Abstract
A method includes: providing position data for a plurality of areas on the sample which are to be inspected; providing a first raster arrangement of the plurality of individual particle beams, with a single field of view on the sample assigned to each individual particle beam; defining the position of a nominal scanning area in each single field of view in relation to the first raster arrangement, with the dimensions of the nominal scanning area smaller than the complete single field of view; determining an individual position deviation between a nominal scanning area and the area to be inspected for the at least one individual particle beam; changing the first raster arrangement based on the determined individual position deviation to produce a second raster arrangement of the plurality of individual particle beams; and area-wise scanning the sample using the plurality of individual particle beams in the second raster arrangement.
Claims
1. A method of area-wise inspecting a sample using a multi-beam particle microscope which generates a plurality of individual charged particle beams, the method comprising: providing position data for a plurality of areas on the sample; providing a first raster arrangement of the plurality of individual particle beams, a single field of view on the sample being assigned to each individual particle beam; defining a position of a nominal scanning area in each individual field of view relative to the first raster arrangement, dimensions of the nominal scanning area being smaller than a complete single field of view; assigning a nominal scanning area to an area to be inspected for at least one individual particle beam; for the at least one individual particle beam, determining an individual position deviation between the nominal scanning area and the area to be inspected assigned to the at least one individual particle beam; changing the first raster arrangement according to the determined individual position deviation to produce a second raster arrangement of the plurality of individual particle beams so that the assigned areas to be inspected are scannable in a targeted fashion; and area-wise scanning the sample using the plurality of individual particle beams in the second raster arrangement.
2. The method of claim 1, wherein producing the second raster arrangement comprises an individual deflection of the at least one individual particle beam.
3. The method of claim 1, further comprising, when area-wise scanning the sample in the second raster arrangement, using a collective scan deflector to deflect all the individual particle beams.
4. The method of claim 1, wherein most of the assigned areas to be inspected are assigned to nominal scanning areas located in the same single field of view relative to the first raster arrangement.
5. The method of claim 1, wherein at least one of the following holds: mutually adjacent single fields of view of the multi-beam particle microscope overlap; and the multi-beam particle microscope comprises a single column.
6. The method of claim 1, wherein providing the first raster arrangement comprises setting of a regular pitch between mutually adjacent individual particle beams.
7. The method of claim 1, wherein setting the pitch is performed according to at least one of the following criteria: increasing a number of areas to be inspected which are located within a multi-field of view; and uniformly distributing the areas to be inspected among the single fields of view (sFOVs).
8. The method of claim 1, wherein providing the first raster arrangement comprises optimizing the first raster arrangement by changing a position, a pitch and/or a rotation of the first raster arrangement.
9. The method of claim 1, wherein the first raster arrangement is optimized according to at least one of the following criteria: arranging each area to be inspected completely within a single field of view of the raster arrangement; maximizing a distance between areas to be inspected and edges of single fields of view; and uniformly distributing areas to be inspected among the single fields of view.
10. The method of claim 7, wherein a predetermined proportion of all multi-fields of view have only single fields of view which have either no areas to be inspected or only a predetermined number of areas to be inspected.
11. The method of claim 10, wherein the predetermined proportion of all single fields of view has exactly one area to be inspected.
12. The method of claim 1, further comprising: producing a distance distribution of areas to be inspected from the provided position data; and optimizing the first raster arrangement based on the produced distance distribution.
13. The method of claim 12, further comprising: choosing a lower limit of a minimum distance between areas to be inspected in the distance distribution so that a predetermined proportion of all areas to be inspected has a minimum distance greater than or equal to this lower limit; and setting a pitch of the first raster arrangement to the lower limit.
14. The method of claim 13, wherein the predetermined proportion is at least 95%.
15. The method of claim 1, wherein the position of the nominal scanning area in each single field of view is defined according to at least one of the following criteria: maximizing the number of nominal scanning areas which already in the first raster configuration at least partially cover the areas to be inspected; minimizing the number of individual particle beams which are positioned differently in the second raster configuration in relation to the first raster configuration; and restricting a position deviation of individual particle beams in the second raster arrangement in comparison with the first raster arrangement.
16. The method of claim 15, wherein the restriction leads to the position deviation of the individual particle beams being less than twice the pitch or less than the single pitch between mutually adjacent individual particle beams in the first raster arrangement.
17. The method of claim 1, wherein, compared to the first raster arrangement, a position deviation of individual particle beams in the second raster configuration is greater than or equal to the pitch in the first raster arrangement only when more areas to be inspected are arranged in the adjacent single field of view relative to the first raster arrangement obtained by the position deviation than in the single field of view relative to the first raster arrangement.
18. The method of claim 1, wherein at least one of the following holds: the position data are generated via an optical inspection for recognizing semiconductor defects; and the position data are generated on the basis of existing prior knowledge about the sample.
19.-24. (canceled)
25. A method of operating a multi-beam particle microscope, the method comprising: setting a regular raster arrangement, the multi-beam particle microscope being technically configured to use a collective beam deflector to scan a sample using the regular raster arrangement; using a multi-stigmator or a multi-deflector to produce an irregular raster arrangement by individually deflecting at least one individual particle beam; and using the collective scan deflector to scan the sample according to the irregular raster arrangement.
