Non-uniform d-shaped focused ion beam

Abstract

To provide a method for generating desirable beam characteristics.SOLUTION: A method includes: directing a charged particle beam toward a target along a beam axis of a charged particle beam column by generating the charged particle beam by using a charged particle beam source; directing the charged particle beam through a long and thin opening positioned by being offset with respect to the beam axis; and focusing the beam on the target so as to generate an asymmetric strength profile of the beam, that is, the asymmetric strength profile having a sharp strength edge in the target on the basis of the offset long and thin opening.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The field is charged particle beam systems and methods for generating charged particle beams. [Background technology]

[0002] Multi-lens systems have been used to image the system aperture onto a sample, or have been used with aperture projection techniques to generate intensity distributions at the sample. However, such approaches are typically inappropriate for applications involving highly focused beams, or they generate inappropriately low-density and wide-area intensity distributions. Improved techniques for generating desirable beam characteristics, and systems for using them, remain needed. Summary of the Invention

[0003] The disclosed apparatus and method can create asymmetrically shaped intensity profiles with sharp edges (e.g., "D-shaped") for charged particle beams (e.g., electron beams, ion beams, etc.) by using offset elongated apertures.

[0004] According to one aspect of the disclosed technology, a method includes generating a charged particle beam using a charged particle beam source, directing the charged particle beam to a target along a beam axis of a charged particle beam column, directing the charged particle beam through an elongated aperture positioned offset with respect to the beam axis, and focusing the beam at the target to generate an asymmetric intensity cross-section of the beam, the cross-section having a sharp intensity edge at the target based on the offset elongated aperture.

[0005] In accordance with another aspect of the disclosed technique, an apparatus includes a charged particle beam source configured to generate a charged particle beam in a charged particle beam column and direct the charged particle beam to a target along a beam axis of the charged particle beam column; an elongated aperture positioned to receive the charged particle beam, the elongated aperture being offset with respect to the beam axis; and an objective lens configured to focus the beam at the target to generate an asymmetric intensity cross-section of the beam, the cross-section having a sharp intensity edge at the target based on the offset elongated aperture.

[0006] The foregoing and other objects, features, and advantages of the disclosed technology will become more apparent from the following detailed description which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0007] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. [Figure 1] 1 shows a plan view of a circular aperture and the corresponding intensity distribution of the beam (cross section) at the target produced after propagation through the circular aperture. [Figure 2] 1 is a plan view of an elliptical aperture and the corresponding intensity distribution (in a cross section) of the beam at the target produced after propagation through the elliptical aperture. [Figure 3] FIG. 10 is a plan view of an offset elliptical aperture and the corresponding intensity distribution (cross section) of the beam at the target produced after propagating through the offset elliptical aperture. [Figure 4] 1 is a cross-sectional intensity distribution of a beam focused at a target and generated using a circular aperture. [Figure 5] 10 is a graph of the lateral intensity distribution of a beam produced using a circular aperture and an offset elliptical aperture. [Figure 6] FIG. 1 is a schematic diagram of a charged particle beam microscope system. [Figure 7A] 10 is a diagram showing the intensity distribution of a beam cross section produced using a circular aperture. [Figure 7B] 10 is a diagram showing the intensity distribution of a beam cross section produced using a circular aperture. [Figure 7C] 10 is a diagram showing the intensity distribution of a beam cross section produced using a circular aperture. [Figure 7D] 10 is a diagram showing the intensity distribution of a beam cross section produced using a circular aperture. [Figure 7E] 10 is a diagram showing the intensity distribution of a beam cross section produced using a circular aperture. [Figure 7F] 10 is a diagram showing the intensity distribution of a beam cross section produced using a circular aperture. [Figure 7G] 10 is a diagram showing the intensity distribution of a beam cross section produced using a circular aperture. [Figure 7H] 10 is a diagram showing the intensity distribution of a beam cross section produced using a circular aperture. [Figure 7I] 10 is a diagram showing the intensity distribution of a beam cross section produced using a circular aperture. [Figure 8A] 1 shows the intensity distribution of the beam cross section produced using an on-axis elliptical aperture. [Figure 8B] 1 shows the intensity distribution of the beam cross section produced using an on-axis elliptical aperture. [Figure 8C] 1 shows the intensity distribution of the beam cross section produced using an on-axis elliptical aperture. [Figure 8D] 1 shows the intensity distribution of the beam cross section produced using an on-axis elliptical aperture. [Figure 8E] 1 shows the intensity distribution of the beam cross section produced using an on-axis elliptical aperture. [Figure 8F] 1 shows the intensity distribution of the beam cross section produced using an on-axis elliptical aperture. [Figure 8G] 1 shows the intensity distribution of the beam cross section produced using an on-axis elliptical aperture. [Figure 8H] 1 shows the intensity distribution of the beam cross section produced using an on-axis elliptical aperture. [Figure 8I] 1 shows the intensity distribution of the beam cross section produced using an on-axis elliptical aperture. [Figure 9A] 10 is an intensity distribution of a beam cross section produced using an off-axis elliptical aperture. [Figure 9B] 10 is an intensity distribution of a beam cross section produced using an off-axis elliptical aperture. [Figure 9C] 10 is an intensity distribution of a beam cross section produced using an off-axis elliptical aperture. [Figure 9D] 10 is an intensity distribution of a beam cross section produced using an off-axis elliptical aperture. [Figure 9E] 10 is an intensity distribution of a beam cross section produced using an off-axis elliptical aperture. [Figure 9F] 10 is an intensity distribution of a beam cross section produced using an off-axis elliptical aperture. [Figure 9G] 10 is an intensity distribution of a beam cross section produced using an off-axis elliptical aperture. [Figure 9H] 10 is an intensity distribution of a beam cross section produced using an off-axis elliptical aperture. [Figure 9I] 10 is an intensity distribution of a beam cross section produced using an off-axis elliptical aperture. [Figure 10] 1 is a flowchart of a method for selecting characteristics of a charged particle system that produces a sharp-edged beam. [Figure 11] 1 is a flowchart of a method for milling a specimen using a shaped beam. DETAILED DESCRIPTION OF THE INVENTION

