DE102013108610A1 - Metal-ceramic substrate and method for producing a metal-ceramic substrate - Google Patents

Abstract

A metal-ceramic substrate having a multilayer, plate-shaped ceramic material or substrate, which consists of an inner base layer made of a silicon nitride ceramic and at least one applied to a surface side of the base layer intermediate layer of an oxide ceramic, and having at least one metallization with the intermediate layer is connected by direct bonding (DCB method).

Description

The invention relates to a metal-ceramic substrate according to the preamble of claim 1 or 2 and to a method according to the preamble of claim 12.

Metal-ceramic substrates or ceramic substrates with metallizations are known in various designs, in particular as printed circuit boards or substrates for electrical and electronic circuits or modules and in particular for high power circuits or modules.

Also known is the so-called DCB method for directly joining metal foils or metallizations with a ceramic material or ceramic substrate for producing the metallization required for printed conductors, terminals, etc. on a ceramic substrate, for example on an aluminum oxide ceramic substrate. In this example, in the US-PS 37 44 120 or in the DE-PS 23 19 854 described methods are metal layers or foils, such as copper layers or foils on their surface sides with a coating of a chemical compound of the metal (eg copper) and a reactive gas (preferably oxygen) provided. This coating forms with a thin layer of the adjacent metal a eutectic (melting layer) with a melting temperature below the melting temperature of the metal (eg copper), so that by laying the metal layer or foil on the ceramic and by heating all the layers they can be joined together , By melting the metal substantially only in the region of the reflow layer or oxide layer. When copper or a copper alloy is used as metal, this process is also referred to as DCB bonding or direct copper bonding (DCB) processes.

• – Oxidieren einer Kupferfolie derart, dass sich eine gleichmäßige Kupferoxidschicht ergibt;
• – Auflegen des Kupferfolie auf die Keramikschicht;
• – Erhitzen des Verbundes auf eine Prozesstemperatur zwischen etwa 1025°C bis 1083°C, z.B. auf ca. 1071°C;
• – Abkühlen auf Raumtemperatur.

This DCB method then has, for example, the following method steps:

• - Oxidizing a copper foil such that a uniform copper oxide layer results;
• - placing the copper foil on the ceramic layer;
• - Heating the composite to a process temperature between about 1025 ° C to 1083 ° C, for example to about 1071 ° C;
• - Cool to room temperature.

Also known is the so-called active soldering method ( DE 22 13 115 ; EP-A-153 618 ) for joining metallization-forming metal layers or metal foils, in particular also copper layers or copper foils with the respective ceramic material or ceramic substrate. In this method, which is also used specifically for the production of metal-ceramic substrates, at a temperature between about 800 ° C-1000 ° C, a connection between a metal foil, such as copper foil, and a ceramic substrate, such as aluminum nitride ceramic, prepared using a brazing alloy which also contains an active metal in addition to a main component such as copper, silver and / or gold. This active metal, which is, for example, at least one element of the group Hf, Ti, Zr, Nb, Ce, establishes a chemical bond between the solder and the ceramic, while the bond between the solder and the metal is a metallic braze joint ,

Also known is a metal-ceramic substrate with an inner layer or base layer of a silicon nitride ceramic ( EP 798 781 ), which has a much higher mechanical strength compared to other ceramics, especially compared to an alumina ceramic (Al3O2 ceramic). In order to enable the metallization to be applied by the DCB method, it has been proposed to apply an intermediate layer of a pure aluminum oxide ceramic to the surface sides of the silicon nitride ceramic base layer. However, this procedure does not lead to a complete, especially not to a defect-free connection between the ceramic material and the metallization. On the contrary, especially when copper metallizations are used, numerous gas inclusions occur between the metallization and the ceramic material, which result from a reaction between the oxygen from the copper or copper oxide eutectic (Cu / Cu 2 O eutectic) and the silicon nitride ceramic, according to the formula below: 6CuO + Si3N4 → 3SiO2 + 6Cu + N2.

