Methods for manufacturing III-V substrates, especially GaAs and InP

Abstract

The invention comprises a method for drying wafers W, W1, W2 immersed in a bath 1, and a device for drying undoped or doped wafers W, W1, W2 and wafers W, W1, W2 according to the invention. Here, care is taken to ensure that the travel distance of the wafers W, W1, and W2 is kept as short as possible, so that few residual droplets remain attached to the wafers W, W1, and W2, thereby ensuring that the wafers W, W1, and W2 exhibit as uniform an oxide surface as possible and reducing the number / area of ​​defect regions resulting from residual droplets remaining attached after Marangoni drying. Accordingly, when crossing the water surface, there is little or ideally no contact between the wafers W and the racks 3; 31, 32 / guiding devices 3a, 3a', 3b, 3b', 3c, 3c'. Additionally, when drying the wafers W (and ideally also the racks 3; 31, 32), continuous overflow can be maintained, i.e., the water level is preferably not lowered.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an improved surface of a III-V substrate, as well as to a method for producing the III-V substrate itself, of which the materials GaAs and InP are particularly relevant. [Background technology]

[0002] III-V substrates, especially gallium arsenide substrates and wafers, are used in a variety of applications and are becoming increasingly economically important. Examples include high-frequency amplifiers and switches, as well as light-emitting components such as semiconductor lasers and diodes. Transistors and diodes, in particular, are primarily fabricated from epitaxially grown monocrystalline compounds. Growth parameters may be specifically tailored to the crystal lattice. Lattice-matched epitaxy ensures high quality and low defect density. However, quality can depend not only on the conditions during epitaxy but also on the characteristics of the substrate itself, which often affect quality. Gallium arsenide, in particular, faces the problem of rapid oxide layer formation on the substrate surface, which can form with heterogeneous compositions (gallium oxide and arsenic oxide in various oxidation states) if proper surface preparation is not performed. The thermal properties of oxides of different compositions are, in part, very different. However, the subsequent epitaxy process must ensure that the oxide layer can be easily removed by heat treatment.

[0003] For example, EP 2629319 teaches that gallium arsenide, known in the state of the art, in particular gallium arsenide, has physical and chemical surface properties that are significantly different from those of other semiconductors such as silicon. Surface reactivity is a particular phenomenon here, since the surface of a gallium arsenide wafer contains gallium and arsenic atoms that exhibit different chemical properties (even in terms of reactivity): the surface layer can consist of gallium dioxide (Ga2O3), arsenic trioxide (As2O3), arsenic pentoxide (As2O5), and small amounts of elemental arsenic. When growing gallium arsenide, the surface must be prepared using the specific method disclosed in this document: by treating with an ammonia solution, hydrogen peroxide, and water, rinsing the wafer with deionized water, treating the wafer with an oxidizing agent, repeatedly rinsing the wafer with deionized water, treating the wafer with a diluted acid or alkaline solution, rinsing the wafer again with deionized water, and finally drying the wafer.

[0004] During gallium arsenide surface treatment, foreign particles adhere very easily, leading to an increase in defects and thus to disadvantages in the subsequent epitaxy process. Further state-of-the-art literature (Klaus Wolke et al., "Marangoni-wafer drying avoids disadvantages," Solid State Technology, August 1996) describes the Marangoni drying method for silicon wafers. It discloses that Marangoni drying is based on physical forces that move liquids away from the surface due to varying surface tensions, thereby establishing equilibrium. A small amount of water with low surface tension (containing absorbed isopropanol) migrates into the bulk liquid with normal surface tension. For example, an isopropanol-nitrogen atmosphere with lower surface tension may be used. In contrast, ordinary water has a higher surface tension. Water tends to form a positive meniscus when the solid crosses the gas-liquid interface, for example, when removing a wafer from the bath. The presence of water-soluble materials in the atmosphere, such as isopropanol, leads to an increased concentration of solvent in the meniscus compared to the rest of the bath. When the wafer is withdrawn from the bath, the water in the meniscus is drawn into the bulk liquid, resulting in a completely dry wafer surface without water droplets adhering to the wafer surface which can cause so-called water spots.

[0005] The Marangoni effect therefore arises from differences in interfacial tension: the fluid (in this case, water) then flows along the wafer in the direction of the higher tension, thus removing the water from the wafer and allowing it to dry without residue.

[0006] Marangoni drying of semiconductor wafers relies on the spatial separation of the wafer and the ultrapure water under the influence of a surface tension gradient in the interfacial layer of ultrapure water in contact with the wafer. Spatial separation is achieved by lifting the wafer out of a bath filled with ultrapure water in a wet processing unit for semiconductor wafers or by lowering the water level.

[0007] WO 2014 / 124980 discloses a method for producing a GaAs substrate and a gallium arsenide substrate produced thereby, which includes Marangoni drying. It has been found that specific surface cleaning steps (acid cleaning, alkaline cleaning, contact with an oxidizing agent) combined with Marangoni drying contribute to a significant improvement in oxide surface uniformity compared to methods that do not involve a drying method based on Marangoni drying following the cleaning step.

[0008] This allows the number of defects and the defect area on the wafer's surface to be significantly reduced compared to methods that do not involve Marangoni drying. Here, such areas are considered defect areas, and their measurement signal, obtained via Candela ellipsometry, is outside a specified threshold. This is a standard feature of the Candela ellipsometer and is output directly by the device.

[0009] Marangoni drying is particularly suitable for drying semiconductor wafers after wet chemical cleaning. Drying is preferably uniform across the entire surface, leaving little residue. Before drying begins, semiconductor wafers are typically positioned vertically on a process carrier, which is placed in a processing bath filled with ultrapure water. Often, this bath is the last bath of a so-called wet bench: a series of successively aligned baths filled with liquid, in which wafers are subjected to the chemical and rinsing steps required for cleaning. In the high-productivity semiconductor industry, process carriers carrying wafers are typically transferred from one bath to another by automated handling systems after the completion of each intended process time. Marangoni drying exists in various configurations. However, all Marangoni methods share a common basic principle: a liquid is added to the water surface, reducing the surface tension of the water inside the bath. Typically, this involves isopropyl alcohol (IPA).

[0010] The actual drying proceeds by a slow spatial separation between the wafer and the upper water layer, which exhibits reduced surface tension due to the presence of isopropanol. This spatial separation can be achieved in a variety of ways, such as by lifting the wafer out of the water, lowering the water level, or a combination of both. To achieve good drying, the relative removal speed of the wafer and the water level will be, for example, in the range of 1 mm / s.

[0011] During Marangoni drying, water droplets, so-called residual droplets, can inevitably adhere to the remaining contact points between the wafer and the clamping device when crossing the phase boundary, resulting in a chemically altered oxide layer that adversely affects the crystalline quality of epitaxial layers deposited on the wafer during device fabrication. Drying of the water in a delayed and uncontrolled manner can damage the wafer surface.

[0012] During the further processing of semiconductor wafers into electronic or optical devices, extremely surface-sensitive coating processes can be applied within the framework of so-called planar technology, in which thin semiconductor layers are deposited in monocrystalline form on the surface of the wafer. This process, called epitaxy, imposes extremely high quality requirements on the surface of the semiconductor wafer.

[0013] So-called III-V semiconductors, especially GaAs and InP, exhibit distinctive features over silicon wafers, such as altered surface tension, significantly increased surface reactivity, and a more complex chemical composition of the oxide layer. In addition, the preferred further processing of these wafers by monocrystalline coating with other III-V materials imposes higher requirements on the lateral uniformity of the composition of the oxide layer compared to silicon wafers.

[0014] Also, residual droplets may form more easily during Marangoni drying for III-V semiconductor wafers and may have a more negative impact on subsequent processes in device fabrication.

[0015] In the dry state, the surface of certain semiconductor wafers (especially GaAs and InP) is always covered by a thin amorphous oxide layer. This layer is typically in the 1-2 nanometer range (sometimes less than 1 nm for InP) and therefore consists of only a few atomic layers. During wet chemical cleaning and rinsing processes, the oxide layer undergoes complex transformations, resulting in its removal, rearrangement, or modification of its composition. The oxide layer formed on the wafer surface after the cleaning, rinsing, and drying processes has a passivating effect and is thermally removed from the wafer surface immediately prior to epitaxial coating in certain applications.

[0016] However, an ideal and laterally uniform composition of the oxide layer is a key requirement, so that the starting surface remaining after thermal desorption of the oxide layer allows for the best crystallographic coupling of the layers deposited across the surface for epitaxy, thereby facilitating ideal current flow in devices subsequently fabricated from these epitaxial layers.

[0017] Delayed and uncontrolled drying of residual water droplets after Marangoni drying can result in an oxide layer with an unfavorably altered composition, with partially crystalline regions within the corresponding area of ​​the wafer surface. In these disturbed areas of the wafer surface, incomplete desorption of the surface oxide can occur during desorption prior to the epitaxy process, resulting in roughening of the wafer surface. As a result, single-crystal growth of the functional layer is hindered, leading to the generation of crystalline defects such as dislocations, grain boundaries, and twin lamellae. This can ultimately disrupt current flow within devices fabricated from the epitaxially grown material, resulting in yield loss.

[0018] In principle, there are several different possibilities for drying the wafer after surface treatment and for withdrawing the wafer from the bath for Marangoni drying.

[0019] In one embodiment, a wafer or a group of wafers is held in a water bath by a rack (a holding mechanism with rods). In this first embodiment, the rinse water (usually after a cleaning step using deionized water) is drained, but as shown in this disclosure, it has been found that residual droplets frequently form at the contact points of one or more wafers, where they become fixed to the rack and prevent uniform drying. This leads to a localized reduction in the quality of the oxide layer on the surface of the wafer, resulting in an uneven surface oxide layer and a reduction in the quality of the subsequently grown epitaxial layer.

[0020] In a second embodiment, the wafer is lifted from the water bath by a wedge that pushes vertically upward, and the wafer is temporarily held by the wedge and a wafer holder located, for example, inside the dryer lid. As shown in this disclosure, this embodiment has been found to prevent residual droplets at multiple contact points. However, droplets typically remain around the wedge as it passes through the water surface. Furthermore, the fixed wafer holder mechanism inside the dryer lid limits drying to a specific wafer diameter.

[0021] A further method for lifting a wafer or group of wafers from a cleaning bath is disclosed in WO 2001 / 078112, in which there are two opposing gripping elements with receiving slots facing each other, said gripping arms being able to grip the wafers as they are lifted out of the water surface by the wedge.

[0022] Furthermore, WO 2001 / 078112 discloses a method for drying a substrate by the Marangoni effect, in which at least one additional fluid is directed laterally onto the substrate and the processing fluid and towards the region between the substrates while the substrate is being lifted.

[0023] Furthermore, German Patent No. 10359320 teaches a method for drying a substrate, in which the substrate is lifted from a tank containing a processing fluid, and a fluid that reduces the surface tension of the processing liquid is applied to the processing liquid through at least two opposing supply devices facing each other, and the supply of the fluid that reduces the surface tension of the processing liquid is controlled so that the opposing supply devices alternately supply the fluid.

[0024] The methods known from the prior art are often complex in terms of equipment and are still associated with, or even intentionally accept, the drawback of leaving residual droplets when the wafer is lifted out of the processing fluid, which leads to the formation of "spots" on the wafer and thus hinders the subsequent epitaxial growth of a thicker crystalline layer. In this disclosure, "spots" refers to surface defects that arise from residual droplets attached to the wafer and can be detected by Candela surface ellipsometry.

