Method for producing a metal-ceramic substrate, ceramic element and metal layer for such a method, and metal-ceramic substrate produced by such a method

Abstract

A method for producing a metal-ceramic substrate (1), comprising – providing at least one first metal layer (10) for forming a component metallization and a ceramic element (30), – bonding the at least one first metal layer (10) to the ceramic element (30) by means of a direct bonding method, more particularly a DCB method or a DAB method, to form a common first bonding layer (12) between the ceramic element (30) and the at least one metal layer (10), a first agent for promoting formation of spinel being provided in a region intended for the formation of the first bonding layer (12) in order to improve adhesive strength between the at least one first metal layer (10) and the ceramic element (30) for the bonding by means of the direct bonding method.

Description

[0001] Method for producing a metal-ceramic substrate, ceramic element and metal layer for such a method and metal-ceramic substrate produced by such a method

[0002] The present invention relates to a method for producing a metal-ceramic substrate, a ceramic element and a metal layer for such a method and a metal-ceramic substrate produced by such a method.

[0003] Metal-ceramic substrates are well known as printed circuit boards or circuit boards from the prior art, for example, from DE 102013 104 739 A1, DE 19 927 046 B4, and DE 102009 033 029 A1. Typically, connection pads for electrical components and conductor tracks are arranged on one component side of the metal-ceramic substrate or the metal-ceramic substrate, wherein the electrical components and the conductor tracks can be interconnected to form electrical circuits. Key components of the metal-ceramic substrates are an insulating layer, preferably made of a ceramic, and at least one metal layer bonded to the insulating layer. Due to their comparatively high insulation strength, insulating layers made of ceramic have proven particularly advantageous in power electronics.By structuring the metal layer, conductor tracks and / or connection surfaces for the electrical components can then be realized.

[0004] For the production of such ceramic substrates, it is typically intended that a metal layer or layer is bonded to a ceramic element. In addition to an active soldering process, a direct bonding process is also known, for example, in the form of a direct copper bonding (DCB) process or a direct aluminum bonding (DAB) process. Such direct bonding processes allow the metal layer to be bonded directly to the ceramic element, in particular without the need for a solder layer arranged between the metal layer and the ceramic element.

[0005] For such metal-ceramic substrates produced using a corresponding direct bonding process, it is becoming increasingly challenging to achieve sufficiently high bond strengths. Bond strength specifies the adhesion strength of the bonded metal layer to the ceramic element. Another challenge is that the trend toward miniaturization, for example, in the form of finer conductor track structures, increases the tendency for the metal layer to delaminate from the ceramic element.

[0006] Furthermore, with metal-ceramic substrates, a backside metallization is formed opposite the component metallization to counteract bending of the metal-ceramic substrate. Such bending would otherwise occur if the metal layer were bonded to the ceramic element on only one side. Due to different expansion coefficients, the thermomechanical stresses would cause distortion in the metal-ceramic substrate. Therefore, a backside metallization that counteracts such bending is advisable. It has been found that the adhesion strength of the component metallization on one side and the backside metallization on the other side often differs.

[0007] Based on this, the present invention aims to produce metal-ceramic substrates manufactured using a DCB or direct bonding process, thereby exhibiting a higher bond strength between the ceramic element and the metal layer. Furthermore, comparable bond strengths should be present on the front and back sides of the metal-ceramic substrate, if possible.

[0008] This object is achieved by the method according to claim 1, the ceramic element according to claim 7, the metal layer according to claim 8 and the metal-ceramic substrate according to claim 9. The figures and the description contain further embodiments of the invention.

[0009] According to a first aspect of the present invention, there is provided a method for producing a metal-ceramic substrate, comprising

[0010] - Providing at least one first metal layer for forming a component metallization and a ceramic element,

[0011] - Bonding the at least one first metal layer to the ceramic element by means of a direct bonding process, in particular a DCB process or a DAB process, by means of which a common first bonding layer is formed between the ceramic element and the at least one metal layer, wherein in order to improve an adhesive strength between the at least one first metal layer and the ceramic element for bonding by means of the direct bonding process, a first means for promoting spinel formation in a region provided for the formation of the first bonding layer is provided and in particular specifically adjusted.

[0012] In contrast to the methods known from the prior art, the invention provides that means for promoting spinel formation are specifically incorporated or added into the bonding process. It has been found that increased spinel formation contributes significantly to improving adhesion. In particular, it has also been found that increased spinel formation in the bonding layer advantageously makes it possible to increase the bending strength. It should be noted that after the bonding process or after bonding using the direct bonding method, a bonding layer is formed between the metal layer and the ceramic element, which bonding layer is made up of two layers, with a first layer forming a eutectic structure, for example of copper and oxygen, and a second layer being a spinel layer. In particular, it has been found that the targeted introduction of chemical elements promotes spinel formation orthe composition and size of the spinel layer can be influenced, whereby with increasing amount of spinels formed the adhesion strength could be increased, the bending-fracture strength could be improved and the thermal shock resistance of the metal-ceramic substrate could be increased.

[0013] The metal-ceramic substrate is preferably designed as a printed circuit board in which, in the manufactured state, the at least one metal layer that is bonded to the ceramic element and thus forms the component metallization is structured. The component metallization comprises a plurality of electrically insulated and spatially separated metal sections. For example, it is provided that after the bonding step, structuring is also carried out, for example by lasering, etching and / or mechanical processing, with which conductor tracks and / or connections for electrical or electronic components are realized. It is preferably provided that on a manufactured metal-ceramic substrate, a further metal layer, in particular a back-side metallization and / or a cooling element, is provided on the ceramic element, on the side opposite the metal layer.The rear-side metallization preferably serves to counteract deflection, and the cooling element serves to effectively dissipate heat generated during operation by electrical or electronic components that are connected to the circuit board or the metal-ceramic substrate.