26.-28. (canceled)
29. A multi-beam particle microscope, comprising: a multi-beam generator configured to generate a first field of a plurality of charged first individual particle beams; a first particle optical unit having a first particle optical beam path, the first particle optical unit configured to image the charged first individual particle beams onto a sample surface in the object plane so that the charged first individual particle beams impinge on the sample surface at incidence locations which form a second field; a detection system comprising a multiplicity of detection regions defining a third field; a second particle optical unit having a second particle optical beam path, the second particle optical unit configured to image second individual particle beams, which emanate from the incidence locations in the second field, onto the third field of the detection regions of the detection system; a magnetic and/or electrostatic objective lens configured so that both the first and the second individual particle beams pass through therethrough; a beam switch disposed in the first particle optical beam path between the multi-beam particle source and the objective lens, the beam switch disposed in the second particle optical beam path between the objective lens and the detection system; a collective scan deflector disposed between the beam switch and the sample surface, the collective scan deflector configured to collectively scan the sample surface using the plurality of charged first individual particle beams; an individual deflector arrangement disposed between the multi-beam generator and the collective scan deflector, the individual deflector configured to, in each case, deflect the first individual particle beams on an individual basis, a deactivated individual deflector arrangement or an individual deflection that is identical for all first individual particle beams corresponding to a first raster arrangement of the first individual particle beams and an activated individual deflection that is not identical for all first individual beams corresponding to a second raster arrangement of the first individual particle beams; and a controller, wherein is configured to provide: low-frequency control of the individual deflector arrangement to produce the second raster arrangement; and high-frequency control of the collective scan deflector so that portions of the sample surface located in a multi-field of view are scanned using the first individual particle beams in the second raster arrangement.
30.-33. (canceled)
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0074] The disclosure will be understood even better with reference to the accompanying figures, in which:
[0075] FIG. 1 shows a schematic representation of a multi-beam particle microscope (MSEM);
[0076] FIGS. 2A-2B schematically show an area inspection of a sample via an individual beam particle microscope;
[0077] FIGS. 3A-3H schematically show the concept according to the disclosure for the area inspection of a sample via a multi-beam particle microscope, and optimization strategies;
[0078] FIG. 4 shows a flowchart of the method according to the disclosure;
[0079] FIG. 5 shows a flowchart of a workflow for the area inspection of a sample;
[0080] FIG. 6: schematically shows a multi-beam electron microscope having a single column for carrying out the method according to the disclosure; and
[0081] FIG. 7: schematically shows a multi-stigmator with a chip, which can be controlled via the clock signal.
DETAILED DESCRIPTION
[0082] FIG. 1 is a schematic representation of a particle beam system 1 in the form of a multi-beam particle microscope 1, which uses a plurality of particle beams. The particle beam system 1 produces a plurality of particle beams which strike an object to be examined in order to generate there interaction products, e.g., secondary electrons, which emanate from the object and are subsequently detected. The particle beam system 1 is of the scanning electron microscope (SEM) type, which uses a plurality of primary particle beams 3 which are incident on a surface of the object 7 at a plurality of locations 5 and produce there a plurality of electron beam spots, or spots, that are spatially separated from one another. The object 7 to be examined can be of any desired type, e.g., a semiconductor wafer or a biological sample, and comprise an arrangement of miniaturized elements or the like. The surface of the object 7 is arranged in a first plane 101 (object plane) of an objective lens 102 of an objective lens system 100.
[0083] The enlarged detail I1 in FIG. 1 shows a plan view of the object plane 101 having a regular rectangular field 103 of incidence locations 5 formed in the first plane 101. In FIG. 1, the number of incidence locations is 25, which form a 5×5 field 103. The number 25 of incidence locations is a number chosen for reasons of simplified illustration. In practice, the number of beams, and hence the number of incidence locations, can be chosen to be significantly greater, such as, for example, 20×30, 100×100 and the like.
[0084] In the depicted embodiment, the field 103 of incidence locations 5 is a substantially regular rectangular field having a constant pitch P1 between adjacent incidence locations. Exemplary values of the pitch P1 are 1 micrometer, 10 micrometres and 40 micrometres. However, it is also possible for the field 103 to have other symmetries, such as a hexagonal symmetry, for example.
[0085] A diameter of the beam spots shaped in the first plane 101 can be small. Exemplary values of said diameter are 1 nanometer, 5 nanometres, 10 nanometres, 100 nanometres and 200 nanometres. The focusing of the particle beams 3 for shaping the beam spots 5 is carried out by the objective lens system 100.
[0086] The primary particles striking the object generate interaction products, e.g., secondary electrons, back-scattered electrons or primary particles that have experienced a reversal of movement for other reasons, which emanate from the surface of the object 7 or from the first plane 101. The interaction products emanating from the surface of the object 7 are shaped by the objective lens 102 to form secondary particle beams 9. The particle beam system 1 provides a particle beam path 11 for guiding the plurality of secondary particle beams 9 to a detector system 200. The detector system 200 comprises a particle optical unit with a projection lens 205 for directing the secondary particle beams 9 at a particle multi-detector 209.
[0087] The detail I2 in FIG. 1 shows a plan view of the plane 211, in which individual detection areas of the particle multi-detector 209 on which the secondary particle beams 9 are incident at locations 213 are located. The incidence locations 213 lie in a field 217 with a regular pitch P2 from one another. Exemplary values of the pitch P2 are 10 micrometres, 100 micrometres and 200 micrometres.
