JPH02177463A - Manufacture of ceramic-metal composite board - Google Patents

Abstract

PURPOSE:To manufacture a composite board at a low price having a highly reliable junction section by a method wherein a copper member is brought into contact with both the sides of a ceramic board via a thin film layer of an active metal, a copper member for joining elements is brought into contact with one side of the copper member which is not brought into contact, and it is heated to a specific temperature and pressurized in a thicknesswise direction. CONSTITUTION:A first and a second copper member 2a, 2b are brought into contact with both the sides of a ceramic board 1 via a thin film layer 21 made of an active metal which is 0.1 to 3mum thick. A copper member 2c for joining semiconductor elements is brought into contact with the not-contacted side of the copper member 2a which is one of the above copper member 2a, 2b via a heat buffer metal board 3. Next, such a board member as above is heated to a temperature from the melting point of an alloy formed by the first and second copper members 2a, 2b and an active metal to temperature not higher than the melting point of the first and second copper members 2a, 2b in an atmosphere which is not likely to react with the active metal and is pressurized in a thicknesswise direction. For example, for the ceramic board 1, an alumina member is used; for the active metal, Ti; and, for the heat buffer metal, molybdenum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a ceramic-metal composite substrate used in manufacturing a semiconductor device.

[Conventional technology]

Conventionally, as a method for manufacturing a ceramic-metal composite substrate for mounting a semiconductor element in which a ceramic base material and a metal member are directly bonded, there is known a method disclosed in Japanese Patent Application Laid-open No. 155580/1983. However, the substrate formed by this manufacturing method has a problem in that it is susceptible to heat cycles when used as a substrate for a semiconductor device. In order to solve this problem, a heat-restricting material such as molybdenum is interposed between the metal member to be bonded to the semiconductor element and the metal member to be bonded to the ceramic base material to form a cladding material. The applicant has proposed a method for manufacturing a ceramic-metal composite substrate in which a ceramic-metal composite substrate is bonded to a ceramic base material. This will be explained using a diagram.

FIGS. 5(a) to 5(c) are cross-sectional views for explaining a conventional method for manufacturing a ceramic-metal composite substrate, in which 1 is a ceramic base material, and 2a, 2b, and 2c form electric circuits. These copper members 2a, 2
b and 2c are each made of copper or a copper alloy, the copper members 2a and 2b are placed on both sides of the ceramic base material 1, and the copper member 2c is placed on the copper member 2a via a restraining member which will be described later. There is. This copper member 2c is added to increase the capacity of the semiconductor element, and the semiconductor element is mounted on this copper member 2c. 3 is a restraining member for restraining the thermal expansion of the copper members 2a and 2c;
This restraint member 3 is made of molybdenum, for example.

Next, a method for manufacturing a ceramic-metal composite substrate using each of these members will be described. Since it is desirable that each of the above-mentioned members be joined without intervening an intermediate layer such as solder, first, as shown in FIG. 5(a), the restraining member 3 is sandwiched between the copper member 2a and the copper member 2C, and these are integrated using a joining method such as explosive welding. At this time, the joint surface 4a between the restraint member 3 and both copper members 2a and 2c,
4b is a material that is mechanically strong. Next, the cladding material produced by the above process is shaped by a method such as punching to form a desired electrical circuit pattern. As shown in FIG. 5(b), the ceramic base material 1 is sandwiched between the clad material and the copper member 2b, and the clad copper members 2a and 2b are attached to the ceramic base material 1.
are joined to each other. The bonding between the ceramic base material 1 and the copper members 2a and 2b can be performed, for example, by
The so-called DB mediated by oxygen shown on the common axis of No. 55580
C method and active metal method are adopted.

In addition, 5 in the figure indicates the ceramic base material l and the copper member 2a +2
This is oxygen to firmly bond b. According to the DBC method and the active metal method, a molten layer with a thickness of approximately several tens of μm is formed on the bonding surfaces 6a and 6b between the copper members 2a and 2b and the ceramic base material 1, and this molten layer forms the copper member 2a and the ceramic base material 1.
, 2b and the ceramic base material 1 are bonded to each other in a wetting manner, so that the copper members 2a, 2b are firmly bonded to the ceramic base material 1.

