Metal-ceramic composite

Abstract

The present invention relates to a metal-ceramic composite, containing: a ceramic substrate which contains aluminium nitride; a metal coating provided on the front side of the ceramic substrate, wherein the metal coating comprises at least one cutout and a surface of the ceramic substrate is exposed in the region of the cutout, and the exposed surface of the ceramic substrate exhibits an Al2p signal in an energy spectrum recorded by X-ray photoelectron spectroscopy, the signal having the following peaks: one or more peaks which each have a maximum in the range of 72.2 eV to 72.7 eV; one or more peaks which each have a maximum in the range of 73.4 eV to 74.6 eV.

Description

[0001] DESCRIPTION

[0002] Metal-ceramic composite

[0003] The present invention relates to a metal-ceramic composite which can be used as a ceramic circuit carrier in power electronics.

[0004] In power electronics, printed circuit boards that carry power components such as MOSFETs must be designed for high currents and be able to dissipate waste heat quickly.

[0005] Since ceramic materials such as aluminum oxide, aluminum nitride and silicon nitride have a significantly higher thermal conductivity than polymers used to manufacture conventional printed circuit boards, ceramic circuit boards are often used in power modules.

[0006] An overview of ceramic substrates used in power electronics for the production of ceramic circuit boards can be found, for example, in the following publication:

[0007] N. Chasserio et al., “Ceramic Substrates for High-Temperature Electronic Integration,” Journal of Electronic Materials, Volume 38 (2009), pp. 164-174

[0008] Ceramic substrates based on aluminum nitride exhibit very high thermal conductivity combined with sufficiently high mechanical strength and are therefore very well suited for applications in power electronics.

[0009] A ceramic circuit board contains a ceramic substrate coated with a metal layer on at least one of its sides, usually on both sides. The semiconductor components are applied to one of these metal layers in the final module, while the metal layer on the opposite side of the ceramic substrate can be thermally connected to a heat sink, for example. The ceramic substrate electrically insulates the metal layers from each other.

[0010] The production of a metallized ceramic substrate functioning as a ceramic circuit board, as is known to those skilled in the art, takes place, for example, by bringing the front and back of the ceramic substrate into contact with a metal foil (e.g. a copper or aluminum foil) and bonding them together. The bonding of the metal foils is achieved, for example, by eutectic bonding or active metal brazing (AMB). If the metal foil is a copper foil, the eutectic bonding is also referred to as the DCB or DBC process (DCB: "Direct Copper Bonding" -, DBC: "Direct Bonded Copper"). In the case of aluminum foil, the term "DAB" (Direct Aluminum Bonding) is also used for eutectic bonding. A metallized ceramic substrate produced using a DCB or AM B process is occasionally referred to as a DCB substrate (alternatively: DBC substrate) or AM B substrate.

[0011] For metallization using the DCB process, aluminum nitride substrates, for example, are first surface oxidized. The copper foil is then applied to this thin aluminum oxide layer on the surface of the aluminum nitride substrate using eutectic bonding.

[0012] For metallization by the active soldering process, active solders are used which, in addition to a main component such as Cu, Ag or Au, usually contain one or more elements that can react with the ceramic to form an adhesion-promoting reaction layer (see, for example, Chapter 8.2.4.3 (“Active Soldering”), pages 203-204, in Brevier Technische Keramik, Verband der Keramischen Industrie eV, 2003, Fahner Verlag). Examples of reactive elements used are hafnium (Hf), titanium (Ti), zirconium (Zr), niobium (Nb), cerium (Ce), tantalum (Ta) and vanadium (V). When metallizing an aluminum nitride substrate by active soldering, the reaction layer contains, for example, a nitride of the reactive element (A. Pönicke et al., “Active Soldering of Copper with Aluminum Nitride and Silicon Nitride Ceramics”, Keramische Zeitschrift, 63(5), 2011, 334-342).

