Patent Application
20240347313
The embodiments provided herein relate to electron sources of charged-particle beam systems, and more particularly to systems and methods of cleaning field-emission electron sources using an optical source.
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, imaging resolution and yield in defect detection become more important. Multiple charged-beams may be employed to address the inspection throughput requirements; however, imaging resolution of multiple charged-beam systems may be compromised, rendering the inspection tools inadequate for their desired purpose. Imaging resolution is also influenced by electron source stability, which is maintained by periodically decontaminating the electron emitter tips. The existing procedures for cleaning the electron emitter tips of the electron sources may necessitate a partial or a complete shutdown of an inspection tool, affecting an overall inspection throughput, among other issues.
Thus, related art systems face limitations in, for example, image resolution and electron source stability due to contamination of the electron source. The existing ways of removing contaminants from the electron source may introduce variability in the current generated after cleaning or shorten the life-span of the electron source, rendering them cost-ineffective or unreliable, or both. Therefore, systems and methods of cleaning an electron source while maintaining the imaging resolution, source stability, and inspection throughput are desired.
Some embodiments of the present disclosure are directed to an electron beam apparatus comprising an electron source and an optical source. The electron source may comprise an emitter tip configured to emit electrons and the optical source may be configured to generate an optical beam illuminating a portion of the emitter tip to excite a surface mode of the optical beam, wherein the excited surface mode facilitates removal of a contaminant from a surface of the illuminated portion of the emitter tip.
Some embodiments of the present disclosure are directed to an electron beam apparatus comprising an electron source and an optical source. The electron source may comprise an emitter tip configured to emit electrons and the optical source may be configured to generate an optical beam illuminating a portion of the emitter tip to remove a contaminant from a surface of the illuminated portion of the emitter tip.
Some embodiments of the present disclosure are directed to a method of removing a contaminant from an emitter tip of an electron source. The method may comprise activating an optical source to generate an optical beam and illuminating a portion of the emitter tip with the optical beam excite a surface mode of the optical beam, wherein the excited surface mode facilitates removal of a contaminant from a surface of the illuminated portion of the emitter tip.
Some embodiments of the present disclosure are directed to a method of removing a contaminant from an emitter tip of an electron source. The method may comprise activating an optical source to generate an optical beam and illuminating a portion of the emitter tip with the optical beam to remove the contaminant bonded to a surface of the illuminated portion of the emitter tip.
Some embodiments of the present disclosure are directed to a non-transitory computer readable medium storing a set of instructions that is executable by one or more processors of an electron beam apparatus to cause the electron beam apparatus to perform a method of removing a contaminant from an emitter tip of an electron source. The method may comprise activating an optical source to generate an optical beam and illuminating a portion of the emitter tip with the optical beam excite a surface mode of the optical beam, wherein the excited surface mode facilitates removal of a contaminant from a surface of the illuminated portion of the emitter tip.
Other advantages of the embodiments of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of the present invention.
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 silicon called a substrate. 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 fit on the substrate. For example, an IC chip in a smart phone 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 extremely small ICs 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, thereby 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 electron microscope (SEM). An SEM can be used to image these extremely small structures, in effect, taking a “picture” of the structures. The image can be used to determine if the structure was formed properly and also if it was formed in the proper location. If the structure is defective, then the process can be adjusted so the defect is less likely to recur.
Obtaining high resolution images with a SEM starts with an electron source that has high brightness, a small energy spread, and a small virtual size. Thermionic emission sources, such as tungsten hairpin filaments, although inexpensive and easy to use, suffer from several drawbacks including short lifetime, high operating temperature, low brightness, broad beam energy spread, among other things, which may result in reduced image quality. In comparison, field-emission sources provide superior brightness due to substantially smaller emission area, small beam energy spread, high longevity, and high image resolution, rendering them a desirable electron source for high resolution imaging in SEMs. However, there are several issues that may limit their efficiency and usability in systems and applications requiring high throughput. Some of these issues include short current-decay time (<100 hours) even at high vacuum conditions, large emission-current variation, and ultra-high or extremely high vacuum requirements to prevent arc-over at the emitter tip.
