Joined body and production method for joined body

Abstract

This joined body comprises a ceramic layer, a metal layer that comprises copper, and a joining layer that joins the ceramic layer and the metal layer and includes titanium but does not include copper.

Description

Joint and method for manufacturing the joint

[0001] The present invention relates to a bonded body and a method for manufacturing the bonded body.

[0002] Conventionally, a bonded structure formed by bonding a heat-resistant and insulating ceramic substrate to a conductive metal has been known as a circuit board used in semiconductor devices and the like (see, for example, Patent Document 1). Patent Document 1 discloses a bonded structure formed by sandwiching a sheet-like titanium material between a ceramic substrate and a copper material and applying pressure. This bonded structure comprises a ceramic substrate, a copper material, and a bonding layer that bonds the ceramic substrate and the copper material. The bonding layer comprises three layers: a first layer primarily composed of titanium, a second layer primarily composed of copper, and a third layer containing a ceramic component and a titanium compound.

[0003] Patent No. 7107591

[0004] When manufacturing a circuit board, an etching process is performed to form a pattern. This etching process involves two steps: a first etching process in which a surface metal layer (a copper layer in the case of Patent Document 1) is etched, and a second etching process in which a bonding layer is etched. In this case, if the bonding layer contains components of the surface metal layer, as in Patent Document 1, there is a risk of etching defects occurring during the etching of the bonding layer.

[0005] The present invention has been made in view of the above, and has an object to provide a bonded body that can suppress etching defects and a method for manufacturing the bonded body.

[0006] In order to solve the above-mentioned problems and achieve the object, the bonded body of the present invention is characterized by comprising a ceramic layer, a metal layer made of copper, and a bonding layer bonding the ceramic layer and the metal layer, the bonding layer containing titanium as a component and not containing copper.

[0007] In addition, the bonded body according to the present invention is characterized in that, in the above invention, the bonding layer is formed using foil-like titanium.

[0008] In addition, the joined body according to the present invention is characterized in that, in the above invention, the ceramic layer is formed using nitride ceramics.

[0009] In addition, the joined body according to the present invention is characterized in that, in the above invention, the nitride ceramic is formed using silicon nitride.

[0010] The bonded body according to the present invention is characterized in that, in the above invention, it forms a part of a component constituting a circuit board used in a power module.

[0011] Furthermore, a method for producing a bonded body according to the present invention is characterized in that a titanium foil is placed between a ceramic layer and a metal layer made of copper, and the titanium foil is pressed through the ceramic layer and the metal layer at a bonding temperature of 875°C or higher and 920°C or lower, a surface pressure of 3 MPa or higher and 20 MPa or lower, and a holding time of more than 0.1 hour and less than 3 hours, thereby forming a bonding layer that bonds the ceramic layer and the metal layer.

[0012] The present invention has the effect of suppressing etching defects.

[0013] FIG. 1 is a diagram illustrating a configuration of a bonded body according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a bonding method for a bonded body according to an embodiment of the present invention. FIG. 3 is a diagram (part 1) illustrating a scanning electron microscope (SEM) image and a backscattered electron image of a cross section of a portion of a bonded body according to an embodiment of the present invention. FIG. 4 is a diagram (part 2) illustrating a SEM image and a backscattered electron image of a cross section of a portion of a bonded body according to an embodiment of the present invention. FIG. 5 is a diagram illustrating a mapping image, a secondary electron image, and a backscattered electron image of each element of a bonded body treated at 905° C., 3 MPa, and 1 hour. FIG. 6 is a diagram illustrating a mapping image, a secondary electron image, and a backscattered electron image of each element of a bonded body treated at 905° C., 10 MPa, and 1 hour. FIG. 7 is a diagram illustrating a mapping image, a secondary electron image, and a backscattered electron image of each element of a bonded body treated at 905° C., 20 MPa, and 1 hour. Fig. 8 shows a mapping image, a secondary electron image, and a backscattered electron image of each element in a bonded body treated at 905°C, 20 MPa, and 3 hours. Fig. 9 shows a mapping image, a secondary electron image, and a backscattered electron image of each element in a bonded body treated at 905°C, 20 MPa, and 15 hours. Fig. 10 shows an SEM image and a backscattered electron image (part 3) of a cross section of a portion of a bonded body according to an embodiment of the present invention. Fig. 11 shows an SEM image of a cross section of a portion of a bonded body produced when titanium foils of different thicknesses are used.

[0014] Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as "embodiments") will be described with reference to the accompanying drawings. Note that the drawings are schematic, and the relationship between the thickness and width of each part, the thickness ratio of each part, etc. may differ from the actual ones, and the drawings may also include parts with different dimensional relationships and ratios.

