Shielding strategies for mitigating stray magnetic fields for permanent magnet arrays

Abstract

The present disclosure provides an inspection system and method for stray magnetic field mitigation. The system includes an array of electron beam columns, a first permanent magnet array, and a plurality of shielding plates. Each of the array of electron beam columns includes an electron source configured to emit electrons toward a stage. The first permanent magnet array is configured to condense electrons from each electron source into an array of electron beams. The first permanent magnet array is disposed at a first end of the array of electron beam columns. The plurality of shielding plates extend across the array electron beam columns downstream of the first permanent magnet array in the electron emission direction. The array of electron beams passes through a plurality of openings in each of the plurality of shielding plates to reduce a radial stray magnetic field of the array of electron beams.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to inspection systems, and more particularly to inspection systems that utilize electron beams and permanent magnet arrays. [Background technology]

[0002] The evolution of the semiconductor manufacturing industry is placing greater demands on yield management, particularly on metrology and inspection systems. As critical dimensions continue to shrink, the industry must reduce the time to achieve high-yield, high-value production. Minimizing the total time from detecting a yield problem to fixing it determines the return on investment for semiconductor manufacturers.

[0003] Fabricating semiconductor devices, such as logic and memory devices, typically involves processing a semiconductor wafer or EUV mask using multiple manufacturing processes to form various features and levels of the semiconductor device. For example, lithography is a semiconductor manufacturing process that involves transferring a pattern from a reticle to a photoresist disposed on a semiconductor wafer. Further examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices can be fabricated in-place on a single semiconductor wafer, which is then separated into individual semiconductor devices.

[0004] Inspection processes are used at various steps during semiconductor manufacturing to detect defects on wafers in order to promote higher yields in the manufacturing process and therefore higher profits. Inspection has always been an important part of manufacturing semiconductor devices, such as integrated circuits (ICs). However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause device failure. For example, as the dimensions of semiconductor devices shrink, detection of reduced-size defects has become necessary because even relatively small defects can cause undesirable aberrations in the semiconductor device.

[0005] One device used in the inspection process is a multi-column system. In a multi-column system, multiple beamlets are generated and focused onto a target. Each beamlet is directed through an optical column that includes upper and lower permanent magnets. However, the permanent magnets generate stray magnetic fields that cause beam deflection. Beam deflection can lead to beam misalignment and reduce the accuracy of the inspection process. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2012 / 0145900 [Patent Document 2] U.S. Patent Application Publication No. 2013 / 0313431 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, there is a need for a method to mitigate stray fields in multi-beam systems. [Means for solving the problem]

[0008] An embodiment of the present disclosure provides an inspection system. The inspection system includes an array of electron beam columns, each of which includes an electron source configured to emit electrons toward a stage. The inspection system further includes a first permanent magnet array configured to condense electrons from each electron source into the array of electron beams. The first permanent magnet array is disposed at a first end of the array of electron beam columns. The inspection system further includes a plurality of shielding plates extending across the array of electron beam columns downstream of the first permanent magnet array in the electron emission direction. Each of the plurality of shielding plates includes a plurality of apertures and has a thickness of 1 μm to 1 mm, and the array of electron beams passes through the plurality of apertures. The plurality of shielding plates reduce a radial stray magnetic field of the array of electron beams.

[0009] According to an embodiment of the present disclosure, the inspection system may further include a second permanent magnet array configured to focus the array of electron beams toward a target on the stage, the second permanent magnet array being disposed at a second end of the array of electron beam columns.

[0010] According to an embodiment of the present disclosure, the plurality of shielding plates includes a first shielding plate positioned proximate to the first permanent magnet array and a second shielding plate positioned proximate to the second permanent magnet array.

[0011] According to an embodiment of the present disclosure, the inspection system further includes a detector configured to detect electrons reflected from the target, the detector being disposed between the first permanent magnet array and the second permanent magnet array, and the plurality of shielding plates further includes a third shielding plate disposed proximate to the detector.

[0012] According to an embodiment of the present disclosure, the plurality of shielding plates further comprises a fourth shielding plate disposed opposite the third shielding plate and proximate to the detector.

[0013] According to an embodiment of the present disclosure, the plurality of shielding plates further includes at least one auxiliary shielding plate disposed between the first shielding plate and the second shielding plate.

[0014] According to an embodiment of the present disclosure, the plurality of shielding plates includes at least seven shielding plates.

[0015] According to one embodiment of the present disclosure, at least one of the plurality of shielding plates is disposed where the stray magnetic field is greatest in the radial direction of the array of electron beams.

[0016] According to one embodiment of the present disclosure, the thickness of each of the plurality of shielding plates is at least 120 μm.

[0017] According to an embodiment of the present disclosure, the plurality of shielding plates are constructed from a magnetic nickel-iron alloy.