[0008] The disclosed embodiments can address problems and difficulties associated with improving focused ion beam (FIB) milling performance by increasing the amount of current at a given diameter on the milling target. The embodiments can provide a sharp edge where the beam intensity drops off rapidly over a short distance (e.g., perpendicular to the edge). This can enable more precise material processing of the target using a charged particle beam, such as a FIB or electron beam. In many of the disclosed embodiments, the aperture used to define the beam is an elongated aperture, such as an elliptical aperture. The aperture is configured to be offset relative to the beam axis, and the elongated aperture can be used to increase the amount of current in the beam while minimizing the increase in beam size in the narrow axis of the aperture.

[0009] FIG. 1 illustrates a commonly used circular aperture 100 that can be located in a charged particle beam column (e.g., FIB, e-beam, etc.) alongside an intensity profile cross-section of a charged particle beam 102 generated at the surface of a target 104 using the circular aperture 100. In a milling example, the beam 102 can be scanned across the surface, e.g., here in the left-right x-direction (indicated by the right-pointing arrow), to remove material from the target 104, forming a cutting edge 106 and a target region 108 adjacent the cutting edge 106 that can be minimally affected by the beam 102. FIG. 2 illustrates an elliptical aperture 200 that can replace the circular aperture 100 in a charged particle beam column, along with the corresponding intensity profile of the charged particle beam cross-section 202 at the target 204. The elliptical aperture 200 can enable a significant increase, e.g., a factor of two or more, in the current contained in a similar beam cross-section at the target 204. The beam 202 may also be scanned along a direction in a milling example that may define a cutting edge 206 and an area 208 adjacent the cutting edge 206 where material is minimally affected.

[0010] An elongated aperture aligned with the beam axis (e.g., aligned with the center point of an ellipse that coincides with the central axis of the beam) can work well for low currents because the image angle is relatively small and spherical aberration does not significantly degrade beam quality at the target. However, at high currents, larger image angles exist and spherical aberrations cause undesirable “bow-tie” effects. Such effects can manifest as beam tails 208 a, 208 b that degrade beam performance at the target 204. These bow-tie lobes generally result from the combination of an aperture extension in one axis, causing beam broadening in the other axis. As can be seen, the lobes 208 a, 208 b introduce a small but significant amount of energy into regions 210 a, 210 b of the target 204 surface adjacent the cutting edge 206, thereby spreading the beam current into areas where such energy is undesirable. For example, in many milling and processing applications, even small amounts of current past the cutting edge 206 will degrade the process target due to damage to the target outside of the area being removed. Lobes can be minimized in various ways, such as using additional corrective lenses that can compensate for or cancel out the lobes 208 a, 208 b. However, such techniques can be expensive and introduce additional complexity into the microscope column and control over the beam.

