Measuring and controlling the working distance from the SEM to the target using a laser beam for SEM-based tools

Abstract

1. A system for processing a sample, the system comprising: a vacuum chamber having a window formed along one wall of the vacuum chamber; a sample support configured to hold the sample within the vacuum chamber during a sample processing step and to move the substrate along X, Y, and Z axes within the vacuum chamber; a charged particle beam column configured to direct a charged particle beam into the vacuum chamber and focus the beam to impinge on a target region on the sample; an optical distance measurement device configured to generate electromagnetic radiation, direct it through the window into the vacuum chamber, detect photons from the electromagnetic radiation reflected from the sample, and determine a working distance between the sample and the charged particle column based on the generated electromagnetic radiation and the detected photons; and one or more mirrors positioned within the vacuum chamber to direct the electromagnetic radiation generated by the optical distance measurement system to a measurement location on the sample proximate the target region, including at least one mirror positioned directly below a portion of the charged particle column.

Description

[Technical Field]

[0001] cross reference

[0001] This application claims priority to U.S. Application No. 18 / 072,451, filed November 30, 2022, the entire contents of which are incorporated herein by reference. [Background technology]

[0002]

[0002] In the study of electronic materials and the processes by which they are fabricated into electronic structures, specimens of the electronic structures may be subjected to microscopic examination for the purposes of failure analysis and device validation. For example, specimens of electronic structures, such as silicon wafers, can be analyzed with a scanning electron microscope (SEM) to examine specific features of the wafer. Such features may include the circuits fabricated and any defects formed during the fabrication process. The electron microscope is one of the most useful instruments for analyzing the microstructure of semiconductor devices.

[0003]

[0003] SEM devices can capture images of areas on a sample by generating a beam of charged particles and irradiating the sample with the beam. The particles emitted by the irradiation can then be detected to generate an SEM image of the area illuminated by the charged particle beam. When acquiring an SEM image, it is important to position the sample at a known working distance from the charged particle column that generates the charged particle beam.

[0004] In some SEM instruments, the working distance between the sample and the charged particle column is measured with a capacitive sensor. This arrangement works very well for conductive samples. However, some semiconductor and other manufacturers build their devices on dielectric samples (e.g., sapphire wafers) that are not conductive. Capacitive sensors cannot easily be used to determine the working distance for such samples.

[0005] Therefore, new and improved methods and systems for determining the working distance between a sample and a charged particle column are desired. Summary of the Invention

[0006]

[0006] Embodiments described herein provide methods and systems for determining the working distance between a sample and a charged particle column that work for both conductive and non-conductive (i.e., dielectric) samples. In some embodiments, a laser and multiple mirrors are used to direct a laser beam generated by the laser to a location on the sample that is in close proximity to the region to be imaged. The laser beam is reflected from the surface of the sample and directed to a detector where interferometric techniques can be used to determine the working distance between the sample and the charged particle column.

[0007]

[0007] While embodiments of the present disclosure can be used to measure the working distance between a charged particle column and many different types of samples, some embodiments are particularly useful when performing measurements on samples that are dielectric or semiconductor wafers or similar specimens.

[0008]

[0008] According to some embodiments, a system for processing a sample is disclosed, the system including: a vacuum chamber having a window formed along one of the walls of the vacuum chamber; a sample support configured to hold the sample within the vacuum chamber during a sample processing step and to move the substrate along the X, Y, and Z axes within the vacuum chamber; a charged particle beam column configured to direct a charged particle beam into the vacuum chamber and focus the beam to impinge on a target area on the sample; an optical distance measurement device configured to generate electromagnetic radiation, direct it into the vacuum chamber through the window, detect photons from the electromagnetic radiation reflected from the sample, and determine a working distance between the sample and the charged particle column based on the generated electromagnetic radiation and the detected photons; and one or more mirrors disposed within the vacuum chamber and positioned to direct the electromagnetic radiation generated by the optical distance measurement system to a measurement location on the sample proximate the target area, including at least one mirror positioned directly below a portion of the charged particle column.

