Contamination handling in metrology systems

Abstract

The present disclosure relates to a metrology system configured for handling contamination within a vacuum chamber. The system comprises a Scanning Electron Microscope (SEM) module for imaging a sample, a sample processing module for processing the sample and generating contaminants, and a contamination handling module configured to prevent the contaminants from reaching the SEM module. The contamination handling module can include various components such as a dynamic shutter, a static contaminant barrier, a contaminant cooling trap, electrostatic collection fields, and a protection gas environment.These components work together to effectively manage contaminants and maintain a clean environment for the SEM module, ensuring high-quality imaging results and reduced maintenance requirements.

Description

[0001] D E S C R I P T I O N

[0002] CONTAMINATION HANDLING IN METROLOGY SYSTEMS

[0003] TECHNICAL FIELD

[0004] Various examples generally relate to contamination handling in metrology systems. Various examples specifically relate to contaminant handling in for example in enclosed sample chambers or vacuum chambers, of optical, electron, and / or x-ray -based metrology systems, more specifically in metrology systems employing a particle beam imaging process, particularly a Scanning Electron Microscope (SEM) process, and / or a beam-induced material removal or deposition or etching process, for example using material abrasive process modules such as a Focused Ion Beam (FIB) module.

[0005] BACKGROUND

[0006] Enclosed sample chambers, specifically vacuum chambers, are commonly used in metrology systems. However, contaminants from physically processing or altering samples inside the vacuum chambers can contaminate an imaging process module, such as a SEM process module. Contaminant accumulation on the sample and the SEM column can significantly degrade image quality and contrast over time. Therefore, effective contamination handling inside vacuum chambers is important for continuous high quality imaging processes.

[0007] From US 2016 / 0343537 A1 , US 2022 / 0208531 A1 , US 2023 / 0350301 A1 , and Buse et al. 'Decontamination in the Electron Probe Microanalysis with a Peltier-Cooled Cold Finger', Microscopy and Microanalysis, 2016, pp. 981-986, vacuum chamber cooling traps and plasma cleaning devices are known.

[0008] SUMMARY

[0009] Accordingly, a need exists for advanced imaging techniques for contamination handling in vacuum chambers of metrology systems that mitigate or reduce at least some of the aboveidentified drawbacks.

[0010] This need is met by the features of the independent claims. The features of the dependent claims define embodiments. In the following, the solution according to the present disclosure will be described with regard to metrology systems as well as with regard to corresponding methods and method steps for operating the metrology systems, wherein features, advantages, or alternative embodiments can be assigned to the other categories and vice versa. Therefore, it is to be understood that the metrology systems can be improved with features described in the context of the methods, and the methods can be improved with features described in the context of the metrology systems.

[0011] A metrology system comprising any one or any combination of process modules such as for example a SEM and / or FIB and / or Gas Injection System (GIS) , is provided, which is configured for contamination handling according to the techniques of the present disclosure. The metrology system may be configured to perform one or more of inspection, imaging, processing, micro-processing, etching, depositing, or other operations on a sample on a sample table in a vacuum chamber, using one or more of the process modules sequentially or in parallel. Therefore, the metrology system comprises one or more contamination handling modules and / or elements of one or more contamination handling modules, in order to provide contamination handling in the vacuum chamber.

[0012] In various examples, a metrology system comprises a vacuum chamber. A vacuum chamber in a metrology system may refer to an enclosed space, in which the sample is located, and / or processed and / or analyzed, where the pressure is significantly reduced compared to the atmospheric pressure surrounding the metrology system. This low-pressure environment enables operation of the SEM module and other components, as it allows electrons to travel with minimal interference from gas molecules.

[0013] In various examples, the metrology system comprises a sample stage within the vacuum chamber configured to hold a sample to be processed. A sample stage within the vacuum chamber may be referred to as a platform or holder designed to position the sample being analyzed or processed by various process modules, such as the imaging module or a sample processing module. It may have the capability to move the sample in various directions (e.g., X, Y, and Z axes) and rotate or tilt it to facilitate the imaging and processing of different areas of the sample.

[0014] In various examples, the metrology system comprises a Scanning Electron Microscope (SEM) module within the vacuum chamber configured to image the sample. A Scanning Electron Microscope (SEM) module is an imaging process module that uses a focused electron beam to scan the sample surface and create high-resolution images. The SEM module operates within a vacuum chamber to maintain the integrity of the electron beam and to prevent contamination of the sample and the SEM components. It is to be understood that prevent may refer to a stop of all contaminants or a stop a relevant part of the contaminants from reaching the SEM module. Here, prevent is used to convey that the contamination handling module significantly reduces the quantity of contaminants that reach the SEM module, thereby mitigating their impact on the imaging process. This may refer to one or more of the facts that the contamination handling module hinders contaminants from reaching the SEM module. It may imply a substantial reduction in the quantity of contaminants that reach the SEM module. The contamination handling module may reduce the quantity of contaminants reaching the SEM module, for example to a very level of lower than 30%, or lower than 20%, or lower than 10%, or lower than 1% of contaminants reaching the SEM module without the contamination handling module.

[0015] In various examples, the metrology system comprises a sample processing module within the vacuum chamber configured to physically process or modify the sample or sample structure, for example by removing material from the sample, thereby generating contaminants within the low-pressure gas atmosphere of the vacuum chamber. A sample processing module within the vacuum chamber may be deployed for altering or modifying the physical structure or manipulating the physical structure of the sample. This processing may include techniques such as focused ion beam (FIB) milling, etching, or deposition, and may be performed by one or more corresponding sample processing modules arranged at least partly within the vacuum chamber. Such processes generate contaminants, such as particles or gases, in other words debris, which may interfere with the SEM imaging if no proper mitigation exists.

[0016] In various examples, the metrology system comprises a contamination handling module, in other words a contamination management module, at least partly within the vacuum chamber, the contamination handling module configured to hinder or prevent contaminants, or at least some, more than 50% or 70% of contaminants, or most or essentially all contaminants, from interfering with the imaging process, in particular from reaching the SEM module, specifically critical SEM module surfaces.

[0017] In various examples, a contamination handling module may be referred to as element or component comprised at least partly within the vacuum chamber, and designed to mitigate the impact of contaminants generated during physical sample processing. Its primary function is to prevent or hinder contaminants from reaching the areas of the SEM module, which could degrade imaging quality or cause damage to the sensitive components, in particular SEM electron emission and detection. The contamination handling module may employ various techniques or combinations of techniques for contamination handling or contamination management, such as dynamic or static physical barriers, protection gas flows, or electrostatic fields, to control and remove the contaminants effectively, as will be described in the following.

[0018] It is to be understood that the disclosed contamination handling techniques can be applied to various imaging and analytical instruments that operate within a vacuum chamber or in more general, a sample processing and analysis chamber. While the claims specifically mention a Scanning Electron Microscope (SEM) module, these techniques are not limited to SEM and can be employed in other systems where contaminants generated during sample processing may interfere with the imaging or analysis process.

[0019] Some non-limiting examples of other imaging and analytical techniques that may also benefit from the disclosed contamination handling methods may include optical imaging modules and apparatuses, Transmission Electron Microscopy (TEM), which operates under vacuum conditions and involves the transmission of electrons through a thin sample to create high- resolution images. Sample preparation techniques for TEM, such as ion milling or focused ion beam (FIB) thinning, can generate contaminants that may affect the imaging quality. Auger Electron Spectroscopy (AES), which is a surface-sensitive analytical technique that uses an electron beam to probe the sample surface and measure the energy of emitted Auger electrons. The electron beam interaction with the sample can cause the release of contaminants, which may interfere with the AES measurements. X-ray Photoelectron Spectroscopy (XPS), which is a further surface analysis technique that uses X-rays to excite electrons from the sample surface, providing information about the elemental composition and chemical states. Contaminants introduced during sample processing or transfer may affect the XPS results. Secondary Ion Mass Spectrometry (SIMS), which is a surface analysis method that uses an ion beam to sputter the sample surface and analyse the emitted secondary ions. The sputtering process can generate contaminants that may interfere with the SIMS measurements or cause undesired artifacts. In such and similar cases, the disclosed contamination handling techniques, such as cooling traps, dynamic shutters, static barriers, electrostatic shielding, protection gas environments, and directional gas flows, can be adapted and implemented to minimize the impact of contaminants on the respective imaging or analysis process modules. By effectively managing the contaminants within the vacuum chamber or sample processing and analysis chamber, the quality and reliability of the results obtained from these instruments can be significantly improved.

[0020] The disclosed contamination handling module can comprise any one or any combination of the following examples, as shown in Table 1 and which are described in further detail in the present disclosure.

[0021] The contamination handling module may comprise a dynamic shutter. The dynamic shutter may be synchronized with the operation of the SEM module and the sample processing module. The dynamic shutter may be configured to block a direct path between the SEM module and the sample during operation of the sample processing module. The dynamic shutter may be further configured to enable imaging of the sample during operation of the SEM module.

[0022] In various examples, the dynamic shutter may comprise a movable component within the contamination handling module that helps prevent contaminants from reaching the SEM module. It may be synchronized with the operation of the SEM module and the sample processing module, ensuring that it blocks the direct path between the SEM and the sample during the processing phase and allows imaging during the SEM operation phase.

[0023] The dynamic shutter may comprise a rotatable blade or an oscillating blade. In various examples, the dynamic shutter may be implemented as a rotatable blade or an oscillating blade. The blade may have an opening that aligns with the direct path between the SEM and the sample in the imaging position, allowing the electron beam to pass through and enabling imaging. In the processing position, the opening is misaligned with the direct path, effectively blocking contaminants from reaching the SEM module.

[0024] It is to be understood that other mechanical shapes and forms of a moving shutter can be employed to achieve the effect of dynamically blocking and protecting the SEM from contaminants generated during sample processing. Some alternative designs for the dynamic shutter may include, but are not limited to, sliding shutters, which may consist of one or more plates that slide in a linear planar motion to block or unblock the direct path between the SEM and the sample. The sliding motion can be synchronized with the operation of the SEM and sample processing modules. An iris diaphragm can be adapted for use as a dynamic shutter. The diaphragm consists of a series of overlapping blades that can be opened or closed to varying degrees. When closed, the diaphragm blocks the direct path between the SEM and the sample, and when opened, it allows the electron beam to pass through for imaging. The dynamic shutter can be designed with a curved or multi-faceted surface to optimize the blocking of contaminants. The curved or angled surfaces may help deflect contaminants away from the SEM module more effectively compared to a flat blade design. A dual-blade shutter system can be employed, where two blades move in opposite directions to block or unblock the path between the SEM and the sample. This design may provide a more complete sealing of the path when the blades are closed, further reducing the risk of contaminants reaching the SEM module. Such designs ensure blocking of contaminants while minimizing interference with the operation of the SEM and sample processing modules. Additionally, the material used for the dynamic shutter could be cooled as to provide a cooling trap, wherein similar considerations as with regard to a disclosed cooling trap are applicable.

[0025] The dynamic shutter may be movable between a first position and a second position. The dynamic shutter may be rotatable between the first position and the second position. The rotation may be synchronized with operating phases of the SEM module and the sample processing module. The dynamic shutter may oscillate between the first position and the second position. The oscillation may be synchronized with the operation of the SEM module and the sample processing module.

[0026] The first position may correspond to an imaging position during imaging operation of the SEM module. The second position may correspond to a processing position during operation of the sample processing module. Movement of the dynamic shutter between a first (imaging) position and the a (processing) position can be achieved through rotation or oscillation. The rotation or oscillation may be synchronized with the operating phases of the SEM module and the sample processing module, ensuring that the shutter is in the correct position at the respective period of times. The dynamic shutter may comprise an opening. In the imaging position, the opening may be aligned with the direct path between the SEM module and the sample. In the processing position, the opening may be misaligned with the direct path between the SEM module and the sample, thereby blocking the direct path and preventing contaminants from reaching the SEM module.

[0027] By using a dynamic shutter, the metrology system can effectively protect the SEM module from contaminants generated during sample processing while still allowing imaging to occur when needed. The synchronized movement of the shutter minimizes the interference with the operation of the SEM and sample processing modules, ensuring efficient and reliable performance of the metrology system.

[0028] The contamination handling module may comprise a static contaminant barrier. The static contaminant barrier may be configured to restrict a volume of the vacuum chamber affected by the contaminants while maintaining a direct path between the SEM module and a processed location on the sample.

[0029] In various examples, a static contaminant barrier may be referred to as a fixed component or element within the contamination handling module that is configured to limit the spread of contaminants within the vacuum chamber. Unlike the dynamic shutter, the static barrier does not dynamically move but instead provides a physical obstruction, by forming or defining a sub-volume or department withing the vacuum chamber, that may limit or restrict movement of contaminants to the specific sub-volume or department of the vacuum chamber. The barrier may be designed to maintain a direct path between the SEM module and the processed location on the sample, wherein imaging can still be performed.

[0030] In various examples, the static contaminant barrier may comprise a fixed wall or partition with an opening that allows the electron beam from the SEM to reach the sample surface. The opening can be positioned and sized to optimize the containment of contaminants while minimizing interference with the SEM imaging process.

[0031] In various examples, the static contaminant barrier may be positioned between the SEM module and the sample processing module. The static contaminant barrier may be configured to divide the vacuum chamber into a first compartment containing the SEM module and a second compartment containing the sample processing module.

[0032] Positioning the static contaminant barrier at least partly between the SEM module and the sample processing module may help to isolate the two modules and minimize the spread of contaminants towards the SEM module. By dividing the vacuum chamber into two compartments, the barrier creates separate environments for the SEM module and / or the sample processing module and / or the sample stage. Such environments may be at least partly open to enable a direct line towards the sample, however thereby restrict the movement of contaminants within the vacuum chamber.

[0033] In various examples, the static contaminant barrier may be a vertical wall or housing placed between the SEM column and the focused ion beam (FIB) or other sample processing modules. The wall can have an aperture or opening that allows the electron beam and the ion beam to reach the sample surface while still maintaining separation between the compartments.

[0034] The static contaminant barrier may comprise an aperture aligned with the direct path between the SEM module and the processed location on the sample. The aperture may be configured to allow the passage of an electron beam from the SEM module to the sample and to allow the passage of secondary electrons or backscattered electrons from the sample to the SEM module.

[0035] The aperture in the static contaminant barrier may enable the SEM imaging process to occur while maintaining the barrier's ability to restrict contaminants. The aperture may be aligned with the direct path between the SEM module and the processed location on the sample, allowing the electron beam to pass through and interact with the sample. The aperture may allow the secondary electrons or backscattered electrons, which are generated by the interaction of the electron beam with the sample, to return to the SEM module for detection and imaging.

[0036] In various examples, the aperture in the static contaminant barrier may be a small hole or slit that is positioned and sized to accommodate the electron beam. The aperture can be optimized to minimize the amount of contaminants that can pass through while still allowing sufficient signal from the sample to reach the SEM detectors.

[0037] The static contaminant barrier may comprise a cooled surface configured to bind contaminants to the barrier. In various examples, including a cooled surface in the static contaminant barrier can enhance its effectiveness in trapping and containing contaminants. By maintaining the surface at a low temperature, contaminants that come into contact with the barrier are more likely to condense or adhere to the surface, preventing them from spreading along the barrier further into direction of the SEM in the vacuum chamber.

[0038] In various examples, the static contaminant barrier may include a cooling system, such as a Peltier cooler or a cryogenic cooling loop, that maintains the barrier's surface at a temperature below the condensation point of the expected contaminants, as described in respect of the Peltier cooling trap according to the disclosure. The cooled surface can be located along a flow path of contaminants from the sample towards the SEM on the barrier to maximize its contaminant trapping. The static contaminant barrier may comprise a plurality of fins configured to deflect a contaminant gas flow away from the SEM module, thereby preventing the contaminants from reaching the SEM module.

[0039] In various examples, adding fins to the static contaminant barrier can help to redirect the flow of contaminant gases away from the SEM module. The fins act as physical obstacles that change the direction of the gas flow, guiding the contaminants towards the edges of the barrier or towards a designated exhaust location. By deflecting the contaminant gas flow, the fins reduce the likelihood of contaminants reaching and accumulating on the sensitive components of the SEM module.

[0040] In various examples, the static contaminant barrier may feature a series of vertical or angled fins positioned on the surface of the barrier facing the sample processing module. The fins can be arranged in a pattern that optimizes the deflection of contaminant gases away from the SEM while avoiding obstruction to the electron beam path. The shape, size, and spacing of the fins can be tailored to the specific characteristics of the expected contaminants and the vacuum chamber geometry. In an example, the fins may comprise a surface angled smaller than 45° or 30° or 20° from the axis defined between the SEM head to the sample.

