Apparatus and method for projecting an array of multiple charged particle beamlets onto a sample

Abstract

An apparatus for inspecting a sample, comprising: a sample holder for holding a sample at a sample plane; and a charged particle column for generating an array of a plurality of charged particle beamlets and directing said array towards the sample holder. The charged particle column comprises an objective for focusing the charged particle beamlets of said array into an array of charged particle beam spots at or near the sample plane. The objective comprises a magnetic lens common to all charged particle beamlets. The apparatus further comprises: a position sensor for providing a signal dependent on a position of the sample along an optical axis of the charged particle column; and a control unit for controlling the position of the sample holder based on the signal from the position sensor to keep a pitch and / or an orientation of the spots on the sample constant.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for projecting an array of multiple charged particle wavelet beams onto a sample. Background Technology

[0002] For example, such an apparatus or method is disclosed in US 2015 / 027095 A1. This patent application describes an apparatus for examining the surface of a sample. The apparatus includes a generator for generating an array of primary charged particle beamlets, and a charged particle optical system having an optical axis. The charged particle optical system includes a lens system for focusing the primary charged particle beamlets onto an array of spots on the sample surface. The lens system includes at least one electromagnetic lens shared by all charged particle beams. Preferably, the objective lens for focusing the array of primary charged particle beamlets includes the electromagnetic lens, which is arranged to rotate the array of primary charged particle beamlets about the optical axis of the charged particle optical system. Summary of the Invention

[0003] When a charged particle optical system includes a magnetic lens shared by all primary charged particle wavelets of an array of primary charged particle wavelets, the array will rotate and / or change its magnification when the excitation and / or intensity of the magnetic lens is changed.

[0004] The object of the present invention is to provide an apparatus and method in which the spacing and / or rotation of an array of primary charged particle wavelets on a sample remain at least substantially constant.

[0005] According to a first aspect, the present invention provides an apparatus for examining a sample, wherein the apparatus comprises: A sample holder, used to hold the sample in the sample plane; A charged particle column for generating an array of multiple charged particle wavelets and guiding the array of multiple charged particle wavelets toward a sample holder, wherein the charged particle column includes an objective lens for focusing the charged particle wavelets of the array of multiple charged particle wavelets into a charged particle beam spot array at or near the sample plane, wherein the objective lens includes a magnetic lens shared by all the charged particle wavelets in the array of multiple charged particle wavelets; A position sensor configured to provide a signal depending on the position of the sample in a direction along the optical axis of the charged particle column; and A control unit is configured to control the position of the sample holder based on signals from the position sensor, at least in a direction parallel to the optical axis of the charged particle column.

[0006] Because of the combined position sensor and control unit in the multi-charged particle beam inspection apparatus of the present invention, the sample holder can be controlled to hold the portion of the sample, which is being inspected by means of an array of multiple charged particle beams, positioned at the sample plane and / or focal plane of the multi-charged particle beam inspection apparatus. When the arrangement of the charged particle columns remains unchanged and the portion of the sample being inspected is held at the sample plane and / or focal plane of the multi-charged particle beam inspection apparatus, the spacing and rotation of the array of multiple charged particle wavelet beams on the sample at the sample plane and / or focal plane of the multi-charged particle beam inspection apparatus can remain constant. It should be noted that, for imaging the sample, the sample plane is preferably arranged at the focal plane of the multi-charged particle beam inspection apparatus.

[0007] It should be noted that when the sample holder is arranged to at least partially position the sample in the magnetic field of the magnetic objective, the array of primary charged particle wavelets will rotate in the magnetic field in its direction toward the sample. This rotation depends particularly on the magnetic field strength of the magnetic lens. Even if the sample holder is configured to position the sample surface in a field-free region, changes in the sample's position along the optical axis of the charged particle beams typically require adjustment of the focus, and therefore the magnetic field strength, to maintain sample focus. Consequently, the orientation of the array of primary charged particle wavelets at the sample surface depends on the sample's position relative to the magnetic lens, particularly its position along the optical axis of the charged particle optical system.

