Dry electron source environment

Abstract

To provide new charged particle microscope systems optimizing the use of Wehnelt electrodes.SOLUTION: A charged particle microscope system comprises: an electron source housing a Wehnelt electrode and a cathode, where the electron source may include a dry environment defining a volume between the Wehnelt electrode and the cathode that may be substantially water-free; a beam column including 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.SELECTED DRAWING: Figure 1B

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Non-Provisional Application No. 18 / 485,133, filed October 11, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a dry electron source environment. [Background technology]

[0003] Electron microscopes are used as imaging tools by focusing an electron beam from an electron emitter onto a sample with sufficient size and then detecting the reflection of those electrons to produce a high resolution image of the sample. One step in focusing and controlling the size of the electron beam can include emitting electrons through an aperture in a Wehnelt electrode. The Wehnelt electrode is charged to a negative bias voltage with respect to the electron emitter to generate an electrostatic field around the Wehnelt electrode, which repels the electrons toward the center of the aperture in the Wehnelt electrode, thus focusing the electron beam emitted through the aperture. New charged particle microscope systems that optimize the use of the Wehnelt electrode are desired. Summary of the Invention

[0004] One aspect of the disclosure provides a charged particle microscope system including an electron source housing a Wehnelt electrode and a cathode, the electron source including a dry environment defining a substantially water-free volume between the Wehnelt electrode and the cathode, a beam column including a plurality of electromagnetic lens elements, and a vacuum chamber including a sample holder. An electron beam axis is defined from the cathode to the sample holder. The dry environment can be substantially water-free if the dry environment can include less than 5% humidity. The dry environment can be substantially oxygen-free. The dry environment can be substantially oxygen-free if the dry environment can include less than 5% oxygen. The charged particle microscope can further include a first cold trap positioned between the beam column and the Wehnelt electrode. The first cold trap can include a first adsorption surface defining a first cold region at a first temperature substantially below the freezing point of water, and a first heat removal element coupled to the first cold surface. The first heat removal element can include a Peltier cooling system. The first heat removal element may include at least one of a circulation element 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 further include a turbo pump in fluid communication with the electron source, and the second cold trap may be positioned between the turbo pump and the electron source. The second cold trap may include a second adsorption surface defining a second cold region at a second temperature substantially below the freezing point of water, and 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 region. The charged particle microscope system may further include an inert gas reservoir containing an inert gas, and 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 for transporting at least a portion of the inert gas into the dry environment. The first turbo pump is capable of generating a first pressure within the electron source that is greater than a second pressure at the outlet.The charged particle microscope system may further include 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 second turbo pump capable of generating a third pressure in the beam column greater than the second pressure. The charged particle microscope system may further include a third turbo pump in fluid communication with the vacuum chamber. The third turbo pump may generate a fourth pressure 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 vessel housing the electron source, the beam column, and the vacuum chamber. The vessel may include a dry interior volume.

[0005] Another aspect of the present disclosure provides a charged particle microscope system comprising an electron source housing a Wehnelt electrode and a cathode in a substantially water-free dry environment, a beam column including a plurality of electromagnetic lens elements, and a vacuum chamber including a sample holder. An electron beam axis is defined from the cathode to the sample holder. The charged particle microscope system may further comprise a turbo pump in fluid communication with the electron source, a first cold trap may be positioned between the beam column and the Wehnelt electrode, and a second cold trap may be positioned between the turbo pump and the electron source. The first cold trap may include a first adsorbent surface defining a first cold region at a first temperature substantially below the freezing point of water, and a first heat removal element may be coupled to the first cold surface. The second cold trap may include a second adsorbent surface defining a second cold region at a second temperature substantially below the freezing point of water, and a second heat removal element may be coupled to the second cold surface. The charged particle microscope system may further include an inert gas reservoir containing an inert gas and 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 transport at least a portion of the inert gas into 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 the 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 including an electron source containing a Wehnelt electrode and a cathode electrode. The electron source includes a dry environment defining a substantially water-free volume between the Wehnelt electrode and the cathode electrode, a beam column including a plurality of electromagnetic lens elements, and a vacuum chamber including a specimen holder. An electron beam axis is defined from the cathode electrode to the specimen holder. [Brief description of the drawings]

