Method of manufacturing a charged particle detector

Abstract

The invention relates to a method of manufacturing a charged particle detector comprising the steps of providing a sensor device, such as an active pixel sensor (APS). The sensor device comprises at least a substrate layer and a sensitive layer. The method further comprises the steps of providing a mechanical support layer and connecting the mechanical support layer to the sensor device. After the connection, the sensitive layer is located between the substrate layer and the mechanical support layer. By connecting the mechanical support layer, it is possible to thin the substrate layer for forming the charged particle detector. The mechanical support layer forms part of the manufactured detector. The detector can be used for charged particle microscopy, such as a transmission electron microscope for direct electron detection.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method of manufacturing a charged particle detector, wherein the charged particle detector comprises a sensor device having a substrate layer and a sensitive layer. BACKGROUND

[0002] Charged particle microscopy is a well-known and increasingly important technology for imaging microscopic objects, in particular in the form of electron microscopy. Historically, the basic family of electron microscopes has undergone a transformation into several well-known device categories, such as transmission electron microscopes (TEM), scanning electron microscopes (SEM) and scanning transmission electron microscopes (STEM), and also into various sub-categories, such as so-called "dual beam" devices (e.g. FIB-SEM) which additionally employ a "machined" focused ion beam (FIB) allowing, for example, supportive activities such as ion beam milling or ion beam induced deposition (IBID). The skilled person will be familiar with the different categories of charged particle microscopes.

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

[0004] In TEM, a beam of electrons is transmitted through a specimen, to form an image from interactions of the electrons with the sample as the beam is transmitted through the specimen. The image is then magnified and focused onto an imaging device such as a phosphor screen, photographic film layer, or a sensor such as a scintillator attached to a charge-coupled device (CCD). The scintillator converts the primary electrons in the microscope into photons, enabling the CCD to detect it.

[0005] A recent development in TEM includes the use of direct electron detectors. These direct electron detectors are able to directly detect imaging electrons in the microscope without the use of a scintillator. Direct electron detectors are based on sensor technology in which the electrons directly impinge on a lightly doped silicon epitaxial layer, which is supported on a more highly doped silicon substrate. A passivation layer sits on top of the epitaxial layer and includes a heavily doped well and electronics and interconnects for readout. With such direct electron detectors, improved resolution, signal-to-noise ratio (SNR) and sensitivity have been achieved (McMullan, Faruqi and Henderson, 2016). This advantageous SNR ratio, combined with high-speed CMOS electronics, enables counting of individual primary electrons. SUMMARY

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

[0007] For this purpose, a method of manufacturing a charged particle detector is provided. The method as defined herein comprises the step of providing a sensor device, such as an active pixel sensor (APS), wherein the sensor device comprises a substrate layer and a sensitive layer. The sensor device with the sensitive layer is capable of detecting incoming charged particles and in particular is arranged for detecting incoming electrons. For example, the substrate layer can be a highly doped silicon substrate. The sensitive layer can comprise an epitaxial layer. The sensor device, such as an APS, can also comprise a passivation layer on top of the sensitive layer. In that case, the sensitive layer can be sandwiched between the passivation layer and the substrate layer. The passivation layer can comprise a heavily doped well and electronics and interconnects for readout.

[0008] According to the method as defined herein, the method comprises the step of providing a mechanical support layer and connecting the mechanical support layer to the sensor device in such a way that the sensitive layer is located between the substrate layer and the mechanical support layer. The mechanical support layer can be provided in such a way that the sensitive layer is directly adjacent to the mechanical support layer. In other embodiments, in which the sensor device, such as an APS, comprises a passivation layer, the passivation layer is located between the sensitive layer and the mechanical support layer.

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

[0010] Providing the mechanical support layer and connecting it to the sensor device enables the substrate layer to be easily thinned. The mechanical support layer provides mechanical support during the thinning process. Due to the use of the mechanical support layer, the charged particle detector is less fragile during the thinning process. Additionally, the mechanical support layer allows a large portion of the substrate layer to be removed. In embodiments, it becomes possible to completely remove the substrate layer. In other words, the mechanical support layer allows the charged particle detector to be back-thinned up to the epitaxial layer. By using such a back-thinned detector, the noise contribution from scattered electrons is reduced.

