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1 SYSTEM AND METHOD FIELD [0001] The embodiments provided herein generally relate charged particle assessment systems and 5 methods of operating charged particle assessment systems. BACKGROUND [0002] When manufacturing semiconductor integrated circuit (IC) chips, undesired pattern defects, as a consequence of, for example, optical effects and incidental particles, inevitably occur on a 10 substrate (i.e. wafer) or a mask during the fabrication processes, thereby reducing the yield. Monitoring the extent of the undesired pattern defects is therefore an important process in the manufacture of IC chips. More generally, the inspection and/or measurement of a surface of a substrate, or other object/material, is an important process during and/or after its manufacture. [0003] Pattern inspection tools with a charged particle beam have been used to inspect objects, for 15 example to detect pattern defects. These tools typically use electron microscopy techniques, such as a scanning electron microscope (SEM). In a SEM, a primary electron beam of electrons at a relatively high energy is targeted with a final deceleration step in order to land on a sample at a relatively low landing energy. The beam of electrons is focused as a probing spot on the sample. The interactions between the material structure at the probing spot and the landing electrons from the beam of 20 electrons cause electrons to be emitted from the surface, such as secondary electrons, backscattered electrons or Auger electrons. The generated secondary electrons may be emitted from the material structure of the sample. By scanning the primary electron beam as the probing spot over the sample surface, secondary electrons can be emitted across the surface of the sample. By collecting these emitted secondary electrons from the sample surface, a pattern inspection tool may obtain an image 25 representing characteristics of the material structure of the surface of the sample. The intensity of the electron beams comprising the backscattered electrons and the secondary electrons may vary based on the properties of the internal and external structures of the sample, and thereby may indicate whether the sample has defects. [0004] When the primary electron beam scans the sample, charges may be accumulated on the 30 sample due to large beam current, which may affect the quality of the image. To regulate the accumulated charges on the sample, an Advanced Charge Controller (ACC) module may be employed to illuminate a light beam, such as a laser beam, on the sample, so as to control the accumulated charges due to effects such as photoconductivity, photoelectric, or thermal effects. It can be difficult to illuminate the light beam on the sample. For example, the dimensions of the pattern inspection tool 35 may make it difficult to reach the sample with the light beam. SUMMARY 2 [0005] It is an object of the present disclosure to provide embodiments that support illuminating the sample with a light beam for an ACC module. [0006] According to a first aspect of the invention, there is provided a charged particle assessment system comprising: a sample holder configured to hold a sample having a surface; a charged particle- 5 optical device configured to project a charged particle beam towards the sample, the charged particle beam having a field of view corresponding to a portion of the surface of the sample, the charged particle-optical device having a facing surface facing the sample holder; and a projection assembly arranged to direct a light beam along a light path such that the light beam reflects off the facing surface up-beam, with respect to the light path, of being incident on the portion of the surface of the 10 sample. BRIEF DESCRIPTION OF FIGURES [0007] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments, taken in conjunction with the accompanying drawings. 15 [0008] FIG. 1 is a schematic diagram illustrating an exemplary electron beam inspection apparatus. [0009] FIG. 2 is a schematic diagram illustrating an exemplary multi-beam charged particle assessment system that is part of the exemplary electron beam inspection apparatus of FIG. 1 . [0010] FIG. 3 is a schematic diagram of an exemplary multi-beam charged particle assessment system according to an embodiment. 20 [0011] FIG. 4 is a schematic diagram of an exemplary charged particle assessment system comprising a macro collimator and macro scan deflector. [0012] FIG. 5 is a schematic diagram of an exemplary multi-beam charged particle assessment system according to an embodiment. [0013] FIG. 6 is a schematic diagram of part of the multi-beam charged particle assessment system 25 of FIG. 5 . [0014] FIG. 7 is a schematic cross-sectional view of an objective lens array of a charged particle assessment system according to an embodiment. [0015] FIG. 8 is a bottom view of a modification of the objective lens array of FIG. 7 . [0016] FIG. 9 is an enlarged schematic cross-sectional view of a detector incorporated in the 30 objective lens array of FIG. 7 . [0017] FIG. 10 is a bottom view of a detector element of a detector. [0018] FIG. 11 is a schematic diagram of an exemplary single beam charged particle assessment system according to an embodiment. [0019] FIG. 12 is a schematic diagram of a light beam entering between the electron-optical device 35 and the sample according to an embodiment. [0020] FIG. 13 is a diagram explaining the focus angle of a light beam entering between the electron-optical device and the sample according to an embodiment. 