Dry electron source environment

Abstract

The present invention discloses a charged particle microscope system comprising: an electron source housing a Venal electrode and a cathode, where the electron source may comprise a dry environment that may be substantially water-free, the dry environment defining a volume between the Venal electrode and the cathode; a beam column comprising a plurality of electromagnetic lens elements; and a vacuum chamber including a sample holder. An electron beam axis may be defined from the cathode to the sample holder.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. non-provisional application No. 18 / 485,133, filed on October 11, 2023, the disclosure of which is incorporated herein by reference in its entirety. Background Art

[0003] Electron microscopes are used as imaging tools by focusing a beam of electrons of sufficient size from an electron emitter onto a sample and then detecting reflections of these electrons to generate a high-resolution image of the sample. One step of focusing the electron beam and controlling its size may include emitting the electrons through an aperture in a Wehnelt electrode. The Wehnelt electrode is charged to a negative bias voltage relative to the electron emitter to generate an electrostatic field around the Wehnelt electrode that repels the electrons toward the center of the aperture in the Wehnelt electrode, thereby concentrating the electron beam emitted through the aperture. A new charged particle microscope system is needed that optimizes the use of the Wehnelt electrode. Summary of the invention

[0004] One aspect of the present disclosure provides a charged particle microscope system, the charged particle microscope system comprising: an electron source, the electron source accommodating a Wehnelt electrode and a cathode, wherein the electron source includes a substantially water-free dry environment, the dry environment defining a volume between the Wehnelt electrode and the cathode; a beam column, the beam column including a plurality of electromagnetic lens elements; and a vacuum chamber, the vacuum chamber including a sample holder. An electron beam axis is defined from the cathode to the sample holder. The dry environment may be substantially water-free when the dry environment may include less than 5% humidity. The dry environment may be substantially oxygen-free. The dry environment may be substantially oxygen-free when the dry environment may include less than 5% oxygen. The charged particle microscope may also include a first cold trap, the first cold trap positioned between the beam column and the Wehnelt electrode. The first cold trap may include: a first adsorption surface, the first adsorption surface defining a first cold zone, the first cold zone being at a first temperature significantly below the freezing point of water; and a first heat removal element, the first heat removal element coupled to the first cold surface. The first heat removal element may include a Peltier cooling system. The first heat removal element may include at least one of the circulation elements in fluid communication with a reservoir containing a coolant. The coolant may include at least one of liquid nitrogen or dry ice in acetone. The charged particle microscope system may also include a turbo pump in fluid communication with the electron source, and a second cold trap may be positioned between the turbo pump and the electron source. The second cold trap may include: a second adsorption surface, the second adsorption surface defining a second cold zone, the second cold zone being at a second temperature significantly below the freezing point of water; and a second heat removal element, the second heat removal element may be coupled to the second cold surface. The second adsorption surface may include a plurality of channels, and the plurality of channels may each define a channel cold zone. The charged particle microscope system may also include an inert gas reservoir containing an inert gas, and the charged particle microscope system may include: an outlet in fluid communication with the electron source; and a first turbo pump in fluid communication with the electron source and the outlet to deliver at least a portion of the inert gas to the dry environment. The first turbo pump may generate a first pressure in the electron source, the first pressure being greater than a second pressure at the outlet. The charged particle microscope system may further include a second turbopump in fluid communication with the vacuum chamber and the beam column. The outlet may be positioned between the electron source and the second turbopump, and the second turbopump may generate a third pressure in the beam column that is greater than the second pressure. The charged particle microscope system may further include a third turbopump in fluid communication with the vacuum chamber. The third turbopump may generate a fourth pressure that is greater than the third pressure. The inert gas may include at least one of argon, nitrogen, dry air, and helium. The outlet may be positioned in the beam column. The charged particle microscope may further include a container that houses the electron source, the beam column, and the vacuum chamber. The container may include a dry internal volume.

[0005] Another aspect of the present disclosure provides a charged particle microscope system, the charged particle microscope system comprising: an electron source, the electron source containing a Wehnelt electrode and a cathode in a substantially water-free dry environment; a beam column, the beam column comprising a plurality of electromagnetic lens elements; and a vacuum chamber, the vacuum chamber comprising a sample holder. An electron beam axis is defined from the cathode to the sample holder. The charged particle microscope system may also include a turbo pump, the turbo pump being in fluid communication with the electron source, a first cold trap being positionable between the beam column and the Wehnelt electrode, and a second cold trap being positionable between the turbo pump and the electron source. The first cold trap may include: a first adsorption surface, the first adsorption surface defining a first cold zone, the first cold zone being at a first temperature significantly below the freezing point of water; and a first heat removal element, the first heat removal element being connectable to the first cold surface. The second cold trap may include: a second adsorption surface, the second adsorption surface defining a second cold zone, the second cold zone being at a second temperature significantly below the freezing point of water; and a second heat removal element, the second heat removal element being connectable to the second cold surface. The charged particle microscope system may further include an inert gas reservoir containing an inert gas, and the charged particle microscope system may include: an outlet in fluid communication with the electron source; a first turbo pump in fluid communication with the electron source and the outlet to deliver at least a portion of the inert gas to the dry environment; and a second turbo pump in fluid communication with the vacuum chamber and the beam column. The outlet may be positioned between the electron source and the second turbo pump, the first turbo pump may generate a first pressure in the electron source that is greater than a second pressure at the outlet, and the second turbo pump may generate a third pressure in the beam column that is greater than the second pressure.

