EP4736211A1 - In-vacuum, in-situ wafer temperature measuring method and apparatus - Google Patents

Abstract

An improved particle beam inspection apparatus, and more particularly, a particle beam inspection apparatus including a contactless temperature sensor for accurately measuring a temperature of a wafer without risk of contamination is disclosed. The charged particle beam apparatus may calibrate the contactless temperature sensor using a temperature adjustable calibration pad, and then use the calibrated contactless temperature sensor to determine a temperature of a sample with an accuracy of 0.01-0.1 °C. The charged particle beam apparatus may further optimize and adjust a thermal conditioning station based on the accurately measured sample temperature.

Description

IN- VACUUM, IN-SITU WAFER TEMPERATURE MEASURING METHOD AND APPARATUS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63/524,568 which was filed on June 30, 2023 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The embodiments provided herein disclose a charged particle beam inspection apparatus, and more particularly, a charged particle beam inspection apparatus including a contactless temperature sensor for measuring a temperature of a wafer.

BACKGROUND

[0003] When manufacturing semiconductor integrated circuit (IC) chips, pattern defects or uninvited particles (residuals) inevitably appear on a wafer or a mask during fabrication processes, thereby reducing the yield. For example, uninvited particles may be troublesome for patterns with smaller critical feature dimensions, which have been adopted to meet the increasingly more advanced performance requirements of IC chips.

[0004] Pattern inspection tools with a charged particle beam have been used to detect the defects or uninvited particles. These tools typically employ a scanning electron microscope (SEM). In a SEM, a beam of primary electrons having a relatively high energy is decelerated to land on a sample at a relatively low landing energy and is focused to form a probe spot thereon. Due to this focused probe spot of primary electrons, secondary electrons will be generated from the surface. The secondary electrons may comprise backscattered electrons, secondary electrons, or Auger electrons, resulting from the interactions of the primary electrons with the sample. By scanning the probe spot over the sample surface and collecting the secondary electrons, pattern inspection tools may obtain an image of the sample surface.

[0005] During operation of an inspection tool, the wafer is typically held by a wafer stage. The inspection tool may comprise a wafer positioning device for positioning the wafer stage and wafer relative to the e-beam. This may be used to position a target area on the wafer, e.g., an area to be inspected, in an operating range of the e-beam.

SUMMARY

[0006] The embodiments provided herein disclose a charged particle beam inspection apparatus, and more particularly, a particle beam inspection apparatus including a contact-less temperature sensor for measuring a temperature of a wafer.

[0007] Some embodiments provide an in-vacuum temperature measurement system. The in-vacuum temperature measurement system comprises a vacuum chamber, a wafer holder located in the vacuum chamber and configured to hold a wafer, a temperature adjustable calibration pad coupled to an internal component of the vacuum chamber, a contactless temperature sensor configured to generate an output signal based on a temperature of the temperature adjustable calibration pad, a contact temperature sensor coupled to the temperature adjustable calibration pad, wherein the contact temperature sensor is configured to determine a temperature of the temperature adjustable calibration pad, and a controller configured to calibrate the contactless temperature sensor based on the output signal from the contactless temperature sensor and the temperature of the temperature adjustable calibration pad determined by the contact temperature sensor.

[0008] In some embodiments, a charged-particle beam apparatus is provided. The charged-particle beam apparatus comprises a vacuum chamber configured to provide a vacuum environment, a sample holder located in the vacuum chamber and configured to hold a sample, a calibration pad coupled to an internal component of the vacuum chamber, an IR sensor configured to generate an output signal based on a temperature of the calibration pad, a contact temperature sensor coupled to the calibration pad, wherein the contact temperature sensor is configured to measure a temperature of the calibration pad, and a controller configured to calibrate the IR sensor based on the output signal from the IR sensor and the temperature of the calibration pad determined by the temperature sensor.

[0009] In some embodiments, a non-transitory computer readable medium including a set of instructions that is executable by one or more processors of a controller to cause the controller to perform operations for measuring a temperature of a sample in vacuum using a charged particle beam apparatus is provided. The operations comprise adjusting a temperature of a temperature adjustable calibration pad to a first temperature, collecting a first set of measurements of the temperature adjustable calibration pad at the first temperature using a contact temperature sensor and a contactless temperature sensor, adjusting a temperature of the temperature adjustable calibration pad to a second temperature, collecting a second set of measurements of the temperature adjustable calibration pad at the second temperature using the contact temperature sensor and the contactless temperature sensor, calibrating the contactless temperature sensor, and measuring a temperature characteristic of a sample to be inspected using the calibrated contactless temperature sensor.

[0010] Other advantages of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of the present disclosure.

BRIEF DESCRIPTION OF FIGURES

[0011] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments, taken in conjunction with the accompanying drawings. [0012] FIG. 1A is a schematic diagram illustrating an exemplary wafer deformation effect in a charged particle beam inspection system. [0013] FIG. IB a schematic diagram illustrating an exemplary charged particle beam inspection system, consistent with embodiments of the present disclosure.

[0014] FIG. 1C is a schematic diagram illustrating an exemplary wafer loading sequence in the charged particle beam inspection system of FIG. IB, consistent with embodiments of the present disclosure.

[0015] FIG. 2 is a schematic diagram illustrating an exemplary electron beam tool, consistent with embodiments of the present disclosure.

[0016] FIG. 3 is an exemplary graph showing a wafer temperature change over time in a charged particle beam inspection system.

[0017] FIG. 4 is a schematic diagram of an exemplary charged particle beam inspection system with a thermal conditioning station, consistent with embodiments of the present disclosure.

[0018] FIGS. 5 and 6 is an exemplary graph showing a wafer temperature change over time in relation to a temperature setpoint of the thermal conditioning process, consistent with embodiments of the present disclosure.

[0019] FIGS. 7A and 7B are exemplary schematic diagrams illustrating a calibration mode and a measurement mode of a contactless temperature sensor and temperature adjustable calibration pad, consistent with embodiments of the present disclosure.

[0020] FIG. 7C is an example schematic diagram of a temperature adjustable calibration pad coupled to an internal component of a vacuum chamber, consistent with embodiments of the present disclosure

[0021] FIG. 7D is an example schematic diagram of a top-view of a temperature adjustable calibration pad, consistent with embodiments of the present disclosure.

[0022] FIG. 7E is an example schematic diagram of a temperature adjustable calibration pad coupled to an internal component in a vacuum chamber, consistent with embodiments of the present disclosure.

[0023] FIG. 8 is a flow chart illustrating an exemplary method for calibrating and measuring a wafer temperature with a contactless temperature sensor, consistent with embodiments of the present disclosure.

DETAILED DESCRIPTION

[0024] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the invention. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the invention as recited in the appended claims. [0025] The enhanced computing power of electronic devices, while reducing the physical size of the devices, can be accomplished by significantly increasing the packing density of circuit components such as transistors, capacitors, diodes, etc. on an IC chip. For example, an IC chip of a smart phone, which is the size of a thumbnail, may include over 2 billion transistors, the size of each transistor being less than l/1000th of a human hair. Thus, it is not surprising that semiconductor IC manufacturing is a complex and time-consuming process, with hundreds of individual steps. Errors in even one step have the potential to dramatically affect the functioning of the final product. Even one “killer defect” can cause device failure. The goal of the manufacturing process is to improve the overall yield of the process. For example, for a 50-step process to get to a 75% yield, each individual step must have a yield greater than 99.4%, and if the individual step yield is 95%, the overall process yield drops to 7%.

[0026] While high process yield is desirable in an IC chip manufacturing facility, maintaining a high wafer throughput, defined as the number of wafers processed per hour, is also essential. High process yield and high wafer throughput can be impacted by the presence of defects, especially if operator intervention is required for reviewing the defects. Thus, high throughput detection and identification of micro and nano-sized defects by inspection tools (such as a SEM) is essential for maintaining high yield and low cost.

[0027] A SEM scans the surface of a wafer with a focused beam of electrons. The electrons interact with the wafer and generate secondary electrons. By scanning the wafer with an electron beam and capturing the secondary electrons with a detector, a SEM creates an image of the wafer that shows the internal device structure in the area of the wafer being inspected.