[0088] The primary particle beams 3 are produced in a beam producing apparatus 300 comprising at least one particle source 301 (e.g. an electron source), at least one collimation lens 303, a multi-aperture arrangement 305 and a field lens 307. The particle source 301 produces a diverging particle beam 309, which is collimated or at least substantially collimated by the collimation lens 303 in order to shape a beam 311 which illuminates the multi-aperture arrangement 305.
[0089] The detail I3 in FIG. 1 shows a plan view of the multi-aperture arrangement 305. The multi-aperture arrangement 305 comprises a multi-aperture plate 313, which has a plurality of openings or apertures 315 formed therein. Midpoints 317 of the openings 315 are arranged in a field 319 that is imaged onto the field 103 formed by the beam spots 5 in the object plane 101. A pitch P3 between the midpoints 317 of the apertures 315 can have exemplary values of 5 micrometres, 100 micrometres, and 200 micrometres. The diameters D of the apertures 315 are smaller than the pitch P3 between the midpoints of the apertures. Exemplary values of the diameters D are 0.2×P3, 0.4×P3, and 0.8×P3.
[0090] Particles of the illuminating particle beam 311 pass through the apertures 315 and form particle beams 3. Particles of the illuminating beam 311 which strike the plate 313 are absorbed by the latter and do not contribute to the formation of the particle beams 3.
[0091] On account of an applied electrostatic field, the multi-aperture arrangement 305 focuses each of the particle beams 3 in such a way that beam foci 323 are formed in a plane 325. Alternatively, the beam foci 323 can be virtual. A diameter of the beam foci 323 can be, for example, 10 nanometres, 100 nanometres and 1 micrometer.
[0092] The field lens 307 and the objective lens 102 provide a first imaging particle optical unit for imaging the plane 325, in which the beam foci 323 are formed, onto the first plane 101 such that a field 103 of incidence locations 5 or beam spots arises there. Should a surface of the object 7 be arranged in the first plane, the beam spots are correspondingly formed on the object surface.
[0093] The objective lens 102 and the projection lens arrangement 205 provide a second imaging particle optical unit for imaging the first plane 101 onto the detection plane 211. The objective lens 102 is thus a lens that is part of both the first and the second particle optical unit, while the field lens 307 belongs only to the first particle optical unit and the projection lens 205 belongs only to the second particle optical unit.
[0094] A beam switch 400 is arranged in the beam path of the first particle optical unit between the multi-aperture arrangement 305 and the objective lens system 100. The beam switch 400 is also part of the second optical unit in the beam path between the objective lens system 100 and the detector system 200.
[0095] Further information relating to such multi-beam particle beam systems and components used therein, such as, for instance, particle sources, multi-aperture plate and lenses, can be obtained from the international patent applications WO 2005/024881 A2, WO 2007/028595 A2, WO 2007/028596 A1, WO 2011/124352 A1 and WO 2007/060017 A2 and the German patent applications DE 10 2013 016 113 A1 and DE 10 2013 014 976 A1, the disclosure of which in the full scope thereof is incorporated by reference in the present application.
[0096] The multi-particle beam system furthermore comprises a computer system 10 configured both for controlling the individual particle-optical components of the multi-particle beam system and for evaluating and analysing the signals obtained by the multi-detector 209. It can also be used to carry out the method according to the disclosure. In this case, the computer system 10 can be constructed from a plurality of individual computers or components.
[0097] FIG. 2 schematically shows an area inspection of a sample via an individual beam particle microscope. In this case, reference sign 50 indicates a single field of view that can be scanned by an individual beam system. The size of such a single field of view 50 is typically 100 μm×100 μm. FIG. 2A shows a full inspection. In this case, a full inspection via an individual beam electron microscope is comparatively time-consuming and the single field of view to be scanned, totaling 10 000 μm.sup.2, is comparatively large. If the areas 51, 52, 53 etc. of the field of view 50 in which defects are to be expected are known, either from prior knowledge about the sample to be examined or from a preceding detection, for example via an optical inspection system, it is possible to home in on these areas in a targeted fashion with the scanner of the individual beam system and scan the areas of interest in a targeted fashion: This area inspection is depicted in FIG. 2B. It is already known in the run-up that defects are to be expected at a total of seven sites. Therefore, the positions are homed in on separately and the associated areas of interest 54, 55, 56— as illustrated in FIG. 2B by the small squares—are then scanned. In this case, the areas of interest 54, 55 and 56 are significantly smaller than the overall field of view 50. They typically have an area of approximately 1 μm.sup.2. Therefore, a speed increase can already be obtained by the area inspection of the sample, approximately by a factor of 1000 here.
[0098] FIGS. 3A-3H schematically show the concept according to the disclosure for the area inspection of a sample via a multi-beam particle microscope. In this case, the individual illustrations a), b), c), d) explain the concept step by step. In the illustrated example, the multi-field of view 60 comprises a total of twelve single fields of view 61 to 72. These single fields of view may directly adjoin one another or slightly overlap one another. This has not been depicted more clearly in FIGS. 3A-3H for graphic reasons. The positions where defects d1 to d7 are to be expected are now known in turn. If a conventional multi-beam particle microscope, for example with a single column system, were now used for the sample inspection, the entire area of the multi-field of view 60 would be scanned according to certain known systems. For example, all single fields of view 61 to 72 would be scanned. However, this would not bring a substantial acceleration of the method. However, it is now possible to choose the areas actually to be scanned to be smaller than the single fields of view 61 to 72. This first approach is depicted in FIG. 3A. Nominal scanning areas 81 to 92, which all have the same size and are all positioned the same in the example shown, are plotted in each single field of view 61 to 72. The size of the nominal scanning areas 81 to 92 has been chosen in such a way that in FIG. 3A all defects d1 to d7 are also in fact located within the nominal scanning areas 81 to 92 and can consequently be scanned. However, this only provides a small speedup since the non-scanned area is very small. Consequently, it would be better to reduce the size of the actual scanning area in each single field of view.
