Shielding strategies for mitigating stray fields in permanent magnet arrays

Abstract

The present disclosure provides an inspection system and a method for stray field mitigation. The system includes an electron beam column array, a first permanent magnet array, and a plurality of shielding plates. The electron beam column arrays each include an electron source configured to emit electrons toward a stage. The first permanent magnet array is configured to converge the electrons from each electron source into an electron beam array. The first permanent magnet array is arranged at a first end of the electron beam column array. The plurality of shielding plates extend across the electron beam column array in the direction of electron emission downstream of the first permanent magnet array. The electron beam array passes through a plurality of apertures in each of the plurality of shielding plates, which reduces the stray magnetic field in the radial direction of the electron beam array.

Description

Technical Field

[0001] The present disclosure relates to inspection systems, and more particularly to inspection systems utilizing an electron beam and a permanent magnet array. Background Art

[0002] The evolution of the semiconductor manufacturing industry places increasing demands on yield management and specifically on metrology and inspection systems. Critical dimensions continue to shrink, but the industry needs to reduce the time to reach high-yield, high-value production. Minimizing the total time from detecting a yield problem to resolving it determines the return on investment for semiconductor manufacturers.

[0003] The manufacture of semiconductor devices, such as logic and memory devices, typically includes processing a semiconductor wafer or EUV mask using a number of manufacturing processes to form various features and multiple levels of the semiconductor device. For example, photolithography is a semiconductor manufacturing process that involves transferring a pattern from a retracted mask to a photoresist disposed on a semiconductor wafer. Additional examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices may be manufactured as one arrangement on a single semiconductor wafer that is separated into individual semiconductor devices.

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

[0005] One device used for inspection processes is a multi-column system. In a multi-column system, hundreds of beamlets are generated and focused onto a target. Each beamlet is guided through an optical column that includes upper and lower permanent magnets. However, the permanent magnets generate stray fields that cause beam deflection. Beam deflection results in poor beam alignment and reduces the accuracy of the inspection process.

[0006] Therefore, there is a need for a method for mitigating stray fields in a multi-beam system. Summary of the invention

[0007] 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 converge electrons from each electron source into an electron beam array. The first permanent magnet array is arranged at a first end of the electron beam column array. The inspection system further includes a plurality of shielding plates extending across the electron beam column array in the direction of electron emission downstream of the first permanent magnet array. Each of the plurality of shielding plates includes a plurality of apertures and has a thickness between 1 μm and 1 mm, and the electron beam array passes through the plurality of apertures. The plurality of shielding plates reduce stray magnetic fields in the radial direction of the electron beam array.

[0008] According to an embodiment of the present disclosure, the inspection system may further include a second permanent magnet array configured to focus the electron beam array toward a target on the stage. The second permanent magnet array is arranged at a second end of the electron beam column array.

[0009] According to an embodiment of the present disclosure, the plurality of shielding plates include a first shielding plate arranged close to the first permanent magnet array, and a second shielding plate arranged close to the second permanent magnet array.

[0010] 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 is arranged between the first permanent magnet array and the second permanent magnet array. The plurality of shielding plates further includes a third shielding plate arranged close to the detector.

[0011] According to an embodiment of the present disclosure, the plurality of shielding plates further include a fourth shielding plate close to the detector and arranged opposite to the third shielding plate.

[0012] According to an embodiment of the present disclosure, the plurality of shielding plates further include at least one supplementary shielding plate arranged between the first shielding plate and the second shielding plate.

[0013] According to an embodiment of the present disclosure, the plurality of shielding plates includes at least seven shielding plates.

[0014] According to an embodiment of the present disclosure, at least one of the plurality of shielding plates is arranged where the stray magnetic field is at a highest magnitude in the radial direction of the electron beam array.

[0015] According to an embodiment of the present disclosure, the thickness of each of the plurality of shielding plates is at least 120 μm.

[0016] According to an embodiment of the present disclosure, the plurality of shielding plates are made of a magnetic nickel-iron alloy.

