Charged particle inspection apparatus

Abstract

To provide a system and apparatus for charged particle inspection.SOLUTION: The load lock system (300) includes a chamber (302) enclosing a support structure (308) configured to support a wafer (310), a gas vent (312) disposed in a ceiling (304) of the chamber (302) and configured to exhaust gas into the chamber (302) at a flow rate of at least 20 normal liters per minute, and a plate (314) secured to the ceiling (304) between the gas vent (312) and the wafer (310).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Patent Application No. 63 / 068,824, filed August 21, 2020, and incorporated herein by reference in its entirety.

[0002] SUMMARY OF THE INVENTION

[0002] Embodiments provided herein disclose a charged particle inspection apparatus, and more particularly, a charged particle inspection apparatus that includes an improved load lock unit. [Background technology]

[0003]

[0003] When manufacturing semiconductor integrated circuit (IC) chips, pattern defects or unwanted particles (residues) inevitably occur on wafers or masks during the manufacturing process, which significantly reduces yield. For example, unwanted particles can be problematic for patterns with smaller critical feature dimensions that are adopted to meet the increasingly higher performance requirements of IC chips.

[0004]

[0004] Pattern inspection tools using one or more charged particle beams are used to detect defects or unwanted particles. These tools typically use scanning electron microscopes (SEMs). In an SEM, a primary electron beam having a relatively high energy is decelerated to land on the sample with a relatively low landing energy and focused to form a probe spot thereon. This focused probe spot of primary electrons causes secondary electrons to be generated from the surface. By scanning the probe spot across the sample surface and collecting the secondary electrons, the pattern inspection tool can obtain an image of the sample surface.

[0005]

[0005] During operation of the inspection tool, the wafer is typically held by a wafer stage. The inspection tool may include a wafer positioning device for positioning the wafer stage and the wafer relative to the charged particle beam. This may be used to position a target area on the wafer, i.e., the area to be inspected, within the operating range of the electron beam. Summary of the Invention

[0006]

[0006] Embodiments of the present disclosure provide systems and apparatus for charged particle inspection. In some embodiments, a load lock system may include a chamber enclosing a support structure configured to support a wafer. The load lock system may also include a gas vent disposed in a ceiling of the chamber and configured to exhaust gas into the chamber at a flow rate of at least 20 normal liters per minute. The load lock system may further include a plate secured to the ceiling between the gas vent and the wafer.

[0007] In some embodiments, the charged particle inspection apparatus may include a load lock system. The load lock system may include a chamber enclosing a support structure configured to support a wafer. The load lock system may also include a gas vent disposed in a ceiling of the chamber and configured to exhaust gas into the chamber at a flow rate of at least 20 normal liters per minute. The load lock system may further include a plate secured to the ceiling between the gas vent and the wafer.

[0008] In some embodiments, an apparatus for reducing wafer contamination in a load lock system may include a wafer holder configured to support a wafer. The apparatus may also include a chamber. The chamber may include a surface. The chamber may also include a gas vent disposed on the surface and configured to exhaust gas into the chamber during pressurization of the chamber, the gas vent having a direction of gas flow perpendicular to the wafer and the surface. The apparatus may further include a baffle disposed between the wafer and the surface, the baffle being substantially parallel to the wafer and configured to deflect the direction of gas flow away from the wafer. [Brief explanation of the drawings]

[0009] [Figure 1A] FIG. 1 is a schematic diagram illustrating an exemplary charged particle beam inspection system according to an embodiment of the present disclosure. [Figure 1B]

[0010] 1B is a schematic diagram illustrating an exemplary wafer loading sequence in the charged particle beam inspection system of FIG. 1A in accordance with an embodiment of the present disclosure. [Figure 2]

[0011] 1B is a schematic diagram illustrating an exemplary electron beam tool according to an embodiment of the present disclosure that may be part of the charged particle beam inspection system of FIG. 1A. [Figure 3]

[0012] FIG. 1 illustrates an exemplary load lock system according to an embodiment of the present disclosure. [Figure 4]

[0013] FIG. 4 is a diagram of an expanded view of a portion of the load lock system of FIG. 3 in accordance with an embodiment of the present disclosure. [Figure 5]

[0014] 4 is an exemplary graphical representation of the relationship between gas velocity reduction rate, plate size, and gap size in the load lock system of FIG. 3 in accordance with an embodiment of the present disclosure. [Figure 6]

[0015] 6 is an exemplary graphical representation of the relationship between volumetric increase rate and the size of the gap of FIG. 5, according to an embodiment of the present disclosure. [Figure 7A]

[0016] 1 illustrates a cross-sectional view showing gas flow velocities for a pressurization process in a load lock system without a particle shield according to an embodiment of the present disclosure. [Figure 7B]

[0017] 4 shows a cross-sectional view illustrating gas flow velocities for a pressurization process in the load lock system of FIG. 3 according to an embodiment of the present disclosure. [Figure 8A]

[0018] 10A-10C illustrate perspective views illustrating shear rates on the top surface of a wafer during a pressurization process of a load lock system without a particle shield according to an embodiment of the present disclosure. [Figure 8B]

[0019] 4 shows a perspective view illustrating shear rates on the top surface of the wafer during a pressurization process of the load lock system of FIG. 3 according to an embodiment of the present disclosure. [Figure 9A]

[0020] FIG. 4 is a diagram of an exemplary particle trap of the load lock system of FIG. 3 in accordance with an embodiment of the present disclosure. [Figure 9B]

[0021] 9B shows a perspective view illustrating a region having a high particle deposition rate in the gap of the load lock system of FIG. 9A according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010]

[0022] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, in which the same numbers in different drawings represent the same or similar elements unless otherwise specified. The implementations described in the following description of exemplary embodiments do not represent all implementations according to the present disclosure. Instead, these implementations are merely examples of apparatus and methods according to aspects related to the subject matter recited in the appended claims. Without limiting the scope of the present disclosure, some embodiments may be described in connection with providing detection systems and methods in systems utilizing electron beams ("e-beams"). However, the present disclosure is not so limited. Other types of charged particle beams (e.g., including protons, ions, muons, or any other particles carrying an electric charge) may be similarly applied. Furthermore, the systems and methods for detection may be used in other imaging systems, such as optical imaging, photon detection, x-ray detection, ion detection, or any system for generating images of surface or sub-surface structures using radiation techniques.