[0007] A further understanding of the nature and advantages of the various embodiments can be realized by reference to the following figures. In the accompanying drawings, similar components or features may have the same reference label. Furthermore, various components of the same type may be distinguished by following the reference label with a dash and a second label that distinguishes between the similar components. If only a first reference label is used herein, the description is applicable to any one of the similar components having the same first reference label, regardless of the second reference label. [Figure 1A] FIG. 1 is a simplified cross-sectional view of an exemplary charged particle microscope system according to an embodiment of the present disclosure. [Figure 1B] 1B is a cross-sectional view of an electron source of the charged particle microscope system of FIG. 1A according to an embodiment of the present disclosure. [Figure 2A] FIG. 1 is a simplified cross-sectional view of an exemplary charged particle microscope system according to an embodiment of the present disclosure. [Figure 2B] 2B is a cross-sectional view of an electron source and cold trap of the charged particle microscope system of FIG. 2A according to an embodiment of the present disclosure. [Diagram 3] FIG. 1 is a simplified cross-sectional view of an exemplary charged particle microscope system according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a simplified cross-sectional view of an exemplary charged particle microscope system according to an embodiment of the present disclosure. [Diagram 5] 1 is an example graph of Wehnelt electrode voltage over time according to an embodiment of the present disclosure. [Figure 6] 1 is an example graph of Wehnelt electrode voltage over time according to an embodiment of the present disclosure. [Figure 7] 1 is an example graph of Wehnelt electrode voltage over time according to an embodiment of the present disclosure. [Figure 8] 1 is an example graph of Wehnelt electrode voltage over time according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Electron microscopy provides high-resolution imaging by detecting backscattered electrons (BSEs) generated by elastic scattering of an electron beam emitted from an electron emitter interacting with atoms of a sample. In one example, electrons can be emitted from a cathode electrode that is heated by an electric current. The emitted electrons are attracted to an anode disposed downstream of the cathode electrode, thus forming an electron beam generally directed toward the sample. However, to achieve a useful image, the electron beam must be further focused with sufficient size toward the sample.

[0009] One means of focusing and controlling the electron beam involves the use of a Wehnelt electrode, which is charged with a negative bias voltage to generate an electric field that not only repels electrons emitted from the cathode electrode, but also controls the current emission of the electron beam. The electron beam emitted from the cathode electrode is directed toward an aperture defined by the Wehnelt electrode, such that the electric field of the Wehnelt electrode allows electrons to be emitted only from an area defined by the electric field surrounding the aperture. In this manner, the Wehnelt electrode can assist in focusing and controlling the electron beam toward the specimen.

[0010] However, the electrons emitted from the cathode electrode may ionize the gas around the cathode electrode and the Wehnelt electrode (e.g., in the electron source). The positively ionized gas particles may be attracted to the electric field generated by the Wehnelt electrode and thus form a deposition layer on the Wehnelt electrode. In particular, the ionized gas particles may be particles evaporated from the cathode electrode due to oxidation of the cathode electrode. This deposition layer may interfere with the electric field generated by the Wehnelt electrode, which in turn may disturb the focus of the electron beam. This disturbance may be so severe that the electron beam cannot be corrected later in the beam column.

[0011] This problem may be especially pronounced in benchtop electron microscopes because the pumps used in these systems are smaller than larger electron microscopes, such as floor type electron microscopes. Thus, these smaller pumps may have a more difficult time pumping gas particles out of the electron source. Additionally, benchtop electron microscopes have smaller beam columns and fewer apertures than floor type models. This may result in higher operating pressures that may lead to contamination concentrations at the electron source.

