Patent Description:
Positioning samples for electron microscopy can be time-intensive and requires operator diligence. Variably-sized samples on a sample holder must be carefully positioned to avoid contact with microscope components such a pole pieces used by magnetic lenses, electron detectors, or other components. In some cases, a sample holder retains multiple samples of differing heights and an operator must move each sample carefully into the microscope field of view. After positioning in the field of view, additional operator time is then required to focus the sample. Sample positioning and focusing thus are both time consuming and prone to error, and the operator skill needed can require supervision of new users who can cause sample/pole piece contact, introducing astigmatism, misalignment, or component or sample damage. For at least these reasons, alternative approaches are needed.

<CIT> discloses generating a surface model of a structure based on detected light rays or particles emanate from the structure, and positioning the object depending on the surface model. <CIT> discloses method of cross-section processing based on sample images acquired by an optical microscope. <CIT> discloses method and system for measuring height of an object of lithography.

Methods comprise illuminating a sample situated 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 situated at an imaging location within the vacuum chamber based on the 3D map. In some examples, the first side is opposite the second side and a plurality of 2D projections of the sample on the second side are detected and the 3D map is generated based on the plurality of projections. Typically, the plurality of 2D projections of the sample on the second side are detected by rotating the sample. In some examples, a set of 3D maps is produced, each 3D map based on a set of rotation angles, wherein the 3D map is based on combining each of the set of 3D maps. In examples, the sample is moved into the imaging location after the 2D projections are detected. In further examples, the sample is loaded into a vacuum chamber of a charged particle microscope and irradiated with light. The sample is moved into the imaging location within the vacuum chamber based on a 3D map generated from the 2D projection. The sample may be processed or imaged with the charged particle beam at the imaging location. In some examples, illuminating the sample comprises directing a collimated beam to the sample and the collimated beam is directing along an axis that is perpendicular to a charged-particle optical axis. The illuminating the sample can be performed with a light source situated within or outside of the vacuum chamber. In some alternatives, illuminating the sample comprises illuminating the sample with beam having a patterned intensity, and further comprising identifying reflective sample surface based on the patterned intensity. In some examples, detecting at least one 2D projection of the sample on the second side, opposite the first side is performed with a telecentric optical system. The telecentric optical system can include an objective lens that is situated within or outside of the vacuum chamber. The telecentric optical system is one or both of object-side telecentric and image-side telecentric. In some examples, the central axis of the detector for acquiring the 2D projections is parallel to the sample platform for holding the samples.

A charged particle microscope comprises an illumination system situated to illuminate samples from a first side and an imaging system situated to produce 2D profiles of the illuminated samples based on the illumination from the first side. A processor is coupled to receive the 2D profiles and generate a 3D map based on the 2D profiles. The imaging system includes an image sensor situated to produce the 2D profile images of the illuminated samples based on the illumination from the first side; and the processor is coupled to a sample stage and is configured to rotate the illuminated samples to produce the 2D profiles. The imaging system can include a telecentric optical system that directs 2D profiles to the image sensor. The illumination system can be situated to direct a diffuse beam to the samples or a collimated beam to the samples. A sample stage is operable to move the sample platform to a charged particle optical axis.

The foregoing and other features, and advantages of the disclosed technology will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

In the following, representative examples of CPB systems such as CPB microscopes and related components, sub-components, and methods are disclosed. In many practical examples, electron beams are of interest, and the examples are described with reference electron beams for convenient illustration. The disclosed approaches can also be used in light microscopy as well. In most examples, additional CPB components such as lenses, deflectors, stigmators, and additional apertures are used, but are not shown for convenient illustration. The disclosed methods and apparatus can be used in both transmission and scanning microscopy. As discussed below, in some examples, a vacuum chamber can be evacuated while one or more samples are profiled at a sample profiling location to produce a 3D map. The samples can be situated on a stage at a charged particle (CP) optical axis or can be tilted with respect to or displaced from the CP optical axis. The samples may be moved to the CP optical axis for imaging or processing after profiled. As used herein, image can refer to a presentation of image data on a display for visual inspection by an operator or data associated with 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 a CP optical axis (a Z-axis). Such axes need not be mutually orthogonal, but orthogonal axes are convenient.

Illumination as used herein refers generally to directing electromagnetic radiation to an object or the electromagnetic radiation itself. Such electromagnetic radiation is typically visible light at wavelengths between about <NUM> and <NUM> which are convenient for use with readily available image sensors and permit operator observation as well as use with a camera. Other wavelengths can also be used, but the range <NUM> to about <NUM> is convenient. In the examples, back-illumination is generally used. Front illumination produces profile images that are generally dependent on sample reflectivity and details of the samples. By contrast, back illumination produces profile images with contrast between light and dark areas (unblocked and blocked areas) that generally depend on sample shape and not sample surface characteristics. Back illumination can be provided by placing a light source behind an object of interest or placing a reflector behind the object and reflecting light to the object.

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

Lenses are shown in the examples as single element lenses but multi-element lenses can also be used. Light optical systems are shown typically along a linear axis, but such an axis can be bent or folded using prisms or mirrors, as desired.

