Method for fixing optical element to substrate in beam path of optoelectronic component, and optoelectronic component

Abstract

The invention relates to a method for fastening an optical element to a substrate in the beam path of an optoelectronic component, comprising the following steps: providing an optical element having a first surface comprising a first surface material, and providing a substrate having a second surface comprising a second surface material, wherein the first surface material and the second surface material are selected independently of one another from a transparent oxide material and a transparent nitride material, applying an alkaline solution to the first surface and / or the second surface, arranging the first surface on the second surface, wherein a tie layer having an inorganic polymer network is formed between the first surface material and the second surface material. The invention further relates to an optoelectronic component. The optoelectronic component can be a light emitting diode, such as an LED.

Description

TECHNICAL FIELD

[0001] A method for fixing an optical element on a substrate in an optical path of an optoelectronic component is proposed as well as an optoelectronic component. SUMMARY

[0002] It is an object of at least one embodiment to propose a method for fixing an optical element on a substrate in an optical path of an optoelectronic component, which has improved properties. It is an object of at least one further embodiment to propose an optoelectronic component having improved properties. These objects are achieved by the method and the optoelectronic component according to the independent claims. Further features and embodiments of the method and the component are subject matter of the dependent claims.

[0003] A method for fixing an optical element on a substrate in an optical path of an optoelectronic component is proposed.

[0004] Here and in the following, "fixing" is understood as a mechanical fastening, which is permanent and in particular irreversible.

[0005] The optical component is provided and configured for generating electromagnetic radiation. To this end, the optical component comprises for example a semiconductor chip or a laser chip, which generates electromagnetic radiation when energized. Depending on the nature of the semiconductor chip or the laser chip, the electromagnetic radiation can have for example a wavelength selected from the UV range and / or the visible light range. In particular, the electromagnetic radiation has a wavelength from the UV-C range, for example between 100 nm and 280 nm.

[0006] The generated electromagnetic radiation is conducted through the means provided for this purpose of the optoelectronic component and in particular coupled out of the optoelectronic component by means of the optical element. The path through which the electromagnetic radiation passes when exiting the optoelectronic component is referred to as the optical path.

[0007] Here and in the following, an optical element is understood as a component of the optoelectronic component, which is capable of coupling out incident electromagnetic radiation and optionally also of changing the electromagnetic radiation. This change can for example consist in that the incident electromagnetic radiation is focused, diverged or its wavelength is completely or partially converted into another wavelength. In accordance therewith, the optical element can for example be selected from a lens, a prism, a conversion foil, a micro-optical device or a sealing window.

[0008] The substrate can be any component of the optoelectronic component, which is provided in the optical path of the component and on which the optical component can be reasonably applied in order to achieve an efficient coupling out of electromagnetic radiation from the optoelectronic component. The substrate can for example be a growth substrate of a semiconductor chip or for example a passivation layer applied on a semiconductor chip.

[0009] According to at least one embodiment, the method comprises the steps of providing an optical element having a first surface comprising a first surface material and providing a substrate having a second surface comprising a second surface material. That is, the optical element and the substrate have a surface comprising a specific surface material, respectively.

[0010] The first surface material can be the base material of the optical element or can also be the material which only forms the first surface. If only the first surface is formed by the first surface material, the first surface material can be configured as a thin layer, for example having a thickness from the range of 10 nm to 10 pm, including the boundary values.

[0011] The second surface material can be the material of the entire substrate or can also be the material which only forms the second surface. If only the second surface is formed by the second surface material, the second surface material can be configured as a thin layer, for example having a thickness from the range of 10 nm to 10 pm, including the boundary values.

[0012] According to at least one embodiment, the first surface material and the second surface material are selected independently of one another from transparent oxide materials and transparent nitride materials. In particular, the first surface material and the second surface material are selected independently of one another from AI2O3, sapphire, Si4N3, ZnO, ITO, ZrO2, HfO2, Ta2O5, Si(O) x N y , TiO2, GaN, quartz, quartz glass, oxide glass, phosphate glass, Si (with natural oxide layer) and GaAs (with natural oxide layer).

[0013] That is, for example, the substrate of an optoelectronic device and an optical element, for example a lens, can be fixed directly against one another, wherein the first surface of the optical element has a first surface material selected from sapphire, quartz, quartz glass, oxide glass and phosphate glass, wherein the second surface of the substrate has a second surface material selected from AI2O3, sapphire, Si4N3, Si, ZnO, ITO, ZrO2, HfO2, GaAs, GaN, Ta2O5, Si(O) x N y 2) and TiO2. Here, the optical element and the substrate can each be formed completely from the mentioned materials or only at their first or second surface to be fixed have these materials. Furthermore, the first and second surfaces can have the same or different materials from one another. In particular, when selecting the material of the optical element, here attention is paid to a high transparency for the radiation emitted by the optoelectronic device, for example radiation from the UV-C range.

[0014] According to at least one embodiment, the method further comprises the step of applying a basic solution onto the first surface and / or the second surface. That is, a basic solution is applied onto the first surface, the second surface or both the first and the second surface. Herein and in the following, a basic solution is understood to be a solution of an inorganic compound which contains or is able to form hydroxide ions and which has an etching effect when in contact with a surface.

[0015] According to at least one embodiment, the method further comprises the step of arranging the first surface on the second surface. In particular, the first and the second surface are arranged successively such that they are superimposed or, if the two surfaces have different lateral extensions, such that the smaller surface is completely covered by the larger surface. Arranging the first surface on the second surface is in particular carried out after the basic solution has been applied to the first and / or the second surface. Thus, in the arranging step, the basic solution is arranged between the first surface and the second surface.

[0016] According to at least one embodiment, in the method, a connection layer comprising an inorganic polymer network is formed between the first surface material and the second surface material.

