Method for evaluating sample, device for evaluating sample

Abstract

The present disclosure relates to devices and methods for evaluating a sample (208) using charged particles. In one arrangement, the degassing is performed by exposing a target region of a sample (208) to charged particles to excite the degassing. The rate of degassing from the target region is measured during the degassing action. The initiation of the evaluation of the sample (208) is controlled based on a characteristic of the measured rate of degassing. The evaluation of the sample (208) includes exposing the target region to charged particles and detecting signal charged particles from the target region.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP Application No. 22184150, filed on July 11, 2020, and incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to methods and apparatus for evaluating samples using charged particles. Background Art

[0004] When manufacturing semiconductor integrated circuit (IC) chips, due to, for example, optical effects and incidental particles, undesirable pattern defects will inevitably appear on the substrate (i.e., wafer) or mask during the manufacturing process, thereby reducing the yield. Therefore, monitoring the degree of undesirable pattern defects is an important process in IC chip manufacturing. More generally, the evaluation (e.g., inspection and / or measurement) of the surface of a substrate or other object / material is an important process during and / or after its manufacture.

[0005] Known evaluation tools (referred to herein as evaluation systems) use charged particle beams to evaluate objects (which may be referred to as samples), for example, to detect pattern defects. These systems typically use electron microscopy techniques, such as scanning electron microscopes (SEMs). In an SEM, a primary electron beam of electrons at relatively high energy is targeted at a final deceleration step so as to land on a sample with a relatively low landing energy. The electron beam is focused onto the sample as a probing spot. The interaction between the material structure at the probing spot and the landing electrons from the electron beam causes signal electrons to be emitted from the surface, such as secondary electrons, backscattered electrons, or Auger electrons. Signal electrons can be emitted from the material structure of the sample. By scanning the primary electron beam as a probing spot on the sample surface, signal electrons can be emitted across the sample surface. By collecting these emitted signal electrons from the sample surface, the pattern inspection system can obtain an image representing the characteristics of the material structure of the sample surface.

[0006] It has been observed that electrons impinging on a surface can stimulate degassing from the surface. Gases generated in this way may result in the deposition of unwanted materials on device components exposed to the gas. Such deposition can be driven by charged particles and is therefore particularly likely to occur when charged particles impinge on components in the presence of a gas. Deposition can be reduced or eliminated by extracting the outgassed gas before it can contribute to deposition, but this is not always possible, particularly where space is limited in the area where degassing occurs. Summary of the invention

[0007] It is an object of the present disclosure to provide methods and apparatus that at least partially address the challenges mentioned above, such as reducing or eliminating contamination caused by material deposition due to outgassing originating from charged particle excitation.

[0008] According to one aspect of the present invention, a method for evaluating a sample using charged particles is provided, comprising: performing degassing by exposing a target area of ​​the sample to charged particles to stimulate degassing; measuring the rate of degassing from the target area during the degassing; and controlling the start of evaluation of the sample based on characteristics of the measured degassing rate, the evaluation of the sample comprising exposing the target area to charged particles and detecting signal charged particles from the target area.

[0009] According to one aspect of the present invention, there is provided an apparatus for evaluating a sample using charged particles, the apparatus comprising: a degassing device configured to expose a target area of ​​the sample to charged particles to stimulate degassing from the target area; a degassing sensor configured to measure the rate of degassing from the target area; an evaluation device configured to perform evaluation of the sample by exposing the target area to the charged particles and detecting signal charged particles from the target area; and a control system configured to control the evaluation device to initiate evaluation of the sample in response to an output from the degassing sensor.

[0010] According to one aspect of the present invention, a method for evaluating a sample using charged particles is provided, comprising: performing degassing by exposing a target area of ​​the sample to charged particles to stimulate degassing until the rate of stimulated degassing is lower than a threshold count of the number of molecules of a component of interest (desirably hydrocarbons) degassed per charged particle impacting the target area, the threshold count desirably being 0.01 moles of molecules degassed per charged particle impacting the target area; and subsequently evaluating the sample by exposing the target area to charged particles and detecting signal charged particles from the target area.

[0011] According to one aspect of the present invention, there is provided an apparatus for evaluating a sample using charged particles, the apparatus comprising: a degassing device configured to expose a target area of ​​the sample to charged particles to stimulate degassing from the target area; an evaluation device configured to perform evaluation of the sample by exposing the target area to the charged particles and detecting signal charged particles from the target area; and a control system configured to control the evaluation device to start evaluation of the sample after the degassing device exposes the target area of ​​the sample to the charged particles until the rate of the stimulated degassing is lower than a threshold count of the number of moles of a component of interest (desirably hydrocarbons) degassed per charged particle impacting the target area, the threshold count desirably being 0.01 moles degassed per charged particle impacting the target area. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and other aspects of the present disclosure will become more apparent through the description of exemplary embodiments with reference to the attached drawings.

[0013] Figure 1 is a schematic diagram illustrating an exemplary charged particle beam inspection apparatus.

[0014] Figure 2 It is illustrated as Figure 1 Schematic diagram of an exemplary multi-beam apparatus of a portion of an exemplary charged particle beam inspection apparatus.

[0015] Figure 3 is a schematic diagram of an exemplary electron optical column including a focusing lens array, an objective lens array, and a detector array.

[0016] Figure 4 is a schematic cross-sectional view of a portion of an exemplary arrangement of a detector array and an objective lens array.

[0017] Figure 5 yes Figure 4 Bottom view of a portion of the detector array.

[0018] Figure 6 yes Figure 4 Bottom view of a modified version of a portion of the objective lens array.

[0019] Figure 7 is a schematic diagram of an exemplary electron optical device including an objective lens array and a beam splitter.

[0020] Figure 8 is a flow chart depicting an example method for evaluating a sample using charged particles.

[0021] Fig. 9 is a flow chart depicting yet another example method of evaluating a sample using charged particles.

[0022] Fig.10 is a flow chart depicting yet another example method of evaluating a sample using charged particles.

[0023] Fig.11 is a schematic diagram of an exemplary apparatus for evaluating a sample having a degassing device, a degassing sensor, and an evaluation device. DETAILED DESCRIPTION

[0024] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description is made with reference to the accompanying drawings, and unless otherwise indicated, the same reference numerals in different drawings represent the same or similar elements. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations consistent with the present invention. Instead, they are merely examples of devices and methods consistent with various aspects of the present invention as recited in the appended claims.

[0025] The enhanced computing power of electronic devices can be achieved by significantly increasing the packaging density of circuit components (such as transistors, capacitors, diodes, etc.) on IC chips, which reduces the physical size of the device. This is achieved by increasing the resolution, which enables the manufacture of smaller structures. For example, the IC chip of a smartphone (which is the size of a thumbnail and available in 2019 or earlier) may include more than 2 billion transistors, each of which is less than 1 / 1000 the size of a human hair. Not surprisingly, semiconductor IC manufacturing is a complex and time-consuming process with hundreds of individual steps. Even an error in one step has the potential to greatly affect the operation of the final product. In some cases, even a single defect can cause device failure. The goal of the manufacturing process is to increase the overall yield of the process. For example, in order to obtain a 75% yield for a 50-step process (where one step can indicate the number of layers formed on the wafer), each individual step must have a yield greater than 99.4%. If each individual step has a 95% yield, the total process yield will be as low as 7%.

[0026] While high process yields are desired in IC chip manufacturing facilities, it is also essential to maintain high substrate (i.e., wafer) throughput, which is defined as the number of substrates processed per hour. The presence of defects may compromise both high process yields and high substrate throughput. This is especially true if operator intervention is required to review the defects. Therefore, high throughput detection and identification of micron and nanometer-scale defects by inspection systems, such as scanning electron microscopes ("SEMs"), is important to maintaining high yields and low costs.

[0027] The SEM includes a scanning device and a detector device. The scanning device includes an irradiation device, which includes an electron source for generating primary electrons and a projection device for scanning a sample such as a substrate using one or more focused primary electron beams. At least the irradiation device or irradiation system and the projection device or projection system together can be collectively referred to as an electron optical device or column. The primary electrons interact with the sample and generate secondary electrons. The detection device captures secondary electrons from the sample as the sample is scanned, so that the SEM can create an image of the scanned area of ​​the sample. For high-throughput inspection, some inspection devices use multiple focused primary electron beams, i.e., multiple beams. The component beams in the multiple beams can be referred to as sub-beams or beam waves. Multiple beams can scan different parts of the sample at the same time. Therefore, a multi-beam inspection device can inspect samples at a much higher speed than a single-beam inspection device.

[0028] The following describes a known implementation of a multi-beam inspection device.

[0029] The drawings are schematic. Therefore, for the sake of clarity, the relative sizes of the components in the drawings are exaggerated. In the following description of the drawings, the same or similar reference numerals refer to the same or similar components or entities, and only the differences with respect to the various embodiments are described. Although the description and drawings refer to electron-optical devices, it is to be understood that the embodiments are not intended to limit the present disclosure to specific charged particles. Therefore, references to electrons throughout this article can be considered more generally as references to charged particles, which are not necessarily electrons.

[0030] Now refer to Figure 1 , Figure 1 is a schematic diagram illustrating an exemplary charged particle beam inspection apparatus 100 , which may also be referred to as a charged particle beam evaluation system or simply an evaluation system. Figure 1 The charged particle beam inspection apparatus 100 includes a main chamber 10, a load lock chamber 20, an electron beam device 40, an equipment front end module (EFEM) 30, and a controller 50. The controller may be distributed between different components of the evaluation system, including, for example, in the electron beam device 40. The electron beam device 40 is located in the main chamber 10.