[0018] An embodiment of the present disclosure provides a method for mitigating stray electric fields applied to a multi-column inspection system. The inspection system includes an array of electron beam columns, each of which includes an electron beam source configured to emit electrons toward a stage. The method includes passing electrons from each electron source through a first permanent magnet array to condense the electrons into an array of electron beams. The first permanent magnet array is disposed at a first end of the array of electron beam columns. The method further includes directing the array of electron beam columns through a plurality of shielding plates extending downstream of the first permanent magnet array. Each of the plurality of shielding plates has a plurality of apertures and a thickness of 1 μm to 1 mm, and the array of electron beams passes through the plurality of apertures. The plurality of shielding plates reduce radial stray magnetic fields of the array of electron beams.

[0019] According to an embodiment of the present disclosure, the method further includes passing the array of electron beams through a second permanent magnet array disposed at a second end of the array of electron beam columns and downstream of the plurality of shielding plates to focus the array of electron beams toward a target on the stage.

[0020] According to an embodiment of the present disclosure, directing the array of electron beams through a plurality of shielding plates includes directing the array of electron beams through a first shielding plate positioned proximate to a first permanent magnet array, and directing the array of electron beams through a second shielding plate positioned proximate to a second permanent magnet array.

[0021] According to an embodiment of the present disclosure, the method further includes directing the array of electron beams through a detector configured to detect electrons reflected from the target, the detector being oscillated between a first permanent magnet array and a second permanent magnet array, and passing the array of electron beams through a plurality of shielding plates further includes passing the array of electron beams through a third shielding plate disposed proximate to the detector.

[0022] According to an embodiment of the present disclosure, the step of directing the array of electron beams through the plurality of shielding plates further includes the step of directing the array of electron beams through a fourth shielding plate positioned opposite the third shielding plate and proximate to the detector.

[0023] According to one embodiment of the present disclosure, the step of directing the array of electron beams through a plurality of shielding plates further includes the step of directing the array of electron beams through at least one auxiliary shielding plate disposed between the first shielding plate and the second shielding plate. [Brief explanation of the drawings]

[0024] For a fuller understanding of the nature and objects of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which: [Figure 1A] FIG. 1 is a schematic diagram of an inspection system of the present disclosure. [Figure 1B] 1 is a schematic diagram of an electron beam column of the present disclosure; [Figure 1C] FIG. 2 is a top view of a shielding plate according to an embodiment of the present disclosure. [Figure 2A] FIG. 10 is a graphical illustration of the reduction of the stray magnetic field Bx according to an embodiment of the present disclosure. [Figure 2B]FIG. 10 is a graphical representation of the reduction of the stray magnetic field By according to an embodiment of the present disclosure. [Figure 2C] FIG. 10 is a graphical illustration of the effect on a magnetic field Bz parallel to the electron beam optical axis according to an embodiment of the present disclosure. [Figure 3] FIG. 1 is a schematic diagram of an electron beam column according to an embodiment of the present disclosure. [Figure 4] FIG. 2 is a schematic diagram of an electron beam column according to another embodiment of the present disclosure. [Figure 5] FIG. 1 is a block diagram of the method of the present disclosure. [Figure 6] FIG. 1 is a block diagram of a method according to an embodiment of the present disclosure. [Figure 7] FIG. 10 is a block diagram of a method according to another embodiment of the present disclosure. [Figure 8] FIG. 10 is a block diagram of a method according to another embodiment of the present disclosure. [Figure 9] FIG. 1 is a schematic diagram of a system according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0025] Although the claimed subject matter is described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features described herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of this disclosure. Accordingly, the scope of this disclosure is defined solely by reference to the appended claims.

[0026] As shown in FIG. 1A, an embodiment of the present disclosure provides a multi-row inspection system 100. The inspection system 100 may include an array of electron beam columns 101. The array of electron beam columns 101 may be a two-dimensional array. Although seven electron beam columns 101 are shown in FIG. 1A, the specific size and number of electron beam columns in the array 101 may vary depending on the application. The electron beam columns in the array 101 may also extend into or out of the page. The electron beam columns 101 may be held by a support structure 102.

[0027] 1B , each electron beam column 101 in the inspection system 100 may include an electron beam source 110. The electron beam source 110 may be configured to emit electrons in a single electron beam or in multiple electron beams arranged in an array. A single electron beam source 110 may be used for all of the electron beam columns 101, each electron beam column 101 may have its own electron beam source 110, or some combination thereof. Electrons from each electron beam source 110 may be directed toward a stage 130. The stage 130 may be configured to hold a target, such as a semiconductor wafer or a reticle.

[0028] The inspection system 100 may further include a first permanent magnet array 140. The first permanent magnet array 140 may be configured to condense electrons from each electron source 110 into an array of electron beams 120. The first permanent magnet array 140 may be disposed at a first end 121 of the array of electron beam columns 101. For example, the first permanent magnet array 140 may be disposed at the top end of the array of electron beam columns 101 in proximity to the electron beam sources 110.

