3D mapping of samples in charged particle microscopy

Abstract

To execute a positioning of a sample in an electron microscopy in a short time without an error.SOLUTION: An arrangement of a sample on an optical shaft 110 of a charged-particle microscope 100 can be made on the basis of a 3D map of the sample. The 3D map is created by using a backside-illumination of the sample and a telecentric imaging for creating a profile image. The 3D map is created by combining the profile image. Since an imaging is made with the charged-particle microscope by using the 3D map, a processor is combined to a sample stage 114 for arranging a selected sample S or a sample part. In some examples, the processor responds to a selection of the sample by using a graphical interface so as to control the selected sample so as to be safely arranged without additional interposition of an operator in the sample stage 114.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to microscopy methods and systems, and more particularly to sample positioning in charged particle microscopes. [Background technology]

[0002] Positioning samples for electron microscopy can be time-consuming and requires careful operator attention. Samples of various sizes on the sample holder must be carefully positioned to avoid contact with microscope components, such as the pole pieces used by the magnetic lenses, electron detectors, or other components. In some cases, the sample holder holds multiple samples of different heights, requiring the operator to carefully move each sample into the microscope's field of view. After placement within the field of view, additional manipulation time is required to focus the sample. Thus, sample positioning and focusing is time-consuming, error-prone, and the required operator skills can be challenging to manage for new users, potentially causing sample / pole piece contact, astigmatism, misalignment, or damage to components or samples. For at least these reasons, an alternative approach is needed. Summary of the Invention

[0003] The method includes illuminating a sample located within a vacuum chamber of a charged particle microscope from a first side and detecting at least one 2D projection of the sample on a second side opposite the first side. A 3D map is generated based on the at least one 2D projection, and the sample is positioned at an imaging position within the vacuum chamber based on the 3D map. In some examples, the first side is opposite the second side, multiple 2D projections of the sample on the second side are detected, and the 3D map is generated based on the multiple projections. Typically, the multiple 2D projections of the sample on the second side are detected by rotating the sample. In some examples, a set of 3D maps is generated, each 3D map based on a set of rotation angles, and the 3D map is based on combining each of the set of 3D maps. In an example, after the 2D projections are detected, the sample is moved to an imaging position. In a further example, the sample is loaded into the vacuum chamber of the charged particle microscope and illuminated with light. The sample is moved to an imaging position within the vacuum chamber based on the 3D map generated from the 2D projections. The sample may be processed or imaged using a charged particle beam at the imaging position. In some examples, illuminating the sample includes directing a collimated beam toward the sample, the collimated beam being directed along an axis perpendicular to the optical axis of the charged particles. Illuminating the sample can be performed using a light source located inside or outside the vacuum chamber. In some alternatives, illuminating the sample includes illuminating the sample with a beam having a patterned intensity, and further includes identifying the reflective sample surface based on the patterned intensity. In some examples, detecting at least one 2D projection of the sample on a second side opposite the first side is performed using telecentric optics. The telecentric optics can include an objective lens located inside or outside the vacuum chamber. The telecentric optics can be one or both of object-side telecentric and image-side telecentric. In some examples, a central axis of a detector for acquiring the 2D projection is parallel to a sample platform for holding the sample.

[0004] The charged particle microscope includes an illumination system arranged to illuminate a sample from a first side and an imaging system arranged to generate a 2D profile of the illuminated sample based on the illumination from the first side. A processor is coupled to receive the 2D profile and generate a 3D map based on the 2D profile. The imaging system includes an image sensor arranged to generate a 2D profile image of the illuminated sample based on the illumination from the first side, and the processor is coupled to the sample stage and configured to rotate the illuminated sample to generate the 2D profile. The imaging system can include telecentric optics that direct the 2D profile to the image sensor. The illumination system can be arranged to direct a diverging beam or a collimated beam toward the sample. The sample stage is operable to move the sample platform toward the optical axis of the charged particle beam.

[0005] The foregoing and other features and advantages of the disclosed technology will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0006] [Figure 1] 1 shows a representative charged particle microscope including surface profiling optics. [Figure 2] 1 shows a representative graphical user interface for adjusting the focus of a charged particle microscope to a selected position. [Figure 3A] A sample placed on a sample platform. [Figure 3B] 3B is a 3D map corresponding to FIG. 3A. [Figure 4A] A representative 3D map of the sample as shown in Figure 3B is shown. [Figure 4B] A representative 3D map of the sample as shown in Figure 3B is shown. [Figure 4C] Here are some typical ways to create a "safer" 3D map. [Figure 5]1 shows a representative optical system for surface profiling using parallel illumination. [Figure 5A] FIG. 6 is a cross-sectional view of the optical system of FIG. 5. [Figure 6] 1 shows a representative optical system for surface profiling using telecentric optics. [Figure 6A] FIG. 7 is a cross-sectional view of the optical system of FIG. [Figure 7] 1 shows a representative optical system for surface profiling using telecentric optics. [Figure 8] 1 shows a representative optical system for surface profiling using telecentric optics. [Figure 9A] An additional representative telecentric optical system is shown fixed to the wall of the vacuum chamber. [Figure 9B] An additional representative telecentric optical system is shown fixed to the wall of the vacuum chamber. [Figure 10] An additional representative telecentric optical system is shown fixed to the wall of the vacuum chamber. [Figure 11] 1 shows a typical telecentric optical system that is object-side and image-side telecentric. [Figure 12] 1 shows a part of a charged particle microscope. [Figure 12A] FIG. 13 is a cross-sectional view of the charged particle microscope shown in FIG. 12. [Figure 12B] A typical 2D profile that can be obtained with an optical system such as that shown in FIGS. 12-12A is shown. [Figure 13] 1 shows a portion of a charged particle microscope with a tiltable sample platform. [Figure 14A] 1 shows a sample with a reflection profile portion. [Figure 14B] 1 shows a sample with a reflection profile portion. [Figure 15] A representative graduated intensity illuminator is shown. [Figure 16] Here are some typical methods for creating 3D maps: [Figure 17]A representative method for creating a 3D map and moving the sample platform along the microscope axis for 3D map-based imaging is shown. [Figure 18] 1 illustrates a representative processing environment for the disclosed method and apparatus. [Figure 19] FIG. 1 is a cross-sectional view of a typical electron microscope. [Figure 20] 2D projections are shown. [Figure 21A] 2D projection with reflective areas. [Figure 21B] 21B shows a portion of FIG. 21A including a reflective area. [Figure 22A] It is a partial 2D projection. [Figure 22B] It is a partial 2D projection. [Figure 22C] This is the complete 2D projection obtained by combining the 2D projections of Figures 22A-22B. [Figure 23] A series of 2D projections at various rotation angles are shown. [Figure 24A] We show how to generate 3D maps from 2D projections. [Figure 24B] We show how to generate 3D maps from 2D projections. [Figure 24C] We show how to generate 3D maps from 2D projections. [Figure 24D] We show how to generate 3D maps from 2D projections. [Figure 24E] We show how to generate 3D maps from 2D projections. [Figure 24F] We show how to generate 3D maps from 2D projections. DETAILED DESCRIPTION OF THE INVENTION