Referring now to <FIG>, in a representative embodiment, a charged particle beam (CPB) system <NUM> includes a CPB microscope <NUM> such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and comprises one or more CPB lenses such as a condenser lens <NUM> that is situated to direct a CPB from a CPB source <NUM> towards an objective lens <NUM>. The CPB source <NUM> can be, for example, a field emitter that produces an electron beam, but other sources can be used. In some embodiments, one or more additional CPB lenses can be provided, and can be magnetic lenses and/or electrostatic lenses. A primary axis <NUM> may be determined during manufacturing of the microscopy system. In use, the CPB propagates along the primary axis <NUM> towards a sample stage <NUM> and a beam deflector <NUM> can be used to scan the beam with respect to samples S situated on a sample stage <NUM>. The sample stage <NUM> generally provides translations and or rotations for positioning the samples S. Typically, the samples S are secured to a sample platform that is then secured to the sample stage <NUM>.

The CPB system <NUM> includes a vacuum chamber housing <NUM> that can be evacuated using vacuum pumps (not shown) and typically defines a first volume 112A that contains the CPB source <NUM> and selected other CPB optical components and a second volume 112B that is situated to receive the sample S and the sample stage <NUM>. A column isolation valve (CIV) <NUM> is situated to separate the first volume 112A and the second volume 112B. Typically, the CIV <NUM> is operable to hermetically isolate the first volume 112A from the second volume 112B during sample exchange. The sample stage <NUM> can be movable in an X-Y plane as shown with respect to a coordinate system <NUM>, wherein a Y-axis is perpendicular to a plane of the drawing. The sample stage <NUM> can further move vertically (along a Z-axis) to compensate for variations in the height of the samples S and to aid in focusing the beam at the samples S. The sample stage <NUM> can also rotate about an axis parallel to the z-axis as well as tilt the sample S. In some cases, sample profiling is done with the sample platform tilted as shown in <FIG>, discussed further below. In some embodiments, the CPB microscope <NUM> can be arranged vertically above the sample S and can be used to image the samples. In some embodiments, the CPB microscope <NUM> can be arranged vertically above the sample S and can be used to image the samples S while an ion beam machines or otherwise processes the samples S.

A light source <NUM> is situated to deliver an illumination beam <NUM> through a window <NUM> in the vacuum chamber housing <NUM>. The illumination beam <NUM> is illustrated as a collimated beam but can be diffuse or uncollimated as well. An optical system comprising one or more lenses such as lens <NUM> is situated to receive portions of the illumination beam <NUM> that are not blocked by the samples S and produce one or more profile images (or 2D projections) of the samples S at or near an image sensor <NUM>. As shown, the lens <NUM> and portions of the optical system extend into the vacuum chamber <NUM>. However, either the optical system, the light source <NUM>, or both can be inside, outside, or partially inside and outside of the vacuum chamber housing <NUM>. Typically, the sample stage <NUM> is rotated about the axis <NUM> (or a parallel axis) and profile images acquired during the rotation. For example, the sample stage <NUM> can be rotated <NUM> degrees and profile images acquired at <NUM> degree intervals.

The CPB system <NUM> can further comprise a computer processing apparatus <NUM> such as a control computer and a CPB system controller <NUM> for controlling beam deflectors, CPB lenses <NUM>, <NUM> and other CPB lenses and other components such as detectors and the sample stage <NUM>, including rotations and translations of the sample stage <NUM>. The computer processing apparatus <NUM> can also control display of information gathered from or more CPB detectors on a display unit. In some cases, the computer processing apparatus <NUM> (e.g., the control computer) establishes various excitations, records image data, and generally controls operation of the CPB microscope <NUM> including the control of profile image acquisition. A so-called "navigational camera" <NUM> is situated to provide top-down images of the sample and the sample stage, typically for viewing by an operator. A camera <NUM> can also be provided to obtain a side view of samples. The camera <NUM> is typically displaced along the Y- axis (into the plane of <FIG>) and is situated to view out of the plane of <FIG>.

The sample stage <NUM> can be translated along the Z-axis for focusing as controlled by one or both of the computer processing apparatus <NUM> and the CPB system controller <NUM> based on the profile images produce with the image sensor <NUM>. In some examples, the sample stage <NUM> can be set to a suitable Z-axis location for imaging a particular sample with or without manual operator adjustment of Z-axis position. Sample imaging can be based on transmitted, reflected, or scattered charged particles, X-rays or other electromagnetic radiation, or secondary emission received by one or more detectors that are not shown in <FIG>.

<FIG> illustrates a portion of a graphical user interface <NUM> that can be provided on a display device associated with a CPB system such as illustrated in <FIG>. In this example, a display area <NUM> contains an image of a substrate surface, display area <NUM> is a side view <NUM> of an electron microscope column that includes a pole piece <NUM> and a sample <NUM> that is secured to a sample platform <NUM> and having a surface <NUM> whose image is shown in the display area <NUM>. The side view <NUM> may be obtained using an optical system and an image sensor such as the lens <NUM> and image sensor <NUM> of <FIG> or any of the optical systems described below. Display area <NUM> illustrates a top surface <NUM> of the sample platform <NUM> indicating a location <NUM> for which beam focus is selected. Display area <NUM> contains a top view of the sample platform <NUM> on which various samples can <NUM>-<NUM> be seen. A display area <NUM> includes display areas for stage X, Y, Z, rotation, and tilt coordinates <NUM>, an area <NUM> used to indicated with a computer pointing device that a CPB is to be turned on (shown as radio buttons), an area <NUM> used to indicated with a computer pointing device that a autofocus is to be activated for the area indicated at <NUM>, and an area <NUM> that can include other controls and data. With this user interface, indicating that the location <NUM> is to be imaged using a computer pointing device causes the sample stage to position the location suitably with respect to the electron microscope optical column based on profile data that permits safe movement (i.e., collision free movement).