[0029] The inspection system 100 may further include a second permanent magnet array 150. The second permanent magnet array 150 may be configured to focus the array of electron beams 120 toward a target. The second permanent magnet array 150 may be disposed at a second end 122 of the array of electron beam columns 101. For example, the second permanent magnet array 150 may be disposed at a lower end of the array of electron beam columns 101 proximate the stage 130.

[0030] According to an embodiment of the present disclosure, the inspection system 100 may include only one permanent magnet array, such as the first permanent magnet array 140. According to another embodiment of the present disclosure, the inspection system 100 may include multiple permanent magnet arrays, such as the first permanent magnet array 140 and the second permanent magnet array 150.

[0031] According to an embodiment of the present disclosure, the support structure 102 can hold a permanent magnet array 140 and a second permanent magnet array 150 .

[0032] According to an embodiment of the present disclosure, the inspection system 100 may include only one of the first permanent magnet array 140 and the second permanent magnet array 150 .

[0033] The inspection system 100 may further include multiple shielding plates 160. The multiple shielding plates 160 may extend across the array of electron beam columns 101 between the first permanent magnet array 140 and the second permanent magnet array 150. Note that while FIG. 1A shows only one shielding plate 160 for ease of illustration, multiple shielding plates 160 may be provided between the first permanent magnet array 140 and the second permanent magnet array 150. As shown in FIG. 1C, each of the multiple shielding plates 160 may include multiple openings 160a. Each opening 160a may be circular, elliptical, or polygonal. The specific size and shape of each opening 160a may depend on the location of the particular shielding plate 160 within each of the electron beam columns 101, the dimensions of the electron beam, and / or the size and shape of other components in the inspection system 100 adjacent to the particular shielding plate. The multiple apertures 160a may be arranged in a regular pattern corresponding to the XY arrangement of the array of electron beam columns 101. While a 2x2 arrangement of the apertures 160a is shown in FIG. 2C, the number and arrangement of the apertures 160a depend on the number and arrangement of the electron beam columns in the array 101. The array of electron beams 120 can pass through the multiple apertures 160a. In this manner, the array of electron beams 120 can pass through each of the multiple shielding plates 160 as the array of electron beams 120 travels through each electron beam column 101 toward the stage 130. Each shielding plate 160 can have a thickness of 1 μm to 1 mm. For example, each shielding plate 160 can have a thickness of at least 125 μm. In certain embodiments, the thickness can be approximately 250 μm. The multiple shielding plates 160 can have the same thickness or different thicknesses. The multiple shielding plates 160 can be made of a nickel-iron alloy. The nickel-iron alloy can be magnetic. For example, the shielding plates 160 may be constructed from Carpenter 49 or Carpenter H yMu "80" alloy. Other mild steel alloys may also be used.

[0034] According to an embodiment of the present disclosure, the support structure 102 can hold multiple shielding plates 160. The multiple shielding plates 160 can be secured to various components within the array of electron beam columns 101. For example, the multiple shielding plates 160 can include mounting holes configured to receive fasteners for securing the multiple shielding plates 160 to the support structure 102 and / or components within the array of electron beam columns 101. The multiple shielding plates 160 can be evenly spaced within the array of electron beam columns 101.

[0035] According to the electron beam column 101 of the present disclosure, the multiple shielding plates 160 can reduce the radial stray magnetic field of the electron beam column 120. For example, the axial direction of the electron beam column 101 may be defined as the Z axis, and the radial directions of the electron beam column 101 may define the X axis and the Y axis. Correspondingly, the magnetic field within each electron beam column 101 can be defined by Bx, By, and Bz. The magnetic fields Bx and By can be reduced to less than 7%. Such a reduction in the magnetic field can result in reduced beam deflection, improve beam alignment, facilitate multi-column setup, and improve the accuracy of the inspection process.

[0036] According to an embodiment of the present disclosure, the plurality of shielding plates 160 may include a first shielding plate 161. The first shielding plate 161 may be disposed proximate to the first permanent magnet array 140. For example, the first shielding plate 161 may be disposed downstream of the first permanent magnet array 140 at the first end 121 of the array of the electron beam column 101.

[0037] According to an embodiment of the present disclosure, the plurality of shielding plates 160 may include a second shielding plate 162. The second shielding plate 162 may be disposed proximate to the second permanent magnet array 150. For example, the second shielding plate 162 may be disposed upstream of the second permanent magnet array 150 at the second end 122 of the array of the electron beam column 101.

[0038] According to an embodiment of the present disclosure, the electron beam array 101 may further include a detector 170. The detector 170 may be configured to detect electrons reflected from the target. The detector 170 may be disposed between the first permanent magnet array 140 and the second permanent magnet array 150.