To mitigate some of the existing issues with the field-emission sources, the electron source is cleaned periodically, such as by resistively (ohmically) heating the electron source periodically to clean the emission surface, or indirectly heating the electron emission source through radiation from resistively heating a filament placed in the vicinity of the electron source. In resistive heating, also known as “flashing” or “flash heating.” large electric current may be passed through the filament and the emitter tip, raising the temperature globally, to decontaminate the emission surface and restore the emission current. Flashing may include mild-heating or hard heating, raising the temperature of the electron source, including the non-emission surfaces, in a range from 700° C. to 2000° C. If a hard-heating procedure is performed, the inspection tool may have to be shut down and the electron optical column may have to be realigned or recalibrated, thereby significantly impacting the throughput. A mild-heating procedure may be performed more frequently to prolong the period between two hard-heating procedures.
In either of the flashing techniques, the inventors of this disclosure have realized that the outgassing due to global temperature increase is significant enough to negatively affect the vacuum in the chamber enclosing the electron source, and in particular, around the electron emitter tip. One of several issues with poor vacuum around the emitter tip is an appreciable reduction in the lifetime of the electron source due to higher rate of contaminant formation on its surface, which would necessitate more and frequent flashing cycles, causing tip blunting and frequent tip replacement. In some cases, the outgassing may be severe enough to “strain” the vacuum pumping mechanism enough to cause longer machine downtime, thereby negatively affecting the throughput as well. Therefore, it may be desirable to remove contaminants from the emission surface of an electron source, while maintaining low outgassing rates and high inspection throughput.
In some embodiments of the present disclosure, an electron beam apparatus comprising an electron source and an optical source is disclosed. The electron source may include an emitter tip configured to generate electrons and the optical source may be used to generate an optical beam to illuminate the emitter tip to remove contaminants adsorbed on the emitter tip. With optical beams, such as a laser beam, the wavelength may be adjusted based on the target contaminant and the beam may be focused on a smaller portion of the tip, such as the apex of the emitter tip. Even if the desired wavelength of the laser beam, such as infrared laser, causes the emitter tip to heat up, the amount of heat generated is appreciably less, resulting in significantly reduced outgassing in the vacuum chamber, and which may also minimize tip blunting. This is in contrast to the existing techniques and prior art, which heat up the entire emitter tip either by passing current through the tip or by heating a filament close to the tip to remove contaminants. Further, the laser beam may be linearly polarized such that the removal of the contaminants may be assisted by the electric field component of the laser beam, further reducing the amount of heat generated.
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.
Reference is now made to
EFEM 30 includes a first loading port 30a and a second loading port 30b. EFEM 30 may include additional loading port(s). First loading port 30a and second loading port 30b receive wafer front opening unified pods (FOUPs) that contain wafers (e.g., semiconductor wafers or wafers made of other material(s)) or samples to be inspected (wafers and samples are collectively referred to as “wafers” hereafter). One or more robot arms (not shown) in EFEM 30 transport the wafers to load-lock chamber 20.
Load-lock chamber 20 is connected to a load/lock vacuum pump system (not shown), which removes gas molecules in load-lock chamber 20 to reach a first pressure below the atmospheric pressure. After reaching the first pressure, one or more robot arms (not shown) transport the wafer from load-lock chamber 20 to main chamber 10. Main chamber 10 is connected to a main chamber vacuum pump system (not shown), which removes gas molecules in main chamber 10 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subject to inspection by electron beam tool 40. In some embodiments, electron beam tool 40 may comprise a single-beam inspection tool. In other embodiments, electron beam tool 40 may comprise a multi-beam inspection tool.
Controller 50 may be electronically connected to electron beam tool 40 and may be electronically connected to other components as well. Controller 50 may be a computer configured to execute various controls of charged particle beam inspection system 100. Controller 50 may also include processing circuitry configured to execute various signal and image processing functions. While controller 50 is shown in
In some embodiments, controller 50 may 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, controller 50 may 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 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.
