Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
  • H01L21/67005—Apparatus not specifically provided for elsewhere
  • H01L21/67011—Apparatus for manufacture or treatment
  • H01L21/67017—Apparatus for fluid treatment
  • H01L21/67063—Apparatus for fluid treatment for etching
  • H01L21/67075—Apparatus for fluid treatment for etching for wet etching
  • H01L21/67086—Apparatus for fluid treatment for etching for wet etching with the semiconductor substrates being dipped in baths or vessels
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
  • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
  • H01L21/3105—After-treatment
  • H01L21/311—Etching the insulating layers by chemical or physical means
  • H01L21/31105—Etching inorganic layers
  • H01L21/31111—Etching inorganic layers by chemical means

Definitions

• the present invention relates to a method for exclusively single-sided wet-chemical removal of passivating and / or dielectric oxide layers present on flat substrates, in particular silicon wafers, by etching the lower side of a substrate transported horizontally through a container filled with an etching liquid. Using this method, no protection of the non-treated substrate side in the form of a coating or mechanical aids is required.
• the slices obtained are prepared after sawing one or both sides, such as. textured, polished, or saw-etched, followed by further, usually one-sided, manufacturing steps. It may be necessary to remove passivation layers formed during a process step, such as, in particular, oxide layers on one side from the substrate, ie to reduce their thickness or to remove them entirely on one side.
• passivation layers formed during a process step such as, in particular, oxide layers on one side from the substrate, ie to reduce their thickness or to remove them entirely on one side.
• silicon dioxide for example, the following processes and etching media known from the prior art are used:
• Hexafluoroethane (C 2 F 6 ), octafluoropropane (C3F 8 ) and / or sulfur hexafluoride (SF 6 );
• DRIE Deep Reactive Ion Etching
• CMP Chemical-mechanical polishing
• KOH potassium hydroxide
• Document DE 10313127 A1 discloses a method according to which the substrates to be treated on one side are transported along the surface of a treatment liquid such that only the substrate underside to be treated comes into contact with the treatment liquid.
• the document WO 2005/093788 shows that in addition to this "active (direct) wetting" procedure also a distance between the surface of the treatment medium and the underside of the substrates may be provided, wherein the treatment liquid by means of corresponding wheels to the Bottom of the substrates is brought (“passive (indirect) wetting").
• the substrate edges can be included in the process or excluded from it.
• the guide discs also serve as a bridge on which undesirably treatment fluid can reach the top of the substrates. Since the flow velocity also decreases with decreasing distance to the substrate surface and practically becomes zero directly at the substrate surface, in this region the exchange of treatment liquid and reaction products can only take place by slow diffusion and not by rapid flow exchange. Thus, a diffusion layer of reaction products is formed on the underside of the substrate with increasing duration of treatment, which hinders the progress of the process.
• Unwanted bubbles may also have been introduced into the treatment liquid other than by chemical reaction, for example, by entry by means of circulating pumps or the like. In this respect, such sources of gas bubbles are included below.
• the known in the prior art etching liquids also have the disadvantage of unfavorable creep, whereby the known liquids with relatively low viscosity tend to creep up at the edges of the substrate and thereby not only the edges, but also the upper non-treated substrate side disadvantageous and unwanted to wet.
• This negative creep behavior proves to be disadvantageous not only for flat substrates with so-called blind or through-holes, but also for substrates with structured structures.
• the object of the invention is therefore to provide an etching process with which the disadvantages of the prior art are overcome.
• the invention is intended to serve to unilaterally ablate passivating and / or dielectric oxide layers, especially on monocrystalline and multicrystalline silicon or Galliumarsenidsubstraten without the surface of the non-treated side is attacked, and without the need for additional protection or masking of the same is required ,
• the object is achieved by the method according to the skin claim.
• Advantageous embodiments are given in the subclaims and in the following detailed description.
• the method according to the invention serves for the one-sided wet-chemical removal of passivation layers on substrates such as in particular silicon wafers using an etching liquid. It should be noted that the method is also suitable for the removal of dielectrics such as silicon nitride and / or silicon dioxide layers. For reasons of clarity, however, only "passivation layers" will be discussed below.