[0025] For example, the "spots" affect the composition of the chemically altered surface oxide layer at the wafer surface compared to areas where no such "spots" are present.

[0026] It is therefore an object of the present invention to provide a method that is not complex in terms of equipment and is easily implementable, that is capable of drying wafers of various sizes, and that minimizes or possibly completely prevents the formation of residual droplets during wafer lift.An additional object of the present invention can be to provide III-V wafers with a highly uniform oxide surface. [Prior art documents] [Patent documents]

[0027] [Patent Document 1] European Patent No. 2629319 [Patent Document 2] International Publication No. 2014 / 124980 [Patent Document 3] International Publication No. 2001 / 078112 [Patent Document 4] International Publication No. 2001 / 078112 [Patent Document 5] German Patent No. 10359320 [Non-patent literature]

[0028] [Non-Patent Document 1] Klaus Wolke et al.,"Marangoni-wafer drying avoids disadvantages",Solid State Technology,August 1996 Summary of the Invention [Problem to be solved by the invention]

[0029] The object is solved by a method according to claim 1, a III-V wafer according to claim 14 or 16, and a device for drying a wafer according to claim 18. Further advantageous embodiments of the invention are the subject of the corresponding dependent claims. [Means for solving the problem]

[0030] Ellipsometry-based surface mapping was performed using a Candela ellipsometer and used to characterize the surface properties of the corresponding wafers. Details of the corresponding measurements are provided in the description and examples where appropriate.

[0031] Without limiting the invention, the following items are provided to illustrate key aspects, preferred embodiments, and special features of the present invention:

[0032] 1. A method for drying a wafer (W) located inside a tank (1) by using a mechanism including at least one wedge (2) and a pair of first lateral guide devices (3a, 3a'), a pair of second lateral guide devices (3b, 3b') and a pair of third lateral guide devices (3c, 3c'), a pair of first lateral guiding devices (3a, 3a') are arranged below a pair of second lateral guiding devices (3b, 3b'), and a pair of second lateral guiding devices (3b, 3b') are arranged below a pair of third lateral guiding devices (3c, 3c'); Follow these steps: i) moving at least one wedge (2) vertically upward until it reaches the lowest point of the wafer, and moving the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b') vertically upward, where the wafer (W) comes into contact with the pair of first lateral guiding devices (3a) and the pair of second lateral guiding devices (3b), and an upper region of the wafer (W) is lifted out of the bath (1), where the pair of third lateral guiding devices (3c) does not come into contact with the wafer; ii) moving the wedge (2) vertically upward until the pair of first lateral guide devices (3a, 3a') and the pair of second lateral guide devices (3b, 3b') are no longer in contact with the wafer (W) while still below the liquid level in the bath (1), and then the pair of third lateral guide devices (3c, 3c') are in contact with the wafer above the liquid level in the bath (1); iii) raising the wafer (W) above the liquid level of the tank (1) where the pair of third lateral guiding devices (3c, 3c') come into contact with the wafer (W).

[0033] In the embodiment, the distance between the pair of first lateral guidance devices (3a, 3a') is shorter than the distance between the pair of second lateral guidance devices (3b, 3b'), and the distance between the pair of second lateral guidance devices (3b, 3b') is shorter than the distance between the pair of third lateral guidance devices (3c, 3c').

[0034] 2.iv) moving the wedge (2) vertically downward until the wafer (W) contacts at least one of the pair of first lateral guiding device (3a) and second lateral guiding device (3b); v) further moving the wedge (2) vertically downward until it no longer contacts the wafer (W); further comprising Item 1. The method for drying a wafer (W) according to item 1, wherein, in parallel with step iv) and / or v), or after step v), the liquid level in the tank (1) is lowered until the liquid level is below the wedge (2).

[0035] 3. The method according to item 1 or 2, wherein the bath contains water and at least one additional surface tension-reducing substance.

[0036] 4. The method of claim 3, wherein the at least one additional surface tension-reducing substance is isopropanol.

[0037] 5. A method according to any one of items 2 to 4, wherein in step i), the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b') remain immersed in the bath (1), and at the end of step v), the pair of third lateral guiding devices (3c, 3c') preferably does not contact the wafers (W, W1, W2).

[0038] 6. A method according to any one of the preceding items, wherein the pair of first lateral guiding devices (3a, 3a'), the pair of second lateral guiding devices (3b, 3b') and / or the pair of third lateral guiding devices (3c, 3c') each comprise a pair of webs arranged to contact opposite sides of the wafer (W).

[0039] 7. A method according to any one of the preceding items, wherein the pair of first lateral guiding devices (3a, 3a'), the pair of second lateral guiding devices (3b, 3b') and the optional pair of third lateral guiding devices (3c, 3c') are further held by a carrier device (3d), and thus the vertical movements of the pair of first lateral guiding devices (3a, 3a'), the pair of second lateral guiding devices (3b, 3b') and the optional pair of third lateral guiding devices (3c, 3c') always occur synchronously.

[0040] 8. A method according to any one of the preceding items, wherein in step i), the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b') are kept immersed in the bath (1).

[0041] 9. The method according to any one of items 2 to 8, wherein at the end of steps iv) and v), the pair of third lateral guiding devices (3c, 3c') is not in contact with the wafer (W).

[0042] 10. A method according to any one of the preceding items, wherein step ii) further comprises clamping the wafer by an additional gripping device (4) mounted above the liquid level of the bath (1).

[0043] 11. The method according to any one of the preceding items, wherein the wedge (2) contains a suction device (6) that applies a vacuum when the upper end of the wedge (2) is located above the liquid level. 12. The method according to item 11, wherein the suction device (6) represents an opening in the wedge (2, 2a, 2b).

[0044] 13. The method according to any one of the preceding items, wherein the wedge (2) is made from plastic, preferably polyetheretherketone (PEEK).

[0045] 14. The method according to any one of the preceding items, wherein the wedge (2) exhibits a surface structure that increases the surface tension.

[0046] The structure can be achieved, for example, via plasma treatment.

[0047] 15. A method according to any one of the preceding items, wherein the pair of first lateral guiding devices (3a, 3a'), the pair of second lateral guiding devices (3b, 3b') and the pair of third lateral guiding devices (3c, 3c') exhibit notches.

[0048] 16. The lifting speed depends on the position of the lowest point of the wafer (W), 16. The method according to any one of items 1 to 15, wherein the moving speed is 0.8 to 1.2 mm / s when the lowest point of the wafer (W) is more than 1.2 cm below the liquid level, or 0.4 to 0.5 mm / s when the lowest point of the wafer (W) is less than 1.2 cm below the liquid level, and becomes at least 30 mm / s, preferably at least 40 mm / s, and more preferably at least 50 mm / s as soon as the lowest point of the wafer (W) reaches the liquid level.

[0049] 17. A pair of first lateral guiding devices (3a, 3a'), a pair of second lateral guiding devices (3b, 3b') and a pair of third lateral guiding devices (3c, 3c') are mounted on the rack (3); 17. The method according to any one of items 1 to 16, wherein in step i), the rack (3) is moved, and in step iii), the wafer (W) is pulled up above the liquid level of the tank (1), where the pair of third lateral guiding devices (3c, 3c') and the wedge (2) come into contact with the wafer (W).

[0050] 18. The method according to any one of items 1 to 16, wherein the pair of third lateral guiding devices (3c, 3c') is located above the liquid level in all process steps and is movable independently from the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b'), and the third lateral guiding devices (3c, 3c') are horizontally movable relative to each other.

[0051] 19. The method according to item 18, wherein the wedge (2) remains below the liquid level in all process steps.

[0052] 20. A method according to item 18 or 19, wherein in step iii) the distance between the points at which the third lateral guiding device (3c, 3c') contacts the wafer is continuously reduced.

[0053] 21. The method according to any one of items 18 to 20, wherein the third lateral guiding devices (3c, 3c') are adapted to perform horizontal movements relative to each other.

[0054] 22. The method according to any one of items 18 to 21, wherein the third lateral guidance device (3c, 3c') is mounted eccentrically or exhibits an oval shape and is designed to perform a rotational movement.

[0055] 23.Oxide surface is 25mm 2 A III-V wafer (W) exhibiting a defect area of ​​less than 1000 nm, said III-V wafer (W) being semi-insulating.

[0056] The term semi-insulating refers to many compounds (e.g., GaAs) whose Fermi level is near the center of the band gap. In GaAs, this can be ensured by the intrinsic point defect EL2 (arsenic antisite at the gallium site) in addition to doping with a certain amount of carbon (C). In InP, iron doping is necessary to achieve semi-insulating properties.

[0057] The following applies to the charge carrier concentration: 1 × 10 10 cm -3 At charge carrier concentrations below 1×10, the wafer is considered semi-insulating. 10 cm -3 A material is considered semiconductive at a charge carrier concentration above 0.05. The determination of charge carrier concentration is described in the standard SEMI M39.

[0058] According to the standard "SEMI M87", the resistivity of a semi-insulating wafer is 1 x 105 above Ωcm, while wafers with values ​​below this value can be considered semiconductive.

[0059] 24. The oxide surface is 15 mm 2 Less than 10 mm, preferably 2 Less than 5 mm, more preferably 2 24. A III-V wafer (W) according to item 23, exhibiting a defect area of ​​less than 100 nm.

[0060] 25. A 5 mm surface having an oxide layer over the entire surface and exhibiting an altered surface oxide composition compared to the remainder of the entire surface of the III-V wafer. 2 A semi-insulating III-V wafer (W) that is polished on at least one side and dried.

[0061] Here, measurements were performed by Candela surface ellipsometry using measurement channel QAbsPhase.

[0062] 26. A III-V wafer (W) according to item 23, 24 or 25, wherein the III element is selected from Ga and In and the V element is selected from As and P.

[0063] 27. A III-V wafer (W) according to item 26, wherein the III-V wafer is made of GaAs or InP, and GaAs and InP may be undoped or doped with carbon (C) and may be doped with iron (Fe), respectively.

[0064] 28. The resistivity is 1 x 10 8 Ωcm~8×10 8 28. The III-V wafer (W) according to any one of items 23 to 27, having a resistivity of Ωcm.

[0065] 29.Oxide surface is 25mm 2 A III-V wafer (W) exhibiting a defect area of ​​less than 1000 nm, said III-V wafer (W) being semi-conductive.

[0066] Here, measurements were performed by Candela surface ellipsometry using measurement channel QAbsPhase.

[0067] The following applies to the charge carrier concentration: 1 × 10 10 cm -3 At charge carrier concentrations below 1×10, the wafer is considered semi-insulating. 10 cm -3 A material is considered semiconductive at a charge carrier concentration above 0.05. The determination of charge carrier concentration is described in the standard SEMI M39.

[0068] 30. A III-V wafer (W) according to item 29, wherein the III-V wafer (W) contains silicon or sulfur as a dopant.

[0069] 31. The III-V wafer (W) according to item 30, wherein the III-V wafer is a GaAs wafer and contains silicon as a dopant.

[0070] 32. A III-V wafer (W) according to item 30, wherein the III-V wafer is an InP wafer and contains sulfur as a dopant.

[0071] 33. A 25 mm surface having an oxide layer over the entire surface and exhibiting an altered surface oxide composition compared to the remainder of the entire surface of the III-V wafer. 2 A semi-insulating III-V wafer (W) that is polished on at least one side and dried.

[0072] Again, measurements were performed by Candela surface ellipsometry using measurement channel QAbsPhase.

[0073] 34. The charge carrier concentration is 1 x 10 18 cm -3 ~9×10 18 cm -3 34. The III-V wafer (W) according to any one of Items 29 to 33.