[0007] Disclosed below are representative examples of CPB systems, such as CPB microscopes and related components, subcomponents, and methods. In many examples, an electron beam is important, and the examples are described using electron beam references for convenience and explanation. The disclosed approaches can also be used with optical microscopy. In most examples, additional CPB components, such as lenses, deflectors, stigmators, and additional apertures, are used but are not shown for convenience and explanation. The disclosed methods and apparatus can be used with both transmission and scanning microscopy. As described below, in some examples, a vacuum chamber can be evacuated while one or more samples are profiled at a sample profiling location to create a 3D map. The sample can be positioned on a stage at the charged particle (CP) optical axis, tilted, or offset relative to the CP optical axis. After profiling, the sample can be moved to the CP optical axis for imaging or processing. As used herein, image can refer to the presentation of image data on a display for visual inspection by an operator, or data related to a visual image, such as stored in a JPG, TIFF, or other data file. As used herein, X and Y refer to axes that are orthogonal to the CP optical axis (Z axis). Such axes need not be mutually orthogonal, although orthogonal axes are convenient.

[0008] As used herein, illumination generally refers to directing electromagnetic radiation toward an object or the electromagnetic radiation itself. Such electromagnetic radiation is typically visible light with wavelengths between approximately 400 nm and 700 nm, convenient for use with readily available image sensors, allowing for operator observation or camera use. While other wavelengths can be used, the range of 300 nm to approximately 2 μm is convenient. In examples, backside illumination is commonly used. Frontside illumination generally produces profile images that depend on the reflectivity and sample detail of the sample. In contrast, backside illumination produces profile images with contrast between light and dark areas (unblocked and blocked areas), which generally depend on the shape of the sample rather than its surface properties. Backside illumination can be achieved by placing a light source behind the object or by placing a reflector behind the object and reflecting light back onto the object.

[0009] Terms such as profile, projection, profile image, and projected image are used to refer to the outline of a sample produced as a shadow or as an image using an optical system. In some cases, these terms refer to the distribution of illumination directed at an image sensor or an associated detected illumination distribution.

[0010] The lenses are shown as single element lenses in the examples, but multiple element lenses can also be used. Although the optical systems are generally shown along linear axes, those axes can be bent or folded as needed using prisms or mirrors. Example 1

[0011] As shown in FIG. 1 , in a representative embodiment, a charged particle beam (CPB) system 100 includes a CPB microscope 102, such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM), with one or more CPB lenses, such as a focusing lens 104, positioned to direct CPB from a CPB source 106 to an objective lens 108. The CPB source 106 may be, for example, a field emitter generating an electron beam, although other sources can be used. In some embodiments, one or more additional CPB lenses can be provided and may be magnetic and / or electrostatic lenses. The primary axis 110 can be determined during fabrication of the microscopy system. In use, the CPB propagates along the primary axis 110 toward a sample stage 114, and a beam deflector 122 can be used to scan the beam relative to a sample S located on the sample stage 114. The sample stage 114 typically translates and / or rotates to position the sample S. Typically, the sample S is fixed to a sample platform, which in turn is fixed to the sample stage 114.

[0012] The CPB system 100 includes a vacuum chamber housing 112 that can be evacuated using a vacuum pump (not shown) and typically defines a first volume 112A containing the CPB source 106 and selected other CPB optical components, and a second volume 112B positioned to receive the sample S and a sample stage 114. A column isolation valve (CIV) 120 is positioned to separate the first volume 112A from the second volume 112B. Typically, the CIV 120 is operable to seal and isolate the first volume 112A from the second volume 112B during sample exchange. The sample stage 114 is movable in the XY plane, as shown with respect to a coordinate system 150, where the Y axis is perpendicular to the plane of the drawing. The sample stage 114 can also move vertically (along the Z axis) to compensate for variations in the height of the sample S and to help adjust the focus of the beam on the sample S. The sample stage 114 can also rotate about an axis parallel to the Z axis, as well as tilt the sample S. In some cases, sample profiling is performed with the sample platform tilted, as shown in FIG. 13 (discussed further below). In some embodiments, the CPB microscope 102 can be positioned vertically above the sample S and used to image the sample. In some embodiments, the CPB microscope 102 can be positioned vertically above the sample S and used to image the sample S while the ion beam machines or otherwise processes the sample S.