FIG. 6 is a perspective view showing a state in which a semiconductor element is bonded to a conventional ceramic-metal composite substrate. In this figure, the same members as those explained in FIG. Further explanation will be omitted. In FIG. 6, 7 is a semiconductor element, and this semiconductor element 7 is a copper member 2C.
It is mounted on the top via solder 8. Reference numeral 9 denotes a copper plate serving as an electrode for external connection, and this copper plate 9 is bonded onto the ceramic base material 1 and is electrically insulated from the copper member 2C. 10 is a bonding wire for connecting the surface bridge (not shown) of the semiconductor element 7 and the copper plate 9, and this bonding wire 10 is made of aluminum.

[Problem to be solved by the invention]

However, the method for manufacturing a ceramic-metal composite substrate as described above requires two steps, one for joining metals together and the other for joining metal and ceramic, resulting in high manufacturing costs. For this reason, although this is an excellent substrate structure, it has been a major hindrance to its practical application in terms of cost.

Moreover, when the copper members 2a, 2c and the restraining member 3 are joined in the previous process, the copper members 2a+20
It was necessary to take a symmetrical shape with the same plate thickness.

That is, if the copper members 2a and 2c are not symmetrical,
This is because warpage may occur due to the difference in thermal expansion between the restraining member 3 and the restraining member 3, and it may become impossible to proceed to the next step.

For this reason, there is no degree of freedom as an electric circuit. For example, the thickness of the copper member 2c is made thinner and the thickness of the copper member 2a is made thicker to reduce thermal stress on the semiconductor element 7 mounted on the electric circuit. This makes it difficult to take measures to prevent damage to the semiconductor element 7.

Further, the surface on which the semiconductor element 7 is mounted is a copper member 2 a +
Conventionally, it is necessary to process the composite material in which the restraining member 2c and the restraining member 3 are integrated into a desired shape to form an electric circuit.
In the processing method using chemical etching, which is often used for small-scale production, processing is difficult because the etching speeds of the copper members 2a, 2c and the restraining member 3 are different.

For this reason, in the past, it was necessary to manufacture an expensive mold and punch it into the desired shape.

In order to solve these problems, it is possible to join each member all at once, but if conventional manufacturing methods are combined into one process, the following problems will occur. First, the case of joining metals together will be described in detail. Copper members 2a, 2c
Since the melting points of the restraining member 3 and the restraining member 3 are greatly different, it is necessary to join them by a joining method such as patent joining or brazing, which is characterized by the above-mentioned explosive pressure welding. In general brazing, considering the quality of the bonding interface, many unbonded parts remain, which not only makes it impossible to make a strong bond, but also increases the thermal resistance between the parts that are closely bonded through the brazing material. It is difficult to obtain a substrate with high thermal conductivity, therefore, the copper member 2a
, 2c and the restraining member 3 must be joined by solid phase joining. The principle of solid phase bonding is to bond the objects by bringing their interfaces close to the atomic distance. must be maintained for a specified period of time until the diffusion reaction occurs. On the other hand, copper members 2a, 2
A DBC method or an active metal method is generally used to bond the ceramic substrate 1 and the ceramic substrate 1. At this time, the bonding interface has a thickness of several tens of μm.
By forming front and rear molten layers and ensuring wetting between the metal and ceramic, stable strength can be obtained in a short time.

In this case, problems that arise when two types of welding methods of 0 or more are performed at the same time and welded at once are shown in Figure 7 (a) and Figure 7 (b). explain. In FIG. 7, the same members as those explained in FIG. 5 are given the same reference numerals, and detailed explanations will be omitted here. FIG. 7(a) shows an example in which pressure is applied to ensure in-phase bonding, and FIG. 7(b) shows an example in which bonding is performed without applying pressure. As shown in Figure 7(a),
When the copper members 2a, 2c and the restraining member 3 are reliably joined by in-phase joining, the ceramic base material l and the copper member 2a
, 2b, the reaction molten layer 11 is discharged from the joint surface, causing a problem that the electric circuit is short-circuited. On the other hand, in Fig. 7(b) where no pressure is applied,
The bonding surfaces 4a and 4b cannot be reliably bonded and bonding strength cannot be obtained. Also, the reaction time and temperature required for bonding are different, and if the copper members 2a+2b and the ceramic base material 1 are kept at high temperatures for a long time, the copper The reaction between the members 2a and 2b and the molten layer progresses too much and the copper members 2a and 2b are altered and deformed.