[0074] 35. The oxide surface is 20 mm 2 Less than 15mm, preferably 2 Less than 10 mm, preferably 2 less than, and even more preferably 5 mm 2 35. An InP wafer (W) according to any one of items 29 to 34, exhibiting a defect area of ​​less than 100 nm.

[0075] 36. A III-V wafer (W) according to any one of items 23 to 35, wherein the diameter of the wafer is at least 150 mm.

[0076] 37. A III-V wafer (W) according to any one of items 23 to 36, wherein the diameter of the wafer is at least 200 mm.

[0077] 38.1×10 18 cm -3 ~3×10 18 cm -3 A silicon-doped GaAs wafer (W) having a charge carrier concentration of 25 mm 2 GaAs wafer (W) showing defect areas below 100 nm.

[0078] 39.1.5×10 18 cm -3 ~9×10 18 cm -3 a sulfur-doped InP wafer (W) having a charge carrier concentration of 25 mm 2 InP wafer (W) showing defect areas below 100 nm.

[0079] 40.1.5×10 18 cm -3 ~9×10 18 cm -3 a sulfur-doped InP wafer having a charge carrier concentration of 20 mm 2 Less than 15mm, preferably 2 Less than 10 mm, preferably 2 less than, and even more preferably 5 mm 2 InP wafer (W) showing defect areas below 100 nm.

[0080] 41. A III-V wafer (W) according to any one of items 23 to 39 or an InP wafer according to item 39 or 40, wherein the defect region is a continuous region.

[0081] 42. A III-V wafer (W) according to item 41, wherein at least some of the defect areas are in contact with the edge of the wafer.

[0082] 43. A III-V wafer (W) according to item 41 or 42, in which at least some of the defect areas are at most 5 mm away from the edge of the wafer.

[0083] 44. A III-V wafer (W) according to any one of items 41 to 43, wherein the entire defect area is located within a circular ring between the edge of the wafer and an imaginary ring line that is at most 10 mm away from the edge of the wafer.

[0084] 45. A III-V wafer (W) according to any one of items 41 to 44, wherein the entire defect area is located within a circular ring between the edge of the wafer and an imaginary ring line that is at most 10.5 mm away from the edge of the wafer.

[0085] 46. ​​A III-V wafer (W) according to any one of items 41 to 45, wherein the entire defect area is located within a circular ring between the edge of the wafer and an imaginary ring line that is at most 10 mm away from the edge of the wafer.

[0086] 47. A III-V wafer (W) according to any one of items 41 to 46, wherein the wafer has a linear grind or notch on part of its edge and the defective area is located opposite the linear grind or notch.

[0087] The linear grind or notch acts as a "recognition feature" to transfer the azimuthal orientation of the crystal lattice, determined by X-ray methods at the wafer manufacturer, to the exposure system in the lithography line when the wafer is used in the manufacture of electronic components (growth of epitaxial layers on the wafer, lithography, etc.).

[0088] 48. A tank (1) containing a liquid, Wedge (2), at least one bearing device capable of vertical movement (5) 1. A device for drying a wafer, comprising: At least one rack (3;31,32) has at least one rack (3;31,32): a pair of first lateral guidance devices (3a, 3a'), a pair of second lateral guidance devices (3b, 3b') and a pair of third lateral guidance devices (3c, 3c'); and the bearing device (5) may comprise: a pair of first lateral guiding devices (3a, 3a') are arranged below a pair of second lateral guiding devices (3b, 3b'), and a pair of second lateral guiding devices (3b, 3b') are arranged below a pair of third lateral guiding devices (3c, 3c'); the distance between the pair of first lateral guidance devices (3a, 3a') is shorter than the distance between the pair of second lateral guidance devices (3b, 3b'), and the distance between the pair of second lateral guidance devices (3b, 3b') is shorter than the distance between the pair of third lateral guidance devices (3c, 3c'); A device in which a wedge (2) is positioned below the rack (3) and is vertically movable separately from the bearing device (5).

[0089] Here, vertical means moving out of or into the tank, i.e., moving parallel to the direction of gravity.

[0090] 49. The device according to item 48, wherein the wedge (2) is vertically movable independently of the bearing device (5) or the rack (3).

[0091] 50. A device according to item 48 or 49, wherein the wedge (2) comprises at least two wedge portions (2a, 2b), both wedge portions (2a, 2b) being vertically movable independently of each other.

[0092] 51. The device described in item 50, wherein at least a first rack (31) can be inserted into the bearing device (5) so that the center of at least the first rack (31) is located above the tip of the first wedge portion (2a), and further, a second rack (32) can be inserted so that the center of the second rack (32) is located above the tip of the second wedge portion (2b).

[0093] 52. The device described in item 51, wherein the first rack (31) is adapted to hold wafers (W1) having a first diameter, and the second rack (32) is adapted to hold wafers (W2) having a second diameter, the first diameter being shorter than the second diameter.

[0094] 53. A device according to any one of items 50 to 52, wherein the tip of the first wedge portion (2a) and / or the second wedge portion (2b) is formed as a triangle, preferably as a right-angled triangle.

[0095] 54. A device according to any one of items 50 to 53, wherein the first wedge portion (2a) is divided into two parts, and there are two parts, and the first wedge portion (2a) and the second wedge portion (2b) are arranged adjacent to each other. [Brief explanation of the drawings]

[0096] [Figure 1a] 1 shows the mechanics of a wafer in a state-of-the-art bath during the process of state-of-the-art Marangoni drying. [Figure 1b] 1 shows the sequence of process steps in the state-of-the-art Marangoni drying process. [Figure 1c] 1 shows the resulting wafer with the corresponding residual droplets according to the state of the art in the process of Marangoni drying according to the state of the art. [Figure 2a] 1 shows the mechanism of the wafer in the state-of-the-art bath during the additional process of state-of-the-art Marangoni drying. [Figure 2b] 1 shows a series of process steps in the additional process of Marangoni drying according to the state of the art. [Figure 2c] 3 shows the resulting wafer with the corresponding residual droplets according to the state of the art in the additional process of Marangoni drying according to the state of the art. [Figure 3a] 1 illustrates the mechanics of a wafer in a bath during a process for producing cleaned and dried wafers, such as GaAs wafers, using Marangoni drying according to one embodiment of the present invention. [Figure 3b] 1 illustrates a series of process steps in a process for producing cleaned and dried wafers, such as GaAs wafers, using Marangoni drying according to one embodiment of the present invention. [Figure 3c] 10 illustrates residual droplets at contact points on the resulting wafers in a process for producing cleaned and dried wafers, such as GaAs wafers, using Marangoni drying according to an embodiment of the present invention. [Figure 4a] 1 illustrates process steps in a process for producing cleaned and dried wafers, such as GaAs or InP wafers, according to one embodiment of the present invention using Marangoni drying according to another embodiment. [Figure 4b] 10A-10C show details of potential structures for clamping a wafer above a liquid level in a process for producing cleaned and dried wafers, such as GaAs or InP wafers, according to one embodiment of the present invention, using Marangoni drying according to another embodiment. [Figure 5] 5 shows details of the exact sequence of step d) of FIG. 4 according to a first variant. [Figure 6] 5 shows details of the exact sequence of step d) of FIG. 4 according to a second variant. [Figure 7] 5 shows details of the exact sequence of step d) of FIG. 4 according to a third variant. [Figure 8] 5 illustrates the concept of step d) of FIG. 4 according to a fourth variant. [Figure 9] 1 shows another embodiment of a device for drying a wafer. [Figure 10] Two examples of racks capable of holding multiple wafers are shown. [Figure 11] An example of an evaluation routine for each wafer or group of wafers is provided, in which data acquired using a Candela surface ellipsometer can be processed accordingly. [Figure 12] Some examples of residual droplets or their residues that can be detected using a Candela surface ellipsometer and measured accordingly in terms of their area are given below. [Figure 13] Another example of an evaluation routine for each wafer or group of wafers is shown, in which data acquired using a Candela surface ellipsometer can be processed accordingly. [Figure 14] A comparison is shown in terms of defect area between a semi-insulating (in this case undoped) GaAs wafer dried using a process according to an embodiment of the invention in FIG. 3 and a wafer dried according to the process according to FIG. [Figure 15] A comparison is shown in terms of defect area between a semiconducting (in this case Si-doped) GaAs wafer dried using a process according to an embodiment of the invention in FIG. 3 and a wafer dried according to the process according to FIG. [Figure 16] A comparison is shown in terms of defect area between a semiconducting (in this case sulfur-doped) InP wafer dried using a process according to an embodiment of the invention in FIG. 3 and a wafer dried according to the process according to FIG. [Figure 17] 1 shows a top view of a device for drying wafers. [Figure 18] 3A-3D show side views of a device for drying wafers (in different states) according to another embodiment of the invention; [Figure 19] A comparison is shown in terms of defect area between a semi-insulating (in this case Fe-doped) InP wafer dried using a process according to an embodiment of the invention in FIG. 3 and a wafer dried according to the process according to FIG. DETAILED DESCRIPTION OF THE INVENTION

[0097] 1a) to 1c) show the process for lifting one or more wafers W from the bath 1. FIG.

[0098] 1a shows a bath 1 (which contains, for example, deionized rinsing water to which a surface-active substance such as isopropanol has been added) in which a wafer W is contained. Above the water surface, holding devices H and H' are located, and the wafer W is held by two pairs of lateral guiding devices 3a and 3a' and 3b and 3b'. Below the wafer, a corresponding wedge 2 is located, which is vertically movable and is used during wafer lifting.

[0099] In Figure 1b the process steps are described in more detail.

[0100] In step a) of the state-of-the-art process, the wafer W is located below the liquid level in the bath 1, and the first lateral guiding device 3a, 3a' and the second lateral guiding device 3b, 3b' are also located below the liquid level. The wedge 2 is located below the wafer W but does not contact it.

[0101] In step b), the wedge 2 moves towards the wafer W while the first and second lateral guide devices 3a, 3a', 3b, 3b' move upward. However, the wedge 2 does not necessarily have to contact the wafer W. A part of the wafer W is now located above the liquid level. However, the first and second lateral guide devices 3a, 3a', 3b, 3b' are still located below the liquid level. The wafer W cannot yet be held by the holding devices H and H'. It has not yet been withdrawn from the bath.

[0102] In step c), only wedge 2 is moved vertically upward, partially pushing wafer W out of the water bath, where wafer W is already in contact with holding devices H and H', which may be located, for example, inside the lid of the dryer. However, first and second lateral guide devices 3a, 3a', 3b, 3b' are still below the liquid level and have not yet moved further since step b). Because wedge 2 has pushed wafer W further upward, first lateral guide devices 3a, 3a' are no longer in contact with wafer W, but second lateral guide devices 3b, 3b' are still in contact with wafer W.

[0103] In step d), the wafer W is pushed further upwards by the wedge 2, and now the second lateral guiding device 3b, 3b' also no longer contacts the wafer W. However, the wafer W is still held by the holding devices H, H'.

[0104] In step e), the liquid is drained from the bath 1. The liquid level is below the wafer W. The wafer W is therefore dried. To ensure that the first and second lateral guide devices 3a, 3a', 3b, 3b' are dry, the water level in the bath is lowered, i.e. the water is drained. The wedge 2 is still in contact with the wafer W. The first and second lateral guide devices 3a, 3a', 3b, 3b' have not moved further since step c).

[0105] In step f), the surface of the water bath 1 is lowered to such an extent that the first and second lateral guiding devices 3a, 3a', 3b, 3b' and the wedge 2 are located above the water level and therefore also dry. The wedge 2 is still in contact with the wafer W.

