mechanical support layer consists of pyrolytic carbon.

[0024] The charged particle detector can include an adhesive layer or a glue layer between the mechanical support layer and the passivation layer. The adhesive layer ensures a good thermal connection between the sensor device and the mechanical support layer. Additionally, the adhesive layer can help establish an electrical insulation layer between the passivation layer and the mechanical support layer.

[0025] According to an alternative aspect, a sensor device such as an APS having a sensitive layer and a passivation layer, and a mechanical support layer connected to the sensor device such that the sensitive layer is positioned between the passivation layer and the mechanical support layer, a charged particle detector is provided. The charged particle detector according to this embodiment is particularly advantageous from the perspective of heat transfer. In one embodiment, the mechanical support layer may be made of a low-Z material with low thermal conductivity. The mechanical support layer can include carbon, especially pyrolytic carbon. In one embodiment, the mechanical support layer consists of pyrolytic carbon. These features may be used to improve the scattering performance of the charged particle detector.

[0026] According to one aspect, a charged particle microscope for inspecting a sample, An optical column including a charged particle source and an illumination device for directing a beam of charged particles emitted from the charged particle source onto a sample, A sample stage positioned downstream of the illumination device and arranged to hold the sample, A detection device for detecting radiation generated from the sample in response to the incidence of charged particles emitted from the charged particle source, A charged particle microscope comprising a control unit for performing the operation of the charged particle microscope.

[0027] The charged particle microscope defined herein includes charged particle detectors described herein, such as the charged particle detector defined in claim 11.

[0028] The charged particle microscope may be a TEM in one embodiment. The charged particle detector may be a direct electron detector.

[0029] In one embodiment, the charged particle detector is arranged such that the sensitive layer is positioned between the particle source and the mechanical support layer. In other words, the sensitive layer faces the particle source directly. The passivation layer is arranged between the sensitive layer and the mechanical support layer.

Brief Description of the Drawings

[0030] The present invention will now be described in more detail based on exemplary embodiments and the accompanying schematic diagrams.

Figure 1

Figure 2

Figure 3a

Figure 3b

Figure 4a

Figure 4b

Figure 4c

Figure 5

Embodiments for Carrying Out the Invention

[0031] FIG. 1 (not to exact scale) is a very schematic view of an embodiment of a charged particle microscope M according to an embodiment of the present invention. More specifically, it shows an embodiment of a transmission microscope M, in this case a TEM / STEM (however, in the context of the present invention, it may also be an SEM (see FIG. 2), or for example an ion-based microscope). In FIG. 1, within the vacuum housing 2, the electron source 4 functions to generate an electron beam B that propagates along the electron optical axis B' and traverses the electron optical illumination device 6, directing / focusing the electrons onto a selected portion of the sample S (for example, it can be (locally) thinned / flattened). A deflector 8 is also shown, which can be used to effect (inter alia) a scanning movement of the beam B.

[0032] The sample S is held in a sample holder H that can be positioned in a plurality of degrees of freedom by a positioning device / stage A that moves a cradle A' to which the holder H is (removably) fixed. For example, the sample holder H can include fingers that can move (inter alia) within the XY plane (see the Cartesian coordinate system shown. Usually, movement parallel to Z and tilting with respect to X / Y are also possible). Such movement enables different portions of the sample S to be illuminated / imaged / inspected by the electron beam B that travels along the axis B' (in the Z direction) (and / or enables the scanning movement to be carried out as an alternative to beam scanning). If desired, an optional cooling device (not shown) can be brought into close thermal contact with the sample holder H to maintain the sample holder H (and the sample S thereon) at, for example, extremely low temperatures.

