Method for the production of a iii-v substrate, in particular a gaas and inp substrate

Abstract

The present invention relates to a method for drying a wafer (W, W1, W2) which is in a bath (1), and to an undoped and doped wafer (W, W1, W2) according to the invention, as well as to a device for drying wafers (W, W1, W2). It is ensured that the travel distance of the wafers (W, W1, W2) is as short as possible, only a few drops remain stuck on the wafer (W, W1, W2), and the wafer (W, W1, W2) thus has an as homogeneous as possible oxide surface, and the number / area of the defective surfaces due to drops remaining stuck after the Marangoni drying process can be minimised. As a result, there is little, or better, no contact between the wafer (W) and the rack (3; 31, 32) / guide device (3a. 3a'; 3b, 3b'; 3c, 3c') on passage through the water surface. As a result, the constant overflow can be maintained, i.e. preferably the water level does not drop as long as the wafers (W) (and ideally also the rack (3; 31, 32)) are being dried.

Description

[0001] METHOD FOR PRODUCING A III-V SUBSTRATE, IN PARTICULAR A GAAS AND INP SUBSTRATE

[0002] The present invention relates to a method for producing improved surfaces of III-V substrates, as well as the III-V substrates themselves, with the materials GaAs and InP being of particular importance here.

[0003] BACKGROUND OF THE INVENTION

[0004] III-V substrates, especially gallium arsenide substrates, and especially their wafers, are used for various applications and are becoming increasingly important economically. Examples include high-frequency amplifiers and switches, but also light-emitting components, semiconductor lasers, and diodes. Transistors and diodes, in particular, are manufactured from single-crystal chemical compounds grown epitaxially. Growth parameters can be adapted to the crystal lattice. Lattice-matched epitaxy guarantees high quality and low defect densities; however, the quality depends not only on the conditions during epitaxy but also on the substrate properties themselves, which often influence the quality.In the case of gallium arsenide, the particular problem is that an oxide layer can quickly form on the substrate surface, which, if not properly treated, can develop into an inhomogeneous composition (gallium oxide and arsenic oxide in different oxidation states). The thermal properties of oxides with different compositions can vary considerably. However, for subsequent epitaxial processes, it must be guaranteed that the oxide layer can be easily removed under thermal conditions. For example, the prior art includes document EP 2 629 319 A1, which shows that gallium arsenide, in particular, has special physical and chemical surface properties that differ significantly from other semiconductors, such as silicon.Because the surface of a gallium arsenide wafer contains gallium atoms and arsenic atoms, which have different chemical properties (including reactivity), surface reactivity is a special phenomenon: The surface layer can consist of gallium dioxide (Ga2O3), arsenic trioxide (AS2O3), arsenic pentoxide (AS2O5), and a small amount of elemental arsenic. When growing gallium arsenide, the surface must be prepared using a specific process described in this document: treatment with 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 dilute acid solution or a dilute alkali solution, washing the wafer again with deionized water, and finally drying the corresponding wafer.

[0005] During the surface treatment of gallium arsenide, foreign particles can easily adhere, which is detrimental to subsequent epitaxial processes because they would cause an increased number of defects. Further prior art (Klaus Wolke et al., "Marangoni wafer drying avoids disadvantages," Solid State Technology, August 1996) describes the Marangoni drying process of silicon wafers. It is disclosed that Marangoni drying is based on a physical force that moves liquids from surfaces with different surface tensions, thus establishing an equilibrium. Small amounts of water with a low surface tension (containing absorbed isopropanol) move into a bulk liquid with a normal surface tension. For example, an isopropanol-nitrogen atmosphere can be used, which has a low surface tension. Normal water, on the other hand, has a higher surface tension.Water forms a positive meniscus when solids cross the gas-liquid interface, for example, when wafers are removed from a bath. When water-soluble materials such as isopropanol are present in the atmosphere, a higher concentration of solvent is found in the meniscus compared to the rest of the bath. Thus, when a wafer is pushed out of the bath, the water in the meniscus is drawn down into the bulk liquid, resulting in a completely dry wafer surface, with no adhering water plugs on the wafer surface that can cause so-called water spots.

[0006] The Marangoni effect is caused by a difference in interfacial tension. A fluid, in this case water, then flows along the wafer in the direction of the higher tension, which causes water to be removed from the wafer, allowing the wafer to dry without residue.

[0007] Marangoni drying of semiconductor wafers is based on the spatial separation of wafers and ultrapure water under the influence of a surface tension gradient in the interface of the ultrapure water that touches the wafer. This spatial separation can be achieved by lifting the wafers from a process tank filled with ultrapure water in a wet process system for semiconductor wafers or by lowering the water level.

[0008] Document WO 2014 / 124980 A2 discloses a method for producing GaAs substrates and a gallium arsenide substrate produced therefrom, wherein the method includes Marangoni drying. It was found that certain surface cleaning steps (acidic cleaning, alkaline cleaning, contact with an oxidizing agent) in combination with Marangoni drying contribute to a significant improvement in the homogeneity of the oxide surface compared to processes in which Marangoni drying is not used as a drying process after the cleaning steps. The number of defects and the defect area on the wafer surface could thus be massively reduced compared to a process that does not use Marangoni drying. Here, the defect areas are those areas where the measurement signal of a candela ellipsometry lies outside defined threshold values.This is a standard function of the candela ellipsometer and is output directly by the device. Marangoni drying is ideal for drying semiconductor wafers after wet-chemical cleaning. Drying is preferably carried out evenly over the entire surface and largely residue-free.

[0009] Before drying begins, the semiconductor wafers are typically positioned vertically in a process carrier located in a process tank filled with deionized water. This tank is often the last tank in a so-called wet bench: a series of sequentially arranged, liquid-filled tanks in which the wafers are subjected to the chemical and rinsing steps required for cleaning. In the high-productivity semiconductor industry, the process carriers containing the wafers are typically transferred from tank to tank by an automatic handling system after the specified process time has elapsed.

[0010] Drying according to the Marangoni process exists in various forms. However, all Marangoni processes are based on common basic principles:

[0011] A liquid suitable for lowering the surface tension of the water in the pool is applied to the surface. This is usually isopropyl alcohol (isopropanol, abbreviated to IPA).

[0012] The actual drying process occurs through the slow spatial separation of the wafers and the upper water layer, whose surface tension is reduced by the isopropanol. This spatial separation can be achieved in various ways, such as by lifting the wafers out of the water, lowering the water level, or a combination of both.

[0013] For a good drying result, the relative speed of wafer removal and water level is in the range of, for example, 1 mm / s.

[0014] Water droplets, so-called residual droplets, can adhere to the inevitable contact points between the wafer and the holding device as they pass through the phase boundary during Marangoni drying. These droplets can lead to a chemically altered oxide layer that negatively impacts the crystalline quality of the epitaxial layers deposited on the wafers during component production. Delayed and uncontrolled drying of water can cause damage to the wafer surface. During the further processing of semiconductor wafers into electronic or optical components, extremely surface-sensitive coating processes can be used within the framework of so-called planar technology, in which thin semiconductor layers are deposited in single-crystalline form on the surface of the wafer. This process, known as epitaxy, places extremely high demands on the surface quality of the semiconductor wafers.

[0015] So-called 111-V semiconductors, especially GaAs and InP, are characterized by a modified surface tension, significantly increased surface reactivity, and a more complex chemical composition of the oxide layer compared to silicon wafers, for example. The preferential further processing of these wafers using monocrystalline coating with other III-V materials also places considerably higher demands on the lateral uniformity of the oxide layer composition than with silicon wafers. Residual droplets during Marangoni drying can therefore form more easily with III-V semiconductor wafers and have a more negative impact on subsequent processes in component manufacturing.

[0016] In the dry state, the surface of certain semiconductor wafers (particularly GaAs and InP) is always covered with a thin, non-crystalline oxide layer. This layer is typically only 1 to 2 nanometers thick (with InP, layer thicknesses below 1 nm are even possible) and therefore consists of only a few atomic layers. During wet-chemical cleaning and rinsing processes, the oxide layer undergoes complex changes, being removed, regenerated, or altered in its composition.

[0017] The oxide layer formed on the wafer surface after the cleaning, rinsing and drying processes has a passivating effect and, in some applications, is only thermally removed from the wafer surface immediately before epitaxial coating.

[0018] However, an optimal and laterally uniform composition of the oxide layer is a crucial prerequisite so that the starting surface for epitaxy remaining after thermal desorption of the oxide layer enables the best possible crystallographic coupling of the layers to be deposited over the entire area, and thus an optimal current flow in the components later produced from these epitaxial layers.

[0019] Delayed and uncontrolled drying of water droplets remaining after Marangoni drying causes an unfavorable change in the composition of the oxide layer in the affected areas of the wafer surface, with partially crystalline regions. In these disturbed areas of the wafer surface, desorption of the surface oxide prior to the epitaxial process can result in incomplete desorption, resulting in a roughening of the wafer surface. The single-crystal growth of the functional layers is subsequently disrupted, leading to the formation of crystal defects such as dislocations, grain boundaries, or twin lamellae. This ultimately disrupts the current flow in the components produced from the epitaxially grown material, and can lead to yield losses.

[0020] In the Marangoni drying process, there are basically different ways of drying a wafer after surface treatment and of removing a wafer from the bath.

[0021] In one variant, a wafer or a group of wafers is held in a water bath by a rack (a holding arrangement with rods). In this first variant, the rinse water is drained (usually after the cleaning step with deionized water). However, within the scope of the present invention, it was recognized that residual drops often occur at the contact points of the wafer or wafers where they are held by the rack, disrupting homogeneous drying. The quality of the surface oxide layer on the wafer surface thus deteriorates locally, and the surface oxide layer becomes inhomogeneous, leading to lower quality in epitaxial layers grown later.

[0022] In the second variant, the wafers are lifted out of the water bath by a vertically pushed wedge. The wafers are temporarily held by this wedge and by wafer holders, for example, in the dryer lid. In this variant, it was recognized within the scope of the present invention that residual droplets can be avoided at many contact points; however, a droplet is usually present in the area of ​​the wedge when passing through the water surface. Furthermore, due to the fixed arrangement of the wafer holder in the dryer lid, only wafers with a specific wafer diameter can be dried.

[0023] Further methods for lifting a wafer or a group of wafers from a cleaning bath are disclosed in document WO 2001 / 078112 A1. This method involves two opposing gripping elements with mutually facing pick-up tips. These gripping arms can grip wafers when they are pushed out of the water surface by a wedge.

[0024] Furthermore, document DE 199 243 02 A1 discloses a method for drying substrates according to the Marangoni effect. Here, when the substrate is removed from the treatment fluid, at least one additional fluid is applied laterally to the substrate and onto the treatment fluid and directed into the areas between the substrates.

[0025] Furthermore, from the document DE 10 359 320 A1 a method for drying substrates is known, wherein substrates are removed from the bath of the treatment liquid and are applied to the treatment liquid by means of at least two opposing feed devices directed towards each other in a fluid which reduces the surface tension of the treatment liquid, which results in the supply of the fluid which reduces the surface tension of the treatment liquid being controlled in such a way that the opposing feed devices are alternately supplied with fluid.

