Abstract:
In a charged-particle multi-beam processing apparatus for exposure of a target with a plurality of parallel particle-optical columns, each column has a beam shaping device forming the shape of the illuminating beam into a desired pattern composed of a multitude of sub-beams, by means of an aperture array device, which defines the shape of a respective sub-beam by means of an array of apertures, and a deflection array device selectively deflecting sub-beams off their nominal paths; thus, only the non-selected sub-beams can reach the target. According to many embodiments of the invention each beam shaping device is provided with a first field-boundary device and a second field-boundary device, which are the first and last plate elements traversed by the beam. One of the first and second field-boundary devices defines a field-free space interval so as to accommodate feeding lines for controlling the deflection array device.

Description:
RELATED APPLICATION 
     The present application claims priority to European Application No. 14165970.6 filed Apr. 25, 2014, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     The invention relates generally to a programmable charged-particle multi-beam apparatus for processing (in particular nanopatterning or semiconductor lithography) or inspection of a target. 
     SUMMARY OF THE INVENTION 
     In more detail, the invention generally relates to a charged-particle multi-beam processing apparatus for exposure of a target with a plurality of beams of electrically charged particles, comprising a plurality of particle-optical columns arranged parallel (along a Z direction) and configured for directing a respective particle beam towards the target, wherein each particle-optical column comprises an illumination system, a beam shaping device, and a projection optics system. The illumination system serves to produce a respective beam and form it into a (preferably, substantially telecentric) beam illuminating the shaping means. The beam shaping device is configured to form the shape of the illuminating beam into a desired pattern composed of a multitude of sub-beams, and includes an aperture array device provided with a multitude of apertures, each of said apertures defining the shape of a respective sub-beam having a nominal path towards the target, as well as a deflection array device for deflecting (only) selected sub-beams off their respective nominal path so that sub-beams thus selected do not reach the target; the remaining sub-beams represent the desired pattern being imaged to the target. The projection optics system serves to project an image of the beam shape defined in the shaping means onto the target. 
     Furthermore, the invention also generally relates to a beam shaping device (also called pattern definition device) for use in a column of such a charged-particle multi-beam processing apparatus, configured to be irradiated by an illuminating beam of electrically charged particles and to form the shape of the illuminating beam into a desired pattern composed of a multitude of sub-beams. This type of multi-column (or “multi-axis”) configuration is described in U.S. Pat. Nos. 7,214,951 and 8,183,543 of the applicant. 
     Embodiments of several solutions and techniques suitable in the field of charged-particle multi-beam lithography and nanopatterning and pertinent technology have been developed, such as the following: when using ion multi-beams coined CHARPAN (charged particle nanopatterning) and when using electron multi-beams coined eMET (electron mask exposure tool) or MBMW (multi-beam mask writer) for mask writing, and coined PML2 (Projection Mask-Less Lithography) for direct write lithography on substrates, in particular silicon wafers. In this context, relevant patent documents in the name of the applicant are U.S. Pat. Nos. 7,199,373, 7,214,951, 8,304,749, 8,183,543, and 8,222,621. 
       FIG. 1  shows a schematic sectional view of a multi-column writer tool  1  in accordance with many embodiments with vacuum housing  10  for the multi-column charged-particle optics  2 , a target chamber  3  onto which the multi-column charged-particle optics is mounted by means of by means of a column base plate  4 . Within the target chamber  3  is an X-Y stage  5 , e.g., a laser-interferometer controlled air-bearing vacuum stage onto which a substrate chuck  6  is loaded using a suitable handling system. The chuck  6 , which preferably is an electrostatic chuck, holds the substrate  7 , such as a silicon wafer. For charged-particle multi-beam lithography the substrate, for instance, is covered with an electron or ion beam sensitive resist layer  8 . 
     The multi-column optics  2  comprises a plurality of sub-columns  9  (the number of columns shown is reduced in the depiction for better clarity, and represent a much larger number of columns that are present in the multi-column apparatus in a realistic implementation). Preferably, the sub-columns  9  have identical setup and are installed side-by-side with mutually parallel axes. Each sub-column has an illuminating system  11  including an electron or ion source  11   a , an extraction system  11   b , and an electrostatic multi-electrode condenser optics  11   c , delivering a broad telecentric charged-particle beam to a pattern definition device (PDD)  12  being adapted to let pass the beam only through a plurality of apertures defining the shape of sub-beams (“beamlets”) permeating said apertures (beam shaping device), and a demagnifying charged-particle projection optics  16  comprising three lenses. In the many embodiments shown, the first lens is an accelerating electrostatic multi-electrode lens  16   a  whereas the second and third lenses  16   b ,  16   c  are either magnetic lenses, in particular when using electrons, or electrostatic lenses, for instance in the case where the particles are ions, as outlined in U.S. Pat. No. 7,214,951. 
     The accelerating first lens of the projection charged-particle optics  16  provides the important advantage of operating the PDD  12  at low kinetic energy of the particles (e.g., 5 keV) whereas providing high beam energy (e.g., 50 keV) at the cross-overs of the demagnifying projection optics, thus minimizing stochastic Coulomb interactions. Further, the high beam energy at the substrate is beneficial to reduce forward scattering of the charged particles when exposing the target, in particular the charged-particle sensitive layer  8 . 
     The first lens of the projection optics forms a first cross-over whereas the second lens forms a second cross-over. At this position in each sub-column there is a stopping plate  15  configured to filter out beams deflected in the PDD. The third lenses  16   c  of the sub-columns as well as the stopping plates  15  are mounted onto a reference plate  17  which is mounted by suitable fastening means  18  onto the column base plate  4 . Mounted onto the reference plate  17  are parts  19  of an off-axis optical alignment system. 