[0008] Because of the combined position sensor and control unit in the multi-charged particle beam inspection apparatus of the present invention, the sample holder can be controlled to hold the portion of the sample being inspected by means of an array of multiple charged particle beams, positioned at a desired distance from the magnetic objective. When the arrangement of the charged particle columns remains unchanged and the portion of the sample being inspected is maintained at the desired distance from the magnetic objective, the spacing and rotation of the array of multiple charged particle wavelet beams on the sample plane can remain constant.

[0009] Furthermore, it should be noted that charged particle inspection devices (such as electron microscopes) have a relatively large depth of focus. Therefore, within at least a portion of the depth of focus range, the sample can be moved in a direction parallel to the optical axis of the charged particle optical system to position the sample at a desired location along the optical axis, wherein the array of multiple charged particle wavelets has a desired orientation in the direction surrounding the optical axis of the charged particle column. The desired orientation of the charged particle beam spot array at or near the sample plane depends, for example, on the direction in which the array of multiple charged particle wavelets can scan the sample and / or on the direction in which the sample can move relative to the charged particle column. Due to the combined position sensor and control unit in the multi-charged particle beam inspection apparatus of the present invention, the sample holder can be controlled to hold the portion of the sample inspected by means of the array of multiple charged particle beams at a desired location, and to hold the charged particle beam spot array at or near the sample plane in the desired orientation.

[0010] In an embodiment, the position sensor is configured such that the signal depends on the position of the sample holder or sample plane relative to the objective lens. Specifically, the signal depends on the distance between the sample holder or sample plane and the objective lens. As described above, the orientation of the array of primary charged particle wavelets at the sample surface depends on the position of the sample relative to the magnetic lens, particularly its position along the optical axis of the charged particle optical system.

[0011] In an embodiment, the device further includes: a photodetector and an optical component, the photodetector being used to detect photons generated by one or more of the array of charged particle wavelets when they strike a sample or when the one or more charged particle wavelets strike a luminescent material layer after passing through the sample; the optical component being used to project or image at least a portion of the photons onto the photodetector along the beam path.

[0012] In this embodiment, the optical components are configured to image the sample plane onto the photodetector. This embodiment provides an improvement in so-called integrated inspection apparatus, characterized by the integration of a multi-beam charged particle inspection device (e.g., a multi-beam scanning electron microscope (multi-beam SEM)) and an optical inspection device (e.g., optical microscope optics). According to the invention, when the arrangement of the charged particle columns remains unchanged and the portion of the sample being inspected is held at a desired distance from the magnetic objective, the spacing and rotation of the array of multiple charged particle wavelets on the sample plane can remain constant. Furthermore, the invention allows for the provision and maintenance of desired alignment and spacing of the charged particle wavelets in the array of multiple charged particle wavelets relative to the optical microscope, particularly relative to the photodetector of the optical microscope.

[0013] In one embodiment, the optical component includes an optical objective for collecting photons from the sample and / or the luminescent material layer.

[0014] In an embodiment, the device further includes an optical focusing sensor configured to provide a signal dependent on the distance between the sample plane and the optical objective, wherein the control unit is configured to control the position of the sample holder based on the signal from the optical focusing sensor, at least in a direction parallel to the optical axis of the charged particle column. In addition to using a position sensor, or as an alternative, the optical focusing sensor can also be used to control the sample holder to hold the portion of the sample, which is positioned on the sample plane and examined by means of an array of charged particle beams. The combination of the optical focusing sensor and the control unit allows the sample to be held within the focal point of the optical assembly by a photodetector, thus holding the portion of the sample, positioned on the sample plane and examined by means of an array of charged particle beams. When the arrangement of the charged particle columns remains unchanged and the portion of the sample being examined is held on the sample plane, the spacing and rotation of the array of multiple charged particle wavelet beams on the sample plane can remain constant.