[0026] The methods known from the prior art are often complex in terms of equipment; they still suffer from, or even knowingly accept, the disadvantage that residual droplets remain when the wafers are removed from the treatment fluid, causing "spots" on the wafer. These spots can disrupt subsequent epitaxial growth of thicker crystal layers. In the context of the present disclosure, "spots" refer to surface defects resulting from droplets adhering to the wafer and detectable using candela surface ellipsometry.

[0027] For example, "spots" chemically mean a changed surface oxide composition on the wafer surface compared to the areas where no such spots occur.

[0028] It is therefore an object of the present invention to provide a method that is not complex in terms of equipment and is easy to implement, with which wafers of various sizes can be dried and in which the formation of residual droplets during wafer removal can be minimized or, if possible, completely avoided. Providing III-V wafers with a very homogeneous oxide surface can be considered a further object of the present invention.

[0029] SUMMARY OF THE INVENTION

[0030] This object is achieved by a method according to claim 1, a III-V wafer according to claim 14 or 16 and a device for drying wafers according to claim 18. Further advantageous embodiments of the present invention are the subject of the corresponding subclaims.

[0031] To characterize the surface properties of the respective wafers, ellipsometric surface mappings were performed using a Candela surface ellipsometer. Details of the corresponding measurements are explained in the description and examples.

[0032] Without limiting the invention, the following points are presented to describe main aspects, preferred embodiments and special features of the present invention as follows:

[0033] 1 . Method for drying a wafer (W) which is located in a bath (1), by means of an arrangement which has 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'), wherein the pair of first lateral guide devices (3a, 3a') is arranged below the pair of second lateral guide devices (3b, 3b'), and the pair of second lateral guide devices (3b, 3b') is arranged below the pair of third lateral guide devices (3c, 3c'), and wherein the method comprises the following steps: i) Vertically moving the at least one wedge (2) upwards until it touches the wafer at its lowest point, vertically moving the pair of first lateral guide devices (3a, 3a') and the pair of second lateral guide devices (3b,3b') upwards, wherein the wafer (W) contacts the pair of first lateral guide devices (3a) and the pair of second lateral guide devices (3b), wherein an upper region of the wafer (W) is pushed out of the bath (1), wherein the pair of third lateral guide devices (3c) does not contact the wafer; ii) Moving the wedge (2) vertically upwards until the pair of first lateral guide devices (3a, 3a') and the pair of second lateral guide devices (3b, 3b') no longer contact the wafer (W) while they are still below the liquid surface of the bath (1), wherein the pair of third lateral guide devices (3c, 3c') contact the wafer above the liquid surface of the bath (1); iii) pushing out the wafer (W) above the liquid level of the bath (1 ), wherein the pair of third lateral guide devices (3c, 3c') touches the wafer (W).

[0034] In one embodiment, the distance between the pair of first lateral guide devices (3a, 3a') is smaller than the distance between the pair of second lateral guide devices (3b, 3b'), and the distance between the pair of second lateral guide devices (3b, 3b') is smaller than the distance between the pair of third lateral guide devices (3c, 3c').Method for drying a wafer (W) according to item 1, further comprising the following steps: iv) moving a wedge (2) vertically downwards until the wafer (W) touches at least one of the pair of first lateral guide devices (3a) and the pair of second lateral guide devices (3b); v) further moving a wedge (2) vertically downwards until it no longer touches the wafer (W); wherein parallel to steps iv) and / or v) or after step v), the liquid level of the bath (1) is lowered until the liquid level is below the wedge (2). Method according to item 1 or 2, wherein the bath contains water and at least one further surface tension-reducing substance. Method according to item 3, wherein at least one further surface tension-reducing substance is isopropanol.Method according to one of the preceding points 2 to 4, wherein in step i) the pair of first lateral guide devices (3a, 3a') and the pair of second lateral guide devices (3b, 3b') remain immersed in the bath (1), and preferably at the end of step v) the pair of third lateral guide devices (3c, 3c') does not touch the wafer (W, W1, W2). Method according to one of the preceding points, wherein the pair of first lateral guide devices (3a, 3a'), the pair of second lateral guide devices (3b, 3b') and / or the pair of third lateral guide devices (3c, 3c') each consist of a pair of webs which are adapted to contact opposite sides of the wafer (W).Method according to one of the preceding points, wherein the pair of first lateral guide devices (3a, 3a'), the pair of second lateral guide devices (3b, 3b'), and optionally the pair of third lateral guide devices (3c, 3c') are further held by a support device (3d), so that a vertical movement of the pair of first lateral guide devices (3a, 3a'), the pair of second lateral guide devices (3b, 3b'), and optionally the pair of third lateral guide devices (3c, 3c') always occurs synchronously. Method according to one of the preceding points, wherein in step i), the pair of first lateral guide devices (3a, 3a') and the pair of second lateral guide devices (3b, 3b') remain immersed in the bath (1).Method according to one of the preceding points 2 to 8, wherein at the end of step iv) and v) the pair of third lateral guide devices (3c, 3c') does not touch the wafer (W). Method according to one of the preceding points, wherein step ii) further comprises fixing the wafer by an additional gripping device (4) provided above the liquid level of the bath (1). Method according to one of the preceding points, wherein the wedge (2) is provided with suction devices (6) to which a negative pressure is applied when the upper tip of the wedge (2) is above the liquid level. Method according to point 11, wherein the suction devices (6) are openings in the wedge (2, 2a, 2b). Method according to one of the preceding points, wherein the wedge (2) is made of plastic, preferably polyetheretherketone (PEEK).Method according to one of the preceding points, wherein the wedge (2) has a surface tension-increasing surface structure.

[0035] This is achieved, for example, by plasma treatment. The method according to any one of the preceding points, wherein the pair of first lateral guide devices (3a, 3a'), the pair of second lateral guide devices (3b, 3b'), and the pair of third lateral guide devices (3c, 3c') have prongs. Method according to one of points 1 to 15, wherein the lifting speed depends on the position of the lowest point of the wafer (W) and 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, 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 at least 30 mm / s, preferably at least 40 mm / s, more preferably at least 50 mm / s, as soon as the lowest point of the wafer (W) has reached the liquid level.Method according to one of items 1 to 16, wherein the pair of first lateral guide devices (3a, 3a'), the pair of second lateral guide devices (3b, 3b') and the pair of third lateral guide devices (3c, 3c') are provided on a tray (3), and in step i) the tray (3) is moved, in step iii) the wafer (W) is pushed out above the liquid level of the bath (1), wherein the pair of third lateral guide devices (3c, 3c') and the wedge (2) touch the wafer (W). 18.Method according to one of points 1 to 16, wherein the pair of third lateral guide devices (3c, 3c') is positioned above the liquid level in all method steps and is movable independently of the pair of first lateral guide devices (3a, 3a') and the pair of second lateral guide devices (3b, 3b'), and the third lateral guide devices (3c, 3c') are horizontally movable relative to one another. Method according to claim 18, wherein the wedge (2) remains below the liquid level in all method steps. Method according to one of points 18 or 19, wherein in step iii) the distance between the points at which the third lateral guide devices (3c, 3c') contact the wafer is continuously reduced. Method according to one of points 18 to 20, wherein the third lateral guide devices (3c, 3c') are adapted to perform a horizontal movement relative to one another.Method according to one of items 18 to 21, wherein the third lateral guide devices (3c, 3c') are either mounted eccentrically or have an oval shape and are adapted to perform a rotational movement. A III-V wafer (W), wherein at least one surface of the wafer has an oxide layer, wherein this surface or its oxide layer has a defect area of ​​less than 25 mm. 2 and wherein the III-V wafer (W) is semi-insulating.

[0036] For many compounds (such as GaAs), semi-insulating means that the Fermi level is located near the middle of the band gap. In the case of GaAs, the intrinsic point defect EL2 (arsenic antisite on gallium site) can provide this, along with a certain amount of carbon (C) doping. In the case of InP, doping with iron is necessary to achieve semi-insulating properties.

[0037] The following applies to the charge carrier concentration: At a charge carrier concentration of less than 1x1010 cm -3 Wafers are considered semi-insulating if the charge carrier concentration is above 1x10 10 cm' 3 semiconducting. The determination of charge carrier concentration is described in the standard "SEMI M39".

[0038] According to the “SEMI M87” standard, the specific resistance for semi-insulating wafers is more than 1x10 5 Qcm, below this value the wafers can be considered semiconducting. III-V wafers (W) according to item 23, where the oxide surface has a defect area of ​​less than 15 mm 2 , preferably less than 10 mm 2 , further preferably under 5 mm 2 A III-V wafer (W) which is final polished on at least one side, dried and semi-insulating and has an oxide layer on the entire surface, wherein a surface which has a modified surface oxide composition compared to the remaining total surface of the III-V wafer is less than 5 mm 2 amounts.

[0039] A measurement is carried out here by candela surface ellipsometry with the measurement channel QAbsPhase. III-V wafer (W) according to item 23, 24 or 25, wherein the Hl element is selected from Ga and In, and the V element is selected from As and P. III-V wafer (W) according to item 26, wherein the III-V wafer consists of GaAs or InP, wherein GaAs can be undoped or doped with carbon (C) or the InP can be doped with iron (Fe). III-V wafer (W) according to any one of items 23 to 27, wherein the specific resistance is between 1x10 8 and 8x10 8 Qcm. III-V wafer (W), wherein at least one surface of the wafer has an oxide layer, wherein this surface or its oxide layer has a defect area of ​​less than 25 mm 2 and wherein the III-V wafer (W) is semiconducting.

[0040] A measurement is carried out here using candela surface ellipsometry with the QAbsPhase measurement channel.

[0041] The following applies to the charge carrier concentration: At a charge carrier concentration of less than 1x10 10 cm' 3 Wafers are considered semi-insulating if the charge carrier concentration is above 1x10 10 cm' 3 Semiconducting. The determination of the charge carrier concentration is described in the standard "SEMI M39". III-V wafer (W) according to item 29, wherein the III-V wafer (W) contains silicon or sulfur as a dopant. III-V wafer (W) according to item 30, wherein the III-V wafer is a GaAs wafer and contains silicon as a dopant. III-V wafer (W) according to item 30, wherein the III-V wafer is an InP wafer and contains sulfur as a dopant. A dried, semiconducting III-V wafer (W) that has been final polished on at least one side and has an oxide layer on the entire surface, wherein a surface that has a different surface oxide composition compared to the remaining total surface of the III-V wafer (W) is less than 25 mm 2 amounts.

