Device and method for calibrating charged-particle beam

Abstract

To determine an exact position of a charged-particle beam with respect to one or more desired positions at a target.SOLUTION: A beam calibration device is presented in relation to a position of a beam with respect to a target. The beam calibration device 140 includes a detector 145 for charged particles that are arriving at registering structures 143 of the device. The beam is deflected towards the device by means of a lateral initial deflection, and thus impinges on at least one of the registering structures. The beam calibration device is scanned with the beam so as to cover a prescribed region including the registering structure. The detector is used for measurement as a current signal, and a central relative position of the beam is determined with respect to an optimal position defined on the beam calibration device surface. This optimal position is used to deflect the beam back to a designated target position by a reverse lateral deflection, which is an inverse of the initial deflection combined with a deflection correction. The deflection correction represents a correction of the lateral beam position to compensate the central relative position.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] This application claims the benefit of Paris Convention priority from European Patent Application No. 23160722.7, filed March 8, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to particular improvements in the control of process parameters in a multi-beam charged particle processing apparatus, more particularly to a method for calibrating a charged particle beam, in particular an electron beam, in a charged particle processing apparatus or a multi-beam charged particle processing apparatus configured for exposing a target with a structured beam of charged particles. [Background technology]

[0003] In a charged particle multi-beam processing apparatus, a particle beam is generated in a charged particle source, directed to and illuminates a pattern definition device that includes an aperture array consisting of a number of blanking apertures through which the particle beam passes, and is imaged onto a target by a projection optical system to write a desired pattern on the target by exposing a number of pixels with the particle beam impinging on the target within the beam field of the target.

[0004] The applicant has developed the above type of charged particle multi-beam tool and corresponding charged particle optics, pattern definition (PD) devices and multi-beam writing methods, in particular a state-of-the-art 50 keV electron multi-beam writer for realizing composite photomasks for 193 nm immersion lithography, masks for EUV lithography and templates (1× masks) for imprint lithography. The system is called eMET (electron Mask Exposure Tool) or MBMW (multi-beam mask writer) for exposing 6″ mask blank substrates. The multi-beam system is called PML2 (Projection Mask-Less Lithography) for electron beam direct writer (EBDW) applied to silicon wafer substrates. The multi-beam column and writing method can also be used for multi-beam inspection applications.

[0005] In Fig. 1 an exemplary schematic structure of a multi-beam writer is shown. Such lithographic apparatus are known in the prior art, such as US 6,768,125, EP 2 187 427 A1 (=US 8,222,621) and EP 2 363 875 A1 (=US 8,378,320). In the following, their details are given only insofar as they are necessary for the disclosure of the present invention. The components are not shown to scale in Fig. 1 for the sake of clarity. The main components of a lithographic apparatus 1 - corresponding to the direction of the lithographic beams lb, pb, which in this example travel from top to bottom in the plane of Fig. 1 - are an illumination system 3 including a charged particle source, a pattern definition (PD) system 4, a projection system 5 and a target station 6 with a substrate 16 serving (used) as a target. The entire apparatus 1 is housed in a vacuum housing 2, which is maintained at high vacuum to ensure unhindered propagation of the beams lb, pb along the optical axis cw of the apparatus. The charged particle optical system 3, 5 is realized using electrostatic and / or magnetic lenses.

[0006] The illumination system 3 includes, for example, an electron gun 7, an extraction system 8 and a condenser lens system 9. It should be noted, however, that instead of electrons, in general, other charged particles can also be used. In addition to electrons, the charged particles can be, for example, hydrogen ions or other heavier ions, charged atomic clusters, or charged molecules.

[0007] The extraction system 8 accelerates the particles to a defined energy, typically of a few keV, for example 5 keV. By means of a condenser lens system 9, the particles emitted from the charged particle source 7 are shaped into a wide, substantially telecentric particle beam 50 that serves (is used) as the lithography beam lb. The lithography beam lb then illuminates the PD system 4, which includes a number of plates with a number of holes or apertures 24 (FIG. 2). The PD system 4 is held at a specific position in the path of the lithography beam lb, which illuminates the number of apertures and is split into a number of beamlets.

[0008] According to Fig. 2, some of the apertures 24 of the PD system 4 are "switched on" or "open" to be transparent to the incident beam in the sense that they allow parts of the incident beam (beamlets 51) to pass through them and reach the target; other apertures are "switched off" or "closed", i.e. the corresponding beamlets 52 cannot reach the target, and thus essentially these apertures and / or holes are non-transparent to the beam. Thus, the lithography beam lb is structured into a patterned beam pb and exits the PD system 4. The pattern of switched on apertures - only parts of the PD system 4 that are transparent to the lithography beam lb - is selected depending on the pattern to be exposed on the target 16. It should be noted that “switching on / off” of beamlets is typically achieved by some kind of deflection means provided on one of the plates of the PD system 4: the “switched-off” beamlets are deflected from their path (by a very small angle) so that they do not reach the target but are simply absorbed somewhere in the lithographic apparatus, for example by an absorbing plate 11.

[0009] The pattern as represented by the patterned beam pb is then projected by an electro-magneto-optical projection system 5 onto a substrate 16, where it forms an image of the "switched-on" apertures and / or holes. The projection system 5 performs, for example, a reduction of 200:1, with two crossovers c1 and c2. The substrate 16 used as target is, for example, a 6" mask blank or a silicon wafer coated with a particle-sensitive resist layer 17. The target is held by a chuck 15 and positioned by a substrate stage 14 in a target station 6. In the following, the terms "substrate" and "target" are used synonymously and refer to any substrate placed at a target position in a processing device.

[0010] Information regarding the pattern to be exposed is provided to the PD system 4 by a data path implemented by an electronic pattern information processing system 18 (see also the data path description below).

[0011] In the embodiment shown in Fig. 1, the projection system 5 is composed of a number of sequentially arranged electromagnetic-optical projection stages 10a, 10b, 10c consisting of electrostatic and / or magnetic lenses and other deflection means, controlled by a projection controller 56, which is for example part of a dedicated control computer or an optical system controller (not shown) of the overall device 1. These lenses and means are shown in schematic form only, since their application is well known in the art. The projection system 5 employs demagnification imaging via crossovers c1, c2. The demagnification ratio for both stages is chosen to achieve an overall demagnification of several hundreds, for example 200:1. This order of demagnification is particularly suitable for lithographic configurations in order to improve the miniaturization problems in PD devices.

[0012] The entire projection system 5 is provided with provisions to largely compensate for chromatic and geometric aberrations. Deflection means 12a, 12b, 12c are provided in the condenser [illumination system] 3 and in the projection system 5 as means for shifting the image generally laterally, i.e. along a direction perpendicular to the optical axis cw. The deflection means can be realized, for example, as a multipole electrode system located near the source extraction system (12a), near the first crossover, as shown by deflection means 12b in FIG. 1, and / or behind (downstream) the final lens 10c of the respective projection device, as in the case of using the stage deflection means 12c in FIG. 1. In this arrangement, the multipole electrode structure is used as a deflection means both for shifting the image with respect to stage movements and for correction of the imaging system in conjunction with the charged particle optics alignment system. These deflection means 12a, 12b, 12c should not be confused with the deflection array means of the PD system 4, which, in cooperation with the stop plate 11, are used to switch "on" or "off" selected beamlets of the patterned beam pb, since the former only deals with the particle beam as a whole. There is also the possibility to rotate the ensemble of programmable beams (plural) using a solenoid 13 ("air-coil") providing an axial magnetic field.

[0013] As can be seen in the detailed (longitudinal) cross-section of FIG. 2, the PD system 4 preferably comprises three plates stacked in a sequential arrangement: an "Aperture Array Plate" (AAP) 20, a "Deflection Array Plate" (DAP) 30 and a "Field-boundary Array Plate" (FAP) 40. It is useful to note that the term "plate" refers to the overall shape of the respective device and does not necessarily imply that a plate is realized as a single plate component, even though the latter is usually the preferred mode of realization; although in some embodiments a "plate" such as an aperture array plate can also be composed of multiple sub-plates, for example two movable sub-plates (see the applicant's US 8,546,767) that allow the beamlet size to be switched in-situ. The plates are preferably arranged parallel to each other at a predetermined mutual distance along the Z direction.

[0014] The flat top surface of the AAP 20 forms a defined potential interface with the condenser optics / illumination system 11 [3]. The AAP may be formed, for example, from a square or rectangular piece (approximately 1 mm thick) 21 of silicon wafer with a thin central portion 22. The plate may be covered by a conductive protective membrane 23, which is particularly advantageous when using hydrogen or helium ions (see US 6,858,118). When using electrons or heavy ions (e.g. argon or xenon), the membrane 23 may be silicon provided by the surface portions 21 and 22, respectively, in which case there is no interface between the membrane 23 and the bulk portions 21, 22, respectively.

[0015] The AAP 20 includes a number of apertures 24, realized as holes traversing the thinned portion 22. In the illustrated embodiment, the apertures 24 are configured with a straight profile and a "retrograde" profile of the bulk layer formed in the membrane 23 of the AP 20 such that the lower exit portions 25 of the holes are wider than the main portion of the apertures 24. Both the straight profile and the retrograde profile can be formed by conventional structuring techniques such as reactive ion etching. The retrograde profile significantly reduces mirror charging effects of the beam passing through the hole.