[0012] One solution to this problem can include increasing the negative bias voltage of the Wehnelt electrode (e.g., increasing the negative value of the voltage supplied to the Wehnelt electrode). While this can address the electric field of the Wehnelt electrode, this still does not address the underlying problem of ionized gas particles forming a deposition layer along the Wehnelt electrode. Ignoring this deposition layer can result in the further problem of the deposition layer flaking off and floating back onto the cathode electrode (e.g., after thermal expansion and cooling of the deposition layer). This additional contamination layer on the cathode electrode can change the direction of electrons emitted from the cathode electrode, further disrupting the focus of the electron beam.

[0013] Another solution may involve dismantling the electron source to physically remove contamination within the electron source. However, this poses additional challenges as dismantling the electron source may expose the chamber to potential contamination. Again, this may be particularly problematic for tabletop electron microscopes, as they are located in areas with different cleanliness standards (e.g., laboratories or offices) and are not generally in controlled, contaminant-free environments. Furthermore, cleaning the electron source increases the risk that the electron microscope system will have alignment problems. Another problem is that the relatively weak vacuum system of a tabletop SEM has a poor ability to degas the interior surfaces from adsorbed species such as organic molecules and water.

[0014] The present disclosure provides a charged particle microscope system having an electron source with a substantially water-free dry environment. Because water is a common vapor species that enters a charged particle microscope system and oxygen is the primary catalyst in the evaporation of material from the cathode electrode, providing a substantially water-free dry environment for the electron source can reduce the evaporation of material from the cathode electrode. This, in turn, reduces the ionization of gas particles in the source portion of the microscope system, which in turn reduces the formation of deposition layers along the Wehnelt and cathode electrodes. Furthermore, because reducing the presence of oxygen also reduces the oxidation and evaporation of the cathode electrode, the lifetime of the cathode electrode can be significantly improved (e.g., from 150 hours of use to over 1,500 hours).

[0015] However, it may also prove difficult to remove water and / or oxygen from the electron source. 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. Thus, a solution to this problem may include both providing a substantially water-free or oxygen-free electron source while still allowing an unobstructed path from the cathode electrode to the sample. Various embodiments that provide such a solution are 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 section. Yet another embodiment includes enclosing the charged particle microscope system in a dry environment.

[0016] The remainder of the description is generally based on the results of scanning electron microscopy. Reference is made to scanning electron microscopes (SEMs), but it will be readily understood by one of ordinary skill in the art that the present technology is not so limited. The present design can be used with other types of charged particle microscopes, such as transmission electron microscopes (TEMs), scanning transmission electron microscopes (STEMs), dual beam systems including ion and electron beam sources, reflection electron microscopes (REMs), circuit edit microscopes, etc. Thus, the present disclosure and claims should not be considered limited to any particular exemplary microscope discussed, but rather can be broadly utilized with any number of electron microscopes that may exhibit some or all of the electrical or chemical properties of the discussed examples.

[0017] 1A-1B depict an exemplary charged particle microscope system 100 illustrating a system for focusing and controlling the emission current of an electron beam using a Wehnelt electrode. Referring to FIG. 1B, the electron microscope 100 can include multiple sections including an electron source 110, a beam column 120, an objective lens 130, and a vacuum chamber 140. The electron source 110 can include high voltage supply components, vacuum system components, and an electron emitter configured to generate an electron beam that is accelerated in the beam column 120. The beam column 120 includes various beam steering components 122, such as electromagnetic lens elements, configured to shape and form the electron beam from the electron source 110 into a substantially circular beam having a substantially uniform profile that is focused onto a sample by the objective lens 130.

[0018] Electron beams are typically characterized by, among other criteria, a beam current and an acceleration voltage applied to generate the beam. The range of beam current and acceleration voltage may vary between instruments and are typically selected based on the material properties of the sample or the type of analysis being performed. In general, however, electron beams are characterized by energies of about 0.1 keV to about 50 keV (e.g., for an acceleration voltage of 0.1 kV) and beam currents of picoamps to microamps.

[0019] The vacuum chamber 140 and / or the 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 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 operatively 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 study and / or image a sample held within the sample holder 144. A vacuum chamber door 142 provides access to the vacuum chamber 140 from outside the charged particle microscope system 100 (e.g., for cleaning, changing samples, etc.).