[0042] A measurement is also carried out here by candela surface ellipsometry with the measurement channel QAbsPhase. III-V wafer (W) according to one of the points 29 to 33, with the charge carrier concentration between 1x10 18 cm' 3 and 9x10 18 cm' 3 InP wafer (W) according to any one of items 29 to 34, whose oxide surface has a defect area of ​​less than 20 mm 2 , preferably less than 15 mm 2 , further preferably less than 10 mm 2 , even further preferably less than 5 mm 2 III-V wafer (W) according to any one of the preceding items 23 to 35, wherein the wafer diameter is at least 150 mm. III-V wafer (W) according to any one of items 23 to 36, wherein the wafer diameter is at least 200 mm. GaAs wafer (W) doped with silicon, a charge carrier concentration between 1x10 18 cm' 3 and 3x10 18 cm' 3, and wherein the oxide surface has a defect area of ​​less than 25 mm 2 InP wafer (W), which is doped with sulfur, has a charge carrier concentration between 1 ,5x10 18 cm' 3 and 9x10 18 cm' 3 , and wherein at least one surface of the wafer has an oxide layer, wherein this surface or its oxide layer has a defect area of ​​less than 25 mm 2 InP wafer (W), which is doped with sulfur, has a charge carrier concentration between 1 ,5x10 18 cm' 3 and 9x10 18 cm' 3 , and wherein at least one surface of the wafer has an oxide layer, wherein this surface or its oxide layer has a defect area of ​​less than 20 mm 2 , preferably less than 15 mm 2 , further preferably less than 10 mm 2 , even further preferably less than 5 mm 2III-V wafer (W) according to one of items 23 to 39 or InP wafer according to one of items 39 or 40, wherein the defect area is a continuous region. III-V wafer (W) according to item 41, wherein at least a part of the defect area contacts the edge of the wafer. III-V wafer (W) according to item 41 or 42, wherein at least a part of the defect area is max. 5 mm from the edge of the wafer. III-V wafer (W) according to one of items 41 to 43, wherein at least a part of the defect area is located in a circular ring between the edge of the wafer and a virtual circular line which is max. 10 mm from the edge of the wafer. III-V wafer (W) according to one of the items 41 to 44, wherein the entire defect area is located in a circular ring between the edge of the wafer and a virtual circular line which is max. 10.5 mm away from the edge of the wafer.The 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 a virtual circular line that is a maximum of 10 mm from the edge of the wafer. The III-V wafer (W) according to any one of items 41 to 46, wherein the wafer has a straight-ground portion or notch at a portion of the edge, and the defect area is opposite the straight-ground portion or notch.

[0043] The straight-ground section or notch serves as a "recognition feature" for transferring the azimuthal orientation of the crystal lattice, determined by X-ray imaging at the wafer manufacturer, to the exposure systems in a lithography line when the wafer is used for the production of electrical components (growth of epitaxial layer on wafer, lithography, etc.). A device for drying wafers, comprising: a bath (1) containing liquid; a wedge (2), at least one storage device (5) which is vertically movable; wherein at least one tray (3; 31, 32) is insertable into the storage device (5), wherein the at least one tray (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'), wherein the pair of first lateral guide devices (3a,3a') is arranged below the pair of second lateral guide devices (3b, 3b'), and the pair of second lateral guide devices (3b, 3b') is arranged below the pair of third lateral guide devices (3c, 3c'), and wherein the distance between the pair of first lateral guide devices (3a, 3a') is smaller than the distance between the pair of second lateral guide devices (3b, 3b'), and the distance between the pair of second lateral guide devices (3b, 3b') is smaller than the distance between the pair of third lateral guide devices (3c, 3c'), wherein the wedge (2) is provided below the tray (3) and is movable vertically separately from the storage device (5).

[0044] Vertical here means out of the bath or into the bath, i.e. parallel to the direction of gravity. Device according to item 48, wherein the wedge (2) can be moved vertically independently of the storage device (5) or tray (3). Device according to item 48 or 49, wherein the wedge (2) comprises at least two wedge sections (2a, 2b), wherein both wedge sections (2a, 2b) can be moved vertically separately from one another; 51. Device according to item 50, wherein at least one first tray (31) can be inserted into the storage device (5) such that the center of the at least first tray (31) is positioned above the tip of the first wedge section (2a), and furthermore a second tray (32) can be inserted such that the center of the second tray (32) is positioned above the tip of the second wedge section (2b).

[0045] 52. Apparatus according to item 51, wherein the first tray (31) is adapted to hold a wafer (W1) having a first diameter, and the second tray (32) is adapted to hold a wafer (W2) having a second diameter, the first diameter being smaller than the second diameter.

[0046] 53. Device according to one of the items 50 to 52, wherein the tip of the first wedge section (2a) and / or second wedge section (2b) is formed as a triangle, preferably a right-angled triangle.

[0047] 54. Device according to one of the items 50 to 53, while the first wedge section (2a) is divided into two parts and there are two regions in which the first wedge section (2a) and the second wedge section (2b) are arranged next to each other.

[0048] DESCRIPTION OF THE CHARACTERS

[0049] In the following, preferred embodiments of the present invention are described in more detail with reference to the accompanying figures.

[0050] Fig. 1 shows a Marangoni drying process according to the prior art.

[0051] Fig. 1 a) shows an arrangement of a wafer in a bath according to the prior art,

[0052] Fig. 1 b) shows the sequence of process steps, and Fig. 1 c) shows a obtained wafer with corresponding residual droplets according to the prior art.

[0053] Fig. 2 shows another method for Marangoni drying according to the prior art.

[0054] Fig. 2a) shows an arrangement of a wafer in a bath according to the prior art,

[0055] Fig. 2b) shows the sequence of process steps, and

[0056] Fig. 2c) shows a obtained wafer with corresponding residual droplets according to the prior art.

[0057] Fig. 3 shows a method according to the invention for producing a cleaned and dried wafer, for example a GaAs wafer, with a Marangoni drying according to one embodiment.

[0058] Fig. 3a) shows an arrangement of a wafer in a bath,

[0059] Fig. 3b) shows the sequence of process steps, and

[0060] Fig. 3c) shows a residual drop at the contact point of a wafer obtained according to the embodiment of the invention.

[0061] Fig. 4 shows a method according to the invention for producing a cleaned and dried wafer, for example, a GaAs or InP wafer, with Marangoni drying according to another embodiment. Fig. 4 a) shows the process steps, while Fig. 4 b) shows possible design details for securing the wafer above the liquid level.

[0062] Fig. 5 shows a detail of the exact sequence of step d) from Fig. 4 according to a first modification. Fig. 6 shows a detail of the exact sequence of step d) from Fig. 4 according to a second modification.

[0063] Fig. 7 shows a detail of the exact sequence of step d) of Fig. 4 according to a third modification.

[0064] Fig. 8 shows a concept for step d) of Fig. 4 according to a fourth modification.

[0065] Fig. 9 shows another embodiment of a device for drying wafers.

[0066] Fig. 10 shows two examples of trays in which several wafers can be held.

[0067] Fig. 11 shows an example of an evaluation routine for wafers or wafer groups, in which data recorded with a Candela surface ellipsometer are processed accordingly.

[0068] Fig. 12 shows several examples of residual plugs or their residues, which can be detected with a Candela surface ellipsometer and are measured accordingly with regard to their area.

[0069] Fig. 13 shows another example of an evaluation routine for wafers or wafer groups, in which data recorded with a Candela surface ellipsometer are processed accordingly.

[0070] Fig. 14 shows a comparison of the defect area between semi-insulating (in this case undoped) GaAs wafers dried using a method according to the invention as shown in Fig. 3 and wafers dried using a method according to Fig. 1. Fig. 15 shows a comparison of the defect area between semiconducting (in this case Si-doped) GaAs wafers dried using a method according to the invention as shown in Fig. 3 and wafers dried using a method according to Fig. 1.

[0071] Fig. 16 shows a comparison between semiconducting (in this case sulfur-doped) InP wafers dried by a method according to the invention as shown in Fig. 3 and wafers dried by a method as shown in Fig. 1, with regard to their defect area.

[0072] Fig. 17 shows a view of an apparatus for drying wafers, viewed from above.

[0073] Fig. 18 shows side views of an apparatus for drying wafers (in different states) according to another embodiment of the present invention.

[0074] Fig. 19 shows a comparison between semi-insulating (in this case Fe-doped) InP wafers dried by a method according to the invention as shown in Fig. 3 and wafers dried by a method as shown in Fig. 1, with regard to their defect area.

[0075] Fig. 1 shows a method for removing one or more wafers W from a bath 1.

[0076] Fig. 1a) shows a bath 1 (containing, for example, deionized rinse water to which a surfactant such as isopropanol has been added), containing a wafer W. Holding devices H and H' are located above the water surface, and the wafer W is held in the bath by two pairs of lateral guide devices 3a and 3a', and 3b and 3b'. A corresponding wedge 2 is located below the wafer, which is vertically movable and is used to lift the wafer.

[0077] The process steps are described in more detail in Fig. 1 b).

[0078] In step a) of the prior art method, the wafer W is located below the liquid surface of the bath 1, and the lateral first guide devices 3a, 3a' and second guide devices 3b, 3b' are also located below the liquid surface. The wedge 2 is located below the wafer W and does not touch it.

[0079] In step b), while the first and second lateral guide devices 3a, 3a', 3b, 3b' are moved upward, the wedge 2 is moved toward the wafer W. However, it does not necessarily have to touch it. Part of the wafer W is now above the liquid surface, but the first and second lateral guide devices 3a, 3a', 3b, 3b' are still below the liquid surface. The wafer W is in a state in which it cannot yet be held by the holding devices H and H'. It has not yet been lifted out of the bath.

[0080] In step c), only the wedge 2 is moved vertically upwards and pushes the wafer W partially out of the water bath; the wafer W already touches the holding devices H, H'. These can be provided, for example, in the lid of the dryer. However, the first and second lateral guide devices 3a, 3a', 3b, 3b' are still below the liquid surface and have not moved any further compared to step b). Because the wedge 2 has moved the wafer W further upwards, the first lateral guide devices 3a, 3a' no longer touch the wafer W - but the second lateral guide devices 3b, 3b' still touch.

[0081] In step d), the wafer W is pushed further upwards by the wedge 2 - the second lateral guide devices 3b, 3b' no longer touch the wafer W. However, the wafer W is held by the holding devices H, H'

[0082] In step e), liquid from bath 1 is drained; the liquid surface is below the wafer W. Therefore, the wafer W is dried. To allow the first and second lateral guide devices 3a, 3a', 3b, 3b' to be dried, the water level of the bath is lowered, thus draining the water. Wedge 2 still touches the wafer W. The first and second lateral guide devices 3a, 3a', 3b, 3b' have not moved any further compared to step c).

[0083] In step f), the surface of the water bath 1 is drained to such an extent that the first and second lateral guide devices 3a, 3a', 3b, 3b' and the wedge are above the liquid surface and thus also dry. The wedge 2 still touches the wafer W.

[0084] In step g), the wedge 2 is lowered. Due to the downward movement of the wedge 2, the wafer W is again held by the already dried first and second lateral guide devices 3a, 3a', 3b, 3b' and therefore touches them.

[0085] To prevent contact of the wafer W with the first and second lateral guide devices 3a, 3a', 3b, 3b' while passing the liquid surface of the bath 1, the wafer is pushed out of the first and second guide devices 3a, 3a', 3b, 3b' by the upwardly moving wedge 2 and is then held only by the holding devices H. Residual drops between the wafer and the first and second lateral guide devices 3a, 3a', 3b, 3b' are avoided. The holders H, H' are always above the water level and are therefore always dry and cannot cause residual drops. When passing the water level, only a residual drop can remain between the wafer W and the wedge 2.

[0086] The disadvantage of this method, however, is that it requires complex process control, with very high requirements for the spatial alignment of the moving parts relative to one another, particularly the wedge 2 and the first and second lateral guide devices 3a, 3a', 3b, 3b'. Since the holding devices H, H' are always adjusted to a single wafer size, wafers of different sizes cannot be dried using this method – a separate drying device would therefore be required for each size.