On the one hand, this reaction consumes the liquid eutectic Cu / Cu 2 phase necessary for the bonding. On the other hand, bubbles are formed by the resulting gaseous nitrogen (N2). This disadvantageous reaction can not be avoided with an intermediate layer of the pure aluminum oxide ceramic. This is according to one of the present invention underlying knowledge, inter alia, on the very different thermal expansion coefficients of silicon nitride (3.0 × 10 ^-6 K ^-1 ) and of alumina (8 × 10 ^-6 K ^-1 ). These differences in the thermal expansion coefficient, for example, during the firing or sintering of the intermediate layer of the alumina ceramic, but also during the bonding of the metallization (DCB method) to cracks in the intermediate layer, so that through these cracks, the above reaction between the Cu / Cu2O eutectic and the silicon nitride ceramic can be done.

It is also known ( EP 0 499 589 ) to provide on a ceramic base layer at least one intermediate layer of pure silicon oxide (SiO 2) and then apply the metallization by means of the DCB method. This procedure likewise does not lead to a usable result since the eutectic melt necessary for the DCB process reacts with the SiO 2 to form liquid Cu 2 O-SiO 2. An intermediate layer of SiO 2 is therefore not useful for the application of the metallizations with the DCB method.

Also known are metal-ceramic substrates with an inner base layer, which is formed by a silicon nitride ceramic and which is provided on both sides with an intermediate layer of an oxide ceramic, to each of which then a metallization is applied by DCB bonding ( DE 10 2005 042 554 A1 ). The intermediate layers consist for example of forsterite, cordierite, mullite or mixtures thereof. Among other things, a balance of the very different expansion coefficients of the silicon nitride ceramic and of the metal (eg copper) of the metallizations is achieved by the intermediate layers. Furthermore, a reaction of the oxygen from the copper or copper oxide eutectic with the silicon nitride ceramic and thus caused by liberated nitrogen vacancies in the eutectic connection between the respective metallization and the intermediate layer is avoided by the intermediate layers during the DCB process. It is also desirable in this known metal-ceramic substrate that the proportion of free silicon oxide at the transition between the intermediate layer and the respective metallization is substantially zero in order to improve the quality of the eutectic connection of the metallization with the intermediate layer and thus the quality of the Metal-ceramic substrate to avoid overall impairing reaction between the free silica and the copper or copper oxide eutectic. This distribution of the free silicon in the intermediate layer requires a special temperature-time profile during firing of the intermediate layer.

The object of the invention is to show a metal-ceramic substrate, which in particular as a circuit board for electrical circuits or modules further improved properties, in particular with regard to the adaptation of the coefficient of thermal expansion by the respective intermediate layer and with respect to the prevention of defects by the DCB bonding having released nitrogen.

To solve this problem, a metal-ceramic substrate according to claims 1 or 2 is formed. A method for producing a metal-ceramic substrate is the subject of claim 12.

A special feature of the metal-ceramic substrate according to the invention is that the respective intermediate layer contains silicon oxide in crystalline form (cristobalite), in an arbitrary distribution. Since the silica is in crystalline form, there is no risk of deteriorating the quality of the eutectic connection between the intermediate layer and the metallization by the reaction between free silica and the copper or copper oxide eutectic because the reaction rate is greatly lowered. A special temperature-time profile when burning the intermediate layer is therefore not required.

In the invention as well, the intermediate layers compensate for the very different coefficients of expansion of the silicon nitride ceramic and of the metal (eg copper) of the metallizations, so that a reaction of the oxygen from the copper or copper oxide through the intermediate layers during the DCB process -Eutectic with the silicon nitride ceramic and thus defects in the eutectic compound, which are caused by (released) nitrogen, between the respective metallization and the intermediate layer can be avoided.