[0031] The EFEM 30 includes a first feed port 30a and a second feed port 30b. The EFEM 30 may include (one or more) additional feed ports. The first feed port 30a and the second feed port 30b may, for example, accommodate a substrate front opening pod (FOUP) containing a substrate to be inspected (e.g., a semiconductor substrate or a substrate made of (one or more) other materials) or a sample (substrate, wafer, and sample are collectively referred to as "sample" hereinafter). One or more robotic arms (not shown) in the EFEM 30 transport the sample to the load lock chamber 20.

[0032] The load lock chamber 20 is used to remove the gas around the sample. This creates a vacuum with a local gas pressure lower than the pressure in the surrounding environment. The load lock chamber 20 can be connected to a load lock vacuum pump system (not shown), which removes the gas particles in the load lock chamber 20. The operation of the load lock vacuum pump system enables the load lock chamber to reach a first pressure lower than atmospheric pressure. After reaching the first pressure, one or more robot arms (not shown) transport the sample from the load lock chamber 20 to the main chamber 10. The main chamber 10 is connected to the main chamber vacuum pump system (not shown). The main chamber vacuum pump system removes the gas particles in the main chamber 10 so that the pressure around the sample reaches a second pressure lower than the first pressure. After reaching the second pressure, the sample is transported to an electron beam device, and the sample can be inspected by the electron beam device. The electron beam device 40 may include a multi-beam electron optical device.

[0033] The controller 50 is connected to the electron beam device 40 in a signal manner (e.g., electronically), for example, as a distributed component of the controller 50. The controller 50 can be a processor (such as a computer) configured to control the charged particle beam inspection device 100. The controller 50 can also include processing circuit devices configured to perform various signal and image processing functions. Although the controller 50 is in Figure 1 Controller 50 is shown as being outside the structure including main chamber 10, loading lock chamber 20 and EFEM 30, but it is understood that controller 50 can be part of the structure. Controller 50 can be located in one of the constituent elements of the charged particle beam inspection device, or it can be distributed on at least two constituent elements. Although the present disclosure provides an example of a main chamber 10 that accommodates an electron beam inspection device, it should be noted that the broadest aspects of the present disclosure are not limited to chambers that accommodate electron beam inspection devices. On the contrary, it is understood that the aforementioned principles can also be applied to other systems and other device arrangements that operate at a second pressure.

[0034] Now refer to Figure 2 , Figure 2 is a schematic diagram illustrating an exemplary charged particle beam evaluation apparatus 40. The electron beam apparatus 40 may be configured as Figure 11. The electron beam device 40 includes an electron source 201 and a charged particle column (or device) 230. The charged particle device 230 may refer to or include a projection device for directing a primary charged particle beam 202 toward a sample 208. The electron source 201 and its associated and constituent charged particle optical elements may be referred to as an irradiation device for generating a primary charged particle beam 202. The evaluation device includes a sample support supporting the sample 208. The sample support in this example includes a sample holder 207. The sample holder 207 holds a sample 208 (e.g., a substrate or mask) for evaluation. The sample holder 207 is supported by a motorized or actuated stage 209. The electron beam device 40 also includes a detector 240. The detector 240 detects signal charged particles (e.g., electrons) from the sample 208. The detector 240 generates a detection signal when the signal charged particles are detected.

[0035] The electron source 201 may include a cathode (not shown) and an extractor or anode (not shown). During operation, the electron source 201 is configured to emit electrons from the cathode as primary electrons. The primary electrons are extracted or accelerated by the extractor and / or the anode to form a primary electron beam 202.

[0036] The charged particle device 230 is configured to convert the primary electron beam 202 into a plurality of charged particle beams 211, 212, 213, and direct each beam onto the sample 208. Although three beams are illustrated for simplicity, there may be tens, hundreds, thousands, tens of thousands or even hundreds of thousands (or more) of beams. A beam may be referred to as a beam wave or a beamlet. A plurality of charged particle beams may be collectively referred to as a multi-beam or a beam grid. A beam grid having such a plurality of beams (e.g., more than one thousand beams) may have, for example, a field of view of more than 0.5 mm, for example, in the range of 0.5 to 30 mm or 1 to 30 mm.

[0037] The controller 50 (e.g., a control system including a distributed controller) may be connected to Figure 1 The controller 50 may be used to control various parts of the charged particle beam inspection apparatus 100, such as the electron source 201, the electron detection device 240, the charged particle device 230, and the motorized stage 209. The controller 50 may perform various image and signal processing functions. The controller 50 may also generate various control signals to manage the operation of the charged particle beam inspection apparatus 100, including the operation of the electron beam device 40.

[0038] The charged particle device 230 can be configured to focus the beams 211, 212, and 213 onto the sample 208 for inspection, and three detection spots 221, 222, and 223 can be formed on the surface of the sample 208. The charged particle device 230 can be configured to deflect the primary beams 211, 212, and 213 to scan the detection spots 221, 222, and 223 across the respective scanning areas in the section of the surface of the sample 208. In response to the primary beams 211, 212, and 213 being incident on the detection spots 221, 222, and 223 on the sample 208, electrons including secondary electrons and backscattered electrons are generated from the sample 208, which can be referred to as signal charged particles. The secondary electrons typically have an electron energy of up to fifty electron volts (≤50 eV), and the electron energy of the backscattered electrons is typically between fifty electron volts (50 eV) and the landing energy of the primary beams 211, 212, and 213.

[0039] The detector 240 can send the detection signal generated in the detector 240 (e.g., as an imaging or detection signal) to the controller 50 or a signal processing system (not shown, which can be part of the controller 50), for example, to construct an image of the corresponding scan area of ​​the sample 208. The detector 240 can be at least partially incorporated into the charged particle device 230, or can be separate from the charged particle device 230, such as in the case where a secondary optical column guides the secondary electrons to the detector 240.

[0040] The controller 50 may include an image processing system including an image acquisition device (not shown) and a storage device (not shown). For example, the controller may include a processor, a computer, a server, a mainframe, a terminal, a personal computer, any kind of mobile computing device, etc., or a combination thereof. The image acquisition device may include at least a portion of the processing function of the controller. Therefore, the image acquisition device may include at least one or more processors. The image acquisition device may be communicatively coupled to a detector 240 that allows signal communication, such as an electrical conductor, a fiber optic cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, radio, etc., or a combination thereof. The image acquisition device may receive a detection signal from the detector 240, may process the data included in the signal, and may construct an image based thereon. The image acquisition device may thus acquire an image of the sample 208. The image acquisition device may also perform various post-processing functions, such as generating a contour, superimposing an indicator on the acquired image, etc. The image acquisition device may be configured to perform adjustments to the brightness and contrast of the acquired image, etc. The storage device may be a storage medium such as a hard disk, a flash drive, a cloud storage device, a random access memory (RAM), other types of computer-readable memory, etc. The storage device may be coupled to the image acquirer and may be used to save the scanned raw image data as a raw image and a post-processed image.

[0041] The image acquirer can acquire one or more images of the sample 208 based on the imaging signal received from the detector 240. The imaging signal can correspond to a scanning operation for performing charged particle imaging. The acquired image can be a single image including multiple imaging areas. The single image can be stored in a storage device. The single image can be an original image that can be divided into multiple areas. Each of the areas can include an imaging area that contains features of the sample 208. The acquired image can include multiple images of a single imaging area of ​​the sample 208 sampled multiple times over a period of time. The multiple images can be stored in a storage device. The controller 50 can be configured to perform an image processing step using multiple images of the same location of the sample 208.

[0042] The controller 50 may include a measurement circuit device (e.g., an analog-to-digital converter) to obtain the distribution of the detected secondary electrons. A portion of the controller for this function may be included in or near the detector. The electron distribution data collected during the detection time window can be used in combination with the corresponding scan path data of each of the primary beams 211, 212, and 213 incident on the sample surface to reconstruct an image of the inspected sample structure. The reconstructed image can be used to reveal various features of the internal or external structure of the sample 208. Therefore, the reconstructed image can be used to reveal any defects that may be present in and / or on the sample.

[0043] The controller 50 may control the actuation stage 209 to move the sample 208 during inspection of the sample 208, for example to provide a scanning motion of the stage relative to the path of the primary beam. The controller 50 may enable the actuation stage 209 to move the sample 208, preferably continuously at a constant speed, at least during inspection of the sample, along a direction such as a portion of the scanning motion of the stage. The controller 50 may control the movement of the actuation stage 209 such that it changes the speed of movement of the sample 208 according to various parameters. For example, the controller may control the speed of the stage (including its direction) according to the characteristics of the inspection step and / or scan of the scanning process, for example as disclosed in EPA 21171877.0 filed on May 3, 2021, which is incorporated herein by reference, at least with respect to the combined step and scan strategy of the stage. When controlling the actuation stage, the actuation of the stage and therefore the sample may enable the sample to be positioned, for example dynamically, relative to the path of the primary beam.

[0044] Figure 3is a schematic diagram of an exemplary charged particle device 41 for evaluating an apparatus. For ease of illustration, the lens array is schematically depicted herein by an array of ellipses. Each ellipse represents one of the lenses in the lens array. By convention, ellipses are used to represent lenses, similar to the biconvex form often used in optical lenses. In the context of charged particle devices such as those discussed herein, it is understood that the lens array will typically operate electrostatically, and therefore any physical elements that adopt a biconvex shape may not be required. As described below, the lens array may alternatively include a plurality of plates with apertures. Each plate with an aperture may be referred to as an electrode. The electrodes may be arranged in series along the path of a beam grid of a plurality of charged particle beams (which may also be referred to as sub-beams). Therefore, the electrodes are also connected in series along the path of the charged particle beam of the beam grid.

