System and method for producing multiple electron beams - Patents.com

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] The present disclosure relates to electron optics, and more particularly to producing multiple electron beams in an electron beam device. [Background technology]

[0002] Scanning electron microscopes (SEMs) have long been used for inspection applications such as semiconductor wafer inspection. Traditionally, SEMs have had a single electron beam. However, more recently, SEMs with multiple electron beams (i.e., beamlets) have been developed (e.g., using an array of Einzel lenses or deflecting dipoles). The throughput of an SEM (or other electron beam device) depends on the number of beamlets, with higher numbers of beamlets resulting in higher throughput. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2017 / 0025241 [Patent Document 2] US Patent Application Publication No. 2008 / 0023643 [Patent Document 3] International Publication No. 2021 / 018332 [Patent Document 4] US Patent Application Publication No. 2003 / 0001095 Summary of the Invention [Problem to be solved by the invention]

[0004] However, increasing the number of beamlets introduces significant problems. For example, the number of beamlets can be limited by poor optical resolution and high electric field strength, which increases the risk of arcing. Moreover, these problems may be mutually exclusive. For example, the electron beam energy can be reduced to reduce the electric field strength and therefore the risk of arcing. However, a reduction in the electron beam energy increases the Coulomb interaction between the electrons, which reduces 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 with a plurality of lenses for adjusting a focus of the plurality of electron beamlets. Each lens of the plurality of lenses adjusts a focus of each electron beamlet of the plurality of electron beamlets. The upper column electron optics further includes a first global lens for adjusting a focus of the plurality of electron beamlets in an inverse manner to the lens array.

[0006] In some embodiments, a method is performed in an 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 a 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 a focus of each electron beamlet of the plurality of electron beamlets using a respective lens of the plurality of lenses. The method further includes adjusting a 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 an inverse manner to the lens array.

[0007] For a better understanding of the various described embodiments, reference should be made to the following detailed description taken in conjunction with the following drawings, in which: [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 illustrates an electron beam device generating multiple electron beams (i.e., multiple beamlets). [Diagram 2] FIG. 1 illustrates a plate that may be used in an electron beam device for generating multiple electron beams. [Diagram 3] FIG. 1 illustrates a portion of the upper column electron optics of an electron beam device (e.g., an SEM) that generates multiple electron beams, defocuses the electron beams using a defocusing lens array, and focuses the electron beams onto an intermediate image plane using a global imaging lens, in accordance with some embodiments. [Figure 4A] 4 illustrates a portion of an example of the upper column electronic optics of FIG. 3 according to some embodiments. [Figure 4B] FIG. 4B is an enlarged view of a region of the upper column electronic optics of FIG. 4A in accordance with some embodiments. [Figure 4C] FIG. 5 illustrates a computer simulation of equipotential lines and main trajectories of electron beamlets for the upper column electron optics of FIGS. 4A and 4B in accordance with some embodiments. [Diagram 5] FIG. 5 illustrates field curvature blur for beamlets generated using the upper column electron optics of FIGS. 4A-4C, according to some embodiments. [Figure 6] FIG. 2 illustrates a portion of an upper column electron optics comprising an aperture array, a first multi-bore plate, a second multi-bore plate, and a global imaging lens in accordance with some embodiments. [Figure 7] 7A-7C show plates that can be used as the first and second plates in the upper column electron optics of FIG. 6 according to some embodiments. [Figure 8A] FIG. 13 illustrates the projection of three respective electron beamlets with field curvature correction according to some embodiments. [Figure 8B] FIG. 13 illustrates the projection of three respective electron beamlets with field curvature correction according to some embodiments. [Figure 8C] FIG. 13 illustrates the projection of three respective electron beamlets with field curvature correction according to some embodiments. [Figure 9] FIG. 13 illustrates simulated spot size across a field with field curvature correction in accordance with some embodiments. [Figure 10] FIG. 1 illustrates a portion of the upper column electron optics of an electron beam device (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, in accordance with some embodiments. [Figure 11] 1 is a flowchart illustrating a method for producing multiple electron beams in an electron beam device, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Like reference characters refer to corresponding parts throughout the drawings and specification.