• the etching liquid contains water, hydrofluoric acid and at least one further component selected from the group consisting of sulfuric and phosphoric acids and their alkali, ammonium and organoammonium hydrogen salts and salts, hexafluorosilicic acid and silicon tetrafluoride.
• the selection and use of the further component is provided according to the invention in order to increase the viscosity of the etching liquid or to influence its creep behavior on the substrate surface.
• the etching liquid are added to it in its detachable, non-reacting mineral and / or organic substances. It is also envisaged to accelerate the chemical reaction by means of appropriate additives. It is not always a separation of the two functionalities "increase in viscosity" and “acceleration The chemical reaction "possible, which is why such additives are preferred, which combine both functionalities in itself.
• the etching liquid contains as further component sulfuric acid, phosphoric acid, ammonium sulfate, ammonium phosphate, ammonium fluoride, silicon tetrafluoride and / or hexafluorosilicic acid and is preferably maintained at a temperature between 15 and 30 ° C during the treatment.
• the concentration of hydrofluoric acid (HF) is increased, but this leads to an undesirable creep of the etching medium due to its low viscosity.
• H 2 S0 4 as an additive to the etching liquid can - at similar high removal rates as in highly concentrated HF - the concentration of HF can be kept low in an advantageous manner, which is why the etching liquid depending on the completely or partially ablated oxide layer between 0.3 and 10% by weight, in a preferred embodiment, 1 to 4% by weight of hydrofluoric acid. This results in a high viscosity of the etching medium due to the low HF concentration, so that the unwanted creep is avoided.
• the etching liquid contains 50 to 70 wt.% Sulfuric acid.
• the substrates are transported horizontally along the surface of the etching liquid such that the substrate undersides are contacted with the etching liquid.
• etching medium creeps up on the peripheral edges of the substrate and subsequently on its prevents top to be treated. Thus, can be dispensed with a separate protection of the top.
• the substrates are first brought into contact with the etching liquid.
• any transport devices can be used for this purpose.
• roller conveyors are particularly suitable, as disclosed, for example, in document WO 2005/093788.
• the treatment liquid for example, as likewise in the document WO 2005 / 093788, is brought by means of appropriate wheels to the underside of the substrates.
• the substrates are transported along the surface of the etching liquid, which preferably also takes place with said roller conveyors.
• transport devices such as grippers are conceivable.
• the critical size of the gas bubbles is about 1 cm.
• other values may apply, depending on the composition of the treatment medium. Thus, this value depends among other things on the actual viscosity of the treatment medium and its surface tension.
• the transport of the substrates along the surface of the etching liquid is therefore preferably carried out using at least one transport roller whose lateral surface (3) has a thread structure (4) with at least one thread (5).
• the thread structure is provided on several, more preferably on all transport rollers of the transport system used.
• the at least one thread preferably has a pitch angle of less than 80 °, as will be explained in more detail below.
• Thread structure means that the shell surface of the roll has one or more spiral protrusions or depressions similar to a screw
• a thread structure may have one or more "threads”.
• the thread structure carries gas bubbles that have accumulated at any location on the underside of the substrate, in the direction of the lateral edge regions of the objects. The reason for this lies in the fact that the gas bubbles always rise due to their low density in the treatment liquid.
• the underside of the substrate forms a barrier, whereby the perpendicular degree of freedom is blocked to move a gas bubble. Further degrees of freedom now run exclusively parallel to the substrate underside. The degree of freedom in the direction of the lateral edge regions block the flanks of the thread.
• the bubbles are also denied the last remaining degree of freedom, which is parallel to the transport direction.
• the bubbles would otherwise have to sink due to the shape of the thread. However, this is also excluded due to their lower compared to the treatment medium density without external effects.
• gas bubbles can only be in the cavity of the thread and at the same time directly on the underside of the substrate. Due to the progressive unwinding of the thread during substrate transport, these possible locations and thus the bubbles trapped in them move in the direction of the lateral edge areas of the substrates, where they finally rise as soon as the vertical degree of freedom is released when leaving the substrate area.