The present invention has been made to solve these problems, and an object of the present invention is to provide a method for manufacturing a ceramic-metal composite substrate having a bonding portion that is inexpensive and highly reliable.

[Means to solve the problem]

The method for manufacturing a ceramic-metal composite substrate according to the present invention includes:
The first and second copper members are brought into close contact with each other through a thin film layer made of active metal with a thickness of 0.1 μm to 3 μm on both sides of the ceramic plate, and the end facing surface of one of the copper members is A substrate member made of a copper member for bonding a semiconductor element brought into close contact with a metal plate for heat supply is heated from the melting point of the alloy formed by the first and second copper members and the active metal. The copper member is heated to a temperature below the melting point of the copper member in an atmosphere where it is unlikely to react with the active metal, and pressure is applied in the thickness direction.

[For production]

Each component of the composite substrate can be bonded all at once.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to FIGS. 1 to 4.

FIG. 1(a) and FIG. 1(b) are diagrams for explaining the method of manufacturing a ceramic-metal composite substrate of the present invention, and FIG. 1(a) is a cross-section of each member showing the state before joining, Same figure (b)
FIG. 3 is a cross-sectional view of each member showing the state after joining. Fig. 2 is a characteristic diagram showing the relationship between beer strength and temperature between the copper member and the restraining member according to the present invention, and Fig. 3 shows the relation between beer strength and temperature between the ceramic base material and the copper member according to the present invention. Characteristic diagram,
FIG. 4 is a characteristic diagram showing the relationship between beer strength and film thickness of the ceramic base material and copper member according to the present invention. In these figures, the same or equivalent members as those explained in FIG. 5 are given the same reference numerals, and detailed explanation will be omitted here. In this example, an example in which an alumina member is used as the ceramic base material 1 will be described. 1st
In figure (a), 21 is a thin film layer made of active metal,
This thin film layer 21 is formed by sequentially vacuum-depositing Ti on one surface of each of the copper members 2a and 2b, and its thickness is set to 0.1 μm to 3 μm.

Next, a method for manufacturing a ceramic-metal composite substrate according to the present invention will be described.

First, in order to ensure the bondability between the ceramic base material 1 and the copper members 2a and 2b, the ceramic base material 1 or the copper member 2 is
A, 2b joint surfaces 6a, 6b have a thickness of 0.1 μm to 3
Thin film layer 2 by precoating with μm of active metal.
form 1. The precoat may be formed on either the ceramic base material 1 or the copper members 2a and 2b, but in consideration of productivity, it is possible to carry out continuous vapor deposition using a rolled plate material for the copper member. Because of this advantage, it is desirable to form them on the copper members 2a and 2b side.

In this embodiment, an example in which the thin film layer 21 is formed on the copper members 2a and 2b side will be explained.

Next, the copper members 2a, 2b, 2c and the restraining member 3
is formed into a predetermined shape by, for example, chemical etching. Ceramic base material 1 formed by the above steps
．． As shown in FIG. 1(a), the tIi4 members 2a, 2b, 2c and the restraining member 3 are stacked and mounted in a predetermined order on a carbon jig. At this time, the copper member 2a is placed so that the thin film 121 is brought into contact with the ceramic base material l.

2b are attached to both sides of the ceramic base material 1. and,
This jig and each member are mounted on a vacuum hot press device as a bonding device. As a bonding device, atmosphere formation,
Any device other than the hot press device may be used as long as it is capable of pressurizing and heating.

After being installed in the bonding device, an atmosphere that does not easily react with the active metal, such as argon gas, nitrogen gas, or a vacuum of about 10-'Torr, is created in the bonding device, and then as shown in FIG. 1(b), , pressurize, and heat. Note that arrow A in the figure indicates the direction of pressurization. At this time, the pressure may be applied before heating or after reaching a certain temperature. Copper members 2a, 2b, 2
It is sufficient if the adhesion can be achieved by applying pressure at a temperature at which c and the restraining member 3 react. In addition, the heating rate does not have a large effect on bonding properties, for example, 50°C/wi
About n is sufficient.