[0013] The light source 152 is positioned to send an illumination beam 154 through a window 156 in the vacuum chamber housing 112. The illumination beam 154 is shown as a collimated beam, but can also be divergent or non-collimated. An optical system, including one or more lenses, such as lens 158, is positioned to receive the portion of the illumination beam 154 that is not blocked by the sample S and generate one or more profile images (or 2D projections) of the sample S at or near the image sensor 160. As shown, the lens 158 and a portion of the optical system extend within the vacuum chamber 112. However, either the optical system, the light source 152, or both can be inside, outside, or partially inside and outside the vacuum chamber housing 112. Typically, the sample stage 114 is rotated about axis 110 (or a parallel axis), and profile images are acquired during the rotation. For example, the sample stage 114 can rotate 360 ​​degrees, with profile images acquired at 1-degree intervals.

[0014] The CPB system 100 includes a computer processing device 144, such as a control computer and CPB system controller 140, for controlling the beam deflectors, CPB lenses 104, 108, and other CPB lenses, as well as other components, such as the detectors and sample stage 114, including the rotation and translation of the sample stage 114. The computer processing device 144 can also control the display of information collected from multiple CPB detectors on a display unit. In some cases, the computer processing device 144 (e.g., a control computer) establishes various excitations, records image data, and generally controls the operation of the CPB microscope 102, including controlling profile image acquisition. A so-called "navigation camera" 137 is typically positioned to provide a top-down image of the sample and sample stage for viewing by an operator. A camera 141 can also be provided to obtain a side view of the sample. The camera 141 is typically offset along the Y axis (into the plane of FIG. 1) and positioned to look out of the plane of FIG. 1.

[0015] The sample stage 114 can be translated along the Z-axis to focus as controlled by one or both of the computer processor 144 and the CPB system controller 140 based on the profile image generated by the image sensor 160. In some examples, the sample stage 114 can be set to an appropriate Z-axis position for imaging a particular sample, with or without manual adjustment of the Z-axis position by an operator. Sample imaging can be based on transmitted, reflected, or scattered charged particles, X-rays or other electromagnetic radiation, or secondary emissions received by one or more detectors not shown in FIG. 1 . Example 2

[0016] FIG. 2 illustrates a portion of a graphical user interface 200 provided on a display device associated with a CPB system such as that shown in FIG. 1. In this example, display area 202 includes an image of a substrate surface, and display area 204 is a side view 205 of an electron microscope column including a pole piece 206 and a sample 208 having a surface 210 fixed to a sample platform 209, the image of which is shown in display area 202. Side view 205 may be acquired using an optical system, an image sensor such as lens 158 and image sensor 160 in FIG. 1, or any of the optical systems described below. Display area 212 illustrates a top surface 214 of sample platform 209 showing a position 216 where a beam focus is selected. Display area 220 includes a top surface of sample platform 209 from which various samples 222-224 can be viewed. Display area 230 includes a display area for stage X, Y, Z, rotation, and tilt coordinates 232, an area 234 (shown as a radio button) used to indicate with a computer pointing device that CPB is turned on, an area 236 used with a computer pointing device to indicate that autofocus is activated for the area indicated at 216, and an area 238 that may contain other controls and data. By using this user interface to indicate that location 216 is to be imaged using a computer pointing device, the sample stage is properly positioned relative to the electron microscope optics column based on profile data that allows for safe movement (i.e., collision-free movement). Example 3

[0017] FIG. 3A shows a representative plan view of a sample platform on which samples 301-303 are fixed. FIG. 3A is captured by a navigation camera, such as navigation camera 137 in FIG. 1. For convenience, 3D coordinate axes are provided. Based on multiple profile images (profiles) obtained as described above, a 3D map 350 is generated in FIG. 3B. The 3D map includes map regions 401-403 corresponding to samples 301-303 shown in FIG. 3A. Images from cameras, such as cameras 137 and 141 in FIG. 1, can be combined with the 3D map for visualization, but such camera images are not required for the 3D map. Example 4

[0018] Typically, multiple 2D projections or profiles of the sample platform and sample are obtained with multiple sample platform rotations of approximately 1 degree across a 360-degree range. In some cases (e.g., when there is a reflection from the sample surface in the profile), a first 3D map is acquired using a series of rotations in first increments (e.g., 6 degrees) across a 360-degree range starting from a first angle. The first angle is then incremented by a second increment to span additional profiles in first increments across a 360-degree range. Thus, multiple series of 2D profiles can be acquired, such as creating a first 3D map at 0, 6, 12, ..., 360 degrees, followed by a second 3D map at 1, 7, 13, ... degrees. This creates six 3D maps, each associated with 60 rotation angles. Each of these maps can display reflections not visible in the other maps. These maps can be combined, preferably using an OR operation, to ensure that the reflective surface of the sample is included in the mapping. This tends to produce a "safe" 3D map for focus adjustment, allowing the stage holder to be moved without the sample coming into contact with other components. As used herein, a safe 3D map refers to a 3D map obtained by taking reflections into account. Figure 4A shows a 3D map generated by 360 rotations in 1-degree increments. Figure 4B shows a 3D map generated by combining six 3D maps generated by 60 incremental rotations. While the 1-degree incremental mapping is suitable for sample visualization, combining the 6-degree incremental mapping provides a safer path for sample movement when reflective surfaces are included as obstacles.