[0013] D. Liu et al., "Fabrication of AIN / Cu composite structure via laser surface metallization assisted direct bonding technology," Journal of Manufacturing Processes, Vol. 119, 2024, pp. 640-648, describe a method for bonding a copper foil to an aluminum nitride ceramic substrate. In this method, the surface of the ceramic substrate is irradiated with a laser emitting pulses with a pulse duration in the nanosecond range. The irradiation parameters are selected such that a significant portion of the surface aluminum nitride is decomposed to form metallic aluminum according to the following reaction equation (1):

[0014] 2 AIN -> 2 AI + N2(1)

[0015] The laser treatment forms a metallic aluminum film on the surface of the aluminum nitride, which is used for the direct bonding of a copper foil. The copper foil is applied to the metallized surface of the ceramic substrate and bonded to the ceramic substrate under pressure and at a temperature of 620°C.

[0016] In a metal-ceramic composite used in power electronics, the metal layer on which the semiconductor components are to be mounted usually has one or more recesses and is therefore also referred to as a structured metal coating. The structuring creates, for example, metallic conductor tracks on the ceramic substrate. Adjacent conductor tracks are spatially separated by the recesses and are therefore electrically insulated from one another. The structuring of AM B substrates can, for example, be carried out in a two-stage process. In a first step, the metal layer is removed in defined areas (e.g. using a first etching solution) and then, in a second step, the adhesion-promoting layer resulting from the active solder process is removed (e.g. using a second etching solution).By removing the metal layer and, if applicable, the adhesion-promoting layer, the ceramic substrate is exposed in defined areas.

[0017] For use in power electronics, a metal-ceramic composite should exhibit high partial discharge resistance. Partial discharges are local discharges that partially bridge the insulation gap between two electrodes or adjacent conductor tracks.

[0018] DE 10 2008 001 220 A1 describes a metal-ceramic composite comprising a ceramic body which is covered with a metallization in at least one area of ​​its surface, wherein the partial discharge resistance between at least two layers of a metallization made of similar or different materials and between the layer of a metallization and the ceramic is < 20 pC and the ceramic body is spatially structured.

[0019] EP 4 407 672 A1 describes a metal-ceramic composite produced by an active soldering process, wherein (i) the solder material layer has an overhang portion extending 80 pm or more outward from a lower edge portion of a side surface of the metallic circuit board, (ii) the side surface of the metal coating has an inclination angle of 75° or more with respect to the surface of the ceramic substrate, and (iii) an insulating layer covers the side surface of the metal coating and the overhanging portion of the solder material layer. As already mentioned above, ceramic substrates based on aluminum nitride are used as circuit carriers in power electronics due to their very high mechanical strength combined with high thermal conductivity. In order to utilize their potential as circuit carriers as comprehensively as possible, it would be desirable to further optimize the partial discharge resistance of metallized aluminum nitride ceramic substrates.

[0020] An object of the present invention is to provide a metallized aluminum nitride-containing ceramic substrate which has a high partial discharge resistance and is therefore suitable for use in power electronics.

[0021] The object is achieved by a metal-ceramic composite comprising a ceramic substrate having a front side and a back side and containing aluminum nitride, a metal coating present on the front side of the ceramic substrate, wherein the metal coating has at least one recess and a surface of the ceramic substrate is exposed in the region of the recess, the exposed surface of the ceramic substrate shows an Al2p signal in an energy spectrum recorded by X-ray photoelectron spectroscopy (hereinafter also referred to as XPS spectrum), which has the following peaks: one or more peaks, each having a maximum in the range from 72.2 eV to 72.7 eV, one or more peaks, each having a maximum in the range from 73.4 eV to 74.6 eV, wherein the following condition is met:

[0022] 0.011 < h / (h + l2) < 0.050 where h is the total intensity of the peaks whose maximum lies in the range from 72.2 eV to 72.7 eV; l2 is the total intensity of the peaks whose maximum lies in the range from 73.4 eV to 74.6 eV.

