Method for carrying out an electron beam examination of at least one preparation, and carrier for such a method
The method of adapting a short-circuit bridge on a carrier to form gaps for individual electrical connections addresses the challenge of preparing TEM samples, enabling efficient and cost-effective electron beam examination of nanostructures.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- HUMBOLDT UNIVET ZU BERLIN
- Filing Date
- 2025-11-20
- Publication Date
- 2026-06-18
Smart Images
Figure DE2025101091_18062026_PF_FP_ABST
Abstract
Description
[0001] HUM118
[0002] Description
[0003] Method for carrying out an electron beam examination of at least one specimen and carrier for such a method
[0004] The invention relates to a method for carrying out an electron beam examination of at least one preparation.
[0005] Electron microscopy, especially transmission electron microscopy (TEM), has become indispensable in development-related research. This is due to the ongoing miniaturization of switchable electronic components down to the micro and nanoscale. The nanostructures in such components, which significantly contribute to increasing their efficiency, encounter real physical limitations during development. Since these limitations are difficult to model, particularly for dynamic processes like switching operations, both industry (R&D, manufacturers) and academia (basic research) are urgently seeking methods for investigating real switching nanostructures.
[0006] Since the preparation of such electrically contacted samples for TEM investigations presents non-trivial challenges, there are currently only a few successful examples in the literature. A simple, reliable, and reproducible method for preparing such samples, which also meets the time constraints of industry, does not yet exist. HUM118
[0007] 2
[0008] The invention is based on the objective of providing a method for carrying out an electron beam examination of a preparation and a particularly suitable carrier for this purpose.
[0009] This problem is solved according to the invention by a method with the features according to claim 1. Advantageous embodiments of the method according to the invention are specified in the dependent claims.
[0010] According to the invention, starting from a sample, the preparation is produced by material removal. A carrier comprising a first terminal electrode, a second terminal electrode, and a short-circuit bridge bridging a carrier material-free area and located electrically between the first and second terminal electrodes is interrupted, thereby forming a gap between a first bridge part and a second bridge part, and electrically separating the two bridge parts. The gap width and / or gap shape is adapted to the position of a first and second terminal of the preparation in a preparation-specific manner, such that the first electrical terminal of the preparation can be electrically connected to the first bridge part and the second terminal to the second bridge part.The first electrical connection of the specimen is electrically connected to the first bridge section and the second connection to the second bridge section, and an electron beam examination of the specimen connected to the connection electrodes via the bridge sections is performed, whereby an electron beam is passed through the specimen and the area free of support material. HUM118
[0011] 3
[0012] A significant advantage of the method according to the invention is that, by using a carrier with an initially uninterrupted short-circuit bridge, the short-circuit bridge can be individually adapted to the size and / or shape of the preparation by separating it into bridge parts, with the gap being individually adapted to the preparation to be examined, and the substrate being connected to the individually manufactured bridge parts. This enables a particularly fast and cost-effective production of the measurement object to be examined in the form of the preparation applied to the carrier.
[0013] It is advantageous if the area free of carrier material is designed as a through hole or through slot, with a through slot being considered particularly advantageous with regard to use in a transmission electron microscope.
[0014] The bridge part can be formed by a section of a conductor track; however, it is particularly advantageous if the short-circuit bridge is designed as a separate part that is placed on conductor track sections of a conductor track layer.
[0015] In one embodiment considered advantageous, the preparation is first produced from a sample before the short-circuit bridge is interrupted, taking into account the actual shape and size of the preparation. This procedure allows for a particularly individual adaptation of the gap to the specific needs of the preparation. HUM118
[0016] 4
[0017] After connecting the preparation to the bridge parts, further material removal can be carried out, at least of the preparation, with further reduction of the preparation thickness and usually with further reduction of the bridge thickness of the adjacent bridge parts.
[0018] With regard to individual adaptation to the preparation, it is advantageous if the bridge width and / or the bridge thickness of the first and / or second bridge part is reduced at least section by removing material from the respective bridge part.
[0019] The narrowing or reduction of the bridge width is preferably carried out in such a way that the first and second bridge sections, viewed in the longitudinal direction of the bridge, are at least partially free of overlap.
