Method for bonding substrates by distributing a bonding material by bringing the substrates close together.

Abstract

Method for bonding a first lower substrate (1) to a second upper substrate (2) by means of a bonding layer (7) made of a bonding material (3, 5) arranged between the substrates (1, 2) comprising the following steps: - Coating the first lower substrate (1) with the bonding material (3, 5) by centrifugal or spray coating, - Applying at least one drop of the compound material (3, 5) to the second upper substrate (2) in liquid form and - after coating the first lower substrate (1) after applying the at least one drop of the compounding material (3, 5) to the second upper substrate (2) the compounding material (3, 5) is distributed between the substrates (1, 2) by bringing the substrates (1, 2) closer together, the distribution occurring automatically by means of the capillary force of the liquid compounding material (3, 5), one of the two substrates (1, 2) being left free after contact of the at least one drop with the compounding material (3, 5) on the first lower substrate (1), and thereby forming the shape of the compounding layer (7) with a thickness t, the compounding material (3, 5) being applied in an excess-free quantity.

Description

[0001] The present invention relates to a method for bonding a first substrate to a second substrate according to claim 1.

[0002] The state of the art reveals a wide variety of processes, technologies and systems that can be used to coat different surfaces, especially bonding surfaces, with liquids, particularly mixtures of viscous polymers with solvents.

[0003] Publication US 2009 / 0 183 819 A1 discloses a method for manufacturing a display device with a translucent substrate which is glued to a display board with a translucent adhesive.

[0004] US 2008 / 0 216 952 A1 discloses a method for bonding a first optical component to a second optical component. JP 2002-285 132 A WO 2011 / 140 469 A1 discloses a method for laminating multiple elements in an adhesive resin without air bubbles when the elements are laminated with the resin.

[0005] US 2011 / 0 130 065 A1 discloses a method for manufacturing a display, wherein the method includes a step of applying a translucent substrate. DE 10 2012 112 385 A1 discloses a transparent bonding of transparent layers, comprising: (i) applying a transparent adhesive to a bonding surface (31) on a display unit (3) to form a transparent adhesive layer.

[0006] WO 2011 / 140469 A1 discloses a polymerizable composition containing at least one monomer and a photoinitiator that can trigger the polymerization of the monomer when exposed to light.

[0007] JP2004010810 A discloses a non-soluble one-component epoxy resin composition which can preferably form a sealing filler in a gap between a chip component and a printed circuit board.

[0008] Adhesives represent an important group of liquids. They are increasingly used in the semiconductor industry to bond substrates together. A distinction is made between temporary and permanent adhesives.

[0009] A temporary adhesive is usually a thermoplastic that softens above a characteristic temperature, the so-called glass transition temperature. Substrates bonded with a thermoplastic can be separated again by heating the thermoplastic above its glass transition temperature. Thermoplastics can be thermally cycled; therefore, they can theoretically be heated and cooled repeatedly without losing their physical and / or chemical properties. This is because, unlike thermosets, thermoplastics do not cross-link. As a result, the polymer chains can shift relative to each other at sufficiently high temperatures, and the temporary adhesive remains malleable.

[0010] Permanent adhesives are polymers whose polymer chains permanently cross-link under chemical, thermal, or electromagnetic influence. The cross-linking process is irreversible. Such polymers are regularly used to bond substrates, especially substrates made of different materials.

[0011] The joining of two substrates can be achieved through a variety of methods. For example, substrates with metallic surfaces are joined via metal diffusion bonding. The bonding between silicon and / or silicon oxide surfaces is achieved through direct or fusion bonding. Glass substrates can also be joined by anodic bonding, provided the necessary ion transport is possible.

[0012] The aforementioned bonding methods have the significant disadvantage of being limited to specific surface properties of the substrates. For example, metal-to-metal surfaces can usually only be bonded using a metal diffusion bond. Furthermore, direct or fusion bonding technology can only be applied between silicon and / or silicon oxide surfaces, or at least surfaces with similar properties. For instance, bonding a metal surface to a silicon surface using a diffusion or direct bond is generally not possible. Therefore, such connections are usually made using permanent adhesives.

[0013] It is generally desirable to minimize the thickness t of the permanent adhesive layer. On the one hand, the thickness t should be large enough to securely and permanently bond the two substrates and preferably to compensate for surface irregularities. On the other hand, the thickness t should be as small as possible to avoid impairing the properties (e.g., transparency, hardness, strength, stiffness, thermal conductivity) of the resulting products.

[0014] The most important technique for applying adhesives is spin coating. In spin coating, a quantity of permanent adhesive is dispensed centrally onto a substrate. The substrate is fixed to a sample holder. After the permanent adhesive has been applied, the sample holder is set into rapid rotation. The centrifugal force distributes the permanent adhesive relatively evenly over the substrate. The thickness t of the permanent adhesive can be adjusted by the amount dispensed, the rotational speed, and the rotational acceleration.

