Systems and methods for generating multiple electron beams

Abstract

The electron beam device includes an upper column electron optics 300 and a lower column electron optics. The upper column electron optics 300 includes an aperture array 110 for splitting an electron beam into a plurality of electron beamlets 312. The upper column electron optics 300 further includes a lens array 302 having a plurality of lenses 304 for adjusting the focus of the plurality of electron beamlets 312. Each of the lenses 304-1 to 304-3 of the plurality of lenses 304 adjusts the focus of each of the plurality of electron beamlets 312. The upper column electron optics 300 further includes a first global lens 306 for adjusting the focus of the plurality of electron beamlets 312 in an inverse manner to the lens array 302.

Description

[Technical Field]

[0001] This disclosure relates to electron optics, and more particularly to generating multiple electron beams in an electron beam apparatus. [Background technology]

[0002] Scanning electron microscopes (SEMs) have long been used for inspection purposes, such as semiconductor wafer inspection. Traditionally, SEMs have had a single electron beam. More recently, however, SEMs with multiple electron beams (i.e., beamlets) have been developed (for example, using arrays of Einzel lenses or deflection dipoles). The throughput of an SEM (or other electron beam device) depends on the number of beamlets; the throughput increases as the number of beamlets increases. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 0025241 [Patent Document 2] U.S. Patent Application Publication No. 2008 / 0023643 [Patent Document 3] International Publication No. 2021 / 018332 [Patent Document 4] U.S. Patent Application Publication No. 2003 / 0001095 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, a serious problem occurs when the number of beamlets increases. For example, the number of beamlets can be limited by poor optical resolution and high electric field strength that increases the risk of arcing. Moreover, these problems may not be compatible with each other. For example, the electron beam energy can be reduced to reduce the electric field strength and thus the arcing risk. However, when the electron beam energy is reduced, the Coulomb interaction between electrons increases, thereby degrading the resolution.

Means for Solving the Problem

[0005] In some embodiments, an electron beam device includes upper column electron optics and lower column electron optics. The upper column electron optics includes an aperture array for splitting an electron beam into a plurality of electron beamlets. The upper column electron optics further includes a lens array having a plurality of lenses for adjusting the focus of the plurality of electron beamlets. Each lens of the plurality of lenses adjusts the focus of each electron beamlet of the plurality of electron beamlets. The upper column electron optics further includes a first global lens for adjusting the focus of the plurality of electron beamlets in a manner opposite to that of the lens array.

[0006] In some embodiments, a method is performed in the upper column electron optics of an electron beam device. The method includes splitting an electron beam into a plurality of electron beamlets using an aperture array. The method further includes adjusting the focus of the plurality of electron beamlets using a lens array including a plurality of lenses. Adjusting the focus of the plurality of electron beamlets includes adjusting the focus of each electron beamlet of the plurality of electron beamlets using each lens of the plurality of lenses. The method further includes adjusting the focus of the plurality of electron beamlets using a first global lens. The first global lens adjusts the focus of the plurality of electron beamlets in a manner opposite to that of the lens array.

[0007] For a better understanding of the various described embodiments, reference will be made to the following forms for carrying out the invention in conjunction with the following drawings.

Brief Description of the Drawings

[0008] [Figure 1] It is a diagram showing an electron beam device that generates a plurality of electron beams (i.e., a plurality of beamlets). [Figure 2] It is a diagram showing a plate that can be used in an electron beam device that generates a plurality of electron beams. [Figure 3] It is a diagram showing a part of the upper column electron optics of an electron beam device (e.g., SEM) that generates a plurality of electron beams, defocuses the electron beams using a defocus lens array, and focuses the electron beams on an intermediate image plane using a global imaging lens, according to some embodiments. [Figure 4A] It is a diagram showing a part of an example of the upper column electron optics of FIG. 3, according to some embodiments. [Figure 4B] It is an enlarged view of a region of the upper column electron optics of FIG. 4A, according to some embodiments. [Figure 4C] It is a diagram showing a computer simulation of equipotential lines and the main trajectories of electron beamlets for the upper column electron optics of FIGS. 4A and 4B, according to some embodiments. [Figure 5] It is a diagram showing image plane curvature blur for beamlets generated using the upper column electron optics of FIGS. 4A to 4C, according to some embodiments. [Figure 6] It is a diagram showing a part of the upper column electron optics including an aperture array, a first multi-bore plate, a second multi-bore plate, and a global imaging lens, according to some embodiments. [Figure 7] It is a diagram showing a plate that can be used as the first plate and the second plate in the upper column electron optics of FIG. 6, according to some embodiments. [Figure 8A] This figure shows the projection of each of the three electron beamlets with image field curvature correction according to several embodiments. [Figure 8B] This figure shows the projection of each of the three electron beamlets with image field curvature correction according to several embodiments. [Figure 8C] This figure shows the projection of each of the three electron beamlets with image field curvature correction according to several embodiments. [Figure 9] This figure shows the simulated spot size across the field of view with image field curvature correction in several embodiments. [Figure 10] This figure shows a portion of the upper column electron optics of an electron beam apparatus (e.g., SEM) that generates multiple electron beams, focuses the electron beams using a focus lens array, and defocuses the electron beams using a global defocus lens, according to several embodiments. [Figure 11] This flowchart shows a method for generating multiple electron beams in an electron beam apparatus according to several embodiments. [Modes for carrying out the invention]

[0009] Throughout the drawings and this specification, similar reference numerals indicate corresponding parts.

