BEAM POSITION DISPLACEMENT CORRECTION IN CHARGED PARTICLE INSPECTION

An improved method and system for correcting inspection image error are disclosed. An improved method comprises acquiring a set of first beam positions on a test wafer while a wafer stage supporting the test wafer moves at a first velocity; acquiring a set of second beam positions, corresponding to the set of first beam positions, on the test wafer while the wafer stage moves at a second velocity; calculating a beam position displacement of a beam while the wafer stage moves at a third velocity in a range of velocities from the first velocity to the second velocity; and adjusting a beam position of the beam based on the calculated beam position displacement.

TECHNICAL FIELD

The embodiments provided herein relate to an image enhancement technology, and more particularly to a beam position displacement calibration or correction for charged particle inspection.

BACKGROUND

In manufacturing processes of integrated circuits (ICs), unfinished or finished circuit components are inspected to ensure that they are manufactured according to design and are free of defects. Inspection systems utilizing optical microscopes or charged particle (e.g., electron) beam microscopes, such as a scanning electron microscope (SEM) can be employed. As the physical sizes of IC components continue to shrink, accuracy and yield in defect detection become more important. Inspection images such as SEM images can be used to identify or classify a defect(s) of the manufactured ICs. To improve defect detection performance, obtaining an accurate SEM image without distortion nor deformation is desired.

SUMMARY

The embodiments provided herein disclose a particle beam inspection apparatus, and more particularly, an inspection apparatus using a plurality of charged particle beams.

Some embodiments provide a method for correcting inspection image error. The method comprises acquiring a set of first beam positions on a test wafer while a wafer stage supporting the test wafer moves at a first velocity; acquiring a set of second beam positions, corresponding to the set of first beam positions, on the test wafer while the wafer stage moves at a second velocity; calculating a beam position displacement of a beam while the wafer stage moves at a third velocity in a range of velocities from the first velocity to the second velocity; and adjusting a beam position of the beam based on the calculated beam position displacement.

Some embodiments provide an apparatus for correcting inspection image error. The apparatus comprises: a memory storing a set of instructions, and at least one processor configured to execute the set of instructions to cause the apparatus to perform: acquiring a set of first beam positions on a test wafer while a wafer stage supporting the test wafer moves at a first velocity; acquiring a set of second beam positions, corresponding to the set of first beam positions, on the test wafer while the wafer stage moves at a second velocity; calculating a beam position displacement of a beam while the wafer stage moves at a third velocity in a range of velocities from the first velocity to the second velocity; and adjusting a beam position of the beam based on the calculated beam position displacement.

DETAILED DESCRIPTION

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. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the disclosed embodiments as recited in the appended claims. For example, although some embodiments are described in the context of utilizing electron beams, the disclosure is not so limited. Other types of charged particle beams may be similarly applied. Furthermore, other imaging systems may be used, such as optical imaging, photo detection, x-ray detection, etc.

Electronic devices are constructed of circuits formed on a piece of semiconductor material called a substrate. The semiconductor material may include, for example, silicon, gallium arsenide, indium phosphide, or silicon germanium, or the like. Many circuits may be formed together on the same piece of silicon and are called integrated circuits or ICs. The size of these circuits has decreased dramatically so that many more of them can be fit on the substrate. For example, an IC chip in a smartphone can be as small as a thumbnail and yet may include over 2 billion transistors, the size of each transistor being less than 1/1000th the size of a human hair.

Making these ICs with extremely small structures or components is a complex, time-consuming, and expensive process, often involving hundreds of individual steps. Errors in even one step have the potential to result in defects in the finished IC, rendering it useless. Thus, one goal of the manufacturing process is to avoid such defects to maximize the number of functional ICs made in the process; that is, to improve the overall yield of the process.

One component of improving yield is monitoring the chip-making process to ensure that it is producing a sufficient number of functional integrated circuits. One way to monitor the process is to inspect the chip circuit structures at various stages of their formation. Inspection can be carried out using a scanning charged-particle microscope (SCPM). For example, an SCPM may be a scanning electron microscope (SEM). A SCPM can be used to image these extremely small structures, in effect, taking a “picture” of the structures of the wafer. The image can be used to determine if the structure was formed properly in the proper location. If the structure is defective, then the process can be adjusted, so the defect is less likely to recur.

As the physical sizes of IC components continue to shrink, accuracy and yield in defect detection become more important. Inspection images such as SEM images can be used to identify or classify a defect(s) of the manufactured ICs. To improve defect detection performance, obtaining an accurate SEM image without distortion nor deformation is desired. A system magnetic field is formed around or in a SEM tool during operation, and thus when a wafer stage including conductor(s) moves in the system magnetic field, eddy currents may be induced in the conductors. By the induced eddy currents, a magnetic field that disturbs the system magnetic field of the SEM tool can be generated. Such magnetic field disturbances may cause displacements of charged particle beams on a sample from targeted positions, which in turn may degrade image quality of resulting SEM images. In an effort to avoid eddy currents from being generated, a wafer stage with an eddy current suppression design has been developed. For example, a non-conductive plate with conductive coating can be utilized as a wafer holder of a wafer stage. However, such alternative design is usually pricy to manufacture and requires frequent maintenance. Moreover, a wafer holder including a conductive material coating may exacerbate arcing effects when conducting a high voltage inspection of a wafer.