While the present disclosure provides examples of main chamber 10 housing an electron beam inspection system, it should be noted that aspects of the disclosure in their broadest sense, are not limited to a chamber housing an electron beam inspection system. Rather, it is appreciated that the foregoing principles may be applied to other chambers as well.
Reference is now made to
In some embodiments, electron emitter may include cathode 203, an anode 222, wherein primary electrons can be emitted from the cathode and extracted or accelerated to form a primary electron beam 204 that forms a primary beam crossover 202. Primary electron beam 204 can be visualized as being emitted from primary beam crossover 202.
In some embodiments, the electron emitter, condenser lens 226, objective lens assembly 232, beam-limiting aperture array 235, and electron detector 244 may be aligned with a primary optical axis 201 of apparatus 40. In some embodiments, electron detector 244 may be placed off primary optical axis 201, along a secondary optical axis (not shown).
Objective lens assembly 232, in some embodiments, may comprise a modified swing objective retarding immersion lens (SORIL), which includes a pole piece 232a, a control electrode 232b, a beam manipulator assembly comprising deflectors 240a, 240b, 240d, and 240c, and an exciting coil 232d. In a general imaging process, primary electron beam 204 emanating from the tip of cathode 203 is accelerated by an accelerating voltage applied to anode 222. A portion of primary electron beam 204 passes through gun aperture 220, and an aperture of Coulomb aperture array 224, and is focused by condenser lens 226 so as to fully or partially pass through an aperture of beam-limiting aperture array 235. The electrons passing through the aperture of beam-limiting aperture array 235 may be focused to form a probe spot on the surface of sample 250 by the modified SORIL lens and deflected to scan the surface of sample 250 by one or more deflectors of the beam manipulator assembly. Secondary electrons emanated from the sample surface may be collected by electron detector 244 to form an image of the scanned area of interest.
In objective lens assembly 232, exciting coil 232d and pole piece 232a may generate a magnetic field. A part of sample 250 being scanned by primary electron beam 204 can be immersed in the magnetic field and can be electrically charged, which, in turn, creates an electric field. The electric field may reduce the energy of impinging primary electron beam 204 near and on the surface of sample 250. Control electrode 232b, being electrically isolated from pole piece 232a, may control, for example, an electric field above and on sample 250 to reduce aberrations of objective lens assembly 232 and control focusing situation of signal electron beams for high detection efficiency, or avoid arcing to protect sample. One or more deflectors of beam manipulator assembly may deflect primary electron beam 204 to facilitate beam scanning on sample 250. For example, in a scanning process, deflectors 240a, 240b, 240d, and 240e can be controlled to deflect primary electron beam 204, onto different locations of top surface of sample 250 at different time points, to provide data for image reconstruction for different parts of sample 250. It is noted that the order of 240a-e may be different in different embodiments.
Backscattered electrons (BSEs) and secondary electrons (SEs) can be emitted from the part of sample 250 upon receiving primary electron beam 204. A beam separator (not shown) can direct the secondary or scattered electron beam(s), comprising backscattered and secondary electrons, to a sensor surface of electron detector 244. The detected secondary electron beams can form corresponding beam spots on the sensor surface of electron detector 244. Electron detector 244 can generate signals (e.g., voltages, currents) that represent the intensities of the received secondary electron beam spots, and provide the signals to a processing system, such as controller 50. The intensity of secondary or backscattered electron beams, and the resultant secondary electron beam spots, can vary according to the external or internal structure of sample 250. Moreover, as discussed above, primary electron beam 204 can be deflected onto different locations of the top surface of sample 250 to generate secondary or scattered electron beams (and the resultant beam spots) of different intensities. Therefore, by mapping the intensities of the secondary electron beam spots with the locations of sample 250, the processing system can reconstruct an image that reflects the internal or external structures of wafer sample 250.
