Multi-charged particle beam irradiation device and adjustment method thereof

Abstract

To adjust the imaging height to allow the multi-beams to be incident perpendicularly on a sample surface while suppressing fluctuations in the beam array distribution.SOLUTION: A multi-charged particle beam irradiation device according to an embodiment includes an optical system including multiple stages of lenses for adjusting the multiple beams, and a lens control circuit. A virtual crossover, as viewed from downstream of the multiple beams, is formed on the front focal plane of the lowest objective lens in the optical system, and the multiple beams are configured to be perpendicularly incident on the sample surface. The multiple stages of lenses include three or more stages of focus correction lenses that perform focus correction according to the height of the sample surface and / or the beam current. An actual crossover (CO2r) is located between the main surface of the topmost focus correction lens and the main surface of the bottommost focus correction lens. The lens control circuit controls the applied voltage or current conditions of the focus correction lenses so as to satisfy a predetermined rotation angle condition, a condition for the virtual crossover (CO2) to be stationary as viewed from downstream, and a focusing condition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-charged particle beam irradiation apparatus and an adjustment method thereof. [Background technology]

[0002] In recent years, with the increasing integration density of LSIs, the circuit line width required for semiconductor devices has become finer year by year. Here, electron beam (EB) lithography technology has inherently excellent resolution, and mask patterns are written onto mask blanks using an electron beam.

[0003] For example, there is a lithography system that uses multiple beams. Compared to lithography using a single electron beam, using multiple beams allows for the irradiation of many beams at once, thereby significantly improving throughput. In a multi-beam lithography system, for example, an electron beam emitted from an electron gun is passed through an aperture array with multiple openings to form multiple beams, each of which is blanked, and the beams that are not blocked by a stopping plate are reduced in size by an optical system, deflected by a deflector, and irradiated onto the desired position on the sample.

[0004] In one example of a conventional optical system, a crossover is formed on the focal plane in front of the objective lens (upstream in the direction of beam travel) so that the beam is perpendicular to the sample surface. By having the beam perpendicularly incident, the beam array distribution does not change even if the height of the sample surface changes. If the objective lens is an electromagnetic lens and a magnetic field is present on the sample surface, a slight deviation in the rotation direction will occur, but if the deviation is within the allowable range, it is considered to be perpendicular incidence.

[0005] Increasing the focusing half-angle of the beams to increase the current of each beam in a multi-beam system results in increased beam blurring when the sample surface height changes. To suppress beam blurring, it is necessary to change the excitation of the objective lens to perform focus correction and align the imaging height with the sample surface height. However, this poses the problem of changing the beam array distribution of the multi-beams as the excitation changes. Furthermore, changes in the multi-beam current cause focus shifts due to the Coulomb effect, and while focus correction of the objective lens is an effective way to correct this effect, similar problems arise. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-332206 [Patent Document 2] Japanese Patent Application Publication No. 6-338445 [Patent Document 3] Japanese Patent Application Publication No. 10-106467 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a multi-charged particle beam irradiation device and an adjustment method thereof that can adjust the imaging height and make multiple beams perpendicularly incident on a sample surface while suppressing fluctuations in the beam array distribution. [Means for solving the problem]

[0008] A multi-charged particle beam irradiation device according to one aspect of the present invention comprises a charged particle source that generates and emits multibeams, an optical system including a plurality of lenses that adjust the emitted multibeams, and a lens control circuit that controls the plurality of lenses. In the optical system, a virtual crossover is formed when viewed from downstream of the multibeams on a front focal plane located on the opposite side of the sample surface of the objective lens, which is the lowest lens among the plurality of lenses, and the multibeams that have passed through the objective lens are configured to be perpendicularly incident on the sample surface. The plurality of lenses has three or more stages of focus correction lenses that perform focus correction of the multibeams in accordance with the height of the sample surface and / or the beam current. Among the three or more stages of focus correction lenses, an actual crossover (C02r) is located between the main surface of the uppermost focus correction lens and the main surface of the lowermost focus correction lens. The lens control circuit controls the applied voltage or current conditions of the focus correction lenses so as to satisfy a predetermined rotation angle condition, a condition that the virtual crossover (C02) is stationary when viewed from downstream, and a focusing condition.