In a further preferred embodiment of the invention, the oxidic ceramic of the intermediate layer consists exclusively or almost exclusively of magnesium silicate with zirconium and / or yttrium silicate and with a proportion of free silicon oxide in crystalline form. Magnesium and zirconium as well as yttrium promote (catalyze) the conversion of glassy silica (no lattice structure) into crystalline silica (cristobalite).

The term "substantially" or "approximately" or "approx." In the context of the invention means deviations from the exact value by +/- 10%, preferably by +/- 5% and / or deviations in the form of for Function insignificant changes.

Further developments, advantages and applications of the invention will become apparent from the following description of exemplary embodiments and from the figures. In this case, all described and / or illustrated features alone or in any combination are fundamentally the subject of the invention, regardless of their summary in the claims or their dependency. Also, the content of the claims is made an integral part of the description.

The invention will be explained in more detail below with reference to the figures of an embodiment. Show it:

1 in a simplified representation of a section through a metal-ceramic substrate according to the invention;

2 Various process steps in the production of the metal-ceramic substrate of 1 ;

3 a schematic representation of a method for determining the adhesion or peel strength applied to the ceramic material or ceramic substrate, formed by a metal foil metallization;

4 in a simplified representation of a section through a structured metal-ceramic substrate according to the invention;

5 similar in a presentation 4 a semiconductor module.

That in the figures with 1 designated metal-ceramic substrate consists of a plate-shaped ceramic material or ceramic substrate 2 , which on both surface sides by means of the DCB method with one each of a metal foil 3.1 respectively. 4.1 , ie an illustrated embodiment of metallization formed by a copper foil 3 respectively. 4 is provided with a thickness dm. The ceramic substrate 2 is in turn made of several layers, consisting of an inner ceramic or base layer 5 made of silicon nitride (Si3N4), which in each case has an intermediate layer on both surface sides 6 and 7 made of an oxide ceramic is provided. The intermediate layers 6 and 7 allow application of the metallizations 3 and 4 with the aid of the DCB method, without the formation of impurities and with high adhesion or peel strength of the metallizations 3 and 4 forming copper on the ceramic material 2 ,

The base layer 5 of silicon nitride has a thickness dc and contains, for example, in addition to silicon nitride, inter alia, sintering aids in the form of at least one oxide of Ho, Er, Yb, Y, Mg, Ca, La, Sc, Pt, Ce, Nd, Dy, Sm and / or Gd , For example, in a proportion of 1.0 to 8.0 weight percent and also Ti, Fe, Cr as impurities, for example in a proportion of 0.1 to 1.0 weight percent, each based on the total mass of the base layer 5 forming ceramics.

In the illustrated embodiment, the two have metallizations 3 and 4 for example, the same thickness dm, which is at most four times the thickness dc of the base layer 5 or the total thickness of the ceramic material 2 can amount. Usually, the thickness dm of the metallizations 3 and 4 in the range between 0.01 mm-1.0 mm. The thickness dc is, for example, in the range between 0.1 mm and 2.0 mm.

The two intermediate layers 6 and 7 are reproduced in the figure with a greatly increased thickness, which allows the representation of these layers. The thickness of these intermediate layers is actually in the range between 0.5 μm and 15 μm, preferably in the range between 2.0 μm and 4.0 μm.

A special feature of the metal-ceramic substrate 1 is that the intermediate layers 6 and 7 Silicon oxide (SiO 2) in crystalline form over their entire layer thickness arbitrarily distributed, preferably also shares of zirconium oxide (ZrO 2) and traces of aluminum silicate (Al 2 SiO 4). In detail, the oxidic interlayers exist 6 and 7 exclusively or substantially exclusively of magnesium silicate (MgSiO3, Mg2Si2O6) with zirconium silicate (ZrSiO4) and / or yttrium silicate (Y2Si2O7), balance silicon oxide (SiO2) in crystalline form, zirconium oxide (ZrO2) and possibly traces of aluminum silicate (Al2SiO4).

