Miniature hybrid electron beam column

Abstract

A miniature electron beam column is combined with a magnetostatic lens to create a miniature electron or ion beam column with very high performance. Silicon-based electron optical components provide high precision formation and alignment of the key optical elements, while magnetic lenses provide the focusing or focusing elements with low aberration. Precision assembly of the silicon and magnetic components can be achieved through multi-layer assembly techniques, thereby enabling high performance to be achieved.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates generally to the field of wafer inspection systems. More specifically, the present disclosure relates to miniature electron beam column detectors. [Background technology]

[0002] Generally, in the semiconductor manufacturing industry, semiconductor materials are layered and patterned on a substrate, such as silicon, to produce integrated circuits with highly sophisticated techniques. Due to the large scale of circuit integration and the shrinking size of semiconductor devices, the devices being manufactured are becoming increasingly sensitive to defects, i.e., the defects that can cause the device to malfunction are becoming smaller and smaller. Devices are generally required to be defect-free before being shipped to an end user or customer.

[0003] That is, it is becoming more and more important to be able to detect smaller and smaller defects. The type of defects, the number of defects, and the signatures found by the inspection system (or inspector) provide valuable semiconductor manufacturing related information to ensure that the manufacturing process established in the R&D phase can be ramped (hardened) so that the process windows identified in the ramp phase can be transferred to high volume manufacturing (HVM) and the day-to-day operation in HVM is stable and under control.

[0004] One method of defect detection is through the use of a scanning electron microscope (SEM). An SEM may have multiple electron beam columns with built-in detectors. As semiconductor devices shrink in size, the size of defects to be detected becomes smaller and the limiting factor of the wavelength of light makes detection by traditional optical methods extremely challenging. One method of detecting these defects is through the use of an electron beam, as the wavelength of the electron beam can be much shorter than the wavelength of light. However, this is slow in terms of throughput, and a single column electron beam inspection of a wafer can take days or even weeks. A solution to this problem is a miniaturized multi-column or multi-beam SEM, which allows for massively parallel inspection of wafers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2014 / 0217282 [Patent Document 2] U.S. Patent No. 6,438,073 Summary of the Invention [Problem to be solved by the invention]

[0006] Previous columns have been constructed with all-silicon elements, or with metal components and permanent magnets. The latter technology (silicon "lens stacks") produces high-resolution columns but limits the operating conditions. While some applications, such as desktop SEM, may tolerate these limitations, high-performance applications, such as lithography, metrology, or inspection, may not. The latter combines conventional machining with permanent magnets (often arrays thereof) and provides an avenue for high-throughput applications, but suffers from lack of alignment accuracy and therefore performance and assembly yield. Thus, a system is needed that circumvents the unique shortcomings of silicon all-electrostatic columns and the difficulties of conventional miniaturized columns by combining silicon columns with permanent magnetic lenses using precision alignment techniques that are largely limited when using silicon lens stacks. [Means for solving the problem]

[0007] The following is a simplified summary of the disclosure in order to provide a basic understanding of certain embodiments of the disclosure. This summary is not an exhaustive overview of the disclosure, and it does not identify key / critical elements of the disclosure or delineate the scope of the disclosure. Its sole purpose is to present certain concepts of the disclosure in a simplified form as a prelude to the more detailed description that is presented later.

[0008] Aspects of the present disclosure relate to an apparatus, system, and miniature electron beam column. The apparatus includes an electron source, a detector in tandem with the electron source, and a magnetic objective lens in tandem with the electron source and detector. The magnetic lens has an aperture. The magnetic objective lens is configured to focus an electron beam emanating from the electron source and passing through the aperture.