[0014] Conceivable materials for the metal layers or metal sections, i.e. for the first metal layer and a second metal layer, include copper, aluminum, molybdenum and / or their alloys, as well as laminates such as CuW, CuMo, CuAl, AlCu and / or CuCu, in particular a copper sandwich structure with a first copper layer and a second copper layer, wherein a grain size in the first copper layer differs from that of a second copper layer. Furthermore, it is preferably provided that the at least one metallization, i.e. the primary component metallization or secondary component metallization, is surface-modified. Conceivable surface modifications include, for example, sealing with a precious metal, in particular silver and / or gold, or ENIG (“electroless nickel immersion gold”) or edge casting on the first or second metallization layer to suppress crack formation or crack widening.

[0015] The ceramic element preferably comprises at least one ceramic layer, wherein the ceramic layer is Al2O3, SiSn^AlN, an HPSX ceramic (i.e. a ceramic with an Al2O3 matrix comprising an x ​​percent ZrO2 content, for example Al2O3 with 9% ZrO2 = HPS9 or Al2O3 with 25% ZrO2 = HPS25), SiC, BeO, MgO, high-density MgO (> 90% of the theoretical density), TSZ (tetragonally stabilized zirconium oxide) or ZTA. It is also conceivable for the insulation layer or the ceramic element to be designed as a composite or hybrid ceramic, in which, in order to combine various desired properties, several ceramic layers, each differing in terms of their material composition, are arranged one above the other and joined together to form an insulation layer. Preferably, a ceramic that is as thermally conductive as possible is used for the lowest possible thermal resistance.It is also conceivable that a metallic intermediate layer is arranged in the ceramic element or in the insulation layer between two ceramic layers.

[0016] Furthermore, it is preferably provided that the method further comprises:

[0017] - Providing at least one second metal layer for forming a backside metallization, wherein the at least one first metal layer and the at least one second metal layer are arranged on opposite sides of the ceramic element, - Bonding the at least one second metal layer to the ceramic element by means of the direct bonding process, by means of which a common second bonding layer is formed between the ceramic element and the at least one second metal layer, wherein in order to improve the adhesive strength between the second metal layer and the ceramic element for bonding by means of the direct bonding process, a second means for promoting spinel formation in a region for forming the second bonding layer is provided, wherein the at least one first metal layer and the at least one second metal layer are bonded in a common bonding process, preferably in a common furnace pass,be connected to the ceramic element.,

[0018] It has advantageously been found that it is possible to achieve adhesive strengths of such a nature that just a single pass through a furnace in which direct metal bonding takes place is sufficient. This advantageously makes it possible to simultaneously bond the at least one first metal layer to the ceramic element and the at least one second metal layer to the ceramic element in a common process step, for example through joint presence or presence in a furnace. This eliminates the need for the at least one first metal layer to be bonded to the ceramic element in a first bonding step and for the at least one second metal layer to be bonded to the ceramic element or the pre-composite of the ceramic element and at least the first metal layer in a second subsequent process step, for example in a second pass through a furnace.In particular, it proves particularly advantageous that the adhesion strength of the at least one first metal layer and the at least one second metal layer to the ceramic element is comparable and / or substantially identical. Accordingly, the adhesion strength for the component metallization and the backside metallization does not differ, as is known, for example, for metal-ceramic substrates produced in a two-stage bonding process using the direct bonding method.

[0019] In particular, an adhesive strength is formed which on average assumes a value which is greater than 6 N / mm, preferably greater than 8 N / mm and particularly preferably greater than 10 N / mm and / or a difference between an adhesive strength for the at least one first metal layer and an adhesive strength for the at least one second metal layer is less than 15%, preferably less than 10% and particularly preferably less than 5% of the adhesive strength of the at least one first metal layer.

[0020] Preferably, the first agent for promoting spinel formation and the second agent for promoting spinel formation are the same element or the same element compositions or compounds, so that the first bonding layer and the second bonding layer are essentially identical or comparable in their composition. In particular, it is provided that a component metallization is provided from the at least first metal layer by the bonding, while a backside metallization is produced by the bonding of the at least one second metal layer. In other words: before and during the bonding, one speaks of the at least one first metal layer or at least one second metal layer, while after the bonding process or bonding, the first metal layer or the second metal layer is referred to as component metallization or backside metallization.In particular, it is provided that, in order to produce the metal-ceramic substrate, it is also provided that the component metallization is structured, for example by removing metal from the component metallization using appropriate etching processes, chemical processes and / or laser treatment processes, in order to thus provide or produce conductor tracks and / or connection surfaces for the metal-ceramic substrate.