[0015] Another coating technique is spray coating or spray painting. This technique involves a nozzle atomizing a liquid to be applied while moving relative to a substrate. This relative movement between the nozzle and the substrate can be a simple rotation, a translation, or more complex movements.

[0016] One of the biggest challenges in bonding two substrates, which in most cases are made of different materials, is creating a defect-free interface. When directly bonding two substrates, especially silicon-silicon or silicon oxide-silicon oxide, the avoidance of inclusions and cavities is paramount. In direct bonding, the bonding surfaces of the two substrates are brought into contact, preferably centrally. A bond wave propagates radially outwards from the center. At the micro and / or nanoscale, distortion can occur in one of the two bonding surfaces. This distortion leads to a bulge in at least one of the bonding surfaces, which remains permanently in the interface.

[0017] Unlike direct bonding methods, the biggest problem with permanent adhesive bonding methods is the entrapment of gases, especially bubble formation. The higher the viscosity of a liquid, the more difficult it is for trapped gas to escape. Once trapped, gas can practically no longer escape and remains in the interface.

[0018] The coating methods used in the state of the art result in the following problems.

[0019] While spin coating produces a relatively homogeneous and bubble-free layer on a substrate, the second substrate must be contacted with this pre-existing permanent adhesive layer. If the permanent adhesive layer exhibits significant inhomogeneity (roughness), gas bubbles are frequently trapped. Furthermore, all types of liquids applied via spin coating form an edge bead at the substrate's perimeter. The permanent adhesive is therefore thicker in the edge bead region than in the center, often resulting in gas inclusions. Most liquids applied via spin coating have such a high viscosity that they must be thinned with a solvent. This solvent must then be removed after spin coating through a heat treatment process.The outgassing of the solvent increases the surface roughness, which in turn can lead to a poorer bonding result.

[0020] Even with spray coating, gas inclusions can occur, for example, due to surface roughness. This roughness is a direct result of the individual droplets agglomerating on the substrate surface.

[0021] The object of the present invention is therefore to provide a method that improves the bonding result and is universally applicable.

[0022] This problem is solved by the features of claim 1. Advantageous embodiments of the invention are specified in the dependent claims. The scope of the invention also includes all combinations of at least two of the features specified in the description, the claims, and / or the figures. Where value ranges are specified, values ​​lying within the stated limits are also considered disclosed limits and may be claimed in any combination.

[0023] The basic idea of ​​the present invention is to apply a bonding material as a liquid, in particular a polymer, or even more preferably a permanent adhesive, between two substrates in such a way that the liquid is distributed at least partially, preferably predominantly, automatically, in particular exclusively by linear movement of one or both substrates towards each other, between the substrates, in particular by concentric or radially symmetrical spreading. A central aspect of the invention is to apply the bonding material in a quantity free of excess. The disclosed embodiment of the invention is in particular self-regulating with regard to • an adjustment of the layer thickness and / or • a wedge fault compensation and / or • a fluid distribution.

[0024] Self-regulating means that no control is required to optimize the aforementioned parameters, particularly from an external source. A system according to the invention, once left to its own devices, strives for a state with a maximally homogeneous layer thickness, a minimal wedge defect, and / or an optimal liquid distribution, particularly through the effect of gravity on the upper substrate and / or through capillary action between the two substrates.

[0025] Excess-free means that the amount of bonding material applied is sufficient to form the complete bonding layer with a specified thickness t, in particular without bonding material extending beyond a circumferential edge of at least one of the substrates.

[0026] Preferably, the applied quantity is applied to an area B that is small compared to the contact area A of the substrates. Preferably, the ratio of area B to A is less than 1 / 2, even more preferably less than 1 / 3, even more preferably less than 1 / 4, even more preferably less than 1 / 5.

[0027] The liquid is distributed automatically, particularly by the weight of one of the two substrates (especially the upper one) and / or by capillary action of the liquid between the two substrates. One of the two substrates is released, particularly after contact between the liquids (in the case of application to both substrates) or between the liquid and one of the substrates.

[0028] This results in a defect-free, efficient, and material-saving distribution of the bonding material and the formation of a bonding layer between two substrates with minimal effort and energy expenditure. The liquid is distributed in such a way that an average thickness t of the cured bonding layer is defined, and the homogeneous, bubble-free distribution ensures that the total thickness of the stack consisting of the first substrate, the second substrate, and the bonding layer remains constant across the surface. In particular, the formation of edge beads is also prevented. When using transparent substrates and liquids that can be cured by electromagnetic radiation, especially permanent adhesives, the liquid can be cured directly by irradiation, particularly with UV light.

[0029] At least two substrates are used to distribute the bonding material, which is intended to remain between the two substrates for a certain period of time. According to the invention, temporary and permanent bonding methods are preferred.

[0030] The bonding material is, in particular, a permanent bonding adhesive. However, according to the invention, the use of a temporary adhesive, a photoresist, a liquid that is subsequently converted into an insulating layer, or a cleaning fluid would also be conceivable. The bonding material is understood to include, in particular, all types of mixtures, preferably adhesives dissolved in solvents.