[0045] The electron source 201 guides the electrons toward the converging lens array 231 forming a part of the charged particle device 230. The electron source 201 is desirably a high brightness thermal field emitter with a good compromise between brightness and total emission current. There may be tens, hundreds or thousands or even tens of thousands of converging lenses 231. The converging lenses in the array 231 may include a multi-electrode lens and have a structure based on EP1602121 A1, which is incorporated herein by reference, and which particularly discloses a lens array for splitting an electron beam into a plurality of sub-beams, wherein the array provides a lens for each sub-beam. The converging lens array may take the form of at least two (preferably three) plates, which act as electrodes, wherein the aperture in each plate is aligned with the aperture in other plates to define the path of the charged particle beam through the plate. At least two plates are maintained at different potentials during operation to achieve the desired lens effect. Between the plates of the converging lens array is an electrically insulating plate, for example, made of insulating materials such as ceramics or glass, with one or more apertures for charged particle beams. Additionally or alternatively, one or more plates may feature apertures each having their own electrodes, for example having an array of electrodes around its periphery, or being arranged as an aperture group with a common electrode. In one variation, one or more of the plates may include multiple sections or strips having multiple apertures. In yet another alternative arrangement, a macro-collimator is provided in place of the converging lens array. The macro-collimator may act on the beam from source 201 before the beam is split into multiple beams. The macro-collimator may be implemented magnetically, electrostatically, or magnetically and electrostatically.

[0046] In some embodiments, the converging lens array is formed by an array of three plates, where the charged particles have the same energy when entering and leaving each lens, and this arrangement can be called a single lens. Therefore, the dispersion only occurs within the single lens itself (between the entry and exit electrodes of the lens), thereby limiting the off-axis chromatic aberration. When the thickness of the converging lens is low (e.g., a few millimeters), the effect of this aberration is small or negligible.

[0047] Each converging lens in the array directs electrons into a respective beam 211, 212, 213 which is focused at a respective intermediate focus 233. A collimator or array of collimators may be positioned to operate on the respective intermediate focus 233. The collimator may take the form of a deflector 235 disposed at the intermediate focus 233. The deflector 235 is configured to bend the respective beam 211, 212, 213 by an amount to ensure that the chief ray (which may also be referred to as the beam axis) is incident on the sample 208 substantially normally (i.e., substantially 90° to the nominal surface of the sample). Note that in an arrangement with a macrocondenser lens, the converging lens may collimate the beam source or assist in the collimation of the source beam, or in an embodiment, collimate multiple beams.

[0048] The objective lens array 401 is arranged down-beam from the deflector 235. The objective lens array 401 comprises an objective lens for each beam 211, 212, 213. The objective lens array 401 projects the beams 211, 212, 213 onto the sample 208. The objective lens array 401 may comprise two or more (preferably at least three) plate electrode arrays connected to respective potential sources.

[0049] Optionally, a control lens array 250 is provided between the deflector 235 and the objective lens array 401. The control lens array 250 comprises a control lens for each beam 211, 212, 213. The control lens array 250 provides an additional degree of freedom for controlling the properties of the beams 211, 212, 213. The control lens array 250 may comprise two or more (preferably at least three) plate electrode arrays connected to respective potential sources. The function of the control lens array 250 is to optimize the beam opening angle relative to the reduction of the beam and / or to control the beam energy delivered to the objective lens, each objective lens directing the respective beam 211, 212, 213 onto the sample 208. In an embodiment, the control lens array may be considered as part of the objective lens, for example in an additional plate associated with the objective lens array.

[0050] Optionally, a scanning deflector array 260 is disposed between the control lens array 250 and the objective lens array 401. The scanning deflector array 260 includes a scanning deflector for each beam 211, 212, 213. Each scanning deflector is configured to deflect the corresponding beam 211, 212, 213 in one or two directions so as to scan the beam across the sample 208 along one or two directions. Alternatively, a macro scanning deflector can be provided to scan the charged particle beam on the sample 208. The macro scanning deflector can be provided upstream (up-beam) of the control lens array 250. In an embodiment, such a macro scanning deflector can operate on the source beam and can exist together with a macro focusing lens.

[0051] The detector module 402 of the detector is arranged in the objective lens or between the objective lens and the sample 208 to detect signal electrons / particles from the sample 208. An exemplary construction of such a detector module 402 is described below. Note that the detector may additionally or alternatively have detector elements upstream along the primary beam path of the objective lens array 401 or even the control lens array 250. The detector module may be an array of detector elements (e.g., a detector array). Each element may be associated with a respective beam, for example, positioned to detect signal particles generated by the respective beam.

[0052] Figure 3 The charged particle device 41 can be configured to control the landing energy of electrons on the sample 208 by changing the potential applied to the electrodes of the control lens and the objective lens. The control lens and the objective lens work together and can be referred to as an objective lens assembly. The landing energy can be selected to increase the emission and detection of secondary electrons according to the properties of the sample being evaluated. The detector module can be included in the objective lens assembly.

[0053] The objective lens can be configured to reduce the electron beam to one-tenth or less, desirably within a range of one-hundredth to one-fiftieth or less. The objective lens can include three electrodes: an intermediate electrode, a lower electrode, and an upper electrode. The upper electrode can be omitted. An objective lens array with only two electrodes can have lower aberrations than an objective lens array with more electrodes. A three-electrode objective lens can have a greater potential difference between the electrodes, thereby achieving a stronger lens. Additional electrodes (i.e., more than two electrodes) provide additional degrees of freedom for controlling the trajectory of electrons, such as to focus secondary electrons as well as the incident beam.

[0054] In some embodiments, the objective lens array assembly includes a detector having a detector module 402 downstream of at least one electrode of the objective lens array 401. The detector module 402 may include or even take the form of a detector array. In an embodiment, at least a portion of the detector is adjacent to and / or integrated with the objective lens array 401. For example, the detector module 402 may be implemented by integrating a CMOS chip detector into the bottom electrode of the objective lens array 401. The secondary column may be replaced by integrating the detector module 402 into the objective lens array. The CMOS chip is preferably oriented to face the sample (because the distance between the sample and the bottom of the electron optical system is very small, for example, it may be in the range of 10 to 400 microns, desirably in the range of 50 to 200 microns, optionally about 100 microns). It should be noted that even in the case where the detector is located upstream of the most downstream electron optical element of the charged particle device, there may also be a close interval between the most downstream electron optical element and the sample, for example, a similar distance (for example, about 100 microns). In an embodiment, an electrode for capturing signal charged particles is formed in the top metal layer of the CMOS device. The electrode may be formed in other layers of the substrate of the CMOS chip, for example. The power supply and control signals of the CMOS can be connected to the CMOS through through-silicon vias. For robustness, preferably, the bottom electrode consists of two components: the CMOS chip and a passive silicon plate with holes. The plate shields the CMOS from high electric fields.

[0055] In an embodiment, a single electrode surrounds at least some of the apertures. In an arrangement, for example, a single electrode is allocated around each aperture. In another embodiment, multiple electrode elements are arranged around each aperture, for example as detector elements. Signal charged particles captured by the electrode elements surrounding an aperture can be combined into a single detection signal or used to generate independent detection signals. The electrode elements can be divided radially (i.e., forming multiple concentric rings), angularly (i.e., forming multiple fan-shaped parts), radially and angularly (providing an arrangement similar to a dart board), or divided in a grid (e.g., as a chessboard) or in any other convenient way.

[0056] exist Figure 4 An exemplary embodiment of a detector integrated into the objective lens array 401 is shown in Figure 4 A portion of an objective lens array 401 is illustrated in schematic cross section. In this embodiment, the detector comprises a detector module 402 comprising a plurality (e.g., an array) of detector elements 405 (e.g., sensor elements, such as capture electrodes), preferably as an array of detector elements (i.e., a plurality of detector elements preferably in a pattern or arrangement on a two-dimensional surface). In this embodiment, the detector module 402 is arranged at the output side of the objective lens array. The output side is the output side of the objective lens array 401. Figure 54 is a bottom view of a detector module 402 including a substrate 404 on which are disposed a plurality of detector elements (or capture electrodes 405) each surrounding a beam aperture 406. The beam aperture 406 may be formed by etching through the substrate 404. Figure 5 In the illustrated arrangement, the beam apertures 406 are shown in a rectangular array. The beam apertures 406 may also be arranged differently, for example, Figure 6 Depicted is a hexagonally packed array.

[0057] The above-described integrated detector module 402 is particularly advantageous when used with an evaluation device (e.g., including an apparatus) having a tunable landing energy, because the secondary electron capture can be optimized for a range of landing energies. Detector modules having an array or in the form of an array can also be integrated into other electrode arrays, not just the lowest electrode array. Further details and alternative arrangements of detector modules integrated into the objective lens can be found in EP application number 20184160.8, which is incorporated herein by reference.

[0058] A power source may be provided to apply corresponding electric potentials to the electrodes of the control lenses in the control lens array 250, the objective lenses in the objective lens array 401, and the converging lenses in the converging lens array, or any electron optical components (e.g., detector modules) of the charged particle device 41 (such as when integrated into the objective lens array, or when the objective lens and the detector module are separate components). The controller 50 may control the electric potentials applied to the electron optical components such as the electrodes of the converging lens array, the objective lens array, and / or the control lens array.

[0059] The charged particle device 41 may include other electron optical components such as charged particle correctors, for example as a corrector array for alignment of the source to the sample and between beams in the multi-beam, and for adjusting the focus of individual beams in different beam grid groups or beam grids. Such correctors may be controlled for dynamic and / or static operation, for example during installation, maintenance or calibration of the charged particle device 41.