[0039] According to an embodiment of the present disclosure, the plurality of shielding plates 160 may further include a third shielding plate 163. The third shielding plate 163 may be disposed proximate to the detector 170. For example, the third shielding plate 163 may be disposed upstream of the detector 170 or downstream of the detector 170.

[0040] According to an embodiment of the present disclosure, the plurality of shielding plates 160 may further include a fourth shielding plate 164. The fourth shielding plate 164 may be disposed adjacent to the detector 170 on the opposite side of the third shielding plate 163. For example, the third shielding plate 163 may be disposed upstream of the detector 170, and the fourth shielding plate 164 may be disposed downstream of the detector 170. Alternatively, the third shielding plate 163 may be disposed downstream of the detector 170, and the fourth shielding plate 164 may be disposed upstream of the detector 170. In both configurations, the third shielding plate 163 and the fourth shielding plate 164 may be disposed on either side of the detector 170.

[0041] According to an embodiment of the present disclosure, the plurality of shielding plates 160 may further include at least one auxiliary shielding plate 165. The auxiliary shielding plate 165 is disposed between the first shielding plate 161 and the second shielding plate 162.

[0042] According to an embodiment of the present disclosure, the plurality of shielding plates 160 may include seven shielding plates. For example, as shown in FIG. 1B , the plurality of shielding plates 160 may include a first shielding plate 161, a second shielding plate 162, a third shielding plate 163, a fourth shielding plate 164, and three auxiliary shielding plates 165. The first shielding plate 161 may be disposed proximate to the first permanent magnet array 140. The second shielding plate may be disposed proximate to the second permanent magnet array 150. The third shielding plate 163 and the fourth shielding plate 164 may be disposed proximate to and on opposite sides of the detector 170. A first auxiliary shielding plate 165a is disposed between the first shielding plate 161 and the third shielding plate 163. A second auxiliary shielding plate 165b is disposed between the fourth shielding plate 164 and the second shielding plate 162. A third auxiliary shielding plate 165c is disposed between the second auxiliary shielding plate 165b and the second shielding plate 162. With this design, the radial stray magnetic field can be reduced by more than 92%. For example, FIGS. 2A and 2B show the stray magnetic fields Bx and By of three columns A, B, and C of the array of electron beam columns 101 with and without the shielding plate 160. Similarly, FIG. 2C shows the magnetic field Bz of three columns A, B, and C of the array of electron beam columns 101 with and without the shielding plate 160.

[0043] According to an embodiment of the present disclosure, the plurality of shielding plates 160 may include more than seven shielding plates. The particular number of shielding plates may depend on the available space in the array of electron beam columns 101. It may be appreciated that adding more shielding plates 160 to the inspection system 100 may further reduce the stray magnetic field.

[0044] According to another embodiment of the present disclosure, the plurality of shielding plates 160 may include four shielding plates. For example, as shown in FIG. 3 , the plurality of shielding plates may include a first shielding plate 161, a second shielding plate 162, a third shielding plate 163, and a fourth shielding plate 164. The first shielding plate 161 may be disposed proximate to the first permanent magnet array 140. The second shielding plate 162 may be disposed proximate to the second permanent magnet array 150. The third shielding plate 163 and the fourth shielding plate 164 may be disposed proximate to and opposite the detector 170. This design can reduce radial stray magnetic fields by more than 90%.

[0045] According to another embodiment of the present disclosure, the plurality of shielding plates 160 may include four shielding plates. For example, as shown in FIG. 4 , the plurality of shielding plates may include a first shielding plate 161, a second shielding plate 162, a first auxiliary shielding plate 165a, and a second auxiliary shielding plate 165b. The first shielding plate 161 may be disposed adjacent to the first permanent magnet array 140. The second shielding plate 162 may be disposed adjacent to the second permanent magnet array 150. The first auxiliary shielding plate 165a and the second auxiliary shielding plate 165b may be disposed so that the leakage magnetic field is greatest in the radial direction of the array of the electron beam 101. For example, referring to FIGS. 2A and 2B , the first auxiliary shielding plate 165a and the second auxiliary shielding plate 165b may be disposed along the Z axis where Bx and By have the largest magnitudes (positive or negative values). With this design, the radial stray field can be reduced by more than 75%. Various other optical components can be included between the first permanent magnet array 140 and the second permanent magnet array 150.

[0046] As shown in FIG. 5 , an embodiment of the present disclosure provides a method 200 for stray magnetic field mitigation. Method 200 may be applied to a multi-column inspection system including an array of electron beam columns. Each electron beam column may include an electron beam source configured to emit electrons. The electrons may be directed toward a stage. The stage may be configured to hold a target. Method 200 may include the following steps:

[0047] In step 210, electrons from each electron source may be directed through a first permanent magnet array. The first permanent magnet array may condense the electrons into an array of electron beams. The first permanent magnet array may be disposed at a first end of the array of electron beam columns. For example, the first permanent magnet array may be disposed at the top end of the electron beam columns, proximate to the electron beam sources.