[0041] The contamination handling module may comprise a contaminant cooling trap configured to capture the contaminants. Such a contaminant cooling trap and the metrology system, especially the sample stage and / or a vacuum pump and / or a plasma cleaning system may be operated in a synchronized manner, as described in further detail throughout the disclosure.

[0042] In various examples, a contaminant cooling trap may be referred to as a component within the contamination handling module that uses low temperatures to condense and trap contaminants from the vacuum chamber atmosphere. By providing a cold surface, the trap effects contaminants to adhere to it, thereby removing them from the atmosphere and preventing them from reaching the SEM module.

[0043] In various examples, the contaminant cooling trap may be a cold plate or a series of cooled baffles positioned near the sample processing module. The trap can be maintained at a temperature well below the condensation point of the expected contaminants, ensuring efficient capture and removal.

[0044] The contaminant trap may comprise a Peltier cooling element configured to maintain a surface of the contaminant trap at a temperature lower than a condensation temperature of the contaminants.

[0045] In various examples, a Peltier cooling element may be referred to as a thermoelectric device that can be used to actively cool the contaminant trap surface. By applying an electrical current to the Peltier element, heat is transferred from one side of the device to the other, creating a cold surface that can condense and trap contaminants. The use of a Peltier cooling element allows for precise temperature control and can be adjusted to optimize the trapping efficiency for specific contaminants.

[0046] In various examples, the contaminant trap may incorporate a Peltier cooling element. A cold plate connected to the Peltier cooling element serves as the trapping surface. The temperature of the cold plate can be regulated by controlling the current supplied to the Peltier element.

[0047] The Peltier cooling element may further be operatively connected to a heat sink located outside the vacuum chamber. The heat sink may be configured to dissipate heat generated by the Peltier cooling element.

[0048] In various examples, in order to maintain the efficiency of the Peltier cooling element and prevent heat buildup within the vacuum chamber, the excess heat generated by the element needs to be dissipated. Connecting the Peltier element to a heat sink located outside the vacuum chamber allows for effective heat removal, as the heat sink can be designed with a larger surface area and can be cooled by external means, such as air or liquid cooling.

[0049] In various examples, the Peltier cooling element may be thermally coupled to a heat sink through a feedthrough in the vacuum chamber wall. The heat sink can be a finned radiator or a water-cooled block that efficiently transfers the heat away from the Peltier element. By locating the heat sink outside the vacuum chamber, the cooling performance of the contaminant trap can be maintained without affecting the vacuum environment.

[0050] The contaminant trap may be positioned between the sample processing module and the SEM module configured to capture contaminants generated by the sample processing module before they reach the SEM module.

[0051] In various examples, arranging the contaminant trap between the sample processing module and the SEM module helps to intercept and capture contaminants before they can reach and accumulate on the SEM module, in other words short SEM. By targeting the contaminants at their source, the trap can more effectively prevent the spread of contamination within the vacuum chamber. By targeting contaminants near the SEM and / or near a gas flow path in a direct line from the sample to the SEM, the cooling trap can more effectively protect the SEM from contaminants.

[0052] In various examples, the contaminant trap may be mounted on a support structure that positions it directly above the sample processing area, such as directly adjacent to the focused ion beam (FIB) or other material removal / deposition modules. As contaminants are generated during the processing operation, they rise and come into contact with the cold surface of the trap, where they condense and adhere, preventing them from reaching the SEM module. It may also be arranged directly adjacent to the SEM head or the SEM endcap, for examples at least partly extending along or around the SEM end-cap.

[0053] The metrology system may further comprise a cleaning module configured to remove accumulated contaminants from the surface of the cooling contaminant trap during a cleaning phase, wherein such cleaning module may correspond to or comprise at least some elements of a directed plasma cleaning system with as described herein.

[0054] In various examples, over time, the contaminant trap may accumulate a significant amount of trapped contaminants on its surface, which can reduce its trapping efficiency and potentially become a source of contamination itself. To address this issue, a cleaning module can be incorporated into the metrology system to periodically remove the accumulated contaminants from the trap surface. The cleaning module can be activated during a dedicated cleaning phase, which may be scheduled between imaging or processing sessions, or as part of a regular maintenance routine.

[0055] In various examples, such a cleaning module may comprise a heating element, or reverse the Peltier cooling element, that can raise the temperature of the contaminant trap surface above the evaporation point of the trapped contaminants, causing them to release from the surface. Alternatively, the cleaning module may employ a mechanical scraper or a gas jet that physically dislodges the contaminants from the trap surface. The released contaminants can then be evacuated from the vacuum chamber through a dedicated pumping system.

[0056] The cleaning module may comprise a plasma generator configured to direct a plasma stream towards the surface of the cooling contaminant trap. The plasma stream may be configured to dissolve the accumulated contaminants from the surface. A vacuum pump may be configured to evacuate the cleaning plasma with the contaminants from the vacuum chamber.

[0057] In various examples, the plasma cleaning is an effective method for removing accumulated contaminants from surfaces. By generating a plasma stream and directing it towards the contaminant trap surface, the high-energy particles in the plasma can interact with the contaminants, breaking down their chemical bonds and facilitating their removal. The plasma cleaning process can be performed in-situ within the vacuum chamber, eliminating the need to disassemble the trap or remove it from the system.

[0058] In various examples, the cleaning module may include a plasma source, such as a radiofrequency (RF) or microwave generator, coupled to a gas delivery system. During the cleaning phase, a cleaning gas, such as oxygen or a mixture of gases, is introduced into the vacuum chamber and ionized by the plasma source. The resulting plasma stream is directed towards the contaminant trap surface, where it reacts with the accumulated contaminants, converting them into volatile compounds. A vacuum pump connected to the chamber then evacuates the cleaning plasma along with the contaminants, leaving the trap surface clean and ready for further use.

[0059] The contamination handling module may comprise a first electrostatic collection field configured to deflect charged contaminant particles away from the SEM module.

[0060] In various examples, an electrostatic collection field can be employed to manipulate the trajectory of charged contaminant particles and prevent them from reaching the SEM module. By applying a voltage to a set of electrodes or plates within the vacuum chamber, an electric field is generated that exerts a force on the charged particles. The direction and strength of the electric field can be adjusted to deflect the contaminants away from sensitive components and guide them towards a designated collection area.

[0061] In various examples, the first electrostatic collection field may be created by a pair of parallel plates positioned near the SEM module. One plate may be positively charged, while the other is negatively charged, creating an electric field perpendicular to the plates. As charged contaminant particles enter the field, they experience a force that deflects them towards the oppositely charged plate, effectively steering them away from the SEM module.

[0062] The contamination handling module may comprise a second electrostatic collection field with a polarity opposite to that of the first electrostatic collection field.

[0063] Incorporating a second electrostatic collection field with an opposite polarity to the first field can enhance the efficiency of contaminant removal. The second electric field may, as the first electric field be located adjacent or around the SEM head. The oppositely charged fields work together to guide differently charged contaminants away from the SEM head, where they can be evacuated from the vacuum chamber.

[0064] In various examples, the second electrostatic collection field may be generated by a second set of parallel plates positioned adjacent to the first set. The polarity of the plates in the second set may be reversed compared to the first set, creating an opposing electric field. Charged contaminant particles that are not deflected by the first field are then deflected by second field. This dual-field configuration can thus improve the contamination handling.

[0065] The first and / or the second electrostatic collection fields may be electric gradient fields with the highest field strength arranged closer to the SEM module.

[0066] In various examples, the contamination handling module may comprise a plurality of electrodes arranged to generate an electrostatic collection field. The electrodes may be arranged such that different potentials are applied to different electrodes to generate the electrostatic collection field. The electrostatic collection field may comprise a first field region and a second field region, wherein the first field region in configured to primarily attract particles of one polarity, while the second field region is configured to primarily attract particles of the opposite polarity.

[0067] Incorporating the first and second field regions that attract oppositely charged particles enhances the efficiency of contaminant removal. The electrodes generating the first and second field regions may be located adjacent to or around the SEM head. The field regions with opposing particle attraction work together to deflect differently charged contaminants away from the SEM head, such that they can be evacuated from the vacuum chamber.

[0068] In various examples, the first field region may be generated by a first set of electrodes, and the second field region may further be generated using a second set of electrodes. The potentials applied to the electrodes in the second set may be configured to generate the second field region for attracting particles of the opposite polarity compared to the potentials applied to the electrodes in the first set. Charged contaminant particles that are not attracted by the first field region may be attracted by the second field region, and vice versa. This dualfield configuration can thus improve the contamination handling.

[0069] In various examples, configuring the electrostatic collection fields as gradient fields, with the highest field strength near the SEM module, can improve deflection of contaminants. In a gradient field, the electric field strength varies with distance, creating a force that pushes charged particles away from the region of highest field strength. By positioning the highest field strength closer to the SEM module, contaminants are stronger repelled from the sensitive components, reducing the likelihood of contamination.

[0070] In various examples, the electrostatic collection fields may be designed with a series of electrodes arranged in a concentric pattern around the SEM module. The electrodes closer to the SEM module may be smaller compared to those further away, creating an electric field gradient. As charged contaminant particles approach the SEM module, they experience an increasingly strong repulsive force that pushes them towards the outer regions of the collection fields, where they can be removed.

[0071] The metrology system may further comprise an ionizer arranged at an end-cap of the SEM module configured to charge neutral contaminant particles. Such neutral contaminant particles, in other words contaminants, may be present in areas near the sample stage or near the SEM module, or near the electric fields, where they can become ionized or charged.

[0072] In various examples, while electrostatic collection fields are effective at managing charged contaminant particles, neutral particles are not influenced by electric fields. To address this limitation, an ionizer can be incorporated into the system to charge neutral contaminant particles near the SEM, in order to make them susceptible to the electrostatic collection fields. The ionizer may be typically positioned near the SEM module, where it can interact with the contaminant particles before they reach sensitive elements.

[0073] For example, the ionizer may be a discharge device or an electron emission source located at the end-cap of the SEM module. As neutral contaminant particles pass through the ionizer, they interact with charged particles (ions or electrons), which transfer charge to the contaminants. Once charged, the contaminant particles can be effectively manipulated by the electrostatic collection fields and directed away from the SEM module.

[0074] The ionizer may comprise a laser source configured to emit laser continuous or pulsed high energy radiation towards the neutral contaminant particles, thereby ionizing the neutral contaminant particles through photoionization.

[0075] In various examples, photoionization using laser radiation is a precise and efficient method for charging neutral contaminant particles. By selecting a laser wavelength that matches the ionization energy of the contaminant particles, the laser can selectively ionize the particles without affecting other components in the vacuum chamber. Photoionization has the advantage of being a non-contact method, minimizing the risk of introducing additional contamination into the system.

[0076] In various examples, the ionizer may incorporate a pulsed ultraviolet (UV) laser source that emits high-energy photons. The laser beam is directed towards SEM and / or to the region in which the electric collection fields are active, where neutral contaminant particles are expected to be present, or near the sample processing area. When a neutral particle absorbs a photon with sufficient energy, an electron is ejected from the particle, resulting in a positively charged ion. The newly charged particle can then be influenced by the electrostatic collection fields and removed from the vicinity of the SEM module.

[0077] The ionizer may comprise an electron source configured to emit electrons towards the neutral contaminant particles.

[0078] In various examples, an electron source ionizer works by colliding neutral contaminant particles with a beam of electrons. When an electron collides with a neutral particle, it can knock out one or more electrons from the particle, creating a positively charged ion. This process, known as electron impact ionization, is a reliable and well-established method for charging particles in vacuum systems.

[0079] In various examples, the ionizer may use a thermionic electron emitter, such as a heated filament or a field emission tip, to generate a focused electron beam. The electron beam is directed towards the path of the neutral contaminant particles, either continuously or in a pulsed manner. As the electrons interact with the particles, they ionize them, allowing the electrostatic collection fields to effectively remove the charged contaminants from the system.

[0080] The ionizer may comprise a plasma generator configured to generate a plasma to charge the neutral contaminant particles through collisions.

[0081] In various examples, plasma-based ionization is a versatile method for charging neutral contaminant particles. A plasma is a partially ionized gas consisting of electrons, ions, and neutral particles. When a neutral contaminant particle collides with an electron or an ion in the plasma, it can gain or lose electrons, becoming charged in the process. Plasma ionization can for example be effective in situations where a high concentration of contaminant particles is present.

[0082] In various examples, the ionizer may include a plasma source. The plasma source may be positioned in the vacuum chamber, near the region where neutral contaminant particles are present, for example near the electrostatic collection fields. The plasma may be generated by applying a high-frequency electric field to a low-pressure gas, such as argon or helium. As the contaminant particles pass through the plasma, they undergo collisions with the charged species, resulting in ionization. The charged particles can then be efficiently managed by the electrostatic collection fields.

[0083] The contamination handling module may comprise a protection gas environment within the vacuum chamber. The protection gas environment may comprise a protection gas inlet configured to supply a protection gas flow to sweep the contaminants and a gas outlet configured to evacuate the contaminants carrying protection gas.

[0084] In various examples, a protection gas environment may refer to an enclosed sub environment within the vacuum chamber in which the atmosphere mainly consists of the protection gas, to mitigate the impact of contaminants on the SEM module. By introducing a controlled flow of protection gas, such as nitrogen or argon, contaminant particles can be kept away from sensitive components and directed towards a gas outlet for evacuation. The protection gas flow comprises a localized higher pressure in the protection gas environment and / or a protection gas flow that hinders the path of the contaminants towards the SEM and thus prevents them from reaching the SEM module.

[0085] In various examples, the protection gas environment may be established by positioning a gas inlet near the sample processing area, where contaminants are generated. The gas inlet is connected to a protection gas supply, such as a nitrogen or argon, through a pressure regulator and a flow controller. During operation, the protection gas is released into the vacuum chamber at a controlled rate, creating a laminar flow that carries the contaminants towards the gas outlet. The gas outlet is connected to a vacuum pump that continuously removes the protection gas and the entrained contaminants from the chamber.

[0086] In various examples, the protection gas environment may further comprise a protection gas enclosure within the vacuum chamber enclosing at least part of the SEM module and / or at least part of the sample stage. The housing may have apertures for the SEM module, the sample processing module, the protection gas inlet, and the gas outlet. In some examples, the protection gas environment is the inner of an enclosure around the SEM head and / or the SEM end-cap. In some examples, the protection gas enclosure encloses at least the part of the SEM head where the emission and detection is performed, and includes an opening for the electron beam and secondary electron detection. The protection gas inlet may be located in the inner of the enclosure, such that a positive pressure inside the enclosure by the protection gas relative to the atmosphere inside the vacuum chamber and / or a gas flow by the protection gas from the inner of the protection gas enclosure into the vacuum chamber may be realized.

[0087] Therefore, in various examples, to enhance the effectiveness of the protection gas environment, an enclosure can be added within the vacuum chamber. The enclosure serves to confine the protection gas flow and create a more localized clean environment around the SEM module and the sample stage. By isolating critical components from the rest of the chamber with a positive pressure and steady protection gas flow out of the enclosure, the enclosure may minimize the interference of the protection gas flow with other processes and reduces the amount of gas required to maintain a stable environment.

[0088] For example, the enclosure may be a cylindrical or rectangular housing made of a nonmagnetic material, such as aluminium or plastic. The housing is designed to fit around the SEM module and the sample stage, with sufficient clearance to allow for sample movement and the operation of the sample processing module. Apertures are provided in the housing for the SEM module, the sample processing module, the protection gas inlet, and the gas outlet. These apertures are carefully positioned and sized to optimize the gas flow pattern and minimize the escape of contaminants into the main vacuum chamber.

[0089] The protection gas inlet may be positioned closer to the SEM module, and the gas outlet may be positioned closer to the sample processing module. This may create a protection gas flow direction from the SEM module towards the sample processing module to sweep the contaminants.

[0090] In various examples, the relative positioning of the protection gas inlet and outlet effect the direction and effectiveness of the protection gas flow. By placing the gas inlet closer to the SEM module and the outlet closer to the sample processing module, a unidirectional flow can be established. This arrangement ensures that the clean protection gas first passes over the sensitive SEM components before sweeping the contaminants generated by the sample processing module towards the outlet.

[0091] In various examples, the protection gas inlet may be located just above or to the side of the SEM module, directing the protection gas flow downwards and across the surface of the SEM components. As the gas moves towards the sample processing area, it encounters the contaminant particles and carries them along its path. The gas outlet may be positioned near the sample processing module, where the concentration of contaminants is highest. The continuous flow of protection gas from the inlet to the outlet creates a flow that effectively sweeps the contaminants away from the SEM module and into the evacuation port.

[0092] The system may be configured such that the gas flow direction is substantially parallel to a top surface of the sample stage.

[0093] In various examples, such a protection gas environment minimizes the interference of the gas flow with the operation of the sample stage, ensuring that the sample remains stable and unaffected by the gas movement. A parallel flow pattern helps to maintain a laminar flow. This configuration allows for efficient sweeping of contaminants from the surface of the sample and the stage preventing deposition onto the SEM module.