[0023] XPS spectroscopy is an established method for analyzing solid surfaces. The signal of an element in the XPS spectrum is influenced by its oxidation state and its chemical environment (e.g., its chemical bonding partners). For example, if the Al atoms present near the surface of a ceramic substrate have a uniform oxidation state and a matching chemical environment, an Al2p signal with a relatively narrow half-width can be expected in the XPS spectrum. However, if the Al atoms have different oxidation states and / or different chemical bonding partners, the Al2p signal in the XPS spectrum will typically comprise two or more peaks.

[0024] In the context of the present invention, it was recognized that the treatment of the aluminum nitride ceramic substrate with an ultrashort pulse laser (i.e. a laser that emits pulses with a pulse duration in the range of pico- or femtoseconds) can lead to a significant improvement in the partial discharge resistance.

[0025] Furthermore, within the scope of the present invention, it was discovered that the Al2p signal of the XPS spectrum of the surface of the aluminum nitride ceramic substrate treated with the ultrashort pulse laser ("UKP laser") exhibits an additional peak with a maximum in the range of 72.2 eV to 72.7 eV, which is not present in the Al2p signal of the untreated aluminum nitride ceramic or aluminum nitride ceramic treated with an etching medium. An improvement in partial discharge resistance is achieved when the following condition is met:

[0026] 0.011 < h / (h + l2) < 0.050 where h is the total intensity of the peaks whose maximum lies in the range from 72.2 eV to 72.7 eV; l2 is the total intensity of the peaks whose maximum lies in the range from 73.4 eV to 74.6 eV.

[0027] The intensity ratio h / (h + l2) can be controlled, for example, by the pulse energy of the pulses of the U KP laser.

[0028] In a preferred embodiment, the following condition is met: 0.020 < h / (l1 + l2) < 0.040, where h and l2 have the meanings given above. In an exemplary embodiment, there is only a single peak, which has a maximum in the range from 72.2 eV to 72.7 eV, and no more than two peaks, each having a maximum in the range from 73.4 eV to 74.6 eV, are present.

[0029] In a further exemplary embodiment, the Al2p signal of the XPS spectrum has the following peaks: one or more peaks, more preferably no more than two peaks, particularly preferably a single peak with a maximum in the range from 72.2 eV to 72.7 eV, one or more peaks, more preferably no more than two peaks, particularly preferably a single peak with a maximum in the range from 73.4 eV to 73.9 eV, one or more peaks, more preferably no more than two peaks, particularly preferably a single peak with a maximum in the range from 74.1 eV to 74.6 eV.

[0030] The following applies preferably:

[0031] I2 = I2-1 + I2-2 where

[0032] I2 has the meaning given above;

[0033] I2-1 is the total intensity of the peaks, each of which has a maximum in the range from 73.4 eV to 73.9 eV;

[0034] I2-2 is the total intensity of the peaks, the maximum of which lies in the range of 74.1 eV to 74.6 eV.

[0035] The ratio I2-2 / I2-1 can be varied over a wide range within the scope of the present invention.

[0036] For example, the following applies:

[0037] 1 / 99 < I2-2 / I2-1 < 99 / 1

[0038] In an exemplary embodiment, the following applies:

[0039] 2 / 1 < I2-2 / I2-1 < 25 / 1

[0040] The I2-2 / I2-1 ratio can be influenced, for example, by the gas atmosphere in which the ceramic surface is treated with the ultrafast laser. An oxygen-containing atmosphere favors higher values ​​for the I2-2 / I2-1 ratio, while a nitrogen-containing or inert atmosphere may favor lower values ​​for the I2-2 / I2-1 ratio.

[0041] The intensity of a peak is the area under that peak.

[0042] For example, if there is only one peak with a maximum in the range from 72.2 eV to 72.7 eV of the AI2p signal, the total intensity h corresponds to the intensity of this peak. If there are two peaks, each with a maximum in the range from 72.2 eV to 72.7 eV, the total intensity h corresponds to the sum of the two peak intensities.