[0011]

[0023] Electronic devices consist of circuits formed on a piece of semiconductor material called a substrate. Semiconductor materials can include, for example, silicon, gallium arsenide, indium phosphide, silicon germanium, or any material with electrical properties intermediate between those of a conductor and an insulator. Many circuits can be formed together on the same piece of silicon and are called integrated circuits, or ICs. The size of these circuits is shrinking dramatically to allow more circuits to fit on a substrate. For example, an IC chip in a smartphone can be about the size of a thumbnail yet contain over 2 billion transistors, each of which can be less than 1 / 1000 the size of a human hair.

[0012]

[0024] The fabrication of these ICs, which have extremely small structures or components, is a complex, time-consuming, and expensive process that often involves hundreds of individual steps. An error in even one step can introduce defects into the finished IC, rendering it unusable. Therefore, one goal of the manufacturing process is to avoid such defects and maximize the number of working ICs produced by the process, i.e., to increase the overall process yield.

[0013]

[0025] One element of improving yield is monitoring the chip manufacturing process to ensure that it produces a sufficient number of working integrated circuits. One way to monitor the process is to inspect the chip circuit structures at various stages in their formation. Inspection can be done using a scanning charged particle microscope ("SCPM"). For example, an SCPM can be a scanning electron microscope (SEM). An SCPM is used to image these extremely small structures, actually taking a "picture" of the structures on the wafer. The image can be used to determine whether the structures were properly formed in the proper locations. If the structures are defective, the process can be adjusted so that the defect is less likely to recur.

[0014]

[0026] In IC chip manufacturing facilities, high process yields are desirable, but maintaining high wafer throughput, defined as the number of wafers processed per hour, is also essential. High process yields and high wafer throughput can be affected by the presence of defects, especially if there is operator intervention to closely examine the defects. Therefore, high-throughput detection and identification of micro- and nano-sized defects by inspection tools (e.g., SCPM) is essential to maintaining high yields and low costs.

[0015]

[0027] The SCPM may inspect wafers in the main chamber. To ensure high wafer throughput and smooth wafer transfer operation, the pressure in the load lock chamber is typically regulated by depressurizing ("pump down") or pressurizing ("vent up") the pressure. "Depressurizing" herein may refer to a process or procedure for lowering the gas pressure in an enclosed space (e.g., a chamber), such as by pumping gas out of the enclosed space. "Pressurizing," also referred to as "repressurizing," as used herein, may refer to a process or procedure for increasing the gas pressure in an enclosed space (e.g., a chamber), such as by pumping gas into the enclosed space. Prior to inspection, a wafer may be loaded (e.g., by a robot arm) from an atmospheric clean room environment into the load lock chamber of the SCPM. The load lock chamber may be connected to a pump for depressurization. When the gas pressure in the load lock chamber is lower than a first threshold pressure (e.g., much lower than atmospheric pressure), the wafer may be moved (e.g., by a robot arm) into the main chamber. The main chamber may be connected to another pump for further depressurization to a lower pressure. When the gas pressure in the main chamber exceeds a second threshold pressure (e.g., 10 -6 When the pressure is below 1000 psi (0.25 psi), wafer inspection can begin. Once inspection is complete, the wafer can be moved from the main chamber to a load lock chamber. The load lock chamber can be vented (e.g., by filling the load lock chamber with gas through a gas vent) to a target pressure (e.g., atmospheric pressure) before the wafer is unloaded into the atmospheric clean room environment. For better depressurization and pressurization, the load lock chamber can use a small volume design that can vent and fill with smaller amounts of gas.

[0016]

[0028] One of the challenges of small-volume designs is that gas flows are stronger in smaller spaces. Strong gas flows can lead to significant particle contamination on the wafer surface during the pressurization process because particles on the chamber surface or gas inlet are lifted by the airflow and transported to the wafer surface, where they appear as contaminants on the wafer and potentially affect the functionality of the semiconductor devices on the wafer. For example, the gas flow can contain undesirable particles (e.g., dust) that can be deposited on the wafer surface and the inner surfaces of the load-lock chamber. Particle contamination can be exacerbated when the gas flow is perpendicular to the wafer surface and particles in the gas flow can directly impinge on the wafer surface. Some existing designs of load-lock chambers use particle shields to divert the gas flow to avoid direct impingement of the gas flow on the wafer surface and reduce particle contamination. However, strong gas flows can create flow disturbances (e.g., circulation) within the load-lock chamber that can induce undesirable particle migration. For example, the flow disturbances may carry foreign particles into the load lock chamber, which may eventually be deposited on the wafer surface and the interior surfaces of the load lock chamber. In another example, the flow disturbances may blow away existing particles in the load lock chamber, causing them to deposit on the wafer surface.

[0017]

[0029] Existing designs of load lock chambers may use large particle shields with complex geometries, which can pose challenges for small-volume designs. Existing designs may not be optimized for flow disturbances within the flow paths and load lock chambers, which can limit the reduction of flow-induced particle contamination. Furthermore, some existing designs may limit the flow rate of pressurization to minimize flow disturbances in order to reduce the risk of flow-induced particle contamination, but this can impair system throughput due to such slow pressurization.

[0018]

[0030] Embodiments of the present disclosure may provide improved designs for load lock chambers. Provided embodiments may include small-volume (e.g., less than 5 liters) chamber designs with compact vertical layouts. To accommodate the compact vertical layout, the small-volume designs may include gas vents in the ceiling that can exhaust gas into the load lock chamber at high flow rates (e.g., greater than 20 normal liters per minute). The ceiling-mounted gas vents allow gas flow to enter the load lock chamber in a direction perpendicular to the wafer. To reduce flow-induced particle contamination, provided embodiments may include a plate secured to the ceiling of the load lock chamber, where the plate may be positioned between the gas vent and the wafer. The space between the ceiling and the plate and the space between the plate and the wafer may be optimized to reduce flow disturbances without compromising the small-volume design. With a small-volume design and high flow rates, pressurization operations may be completed in a shorter time (e.g., reduced from 30 seconds to 15 seconds) to improve throughput, enabling effective overpressurization of the load lock. Optimized plates can minimize flow-induced particle contamination.