[0006] Another aspect of the present disclosure provides a charged particle microscope system, the charged particle microscope system including an electron source, the electron source accommodating a Wiener electrode and a cathode electrode. The electron source includes a substantially water-free dry environment, the dry environment defining a volume between the Wiener electrode and the cathode; a beam column, the beam column including a plurality of electromagnetic lens elements; and a vacuum chamber, the vacuum chamber including a sample holder. An electron beam axis is defined from the cathode electrode to the sample holder. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A further understanding of the nature and advantages of the various embodiments may be achieved by reference to the following drawings. In the drawings, similar components or features may have the same reference numeral. In addition, various components of the same type may be distinguished by following the reference numeral with a hyphen and a second reference numeral to distinguish between similar components. If only the first reference numeral is used in the specification, the description applies to any of the similar components having the same first reference numeral, regardless of the second reference numeral.

[0008] Figure 1ADepicted is a simplified cross-sectional view of an example charged particle microscope system in accordance with an embodiment of the present disclosure.

[0009] Figure 1B Describes an embodiment of the present disclosure Figure 1A Cross-sectional view of the electron source of a charged particle microscope system.

[0010] Figure 2A Depicted is a simplified cross-sectional view of an example charged particle microscope system in accordance with an embodiment of the present disclosure.

[0011] Figure 2B Describes an embodiment of the present disclosure Figure 2A and a cross-sectional view of the electron source and cold trap of a cold charged-particle microscope system.

[0012] Figure 3 Depicted is a simplified cross-sectional view of an example charged particle microscope system in accordance with an embodiment of the present disclosure.

[0013] Figure 4 Depicted is a simplified cross-sectional view of an example charged particle microscope system in accordance with an embodiment of the present disclosure.

[0014] Figure 5 Depicted is an example graph of Wehnelt electrode voltage over time in accordance with an embodiment of the present disclosure.

[0015] Figure 6 Depicted is an example graph of Wehnelt electrode voltage over time in accordance with an embodiment of the present disclosure.

[0016] Figure 7 Depicted is an example graph of Wehnelt electrode voltage over time in accordance with an embodiment of the present disclosure.

[0017] Figure 8 Depicted is an example graph of Wehnelt electrode voltage over time in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION

[0018] Electron microscopy provides high-resolution imaging by detecting backscattered electrons (BSE) generated by elastic scattering of an electron beam emitted from an electron emitter that interacts with atoms of the sample. In one example, electrons may be emitted from a cathode electrode heated by an electric current. The emitted electrons are attracted to an anode placed downstream of the cathode electrode, thereby forming an electron beam that is generally directed toward the sample. However, in order to obtain a useful image, the electron beam must be further focused toward the sample with a sufficient size.

[0019] One means of focusing and controlling an electron beam includes the use of a Wehner electrode. The Wehner electrode is charged with a negative bias voltage to generate an electric field that repels electrons emitted from a cathode electrode and controls the current emission of the electron beam. The electron beam emitted from the cathode electrode can be directed toward an aperture defined by the Wehner electrode so that the electric field of the Wehner electrode allows electron emission only from an area defined by the electric field surrounding the aperture. In this way, the Wehner electrode can help focus and control the electron beam toward a sample.

[0020] However, the electrons emitted from the cathode electrode may ionize the gas around the cathode electrode and the Wiener electrode (e.g., in an electron source). The positively ionized gas particles may be attracted to the electric field generated by the Wiener electrode, thereby forming a deposit layer on the Wiener electrode. In particular, the ionized gas particles may be particles that have evaporated from the cathode electrode by oxidation of the cathode electrode. The deposit layer may interfere with the electric field generated by the Wiener electrode, which in turn may disturb the focusing of the electron beam. This disturbance may be severe enough that the electron beam cannot be corrected later in the beam column.

[0021] This problem is particularly evident for desktop electron microscopes because the pumps used in these systems are smaller than those used in larger electron microscopes, such as floor-standing electron microscopes. As a result, these smaller pumps may have a harder time pumping gas particles out of the electron source. In addition, desktop electron microscopes have smaller beam columns and fewer orifices than floor-standing models. This can result in higher operating pressures, which can lead to a certain level of contamination in the electron source.

[0022] One solution to this problem may include increasing the negative bias voltage of the Wehner electrode (e.g., increasing the negative value of the voltage supplied to the Wehner electrode). Although this may solve the problem of the electric field of the Wehner electrode, this still does not solve the fundamental problem of the ionized gas particles forming a deposit layer along the Wehner electrode. Ignoring this deposit layer may lead to further problems: the deposit layer flakes off (e.g., after thermal expansion and cooling of the deposit layer) and floats back onto the cathode electrode. This additional contamination layer on the cathode electrode may change the direction of the electrons emitted from the cathode electrode and further disrupt the focusing of the electron beam.