[0009] A method for adjusting a multi-charged particle beam irradiation device according to one aspect of the present invention adjusts the focal length of the focus correction lens in the above-mentioned multi-charged particle beam irradiation device while maintaining the magnification change of the multi-beam distribution smaller than an allowable amount. [Effects of the Invention]

[0010] According to the present invention, it is possible to adjust the imaging height while suppressing fluctuations in the beam array distribution, and to make the multibeams perpendicularly incident on the sample surface. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram of a multi-beam drawing apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram of a shaping aperture array substrate. [Figure 3] FIG. 10 is a diagram illustrating a crossover. [Figure 4]FIG. 10 is a diagram illustrating an example of focus correction. [Figure 5] FIG. 10 is a schematic diagram of a modified focus correction lens. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiment, a configuration using an electron beam as an example of a beam will be described. However, the beam is not limited to an electron beam, and other charged particle beams such as an ion beam may also be used.

[0013] 1 includes a drawing unit 10 that draws a desired pattern by irradiating a sample such as a mask or a wafer with an electron beam, and a control unit 60 that controls the operation of the drawing unit 10. The drawing unit 10 includes an electron optical lens barrel 12 and a drawing chamber 40. In this embodiment, a multi-beam drawing apparatus will be described as an example of a multi-beam irradiation apparatus.

[0014] Arranged within the electron optical column 12 are an electron source 14, an illumination lens 16, a shaping aperture array substrate 18, a blanking aperture array substrate 20, a projection lens 22, a stopping aperture (limiting aperture member) 24, a first objective lens 26, a positioning deflector 28, a second objective lens 30, and three-stage focus correction lenses 32-34. An XY stage 42 is arranged within the writing chamber 40. A mask blank or the like, which is a sample 44 to be written, is placed on the XY stage 42. The multi-beam writing device irradiates the sample 44 with multiple beams using an optical system including multiple stages of lenses, such as the illumination lens 16, the projection lens 22, the first objective lens 26, the second objective lens 30, and the three-stage focus correction lenses 32-34.

[0015] As shown in Fig. 2, apertures (first apertures) 18A are formed in m columns by n rows (m, n ≥ 2) at a predetermined arrangement pitch on the shaping aperture array substrate 18. Each aperture 18A is formed as a rectangle of the same dimensions. The shape of the apertures 18A may be circular. Multiple beams MB are formed by portions of the electron beams B passing through each of the plurality of apertures 18A.

[0016] Also provided is a sample surface height measuring means (not shown). For example, an optical lever-type sample surface height measuring device is used as the sample surface height measuring means. This device measures the sample surface height using reflected light obtained by irradiating light onto an area on the sample surface that includes the electron beam irradiation position. Using this, the height of the position on the sample surface that is irradiated with the electron beam can be determined.

[0017] Furthermore, a Faraday cup (not shown) is provided on the XY stage 42, and the beam current can be measured.

[0018] The blanking aperture array substrate 20 is provided below the shaping aperture array substrate 18, and has formed therein passage holes 20A (second openings) corresponding to the respective openings 18A of the shaping aperture array substrate 18. A blanker (not shown), consisting of a pair of two electrodes, is disposed in each passage hole 20A. One of the blankers is fixed at ground potential, and the other is switched to a potential different from ground potential. The electron beams passing through each passage hole 20A are deflected independently by the voltage applied to the blanker. In this manner, the multiple blankers perform blanking deflection on the corresponding beams among the multi-beams MB that have passed through the multiple openings 18A of the shaping aperture array substrate 18.