Embodiments of the disclosure may provide a beam position displacement compensation or correction technique for SEM inspection. According to some embodiments of the present disclosure, eddy current effects can be offset. According to some embodiments of the present disclosure, a wafer stage having conductor(s) can still be utilized while suppressing or minimizing eddy current effects. According to some embodiments of the present disclosure, a beam position displacement from a target position can be corrected. According to some embodiments of the present disclosure, effects of a disturbance magnetic field can be offset. Embodiments of the disclosure may provide a beam position displacement compensation or correction method or system based on a linear relationship between a movement velocity of a conductor and eddy current density induced in the conductor.

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 component may include A or B, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or A and B. As a second example, if it is stated that a component may include A, B, or C, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

FIG.1illustrates an example electron beam inspection (EBI) system100consistent with embodiments of the present disclosure. EBI system100may be used for imaging. As shown inFIG.1, EBI system100includes a main chamber101, a load/lock chamber102, a beam tool104, and an equipment front end module (EFEM)106. Beam tool104is located within main chamber101. EFEM106includes a first loading port106aand a second loading port106b.EFEM106may include additional loading port(s). First loading port106aand second loading port106breceive 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 may be used interchangeably). A “lot” is a plurality of wafers that may be loaded for processing as a batch.

One or more robotic arms (not shown) in EFEM106may transport the wafers to load/lock chamber102. Load/lock chamber102is connected to a load/lock vacuum pump system (not shown) which removes gas molecules in load/lock chamber102to reach a first pressure below the atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) may transport the wafer from load/lock chamber102to main chamber101. Main chamber101is connected to a main chamber vacuum pump system (not shown) which removes gas molecules in main chamber101to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subject to inspection by beam tool104. Beam tool104may be a single-beam system or a multi-beam system.

A controller109is electronically connected to beam tool104. Controller109may be a computer configured to execute various controls of EBI system100. While controller109is shown inFIG.1as being outside of the structure that includes main chamber101, load/lock chamber102, and EFEM106, it is appreciated that controller109may be a part of the structure.

In some embodiments, controller109may include one or more processors (not shown). A processor may be a generic or specific electronic device capable of manipulating or processing information. For example, the processor may include any combination of any number of a central processing unit (or “CPU”), a graphics processing unit (or “GPU”), an optical processor, a programmable logic controllers, a microcontroller, a microprocessor, a digital signal processor, an intellectual property (IP) core, a Programmable Logic Array (PLA), a Programmable Array Logic (PAL), a Generic Array Logic (GAL), a Complex Programmable Logic Device (CPLD), a Field-Programmable Gate Array (FPGA), a System On Chip (SoC), an Application-Specific Integrated Circuit (ASIC), and any type circuit capable of data processing. The processor may also be a virtual processor that includes one or more processors distributed across multiple machines or devices coupled via a network.

In some embodiments, controller109may further include one or more memories (not shown). A memory may be a generic or specific electronic device capable of storing codes and data accessible by the processor (e.g., via a bus). For example, the memory may include any combination of any number of a random-access memory (RAM), a read-only memory (ROM), an optical disc, a magnetic disk, a hard drive, a solid-state drive, a flash drive, a security digital (SD) card, a memory stick, a compact flash (CF) card, or any type of storage device. The codes and data may include an operating system (OS) and one or more application programs (or “apps”) for specific tasks. The memory may also be a virtual memory that includes one or more memories distributed across multiple machines or devices coupled via a network.

FIG.2illustrates a schematic diagram of an example multi-beam tool104(also referred to herein as apparatus104) and an image processing system290that may be configured for use in EBI system100(FIG.1), consistent with embodiments of the present disclosure.

Beam tool104comprises a charged-particle source202, a gun aperture204, a condenser lens206, a primary charged-particle beam210emitted from charged-particle source202, a source conversion unit212, a plurality of beamlets214,216, and218of primary charged-particle beam210, a primary projection optical system220, a motorized wafer stage280, a wafer holder282, multiple secondary charged-particle beams236,238, and240, a secondary optical system242, and a charged-particle detection device244. Primary projection optical system220can comprise a beam separator222, a deflection scanning unit226, and an objective lens228. Charged-particle detection device244can comprise detection sub-regions246,248, and250.

Charged-particle source202, gun aperture204, condenser lens206, source conversion unit212, beam separator222, deflection scanning unit226, and objective lens228can be aligned with a primary optical axis260of apparatus104. Secondary optical system242and charged-particle detection device244can be aligned with a secondary optical axis252of apparatus104.

Charged-particle source202can emit one or more charged particles, such as electrons, protons, ions, muons, or any other particle carrying electric charges. In some embodiments, charged-particle source202may be an electron source. For example, charged-particle source202may include a cathode, an extractor, or an anode, wherein primary electrons can be emitted from the cathode and extracted or accelerated to form primary charged-particle beam210(in this case, a primary electron beam) with a crossover (virtual or real)208. For ease of explanation without causing ambiguity, electrons are used as examples in some of the descriptions herein. However, it should be noted that any charged particle may be used in any embodiment of this disclosure, not limited to electrons. Primary charged-particle beam210can be visualized as being emitted from crossover208. Gun aperture204can block off peripheral charged particles of primary charged-particle beam210to reduce Coulomb effect. The Coulomb effect may cause an increase in size of probe spots.