In some embodiments, controller 50 may comprise an image processing system that includes an image acquirer (not shown) and a storage (not shown). The image acquirer may comprise one or more processors. For example, the image acquirer may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, and the like, or a combination thereof. The image acquirer may be communicatively coupled to electron detector 244 of apparatus 40 through a medium such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, among others, or a combination thereof. In some embodiments, the image acquirer may receive a signal from electron detector 244 and may construct an image. The image acquirer may thus acquire images of regions of sample 250. The image acquirer may also perform various post-processing functions, such as generating contours, superimposing indicators on an acquired image, and the like. The image acquirer may be configured to perform adjustments of brightness and contrast, etc. of acquired images. In some embodiments, the storage may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), other types of computer readable memory, and the like. The storage may be coupled with the image acquirer and may be used for saving scanned raw image data as original images, and post-processed images.
In some embodiments, controller 50 may include measurement circuitries (e.g., analog-to-digital converters) to obtain a distribution of the detected secondary electrons and backscattered electrons. The electron distribution data collected during a detection time window, in combination with corresponding scan path data of a primary beam 204 incident on the sample (e.g., a 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 sample 250, and thereby can be used to reveal any defects that may exist in the wafer.
In some embodiments, controller 50 may control motorized stage 234 to move sample 250 during inspection. In some embodiments, controller 50 may enable motorized stage 234 to move sample 250 in a direction continuously at a constant speed. In other embodiments, controller 50 may enable motorized stage 234 to change the speed of the movement of sample 250 over time depending on the steps of scanning process.
An exemplary configuration 300 of an electron source in an electron beam inspection tool is illustrated in
In some embodiments, chamber 310 may comprise a vacuum chamber and may be a part of electron-optics column (not shown) of apparatus 40. Chamber 310 may enclose electron source 330 and extractor electrode 338. Chamber 310 may be constructed from a high-vacuum or UHV compatible material such as, but not limited to, stainless steel, and may be evacuated using one or more vacuum pumps of vacuum pumping mechanism 320. In some embodiments, chamber 310 may be pumped to ultra-high vacuum (UHV) or extreme high vacuum (XHV) conditions to provide a long mean free path for the electrons traveling downstream in the electron-optics column, to improve the reliability and stability of electron sources, to prolong the operating lifetime of electron sources, among other advantages.
In some embodiments, chamber 310 may include a view port 350 configured to allow an optical beam 345 generated by an optical source 340 to pass through. View port 350 may be mounted on an exterior surface of chamber 310 such that optical beam 345 passing through may be incident on emitter tip 335 without hinderances. In some embodiments, view port 350 may be made from a material substantially transparent to a broad range of wavelengths of electromagnetic radiation. For example, view port 350 may be made from borosilicate glass having an optical transmission greater than 90% over a wavelength range of 375 nm to 1900 nm. It is to be appreciated that other materials with desirable characteristics may be used as well, as appropriate. In some embodiments, in addition to being substantially transparent, view port 350 may be made from a low outgassing material compatible with high-vacuum or UHV operating conditions.
Vacuum pumping mechanism 320 may be in fluidic connection with chamber 310 such that chamber 310 may be evacuated efficiently. In some embodiments, vacuum pumping mechanism 320 may comprise a plurality of vacuum pumps including, but not limited to, a diaphragm pump, a scroll pump, an adsorption pump, a diffusion pump, a turbomolecular pump, a cryogenic pump, an ion getter pump, a titanium sublimation pump, among other vacuum pumps. In operation, one or more pumps may be used in combination to achieve the desired vacuum levels. In some embodiments, the choice of vacuum pumps or combinations of vacuum pumps may be based on factors including, but not limited to, the end-use application, the gases to be evacuated, the surfaces that contribute to outgassing, or the desired vacuum levels.
In currently existing SEMs, an electron source may include a thermionic emission source or a field-emission source. In general, thermionic emission sources rely on resistive heating to generate electrons from a cathode such as a tungsten filament, a LaB6, or a CeB6 crystal. Large currents are passed through the filament (cathode), generating heat based on the resistance of the filament, and thereby providing energy to the electrons to escape the solid surface. Although cheap and easy to maintain, such sources of electrons suffer from low brightness and broad energy distribution, resulting in inadequate image quality. On the other hand, field emission sources use an electrostatic field to induce electron emission. This electrostatic field is applied to an apex of an emitter tip made of an electrically conducting wire, where quantum mechanical tunneling allows high-energy electrons to be released. The emission area is substantially smaller for a field-emission source, typically in nanometers, than a thermionic source, resulting in superior brightness and, in turn, enhanced image quality including higher spatial resolution and increased signal to noise.