[0099] FIG. 3B illustrates this approach: The single fields of view 61 to 72 of the multi-field of view 60 are identical, as are the plotted defects d1 to d7. However, unlike in FIG. 3A, provision is made of nominal scanning areas 81 to 92 which are significantly smaller than those depicted in FIG. 3A. The defects d1 to d7 appear to be comparatively large in the schematic figures. In reality, the defects d1 to d7 are significantly smaller in this context. However, the following circumstances are schematically indicated in the figures: The mechanism which aids in the detection of the defects only have a certain accuracy with which they can find the position of the defects, which generally have a size of only a few nanometres. In principle, this accuracy is already limited by the wavelength of the optical light used to find the defects. Furthermore, the relative positioning accuracy between the optical mechanism and the multi-beam particle microscope is relevant, with this relative positioning accuracy being given for example by the positioning accuracy of the two stages and the positioning accuracy of the individual particle beams with respect to the stage, as well as by further factors. Thus, it is desirable to ensure that a defect d1 to t7 is located in the area to be inspected. An area to be inspected can typically have edge lengths between 250 nm and 2 μm.
[0100] However, in relation to the exemplary embodiment in FIG. 3B, it is not the case that a defect d1 to d7 in fact also comes to rest under each nominal scanning area 81 to 92. This is because the pattern of the defects d1 to d7 does not orient itself on the pattern of the nominal scanning areas 81 to 92. Instead, it is the case that only defects d2 and d3 in single fields of view 64 and 66 overlap with the nominal scanning areas 84 and 86. If the sample were now to be scanned collectively area-wise with the first raster arrangement of the individual particle beams, that is to say in the case of scanning the nominal scanning areas 81 to 92, numerous defects would remain undetected. This, in general, is to be avoided.
[0101] The appropriate approach to this end is illustrated in FIG. 3C: In FIG. 3C, nominal scanning areas were largely assigned to areas to be inspected, that is to say to defects d1 to d7 in this case: The nominal scanning area 81 was assigned to the defect d1. The nominal scanning area 81 are displaced in order to in fact scan the defect d1, a new position is the scanning area 81′ in FIG. 3C. Likewise, in field of view 67, the nominal scanning area 87 was displaced to the new position 87′ and now covers defect d4. A corresponding statement applies to the nominal scanning area 91, 91′ and the defect d5, and to the nominal scanning area 92, 92′ and the defect d7. Here, in the example according to FIG. 3C, it is the case that a defect d6 has not been assigned in the single field of view 72. This is because two defects, d6 and d7, are situated in the field of view 72. Moreover, the nominal scanning area 88 in FIG. 3C has not been assigned and therefore not displaced either as there is no defect in the single field of view 68.
[0102] Therefore, a further improvement in the situation has been depicted in FIG. 3D: The depicted situation is identical to that depicted in FIG. 3C, with the exception of the situation depicted in the single fields of view 68 and 72. The nominal scanning area 88 of the field of view 68 is displaced into the single field of view 72 and forms the displaced nominal scanning area 88′ there. This now covers the defect d6, which had not been assigned previously. In this way, all defects d1 to d7 have now experienced a respective assignment to nominal scanning areas and as a result of the displacement of the latter it is possible to also in fact inspect defects d1 to d7 when scanning the sample surface.
[0103] In FIGS. 3A and 3B, the nominal scanning areas 81 to 92, each of which is non-displaced, correspond to a first regular raster configuration. By contrast, FIGS. 3C and 3D show two different second raster arrangements. According to FIG. 3C, a total of six positions of individual particle beams are displaced in the second raster arrangement in relation to the first raster configuration. In FIG. 3D, a total of seven individual particle beams are displaced in the second raster configuration in relation to the first raster arrangement. The remaining individual particle beams remain unchanged in terms of position; they likewise scan the sample without however scanning defects in the process.
[0104] In FIG. 3C, all displacements from nominal scanning areas to actual or displaced scanning areas are smaller than the pitch between the individual particle beams in relation to the first raster configuration. This does not apply to all displaced individual particle beams in FIG. 3D: The exception is formed by the individual particle beam associated with the single field of view 68, which has been displaced beyond the field of view boundary between fields of view 68 and 72 (displaced scanning area 88′). Thus, there now is the situation in FIG. 3D in which secondary beams emanating simultaneously from the same single field of view 72 have to be separated again in the detection path of the multi-beam particle microscope. This can be achieved by virtue of the fact that the resolution in the secondary path is chosen to be high enough such that second individual particle beams between the areas to be inspected can be separated even if they are located close together, and for example are to be assigned to the same single field of view (sFOV) on the sample. By way of example, it is also possible to arrange a multi-deflector array in the secondary path in order to steer one of the second individual particle beams back to the detection unit which is to be assigned to the original field of view (in this case: field of view 58). Alternatively or in addition, a skillful choice of the rotation, magnification and shift parameters of a multi-field of view may contribute to separating the secondary beams again in the detection path. A further option is using a detection system with a plurality of detection regions, the number of detection regions being greater than the number of individual particle beams in the primary path or secondary path of the system. It is also possible to choose a detection region per individual particle beam pair (made up of primary beam and secondary beam), with said detection region in turn being able to be subdivided into sub-detection regions. In this context, reference is made anew to the details in DE 10 2015 202 172 A1 disclosed in relation to the detection system and, for example, in relation to a dynamic detection system, the disclosure of this document being incorporated in full in this patent application by reference.