[0019] The stopping aperture 24 blocks the beam deflected by the blanker. The beam not deflected by the blanker passes through an opening 24A (third opening) formed in the center of the stopping aperture 24. In order to reduce beam leakage during individual blanking by the blanking aperture array substrate 20, the stopping aperture 24 is placed on the image plane of the crossover (light source image) CO1, where the beam divergence becomes smaller.

[0020] The control unit 60 has a control computer 62, a deflection control circuit 64, a lens control circuit 66, and a memory 68. The deflection control circuit 64 controls the voltages applied to the blanker provided on the blanking aperture array substrate 20 and the electrodes of the positioning deflector 28. The lens control circuit 66 controls the voltages applied to the illumination lens 16, the projection lens 22, the first objective lens 26, the second objective lens 30, and the focus correction lenses 32 to 34.

[0021] Electron beam B emitted from electron source 14 is illuminated almost perpendicularly onto the entire shaping aperture array substrate 18 by illumination lens 16. Electron beam B passes through multiple apertures 18A in shaping aperture array substrate 18, forming a multibeam MB consisting of multiple electron beams. The multibeam MB passes through the corresponding blankers in blanking aperture array 20.

[0022] The multi-beams MB that pass through the blanking aperture array substrate 20 are reduced in size by the projection lens 22 and travel toward the central opening 24A of the stopping aperture 24, forming a crossover CO1. Here, the electron beams deflected by the blanker of the blanking aperture array substrate 20 move out of position with respect to the opening 24A of the stopping aperture 24 and are blocked by the stopping aperture 24. On the other hand, the electron beams that are not deflected by the blanker pass through the opening 24A of the stopping aperture 24. Blanking control is performed by turning the blanker on and off, and the on / off of the beams is controlled.

[0023] In this way, the stopping aperture 24 blocks each beam deflected by the blanker of the blanking aperture array substrate 20 to be in the beam OFF state.

[0024] The multi-beams MB that have passed through the stopping aperture 24 are focused by the first objective lens 26, the second objective lens 30, and the focus correction lenses 32 to 34 to form a pattern image with a desired reduction ratio, which is then irradiated onto the sample 44.

[0025] Specifically, the multibeams MB that have passed through the stopping aperture 24 are reduced in size by the first objective lens 26 and form a virtual crossover CO2 on the front focal plane of the second objective lens 30 when viewed from downstream. Here, the front focal plane of the second objective lens 30 refers to a focal plane located on the opposite side of the sample 44 from the second objective lens 30, in other words, a focal plane located upstream in the beam traveling direction from the second objective lens 30. The multibeams MB2 that have formed the virtual crossover CO2 on the front focal plane of the second objective lens 30 when viewed from downstream are refracted by the second objective lens 30 to be parallel to the optical axis and are incident perpendicularly on the sample 44.

[0026] The second objective lens 30 is the lowest lens among the multiple stages of lenses included in the optical system.

[0027] The positioning deflector 28, which is disposed between the first objective lens 26 and the second objective lens 30, deflects and irradiates the multibeam MB onto a desired position on a sample 44 placed on a continuously moving XY stage 42. The positioning deflector 28 has a plurality of electrodes, and may be, for example, a quadrupole deflector with four electrodes or an octupole deflector with eight electrodes. The beam deflection position (the beam irradiation position on the sample 44) can be changed by changing the voltage applied to each electrode of the positioning deflector 28.

[0028] Three stages of focus correction lenses 32 to 34 are provided between the second objective lens 30 and the positioning deflector 28. For example, the focus correction lenses 32, 33, and 34 are arranged in this order from the positioning deflector 28 toward the second objective lens 30 (along the beam traveling direction). Hereinafter, the focus correction lens 32 will also be referred to as the upper (top) stage focus correction lens, the focus correction lens 33 as the middle stage focus correction lens, and the focus correction lens 34 as the lower (bottom) stage focus correction lens.