[0094] In various examples, the protection gas inlet and outlet may be positioned at opposite ends of the sample stage, with the inlet slightly higher than the outlet. The gas flow is directed parallel to the top surface of the stage, creating a laminar flow pattern towards the sample. In this regard, the protection gas has the effect of a cleaning gas for the sample. As the gas moves across the stage, it collects contaminant particles that may have settled on the surface or are being generated by the sample processing module. The flow minimizes any vertical paths of the contaminants, ensuring that they are efficiently carried towards the outlet and evacuated from the system.

[0095] In various examples, the gas flow may be directed parallel to the top surface of the stage, creating a flow pattern that depends on the ratio of the mean free path of the gas molecules to the characteristic spatial dimensions of the system. In various examples, the flow may be in a continuum regime, where molecule-molecule scattering dominates. In this case, the gas flow may be a laminar flow. In various examples, the flow may be in a free molecular regime, where molecule-wall scattering dominates. In this case, the gas molecules rarely collide with each other, and their motion is governed by their interactions with the walls of the system. In various examples, the flow may considered to be in a transitional regime, where both molecule-molecule and molecule-wall scattering significantly occur. In each flow regime, the protection gas has the effect of a cleaning gas for the sample. As the gas moves across the stage, it collects contaminant particles that may have settled on the surface or are being generated by the sample processing module. The flow direction parallel to the stage surface minimizes vertical paths of the contaminants, ensuring that they are efficiently carried towards the outlet and evacuated from the system.

[0096] In various examples, the metrology system may be configured such that the protection gas environment includes the head of the SEM module having an opening for the SEM beam. The protection gas flow may be configured to maintain a positive pressure of the protection gas within the protection gas environment relative to the vacuum chamber, thereby preventing the contaminants from entering the protection gas environment.

[0097] In various examples, constructing the protection gas environment to only the head of the SEM module may provide additional protection against contaminants. By maintaining a positive pressure of the protection gas within this environment, relative to the surrounding vacuum chamber, contaminants are actively prevented from entering the region around the SEM module. This positive pressure creates an outward flow of protection gas through the opening for the SEM beam, effectively blocking the ingress of contaminants.

[0098] In a typical SEM application, the operating pressure in a main operating chamber may, for example, range from 10A-5 to 10A-6 mbar. Other variable pressure SEMs (VPSEMs) may, for example, operate at pressures up to 100 mbar or higher. In some examples, the head of the SEM module may be enclosed within a compartment that is sealed to the SEM housing and connected to the protection gas inlet. The compartment may be designed to maintain a higher pressure than the main vacuum chamber, for example >1 * 10A-6 mbar, or > 1 x 10A- 5 mbar, or > 1 10A-2, or even >1 mbar, or <10 mbar, above the main chamber pressure.

[0099] This pressure difference is achieved by balancing the gas inflow rate with the pumping speed of the vacuum system. The opening for the SEM beam is the only pathway for the pressurized gas to flow out, creating a localized outward flow that prevents contaminants from entering the compartment. Any contaminants that may have been present in the compartment are continuously flushed out by the protection gas flow, maintaining a clean protection gas environment around the SEM module. The contamination handling module may comprise a directional protection gas system configured to direct a protection gas flow from the SEM module head towards the sample stage.

[0100] In various examples, a directional protection gas system is designed to create a controlled gas flow that originates from the SEM module head and is directed towards the sample stage. This configuration establishes a clean environment around the SEM module and actively sweeps contaminants away from the sensitive components. By directing the gas flow from the SEM module head, the system ensures that the protection gas first passes over the critical parts of the SEM before encountering the contaminants generated by the sample processing module.

[0101] In various examples, the directional protection gas system may include a gas inlet manifold integrated into the SEM module head. The manifold is designed to distribute the protection gas evenly around the perimeter of the SEM module, creating a uniform, downward flow towards the sample stage. As the protection gas passes over the SEM components, it creates a protective barrier that prevents contaminants from reaching the sensitive surfaces. The gas flow continues towards the sample stage, where it collects the contaminants generated by the sample processing module and carries them away from the SEM module.

[0102] The directional protection gas system may comprise a protection gas inlet integrated into the SEM module configured to direct the protection gas flow towards the sample stage.

[0103] In various examples, integrating the protection gas inlet directly into the SEM module allows for a more targeted delivery of the protection gas flow. By positioning the inlet close to the SEM components, the system ensures that the protection gas flow reaches the critical areas effectively. This direct integration also minimizes the distance the gas has to travel, reducing the potential for contamination along the way.

[0104] In various examples, the protection gas inlet may be incorporated into the SEM module head as a series of nozzles or a circular slot surrounding the electron beam aperture. The inlet may be connected to a protection gas supply line that delivers the protection gas at a controlled pressure and flow rate. As the gas exits the inlet, it is directed downwards towards the sample stage, creating a directed gas flow that sweeps contaminants away from the SEM module. The close proximity of the inlet to the SEM components ensures that the protection gas has higher concentration and / or velocity and integrity.

[0105] The directional protection gas system may comprise a gas outlet positioned below the sample stage configured to remove the protection gas from the vacuum chamber.

[0106] In various examples, a gas outlet is positioned below the sample stage to remove the gas and entrained contaminants from the vacuum chamber. The placement of the outlet below the stage ensures that the gas flow is directed away from the SEM module. This configuration helps to prevent the circulation of contaminants and maintains a clean protection gas environment around the SEM module.

[0107] In various examples, the gas outlet may be integrated into the base of the vacuum chamber, directly beneath the sample stage. The outlet may be connected to a vacuum pumping system that continuously removes the protection gas and contaminants from the chamber. As the gas flow from the SEM module head reaches the sample stage, it is drawn downwards by the vacuum pumping action, carrying the contaminants towards the outlet. The placement of the outlet below the stage creates an efficient, unidirectional flow pattern that minimizes the chances of contaminants being recirculated back towards the SEM module.

[0108] The SEM module may comprise an end-cap facing the sample stage. The end-cap may have a plurality of internal gas channels configured to direct the protection gas flow towards the protection gas inlet integrated into the end-cap.

[0109] In various examples, the SEM module may comprise an end-cap with internal gas channels. These channels are designed to guide the protection gas from the supply line to the gas inlet nozzles or slots in the end-cap. By evenly distributing the gas flow through multiple channels, the system creates a consistent, laminar flow pattern that provides optimal protection against contaminants.

[0110] In various examples, the end-cap of the SEM module may comprise a network of internal gas channels. These channels may be connected to the protection gas supply line and terminate at inlet openings, such as protection gas inlet nozzles or slots around the end-cap. As the protection gas enters the channels, it is distributed and directed towards the inlet openings. The geometry of the channels provide a constant gas velocity and minimize turbulence.

[0111] The end-cap may further comprise a central aperture configured to allow passage of an electron beam from the SEM module to the sample. The protection gas channels may be arranged around the central aperture. This configuration ensures that the gas flow does not interfere with the electron beam path and maintains a clean environment in the immediate vicinity of the aperture.

[0112] In various examples, the end-cap of the SEM module may comprise a central aperture that is aligned with the electron beam column. The aperture may be sized to allow the passage of the focused electron beam while minimizing the escape of protection gas. The internal gas channels may be arranged symmetrically arranged around the central aperture and / or forming a circular pattern. As the protection gas exits the channels and flows through the inlet nozzles or slots, it creates an annular flow. This configuration provides a protective stream of gas, preventing contaminants from entering the aperture and interfering with the imaging process.

[0113] The protection gas may be an inert gas selected from the group consisting of noble gases and nitrogen. Inert gases, such as noble gases (e.g., argon, helium, neon) and nitrogen, are preferred due to their chemical stability and non-reactivity. These gases do not interact with the sample, the SEM components, or the contaminants.

[0114] The sample processing module may be configured to mill the sample or etch the sample or deposit material onto the sample. In various examples, the sample processing module is responsible for performing various physical or material operations on the sample, such as for example milling, etching, or material deposition. These processes are essential for preparing the sample for imaging, analyzing its composition, or fabricating nano-scale structures. However, these processes can also generate contaminants that may interfere with the SEM imaging. The contamination handling system is designed to mitigate the impact of these contaminants and ensure a clean environment for the SEM.

[0115] In general, the sample processing module can include various functionalities. In various examples, the sample processing module may comprise a focused ion beam (FIB) system for example for milling the sample. The FIB system uses a focused beam of ions to remove material from the sample surface. This process can generate contaminants such as sputtered material, redeposited debris, or residual precursor gases, which the contamination handling system must effectively manage to maintain the integrity of the SEM imaging. In various examples, the sample processing module may comprise one or more of a focused ion beam (FIB) module, or a gas injection system (GIS), or a laser processing module.

[0116] A gas injection system (GIS) is used for site-specific deposition of materials onto the sample surface. The GIS introduces a precursor gas into the vacuum chamber, which is then decomposed by the electron beam or ion beam to deposit the desired material. Common applications include the deposition of protective coatings, conductive layers, or insulating materials. The GIS can generate contaminants in the form of residual precursor gases or unwanted deposition on the SEM components.

[0117] A laser processing module may be used a focused laser beam to modify the sample surface through ablation, melting, or selective heating. Laser processing is often used for micromachining, surface texturing, or material removal. The laser-material interaction can generate debris, vapours, or plasma plumes that may contaminate the SEM module if not properly managed.

[0118] Such types of sample processing modules include the risk to generate contaminants that can interfere with the SEM imaging process. The contamination handling module is designed to ensure a clean and stable environment for the SEM imaging process.

[0119] The disclosed techniques can further be described using the following examples:

[0120] In the following, some general examples and some examples with regard to a Peltier cooling trap for contaminants in the vacuum chamber will be described in further detail.

[0121] In various examples, the metrology system comprises a vacuum chamber. In various examples, the system comprises a sample stage arranged within the vacuum chamber. The sample stage can be configured to hold a sample on a sample stage surface. The sample stage can be configured to position the sample in an operational position inside the vacuum chamber during an operational phase of the metrology system.

[0122] In various examples, the system comprises a Peltier element arranged at least partly within the vacuum chamber. The Peltier element can act as a cooling or cryo- trap for contaminants present within the vacuum chamber. The Peltier element can be arranged fully in the vacuum chamber, wherein one surface of the Peltier element that is cooled or heated by the Peltier effect, is thermally connected to the vacuum chamber housing, such that heat can effectively be transferred from and to the Peltier element, and the other complementary cooled or heated surface of the Peltier element is facing the inside of the vacuum chamber for trapping contaminants. In other words, the Peltier element's collection surface for cryogenically trapping contaminants represents one part of the overall Peltier thermoelectric module. This collection surface is actively cooled or heated according to the applied voltage polarity across the Peltier junction.

[0123] An opposing complementary part of the Peltier element is heated or cooled respectively by the Peltier effect during operation. This complementary part can be positioned either inside or outside the vacuum chamber to facilitate heat transfer and dissipation.

[0124] In various examples, the complementary Peltier part can be thermally connected to and mounted to the vacuum chamber housing, while the collection surface is located within the inner vacuum environment facing towards the sample stage and sample. The housing wall thereby connects the complementary Peltier part to / from the ambient external environment surrounding the vacuum chamber.

[0125] In other words, for binding contaminants present within the vacuum chamber, the Peltier element comprises a collection surface inside the vacuum chamber, which can be cooled relative to the inside of the vacuum chamber. The collection surface may face in the direction of the sample stage. The collection surface may surround at least partly the sample stage. The collection surface is configured to be cooled below 0° Celsius, for binding contaminants within the vacuum chamber onto the collection surface. The collection surface may be closer than 5 cm, or 10 cm, from the sample stage surface holding the sample. The collection surface may extend along at least 20%, or 50%, of the sample stage surface. The collection surface may extend at least partly around one or more process modules for inspecting and processing the sample on the sample stage surface, such as a concave surface. The collection surface may be formed, at least partly by a heat conductive material such as copper or aluminium, particularly in a core layer for efficient heat transfer within the plate. A surface of the plate may comprise a layer of a different material, e.g. titanium. In various examples, when the sample is being inspected or processed, this Peltier collection surface is actively cooled to a low temperature. The cooling causes contaminant molecules within the vacuum chamber to lose kinetic energy and cryogenically bind to the collection surface. The Peltier collection surface thereby effectively functions as a cooling trap, binding contaminants on the surface before they can accumulate on and interfere with the metrology system optics, sample, or chamber walls.

[0126] In various examples, the metrology system may optionally comprise a plasma cleaning system. The plasma cleaning system may comprise a cleaning plasma source, a cleaning plasma inlet for injecting the cleaning plasma into the vacuum chamber, and a cleaning plasma outlet from the vacuum chamber for extracting the cleaning plasma with contaminants. The plasma cleaning system may be configured to clean the collection surface of the Peltier element.

[0127] In various examples, the system comprises a plasma inlet of the vacuum chamber connected to a plasma source for providing a cleaning plasma stream into the vacuum chamber. The system comprises a plasma outlet of the vacuum chamber opposite to the plasma inlet for evacuating the cleaning plasma stream with released contaminants, by a vacuum pump.

[0128] In various examples, the cleaning plasma stream may be directed towards or onto the collection surface of the Peltier cooling trap. In various examples, the cleaning plasma stream may essentially extend along a cleaning plasma direction, or axis, from the cleaning plasma inlet towards the collection surface. The plasma axis may be directed in parallel to, i.e., along, or in a small angle of preferably <20° relative to the collection surface. In some examples <15°, or <10° would also be possible.

[0129] The plasma composition injected into the vacuum chamber environment comprises ionized gas mixtures can be designed to release or push contaminants, or chemically react with and break down contaminant species. Common gases like oxygen, hydrogen, or nitrogen can be ionized into the cleaning plasma stream. These reactive plasma flows energetically impinge on the accumulated contaminants, gradually pushing and releasing the molecular contaminants from the collection surface and towards the cleaning plasma outlet for evacuation.

[0130] In addition to chemical decomposition of contaminants, the physical momentum transfer of the directed plasma streams may also serve to sputter etch the collection surface itself. This helps maintain a refreshed, activated surface optimized for cryogenically trapping additional contaminants once cooled again after the cleaning process completes and the next operational metrology phase commences. Optionally in this regard, as will be described in detail, in this case a replaceable sacrificial plate may be used as collection surface, which is mounted onto the cooled surface of the Peltier element.

[0131] Optionally, before or while injecting the plasma, the Peltier element can be switched to and operated in a heating mode, wherein the collection surface is heated, in order to first release the previously bound contaminants, or at least facilitate the cleaning process by the cleaning plasma. This allows the plasma streams to interact with the released contaminants more effectively to facilitate removal. However, the heating step is not essential, and contaminants can still be released and evacuated even while partially bound to the cooled collection surface.

[0132] The integrated contamination handling through a Peltier cooling trap combined with plasma cleaning provides improved contamination control. Keeping optical and semiconductor components substantially free of contaminants enables precise metrology measurement and processing within the vacuum chamber.

[0133] In various examples, the metrology system may optionally comprise a sample stage movement mechanism connected to the sample stage, which is configured to move the sample stage out of the plasma cleaning stream.

[0134] In other words, the metrology system can include a movable sample stage, movable by precision actuators, which can be located and moved in an operational position for measurement or inspection. To protect the sample stage from exposure to the cleaning plasma used to remove contaminants from the Peltier cooling trap, the system may further provide an additional sample stage movement mechanism to translate the sample stage further away from the plasma flow paths during the cleaning process, additionally to the regular precision sample stage movement. In various examples, the sample stage movement mechanism may be configured to move the sample stage over a distance of preferably more than 15 cm in one or more directions, for example in the horizontal direction. However, it is to be understood that the disclosure is not limited in this regard, and any linear or even nonlinear movement, in any direction out of the direct impact region of the cleaning plasma stream can be realized. In some examples a horizontal movement of more than 5 cm, or more than 10 cm, or more than 20 cm, or more than 30 cm in horizontal direction can be realized. In some examples, this could be combined with additional linear movement in vertical direction, or even rotational movement.

[0135] In various examples, during the operational phase, the sample stage surface overlaps the collection surface of the Peltier element in a horizontal direction, and during the cleaning phase, the sample stage is positioned with a horizontal distance greater than 5 cm, or 10 cm, or 15 cm, or 20 cm, or 25 cm, between the sample stage surface and the collection surface of the Peltier element.

[0136] In various examples, the sample stage which supports semiconductor wafers, substrates, or other inspection pieces can be moved bi-directionally from an operational position to an alternate safe cleaning position. This movement may be enabled by a motorized rail system or equivalently by other transport mechanics integrated internally within the vacuum chamber environment.