[0048] In step 220, the array of electron beams may be directed through a plurality of shielding plates extending across the array of electron beam columns downstream of the first permanent magnet array. Each of the plurality of shielding plates may include a plurality of apertures. The apertures may be circular, elliptical, or polygonal. The specific size and shape of each aperture may depend on the position of the particular shielding plate within the array of electron beam columns and / or the size and shape of other components in the array of electron beam columns adjacent to the particular shielding plate. The array of electron beams may pass through the plurality of apertures. In this manner, the array of electron beams may pass through each of the plurality of shielding plates as the array of electron beams passes through the array of electron beam columns. Each shielding plate may have a thickness between 1 μm and 1 mm. For example, each shielding plate may have a thickness of at least 120 μm. In certain embodiments, each shielding plate may have a thickness of approximately 250 μm. Each shielding plate may have the same or different thicknesses. The plurality of shielding plates may be constructed of a nickel-iron alloy. For example, the shielding plates may be constructed from Carpenter 49 or Carpenter HyMu "80" alloy. Other mild steel alloys may also be used.

[0049] The inspection system of the present disclosure may include only one permanent magnet array (e.g., a first permanent magnet array), or the inspection system may include multiple permanent magnet arrays (e.g., a first permanent magnet array and a second permanent magnet array). According to an embodiment of the present disclosure in which multiple permanent magnet arrays are provided, method 200 may further include step 230. In step 230, the array of electron beams may be directed through the second permanent magnet array. The second permanent magnet array may be configured to focus the array of electron beams toward a target on the stage. The second permanent magnet array may be disposed at a second end of the array of electron beam columns, downstream of the multiple shielding plates. For example, the second permanent magnet may be disposed at a lower end of the array of electron beam columns, proximate to stage 130.

[0050] In the method 200 of the present disclosure, the multiple shielding plates can reduce the stray magnetic field in the radial direction of the electron beam array. For example, the axial direction of each electron beam column may be defined as the Z axis, and the radial direction of each electron beam column may define the X axis and the Y axis. Correspondingly, the magnetic field within each electron beam column may be defined by Bx, B y, and Bz. The magnetic fields Bx and B ym may be reduced to less than 7%. Such a reduction in the magnetic field can result in reduced beam deflection, improving beam alignment and improving the accuracy of the inspection process.

[0051] According to an embodiment of the present disclosure, step 220 may further include the following steps.

[0052] In step 221, the array of electron beams may be directed through a first shielding plate. The first shielding plate may be located proximate to the first permanent magnet array. For example, the first shielding plate may be located downstream of the first permanent magnet array and at a first end of the array of electron beam columns.

[0053] In step 229, the array of electron beams may be directed through a second shielding plate. The second shielding plate may be positioned proximate to the second permanent magnet array. For example, the second shielding plate may be positioned upstream of the second permanent magnet array and at a second end of the array of electron beam columns.

[0054] According to an embodiment of the present disclosure, the method 200 may further include step 224. In step 224, the array of electron beams may be directed through a detector. The detector may be disposed between the first permanent magnet array and the second permanent magnet array. The detector may be configured to detect backscattered electrons reflected from the target.

[0055] According to an embodiment of the present disclosure, step 220 may further include step 223. In step 223, the array of electron beams may be directed through a third shielding plate. The third shielding plate may be located proximate to the detector. For example, the third shielding plate may be located upstream of the detector or downstream of the detector.

[0056] According to an embodiment of the present disclosure, step 220 may further include step 225. In step 225, the array of electron beams may be directed through a fourth shielding plate. The fourth shielding plate may be positioned adjacent to the detector on the opposite side of the third shielding plate. For example, the third shielding plate may be positioned upstream of the detector, and the fourth shielding plate may be positioned downstream of the detector. Alternatively, the third shielding plate may be positioned downstream of the detector, and the fourth shielding plate may be positioned upstream of the detector. In both configurations, the third shielding plate and the fourth shielding plate may be positioned on either side of the detector.

[0057] According to an embodiment of the present disclosure, step 220 may further include step 226. In step 226, the array of electron beams may be directed through at least one auxiliary shielding plate. The at least one auxiliary shielding plate may be disposed between the first shielding plate and the second shielding plate.

[0058] According to an embodiment of the present disclosure, the plurality of shielding plates may include seven shielding plates. For example, the plurality of shielding plates may include a first shielding plate, a second shielding plate, a third shielding plate, a fourth shielding plate, and three auxiliary shielding plates. The first shielding plate may be disposed proximate to the first permanent magnet array. The second shielding plate may be disposed proximate to the second permanent magnet array. The third shielding plate and the fourth shielding plate may be disposed proximate to the detector and on both sides of the detector. The first auxiliary shielding plate may be disposed between the first shielding plate and the third shielding plate. The second auxiliary shielding plate may be disposed between the fourth shielding plate and the second shielding plate. The third auxiliary shielding plate may be disposed between the second auxiliary shielding plate and the second shielding plate. 6, the method 201 may be performed in the following ordered steps: step 210, step 221, step 223, step 224, step 225, step 226, step 229, and step 230. With this design, the radial stray field may be reduced by more than 92%.

