Method and system for imaging multiple electron beams

Abstract

A multi-electron beam system that forms hundreds of beamlets can focus the beamlets, reduce Coulomb interaction effects, and improve the resolution of the beamlets. A Wien filter with electrostatic and magnetic deflection fields can separate the secondary electron beam from the primary electron beam and can correct for astigmatism and source energy dispersion blur for all the beamlets simultaneously.

Description

Technical Field

[0001] The present disclosure relates to electron beam systems. Background Art

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

[0003] The manufacture of semiconductor devices such as logic and memory devices typically includes processing semiconductor wafers using a number of manufacturing processes to form various features and multiple levels of semiconductor devices. For example, photolithography is a semiconductor manufacturing process that involves transferring a pattern from a 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. An arrangement of multiple semiconductor devices manufactured on a single semiconductor wafer may be separated into individual semiconductor devices.

[0004] Inspection processes are used at various steps during semiconductor manufacturing to detect defects on wafers to facilitate 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 more important for the successful manufacture of acceptable semiconductor devices because smaller defects may cause device failures. For example, as the size of semiconductor devices decreases, detection of defects of reduced size has become necessary because even relatively small defects may still cause undesirable aberrations in semiconductor devices.

[0005] However, as design rules shrink, semiconductor manufacturing processes can operate closer to the limits of the performance capabilities of the process. In addition, as design rules shrink, smaller defects may have an impact on the electrical parameters of the device, which drives more sensitive inspection. As design rules shrink, the population of potential yield-related defects detected by inspection grows dramatically, and the population of disturbing point defects detected by inspection also grows dramatically. Therefore, more defects can be detected on the wafer, and correcting the process to eliminate all defects can be difficult and expensive. Determining which of the defects actually has an impact on the electrical parameters and yield of the device can allow the process control method to focus on the defect and largely ignore other defects. In addition, under smaller design rules, process-induced failures tend to be systematic in some cases. That is, process-induced failures tend to fail at predetermined design patterns that are usually repeated many times within the design. Eliminating spatially systematic electrical related defects can have an impact on yield.

[0006] Focused electron beam systems are commonly used to create or inspect microstructures of items such as silicon wafers used in the manufacture of integrated circuits. The electron beam is formed with electrons emitted from an emitter in an electron gun, which acts as a fine probe as it interacts with the wafer to inspect the microstructure. Single electron beams were previously used for wafer inspection and re-inspection to inspect finished or unfinished IC components at the nanometer critical dimension (CD) level. The throughput of a single electron beam device is quite low. Semiconductor manufacturers are seeking higher throughput systems.

[0007] The throughput of a multi-electron beam device is characterized by the number of sub-beams or the number of total electron beamlets. The larger the number of beamlets, the higher the throughput will be. However, increasing the number of beamlets is prevented by the imaging projection optics, which consists of global optical elements including a global objective and a Wien filter. In the case of an increased demand for more electron beamlets to achieve higher throughput, it is difficult to provide imaging uniformity across a larger field of view (FOV) using an imaging projection system due to off-axis aberrations from outer beamlets, source energy dispersion blur, optical astigmatism due to the presence of Wien filters, and strong Coulomb interaction effects due to higher beam currents with more beamlets.

[0008] Previous electron beam systems suffered from low resolution due to the effects of Coulomb interactions. The resolution of multi-electron beam systems is largely limited by the imaging projection optics from the intermediate image plane (IIP) to the wafer, which is the beam crossover close to the wafer. The beamlet imaging resolution is mainly gated by the Coulomb interaction effects around the crossover.

[0009] Previous electron beam systems also suffer from the problem of having source energy dispersion blur and astigmatism blur due to the presence of Wien filters. To remove the crosstalk between beamlet signals in a multi-electron beam apparatus, the Wien filter separates the secondary electron beam (SEB) from the primary electron beam (PEB) by a high Wien filter strength at a large SEB deflection angle. This causes heavier source energy dispersion blur and astigmatism blur for each beamlet across a large FOV.

[0010] Improved systems and methods are needed. Summary of the invention

[0011] In a first embodiment, a system is provided. The system includes an electron beam source that generates an electron beam. The electron beam source includes a tip, a suppression electrode, and an extraction electrode. The system further includes: a stage configured to hold a wafer in a path of the electron beam; an objective lens in the path of the electron beam; a Wien filter in the path of the electron beam between the objective lens and the electron beam source; a transfer lens in the path of the electron beam between the Wien filter and the electron beam source; and a detection array configured to receive at least one secondary electron beam from the wafer on the stage. The transfer lens includes a pole piece and a transfer lens coil. The objective lens includes: an upper pole piece; a lower pole piece; an objective coil disposed on the upper pole piece; a charge control plate disposed on the lower pole piece; an accelerating electrode disposed in the path of the electron beam between the upper pole piece and the lower pole piece; and a scanner disposed on the upper pole piece.

[0012] Wien filters can include electrostatic deflectors and magnetic deflectors.

[0013] The system may further include a collimating lens in a path of the electron beam and a beam-limiting aperture in the path of the electron beam between the collimating lens and an electron beam source.