In some embodiments, apparatus 40 may include electron source 330, which comprises a field-emission source, also referred to as a field-emission gun (FEG) or a cold field emitter. Electron source 330 may include emitter tip 335 attached to a filament and shaped to have a tapered end. An apex 336 of the tapered end of emitter tip 335 may be sharpened to a tip radius of 0.5 μm or less, 0.4 μm or less, 0.3 μm or less, 0.2 μm or less, or 0.1 μm or less, such that the electrostatic field is extremely high, in the order of 108 V/cm, facilitating “quantum tunneling” of electrons. The emission current in a field-emission source is purely due to tunneling and is temperature-independent.
For a field emitter such as electron source 330, it may be desirable to have a clean emitter tip surface, essentially free of contaminants and adsorbates. One of several ways to maintain a clean emitter tip surface includes maintaining high levels of vacuum, and in some cases, extremely high vacuum around electron source 330. As an example, at a negative pressure of 106 Torr, a monolayer of gas is adsorbed on an exposed surface every 1-2 seconds. Although the monolayer formation rate may be prolonged to 5-10 minutes, for example, by operating at vacuum conditions of 10−10 Torr or below, the monolayer formation rate may still be unacceptable, rendering the tool and the inspection process inefficient.
Some of the currently existing techniques of cleaning emitter tip surfaces include a “flashing” process that involves resistively heating the emitter tip and the supporting filament to which the emitter tip is attached, by passing current through the emitter tip, to temperatures ranging from 700° C. to 2000° C. for short periods. While mild flashing may be performed at lower temperatures and more frequently compared to hard flashing, which is performed at higher temperatures and may require tool shut-down, the flash heating technique has several disadvantages and challenges. Some of the challenges include, but are not limited to, higher outgassing due to appreciable overall temperature increase of the chamber, temporary reduction of vacuum levels allowing re-adsorption of contaminants on the emitter tip, reduction in operating lifetime of the electron source, emission current instability, or short current-decay time of the electron source, among other issues. Other techniques may include radiative heating of a filament positioned in the vicinity of the emitter tip; however, radiative and resistive heating include heating procedures that increase the outgassing rate or high-voltage breakdown risk, or both. Therefore, it may be desirable to clean the field-emission source emitter tips with a technique that may mitigate one or more issues associated with existing cleaning techniques, while maintaining imaging resolution and inspection throughput.
As illustrated in
In some embodiments, optical source 340 may be fixedly coupled with chamber 310 such that optical beam 345 generated from optical source 340 may pass through view port 350 and be incident on a portion of the tapered end of emitter tip 335. In some embodiments, optical beam 345 may be aligned to illuminate apex 336 of emitter tip 335 such that upon illumination, one or more contaminants may be dislodged from the exposed surface of emitter tip 335, rendering the surface substantially clean from contaminants or adsorbates. Once aligned, the fixed coupling between optical source 340 and chamber 310 may ensure that the alignment is maintained until a replacement of emitter tip 335 is warranted, or a scheduled tool maintenance needs to be performed. In some embodiments, optical source 340 may comprise a beam polarizer (not shown). Beam polarizer may be configured to polarize optical beam 345 generated by optical source 340. In some embodiments, optical beam 345 may be linearly polarized, circularly polarized, elliptically polarized, or randomly polarized. Polarization of a beam, for example a light beam, as used herein, refers to the direction of the electric field oscillation of the light beam. For example, in a linearly polarized light beam, the electric field oscillates in a linear direction perpendicular to the propagation axis of the light beam, and the magnetic field oscillates in a direction perpendicular to the propagation axis of the light beam and to the electric field direction.
In some embodiments, although not illustrated, apparatus 40 may include more than one optical source 340 configured to illuminate emitter tip 335 with optical beams such as optical beam 345. The plurality of optical sources 340 may be positioned such that the plurality of optical beams may be incident on apex 336 of emitter tip 335 at different locations around the axis of emitter tip 335. It is to be appreciated that a configuration comprising more than one optical source 340 may also comprise a corresponding view port 350 for a corresponding optical beam to pass through. In some embodiments, the number of optical sources employed may be determined based on the mechanical, structural, spatial, or functional design considerations of chamber 310.