[0017] Embodiments of the present disclosure provide a method for stray field mitigation applied to a multi-column inspection system. The inspection system includes an electron beam column array, each electron beam column including an electron beam source configured to emit electrons toward a stage. The method includes guiding electrons from each electron source through a first permanent magnet array to converge the electrons into an electron beam array. The first permanent magnet array is arranged at a first end of the electron beam column array. The method further includes guiding the electron beam array through a plurality of shielding plates extending across the electron beam column array downstream of the first permanent magnet array. The plurality of shielding plates each include a plurality of apertures and have a thickness between 1 μm and 1 mm, and the electron beam array passes through the plurality of apertures. The plurality of shielding plates reduce the stray magnetic field in the radial direction of the electron beam array.

[0018] According to an embodiment of the present disclosure, the method further comprises directing the electron beam array through a second permanent magnet array to focus the electron beam array toward a target on the stage. The second permanent magnet array is arranged at a second end of the electron beam column array, downstream of the plurality of shielding plates.

[0019] According to an embodiment of the present disclosure, guiding the electron beam array through a plurality of shielding plates includes: guiding the electron beam array through a first shielding plate arranged close to the first permanent magnet array, and guiding the electron beam array through a second shielding plate arranged close to the second permanent magnet array.

[0020] According to an embodiment of the present disclosure, the method further includes directing the electron beam array through a detector configured to detect electrons reflected from the target. The detector is arranged between the first permanent magnet array and the second permanent magnet array. Directing the electron beam array through a plurality of shielding plates further includes directing the electron beam array through a third shielding plate arranged near the detector.

[0021] According to an embodiment of the present disclosure, directing the electron beam array through a plurality of shielding plates further includes: directing the electron beam array through a fourth shielding plate disposed near the detector and opposite to the third shielding plate.

[0022] According to an embodiment of the present disclosure, directing the electron beam array through a plurality of shielding plates further includes: directing the electron beam array through at least one supplementary shielding plate disposed between the first shielding plate and the second shielding plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] For a more complete 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, wherein:

[0024] Figure 1A is a schematic diagram of an inspection system of the present disclosure;

[0025] Figure 1B is a schematic diagram of an electron beam column of the present disclosure;

[0026] Figure 1C is a top view of a shielding plate according to an embodiment of the present disclosure;

[0027] Figure 2A is the stray magnetic field B according to the embodiment of the present disclosure x A graphical illustration of the reduction in

[0028] Figure 2B is the stray magnetic field B according to the embodiment of the present disclosure y A graphical illustration of the reduction in

[0029] Figure 2C is a magnetic field B parallel to the electron beam optical axis according to an embodiment of the present disclosure. z Graphical illustration of the impact of

[0030] Figure 3 is a schematic diagram of an electron beam column according to an embodiment of the present disclosure;

[0031] Figure 4 is a schematic diagram of an electron beam column according to another embodiment of the present disclosure;

[0032] Figure 5 is a block diagram of the method of the present disclosure;

[0033] Figure 6 is a block diagram of a method according to an embodiment of the present disclosure;

[0034] Figure 7 is a block diagram of a method according to another embodiment of the present disclosure;

[0035] Figure 8 is a block diagram of a method according to another embodiment of the present disclosure; and

[0036] Fig. 9 is a schematic diagram of a system according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0037] Although the claimed subject matter will be described in terms of specific embodiments, other embodiments (including embodiments that do not provide all of the advantages and features set forth herein) are also within the scope of the present disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the present disclosure. Accordingly, the scope of the present disclosure is defined solely by reference to the appended claims.

[0038] like Figure 1AAs shown in , an embodiment of the present disclosure provides a multi-column 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. Figure 1A 1. Seven electron beam columns 101 are illustrated in FIG. 1, but the specific size and number of electron beam columns 101 in the array may vary depending on the application. The electron beam columns 101 in the array may also extend into or out of the page. The electron beam columns 101 may be held by a support structure 102.

[0039] like Figure 1B , each electron beam column 101 of 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 multiple electron beams arranged in an array. A single electron beam source 110 may be used for all 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 retracted mask.

[0040] The inspection system 100 may further include a first permanent magnet array 140. The first permanent magnet array 140 may be configured to focus electrons from each electron source 110 into the electron beam array 120. The first permanent magnet array 140 may be disposed at a first end 121 of the electron beam column 101 array. For example, the first permanent magnet array 140 may be disposed at an upper end of the electron beam column 101 array close to the electron beam source 110.

