JPH03112874A - Junction between ceramic base and copper - Google Patents

Abstract

PURPOSE:To improve the wetability of the surface of a ceramic base and enable a strong junction between copper by forming a zygote containing specified elements on the surface of the ceramic base before heat junction between the ceramic base and copper. CONSTITUTION:In forming a conductive circuit composed of a copper metal layer on a circuit base such as an alumina base, etc., a zygote (e.g. SiO2 layer prepared by oxidative destruction by heat treatment of silane coupling agent) containing one or more elements of Be, Mg, Ca, Sr, Ba, B, Al, Y, Si, Ti, Zr and Cu is formed after preferably chemical or physical roughening of the surface of the ceramic base and heat junction between the ceramic base and copper is subsequently carried out. The condition of the heat junction is preferably about 1-10min. at < eutectic point of copper and copper oxide in an inert atmosphere containing <=1000ppm oxygen.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for bonding a ceramic substrate and copper, and more specifically, when forming a copper metal layer to serve as a conductor circuit on the surface of a ceramic circuit board, etc. The present invention relates to a method for joining a ceramic substrate, which is a non-metallic material, and copper, which is a metallic material, in the field of manufacturing circuit components and other products.

[Conventional technology]

Conventionally, in the field of manufacturing semiconductors and printed circuit boards, a copper conductor layer has been formed on a ceramic substrate by bonding copper foil, chemical plating, sputtering, or the like.

In such cases, the copper layer must be extremely thin, on the order of microns, and must accurately transmit high-density electrical signals, and must not cause conduction defects such as disconnections, so it is It is necessary to bond the copper firmly and tightly.

Therefore, various methods have been proposed to improve the adhesion between the ceramic substrate and copper.

For example, Japanese Unexamined Patent Publication No. 57-36892 discloses a method of forming a copper conductor layer on a ceramic substrate by chemical plating or sputtering, and then performing heat treatment to improve the adhesion between the ceramic substrate and the copper. has been done.

In addition, Japanese Patent Publication No. 57-13515 discloses that a thin copper plate is stacked on a ceramic substrate and heated in a reactive gas atmosphere to form a eutectic of copper and copper oxide. A method for improving the adhesion between a substrate and copper is disclosed.

[Problem to be solved by the invention]

However, even with the above-mentioned prior art methods, the adhesion between the ceramic substrate and copper is insufficient, and further improvements are desired.

For example, in the above-mentioned method of improving adhesion using the eutectic of copper and copper oxide, when attempting to bond a thin copper plate or copper film of approximately 15 μm or less to a ceramic substrate, it is necessary to heat it above the eutectic temperature. There is a problem in that the thin copper layer melts due to the process, and in order to generate enough eutectic without melting the copper layer, technically extremely difficult operations are required. Furthermore, the bonding method using heating has a problem in that blisters are likely to occur.

On the other hand, depending on the intended use of the ceramic substrate, it may be used with a roughened surface, but when attempting to bond copper to the surface of such a roughened ceramic substrate, sufficient adhesion may not be achieved. The problem was that I couldn't get it. This is achieved by roughening the surface of the ceramic substrate.
It is thought that this is because the eutectic melt, which contributes to improving adhesion in the above method, cannot sufficiently wet the surface of the ceramic substrate because the flux on the surface of the substrate is removed. The reason for this will be explained in more detail below.

Table 1 below shows the results of an Auger analysis (AE
This is publicly known data showing the results of compositional analysis by S). C.P., F., Becher & J., S., Murday.
: Proc, IStlM Int, Microel
Quoted from electronicSymp, (1976)].

Looking at the above table, it can be seen that the surface of the untreated alumina substrate contains the flux of the alumina substrate, for example, 5iOt, MgO,
It can be seen that CaO etc. are segregated. When such an alumina substrate is surface-treated with HF to make the surface rough, the segregated flux, especially 5iO=, is removed and the A1
□0. It can be seen that it has a rich composition. Therefore, even if the eutectic described above is applied to the surface of the alumina substrate, the eutectic melt cannot sufficiently wet the ceramic substrate. In other words, the presence of the flux component improves the wettability of the eutectic to the alumina substrate surface, and the eutectic becomes A1. This means that it combines not only with O, but also with the flux to obtain a strong bond, which is an extremely important function, and is also the reason why the adhesion between the roughened ceramic substrate and copper is poor. is there.

Furthermore, in the case of non-oxide ceramic substrates such as SiC and AIN, conventionally, an oxide layer is formed on the surface by heat treatment in the atmosphere, and this oxide layer improves the adhesion with copper. However, it had the disadvantage of causing a crack between the eyebrows.

Therefore, an object of the present invention is to provide a method for bonding a ceramic substrate and copper as described above, in which even a thin layer of copper can be reliably and firmly bonded to a ceramic substrate without melting or deforming. The object of the present invention is to provide a method that can firmly bond copper even to a ceramic substrate having a roughened surface without causing blisters or cracks during the process.