[0019] One approach to providing a secure 3D map is to combine 3D maps acquired at different angles, such as different initial angles, with fixed angle increments. As shown in FIG. 4C, an exemplary method 450 includes selecting a set of initial angles and angle increments at 452. At 454, 2D projections associated with each initial angle are combined at multiples of the angle increment to generate multiple 3D maps. For example, for n initial angles θ,...,θ n and the initial angle θ of the set of angle increments Δθ iFor θ, all integer values ​​of j provide angles within a complete rotation i The 2D projections corresponding to +jΔθ are combined for each initial angle to generate n 3D maps. At 456, the 3D maps can be logically ORed within an angular range corresponding to the angular increment Δθ to obtain a safe 3D map. For example, five 3D maps created with an angular increment Δθ = 5 degrees can be obtained using 2D projections created at 1-degree increments. The first 3D map can include values ​​of 62, 67, 72, and 77 degrees (and other angles across the full 360 degrees), while the second can include values ​​of 63, 68, 73, and 78 degrees (and other angles across the full 360 degrees). These 3D maps can be combined; that is, map values ​​within the angular increment Δθ are processed to retain values ​​corresponding to obstacles (unilluminated areas of the sensor). For a typical 3D map for back-illuminated applications, the 3D map values ​​are 0 or 1 (unobstructed or obstructed, respectively), and the 3D maps are combined using a logical OR operation. Some 3D maps show obstacles not present in other maps. The combination of such 3D maps provides a safe 3D map in which actual obstacles are not lost due to reflections. The resulting safe 3D map may be a lower-resolution map, but generally does not appear visually very different from a higher-resolution 3D map, as shown in Figures 4A-4B. Multiple 3D maps can be acquired using different sets of angles; the disclosed example is chosen for convenience of illustration. The selection of angles for combining map values ​​need not be the same as the angular increment. Typically, 2D projections are acquired at a predetermined angular resolution, and the 2D projections are combined to create multiple 3D maps used to create the safe 3D map. At 458, the 3D safe map is output for use in the electron microscope. Example 5

[0020] FIG. 5 is a plan view, and FIG. 5A is a cross-sectional view along AA, of an exemplary profile measurement system 500 including a light source 502 configured to generate a collimated beam 504 that is directed toward a sample platform 506 on which representative samples 508, 509 are disposed. A transmitted beam portion 510 is directed toward an image sensor 512 to generate a 2D profile image. As shown, a portion of the collimated beam 504 is blocked by the sample 508, generating a corresponding dark or shaded region 514 on the image sensor 512. The sample platform rotates about an axis 520 such that the light and dark regions on the image sensor change, resulting in different profile images. The samples 508, 509 move in and out of the beam 504 during rotation. Example 6

[0021] FIG. 6 is a plan view, and FIG. 6A is a cross-sectional view, of an exemplary profile measurement system 600 including a light source 602 configured to generate a beam 604 that is directed toward a sample platform 606 on which representative samples 608 and 609 are disposed. A transmitted beam portion 610 is directed toward an image sensor 612 via telecentric optics 611 (shown as a single lens for illustrative purposes) to generate a 2D profile image. As shown, a portion of the beam 604 is blocked by the sample 608, generating a corresponding dark or shaded region 614 on the image sensor 612. The sample platform rotates about an axis 620 such that the light and dark regions on the image sensor change and the samples 608 and 609 move relative to the image sensor 612. In this example, the light source 602 is shown as generating a parallel beam, although a diverging or diverging beam could be used. As described in more detail below, collimation is not required because the telecentric optics 611 eliminates or reduces perspective error. Diverging or diverging beams can be used, but such beams can produce reflections from the sample surface that can be overlooked and inappropriately considered as unobstructed areas. Example 7

[0022] FIG. 7 illustrates a portion of a representative profile measurement system including a telecentric optical system 700 arranged to generate images of a sample that can be positioned at various positions along an optical axis 701, such as 702A and 702B. The sample is fixed to a rotatable sample platform 704 so that the sample position can be varied along both the X and Y axes of a representative coordinate system 750. For convenience, the optical axis 701 is shown as being parallel to the X axis, while the electron microscope axis is parallel to the Z axis. The telecentric optical system includes an objective lens 710 mounted within a vacuum chamber. The objective lens 710 is secured to a lens tube 712, which is secured to a vacuum chamber wall 714 with an optical window 716. To achieve telecentricity, an imaging lens 718 and aperture stop 720 are positioned at the focal length F of the objective lens 710. As shown, the imaging lens 718 and aperture stop 720 are contained within a camera 722, which also includes an image sensor 724 and associated electronics for acquiring, processing, storing, and communicating images. In this example, the chief rays are parallel on the object side of the optical system, so the optical system can be called object-side telecentric.

[0023] In this telecentric arrangement, the apparent size of the sample does not change with distance to the optical system, and magnification is the same at all object distances. An out-of-focus sample results in a blurred image, but the size of the blurred image corresponds to the size of an in-focus image of the sample. The edges of the sample may appear blurred but are easily visible. Parallax error is avoided. In some instances, due to the available depth of field, all of the sample is in focus. Placing an aperture stop at the focal point of the lens is a typical approach to achieving telecentricity. As shown in Figure 7, if the sample is located at either 702A or 702B, the associated chief rays 730A and 730B pass through the center of the aperture stop 720, respectively. For clarity, imaging by the imaging lens 718 is not shown so that the chief rays can be easily seen. As noted above, some or all parts of the telecentric optical system 700 can be located inside or outside the vacuum chamber for convenience.

[0024] In the arrangement of Figure 7, the inspected object can be illuminated from either the front or back. Typically, backside illumination is used so that the sample blocks the illumination and the image of the sample appears as a dark area with edges. Using a mirror or other reflector, front or backside illumination of the sample can be provided using a light source placed either in front or behind the sample. Side illumination can also be used, but typically requires processing to properly identify reflective areas for a safe 3D map. Example 8

[0025] FIG. 8 illustrates a portion of a representative profile measurement system, including a telecentric optical system 800 arranged to generate images of a sample that can be positioned at various locations along an optical system axis 801, such as 802A and 802B. The sample is fixed to a rotatable sample platform 804, allowing for variation of the sample position along both the X and Y axes of a representative coordinate system 850. For convenience, the optical system axis 801 is shown parallel to the X axis, and the electron microscope axis is parallel to the Z axis. The telecentric optical system includes an objective lens 810 and an imaging lens 818 arranged around an aperture stop 820 located at focal lengths F1 and F2 of the objective lens 810 and imaging lens 818, respectively, to obtain telecentricity and generate an image on an image sensor 824. Associated electronics for acquiring, processing, storing, and communicating the images are not shown. In this example, when the chief rays are parallel on the object and image sides of the optical system, the optical system can be referred to as object-side telecentric and image-side telecentric.