[0041] 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 electron beam array 120 toward a target. The second permanent magnet array 150 may be disposed at the second end 122 of the electron beam column 101 array. For example, the second permanent magnet array 150 may be disposed at the lower end of the electron beam column 101 array near the stage 130.

[0042] According to an embodiment of the present disclosure, the inspection system 100 may include only one permanent magnet array (e.g., the first permanent magnet array 140). According to another embodiment of the present disclosure, the inspection system 100 may include more than one permanent magnet array (e.g., the first permanent magnet array 140 and the second permanent magnet array 150).

[0043] According to an embodiment of the present disclosure, the support structure 102 can hold the permanent magnet array 140 and the second permanent magnet array 150 .

[0044] 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 .

[0045] The inspection system 100 may further include a plurality of shielding plates 160. The plurality of 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. Figure 1A Only one shielding plate 160 is described in the figure (for ease of description), but multiple shielding plates 160 may be disposed between the first permanent magnet array 140 and the second permanent magnet array 150. Figure 1C , the plurality of shielding plates 160 may each include a plurality of apertures 160a. Each aperture 160a may be circular, elliptical, or polygonal. The specific size and shape of each aperture 160a may depend on the location of the particular shielding plate 160 within each of the electron beam columns 101, the size of the electron beam, and / or the size and shape of other components within the inspection system 100 adjacent to the particular shielding plate. The plurality of apertures 160a may be arranged in a regular pattern corresponding to the XY arrangement of the array of electron beam columns 101. Although Figure 1C , but the number and arrangement of the apertures 160a depends on the number and arrangement of the electron beam columns 101 in the array. The electron beam array 120 may pass through multiple apertures 160a. In this way, when the electron beam array 120 travels through each electron beam column 101 toward the stage 130, the electron beam array 120 may pass through each of the multiple shielding plates 160. Each shielding plate 160 may have a thickness between 1 μm and 1 mm. For example, each shielding plate 160 may have a thickness of at least 125 μm. In a specific embodiment, the thickness may be about 250 μm. Multiple shielding plates 160 may have the same or different thicknesses. Multiple shielding plates 160 may include nickel-iron alloys. Nickel-iron alloys may be magnetic. For example, multiple shielding plates 160 may include Carpenter 49 or Carpenter HyMu "80" alloys. Other soft iron alloys may also be used.

[0046] According to an embodiment of the present disclosure, the support structure 102 may hold a plurality of shielding plates 160. The plurality of shielding plates 160 may be secured to various components within the electron beam column 101 array. For example, the plurality of shielding plates 160 may include mounting holes configured to receive fasteners to secure the plurality of shielding plates 160 to the support structure 102 and / or components within the electron beam column 101 array. The plurality of shielding plates 160 may be evenly spaced within the electron beam column 101 array.

[0047] Using the electron beam column 101 of the present disclosure, the plurality of shielding plates 160 can reduce the stray magnetic field in the radial direction of the electron beam array 120. For example, the axial direction of each electron beam column 101 can define the Z axis, and the X axis and the Y axis can be defined by the radial direction of each electron beam column 101. Correspondingly, the magnetic field in each electron beam column 101 can be defined by B x , B yand B z Definition. Magnetic field B x and B y This magnetic field reduction can result in reduced beam deflection, which improves beam alignment, facilitates multi-column setups and improves the accuracy of the inspection process.

[0048] 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 arranged close to the first permanent magnet array 140. For example, the first shielding plate 161 may be arranged at the first end 121 of the electron beam column 101 array, downstream of the first permanent magnet array 140.

[0049] 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 arranged close to the second permanent magnet array 150. For example, the second shielding plate 162 may be arranged at the second end 122 of the electron beam column 101 array, upstream of the second permanent magnet array 150.

[0050] According to an embodiment of the present disclosure, the electron beam column 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 arranged between the first permanent magnet array 140 and the second permanent magnet array 150 .

[0051] 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 arranged close to the detector 170. For example, the third shielding plate 163 may be arranged upstream of the detector 170 or downstream of the detector 170.