[0029] In this embodiment, the focus correction lenses 32 to 34 are arranged so that a virtual crossover position, as viewed from downstream, corresponding to the front focal plane (or its conjugate point) of the second objective lens 30 is located at the height between the principal plane of the upper focus correction lens 32 and the principal plane of the lower focus correction lens 34. Here, the virtual crossover position, as viewed from downstream, refers to the crossover position obtained by tracing the trajectory from downstream of the focus correction mechanism back and assuming that there is no electromagnetic field at the focus correction mechanism position. On the other hand, when simply referred to as the crossover position, it is used to mean the position where the paraxial trajectory passes through the optical axis. When there is no electromagnetic field near the crossover, as in the case where there is no focus correction mechanism, the paraxial trajectory that gives the crossover becomes a straight line near the crossover position, and the crossover position and the virtual crossover position as viewed from downstream coincide.

[0030] The focus correction lenses 32 to 34 are non-rotating lenses, and may be electrostatic lenses such as electrostatic Einzel lenses. The voltages applied to each of the focus correction lenses 32 to 34 that satisfy the conditions for a virtual crossover CO2 to be stationary when viewed from downstream and for the focusing point are determined in advance by experiment or simulation, and a table defining the determined applied voltages is stored in memory 68.

[0031] Here, the immobility of the virtual crossover CO2 as viewed from downstream means that when the trajectory corresponding to the virtual crossover CO2 image as viewed from downstream enters the focus correction mechanism FA, it matches the position before the focus correction operation within the required accuracy range, even after the focus correction operation is performed downstream of the focus correction mechanism FA, as shown in Figure 3. In other words, this means that the virtual crossover position obtained by tracing the trajectory from downstream of the focus correction mechanism FA (the virtual crossover position as viewed from downstream) does not change within the required accuracy range.

[0032] In contrast, the position defined as the point where the trajectory corresponding to the virtual crossover CO2 image when viewed from downstream passes through the optical axis when it enters the focus correction mechanism FA is called the actual crossover, and this position is denoted as CO2r. CO2r is set to be inside the focus correction mechanism FA. The virtual crossover position CO2 when viewed from downstream can be either outside or inside the focus correction mechanism FA.

[0033] The allowable variation in the crossover position is determined by the allowable change in magnification of the multi-beam. In this example, the focus correction mechanism FA consists of correction lenses 32 to 34. The focus correction mechanism FA is defined as the area where the electromagnetic field of the correction lens is strong enough to affect the trajectory. Outside the boundary of the focus correction mechanism FA, the boundary is set so that the trajectory of the electron beam can be approximated as a straight line. In the case of an Einzel lens, if the lens electric field can be ignored outside the grounded aperture, the outer edge of the external grounded aperture can be set as the boundary. In the case of a magnetic lens, if the leakage of the lens magnetic field at the opening at the outer edge of the area surrounded by the pole piece or magnetic material is sufficiently small, the outer edge opening can be set as the boundary.

[0034] The lens control circuit 66 references a table stored in memory 68 and controls the voltage applied to the focus correction lenses 32-34 based on the surface height of the sample 44 detected by the Z sensor (not shown), thereby performing focus correction (dynamic focus). If a focus correction amount not listed in the table is required, the appropriate voltage can be determined, for example, by interpolating values ​​listed in the table. Interpolation can be performed by interpolating two data items listed in the table, or by fitting multi-point data to a polynomial, which can then be used to obtain lens control values. Since the excitation of the second objective lens 30 is not changed, the normal incidence condition is maintained.

[0035] This allows focus correction to be performed without changing the beam array distribution of the multi-beams and while maintaining the normal incidence condition, allowing the imaging height to be changed to match the height of the sample surface, as shown in Figure 4. In Figure 4, the solid line indicates the central trajectory and the dashed line indicates the off-axis trajectory. If the irradiation position of the entire multi-beams on the sample surface fluctuates due to focus correction, this can be corrected using the positioning deflector 28.

