Method of producing a vacuum chuck for semiconductor workpieces and vacuum chuck

Abstract

The present invention relates to a method for producing a vacuum clamp (100) for semiconductor workpieces, wherein the vacuum clamp (100) is produced from at least one substrate by means of an additive manufacturing method, and relates to a vacuum clamp (100) of this type.

Description

Technical Field

[0001] The present invention relates to a method for producing a vacuum clamp for semiconductor workpieces and such a vacuum clamp for semiconductor workpieces. Background Technology

[0002] Vacuum grippers (also commonly referred to as "chucks," suction grippers, or vacuum suction grippers) are used in the production and processing of semiconductor workpieces such as wafers (crystals) of silicon or other semiconductor materials to secure and / or transport these workpieces and / or hold them in a specific arrangement during various process steps (processes). However, while the semiconductor workpieces are arranged or held on the vacuum gripper, they are also processed. This includes, for example, polishing, etching, cleaning, dimensionaling, and surface grinding.

[0003] Such vacuum grippers for semiconductor workpieces can be manufactured as devices through casting, welding, and machining processes. However, as has been shown, these manufacturing processes only allow for limited realization of the vacuum gripper's shape and functional features.

[0004] Document US 2019 / 272982 A1 discloses a method for producing a vacuum gripper for semiconductor workpieces, wherein the vacuum gripper is created from at least one substrate (base material) by means of an additive deposition process.

[0005] Document US 2019 / 080954 A1 discloses an apparatus for holding (holding) a semiconductor wafer using a vacuum.

[0006] Document US 2017 / 345692 A1 also discloses a device for using vacuum to hold semiconductor wafers, which is produced by means of 3D printing.

[0007] Therefore, there is a need for improved vacuum grippers for semiconductor workpieces and / or their production. Summary of the Invention

[0008] According to the present invention, a method for producing an apparatus suitable for holding (holding) semiconductor workpieces by means of a vacuum is provided. Advantageous embodiments are the subject of the dependent claims and the description below.

[0009] This invention relates to the manufacture of vacuum grippers for semiconductor workpieces such as, for example, silicon wafers, and consequently, to their structural design. As mentioned in the opening section, a vacuum gripper is a device by virtue of its ability to securely hold semiconductor workpieces, particularly wafers. For this purpose—as its name suggests—a vacuum is generated, by virtue of which the semiconductor workpiece can be drawn onto the vacuum gripper.

[0010] This vacuum holder preferably has: a (at least generally) flat area on which a semiconductor workpiece can be arranged, one or more suction openings, and one or more channels connected thereto. In this case, these channels should be correspondingly connected to the suction openings. The suction openings should be located as close as possible to the area (site) where the flat area is situated, so that the semiconductor workpiece can be positioned thereon. Furthermore, in this case, the channels should be able to connect to, or have already connected to, a negative pressure source so that a negative pressure (or vacuum) can be created in the channels. The flat area may have, for example, a circular shape so that a typical wafer can be placed thereon. The diameter of this circular area or the entire vacuum holder can then be, for example, 300 mm or even larger.

[0011] In the proposed method, the vacuum gripper is created by means of additive deposition or manufacturing processes—which may particularly be so-called 3D printing—and in fact, specifically, from at least one substrate in or according to a predetermined shape. The substrates are thus, for example, bonded together layer by layer until the desired, predetermined shape is finally produced. In this respect, as explained above as a convenient (suitable) embodiment of the vacuum gripper, the vacuum gripper is preferably designed such that it has at least a generally flat area, one or more suction openings, and one or more channels connected thereto.

[0012] The vacuum clamp is also preferably designed to include a reinforcing structure, which is formed, in particular, from a substrate. Such reinforcing structures, such as struts, thickened sections, etc., can be created in a particularly simple manner by means of additive manufacturing processes or by means of 3D printing, and can also be more or less in any desired shape. However, the reinforcing structure can also be formed from another material having, for example, a different material hardness than the substrate.

[0013] At least one additive (by means of which the material hardness can be adjusted) is preferably added to the substrate. In this way, the mechanical properties of the vacuum gripper can be influenced in a targeted manner (particularly selectively at specific points or in specific regions), similar to the formation of the reinforcing structure.

[0014] Similarly, it is convenient when a predetermined area of ​​the vacuum gripper is created from a material different from the substrate using an additive deposition process. In this way, flexible regions can be created, for example, that function as seals.