[0052] 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 arranged near the detector 170 and opposite to the third shielding plate 163. For example, the third shielding plate 163 may be arranged upstream of the detector 170, and the fourth shielding plate 164 may be arranged downstream of the detector 170. Alternatively, the third shielding plate 163 may be arranged downstream of the detector 170, and the fourth shielding plate 164 may be arranged upstream of the detector 170. In both configurations, the third shielding plate 163 and the fourth shielding plate 164 may be arranged on opposite sides of the detector 170.

[0053] According to an embodiment of the present disclosure, the plurality of shielding plates 160 may further include at least one supplementary shielding plate 165 (including supplementary shielding plates 165a, 165b, and 165c). At least one supplementary shielding plate 165 (including supplementary shielding plates 165a, 165b, and 165c) may be arranged between the first shielding plate 161 and the second shielding plate 162.

[0054] According to an embodiment of the present disclosure, the plurality of shielding plates 160 may include seven shielding plates. Figure 1B As shown in , 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 supplementary shielding plates 165a, 165b and 165c. The first shielding plate 161 may be arranged close to the first permanent magnet array 140. The second shielding plate may be arranged close to the second permanent magnet array 150. The third shielding plate 163 and the fourth shielding plate 164 may be arranged close to the detector 170 and on opposite sides of the detector 170. The first supplementary shielding plate 165a may be arranged between the first shielding plate 161 and the third shielding plate 163. The second supplementary shielding plate 165b may be arranged between the fourth shielding plate 164 and the second shielding plate 162. The third supplementary shielding plate 165c may be arranged between the second supplementary shielding plate 165b and the second shielding plate 162. According to this design, the stray magnetic field in the radial direction may be reduced by more than 92%. For example, Figure 2A and Figure 2B The stray magnetic field B of the three columns A, B, and C of the electron beam column 101 array with and without the shielding plate 160 is shown in FIG. x and B y Similarly, Figure 2C The magnetic field B of the three columns A, B, and C of the electron beam column 101 array with and without the shielding plate 160 is shown in FIG. z .

[0055] According to an embodiment of the present disclosure, the plurality of shielding plates 160 may include more than seven shielding plates. The specific number of shielding plates may depend on the available space within the array of electron beam columns 101. It can be appreciated that adding more shielding plates 160 to the inspection system 100 may further reduce stray magnetic fields.

[0056] According to another embodiment of the present disclosure, the plurality of shielding plates 160 may include four shielding plates. Figure 3 As shown in FIG. 1 , 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 arranged close to the first permanent magnet array 140. The second shielding plate 162 may be arranged close to the second permanent magnet array 150. The third shielding plate 163 and the fourth shielding plate 164 may be arranged close to the detector 170 and on opposite sides of the detector 170. According to this design, the stray magnetic field in the radial direction may be reduced by more than 90%.

[0057] According to another embodiment of the present disclosure, the plurality of shielding plates 160 may include four shielding plates. Figure 4As shown in FIG. 1 , the plurality of shielding plates may include a first shielding plate 161, a second shielding plate 162, a first supplementary shielding plate 165a, and a second supplementary shielding plate 165b. The first shielding plate 161 may be arranged close to the first permanent magnet array 140. The second shielding plate 162 may be arranged close to the second permanent magnet array 150. The first supplementary shielding plate 165a and the second supplementary shielding plate 165b may be arranged where the stray magnetic field is at the highest magnitude in the radial direction of the electron beam array 120. For example, referring to Figure 2A and 2B The first supplementary shielding plate 165a and the second supplementary shielding plate 165b may be arranged along the Z axis at B x and B y At the highest magnitude (positive or negative). According to this design, the stray magnetic field in the radial direction 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.

[0058] like Figure 5 As shown in , an embodiment of the present disclosure provides a stray field mitigation method 200. The 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. The method 200 may include the following steps.

[0059] At step 210, electrons from each electron source may be directed through a first permanent magnet array. The first permanent magnet array may focus the electrons into an electron beam array. The first permanent magnet array may be disposed at a first end of the electron beam column array. For example, the first permanent magnet array may be disposed at an upper end of the electron beam column, near the electron beam source.