[0033] The electron beam B interacts with the sample S such that the sample S emits various types of "induced" radiation, including (for example) secondary electrons, backscattered electrons, X-rays, and optical radiation (cathodoluminescence). If desired, one or more of these types of radiation can be detected, for example, with the aid of an analytical device 22 combined with a scintillator / photomultiplier tube or an EDX or EDS (energy-dispersive X-ray spectroscopy) module, and in such cases an image can be constructed using essentially the same principle as in an SEM. However, alternatively or additionally, electrons that traverse (pass through) the sample S and are emitted / released from the sample S and continue to propagate along the axis B' (substantially, though generally with some deflection / scattering) can be investigated. Such a transmitted electron beam is incident on an imaging system (projection lens) 24, which generally includes various electrostatic / magnetic lenses, deflectors, correctors (such as a stigmator), etc. In the normal (non-scanning) TEM mode, this imaging system 24 can focus the transmitted electron beam onto a fluorescent screen 26, and the fluorescent screen 26 can be retracted / retrieved (as schematically indicated by the arrow 26') to move the fluorescent screen 26 away from the axis B' if desired. An image (or a diffractogram) of (a part of) the sample S is formed on the screen 26 by the imaging system 24, and this image can be viewed through a viewing port 28 located in an appropriate part of the wall of the housing 2. The retraction mechanism of the screen 26 is, for example, an essentially mechanical and / or electrical mechanism, which is not shown here.

[0034] As an alternative to viewing the image on the screen 26, instead, the fact that the focusing depth of the electron beam emerging from the imaging system 24 is generally extremely deep (for example, about 1 meter) can be utilized. As a result, At the position of the camera 30 where various other types of analyzers such as the TEM camera 30 can be used downstream of the screen 26, the electron beam can form a still image (or a diffraction pattern), and the still image can be processed by the control device / processor 20 and displayed on a display device 14 such as a flat panel display. If not necessary, the camera 30 can be retracted / withdrawn (as schematically indicated by the arrow 30') so that the camera is off the axis B'. - STEM camera 32. The output from the camera 32 can be recorded as a function of the (X, Y) scanning position of the beam B on the sample S, and an image that is a "map" of the output from the camera 32 as a function of X and Y can be constructed. The camera 32 can include, for example, a single pixel having a diameter of 20 mm, in contrast to the matrix of pixels typically present in the camera 30. Further, the camera 32 generally has an acquisition rate (e.g., 10 2 points / second) that is much higher than that of the camera 30 (e.g., 10 6 images / second). Also in this case, if not necessary, the camera 32 can be retracted / withdrawn (as schematically indicated by the arrow 32') so that the camera is off the axis B' (such a retraction is not necessary, for example, in the case of a donut-shaped annular dark field camera 32, but in such a camera, the central hole allows the passage of flux if the camera is not being used). - As an alternative to imaging using the camera 30 or 32, for example, a spectrometer 34 that can be an EELS module can also be called.

[0035] Note that the order / position of the components 30, 32, and 34 is not strict, and many possible variations are conceivable. For example, the spectrometer 34 can also be integrated with the imaging system 24.

[0036] In the illustrated embodiment, the microscope M further includes a retractable X-ray computed tomography (CT) module, generally indicated at reference 40. In computed tomography (also referred to as tomographic imaging), a source and a detector (at the opposite pole) are used to examine the sample along different lines of sight so as to obtain transmission observations of the sample from various viewpoints.

[0037] Note that the controller (computer processor) 20 is connected to the various components shown via a control line (bus) 20'. This controller 20 can provide various functions such as synchronizing operations, providing set points, processing signals, performing calculations, and displaying messages / information on a display device (not shown). Needless to say, the controller 20 (shown schematically) can be located (partially) inside or outside the housing 2 and can have a single-piece or composite structure as desired.

[0038] Those skilled in the art will understand that the interior of the housing 2 need not be maintained in a strict vacuum. For example, in so-called "environmental TEM / STEM", a background atmosphere of a given gas is intentionally introduced / maintained inside the housing 2. Those skilled in the art will also understand that in practice, it is advantageous to enclose the volume of the housing 2 and, if possible, have the housing 2 essentially enclose the axis B' such that the electron beam employed passes through a small-diameter tube and spreads out to accommodate structures such as the source 4, the sample holder H, the screen 26, the cameras 30, 32, the spectrometer 34, etc., in the form of a small-diameter tube (e.g., about 1 cm in diameter).