Source conversion unit212can comprise an array of image-forming elements and an array of beam-limit apertures. The array of image-forming elements can comprise an array of micro-deflectors or micro-lenses. The array of image-forming elements can form a plurality of parallel images (virtual or real) of crossover208with a plurality of beamlets214,216, and218of primary charged-particle beam210. The array of beam-limit apertures can limit the plurality of beamlets214,216, and218. While three beamlets214,216, and218are shown inFIG.2, embodiments of the present disclosure are not so limited. For example, in some embodiments, the apparatus104may be configured to generate a first number of beamlets. In some embodiments, the first number of beamlets may be in a range from 1 to 1000. In some embodiments, the first number of beamlets may be in a range from 200-500. In an exemplary embodiment, an apparatus104may generate 400 beamlets.

Condenser lens206can focus primary charged-particle beam210. The electric currents of beamlets214,216, and218downstream of source conversion unit212can be varied by adjusting the focusing power of condenser lens206or by changing the radial sizes of the corresponding beam-limit apertures within the array of beam-limit apertures. Objective lens228can focus beamlets214,216, and218onto a wafer230for imaging, and can form a plurality of probe spots270,272, and274on a surface of wafer230.

Beam separator222can be a beam separator of Wien filter type generating an electrostatic dipole field and a magnetic dipole field. In some embodiments, if they are applied, the force exerted by the electrostatic dipole field on a charged particle (e.g., an electron) of beamlets214,216, and218can be substantially equal in magnitude and opposite in a direction to the force exerted on the charged particle by magnetic dipole field. Beamlets214,216, and218can, therefore, pass straight through beam separator222with zero deflection angle. However, the total dispersion of beamlets214,216, and218generated by beam separator222can also be non-zero. Beam separator222can separate secondary charged-particle beams236,238, and240from beamlets214,216, and218and direct secondary charged-particle beams236,238, and240towards secondary optical system242.

Deflection scanning unit226can deflect beamlets214,216, and218to scan probe spots270,272, and274over a surface area of wafer230. In response to the incidence of beamlets214,216, and218at probe spots270,272, and274, secondary charged-particle beams236,238, and240may be emitted from wafer230. Secondary charged-particle beams236,238, and240may comprise charged particles (e.g., electrons) with a distribution of energies. For example, secondary charged-particle beams236,238, and240may be secondary electron beams including secondary electrons (energies≤50 eV) and backscattered electrons (energies between 50 eV and landing energies of beamlets214,216, and218). Secondary optical system242can focus secondary charged-particle beams236,238, and240onto detection sub-regions246,248, and250of charged-particle detection device244. Detection sub-regions246,248, and250may be configured to detect corresponding secondary charged-particle beams236,238, and240and generate corresponding signals (e.g., voltage, current, or the like) used to reconstruct an SCPM image of structures on or underneath the surface area of wafer230.

The generated signals may represent intensities of secondary charged-particle beams236,238, and240and may be provided to image processing system290that is in communication with charged-particle detection device244, primary projection optical system220, and motorized wafer stage280. The movement speed of motorized wafer stage280may be synchronized and coordinated with the beam deflections controlled by deflection scanning unit226, such that the movement of the scan probe spots (e.g., scan probe spots270,272, and274) may orderly cover regions of interests on the wafer230. The parameters of such synchronization and coordination may be adjusted to adapt to different materials of wafer230. For example, different materials of wafer230may have different resistance-capacitance characteristics that may cause different signal sensitivities to the movement of the scan probe spots.

The intensity of secondary charged-particle beams236,238, and240may vary according to the external or internal structure of wafer230, and thus may indicate whether wafer230includes defects. Moreover, as discussed above, beamlets214,216, and218may be projected onto different locations of the top surface of wafer230, or different sides of local structures of wafer230, to generate secondary charged-particle beams236,238, and240that may have different intensities. Therefore, by mapping the intensity of secondary charged-particle beams236,238, and240with the areas of wafer230, image processing system290may reconstruct an image that reflects the characteristics of internal or external structures of wafer230.

In some embodiments, image processing system290may include an image acquirer292, a storage294, and a controller296. Image acquirer292may comprise one or more processors. For example, image acquirer292may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, or the like, or a combination thereof. Image acquirer292may be communicatively coupled to charged-particle detection device244of beam tool104through a medium such as an electric conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, or a combination thereof. In some embodiments, image acquirer292may receive a signal from charged-particle detection device244and may construct an image. Image acquirer292may thus acquire SCPM images of wafer230. Image acquirer292may also perform various post-processing functions, such as generating contours, superimposing indicators on an acquired image, or the like. Image acquirer292may be configured to perform adjustments of brightness and contrast of acquired images. In some embodiments, storage294may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), other types of computer-readable memory, or the like. Storage294may be coupled with image acquirer292and may be used for saving scanned raw image data as original images, and post-processed images. Image acquirer292and storage294may be connected to controller296. In some embodiments, image acquirer292, storage294, and controller296may be integrated together as one control unit.