[0105] FIGS. 3E to 3H illustrate optimization strategies within the scope of carrying out the method according to the disclosure. In this context, it is firstly possible to optimize the first raster arrangement and secondly possible to optimize the relative position of the nominal scanning areas. FIG. 3E in this case shows an optimization strategy that is based on a displacement/shift of the first raster arrangement: This displacement is evident from a comparison of the illustration according to FIG. 3D with the illustration according to FIG. 3E: In comparison with the illustration in FIG. 3D, the raster arrangement or the multi-field of view 60 has been displaced downward, to be precise by approximately half the pitch, in FIG. 3E. As a consequence, defects d6 and d7 are no longer assigned to the same single field of view 72 as a result of the displacement of the first raster arrangement. Instead, the defect d6 is in the single field of view 72 and the defect d7 is in the adjacent single field of view 76. Thus, there is a more uniform distribution of the defects d1 to d7 among the single fields of view 61 to 76 as a result of this displacement. Each single field of view has a maximum of one defect d1 to d7. In this case, no defect d1 to d7 is cut by the boundaries of the raster configuration. Moreover, the relative position of the nominal scanning areas 81 to 96 in FIG. 3E is different to the relative position of the nominal scanning areas 81 to 88 according to FIG. 3D: If the nominal scanning areas 81 to 92 of FIG. 3D are located top left in each single field of view 61 to 72, these now are bottom left in the single fields of view 61 to 76 in FIG. 3E. Thus, two things were changed: Firstly, the first raster arrangement was displaced for optimization purposes and secondly the arrangement of the nominal scanning areas in the single fields of view was changed or likewise optimized. In this case, 16 sFOVs were shown here instead of the previous 12, without this representing a loss of generality.
[0106] FIG. 3F now illustrates a further optimization strategy by adjusting a magnification of the first raster arrangement. The adjustment of the magnification of the first raster arrangement in this case corresponds to the adjustment of the pitch between the individual particle beams and moreover corresponds to the size of the respective single fields of view 61 to 72, which should be scanned by the plurality of the first individual particle beams. As a result of the magnification or the increase in the pitch, it also is the case in FIG. 3F that each single field of view 61 to 72 has, if at all, only a single defect. However, the same area (even if this includes breaks) can now be scanned with a smaller number of individual particle beams: While seven defects are distributed among a total of 16 single fields of view in FIG. 3E, seven defects are distributed among only 12 single fields of view and, in the process, these defects are distributed uniformly in the example in FIG. 3F. Thus, the variation of the pitch can also decisively contribute to a speedup of the method according to the disclosure.
[0107] FIG. 3G discloses a further optimization strategy, specifically a rotation of the first raster arrangement. In a manner similar to a displacement of the raster arrangement according to FIG. 3E, what an additional or alternative rotation of the first raster arrangement is also able to achieve is that only a precisely defined number of defects are provided for each single field of view, for example exactly one defect per single field of view in this case here. Thus, the choice of the orientation of the raster arrangement and, linked therewith, the choice of the orientation of a multi-field of view overall is also an important parameter for attaining the best possible speedup.
[0108] In exemplary fashion, FIG. 3H illustrates the production of a distance distribution of areas to be inspected, or of defects, from the provided position data, and explains further optimization strategies of the method according to the disclosure: A diagram is plotted as to how the pairwise spacing of areas to be inspected, or of defects, is distributed in respect of its frequency. Plotted on the x-axis is the pairwise spacing between adjacent defects, abbreviated to ROI D, while the y-axis plots the number or frequency.
[0109] By way of example, to generate such a histogram in relation to FIG. 3F, the distance of the defect d3 from the defects d1, d2, d4 and d5 could be determined. A similar procedure could be carried out for defect d4: In this case, it would be possible for example to determine the distance of the defect d4 from the defects d3, d2, d5 and d6 in each case, etc. It is important here that distances are not counted twice. It allows the case in the histogram depicted in FIG. 3H that there is a most probable distance between areas to be inspected or defects d. As the distribution narrows, a minimum distance between mutually adjacent defects is definable more characteristically and more significantly. Furthermore, FIG. 3H plots a lower limit c. This lower limit or this cut-off c can be used to define the pitch of the first raster arrangement: Only a small number of defects have a minimum distance from adjacent defects that is smaller than the limit c. By way of example, it is possible that more than 95%, more than 98% or even more than 99% of all defects have a distance from their closest neighbour that is greater than or equal to this limit c. It is now possible to set the pitch to be the limit c. As a consequence, what applies to the vast majority of all defects is that these are in each case arranged as a single defect in a single field of view.
[0110] In a further variant, the pitch for defining the first raster arrangement is chosen in such a way that a distance distribution of areas to be inspected represents a certain fraction of the pitch to be set: for example exactly ½ pitch or ⅓ pitch or generally 1/n pitch. If the distribution of the histogram is narrow enough, a very large majority of all single fields of view then has either exactly 2, exactly 3 or exactly n defects, or has no defect at all. Thus, in this case it is also possible to obtain a very uniform distribution of areas to be inspected among single fields of view. This very uniform distribution then in turn leads to the desired speedup of the inspection method.