[0031] According to the invention, defect formation, in particular bubble formation, is prevented even in compound materials with high to very high viscosity. Furthermore, the embodiment according to the invention achieves a liquid distribution with a very homogeneous layer thickness t.

[0032] The substrates can have any shape, but are preferably circular. In particular, according to the invention, the substrates have no projections or edges extending beyond the contact surfaces. The contact surface is designed to be, in particular, completely flat. The diameter of the substrates is, in particular, industrially standardized. For wafers (preferred substrates), diameters of 1 inch, 2 inches, 3 inches, 4 inches, 5 inches, 6 inches, 8 inches, 12 inches, and 18 inches are particularly preferred. However, the embodiment according to the invention can, in principle, handle any substrate, regardless of its diameter. The embodiment according to the invention is particularly suitable for coating and bonding rectangular substrates, preferably glass substrates. In a first process step according to the invention, a defined quantity of the bonding material is deposited or applied to the first and / or the second substrate.The liquid is preferably deposited / applied centrally, forming a puddle or a droplet. The application is carried out in such a way as to create a smooth and clean liquid surface, taking into account, in particular, the choice of material and / or other process conditions such as temperature and pressure, according to the invention. Irregularities in the liquid surface can lead to unwanted inclusions.

[0033] In a specific embodiment of the invention, the liquid is applied to the substrate surface not as drops, but as a geometric pattern. By selectively depositing a liquid pattern, the distribution of the liquid during the distribution process according to the invention can be influenced. This specific embodiment of the invention offers particular advantages for the uniform distribution of the liquid on non-circular, especially rectangular, for example, square, substrates. Rectangular substrates do not possess radial symmetry. The path to a corner of such a rectangular substrate is therefore longer from the geometric center of the substrate than the path to some of the edges. In general, the paths are therefore dependent on the direction in which the liquid is distributed.In order to distribute the liquid evenly, and especially simultaneously, over the substrate surface, according to the invention more liquid is deposited in the direction of longer paths.

[0034] According to one embodiment of the invention, in particular by depositing the liquid in a cross shape, with the corners of the cross pointing towards the corners of the rectangular substrate, an initial situation can be created which, with the distribution of the liquid according to the invention, results in the liquid reaching every point of the rectangular substrate approximately, preferably exactly, simultaneously. Analogous considerations apply to substrates of arbitrary shape, wherein the pattern of the liquid is calculated or determined experimentally for each substrate shape individually. In most specific extensions of the invention, the pattern will be composed of combinations of lines and / or points. In a particular extension of the invention, the line thicknesses of the lines of the pattern are varied during deposition.By generating such a pattern, it can also be ensured that a contact wave of the process according to the invention starts from the correct contact point. Generating such patterns enables faster and, above all, more homogeneous coating by the process according to the invention. A deposited droplet can again be located on the substrate surface of the second substrate, which then contacts the pattern on the substrate surface of the first substrate.

[0035] In particular, the amount of liquid deposited / applied with respect to the desired thickness t at the end of the process, i.e., especially after the liquid has hardened, is determined, and in particular calculated. Assuming a homogeneous distribution of the liquid between the substrates, a 100% incompressible liquid with constant density, and a correspondingly predetermined substrate area, the amount of liquid to be deposited is calculated, in particular, as follows. The volume V of the compound layer with thickness t over the base area A (connection area of ​​the first and / or second substrate) after completion of the process according to the invention is: V=t*A

[0036] In the case of circular substrates, the area A is equal to the square of the circle radius (or half the diameter) times the number π, i.e. V=t*r2*π=t*(d2)2*π

[0037] In the case of an incompressible liquid, the volume is independent of the pressure. Specifically, the amount of liquid bonding material is deposited / applied by volume control, whereby, given a specific substrate area A and a desired or set layer thickness t, the volume to be deposited is dispensed, particularly after accounting for shrinkage caused by curing. This shrinkage, which is primarily polymerization shrinkage, is specified by the shrinkage parameter s. Polymerization shrinkage refers to the decrease in volume or compaction of a polymer due to the progressive cross-linking of the polymer chains. This irreversible process occurs primarily in permanent bonding adhesives. Another reason for the decrease in volume is the outgassing of liquid components.In the embodiments according to the invention, outgassing of a liquid would be difficult or even impossible, since the distributed liquid is located between two substrates that are generally gas-tight. Outgassing would only be possible via the relatively narrow area between the circumferential contours of the two substrates. Therefore, this type of shrinkage will not be discussed in further detail. The shrinkage parameter s is defined as the difference between 1 and the ratio of the volume V after shrinkage to the volume V0 before shrinkage, hence: s=1−VV0

[0038] The shrinkage is less than 0.2, preferably less than 0.1, even more preferably less than 0.01, most preferably less than 0.001, and most preferably 0.