[0028] One of the problems with a conventional inspection system is that a wafer being scanned may change its shape or size while the scanning is in progress. For example, when the wafer is placed on an inspection platform, the temperature of wafer can be different from the temperature of the platform. This temperature difference may cause a wafer temperature drift (e.g., the temperature of the wafer gradually and continuously changes towards a stable point, which is usually close to the temperature of the inspection system), thereby resulting in the change in the shape or size of the wafer. If the wafer temperature increases, the wafer would expand; if the wafer temperature decreases, the wafer would shrink. This change in the shape or size of the wafer can cause inaccurate inspection results.

[0029] Therefore, an operator, who is inspecting a wafer using a conventional particle beam inspection system, needs to wait for the wafer to become temperature- stabilized before starting the inspection. This temperature stabilization is required because the wafer changes size as the temperature changes, which causes elements on the wafer to move as the wafer expands or contracts. For example, FIG. 1A shows that elements 180, 182, 184, and 186 can move to new locations 170, 172, 174, and 178 as a wafer 160 expands due to the temperature change. And when the precision for inspecting a wafer is in nanometers, this change in location is material. Accordingly, for the operator to precisely locate and inspect the elements on the wafer, the operator must wait until the wafer temperature stabilizes. Therefore, for high throughput inspection, some of the newer inspection systems perform a thermal conditioning of a wafer before placing the wafer on the inspection platform. By making the wafer temperature close to the temperature of the wafer stage before placing the wafer onto the wafer stage, the inspection can begin with much less delay. Therefore, the operator can inspect more wafers within a given period of time, thereby achieving an increased throughput. [0030] If the inspection system can use the actual temperature of the wafer, the thermal conditioning process can be further optimized. However, measuring the actual wafer temperature is difficult. Placing a thermometer on the wafer can contaminate the inspection environment with unwanted particles (e.g., dust), which can degrade the accuracy of wafer inspection. Additionally, attaching a thermometer on the wafer may increase the amount of wiring in the system, which may increase the overall noise in measurements of the wafer. Moreover, as the thermometer is attached to the wafer and may move with the wafer during inspection, there may be increased risk of the wiring detaching and prompting repair of the thermometer. This may require venting the vacuum chamber to atmospheric conditions for the repair, and thus significantly reduce throughput. Contactless thermometers, like Infrared (IR) temperature sensors, may avoid the contamination problem, but the accuracy of IR sensors is undesirably low. A contactless temperature sensor is calibrated under atmospheric conditions, so accuracy of an in-situ, in-vacuum contactless temperature sensor may not be accurate.

[0031] Embodiments of the present disclosure may provide systems and methods that can accurately measure the temperature characteristics of the wafer without contact to the wafer and without using any component that can contaminate the inspection environment. Some embodiments of the present disclosure may provide systems and methods for in-situ, in-vacuum calibration of a contactless temperature sensor using a temperature adjustable calibration pad. In some embodiments, the calibrated contactless temperature sensor may measure a temperature of a wafer in- vacuum and in-situ with an accuracy of 0.1 °C or better (e.g., 0.1 - 0.01 °C). In some embodiments, the temperature adjustable calibration pad is a same material of a wafer to be inspected. In some embodiments, the temperature adjustable calibration pad is a same material of a component in a vacuum chamber that is contacted to a sample to be inspected. In some embodiments, the contactless temperature sensor may be an IR temperature sensor. In some embodiments, a calibrated contactless temperature sensor may be used in a charged particle system or apparatus to accurately measure a temperature of a wafer during inspection. Some embodiments of the present disclosure may provide a method to increase defect inspection accuracy and yield of defect-free wafers throughout high volume manufacturing (HVM).

[0032] Relative dimensions of components in drawings may be exaggerated for clarity. Within the following description of drawings the same or like reference numbers refer to the same or like components or entities, and only the differences with respect to the individual embodiments are described. As used herein, unless specifically stated otherwise, the term “or” encompasses all possible combinations, except where infeasible. For example, if it is stated that a database can include A or B, then, unless specifically stated otherwise or infeasible, the database can include A, or B, or A and B. As a second example, if it is stated that a database can include A, B, or C, then, unless specifically stated otherwise or infeasible, the database can include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0033] Reference is now made to FIG. IB, which is a schematic diagram illustrating an exemplary charged particle beam inspection system 100, consistent with embodiments of the present disclosure. As shown in FIG. IB, charged particle beam inspection system 100 may include a main chamber 10, a load lock chamber 20, an electron beam tool 40, and an equipment front end module (EFEM) 30. Electron beam tool 40 may be located within main chamber 10. While the description and drawings are directed to an electron beam, it is appreciated that the embodiments are not used to limit the present invention to specific charged particles. It is further appreciated that electron beam tool 40 can be a single-beam tool utilizing a single electron beam or a multi-beam tool utilizing multiple electron beams.

[0034] EFEM 30 may include a first loading port 30a and a second loading port 30b. EFEM 30 may include additional loading port(s). First loading port 30a and second loading port 30b may, for example, receive wafer front opening unified pods (FOUPs) that contain wafers (e.g., semiconductor wafers or wafers made of other material(s)) or samples to be inspected (wafers and samples are collectively referred to as “wafers”). One or more robot arms (e.g., robot arm 11 shown in FIG. 1C) in EFEM 30 transport the wafers to load lock chamber 20.

[0035] Load lock chamber 20 may be connected to a load lock vacuum pump system (not shown), which removes gas molecules in load lock chamber 20 to reach a first pressure below the atmospheric pressure. After reaching the first pressure, one or more robot arms (e.g., robot arm 12 shown in FIG. 1C) transport the wafer from load lock chamber 20 to main chamber 10. Main chamber 10 is connected to a main chamber vacuum pump system (not shown), which removes gas molecules in main chamber 10 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subject to inspection by electron beam tool 40.

[0036] A controller 50 may be electronically connected to electron beam tool 40 or any other parts of charged particle beam inspection system 100. Controller 50 may be a computer configured to execute various controls of charged particle beam inspection system 100. Controller 50 may also include a processing circuitry configured to execute various signal and image processing functions. While controller 50 is shown in FIG. IB as being outside of the structure that includes main chamber 10, load lock chamber 20, and EFEM 30, it is appreciated that controller 50 may be part of the structure. While the present disclosure provides examples of main chamber 10 housing an electron beam inspection tool, it should be noted that aspects of the disclosure in their broadest sense are not limited to a chamber housing an electron beam inspection tool. Rather, it is appreciated that the foregoing principles may also be applied to other tools that operate under the second pressure.

[0037] Reference is now made to FIG. 1C, which is a schematic diagram illustrating an exemplary wafer loading sequence in charged particle beam inspection system 100 of FIG. IB, consistent with embodiments of the present disclosure. In some embodiments, charged particle beam inspection system 100 may include a robot arm 11 located in EFEM 30 and a robot arm 12 located in main chamber 10. In some embodiments, EFEM 30 may also include a pre-aligner 60 configured to position a wafer accurately before transporting the wafer to load lock chamber 20.

[0038] In some embodiments, first loading port 30a and second loading port 30b, for example, may receive wafer front opening unified pods (FOUPs) that contain wafers. Robot arm 11 in EFEM 30 may transport the wafers from any of the loading ports to pre-aligner 60 for assisting with the positioning. Pre-aligner 60 may use mechanical or optical aligning methods to position the wafers. After pre-alignment, robot arm 11 may transport the wafers to load lock chamber 20.

[0039] After the wafers are transported to load lock chamber 20, a load lock vacuum pump (not shown) may remove gas molecules in load lock chamber 20 to reach a first pressure below the atmospheric pressure. After reaching the first pressure, a robot arm 12 may transport the wafer from load lock chamber 20 to a wafer stage 80 of electron beam tool 40 in main chamber 10. Main chamber 10 is connected to a main chamber vacuum pump system (not shown), which removes gas molecules in main chamber 10 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer may be subject to inspection by electron beam tool.

[0040] In some embodiments, main chamber 10 may include a parking station 70 configured to temporarily store a wafer before inspection. For example, when the inspection of a first wafer is completed, the first wafer may be unloaded from wafer stage 80, and then robot arm 12 may transport a second wafer from parking station 70 to wafer stage 80. Afterwards, robot arm 12 may transport a third wafer from load lock chamber 20 to parking station 70 to temporarily store the third wafer until the inspection for the second wafer is finished.