[0009] In certain embodiments, the apparatus comprises silicon MEMS technology. In certain embodiments, the magnetic static objective lens is lithographically positioned to align with other elements of the apparatus. In certain embodiments, the magnetic static objective lens is positioned using lithographically positioned fiducials configured to align with other lithographically positioned fiducials on other elements of the apparatus. In certain embodiments, stray magnetic fields caused by the magnetic static objective lens are attenuated using high mu metal strategically placed around the periphery of the apparatus. In certain embodiments, the magnetic static lens is rounded. In certain embodiments, the apparatus is a miniature electron beam column.

[0010] These and other aspects of the disclosure are further described below with reference to the drawings. [Brief description of the drawings]

[0011] [Figure 1A] FIG. 1 illustrates an example configuration of a miniature column according to embodiments of the present disclosure. [Figure 1B] FIG. 1 illustrates another example configuration of a miniature column according to embodiments of the present disclosure. [Figure 1C] 1A-1C depict examples of how a magnetic lens affects an electron beam column according to embodiments of the present disclosure. [Figure 1D] 1A-1C depict examples of how to address the effects of a magnetic lens on an electron beam column according to embodiments of the present disclosure. [Figure 2A] 1A-1C depict alternative configurations of miniature columns according to embodiments of the present disclosure. [Figure 2B] FIG. 13 illustrates another alternative configuration of a miniature column according to embodiments of the present disclosure. [Figure 3A] 1 is a flowchart illustrating an example operational flow of an electron beam column according to embodiments of the present disclosure. [Figure 3B]1 is a flowchart illustrating an example operational flow of an electron beam column in conjunction with system level calibration according to embodiments of the present disclosure. [Figure 4A] FIG. 1 illustrates an exemplary output of an electron beam column according to embodiments of the present disclosure. [Figure 4B] FIG. 1 illustrates an exemplary output of an electron beam column according to embodiments of the present disclosure. [Figure 4C] FIG. 1 illustrates an exemplary output of an electron beam column according to embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In the following description, numerous specific details are set forth in order to provide a consistent understanding of the present disclosure. The present disclosure may be practiced without some or all of these specific details. In addition, for example, well-known process operations are not detailed to avoid unnecessarily obscuring the present disclosure. Although the present disclosure will be described in connection with specific embodiments, it will be understood that there is no intent to limit the present disclosure to those embodiments.

[0013] As mentioned above, there is a need to obtain a high throughput electron beam system. In general, this can be achieved by miniaturizing the column itself, allowing multiple columns to be used in parallel. Column miniaturization can be achieved by using electrostatics, magnetics, or magnetostatics. Electrostatics, although successful, has limitations. The biggest limitation with electrostatics is that it has a limited resolution quality due to various constraints. Therefore, the use of magnetics is an alternative. However, magnetics involves the use of coils and electromagnets, which inevitably leads to larger systems and equipment. As mentioned above, miniaturized columns are needed to increase throughput. Therefore, the use of magnetics is a third option. With magnetics, it is possible to obtain high resolution by using stationary magnets to basically shape the magnetic field. Therefore, a solution to the problems presented would be to use silicon MEMS technology or any "miniature" technology in conjunction with small, compact magnetostatic elements to build a miniature column to obtain a very high resolution system.

[0014] According to various embodiments, as described by the techniques and mechanisms of the present disclosure, miniature silicon-based electron-optical elements can be used in conjunction with magnetostatic (permanent magnet) lenses to create very high performance miniature electron or ion beam columns. This combination provides high precision formation and alignment of the critical optical elements, while the magnetic lenses provide a focusing or focusing element with low aberration. According to various embodiments, precise assembly of silicon and magnetic components can be achieved (via multi-layered assembly techniques), and importantly, the best performance (e.g., spot size, beam current, and field of view or FOV) can be achieved.

[0015] One of the biggest hurdles in incorporating magnetostatics into silicon MEMS technology has been alignment during fabrication. Another very high hurdle is the generation of stray magnetic fields. Traditionally, electrostatic columns have been made using conventional machining technology. However, conventional machining technology cannot produce the precision required for miniature electron columns. At best, conventional machining technology can produce micrometer-order precision. However, miniature electron beam columns require nanometer-order precision.

