KR-102963760-B1 - Electron microscope, electron source for electron microscope, and methods to operate electron microscope

KR102963760B1KR 102963760 B1KR102963760 B1KR 102963760B1KR-102963760-B1

Abstract

An electron microscope (100) is described. The electron microscope comprises an electron source (110) for generating an electron beam, a focusing lens (130) for collimating the electron beam downstream of the electron source, and an objective lens (140) for focusing the electron beam onto a specimen (16). The electron source comprises a cold field emitter having an emission tip (112), an extractor electrode (114) for extracting the electron beam (105) from the cold field emitter for propagation along the optical axis (A)—the extractor electrode has a first aperture (115) configured as a first beam-limiting aperture—a first cleaning array (121) for cleaning the emission tip (112) by heating the emission tip, and a second cleaning array (122) for cleaning the extractor electrode (114) by heating the extractor electrode. A method of operating such an electron microscope is further described.

Inventors

아다멕, 파벨

Assignees

아이씨티 인티그레이티드 써킷 테스팅 게젤샤프트 퓌어 할프라이터프뤼프테크닉 엠베하

Dates

Publication Date: 20260513
Application Date: 20221013
Priority Date: 20211221

Claims (20)

As an electron microscope (100), Electronic source (110) - The electronic source is: Cold field emitter having a discharge tip (112); An extractor electrode (114) for extracting an electron beam (105) from the cold field emitter for propagation along an optical axis (A) - the extractor electrode has a first aperture (115) configured as a first beam limiting aperture -; A suppressor electrode (113) arranged at least partially between the above-mentioned discharge tip (112) and the heating wire (126); A first cleaning array (121) for cleaning the discharge tip (112) by heating the discharge tip - the first cleaning array (121) includes a heating filament (125) in thermal contact with the discharge tip -; and A second cleaning array (122) for cleaning the extractor electrode (114) by heating the extractor electrode - the second cleaning array (122) includes the heating wire (126) located adjacent to the extractor electrode -; A focusing lens (130) for collimating the electron beam downstream of the electron source; An objective lens (140) for focusing the above electron beam onto a specimen; A second beam limiting aperture (132) between the focusing lens (130) and the objective lens (140); and A third aperture (133) between the second beam limiting aperture (132) and the objective lens (140) Includes, The first beam limiting aperture is arranged to function as a first differential pumping aperture, the second beam limiting aperture is arranged to operate as a second differential pumping aperture, and the third aperture is arranged to operate as a third differential pumping aperture; The above inhibitor electrode (113) is configured to be set to a potential for deflecting electrons emitted by the heating wire (126) away from the emission tip (112), in an electron microscope.
In paragraph 1, The above-mentioned emission tip is attached to or bonded to the above-mentioned heating filament, electron microscope.
In paragraph 1, The electron microscope, wherein the heating wire (126) is configured to be heated to a temperature of 1500°C or higher.
In paragraph 3, The above heating wire is arranged to at least partially surround the first opening (115) of the extractor electrode, in an electron microscope.
In paragraph 3, The heating wire (126) above is an electron microscope containing tantalum or made of tantalum.
In any one of paragraphs 1 through 5, It includes a cleaning controller (128), and the cleaning controller, In the first cleaning mode, configured to allow current to flow through the heating filament (125) in thermal contact with the discharge tip to heat the discharge tip to a temperature exceeding 1500°C, or An electron microscope configured to allow current to flow through the heating wire (126) of the second cleaning array for at least one of heating the extractor electrode to a temperature of at least partially greater than 500°C and causing electron stimulation desorption on the surface of the extractor electrode in a second cleaning mode.
In any one of paragraphs 1 through 5, An electron microscope in which the distance between the first opening (115) of the extractor electrode (114) and the emission tip (112) is 5 mm or less.
In any one of paragraphs 1 through 5, The above focusing lens (130) is a magnetic focusing lens having a first inner pole and a first outer pole, and the first axial distance (D1) between the emission tip and the first inner pole is greater than the second axial distance (D2) between the emission tip and the first outer pole, electron microscope.
In any one of paragraphs 1 through 5, The above objective lens (140) is a magnetic objective lens having a second inner pole and a second outer pole, and the third axial distance between the second inner pole and the sample stage is greater than the fourth axial distance between the second outer pole and the sample stage, electron microscope.
In any one of paragraphs 1 through 5, An acceleration section for accelerating the electron beam to an energy of 5 keV or more—the acceleration section is located upstream of the focusing lens or at least partially overlaps with the focusing lens—; and An electron microscope comprising a deceleration section for decelerating the electron beam from an energy of 5 keV or more to a landing energy of 2 keV or less—the deceleration section being downstream of the objective lens or at least partially overlapping with the objective lens.
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In any one of paragraphs 1 through 5, The above-mentioned emission tip (112) is arranged in a first vacuum region (10a), the above-mentioned focusing lens (130) is arranged in a second vacuum region (10b), and the electron microscope comprises an ion getter pump (13) and a non-evaporative getter pump (14) for pumping the first vacuum region (10a).
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As a method of operating an electron microscope having an electron source having a cold field emitter, In a first cleaning mode, a step of cleaning the emission tip of the cold field emitter by heating the emission tip; In a second cleaning mode, a step of cleaning the extractor electrode of the electron source by heating the extractor electrode using a heating wire—a suppressor electrode at least partially arranged between the emission tip and the heating wire is set to a potential to deflect electrons emitted by the heating wire away from the emission tip during heating using the heating wire—; and In operating mode: A step of extracting an electron beam from the cold field emitter for propagation along an optical axis—the electron beam is shaped by a first aperture provided at the extractor electrode, and the first aperture acts as a first differential pumping aperture—; A step of collimating the electron beam using a focusing lens; and A step of focusing the electron beam onto a specimen using an objective lens - a second beam limiting aperture is provided between the focusing lens and the objective lens to operate as a second differential pumping aperture, and a third aperture is provided between the second beam limiting aperture and the objective lens to operate as a third differential pumping aperture -; A method including
In paragraph 15, In the first cleaning mode above, the current flows through a heating filament to which the discharge tip is bonded to heat the discharge tip to a temperature of more than 1500°C.
In paragraph 15 or 16, A method in which, in the second cleaning mode, current flows through a heating wire located adjacent to the extractor electrode to cause thermal emission of electrons from the heating wire for cleaning of the extractor electrode by at least one or both of electron stimulation desorption and thermal gas emission.
In paragraph 15 or 16, A method comprising the step of switching from the operating mode to the first cleaning mode after a predetermined period in the operating mode.
In paragraph 15 or 16, The emission tip is arranged in a first vacuum region, the focusing lens is arranged in a second vacuum region downstream of the first vacuum region, the first aperture acts as the first differential pumping aperture between the first vacuum region and the second vacuum region, and the method is: A method comprising the step of differentially pumping the third vacuum region through a second differential pumping aperture arranged between the first vacuum region and the second vacuum region, and optionally, between the second vacuum region and a third vacuum region arranged downstream of the second vacuum region.
In paragraph 15 or 16, In the above operating mode: A step of accelerating electrons of the electron beam to an energy of 5 keV or more in an acceleration section - said acceleration section is upstream of the focusing lens or at least partially overlaps with the focusing lens -; A step of collimating the electron beam using the focusing lens having a first inner electrode and a first outer electrode - the first axial distance between the emission tip and the first inner electrode is greater than the second axial distance between the emission tip and the first outer electrode -; and A method further comprising the step of decelerating electrons of the electron beam to a landing energy of 3 keV or less in a deceleration section—wherein the deceleration section is downstream of the objective lens or at least partially overlaps with the objective lens.