[0011] According to an embodiment of the disclosed technology, FIG. 3 illustrates an example of an offset elongated aperture 300 (here, elliptical) that can be used in a charged particle beam column to generate a charged particle beam 302 at the surface of a target 304. The aperture 300 is offset a small distance 308 along a direction perpendicular to the elongation direction, away from a position 310 corresponding to the central beam axis of the charged particle beam column. In some embodiments, the elongated aperture 300 can be elliptical with associated major and minor axes 311 a and 311 b. The offset can be along the direction of the minor axis 311 a. Based on the elongated offset characteristic of the aperture 300, the beam 302 can be formed at the target 304 with asymmetric characteristics, for example, such that the intensity decreases rapidly on one side of the beam 302, as can be seen from a cross-section of the intensity of the beam 302 at the surface of the target 304. This can enable accurate formation of cutting edge 306 because the beam is scanned in a selected direction (left to right in FIG. 3 ) aligned with cutting edge 306 without accumulating significant beam current in region 312 adjacent cutting edge 306. In an exemplary embodiment, additional compensators that might otherwise be required to remove undesirable bow ties are no longer needed due to offset 308.

[0012] The offset 308 can be selected in relation to other variables to optimize the current distribution generated at the target 304. In selected embodiments, the offset 308 is selected in relation to the column magnification and the elongation ratio of the aperture 300. The aperture and column variables can be selected to minimize one or more parameters of the beam 302 at the target 304. For example, FIG. 4 shows a typical circular beam 400 generated using a circular, non-offset aperture, such as aperture 100. The circular beam 400 matches a FIB source object size of approximately 50 nm (approximate distance between the dashed lines 401 a, 401 b shown). However, spherical aberration in the beam 400 causes significant beam energy 402 to be rotated around the center 404 of the beam 400. FIG. 5 shows side cross-sectional beam intensity profiles generated at the target for different beams 500, 502. The beam 500 is generated using a circular aperture and can correspond to the beam 400 of FIG. 4. Similar to beam 400, beam 500 has a central portion 503 with a large current density, but beam 500 contains significant beam energy in tail sections 504a, 504b. In contrast, beam 502 is generated using an offset elliptical aperture (in this case, using a 1:3 aspect ratio). Beam 502 can correspond to beam 302 of FIG. 3 generated using aperture 30; thus, beam 502 has a significant central portion 506 and includes asymmetric tail portions 508a, 508b. Portions 506, 508a, 508b match the profile of beam 302 of FIG. 3; for example, the lower half of beam 302 of FIG. 3 corresponds to left tail portion 508a, and the upper half of beam 302 of FIG. 3 corresponds to right tail portion 508b. Shifting aperture 300 by offset 308 can operate to remove beam rays with large image angles, which can then reduce or move tail 508b. For example, various offsets may be used, such as about 0.25-2 times, 0.1-5 times, 0.5-1.5 times the beam diameter at the aperture, etc. The elongation of the elongated aperture 300 may also vary, having aspect ratios of, for example, 1:1.5, 1:2, 1:3, 1:5, 1:10, etc.

[0013] The disclosed embodiments can have aperture and column characteristics selected relative to one another to provide optimization for quantifiable characteristics that describe tail 508b. One such metric can be referred to as “asymmetric” full-width 90 (FW90) or asymmetric full-width 50, which can correspond to the distance of a tail (such as tail 508b) containing 90% of the current, measured only from a central peak, such as line 510 centered on central portions 503, 506. The metric is asymmetric because the complementary FW90 on the other side of the central peak is often many times larger. Such a metric can specifically capture this concentrated sharpness on one side of an asymmetric beam, such as beam 502. Thus, in selecting values ​​for the aperture and column components relative to one another, the distance capturing 90% of the current measured from the peak to one side can be minimized, while the FW90 on the other side can remain the same or be made larger. As shown, the asymmetric FW90 distance 512 for beam 500 is relatively large (approximately 1000 nm), while the asymmetric FW90 distance 514 for beam 502 is significantly smaller (approximately 50 nm). Thus, even though the current density is lower for beam 502 at its peak (e.g., at its central portion 506) than for beam 500, the asymmetric FW90 is many times smaller. Exemplary asymmetric FW90 for a sharp edge of a cross section can vary from beam to beam and from system to system, with values ​​including 100 nm, 50 nm, 20 nm, 10 nm, 5 nm, 2 nm, or 1 nm or less, etc.

[0014] The edge of the beam 502 is typically relatively straight (as can be seen for the intensity profile 302 and corresponding cutting edge 306); therefore, when the beam 502 is rastered along the direction of the straight edge in the same manner as a circular beam (such as beam 500), the beam 502 mills a pattern into the target surface, producing a well-defined edge. In embodiments where the intensity edge formed is somewhat curved, the edge generally bends toward the beam 502 rather than away from it (convex rather than concave), again enabling the formation of a well-defined edge through scanning. The shape of the beam 302, 502 can also be optimized in relation to the properties of the target sample to provide the highest throughput at a fixed damage threshold, enabling faster milling with less damage in transmission electron microscope (TEM) sample preparation.