[0043] For example, the ceramic substrate contains the aluminum nitride in a proportion of at least 70 wt%, more preferably at least 80 wt%. Optionally, the ceramic substrate can be surface oxidized, i.e., the surface of the ceramic substrate comprises an aluminum oxide and / or an aluminum oxynitride in addition to the aluminum nitride or instead of the aluminum nitride.

[0044] Optionally, the ceramic substrate may contain one or more metal oxides. These were added, for example, as sintering aids during the production of the ceramic substrate. For example, the ceramic substrate contains one or more of the following oxides: one or more alkaline earth metal oxides such as magnesium oxide, one or more transition metal oxides (e.g., one or more rare earth oxides such as yttrium oxide or erbium oxide), a silicon oxide (e.g., SiO2), or a silicate.

[0045] The ceramic substrate has, for example, a thickness in the range of 0.1 mm to 1.5 mm, more preferably 0.2 mm to 1.0 mm.

[0046] Aluminum nitride ceramic substrates usable in the present invention are commercially available.

[0047] A metal coating is present on the front side of the ceramic substrate, wherein the metal coating has at least one recess and a surface of the ceramic substrate is exposed in the region of the recess (i.e. an exposed surface of the ceramic substrate is present in the region of the recess of the metal coating). This metal coating is also referred to below as a structured metal coating. Semiconductor components can be applied to the structured metal coating. For example, the metal coating is separated by the recess into at least two metallic conductor tracks. The distance between adjacent metallic conductor tracks separated from one another by the recess is, for example, at least 0.3 mm, e.g., 0.3 mm to 2 mm. For example, the recess is linear and has a width of at least 0.3 mm, e.g., 0.3 mm to 2 mm.

[0048] Optionally, a metal coating is also present on the back of the ceramic substrate. This back metal coating can optionally also have at least one recess through which a surface of the ceramic substrate is exposed. To achieve the most efficient heat dissipation possible, it may be preferable for the back metal coating not to have such a recess.

[0049] The metal coating present on the front side and optionally the back side of the ceramic substrate is, for example, a copper coating or an aluminum coating. The metal coating has a thickness in the range of 0.05 mm to 1.5 mm, for example, and more preferably 0.2 mm to 0.8 mm.

[0050] If the metal coating is a copper coating, it has, for example, a copper content of at least 97% by weight, more preferably at least 99% by weight.

[0051] If the metal coating is an aluminum coating, it has, for example, an aluminum content of at least 97% by weight, more preferably at least 99% by weight.

[0052] The metal coating can be applied to the front and optionally the back of the ceramic substrate using methods known to those skilled in the art.

[0053] For example, a metal foil (e.g. a copper or aluminum foil) is bonded to the front side of the ceramic substrate by active soldering.

[0054] In active soldering, for example, a bond is created between the metal foil and the ceramic substrate using an active solder at a temperature of approximately 600-1000°C. Due to their alloy composition, active solders are capable of wetting non-metallic, inorganic materials such as ceramic substrates. In addition to a main component such as copper, silver, and / or gold, active solders also contain one or more active metals such as Hf, Ti, Zr, Nb, V, Ta, or Ce, which can react with the ceramic substrate to form a reaction layer.

[0055] Preferably, a reaction layer resulting from the active soldering is present between the metal coating and the front side of the ceramic substrate. The reaction layer contains, for example, one or more ERS elements selected from Hf, Ti, Zr, Nb, V, Ta, and Ce, preferably selected from Hf, Ti, Zr, Nb, and Ce, more preferably selected from Hf, Ti, and Zr. The ERS element in the reaction layer is particularly preferably titanium. For example, the ERS elements are present in the reaction layer in the form of a nitride, an oxynitride, and / or an aluminide. For example, the reaction layer contains the ERS elements in a total amount of at least 50 wt%. For example, the reaction layer contains the nitrides, oxynitrides, and / or aluminides of the ERS elements in a total amount of at least 70 wt%, more preferably at least 85 wt%. In a semiconductor module for power electronics, the migration of silver can lead to problems.It may therefore be preferred that the reaction layer contains silver in a proportion of not more than 5 wt%, more preferably not more than 1 wt%, or is even silver-free.