[0016] According to various embodiments, alignment accuracy is key to the assembly process. During manufacturing, all pattern placement is done lithographically. For example, apertures are placed lithographically, allowing for very high accuracy in both geometry and location. In certain embodiments, fiducials are also placed lithographically on the members, allowing for highly accurate lens-to-lens placement. This is because fiducial-to-fiducial alignment is much more accurate than attempting to capture miscellaneous size shapes or circles.

[0017] That is, the disclosed techniques and mechanisms provide a miniature silicon column design with electro-optical performance that is compatible with permanent magnets. According to various embodiments, this requires a) designing with bore diameters, spacing, and silicon thicknesses that are compatible with standard micromachining (MEMS or microelectromechanical systems) and IC technologies and are compatible with generally accepted high magnetic field practices, b) incorporating sufficient fiducials throughout the components (including the magnets) to ensure accurate inter-element alignment, c) designing magnet size, performance, and structure to ensure maximum performance (possibly including bias magnets for the E×B field), and d) understanding the tolerance requirements of the individual components. In certain embodiments, assembly techniques are utilized that ensure that each component is precisely aligned within the column and within the specifications detailed above. In certain embodiments, precise calibration is required on the tools required for column assembly.

[0018] According to various embodiments, magnetostatic lenses are prone to magnetic leakage, meaning it is difficult to precisely control what environment the electrons encounter as they move down the column, which leads to distortions. One solution to this is the use of shielding. In certain embodiments, additional strategically placed components essentially shield the beam itself from the magnet's leakage field, thereby improving resolution.

[0019] Details of example techniques and example system implementations provided by the techniques and mechanisms described herein will now be described with reference to the following drawings.

[0020] 1A and 1B depict examples of miniature columns according to embodiments of the present disclosure. FIG 1A depicts an example miniature electron beam column 100 according to embodiments of the present disclosure. FIG 1B depicts an alternative miniature electron beam column 102 according to embodiments of the present disclosure.

[0021] In some embodiments, the electron beam is emitted from the electron source 104. In some embodiments, the electron source 104 is a thermal electron emitter. In some embodiments, the electrons are extracted from the electron source 104 by the extractor / condenser 106. In some embodiments, the extractor portion (the first half of the extractor / condenser 106) is an anode, and a high voltage is applied to it to generate an electric field that extracts the electrons from the electron source 104. In some embodiments, the condenser portion of the extractor / condenser 106 is below the extractor portion. In some embodiments, the condenser portion moves the electrons parallel down the column. Below the extractor / condenser 106 is a steering deflector / limiting aperture 108. The deflector portion effectively steers the electron beam into the limiting aperture. In some embodiments, the limiting aperture defines the acceptance angle at the electron source. In some embodiments, the limiting aperture defines the numerical aperture (NA), which determines the resolution and beam current of the system. In certain embodiments, the limiting aperture filters the beam to be on the order of tens of micrometers.

[0022] In some embodiments, the electron beam then passes through a through hole in detector 110. In some embodiments, detector 110 is positioned face down towards specimen 130. In some embodiments, detector 110 is a silicon diode, e.g., a PIN diode. In some embodiments, the electron beam then passes through a dual scanning deflector 112. In some embodiments, dual scanning deflector 112 is a scanning coil that rasters the electron beam over specimen 130. In some embodiments, magnetic objective lens 114 then focuses the electron beam onto specimen 130. In some embodiments, magnetostatic lens 114 incorporates a high mu metal that is configured to direct a magnetic field to form a focusing magnetic field to further focus the electron beam. In some embodiments, magnetostatic lens 114 is designed to better align e-beam column 100 and improve performance.