[0009] In some embodiments, a method for processing a sample in a vacuum chamber with a charged particle column is provided. The method can include positioning the sample on a sample support in the vacuum chamber such that a region of interest is directly beneath a tip of the charged particle column, directing electromagnetic radiation to a measurement location on the sample proximate the region of interest and directly beneath a portion of the charged particle column, detecting photons reflected from the measurement location, and determining a working distance between the charged particle column and the sample at the measurement location based on the emitted electromagnetic radiation and the detected photons. The electromagnetic radiation can be generated by a device external to the vacuum chamber and directed to the measurement location through a window in the vacuum chamber by one or more mirrors, at least one of which is positioned directly beneath the portion of the charged particle column.

[0010] In some additional embodiments, a non-transitory computer-readable memory is provided that stores instructions for processing a sample in a vacuum chamber with a charged particle column, the instructions causing the sample to be processed in the vacuum chamber by positioning the sample on a sample support in the vacuum chamber so that a region of interest is directly beneath a tip of the charged particle column, directing electromagnetic radiation to a measurement location on the sample proximate the region of interest and directly beneath a portion of the charged particle column, detecting photons reflected from the measurement location, and determining a working distance between the charged particle column and the sample at the measurement location based on the emitted electromagnetic radiation and the detected photons. The electromagnetic radiation may be generated by a device external to the vacuum chamber and directed to the measurement location through a window in the vacuum chamber by one or more mirrors, at least one of which is positioned directly beneath the portion of the charged particle column.

[0011] Various implementations of the disclosed embodiments may include one or more of the following features: The charged particle column may be a scanning electron microscope (SEM) column, and the charged particle beam may be an electron beam. The optical distance measurement device may be configured to generate and direct a laser beam into the vacuum chamber through a window. The window may be formed in a chamber lid of the vacuum chamber, and the optical distance measurement device may be attached directly to the chamber lid and aligned to project the laser beam through the window. The system for processing a sample may further include one or more processors and computer-readable memories operably coupled to the one or more processors. The one or more computer-readable memories may include instructions that, when executed by the one or more processors, cause the system to adjust a vertical spacing between the charged particle column and the sample based on a difference between the determined working distance and the intended working distance. The optical distance measurement device may determine a working distance between the charged particle column and the sample at the measurement position using an interferometric measurement technique. The one or more mirrors may each include a reflective ceramic material.

[0012]

[0012] For a better understanding of the nature and advantages of the present disclosure, reference should be made to the following description and accompanying drawings. It should be understood, however, that each figure is provided for illustrative purposes only and is not intended as a definition of the limits of the scope of the present disclosure. Also, as a general rule, and unless clearly inconsistent with the description, when elements in different figures use the same reference numerals, the elements are generally identical, or at least similar in function or purpose. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a simplified diagram of a sample evaluation system including a scanning electron microscope (SEM) column. [Figure 2] 1 is a simplified diagram of an evaluation chamber according to some embodiments. [Figure 3] FIG. 1 is a simplified schematic diagram of an optical distance measuring device that can be used with embodiments described herein. [Figure 4] 1 is a simplified diagram of an evaluation chamber according to some embodiments. [Figure 5] 1 is a simplified diagram of an evaluation chamber according to some embodiments. [Figure 6] 1 is a simplified diagram of an evaluation chamber according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0014]

[0019] The embodiments described herein provide methods and systems for determining the working distance between a sample and a charged particle column that work for both conductive and non-conductive (i.e., dielectric) samples. In some embodiments, a laser and one or more mirrors are used to direct a laser beam generated by the laser to a location on the sample that is very close to the area to be imaged (i.e., the area scanned by the charged particle beam). Photons from the laser beam are then reflected from the surface of the sample and directed to a detector where interferometric techniques can be used to determine the working distance between the sample and the charged particle column. While embodiments of the present disclosure can be used to measure the working distance between a charged particle column and many different types of samples, some embodiments are particularly useful when performing measurements on samples that are dielectric or semiconductor wafers or similar specimens.

[0015]

[0020] As used herein, the "working distance" between the charged particle column and the sample is the distance between the electrode of the lens arrangement closest to the plane of the sample (i.e., the cap electrode in some of the examples below) and the plane of the sample.

[0016] Sample assessment tool example

[0021] To better understand and appreciate the present disclosure, reference is first made to Figure 1, which is a simplified schematic diagram of a conventionally known sample evaluation system 100. The sample evaluation system 100 can be used for defect review and analysis of structures formed on a sample, such as a semiconductor wafer, among other processes.