<FIG> illustrates a representative plan view of a sample platform to which samples <NUM>-<NUM> are secured. <FIG> is captured with a navigational camera, such as the navigational camera <NUM> of <FIG>. 3D coordinate axes are provided for convenience. Based on plurality of profile images (profiles) obtained as discussed a 3D map <NUM> is produced in <FIG>. The 3D map includes map regions <NUM>-<NUM> corresponding to the samples <NUM>-<NUM> shown in <FIG>. Images from cameras such as the cameras <NUM>, <NUM> of <FIG> can be combined with the 3D map for visualization, but the 3D map does not require such camera images.

Typically, multiple 2D projections or profiles of the sample platform and the samples are obtained with a plurality of sample platform rotations of about <NUM> degree through a range of <NUM> degrees. In some cases (such as in the presence of reflections from sample surface in profiles), a series of rotations at a first increment (such as <NUM> degrees) through a <NUM> degree range beginning at a first angle is used to obtain a first 3D map. The first angle is then incremented at a second increment and the <NUM> degree range is spanned by additional profiles at the first increment. Thus, multiple series of 2D profiles can be obtained such as at <NUM>, <NUM>, <NUM>,. , <NUM> degrees to produce a first 3D map, then , the at <NUM>, <NUM>, <NUM>,. to produce a second 3D map, etc. This can produce <NUM>3D maps, each associated with <NUM> rotation angles. Each of these maps can show reflections that are not shown on the other maps. These maps can be combined, preferably using an OR operation so that any reflective surfaces of a sample are included in mapping This tends to produce a "safe" 3D map for focus adjustment and the stage holder can be moved without the sample contacting other components. As used herein, safe 3D map refers to a 3D map obtained by accounting for reflections. <FIG> shows a 3D map produced with <NUM> rotations incremented by <NUM> degree. <FIG> shows a 3D map produced by combining <NUM>3D maps produced with <NUM> incremented rotations. The <NUM> degree incremented mapping is better for visualizing the samples but the combined <NUM> degree incremented mapping is safer for sample movements as reflective surfaces are included as possible obstructions.

One approach to providing safe 3D maps is to combine 3D maps obtained at different angles such as differing initial angles with a fixed angular increment. As shown in <FIG>, a representative method <NUM> includes selecting a set of initial angles and an angular increment at <NUM>. At <NUM>, 2D projections associated with each initial angle at multiples of the angular increment are combined to produce multiple 3D maps. For example, for initial angles θi of a set of n initial angles θ<NUM>,. , θn, and an angular increment Δθ, 2D projections corresponding to θi + j Δθ for all integer values of j that provide angles within a full rotation are combined for each initial angle to produce n 3D maps. At <NUM>, the 3D maps can be processed with a logical OR within angular range corresponding to the angular increment Δθ to obtain a safe 3D map. For example, five 3D maps made with the angular increment Δθ = <NUM> degrees can be obtained using 2D projections made at <NUM> degree increments. A first 3D map can contain values for <NUM>, <NUM>,<NUM>, and <NUM> degrees (and other angles over a full <NUM> degrees), a second 3D can contain values for <NUM>, <NUM>,<NUM>, and <NUM> (and other angles over a full <NUM> degrees, and so on. These 3D maps can be combined, i.e., map values within the angular increment Δθ are processed to retain the values corresponding to obstructions (unilluminated region of the sensor). In typical 3D maps with back illumination, 3D map values are either <NUM> or <NUM> (unobstructed or obstructed, respectively) and the 3D maps are combined through a logical OR operation. Some 3D maps show obstructions that are not in other maps, and such a combination of 3D maps provides a safe 3D map in which reflections do not result in missing real obstructions. The resulting safe 3D map can be a lower resolution map, but generally does not appear too visually different from a higher resolution 3D map as shown in <FIG>. Different sets of angles can be used to obtain the multiple 3D maps, and the disclosed example is chosen for convenient explanation. Choices of the angle over which map values are combined need not be the same as the angular increment. Typically, 2D projections are obtained at a predetermined angular resolution and then combined to make multiple 3D maps for use in making a safe 3D map. At <NUM>, the 3D safe map is output for use in an electron microscope.

<FIG> is a plan view and <FIG> is a sectional view along A-A of a representative profile measurement system <NUM> that includes a light source <NUM> that is configured to produce a collimated beam <NUM> that is directed to a sample platform <NUM> on which representative samples <NUM>, <NUM> are situated. A transmitted beam portion <NUM> is directed to an image sensor <NUM> to produce a 2D profile image. As shown, a portion of the collimated beam <NUM> is blocked by the sample <NUM> and produces a corresponding dark or shaded area <NUM> at the image sensor <NUM>. The sample platform is rotated about an axis <NUM> so that the light and dark areas on the image sensor change and different profile images are obtained. The samples <NUM>, <NUM> are moved into and out the beam <NUM> during the rotation.