[0020] The narrowing or reduction of the bridge width preferably involves the gap deviating from a rectangular shape when viewed from above. The narrowing of the bridge width is achieved, for example, by ensuring that the gap contour, when viewed from above, has at least one corner or at least one curved section in the area of the bridge's center.
[0021] For example, it may be advantageous if the tapering or reduction of the bridge width of the first and / or second bridge part is adapted to the shape, in particular the spatial position of the first and / or second connection, of the specimen, preferably in such a way that an overlap of non-contacting areas of the specimen with the bridge parts is avoided or minimized. HUM118
[0022] 5
[0023] It can also be advantageously provided that the support has a third terminal electrode and a second short-circuit bridge connected to the third terminal electrode, which also bridges the area free of support material, and that a third electrical connection of the preparation is electrically connected to the second short-circuit bridge or at least to a bridge part of the second short-circuit bridge.
[0024] The first and second short-circuit bridges are preferably parallel.
[0025] It is also advantageous if the bridge width and / or the bridge thickness of the second short-circuit bridge is reduced, at least section by section, by material removal, viewed in the longitudinal direction of the bridge.
[0026] It is advantageous if the second short-circuit bridge connects the third terminal electrode with a fourth terminal electrode, at least in the initial state before any material removal.
[0027] In a preferred embodiment, the second short-circuit bridge is provided to remain uninterrupted in the longitudinal direction of the bridge.
[0028] In another preferred embodiment, the second short-circuit bridge is interrupted by material removal to form a second gap, a third electrical connection of the preparation is electrically connected to a first bridge part of the second short-circuit bridge, and a fourth electrical connection of the HUM118
[0029] 6
[0030] The preparation is electrically connected to a second bridge part of the second short-circuit bridge.
[0031] In a further method variant considered advantageous, it is provided that, starting from the same or a second sample, a second preparation is produced by material removal, the support is electrically interrupted in the area of a further short-circuit bridge, thereby forming a further gap between a first bridge part of the further short-circuit bridge and a second bridge part of the further short-circuit bridge, and the two bridge parts are electrically separated from each other, wherein the gap width and / or gap shape is adapted to the position of a first and second connection of the second preparation such that the first electrical connection of the second preparation can be electrically connected to the first bridge part of the further short-circuit bridge and the second connection to the second bridge part of the further short-circuit bridge.the first electrical connection of the second preparation is electrically connected to the first bridge part of the further short-circuit bridge and the second connection of the second preparation is electrically connected to the second bridge part of the further short-circuit bridge, and an electron beam examination includes the second preparation connected to the connecting electrodes via the bridge parts of the further short-circuit bridge.
[0032] It is advantageous if TEM lamellae are examined as the preparation(s). The preparations are preferably cut from a wafer or chip using a focused ion beam method, or at least also using such a method. HUM118
[0033] 7
[0034] As already mentioned at the outset, the invention also relates to a carrier suitable for a method as described above. According to the invention, the carrier is provided to have a first terminal electrode, a second terminal electrode, and an electrical short-circuit bridge between the first and second terminal electrodes, bridging a carrier-material-free area.
[0035] Regarding the advantages of the carrier according to the invention and its advantageous embodiments, reference is made to the above statements in connection with the method according to the invention and its advantageous embodiments.
[0036] With regard to the support, it is considered advantageous if the support has two or more short-circuit bridges, at least two of which are parallel to each other and bridge one and the same support material-free area.
[0037] The invention is explained in more detail below using exemplary examples; these include, by way of example:
[0038] Fig. 1-5 shows an exemplary embodiment of a support according to the invention.
[0039] Figs. 6-10 show an exemplary embodiment for the production of a preparation and the application of the preparation to the carrier shown in Figures 1 to 5.
[0040] Figure 11 shows an electron beam examination of the preparation applied to the support according to Figures 1 to 10, HUM118
[0041] 8
[0042] Figs. 12-16 show a second exemplary embodiment for the production of a preparation and the application of the preparation to the carrier according to Figures 1 to 5.
[0043] Figs. 17-19 show a third exemplary embodiment for a carrier according to the invention, the production of a preparation and the application of the preparation to the latter carrier, and
[0044] Figure 20 shows a production of beams, for example beams according to Figures 1 to 5, wherein a beam material-free section is first produced in the form of a through hole and this through hole is subsequently subdivided to form a through slot for two adjacent beams.