[0014] The system may further include: an aperture array disposed in the path of the electron beam; a microstigmator array disposed in the path of the electron beam between the aperture array and a transfer lens; a microdeflector array disposed in the path of the electron beam between the microstigmator array and the transfer lens; and a microlens array disposed in the path of the electron beam between the microdeflector array and the transfer lens. The aperture array separates the electron beam into a plurality of beamlets. The plurality of beamlets includes at least 100 of the beamlets. The electron beam may be a telecentric beam upstream of the aperture array.

[0015] In an example, a path of the electron beam exits the transfer lens in a first orientation and exits the Wien filter in a second orientation different from the first orientation such that the first orientation is at a non-parallel angle to the second orientation.

[0016] The system may include a second Wien filter in the path of the electron beam between the Wien filter and the transfer lens. The second Wien filter may include a second electrostatic deflector and a second magnetic deflector.

[0017] In a second embodiment, a method is provided. The method comprises directing a plurality of beamlets through a transfer lens downstream of an electron beam source, thereby focusing the electron beam. Directing the beamlets through a Wien filter downstream of the transfer lens, thereby separating one or more secondary electron beams from the beamlets. Directing the beamlets through an upper pole piece of an objective lens. The objective lens is downstream of the Wien filter. Directing the beamlets through an accelerating electrode downstream of the upper pole piece. Directing the beamlets through a charge control plate disposed in a lower pole piece of the objective lens. The charge control plate is disposed on a side of the objective lens opposite to the upper pole piece. Directing the beamlets at a wafer. Receiving at least one secondary electron beam from the wafer at a detection array.

[0018] The plurality of beamlets may comprise at least 100 beamlets.

[0019] The method may further include generating an electron beam using an electron beam source and converting the electron beam into a plurality of beamlets.

[0020] The method may further include directing the electron beam through a collimating lens and a beam-limiting aperture disposed in a path of the electron beam between the electron beam source and the transfer lens.

[0021] The method may further include scanning the beamlet using a scanner disposed on the upper pole piece.

[0022] Wien filters can include electrostatic deflectors and magnetic deflectors.

[0023] The method may further include: separating the electron beam into beamlets using an aperture array; directing the beamlets through a micro-astigmatism corrector array disposed in the path of the beamlets between the aperture array and a transfer lens; directing the beamlets through a micro-deflector array disposed in the path of the beamlets between the micro-astigmatism corrector array and the transfer lens; and directing the beamlets through a micro-lens array disposed in the path of the beamlets between the micro-deflector array and the transfer lens. The aperture array is disposed in the path of the electron beam between an electron beam source and the transfer lens. The plurality of beamlets may include at least 100 of the beamlets. The electron beam may be a telecentric beam upstream of the aperture array.

[0024] The method may further include changing the direction of the beamlet using a Wien filter such that the beamlet is directed out of the Wien filter at an angle relative to the orientation in which it entered the Wien filter.

[0025] The method may further include directing the beamlet through a second Wien filter in the path of the beamlet between the Wien filter and the transfer lens.

[0026] The accelerating electrodes can be configured to vary the resolution of the beamlet.

[0027] The Wien filter can be configured to adjust both the divergence and astigmatism of the beamlets. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] For a fuller understanding of the nature and purpose of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0029] Figure 1 is an embodiment of a system according to the present disclosure;

[0030] Figure 2 is an embodiment of an imaging optic according to the present disclosure;

[0031] Figure 3 is an embodiment of a Wien filter having an octupole electrostatic deflector and an octupole magnetic deflector;

[0032] Figure 4 Explain the electrostatic deflection field in the octopole electrostatic deflector;

[0033] Figure 5 Description does not exist Figure 1 and Figure 2 In the case of Wien filters, such as the multi-electron spot size of the wafer;

[0034] Figure 6 is a graph showing the improvement of multi-electron beam resolution with accelerating voltage (Va);

[0035] Figure 7 Demonstrates source energy dispersion blurring due to the presence of a Wien filter;

[0036] Figure 8 is an embodiment of a globally tilted optical column that corrects source energy dispersion blur according to the present disclosure;

[0037] Fig. 9 Demonstrates astigmatic blur due to the presence of a Wien filter;

[0038] Fig.10 A global electrostatic astigmatism corrector including an octupole deflection plate in a Wien filter is described;

[0039] Fig.11 Demonstrates image uniformity across a large field of view with 331 beamlets after correction for energy dispersion and astigmatism;

[0040] Fig.12 is another embodiment of the system according to the present disclosure; and

[0041] Fig.13 is a flow chart of an embodiment of a method according to the present disclosure. DETAILED DESCRIPTION

[0042] 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. Therefore, the scope of the present disclosure is defined solely by reference to the appended claims.