     The reference plate is fabricated from a suitable base material having low thermal expansion, such as a ceramic material based on silicon oxide or aluminum oxide, which has the advantage of little weight, high elasticity module and high thermal conductivity, and may suitably be covered with an electrically conductive coating, at least at its relevant parts, in order to avoid charging (by allowing electrostatic charges being drained off). 
     As can be seen in the longitudinal sectional detail of  FIG. 2 , a PDD  12  according to prior art comprises three plates stacked in a consecutive configuration. An aperture array plate  20  (AAP), a deflection array plate  30  (DAP, also referred to as blanking array plate) and a field-boundary array plate  40  (FAP). It is worthwhile to note that the term ‘plate’ is refers to an overall shape of the respective device, but does not necessarily indicate that a plate is realized as a single plate component even though the latter is usually the preferred way of implementation; still, in certain embodiments, a ‘plate’, such as the AAP, may be composed of a number of sub-plates. The plates are preferably arranged parallel to each other, at mutual distances along the Z direction. 
     The flat upper surface of AAP  20  forms a defined potential interface to the condenser optics  11 . The AAP may, e.g., be made from a square or rectangular piece of a silicon wafer (approx. 1 mm thickness)  21  with a thinned center part  22 . The plate may be covered by an electrically conductive protective layer  23 , which will be particularly advantageous when using hydrogen or helium ions (line in U.S. Pat. No. 6,858,118). When using electrons or heavy ions (e.g., argon or xenon), the layer  23  may also be silicon, provided by the surface section of  21  and  22 , respectively, so that there is no interface between layer  23  and bulk parts  21 / 22 , respectively. 
     The AAP  20  is provided with a plurality of apertures  24  formed by openings traversing the thinned part  22 . In the embodiments shown the apertures  24  are realized having a straight profile fabricated into the layer  23  and a “retrograde” profile in the bulk layer of the AAP  20  such that the downward outlets  25  of the openings are wider than in the main part of the apertures  24 . Both the straight and retrograde profiles can be fabricated with state-of-the-art structuring techniques such as reactive ion etching. The retrograde profile strongly reduces mirror-charging effects of the beam passing through the opening. 
     The DAP  30  is a plate provided with a plurality of openings  33 , whose positions correspond to those of the apertures  24  in the AAP  20 , and which are provided with electrodes  35 ,  38  configured for deflecting the individual sub-beams passing through the openings  33  selectively from their respective paths. The DAP  30  can, for instance, be fabricated by post-processing a CMOS wafer with an ASIC circuitry. The DAP  30  is, for instance, made from a piece of a CMOS wafer having a square or rectangular shape and comprises a thicker part  31  forming a frame holding a center part  32  which has been thinned (but may be suitably thicker as compared to the thickness of  22 ). The aperture openings  33  in the center part  32  are wider compared to  24  (by approx. 2 μm at each side for instance). CMOS electronics  34  is used to control the electrodes  35 ,  38 , which are provided by means of MEMS techniques. Adjacent to each opening  33 , a “ground” electrode  35  and a deflection electrode  38  are provided. The ground electrodes  35  are electrically interconnected, connected to a common ground potential, and comprise a retrograde part  36  to prevent charging and an isolation section  37  in order to prevent unwanted shortcuts to the CMOS circuitry. The ground electrodes  35  may also be connected to those parts of the CMOS circuitry  34  which are at the same potential as the silicon bulk portions  31  and  32 . 
     The deflection electrodes  38  are configured to be selectively applied an electrostatic potential; when such electrostatic potential is applied to an electrode  38 , this will generate an electric field causing a deflection upon the corresponding sub-beam, deflecting it off its nominal path. The electrodes  38  as well may have a retrograde section  39  in order to avoid charging. Each of the electrodes  38  is connected at its lower part to a respective contact site within the CMOS circuitry  34 . 
     The height of the ground electrodes  35  is higher than the height of the deflection electrodes  38  in order to suppress cross-talk effects between the beams. 
     The third plate  40  serving as FAP has a flat surface facing downstream to the first lens part of the demagnifying charged-particle projection optics  16 , thus providing a defined potential interface to the first lens  16   a  of the projection optics. The thicker part  41  of FAP  40  is a square or rectangular frame made from a part of a silicon wafer, with a thinned center section  42 . The FAP  40  is provided with a plurality of openings  43  which correspond to the openings  24 ,  33  of the AAP  20  and DAP  30  but are wider as compared to the latter. 
     The PDD  12 , and in particular the first plate of it, the AAP  20 , is illuminated by a broad charged particle beam  50  (herein, “broad” beam means that the beam is sufficiently wide to cover the entire area of the aperture array formed in the AAP), which is thus divided into many thousands of micrometer-sized beams  51  when transmitted through the apertures  24 . The beams  51  will traverse the DAP and FAP unhindered. 
     As already mentioned, whenever a deflection electrode  38  is powered through the CMOS electronics, an electric field will be generated between the deflection electrode and the corresponding ground electrode, leading to a small but sufficient deflection of the respective beam  52  passing through ( FIG. 2 ). The deflected beam can traverse the DAP and FAP unhindered as the openings  33  and  43 , respectively, are made sufficiently wide. However, the deflected beam  52  is filtered out at the stopping plate  15  of the sub-column ( FIG. 1 ). Thus, only those beams which are unaffected by the DAP will reach the substrate. 
     The reduction factor of the demagnifying charged-particle optics  16  is chosen suitably in view of the dimensions of the beams and their mutual distance in the PDD  12  and the desired dimensions of the structures at the target. This will allow for micrometer-sized beams at the PDD whereas nanometer-sized beams are projected onto the substrate. 