[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 connected to the sensor device in a permanent way and is not removed to complete the manufacturing process. The connection between the mechanical support layer and the sensor device can be designed in such a way that the permanent connection is maintained or enhanced. By having the mechanical support layer become part of the final charged particle detector, the speed of the manufacturing process is improved and also the strength and durability of the charged particle detector are improved.

[0012] It is noted that, in principle, it is advantageous to use a thinner sensor, and thus it seems counterintuitive to add a mechanically supporting layer that remains attached (making the charged particle sensor thicker). However, the inventors found that by attaching a mechanical support layer to the sensor device and thinning the substrate layer up to the sensing layer, it becomes possible to use the manufactured charged particle detector in so-called backside illumination mode. In backside illumination, the sensing layer is the outermost layer of the charged particle detector. The sensing layer can be arranged to face the incoming flow of expected charged particles, and the mechanical support layer is positioned on the backside of the sensing layer and has reduced the influence of scattering. Thus, the application of a mechanical support layer, and the maintenance of this layer in the final charged particle detector, is not really a disadvantage, as the adverse effects are small enough to compensate for the advantages it provides.

[0013] The maintenance of a mechanical support layer is also advantageous in case the sensor device comprises a sensing layer and a passivation layer containing heavily doped wells and electronics and interconnects for readout. In this case, the epitaxial layer of the sensing layer faces the incoming flow of (expected) charged particles, such as electrons. The mechanical support layer is directed away from the incoming flow of charged particles, and the passivation layer is sandwiched between the mechanical support layer and the sensing layer. The passivation layer is mechanically protected by both surrounding layers. Detection of charged particles can also be done in a more direct way, as the passivation layer is not the first layer that is hit by incoming charged particles, which can lead to scattering and other undesired effects.

[0014] To prevent the mechanical support layer from influencing the signal detected by the charged particle detector, such as can occur due to backscattered electrons originating from the mechanical support layer, in an embodiment, the mechanical support layer comprises a low-Z material. Such a low-Z material can comprise, for example, materials comprising carbon, beryllium, and / or boron. The low-Z material can also comprise other materials. For example, the low-Z material can also contain 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 are typically operated in vacuum and need to dissipate thermal power of about 0.2 - 20 W. It is known that heat transfer in vacuum is a challenge. The amount of power typically also increases with increasing frame rate. In an embodiment, the sensor device backside can be thinned to a thickness of approximately 20-40 pm. If the sensor device backside is thinned to these dimensions, the cross-sectional area becomes smaller and thus the heat flux due to thermal conduction is reduced as well. In practice, this leads to cooling as a major challenge for these backside thinned detectors. For this purpose, the mechanical support layer can in an embodiment comprise or can be made of a thermally conductive material which is arranged for (e.g. by means of conduction) transferring the above-mentioned 0.2-20 W of thermal power away from the detector, e.g. to a heat sink, or at least distributing the thermal power evenly to prevent hot spots. The thermally conductive material can have a thermal conductivity of at least 500 W / m K, and in particular at least 1000 W / m K. The thickness of the mechanical support layer can be similar to the thickness of the backside thinned layer, such as e.g. in the range of 10 - 50 pm, in particular approximately 25 pm. The connection to the sensor device and the properties of the mechanical support layer enable the mechanical support layer to transfer the above-mentioned thermal power via conduction. The charged particle detector can comprise a heat sink connected to the mechanical support layer and arranged for active cooling, e.g. using water cooling and / or Peltier cooling.