Description

Electron microscope, electron source for electron microscope, and methods to operate electron microscope The embodiments described herein relate to electronic devices, in particular, electron microscopes, and more specifically, to scanning electron microscopes (SEMs) for inspection or imaging system applications, test system applications, lithography system applications, etc. The embodiments described herein specifically relate to electron microscopes having a cold field emitter that provides a high-intensity electron beam for high-resolution and high-throughput applications. More specifically, a high-throughput wafer inspection SEM is described. The embodiments described herein also relate to electron sources for electron microscopes as well as methods for operating electron microscopes. Electron microscopes have many functions in multiple industrial fields, including but not limited to the inspection or imaging of semiconductor substrates, wafers, and other specimens, critical dimensions, defect inspection, exposure systems for lithography, detector arrays, and test systems. There is a high demand for structuring, testing, inspecting, and imaging specimens at the micrometer and nanometer scales. Electron microscopes provide superior spatial resolution compared to, for example, photon beams, and enable high-resolution imaging and inspection. An electron microscope includes an electron source, or "electron gun," that generates an electron beam that strikes a specimen. Different types of electron sources are known, including hot field emitters, Schottky emitters, thermally assisted field emitters, and cold field emitters. A cold field emitter (CFE) includes an emission tip that is cold (= not heated) during operation, and the emission tip emits electrons by applying a high electrostatic field between the emission tip and the extractor electrode. Hot field emitters can typically provide high-current electron beams, whereas cold field emitters have the potential to provide high-intensity electron beam probes suitable for achieving high resolutions. However, CFEs are particularly sensitive to contamination and therefore must be operated in an evacuated gun housing under extremely good vacuum conditions, specifically ultra-high vacuum conditions. Still, unwanted ions, ionized molecules, or other contaminant particles may be present in the evacuated gun housing. For example, charged contaminant particles can be accelerated toward the emitter, thereby mechanically deforming the emission tip or negatively affecting it in other ways. Furthermore, the accumulation of particles on the surface of the emitter or on other surfaces of the electron source can introduce noise and other beam instabilities. Specifically, contaminant particles in the electron gun region can lead to an unstable or noisy electron beam, for example, a variable beam current or a variable beam profile. Therefore, vacuum conditions within the electron microscope, specifically within the gun housing housing the CFE, are important. Considering the above, it would be beneficial to improve the beam stability of electron beams in electron microscopes and reduce the amount of contaminant particles within the total housing. Specifically, it would be beneficial to provide a compact electron microscope having a CFE electron gun that emits a high-intensity electron beam with improved stability, which can further improve achievable resolution and throughput. Additionally, it would be beneficial to provide a method for operating the electron microscope to provide, for example, a high-intensity electron beam with improved beam stability. With the foregoing in mind, electron microscopes, electron sources, and methods for operating electron microscopes are provided according to the independent claims. Further aspects, advantages, and features are apparent from the dependent claims, the detailed description, and the accompanying drawings. According to one aspect, an electron microscope is provided. The electron microscope comprises an electron source, a focusing lens, and an objective lens. The electron source comprises a cold field emitter (CFE) having an emission tip; an extractor electrode for extracting an electron beam from the cold field emitter for propagation along an optical axis—the extractor electrode has a first aperture configured as a first beam-limiting aperture—; a first cleaning array for cleaning the emission tip by heating the emission tip; and a second cleaning array for cleaning the extractor electrode by heating the extractor electrode. The focusing lens is for collimating the electron beam downstream of the electron source, and the objective lens is for focusing the electron beam onto a specimen. According to one aspect, an electron source for an electron microscope as described herein is provided. The electron source comprises: a cold field emitter (CFE) having an emission tip; an extractor electrode for extracting an electron beam from the