[0137] In an operational position and / or in the operational phase, the sample is aligned for metrology measurements, situated closer than 10 cm, to process module heads for inspection or processing. In various examples, the sample could be situated closer than 5 cm, or 2 cm, or 1 cm, or 5 mm. Thus prior to initiating a plasma cleaning sequence, the system controller transmits control signals that activates the sample stage movement to a cleaning position, which is in use during a cleaning phase of the metrology system. This moves the sample stage away from exposed regions to the cleaning plasma, for example by lowering the sample stage horizontally and / or vertically, and / or rotating the stage to a more protected cleaning position. During the cleaning phase, and / or in the cleaning position, the samples stage may not hold a sample.

[0138] During the cleaning phase, when the cleaning plasma stream enters the vacuum chamber, the sample stage may remain outside the direct plasma path through the vacuum chamber. It may also be possible, that the sample stage remains in an operational phase, therefore moving the sample stage may be considered optional. After the cleaning phase, the controller then returns the transport mechanism to move the sample stage back into the prior operational position. During the plasma cleaning phase, the sample may be situated outside the vacuum chamber.

[0139] In various examples, the stage movement mechanism is configured to move the sample stage from the operational position during the operational phase to the cleaning position for or during the cleaning phase. The cleaning position is outside a path of the cleaning plasma stream. The system comprises a controller. During the operational phase, the controller is configured to operate the Peltier element in a cooling mode to cool the collection surface for binding contaminants within the vacuum chamber onto the collection surface, while the sample stage is in the operational position. After the operational phase, the controller is configured to control the stage movement mechanism to move the sample stage from the operational position to the cleaning position. During the cleaning phase, the controller is configured to operate the plasma source to direct a cleaning plasma stream towards the collection surface to release contaminants and evacuate the cleaning plasma stream together with released contaminants through the plasma outlet, while the sample stage is positioned in the cleaning position outside the path. For evacuating the plasma with released contaminants through the plasma outlet, one or more vacuum pumps, such as a turbo molecular pump and a rough pump, may be applied.

[0140] The techniques according to the present disclosure may combine a Peltier cooling trap and plasma cleaning stream, while optionally moving sensitive elements within the vacuum chamber out of the cleaning plasma stream, which provides at least the following advantages. The disclosed techniques prolong the operational time of the metrology system between required maintenance cycles. The disclosed techniques shorten the maintenance time of the metrology system between operational phases. By collecting contaminants on a plasma-cleanable Peltier cooling trap, the metrology system can operate continuously for longer duration before a full cleaning of the vacuum chamber is necessary. The disclosed techniques avoid the need to vent the vacuum chamber to atmospheric pressure for cleaning the cooling trap. Venting the chamber could allow inflow of moisture and additional contaminants from the atmosphere into the chamber. By instead using, in vacuum, a cleaning plasma stream for cleaning, directed only at the removable contaminant trap itself while inside the vacuum chamber and evacuating the plasma continually by the vacuum pump, optionally simultaneously to plasma injection, the vacuum of the chamber can be essentially maintained. The use of a plasma stream provides efficient cleaning of the cooling trap comparable to extracting and cleaning outside the vacuum chamber. The cyclical process of cooling the trap to collect contaminants then heating and plasma-cleaning allows a more continuous operation of the metrology system without venting the vacuum chamber. This improves throughput and productivity. Keeping contaminants concentrated on the collection surface of the Peltier cooling trap protects other instruments, detectors, and positioning stages inside the vacuum chamber from degradation. If the trap unit itself degrades after extensive plasma cleaning cycles, only that modular unit needs replacement rather than internal chamber elements. The contaminant trapping and collection concept could be adapted to many different vacuum chamber devices and applications beyond metrology - the principles remain valid whether optical instruments, electron microscopes, or other analytical tools are used in a chamber system.

[0141] An optional advantage of a plasma-cleaned Peltier element is its configurability between heating or cooling by changing the polarity of voltage applied over the Peltier junction, for assisting the plasma cleaning process. Therefore, after an operational phase with the collection surface cooled to bind contaminants, the system controller can switch the Peltier element into heating mode. The collection surface is selectively heated to a high enough temperature that previously bound contaminants are re-vaporized and released back into the vacuum chamber environment. Before or while injecting the plasma, the Peltier element can be switched into heating mode in order to first release the previously bound contaminants back into the vacuum environment. This allows the plasma streams to interact with the released contaminants more effectively to facilitate removal.

[0142] A further optional advantage of the Peltier element is, that a sacrificial plate can be mounted onto the cooled / heated surface facing the sample stage, which can easily be replaced when it is degraded by the cleaning plasma, and which provides, or comprises the collection surface.

[0143] In other words, the Peltier element or more general the metrology system, can include a removable sacrificial plate mounted onto the Peltier cooling trap, forming the collection surface to which the contaminants bind, and which is exposed to the cleaning plasma. This plate mounts onto the cooling face of the Peltier element while exposed to the internal vacuum environment.

[0144] The sacrificial plate can comprise high surface area materials, for example optimized for adsorption of common contaminant species encountered in the metrology vacuum chamber. Example materials for the plate include but are not limited to titanium, platinum, ceramics, and other alloys that have affinity for organic contaminant molecules under cooled conditions.

[0145] A key advantage of the detachable sacrificial plate functioning as the collection surface is an easier replacement after contaminant exposure from numerous cleaning phases. Rather than needing to replace the entire Peltier element, just the sacrificial plate can be switched, possibly to a new plate with same material specification or another material composition. The sacrificial plate can thus improve collection capacity, and further can be tailored with a roughened surface texturing to maximize surface area.

[0146] The described metrology systems and devices can be configured to perform any method, method step, or combination of methods of method steps as described in the present disclosure.

[0147] A corresponding method for contaminant removal in a metrology system is provided.

[0148] The metrology system comprises an enclosed sealed chamber, in other words a vacuum chamber, in which a movable sample stage is arranged. On the sample stage, on a sample stage surface configured for holding a sample, a sample to be inspected or processed can be arranged. Further, at least partly within the vacuum chamber, a Peltier element is arranged, such that a part or surface of the Peltier element that can be cooled or heated is arranged within the vacuum chamber.

[0149] The disclosed techniques enable a two-cycle iterative operation / cleaning sequence including an operational phase and a cleaning phase. In a step, during an operational phase of the metrology system, the Peltier element is operated in a cooling mode, wherein a collection surface of the Peltier element is arranged inside the vacuum chamber facing the sample stage and is cooled for binding contaminants present within the vacuum chamber onto the collection surface. During the operational phase, the sample stage is positioned in an operational position that allows a sample on the sample stage to be inspected or processed. During the operational phase, the collection surface of the Peltier element is arranged in proximity and facing the sample stage surface and / or the sample, in other words adjacent to the sample stage surface and / or sample, such that contaminants, that would otherwise bind to the sample surface can be collected and bound to the cooled collection surface of the Peltier element acting as a cooling trap for contaminants.

[0150] In various examples, the cooling trap takes advantage of temperature differences to trap or bind contaminant molecules from a gas or vacuum onto a cold surface. In this case, the collection surface of the Peltier element provides the cold trapping surface within the vacuum chamber. The Peltier element generally creates cooled and / or a heated elements separate from each other. When an electric current is applied, i.e. , when the Peltier element is powered by electric energy, one side gets cooler while the other side gets warmer. In the cooling mode, the Peltier element pumping action transfers heat from the collection surface to the other warmer side of the Peltier. The warm elements of the Peltier element may be located outside the vacuum chamber. This makes the collection surface colder than surrounding chamber walls and components inside the vacuum chamber, such that contaminants can be collected from the inside atmosphere by the collection surface. The contaminant molecules present in the vacuum chamber - especially hydrocarbons or other organic compounds given off from samples - will preferentially move toward and condense or freeze onto the cooled collection surface as they collide randomly due to kinetic energy. The contaminants thus get bound and trapped on the cooling Peltier surface rather than deposit elsewhere in the chamber. Stopping the cooling, or even reversing the electric power, may allow the surface to warm back up so the contaminants desorb or evaporate back into the chamber for evacuation.

[0151] In an optional step, at least partly after the operational phase and at least in preparation for a subsequent cleaning phase, in various examples, in a moving phase, the sample stage is moved away from the Peltier cooling element. In this optional step, the sample stage is moved from an operational position it was in during the operational phase to a designated cleaning position. It may also be possible that the Peltier element is moved to a cleaning position, additionally to the sample stage being moved. Such a moving phase may be considered optional, as it may at least partly be included or in parallel to the operational and / or cleaning phase. In a step, during a cleaning phase, contaminants are removed from the Peltier cooling trap, specifically the collection surface of the Peltier element, and the vacuum chamber. During the cleaning phase, a cleaning plasma stream is directed into the vacuum chamber from a cleaning plasma inlet. The cleaning plasma stream flows along a defined cleaning plasma path towards the collection surface of the Peltier element. Thereby, contaminants that were bound onto the collection surface are released pushed away by the cleaning plasma stream during the operational phase. The cleaning plasma stream together with contaminants is evacuated from the vacuum chamber through a cleaning plasma outlet, carrying the released contaminants. During this step, the sample stage remains positioned in the cleaning position, outside the cleaning plasma path.

[0152] Optionally, after the operational metrology phase, the sample stage holding analyzed samples can be moved from its original operational position to a designated cleaning position. This movement intentionally positions the sample stage away from the path of the incoming cleaning plasma stream directed at the Peltier cooling trap.

[0153] In various examples, while inspecting samples, the stage may be located in close vertical proximity facing the collection surface of the Peltier cooling trap to allow contaminants easy migration to the cold collection surface. In various examples, the sample stage surface and the collection surface may overlap in a horizontal direction, which may be in a direction parallel to the sample stage surface. The collection surface and the sample stage surface may face each other directly. The collection surface and the sample stage surface may be essentially parallel to each other. The vertical distance between the sample stage surface and the collection surface may be less than 10%, or 20% or 30% of the dimension of the sample stage and / or the dimension of the collection surface, in a direction parallel to the sample stage surface (e.g., in a horizontal direction). In some examples, the sample stage surface, on which a sample can be held, can have a horizontal overlap with the Peltier collection surface of more than 20%, or 40% or 60%, or 80%, of the dimension of the sample stage and / or the dimension of the collection surface. Prior to the plasma cleaning phase, a stage translation mechanism such as one or more actuators, e.g., a motorized rail, or a combination of linear and non-linear actuators, can shift the stage away from its original operational position, in a vertical direction and / or a horizontal direction. This provides separation from the cleaning plasma stream during plasma cleaning.

[0154] In various examples, during the operational phase, the sample stage surface, where the sample can be held, can be positioned preferably closer than 10 cm from of the Peltier element collection surface. In some examples, the collection surface could also be positioned closer than 5 cm, or more general closer than 20 cm, from the sample stage surface. This allows contaminants in the atmosphere around the inspected samples to diffuse over and adhere to the cooled Peltier surface which acts as a cryotrap.

[0155] To prepare for the cleaning phase, where a cleaning plasma stream is directed towards the collection surface, the sample stage then moves away from the collection surface and the cleaning plasma path, for example perpendicular out of the path of the incoming plasma stream.

[0156] The cleaning plasma inlet may be located at any suitable position in the vacuum chamber housing. In various examples, it may be attached horizontally. It may be located on a vertical vacuum chamber housing wall. In some examples, the incoming cleaning plasma stream may be directed essentially in a horizontal direction. In some examples, the cleaning plasma stream may be directed towards the Peltier collection surface.

[0157] The cleaning plasma outlet may be located at any at any suitable position in the vacuum chamber housing. In various examples, it may be located on a bottom vacuum chamber housing wall, such that the cleaning plasma stream path is directed towards the bottom surface of the vacuum chamber. However, it would also be possible to arrange it at different positions within the vacuum chamber, for example also in a horizontal position across the Peltier collection surface.

[0158] In various examples, the distance between the plasma inlet and the Peltier collection surface can be between 10 cm and 30 cm. In various examples the plasma outlet can be located vertically below the Peltier collection surface.

[0159] In various examples, the sample stage can move laterally, i.e., horizontally more than 5 cm, or more than 10 cm, or more than 15 cm or 30 cm, away from the centre of the cleaning plasma flow path. Optionally, the stage may be moved vertically in direction along the plasma stream to further protect the sample stage from high cleaning plasma impact. Also, a combination of vertical, and / or horizontal translational movement, and / or rotational movement would be possible, such that impact of the cleaning plasma onto the sample stage can be reduced.

[0160] In some examples, it would even be possible to move the Peltier cooling trap translationally towards the cleaning plasma inlet, i.e., higher plasma concentrations, or rotate the collection surface towards higher angle impact directions, in order to realize a better cleaning effect with a reduced plasma stream.

[0161] In various examples, during the operational phase the perpendicular distance from the collection surface to sample stage may be preferably closer than 10 cm, then the actuators relocate the stage horizontally more than 20 cm away in perpendicular direction and optionally more than 20 cm away in horizontal direction. This protects samples from plasma backscatter while opening full exposure for complete cleaning plasma diffusion to / from the inlet / outlet across the entire collection surface.

[0162] Additionally, the stage may be moved vertically and / or horizontally to an at least partly closed inner space within the vacuum chamber, which may be a sheltered cavity region of the vacuum chamber, during plasma cleaning. Optionally, the sample stage may be moved behind at least a wall separating the sample stage, with respect to a direct line, or line of view, from the cleaning plasma inlet. This may provide a sheltering from inlet of the incoming cleaning plasma stream.

[0163] In various examples, during the cleaning phase, the method can further comprise operating the Peltier element in a heating mode to heat, i.e. , to raise the temperature, of the collection surface and release contaminants bound thereon to facilitate removal by the cleaning plasma stream. The application of heat serves to provide thermal energy capable of breaking any residual chemical and physical bonds between said contaminants and the collection surface as bound during the operational phase. Facilitating release and evacuation of contaminants in this manner can minimize surface residues prior to subsequent operational phases and can sustain optimal operational conditions over extended operational-cleaning cycles.

[0164] The collection surface of the Peltier element can further comprise a replaceable sacrificial plate to accumulate contaminants during the operational phase, wherein said sacrificial plate can be removed and replaced after exposure to the directional cleaning plasma stream over a plurality of cleaning cycles. In other words, the sacrificial plate can be placed onto the cooled or heated surface of the Peltier element inside the vacuum chamber and can thus form a replaceable collection surface for contaminants.

[0165] The sacrificial plate thereby provides a renewable contamination accumulation layer to preserve optimal functioning of said Peltier element. When degradation due to extensive plasma exposure occurs on the plate after repeated cleaning phases, only the modular sacrificial plate requires replacement rather than the integrated Peltier element.

[0166] The collection surface of the sacrificial plate can have a roughness (Ra) between 1-5 micrometer, or more specifically 2-3 micrometer, to provide optimal contaminant adsorption. The roughened surface enhances contaminant adsorption during operational phases through greater surface area.

[0167] The sacrificial plate optionally can comprise or have a collection surface made out of materials like aluminum or titanium. Aluminum may provide good heat transfer owing to high thermal conductivity, while remaining cost-effective as a replaceable unit. Titanium offers good plasma resistance, sustaining more cleaning exposure over time. The collection surface may comprise material layers or coatings to further enhance specific properties. In various examples, aluminum core and titanium layer. The sacrificial plate can be improved by selecting a combination of materials with a roughness between 1-5 micrometer of suitable base metals, alloys, or surface coatings.

[0168] The cleaning plasma outlet can be located on an opposite side of the vacuum chamber with regard to the collection surface of the Peltier element and the cleaning plasma inlet. The cleaning plasma path is able to extend in essentially a straight path from the cleaning plasma inlet towards the collection surface and continue towards the cleaning plasma outlet.

[0169] Positioning the plasma outlet opposite the plasma inlet allows the introduced plasma stream to traverse horizontally directly towards and interact with the entire face of the collection surface. The contaminants released by the plasma can then be pushed or carried through the chamber towards the cleaning plasma outlet located on the bottom of the vacuum chamber.

[0170] The cleaning phase can be carried out without venting the vacuum chamber, i.e., essentially maintaining the vacuum or inside pressure of the vacuum chamber.

[0171] Thereby, faster cleaning processes can be realized by cleaning the plasma stream, and avoiding venting eliminates the risk of humidity, oxygen, and other contaminants getting into the chamber prior to reestablishing vacuum conditions. Performing the cleaning protocol at vacuum further allows the contaminant removal process faster since time-intensive pump down and purge steps are not required between operational and cleaning phases. Thereby, uptime and sample throughput can be enhanced.

[0172] In general, during an operational phase, the working distance, which is the distance between sample surface and process module (e.g., SEM pole piece) can be typically 5 mm. The maximum travel range of the stage in vertical direction can be 5 mm, or 10 mm, in some examples also 20 mm or 30 mm. During the operational phase, the sample stage can be positioned less than 15 cm, specifically less than 10 cm, or 5 cm, away from the collection surface of the Peltier element. This allows efficient collection of contaminants from the proximity of samples. The collection surface of the Peltier element may extend at least partially along the sample stage surface, where the sample is mounted, specifically along more than 50%, or 70% or 80% of the sample stage surface area.