[0041] In some embodiments, to improve the overall throughput of inspection system, charged particle beam inspection system 100 may perform a thermal conditioning of a wafer before loading the wafer onto wafer stage 80. This pre-inspection thermal conditioning may occur in pre-aligner 60, load lock chamber 20, parking station 70, or any other place suitable for thermally conditioning the wafer before moving it to wafer stage 80.

[0042] Reference is now made to FIG. 2, which is a schematic diagram illustrating an exemplary inspection system 200 that may be part of the charged particle beam inspection system of FIGS. IB and 1C, consistent with embodiments of the present disclosure. Inspection system 200 may include an electron beam tool 40 and a controller 50.

[0043] Electron beam tool 40 may include a motorized wafer stage 201 (similar to wafer stage 80 of FIG. 1C). Electron beam tool 40 may also include a wafer holder 202 supported by motorized wafer stage 201 to hold a wafer 203 to be inspected. Electron beam tool 40 may further include a compound objective lens 204, electron detector 206 (which includes electron sensor surfaces), an objective aperture 208, a condenser lens 210, a beam limit aperture 212, a gun aperture 214, an anode 216, and a cathode 218, one or more of which may be aligned with an optical axis 217 of electron beam tool 40. In some embodiments, detector 206 may be arranged off axis 217.

[0044] Compound objective lens 204, in some embodiments, may include a modified swing objective retarding immersion lens (SORIL), which may include a pole piece 204a, a control electrode 204b, a deflector or a set of deflectors 204c, and an exciting coil 204d. In some embodiments, electron beam tool 40 may additionally include an energy dispersive X-ray spectrometer (EDS) detector (not shown) to characterize the materials on the wafer.

[0045] A primary electron beam 220 may be emitted from cathode 218 by applying a voltage between anode 216 and cathode 218. Primary electron beam 220 may pass through gun aperture 214 and beam limit aperture 212, both of which may determine the current of electron beam entering condenser lens 210, which resides below beam limit aperture 212. Condenser lens 210 may focus primary electron beam 220 before the beam enters objective aperture 208 to set the current of the electron beam before entering compound objective lens 204.

[0046] Compound objective lens 204 may focus primary electron beam 220 onto wafer 203 for inspection and can form a probe spot 222 on surface of wafer 203. Deflector(s) 204c may deflect primary electron beam 220 to scan probe spot 222 over wafer 203. For example, in a scanning process, deflector(s) 204c may be controlled to deflect primary electron beam 220 sequentially onto different locations of top surface of wafer 203 at different time points, to provide data for image reconstruction for different parts of wafer 203. Moreover, in some embodiments, deflector 204c may also be controlled to deflect primary electron beam 220 onto different sides of wafer 203 at a particular location, at different time points, to provide data for stereo image reconstruction of the wafer structure at that location. Further, in some embodiments, anode 216 and cathode 218 may be configured to generate multiple primary electron beams 220, and electron beam tool 40 may include a plurality of deflectors 204c to project the multiple primary electron beams 220 to different parts/sides of wafer 203 at the same time.

[0047] When a current is applied onto exciting coil 204d, an axially-symmetric (i.e., symmetric around optical axis 217) magnetic field may be generated in the wafer surface area. A part of wafer 203 being scanned by primary electron beam 220 may be immersed in the magnetic field. In some embodiments, different voltages may be applied onto wafer 203, pole piece 204a, and control electrode 204b, to generate an axial symmetric retarding electric field near the wafer surface. The electric field may reduce the energy of impinging primary electron beam 220 near the surface of the wafer before electrons of the beam collide with wafer 203. Control electrode 204b, being electrically isolated from pole piece 204a, may control an axially-symmetric electric field on the wafer to prevent micro-arcing of the wafer and to ensure proper beam focus at the wafer surface with the axially- symmetric magnetic field together.

[0048] A secondary electron beam 230 may be emitted from the part of wafer 203 upon receiving primary electron beam 220. Secondary electron beam 230 may comprise backscattered electrons, secondary electrons, or Auger electrons, resulting from the interactions of the primary electrons with wafer 203. Secondary electron beam 230 may be received by sensor surfaces of electron detector 206. In some embodiments, electron detector 206 may generate a signal (e.g., a voltage, a current, etc.) that represents an intensity of secondary electron beam 230 and may provide the signal to controller 50 in communication with electron detector 206. The intensity of secondary electron beam 230 may vary according to the external or internal structure of wafer 203, and thus may indicate whether wafer 203 includes defects. Moreover, as discussed above, primary electron beam 220 may be projected onto different locations of the top surface of wafer 203, or different sides of wafer 203 at a particular location, to generate secondary electron beams 230 of different intensities. Therefore, by mapping the intensity of secondary electron beam 230 with the areas of wafer 203, image processing circuitry in controller 50 may reconstruct an image that reflects the characteristics of internal or external structures of wafer 203.

[0049] In some embodiments, controller 50 may comprise image processing system that includes an image acquirer (not shown) and a storage (not shown). The image acquirer may comprise one or more processors. For example, the image acquirer may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, and the like, or a combination thereof. The image acquirer may be communicatively coupled to electron detector 206 of electron beam tool 40 through a medium such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, among others, or a combination thereof. In some embodiments, the image acquirer may receive a signal from electron detector 206 and may construct an image. The image acquirer may thus acquire images of wafer 203. The image acquirer may also perform various post-processing functions, such as generating contours, superimposing indicators on an acquired image, and the like. The image acquirer may be configured to perform adjustments of brightness and contrast, etc. of acquired images. In some embodiments, the storage may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), other types of computer readable memory, and the like. The storage may be coupled with the image acquirer and may be used for saving scanned raw image data as original images, and post-processed images.

[0050] In some embodiments, the image acquirer may acquire one or more images of wafer 203 based on an imaging signal received from detector 206. An imaging signal may correspond to a scanning operation for conducting charged particle imaging. An acquired image may be a single image comprising a plurality of imaging areas. The single image may be stored in the storage. The single image may be an original image that may be divided into a plurality of regions. Each of the regions may comprise one imaging area containing a feature of wafer 203. The acquired images may comprise multiple images of a single imaging area of wafer 203 sampled multiple times over a time sequence. The multiple images may be stored in storage 270. In some embodiments, controller 50 may be configured to perform image processing steps with the multiple images of the same location of wafer 203.

[0051] In some embodiments, controller 50 may include measurement circuitries (e.g., analog-to- digital converters) to obtain a distribution of the detected secondary electrons. The electron distribution data collected during a detection time window, in combination with corresponding scan path data of primary electron beam 220 incident on the wafer surface, can be used to reconstruct images of the wafer structures under inspection. The reconstructed images can be used to reveal various features of the internal or external structures of wafer 203, and thereby can be used to reveal any defects that may exist in the wafer.

[0052] In some embodiments, controller 50 may perform a calibration process of a contactless temperature sensor using a temperature adjustable calibration pad. Controller 50 may further perform a temperature measurement process of a wafer using the calibrated temperature sensor.

[0053] Moreover, although FIG. 2 shows that electron beam tool 40 uses a single primary electron beam, it is appreciated that electron beam tool 40 may also be a multi-beam inspection tool that uses multiple primary electron beams. The present disclosure does not limit the number of primary electron beams used in electron beam tool 40.

[0054] Reference is now made to FIG. 3, which is an exemplary graph showing a wafer temperature change over time for a charged particle beam inspection system. The vertical axis represents temperature change, and the horizontal axis represents passage of time. The graph shows that the wafer temperature changes over time while the wafer is processed through multiple stages of wafer load sequence. At time 330, the wafer is loaded to a load lock chamber. At time 340, the wafer is transported and loaded to wafer stage. At time 345, a wafer inspection begins. At time 350, the wafer inspection ends, and the wafer is unloaded from the wafer stage. During period 320, the wafer stays on the wafer stage.

[0055] According to the exemplary data shown in FIG. 3, when a wafer is loaded to the load lock chamber at time 330, the temperature of the wafer is approximately 22 degrees Celsius (annotated as 312). After the wafer is transported to a load lock chamber, the wafer temperature sharply drops from temperature 312 to temperature 314. Exemplary data show that this temperature drop, which occurs when the load lock chamber is pumped down to a vacuum, may be approximately one to two degrees. This sudden temperature drop is referred to as a pump-down effect.