<FIG> is a plan view and <FIG> is a sectional view of a representative profile measurement system <NUM> that includes a light source <NUM> that is configured to produce a beam <NUM> that is directed to a sample platform <NUM> on which representative samples <NUM>, <NUM> are situated. A transmitted beam portion <NUM> is directed to an image sensor <NUM> via a telecentric optical system <NUM> (shown as a single lens for purposes of illustration) to produce a 2D profile image. As shown, a portion of the beam <NUM> is blocked by the sample <NUM> and produces a corresponding dark or shaded area <NUM> at the image sensor <NUM>. The sample platform is rotated about an axis <NUM> so that the light and dark areas on the image sensor change, and the samples <NUM>, <NUM> move with respect the image sensor <NUM>. In this example, the light source <NUM> is shown as producing a collimated beam but diffuse beams or diverging beams can be used. Collimation is not required as the telecentric optical system <NUM> eliminates or reduces perspective errors as discussed in detail below. While diverging or diffuse beams can be used, such beams may produce reflections from sample surfaces that can be overlooked and inappropriately considered as unobstructed areas.

<FIG> illustrates a portion of representative profile measurement system that includes a telecentric optical system <NUM> situated to produce an image of a sample that can be situated at various locations along an optical system axis <NUM> such as at 702A, 702B. The sample is secured to a rotatable sample platform <NUM> so that sample position along both X- and Y-axes of a representative coordinate system <NUM> can vary. For convenience, the optical system axis <NUM> is shown as parallel to the X-axis and an electron microscope axis is parallel to the Z-axis. The telecentric optical system includes an objective lens <NUM> that is mounted within a vacuum chamber. The objective lens <NUM> is fixed to a lens tube <NUM> that is secured to a vacuum chamber wall <NUM> at an optical window <NUM>. An imaging lens <NUM> and an aperture stop <NUM> are situated at the focal length F of the objective lens <NUM> to obtain telecentricity. As shown, the imaging lens <NUM> and the aperture stop <NUM> are included in a camera <NUM> that also includes an image sensor <NUM> and associated electronics for acquiring, processing, storing, and communicating images. In this example, the optical system can be referred to as object-side telecentric as chief rays are parallel on the object-side of the optical system.

With this telecentric arrangement, the apparent size of a sample does not vary with distance to the optical system and magnification is the same for all object distances. A sample that is out of focus will have a blurry image but the size of the blurry image corresponds to that of an in-focus image of the sample. Sample edges can appear blurred, but can be readily located. Parallax errors are avoided. In some examples, all samples are in focus due to the available focal depth of field. Placement of the aperture stop at the focus of the lens is a representative approach to achieving telecentricity. As shown in <FIG>, with the sample situated at either 702A or 702B, associated chief rays 730A, 730B, respectively, pass through the center of the aperture stop <NUM>. For clarity of illustration, image formation by the imaging lens <NUM> is not shown so that chief rays can be readily seen. As discussed above, some or all portions of the telecentric optical system <NUM> can be inside or outside of a vacuum chamber as may be convenient.

In the arrangement of <FIG>, the specimen can be illuminated either from the front side or the back side. In typical examples, back side illumination is used so that samples block illumination and images of samples are shown as dark regions with edges. Using mirrors or other reflectors, front or back side illumination can be provided with sources located on either the front side or the back side of a sample. Side illumination can also be used, but typical requires processing to properly identify reflective areas for a safe 3D map.

<FIG> illustrates a portion of representative profile measurement system that includes a telecentric optical system <NUM> situated to produce an image of a sample that can be situated at various locations along an optical system axis <NUM> such as at 802A, 802B. The sample is secured to a rotatable sample platform <NUM> so that sample position along both X- and Y-axes of a representative coordinate system <NUM> can vary. For convenience, the optical system axis <NUM> is shown as parallel to the X-axis and an electron microscope axis is parallel to the Z-axis. The telecentric optical system includes an objective lens <NUM> and an imaging lens <NUM> that are situated about an aperture stop <NUM> located at the respective focal lengths F1, F2 of the objective lens <NUM> and the imaging lens <NUM> to obtain telecentricity and produce an image at an image sensor <NUM>. Associated electronics for acquiring, processing, storing, and communicating images are not shown. In this example, the optical system can be referred to as object-side telecentric and image-side telecentric as chief rays are parallel on the object-side and the image-side of the optical system.

With this telecentric arrangement, the apparent size of a sample does not vary with distance to the optical system and magnification is the same for all object distances due to object-side telecentricity. With image-side telecentricity, chief ray position at the image sensor does not depend on object distance and magnification is constant. As shown in <FIG>, with the sample situated at either 802A or 802B, associated chief rays 830A, 830B , respectively, pass through the center of the aperture stop <NUM> and are parallel on the image-side of the imaging lens <NUM>. As above, for clarity of illustration, image formation by the imaging lens <NUM> is not shown so that chief rays can be readily seen. Some or all portions of the telecentric optical system <NUM> can be inside or outside of a vacuum chamber as may be convenient. In addition, the specimen can be illuminated either from the front side or the back side. In typical examples, back side illumination is used so that samples block illumination and images of samples are shown as dark regions with edges.