[0087] In Fig. 1c) it is clear that a residual drop T is present at the lower edge of the wafer W, which is created between the contact between wafer W and wedge 2. Fig. 2 shows an alternative method for drying one or more wafers from a bath 1, this method is also known from the prior art.

[0088] From Fig. 2 a), it is clear that the wafer W is again held by two pairs of first and second lateral guide devices 3a, 3a', and 3b, 3b'. These are again located in a bath 1.

[0089] The individual steps of the process are shown in Fig. 2 b):

[0090] In step a), the wafer is located below the water surface and is held by the first and second lateral guide devices 3a, 3a' and 3b, 3b'. Here, the first and second lateral guide devices 3a, 3a' and 3b, 3b' are not moved. The water bath 1, which contains water enriched with isopropanol in its near-surface layer, is drained at a predetermined rate.

[0091] In step b), the liquid surface is located above the pair of second guide devices 3b, 3b'.

[0092] In step c), the water is located below the wafer W, the first and second lateral guide devices 3a, 3a' and 3b, 3b' are above the liquid surface.

[0093] Due to the contact between the first and second lateral guide devices 3a, 3a', 3b, 3b' when lowering the liquid level, the contact points of the wafer with the first and second lateral guide devices 3a, 3a', 3b, 3b' often contain residual droplets, which accordingly impair the quality of the wafers. The quality of subsequently grown epitaxial layers is also compromised, which can lead to a poorer component yield. However, one advantage of this process is that it is technically less demanding and also allows for the drying of wafers of various sizes.

[0094] Fig. 2 c) shows a wafer W with residual droplets T at all four contact points. Fig. 3 shows a wafer drying method according to the present invention.

[0095] Fig. 3a) shows a state in which the wafer W is completely in bath 1.

[0096] Here, however, there are three pairs of lateral guide devices 3a, 3a', 3b, 3b', and 3c, 3c', which hold the wafer accordingly, wherein the pair of first lateral guide devices 3a, 3a' is arranged below the pair of second lateral guide devices 3b, 3b', and the pair of second lateral guide devices 3b, 3b' is arranged below the pair of third lateral guide devices 3c, 3c'.

[0097] The distance between the pair of first lateral guide devices 3a, 3a' is smaller than the distance between the pair of second lateral guide devices 3b, 3b', and the distance between the pair of second lateral guide devices 3b, 3b' is smaller than the distance between the pair of third lateral guide devices 3c, 3c'. In Fig. 3 a), the third lateral guide devices 3c, 3c' do not touch the wafer W. A wedge 2 is provided below the wafer.

[0098] The individual steps are described in more detail in Fig. 3b).

[0099] In step a), the wafer W is located below the liquid surface of the bath 1 and is held by the first pair of first lateral guide devices 3a, 3a' and the second pair of second lateral guide devices 3b, 3b'. The wedge does not touch the wafer. The pair of third lateral guide devices 3c, 3c' does not touch the wafer W. In step b), the wedge is moved to the wafer so that the tip of the wedge touches the wafer.

[0100] In step c), the lateral guide devices 3a, 3a', 3b, 3b' and 3c, 3c' as well as the wedge 2 are moved upwards. Here, the third lateral guide devices 3c, 3c' have already passed the water surface, but have no contact with the wafer W, i.e. they do not touch it. The wedge 2 remains moved towards the wafer W and touches it, but still below the water surface. In step d), the water level is still between the pair of second lateral guide devices 3b, 3b' and the third lateral guide devices 3c, 3c'. The wafer W is only slightly raised by the wedge 2, so that the wafer no longer touches the first pair of lateral guide devices 3a, 3a' and the second pair of lateral guide devices 3b, 3b'. For this purpose, the wafer W is in contact with the third pair of lateral guide devices 3c, 3c' above the liquid surface.The wafer is now held by the wedge 2 and the third pair of lateral guide devices 3c, 3c'.

[0101] In step e), the wafer W as well as the tip of the wedge 2 as well as the first pair of lateral guide devices 3a, 3a', the second pair of lateral guide devices 3b, 3b' and the third pair of lateral guide devices 3c, 3c' are above the water surface.

[0102] In step f), the wedge 2 is lowered, and the wafer is again held by the wedge 2 and the first pair of lateral guide devices 3a, 3a' and the second pair of lateral guide devices 3b, 3b', which have since dried. The third lateral guide devices 3c, 3c' no longer touch the wafer W.

[0103] In step g), the water level was lowered, the position of the wafer W relative to the three guide devices 3a, 3a', 3b, 3b' and 3c, 3c' as well as the wedge 2 has not changed compared to step f).

[0104] When passing through the liquid surface, there is only one contact point between the wafer W and the wedge 2 at which a residual drop can form.

[0105] In Fig. 3c) a residual drop is shown at the bottom of the contact point of the wedge 2, this does not have to occur, however, and if it does occur, it is smaller compared to the method according to Fig. 1 and Fig. 2. The speed of movement of the lateral guide devices 3a, 3a', 3b, 3b' and 3c, 3c' as well as the wedge 2 are always coordinated with one another such that the resulting travel speed for the wafers is always constant and can thus be adjusted. The travel path of the wafers during removal is significantly shorter compared to Fig. 1, which leads to a shorter process time. As a result, the contact time between the lower edge of the wafer W and the movable wedge 2, which is subject to residual moisture, is also shortened by several minutes. As a result, the risk of residual droplets forming at the contact points is also fundamentally reduced.Due to the shortened vertical distance between the wafer and the lateral guide devices 3a, 3a', 3b, 3b' and 3c, 3c', the wafer and the lateral guide devices can be dried almost simultaneously, which further shortens the process time.

[0106] This leads to a significantly higher productivity of the entire cleaning process, since drying is usually the slowest process step and thus the limiting step for the speed of the entire process.

[0107] The adjustment effort required to set up and correct the position of all components (wedge and lateral guide devices) is significantly reduced, complicated alignment between lateral guide devices is eliminated, and no inclined travel path is necessary. Furthermore, there is less risk of the wafer being subjected to mechanical stress due to inaccurate adjustment, which can lead to scratches on the wafer, damage to the wafer edge, and wafer breakage.

[0108] The reduced risk of residual drops and mechanical stress on the wafers due to inaccurate adjustment is particularly important for the drying of larger wafers (e.g., over 150 mm), since the unfavorable leverage ratios would require significantly more adjustment effort and lower tolerances compared to smaller wafer diameters in order to ensure consistent wafer quality.

[0109] Compared to the process in Fig. 1, the contact time between wedge 2 and wafer W can be reduced from several minutes to a few seconds, which significantly reduces the probability of residual droplets forming at the only remaining initial contact point (between wedge 2 and wafer W). If these residual droplets do occur, they are significantly smaller.

[0110] Preferably, the wafers are lifted at a speed of approximately 1 mm / s. For drying the lower section of the wafer (approximately 1 cm), the lift speed is significantly reduced to below 0.5 mm / s to reduce contact droplets.

[0111] The lift-off speed is the speed at which the wafer moves relative to the liquid level.

[0112] Since excessive fluctuations in the water level can be reflected in the chemical composition of the oxide layer, this speed reduction must be carried out gradually.

[0113] Exactly when the lower edge of the wafer W has reached the water level, the wafers W must be separated from the water level at high speeds (> 30 mm / s, preferably > 40 mm / s, more preferably > 50 mm / s) and, at the same time, the wedge 2 must be separated from the lower edge of the wafers W in the opposite direction.

[0114] Particularly with n-doped GaAs, precise adherence to this boundary condition is necessary due to its high surface tension. This is the only way to prevent water from the water level and residual moisture from wedge 2 from being drawn back onto the wafer surface.

[0115] Fig. 4 shows another embodiment of a method for Marangoni drying. In particular, Fig. 4 a) shows the sequence of process steps. In step a), the wafer W is located below the liquid surface and is held by pairs of first and second lateral guide devices 3a, 3a' and 3b, 3b'. The water bath 1 contains water enriched with isopropanol on its surface.

[0116] A pair of third lateral guide devices 3c, 3c' are located above the liquid surface. These function as dry receivers, so to speak.

[0117] In step b), the wafer W is slightly lifted by a wedge 2. A portion of the wafer is above the water surface, and the wedge 2 is in contact with the lower edge of the wafer W. The wafer is still held below the water surface by the lateral guide devices 3a, 3a' and 3b, 3b', which have, however, moved slightly upward. The pair of third lateral guide devices 3c, 3c' is still above the water surface and is not in contact with the wafer.

[0118] In step c), the position of the pair of first lateral guide devices 3a, 3a' and the pair of second lateral guide devices 3b, 3b' remains constant. However, the wedge 2 has further raised the wafer so that it is only in contact with the pair of second lateral guide devices 3b, 3b', but not with the pair of first lateral guide devices 3a, 3a'. The position of the pair of third lateral guide devices 3c, 3c' has not changed compared to step b).

[0119] In step d), the wafer W was completely lifted out of the liquid bath. However, the wedge 2 remains below the liquid surface. The pair of third lateral guide devices 3c, 3c' has moved horizontally, and the distance between the third lateral guide devices 3c, 3c' has decreased. Either the third lateral guide devices 3c, 3c' can have a holding function, or an additional gripping device 4, as shown in Fig. 9 (but not in the present figure), can be used to hold the wafer W above the liquid surface.

[0120] These hold the wafer W above the water surface. In step e), the liquid level is now lowered by draining water. In step f), the position of the first and second lateral guide devices 3a, 3a', 3b, 3b' remains unchanged, but the pair of third lateral guide devices 3c, 3c' is moved horizontally, and the distance between the third lateral guide devices 3c, 3c' increases again, so that the wafer W now rests, among other things, on the wedge 2. The wafer W is then held by the wedge 2 and the second lateral guide devices 3b, 3b' from the moment the third lateral guide devices 3c, 3c' no longer touch the wafer. Thus, both the wedge 2 and all guide devices 3a, 3a', 3b, 3b' and 3c, 3c' are dried.In step g), the wedge 2 is lowered so that the wafer W is again held by the pair of first lateral guide devices 3a, 3a' and the second pair of lateral guide devices 3b, 3b'.

[0121] This process has the special feature that it is possible for the wafer to pass through the water surface without any contact with any tool, i.e. neither with any of the guide devices 3a, 3a', 3b, 3b' and 3c, 3c', nor with the wedge 2. The wedge 2 remains below the liquid surface during all wafer removal steps, while the pair of third lateral guide devices 3c, 3c' always remains above the liquid surface and thus never gets wet.

[0122] Fig. 4 b) shows how, for example, starting from step d) in Fig. 4 a), the wafer can be additionally held. On the left, the third lateral guide devices 3c, 3c' are shown in a T-shape, which allows for better holding of the wafer W. The right-hand view shows gripping devices 4, which can additionally hold the wafer W above the liquid surface and are also adjustable with respect to the wafer diameter.

[0123] In general, the embodiments of the method according to the invention (Figs. 3 and 4) operate by draining the water in the process tank only when the wafer is completely above the liquid surface. This allows for a constant flow of ultrapure water (so-called overflow). The surface of the liquid level, on which particles can float, is thus always well permeated, and liquid exchange takes place. In a method according to Fig. 2, the liquid level is lowered while the wafer W is still at least partially immersed in the bath. An overflow at the liquid surface is then no longer possible, where particles can easily accumulate and adhere to the wafers W to be dried – this then degrades the quality of the epitaxial layer.