[0015] In this case, it is also preferable to form a layer of material with a lower hardness or degree of hardness than the substrate in the region or side of the vacuum gripper facing the semiconductor workpiece. This layer can then include flat areas. This layer can then be used to prevent potential damage to the semiconductor workpiece and can thus serve as an alternative to a so-called "chuck pad." This "chuck pad" is typically a section of fabric or textile, and if suitable, can be made of polyurethane, which is placed on—in conventional vacuum grippers—a hard surface to prevent damage to the semiconductor workpiece. In the design of the layer described above, this chuck pad is no longer necessary.

[0016] Then, that is, after the vacuum gripper is manufactured in a predetermined shape (form) from a substrate or alternative material, a coating material for chemical protection can be applied (in this way, deposited) entirely or in a predetermined area on the body surface. This coating (which acts as a protective layer) makes the vacuum gripper chemically resistant and reduces surface roughness. The relevant areas of the surface to which the coating material is applied are particularly those areas that will subsequently come into contact with the corresponding medium or chemicals during use and therefore should be protected. This particularly relates to the top side surface used to hold semiconductor workpieces (especially the already mentioned flat area). In this respect, preferred coating materials are polytetrafluoroethylene, PTFE, perfluoroalkoxy polymers, PFA, polyvinylidene fluoride, PVDF, DLC (diamond-like carbon), or silicon carbide.

[0017] The reason for preferring this coating is that, in the case of parts produced by additive manufacturing processes such as 3D printing, and in the case of vacuum grippers (which may simply be) made of substrates—depending on the desired application—the surface roughness may be too pronounced, i.e., the surface may be generally too rough for the intended use. Therefore, organic and inorganic contaminants (which, for example, are generated when the semiconductor workpiece held by the vacuum gripper is polished) are deposited in and on the surface, and in some cases negatively impact the quality of the semiconductor workpiece to be processed.

[0018] However, coating the relevant surfaces of vacuum grippers, such as with PTFE, produced by additive deposition processes now allows for the combination of the positive properties of conventionally produced vacuum grippers (i.e., chemical resistance in particular) with those of vacuum grippers produced by additive deposition processes for silicon wafers (i.e., freeformability in particular).

[0019] Because vacuum grippers manufactured using additive deposition processes are subjected to high heat loads and would therefore deform under conventional coating processes, low-temperature coating processes can be combined with additive deposition processes in a targeted manner. In the case of semiconductor workpieces, the high-purity coatings required for the process (i.e., coatings with particularly high purity) are conventionally applied to the surface at high temperatures.

[0020] The targeted use of low-temperature coating processes (preferably at temperatures below 150°C) allows for the application of high-purity coatings even to surfaces with poor thermal stability, such as those of 3D-printed parts (e.g., vacuum grippers), thereby combining advantages such as freeformability, targeted positioning of suction openings, and chemical and physical properties. For example, according to ISO 75-1 / -2, the material PA3200GF has a heat distortion temperature of up to 157°C (at a pressure of 0.45 MPa and in the X direction). A comparable situation applies to preferred substrates including polyamides (particularly those filled with glass beads). Above this temperature, the plastic profile typically collapses on its own. For example, PTFE coatings are typically molded and sintered in an oven at temperatures ranging from approximately 220°C to 420°C. Low-temperature sintering processes (which typically extend for a relatively long time, for example at 100°C) make it possible to achieve 3D-printed vacuum grippers for silicon wafers that are resistant to chemicals and dust.

[0021] The surface roughness of vacuum grippers produced using additive deposition processes can be reduced through cryogenic coatings—Rz and Ra values ​​(which specify roughness) are typically reduced by about 70% compared to corresponding values ​​for vacuum grippers without cryogenic coatings. This also helps liquid particles or other organic or inorganic components on the vacuum gripper adhere to the surface to a much smaller extent, and thus can be removed in a much easier and more targeted manner.

[0022] Vacuum grippers can be produced using additive manufacturing processes or 3D printing, achieving optimizations in all aspects compared to conventional manufacturing processes. Improved forming (i.e., the actual producible shape) allows for better-than-usable optimal shapes than conventional manufacturing processes, and, for example, more efficient suction openings (e.g., in the form of suction funnels) can be adapted to specific desired applications compared to conventionally manufactured vacuum grippers. Freeform forming allows for setting the required holding force created by vacuum or negative pressure in a particularly precise manner. With this application-optimized and variable forming, the area to be evacuated (channel) can be kept as small as possible, which helps the holding force accumulate and decrease more quickly, and thus, for example, accelerates the transfer of semiconductor workpieces.