[0036] In the above embodiment, focus correction is performed when the height of the sample surface changes. However, focus correction may also be necessary when the beam current changes significantly. In a multi-beam lithography system, the number of beams varies depending on the pattern being written, which changes the total beam current irradiated onto the sample surface. As the beam current increases, the electron beam tends to expand due to the Coulomb force between the electrons constituting the electron beam. This effect generally manifests as a downstream shift of the image plane. Here, this is referred to as Coulomb effect-induced focus shift. To suppress this Coulomb effect-induced focus shift, the focal length of the lens is adjusted to correct the image plane to the sample surface. In this case, as described in the above embodiment, adjustments are made to ensure that the crossover position remains stationary and non-rotating. In this case, the total beam current value is required, rather than the height of the sample surface. For example, the beam current can be determined from the blanker control signal of the blanking aperture array board 20. The focal length of the objective lens can then be adjusted according to the determined beam current. In this case as well, the lens control circuit 66 may refer to the table stored in the memory 68, and control the voltages applied to the focus correction lenses 32 to 34 based on the beam current to perform focus correction.

[0037] In some cases, both a change in the specimen surface height and a change in the beam current occur. Similarly, a table corresponding to the conditions can be stored in the memory 68, and the voltages to be applied to the focus correction lenses 32 to 34 can be determined.

[0038] In the above embodiment, an example was described in which a three-stage electrostatic lens is used as a non-rotating lens that serves as a focus correction lens constituting the focus correction mechanism, but the electrostatic lens may be four or more stages. Also, an electromagnetic lens with four or more stages may be used as the focus correction lens.

[0039] For example, currents are passed through the multiple loops so that the sum of the currents in the rotational directions surrounding the optical axis is zero. In this case, a table showing the currents to be passed through the multiple loops to satisfy the conditions for no rotation and for the virtual crossover CO2 to remain stationary when viewed from downstream, and the focusing conditions, is prepared in advance and stored in memory 68. The lens control circuit 66 refers to the table stored in memory 68, controls the amount of current in the multiple loops based on the surface height of the sample 44, and performs focus correction (dynamic focus).

[0040] As shown in FIG. 5, the focus correction lens may include an antisymmetric magnetic doublet lens 70, a cylindrical electrode 72 surrounding the axis of the antisymmetric magnetic doublet lens 70 and positioned so that its front-to-back center position coincides with the center position of the antisymmetric magnetic doublet lens 70, and a ground electrode 74. The arrows in FIG. 5 indicate an example of the direction of the magnetic field. Magnetic fields in opposite directions are formed alternately. While FIG. 5 shows an example of four stages of focus correction lenses, five or more stages may also be used.

[0041] When a voltage is applied to the electrodes 72, the electron energy changes, which in turn changes the focal length and amount of rotation of the lens. The voltages applied to the four electrodes 72 are changed so as to satisfy the conditions that the virtual crossover CO2 is stationary as a whole when viewed from downstream and without rotation. The voltages to be applied to each electrode 72 that satisfy the conditions that the virtual crossover CO2 is stationary when viewed from downstream and without rotation and the focusing condition are determined in advance, and a table defining these voltages is stored in memory 68. The lens control circuit 66 refers to the table stored in memory 68 and controls the voltages applied to each electrode 72 based on the surface height of the sample 44, thereby performing focus correction (dynamic focus).

[0042] When the magnetic field of the electromagnetic lens is present on the sample surface, the incident electrons have a velocity in the rotational direction and therefore usually enter the sample surface at an angle to the rotational direction. Therefore, by installing a magnetic field canceling lens with an excitation direction opposite to that of the second objective lens 30 below the stage 42 (downstream in the beam travel direction), and using an objective lens that cancels out the magnetic field on the sample surface and eliminates the tilt in the rotational direction, it is possible to suppress fluctuations in the rotational direction of the beam acquisition position due to fluctuations in the height of the sample surface.

[0043] In the above embodiment, an example was described in which a non-rotational lens was used as the focus correction lens, but the rotation angle condition for the focus correction lens is not limited to a non-rotational condition, and it may also be one that performs rotation correction.