[0045] For the sake of clarity, the same reference symbols are always used in the figures for identical or comparable components.
[0046] Figures 1 to 5 show an exemplary embodiment of a support 100 according to the invention, which is suitable for carrying out electron beam examination methods according to the invention.
[0047] Figure 1 shows a top view (xy-plane) of the support 100, which comprises a first terminal electrode 110 and a second terminal electrode 111. The two terminal electrodes 110 and 111 can be configured as conductive traces supported by a substrate. The substrate can, for example, be a silicon substrate 101, which is insulated by an insulating layer applied to it.
[0048] 9 for example in the form of a silicon oxide or silicon nitride layer is separated from a conductor layer 115 forming the conductor tracks.
[0049] The support 100 also comprises a short-circuit bridge 120, which is electrically connected to the first terminal electrode 110 and the second terminal electrode 111 and bridges a carrier-material-free area 130. The carrier-material-free area 130 is preferably a through-slot 131 extending to the outer edge of the support 100; alternatively, the carrier-material-free area 130 can be a through-hole spaced apart from the outer edge of the support 100.
[0050] The short-circuit bridge 120 can be a further conductor track of the conductor track layer 115 applied to the insulation layer. However, for reasons of stability, it is particularly advantageous if the short-circuit bridge 120 is a separate part, in particular a metal part, which is applied to the end sections of the two terminal electrodes 110 and 111 and electrically connected to them, for example by soldering.
[0051] Figure 2 shows a section of the support marked with the reference sign E in Figure 1 in the same top view (xy-plane) in more detail.
[0052] Figure 3 shows the beam section marked with reference sign E in Figure 1 in a cross-sectional view (x-z plane) in more detail.
[0053] Figure 4 shows the entire support 100 including the support section designated with reference sign E in Figure 1 - HUM118
[0054] 10
[0055] The section in the same cross-sectional view (x-z plane) is shown in more detail. In the embodiment shown in Figure 4, the through slot 131 is bounded by vertical surfaces arranged perpendicular to the surface of the support 100.
[0056] Figure 5 shows another preferred embodiment of the through-slot 130. In the embodiment shown in Figure 5, the through-slot 131 is bounded by inclined surfaces. For example, these can be (1, 1, 1) surfaces if they are produced by anisotropic etching of a (1, 0, 0)-oriented silicon substrate 101.
[0057] The carriers 100 shown in connection with Figures 1 to 5 can be produced, for example, by coating a silicon substrate 101 with an insulating layer such as silicon oxide or silicon nitride. The through-slot 131 can then be produced, for example, by sawing and / or etching. Before or after this, the conductive layer 115 can be applied to the insulating layer and structured accordingly to form the conductive tracks. Before or after completion of the through-slot 131, the short-circuit bridge 120 is placed on the end sections of the two terminal electrodes 110 and 111. The same applies to the carrier 100 described below in connection with Figures 17-20, which has two short-circuit bridges 120 and 120a.
[0058] As part of wafer processing, as illustrated by Figure 20, a large number of carriers 100 can be produced simultaneously. The carrier-free areas 130 can be produced in two stages. For example, through-holes 132 can first be etched, and then the short-circuit bridges 120 and 120a can be positioned. During the singulation or splitting of the wafer into the individual carriers 100, the cutting or sawing edge SK between the short-circuit bridge areas of adjacent carriers 100 can be placed through the through-holes 132, so that each through-hole of two adjacent carriers 100 is modified into two through-slots 131, one for each of the two carriers 100.
[0059] Figure 6 shows an example of the fabrication of a preparation 200 from a sample 205. The sample 205 is, for example, a wafer carrying a multitude of electronic components. In the embodiment according to Figure 6, a section of the wafer with an electrical component having two electrical connections 210 is separated by material removal, for example by sawing or a focused ion beam process, and then thinned by further material removal to form the preparation 200. The further material removal can, for example, also be carried out by a focused ion beam process. In other words, the preparation 200 can, for example, be a so-called TEM lamella.