[0019]

[0031] The relative dimensions of components in the drawings may be exaggerated for clarity. In the following description of the drawings, the same or similar reference numbers refer to the same or similar components or entities, and only the differences with respect to individual embodiments are described.

[0020]

[0032] As used herein, unless specifically stated otherwise, the term "or" includes all possible combinations unless impracticable. For example, if a component is stated to include A or B, the component may include A or B, or A and B, unless specifically stated otherwise or impracticable. As another example, if a component is stated to include A, B, or C, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A, B, and C, unless specifically stated otherwise or impracticable.

[0021]

[0033] FIG. 1A illustrates an exemplary charged particle beam inspection system 100 according to an embodiment of the present disclosure. The system 100 may be used for imaging. As shown in FIG. 1A, the system 100 includes a main chamber 101, a load lock chamber 102, a beam tool 104, and a front-end equipment module (EFEM) 106. The beam tool 104 is disposed within the main chamber 101 and may be a single-beam system or a multi-beam system. The EFEM 106 includes loading ports 106a and 106b. The EFEM 106 may include one or more additional loading ports. The loading ports 106a and 106b may accept a front-opening integrated wafer pod (FOUP) containing wafers (e.g., semiconductor wafers or wafers made of one or more other materials) or samples to be inspected (the terms wafer and sample may be used interchangeably). A "lot" is a plurality of wafers that may be loaded for processing as a batch. One or more robotic arms (not shown in FIG. 1A) of the EFEM 106 may transfer wafers to the load lock chamber 102 .

[0022]

[0034] A controller 109 is electronically connected to the beam tool 104. The controller 109 may be a computer configured to perform various controls of the system 100. While the controller 109 is shown in Figure 1A as being external to the structure including the main chamber 101, the load lock chamber 102, and the EFEM 106, it should be understood that the controller 109 may be part of the structure.

[0023]

[0035] In some embodiments, the controller 109 may include one or more processors (not shown). A processor may be a general-purpose or special-purpose electronic device capable of manipulating or processing information. For example, a processor may include a central processing unit (or "CPU"), a graphics processing unit (or "GPU"), an optical processor, a programmable logic controller, a microcontroller, a microprocessor, a digital signal processor, an intellectual property (IP) core, a programmable logic array (PLA), a programmable array logic (PAL), a generic array logic (GAL), a complex programmable logic device (CPLD), a field programmable gate array (FPGA), a system-on-chip (SoC), an application-specific integrated circuit (ASIC), and any number or combination of any type of circuit capable of processing data. A processor may also be a virtual processor, including one or more processors distributed across multiple machines or devices coupled via a network.

[0024]

[0036] In some embodiments, the controller 109 may further include one or more memories (not shown). Memory may be a general-purpose or special-purpose electronic device capable of storing code and data accessible by a processor (e.g., via a bus). For example, memory may include any number or combination of random access memory (RAM), read-only memory (ROM), optical disks, magnetic disks, hard drives, solid-state drives, flash drives, security digital (SD) cards, memory sticks, CompactFlash (CF) cards, or any type of storage device. Code may include an operating system (OS) and one or more application programs (or "apps") for specific tasks. Memory may also be virtual memory, including one or more memories distributed across multiple machines or devices coupled via a network.

[0025]

[0037] 1B is a schematic diagram illustrating an exemplary wafer loading sequence in the system 100 of FIG. 1A in accordance with an embodiment of the present disclosure. In some embodiments, the charged particle beam inspection system 100 may include a robot arm 108 located within the EFEM 106 and a robot arm 110 located within the main chamber 101. The load lock chamber 102 may be attached to the EFEM 106 via a gate valve 105 and may be attached to the main chamber 101 using a gate valve 107. In some embodiments, the EFEM 106 may also include a pre-aligner 112 configured to precisely position the wafer before transferring the wafer to the load lock chamber 102.

[0026]

[0038] In some embodiments, loading ports 106a and 106b can accept a FOUP. A robot arm 108 within EFEM 106 can transfer the wafer from either loading port 106a or 106b to a pre-aligner 112 for positioning assistance. The pre-aligner 112 can use mechanical or optical alignment methods to position the wafer. After pre-alignment, robot arm 108 can transfer the wafer to load lock chamber 102 via gate valve 105.

[0027]

[0039] The load lock chamber 102 may include a sample holder (e.g., a support structure, not shown) capable of holding one or more wafers. After the wafer is transferred to the load lock chamber 102, a load lock vacuum pump (not shown) may remove gas molecules within the load lock chamber 102 to reach a first pressure lower than atmospheric pressure. After the first pressure is reached, a robot arm 110 may transfer the wafer from the load lock chamber 102 via a gate valve 107 to a wafer stage 114 of the beam tool 104 within the main chamber 101. The main chamber 101 is connected to a main chamber vacuum pump system (not shown) that may remove gas molecules within the main chamber 101 to reach a second pressure lower than the first pressure. After the second pressure is reached, the wafer may undergo inspection by the beam tool 104.

[0028]

[0040] In some embodiments, main chamber 101 may include a parking station 116 configured to temporarily store wafers prior to inspection. For example, once inspection of a first wafer is complete, the first wafer may be unloaded from wafer stage 114, and then robot arm 110 may transfer a second wafer from parking station 116 to wafer stage 114. Thereafter, robot arm 110 may transfer a third wafer from load lock chamber 102 to parking station 116 for temporary storage until inspection of the second wafer is complete.

[0029]

[0041] FIG. 2 illustrates an exemplary imaging system 200 according to an embodiment of the present disclosure. The electron beam tool 104 of FIG. 2 can be configured for use in the system 100. The electron beam tool 104 can be a single-beam device or a multi-beam device. As shown in FIG. 2, the electron beam tool 104 includes a motorized sample stage 201 and a wafer holder 202 supported by the motorized sample stage 201 to hold a wafer 203 to be inspected. The electron beam tool 104 further includes an objective lens assembly 204, an electron detector 206 (including electron sensor faces 206 a and 206 b), an objective aperture 208, a condenser lens 210, a beam-limiting aperture 212, a gun aperture 214, an anode 216, and a cathode 218. The objective lens assembly 204 may, in some embodiments, include a modified rebound immersion phase contrast objective lens (SORIL) including a pole piece 204 a, a control electrode 204 b, a deflector 204 c, and an excitation coil 204 d. Additionally, the electron beam tool 104 may include an energy dispersive X-ray spectrometer (EDS) detector (not shown) for characterizing materials on the wafer 203.