[0017]

[0022] The system 100 may include a vacuum chamber 110 along with a scanning electron microscope (SEM) column 120. A support element 140 may support a sample 150 (e.g., a semiconductor wafer) within the chamber 110 during a processing step in which the sample 150 (which may also be referred to herein as an "object" or "specimen") is subjected to a charged particle beam 126 from the SEM column.

[0018]

[0023] The SEM column 120 is connected to the vacuum chamber 110 so that a charged particle beam generated by the column propagates through a vacuum environment created within the vacuum chamber 110 before impinging on the sample 150. The SEM column 120 can generate an image of a portion of the sample 150 by irradiating the sample with the charged particle beam 125, detecting particles emitted by the irradiation, and generating a charged particle image based on the detected particles. To this end, the SEM column 120 can include an electron beam source 122 (i.e., an "electron gun"), an anode tube 126 that defines an electron beam drift space, a condenser lens arrangement 124, one or more deflection lenses, such as lenses 130, 132, one or more focusing lenses 134, and a column cap 136.

[0019]

[0024] During the imaging process, electron beam source 122 generates electron beam 125, which passes through condenser lens 124 and is first focused by condenser lens 124, then focused by lens 134, before impinging on sample 150. Condenser lens 124 defines the aperture and current of the electron beam (along with the final aperture), which directly relates to the resolution, and focusing lens 134 focuses the beam onto the sample. Column cap 136, located between the bottom end of anode tube 126 (first electrode) and sample 150 (second electrode), can be a third electrode in the system that adjusts the electric field formed in the vicinity of the wafer.

[0020]

[0025] 1 shows an SEM column 120 producing a charged particle beam 125 that is generally perpendicular to a sample 150 when the beam strikes the sample. In various embodiments, the SEM column 120 can be operated in a tilted mode, where the charged particle beam 125 strikes the sample 150 at a non-perpendicular angle, for example, a 45 degree angle.

[0021]

[0026] In both normal and tilt modes, the particle imaging process typically involves scanning a charged particle beam back and forth (e.g., in a raster or other scan pattern) across a specific portion of the sample to be imaged. The deflection lenses 130, 132 may be magnetic, electrostatic, or a combination of both electric and magnetic lenses to implement scan patterns known to those skilled in the art. The scanned portion is typically a small portion of the sample's total area. For example, the sample may be a 200 mm or 300 mm diameter semiconductor wafer, and each scanned portion on the wafer may be a rectangular portion with a width and / or length measured in microns or tens of microns.

[0022]

[0027] The SEM column 120 can also include one or more detectors for detecting charged particles emanating from the sample during the imaging process. For example, the SEM column 120 can include an in-lens detector 128 and a top detector 138, which can be configured to detect secondary and backscattered electrons emitted as a result of the sample being irradiated with the charged particle beam 126. The in-lens detector 128 can include a central hole that allows the charged particle beam 126 to pass through the detector and allows both secondary and backscattered electrons incident on the charged particle column 120 to pass through the detector 128 and reach the top detector 138. In some embodiments, the sample evaluation system 120 can also include an external detector that can be configured to detect secondary and backscattered electrons or that can be configured to detect x-rays, such as an x-ray spectroscopy (EDX) detector.

[0023]

[0028] During operation of system 100, sample support 140 (also referred to herein as a "stage") can move the sample so that different portions (e.g., different regions of interest or "ROIs") are positioned directly beneath the field of view of SEM column 120. Sample support 140 can move sample 150 left and right and front and back (i.e., along both the X and Y axes) within chamber 110, and can also raise and lower sample 150 to move the sample along the Z axis.

[0024]

[0029] Because many features formed on the sample 150 have micron-sized or smaller dimensions, it is important to accurately know the location of the sample relative to the focal point of the SEM column 120. To accurately determine the position of the sample 150, some embodiments can use a stage-accurate navigation, interferometry system 160. The system 160 is attached to the lid 112 of the chamber 110 and can direct collimated light (e.g., a laser beam) through a window 114 formed in the lid to target sites on the sample support 140 that are encoded with various linear or other marks. The system can detect (e.g., using an array of photodetectors) the light from the collimated light pulse after it reflects off the encoded target sites on the sample support 140 and returns to the system 160. A processor (e.g., a digital signal processor) within the system 160 can then analyze the detected optical signals to determine a highly accurate position of the sample along the X and Y axes.