[0017] Herein and in the following, an inorganic polymer network is understood to be a network composed of three-dimensionally linked inorganic polymer chains. The connection layer can comprise, in particular be composed of, an inorganic polymer network. This means that an inorganic compound is formed between the first surface or the first surface material and the second surface or the second surface material. The connection layer does not necessarily mean that there is a precisely definable boundary between the connection layer and the first surface material or between the connection layer and the second surface material. Rather, the inorganic polymer network can also gradually transition into the first surface material or the second surface material. In any case, by the connection layer composed between the surface materials to be joined, a firm covalent connection exists between the surface materials to be joined. According to one embodiment, the polymer network can comprise and / or be composed of Si-O bonds.

[0018] According to at least one embodiment, a method for fixing an optical element on a substrate in an optical path of an optoelectronic device comprises the following steps:

[0019] - providing an optical element having a first surface comprising a first surface material; and providing a substrate having a second surface comprising a second surface material, wherein the first surface material and the second surface material are independently of each other selected from a transparent oxide material and a transparent nitride material,

[0020] - applying a basic solution onto the first surface and / or the second surface,

[0021] - disposing the first surface on the second surface, wherein a connection layer with an inorganic polymer network is formed between the first surface material and the second surface material.

[0022] In the field of optoelectronic devices, for example LEDs (light emitting diodes) or laser-based systems, it is common to integrate additional optical elements, for example lenses, prisms, conversion foils or sealing windows, in order to improve the light coupling output of the device and / or the durability and lifetime of the device. Depending on the application of the device, a specific connection technology and a material are required which have sufficient transparency in the desired wavelength range and which enable a sufficiently stable connection, especially also with respect to electromagnetic radiation.

[0023] Especially in devices provided for generating UV-C radiation, for example UV-C LEDs, a reliable radiation stability of the connection material is also necessary over a long period of time. UV-C LEDs emit electromagnetic radiation with a wavelength usually in the range of 100 nm to 280 nm, which can effectively inactivate viruses, bacteria and other pathogens within seconds, thus enabling disinfection of surfaces, air and water without the use of chemicals. In addition, the mentioned devices with increased efficiency have the potential to replace conventional mercury discharge lamps. In order to improve their performance, optical elements such as hemispherical lenses can be placed on such LEDs emitting UV-C radiation. However, for fixing the lenses a connection material is required which has a high radiation stability with respect to high-energy electromagnetic radiation.

[0024] The inventors have recognized that with the method described here a connection layer can be produced which has a high mechanical and chemical stability and a high transparency with respect to electromagnetic radiation, especially in the UV and visible range of the electromagnetic spectrum. At the same time, the connection layer is stable with respect to high-energy electromagnetic radiation, for example UV, especially UV-C radiation. Therefore, such a connection layer is also suitable for use in the optical path of an optoelectronic device.

[0025] Therefore, the method can be used, for example, in the field of UV-C LEDs, in which a high, durable and uniform stability of the connection layer with respect to high-energy UV-C radiation is necessary.

[0026] The method described here does not require fluorine-containing polymers or other organic materials. In addition, the method has with respect to the quality of the materials involved and with respect to the conditions to be implemented, which are easier to achieve, with respect to conventional methods, such as ADB (Atomic Diffusion Bonding) or SAB Surface Activated Bonding. In addition, with the method described here a large number of the same or different materials can be fixed next to each other.

[0027] By using a basic solution, the formation of the connecting layer is achieved, which leads to the formation of a chemical connection between the substrate and the optical element. This leads to a three-stage process. In a first step, the respective surface is etched when the basic solution is brought into contact with the first and / or the second surface, which is achieved, inter alia, by selecting the first and the second surface material from transparent oxide materials or nitride materials. The OH⁻ groups present in the basic solution lead to the hydration of these materials. This leads, in a further step, to the dissociation of the hydrated molecules of the first or the second surface material and, ultimately, to their cross-linking by polymerization and / or dimerization, whereby water is split off as a by-product to form an inorganic polymer network.

[0028] On the basis of these processes, inter alia, a connecting layer can be formed which comprises an inorganic polymer network which gradually and uniformly transitions into the first or the second surface material at the edge range of the connecting layer and can be a mixture in the center. That is to say, according to one embodiment, a connecting layer is formed which comprises an inorganic polymer network mixture or an inorganic polymer network in a central region parallel to the lateral extension and does not comprise pure first or second surface material, whereas the proportion of the first or the second surface material continuously increases with increasing distance from the central region until there is no longer a proportion of the inorganic polymer network mixture or the inorganic polymer network. This gradual transition means that there is a lack of strictly and clearly separable contact surfaces, whereby an approximately integral system can be formed which has a high mechanical stability and a high stability with respect to, inter alia, high-energy electromagnetic radiation. The high mechanical and chemical stability is determined here, inter alia, by the degree of cross-linking and leads to the fact that the inorganic polymer network produced is hydrolysis-stable.

[0029] Due to the gradual transition, the refractive index of the material of the connecting layer or of the adjoining surface material also gradually changes, which leads to a high transparency of the connecting layer by reducing the undesired reflection effects.

[0030] The high transparency and the high stability of the connecting layer produced by means of the method make the connecting layer and thus also the method suitable, inter alia, for use in the optical path of an optoelectronic device.

[0031] The use of a basic solution also offers the advantage that when two surfaces to be connected are arranged on top of one another, these two surfaces to be connected form a self-adjusting system, so that the necessary outlay in terms of their orientation relative to one another is less. Furthermore, the cost of the basic solution is negligible, so that the method can be carried out at low cost.

[0032] Finally, the use of a basic solution requires only a moderate surface quality. Thus, an average roughness of up to 100 nm, in particular in the range from 10 nm to 50 nm, is sufficient for carrying out the method described here.