[0056] Subsequently, when the wafer is transported and loaded onto the wafer stage (e.g., wafer stage 80 of FIG. 1C) at time 340, the wafer temperature (annotated 314) and the wafer stage temperature (not shown, but close to an equilibrium temperature 310) may be at different temperatures. Exemplary data show that this difference may be approximately up to three degrees. [0057] This temperature difference between the wafer and the wafer stage causes wafer temperature drift towards the wafer stage temperature. For example, the graph in FIG. 3 shows that the wafer temperature changes during period 320. Under such circumstances, heat transfer occurs between the wafer and the wafer stage, thereby resulting in a deformation (e.g., a thermal expansion shown in FIG. 1A) of the wafer (or the wafer stage). While the wafer stage or wafer is undergoing a thermal deformation, the inspection of the target area may not be possible or may have a reduced accuracy. Thus, to perform a more accurate inspection, the system waits for a significant period of time (waiting period 325) until the wafer temperature stabilizes at an equilibrium temperature 310 before an inspection can commence at time 345. Therefore, reducing waiting period 325 may improve the throughput of the inspection system. In some embodiments, the wafer may be thermally preconditioned to reduce temperature difference 360, thereby resulting in shorter waiting period 325. [0058] An example of wafer stage for quicker temperature stabilization may be found in European Patent Application No. EP18174642.1, titled PARTICLE BEAM APPARATUS and filed on May 28, 2018, which is incorporated by reference in its entirety. Another way to cope with this long stabilization time is conditioning the wafer temperature by pre-heating or pre-cooling the wafer to match the temperature of the wafer stage before the wafer is loaded onto the wafer stage. Examples of such embodiments may be found in U.S. Patent Application No. 62699643, titled PARTICLE BEAM INSPECTION APPARATUS and filed on July 17, 2018, which is incorporated by reference in its entirety.

[0059] Reference is now made to FIG. 4, which shows an exemplary charged particle beam inspection system 400 with a thermal conditioning station 410, consistent with embodiments of the present disclosure. In some embodiments, inspection system 400 may include thermal conditioning station 410, a main chamber 490, a controller 450, and a heater/cooler 460. Main chamber 490 may include an electron beam tool (not shown; such as electron beam tool 40 of FIG. 2) to obtain images of a wafer 480 (a wafer currently under inspection). While inspection of wafer 480 is in progress, thermal conditioning station 410 may perform a thermal conditioning of a wafer 420 (a wafer in line to be inspected after wafer 480 inspection is completed) to change the temperature of wafer 420 in preparation for the inspection step.

[0060] In some embodiments, thermal conditioning station 410 may include a plurality of supporting structures 425 and a conditioning plate 415 configured to transfer heat to wafer 420. In other embodiments, conditioning plate 415 may be configured to additionally or alternatively transfer heat from wafer 420. Supporting structures 425, coupled to conditioning plate 415, may support wafer 420 such that there is a space between wafer 420 and conditioning plate 415. While it is appreciated that more efficient heat transfer may be achieved as wafer 420 is positioned closer to conditioning plate 415, in some embodiments, it may be desirable to have sufficient distance in between wafer 420 and conditioning plate 415 to provide space for a robot arm to lift or transport wafer 420. In some embodiments, the distance between wafer 420 and conditioning plate 415 may be in a range of 1.5 mm to 10 mm to provide space to accommodate a variety of robot arm sizes in lifting or transporting a wafer. In some embodiments, the distance between wafer 420 and conditioning plate 415 may be in a range of 3 mm to 5 mm to provide space to accommodate a certain type of robot arms while providing more efficient heat transfer, without requiring a special treatment for robot arm transportation. In some embodiments, a special mechanism for lifting wafer 420 may be used, allowing the distance to be narrower.

[0061] Furthermore, even if two supporting structures 425 are shown in FIG. 4, it is appreciated that thermal conditioning station 410 may include any number of supporting structures 425. In some embodiments, wafer 420 may be passively placed on top of supporting structures 425 without any means of active coupling (e.g. electrostatic clamping). In other embodiments, wafer 420 may be held onto supporting structures 425 using an active holding mean, such as electrostatic clamping.

[0062] In some embodiments, a pre-aligner (such as pre-aligner 60 of FIG. 1C) may function as thermal conditioning station 410. In some embodiments, a parking station (such as parking station 70 of FIG. 1C) may function as thermal conditioning station 410.

[0063] In some embodiments, a load lock chamber (such as load lock chamber 20 of FIG. 1C) may function as thermal conditioning station 410. In such embodiments, the load lock chamber (i.e., thermal conditioning station 410) may be configured to change the internal pressure between atmospheric and vacuum. A pump, such as a turbo pump (not shown), may be connected to the load lock chamber to maintain a vacuum level at an appropriate level for conditioning the temperature of wafer 420. It is appreciated that the pump may be a type of pump different from a turbo pump as long as the pump is suitable for establishing a vacuum in the load lock chamber.

[0064] In some embodiments, conditioning plate 415 may include a heat transfer element 440 configured to change the temperature of conditioning plate 415, which in turn affect the temperature of wafer 420. Heat transfer element 440 may be coupled to heater/cooler 460. In some embodiments, heater/cooler 460 may be placed outside of thermal conditioning station 410. In other embodiments, heater/cooler 460 may be placed inside of thermal conditioning station 410.

[0065] Controller 450 may be configured to adjust heater/cooler 460 or heat transfer element 440, via a control signal 434, to change the temperature of conditioning plate 415, which in turn affects the temperature of wafer 420. In some embodiments, controller 450 may perform various analyses based on multiple data inputs (e.g., via communication channels 431, 432, and 433) to adjust a temperature setpoint for the thermal conditioning process, thereby controlling heater/cooler 460 or heat transfer element 440 via control signal 434.

[0066] In some embodiments, controller 450 may receive a stage-temperature data about the temperature of wafer stage 495 in a main chamber 490. For example, controller 450 may receive, via communication channel 431, an electric signal conveying the stage-temperature data from a temperature sensor 496 configured to measure the temperature of wafer stage 495. In such embodiments, controller 450 may adjust the temperature setpoint of thermal conditioning process based on the received stage-temperature data of wafer stage 495 and control heater/cooler 460 to adjust the temperature of conditioning plate 415 according to the adjusted temperature setpoint.

[0067] Controller 450 may additionally or alternatively use information from the electron beam tool to adjust thermal conditioning station 410. Wafer 480 may have already been thermally conditioned in thermal conditioning station 410 before being transported to wafer stage 495 for inspection. Therefore, by obtaining and processing the temperature characteristics of the wafer 480 that has been already thermally preconditioned, controller 450 may determine the effectiveness of thermal conditioning process and reconfigure thermal conditioning station 410 to treat the wafers in pipeline (e.g., wafer 420 and other wafers in FOUPs) more efficiently, thereby improving the overall throughput of charged particle beam inspection system 400. For example, controller 450 may adjust the temperature setpoint of the thermal conditioning process based on the temperature characteristic of wafer 480.

[0068] To determine the temperature characteristic of wafer 480, controller 450 may receive, via communication channel 433, some measured characteristics of wafer 480. These characteristics of wafer 480 may include temperatures determined from contact temperature sensor coupled to a temperature adjustable calibration pad, and an output signal from a contactless temperature sensor. These characteristics of wafer 480 may also include an output signal from a calibrated contactless temperature sensor.