[0010] Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the various described embodiments. However, it will be apparent to those skilled in the art that the various described embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.

[0011] In electronic optics, lensing is provided by electric and / or magnetic fields. Both fields and the components used to generate them are referred to herein 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] FIG. 1 shows an electron beam device 100 that generates multiple electron beams (i.e., beamlets). The electron beam device 100 includes upper column electron optics 126 and 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 an emitter tip 102. A gun lens (GL) 104 focuses the electrons into an electron beam 108, which collimates the electrons emitted by the emitter tip 102 into a telecentric illumination beam (TIB) 108 that illuminates an aperture array (AA) 110. A beam-limiting aperture (BLA) 106 selects the current of the electron beam 108 that illuminates the aperture array (AA) 110. The beam limiting aperture, like the gun lens 104, is disposed along the optical axis z between the emitter tip 102 and the aperture array 110. The aperture array 110 splits the electron beam 108 into multiple electron beamlets 112 by allowing the electron beamlets 112 to pass through respective apertures in the aperture array 110 while blocking the remainder of the electron beam 108 (for simplicity, three electron beamlets 112-1 to 112-3 are shown in FIG. 1). The lens array 114, also referred to as a microlens array (MLA), follows the aperture array 110. The lens array 114 includes multiple lenses, each of which focuses a respective one of the multiple electron beamlets 112 onto an intermediate image plane (IIP) 116. The multiple electron beamlets 112 are focused into a field of view (FOV) within the intermediate image plane 116. oand each 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 the 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 by the transfer lens 118 and the objective lens 122 onto a wafer 124 (or other substrate) for inspection (e.g., at an optimal magnification where beam blur for the multiple electron beamlets 112 is minimized at the wafer (WF) 124). The multiple electron beamlets 112 form a field of view (FOV) on the surface of the wafer 124. i and each electron beamlet 112 has a numerical aperture (NA) β i For inspection of a wafer 124 (or other substrate), secondary electrons (SE) and / or backscattered electrons emitted from the wafer 124 upon bombardment of the wafer 124 by the multiple electron beamlets 112 may be split off from the optical axis and deflected by a Wien filter (not shown) towards a detection system (not shown).

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

[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. For the hexagonal pattern of FIG. 2, the total number of electron beamlets 112 in the plurality of electron beamlets 112 is MEB tot teeth,

number

[0016] 2 can further illustrate the pattern of the multiple electron beamlets 112 at the intermediate image plane 116 and at 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 multiple electron beamlets 112 is reduced by 1 / M, where 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 multiple electron beamlets 112, respectively. FOV o =2np (3) where n is the number of hexagonal rings of electron beamlets 112 (and therefore of apertures 202) and p is the spacing between the electron beamlets 112.

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

[0018] FIG. 3 shows a portion of an upper-column electron optics 300 of such an electron beam device (e.g., SEM) according to some embodiments. In the upper-column electron optics 300, the aperture array 110 (e.g., plate 200, FIG. 2) splits the electron beam 108, which is a telecentric illumination beam (TIB) and therefore collimated, into multiple electron beamlets 312 with trajectories parallel to the optical axis. (For simplicity, three electron beamlets, 312-1 to 312-3, are shown in FIG. 3. The upper-column electron optics 300 can further include the emitter tip 102, gun lens 104, and beam-limiting aperture 106 of FIG. 1, but for simplicity, they are not shown in FIG. 3.) The electron beamlets 312 are then separately defocused by respective defocus lenses 304 in the defocus lens array (DLA) 302. (For simplicity, three lenses, 304-1 through 304-3, corresponding to electron beamlets 312-1 through 312-3, are shown in FIG. 3.) A first global lens (i.e., GIL) 306 then focuses and deflects the defocused electron beamlets 312. The deflected electron beamlets 312 form a crossover 308 and then form an image at an intermediate image plane 316. A second global lens 310 (also referred to as a global field lens or GFL) collimates the deflected electron beamlets 312 and telecentrically illuminates the lower column electron optics 128 (shown in FIG. 1 but not shown in FIG. 3).