[0044] When four or more stages of electromagnetic lenses are used, focus correction is possible while satisfying the condition that the virtual crossover CO2 is stationary when viewed from downstream, and correction of the rotation angle is also possible. The current to be passed through each electromagnetic lens so that the virtual crossover CO2 is stationary when viewed from downstream and the rotation amount and focusing conditions are satisfied is determined in advance, and a table defining the determined currents is stored in memory 68. The lens control circuit 66 refers to the table stored in memory 68 and controls the current of the electromagnetic lens based on the surface height of the sample 44, thereby performing focus correction (dynamic focus) and rotation correction.

[0045] In the above embodiment, the configuration of a multi-beam lithography device has been described, but the present invention can also be applied to other multi-beam irradiation devices such as a multi-beam inspection device. It is not limited to multi-beams, and can also be applied to a case where a single variable shaped beam is used. When correcting positional deviation due to the Coulomb effect with a variable shaped beam, the beam current can be calculated from the beam dimension.

[0046] Furthermore, the same effect can be achieved by arranging the focus correction lens groups on either side of the conjugate point of the upstream crossover, rather than at the most downstream crossover position. In this case, the actual crossover is fixed downstream of the focus correction mechanism.

[0047] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined. [Explanation of symbols]

[0048] 10 Drawing section 12 Electron Optical Tube 14 Electron gun 16 Lighting lens 18 Molded aperture array substrate 20 Blanking aperture array substrate 22 Projection lens 24 Stopping Aperture 26 First objective lens 28 Positioning deflector 30 Second objective lens 32~34 Focus correction lens 40 Drawing room 42 XY stage 44 samples 60 Control Unit

Claims

1. a charged particle source that generates and emits multiple beams; an optical system including multiple stages of lenses for adjusting the emitted multiple beams; a lens control circuit for controlling the plurality of stages of lenses; Equipped with In the optical system, a virtual crossover is formed when viewed from downstream of the multi-beams on a front focal plane located on the opposite side of the sample surface from the objective lens, which is the lowest lens among the plurality of stages of lenses, and the multi-beams that have passed through the objective lens are configured to be perpendicularly incident on the sample surface, the multi-stage lens includes three or more stages of focus correction lenses that perform focus correction of the multi-beams in accordance with the height of the sample surface and / or the beam current; Among the three or more stages of focus correction lenses, an actual crossover (CO2r) is located between a principal surface of an uppermost focus correction lens and a principal surface of a lowermost focus correction lens, The lens control circuit controls the applied voltage or current conditions of the focus correction lens so as to satisfy the predetermined rotation angle conditions, the condition that the virtual crossover (CO2) is stationary when viewed from downstream, and the focusing condition.

2. a memory for storing a table defining voltage or current conditions for the focus correction lens that satisfy the predetermined rotation angle condition, the condition under which the virtual crossover is immovable when viewed from downstream, and the in-focus condition; 2. The multi-charged particle beam irradiation equipment according to claim 1, wherein the lens control circuit refers to the table and controls the amount of voltage or current applied to the focus correction lens based on the height of the sample surface.

3. 2. The multi-charged particle beam irradiation system according to claim 1, wherein the three or more stages of focus correction lenses are non-rotating lenses.

4. The multi-charged particle beam irradiation device according to claim 3 , wherein the non-rotating lens is an electrostatic lens.

5. the optical system has four or more stages of the focus correction lenses, 4. The multi-charged particle beam irradiation device according to claim 3, wherein the non-rotating lens is a non-rotating electromagnetic lens formed by current loops having the same magnitude but in opposite directions.

6. the optical system has four or more stages of the focus correction lenses, 4. The multi-charged particle beam irradiation device according to claim 3, wherein the non-rotational lens is a non-rotational electromagnetic lens in which currents are passed through a plurality of loops so that the sum of currents in one rotational direction surrounding the optical axis is zero.

7. 2. A method for adjusting a multi-charged particle beam irradiation system according to claim 1, wherein the focal length of the focus correction lens is adjusted while a change in magnification of the multi-beam distribution is maintained smaller than a tolerance.

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