[0039] Alternatively, the amount of liquid is separated / applied in particular by mass control, whereby the calculated volume is multiplied by the (in particular constant) density of the bonding material. m=ρ*V=ρ*t*r2*π=ρ*t(d2)2*π

[0040] According to the invention, it is particularly important to ensure that the density of the liquid is a function of the temperature. Preferably, the thickness t of the compound layer is minimized in order to optimize the transmission of electromagnetic radiation through the compound layer, i.e., to reduce absorption.

[0041] As an example, but not an exhaustive one, the amount of liquid to be deposited for different layer thicknesses and a given substrate diameter is presented in tabular form. The density is expressed as 1 g / cm³. 3The chosen value is a realistic value for the density of the polymers according to the invention. The actual density of a thermoplastic, in particular a thermoplastic dissolved in a solvent, may deviate from this.

[0042] Tabular representation of a series of liquid quantities to be separated with volume V (or correspondingly converted mass m) for a 200mm substrate and different thicknesses t. Radius rm Area Am 2 Density ρg / cm³ 3 Dicke tµm Volume Vm 3 Masse mkg 0,1 0,031416 1 1 3,14159E-08 3,14159E-05 0,1 0,031416 1 2 6,28319E-08 6,28319E-05 0,1 0,031416 1 5 1,5708E-07 0,00015708 0,1 0,031416 1 10 3,14159E-07 0,000314159 0,1 0,031416 1 50 1,5708E-06 0,001570796 0,1 0,031416 1 100 3,14159E-06 0,003141593

[0043] The thickness t of the compound layer according to the invention is particularly between 100µm and 0.001 µm, preferably between 75 µm and 0.01 µm, even more preferably between 50 µm and 0.1 µm, most preferably between 25 µm and 1 µm, and most preferably between 10 µm and 1 µm.

[0044] In a further, particularly second, process step, the two substrates are brought closer together. Before and / or during this approach, wedge error compensation between the substrates can be performed. Preferably, the two substrates are rapidly brought close to a first position to accelerate the process. During this approach process to the first position, the relative approach speed of the two substrates is particularly greater than 0.01 mm / s, preferably greater than 0.1 mm / s, even more preferably greater than 1 mm / s, and most preferably greater than 10 mm / s. However, the embodiment according to the invention has the advantage that wedge error correction can usually be completely dispensed with. The wedge error is completely, or at least almost completely, compensated automatically by the self-distributing liquid between the two substrates.

[0045] The first position preferably ends with the contact of the liquids (when applied to both substrates) or of the liquid with one of the two substrates.

[0046] The relative approach speed is reduced upon reaching the first position and is particularly less than 1 mm / s, preferably less than 0.1 mm / s, more preferably less than 0.01 mm / s, and most preferably less than 0.001 mm / s. In a particularly preferred embodiment, the process according to the invention is therefore carried out in a two-stage process as described above.

[0047] In a further, and in particular third, process step according to the invention, one of the substrates, especially the second substrate, is released from its fixation (receiving device). If the two substrates are stored horizontally, the force of gravity and the capillary force acting through the liquid between the two substrates pull the upper substrate towards the lower substrate. The resulting pressure distribution within the liquid causes it to spread automatically along the interface. The spreading liquid wave pushes the air ahead of it and removes all types of gases from the substrate interface. The liquid distribution is particularly uniform, more preferably radially symmetrical, and preferably concentric. With appropriate storage and selection of a liquid viscosity high enough to prevent the liquid from spreading when exposed to transverse or vertical forces, the distribution of the liquid is further enhanced.While the substrates are positioned vertically, a transverse or vertical orientation is also conceivable. In such a specific embodiment according to the invention, capillary action alone would ensure the automatic approach of the substrates to one another and the distribution of the liquid between them.

[0048] In a further, and in particular a fourth, step according to the invention, the liquid reaches the edge of the two substrates, and due to the predetermined quantity and the absence of capillary action, the distribution is automatically terminated. The liquid (connecting material) possesses, in particular, a viscosity that is low enough to allow it to spread between the two substrates, but high enough to prevent it from escaping the substrates held together by the surface tension present at the edge. Viscosity is a physical property that is strongly temperature-dependent. The viscosity of liquids, especially polymers, generally decreases with increasing temperature. The viscosity of the connecting material according to the invention is, in particular, between 10 at room temperature. 6 Pa*s and 1 Pa*s, preferably between 10 5 Pa*s and 1 Pa*s, even more preferably between 10 4Pa*s and 1 Pa*s, preferably between 10 3 Pa*s and 1 Pa*s.

[0049] The processes according to the invention generally function with any hydrophilicity value of the substrate surfaces. The hydrophilicity values ​​of the substrate surfaces can also differ, particularly through the use of different substrate materials and / or different surface treatment processes. Thus, broadly distinguishing between hydrophobic and hydrophilic, the following combinations are generally possible for the first and second substrates. • hydrophobic-hydrophobic • hydrophilic-hydrophilic • hydrophobic-hydrophilic • hydrophilic-hydrophobic

[0050] According to the invention, hydrophilic substrate surfaces are used primarily when a corresponding wetting effect, and thus a larger contact area and correspondingly higher adhesion strength, between the liquid and the substrate surface is desired. In particular, substrates on whose underside liquids are to be deposited in the form of droplets exhibit a correspondingly high hydrophilicity.