[0111] It is possible to further refine or complement the above-described optimization strategies, or to wholly or partly combine these with one another.
[0112] FIG. 4 now shows a flowchart of the method according to the disclosure, within the scope of which the concepts described according to FIGS. 3A-3H are applied. The method for area-wise inspecting a sample via a multi-beam particle microscope which operates using a plurality of individual charged particle beams, in this case comprises the following steps:
[0113] The provision of position data for a plurality of areas to be inspected d1 to d7 on the sample is implemented in method step S1. These position data may already be known, but it is also possible that these are only determined within the scope of the method according to the disclosure. By way of example, the position data can be generated via an optical inspection for recognizing semiconductor defects, and/or the position data can be generated on the basis of existing prior knowledge about the sample.
[0114] The provision of a first raster arrangement of the plurality of individual particle beams is implemented in a further method step S2, each individual particle beam being assigned a single field of view 61 to 72 on the sample 7. In this case, the first raster arrangement can be a regular hexagonal raster arrangement for example. However, any other regular embodiment of the raster arrangement or even an irregular arrangement of the raster arrangement is also possible. In this case, the first raster arrangement can be defined in a targeted manner or can be chosen according to optimization strategies—for example as described above with reference to FIGS. 3E to 3H— in order to speed up the method.
[0115] In a further method step S3, the position of a nominal scanning area 81 to 92 in each single field of view 61 to 72 is defined in relation to the first raster arrangement, with the dimensions of the nominal scanning area 81 to 92 being smaller than the complete single field of view 61 to 72. The position of the nominal scanning area in each single field of view 61 to 72 can in this case be defined on the basis of desirable criteria. By way of example, such criteria are maximizing the number of nominal scanning areas 81 to 92 which already in the first raster configuration at least partially cover, such as completely cover, the areas to be inspected d1 to d7. A further criterion is minimizing the number of individual particle beams 3 which are positioned differently in the second raster configuration in relation to the first raster configuration. A further criterion is restricting a position deviation of individual particle beams in the second raster arrangement in comparison with the first raster arrangement. These strategies also contribute to the speedup of the method.
[0116] Moreover, it is possible to choose the first raster arrangement, for example set a regular pitch between mutually adjacent individual particle beams in a targeted manner. As a result, it is possible for example to increase the number of areas to be inspected d1 to d7 which are located within a multi-field of view 60. Moreover, it can be desirable to distribute the areas to be inspected d1 to d7 as uniformly as possible among the single fields of view 61 to 72. Therefore—if there even is a defect—only a single defect d1 to d7 is present in most single fields of view 61 to 72 in FIGS. 3A-3H.
[0117] A nominal scanning area 81 to 92 is assigned to an area to be inspected d1 to d7 for at least one individual particle beam 3 in a further method step S4. There is a total of seven assignments in the example according to FIG. 3D.
[0118] An individual position deviation is determined in a further method step S5 between the nominal scanning area 81 to 92 and the area to be inspected d1 to d7, assigned thereto, for the at least one individual particle beam 3. Thus, this individual position deviation is determined for all pairs of nominal scanning areas and areas to be inspected. In this case, this position deviation may also be zero, specifically if the nominal scanning area already covers the area to be inspected (cf. nominal scanning areas 84 and 86 in FIG. 3D). Ultimately, the individual position deviation corresponds to the displacement of the nominal scanning area in the second raster arrangement in comparison with the first raster arrangement. By way of example, the individual position deviation is the displacement of the nominal scanning area 81 according to FIG. 3B comparison with the displaced nominal scanning area 81′ in FIG. 3D.
[0119] The first raster arrangement is changed in accordance with the respectively determined individual position of the deviation and a second raster arrangement of the plurality of individual particle beams 3 is produced thereby in a further method step S6, such that the assigned areas to be inspected d1 to d7 can be scanned in a targeted fashion. An exemplary second raster arrangement is evident in FIG. 3C from the position of the nominal scanning areas or optionally the displaced nominal scanning areas. A corresponding statement applies to the illustration according to FIGS. 3D to 3E.
[0120] In a further method step S7, the sample 7 is scanned area-wise using the plurality of individual particle beams 3 in the second raster arrangement. As many as possible of the areas to be inspected d1 to d7, for example all, are scanned in the process. In the illustrated example of FIG. 3, this is successful using the raster configuration according to FIG. 3D but only partially successful via the second raster configuration according to FIG. 3C since the defect d6 was not scanned in FIG. 3C. Thus, the second raster configuration according to FIG. 3D can be more desirable overall, with a greater position deviation or a greater deflection of an individual particle beam 3 for the purposes of generating the second raster arrangement having to be accepted only in one case: Only the individual particle beam assigned to the field of view 68 is deflected by more than the single pitch. Nevertheless, the deflection in that case is less than twice the pitch in relation to the first raster arrangement. What generally holds true is that a position deviation of individual particle beams 3 in the second raster configuration in comparison with the first raster arrangement is only greater than or equal to the pitch in the first raster arrangement if more areas to be inspected (in this case: d6, d7) are arranged in the adjacent single field of view (sFOV), in relation to the first raster arrangement, obtained by this position deviation than in the single field of view (sFOV 68), in relation to the first raster arrangement, originally assigned to the individual electron beam 3. Specifically, no defect was present there.