[0016] In an advantageous embodiment, the mechanical support layer comprises a low-Z thermally conductive material. In an embodiment, a carbon material is used, such as graphite and carbon fiber composite. In an embodiment, pyrolytic carbon is used. In addition to the support, it also provides an excellent thermal conductivity (~ 1950 W / m K) and has a very low mass (low-Z). This allows an excellent heat transfer from the detector towards the heat sink and minimizes the amount of (unwanted) scattering of electrons. In this regard, it is noted that pyrolytic carbon also provides an improvement in thermal conductivity relative to the materials currently used. Additionally, pyrolytic carbon is also a vacuum compatible material which allows the use of the obtained charged particle detector in a charged particle microscope. The thickness of the mechanical support layer can be in the range of approximately 10 to 50 pm, such as approximately 25 pm.

[0017] To allow the mechanical support layer to act as a heat conducting material, it is advantageous when the mechanical support layer is in good thermal contact with the sensor device. For this purpose, the method can comprise the step of connecting said mechanical support layer to said sensor device by means of an adhesive. Said 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; heat adhesives) or reactive (anaerobic adhesives; multi-part adhesives; pre-mixed and refrigerated adhesives; one-part adhesives). In an advantageous embodiment, a liquid or flowable adhesive is used. By using such an adhesive, it is possible to ensure that a good thermal contact is established between the sensor device and the mechanical support layer. The use of an adhesive that is able to adapt itself to any non-flat surface (e.g. such as occurs at the APS) will help to provide a good thermal contact, but will also improve the structural strength of the final direct electron detector.

[0018] In an embodiment, the mechanical support layer is directly connected to at least a portion of said sensitive layer. In other embodiments, when said sensor device comprises a passivation layer, said mechanical support layer is directly connected to said passivation layer. Direct connection includes direct connection in which an adhesive is used. Said adhesive can have a certain thickness and be located between the mechanical support layer and the layer to which the mechanical layer is directly connected. Direct connection to the relevant layer keeps the sensor relatively compact, but also helps to dissipate heat.

[0019] According to an aspect, there is provided a charged particle detector comprising:

[0020] - a sensor device having a sensitive layer and a passivation layer, such as an APS; and

[0021] - a mechanical support layer connected to said sensor device in such a way that the passivation layer is located between said sensitive layer and said mechanical support layer.

[0022] The sensor device of the charged particle detector can consist of a sensitive layer and a passivation layer. The sensitive layer can comprise or consist of a lightly doped silicon epitaxial layer. The passivation layer can be connected to the epitaxial layer. The passivation layer can comprise a heavily doped well and electronics and interconnects for readout. The sensor device can be free of any substrate layer and in particular free of a higher doped silicon substrate. The sensor device can be based on active pixel sensor (APS) technology, such as monolithic active pixel sensor (MAPS) technology. The sensitive layer, and in particular the epitaxial layer, can form the outermost layer of the charged particle detector. By having the sensitive layer (e.g. the epitaxial layer) as the outermost layer of the charged particle detector, a detector with improved noise characteristics is obtained. The mechanical support layer contributes to the robustness of the charged particle detector and, as explained before, can help to provide sufficient heat transfer from the charged particle detector to the surrounding environment or at least distribute it more evenly over the sensor device.

[0023] Such a charged particle detector shows improved resolution, signal-to-noise ratio and sensitivity and is generally particularly useful as a direct electron detector in a TEM or charged particle microscope and even more so in case of electron counting.

[0024] The total thickness of the charged particle detector can be in the range of approximately 30 - 100 pm, more particularly in the range of 40 - 60 pm. The thickness of the mechanical support layer can be similar to the thickness of the sensor device. The mechanical support layer can have a thickness of approximately 10 to 50 pm, for example such as approximately 25 pm.

[0025] As explained before, in an embodiment the mechanical support layer can be made of a thermally conductive low-Z material. The mechanical support layer can comprise carbon, in particular pyrolytic carbon. In an embodiment the mechanical support layer consists of pyrolytic carbon.

[0026] The charged particle detector can comprise an adhesive or 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 to establish an electrical isolation layer between the passivation layer and the mechanical support layer.