[0023] Another solution may include disassembling the electron source to physically clean the contamination from the electron source. However, this presents additional challenges, as disassembling the electron source may expose the chamber to potential contamination. This is also a particular problem for desktop electron microscopes, as such microscopes are located in areas with different cleanliness standards (e.g., laboratories or offices) and are not typically placed in a controlled, contaminant-free environment. In addition, cleaning the electron source increases the risk that the electron microscope system has alignment problems. Another problem is that the relatively weak vacuum system of a desktop SEM is less able to degas adsorbed substances (such as organic molecules and water) from the interior surfaces.

[0024] The present disclosure provides a charged particle microscope system having an electron source having a substantially water-free dry environment. Since water is a common vapor species entering a charged particle microscope system and oxygen is the primary catalyst for evaporation of material from a cathode electrode, providing a substantially water-free dry environment for the electron source can reduce evaporation of material from the cathode electrode. This in turn mitigates ionization of gas particles in the source portion of the microscope system, and in turn reduces the formation of a deposited layer along the Wiener electrode and the cathode electrode. In addition, since reducing the presence of oxygen also mitigates oxidation and evaporation of the cathode electrode, the life of the cathode electrode can be significantly improved (e.g., from 150 hours of use to greater than 1,500 hours).

[0025] However, removing water and / or oxygen from the electron source may also prove to be challenging. Because the electron source defines a first end of an unobstructed beam path between the cathode electrode and the sample position, the electron source is not sealed (e.g., airtight) during operation of the electron source. Therefore, a solution to this problem may include providing an electron source that is substantially water-free or oxygen-free while still allowing an unobstructed path from the cathode electrode to the sample. Various embodiments for providing such a solution will be discussed further below. One embodiment includes using a cold trap to condense water vapor that may enter the electron source. Another embodiment includes introducing an inert gas into the electron source portion. Yet another embodiment includes enclosing the charged particle microscope system in a dry environment.

[0026] Although the remainder of this specification will conventionally refer to a scanning electron microscope (SEM), those skilled in the art will readily appreciate that the technology is not limited thereto. The designs of the present invention may be used with other types of charged particle microscopes, such as a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), a dual beam system including an ion beam source and an electron beam source, a reflection electron microscope (REM), a circuit editing microscope, etc. Therefore, the present disclosure and claims should not be considered limited to any particular example microscope discussed, but rather may be used broadly with any number of electron microscopes that may exhibit some or all of the electrical or chemical properties of the examples discussed.

[0027] Figure 1A to Figure 1B An example charged particle microscope system 100 is depicted, illustrating a system that utilizes a Wehner electrode to focus an electron beam and control its emission current. Figure 1B , the electron microscope 100 may include multiple parts, including an electron source 110, a beam column 120, an objective lens 130, and a vacuum chamber 140. The electron source 110 may include high voltage supply components, vacuum system components, and electron emitters configured to generate an electron beam that is accelerated into the beam column 120. The beam column 120 includes various beam manipulation components 122, such as electromagnetic lens elements, that are configured to shape and form the electron beam from the electron source 110 into a substantially circular beam having a substantially uniform profile so as to be focused by the objective lens 130 onto a sample.

[0028] Electron beams are often characterized by the beam current and the accelerating voltage applied to produce the beam, among other criteria. The range of beam current and accelerating voltage can vary between instruments and are often selected based on the material properties of the sample or the type of analysis being performed. However, typically, electron beams are characterized by energies ranging from about 0.1 keV (e.g., for an accelerating voltage of 0.1 kV) to about 50 keV and beam currents ranging from picoamperes to microamperes.

[0029] The vacuum chamber 140 and / or beam column 120 may include multiple detectors for various signals, including but not limited to secondary electrons generated by the interaction of the electron beam with the sample, x-ray photons (e.g., energy dispersive x-ray spectroscopy), other photons (e.g., visible and / or infrared light cameras), and / or molecular species (e.g., time-of-flight secondary ion mass spectrometry). The vacuum chamber 140 may also include a sample holder 144 that may be operably coupled to a holder motion system 170 (e.g., a multi-axis translation / rotation control system) such that the sample holder 144 may be repositioned relative to the electron beam to optimally investigate and / or image a sample held in the sample holder 144. A vacuum chamber door 142 allows access to the vacuum chamber 140 from outside the charged particle microscope system 100 (e.g., for cleaning, sample replacement, etc.).