[0023] In contrast to conventional manufacturing processes limited by the use of machining tools (which can only create holes of limited length, such as thin and deep ones), additive manufacturing processes allow for the direct production of vacuum reservoirs, for example, within a vacuum holder (e.g., as a result of a relatively large local cross-section of the channels within the vacuum holder). Therefore, this vacuum holder is less sensitive to temporary vacuum leaks, and the risk of damage to the semiconductor workpiece is reduced if the holding force decreases during surface processing. Compared to conventional manufacturing processes, the personalized (unique) design and arrangement of the suction openings and channels allow for the targeted setting of the holding force for the semiconductor workpiece, for example, setting a higher holding force in the peripheral region during processing compared to other areas (this involves specific force application at the workpiece edges).

[0024] Additive manufacturing processes allow for the targeted selection of the number of suction openings and channels based on the area of ​​the vacuum gripper, thereby increasing the number of suction openings and channels in the peripheral area compared to conventionally manufactured vacuum grippers. In this way, media (such as polishing agents) that are sucked up during the processing of semiconductor workpieces can be extracted more quickly through suction. Peripheral corrosion is thus avoided.

[0025] Compared to conventional manufacturing processes, the proposed method also enables the formation of suction openings in the peripheral region that can be designed in a targeted manner and adapted to the corresponding processing techniques of semiconductor workpieces. In the case of processes used to process the edges of semiconductor workpieces (e.g., edge polishing), process media typically also enter the region between the vacuum holder and the semiconductor workpiece due to the forces acting on the edges. The suction openings, designed as annular channels on the top side of the vacuum holder, allow for the rapid removal, for example, of the already infiltrated media, thus avoiding undesirable chemical or physical reactions of the media on the surface of the semiconductor workpiece.

[0026] Compared to conventional manufacturing processes for vacuum grippers, the use of additive manufacturing processes allows for the direct integration or subsequent attachment of, for example, even flexible seals (as mentioned above). For instance, 3D-printed sealing elements can (compared to conventional seals) precisely adapt to the processing techniques used on semiconductor workpieces, thereby preventing process media, for example, from seeping into the edge region between the support area and the semiconductor workpiece during edge polishing processes. The use of vacuum grippers manufactured using additive manufacturing processes and featuring integrated or separate seals (however, these are also manufactured using additive manufacturing processes) allows for more versatile and faster adaptation of seals to varying processing techniques for semiconductor workpieces compared to conventional manufacturing processes.

[0027] In contrast to conventional manufacturing processes, targeted manufacturing using additive deposition processes allows for the creation of suction openings with any desired shape. Therefore, by utilizing suction openings and support areas formed in any desired manner on the semiconductor workpiece, such as by using curved (radius) edges instead of milled edges, sharp edge transitions can be avoided. In the case of conventionally manufactured vacuum chucks, sharp edge transitions are a significant cause of markings, scratches, or other damage to the surface of the semiconductor workpiece. As a result of evacuation, the surface is pressed against the support area, and sharp edge transitions leave marks (i.e., so-called "chuck marks") on the semiconductor workpiece or wafer due to the high holding forces (which are necessary, for example, when the edges are polished).

[0028] Compared to vacuum grippers manufactured using conventional methods (e.g., machining processes), additive manufacturing processes can achieve, for example, optimized channels or channel guides and suction openings. This helps maintain sufficient holding force between the vacuum gripper and the semiconductor workpiece in the event of time-limited vacuum leaks, such as those caused by polishing forces and lifting of the semiconductor workpiece edges. Furthermore, the variable arrangement of active holding elements (i.e., suction openings) on the top side or holding area of ​​the vacuum gripper enables a (as uniform as possible) distribution of forces acting during the process. Therefore, with constant system power, the load on the substrate is kept low, and the risk of semiconductor workpiece breakage (wafer fracture) is significantly reduced.