[0039] Accordingly, the charged particle microscope M shown in FIG. 1 generally includes an optical column O including a charged particle source 4 and an illumination device 6 that directs a beam B of charged particles emitted from the charged particle source 4 onto a sample S, a sample stage A, H positioned downstream of the illumination device 6 and arranged to hold the sample S, One or more detection devices 22, 26, 30, 32, 34 for detecting radiation arising from the sample in response to the incidence of charged particles emitted from the charged particle source, and a control unit for performing the operation of the charged particle microscope, a charged particle microscope comprising the same.

[0040] The charged particle microscope M of FIG. 1 also includes a charged particle detector 130 as defined herein. The charged particle detector 130 defined herein is particularly useful as a direct electron detector. The charged particle detector 130 can be used as the TEM camera 30 of FIG. 1. The complete details of an embodiment of the charged particle detector 130 are illustrated by FIG. 3.

[0041] Now first, referring to FIG. 2, another embodiment of the apparatus according to the present invention is shown. FIG. 2 (not to scale) is a very schematic depiction of a charged particle microscope M according to the present invention, and more specifically, in this case, an embodiment of a non-transmission microscope M, which is an SEM (however, in the context of the present invention, for example, an ion-based microscope may also be equally effective). In the figure, parts corresponding to the parts of FIG. 1 are shown using the same reference numerals and are not described separately here. In addition to FIG. 1, the following parts are added. -2a: A vacuum port that can be opened to introduce / remove components (constituents, samples) into / from the interior of the vacuum chamber 2, or on which, for example, auxiliary devices / modules can be mounted. The microscope M can include a plurality of such ports 2a if desired. -10a, 10b: Lenses / optical elements within the illumination device 6 schematically illustrated. -12: A voltage source that enables the sample holder H or at least the sample S to be biased (floating) at a certain potential with respect to ground if desired. -14: A display such as an FPD or a CRT. -22a, 22b: A segmented electron detector 22a including a plurality of independent detection segments (e.g., quadrants) arranged around a central opening 22b that allows passage of the beam B. Such a detector can be used, for example, to investigate the output (secondary or backscattered) electron beam (and its angular dependence) emitted from the sample S.

[0042] Thus, a charged particle microscope M as shown in FIG. 2 generally includes an optical column O including a charged particle source 4 and an illumination device 6 that directs a beam B of charged particles emitted from the charged particle source 4 onto the sample S, a sample stage A, H positioned downstream of the illumination device 6 and arranged to hold the sample S, one or more detection devices 22, 26, 30, 32, 34 for detecting the radiation generated from the sample in response to the incidence of the charged particles emitted from the charged particle source, and a control unit for performing the operation of the charged particle microscope.

[0043] The charged particle microscope M of FIG. 2 further includes a scanner 8 for focusing the beam B of charged particles emitted from the charged particle source 4 onto the sample S.

[0044] The charged particle microscope M of FIG. 2 also includes a charged particle detector 130 as defined herein. The charged particle detector 230 as defined herein is particularly useful as a direct electron detector. The charged particle detector 130 may be used as the segmented electron detector 22a and - virtually - provides a pixelated segmented electron detector 22a. The complete details of the embodiments of the charged particle detector 130 are illustrated by FIG. 3.

[0045] Next, with reference to FIGS. 3a and 3b, an embodiment of the charged particle detector 130 as defined herein will be described. The charged particle detector 130 includes a sensor device 120 such as an active pixel sensor or a monolithic active pixel sensor. The sensor device 120 includes a sensitive layer 140 and a passivation layer 150. The sensitive layer 140 includes an epi layer 141, and the passivation layer 150 includes sub-layers of highly doped wells 152; 155; 156 and further sub-layers 151 for insulation and passivation. The sub-layer 151 may include an oxide and a metal layer. The highly doped wells 152, 155, 156 can include a P well 152 and N wells 156, 156, and the N wells are used to detect electrons generated in the epi layer by incoming electrons 101. The pixel pitch of the charged particle detector 130 is determined by the spacing between the diodes formed by the well-doped regions (N wells 155, 156). The trajectory of the incoming electrons 101 and the diffusion collection of the mobile electrons generated by electron-hole pair excitation by the N well 156 are schematically shown.