[0021] Preferably, the first agent for promoting spinel formation and / or the second agent for promoting spinel formation comprises magnesium, chromium, iron, barium, calcium, aluminum and / or manganese, in particular in oxidized form. It has proven particularly advantageous for spinel formation if divalent, trivalent or even tetravalent elements are provided in corresponding compounds, since these promote spinel formation. For example, manganese oxide, magnesium oxide or aluminum oxide is deliberately introduced into the region in which the bonding layer or the second bonding layer is provided. In particular, it is provided that, with regard to the oxidation state, the inserted metals are at least divalent, preferably trivalent or tetravalent. Examples of tetravalent elements, which in particular have a high affinity for oxygen, are titanium, yttrium, hafnium and / or zirconium.This advantageously also reduces the first layer from the eutectic structure, which has also proven advantageous for the bonding process and bonding behavior with regard to the adhesive strengths to be achieved. Preferably, the first agent for promoting spinel formation and / or the second agent for promoting spinel formation is / are essentially free of an aluminum compound and / or an aluminum oxide compound. It has been found that the first and / or second agent for promoting spinel formation significantly influences the frequency distribution of spinel types, in particular a first spinel type and / or a second spinel type, in the manufactured first or second bonding layer. This, in turn, can influence the properties of the first or second bonding layer.As will be described in detail later, it has been found that components of the first agent and / or the second agent are preferentially incorporated into the spinels in the bond layer, thereby displacing spinels that would otherwise be formed, i.e. reducing their abundance. It has also been found that aluminum-containing spinels are generally undesirable and less beneficial than other spinels, particularly for adhesion and resistance to thermal shock. It is therefore particularly advantageous if - for example for an aluminum-containing ceramic element - the first agent for promoting spinel formation and / or the second agent for promoting spinel formation is substantially free of an aluminum compound and / or an aluminum oxide compound.In this case, the person skilled in the art understands that essentially free means that a proportion of aluminum compounds and / or aluminum oxide compounds in the first agent and / or second agent is less than 5% by weight, preferably less than 1% by weight and particularly preferably less than 0.5% by weight.

[0022] In particular, it is envisaged that a concentration of the first agent for promoting spinel formation is greater than 20 g / l, preferably greater than 50 g / l and particularly preferably greater than 150 g / l and / or wherein a concentration of the second agent for promoting spinel formation is greater than 20 g / l, preferably greater than 50 g / l and particularly preferably greater than 150 g / l. It has been found that from about 20 g / l onwards, the incorporation of components of the first agent and / or the second agent for promoting spinel formation into the spinels of the bonding layer is significantly promoted. In addition, a corresponding proportionality can be set for this from this value onwards. For amounts exceeding 150 g / l, a type of saturation can be assumed for Mg, for example, so that a maximum preference for a certain spinel type can advantageously be achieved if correspondingly very high amounts of agents for promoting spinel formation are used.Furthermore, it is preferably provided that the first agent for promoting spinel formation is used to adjust the frequency of a first spinel type in the manufactured metal-ceramic substrate. In other words: a type and / or amount of the first and / or second agent for promoting spinel formation is used in a targeted manner, for example to specifically promote a first spinel type and reduce the frequency of a second spinel type. This advantageously allows the spinel type proportions or their ratios and thus the properties of the bonding layer to be specifically adjusted and manipulated. This also allows, for example, the color of the bonding layer, adhesion, and / or thermal shock resistance to be specifically and, in particular, controlled to be adjusted.

[0023] In particular, it is intended that the proportion or quantity of first agents and / or second agents exceeds those values ​​that can be achieved, for example, in a wet-chemical oxidation prior to the bonding process. In this regard, it should be noted that the usual wet-chemical processes for the oxidation of metal layers or metal coatings also contain corresponding agents as described above, which have so far promoted spinel formation to a small extent, particularly in an uncontrolled manner. Through the targeted additional introduction of such elements or chemical agents, it is advantageously possible to promote spinel formation and thereby increase or initiate the positive effects on adhesive strength, fracture strength, and thermal shock resistance.

[0024] In particular, it is provided that the first agent for promoting spinel formation and / or the second agent for promoting spinel formation is applied to an outer side of the ceramic element of the at least one metal layer and / or the second metal layer, for example by gas-physical deposition, a chemical process and / or a mechanical process. It is conceivable, for example, that the first agent and / or second agent for promoting spinel formation are introduced by means of a sputtering process, a CVD process or a comparable process, in particular by coating the respective layers. Preferably, both the ceramic elements and the first metal layer or second metal layer are coated with the first agent and / or second agent.Alternatively, it is also conceivable that the ceramic element and / or the at least one first metal layer and / or the at least one second metal layer is doped with the agent for promoting spinel formation. In other words, a coating of the outer surface is not necessarily required to introduce the corresponding promoting agents into the region; rather, the agents for promoting spinel formation can already be present in the body of the at least one first metal layer, the at least one second metal layer, and / or the ceramic element and thus flow or diffuse into the region for the subsequent bonding layer.

[0025] Preferably, the thickness of the deposited first spinel formation-promoting agent and / or the deposited second spinel formation-promoting agent assumes a value greater than 100 nm, preferably greater than 500 nm, and particularly preferably greater than 1000 nm. It has been found advantageous to provide comparatively thick layers of the first agent and the second agent, which is also beneficial for improving adhesion and / or thermal shock resistance. Finally, a thicker layer of spinel formation-promoting agents is characterized by increasing the amount of elements provided to promote spinel formation.

[0026] Preferably, the at least one first metal layer is treated in such a way that different sizes for the first agent for promoting spinel formation are established on opposite sides of the first metal layer, and / or the at least one second metal layer is treated in such a way that different sizes for the second agent for promoting spinel formation are established on opposite sides of the second metal layer. This advantageously makes it possible to also influence the outer side opposite the ceramic element as desired and to determine the respective spinel content.In particular, it has been found that the second layer in the bonding layer, which forms the spinel portion, is again two-part and comprises both a first spinel component and a second porous spinel component. As a result, the spinel formation can be adjusted as needed and, in particular, a smaller proportion of agents for promoting spinel formation can be adjusted on the outside, which has proven to be advantageous for the surface quality of the bonded first metal layer or second metal layer, ie for the component metallization and / or backside metallization.