[0069] The temperature characteristic of wafer 480, in some embodiments, may be information about temperature of wafer 480, which may be a temperature of wafer 480 or thermal radiation emitted from wafer 480 The temperature information of wafer 480 may be obtained by direct measurement (e.g., using a contact- or contactless- temperature sensor). As described above, a contact temperature sensor may be more accurate than a contactless temperature sensor. However, a contact temperature sensor may contaminate wafer 480. Furthermore, a contact temperature sensor may require a greater number of wiring in the system, which may decrease a signal-to-noise ratio in collected images of wafer 480, and may malfunction as the contact temperature sensor is connected to the movable wafer stage 495. A contactless temperature sensor may avoid contaminating wafer 480, but a contactless temperature sensor is less accurate than a contact temperature sensor. As described above, a contactless temperature sensor (e.g, an IR temperature sensor) may be calibrated to improve accuracy, but calibration must be done at atmospheric conditions. A calibrated contactless temperature sensor installed into a vacuum chamber (e.g., vacuum chamber 490 in FIG. 4) and pumped down to vacuum may not measure a temperature of wafer 480 according to the calibration under atmospheric conditions. In some embodiments of the present disclosure, a temperature adjustable calibration pad may be installed into a vacuum chamber (e.g., vacuum chamber 490 of FIG. 4) to calibrate a contactless temperature sensor in-vacuum. A contactless temperature sensor may then accurately measure a temperature of wafer 480 in-situ and in-vacuum. In some embodiments, controller 450 may receive one or more temperatures of wafer 480 measured by a calibrated contactless temperature sensor via communication channel 433. This indirect calibration and measurement process is described in further detail with respect to FIGS. 7A-7E and FIG. 8 in the following sections. [0070] In some embodiments, controller 450 may receive a heater-temperature data about the temperature of output of heater/cooler 460 via communication channel 432. In such embodiments, controller 450 may dynamically adjust heater/cooler 460 with control signal 434 based on the feedback information (the received heater-temperature data) to control the temperature of conditioning plate 415. For example, in some embodiments, heater/cooler 460 may be a water heater or water cooler. In such embodiments, heated or cooled water flows through heat transfer elements 440 in conditioning plate 415, and controller 450 may receive the heater-temperature data about the temperature of water at the output of heater/cooler 460. Controller 450 may adjust heater/cooler 460 based on the water temperature. Controller 450 may receive an electric signal conveying the heatertemperature data from a temperature sensor 465 configured to measure the temperature of water, via communication channel 432. In some embodiments, controller 450 may use the received heatertemperature data to adjust the temperature setpoint of the thermal conditioning process.

[0071] In some embodiments, communication channels 431, 432, and 433 and control signal 434 may comprise a medium such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, among others, or a combination thereof. In some embodiments, controller 450 may be further optimized with additional temperature sensors. For example, in some embodiments, system may additionally include one or more sensors configured to measure the temperature of wafer 420, wafer 480, or conditioning plate 415.

[0072] FIG. 5 shows an exemplary graph showing a wafer temperature change over time in a thermal conditioning station (such as thermal conditioning station 410 in FIG. 4), in relation to a temperature setpoint of the thermal conditioning process. The thermal conditioning process begins at time 530. As the heat is transferred to the wafer, the temperature of wafer gradually approaches an equilibrium temperature 510. The thermal conditioning process may continue until time 540, at which the temperature of wafer stabilizes approximately at equilibrium temperature 510. The thermal conditioning station may be controlled by a controller (such as controller 450 of FIG. 4) with a temperature setpoint 520. As shown in FIG. 5, in some embodiments, the controller may drive temperature setpoint 520 to a constant value.

[0073] FIG. 6 shows another exemplary graph showing a wafer temperature change over time during wafer temperature conditioning. Similar to an embodiment in FIG. 5, the thermal conditioning process begins at time 630 and ends at time 640, when the temperature of wafer stabilizes approximately at an equilibrium temperature 610. In this embodiment, the controller may adjust a temperature setpoint 620 dynamically in real-time to reduce the time needed for thermal conditioning. For example, temperature setpoint 620 may be set high initially to quickly change the temperature of wafer, then gradually lowered as the wafer temperature approaches towards equilibrium temperature 610. [0074] Reference is now made to FIGS. 7A and 7B, which are schematic diagrams illustrating an exemplary vacuum chamber 701 including a contactless temperature sensor 702, with a field of view 702_l, and a temperature adjustable calibration pad 703, consistent with embodiments of the present disclosure. FIG. 7A may illustrate a “calibration mode” where temperature adjustable calibration pad 703 is positioned within field of view 702_l of contactless temperature sensor 702. Contactless temperature sensor 702 may be coupled to an interior upper side of vacuum chamber 701 and may be in communication with a controller (e.g., controller 450 of FIG. 4). Temperature adjustable calibration pad 703 may be coupled to a component 704 of vacuum chamber 701. In some embodiments, component 704 may be movable. In some embodiments, component 704 may be rotated about an axis, shifted along an axis, inserted into vacuum chamber 701, or retracted from vacuum chamber 701. Component 704 may be a robot arm (e.g., robot arm 12 of FIG. 1C). Component 704 may carry a wafer 705 into vacuum chamber 701 and load wafer 705 onto a wafer holder 706, which may be placed on top of a Z-stage 707, X-stage 708, and Y-stage 709.

[0075] Reference is now made to FIG. 7B, which may illustrate a “measurement mode.” FIG. 7B illustrates that component 704 may be moved, which may remove temperature adjustable calibration pad 703 from field of view 702_l of contactless temperature sensor 702. It is appreciated that component 704 may be moved such that temperature adjustable calibration pad 703 is within vacuum chamber 701 or removed from vacuum chamber 701 (e.g., in load lock chamber 20 of FIG. 1). Component 704 may be moved by rotation or extraction from vacuum chamber 701. Wafer 705 may be moved to a position within field of view 702_l of contactless temperature sensor 702 for a temperature measurement. In some embodiments, wafer holder 706 may be moved to a position within field of view 702_l of contactless temperature sensor 702 for a temperature measurement before wafer 705 is loaded into vacuum chamber 701. It is appreciated that the representation of temperature adjustable calibration pad 703 and component 704 as shown in FIGS. 7A and 7B are for illustrative purposes. A more detailed representation and description follows below.

[0076] Reference is now made to FIG. 7C, which is an example schematic diagram of a temperature adjustable calibration pad coupled to a component of a vacuum chamber, consistent with embodiments of the present disclosure. FIG. 7C illustrates an upper surface of a temperature adjustable calibration pad 703 may be coupled to a lower surface of component 704 wherein a portion of the upper surface of temperature adjustable calibration pad 703 may be exposed to contactless temperature sensor 702. A temperature adjusting element 710 may be positioned between the upper surface of temperature adjustable calibration pad 703 and the lower surface of component 704. In some embodiments, temperature adjusting element 710 may be an electric temperature adjusting element. An electric temperature adjusting element may apply an electrical signal to change a temperature of temperature adjustable calibration pad 703. The electrical signal may be a voltage or current. In some embodiments, temperature adjusting element 710 may be a thermoelectric temperature adjusting element. Non-limiting examples of a thermoelectric temperature adjusting element may include a Peltier effect material, a Seebeck effect material, a Thomson effect material, or any other material that may reversibly generate a thermal gradient via an electrical signal. In some embodiments, component 704 may serve as a heat sink as component 704 may have a larger thermal mass than temperature adjustable calibration pad 703. A heat sink with a larger thermal mass may enable rapid heat transfer. This may also enable rapid temperature adjustment of temperature adjustable calibration pad 703 over a wide temperature range useful for wafer inspection (e.g., 20- 30 °C). In some embodiments, component 704 may comprise aluminum. A temperature of temperature adjustable calibration pad 703 may be adjusted by applying an electrical signal to temperature adjusting element 710 to transfer heat between component 704 and temperature adjustable calibration pad 703. In some embodiments, the electrical signal applied to temperature adjusting element 710 is a volage or a current.

[0077] The upper surface of temperature adjustable calibration pad 703 may be exposed to contactless temperature sensor 702 wherein temperature adjustable calibration pad 703 is positioned within field of view 702_l of contactless temperature sensor 702. A contact temperature sensor 711 may be coupled to a lower surface of temperature adjustable calibration pad 703. Contact temperature sensor 711 may be in communication with a controller (e.g., controller 450 of FIG. 4). In some embodiments, contact temperature sensor 711 may be a thermocouple.

[0078] Reference is now made to FIG. 7D, which is an example schematic diagram of a top- view of a temperature adjustable calibration pad, consistent with embodiments of the present disclosure. FIG. 7D illustrates temperature adjusting element 710 and contact temperature sensor 711 are coupled to temperature adjustable calibration pad 703. It is appreciated that the dashed line representing temperature adjusting element 710 indicates temperature adjusting element 710 is above temperature adjustable calibration pad 703. It is also appreciated that the dotted line representing contact temperature sensor 711 indicates contact temperature sensor is below temperature adjustable calibration pad 703. In some embodiments, temperature adjusting element 710 may be coupled to an upper surface of temperature adjustable calibration pad 703. In some embodiments, contact temperature sensor 711 may be coupled to a lower surface of temperature adjustable calibration pad 703. It is appreciated that FIG. 7D is a non-limiting schematic diagram of an orientation, shape, and relative positions of temperature adjustable calibration pad 703, temperature adjusting element 710, and contact temperature sensor 711. Other orientations, shapes, and relative positions of the above components may be considered as embodiments of the present disclosure.