[0121] Likewise second raster configurations can be gathered from FIGS. 3E, 3F, 3G, with setting the magnification bringing the greatest speedup in the illustrated example (cf. the explanations above).
[0122] The method can be carried out via a multi-beam electron microscope having a single column. In this case, the adjacent single fields of view 61 to 72 of the multi-beam particle microscope 1 overlap one another. Moreover, the area-wise scanning of the sample according to step S7 is implemented via a collective scan deflector for the individual particle beams. By contrast, an individual deflector, for example in the form of an individual deflector arrangement, is used for the individual deflection of single individual particle beams for the purposes of generating the second raster arrangement. By way of example, these might be a multi-stigmator elements in this case. However, it is also possible to provide a separate individual deflector arrangement.
[0123] FIG. 5 shows a flowchart of a workflow for the area inspection of a sample. In this case, it is not only a single multi-field of view 60 that is scanned area-wise but a plurality of multi-fields of view, for example n multi-fields of view, that are successively scanned area-wise. In a method step W1, control signals assigned to the position data in relation to a first multi-field of view mFOV1 are loaded into the collective scan deflector and into an individual deflector arrangement via a controller. In a method step W2, there then is—as described above in conjunction with FIG. 4—an area inspection of the mFOV1. Following the completion of this inspection, there is a sample movement or a stage move, within the scope of which the sample to be inspected is displaced relative to the multi-beam particle microscope 1. As a result, it is possible to area-wise inspect a further multi-field of view mFOV2: Once again, the control signals which are for the areas to be inspected and which are assigned to the position data are uploaded in a method step W4 and the individual deflector arrangement and the collective scan deflector 110 are controlled accordingly. The corresponding inspection of the second multi-field of view mFOV2 is then implemented in step W5. Subsequently, there is again a displacement of the sample 7 in relation to the multi-beam particle microscope 1 (stage move). This can be accordingly continued until the last multi-field of view, in this case the n-th multi-field of view mFOVn, has been area-wise inspected. Instead of uploading the position data per multi-field of view into the collective scan deflector and into the individual deflector arrangement, it is also possible to upload all control signals at once and then call/enable these via a trigger signal following a sample movement.
[0124] FIG. 6 schematically shows a multi-beam electron microscope having a single column for carrying out the method according to the disclosure. FIGS. 1 and 6 correspond to one another but FIG. 6 shows more details in respect of the particle-optical elements. In FIG. 6, a collective scan deflector 110 is arranged in the area of the crossover 108. All individual particle beams are deflected equally via this collective scan deflector 110 and the scan deflector 110 is controlled via the controller 10 in such a way that the plurality of individual particle beams scan the sample surface 25 as desired. According to the method according to the disclosure, this scanning is implemented area-wise, with the plurality of the individual particle beams 3 being arranged according to the second irregular raster arrangement, which deviates from the regular first raster arrangement.
[0125] The second (irregular) raster arrangement is generated by a targeted deflection of selected individual particle beams. To this end, a deflection of the individual particle beams assigned to the selected area/areas to be inspected is carried out once (once provided a single set of nominal sample areas is provided), and this deflection is then maintained during the area scan in the multi-field of view (mFOV). Therefore, the adjustment is technically simple or can be implemented in low-frequency fashion at a rate of only a few hertz, for example 5 or 10 Hz. In the example shown in FIG. 6, the controller 10 can obtain the described beam deflection by way of controlling a multi-stigmator. The multi-stigmator is a constituent part of the micro-optics 306 and comprises the components 306.1 and 306.2 in the example shown. One or both of these components 306.1, 306.2 can be used to set the second raster arrangement. Additionally or alternatively, the individual deflector array 390 can also be controlled by way of the controller 10 for the purposes of setting the second raster arrangement. In the example shown, this is situated just downstream of the intermediate image plane 325, an arrangement within the intermediate image plane is not reasonable as only a very small positional change of the beams could be brought about in that case. In both discussed cases, the mechanism for the individual beam deflection are located at a position in which, firstly, the individual particle beams are well separated from one another and, secondly, the particle beam diameter of the individual particle beams is small in each case; however, in principle, other arrangements of the one-part or multi part individual deflector array are also possible.
[0126] FIG. 6 also shows details of the projection system 205. In addition to the projection lens system having a plurality of projection lenses 205.1, 205.2 and 205.3, this also comprises a further collective scan deflector 222, the so-called anti-scan. The latter is configured to guide the plurality of second individual particle beams which emanate from the sample 7 over the detection device 200. It is likewise controlled via the controller 10.
[0127] Positions of the second individual particle beams on the detection unit 200 can optionally be adjusted via an individual deflector array 220 which can be controlled in low-frequency fashion by way of the controller 1—whether this is used depends on the type of utilized detection unit 200. If a CMOS-type electron detector with a plurality of pixels is used, there is no need to use the individual deflector array 220 since only the assignment of the sensor pixels to the beam spots is different in that case.