[0015] In one embodiment, the optical component, particularly its optical objective, includes an optical axis, wherein the device is configured such that the optical axis is substantially parallel to the optical axis of the charged particle column. In this embodiment, a change in the position of the sample along the direction of the optical axis of the charged particle column results in the same change in the position of the sample along the optical axis. Therefore, when the optical component is used to hold the sample in a substantially constant position along the optical axis, this also holds the sample in a substantially constant position along the optical axis of the charged particle column.

[0016] It should be noted that the depth of focus of this optical assembly at the sample is typically much smaller than that of the charged particle inspection device. Therefore, by positioning and / or holding the sample in the focal point of the optical assembly, the portion of the sample to be inspected by means of the array of multiple charged particle beams is also positioned and / or held at a substantially fixed distance from the magnetic objective. When the arrangement of the charged particle columns remains unchanged and the portion of the sample to be inspected is held at the desired distance from the magnetic objective, the spacing and rotation of the array of multiple charged particle wavelet beams on the sample plane can remain constant.

[0017] According to a second aspect, the present invention provides an apparatus for examining a sample, wherein the apparatus comprises: A sample holder, used to hold the sample in the sample plane; A charged particle column for generating an array of multiple charged particle wavelets and guiding the array of multiple charged particle wavelets toward the sample holder, wherein the charged particle column includes an objective lens for focusing the charged particle wavelets of the array of multiple charged particle wavelets into a charged particle beam spot array at or near the sample plane, wherein the objective lens includes a magnetic lens shared by all the charged particle wavelets in the array of multiple charged particle wavelets; A photodetector for detecting photons generated by one or more of the charged particle wavelets in the array of the plurality of charged particle wavelets when one or more of the charged particle wavelets strike the sample, or when the one or more charged particle wavelets strike the luminescent material layer after passing through the sample; An optical component for projecting or imaging at least a portion of the photons onto the photodetector along a beam path, wherein the optical component includes an optical objective for collecting photons from the sample and / or the luminescent material layer; An optical focusing sensor configured to provide a signal dependent on the distance between the sample holder or sample plane and the optical objective; and A control unit is configured to control the position of the sample holder based on signals from the optical focusing sensor, at least in a direction parallel to the optical axis of the charged particle column.

[0018] The optical inspection equipment can be used in combination with multi-beam charged particle equipment and optical inspection equipment.

[0019] The combination of the optical focusing sensor and the control unit allows the photodetector to hold the sample within the focal point of the optical assembly and / or to hold the portion of the sample positioned on the sample plane for inspection by means of the array of multiple charged particle beams. When the configuration of the charged particle beams remains unchanged and the portion of the sample being inspected remains on the sample plane, the spacing and rotation of the array of multiple charged particle wavelet beams on the sample plane can remain constant.

[0020] In one embodiment, the optical objective includes an optical axis, wherein the device is configured such that the optical axis is substantially parallel to the optical axis of the charged particle column.

[0021] In one embodiment, the optical component is configured to image the sample plane onto the photodetector. This embodiment provides an improvement in so-called integrated inspection apparatus, characterized by the integration of a multi-beam charged particle inspection device (such as a multi-beam scanning electron microscope (SEM)) and an optical inspection device (such as optical microscope optics), wherein the optical microscope is used to set and maintain the alignment of the array of charged particles on the sample at least substantially constant during the inspection of the sample.

[0022] According to a third aspect, the present invention provides a method for examining a sample, wherein the method includes the following steps: Arrange the sample on the sample holder; An array of multiple charged particle wavelets is generated using a charged particle column and the array of multiple charged particle wavelets is directed toward the sample. The charged particle column includes an objective lens that focuses the charged particle wavelets of the array of multiple charged particle wavelets into a spot array of charged particle beams at or near the sample plane. The objective lens includes a magnetic lens shared by all the charged particle wavelets of the array of multiple charged particle wavelets. A position sensor is used to provide a signal that depends on the sample's position along the optical axis of the charged particle column; and Based on the signal from the position sensor, a control unit is used to control the position of the sample holder at least in the direction parallel to the optical axis of the charged particle column.