[0033] By means of the method, it is possible, inter alia, to realize a connection layer in an optoelectronic component configured as a surface emitter, since the connection layer produced by means of the method is mechanically and radiation-stable over a large lateral extension, for example an extension of at least 1 mm 2 .

[0034] According to at least one embodiment, a connection layer is produced by means of the method, the connection layer having a thickness selected from the range of 50 nm to 800 nm, including the boundary values. The thickness relates to a region of the connection layer in which a certain proportion of the inorganic polymer network still exists in the case of a gradual transition of the inorganic polymer network into the first or second surface material.

[0035] According to at least one embodiment, the alkaline solution has a pH value of greater than 11. The alkaline solution is thus a strong base, by means of which the method described above can be carried out particularly effectively.

[0036] According to at least one embodiment, the alkaline solution is selected from the group consisting of an aqueous alkali metal silicate solution, an aqueous alkali metal aluminate solution and an aqueous alkali metal phosphate solution. The alkaline solution thus contains an additive selected from the group consisting of silicates, aluminates and phosphates.

[0037] According to at least one embodiment, the alkaline solution comprises an aqueous alkali metal silicate solution. According to at least one embodiment, the alkali metal silicate solution comprises a silicate component in a concentration of 2 to 40 percent by weight, including the boundary values, and a water content of 60 - 98% by weight, in particular deionized water (DI). The alkali metal silicate contained in the solution can have the general formula n(Si02) [mol] / n(R20) [mol], where R is selected from the group consisting of Na, K, Li and mixtures thereof. The molar ratio of silicate Si02 to alkali metal oxide R20 is from 1.0 to 7.8, in particular from 1.6 to 4.0, including the boundary values.

[0038] The alkaline solution is thus additionally enriched with silicates in this embodiment, which accelerate the profile of the inorganic polymer network, which can in particular be a three-dimensional network, and which can lead to a thicker connection layer, which reduces the requirements for the surface roughness of the surfaces to be connected in relation to an alkaline solution without silicate additives.

[0039] According to at least one embodiment, the alkaline solution comprises at least one of NaOH, KOH and LiOH. Here, the ratio of alkali hydroxide (NaOH, KOH, LiOH) to water can be between 1 : 100 and 1 : 300. The method described here can thus be carried out by means of an alkaline solution without silicates or without additives.

[0040] According to at least one embodiment, in the method, prior to the providing step, a first auxiliary layer is applied on the optical element to form the first surface comprising the first surface material, and / or a second auxiliary layer is applied on the substrate to form the second surface comprising the second surface material. Thus, after the application, the first or second auxiliary layer corresponds to the first or second surface.

[0041] The application of the auxiliary layer on the one hand can facilitate the profile of the inorganic polymer network and thus the formation of the connection layer, and on the other hand can also make the method available for substrates and / or optical elements, which auxiliary layer itself does not have a material which can constitute the connection layer by means of an alkaline solution. For example, a lens composed of MgF2 can be provided with such an auxiliary layer and fixed on a substrate by means of the method described here.

[0042] According to at least one embodiment, the first and / or second auxiliary layer has a layer thickness selected from the range of 5 nm to 10 pm, in particular from the range of 5 nm to 100 nm, including the boundary values. For example, the layer thickness of the first and / or second auxiliary layer is 20 nm.

[0043] According to at least one embodiment, as the first and / or second auxiliary layer, a transparent oxide material is applied independently of one another. In particular, the transparent oxide material is selected from SiO2, ZrO2 and Al2O3. These oxides are in particular transparent and do not show an absorption in the spectral range of short waves at wavelengths less than 280 nm, whereby the oxides are light-stable, for example with respect to UV-C radiation, and thus in particular suitable for application in the field of UV-C LED encapsulation.

[0044] According to at least one embodiment, the transparent oxide material of the first and / or second auxiliary layer is amorphous and / or porous. For example, as the first and / or second auxiliary layer, amorphous SiO2, amorphous ZrO2 or amorphous Al2O3 is applied. Thus, the first and / or second surface has a first or second surface material comprising amorphous SiO2, amorphous ZrO2 or amorphous Al2O3. The amorphous and / or porous structure of the one or both surface materials makes it easy for the alkaline etching attack of the first or second surface by an alkaline solution, thus facilitating the formation of a homogeneous, stable connection layer.

[0045] According to at least one embodiment, the method comprises the step of cleaning the first and second surfaces prior to applying the alkaline solution. Cleaning can be performed, inter alia, by means of dry-chemical or wet-chemical oxidation methods. For example, the first and second surfaces can be treated by means of ozone, oxygen plasma or by means of UV wet oxidation for cleaning. The cleaning step on the one hand ensures that the surfaces are free of contaminants, in particular free of organic deposits, and on the other hand the cleaning step can also prepare or activate the surfaces for the further method.

[0046] According to at least one embodiment, the first surface and / or the second surface to which the alkaline solution is applied has an area which is at least 100 pm 2 , for example 1 mm 2 in size. Thus, by means of the method it is possible to form a connection layer between the substrate and the optical element which is of large area and which has a high stability over a large range. For example, a drop of alkaline solution is applied with a weight in the range from 1 pg to 50 pg per mm 2 of surface area, with the boundary values included. The coating can be performed here by means of spot or drop application. The liquid drop can be applied, for example, in the lateral center of the respective surface, from which the liquid drop is distributed uniformly over the entire surface. Alternatively, however, the coating can also be applied over a large area, for example by means of spraying, blade coating, stamping, slot coating, etc.

[0047] According to at least one embodiment, the method, in particular the step of arranging the first surface on the second surface, is performed under controlled conditions. Here, the controlled conditions can comprise, for example, temperature, time (staging time), ambient pressure, load pressure, ambient humidity and standing time and concentration of the alkaline solution.