[0027] The present invention further provides a ceramic element for the process according to the invention, wherein the ceramic element comprises a first agent for promoting spinel formation, for example, on an outer side or within the ceramic element. All described advantages and properties of the process can be applied analogously to the ceramic element.

[0028] The present invention further provides a metal layer for a process according to the invention, wherein the metal layer comprises an agent for promoting spinel formation, for example, on an outer side or within the metal layer. All properties and advantages described for the process can be applied analogously to the metal layer, and vice versa.

[0029] A further subject of the present invention is a metal-ceramic substrate produced by a method according to the invention comprising a ceramic element, a component metallization and a backside metallization, wherein, viewed along a stacking direction, the ceramic element is arranged between the component metallization and the backside metallization, a bonding layer is formed between the ceramic element and the component metallization with a first spinel content per volume and a second bonding layer is formed between the ceramic element and the backside metal layer with a second spinel content per volume, wherein an adhesive strength is formed for the component metallization and / or the backside metallization, which on average assumes a value that is greater than 6 N / mm,preferably greater than 8 N / mm and particularly preferably greater than 10 N / mm and / or a difference between an adhesive strength for the component metallization and an adhesive strength for the backside metallization is less than 15%, preferably 10% and particularly preferably less than 5% of the adhesive strength of the component metallization.

[0030] Preferably, the thickness of the formed spinel layer assumes a value of at least 200 nm, preferably of at least 500 nm and particularly preferably of at least 1000 nm.

[0031] All of the described advantages and properties of the process can be applied analogously to the metal-ceramic substrate and vice versa. In particular, the ratio between the difference and the mean value indicates that the spinel fractions formed are comparable in size and that no significant deviations exist between the two bonding layers. This can only be the case if the at least one metal layer and at least one other metal layer have experienced comparable temperature influences.

[0032] A further subject matter of the present invention is a metal-ceramic substrate produced by the method according to the invention, wherein in the produced metal-ceramic substrate, a bonding layer comprising spinels, in particular the first bonding layer and / or the second bonding layer, is formed between the ceramic element and the metal layer, wherein the layer comprising spinels has at least a first spinel type which contains at least one component of the first and / or second agent for promoting spinel formation, wherein the proportion of spinels of the first spinel type is at least 1.3 times, preferably at least 3 times and particularly preferably at least 5 times as large as the proportion of spinels of the first spinel type in a bonding layer in a reference substrate,in which a bond between the metal layer and the ceramic element has been formed by means of a direct bonding process without the introduction of a first and / or second agent to promote spinel formation.

[0033] All described advantages and properties of the process can be transferred analogously to the metal-ceramic substrates and vice versa.

[0034] For the sake of simplicity, the following will also refer to the bonding layer (instead of the first or second bonding layer) and to a means for promoting spinel formation. The following explanations apply independently to the first means or the second means, or to the first and second bonding layers, as already introduced above. Therefore, if properties and findings are described that relate to the type of bonding layer and not its side on the ceramic element, the terms bonding layer and means for promoting spinel formation will be referred to for the sake of simplicity, without diminishing their significance for the first bonding layer and the second bonding layer, or for the first and second means for promoting spinel formation.

[0035] Compared to the prior art processes, which also generate spinel formation during the conventional direct bonding process, it has been found that by additionally introducing spinel formation-promoting agents, particularly above a threshold value, it is possible to influence the composition of the spinel types in the first or second bonding layer. In other words, if a sufficient amount of spinel formation-promoting agents is introduced between the ceramic element and the metal layer, exceeding a threshold value, this can influence the composition of the spinel types and thus the properties of the bonding layer and thus the overall properties of the metal-ceramic substrate.

[0036] It has been found that, for example, by introducing additional magnesium between the ceramic element and the metal layer, magnesium is specifically recruited as a component for spinel formation in the bonding layer. This preferentially produces spinels of a first type, i.e. a first spinel type that contains magnesium, while other spinel types, which contain, for example, copper or calcium, are produced to a lesser extent in the bonding layer. This is a phenomenon that is unknown in the context of the usual direct bonding processes of the metal layer to the ceramic element and does not arise from them. Even if it is believed that a normal eutectic layer leads to a corresponding promotion of spinel formation, this does not, however, result in a targeted manipulation in which a certain specific type of spinel formation is favored in the subsequent bonding layer.Therefore, in the present case, the proportion of identified first spinel types is preferably specifically compared with the first spinel type proportion in a reference substrate in which the metal layer and the ceramic element are simply bonded to one another, without an additional agent for promoting spinel formation having been introduced prior to the direct bonding for the same material combination. It has been found that it is even possible, by means of a correspondingly large proportion of agents for promoting spinel formation, for example magnesium, to increase the proportion of the first spinel type by at least a factor of 1.3, preferably by a factor of 3, and particularly preferably by a factor of 5, compared to the reference substrate in which spinel formation also occurs and, in particular, is promoted, but in which promotions that favor a specific first spinel type do not specifically occur.As already shown, this can significantly contribute to improving adhesion and thermal shock resistance.