In some embodiments, image acquirer292may acquire one or more SCPM images of a wafer based on an imaging signal received from charged-particle detection device244. 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 storage294. 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 wafer230. The acquired images may comprise multiple images of a single imaging area of wafer230sampled multiple times over a time sequence. The multiple images may be stored in storage294. In some embodiments, image processing system290may be configured to perform image processing steps with the multiple images of the same location of wafer230.

In some embodiments, image processing system290may include measurement circuits (e.g., analog-to-digital converters) to obtain a distribution of the detected secondary charged particles (e.g., secondary electrons). The charged-particle distribution data collected during a detection time window, in combination with corresponding scan path data of beamlets214,216, and218incident 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 wafer230, and thereby can be used to reveal any defects that may exist in the wafer.

In some embodiments, the charged particles may be electrons. When electrons of primary charged-particle beam210are projected onto a surface of wafer230(e.g., probe spots270,272, and274), the electrons of primary charged-particle beam210may penetrate the surface of wafer230for a certain depth, interacting with particles of wafer230. Some electrons of primary charged-particle beam210may elastically interact with (e.g., in the form of elastic scattering or collision) the materials of wafer230and may be reflected or recoiled out of the surface of wafer230. An elastic interaction conserves the total kinetic energies of the bodies (e.g., electrons of primary charged-particle beam210) of the interaction, in which the kinetic energy of the interacting bodies does not convert to other forms of energy (e.g., heat, electromagnetic energy, or the like). Such reflected electrons generated from elastic interaction may be referred to as backscattered electrons (BSEs). Some electrons of primary charged-particle beam210may inelastically interact with (e.g., in the form of inelastic scattering or collision) the materials of wafer230. An inelastic interaction does not conserve the total kinetic energies of the bodies of the interaction, in which some or all of the kinetic energy of the interacting bodies convert to other forms of energy. For example, through the inelastic interaction, the kinetic energy of some electrons of primary charged-particle beam210may cause electron excitation and transition of atoms of the materials. Such inelastic interaction may also generate electrons exiting the surface of wafer230, which may be referred to as secondary electrons (SEs). Yield or emission rates of BSEs and SEs depend on, e.g., the material under inspection and the landing energy of the electrons of primary charged-particle beam210landing on the surface of the material, among others. The energy of the electrons of primary charged-particle beam210may be imparted in part by its acceleration voltage (e.g., the acceleration voltage between the anode and cathode of charged-particle source202inFIG.2). The quantity of BSEs and SEs may be more or fewer (or even the same) than the injected electrons of primary charged-particle beam210.

The images generated by SEM may be used for defect inspection. For example, a generated image capturing a test device region of a wafer may be compared with a reference image capturing the same test device region. The reference image may be predetermined (e.g., by simulation) and include no known defect. If a difference between the generated image and the reference image exceeds a tolerance level, a potential defect may be identified. For another example, the SEM may scan multiple regions of the wafer, each region including a test device region designed as the same, and generate multiple images capturing those test device regions as manufactured. The multiple images may be compared with each other. If a difference between the multiple images exceeds a tolerance level, a potential defect may be identified.

FIG.3illustrates a magnetic field generation system of an inspection apparatus, consistent with embodiments of the present disclosure. A magnetic field generation system300ofFIG.3may be a part of EBI system100ofFIG.1or electron beam tool104ofFIG.2. In some embodiments, magnetic field generation system300can generate a system magnetic field of EBI system100ofFIG.1or electron beam tool104during operation. As shown inFIG.3, magnetic field generation system300can include an objective lens (e.g., objective lens228ofFIG.2), and objective lens228can include a pole piece228a,an exciting coil228b,and a control electrode228c.In some embodiments, objective lens228can be a modified SORIL lens. In a detection or imaging process, a beam (e.g., beamlet216) can be focused into a probe spot (e.g., probe spot272) by objective lens228and impinge onto the surface of wafer230. As discussed, probe spot272may be scanned across the surface of wafer230by a deflection scanning unit, such as deflection scanning unit226or other deflectors in the SORIL lens. WhileFIG.3illustrates only one beam216, it will be appreciated that multiple beams can simultaneously scan the surface of wafer230as shown inFIG.2.

In some embodiments, magnetic field generation system300including objective lens228may be configured to generate a magnetic field around or in beam tool104during operation.FIG.4Aillustrates a static magnetic field generated by magnetic field generation system300ofFIG.3, consistent with some embodiments of the present disclosure. As shown inFIG.4A, at least part of a motorized stage280and wafer holder282may be positioned in a magnetic field of a beam tool. In this disclosure, a motorized stage280and wafer holder282can be collectively referred to as a wafer stage.

When a conductor moves in a magnetic field, eddy currents may be induced in the conductor according to Faraday's law of induction. Eddy currents flow in closed loops within a conductor. In some embodiments in which a conductor(s) is included in a wafer stage, eddy currents can be induced in the conductor during operation of a beam tool as motorized stage280moves for scanning a wafer. In some embodiments, a wafer stage can be implemented to include a conductor(s). For example, wafer holder282can be made of a conductive material(s) such as aluminum, titanium, etc. When wafer holder282is a conductor, eddy currents may be induced in wafer holder282as wafer holder282moves in a magnetic field generated by magnetic field generation system300of a beam tool.