[0106] In step g), the wedge 2 is lowered. Through the downward movement of the wedge 2, the wafer W is again held by and thus comes into contact with the first and second lateral guiding devices 3a, 3a', 3b, 3b', which are already dry.

[0107] To prevent contact between the wafer W and the first and second lateral guide devices 3a, 3a', 3b, 3b' while passing through the liquid surface of the bath 1, the wafer W is pushed out of the first and second lateral guide devices 3a, 3a', 3b, 3b' by the vertically upwardly moving wedge 2 and subsequently held only by the holding devices H, H'. This prevents residual droplets from forming between the wafer W and the first and second lateral guide devices 3a, 3a', 3b, 3b'. The holding devices H, H' are now above the water level and therefore still dry, preventing any residual droplets from forming. While passing through the water surface, residual droplets may only exist between the wafer W and the wedge 2. However, a disadvantage of this method is that there are very strict requirements for the spatial alignment of the moving parts relative to each other, particularly for the wedge 2 and the first and second lateral guide devices 3a, 3a', 3b, 3b', making process control difficult. Since the holding devices H, H' are adjusted successively to wafers of one size, wafers having different sizes cannot be dried according to this method, and a separate drying apparatus is required for each size.

[0108] FIG. 1c clearly shows that a residual droplet T is present on the lower edge of the wafer W, which occurs at the contact point between the wafer W and the wedge 2.

[0109] 2a-c show an alternative process for drying single or multiple wafers from a bath 1, also known in the prior art.

[0110] 2a clearly shows that the wafer W is held by two pairs of first and second lateral guide devices 3a, 3a', 3b, 3b', which are in turn located within the bath 1. Figure 2b reveals the individual steps of the process:

[0111] In step a), the wafer is below the water surface and is held by the first and second lateral guide devices 3a, 3a', 3b, 3b', which have not yet moved. The water bath 1, which contains water enriched with isopropanol near its surface layer, is drained at a predetermined rate.

[0112] In step b), the liquid level is above the pair of second lateral guiding devices 3b, 3b'.

[0113] In step c), water is below the wafer W and the first and second lateral guiding devices 3a, 3a' and 3b, 3b' are above the liquid surface.

[0114] Due to contact between the first and second lateral guide devices 3a, 3a', 3b, 3b' when the liquid level is lowered, residual liquid droplets often remain at the contact points between the wafer and the first and second lateral guide devices 3a, 3a', 3b, 3b', which adversely affects the quality of the wafer. This also adversely affects the quality of the subsequently grown epitaxial layer, which can lead to a decrease in component yield. However, the advantage of this method is that it is not technically very difficult and can potentially dry wafers of different sizes.

[0115] FIG. 2c shows a wafer W with residual droplets T at all four contact points.

[0116] 3a-c show a wafer drying method according to the present invention.

[0117] 3a shows a wafer W fully immersed in the bath 1. However, here, there are three pairs of lateral guidance devices 3a, 3a', 3b, 3b', and 3c, 3c' to hold the wafer, with the first pair of lateral guidance devices 3a, 3a' positioned below the second pair of lateral guidance devices 3b, 3b', which in turn are positioned below the third pair of lateral guidance devices 3c, 3c'. The distance between the pair of first lateral guidance devices 3a, 3a' is shorter than the distance between the pair of second lateral guidance devices 3b, 3b', which in turn is shorter than the distance between the pair of third lateral guidance devices 3c, 3c'.

[0118] In Figure 3a, the third lateral guiding device 3c, 3c' does not contact the wafer W. A wedge 2 is provided below the wafer.

[0119] In Figure 3b, the individual steps are described in more detail.

[0120] In step a), the wafer W is positioned below the liquid level in the bath 1 and is held by a pair of first lateral guiding devices 3a, 3a' and a pair of second lateral guiding devices 3b, 3b'. The wedges do not contact the wafer. The pair of third lateral guiding devices 3c, 3c' do not contact the wafer.

[0121] In step b), the wedge is moved towards the wafer so that the tip of the wedge contacts the wafer.

[0122] In step c), the lateral guide devices 3a, 3a', 3b, 3b' and 3c, 3c' and wedge 2 are moved upward. Now, the third lateral guide device 3c, 3c', which has already passed the water surface, is not in contact with the wafer, i.e., 3c, 3c' does not touch the wafer. Wedge 2 moves towards the wafer W and remains in contact with it, but is still below the water surface.

[0123] In step d), the water level is still located between the pair of second lateral guiding devices 3b, 3b' and the pair of third lateral guiding devices 3c, 3c'. However, the wafer W is only slightly raised by the wedge 2, so the wafer is no longer in contact with the pair of first lateral guiding devices 3a, 3a' and the pair of second lateral guiding devices 3b, 3b'. Rather, the wafer W is in contact with the pair of third lateral guiding devices 3c, 3c' above the liquid surface. Therefore, the wafer is now held by the wedge 2 and the pair of third lateral guiding devices 3c, 3c'.

[0124] In step e), the wafer W, the tip of the wedge 2, the pair of first lateral guiding devices 3a, 3a', the pair of second lateral guiding devices 3b, 3b' and the pair of third lateral guiding devices 3c, 3c' are above the water surface.

[0125] In step f), the wedge 2 is lowered and the wafer W is held by the wedge 2 and the now already dry first and second lateral guide devices 3a, 3a' and 3b, 3b'. The third lateral guide device 3c, 3c' is no longer in contact with the wafer W.

[0126] In step g), the water level is lowered and the position of the wafer W relative to the three lateral guiding devices 3a, 3a', 3b, 3b' and 3c, 3c' and the wedge 2 remains unchanged compared to step f).

[0127] During the passage through the water surface, there is only one contact point between the wafer W and the wedge 2, where residual droplets can form.

[0128] In FIG. 3c, a residual droplet is shown at the contact point of the lower wedge 2, but this does not necessarily occur and, if it does, is small compared to the method according to FIGS.

[0129] The movement speeds of the lateral guide devices 3a, 3a', 3b, 3b', and 3c, 3c' and the wedge 2 are always synchronized, thereby ensuring that the resulting wafer movement speed is always constant and therefore controllable. The wafer's movement path during lifting is shorter compared to that shown in FIG. 1, leading to shorter process times. As a result, the contact time between the lower edge of the wafer W and the movable wedge 2 (containing residual moisture) is reduced by several minutes. As a result, the risk of residual droplets forming at the contact point is significantly reduced. Due to the short vertical distance between the wafer and the lateral guide devices 3a, 3a', 3b, 3b', and 3c, 3c', both the wafer and the lateral guide devices can dry almost simultaneously, further shortening the process time. This significantly improves the productivity of the overall cleaning process, since drying is typically the most time-consuming process step and therefore the step that limits the overall process speed.

[0130] The adjustment effort for setting and correcting the positions of all components (wedges and lateral guide devices) is greatly reduced, the complicated alignment between the lateral guide devices is omitted, and the inclined movement path is not required. Furthermore, the risk of the wafer being subjected to mechanical stress in case of inaccurate adjustment, which may lead to scratches on the wafer, damage to the wafer edge, and breakage of the wafer, is reduced.

[0131] The risk of residual droplets and reduced mechanical stress on the wafer due to imprecise alignment are disadvantageous for larger wafers (e.g., over 150 mm) compared to smaller wafer diameters, requiring a significant increase in alignment effort and tighter tolerances to ensure consistent wafer quality.

[0132] The contact time between wedge 2 and wafer W can be reduced from minutes to seconds compared to the method of Figure 1, greatly reducing the likelihood of residual droplets forming at the only remaining first contact point (the contact point between wedge 2 and wafer W). If these residual droplets still form, they will be significantly fewer.

[0133] Preferably, the wafer is pulled up at a speed of approximately 1 mm / s. To dry the lower part of the wafer (approximately 1 cm), the pulling speed is significantly reduced to less than 0.5 mm / s to reduce droplets due to contact. The pulling speed is the speed at which the wafer moves relative to the liquid level. This reduction must be carried out in stages, since excessively strong fluctuations in the liquid level may indicate a change in the chemical composition of the oxide layer. Just as the lower edge of the wafer W reaches the liquid level, the wafer W must move away from the liquid level at high speed (>30 mm / s, preferably >40 mm / s, more preferably >50 mm / s), while the wedge 2 simultaneously moves away from the lower edge of the wafer W in the opposite direction. Strict adherence to this boundary condition is particularly necessary for n-doped GaAs due to its high surface tension. Only in this way can water from the liquid level, on the one hand, and residual moisture from the wedge 2, on the other hand, be prevented from being drawn back onto the wafer surface.

[0134] 4a, b show another embodiment of the Marangoni drying method, in particular the sequence of process steps is shown in FIG.

[0135] In step a), the wafer W is below the liquid level and is held by the first and second lateral guide devices 3a, 3a' and 3b, 3b'. The water bath 1 contains water enriched with isopropanol at its surface. A pair of third lateral guide devices 3c, 3c' are located above the liquid level and function as a dry transfer unit.

[0136] In step b), the wafer W is slightly raised by the wedge 2, with part of the wafer above the water surface and the wedge 2 in contact with the lower edge of the wafer W. Below the water surface, the wafer is still held by the lateral guide devices 3a, 3a' and 3b, 3b', which have further moved slightly upward. A third pair of lateral guide devices 3c, 3c' are still above the water surface and are not in contact with the wafer.

[0137] In step c), the positions of the pair of first lateral guidance devices 3a, 3a' and the pair of second lateral guidance devices 3b, 3b' remain constant. However, the wedge 2 further pulls the wafer up, so that the wafer contacts only the pair of second lateral guidance devices 3b, 3b', but not the pair of first lateral guidance devices 3a, 3a'. The position of the pair of third lateral guidance devices 3c, 3c' remains unchanged compared to step b).

[0138] In step d), the entire wafer W is lifted out of the liquid bath. At this time, the wedge 2 remains below the liquid surface. Here, the pair of third lateral guiding devices 3c, 3c' moves horizontally, and the distance between the third lateral guiding devices 3c, 3c' decreases. The third lateral guiding devices 3c, 3c' may have a holding function, or additional gripping devices 4 (not shown in this drawing) as exemplified in FIG. 9 can be used to keep the wafer W above the liquid surface. These hold the wafer W above the water surface.

[0139] In step e) the liquid level is lowered by draining the water.

[0140] In step f), the positions of the first and second lateral guiding devices 3a, 3a', 3b, 3b' remain unchanged, but the pair of third lateral guiding devices 3c, 3c' move horizontally, widening the distance between the third lateral guiding devices 3c, 3c' again, and the wafer W is now placed on the wedge 2. From the moment the third lateral guiding devices 3c, 3c' are no longer in contact with the wafer, the wafer W is held by the wedge 2 and the second lateral guiding devices 3b, 3b'. Thus, the wedge 2 and all the lateral guiding devices 3a, 3a', 3b, 3b' and 3c, 3c' are dried.

[0141] In step g), the wedge 2 is lowered so that the wafer W is again held by the pair of first lateral guiding devices 3a, 3a' and the pair of second lateral guiding devices 3c, 3b'.

[0142] This method is characterized in that the passage of the wafer through the water level is possible without a single contact with any of the tools, i.e., with any of the guiding devices 3a, 3a', 3b, 3b' and 3c, 3c', or with the wedge 2. The wedge 2 remains below the liquid level during all process steps of lifting the wafer, while the pair of third lateral guiding devices 3c, 3c' always remain above the liquid level and therefore never get wet.