3 [0021] FIG. 14 is a schematic diagram of a projection assembly projecting a light beam entering between the electron-optical device and the sample according to an embodiment. [0022] FIG. 15 is a schematic diagram of a light beam entering between the electron-optical device and the sample according to an embodiment. 5 [0023] The schematic diagrams and views show the components described below. However, the components depicted in the figures are not to scale. DETAILED DESCRIPTION [0024] Reference will now be made in detail to exemplary embodiments, examples of which are 10 illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the invention. Instead, they are merely examples of apparatuses and methods consistent with the spirit and scope of the 15 invention. [0025] The enhanced computing power of electronic devices, which reduces the physical size of the devices, can be accomplished by significantly increasing the packing density of circuit components such as transistors, capacitors, diodes, etc. on an IC chip. This has been enabled by increased resolution enabling yet smaller structures to be made. For example, an IC chip of a smart phone, 20 which is the size of a thumbnail and available in, or earlier than, 2019, may include over 2 billion transistors, the size of each transistor being less than 1/1000th of a human hair. Thus, it is not surprising that semiconductor IC manufacturing is a complex and time-consuming process, with hundreds of individual steps. Errors in even one step have the potential to dramatically affect the functioning of the final product. Just one “killer defect” can cause device failure. The goal of the 25 manufacturing process is to improve the overall yield of the process. For example, to obtain a 75% yield for a 50-step process (where a step can indicate the number of layers formed on a wafer), each individual step must have a yield greater than 99.4%,. If each individual step had a yield of 95%, the overall process yield would be as low as 7%. [0026] While high process yield is desirable in an IC chip manufacturing facility, maintaining a high 30 substrate (i.e. wafer) throughput, defined as the number of substrates processed per hour, is also essential. High process yield and high substrate throughput can be impacted by the presence of a defect. This is especially true if operator intervention is required for reviewing the defects. Thus, high throughput detection and identification of micro and nano-scale defects by inspection tools (such as a Scanning Electron Microscope (‘SEM’)) is essential for maintaining high yield and low cost. 35 [0027] A SEM comprises a scanning device and a detector apparatus. The scanning device comprises an illumination apparatus that comprises an electron source, for generating primary electrons, and a projection apparatus for scanning a sample, such as a substrate, with one or more 4 focused beams of primary electrons. Together at least the illumination apparatus, or illumination system, and the projection apparatus, or projection system, may be referred to together as the electron- optical system or apparatus. The primary electrons interact with the sample and generate secondary electrons. The detection apparatus captures the secondary electrons from the sample as the sample is 5 scanned so that the SEM can create an image of the scanned area of the sample. For high throughput inspection, some of the inspection apparatuses use multiple focused beams, i.e. a multi-beam, of primary electrons. The component beams of the multi-beam may be referred to as sub-beams or beamlets. A multi-beam can scan different parts of a sample simultaneously. A multi-beam inspection apparatus can therefore inspect a sample at a much higher speed than a single-beam 10 inspection apparatus. [0028] An implementation of a known multi-beam inspection apparatus is described below. [0029] The figures are schematic. Relative dimensions of components in drawings are therefore exaggerated for clarity. Within the following description of drawings the same or like reference numbers refer to the same or like components or entities, and only the differences with respect to the 15 individual embodiments are described. While the description and drawings are directed to an electron-optical system, it is appreciated that the embodiments are not used to limit the present disclosure to specific charged particles. References to electrons throughout the present document may therefore be more generally be considered to be references to charged particles, with the charged particles not necessarily being electrons. 20 [0030] Reference is now made to FIG. 1 , which is a schematic diagram illustrating an exemplary charged particle beam inspection apparatus 100. The charged particle beam inspection apparatus 100 of FIG. 1 includes a main chamber 10, a load lock chamber 20, a charged particle assessment system ...