[0023] It should be noted that, given the state of the art, it is very difficult to insert a magnetostatic lens into an electron beam column. Normally, a magnetostatic lens would have a destructive effect on the functioning of the electron beam column, since the magnetic field emanating from the magnet would interact with the electron field at the top of the column. For example, the measured or model-derived transverse magnetic field at the back of the magnetostatic lens can reach 3-5 Gauss, depending on the distance from the optical axis. For reference, the magnetic field of the Earth is about 0.5 Gauss. Under these conditions, using the well-known equation of motion for an electron in a stationary magnetic field, r=mv / qB, where r=radius of curvature, m=mass of the electron, v=velocity of the electron, q=charge on the electron, and B=magnetic field, the expected deflection of a 1 keV electron is 7 μm per mm of travel in the column. If the column aperture is about 10 μm in diameter, then electrons traveling more than 2 mm will be blocked. In addition, this additional magnetic field problem can usually be addressed by using an electromagnet lens. However, electromagnet lenses have too much power requirement and are too large for miniature electron beam columns.

[0024] In some embodiments, these challenges are addressed by first arranging the columns in an array and then adding shielding. In some embodiments, the shielding is also made of mu-metal. In some embodiments, each electron beam column is fitted with two mu-metal magnetic termination shields near the electron source. In some embodiments, an additional shield is placed in the electron column system to short-circuit the additional magnetic fields and provide a return path for them so that they do not interact with the electron beam of the column that is in the middle of the column. Without the additional shielding in such an embodiment, the magnetic field generated by the magnetostatic lens would leak into the electron beam path and distort or deflect the beam as it tries to pass through the column incorrectly. In some embodiments, the column is constructed with a mu-metal layer that is placed horizontally (i.e., perpendicular to the beam). In some other embodiments, multiple shielding layers, such as a shield-in-shield, can be added to improve attenuation of stray magnetic fields.

[0025] In some embodiments, the column comprises a lens stack (lens), permanent magnets (magnets), and a multi-layer board (substrate). In some embodiments, the lens stack is a micromachined multi-layer structure composed of silicon apertures and glass isolators. In some embodiments, the multi-layer board is composed of multi-layer ceramics, metal support structures, and connectors. In some embodiments, each lens and magnet has a lithographic alignment fiducial designed to mate with a vertically neighboring lens. In some embodiments, the lenses and magnets are assembled onto the board using a pick-and-place assembly tool with high alignment accuracy.

[0026] According to various embodiments, the performance of the column depends in part on precisely locating the centers of the individual lenses and magnets relative to the optical axis. In certain embodiments, using a coordinate system in which the x and y axes form a Cartesian plane, the optical axis is perpendicular to the xy plane. In certain embodiments, the location of the optical axis is defined by the location of the center of the first lens.

[0027] According to various embodiments, the columns are designed so that each lens is aligned with the lens directly beneath it. In such embodiments, the placement of the center of each lens relative to the optical axis is determined by the placement of a lithographic alignment fiducial and the accuracy of the pick-and-place tool. In many cases, lens-to-lens alignment is the most precise method to minimize the total stack-up misalignment of the lens assembly.

[0028] In some embodiments, each lens must be linearly and rotatably aligned to contact pads printed on the board. In such embodiments, board-to-board alignment must be controlled since the lenses are aligned to the lens and not to the board, and the optical axis is determined by the placement of the first lens. In some embodiments, this is done using pin-and-slot alignment.

[0029] An example alignment process includes: (1) aligning lens 1 with board 1. The center of lens 1 defines its optical axis. (2) attaching board 2 to board 1. (3) aligning and placing lens 2 with lens 1 using fiducials on lens 2 and lens 1. (4) attaching board 3 to board 2. (5) continuing this process until all lenses and boards are assembled. According to various embodiments, there are many suitable bonding techniques to securely attach the lenses to the boards, including adhesive, eutectic, or solder processes.

[0030] In some embodiments, an array of lenses is utilized with a single electron column. In other embodiments, a single magnetostatic lens is utilized with a single electron column. With only one lens, the bore diameter of the lens can be made quite large. The larger bore of the magnetic lens allows for the collection of backscattered electrons at the detector.