[0019] The defocusing lens array 302 is disposed along the optical axis between the aperture array 110 and a first global lens 306. The first global lens 306 is disposed along the optical axis between the defocusing lens array 302 and a second global lens 310. The second global lens 310 is disposed along the optical axis between the first global lens 306 and the lower column electron optics 128 (FIG. 1). A crossover 308 occurs along the optical axis between the first global lens 306 and the second global lens 310 (and also between the first global lens 306 and an intermediate image plane 316).

[0020] The upper-column electron optics 300 may be considered as projection optics, where 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 defocusing lens 304 in the defocusing lens array 302, as shown by the dotted line in FIG. 3. The imaging relationship of the electron beamlets 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 (e.g., exactly 1x if 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] FIG. 4A illustrates a portion of an upper-column electron optics 400, according to some embodiments. The upper-column electron optics 400 may be an example of the upper-column electron optics 300 (FIG. 3), according to some embodiments. The upper-column electron 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 FIG. 1, but not shown in FIG. 4). In addition to the aperture array 110, the upper-column electron optics 400 includes a first plate 402, a second plate 404, and a third plate 408, each plate arranged sequentially along an optical axis, perpendicular to the optical axis. The first plate 402 is disposed between the aperture array 110 and the second plate 404. The second plate 404 is disposed between the first plate 402 and the third plate 408. The first plate 402 and the second plate 404 are an example of a defocusing lens array 302 (FIG. 3). The second plate 404 and the third plate 408 are an example of a first global lens 306 (FIG. 3). The second plate 404 and the third plate 408 have respective bores 406 and 410 that allow the passage of multiple beamlets 312 (FIG. 3) according to some embodiments, i.e., during operation, all beamlets 312 pass through the bores 406 and 410. 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 elimination of spherical aberration of the beamlets 312 (e.g., having a size of tens of microns).

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

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

[0025] In some embodiments, the plurality of bores 424 are surrounded by dummy holes 426 in the first plate 402. The dummy holes 426 are outer bores that do not correspond to the respective apertures 422 such that the electron beamlets 312 do not pass through the dummy holes 426. The bores 424 may also be 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 their respective electrodes. To achieve the desired defocus by the defocus lens array 302 and the desired focus by the first global lens 306 (FIG. 3), the second plate 404 is coupled to a negative imaging voltage V IMG (FIG. 4A) (e.g., in the range of −17 kV to −24 kV with a beam energy of approximately 30 kV), the aperture array 110, the first plate 402, and the third plate 408 are grounded. Thus, according to some embodiments, the second plate 404 can be configured to be negatively biased. The second plate 404 may be separated along the optical axis by 6-12 mm from the first plate 402 and by 6-12 mm from the third plate 408. These gaps result in a 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 , the first global lens 306 can be implemented.

[0027] FIG. 4C shows a computer simulation of equipotential lines 430 and main trajectory 432 of electron beamlets 312 for upper-column electron optics 400 according to some embodiments. The components of upper-column electron optics 400 are biased as shown in FIG. 4A. The first plate 402 and the second plate 404 create a defocus field 434, and the second plate 404 and the third plate 408 create a focus (i.e., imaging) field 436. The defocus field 434 and the focus field 436 are electric fields. The computer simulation establishes that the resulting electron beamlets 132 (i.e., electron beamlets 132 with main trajectory 432) have negligible spherical aberration and negligible Coulomb interaction. The Coulomb interaction is negligible. Because the crossover position 438 (between the third plate 408 and the magnetic lens 414) is in a free electric field space with a negative potential so that the energy of the electron beamlets 132 around the crossover position 438 is not reduced, and the crossover angle is quite high compared to the numerical aperture of the electron beamlets 132. Thus, the upper column electron optics 400 produces multiple electron beamlets 132 with negligible blurring due to spherical aberration and Coulomb interactions.