[0048] According to at least one embodiment, the method is performed at a temperature selected from the range from 10 °C to 60 °C, with the boundary values included. In particular, the method can be performed at room temperature. A low temperature prevents possible damage at the optoelectronic device during the fixing of the optical element at the substrate. Furthermore, at low temperatures the possible differences in the coefficients of thermal expansion of the different materials, for example of the first and second surface materials, play a negligible role. Furthermore, at low temperatures it is ensured that the build-up of the connection layer takes place sufficiently slowly so that the water produced by the dehydration can escape completely or to a sufficient extent.

[0049] According to at least one embodiment, the method is performed at a pressure selected from the range from 1 bar to 1 mbar, with the boundary values included. Thus, the method can be performed with slight underpressure or also without vacuum at ambient pressure. Super-high vacuum conditions are not required, which simplifies the performance of the method. Water can also be removed by freeze-drying.

[0050] According to at least one embodiment, the method is carried out at an ambient humidity selected from the range of 20% to 60% relative air humidity, including the boundary values.

[0051] According to at least one embodiment, the method is carried out without the application of additional load forces. Thus, the connection layer can be formed only under the action of the self-weight of the optical element or the substrate. It is thus possible to prevent mechanical damage at the substrate and / or the optical element.

[0052] According to at least one embodiment, the formation of the connection layer is carried out within a time period selected from the range of 3 hours to 30 days, including the boundary values. This time period enables the water to sufficiently or completely drain off during the formation of the inorganic polymer network.

[0053] According to at least one embodiment, the method is carried out without the use of additional carrier layers, as is partly customary in conventional methods.

[0054] A kind of optoelectronic device is also proposed. The optoelectronic device can be manufactured in particular using the method described herein. Thus, all features and embodiments disclosed in connection with the method also apply to the optoelectronic device and vice versa.

[0055] According to at least one embodiment, the optoelectronic device has a semiconductor chip which generates electromagnetic radiation in operation.

[0056] The semiconductor chip is for example a light emitting diode chip or a laser diode chip. Thus, the device can be a light emitting diode (LED) or a laser. Preferably, the semiconductor chip has an epitaxially grown semiconductor layer sequence which has an active region which is suitable for generating electromagnetic radiation. To this end, the active region has for example a pn junction, a double heterostructure, a single quantum well or a multiple quantum well structure. The generated electromagnetic radiation can for example have a wavelength from the visible or UV range, in particular from the UV-C range.

[0057] According to at least one further embodiment, the optoelectronic device also has an optical element which is arranged on the substrate.

[0058] Here and in the following, a "substrate" is understood to be the component from which the electromagnetic radiation first exits and is then diverted by or onto the optical element. The generated electromagnetic radiation exits the semiconductor chip in particular via a radiation exit face. Depending on the chip technology on which it is based and the architecture of the semiconductor element, the radiation exit face can be a passivation layer or a mirror layer or an epitaxially grown substrate.

[0059] An optical element is arranged on the substrate. An optical element is to be understood as a component which couples out the incident radiation from the optoelectronic device and optionally changes the radiation, for example bunches, diverges or converts it. The optical element can thus have different geometric configurations and functions.

[0060] According to at least one embodiment, the optical element is fixed at the substrate in the optical path of the optoelectronic device by means of the connecting layer. The optical path is to be understood as the path through which the electromagnetic radiation passes through the device until it is coupled out. That is to say, in this case the electromagnetic radiation radiates through the substrate, the connecting layer and the optical element. The expression "fixed" is to be understood as a permanent mechanical connection which directly connects the substrate and the optical element to one another.

[0061] According to at least one embodiment, the connecting layer comprises an inorganic polymer network. That is to say, there is an inorganic compound between the substrate and the optical element.

[0062] According to at least one embodiment, an optoelectronic device is proposed which has a semiconductor chip which generates electromagnetic radiation in operation and an optical element which is arranged on a substrate, wherein the optical element is fixed at the substrate in the optical path of the optoelectronic device by means of a connecting layer, which comprises an inorganic polymer network.

[0063] The connecting layer comprising an inorganic polymer network or its structural configuration in the form of covalent chemical bonds thus results in a firm, rigid anchoring of the substrate and the optical element, which has a high mechanical stability, so that the unit consisting of the substrate, the connecting layer and the optical element can also be referred to as approximately monolithic. Furthermore, the inorganic polymer network results in a chemical stability with respect to hydrolysis, which likewise contributes to the stability of the connecting layer. Furthermore, the connecting layer is stable with respect to high-energy electromagnetic radiation, for example UV-C radiation. The connecting layer can thus be well combined with semiconductor chips which emit high-energy radiation, for example UV-C radiation.

[0064] According to at least one embodiment, the inorganic polymer network gradually transitions into a first surface material towards the optical element and into a second surface material towards the substrate. Here and in the following, "gradually" is to be understood as the connecting layer comprising up to 100% of the inorganic polymer network in a lateral central range parallel to the main extension plane and the proportion of the first surface material or the second surface material increasing with increasing distance from the central region of the connecting layer until the proportion of the inorganic polymer network is 0%.

[0065] Herein, the first surface material can be the material of the optical element or at least the material of a first surface layer of the optical element, wherein the first surface layer is a layer of the optical element which adjoins the connecting layer. Herein, the second surface material can be the material of the substrate or at least the material of a second surface layer of the substrate, wherein the second surface layer is a layer of the substrate which adjoins the connecting layer.

[0066] The gradual transition of the inorganic polymer network also causes a gradual change of the refractive index of the material, so that a high transparency of the connecting layer can be achieved.

[0067] According to at least one embodiment, the connecting layer has a thickness selected from the range of 50 nm to 800 nm, wherein the boundary values are included. The thickness relates to the region of the connecting layer in which the inorganic polymer network is present, i.e. the region which has not yet been completely replaced by the first or second surface material.