[0037] It is preferably provided that the bonding layer comprising spinels comprises a second spinel type, wherein the proportion of spinels of the second spinel type is at least 1.3 times, preferably at least 2.5 times and particularly preferably 3.5 times smaller than the proportion of spinels of the second spinel type in the reference substrate. It has thus also been found that in the example mentioned, not only can the magnesium proportion be increased, but the proportion of copper- and / or calcium-containing spinels can also be specifically reduced, for example when bonding a metal layer to an HPS ceramic. This is particularly advantageous because calcium- and copper-containing spinels not only lead to undesirable discoloration in the red or brown range, but these spinels are also detrimental to improved adhesive strength and resistance to thermal shock.In other words, by introducing an agent to promote spinel formation, it is possible to specifically target the properties of the bonding layer and thus of the metal-ceramic substrate itself, in particular to improve the adhesion strength for the specific metal layer-ceramic element combination, as would be expected for a conventional direct bond between metal layer and ceramic element in the corresponding material constellation.

[0038] Preferably, a resistance across an isolation trench in the manufactured metal-ceramic substrate is at least 1.5 times, preferably at least 2.5 times, and particularly preferably at least five times as great as the resistance across a comparison isolation trench on the reference substrate. A comparison isolation trench is understood, in particular, to be an isolation trench with the same dimensions. The isolation trench separates two adjacent metal sections. The resistance between these two metal sections is typically in the TQ range, and it has been found that, in particular by reducing copper spinels in the bonding layer, this resistance can be further increased, in particular by at least the factors claimed.

[0039] Preferably, the roughness of the spinel layer in the manufactured metal-ceramic substrate is less than the roughness in the reference substrate. It has been found that the use of spinel-promoting agents results in a lesser increase in roughness compared to the raw ceramic element than in the case of direct bonding, where no other agent contributes to promoting spinel formation between the metal layer and the ceramic element other than the specifically produced eutectic.

[0040] In particular, it is intended that means for promoting spinel formation be excluded that arise exclusively and simply through the oxidation of the metal layer. It is preferably intended that a surface roughness S aassumes a value that is less than 0.62 pm, preferably less than 0.6 pm and particularly preferably less than 0.58 pm. In particular, it can be observed that the value for S a by a value of at least 10% and preferably at least 12% compared to the value for S a of the raw ceramic (i.e. the ceramic element before bonding) increases when no agent is introduced to promote spinel formation between the metal layer and the ceramic element. In contrast, the value for S a by less than 8%, preferably less than 5% and particularly preferably less than 3% compared to the value for S a for the raw ceramic if an agent is added to promote spinel formation.

[0041] Further advantages and features will become apparent from the following description of preferred embodiments of the subject matter of the invention with reference to the attached figure. It shows:

[0042] Fig. 1 : Metal-ceramic substrate according to a first exemplary embodiment of the present invention;

[0043] Fig. 2 Detailed view of the bonding layer in a metal-ceramic substrate

[0044] Fig. 3 Dependence of magnesium bound in a spinel in a bonding layer on the magnesium content in the first or second agent for promoting spinel formation,

[0045] Fig. 4 Dependence of calcium bound in a spinel or

[0046] Copper in a bonding layer of magnesium content in the first or second agent to promote the formation of spiders

[0047] Fig. 5 Dependence of the resistance over an isolation trench in a

[0048] Binding layer of magnesium content in the first or second agent to promote the formation of spiders and

[0049] Fig. 6 Representation of a spinel layer in the manufactured substrate and Fig. 7 Dependence of the roughness in a bonding layer on the magnesium content in the first or second agent for promoting spinel formation

[0050] Figure 1 shows a metal-ceramic substrate 1 according to a first exemplary embodiment of the present invention. Such metal-ceramic substrates 1 preferably serve as a carrier or circuit board for electronic or electrical components, which can be connected to the at least one first metal layer 10 of the metal-ceramic substrate 1 on its component side. In this case, it is preferably provided that the at least one first metal layer 10 is structured in order to form corresponding conductor tracks and / or connection surfaces, i.e. in the manufactured metal-ceramic substrate 1, the at least one first metal layer 10 comprises a plurality of metal sections which are electrically insulated from one another and which then forms the component metallization. The at least one metal layer 10 orComponent metallization and a ceramic element 30 extending along the main extension plane HSE are arranged one above the other along a stacking direction S running perpendicular to the main extension plane HSE and are preferably joined or connected to one another via a first bonding layer 12. Preferably, the metal-ceramic substrate 1 comprises, in addition to the at least one first metal layer 10, at least one second metal layer 20, which, viewed in the stacking direction S, is arranged on the side of the ceramic element 30 opposite the at least one first metal layer 10 and is bonded to the ceramic element 30 via a second bonding layer 14.

[0051] In this case, the at least one second metal layer 20, which is referred to as backside metallization after bonding, serves, wherein the at least one second metal layer counteracts a bending of the metal-ceramic substrate 1, in particular of the metal-ceramic element 1, and / or at least as part of a heat sink which is designed to dissipate heat input caused by electrical or electronic components on the metal-ceramic substrate 1.

[0052] Figure 2 shows a detailed view of the bonding layer 12, 14 between the metal layer

[0053] 10, 20 and the ceramic element 30. In particular, this illustration serves the purpose of showing that the bonding layer 12, 14, which forms as a result of the eutectic in a direct bonding process, such as a DCB process, and extends between the metal layer 10, 20 and the ceramic element 30 in the manufactured metal-ceramic substrate 1. This bonding layer 12, 14 contains a large number of different spinels. These are molecular complexes in which individual components are incorporated, which arise in particular from the joining partners. In particular, impurities in the ceramic element 30 and / or the copper of a metal layer 10, 20 formed as a copper layer are also incorporated into these spinels. Typically, when an aluminum oxide ceramic is bonded to a copper layer, spinel types such as CuAIO, CuAIC>2, CuAI2C>4, CaAhC and / or MnAhC or MgAhC are formed.Thus, various spinel types form within the bonding layer 12, 14.