[0173] Then, during the cleaning phase, the sample stage is moved preferably more than 15 cm away from the collection surface of the Peltier element and / or from the path of the cleaning plasma, particularly away from a cleaning plasma path between the cleaning plasma inlet and outlet. The sample stage may be moved, such that the collecting surface of the Peltier element is no longer extending along the sample stage surface, i.e., no longer overlapping in a horizontal direction. In some examples, the sample stage can be move in a horizontal direction over a distance greater than 10 cm, or 15 cm, or 20 cm, or 25 cm, or up to 30 cm away from the operational position. Further, with regard to the cleaning plasma stream path, if the cleaning plasma stream has a perpendicular cross-section area, which is oriented essentially perpendicular to the cleaning plasma path of the cleaning plasma stream through the vacuum chamber, then this cross-sectional area of the cleaning plasma stream may be defined as region, in which the cleaning plasma has more than 60%, or 70% or 80%, of plasma particle concentration compared to the particle concentration in the center of the plasma stream. The sample stage can be moved out of this high concentration area. This defined displacement protects the sample stage, which could otherwise be gradually degraded by repetitive cleaning plasma exposure. The movement may also fully expose the entire Peltier cooling trap to the cleaning plasma stream.

[0174] The collection surface of the Peltier element can extend substantially parallel, or in a small angular range of >0°, or >5°, and / or <10° or <20° relative to the horizontal direction and / or sample stage surface, and facing the sample stage surface holding a sample during the operational phase, such that during the operational phase molecular contaminants released from the sample on the sample stage, an / or are moving towards the sample, can easily be captured on the collection surface.

[0175] The sample can be a semiconductor wafer or substrate. The metrology system can be configured for at least one of: semiconductor wafer inspection, measurement, analysis, or processing.

[0176] The metrology system can comprise a scanning electron microscope (SEM) module configured to image a sample, for example a semiconductor wafer, within the vacuum chamber during the operational phase. The metrology system can further comprise at least one of a Focused Ion Beam (FIB) system and a Gas Injection System (GIS) for processing the sample. In this regard, the operational phase may also be regarded as acquisition phase and / or processing phase of the metrology system.

[0177] The method can further comprise monitoring the temperature of the collection surface of the Peltier element during the cleaning phase and adjusting heating to maintain a temperature above 100 degrees Celsius.

[0178] Maintaining the elevated temperature facilitates desorption of contaminants during plasma exposure and prevents re-adherence and accumulation between cleaning cycles. The higher heat better enables the plasma stream to dislodge and evacuate trapped particles for sustained optimal operation. The method can further include monitoring the temperature of the collection surface of the Peltier element during the operational phase and adjusting the cooling to maintain a temperature below 0 degrees Celsius.

[0179] Maintaining a sub-zero Celsius temperature on the collection surface allows more efficient trapping of vapor phase contaminants, increasing adsorption rate and capacity through cryogenic effects. Fine-tuning and sustaining the cooling facilitates accumulation of molecular contaminants during operational metrology work rather than allowing dispersal within the vacuum chamber volume.

[0180] In the following some examples are provided with regard to a Peltier Cooling Trap:

[0181] 1. A method for contaminant removal in a metrology system, the metrology system comprising a sample stage within a vacuum chamber and a Peltier element arranged at least partly within the vacuum chamber, comprising the following steps:

[0182] - during an operational phase of the metrology system: operating the Peltier element in a cooling mode, in which a collection surface of the Peltier element arranged inside the vacuum chamber and facing the sample stage is cooled for binding molecular contaminants present within the vacuum chamber onto the collection surface, wherein the sample stage is in an operational position allowing a sample on the sample stage to be inspected or processed;

[0183] - after the operational phase of the metrology system, and in preparation of a cleaning phase of the metrology system: moving the sample stage from the operational position to a cleaning position;

[0184] - during the cleaning phase of the metrology system: directing a cleaning plasma stream from a cleaning plasma inlet of the vacuum chamber along a cleaning plasma path towards the collection surface of the Peltier element to release contaminants from the collection surface, and evacuating the cleaning plasma with the released contaminants through a cleaning plasma outlet of the vacuum chamber, wherein the sample stage is positioned outside the cleaning plasma path of the cleaning plasma stream.

[0185] 2. The method of Example 1 , wherein during the cleaning phase, the method further comprises: operating the Peltier element in a heating mode to heat the collection surface and release contaminants bound thereon to facilitate removal by the cleaning plasma stream.

[0186] 3. The method of one of the preceding examples, further comprising: mounting a replaceable sacrificial plate on the Peltier element, which provides the collection surface to collect contaminants during the operational phase, and replacing the sacrificial plate after a predefined number of cleaning cycles.

[0187] 4. The method of example 3, wherein the sacrificial plate provides the collection surface with a surface roughness (Ra) between 1 micrometers and 5 micrometers.

[0188] 5. The method of example 3 or 4 wherein the sacrificial plate is provided with an outer layer of a first adsorbent material over an inner layer of a higher heat-conducting material.

[0189] 6. The method according to one of the preceding examples, wherein the cleaning phase is carried out without venting the vacuum chamber.

[0190] 7. The method according to one of the preceding examples, wherein during the operational phase, the sample stage surface overlaps the collection surface of the Peltier element in a horizontal direction, and during the cleaning phase, the sample stage is positioned with a horizontal distance greater than 15 cm between the sample stage surface and the collection surface of the Peltier element.

[0191] 8. The method according to one of the preceding examples, further comprising monitoring the temperature of the collection surface of the Peltier element during the operational phase and adjusting the cooling to maintain a temperature below 0 degrees Celsius.

[0192] 9. The method according to one of the preceding examples, further comprising monitoring the temperature of the collection surface of the Peltier element during the cleaning phase and adjusting heating to maintain a temperature above 100 degrees Celsius.

[0193] 10. A metrology system comprising:

[0194] - a vacuum chamber;

[0195] - a sample stage arranged within the vacuum chamber, the sample stage configured to hold a sample and position the sample inside the vacuum chamber in an operational position during an operational phase of the metrology system;

[0196] - a Peltier element arranged at least partly within the vacuum chamber, the Peltier element comprising a collection surface inside the vacuum chamber facing the sample stage and configured to be cooled during the operational phase for binding contaminants within the vacuum chamber onto the collection surface;

[0197] - a plasma inlet of the vacuum chamber and connected to a plasma source for providing a cleaning plasma stream into the vacuum chamber during a cleaning phase;

[0198] - a plasma outlet of the vacuum chamber for evacuating the cleaning plasma stream with released contaminants;

[0199] - a stage movement mechanism connected to the sample stage configured to move the sample stage from the operational position during the operational phase to a cleaning position during the cleaning phase, the cleaning position being outside a path of the cleaning plasma stream;

[0200] - a controller configured to: during the operational phase, operate the Peltier element in a cooling mode, in which the collection surface of the Peltier element is cooled for binding contaminants within the vacuum chamber onto the collection surface of the Peltier element, while the sample stage is in the operational position; after the operational phase, control the stage movement mechanism to move the sample stage from the operational position to the cleaning position; during the cleaning phase, operate the plasma source to direct a cleaning plasma stream from the plasma inlet along a cleaning plasma path towards the collection surface of the Peltier element to release contaminants, and evacuate the cleaning plasma stream together with released contaminants through the plasma outlet, while the sample stage is positioned in the cleaning position outside the path of the cleaning plasma stream.

[0201] 11. The system according to example 10, wherein the cleaning plasma outlet is located on an opposite side of the vacuum chamber with regard to the collection surface of the Peltier element and the cleaning plasma inlet, and wherein the cleaning plasma path extends essentially along a line from the cleaning plasma inlet towards the collection surface and further towards the cleaning plasma outlet.

[0202] 12. The system according to one of examples 10 to 11 , wherein the collection surface of the Peltier element extends substantially parallel and facing the sample stage surface holding a sample during the operational phase, such that during the operational phase molecular contaminants within the space between the sample on the sample stage and the Peltier element are captured by the extended parallel collection surface. 13. The system according to one of examples 10 to 12, wherein the sample is a semiconductor wafer or substrate, wherein the metrology system is configured for semiconductor wafer inspection, measurement, analysis, or processing.

[0203] 14. The system according to one of examples 10 to 13, wherein the metrology system comprises a scanning electron microscope (SEM) configured to image the semiconductor wafer within the vacuum chamber during the operational phase.

[0204] 15. The system according to one of examples 10 to 14, wherein the metrology system further comprises at least one of a Focused Ion Beam (FIB) system and a Gas Injection System (GIS) for processing the semiconductor wafer.

[0205] The techniques can comprise operating one or more Peltier elements, during an operational phase and cleaning phase, as cryo-traps binding contaminants using an electrical power supply.

[0206] A vacuum chamber can also be referred to as sealed or enclosed sample chamber, which has a lower inside pressure than the local environment. The vacuum pump may or may not be operated during the operational phase.

[0207] During the operational phase, a collection surface can be inside the vacuum chamber, in other words it can form part of the inside surface of the vacuum chamber. A corresponding warmed surface can be located outside the vacuum chamber, or thermally coupled the vacuum chamber wall or another heat dissipating system. During the cleaning phase, the inside surface may be heated, and the corresponding other surface may be cooled, vice versa.

[0208] The method can comprise directing the cleaning plasma stream onto the collection surface, or along the collection surface, in particular in an angle smaller than 10° or 20° with regard to the collection surface, in order to release and push contaminants from the collection surface towards a vacuum pump outlet for evacuation. With regard to the flow direction of the plasma, the collection surface may be arranged in the center of the cleaning plasma stream, where the concentration of the cleaning plasma is within 80%, or 60%, or 40% of its maximum concentration in a cross-sectional plane through the collection surface.

[0209] The method can comprise moving or positioning the sample stage outside of an area impacted by the cleaning plasma stream. In particular, outside a region within 15 cm, or 20 cm, from a connection line between the cleaning plasma inlet and outlet.

[0210] The method can comprise covering the Peltier collection surface with a replaceable collection surface or plate, which is cooled or heated by the Peltier element and acts to collect contaminants. In other words, the collection plate can further comprise or be covered by a replaceable sacrificial collection plate positioned to cover the cooling surface of the Peltier element. The collection plate can have a rough surface, or a concave surface around the sample stage, configured to improve adherence of molecular contaminants.

[0211] The method can comprise reversing a polarity of power to the Peltier element to release collected contaminants, wherein the reversing may be controlled by the controller according to a predefined temperature curve.

[0212] A SEM process module in the metrology system can be configured to image the sample at an accelerating voltage between 500 V and 30 kV. The SEM process module can comprise a low-vacuum SEM configured to image the sample at pressures between 10 Pa and 1000 Pa. Additionally, a FIB process module can be configured to mill or deposit material on the sample surface during the operational phase. Additionally, a GIS process module can be configured to provide a gas to the sample surface during the operational phase.

[0213] The method can comprise measuring the pressure within the vacuum chamber and initiating the cleaning phase in response to determining the pressure rises above a threshold pressure.

[0214] The method can comprise visually inspecting the collection surface and initiating replacement of the sacrificial plate in response to determining a predefined degree of degradation from plasma exposure.

[0215] The operational phase can comprise an image acquisition phase, and / or a sample processing phase, in some embodiments in parallel to each other.

[0216] In general, corresponding methods for operating the metrology systems and / or contamination handling modules or any one or any combination of described examples are understood to be disclosed, wherein the functional and / or structural elements, specifically one or more controllers are provided within or at least partly within a metrology system and / or vacuum chamber, to control the system and / or module to perform the described operational steps.

[0217] For the disclosed contamination handling methods for a metrology system, advantages may be realized, which correspond to the advantages described for the described metrology systems.

[0218] It is to be understood that the features and examples mentioned above and features and examples yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without departing from the scope of the present disclosure. In particular, features of the disclosed embodiments may be combined with each other in further embodiments. The above summary is therefore only intended to give a brief overview of some features of some embodiments and implementations and is not to be understood as a limitation. Other embodiments may include features other than those described above.

[0219] BRIEF DESCRIPTION OF THE DRAWINGS

[0220] These and other objects of the disclosure will be appreciated and understood by those skilled in the art from the detailed description of the preferred embodiments and the following drawings in which like reference numerals refer to like elements.

[0221] FIG. 1 schematically illustrates a metrology system including an SEM module and a FIB module operating on a sample in a vacuum chamber, in which the techniques according to the present disclosure can be applied.

[0222] FIGS. 2-6 schematically illustrate examples of a contamination handling module comprising a cooling trap for capturing contaminants in a vacuum chamber, according to various examples.

[0223] FIG. 2 schematically illustrates a metrology system in an operating phase, according to various examples.

[0224] FIG. 3 schematically illustrates the metrology system in a cleaning phase, according to various examples.

[0225] FIG. 4 schematically illustrates a further metrology system in an operating phase, wherein the cleaning plasma outlet is arranged at a bottom side of the vacuum chamber, according to various examples.

[0226] FIG. 5 schematically illustrates the metrology system of FIG. 4 in a cleaning phase, according to various examples.

[0227] FIG. 6 schematically illustrates steps of a method for contaminant removal in a metrology system, according to various examples.

[0228] FIG. 7 schematically illustrates a dynamic shutter blade included in a contamination handling module of a metrology system, according to various examples.

[0229] FIG. 8 schematically illustrates a static blade of a contaminant barrier included in a contamination handling module of a metrology system, according to various examples.

[0230] FIG. 9 schematically illustrates electrostatic shielding of a SEM head included in a contamination handling module of a metrology system, according to various examples. FIG. 10 schematically illustrates a protective gas environment of a contamination handling module in a vacuum chamber of a metrology system, according to various examples.

[0231] FIG. 11 schematically illustrates a directional protection gas flow of a contamination handling module in a metrology system, according to various examples.

[0232] DETAILED DESCRIPTION

[0233] In the following, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. It should be understood that the following description of embodiments is not to be taken in a limiting sense. The scope of the disclosure is not intended to be limited by the embodiments described hereinafter or by the drawings, which are taken to be illustrative examples of the general inventive concept. The features of the various embodiments may be combined with each other, unless specifically noted otherwise.

[0234] The drawings are to be regarded as being schematic representations and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to a person skilled in the art. Any connection or coupling between functional blocks, devices, components, or other physical or functional units shown in the drawings or described herein may also be implemented by an indirect connection or coupling. A coupling between components may also be established over a wireless connection. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof.

[0235] Some examples of the present disclosure generally provide for a plurality of modules or other electrical devices of a metrology system. All references to the modules and other electrical devices and the functionality provided by each are not intended to be limited to encompassing only what is illustrated and described herein. While particular labels may be assigned to the various modules or other electrical devices disclosed, such labels are not intended to limit the scope of operation for the modules and the other electrical devices. Such modules and other electrical devices may be combined with each other and / or separated in any manner based on the particular type of mechanical and / or electrical implementation that is desired. It is recognized that any process module or other electrical device disclosed herein may include any number of microcontrollers, a graphics processor unit (GPU), integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read only memory (ROM), electrically programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), or other suitable variants thereof), and software which co-act with one another to perform operation(s) disclosed herein. In addition, any one or more of the electrical devices may be configured to execute a program code that is embodied in a non-transitory computer readable medium programmed to perform any number of the functions as disclosed.

[0236] Hereinafter, techniques for contamination handling, or contaminant removal, in a metrology system, which may be used for imaging and processing microscopic samples using charged- particle scanning systems such as SEMs and FIBs, are disclosed. It is to be understood that the described techniques may be applied to any metrology system that employs an enclosed and / or sealed sample chamber, specifically a vacuum chamber, including an imaging process, such as particle beam imaging technique, and a material abrasive process, which generates contaminants in the vacuum chamber, which interfere with imaging processes, such as beam-induced material removal techniques or beam-induced deposition or etching techniques.

[0237] In the semiconductor industry, 300-mm platforms refer to a wafer fabrication facility designed to process silicon wafers with a diameter of 300 millimeters. These platforms are equipped with advanced process modules, including metrology systems, to manufacture cutting-edge integrated circuits. One such metrology system is a dual beam system, which combines a Focused Ion Beam (FIB) for milling and a Scanning Electron Microscope (SEM) for imaging within the same vacuum chamber. This optimized setup allows for precise material removal and high-resolution imaging, which is crucial for process control and failure analysis in semiconductor manufacturing.

[0238] However, this integration of FIB and SEM in a single chamber leads to the problem that material debris is generated during the FIB milling process, which can also be referred to as contaminants in the gas within the vacuum chamber, which can then get deposited on the SEM column. This contamination of the SEM column has detrimental effects on the imaging quality, which can significantly impact the accuracy and reliability of the metrology system.