[0059] According to an embodiment of the present disclosure, the plurality of shielding plates may include four shielding plates. For example, the plurality of shielding plates may include a first shielding plate, a second shielding plate, a third shielding plate, and a fourth shielding plate. The first shielding plate may be disposed proximate to the first permanent magnet. The second shielding plate may be disposed proximate to the second permanent magnet. The third shielding plate may be disposed proximate to the detector. Thus, as shown in FIG. 7 , method 202 may be performed in the following ordered steps: step 210, step 221, step 223, step 224, step 225, step 229, and step 230. This design can reduce radial stray magnetic fields by more than 90%.

[0060] According to an embodiment of the present disclosure, the plurality of shielding plates may include four shielding plates. For example, the plurality of shielding plates may include a first shielding plate, a second shielding plate, a first auxiliary shielding plate, and a second auxiliary shielding plate. The first shielding plate may be disposed adjacent to the first permanent magnet. The second shielding plate may be disposed adjacent to the second permanent magnet. The first auxiliary shielding plate 165a and the second auxiliary shielding plate 165b may be disposed so that the stray magnetic field is greatest in the radial direction of the array of electron beams 101. For example, see FIGS. 2A and 2B. The first auxiliary shielding plate 165a and the second auxiliary shielding plate 165b may be disposed along the Z-axis where Bx and By are greatest (positive or negative values). Therefore, method 203 may be performed in the following ordered steps, as shown in FIG. 8: step 210, step 221, step 226, step 229, and step 230. With this design, the radial stray field can be reduced by more than 75%.

[0061] 9 is a block diagram of an embodiment of a system 300. The system 300 includes a wafer inspection tool (including an electron column 301) configured to generate an image of a wafer 304.

[0062] The wafer or mask inspection tool includes an output acquisition subsystem including at least an energy source and a detector. The output acquisition subsystem may be an electron beam-based output acquisition subsystem. For example, in one embodiment, the energy directed at the wafer 304 includes electrons, and the energy detected from the wafer 304 includes electrons. In this manner, the energy source may be an electron beam source. In one such embodiment shown in FIG. 9, the output acquisition subsystem includes an electron column 301 coupled to a computer subsystem 302. A stage 310 may hold the wafer 304.

[0063] As also shown in FIG. 9, electron column 301 includes an electron beam source 303 configured to generate electrons that are focused onto wafer 304 by one or more elements 305 . The electron beam source 303 may include, for example, a cathode source or an emitter tip. The one or more elements 305 may include, for example, a gun lens, an anode, a beam limiting aperture, a gate valve, a beam current selection aperture, an objective lens, and a scanning subsystem, all of which may include any such suitable elements known in the art. The one or more elements 305 may further include a plurality of shielding plates 160, which may reduce stray magnetic fields within the electron column 301.

[0064] Electrons returning from wafer 304 (e.g., secondary electrons) may be focused onto detector 307 by one or more elements 306. One or more elements 306 may include a scanning subsystem, which may be, for example, the same scanning subsystem included in element 305.

[0065] Electron train 301 may also include any other suitable elements known in the art.

[0066] 9 as being configured such that electrons are directed at wafer 304 at an oblique angle of incidence and scattered from wafer 304 at another oblique angle, the electron beam may be directed at and scattered from wafer 304 at any suitable angle. Additionally, the electron beam-based output acquisition subsystem may be configured to use multiple modes to generate images of wafer 304 (e.g., with different illumination angles, collection angles, etc.). The multiple modes of the electron beam-based output acquisition subsystem may differ in any image-generating parameter of the output acquisition subsystem.

[0067] The computer subsystem 302 may be coupled to the detector 307 as described above. The detector 307 may detect electrons returning from the surface of the wafer 304, thereby forming an electron beam image of the wafer 304. The electron beam image may include any suitable electron beam image. The computer subsystem 302 may be configured to perform any of the functions described herein using the output of the detector 307 and / or the electron beam image. The computer subsystem 302 may be configured to perform any additional steps described herein. The system 300 including the output acquisition subsystem shown in FIG. 9 may be further configured as described herein.

[0068] It should be noted that FIG. 9 is provided herein to schematically illustrate an electron beam-based power acquisition subsystem configuration that may be used in the embodiments described herein. The electron beam-based power acquisition subsystem configuration described herein may be modified to optimize the performance of the power acquisition subsystem, as is typically done when designing commercial power acquisition systems. In addition, the systems described herein may be implemented using existing systems (e.g., by adding the functionality described herein to the existing system). For some such systems, the methods described herein may be provided as optional functionality of the system (e.g., in addition to other functions of the system). Alternatively, the systems described herein may be designed as entirely new systems.