[0068] According to at least one embodiment, the connecting layer has an area of at least 100 pm 2 . For example, the connecting layer has an area of 1 mm 2 . Thus, the optoelectronic component can be a surface emitter, wherein the connecting layer has its high stability over the entire area.

[0069] According to at least one embodiment, the connecting layer has a transparency of more than 95% for electromagnetic radiation from the range of 200 nm to 600 nm. Thus, the connecting layer can be well used in optoelectronic components which emit electromagnetic radiation in the visible range but also in the high-energy UV and UV-C range. On the one hand, the connecting layer has sufficient stability with respect to electromagnetic radiation, in particular with respect to high-energy electromagnetic radiation, on the other hand, due to its high transparency with respect to electromagnetic radiation, the connecting layer improves the light coupling-out efficiency of the optoelectronic component.

[0070] According to at least one embodiment, the connecting layer has a mechanical stability which is at least 60% of the mechanical stability of the first and second surface material. Thus, the optoelectronic component has a high mechanical stability and thus an increased service life.

[0071] According to at least one embodiment, the connecting layer is hydrolysis-stable. Thus, the connecting layer does not dissolve or partially dissolve due to moisture transport, in particular also not due to air humidity. This in particular contributes to the mechanical stability of the connecting layer and thus of the optoelectronic component.

[0072] According to at least one embodiment, the optical element is selected from the group consisting of a lens, a prism, a sealing window, a micro-optical element and a conversion foil. However, it is also conceivable to fix other optical elements by means of the connection layer. For example, the optical element is a lens. The lens itself can also have a material selected from the group consisting of sapphire, quartz, quartz glass, oxide glass, phosphate glass or also MgF2, to which a first surface layer comprising an oxide material or a nitride material is applied before the lens is fixed to the substrate. Such a lens can be applied to a substrate, for example, which is a growth substrate of a semiconductor chip, for example a III / V semiconductor chip, or a passivation layer applied on a semiconductor chip. The substrate can comprise, for example, a material selected from the group consisting of Al2O3, sapphire, Si4N3, silicon, ZnO, ITO, ZrO2, HfO2, GaAs, GaN, Ta2O5, Si(O)xN y In other words, in optoelectronic devices, a plurality of materials can be fixed next to one another by means of the connection layer, wherein the materials can be the same or different from one another.

[0073] According to at least one embodiment, the optoelectronic device is a light emitting diode or a laser. The laser can be, in particular, a UV laser. The light emitting diode can be, in particular, a µ-LED.

[0074] In a µ-LED or micro LED, the growth substrate is removed, so that the typical height of such a µ-LED is, for example, in the range of 1.5 µm to 10 µm. In principle, the µ-LED does not necessarily have to have a rectangular radiation emission face. Overall, the LED can have, for example, a radiation emission face in which, in a plan view of the layer stack, each lateral extension of the radiation emission face is less than or equal to 100 µm or less than or equal to 70 µm. In most cases, such µ-LEDs are provided on a wafer, which has a (non-destructive) detachable holding structure for the µ-LEDs.

[0075] According to at least one embodiment, the optoelectronic device is a light emitting diode which emits electromagnetic radiation from the range of 100 nm to 300 nm. Thus, the light emitting diode is a UV-C diode, which emits high-energy UV-C radiation. Due to the high stability of the connection layer with respect to mechanical influences and with respect to electromagnetic radiation, such an optoelectronic device has a high stability, which has a positive effect, for example, on long-term stability and thus on the lifetime. Furthermore, the optoelectronic device has a high coupling-out efficiency, since, as has been set out, the connection layer is not only stable over its entire area, but also has a high transparency.

[0076] Further advantageous embodiments and improvements of the device and the method result from the embodiments described in the following with reference to the drawings. Attached Figure Description

[0077] Figure 1 A schematic cross-sectional view of an optoelectronic device according to one embodiment is shown.

[0078] Figure 2 illustrates the method steps of a method for fixing an optical element on a substrate in the optical path of an optoelectronic device according to an embodiment.

[0079] Figure 3 illustrates the fabrication and optical properties of the bonding layer according to one embodiment.

[0080] In the accompanying drawings, identical, similar, or functionally equivalent elements are given the same reference numerals. The size relationships between the elements shown in the drawings should not be considered to be proportional. Rather, individual elements, especially layer thicknesses, are exaggerated for better illustration and / or for better understanding. Detailed Implementation

[0081] Figure 1 A schematic cross-sectional view of an optoelectronic device 100 according to one embodiment is shown. An electrical interface 60 is provided on a carrier 50. A semiconductor chip 40 is provided in electrical contact with the interface 60. The semiconductor chip 40 can be a light-emitting diode chip or a laser chip. Here, in this embodiment, an LED chip emitting electromagnetic radiation in the UV-C wavelength range is involved. A substrate 20 is provided on the semiconductor chip 40, and an optical element 10 is disposed directly on the substrate 20 by means of a bonding layer 30. In this embodiment, the substrate 20 is the growth substrate of the LED chip. In principle, any type of optical element 10 that couples electromagnetic radiation from the optoelectronic device is suitable as an optical element. Figure 1 In the example shown, optical element 10 is a hemispherical lens.

[0082] The substrate 20, particularly at its second surface 22 facing the optical element 10, or throughout its entirety, comprises an oxide or nitride material. In this embodiment, the entire substrate 20 comprises sapphire.

[0083] The optical element 10, particularly on its first surface 12 facing the substrate 20, or throughout its entirety, comprises an oxide or nitride material. In this embodiment, the entire lens is made of quartz glass.