[0023] In one embodiment, the position sensor is configured such that the signal depends on the distance between the sample holder or sample plane and the objective lens.

[0024] In this embodiment, the method includes the following steps: At least in the direction parallel to the optical axis of the charged particle column, adjust the position of the sample holder and / or the charged particle column relative to each other, and / or focus and set the desired spacing and orientation of an array of multiple charged particle wavelets in the sample plane.

[0025] According to a fourth aspect, the present invention provides a method for examining a sample, wherein the method includes the following steps: Arrange the sample on the sample holder; An array of multiple charged particle wavelets is generated using a charged particle column and the array of multiple charged particle wavelets is directed toward the sample. The charged particle column includes an objective lens that focuses the charged particle wavelets of the array of multiple charged particle wavelets into a spot array of charged particle beams at or near the sample plane. The objective lens includes a magnetic lens shared by all the charged particle wavelets of the array of multiple charged particle wavelets. A photodetector is used to detect photons generated by one or more of the charged particle wavelets in the array of the plurality of charged particle wavelets when one or more of the charged particle wavelets strike the sample, or when one or more of the charged particle wavelets strike the luminescent material layer after passing through the sample; At least a portion of the photons is projected or imaged onto the photodetector along the beam path using an optical component, wherein the optical component includes an optical objective for collecting photons from the sample and / or the luminescent material layer; An optical focusing sensor is used to provide a signal that depends on the distance between the sample holder or sample plane and the optical objective; and Based on the signal from the optical focusing sensor, the position of the sample holder is controlled by the control unit at least in the direction parallel to the optical axis of the charged particle column.

[0026] According to a fifth aspect, the present invention provides a computer-readable medium having computer-executable instructions adapted to cause the apparatus or embodiments thereof described above to perform the methods or embodiments thereof described above.

[0027] The aspects and features described and illustrated in this specification may be applied individually in any possible circumstances. These individual aspects, particularly those described in the appended dependent claims, may be the subject of a divisional patent application. Attached Figure Description

[0028] The invention will be explained based on exemplary embodiments shown in the accompanying drawings, in which: Figure 1 A first exemplary embodiment of a device typically improved by the present invention is illustrated schematically; and Figure 2 A second exemplary embodiment of the device, typically improved by the present invention, is illustrated schematically. Detailed Implementation

[0029] Figure 1 A first exemplary embodiment of a device typically improved by the present invention is illustrated schematically. The device according to this first example includes a multi-beam scanning electron microscope (MBSEM). MBSEM 1 includes a multi-beam charged particle generator 2 for generating an array of primary charged particle wavelets (in this case, an array of primary electron wavelets 3). The multi-beam electron generator includes at least one electron source 4 for generating a diverging electron beam 5. The diverging electron beam 5 is split into an array of focused primary electron wavelets 3 by an aperture lens array 6. As schematically indicated by arrow P, the primary electron wavelets 3 are then directed toward a sample 15 in a sample holder 17.

[0030] Multiple images from source 4 are positioned on the object-side principal plane of accelerator lens 7. Accelerator lens 7 guides the primary electron wavelet 3 toward optical axis 8 and generates a first common crossover 9 for all primary electron wavelet 3. The first common crossover 9 is imaged onto a variable aperture 16, which acts as a current-limiting aperture, by magnetofocusing lens 10. At the variable aperture 16, a second common crossover for all primary electron wavelet 3 is generated.

[0031] The MBSEM includes a lens system for guiding the primary charged particle wavelets 3 from a common intersection at the variable aperture 16 toward the sample surface and for focusing all the primary charged particle wavelets 3 onto a single spot array on the sample surface. The lens system includes an intermediate magnetic lens 13 for imaging the variable aperture 16 onto the coma-free plane of the objective lens 14, which generates an array of focused primary electron wavelets on the sample surface.