[0056] Exposing a surface of the ceramic substrate, for example, occurs in several steps. First, the metal coating is removed, for example, by etching, and the reaction layer formed during active soldering is exposed. Subsequently, the exposed reaction layer is removed. Preferably, the exposed reaction layer is removed using an ultrashort pulse laser with a pulse duration in the picosecond or femtosecond range (e.g., an IR picosecond or femtosecond laser).

[0057] In order to electrically isolate the areas of the metal coating separated by the recess, it would be sufficient to carry out the material removal with the pulsed laser only for such a time or under such conditions until the electrically conductive material has been essentially completely removed in the treated areas, but a modification of the surface of the ceramic substrate is essentially avoided.

[0058] Within the scope of the present invention, however, treatment with the pulsed laser not only exposes a surface of the ceramic substrate, but also modifies this surface. As a result of this modification, the surface of the ceramic substrate exposed in the region of the recess exhibits the inventive Al2p signal in the XPS spectrum. For the production of a metal-ceramic substrate exhibiting the inventive XPS spectrum, it has proven advantageous if the pulses of the laser beam have a pulse duration of <100 picoseconds (e.g., 1 ps to 100 ps or 1 fs to <1000 fs) and a pulse energy in the range of 18 pJ to 75 pJ, more preferably 30 pJ to 65 pJ. The total fluence applied by the pulsed laser beam is, for example, 70 J / cm 2 up to 350 J / cm 2 , preferably 100 J / cm 2 up to 200 J / cm 2 .

[0059] Within the scope of the present invention, it is also possible to first expose the ceramic substrate surface by a single- or multi-stage etching process and then to treat the exposed ceramic substrate surface with the pulsed laser beam until the groove structure according to the invention is realized.

[0060] However, for reasons of process efficiency, it may be preferable to use the pulsed laser both for exposing the ceramic substrate surface and for modifying this surface.

[0061] For example, at least 50%, more preferably at least 70% of the area of ​​the surface of the ceramic substrate exposed in the region of the recess has the AI2p signal according to the invention.

[0062] The present invention also relates to a semiconductor module comprising the metal-ceramic composite described above and one or more semiconductor components.

[0063] Optionally, the semiconductor module contains a potting compound, which contacts the surface of the ceramic substrate of the metal-ceramic composite exposed in the area of ​​the metal coating recess. Potting compounds for electronic components are known to those skilled in the art. The potting compound contains, for example, a polymer (e.g., a thermoplastic or thermosetting polymer). For example, the potting compound contains an optionally cured epoxy resin or silicone resin, a polyurethane, or an inorganic cement (e.g., a phosphate cement). Measurement methods

[0064] Measurement of XPS spectra

[0065] The XPS energy spectra were recorded and analyzed as follows: The X-ray photoelectron spectra were recorded on a Physical Electronics PHI 5800 ESCA with a Mg anode (monochromatic Ka = 1.253 keV) as the source. First, overview spectra (range 0–1400 eV) were recorded from the samples. The elements present on the examined upper surface of the samples were determined from the overview spectra. Subsequently, detailed spectra were recorded from the samples in the energy ranges where signals could be identified in the overview spectrum. To record the detailed spectrum of the AI2p signal, an X-ray beam (200 pm diameter; 50 W at 15 kV; measurement time: 25 - 40 min (for example: 30 min); 20 ms integration time per measurement point) was used with the peak-to-noise setting activated and using a neutralizer (combination of Ar+ and e-, at low kinetic energy).The spectra were analyzed using the CasaXPS analysis software (version 52.3.224PR1.0; Casa Software Ltd.). The CC / CH component of the C 1s signal (ubiquitously present) was normalized to 284.8 eV as a reference, and the binding energies of the detailed spectra were shifted accordingly. A Shirley function was used for background correction. Peaks were generated from the obtained signals using the analysis software. The number of peaks was adjusted based on fitting models from the literature (XPS-NIST10 database). The analysis software was used to calculate the peak areas for the generated peaks, taking the relative sensitivity factors into account.