[0143] FIG. 4b exemplarily illustrates how the wafer from step d) can be further held. On the left side, a third lateral guide device 3c, 3c' is illustrated in a T-shape, which provides better holding of the wafer W. On the right side of FIG. 4b, a gripping device 4 is shown, which can further hold the wafer W above the liquid level and can be adjusted to the wafer's diameter. Generally, the embodiment of the method with water drainage in the process bath (FIGS. 3 and 4) only works when the wafer is completely above the liquid level. This allows a continuous flow of ultrapure water (so-called overflow). Therefore, the liquid level, on which particles can float, is always sufficiently circulated and the liquid is exchanged. In the method according to FIG. 2, the liquid level is lowered while the wafer W is still at least partially in the bath. Overflow at the liquid level is then no longer possible, and particles can easily accumulate there and adhere to the dried wafer W, thereby degrading the quality of the epitaxial layer.

[0144] FIG. 5 provides a more detailed diagram of the sequence of step d) of FIG. 4a according to the first variant, illustrating the substeps, so to speak. Here, in step d-1), the wafer W is positioned almost completely above the liquid level. The wedge 2 is positioned below the liquid level, and the pair of third lateral guide devices 3c, 3c' is positioned above the liquid level and adjacent to the wafer W. In steps d-2), d-3), and d-4), the distance between the pair of third lateral guide devices 3c, 3c' is continuously reduced, while the wedge 2 remains below the liquid level. In step d-3), the entire wafer is already above the water surface. In step d-4), the wafer has moved slightly further upward. Therefore, the third lateral guide devices 3c, 3c' are dry transfer units that are always above the liquid level and therefore never get wet. Only horizontal movement of the third lateral guide devices 3c, 3c' is required. The wafer slides over a third lateral guiding device 3c, 3c'.

[0145] FIG. 6 provides a more detailed illustration of the sequence of step d) of FIG. 4a according to the second variant, illustrating the substeps, so to speak. Here, only the structure of the third lateral guide devices 3c, 3c' differs. They are oval in shape, and horizontal and rotational movements are required to move the wafer W. Here, the lifting of only the remaining few millimeters of the entire wafer W from the liquid bath, illustrated in step d) of FIG. 4a, will be described in more detail accordingly. In step d-1), the wafer is placed on two obliquely arranged oval-shaped third lateral guide devices 3c, 3c', with the larger side of the oval resting on the wafer. The wafer is almost completely lifted out of the water bath, with only one millimeter still immersed in the water. The wedge 2 remains below the water at all times. Now, in step d-2), the oval-shaped third lateral guide devices 3c, 3c' are rotated so that the wafer is rotated slightly upwards. In steps d-3) and d-4), the third lateral guiding device 3c, 3c' is further rotated until the wafer is positioned completely above the liquid level.

[0146] FIG. 7 provides a more detailed diagram of the sequence of step d) of FIG. 4a according to the third variant, illustrating the substeps, so to speak. Here, the dry transfer unit, i.e., the third lateral guide device 3c, 3c', exhibits an eccentric axis. Horizontal and rotational movements are required to move the wafer W. In step d-1), only a small portion of the wafer is still below the liquid level; in step d-2), the third lateral guide device 3c, 3c' rotates, which causes the wafer to move slightly upward; in step d-3), the third lateral guide device 3c, 3c' is further rotated so that the wafer is already above the liquid level; and in step d-4), the wafer is pulled up slightly above the liquid surface. The wedge 2 always remains below the water.

[0147] Figure 8 shows a diagram of AI-assisted adaptive control for wafer lifting. Here, a wafer W with a radius R is shown, and a pair of third lateral guide devices 3c, 3c' are asymmetrically positioned. The interrelationship between the movement of the wedge 2 (not shown here), the movement of the third lateral guide devices 3c, 3c', and the movement of the wafer relative to the water level is complex, especially when drying wafers of different diameters. According to conventional methods, complex movement patterns must be developed, and the mechanics must be extensively calibrated for each diameter. Here, AI-assisted adaptive control can be utilized. Wafers placed on a rack, i.e., at least the first and last wafers on the rack, are recorded using a camera (not shown here). The camera is fixed and installed above the water surface, and the third lateral guide devices 3c, 3c' are highlighted in color to facilitate image recognition. A trained neural network with AI-based image recognition can then determine the distance (parameter z in FIG. 8 ) between the wafer center and the water level, the position (parameters x and y in FIG. 8 ), and possibly the rotational position of the third lateral guiding device 3 c, 3 c′. These data can then control the program flow, in particular the vertical movement of the wedge 2, the movement (horizontal movement and possibly rotation) of the third lateral guiding device 3 c, 3 c′, and accordingly further additional important process parameters (such as drainage or deionized water supply). By monitoring the first and last wafers in the rack, it is possible to detect any tilt of the rack axis relative to the plane of the water surface and, if necessary, take appropriate measures.

[0148] Figure 9 shows another embodiment of a corresponding device for drying wafers. Apart from the rack 3 and wedge 2, a gripping device 4 is provided, which is designed to grip the wafer as long as it is raised above the water surface. As soon as the gripping device 4 grips the wafer, the wedge 2, which is still below the water surface, can be lowered (not shown). The rack and gripper move upward at the same speed, and the wafer passes through the water surface without being held by the wedge 2 at the passing point. Thus, the formation of residual droplets is prevented. Here, a suction device 6 is provided within the wedge 2.

[0149] FIG. 10 shows two racks. FIG. 10(a) shows, as an example, a state-of-the-art rack 3 that can be used in the method according to FIG. 1. Here, there are two heads 3d, 3d', between which two pairs of lateral guide devices 3a, 3a' and 3b, 3b' are arranged. These can hold wafers W (not shown here). The first lateral guide devices 3a, 3a' and the second lateral guide devices 3b, 3b' each have protrusions (not shown in detail here), which form a comb-like structure that cannot hold individual wafers W (not shown here) so that the wafers cannot touch each other or tilt. The pair of first lateral guide devices 3a, 3a' is arranged below the second lateral guide devices 3b, 3b'. The distance between the pair of first lateral guide devices 3a, 3a' is shorter than the distance between the second lateral guide devices 3b, 3b'.

[0150] 10(b) shows a rack 3 that can be used in the method of the present invention according to FIG. 3. In contrast to FIG. 4a, here, a pair of third lateral guide devices 3c, 3c' is arranged above a pair of second lateral guide devices 3b, 3b'. The distance between the pair of first lateral guide devices 3a, 3a' is shorter than the distance between the second lateral guide devices 3b, 3b', and the distance between the pair of second lateral guide devices 3b, 3b' is shorter than the distance between the third lateral guide devices 3c, 3c'. Thus, unlike FIG. 4a, there is the possibility of holding the wafer (not shown here) at multiple points. The first lateral guiding device 3a, 3a', the second lateral guiding device 3b, 3b' and the third lateral guiding device 3c, 3c' each exhibit ridges (not shown in detail here) which form a comb-like structure capable of holding individual wafers W (not shown here) so that the wafers cannot touch each other or tilt.

[0151] Figure 11 shows the corresponding evaluation routine for a measurement that can evaluate the uniformity of the oxide surface layer of a wafer according to the present invention: A Candela surface ellipsometer is used to generate a raw data file. Within the Candela ellipsometer's software, a corresponding contrast maximization is performed and applied to the entire mapping (for example, in image processing software for pixel graphics, the contrast is varied until the droplet residue is clearly visible on the shown photograph, ensuring that areas with the droplet's characteristic shape are more prominent than their surroundings). The corresponding image file is then exported. Then, for all wafers, areas of different contrast are manually marked, with particular attention paid to the peripheral areas.

[0152] In locations where residual droplets may form during the drying process due to the wafer's orientation, a 9 cm wide and 1.9 cm high square is placed on the wafer for evaluation. Droplets are identified and evaluated within this square. This ensures that all possible residual droplets within a 1 cm wide ring at the wafer's outer edge are recorded. The use of an imaginary square is more useful and accurate than a ring (a full-circumference stripe), which does not easily distinguish residual droplets from possible laser markings on the front side of the wafer during image processing.

[0153] The determination of the area of ​​the defect area is then carried out using image processing, which allows the area to be measured accordingly, thereby measuring the area of ​​the delimited area.

[0154] Here, typically, the corresponding defects can be essentially avoided by improved Marangoni drying methods, so that the entire wafer can still be used, rather than eliminating a margin in certain areas of the wafer.

[0155] Now, any residual droplets or defect areas showing their effect on the compositional change of the oxide layer are marked and measured based on the following criteria: The area must be on the edge of the wafer Irregular shapes exist Areas exhibit a different brightness than the surrounding areas (usually brighter than the surrounding areas; smaller darker areas are also possible) The shape of the domain is the typical shape of the remaining water (droplet shape, spherical / elliptical / ovoid elements, elongated and branched shapes, etc.).

[0156] This provides a frequency distribution of the determined defective areas.

[0157] Figures 12(a) and (b) show two examples of droplets at the edge of a wafer, marked and measured for area, respectively. Automatic evaluation is difficult here because, for example, contrast variations on the wafer may occur due to other effects (shown in black in Figure 12), which should not be confused with droplets at the edge of the wafer. Therefore, manual evaluation must be performed here, always paying attention to the fact that droplets originate from the edge of the wafer and that corresponding shapes can necessarily be assigned to droplet shapes. Therefore, shapes with sharp angles throughout cannot be assigned to droplets. For example, edges with fine serrated notches cannot be assigned to droplets because the surface tension of water does not allow such shapes to develop. However, shapes with irregular edges are possible, as seen in the left image of Figure 12(a).

[0158] During drying, defects occur due to the wafer coming into contact with the rack or wedge as it passes through the liquid surface, causing droplets to adhere, which cause spots and therefore "defects." However, the present invention leaves fewer spots, preferably only one spot, and / or an overall minimized spot area, whereas state-of-the-art drying methods typically leave multiple and overall larger spot areas.

[0159] Figure 13 presents an alternative evaluation routine. Here, manual marking of areas with different contrast is performed on only a few wafers. Then, with the help of neural network training, all remaining wafers are evaluated and the defect areas are assessed accordingly. Because the appearance of droplet residues can reveal very different contrasts, droplet region segmentation was performed with the help of a neural network. The neural network was trained using the TensorFlow-Keras platform. A UNet structure with a resnet34 skeleton was used as the model ("U-Net: Convolutional Networks for Biomedical Image Segmentation," Olaf Ronneberger, Philipp Fischer, Thomas Brox, arXiv 2015, 1752118795841_0.04597; http: / / lmb.informatik.uni-freiburg.de / people / ronneber / u-net).

[0160] The segmented regions were visually checked for validity on all images, and additional training datasets were added to retrain the network if necessary. This process was repeated until the automated segmentation matched the visual assessment for over 98% of all images. Regions segmented in this way were then selected and measured within those regions using conventional image processing (e.g., OpenCV: https: / / opencv.org / ) in a second step.

[0161] Therefore, contrast is not assessed based on a threshold, but rather on its degree, either visually or by a trained algorithm or neural network, where the absolute value of the measurement signal is not taken into account, but only the visibility of the droplet area. The assessment proceeds outside the Candela ellipsometer.

[0162] FIG. 14 shows the defect area measurements of two corresponding groups of semi-insulating undoped GaAs wafers, 150 mm in diameter, dried using conventional Marangoni drying (according to FIG. 1) (right) and using the improved Marangoni drying according to the present invention (FIG. 3) (left).