[0060] In step 220, the electron beam array may be directed through a plurality of shielding plates extending across the electron beam column array downstream of the first permanent magnet array. The plurality of shielding plates may each include a plurality of apertures. The plurality of 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 electron beam column array and / or the size and shape of other components adjacent to the particular shielding plate within the electron beam column array. The electron beam array may pass through the plurality of apertures. In this way, the electron beam array may pass through each of the plurality of shielding plates as the electron beam array travels through the electron beam column array. 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 a particular embodiment, 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 include a nickel-iron alloy. For example, the plurality of shielding plates may include Carpenter 49 or Carpenter HyMu "80" alloy. Other soft iron alloys may also be used.

[0061] 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 more than one permanent magnet array (e.g., a first permanent magnet array and a second permanent magnet array). According to embodiments of the present disclosure in which more than one permanent magnet array is provided, method 200 may further include step 230. At step 230, the electron beam array may be directed through the second permanent magnet array. The second permanent magnet array may be configured to focus the electron beam array toward a target on the stage. The second permanent magnet array may be disposed at a second end of the electron beam column array, downstream of the plurality of shielding plates. For example, the second permanent magnet may be disposed at a lower end of the electron beam column array near stage 130.

[0062] Using the method 200 of the present disclosure, a plurality of 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 can define the Z axis, and the X axis and the Y axis can be defined by the radial direction of each electron beam column. Correspondingly, the magnetic field in each electron beam column can be defined by B x , B y and B z Definition. Magnetic field B x and B y This magnetic field reduction can result in reduced beam deflection, which improves beam alignment and improves the accuracy of the inspection process.

[0063] According to an embodiment of the present disclosure, step 220 may further include the following steps.

[0064] At step 221, the electron beam array may be directed through a first shielding plate. The first shielding plate may be arranged near the first permanent magnet array. For example, the first shielding plate may be arranged at a first end of the electron beam column array, downstream of the first permanent magnet array.

[0065] At step 229, the electron beam array may be directed through a second shielding plate. The second shielding plate may be arranged near the second permanent magnet array. For example, the second shielding plate may be arranged at the second end of the electron beam column array, upstream of the second permanent magnet array.

[0066] According to an embodiment of the present disclosure, method 200 may further include step 224. At step 224, the electron beam array 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 off the target.

[0067] According to an embodiment of the present disclosure, step 220 may further include step 223. In step 223, the electron beam array may be guided through a third shielding plate. The third shielding plate may be arranged close to the detector. For example, the third shielding plate may be arranged upstream of the detector or downstream of the detector.

[0068] According to an embodiment of the present disclosure, step 220 may further include step 225. In step 225, the electron beam array may be directed through a fourth shielding plate. The fourth shielding plate may be arranged near the detector and opposite to the third shielding plate. For example, the third shielding plate may be arranged upstream of the detector, and the fourth shielding plate may be arranged downstream of the detector. Alternatively, the third shielding plate may be arranged downstream of the detector, and the fourth shielding plate may be arranged upstream of the detector. In both configurations, the third shielding plate and the fourth shielding plate may be arranged on opposite sides of the detector.

[0069] According to an embodiment of the present disclosure, step 220 may further include step 226. In step 226, the electron beam array may be directed through at least one supplementary shielding plate. The at least one supplementary shielding plate may be arranged between the first shielding plate and the second shielding plate.

[0070] 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 supplementary shielding plates. The first shielding plate may be arranged close to the first permanent magnet array. The second shielding plate may be arranged close to the second permanent magnet array. The third shielding plate and the fourth shielding plate may be arranged close to the detector and on opposite sides of the detector. The first supplementary shielding plate may be arranged between the first shielding plate and the third shielding plate. The second supplementary shielding plate may be arranged between the fourth shielding plate and the second shielding plate. The third supplementary shielding plate may be arranged between the second supplementary shielding plate and the second shielding plate. Therefore, method 201 may be performed in the following sequential steps, as Figure 6 : step 210, step 221, step 223, step 224, step 225, step 226, step 229 and step 230. According to this design, the stray magnetic field in the radial direction can be reduced by more than 92%.

[0071] 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 arranged close to the first permanent magnet. The second shielding plate may be arranged close to the second permanent magnet. The third shielding plate may be arranged close to the detector. Therefore, the method 202 may be performed in the following sequential steps, such as Figure 7 : step 210, step 221, step 223, step 224, step 225, step 229 and step 230. According to this design, the stray magnetic field in the radial direction can be reduced by more than 90%.