[0026] In this telecentric arrangement, the apparent size of the sample does not change with distance to the optical system, and magnification is the same at all object distances due to object-side telecentricity. Image-side telecentricity also ensures that the chief ray position at the image sensor is independent of object distance, and magnification is constant. As shown in Figure 8, if a sample is placed in either 802A or 802B, the associated chief rays 830A and 830B pass through the center of the aperture stop 820 and are parallel on the image side of the imaging lens 818. As noted above, for clarity of illustration, imaging by the imaging lens 818 is not shown so that the chief rays are easily visible. Some or all parts of the telecentric optical system 800 can be inside or outside the vacuum chamber for convenience. Additionally, the specimen can be illuminated from either the front or back. Typically, backside illumination is used, such that the sample blocks illumination, causing the image of the sample to appear as a dark, edged area. Example 9

[0027] Referring to FIG. 9A , a representative profile system 900 includes an objective lens 910 and an imaging lens 912 arranged around an aperture stop 914 to form a sample profile image on an image sensor 924. The aperture stop 914 is positioned at the focal point of the objective lens 910 so that the lenses 910 and 912 form an object-space telecentric optical system. The telecentric objective lens 910 is separated from a vacuum chamber 916 by a vacuum-tight transparent window 913. The imaging lens 912, aperture stop 914, and objective lens 910 are secured in a lens tube 918, which is secured to the vacuum chamber 916 with one or more bolts 920 or other fasteners. The lens tube is curved to conserve space outside the vacuum chamber 916. To this end, a mirror 911 redirects the beam from the vacuum chamber 916 to the telecentric objective lens 910. A rotatable sample stage 904 holds samples 902, 906, with sample 906 shown positioned within the image field of objective lens 910. Representative chief rays 930, 931 are shown, but the ray paths associated with image formation by imaging lens 912 are not shown.

[0028] As shown in FIG. 9B, an exemplary profile system 950 includes an objective lens 960 and an imaging lens 962 arranged around an aperture stop 964. The aperture stop 964 is positioned at the focal point of the objective lens 960 so that the lenses 960, 962 form an object-space telecentric optical system. The objective lens 960 serves as a window within a vacuum chamber 966. The imaging lens 962 and aperture stop 964 are secured to a lens tube 968, which is secured to the vacuum chamber 966 with one or more bolts 970 or other fasteners. Gaskets or other components necessary to ensure a vacuum seal are not shown. A rotatable sample stage 954 holds samples 952, 956, with the sample 956 shown positioned within the image field of the objective lens 960. Representative chief rays 980, 981 are shown, but the ray paths associated with image formation by the imaging lens 962 are not shown. Example 10

[0029] As shown in FIG. 10 , a representative profile system 1000 includes an objective lens 1010 and an imaging lens 1012 arranged around an aperture stop 1014 to form a sample profile image on an image sensor 1024. The aperture stop 1014 is positioned at the focal point of the objective lens 1010 and the focal point of the imaging lens 1012 such that the lenses 1010, 1012 form an object-side and image-side telecentric optical system. The objective lens 1010 and aperture stop 1014 are disposed within a vacuum chamber and held by a lens tube 1018 that extends through a wall 1016 of the vacuum chamber. The lens tube 1018 is secured to the vacuum chamber wall 1016 with one or more bolts 1020 or other fasteners. Gaskets or other components necessary to ensure a vacuum seal are not shown. Example 11

[0030] As shown in Figure 11, another exemplary telecentric optical system 1100 includes an objective lens 1112, an intermediate lens 1004, and an imaging lens 1106 arranged on an axis 1101. An aperture stop 1108 is located at the focus of the objective lens 1102 and positioned relative to the lenses 1104 and 1106 to achieve object-side and image-side telecentricity. In this example, three lenses are used, one of which (the intermediate lens 1004) has negative refractive power. Chief rays 1112 and 1113 are shown. Example 12

[0031] As shown in FIGS. 12-12A, portion 1200 of the electron microscope includes a sample chamber 1202 defined by a vacuum chamber 1204. Electron optics extend along a column 1206, but are not further shown. A sample profile is obtained using an illuminator 1212 that directs an illumination beam 1214 toward a sample fixed to a rotatable sample platform 1220 that can translate along the X and Y axes of a coordinate system 1201 with translation stages 1226 and 1224, respectively. An approximate center 1228 of the electron optics is offset from the illumination beam 1214. The sample is profiled with the illumination beam 1214 and can then be imaged or processed with the electron optics by translating an imaging location, such as the center 1228. The illumination beam 1214 can be a parallel or divergent beam and is shown as rectangular in shape for convenience of illustration.

[0032] 12B is an image 1280 showing 2D profiles obtained with telecentric optics for three objects 1282 of the same size placed on a sample platform 1284 at different distances from the telecentric optics. As shown, the three objects 182 have profiles of the same size so that the profiles can be used to provide guidance for safe sample stage movement and focus adjustment. Example 13

[0033] As shown in FIG. 13, portion 1300 of the electron microscope includes a sample chamber defined by a vacuum chamber 1320 that can be evacuated through passageway 1322. The electron optics, including the objective pole piece 1324, are not further shown. 2D sample profiles are obtained using an illuminator 1306 that directs an illumination beam 1308 toward a sample 1312 fixed to a rotatable sample platform 1308 that can translate along any axis of a coordinate system 1301 and tilt to a sample position 1313 for profiling. The sample platform 1311 is typically coupled to a sample stage 1309 for translating the sample along the axis 1340 of the electron optics. The sample can be tilted, profiled as shear and tilt, and translated to remove tilt and imaged with the electron optics. The illumination beam 1308 can be a parallel or divergent beam. The objective 1302 is positioned against the wall of the vacuum chamber 1320, and a camera 1305 is positioned to form a telecentric optical system and record the sample profile. The central axis of the profile system 1304 is parallel to the sample platform plane during profiling. Example 14