[0084] The optical element 10 is fixed, or permanently attached, to the substrate 20 by means of a bonding layer 30. The bonding layer 30 comprises an inorganic polymer network, particularly a three-dimensional cross-linked polymeric silicate network or an aluminosilicate network. Even in Figure 1The connection layer 30 is shown as a layer with a clear delimitation of the interface with respect to the optical element 10 and the substrate 20, the material of the connection layer can also gradually and uniformly transition into the material of the first surface 12 or the second surface 22. This means that the connection layer 30 has, in particular in its central region, an inorganic polymer network, the content of the first surface material of the optical element 10, in this example quartz glass, or the content of the second surface material of the substrate 20, in this example sapphire, gradually increasing as the distance to the optical element 10 or to the substrate 20 decreases. Thus, there is an approximately integral connection in the device 100. The thickness of the connection layer 30, i.e. the range in which the inorganic polymer network is present, is, for example, between 50 nm and 800 nm.

[0085] Furthermore, the connection layer 30 is located in the optical path 11 of the optoelectronic device, which is indicated by the dashed arrow. Figure 1

[0086] The connection layer 30 is hydrolysis-stable due to its inorganic polymer network. In particular due to the controlled conditions under which the connection layer 30 is formed between the substrate 20 and the optical element 10, there is hardly any water left in the connection layer 30. Furthermore, the connection layer 30 has a high mechanical stability, at least 60% of the stability of the material adjoining it. The material adjoining the connection layer is, in particular, the first surface material of the optical element 10 or the first surface 12 of the optical element 10, and the second surface material of the substrate 20 or the second surface 22 of the substrate 20. Furthermore, the connection layer 30 with the inorganic polymer network is stable with respect to high-energy electromagnetic radiation, so that it can be well combined with semiconductor chips 40 that emit UV-C radiation. Due to its high transparency, the connection layer 30 also achieves an improved light coupling-out efficiency of more than 80% through the optical element 10, in this example a lens, which is fixed on the substrate 20.

[0087] Although sapphire is listed as the material of the substrate 20 and quartz glass as the material of the optical element 10 shaped as a lens in this embodiment, the fixing of other geometrical and / or functional optical elements 10 is also possible and conceivable, alternatively or additionally, the optical element 10 and the substrate 20 can contain other materials as already mentioned above independently of one another. The first and second surfaces 12, 22 fixed to one another by means of the connection layer 30 have here oxide and / or nitride materials.

[0088] Figure 2 shows the method steps of a method for fixing an optical element 10 on a substrate 20 in the optical path 11 of an optoelectronic device 100 according to an embodiment. In the following, the same reference signs denote the same elements as with respect to Figure 1 the already explained. Some reference signs can be omitted for the sake of clarity.

[0089] In​Figure 2a In an embodiment of the method, a substrate 20 is provided, which is a growth substrate on a semiconductor chip 40, and an optical element 10 is provided, in the present example a lens. The optical element 10 has a first surface 12, which shall be arranged and fixed on a second surface 22 of the substrate 20.

[0090] In principle, the method is used for homogeneous and inhomogeneous bonding. This shall mean that the substrate 20 and the optical element 10 can comprise the same material (homogeneous bonding) or different materials (inhomogeneous bonding). The material of the optical element 10 and then of the substrate 20 is an oxide material or a nitride material.

[0091] However, in principle it is important which material is at the first surface 12, the first surface material, and which material is at the second surface 22, the second surface material. In order to improve the method described here and / or in order to fix optical elements 10 with a substrate 20 having a non-oxide material or a non-nitride material next to each other, an auxiliary layer 32 can be applied in step I to form the first and / or the second surface 12, 22. However, this step I is optional or only necessary when there is a non-oxide material or a non-nitride material at the surface of the optical element 10 or the substrate 20 to be fixed. Therefore, step I is shown in brackets in Figure 2a and is explained in detail in connection with Figure 2b .

[0092] Irrespective of whether an auxiliary layer 32 is applied or not, in step II of the method both the first and the second surface 12, 22 can be cleaned. The cleaning is in particular a dry or wet-chemical oxidation cleaning and can be performed, for example, by means of ozone, oxygen plasma or by means of UV wet oxidation. By cleaning, the first and the second surface 12, 22 are freed of contaminants and organic substances and are activated for the subsequent method.

[0093] Basically, the quality requirements for the first and the second surface 12, 22 in the present method are not as high as in alternative direct bonding methods, for example the so-called surface-activated bonding (SAB). Therefore, a roughness of, for example, 10 nm to 50 nm is already sufficient, with an auxiliary layer 32 of even only 20 nm to 100 nm.

[0094] In step III of the method, the alkaline solution 3 is applied to the first and / or second surface 12, 22. It is possible to use a solution free of silicates as the alkaline solution, which for example contains NaOH, LiOH or KOH, with a molar ratio of between 1 : 100 and 1 : 300. Alternatively, it is also possible to use an additive-rich, for example silicate-rich, aqueous alkali metal oxide solution. The molar ratio of silicate Si02to alkali metal oxide R20(R = Na, K or Li) is for example 2.6 here, with an aqueous alkali metal silicate concentration of 2 to 40% by weight in order to ensure a good quality of the connection layer 30 to be formed.

[0095] The alkaline solution 3 is applied to the central region of the first and / or second surface 12, 22, for example in the form of droplets. Typically, 1 to 50 pg, in particular 4 to 10 pg, of alkaline solution 3 per mm2of surface is applied. Here, the lateral extension of the first and / or second surface 12, 22 is typically 1 mm 2 When the two surfaces are subsequently arranged one after the other, the alkaline solution 3 ensures a self-adjusting system, so that it is not necessary or less necessary to arrange the first and second surfaces 12, 22 one above the other in register and / or centrally or to arrange the first and second surfaces 12, 22 one above the other in register and / or centrally.

[0096] The alkaline solution 3 initiates a multi-stage chemical process by means of which the connection layer 30 is formed and which is described in more detail in Figure 2c . First of all, the alkaline solution 3 ensures etching of the surface to which it is applied. In the example shown in Figure 2a , the first and second surfaces 12, 22 are etched by the alkaline solution 3, which is indicated by the hatched surfaces 12, 22.