[0016] The DAP 30 is a plate with a number of holes 33, each of whose positions corresponds to the position of the apertures 24 of the AAP 20. These holes 33 are equipped with electrodes 35, 38 configured to selectively deflect individual sub-beams passing through the holes 33 from their respective paths. The DAP 30 can be manufactured, for example, by post-processing of a CMOS wafer with ASIC circuitry. The DAP 30 is made, for example, from a single CMOS wafer having a square or rectangular shape and includes a thickened portion 31 forming a frame holding a thinned (but possibly thicker than the thickness of 22) central portion 32. The aperture holes 33 in the central portion 32 are wider than the apertures 24 (for example by approximately 2 μm on each side). The CMOS electronics 34 are used to control the electrodes 35, 38 provided by MEMS technology. Near each hole 33, a "ground" electrode 35 and a deflection electrode 38 are provided. The ground electrodes 35 are electrically connected to each other, connected to a common ground potential, and include a downwardly flared (widened) portion 36 to prevent charging and an insulating portion 37 to prevent undesired shortcuts to the CMOS circuitry. The ground electrodes 35 may also be connected to portions of the CMOS circuitry 34 that are at the same potential as the silicon bulk portions 31 and 32.

[0017] The deflection electrodes 38 are configured to have an electrostatic potential selectively applied to them; when such an electrostatic potential is applied to an electrode 38, the electrode generates an electric field that induces a deflection in the corresponding sub-beam, causing the sub-beam to deviate from its nominal path. The electrodes 38 may also have a downward flared portion 39 to avoid charging. Each of the electrodes 38 is connected at its base to a respective contact within the CMOS circuitry 34.

[0018] The height (length) of the earth electrode 35 is greater (longer) than the height (length) of the deflection electrode 38 in order to suppress the crosstalk effect between the beams.

[0019] The configuration of the PD system 12 with a DAP 30 having downstream oriented electrodes as shown in Figure 2 is only one of several possibilities. Additional DAP configurations, such as those with embedded ground and deflection electrodes, can be readily devised by one skilled in the art (see other patents in the applicant's name, such as US 8,198,601).

[0020] The third plate 40 serving as the FAP has a flat surface facing the first lens portion of the downstream charged particle reduction projection optics and thus providing a defined potential interface to the first lens 16a of said projection optics. The thickened portion 41 of the FAP 40 is a square or rectangular frame made of a portion of a silicon wafer and having a thinned central portion 42. The FAP 40 is provided with a number of holes 43 which correspond to the holes 24, 33 of the AAP 20 and the DAP 30 but are wider than these.

[0021] The PD system 4, and in particular its first plate, the AAP 20, is illuminated by a wide charged particle beam 50 (where "broad" means that the beam is wide enough to cover the entire area of ​​the aperture array formed in the AAP 20), such that upon being sent through the apertures 24, the beam 50 is split into thousands (a very large number) of micrometer-sized (diameter) beams 51. The beamlets 51 and 52 will traverse (pass) the DAP and FAP unimpeded.

[0022] As already mentioned, when the deflection electrodes 38 are powered by the CMOS electronics, an electric field is generated between the deflection electrodes and the corresponding ground electrodes, which causes a small but sufficient deflection of each passing beam 52 (Fig. 2). The deflected beam can traverse (pass) the DAP and FAP unhindered, because the respective holes 33 and 34 are made wide enough. However, the deflected beam 52 is filtered out at the blocking plate 15 of the sub-column (Fig. 1). Therefore, only the beam unaffected by the DAP reaches the target.

[0023] The demagnification ratio of the charged particle demagnification optics 5 is appropriately selected in view of the size of the beams and their distance from one another at the PD device 4 and the desired size of the structures at the target, allowing for micrometer-sized beams in the PD system while nanometer-sized beams are projected onto the target.

[0024] The bundle of (unaffected) beams 51 formed by the AAP is projected onto the target with a preset demagnification ratio R of the charged particle projection optics.

[0025] It is instructive to note that the individual beams 51, 52 shown in FIG. 2 are representative of a very large number of sub-beams, typically many thousands of sub-beams, arranged in a two-dimensional XY array.

[0026] As a typical implementation of MBMW, the applicant has already realized a 50 keV electron MBMW with charged particle optics providing a reduction ratio of R=200 for 512×512 (262,144) programmable beamlets with 20 nm beam size inside a beam field of 81.92 μm×81.92 μm at the target, which corresponds to a hole size of 4 μm×4 μm in the aperture array plate (AAP). In the realized writer system, the target is a substrate realized, for example, with a 6″ mask blank (area: 6″×6″=152.4 mm×152.4 mm, thickness: 1″ / 4=6.35 mm) coated with an electron beam sensitive resist. Moreover, in the applicant's realized system, multi-beam writing is possible on resist-coated 150 mm Si wafers.

[0027] First generation MBMW production tools are targeted to use 20nm and 10nm beams providing approximately 1μA of current to turn all 262,144 programmable beams “on.” Subsequent generations of MBMW production tools are planned to use even smaller beam sizes, e.g., 8nm, and provide, e.g., 640×640=409,600 beamlets within a 81.92μm×81.92μm beam field at the target. [Prior art documents] [Patent documents]

[0028] [Patent Document 1] US6,768,125 [Patent Document 2] EP2 187 427 A1 [Patent Document 3] US8,222,621 [Patent Document 4] EP2 363 875 A1 [Patent Document 5] US8,378,320 [Patent Document 6] US8,546,767 [Patent Document 7] US6,858,118 [Patent Document 8] US8,198,601 Summary of the Invention [Problem to be solved by the invention]

[0029] The inventors have found that proper control of imaging errors can be improved by a dedicated in-situ device for measuring the exact position of the beam relative to the surface (the "target surface") on which the target is to be positioned in the respective writing machine system (charged particle processing device).

[0030] It is therefore an object of the present invention to provide an approach for determining the precise positioning of a charged particle (electron) beam relative to one or more desired locations on a target. [Means for solving the problem]