[0032] In addition, the MBSEM is equipped with a scanning coil 18 for scanning an array of focused primary electron wavelets on the sample surface.

[0033] Therefore, the MBSEM includes a charged particle column for generating an array of multiple charged particle wavelet beams 3 and guiding the array of multiple charged particle wavelet beams 3 toward the sample holder 17. The charged particle column includes an objective lens 14 for focusing the charged particle wavelet beams of the array of multiple charged particle wavelet beams into a charged particle beam spot array at or near the sample surface. The objective lens 14 includes a magnetic lens shared by all the charged particle wavelet beams of the array of multiple charged particle wavelet beams 3.

[0034] Figure 1The apparatus further includes a position sensor 19 and a control unit 20. The position sensor 19 is configured to provide a signal depending on the position of the sample 15 in the direction parallel to the optical axis 8 of the charged particle column. The control unit 20 is connected to the position sensor 19 to receive the signal and is also connected to a sample holder 17 to control actuators in the sample holder 17 to move the sample 15. The control unit 20 is configured to control the position of the sample holder 17, at least in the direction parallel to the optical axis 8 of the charged particle column, based on the signal from the position sensor 19. The position sensor 19, control unit 20, and sample holder 17 are configured to provide a control loop to position the sample 15 in the direction parallel to the optical axis 8. In this way, the sample 15 can be arranged along the optical axis 8 at a desired location where the array of charged particle wavelets 3 has a desired orientation or alignment, and the control loop can be used to hold the sample 15 at the desired location. During the inspection of sample 15, the MBSEM setup is preferably kept constant, so that the spacing and orientation of the array of multiple charged particle wavelet beams 3 remain constant.

[0035] It should be noted that the position sensor 19 preferably measures the position of the sample 15 on the sample holder 17, which is aligned with the optical axis 8. Because the position sensor 19 is arranged spaced apart from the optical axis 8 in a direction perpendicular to the optical axis 8, the distance between the sensor 19 and the sample holder 17 is sensitive to tilt errors. This tilt error can be substantially mitigated by using a method such as... Figure 1 The two position sensors 19 and 19' shown schematically are used to prevent this.

[0036] Alternatively, the two position sensors 19, 19' can be configured to use triangulation to determine the position of the sample 15 along the optical axis 8.

[0037] Further attention should be paid to, such as Figure 1 The MBSEM presented here is typically arranged in a vacuum chamber. In addition, the MBSEM is usually equipped with sensors for detecting secondary charged particles and / or electromagnetic radiation originating from sample 15 when a primary charged particle wavelet 3 strikes sample 15.

[0038] Figure 2 A second exemplary embodiment of a device typically improved by the present invention is illustrated schematically. The device according to this second example is characterized by the integration of a multi-beam charged particle inspection device (e.g., a multi-beam scanning electron microscope 30 (MBSEM)) and an optical inspection device (e.g., an optical microscope 50). The multi-beam scanning electron microscope 30 (MBSEM) and the optical inspection device (such as the optical microscope 50) are mechanically coupled.