[0043] A multi-electron beam system that forms hundreds of beamlets is disclosed herein. A transfer lens (TL) field focuses the beamlets to an optimal optical magnification. An energy accelerator booster field reduces Coulomb interaction effects and improves the resolution of the beamlets. Electron energy delay (deceleration) and substrate charging fields may be used to obtain desired wafer charging, extraction fields, and landing energies. A magnetic objective field may minimize optical aberrations to image the multi-electron beams at the wafer. A Wien filter with electrostatic and magnetic deflection fields may separate one or more secondary electron beams (SEBs) from one or more primary electron beams and may correct source energy dispersion blur for all beamlets simultaneously. The Wien filter may include an electrostatic (or magnetic) astigmatism corrector field to correct beamlet astigmatism simultaneously. The transfer lens may select the optical magnification and the accelerating electrode may reduce Coulomb interactions. In an embodiment, source energy dispersion blur for the beamlets may be corrected due to the presence of the Wien filter. In another embodiment, astigmatism blur for the beamlets may be corrected due to the presence of the Wien filter. In yet another embodiment, the source energy spread between two Wien filters can be compensated such that all energy spread blurring of the beamlets is removed and at the same time the secondary electron beam is deflected to the side detection array.

[0044] Figure 1 The optics of an embodiment of a multi-electron beam apparatus are shown. It includes four optical modules of an electron gun ("Gun"), a collimating lens ("CL"), a multi-electron beam creation ("MBC"), and projection imaging ("Projection").

[0045] like Figure 1 , system 100 includes an electron beam source that generates an electron beam 113. The electron beam source may include a tip 101. The electron beam source may also include a suppression electrode and an extraction electrode. The electron beam source may be a thermal field emission (TFE) or cold field emission (CFE) source that emits electrons from the emitter tip. The electrons are focused by a gun lens (GL) 102 into a large size electron beam 113. The high current electron beam 113 is collimated by a collimating lens 126 into a telecentric beam to illuminate an aperture array 103 (AA). The aperture array 103 may also be referred to as a micro-aperture array. Additional electron energy accelerating elements such as anodes may be used with the electron beam source.

[0046] The beam limiting aperture (BLA) 125 after the gun lens 102 can select the total beam current of the illumination aperture array 103, which separates the electron beam 113 into beamlets 114. The aperture array 103 is used to select the beam current of each individual beamlet 114. For each beamlet 114, there is one hole in the aperture array 103. The holes can be circular, hexagonal or other shapes. For simplicity, Figure 1 1 , three beamlets 114 are illustrated, but other numbers are possible. For example, there may be at least 100 beamlets 114 (e.g., greater than 300). Downstream of the aperture array 103, a microlens array (MLA) 106 focuses each beamlet 114 onto an intermediate image plane (IIP). Each microlens in the microlens array 106 may be a magnetic lens or an electrostatic lens. The magnetic microlens may be a number of magnetic pole pieces powered by coil excitation or permanent magnets. The electrostatic microlens may be an electrostatic single lens or an electrostatic acceleration / deceleration single potential lens.

[0047] The system 100 includes a collimating lens 126 in the path of the electron beam 113. The collimating lens 126 can be an electrostatic lens or a magnetic lens that is used to focus the diverging electron beam from the gun into a telecentric beam before illuminating the MBC module. The collimating lens 126 can reduce the gun spherical aberration of the outer electron beamlets, which can help increase the number of beamlets for higher throughput. A beam limiting aperture 125 is in the path of the electron beam 113 between the collimating lens 126 and the electron beam source.

[0048] A micro-astigmatism corrector array 104 (MSA) is disposed in the path of the electron beam 113 between the aperture array 103 and the transfer lens 112 and can correct the astigmatism of each beamlet 114. A micro-deflector array 105 (MDA) is disposed in the path of the electron beam 113 between the micro-astigmatism corrector array 104 and the transfer lens 112. The micro-deflector array 105 can correct the distortion of each beamlet 114 and / or scan each beamlet 114 over the wafer 107 with a given sub-FOV. A micro-lens array 106 (MLA) is disposed in the path of the electron beam 113 between the micro-deflector array 105 and the transfer lens 112. The term "micro" can refer to the size of the components, but can also indicate that these components are used with beamlets 114. The beamlets 114 are smaller than the electron beam 113.

[0049] The stage 108 is configured to hold the wafer 107 in the path of the beamlet 114 of the electron beam 113. Upstream of the stage 108 are an objective lens 109 and a Wien filter 110.

[0050] The electron source emits electrons from the tip 101 and then the electrons are accelerated and focused by the gun lens 102 into a large size electron beam 113. The electron beam 113 with a high beam current is collimated by the collimating lens 126 into a telecentric beam to illuminate the aperture array 103. With a given source brightness or angular intensity, the electron beam 113 is Figure 1 The tip emission angle α in α is characterized. The beam limiting aperture 125 after the gun lens 102 is used to select the total beam current of the illumination aperture array 103. The aperture array 103 is used to select the beam current of each single beamlet 114. After the aperture array 103, the micro-astigmatism corrector array 104 and the micro-deflector array 105, the micro-lens array 106 focuses each beamlet 114 onto the intermediate image plane. The intermediate image plane is the object plane of the projection imaging optics in the lower column.