[0030] The turbo pump 160 can create a pressure differential by drawing material from within the vacuum chamber 140, thereby creating a vacuum in the vacuum chamber 140. The vacuum chamber 140 can be free of matter to minimize the risk of any intermediate matter within the vacuum chamber 140 disrupting the electron beam to the sample. The turbo pump 160 can pump the vacuum chamber 140 (and any intermediate components) to less than about 10 -10 Torr (such as less than or about 10 -11 Torr, such as less than or about 10 -12 Torr, or such as less than or about 10 -13The turbo pump 160 may be in fluid communication with the vacuum chamber 140, the objective lens 130, the beam column 120, and the electron source 110 to draw gas from the vacuum chamber 140. A path may be defined from the turbo pump 160 through the electron source 110, the beam column 120, the objective lens 130, and to the sample holder 144, wherein the turbo pump 160 defines the most upstream point and the sample holder 144 defines the most downstream point. In this manner, "downstream" and "upstream" may be relative terms used to describe the location of various components along the path.

[0031] Steering Figure 1B , the electron source 110 may include a Wiener electrode 112 and a cathode electrode 114 (e.g., a cathode crystal). The cathode electrode 114 may be heated using a voltage (e.g., heated to approximately 1700 Kelvin to 1800 Kelvin) to emit an electron beam A from the tip of the cathode electrode 114. The cathode electrode 114 may be cerium hexaboride, lanthanum hexaboride, or other materials that may be used as an electron emitter source. The Wiener electrode 112 may define an orifice 116 downstream of the cathode electrode 114 to allow the electron beam A to pass through. The Wiener electrode 112 may be charged to have a negative bias voltage that is more negative than the voltage of the cathode electrode 114 to generate an electric field. The electric field focuses the electron beam A and controls its current emission by surrounding the orifice 116 with the electric field, so that any stray electrons leaving the electron beam A are repelled by the electric field toward the center line of the orifice 116. In this way, the electron beam axis from the cathode electrode 114 to the sample holder 144 may be defined. The amount of negative bias voltage provided to the Wehnelt electrode 112 may be related to the amount of energy of the electron beam emitted from the cathode electrode 114 .

[0032] However, as noted above, the emitted electrons may ionize gas particles that may be present in the electron source 110. Such gas particles may be materials that evaporate from the cathode electrode 114, such as due to oxidation of the cathode electrode 114. In other words, at least some of the gas particles within the electron source 110 may be byproducts (e.g., cerium, borides, oxides, etc.) of the reaction of the cathode electrode 114 with oxygen in the electron source 110. However, while oxidation may play a role in contamination, it is not the only chemical mechanism that causes performance degradation of the electron source 110. These gas particles may be ionized to have an electrical charge. At least some of these ionized gas particles B may be ionized to have a positive charge, resulting in the ionized gas particles B being attracted to the Wiener electrode 112. The ionized gas particles B may form a deposited layer 118 that extends along the Wiener electrode 112 and partially within the orifice 116.

[0033] The deposited layer 118 reduces the potential and electric field of the Wiener electrode 112. To offset the reduction in potential, the Wiener electrode 112 may require a larger negative voltage to maintain the desired electric field to focus the electron beam A and control its current emission. In addition, during thermal expansion and cooling of the Wiener electrode 112 and the deposited layer 118, portions of the deposited layer 118 may flake off. These flakes may float to the cathode electrode 114 to form another deposited layer, which may further change the direction of the electron beam A. Therefore, the presence of oxygen in the electron source 110 not only causes the cathode electrode 114 to degrade faster, but oxygen also causes the formation of the deposited layer 118 and causes the electron beam A to be misaligned.

[0034] Since oxygen is a chemical component of water, which is a common vapor that can penetrate the electron source 110, removing water from the electron source 110 (e.g., from the volume between the Wiener electrode 112 and the cathode electrode 114) so ​​that the electron source 110 is a dry environment can be beneficial to prevent degradation of the cathode electrode 114. For example, the electron source 110 can be a dry environment when it includes less than about 5% humidity, less than about 4% humidity, less than about 3% humidity, less than about 2% humidity, less than about 1% humidity, or no humidity at all. In one example, the electron source 110 can be a dry environment when it includes 0.01% humidity. In other embodiments, the electron source 110 can be a dry environment when the electron source 110 is substantially free of oxygen. For example, the electron source 110 can include less than about 5% oxygen, less than about 4% oxygen, less than about 3% oxygen, less than about 2% oxygen, less than about 1% oxygen, or no oxygen at all.

[0035] Figure 2A and 2BAn example charged particle microscope system 200 is depicted. It should be understood that features ending with similar reference numerals to features discussed above are similar unless otherwise noted below. The charged particle microscope system 200 includes a first cold trap 280a and a second cold trap 280b. The first cold trap 280a may be positioned downstream of the electron source 210, between the electron source 210 and the beam column 220. However, in some embodiments, the first cold trap may be positioned in the beam column, downstream of the electron source. The second cold trap 280b may be positioned upstream of the electron source 210, between the electron source 210 and the turbo pump 260. The cold traps 280a, 280b may condense and capture water vapor in the charged particle microscope system 200 just upstream and downstream of the electron source 210 to prevent water from entering the electron source 210, so that the electron source 210 is substantially free of water. The first cold trap 280a can be positioned just downstream of the electron source 210 so that any water vapor in the gas flowing into the electron source 210 from the beam column 220 can be condensed and trapped before the water enters the electron source 210. The second cold trap 280b can be positioned just upstream of the electron source 210 so that any water vapor in the gas that may flow back into the electron source 210 from the turbo pump 260 can be condensed and trapped before entering the electron source 210. Although two cold traps 280a, 280b are depicted, in some embodiments, only one cold trap (e.g., a cold trap located downstream of the electron source) is included in the microscope system.