[0079] It is appreciated that an upper surface of temperature adjustable calibration pad 703 may be coupled to a lower surface of component 704 in any orientation such that a portion of the upper surface of temperature adjustable calibration pad 703 may be exposed to contactless temperature sensor 702. It is appreciated that temperature adjustable calibration pad 703 may be coupled to the lower surface of component 704 at more than one position. Some embodiments include, and are not limited to, one or more positions where the upper surface of temperature adjustable calibration pad 703 is coupled to component 704. In some embodiments, one or more temperature adjusting elements

710 may be positioned between the one or more positions where the upper surface of temperature adjustable calibration pad 703 is coupled to component 704.

[0080] Reference is now made to FIG. 7E, which is an example schematic diagram of a temperature adjustable calibration pad coupled to a component in a vacuum chamber, consistent with embodiments of the present disclosure. It is appreciated that FIG. 7E illustrates one orientation of a temperature adjustable calibration pad coupled to a component of a vacuum chamber, and other orientations may be considered. FIG. 7E illustrates an upper surface of temperature adjustable calibration pad 703 may be coupled to a lower surface of component 704. It is appreciated that the dotted line portion of temperature adjustable calibration pad 703 represents a portion of the upper surface of temperature adjustable calibration pad 703 that is coupled to, and beneath, the lower surface of component 704. Temperature adjusting element 710 may be positioned between temperature adjustable calibration pad 703 and component 704. Temperature adjusting element 710 may be connected to wiring (not shown) which may be connected to a processor (e.g., controller 450 in FIG. 4). As described above, temperature adjusting element 710 may be positioned between temperature adjustable calibration pad 703 and component 704. It is appreciated that the dashed line representing temperature adjusting element 710 indicates temperature adjusting element 710 is beneath component 704 and above temperature adjustable calibration pad 703. In some embodiments, a portion of temperature adjusting element 710 is positioned between component 704 and temperature adjustable calibration pad 703. As described above, the upper surface of a temperature adjustable calibration pad 703 may be underneath and exposed to field of view 702_l of a contactless temperature sensor 702. Contactless temperature sensor 702 is illustrated as being coupled to an upper interior surface of vacuum chamber 701 (not shown) by a bracket 712. Contact temperature sensor

711 is coupled to a lower surface of temperature adjustable calibration pad 703, as illustrated by the dotted line. It is appreciated that other material shapes and arrangement orientations as illustrated in FIG. 7E may be considered as embodiments of the present disclosure.

[0081] Reference is now made to FIG. 8, which is an example flow diagram illustrating a method 800 of calibrating a contactless temperature sensor and measuring a temperature of a sample, consistent with embodiments of the present disclosure. The method may be performed by a charged particle beam inspection system (e.g., charged particle beam inspection system 400 of FIG. 4) and by a controller (e.g., controller 450 of FIG. 4). It is appreciated that the illustrated method 800 may be altered to modify the order of steps and to include the additional steps.

[0082] Steps 801 to 805 of method 800 may be considered a calibration mode 800_l, and step 806 of method 800 may be considered a measurement mode 800_2. Calibration mode 800_l and measurement mode 800_2 may be performed by system 400 in FIG. 4.

[0083] In step 801, a temperature adjustable calibration pad at a first temperature is positioned within a field of view of a contactless temperature sensor. The temperature adjustable calibration pad (e.g., temperature adjustable calibration pad 703) may be a same material of a material to be inspected. The temperature adjustable pad may be a same material of a component in a vacuum system that may contact a sample to be inspected (e.g., wafer holder 706 in FIGS. 7A and 7B). The temperature adjustable calibration pad may be coupled to a contact temperature sensor (e.g., contact temperature sensor 711 in FIGS. 7C- 7E). The contact temperature sensor may be coupled to a side of the temperature adjustable calibration pad opposite to the contactless temperature sensor.

[0084] In step 802, a first set of measurements of the temperature adjustable calibration pad is collected. The first set of measurements may correspond to a first temperature of the temperature adjustable calibration pad. The first set of measurements may include a measured first temperature of the temperature adjustable calibration pad determined by the contact temperature sensor, and a measured first electrical signal determined by the contactless temperature sensor. The measured first electrical signal may be a voltage or a current.

[0085] In step 803, the temperature adjustable calibration pad is adjusted to a second temperature and step 802 is repeated, but with respect to the second temperature. The temperature adjustable calibration pad may be adjusted to a second temperature by a temperature adjusting element (e.g., temperature adjusting element 710 in FIGS. 7C-7E). A second set of measurements of the temperature adjustable calibration pad may correspond to the second temperature of the temperature adjustable calibration pad. The second set of measurements may be collected and may be as described above.

[0086] In step 804, the temperature adjustable calibration pad is adjusted to a third temperature, and step 802 is repeated, but with respect to the third temperature. A third set of measurements of the temperature adjustable calibration pad may correspond to the third temperature of the temperature adjustable calibration pad. The third set of measurements may be as collected and may be as described above.

[0087] In step 805, a relationship between the first, second, and third sets of measurements is determined. The relationship may be a relationship between a measured temperature and a measured electrical signal for each temperature of the temperature adjustable calibration pad. The relationship may be a linear relationship. The first, second, and third temperature of the temperature adjustable calibration pay may cover a temperature range of a sample during inspection. The temperature range may be from 20 to 30 °C. The determined relationship between the first, second, and third sets of measurements may calibrate the measured electrical signal determined by the contactless-temperature sensor. The measured electrical signal may be correlated to a measured temperature with an accuracy of about 0.01 to 0.1 °C. The measured electrical signal may be correlated to a measured temperature with an accuracy of about 0.01 °C.

[0088] It is appreciated that steps 801-805 (e.g., calibration mode 800_l) may be performed while a sample (e.g., wafer 705 in FIGS. 7A and 7B) is loaded onto a wafer holder (e.g., wafer holder 706 in FIGS. 7A and 7B), before a sample is loaded onto a wafer holder (e.g., coupled to component 704 in FIGS. 7A-7E) or before a sample is loaded into a vacuum chamber (e.g., vacuum chamber 701 in FIGS. 7A and 7B).

[0089] In step 806, a temperature of a sample of interest is determined using the calibrated contactless temperature sensor. A sample of interest may be positioned within a field of view of the contactless temperature sensor and a measured electrical signal is obtained by the contactless temperature sensor. A temperature of the sample is determined from the measured electrical signal. The temperature of the sample may be determined by correlating the measured electrical signal from the calibrated contactless temperature sensor to the relationship between measured electrical signal and measured temperature (e.g., step 805).

[0090] It is appreciated that step 806 (measurement mode 800_2) may be performed to measure a temperature of a sample during inspection to qualify the effectiveness of the sample temperature conditioning sequence as described above and avoid undesirable temperature discrepancies between the sample and the sample holder (e.g., sample holder 706 in FIGS. 7A and 7B) upon contact. A temperature time history may be recorded upon each measurement from step 806 and a temperature variation of a sample during inspection may be determined with an accuracy of about 0.01 - 0.1 °C. [0091] Method 800 may also be performed to calibrate a temperature adjustable calibration pad of a same material of a component in a vacuum system to determine a temperature of a component that may contact a sample to be inspected (e.g., wafer holder 706 in FIGS. 7A and 7B). This may determine a temperature of a component in the vacuum chamber (e.g., wafer holder 706 in FIGS. 7A and 7B) prior to the sample to be inspected is contacted to the component. The measured temperature of the component may be provided to a controller (e.g., controller 450 in FIG. 4) to optimize a thermal condition sequence as described above and avoid an undesirable temperature discrepancy upon contact. The temperature adjustable calibration pad may then be removed from the vacuum chamber as described above and replaced with a temperature adjustable calibration pad of a same material as the sample to be inspected. This way, the vacuum chamber (e.g., vacuum chamber 701 in FIGS. 7A and 7B) may not need to be vented to atmospheric conditions and a desirable throughput may be maintained.