[0020] The turbo pump 160 can create a vacuum within the vacuum chamber 140 by creating a pressure differential by pumping material from within the vacuum chamber 140. The vacuum chamber 140 can be free of material to minimize the risk of any intervening material within the vacuum chamber 140 interfering with the electron beam to the specimen. The turbo pump 160 can operate at a speed of approximately 10 -10 Less than Torr, e.g., about 10 -11 Torr or less, e.g., about 10 -12 Torr or less, or, for example, about 10 -13The vacuum chamber 140 (as well as any intervening components) may be pumped to a pressure of sub-Torr. A 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 pump gases out of 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, to the sample holder 144, with the turbo pump 160 defining the most upstream point and the sample holder 144 defining the most downstream point. In this manner, "downstream" and "upstream" may be relative terms used to describe the location of various components along this path.

[0021] 1B, the electron source 110 can include a Wehnelt electrode 112 and a cathode electrode 114 (e.g., a cathode crystal). The cathode electrode 114 can be heated (e.g., to about 1700-1800 Kelvin) with a voltage to emit an electron beam A from the tip of the cathode electrode 114. The cathode electrode 114 can be cerium hexaboride, lanthanum hexaboride, or other material that can be used as an electron emitter source. The Wehnelt electrode 112 can define an opening 116 downstream of the cathode electrode 114 to allow the electron beam A to pass therethrough. The Wehnelt electrode 112 can be charged with a negative bias voltage to generate an electric field that is more negative than the voltage of the cathode electrode 114. This electric field focuses and controls the current emission of electron beam A by surrounding the aperture 116 with the electric field, so that any stray electrons leaving electron beam A are repelled by the electric field toward the centerline of the aperture 116. In this manner, the electron beam axis can be defined from the cathode electrode 114 to the specimen holder 144. The amount of negative bias voltage supplied to the Wehnelt electrode 112 can be correlated to the amount of electron beam energy emitted from the cathode electrode 114.

[0022] However, as mentioned above, the emitted electrons may ionize gas particles that may be present within the electron source 110. Such gas particles may be material evaporated from the cathode electrode 114, such as from oxidation of the cathode electrode 114. In other words, at least some of the gas particles within the electron source 110 may be by-products of the cathode electrode 114 (e.g., cerium, borides, oxides, etc.) reacting with oxygen within the electron source 110. However, while oxidation may play a role in contamination, it is not the only chemical mechanism by which the performance of the electron source 110 degrades. These gas particles may be ionized and have an electric charge. At least some of these ionized gas particles B may be ionized and have a positive charge, leading to the ionized gas particles B being attracted to the Wehnelt electrode 112. The ionized gas particles B may form a deposition layer 118 along the Wehnelt electrode 112 and extend partially into the opening 116.

[0023] This deposition layer 118 reduces the potential and electric field of the Wehnelt electrode 112. To counter this reduction in potential, the Wehnelt electrode 112 may require a larger negative voltage to maintain a desired electric field that focuses and controls the current emission of the electron beam A. Furthermore, portions of the deposition layer 118 may flake off during thermal expansion and cooling of the Wehnelt electrode 112 and the deposition layer 118. These flakes may float to the cathode electrode 114 and form another deposition layer, which may further redirect the electron beam A. Thus, the presence of oxygen in the electron source 110 not only causes faster degradation of the cathode electrode 114, but oxygen also causes the formation of the deposition layer 118, resulting in misalignment of the electron beam A.

[0024] Because oxygen is a chemical component of water, which is a common vapor that may permeate the electron source 110, removing water from the electron source 110 (e.g., from the volume between the Wehnelt electrode 112 and the cathode electrode 114) so ​​that the electron source 110 is a dry environment may be beneficial to prevent degradation of the cathode electrode 114. For example, the electron source 110 may be a dry environment if the electron source 110 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 may be a dry environment if the electron source includes 0.01% humidity. In other embodiments, the electron source 110 may be a dry environment if the electron source 110 is substantially free of oxygen. For example, the electron source 110 may 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.