     The ensemble of (unaffected) beams  51  as formed by AAP is projected to the substrate with a predefined reduction factor R of the projection charged-particle optics. Thus, at the substrate a “beam array field” (BAF) is projected having widths BX=AX/R and BY=AY/R, respectively, where AX and AY denote the sizes of the aperture array field along the X and Y directions, respectively. The beam size of an individual sub-beam at the substrate is given by bX=aX/R and by=aY/R, respectively, where aX and aY denote the sizes of the beam  51  as measured along the X and Y directions, respectively, at the level of the DAP  30 . 
     It is worthwhile to note that the individual beams  51 ,  52  depicted in  FIG. 2  (as well as in the analogous figures below) represent a much larger number of sub-beams, typically many thousands, arranged in a two-dimensional X-Y array. The applicant has, for instance, realized multi-beam charged-particle optics with a reduction factor of R = 200  for ion as well as electron multi-beam columns with many thousands (e.g., 262,144) programmable beams. The applicant has realized such columns with a beam array field of approx. 82 μm×82 μm at the substrate. These examples are stated for illustrative purpose, but are not to be construed as limiting examples. 
     The arrangement outlined in  FIGS. 2  is used to implement sub-columns with such a diameter that a large number of sub-columns of the above-described kind fit within the area of a substrate, such as a 300 mm silicon wafer used as a substrate for leading-edge integrated circuit device production. There is ongoing development of 193 nm immersion optical lithography, EUV and nano-imprint lithography tools for 450 mm silicon wafer size. Without loss of throughput, the multi-column configuration as presented here can easily be adapted to any other wafer size, such as a 450 mm diameter silicon wafer size, by providing a corresponding higher number of sub-columns. 
     The recent progress of integrated circuits, in particular microprocessors, was made possible not only by novel lithographic, deposition, and etching techniques, but also by innovative circuit design. A most powerful innovation was to proceed from a two-dimensional to a one-dimensional circuit design, as was described by Yan Borodovsky in “EUV, EBDW—ARF Replacement or Extension?”, KLA-Tencor Lithography User Forum, Feb 21, 2010, San Jose, Calif., USA, as well as “MPProcessing for MPProcessors”, SEMATECH Maskless Lithography and Multibeam Mask Writer Workshop, May 10, 2010, New York, N.Y., USA. For this end regular line patterns are fabricated using e.g., 193 nm (water) immersion optical lithography, layer deposition and etching steps, and then “complementary lithography” exposure and subsequent etching steps are performed to generate cuts in the regular line pattern according to a desired structured line pattern. 
     To date development of EUV (extended ultra-violet) lithography, based on 13.5 nm wavelength, is delayed, and therefore, in 2015 there will be the necessity to expose the cutting pattern with 193 nm immersion optical lithography. As the minimum pitch for this technique is ca. 80 nm. As a consequence there is the need to expose the cutting pattern with 4 different masks (cf. Yan Borodovsky in KLA-Tencor Lithography User Forum op.cit.). Thus, in the context of EUV lithography there is a need for new techniques allowing to expose the cutting pattern on the mask with one mask only. Therefore, there is continued strong industrial interest in EUV lithography, even though it might not be ready for production at the 10 nm logic node. Still, there are major hurdles for EUV lithography to overcome, which is why the semiconductor industry is increasingly and seriously interested in alternative lithographic possibilities for cutting pattern exposure. Nano-imprint lithography is one possibility but there are several difficulties, such as master template fabrication, lifetime of working stamp replicas, defect inspection and repair of the stamps, and the possible occurrence of defect generation during imprinting. As another alternative, electron multi-beam direct write has obtained increasing industrial attention because it offers sub-10 nm resolution potential and no masks are needed. 
     Evidently, the multi-column layout described above requires that, in order to properly control the multitude of deflector devices in the DAPs  30  of the multicolumn apparatus, a large number of data and controlling signals are supplied as input signals to the DAPs. Further, additional control lines for reading out the deflector devices may be present to provide output signals. These input and output lines of the DAPs are referred to as ‘data path’. 
     The layout of the multi-column apparatus underlying many embodiments of the invention, such as the one illustrated in  FIG. 1 , has a compact arrangement where the charged-particle optical columns are positioned closely together, which is advantageous with respect to its ability to perform writing and structuring patterns onto the target in an efficient manner; however, this compact arrangement makes it highly difficult to provide data path access to the plurality of sub-columns. This is because the compact arrangement of the sub-columns leaves only little space between them through which the required data lines can pass; further aggravating this problem is that the data lines forming the data path are of a considerable number, since for each aperture field data must be supplied to each row of apertures simultaneously. Therefore, it is an aim of many embodiments of the invention to provide access possibilities for the data path from the sides of the PDDs of the sub-columns, without the need of modifying—and very likely deteriorating—the optical properties of the highly optimized lens elements. 
     This aim is met by a beam shaping device, as well as a charged-particle multi-beam processing apparatus incorporating such a beam shaping device layout, wherein the beam shaping device is provided with
         a first field-boundary device as the first element of the respective beam shaping device traversed by the beam, the first field-boundary device having a first surface oriented towards the illumination system,   a second field-boundary device as the last element of the respective beam shaping device traversed by the beam, the second field-boundary device having a second surface oriented towards the projection optics system, and the first and/or second field-boundary devices define—i.e., delimit—a field-free space interval within the respective beam shaping device, which field-free space interval is configured to accommodate feeding lines for controlling the deflection array device of the respective beam shaping device (i.e., the data path lines). The field-free space interval includes at least the free space which is formed between the respective first or second field-boundary device and a consecutive component devices of the beam shaping device, which preferably are plate-shaped components of the beam shaping device, such as the mentioned aperture array device or deflection array device. Herein “consecutive component device” is understood to mean a component device which is located adjacent but at a distance to the relative field-boundary device within the beam shaping device.       