[0031] In a first aspect of the invention, a method is provided for calibrating a beam of charged particles in a charged particle processing apparatus with respect to positioning of the beam relative to a target surface of the processing apparatus. The method includes the steps of: providing a beam calibration apparatus, the beam calibration apparatus including a detector for charged particles impinging on the beam calibration apparatus and reaching at least one alignment structure provided on a surface of the beam calibration apparatus, and positioning the beam calibration apparatus to have said surface substantially in a target surface of the processing apparatus; generating a beam of charged particles in said processing device, said beam having a predetermined shape, and imaging said beam onto a designated target location on said target surface; deflecting said beam from said designated target location to said beam calibration device with a predetermined lateral initial deflection, said lateral (initial) deflection being transverse to the beam direction, thereby causing said beam to impinge on at least one of said (at least one) alignment structures; performing a scan of the beam on the beam calibration device, thus covering a predetermined area of ​​the beam calibration device including the at least one alignment structure; measuring, with said detector, an electrical current generated by said beam during said scan to obtain a current signal as a function of position in said region; Evaluating the current signal so measured and determining therefrom the relative position of the centre of the beam with respect to a predefined optimum position on the surface of the beam calibration device. In a second aspect of the present invention, a beam calibration apparatus for calibrating a charged particle beam of a given type is provided. The beam calibration device is intended for use in a charged particle processing device that uses a charged particle beam of the given type. The beam calibration device comprises: an alignment surface having at least one alignment structure disposed thereon, the alignment surface being oriented substantially perpendicular to an axial direction along which the beam is to be emitted into the beam calibration device; and a detector configured to measure an amount of charged particles that reach the at least one alignment structure when illuminated by the beam as an output signal. Contains; The beam calibration device is configured to transmit the output signal to a calibration controller connectable to the beam calibration device for evaluating the output signal. In a third aspect of the present invention, there is provided a charged particle optical device configured as a multi-column system including a plurality of particle optical columns configured to simultaneously process the same target positioned at a target plane within the charged particle optical device. the charged particle optical device further comprising a plurality of beam calibration devices according to the invention positioned longitudinally in or near the surface of the target, laterally of the target or at a distance from the target, respectively; Each of the plurality of beam calibration devices is associated with a respective one of the plurality of particle-optical columns or with a respective one of a plurality of mutually disjoint (i.e., having no common elements (in this case, particle-optical columns): disjunct) groups of particle-optical columns. In a fourth aspect of the invention, there is provided a charged particle processing apparatus including a beam calibration device according to the invention. the beam calibration device is positioned longitudinally at or near a surface of a target in the processing device and at a position laterally offset from a position intended for a target to be processed by the processing device; The charged particle processing device further includes a calibration controller to which the beam calibration device is connectable; The calibration controller is configured to receive a position signal relating to a relative position of the beam impinging on the beam calibration device, record the output signal as a function of the relative position, and determine an optimal relative position of the beam from the output signal as a function of the relative position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] (Mode 1) See the first aspect of the present invention above. (Mode 2) In the method according to mode 1, the method is used in a charged particle optical device configured as a multi-column system including a plurality of particle optical columns configured for simultaneous processing on the same target; a plurality of beam calibration devices are provided and positioned longitudinally on or near the face of the target, laterally of the target or at a distance from the target; for each beam of a plurality of said particle-optical columns and for one beam calibration device associated with each of said plurality of beam calibration devices, the following steps of said method: deflecting the beam, performing a scan, and measuring the electrical current generated by said beam are performed using the respective associated beam calibration device. is preferred. (Mode 3) In the method according to mode 1, the beam being formed from a plurality of beamlets; wherein in the step of performing the scan, the beam is deflected across the alignment structure to pass through a plurality of scan positions according to a grid of predetermined positions; the grid having a grid pitch that is smaller than a nominal size of a beamlet spot as produced by a single beamlet at the target plane; is preferred. (Mode 4) In the method according to mode 1, the beam being formed from a plurality of beamlets; wherein in the step of performing the scan, the beam is deflected across the alignment structure to pass through a plurality of scan positions according to a grid of predetermined positions; the grid having a grid pitch equal to a nominal size of a beamlet spot as produced by a single beamlet at the target plane; is preferred. (Mode 5) In the method according to mode 1, the beam being formed from a plurality of beamlets; In the step of performing the scan, the beam is deflected across the alignment structure through a plurality of scan positions according to a grid of predetermined positions; based on a predefined division of said grid of locations into distinct subsets, one of said subsets is used, and thus said beam is deflected to pass only through scan positions corresponding to said subset; If the step of performing the scan is repeated at subsequent times, each subsequent time uses a different subset, and the plurality of subsets are repeated. is preferred. (Mode 6) In the method according to Mode 5, The distinct subsets represent substantially equivalent sub-grids. is preferred. (Mode 7) In the method according to any one of Modes 1 to 6, particularly Mode 1, wherein in the step of performing the scan, the beam is deflected across the alignment structure to pass through a plurality of scan positions according to a grid of predetermined positions; the grid is composed of at least two grid areas having different grid pitches; Grid areas with larger grid pitches are defined in areas where less importance is placed on the quality of the center relative position determination. is preferred. (Mode 8) In the method according to any one of Modes 1 to 7, particularly Mode 1, the different beam portions of the beam being used for corresponding subsequent calibrations; the results of each of the center relative positions so determined from said plurality of calibrations are used to derive a distortion map, said distortion map describing how different portions of said beams are positioned relative to one another at said designated target location. is preferred. (Mode 9) In the method according to mode 8, a plurality of alignment structures are used, each of the alignment structures being located at a respective predetermined position on a beam calibration device, for the plurality of calibrations performed after using the plurality of different beam portions; the plurality of alignment structures being substantially aligned with positions of the plurality of distinct beam portions when projected onto the plurality of alignment structures; is preferred. (Mode 10) In the method according to any one of Modes 1 to 9, particularly Mode 1, The method is performed during or immediately prior to a writing process for a substrate provided at the designated target location. is preferred. (Mode 11) In the method according to any one of Modes 1 to 10, particularly Mode 1, In the step of performing the scan, the beam is deflected by a beam deflection device of the charged particle processing device so as to traverse the alignment structure. is preferred. (Mode 12) See the second aspect of the present invention above. (Feature 13) In the beam calibration device according to feature 12, the alignment surface being configured as a free-standing membrane member having at least one alignment structure; the alignment structure being transparent to the charged particles impinging on the alignment surface, but otherwise impermeable to the charged particles; the detector is positioned downstream of the at least one alignment structure and configured to measure a quantity of charged particles passing through the alignment surface. is preferred. (Feature 14) In the beam calibration device according to feature 12 or 13, particularly according to feature 12, the alignment surface is provided with a plurality of alignment structures having the same shape when viewed along the axial direction; is preferred. (Mode 15) In the method according to any one of Modes 1 to 11, the beam calibration device is configured as the beam calibration device according to any one of Modes 12 to 14. is preferred. (Mode 16) See the third aspect of the present invention above. (Feature 17) In the charged particle optical device according to feature 16, Each of the plurality of beam calibration devices is disposed on a respective movable stage. is preferred. (Feature 18) The charged particle optical device according to feature 16 or 17, particularly according to feature 16, The multi-column system further includes a calibration controller connected to the beam calibration devices and configured to calibrate the charged particle beams of the particle-optical columns. is preferred. (Mode 19) See the fourth aspect of the present invention above.

[0033] The above object is achieved by a method for calibrating a charged particle beam in a charged particle processing device with respect to its positioning relative to a target surface of the device, the method comprising the steps of: providing a beam calibration device, the beam calibration device including a detector for charged particles impinging on the beam calibration device and reaching at least one alignment structure provided on a surface of the beam calibration device, and positioning the beam calibration device to have a surface of the device substantially in a target plane of the processing device; generating a beam of charged particles in said processing device, said beam having a predetermined shape, and imaging said beam onto a designated target location on said target surface; deflecting said beam from said designated target location to said beam calibration device with a predetermined lateral initial deflection, said lateral (initial) deflection being transverse to the beam direction, thereby causing said beam to impinge on at least one of said (at least one) alignment structures; performing a scan of the beam on the beam calibration device, thus covering a predetermined area of ​​the beam calibration device including the at least one alignment structure; measuring, with said detector, an electrical current generated by said beam during said scan to obtain a current signal as a function of position in said region; Evaluating the current signal so measured and determining therefrom the relative position of the centre of the beam with respect to a predefined optimum position on the surface of the beam calibration device.

[0034] Furthermore, advantageously, the central relative position obtained in the last step above can be used to deflect the beam back to the designated target position using a reverse lateral deflection comprising the inverse of the initial deflection combined with a deflection correction, which represents a correction of the lateral beam position to compensate for the central relative position, which is useful, among other things, to compensate for drifts in the lateral position of the beam.

[0035] This method provides an effective approach to determine and / or implement the calibration position of the beam, which also allows compensation of drifts in charged particle processing devices. Here, "particles arriving (at the registering structure)" means that these particles impinge on the shape of the respective registering structure so as to contribute (be reflected) to the signal of the measurement. In one typical special case, the charged particles can be electrons, in which case the beam calibration device is configured to detect electrons. The method according to the invention can also be used to determine the "distortion" of the beam at the target position. Here, "distortion" means a change in the nature of the focus over the area of ​​the beam (the different beamlets that make up the beam), which can thus contribute to a better detection of the presence and amount of imaging defects of the image field generated by the beam on the target.

[0036] The invention, in particular the method according to the invention, can also comprise in particular one or more of the following developments.

[0037] Advantageously, the step of evaluating may include fitting a preselected function to the measured current signal, obtaining optimal fitting parameters and determining therefrom the location of the center of the signal curve (representing signal strength as a function of position).

[0038] In many configurations, the steps of deflecting the beam and performing the scan are realized using a beam deflection device of the charged particle processing device (which is typically positioned upstream of the target plane), and in the step of performing the scan, the beam is deflected across the alignment structure through a plurality of scan positions according to a grid of predefined positions. The grid preferably has a grid pitch (mesh width) smaller than the nominal size of the beamlet spot as generated by a single beamlet at the target plane (e.g., 1 / 2 n The grid pitch (mesh width) may be equal to or smaller than the nominal size of the beamlet spots, for example, twice the size or a convenient multiple (e.g., 2× n), where n is an integer or half integer in the case of a double-centered grid raster as shown in FIG. 8C of our US 10,651,010. In other configurations, the grid pitch may be greater than the nominal size of the beamlet spots, for example, twice the size or a convenient multiple (e.g., 2× n). n It is possible for n to be an integer or half integer in the case of double-centered grid rasters.

[0039] Furthermore, in particular when the step of performing a scan is repeated to have several scanning steps, based on a predefined (conceptual) division of the grid of positions into distinct subsets, which preferably represent substantially equivalent sub-grids, one of these sub-grids is used in each iteration of the step of performing a scan; this means that the beam is deflected only through the scanning positions corresponding to the respective subset (in one iteration); when the scanning step is repeated, the subsequent iterations of the step of performing a scan use respectively different subsets, so that the iterations are performed according to the number of subsets. Furthermore, the grid used to perform the scan can be composed of grid areas with different mesh widths, i.e. at least two grid areas with different grid pitches; preferably, the grid areas with a larger grid pitch are defined in areas that are less important for the quality of the determination of the center relative position.

[0040] The calibration method of the present invention can be suitably performed during or immediately before a writing process on a substrate provided at a specified target position, which can ensure an improved accuracy of the respective writing process and prevent intrusive disturbing contributions to drift.

[0041] The calibration method of the invention is particularly advantageous for use in a charged particle optical device configured as a multi-column system. Such a system includes a plurality of particle optical columns configured for simultaneous operation on the same target positioned in the target plane: advantageously, a plurality of beam calibration devices can be provided, which can be positioned longitudinally in or near the target plane, at a lateral position relative to the target and preferably at a position remote from the target; for each of the beams, or for each of a selected subset of the beams, belonging to the plurality of particle optical columns (the number of which preferably corresponds to the number of beam calibration devices), the above-mentioned method steps of deflecting the beam, performing a scan and measuring the electric current generated by the beam will be performed using a respective one of the beam calibration devices. Thus, a plurality of beams (particle optical columns) can be simultaneously calibrated using a plurality of beam calibration devices.