[0015] FIG. 6 illustrates an exemplary charged particle beam microscope 600 including a charged particle beam column 602. The microscope 600 can include FIB, SEM, STEM, TEM, and multi-beam / column systems, such as systems with a large, main electron column and a smaller FIB column positioned at an angle to the electron column and directed toward a common sample chamber. For ease of illustration, only one column is shown. The column 602 can include a charged particle beam source 604 configured to generate and direct a charged particle beam 606 along a column beam axis 608. The column 602 can include an arrangement of column components that manipulate the beam 606 and direct the beam to a target 610 coupled to a stage 612 that can support the target 610 and provide other functions such as movement, temperature control, etc. The target 610 and stage 612 are typically located within an environmental control chamber 614, which controls, for example, the presence of gas species, pressure, temperature, etc.

[0016] The column components may include a condenser lens 616 positioned to collect and focus the beam 606 after it diverges from the beam source 604. The condenser lens typically includes one or more electrostatic and / or magnetostatic lens components. In exemplary embodiments, the condenser lens 616 is configured to collimate the beam 606, e.g., so that the beam 606 propagates with minimal convergence / divergence. In further embodiments, the condenser lens 616 may be configured to converge the beam 606 and / or bring the beam 606 to an intermediate focus. In many embodiments, an intermediate focus is avoided or unnecessary. For example, because object sizes are very small (e.g., about 50 nm), further reduction in object size is often not necessary, thus providing something approaching a 1:1 magnifier.

[0017] The elongated aperture 618 can be located close to the condenser lens 616, for example, immediately after the condenser lens 616, or after the beam is collimated. In some embodiments, the elongated aperture 618 can be located immediately before the condenser lens. In many embodiments, the location of the aperture 618 is selected to be as far upstream in the column 602 as possible, thereby reducing the beam current as quickly as possible to minimize Coulomb interactions. Thus, while allowing the beam to diverge may be a consideration for aperture placement, limiting the beam current may be a higher priority because the beam is continuously degrading in high-current regions before it reaches the aperture 618. In representative embodiments, the elongated aperture 618 is not located in the image or focal plane of the lens 618 or other lenses in the column 602, as may be used in aperture imaging / projection techniques.

[0018] The elongated aperture 618 is offset from the beam axis 608 in the X and / or Y directions, such that the center of the elongated aperture 618 is not coaxial with the beam axis 608. As discussed elsewhere herein, the offset can be used to generate an asymmetric intensity cross-section of the beam 606 at a target 610 having a sharp edge. The cross-section can correspond to a central cross-section of the beam along the direction of the offset. For example, if the elongated aperture 618 is an elliptical aperture, the offset can be along the direction of the elliptical aperture's minor axis, which extends approximately perpendicular to the aperture's major axis and corresponding elongation direction. Thus, scanning the beam 606 across the target along a direction perpendicular to the offset (e.g., along the direction of the aperture's elongation) can generate a well-defined cutting edge with minimal damage to portions of the target adjacent the sharp edge. The aperture 618 can be coupled to a support 620. In some examples, the support 620 can include a translation stage that can be configured to change the positioning of the aperture 618, for example, by rotating the aperture 618 about the axis 608. Rotation can adjust the positioning of the beam edge at the target 610. Other movements can be applied, such as changing the offset, swapping and interchanging with other apertures, other angles (e.g., relative to the XY plane), etc.

[0019] The perimeter defining the aperture 618 may be made of a thin foil such as molybdenum, although other materials may also be used. The dimensions of the aperture are typically on the order of tens to hundreds of microns. For example, an example elliptical aperture may be 200 μm by 300 μm (aspect ratio 1.5). An exemplary offset may be on the same order as the aperture size, such as 100 microns for a 200 μm by 300 μm aperture. Generally, the offset may be on the order of the beam diameter.

[0020] Column 602 may also include an objective lens 622 located downstream from condenser lens 616 and aperture 618 to receive beam 606 and focus the beam onto target 610. In many embodiments, column 602 may include a beam scanner 624 that may be positioned to direct beam 606 relative to target 610, for example, by raster scanning a path across the surface of target 610. Beam scanner 624 may include, for example, one or more beam deflection coils.