[0028] However, the upper column electron optics 400 may have blurring caused by field curvature over a large field of view. The field curvature in the intermediate image plane 316 (FIG. 3) (e.g., in the intermediate image plane 416, FIG. 4A) is caused by the deflection of the electron beamlets 312 that are off-axis (i.e., off the optical axis). FIG. 5 shows the field curvature blurring at the intermediate image plane 416 (FIG. 4) over the field of view for a defocused lens array 302 with 331 electron beamlets 312 implemented according to the plate 200 (FIG. 2) and the upper column electron optics 400 (FIGS. 4A-4C) sized with 50 μm apertures and 100 μm aperture spacing, according to some embodiments. The field of view is therefore 1414 μm×1414 μm. The field curvature blurring in FIG. 5 is determined by computer simulation. FIG. 5 shows the field curvature blur for the central electron beamlet 312-a, the farthest electron beamlet 312-b along the x-axis and y-axis, and the farthest corner electron beamlet 312-c. FIG. 5 has two scales: a first scale for the electron distribution in each electron beamlet 312 and a larger scale for the distance between the electron beamlets 312. The five rings for each electron beamlet 312 show 20%, 40%, 60%, 80%, and 100% electron distribution 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, etc.). As shown in FIG. 5, the farthest corner electron beamlet 312-c has a larger spot size along the x-axis and y-axis than the farthest electron beamlet 312-b, which has a larger spot size than the electron central beamlet 312-a.

[0029] To help correct the field curvature blur of FIG. 5, according to some embodiments, two multi-bore plates are used instead of a single multi-bore plate. The first multi-bore plate is grounded and connected to an auxiliary voltage V FCC (also referred to as the field curvature correction voltage) is applied to the second multi-bore plate. V FCC VIMG It is called the auxiliary voltage because it is separate from the V FCC The magnitude of can be on the order of hundreds of volts (eg, in the range of 0 to 1 kV).

[0030] 6 shows a portion of an upper column electron optics 600 of an electron beam device (e.g., an SEM) comprising an aperture array 110, a first plate 602, and a second plate 606, according to some embodiments. The first plate 602 is disposed 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 along the optical axis by a gap on the order of tens of microns.

[0031] The first plate 602 and the second plate 606 are both conductive (e.g., metallic) multi-bore plates, with the first plate 602 having a first plurality of bores 604 and the second plate 606 having a second plurality of bores 608. The first plurality of bores 604 correspond to respective apertures (e.g., apertures 422, FIG. 4B) in the aperture array 110. The second plurality of bores 608 correspond to the first plurality of bores 604 and also correspond to respective apertures 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 plurality of bores 604 and the second plurality of bores 608 are aligned with each other and with the respective apertures in the aperture array 110 (i.e., each bore 608 is aligned with each bore 604 and each 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., of the aperture with which they are aligned). One example of an aperture size is 50 μm with a spacing between the apertures 422 of 100 μm. Other examples are possible. Each bore 608 in the second plurality of bores 608 may have the same bore size as the corresponding bore 604 in the plurality of bores 604. The first plurality of bores 604 and the second plurality of bores 608 may be surrounded by respective dummy holes 426 (FIG. 4B) in the first and second plates 602 and 606, respectively.