[0051] There is a beam crossing (xo) between the transfer lens 112 and the objective lens 109. The beamlets 114 formed by the upper column at the intermediate image plane are projected onto the wafer (WF) 107 by the transfer lens 112 and the objective lens 109 at the desired magnification. The magnification can be configured to minimize all beam blurring for each beamlet at the wafer. The optimal magnification is given as D i / D o , where D i and D o The multi-electron beam (MB) FOV in the wafer plane (image plane) and the intermediate image plane (object plane), respectively. The transfer lens 112 can select the desired position (or crossing angle θ) of the beam crossing (xo) where the total spot size of each beamlet 114 is minimum while balancing axial aberrations, off-axis aberrations, and Coulomb interactions between electrons.

[0052] To inspect and recheck the wafer, secondary electrons (SE) and / or backscattered electrons (BSE) emitted from the wafer 107 due to bombardment by each primary beamlet 114 electrons may be separated from the optical axis and deflected by a Wien filter 110 toward a detection array 111 .

[0053] like Figure 2 , the objective lens 109 is in the path of the beamlets 114 of the electron beam 113. The objective lens 109 includes an upper pole piece 115 and a lower pole piece 116. The objective lens coil 117 is disposed on the upper pole piece 115. The charge control plate 118 is disposed on the lower pole piece 116. The accelerating electrode 119 is disposed in the path of the electron beam 113 between the upper pole piece 115 and the lower pole piece 116. The scanner 120 is disposed on the upper pole piece 115. The scanner 120 can scan all the beamlets 114 simultaneously in the same way (e.g., raster scanning) and the same scanning FOV. The scanning FOV size is given by the beamlet spacing on the wafer 107.

[0054] The Wien filter 110 is in the path of the beamlets 114 of the electron beam 113 between the objective lens 109 and the electron beam source. In an embodiment, the Wien filter 110 comprises an electrostatic deflector 121 and a magnetic deflector 122.

[0055] The Wien filter 110 may be removed or inactivated during operation. This may be beneficial for multi-electron beam lithography or multi-electron beam retesting and inspection using an annular detection array (e.g., with a central detector axis that is the same as the primary beam optical axis). Lithography is direct writing on wafer photoresist without collecting secondary electrons or separating primary electrons (PE) from secondary electrons. If an annular detection array is used, each SE beamlet hits a fixed sub-detector directly without changing direction (deflection). Therefore, these applications may not require a Wien filter. For example, for simpler applications, the beam energy and landing energy are fixed for a special purpose, and the SE trajectory is fixed. If the conditions of use change, the SE trajectory also changes. In this case, a fixed annular detection array may not be sufficient to meet all applications.

[0056] A transfer lens 112 (TL) is in the path of beamlets 114 of the electron beam 113 between the Wien filter 110 and the electron beam source. The transfer lens 112 includes a pole piece 123 and a transfer lens coil 124. The transfer lens 112 may be a magnetic lens for improving off-axis optical performance with a shaped beam or multiple electron beams.

[0057] The objective lens 109 may include an electrostatic section and a magnetic section. The electrostatic section of the objective lens 109 may include a ground electrode, an accelerating electrode 119 having a voltage Va, a charge control plate 118, and a stage 108. One or more of these components may be used to charge the wafer 107 and delay (decelerate) the electrons from the beam energy to the landing energy on the wafer 107. For example, if the electron beam is 30 keV in the column, the wafer 107 may be biased at -29 kV for an electron beam landing energy of 1 keV. 1 keV may be used for electron beam inspection and re-inspection, but other values ​​are possible. To charge the wafer 107 using an extraction field on the wafer surface, the charge control plate 118 should be biased according to the application requirements. The magnetic section of the objective lens 109 may include an upper pole piece 115, a lower pole piece 116, and a coil. The upper pole piece 115 and the lower pole piece 116 may be made of a magnetic material. The upper pole piece 115 may be connected to a ground electrode, such as a Wien filter shield or a scanner shield. The lower pole piece 116 may be connected to a charge control plate 118 electrode. The outer gap between the lower pole piece 116 and the upper pole piece 115 may be sealed with an insulator material.

[0058] The detection array 111 (DA) is configured to receive the secondary electron beam from the wafer 107 on the stage 108. Signals from the detection array 111 may be used to generate measurements or images. The detection array 111 may be in electronic communication with a processor for image generation, inspection, metrology, or other functions.

[0059] Figure 1 The multi-electron beam crossover (xo) in the embodiment is arranged around the accelerating electrode 119 to reduce the Coulomb interaction (CI), because the optical blur induced by CI may dominate the resolution of each beamlet 114 at the wafer 107. The Coulomb interaction may be mainly generated at the crossover. Arranging the crossover around the accelerating electrode 119 can accelerate the electrons, which can reduce the Coulomb effect.

[0060] Figure 2 The scanner 120 in the embodiment can scan all electron beamlets 114 in the FOV at the same time. Figure 1 A micro-deflector array 105 in the system scans each beamlet separately, wherein each micro-deflector can be controlled independently.