[0015] (Embodiment) Fig. 1 is a diagram showing the configuration of a bonded body according to one embodiment of the present invention. The bonded body 1 is used, for example, as a circuit board in a semiconductor device or the like. The bonded body 1 includes a metal layer 11 formed using a metal material, a ceramic layer 12 formed using a ceramic, and a bonding layer 13 provided between the metal layer 11 and the ceramic layer 12 to bond them together, forming a three-layer structure (metal layer / ceramic layer / metal layer) in which the ceramic layer 12 is located between the two metal layers 11. The bonded body 1 is used, for example, in a circuit board for a power module. Specifically, the bonded body 1 forms part of a component constituting the circuit board for the power module, and a pattern is formed by etching or the like.

[0016] The metal layer 11 has, for example, a plate shape and is made of, for example, copper (Cu).

[0017] The ceramic layer 12 has, for example, a plate shape and is formed using, for example, ceramics containing an oxide such as alumina, or nitride-based ceramics containing a nitride such as aluminum nitride or silicon nitride.

[0018] The bonding layer 13 is a single layer containing titanium as a main component, and is formed using titanium (Ti) foil (hereinafter also referred to as titanium foil).

[0019] Next, a method for joining a bonded body according to this embodiment will be described with reference to Fig. 2. Fig. 2 is a diagram illustrating a method for joining a bonded body according to one embodiment of the present invention. Fig. 2 shows the configuration of one side (the lower side in Fig. 1) of the bonded body 1 between the metal layer 11 and the ceramic layer 12. The other side is joined in the same manner. The one side and the other side may be joined simultaneously or at different times.

[0020] First, a titanium foil 13a is disposed on the surface of the metal layer 11 (see FIG. 2(a)). Here, the thickness of the titanium foil 13a is, for example, 2 μm or more and 10 μm or less.

[0021] After disposing titanium foil 13a on the surface of metal layer 11, ceramic layer 12 is placed on the side of titanium foil 13a opposite to metal layer 11, and diffusion bonding is performed (see FIG. 2(b)). The diffusion bonding conditions are as follows: the bonding temperature is set to be equal to or higher than the titanium-copper eutectic temperature (approximately 875°C), e.g., 875°C to 920°C, the surface pressure is set to be 3 MPa to 20 MPa, and the holding time is set to be longer than 0.1 hours and shorter than 3 hours. A load is applied in the direction that brings metal layer 11 and ceramic layer 12 closer to each other. This diffusion bonding causes titanium foil 13a to form bonding layer 13.

[0022] The joined body 1 according to this embodiment is produced by placing a titanium foil 13a on the copper material that constitutes the metal layer 11, and then sandwiching the titanium foil 13a between the ceramic material and copper material that constitute the ceramic layer 12 and diffusion bonding them together. Therefore, the joined body 1 according to this embodiment can be produced by a simpler process than in the conventional case where a brazing filler metal is applied or a brazing filler metal is disposed by screen printing.

[0023] Next, an example of a bonding interface in a bonded body will be described with reference to FIGS. 3 to 11. FIGS. 3 and 4 are diagrams showing SEM (Scanning Electron Microscope) images and backscattered electron images of a cross section of a portion of a bonded body according to an embodiment of the present invention. FIG. 3 shows SEM images at various magnifications (1000x, 3000x, and 5000x) of a bonded portion when bonding was performed at a bonding temperature of 905°C, a holding time of 1 hour, and surface pressures of 3 MPa, 10 MPa, and 20 MPa. FIG. 4 shows SEM images at various magnifications (1000x, 3000x, and 5000x) of a bonded portion when bonding was performed at a bonding temperature of 905°C, a surface pressure of 20 MPa, and a holding time of 1 hour, 3 hours, and 15 hours. FIGS. 3 and 4 show SEM images of a bonded portion when bonding was performed at a metal layer made of copper on the top and a metal layer made of Si on the bottom. ３ N ４ A ceramic layer made of titanium foil is placed between the metal layer and the ceramic layer. ３ N ４ The substrate was bonded with 0.4 mm thick copper and 4 μm thick titanium foil.

[0024] FIG. 5 shows a mapping image, a secondary electron image, and a backscattered electron image of each element in a bonded body treated at 905°C, 3 MPa, and 1 hour. FIG. 6 shows a mapping image, a secondary electron image, and a backscattered electron image of each element in a bonded body treated at 905°C, 10 MPa, and 1 hour. FIG. 7 shows a mapping image, a secondary electron image, and a backscattered electron image of each element in a bonded body treated at 905°C, 20 MPa, and 1 hour. FIG. 8 shows a mapping image, a secondary electron image, and a backscattered electron image of each element in a bonded body treated at 905°C, 20 MPa, and 3 hours. FIG. 9 shows a mapping image, a secondary electron image, and a backscattered electron image of each element in a bonded body treated at 905°C, 20 MPa, and 15 hours. The mapping images show the distribution of elements in a cross section of the bonded body, as measured by an electron probe microanalyzer (EPMA). The secondary electron image and the backscattered electron image are images taken by an SEM.