[0031] In certain embodiments, the objective lens 114 is actually rounded. In such embodiments, the round shape, as opposed to the traditional square shape, allows the lens to be turned on a lathe, improving the precision and accuracy of lens manufacturing. The greater precision means that the magnetic field itself will ultimately be more precise, resulting in higher resolution, and introducing less aberrations. Magnets with this improved geometry can be placed with greater precision.

[0032] In certain embodiments, after the electron beam is raster scanned over the specimen 130, the electrons are reflected back as secondary / backscattered electrons and directed in a diffusive manner towards the detector 110. In certain embodiments, the dual deflector 112 steers the beam to the side.

[0033] As shown in FIG. 1B, certain embodiments of the miniature electron beam column 102 include a post-lens element 120 to control the SE and BSE signals on the detector 110. In certain embodiments, the post-lens element 120 is a post-lens deflector / dynamic focus element. In certain embodiments, the deflector is placed after the lens to reduce additional aberrations or distortions from the lens itself. In addition, in certain embodiments, the post-lens element 120 also performs dynamic focusing to keep the beam focused at all times. Also shown in FIG. 1B, certain embodiments of the electron beam column 102 replace the steering deflector / limiting aperture 108 with a separate dual steering deflector 107 and a separate limiting aperture 109. In such embodiments, the separate dual steering deflector 107 gives the column a unique ability to steer the beam away from the axis to improve resolution.

[0034] FIG. 1C shows how the magnetic field 140 from the magnetostatic lens 114 can affect the trajectory of the electron beam 150. Magnetostatic lenses tend to "leak" stray transverse magnetic fields (Bx and By) that can cause the electron beam 150 to be deflected off-axis. This can be especially true in miniature columns because their low voltage operation makes them more sensitive to transverse magnetic fields. In addition, the design of the magnetostatic lens can greatly affect the magnitude of this effect. It should be noted that "conventional" electromagnet lenses are self-shielding and avoid these complications. As shown in FIG. 1C, the electron beam 150 is bent by the magnetic field 140, which causes the electron beam 150 to be turned off-axis. For convenience, only one magnetic field (Bx) is shown. However, it should be noted that the By field (not shown) can also bend the electron beam 150 off-axis.

[0035] 1D illustrates an example embodiment in which a shield 136 is inserted into the system at the correct location during assembly. The shield 136 blocks or attenuates the magnetic field 140, allowing the electron beam 150 to travel straight and undistorted along its axis. According to various embodiments, the size and placement of the shield (which can be an extremely high magnetic permeability composition) is dictated by the specific design of the column and objective lens.

[0036] In certain embodiments, the centerline of the electron beam 150 must be aligned very precisely with respect to the center of the magnetostatic lens 114. In such embodiments, achieving precise alignment between the MEMS column and the mechanically assembled magnets can be very difficult. Therefore, in certain embodiments, alignment marks 172 are patterned on the lens 114 and are matched with alignment marks 182 at corresponding locations on the electron beam column 100. In certain embodiments, the alignment marks 182 and 172 are fiducials lithographically placed on the lens and column and are configured to mate with each other (thereby overlapping and forming concentric circles). The alignment of the two pairs of alignment marks at two separate locations aligns the magnetostatic lens 114 with respect to the rest of the electron beam column 100. In certain embodiments, because the electron beam column 100 is a miniature electron beam column, the required accuracy is on the nanometer scale as opposed to the micrometer scale of conventional electron beam columns. Due to this high accuracy requirement, the only fiducial alignment method is through silicon MEMS technology, and more specifically lithography, as conventional machining processes are unable to achieve nanometer-scale accuracy.