[0036] Go to Figure 2B, the first cold trap 280a may include a first cold structure 282a and a first heat removal element 284a coupled to the first cold structure 282a. The second cold trap 280b may include a second cold structure 282b and a second heat removal element 284b coupled to the second cold structure 282b. The first cold structure 282a and the second cold structure 282b may be made of glass, steel, etc. The heat removal elements 284a, 284b may include a coolant (e.g., liquid nitrogen, dry ice in acetone, cold water, etc.) that circulates within the heat removal elements 284a, 284b to remove heat from the cold structures 282a, 282b, so that the cold structures 282a, 282b may have a temperature that cools water vapor entering the cold structures 282a, 282b into a solid or liquid. For example, the heat removal elements 284a, 284b may each include a circulation element (e.g., a coil, a tube, a channel, etc., and one or more pumps for circulating the coolant in the coil, the tube, the channel, etc.) that circulates the coolant from the reservoir so that the coolant absorbs heat from the cold structure 282a, 282b and is then circulated away. In some embodiments, the heat removal elements 284a, 284b may be fluidly coupled to a reservoir containing the coolant, however, in other embodiments, the heat removal element may include a reservoir with the coolant. In some embodiments, the heat removal elements 284a, 284b may use thermoelectric cooling (such as using a Peltier cooling system) to transfer heat away from the cold structure 282a, 282b. In other embodiments, other means of removing heat using a heat removal system are contemplated.

[0037] The first cold structure 282a and the second cold structure 282b include a first cold surface 288a and a second cold surface 288b, respectively, that capture condensed water. For example, the cold surfaces 288a, 288b can be adsorptive, such that the cold surfaces 288a, 288b are adsorptive surfaces that collect condensed water along the cold surfaces 288a, 288b. However, in other embodiments, the cold surfaces can be made of an absorbent material, such that the cold surfaces are absorbent surfaces that absorb condensed water within the cold surfaces. The cold surfaces 288a, 288b can be cylindrical, however, in other embodiments, the cold surfaces can have any geometric shape, including conical, cubic, etc.

[0038] The first cold surface 288a and the second cold surface 288b can define the area cooled by the heat removal elements 284a and 284b in the cold structure 282a and 282b as the first cold area 286a and the second cold area 286b, respectively. The cold structure 282a and 282b can be cooled to a temperature significantly lower than the freezing point of water at the pressure generated by the turbo pump 260, such as below about -50°C, such as below about -85°C, or below about -105°C. In this way, any water vapor entering the cold zone 286a and 286b can be quickly cooled and condensed, and then captured along the cold surface 288a and 288b. In some embodiments, the cold structure can be cooled to a temperature significantly lower than the freezing point of oxygen at the pressure generated by the turbo pump, such as below about -180°C, such as below about -190°C, or such as below about -200°C. In this way, oxygen can be cooled and condensed, and then captured along the cold surface of the cold trap.

[0039] In some embodiments, the cold structures 282a, 282b may include a mesh structure to increase the surface area to volume ratio of the cold structures 282a, 282b. The mesh structure may define a plurality of channels for gas to enter and exit the electron source 210, and a plurality of cold zones are defined within these channels to condense water vapor on the surface of the channels. Therefore, the mesh structure may increase the amount of surface for capturing any condensed water vapor passing through the cold zones 286a, 286b. The mesh structure may include a honeycomb shape defining hexagonal channels, however, in other embodiments, the mesh structure may have other shapes, such as defining cylindrical channels, rectangular channels, tapered channels, multiple baffles, etc. In some embodiments, the first cold structure 282a of the first cold trap 280a may additionally define a central aperture through this mesh structure to allow electrons to pass from the electron source 210 to the beam column 220 without inhibition. The second cold structure 282b of the second cold trap 280b may not define a central aperture, but may be substantially entirely a mesh structure to maximize the interception of reflowing water vapor.

[0040] Figure 3 An example charged particle microscope system 300 is depicted. It should be understood that features ending with similar reference numerals as features discussed above are similar unless otherwise noted below. The charged particle microscope system 300 includes a first turbopump 360a, a second turbopump 360b, and a gas reservoir 324. The second turbopump 360b can be similar to the first turbopump 360a, except that the second turbopump 360b can pump to a higher pressure than the first turbopump 360a. For example, the first turbopump 360a can pump to a pressure below about 10 -10 Torr (such as less than or about 10 -11 Torr, such as less than or about 10 -12 Torr, or such as less than or about 10 -13 The second turbo pump 360b may pump to a first pressure greater than about 10-13 Torr and less than about 10 -6 For example, the second pressure may be greater than or about 10 -12 Torr, greater than or about 10 -11 Torr, or greater than or about 10 -10 The second pressure may be less than or about 10 -6 Torr, less than or about 10 -7 Torr, less than or about 10 -8 Torr, or less than or about 10 -9 However, other pressure values ​​are contemplated. In this way, a consistent gas flow path from the vacuum chamber 340, through the second turbo pump 360b, and to the first turbo pump 360a can be maintained.