[0010] Next, we will refer in detail to various embodiments having examples illustrated in the accompanying drawings. The following detailed description includes many specific details to ensure a complete understanding of the various described embodiments. However, it will be apparent to those skilled in the art that the various described embodiments can be practiced without these specific details. In other examples, well-known methods, procedures, components, circuits, and networks are not described in detail so as not to unnecessarily obscure the aspects of the embodiments.

[0011] In electronic optics, lensing is brought about by electric and / or magnetic fields. Both fields and components used to generate those fields are referred to as lenses, depending on the context. A particular component may be part of multiple lenses. For example, a particular component may be both a final component of a first lens and an initial component of a second lens.

[0012] Figure 1 shows an electron beam apparatus 100 that generates multiple electron beams (i.e., beamlets). The electron beam apparatus 100 includes an upper column electron optics 126 and a lower column electron optics 128. The upper column electron optics 126 includes optics for forming multiple electron beamlets 112. In the upper column electron optics 126, an electron source (e.g., a thermal field emission (TFE) source or a cold field emission (CFE) source) emits electrons from the emitter tip 102. A gun lens (GL) 104 focuses the electrons into an electron beam 108, and the gun lens 104 collimates the electrons emitted by the emitter tip 102 into a telecentric irradiation beam (TIB) 108 that irradiates the aperture array (AA) 110. A beam limiting aperture (BLA) 106 selects the current of the electron beam 108 that irradiates the aperture array (AA) 110. The beam-limiting aperture, like the gun lens 104, is positioned along the optical axis z between the emitter tip 102 and the aperture array 110. The aperture array 110 divides the electron beam 108 into multiple electron beamlets 112 by blocking the rest of the electron beam 108 while allowing each electron beamlet 112 to pass through its respective aperture in the aperture array 110 (for simplicity, three electron beamlets, 112-1 to 112-3, are shown in Figure 1). Following the aperture array 110 is the lens array 114, also called a microlens array (MLA). The lens array 114 contains multiple lenses, each of which focuses one of the multiple electron beamlets 112 onto the intermediate image plane (IIP) 116. The multiple electron beamlets 112 have a field of view (FOV) within the intermediate image plane 116. oEach electron beamlet 112 has a numerical aperture (NA)β0.

[0013] The lower column electron optics 128 includes a transfer lens (TL) 118 and an objective lens (OL) 122. The transfer lens 118 is configured to create a crossover (xo) 120 of multiple electron beamlets 112 between the transfer lens 118 and the objective lens 122. The lower column electron optics 128 is a projection optics. For example, the multiple electron beamlets 112 are projected onto the wafer 124 (or other substrate) by the transfer lens 118 and the objective lens 122 for inspection (e.g., at an optimal magnification where beam deflection for the multiple electron beamlets 112 is minimized on the wafer (WF) 124). The multiple electron beamlets 112 are projected onto the surface of the wafer 124 in a field of view (FOV). i Each electron beamlet 112 has a numerical aperture (NA) β i The wafer 124 (or other substrate) is bombarded by multiple electron beamlets 112, and secondary electrons (SE) and / or backscat electrons emitted from the wafer 124 can be split from the optical axis and deflected toward a detection system (not shown) by a Wien filter (not shown).

[0014] Figure 2 shows a plate 200 that may be used in an electron beam apparatus that generates multiple electron beams. For example, plate 200 may be an example of an aperture array 110 of an electron beam apparatus 100 (Figure 1). Plate 200 is arranged in the xy plane perpendicular to the optical axis (i.e., the z axis). Plate 200 includes an array of apertures 202. The apertures 202 may further be referred to as bores or holes. (As used herein, the terms “aperture,” “bore,” and “hole” are interchangeable.) The apertures 202 may be circular. Plate 200 is conductive (e.g., metallic) so that it can function as an electrode in an electron beam apparatus.

[0015] In some embodiments, the apertures 202 are distributed in a hexagonal pattern, which is desirable because hexagons have a relatively high degree of rotational symmetry. Alternatively, the apertures 202 are distributed in a different pattern (e.g., with a different degree of rotational symmetry). The size (e.g., diameter) of each aperture 202 determines the current of the corresponding electron beamlet 112. The number of apertures 202 determines the number of electron beamlets 112 in the plurality of electron beamlets 112. In the case of the hexagonal pattern of FIG. 2, the total number MEB of electron beamlets 112 in the plurality of electron beamlets 112[[ID=I]] tot is [Number] where M x is the number of apertures 202 along the axis of the hexagon (e.g., the x-axis). For example, in FIG. 2, within the 5 rings of apertures 202 distributed in a hexagon (i.e., M x = 11), the total number of beamlets 112 is 91 (i.e., MEB tot = 91). Within the complete 10 rings of FIG. 2 (i.e., M x = 21), the total number of beamlets 112 is 331 (i.e., MEB tot = 331).

[0016] The circular array in FIG. 2 can further show the pattern of the plurality of electron beamlets 112 at the intermediate image plane 116 and the plane of the wafer 124 (e.g., on the surface of the wafer 124) (FIG. 1). From the intermediate image plane 116 to the plane of the wafer 124, the field of view of the plurality of electron beamlets 112 is reduced by 1 / M. Here, M = FOV i / FOV o = (β0 / β i ) * (BE / LE) 1 / 2 (2) where BE and LE are the beam energy and landing energy of the plurality of electron beamlets 112, respectively. Further, FOV o = 2np (3) Hereinafter, n is the number of hexagonal rings (and therefore apertures 202) of the electron beamlet 112, and p is the spacing between the electron beamlets 112.