[0042] A further advantageous development of the method can use a number of different beam portions of the beam (each of which may be represented by a beamlet or a group of beamlets, but the groups of beamlets representing the beam portions are preferably arranged according to the same arrangement), which are used for corresponding calibrations performed subsequently (preferably, but not necessarily immediately); and the results of the respective relative center positions so determined (from said calibrations) are then used to derive a distortion or distortion map describing how the different portions of the beam are positioned relative to one another at a specified target position. This can be used to determine (obtain) the "distortion" of the beam at the target position, as already mentioned. In particular, for said calibrations performed subsequently with said different beam portions, a number of alignment structures are used, which are arranged at respective predetermined positions of the beam calibration device, advantageously the alignment structures being substantially aligned with the positions of the different beam portions projected onto said alignment structures. Here, "substantially aligned" means that small deviations are tolerated that do not impair the accuracy of the calibration measurements.

[0043] A further aspect of the invention is directed to a beam calibration device for calibrating a charged particle beam in a charged particle processing device (particularly an electron beam in a processing device using an electron beam), in particular for use during (the performance of) the method of the invention, for use in a charged particle processing device using a charged particle beam, the beam calibration device being configured / intended for use in a charged particle processing device using a charged particle beam of a given type (particularly an electron beam), the beam calibration device being configured to detect particles of a particular type, and the beam calibration device being configured to include an alignment structure in which at least one alignment structure is arranged. an alignment surface, where the alignment surface (or alignment structure) is oriented substantially perpendicular to the axial direction along which the beam is to be irradiated into the beam calibration device; and a detector configured to measure the amount of charged particles (which may typically be electrons) that reach at least one alignment structure as an output signal when irradiated by the beam (again, "particles that reach the alignment structure" means that these particles impinge on the shape of the respective alignment structure so as to contribute (affect) the measurement signal); the beam calibration device is configured to send an output signal to a calibration controller connectable to the beam calibration target for evaluation of the output signal.

[0044] The inventive devices may in particular include one or more of the following developments:

[0045] Advantageously, the alignment surface can be configured as a membrane member, in particular as a free-standing membrane member, with at least one alignment structure, in which case such alignment structure is transparent to the charged particles impinging on the alignment surface but otherwise non-transparent to said charged particles; a detector is positioned (arranged) downstream of the (one or more) alignment structures and configured to measure the amount of charged particles passing through the alignment surface.

[0046] Furthermore, the alignment surface may suitably comprise a number of alignment structures which may have different shapes or the same shape when viewed along the optical axis, i.e., the axial direction along which the illuminated beam should run.

[0047] Furthermore, the invention also includes a charged particle optical device comprising at least one beam calibration device according to the invention; preferably, the beam calibration device is positioned longitudinally at or near the surface of the target in the processing device and preferably laterally offset from the intended position for the target to be processed by the processing device; in particular, one or more beam calibration devices can be arranged at a position outside the target. Here, "close to" means that the (calibration) device can be at a small distance to the relevant surface that does not have a significant effect on the imaging properties with respect to the calibration method, in particular that no optical components of the (processing) device are present between the (calibration) device and the target surface when viewed longitudinally. The charged particle processing device can further include a calibration controller to which the beam calibration device can be connected, such calibration controller being suitably configured to receive a position signal related to the relative position of the beam impinging on the beam calibration device, to record an output signal as a function of the relative position and to determine therefrom an optimal relative position of the beam.

[0048] The charged particle optical device can also be configured as a multi-column system including a plurality of particle optical columns, each including a respective beam calibration device according to the invention positioned longitudinally at or near the plane of the target in the respective column and preferably laterally offset from the target position in the respective column (next to the target in the multi-column system), the multi-column system preferably including a calibration controller connected to the beam calibration devices, which is provided for calibrating the charged particle beams of the particle optical columns and advantageously uses the respective output signals provided by the respective beam calibration devices and the respective position signals relating to the relative positions of the respective beams impinging on the respective corresponding beam calibration devices. In such a system with a plurality of (multiple) beam calibration devices, it is also possible that all of the beam calibration devices are arranged in a fixed arrangement or that each of the beam calibration devices is arranged on a respective movable stage to allow correction of misalignment between the beam calibration devices according to the arrangement of the single columns. The multiple beam calibration devices can preferably be positioned not only longitudinally in or near the plane of the target, but also laterally relative to the target and, possibly advantageously, at a distance from the target. Furthermore, the multiple particle-optical columns can preferably be configured to operate simultaneously on the same target, in which case each of the multiple beam calibration devices can be appropriately associated with a respective one of the multiple particle-optical columns or with a respective one of multiple groups of particle-optical columns that are separate from each other (i.e. have no elements (particle-optical columns in this case) in common: disjunct) and used to perform a calibration for the respectively associated column of these columns (or respectively for one of the columns of the respectively associated group).

[0049] In the following, reference will be made to exemplary, non-limiting embodiments (or examples) illustrated in the drawings in order to further explain the invention. [Brief description of the drawings]

[0050] [Figure 1] FIG. 1 is a longitudinal sectional view of an example of a charged particle multi-beam system. [Diagram 2] 1 is a vertical cross-sectional view of an example of a prior art pattern definition system; [Diagram 3] 3A and 3B are cross-sectional and plan views, respectively, of an example layout of a BCT according to an embodiment of the present invention. [Figure 4] FIG. 4. Plan view of the BCT in FIG. 3 with beam images projected onto the BCT during scanning. [Diagram 5] Some examples of suitable shapes for registering structures, among others Fig. 5(A) shows a cross, Fig. 5(B) shows an L-shape, Fig. 5(C) shows a rectangular or square shape, and Fig. 5(D) shows a box shape. [Figure 6] An example of a one-dimensional signal generated by a slit-shaped alignment structure. [Figure 7] 13 is an example of a signal profile produced by a cross-shaped alignment structure and a point beam. [Figure 8] Example of a cross-shaped alignment structure and signal profiles produced by two different sized cross-shaped beams. [Figure 9] FIG. 1 shows a top view of an example alignment structure with material deposited on its inner long edges due to aging. [Figure 10] 1 is an example of a dense grid of grid points used during a calibration scan. [Figure 11] An example of overlap of two beam spots in interlocking grids. [Figure 12A] A one-dimensional example of a grid that includes "thinned-out" grid areas. [Figure 12B]A 2D example of a grid, including "thinned-out" grid areas. [Figure 13] Deflection vectors for an example calibration method for BCT and target. [Figure 14A] 1 illustrates an exemplary layout (plan view) of one example of a BCT having an array of registration structures. [Figure 14B] Beam cross section of the beam corresponding to the BCT in Figure 14A. [Figure 15A] FIG. 1 is a schematic longitudinal cross-sectional view of a multi-column writer tool including a BCT. [Figure 15B] FIG. 15B is a detailed view of the BCT in the drawing machine tool of FIG. 15A. [Figure 16] FIG. 1 is a detailed view of an example of a multiple BCT arrangement where each BCT is mounted on a moveable stage within a common frame. EXAMPLES

[0051] The detailed discussion of exemplary embodiments of the present invention given below discloses the basic idea, realization and further advantageous developments of the present invention. It is clear to a person skilled in the art to combine any of some or all of the embodiments discussed herein as deemed suitable for a particular application of the present invention. Throughout this disclosure, terms such as "advantageous", "exemplary", "typical", "preferably" or "preferable" refer to elements or dimensions that are particularly suitable - but not essential - for the present invention or an embodiment thereof, and can be modified, unless expressly required, if deemed suitable by a person skilled in the art. It is understood that the present invention is not limited to the exemplary embodiments discussed below, which are given for the purpose of illustrating the present invention and merely present preferred embodiments of the present invention. Within the scope of this disclosure, terms relating to the vertical direction, such as "up" or "down", should be understood with respect to the direction of a particle beam traversing an electromagnetic lens, which is considered to travel downward ("vertically") along a central (or vertical) axis. This vertical axis is generally identified by the Z direction, which intersects the X and Y directions.

[0052] Electro-Optical System

[0053] In a preferred embodiment of the invention, a beam calibration method is applied to a multi-beam writer tool, such as that shown in Figure 1, to calibrate the lateral positioning of a shaped charged particle (electron) beam on an image plane relative to a reference point that can be used, among other things, for proper positioning of the beam on a mask substrate loaded into the tool at a desired target location. The method preferably uses the following tool components: · an electron-optical system 5 of the writing machine tool, which is capable of defining a beam or a bundle of beams by means of a pattern definition device 4; a beam calibration target 19 (BCT) arranged in a target plane of the electron optical system, including an electron current measuring device and configured to generate an output signal s1 having an intensity (magnitude) describing (defining) the degree to which the beam illuminates a structure on the BCT; an electron-optical deflection device 12c of the writing machine tool, which is able to deflect the group of electron beams across the target surface and is usually positioned in the beam path just before the target surface (i.e. as the final (most downstream) particle-optical component);

[0054] The above mentioned components are controlled by a controller 56 of the imaging apparatus 1. The beam calibration method according to the invention uses a signal s1 generated by the BCT 19 and a signal s2 that specifies the relative position of the beam when it hits the target, such as a signal branched off from a deflection signal that controls a deflection device (symbolically shown by a wavy line in FIG. 1). Preferably, the beam calibration is performed in a program module of the controller 56 or in a special calibration controller 59 that cooperates with the controller 56 and that may preferably be located in the housing 2 of the imaging apparatus 1.