[0021] A system controller 626 (which may be part of a larger control system or environment of system 600 or may be separate therefrom) may be configured to control various components of charged particle beam system 600. For example, controller 626 may be coupled to beam source 604 to control the emission of beam 606 and characteristics of the emitted beam (e.g., source selection, beam current, timing, pulse generation, etc.). Controller 626 may also be coupled to condenser lens 616, objective lens 622, beam scanner 624, and other lens and beam control components to control beam characteristics at target 610, such as focus position, aberration correction, magnification, deflection position, etc. For example, controller 626 may include a beam scan map 628 stored in memory that may be used to direct beam 606 during various material processes, such as FIB milling.

[0022] A controller 626 may further be coupled to the stage 612 to control the movement and positioning of the target 610 relative to the beam 606. In many embodiments, the stage movement 630 may be stored in memory and executed during the ion milling process flow. In some embodiments, the controller 626 may be coupled to a movement stage coupled to the support 620 to control the selection, movement, and / or positioning of the aperture 618 relative to the beam 606, for example, to change the angle or other characteristics of the beam edge of the beam 606 at the target. The selected aperture adjustment 632 may be stored in memory as part of a workflow, such as part of the milling process.

[0023] In many embodiments, because beam 606 is brought to a focal position at target 610 using objective lens 622 to produce an intensity profile with sharp edges that may be desirable for various processes, certain other focal positions above and / or below the selected focal position (e.g., corresponding to certain positions in the through-focus sequence) may produce an undesired intensity profile, e.g., a profile with a significant (or even substantial) amount of energy beyond the intended edge that may damage the surface of target 610. Focal position 634 (or a position to be avoided) may be stored in memory so that undesired intensity profiles at the surface of target 610 may be avoided.

[0024] In general, the elongated aperture (e.g., 1.5-5x) 618 may be offset to remove lobes in the intensity profile at the target 610, and the magnification of the condenser lens may be selected to balance aberrations against the spot size at the target 610 to deliver a sharp-edged beam. Thus, in some embodiments, the controller 626 may be configured to provide adjustment of the sharp-edged characteristics of the beam 606 by adjusting the offset of the aperture 618 (or the aperture itself to change its elongation or shape) and the magnification provided by the lens components of the column 602.

[0025] Figures 7A-9I show three through-focus image series for beams generated at a target using a circular aperture (Figures 7A-7I), an elliptical aperture (Figures 8A-8I), and an offset elliptical aperture (Figures 9A-9I). The progression through each image series shows the cross section of the respective beam as the objective lens intensity changes. Thus, the through-focus series can be understood as a change in the focus adjustment of the beam, and the images of the beam with each of these focus settings can be understood as, for example, a slice in space through the z-axis or an adjustment of the focus control. Figures 7A-7I show a beam cross section that is circular and remains circular throughout the through-focus series. Figures 8A-8I show a relatively linear or hourglass-shaped beam cross section in the vertical direction, with some variation in the high-intensity regions on opposite ends of the through-focus series. A significant portion of the beam energy may extend beyond the left or right edge of the central high-intensity region.

[0026] 9A-9I illustrate beam cross sections that vary significantly over a through-focus sequence according to many disclosed embodiments. As shown, beam convergence is achieved in FIG. 9F, while the beam cross sections in FIGS. 9F-9G have a clearly defined beam edge on the left side of the beam cross section, with little or no ion energy deposited to the left of the edge. Throughout the focus sequence, there are several through-focus positions (see FIGS. 9A-9E), where some or most of the beam energy arrives to the left of the edge shown in FIGS. 9F-9G. Such focus positions can be avoided according to many process embodiments herein. As discussed above, elongating the beam defining the aperture can result in large beam tails with significant spherical aberration, and aperture offset can be used to remove high-image-angle rays. Disclosed embodiments use an offset elongated aperture along with the appropriate column magnification and aperture aspect ratio to generate an asymmetric, sharp-edged beam. The amount of defocus can also be optimized in terms of offset, elongation, and magnification to generate a sharp edge at the selected focus position of the beam. Typically, the selected focus position corresponds to a spot or in-focus position, although in some instances the selected defocus position may be selected and optimized with respect to offset, elongation, and magnification. As shown in Figures 9A-9I, sharp edges may be produced in the beam at the beam focus, and various defocus positions or ranges of defocus positions may be specifically avoided.

[0027] FIG. 10 illustrates an exemplary process 1000 that can be used to select system parameter values ​​that can produce an asymmetric, sharp-edged beam intensity profile for a charged particle beam at a target. At 1002, values ​​for the aperture major and minor axes, aperture offset, and column magnification can be selected. The presence of offsets tends to degrade beam performance, many values ​​for the minor / major axes are inappropriate and may result in degraded performance, and many values ​​for the column magnification may degrade performance. Thus, many combinations may produce poor or undesirable simulation results. However, some sets can produce sharp edges that can exhibit superior performance to a circular beam, for example, with excellent beam milling characteristics and no energy deposition in undesired areas.