Note that after the objects to be bonded reach a predetermined temperature, a sufficient reaction time (bonding time) is required for bonding. After the bonding is completed, a ceramic-metal composite substrate is obtained by cooling the ceramic substrate 1 at a cooling rate of, for example, 10° C./s+in, which does not cause cracks.

Next, we will discuss in detail the phenomena during welding when performing -bracket welding.

First, the connection between the copper members 2a, 2c and the restraining member 3 will be explained with reference to FIG. Below, the copper member 2a.

An example will be described in which the restraining member 2c is made of copper and the restraining member 3 is made of molybdenum. FIG. 2 is a characteristic diagram showing the relationship between temperature on the horizontal axis and beer strength on the vertical axis. In the figure, A indicates the case where the pressurizing force is 1 MPa, and B
indicates the case where the applied pressure is 20 MPa. Note that since copper and molybdenum are bonded in a solid state, a relatively long bonding time is required, and the bonding time is set to 20 minutes, which is about the same as conventional solid phase bonding (diffusion bonding). As shown in FIG. 2, stable values of bonding strength were obtained from around 900°C. If the pressing force is less than 1 MPa, adhesion will be insufficient and stable strength will not be obtained. Moreover, if the pressing force is 20 MPa or more, not only will the strength not be improved, but the copper members 2a and 2c will be deformed and their practical value will be reduced.On the other hand, the copper member 2a.

In order to reliably bond 2b and ceramic base material 1, it is necessary to match the reaction rate at the bonding surfaces 6a and 6b with the rate of solid phase bonding.

Similar to FIG. 2, FIG. 3 is a characteristic diagram showing the relationship between copper and alumina, with temperature on the horizontal axis and beer strength on the vertical axis, using titanium as an example of the active metal. In the same figure, A,
B shows the case where the pressing force is IMPa, and C and D show the case where the pressing force is 20 MPa. Further, the solid line indicates the case where the thickness of the thin film layer 21 is 1 μm, and the broken line indicates the case where the thickness is 3 μm. The eutectic temperature of copper and titanium is approximately 880° C., which is lower than the melting points of copper and titanium, and the eutectic composition starts to melt at temperatures above this temperature. The conventional brazing method uses a thick brazing filler metal with a thickness of several tens of micrometers, which is a mixture of several materials and has a melting point lower than the melting point of the objects to be joined, and the brazing filler metal is heated to a temperature above its melting point. However, in the present invention, a molten layer is formed only after the thin film layer 21 made of active metal and the copper members 2a + 2b react, so the thickness of this thin film layer 21 is changed. By doing so, the amount of the molten layer can be varied and the reaction rate can also be controlled. As shown in FIG. 3, when the thickness of the thin film layer 21 made of titanium is 1 μm, the difference in beer strength due to the difference in pressing force is larger than when the thickness is 3 μm. That is, when the film thickness is thin, the molten layer formed by the reaction is also thin (this indicates that pressure is required to promote adhesion and bonding with alumina).

In addition, as the film thickness increases, the molten layer that is more likely to flow increases, so it is less affected by pressure and adhesion and bonding can be easily achieved even at low temperatures, but if the molten layer is made too thick, the molten layer will be expelled. A problem arises. Figure 4 is a characteristic diagram showing the influence of bonding time, with film thickness on the horizontal axis and beer strength on the vertical axis. The case of minutes is shown. In addition, the pressing force was 10 MPa in both cases.

The figure clearly shows that the thinner the film, the longer it takes to bond. If the film thickness is 0.1 μm or less, even if the pressing force is increased to the limit where copper is deformed, the reaction will be slow and the industrial value will be low. On the other hand, if the film thickness is 3 μm or more, the reaction proceeds quickly, but the molten layer is discharged even at IMPa, which is the lowest pressure for solid phase bonding, making it difficult to use as an electric circuit.

From the above, the copper members 2a, 2b and the ceramic base material 1
The connection with is thin 11! The thickness of JIi21 is 0.1 μm.
~3 μm, the bonding pressure is set to 1 to 20 MPa, and the bonding temperature is set to a range that is higher than the melting point of the alloy formed by the thin film 21 and the copper members 2a and 2b and lower than the melting point of the copper members 2a + 2b. This can be done at the same time as joining 2a, 2c and the restraining member 3.