[0027] According to an alternative aspect, there is provided a charged particle detector comprising:

[0028] - a sensor device with a sensitive layer and a passivation layer, such as an APS; and

[0029] - a mechanical support layer connected to the sensor device in such a way that the sensitive layer is located between the passivation layer and the mechanical support layer. The charged particle detector according to this embodiment is particularly advantageous in view of heat transfer. In an embodiment, the mechanical support layer can be made of a thermally conductive low-Z material. The mechanical support layer can comprise carbon, in particular pyrolytic carbon. In an embodiment, the mechanical support layer consists of pyrolytic carbon. These features can be used to improve the scattering performance of the charged particle detector.

[0030] According to an aspect, a charged particle microscope for inspecting a sample comprises:

[0031] - an optical column comprising a charged particle source and an illuminator for directing a beam of charged particles emitted from the charged particle source onto a sample;

[0032] - a sample stage positioned downstream of the illuminator and arranged for holding the sample;

[0033] - a detector device for detecting emissions originating from the sample in response to the incidence of charged particles emitted from the charged particle source; and

[0034] - a control unit for carrying out the operation of the charged particle microscope.

[0035] A charged particle microscope as defined herein comprises a charged particle detector as described herein, such as a charged particle detector as defined in the embodiments.

[0036] In an embodiment, the charged particle microscope can be a TEM. The charged particle detector can be a direct electron detector.

[0037] In an embodiment, the charged particle detector is placed in such a way that the sensitive layer is positioned between the particle source and the mechanical support layer. In other words, the sensitive layer directly faces the particle source. The passivation layer is located between the sensitive layer and the mechanical support layer. BRIEF DESCRIPTION OF DRAWINGS

[0038] The application will now be explained in more detail on the basis of exemplary embodiments and the accompanying schematic drawings, in which:

[0039] Figure 1 A longitudinal cross-sectional view of a charged particle microscope according to a first embodiment of the application is shown;

[0040] Figure 2 A longitudinal cross-sectional view of a charged particle microscope according to a second embodiment of the application is shown;

[0041] Figure 3a-b illustrates an embodiment of a charged particle detector as disclosed herein;

[0042] Figure 4a -c illustrates an embodiment of a method for manufacturing a charged particle detector as disclosed herein;

[0043] Figure 5 The use of charged particle detectors in charged particle microscopy is shown. Detailed Implementation

[0044] Figure 1 (Not to scale) is a highly schematic depiction of an embodiment of a charged particle microscope M according to an embodiment of the invention. More specifically, it shows an embodiment of a transmission microscope M, which in this case is TEM / STEM (although in the context of the invention, it can be just as effectively a SEM, for example (see...) Figure 2 (or ion-based microscopy). Figure 1 Within the vacuum enclosure 2, an electron source 4 generates an electron beam B that propagates along the electron-optical axis B' and passes through an electron-optical illuminator 6, serving to guide / focus the electrons onto a selected portion of the sample S (which may, for example, be (locally) thinned / planarized). A deflector 8 is also depicted, which can (in particular) be used to implement the scanning motion of the beam B.

[0045] Sample S is held on sample holder H, which can be positioned with multiple degrees of freedom by a positioning device / stand A that moves a bracket A', and the holder H is (removably) fixed to the bracket A'; for example, sample holder H may include ( In particular A finger-like object moving in the XY plane (see the depicted Cartesian coordinate system; typically, movement parallel to Z and tilted about X / Y is also possible). Such movement allows different portions of the sample S to be illuminated / imaged / examined by an electron beam B traveling along axis B' (in the Z direction) (and / or allows for scanning motion as an alternative to beam scanning). If desired, an optional cooling device (not depicted) can be brought into close thermal contact with the sample holder H to, for example, maintain it (and the sample S thereon) at a low temperature.