[0060] In an embodiment, a charged particle device array (or device array) is provided. The array may include a plurality of any charged particle devices described herein (e.g., electron optical columns). Each charged particle device in the charged particle devices in the array focuses a corresponding plurality of charged particle beams onto different regions of the same sample 208. Each charged particle device in the array may derive a corresponding plurality of charged particle beams from different corresponding sources 201. Each corresponding source 201 may be a source in a plurality of sources 201. At least one subset of a plurality of sources 201 may be set as a source array. The source array may include a plurality of emitters on a common substrate. Focusing a plurality of charged particle beams from different charged particle devices simultaneously onto different regions of the same sample allows the increased area of ​​the sample 208 to be exposed to the charged particle beams simultaneously. Therefore, an increased sample area may be processed (e.g., evaluated) at one time. The charged particle devices in the device array may be arranged adjacent to each other so that a corresponding plurality of beams are projected onto adjacent regions of the sample 208. Any number of charged particle devices may be used in the array. Preferably, the number of charged particle devices is in the range of 9 to 200. When referring to a single charged particle device, electron-optical device or system or column, each charged particle device in the array may be configured in any way described herein.Alternatively or additionally, one or more charged particle devices in the array may be configured to project a single beam.

[0061] Figure 7 A further example of a charged particle device 41 is schematically depicted. Features identical to those described above are given the same reference numerals. For the sake of brevity, reference is not made to Figure 7 Such features are described in detail. For example, the source 201, the focusing lens 231, the objective lens array 401 and the sample 208 (e.g., on the sample support 207) can be as described above. In this example, a macro collimator 270 is provided instead of the one described above with reference to Figure 3 A deflector array of the type described. Such a macro-collimator can be a macro lens, which can be magnetic, electrostatic, or both. In other embodiments, the deflector array can be used to at least assist in the collimation of the beam, so that the deflector array is used to deflect toward collimation more finely than the action of the macro-collimator 270. This arrangement can also include multiple deflector arrays (for example, each aperture having multiple electrodes) to achieve finer collimation. In the arrangement, the converging lens 231 can include a single plate defining a beam-limiting aperture array, in which multiple apertures and one or more associated macro electrodes with a single aperture are defined. Such a beam-limiting aperture array and associated macro electrodes can also form a converging lens array to focus the generated beam at an intermediate focus, which desirably corresponds to the position of the collimator 270.

[0062] As described above, in some embodiments, the detector may be disposed between the objective lens array 401 and the sample 208. The detector may face the sample 208. Alternatively, as Figure 7 As shown, the detector 240 can be implemented so that the objective lens array 401 is between the detector 240 and the sample 208.

[0063] In an embodiment, the deflector array 95 is disposed between the detector 240 and the objective lens array 401. In an embodiment, the deflector array 95 includes an array of Wien filters, so that the deflector array 95 can be referred to as a beam splitter. The deflector array 95 is configured to provide a magnetic field and an electrostatic field. The electrostatic field and the magnetic field operate together to separate the charged particles projected onto the sample 208 relative to the signal particles (e.g., electrons from the sample 208). The operation of the field directs the signal particles toward the detector 240.

[0064] In an embodiment, the detector 240 is configured to detect signal particles by referring to the energy of the charged particles (i.e., according to the band gap), such a semiconductor-based detector. Such a detector 240 may be referred to as an indirect current detector. The secondary electrons emitted from the sample 208 obtain energy from the field between the electrodes. The secondary electrons have sufficient energy once they reach the detector 240. In a different arrangement, the detector 240 may be an electron-photon converter, such as a scintillator array, such as a fluorescent stripe between beams, which are positioned upstream along the primary beam path relative to the Wien filter. The primary beam passing through the Wien filter array (magnetic and electrostatic stripes orthogonal to the primary beam path) has a path upstream and downstream of the Wien filter array that is substantially parallel, and the signal electrons from the sample are guided by the Wien filter array toward the scintillator array. The electron-photon converter may be photon-coupled to the photon-electronic converter to convert any photons generated in the electron-photon converter and emitted by it. The photon-electronic converter may be electrically connected to an electronic circuit device to process the detection signal. In different embodiments, the photon-to-electron converter may be internal or external to the charged particle device.In an embodiment, photon coupling may be via a photon transport unit (eg, an optical fiber array) to a remote optical detector that generates a detection signal when a photon is detected.

[0065] As mentioned in the introductory portion of the description, degassing stimulated by charged particles impinging upon the sample may result in the deposition of unwanted materials on components exposed to the gases generated by the degassing. This is particularly problematic in arrangements where it is difficult to adequately pump out the gases. This may be the case where the gap between the sample and the charged particle apparatus used to direct the charged particles onto the sample is very small and / or where contamination sensitive components are positioned near the sample. An example of a contamination sensitive component is a detector. Thus, particularly in arrangements where the detector is positioned close to the sample 208, such as between the sample 208 and the objective lens array 401 (e.g., Figure 3 Problems may arise, for example, at distances less than about 200 microns, such as less than about 100 microns, less than about 75 microns, less than about 50 microns, less than about 20 microns, or equal to or less than about 10 microns, within the objective lens array 401. In these cases, it may be difficult or impossible to prevent a significant portion of the gas from the degassing (also referred to as charged particle excited desorption, or in the case of electrons, electron excited desorption) from entering the charged particle device adjacent to the sample. The gas may pass through vias in the charged particle device, such as via apertures used to implement electrostatic lenses or act as beam limiting apertures. The gas may reach contamination sensitive components via the apertures.

[0066] Hydrocarbon (C x H y ), particularly hydrocarbons with a molecular weight of about 50 or greater, are typically of greatest concern in the degassing gas, as these can result in destructive deposition of carbon on contamination-sensitive components, such as detectors. Degassing is typically higher when performing post-development inspection (ADI) using charged particles than when performing post-etch inspection (AEI). However, in both cases, if countermeasures are not taken, there will be scenarios where the outgassing of hydrocarbons is too high to avoid deposition problems. For example, even in AEI, outgassing rates of up to about 0.3 moles per electron or more have been observed. If about 1% of the degassed molecules are hydrocarbons, this will result in a partial pressure of the hydrocarbons that is 1 to 10 times too high to avoid significant growth of carbon on contamination-sensitive components. The embodiments of the present disclosure described below are intended to address these issues, and in particular to reduce or avoid problematic deposition of materials on contamination-sensitive components.

[0067] Figure 8 An apparatus for evaluating a sample 208 using charged particles (e.g., electrons) is depicted. The apparatus includes a degassing device 102, a degassing sensor 104, an evaluation device 106, and a control system 500. The control system 500 controls the apparatus to perform various functions described below. The control system 500 may include or consist of a controller 50, which uses the above-referenced Figure 1The control system 500 may comprise a single unit configured to perform all control functionality, or may comprise a system of distributed units that together allow the desired functionality to be achieved. The control system 500 may be at least partially computer-implemented. Any suitable combination of elements (e.g., CPU, RAM, data storage devices, data connection devices, sensors, etc.) may be provided and appropriately programmed to achieve some or even all of the specified functionality. Any reference herein to an apparatus, device or system configured to perform functionality is intended to cover the case where the control system 500 is configured to cause the functionality to be performed (e.g., by being appropriately programmed to provide control signals that cause the functionality to occur). The apparatus is a device that can be used to perform the functions described below with reference to Figures 9 to 11 An example of an apparatus for the described method.

[0068] In an embodiment, Fig. 9 As illustrated in the flowchart of , the sample is evaluated by executing steps S1 and S2.

[0069] In step S1, degassing is performed by exposing a target area of ​​the sample to charged particles. The charged particles stimulate degassing (e.g., via electron-stimulated desorption). Degassing can be performed by Figure 8 The degassing device 102 shown is performed. Thus, the degassing device 102 can be configured to expose a target area of ​​the sample 208 to the charged particles to stimulate degassing from the target area. During the degassing action, for example, Figure 8 The degassing sensor 104 shown measures the rate of degassing from the target area. Thus, when the target area is exposed by the degassing device 102, the rate of degassing can be measured.

[0070] In step S2, for example, using Figure 8 The evaluation device 106 performs the evaluation of the sample 208. The evaluation is initiated by, for example, Figure 8 The control system 500 is controlled based on the characteristic of the measured rate of degassing. The characteristic of the measured rate of degassing can be, for example, the amplitude of the measured rate of degassing or the rate of change of the amplitude of the measured rate of degassing over time or a combination thereof. The evaluation includes exposing the target area to charged particles and detecting signal charged particles from the target area. The evaluation can include evaluating defects in the target area of ​​the sample 208 and / or evaluating the relative size of structures in and / or on the target area of ​​the sample, such as measured values. The evaluation can be referred to as an inspection process and / or a measurement process.

[0071] Thus, a method is provided in which degassing of a target area on a sample 208 is intentionally stimulated by charged particles, and the results of the stimulation are monitored by measuring the rate of degassing. As particles susceptible to charged particle stimulated degassing leave the sample 208 during the degassing action, the rate of stimulated degassing will gradually decrease. In any subsequent exposure of the target area to charged particles, the rate of expected degassing will also decrease. Thus, measuring the rate of degassing during the degassing action in step S1 provides information about the extent to which degassing will be reduced in step S2 during the evaluation of the sample via charged particle exposure. Thus, controlling the initiation of the evaluation of the sample 208 in step S2 based on the characteristics of the measured rate of degassing allows the evaluation of the sample 208 to be initiated only when the degassing will be at an acceptably low level. For example, an acceptably low level may correspond to a level at which the deposition of carbon on contamination sensitive components due to degassing will be at an acceptably low level or will not occur at all to a large extent. An acceptably low level may correspond to a threshold count of moles of degassing per charged particle impinging on the target area, for example, a rate of about 0.01, desirably about 1×10, of degassing hydrocarbon molecules per charged particle impinging on the target area. -3 , desirably about 1×10 -4 , desirably about 1×10 -5 .