[0055] Beam calibration target (BCT)

[0056] The BCT serves to indicate the alignment of the beam with a predefined nominal position on the BCT top surface. The BCT is embodied as a component on the mask chuck 15 and / or target stage 14 that holds the substrate 16 (or target). This allows the BCT to be positioned to the side of the substrate 16 position. Vertically, the BCT is arranged so that its top surface is positioned at the target plane of the electron optical system. The BCT top surface preferably includes a registering surface oriented towards the incoming (incident) beam as described below.

[0057] One preferred embodiment of a BCT is shown in Figure 3. The BCT 140 includes an alignment surface, such as a structured top membrane member 144, having a number of alignment structures (such as apertures 143 formed in a membrane member 144, or a number of such apertures arranged in a particular two-dimensional layout), and an electronic current measurement device 145 disposed below the alignment surface (or membrane member).

[0058] Each alignment structure is preferably embodied as a recess and / or hole formed in the surface of the BCT 19, for example as an aperture in the top membrane member of the BCT. In the embodiment shown in Figures 3(A) and 3(B), the alignment structure is an aperture 143 that allows the electrons to pass, while other areas of the membrane member 144 block (by absorption and / or reflection) any incoming electrons. In other embodiments, the alignment structure can be formed as a shaped recess, such that the membrane member at the recess is thinned to a thickness that can be penetrated by (highly) energetic electrons, while other areas of the membrane member have a significantly larger thickness (and preferably an additional cover layer as described below), so that the electrons cannot pass through the membrane member in the latter areas. The shape of the alignment structure can be any suitable shape, such as a narrow rectangle (i.e., a slit), an L-shape (FIG. 5(B)), a rectangle or square (FIG. 5(C)), a box shape (FIG. 5(D)) or a cross (FIGS. 5(A), 3(B)), as seen in a plan view of the BCT surface.

[0059] Calibration Method

[0060] In an exemplary embodiment of the present invention, and with reference to FIG. 13, a preferred method of lateral position calibration includes the following steps: Generating an electron beam embodied as a single beamlet or multiple beamlets in a charged particle multi-beam writer tool using a PD device that defines the beamlet(s) according to a specific beam pattern (as described further below); Appropriate "initial deflection" towards the BCT 70 and, preferably, specific alignment features 71 of the BCT (as further described below). deflecting the electron beam by TIFF2024127864000002.tif4170, where the "initial deflection" corresponds to a (pre-measured or pre-calculated) relative position of the BCT with respect to a pre-defined target reference position 73 ("designated target position") on the target 72; this deflection is preferably achieved by a deflection device of the writer tool, typically a multi-pole deflector, such as deflection device 12c of the multi-beam system of FIG. 1, and may additionally include a movement generated by the substrate stage 14, especially if the initial deflection is large; · Irradiating the BCT 70 with an electron beam 75 within proximity of the particular alignment structure(s) 71; performing a scan using said deflection device to deflect the beam across the alignment structure according to a grid of positions, the scan being suitably performed over a sufficiently large area to ensure that the scan covers the alignment structure, preferably using a set of discrete scan grid positions according to a predefined grid (see below for a description of a suitable grid); measuring the electron current that can pass through the BCT alignment structure using an electron current measurement device, taking advantage of the fact that the measured current signal s1 forms a curve that corresponds to the convolution of the electron beam and the alignment structure as a function of the grid point position of the scan (see Figures 6 to 8(B)); · Determining the center (middle) position of the signal curve s1 (xc in Figure 6) by fitting an appropriate function to the measured current signal; From the central position thus determined, the deviation of the electron beam 75 from its desired (nominal) position on the BCT. TIFF2024127864000003.tif4170 (this offset is also referred to as the "central relative position"), which can then be used to determine the deflection correction needed to reposition (or center) the electron beam with respect to the alignment structure; and Using the deflection device described above, deflect the electron beam back from the BCT to the designated target location by a suitable reverse deflection (reverse deflection) 74, where the reverse deflection 74 is a basic reverse deflection (corresponding to the reverse of the "initial deflection"). TIFF2024127864000004.tif4170, and further including the deflection correction determined in the previous step. Also includes TIFF2024127864000005.tif4170.

[0061] Thus, the electron beam is repositioned as needed to accurately position the electron beam at a particular target location on the target 72 as required for a subsequent writing process on a substrate disposed at the target location.

[0062] The calibration process is controlled by a calibration controller 59 which controls the mask stage position and the deflection device (e.g. by controlling the supply voltages of the deflection device). This is advantageous since, in the inventor's opinion, in general the positioning accuracy of the target stage is less than, and often significantly worse than, the positioning accuracy of the optical deflection elements. The stage is therefore moved roughly (coarse) so that the electron beam can impinge on the BCT, and the deflection device is used for fine positioning of the beam position on the target and to perform scanning steps as required during the writing process. To perform the desired spatial deflection, the method may also involve the use of a sensitivity matrix which indicates (specifies) the required voltages supplied to the deflection device, as will be explained in more detail below.

[0063] The calibration controller 59 may be embodied as a program module of the controller 56 or as a specific controller device cooperating with the controller 56, and may preferably be located within the housing 2 of the imaging apparatus 1. For the beam calibration process according to the present invention, the calibration controller 59 uses a signal s1 generated by the BCT 19 and a signal s2 that identifies the relative position of the beam when it strikes the target surface (note that the signal s2 is symbolically shown in FIG. 1 by a wavy line, since in general this signal s2 may be a control signal for the deflection device 12c or a signal that is branched off from the deflection device control signal).

[0064] Pattern of BCT alignment structure

[0065] In an exemplary embodiment of the invention, a scan is performed on a beam, as formed in a PD device, defined by a single beamlet. The beam traverses the electron-optical system of the writer tool to perform a lateral position calibration according to the invention. It should be seen that if the size of the single beamlet is small compared to the typical dimensions of the alignment structures of the BCT, the resulting measurement current signal scan will generate a map that generally looks like the shape of the structure itself (since the convolution of a point-like function with a specific shape simplifies to a very equal shape). In the exemplary case where the shape of the alignment structure is a cross (FIG. 3(B)), the measurement current pattern as a function of the abscissas x and y will reproduce this (cross) shape as shown in FIG. 7, if the lateral size of the beam is negligible compared to the feature size of the cross.

[0066] Since typical electron beamlets formed by a pattern definition device have a non-zero (finite) size, there will be transition zones at the boundaries of the BCT pattern in the current measurement, as shown in Figure 6. Note that Figure 6 shows the intensity (one-dimensional signal) generated by a simple slit-shaped structure when traversing in a direction perpendicular to the elongation direction of the slit shape. Since real electron beamlets formed by a pattern definition device have a non-zero blur, the resulting signal will additionally blur out the corners (rather than the straight hypotenuses as shown in Figure 6) outwards (spreading out).

[0067] The use of a single beamlet for calibration may suffer from a low signal-to-noise ratio in the current measurement, which is highly dependent on the current measurement method, as described in more detail below. The use of a beam including multiple beamlets can improve this problem. Furthermore, when multiple beamlets are used to perform the calibration, this provides the additional advantage that the beam may have a suitable pattern structure.

[0068] FIG. 3(A) shows a detailed longitudinal section of the BCT 140 at an aperture 144 of the BCT 140, and FIG. 3(B) shows a plan view of the BCT aperture. Furthermore, FIG. 4 shows an example of scanning using a shaped beam 142 composed of multiple beamlets, where the beam (or more precisely, the image of the beam, shown as a black cross in FIG. 4) scans across the alignment structure 143 (throughout the alignment structure 143) along the direction indicated by the arrow. Depending on the position of the beam relative to the alignment structure, only some of the beamlets are transmitted through the membrane 144 towards the current measurement device 145. Due to an exemplary pattern of beamlets arranged in a cross and an aperture of the BCT membrane in a similar cross shape, a two-dimensional measurement current pattern would typically look like that used in FIG. 8(A) and FIG. 8(B). Figure 8(A) shows an example where the cross-shaped electron beam pattern has exactly the same size as the BCT pattern, while in Figure 8(B) the cross-shaped electron beam pattern is smaller. As can be seen in the figures, the current patterns in Figures 8(A) and 8(B) contain substantial transition zones, which are generated by partial propagation of the groups of beamlets at the edges of the aperture. The calibration results include the average deflection of the beamlets.

[0069] In general, the pattern of the beamlets is not required to resemble the shape of the aperture (or, more generally, the alignment structure).