[0025]

[0030] Additionally, system 100 may include a voltage supply 165 and one or more controllers 170, such as a processor or other hardware unit. The voltage supply 165 may be operated to provide a desired effective voltage for the column, thereby improving image resolution. This may be achieved by appropriately distributing the voltage supply between the first and second electrodes (i.e., between the anode tube and the sample). The controller(s) 170 may control system operation, including the voltage supply, by executing computer instructions stored in one or more computer-readable memories 180, as is well known to those skilled in the art. By way of example, the computer-readable memory may include solid-state memory (such as random-access memory (RAM) and / or read-only memory (ROM) that may be programmable, flash-updateable, etc.), a disk drive, an optical storage device, or similar non-transitory computer-readable storage medium.

[0026]

[0031] The system 100 may further include a user interface 190 that may allow one or more users to interact with the system. For example, the user interface 190 may allow a user to set parameters of an SEM column or detector that may be used when analyzing a sample. The user interface 190 may include any known device or devices that allow a user to input information to interact with a computer system, such as a keyboard, mouse, monitor, touch screen, touch pad, voice-activated input controller, etc.

[0027] Continuous height measurement

[0032] When an SEM device such as system 100 is used to image or otherwise evaluate a sample, it can be important to know precisely the working distance between the tip of the column and the sample, and it is also important that the working distance be maintained at a consistent distance even when different regions of the sample that are relatively far apart are evaluated.

[0028]

[0033] As mentioned above, some SEM systems use capacitive distance measurement systems to detect the working distance and provide feedback that can be used to appropriately adjust the height of the substrate support to maintain the desired working distance. However, capacitive sensors cannot easily be used to determine the working distance of dielectric (non-conductive) samples.

[0029]

[0034] In some cases, it can be important to measure the working distance very close to where the charged particle beam focuses on the sample. For example, although a 200 mm or 300 mm wafer appears very flat to the naked eye, such wafers typically exhibit some degree of bowing, sometimes exceeding 200 microns. Therefore, when using an SEM instrument to image or otherwise characterize areas at different locations on the wafer, the working distances at the different areas may differ slightly from each other unless the height of the sample support or SEM column is adjusted. Even a few microns of deviation in the actual working distance from the expected working distance can adversely affect imaging.

[0030]

[0035] The embodiments disclosed herein provide systems and methods for measuring working distance in real time that work with both conductive and non-conductive samples. Furthermore, the embodiments can measure the working distance directly beneath a portion of the charged particle column, very close to the focal point of the charged particle beam. For example, in some embodiments, the working distance can be measured within 20 mm, 10 mm, or 5 mm of the focal point of the charged particle beam. Measuring the working distance in such close proximity to the actual area being imaged or otherwise evaluated by the charged particle beam allows a characterization system, such as system 100, to adjust the height of the stage and / or the tip of the charged particle column to control and set the working distance to a desired distance.

[0031] SEM equipment equipped with an optical distance measurement device on the chamber lid

[0036] FIG. 2 is a simplified schematic diagram of an SEM apparatus 200 according to some embodiments. The SEM apparatus 200 can perform various functions described above with respect to the system 100, and can implement many of the same elements that, for simplicity, will not be further described in conjunction with FIG. 2 . As shown in FIG. 2 , the SEM apparatus 200 can include, among other elements, a vacuum chamber 210, a scanning electron microscope column 220, and a sample support 240. The sample support 240 can support a sample 250 and move the sample along the X, Y, and Z axes below the SEM column 220, and a precision stage navigation, interferometry system (not shown) tracks the position of the substrate support 240 and sample 250 along the X and Y axes. The SEM column 220 can generate a charged particle beam 225 (e.g., an electron beam) and direct the beam to impinge on a region of interest on the top surface of the sample 250.

[0032]

[0037] The SEM apparatus 200 can also include an optical distance measurement device 260 that can measure a working distance along the Z-axis between the column tip 236 of the SEM column 220 and the sample 250. In some embodiments, the optical distance measurement device 260 can measure the working distance in real time, for example, while the sample 250 is being moved from a first position where a first region of interest on the sample 250 is imaged to a second position where the SEM apparatus 200 images a second region of interest on the sample. As shown, the optical distance measurement device 260 can be positioned outside the chamber 210 and generate a collimated light beam 262 (e.g., a laser beam) and direct it into the vacuum chamber through the window 214. A series of mirrors 264, 266 can then redirect the laser beam 262 so that it contacts and reflects off the top surface of the sample 250 at a position (which may be referred to herein as the “measurement position”) directly below a portion of the charged particle column 220 and in close proximity to where the charged particle beam 225 focuses on the sample. As shown, each mirror 264, 266 changes the path of the laser beam (and the reflected beam) by 90 degrees, directing laser beam 262 to strike sample 250 at an angle perpendicular to the sample's top surface. With this configuration, reflected beam 268 travels generally the same path as laser beam 262 in reverse, reflecting back through window 214 to optical distance measurement device 260.