FIG.4Billustrates eddy currents in a conductor resulting from movement of a wafer stage, consistent with embodiments of the present disclosure. InFIG.4B, it is assumed that wafer holder282is a conductor for illustration purposes. InFIG.4B, current density J A/m2 is defined by a contrast bar at the bottom. In this example, a first current density J1is lower than a second current density J2, which in turn is lower than a third current density J3. InFIG.4B, eddy current density induced in wafer holder282is indicated in wafer holder282when wafer holder282made of titanium moves at a speed 400 mm/s. As shown inFIG.4B, eddy current density is not uniform across wafer holder282. For example, eddy current density may vary depending on a location on wafer holder282.

In turn, the induced eddy currents in wafer holder282can generate a magnetic field that disturbs beam tool's magnetic field generated by magnetic field generation system300.FIG.4Cillustrates a disturbance magnetic field caused by eddy currents in a conductor, consistent with embodiments of the present disclosure. InFIG.4C, an X-axis indicates a distance from the left end of a wafer (e.g., wafer230) held by wafer holder282to the right end of the wafer, and a Y-axis indicates a magnitude of a disturbance magnetic field on the wafer caused by eddy currents in wafer holder282. As shown inFIG.4C, a disturbance magnetic field caused by eddy currents in moving wafer holder282exerts an influence on a point of interest on a wafer and thus disturbs a system magnetic field of a beam tool, for example, generated by magnetic field generation system300.

However, an inspection apparatus (e.g., EBI system100ofFIG.1or electron beam tool104) is susceptible to such magnetic field disturbances. For example, such disturbance magnetic field can cause a beam displacement from a target beam position on a wafer when scanning the wafer, which in turn leads to image quality degradation. In order to prevent eddy currents from being induced, a wafer stage with an eddy current suppression design has been utilized. An eddy current suppression design may include a non-conductive wafer holder instead of a conductive wafer holder. In this case, a non-conductive plate can be coated with a conductive material to be used as a wafer holder, e.g., for surface charge suppression. For example, chromium coated ceramic is used as a wafer holder. However, such alternative design is usually pricy to manufacture due to materials used for coating (e.g., chromium) or a non-conductive material (e.g., ceramic). Further, such coating requires frequent maintenance.

In addition to the cost and cumbersome reasons, using a non-conductive plate coated with a conductive material as a wafer holder may exacerbate arcing issues when conducting a high voltage inspection of a wafer. Arcing can occur on conductive coating when inspecting a wafer with a high voltage, and the arcing can cause particles of the coating to make a breakaway. Particles left from the coating may contaminate an inspection as well as a wafer, and thereby worsen the arcing effects. Embodiments of the present disclosure may provide methods or systems to offset eddy current effects while utilizing a wafer stage including conductor(s), e.g., a conductor wafer holder.

FIG.5is a block diagram of a beam displacement compensation system, consistent with embodiments of the present disclosure. In some embodiments, a beam displacement compensation system500comprises one or more processors and memories. It is appreciated that in various embodiments beam displacement compensation system500may be part of or may be separate from a charged-particle beam inspection system (e.g., EBI system100ofFIG.1). In some embodiments, beam displacement compensation system500may include one or more components (e.g., software modules) that can be implemented in controller109or system290as discussed herein. As shown inFIG.5, beam displacement compensation system500may comprise a first beam position acquirer510, a second beam position acquirer520, a beam displacement calculator530, and beam displacement calibrator540.

According to some embodiments of the present disclosure, first beam position acquirer510can acquire a first beam position on a test wafer while a wafer stage supporting the test wafer moves at a first velocity. In some embodiments, a first beam position on a test wafer can be measured from a first inspection image acquired while a wafer stage moves at a first velocity V1. While velocity can represent both a speed at a wafer stage moves and a direction of the wafer stage's movement in this disclosure, it will be appreciated that velocity can also be used to refer to a speed in some embodiments. In some embodiments, an inspection image is a SEM image of a sample or a wafer. In some embodiments, an inspection image can be an inspection image generated by, e.g., EBI system100ofFIG.1or electron beam tool104ofFIG.2. In some embodiments, an inspection image can be obtained from a storage device or system storing the inspection image.

According to some embodiments of the present disclosure, a first inspection image can be acquired when a wafer stage is stationary, i.e., a first velocity V1is zero. In some embodiments, a first inspection image can be acquired when a disturbance magnetic field, e.g., caused by eddy currents in a moving conductor does not exist.FIG.6Aillustrates an example first inspection image610, consistent with some embodiments of the present disclosure. InFIG.6A, a position on a test wafer can be represented by x and y coordinates where a center of the test wafer is represented as (0,0).FIG.6Ashows a first beam611positioned at a center of first inspection image610, which indicates first beam611impinges on a test wafer at a center of the test wafer. While first beam611positioned at the wafer center is described, it will be appreciated that first beam611can be positioned on any part of a wafer.