[0028] At 1004, a simulation may be performed of a charged particle beam propagating in a charged particle beam column from a particle beam source to a target using the set of values ​​selected in 1002 and variations of the selected values. For example, the aperture offset may be increased and decreased by incremental values ​​or percentages, the aperture aspect ratio may be increased and decreased by incremental values ​​or percentages, and the column magnification may be increased and decreased by incremental values ​​or percentages. The results of the simulation may be analyzed to select a parameter set exhibiting preferred beam characteristics, which may optionally be further refined for additional degrees of freedom. At 1006, values ​​having a sufficiently small asymmetric full width 90 for the intensity cross section of the beam at the target and a sufficiently large beam current may be selected. The values ​​may be stored in memory and used in milling or other sample processing workflows.

[0029] FIG. 11 illustrates an exemplary milling process 1100 that can be used with various charged particle beams and samples. At 1102, a sample can be positioned for charged particle beam milling. The sample is typically placed in an environmentally controlled chamber on a sample stage. At 1104, a charged particle beam can be directed to the sample by directing the beam through an offset elongated aperture. The beam can be collected using a condenser lens and focused onto a target at 1106, for example, using an objective lens, to form an asymmetric beam intensity distribution with a sharp edge at the sample. At 1108, the beam can be scanned across the sample along a direction corresponding to the sharp edge to mill material from the sample.

[0030] General Considerations As used in this application and the claims, the singular forms "a," "an," and "the" include the plural forms unless the content clearly dictates otherwise. Additionally, the term "includes" means "comprises." Furthermore, the term "coupled" does not exclude the presence of intermediate elements between the coupled items.

[0031] The systems, devices, and methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with one another. The disclosed systems, methods, and devices are not limited to any specific aspect or feature or combination thereof, and the disclosed systems, methods, and devices do not require that any one or more specific advantages be present or problems be solved. While any theory of operation is provided for ease of explanation, the disclosed systems, methods, and devices are not limited to such theory of operation.

[0032] Although some operations of the disclosed methods are described in a particular sequential order for convenient presentation, it should be understood that this description style encompasses reordering unless a particular ordering is required by specific language set forth below. For example, operations described in sequence may in some cases be reordered or performed simultaneously. Moreover, for simplicity, the accompanying figures may not show the various ways in which the disclosed systems, methods, and apparatuses can be used in conjunction with other systems, methods, and apparatuses. Additionally, the description may use terms such as "produce" and "provide" to describe the disclosed methods. These terms are high-level abstractions of actual operations that take place. The actual operations corresponding to these terms will vary depending on the particular implementation and are readily discernible by those skilled in the art.

[0033] In some instances, values, procedures, or devices are referred to as "lowest," "best," "smallest," etc. Such descriptions are intended to indicate that a selection may be made from among many functional alternatives used, but it will be understood that such a selection need not be better, smaller, or otherwise preferred than other selections.

[0034] Portions of the disclosed techniques and processes may be embodied as software or firmware instructions executed by one or more controllers, such as a digital computer. For example, any of the control over the disclosed beam processing or system parameter selection techniques may be performed by a computer or other computing hardware (e.g., an ASIC or FPGA) that is part of the charged particle microscope system. The charged particle microscope system may be connected to or otherwise communicate with various system components to perform ion milling or other material processing workflows. The computer may be a computer system including one or more processors (processing devices) and tangible, non-transitory computer-readable media (e.g., one or more optical media disks, volatile memory devices (such as DRAM or SRAM), or non-volatile memory or storage devices (such as hard drives, NVRAM, and solid-state drives (e.g., flash drives)). The one or more processors may execute computer-executable instructions stored on one or more of the tangible, non-transitory computer-readable media, thereby performing any of the disclosed techniques. For example, software for performing any of the disclosed embodiments may be stored in one or more volatile, non-transitory computer-readable media as computer-executable instructions that, when executed by one or more processors, cause the one or more processors to perform any of the disclosed techniques. Scan maps and beam edge alignments of asymmetric beams may be adjusted to mill or process a target and may be stored in one or more tangible, non-transitory computer-readable storage media. [Example]

[0035] Additional Examples The following are additional examples of the disclosed technology.