[0033]

[0038] In the illustrated embodiment, optical distance measurement device 260 is located on and directly attached to chamber cover 212. The chamber cover is electrically grounded, kept at or near room temperature, and can be a very heavy component, weighing over 100 kg, and in some embodiments, over 200 kg. SEM column 220 can also be directly attached to chamber cover 212. In this way, any vibrations in the fabrication facility that are transferred to SEM column 220 (and therefore to charged particle beam 222) are equally transferred to optical distance measurement device 260 (and laser beam 262) and can therefore be canceled out.

[0034]

[0039] As shown in FIG. 2 , the charged particle column 220 is quite large and may obstruct a direct line of sight between the laser beam 262 introduced into the chamber 210 from a position above the chamber lid 212 and the target area. The embodiments described herein can use a series of mirrors to direct the laser beam 262 to a spot on the sample 250 near where the charged particle beam 225 focuses on the sample 250. For example, the SEM apparatus 200 uses mirrors 264 and 266 to direct the laser beam 262 from an initial position where the beam is outside the periphery of the charged particle column 220 to a “measurement position” directly below a portion of the charged particle column and very close to the target area on the sample 250 being imaged. In some embodiments, “very close” means 40 mm or less, 20 mm or less, 10 mm or less, or 5 mm or less. Directing the laser beam 262 to a measurement position very close to the target area minimizes the effects of any potential warping of the sample 250.

[0035]

[0040] As shown, mirrors 264 and 266 are each positioned within chamber 210 relatively close to charged particle beam 225, which may be highly sensitive to magnetic fields. To prevent mirrors 264, 266 from adversely affecting the trajectory of charged particle beam 225, the mirrors may be made of a non-conductive and non-magnetic material. In some embodiments, mirrors 264, 266 are made of a reflective ceramic material, and in some embodiments, mirrors 264, 266 may include a ceramic reflective surface held in place by an aluminum holder.

[0036]

[0041] After mirrors 264, 266 direct laser beam 262 into contact with sample 250, some of the photons of laser beam 262 reflect back through mirror 266 and then 264 to optical distance measurement device 260, as shown by reflected beam 268. System 260 can then compare emitted laser beam 262 and reflected beam 268 and use known phase interferometry techniques to determine the vertical position (with respect to the Z axis) of the top surface of sample 240 in the measured area, which system 260 can then use to calculate the working distance between SEM column 220 and the area of ​​interest on sample 240. The optical distance measurement device 260 continuously projects or pulses a laser beam 262, continuously measures the reflected photons 268 directed at the spot, and samples the phase difference between the two at very high speeds, thereby measuring distance in real time and adjusting the vertical height of the sample 240 in real time to maintain a constant working distance as multiple regions of interest are imaged or otherwise sampled across the surface of the sample 250.

[0037]

[0042] In some embodiments, the optical radiation beam 262 emitted by the ODMD 260 can include two laser beams of different wavelengths combined into a single beam. The reflected beam 268 can also include reflections from each of the different wavelengths. Such a configuration can be beneficial in overcoming "dead spots" or other potential problems that can lead to signal loss when imaging transparent samples.

[0038]

[0043] Note that Figure 2 is not drawn to scale. Rather, Figure 2 is a schematic diagram of the SEM apparatus 200. Thus, although the beam 262 is shown as being approximately half a radius of the sample away from the location where the charged particle beam 225 contacts the sample 240, in some embodiments, the beam 262 is directed much closer to the focal point of the charged particle beam 225 than is shown. For example, in some embodiments, the distance between the location where the charged particle beam 225 and the laser beam 262 contact the sample 250 may be less than 20 mm, less than 10 mm, or less than 5 mm, and the sample 250 may be a 200 mm or 300 mm wafer.