In some embodiments, a wafer having known patterns at corresponding locations on the wafer can be used as a test wafer. In some embodiments, a beam position on a wafer can be determined by matching a pattern of an SEM image taken by a first beam with a corresponding pattern on the wafer and by identifying a location of the corresponding pattern on the wafer. In some embodiments, a reference image of a test wafer can be utilized to determine patterns of a test wafer and corresponding locations of the patterns on the test wafer. In some embodiments, a reference image can be a golden image or a layout file for a wafer design corresponding to a test wafer. The layout file can be in a Graphic Database System (GDS) format, Graphic Database System II (GDS II) format, an Open Artwork System Interchange Standard (OASIS) format, a Caltech Intermediate Format (CIF), etc. The wafer design may include patterns or structures for inclusion on the wafer. The patterns or structures can be mask patterns used to transfer features from the photolithography masks or reticles to a wafer. In some embodiments, a layout in GDS or OASIS format, among others, may comprise feature information stored in a binary file format representing planar geometric shapes, text, and other information related to the wafer design. In some embodiments, a reference image can be an image rendered from the layout file.

Referring back toFIG.5, according to some embodiments of the present disclosure, second beam position acquirer520can acquire a second beam position on a test wafer while a wafer stage supporting the test wafer moves at a second velocity. In some embodiments, a second beam position on the test wafer can be measured from a second inspection image acquired while a wafer stage moves at a second velocity V2. In some embodiments, a second inspection image is a SEM image of a sample or a wafer. In some embodiments, a second inspection image can be an inspection image generated by, e.g., EBI system100ofFIG.1or electron beam tool104ofFIG.2. In some embodiments, a second inspection image can be obtained from a storage device or system storing the second inspection image.

According to some embodiments of the present disclosure, a second inspection image can be acquired when a wafer stage moves at a second velocity that is different from a first velocity. In some embodiments, a second velocity can be set as a maximum velocity of a wafer stage of a beam tool. In some embodiments, a second inspection image can be acquired when a disturbance magnetic field, e.g., caused by eddy currents in a moving conductor exists. In some embodiments, a second inspection image can be acquired under a same inspection condition as the first inspection image except that a wafer stage moves at a different velocity. In some embodiments, an inspection condition includes, but is not limited to, a beam deflection degree, a system magnetic field, an operation voltage, a beam current, a target beam position on a wafer, etc.FIG.6Billustrates an example second inspection image620and a second beam621, consistent with some embodiments of the present disclosure. It is assumed that a target beam position of second beam621is the same as first beam611, i.e., the wafer center (0,0) as shown inFIG.6Ain that second inspection image620is acquired under the same condition as first inspection image610except the wafer stage's movement.FIG.6Bshows second beam621positioned at a position (xd, yd) on second inspection image620, which is displaced from the target beam position, i.e., the wafer center (0, 0).

Referring back toFIG.5, beam displacement calculator530can calculate a beam position displacement of a beam when inspecting a wafer while a wafer stage moves at a third velocity in a range of velocities from a first velocity to a second velocity. While some embodiments will be explained by assuming a first velocity is zero, it will be appreciated that the present disclosure can also be applied to some embodiments in which a first velocity is non-zero.

In some embodiments where a third velocity is equal to a second velocity, a beam position displacement of a beam can be equal to a beam position displacement of a second beam with respect to a first beam. As shown inFIG.6C, which illustrates a beam position displacement between first beam611and second beam621, second beam621is displaced from first beam611by displacement D2. In some embodiments, a beam position displacement can be measured in an X-Y plane. As shown inFIG.6C, a position of second beam621is deviated from a position of first beam611by distance xdin an X-direction and distance ydin a Y-direction. In some embodiments, displacement D2can represent a displacement scalar quantity or both a displacement scalar quantity and a direction of the displacement. In some embodiments, a beam position displacement of a second beam with respect to a first beam can also be measured in a z-direction. In some embodiments, a beam position displacement in a z-direction can be measured by a focal point displacement of a second beam from a focal point of a first beam. For example, while a focal point of a first beam may be placed on a surface of a wafer that is a target for inspection, a focal point of a second beam may be placed on a plane lower or higher than the wafer surface in a z-direction. In some embodiments, a focal point of a beam can be determined based on a degree of inspection image blurring. In some embodiments, a focal point of a beam can be determined based on a size of a beam spot on an inspection image. While some embodiments will be explained for a position displacement in an X-Y plane, it will be appreciated that the present disclosure can be applied to some embodiments where a beam position is displaced in a z-direction.

In some embodiments where a third velocity is greater than a first velocity and less than a second velocity, a beam position displacement of a beam can be calculated based on a beam displacement of a second beam. In some embodiments, displacement D2of second beam621can be understood to result from a disturbance magnetic field caused by eddy currents in a moving conductor as first inspection image610and second inspection image620are obtained under the inspection conditions but wafer stage's velocity. Since eddy current density in a moving conductor has a linear relationship with a velocity of the moving conductor, a beam position displacement can be determined based on the velocity of the moving conductor. As described referring toFIG.4B, since eddy current density is not uniform in a moving conductor and thus a disturbance magnetic field varies depending on an X-Y location of a wafer, a beam position displacement can further be determined based on an X-Y position of a beam on a wafer.