[0070] Charged particle current measurement

[0071] The BCT further includes a device for accurately measuring the electron current transmitted through the BCT alignment structure; preferably, this measurement device should have high accuracy and a large signal-to-noise ratio. In one exemplary embodiment of the invention, the measurement device may be a Faraday cup positioned downstream of the membrane member containing the alignment structure. In other embodiments, other suitable types of devices may be used, such as a channeltron or semiconductor detector.

[0072] Material Selection for BCT

[0073] The choice of material for the BCT can affect the performance of the BCT. The highest priority for the function of the BCT is opacity (non-transmittance) to electrons in areas different from the alignment structures, which can be optimized by choosing an appropriate (sufficient) thickness of the material. In one exemplary form, the bulk material can be silicon coated with a metal such as titanium. Silicon has the advantage of having good processability (utilizing best practice in the processing industry) and strongly facilitating the formation of alignment structures. A coating, such as a titanium coating, is advantageous because it protects the silicon from oxidation. Furthermore, a conductive coating helps to protect the BCT surface from charging during electron exposure. Furthermore, it is advantageous for the coating to be vacuum-compatible. Those skilled in the art should appreciate that the choice of material also has an impact on the backscattering of electrons generated on the BCT surface, which can affect other parts of the writer tool.

[0074] Aging - Adhesion of material to alignment structures

[0075] Due to the interaction of electrons with residual gases and other effects, material (e.g. carbon compounds) may deposit on or at the boundaries of the alignment structure, hereinafter referred to as aging. In particular, recesses or openings may close. In general, this aging may be non-uniform along the edges of the alignment structure for exposure positioning of the beamlets. An example of aging is shown in FIG. 9, which shows a top view of a slit-shaped alignment structure 60 with an irregularly shaped material 61 deposited on its inner long edge. This aging will disturb the current measurements and therefore the center position determined with the "aged" alignment structure, until the measurements become unreliable. By choosing the calibration scan grid positions in a particular way, the aging can be reduced and uniformed so that the problem is reduced or even eliminated, as explained in the following section.

[0076] Calibration Scan Method

[0077] The choice of grid locations used during the calibration scan can strongly affect the performance of the calibration and the aging effects mentioned above. On the one hand, a larger number of grid points provides finer data to be fitted and improves the quality of the fitting, but on the other hand, the scan is longer. The aging effects depend on the position of the beamlets along the edge of the alignment structure. One possible improvement is to define a dense grid as shown in FIG. 10 so that the electron beam dose deposited is uniform for all scan points. In FIG. 10, each square corresponds to one beam spot generated by the beam during the scan, so that the whole area is completely covered by the beam spots of the grid ("dense grid") as also shown in FIG. 10.

[0078] To reduce the total number of grid points used during each one of the calibration processes, only one subgrid of the grid may be used, but if the calibration process is performed multiple times, multiple different subgrids of the same grid are used; this is also referred to as "spreading out" the grid for multiple calibrations. For example, referring again to FIG. 10, only beam spots numbered "1" are used in one loop of the calibration process, while beam spots numbered "2" are used in the next loop of the calibration, beam spots numbered "3" are used in the third loop, and then "1" again, etc. Thus, the entire dense grid is used by subsequent sets of multiple calibrations (three calibrations in this example). This allows the number of grid points used during each individual instance of the calibration process to be reduced, thus reducing the time used by the scan and the complexity of the calibration.

[0079] Overlapping beam spots, interlocking grid

[0080] In another preferred development of the invention, in addition to the dense grid described above, aging can also be suppressed (by counter-action) by using overlapping beam spots, for example in conjunction with so-called "interlocking grids", where the interlocking grids are multiple grids positioned interdigitated with each other with a mutual offset that is only a small fraction of the grid spacing (corresponding to the nominal size of the beamlet spot on the target), which allows the beamlet spots to overlap (for example by 25 or 50 percent of a pixel on the target) to form sub-pixels and thus sub-pixels in the pattern raster generated by the beamlets. Interlocking grids are described in more detail in the applicant's US Pat. No. 7,276,714 and US Pat. No. 9,053,906. A simple example of overlapping beam spots is shown in Figure 11, where a pixel 70 formed by a first beamlet overlaps with another pixel 71, the overlapping region forming a sub-pixel 77 to which the combined dose from the two pixels 70 and 71 is applied. The interlocking grid can also be "rolled out" over multiple calibrations. This has the advantage of further uniforming the electron beam dose applied to the edges of the alignment structure, since local non-uniformities of the beamlets are averaged out to a large extent.

[0081] Thinning out the scan grid

[0082] In the scan grid used in the above scanning method, which is mainly focused on aging uniformity, there are regions in the grid that do not affect aging but are less significant or even in some cases irrelevant for the quality of the subsequent fitting. Such regions can be scanned with a reduced number of grid points; thus, these regions are covered by grid areas in which the grid is "thinned out" by making the grid pitch (in such grid areas corresponding to regions less significant for fitting to determine the center relative position) larger than the grid pitch in grid areas corresponding to regions more significant (i.e., generally more important for determining the center relative position) for achieving a good quality of fitting.

[0083] 12A and 12B show examples of "thinned" scan grids. FIG. 12A shows an example of a linear scan where the beam pattern illuminates a larger alignment structure. In this case, there is a central region 121 in the scan where the full beam passes through the alignment structure, and the grid points in this region 121 have negligible effect on aging. Therefore, the grid points falling on the region 121 have little significance on the quality of the fitting. To reduce the time required for the scan, the grid points in such regions can be thinned out. Such thinning is shown in FIG. 12A, where the grid points in an example of a 1D scan are thinned out in a grid area 122 that is located within the expected range of the plateau. FIG. 12B shows an example of a 2D scan for a rectangular alignment structure. In this example, only the ring-shaped region 123 that is expected to coincide with the site(s) where signal changes occur is performed using a grid with a small grid pitch, while other regions 124, 125, in this case the regions inside and outside region 123 shown in FIG. 12B, are "thinned out".

[0084] deflection device

[0085] Deflection devices are used to perform fine deflections for the scan. Deflection devices are for example electrostatic multipole electrode systems, which allow the realization of deflections by applying electric potentials (voltages) to individual electrodes. In its simplest form, the deflection element is a plate capacitor. For deflection in two directions at right angles, a double plate capacitor can be realised. Advantageously, the deflection device is a multipole system with an appropriate number of electrodes. To measure the deflection sensitivity of the deflection element, i.e. the transversal deflection is determined by the vector In the case of the beamlet 100, a pre-calibration method can be used to determine which voltages V1, V2 are required to perform a particular lateral deflection of the beamlet(s). The deflection sensitivity can be expressed by a sensitivity matrix, which can be expressed as: TIFF2024127864000007.tif6170

[0086] The elements of this sensitivity matrix can be measured by the pre-calibration method described above. Using the sensitivity matrix, TIFF2024127864000008.tif4170 or This allows for a suitable approach to control predefined deflections, such as TIFF2024127864000009.tif4170.

[0087] Fitting Method

[0088] The fitting method is a step in the calibration process according to the present invention, and involves fitting an offset vector between the expected position of the beam center and the actual beam center located as measured. TIFF2024127864000010.tif4170 (see FIG. 13). It is clear that the function used for fitting is appropriately selected to describe the overall shape of the convolved measured electron current pattern with sufficient accuracy. Preferably, the fitting method involves a translation, described by an offset in two lateral coordinates x and y. The accuracy of the fitted offset is determined by the quality of the fitting function, the grid points (number and arrangement) and the potential noise on the measured current signal. A determined non-zero offset indicates a deflection correction in the optical system (e.g. caused by drift over time). The offset measurement can therefore be used to recalibrate the entire electron beam to a central (middle) position. An example of a fitting function that can be used for the one-dimensional example of FIG. 6 is the base level TIFF2024127864000011.tif4170, its length TIFF2024127864000012.tif4170, Plateau Level TIFF2024127864000013.tif4170, its length TIFF2024127864000014.tif4170 and center Piecewise definition with TIFF2024127864000015.tif4170: A trapezoid function embodied by TIFF2024127864000016.tif30170. Another example is a fitting function with curved flanks, which can be modeled by stitching together suitable functions such as a first sigmoid function for the rising hypotenuse and a second sigmoid function for the falling hypotenuse. Suitable fitting functions for two or more dimensional fittings can be easily provided by one skilled in the art by stitching suitable one-dimensional functions.

[0089] Beamlet distortion measurement

[0090] 14A and 14B, using different beamlet sections of the image field, distortion measurements can be performed, i.e. it is determined (measured) how different segments of the beamlets across the image field are positioned relative to each other and relative to the ideal positions. For this, preferably multiple alignment structures can be used. For example, as shown in FIG. 14A, a composite BCT with an array of 6×6 alignment structures 81, which may preferably have the same shape but may also have different shapes, is used in combination with a beam 80 as shown in FIG. 14B, which may have a suitable shape and in particular be composed of a corresponding array of sub-beams, which are preferably formed.