[0017] To improve the final focus of the electron beamlet 112 (for example, to reduce spherical aberration), the electron beam apparatus 100 may be replaced with an electron beam apparatus that uses a defocus lens array to defocus multiple electron beamlets and a first global lens (also referred to as a global imaging lens or GIL) to focus multiple electron beamlets onto an intermediate image plane. Thus, the defocus lens array adjusts the focus of multiple electron beamlets in a first manner (i.e., by defocusing them), and the first global lens adjusts the focus of multiple electron beamlets in a second manner, which is the opposite of the first manner (i.e., by focusing them).

[0018] Figure 3 shows a portion of the upper column electron optics 300 of such an electron beam apparatus (e.g., SEM) according to several embodiments. In the upper column electron optics 300, the aperture array 110 (e.g., plate 200, Figure 2) divides the telecentric irradiation beam (TIB) and therefore collimated electron beam 108 into a plurality of electron beamlets 312 having trajectories parallel to the optical axis. (For simplicity, three electron beamlets, 312-1 to 312-3, are shown in Figure 3. The upper column electron optics 300 may further include the emitter tip 102, gun lens 104, and beam limiting aperture 106 in Figure 1, but for simplicity, they are not shown in Figure 3.) The electron beamlets 312 are then individually defocused by their respective defocus lenses 304 in the defocus lens array (DLA) 302. (For simplicity, three lenses, 304-1 to 304-3, corresponding to electron beamlets 312-1 to 312-3, are shown in Figure 3.) Next, the first global lens (i.e., GIL) 306 focuses and deflects the defocused electron beamlet 312. The deflected electron beamlet 312 forms a crossover 308 and then forms an image on the intermediate image plane 316. The second global lens 310 (also called the global field lens or GFL) collimates the deflected electron beamlet 312 and telecentrically illuminates the lower column electron optics 128 (shown in Figure 1 but not in Figure 3).

[0019] The defocus lens array 302 is positioned along the optical axis between the aperture array 110 and the first global lens 306. The first global lens 306 is positioned along the optical axis between the defocus lens array 302 and the second global lens 310. The second global lens 310 is positioned along the optical axis between the first global lens 306 and the lower column electronic optics 128 (Figure 1). A crossover 308 occurs along the optical axis between the first global lens 306 and the second global lens 310 (and further between the first global lens 306 and the intermediate image plane 316).

[0020] The upper column electron optics 300 may be considered a projection optics in which the object plane is a virtual object plane (VOP) 301 and the image plane is an intermediate image plane 316. The virtual object plane 301 is the image plane of the defocus lens 304 in the defocus lens array 302, as shown by the dotted line in Figure 3. The image formation relationship of the electron beamlet 312 in the upper column electron optics 300 is:

number

[0021] In some embodiments, the optical magnification of the upper column electronic optics 300 is approximately 1x (for example, exactly 1x when the field of view at the virtual object plane 301 is equal to the field of view at the intermediate image plane 316). The numerical aperture (NA) is,

number

[0022] Figure 4A shows a portion of the upper column electronic optics 400 according to several embodiments. The upper column electronic optics 400 may be an example of the upper column electronic optics 300 (Figure 3) according to several embodiments. The upper column electronic optics 400 includes an aperture array 110 and may further include an emitter tip 102, a gun lens 104, and a beam limiting aperture 106 (shown in Figure 1 but not in Figure 4). In addition to the aperture array 110, the upper column electronic optics 400 includes a first plate 402, a second plate 404, and a third plate 408, each plate arranged sequentially along the optical axis perpendicular to the optical axis. The first plate 402 is positioned between the aperture array 110 and the second plate 404. The second plate 404 is positioned between the first plate 402 and the third plate 408. The first plate 402 and the second plate 404 are examples of a defocus lens array 302 (Figure 3). The second plate 404 and the third plate 408 are examples of a first global lens 306 (Figure 3). The second plate 404 and the third plate 408 have bores 406 and 410 respectively, which, according to some embodiments, allow the passage of multiple beamlets 312 (Figure 3), i.e., all beamlets 312 pass through the bores 406 and 410 during operation. Thus, the second plate 404 and the third plate 408 are single-bore plates. In some embodiments, the bores 406 and 410 have a diameter of 10 mm or more to ensure effective removal of spherical aberration of the beamlets 312 (e.g., having a size of several tens of microns).

[0023] The upper column electronic optics 400 further includes a magnetic lens 414, which is an example of a second global lens 310. The magnetic lens 414 includes a pole piece 418 and a coil 420. An intermediate image plane 416 is located midway between the magnetic lens 414 and perpendicular to the optical axis. The intermediate image plane 416 is an example of an intermediate image plane 316 (Figure 3). The magnetic lens 414 is positioned along the optical axis between the third plate 408 and the lower column electronic optics 128 (shown in Figure 1, but not in Figure 4A).

[0024] Figure 4B is an enlarged view of region 412 (Figure 4A) of the upper column electron optics 400 according to several embodiments. As shown in Figure 4B, the aperture array 110 has a plurality of apertures 422 (e.g., aperture 202, Figure 2), each corresponding to a respective electron beamlet 312 (Figure 3). Each electron beamlet 312 passes through and is thus produced by each aperture 422. The first plate 402 has a plurality of bores 424 corresponding to each aperture 422 in the aperture array 110, and each electron beamlet 312 passes through a respective bore 424. Thus, the first plate 402 is a multi-bore plate. Plate 200 (Figure 2) may be an example of the first plate 402, where aperture 202 is a bore 424. In some embodiments, multiple bores 424 are aligned with their respective apertures 422 (i.e., each bore 424 is aligned with its respective aperture 422). The multiple bores 424 may have a bore size (e.g., the diameter of each bore 424) that is larger than the aperture size of the apertures 422 (e.g., the diameter of each aperture 422). An example of an aperture size for the apertures 422 is 50 μm when the spacing between the apertures 422 is 100 μm. Other examples are possible.