[0039]

[0044] 3 is a simplified schematic diagram of one embodiment of an optical distance measurement device 300 (which may be referred to herein for short as "ODMD 300") according to some embodiments. Optical distance measurement device 300 may represent optical distance measurement device 260 described above with respect to FIG. 2. It is important to note that ODMD 300 is merely one non-limiting example of an optical distance measurement device that may be used as optical distance measurement device 260. The embodiments disclosed herein are not limited to any particular type of optical measurement device, and other suitable types of optical measurement devices may be used in place of ODMD 300, as may be determined by one of ordinary skill in the art based on this disclosure.

[0040]

[0045] As shown, ODMD 300 includes an emitter 310 and a detector 320. Emitter 310 may be an LED or a laser, such as a vertical cavity surface emitting laser (VCSEL) or edge emitting laser (EEL), that generates a beam of optical radiation 312. In some embodiments, one or more lenses 314 may shape beam 312, for example, by collimating the beam, before the beam is reflected by mirror 332 and beam splitter 334 through window 214 into a sample processing chamber, such as vacuum chamber 210.

[0041]

[0046] Photons from reflected beam 312 from an object (e.g., sample 240) may return to ODMD 300 as represented by reflected beam 322 and be detected by detector 320 (e.g., an array of photodiodes). A processor (not shown) may then calculate the distance to the object from the photons of beam 322 based on the interference between beam 312 and reflected beam 322 using optical interferometry techniques known to those skilled in the art.

[0042] SEM equipment equipped with an optical distance measurement device on the chamber sidewall

[0047] 4 is a simplified schematic diagram of an SEM apparatus 400 according to some additional embodiments. SEM apparatus 400 is similar in many respects to SEM apparatus 200, and like reference numerals are used to represent substantially similar elements that, for brevity, are not further described in conjunction with FIG. 4. As shown, SEM apparatus 400 includes an optical distance measurement device (ODMD) 460 mounted on a sidewall 416 of chamber 210. ODMD 460 is configured to direct a light beam 462 (e.g., a laser beam) into chamber 210 through a window 414 formed along sidewall 416.

[0043]

[0048] The location of ODMD 460 on the sidewall of chamber 210 allows laser beam 462 to be directed to a measurement location on sample 250 with a single mirror 466. Similarly, single mirror 466 can be directed to reflect beam 462 back to ODMD 460 so that an optical measurement device can determine the working distance between SEM column 220 and sample 250 as described above.

[0044]

[0049] 5 is a simplified schematic diagram of an SEM apparatus 500 according to some additional embodiments. SEM apparatus 500 is similar in many respects to SEM apparatus 200 and 400, and like reference numerals are used to denote substantially similar elements that, for brevity, are not further described in conjunction with FIG. 5. As shown, SEM apparatus 500 includes an optical distance measurement device (ODMD) 560 mounted to a sidewall 516 of chamber 210. Similar to ODMD 460, ODMD 560 is configured to direct a light beam 462 (e.g., a laser beam) into chamber 210 through window 514.

[0045]

[0050] However, ODMD 560 is positioned on a sidewall of chamber 210 at a lower vertical height than sample 250. Thus, three separate mirrors 564, 566, 568 can be used to direct laser beam 562 to a measurement location on sample 250, as shown. Similarly, the same series of three mirrors 564, 566, 568 directs a reflection of beam 562 back to ODMD 560, allowing the optical measurement device to determine the working distance between SEM column 220 and sample 250, as described above.

[0046]

[0051] For each of ODMD 460 and ODMD 560, the "measurement location" is directly beneath a portion of charged particle column 220 and in close proximity to where charged particle beam 225 is focused onto sample 250, as described above with respect to the optical path associated with optical distance measurement device 260. Furthermore, the depicted mirrors 466, 562, 564, and 566 may each be made from a non-conductive and non-magnetic material. In some embodiments, the mirrors may be made from a reflective ceramic material, and in some embodiments, mirrors 466, 562, 564, and 566 may include a ceramic reflective surface held in place by an aluminum holder.

[0047] SEM equipment equipped with a magnetic shield

[0052] In some embodiments, the SEM device may include a magnetic shield that surrounds the tip of the SEM column. Figure 6 is a simplified schematic diagram of some such embodiments of an SEM device 600. The SEM device 600 is similar to the SEM device 200, except that the SEM device 600 includes a magnetic shield 610 that completely surrounds the periphery of the tip 236 of the SEM column 220.