[0030]

[0042] Applying an accelerating voltage between the anode 216 and the cathode 218 emits a primary electron beam 220 from the cathode 218. The primary electron beam 220 passes through a gun aperture 214 and a beam-limiting aperture 212. Both the gun aperture 214 and the beam-limiting aperture 212 can determine the size of the electron beam incident on a condenser lens 210 located below the beam-limiting aperture 212. After the condenser lens 210 focuses the primary electron beam 220, the beam enters an objective aperture 208, which sets the size of the electron beam, before entering the objective lens assembly 204. A deflector 204c deflects the primary electron beam 220 to facilitate beam scanning over the wafer. For example, during a scanning process, the deflector 204c can be controlled to sequentially deflect the primary electron beam 220 onto different positions on the top surface of the wafer 203 at different times to provide data for image reconstruction for different portions of the wafer 203. Additionally, the deflector 204c may also be controlled to deflect the primary electron beam 220 at a specific location onto different sides of the wafer 203 at different times to provide data for three-dimensional image reconstruction of the wafer structures at that specific location. Furthermore, in some embodiments, the anode 216 and cathode 218 may generate multiple primary electron beams 220, and the electron beam tool 104 may include multiple deflectors 204c that simultaneously project the multiple primary electron beams 220 onto different portions / sides of the wafer 203 to provide data for image reconstruction of different portions of the wafer 203.

[0031]

[0043] The excitation coil 204d and pole piece 204a generate a magnetic field that starts at one end of the pole piece 204a and ends at the other end of the pole piece 204a. The portion of the wafer 203 scanned by the primary electron beam 220 may be immersed in this magnetic field and may become charged, generating an electric field. The electric field reduces the energy of the incident primary electron beam 220 near the wafer's surface before it impacts the wafer 203. A control electrode 204b, electrically isolated from the pole piece 204a, controls the electric field on the wafer 203 to prevent micro-arching of the wafer 203 and ensure proper beam focus.

[0032]

[0044] Upon receiving the primary electron beam 220, a secondary electron beam 222 may be emitted from a portion of the wafer 203. The secondary electron beam 222 may form a beam spot on the sensor surfaces 206a and 206b of the electron detector 206. The electron detector 206 may generate a signal (e.g., a signal indicative of a voltage, a current, or any electrical property) representing the intensity of the beam spot and provide this signal to the image processing system 250. The intensity of the secondary electron beam 222 and the resulting beam spot may vary depending on the external or internal structure of the wafer 203. Furthermore, as discussed above, the primary electron beam 220 may be projected onto different locations on the top surface of the wafer or onto different sides of the wafer at specific locations to generate secondary electron beams 222 (and resulting beam spots) of different intensities. Thus, by mapping the intensity of the beam spot with respect to the position on the wafer 203, the processing system may reconstruct an image reflecting the internal or external structure of the wafer 203.

[0033]

[0045] The imaging system 200 may be used to inspect a wafer 203 on a motorized sample stage 201 and includes the electron beam tool 104 discussed above. The imaging system 200 may also include an image processing system 250, which includes an image acquisition device 260, storage 270, and a controller 109. The image acquisition device 260 may include one or more processors. For example, the image acquisition device 260 may include a computer, a server, a mainframe host, a terminal, a personal computer, any type of mobile computing device, etc., or a combination thereof. The image acquisition device 260 may be connected to the detector 206 of the electron beam tool 104 via a medium such as electrical conductors, fiber optic cables, portable storage media, IR, Bluetooth, the Internet, a wireless network, a radio, or a combination thereof. The image acquisition device 260 may receive signals from the detector 206 and construct an image. Thus, the image acquisition device 260 may acquire an image of the wafer 203. The image capture device 260 may also perform various post-processing functions, such as generating contours and overlaying indices on the captured image. The image capture device 260 may adjust the brightness and contrast of the captured image or any other image characteristic. The storage 270 may be a storage medium such as a hard disk, cloud storage, random access memory (RAM), or other type of computer-readable memory. The storage 270 may be coupled to the image capture device 260 and may be used to store raw scanned image data as original images or to store post-processed images. The image capture device 260 and the storage 270 may be connected to the controller 109. In some embodiments, the image capture device 260, the storage 270, and the controller 109 may be integrated together as a single control unit.

[0034]

[0046] In some embodiments, the image acquisition device 260 may acquire one or more images of the sample based on an imaging signal received from the detector 206. The imaging signal may correspond to a scanning motion for performing charged particle imaging. The acquired image may be a single image including multiple imaging regions. The single image may be stored in the storage 270. The single image may be an original image that may be divided into multiple regions. Each of the regions may include one imaging region that includes a feature of the wafer 203.

[0035]

[0047] FIG. 3 is a diagram of an exemplary load lock system 300 in accordance with an embodiment of the present disclosure. In FIG. 3, the load lock system 300 includes a chamber 302 including a ceiling 304 and a floor 306. In some embodiments, the chamber 302 may have a cylindrical shape. The chamber 302 may enclose one or more support structures (e.g., wafer pedestals) disposed on the floor 306, including a support structure 308. The support structure may be used to support a wafer 310. For ease of explanation, a wafer 310 is shown in FIG. 3, but it should be noted that the load lock system 300 may or may not include a wafer 310. The load lock system 300 may further include a gas vent 312 in the ceiling 304. The gas vent 312 may be used to exhaust gas into the chamber 302 at a high flow rate (e.g., in pressurized operation). For example, the flow rate may be at least 20 normal liters per minute (NL / min). One normal liter is one liter of gas at one atmosphere pressure and standard temperature (e.g., 0°C or 20°C). In some embodiments, the flow rate may be greater than 20 NL / min (e.g., 40 NL / min or 60 NL / min). The load lock system 300 may further include a plate 314 secured to the ceiling 304 between the gas vent 312 and the wafer 310. As an example, as shown in FIG. 3 , the load lock system 300 may include one or more suspension structures (including suspension structure 316) secured to the ceiling 304, which may be used to secure the plate 314. In some embodiments, the load lock system 300 may further include a gas supply system (e.g., a pump, gas reservoir, or any system for providing gas, not shown in FIG. 3 ) coupled to the gas vent 312 for extracting, filling, or regulating gas.