[0163] For undoped wafers, the spread of different defect areas is smaller and the absolute defect area is smaller (5 mm 2 It can be shown that

[0164] The defect area corresponds to the area measured by measuring the surface using Candela ellipsometry. From a chemical point of view, there is a non-uniform composition of the surface oxide, and accordingly, the defect area is an area of ​​the surface oxide with a non-uniform oxide composition.

[0165] Because the droplet sizes in the data are not normally distributed, a standard t-test cannot be performed. In these cases, a Wilcoxon test is appropriate, as it makes no assumptions about the underlying distribution. This test calculates the rank sum of the observations, which is approximately normally distributed and allows for statistical statements. Because the droplet sizes of both methods are significantly different, a one-sided test with a confidence interval of 0.95 was performed. The parameter n indicates the total number of values. If the p-value is below the typical value of 0.05, the null hypothesis can be rejected (in this case: the droplet sizes obtained by the method according to Figure 3 are larger than those obtained by the method according to Figure 1). Therefore, a very small p-value (<0.0001) in the data significantly indicates that the droplet sizes obtained by the method according to Figure 3 are smaller. The parameter W refers to the rank sum of one of the two groups.

[0166] FIG. 15 shows the defect area measurements for two corresponding groups of semi-insulating silicon-doped GaAs wafers, 150 mm in diameter, dried using conventional Marangoni drying (according to FIG. 1) (right) and using the improved Marangoni drying according to the invention (FIG. 3) (left). The spread is significantly smaller in the Si-doped wafers when the method according to the invention is used, and the defect area is significantly smaller (25 mm 2 It can also be shown that

[0167] Because the droplet sizes in the data are not normally distributed, a standard t-test cannot be performed. In these cases, a Wilcoxon test is appropriate, as it makes no assumptions about the underlying distribution. This test calculates the rank sum of the observations, which is approximately normally distributed and allows for statistical statements. Because the droplet sizes of both methods are significantly different, a one-sided test with a confidence interval of 0.95 was performed. The parameter n indicates the total number of values. If the p-value is below the typical value of 0.05, the null hypothesis can be rejected (in this case: the droplet sizes obtained by the method according to Figure 3 are larger than those obtained by the method according to Figure 1). Therefore, a very small p-value (<0.0001) in the data significantly indicates that the droplet sizes obtained by the method according to Figure 3 are smaller. The parameter W refers to the rank sum of one of the two groups.

[0168] FIG. 16 shows the defect area measurements for two corresponding groups of 100 mm diameter InP wafers doped with semiconducting sulfur, dried using conventional Marangoni drying (according to FIG. 1) (right) and using the improved Marangoni drying according to the present invention (FIG. 3) (left). The spread is significantly smaller and the defect area is significantly smaller (5 mm) in the sulfur doped wafers when the method according to the present invention is used. 2 It can also be shown that

[0169] The defect area corresponds to the area measured by measuring the surface using Candela ellipsometry. From a chemical point of view, there is a non-uniform composition of the surface oxide, and accordingly, the defect area is an area of ​​the surface oxide with a non-uniform oxide composition.

[0170] Because the droplet sizes in the data are not normally distributed, a standard t-test cannot be performed. In these cases, a Wilcoxon test is appropriate, as it makes no assumptions about the underlying distribution. This test calculates the rank sum of the observations, which is approximately normally distributed and allows for statistical statements. Because the droplet sizes of both methods are significantly different, a one-sided test with a confidence interval of 0.95 was performed. The parameter n indicates the total number of values. If the p-value is below the typical value of 0.05, the null hypothesis can be rejected (in this case: the droplet sizes obtained by the method according to Figure 3 are larger than those obtained by the method according to Figure 1). Therefore, a very small p-value (<0.0001) in the data significantly indicates that the droplet sizes obtained by the method according to Figure 3 are smaller. The parameter W refers to the rank sum of one of the two groups.

[0171] FIG. 17 shows an embodiment of a device for drying wafers according to the present invention. Here, a bearing unit 5 is provided, on which several different racks 3, 31, and 32 can be suspended. The racks themselves use guide devices (comb rods) to hold the wafers. In this figure, either a first rack 31 or a second rack 32 can be suspended. The first rack 31 is useful for drying wafers with a smaller diameter than the rack 32. Here, the wedge is composed of two wedges, a first wedge portion 2a and a second wedge portion 2b, which can be moved vertically independently of each other. The center of the first rack 31 is located directly above the tip of the first wedge portion 2a, and the center of the second rack 32 is located above the tip of the second wedge portion 2b. The first and second wedges 2a and 2b also exhibit corresponding ridges 2c that form a comb-like structure. For example, for large wafers with a diameter of 200 mm or more, a second rack 32 is provided, and the raised portion 2c has a longer distance compared to the first rack 31. Therefore, the rack 32 is longer than the first rack 31, and the wafers, unlike small-diameter wafers, can no longer be lifted using the same wedges. The wedges 2a and 2b must be positioned in the center of the rack to hold the wafer at its lower point. Therefore, for example, lifting wafers with a diameter of up to 150 mm on the one hand and wafers with a diameter of 200 mm or more on the other hand in a dryer is impossible according to the state of the art. In the device according to the present invention, individual wedges (2a for small wafers W1 and 2b for large wafers W2) with a suitably long length and a properly adjusted raised portion 2c distance are used for small wafers (e.g., diameters of 150 mm or less) and large wafers (e.g., diameters of 200 mm or more), respectively. Since the 200 mm wafer has a larger diameter, the distance of the ridges 2c must be longer than for smaller diameter wafers, so that the wafers W2 do not touch each other if tilted slightly.

[0172] 18 shows a side view of a wedge 2 of a device according to the present invention. Here, the left image shows the structure of a first wedge portion 2a and a second wedge portion 2b. The center image shows a small diameter wafer W1 (e.g., a 3-inch or 150 mm wafer) being pulled upward by the first wedge portion 2a. The right image shows a large diameter wafer W2 (e.g., a 200 mm wafer) being pulled upward with the help of the second wedge portion.

[0173] Figure 19 shows the defect area measurements for two corresponding groups of semi-insulating Fe-doped InP wafers, 150 mm in diameter, dried using conventional Marangoni drying (according to Figure 1) (right) and using the improved Marangoni drying according to the present invention (Figure 3) (left). In the case of the Fe-doped wafers, it can be shown that the extent of the different defect areas is similarly small in the wafers produced according to the existing new method, and that any defect areas are barely visible.

[0174] The defect area corresponds to the area measured by measuring the surface using Candela ellipsometry.

[0175] The method for drying wafers according to the present invention includes a bath having at least one wedge and at least one rack arrangement.

[0176] a pair of first lateral guidance devices 3a, 3a', a pair of second lateral guidance devices 3b, 3b' and a pair of third lateral guidance devices 3c, 3c'.

[0177] The pair of first lateral guiding devices 3a, 3a' are arranged below the pair of second lateral guiding devices 3b, 3b', and the pair of second lateral guiding devices 3b, 3b' are arranged below the pair of third lateral guiding devices 3c, 3c'.

[0178] The distance between a pair of first lateral guidance devices 3a, 3a' is preferably shorter than the distance between a pair of second lateral guidance devices 3b, 3b', and the distance between a pair of second lateral guidance devices 3b, 3b' is preferably shorter than the distance between a pair of third lateral guidance devices 3c, 3c'.

[0179] The method according to the invention comprises the following steps: i) moving at least one wedge 2 vertically upward until it contacts the lowest point of the wafer, and moving the pair of first lateral guiding devices 3a, 3a' and the pair of second lateral guiding devices 3b, 3b' vertically upward, where the wafer W contacts the pair of first lateral guiding devices 3a, 3a' and the pair of second lateral guiding devices 3b, 3b', and an upper region of the wafer W is lifted out of the bath 1, where the pair of third lateral guiding devices 3c, 3c' do not contact the wafer; ii) moving the wedge 2 vertically upward until the pair of first lateral guide devices 3 a, 3 a′ and the pair of second lateral guide devices 3 b, 3 b′ are out of contact with the wafer W while still below the liquid level in the bath 1, and then the pair of third lateral guide devices 3 c, 3 c′ are in contact with the wafer above the liquid level in the bath 1; iii) raising the wafer W above the liquid level of the bath 1, where the pair of third lateral guiding devices 3c, 3c' contact the wafer W;

[0180] Compared to the state of the art (Figure 1), the wafer is no longer held by fixed holding devices H and H', which are limited to the diameter of the wafer (and therefore, for example, the interior of the dryer lid), but rather is held specifically by a pair of third lateral guiding devices 3c, 3c'.

[0181] Thus, contact between the wafers and, in particular, the first and second lateral guide devices 3a, 3a', 3b, 3b' of the racks 3, 31, 32 is accordingly prevented when the water level passes through said first and second lateral guide devices. The wafers W, W1, W2 are held by the third lateral guide devices 3c, 3c', which are located above the water level and already dry. During drying according to the present invention, the vertical movement path of the wafers is significantly shorter, down to a few seconds. Therefore, droplets that may form during contact between the wafers and the wedges 2, 2a, 2b occur significantly less frequently and are smaller. Residual droplets found in Candela measurements of wafers dried in this manner are fewer and smaller.

[0182] Preferably, the method according to the invention comprises the following steps: iv) moving the wedge 2 vertically downward until the wafer W contacts at least one of the pair of first lateral guiding devices 3 a, 3 a′ and the pair of second lateral guiding devices 3 b, 3 b′; v) further moving the wedge 2 vertically downward until it no longer contacts the wafer W; In parallel with steps iv) and / or v), or after step v), the liquid level in tank 1 is lowered until the liquid level is below wedge 2.

[0183] Thus, the lateral guidance devices 3a, 3a', 3b, 3b' or racks 3, 31, 32 and wedges 2, 2a, 2b can dry until the wafers are ready for the follow-up drying operation.

[0184] Preferably, the reservoir 1 contains water and at least one additional surface tension reducing substance, preferably isopropanol.

[0185] Thus, in the method according to the invention, an optimal exploitation of the Marangoni effect can be achieved.

[0186] Preferably, the pair of first lateral guiding devices 3a, 3a', the pair of second lateral guiding devices 3b, 3b' and / or the pair of third lateral guiding devices 3c, 3c' consist of a pair of webs that are arranged to contact opposite sides of the wafers W, W1, W2, respectively, at different process steps.

[0187] Thus, wafers W, W1, W2 can be held from the sides to ensure that they do not touch each other during the drying process (i.e., they do not tip over in the dryer). Wafers that do touch each other during drying may "stick" together, thereby preventing drying (i.e., the wafers remain wet).

[0188] Preferably, in step i), a pair of first lateral guiding devices 3a, 3a' and a pair of second lateral guiding devices 3b, 3b' are immersed in the bath 1, and preferably, at the end of step v), a pair of third lateral guiding devices 3c, 3c' are not in contact with the wafers W, W1, W2.

[0189] Since there is almost no contact between the wedge and the wafer (or the wafer may even have no contact at all with any of the guiding devices or wedges) while passing through the liquid surface of the bath, it can be ensured that there are no droplets of liquid adhering to the wafers W, W1, W2 within the area of ​​the first, second and third guiding devices that could reduce the surface uniformity of the wafer surface.

[0190] Preferably, the wedges 2, 2a, 2b are equipped with at least one suction device 6 capable of applying a vacuum when the upper ends of the wedges 2, 2a, 2b are located above the liquid level, thus sucking out any remaining water at the tips of the wedges 2, 2a, 2b, thereby ensuring that no droplets reach the wafers W, W1, W2, which may therefore result in non-uniformity of the oxide surface.