[0051] Hydrophobic surfaces, on the other hand, are used according to the invention primarily to create point contact between a deposited liquid and the substrate surface. Such point contacts can be particularly advantageous in those embodiments of the invention where the liquid is deposited only on the hydrophilic underside of the upper substrate, while the upper surface of the hydrophobic lower substrate makes only point contact with the convex droplet. The weight of the upper substrate then spreads the droplet between the two substrate surfaces from this point contact.

[0052] Hydrophilicity is determined using the contact angle method. This involves measuring the angle between the tangent to a liquid droplet and the wetted surface using an optical instrument. The method is known to those skilled in the art. The measured angle is acute for high hydrophilicity and obtuse for high hydrophobicity. The preferred contact angle between the liquid compound and the contact surfaces is, in particular, less than 90° for hydrophilic substrate surfaces according to the invention, preferably less than 70°, even more preferably less than 50°, and most preferably less than 30°. The preferred contact angle between the liquid compound and the contact surfaces is, in particular, greater than 90° for hydrophobic substrate surfaces according to the invention, preferably greater than 125°, even more preferably greater than 150°, and most preferably greater than 175°.

[0053] Should it be necessary to convert a hydrophobic substrate surface into a hydrophilic one (or a hydrophilic substrate surface into a hydrophobic substrate surface), this can be carried out using any known technique before performing the process according to the invention. Possible techniques include plasma treatments, surface etching, chemical treatments, coatings, sputtering, increasing the surface roughness, etc.

[0054] In the following, both substrate surfaces are assumed to be hydrophilic (preferred embodiment).

[0055] To ensure the distribution of the liquid and, above all, optimal wetting of the interfaces, the substrate surface is preferably hydrophilic. If the deposition / application of a droplet occurs, particularly onto the upper / second substrate, excessive hydrophobicity (i.e., insufficient hydrophilicity) can adversely affect the adhesion between the liquid and the substrate surface. The hydrophilicity (i.e., the adhesive force) between the liquid and the substrate surface is preferably at least high enough that the liquid is not pulled away from the substrate surface by gravity. In this case, a hydrophilicity is therefore chosen at which the contact angle is at least greater than 0°, particularly greater than 10°, and preferably greater than 20°.

[0056] Another relevant physical parameter according to the invention is the adhesion between the bonding layer and the substrates. Adhesion is preferably defined by the energy per unit area required to separate two bonded surfaces. This energy is expressed in J / m². 2 The bonding layer and the substrates are specifically selected such that the energy per unit area is less than 2.5 J / m². 2 , preferably less than 0.1 J / m² 2 , with greater preference for values ​​less than 0.01 J / m 2 , preferably less than 0.001 J / m² 2 , preferably smaller than 0.0001 J / m² 2 , preferably less than 0.00001 J / m² 2A preferred, and in particular empirically determined, average value of the energy per unit area between a coating material, in particular one applied to at least one of the substrates, and a polymer as a bonding material, is approximately 0.1 J / m². 2 A typical, empirically measured average value of energy per unit area, between pure silicon and the same polymer, is approximately 1.2 J / m². 2 The corresponding values ​​can vary depending on the coating material, substrate material, and impurities, in this case a polymer. Far more efficient coating materials are expected in the future.

[0057] In a particular embodiment according to the invention, the connecting surfaces, in particular before a coating of the surfaces according to the invention, can be treated with a plasma and / or coated in order to change or selectively adjust the surface properties, in particular the hydrophilicity or hydrophobicity.

[0058] The types of plasma that can be used are preferably • Inductive plasma • Capacitive plasma • Remote plasma

[0059] The contact angle or the desired adhesion is set by selecting the plasma parameters.

[0060] According to an advantageous embodiment of the invention, by separating the exact amount of liquid from the bonding material and / or by knowing the density, viscosity, and / or surface properties of the bonding material, the process is carried out in such a way that the liquid does not leave the circumferential edge of the two substrates. This prevents the system in which the process according to the invention is carried out from being contaminated by the liquid.