FIG.7illustrates an example beam displacement table, consistent with some embodiments of the present disclosure. InFIG.7, a displacement table700lists positions P1to Pnon a wafer in a first row. In some embodiments, positions P1to Pnon a wafer can be a beam position on a X-Y plane of a wafer. For example, position (0, 0) of first beam611in first inspection image610can be a first position P1. Positions P2to Pncan be positions on a wafer other than first position P1. In some embodiments, positions P1to Pncan be target positions of beams on a wafer. While acquiring a beam position displacement of second beam621from first beam611targeting at one position (e.g., first position P1) has been illustrated, it will be appreciated that the present disclosure can also be utilized to acquire multiple beam position displacements of second beam621from first beam611targeting at multiple positions (e.g., positions P2to Pn) on a wafer.

InFIG.7, displacement table700further lists a velocity V2in a first column. In some embodiments, velocity V2inFIG.7can be a maximum velocity of a wafer stage of a beam tool. InFIG.7, displacement values D21to D2nin a second row can be beam position displacements of a second beam with respect to a first beam. For example, a beam position displacement (e.g., by distance xdin an X-direction and distance ydin a Y-direction) of second beam621from first beam611can be a first displacement D21. Similarly, beam position displacements of second beams with respect to corresponding first beams on different positions P2to Pnon a wafer can be beam position displacements D22to D2n.

According to some embodiments where a third velocity is greater than a first velocity and less than a second velocity, a beam position displacement of a beam can be calculated based on a beam location on a wafer and the first to third velocities. In some embodiments, a beam position displacement of a beam can be calculated based on beam displacement table700. As described, eddy currents generated in a conductor are proportional to a velocity of the conductor, and thus a beam displacement caused by eddy currents also has a linear relationship with a velocity. In some embodiments, a beam position displacement of a beam for inspecting a wafer while a wafer stage moves at a third velocity V3can be calculated by a ratio of third velocity V3to second velocity V2. For example, a beam position displacement D31of a third beam targeting at first position P1while a wafer stage moves at third velocity V3can be determined by multiplying first beam displacement of second beam621targeting at first position P1by a ratio V3/V2, i.e., D31=D21*V3/V2. Similarly, beam position displacements D32to D3nof a third beam targeting at positions P2to Pncan be determined based on a ratio V3/V2and corresponding beam displacements D22to D2nof a second beam.

Referring back toFIG.5, beam displacement calibrator540can adjust a beam position on a wafer for inspecting a wafer while a wafer stage moves at a third velocity. In some embodiments, beam displacement calibrator540can adjust a beam position based on a beam displacement for a beam determined by beam displacement calculator530.

In some embodiments, beam displacement calibrator540can adjust a beam position to offset a beam position displacement of a beam. In some embodiments, beam displacement calibrator540can generate a control signal to offset a beam position displacement of a beam. For example, beam displacement calibrator540can generate a control signal to adjust an operational parameter(s) of a deflection scanning unit, e.g., deflection scanning unit226ofFIG.2. In some embodiments, the control signal to offset the beam displacement can be sent to a driver for a deflection scanning unit. In some embodiments in which a beam position is displaced in a Z-direction, beam displacement calibrator540can generate a control signal to offset a beam position displacement in a Z-direction. For example, beam displacement calibrator540can generate a control signal to adjust a height of a wafer, and the control signal can be sent to a wafer stage controller.

According to some embodiments, a beam displacement of a beam may be caused by a disturbance magnetic field, e.g., induced by movement of a wafer stage at a third velocity. In some embodiments, beam displacement calibrator540can adjust a system magnetic field of beam tool104to offset the disturbance magnetic field. For example, beam displacement calibrator540can generate a control signal to adjust an operational parameter(s) of an objective lens, e.g., objective lens228ofFIG.2andFIG.3to cancel or minimize the disturbance magnetic field. In some embodiments, the control signal to offset effects of the disturbance magnetic field can be sent to a driver for an objective lens.

In some embodiments, beam displacement calibrator540can generate a control signal to adjust an operational parameter(s) of any components of an inspection apparatus (e.g., EBI system100ofFIG.1or electron beam tool104ofFIG.2) to compensate a beam displacement of a beam or to offset disturbance magnetic fields. For example, beam displacement calibrator540can generate a control signal to adjust an operation voltage, a beam current, a magnetic field generation current, etc. In some embodiments, beam displacement calibrator540can generate a control signal to adjust an operation parameter of an external apparatus other than an inspection apparatus (e.g., EBI system100ofFIG.1or electron beam tool104ofFIG.2) to compensate a beam displacement of a beam or to offset disturbance magnetic fields. For example, an external apparatus can be utilized to cancel disturbance magnetic fields or to offset beam displacements.

FIG.8is a process flowchart representing an exemplary beam displacement compensation method, consistent with embodiments of the present disclosure. The steps of method800can be performed by a system (e.g., system500ofFIG.5) executing on or otherwise using the features of a computing device, e.g., controller109ofFIG.1. It is appreciated that the illustrated method800can be altered to modify the order of steps and to include additional steps.