In a preferred embodiment of the metal-ceramic substrate according to the invention, the intermediate layers 6 and 7 then the following composition: 40 percent by weight Magnesium silicate (MgSiO3 / Mg2Si2O6) 10 weight percent Weight percent zirconium silicate (ZrSiO4) and / or yttrium silicate (Y2Si2O7) Rest: SiO2 in crystalline form + ZrO2 + traces of Al2SiO4, in each case based on the total mass of the respective intermediate layer 6 respectively. 7 ,

The production of the ceramic material 2 consisting of the base layer 5 and the intermediate layers 6 and 7 for example, as follows:
On the base layer 5 ( 2 , Position a), a starting solution or dispersion is applied, which contains at least Zr, Mg, Y, Al, crystallizers, Ca, Si, Ca. The application is carried out for example by spraying, dipping or in a sol-gel process. This is followed by baking and dense sintering of the intermediate layers 6 and 7 in an oxidic atmosphere, at a temperature and with a process duration which are well above the process temperature and process time of the DCB process, ie at a temperature in the range between 1100 ° C and 1400 ° C and with a combustion or process duration, for example for several hours, eg from about one to six hours. The in this baking and dense sintering of the silicon nitride of the base layer 5 liberated nitrogen can via free lattice sites in the resulting intermediate layer 6 respectively. 7 escape to the outside, leaving dense intermediate layers 6 and 7 can be achieved without defects. After firing and dense sintering is the ceramic material 2 receive ( 2 , Position b).

The components of the intermediate layers 6 and 7 thus come partially from the on the base layer 5 applied starting solution or Ausgangsdispersion, but partially from the base layer 5 itself. In a preferred embodiment, the base layer contains 5 also magnesium and / or yttrium, so that the magnesium silicates (MgSiO3, Mg2Si2O6) and / or yttrium silicates (Y2Si2O7) of the intermediate layers 6 and 7 at least in part from the magnesium or yttrium of the base layer 5 be formed.

After producing the intermediate layers 6 and 7 become the metallizations by means of the DCB process 3 and 4 applied, by applying pre-oxidized copper foils 3.1 and 4.1 (Position c the 2 ) and then heating the ceramic material 2 and the copper foils 3.1 and 4.1 formed to the DCB bond or process temperature between about 1025 ° C to 1083 ° C, for example 1071 ° C over a period shorter than 20 minutes. (Position d the 2 ).

After DCB bonding of the metallizations 3 and 4 Preferably, a further treatment of the metal-ceramic substrate produced 1 in a printing process, further reduction of defects (pores or voids) in the bonding layer, eg in the eutectic bonding layer between the metallizations 3 and 4 and the respective intermediate layer 6 respectively. 7 , the metal-ceramic substrate 1 In this case, in a protective gas atmosphere (eg argon) at a temperature between 500 ° C and 1000 ° C applied with such a pressure that results in a volume reduction of 5% to 20% of the eutectic compound layer, for example, with a pressure up to 1000bar. With the pressure treatment, not only defects in the bonding layer are reduced, but in the pressure treatment is also material of the metallizations 3 and 4 by permanent deformation pressed into depressions or open pores of the bonding layer, whereby the adhesion of the metallizations 3 and 4 additionally improved.

It has been shown that the intermediate layers 6 and 7 in the described composition advantageously a compensation of the very different thermal expansion coefficients of the metal or copper of the metallizations 3 and 4 and the silicon nitride of the base layer 5 cause no thermally induced cracks in the intermediate layers during the DCB process 6 and 7 which could affect the tightness of these layers. The intermediate layers 6 and 7 thus effectively prevent oxygen from the copper or copper-oxide eutectic (Cu / Cu2O eutectic) to the base layer during the DCB process 5 and react there with the silicon nitride to release nitrogen, resulting in blistering or the formation of voids in the connection between the metallizations 3 and 4 and the ceramic material would lead. This barrier effect of the intermediate layers 6 and 7 Oxygen during the DCB process is particularly supported by the fact that the process temperature and the process time of the DCB process are substantially smaller than the process temperature and the process time during firing or dense sintering of the intermediate layers 6 and 7 ,