[0061] According to a preferred embodiment of the invention, the two substrates are joined by the combination of the bonding material applied to the lower / first substrate with the bonding material applied to the upper / second substrate, particularly in the form of a droplet. The droplet can be deposited, for example, by a device for depositing liquids against the direction of gravity, as described in German patent DE 102013113241.3. The droplet can also be applied manually. This embodiment of the invention is particularly preferred because the droplet has a perfectly convex shape at the bonding surface (contact surface) of the second, upper substrate due to the force of gravity acting on the droplet. In contrast, the liquid at the bonding surface of the first, lower substrate can exhibit concave areas, especially if it was poorly deposited.Concave areas arise primarily, but not exclusively, from multiple deposition of liquid at different, particularly non-centric, positions on the first, lower substrate. Since these multiple depositions can be largely minimized by appropriately calibrated deposition systems, concave areas in the submillimeter or submicrometer range are particularly important. Occasionally, local surface tension changes (e.g., caused by grease particles, dust particles, ions, organic molecules, etc.) can create local, very small (barely perceptible to the naked eye) concave areas on the liquid surface, which can act as nucleation sites for defect or bubble formation.Regardless of the cause of the formation of an imperfect convex liquid surface, this embodiment of the process can prevent the formation of defects. This embodiment results in the merging of the droplet at the interface of the second, upper substrate with the liquid at the interface of the first, lower substrate, which exhibits concave areas. The continuous, and in particular slow, approach allows sufficient time for defects, especially gas inclusions, to be forced outwards.

[0062] According to the invention, the liquid is deposited on the substrate surface of the lower / first substrate by centrifugal coating or spray coating. The bonding material is then applied as droplets to the substrate surface of the upper / second substrate.

[0063] In a further embodiment of the invention, the bonding material is applied to the lower / first substrate in the form of a pattern. The pattern is selected such that the distribution of the bonding material according to the invention results in optimal, rapid, and, above all, simultaneous wetting of the substrate surfaces. This type of distribution is particularly preferred for non-circular, especially rectangular, substrates, since the length of the path that the bonding material travels from the center to the edge depends on the direction. Therefore, a deposition of the bonding material adapted to the geometry of the substrate, particularly on the lower / first substrate, is advantageous. On the upper / second substrate, a droplet of the bonding material is deposited, in particular, to facilitate the contacting according to the invention.

[0064] In a particular embodiment, it is conceivable according to the invention to deposit / apply geometric figures, in particular a (or several, preferably intersecting) rectangle, instead of a drop and / or a puddle. This accelerates the distribution process of the liquid between the two substrates according to the invention due to the improved pre-distribution and the resulting increased capillary action.

[0065] The specifically deposited geometric shapes pre-distribute the liquid over a longer distance (e.g., a line) or over several longer distances (e.g., a cross). These geometric shapes preferentially accelerate the liquid wave generated and driven by capillary forces, thus accelerating the liquid distribution process according to the invention.

[0066] In a further, particularly preferred, embodiment of the invention, the dispensing of the liquid at the lower / first substrate is omitted. Dispensing occurs exclusively at the interface / contact surface of the second / upper substrate, particularly as a single droplet. The single droplet dispensed at the interface of the second, upper substrate is particularly advantageous for producing extremely thin liquid layers. Due to the dispensing of the droplet at the interface of the second, upper substrate, gravity acts upon the droplet, causing it to have a perfectly convex shape and no concave areas. The point-like contact between the droplet and the interface of the first, lower substrate is correspondingly precise. In this embodiment, dispensing only needs to occur once, thus saving time and costs.

[0067] The distribution of the liquid compound material (liquid) at room temperature according to the invention is the preferred embodiment. Alternatively, temperature control of the first and / or second substrate is conceivable according to the invention. By temperature control of the first and / or second substrate, the viscosity of the liquid can be specifically adjusted and thus the flow behavior regulated. The first / upper and / or second / lower substrate is / are temperature-controlled depending on the desired viscosity of the liquid. The temperature range according to the invention is particularly between -100°C and 300°C, preferably between -50°C and 300°C, more preferably between 0°C and 300°C, most preferably between 50°C and 300°C, and even more preferably between 100°C and 300°C. In particular, no permanent cross-linking of the liquid takes place in the temperature range of the temperature control of the first and / or second substrate.

[0068] The compound material to be distributed between the two substrates according to the process of the invention is preferably cured, particularly during and / or after the distribution of the compound material between the substrates. Curing is carried out either by means of electromagnetic radiation and / or by means of heat. The electromagnetic radiation has a wavelength in the range between 10 nm and 2000 nm, preferably between 10 nm and 1500 nm, more preferably between 10 nm and 1000 nm, most preferably between 10 nm and 750 nm, and most preferably between 10 nm and 500 nm.

[0069] In the case of thermal curing, the liquid is heated to a temperature greater than 100°C, preferably greater than 200°C, even more preferably greater than 300°C, most preferably greater than 400°C, and most preferably greater than 500°C. In this embodiment, the thermal conductivity of the substrates is preferably as high as possible in order to transfer the heat quickly and efficiently to the bonding material. The thermal conductivity of at least one of the two substrates is preferably between 0.1 W / (mK) and 5000 W / (mK), preferably between 1 W / (mK) and 2500 W / (mK), even more preferably between 10 W / (mK) and 1000 W / (mK), and most preferably between 100 W / (mK) and 450 W / (mK).

[0070] In a particularly preferred embodiment, the liquid is separated against gravity by generating a droplet, held together in particular by surface tension, at the end of a separation tube, especially a needle, and by transferring this droplet through contact with a substrate surface. The droplet size can be determined by precisely selecting the diameter of the outlet opening.

