JP2652074B2 - Method for producing bonded body of copper plate and ceramic substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for directly bonding a copper plate to a ceramic substrate, and more particularly, to a method for heating a copper plate in an inert gas atmosphere without oxidizing the copper plate. (1) The present invention relates to a method for producing a joined body of a copper plate and a ceramic substrate, which is joined by reacting copper (Cu ₂ O) with SiO _{2 in a} ceramic substrate.

[Prior art] With the recent development of semiconductor technology, a method of directly joining a copper circuit board on a ceramic substrate has been used,
Many proposals have been made for such a method.
With respect to these proposed methods, including the problems contained therein, methods for directly joining a metal piece or the like to a conventional ceramic substrate are listed below.

The copper plate is oxidized in advance and placed so as to be in contact with the ceramic substrate, and in an inert gas atmosphere, a hypoeutectic melt of copper oxide and copper is formed, so that wetting occurs on the ceramic substrate and direct bonding is performed. The technology to make it
It is known by "Method of bonding a copper member to a substrate made of ceramic" of JP-A-60-4154.

However, this method requires a minimum oxygen partial pressure in order to prevent decomposition of pre-oxidized copper oxide. Japanese Unexamined Patent Application Publication No. 58-217475 discloses a "method of directly joining a metal piece and an oxide ceramic substrate". Is disclosed.

Japanese Patent Publication No. 60-4154 discloses the use of an oxygen-containing copper member.In this case, too, Japanese Patent Application Laid-Open No. 58-217475 discloses that a minimum oxygen partial pressure is maintained in a furnace atmosphere. Otherwise, the bond between the copper and the ceramic substrate will not only occur, but the oxygen dissolved in the copper will diffuse to the contact surface between the copper and the ceramic and be encapsulated there, resulting in the formation of air bubbles and the interaction between the metal and the ceramic. It has been pointed out that this leads to bonding defects.

Japanese Patent Publication No. 57-13515 discloses a method of bonding a metal directly to a non-metal substrate by bonding a copper foil to an oxide ceramic substrate in a reactive atmosphere such as an oxygen-containing atmosphere without using pre-oxidation. Is known. In this method, oxygen in the atmosphere must first oxidize copper before the original bonding process proceeds, but a sufficient amount of oxygen can be removed from the ceramic, especially when the bonding area between ceramic and copper is large. Cannot enter the gap between the copper and the copper, so that a bubble-shaped non-adhered portion is generated. In addition, since the atmosphere has an oxygen content in the range of 0.01 to 0.5% by volume, the surface of the copper foil in contact with the ceramic substrate (the surface in contact with the atmosphere gas) is covered with a thick black copper oxide film. Become. Therefore, in order to make full use of the inherent properties of the copper material, a step of removing the copper oxide film is required (see Japanese Patent Application Laid-Open No. 58-217475).

On the other hand, as another joining means, Japanese Patent Publication No. 60-28785, `` Method of Bonding Metal to Ceramic, '' discloses a joining method using a eutectic melt of copper oxide and copper, in which case, it is oxidized in advance. Metal pieces are used. Since this metal piece is formed into a curved body in advance so that it gradually comes into contact with the ceramic substrate during heating, it can sequentially extrude bubbles generated between the metal piece and the ceramic substrate during bonding. It is.

However, this method has a problem that the cost is high and the process control is complicated. That is, when the metal piece or the ceramic substrate is complicatedly preformed,
In addition to the inability to bend the metal, the metal piece does not contact the ceramic substrate in a sufficiently uniform state. Also in this method, about 0.
Since the exposed surface of the metal is covered with the oxide layer when oxygen of 01 to 0.5% by volume is present, it is necessary to remove the oxide layer in a later step as described above (Japanese Patent Laid-Open No. 58-1983). 217475
No.).

As means for improving the problems of the above-mentioned known techniques, Japanese Patent Application Laid-Open No. 58-217475 described above discloses that a bubble-free perfect bond can be obtained between a metal piece and a ceramic substrate, and that there is no oxide. It discloses a direct bonding method in which a metal surface can be easily obtained.

However, in this joining method, it is necessary to constantly control the oxygen concentration of the atmosphere in the continuous furnace to 20 to 50 ppm, and it is necessary to avoid mixing of the atmosphere into the furnace as much as possible. In addition, it is necessary to install gas curtains at the entrance and the exit in order to prevent air from being mixed. In addition, the metal pieces used for bonding require pre-oxidation in advance, and the oxide layer requires a considerable amount of labor to adjust so that about one-tenth of the surface roughness is preferable.

As described above, in the prior art, since preliminary oxidation is required in advance, it is necessary to uniformly control the thickness of the oxide film, and the removal operation has been performed before the joining step. Further, the formation of the hypoeutectic melt starts from the interface between copper oxide and copper formed on the surface of the placed copper plate, and shifts to the copper oxide film side. The progress of this dissolution proceeds to the copper plate side, and a eutectic melt almost double that of the copper oxide film is generated.
It has been confirmed by experiments of the present inventors that the eutectic melt undergoes solidification shrinkage due to solidification, which causes small voids at the bonding interface.