     This solution creates sufficient space for the data path access while maintaining a compact arrangement of the multiple columns. The compact arrangement is key to achieve high throughput. Many embodiments of the invention allow for the accommodation of the feeding lines which realize the data path access within the field-free space and separately from the deflection array device, and possibly also separately from the other component devices of the beam shaping device as well. Further, the embodiments of the invention facilitate effective cooling of the PDDs to keep them at a desired temperature within a narrow tolerance range. 
     According to an advantageous development of many embodiments of the invention, the feeding lines (i.e., the data path lines) may come at multiple levels of height with regard to the Z direction within the field-free space interval. This reduces the space the lines need within a given X-Y plane, thus reducing the need for space. 
     Another possible aspect of many embodiments of the invention may provide for shielding tubes which shield the sub-beams and the data path lines against each other. Thus, each shielding tube may be locate within a respective beam shaping device in the respective field-free space, entirely surrounding the beam traversing the respective beam shaping device. The shielding tube will be made of a material suitable to provide a magnetic and/or electric shielding of the beam. Their shape will usually be a generally cylindrical or prismatic shape coaxial with the Z direction, which includes shapes of circular, oval, polygonal and rounded-polygonal cross-sections, such as squares or rectangles with rounded corners. 
     In one particularly advantageous development in accordance with embodiments of the invention the first and/or second field-boundary devices are arranged at a distance (along the Z direction) to the other components of the respective beam shaping device, so as to provide a field-free space with regard to electric fields within the respective pattern definition device, wherein the dimension of this distance is chosen so as to be sufficient for accommodating the feeding lines. 
     In one typical implementation according to embodiments the first field-boundary device will be a device separate from the aperture array device of the respective column, so as to allow a separation of the functions and facilitate replacement processes of worn out components. However, the first field-boundary device may be realized by the aperture array device of the respective column, which will reduce the number of components. 
     According to a suitable implementation of embodiments of the invention, the first and second field-boundary devices are realized as generally plate-shaped components, which may further be arranged parallel to each other and at a mutual distance along the Z direction. 
     In another advantageous development of embodiments of the invention, the DAPs may be located at different Z locations (“tiers”). In this case, the first field-boundary devices of the columns are arranged at a uniform first height with regard to the Z direction, and the second field-boundary devices of the columns are arranged at a uniform second height; for each column a blanking unit including the respective deflection array device is arranged at a height level different from the height levels of the blanking unit of the columns adjacent to the respective column. Thus, the blanking units/the deflection array devices are arranged at a number of height levels between the first and second heights. 
     The first and second field-boundary devices will include respective arrays of openings that correspond to the apertures of the aperture array device of the respective column. Advantageously, these first and second surfaces may be flat with the exception of the respective array of openings, so as to define a clear limiting surface vis-à-vis the illuminating system and/or the projection system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, several embodiments of the present invention are described in more detail with reference to the drawings, which illustrate several embodiments of the invention given by way of example and representing suitable implementations of the invention, which are not to be construed as restrictive to invention. The drawings schematically show: 
         FIG. 1  a multi-column writer tool in a schematic sectional view in accordance with many embodiments; 
         FIG. 2  is a longitudinal sectional view of a PDD of one of the columns of the tool of  FIG. 1 ; 
         FIG. 3A  shows a first arrangement of the columns with regard to the target in a partial plan view (rectangular arrangement); 
         FIG. 3B  shows a second arrangement of the columns (rhombic arrangement); 
         FIG. 4  illustrates a multi-column writer tool incorporating an embodiment of the invention in a sectional view; 
         FIG. 5A  shows a PDD according to an embodiment; 
         FIG. 5B  shows how several PDDs of the type shown in  FIG. 5A  are arranged in parallel in the tool of  FIG. 4 ; 
         FIG. 6  shows a PDD according to other embodiments; 
         FIG. 7  shows a PDD according to further embodiments; 
         FIG. 8A  depicts several PDDs in a rectangular arrangement, in a cross sectional view detail along line  8 A- 8 A in  FIG. 5B ; 
         FIG. 8B  depicts PDDs in a cross sectional view detail like that of  FIG. 8A , but in a rhombic arrangement; 
         FIG. 9  shows another embodiment where the PDDs have a Z-staggered arrangement of the AAP-DAP packages; 
         FIG. 10  is a longitudinal sectional view of one of the AAP-DAP packages of  FIG. 9 ; 
         FIG. 11  is a plan view of the AAP-DAP package of  FIG. 10 ; 
         FIGS. 12A-12D  depict the mutual arrangement of the AAP-DAP packages in the various tiers of the Z-staggered arrangement. 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments shown in the following relate to a multi-beam tool for cutting patterns used for mix-and-max lithography, where the substrate (e.g., silicon wafer) is exposed e.g., with a 193 nm immersion scanner tool with die-fields having length DX and width DY of typically DX=33 mm and DY=26 mm. One die field may, and typically will, comprise several chips. The many embodiments are not limiting, and thus the invention may refer to other layouts and applications as well. Within this disclosure, the terms “upper”, “lower” and related terms like “top” or “bottom” are to be understood with regard to the direction of the beam, which is thought to run downwards along a “vertical” axis. This vertical axis, in turn, is identified with the Z direction (longitudinal direction), to which the X and Y directions are transversal. 
     Examples of embodiments of compact sub-columns arrangements  60  and  70  suitable for the invention are shown in  FIGS. 3A and 3B , respectively, which show plan view details of the arrangements with regard to the plane of the target. In  FIG. 3A  a “rectangular” layout is depicted, wherein one sub-column  61  (symbolically represented by a circle) with an aperture array field  62  is respectively used to expose the area  63  of one die field (as illustrated by different ways of hatching); consequently, the mutual arrangement of columns reflected the mutual arrangement of the die fields.  FIG. 3B  illustrates a “rhombic” arrangement of the columns, where one sub-column  71  with an aperture array field  72  is respectively used to expose the area  73  of two die fields, and the distance between two neighboring columns corresponds to a diagonal of a single die field. 