[0039] MBSEM 30 can be substantially the same device as presented in the first example above. Thus, MBSEM 30 includes a multi-beam charged particle generator 32 for generating an array of primary charged particle wavelets (in this case, an array of primary electron wavelets 33). The multi-beam electron generator includes at least one electron source 34 for generating a diverging electron beam 35. The diverging electron beam 35 is split into an array of focused primary electron wavelets 33 by an aperture lens array 36. The primary electron wavelets 33 are then directed toward the sample 45 on the sample holder 47. Multiple images of the source 34 are positioned on the object-side principal plane of the accelerator lens 37. The accelerator lens 37 directs the primary electron wavelets 33 toward the optical axis 38 and generates a first common cross 39 of all the primary electron wavelets 33. The first common cross 39 is imaged onto a variable aperture 46, which acts as a current-limiting aperture, by a magnetic focusing lens 40. At the variable aperture 46, a second common cross of all the primary electron wavelets 33 is generated. The MBSEM includes a lens system for guiding a common cross of primary charged particle wavelets 33 from a variable aperture 46 toward the sample surface and for focusing all the primary charged particle wavelets 33 onto a single spot array on the sample surface. The lens system includes an intermediate magnetic lens 43 for imaging the variable aperture 46 onto the coma-free plane of an objective lens 44, which generates an array of focused primary electron wavelets on the sample surface. Furthermore, the MBSEM is equipped with a scanning coil 48 for scanning the array of focused primary electron wavelets 33 on the surface of the sample 45.

[0040] Preferably, the MBSEM also includes a charged particle sensor 49 configured to detect secondary charged particles and / or electromagnetic radiation originating from the sample when the primary charged particle wavelet 33 strikes the sample 45. For clarity, the trajectory of the secondary charged particles is not shown in the figure, and the charged particle sensor 49 is also presented very schematically.

[0041] like Figure 2 As shown, the MBSEM is arranged inside a vacuum chamber 31, which includes an output port 70 for connecting the vacuum chamber 31 to a vacuum pump (not shown).

[0042] Below the sample holder 47, an optical microscope 50 is arranged. The optical microscope 50 includes a microscope objective 51 arranged inside the vacuum chamber 31. The other main parts of the optical microscope system are arranged outside the vacuum chamber 31. Light from the sample 45 is collected by the microscope objective 51 and imaged onto a light detector 54 (e.g., a CCD sensor) via a mirror 52, a window 53, and a translucent mirror or dichroic mirror 56.

[0043] It should be noted that an optical microscope 50, including a light source 55 (e.g., an LED), may also be used. The emitted light from the light source 55 is directed toward a translucent mirror or dichroic mirror 56 and is guided into the vacuum chamber 31 via a window 53. This light is coupled to the microscope objective 51 via a mirror 52 to illuminate the sample 45 from the bottom.

[0044] In use, the photodetector 54 is configured to detect reflected light from the sample 45. Furthermore, the photodetector 54 is configured to detect photons generated by one or more of the charged particle wavelets 33 when one or more of the charged particle wavelets strike the sample 45, or when the one or more charged particle wavelets strike the luminescent material layer 42 after passing through the sample 45.

[0045] The photodetector 54 can be used as an optical focusing sensor, for example by providing a signal depending on whether the sample 45 is in focus on the photodetector 54. Alternatively, the optical microscope may be equipped with a separate optical focusing sensor configured to provide a signal depending on the distance between the sample holder 47 or the sample surface and the optical objective, for example using well-known techniques for providing autofocus (such as triangulation, phase detection, or contrast detection).

[0046] Signals from photodetector 54 or a separate optical focusing sensor are provided to control unit 60, which is configured to control the position of sample holder 47 based on signals from photodetector 54 or a separate optical focusing sensor, at least in a direction parallel to the optical axis 38 of MBSEM 30.

[0047] It should be noted that the optical focusing sensor preferably uses a wavelength that is at least substantially different from the wavelength of the emitted light from the sample. In this way, the optical focusing sensor does not interfere with the collection of the emitted light from the sample.

[0048] As described above, the final MBSEM lens (also referred to as objective 44) comprises a magnetic lens shared by all charged particle wavelets of the array of the plurality of charged particle wavelets 33. The pattern of the array of the plurality of charged particle wavelets 33 projected onto the sample 45 by the magnetic lens is typically non-telecentric. Even if the sample holder 47 is configured to place the sample 45 in a field-free region, changes in the position of the sample 45 along the direction of the optical axis 38 typically require adjustment of the focus, thus adjusting the magnetic field strength of the magnetic lens to keep the sample 45 focused. Therefore, if the excitation / intensity of the magnetic lens changes (e.g., for focusing), the pattern of the array of the plurality of charged particle wavelets 33 will rotate and / or change the magnification. To address this problem, the present invention provides a method comprising the following steps: a. Adjust the position of sample 45 along the optical axis of MBSEM 30 so that sample 45 is at the focal point of photodetector 54.