[Means to solve the problem]

A method for bonding a ceramic substrate and copper according to the present invention that solves the above-mentioned problems has a method of bonding Be, Mg, C, etc.
a, Sr, Ba, B, A1. Y.

After forming a bonded body containing at least one element among Si, Ti, Zr, and Cu, the ceramic substrate and copper are bonded by heating through this bonded body.

As the ceramic substrate, those made of various ordinary ceramic materials such as oxide-based and non-oxide-based ceramic materials can be used. The ceramic substrate can be in any shape, such as a plate or a block, depending on the purpose of use.

As the copper to be bonded to the ceramic substrate, a pre-manufactured copper material such as a copper plate or copper foil may be used as in the illustrated example, or a film may be directly applied to the surface of the ceramic substrate by chemical plating or sputtering. It may be formed. The thickness of the copper layer is not particularly limited, but is preferably 5n.
Execute the above steps. In addition to covering the entire surface of the ceramic substrate, the copper layer may be formed by punching or etching copper foil into a predetermined shape.

When forming a copper film on the surface of a ceramic substrate by chemical plating or sputtering, the initial adhesion to the copper can be improved by chemically or physically roughening the surface of the ceramic substrate. This is a preferable method because it reduces the possibility of blistering or peeling when the temperature is raised in the heat bonding process.

The bonded body formed on the surface of the ceramic base is made of Be, Mg
, Ca, Sr, Ba, B, Al, Y,
A material containing at least one element selected from Si, 'rt, Zr, and Cu is used. Among them, MgCa, AI
, Si, Ti, 7. Particularly preferred are those containing r. These elements are effective as flux components on the surface of the ceramic substrate. The bonded body is formed on the surface of the ceramic substrate before bonding the copper layer such as copper foil or copper film as described above to the surface of the ceramic substrate.

In order to form a bonded body on the surface of a ceramic substrate, the surface of the ceramic substrate is treated with a compound containing the above-mentioned elements.

The compound may be a simple substance of the above-mentioned element, or may be an oxide, an organometallic compound, a nitrate, a halide, etc., and preferably one that easily becomes an oxide by heat treatment in the atmosphere.

As a treatment method for forming a bond by treating the surface of a ceramic substrate with a compound, when the compound is a simple substance or an oxide, it is attached to the surface of the substrate by vapor deposition, sputtering, or the like. In particular, in the case of a single substance, it is heat-treated in the atmosphere to convert it into an oxide and adhere to the surface of the substrate. In the case of oxides, they may be simply deposited as is, but in order to improve their compatibility with the substrate surface, it is preferable to heat-treat them in the atmosphere.

In addition, in the case of compounds that are soluble in water or organic solvents, such as nitrates, halides, organometallic compounds, etc., after applying the solution to the substrate surface, it can be exposed to temperatures above the decomposition temperature of the compound in the atmosphere. A heating method can be used. By performing such a treatment, the compound is decomposed into an oxide, which adheres to the surface of the substrate.

Among the above methods, the most preferred method is to apply an organometallic compound such as a metal alkoxide or a coupling agent to the surface of the substrate and then heat treat it.

It is sufficient that the amount of bonded material formed on the surface of the ceramic substrate is small enough to be effective as a flux component.
Specifically, it is preferable to form the film so that the film thickness is approximately lfm or less at most.

After forming a copper foil or a copper film on the surface of a ceramic substrate via a bonded body, the ceramic substrate and copper are bonded together by heating. The heat bonding conditions include heating at a temperature below the melting point of copper and holding for 1 to 20 minutes in an inert atmosphere with an oxygen concentration of 11,000 pp or less. Further, preferably, the heating temperature is lower than the eutectic temperature of copper and copper oxide, and the heating temperature is maintained for 1 to 10 minutes in an inert atmosphere with an oxygen concentration of 100 ppn+ or less. Since the ceramic substrate has improved wettability due to the formation of the bonded body, it can be bonded sufficiently firmly even at a heating temperature below the eutectic temperature. Also, it is better to carry out at a lower temperature.
It is also effective in preventing blisters. In particular, the thickness of the copper is 25.
In the case of a thin copper layer with a thickness of about 50% or less, it is easily melted by a copper oxide-copper eutectic melt. A method of heating and bonding under an inert atmosphere is preferred.

[For production]

When a bonded body containing the above-mentioned elements is formed on the surface of a ceramic substrate, the bonded body performs the same function as a type of flux component, and the wettability of the surface of the substrate is improved. As a result, the copper and ceramic substrate are firmly bonded via the bonded body. The presence of the bonded body improves the bondability between the copper and the ceramic substrate, so there is no need to heat to a high temperature in the heat bonding process, and a strong bonding force can be exerted even at a relatively low temperature. As a result, there is no risk of blistering or cracking during the heating bonding process, and there is no risk of melting even a thin copper layer.