[0060] Before or after the production of the preparation 200, or simultaneously, the short-circuit bridge 120 of the support 100 described in connection with Figures 1 to 5 (see Figures 7 and 8) spanning the through-slot 131 is interrupted, thereby creating a gap 300 between a first bridge part
[0061] 121 of the short-circuit bridge 120 and a second bridge section
[0062] 122 of the short-circuit bridge 120 is formed and the two bridge parts 121 and 122 are electrically separated from each other. 12
[0063] Figure 7 shows the beam section E marked in Figure 1 in a top view (xy-plane) after the interruption of the short-circuit bridge 120 in more detail. Figure 8 shows the beam section E in a cross-sectional view (x-z-plane).
[0064] After the short-circuit bridge 120 is interrupted and the two bridge parts 121 and 122 are separated from each other, the preparation 200 shown in Figure 6 is placed on the two bridge parts 121 and 122 and connected to it, for example, by soldering.
[0065] Figure 9 shows the support section E marked in Figure 1 in a top view (xy-plane) after the application of preparation 200 in more detail. Figure 10 shows the support section E in a cross-sectional view (x-z-plane).
[0066] Figures 9 and 10 show that the gap width is adapted to the later position of a first and second connection of the preparation 200 in such a way that the first electrical connection 210 of the preparation 200 can be electrically connected to the first bridge part 121 and the second connection 210 can be electrically connected to the second bridge part 122.
[0067] In the embodiment shown in Figures 6 to 10, the connections 210 of the preparation 200 lie on a line L parallel to the bridge longitudinal direction BLR and the bridge width B (x ) of the two bridge parts 121 and 122 is constant .
[0068] Figure 11 shows a simplified representation of an embodiment of an invention- HUM118
[0069] Figure 13 shows a conventional electron beam examination method. Components of a transmission electron microscope 500 are depicted, comprising an electron beam source 510 and an electron measuring device 520. The support 100, provided with the specimen 200 according to Figures 9 to 10, is located, for example, in a high-vacuum section of the transmission electron microscope 500.
[0070] Regarding the measurement operation of the transmission electron microscope 500, conventional methods can be used; the inventive concept of the exemplary embodiment of an inventive method shown in connection with Figures 1 to 11 consists in the production of the measurement object, i.e. the carrier 100 with the preparation 200 located on it.
[0071] Figure 12 shows an example of the fabrication of another preparation 200 from a sample 205. The sample 205 is, for example, a diode, such as a laser diode. In the embodiment according to Figure 12, a section of the laser diode is separated by material removal, for example by sawing or a focused ion beam process, and then thinned by further material removal to form the preparation 200. The further material removal can also be carried out, for example, by a focused ion beam process. In other words, the preparation 200 can, for example, be a so-called TEM lamella of a laser diode. The further material removal or thinning of the preparation can also be carried out after the preparation has been placed on the bridge parts; in such a case, the adjacent bridge parts are usually also thinned. HUM118
[0072] 14
[0073] Before or after the preparation of the preparation 200, or simultaneously, the short-circuit bridge 120 of the carrier 100 described in connection with Figures 1 to 5 (see Figures 13 and 14) spanning the through-slot 131 is interrupted, thereby forming a gap 300 individually adapted to the preparation between a first bridge part 121 of the short-circuit bridge 120 and a second bridge part 122 of the short-circuit bridge 120 and electrically isolating the two bridge parts 121 and 122 from each other.
[0074] Figure 13 shows the beam section E marked in Figure 1 in a top view (xy-plane) after the interruption of the short-circuit bridge 120 in more detail. Figure 14 shows the beam section E in a cross-sectional view (x-z-plane).
[0075] To simplify the placement of the specimen 200 onto the two bridge sections 121 and 122, or to increase the space between the two bridge sections for the specimen 200, the shape of the gap 300 is adapted to the shape of the specimen 200 by reducing the bridge width B(x) of the first and second bridge sections, at least section by removing material from the respective bridge section – along the bridge longitudinal direction BLR or the bridge section longitudinal direction. Thus, unlike in the embodiment shown in Figures 6 to 10, the bridge width B(x) is not constant, but depends on the respective location x on the respective bridge section 121 or 122. The resulting gap 300 is therefore not rectangular as in the embodiment shown in Figures 6 to 10, but polygonal and has corners or... Curvature areas EK in the middle area of the gap 300 on . HUM118
[0076] 15
[0077] In the embodiment shown in Figures 12 to 16, the narrowing of the bridge width B is carried out in such a way that the first and second bridge sections 121 and 122 are at least partially free of overlap when viewed in the longitudinal direction of the bridge BLR.