[0025] In some embodiments, multiple bores 424 are surrounded by dummy holes 426 within a first plate 402. The dummy holes 426 are outer bores that do not correspond to each aperture 422, so that the electron beamlet 312 does not pass through the dummy holes 426. The bores 424 are sometimes further referred to as effective holes, in contrast to the dummy holes 426. The dummy holes 426 are used to ensure that the electric field distribution across the bores 424 is uniform.

[0026] The first plate 402, the second plate 404, and the third plate 408 are conductive (e.g., metallic) plates that function as electrodes, respectively. The second plate 404 provides a negative imaging voltage V to achieve the desired defocus by the defocus lens array 302 and the desired focus by the first global lens 306 (Figure 3). IMG (Figure 4A) The aperture array 110, the first plate 402, and the third plate 408 are grounded while being biased at (for example, in the range of -17kV to -24kV at a beam energy of approximately 30kV). Thus, according to some embodiments, the second plate 404 can be configured to be negatively biased. The second plate 404 may be separated from the first plate 402 by only 6 to 12 mm and from the third plate 408 by only 6 to 12 mm along the optical axis. These gaps result in relatively low electric field strength between the plates, thus reducing or avoiding the risk of arcing. Furthermore, these designs allow for a single global voltage V IMG This allows for the implementation of the first global lens 306.

[0027] Figure 4C shows computer simulations of equipotential lines 430 and the main orbit 432 of the electron beamlet 312 for the upper column electron optics 400 according to several embodiments. The components of the upper column electron optics 400 are biased as shown in Figure 4A. The first plate 402 and the second plate 404 produce a defocus field 434, and the second plate 404 and the third plate 408 produce a focus (i.e., imaging) field 436. The defocus field 434 and the focus field 436 are electric fields. The computer simulations demonstrate that the resulting electron beamlet 132 (i.e., the electron beamlet 132 with the main orbit 432) has negligible spherical aberration and negligible Coulomb interaction. The Coulomb interaction is negligible. This is because the crossover position 438 (between the third plate 408 and the magnetic lens 414) is located in a free electric field space with a negative potential, so that the energy of the electron beamlet 132 around the crossover position 438 is not reduced, and moreover, the crossover angle is considerably higher than the numerical aperture of the electron beamlet 132. Therefore, the upper column electron optics 400 produces multiple electron beamlets 132 with negligible wobble due to spherical aberration and Coulomb interaction.

[0028] However, the upper column electron optics 400 may experience blurring due to field curvature over a large field of view. Field curvature within the intermediate image plane 316 (Figure 3) (e.g., within the intermediate image plane 416, Figure 4A) is caused by the deflection of an off-axis (i.e., off-axis) electron beamlet 312. Figure 5 shows the field curvature blur in the intermediate image plane 416 (Figure 4) over a field of view in a defocus lens array 302 using 331 electron beamlets 312 implemented according to a plate 200 (Figure 2) and an upper column electron optics 400 (Figures 4A-4C) sized to a 50 μm aperture with a 100 μm aperture spacing, according to several embodiments. Thus, the field of view is 1414 μm × 1414 μm. The field curvature blur in Figure 5 is determined by computer simulation. Figure 5 shows the field curvature for the central electron beamlet 312-a, the furthest electron beamlet 312-b along the x and y axes, and the furthest corner electron beamlet 312-c. Figure 5 has two scales: a first scale for the electron distribution in each electron beamlet 312 and a larger scale for the distance between electron beamlets 312. The five rings for each electron beamlet 312 represent the 20%, 40%, 60%, 80%, and 100% electron distributions for the electron beamlet 312 (i.e., 20% of the electrons for the electron beamlet 312 are in the first ring, 40% are in the second ring, and so on). As shown in Figure 5, the furthest corner electron beamlet 312-c has a larger spot size along the x and y axes than the furthest electron beamlet 312-b, and the furthest electron beamlet 312-b has a larger spot size than the central electron beamlet 312-a.

[0029] To help correct the image field curvature in Figure 5, in some embodiments, two multi-bore plates are used instead of a single multi-bore plate. The first multi-bore plate is grounded and an auxiliary voltage V FCC Furthermore, a voltage (also called the image field curvature correction voltage) is applied to the second multi-bore plate. FCC VIMG Since it is separate from the other voltage, it is called an auxiliary voltage. FCC The magnitude can be in the order of several hundred volts (for example, in the range of 0 to 1 kV).

[0030] Figure 6 shows a portion of the upper column electron optics 600 of an electron beam apparatus (e.g., SEM) comprising an aperture array 110, a first plate 602, and a second plate 606, according to several embodiments. The first plate 602 is positioned along the optical axis between the aperture array 110 and the second plate 606. The first plate 602 may be separated from the second plate 606 by a gap of several tens of microns along the optical axis.