In some embodiments, optical beam 345 may be incident on apex 336 or on regions close to apex 336 of emitter tip 335 at an incidence angle between 0° to 90° with respect to axis of emitter tip 335, which may substantially coincide with primary optical axis 301. The incidence angle of optical beam 345 may be determined based on the location of optical source 340, path of optical beam 345, location of view port 350, position of emitter tip 335 within chamber 310, among other things.
In some embodiments, in a configuration comprising multiple optical sources 340, two or more optical sources 340 may be configured to illuminate emitter tip 335 with optical beams of similar or dissimilar characteristics such as, but not limited to, wavelength, frequency, intensity, power density, incidence angle, among other characteristics. For example, a first optical source may generate a first optical beam in the ultraviolet wavelength range at a 45º incidence angle on a first portion of the emitter tip, and a second optical source may generate a second optical beam in the infrared wavelength range at a 30º incidence angle on a second portion of the emitter tip. A characteristic of optical beam 345 may be determined based on the contaminant, type of bonding between the contaminant and the surface of emitter tip 335, location of the contaminant on or around apex 336 of emitter tip 335, among other things. One or more optical beams 345 from a corresponding optical source 340 may be incident on emitter tip 335 simultaneously or substantially simultaneously. In some embodiments, multiple optical beams may illuminate emitter tip 335 sequentially with a regular or an irregular timing offset between successive incidences. One of several advantages of illuminating emitter tip 335 with multiple optical beams from multiple optical sources simultaneously includes improved cleaning efficiency and enhanced throughput by reducing the time required to clean emitter tip 335.
In operation of apparatus 40 for inspection or imaging, power supply 360 may be configured to generate electrostatic field to extract electrons from emitter tip 335, or configured to focus the extracted electrons, or both. The extracted electrons may form an electron beam 302 traveling along primary optical axis 301. In some embodiments, power supply 360 may be controlled by controller 50. Controlling power supply 360 may include adjusting the voltage, the current, or the power generated by power supply 360 to regulate the electron beam characteristics including, but not limited to, number of electrons, electron beam distribution, among other things.
Reference is now made to
As shown in
In some embodiments, optical beam 445, upon illuminating a portion of apex 436, may break the bond between one or more contaminants 420 and the surface of emitter tip 435. Breaking the bond may include desorption of adsorbed molecules, or cleavage of a physical or a chemical bond, or dissociation of a molecule into individual atoms before removal from the surface. In some embodiments, breaking the bond may include a photon-assisted quantum process, also referred to as photon-contaminant resonance, to remove atoms or molecules from a surface. In the example shown in
In some embodiments, a photon-contaminant resonance mechanism for cleaning emitter tips may include adjusting a wavelength of optical beam 445 comprising photons to break the bond between contaminant 420 and the surface of emitter tip 435 or apex 436. The wavelength may be adjusted to be resonant with the bond formed between contaminant 420 and surface of emitter tip 435.
In some embodiments, breaking the bond to remove contaminant 420 from surface of apex 436 by photon-contaminant resonance mechanism may generate heat based on characteristics of optical beam 445 such as power, wavelength, frequency, duration of exposure, intensity, target material, target contaminant, or type of bond between the contaminant and the surface of the emitter tip, among other factors. However, the amount of heat generated may be considerably less compared to the existing techniques of resistive or radiative heating to clean emitter tips of electron sources.
In some embodiments, propagation of an optical beam or a light beam may be considered as a wave phenomenon where light waves may be recognized as electromagnetic transverse waves. In electromagnetic transverse waves, the electric field and the magnetic field oscillate orthogonal to each other and to the direction of the propagation of the light wave. A light beam may be linearly polarized, circularly polarized, elliptically polarized, or randomly polarized.