[0239] One such effect is the occurrence of jumping images, where quick accumulation of charge on contaminants inside the SEM column causes subsequent images to capture a different field- of-view (FoV) than the previous ones. This results in a sudden shift of the imaged area, deviating from the expected FoV, especially over small milling depths. Another issue is the presence of drifting images, where a slow buildup of charge on contaminants inside the SEM column leads to a gradual drift of the imaged FoV, causing a deviation from the expected FoV over large milling depths. Consequently, the imaged FoV of the volume differs from the intended one, which can lead to inaccurate measurements and analyses.

[0240] Furthermore, charged particles can deflect the primary beams, causing imaging artifacts by varying the focus and beam support, a phenomenon known as astigmatism. Astigmatism occurs when the electron beam is not perfectly round, leading to distortions in the image. This can be particularly problematic in metrology systems, where high-resolution imaging is essential for accurate measurements and inspections.

[0241] To mitigate these issues, the SEM column requires frequent cleaning. However, this process poses several challenges in the context of vacuum chambers and contamination handling. Cleaning the SEM column is labor-intensive, expensive, and unreliable, as the precise removal of minute particles cannot be guaranteed. Moreover, it necessitates a broad supporting supply chain, including specialized tools and trained personnel. Additionally, exposing the vacuum chamber to the natural environment while addressing the contamination issue can lead to downstream problems, such as the introduction of new contaminants or difficulty in re-establishing the required vacuum level.

[0242] The present disclosure is based on the finding that the optimal approach to the debris deposition problem in dual beam systems is to prevent the contaminants from reaching the SEM column in the first place, rather than trying to remove them after. Therefore, the examples of the present disclosure represent various solutions to collect and present to protect the SEM column from contamination caused by FIB-generated debris or in from general contaminants that may be present (in the gas) within a vacuum chamber.

[0243] Various examples relate to protecting SEM Columns from Milling generated contaminants, in other words debris, in Dual Beam Systems. Various examples relate to metrology systems comprising at least one of or both of a SEM process module and a FIB process module.

[0244] A SEM process module may refer to a component of the metrology system that is configured to image a sample, such as a semiconductor wafer, within the vacuum chamber during an operational phase. The SEM column may refer to the vertical portion of the SEM that extends into the vacuum chamber and contains the electron beam optics. The SEM head and / or SEM end-cap may refer to the bottom part of the SEM column that is closest to the sample and most susceptible to contamination from particles generated during sample processing. A housing or shielding around the SEM head or end-cap may be used to protect it from contaminants.

[0245] A FIB process module, which may include a FIB column, may refer to a material abrasive process module in a metrology system configured to mill (i.e. remove material from) the sample surface during an operational phase of the metrology system. The FIB column generates a focused ion beam that impinges on the sample surface at an angle, allowing it to process the sample in coordination with the SEM imaging. Together, the SEM and FIB process modules enable the metrology system to both image and physically process the sample, such as a semiconductor wafer, within the vacuum chamber. Other process modules, such as a GIS process module may configured to provide a gas to the sample surface during the operational phase of the metrology system. This gas can be used for various purposes, such as an etching process or providing a source of material to be deposited onto the sample surface. The GIS may work in coordination with the FIB and SEM modules to enable localized processing of the sample within the vacuum chamber.

[0246] FIG. 1 schematically illustrates a dual beam metrology system 1000 including an SEM process module 1040 and a FIB process module 1050 operating on a sample in a vacuum chamber, in which the techniques according to the present disclosure can be applied.

[0247] As can be seen in FIG. 1 , the metrology system 1000 comprises a wafer inspection system configured for a slice- and imaging method with a dual beam configuration. Processing a sample in the metrology system is typically performed in a sealed environment, such as a process chamber, specifically in a vacuum chamber 10, which his schematically depicted around the metrology system 1000.

[0248] The metrology system 1000, specifically in or at least partly in the vacuum chamber 10 may comprise one or more contamination handling modules and any corresponding apparatuses, systems or devices or elements for contamination handling as described in the present disclosure, wherein the metrology system 1000 can further be configured to perform any method or combinations of methods according to the present disclosure. In various examples, the metrology system may comprise a controller configured for controlling the various elements for executing one or more contamination handling methods.

[0249] Process modules comprising for example SEM-column 1040, FIB-column 1050 and particle detector 1017 may extend from an exterior of the vacuum chamber through the vacuum chamber housing 10 to the interior of the vacuum chamber housing 10 according to the techniques of the present disclosure.

[0250] For a wafer 1008, several measurement sites, comprising measurement sites 1006.1 and 1006.2, are defined in a location map or inspection list generated from an inspection tool or from design information. The wafer 1008 is placed on a sample stage 1015. The sample stage 1015 is mounted on a stage movement mechanism 1155 with actuators and position control 1021 . Actuators and means for precision control 1021 for a stage movement mechanism 1155 such as laser interferometers are known in the art. A control unit 1016 receives information about the actual position of the stage movement mechanism 1155 and is configured to control the stage movement mechanism 1155 and to adjust a measurement site 1006.1 of the wafer 1008 at the intersection point 1043 of the dual-beam device 1001. The dual beam device 1001 is comprising a FIB column 1050 with a FIB optical axis 1048 and a charged particle beam (CPB) imaging system 1040 (e.g., SEM or HIM; cf. FIG. 3: charged-particle scanning microscope 160) with optical axis 1042. At the intersection point 1043 of both optical axes of FIB and CPB imaging system, the wafer surface 1055 is arranged at a slant angle GF to the FIB axis 1048. FIB and CPB co-observe the sample. FIB axis 1048 and CPB imaging system axis 1042 include an angle GFE. In the coordinate system of FIG. 1 , the normal to the wafer surface is given by the z-axis. The focused ion beam (FIB) 1051 is generated by the FIB-column 1050 and is impinging under angle GF on the surface 1055 of the wafer 1008. Slanted cross-section surfaces may be milled into the wafer by ion beam milling at the inspection site 1006.1 under approximately the slant angle GF at a predetermined y-position, which is controlled by the stage movement mechanism 1155 and position control 1021. In the illustrated example, the slant angle GF is approximately 30°. The actual slant angle of the slanted cross-section surface can deviate from the slant angle GF by up to 1° to 4° due to the beam divergency of the focused ion beam, for example a Gallium-lon beam, or due to variable material properties with respect to milling along the cross-section surface. With the charged particle beam imaging system 1040, images of the milled surfaces are acquired. In the example of FIG. 1, the charged particle beam imaging system 1040 is arranged with its charged particle beam 1044 perpendicular to the wafer surface 1055 and parallel to the z-axis. In other configurations, the optical axis 1042 of the charged particle beam imaging system 1040 is arranged at an angle to the z-axis.

[0251] During imaging, a beam of charged particles 1044 is scanned by a scanning unit of the charged particle beam imaging system 1040 along a scan path over a cross-section surface of the wafer at measurement site 1006.1 , and secondary particles as well as backscattered particles are generated. Particle detector 1017.1 and optional internal particle detector 1017.2 collect at least some of the secondary particles and / or backscattered particles and communicate the particle count with a control unit 1019. Other detectors for other kinds of interaction products such as x-rays or photons may be present as well. Control unit 1019 is in control of the charged particle beam imaging column 1040 and of the FIB column 1050 and connected to a control unit 1016 to control the position of the wafer mounted on the sample stage 1015 via the stage movement mechanism 1155. Operation control unit 1002 communicates with control unit 1019, which triggers placement and alignment for example of measurement site 1006.1 of the wafer 1008 at the intersection point 1043 via stage movement mechanism movement and triggers repeatedly operations of FIB milling, image acquisition and stage movements. Control unit 1019 and operation control unit 1002 comprises a memory for storing instructions in form of software code and at least one processer to execute during operation the instructions. A memory is further provided to store digital image data. Operation control unit 1002 may further comprise a user interface or an interface to other communication interfaces to receive instructions, prior information and to transfer inspection results.

[0252] In such an exemplary metrology system 1000 as described in FIG. 1, contamination handling according to the techniques of the present disclosure can be deployed.

[0253] FIGS. 2-6 schematically illustrate examples of a contamination handling module comprising a cooling trap for capturing contaminants in a vacuum chamber, according to various examples.

[0254] The contamination handling module of the metrology system may comprise a cooling trap configured to capture contaminants within the vacuum chamber. The cooling trap can be embodied as a Peltier cooling trap, which utilizes the Peltier effect to achieve efficient cooling and contaminant capture.

[0255] The Peltier cooling trap can comprise a Peltier cooling element configured to maintain a surface of the contaminant trap at a temperature lower than the condensation temperature of the contaminants present in the vacuum chamber.

[0256] In terms of placement, the contaminant trap may be positioned between the sample processing module (e.g., FIB module) and the SEM module, for example as a static contamination barrier, or in another location in the vacuum chamber. This arrangement allows the trap to capture contaminants generated by the sample processing module before they can reach and potentially damage or interfere with the SEM module.

[0257] To further enhance the functionality of the cooling trap, the metrology system may include a cleaning module configured to remove accumulated contaminants from the surface of the cooling trap during a cleaning phase. The cleaning module may comprise a plasma generator that directs a plasma stream towards the surface of the cooling trap. The plasma stream interacts with the accumulated contaminants, effectively removing them from the trap surface. A vacuum pump is then used to evacuate the cleaning plasma along with the removed contaminants from the vacuum chamber, maintaining the cleanliness and performance of the cooling trap over extended periods of operation.

[0258] By incorporating a Peltier cooling trap with an associated cleaning module, the contamination handling module of the metrology system provides an efficient and reliable means of capturing and removing contaminants from the vacuum chamber, ensuring a clean and stable environment for the SEM imaging process.

[0259] The cleaning module, embodied as a plasma cleaning system, is operated according to a sequence of method steps that alternate between imaging / processing phases and cleaning phases. This sequential approach ensures that the contaminants generated during the imaging and processing of the sample are effectively removed, maintaining the cleanliness of the vacuum chamber and the performance of the SEM module.

[0260] During the imaging / processing phase, the metrology system operates as in an operation mode, with the SEM module imaging the sample and the sample processing module (e.g., FIB module) performing any necessary modifications or analyses. Throughout this phase, the Peltier cooling trap remains active, continuously capturing contaminants generated by the sample processing module.

[0261] Once the imaging / processing phase is complete, the system transitions to the cleaning phase. During this phase, the plasma generator of the cleaning module is activated, directing a plasma stream towards the surface of the Peltier cooling trap. The plasma stream interacts with the accumulated contaminants on the trap surface, breaking them down and releasing them from the surface.

[0262] To facilitate the cleaning process, the Peltier cooling element can be temporarily deactivated or even reversed in polarity, allowing the trap surface to warm up. This temperature change enhances the effectiveness of the plasma stream in removing the contaminants by promoting their desorption from the surface.

[0263] As the plasma stream removes the contaminants from the trap surface, the vacuum pump continuously evacuates the cleaning plasma and the released contaminants from the vacuum chamber. This ongoing evacuation process ensures that the contaminants are effectively removed from the system, preventing them from re-depositing on the trap surface or interfering with the SEM module.

[0264] Once the cleaning phase is complete, the plasma generator is deactivated, and the Peltier cooling element is returned to its normal operating state, cooling the trap surface to its optimal temperature for contaminant capture. The system is then ready to begin another imaging / processing phase, with the cleaned Peltier cooling trap effectively capturing contaminants once again.

[0265] By cyclically alternating between the imaging / processing phases and the cleaning phases, the metrology system maintains a clean and contaminant-free environment within the vacuum chamber. This sequential approach, facilitated by the plasma cleaning module and the Peltier cooling trap, ensures that the SEM module can operate at peak performance, providing high-quality imaging results without interference from contaminants generated during sample processing.

[0266] FIG. 2 schematically illustrates a metrology system 1000 in an operating phase, according to various examples. As can be seen in FIG. 2, a metrology system 1000 includes a vacuum chamber 10, wherein the vacuum chamber housing includes a cleaning plasma inlet 11 for injecting a cleaning plasma stream from a plasma source of a plasma cleaner, further in the vacuum chamber housing is a cable feedthrough 4 for electrically powering a Peltier element 1 arranged within the vacuum chamber 10. The Peltier element 1 has a collection surface 2 implemented by a thermoconductive and replaceable sacrificial material plate 2 facing the sample stage 3 while the sample stage 3 is arranged adjacent to the collection surface 2 in vertical direction at a distance of less than 15 cm and facing the collection surface 2 which extends substantially parallel to the sample stage surface. The corresponding other surface, that is heated respectively cooled of the Peltier element 1 is thermally connected to the vacuum chamber housing by a vacuum suitable thermoconductive paste. On the other side of the vacuum chamber housing there is a cleaning plasma outlet 12 which is arranged on the opposite side to the inlet 11 , defining a cleaning plasma path in between, for extracting the plasma and released contaminants. In FIG. 2, the sample stage is in an operational position 5 near the Peltier Device 1 and in between the cleaning plasma inlet and outlet. The sample stage is configured to hold a semiconductor wafer sample and position the sample in an operational position 5 inside the vacuum chamber during an operational phase of the metrology system, which can comprise an SEM and FIB system such as depicted in FIG. 1. The Peltier element is operated in a cooling mode to maintain the collection surface at a low temperature, for example below 0 degrees Celsius, in which the collection surface of the Peltier element is cooled for binding contaminants within the vacuum chamber onto the collection surface of the Peltier element. While the sample stage is in the operational position 5 adjacent and facing the Peltier collection surface, it extends at least partly along the sample stage and sample surface.

[0267] FIG. 3 schematically illustrates the metrology system 1000 of FIG. 2 in a cleaning phase, according to various examples.

[0268] As can be seen in FIG. 3, the metrology system 1000 comprises the same features as in FIG. 2, however the sample stage 3 is moved by a stage movement mechanism (not depicted) to the cleaning position 6, i.e. , a stage parking position for the cleaning process, at a distance greater than, for example 30 cm, from the Peltier element 1 and collection surface 2, and also outside the cleaning plasma path between the plasma inlet 11 and outlet 12. A plasma stream 7 is directed from the plasma inlet 11 towards the collection surface 2 along the defined cleaning plasma path. The Peltier device 1 is operated in heating mode to heat the collection surface to a high temperature, for example above 100 degrees Celsius, and release the bound contaminants. The released contaminants are pushed by the cleaning plasma in the plasma stream 7 flowing directly along collection surface 2, and the contaminants in the gas phase are evacuated through the plasma outlet 12 on the opposite side of the vacuum chamber. The cleaning phase is carried out without venting the vacuum chamber, i.e., while essentially maintaining the vacuum or inside pressure.

[0269] FIG. 4 schematically illustrates a further metrology system in an operating phase, wherein the cleaning plasma outlet is arranged at a bottom side of the vacuum chamber, according to various examples.

[0270] As can be seen in FIG. 4, the cleaning plasma outlet 12 connected to the one or more vacuum pumps for evacuating the cleaning plasma and the contaminants in gas phase, is arranged at a bottom side of the vacuum chamber. In this example, the plasma outlet is arranged under the operational position of the sample stage and / or under the collection surface of the Peltier element.

[0271] FIG. 5 schematically illustrates the metrology system of FIG. 4 in a cleaning phase, according to various examples.

[0272] As can be seen in FIG. 5, the cleaning plasma path is directed from the plasma inlet in a horizontal direction towards the collection surface 2 of the Peltier device 1 , wherein the sample stage 3 is located in the cleaning position, i.e., outside of the cleaning plasma path. The contaminants in the gas phase in the cleaning plasma is evacuated through the bottom plasma outlet.

[0273] In general, by the arrangement of directing the cleaning plasma past the collection surface 2 of the Peltier element 1 towards the plasma outlet 12, the released contaminants can be effectively evacuated. As can be seen in FIGS. 3 and 5, the sample stage 3 is moved to a parking position 6 during the cleaning phase. This parking position 6 is located outside of the main cleaning plasma path between the plasma inlet 11 and plasma outlet 12. By locating the sample stage 3 outside of this primary cleaning plasma stream 7, the concentration and velocity of the plasma at the parking position 6 is maintained under certain thresholds that could otherwise lead to undesired effects on the sample stage.

[0274] In various examples, parking position 6 may be a region where the cleaning plasma has a concentration less than 50% or the concentration at the collection surface of the Peltier element, or less than 1012ions / cm3, and / or less than 50% of the plasma velocity at the collection surface of the Peltier element, or lower than 10 m / s. High energy plasma exposure could damage components of the sample stage. By situating the sample stage parking position 6 away from the main cleaning plasma path and orientation, undesired effects of the cleaning plasma on the sample stage can be avoided while still effectively cleaning the Peltier cooling trap.