[0048]

[0053] The magnetic shield 610 is made of a material that blocks magnetic fields that may arise from materials or objects outside the chamber 210, preventing such magnetic fields from adversely affecting the trajectory of the charged particle beam 225. The magnetic shield is positioned between the optical distance measurement device 260 and the measurement location. To allow the laser beam 262 to reach the measurement location, an embodiment includes a channel 612 that extends linearly through the magnetic shield 610. As shown, the channel 612 also provides a return path for the reflected beam 268 to reach the optical distance measurement device 260.

[0049]

[0054] In some embodiments, the channel 612 may have a circular cross-section and may be formed, for example, by drilling a hole through the width of the magnetic shield, however, embodiments are not limited to any particular cross-sectional shape for the channel 612, and in other embodiments, the channel 612 may have a rectangular, square, oval, or other cross-sectional shape.

[0050]

[0055] While FIG. 6 illustrates SEM apparatus 600 with the addition of a magnetic shield to SEM apparatus 200, in other embodiments, similar magnetic shields can be included in SEM apparatus 400 and 500 described above with respect to FIGS. 4 and 5, respectively.

[0051] Example of sample to be imaged

[0056] As described above, embodiments of the present disclosure can be used to accurately set the working distance between the SEM column and the sample being imaged to a desired distance. Embodiments can be used to measure and adjust the working distance when imaging many different types of samples, including electronic circuits formed on semiconductor structures, solar cells formed on polycrystalline or other substrates, nanostructures formed on various substrates, etc.

[0052] Additional Embodiments

[0057] In the preceding description, for purposes of explanation, specific nomenclature was used to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that specific details are not required to practice the described embodiments. For example, while the above examples describe optical distance measurement devices that use optical interferometry techniques to determine the measured working distance, other embodiments may include optical distance measurement devices that use other suitable techniques, such as detecting the time-of-flight of a reflected radiation beam. As another example, while the systems described above included a scanning electron microscope as the charged particle column, in other embodiments, the charged particle column may be a focused ion beam column, and in still other embodiments, the system may include both an SEM column and a FIB column as part of an SEM / FIB tool.

[0053]

[0058] Moreover, while various embodiments of the present disclosure have been disclosed above, the specific details of particular embodiments can be combined in any suitable manner without departing from the spirit and scope of the embodiments of the present disclosure. Moreover, many modifications and variations will be apparent to those skilled in the art in light of the above teachings. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and variations that fall within the true spirit of the embodiments of the present disclosure.

[0054]

[0059] Furthermore, while the exemplary embodiments of the present disclosure may, for the most part, be implemented using electronic components and circuits known to those skilled in the art, such details have not been described beyond the extent deemed necessary for an understanding and appreciation of the concepts underlying the present disclosure and in order not to obscure or deviate from the teachings of the present disclosure, as exemplified above.

[0055]

[0060] Furthermore, any reference in the specification to a method should apply mutatis mutandis to a system capable of carrying out the method, and should apply mutatis mutandis to a computer program product storing instructions that, once executed, result in the performance of the method. Similarly, any reference in the specification to a system should apply mutatis mutandis to a method that may be performed by the system, and should apply mutatis mutandis to a computer program product storing instructions that may be executed by the system. Also, any reference in the specification to a computer program product should apply mutatis mutandis to a method that may be performed when executing instructions stored in the computer program product, and should apply mutatis mutandis to a system configured to execute instructions stored in the computer program product.

Claims

1. 1. A system for processing a sample, comprising: a vacuum chamber having a window formed along one of the walls of the vacuum chamber; a sample support configured to hold a sample within the vacuum chamber during sample processing steps and to move the substrate along X, Y, and Z axes within the vacuum chamber; a charged particle beam column configured to direct a charged particle beam into the vacuum chamber and focus the beam to impinge on a region of interest on a sample; an optical distance measurement device configured to generate and direct electromagnetic radiation into the vacuum chamber through the window, detect photons from the electromagnetic radiation reflected from the sample, and determine a working distance between the sample and the charged particle column based on the generated electromagnetic radiation and the detected photons; one or more mirrors disposed within the vacuum chamber and positioned to direct the electromagnetic radiation generated by the optical distance measurement device to a measurement location on the sample proximate the region of interest, including at least one mirror positioned directly below a portion of the charged particle column; A system for processing a sample, comprising:

2. 2. The system for processing a sample of claim 1, wherein the charged particle column is a scanning electron microscope (SEM) column and the charged particle beam is an electron beam.