• the advantage of discharging the gaseous reaction products in the direction of the lateral edge regions of the substrates is that the bubbles are no longer pushed along in the area of the migrating contact surface to the (threadless) roll on the substrate bottom. There, they continuously increase until they reach the rear substrate edge, where they then rise and collapse at the same time, which in particular can also lead to undesired wetting of the upper side of the following substrate. Instead, the bubbles are promptly discharged to their formation in areas that are not behind, but (as seen in the transport direction) from the side of the substrate. Since the removal is continuous, the bubbles also continuously emerge on the sides of the substrates. Because the Residence time of the bubbles is shortened below the substrate, the risk of accumulation and thus growth of the initially very small bubbles is reduced. Below a critical size of the then bursting bubbles but no risk of wetting the substrate top more.
• the invention provides also that at least one thread preferably has a slope angle "of less than 80 °.
• the angle of inclination is the angle between Gewindegang- wall and the circumferential surface of the cylinder force that is the roll, in a plan view
• the pitch angle in a plan view is the angle between the axis of the feed roller and the direction in which the flanks of the thread are pointing. The further it moves into the area around 45 degrees or below (steep, coarse thread) .A small angle thus also leads to a faster lateral discharge of the bubbles.
• the pitch angle should be selected so that a gas bubbles still safely led to the side can be and not due to a too large pitch angle of (for Side directed) discharge speed can no longer follow.
• a too small pitch angle may thus be a crossing of the gas bubbles over the thread limiting flank into an upstream or downstream region of the same thread turn.
• the pitch angle should be chosen so large that a gas bubbles in the context of the complete transport of a substrate over a certain role actually up to beyond the lateral edge of the substrate is also promoted. If the pitch angle chosen too large, the lateral discharge is too slow. The gas bubbles are not exiting the substrate from the roll the lateral edge, but in the area of the trailing edge.
• the pitch angle is 20 ° -40 °. Experiments have shown that in this area a particularly good and safe removal of the gaseous reaction products is achieved. Particularly preferably, the pitch angle is about 30 °.
• a thread structure comprises a thread which is arranged to extend uniformly and in the same direction of rotation from one end of the roll to the other.
• the thread structure of the same lateral surface comprises two opposing threads.
• the directions of rotation of the two threads are chosen so that they point away from each other at a necessary for the transport of the substrates rotation of the respective role. Thought and inhibited in their rotation screws that are attached to these threads would thus also move away from each other.
• the boundary region of both threads is preferably arranged such that it divides the track on which the substrates are transported into two halves of approximately equal size ("tractor profile"), which results in bubbles forming in the region of the underside of the substrates are continuously conveyed from the center of the track to their sides, thus avoiding the above-described enlargement, and in each case evenly discharging the bubbles to both sides, so that the bubbles formed at the bottom are approximately
• a further advantage of this embodiment is that the respective travel distance of a given gas bubble to the substrate side is reduced.
• it can be provided, for example, that the height of the elevations above the bottom of the thread at the edge of the track is slightly greater than in the middle of the track in the direction of the edge and thus "out of the track
• a transport roller can have one or even several tracks running parallel to each other.
• the same variations of a concrete embodiment exist mutatis mutandis for each of the tracks.
• the distance of the tracks should be at least slightly greater than the width of the substrates to be transported.
• the distance between two substrates transported side by side is at least 1 cm.
• the spacing of the individual tracks from each other must be adapted to the largest substrate width.
• tracks of different widths can be provided side by side on a roll, so that substrates of different widths can be transported side by side. Each track is then provided for the transport always the same width substrates.
• the device comprises a plurality of transport rollers each having a threaded structure, wherein the thread structures of two consecutive roles in the transport direction are formed in opposite directions with respect to their direction of rotation.
• the direction of rotation of the thread or turns of successive transport rollers alternates.
• substrates of different widths can be transported both behind and next to each other in this way.
• This embodiment is therefore particularly suitable for substrates with standard geometries (round, square) and / or standard dimensions (eg 30 cm substrates, 11 inch wafers).