[0124] Fig. 5 shows a more detailed representation of the sequence of step d) from Fig. 4 according to a first variation - sub-steps are shown, so to speak. Here, in step d-1), the wafer W is almost completely above the liquid level, the wedge 2 is below the liquid level, and the pair of third lateral guide devices 3c, 3c' is above the liquid level and rests on 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 continually reduced, but the wedge 2 always remains below the liquid surface. In step d-3), the entire wafer is already above the water surface, while in step d-4) the wafer has moved slightly upwards. The third lateral guide devices 3c, 3c' are thus dry transfer devices, they are always above the liquid surface and therefore never get wet.Only a horizontal movement of the third lateral guide devices 3c, 3c' is necessary. The wafer slides along the third lateral guide devices 3c, 3c'.

[0125] Fig. 6 shows a more detailed representation of the sequence of step d) from Fig. 4 according to a second modification - sub-steps are shown, so to speak. Here, only the structure of the third lateral guide devices 3c, 3c' is different. These are oval here, and a horizontal movement and a rotational movement are necessary to move the wafer W. Here, too, only the lifting of the last few millimeters of the entire wafer W from the liquid bath, as shown in step d) in Fig. 4, is carried out in correspondingly more detail. In step d-1 ), the wafer rests against two inclined oval third lateral guide devices 3c, 3c', the long side of the oval shape rests against the wafer. The wafer is almost completely lifted out of the water bath, only submerged in the water by one millimeter. The wedge 2 always remains under water.Now, in step d-2), the oval third lateral guide devices 3c, 3c' rotate, so that the wafer is rotated slightly further upward. In steps d-3) and d-4), the third lateral guide devices 3c, 3c' are rotated further until the wafer is completely above the liquid level.

[0126] Fig. 7 shows a more detailed representation of the sequence of step d) from Fig. 4 according to a third modification – sub-steps are shown, so to speak. Here, the dry transfer devices, i.e., the third lateral guide devices 3c, 3c', have an eccentric axis, requiring a horizontal movement and a rotational movement to move the wafer W. In step d-1), the wafer is still slightly below the liquid level. In step d-2), the third lateral guide devices 3c, 3c' rotate, which is why the wafer is lifted slightly upwards. In step d-3), the third lateral guide devices 3c, 3c' have rotated further, so that the wafer is already above the liquid level. In step d-4), it is lifted slightly above the liquid surface. The wedge 2 always remains underwater. Fig. 8 shows an illustration of a K1-supported adaptive control system for wafer lifting.Here, wafer W is shown, which has a radius R. Furthermore, the pair of third lateral guide devices 3c, 3c' is shown asymmetrically. The interaction of the movements of the wedge 2 (not shown here), the third lateral guide devices 3c, 3c', and the wafer with respect to the position of the water level is complex, especially for drying wafers of different diameters. Conventional methods would require complex motion sequences, and the mechanics would have to be laboriously calibrated for each diameter. AI-assisted adaptive control can be used here. Wafers arranged in a tray are imaged by cameras (not shown here), specifically at least the first and last wafers of a tray. The cameras are permanently installed above the water surface, and the third lateral guide devices 3c, 3c' are color-coded to facilitate image recognition.A trained neural network with AI image recognition can then determine the wafer diameter as well as the distance between the wafer center and the water level (parameter z in Fig. 18), the position (parameters x, y in Fig. 18), and possibly the rotational position of the third lateral guide devices 3c, 3c'. These data can then control the program sequence, in particular the movement of the wedge 2 in the vertical direction, the movement of the third lateral guide devices 3c, 3c' (horizontal movement and possibly rotation), and other important process parameters (e.g., drainage or DI water inflow) can be controlled accordingly. Observing the first and last wafers in a tray makes it possible to detect any tilt of the tray axis relative to the water level and, if necessary, initiate appropriate countermeasures.

[0127] Fig. 9 shows a further embodiment of a corresponding device for drying wafers. In addition to the tray 3 and the wedge 2, gripping devices 4 are also provided, which are designed to grip the wafer as long as it rises above the water surface. As soon as the gripping devices 4 have gripped the wafer, the wedge 2, which is still underwater, can be lowered (not shown in this figure). The tray and the gripper move upwards at the same speed, and the wafer passes through the water surface without being held at the point of passage by the wedge 2. This means that no residual drops are formed. A suction device 6 is provided in the wedge 2.

[0128] Fig. 10 shows two trays - Fig. 10 a) shows a tray 3 according to the prior art, which can be used, for example, in a method according to Fig. 1. Here, two head parts 3d, 3d' are provided, between which two pairs of lateral guide devices 3a, 3a' and 3b, 3b' are arranged. The wafers W (not shown here) can be held by these. The first lateral guide devices 3a, 3a' and the second lateral guide devices 3b, 3b' each have elevations (not shown in detail here) - these form a comb-like structure which can hold individual wafers W (not shown here) - so that wafers do not touch each other or tip over.

[0129] The pair of first lateral guide devices 3a, 3a' is arranged below the pair of second lateral guide devices 3b, 3b'.

[0130] The distance between the pair of first lateral guide devices 3a, 3a' is smaller than the distance between the pair of second lateral guide devices 3b, 3b'.

[0131] Fig. 10 b) shows a tray 3 which can be used in a method according to the invention as shown in Fig. 3.

[0132] In contrast to Fig. 4 a), here a pair of third lateral guide devices 3c, 3c' is arranged above the pair of second lateral guide devices 3b, 3b'.

[0133] The distance between the pair of first lateral guide devices 3a, 3a' is smaller than the distance between the pair of second lateral guide devices 3b, 3b', and the distance between the pair of second lateral guide devices 3b, 3b' is smaller than the distance between the pair of third lateral guide devices 3c, 3c'. This makes it possible to hold a wafer W (not shown here) at multiple locations compared to Fig. 4 a).

[0134] The first lateral guide devices 3a, 3a', the second lateral guide devices 3b, 3b' and the third lateral guide devices 3c, 3c' each have elevations (not shown in detail here) - these form a comb-like structure which can hold individual wafers W (not shown here) - so that wafers do not touch each other or cannot tilt.

[0135] Fig. 11 shows a corresponding evaluation routine for measurements in which the homogeneity of the surface oxide layer of wafers according to the invention can be measured: Raw data files are generated using the candela surface ellipsometer. Within the candela ellipsometer software, a corresponding contrast maximization is performed, which is applied to the entire mapping (the contrast is varied – for example, in an image processing program for pixel graphics – until droplet residues are clearly visible in the displayed images; here, it must be ensured that an area with a typical droplet shape stands out clearly from its surroundings).

[0136] The corresponding image files are then exported. The surfaces are then manually marked with a different contrast for all wafers, with particular attention paid to the edge areas.

[0137] At the point where the residual droplet can form due to the alignment of the wafer during the drying process, a 9 cm wide and 1.9 cm high rectangle was placed in the wafer for evaluation. The droplet is identified and evaluated within this rectangle. This ensures that all possible residual droplets within a 1 cm wide ring on the outer edge of the wafer are detected. Using a fictitious rectangle is more useful and accurate than using a ring (circumferential strip), which would make it difficult to distinguish the residual droplet from a possible laser marking on the front of the wafer during image processing.

[0138] The defect areas are then determined using image processing, which allows the areas to be measured accordingly. This measures the area of ​​an adjacent area.

[0139] Typically, there is no edge exclusion of specific areas of the wafer—instead, the entire wafer can be reused—because the improved Marangoni drying process largely eliminates such defects. Here, the defect areas exhibiting residual droplets or their effects, such as changes in the oxide layer composition, are selected, marked, and measured based on the following criteria:

[0140] • Area must be at the edge of the wafer

[0141] • It has an irregular shape

[0142] • Area has a different brightness from surrounding areas (usually brighter than surrounding areas; however, smaller darker areas are also possible)

[0143] • The shape of the surface is typical for a water residue (e.g. drop shape, shape with round / elliptical / oval elements, elongated and branched shape).

[0144] This results in a frequency distribution of the identified defect areas.

[0145] Fig. 12 shows two examples of drops at the edge of the wafers, each of which is marked and whose area is measured. It is difficult to carry out an automated evaluation here because, for example, contrast variations can occur in the wafers due to other effects (shown in black in Fig. 12), which, however, must not be confused with the drop at the edge of the wafer. Therefore, a manual evaluation is required here, always ensuring that the drops emanate from the edge of the wafer and that a corresponding shape can be logically assigned to the shape of a drop. A completely angular shape cannot therefore be assigned to a drop. Likewise, edges with delicate jagged edges cannot be assigned to a drop because the surface tension of water would not allow the formation of such a shape.However, a shape with irregular edge sections is possible, as can be seen in the left illustration of Fig. 12.

[0146] Defects arise from contact between the wafer and the tray or wedge as it passes through the liquid surface during drying due to adhering droplets, which can cause spots and thus "defects." However, according to the invention, fewer spots remained, advantageously only a single spot, and / or an overall minimized spot area, whereas prior art drying processes generally left multiple and overall larger spot areas.

[0147] Fig. 13 shows an alternative for the evaluation routine. Here, only a manual marking of the areas with a different contrast is carried out for some wafers, and with the help of training a neural network, all other wafers are then evaluated and the defect areas are evaluated accordingly.

[0148] Since the appearance of droplet residues can exhibit very different contrasts, the droplet regions were segmented using a neural network. The neural network was trained in a Tensorflow-Keras environment. A UNet structure with a resnet34 backbone was used as the model (U-Net: Convolutional Networks for Biomedical Image Segmentation, Olaf Ronneberger, Philipp Fischer, Thomas Brox, arXiv 2015).

[0149] The segmented regions were visually checked for plausibility for all images and, where appropriate, included in the training dataset for retraining the network. This process was repeated iteratively until the automatic segmentation matched the visual assessment for more than 98% of all images. The regions segmented in this way were then processed in a second step using conventional image processing (e.g., OpenCV: ) are automatically selected and their areal extent is measured.

[0150] The contrasts are therefore not evaluated by threshold values, but rather by their intensity, either visually or by a trained algorithm or by a neural network. Here, the focus is not on the absolute value of the measurement signal, but only on the detectability of droplet areas. This evaluation takes place outside the candela ellipsometer.

[0151] Fig. 14 shows a result of the measurement of the defect areas of two corresponding wafer groups of semi-insulating, undoped GaAs wafers with a diameter of 150 mm. On the right, wafers dried using a conventional Marangoni drying process (according to the method in Fig. 1 ) and, on the left, wafers dried using an improved Marangoni drying process according to the inventive method (Fig. 3). For undoped wafers, it was shown that the scattering of different defect areas of the wafers produced using the new method is significantly lower, and that the absolute defect area is significantly lower (less than 5 mm 2 ).

[0152] The defect area corresponds to the area measured by surface measurement using candela ellipsometry. Chemically speaking, the surface oxide composition is inhomogeneous—defect areas are areas of the surface oxide where the oxide composition is inhomogeneous.