[0061] The Wien filter 110 may include an electrostatic deflector and a magnetic deflector with orthogonal electrostatic fields (E fields) and magnetic fields (B fields), as shown by the electrostatic dipole 121 and the magnetic dipole 122 . Figure 3 Demonstrates the construction of a Wien filter consisting of an octupole electrostatic deflector and an octupole magnetic deflector. Using the magnetic deflection field as an example, Figure 3 A cross-sectional view of an octupole magnetic deflector (MD) is shown. The eight magnetic pole pieces are arranged in a rotationally symmetrical manner to form an octupole deflector, and the same number of coil turns are wound around each pole piece. Figure 3 , are generally shielded as shown in FIG. 1 . With appropriate settings of the current through the coils, the distribution of the magnetic deflection field in a large central region can be quite uniform to minimize coma blurring of the outer beams among hundreds of beamlets. For example, for a uniform B field in the y-axis direction, the coil currents can be applied as Iy=1 unit, Ix=0 units, and a scaling factor a=1 / √2. In another example, for a uniform B field in the x-axis direction, the coil currents can be applied as Ix=1 unit, Iy=0 units, and a=1 / √2.

[0062] Figure 4 An octopole electrostatic deflector (ED) is shown in Figure 3 If the deflection voltage is set to Vx = 1 unit, Vy = 0 units and the scaling factor a = 1 / √2, then a fairly uniform field distribution in a larger central area is used to generate an electrostatic deflection field in the x-axis direction, as can be seen in the straight equipotential lines.

[0063] Computer simulations were performed to demonstrate that hundreds of electron beamlets were imaged at the wafer, e.g. Figure 5 As shown in . Figure 5 The example in FIG. 1 is for 331 electron beamlets having a hexagonal distribution, but other numbers of beamlets or distributions are possible. The multi-electron beam FOV at the wafer 107 (i.e., Figure 1 D i ) is defined as the farthest corner beam to the farthest corner beam, if the optical demagnification from IIP to wafer is 8X, then it can be Figure 1 The D of the wafer 107 is from about 200 microns to 300 microns. i or D from about 1600 microns to 2400 microns at IIP o .

[0064] Further computer simulations were performed to confirm the relationship between spot size and beam current, such as Figure 6 The total beam current is the sum of all beamlets (e.g. Figure 5 The beam current of the 331 beams in the beam is summed, and the spot size reflects the optical performance (resolution) including taking into account all optical blurs (e.g., blurs due to lens aberrations and due to Coulomb interactions between electrons). In the simulation, the accelerating voltage Va was applied with 0 kV, 25 kV, 50 kV and 100 kV, respectively. For each accelerating voltage Va, the magnetic excitation (coil current) of the objective lens 109 is used to focus the beam on the wafer 107. The crossover (xo) is set around the accelerating electrode 119 (Va) for increasing the beam energy around the crossover to (BE+Va), where BE is the beam energy in the column before the electrons are accelerated. Based on Figure 6 , the accelerating voltage Va on the booster can help improve the multi-electron beam resolution.

[0065] although Figure 5 The distribution of the electron beam spot at the wafer 107 is shown, but it can be further used to illustrate Figure 1 and Figure 2 Some properties of the optical device in the xy plane.

[0066] Figure 5 exhibit Figure 1 The aperture array 103 in the aperture array 103. The holes of the aperture array 103 can be hexagonally distributed, because the hexagon is close to rotational symmetry in optics. Other shapes are possible. The size of each hole in the aperture array 103 is the electron current used to select the beamlet. The number of holes in the aperture array 103 is the number of beamlets.

[0067] It can be scaled according to equation (1) Figure 1 Total MB (multiple electron beams) in MB tot).

[0068]

[0069] In equation (1), M x yes Figure 5 The number of all beamlets on the x-axis in . For example, Figure 5 The number of all beamlets on the x-axis in the five rings of the hexagonal distribution of beamlets is M x = 11, and gives the total number of beamlets MB tot =91. In 10 rings, M x =21, and MB tot =331.

[0070] Figure 5 Can also display Figure 1 The position and size of each micro-astigmatism corrector in the micro-astigmatism corrector array 104, each micro-deflector in the micro-deflector array 105, and each micro-lens in the micro-lens array 106. Figure 5 Can also display Figure 1 and Figure 2 An intermediate image plane in which the multiple electron beams are imaged to have an array of intermediate spot sizes distributed in a hexagonal pattern.

[0071] Figure 5 Also displayed Figure 1 and Figure 2 The sample (wafer) plane in the image plane, where the multi-electron beam is imaged with a hexagonal array of final spot sizes. From the intermediate image plane to the wafer plane, the multi-electron beam FOV is reduced to 1 / M. M is the optical magnification from IIP to wafer. Figure 1 In the optical magnification, M = D i / D o , where D i and D o These are called the FOV in the image plane and object plane of the projection optics, respectively. o =2xn=2np, where n is the number of hexagonal rings and p is the spacing between beamlets.