[0025] 2A and 2B depict an exemplary charged particle microscope system 200. Features ending with similar reference numbers to features discussed above are understood to be similar, except as 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, and 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 trap water vapor within the charged particle microscope system 200 immediately upstream and downstream of the electron source 210 to prevent water from entering the electron source 210, such that the electron source 210 is substantially water-free. The first cold trap 280a can be positioned just downstream of the electron source 210 so that any water vapor in the gas flowing from the beam column 220 to the electron source 210 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 from the turbo pump 260 to the electron source 210 can be condensed and trapped before it enters the electron source 210. Although two cold traps 280a, 280b are depicted, in some embodiments only one cold trap (e.g., the cold trap downstream of the electron source) is included in the microscope system.

[0026] 2B, the first cold trap 280a can 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 can 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 can be made of glass, steel, etc. The heat removal elements 284a, 284b can include a coolant (e.g., liquid nitrogen, dry ice in acetone, cold water, etc.) circulated within the heat removal elements 284a, 284b to remove heat from the cold structures 282a, 282b such that the cold structures 282a, 282b can have a temperature that cools water vapor entering the cold structures 282a, 282b to a solid or liquid. For example, the heat removal elements 284a, 284b may each include a circulation element (e.g., a coil, tube, channel, etc., and one or more pumps for circulating the coolant within the coil, tube, channel, etc.) that circulates the coolant from a reservoir such that the coolant absorbs heat from the cold structures 282a, 282b before being circulated away. In some embodiments, the heat removal elements 284a, 284b may be fluidly coupled to a reservoir that contains the coolant, while in other embodiments, the heat removal elements may include a reservoir having a 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 structures 282a, 282b. In other embodiments, other means of removing heat using a heat removal system are contemplated.

[0027] The first cold structure 282a and the second cold structure 282b each include a first cold surface 288a and a second cold surface 288b that trap condensed water. For example, the cold surfaces 288a, 288b may be adsorbent such that the cold surfaces 288a, 288b are adsorbent surfaces that collect condensed water along the cold surfaces 288a, 288b. However, in other embodiments, the cold surfaces may 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 may be cylindrical, but in other embodiments, the cold surfaces may have any geometric shape, including conical, cubic, etc.

[0028] The first cold surface 288a and the second cold surface 288b can define regions within the cold structures 282a, 282b that are cooled by the heat removal elements 284a, 284b as the first cold region 286a and the second cold region 286b, respectively. The cold structures 282a, 282b can be cooled to a temperature substantially below the freezing point of water at the pressure generated by the turbo pump 260, such as below about -50°C, below about -85°C, or below about -105°C. In this manner, any water vapor that enters the cold regions 286a, 286b can be rapidly cooled and condensed before being trapped along the cold surfaces 288a, 288b. In some embodiments, the cold structures can be cooled to a temperature substantially below 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 below about -200°C. In this way, the oxygen can be cooled and condensed before being trapped along the cold surface of the cold trap.

[0029] In some embodiments, the cold structures 282a, 282b may include a mesh structure to increase the surface-to-volume ratio of the cold structures 282a, 282b. The mesh structure may define multiple channels for the passage of gas to and from the electron source 210, and multiple cold regions are defined within these channels to condense water vapor on the surfaces of the channels. Thus, the mesh structure may increase the amount of surface available to trap any condensed water vapor passing through the cold regions 286a, 286b. The mesh structure may include a honeycomb shape defining hexagonal channels, although in other embodiments, the mesh structure may have other shapes, such as defining cylindrical channels, rectangular channels, tapered channels, multiple baffles, and the like. In some embodiments, the first cold structure 282a of the first cold trap 280a may additionally define a central opening through the mesh structure to allow electrons to pass unimpeded from the electron source 210 to the beam column 220. The second cold structure 282b of the second cold trap 280b may not define a central opening, and may instead be a substantially complete mesh structure to maximize trapping of backflowing water vapor.