Referring to <FIG>, a representative profile system <NUM> includes an objective lens <NUM> and an imaging lens <NUM> situated about an aperture stop <NUM> to form sample profile images at an image sensor <NUM>. The aperture stop <NUM> is situated at a focus of the objective lens <NUM> so that the lenses <NUM>, <NUM> form an object-side telecentric optical system. The telecentric objective <NUM> is separated from the vacuum chamber <NUM> by a vacuum sealed transparent window <NUM>. The imaging lens <NUM>, the aperture stop <NUM>, and the objective lens <NUM> are secured in a lens tube <NUM> that is secured to the vacuum chamber <NUM> with one or more bolts <NUM> or other fasteners. The lens tube is bent to save a space outside of the vacuum chamber <NUM>. For this purpose, a mirror <NUM> redirects the beams from the vacuum chamber <NUM> to the telecentric objective <NUM>. Rotatable sample stage <NUM> retains samples <NUM>, <NUM> with the sample <NUM> shown positioned in an imaging field of view of the objective lens <NUM>. Representative chief rays <NUM>, <NUM> are shown, but ray paths associated with image formation by the imaging lens <NUM> are not shown.

Referring to <FIG>, a representative profile system <NUM> includes an objective lens <NUM> and an imaging lens <NUM> situated about an aperture stop <NUM>. The aperture stop <NUM> is situated at a focus of the objective lens <NUM> so that the lenses <NUM>, <NUM> form an object-side telecentric optical system. The objective lens <NUM> serves as a window in a vacuum chamber <NUM>. The imaging lens <NUM> and the aperture stop <NUM> are secured in a lens tube <NUM> that is secured to the vacuum chamber <NUM> with one or more bolts <NUM> or other fasteners. Gaskets or other components needed to ensure a vacuum seal are not shown. A rotatable sample stage <NUM> retains samples <NUM>, <NUM> with the sample <NUM> shown positioned in an imaging field of view of the objective lens <NUM>. Representative chief rays <NUM>, <NUM> are shown, but ray paths associated with image formation by the imaging lens <NUM> are not shown.

Referring to <FIG>, a representative profile system <NUM> includes an objective lens <NUM> and an imaging lens <NUM> situated about an aperture stop <NUM> to form sample profile images at an image sensor <NUM>. The aperture stop <NUM> is situated at a focus of the objective lens <NUM> and a focus of the imaging lens 1012so that the lenses <NUM>, <NUM> form an object-side and image-side telecentric optical system. The objective lens <NUM> and the aperture stop <NUM> are situated in a vacuum chamber and are retained by a lens tube <NUM> that extends through a wall <NUM> of the vacuum chamber. The lens tube <NUM> is secured to the vacuum chamber wall <NUM> with one or more bolts <NUM> or other fasteners. Gaskets or other components needed to ensure a vacuum seal are not shown.

Referring to <FIG>, another representative telecentric optical system <NUM> includes an objective lens <NUM>, an intermediate lens <NUM>, and an imaging lens <NUM> situated on an axis <NUM>. An aperture stop <NUM> is located at the focus of the objective lens <NUM> and located with respect to the lenses <NUM>, <NUM> to achieve object-side and image-side telecentricity. In this example, three lenses are used, one of which (the intermediate lens <NUM>) has negative optical power. Chief rays <NUM>, <NUM> are shown.

Referring to <FIG>, a portion <NUM> of an electron microscope includes a sample chamber <NUM> defined by a vacuum chamber <NUM>. An electron optical system extends along a column <NUM>, but is not shown further. Sample profiles are obtained using an illuminator <NUM> that directs an illumination beam <NUM> toward samples secured to a rotatable sample platform <NUM> that is translatable along X- and Y-axes of a coordinate system <NUM> with translation stages <NUM>, <NUM>, respectively. An approximate center <NUM> of the electron optical system is displaced from the illumination beam <NUM>. Samples can be profiled with the illumination beam <NUM> and then translated an imaging location, such as the center <NUM>, to be imaged or processed with the electron optical system. The illumination beam <NUM> can be a collimated or diffuse beam and is shown as a rectangular shape for convenient illustration.

<FIG> is an image <NUM> that illustrates a 2D profile obtained with a telecentric optical system for three objects <NUM> of the same size situated on a sample platform <NUM> at different distances from the telecentric optical system. As shown, the three objects <NUM> have profiles that are of the same size so that their profiles can be used to provide guidance for safe sample stage movements and focusing.