[0191] Preferably, the wedges 2, 2a, 2b are provided with a structure that increases the surface tension, for example by plasma treatment of the PEEK from which the wedges 2, 2a, 2b can be manufactured. The increase in the surface tension of the wedges 2, 2a, 2b can lead to residual droplets remaining on the wedges 2, 2a, 2b and not spreading onto the wafers W, W1, W2.

[0192] Preferably, the lifting speed depends on the position of the wafer's lowest point. If the wafer's lowest point is more than 1.2 cm below the liquid level, it is 0.8 to 1.2 mm / s. If the wafer's lowest point is less than 1.2 cm below the liquid level, it is 0.4 to 0.5 mm / s, resulting in a significant reduction in contact-induced droplets. This speed reduction should be carried out gradually, as excessively large fluctuations in the water level may be indicated in the chemical composition of the oxide layer. As soon as the wafer's lowest point reaches the water level, the lifting speed is increased to at least 30 mm / s (preferably 40 mm / s or 50 mm / s). This prevents water from the water level, on the one hand, and residual moisture from the wedge, on the other hand, from being drawn back onto the wafer surface. This allows the wedge to move away from the lower edge of the wafer in the opposite direction.

[0193] According to the embodiment, a pair of first lateral guiding devices 3a, 3a', a pair of second lateral guiding devices 3b, 3b', and a pair of third lateral guiding devices 3c, 3c' are provided on a rack 3, and in step i), the entire rack 3 is moved, and in step iii), the wafer W is raised above the liquid level in the tank 1, so that the pair of third lateral guiding devices 3c, 3c' (already above the liquid level) and the wedge 2 come into contact with the wafer W. While passing through the liquid level, there is only one contact point between the wedge and the wafer, and the area of ​​the liquid droplet can be minimized.

[0194] According to another embodiment, the pair of third lateral guide devices 3c, 3c' remain above the liquid level during all process steps and are movable independently of the pair of first lateral guide devices 3a, 3a' and the pair of second lateral guide devices 3b, 3b', while the third lateral guide devices 3c, 3c' are horizontally movable relative to each other. Thus, the third lateral guide devices 3c, 3c' always remain dry and can grip the wafer W above the liquid level. While passing through the liquid level, there are no contact points between the wedge and the wafer, and thus the liquid droplet area can even be completely avoided. Preferably, the wedge 2 remains below the liquid level during all process steps. This is why no residual liquid droplets remain on the wafer in the wedge area.

[0195] Preferably, in step iii), the distance between the points at which the third lateral guiding devices 3c, 3c' contact the wafer is continuously reduced, thereby enabling the horizontal movement of the third lateral guiding devices 3c, 3c' to vertically move the wafer W. The third lateral guiding devices 3c, 3c' are more preferably arranged to perform horizontal movements relative to each other.

[0196] More preferably, the third lateral guide device 3c, 3c' is mounted eccentrically or oval-shaped and arranged to perform a rotational movement, so that the vertical movement of the wafer can be effected by the rotational movement of the third lateral guide device 3c, 3c', which can be useful in the area of ​​lifting the last wafer out of the bath, at which moment the wedge 2 is not required for the vertical movement of the wafer, thereby avoiding contact points between the wafer W and the wedge 2 during the passage through the liquid surface.

[0197] Additional process parameters can affect the oxide surface uniformity of III-V wafers: The concentration of a substance that reduces the surface tension of ultrapure water, preferably isopropyl alcohol (IPA), emerged as an additional parameter that needs to be controlled for Marangoni drying to reduce residual droplets. Reducing the IPA supply during the final stages of drying creates a larger vertical gradient in the surface tension, reducing the risk of residual droplets forming. Because the effect of reducing the IPA supply on the IPA concentration in the gas phase and subsequently on the magnitude of the concentration gradient is delayed, it can be beneficial to gradually reduce the IPA supply after the interphase boundary (liquid surface) has passed the center of the wafer. A more significant reduction in the IPA supply can be beneficial, especially for n-doped GaAs. The IPA gradient at the interface results from the interaction of the regulated IPA supply with the deionized water (ultrapure water) flooding in the process bath. At the same time, the flood strength influences the particles that remain attached to the wafer. Wafers made of InP exhibit a high surface tension (with the same pretreatment) and a significantly higher particle adhesion capacity than GaAs. To achieve a lower level of residual particles, for example, a flow rate of at least 0.1 l / h / cm 2 of ultrapure water (liquid surface area in the tank: 1 cm 2 A flood of 0.1 liters of ultrapure water per hour per GaAs substrate is required. The flood can exceed this value only slightly, since the concentration of IPA at the interface is sufficient. Accordingly, the IPA / N flow should be increased to 0.003-0.007 l / h / cm compared to GaAs to compensate for the large amount of IPA extraction due to flooding, and thereby to keep the IPA concentration stable at the interface. 2 It needs to be increased.

[0198] Besides the technological and chemical influences of the Marangoni drying itself, the treatment of the III-V semiconductor wafer in the process bath before drying influences the quality of the Marangoni drying and the size of the residual droplets that form at the contact point with the wedge used for pulling. Depending on the cleaning sequence, the final cleaning step can consist of an acid, alkaline, or neutral solution (e.g., with a non-ionic surfactant). The pH value of the final chemical cleaning step before Marangoni drying determines the surface tension of the wafer surface during the drying process. To optimize drying, the IPA concentration may be adjusted to the surface tension of the wafer to be dried. In this context, hydrophobic wafers require less isopropanol than hydrophilic wafers (e.g., hydrophobic: <0.01 l / h / cm). 2 IPA / N2, e.g., hydrophilic: >0.01 l / h / cm 2 IPA / N2).

[0199] Adjustment of the surface tension of the drying wafer can be achieved, for example, by adding small amounts of acidic or basic additives.

[0200] The wafer according to the invention has an oxide layer on at least one surface, said surface being 25 mm deep in the oxide layer. 2 The wafer has a defect area of ​​less than 1000 nm. The wafer is semi-insulating or semi-conducting. A surface having an oxide layer is also called an oxide surface.

[0201] In the case of semi-insulating wafers, even smaller defect areas are possible: here the defect area is preferably less than 15 mm 2 Less than 10 mm, preferably 2 less than, and even more preferably 5 mm 2 More preferably, such wafers are preferably composed of GaAs or InP, even more preferably undoped or carbon-doped GaAs or iron-doped InP.

[0202] The semiconducting wafer may be a GaAs wafer and contain silicon as a dopant, or an InP wafer and contain sulfur as a dopant.

[0203] Preferably, the defect area is a continuous area, as exemplarily shown in Figure 12, where at least a portion of the defect area may contact the edge of the wafer.

[0204] Preferably, at least some of the defect areas are a maximum of 5 mm from the edge of the wafer.

[0205] More preferably, at least a portion of the defect area is located within a circular ring between the edge of the wafer and an imaginary ring line that is a maximum of 10 mm away from the edge of the wafer.

[0206] Also, preferably, the entire defect area is located within a circular ring between the edge of the wafer and an imaginary ring line that is a maximum of 10.5 mm away from the edge of the wafer.

[0207] Even more preferably, the entire defect area is located within a circular ring between the edge of the wafer and an imaginary ring line that is a maximum of 10 mm away from the edge of the wafer.

[0208] Optionally, the wafer has a linear grind or notch on a portion of its edge, and the defective area is located opposite the linear grind or notch.

[0209] Corresponding wafers can be produced using the method according to the invention, since droplets can be minimized during drying and are contained in particularly small defect areas.

[0210] The device according to the invention for drying wafers comprises: a reservoir 1 containing a liquid; Wedge 2 and at least one vertically movable bearing device 5; At least one rack 3; 31, 32 is mounted in a bearing device 5, At least one rack 3; 31, 32 comprises a pair of first lateral guide devices 3a, 3a', a pair of second lateral guide devices 3b, 3b' and a pair of third lateral guide devices 3c, 3c'; the pair of first lateral guidance devices 3a, 3a' are arranged below the pair of second lateral guidance devices 3b, 3b', the pair of second lateral guidance devices 3b, 3b' are arranged below the pair of third lateral guidance devices 3c, 3c'; the distance between the pair of first lateral guidance devices 3a, 3a' is shorter than the distance between the pair of second lateral guidance devices 3b, 3b', the distance between the pair of second lateral guidance devices 3b, 3b' is shorter than the distance between the pair of third lateral guidance devices 3c, 3c'; a wedge 2 is arranged below the rack 3 and is vertically movable separately from the bearing device 5; the wedge 2 comprises at least two wedge portions 2 a, 2 b, both of which are vertically movable independently of each other; At least the first rack 31 can be suspended in the bearing device 5 so that the center of at least the first rack 31 is located above the tip of the first wedge portion 2a, and further, the second rack 32 can be suspended so that the center of the second rack 32 is located above the tip of the second wedge portion 2b.

[0211] Compared to the prior art, the two additional lateral guide devices (third lateral guide devices 3c, 3c') result in the fact that the wafers W, W1, W2 can already be held from the sides when they are raised above the liquid surface, so that when the wafers W, W1, W2 pass through the liquid surface, holding can be achieved by the third lateral guide devices 3c, 3c' (above the liquid surface) and the wedges 2, 2a, 2b (below the liquid surface). The first lateral guide devices 3a, 3a' and the second lateral guide devices 3b, 3b' do not come into contact with the wafers W, W1, W2 below the liquid surface, and also do not come into contact with them while they pass through the liquid surface, thereby avoiding the risk of droplets forming in these areas.

[0212] In the device according to the present invention, individual wedges (2a for small wafer W1 and 2b for large wafer W2) with a suitable length and a properly adjusted distance of the raised portions 2c are used for small wafers (e.g., diameters of 150 mm or less) and large wafers (e.g., diameters of 200 mm or more), respectively. Because the 200 mm wafer has a larger diameter, the distance of the raised portions 2c must be longer than that for smaller diameter wafers, so that the wafers W2 do not come into contact with each other when tilted slightly.

[0213] Such a device is suitable for drying wafers of multiple diameters without additional construction effort. [Example]

[0214] Wet chemical cleaning methods were used to clean the GaAs wafers, and all wafers were pre-polished on both sides and final polished on one side.

[0215] Pre-cleaning was performed using NH3 and HCl.

[0216] The final cleaning was performed using the method according to WO 2014 / 124980: the wafer was subjected to alkaline cleaning (dilute NH3 solution and megasonics), rinsed with deionized water and subsequently dried using Marangoni drying.

[0217] Example 1: Semi-insulating, undoped GaAs wafers with a diameter of 150 mm were cleaned in a bath and subsequently dried using Marangoni drying. The undoped wafers were fabricated from crystals grown via the VGF process and had a 1 × 10 8 Ωcm~8×10 8 It had a resistivity of Ωcm.

[0218] 48 GaAs wafers were dried using the method of the present invention according to Figure 3. The wafer process speed was approximately 1 mm / s (which may vary at individual stages of pulling, see above and claim 8). "Process speed" refers to the speed at which the wafer moves relative to the water surface.

[0219] Comparative Example 1: Semi-insulating, undoped GaAs wafers with a diameter of 150 mm were cleaned in a bath and subsequently dried using Marangoni drying. The undoped wafers were fabricated from crystals grown via the VGF process and had a 1 × 10 8 Ωcm~8×10 8 It had a resistivity of Ωcm.

[0220] 46 GaAs wafers were dried using the method according to Figure 1 (state of the art). The wafer process speed was approximately 1 mm / s (which may vary at individual stages of pulling, see above and claim 8).