[0097] The first and second surfaces 12, 22 are finally arranged one after the other in step IV and the connection layer 30 is formed under controlled conditions. Here, the controlled conditions include a pressure of 1 mbar to 1 bar, a temperature of 10°C to 60°C, an ambient humidity of 20% to 60% and do not include or only include a small load pressure. Under these conditions, the chemical reactions initiated by the alkaline solution 3 can be controlled and proceed completely, which leads to the formation of a stable inorganic polymer network. Furthermore, the optoelectronic component, in particular the semiconductor chip 40, is not damaged by excessive load pressure and / or high temperatures. The formation of the connection layer 30 takes place in a period of 3 hours to 30 days, for example 10 days. Under these controlled conditions, the possible different coefficients of thermal expansion of the materials involved or adjoining do not play a role.

[0098] Figure 2bThe optional or potentially necessary step I is described, namely, applying the auxiliary layer 32 to the substrate 20 and / or the optical element 10. Depending on the properties of the optical element 10 and the substrate 20, the first and second surfaces 12, 22, comprising oxide or nitride materials, can be formed by means of the auxiliary layer 32. Here, the auxiliary layer 32 can be applied to the substrate 20 ( Figure 2b (upper part), applied to optical element 10 ( Figure 2b (middle) or both sides apply ( Figure 2b (Lower part). The auxiliary layer 32 comprises an oxide or nitride material, such as an oxide material like SiO2, ZrO2, or Al2O3, which is preferably amorphous and / or porous. The typical thickness of the auxiliary layer 32 is between 5 nm and 10 µm, especially between 5 nm and 100 nm, for example, 20 nm. The auxiliary layer 32, especially when it comprises an amorphous oxide material, simplifies and accelerates the etching of the first and / or second surfaces 12, 22 by the alkaline solution 3, and can induce a thicker and more stable bonding layer 30. After step I, it is possible to... Figure 2a Continue the method as described in the document.

[0099] Figure 2c The chemical process of step III is described after the alkaline solution 3 is applied to the first surface 12 and / or the second surface 22. If, as described above, the optical element 10 comprises quartz glass, i.e., SiO2 (… Figure 2c (left side), and substrate 20 contains sapphire, namely Al2O3 ( Figure 2c (right side), then the first thing to cause the alkaline solution 3 to react with OH- - The groups hydrate and etch the corresponding materials, thereby releasing silicate and aluminate ions.

[0100] Subsequently, the dissociation of silicate or aluminate ions and the polymerization or dimerization of the dissociated molecules occur, producing water as a byproduct. Finally, water molecules leak out of the system, causing dehydration and forming an inorganic polymer network, in this case, an aluminosilicate network. In particular, the formed polymer network is almost free of alkali metal ions and is hydrolyzed stable.

[0101] Figure 3 illustrates the optical properties of the bonding layer 30 with respect to sample substrates 21 and 23, which are fixed close together. Two sapphire flakes, serving as sample substrates 21 and 23 (each with a thickness of 400 µm and a thickness of 1.5 cm, respectively), were treated with an alkaline solution 3 using the method described above. 2 The dimensions), and the connecting layer 30 is manufactured under controlled conditions ( Figure 3a). In the present example, as the alkaline solution 3 a silicate solution (Na) is used, wherein n = 2.6 and the dilution in deionized water is 2 to 10 wt.%, in this example 5.3 wt.%. With this configuration, a total energy dose of 45 kJ / cm 2 of UV-C radiation is guided, and the optical transparency and its change is determined in the range from 200 nm to 600 nm by means of UVvis spectroscopy (detection unit 70 of a UVvis spectrometer is shown schematically) Figure 3b . Additionally, the resistance to moisture of the configuration is examined.

[0102] Here, the transmittance of the sapphire wafer configuration is additionally determined for different time periods and after one week, in which the sample substrate 21, 23 fixed by means of the connecting layer 30 is exposed to a temperature of 60°C and an air humidity of 93%. Figure 3c The measurement results, i.e. the relative transparency in % in relation to the wavelength λ in nm, are shown.

[0103] As a reference example S1 the transparency of a single sapphire wafer with a thickness of 800 pm is shown, which is set to 100%. The reference example S2 shows the transparency of two stacked sapphire wafers with a thickness of 400 pm each, but without a connecting layer 30. The transmission curves Ex1, Ex2, Ex3 and Ex4 show the transmittance of the configurations exposed to different stress influences according to Figure 3a . The transmission curve Ex1 shows the transmittance of the connecting layer 30 with an age of 24 hours, Ex2 shows the transmittance of the connecting layer 30 with an age of 260 hours. Ex3 shows the transmittance under additional UV-C stress at 255 nm and a dose of 45 kJ, Ex4 shows the transmittance under UV-C stress at 255 nm and a dose of 45 kJ, additional water cleaning and humidity stress in 93% relative humidity at 60°C for 168 hours. It can be seen that the transparency of the connecting layer remains almost unchanged at a high level for wavelengths in the range from 200 nm to 600 nm under all stress conditions.

[0104] As reference values S1 and S2, in this case the spectrum of a sapphire wafer with a thickness of 800 pm (S1) and the spectrum of an unconnected stack of two mutually stacked sapphire wafers with a single layer thickness of 400 pm each (S2) are additionally listed.

[0105] Even when the connecting layer 30 is examined macroscopically, no difference between the newly manufactured connecting layer 30 and the connecting layer 30 exposed to the above-mentioned stress conditions (UVC radiation, humidity stress) can be identified.

[0106] The UV-C stability of the connection layer and its suitability in the optical path of the optoelectronic component 100 can thereby be proven.