[0029] As mentioned earlier, providing a material layer with a lower hardness than the substrate eliminates the need for a so-called "chuck pad." Even if this layer is not provided and / or a "chuck pad" is intended to be used, its production can still be simplified. This is because, in the case of a "chuck pad" used in a conventional vacuum gripper, a ring-shaped cut is typically required to expose the suction opening within the vacuum gripper. The significantly more versatile design of the suction opening in a vacuum gripper produced using additive deposition processes allows for a correspondingly simpler cut in the "chuck pad," such as a circular cut. Furthermore, it is conceivable to produce the "chuck pad" itself using additive deposition processes.

[0030] Additive manufacturing, or 3D printing, allows for freedom—especially compared to casting or machining processes used to date—in terms of the number of items (projects), optimized material usage, and lower tooling costs. Therefore, the production cost of vacuum grippers is significantly lower than that of conventional manufacturing processes. For example, modifications to the underlying 3D CAD data used to control 3D printing are sufficient to produce or print the modified design of the vacuum gripper without requiring additional tooling instances (such as casting models and specific milling heads) as in conventional manufacturing processes.

[0031] As mentioned earlier, additive manufacturing processes or 3D printing allow for freeform shaping, and therefore, for example, also allow for targeted mass distribution of materials or substrates used for the purpose of avoiding vibrations (which might otherwise be caused by, for example, imbalances). For example, by using honeycomb structures, mass-reduced struts instead of solid materials, and applications-optimized designs generated by FEM (“finite element method”), reduced material usage can be achieved while maintaining mechanical stiffness. Furthermore, the use of fillers (fillers) for targeted settings of mechanical properties can be considered. In this case, for example, a fiber share (such as carbon fiber, glass fiber, or ceramic fiber) can be preferably used for targeted stiffness settings, which can vary even within the vacuum holder in the case of additive manufacturing processes. In this way, the vacuum holder can be designed to be more wear-resistant, for example, at mechanical fastening points than at the periphery.

[0032] As mentioned earlier, additives can be used for targeted adjustments to the material hardness, which can also be variably set in the case of additive manufacturing processes. Thus, for example, certain areas of a vacuum clamp can be produced in a flexible or flexible manner (e.g., produced as a seal), while other areas can be produced, for example, to be more robust and rigid.

[0033] In contrast to conventional manufacturing processes, additive manufacturing or 3D printing allows different materials to be combined without the need for bonding techniques, thereby achieving the desired properties for the specific application. This preferably enables the achievement of mechanisms of action that would otherwise require additional actuators in conventionally manufactured vacuum grippers, through material bonding. For example, in the case of 3D printing, the peripheral area of ​​the vacuum gripper can be produced from a resilient and springy material that provides better support to the peripheral area when the edges are polished.

[0034] Furthermore, application-specific smoothing (treatment) of specific areas (such as, for example, the surface of a vacuum gripper) is preferably achieved through a specific polishing process (particularly by means of ultrasonic waves and polishing additives) that conveniently reduces the surface roughness of all surfaces of the vacuum gripper, and even the internal channels. This results in reduced adhesion of media (e.g., polishing agents) to the surface, thereby preventing damage to the semiconductor workpiece.

[0035] The present invention also relates to a vacuum holder for semiconductor workpieces, said vacuum holder being manufactured by means of an additive deposition process, particularly from a substrate in a predetermined shape or according to a predetermined form. In this respect, the vacuum holder conveniently has at least a generally flat area thereon on which a semiconductor workpiece can be arranged, one or more suction openings, and one or more channels connected thereto. In this case, such a vacuum holder is preferably manufactured by means of the method according to the invention. For further preferred embodiments and advantages, to avoid repetition, reference should be made to the above description relating to the method, which applies accordingly herein.

[0036] Further advantages and embodiments of the present invention will become apparent from the description and drawings.

[0037] It is understood that, without departing from the scope of the invention, the features pointed out above and those explained below may be used not only in the specific combinations indicated, but also in other combinations, or individually.

[0038] The present invention is schematically illustrated in the accompanying drawings by way of exemplary embodiments, and is described below with reference to the accompanying drawings. Attached Figure Description

[0039] Figure 1 A schematic diagram of the procedure (flow) of the method according to the present invention in a preferred embodiment is shown.

[0040] Figure 2 A schematic diagram of a vacuum clamp according to the present invention in a preferred embodiment is shown.

[0041] Figure 3 Shown in sectional view Figure 2 Vacuum clamp in the middle.