[0066] Composition of the adhesion promoter layer

[0067] The composition of the adhesion-promoting layer is determined by energy-dispersive X-ray spectroscopy (EDX) coupled with scanning electron microscopy (SEM-EDX).

[0068] In SEM-EDX, a focused primary electron beam is scanned point by point across the sample surface. The scattered electrons are recorded by a detector, with the number of electrons per pixel producing a microscopic image of the sample surface in grayscale. In addition, the primary electron beam excites the sample to emit characteristic X-rays, allowing the elements in the sample and their weight fraction to be determined by analyzing the energy spectrum with an EDX detector. For the examination, a scanning electron microscope (JSM-6060 SEM, JEOL Ltd) with a silicon drift EDX detector (NORAN, Thermo Scientific Inc) and analysis software (Pathfinder Mountaineer EDS System, e.g., version 2.8, Thermo Scientific Inc) is used.The following settings were used for scanning electron microscopy: magnification: 1000x, accelerating voltage = 15 kV, working distance = 10 mm, spot size (50 - 60) (adjusted to achieve 25% + / - 5% of the EDX detector dead time). The EDX spectrum was acquired using the following EDX detector settings: live time = 30 s, rate = auto, low energy cutoff = 100 keV, high energy cutoff = auto (per SEM accelerating voltage).

[0069] SEM-EDX allows the composition of the adhesion promoter layer to be determined both qualitatively (detection of specific elements and phases, e.g., a metal nitride phase present in the adhesion promoter layer) and quantitatively. The measurement is performed, for example, at at least 10 locations on the adhesion promoter layer.

[0070] Determination of partial discharge

[0071] To determine the partial discharge of the respective copper-ceramic composites, they were clamped in insulating frames that completely enclosed the respective top and bottom surfaces, thus isolating the top and bottom of the copper-ceramic composites. The central recess in the insulating frame allowed contacting of the individual copper areas on the top and bottom of the copper-ceramic composites using spring contacts. The contacted copper-ceramic composites were then placed in a plastic container containing an insulating liquid (Galden HS 240) so that the individual copper areas were completely covered with the insulating liquid. The spring contacts protruding from the insulating liquid were connected to the MPD600 measurement and analysis system from OMICRON Electronics.The partial discharge measurements were performed in accordance with the IEC 61287 standard using a different operating voltage of 3.6 kV (50 Hz) (instead of 2.4 kV). The AC voltage was ramped up to 3.6 kV within 10 s and applied for 60 s. The specified partial discharge values ​​were determined by averaging the last 10 s. Examples

[0072] For the examples, metal-ceramic composites were used, in which an aluminum nitride ceramic measuring 177.8 x 139 x 0.32 mm was bonded on both sides to a copper layer measuring 170 x 132 x 0.3 mm. The copper coating was applied using an active solder process, creating a reaction layer between the ceramic substrate and the copper coating.

[0073] Etching masks were applied to the copper coatings of the metal-ceramic composites. The unmasked areas of the copper layers of the copper-ceramic composites were wet-chemically etched using a hydrochloric acid copper chloride solution (copper ion content = 160 g / l) containing hydrogen peroxide. Etching was performed at a temperature of 50°C. The etching exposed the reaction layer resulting from the active soldering process.

[0074] The reaction layer exposed by etching was then removed.

[0075] For this purpose, in the inventive examples EB1, EB2, and EB3, as well as in the comparative examples VB1 and VB2, the reaction layer was removed by laser treatment with a pulsed laser beam from an IR picosecond laser. The applied total fluence in each case was 150 J / cm 2 , however, the pulse energies in the examples EB1, EB2, EB3, VB1 and VB2 differed from each other.