• it is also suitable for transporting and handling significantly larger objects, for example 90 cm ⁇ 120 cm glass substrates, such as those used for solar cell production.
• the at least one thread has a profile depth of at least 1 mm and / or at most 10 mm and a profile shape whose cross-section round, rectangular, triangular, or can be produced with a standard threading tool.
• the “profile shape” is the geometry of a thread turn that results when looking at a cut surface running through the roll axis.
• “Tread depth” refers to the distance between the unstructured surface of the roll and the deepest point of a thread turn. The tread depth should not be less than a minimum depth. At a lower than the minimum depth effective removal of the gas bubbles is no longer guaranteed. It is also provided that the maximum depth of the thread is 10 mm. Particularly preferred here is the range of 1.5 to 5 mm profile depth. Most preferred is a square profile with a depth and a clear width of 5 mm each. Alternatively, it is provided that either the width or the depth of the profile is less than 1 cm.
• Both the shape of the cross section and the profile depth preferably remain the same over the entire length of the thread.
• the cross-sectional profile can be produced with a standard threading tool.
• the flat objects are silicon substrates or glass sheets. According to the invention, however, other substrate materials such as ceramic, metal or plastic are conceivable.
• the method according to the invention therefore also makes possible, in one of its preferred embodiments, controlled lateral discharge of gaseous reaction products from the underside of flat objects which are transported horizontally in the context of a production line through a wet-chemical treatment container.
• the at least one thread of a transport roller has a tread depth of at least 1 mm and / or at most 10 mm and a profile shape whose cross section is round, rectangular, triangular, or can be produced with a standard threading tool.
• a chemical additive is added to the etching medium, which prevents gas formation.
• the substrates are transported rotated by approximately 45 degrees in the event that they are rectangular, so that not an edge but a tip of the substrate points in the transport direction.
• At least one transport roller is used for transport, and preferably a multiplicity of such rollers arranged one behind the other (roller conveyor) is used. It is particularly preferred that for the transport and removal of the bubbles and / or reaction products at least one designed as a full roll transport roller is provided.
• the etching process preferably takes place in a temperature range of 15-30 ° C.
• the process requires less energy than comparable processes, which start only at higher temperatures.
• temperatures below 15 ° C occurs on the non-treated side on a condensation of the etching medium, so that the surface of the substrate top is attacked.
• Temperatures of more than 30 ° C can lead to premature depletion of the etching medium.
• the undersides of the substrates are selectively supplied with etching liquid during transport.
• a water rinse is used to remove the etching liquid and to stop the reaction. 'This step is advantageous in order to determine a defined endpoint of the reaction, and also the entrainment of etching medium if necessary to avoid in subsequent liquid baths or other processes.
• deionized water is used for rinsing.
• other detergents can be used.
• ultrasound and / or egaschall acts on the substrates at least temporarily to assist the etching process.
• the action can be done preferably from below, but also from above and / or from the side.
• the etching medium is brought to the surface to be treated more effectively and the media exchange is improved. This results in an improvement of the treatment result or a shortening of the treatment time.
• the side of the substrates to be treated is at least temporarily irradiated with light. In certain cases, an increase in the removal rate can be achieved by supplying light energy.
• the light radiates at a wavelength which is in the range of the natural frequency of the molecular bonds of the passivation layer.
• the light source should preferably emit in the infrared range, and particularly preferably in the wavelength range around 5000 nm.
• both monochrome laser light and light with a continuous spectrum can be used.
• a chemical attack of the substrate top side is reduced by a venting device.
• This deaerator serves as a gas displacer which displaces the reaction gas liberated in the reaction from the region of the upper side of the substrates or sucks it from there.
• the etching process is stopped uniformly by a stripping process.
• a stripping process is particularly preferably proposed.
• such a step should, however, be provided preferably only if the passivation layer is not to be completely removed. Otherwise, the removal is sufficient by means of the above-described Di-rinsing process.
• the substrates are finally dried with a gas stream.
• "Final” means after the etching process and the possibly existing subsequent cleaning steps.
• This gas stream may be at room temperature or at an elevated temperature.