In the above embodiment, an example was shown in which the thin film layer 21 to be precoated was formed of titanium, but it is not limited to titanium, and other active metals such as zirconium may be used, and its components may be of one type. There is no limitation, and for example, silver or the like may be precoated at the same time. However, the bonding strength between the copper members 2a and 2c and the restraining member 3 is 900°C.
Since stable values can be obtained at temperatures higher than
It is desirable that the melting point of the alloy formed by a, 2b and the thin film layer 21 be close to 900° C. in order to suppress discharge phenomena.

Further, in the above embodiment, an example was shown in which the active metal pre-coat was formed by vacuum evaporation, but the present invention is not limited to this. Even if other methods are used, the same effects as the present invention can be obtained.

Furthermore, in the above embodiment, an alumina member is used as the ceramic base material 1, and a molybdenum member is used as the restraining member 3. The same effect as the present invention can be obtained by using metal, and instead of the molybdenum member, a tungsten member having substantially the same bonding properties as a copper member can also be used.

The ceramic member, copper member, and restraint member used in this example do not need to be made of the same material with 100% purity (for example, unless the bonding properties are significantly changed, an alloy material mainly composed of the above components, etc.) is not required. , copper alloy, or molybdenum alloy.

〔Effect of the invention〕

As explained above, in the method for manufacturing a ceramic-metal composite substrate according to the present invention, a thickness of 0.1 μm is formed on both sides of the ceramic plate.
The first and second copper members are brought into close contact with each other through a thin film layer made of active metal with a thickness of ~3 μm, and a semiconductor element is placed on the uncontacted surface of one of the two copper members through a thermal buffer metal plate. A substrate member formed by bringing bonding copper members into close contact with each other is heated to a temperature below the melting point of the first and second copper members from the melting point of the alloy formed by the first and second copper members and the active metal. Since it is heated in an atmosphere that does not easily react with metal and pressurized in the thickness direction, each component of the composite substrate can be bonded all at once. Therefore, a ceramic-metal composite substrate having a highly reliable joint can be obtained at low cost.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are diagrams for explaining the method of manufacturing a ceramic-metal composite substrate of the present invention, in which FIG. ) is a sectional view of each member showing the state after joining. Fig. 2 is a characteristic diagram showing the relationship between beer strength and temperature between the copper member and the restraining member according to the present invention, and Fig. 3 shows the relation between beer strength and temperature between the ceramic base material and the copper member according to the present invention. A characteristic diagram, FIG. 4 is a characteristic diagram showing the relationship between beer strength and film thickness of the ceramic base material and copper member according to the present invention, and FIGS. 5(a) to (c) are characteristic diagrams of the conventional ceramic-metal composite substrate. These are diagrams for explaining the manufacturing method. Figure (a) is a cross-sectional view showing a state where a restraining member and a copper member are joined, and Figure (b) is a diagram showing a state where a ceramic base material and a copper member are joined. FIG. 3(c) is a sectional view showing the state after the bonding is completed. Fig. 6 is a perspective view showing the state in which semiconductor elements are bonded to a conventional ceramic-metal composite substrate, and Fig. 7 (a) and (b) are the states of each member when they are collectively bonded by the conventional manufacturing method. FIG. 3A is a cross-sectional view showing the case where pressure is applied, and FIG. l...ceramic base material, 2a, 2b, 2c...
...Copper member, 3...Restraint member, 21...Thin film layer.

Claims (1)

[Claims] The first and second copper members are brought into close contact with each other through a thin film layer made of active metal with a thickness of 0.1 μm to 3 μm on both sides of the ceramic plate, and heat is applied to the non-contact surface of one of the copper members. A substrate member in which a copper member for bonding semiconductor elements is brought into close contact with each other via a buffering metal plate is heated by heating the first and second copper members from the melting point of the alloy formed by the first and second copper members and the active metal. A method for producing a ceramic-metal composite substrate, which comprises heating the member to a temperature below the melting point of the member in an atmosphere that does not easily react with the active metal, and applying pressure in the thickness direction.