[0091] Multi-column System

[0092] 15A and 15B show an example of a multi-column writer tool 100. The writer tool uses multiple charged particle beams, which may consist of electrons or ions (e.g. positively charged ions). As can be seen in FIG. 15A, which shows a schematic longitudinal cross-section of the multi-column writer tool 100, the writer tool 100 comprises a vacuum housing 48 for the multi-column charged particle optics, a base 47 on which the multi-column charged particle optics is arranged. On top of the base, an XY stage 46, e.g. a laser interferometer controlled air-bearing vacuum stage, is arranged with a suitable manipulation system. On the stage, a target 45, preferably a mask for lithography purposes or a silicon wafer in a direct write writer tool, is placed. The target then comprises, e.g. a resist layer, which may be exposed by the charged particle beams of the writer. The multi-column writer tool 100 further comprises, preferably for each column or for each subset of the columns, a respective instance of a BCT 90 according to an embodiment of the present invention. Each BCT 90 (symbolically shown as cross-hatched squares in FIG. 15B) may be positioned next to a target 45 on a stage 46 .

[0093] This form of multi-column optical system includes a number of sub-columns 400 (the number of columns shown has been reduced for clarity, but is representative of the much larger number of columns that would be present in a multi-column device in a real implementation). Preferably, the sub-columns have the same setups and are arranged side-by-side with their axes c5 parallel to one another. Each sub-column comprises an illumination system 412 including a charged particle source 411 supplying a wide, telecentric charged particle beam to a pattern definition device 413, which is configured to pass only through a number of apertures (beam shaping devices) that define the shape of the sub-beams ("beamlets") passing through said apertures, typically a reducing and even energizing type of charged particle projection optics 44, which preferably comprises a number of sequentially arranged charged particle lenses including electrostatic and / or magnetic lenses, and possibly further other charged particle devices. In the embodiment of Figure 15, the projection optics comprises, for example, a first charged particle lens 44a, e.g. an electrostatic immersion lens, while a second lens 44b arranged downstream of the first lens may be embodied using a charged particle electromagnetic lens.

[0094] FIG. 15B details a top view of the lower portion of a multi-column writer tool 40

[0100] in which multiple BCT devices 90 are positioned beside the target on the stage. Each BCT is positioned longitudinally (vertically) at or near the surface of the target. A common calibration controller (not shown; see controller 59 in FIG. 1) is provided to perform and control a calibration method for the charged particle beams of the charged particle columns. Notably, if there is one BCT per column and the BCT devices are positioned corresponding to the lateral positions of the columns, the calibration method can be performed simultaneously for all of the columns; alternatively, if there is not one BCT per column, a suitable subset of the columns can be calibrated simultaneously and the other columns can be calibrated in subsequent steps. To cause the initial deflection of the beam(s) of each column(s) onto the BCT(s) 90 and reverse deflection back to the exposure area on the substrate, the target stage 46 cooperates, for example, with a multi-pole deflector component of the final lens of each column to form the appropriate total deflection of the beam between the target position and the position of each BCT 90.

[0095] The grid of the BCT devices 90 and the grid of the columns in a multi-column system may not be perfectly aligned in the plane transverse to the beam. Therefore, in another illustrative example of a multi-column configuration of the present invention, the multiple BCT devices are each mounted on a movable stage 91 so that the BCT position can be adjusted to match the grid arrangement of the columns. Figure 16 shows a detailed view of an example of this type of multi-column configuration, showing three BCTs 90 (out of a larger number of BCT devices). Each BCT 90 includes an alignment structure 92 on a movable stage 91 that ensures that each BCT can be adjusted in the plane transverse to the beam with the help of a piezoelectric element 93 connected to a common frame 94 of the BCT devices.

[0096] All or part of the above embodiments and examples can be described as the following supplementary notes, but are not limited thereto. [Appendix 1] A method for calibrating a beam of charged particles in a charged particle processing device with respect to the positioning of the beam relative to a target surface of the processing device. The method includes the steps of: providing a beam calibration apparatus, the beam calibration apparatus including a detector for charged particles impinging on the beam calibration apparatus and reaching at least one alignment structure provided on a surface of the beam calibration apparatus, and positioning the beam calibration apparatus to have said surface substantially in a target surface of the processing apparatus; generating a beam of charged particles in said processing device, said beam having a predetermined shape, and imaging said beam onto a designated target location on said target surface; deflecting said beam from said designated target location to said beam calibration device with a predetermined lateral initial deflection, said lateral (initial) deflection being transverse to the beam direction, thereby causing said beam to impinge on at least one of said (at least one) alignment structures; performing a scan of the beam on the beam calibration device, thus covering a predetermined area of ​​the beam calibration device including the at least one alignment structure; measuring, with said detector, an electrical current generated by said beam during said scan to obtain a current signal as a function of position in said region; Evaluating the current signal so measured and determining therefrom the relative position of the centre of the beam with respect to a predefined optimum position on the surface of the beam calibration device. [Appendix 2] In the method according to appendix 1, The method is used in a charged particle optical device configured as a multi-column system including multiple particle optical columns configured to simultaneously operate on the same target; A plurality of beam calibration devices are provided and positioned longitudinally at or near the face of the target, laterally of the target or at positions spaced from the target; For each beam of a plurality of said particle-optical columns and for one beam calibration device associated with each of said plurality of beam calibration devices, the following steps of the method: deflecting the beam, performing a scan, and measuring the electrical current generated by the beam are performed using the respectively associated beam calibration device. [Appendix 3] In the method according to appendix 1, the beam being formed from a plurality of beamlets; In the step of performing the scan, the beam is deflected across the alignment structure to pass through a plurality of scan locations according to a grid of predetermined locations; The grid has a grid pitch that is smaller than a nominal size of a beamlet spot as produced by a single beamlet at the target plane. [Appendix 4] In the method according to Appendix 1, the beam being formed from a plurality of beamlets; In the step of performing the scan, the beam is deflected across the alignment structure to pass through a plurality of scan locations according to a grid of predetermined locations; The grid has a grid pitch equal to a nominal size of a beamlet spot as produced by a single beamlet at the target plane. [Appendix 5] In the method according to appendix 1, the beam being formed from a plurality of beamlets; In the step of performing the scan, The beam is deflected across the alignment structure to pass through a plurality of scan locations according to a grid of predetermined locations; based on a predefined division of the grid of locations into different subsets, one (of) the subsets is used, such that the beam is deflected to pass only through scan locations corresponding to said subset; If the step of performing the scan is repeated at subsequent times, each subsequent time of the step of performing the scan uses different subsets and repeats the subsets. [Appendix 6] In the method according to Appendix 5, The distinct subsets represent substantially equivalent sub-grids. [Appendix 7] In the method according to any one of appendices 1 to 6, In the step of performing the scan, the beam is deflected across the alignment structure to pass through a plurality of scan locations according to a grid of predetermined locations; The grid is composed of at least two grid areas having different grid pitches; Grid areas with larger grid pitch are defined in areas where there is less importance for the quality of the center relative position determination. [Appendix 8] In the method according to any one of appendices 1 to 7, the different beam portions of the beam being used for corresponding subsequent calibrations; The results of each central relative position so determined from the multiple calibrations are used to derive a distortion map, which describes how different portions of the beam are positioned relative to each other at the specified target location. [Appendix 9] In the method according to Appendix 8, for the calibrations performed after using the different beam portions, a plurality of alignment structures are used, each of which is disposed at a predetermined position on a beam calibration device; The alignment structures substantially align with positions of the different beam portions when projected onto the alignment structures. [Appendix 10] In the method according to any one of appendices 1 to 9, The method is performed during or immediately prior to a writing process on a substrate provided at the designated target location. [Appendix 11] In the method according to any one of appendices 1 to 10, In the step of performing the scan, the beam is deflected by a beam deflection device of the charged particle processing device so as to traverse the alignment structure. [Appendix 12] A beam calibration device for calibrating a charged particle beam of a given type. the beam calibration device is for use in a charged particle processing device that uses the predetermined type of charged particle beam; The beam calibration device comprises: an alignment surface having at least one alignment structure disposed thereon, the alignment surface being oriented substantially perpendicular to an axial direction along which the beam is to be emitted into the beam calibration device; and a detector configured to measure an amount of charged particles that reach the at least one alignment structure when illuminated by the beam as an output signal. Contains; The beam calibration device is configured to transmit the output signal to a calibration controller connectable to the beam calibration device for evaluating the output signal. [Supplementary Note 13] In the beam calibration device according to Supplementary Note 12, the alignment surface is configured as a free-standing membrane member having at least one alignment structure; the alignment structure is transparent to the charged particles impinging on the alignment surface, but is otherwise impermeable to the charged particles; The detector is positioned downstream of the at least one alignment structure and is configured to measure an amount of charged particles passing through the alignment surface. [Appendix 14] In the beam calibration device according to appendix 12 or 13, The alignment surface is provided with a plurality of alignment structures having the same shape when viewed along the axial direction. [Supplementary Note 15] In the method according to any one of Supplements 1 to 11, the beam calibration device is configured as the beam calibration device according to any one of Supplements 12 to 14. [Appendix 16] A charged particle optical device configured as a multi-column system including multiple particle optical columns configured to simultaneously process the same target positioned on a target surface within the charged particle optical device. The charged particle optical apparatus further includes a plurality of beam calibration devices according to any one of claims 12 to 14 positioned longitudinally at or near the surface of the target, laterally of the target or at a position spaced from the target, respectively; Each of the plurality of beam calibration devices is associated with a respective one of the plurality of particle-optical columns or with a respective one of a plurality of mutually disjoint (i.e., having no common elements (in this case, particle-optical columns): disjunct) groups of particle-optical columns. [Appendix 17] In the charged particle optical apparatus according to appendix 16, Each of the plurality of beam calibration devices is disposed on a respective moveable stage. [Appendix 18] In the charged particle optical apparatus according to appendix 16 or 17, The multi-column system further includes a calibration controller connected to the beam calibration devices and configured to calibrate the charged particle beams of the particle-optical columns. [Supplementary Note 19] A charged particle processing apparatus including the beam calibration device according to any one of Supplementary Notes 12 to 14. the beam calibration device being positioned longitudinally at or near a plane of a target in the processing device and at a position laterally offset from a position intended for a target to be processed by the processing device; The charged particle processing device further includes a calibration controller to which the beam calibration device is connectable; The calibration controller is configured to receive a position signal relating to the relative position of the beam impinging on the beam calibration device, record the output signal as a function of the relative position, and determine an optimal relative position of the beam from the output signal as a function of the relative position (although possibly other signals such as the position signal may also be used together).