[0072] use Figure 5 , the total beamlets are calculated using equation (1) and each beamlet is addressed by the ring number (nth ring, n=0, 1, 2, 3, ...) and the polar angle. For example, (10th ring, 60°) and (10th ring, 120°) address the farthest corner beamlets of 60° and 120°, respectively.

[0073] In cases where higher throughput with more electron beamlets is desired, Figure 1 and Figure 2The secondary electron beams in may be separated from the optical axis and deflected toward the side detection array 111 for reducing crosstalk between the secondary electron beams. Figure 1 and Figure 2 A Wien filter in may achieve this separation. However, this may introduce energy dispersion blurring of the beamlets at the wafer 107, since all electrons emitted from the electron source have an energy spread (eg, about 1 eV for a TFE source).

[0074] Figure 1 and Figure 2 Computer simulation of the optical system in Figure 2 shows that the electrons of the small beam spot at the wafer expand and distribute in the same direction, as shown in Figure 2. Figure 7 This is because the energy dispersion angle of the electrons is distributed only in the direction of the Wien filter equilibrium between the electrostatic force and the magnetic force (e.g., the x-axis or y-axis direction). Even in the case of the rotation of the electrons when the electrons are focused by the magnetic objective lens 109, the electrons still maintain the same direction of energy dispersion distribution. Figure 7 Seven source energy dispersion blurs of typical beamlets at the center (0th ring) and 10th ring with 0°, 60°, 120°, 180°, 240° and 300° respectively are shown.

[0075] A global tilt optical column may be employed to correct for the source energy dispersion blur of all beamlets due to the presence of the Wien filter 110, such as Figure 8 As shown in p is the column tilt angle of the primary multi-electron beam relative to the center of the Wien filter 110, and θ s θ is the secondary electron beam (SEB) angle toward the detection array 111. The path of the electron beam 114 exits the transfer lens 112 in a first orientation and exits the Wien filter 110 in a second orientation different from the first orientation such that the first orientation is at a non-parallel angle to the second orientation. s is the deflection angle of the secondary electron beam passing through the Wien filter 110. If the angle θ p and θ s If certain conditions are met, then correction can be made Figure 7 The total energy in the beam is dispersed and blurred. For multi-beam applications, the secondary electron angle θ s The primary electron beam angle θ can be approximately 10° to 45° and is given by the equation s .

[0076] if Figure 8 The angle θ p and θ s The source energy dispersion blurring caused by the electrostatic and magnetic deflection fields in the Wien filter 110 can cancel each other out by satisfying the relationship defined in equation (2). Equations (2) and (3) can be used to balance the correction of energy dispersion.

[0077]

[0078]

[0079] In equations (2) and (3), V p and V s is the energy voltage of the primary electron beam and the secondary electron beam in the Wien filter region, and LE is the landing energy of the primary electron beam on the wafer. For example, if LE = 1 kV and Vp = 30 kV, then ρ = 1 / 30, giving θ p / θ s = 0.33. Therefore, the column inclination angle θ p is the detection array angle θ s For a multi-electron beam system with hundreds of beamlets, the SEB angle θ s may be relatively large (e.g., θ s =15°), so the tilt column angle can be θ p =5°.

[0080] Equation (2) not only meets the cancellation condition of source energy dispersion, but also meets the alignment condition of the primary beam. If the alignment condition is met, then we have Figure 8 The angle θ p The tilted primary beam is aligned to the optical axis of the objective lens 109. The alignment condition may require that the electrostatic field of the Wien filter 110 is deflected in the y direction by an angle θ p It is required that the magnetic field of the Wien filter 110 is deflected by an angle of 2θ in the -y direction. p This assumption Figure 8 The cross section is in the yz plane.

[0081] The electrostatic and magnetic deflection fields of the Wien filter 110 can be respectively Figure 3 and Figure 4 The octupole is generated in the . It is attributed to the deflection field in the larger central area (i.e., Figure 4 The fact that the energy dispersion is fairly uniform in the larger area (the equipotential lines in the middle) can make the energy dispersion cancellation fairly uniform in the larger area, so that the global Wien filter can be used to cancel out Figure 7 The energy of the hundreds of small beams in the beam is dispersed and blurred.

[0082] If the primary beam landing energy (LE) varies within the range, then the angle θ with respect to a given (ie, fixed) detection array 111 is s In comparison, the secondary electron beam may be over-deflected or under-deflected. However, an aligner (ie, a deflector) in the secondary electron collection optics (not shown) may be employed to correct this misaligned secondary electron beam.

[0083] Figure 8The presence of the Wien filter 110 in FIG. 1 introduces astigmatic blurring of the beamlets at the wafer 107 . Figure 8 Computer simulation on the optical system in FIG. 1 shows that the electron distribution of the astigmatic spot (elliptical spot) at the wafer 107 is in the same direction, as shown in FIG. Fig. 9 Even though the electrons rotate as they experience the focusing of the magnetic objective lens 109, the electrons still maintain the same direction at the wafer 107 as they experience the Wien filter 110. Fig. 9 Seven astigmatic blurs of typical beamlets at the center (0th ring) and the 10th ring with 0°, 60°, 120°, 180°, 240° and 300° respectively are shown.