[0072] 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 supplementary shielding plate, and a second supplementary shielding plate. The first shielding plate may be arranged close to the first permanent magnet. The second shielding plate may be arranged close to the second permanent magnet. The first supplementary shielding plate 165a and the second supplementary shielding plate 165b may be arranged where the stray magnetic field is at the highest magnitude in the radial direction of the electron beam array 120. For example, referring to Figure 2A and 2B The first supplementary shielding plate 165a and the second supplementary shielding plate 165b may be arranged along the Z axis at B x and B y At the highest value (positive or negative). Therefore, method 203 can be performed in the following sequential steps, such as Figure 8 : step 210, step 221, step 226, step 229 and step 230. According to this design, the stray magnetic field in the radial direction can be reduced by more than 75%.

[0073] Fig. 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.

[0074] The wafer or mask inspection tool includes an output acquisition subsystem that includes at least one energy source and a detector. The output acquisition subsystem can be an electron beam based output acquisition subsystem. For example, in one embodiment, the energy directed to the wafer 304 includes electrons, and the energy detected from the wafer 304 includes electrons. In this manner, the energy source can be an electron beam source. Fig. 9 In one such embodiment shown in , the output acquisition subsystem includes an electron column 301 coupled to a computer subsystem 302. A stage 310 may hold a wafer 304.

[0075] Another example Fig. 9 , the electron column 301 includes an electron beam source 303 configured to generate electrons that are focused to a wafer 304 by one or more elements 305. The electron beam source 303 may include, for example, a cathode source or 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 that may reduce stray magnetic fields in the electron column 301.

[0076] Electrons returning from wafer 304 (eg, secondary electrons) may be focused by one or more elements 306 onto detector 307. One or more elements 306 may include, for example, a scanning subsystem, which may be the same scanning subsystem included in element 305.

[0077] The electron column 301 may also include any other suitable elements known in the art.

[0078] although Fig. 9 301 is shown as being configured so that electrons are directed to wafer 304 at an oblique angle of incidence and scattered from wafer 304 at another oblique angle, but the electron beam may be directed to wafer 304 and scattered from wafer 304 at any suitable angle. In addition, the electron beam-based output acquisition subsystem may be configured to use multiple modes to generate images of wafer 304 (e.g., employing different illumination angles, collection angles, etc.). The multiple modes of the electron beam-based output acquisition subsystem may differ in any image generation parameters of the output acquisition subsystem.

[0079] Computer subsystem 302 may be coupled to detector 307 as described above. Detector 307 may detect electrons returning from the surface of wafer 304, thereby forming an electron beam image of wafer 304. The electron beam image may include any suitable electron beam image. Computer subsystem 302 may be configured to use the output of detector 307 and / or the electron beam image to perform any of the functions described herein. Computer subsystem 302 may be configured to perform any additional steps described herein. Fig. 9 The system 300 of output acquisition subsystems shown in FIG. 3 may be further configured as described herein.

[0080] It should be noted that this article provides Fig. 9 To generally illustrate configurations of electron beam-based output acquisition subsystems that may be used in the embodiments described herein. Configurations of the electron beam-based output acquisition subsystems described herein may be altered to optimize the performance of the output acquisition subsystem, as is typically performed when designing commercial output acquisition systems. Additionally, the systems described herein may be implemented using existing systems (e.g., by adding the functionality described herein to the existing systems). For some such systems, the methods described herein may be provided as optional functionality of the system (e.g., in addition to other functionality of the system). Alternatively, the systems described herein may be designed as completely new systems.

[0081] Although the output acquisition subsystem is described above as an electron beam-based output acquisition subsystem, the output acquisition subsystem may be an ion beam-based output acquisition subsystem. Fig. 9, except that the electron beam source can be replaced by any suitable ion beam source known in the art. In addition, the output acquisition subsystem can be any other suitable ion beam-based output acquisition subsystem, such as the ion beam-based output acquisition subsystem included in commercially available focused ion beam (FIB) systems, helium ion microscope (HIM) systems, and secondary ion mass spectrometer (SIMS) systems.