[0069] Although the output acquisition subsystem is described above as an electron beam-based output acquisition subsystem, the output acquisition subsystem may also be an ion beam-based output acquisition subsystem. Such an output acquisition subsystem may be configured as shown in FIG. 9, except that the electron beam source may be replaced with any suitable ion beam source known in the art. In addition, the output acquisition subsystem may be any other suitable ion beam-based output acquisition subsystem, such as those included in commercially available focused ion beam (FIB) systems, helium ion microscope (HIM) systems, and secondary ion mass spectrometry (SIMS) systems.

[0070] The computer subsystem 302 includes a processor 308 and an electronic data storage unit 309. The processor 308 may include a microprocessor, microcontroller, or other device.

[0071] Computer subsystem 302 may be coupled to the components of system 300 in any suitable manner (e.g., via one or more transmission media, which may include wired and / or wireless transmission media) such that processor 308 can receive the output. Processor 308 may be configured to perform several functions using the output. A wafer inspection tool may receive instructions or other information from processor 308. Processor 308 and / or electronic data storage unit 309 may optionally be in electronic communication with another wafer inspection tool, wafer metrology tool, or wafer review tool (not shown) to receive additional information or send instructions.

[0072] The processor 308 is in electronic communication with a wafer inspection tool, such as the detector 307. The processor 308 may be configured to process images generated using measurements from the detector 307. For example, the processor may perform an embodiment of the method 200.

[0073] The computer subsystem 302, other systems, or other subsystems described herein may be part of a variety of systems, including a personal computer system, an image computer, a mainframe computer system, a workstation, a network appliance, an Internet appliance, or other devices. The subsystem or system may include any suitable processor known in the art, such as a parallel processor. Additionally, the subsystem or system may include a platform with high-speed processing and software, either as a standalone tool or a network tool.

[0074] The processor 308 and electronic data storage unit 309 may be located within or otherwise part of the system 300 or another device. In one example, the processor 308 and electronic data storage unit 309 may be part of a stand-alone control unit or may be a centralized quality control unit. Multiple processors 308 or electronic data storage units 309 may be used.

[0075] The processor 308 may actually be implemented by any combination of hardware, software, and firmware. Also, its functions as described herein may be performed by one unit or divided among different components, each of which may in turn be implemented by any combination of hardware, software, and firmware. Program codes or instructions for the processor 308 to implement the various methods and functions may be stored in a readable storage medium, such as memory in the electronic data storage unit 309 or other memory.

[0076] Where system 300 includes multiple computer subsystems 302, the different subsystems may be coupled to one another such that images, data, information, instructions, etc. may be transmitted between the subsystems. For example, one subsystem may be coupled to additional subsystems by any suitable transmission medium, which may include any suitable wired and / or wireless transmission medium known in the art. Two or more of such subsystems may also be effectively coupled by a shared computer-readable storage medium (not shown).

[0077] The processor 308 may be configured to perform some function using the output of the system 300 or other outputs. For example, the processor 308 may be configured to send the output to an electronic data storage unit 309 or another storage medium. The processor 308 may be further configured as described herein.

[0078] Processor 308 or computer subsystem 302 may be part of a defect review system, an inspection system, a metrology system, or some other type of system. Accordingly, the embodiments disclosed herein describe several configurations that can be tailored in several ways for systems with different capabilities that are more or less suitable for different applications.

[0079] Processor 308 may be configured according to any of the embodiments described herein. Processor 308 may also be configured to perform other functions or additional steps using the output of system 300 or using images or data from other sources.

[0080] Processor 308 may be communicatively coupled to any of the various components or subsystems of system 300 in any manner known in the art. Additionally, processor 308 may be configured to receive and / or acquire data or information from other systems (e.g., inspection results from an inspection system such as a review tool, a remote database containing design data, etc.) via a transmission medium, which may include wired and / or wireless portions. In this manner, the transmission medium may serve as a data link between processor 308 and other subsystems of system 300 or systems external to system 300.

[0081] The various steps, functions, and / or operations of the system 300 and methods disclosed herein may be performed by one or more of the following: electronic circuits, logic gates, multiplexers, programmable logic devices, ASICs, analog or digital controls / switches, microcontrollers, or computing systems. Program instructions implementing methods such as those described herein may be transmitted over or stored on a carrier medium. The carrier medium may include a storage medium such as a read-only memory, a random-access memory, a magnetic or optical disk, a non-volatile memory, a solid-state memory, or a magnetic tape. The carrier medium may include a transmission medium such as a wire, a cable, or a wireless transmission link. For example, the various steps described throughout this disclosure may be accomplished by a single processor 308 (or computer subsystem 302) or, alternatively, by multiple processors 308 (or multiple computer subsystems 302). Furthermore, different subsystems of the system 300 may include one or more computing or logic systems. Therefore, the above description should not be construed as a limitation on the present disclosure, but merely as illustrative.