[0084] A global astigmatism corrector may be employed to correct the astigmatism blur of all beamlets due to the presence of the Wien filter 110, such as Fig.10 . Fig.10 The eight plates of the octupole (electrostatic) deflector in the figure act as two astigmatism correctors applying two groups of voltages ±Va and ±Vb. For example, in the case of applying voltages Va = 1 unit and Vb = 0 units, a computer simulation gives Fig.10 . This example produces an electrostatic field distribution that focuses the electron beam in the y-axis direction and defocuses the electron beam in the x-axis direction. Changing Va and Vb can change the combined electrostatic force around the polar angle from 0 degrees to 360 degrees, so that astigmatic blur in any direction can be corrected by selecting the Va and Vb voltages.

[0085] In use Figure 8 The global tilt column and Fig.10 After correcting the source energy dispersion and astigmatism with the global astigmatism corrector, the final spot size across the large field of view of 331 beamlets can meet the required resolution and imaging uniformity, such as Fig.11 Computer simulations further demonstrate that Figure 6 The plot in characterizes the spot size vs. beam current, which means that source energy spread and astigmatism are all removed without affecting the final resolution. Figure 7 and 9 , Fig.11 (a), (b), (c), (d), (e), (f) and (g) are the final spots of small beams with angles of 0°, 60°, 120°, 180°, 240° and 300° at the center (0th ring) and the 10th ring respectively.

[0086] like Fig.12 As shown in FIG. 1 , a second Wien filter 127 can be added along the path of the beamlet between the Wien filter 110 and the transfer lens 112. The second Wien filter includes a second electrostatic deflector 128 and a second magnetic deflector 129.

[0087] Two Venn filters can be used to correct for Figure 7 The existence of the Wien filter in the source energy dispersion blurs. Fig.12 1, a lower Wien filter 110 closer to the wafer 107 can be used to deflect the secondary electron beam toward the side detection array 111. A second (or upper) Wien filter 127 closer to the transfer lens 112 can be used to compensate for energy dispersion. The energy dispersion generated in the Wien filter 127 can be used to compensate for the energy dispersion generated in the Wien filter 110. The use of two Wien filters is further described in U.S. Patent No. 10,090,131, which is incorporated by reference in its entirety.

[0088] use Figure 2 and Figure 8 The accelerating magnetic objective lens scheme in the embodiment of the present invention improves the resolution of multiple electron beamlets by increasing the accelerating voltage Va. The accelerating voltage Va can be increased to a level without arcing and the electron beamlets can be stably focused on the wafer using magnetic excitation.

[0089] Use two Venn filters to correct Figure 7 The source energy in the beam is dispersed and blurred. The primary beam optical column is a vertical column, but it can provide Figure 8 Similar correction performance for tilted columns in .

[0090] Fig.13 200. In 201, a plurality of beamlets are directed through a transfer lens downstream of an electron beam source, thereby focusing the electron beam. For example, there may be at least 100 beamlets (e.g., greater than 300 beamlets). In 202, the beamlets are directed through a Wien filter downstream of the transfer lens, thereby separating the secondary electron beam from the beamlets. The Wien filter may have an electrostatic deflector and a magnetic deflector. In 203, the beamlets are directed through an upper pole piece of an objective lens. The objective lens is downstream of the Wien filter. The Wien filter may be configured to simultaneously adjust the dispersion and astigmatism of the beamlets. In 204, the beamlets are directed through an accelerating electrode downstream of the upper pole piece. The accelerating electrode may be configured to change the resolution of the beamlets. In 205, the beamlets are directed through a charge control plate disposed in a lower pole piece of the objective lens. The charge control plate is disposed on the side of the objective lens opposite to the upper pole piece. In 206, the beamlets are directed at a wafer. At 207, one or more secondary electron beams are received from the wafer at a detection array.

[0091] The method 200 may further include generating the electron beam using an electron beam source and converting the electron beam into a plurality of beamlets.The electron beam may be directed through a collimating lens and a beam-limiting aperture disposed in a path of the electron beam between the electron beam source and the transfer lens.

[0092] The method 200 may further include scanning the beamlet using a scanner (ie, deflector) disposed on the upper pole piece.

[0093] The method 200 may further include separating the electron beam into beamlets using an aperture array. The aperture array is disposed in a path of the electron beam between an electron beam source and a transfer lens. The beamlets are directed through: a micro-astigmatism corrector array disposed in the path of the beamlets between the aperture array and the transfer lens; a micro-deflector array disposed in the path of the beamlets between the micro-astigmatism corrector array and the transfer lens; and a micro-lens array disposed in the path of the beamlets between the micro-deflector array and the transfer lens. The electron beam may be a telecentric beam upstream of the aperture array.

[0094] The method 200 may further include changing the direction of the beamlet using the Wien filter such that the beamlet is directed out of the Wien filter at an angle relative to the orientation in which it entered the Wien filter.

[0095] The method 200 may include directing the beamlet through a second Wien filter in the path of the beamlet between the Wien filter and the transfer lens.