[0092] It is appreciated that a controller of the wafer temperature measurement system could use software to control the functionality described above. For example, the controller may analyze multiple sets of measurements collected by a contactless temperature sensor and a contact temperature sensor and determine a relationship between measured electrical signal and measured temperature. The controller may send instructions to a heater/cooler (such as heater/cooler 460 of FIG. 4) to adjust the temperature of heat transfer elements. The software may be stored on a non-transitory computer readable medium. Common forms of non-transitory media include, for example, a floppy disk, a flexible disk, hard disk, solid state drive, magnetic tape, or any other magnetic data storage medium, a CD-ROM, any other optical data storage medium, any physical medium with patterns of holes, a RAM, a PROM, and EPROM, cloud storage, a FLASH-EPROM or any other flash memory, NVRAM, a cache, a register, any other memory chip or cartridge, and networked versions of the same.

[0093] The embodiments may further be described using the following clauses:

1. An in-vacuum temperature measurement system comprising: a vacuum chamber; a wafer holder located in the vacuum chamber and configured to hold a wafer; a temperature adjustable calibration pad coupled to an internal component of the vacuum chamber; a contactless temperature sensor configured to generate an output signal based on a temperature of the temperature adjustable calibration pad; a contact temperature sensor coupled to the temperature adjustable calibration pad, wherein the contact temperature sensor is configured to determine a temperature of the temperature adjustable calibration pad; and a controller configured to calibrate the contactless temperature sensor based on the output signal from the contactless temperature sensor and the temperature of the temperature adjustable calibration pad determined by the contact temperature sensor.

2. The system of clause 1, wherein the temperature adjustable calibration pad is a same material as a wafer held by the wafer holder.

3. The system of clause 1, wherein the temperature adjustable calibration pad is a same material of a component of the charged particle beam apparatus that is contacted to a sample to be inspected.

4. The system of clause 3, wherein the temperature adjustable calibration pad is a same material as the wafer holder.

5. The system of any one of clauses 1 to 4, further comprising a temperature adjusting element positioned between the temperature adjustable calibration pad and the component of the vacuum chamber.

6. The system of clause 5, wherein the temperature adjusting element is an electric temperature adjusting element.

7. The system of clause 5, wherein the temperature adjusting element is a thermoelectric temperature adjusting element.

8. The system of any one of clauses 1 to 7, wherein the temperature adjustable calibration pad is coupled to a lower surface of the internal component of the vacuum chamber.

9. The system of any one of clauses 1 to 8, wherein the temperature adjustable calibration pad is within a field of view of the contactless temperature sensor.

10. The system of clause 9, wherein an upper surface of the temperature adjustable calibration pad is within a field of view of the contactless temperature sensor. 11. The system of any one of clauses 1 to 10, wherein the contact temperature sensor is coupled to a lower surface of the temperature adjustable calibration pad.

12. The system of any one of clauses 1 to 11, wherein the internal component of the vacuum chamber to which the temperature adjustable calibration pad is coupled is movable.

13. The system of clause 12, wherein the internal component of the vacuum chamber is rotatable.

14. The system of clause 12, wherein the internal component of the vacuum chamber is retractable.

15. The system of any one of clauses 12 to 14, wherein the internal component of the vacuum chamber is configured to move the temperature adjustable calibration pad within a field of view of the contactless temperature sensor.

16. The system of any one of clauses 12 to 14, wherein the internal component of the vacuum chamber is configured to move the temperature adjustable calibration pad outside a field of view of the contactless temperature sensor.

17. The system of any one of clauses 1 to 16, wherein the wafer holder is configured to move within a field of view of the contactless temperature sensor.

18. The system of any one of clauses 1 to 17, wherein the internal component of the vacuum chamber to which the temperature adjustable calibration pad is coupled is configured to load a wafer onto the wafer holder.

19. The system of any one of clauses 1 to 18, wherein the component of the vacuum chamber to which the temperature adjustable calibration pad is coupled is a robot arm.

20. The system of any one of clauses 1 to 19, wherein the contactless temperature sensor is an infrared (IR) sensor.

21. The system of any one of clauses 1 to 20, wherein the output signal of the contactless temperature sensor is an electrical signal.

22. The system of any one of clauses 1 to 21, wherein the electrical signal is a voltage or a current.

23. A method of measuring a temperature of a wafer in vacuum using a charged particle beam apparatus, the method comprising: adjusting a temperature of a temperature adjustable calibration pad to a first temperature; collecting a first set of measurements of the temperature adjustable calibration pad at the first temperature using a contact temperature sensor and a contactless temperature sensor; adjusting a temperature of the temperature adjustable calibration pad to a second temperature; collecting a second set of measurements of the temperature adjustable calibration pad at the second temperature using the contact temperature sensor and the contactless temperature sensor; calibrating the contactless temperature sensor; and determining a temperature of a sample to be inspected using the calibrated contactless temperature sensor.

24. The method of clause 23, wherein the temperature adjustable calibration pad is a same material of the sample be inspected.

25. The method of clause 23, wherein the temperature adjustable calibration pad is a same material of a component of the charged particle beam apparatus that is contacted to a sample to be inspected.

26. The method of any one of clauses 23 to 25, wherein the temperature adjustable calibration pad is coupled to an internal component of the charged particle beam apparatus.

27. The method of clause 26, wherein the internal component of the vacuum chamber is configured to move the temperature adjustable calibration pad within a field of view of the contactless temperature sensor.

28. The method of clause 26, wherein the internal component of the vacuum chamber is configured to move the temperature adjustable calibration pad outside a field of view of the contactless temperature sensor.

29. The method of any one of clauses 26 to 28, wherein a temperature adjusting element is positioned between the temperature adjustable calibration pad and the internal component of the charged particle beam apparatus.

30. The method of clause 29, wherein the temperature adjusting element is an electric temperature adjusting element.

31. The method of clause 29, wherein the temperature adjusting element is a thermoelectric temperature adjusting element.

32. The method of any one of clauses 23 to 31, wherein the contact temperature sensor is coupled to a lower surface of the temperature adjustable calibration pad.

33. The method of any one of clauses 23 to 32, wherein the temperature adjustable calibration pad is positioned within a field of view of the contactless temperature sensor.

34. The method of clause 33, wherein an upper surface of the temperature adjustable calibration pad is positioned within the field of view of the contactless temperature sensor.

35. The method of any one of clauses 23 to 34, wherein the measurements collected by the contact temperature sensor comprise a temperature.

36. The method of any one of clauses 23 to 34, wherein the measurements collected by the contactless temperature sensor comprise an electrical signal.

37. The method of clause 36, wherein the electrical signal is a voltage or a current.

38. The method of any one of clauses 23 to 37, wherein calibrating the contactless temperature sensor comprises: determining a relationship between the measurements of the temperature adjustable calibration pad collected by the contact temperature sensor and the contactless temperature sensor at the first temperature and the second temperature.

39. The method of clause 23, wherein determining a temperature of a sample to be inspected using the calibrated contactless temperature sensor comprises: moving the temperature adjustable calibration pad outside the field of view of the calibrated contactless temperature sensor; moving the sample to be inspected within the field of view of the calibrated contactless temperature sensor; and collecting a measurement of the sample to be inspected using the calibrated contactless temperature sensor.

40. The method of any one of clauses 23 to 39, wherein the sample to be inspected is a wafer.

41. The method of any one of clauses 23 to 40, wherein the contactless temperature sensor is an IR sensor.

42. A charged particle beam apparatus, comprising: a vacuum chamber configured to provide a vacuum environment; a sample holder located in the vacuum chamber and configured to hold a sample; a calibration pad coupled to an internal component of the vacuum chamber; an IR sensor configured to generate an output signal based on a temperature of the calibration pad; a contact temperature sensor coupled to the calibration pad, wherein the contact temperature sensor is configured to measure a temperature of the calibration pad; and a controller configured to calibrate the IR sensor based on the output signal from the IR sensor and the temperature of the calibration pad determined by the contact temperature sensor.

43. The apparatus of clause 42, wherein the calibration pad is a same material of the sample.

44. The apparatus of clause 42, wherein the calibration pad is a same material of a component of the charged particle beam apparatus that is contacted to a sample.

45. The apparatus of clause 44, wherein the calibration pad is a same material as the wafer holder.

46. The apparatus of any one of clauses 42 to 45, further comprising a temperature adjusting element positioned between the calibration pad and the internal component of the vacuum chamber.

47. The apparatus of clause 46, wherein the temperature adjusting element is an electric temperature adjusting element. 48. The apparatus of clause 46, wherein the temperature adjusting element is a thermoelectric temperature adjusting element.