The base layer 5 indicates its with the respective intermediate layer 6 respectively. 7 surface to be provided with a mean surface roughness Ra after DIN 4760 which ranges between 0.2 Ra and 0.7 Ra, for example, 0.4 Ra. Only at a sufficient surface roughness, can be for the intermediate layers 6 and 7 and the metallizations associated with them 3 and 4 achieve a sufficiently high adhesion or peel strength, for example, a peel strength greater than 40 N / cm. This peel strength is with in the 3 measured method. A test object 1.1 , which corresponds in structure to the metal-ceramic substrate, but only with the metallization 3 and the intermediate layer 6 is prepared is prepared in the manner described above. The metallization 3 is made as a strip with a width of 1 cm and a thickness of 0.3 mm. At an upstanding end of the strip-shaped metallization 3 is when the test specimen is clamped 1.1 exerted a force, and with such a size that the strip-shaped metallization 3 at a rate of 0.5 cm / min from the ceramic material 2 is deducted. The required force F then determines the adhesion or peel strength.

The 4 shows the metal-ceramic substrate 1 with structured metallization 3 for the formation of structured metal areas 3s eg in the form of printed conductors, contact and / or attachment surfaces. The structuring is done with the usual techniques.

The 5 shows the metal-ceramic substrate 1 with structured metallization 3 , with the textured metal areas 3s and with electrical or electronic components 8th on the structured metallization 3 ,

The invention has been explained in more detail above using an exemplary embodiment. It is understood that changes and modifications are possible without thereby departing from the inventive concept underlying the invention.

LIST OF REFERENCE NUMBERS

1

Metal-ceramic substrate

1.1

examinee

2

ceramic material

3, 4

metallization

3s

Metal area of textured metallization 3

3.1, 4.1

metal foil

5

base layer

6, 7

interlayer

8th

module

F

force

_c

Thickness of the base layer 5

d _m

Thickness of the metallizations

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 3744120 [0003]
• DE 2319854 [0003]
• DE 2213115 [0005]
• EP 153618 A [0005]
• EP 798781 [0006]
• EP 0499589 [0008]
• DE 102005042554 A1 [0009]

Cited non-patent literature

• DIN 4760 [0034]

Claims (18)