Referring to <FIG>, a portion <NUM> of an electron microscope includes a sample chamber defined by a vacuum chamber <NUM> that can be evacuated through a passage <NUM>. An electron optical system includes an objective lens pole piece <NUM> but is not shown further. 2D sample profiles are obtained using an illuminator <NUM> that directs an illumination beam <NUM> toward samples <NUM> secured to a rotatable sample platform <NUM> that is translatable along any of the axis of a coordinate system <NUM> and tiltable into a sample position <NUM> for profiling. The sample platform 1311is typically coupled to a sample stage <NUM> for translation of samples to an axis <NUM> of the electron optical system. Samples can be tilted, profiled as displaced and tilted, and then translated with the tilt removed to be imaged with the electron optical system. The illumination beam <NUM> can be a collimated or diffuse beam. An objective lens <NUM> is situated at the wall of the vacuum chamber <NUM> and a camera <NUM> is situated to form a telecentric optical system and record sample profiles. The central axis of the profile system <NUM> is parallel to the sample platform plane during profiling.

<FIG> illustrates aspects of sample profile images. In typical examples, samples such as samples <NUM>, <NUM> are secured to a sample platform <NUM> and back-illuminated with an illumination system <NUM>. The outlines of the samples generally appear dark due to the backside illumination such as sample area <NUM>, but some portions such as sample area <NUM> appear to be brighter because of sample reflexivity and a surface sample tilt. This sample area <NUM> reflects light from the illumination system <NUM>. In order to position samples safely (without collision with components in the electron optical system or other components), intermediate areas such as the sample area <NUM> can be processed in the same manner as dark areas such as <NUM>, <NUM>. Processing is simple if areas such as the sample area <NUM> were appeared darker, but they are still recognizable as possible obstructions to be avoided in moving samples into position for imaging.

<FIG> illustrates the sample arrangement of <FIG> but using an illuminator <NUM> that provides variable illumination in a Z-axis direction <NUM>. As shown, the illuminator <NUM> includes a relatively bright area (higher intensity) <NUM> and relatively dark area (lower intensity) <NUM> that produces a relatively darker area <NUM> - if used with the illumination system <NUM> of <FIG>, the area <NUM> would appear brighter in the 2D profile and be more difficult to recognize as a possible obstruction. Reflection from the area1456 is associated with sample surface reflexivity and a surface sample tilt. By varying the illumination intensity in the z-direction, the top portion of the samples may be imaged with higher contrast, and therefore identified with higher accuracy in a 3D map. Other stepped or gradual increases or decreases in illumination intensity along Z-axis can be used and provided for by suitable numbers of light emitters, variations in light scattering, or light attenuation, or other approaches. Because obstructions should appear dark, reflective obstructions such as sides of a sample can appear relatively bright in comparison with obstructions that completely block illumination. These relatively bright areas (such as area <NUM>) should be identified as obstructions.

<FIG> illustrates a representative illuminator <NUM> that includes one or more light emitters such as LED <NUM> that couple light into an edge of a transparent sheet <NUM> that serves as a light guide. Coordinates axes <NUM> indicate a Z-axis associated with a charged particle beam optical axis and a Y-axis associated with an axis of an optical system used to obtain 2D profiles. A major surface of the sheet <NUM> is optically roughen by grinding, sanding, bead blasting or other processes to scatter light for illumination. As light introduced at an edge <NUM> propagates toward an opposing edge <NUM>, the light is attenuated by scattering. To permit uniform illumination, zones <NUM>-<NUM> of the surface of the sheet <NUM> can be provided with increasing roughness to increase scattering to compensate for loss in light intensity as light propagates from the LED <NUM> to the edge <NUM>. Roughness or other scattering characteristic can change smoothly or stepwise (as shown) or both. Intensity of output light can be further customized as well with an illumination gradient from top to bottom (stepwise or continuous) so that, for example, a top edge and a bottom edge of the illuminator surface are associated with different intensities. Variable (stepped or gradient attenuators) can also be used having higher optical densities near the edge <NUM> and lower optical densities near the edge <NUM>. Other illumination patterns can be used in addition to stepped or continuous gradients.

Referring to <FIG>, a representative method <NUM> of producing a 3D map comprises selecting a number of sample views (rotation angles) at <NUM> and selecting an initial view height and view width at <NUM>. In some cases, optical system field of view is not large enough to obtain a complete profile and the sample platform or optical system is adjusted to capture full specimen height. At <NUM>, a rotation angle is selected and at <NUM>, the sample platform is set at the initial height and rotation angle. At <NUM>, a 2D profile is obtained. In some examples, the 2D profile or 2D projection, is an image with binary contrast. The binary 2D profile may be converted by thresholding the image detected by the detector. For example, the 2D profile exhibits a first intensity corresponding to light directly received from the light source, without being blocked by the samples and/or the sample platform. The binary 2D profile can also exhibit a second intensity, less than the first intensity in areas corresponding to shadows generated by the light obstruction samples. At <NUM>, it is determined in additional angles are to be used to obtain additional profiles. If so, the method <NUM> returns to <NUM> to select a rotation angle and the necessary steps repeated. At <NUM>, it is determined if view height is to be adjusted. If so, view height is adjusted at <NUM> and processing returns to <NUM>. View width can be changed at <NUM> as determined at <NUM> and processing can return to <NUM>. Once all profiles are available, the profiles can be combined at <NUM> to produce a 3D map. The 3D map may be produced as illustrated below with reference to <FIG>. If desired, the 3D map can optionally be combined with a camera image, such as the image acquired with the navigational camera, at <NUM>. Method <NUM> may be executed after loading the samples into the vacuum chamber and before being imaged or processed with the charged particle beams. In one example, method <NUM> may be executed while pumping down the vacuum chamber for charged particle beam imaging or processing. The 3D sample profile may be generated when the samples or the sample platform is positioned in a profiling location. The sample platform is then moved from the profiling location to a sample imaging location for imaging or processing one or more samples held by the sample platform. The sample platform is moved based on the 3D sample profile from the profiling location to the imaging location to avoid sample collision with internal structures of the CPM.