[0041] When the second turbopump 360b draws gas from the vacuum chamber 340, the second turbopump 360b can collect water vapor. Therefore, the second turbopump 360b can reduce the amount of water vapor that can enter the electron source 310 by collecting at least some (if not all) of the water vapor downstream of the electron source 310. Therefore, the gas entering the electron source 310 upstream of the second turbopump 360b can be substantially anhydrous. In other embodiments, there may be more than two turbopumps, such as three, four, etc. For example, for each of the beam column, the objective lens and / or the vacuum chamber, there may be one or more turbopumps. These other turbopumps may be positioned downstream of the second turbopump, and the farther downstream of the turbopump, the greater the pressure that these other turbopumps can each be pumped to. In this way, a consistent gas flow path from the vacuum chamber, through multiple turbopumps and reaching the first turbopump can still be maintained.

[0042] The gas reservoir 324 may contain an inert gas and may be fluidly connected to the first turbo pump 360a so that the first turbo pump 360a delivers at least a portion of the inert gas from the gas reservoir 324 to the electron source 310. The inert gas may be a gas that is not easily ionized. For example, the inert gas may be argon, nitrogen, dry air, helium, etc. The gas reservoir 324 may be positioned in the beam column 320, however, in other embodiments, the gas reservoir may be a separate component housed outside the beam column. In some embodiments, the outlet 325 may be positioned in the beam column 320, downstream of the electron source 310 and upstream of the second turbo pump 360b. In other embodiments, the outlet may be positioned upstream of the beam column. Therefore, the pressure at the outlet 325 may be less than the pressure generated by the second turbo pump 360b and greater than the pressure generated in the electron source 310 by the first turbo pump 360a. In this way, the inert gas from the gas reservoir 324 may be delivered to the electron source 310 by the first turbo pump 360a. When the second turbo pump 360b collects water vapor downstream of the gas reservoir 324, the gas entering the electron source 310 can be substantially completely inert gas and can be substantially free of water. Therefore, degradation of the cathode electrode can be minimized and the life of the cathode electrode can be increased.

[0043] In some embodiments, one or more cold traps (e.g., similar to FIG. 2A to FIG. 2B The cold trap 260a, 260b of the second turbo pump) is further ensured that the electron source 310 is substantially anhydrous. For example, the cold trap may be positioned downstream of the second turbo pump and just upstream of the second turbo pump, but downstream of the outlet of the gas reservoir. Therefore, any water vapor that has not yet been collected by the second turbo pump may be condensed and captured in a cold trap in the first cold trap or the second cold trap before entering the electron source. In addition, similar to the second cold trap 280b, the third cold trap may be positioned between the first turbo pump and the electron source to condense and capture any reflux water vapor from the first turbo pump. In yet another embodiment, one or more cold traps and one or more pumps may be present, as discussed above, but there is no gas reservoir for accommodating inert gas.

[0044] Figure 4An example charged particle microscope system 400 is depicted. It should be understood that features ending with similar reference numerals as features discussed above are similar unless otherwise noted below. The electron source 410, beam column 420, objective lens 430, vacuum chamber 440, sample holder 444, turbo pump 460, and holder motion system 470 can be positioned in a substantially water-free container 490. The container 490 can be a substantially water-free glove box, room, etc. Conversely, the container 490 can be completely filled with an inert gas, such that the electron source 410 can include only the inert gas. For example, an external pump can draw substantially all of the water from within the container 490 while simultaneously drawing the inert gas into the container until the entire interior volume of the container 490 is substantially free of water (e.g., until the container includes a dry interior volume), including the electron source 410.

[0045] Figure 5 and Figure 6 Example graphs 500, 600 are depicted, respectively, for a charged particle microscope system that does not have a substantially anhydrous electron source. The graphs 500, 600 depict that the voltage applied to the Wehner electrode (e.g., the Wehner voltage) decreases over time. In other words, the negative bias voltage of the Wehner electrode increases over time. As described above, this is caused by the deposition of a contamination layer on the Wehner electrode. Since this deposition layer interferes with the electric field generated by the Wehner electrode, the negative bias voltage of the Wehner electrode must increase over time to ensure that the electron beam current is stable. Therefore, these graphs 500, 600 provide a numerical representation of the results of an electron microscope system that does not have a substantially anhydrous electron source.