Turning back to
In some embodiments, a surface mode of linearly polarized optical beam 445 may be excited upon illumination of a surface of emitter tip 435 including grating structure 455. The surface mode of linearly polarized optical beam 445 may comprise a propagating surface wave 452, which may enhance optical energy absorption, upon irradiation of emitter tip 435. Propagating surface wave 452, propagating along grating structure 455 on tapered edge of emitter tip 435 may enable debonding of contaminant 420 from surface of emitter tip 435. Propagating surface wave 452 may be excited upon incidence of linearly polarized optical beam 445 on grating structure 455. One of several advantages of the propagating surface wave of optical beam 445 includes reduction in reflected or scattered photons from emitter tip 435 and thereby reducing outgassing from neighboring regions of emitter tip 435. Although not illustrated, it is to be appreciated that grating structure 455 may be formed on one or more surfaces of emitter tip 435. In some embodiments, grating structure 455 may be formed on a small region on or around apex 446. Alternatively, or additionally, grating structure 455 may be formed on a majority of the tapered edges of emitter tip 435.
Reference is now made to
In some embodiments, optical beam 545, upon illuminating a portion of apex 536, may break the bond between one or more contaminants 520 and the surface of emitter tip 535. Breaking the bond between contaminant 520 and a surface of emitter tip 535 to clean emitter tip 535 may include a localized optical radiation heating mechanism. In this mechanism, optical beam 545 may be focused on apex 536 of emitter tip 535, causing the temperature of apex 536 to rise locally such that one or more contaminants 520 may be desorbed from the surface. In some embodiments, optical beam 545 may comprise a near-infrared laser beam, or a mid-infrared laser beam. The wavelength of optical beam 545 may be chosen based on type of contaminant 520, or nature of the bond formed between contaminant 520 and surface of apex 536. For example, an infrared laser beam having a wavelength of 800 nm may be used to desorb water molecules from apex 536 and a near-infrared laser beam having a wavelength of 1500 nm may be used to remove a carbon monoxide molecule bonded to apex 536. It is to be appreciated that these exemplary wavelengths are non-limiting and non-specific. Other laser wavelengths and intensities may be used, as appropriate. Although the local temperature of emitter tip 535 may be increased by exposure to optical beam 545, the temperature rise is significantly less compared to resistive and radiative heating techniques. This is because the heating is localized and confined to the emission surface or apex 536 of emitter tip 535. Additionally, because only a small targeted area (e.g., apex 536) of emitter tip 535 is cleaned, the number of contaminants released may not burden the vacuum pumping mechanism to cause significant reduction in vacuum levels around emitter tip 535.
Turning back to
An electron emitter tip cleaning technique using optical beams such as a laser, may have some or all of the advantages discussed herein:
Reference is now made to
In step 610, an optical source (e.g., optical source 340 of
In step 620, the optical beam may be directed to illuminate a portion of an emitter tip (e.g., emitter tip 335 of
In some embodiments, breaking the bond may include a photon-assisted quantum process, also referred to as photon-contaminant resonance, to remove atoms or molecules from a surface of the emitter tip. A photon-contaminant resonance mechanism for cleaning emitter tips may include adjusting a wavelength of the optical beam comprising photons to break the bond between the contaminant and the surface of emitter tip or apex (e.g., apex 436 of
In some embodiments, breaking the bond between the contaminant and a surface of the emitter tip to clean emitter tip may include a localized optical radiation heating mechanism. In this mechanism, the optical beam may be focused on the apex of the emitter tip, causing the temperature of the apex to rise locally such that one or more contaminants may be desorbed from the surface. In some embodiments, optical beam may comprise a near-infrared laser beam, or a mid-infrared laser beam.
A non-transitory computer readable medium may be provided that stores instructions for a processor of a controller (e.g., controller 50 of
The embodiments of the present disclosure may further be described using the following clauses:
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 technology 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.
The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.
This application claims priority of International application PCT/EP2022/083068, filed on 24 Nov. 2022, which claims priority of U.S. application 63/293,615, filed on Dec. 23, 2021. These applications are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 63293615 | Dec 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2022/083068 | Nov 2022 | WO |
| Child | 18751031 | US |