[0078] After the short-circuit bridge 120 is interrupted and the two bridge parts 121 and 122 are separated from each other, the preparation 200 shown in Figure 12 is placed on the two bridge parts 121 and 122 and preferably connected to it, for example by soldering.
[0079] Figure 15 shows the support section E marked in Figure 1 in a top view (xy-plane) after the application of preparation 200 in more detail. Figure 16 shows the support section E in a cross-sectional view (x-z-plane).
[0080] It can be seen in the figures that a virtual connecting line L between the two terminals 210 of the preparation 200 is not arranged parallel to the bridge longitudinal direction BLR of the two bridge parts 121 and 122, but is inclined to it.
[0081] Figures 17, 18a and 19a show a further embodiment of a support 100 according to the invention, which is suitable for carrying out electron beam examination methods according to the invention.
[0082] The carrier 100 according to Figures 17, 18a and 19a, unlike the carrier 100 according to Figures 1 to 5, has four connecting electrodes 110-113 and two short-circuit bridges 120 and 120a, which can be selectively cut and thus HUM118
[0083] 16 can be used for connecting an electrical preparation 200 with three or four connections.
[0084] Figures 18b and 19b below illustrate, by way of example, that a sample 200 with three electrical connections is to be examined, such that it is sufficient to cut only one of the two short-circuit bridges 120. The other short-circuit bridge 120a can remain intact, but its width can be adjusted if this appears advantageous with regard to the sample 200, resulting in a width that depends on the location x.
[0085] Figures 18c and 19c show the support 100 after the preparation 200 has been placed on the two separate bridge parts 121 and 122 of the severed short-circuit bridge 120 and the other short-circuit bridge 120a, which has only been reduced in width.
[0086] Finally, it should be mentioned that the features of all the exemplary embodiments described above can be combined with each other in any way to form further other exemplary embodiments of the invention.
[0087] Furthermore, all features of dependent claims can each be combined individually with each of the dependent claims, either alone or in any combination with one or more other dependent claims, to obtain further embodiments. HUM118
[0088] Reference character list
[0089] 100 carriers
[0090] 101 Silicon substrate
[0091] 110 first connecting electrode
[0092] 111 second connecting electrode
[0093] 112 third connection electrode
[0094] 113 fourth terminal electrode
[0095] 115 conductor layer
[0096] 120 Short-circuit bridge
[0097] 120a Short-circuit bridge
[0098] 121 first bridge section
[0099] 122 second bridge section
[0100] 130 carrier material-free area
[0101] 131 through-slot
[0102] 132 through holes
[0103] 200 preparation
[0104] 210 electrical connection
[0105] 205 Sample
[0106] 300 gap
[0107] 500 transmission electron microscope
[0108] 510 electron beam source
[0109] 520 electron measuring device
[0110] BLR bridge longitudinal direction
[0111] B / B (x ) bridge width
[0112] E Carrier section
[0113] EB electron beam
[0114] EK Curvature Area
[0115] L line
[0116] SK saw edge x location xy-plane top view x-z plane cross-sectional view
Claims
Patent claims 1. Method for carrying out an electron beam examination of at least one preparation (200) , characterized in that - starting from a sample (205) the preparation (200) is produced by material removal, - a support (100) comprising a first terminal electrode (110), a second terminal electrode (111) and a short-circuit bridge (120, 120a) bridging a support-material-free region (130) and electrically located between the first and second terminal electrodes (110, 111), is interrupted, thereby forming a gap (300) between a first bridge part (121) of the short-circuit bridge (120, 120a) and a second bridge part (122) of the short-circuit bridge (120, 120a) and electrically separating the two bridge parts (121, 122) from each other, wherein the gap width and / or gap shape is adapted to the position of a first and second terminal (210) of the preparation (200) in a preparation-specific manner such that the first electrical terminal (210) of the preparation (200) is electrically connected to the first bridge part (121) and the second terminal (210) can be electrically connected to the second bridge part (122), - the first electrical connection (210) of the preparation (200) is electrically connected to the first bridge part (121) and the second connection (210) is electrically connected to the second bridge part (122) and - an electron beam examination of the preparation (200) connected to the connecting electrodes (110, 111) via the bridge parts (121, 122) is carried out, whereby an electron beam (EB) is passed through the preparation (200) and the support-free area (130). HUM118 19 2. Method according to claim 1, characterized in that after connecting the connections (210) of the preparation (200) to the bridge parts (121, 122) a further material removal of at least the preparation (200) is carried out with further reduction of the preparation thickness.