[0031] The first plate 602 and the second plate 606 are both coconductive (e.g., metallic) multi-bore plates, where the first plate 602 has a first plurality of bores 604 and the second plate 606 has a second plurality of bores 608. The first plurality of bores 604 correspond to each aperture in the aperture array 110 (e.g., aperture 422, Figure 4B). The second plurality of bores 608 correspond to the first plurality of bores 604 and also correspond to each aperture in the aperture array 110. Thus, the second plurality of bores 608 and the first plurality of bores 604 have the same number of bores. For example, the first set of bores 604 and the second set of bores 608 are aligned with each other and also with their respective apertures in the aperture array 110 (i.e., each bore 608 is aligned with its respective bore 604 and its respective aperture). Each bore 604 (e.g., each bore 604) and each bore 608 (e.g., each bore 608) may have a bore size larger than the aperture size of the corresponding aperture in the aperture array 110 (e.g., the aperture to which they are aligned). An example of an aperture size is 50 μm when the spacing between apertures 422 is 100 μm. Other examples are possible. Each bore 608 in the second set of bores 608 may have the same bore size as the corresponding bore 604 in the set of bores 604. The first plurality of bores 604 and the second plurality of bores 608 may each be surrounded by their respective dummy holes 426 (Figure 4B) in the first and second plates 602 and 606.

[0032] The upper column electron optics 600 may further include an emitter tip 102 (Figure 1), a gun lens 104 (Figure 1), a beam limiting aperture 106 (Figure 1), a first global lens 306 (Figure 3), and a second global lens 310 (Figure 3). (For simplicity, the emitter tip 102, gun lens 104, beam limiting aperture 106, and second global lens 310 are not shown in Figure 6.) An electron beam apparatus including the upper column electron optics 600 (e.g., SEM) may further include a lower column electron optics 128 (Figure 1). A magnetic lens 414 may be used to mount the second global lens 310.

[0033] The first global lens 306 can be implemented using plates 404 and 408 as shown in Figures 4A-B. Thus, the upper column electronic optics 600 can be implemented according to several embodiments by replacing plate 402 in the upper column electronic optics 400 (Figures 4A-4C) with the first and second plates 602 and 606. In this example, plate 404 is a third plate and plate 408 is a fourth plate. The third plate 404 is positioned between the second plate 606 and the fourth plate 408. The fourth plate 408 is positioned between the third plate 404 and the magnetic lens 414. The second plate 606 is positioned between the first plate 602 and the third plate 404.

[0034] The first plate 602, the second plate 606, and the third plate 404 constitute a lens array disposed between the aperture array 110 and the first global lens 306 (although the third plate 404 is considered to be part of both the lens array and the first global lens 306). The lens array may be configured to act as a defocusing lens that defocuses multiple electron beamlets 612. The first global lens 306 may be configured to act as a focusing lens that focuses the multiple electron beamlets 612 that have been defocused by the lens array. These functions are achieved through proper biasing: the aperture array 110 and the first plate 602 are grounded, and the second plate 606 is V FCC Biased by, the third plate 404 has a negative voltage V IMG The fourth plate 408 is biased and grounded. Thus, according to some embodiments, the second plate 606 is V FCC It can be configured to be biased by the third plate 404 with voltage V IMG It can be configured to be negatively biased.

[0035] In some embodiments, the bore size of each bore in the first plurality of bores 604 and the second plurality of bores 608 increases as the value of the radial coordinate for each bore increases. The radial coordinate is measured from the center of the bore pattern. Figure 7 shows a plate 700 that can be used as the first plate 602 and the second plate 606 according to some embodiments. Thus, the bore 702 in plate 700 is an example of the first plurality of bores 604 and the second plurality of bores 608. The bore size (e.g., diameter) of the bore 702 in plate 700 is variably distributed: the bore size increases as the distance from the origin (i.e., the intersection of the x and y axes) increases, and therefore as the value of the radial coordinate r increases. In the example in Figure 7, the bore size increases as a linear function of the radial coordinate (and its linear relationship). Other examples are possible. The smaller the bore size, the stronger the focus intensity; conversely, the larger the bore size, the weaker the focus intensity.

[0036] This difference in focus intensity results in different optical axis coordinates zo0, zo1, and zo2 for the virtual objects corresponding to electron beamlets 612-3, 612-2, and 612-1, respectively, as shown in Figure 6, V FCC When is zero, the virtual object positions of each electron beamlet 312 will be different. The images of the virtual objects located at zo0, zo1, and zo2 have their respective optical axis coordinates zi0, zi1, and zi2 on the image side of the first global lens 306 (Figure 6). FCC When V is zero, the electron beamlet 312 is underfocused by the first global lens 306: as shown in Figure 6, the image positions zi0, zi1, and zi2 are to the right of the intermediate image plane (IIP) 616, and the defocus relationship is (zi0-IIP)>(zi1-IIP)>(zi2-IIP)>0. However, when a certain optimized V is applied to the second plate 606, FCCFor a value (negative or positive), the defocus relationship is (zi0-IIP)=(zi1-IIP)=(zi2-IIP) such that the image positions for multiple electron beamlets 612 are equal. A negative voltage V is applied to the third plate 404. IMG By optimally adjusting this, the defocus relationship becomes (zi0-IIP)=(zi1-IIP)=(zi2-IIP)=0, such that the image positions for all of the electron beamlets 612 are within the intermediate image plane 616 and all image plane curvature of the electron beamlets 612 is corrected.

[0037] Figures 8A-8C and 9 show the correction of field curvature by computer-simulated operation of the upper column electronic optics 600 in several embodiments. In these simulation results, the first global lens 306 is implemented using plates 404 and 408 (Figures 4A-4B), and the second global lens 310 (shown in Figure 3 but not in Figure 6 for simplicity) is implemented using magnetic lens 414.