[0054] It has now been found that in the process presented here, in which a first agent and / or a second agent for promoting spinel formation is arranged between the metal layer 10, 20 and the ceramic element 30 before the direct bonding process, various effects on the manufactured metal-ceramic substrate 1 can be observed, which are summarized below using an example and various analyses.

[0055] In the following, a metal-ceramic substrate 1 is investigated in which a copper layer is bonded to an HPS9 ceramic using a DCB (direct copper bonding) process. Four different cases were examined. In the first case, no agent to promote spinel formation was placed between the copper layer and the ceramic element 30. This represents the case of the reference substrate. In three further cases, 1) a small amount (50 g / l Mg via MgSC) of agent to promote spinel formation, 2) a large amount (100 g / l Mg via MgSC) of agent to promote spinel formation, and 3) a very large amount (100 g / l Mg via MgSC) of agent to promote spinel formation was placed between the ceramic element and the copper layer. Subsequently, certain properties of the manufactured metal-ceramic substrate were investigated.

[0056] First, the material compositions of the respective bonding layers 12, 14 were investigated. For this purpose, the bonded copper layer was first etched away until the bonding layer 12, 14 was exposed on the ceramic element. This allowed EDX methods to be performed using a scanning electron microscope, i.e., element-sensitive methods that reveal the chemical composition of the bonding layer. An excitation voltage of 5 kV and a radiation intensity of 15 were used as parameters. This made it possible to identify different spinel types in the bonding layer. The results are summarized in Figures 3 and 4.

[0057] The following picture emerges: It has been found that when using a supplemental agent to promote spinel formation, which is applied between the ceramic layer and the metal layer before the actual direct bonding process, a component of the agent is increasingly incorporated into the spinels of the bonding layer 12, 14. This leads to a first spinel type being found more frequently in this bonding layer 12, 14 compared to a reference substrate in which the metal layer 10, 20 and the ceramic element 30 are bonded together without this agent to promote spinel formation being placed between the ceramic element 30 and the metal layer 10, 20. In particular, it has been found that this first spinel type is present at least 1.3 times, preferably more than 3 times, and particularly preferably more than 5 times as often as in the case of the reference substrate.

[0058] The graph in Figure 3 shows the respective proportion of spinels with magnesium in the bonding layers 12, 14 as a function of the magnesium content, when a corresponding agent for promoting spinel formation contains magnesium or is predominantly composed of magnesium or a magnesium-containing molecule, such as MgSC. It has been shown that the agent introduced to promote spinel formation, in the exemplary documented and proven case from Figure 3, displaces other incorporated elements in the spinel and takes their place. In other words: it is possible to significantly influence the spinel type distribution with the agent for promoting spinel formation. Components of the introduced agent substitute for components that are usually introduced into the spinels through the ceramic element 30 or the metal layer 10, 20, in this case the copper layer.In the present case, with increasing proportion of magnesium in the agent introduced to promote spinel formation, the proportion of magnesium incorporated in the bonding layer 12, 14 in corresponding spinels is increased.

[0059] To form the representation in Figure 3, the proportion of spinels containing magnesium identified in the bonding layer 12, 14 was plotted against the amount of magnesium that was additionally and intentionally introduced between the ceramic element 30 and the metal layer 10, 20 prior to the actual bonding process. It can be seen that with increasing absolute magnesium content in the agent for promoting spinel formation, a correspondingly larger relative proportion of magnesium-containing spinels can be found in the bonding layer 12, 14, in particular to a much greater extent than is the case in cases where no agent for promoting spinel formation is introduced therebetween, ie in the case of the reference substrate.

[0060] At the same time, it has also been found that with increasing magnesium content or with increasing amount of magnesium introduced between ceramic element 30 and metal layer 10, 20, the proportion of spinels with copper or with calcium in the corresponding bonding layer 12, 14 decreases. This is illustrated in Figure 4. In other words, elements such as calcium and / or copper, which would otherwise be bound into specific spinels within the bonding layer 12, 14, are reduced. Thus, it has been shown that by introducing a special agent to promote spinel formation, the composition of the spinel layer in particular can be significantly impaired and, in particular, magnesium content in this case can be specifically increased and calcium and copper content in the respective spinels can be reduced.

[0061] This is particularly advantageous considering that it allows for the targeted avoidance of undesirable spinel phases. For example, CuAlC>2 is undesirable because it is a high-temperature semiconductor. Furthermore, it contributes significantly to the red coloration of the ceramic element 30 or the bonding layer 12, 14.

[0062] Regarding the CuAhC phase, it can be seen that this leads to lower adhesion strength and lower thermal shock resistance. The same applies to CaAhO4 and to spinels, into which calcium is partially incorporated by replacing the otherwise usual cation. Both lead to an undesirable reduction in thermal shock resistance and adhesion. In the case of CUAl2O4, a brown coloration is also observed. In contrast, MgAl2O4 phases are desirable because they promote adhesion strength and thermal shock resistance. They are also characterized by being colorless and do not cause any additional coloration in the area of ​​the bonding layer 12, 14. Thus, the agent for promoting spinel formation can also be used to optically influence the bonding layer 12, 14 by specifically manipulating the spinel type composition.In particular, it is advantageous if an agent promoting spinel formation, such as magnesium, is introduced, resulting in the first spinel type increasingly displacing magnesium and second spinel types, which, for example, are copper- or calcium-rich. This specifically modifies and manipulates the spinel type composition of the bonding layer 12, 14, thereby increasing the bond strength, particularly compared to a case in which no agent promoting spinel formation is introduced between the ceramic element 30 and the metal layer 10, 20.