3. 2. The system for processing a sample of claim 1, wherein the optical distance measurement device is configured to generate and direct a laser beam through the window into the vacuum chamber.

4. 4. The system for processing a sample as described in claim 3, wherein the window is formed in a chamber lid of the vacuum chamber, and the optical distance measuring device is mounted directly to the chamber lid and aligned to project the laser beam through the window.

5. 5. The system for processing a sample according to claim 1, further comprising one or more processors and a computer-readable memory operably coupled to the one or more processors, the computer-readable memory comprising instructions that, when executed by the one or more processors, cause the system to adjust the vertical spacing between the charged particle column and the sample based on a difference between the determined working distance and an intended working distance.

6. The system for processing a sample according to claim 1 , wherein the optical distance measurement device uses an interferometric measurement technique to determine a working distance between the charged particle column and the sample at the measurement position.

7. The system for processing a sample of claim 1 , wherein the one or more mirrors each comprise a reflective ceramic material.

8. 1. A method for processing a sample in a vacuum chamber equipped with a charged particle column, comprising: positioning the sample on a sample support in the vacuum chamber such that a region of interest is directly beneath a tip of the charged particle column; directing electromagnetic radiation to a measurement location on the sample proximate the region of interest and directly beneath a portion of the charged particle column; detecting photons reflected from the measurement location; determining a working distance between the charged particle column and the sample at the measurement location based on the emitted electromagnetic radiation and the detected photons; Including, The method of claim 1, wherein the electromagnetic radiation is generated by a device external to the vacuum chamber and directed to the measurement location through a window in the vacuum chamber by one or more mirrors, at least one of which is positioned directly beneath a portion of the charged particle column.

9. The method of claim 8 , further comprising adjusting the vertical spacing between the charged particle column and the sample based on a difference between the determined working distance and an intended working distance.

10. The method of claim 8 , further comprising imaging the region of interest by scanning a charged particle beam produced by the charged particle column across the region of interest.

11. The method of claim 8 , wherein the electromagnetic radiation is in the visible spectrum or the infrared spectrum.

12. The method of claim 8 , wherein the device generating the electromagnetic radiation uses an interferometric measurement technique to determine a working distance between the charged particle column and the sample at the measurement position.

13. The method of claim 12 , wherein the electromagnetic radiation generated by the device is in the form of a laser beam.

14. The method of claim 8 , wherein the measurement location is within 20 mm of the region of interest.

15. The method of claim 8 , wherein the measurement location is within 10 mm of the region of interest.

16. 16. The method of any one of claims 8 to 15, wherein the sample is a non-conductive wafer.

17. 1. A non-transitory computer-readable memory, comprising: positioning the sample on a sample support in a vacuum chamber such that the region of interest is directly under the tip of the charged particle column; directing electromagnetic radiation to a measurement location on the sample proximate to the region of interest and directly beneath a portion of the charged particle column; detecting photons reflected from the measurement location; determining a working distance between the charged particle column and the sample at the measurement location based on the emitted electromagnetic radiation and the detected photons; storing instructions for processing a sample in a vacuum chamber with a charged particle column by the electromagnetic radiation is generated by a device external to the vacuum chamber and directed to the measurement location through a window in the vacuum chamber by one or more mirrors, at least one of which is positioned directly below a portion of the charged particle column.

18. 20. The non-transitory computer-readable memory of claim 17, wherein the instructions for processing a sample in a vacuum chamber with the charged particle column further comprise instructions for adjusting a vertical spacing between the charged particle column and the sample based on a difference between the determined working distance and an intended working distance.

19. 20. The non-transitory computer-readable memory of claim 17, wherein the instructions for processing a sample in a vacuum chamber with a charged particle column further comprise instructions for imaging the region of interest by scanning a charged particle beam produced by the charged particle column across the region of interest.

20. 20. The non-transitory computer-readable memory of claim 17, wherein the device that generates the electromagnetic radiation uses an interferometric measurement technique to determine a working distance between the charged particle column and the sample at the measurement position, and the electromagnetic radiation generated by the device is in the form of a laser beam.

Images