[0038] Figures 8A-8C show projections 800A, 800B, and 800C on the yz plane of three electron beamlets 612-3, 612-2, and 612-1 in an image plane curvature-corrected state according to several embodiments. The deflection of electron beamlets 612-1, 612-2, and 612-3 occurs in the xz plane. The y-axis corresponds to the second plate 606 and the second multiple bores 608. The image positions of the three electron beamlets 612-1, 612-2, and 612-3 are zi2, zi1, and zi0, respectively. Each projection 800A, 800B, and 800C includes multiple computer ray tracing simulations of the electron trajectory. V used in the simulations for Figures 8A-8C FCC To determine the desired value of V, FCCThe voltage is increased in steps (for example, up to several hundred volts). At each step, the residual image plane curvature (zi0-IIP) > (zi1-IIP) > (zi2-IIP) is reduced until (zi0-IIP) ≈ (zi1-IIP) ≈ (zi2-IIP) ≈ 0 (for example, the image positions of electron beamlets 612-1, 612-2, and 612-3 are substantially within the intermediate image plane 616 to within an acceptable error).

[0039] As shown in Figures 8A-8C, the electron beamlets 612-1, 612-2, and 612-3 are first defocused by a lens array including a first plate 602, a second plate 606, and a third plate 404. Then, the electron beamlets 612-1, 612-2, and 612-3 are focused (and defocused) by the first global lens 306. The electron beamlets 612-1, 612-2, and 612-3 are well focused at zi2, zi1, and zi0, and exhibit good image-forming performance with spherical aberration elimination. This image-forming performance is achieved by using two voltages V in some embodiments. IMG and V FCC This is achieved using only (plus biasing against the second global lens 310), thereby allowing the upper column electronic optics 600 to be implemented with minimal power supply and a simple power path.

[0040] Figure 9 shows simulated spot sizes across the field of view with image field curvature correction in several embodiments. The spot sizes include spot sizes along the x and y axes for the central electron beamlet 612-a and the furthest electron beamlet 612-b, as well as the spot size for the furthest corner electron beamlet 612-c. Similar to Figure 5, Figure 9 has two scales: a first scale for electron distribution in each beamlet 312 and a larger second scale for distance between electron beamlets 312. The first scale in Figure 9 is 1 / 5 of the first scale in Figure 5. As image field curvature is eliminated, the spot sizes of electron beamlets 612-b and 612-c approach the spot size of the central electron beamlet 612-a, although certain astigmatic blur and distortion remain. The distortion may be smaller than the pixel size. Therefore, Figure 9 shows a significant improvement in electron beamlet resolution compared to Figure 5.

[0041] Image field curvature also exists within the lower column electronic optics 128 (Figure 1) from the intermediate image plane to the wafer (or other substrate) under inspection. Off-axis aberrations, including image field curvature within the lower column electronic optics 128, can be minimized by optimizing the projected optical attenuation ratio. For example, the optical attenuation ratio can be in the range of 5 to 10 times or approximately that range, depending on the landing energy for a particular use. Thus, the FOV on the surface of wafer 124. i For an intermediate image plane of 1414 μm × 1414 μm, the FOV0 can be in the range of 282 μm × 282 μm to 141 μm × 141 μm or approximately within that range. i The field curvature in the lower column electron optics 128 may be significant with respect to the value. The upper column electron optics 600 (Figure 6) overcorrects the field curvature in the intermediate image plane 616 so that (zi2-IIP)>(zi1-IIP)>(zi0-IIP)=0. FCCThe values ​​of may be selected to compensate for image field curvature in the lower column electron optics 128. The amounts of overcompensation (zi2-IIP) and (zi1-IIP) compensate for the image field curvature distance in the lower column electron optics 128 for the respective electron beamlets 612-1 and 612-2.

[0042] In some embodiments, to improve the final focus of the electron beamlet 112 (Figure 1), the electron beam apparatus 100 (Figure 1) may be replaced with an electron beam apparatus that uses a focus lens array to focus multiple electron beamlets and a first global lens (also referred to as a global defocus lens or GIL) to defocus multiple electron beamlets. Thus, the focus lens array adjusts the focus of multiple electron beamlets in a first manner (i.e., by focusing them), and the first global lens adjusts the focus of multiple electron beamlets in a second manner, which is the opposite of the first manner (i.e., by defocusing them).

[0043] Figure 10 shows a portion of the upper column electron optics 1000 of such an electron beam apparatus (e.g., SEM) according to several embodiments. In the upper column electron optics 1000, the aperture array 110 (e.g., plate 200, Figure 2) divides the telecentric irradiation beam (TIB) and thus collimated electron beam 108 into a plurality of electron beamlets 1012 having trajectories parallel to the optical axis. (For simplicity, three electron beamlets, 1012-1 to 1012-3, are shown in Figure 10. The upper column electron optics 1000 may further include the emitter tip 102, gun lens 104, and beam limiting aperture 106 in Figure 1, but for simplicity, they are not shown.) The electron beamlets 1012 are then individually focused by their respective focus lenses 1004 in the focus lens array (FLA) 1002. (For simplicity, Figure 10 shows three lenses, 1004-1 to 1004-3, corresponding to electron beamlets 1012-1 to 1012-3.) The focus lens array 1002 focuses the electron beamlet 1012 onto a virtual object plane (VOP) 1008 between the first global lens 1006 and the second global lens 310 (i.e., between the first global lens 1006 and the intermediate image plane 1016). The first global lens (i.e., GDL) 1006 then defocuses and deflects the focused electron beamlet 1012. The deflected electron beamlet 1012 forms an image on the intermediate image plane 1016. The focusing performed by the focus lens array 1002 is stronger than the defocusing performed by the first global lens 1006, thereby enabling the electron beamlet 1012 to form an image on the intermediate image plane 1016. The second global lens 310 collimates the deflected beamlet 1012 and telecentrically illuminates the lower column electron optics 128 (shown in Figure 1, but not in Figure 10).