[0063] As Figure 4 illustrates, in the example shown, in which an HPS9 ceramic was bonded to a metal layer 10, 20, the proportion of the spinel formation promoter also plays a decisive role in the formation of the copper and calcium spinels. It can be seen that with increasing absolute magnesium content in the spinel formation promoter, the copper and calcium content in the spinels decreases, thus resulting in a desired manipulation that is beneficial for the adhesion or bond strength and thermal shock resistance of the bonded, i.e., the manufactured metal-ceramic substrate 1.

[0064] Another observation concerns a resistance that occurs between two metal sections separated by an isolation trench. The results are summarized graphically in Figure 5.

[0065] It has been found that, particularly due to the reduction of copper spinels in the bonding layer 12, 14, the resistance can be increased accordingly with increasing amounts of spinel-promoting agent between the metal sections. In particular, it has been shown that the resistance between two metal sections electrically isolated from each other by an insulation trench can be at least doubled, preferably tripled, if an agent for promoting spinel formation has been used. This is illustrated in Figure 5, which shows a sheet resistance for the variously manufactured metal-ceramic substrates 1, which differ with regard to the proportion of incorporated magnesium.

[0066] Figure 6 shows microscopic images of the bonding layer in a top view. The top image shows what the bonding layer 12, 14 looks like when no agent for promoting spinel formation is applied between the ceramic element 30 and the metal layer 10, 20. The bottom image, however, shows the same image in the case where an agent for promoting spinel formation was applied between the ceramic element 30 and the metal layer 10, 20 before a direct bonding process bonded the metal layer 10, 20 and the ceramic element. To take this image, the metal layers were etched away again in order to visually capture the surfaces of the bonding layers. It can be seen that individual grains are no longer recognizable in the image shown above, and determining the grain size of the ceramic element 30, for example, would be difficult.In contrast, the grain sizes of ceramic element 30 are clearly visible in the lower image. In particular, it has been shown that the grain sizes, when a spinel-promoting agent is used, essentially correspond to those expected for a raw ceramic element. This can also be determined, for example, along a fracture edge, in order to then examine a cross-section for grain size.

[0067] Figure 7 concerns the determined roughness S ain the bonding layer. In particular, it has been found that the roughness values ​​attributable to this surface essentially correspond, i.e., within certain tolerances, to those attributable to the raw ceramic, i.e., the ceramic element before the bonding process, when an agent to promote spinel formation was added. In contrast, in the surface structure after the bonding process, without the agent to promote spinel formation, the roughness is significantly increased, in particular by at least a factor of 1.5, preferably by a factor of 2.5, and particularly preferably by a factor of more than 3.5. This is illustrated in the upper graph of Figure 7. It can be seen that with a roughness of 0.58 pm of the raw ceramic, this roughness value increases by 10% - 12% if the bonding process is carried out without the agent to promote spinel formation. With increasing absolute proportion of Mg, i.e.Agents to promote spinel formation, the roughness decreases again and approaches the value of the raw ceramic or even falls below it in the case of a very large amount of agents to promote spinel formation.

[0068] In particular, a surface roughness S a which is less than 0.62 pm, preferably less than 0.6 pm and particularly preferably less than 0.58 pm. In particular, it can be observed that the value for S a by a value of at least 10% and preferably at least 12% compared to the value for S a of the raw ceramic (i.e. the ceramic element before bonding) increases when no agent is introduced to promote spinel formation between the metal layer and the ceramic element. In contrast, the value for S a by less than 10%, preferably less than 5% and particularly preferably less than 3% compared to the value for S afor the raw ceramic if an agent is added to promote spinel formation.

[0069] In particular, a parameter can be defined that indicates the influence of the agent on promoting spinel formation. This is defined by

[0070] The graph below illustrates this parameter for different amounts of spinel formation promoters. It can be seen that the parameter decreases with increasing amounts of spinel formation promoters. In particular, the parameter exhibits values ​​that are less than 10%, preferably less than 5%, and particularly preferably less than 2% or even less than 1.5%.

[0071] In summary, it can be stated that the targeted introduction of additional agents to promote spinel formation, which do not originate from the ceramic element 30 or the metal layer 10, 20 themselves and exceed a threshold value, can significantly influence the bonding layer 12, 14 between the metal layer 10, 20 and the ceramic element 30, which is also reflected in the manufactured metal-ceramic substrate 1. In particular, it can be seen that in this way, a targeted adjustment of the adhesive strength and the thermal shock resistance as well as a resistance can be achieved, in particular to an extent that goes beyond what occurs when the ceramic element 30 is bonded to the metal layer 10, 20 as usual.