[0034] FIG. 14A shows an embodiment of a sample profile image. In a typical example, samples such as samples 1406 and 1420 are fixed to a sample platform 1402 and back-illuminated with an illumination system 1410. Back-illumination, such as sample region 1407, generally causes the outline of the sample to appear dark, while portions, such as sample region 1455, appear bright due to the sample's reflectivity and the tilt of the surface sample. This sample region 1455 reflects light from the illumination system 1410. To safely position the sample (without colliding with components of the electron-optics system or other components), intermediate regions, such as sample region 1455, can be treated in the same way as dark regions, such as 1407 and 1421. If regions such as sample region 1455 appeared darker, processing would be simpler, but they would still be recognizable as potential obstacles to avoid when moving the sample into position for imaging.

[0035] Figure 14B shows the sample arrangement of Figure 14A, but uses an illuminator 1450 that provides variable illumination in the Z-axis direction 1454. As shown, the illuminator 1450 includes a relatively bright region (higher intensity) 1451 and a relatively dark region 1452 (lower intensity), which produces a relatively dark region 1456. When used with the illumination system 1410 of Figure 14A, region 1456 appears brighter in the 2D profile and is more difficult to recognize as a possible obstruction. The reflection from region 1456 is related to the sample's surface reflectivity and the tilt of the surface sample. By varying the illumination intensity in the z-axis, the top of the sample can be imaged with higher contrast and therefore more accurately identified in the 3D map. Other stepwise or gradual increases or decreases in illumination intensity along the Z-axis can be used and can be provided by an appropriate number of illuminators, changes in light scattering, or light attenuation, or other approaches. Obstacles should appear dark; reflective obstructions, such as the sides of the sample, may appear relatively bright compared to obstructions that completely block illumination. These relatively bright areas (such as area 1456) should be identified as obstacles. Example 15

[0036] FIG. 15 illustrates a representative illuminator 1500, including one or more light emitters, such as LEDs 1502, that couple light into the edge of a transparent sheet 1504, which acts as a light guide. Coordinate axes 1550 indicate the Z axis, which corresponds to the optical axis of the charged particle beam, and the Y axis, which corresponds to the axis of the optical system used to acquire the 2D profile. The major surface of sheet 1504 is optically roughened by grinding, polishing, bead blasting, or other processes to scatter light during illumination. When light introduced at edge 1506 propagates toward the opposite edge 1507, the light is attenuated by scattering. To enable uniform illumination, zones 1510-1514 of the sheet's surface can be given increased roughness to increase scattering and compensate for the loss of light intensity as the light propagates from LEDs 1502 to edge 1507. The roughness, or other scattering characteristics, can vary smoothly or in a stepwise manner (as shown), or both. The intensity of the output light can also be further customized using an illumination gradient (stepped or continuous) from top to bottom, for example, so that the top and bottom of the illuminator face are associated with different intensities. A variable (stepped or gradient attenuator) can also be used, with a higher optical density near edge 1506 and a lower optical density near edge 1507. Other illumination patterns can be used in addition to stepped or continuous gradients. Example 16

[0037] As shown in FIG. 16, an exemplary method 1600 for generating a 3D map includes selecting several sample views (rotation angles) in 1602 and selecting an initial view height and view width in 1604. In some cases, the field of view of the optical system is not large enough to acquire a complete profile, and the sample platform or optical system is adjusted to capture the complete inspected object height. A rotation angle is selected in 1606, and the sample platform is set at the initial height and rotation angle in 1608. A 2D profile is acquired in 1610. In some examples, the 2D profile or 2D projection is a binary contrast image. A binary 2D profile can be converted by thresholding the image detected by the detector. For example, the 2D profile shows a first intensity corresponding to light received directly from the light source without being blocked by the sample and / or sample platform. The binary 2D profile can also show a second intensity, lower than the first intensity, in areas corresponding to shadows cast by light obstructions. In 1612, it is determined to use additional angles to acquire additional profiles. If so, method 1600 returns to 1606 to select a rotation angle, and the necessary steps are repeated. At 1614, it is determined whether to adjust the view height. If so, the view height is adjusted at 1618, and processing returns to 1606. The view width, if determined at 1616, can be changed at 1620, and processing can return to 1606. Once all profiles are available, the profiles can be combined to create a 3D map at 1630. The 3D map can be created as shown below with reference to FIG. 24. If desired, the 3D map can be optionally combined with camera images, such as images acquired by a navigation camera, at 1632. Method 1600 can be performed after loading the sample into the vacuum chamber, but before imaging or processing with a charged particle beam. In one example, method 1600 can be performed while the vacuum chamber is pumped down for charged particle beam imaging or processing.The 3D sample profile may be generated when a sample or sample platform is placed in a profiling position. The sample platform is then moved from the profiling position to a sample imaging position to image or process one or more samples held by the sample platform. The sample platform is moved from the profiling position to the imaging position based on the 3D sample profile to avoid collision of the sample with internal structures of the CPM. Example 17