[0153] Since the droplet size in the data is clearly not normally distributed, a normal t-test cannot be carried out. In these cases, the Wilcoxon test is suitable, which makes no assumptions about the underlying distributions. In this test, rank sums of the observed values ​​are calculated, which in turn are approximately normally distributed and allow for statistical conclusions. Since the droplet sizes of the two methods are significantly different, a one-sided test with a confidence level of 0.95 was carried out. The parameter n specifies the total number of values. If the p-value of this is below a typical value of 0.05, the null hypothesis (in this case: the droplet sizes obtained with the method according to Fig. 3 are larger than the droplet sizes obtained with the method according to Fig. 1) can be rejected. The very small p-values ​​(< 0.0001) of the data therefore show very significantly that the droplet sizes obtained with the method according to Fig.3 are smaller. The parameter W refers to the rank sum of one of the two groups.

[0154] Fig. 15 shows a result of the measurement of the defect areas of two corresponding wafer groups of semiconducting, silicon-doped GaAs wafers with a diameter of 150 mm, on the right wafers that were dried using a conventional Marangoni drying process (according to the method in Fig. 1 ) and on the left wafers that were dried using an improved Marangoni drying process according to the invention as shown in Fig. 3. It could also be shown for Si-doped wafers that the scattering is significantly lower with the method according to the invention and the defect area (less than 25 mm 2 ) is significantly lower.

[0155] Since the droplet size in the data is clearly not normally distributed, a normal t-test cannot be carried out. In these cases, the Wilcoxon test is suitable, which makes no assumptions about the underlying distributions. In this test, rank sums of the observed values ​​are calculated, which in turn are approximately normally distributed and allow for statistical conclusions. Since the droplet sizes of the two methods are significantly different, a one-sided test with a confidence level of 0.95 was carried out. The parameter n specifies the total number of values. If the p-value of this is below a typical value of 0.05, the null hypothesis (in this case: the droplet sizes obtained with the method according to Fig. 3 are larger than the droplet sizes obtained with the method according to Fig. 1) can be rejected. The very small p-values ​​(< 0.0001) of the data therefore show very significantly that the droplet sizes obtained with the method according to Fig.3 are smaller. The parameter W refers to the rank sum of one of the two groups.

[0156] Fig. 16 shows a result of the measurement of the defect areas of two corresponding wafer groups of semiconducting, sulfur-doped InP wafers with a diameter of 100 mm. On the right, wafers dried using a conventional Marangoni drying process (according to the method in Fig. 1 ) and on the left, wafers dried using an improved Marangoni drying process according to the method according to the invention (Fig. 3). For sulfur-doped wafers, it was shown that the scattering of different defect areas of the wafers produced using the new process is significantly lower, and that the absolute defect area is significantly lower (less than 5 mm 2 ).

[0157] The defect area corresponds to the area measured by surface measurement using candela ellipsometry. Chemically speaking, the surface oxide composition is inhomogeneous—defect areas are areas of the surface oxide where the oxide composition is inhomogeneous.

[0158] Since the droplet size in the data is clearly not normally distributed, a normal t-test cannot be carried out. In these cases, the Wilcoxon test is suitable, which makes no assumptions about the underlying distributions. In this test, rank sums of the observed values ​​are calculated, which in turn are approximately normally distributed and allow for statistical conclusions. Since the droplet sizes of the two methods are significantly different, a one-sided test with a confidence level of 0.95 was carried out. The parameter n specifies the total number of values. If the p-value of this is below a typical value of 0.05, the null hypothesis (in this case: the droplet sizes obtained with the method according to Fig. 3 are larger than the droplet sizes obtained with the method according to Fig. 1) can be rejected. The very small p-values ​​(< 0.0001) of the data therefore show very significantly that the droplet sizes obtained with the method according to Fig.3 are smaller. The parameter W refers to the rank sum of one of the two groups.

[0159] Figure 17 shows an embodiment of a wafer drying device according to the invention. It includes a storage device 5 into which various trays 3, 31, 32 can be suspended.

[0160] The trays themselves hold the wafers with guide devices (comb rods). In the present view, either two first trays 31 or a second tray 32 can be suspended. A first tray 31 is used to dry wafers with a smaller diameter than tray 32. The wedge here consists of two first wedge sections 2a and a second wedge section 2b, which can be moved vertically separately from one another. The centers of the first trays 31 are positioned directly above the tip of the first wedge section 2a, and the center of the second tray 32 is positioned above the tip of the second wedge section 2b. The first wedge section 2a and the second wedge section 2b also have corresponding elevations 2c, which form a comb-like structure.

[0161] The second tray 32 is provided for larger wafers, for example with a diameter greater than or equal to 200 mm, and the elevations 2c have a greater spacing compared to the first trays 31; thus, the trays 32 are longer than the first trays 31 and the wafers can no longer be lifted out with the same wedges as wafers with small diameters. The wedge sections 2a, 2b must always be mounted centrally to the trays, since they must grip the wafers at a lower point. The lifting of, for example, wafers with a diameter of up to 150 mm on the one hand and wafers greater than or equal to 200 mm on the other hand in a dryer is therefore not possible according to the prior art. In the device according to the invention, therefore, for smaller wafers (e.g. diameter of 150 mm or less) and larger (e.g.For each wafer (diameter of 200 mm or larger), a separate wedge section (2a for smaller wafers W1, 2b for larger wafers W2) is used, with a correspondingly suitable length and adjusted distances from the projections 2c. Since the 200 mm wafers have a larger diameter, the distance between the projections 2c must be greater than for smaller wafer diameters, so that wafers W2 do not touch each other when they tilt slightly.

[0162] Fig. 18 shows a side view of the wedges 2 of a device according to the invention. The left view shows the structure of a first wedge section 2a and a second wedge section 2b.

[0163] The middle view shows a small-diameter wafer W1 (e.g., a 3-inch or 150 mm wafer) being lifted upwards using the first wedge section 2a. The right view shows a larger-diameter wafer W2 (e.g., a 200 mm wafer) being lifted upwards using the second wedge section.

[0164] Fig. 19 shows a result of measuring the defect areas of two corresponding wafer groups of semi-insulating, Fe-doped InP wafers with a diameter of 150 mm. On the right, wafers dried using a conventional Marangoni drying process (according to the method in Fig. 1) and, on the left, wafers dried using an improved Marangoni drying process according to the inventive method (Fig. 3). For the Fe-doped wafers, it was shown that the scattering of different defect areas between the wafers produced using the previous and the new processes is similarly small; almost no defect area is visible.

[0165] The defect area corresponds to the area measured by surface measurement using candela ellipsometry. A method according to the invention for drying a wafer includes a bath with an arrangement of at least one wedge and at least one tray. A tray has the following:

[0166] 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'.

[0167] The pair of first lateral guide devices 3a, 3a' is arranged below the pair of second lateral guide devices 3b, 3b', and the pair of second lateral guide devices 3b, 3b' is arranged below the pair of third lateral guide devices 3c, 3c'.

[0168] The distance between the pair of first lateral guide devices 3a, 3a' is preferably smaller than the distance between the pair of second lateral guide devices 3b, 3b', and the distance between the pair of second lateral guide devices 3b, 3b' is smaller than the distance between the pair of third lateral guide devices 3c, 3c'.

[0169] The method according to the invention comprises the following steps: i) Vertically moving the at least one wedge 2 upwards until it touches the wafer at its lowest point, vertically moving the pair of first lateral guide devices 3a, 3a' and the pair of second lateral guide devices 3b, 3b' upwards, wherein the wafer W touches the pair of first lateral guide devices 3a and the pair of second lateral guide devices 3b, wherein an upper region of the wafer W is pushed out of the bath 1, wherein the pair of third lateral guide devices 3c does not touch the wafer;ii) Moving the wedge 2 vertically upwards until the pair of first lateral guide devices 3a, 3a' and the pair of second lateral guide devices 3b, 3b' no longer touch the wafer W while they are still below the liquid surface of the bath 1, wherein the pair of third lateral guide devices 3c, 3c' touch the wafer above the liquid surface of the bath 1; iii) Pushing out the wafer W above the liquid level of the bath 1, wherein the pair of third lateral guide devices 3c, 3c' touch the wafer W;

[0170] Compared to the prior art (see Fig. 1 ), the wafers are no longer held by the fixed holders H and H' limited to a wafer diameter, for example in the lid of the dryer, but in particular by the pair of third lateral guide devices 3c, 3c'

[0171] Thus, contact of the wafers with, in particular, the first and second lateral guide devices 3a, 3a', 3b, 3b' of the tray 3, 31, 32 is avoided, while the water level passes the aforementioned first and second lateral guide devices accordingly. The wafers W, W1, W2 are held by the third lateral guide devices 3c, 3c', which are located above the water level and are already dried. The vertical travel path of the wafers during drying according to the invention is significantly shorter and can be limited to a few seconds. Drops that would otherwise form upon contact between the wafer and the wedge 2, 2a, 2b therefore occur much less frequently and are also smaller. A candela measurement of dried wafers according to this method shows fewer and smaller residual droplets.

[0172] Preferably, the method according to the invention further comprises the following steps: iv) moving a wedge 2 vertically downwards until the wafer W touches at least one of the pair of first lateral guide devices 3a and the pair of second lateral guide devices 3b; v) further moving a wedge 2 vertically downwards until it no longer touches the wafer W; wherein parallel to steps iv) and / or v) or after step v), the liquid level of the bath 1 is lowered until the liquid level is below the wedge 2.

[0173] In this way, the guide devices 3a, 3a', 3b, 3b' or the tray 3, 31, 32 and the wedge 2, 2a, 2b can also be dried until they are ready for the next wafer drying operation.

[0174] Preferably, the bath 1 contains water and at least one further surface tension reducing substance, preferably isopropanol.

[0175] In this way, the Marangoni effect can be optimally used in the process according to the invention.

[0176] Preferably, the pair of first lateral guide devices 3a, 3a', the pair of second lateral guide devices 3b, 3b' and / or the pair of third lateral guide devices 3c, 3c' each consist of a pair of webs which are adapted to touch opposite sides of the wafer W, W1, W2 during different process steps. In this way, it can be ensured that the wafers W, W1, W2 are held laterally and do not touch one another during the drying process (i.e., they cannot tip over in the dryer). Otherwise, wafers which touch one another during drying could "stick" to one another and thus prevent drying, i.e., the wafers would then remain wet.

[0177] Preferably, in step i), the pair of first lateral guide devices 3a, 3a' and the pair of second lateral guide devices 3b, 3b' are immersed in the bath 1, and preferably, at the end of step v), the pair of third lateral guide devices 3c, 3c' does not touch the wafer W, W1, W2.

[0178] Because there is only maximum contact between the wedge and the wafer when passing through the liquid surface of the bath (or even no contact at all between the wafer and any guide device or the wedge), it can be ensured that no residual drops adhere to the wafer W, W1, W2 in the area of ​​the first, second and third guide devices, which could correspondingly impair the surface homogeneity of the wafer surface.

[0179] Preferably, the wedge 2, 2a, 2b is provided with at least one suction device 6, to which a vacuum can be applied when the upper tip of the wedge 2, 2a, 2b is located above the liquid level. This ensures that the water remaining at the tips of the wedge 2, 2a, 2b is suctioned away, preventing the drop from reaching the wafer W, W1, W2 and thus causing inhomogeneity in the oxide surface.