[0046] The electron beam B will interact with the sample S in a manner that causes various types of "stimulated" radiation to emanate from the sample S, including, for example, secondary electrons, backscattered electrons, X-rays, and optical radiation (catholuminescence). If desired, one or more of these radiation types can be detected by means of an analytical device 22, which can be, for example, a combined scintillator / photomultiplier tube or an EDX or EDS (energy-dispersive X-ray spectroscopy) module; in such cases, images can be constructed using essentially the same principles as in SEM. However, alternatively or additionally, one can study electrons that pass through (through) the sample S, exit from / emit from it, and (essentially, although usually with some deflection / scattering) continue to propagate along axis B'. This transmitted electron flux enters the imaging system (projection lens) 24, which will typically include a variety of electrostatic / magnetic lenses, deflectors, correctors (such as astigmatism correctors), etc. In normal (non-scanning) TEM mode, this imaging system 24 can focus the transmitted electron flux onto the fluorescent screen 26, which can be retracted / retracted if desired (as schematically indicated by arrow 26') to avoid the path of axis B'. An image (or diffraction pattern) of a portion of the sample S will be formed on the screen 26 by the imaging system 24, and this can be viewed through an observation port 28 located in a suitable portion of the wall of the housing 2. The retraction mechanism for the screen 26 can be, for example, mechanical and / or electrical in nature, and is not depicted here.

[0047] As an alternative to viewing the image on screen 26, one can take advantage of the fact that the focusing depth of the electron flux exiting imaging system 24 is typically quite large (e.g., about 1 meter). Therefore, various other types of analytical devices, such as:

[0048] - TEM camera 30. At camera 30, the electron flux can form a still image (or diffraction pattern), which can be processed by controller / processor 20 and displayed on display device 14, such as, for example, a flat panel display. When not needed, camera 30 can be retracted / retreated (as schematically indicated by arrow 30') so that camera 30 avoids the path of axis B'.

[0049] STEM camera 32. The output from camera 32 can be recorded as a function of the (X, Y) scan orientation of beam B on sample S, and an image can be constructed that is a "graph" of the output from camera 32 as a function of X and Y. Camera 32 may include individual pixels with, for example, a diameter of 20 mm, rather than a matrix of pixels typically present in camera 30. Furthermore, camera 32 will typically have a larger diameter than camera 30. For example 10 per second2 A much higher acquisition rate (per image) For example, 10 per second 6 (Points). Again, when not needed, camera 32 can be retracted / retracted (as schematically indicated by arrow 32') so that camera 32 avoids the path of axis B' (although such retraction is not necessary, for example, in the case of a donut-shaped annular dark field camera 32; in such a camera, the central aperture will allow the flow when the camera is not in use).

[0050] As an alternative to using cameras 30 or 32 for imaging, one can also invoke a beam splitter device 34, which can be, for example, an EELS module.

[0051] It should be noted that the order / position of parts 30, 32, and 34 is not strict, and many possible variations are conceivable. For example, the beam splitter assembly 34 could also be integrated into the imaging system 24.

[0052] In the illustrated embodiment, the microscope M further includes a retractable X-ray computed tomography (CT) module, generally indicated by reference numeral 40. In computed tomography (also known as computed tomography imaging), a source and (diametrically opposed) detectors are used to carefully examine the sample along different lines of sight in order to obtain penetrating observations of the sample from a wide variety of perspectives.

[0053] Note that the controller (computer processor) 20 Via The control line (bus) 20' connects to various components shown in the diagram. The controller 20 can provide a wide range of functions, such as synchronizing actions, providing setpoints, processing signals, performing calculations, and displaying messages / information on a display device (not shown). Needless to say, the controller 20 (schematically depicted) can be (partially) inside or outside the housing 2, and can have a single or combined structure as desired.

[0054] Those skilled in the art will understand that the interior of housing 2 does not necessarily need to be maintained under a strict vacuum; for example, in so-called “environmental TEM / STEM,” a background atmosphere of a given gas is intentionally introduced / maintained within housing 2. Those skilled in the art will also understand that, in practice, it may be advantageous to limit the volume of housing 2 such that, where possible, it substantially hugs axis B', taking the form of a small conduit (e.g., with a diameter of approximately 1 cm) (through which the electron beam employed passes), but widening it to accommodate structures such as source 4, sample holder H, screen 26, camera 30, camera 32, beam splitter assembly 34, etc.