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

[0033] The first global lens 306 may be implemented as shown in Figures 4A-B using plates 404 and 408. Thus, the upper column electronic optics 600 may be implemented according to some embodiments by replacing plate 402 in the upper column electronic optics 400 (Figures 4A-4C) with first and second plates 602 and 606. In this example, plate 404 is the third plate and plate 408 is the fourth plate. The third plate 404 is disposed between the second plate 606 and the fourth plate 408. The fourth plate 408 is disposed between the third plate 404 and the magnetic lens 414. The second plate 606 is disposed 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 part of both the lens array and the first global lens 306). The lens array may be configurable to operate as a defocusing lens to defocus the plurality of electron beamlets 612. The first global lens 306 may be configurable to operate as a focusing lens to focus the plurality of electron beamlets 612 that have been defocused by the lens array. These functions are achieved through appropriate biasing: the aperture array 110 and the first plate 602 are grounded, and the second plate 606 is biased to V FCC and the third plate 404 is biased at a negative voltage V IMG and the fourth plate 408 is grounded. Thus, according to some embodiments, the second plate 606 is biased at V FCC and the third plate 404 can be configured to be biased at a voltage V IMG The input can be configured to be negatively biased at

[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 the respective bore increases. The radial coordinate is measured from the center of the pattern of bores. FIG. 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 bores 702 in the plate 700 are examples of the first plurality of bores 604 and the second plurality of bores 608. The bore sizes (e.g., diameters) of the bores 702 in the plate 700 are variably distributed: the bore size increases as the distance from the origin (i.e., the intersection of the x-axis and the y-axis) increases, and thus as the value of the radial coordinate r increases. In the example of FIG. 7, the bore size increases as a linear function of (and in a linear relationship with) the radial coordinate. Other examples are possible. The smaller the bore size, the stronger the focus intensity, and 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, resulting in a difference in V, as shown in FIG. FCC When V is zero, the virtual object position of each electron beamlet 312 is different. The images of the virtual objects located at zo, zo, and zo have respective optical axis coordinates zi, zi, and zi on the image side of the first global lens 306 (FIG. 6). FCC When V is zero, the electron beamlet 312 is underfocused by the first global lens 306: as shown in FIG. 6, 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, for a certain optimized V applied to the second plate 606, FCCFor values ​​of V (negative or positive), the defocus relationship is (zi0-IIP)=(zi1-IIP)=(zi2-IIP) such that the image positions for the multiple electron beamlets 612 are equal. IMG By optimally adjusting the IIP, the defocus relationship is (zi0-IIP)=(zi1-IIP)=(zi2-IIP)=0 such that the image positions for the multiple electron beamlets 612 are all within the intermediate image plane 616 and all field curvatures of the electron beamlets 612 are corrected.

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

[0038] 8A-8C show projections 800A, 800B, and 800C on the yz plane of three respective electron beamlets 612-3, 612-2, and 612-1 with field curvature correction, according to some embodiments. The deflection of the 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 plurality of 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 electron trajectories. The V used in the simulations for FIGS. 8A-8C FCC To determine the desired value of V FCCis increased in steps (e.g., to several hundred volts). With each step, the residual field curvature (zi0-IIP)>(zi1-IIP)>(zi2-IIP) is reduced until (zi0-IIP)≈(zi1-IIP)≈(zi2-IIP)≈0 (e.g., the image positions of electron beamlets 612-1, 612-2, and 612-3 are substantially within intermediate image plane 616 to within an acceptable error).

[0039] As shown in FIGS. 8A-8C, electron beamlets 612-1, 612-2, and 612-3 are first defocused by a lens array including the first plate 602, the second plate 606, and the third plate 404. Then, electron beamlets 612-1, 612-2, and 612-3 are focused (and defocused) by the first global lens 306. Electron beamlets 612-1, 612-2, and 612-3 are well focused at zi2, zi1, and zi0, exhibiting good imaging performance with elimination of spherical aberration. This imaging performance is achieved by using two voltages V according to some embodiments. IMG and V FCC This is achieved using only the 1.0 V power supply (plus biasing for the second global lens 310), thereby allowing the upper column electron optics 600 to be implemented with a small power supply and simple power path.