[0096] The method 200 may be used when conditions of the system change. For example, the method 200 may be used when beam energy, landing energy, beam current, FOV, or other parameters are changed.

[0097] Although the present disclosure has been described with respect to one or more specific embodiments, it will be appreciated 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 system for an electron beam, comprising: an electron beam source that generates an electron beam, wherein the electron beam source comprises a tip, a suppression electrode, and an extraction electrode; a stage configured to hold a wafer in a path of the electron beam; an objective lens in the path of the electron beam, wherein the objective lens comprises: Upper pole piece; Lower pole piece; an objective lens coil, which is arranged on the upper pole piece; a charge control plate disposed on the lower pole piece; an accelerating electrode disposed in the path of the electron beam between the upper pole piece and the lower pole piece; and a scanner, which is disposed on the upper pole piece; a Wien filter in the path of the electron beam between the objective lens and the electron beam source; a transfer lens in the path of the electron beam between the Wien filter and the electron beam source, wherein the transfer lens comprises a pole piece and a transfer lens coil; and A detection array is configured to receive at least one secondary electron beam from the wafer on the stage.

2. The system of claim 1, wherein the Wien filter comprises an electrostatic deflector and a magnetic deflector.

3. The system of claim 1, further comprising: a collimating lens in the path of the electron beam; and A beam-limiting aperture is in the path of the electron beam between the collimating lens and the electron beam source.

4. The system of claim 1, further comprising: an aperture array disposed in the path of the electron beam, wherein the aperture array separates the electron beam into a plurality of beamlets; a micro-astigmatism corrector array disposed in the path of the electron beam between the aperture array and the transfer lens; a microdeflector array disposed in the path of the electron beam between the microastigmatism corrector array and the transfer lens; and A microlens array is disposed in the path of the electron beam between the microdeflector array and the transfer lens.

5. The system of claim 4, wherein the plurality of beamlets comprises at least 100 of the beamlets.

6. The system of claim 4, wherein the electron beam is a telecentric beam upstream of the aperture array.

7. The system of claim 1, wherein the path of the electron beam exits the transfer lens in a first orientation and exits the Wien filter in a second orientation different from the first orientation such that the first orientation is at a non-parallel angle to the second orientation.

8. The system of claim 1, further comprising a second Wien filter in the path of the electron beam between the Wien filter and the transfer lens.

9. The system of claim 8, wherein the second Wien filter comprises a second electrostatic deflector and a second magnetic deflector.

10. A method for imaging multiple electron beams, comprising: directing a plurality of beamlets through a transfer lens downstream of an electron beam source, thereby focusing the electron beam; directing the beamlets through a Wien filter downstream of the transfer lens, thereby separating at least one secondary electron beam from the beamlets; directing the beamlet through an upper pole piece of an objective lens, wherein the objective lens is downstream of the Wien filter; directing the beamlet through an accelerating electrode downstream of the upper pole piece; directing the beamlet through a charge control plate disposed in a lower pole piece of the objective lens, wherein the charge control plate is disposed on a side of the objective lens opposite the upper pole piece; directing the beamlet at a wafer; and The at least one secondary electron beam is received from the wafer at a detection array. The method of claim 10 , wherein the plurality of beamlets comprises at least 100 beamlets.

12. The method according to claim 10, further comprising: generating an electron beam using the electron beam source; and The electron beam is converted into the plurality of beamlets.

13. The method according to claim 11, further comprising: The electron beam is directed through a collimating lens and a beam limiting aperture positioned in the path of the electron beam between the electron beam source and the transfer lens.

14. The method of claim 10, further comprising scanning the beamlet using a scanner disposed on the upper pole piece.

15. The method of claim 10, wherein the Wien filter comprises an electrostatic deflector and a magnetic deflector.

16. The method of claim 10, further comprising: separating the electron beam into the beamlets using an aperture array, wherein the aperture array is disposed in a path of the electron beam between the electron beam source and the transfer lens; directing the beamlets through a micro-astigmatism corrector array disposed in the path of the beamlets between the aperture array and the transfer lens; directing the beamlets through an array of microdeflectors positioned in the path of the beamlets between the micro-astigmatism corrector array and the transfer lens; and The beamlets are directed through a microlens array disposed in the path of the beamlets between the microdeflector array and the transfer lens. The method of claim 16 , wherein the plurality of beamlets comprises at least 100 beamlets.

18. The method of claim 16, wherein the electron beam is a telecentric beam upstream of the aperture array.

19. The method of claim 10, further comprising changing the direction of the beamlet using the Wien filter so that the beamlet is directed out of the Wien filter at an angle relative to the orientation in which it entered the Wien filter.

20. The method of claim 10, further comprising directing the beamlet through a second Wien filter in the path of the beamlet between the Wien filter and the transfer lens.

21. The method of claim 10, wherein the accelerating electrodes are configured to change a resolution of the beamlets.

22. The method of claim 10, wherein the Wien filter is configured to simultaneously adjust the dispersion and astigmatism of the beamlets.

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