[0055] therefore, Figure 1 The charged particle microscope M shown typically includes:

[0056] - an optical column O comprising a source of charged particles 4 and an illuminator 6 for directing a beam B of charged particles emitted from said source of charged particles 4 onto a sample S;

[0057] - a sample stage A, H positioned downstream of said illuminator 6 and arranged for holding said sample S;

[0058] - one or more detector devices 22, 26, 30, 32, 34 for detecting emissions originating from said sample in response to the incidence of charged particles emitted from said source of charged particles; and

[0059] - a control unit for carrying out the operation of the charged particle microscope.

[0060] Figure 1 The charged particle microscope M of Fig. 1 further comprises a charged particle detector 130 as defined herein. The charged particle detector 130 as defined herein is in particular usable as a direct electron detector. The charged particle detector 130 can be used as Figure 1 the TEM camera 30 of Fig. 1. All details of embodiments of the charged particle detector 130 will be explained by means of Fig. 3.

[0061] Reference is now first made to Figure 2 Fig. 2, showing another embodiment of an apparatus according to the present invention. Figure 2 Fig. 1 (not to scale) is a highly schematic depiction of a charged particle microscope M according to the present invention; more specifically, it shows an embodiment of a non-transmission type microscope M, which in this case is a SEM (although in the context of the present invention it can equally well be an ion-based microscope). In the figure, the same reference numerals are used to indicate parts corresponding to those in Figure 1 Fig. 1, and will not be discussed separately here. In addition to Figure 1 the following parts, in particular:

[0062] - 2a: a vacuum port, which can be opened in order to introduce parts (components, samples) into / from the interior of the vacuum chamber 2, or onto which e.g. auxiliary equipment / modules can be mounted. If desired, the microscope M can comprise a plurality of such ports 2a.

[0063] 10a, 10b: schematically depict lenses / optical elements in the illuminator 6;

[0064] - 12: a voltage source, which if desired can allow the sample holder H or at least the sample S to be biased (floating) to a potential with respect to ground;

[0065] - 14: a display, such as an FPD or CRT;

[0066] - 22a, 22b: segmented electron detector 22a comprising a plurality of independent detection segments (e.g. quadrants) arranged around a central aperture 22b which allows the passage of the beam 5. Such a detector can for example be used to study the flux (angular dependence) of the outgoing (secondary or backscattered) electrons from the sample 13.

[0067] Thus, as Figure 2 The charged particle microscope M as shown generally comprises:

[0068] - an optical column O comprising a charged particle source 4 and an illuminator 6 for directing a beam B of charged particles emitted from said charged particle source 4 onto a sample S;

[0069] - a sample stage A, H positioned downstream of said illuminator 6 and arranged for holding said sample S;

[0070] - one or more detector devices 22, 26, 30, 32, 34 for detecting emissions originating from said sample in response to the incidence of charged particles emitted from said charged particle source; and

[0071] - a control unit for carrying out the operation of the charged particle microscope.

[0072] Figure 2 The charged particle microscope M as shown additionally comprises a scanner 8 for focusing the beam B of charged particles emitted from said charged particle source 4 onto a sample S.

[0073] Figure 2 The charged particle microscope M as shown further comprises 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 can be used as a segmented electron detector 22a, in fact providing a pixelated segmented electron detector 22a. All the details of an embodiment of the charged particle detector 130 will be explained by means of Fig. 3.