[0049] b. Focus an array of multiple charged particle wavelet beams 33 onto the sample 45, setting the desired spacing (magnification). The sample 45, the optical focus, and the MBSEM focus are now in the same plane.

[0050] c. Provide a photodetector 54 and / or a separate optical focusing sensor, the photodetector 54 and / or the separate optical focusing sensor being configured to provide a signal measuring the distance between the optical focus and the sample surface.

[0051] d. This signal is used in the control unit to control the sample holder 47 to keep the sample surface within the focal point of the photodetector 54.

[0052] In this way, sample 45 is held within the focal point of photodetector 54, and therefore also within the focal point of MBSEM. During the examination of sample 45, the MBSEM setup remains substantially constant, and thus the spacing and orientation of the array of charged particle beams on the sample surface (especially the rotation about optical axis 8) remain substantially constant.

[0053] It should be noted that steps a and b above can be repeated to obtain the desired alignment.

[0054] It should be understood that the above description is intended to illustrate the operation of preferred embodiments and does not imply limitation of the scope of the invention. Many variations will be apparent to those skilled in the art from the above discussion, and these variations will still be covered by the scope of the invention.

[0055] In summary, the present invention provides an apparatus for examining a sample, comprising: a sample holder and a charged particle column, the sample holder for holding the sample in a sample plane; the charged particle column for generating an array of multiple charged particle wavelets and guiding the array toward the sample holder. The charged particle column includes an objective lens for focusing the array of charged particle wavelets onto a spot array of charged particle beams in or near the sample plane. The objective lens includes a magnetic lens shared by all charged particle wavelets. The apparatus further includes: a position sensor and a control unit, the position sensor for providing a signal depending on the position of the sample along the optical axis of the charged particle column; the control unit for controlling the position of the sample holder based on the signal from the position sensor to maintain a constant spacing and / or orientation of the spots on the sample.

Claims

1. An apparatus for inspecting a sample, wherein, The device includes: A sample holder for holding the sample in a sample plane; A multi-beam charged particle inspection device includes a charged particle column for generating multiple charged particle wavelet arrays and guiding the multiple charged particle wavelet arrays toward a sample holder. The charged particle column includes an objective lens for focusing the charged particle wavelets of the multiple charged particle wavelet arrays into a charged particle beam spot array at or near the sample plane. The objective lens includes a magnetic objective lens shared by all the charged particle wavelets in the multiple charged particle wavelet arrays. An optical inspection apparatus, the optical inspection apparatus comprising: A photodetector for detecting photons generated by one or more of the charged particle wavelets in the plurality of charged particle wavelet arrays when one or more of the charged particle wavelets strike the sample, or when one or more of the charged particle wavelets strike the luminescent material layer after passing through the sample; An optical component for projecting or imaging at least a portion of the photons onto the photodetector along a beam path, wherein the optical component includes an optical objective for collecting photons from the sample and / or the luminescent material layer; An optical focusing sensor configured to provide a signal that depends on the distance between the sample holder or sample plane and the optical objective; The multi-beam charged particle inspection device and the optical inspection device are mechanically coupled, and A control unit is configured to control the position of the sample holder based on a signal from the optical focusing sensor of the optical inspection apparatus, at least in a direction parallel to the optical axis of the charged particle column of the multi-beam charged particle inspection apparatus, so as to keep the portion of the sample inspected by means of the array of multiple charged particle beams of the multi-beam charged particle inspection apparatus positioned at a desired distance from the magnetic objective of the multi-beam charged particle inspection apparatus, thereby maintaining the multiple charged particle beam spot array in or near the sample plane in a desired orientation.