[0107] The features and embodiments described in connection with the drawings can be combined with each other according to further embodiments, even if not all combinations are explicitly described. Furthermore, the embodiments described in connection with the drawings can alternatively or additionally have other features according to the description in the SUMMARY.

[0108] The application is not limited to the embodiments described according to the description. Rather, the application comprises every new feature and every combination of features, even if this feature or combination is not explicitly stated in the patent claims, the application or the embodiments. The application comprises in particular every combination of the features in the patent claims, even if this combination is not explicitly stated in the patent claims, the application or the embodiments.

[0109] This patent application claims priority to German patent application 102023131829.2, the disclosure of which is incorporated herein by reference.

[0110] List of reference signs

[0111] 10 optical element

[0112] 11 optical path

[0113] 12 first surface

[0114] 20 substrate

[0115] 21 sample substrate

[0116] 22 second surface

[0117] 23 sample substrate

[0118] 3 alkaline solution

[0119] 30 connection layer

[0120] 32 auxiliary layer

[0121] 40 semiconductor chip

[0122] 50 carrier

[0123] 60 electrical interface

[0124] 70 detection unit

[0125] 100 optoelectronic component

[0126] I method step

[0127] II method step

[0128] III method step

[0129] IV method step

[0130] T rel Relative transparency

[0131] λ wavelength

[0132] S1 Reference Example 1

[0133] S2 Reference Example 2

[0134] Ex1 Transmittance curve 1

[0135] Ex2 Transmittance curve 2

[0136] Ex3 Transmittance curve 3

[0137] Ex4 Transmittance curve 4

Claims

1. A method for fixing an optical element (10) on a substrate (20) in an optical path (11) of an optoelectronic device (100), comprising the following steps: - providing an optical element (10) having a first surface (12) comprising a first surface material, and providing a substrate (20) having a second surface (22) comprising a second surface material, wherein the first surface material and the second surface material are independently of each other selected from a transparent oxide material and a transparent nitride material, - applying a basic solution (3) to the first surface (12) and / or the second surface (22), - arranging the first surface (12) on the second surface (22), wherein a connection layer (30) having an inorganic polymer network is formed between the first surface material and the second surface material.

2. The method according to the preceding claim, wherein the basic solution (3) has a pH value greater than 11.

3. The method according to any one of the preceding claims, wherein the basic solution (3) is selected from an aqueous alkali metal silicate solution, an aqueous alkali metal aluminate solution and an aqueous alkali metal phosphate solution.

4. The method according to any one of claims 1 and 2, wherein the basic solution (3) comprises at least one of NaOH, KOH and LiOH.

5. The method according to any one of the preceding claims, wherein prior to the providing step, a first auxiliary layer (32) is applied on the optical element (10) to form the first surface (12) comprising the first surface material, and / or a second auxiliary layer (32) is applied on the substrate (20) to form the second surface (22) comprising the second surface material.

6. The method according to the preceding claim, wherein as first and / or second auxiliary layer (32), a transparent oxide material is applied independently of each other.

7. The method according to the preceding claim, wherein the transparent oxide material is amorphous and / or porous.

8. The method according to any one of the preceding claims 5 to 7, wherein the first and / or second auxiliary layer (32) has a layer thickness selected from the range comprising 5 nm to comprising 100 nm.

9. The method according to any one of the preceding claims, wherein the first surface (12) and / or the second surface (22) on which the alkaline solution (3) is applied has an area of at least 100 pm2. 2 of at least 100 pm2.

10. The method according to any one of the preceding claims, the method is performed at a temperature selected from the range of 10 °C to 60 °C, wherein the boundary values are included, and / or the method is performed at a pressure selected from the range of 1 bar to 1 mbar, wherein the boundary values are included, and / or the method is performed at an ambient humidity selected from the range of a relative air humidity of 20 % to 60 %, wherein the boundary values are included.

11. The method according to any one of the preceding claims, wherein the formation of the connection layer (30) is carried out over a period of time selected from the range of 3 hours to 30 days, wherein the boundary values are included.

12. An optoelectronic device (100) having: a semiconductor chip (40) which generates electromagnetic radiation in operation, and a An optical element (10) arranged on a substrate (20), wherein in the optical path (11) of the optoelectronic device (100), the optical element (10) is fixed at the substrate (20) by means of a connecting layer (30) comprising an inorganic polymer network.

13. The optoelectronic device (100) according to the preceding claim, wherein the inorganic polymer network gradually transitions into a first surface material towards the optical element (10) and into a second surface material towards the substrate (20).

14. The optoelectronic component (100) according to claim 12 or 13, wherein the connection layer (30) has a thickness selected from the range of 50 nm to 800 nm, inclusive, and / or wherein the connection layer (30) has an area of at least 100 pm2. 2 of 50 nm to 800 nm, inclusive, and / or wherein the connection layer (30) has an area of at least 100 pm2.

15. The optoelectronic device (100) according to any one of claims 12 to 14, wherein the connecting layer (30) has a transparency of more than 95% for electromagnetic radiation out of the range from 200 nm to 600 nm.

16. The optoelectronic device (100) according to any one of claims 13 to 15, wherein the connecting layer (30) has a mechanical stability which is at least 60% of the mechanical stability of the first and second surface materials.

17. The optoelectronic device (100) according to any one of claims 12 to 16, wherein the connecting layer (30) is hydrolysis-stable.

18. The optoelectronic device (100) according to any one of claims 12 to 17, wherein the optical element (10) is selected from the group consisting of lenses, prisms, sealing windows, micro-optical elements and conversion foils.

19. The optoelectronic device (100) according to any one of claims 12 to 18, which is a light emitting diode, in particular a µ-LED, or a laser.

20. The optoelectronic device (100) according to the preceding claim, wherein the light emitting diode emits electromagnetic radiation out of the range from 100 nm to 300 nm.

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