[0038] As shown in FIG. 17 , an exemplary method 1700 includes determining whether a 3D map to address reflections should be acquired at 1702. Such a 3D map is referred to herein as a “safe” 3D map. A safe 3D map may be generated for highly reflective samples whose surfaces are oriented in a manner that could cause light reflections. As described above, the 3D map defines an area around a magnetic pole piece or other component within a vacuum chamber. In this area, the sample can be moved for imaging or other evaluation placement without contacting other components. Reflective surfaces may be missed in the mapping if they are sufficiently reflective to appear as direct illumination from a light source. Creating a map for a reflective sample requires taking the sample's reflectivity into account. If a safe map is to be created, mutually shifted 3D maps are acquired at 1712 and combined at 1714 using OR logic to create the safe 3D map. The shifted 3D maps are typically based on several angles spanning a full rotation, with each map covering a different set of angles, e.g., 0, 5, 10, 360 degrees, and 1, 6, 11, 16 degrees. Otherwise, 2D projections spanning the desired range and resolution (i.e., angular increments) are acquired at 1706 and combined at 1708 to generate a 3D map. For non-reflective samples, the 3D map allows safe navigation without consideration of reflections. However, the created 3D map (i.e., whether it is a safe 3D map or not) can optionally be combined with a camera image at 1710. A sample position can be selected at 1722, and the sample can be positioned at the selected location for focusing using the 3D map at 1724. For example, a sample platform or other mechanical or electro-optical component can be moved without operator intervention by moving within the unoccupied area of ​​the 3D map. This ensures that the selected focal position is in the imaging position and aligned with the CP beam under the CPM pole pieces for imaging or processing. The 3D map therefore allows for the determination of a safe path to avoid collisions between the sample and the optics.

[0039] Using the full 3D map, a system controller, such as a control computer, can automatically check and control the position of the sample, sound alarms, disable sample movements into areas where collisions may occur, and operate to guide manual operations.

[0040] It will be appreciated that generation of the 3D map can be performed outside the electron microscope chamber, or during or after pump-down of the microscope. The sample location can be indicated using a visual interface such as that shown in Figure 2. In some cases, the 3D map can be processed to remove areas that appear to be occupied by the sample. Example 18

[0041] Referring to FIG. 18 , an exemplary system for implementing the disclosed technology includes a general-purpose computing device in the form of an exemplary conventional PC 1800, including one or more processing units 1802, a system memory 1804, and a system bus 1806 coupling various system components, including the system memory 1804, to the one or more processing units 1802. The system bus 1806 can be any of several types of bus structures, including a memory bus, a memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The exemplary system memory 1804 includes read-only memory (ROM) 1808 and random access memory (RAM) 1810. A basic input / output system (BIOS) 1812, containing basic routines that facilitate the transfer of information between elements within the PC 1800, is stored in the ROM 1808. The memory 1804 also includes portions 1871-1875, which include computer-executable instructions and data for 2D profile acquisition (including sample stage control), 3D profile determination based on acquired 2D profile determination of a safe sample path, a graphical user interface for operator input / output, and general instrument control.

[0042] The exemplary PC 1800 further includes one or more storage devices 1830, such as memory devices, such as a hard disk drive or thumb drive. Such storage devices may be connected to the system bus 1806 by an appropriate interface. Such computer-readable media provide non-volatile storage of computer-readable instructions, data structures, program modules, and other data for the PC 1800. Other types of computer-readable media capable of storing data accessible by a PC, such as magnetic cassettes, flash memory cards, digital video disks, CDs, DVDs, RAM, ROM, etc., may also be used in the exemplary operating environment.

[0043] A number of program modules, including an operating system, one or more application programs, other program modules, and program data, may be stored on storage device 1830. A user may enter commands and information into PC 1800 through one or more input devices 1840, such as a keyboard, and a pointing device, such as a mouse, touchpad, digital camera, microphone, jog stick, or game pad. These and other input devices are often connected to the processing unit(s) 1802 through a serial port interface connected to the system bus 1806, but may also be connected by other interfaces, such as a parallel port, game port, or universal serial bus (USB). A monitor 1846 or other type of display device is also connected to system bus 1806 through an interface, such as a video adapter. Other peripheral output devices, such as speakers and a printer (not shown), may be included.

[0044] The PC 1800 may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer 1860. In some examples, one or more network or communication connections 1850 are included. The remote computer 1860 may be another PC, a server, a router, a network PC, a peer device, or other common network node, and typically includes many or all of the elements described above in connection with the PC 1800, although only the memory storage device 1862 is illustrated in FIG. 18 . The personal computer 1800 and / or the remote computer 1860 can be connected to logical local area networks (LANs) and wide area networks (WANs). Such networked environments are commonplace in offices, enterprise-wide computer networks, intranets, and the Internet.

[0045] When used in a LAN networking environment, the PC 1800 is connected to the LAN via a network interface. When used in a WAN networking environment, the PC 1800 typically includes a modem or other means for establishing communications over the WAN, such as the Internet. In a networked environment, program modules depicted relative to the personal computer 1800, or portions thereof, may be stored in a remote memory storage device or elsewhere on the LAN or WAN. The network connections shown are exemplary, and other means of establishing a communications link between computers may be used. Example 19

[0046] As shown in FIG. 19, a representative electron microscope 1900 includes a pole piece 1902 that directs a beam toward a sample platform 1904 coupled to translation stages 1906, 1908 and a translation / rotation stage 1910. An electron optical column 1901 includes lenses, deflectors, and other electron optical components, not shown. Representative samples 1912-1914 are fixed to the sample platform 1904. An illuminator 1920 directs a beam 1922 toward the samples 1912-1914 and a transparent window 1924 within a vacuum chamber housing 1925. Telecentric optics 1926 are positioned to generate profile images on an image sensor 1928 based on backside illumination of the samples 1912-1914 for various rotation angles provided by the translation / rotation stage 1910. Example 20

[0047] Figure 20 shows a sequence 2000 of profile images acquired during rotation of a sample used to generate a 3D map, such as 3D map 350 of Figure 3B. Representative samples 2001-2003 are shown. Each profile image corresponds to a different angle of rotation.