     Assuming DX=33 mm and DY=26 mm, then in case of  FIG. 3A  the diameter of a sub-column  61  is approx. 24 mm and the size of the aperture array field  62  is approx. 8.2 mm×8.2 mm, whereas in case of  FIG. 3B  the diameter of a sub-column  71  is approx. 40 mm and the aperture array field  72  is approx. 16.4 mm×16.4 mm. Assuming the periodicity of the apertures is 16 μm, the aperture array field  62  is able to provide 512×512=262,144 beams, whereas the aperture array field  72  is able to provide 1024×1024=1,048,576 beams. 
     The aperture array field may also, in a variant, be chosen to be rectangular, preferably having the same diagonal length as a corresponding square aperture array field. 
     As mentioned above, a large number of input signals, which include data and controlling signals for the DAPs (or in general, the beam shaping devices of the columns), as well as output signals from the deflector devices and other control sensors, need to be supplied as data path to and from the DAPs (beam shaping devices). However, the compact arrangement of the sub-columns causes a space problem for the data path. The many embodiments of the invention solve this problem, i.e., supplying additional space within the arrangement of the PDD device, by providing a first second field-boundary device and a second field-boundary device as first and last components of the PDD, which serves as field boundaries against the electromagnetic fields of the illumination system  11  and the projection optics system  16 , respectively. Thus, the first and second field-boundary device define a “free drift region” between them, which is protected against the high electric and magnetic fields of the particle optical systems  11  and  16 . It should be noted, however, that this “free drift region” will contain the transversal fields of the deflecting devices in the DAPs, which of course are only local and of limited spatial extension. In particular, one or both of the field-boundary devices is positioned at a substantial distance to the preceding and/or subsequent plate component of the PDD, creating a field-free space through which the beam can travel undisturbed, and which creates a space allowing sufficient access possibilities for the data path  101  entering from the sides of the particle optical columns  9  towards the DAPs. 
       FIG. 4  illustrates an embodiment of the invention in a sectional view corresponding to  FIG. 1 . The apparatus  100  comprises a free-drift region FF between the condenser optics  11  and the projection optics  16 . In this free-drift region FF, the (high) electric fields of the charged-particle optical systems  11  and  16  are shielded off so as to guard the data path lines as well as the local deflection devices. Furthermore, the free-drift region FF has a considerably enhanced height as compared to that of a single PDD  112  of  FIG. 1 . The large free-drift region FF advantageously offers the possibility of sufficient access of the data path  101  regardless of the large number of lines contained therein. The data path  101  comprises a number of line bundles  102 , which enter through vacuum locks  103  into the vacuum chamber  10 ′; a vacuum portion  104  of the data path/line bundles reaches the respective PDDs  112  and feeds the data to the PDDs of the individual columns  9 . 
     The data path comprises, for instance, fiber optical and/or electrical line components (e.g., flatband cables) as known in prior art. An implementation of an optical data path suitable for embodiments of the invention is described in the article of A. Paraskevopoulos et al., “Scalable (24-140 Gbps) optical data link, well adapted for future maskless lithography applications”, Proc. SPIE Vol. 7271, 72711 I (2009). These techniques can be combined with modern packaging techniques, in particular using suitable connections such as flip-chip bonding instead of using bonding wires to the DAP as outlined below in more detail. 
       FIG. 5A  illustrates one realization of a PDD arrangement  512  serving as one of the beam shaping devices  112  of the apparatus  100  of  FIG. 4 , in a longitudinal sectional detail view. In addition to the AAP  520  and DAP  530 , an additional plate  510  is provided as a first plate (i.e., topmost plate) of the PDD arrangement  512 , as well as a plate  540  as a lowermost plate of the PDD arrangement  512  as seen along the direction of the beam. The plate  510  realizes a first field-boundary device according to embodiments of the invention, and is referred to as first or top field-boundary array plate, abbreviated tFAP (or top FAP); likewise, the plate  540  realizes a second field-boundary device according to embodiments of the invention, referred to as second or bottom field-boundary array plate, abbreviated bFAP (or bottom FAP; “bottom” referring to the position as lowermost plate of the PDD). In an embodiment shown in  FIG. 5A , the tFAP  510  is at a considerable distance h 1  to the AAP  520  and the subsequent DAP  530  and bFAP  540 . The tFAP  510  and bFAP  540  define a free-drift region F 1  between them, more exactly between the outwardly facing surfaces  513 ,  514  of the FAPs  510 ,  540 . Preferably, the surfaces  513 ,  514  are flat except for the aperture openings  511 ,  541  provided in the plates so as to allow passage of the illuminating beam  50   a  through the PDD arrangement  512 , as a multitude of sub-beams  57 . The aperture openings  511  in the tFAP  510  may have the same size as the corresponding aperture openings  541  of the bFAP  540 , or a similar size, under the condition that they are larger than the apertures  24  of the AAP  520 . Thus, the sub-beams  50   a  formed by the tFAP are larger compared to the aperture opening size  24  of the AAP, which define the ultimate shape of the individual sub-beams  51 ,  52 . 
     The enhanced height of the free-drift region F 1  allows the adequate access of data path lines  104  to the DAP  530 , as described in more detail below. A large distance h 1  is present between two subsequent plates, here the tFAP  510  and AAP  520 . This distance h 1 , on the one hand, creates a field-free space for the sub-beams  50   a  in the areas of the aperture fields, and on the other hand outside of the regions of the sub-beams (i.e., between the columns) it offers sufficient space for the data path lines  104  supplying the DAPs  530 . The arrows  104  symbolize data path bundles which approach the PDD arrangement at one or more levels of height and enter the respective DAP passing the corresponding AAP (bypassing the outer rim of the AAP and/or traversing through-holes provided therein). The deflection devices of the DAP may be oriented downstream as shown in  FIG. 5A  or upstream (cf.  FIG. 7 ) without this having an effect upon the layout according to embodiments of the invention. 