• the flow rate is so high that the liquid is not only dried, ie evaporated, but also stripped off. It should be ensured that stripped liquid droplets can not get back to already dried surface areas of the substrates.
• the method according to the invention can also be used for materials other than silicon using suitable etching liquids, the method always offering itself when etching liquids with comparatively low viscosity lead to undesired wetting and / or within the scope of a treatment those described above Problems (blistering, spraying, excessive fluid exchange, etc.) are present.
• Example The process was used to treat 125 and 156 mm 2 square monowafes.
• One group of seeds was polished on one side and on the other side had an alkaline induced texturing while another group of wafers were acid etched on both sides.
• the wafers each carried on the front and back of an oxide layer of 100 to 300 nm.
• equally dimensioned wafers were processed with through holes, said holes having a respective distance from each other of about 1 cm and a respective diameter of about 50 ⁇ had.
• the wafers were processed in an in-line system in such a way that the texturized or saw-damaged side was completely removed.
• the etching liquids used were mixtures of HF / H 2 SO 4 / H 2 O, HF / H 3 PO 4 / H 2 O, HF / NH 4 F / H 2 SO 4 / H 2 O, HF / NH 4 F / H 3 PO 4 / H 2 O, HF / NH 4 F / H 2 0 and HF / HCI / H2O used, wherein the mixtures of 50% HF solution, 95-97% H 2 S0 4 solution, 85% H 3 P0 4 solution, 40% NH 4 Solution, and 35% HCl solution were prepared.
• the etching machine had suitable board disc transport rollers and a basin with an active length of 1600 mm.
• the flow rate in the caustic was set at about 35 L / min, and the fill level was regulated via bypasses. At speeds below 21L / min, no oxide-free surface could be obtained.
• the gas displacer used was adjusted to a pressure drop of at least 0.3 KPascal, with a value of 0.5 KPascal proved to be particularly suitable.
• the 3 exhaust flaps on the etching basin were set to 45 ° each.
• An air scraper was installed in the outlet area of the etching basin, which minimized the carryover of etching solution into the dishwashers.
• the subsequent Di-dishwasher had a length of 620 mm. Downstream, followed by an air dryer and a discharge area.
• etch times needed to remove the oxide from the wafer's bottom were dependent on the thickness of the oxide and the nature of the wafer surface.
• Saw damage etched surfaces were faster oxide free than textured surfaces.
• Oxide thicknesses of 300 nm were completely removed in saw-damaged etched surfaces at a temperature of 16 ° C and a transport speed of 1.2 m / min; at layer thicknesses of 200 nm, the same result could be achieved with a transport speed of 1.5 m / min.
• 300 nm thick layers at 1.3 m / min and 200 nm thick layers at 1.0-1.3 m / min were removed.
• higher transport speeds of 1.5 m / min resulted in 300 nm Oxide thickness and from 1.8 m / min for 200 nm oxide thickness to no complete removal.
• Vias with contact holes and an oxide thickness of 210 to 230 nm on the textured side were successfully treated at 20 ° C, a transport speed of 0.85 m / min and a flow rate of 26 L / min, without the etching liquid passing through the holes pulled up.
• the invention preferably proposed at least
• FIG. 1A schematically shows a roll with a thread structure.
• FIG. 1B schematically shows the roller according to FIG. 1A at a later method time.
• Figure 2 shows a roll with several tracks.
• FIG. 3 shows a roller whose thread structure has two opposing threads.
• FIG. 4 shows a schematic representation of a roller 1 with a plurality of parallel threads 5, 5 'on a lateral surface 3 as a right-hand thread (FIG. 4A) and as
• FIG. 5 shows various diagrammatic cross sections
• Moldings for a thread namely a rectangular profile (Fig. 5A), a semi-circular profile (Fig. 5B), and a triangular profile (Fig. 5C).
• FIG. 1A schematically shows a roller 1 with a thread structure 4.
• the roller 1 is designed as a cylinder and has a base 2 and a lateral surface 3. Not shown are other features such as the axis on which the roller 1 is rotatably mounted, and possibly existing drive elements, etc ..