[Problems to be Solved by the Invention] As described above, in the related art, since pre-oxidation has to be performed, various operations associated with the pre-oxidation have been required, which has caused a cost increase. Therefore, it is possible to eliminate the step of pre-oxidizing the copper plate, which is a disadvantage of the conventional method, and to eliminate the formation of a eutectic or hypoeutectic melt at the bonding interface or the generation of voids at the time of solidification. Development of a direct bonding method has been desired.

An object of the present invention is to solve the above-mentioned problems, to eliminate the need for a pretreatment step by pre-oxidation of a copper member, and to produce a bonded body having excellent adhesiveness at low cost and in a large amount by a method in which atmosphere control is easy. An object of the present invention is to provide a method for manufacturing a joined body of a copper plate and a ceramic substrate.

[Means and Actions for Solving the Problems] As a result of research to achieve the above object, the present inventors have found that oxygen in copper generates Cu ₂ O particles when the temperature rises, and that the Cu ₂ O particles As described above, the present inventors have found that it reacts with SiO ₂ in the ceramic substrate, thereby obtaining a strong bond at the boundary between the copper plate and the ceramic substrate, and reached the present invention.

That is, in the present invention, a copper plate having an oxygen concentration of 50 ppm or more is disposed on a ceramic substrate surface containing 0.5% or more of SiO ₂ , and these are placed in an inert gas atmosphere, preferably 1,060 ° C.
Heat treatment in an atmosphere containing oxygen that does not form copper oxide and cuprous oxide on the surface of the copper plate at a lower temperature, and raise the temperature while generating Cu ₂ O particles by utilizing oxygen in the copper plate to 1,060. The reaction between SiO ₂ in the ceramic substrate and Cu ₂ O in the copper plate in a temperature range of not less than 1,065 ° C. and less than 1,065 ° C. to directly join the copper plate and the ceramic substrate. It provides a manufacturing method.

Generally, when sintering ceramics, SiO ₂ is often used for the purpose of further improving sinterability. In this case, SiO ₂ often reacts with a ceramic material as a base material during sintering to form a compound, but in the case of sintering of alumina ceramics, SiO ₂ is present at a grain boundary of alumina particles. It is known that relatively large amounts of SiO ₂ exist on the surface of a sintered alumina substrate.

On the other hand, as a metal plate used in the method of the present invention, a copper member containing oxygen in copper (tough pitch copper) is used. This tough pitch copper is a material that can be easily and inexpensively obtained by industrial means as specified in JIS. This material usually has extremely small Cu ₂ O inside and at the grain boundaries.
It is known that only particles are present.

However, during the heating, as the crystallization of the Cu ₂ O particles progresses, the oxygen present in the copper will grow as Cu ₂ O particles, and if the heating rate is relatively high, Cu and Cu
_As can be understood from FIG. 1 which shows a part of a two-phase equilibrium diagram with ₂ O, the Cu ₂ O + Cu phase mixed region is located on the lower concentration side of Cu ₂ O.
For example, it is considered that they shift as shown by a vertical dotted line. In this case, before Cu ₂ O decomposes and the size of O ₂ diffused into Cu increases,
It was confirmed that when the temperature reached 1,060 ° C., Cu ₂ O in the tough pitch copper and SiO ₂ in the ceramic substrate reacted with each other to cause bonding.

Therefore, it is necessary to use a copper plate having an oxygen concentration of 50 ppm or more as the copper plate used in the method of the present invention, because the tough pitch copper obtained industrially stably is 50 pp.
m or more, preferably 200 to 400 ppm of oxygen, and at the same time, when the amount of Cu ₂ O particles in the copper is small, the reliability of the joined body is inferior.

If the heating temperature is further increased to 1,065 ° C. or higher, Cu and Cu ₂ O in the copper material become eutectic, so that the temperature may be maintained at a temperature lower than 1,065 ° C. for several seconds to several hours. It is possible to manufacture a joined body stably by the degree. According to the test of the method of the present invention, it was manufactured with a holding time of about 1 to 10 minutes to obtain a good bonded body. The heating rate is 10
It has been confirmed that the presence of Cu ₂ O particles at a high temperature is possible if it is 50 ° C./min.
If the speed is high, cracks will occur on the ceramic substrate itself as well as the temperature rise, and the lower limit will be set in terms of industrial productivity.
Since the temperature should be about 10 ° C / min, the cooling rate should be 10-50 ° C
/ Min.

Cu ₂ O particles existing in copper and Si in ceramics
The reaction with O ₂ is a reaction in which eutectic occurs at 1,060 ° C. and a melt is generated, but this melt is generated very little and exists only thinly at the copper-ceramics contact interface.

Bonding is enabled by the reaction of Cu ₂ O-SiO ₂ , in which case, of course, the reacting Cu ₂ O and SiO ₂ are present on the surfaces in contact with each other, and are included in the member. Not all that is.