[0082] Computer subsystem 302 includes processor 308 and electronic data storage unit 309. Processor 308 may include a microprocessor, microcontroller, or other device.

[0083] Computer subsystem 302 may be coupled to components of system 300 in any suitable manner (e.g., via one or more transmission media that may include wired and / or wireless transmission media) such that processor 308 may receive output. Processor 308 may be configured to perform a number of functions using the output. 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 illustrated) to receive additional information or send instructions.

[0084] Processor 308 is in electronic communication with a wafer inspection tool, such as detector 307. Processor 308 may be configured to process images generated using measurements from detector 307. For example, processor 308 may perform an embodiment of method 200.

[0085] The computer subsystem 302, other systems, or other subsystems described herein may be part of a variety of systems, including personal computer systems, image computers, mainframe computer systems, workstations, network appliances, Internet appliances, or other devices. The subsystem or system may also include any suitable processor known in the art, such as a parallel processor. In addition, the subsystem or system may include a platform with high-speed processing and software as a stand-alone or network-connected tool.

[0086] The processor 308 and the electronic data storage unit 309 may be disposed in or otherwise be part of the system 300 or another device. In an example, the processor 308 and the electronic data storage unit 309 may be part of an independent control unit or in a centralized quality control unit. Multiple processors 308 or electronic data storage units 309 may be used.

[0087] Processor 308 may be implemented in practice by any combination of hardware, software, and firmware. Furthermore, its functions as described herein may be performed by one unit, or divided among different components (each of which in turn may be implemented by any combination of hardware, software, and firmware). Program code or instructions for processor 308 to implement various methods and functions may be stored in a readable storage medium, such as a memory in electronic data storage unit 309 or other storage.

[0088] If the system 300 includes more than one computer subsystem 302, the different subsystems may be coupled to each other so that images, data, information, instructions, etc. may be sent between the subsystems. For example, one subsystem may be coupled to an additional subsystem by any suitable transmission media, which may include any suitable wired and / or wireless transmission media known in the art. Two or more of these subsystems may also be operatively coupled by a shared computer-readable storage medium (not shown).

[0089] Processor 308 may be configured to perform a number of functions using the output of system 300 or other output. For example, processor 308 may be configured to send the output to electronic data storage unit 309 or another storage medium. Processor 308 may be further configured as described herein.

[0090] 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. Thus, the embodiments disclosed herein describe some configurations that may be customized in several ways for systems having different capabilities that are more or less suitable for different applications.

[0091] 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.

[0092] The processor 308 may be communicatively coupled to any of the various components or subsystems of the system 300 in any manner known in the art. In addition, the processor 308 may be configured to receive and / or obtain data or information (e.g., test results from an inspection system such as a review tool, a remote database containing design data, and the like) from other systems via a transmission medium that may include wired and / or wireless portions. In this manner, the transmission medium may serve as a data link between the processor 308 and other subsystems of the system 300 or systems external to the system 300.

[0093] The various steps, functions and / or operations of the system 300 and methods disclosed herein are implemented 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 for implementing methods (such as the methods described herein) may be transmitted via or stored on a carrier medium. The carrier medium may include storage media such as read-only memory, random access memory, magnetic or optical disks, non-volatile memory, solid-state memory, magnetic tape, and the like. The carrier medium may include transmission media such as wires, cables, or wireless transmission links. For example, the various steps described throughout the present disclosure may be implemented by a single processor 308 (or computer subsystem 302) or alternatively multiple processors 308 (or multiple computer subsystems 302). In addition, different subsystems of the system 300 may include one or more computing or logic systems. Therefore, the above description should not be construed as limiting the present disclosure but is merely illustrative.

[0094] In an example, electron beam column 101 is incorporated into electron column 301 or otherwise in system 300. Various components of system 300 may be duplicated or otherwise adapted to use an electron beam column.

[0095] Although the present disclosure has been described with respect to one or more specific embodiments, it will be understood that other embodiments of the present disclosure may be made without departing from the scope of the present disclosure. Therefore, the present disclosure is deemed to be limited only by the appended claims and reasonable interpretation thereof.