[0044] The focus lens array 1002 is positioned along the optical axis between the aperture array 110 and the first global lens 1006. The first global lens 1006 is positioned along the optical axis between the focus lens array 1002 and the second global lens 310. The second global lens 310 is positioned along the optical axis between the first global lens 1006 and the lower column electronic optics 128.

[0045] The defocus field of the first global lens 1006 deflects the electron beamlets 1012 that are off-axis (e.g., electron beamlets 1012-1 and 1012-3, but not 1012-2), thereby increasing the FOV in the virtual object plane. o Larger FOV i This is generated at the intermediate image plane 1016. Therefore, the projection optical magnification is greater than 1x. M=FOV i / FOV o >1x (6) That is the case.

[0046] In some embodiments, the upper column electronic optics 1000 uses the upper column electronic optics 300 (Figure 3), which includes the upper column electronic optics 400 (Figures 4A-4B), V IMG This is implemented by making the positive voltage V IMG The voltage is applied to plate 404, and the other components are biased as shown in Figure 4A. IMG By changing the bias from negative to positive, the defocus lens array 302 (Figure 3) becomes the focus lens array 1002, and the global imaging lens (i.e., the first global lens 306) becomes the global defocus lens (i.e., the first global lens 1006). Thus, plate 404 can be configured to be positively biased.

[0047] In some embodiments, the upper column electronic optics 1000 uses an upper column electronic optics 600 (Figure 6) including plates 404 and 408 (Figure 4A), VIMG This is implemented by making the voltage positive. The aperture array 110 and the first plate 602 are grounded, and the second plate 606 is connected to the auxiliary voltage V FCC Biased with (for example, on the order of several hundred volts), the third plate 404 is positive voltage V IMG The fourth plate 408 is biased and grounded.

[0048] Figure 11 is a flowchart illustrating a method 1100 for generating multiple electron beams in an electron beam apparatus (e.g., a scanning electron microscope) according to several embodiments. The method 1100 may be performed using an upper column electron optics within an electron beam apparatus (e.g., an upper column electron optics 300, Figure 3; 400, Figures 4A-4C; 600, Figure 6 and / or 1000, Figure 10).

[0049] In method 1100, an electron beam (e.g., TIB108, Figures 3, 4C, 6, and / or 10) is split into multiple electron beamlets (e.g., electron beamlets 312, Figures 3; 612, Figure 6; or 1012, Figure 10) using an aperture array (e.g., aperture array 110, Figures 3, 4A-4C, 6, and / or 10) (1102).

[0050] The focus of multiple electron beamlets is adjusted using a lens array containing multiple lenses (e.g., defocus lens array 302, Figure 3; lens array in Figure 6; focus lens array 1002, Figure 10) (1104). Each lens of the multiple lenses is used to adjust the focus of each electron beamlet of the multiple electron beamlets. In some embodiments (e.g., as in Figures 3 and 6), the multiple electron beamlets are defocused (1106). Alternatively (e.g., as in Figure 10), the multiple electron beamlets are focused (1108).

[0051] The focus of multiple electron beamlets is adjusted using a first global lens (e.g., first global lens 306, Figure 3 or 6; first global lens 1006, Figure 10) (1110). The first global lens adjusts the focus of the multiple electron beamlets in the opposite manner to that of the lens array (but not at the same magnification; the focus may be stronger than the defocus). In some embodiments (e.g., as in Figures 3 and 6), multiple electron beamlets defocused by the lens array in step 1106 are focused by the first global lens (1112). Alternatively (e.g., as in Figure 10), multiple electron beamlets focused by the lens array in step 1108 are defocused by the first global lens (1114).

[0052] Multiple electron beamlets are collimated (1116) and fed (1118) into the lower column electron optics of the electron beam apparatus (e.g., lower column electron optics 128, Figure 1). For example, a second global lens (e.g., second global lens 310, Figure 3 or 10) (e.g., magnetic lens 414, Figure 4A) collimates the multiple electron beamlets and feeds them into the lower column electron optics.

[0053] Method 1100 enables the generation of multiple electron beamlets (e.g., more than 100 electron beamlets, such as 331 beamlets in plate 200, as shown in Figure 2) with high resolution using a relatively simple optical design with minimal power supply and low arcing risk.

[0054] The preceding description, intended for explanatory purposes, has been based on reference to specific embodiments. However, the above exemplary considerations are not intended to be exhaustive or to limit the claims to any precise form disclosed. Many variations and variants are feasible in light of the above teachings. The embodiments have been selected to best illustrate the principles underlying the claims and their practical application, so that those skilled in the art can best utilize the various variations of the embodiments suitable for their particular intended use.