[0040] FIG. 9 shows simulated spot sizes across the field with field curvature correction according to some embodiments. The spot sizes include spot sizes along the x-axis and y-axis for the central electron beamlet 612-a and the farthest electron beamlet 612-b, as well as the spot size for the farthest corner electron beamlet 612-c. As in FIG. 5, FIG. 9 has two scales: a first scale for the electron distribution in each beamlet 312 and a larger second scale for the distance between the electron beamlets 312. The first scale in FIG. 9 is 1 / 5 of the first scale in FIG. 5. As the field curvature disappears, the spot sizes of the electron beamlets 612-b and 612-c approach the spot size of the central electron beamlet 612-a, but there is some astigmatic blurring and distortion. The distortion may be smaller than the pixel size. Thus, FIG. 9 shows a significant improvement in electron beamlet resolution compared to FIG. 5.

[0041] Field curvature is also present in the lower column electron optics 128 (FIG. 1) from the intermediate image plane to the wafer (or other substrate) being inspected. Off-axis aberrations, including field curvature, in the lower column electron optics 128 can be minimized by optimizing the projection optical reduction factor. For example, the optical reduction factor can be in the range of 5-10x or approximately, depending on the landing energy for a particular application. Thus, the FOV at the plane of the wafer 124 is i may range or approximately range from 282 μm×282 μm to 141 μm×141 μm for an FOV0 at an intermediate image plane of 1414 μm×1414 μm. i The field curvature at the lower column electron optics 128 relative to the value can be significant. The upper column electron optics 600 (FIG. 6) overcorrects the field curvature at the intermediate image plane 616 such that (zi2-IIP)>(zi1-IIP)>(zi0-IIP)=0. FCCmay be used to correct for the field curvature in the lower column electron optics 128 by selecting the values ​​of (zi2-IIP) and (zi1-IIP). The amount of overcorrection (zi2-IIP) and (zi1-IIP) compensate for the 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 beamlets 112 (FIG. 1), the electron beam device 100 (FIG. 1) may be replaced with an electron beam device that uses a focus lens array to focus the electron beamlets and a first global lens (also referred to as a global defocus lens or GIL) to defocus the electron beamlets. Thus, the focus lens array adjusts the focus of the electron beamlets in a first manner (i.e., by focusing them), and the first global lens adjusts the focus of the electron beamlets in a second manner that is opposite to the first manner (i.e., by defocusing them).

[0043] FIG. 10 shows a portion of an upper-column electron optics 1000 of such an electron beam device (e.g., SEM) according to some embodiments. In the upper-column electron optics 1000, an aperture array 110 (e.g., plate 200, FIG. 2) splits an electron beam 108, which is a telecentric illumination beam (TIB) and therefore collimated, into multiple electron beamlets 1012 having trajectories parallel to the optical axis. (For simplicity, three electron beamlets, 1012-1 to 1012-3, are shown in FIG. 10. The upper-column electron optics 1000 can further include the emitter tip 102, gun lens 104, and beam-limiting aperture 106 of FIG. 1, but for simplicity, they are not shown.) The electron beamlets 1012 are then separately focused by respective focus lenses 1004 in a focus lens array (FLA) 1002. (For simplicity, three lenses 1004-1 to 1004-3 corresponding to electron beamlets 1012-1 to 1012-3 are shown in FIG. 10 .) The focus lens array 1002 focuses the electron beamlets 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 beamlets 1012. The deflected electron beamlets 1012 form an image at 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 allowing the electron beamlets 1012 to be imaged at the intermediate image plane 1016. A second global lens 310 collimates the deflected beamlet 1012 and telecentrically illuminates the lower column electron optics 128 (shown in FIG. 1, but not shown in FIG. 10).

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

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

[0046] In some embodiments, upper-column electron optics 1000 uses upper-column electron optics 300 (FIG. 3), which includes upper-column electron optics 400 (FIGS. 4A-4B), to IMG is implemented by making V positive, IMG is applied to plate 404 and the other components are biased as shown in FIG. IMG By changing from negative to positive, the defocus lens array 302 (FIG. 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, the plate 404 may be configurable to be positively biased.