Claims

1. A testing system, comprising: an array of electron beam columns, each of the electron beam columns comprising an electron source configured to emit electrons toward a stage; a first permanent magnet array configured to focus the electrons from each electron source into an electron beam array, wherein the first permanent magnet array is disposed at a first end of the electron beam column array; a second permanent magnet array configured to focus the electron beam array toward a target on the stage, wherein the second permanent magnet array is disposed at a second end of the electron beam column array; and a plurality of shielding plates extending across the electron beam column array in the direction of electron emission between the first permanent magnet array and the second permanent magnet array; wherein each of the plurality of shielding plates comprises a plurality of apertures and has a thickness between 1 μm and 1 mm, and the electron beam array passes through the plurality of apertures; and The plurality of shielding plates thereby reduce the stray magnetic field in the radial direction of the electron beam array.

2. The inspection system of claim 1, wherein the plurality of shielding plates comprises: a first shielding plate, arranged close to the first permanent magnet array; and The second shielding plate is arranged close to the second permanent magnet array.

3. The inspection system according to claim 2, further comprising: a detector configured to detect electrons reflected from the target, wherein the detector is disposed between the first permanent magnet array and the second permanent magnet array; and The plurality of shielding plates further include: A third shielding plate is arranged close to the detector.

4. The inspection system of claim 3, wherein the plurality of shielding plates further comprises: A fourth shielding plate is close to the detector and arranged opposite to the third shielding plate.

5. The inspection system of claim 4, wherein the plurality of shielding plates further comprises: At least one supplementary shielding plate is arranged between the first shielding plate and the second shielding plate.

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

7. The inspection system of claim 1, wherein at least one of the plurality of shielding plates is arranged where the stray magnetic field is at a highest magnitude in the radial direction of the electron beam array.

8. The inspection system of claim 1, wherein the thickness of each of the plurality of shielding plates is at least 120 μm.

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

10. A method for stray field mitigation applied to a multi-column inspection system, the multi-column inspection system comprising an array of electron beam columns, each electron beam column comprising an electron beam source configured to emit electrons toward a stage, the method comprising: directing the electrons from each electron source through a first permanent magnet array to focus the electrons into an electron beam array, wherein the first permanent magnet array is disposed at a first end of the electron beam column array; and directing the electron beam array through a plurality of shielding plates extending across the electron beam column array between the first permanent magnet array and the second permanent magnet array; directing the electron beam array through a second permanent magnet array to focus the electron beam array toward a target on the stage, wherein the second permanent magnet array is disposed at a second end of the electron beam column array, downstream of the plurality of shielding plates; wherein each of the plurality of shielding plates comprises a plurality of apertures and has a thickness between 1 μm and 1 mm, and the electron beam array passes through the plurality of apertures; and The plurality of shielding plates thereby reduce the stray magnetic field in the radial direction of the electron beam array.

11. The method of claim 10, wherein directing the electron beam array through a plurality of shielding plates comprises: directing the electron beam array through a first shielding plate disposed proximate to the first permanent magnet array; and The electron beam array is directed through a second shielding plate disposed proximate to the second permanent magnet array.

12. The method according to claim 11, further comprising: directing the electron beam array through a detector configured to detect electrons reflected from the target, wherein the detector is disposed between the first permanent magnet array and the second permanent magnet array; and Wherein directing the electron beam array through a plurality of shielding plates further comprises: The electron beam array is directed through a third shielding plate disposed proximate to the detector.

13. The method of claim 12, wherein directing the electron beam array through a plurality of shielding plates further comprises: The electron beam array is directed through a fourth shielding plate disposed adjacent to the detector and opposite to the third shielding plate.

14. The method of claim 13, wherein directing the electron beam array through a plurality of shielding plates further comprises: The electron beam array is directed through at least one supplemental shielding plate disposed between the first shielding plate and the second shielding plate.

15. The method of claim 10, wherein the plurality of shielding plates comprises at least seven shielding plates. 16 . The method of claim 10 , wherein at least one of the plurality of shielding plates is arranged where the stray magnetic field is at a highest magnitude in the radial direction of the electron beam array.

17. The method of claim 10, wherein the thickness of each of the plurality of shielding plates is at least 120 μm.

18. The method of claim 10, wherein the plurality of shielding plates are comprised of a magnetic nickel-iron alloy.

Images