[0030] FIG. 3 depicts an exemplary charged particle microscope system 300. Features ending with similar reference numbers to features discussed above are understood to be similar, except as noted below. The charged particle microscope system 300 includes a first turbo pump 360a, a second turbo pump 360b, and a gas reservoir 324. The second turbo pump 360b can be similar to the first turbo pump 360a, except that the second turbo pump 360b can pump to a higher pressure than the first turbo pump 360a. For example, the first turbo pump 360a can pump to a pressure of approximately 10 -10 Less than Torr, e.g., about 10 -11 Torr or less, e.g., about 10 -12 Torr or less, or, for example, about 10 -13 The second turbo pump 360b can pump to a first pressure of about 10 Torr or less. -13Torr and approximately 10 -6 The second pressure can be pumped to a second pressure that is less than about 10 Torr. -12 Torr or higher, approximately 10 -11 Torr or above, or about 10 -10 The second pressure may be about 10 Torr or more. -6 Torr or less, about 10 -7 Torr or less, about 10 -8 Torr or less, or about 10 -9 Torr or less, although other pressure values ​​are contemplated. In this manner, a consistent gas flow path from the vacuum chamber 340 through the second turbo pump 360b to the first turbo pump 360a can be maintained.

[0031] The second turbo pump 360b may collect water vapor as it pumps gas from the vacuum chamber 340. Thus, the second turbo pump 360b may reduce the amount of water vapor that may enter the electron source 310 by collecting at least some, if not all, of the water vapor downstream of the electron source 310. Thus, the gas entering the electron source 310 upstream of the second turbo pump 360b may be substantially free of water. In other embodiments, there may be more than two turbo pumps, such as three, four, etc. For example, there may be one or more turbo pumps for each of the beam column, objective lens, and / or vacuum chamber. These other turbo pumps may be positioned downstream of the second turbo pump, and each of these other turbo pumps may pump to a higher pressure the further downstream the turbo pump. In this manner, a consistent gas flow path from the vacuum chamber through the multiple turbo-type turbo pumps to the first turbo pump may still be maintained.

[0032] The gas reservoir 324 can contain an inert gas and can be in fluid communication with the first turbo pump 360a such that the first turbo pump 360a transports at least a portion of the inert gas from the gas reservoir 324 into the electron source 310. The inert gas can be a gas that does not easily ionize. For example, the inert gas can be argon, nitrogen, dry air, helium, etc. The gas reservoir 324 can be located within the beam column 320, although in other embodiments the gas reservoir can be a separate component housed outside the beam column. In some embodiments, the outlet 325 can be located within the beam column 320 downstream of the electron source 310 and upstream of the second turbo pump 360b. In other embodiments the outlet can be located upstream of the beam column. Thus, the pressure at the outlet 325 can be less than the pressure generated by the second turbo pump 360b in the electron source 310 and greater than the pressure generated by the first turbo pump 360a. In this manner, the inert gas from the gas reservoir 324 can be transported by the first turbo pump 360a into the electron source 310. Because the second turbo pump 360b collects water vapor downstream of the gas reservoir 324, the gas entering the electron source 310 can be substantially entirely inert gas and substantially free of water. Thus, degradation of the cathode electrode can be minimized and the life of the cathode electrode can be extended.

[0033] In some embodiments, one or more cold traps (e.g., similar to cold traps 260a, 260b of FIGS. 2A-2B) may be used to further ensure that the electron source 310 is substantially free of water. For example, a cold trap may be positioned downstream of the second turbo pump and immediately upstream of the second turbo pump, but downstream of the outlet of the gas reservoir. Thus, any water vapor that may not have been collected by the second turbo pump may be condensed and trapped in one of the first or second cold traps before entering the electron source. Additionally, similar to the second cold trap 280b, a third cold trap may be positioned between the first turbo pump and the electron source to condense and trap any backflow water vapor from the first turbo pump. In yet another embodiment, there may be one or more cold traps and one or more pumps, as discussed above, but there may not be a gas reservoir containing an inert gas.

[0034] FIG. 4 depicts an exemplary charged particle microscope system 400. Features ending with similar reference numbers to features discussed above are understood to be similar, except as 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 within a substantially water-free vessel 490. The vessel 490 may be a substantially water-free glove box, room, etc. Alternatively, the vessel 490 may contain entirely inert gas, such that the electron source 410 may contain only inert gas. For example, an external pump can pump substantially all of the water out of the vessel 490 while drawing inert gas into the vessel until the entire interior volume of the vessel 490 containing the electron source 410 is substantially water-free (e.g., until the vessel contains a dry interior volume).