[0072] In an embodiment, the time-averaged current of charged particles received by the target area during exposure of the target area during the degassing in step S1 is higher than during exposure of the target area during evaluation of the sample in step S2, optionally at least 2 times, optionally at least 5 times, optionally at least 10 times, optionally at least 50 times, optionally at least 75 times, optionally at least 100 times. Providing a higher charged particle current accelerates degassing, thereby improving throughput. For example, by providing 100 times the current during degassing, 10 times the charged particle dose can be provided to the target area in a time period of, for example, one-tenth of the time used for evaluation or less. It has been observed that exposing the sample to charged particles to stimulate degassing in a degassing process prior to evaluating the sample reduces degassing during sample evaluation in a manner related to (typically proportional to) the charged particle dose used in the degassing process.

[0073] Alternatively or additionally, the landing energy of the charged particles received by the target area during the degassing of step S1 may be lower than during the evaluation of the sample in step S2, optionally at most one-half, optionally at most one-fifth, optionally at most one-tenth, optionally at most one-fiftieth, optionally at most one-seventy-fifth, optionally at least one-hundredth. In an embodiment, the landing energy of the charged particles received by the target area during the degassing of step S1 is equal to or lower than 1000 eV, optionally equal to or lower than 500 eV, optionally equal to or lower than 250 eV, optionally equal to about 100 eV. Reducing the landing energy during degassing can accelerate degassing by increasing the efficiency of degassing stimulated by the charged particles, thereby increasing throughput. Reducing the landing energy can also make the charged particles more difficult to focus, so it is desirable not to reduce the landing energy too much. Typically, landing energies of about 100 eV or higher will allow adequate control of the spot size during degassing (typically only relatively coarse focusing is required).

[0074] In an embodiment, exposure of a target area during a degassing process comprises a flood exposure. The parameters of the flood exposure used in the degassing process may be different from the parameters of the flood exposure used to flood the sample. That is, the flood exposure of the flood column used for the degassing process may be a specific type of flood exposure. This flood exposure has beam exposure parameters to achieve the desired degassing effect. (It should be noted that embodiments of the degassing process within the beam parameter range of the degassing process may be different from and overlap with the parameters of the flood exposure used to achieve flooding of the sample or at least a target area of ​​the sample). The degassing device 102 may include a flood column configured to provide a flood exposure. Figure 8 An example configuration of a flood column in a degassing device 102 is depicted, but other electron optical designs of flood columns may also be used. In this example, the flood column may include a charged particle source 301, a converging lens 320, a blanker electrode 330, an objective lens 340, and an aperture body 350. The flood column 300 may also include additional components for manipulating the charged particle beam 302, such as a scanning element (not shown) and a field lens (not shown). The components of the flood column 300 may be arranged substantially along an axis 304.

[0075] The charged particle source 301 may be an electron source. The charged particle source 301 may include a charged particle emitting electrode (e.g., a cathode) and an accelerating electrode (e.g., an anode). The charged particles are extracted or accelerated from the charged particle emitting electrode by the accelerating electrode to form a charged particle beam 302. The charged particle beam 302 may propagate along a beam path 302. For example, in the case where the charged particle beam 302 is not deflected away from the axis 304, the beam path 302 may include the axis 304.

[0076] The converging lens 320 is positioned downstream of the charged particle source 301, that is, the converging lens 320 is positioned downstream relative to the charged particle source 301. The converging lens 320 can focus or defocus the charged particle beam 302. Figure 8 As shown, converging lens 320 may be used to collimate charged particle beam 302. However, converging lens 320 may also be used to steer charged particle beam 302 to create a diverging beam or a converging beam.

[0077] The aperture body 350 may be positioned downstream of the converging lens 320. The aperture body 350 may allow a portion of the charged particle beam propagating along the axis 304 to pass through, or only a portion but not all of it. The aperture body 350 may limit the lateral extent of the charged particle beam 302, such as Figure 8 As depicted. Aperture body 350 can also be used to selectively blank charged particle beam 302 to prevent any portion of charged particle beam 302 from passing through. Aperture body 350 can define an opening. If the lateral extent (or diameter) of charged particle beam 302 is greater than the lateral extent (or diameter) of the opening, only a portion of charged particle beam 302 will pass through the opening. Aperture body 350 can therefore limit the lateral extent of charged particle beam 302, thereby acting as a beam-limiting aperture.

[0078] The blanking electrode 330 may be positioned downstream of the converging lens 320 and upstream of the aperture body 350. The blanking electrode 330 may selectively deflect the charged particle beam 302, for example, deflecting the charged particle beam 302 away from the axis 304. The blanking electrode 330 may deflect the charged particle beam 302 away from the opening in the aperture body 350, for example, onto a portion of the aperture body 350 that does not include the opening, to prevent any portion of the charged particle beam 302 from passing through the opening defined by the aperture body 350. The blanking electrode 330 may blank the beam so that the beam does not pass through the opening of the aperture body 350. However, the combination of the blanking electrode 330 and the aperture body 350 may also be used to selectively blank the charged particle beam 302, i.e., selectively prevent at least a portion of the charged particle beam 302 from passing through the opening in the aperture body 350. That is, the combination of the blanking electrode 330 and the aperture body 350 can selectively control the proportion of the charged particle beam 302 passing through the opening.

[0079] The objective lens 340 is positioned downstream of the aperture body 350. The objective lens 340 can focus or defocus the charged particle beam 302. Figure 8As shown, objective lens 320 can be used to control charged particle beam 302 to create a divergent beam, thereby increasing the spot size on sample 208 and increasing the surface area flooded with charged particles on sample 208. However, in some cases, objective lens 340 can be used to control charged particles 302 to create a converging beam, thereby focusing charged particle beam 302 onto sample 208.

[0080] In an embodiment, the evaluation device 106 exposes the sample 208 to a plurality of beams of charged particles, the plurality of beams comprising a plurality of individual charged particle beams. Figure 8 The example of shows a multi-bundle comprising three individual bundles, but in reality, the multi-bundle may comprise tens, hundreds or thousands of bundles.

[0081] In an embodiment, the evaluation device 106 comprises a charged particle device 41. The charged particle device 41 may be, for example, Figure 3 and Figure 7 Any form of description. Figure 8 In the specific example of Figure 3 The arrangement and can be operated and / or adopted as mentioned above Figure 3 any form described. A charged particle device 41 is used during the evaluation of the sample 208 in step S2 to direct charged particles onto the sample 208 and detect signal charged particles from the sample 208. The charged particle device 41 includes a contamination sensitive component. In an embodiment, the detection of the signal charged particles is performed using a contamination sensitive component. Therefore, the contamination sensitive component may include or consist of at least a portion of the detector. The charged particle device 41 is arranged so that the contamination sensitive component is less susceptible to contamination from deposition caused by charged particle excitation due to degassing from the target area during the degassing action in step S1 than during the evaluation of the sample 208 in step S2. Therefore, for a given rate of degassing from the target area, the contamination sensitive component is less susceptible to contamination caused by deposition during step S1 than during step S2.

[0082] The contamination-sensitive components may be less susceptible to contamination during the degassing in step S1 due to being further away from the target area than during the evaluation of the sample 208 in step S2. Alternatively or additionally, the contamination-sensitive components may be less susceptible to contamination during the degassing in step S1 by reducing or eliminating the impact of charged particles on the contamination-sensitive components as compared to during the evaluation of the sample 208 in step S2. For example, the charged particle device 41 may inhibit the propagation of charged particles from the source 201 of the charged particle device 41 to the contamination-sensitive components. In an embodiment, during at least a portion of the degassing in step S1 (e.g., during exposure of the target area of ​​the sample to the charged particles by the degassing device 102), the control system 500 switches the evaluation device to a blocking mode. The blocking mode may be implemented using any suitable technique to block the propagation of charged particles from the source 201 to the contamination-sensitive components. For example, during Figure 8 In the arrangement shown, the blocking mode can be achieved by controlling the potential applied to the electrodes of the converging lens array 231 so that the converging lens array 231 repels the charged particles back to the source 201 and / or redirects the charged particles to be absorbed in the charged particle sink and / or otherwise does not cross the aperture in the control lens array 250 and / or the objective lens array 401 to reach the detector module 402. Additionally or alternatively, the charged particle device may include a deflector configured to deflect the charged particles so that they do not reach the sample. For example, the deflector array is positioned along the path of multiple beams downstream of the converging lens array. During blocking, such a deflector array can be controlled to direct the beam away from the corresponding aperture of each beam in the objective lens array so that the beam impacts the blocking surface of the objective lens array or a plate along the path of the charged particle beam, the plate having an aperture for each beam and serving as a blocking surface.

[0083] In an embodiment, Figure 8 As illustrated, the degassing in step S1 and the evaluation of the sample 208 in step S2 are performed using charged particle beams from sources 301, 201 in different respective charged particle devices to expose the target area to the charged particles. In such an embodiment, when the target area of ​​the sample 208 is positioned in the processing area of ​​the degassing device 102, the degassing device 102 can perform the exposure of the target area of ​​the sample with charged particles to stimulate degassing (i.e., the degassing in step S1). Figure 8 In the example of FIG. 1 , the processing zone of the degassing device 102 corresponds to the area where the sample 208 is opposite to the charged particle device of the degassing device 102 (ie, in Figure 8 ). When the target area of ​​the sample 208 is positioned in the processing area of ​​the evaluation device 106 (i.e., at Figure 8), the evaluation device 106 performs exposure of the target area of ​​the sample with charged particles and detects signal charged particles from the target area (i.e., sample evaluation in step S2). Between the exposure of the target area to the charged particles by the degassing device 102 and the exposure of the target area to the charged particles by the evaluation device 106, the control system 500 controls the sample supports 207, 209 to move the sample 208 from the processing area of ​​the degassing device 102 to the processing area of ​​the evaluation device 106. Therefore, the control system 500 can control the sample supports 207, 209 to move the sample 208 along a direction having a lateral component (in Figure 8 from left to right), such as Figure 8 In this embodiment, when the target area is located in the processing area of ​​the degassing device 102 (i.e., in Figure 8 ), the degassing sensor 104 measures the rate of degassing.