[0275] Various embodiments may utilize different orientation arrangements between plasma inlet 11 , collection surface 2, sample stage parking position 6, and plasma outlet 12 to effectively clean the Peltier element 1 while protecting the sample stage 3. Position 6 is merely exemplary and parking locations having various plasma concentrations and velocities can be selected according to cleaning and contamination constraints of a given metrology system.

[0276] In some embodiments, the sample stage 3 may be further protected at the parking position 6 by using plasma shields or plasma baffles. A plasma shield can be positioned between the main cleaning plasma stream 7 and the sample stage parking position 6. The plasma shield creates a shadowed region that prevents direct exposure of the sample stage 3 to the cleaning plasma.

[0277] The plasma shield can take various forms, ranging from a simple rigid plate obstruction in between position 6 and the plasma inlet to a localized plasma containment system. By utilizing shields or baffles, cleaning plasma cannot reach the sample stage 3 in a direct path, i.e. in a direct line. This minimizes or eliminates any potential undesired contamination, material release, or degradation of sensitive sample stage components during the cleaning phase while the main optics path is exposed to concentrated direct plasma.

[0278] Additionally, plasma suppressors based on magnetic, electrostatic, or fluid flow control methods could be implemented around position 6. By counteracting or diverting the propagation of the cleaning plasma locally, its effective concentration and velocity around the shielding zone can be reduced compared to the main chamber. Combinations of physical obstruction shields and active plasma suppression systems can maximize protection of the sample stage in the parking position 6 during cleaning exposure of the Peltier element.

[0279] FIG. 6 schematically illustrates steps of a method for contaminant removal in a metrology system, according to various examples.

[0280] The method starts in step S10.

[0281] A metrology system comprises a sample stage inside a vacuum chamber and a Peltier element arranged at least partly within the vacuum chamber.

[0282] In step S20, during an operational phase, the Peltier element collection surface inside the chamber and facing the sample stage is cooled to cryogenically bind contaminants present within the vacuum chamber environment onto the collection surface. While the Peltier cooling trap is operational to bind contaminants, the sample stage is in an operational position allowing a sample to be inspected or processed.

[0283] In step S30, which is an optional step, after completing the operational metrology phase, the sample stage transport mechanism moves the sample stage from the operational position to defined cleaning position outside and protected from the subsequent plasma cleaning exposure area. In step S40, a cleaning plasma stream is directed into the vacuum chamber from a plasma inlet, flowing along a cleaning plasma path towards and along the Peltier element collection surface in order to release accumulated contaminants. The cleaning plasma and released contaminants are evacuated via a plasma outlet on the opposite side of the vacuum chamber. The sample stage remains positioned in the protected cleaning position outside the flow path during this plasma cleaning exposure.

[0284] The method ends in step S50.

[0285] Upon concluding the cleaning phase, the sample stage mechanism returns the sample stage back to the operational position, enabling for the next metrology operational phase with the cleaned Peltier cooling trap.

[0286] In various examples spatial separation may be used for protecting the SEM column, in particular spatial separation between the milled point and the SEM head.

[0287] As both FIB and SEM focus on the same location on the sample, they both have unobscured lines of sight to the debris generation position. This generates opportunities for debris created while milling to be launched into the direction of the SEM. Unobscured lines of sight during milling can be avoided by e.g., introducing a dynamic physical shutter, as shown in FIGS. 7 and 8.

[0288] The techniques illustrated in FIGS. 7-11 can further be included in any metrology system, such as the metrology system 1000 of FIG. 1.

[0289] As appreciated for all Figs. 1-11, the metrology system 1000 comprises at least a vacuum chamber, a sample stage within the vacuum chamber configured to hold a sample 16 to be processed, a Scanning Electron Microscope (SEM) module 13 within the vacuum chamber configured to image the sample 16, and a focused ion beam (FIB) module 14 within the vacuum chamber configured to physically process the sample 16, thereby generating contaminants within the vacuum chamber.

[0290] FIG. 7 schematically illustrates a dynamic shutter blade 15 included in a contamination handling module of a metrology system 1000, according to various examples.

[0291] The metrology system 1000 comprises a vacuum chamber (not depicted), a sample stage (not shown) within the vacuum chamber configured to hold a sample 16 to be processed, a Scanning Electron Microscope (SEM) module 13 within the vacuum chamber configured to image the sample 16, and a focused ion beam (FIB) module 14 within the vacuum chamber configured to process the sample 16, thereby generating contaminants within the vacuum chamber. The contamination handling module comprises the dynamic shutter 15, which is synchronized with the operation of the SEM module 13 and the FIB module 14. The dynamic shutter 15 is configured as a rotatable blade arranged in front of the SEM head, with an opening that can be positioned in a first position and a second position by rotating the blade along a rotation axis that is essentially oriented along the axis of the SEM module 13.

[0292] By rotating the blade, the opening can be arranged to block and open the direct path between the SEM module 13 and the sample 16. When the sample 16 is materially processed or altered by the FIB module 14, the opening is arranged such that the direct path from the sample 16 to the SEM module 13 is blocked, preventing contaminants generated by the FIB module 14 from reaching the SEM module 13.

[0293] As can be seen in FIG. 7, the shutter's opening is rotated in sync with the FIB-SEM operation. During the FIB operation, the opening blocks a direct optical path between the SEM module 13 and the sample 16. During the SEM operation, the shutter rotates to enable imaging of the sample 16. The first position corresponds to an imaging position during operation of the SEM module 13, while the second position corresponds to a processing position during operation of the FIB module 14.

[0294] The dynamic shutter 15 comprises an opening, and in the imaging position, the opening is aligned with the direct path between the SEM module 13 and the sample 16. In the processing position, the opening is misaligned with the direct path between the SEM module 13 and the sample 16, thereby blocking the direct path and preventing contaminants from reaching the SEM module 13.

[0295] The dynamic shutter 15 is rotatable between the first position and the second position, with the rotation synchronized with the operating phases of the SEM module 13 and the FIB module 14. Alternatively, the dynamic shutter 15 may oscillate between the first position and the second position, with the oscillation synchronized with the operation of the SEM module 13 and the FIB module 14.

[0296] Other variants of a dynamic blade can be realized, such as blades that move in one direction (to-and-from) to cut off direct contamination paths between the SEM module 13 and the milled location on the sample 16. The example setup involves a synchronized rotatable shutter that cuts away paths between the sample 16 and the SEM module 13 during the FIB milling stage, and reintroduces an optical path during the SEM imaging stage of operation.

[0297] FIG. 8 schematically illustrates a static blade of a contaminant barrier 17 included in a contamination handling module of a metrology system 1000, according to various examples.

[0298] As described for FIG. 7, the static blade 17 can be employed in metrology system 1000 of Fig 1. The contamination handling module comprises a static contaminant barrier 17 configured as a static blade arranged in front of the SEM head. The static blade has an opening that is arranged in front of the SEM module 13 to allow a direct path between the SEM module 13 and the sample 16. The static contaminant barrier 17 is positioned between the SEM module 13 and the FIB module 14, dividing the vacuum chamber into a first compartment containing the SEM module 13 and a second compartment containing the FIB module 14.

[0299] When the sample 16 is materially processed or altered by the FIB module 14, the static contaminant barrier 17 restricts the volume of the vacuum chamber affected by the generated contaminants, thereby hindering the contaminants from reaching and contaminating the SEM head. The static contaminant barrier 17 comprises an aperture aligned with the direct path between the SEM module 13 and the processed location on the sample 16. The aperture is configured to allow the passage of an electron beam from the SEM module 13 to the sample 16 and to allow the passage of secondary electrons or backscattered electrons from the sample 16 to the SEM module 13.

[0300] As can be seen in FIG. 8, the static blade is designed to avoid debris on the SEM module 13 while not restricting the direct optical path between the SEM module 13 and the milled location on the sample 16. While debris targeted at the SEM column directly from the milled location cannot be avoided, the diffusing debris from all other directions is physically shielded off by the static blade.

[0301] Variations of the blade afford handling various sorts of debris. For example, the static contaminant barrier 17 may comprise a cooled surface configured to bind contaminants to the barrier, preventing debris from sticking to it. Additionally, the static contaminant barrier 17 may comprise a plurality of fins (not shown) configured to deflect a contaminant gas flow away from the SEM module 13, further preventing the contaminants from reaching the SEM module 13.

[0302] Direct paths between the FIB module 14 and the SEM module 13 may be unrestricted. However, the volume of the chamber affected by diffusing debris is restricted via the static blade of the contaminant barrier 17, thereby hindering the contaminants from reaching the SEM module 13.

[0303] In addition to the static blade configuration, the static contaminant barrier 17 can take other forms, such as a partial enclosure or encapsulation around the SEM module or the sample processing area. This enclosure can be connected to the vacuum chamber housing walls to create a more isolated environment for the SEM module.

[0304] For example, the static contaminant barrier could be designed as a housing that surrounds the SEM module, with an opening for the electron beam to pass through and reach the sample. This enclosure can be attached to the vacuum chamber walls, effectively creating a separate compartment within the vacuum chamber that minimizes the interaction between the SEM module and the contaminants generated by the sample processing module.

[0305] Another variation could involve an encapsulation of the sample processing area, with or without the FIB module, with the static contaminant barrier connected to the vacuum chamber walls. This configuration would confine the contaminants generated during sample processing to a specific region of the vacuum chamber, reducing their ability to spread and reach the SEM module.

[0306] These alternative forms of the static contaminant barrier, involving partial enclosures or encapsulations connected to the vacuum chamber walls, provide an additional level of protection for the SEM module by physically segregating it from the contaminant-generating processes. By creating separate compartments or confined spaces within the vacuum chamber, the interaction between the contaminants and the SEM module can be further minimized, enhancing the overall effectiveness of the contamination handling module in maintaining a clean imaging environment.

[0307] FIG. 9 schematically illustrates electrostatic shielding of a SEM head included in a contamination handling module of a metrology system 1000, according to various examples.

[0308] As can be seen in FIG. 9 an electrostatic shielding configuration included in a contamination handling module is depicted, which can be deployed in a metrology system 1000, such as for example the one described in Fig 1.

[0309] The contamination handling module comprises a first electrostatic collection electrode 18 and a second electrostatic collection electrode 19 with opposite polarity, arranged around the SEM module 13, particularly around the SEM head of the SEM column and around the SEM end-cap. The field generated by the opposite polarities of the electrostatic electrodes allow charged contamination particles of both polarities to be deflected or drawn away from the SEM end-cap along the SEM head / column housing towards a respective outlet 20 where they can be evacuated from the vacuum chamber by a vacuum pump.

[0310] The first and second electrostatic collection electrodes (18, 19) can be configured as generating electric, or electrostatic, fields for deflecting and guiding the charged contaminants of both polarities away from the sensitive components of the SEM module.

[0311] To exert forces on neutrally charged debris particles, the contamination handling module may further comprise an ionizer (not depicted) arranged near the end-cap of the SEM module 13. The ionizer is configured to charge the neutral contaminant particles, making them susceptible to the influence of the electrostatic collection fields. For example, the ionizer can be integrated below or attached to the end-cap of the SEM module. The ionizer can take various forms, such as a laser source configured to emit laser radiation towards the neutral contaminant particles, ionizing them through photoionization. Alternatively, the ionizer may comprise an electron source configured to emit electrons towards the neutral contaminant particles, or a plasma generator configured to generate a plasma to charge the neutral contaminant particles through collisions.

[0312] During the FIB milling process, atoms and ions are produced as contaminants. The ions can be deflected or drawn by the static electrostatic fields (18, 19) away from the SEM module 13. The electric collection fields, being close to the major flight path of the ions, essentially create a trap that guides the ions towards a vent or outlet for evacuation from the vacuum chamber. The directing electric fields can be switched off during the milling process to avoid interfering with the FIB operation. For example, they can be also switched off during an imaging process. In various examples, they can only be switched on in a cleaning or sweeping phase of the metrology system, in which additionally a protection or cleaning gas flow is used to sweep contaminants away, such that during non-imaging phases they can be operated with higher power.

[0313] Therefore, the electrostatic shielding of the SEM column, as illustrated in FIG. 9, utilizes positive and negative electric electrodes (18, 19) to direct ion debris generated by the FIB milling process away from the sensitive areas of the SEM module 13. The electric electrodes (18, 19) are positioned and configured to maximize the deflection and removal of charged contaminants. Neutral contaminants can be addressed by an ionizer (not shown) integrated near the SEM end-cap, which charges the particles and makes them responsive to the electrostatic fields. During the SEM imaging phase, the electric fields can be turned off to leave the imaging quality unaffected.

[0314] In other words, the ions can be deflected by static fields away from the SEM. A collection field close to the major flight path of ions, essentially creating a trap and eventually leading to a vent or evacuation path, which leads for examples into the SEM column. In some examples, primary electron beams, with the right energy and defocus to maximize the ionization directly below the column, can be used to ionize neutral particles in a sample processing or cleaning phase.

[0315] FIG. 10 schematically illustrates a protective gas environment of a contamination handling module in a vacuum chamber of a metrology system 1000, according to various examples.

[0316] As in previous figures, the metrology system 1000 comprises a vacuum chamber (not shown), a sample stage (not shown) within the vacuum chamber configured to hold a sample 16 to be processed, a Scanning Electron Microscope (SEM) module 13 within the vacuum chamber configured to image the sample 16, and a focused ion beam (FIB) module 14 within the vacuum chamber configured to process the sample 16, thereby generating contaminants within the vacuum chamber.

[0317] The contamination handling module comprises a protection gas environment 21 within the vacuum chamber. The protection gas environment 21 includes at least parts of the FIB module 14, at least part of the SEM module 13, and at least part of the sample 16. The protection gas environment 21 is supplied with a protection gas flow via a protection gas inlet

[0318] 22 and is configured to sweep contaminants towards a gas outlet 23, where they can be evacuated from the protection gas environment and potentially also from the vacuum chamber.

[0319] The protection gas environment 21 further comprises an enclosure within the vacuum chamber that encloses at least part of the SEM module 13 and the sample stage. The housing has apertures for the SEM module 13, the FIB module 14, the protection gas inlet 22, and the gas outlet 23. This enclosure helps to confine the protection gas flow and create a more localized clean environment around the SEM module and the sample stage, where the concentration of protective gas in the inner atmosphere of the protective gas environment is more homogenous and higher than outside. The protective gas environment may comprise the complete vacuum chamber or just a part of it.

[0320] The protection gas inlet 22 is positioned closer to the SEM module 13, while the gas outlet

[0321] 23 is positioned closer to the FIB module 14. This arrangement creates a protection gas flow direction from the SEM module 13 towards the FIB module 14, effectively sweeping contaminants away from the SEM module and towards the outlet for evacuation. The gas flow direction can be substantially parallel to a top surface of the sample stage, aligning with the (tilt) direction of the SEM electron beam, or perpendicular to it.

[0322] The protection gas environment 21 is designed to maintain a positive pressure of the protection gas relative to the surrounding vacuum chamber. This positive pressure prevents contaminants from entering the protection gas environment, as the gas flow continuously exits through the apertures, creating a barrier against contaminant ingress.

[0323] During or after the FIB milling stage, neutral gases such as nitrogen are pumped into the protection gas environment 21 via the gas inlet 22. These gases sweep away the resulting atoms and ions generated by the milling process, carrying them out of the protective gas environment through the gas outlet 23. The housing of the protection gas environment is constructed to allow the passage of the SEM beam and the FIB beam while minimizing the escape of contaminants.

[0324] To maintain the desired pressure within the protection gas environment 21 , appropriate design considerations are taken, such as narrowing all openings of the protective gas environment. This helps to minimize the gas flow required to maintain the positive pressure and reduces the impact on the vacuum level within the main chamber.

[0325] Thereby, the protective gas environment 21, as illustrated in FIG. 10, creates a localized clean environment within the vacuum chamber of the metrology system 1000. By supplying a protection gas flow from the SEM module 13 towards the FIB module 14 and sweeping contaminants towards the gas outlet 23, the SEM module is effectively shielded from contamination generated during the FIB milling process. The enclosure design, with positioned gas inlet and outlet, and the maintenance of a positive pressure relative to the vacuum chamber, further enhances the effectiveness of the contamination handling module in preventing contaminants from reaching the SEM module.

[0326] FIG. 11 schematically illustrates a directional protection gas flow of a contamination handling module in a metrology system 1000, according to various examples.

[0327] As in previous figures, the metrology system 1000 comprises a vacuum chamber (not shown), a sample stage (not shown) within the vacuum chamber configured to hold a sample 16 to be processed, a Scanning Electron Microscope (SEM) module 13 within the vacuum chamber configured to image the sample 16, and a focused ion beam (FIB) module 14 within the vacuum chamber configured to process the sample 16, thereby generating contaminants within the vacuum chamber.

[0328] The contamination handling module comprises a directional protection gas system configured to direct a protection gas flow, in other words purge gas, from the SEM module 13 towards the sample 16. The directional protection gas system includes a protection gas inlet integrated into the SEM module 13, which is configured to direct the protection gas flow towards the sample stage 16.