[0037] FIG. 2A illustrates an alternative configuration of a miniature column according to embodiments of the present disclosure. FIG. 2B illustrates another alternative configuration of a miniature column according to embodiments of the present disclosure. Electron beam columns 200 and 202 are similar to columns 100 and 102, except that extractor / condenser 204 is implemented using a separate magnetostatic lens. In certain embodiments, lens 204 is just an inverted (upside-down) version of lens 214. The remaining elements 206, 207, 208, 209, 210, 212, 214, 220, and 230 are similar to the corresponding features in FIG. 1A and FIG. 1B. In certain embodiments, the use of a separate magnetostatic lens 204 helps eliminate stray magnetic fields from magnetostatic lens 214. However, columns 200 and 202 are more difficult to assemble than columns 100 and 102.

[0038] FIG. 3A is a flow chart depicting an example 300 operational flow of an electron beam column according to embodiments of the present disclosure. At 302, a basic setup is established. In certain embodiments, this is accomplished by applying voltage to all electrodes, including the magnetic objective lens. It should be noted that the lens is not grounded and neither is the wafer. At 304, the tip is aligned. In certain embodiments, this is done using a fixture, e.g., a stage, separate from the column itself, since the tip needs to be aligned with the column on the optical axis at the column. In certain embodiments, the tip is moved in a circular motion until it is aligned with the extractor. In certain embodiments, this can be accomplished by measuring the current as it moves further down the column, so that the system knows when the tip is exactly centered on the extractor. In other embodiments, the tip can be aligned by fixing the tip in a locked position with respect to the extractor and then using a dual deflector to adjust the alignment with the limiting aperture. At 306, the calibration values ​​are loaded into the database. In certain embodiments, calibration values ​​can tell the system how much voltage to apply, how to focus the lens, and how to bring the beam to a particular location. For example, calibration values ​​must be loaded into the system to account for distortion. Finally, in 308, the wafer is scanned in the column by sweeping the beam back and forth to obtain an image.

[0039] FIG. 3B is a flow chart illustrating an example operation flow 310 of an electron beam column according to embodiments of the present disclosure, along with system level calibration. In practice, the system usually needs to scan multiple locations. In such cases, system level calibration is essential for the operation of the electron beam column. Operation flow 310 is similar to operation flow 300, with basic setup 312 and tip alignment 314 being analogous to basic setup 302 and tip alignment 304, respectively. However, instead of a one-time calibration load, the beam needs to be calibrated at 316, the magnetic field needs to be calibrated at 318, and the stage needs to be calibrated at 320. This is because it needs to be calibrated when the resolution is uncertain. When the beam is deflected, it needs to be calibrated. Similarly, when the stage is moving, it needs to be calibrated.

[0040] In some embodiments, the system can calibrate the stage by measuring the velocity of the stage (e.g., with an interferometer) as it moves. That data can then be fed back to the column, allowing the column to calculate how much voltage to apply to deflect the beam to follow the stage. In some embodiments, to calibrate the beam, the system takes a high resolution image, scans over the edge, and from that profile the system knows what the beam profile is. In some embodiments, to measure the beam current, the system brings the beam into a Faraday cup and measures how much current is going through the beam. In some embodiments, system calibration is an iterative process to get the system ready, and once the system is set up, it can be used to scan multiple features of interest.

[0041] The versatility of MEMS columns coupled with magnetostatic lenses is illustrated in Figures 4A-C. Figure 4A is an example image showing the large distortion-free field of view (FOV) that can be obtained with a simple magnetostatic lens. The image consists of a 1 μm silicon square etched on a silicon substrate. Figure 4B shows high resolution <7 nm 20%-80% acquisition imaging of a Sn sphere on a carbon substrate with a landing energy of 1 keV. The FOV in this case is 1.2 μm. And Figure 4C shows the ability of the magnetic-electric column to tune the landing energy to 0.4 keV while maintaining the beam resolution (approximately 7.5 nm, 20%-80%). The practical tunability of these columns is typically 0.5 keV-3 keV.

[0042] Certain embodiments of the present disclosure presented herein generally address the field of electron beam columns and are not limited to their hardware, algorithmic / software implementations and architectures, and examples of use outlined above.