[0221] A comparison between Example 1 and Comparative Example 1 is shown in FIG.

[0222] Example 2: A 150 mm diameter silicon-doped GaAs wafer (semiconducting) was cleaned in a bath and subsequently dried using Marangoni drying. The doped wafer was fabricated from a crystal grown via the VGF process and had a Si doping of 1 × 10. 18 ~3×10 18 cm -3 The charge carrier concentration was

[0223] 84 silicon-doped GaAs wafers were dried using the method of the invention according to Figure 3. The wafer process speed was approximately 1 mm / s (which may vary at individual stages of pulling, see above and claim 8).

[0224] Comparative Example 2: A 150 mm diameter silicon-doped GaAs wafer (semiconductive) was cleaned in a bath and subsequently dried using Marangoni drying.

[0225] 88 silicon-doped GaAs wafers were dried using the method according to Figure 1 (state of the art). The wafer process speed was approximately 1 mm / s (which may vary at individual stages of pulling, see above and claim 8).

[0226] A comparison between Example 2 and Comparative Example 2 is shown in FIG.

[0227] Example 3: A 100 mm diameter sulfur-doped InP wafer (semiconducting) was cleaned in a bath and subsequently dried using Marangoni drying. The sulfur-doped wafer was fabricated from a crystal grown via the VGF process and had a sulfur doping of 1.5 × 10. 18 ~9×10 18 cm -3 The charge carrier concentration was

[0228] Nineteen sulfur-doped InP wafers were dried using the method of the invention according to Figure 3. The wafer process speed was approximately 1 mm / s (which may vary at individual stages of pulling, see above and claim 8).

[0229] Comparative Example 3: A 100 mm diameter sulfur-doped InP wafer (semiconducting) was cleaned in a bath and subsequently dried using Marangoni drying. The sulfur-doped wafer was fabricated from a crystal grown via the VGF process and had a sulfur doping of 1.5 × 10. 18 ~9×10 18 cm -3 The charge carrier concentration was

[0230] 29 InP wafers were dried using the method according to Figure 1 (state of the art). The wafer process speed was approximately 1 mm / s (which may vary at individual stages of pulling, see above and claim 8).

[0231] A comparison between Example 3 and Comparative Example 3 is shown in FIG.

[0232] Example 4: A 150 mm diameter semi-insulating Fe-doped InP wafer was cleaned in a bath and subsequently dried using Marangoni drying. The Fe-doped wafer was fabricated from a crystal grown via the VGF process and had an iron doping of 2.8 × 10. 7 ~3.8×10 7 cm -3 The charge carrier concentration was 4.9×10 7 Ωcm~8.7×10 7 The dislocation density was 290 to 480 cm -2 It was.

[0233] 23 InP wafers were dried using the method of the invention according to Figure 3. The wafer process speed was approximately 1 mm / s (which may vary at the individual stages of pulling, see above and claim 8).

[0234] Comparative Example 4: A 150 mm diameter semi-insulating Fe-doped InP wafer was cleaned in a bath and subsequently dried using Marangoni drying. The Fe-doped wafer was fabricated from a crystal grown via the VGF process and had an iron doping of 2.8 × 10. 7 ~3.8×10 7 cm -3 The charge carrier concentration was 4.9×10 7 Ωcm~8.7×10 7 The dislocation density was 290 to 480 cm -2 It was.

[0235] 12 InP wafers were dried using the method (state of the art) according to Figure 1. The wafer process speed was approximately 1 mm / s (which may vary at individual stages of pulling, see above and claim 8).

[0236] A comparison between Example 4 and Comparative Example 4 is shown in FIG.

[0237] Wafer surface characterization: The surface quality of the wafer (oxide surface quality on the wafer) is characterized after drying by an optical surface analyzer (Candela ellipsometer). For the characterization of the uniformity of the surface quality, the mapping of the measurement channel QAbsPhase of a Candela CS20 manufactured by KLA is evaluated. The radial resolution of the Candela measurement is 50 μm, and the lateral resolution is <30 μm.

[0238] The mapping shows bright and dark areas, as well as stripe structures that can be attributed to inhomogeneities or, in general, "defects." The intensity and number of deviations from the background characterize the uniformity of the surface. In assessing the droplet size, contrast is not derived from a threshold, but rather based on their magnitude either visually or by a trained algorithm or, respectively, by a neural network (see above), where the absolute value of the measurement signal is not taken into account, but only the clearly identifiable droplet area. This assessment then proceeds outside the Candela ellipsometer.

[0239] A boundary exclusion of up to 0.5 mm is applied. The inward spread of the droplets found is up to approximately 1 cm, so this region covers radii ranging from 65 mm to 74.5 mm for 150 mm wafers and 40 mm to 49.5 mm for 100 mm wafers. [Explanation of symbols]

[0240] 1 tank 2,2a,2b Wedge 2c ridge 3 racks 31 First Rack 32 Second Rack 3a, 3a' First lateral guidance device 3b, 3b' Second lateral guidance device 3c, 3c' Third lateral guidance device 3d,3d' head section 4. Grasping Device 5. Bearing Device 6. Suction Device W wafer H, H' holding device

Claims

1. At least one wedge (2) and a pair of first lateral guide devices (3a, 3a'), a pair of second lateral guide devices (3b, 3b') and a pair of third lateral guide devices (3c, 3c'). A method for drying a wafer (W) located inside a tank (1) by using a mechanism comprising: the pair of first lateral guidance devices (3a, 3a') are arranged below the pair of second lateral guidance devices (3b, 3b'), and the pair of second lateral guidance devices (3b, 3b') are arranged below the pair of third lateral guidance devices (3c, 3c'); The method comprises the steps of: i) moving the at least one wedge (2) vertically upward until it reaches the lowest point of the wafer, and moving the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b') vertically upward, where the wafer (W) comes into contact with the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b'), and an upper region of the wafer (W) is lifted out of the bath (1), where the pair of third lateral guiding devices (3c, 3c') does not come into contact with the wafer; ii) moving the wedge (2) vertically upward until the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b') are no longer in contact with the wafer (W) while still below the liquid level of the bath (1), and then the pair of third lateral guiding devices (3c, 3c') contacts the wafer above the liquid level of the bath (1); iii) raising the wafer (W) above the liquid level of the tank (1) where the pair of third lateral guiding devices (3c, 3c') contact the wafer (W).

2. iv) moving the wedge (2) vertically downward until the wafer (W) comes into contact with at least one of the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b'); v) further moving the wedge (2) vertically downward until it no longer contacts the wafer (W); further comprising 2. The method for drying a wafer (W) according to claim 1, wherein the liquid level in the tank (1) is lowered until the liquid level is below the wedge (2) in parallel with steps iv) and / or v) or after step v).

3. 3. The method according to claim 1 or 2, wherein the bath (1) contains water and at least one additional surface tension reducing substance, preferably isopropanol.

4. 10. The method according to any one of the preceding claims, wherein the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b') and / or the pair of third lateral guiding devices (3c, 3c') consist of a pair of webs arranged in contact with opposite sides of the wafer (W, W1, W2).

5. 5. The method according to claim 2, wherein in step i) the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b') remain immersed in the bath (1), and at the end of step v) the pair of third lateral guiding devices (3c, 3c') preferably does not contact the wafers (W, W1, W2).

6. 10. The method according to any one of the preceding claims, wherein the wedge (2, 2a, 2b) is provided with a suction device (6) capable of applying a vacuum when the upper end of the wedge (2, 2a, 2b) is located above the liquid level.

7. 10. The method according to any one of the preceding claims, wherein the wedges (2, 2a, 2b) exhibit a surface structure that increases the surface tension.

8. The lifting speed depends on the position of the lowest point of the wafer (W), The method according to any one of claims 1 to 7, wherein the speed is between 0.8 and 1.2 mm / s when the lowest point of the wafer (W) is more than 1.2 cm below the liquid level, or between 0.4 and 0.5 mm / s when the lowest point of the wafer (W) is less than 1.2 cm below the liquid level, and becomes at least 30 mm / s, preferably at least 40 mm / s, and more preferably at least 50 mm / s as soon as the lowest point of the wafer (W) reaches the liquid level.

9. the pair of first lateral guiding devices (3a, 3a'), the pair of second lateral guiding devices (3b, 3b') and the pair of third lateral guiding devices (3c, 3c') are provided on a rack (3); 9. The method according to claim 1, wherein in step i) the rack (3) is moved, and in step iii) the wafer (W) is raised above the liquid level of the tank (1), where the pair of third lateral guiding devices (3c, 3c') and the wedge (2) come into contact with the wafer (W).

10. 9. The method according to claim 1, wherein the pair of third lateral guiding devices (3c, 3c') is located above the liquid level in all process steps and is movable independently from the pair of first lateral guiding devices (3a, 3a') and the pair of second lateral guiding devices (3b, 3b'), and the third lateral guiding devices (3c, 3c') are horizontally movable relative to each other.

11. 11. The method according to claim 10, wherein the wedge (2) remains below the liquid level in all process steps.

12. 12. A method according to claim 10 or 11, wherein in step iii) the distance between the points at which the third lateral guiding device (3c, 3c') contacts the wafer (W) is continuously reduced.

13. The method according to any one of claims 10 to 12, wherein the third lateral guiding device (3c, 3c') is mounted eccentrically or presents an oval shape and is adapted to perform a rotational movement.

14. Oxide surface is 25 mm ２ III-V wafers (W, W1, W2) exhibiting a defect area of ​​less than 1000 nm, and the III-V wafer (W) is semi-insulating or semi-conductive.

15. The oxide surface is 15 mm ２ Less than 10 mm, preferably ２ less than, more preferably 5 mm ２ 15. III-V wafer (W, W1, W2) according to claim 14, which exhibits a defect area of ​​less than 1000 Å, and which is semi-insulating and preferably made of GaAs or InP, more preferably made of undoped or carbon-doped GaAs or iron-doped InP.

16. 15. The III-V wafer (W, W1, W2) according to claim 14, wherein the III-V wafer is semiconducting, the wafer being a GaAs wafer and containing silicon as a dopant, or the III-V wafer being an InP wafer and containing sulfur as a dopant.

17. 1. A device for drying a wafer, comprising: a reservoir (1) containing a liquid; Wedge (2) and At least one vertically movable bearing device (5), said at least one rack 3; 31, 32 is mounted in said bearing device (5) and comprises a pair of first lateral guide devices (3a, 3a'), a pair of second lateral guide devices (3b, 3b') and a pair of third lateral guide devices (3c, 3c'); the pair of first lateral guidance devices (3a, 3a') are arranged below the pair of second lateral guidance devices (3b, 3b'), and the pair of second lateral guidance devices (3b, 3b') are arranged below the pair of third lateral guidance devices (3c, 3c'); the distance between the pair of first lateral guidance devices (3a, 3a') is shorter than the distance between the pair of second lateral guidance devices (3b, 3b'), and the distance between the pair of second lateral guidance devices (3b, 3b') is shorter than the distance between the pair of third lateral guidance devices (3c, 3c'); a wedge (2) is provided below the rack (3) and is vertically movable separately from the bearing device (5); wherein the wedge (2) comprises at least two wedge portions (2a, 2b), both of which are vertically movable independently of each other; At least a first rack (31) can be suspended in the bearing device (5) such that the center of the at least first rack (31) is located above the tip of the first wedge portion (2a), and further, a second rack (32) can be suspended in the bearing device (5) such that the center of the second rack (32) is located above the tip of the second wedge portion (2b).

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