[0046] Figure 7 and Figure 8 Example graphs 700, 800 of charged particle microscope systems with substantially anhydrous electron sources are depicted, respectively. Specifically, graph 700 depicts an example charged particle microscope system with a substantially anhydrous electron source using argon, and graph 800 depicts an example charged particle microscope system with a substantially anhydrous electron source using dry air. As shown, for both systems, the negative bias of the voltage provided to the Wiener does not increase but decreases (i.e., the value of the voltage increases). This indicates that the cathode electrode of the charged particle microscope system of graphs 700, 800 degrades significantly less over time than the cathode electrode of the charged particle microscope system of graphs 500, 600. Depending on the sample (e.g., the reactivity of the sample to the gas type), the environment of the charged particle microscope system, and the type of the charged particle microscope system, either argon or dry air may be preferred. Although the life of cathode electrodes for substantially water-free electron sources may be about 150 hours, in substantially water-free electron sources, degradation of the cathode electrodes may be minimized such that the life of these cathode electrodes may be increased to about 1500 hours (or even longer).

[0047] In the foregoing description, embodiments of the present disclosure have been described with reference to many specific details, which may vary depending on the embodiment. Therefore, the description and drawings are to be considered illustrative rather than restrictive. The only and exclusive indication of the scope of the present disclosure, and what the applicant intends as an indication of the scope of the present disclosure, is the literal and equivalent range of the set of claims issued from this application in the specific form in which these claims are issued, including any subsequent amendments. The specific details of a particular embodiment may be combined in any suitable manner without departing from the spirit and scope of the embodiments of the present disclosure.

[0048] In addition, spatially relative terms such as "bottom" or "top" may be used to describe the relationship of an element and / or feature to another element and / or feature, as illustrated, for example, in the accompanying drawings. It should be understood that spatially relative terms are intended to cover different orientations of the device in use and / or operation in addition to the orientation depicted in the accompanying drawings. For example, if the device in the accompanying drawings is turned over, the element described as the "bottom" surface may be oriented "above" other elements or features. The device may be oriented in other ways (e.g., rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

[0049] As used herein, the terms "and", "or" and "and / or" may include multiple meanings, which are also expected to depend at least in part on the context in which such terms are used. Generally, if used in an associative list such as A, B, or C, "or" is intended to mean A, B, and C (used herein in an inclusive sense), as well as A, B, or C (used herein in an exclusive sense). In addition, as used herein, the term "one or more" may be used to describe any feature, structure, or characteristic in the singular, or may be used to describe a certain combination of features, structures, or characteristics. However, it should be noted that this is merely an illustrative example, and the subject matter claimed is not limited to this example. In addition, if used in an associative list such as A, B, or C, the term "at least one of" may be interpreted to mean any combination of A, B, and / or C, such as A, B, C, AB, AC, BC, AA, AAB, ABC, AABBCCC, etc.

[0050] References throughout this specification to "one example," "example," "some examples," or "exemplary implementations" mean that a particular feature, structure, or characteristic described in conjunction with that feature and / or example may be included in at least one feature and / or example of the claimed subject matter. Thus, the appearances of the phrases "in one example," "example," "in some examples," "in some implementations," or other similar phrases throughout this specification do not necessarily all refer to the same features, examples, and / or limitations. Furthermore, particular features, structures, or characteristics may be combined in one or more examples and / or features.

[0051] In some specific implementations, operation or processing may involve physical manipulation of physical quantities. Typically, but not necessarily, such quantities may take the form of electrical or magnetic signals that can be stored, transferred, combined, compared, or otherwise manipulated. Mainly for the reasons of common usage, it has been proven that it is convenient to sometimes refer to such signals as bits, data, values, elements, symbols, characters, items, quantities, numbers, etc. However, it should be understood that all of these or similar terms will be associated with appropriate physical quantities and are merely convenient markers. Unless otherwise specifically stated, as will be apparent from the discussion herein, it should be understood that throughout this specification, discussions using terms such as "processing", "calculating", "estimating", "determining", etc. refer to the actions or processes of specific devices (such as special-purpose computers, special-purpose computing devices, or similar special-purpose electronic computing devices). Therefore, in the context of this specification, special-purpose computers or similar special-purpose electronic computing devices are capable of manipulating or transforming signals, which are typically represented as physical electronic quantities or magnetic quantities in the memory, registers, or other information storage devices, transmission devices, or display devices of special-purpose computers or similar special-purpose electronic computing devices.

[0052] In the foregoing detailed description, many specific details have been set forth to provide a thorough understanding of the claimed subject matter. However, those skilled in the art will appreciate that the claimed subject matter may be practiced without these specific details. In other cases, methods and apparatus that would be understood by those skilled in the art are not described in detail so as not to obscure the claimed subject matter. Therefore, it is intended that the claimed subject matter is not limited to the specific examples disclosed, but that the claimed subject matter may also include all aspects falling within the scope of the appended claims and their equivalents.

Claims

1. A charged particle microscope system, comprising: an electron source housing a Wehnelt electrode and a cathode, wherein the electron source comprises a substantially water-free dry environment defining a volume between the Wehnelt electrode and the cathode; a beam column comprising a plurality of electromagnetic lens elements; and A vacuum chamber includes a sample holder, wherein an electron beam axis is defined from the cathode to the sample holder.