49. The apparatus of any one of clauses 42 to 48, wherein the contact temperature sensor is coupled to a lower surface of the calibration pad.

50. The apparatus of any one of clauses 42 to 49, wherein the calibration pad is coupled to a lower surface of the internal component of the vacuum chamber.

51. The apparatus of any one of clauses 42 to 50, wherein the calibration pad is positioned within a field of view of the IR sensor.

52. The apparatus of clause 51, wherein an upper surface of the calibration pad is positioned within the field of view of the IR sensor.

53. The apparatus of any one of clauses 42 to 52, wherein the contact temperature sensor is coupled to a lower surface of the calibration pad.

54. The apparatus of any one of clauses 42 to 53, wherein the internal component of the vacuum chamber to which the calibration pad is coupled is movable.

55. The apparatus of clause 54, wherein the internal component of the vacuum chamber is rotatable.

56. The apparatus of clause 54, wherein the internal component of the vacuum chamber is retractable.

57. The apparatus of any one of clauses 54 to 56, wherein the internal component of the vacuum chamber is configured to move the calibration pad within a field of view of the IR sensor.

58. The apparatus of any one of clauses 54 to 56, wherein the internal component of the vacuum chamber is configured to move the calibration pad outside a field of view of the IR sensor.

59. The apparatus of any one of clauses 42 to 58, wherein the sample holder is configured to move within a field of view of the IR sensor.

60. The apparatus of any one of clauses 42 to 59, wherein the internal component of the vacuum chamber to which the calibration pad is coupled is configured to load a sample onto the sample holder.

61. The apparatus of any one of clauses 42 to 60, wherein the internal component of the vacuum chamber to which the calibration pad is coupled is a robot arm.

62. The apparatus of any one of clauses 42 to 61, wherein the output signal of the IR sensor is an electrical signal.

63. The apparatus of clause 62, wherein the electrical signal is a voltage or a current.

64. The apparatus of any one of clauses 42 to 63, wherein the sample is a wafer.

65. A non-transitory computer readable medium including a set of instructions that is executable by one or more processors of a controller to cause the controller to perform operations for measuring a temperature of a sample in vacuum using a charged particle beam apparatus, the operations comprising: adjusting a temperature of a temperature adjustable calibration pad to a first temperature; collecting a first set of measurements of the temperature adjustable calibration pad at the first temperature using a contact temperature sensor and a contactless temperature sensor; adjusting a temperature of the temperature adjustable calibration pad to a second temperature; collecting a second set of measurements of the temperature adjustable calibration pad at the second temperature using the contact temperature sensor and the contactless temperature sensor; calibrating the contactless temperature sensor; and measuring a temperature characteristic of a sample to be inspected using the calibrated contactless temperature sensor.

66. The non-transitory computer readable medium of clause 65, wherein the temperature adjustable calibration pad is a same material of the sample be inspected.

67. The non-transitory computer readable medium of clause 65, wherein the temperature adjustable calibration pad is a same material of a component of the charged particle beam apparatus that is contacted to a sample to be inspected.

68. The non-transitory computer readable medium of any one of clauses 65 to 67, wherein the temperature adjustable calibration pad is coupled to an internal component of the charged particle beam apparatus.

69. The non-transitory computer readable medium of clause 68, wherein the internal component of the vacuum chamber is configured to move the temperature adjustable calibration pad within a field of view of the contactless temperature sensor.

70. The non-transitory computer readable medium of clause 68, wherein the internal component of the vacuum chamber is configured to move the temperature adjustable calibration pad outside a field of view of the contactless temperature sensor.

71. The non-transitory computer readable medium of any one of clauses 65 to 70, wherein the measurements collected by the contact temperature sensor comprise a temperature.

72. The non-transitory computer readable medium of any one of clauses 65 to 70, wherein the measurements collected by the contactless temperature sensor comprise an electrical signal.

73. The non-transitory computer readable medium of clause 72, wherein the electrical signal is a voltage or a current.

74. The non-transitory computer readable medium of any one of clauses 65 to 73, wherein the operations further comprise: determining a relationship between the measurements of the temperature adjustable calibration pad collected by the contact temperature sensor and the contactless temperature sensor measured at the first temperature and the second temperature. 75. The non-transitory computer readable medium of clause 65, wherein the operations for determining a temperature of a sample to be inspected using the calibrated contactless temperature sensor comprise: moving the temperature adjustable calibration pad outside the field of view of the calibrated contactless temperature sensor; moving the sample to be inspected within the field of view of the calibrated contactless temperature sensor; and collecting a measurement of the sample to be inspected using the calibrated contactless temperature sensor 76. The non-transitory computer readable medium of any one of clauses 65 to 75, wherein the sample to be inspected is a wafer.

77. The non-transitory computer readable medium of any one of clauses 65 to 76, wherein the contactless temperature sensor is an IR sensor.

[0094] Although the disclosed embodiments have been explained in relation to its preferred embodiments, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the subject matter as hereafter claimed.

Claims

1. An in-vacuum temperature measurement system comprising: a vacuum chamber; a wafer holder located in the vacuum chamber and configured to hold a wafer; a temperature adjustable calibration pad coupled to an internal component of the vacuum chamber; a contactless temperature sensor configured to generate an output signal based on a temperature of the temperature adjustable calibration pad; a contact temperature sensor coupled to the temperature adjustable calibration pad, wherein the contact temperature sensor is configured to determine a temperature of the temperature adjustable calibration pad; and a controller configured to calibrate the contactless temperature sensor based on the output signal from the contactless temperature sensor and the temperature of the temperature adjustable calibration pad determined by the contact temperature sensor.

2. The system of claim 1, wherein the temperature adjustable calibration pad is a same material as a wafer held by the wafer holder.

3. The system of claim 1, wherein the temperature adjustable calibration pad is a same material of a component of the charged particle beam apparatus that is contacted to a sample to be inspected.

4. The system of claim 1, further comprising a temperature adjusting element positioned between the temperature adjustable calibration pad and the component of the vacuum chamber.

5. The system of claim 1, wherein the temperature adjustable calibration pad is coupled to a lower surface of the internal component of the vacuum chamber.

6. The system of claim 1, wherein the temperature adjustable calibration pad is within a field of view of the contactless temperature sensor.

7. The system of claim 6, wherein an upper surface of the temperature adjustable calibration pad is within a field of view of the contactless temperature sensor.

8. The system of claim 1, wherein the contact temperature sensor is coupled to a lower surface of the temperature adjustable calibration pad.

9. The system of claim 1, wherein the internal component of the vacuum chamber to which the temperature adjustable calibration pad is coupled is movable.

10. The system of claim 9, wherein the internal component of the vacuum chamber is configured to move the temperature adjustable calibration pad within a field of view of the contactless temperature sensor.

11. The system of claim 9, wherein the internal component of the vacuum chamber is configured to move the temperature adjustable calibration pad outside a field of view of the contactless temperature sensor.

12. The system of claim 1, wherein the contactless temperature sensor is an infrared (IR) sensor.

13. The system of claim 1, wherein the output signal of the contactless temperature sensor is an electrical signal.

14. A charged particle beam apparatus, comprising: a vacuum chamber configured to provide a vacuum environment; a sample holder located in the vacuum chamber and configured to hold a sample; a calibration pad coupled to an internal component of the vacuum chamber; an IR sensor configured to generate an output signal based on a temperature of the calibration pad; a contact temperature sensor coupled to the calibration pad, wherein the contact temperature sensor is configured to measure a temperature of the calibration pad; and a controller configured to calibrate the IR sensor based on the output signal from the IR sensor and the temperature of the calibration pad determined by the contact temperature sensor.

15. A non- transitory computer readable medium including a set of instructions that is executable by one or more processors of a controller to cause the controller to perform operations for measuring a temperature of a sample in vacuum using a charged particle beam apparatus, the operations comprising: adjusting a temperature of a temperature adjustable calibration pad to a first temperature; collecting a first set of measurements of the temperature adjustable calibration pad at the first temperature using a contact temperature sensor and a contactless temperature sensor; adjusting a temperature of the temperature adjustable calibration pad to a second temperature; collecting a second set of measurements of the temperature adjustable calibration pad at the second temperature using the contact temperature sensor and the contactless temperature sensor; calibrating the contactless temperature sensor; and measuring a temperature characteristic of a sample to be inspected using the calibrated contactless temperature sensor.