<FIG>, a representative method <NUM> includes determining if a 3D map to accommodate reflections is to be obtained at <NUM>. Such a 3D map is referred to herein as a "safe" 3D map. The safe 3D map may be generated for high reflectivity samples with surfaces orientated in ways that may cause light reflection. As discussed above, a 3D map defines regions about a pole piece or other components within a vacuum chamber in which samples can travel to be situated for imaging or other evaluation without contacting other components. Reflective surfaces can be missed in mapping if they are sufficiently reflective to appear similar to direct illumination from a light source. Consideration of sample reflectivity can be needed in producing maps for reflective samples. If a safe map is to be produced, mutually shifted 3D maps are obtained at <NUM> and combined at <NUM> using OR logic to produce a safe 3D map. Shifted 3D maps are generally based on a number of angles that span a full rotation but with each map covering a different set of angles, for example, <NUM>, <NUM>, <NUM>,. , <NUM> degrees and <NUM>, <NUM>, <NUM>,. degrees, etc. Otherwise, 2D projections over a desired range and resolution (i.e., angle increment) are obtained at <NUM> and combined to produce a 3D map at <NUM>. For non-reflective samples, the 3D map permits safe movement without consideration of reflections. The 3D map however produced (i.e., whether or not a safe 3D map) can optionally be combined with a camera image at <NUM>. At <NUM>, a sample location can be selected, and at <NUM>, the selected location can be situated for focusing using the 3D map. For example, the sample platform or other mechanical or electron optical components can be moved without operator intervention by moving within unoccupied regions in the 3D map, so that the selected focus location is at the imaging location, aligned with the CP beam under the pole piece of the CPM, for imaging or processing. The 3D map thus permits determination of a safe path that avoids collisions among samples and optical components.

A system controller such us such as a control computer can be operable to automatically check and control sample positioning using the full 3D map or to guide manual operation by sounding alarms or disabling sample movement into regions in which collisions are likely.

It will be appreciated that generation of the 3D map can be done outside of an electron microscope chamber or during or after microscope pump down. Sample locations can be indicated using a visual interface such as shown in <FIG>. In some cases, 3D maps can be processed to remove areas that otherwise appear occupied by samples.

With reference to <FIG>, an exemplary system for implementing the disclosed technology includes a general purpose computing device in the form of an exemplary conventional PC <NUM>, including one or more processing units <NUM>, a system memory <NUM>, and a system bus <NUM> that couples various system components including the system memory <NUM> to the one or more processing units <NUM>. The system bus <NUM> may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The exemplary system memory <NUM> includes read only memory (ROM) <NUM> and random access memory (RAM) <NUM>. A basic input/output system (BIOS) <NUM>, containing the basic routines that help with the transfer of information between elements within the PC <NUM>, is stored in ROM <NUM>. The memory <NUM> also contains a portions <NUM>-<NUM> that include computer-executable instructions and data for 2D profile acquisition (including sample stage control), determination of 3D profiles based on the acquired 2D profiles determination of safe sample paths, graphical user interfaces for operator inputs and outputs, and instrument control generally.

The exemplary PC <NUM> further includes one or more storage devices <NUM> such as a hard disk drive or a memory device such as a thumb drive. Such storage devices can be connected to the system bus <NUM> by a suitable interface. Such computer-readable media provide nonvolatile storage of computer-readable instructions, data structures, program modules, and other data for the PC <NUM>. Other types of computer-readable media which can store data that is accessible by a PC, such as magnetic cassettes, flash memory cards, digital video disks, CDs, DVDs, RAMs, ROMs, and the like, may also be used in the exemplary operating environment.

A number of program modules may be stored in the storage devices <NUM> including an operating system, one or more application programs, other program modules, and program data. A user may enter commands and information into the PC <NUM> through one or more input devices <NUM> such as a keyboard and a pointing device such as a mouse, touch pad, digital camera, microphone, joystick, game pad, or the like. These and other input devices are often connected to the one or more processing units <NUM> through a serial port interface that is coupled to the system bus <NUM>, but may be connected by other interfaces such as a parallel port, game port, or universal serial bus (USB). A monitor <NUM> or other type of display device is also connected to the system bus <NUM> via an interface, such as a video adapter. Other peripheral output devices, such as speakers and printers (not shown), may be included.

The PC <NUM> may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer <NUM>. In some examples, one or more network or communication connections <NUM> are included. The remote computer <NUM> may be another PC, a server, a router, a network PC, or a peer device or other common network node, and typically includes many or all of the elements described above relative to the PC <NUM>, although only a memory storage device <NUM> has been illustrated in <FIG>. The personal computer <NUM> and/or the remote computer <NUM> can be connected to a logical a local area network (LAN) and a wide area network (WAN). Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets, and the Internet.