3. Method according to one of the preceding claims, characterized in that the bridge width (B) and / or the bridge thickness of the first and / or second bridge part (121, 122) is reduced at least section by material removal from the respective bridge part (121, 122).
4. Method according to one of the preceding claims, characterized in that the reduction of the bridge width (B) is carried out in such a way that the first and second bridge part (121, 122) are at least partially free of overlap when viewed in the longitudinal direction of the bridge (BLR).
5. Method according to one of the preceding claims, characterized in that the reduction of the bridge width (B) is carried out such that the gap (300) deviates from a square shape when viewed from above.
6. Method according to one of the preceding claims, characterized in that the reduction of the bridge width (B) is carried out such that the gap contour of the gap (300) is seen in the top view. HUM118 20 hen has at least one corner or at least one curvature area (EC) in the area (130) of the bridge center.
7. Method according to one of the preceding claims, characterized in that - the carrier (100) has a third terminal electrode (112) and a second short-circuit bridge (120a) connected to the third terminal electrode (112), which bridges the carrier material-free area (130) and - a third electrical connection (210) of the preparation (200) is electrically connected to the second short-circuit bridge (120a) or at least to a bridge part of the second short-circuit bridge (120a).
8. Method according to claim 7, characterized in that the first and second short-circuit bridge (120, 120a) are parallel.
9. Method according to one of the preceding claims 7 to 8, characterized in that the bridge width (B) and / or the bridge thickness of the second short-circuit bridge (120a) is reduced at least sectionally by material removal in the longitudinal direction (BLR) of the bridge.
10. Method according to any one of the preceding claims 7 to 9, characterized in that the second short-circuit bridge (120a) connects the third terminal electrode (112) to a fourth terminal electrode (113) at least in the initial state before any material removal. HUM118 21 11. Method according to any one of the preceding claims 7 to 10, characterized in that the second short-circuit bridge (120a) remains uninterrupted in the longitudinal direction of the bridge (BLR).
12. Method according to any one of the preceding claims 7 to 10, characterized in that the second short-circuit bridge (120a) is interrupted by material removal, forming a second gap (300), - a third electrical connection (210) of the preparation (200) is electrically connected to a first bridge part (121) of the second short-circuit bridge (120a) and - a fourth electrical connection (210) of the preparation (200) is electrically connected to a second bridge part (122) of the second short-circuit bridge (120a).
13. Method according to one of the preceding claims, characterized in that - starting from the same or a second sample (205), a second preparation (200) is produced by material removal, - the support (100) is electrically interrupted in the area (130) of a further short-circuit bridge, thereby forming a further gap (300) between a first bridge part (121) of the further short-circuit bridge (120a) and a second bridge part of the further short-circuit bridge (120a) and electrically isolating the two bridge parts (121, 122) from each other, whereby the gap width and / or HUM118 22 The gap shape is adapted to the position of a first and second connection of the second preparation (200) such that the first electrical connection (210) of the second preparation (200) can be electrically connected to the first bridge part (121) of the further short-circuit bridge (120a) and the second connection (210) can be electrically connected to the second bridge part (121) of the further short-circuit bridge (120a), - the first electrical connection (210) of the second preparation (200) electrically with the first bridge part (121) of the further short-circuit bridge (120a) and the second connection (210) of the second preparation (200) is electrically connected to the second bridge part (121) of the further short-circuit bridge (120a) and - an electron beam examination includes the second preparation (200) connected to the connecting electrodes (110, 111) via the bridge parts (121, 122) of the further short-circuit bridge (120a).
14. Carrier (100) suitable for a method according to one of the preceding claims, characterized in that the carrier (100) is a carrier (100) having a first terminal electrode (110), a second terminal electrode (111) and a short-circuit bridge (120, 120a) bridging a carrier material-free area (130) electrically between the first and second terminal electrode (110-113).
15. Support (100) according to claim 14, characterized in that the support (100) has two or more short-circuit bridges, at least two of which are parallel to each other and bridge one and the same support material-free area (130).