[0035] 5 and 6 depict exemplary graphs 500, 600, respectively, of a charged particle microscope system without a substantially water-free electron source. The graphs 500, 600 depict that the voltage (e.g., Wehnelt voltage) applied to the Wehnelt electrode decreases over time. In other words, the negative bias voltage of the Wehnelt electrode increases over time. As discussed above, this is caused by a contamination layer buildup on the Wehnelt electrode. Because this buildup layer interferes with the electric field generated by the Wehnelt electrode, the negative bias of the Wehnelt electrode must be increased over time to ensure that the electron beam current is stable. Thus, these graphs 500, 600 provide a numerical representation of the results of an electron microscope system without a substantially water-free electron source.

[0036] 7 and 8 depict exemplary graphs 700, 800 of charged particle microscope systems having substantially water-free electron sources, respectively. Specifically, graph 700 depicts an exemplary charged particle microscope system having a substantially water-free electron source using argon, and graph 800 depicts an exemplary charged particle microscope system having a substantially water-free electron source using dry air. As shown, for both of these systems, the negative bias of the voltage supplied to the Wehnelt does not increase, but rather decreases (i.e., the voltage increases in value). This indicates that the cathode electrodes of the charged particle microscope systems of graphs 700, 800 have significantly less degradation over time compared to the cathode electrodes of the charged particle microscope systems of graphs 500, 600. Depending on the sample (e.g., the reactivity of the sample to the type of gas), the environment of the charged particle microscope system, and the type of charged particle microscope system, either argon or dry air may be preferred. The lifetime of the cathode electrodes of a substantially water-containing electron source may be about 150 hours, whereas in a substantially water-free electron source, degradation of the cathode electrodes can be minimized, such that the lifetime of these cathode electrodes can be extended to about 1,500 hours (or even longer).

[0037] In the foregoing specification, the embodiments of the present disclosure have been described with reference to numerous specific details that may vary from one embodiment to another. Therefore, the specification and drawings should be regarded in an illustrative sense, not a restrictive sense. The sole and exclusive indication of the scope of the present disclosure, and what the applicant intends the scope of the present disclosure to be, is the literal and equivalent scope of a set of claims issued from this application, in the specific form in which such claims are issued, including any subsequent amendments. The specific details of specific embodiments can be combined in any suitable manner without departing from the spirit and scope of the embodiments of the present disclosure.

[0038] In addition, spatially relative terms such as "bottom" or "top" can be used to describe the relationship of an element and / or feature to another element and / or feature, for example, as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device during use and / or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, an element described as a "bottom" surface can then be oriented "above" the other element or feature. The device can be oriented differently (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can be interpreted accordingly.

[0039] The terms "and," "or," and "and / or" as used herein may include various meanings that are expected to depend, at least in part, on the context in which such terms are used. Typically, when "or" is used to associate a list, such as A, B, or C, it is intended to mean A, B, and C, which are used herein in an inclusive sense, as well as A, B, or C, which are used herein in an exclusive sense. In addition, the term "one or more" as used herein may be used to describe any feature, structure, or characteristic in the singular or may be used to describe any combination of features, structures, or characteristics. However, it should be noted that this is merely an illustrative example, and claimed subject matter is not limited to this example. Furthermore, the term "at least one of," when used to associate a list, such as A, B, or C, 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.

[0040] References throughout this specification to "one example," "an example," "a particular example," or "an exemplary embodiment" mean that a particular feature, structure, or characteristic described in connection with a feature and / or example may be included in at least one feature and / or example of the claimed subject matter. Thus, appearances of the phrases "in one example," "in an example," "in a particular example," "in a particular embodiment," 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 characteristics.