[0076] In comparative example VB3, the bonding layer was removed wet-chemically using an etching solution containing ammonium fluoride, fluoroboric acid and hydrogen peroxide.

[0077] XPS spectra were recorded on the exposed ceramic surfaces of the inventive examples EB1, EB2, and EB3 and the comparative examples VB1, VB2, and VB3. An XPS spectrum was also recorded from the surface of the starting substrate.

[0078] The XPS spectra were analyzed for the Al2p signal. Furthermore, the partial discharge was determined for the metal-ceramic composites of the inventive examples EB1, EB2, and EB3 and the comparative examples VB1, VB2, and VB3.

[0079] The results are summarized in Table 1 below.

[0080] Table 1: XPS-AI2p signals of the surface of the ceramic substrates and partial discharges of the metal-ceramic composites

[0081] The AI2p signal of the XPS spectrum of the ultrashort pulse laser-treated aluminum nitride substrate surface exhibits a peak with a maximum in the range of 72.2 eV to 72.7 eV, which is not present in the AI2p signal of the untreated or etched aluminum nitride ceramic. An improvement in partial discharge resistance is achieved when the relative intensity of this peak, expressed as the ratio h / (h + I2), is increased.

[0082] - on the one hand, exceeds a certain lower limit (see the inventive example EB1 (h / (h + I2) = 0.013) compared to the comparative examples VB3 (h / (h + I2) = 0) and VB1 (h / (h + I2) = 0.009),

[0083] - on the other hand, does not exceed a certain upper limit (see the inventive example EB3 (h / (h + I2) = 0.033) compared to the comparative example VB2 (h / (h + I2) = 0.064).

[0084] In the examples according to the invention, the partial discharge was significantly reduced. Consequently, the risk of electrical breakdown between adjacent copper areas is significantly reduced, thus increasing the reliability of the electrical module.

Claims

CLAIMS 1. A metal-ceramic composite comprising a ceramic substrate having a front side and a back side and containing aluminum nitride, a metal coating present on the front side of the ceramic substrate, wherein the metal coating has at least one recess and a surface of the ceramic substrate is exposed in the region of the recess, the exposed surface of the ceramic substrate shows an Al2p signal in an energy spectrum recorded by X-ray photoelectron spectroscopy, which has the following peaks: one or more peaks, each having a maximum in the range from 72.2 eV to 72.7 eV, one or more peaks, each with a maximum in the range of 73.4 eV to 74.6 eV, where the following condition is met: 0.011 < h / (h + l 2 ) < 0.050 where h is the total intensity of the peaks whose maximum is in the range of 72.2 eV to 72.7 eV; l2 is the total intensity of the peaks whose maximum is in the range of 73.4 eV to 74.6 eV.

2. The metal-ceramic composite according to claim 1, wherein there is only a single peak having a maximum in the range of 72.2 eV to 72.7 eV and no more than two peaks each having a maximum in the range of 73.4 eV to 74.6 eV.

3. The metal-ceramic composite according to claim 1 or 2, wherein the following applies to the peaks having a maximum in the range of 73.4 eV to 74.6 eV: at least one of the peaks has a maximum in the range of 73.4 eV to 73.9 eV, at least one of the peaks has a maximum in the range of 74.1 eV to 74.6 eV.

4. The metal-ceramic composite according to any one of the preceding claims, wherein the ceramic substrate contains the aluminum nitride in a proportion of at least 70% by weight.

5. The metal-ceramic composite according to any one of the preceding claims, wherein the metal coating is a copper or aluminum coating.

6. The metal-ceramic composite according to any one of the preceding claims, wherein a reaction layer is present between the ceramic substrate and the metal coating, the reaction layer containing one or more elements ERS selected from Ti, Hf, Zr, Nb, V, Ta and Ce.

7. A semiconductor module comprising the metal-ceramic composite according to any one of claims 1-6, one or more semiconductor components.

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