[0084] In alternative embodiments, the degassing device 102 and the evaluation device 104 comprise a common charged particle device 41 with a common source 201, 301 or an arrangement with two different sources 201, 301 with a primary charged particle device for evaluation having a merged secondary column for the degassing device 102. For example, Figure 3 The arrangement can be used to perform the degassing action of step S1 and the sample evaluation of step S2. In this type of embodiment, between exposing the target area to charged particles to stimulate degassing (i.e., the degassing action of step S1) and exposing the target area to charged particles and detecting signal charged particles (i.e., the sample evaluation of step S2), the control system 500 can control the sample supports 207, 209 and the evaluation device 106 to move the sample 208 or at least a portion of the common charged particle device 41 so that the sample 208 is farther away from the common charged particle device. Therefore, a larger gap can be provided above the sample 208 during the degassing action of step S1 than during the evaluation of the sample 208 of step S2. The larger gap may help to extract particles during the degassing action, thereby reducing or avoiding any contamination of the components during the degassing action.

[0085] In an embodiment, the degassing sensor 104 is configured to measure the gas properties in the volume of the target area of ​​the fluid connected to the sample 208 when the target area is exposed to charged particles by the degassing device 102 (e.g., during the degassing action of step S1). The volume is the volume affected by the degassing action. The gas generated by the degassing action enters the volume and is detectable in the volume. The degassing sensor 104 can be positioned and / or mounted in any manner that allows the functionality to be performed. For example, the degassing sensor 104 can be supported by a vacuum wall, such as on a flange, to which the charged particle device is mounted. Alternatively, the degassing sensor 104 can be provided as part of a charged particle device, such as a charged particle device configured to expose the target area to charged particles during the degassing action of step S1 (e.g., as part of a flood column). In an embodiment, the degassing sensor 104 is configured to measure the partial pressure of the component of interest in the gas. The degassing sensor 104 may include a residual gas analyzer (RGA). The component of interest in the gas may include hydrocarbons, particularly hydrocarbons having a molecular weight equal to or greater than about 50. It has been found that the change in hydrocarbon partial pressure caused by degassing is high enough to be detected with high accuracy. This is particularly true when high charged particle currents are used during degassing. For example, in an example implementation, where hydrocarbon (C x H y ) is 1% with an initial degassing rate of 0.3 mol per charged particle, and hydrocarbon (C x H y ) is 1% and the final degassing rate is 0.03 mol per charged particle, and the current of the charged particles striking is 200 μA. It is given by the following expression:

[0086]

[0087] where k B is the Boltzmann constant, and Q e is the charge of the electron. If the volume above the sample is pumped at 10 L / s, then C x H y Pressure will be given by the following expression:

[0088]

[0089] For example, using an RGA (residual gas analyzer) one can measure the relative x H y This is particularly true because the partial pressure will undergo a dramatic change once the exposure of the sample to the charged particles in the degassing is interrupted. It is therefore easy to distinguish the contribution of the degassing to the partial pressure from that of C x Hy The background level of C contributes to the partial pressure. x H y The partial pressure change caused by degassing can also be observed if the background level is larger than the partial pressure change caused by degassing.

[0090] Background levels of gases of interest (e.g., hydrocarbons having a molecular weight equal to or greater than a threshold weight (e.g., 50)) may exist independently of degassing. In this case, the measurement of the partial pressure of the component of interest may include contributions from the background and contributions from the degassing of step S1. In some embodiments, background properties of the gas in the volume may be measured. Background properties of the gas in the volume may be measured outside the time period of the degassing in step S1 (i.e., when degassing is not performed). Background properties may include the partial pressure of the component of interest in the gas. Measuring the partial pressure of the component of interest during and outside of degassing may separate the background level of the component of interest from the partial pressure of the component of interest resulting from degassing (excitation by exposure to charged particles in step S1). Thus, the sample evaluation in step S2 may be initiated based on: gas properties measured during the degassing in step S1; and background properties of the gas measured outside the time period of degassing. Fig.10 and Fig.11 Depicted Fig. 9 An example variation of the method that includes such measurement of background properties.

[0091] exist Fig.10 In a variant of the invention, the background characteristics of the gas are measured in a preliminary step S11 before the degassing is performed in step S12. The degassing in step S12 may be performed using the method described above with reference to Fig. 9 The degassing action of step S12 may be followed by step S13, which evaluates sample 208 by exposing a target area to charged particles and detecting signal charged particles from the target area. Step S11 provides background characteristics of the measurement, so step S13 (e.g., via control system 500) can directly take into account the background characteristics of the measurement to control the initiation of the evaluation of sample 208. Otherwise, step S13 may adopt the above reference to Fig. 9 Any form described in step S2.

[0092] exist Fig.11 In a variant of the present invention, the degassing is performed in step S21 and can be carried out using the method described above with reference to Fig. 9in any form as described in step S1. After the degassing in step S21, background properties of the gas are measured in step S22. Thus, in this embodiment, background properties of the gas are measured after the degassing in step S21. In step S23, the measured background properties of the gas (e.g., background partial pressure of hydrocarbons) are compared to (e.g., subtracted from) the gas properties measured during the degassing (e.g., partial pressure of hydrocarbons including contribution from the degassing). This allows a more accurate inference of the rate of degassing due to degassing. If it is determined that the rate of degassing due to degassing is sufficiently low, the method continues to step S24. Step S24 includes evaluating the sample 208 by exposing a target area to charged particles and detecting signal charged particles from the target area. Step S24 may be performed in the manner described above with reference to Fig. 9 Any form of the description of step S2 of step S2. If it is determined in step S23 that the rate of degassing due to degassing is not low enough, then step S21 (degassing) and optionally step S22 (measuring background) can be repeated, and then step S23 can be performed again to check whether the degassing due to degassing is low enough to proceed to step S24 (evaluating sample 208). Therefore, steps S21, S22 and S23 can be repeatedly performed, for example iteratively, until it is determined that degassing has sufficiently reduced degassing to allow safe continuation of the evaluation of sample 208 in step S24. Repeating step S22 can allow monitoring of drift in the background level of the component of interest, thereby improving accuracy. However, in some embodiments, step S22 can be omitted from the repetition. This may be appropriate, for example, in cases where the background characteristics of the gas are expected to be less important (e.g., containing levels of problematic hydrocarbons significantly lower than those produced by degassing) and / or relatively stable over time (such that a single execution of step S22 provides a measure of the background characteristics of the gas that remains sufficiently accurate on a relevant time scale).

[0093] In an embodiment, measuring the property of the gas includes measuring the pressure of the gas. Although the components of interest (e.g., hydrocarbons) in the gas may only account for a relatively small proportion of the gas (e.g., about 1%), measuring the total pressure of the gas can still provide useful information about the level of degassing caused by degassing. The rate of degassing of the components of interest (e.g., hydrocarbons) can be, for example, proportional to or otherwise related to the rate of total degassing.

[0094] In an embodiment, in response to the characteristic of the rate of degassing being determined to satisfy a condition, sample evaluation (e.g., in steps S2, S13, S24) is initiated. Therefore, the method may include determining when the characteristic of the rate of degassing satisfies a condition. In an embodiment, the determination process is performed continuously or at regular intervals during the degassing action until the condition is satisfied. In an embodiment, the condition includes that the rate of degassing has reached or is below a predetermined threshold. The degassing action may be stopped in response to the characteristic of the rate of degassing being determined to satisfy a condition. The predetermined threshold may, for example, include a rate of degassing that is too low to produce any significant deposition of problematic materials (e.g., carbon) on contamination-sensitive components (e.g., components of a detector). In some embodiments, the predetermined threshold may be about 0.01 moles of degassing per charged particle that impacts the target area.

[0095] In the above-described embodiments, the rate of outgassing caused by degassing is measured and used to determine when to initiate evaluation of sample 208. For example, evaluation of sample 208 is initiated only when it is determined that the rate of outgassing during degassing is low enough that outgassing during evaluation of sample 208 will not cause problems (such as carbon deposition on contamination sensitive components such as components associated with detectors). However, it is not necessary to measure outgassing during degassing to ensure that outgassing during evaluation of sample 208 will be low enough. For example, calibration measurements and / or computational modeling can be performed to determine parameters of degassing that will be sufficient to cause degassing during evaluation of sample 208 to be low enough. The parameters of degassing determined may include one or more of the following: duration of degassing, current of charged particles during degassing, and landing energy of charged particles during degassing. In an embodiment, degassing is performed until the rate of degassing stimulated is below a threshold count of moles of a component of interest (optionally hydrocarbons) degassed per charged particle impinging on the target region, desirably 0.01 moles degassed per charged particle impinging on the target region. Subsequently, evaluating the sample 208 by exposing the target region to the charged particles and detecting signal charged particles from the target region is performed.

[0096] Prior to evaluation using an evaluation device, degassing is applied to a portion of the sample surface. In a subsequent evaluation, the surface area of ​​the degassed portion is as large as or larger than the surface of the sample. In the case of evaluating two or more different areas of the sample surface (e.g., dies), for example, simultaneously, such as in a die-to-die mode inspection, two or more different areas of the sample surface are evaluated. Prior to performing such an evaluation, corresponding portions of the different areas are degassed. The different portions may be as large as, if not larger than, the corresponding areas being evaluated. Typically, the degassed surface area may correspond to the surface area that is subsequently evaluated simultaneously in one or more areas of the sample surface.