[0074] Reference is now made to Figure 3a and Figure 3bAn embodiment of a charged particle detector 130 as defined herein will be discussed. The charged particle detector 130 comprises a sensor device 120, such as an active pixel sensor or a monolithic active pixel sensor. The sensor device 120 comprises a sensitive layer 140 and a passivation layer 150. The sensitive layer 140 comprises an epitaxial layer 141 and the passivation layer 150 comprises sub-layers of heavily doped wells 152; 155; 156 and a further sub-layer 151 for insulation and passivation. The sub-layer 151 can comprise an oxide and a metal layer. The heavily doped wells 152; 155; 156 can comprise P-wells 152 and N-wells 156, 156, wherein the N-wells are used to detect electrons generated in the epitaxial layer due to incoming electrons 101. The pixel spacing of the charged particle detector 130 is determined by the spacing between the diodes formed by the well doping regions (N-wells 155, 156). The trajectory of an incident electron 101 is schematically indicated, as well as the diffusion collection of mobile electrons generated by the N-wells 156 in an electron-hole pair excitation.

[0075] It is noted that the basic construction of such an active pixel sensor comprising an epitaxial layer, heavily doped well layers and an insulation and passivation layer is known per se to the person skilled in the art. It is further noted that the structure of such an active pixel sensor can differ in certain embodiments. In general, however, the sensor device 120 comprises a sensitive layer 140 and a passivation layer 150.

[0076] According to the present disclosure, and as shown in Figure 3a and 3b The charged particle detector 130 comprises a mechanical support layer 160 which is connected to the sensor device 120 in such a way that the passivation layer 150 is located between the sensitive layer 150 and the mechanical support layer 160. As indicated before, the mechanical support layer provides mechanical support to the charged particle detector 130 and allows the sensitive layer to be very thin, enabling accurate detection of incoming electrons 101. Due to the presence of the mechanical support layer 160, the total thickness of the charged particle detector can for example be about 10 to 100 pm, such as 50 pm. In an embodiment, the sensor device 120 has an approximate thickness of 30 pm and the mechanical support layer has an approximate thickness of 25 pm. The mechanical support layer 160 is connected to the sensor device 120 by a layer of glue 170. The thickness of the glue can be approximately 5 pm. This results in a total thickness of the charged particle detector 130 of approximately 60 pm. Other dimensions are of course conceivable.

[0077] The mechanical support layer 160 can comprise a low-Z thermally conductive material, which can comprise carbon materials such as graphite and carbon fiber composites. In an embodiment, pyrolytic carbon is used. In addition to support, it also provides an excellent thermal conductivity (~1950 W / m K) and has a very low mass (low-Z). This allows for excellent cooling of the detector and minimizes the amount of electron (unwanted) scattering.

[0078] Figures 4a-4c An embodiment of a method of manufacturing a charged particle detector 130 is shown. The shown method comprises the following subsequent steps: Figure 3a and 3b An embodiment of a method of manufacturing a charged particle detector 130 is shown. The shown method comprises the following subsequent steps:

[0079] 1) As shown in Figure 4a , a sensor device 120 is provided, wherein the sensor device 120 comprises a substrate layer 180 and a sensitive layer 140;

[0080] 2) As shown in Figure 4b , a mechanical support layer 160 is provided and connected to the sensor device 120 in such a way that the sensitive layer 140 is located between the substrate layer 180 and the mechanical support layer 160; and

[0081] 3) As shown in Figure 4c schematically, the substrate layer 180 is thinned for forming the charged particle detector 130.

[0082] The use of a mechanical support layer 160 allows for easy and heavy backside thinning of the substrate layer 180 up to the sensitive layer (e.g. up to its epitaxial layer). In other words, the substrate layer 180 can be completely removed. This allows for using the obtained charged particle detector in so-called back-illumination mode, wherein the epitaxial layer faces the incoming charged particles (such as electrons) and the passivation layer is (partly) shielded from these incoming charged particles by the epitaxial layer. This results in improved detector properties.

[0083] In an embodiment, and as shown in Figure 4b , an adhesive 170 is used for connecting the mechanical support layer 160 to the sensor device 120. This can comprise applying 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 can be covered with adhesive. This ensures that unevenness in the surface is filled with adhesive to ensure good thermal contact between the sensor device 120 and the mechanical support layer 160.