[0036]

[0048] In some embodiments, the load lock system 300 may use a small volume design. For example, the volume of the chamber 302 may be 5 liters or less. In some embodiments, the load lock system 300 may use a compact vertical layout to accommodate the small volume design. For example, as shown in FIG. 3, the chamber 302 may have a height of up to 35 millimeters (mm) between the ceiling 304 and the floor 306. In some embodiments, the height of the chamber 302 may be 30-34 mm.

[0037]

[0049] In some embodiments, the gas vent 312 may be located at the center of the ceiling 304. For example, if the chamber 302 has a cylindrical shape, the ceiling 304 may be substantially circular and the gas vent 312 may be located at the center of the circle of the ceiling 304. In some embodiments, the gas vent 312 may direct the gas flow through the gas vent 312 perpendicular to the plate 314, as shown by the arrow in Figure 3. In some embodiments, the gas may include nitrogen, helium, hydrogen, argon, carbon dioxide, or compressed air.

[0038]

[0050] The plate 314 may be used to inhibit, divert, or adjust the gas flow entering the chamber 302 through the gas vent 312. The plate 314 may be used as a particle shield to reduce exposure of the wafer 310 to a potentially contaminated environment (e.g., an atmospheric environment with airborne dust suspended above the wafer 310), such as through flow-induced particle contamination or gravity-induced deposition. In some embodiments, as shown in FIG. 3 , the plate 314 may be substantially parallel to the ceiling 304 and the wafer 310 (e.g., with a slope of at most 2 degrees measured from the center of the plate 314). In some embodiments, the plate 314 may have the same shape as the wafer 310. For example, if the wafer 310 has a circular shape, the plate 314 may also have a circular shape. In some embodiments, the plate 314 may be centered at the gas vent 312. For example, if the plate 314 is circular, the center of the circle of the plate 314 may be aligned (e.g., vertically aligned) with the gas vent 312. In some embodiments, the plate 314 may have substantially the same size as the wafer 310. For example, the edges of the plate 314 may deviate from the edges of the wafer 310 within a positive or negative error tolerance (e.g., 6 mm). In another example, if the wafer 310 is round, the diameter of the plate 314 may be longer, shorter, or exactly the same as the diameter of the wafer 310 within a positive or negative error tolerance (e.g., 2% of the diameter of the wafer 310). For example, if the wafer 310 is round and has a diameter of 300 mm, the plate 314 may also be round and have a diameter of 300 mm ± 6 mm. In some embodiments, the size of the plate 314 may have a predetermined size that is independent of the size of the wafer 310. For example, plate 314 may be round and have a predetermined diameter with a predetermined tolerance (e.g., 300±6 mm), while wafer 310 may be round and have a diameter smaller than the predetermined diameter (e.g., 100 mm, 125 mm, 150 mm, 200 mm, or any length less than 300 mm). Note that the size and shape of plate 314 can be determined based on the effect of gas velocity reduction (described in connection with FIG. 5) and is not limited to the above example.In some embodiments, the plate 314 may be a metal plate. For example, the plate 314 may be made of stainless steel.

[0039]

[0051] In some embodiments, the placement of the plate 314 may be optimized to balance the efficiency of depressurizing the chamber 302 (e.g., extracting gas out of the chamber 302) and minimizing the volume of the chamber 302. FIG. 4 is a diagram of a close-up view of a portion 318 of the load lock system 300, in accordance with an embodiment of the present disclosure. As shown in FIG. 4, a gap 402 is between the ceiling 304 and the upper surface of the plate 314, and a gap 404 is between the lower surface of the plate 314 and the upper surface of the wafer 310. In some embodiments, the gap 402 may be between 3 and 10 mm. In some embodiments, the gap 402 may be substantially 6 mm (e.g., 6 ± 0.2 mm). In some embodiments, the gap 404 may be between 5 and 10 mm. In some embodiments, the gap 404 may be substantially 5 mm (e.g., 5 ± 0.2 mm).

[0040]

[0052] As shown in FIGS. 3-4, the load lock system 300 may employ a small-volume design with a compact vertical layout. The plate 314 may be substantially the same size as the wafer 310 so that the wafer 310 can be protected from the gas flow entering the chamber 302 through the gas vent 312 in a direction perpendicular to the wafer 310. The gas flow may have a high flow rate (e.g., at least 20 nL / min), but the velocity of the gas flow can be sufficiently slowed by the configured plate 314 before reaching the wafer 310 and steadily filling the chamber 302 by moving over the edge of the plate 314. By doing so, flow disturbances (e.g., flow circulation) can be suppressed within the chamber 302, and the small volume of the chamber 302 and the high gas flow rate can significantly reduce the time required for vacuum pressurization (e.g., less than 30 seconds, such as 15 seconds), thereby maintaining a high level of wafer throughput while reducing or minimizing flow-induced particle contamination of the wafer 310. Additionally, the compact vertical layout may facilitate easier integration of the load lock system 300 into a charged particle inspection apparatus (eg, the charged particle beam inspection system 100).

[0041]

[0053] The gap 402 in FIG. 4 can be optimized. In some embodiments, the gap 402 can be configured to be at least 3 mm to avoid compromising pressure reduction (e.g., “pump down”) efficiency while ensuring effective deceleration of the incoming gas flow. FIG. 5 is an exemplary graphical representation of the relationship between gas velocity reduction rate, plate size, and gap 402 size, according to an embodiment of the present disclosure. In FIG. 5, the horizontal axis represents the size of the plate 314, the vertical axis on the left represents the size of the gap 402, and the vertical legend on the right represents a grayscale corresponding to the reduction rate of the average flow velocity, with the grayscale color of the graph representing the reduction rate of the average flow velocity of the gas flow entering the chamber 302 through the gas vent 312. A positive reduction rate indicates that the average flow velocity of the gas flow is reduced by the plate 314, while a negative reduction rate indicates that the average flow velocity of the gas flow is actually increased by the plate 314 due to aerodynamic properties. As indicated by the light-to-dark color legend, the grayscale represents a reduction rate ranging from positive to negative, respectively. The dashed lines on the grayscale color in FIG. 5 represent iso-rate contours, including contours 504 (representing a 77.4713% reduction), 506 (representing a 66.3711% reduction), and 508 (representing a 55.2709% reduction). For example, a point on contour 504 can represent a combination of gap 402 size and plate 314 size, and contour 504 can represent that all points on contour 504 (i.e., all corresponding combinations of gap 402 size and plate 314 size) can result in a 77.4713% reduction in average flow velocity. All iso-rate contours in FIG. 5 can have similar representations. Contour 504 includes point 502, which represents the size (e.g., height) of gap 402 as 6 mm and the size (e.g., diameter) of plate 314 as 300 mm. As shown in FIG. 5, for some combinations of gap 402 size and plate 314 size, the reduction in average flow velocity can exceed 80%.