[0071] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. These show: Fig. 1a a schematic, not to scale cross-section of a first process step of a first embodiment according to the invention, Fig. 1b a schematic, not to scale cross-section of a second process step of the first embodiment, Fig. 1c a schematic, not to scale cross-section of a third process step of the first embodiment, Fig. 1d a schematic, not to scale cross-section of a fourth process step of the first embodiment, Fig. 2a a schematic, not to scale cross-section of a first process step of a second embodiment according to the invention with a less than optimally separated amount of liquid, Fig. 2b a schematic, not to scale cross-section of a first process step of the second embodiment according to the invention with an optimally separated amount of liquid, Fig. 2c a schematic, not to scale cross-section of a first process step of the second embodiment according to the invention with an optimally distributed quantity of liquid, Fig. 2d a schematic, not to scale cross-section, as well as a corresponding top view, of a first process step of the second embodiment according to the invention with a generated pattern, Fig. 3 a schematic, not to scale cross-section of a first process step of a third embodiment according to the invention and Fig. 4 a schematic, not to scale cross-section of an embodiment according to the invention for droplet separation.

[0072] In the figures, identical or equivalent features are marked with the same reference symbols.

[0073] Fig. Figure 1a shows the initial state of a first process step according to the invention under ideal conditions. A centrally deposited quantity of liquid of a compounding material 3 with an ideal, convex liquid surface 3o is deposited on the bonding surface 1o of a first, lower substrate 1o. A second, upper substrate 2 is aligned with its bonding surface 2o opposite the bonding material 3. Alignment refers in particular to wedge error compensation and / or alignment with respect to circumferential contours 1u / 2u of the substrates 1, 2 and / or alignment marks of the substrates 1, 2 (not shown). The alignment of the substrates 1, 2 is carried out in particular by a suitable alignment system. However, wedge error compensation can preferably be omitted, since automatic wedge error compensation takes place in the later process steps of the process according to the invention.

[0074] In a second process step according to the invention, Fig. 1b The two substrates 1 and 2 are brought relatively close to each other. In a first embodiment of the invention, in which the second, upper substrate 2 is held by a mechanism (not shown) on a corresponding second receiving device, it is preferred that the first, lower substrate 1 be brought close to the sample holder by moving a lower sample holder (first receiving device). However, it would also be conceivable that the first, lower substrate 1 remains fixed on a lower sample holder and the upper, second substrate 2 is brought close to the sample holder.

[0075] When the connecting surface 2o of the upper substrate 2 comes into contact with the liquid surface 3o at the contact point 4, the fixation of the upper substrate 2 is released and the weight force G acting on the upper substrate 2, as well as a, in particular, lesser, capillary force K, pulls the two substrates 1 and 2 according to Fig. 1c together. An inclined or even vertical mounting of the two substrates 1 and 2 is less preferred, as this could distort the liquid. The continuous approach of the two substrates 1 and 2 also ensures that the liquid is evenly distributed between them; in particular, this distribution is supported or improved by capillary action. In this process step according to the invention, the interaction of gravity and capillary force homogenizes the connecting material 3 and thus automatically compensates for wedge errors. With appropriately precisely manufactured, geometrically equivalent substrates, automatic alignment of the two substrates relative to each other can even occur.

[0076] In a final step according to the invention, according to Fig. 1d, which occurs primarily when using curable liquids as the bonding material 3, the first substrate 1 and / or the second substrate 2, and thus in particular also the bonding material 3, are subjected to electromagnetic radiation and / or heat. The subjection of the first substrate 1 and / or the second substrate 2 is carried out in Fig. 1d is symbolized by the arrows acting on the two substrates 1 and 2.

[0077] Fig. Figure 2a shows a preferred embodiment of the invention in which a droplet is applied as a bonding material 5 to the bonding surface 2o of the second substrate 2. Due to the gravitational force acting upon it, the droplet 5 has a perfectly convex droplet surface 5o. The liquid 3' additionally deposited on the lower bonding surface 1o was deposited by a faulty or poorly calibrated deposition system. The liquid surface 3o' therefore does not have a perfectly, purely convex liquid surface 3o'. This type of faulty deposition is primarily caused by incorrectly calibrated, outdated, or contaminated nozzles on the deposition system (not shown).

[0078] According to the invention, it would also be conceivable to deposit several puddles / droplets distributed over the substrate surfaces 10, 20, which would then combine to form the one in Fig. Combine the liquid shown in 2a with 3'.

[0079] The extreme situation of the disadvantageously deposited liquid 3' on the interface 1o of the lower substrate 1 in Fig. 2a practically does not occur in correctly calibrated and cleanly functioning deposition systems. However, the formation of several local convex regions 4, 4' between which corresponding concave regions 6 are located is quite conceivable ( Fig. 2b). These areas 4, 4', 6 are primarily caused by particles in the millimeter, micrometer, and nanometer range, which can lead to a change in surface tension. If such a liquid surface were to come into direct contact with an extremely flat substrate surface 2o, small bubbles in the millimeter, micrometer, and nanometer range would form.