[0084] As shown in Figures 4a-4cAs shown, the sensor device 120 can comprise a passivation layer 150. As indicated earlier, the passivation layer 150 comprises a heavily doped well, and electronics and interconnects for reading out a signal induced by an incoming electron in the sensitive layer 140. The passivation layer 150 can also comprise an isolation (metal oxide) layer. A mechanical support layer 160 is connected to the passivation layer 150, but the sensitive layer 140 is still located between the substrate layer 180 and the mechanical support layer 160.

[0085] The sensor device provided in step 1) and as shown in Figure 4a may be an active pixel sensor (APS), such as a monolithic active pixel sensor (MAPS).

[0086] Turning now to Figure 5 , an embodiment of a detector unit 201 comprising a charged particle detector 130 as described herein is shown. As generally indicated, the charged particle detector 130 has a sensitive layer 140 and a mechanical support layer 160. The sensitive layer 140 faces an incoming stream of charged particles B'. The mechanical support layer 160 is provided downstream of the charged particle beam B'.

[0087] The detector unit 201 further comprises a sensor PCB 211 and a feedthrough PCB 221 for providing I / O connections for the charged particle detector 130 to the controller 20. An 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, which contains Peltier cooling elements 216 for cooling the charged particle device in its use. The use of pyrolytic carbon provides improved heat transfer characteristics, so that the power generated during use of the device can be dissipated.

[0088] The desired protection is given by the attached claims.

[0089] Cited documents:

[0090] [1] McMullan, G and Faruqi, A. R. and Henderson, Richard. (2016). Direct electron detectors. 10.1016 / bs.mie.2016.05.056.

Claims

1. A method of manufacturing a direct charged particle detector, comprising the steps of: - providing a sensor device, wherein the sensor device comprises a substrate layer, a sensitive layer and a passivation layer on top of the sensitive layer; - providing a mechanical support layer and connecting the mechanical support layer to the passivation layer in such a way that the sensitive layer is located between the substrate layer and the mechanical support layer; and - thinning the substrate layer for forming the charged particle detector; wherein the passivation layer comprises electronics and interconnects for reading out signals induced by incoming electrons in the sensitive layer and comprises a first sub-layer comprising a more heavily doped well than the sensitive layer and a second sub-layer comprising an oxide and a metal layer, and wherein the mechanical support layer comprises carbon.

2. The method of claim 1, comprising the step of: The mechanical support layer is connected to the sensor device using an adhesive.

3. The method of claim 1, wherein, The mechanical support layer comprises pyrolytic carbon.

4. The method of any one of claims 1-3, wherein, The sensor device is an active pixel sensor (APS).

5. A direct charged particle detector, comprising: - a sensor device having a sensitive layer and a passivation layer on top of the sensitive layer; - a mechanical support layer connected to the sensor device in such a way that the passivation layer is located between the sensitive layer and the mechanical support layer; wherein the passivation layer comprises electronics and interconnects for reading out signals induced by incoming electrons in the sensitive layer and comprises a first sub-layer comprising a more heavily doped well than the sensitive layer and a second sub-layer comprising an oxide and a metal layer, and wherein the mechanical support layer comprises carbon. The mechanical support layer comprises pyrolytic carbon.

6. The charged particle detector of claim 5, wherein, The charged particle detector comprises an adhesive layer between the mechanical support layer and the passivation layer.

7. The charged particle detector according to any one of claims 5-6, wherein, The sensor device is an active pixel sensor (APS).

8. The charged particle detector according to any one of claims 5-6, wherein, 9. A charged particle microscope for inspecting a sample, comprising: - an optical column comprising a charged particle source and an illuminator for directing a beam of charged particles emitted from the charged particle source onto a sample; - a sample stage positioned downstream of the illuminator and arranged for holding the sample; - a detector device for detecting emissions originating from the sample in response to an incidence of charged particles emitted from the charged particle source; and - a control unit for carrying out operations of the charged particle microscope; characterized in that the detector device comprises a charged particle detector as defined in one of claims 5-8. The charged particle detector is placed in such a way that the sensitive layer is positioned between the particle source and the mechanical support layer.

10. The charged particle microscope of claim 9, wherein, ​

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