[0042]

[0054] In some embodiments, the gap 402 may be configured to be at most 10 mm to avoid substantially increasing the volume of the chamber 302 of FIG. 3 . The increased volume of the chamber 302 may impair wafer throughput because it may require a longer time for the pressurization ("vent-up") operation in the chamber 302. FIG. 6 is an exemplary graphical representation of the relationship between the volume increase rate and the size of the gap 402 according to an embodiment of the present disclosure. In FIG. 6 , the horizontal axis represents the size of the gap 402, and the vertical axis represents the volume increase rate of the chamber 302 of FIG. 3 . As shown in FIG. 6 , when the size of the gap 402 increases, the volume of the chamber 302 also increases along a line 602. The line 602 includes a point 604 that corresponds to a 6 mm size (e.g., height) of the gap 402. As shown in FIG. 6 , the increase in the volume of the chamber 302 corresponding to point 604 is approximately 10.5%.

[0043]

[0055] 3, the gap 402 and the plate 314 may be 6 mm and 300 mm, respectively. As shown in FIGS. 5-6, such a combination may result in a 77.4713% reduction in the average gas flow velocity and a 10.5% increase in the volume of the chamber 302. Such a combination may achieve an excellent balance between pressure reduction efficiency, the effectiveness of slowing down the incoming gas flow, the suppression of flow-induced particle contamination, and a small volume of the chamber 302.

[0044]

[0056] The gap 404 in FIG. 4 may also be optimized. In some embodiments, the gap 404 may be configured to be at least 5 mm to ensure sufficient operating space for a robot arm (e.g., the robot arm 110 in FIG. 1B ) to move the wafer 310 into and out of the chamber 302 between other parts of the charged particle inspection apparatus (e.g., the charged particle beam inspection system 100), such as the wafer stage 114 or the parking station 116 in FIG. 1B . In some embodiments, the gap 404 may be configured to be at most 10 mm to avoid substantially increasing the volume of the chamber 302 in FIG. 3 . In one embodiment of the load lock system 300 in FIG. 3 , the gap 404 may be 5 mm, which may achieve a good balance between pressure reduction efficiency, the effectiveness of slowing down the incoming gas flow, suppression of flow-induced particle contamination, and a small volume of the chamber 302.

[0045]

[0057] In some embodiments, with an optimized configuration, the plate 314 of FIG. 3 can protect the wafer 310 from direct impingement of airborne particles, substantially reducing the gas flow rate in the chamber 302 without compromising the duration for pressurizing the chamber 302. FIG. 7A shows a cross-sectional view illustrating the gas flow rate during a pressurization process in a load lock system without a particle shield for the wafer 310, according to an embodiment of the present disclosure. FIG. 7B shows a cross-sectional view illustrating the gas flow rate during a pressurization process in a load lock system 300 with a plate 314 for the wafer 310, according to an embodiment of the present disclosure. The legends at the bottom of FIGS. 7A-7B represent grayscales corresponding to different flow rates. As shown in the legends, a darker grayscale may represent a higher flow rate, and a lighter grayscale may represent a lower flow rate. Note that the numbers representing flow rates in the legends of FIGS. 7A-7B are merely examples, and the present disclosure does not intend to limit the flow rates as such. FIGS. 7A-7B may be graphical representations of computational fluid dynamics simulations.

[0046]

[0058] As shown in Figures 7A-7B, a high rate (e.g., at least 20 NL / min) of gas flow can enter chamber 302 through gas vent 312. The difference between Figures 7A and 7B is that the load lock system of Figure 7B (e.g., load lock system 300 as shown in Figures 3-4) includes a plate (e.g., plate 314) above wafer 310 as a particle shield. Gas flow can fill chamber 302 by moving over the edge of wafer 310 (as shown in Figure 7A) or the edge of plate 314 (as shown in Figure 7B).

[0047]

[0059] In FIG. 7A, the gas flow directly impinges on the wafer 310, which can result in significant particle contamination of the wafer 310. In contrast, in FIG. 7B, the gas flow is shielded from the wafer 310 by the plate 314, which can reduce particle contamination due to direct gas flow impingement. The plate 314 can also substantially reduce flow disturbances within the chamber 302 during the pressurization process. The grayscale colors in FIGS. 7A-7B represent flow velocity. As shown in regions 702 and 704 in FIGS. 7A-7B, the flow velocity in region 704 is significantly lower than the flow velocity in region 702 due to the plate 314. The lower flow velocity can reduce flow disturbances (e.g., flow circulation) within the chamber 302, which can result in reduced particle contamination due to particles agitated by the high-velocity gas flow (e.g., from the interior surfaces of the chamber 302). If there are particles originally attached to the surface of the wafer 310, a lower flow rate can also reduce the likelihood of those particles being entrained within the chamber 302, which can result in reduced cross-contamination of other wafers.