     The field-free space interval formed by the distance h 1  is a region of evacuated space inside the optical column, not obstructed by mechanical components. It is, therefore, suitable for the beam path of the charged particles near the axis of the optical column, and for accommodating feeding lines in the off-axis regions which are not traversed by the charged particles. The field-free space is, as its name insinuates, essentially free of electromagnetic fields, in particular of free of fields that are technically generated. The latter—i.e., the absence of technically generated electromagntic fields—is achieved by means of the FAPs field-boundary devices. As mentioned above, the bFAP and tFAP are held at a common electrostatic potential (usually reference ground potential), and as a consequence the space or “interval” between those two plate-like devices is free from technically generated electrostatic fields, including in particular the electrostatic fields of the charged-particle optical systems  11  and  16 . 
     Other fields such as magnetic fields are avoided by avoiding their sources ( magnetic materials, conductive elements carrying a current). Furthermore, a magnetic field shielding tube  120  may be provided, positioned in the field-free space formed by the distance h 1  between the tFAP  510  and AAP  520  and surrounding the sub-beams  50   a  traversing this region. The tube  120  is made of a material suitable for magnetic shielding, such as mu-metal with a thickness of approx. 1 mm. The shape of the tube  120  preferably is a cylindrical/prismatic shape derived from a suitable cross-section shape, extending along the Z direction so as to be parallel to the beam. This magnetic field shielding tube  120  helps to avoid cross talk of the beams between the sub-columns, as described in more detail below. Other embodiments (not shown) may be realized without magnetic field shielding tubes. 
       FIG. 5B  shows a number of PDD arrangements of the type shown in  FIG. 5A , in its parallel arrangement within the apparatus  100 . The tFAPs are mounted on a common base plate  131 . The base plate  131  is made of a base material like that of the reference plate, and extends through the entire width of the multi-column device, provided with holes  130  at the positions of the individual columns  9 . In a similar manner, the bFAPs are mounted on a common base plate  132 , preferably made of the same base material. The AAPs and DAPs are mounted on respective positions of the inner surface of a base plate as well, in this case of the second base plate  132 . The data path is supplied in one or more portions  104  to the individual DAPs  530 , possibly at different levels of height, illustrating the improved space situation by virtue of the embodiments of the invention.  FIG. 5B  also illustrates one possible realization of the attachment of the shielding tubes  120  within the PDD arrangement; in this case, each tube  120  is fixed at its upper end to the inner rim of the corresponding hole  130  in the base plate  131  by means of suitable attachment devices  123 . 
     The base plates  131 ,  132  may further include a cooling system as a way to control the temperature of the plates  510 ,  520 ,  530 ,  540  mounted on them. The cooling system may be realized, for instance, by a number of vacuum-tight coolant lines formed in the base plates, which lines are connected to a coolant supply. 
       FIG. 6  shows another embodiment of a PDD arrangement  612  where the AAP  620  is in proximity to the tFAP  610  while the DAP  630  is positioned between the bFAP  640  and the AAP  620  (preferably in close vicinity of the latter), leaving a large distance h 2  above the bFAP  640 . Again a magnetic field shielding tube  120  is provided, in this case located in the field-free space formed by the large distance h 2  between the DAP and bFAP. The data path  104  is supplied to the DAP via the space formed by the large distance outside the shielding tube  120 . 
       FIG. 7  shows a further embodiment of a PDD arrangement  712  where the AAP  710  is the first plate and thus also realizes the first field-boundary device of embodiments of the invention. Consequently, in this case the free-drift region F 2  is formed between the upper surface  713  of the AAP  710  and the lower surface  714  of a bFAP  740 . In this case the apertures  711  of the AAP  710  formed in the surface  713  define the shape of the sub-beams  57 . The aperture openings of the other plates, in particular the corresponding aperture openings  741  of the bFAP  740 , are suitably wider than the apertures  711 . The data path  104  is supplied via the space which, in this case, is defined by the large distance h 2 ′ between the DAP  730  and the bFAP  740 . 
     In each variant of the PDD arrangement, the orientation of the DAP may be with the ground and deflection electrodes  35 ,  38  oriented downstream (“inverted” orientation as shown in  FIGS. 2 and 5A ), or with the electrodes oriented upstream (“upright” orientation, see  FIG. 7 ); the orientation can be chosen as deemed suitable for each case. Further DAP configurations, e.g., with embedded ground and deflection electrodes, can easily be devised by the skilled person (see other patents in the name of the applicant, such as U.S. Pat. No. 8,198,601 B2). 
       FIG. 8A  shows a cross sectional view of the PDDs of several adjacent columns, along a transversal sectional plane as indicated by line  8   A - 8   A  in  FIG. 5B . The arrangement  80  illustrated in  FIG. 8A  realizes a rectangular layout of columns (cf.  FIG. 3A ). The shape of the magnetic field shielding tube  120  may be chosen as needed, preferably having a suitable cross-section shape, extending along the Z direction so as to be parallel to the beam. For instance, the cross-section shape of the tube may be quadratic with rounded inner corners so as to facilitate fabrication of the tube. This shape allows that the tube  120  is positioned in close distance to the ensemble  81  of sub-beams (aperture array field). If the aperture array field is rectangular then the cross-section of the magnetic field tube may advantageously be (rounded) rectangular. The distance between the inner surface of the tube  120  and the sub-beams ensemble  81  may be about 0.5 to 1.0 mm, for instance. 