[0041] In some implementations, operations or processing may involve physical manipulation of physical quantities. Usually, though not necessarily, such quantities may take the form of electrical or magnetic signals that can be stored, transferred, combined, compared, or otherwise manipulated. It has proven convenient at times, primarily for reasons of common usage, to refer to such signals as bits, data, values, elements, symbols, characters, terms, numbers, numerals, or the like. It should be understood, however, that all of these or similar terms are to be associated with the appropriate physical quantities and are merely convenient labels. Unless otherwise indicated, as will be apparent from a discussion of this specification, discussions throughout this specification utilizing terms such as "processing," "computing," "calculating," "determining," or the like, should be understood to refer to operations or processes of a special purpose apparatus, such as a special purpose computer, a special purpose computing apparatus, or a similar special purpose electronic computing device. Thus, in the context of this specification, a special purpose computer or a similar special purpose electronic computing device can manipulate or transform signals that are typically represented as physical electronic or magnetic quantities in the memories, registers, or other information storage devices, transmission devices, or display devices of the special purpose computer or a similar special purpose electronic computing device.

[0042] In the foregoing detailed description, numerous specific details are set forth to provide a thorough understanding of the claimed subject matter. However, it will be understood by those skilled in the art that the claimed subject matter can be practiced without these specific details. In other instances, methods and apparatuses that would be known by those skilled in the art have not been described in detail so as not to obscure the claimed subject matter. Therefore, it is intended that the claimed subject matter not be limited to the particular examples disclosed, but that such claimed subject matter also includes all aspects falling within the scope of the appended claims, and their equivalents.

Claims

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

2. The charged particle microscope system of claim 1 , wherein the dry environment is substantially free of water if the dry environment contains less than 5% humidity.

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

4. The charged particle microscope system of claim 3 , wherein the dry environment is substantially free of oxygen if the dry environment contains less than 5% oxygen.

5. a first cold trap positioned between the beam column and the Wehnelt electrode; The first cold trap comprises: a first adsorbent surface defining a first cold region at a first temperature substantially below the freezing point of water; a first heat removal element 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 a circulation element 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. a turbopump in fluid communication with the electron source; a second cold trap positioned between the turbo pump and the electron source; The second cold trap comprises: a second adsorbent surface defining a second cold region at a second temperature substantially below the freezing point of water; a second heat removal element coupled to the second cold surface.

10. the second adsorption surface includes a plurality of channels; The charged particle microscope system of claim 9 , wherein the plurality of channels each define a channel cold region.

11. 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 for transporting at least a portion of the inert gas into the dry environment; 2. The charged particle microscope system of claim 1, wherein the first turbopump creates a first pressure in the electron source that is greater than a second pressure at the outlet.

12. a second turbo pump in fluid communication with the vacuum chamber and the beam column; the outlet is located between the electron source and the second turbo pump; The charged particle microscope system of claim 11 , wherein the second turbopump creates a third pressure in the beam column that is greater than the second pressure.

13. 13. The charged particle microscope system of claim 12, further comprising a third turbo pump in fluid communication with the vacuum chamber, the third turbo pump generating a fourth pressure 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 within the beam column.

16. The charged particle microscope system of claim 1 , further comprising a vessel housing the electron source, the beam column, and the vacuum chamber, the vessel including a dry interior volume.

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

18. a turbopump in fluid communication with the electron source; a first cold trap positioned between the beam column and the Wehnelt electrode; a second cold trap positioned between the turbo pump and the electron source; The first cold trap comprises: a first adsorbent surface defining a first cold region at a first temperature substantially below the freezing point of water; a first heat removal element coupled to the first cold surface; The second cold trap comprises: a second adsorbent surface defining a second cold region at a second temperature substantially below the freezing point of water; a second heat removal element coupled to the second cold surface.

19. 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 transport at least a portion of the inert gas into the dry environment; a second turbopump in fluid communication with the vacuum chamber and the beam column; the outlet is located between the electron source and the second turbo pump; the first turbo pump creates a first pressure within the electron source that is greater than a second pressure at the outlet; 20. The charged particle microscope system of claim 17, wherein the second turbopump creates a third pressure in the beam column that is greater than the second pressure.

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

Images