[0043] Although the above disclosure has been described in some detail for clarity of understanding, it is understood that certain changes and modifications can be made within the scope of the appended claims. It should be noted that there are various alternative implementations of the process, system and device of the present disclosure. Therefore, the presented embodiments should be considered as illustrative rather than restrictive, and the present disclosure should not be limited to the details given in this application.

Claims

1. 1. An apparatus comprising: an electron source; a detector in tandem with the electron source; a magnetostatic objective lens in tandem with the electron source and the detector; wherein the magnetostatic lens has an aperture, and the magnetostatic objective lens is configured to focus an electron beam emanating from the electron source and passing through the aperture.

2. 10. The device of claim 1, comprising silicon MEMS technology.

3. 10. The apparatus of claim 1, wherein the magnetostatic objective lens is lithographically positioned to align with other elements of the apparatus.

4. 10. The apparatus of claim 1, wherein the magnetostatic objective lens is positioned using a lithographic alignment fiducial configured to align with other lithographic alignment fiducials on other elements of the apparatus.

5. 10. The apparatus of claim 1, wherein stray magnetic fields caused by the magnetostatic objective lens are attenuated using high-mu metal strategically placed around the apparatus.

6. 10. The apparatus of claim 1, wherein the magnetostatic lens is rounded.

7. 10. The apparatus of claim 1, wherein the apparatus is a miniature electron beam column.

8. 1. A system comprising: an electron source; a detector in tandem with the electron source; a magnetostatic objective lens in tandem with the electron source and the detector; wherein the magnetostatic lens has an aperture, and the magnetostatic objective lens is configured to focus an electron beam emanating from the electron source and passing through the aperture.

9. 10. The system of claim 8, comprising silicon MEMS technology.

10. 9. The system of claim 8, wherein the magnetostatic objective lens is lithographically positioned to align with other elements of the system.

11. 10. The system of claim 8, wherein the magnetostatic objective lens is positioned using a lithographic alignment fiducial configured to align with other lithographic alignment fiducials on other elements of the system.

12. 9. The system of claim 8, wherein stray magnetic fields caused by the magnetostatic objective lens are attenuated using high-mu metal strategically placed around the system.

13. 9. The system of claim 8, wherein the magnetostatic lens is rounded.

14. 10. The system of claim 8, wherein the system is a miniature electron beam column.

15. 1. A miniature electron beam column comprising: an electron source; a detector in tandem with the electron source; a magnetostatic objective lens in tandem with the electron source and the detector; wherein the magnetostatic lens has an aperture, and the magnetostatic objective lens is configured to focus an electron beam emanating from the electron source and passing through the aperture.

16. 16. The miniature electron beam column of claim 15, comprising silicon MEMS technology.

17. 16. A miniature electron beam column as recited in claim 15, wherein the magnetostatic objective lens is lithographically positioned to align with other elements of the electron beam column.

18. 16. A miniature electron beam column as described in claim 15, wherein the magnetostatic objective lens is positioned using a lithographic alignment fiducial configured to align with other lithographic alignment fiducials on other elements of the electron beam column.

19. 16. The miniature electron beam column of claim 15, wherein stray magnetic fields caused by the magnetostatic objective lens are attenuated using high-mu metal strategically placed around the electron beam column.

20. 16. The miniature electron beam column of claim 15, wherein the magnetostatic lens is rounded.

21. The apparatus of claim 1, further comprising a stack of silicon micro-electro-mechanical lenses between the detector and the electron source.

22. An apparatus as in claim 21, wherein one or more of the silicon micro-electro-mechanical lenses in the stack have lithographic alignment fiducials configured to align with other lithographic alignment fiducials on at least one adjacent silicon micro-electro-mechanical lens in the stack.

23. The apparatus of claim 1, further comprising one or more electromagnetic shields between the static magnetic objective lens and one or more other elements of the apparatus.

24. The apparatus of claim 1, wherein the post-lens element is configured to deflect and / or focus the electron beam.

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