Metal-ceramic substrate comprising a multilayer, plate-shaped ceramic material or substrate ( 2 ), which consists of an inner base layer ( 5 ) of a silicon nitride ceramic and of at least one on a surface side of the base layer ( 5 ) applied intermediate layer ( 6 . 7 ) consists of an oxide ceramic, and at least one metallization ( 3 . 4 ), with the intermediate layer ( 6 . 7 ) is connected by direct bonding (DCB method), characterized in that the at least one intermediate layer ( 6 . 7 ) of the oxide ceramic contains silica (SiO 2) in crystalline form in an arbitrary distribution. Metal-ceramic substrate comprising a multilayer, plate-shaped ceramic material or substrate ( 2 ), which consists of an inner base layer ( 5 ) of a silicon nitride ceramic and of at least one on a surface side of the base layer ( 5 ) applied intermediate layer ( 6 . 7 ) consists of an oxide ceramic, and at least one metallization ( 3 . 4 ), with the intermediate layer ( 6 . 7 ) is connected by direct bonding (DCB method), characterized in that the at least one intermediate layer ( 6 . 7 ) consists of magnesium silicate (MgSiO3 / Mg2Si2O6) with zirconium silicate (ZrSiO4) and / or yttrium silicate (Y2Si2O3), balance silicon oxide (SiO2) in crystalline form and zirconium oxide (ZrO2). Metal-ceramic substrate according to claim 1, characterized in that the at least one intermediate layer ( 6 . 7 ) additionally consists of magnesium silicate (MgSiO3 / Mg2Si2O6) with zirconium silicate (ZrSiO4) and / or yttrium silicate (Y2Si2O3). Metal-ceramic substrate according to one of the preceding claims, characterized in that the at least one intermediate layer ( 6 . 7 ) exclusively or substantially exclusively, ie up to at least 40% by weight of magnesium silicate (MgSiO3 / Mg2Si2O6) with zirconium silicate (ZrSiO4) and / or yttrium silicate (Y2Si2O3), balance silicon oxide (SiO2) in crystalline form and zirconium oxide (ZrO2). Metal-ceramic substrate according to one of the preceding claims, characterized in that the at least one intermediate layer ( 6 . 7 ) Contains traces of aluminum silicate (Al2SiO4). Metal-ceramic substrate according to one of the preceding claims, characterized in that the at least one intermediate layer has the following composition: 40 percent by weight magnesium silicate 10 weight percent Zirconium silicate and / or yttrium silicate 50 weight percent Silica in crystalline form, zirconium oxide and traces of aluminum silicate and possibly other components in each case based on the total mass of the intermediate layer. Metal-ceramic substrate according to one of the preceding claims, characterized in that the at least one intermediate layer has a thickness in the range between 0.5 and 15 microns, preferably in the range between 2 and 4 microns. Metal-ceramic substrate according to one of the preceding claims, characterized in that the base layer ( 5 ) at the transition to the at least one intermediate layer ( 6 . 7 ) has an average surface roughness in the range between 0.2 Ra and 0.7 Ra, preferably has an average surface roughness of 0.4 Ra. Metal-ceramic substrate according to one of the preceding claims, characterized in that the base layer ( 5 ) at its two, opposite surface sides with the intermediate layer ( 6 . 7 ), and that in each case at least one metallization by DCB bonding is applied to each intermediate layer. Metal-ceramic substrate according to one of the preceding claims, characterized in that the at least one metallization ( 3 . 4 ) forms the exposed outer surface of the metal-ceramic substrate. Metal-ceramic substrate according to one of the preceding claims, characterized in that at least one metallization ( 3 . 4 ) struturiert and, for example, with at least one component ( 8th ) is provided. Method for producing a metal-ceramic substrate ( 1 ) according to any one of claims 2-11, characterized in that the at least one intermediate layer ( 6 . 7 ) is produced from the oxide ceramic in a combustion and / or sintering process at a process temperature and / or process duration greater than the process temperature and / or process time of the DCB process. Method according to claim 12, characterized in that the at least one intermediate layer ( 6 . 7 ) is produced by applying a magnesium and / or zirconium and / or silicon-containing solution or dispersion, for example by spraying, dipping or in a sol-gel process. Process according to claim 12 or 13, characterized in that the magnesium silicate of the at least one intermediate layer ( 6 . 7 ) at least partially from that in the base layer ( 5 ) during the firing and / or sintering of the intermediate layer ( 6 . 7 ) is generated in an oxygen-containing atmosphere. Method according to one of the preceding claims, characterized in that the base layer ( 5 ) at its with the at least one intermediate layer ( 6 . 7 ) to be provided surface side with an average surface roughness in the range between 0.2 Ra and 0.7 Ra is provided. Method according to one of the preceding claims, characterized in that the base layer ( 5 ) on its two surface side, each with an intermediate layer ( 6 . 7 ) and at least one metallization ( 3 . 4 ) is applied by DCB bonding. Method according to one of the preceding claims, characterized in that at least one metallization ( 3 . 4 ) is strutured. Method according to one of the preceding claims, characterized in that after the application of the metallizations ( 3 . 4 ) a post or pressure treatment of the produced metal-ceramic substrate ( 1 ) in a protective gas atmosphere (eg argon) at a temperature between 500 ° C and 1000 ° C, preferably with such a pressure, that a volume reduction of the bonding layer between the metallizations ( 3 . 4 ) and the ceramic material or substrate ( 2 ) from 5% to 20%, for example with a pressure of up to 1000 bar.

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