2. The apparatus according to claim 1, wherein, The photodetector is used as an optical focusing sensor.

3. The apparatus according to claim 1, wherein, The optical components include an optical microscope, wherein the optical microscope is equipped with an independent optical focusing sensor.

4. The apparatus according to claim 1, 2, or 3, wherein, The optical objective includes an optical axis, wherein the device is configured such that the optical axis is substantially parallel to the optical axis of the charged particle column.

5. The apparatus according to claim 1, 2, or 3, wherein, The device is configured to provide a fixed distance between the magnetic objective and the focal point of the optical component.

6. The apparatus according to claim 1, 2, or 3, wherein, The optical components are also configured to image the sample plane onto the photodetector.

7. The apparatus according to claim 1, 2, or 3, wherein, The device further includes a position sensor configured to provide a signal depending on the position of the sample in a direction along the optical axis of the charged particle column, and The control unit is configured to control the position of the sample holder based on signals from the position sensor, at least in a direction parallel to the optical axis of the charged particle column.

8. The apparatus according to claim 7, wherein, The position sensor is configured such that the signal depends on the position of the sample holder or sample plane relative to the magnetic objective.

9. A method for examining a sample using the apparatus of any one of claims 1-8, wherein, The method includes the following steps: Arrange the sample on the sample holder; The charged particle column of the multi-beam charged particle inspection device generates multiple charged particle wavelet arrays and guides the multiple charged particle wavelet arrays toward the sample. The charged particle column includes an objective lens that focuses the charged particle wavelets of the multiple charged particle wavelet arrays into a charged particle beam spot array at or near the sample plane. The objective lens includes a magnetic objective lens shared by all the charged particle wavelets in the multiple charged particle wavelet arrays. The photodetector of the optical inspection device is used to detect photons generated by one or more of the charged particle wavelet beams in the plurality of charged particle wavelet beam arrays when one or more of the charged particle wavelet beams strike the sample, or when one or more of the charged particle wavelet beams strike the luminescent material layer after passing through the sample; The optical components of the optical inspection device project or image at least a portion of the photons onto the photodetector along the beam path, wherein the optical components include an optical objective for collecting photons from the sample and / or the luminescent material layer; The optical focusing sensor of the optical inspection apparatus is used to provide a signal that depends on the distance between the sample holder or sample plane and the optical objective of the optical inspection apparatus; and Based on the signal from the optical focusing sensor of the optical inspection apparatus, the position of the sample holder is controlled by the control unit at least in the direction parallel to the optical axis of the charged particle column of the multi-beam charged particle inspection apparatus, so as to keep the portion of the sample inspected by means of the array of multiple charged particle beams of the multi-beam charged particle inspection apparatus positioned at a desired distance from the magnetic objective of the multi-beam charged particle inspection apparatus, thereby maintaining the desired orientation of the array of multiple charged particle beam spots on or near the sample plane.

10. The method of claim 9, further comprising the step of: The photodetector or a separate optical focusing sensor is used to provide a signal measuring the distance between the optical focus and the sample plane, wherein the control unit is configured to control the position of the sample holder at least in a direction parallel to the optical axis of the charged particle column based on the signal from the photodetector or the separate optical focusing sensor.

11. The method according to claim 9 or 10, wherein, The focal point of the optical component is kept at a fixed distance from the magnetic objective lens.

12. The method according to claim 9 or 10, further comprising the step of: A position sensor is used to provide a signal that depends on the position of the sample in the direction along the optical axis of the charged particle column, wherein the position sensor is configured such that the signal depends on the position of the sample holder or sample plane relative to the magnetic objective. The position of the sample holder is controlled by a control unit based on signals from the position sensor, at least in a direction parallel to the optical axis of the charged particle column.

13. A computer-readable medium having computer-executable instructions adapted to cause a device to perform the method according to any one of claims 9-12.

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