[0082] In one example, electron beam column 101 is incorporated into electron column 301 or is incorporated into system 300. Various components of system 300 may be replicated or otherwise adapted to use with the electron beam column.

[0083] Although the present disclosure has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present disclosure may be made without departing from the scope of the present disclosure.

Claims

1. 1. An inspection system comprising: an array of electron beams, each including an electron source configured to emit electrons toward the stage; a first permanent magnet array configured to focus electrons from each of the electron sources into an array of electron beams, the first permanent magnet array being positioned at a first end of the array of electron beams; a plurality of shielding plates extending across the array of electron beams downstream of the first permanent magnet array in a direction of electron emission, each of the shielding plates including a plurality of apertures and having a thickness of 1 μm to 1 mm, the array of electron beams passing through the plurality of apertures; an electron beam array configured to focus the electron beam array toward a target on the stage and a second permanent magnet array positioned at a second end of the electron beam array, wherein the plurality of shielding plates include a first shielding plate positioned proximate to the first permanent magnet array and a second shielding plate positioned proximate to the second permanent magnet array, and the plurality of shielding plates reduce a radial leakage magnetic field of the electron beam array.

2. a detector configured to detect electrons reflected from the target and disposed between the first permanent magnet array and the second permanent magnet array; Furthermore, The plurality of shielding plates include: a third shielding plate disposed adjacent to the detector; The inspection system of claim 1 further comprising:

3. The plurality of shielding plates include: a fourth shielding plate disposed adjacent to the detector on the opposite side of the third shielding plate; The inspection system of claim 2 further comprising:

4. The plurality of shielding plates include: at least one auxiliary shielding plate disposed between the first shielding plate and the second shielding plate; The inspection system of claim 3 further comprising:

5. The inspection system of claim 1 , wherein the plurality of shielding plates includes at least seven shielding plates.

6. 2. The inspection system according to claim 1, wherein at least one of the plurality of shielding plates is disposed at a position where the stray magnetic field is greatest in a radial direction of the array of electron beams.

7. 2. The inspection system of claim 1, wherein each of the plurality of shielding plates has a thickness of at least 120 [mu]m.

8. 2. The inspection system of claim 1, wherein the plurality of shielding plates are made of a magnetic nickel-iron alloy.

9. 1. A method of stray magnetic field mitigation applied to a multi-row inspection system including an array of electron beams, each electron beam comprising an electron beam source configured to emit electrons toward a stage, the method comprising: focusing the electrons from each electron source into an array of electron beams by passing the electrons through a first permanent magnet array, the first permanent magnet array being positioned at a first end of the array of electron beams; directing the array of electron beams through a plurality of shielding plates extending across the array of electron beams downstream of the first permanent magnet array; Equipped with each of the plurality of shielding plates includes a plurality of apertures and has a thickness of 1 μm to 1 mm, the array of electron beams passes through the plurality of apertures; and focusing the array of electron beams toward a target on the stage through a second permanent magnet array, the second permanent magnet array being disposed downstream of the plurality of shielding plates at a second end of the array of electron beams; passing the array of electron beams through a first shielding plate positioned proximate to the first permanent magnet array; passing the array of electron beams through a second shielding plate positioned proximate to the second permanent magnet array; Equipped with the plurality of shielding plates reduce a radial stray magnetic field of the electron beam array; method.

10. directing the array of electron beams through a detector configured to detect electrons reflected from the target, the detector being positioned between the first permanent magnet array and the second permanent magnet array; Furthermore, directing the array of electron beams through the plurality of shielding plates comprises: passing the array of electron beams through a third shielding plate positioned proximate to the detector; The method of claim 9 further comprising:

11. passing the array of electron beams through the plurality of shielding plates includes: passing the array of electron beams through a fourth shielding plate positioned opposite the third shielding plate and adjacent to the detector; The method of claim 10 further comprising:

12. passing the array of electron beams through the plurality of shielding plates includes: passing the array of electron beams through at least one auxiliary shielding plate disposed between the first shielding plate and the second shielding plate; The method of claim 11 further comprising:

13. The method of claim 9 , wherein the plurality of shielding plates comprises at least seven shielding plates.

14. 10. The method of claim 9, wherein at least one of the plurality of shielding plates is disposed where the stray magnetic field is greatest in the radial direction of the electron beam array.

15. 10. The method of claim 9, wherein each of the plurality of shielding plates has a thickness of at least 120 μm.

16. The method of claim 9, wherein the plurality of shielding plates are made of a magnetic nickel-iron alloy.

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