Claims

1. An electron beam apparatus comprising an upper column electron optics and a lower column electron optics, wherein the upper column electron optics is An aperture array for splitting an electron beam into multiple electron beamlets, A lens array comprising a plurality of lenses for adjusting the focus of the plurality of electron beamlets, wherein each lens of the plurality of lenses adjusts the focus of each electron beamlet of the plurality of electron beamlets, A first global lens for adjusting the focus of the plurality of electron beamlets by focusing them in the opposite direction when the lens array is defocused, and defocusing them in the opposite direction when the lens array is focused, Equipped with, The lens array is disposed between the aperture array and the first global lens. The system further comprises a second global lens for collimating the plurality of electron beamlets and supplying the plurality of electron beamlets to the lower column electron optics, The first global lens is disposed between the lens array and the second global lens. An electron beam apparatus characterized in that the lower column electron optics includes a transfer lens and an objective lens, wherein the transfer lens is configured to create a crossover of the electron beamlet between the transfer lens and the objective lens.

2. An electron beam apparatus according to claim 1, characterized in that the second global lens includes a magnetic lens.

3. An electron beam apparatus according to claim 1, The aforementioned lens array A first plate having a plurality of bores corresponding to each aperture in the aperture array, The system comprises a second plate having a bore for allowing the passage of the plurality of electron beamlets, The first plate is disposed between the aperture array and the second plate. The first global lens described above, The second plate and, The system comprises a third plate having a bore for allowing the passage of the plurality of electron beamlets, An electron beam apparatus characterized in that the second plate is disposed between the first plate and the third plate.

4. An electron beam apparatus according to claim 3, The plurality of bores in the first plate are positioned relative to the respective apertures in the aperture array. An electron beam apparatus characterized in that the plurality of bores in the first plate have a bore size larger than the aperture size of each of the apertures in the aperture array.

5. An electron beam apparatus according to claim 3, The aperture array is grounded, The first plate is grounded, The second plate can be configured to be negatively biased, An electron beam apparatus characterized in that the third plate is grounded.

6. An electron beam apparatus according to claim 3, The aperture array is grounded, The first plate is grounded, The second plate can be configured to be positively biased, An electron beam apparatus characterized in that the third plate is grounded.

7. An electron beam apparatus according to claim 3, wherein the first plate further has a plurality of dummy holes surrounding the plurality of bores, and the plurality of dummy holes do not correspond to each aperture in the aperture array.

8. An electron beam apparatus according to claim 1, The aforementioned lens array A first plate having a plurality of first bores corresponding to each aperture in the aperture array, A second plate having the first plurality of bores and a second plurality of bores corresponding to each of the apertures in the aperture array, It includes a third plate having a bore for allowing the passage of the plurality of electron beamlets, The first plate is disposed between the aperture array and the second plate, and the second plate is disposed between the first plate and the third plate. The first global lens described above, The third plate and, It includes a fourth plate having a bore for allowing the passage of the plurality of electron beamlets, An electron beam apparatus characterized in that the third plate is disposed between the second plate and the fourth plate.

9. An electron beam apparatus according to claim 8, The first plurality of bores and the second plurality of bores are positioned relative to each other and relative to each of the apertures in the aperture array. An electron beam apparatus characterized in that each bore in the first plurality of bores and each bore in the second plurality of bores have a bore size larger than the aperture size of each aperture in the aperture array.

10. An electron beam apparatus according to claim 9, characterized in that the bore size of each bore in the first plurality of bores and the second plurality of bores increases as the value of the radial coordinate of each bore increases.

11. An electron beam apparatus according to claim 8, The aperture array is grounded, The first plate is grounded, The second plate can be configured to be biased with an auxiliary voltage, The third plate can be configured to be negatively biased, An electron beam apparatus characterized in that the fourth plate is grounded.

12. An electron beam apparatus according to claim 8, The aperture array is grounded, The first plate is grounded, The second plate can be configured to be biased with an auxiliary voltage, The third plate can be configured to be positively biased, An electron beam apparatus characterized in that the fourth plate is grounded.

13. An electron beam apparatus according to claim 1, The lens array can be configured to defocus the plurality of electron beamlets, An electron beam apparatus characterized in that the first global lens can be configured to focus the plurality of electron beamlets that have been defocused by the lens array.

14. An electron beam apparatus according to claim 1, The lens array can be configured to focus the plurality of electron beamlets, An electron beam apparatus characterized in that the first global lens can be configured to defocus the plurality of electron beamlets focused by the lens array.

15. A method, in the upper column electron optics of an electron beam apparatus, Using an aperture array, the electron beam is split into multiple electron beamlets, Focusing a plurality of electron beamlets using a lens array comprising a plurality of lenses, comprising using each lens of the plurality of lenses to focus each electron beamlet of the plurality of electron beamlets, Using a first global lens to adjust the focus of the multiple electron beamlets, The first global lens adjusts the focus of the plurality of electron beamlets by focusing in the opposite direction when the lens array is defocused and defocusing in the opposite direction when the lens array is focused. The lens array is disposed between the aperture array and the first global lens. A second global lens is provided for collimating the plurality of electron beamlets and supplying the plurality of electron beamlets to the lower column electron optics of the electron beam apparatus. The first global lens is disposed between the lens array and the second global lens. The lower column electron optics includes a transfer lens and an objective lens, wherein the transfer lens creates a crossover of the electron beamlet between the transfer lens and the objective lens. A method characterized by the following:

16. The method according to claim 15, Adjusting the focus of the plurality of electron beamlets using the lens array includes defocusing the plurality of electron beamlets. A method characterized in that adjusting the focus of the plurality of electron beamlets using the first global lens includes focusing the plurality of electron beamlets that have been defocused by the lens array.

17. The method according to claim 15, Adjusting the focus of the plurality of electron beamlets using the lens array includes focusing the plurality of electron beamlets. A method characterized in that adjusting the focus of the plurality of electron beamlets using the first global lens includes defocusing the plurality of electron beamlets that have been focused by the lens array.

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