[0180] Preferably, the wedge 2, 2a, 2b has a surface tension-increasing surface structure, for example, through a plasma treatment of PEEK, from which a wedge 2, 2a, 2b can be made. An increased surface tension of the wedge 2, 2a, 2b can result in the residual droplet remaining on the wedge 2, 2a, 2b and not transferring to the wafer W, W1, W2.

[0181] Preferably, the lifting speed depends on the position of the lowest point of the wafer and is between 0.8 and 1.2 mm / s if the lowest point of the wafer is more than 1.2 cm below the liquid level, and is between 0.4 and 0.5 mm / s if the lowest point of the wafer is less than 1.2 cm below the liquid level, which leads to a significant reduction in contact droplets. Since excessive fluctuations in the water level can be reflected in the chemical composition of the oxide layer, this speed reduction should be carried out gradually. The lifting speed is at least 30 mm / s (preferably 40 mm / s or 50 mm / s) as soon as the lowest point of the wafer W has reached the liquid level. This prevents water from the water level and residual moisture from the wedge from being drawn back onto the wafer surface.At the same time, the wedge can be separated from the lower edge of the wafer in the opposite direction. According to one embodiment, the pair of first lateral guide devices 3a, 3a', the pair of second lateral guide devices 3b, 3b', and the pair of third lateral guide devices 3c, 3c' are provided on a tray 3, and in step i), the entire tray 3 is moved. In step iii), the wafer W is pushed out above the liquid level of the bath 1, with the pair of third lateral guide devices 3c, 3c' (already above the liquid level) and the wedge 2 touching the wafer W. Thus, when passing through the liquid level, there is only one contact point between the wedge and the wafer - the droplet area can be minimized.

[0182] According to another embodiment, the pair of third lateral guide devices 3c, 3c' is positioned above the liquid level during all process steps and is movable independently of the pair of first lateral guide devices 3a, 3a' and the pair of second lateral guide devices 3b, 3b', and 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. When passing through the liquid level, there is no contact point between the wedge and the wafer – the droplet surface can then even be completely avoided.

[0183] Preferably, wedge 2 remains below the liquid level throughout all process steps. This is the reason why no residual droplets remain on the wafer in the area of ​​the wedge.

[0184] Preferably, in step iii), the distance between the points at which the third lateral guide devices 3c, 3c' contact the wafer is continuously reduced. Thus, the wafer W can be moved vertically by horizontal movement of the third lateral guide devices 3c, 3c'. The third lateral guide devices 3c, 3c' are further preferably adapted to perform a horizontal movement relative to one another.

[0185] Further preferably, the third lateral guide devices 3c, 3c' are either mounted eccentrically or have an oval shape and are adapted to perform a rotational movement. Thus, the rotational movement of the third lateral guide devices 3c, 3c' can induce a vertical movement of the wafer, and can be helpful in the area where the last piece of the wafer is lifted out of the bath—at this moment, the wedge 2 is not required for the vertical movement of the wafer, thus avoiding a contact point between the wafer W and the wedge 2 when passing through the liquid level.

[0186] Other process parameters can influence the homogeneity of the oxide surface of a III-V wafer:

[0187] • Another parameter to be controlled for droplet-free Marangoni drying was the concentration of the substance that lowers the surface tension of the ultrapure water, preferably isopropyl alcohol (IPA). Reducing the IPA supply in the final drying phase leads to a stronger vertical gradient in surface tension and thus reduces the risk of residual droplet formation. Due to the delayed effect of reducing the IPA supply on the IPA concentration in the headspace and subsequently on the magnitude of the concentration gradient, it may be advisable to gradually reduce the IPA supply after the phase interface (liquid surface) has passed the wafer center.

[0188] Especially for n-doped GaAs, a greater reduction of the IPA supply may be useful.

[0189] • The IPA gradient at the interface results from the interaction between the adjusted IPA supply and the counteracting overflow of deionized water (ultrapure water) in the process tank. At the same time, the strength of the overflow influences the particles adhering to the wafers. With the same pretreatment, indium phosphide wafers exhibit a higher surface tension and a significantly higher adhesion capacity for particles than GaAs. For a lower level of residual particles, an ultrapure water overflow of at least 0.1 l / h / cm is recommended. 2 required (0.1 litres of ultrapure water per hour per cm 2 liquid surface in the tank). To ensure sufficient IPA concentration at the interface, the overflow may only slightly exceed this value. At the same time, the IPA / N2 flow must be increased by 0.003 to 0.007 l / h / cm compared to GaAs. 2increased to compensate for the increased IPA discharge due to the overflow - so that the IPA concentration at the interface remains stable.

[0190] • In addition to the technical and chemical factors influencing the Marangoni drying process itself, the treatment of the III-V semiconductor wafers in the process tanks prior to drying also influences the quality of the Marangoni drying process and the strength of the residual droplets that occur at the point of contact with the wedge used for removal.

[0191] Depending on the cleaning sequence, the final cleaning step can consist of an acidic, basic, or neutral solution (e.g., using 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 can be adjusted to the surface tension of the wafers to be dried. Hydrophobic wafers require less isopropanol than hydrophilic wafers (e.g., hydrophobic: < 0.01 l / h / cm 2 IPA / N2, hydrophilic: e.g. > 0.01 l / h / cm 2 IPA / N2).

[0192] Control of the surface tension of the wafers to be dried can also be achieved, for example, by adding small amounts of acidic or basic additives.

[0193] A wafer according to the invention has an oxide layer on at least one surface. This surface has a defect area in the oxide layer of less than 25 mm 2 The wafer is semi-insulating or semiconducting. The surface with the oxide layer is also called the oxide surface.

[0194] For semi-insulating wafers, even smaller defect areas are possible: Here, the defect area is preferably less than 15 mm 2 , further preferably under 10 mm 2 , even further preferably below 5 mm 2 . Such a wafer is further preferably made of GaAs or InP, even more preferably of undoped or carbon-doped GaAs or of iron-doped InP.

[0195] Semiconducting wafers can be GaAs wafers and contain silicon as a dopant, or an InP wafer and contain sulfur as a dopant.

[0196] Preferably, the defect area is a continuous region, as shown, for example, in Fig. 12. At least a portion of the defect area may contact the edge of the wafer.

[0197] Preferably, at least a part of the defect area is max. 5 mm away from the edge of the wafer.

[0198] Further preferably, at least a part of the defect area is located in a circular ring between the edge of the wafer and a virtual circular line which is max. 10 mm away from the edge of the wafer.

[0199] Furthermore, the entire defect area is preferably located in a circular ring between the edge of the wafer and a virtual circular line which is max. 10.5 mm away from the edge of the wafer.

[0200] Further preferably, the entire defect area is located in a circular ring between the edge of the wafer and a virtual circular line, which is max. 10 mm away from the edge of the wafer.

[0201] Optionally, the wafer has a straight-ground section or notch on a part of the edge, and the defect area is opposite the straight-ground section or notch.

[0202] Corresponding wafers can be produced using the method according to the invention, since drops during drying can be minimized, which results in a particularly low defect area.

[0203] A wafer drying device according to the invention comprises: a bath 1 containing liquid; a wedge 2; at least one vertically movable storage device 5; wherein at least one tray 3, 31, 32 can be inserted into the storage device 5, wherein the at least one tray 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', wherein the pair of first lateral guide devices 3a, 3a' is arranged below the pair of second lateral guide devices 3b, 3b', and the pair of second lateral guide devices 3b, 3b' is arranged below the pair of third lateral guide devices 3c, 3c', and wherein the distance between the pair of first lateral guide devices 3a, 3a' is smaller than the distance between the pair of second lateral guide devices 3b,3b' from each other, and the distance between the pair of second lateral guide devices 3b, 3b' from each other is smaller than the distance between the pair of third lateral guide devices 3c, 3c' from each other, wherein the wedge 2 is provided below the tray 3 and is vertically movable separately from the storage device 5, wherein the wedge 2 comprises at least two wedge sections 2a, 2b, wherein both wedge sections 2a, 2b are vertically movable separately from each other, wherein at least one first tray 31 is insertable into the storage device 5 such that the center of the at least first tray 31 is positioned above the tip of the first wedge section 2a, and furthermore a second tray 32 is insertable such that the center of the second tray 32 is positioned above the tip of the second wedge section 2b.

[0204] Compared to the prior art, the two additional lateral guide devices (third lateral guide devices 3c, 3c') mean that they can hold the wafer W, W1, W2 laterally even at the time when they have risen above the liquid surface. Thus, once the wafer W, W1, W2 has passed the liquid surface, it can be held by the third lateral guide devices 3c, 3c' (above the liquid surface) and the wedge 2, 2a, 2b (below the liquid surface). The first lateral guide devices 3a, 3a' and the second lateral guide devices 3b, 3b' do not touch the wafer W, W1, W2 below the liquid surface and do not touch it during its passage through the liquid surface, thus preventing any risk of droplet formation in these areas.

[0205] In the device according to the invention, therefore, a separate wedge section (2a for smaller wafers W1, 2b for larger wafers W2) is used for smaller wafers (e.g., diameters of 150 mm or smaller) and larger wafers (e.g., diameters of 200 mm or larger), with a correspondingly suitable length and respectively adjusted distances from the elevations 2c. Since the 200 mm wafers have a larger diameter, the distance between the elevations 2c must be greater than for smaller wafer diameters, so that wafers W2 do not touch each other when they tilt slightly.

[0206] Such a device is suitable for drying wafers of several diameters without increased design effort.

[0207] Examples

[0208] GaAs wafers were cleaned using a wet chemical cleaning process - All wafers were pre-polished on both sides and final polished on one side.

[0209] Pre-cleaning was carried out using NH3 and HCl.

[0210] The final cleaning was carried out using the method according to WO 2014 / 124980 A2: The wafers were subjected to basic cleaning (diluted NHs solution plus megasonics), rinsed with deionized water and then dried using the Marangoni drying method.

[0211] Example 1 :

[0212] Semi-insulating, undoped GaAs wafers with a diameter of 150 mm were cleaned in a bath and then dried using the Marangoni drying method. The undoped wafers were made from crystals grown using the VGF method and had a resistivity between 1x10 8 and 8x10 8 Qcm.

[0213] Forty-eight GaAs wafers were dried using a process according to the invention as shown in Fig. 3. The wafer travel speed was mostly 1 mm / s (variations are possible for individual phases of the removal process, see above and claim 8). Travel speed refers to the speed of the wafers relative to the water surface.

[0214] Comparative Example 1: Semi-insulating, undoped GaAs wafers with a diameter of 150 mm were cleaned in a bath and then dried using the Marangoni drying method. The undoped wafers were made from crystals grown using the VGF method and had a resistivity between 1x10 8 and 8x10 8 Qcm.

[0215] 46 GaAs wafers were dried using a process according to Fig. 1 (prior art). The wafer travel speed was mostly 1 mm / s (variations are possible for individual phases of the removal process, see above and claim 8).

[0216] The comparison of Example 1 and Comparative Example 1 is shown in Fig. 14.