[0097] Although this article focuses on Figure 3 and Figure 7 Depicted and referenced Figure 3 and Figure 7 The invention is described with reference to a charged particle device 41, but the invention can be applied to a charged particle system having a single beam device or a multi-beam device (having a common single magnetic objective lens). Although such a system has components of a charged particle device 41, these components are not like Figure 3 and Figure 7 Shown and referenced Figure 3 and Figure 7 Although the arrangement described above is close to the sample, contamination may still occur over time and with use. Figure 3 and Figure 7 The delicate components of the charged particle device 41 shown are developed on components further away from the sample, the growth of contamination thereof can be suppressed by embodiments of the present disclosure.

[0098] Mention of the assembly or assembly system or element that can be controlled to manipulate the charged particle beam in some way includes configuring a controller or control system or control unit to control the assembly to manipulate the charged particle beam in the described manner, and optionally using other controllers or devices (such as voltage supply and / or current supply) to control the assembly to manipulate the charged particle beam in this manner. For example, a voltage supply device can be electrically connected to one or more assemblies to apply an electric potential to the assembly, such as in a non-limiting list including control lens array 250 and objective lens array 241.

[0099] References to up and down, upward and downward, above and below, etc. should be understood to refer to directions parallel (usually but not always vertical) to the upstream and downstream directions of the charged particle beam impinging on the sample 208. Thus, references to upstream and downstream are intended to refer to directions about the beam path that are independent of any present gravitational field.

[0100] The electron optical device described herein can take the form of a series of aperture arrays or electron optical elements, which are arranged in an array along a beam or multi-beam path. Such electron optical elements can be electrostatic. In an embodiment, all electron optical elements (e.g., the last electron optical element in the beam path before the beam-limiting aperture array to the sample) can be electrostatic and / or can be in the form of an aperture array or a plate array. In some arrangements, one or more electron optical elements are manufactured as a micro-electromechanical system (MEMS) (i.e., using MEMS manufacturing technology). The electron optical element can have a magnetic element and an electrostatic element. For example, a composite array lens can have a micro-spacing magnetic lens that covers a multi-beam path, wherein the upper pole plate and the lower pole plate are in the magnetic lens and arranged along the multi-beam path. In the pole plate can be an aperture array for the beam path of the multi-beam. Electrodes can be present above, below, or between the pole plates to control and optimize the electromagnetic field of the composite lens array.

[0101] Evaluation devices, tools or systems according to the present disclosure may include devices for qualitative evaluation of samples (e.g., pass / fail), devices for quantitative measurement of samples (e.g., size of features), or devices for generating a mapped image of a sample. Examples of evaluation devices, tools or systems are inspection tools (e.g., for identifying defects), review tools (e.g., for classifying defects), and metrology tools or tools capable of performing any combination of evaluation functionality associated with inspection tools, review tools, or metrology tools (e.g., subway inspection tools).

[0102] The functionality provided by a controller or control system or control unit can be computer-implemented.Any suitable combination of components can be used to provide the required functionality, including, for example, CPU, RAM, SSD, mainboard, network connection, firmware, software and / or other components known in the art that allow the required computing operations to be performed.Required computing operations can be defined by one or more computer programs.One or more computer programs can be arranged in the form of a medium (optionally non-transient medium) storing computer-readable instructions.When the computer-readable instructions are read by a computer, the computer executes the required method steps.The computer can be composed of an independent unit or a distributed computing system, and the distributed computing system has a plurality of different computers connected to each other via a network.

[0103] Although the present invention has been described in conjunction with various embodiments, other embodiments of the present invention will be apparent to those skilled in the art in view of the specification and practice of the invention disclosed herein. The specification and examples are intended to be considered exemplary only, with the true scope and spirit of the present invention being indicated by the following claims and clauses.

[0104] The following terms are provided:

[0105] Item 1. A method for evaluating a sample using charged particles, comprising: performing degassing by exposing a target area of ​​the sample to charged particles to stimulate degassing; measuring the rate of degassing from the target area during the degassing; and controlling the start of evaluation of the sample based on characteristics of the measured degassing rate, wherein the evaluation of the sample includes exposing the target area to charged particles and detecting signal charged particles from the target area.

[0106] Item 2. A method according to Item 1, wherein a charged particle device used during the evaluation of the sample is arranged so that contamination-sensitive components of the charged particle device are less susceptible to contamination caused by deposition stimulated by charged particles during the degassing action due to degassing from the target area than during the evaluation of the sample.

[0107] Clause 3. The method of clause 2, wherein the contamination-sensitive component is less susceptible to contamination by being further away from the target area during the degassing than during the evaluation of the sample.

[0108] Item 4. A method according to Item 2 or 3, wherein during the degassing period, the charged particle device is configured to reduce or eliminate the impact of charged particles on the contamination-sensitive component, making the contamination-sensitive component less susceptible to contamination, compared to during the evaluation of the sample.

[0109] Clause 5. The method of clause 4, wherein the charged particle device is configured to reduce or eliminate the impact of charged particles on the contamination sensitive component by inhibiting propagation of charged particles from a source of the charged particle device to the contamination sensitive component.

[0110] Clause 6. The method of any one of Clauses 2 to 5, wherein the detecting of the signal charged particles is performed using the contamination sensitive component.

[0111] Clause 7. The method of any preceding clause, wherein the degassing and the evaluating of the sample are performed using charged particle beams from sources in different respective charged particle devices to expose the target area to the charged particles.

[0112] Clause 8. A method according to Clause 7, wherein the sample is moved between the degassing and the evaluation of the sample from a position where the target area is located in a processing area of ​​the charged particle device performing the degassing to a position where the target area is located in a processing area of ​​the charged particle device performing the evaluation of the sample.

[0113] Clause 9. The method of Clause 8, wherein the sample is moved in a direction having a lateral component between the degassing and the evaluating of the sample.

[0114] Clause 10. The method of clause 8 or 9, wherein measuring the rate of the degassing is performed while the target region is located in the processing region of the charged particle device performing the degassing.

[0115] Clause 11. The method of any one of clauses 1 to 6, wherein a common charged particle device is used to expose the target area to charged particles to perform the degassing and the evaluating of the sample.

[0116] Clause 12. A method according to clause 11, wherein the sample or at least a portion of the common charged particle device is moved between the degassing and the evaluation of the sample so that the sample is positioned farther away from the common charged particle device during the degassing than during the evaluation of the sample.

[0117] Clause 13. A method according to any preceding clause, wherein the time-averaged current of charged particles received by the target area during exposure of the target area during the degassing is at least twice as high as during exposure of the target area during the evaluation of the sample.

[0118] Clause 14. A method according to any preceding clause, wherein the landing energy of charged particles received by the target area during exposure of the target area during the degassing period is at most one-half of the exposure of the target area during the evaluation of the sample.

[0119] Clause 15. The method of any preceding clause, wherein a landing energy of charged particles received by the target region is equal to or lower than 1000 eV during exposure of the target region during the degassing.

[0120] Clause 16. The method of any preceding clause, wherein the exposing of the target area during the degassing process comprises a flood exposure.

[0121] Clause 17. The method of any preceding clause, wherein the exposing of the target area during the evaluation of the sample comprises exposing with multiple beams.

[0122] Clause 18. The method of any preceding clause, wherein the measuring of the rate of the degassing comprises measuring a property of gas in a volume affected by the degassing during the degassing.

[0123] Clause 19. The method of Clause 18, further comprising: measuring background properties of the gas in the volume affected by the degassing effect outside of a period of time for the degassing effect.

[0124] Clause 20. A method according to clause 19, wherein the initiation of the evaluation of the sample is controlled based on the characteristic of the measured rate of degassing using both: the characteristic of the gas measured during the degassing action; and the background characteristic of the gas measured outside the time period of the degassing action.

[0125] Clause 21. The method of any one of Clauses 18 to 20, wherein the measuring of the property of the gas comprises measuring the pressure of the gas.

[0126] Clause 22. A method according to any one of clauses 18 to 21, wherein the measurement of the property of the gas comprises measuring the partial pressure of a component of interest in the gas, desirably a hydrocarbon, desirably the hydrocarbon having a molecular weight equal to or greater than a weight threshold, desirably the weight threshold being approximately 50.

[0127] Clause 23. A method according to any preceding clause, comprising: determining when the characteristic of the measured rate of outgassing satisfies a condition, wherein the evaluation of the sample is initiated in response to the characteristic of the measured rate of outgassing being determined to satisfy the condition.

[0128] Clause 24. The method of clause 23, wherein the condition comprises the measured rate of the degassing reaching or falling below a predetermined threshold.

[0129] Clause 25. The method of clause 23 or 24, comprising stopping degassing in response to a characteristic of the measured rate of degassing being determined to satisfy the condition.

[0130] Clause 26. The method of any preceding clause, wherein the target area on the sample is an area that has been processed by an etching process.

[0131] Clause 27. The method of Clause 26, comprising performing the etching process.

[0132] Clause 28. A computer program comprising instructions configured to control a processor to perform the method of any one of clauses 1 to 27.

[0133] Item 29. An apparatus for evaluating a sample using charged particles, the apparatus comprising: a degassing device configured to expose a target area of ​​the sample to charged particles to stimulate degassing from the target area; a degassing sensor configured to measure the rate of degassing from the target area; an evaluation device configured to perform the evaluation of the sample by exposing the target area to charged particles and detecting signal charged particles from the target area; and a control system configured to control the evaluation device to initiate the evaluation of the sample in response to an output from the degassing sensor.

[0134] Item 30. An apparatus according to Item 29, wherein the evaluation device includes a contamination-sensitive component and is configured such that the contamination-sensitive component is less susceptible to contamination from deposition stimulated by charged particles during exposure of the target area by the degassing device than during evaluation of the target area by the evaluation device due to degassing from the target area.