       FIG. 8B  shows a variant arrangement  80 ′ of several columns in a rhombic layout (cf.  FIG. 3B ) in a cross sectional view analogous to  FIG. 8A . The tubes  129  are suitably shaped surrounding the respective ensemble  81 ′ of sub-beams, for instance, having a cross-section of quadratic shape with rounded inner corners 
     From the above it will become clear that the free-drift region F 1 , F 2  and in particular the free-field space created by the distance h 1 , h 2 , offers considerable space between the beams  81 ,  81 ′ of the sub-columns, which allows for sufficient space enabling data path access from the side to the individual columns and the DAPs therein. In contrast, in the PDDs of prior art the plate components AAP, DAP, and FAP were arranged closely packed, in order to avoid possible deviations of the sub-beams, which renders a data-path access in the prior-art PDDs difficult. The condenser optic components of the illuminating system have a circular shape (corresponding to the circles depicted in  FIGS. 3A and 3B ) and will come very near to each other in the compact arrangement of columns required for an efficient throughput. Thus, the illuminating systems of the columns hinder a sufficient data path access to the PDD system from the upstream side. The same considerations apply mutatis mutandis for the projections system and data path access from the downstream side. The embodiments of the invention solve this problem by creating additional space within the PDD system through the provision of the tFAPs and bFAPs. 
     The DAP of each column is located in a blanking unit of the respective PDD arrangement. In the simplest case, the blanking unit is represented by the DAP only; the blanking unit may include further plate components of the PDD arrangement, for instance the respective AAP. According to an advantageous variant embodiments of the invention, the AAP and DAP of a PDD arrangement of a single column are positioned in close vicinity to each other and mounted within a structural unit  200 , referred to as blanking “package” or simply “package” ( FIGS. 10 and 11 ); the package is arranged at a respective distance to the FAP, with the distance chosen suitably so as to provide sufficient data path access. 
     Another aspect of many embodiments of the invention addresses a possible problem with the width of the PDD arrangements transversal to the beams, since the width may be large enough that it is not possible to arrange the PDDs side-by-side as shown in  FIG. 5B . In order to relieve this problem, this aspect provides that the blanking units of the PDDs (beam shaping devices) of the columns are positioned not at one uniform distance to the respective FAP, but such that different blanking units may be positioned at different Z levels. (Obviously, this aspect can be combined with the implementation of packages as discussed above.) This will result in a Z-staggered arrangement. This is illustrated in  FIG. 9 , which shows a PDD arrangement  912  of the PDDs of several columns in a schematic longitudinal section. Again, only a small number of columns are shown, to represent a much larger number of columns that are present in the multi-column apparatus. 
     The example depicted in  FIG. 9  relates to a sub-column configuration where each sub-column exposes one die field according to a rectangular arrangement of columns (cf.  FIG. 3A ); the field-free region F 3  is segmented into several segments in consecutive order along the Z direction, in this example five segments, which define several tiers for the plate components of the PDD arrangements, in the example six tiers T 0  . . . T 5 . In particular, the DAPs of adjacent columns are distributed over different tiers. Thus, the Z-staggered arrangement accomplishes a considerably increased space available around each DAP for the data path access. 
     In tier T 0  the tFAP units  110  for each sub-column are mounted onto a common base plate  301 . The base plate  301  is fabricated from a suitable base material preferably, a material is chosen which has high elasticity module and high thermal conductivity; this allows that the base plate  301  can be cooled with state-of-the-art techniques and thus kept precisely at desired temperature. Further, the base plate  301  may be covered with an electrically conductive coating, at least at its relevant parts, in order to allow draining off accumulated electrostatic charges, so as to avoid charging effects. Furthermore, magnetic shielding tubes  302  are mounted to the base plate  301 , by means of suitable attachment devices  313 , for each sub-column, traversing the segment spanning from tier T 0  to T 1 . 
     In tier T 1 , several AAP/DAP packages  200  are provided. The packages  200  are mounted onto a common base plate  311  provided with holes  310 , one for each column. This base plate  311 , as well, can be cooled and kept precisely at desired temperature, and may be covered with a conductive layer to avoid charging effects. Magnetic field shielding tubes  312  are mounted by means of respective attachment devices  313  at the holes  310 , traversing the latter and surrounding the beam of the respective column. 
     Likewise, in tiers T 2 , T 3 , and T 4  further packages  200  are mounted onto respective base plates  321 ,  331 ,  341 , which can be cooled and kept precisely at desired temperature. In  FIG. 9  the tiers T 2  and T 4  appear to contain no package  200 , but in fact those tiers contain packages at other vertical planes, due to the staggered arrangement and as will become clear from the explanation given below with  FIGS. 12A   12 D. At each tier magnetic field shielding tubes  322 ,  332 ,  342  are mounted so as to span from one segment to the next through respective holes in the respective base plate. 
     In order to further increase the effect of the magnetic shielding tubes, the tubes may be provided with sockets  304  where they continue from a preceding tube, so as to ensure a good joining of subsequent tubes wherever no package  200  is present at the respective location. The sockets  304  serve to achieve a virtually seamless magnetic shielding of the beams passing the columns and thus avoid cross talk between the sub-columns. 
     In the final, lowermost tier T 5  the bFAPs  140  are present. They are mounted onto a common base plate  351  (corresponding to base plate  132  of  FIG. 5B ) by means of suitable attachment devices  353 . Magnetic field shielding tubes  352  may be provided to ensure a proper magnetic shielding down to the bFAPs. The base plate  351 , as well, can be cooled and kept precisely at desired temperature. 
     The data path lines (not shown in  FIG. 9 ) extend through the ample space of the segments formed between the tiers T 0  . . . T 5 , and within each segment outside the regions traversed by the sub-beams (i.e., outside the shielding tubes if those are implemented). 
       FIGS. 10 and 11  show a “package”  200  of one PDD of the arrangement of  FIG. 9  in a longitudinal section and a plan view, respectively. The package  200  includes an AAP  320  and DAP  330  and is mounted onto a support board  240 , which may be realized as a PCB and is in turn positioned on the base plate  241  of the respective tier, or in a (not shown) variant directly to said base plate. Two consecutive shielding tubes  302   a ,  302   b  surround the beam  50   a ,  57 . 