2. The charged particle microscope system of claim 1, wherein the dry environment is substantially anhydrous when the dry environment comprises less than 5% humidity.

3. The charged particle microscope system of claim 1, wherein the dry environment is substantially oxygen-free.

4. A charged particle microscope system according to claim 3, wherein the dry environment is substantially oxygen-free when the dry environment comprises less than 5% oxygen.

5. The charged particle microscope system according to claim 1, The charged particle microscope system further includes a first cold trap positioned between the beam column and the Wöhner electrode, and Wherein the first cold trap comprises: a first adsorption surface, the first adsorption surface defining a first cold zone, the first cold zone being at a first temperature significantly below the freezing point of water; and A first heat removing element is coupled to the first cold surface.

6. The charged particle microscope system of claim 5, wherein the first heat removal element comprises a Peltier cooling system.

7. The charged particle microscope system of claim 5, wherein the first heat removal element comprises at least one of the circulation elements in fluid communication with a reservoir containing a coolant.

8. The charged particle microscope system of claim 7, wherein the coolant comprises at least one of liquid nitrogen or dry ice in acetone.

9. The charged particle microscope system according to claim 5, The charged particle microscope system further comprises: a turbo pump in fluid communication with the electron source; a second cold trap, the second cold trap being positioned between the turbo pump and the electron source, Wherein the second cold trap comprises: a second adsorption surface, the second adsorption surface defining a second cold zone, the second cold zone being at a second temperature significantly below the freezing point of water; and A second heat removing element is coupled to the second cold surface.

10. The charged particle microscope system of claim 9, wherein: The second adsorption surface comprises a plurality of channels; and The plurality of channels each define a channel cold zone.

11. The charged particle microscope system according to claim 1, The charged particle microscope system further comprises: an inert gas reservoir containing an inert gas and including an outlet in fluid communication with the electron source; and a first turbo pump in fluid communication with the electron source and the outlet for delivering at least a portion of the inert gas into the dry environment, and The first turbo pump generates a first pressure in the electron source, and the first pressure is greater than a second pressure at the outlet.

12. The charged particle microscope system according to claim 11, The charged particle microscope system further comprises a second turbo pump in fluid communication with the vacuum chamber and the beam column, wherein: the outlet is positioned between the electron source and the second turbo pump; and The second turbopump generates a third pressure in the bundle column, the third pressure being greater than the second pressure.

13. The charged particle microscope system according to claim 12 further comprises a third turbopump, wherein the third turbopump is fluidically connected to the vacuum chamber, wherein the third turbopump generates a fourth pressure, and the fourth pressure is greater than the third pressure.

14. The charged particle microscope system of claim 11, wherein the inert gas comprises at least one of argon, nitrogen, dry air, and helium.

15. The charged particle microscope system of claim 11, wherein the outlet is positioned in the beam column.

16. The charged particle microscopy system of claim 1, further comprising a container housing the electron source, the beam column, and the vacuum chamber, wherein the container comprises a dry interior volume.

17. A charged particle microscope system, comprising: an electron source containing a Wehner electrode and a cathode in a substantially water-free dry environment; a beam column comprising a plurality of electromagnetic lens elements; and A vacuum chamber includes a sample holder, wherein an electron beam axis is defined from the cathode to the sample holder.

18. The charged particle microscope system according to claim 17, The charged particle microscope system further comprises: a turbo pump in fluid communication with the electron source; a first cold trap positioned between the beam column and the Weiner electrode; a second cold trap, the second cold trap being positioned between the turbo pump and the electron source, in: The first cold trap comprises: a first adsorption surface defining a first cold zone at a first temperature significantly below the freezing point of water; and a first heat removing element coupled to the first cold surface; and The second cold trap comprises: a second adsorptive surface defining a second cold zone at a second temperature significantly below the freezing point of water; and A second heat removing element is coupled to the second cold surface.

19. The charged particle microscope system according to claim 17, The charged particle microscope system further comprises: an inert gas reservoir containing an inert gas and including an outlet in fluid communication with the electron source; a first turbo pump in fluid communication with the electron source and the outlet to deliver at least a portion of the inert gas into the dry environment; and a second turbopump in fluid communication with the vacuum chamber and the beam column, in: the outlet being positioned between the electron source and the second turbo pump; The first turbo pump generates a first pressure in the electron source, the first pressure being greater than a second pressure at the outlet; and The second turbopump generates a third pressure in the bundle column, the third pressure being greater than the second pressure.

20. A charged particle microscope system, comprising: an electron source housing a Wehnelt electrode and a cathode electrode, wherein the electron source comprises a substantially water-free dry environment defining a volume between the Wehnelt electrode and the cathode electrode; a beam column comprising a plurality of electromagnetic lens elements; and A vacuum chamber includes a sample holder, wherein an electron beam axis is defined from the cathode electrode to the sample holder.

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