[0036] Example 1 is a method that includes generating a charged particle beam using a charged particle beam source, directing the charged particle beam to a target along a beam axis of a charged particle beam column, directing the charged particle beam through an elongated aperture positioned offset with respect to the beam axis, and focusing the beam at the target to generate an asymmetric intensity cross-section of the beam, the cross-section having a sharp intensity edge at the target based on the offset elongated aperture.

[0037] Example 2 includes the subject matter of example 1, wherein the sharp edge is defined such that a 90% full width of a tail of beam intensity extending from a position of the peak of the beam intensity is 100 nm, 50 nm, 20 nm, 10 nm, 5 nm, 2 nm, or 1 nm or less.

[0038] Example 3 includes the subject matter of any of Examples 1-2, wherein the elongated aperture is an elliptical aperture, and the offset is along the direction of the minor axis of the elliptical aperture.

[0039] Example 4 includes the subject matter of any of Examples 1-3, wherein the elliptical opening has an ellipticity of 3-5.

[0040] Example 5 includes the subject matter of any of Examples 3-4, wherein the elongation of the elliptical aperture, the offset of the aperture, and the column magnification applied to the beam are selected relative to one another to produce a sharp edge.

[0041] Example 6 includes the subject matter of any of Examples 1-5, wherein the offset is greater than 0.25 times the diameter of the beam at the aperture and less than or equal to 2 times the diameter of the beam at the aperture.

[0042] Example 7 includes the subject matter of any of Examples 1-6, further including directing the charged particle beam through a condenser lens, wherein the aperture is located proximate to the condenser lens, and the aperture is not located at an intermediate focal plane of the charged particle beam column.

[0043] Example 8 includes the subject matter of any of Examples 1-7, further including scanning the beam across the target along the direction of the sharp edge.

[0044] Example 9 includes the subject matter of example 8, wherein scanning the beam includes milling the target to remove material from the target and form sharp material edges on the target at locations of the sharp edges of the beam cross section.

[0045] Example 10 includes the subject matter of any of Examples 1-9, further including controlling focusing of the beam at the target by preventing focusing of the beam at a range of focal positions at the target associated with significant beam energy existing beyond a sharp edge, the range of focal positions being axially close to a position or range of focal positions that produces a sharp edge.

[0046] Example 11 is an apparatus comprising: a charged particle beam source configured to generate a charged particle beam in a charged particle beam column and direct the charged particle beam to a target along a beam axis of the charged particle beam column; an elongated aperture positioned to receive the charged particle beam, the elongated aperture being offset with respect to the beam axis; and an objective lens configured to focus the beam at the target to generate an asymmetric intensity cross-section of the beam, the cross-section having a sharp intensity edge at the target based on the offset elongated aperture.

[0047] Example 12 includes the subject matter of example 11, wherein the sharp edge is defined such that a full width at 90% of a tail of beam intensity extending from a position of the peak of the beam intensity is 100 nm, 50 nm, 20 nm, 10 nm, 5 nm, 2 nm, or 1 nm or less.

[0048] Example 13 includes the subject matter of any of Examples 11-12, wherein the elongated aperture is an elliptical aperture, and the offset is along the direction of the minor axis of the elliptical aperture.

[0049] Example 14 includes the subject matter of example 13, wherein the elliptical opening has an ellipticity of 3-5.

[0050] Example 15 includes the subject matter of any of Examples 13-14, wherein the elongation of the elliptical aperture, the offset of the aperture, and the column magnification applied to the beam are selected relative to one another to produce a sharp edge.

[0051] Example 16 includes the subject matter of any of Examples 11-15, wherein the offset is greater than 0.25 times the diameter of the beam at the aperture and less than or equal to 2 times the diameter of the beam at the aperture.

[0052] Example 17 includes the subject matter of any of Examples 11-16, further including a condenser lens disposed between the charged particle beam source and the objective lens and positioned to receive the charged particle beam, wherein the aperture is located proximate to the condenser lens, and the aperture is not located at an intermediate focal plane of the charged particle beam column.

[0053] Example 18 includes the subject matter of any of Examples 11-17, further including a beam scanner coupled to the charged particle beam column and configured to scan the beam across the target along the direction of the sharp edge.

[0054] Example 19 includes the subject matter of example 18, wherein the beam scanner is configured to scan the beam to mill the target to remove material from the target and form sharp material edges on the target at locations of the sharp edges of the beam cross section.

[0055] Example 20 includes the subject matter of any of Examples 11-19, further including a controller coupled to the objective lens that prevents the objective lens from focusing the beam to a range of focus positions at the target associated with significant beam energy present beyond a sharp edge, the range of focus positions being axially close to a position or range of focus positions that produces a sharp edge.