[0048]

[0060] In some embodiments, with an optimized configuration, the plate 314 of FIG. 3 can reduce the shear rate on the wafer 310. Shear rate (also referred to as "friction rate") can express shear stress in velocity units to describe shear-related motion (e.g., particle diffusion or dispersion) in a moving gas or fluid. The shear rate can depend on the shear between layers of the flow. For example, the shear rate on the wafer 310 can be directly correlated with the magnitude of flow-induced particle movement within the chamber 302. FIG. 8A shows a perspective view illustrating the shear rate on the top surface of the wafer 310 during a pressurization process in a load lock system without a particle shield for the wafer 310, according to an embodiment of the present disclosure. FIG. 8B shows a perspective view illustrating the shear rate on the top surface of the wafer 310 during a pressurization process in a load lock system 300 with a plate 314 for the wafer 310, according to an embodiment of the present disclosure. FIGS. 8A-8B may be graphical representations of computational fluid dynamics simulations. The legends at the bottom of FIGS. 8A-8B represent grayscales corresponding to different shear rate values. As shown in the legends, the darker the grayscale, the higher the shear rate may be, and the lighter the grayscale, the lower the shear rate may be. Note that the numbers representing shear rates in the legends of FIGS. 8A-8B are merely examples, and the present disclosure is not intended to limit the shear rates as such. Compared to FIG. 8A, FIG. 8B shows a significantly lower shear rate on the top surface of wafer 310. For example, the maximum shear rate on the top surface of wafer 310 in FIG. 8A is 0.12 m / s, while the maximum shear rate on the top surface of wafer 310 in FIG. 8B is 0.01 m / s. In some embodiments, the maximum shear rate on the top surface of wafer 310 may be reduced by at least 90%.

[0049]

[0061] 8A-8B, plate 314 can reduce the shear rate, where the resuspension rate of micron-scale particles (e.g., having a size of up to 10 microns or μm) can be significantly suppressed (e.g., to a negligible level) on the interior surfaces of chamber 302 and wafer 310. In some embodiments, without plate 314, particles greater than 5 μm in size can be resuspensioned from the interior surfaces of chamber 302 and wafer 310, causing particle contamination or cross-contamination on wafer 310.

[0050]

[0062] 3 can capture a significant portion of particles within the chamber 302. FIG. 9A is a diagram of an exemplary particle trap of the load lock system 300, according to an embodiment of the present disclosure. When a high-velocity (e.g., at least 20 NL / min) gas flow enters the chamber 302 through the gas vent 312, it can carry foreign particles (e.g., dust), including particles 902. The high-velocity flow can deposit the foreign particles on the plate 314, and the gap 402 can function as a particle trap that can effectively capture the foreign particles to reduce the likelihood of the foreign particles being dispersed to the wafer 310.

[0051]

[0063] In some embodiments, even if the gas flow is not filtered (e.g., by a filter upstream of the gas vent 312) or the chamber 302 is not sufficiently clean (e.g., containing internal particles), particles having a size greater than 4 μm may still be trapped and retained in the gap 402. FIG. 9B shows a perspective view illustrating a region 904 of the gap 402 having a high particle deposition rate, according to an embodiment of the present disclosure. FIG. 9B may be a graphical representation of a computational fluid dynamics simulation. The deposition rate (also referred to as the "deposition rate") in FIG. 9B is normalized to the normalized relaxation time with respect to particle properties. The legend at the bottom of FIG. 9B represents grayscales corresponding to different deposition rate values. As shown in the legend, a darker grayscale may represent a higher deposition rate, and a lighter grayscale may represent a lower deposition rate. Note that the numbers representing deposition rates in the legend of FIG. 9B are merely examples, and the present disclosure is not intended to limit the deposition rate as such. As shown in FIG. 9B, due to the high particle deposition rate in region 904, particles having a size greater than 4 μm can still be captured and retained in gap 402.

[0052]

[0064] As shown in FIGS. 9A-9B, such a design and configuration can minimize particle contamination of the wafer 310 and improve the robustness of the charged particle inspection apparatus (e.g., charged particle beam inspection system 100). Due to the improved robustness and effective protection from particle contamination, in some embodiments, aggressive acceleration (e.g., having a flow rate of at least 40 NL / min, such as 60 NL / min) can be applied without causing significant particle contamination. In such cases, pressurizing the chamber 302 to a threshold pressure (e.g., 10 -6 The duration for the ionizing radiation (from 100 Torr to 760 Torr) can be significantly reduced (e.g., from 30 seconds to 15 seconds).

[0053]