[0128] FIG. 7 schematically shows a multi-stigmator, which comprises a chip with a memory. Specifically, FIG. 7 shows a multi-stigmator mDEF, which is arranged in vacuo. In the example shown, the multi-stigmator mDEF comprises two constituent parts or plates. Firstly, it comprises a plate with an application-specific integrated circuit (ASIC) and secondly comprises a plate with a microelectromechanical system (MEMS). The two plates may be, but need not be, fastened to one another. In the example shown, the ASIC plate comprises a CPU, a RAM, a ROM, an analogue-to-digital converter D/A and an input/output I/O. Control signals CTRL are fed to the CPU via the input/output I/O. These are guided into the vacuum from outside of the vacuum in which the multi-stigmator with Chip mDEF is situated. Additionally, a clock signal CLK is transmitted via a clock line via the I/O to the CPU. The control signals CTRL can be stored in the RAM and the CPU is used to control, via the digital-to-analogue converter D/A, the MEMS plate with the electrodes (in this case: octupoles) of the multi-stigmator or of the multi-stigmator array mDEF.
[0129] The provision of a clock line can result in limiting the number of control lines CTRL from outside of the vacuum into the vacuum in terms of their number or comparatively low. Moreover, it is not necessary to transmit the control signals synchronized in time with the scanning of the sample to the multi-stigmator mDEF: Instead, it is possible to upload the control signals CTRL and store these in the RAM memory in advance, for example during the calibration of the system or during a change in the field of view (multi-field of view change, often coupled to a stage movement). Then all that is still used is to transmit the clock signal CLK to the CPU at the right time so that the corresponding control signals CTRL are called from the RAM and transmitted via the D/A converter to the connectors of the MEMS plate or to the octupoles. FIG. 7 only shows 4 lines for an octupole in exemplary fashion; the wiring of the other octupoles on the MEMS plate is implemented accordingly.
[0130] Thus, using the exemplary embodiment depicted in FIG. 7, it is possible to upload into the RAM memory a sequence of control signals for the multi-stigmator mDEF for the purposes of producing the second raster arrangement and to activate the next control signal via a trigger signal, in this case the CLK signal. Thus, the sequence of control signals CTRL is stored or buffered in the RAM memory of the chip, the storing process itself can be implemented once. However, it is alternatively also possible to supply the multi-stigmator mDEF after each stage move, that is to say before the scanning of the next multi-field of view starts, with control signals CTRL or data for the specific control.
LIST OF REFERENCE SIGNS
[0131] 1 Multi-beam particle microscope [0132] 3 Primary particle beams (individual particle beams) [0133] 5 Beam spots, incidence locations [0134] 7 Object [0135] 8 Sample stage [0136] 9 Secondary particle beams [0137] 10 Computer system, controller [0138] 11 Secondary particle beam path [0139] 13 Primary particle beam path [0140] 25 Sample surface, wafer surface [0141] 50 Single field of view (individual beam system) [0142] 51 Area of the single field of view 50 [0143] 51 Area of the single field of view 50 [0144] 52 Area of the single field of view 50 [0145] 53 Area of the single field of view 50 [0146] 54 Area to be inspected of the single field of view 50 [0147] 55 Area to be inspected of the single field of view 50 [0148] 56 Area to be inspected of the single field of view 50 [0149] 60 Multi-field of view (mFOV) [0150] 61 to 76 Single field of view (multi beam system) [0151] 81 to 96 Nominal scanning area [0152] 81′ to 96′ Displaced nominal scanning area [0153] d1 to d7 Defect, area to be inspected [0154] 100 Objective lens system [0155] 101 Object plane [0156] 102 Objective lens [0157] 103 Field [0158] 105 Optical axis of the multi-beam particle microscope [0159] 108 Cross-over [0160] 110 Collective scan deflector [0161] 200 Detector system [0162] 205 Projection lens [0163] 206 Electrostatic lens [0164] 207 Detection region [0165] 208 Deflector [0166] 209 Particle multi-detector [0167] 211 Detection plane [0168] 212 Cross-over [0169] 213 Incidence locations [0170] 214 Aperture filter [0171] 215 Detection region [0172] 216 Active element [0173] 217 Field [0174] 218 Deflector system [0175] 220 Multi-aperture corrector, individual deflector array [0176] 222 Collective deflection system, anti-scan [0177] 300 Beam producing apparatus [0178] 301 Particle source [0179] 303 Collimation lens system [0180] 305 Multi-aperture arrangement [0181] 306 Micro-optics [0182] 307 Field lens [0183] 308 Field lens [0184] 309 Diverging particle beam [0185] 311 Illuminating particle beam [0186] 313 Multi-aperture plate [0187] 315 Openings in the multi-aperture plate [0188] 317 Midpoints of the openings [0189] 319 Field [0190] 323 Beam foci [0191] 325 Intermediate image plane [0192] 326 Field lens system [0193] 390 Individual deflector array, individual deflector arrangement [0194] 400 Beam switch [0195] 420 Magnetic element [0196] 500 Sample stage [0197] 503 Voltage supply for the sample [0198] c Lower limit, cut-off [0199] MAX Maximum value of the distribution [0200] ROI d Minimum distance of the nearest neighbour for areas to be inspected/defects [0201] S1 Position data for areas to be inspected [0202] S2 Providing a first raster arrangement [0203] S3 Defining nominal scanning areas [0204] S4 Assigning nominal scanning areas to areas to be inspected [0205] S5 Determining position deviations [0206] S6 Producing a second raster arrangement [0207] S7 Area inspection [0208] W1 Position data mFOV1 [0209] W2 Inspection mFOV1 [0210] W3 Sample movement [0211] W4 Position data mFOV2 [0212] W5 Inspection mFOV2 [0213] W6 Sample movement [0214] W7 Inspection mFOVn