[0048] 21A-21B show an exemplary 2D projection 2100 of samples 2102, 2104 fixed to a sample platform 2106. FIG. 21B shows a reflective region 2107 associated with the edge of the sample platform 2106. For safe navigation within the vacuum chamber, the reflective region 2107 does not appear as dark as the rest of the 2D projection of the sample platform 2106, but should be identified as an obstacle. Reflective regions such as reflective region 2107 typically appear at selected rotation angles and associated 2D projections.

[0049] 22A-22B show a sample 2201 and 2D projections 2200, 2202 acquired using telecentric optics with a field of view smaller than the sample platform. The 2D projections 2202, 2204 can be combined to generate the complete 2D profile 2206 of FIG. 22C.

[0050] Figure 23 shows a sequence of 2D projections obtained at different rotation angles. Representative samples 2302 and 2304 are shown. At rotation angles of 68, 69, 70, and 71 degrees, sample 2302 has reflective regions 2308 that can be identified as obstacles in the 3D mapping. The reflective regions 2308 appear with a similar intensity to unobstructed regions. If the 2D projection values ​​are thresholded at an appropriate value that distinguishes reflections from unobstructed regions, such regions can be properly identified as obstacles. Parallel illumination or increasing the distance between the light source and the sample can reduce reflections. Alternatively, patterned illumination can be used to simplify the identification of reflective regions or the approach described above with reference to Figures 4A-4B. Example 21

[0051] Figures 24A-24E illustrate the processing of 2D profiles to generate a 3D map. Figure 24A shows a representative 2D projection 2402 at a selected angle, and Figure 24B shows a cylindrical volume 2404 representing the initial fully occupied sample space, i.e., space potentially available for movement but including portions that are unsafe for movement because they are occupied by the sample. As shown in Figure 24B, the initial size of the cylindrical volume 2404 is based on the size of the sample holder and microscope configuration and represents the maximum volume in which a sample can be placed. Using the 2D projection 2402, a portion of the cylindrical volume 2404 is removed, as shown in Figures 24D and 24F. In Figure 24C, the unoccupied space 2406 in the 2D projection 2402 is used to define a corresponding feature 2416 indicating an area where movement is permitted. The unoccupied space 2406 extends through the cylindrical volume 2404, removing portions of the cylindrical volume 2404, so that the feature 2416 extends through the cylindrical volume 2404. Other unoccupied space indicated by 2D projection 2402 defines corresponding features and extends through cylindrical volume 2404. The resulting volume 2405 (FIG. 24D) indicates a safe area for movement. In this example, the upper boundary of 2D projection 2402 is used; this approach can be called an "envelope" approach. Additional 2D projections at other rotation angles are then used to define features within cylindrical volume 2404 to generate a 3D map. Alternatively, the full 2D projection data can be used, as shown in FIGS. 24E-24F. In this case, lower unoccupied space 2408 within 2D projection 2402 is used to define corresponding features 2418 within volume 2404. Additional 2D projections at other angles are then used to define features within volume 2404 to create a 3D map. This approach can be more computationally intensive than the envelope approach.

[0052] In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it is recognized that the illustrated embodiments are preferred examples only and should not be considered limiting in scope, and we therefore claim all that comes within the scope and spirit of the appended claims.

Claims

1. illuminating a sample located within a vacuum chamber of a charged particle microscope from a first side with an illumination beam from a light source; detecting at least one 2D projection of the sample on a second side opposite the first side based on illumination from the first side; generating a 3D map based on a plurality of the 2D projections detected by rotating the sample; placing the sample at an imaging location within the vacuum chamber based on the 3D map; A method comprising:

2. The method of claim 1 , wherein the sample is illuminated from the first side with a light source and the sample is imaged or processed with a charged particle beam at the imaging location.

3. 3. The method of claim 1, further comprising detecting a plurality of 2D projections of the sample at the second side by rotating the sample, and wherein the 3D map is generated based on the plurality of 2D projections.

4. 4. The method of claim 3, further comprising: detecting a set of initial 3D maps, each of the initial 3D maps being based on a different set of rotation angles, and the 3D maps being based on combining the initial 3D maps such that the 3D map is a safe 3D map.

5. The method of any one of claims 1 to 4, wherein the sample is illuminated at a profiling position, and the sample is moved from the profiling position to the imaging position based on the 3D map.

6. The method of claim 1 , wherein the step of irradiating the sample is performed using an irradiation source located within the vacuum chamber.

7. The method of any one of claims 1 to 6, wherein the step of irradiating the sample comprises directing a collimated beam at the sample.

8. The method of any one of claims 1 to 6, wherein the step of irradiating the sample comprises irradiating the sample with a beam having a patterned intensity.

9. 9. The method according to claim 1, wherein detecting at least one 2D projection of the sample on a second side opposite the first side is performed using telecentric optics.

10. 10. The method of claim 9, wherein when the sample is illuminated, a central axis of the telecentric optical system is parallel to a sample platform that holds the sample.

11. an illumination system positioned to illuminate the sample with light from a first side; an imaging system arranged to generate a 2D projection of the illuminated sample based on illumination from the first side; a processor coupled to receive the 2D projections and generate a 3D map of the sample for positioning the sample based on a plurality of the 2D projections detected by rotating the sample; Equipped with The imaging system includes an image sensor positioned on a second side of the sample opposite the first side to generate a 2D profile image of the illuminated sample, and the processor is coupled to a sample platform and configured to rotate the sample to generate the 2D projection.

12. 12. The charged particle microscope of claim 11, wherein the illumination system is arranged to direct a divergent beam towards the sample, and the imaging system includes telecentric optics to direct a 2D projection towards the image sensor.

13. 12. The charged particle microscope of claim 11, wherein the illumination system is arranged to direct a collimated beam towards the sample.

14. The charged particle microscope of any one of claims 11 to 13, wherein the processor is coupled to initiate evacuation of a vacuum chamber of the charged particle microscope during acquisition of the 2D projections.

15. 10. A computer-readable medium storing processor-executable instructions for the method of claim 1.

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