[0072] List of reference symbols:

[0073] 1 metal-ceramic substrate

[0074] 10 first metal layer

[0075] 12 first binding layer

[0076] 14 second binding layer

[0077] 20 second metal layer 30 ceramic layer

Claims

Claims 1. A method for producing a metal-ceramic substrate (1), comprising - Providing at least one first metal layer (10) for forming a component metallization and a ceramic element (30), - Bonding the at least one first metal layer (10) to the ceramic element (30) by means of a direct bonding method, in particular a DCB method or a DAB method, by means of which a common first bonding layer (12) is formed between the ceramic element (30) and the at least one metal layer (10), wherein in order to improve an adhesive strength between the at least one first metal layer (10) and the ceramic element (30) for bonding by means of the direct bonding method, a first means for promoting spinel formation is provided in a region provided for the formation of the first bonding layer (12). 2 Method according to claim 1 , further comprising: - providing at least one second metal layer (20) for forming a backside metallization, wherein the at least one first metal layer (10) and the at least one second metal layer (20) are arranged on opposite sides of the ceramic element (30), - bonding the at least one second metal layer (20) to the ceramic element (30) by means of the direct bonding method, by means of which a common second bonding layer (14) is formed between the ceramic element (30) and the at least one second metal layer (20), wherein in order to improve an adhesive strength between the second metal layer (20) and the ceramic element (30) for bonding by means of the direct bonding method, a second means for promoting spinel formation in a region for forming the second bonding layer (14) is provided, wherein the at least one first metal layer (10) and the at least one second metal layer (20) are bonded to the ceramic element (30) in a common bonding process, preferably in a common furnace pass.

3. A method according to any one of the preceding claims, wherein the first agent for promoting spinel formation and / or the second agent for promoting spinel formation comprises magnesium, iron, barium, calcium, aluminum and / or manganese, in particular in oxidized form.

4. A method according to any one of the preceding claims, wherein the first agent for promoting spinel formation and / or the second agent for promoting spinel formation is substantially free of an aluminum compound and / or an aluminum oxide compound.

5. The method according to any one of the preceding claims, wherein a concentration of first agent for promoting spinel formation is greater than 20 g / l, preferably greater than 50 g / l and particularly preferably greater than 150 g / l and / or wherein an amount of second agent for promoting spinel formation is greater than 20 g / l, preferably greater than 50 g / l and particularly preferably greater than 150 g / l.

5. Method according to one of the preceding claims, wherein the first means for promoting spinel formation sets a frequency of a first spinel type in the manufactured metal-ceramic substrate.

6. The method according to claim 5, wherein a thickness of the deposited first spinel formation promoting agent and / or the deposited second spinel formation promoting agent assumes a value that is greater than 100 nm, preferably greater than 500 nm and particularly preferably greater than 1000 nm.

7. Method according to one of the preceding claims, wherein - the at least one first metal layer (10) is treated in such a way that different amounts of first agents for promoting spinel formation are provided on opposite sides of the first metal layer (10) and / or - the at least one second metal layer (20) is treated such that different amounts of the second agent for promoting spinel formation are provided on opposite sides of the second metal layer (10).

8. Ceramic element (30) for a method according to one of the preceding claims, wherein the ceramic element (30) comprises a first means for promoting spinel formation, for example on an outer side of the ceramic element (30) and / or within the ceramic element (30).

9. Metal layer (10, 20) for a method according to one of claims 1 to 6, wherein the metal layer (10, 20) comprises an agent for promoting spinel formation, for example on an outer side and / or within the metal layer (10, 20).

10. Metal-ceramic substrate (1) produced by a method according to one of claims 1 to 8, wherein in the manufactured metal-ceramic substrate (1) between the ceramic element (30) and the metal layer (10, 20) a bonding layer comprising spinels, in particular the first bonding layer (12) and / or the second bonding layer (14), is formed, wherein the bonding layer comprising spinels has at least a first spinel type, which comprises at least one component of the first and / or second means for promoting spinel formation, wherein the proportion of spinels of the first spinel type is at least 1.3 times, preferably at least 3 times and particularly preferably at least 5 times as large as the proportion of spinels of the first spinel type in a reference substrate in which a bond between the metal layer (10,20) and the ceramic element (30) by means of a direct bonding process without introducing a first and / or second agent to promote spinel formation.

11. Metal-ceramic substrate (1) according to claim 10, wherein the bonding layer (12, 14) comprising spinels comprises a second spinel type, wherein the proportion of spinels of the second spinel type is at least 1.3 times, preferably at least 5 times and particularly preferably 15 times as small as the proportion of spinels of the second spinel type in the reference substrate.

12. Metal-ceramic substrate (1) according to claim 11 or 12, wherein a resistance across an isolation trench in the fabricated substrate is at least 1.5 times, preferably at least 2.5 times and particularly preferably at least 3.5 times as large as the resistance across a comparison isolation trench on the reference substrate.

13. Metal-ceramic substrate (1) according to one of claims 10 to 12, wherein a roughness of the spinel layer in the manufactured metal-ceramic substrate (1) is smaller than a roughness in the reference substrate and / or in the manufactured metal-ceramic substrate a surface roughness assumes a value that is greater than 14. Metal-ceramic substrate (1) produced by a method according to one of claims 1 to 8, comprising - a ceramic element (30), a component metallization (10) and a backside metallization (20), wherein, viewed along a stacking direction (S), the ceramic element (30) is arranged between the component metallization (10) and the backside metallization (20), - a first bonding layer (12) between the ceramic element (30) and the component metallization (10) with a first spinel content / volume and - a second bonding layer (14) between the ceramic element (30) and the backside metal layer (30) with a second spinel content / volume, wherein an adhesive strength for the component metallization (10) and / or the backside metallization (20) is formed which on average assumes a value which is greater than 6 N / mm, preferably greater than 8 N / mm and particularly preferably greater than 10 N / mm and / or a difference between an adhesive strength for the component metallization (10) and an adhesive strength for the backside metallization (20) is less than 15%, preferably less than 10% and particularly preferably less than 5% of the adhesive strength of the component metallization (10).

15. Metal-ceramic substrate (1) according to claim 14, wherein a thickness of a spinel layer is greater than 200 nm, preferably greater than 500 nm and particularly preferably greater than 1000 nm.

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