When used in a LAN networking environment, the PC <NUM> is connected to the LAN through a network interface. When used in a WAN networking environment, the PC <NUM> 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 <NUM>, or portions thereof, may be stored in the remote memory storage device or other locations on the LAN or WAN. The network connections shown are exemplary, and other means of establishing a communications link between the computers may be used.

Referring to <FIG>, a representative electron microscope <NUM> includes a pole piece <NUM> that directs a beam to a sample platform <NUM> that is coupled to translation stages <NUM>, <NUM> and a translation/rotation stage <NUM>. An electron optical column 1901includes lenses, deflectors, and other electron optical components that that are not shown. Representative samples <NUM>-<NUM> are secured to the sample platform <NUM>. An illuminator <NUM> directs a beam <NUM> toward the samples <NUM>-<NUM> and a transparent window <NUM> in a vacuum chamber housing <NUM>. A telecentric optical system <NUM> is situated to form profile images on an image sensor <NUM> based on back-side illumination of the samples <NUM>-<NUM> for various rotation angles provided by the translation/rotation stage <NUM>.

<FIG> illustrates a sequence <NUM> of profile images obtained during rotation of a sample use to produce a 3D map such as the 3D map <NUM> of <FIG>. Representative samples <NUM>-<NUM> are shown. Each profile image corresponds to a different rotation angle.

<FIG> illustrate an example 2D projection <NUM> of samples <NUM>, <NUM> secured to a sample platform <NUM>. <FIG> illustrates a reflective area <NUM> associated with an edge of the sample platform <NUM>. For safe movement within a vacuum chamber, the reflective area <NUM> should be identified as an obstruction although it does not appear as dark as the remainder of the 2D projection of the sample platform <NUM>. Reflective areas such as the reflective area <NUM> typically appear at selected rotation angles and in the associated 2D projections.

<FIG> illustrate 2D projections <NUM>, <NUM> showing a sample <NUM> and obtained using a telecentric optical system having a field of view smaller than the sample platform. The 2D projections <NUM>, <NUM> can be combined to produce a full 2D profile <NUM> in <FIG>.

<FIG> illustrates a sequence of 2D projections obtained at different rotation angles. Representative samples <NUM>, <NUM> are illustrated. At rotation angles of <NUM>, <NUM>, <NUM>, and <NUM> degrees, the sample <NUM> has a reflective area <NUM> which can be identified as an obstruction in 3D mapping. The reflective area <NUM> appears with an intensity similar to that of unobstructed areas. Such areas can be identified properly as obstructions if 2D projection values are subject to thresholding with a suitable value that distinguishes reflections from unobstructed areas. Reflections can be reduced with collimated illumination or increasing a distance between a light source and samples. Alternatively, patterned illumination can be used to simplify identification of reflective areas or the approach discussed above with reference to <FIG> can be used.

<FIG> illustrate processing of 2D profiles to produce a 3D map. <FIG> shows a representative 2D projection <NUM> at a selected angle and <FIG> shows a cylindrical volume <NUM> indicating an initial, fully occupied sample space, i.e., a space that is potentially available for movement but can include portions that are occupied by samples and are thus not safe for movement. As shown in <FIG>, the initial size of the cylindrical volume <NUM> is based on a size of the sample holder and microscope configuration and indicates a maximum volume in which samples can be positioned. Using the 2D projection <NUM>, portions of the cylindrical volume <NUM> are removed as shown in <FIG>. As shown in <FIG>, an unoccupied space <NUM> in the 2D projection <NUM> is used to define a corresponding feature <NUM> indicating a region in which movement can be permitted. The unoccupied space <NUM> is extended through the cylindrical volume 24D to remove portions of the cylindrical volume <NUM> so that the feature <NUM> extends through the cylindrical volume <NUM>. Other unoccupied spaces indicated by the 2D projection <NUM> define corresponding features and are extended through the cylindrical volume <NUM>. A resulting volume <NUM> (<FIG>) indicates safe areas for movement. In this example, the upper borders of the 2D projection <NUM> are used and this approach can be referred to as an "envelope" approach. Additional 2D projections at other rotation angles are then used to define features in the cylindrical volume <NUM> to produce a 3D map. Alternatively, full 2D projection data can be used as shown in <FIG>. In this case, a lower unoccupied space <NUM> in the 2D projection <NUM> is used to define a corresponding feature <NUM> in the volume <NUM>. Additional 2D projections at other angles are then used to define features in the volume <NUM> to produce a 3D map. This approach can be more computationally intensive than the envelope approach.

Claim 1:
A method, comprising:
illuminating the sample situated within a vacuum chamber (<NUM>) of a charged-particle microscope (<NUM>, <NUM>) from a first side with a light (<NUM>, <NUM>, <NUM>);
detecting a plurality of 2D projections (<NUM>, <NUM>, <NUM>, <NUM>) of the sample;
generating a 3D map (<NUM>) based on the 2D projections; and
situating the sample at an imaging location within the vacuum chamber based on the 3D map, wherein the sample is processed or imaged with a charged particle beam at the imaging location,
characterized in:
wherein the 2D projections of the sample are detected on a second side, opposite the first side, and wherein the 2D projections are produced by receiving the light not blocked by the sample.