[0056] Example 21 includes a computer-readable medium including processor-executable instructions for performing any of Examples 1-10.

[0057] In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are merely representative examples and should not be construed as limiting the scope of the present disclosure. The alternatives specifically addressed in these sections are merely exemplary and do not constitute all possible alternatives to the embodiments described herein. For example, various components of the systems described herein may be combined in function and use. We therefore claim all that comes within the scope of the following claims.

Claims

1. 1. A method comprising: generating a charged particle beam using a charged particle beam source and directing the charged particle beam along a beam axis of a charged particle beam column toward a target; directing the charged particle beam through an elongated aperture positioned offset relative to the beam axis; focusing the beam at the target to generate an asymmetric intensity cross-section of the beam, the cross-section having a sharp intensity edge at the target based on the offset elongated aperture.

2. 10. The method of claim 1, wherein the sharp edge is defined such that a full width at 90% of the beam intensity tail extending from a position of peak beam intensity is less than or equal to 100 nm, 50 nm, 20 nm, 10 nm, 5 nm, 2 nm, or 1 nm.

3. The method of claim 1 , wherein the elongated aperture is an elliptical aperture, and the offset is along the direction of a minor axis of the elliptical aperture.

4. The method of claim 3, wherein the elliptical opening has an ellipticity of 3-5.

5. The method of claim 3 , wherein the extension of the elliptical aperture, the offset of the aperture, and a column magnification applied to the beam are selected relative to one another to produce the sharp edge.

6. 2. The method of claim 1, wherein the offset is greater than 0.25 times the diameter of the beam at the aperture and less than or equal to 2 times the diameter of the beam at the aperture.

7. 10. The method of claim 1, further comprising directing the charged particle beam through a condenser lens, the aperture being located proximate to the condenser lens and the aperture not being located at an intermediate focal plane of the charged particle beam column.

8. The method of claim 1 , further comprising scanning the beam across the target along the direction of the sharp edge.

9. 9. The method of claim 8, wherein said scanning said beam comprises milling said target to remove material from said target and form a sharp material edge on said target at the location of said sharp edge of a beam cross section.

10. 10. The method of claim 1, further comprising controlling the focusing of the beam at the target by preventing the beam from focusing to a range of focal positions at the target associated with significant beam energy present beyond the sharp edge, the range of focal positions being axially close to a position or range of focal positions that produces the sharp edge.

11. 1. An apparatus comprising: a charged particle beam source configured to generate a charged particle beam in a charged particle beam column and direct the charged particle beam along a beam axis of the charged particle beam column to a target; an elongated aperture positioned to receive the charged particle beam, the elongated aperture being offset with respect to the beam axis; an objective lens configured to focus the beam at the target to generate an asymmetric intensity cross-section of the beam, the cross-section having a sharp intensity edge at the target based on the offset elongated aperture.

12. 12. The apparatus of claim 11, wherein the sharp edge is defined such that a full width at 90% of the beam intensity tail extending from a position of peak beam intensity is less than or equal to 100 nm, 50 nm, 20 nm, 10 nm, 5 nm, 2 nm, or 1 nm.

13. The apparatus of claim 11 , wherein the elongated opening is an elliptical opening and the offset is along a minor axis of the elliptical opening.

14. 14. The apparatus of claim 13, wherein the elliptical opening has an ellipticity of 3 to 5.

15. The apparatus of claim 13 , wherein the extension of the elliptical aperture, the offset of the aperture, and a column magnification applied to the beam are selected relative to one another to produce the sharp edge.

16. 12. The apparatus of claim 11, wherein the offset is greater than 0.25 times the diameter of the beam at the aperture and less than or equal to 2 times the diameter of the beam at the aperture.

17. 12. The apparatus of claim 11, further comprising a condenser lens disposed between the charged particle beam source and the objective lens and positioned to receive the charged particle beam, wherein the aperture is located proximate to the condenser lens and the aperture is not located at an intermediate focal plane of the charged particle beam column.

18. 12. The apparatus of claim 11, further comprising a beam scanner coupled to the charged particle beam column and configured to scan the beam across the target along the direction of the sharp edge.

19. 20. The apparatus of claim 18, wherein the beam scanner is configured to scan the beam to mill the target to remove material from the target and form a sharp material edge on the target at the location of the sharp edge of the beam cross section.

20. 12. The apparatus of claim 11, further comprising a controller coupled to the objective lens that prevents the objective lens from focusing the beam to a range of focus positions at the target associated with significant beam energy present beyond the sharp edge, the range of focus positions being axially close to a position or range of focus positions that produces the sharp edge.

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