[0046] Note that the basic structure of such an active pixel sensor, including an epi layer, a layer of highly doped wells, and a layer for insulation and passivation, is known per se to those skilled in the art. Further note that the structure of such an active pixel sensor may vary in some embodiments. However, generally speaking, the sensor device 120 includes a sensitive layer 140 and a passivation layer 150.

[0047] According to the present disclosure, as shown in FIGS. 3a and 3b, the charged particle detector 130 includes a mechanical support layer 160 connected to the sensor device 120 such that the passivation layer 150 is positioned between the sensing layer 150 and the mechanical support layer 160. As described above, the mechanical support layer provides mechanical support to the charged particle detector 130, enables the sensing layer to be made very thin, and enables accurate detection of incoming electrons 101. Due to the presence of the mechanical support layer 160, the overall thickness of the charged particle detector can be on the order of 10 to 100 μm, for example, 50 μm. In one embodiment, the sensor device 120 has a thickness of about 30 μm, and the mechanical support layer has a thickness of about 25 μm. The mechanical support layer 160 is connected to the sensor device 120 by an adhesive layer 170. The thickness of the adhesive is about 5 μm. Thereby, a total thickness of the charged particle detector 130 of about 60 μm is obtained. Of course, other dimensions are also conceivable.

[0048] The mechanical support layer 160 can include a low-Z thermal conductive material that can include a carbon material such as graphite and a carbon fiber composite. In one embodiment, pyrolytic carbon is used. In addition to providing support, it has excellent thermal conductivity (~1950 W / mK) and a very low mass (low Z). This enables excellent cooling of the detector and minimizes the amount of (unwanted) scattering of electrons.

[0049] FIGS. 4a-4c show an embodiment of a method for manufacturing the charged particle detector 130 of FIGS. 3a and 3b. The method shown is 1) As shown in FIG. 4a, providing a sensor device 120, the sensor device 120 including a substrate layer 180 and a sensing layer 140, 2) As shown in FIG. 4b, providing a mechanical support layer 160 and connecting the mechanical support layer 160 to the sensor device 120 such that the sensing layer 140 is positioned between the substrate layer 180 and the mechanical support layer 160, 3) As schematically shown in FIG. 4c, thinning the substrate layer 180 for forming the charged particle detector 130.

[0050] By using the mechanical support layer 160, a heavy back-thinning to the sensor layer (e.g., up to its epi layer) can be enabled easily. In other words, the substrate layer 180 may be completely removed. Thereby, the obtained charged particle detector can be used in a so-called back-illumination mode. In this mode, the epi layer faces the (expected) incident (coming-in) charged particles such as electrons, and the passivation layer is shielded (partially) from these incoming charged particles by the epi layer. Thereby, the characteristics of the detector are improved.

[0051] In an embodiment, as shown in FIG. 4b, the adhesive 170 is used to connect the mechanical support layer 160 to the sensor device 120. This may include the application of an adhesive to one or more of the sensor device 120 and the support layer 160. In particular, the entire surface of the sensor device 120 and / or the support layer 160 may be covered with an adhesive. This ensures that the surface irregularities are filled with the adhesive and ensures good thermal contact between the sensor device 120 and the mechanical support layer 160.

[0052] As shown in FIGS. 4a to 4c, the sensor device 120 may include a passivation layer 150. As shown previously, the passivation layer 150 includes electronics and interconnections for reading out signals induced by the incoming electrons in the highly doped wells and the sensor layer 140. The passivation layer 150 may also include a separation (metal oxide) layer. The mechanical support layer 160 is connected to the passivation layer 150, yet the sensor layer 140 is located between the substrate layer 180 and the mechanical support layer 160.

[0053] The sensor device provided in step 1) may be an active pixel sensor (APS) such as a monolithic active pixel sensor (MAPS), as shown in FIG. 4a.

[0054] Next, referring to FIG. 5, an embodiment of a detector unit 201 including a charged particle detector 130 described in this specification is shown. The charged particle detector 130 generally has a sensitive layer 140 and a mechanical support layer 160. The sensitive layer 140 faces the incoming stream of charged particles B'. The mechanical support layer 160 is provided downstream of the charged particle beam B'.