[0135] Clause 31. An apparatus according to clause 30, wherein the degassing device and the evaluation device are configured such that the contamination-sensitive component is farther away from the target area when the target area is exposed to charged particles through the degassing device than when the target area is exposed to charged particles through the evaluation device.

[0136] Clause 32. The apparatus of clause 30 or 31, wherein the evaluation device comprises a source, and the evaluation device is configured to be selectively switchable to a blocking mode in which propagation of charged particles from the source to the contamination-sensitive component is suppressed.

[0137] Clause 33. An apparatus according to any one of clauses 30 to 32, wherein the control system is configured to place the evaluation device in the blocking mode during exposure of the target area of ​​the sample to at least a portion of charged particles by the degassing device.

[0138] Clause 34. Apparatus according to any one of clauses 30 to 33, wherein the evaluation device comprises a detector configured to perform the detection of the signal charged particles, and the contamination sensitive component comprises at least a portion of the detector.

[0139] Clause 35. Apparatus according to any one of clauses 29 to 34, wherein the degassing device and the evaluation device comprise different charged particle sources and different corresponding charged particle devices to direct the charged particles from the sources to the sample.

[0140] Item 36. An apparatus according to Item 35, wherein: the apparatus includes a sample support configured to support the sample; the degassing device is configured to, when the target area of ​​the sample is positioned in a processing area of ​​the degassing device, expose the target area of ​​the sample to charged particles to stimulate degassing; the evaluation device is configured to, when the target area of ​​the sample is positioned in the processing area of ​​the evaluation device, expose the target area of ​​the sample to charged particles and detect signal charged particles from the target area; and the control system is configured to: control the sample support to move the sample from the processing area of ​​the degassing device to the processing area of ​​the evaluation device between exposing the target area to charged particles by the degassing device and exposing the target area to charged particles by the evaluation device.

[0141] Clause 37. The apparatus of Clause 36, wherein the control system is configured to control the sample support to move the sample in a direction having a lateral component.

[0142] Clause 38. The apparatus of clause 36 or 37, wherein the degassing sensor is configured to measure the rate of degassing when the target area is in the processing zone of the degassing device.

[0143] Clause 39. The apparatus of any one of Clauses 29 to 34, wherein the degassing device and the evaluation device comprise a common charged particle device configured to expose the target area to charged particles.

[0144] Item 40. An apparatus according to Item 39, wherein: the apparatus includes a sample support configured to support the sample; and the control system is configured to control the sample support and / or the evaluation device to move the sample or at least a portion of the common charged particle device so that the sample is farther away from the common charged particle device between exposing the target area to charged particles to stimulate degassing and exposing the target area to charged particles and detecting signal charged particles.

[0145] Clause 41. An apparatus according to any one of clauses 29 to 40, wherein the control system, degassing device and / or evaluation device is configured such that the time-averaged current of charged particles received by the target area during exposure of the target area to charged particles to stimulate degassing is at least twice as high as during exposure of the target area to charged particles and detection of signal charged particles.

[0146] Clause 42. An apparatus according to any one of clauses 29 to 41, wherein the control system is configured to control the degassing device so that the landing energy of the charged particles received by the target area during the period of exposing the target area to the charged particles to stimulate degassing is at most one-half of that during the period of exposing the target area to the charged particles and detecting signal charged particles.

[0147] Clause 43. An apparatus according to any one of clauses 29 to 42, wherein the control system is configured to control the degassing device so that the landing energy of the charged particles received by the target area is equal to or less than 1000 eV during exposure of the target area to the charged particles to stimulate degassing.

[0148] Clause 44. The apparatus of any one of Clauses 29 to 43, wherein the degassing device comprises a flood column configured to provide a flood exposure.

[0149] Clause 45. Apparatus according to any one of Clauses 29 to 44, wherein the evaluation device is configured to expose the sample with a multi-beam of charged particles, the multi-beam comprising a plurality of individual charged particle beams.

[0150] Clause 46. An apparatus according to any one of clauses 29 to 45, wherein the degassing sensor is configured to measure a property of a gas in a volume of the target area of ​​the sample connected to a fluid when the target area is exposed to charged particles by the degassing device.

[0151] Clause 47. The apparatus of Clause 46, wherein the control system is configured to cause the degassing sensor to measure background properties of the gas in the volume outside of a period of time during which the target area is exposed to charged particles by the degassing device.

[0152] Clause 48. An apparatus according to clause 47, wherein the control system is configured to control the evaluation device to initiate the evaluation of the sample in response to the output from the degassing sensor using both: the characteristics of the gas measured when the target area is exposed to charged particles through the degassing device; and the background characteristics of the gas measured outside the time period when the target area is exposed to charged particles through the degassing device.

[0153] Clause 49. The apparatus of any one of clauses 46 to 48, wherein the degassing sensor is configured to measure the pressure of the gas.

[0154] Clause 50. The apparatus of any one of clauses 46 to 49, wherein the degassing sensor is configured to measure the partial pressure of a component of interest in the gas, desirably a hydrocarbon, desirably having a molecular weight equal to or greater than 50.

[0155] Clause 51. An apparatus according to any one of clauses 29 to 50, wherein the control system is configured to: determine when a characteristic of the measured rate of degassing satisfies a condition; and initiate the evaluation of the sample in response to the characteristic of the measured rate of degassing being determined to satisfy a condition.

[0156] Clause 52. The apparatus of clause 51, wherein the condition comprises a measured rate of the outgassing reaching or falling below a predetermined threshold.

[0157] Clause 53. The apparatus of clause 51 or 52, wherein the control system is configured to stop exposing the target area by the degassing device in response to a characteristic of the measured rate of the degassing being determined to satisfy the condition.

[0158] Item 54. A method for evaluating a sample using charged particles, comprising: performing degassing by exposing a target area of ​​the sample to charged particles to stimulate degassing until the rate of the stimulated degassing is lower than a threshold count of the number of moles of a component of interest degassed per charged particle impacting the target area, the component of interest being desirably hydrocarbons, the threshold count being desirably 0.01 moles degassed per charged particle impacting the target area; and subsequently evaluating the sample by exposing the target area to charged particles and detecting signal charged particles from the target area.

[0159] Item 55. An apparatus for evaluating a sample using charged particles, the apparatus comprising: a degassing device configured to expose a target area of ​​the sample to charged particles to stimulate degassing from the target area; an evaluation device configured to perform evaluation of the sample by exposing the target area to charged particles and detecting signal charged particles from the target area; and a control system configured to control the evaluation device to start the evaluation of the sample after the degassing device exposes the target area of ​​the sample to charged particles until the rate of the stimulated degassing is lower than a threshold count of the number of moles of a component of interest degassed per charged particle impacting the target area, the component of interest being desirably hydrocarbons, the threshold count being desirably 0.01 moles of degassing per charged particle impacting the target area.

Claims

1. A method for evaluating a sample using charged particles, comprising: Degassing is performed by exposing targeted areas of the sample to charged particles to stimulate degassing; measuring a rate of outgassing from the target area during the degassing action; as well as Initiation of evaluation of the sample is controlled based on a characteristic of the measured rate of the outgassing, the evaluation of the sample comprising exposing the target region to charged particles and detecting signal charged particles from the target region.

2. A method according to claim 1, wherein the charged particle device used during the evaluation of the sample is arranged so that: the contamination-sensitive components of the charged particle device are less susceptible to contamination caused by deposition stimulated by charged particles during the degassing action due to degassing from the target area than during the evaluation of the sample.

3. The method of claim 2, wherein the contamination sensitive component is less susceptible to contamination by being further away from the target area during the degassing than during the evaluation of the sample.

4. A method according to claim 2 or 3, wherein during the degassing period, the charged particle device is configured to reduce or eliminate the impact of charged particles on the contamination-sensitive component, making the contamination-sensitive component less susceptible to contamination, compared to during the evaluation of the sample.

5. The method of claim 4, wherein the charged particle device is configured to reduce or eliminate the impact of charged particles on the contamination sensitive component by inhibiting propagation of charged particles from a source of the charged particle device to the contamination sensitive component.

6. The method according to any one of claims 2 to 5, wherein the detection of the signal charged particles is performed using the contamination sensitive component.

7. A method according to any preceding claim, wherein said degassing and said evaluating of said sample are performed using charged particle beams from sources in different respective charged particle devices to expose said target area to charged particles.

8. A method according to claim 7, wherein the sample moves between the degassing and the evaluation of the sample from a position where the target area is located in a processing area of ​​the charged particle device performing the degassing to a position where the target area is located in a processing area of ​​the charged particle device performing the evaluation of the sample.

9. The method of claim 8, wherein the sample is moved in a direction having a lateral component between the degassing and the evaluating of the sample.

10. A method according to claim 8 or 9, wherein said measuring of the rate of said degassing is performed while said target region is located in said processing region of said charged particle device performing said degassing.

11. A method according to any preceding claim, wherein the time-averaged current of charged particles received by the target area during exposure of the target area during the degassing effect is at least twice as high as during exposure of the target area during the evaluation of the sample.

12. The method of any preceding claim, wherein the exposing of the target area during the degassing process comprises a flood exposure.

13. The method of any preceding claim, wherein the exposing of the target area during the evaluation of the sample comprises exposing with multiple beams.

14. A method according to any preceding claim, wherein the measuring of the rate of degassing comprises measuring a property of gas in a volume affected by the degassing during the degassing.

15. A method according to any preceding claim, comprising: determining when said characteristic of said measured rate of said outgassing satisfies a condition, wherein the evaluation of the sample is initiated in response to the characteristic of the measured rate of the outgassing being determined to satisfy the condition.

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