[0097] Within the scope of the entire disclosure of the present invention (including the claims and drawings), modifications and adjustments of the embodiments are possible based on the basic technical ideas. Furthermore, within the scope of the entire disclosure of the present invention, various combinations or selections (including "non-selection") of various disclosed elements (including each element of each claim, each element of each embodiment, each element of each drawing, etc.) are possible. In other words, the present invention naturally includes various modifications and corrections that a person skilled in the art would be able to make in accordance with the entire disclosure including the claims and drawings and the technical ideas of the present invention. In particular, with regard to the numerical ranges described in this specification, any numerical value or subrange included in the range should be interpreted as being specifically described even if not otherwise specified.

[0098] Furthermore, the reference numerals in the drawings attached in the claims are intended solely to aid in the understanding of the invention, and are not intended to limit the invention to the embodiments and examples shown.

[0099] Furthermore, the entire contents of each of the above references are hereby incorporated by reference.

Claims

1. 1. A method for calibrating a beam of charged particles in a charged particle processing device with respect to a position of the beam relative to a target surface of the processing device, comprising: The method comprises the steps of: providing a beam calibration apparatus, the beam calibration apparatus including a detector for charged particles impinging on the beam calibration apparatus and reaching at least one alignment structure provided on a surface of the beam calibration apparatus, and positioning the beam calibration apparatus to have said surface substantially in a target surface of the processing apparatus; generating a beam of charged particles in said processing device, said beam having a predetermined shape, and imaging said beam onto a designated target location on said target surface; deflecting the beam from the designated target location to the beam calibration device with a predetermined lateral initial deflection, the lateral initial deflection being transverse to a beam direction, thereby causing the beam to impinge on at least one of the alignment structures; performing a scan of the beam on the beam calibration device, thus covering a predetermined area of ​​the beam calibration device including the at least one alignment structure; measuring, with the detector, an electrical current generated by the beam during the scan to obtain a current signal as a function of position in the region; evaluating the current signal so measured and determining therefrom the relative position of the centre of the beam with respect to a predefined optimum position on the surface of the beam calibration device. A method comprising:

2. 10. The method of claim 1 , the method is used in a charged particle optical device configured as a multi-column system including a plurality of particle optical columns configured for simultaneous processing on the same target; a plurality of beam calibration devices are provided and positioned longitudinally on or near the face of the target, laterally of the target or at a distance from the target; for each beam of a plurality of said particle-optical columns and for one beam calibration device associated with each of said plurality of beam calibration devices, the following steps of said method are performed using the respective associated beam calibration device: deflecting the beam, performing a scan, and measuring the electrical current generated by said beam. A method comprising:

3. 10. The method of claim 1 , the beam being formed from a plurality of beamlets; wherein in the step of performing the scan, the beam is deflected across the alignment structure to pass through a plurality of scan positions according to a grid of predetermined positions; the grid having a grid pitch that is smaller than a nominal size of a beamlet spot as produced by a single beamlet at the target plane; A method comprising:

4. 10. The method of claim 1 , the beam being formed from a plurality of beamlets; wherein in the step of performing the scan, the beam is deflected across the alignment structure to pass through a plurality of scan positions according to a grid of predetermined positions; the grid having a grid pitch equal to a nominal size of a beamlet spot as produced by a single beamlet at the target plane; A method comprising:

5. 10. The method of claim 1 , the beam being formed from a plurality of beamlets; In the step of performing the scan, the beam is deflected across the alignment structure through a plurality of scan positions according to a grid of predetermined positions; based on a predetermined division of the grid of locations into different subsets, a subset of the plurality of subsets is used, and thus the beam is deflected to pass only through scan locations corresponding to said subset; and if the step of performing the scan is repeated in subsequent times, each subsequent time of the step of performing the scan uses a different number of subsets, and repeats the number of subsets. A method comprising:

6. 6. The method of claim 5, the distinct subsets representing substantially equivalent sub-grids; A method comprising:

7. 10. The method of claim 1 , wherein in the step of performing the scan, the beam is deflected across the alignment structure to pass through a plurality of scan positions according to a grid of predetermined positions; the grid is composed of at least two grid areas having different grid pitches; Grid areas with larger grid pitches are defined in areas where less importance is placed on the quality of the center relative position determination. A method comprising:

8. 10. The method of claim 1 , the different beam portions of the beam being used for corresponding subsequent calibrations; the respective center relative positions so determined from said plurality of calibrations are used to derive a distortion map, said distortion map describing how different portions of said beam are positioned relative to one another at said designated target location. A method comprising:

9. 9. The method of claim 8, a plurality of alignment structures are used, each of the alignment structures being located at a respective predetermined position on a beam calibration device, for the plurality of calibrations performed after using the plurality of different beam portions; the plurality of alignment structures being substantially aligned with positions of the plurality of distinct beam portions when projected onto the plurality of alignment structures; A method comprising:

10. 10. The method of claim 1 , The method is performed during or immediately prior to a writing process for a substrate provided at the designated target location. A method comprising:

11. 10. The method of claim 1 , In the step of performing the scan, the beam is deflected by a beam deflection device of the charged particle processing device so as to traverse the alignment structure. A method comprising:

12. 1. A beam calibration apparatus for calibrating a charged particle beam of a given type, comprising: the beam calibration device is for use in a charged particle processing device that uses the predetermined type of charged particle beam; The beam calibration device comprises: an alignment surface (144) on which at least one alignment structure (143) is arranged, said alignment surface being oriented substantially perpendicular to an axial direction along which the beam is to be emitted into the beam calibration device; and When illuminated by the beam, the output signal (s １ a detector (145) configured to measure an amount of charged particles reaching said at least one alignment structure as a containing, The beam calibration device detects the output signal (s １ ) to evaluate the output signal (s １ ) to a calibration controller (59) connectable to said beam calibration device. An apparatus comprising:

13. 13. The beam calibration device of claim 12, the alignment surface being configured as a free-standing membrane member (144) having at least one alignment structure (143); the alignment structure being transparent to the charged particles impinging on the alignment surface but otherwise impermeable to the charged particles; the detector (145) is positioned downstream of the at least one alignment structure and configured to measure an amount of charged particles passing through the alignment surface. An apparatus comprising:

14. 13. The beam calibration device of claim 12, the alignment surface is provided with a plurality of alignment structures having the same shape when viewed along the axial direction; An apparatus comprising:

15. In the method according to any one of claims 1 to 11, the beam calibration device is configured as a beam calibration device according to any one of claims 12 to 14. A method comprising:

16. A charged particle optical device configured as a multi-column system including a plurality of particle optical columns configured to simultaneously process the same target positioned at a target surface in the charged particle optical device, The charged particle optical apparatus further comprises a plurality of beam calibration devices according to any one of claims 12 to 14, positioned longitudinally in or near the surface of the target, laterally of the target or at a position spaced from the target, respectively; each of said plurality of beam calibration devices being associated with a respective one of said plurality of particle-optical columns or with a respective one of a plurality of mutually disjunct groups of particle-optical columns; A charged particle optical device comprising:

17. 17. A charged particle optical apparatus according to claim 16, Each of the plurality of beam calibration devices (90) is disposed on a respective movable stage (91). A charged particle optical device comprising:

18. 17. A charged particle optical apparatus according to claim 16, The multi-column system further includes a calibration controller connected to the beam calibration device and configured to calibrate the charged particle beam of the particle-optical column. A charged particle optical device comprising:

19. A charged particle processing apparatus including the beam calibration device according to any one of claims 12 to 14, said beam calibration device being positioned longitudinally at or near a plane of a target in said processing device and at a position laterally offset from a position intended for a target to be processed by said processing device; the charged particle processing device further comprising a calibration controller (59) to which the beam calibration device is connectable; The calibration controller generates a position signal (s ２ ), and receiving the output signal (s １ ) as a function of the relative position, and recording the output signal (s １ ) determining an optimal relative position of the beam from the A charged particle processing device comprising:

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