Due to the presence of SiO _{2 at} the grain boundaries of the alumina substrate,
The compound formed by reacting with Cu ₂ O in the copper material does not separate and separate from the alumina substrate because it has a strong adhesive force with Cu ₂ O or SiO _2, and conversely, Cu ₂ O Since the particles are dispersed in the grain boundaries and in the grains in the copper, the same effect as when a wedge is driven into the copper is achieved, and the adhesive strength is maintained. In other words, a strong bond cannot be obtained only by reacting by contacting the single phase of Cu ₂ O and the single phase of SiO ₂ , and Cu ₂ O and SiO ₂ are unevenly distributed and dispersed at the grain boundaries and grains. It is a feature of the present invention that a strong bonded body is obtained by the above.

As the atmosphere in the method of the present invention, an inert gas atmosphere such as N ₂ gas is used.In this case, it is not necessary to be in a pure inert state, and the copper plate surface is not oxidized at a heating temperature of 1,060 ° C. or less. It has been confirmed that a good bonded body can be obtained even if a small amount of oxygen is mixed.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples.

[Example] As shown in Table 1, 99.5% ceramic substrate was used.
%, 96% and 92% alumina sintered body and sapphire (alumina single crystal) are prepared, and a 0.3 mm thick tough pitch copper plate (oxygen concentration 280 ppm) as a copper plate to be joined and an oxygen-free copper plate as a comparative material ( Oxygen concentration of 8 ppm).

The furnace used for joining is a conveyor type continuous furnace,
Heating and cooling rates 10, 20, 50 and 100 ° C /
The test was performed with a change in minutes.

X-ray diffraction confirmed that SiO ₂ phase was present on the ceramic substrate used, and the test was performed.
No SiO ₂ phase is included.

The atmosphere in the conveyer furnace was controlled by using an N ₂ gas obtained by evaporating liquid nitrogen, and controlling the oxygen concentration in the furnace to about 10 ppm.

Place the tough pitch copper plate and oxygen-free copper plate on the above ceramic substrate at the same time
A temperature profile was created so that the temperature profile could be maintained at 1,063 ° C. for 7 minutes, and a bonding test was performed at each of the heating rate and the cooling rate shown in Table 1. Table 1 shows the test results.

In the test results shown in Table 1, a case where a good joined body was obtained was indicated by a circle, a case where cracks occurred on the ceramic substrate was indicated by a mark, and a case where no joining was performed was indicated by a mark x. .

From the test results shown in Table 1, the following was confirmed.
In other words, when the heating rate is fast (for example, 100 ° C./min),
It was found that the ceramic substrate itself could not be moved at a high temperature and was destroyed. Further, since the equipment of the furnace itself is expensive to perform the high-speed heating, it is not suitable as an apparatus for mass production. Further, if the temperature drop rate is high, the ceramic substrate itself cracks and breaks, as in the case of temperature rise. Therefore, the rate of temperature rise and temperature drop is preferably at most 50 ° C./min. On the other hand, the lower limit of the speed was set to 10 ° C./min or more in consideration of industrial productivity. However, when the speed was lower than 10 ° C./min, the temperature rise to 1,060 ° C. and the temperature decrease from this temperature were 100 It takes more than one minute, so that the furnace itself must be long, so the lower limit speed is preferably 10 ° C./min for both temperature rise and temperature decrease.

In the above test, those using sapphire containing no SiO ₂ and those using oxygen-free copper were all not joined.

Comparative Example A tough pitch copper plate was placed on a blazed substrate having only an SiO ₂ layer formed on an alumina substrate, and bonding was performed according to the procedure described in the example. As a result, a tough pitch copper was confirmed to be bonded to the SiO ₂ layer, and cracks are present in performance due to causes seems to differential thermal expansion at the interface between the alumina substrate and the SiO ₂ layer, a conjugate It could not withstand use due to weak adhesion.

[Effects of the Invention] As described above, the method of the present invention is a method of obtaining a ceramic-metal bonded body by combining an SiO ₂ -containing ceramic substrate obtained by an industrially easy sintering method with a tough pitch copper plate. Therefore, a joined body having excellent adhesiveness can be mass-produced inexpensively by a method that does not require a pretreatment step of a copper member as in the related art and that can easily control the atmosphere.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main part of a two-phase equilibrium diagram of Cu and Cu ₂ O.

Claims (2)

(57) [Claims] The method according to claim 1 oxygen concentration is not less than 50ppm copper plate, a SiO ₂ 0.5
% Or more, and heat-treat them in an inert gas atmosphere to raise the temperature while generating Cu ₂ O particles by utilizing oxygen in the copper plate.
A bonded body of a copper plate and a ceramic substrate, wherein the copper plate and the ceramic substrate are directly bonded by reacting SiO ₂ in the ceramic substrate with Cu ₂ O in the copper plate in a temperature range of 060 ° C. or more and less than 1,065 ° C. Manufacturing method. 2. The method according to claim 1, wherein the inert gas atmosphere is an atmosphere containing oxygen that does not form copper oxide and cuprous oxide on the surface of the copper plate at a temperature lower than 1,060 ° C.