     The DAP  330  is bonded to an interposer  210 , which consists of a silicon chip  211  with CMOS electronics  212 . Bonding contacts  213  provide electrical contacts from the electronics  212  to the CMOS circuitry  34  of the DAP. Suitable implementations of state-of-the-art interposer and packaging techniques are described in H. Y. Li et al., “Through-Silicon Interposer Technology for Heterogeneous Integration”, Future Fab Intl., Issue 45 (Apr. 25, 2013). 
     The interposer  210  further comprises, on the outer region of the electronics  212 , additional contacts  214  onto which receiver devices  220  for data path access are mounted. The receiver device  220  is realized as, e.g., an optical receiver chip  221  having an array of photodiodes  223 , in the case that the data path access  104  is achieved via optical beams. In case of electrical access (e.g., via ribbon cable) the receiver device  220  may include a multi-wire connector. The electric connection from the top of the receiver device  220  to the bottom wiring layer  225  is possible through TSV (Through Silicon Via)  224  so as to allow that the device  220  can be bonded and electrically connected at the bonding contacts  214 . 
     As mentioned earlier, the base plate  241  may be cooled and kept at desired temperature. In addition, in a further embodiment of the invention a cooling device  230  may be provided for each PDD with vacuum-tight chambers  231  which are configured for a cooling fluid being directed through them, such as a cooling liquid having, preferably, low viscosity but high heat capacity (e.g., de-ionized water) or a cooling gas (e.g., Helium). Vacuum-tight flexible cooling media access (not shown) are used to pass the cooling liquid or cooling gas through chambers  231 . Cooling devices, connections and coolant fluids suitable for this purpose are well known from prior art. 
     There is no direct mechanical connection between the AAP  320  and the DAP  330 . Instead, the AAP  320  is mounted on a mechanical device  250 , schematically depicted in  FIG. 10 . For each AAP/DAP-package  200  the respective AAP  320  will be fine-positioned relative to the respective DAP  330  prior to mounting the packages  200  to the support board  240  and insertion into the multi-beam multi-column system. Alternatively, as already realized by the applicant and topic of U.S. Pat. No. 8,546,767, the AAP  320  may be adjustable in situ with regard to fine-positioning in X, Y position and/or rotation, e.g., by means of piezo-drives provided as components of the device  250 , in order to ensure that the sub-beams generated by the apertures of AAP, upon illumination with the wide beam  50   a , will all pass through the corresponding aperture openings  33  of the DAP  330 . 
     In variant embodiments, cooling means may be provided to the AAP as well. However, it is expected that for a multi-beam multi-column system a cooling of the AAP is not necessary. Even when using the arrangement according to  FIG. 7  where the top surface of the AAP  20  is illuminated by the broad beam  50  the power load is low, (i) due to the low energy (e.g., 5 keV) of the beam  50 , and (ii) by the fact that the current density at the AAP is 40,000-times smaller than at the substrate when using a projection optics with 200:1 reduction. The current density of a multi-beam multi-column system at the substrate is lower than 8 A/cm 2  (when using electrons, much lower when using ions). Therefore, the current density at the AAP is &lt;0.2 mA/cm 2 , and the corresponding power load of &lt;1 W/cm 2  will lead to an AAP temperature increase of only a few degrees. The corresponding expansion of the aperture array field is small and can be compensated by electronically adjusting the size of the beam array field  62 ,  72  at the substrate. Since the aperture openings  33  in the DAP are wider than the aperture openings  24  in the AAP there is sufficient tolerance so as to avoid obstruction of the beams passing through the aperture openings  33  of the DAP. 
     As can be seen from the plan view of  FIG. 11 , the AAP-DAP package  200  is mounted onto the base plate  241 . The magnetic field shielding tube  302   a  ends just above the aperture array field  62  of the AAP  320 . The shielding tubes  402  of the neighboring columns are visible in  FIG. 11  as well. The DAP  330  is positioned below the AAP  320  and mounted onto the interposer  210  as described above. Advantageously, four receiver devices  220  may be provided, one at each side of the square (rectangle) shape of the DAP  330 . Furthermore, additional member and/or logic chips  260  may be provided placed on the interposer  210 . The magnetic field shielding tubes  402  are mounted at the base plate  241  by means of attachment components  403 . 
     As visible in  FIG. 11  there may be further space on the support board  240 , which can be used for accommodating additional memory and logic chips and additional devices of the optical data path, which do not form part of the embodiments of the present invention. 
       FIGS. 12A to 12D  show a series of partial plan views of the tiers T 1  to T 4 , respectively, corresponding to respective sections along planes indicated in  FIG. 9  by lines A-A, B-B, C-C, and D-D, respectively. Each partial plan view shows the area of several columns (6 DX×5 DY) at the same position with respect to X and Y coordinates. The packages  200  are arranged with a periodicity of 2*DX in X-direction and of 2*DY in Y-direction within each tier, but there is an offset along DX and/or DY between consecutive tiers. From the combination of these figures it will be clear that in each tier the packages  200  are positioned such that for each pair of directly adjacent columns, the packages are at different tiers. 
     In a further embodiment of the invention, the AAP/DAP-package  200  may be positioned on the base plate  241  by means of a kinematic mount  270  constituted by four 45° openings  271  in the support board  240 . There are four 45° sockets  404  in the base plate  241  into three of which positioning pins  405  are inserted. A thermal expansion of the support board  240 , which may be caused by heat generated in the electronics of the DAP CMOS layer and receiver device, will not change the X, Y and rotation positions of the DAP. As mentioned above, below the silicon interposer  210  there may be a cooling device  230  in order to minimize any change of temperature of the support board  240 .