[0042] Figure 4 It shows Figure 3 The magnified details.

[0043] Figure 5 A schematic diagram of a vacuum clamp according to the invention in another preferred embodiment is shown.

[0044] Figure 6 A schematic diagram of a vacuum clamp according to the invention in another preferred embodiment is shown.

[0045] Figure 7 Shown in different views Figure 6 Vacuum clamp in the middle.

[0046] Figure 8 It shows Figure 7 Different views of the vacuum clamp shown. Detailed Implementation

[0047] Figure 1 A schematic diagram of the procedure of the method according to the invention in a preferred embodiment is illustrated. For this purpose, image (a) first illustrates, in a rough schematic diagram, an apparatus 150 for the additive deposition process, such as a 3D printer having a print head 155 to which a substrate 160 is supplied. Optionally, an additive 161 and / or another material (which in this case is used particularly separately from the substrate) may also be supplied to the print head 155. The print head 155 then first applies a first layer 101 of the vacuum holder to be produced onto the carrier 151.

[0048] In the further progress of the procedure, further layers are applied, in particular by applying a new layer on top of a previous layer. For example, image (b) shows a further layer 102 that is applied to layer 101, while image (c) shows a further layer 103 that is applied to layer 102.

[0049] In this manner, the vacuum gripper 100 is produced from a substrate in a desired or predetermined shape (form) by means of an additive deposition process, as shown in a rough schematic diagram in Figure (d). For a more detailed view, please refer to the following figures. Also as shown in Figure (d), a coating material 180 is applied, for example, to the top side of the vacuum gripper 100 by means of an application tool 175, wherein the coating material 180 is supplied from the tank 170 to the application tool 175.

[0050] Then, as shown in image (e), the vacuum holder 100 coated in this manner is dried (particularly sintered) for a predetermined period of time, for example, in an oven 190 at a predetermined temperature range (e.g., at 150°C) below the heat distortion (deformation) temperature of the substrate 160. This produces a finished coated vacuum holder that is also chemically resistant.

[0051] Figure 2 A schematic diagram of a vacuum clamp 100 according to the invention in a preferred embodiment is shown, which can be, for example, by means of... Figure 1 The method described herein is shown and used for production. Figure 2 A perspective view of the top side of the vacuum gripper 100 is shown. Figure 3 A matching sectional view is shown. Figure 3 The axis of symmetry A shown passes through Figure 2 The central opening extends in the view. Figure 2 and Figure 3 This will be described in full below.

[0052] The vacuum gripper 100 has a circular shape (relative to the axis of symmetry A), and its top side has a (at least substantially) flat region 110 or is designed to be such a flat region. During use of the vacuum gripper 100, semiconductor workpieces (such as, for example, wafers) are placed indirectly or directly on this flat region 110. In this respect, reference should also be made to... Figure 5 .

[0053] Multiple suction openings 120 are introduced on the top side of the vacuum gripper 100. Figure 2 As can be seen, these suction openings 120 are (particularly uniformly) distributed on the top side or within the flat area 110. Figure 3 The configuration within the vacuum holder is shown. Starting from the top side, the suction openings 120 narrow in an approximately conical shape toward the interior of the vacuum holder 100, then open into the channel 130. Each of the suction openings 120 can be attached to the channel 130, and in particular, the suction openings located on a radial line are attached to the common channel 130. In this respect, reference should also be made to 7.

[0054] Channel 130 and all further channels open at the center or along the axis of symmetry A into an opening 135 located opposite the top side or flat region 110. There (in opening 135), suitable equipment can then be placed to generate a negative pressure or vacuum that propagates through channel 130 to (and as far as) the suction opening 120. In this way, a negative pressure or vacuum can be created at suction opening 120, resulting in the wafer abutting against flat region 110 being sucked onto flat region 110 or vacuum holder 100 and thus held in place.

[0055] Figure 4 It shows Figure 3 Enlarged details of the vacuum gripper 100 in the figure. Based on the example of the suction opening 120 located on the far right, i.e., the radially outermost part, in this figure, a transition portion 122 is shown where the suction opening 120 transitions to the flat region 110. It can be seen here that the transition portion is not a sharp edge (which would be a sharp edge in conventionally manufactured vacuum grippers), but rather has a rounded (arc) design or is designed to be arc-shaped. These can be created particularly well, or simply by means of an additive deposition process, resulting in the fact that no damage is caused to the wafer resting thereon, or that damage to the wafer resting thereon can be at least significantly reduced.