[0217] Example 2:

[0218] Silicon-doped GaAs wafers (semiconducting) with a diameter of 150 mm were cleaned in a bath and then dried using the Marangoni drying technique. The doped wafers were made from crystals grown using the VGF process and had a Si doping with a charge carrier concentration between 1x10 18 and 3x10 18 cm" 3 .

[0219] 84 silicon-doped GaAs wafers were dried using a method according to the invention as shown in Fig. 3. The wafer travel speed was mostly 1 mm / s (changes are possible for individual phases of the removal process, see above and claim 8).

[0220] Comparison example 2:

[0221] Si-doped GaAs wafers (semiconducting) with a diameter of 150 mm were cleaned in a bath and then dried using the Marangoni drying method.

[0222] 88 silicon-doped GaAs wafers were dried using a process according to Fig. 1 (prior art). The wafer travel speed was mostly 1 mm / s (variations are possible for individual phases of the removal process, see above and claim 8). A comparison of Example 2 and Comparative Example 2 is shown in Fig. 15.

[0223] Example 3:

[0224] S-doped, semiconducting InP wafers with a diameter of 100 mm were cleaned in a bath and then dried using the Marangoni drying method. The sulfur-doped wafers were produced from crystals grown using the VGF process and had a sulfur doping with a charge carrier concentration between 1.5 x 10 18 and 9x10 18 cm' 3 .

[0225] 19 InP wafers were dried using a method according to the invention as shown in Fig. 3. The wafer travel speed was mostly 1 mm / s (changes are possible for individual phases of the removal process, see above and claim 8).

[0226] Comparison example 3:

[0227] S-doped, semiconducting InP wafers with a diameter of 100 mm were cleaned in a bath and then dried using the Marangoni drying method. The sulfur-doped wafers were produced from crystals grown using the VGF method and had an S doping with a charge carrier concentration between 1.5 x 10 18 and 9x10 18 cm' 3 .

[0228] 29 InP wafers were dried using a process according to Fig. 1 (prior art). The wafer travel speed was mostly 1 mm / s (variations are possible for individual phases of the removal process, see above and claim 8).

[0229] The comparison of Example 3 and Comparative Example 3 is shown in Fig. 16.

[0230] Example 4:

[0231] Fe-doped, semi-insulating InP wafers with a diameter of 150 mm were cleaned in a bath and then dried using the Marangoni drying method. The Fe-doped wafers were produced from crystals grown using the VGF method and had an iron doping with a charge carrier concentration between 2.8 x 10 7 and 3.8x10 7 cm' 3 . The specific resistance was 4.9 x10 7 up to 8.7 x10 7 Q*cm. The dislocation density was 290 to 480 cm' 2

[0232] 23 InP wafers were dried using a method according to the invention as shown in Fig. 3. The wafer travel speed was mostly 1 mm / s (changes are possible for individual phases of the removal process, see above and claim 8).

[0233] Comparison example 4:

[0234] Fe-doped, semi-insulating InP wafers with a diameter of 150 mm were cleaned in a bath and then dried using the Marangoni drying method. The Fe-doped wafers were produced from crystals grown using the VGF method and had an iron doping with a charge carrier concentration between 2.8 x 10 7 and 3.8x10 7 cm -3 . The specific resistance was 4.9 x10 7 up to 8.7 x10 7 Q*cm. The dislocation density was 290 to 480 cm- 2 .

[0235] Twelve InP wafers were dried using a process according to Fig. 1 (prior art). The wafer travel speed was mostly 1 mm / s (variations are possible for individual phases of the removal process, see above and claim 8).

[0236] The comparison of Example 4 and Comparative Example 4 is shown in Fig. 19.

[0237] Surface characterization of the wafers:

[0238] The surface properties of the wafer (the nature of the oxide surface on the wafer) are characterized after drying using an optical surface analyzer (candela ellipsometer). To characterize the homogeneity of the surface properties, a mapping of the QAbsPhase measurement channel of the KLA Candela CS20 is evaluated. The radial resolution of the candela measurement is 50 pm, and the azimuthal resolution is <30 pm.

[0239] The mappings show bright and dark areas as well as striped structures that can be attributed to inhomogeneities or, more generally, "defects." The intensity and number of deviations from the background characterize the homogeneity of a surface.

[0240] When determining droplet sizes, contrasts are evaluated visually, using a trained algorithm, or a neural network (see above), not by threshold values, but by their intensity. Here, the absolute value of the measurement signal is not considered, but only clearly recognizable droplet areas, and this evaluation takes place outside the candela ellipsometer.

[0241] An edge exclusion of a maximum of 0.5 mm is performed. The inward extension of the droplets detected is a maximum of approximately 1 cm, so that the area under consideration covers a radius range between 65 mm and 74.5 mm for a 150 mm wafer, and a radius range between 40 mm and 49.5 mm for a 100 mm wafer.

[0242] LIST OF REFERENCE SYMBOLS

[0243] 1 bathroom

[0244] 2, 2a, 2b wedge

[0245] 2c Survey

[0246] 3 Horde

[0247] 31 first horde

[0248] 32 second horde

[0249] 3a, 3a' first lateral guide device

[0250] 3b, 3b' second lateral guide device

[0251] 3c, 3c' third lateral guide device

[0252] 3d, 3d' headboard

[0253] 4 gripping device

[0254] 5 Storage device

[0255] 6 Suction device

[0256] W wafers

[0257] H, H' holding device

Claims

Claims 1 . Method for drying a wafer (W) which is located in a bath (1), by means of an arrangement which has 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'), wherein the pair of first lateral guide devices (3a, 3a') is arranged below the pair of second lateral guide devices (3b, 3b'), and the pair of second lateral guide devices (3b, 3b') is arranged below the pair of third lateral guide devices (3c, 3c'), and wherein the method comprises the following steps: i) Vertically moving the at least one wedge (2) upwards until it touches the wafer at its lowest point, vertically moving the pair of first lateral guide devices (3a, 3a') and the pair of second lateral guide devices (3b,3b') upwards, wherein the wafer (W) contacts the pair of first lateral guide devices (3a) and the pair of second lateral guide devices (3b), wherein an upper region of the wafer (W) is pushed out of the bath (1), wherein the pair of third lateral guide devices (3c) does not contact the wafer; ii) Moving the wedge (2) vertically upwards until the pair of first lateral guide devices (3a, 3a') and the pair of second lateral guide devices (3b, 3b') no longer contact the wafer (W) while they are still below the liquid surface of the bath (1), wherein the pair of third lateral guide devices (3c, 3c') contact the wafer above the liquid surface of the bath (1); iii) pushing out the wafer (W) above the liquid level of the bath (1 ), wherein the pair of third lateral guide devices (3c, 3c') touches the wafer (W).

2. A method for drying a wafer (W) according to claim 1, further comprising the following steps: iv) moving a wedge (2) vertically downwards until the wafer (W) touches at least one of the pair of first lateral guide devices (3a) and the pair of second lateral guide devices (3b); v) further moving a wedge (2) vertically downwards until it no longer touches the wafer (W); wherein parallel to steps iv) and / or v) or after step v), the liquid level of the bath (1) is lowered until the liquid level is below the wedge (2).

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

4. Method according to one of the preceding claims, wherein the pair of first lateral guide devices (3a, 3a'), the pair of second lateral guide devices (3b, 3b') and / or the pair of third lateral guide devices (3c, 3c') each consist of a pair of webs which are adapted to contact opposite sides of the wafer (W, W1, W2).

5. Method according to one of the preceding claims 2 to 4, wherein in step i) the pair of first lateral guide devices (3a, 3a') and the pair of second lateral guide devices (3b, 3b') remain immersed in the bath (1), and preferably at the end of step v) the pair of third lateral guide devices (3c, 3c') do not touch the wafer (W, W1, W2).

6. Method according to one of the preceding claims, wherein the wedge (2, 2a, 2b) is provided with suction devices (6) to which a negative pressure can be applied when the upper tip of the wedge (2, 2a, 2b) is above the liquid level.

7. Method according to one of the preceding claims, wherein the wedge (2, 2a, 2b) has a surface tension-increasing surface structure.

8. The method according to any one of claims 1 to 7, wherein the lifting speed depends on the position of the lowest point of the wafer (W) and 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, 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 at least 30 mm / s, preferably at least 40 mm / s, more preferably at least 50 mm / s, as soon as the lowest point of the wafer (W) has reached the liquid level.

9. The method according to any one of claims 1 to 8, wherein the pair of first lateral guide devices (3a, 3a'), the pair of second lateral guide devices (3b, 3b') and the pair of third lateral guide devices (3c, 3c') are provided on a tray (3), and in step i) the tray (3) is moved, in step iii) the wafer (W) is pushed out above the liquid level of the bath (1), the pair of third lateral guide devices (3c, 3c') and the wedge (2) touching the wafer (W).

10. Method according to one of claims 1 to 8, wherein the pair of third lateral guide devices (3c, 3c') is positioned above the liquid level in all process steps and is independent of the Pair of first lateral guide devices (3a, 3a') and the pair of second lateral guide devices (3b, 3b'), and the third lateral guide devices (3c, 3c') are horizontally movable relative to each other.

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

12. The method according to claim 10 or 11, wherein in step iii) the distance between the points at which the third lateral guide devices (3c, 3c') contact the wafer is continuously reduced.

13. Method according to one of claims 10 to 12, wherein the third lateral guide devices (3c, 3c') are either mounted eccentrically or have an oval shape and are adapted to perform a rotary movement.

14. III-V wafer (W, W1, W2), wherein at least one surface of the wafer has an oxide layer, said surface having a defect area of ​​less than 25 mm 2 and wherein the III-V wafer (W) is semi-insulating or semiconducting.

15. III-V wafer (W, W1, W2) according to claim 14, wherein the oxide surface has a defect area of ​​less than 15 mm 2 , preferably less than 10 mm 2 , further preferably under 5 mm 2 wherein the III-V wafer (W, W1, W2) is semi-insulating and preferably consists of GaAs or InP, more preferably of undoped or carbon-doped GaAs or of iron-doped InP.

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

7. Apparatus for drying wafers, comprising: a bath (1) containing liquid; a wedge (2), at least one storage device (5) which is vertically movable; wherein at least one tray (3; 31, 32) can be inserted into the storage device (5), wherein the at least one tray (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'), wherein the pair of first lateral guide devices (3a, 3a') is arranged below the pair of second lateral guide devices (3b, 3b'), and the pair of second lateral guide devices (3b, 3b') is arranged below the pair of third lateral guide devices (3c, 3c'), and wherein the distance between the pair of first lateral guide devices (3a,3a') from each other is smaller than the distance between the pair of second lateral guide devices (3b, 3b') from each other, and the distance between the pair of second lateral guide devices (3b, 3b') from each other is smaller than the distance between the pair of third lateral guide devices (3c, 3c'), wherein the wedge (2) is provided below the tray (3) and can be moved vertically separately from the storage device (5), wherein the wedge (2) comprises at least two wedge sections (2a, 2b), wherein both wedge sections (2a, 2b) can be moved vertically separately from each other, wherein at least one first tray (31) can be inserted into the storage device (5) such that the center of the at least first tray (31) is positioned above the tip of the first wedge section (2a), and furthermore a second tray (32) can be inserted such that the center of the second tray (32) is positioned above the tip of the second wedge section (2b) is.,

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