[0055] The detector unit 201 further includes a sensor PCB 211 and a feedthrough PCB 221 to provide an I / O connection for the charged particle detector 130 to the controller 20. The assembly of the sensor PCB 211 and the charged particle detector 130 is supported by a carrier element 212. The carrier element 212 is connected to a cooling device 214 including a Peltier cooling element 216 for cooling the charged particle device during use. Using pyrolytic carbon improves heat transfer characteristics, so that the power generated during the use of the device can be consumed.

[0056] The desired protection is conferred by the appended claims.

[0057] References: [1] McMullan, G & Faruqi, A.R. & Henderson, Richard. (2016). Direct Electron Detectors. 10.1016 / bs.mie.2016.05.056.

[0058] [Appendix 1] A method of manufacturing a charged particle detector, comprising: providing a sensor device, wherein the sensor device comprises a substrate layer and a sensitive layer; providing a mechanical support layer and connecting the mechanical support layer to the sensor device such that the sensitive layer is positioned between the substrate layer and the mechanical support layer; thinning the substrate layer for forming the charged particle detector. [Appendix 2] The method according to appendix 1, comprising the step of using an adhesive to connect the mechanical support layer to the sensor device. [Appendix 3] The method according to appendix 1 or 2, comprising the step of directly connecting the mechanical support layer to the sensitive layer. [Appendix 4] The method according to appendix 1 or 2, wherein the sensor device comprises a passivation layer on top of the sensitive layer. [Appendix 5] The method according to appendix 4, comprising the step of connecting the mechanical support layer to the passivation layer. [Appendix 6] The method according to any one of appendices 1 to 5, wherein the mechanical support layer comprises a low-Z material. [Appendix 7] The method according to any one of appendices 1 to 6, wherein the mechanical support layer comprises a heat conductor. [Appendix 8] The method according to appendix 6 or 7, wherein the mechanical support layer comprises a low-Z material with low thermal conductivity. [Appendix 9] The method according to appendix 8, wherein the mechanical support layer comprises carbon, particularly pyrolytic carbon. [Appendix 10] The method according to any one of appendices 1 to 9, wherein the sensor device is an active pixel sensor (APS). [Appendix 11] A charged particle detector, comprising: a sensor device having a sensitive layer and a passivation layer; and a mechanical support layer connected to the sensor device such that the passivation layer is located between the sensitive layer and the mechanical support layer. [Appendix 12] The charged particle detector according to appendix 11, wherein the mechanical support layer is made of a low-Z material with low thermal conductivity. [Appendix 13] The charged particle detector according to appendix 12, wherein the mechanical support layer comprises carbon, particularly pyrolytic carbon. [Appendix 14] The charged particle detector according to any one of appendices 11 to 13, wherein the charged particle detector includes an adhesive layer between the mechanical support layer and the passivation layer. [Appendix 15] The charged particle detector according to any one of appendices 11 to 14, wherein the sensor device is an active pixel sensor (APS). [Appendix 16] A charged particle microscope for inspecting a sample, including an optical column including a charged particle source and an illumination device for directing a beam of charged particles emitted from the charged particle source onto the sample, a sample stage positioned downstream of the illumination device and arranged to hold the sample, a detection device for detecting radiation generated from the sample in response to incidence of charged particles emitted from the charged particle source, and a control unit for executing the operation of the charged particle microscope, The charged particle microscope, characterized in that the detection device includes a charged particle detector defined in any one of appendices 11 to 15. [Appendix 17] The charged particle microscope according to appendix 16, wherein the charged particle detector is arranged such that the sensitive layer is positioned between the charged particle source and the mechanical support layer.

Claims

[Claim 1] 1. A method of manufacturing a charged particle detector, comprising the steps of: Providing a sensor device, the sensor device comprising a substrate layer and a sensitive layer; providing a mechanical support layer and connecting the mechanical support layer to the sensor device such that the sensitive layer is located between the substrate layer and the mechanical support layer; and thinning the substrate layer to form the charged particle detector.

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