[0047] In some embodiments, upper-column electron optics 1000 uses upper-column electron optics 600 (FIG. 6), which includes plate 404 and plate 408 (FIG. 4A), toIMG is implemented by making V positive. The aperture array 110 and the first plate 602 are grounded, and the second plate 606 is connected to an auxiliary voltage V FCC (e.g., on the order of several hundred volts), and the third plate 404 is biased at a positive voltage V IMG and the fourth plate 408 is biased at ground.

[0048] 11 is a flow chart illustrating a method 1100 of generating multiple electron beams in an electron beam device (e.g., an SEM) according to some embodiments. Method 1100 may be performed using upper column electron optics in the electron beam device (e.g., upper column electron optics 300, FIG. 3; 400, FIG. 4A-4C; 600, FIG. 6, and / or 1000, FIG. 10).

[0049] In method 1100, an electron beam (e.g., TIB 108, Figures 3, 4C, 6, and / or 10) is split (1102) into multiple electron beamlets (e.g., electron beamlets 312, Figure 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).

[0050] The focus of the multiple electron beamlets is adjusted (1104) using a lens array including multiple lenses (e.g., defocus lens array 302, FIG. 3; lens array of FIG. 6; focus lens array 1002, FIG. 10). 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 FIGS. 3 and 6), the multiple electron beamlets are defocused (1106). Alternatively (e.g., as in FIG. 10), the multiple electron beamlets are focused (1108).

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

[0052] The multiple electron beamlets are collimated (1116) and provided (1118) to lower column electron optics (e.g., lower column electron optics 128, FIG. 1) of the electron beam device. For example, a second global lens (e.g., second global lens 310, FIG. 3 or 10) (e.g., magnetic lens 414, FIG. 4A) collimates the multiple electron beamlets and provides the multiple electron beamlets to the lower column electron optics.

[0053] Method 1100 enables multiple electron beamlets (e.g., more than 100 electron beamlets, such as 331 beamlets per plate 200, FIG. 2) to be generated with high resolution using a relatively simple optical design with low power supply and low arcing risk.

[0054] The previous description for purposes of illustration has been described with reference to specific embodiments. However, the above exemplary discussion is not intended to be exhaustive or to limit the scope of the claims to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. The embodiments have been selected to best explain the principles underlying the claims and their practical application, so that those skilled in the art can best use the embodiments with various modifications as appropriate for the particular use envisaged.

Claims

1. 1. An electron beam device comprising upper column electron optics and lower column electron optics, the upper column electron optics comprising: an aperture array for splitting the electron beam into a plurality of electron beamlets; a lens array comprising a plurality of lenses for adjusting a focus of the plurality of electron beamlets, each lens of the plurality of lenses adjusting a focus of a respective electron beamlet of the plurality of electron beamlets; and a first global lens for adjusting the focus of the plurality of electron beamlets in an inverse manner to the lens array; Equipped with the lens array is disposed between the aperture array and the first global lens; Electron beam device characterized by:

2. 10. The electron beam device of claim 1, further comprising a second global lens for collimating the plurality of beamlets and delivering the plurality of beamlets to the lower column electron optics; Electron beam apparatus, characterized in that the first global lens is disposed between the lens array and the second global lens.

3. 3. The electron beam device of claim 2, wherein the second global lens comprises a magnetic lens.

4. 3. The electron beam device of claim 2, wherein the lower column electron optics includes a transfer lens and an objective lens, the transfer lens configured to create a crossover of the electron beamlets between the transfer lens and the objective lens.

5. 2. The electron beam device according to claim 1, The lens array is a first plate having a plurality of bores corresponding to each aperture in the aperture array; a second plate having a bore for allowing passage of the plurality of beamlets; the first plate is disposed between the aperture array and the second plate; The first global lens comprises: The second plate; a third plate having a bore for allowing passage of the plurality of beamlets; Electron beam apparatus, characterized in that the second plate is disposed between the first plate and the third plate.