[0065] Aspects of the present disclosure are set forth in the following numbered clauses. 1. A load lock system comprising: a chamber enclosing a support structure configured to support a wafer; a gas vent disposed in the ceiling of the chamber and configured to exhaust gas into the chamber at a flow rate of at least 20 normal liters per minute; A plate fixed to the ceiling between the gas vent and the wafer Load lock system including. 2. The load lock system of clause 1, wherein the plate is substantially parallel to the ceiling and the wafer. 3. The load lock system according to clause 2, wherein the first gap between the plate and the ceiling is 3 to 10 millimeters. 4. The load lock system according to clause 3, wherein the first gap is 6 mm. 5. A load lock system according to any one of clauses 2 to 4, wherein the second gap between the plate and the wafer is 5 to 10 millimeters. 6. The load lock system according to clause 5, wherein the second gap is 5 mm. 7. A load lock system according to any one of clauses 1 to 6, wherein the chamber has a cylindrical shape. 8. A load lock system according to any one of clauses 1 to 7, wherein the chamber has a maximum height of 35 millimeters between the ceiling and floor of the chamber. 9. The load lock system of clause 8, wherein the height is 30 to 34 millimeters. 10. A load lock system according to any one of clauses 1 to 9, wherein the chamber has a maximum volume of 5 liters. 11. A load lock system as described in any one of clauses 1 to 10, wherein the gas vent is located in the center of the ceiling. 12. A load lock system as described in any one of clauses 1 to 11, wherein the gas vent is configured to direct gas flow through the gas vent perpendicular to the plate. 13. A load lock system according to any one of clauses 1 to 12, wherein the gas comprises nitrogen, helium, hydrogen, argon, carbon dioxide or compressed air. 14. A load lock system according to any one of clauses 1 to 13, wherein the plate is configured to center a gas vent. 15. A load lock system according to any one of clauses 1 to 14, wherein the plate has a shape substantially the same as the shape of the wafer. 16. A load lock system according to any one of clauses 1 to 15, wherein the plate has substantially the same size as the wafer. 17. A load lock system as described in any one of clauses 1 to 16, wherein the plate is round and has a diameter of 300 millimeters. 18. A load lock system according to any one of clauses 1 to 17, wherein the plate is a metal plate. 19. A load lock system as described in any one of clauses 1 to 18, wherein the plate is made from stainless steel. 20. A load lock system as described in any one of clauses 1 to 19, further comprising a suspension structure fixed to the ceiling, the suspension structure configured to secure the plate. 21. The load lock system of any one of clauses 1 to 20, further comprising a gas supply system configured to couple to the gas vent. 22. A load lock system as described in any one of clauses 1 to 21, wherein the time to evacuate gas into the chamber to the threshold pressure is less than 30 seconds. 23. The load lock system of clause 22, wherein the threshold pressure is atmospheric pressure. 24. A load lock system according to clause 22 or 23, wherein the time is reduced to 15 seconds. 25. A charged particle inspection apparatus including a load lock system according to any one of clauses 1 to 24. 26. An apparatus for reducing wafer contamination in a load lock system, comprising: a wafer holder configured to support a wafer; A chamber comprising: The surface and a gas vent disposed on the surface and configured to exhaust gas into the chamber during pressurization of the chamber, the gas flow direction being perpendicular to the wafer and the surface; a chamber containing a baffle disposed between the wafer and the surface and substantially parallel to the wafer, the baffle configured to deflect the gas flow away from the wafer; An apparatus comprising: 27. The apparatus of clause 26, wherein the gas flow has a flow rate of at least 20 normal liters per minute. 28. The apparatus of clause 26 or 27, wherein the baffle is substantially parallel to the surface and the wafer. 29. The apparatus of clause 28, wherein the first gap between the baffle and the surface is between 3 and 10 millimeters. 30. The apparatus of clause 29, wherein the first gap is substantially 6 millimeters. 31. The apparatus of any one of clauses 28-30, wherein the second gap between the baffle and the wafer is 5-10 millimeters. 32. The apparatus of clause 31, wherein the second gap is 5 millimeters. 33. An apparatus according to any one of clauses 26 to 32, wherein the chamber has a cylindrical shape. 34. An apparatus according to any one of clauses 26 to 33, wherein the chamber has a maximum height of 35 millimeters between the surface of the chamber and the floor. 35. The device according to clause 34, wherein the height is 30 to 34 millimeters. 36. A device according to any one of clauses 26 to 35, wherein the volume of the chamber is at most 5 liters. 37. An apparatus according to any one of clauses 26 to 36, wherein the gas vent is positioned at the centre of the surface. 38. An apparatus according to any one of clauses 26 to 37, wherein the gas vent is configured to direct gas flow through the gas vent perpendicular to the baffle. 39. An apparatus according to any one of clauses 26 to 38, wherein the gas comprises nitrogen, helium, hydrogen, argon, carbon dioxide or compressed air. 40. The apparatus of any one of clauses 26 to 39, wherein the baffle is configured to center the gas vent. 41. The apparatus of any one of clauses 26 to 40, wherein the baffle has a shape substantially the same as the shape of the wafer. 42. The apparatus of any one of clauses 26-41, wherein the baffle has substantially the same size as the wafer. 43. An apparatus according to any one of clauses 26 to 42, wherein the baffle is round and has a diameter of 300 millimeters. 44. An apparatus according to any one of clauses 26 to 43, wherein the baffle is a metal baffle. 45. An apparatus according to any one of clauses 26 to 44, wherein the baffle is made from stainless steel. 46. ​​The apparatus of any one of clauses 26 to 45, further comprising a suspension structure secured to the surface, the suspension structure configured to secure the baffle. 47. The apparatus of any one of clauses 26 to 46, further comprising a gas supply system configured to couple to the gas vent. 48. An apparatus as described in any one of clauses 26 to 47, wherein the time to discharge gas into the chamber to the threshold pressure is less than 30 seconds. 49. The device according to clause 48, wherein the threshold pressure is atmospheric pressure. 50. The device of clause 48 or 49, wherein the time is reduced to 15 seconds.

[0054]

[0066] The block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code, including one or more executable instructions for implementing the specified logical function(s). It should be understood that in some alternative implementations, the functions shown in the blocks may occur in a different order than depicted in the figures. For example, two blocks shown in succession may be executed or performed substantially simultaneously, or the two blocks may possibly be executed in reverse order, depending on the functionality involved. Also, some blocks may be omitted. It should be understood that each block and combination of blocks in the block diagrams may also be implemented by a dedicated hardware-based system that performs the specified functions or acts, or a combination of dedicated hardware and computer instructions.

[0055]

[0067] It will be understood that the embodiments of the present disclosure are not limited to the exact constructions described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope of the present disclosure.

Claims

1. 1. A load lock system comprising: a chamber enclosing a support structure for supporting a wafer; a gas vent disposed in the ceiling of the chamber and configured to exhaust gas into the chamber at a flow rate of at least 20 normal liters per minute; a plate fixed to the ceiling between the gas vent and the wafer; Load lock system including.

2. The load lock system of claim 1 , wherein the plate is substantially parallel to the ceiling and the wafer.

3. The load lock system of claim 2 , wherein the first gap between the plate and the ceiling is between 3 and 10 millimeters.

4. The load lock system of claim 3 , wherein the first gap is 6 millimeters.

5. The load lock system of claim 2 , wherein the second gap between the plate and the wafer is between 5 and 10 millimeters.

6. The load lock system of claim 5 , wherein the second gap is 5 millimeters.

7. The load lock system of claim 1 , wherein the chamber has a cylindrical shape.

8. 10. The load lock system of claim 1, wherein the chamber has a maximum height of 35 millimeters between the ceiling and floor of the chamber.

9. The load lock system of claim 8, wherein the height is between 30 and 34 millimeters.

10. 10. The load lock system of claim 1, wherein the chamber has a maximum volume of 5 liters.

11. The load lock system of claim 1 , wherein the gas vent is located at the center of the ceiling.

12. The load lock system of claim 1 , wherein the gas vent directs gas flow through the gas vent perpendicular to the plate.

13. The load lock system of claim 1 , wherein the gas comprises nitrogen, helium, hydrogen, argon, carbon dioxide, or compressed air.

14. The load lock system of claim 1 , wherein the plate is centered on the gas vent.

15. The load lock system of claim 1 , wherein the plate has a shape substantially the same as a shape of the wafer.

Images