[0056] Figure 5 A schematic diagram of a vacuum clamp 100' according to another preferred embodiment of the invention is shown. This vacuum clamp 100' substantially corresponds to the embodiment according to... Figure 2 , 3And 4 vacuum clamps 100. The view shown here corresponds to Figure 4 The view shown in the image.

[0057] As can be seen here, a seal 140 is introduced at the radially outer end of the vacuum gripper 100'. The seal may be particularly flexible and extends, for example, around the periphery of the vacuum gripper in one or more sections. The seal 140 may be produced, for example, by means of an additive manufacturing process; however, in this case, a different material is preferably used as the substrate.

[0058] Furthermore, a pad 155 (or so-called "chuck pad") on which a semiconductor workpiece 150 in the form of a wafer is placed is applied to or placed on the top side or flat area 110. Suction openings and suitable openings, such as in the pad 155 (one of which can be seen in the area of ​​the suction opening 120), allow the wafer 150 to be held together with the pad 155. It can also be seen that the wafer 150 contacts the seal 140, resulting in a seal, and thus the negative pressure can generate a greater effect.

[0059] Figure 6 The illustration shows a schematic diagram of a vacuum clamp 100” according to another preferred embodiment of the invention. The vacuum clamp 100” substantially corresponds to, for example, in Figure 5 The vacuum chuck 100' shown in the diagram, however, has a layer 105 formed on the side of the vacuum chuck facing the wafer 150 and serving as a "chuck pad". Therefore, a separate "chuck pad" is not necessary.

[0060] Figure 7 Specifically with Figure 2 The view in the figure is a perspective view illustrating a schematic diagram of a vacuum clamp 100"' according to another preferred embodiment of the invention. In this respect, the vacuum clamp 100"' substantially corresponds to the view according to the invention. Figure 2 , 3 And the vacuum clamp 100 of 4, however—as can be compared Figure 2 As can be seen, more suction openings 120 are provided. This indicates that the suction openings 120 can be provided as needed so that, for example, the contact pressure created by the negative pressure at the suction openings can be distributed as evenly as possible across the wafer or its surface area.

[0061] Figure 8 In different views, specifically perpendicular to the axis of symmetry (which is located as according to...) Figure 2 The cross-section at the location of the vacuum clamp is shown. Figure 7 The vacuum clamp 100”' is shown in the figure. Several channels 130 are illustrated by way of example, extending radially and coinciding at the center in a star-shaped manner. For example, in… Figure 7 As seen in the image, each of the suction openings can be connected via these channels 130.

Claims

1. A method for producing an apparatus (100, 100', 100'', 100''') suitable for holding semiconductor workpieces by means of vacuum, wherein the apparatus (100) is formed from at least one substrate (160) by means of 3D printing. The device (100, 100', 100'', 100''') is designed to have a generally flat area (110), one or more suction openings (120), and one or more channels (130) connected thereto, wherein a semiconductor workpiece (150) can be arranged on the generally flat area (110), and The device (100', 100'') is designed to have one or more seals (140) that are capable of contacting a semiconductor workpiece (150) to be disposed on the device, and The device (100, 100', 100', 100'''') is designed such that it includes a reinforcing structure, and The device (100''') is designed such that a material layer (105) with a lower hardness than the substrate (160) is formed on the side facing the semiconductor workpiece (150).

2. The method according to claim 1, wherein, The one or more seals (140) are flexible seals.

3. The method according to claim 1, wherein, The reinforcing structure is formed from the substrate (160).

4. The method according to claim 1, wherein, The predetermined areas of the device (100, 100', 100'', 100''') are created by means of 3D printing from a material different from the substrate (160).

5. The method according to claim 1, wherein, The coating material (180) is applied by means of a low-temperature coating process.

6. The method according to claim 5, wherein, The coating material (180) is applied by means of a low-temperature sintering process.

7. The method according to claim 5, wherein, The coating material (180) is applied at a temperature below 150°C.

8. The method according to any one of the preceding claims, wherein, The device (100, 100', 100'', 100''') is smoothed at least in a predetermined area.

9. The method according to claim 8, wherein, The device (100, 100', 100'', 100''') is smoothed using ultrasound and abrasive additives at least in a predetermined area.

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