6. 6. The electron beam device according to claim 5, the plurality of bores in the first plate are aligned with the respective apertures in the aperture array; 11. An electron beam device, comprising: a first plate having a bore size that is greater than an aperture size of each of the apertures in the aperture array;

7. 6. The electron beam device according to claim 5, the aperture array is grounded; the first plate is grounded; the second plate can be configured to be negatively biased; Electron beam apparatus, wherein the third plate is grounded.

8. 6. The electron beam device according to claim 5, the aperture array is grounded; the first plate is grounded; the second plate can be configured to be positively biased; Electron beam device, wherein the third plate is grounded.

9. 6. The electron beam apparatus of claim 5, wherein the first plate further comprises a plurality of dummy holes surrounding the plurality of bores, the plurality of dummy holes not corresponding to respective apertures in the aperture array.

10. 2. The electron beam device according to claim 1, The lens array is a first plate having a first plurality of bores corresponding to each aperture in the aperture array; a second plate having a second plurality of bores corresponding to the first plurality of bores and to the respective apertures in the aperture array; a third plate having a bore for allowing passage of the plurality of 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 comprises: the third plate; a fourth plate having a bore for allowing passage of the plurality of beamlets; Electron beam apparatus, characterized in that the third plate is disposed between the second plate and the fourth plate.

11. 11. The electron beam device according to claim 10, the first and second plurality of bores are aligned with one another and with the respective apertures in the aperture array; 11. An electron beam device, comprising: each bore in the first plurality of bores and each bore in the second plurality of bores having a bore size greater than an aperture size of a respective aperture in the aperture array.

12. 12. The electron beam device of claim 11, wherein 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 the each bore increases.

13. 11. The electron beam device according to claim 10, the aperture array is grounded; the first plate is grounded; the second plate is configurable to be biased with an auxiliary voltage; the third plate can be configured to be negatively biased; Electron beam apparatus, wherein the fourth plate is grounded.

14. 11. The electron beam device according to claim 10, the aperture array is grounded; the first plate is grounded; the second plate is configurable to be biased with an auxiliary voltage; the third plate can be configured to be positively biased; Electron beam apparatus, wherein the fourth plate is grounded.

15. 2. The electron beam device according to claim 1, the lens array can be configured to defocus the plurality of electron beamlets; Electron beam device, characterized in that the first global lens is configurable to focus the plurality of electron beamlets defocused by the lens array.

16. 2. The electron beam device according to claim 1, the lens array is configurable to focus the plurality of electron beamlets; 2. An electron beam device, comprising: a first global lens configured to defocus the plurality of electron beamlets focused by the lens array; 17. A method, in upper column electron optics of an electron beam apparatus, comprising: splitting the electron beam into a plurality of electron beamlets using an aperture array; adjusting a focus of the plurality of electron beamlets using a lens array including the plurality of lenses, wherein adjusting a focus of each electron beamlet of the plurality of electron beamlets using a respective lens of the plurality of lenses; adjusting a focus of the plurality of electron beamlets using a first global lens; and the first global lens adjusts the focus of the plurality of electron beamlets in an inverse manner to the lens array; the lens array is disposed between the aperture array and the first global lens; A method comprising:

18. 20. The method of claim 17, wherein the upper column electron optics further comprises: Collimating the plurality of beamlets; and providing the collimated beamlets to lower column electron optics of the electron beam device.

19. 20. The method of claim 17, adjusting the focus of the plurality of electron beamlets using the lens array includes defocusing the plurality of electron beamlets; 22. The method of claim 21, wherein adjusting the focus of the plurality of electron beamlets using the first global lens comprises focusing the plurality of electron beamlets that were defocused by the lens array.

20. 20. The method of claim 17, adjusting the focus of the plurality of electron beamlets using the lens array comprises focusing the plurality of electron beamlets; 22. The method of claim 21, wherein adjusting the focus of the plurality of electron beamlets using the first global lens comprises defocusing the plurality of electron beamlets focused by the lens array.

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