In step S810, a first beam position can be acquired. Step S810can be performed by, for example, first beam position acquirer510, among others. According to some embodiments of the present disclosure, a first beam position on a test wafer can be acquired while a wafer stage supporting the test wafer moves at a first velocity. In some embodiments, a first beam position on a test wafer can be measured from a first inspection image acquired while a wafer stage moves at a first velocity V1. In some embodiments, a first inspection image can be acquired when a wafer stage is stationary, i.e., a first velocity V1is zero.

In step S820, a second beam position can be acquired. Step S820can be performed by, for example, second beam position acquirer520, among others. According to some embodiments of the present disclosure, a second beam position on a test wafer can be acquired while a wafer stage supporting the test wafer moves at a second velocity. In some embodiments, a second beam position on the test wafer can be measured from a second inspection mage acquired while a wafer stage moves at a second velocity V2. According to some embodiments of the present disclosure, a second inspection image can be acquired when a wafer stage moves at a second velocity that is different from a first velocity. In some embodiments, a second velocity can be set as a maximum velocity of a wafer stage of a beam tool. In some embodiments, a second inspection image can be acquired when a disturbance magnetic field, e.g., caused by eddy currents in a moving conductor exists. In some embodiments, a second inspection image can be acquired under a same inspection condition as the first inspection image except that a wafer stage moves at a different velocity. In some embodiments, a target position of a second beam is the same as a first beam.

In step S830, a beam position displacement of a beam can be calculated. Step S830can be performed by, for example, beam displacement calculator530, among others. According to some embodiments of the present disclosure, a beam position displacement of a beam when inspecting a wafer while a wafer stage moves at a third velocity can be calculated. In some embodiments, the third velocity is in a range of velocities from a first velocity to a second velocity.

In some embodiments where a third velocity is equal to a second velocity, a beam position displacement of a beam can be equal to a beam position displacement of a second beam with respect to a first beam. In some embodiments where a third velocity is greater than a first velocity and less than a second velocity, a beam position displacement of a beam can be calculated based on a beam displacement of a second beam. Since eddy current density in a moving conductor has a linear relationship with a velocity of the moving conductor, a beam position displacement can be determined based on the velocity of the moving conductor. As described referring toFIG.4B, since eddy current density is not uniform in a moving conductor and thus a disturbance magnetic field varies depending on an X-Y location of a wafer, a beam position displacement can further be determined based on an X-Y position of a beam on a wafer. The process of calculating a beam position displacement has been described referring toFIG.6CandFIG.7, and thus the detailed explanation will be omitted here for simplicity purposes.

In step S840, a beam position of a beam can be adjusted. Step S840can be performed by, for example, beam displacement calibrator540, among others. According to some embodiments, a beam position on a wafer for inspecting a wafer while a wafer stage moves at a third velocity can be adjusted. In some embodiments, a beam position can be adjusted based on a beam displacement for the beam determined at step S830. In some embodiments, a beam position can be adjusted to offset a beam position displacement of a beam. In some embodiments, a control signal to offset a beam position displacement of a beam can be generated. In some embodiments, a system magnetic field of beam tool104can be adjusted to offset the disturbance magnetic field. In some embodiments, a control signal to adjust an operational parameter(s) of any components of an inspection apparatus (e.g., EBI system100ofFIG.1or electron beam tool104ofFIG.2) can be generated to compensate a beam displacement of a beam or to offset disturbance magnetic fields. In some embodiments, a control signal can be generated to adjust an operation parameter of an external apparatus other than an inspection apparatus (e.g., EBI system100ofFIG.1or electron beam tool104ofFIG.2) to compensate a beam displacement of a beam or to offset disturbance magnetic fields.

A non-transitory computer readable medium may be provided that stores instructions for a processor of a controller (e.g., controller109ofFIG.1) to carry out, among other things, image inspection, image acquisition, stage positioning, beam focusing, electric field adjustment, beam bending, condenser lens adjusting, activating charged-particle source, beam deflecting, and method800. 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 Compact Disc Read Only Memory (CD-ROM), any other optical data storage medium, any physical medium with patterns of holes, a Random Access Memory (RAM), a Programmable Read Only Memory (PROM), and Erasable

Programmable Read Only Memory (EPROM), a FLASH-EPROM or any other flash memory, Non-Volatile Random Access Memory (NVRAM), a cache, a register, any other memory chip or cartridge, and networked versions of the same.

Block diagrams in the figures may illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. In this regard, each block in a schematic diagram may represent certain arithmetical or logical operation processing that may be implemented using hardware such as an electronic circuit. Blocks may also represent a module, segment, or portion of code that comprises one or more executable instructions for implementing the specified logical functions. It should be understood that in some alternative implementations, functions indicated in a block may occur out of the order noted in the figures. For example, two blocks shown in succession may be executed or implemented substantially concurrently, or two blocks may sometimes be executed in reverse order, depending upon the functionality involved. Some blocks may also be omitted. It should also be understood that each block of the block diagrams, and combination of the blocks, may be implemented by special purpose hardware-based systems that perform the specified functions or acts, or by combinations of special purpose hardware and computer instructions.

It will be appreciated that the embodiments of the present disclosure are not limited to the exact construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The present disclosure has been described in connection with various embodiments, other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.