[0080] The second embodiment according to the invention can eliminate both problems by depositing a droplet 5 at the interface 2o of the upper substrate 2. The inventive deposition of a droplet at the substrate surface 2o of the substrate 2 allows, in particular, the direct contact of two liquids, the compounding material 3'' and the droplet-shaped compounding material 5. This allows any bubbles that might potentially form during contact to escape from the interface of both compounding materials 3'' and 5 through fluid-dynamic relaxation processes, and the resulting combined compounding material remains bubble-free.

[0081] In a further embodiment according to the invention Fig. 2c the liquid 3''' can be deposited uniformly over the substrate surface 1o of the substrate 1 by a coating process, in particular by centrifugal coating or spray coating.

[0082] The Fig. Figure 2d shows a further, non-scale, transverse or top view according to the invention of two rectangular substrates 1', 2', on which a bonding material 3 is applied. IV was applied in the form of a pattern. The pattern allows, after contacting the connecting materials, 3 IV and 5 a faster, more efficient, more homogeneous and, most importantly, simultaneous distribution of the combined bonding material between the two rectangular substrates 1' and 2'.

[0083] Then a procedure will be carried out in accordance with the Fig. 1c-1d analogous procedure.

[0084] In a particularly preferred embodiment of the invention, only a single droplet 5 is deposited at the interface 20 of the upper substrate 2. Due to the force of gravity, the droplet 5 has a purely convex shape. The amount of liquid in the droplet 5 is calculated to be sufficient to create the bonding layer 7 between the two substrates 1 and 2 according to the invention.

[0085] After the deposition of droplet 5, a further process takes place according to the Fig. 1c-1d analogous procedure of approach, contacting, distribution and curing.

[0086] Fig.Figure 4 shows a particularly preferred embodiment for depositing the compound material 5 in the form of a droplet onto a substrate surface 2o. The droplet is generated by a deposition tube 8 at a deposition tube opening 8o. The surface tension of the compound material holds the droplet together. After the formation of a droplet at the end of such a deposition tube 8, in particular a needle or a syringe opening, a relative approach occurs between the droplet 5 or the deposition tube opening 8o and the substrate 2. The droplet finally touches the substrate 2 and is transferred from the deposition tube opening 8o to the substrate surface 2o. According to the invention, a deposition tube diameter D is in particular less than 5 mm, preferably less than 2 mm, even more preferably less than 1 mm, most preferably less than 0.1 mm, and most preferably less than 0.01 mm. Reference symbol list 1, 1' First substrate 10, 10' First connecting surface 1u perimeter contour 2.2' Second substrate 20, 20' Second connecting surface 2u perimeter contour 3, 3', 3'', 3''', 3 IV Connecting material 30, 30', 30'', 30''', 30 IV liquid surface 4.4' Convex area 5 (drop-shaped) bonding material 50 drop surface area 6 Concave Area 7. Compound layer 8 Separation tube 8o Separator pipe opening t thickness G Gravitational force K Capillary force D separation tube diameter

Claims

[1] Method for bonding a first lower substrate (1) to a second upper substrate (2) by means of a bonding layer (7) made of a bonding material (3, 5) arranged between the substrates (1, 2) comprising the following steps: - Coating the first lower substrate (1) with the bonding material (3, 5) by centrifugal or spray coating, - Applying at least one drop of the compound material (3, 5) to the second upper substrate (2) in liquid form and - after coating the first lower substrate (1) after applying the at least one drop of the compounding material (3, 5) to the second upper substrate (2) the compounding material (3, 5) is distributed between the substrates (1, 2) by bringing the substrates (1, 2) closer together, the distribution occurring automatically by means of the capillary force of the liquid compounding material (3, 5), one of the two substrates (1, 2) being left free after contact of the at least one drop with the compounding material (3, 5) on the first lower substrate (1), and thereby forming the shape of the compounding layer (7) with a thickness t, the compounding material (3, 5) being applied in an excess-free quantity. [2] Method according to claim 1, wherein the bonding material (3, 5) is applied in an amount, in particular without excess, which is determined by the thickness t of the bonding layer (7) and a diameter of at least one of the substrates (1, 2). [3] Method according to one of the preceding claims, wherein the bonding material (3, 5) is applied to both substrates in corresponding areas. [4] Method according to one of the preceding claims, wherein the distribution and / or approximation is carried out at least partially exclusively by the capillary force of the liquid compound material (3, 5) and / or by the gravitational force G of one of the substrates (1, 2). [5] Method according to one of the preceding claims, wherein the connecting surfaces (1o, 2o) of the substrates (1, 2) are coated with a coating and / or treated with a plasma before the application of the connecting material (3, 5). [6] Method according to one of the preceding claims, wherein the bonding material (3, 5) is cured during and / or after the distribution and approximation of the substrates (1, 2).

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