[0025] As shown in Figures 3 and 5 to 7, when the bonding temperature is 905°C and the holding time is 1 hour, no copper is seen to penetrate into the bonding layer even when the bonding surface pressure is changed in the range of 3 MPa to 20 MPa.

[0026] On the other hand, when the bonding temperature was 905°C and the surface pressure was 20 MPa, copper infiltration into the bonding layer was observed as the bonding time increased, as shown in Figures 4, 7 to 9. Specifically, a small amount of copper infiltration was observed when the holding time was 3 hours, and it was confirmed that copper infiltrated and formed a roughly layered structure when the holding time was 15 hours.

[0027] Here, nitrogen (N) in the bonded body reacts with Ti as SiN to form TiN, resulting in the appearance of an N-enriched layer. The decomposed Si diffuses into Ti to become more stable. Simultaneously with the Si diffusion, Ti also diffuses into Cu, dissolving Ti up to its solubility limit in Cu. Conversely, because diffusion from Cu to Ti also occurs, extending the holding time or increasing the temperature causes Cu to appear in the Ti layer. The difference between the dissolution of Ti into Cu and the appearance of Cu in the Ti layer is due to the difference in the diffusion coefficient and diffusion rate from Cu to Ti and the diffusion coefficient and diffusion rate from Ti to Cu, as well as the difference in the solid solubility limit of Ti in Cu and the solid solubility limit of Cu in Ti. In this embodiment, it is important to complete the bonding before a Ti layer containing Cu appears, which could become an etching inhibition layer. Magnesium (Mg), yttrium (Y) and oxygen (O) are components contained in silicon nitride, and carbon (C) is the main component of the embedding resin used for SEM observation.

[0028] Next, the cases where the bonding temperatures were 845°C and 875°C will be described with reference to Fig. 10. Fig. 10 shows an SEM image and a backscattered electron image of a cross section of a portion of a bonded body according to an embodiment of the present invention. Fig. 10 shows an SEM image of a cross section of a bonded body bonded using a titanium foil with a thickness of 4 µm. As shown in Fig. 10, when the bonding temperature was lowered, a striped layer was confirmed in the bonding layer.

[0029] Next, the cases where the titanium foil thickness was 2 μm, 4 μm, and 10 μm will be described with reference to FIG. 11. FIG. 11 shows an SEM image of a cross section of a portion of a bonded body produced when titanium foils of different thicknesses were used. As shown in FIG. 11, even when the titanium foil thickness was changed, the layer thickness itself was approximately the same. This is thought to be because the titanium foil leaked to the periphery when pressure was applied. The bonding condition was good for each thickness.

[0030] In the embodiment of the present invention described above, a bonding layer formed using titanium foil is formed from a single layer primarily composed of titanium, which bonds a metal layer made of copper to a ceramic layer, and the metal layer and ceramic layer can be bonded by this bonding layer. This bonding layer is a copper-free layer that does not contain copper, a component of the metal layer. According to this embodiment, since the bonding layer does not contain components of the surface metal layer, there is no risk of etching defects during the etching process of the bonding layer, and etching defects can be suppressed.

[0031] Although the embodiments for carrying out the present invention have been described above, the present invention should not be limited to only the above-described embodiments.

[0032] As such, the present invention may include various embodiments not described here, and various design changes may be made within the scope of the technical idea specified by the claims.

[0033] As described above, the bonded body and the method for manufacturing the bonded body according to the present invention are suitable for suppressing etching defects.

[0034] REFERENCE SIGNS LIST 1 Bonded body 11 Metal layer 12 Ceramic layer 13 Bonding layer 13a Titanium foil

Claims

a ceramic layer; a metal layer made of copper; a bonding layer that bonds the ceramic layer and the metal layer, the bonding layer containing titanium as a component and not containing copper; A bonded body comprising: 　 The bonding layer is formed using foil-shaped titanium.

2. The bonded body according to claim 1 . 　 The ceramic layer is formed using a nitride-based ceramic.

2. The bonded body according to claim 1 . 　 The nitride ceramic is formed using silicon nitride.

4. The bonded body according to claim 3. 　 It forms part of the components that make up the circuit board used in the power module.

2. The bonded body according to claim 1 . 　 A titanium foil is disposed between the ceramic layer and the copper metal layer, a bonding temperature of 875°C or higher and 920°C or lower, a surface pressure of 3 MPa or higher and 20 MPa or lower, and a holding time of more than 0.1 hours and less than 3 hours, and pressurizing the foil-shaped titanium through the ceramic layer and the metal layer to form a bonding layer that bonds the ceramic layer and the metal layer; A method for producing a bonded body, comprising:

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