[0329] The protection gas inlet is directly connected to the SEM's direct path and is designed in a manner that does not affect the SEM lens or electron source setup. The purge gas is pumped towards the sample 16 at a higher pressure than the sample environment, creating a localized high-pressure region that hinders debris from entering the SEM module 13. It may also be turned off during imaging phases of the metrology system.

[0330] The SEM module 13 comprises an end-cap facing the sample stage, and the end-cap may have one or more internal or external gas channels 24 configured to direct the protection gas flow towards the protection gas inlet integrated into the end-cap. The end-cap may comprise a central aperture configured to allow passage of an electron beam from the SEM module 13 to the sample 16, with the protection gas channels 24 arranged around the central aperture.

[0331] The directional protection gas system may also include a gas outlet (not depicted) for example positioned below the sample stage, which is configured to remove the protection gas from the vacuum chamber. The protection gas flow, directed from the SEM module 13 towards the sample 16, serves to sweep away contaminants generated during the FIB milling process, preventing them from reaching and accumulating on the SEM module components.

[0332] The protection gas used in the directional protection gas system or protection gas environment is a neutral gas selected from the group consisting of nitrogen, argon, xenon, and other inert gases. The choice of the specific gas is based on the expected masses of the debris particles, aiming to maximize momentum transfer and optimize the removal of contaminants from the vicinity of the SEM module 13.

[0333] The protective gas is injected at a higher pressure than the surrounding sample environment, creating a gas flow and a protective barrier that carries contaminants away from the sensitive components of the SEM module 13.

[0334] Thereby, the directional protection gas system, as illustrated in FIG. 11 , provides a directed and targeted gas flow in the metrology system 1000. By directing a protection gas flow from the SEM module 13 towards the sample 16 and out through the gas outlet, the system creates a localized high-pressure region that shields the SEM module from contaminants generated during sample processing. The integration of the protection gas inlet into the SEM module end-cap, along with the arrangement of gas channels and the central aperture, ensures that the gas flow is efficiently directed without interfering with the electron beam. The choice of neutral gases, based on the expected contaminant particle masses, further enhances the effectiveness of the protection gas system in removing debris and maintaining a clean environment for the SEM imaging process.

[0335] From the above said, some general conclusions can be drawn:

[0336] The contamination handling module may be referred to as component of the metrology system designed to restrict or hinder free movement of contaminants in the vacuum chamber, especially movement and interference with an imaging module such as the SEM module. This can be achieved through the implementation of either active modules or mechanisms, passive modules or mechanisms, or a combination of both, comprised in the contamination handling module. The contamination handling module may prevent, in other words hinder, contaminants in the vacuum chamber from reaching the SEM module through the use of active mechanisms, which actively control or move contaminants, and / or passive mechanisms, which rely on physical barriers or geometric design to block contaminants. This ensures a clean and stable environment for the SEM imaging process.

[0337] For example, active modules may refer to components or systems that actively control, redirect, or remove contaminants from the path of the SEM module. These modules typically may comprise an external power source, control system, or triggering mechanism to function effectively. Examples of active modules may include one or more of the following examples, electrostatic fields, in other words, electric fields, wherein charged particles, such as ions or electrons, can be actively deflected or drawn, within the low-pressure gas atmosphere in the vacuum chamber, in a direction away from the SEM module using electrostatic fields. By applying a voltage to a set of electrodes or plates, an electric field is generated that alters the trajectory of the charged contaminants, directing them away from sensitive components. Plasma cleaning, wherein a plasma source can be used to actively remove contaminants from the vacuum chamber. The plasma generates reactive species that interact with the contaminants, breaking them down into volatile compounds that can be easily pumped out of the system. Protection gas flow, wherein an active gas flow system can be used to create a positive pressure environment around the SEM module, preventing contaminants from reaching the sensitive components. The gas flow is typically controlled by valves, mass flow controllers, or pressure regulators to maintain a stable and effective protective environment. Cooling traps, wherein cold surfaces can be used to condense and trap contaminants, effectively removing them from the vacuum environment. By placing a cold trap in the path of the contaminants, such as a liquid nitrogen-cooled surface, the contaminants are encouraged to stick to the trap instead of reaching the SEM module.

[0338] Passive mechanisms, on the other hand, rely on physical barriers, geometric configurations, or material properties to prevent contaminants from reaching the SEM module. These mechanisms do not require an external power source or active control system, making them simpler and more reliable in some cases. Examples of passive mechanisms may include one or more of the following. Physical barriers, which may comprise fixed shields, baffles, or apertures can be used to block the direct path of contaminants towards the SEM module. These barriers can be designed to allow the passage of the electron beam while preventing the majority of contaminants from reaching the sensitive components. Geometric design of the vacuum chamber can minimize the direct path of contaminants towards the SEM module. By carefully positioning the sample processing module, SEM module, and other components, the system can be designed to naturally direct contaminants away from sensitive areas.

[0339] The various solutions that can be comprised in the contamination handling module, including active modules and passive mechanisms, can be combined in the contamination handling module to work together and enhance the overall effectiveness of the system in preventing contaminants from reaching the SEM module.

[0340] For example, a synergistic effect may arise from an interaction between electrostatic fields and physical barriers. Electrostatic fields are effective at deflecting charged contaminants, such as ions or charged particles, but may have limited influence on neutral contaminants. Physical barriers, on the other hand, can block both charged and neutral contaminants, but may not provide complete coverage or may interfere with the electron beam path. By combining electrostatic fields with placed physical barriers, the system can achieve better control of contaminant paths. The electrostatic fields can deflect charged contaminants away from the barriers, reducing the accumulation of contaminants on their surfaces and prolonging their effectiveness. For example, such electrostatic, or electric, collection fields can be realized with one or more elements of a barrier as electrode for hindering contaminants in the remaining contaminant path towards the SEM. The combination of protection gas and cleaning gas flows with passive physical barriers can also lead to synergistic effects. Plasma cleaning is effective at removing contaminants from surfaces but may have limited reach. Physical barriers and geometric design can help to confine the contaminants to specific areas of the vacuum chamber, and to define protection and / or cleaning plasma flow paths.

[0341] The following aspects of maintenance may be combined with any described system or method.

[0342] A regular maintenance schedule may be used to periodically replace components such as cooling traps, electric fields, and blades that are directly affected by the accumulation of debris during the system's operation. This scheduled maintenance ensures that these critical components are replaced before they become ineffective or damaged due to the buildup of debris. The system includes appropriate mechanisms for reporting the status of these components and triggering maintenance actions when necessary.

[0343] The system may perform predictive maintenance techniques to estimate when the next cleaning or replacement of components should occur. This may be achieved by monitoring and tracking various measurements related to the system's operation, such as the volume of milled sample processed, the amount of debris collected, and the total exposure time of pumps and electric fields. By analyzing this data, the system can predict when maintenance will be required and schedule it accordingly. The system also includes reporting mechanisms to alert operators of the predicted maintenance needs and request appropriate remedial actions.

[0344] The metrology system may be configured to monitor and / or track sensor measurements related to the system's operational state and / or performed processes, including the measurements of the volume of milled sample processed, the amount of debris collected, and the total exposure time of pumps and electric fields. Further, the metrology system may be configured to process the monitored data to estimate the next required cleaning or replacement of components, and / or to perform reporting mechanisms to alert operators of the predicted maintenance needs and request maintenance actions. Summarizing, metrology system and methods for handling contamination within a vacuum chamber are provided. The metrology system comprises a Scanning Electron Microscope (SEM) module and a sample processing module, such as a Focused Ion Beam (FIB) module, operating within the vacuum chamber. To prevent contaminants generated by the sample processing module from reaching and interfering with the SEM module, the system includes a contamination handling module.

[0345] The contamination handling module can comprise any one or any combination or components, including a dynamic shutter synchronized with the operation of the SEM and sample processing modules, a static contaminant barrier with an aperture for the SEM beam, a contaminant cooling trap with a Peltier cooling element, electrostatic collection fields for deflecting charged contaminants, and a protection gas environment with a directional gas flow.

[0346] These components work together to effectively manage contaminants, maintaining a clean environment for the SEM module and ensuring high-quality imaging results. The dynamic shutter blocks the direct path between the SEM and the sample during processing, while the static barrier restricts the volume affected by contaminants. The cooling trap captures contaminants, and the electrostatic fields deflect charged particles away from sensitive components. The protection gas flow sweeps contaminants away from the SEM module and towards an outlet for evacuation.

[0347] By implementing these systems and methods, the metrology system can effectively mitigate the impact of contaminants, extending the operational lifetime of the SEM module and reducing the need for frequent maintenance. This leads to improved efficiency, reliability, and productivity in semiconductor manufacturing and other applications involving vacuum chamber-based metrology systems.

[0348] Although the disclosure has been shown and described with respect to certain preferred embodiments, equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present disclosure includes all such equivalents and modifications and is limited only by the scope of the appended claims.

Claims

C L A I M S1. A metrology system, comprising: a vacuum chamber; a sample stage within the vacuum chamber configured to hold a sample to be processed; a Scanning Electron Microscope (SEM) module within the vacuum chamber configured to image the sample; a sample processing module within the vacuum chamber configured to process the sample, thereby generating contaminants within the vacuum chamber; and a contamination handling module within the vacuum chamber, the contamination handling module configured to prevent the contaminants from reaching the SEM module.

2. The metrology system of claim 1 , wherein the contamination handling module comprises a dynamic shutter configured to be synchronized with an operation of the SEM module and the sample processing module, the dynamic shutter configured to block a direct path between the SEM module and the sample during operation of the sample processing module and to enable imaging of the sample during operation of the SEM module.

3. The metrology system of claim 2, wherein the dynamic shutter comprises a rotatable blade or an oscillating blade.

4. The metrology system of claim 2 or 3, wherein the dynamic shutter is movable between a first position and a second position, the first position corresponding to an imaging position during operation of the SEM module, and the second position corresponding to a processing position during operation of the sample processing module.

5. The metrology system of claim 4, wherein the dynamic shutter comprises an opening, and wherein the opening is aligned with the direct path between the SEM module and the sample in the imaging position.

6. The metrology system of claim 5, wherein the opening is misaligned with the direct path between the SEM module and the sample in the processing position, thereby blocking the direct path and preventing contaminants from reaching the SEM module.

7. The metrology system of one of claims 2 to 6, wherein the dynamic shutter is rotatable between the first position and the second position, wherein a rotation is synchronized with operating phases of the SEM module and the sample processing module.

8. The metrology system of one of claims 2 to 6, wherein the dynamic shutter is configured to oscillate between the first position and the second position, wherein the oscillation is synchronized with the operation of the SEM module and the sample processing module.

9. The metrology system of any one of the preceding claims, wherein the contamination handling module comprises a static contaminant barrier configured to restrict a volume of the vacuum chamber affected by the contaminants while maintaining a direct path between the SEM module and a processed location on the sample.

10. The metrology system of claim 9, wherein the static contaminant barrier is positioned between the SEM module and the sample processing module, the static contaminant barrier being configured to divide the vacuum chamber into a first compartment containing the SEM module and a second compartment containing the sample processing module.

11. The metrology system of claim 9 or 10, wherein the static contaminant barrier comprises an aperture aligned with the direct path between the SEM module and the processed location on the sample, the aperture being configured to allow passage of an electron beam from the SEM module to the sample and to allow the passage of secondary electrons or backscattered electrons from the sample to the SEM module.

12. The metrology system of one of claims 9 to 11 , wherein the static contaminant barrier comprises a cooled surface configured to bind contaminants to the barrier.

13. The metrology system of one of claims 9 to 12, wherein the static contaminant barrier comprises a plurality of fins configured to deflect a contaminant gas flow away from the SEM module, thereby preventing the contaminants from reaching the SEM module.

14. The metrology system of any one of the preceding claims, wherein the contamination handling module comprises a contaminant cooling trap configured to capture the contaminants.

15. The metrology system of claim 14, wherein the contaminant trap comprises a Peltier cooling element configured to maintain a surface of the contaminant trap at a temperature lower than a condensation temperature of the contaminants.

16. The metrology system of claim 15, wherein the Peltier cooling element is operatively connected to a heat sink located outside the vacuum chamber, the heat sink configured to dissipate heat generated by the Peltier cooling element.

17. The metrology system of any one of claims 14 to 16, wherein the contaminant trap is positioned between the sample processing module and the SEM module configured to capture contaminants generated by the sample processing module before they reach the SEM module.

18. The metrology system of any one of claims 14 to 17, further comprising a cleaning module configured to remove accumulated contaminants from the surface of the cooling contaminant trap during a cleaning phase.

19. The metrology system of claim 18, wherein the cleaning module comprises a plasma generator configured to direct a plasma stream towards the surface of the cooling contaminant trap, the plasma stream configured to dissolve the accumulated contaminants, and a vacuum pump configured to evacuate the plasma stream with the contaminants from the vacuum chamber.

20. The metrology system of any one of the preceding claims, wherein the contamination handling module comprises a first electrostatic collection field configured to deflect charged contaminant particles away from the SEM module.

21. The metrology system of claim 20, wherein the contamination handling module comprises a second electrostatic collection field with a polarity opposite to that of the first electrostatic collection field.

22. The metrology system of claim 20 or 21 , wherein the first and / or the second electrostatic collection fields are electric gradient fields with the highest field strength arranged closer the SEM module.

23. The metrology system of any one of claims 20 to 22, further comprising an ionizer arranged at an end-cap of the SEM module configured to charge neutral contaminant particles.

24. The metrology system of claim 23, wherein the ionizer comprises a laser source configured to emit laser radiation towards the neutral contaminant particles, thereby ionizing the neutral contaminant particles through photoionization.

25. The metrology system of claim 23, wherein the ionizer comprises an electron source configured to emit electrons towards the neutral contaminant particles.

26. The metrology system of claim 23, wherein the ionizer comprises a plasma generator configured to generate a plasma to charge the neutral contaminant particles through collisions.

27. The metrology system of any one of the preceding claims, wherein the contamination handling module comprises a protection gas environment within the vacuum chamber, the protection gas environment comprising a protection gas inlet configured to supply a protection gas flow to sweep the contaminants and a gas outlet configured to evacuate the contaminants carrying protection gas.

28. The metrology system of claim 27, wherein the protection gas environment further comprises an enclosure within the vacuum chamber enclosing at least part of the SEM module and the sample stage, the enclosure having apertures for the SEM module, the sample processing module, the protection gas inlet, and the gas outlet.

29. The metrology system of claim 27 or 28, wherein the protection gas inlet is positioned closer to the SEM module, and the gas outlet is positioned closer the sample processing module, thereby creating a protection gas flow direction from the SEM module towards the sample processing module to sweep the contaminants.

30. The metrology system of any one of claim 27 to 29, wherein the gas flow direction is substantially parallel to a top surface of the sample stage.

31. The metrology system of claim 27, wherein the protection gas environment includes a head of the SEM module having an opening for an electron beam and the protection gas flow configured to maintain a positive pressure of the protection gas within the protection gasenvironment relative to the vacuum chamber, thereby preventing the contaminants from entering the protection gas environment.

32. The metrology system of any one of the preceding claims, wherein the contamination handling module comprises a directional protection gas system configured to direct a protection gas flow from a head of the SEM module towards the sample stage.

33. The metrology system of claim 32, wherein the directional protection gas system comprises a protection gas inlet integrated in the SEM module configured to direct the protection gas flow towards the sample stage.

34. The metrology system of claim 32 or 33, wherein the directional protection gas system further comprises a gas outlet positioned below the sample stage configured to remove the protection gas from the vacuum chamber.

35. The metrology system of any one of claims 32 to 34, wherein the SEM module comprises an end-cap facing the sample stage, the end-cap having a plurality of internal gas channels configured to direct the protection gas flow towards the protection gas inlet integrated in the end-cap.

36. The metrology system of claim 35, wherein the end-cap further comprises a central aperture configured to allow passage of an electron beam from the SEM module to the sample, the protection gas channels being arranged around the central aperture.

37. The metrology system of any one of claims 27 to 36, wherein the protection gas is an inert gas selected from the group consisting of noble gases and nitrogen.

38. The metrology system of any one of the preceding claims, wherein the sample processing module is configured to mill the sample or to etch the sample or to deposit material onto the sample.

39. The metrology system of any one of the preceding claims, wherein the sample processing module is one of a focused ion beam (FIB) module, or a gas injection system (GIS), or a laser processing module.

40. The metrology system of claim 19, further comprising:- a stage movement mechanism configured to move the sample stage from an operating position during an operating phase to a cleaning position during the cleaning phase, wherein, in the cleaning position, the sample stage is positioned outside of a path of the plasma stream directed towards the surface of the cooling contaminant trap.

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