• the threaded structure 4 On the lateral surface 3 there is a threaded structure 4. The parts hidden by the roller 1 are shown as a dashed line.
• the threaded structure 4 has, according to FIG. 1, a continuous thread 5.
• the roller 1 rotates during conveyance of a substrate 6 (shown as a dotted line) in the direction of rotation 7.
• the transport direction 8 is formed. This has parallel to the base 2 of the roll 1.
• the thread 5 is not in the transport direction 8, but forms with the lateral surface 3 a pitch angle 9.
• the pitch angle 9 is approximately 70 °.
• a gas bubble 10 is trapped in the area between the underside of the substrate 6 and the lateral surface 3 of the roller 1. Due to its density, it tries to ascend, but strikes against the underside of the substrate 6. A lateral breaking is also not possible, since it can move only in the interior of the thread 5, which is provided as a notch or recess in the lateral surface 3 of the roller 1 ,
• FIG. 1B shows the situation from FIG. 1A after a few rotations of the roll 1 in the direction of rotation 7.
• the substrate 6 has moved further in the transport direction 8.
• the gas bubble 10, which is trapped in the thread 5 migrates in the direction of the lateral edge region 6 'of the substrate 6. Since further gas bubbles (not shown) also form continuously on the underside of the substrate 6 due to the continuous chemical reaction, there is thus a continuous discharge of the gas bubbles. Due to the barrier that form the flanks of the thread 5, multiple gas bubbles can not unite to one or more large gas bubbles.
• FIG. 2 shows two rollers 1, 1 'which are provided for transport on a plurality of (here two) tracks.
• a track is characterized by a respective thread 5 and 5 '.
• the rollers 1 and 1 'and the threads 5, 5' are dimensioned so that a plurality of substrates (not shown) can be transported side by side.
• the tracks are different in width.
• the pitch angle 9 of the threads 5, 5 ' are the same on both rollers 1 and 1' in magnitude. So that the substrates do not run off the track during continuous rotation of the rollers 1, 1 'due to the transport component pointing in the axial direction of the rollers, the pitch angles 9 of the two rollers 1 and 1' are formed in exactly opposite directions.
• the directions of rotation 7 of the rollers 1 and 1 ' are identical.
• the threads 5 and 5 'of two consecutive in the transport direction 8 rollers 1, 1' are formed in opposite directions with respect to their direction of rotation 11. In this way, although substrates are transported slightly out of the track by a first roller 1, the subsequent roller 1 'leads the substrates back into the track again.
• FIG. 3 shows a roller 1 with a thread structure 4 with two opposing threads 5, 5 '.
• the threads 5, 5 ' together form a track.
• the pitch angle 9 of the two threads 5, 5 ' are the same size, but have opposite signs.
• the roller 1 rotates in the direction of rotation 7.
• the directions of rotation 11, 11 ' which thus result, lead to imaginary and inhibited in their rotation screws that are attached to the threads 5 and 5', upon rotation of the roll from each other would move away.
• FIG. 4 shows a schematic representation of a roller 1 with several parallel threads 5, 5 ', 5 ", 5" on a lateral surface 3 as a right-hand thread (FIG. 4A) and as a left-hand thread (FIG. 4B).
• FIG. 4A right-hand thread
• FIG. 4B left-hand thread
• the lateral surface 3 at a constant pitch angle 9 a larger number of corresponding recesses, which serve to discharge the gas bubbles (not shown).
• FIG. 5 shows various profile shapes for a thread 5 on the basis of schematic cross sections.
• FIG. 5A shows a rectangular profile
• FIG. 5B shows a semicircular profile
• Fig. 5C shows a triangular profile.
• the value a represents in each case the profile depth
• the value b the profile width.

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• 2009
  • 2009-12-18 EP EP09799542A patent/EP2460176A1/de not_active Withdrawn
  • 2009-12-18 CN CN2009801630049A patent/CN102714132A/zh active Pending
  • 2009-12-18 WO PCT/EP2009/009138 patent/WO2011072706A1/de active Application Filing
• 2010
  • 2010-01-21 TW TW099101651A patent/TWI427693B/zh not_active IP Right Cessation

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