In particular, even if the surface of the ceramic substrate is roughened, the bonded body will improve its adhesion to the copper in place of the flux component lost due to the roughening, so the bonding strength will decrease due to the roughening. The problem of doing so is solved.

〔Example〕

Next, embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In step (a), 96% of commercially available ceramic substrates are used.
An Al201 substrate 10 is prepared.

In step (bl), the ceramic substrate 10 is immersed in a commercially available silane cuffling agent containing Si as a treatment agent containing a compound for forming a bonded body, and the silane cuffling agent 20 is applied to the surface of the ceramic substrate 10. Apply.

In step (C), the substrate 10 coated with the silane coupling agent 20 is heat-treated in the atmosphere. With this process,
The silane coupling agent 20 is oxidized and decomposed to form a bonded body 21 made of Sing on the surface of the substrate 10.

In step (d), a copper plate 30 with a thickness of 10 to 200 nm is placed on the ceramic substrate 10 from above the bonded body 21, and heated for 1 to 20 minutes at a heating temperature below the melting point of copper in an inert atmosphere with an oxygen concentration of 11,000 pp or less. By holding for a minute, the copper plate 30 is thermally bonded to the ceramic substrate 10.

More specific examples will be described below.

Example 1 - Commercially available 96% alumina substrate (100 mm square x thickness 0.8
m), and Si-containing compound 5t(0C,H,)
, the metal alkoxide S i
(OC-Hs) 4 was applied to the surface of the substrate, and heat treatment was performed at 900° C. for 1 hour in the air to form a bonded body.

Next, a copper layer of about 10 nm thick was formed on the bonded body on the surface of the substrate by high-speed sputtering. Thereafter, the copper layer was etched into a predetermined circuit pattern.

Next, a heating bonding process was performed. That is, Ol is 30
After holding at 1000° C. for 10 minutes in an Nt atmosphere containing ppm, the copper layer and ceramic substrate were then held at 1064° C. for 5 minutes in a N2 atmosphere to completely bond the copper layer and the ceramic substrate.

When the adhesion force between the obtained ceramic substrate and the copper layer was measured, it showed an adhesion force of 7 kg/im'' or more and was broken within the ceramic substrate, indicating that the adhesion force between the ceramic substrate and the m-layer was extremely high. It was demonstrated that #i4
No defects such as layer blisters were observed.

Example 2 - Commercially available 96% alumina substrate (10 (in square x thickness 0.8
m) was immersed in phosphoric acid heated to 300° C. for 5 minutes to roughen the substrate surface. Next, after immersing the substrate in a silane coupling agent containing Si,
A bonded body was formed by heat treatment at 0° C. for 1 hour.

Next, the Pd core was treated using the known Scentsy Act method, and then a copper layer of about 10 g was formed using high-speed electroless copper plating, and a predetermined circuit pattern was formed using etching processing.

Next, as a heating bonding step, N containing 20 ppm of 08
The &v4 layer and the ceramic substrate were completely bonded by first holding the temperature at 1000° C. for 10 minutes in an N8 atmosphere, and then holding the temperature at 1063° C. for 3 minutes in an N8 atmosphere.

The adhesion and bonding state between the obtained ceramic substrate and the copper layer were as good as in Example 1.

Example 3 In Example 2 above, instead of the silane coupling agent, an ethanol solution of Zr (QC, H%)4 was applied to the substrate surface and then heat treated under the same conditions to form a bonded body.

After placing a copper foil of about 20p on this substrate, it was bonded by heating. The heating bonding conditions were 0□ to 4. N including Oppm
Heat treatment was performed at 1064° C. for 5 minutes under two atmospheres.

As a result, excellent bonding strength similar to that of Example 1 was obtained.

Example 4 - Commercially available SiC ceramic substrate (50+cm square x thickness 0.
After sputtering 5ift on the substrate surface using a 64m) to form a 0.1 via thick Sin layer,
Heat treatment was performed at 1000° C. for 1 hour in a nitrogen atmosphere. Then, in the same process as in Example 3, about 20 μl of copper foil was heat-bonded.

As a result, excellent bonding strength similar to that of Example 1 was obtained.

Example 5 In Example 2, instead of the silane coupling agent,
T i (iso-OCs Ht ) 4 and 5i (Q
The fI layer was bonded to the ceramic substrate through the same steps as in Example 2, except that a solution containing C and Hi was used and the substrate was immersed in this solution.

As a result, excellent bonding strength similar to that of Example 1 was obtained.

Comparative Example 1 - Commercially available 96% alumina substrate (100++ m square x thickness 0.
8■■) with a thickness of 25μ formed in a predetermined shape on the surface.
Place the copper foil of l, and 0! N containing 30 ppm.

The copper foil was heated and bonded to the substrate by holding it at 1068° C. for 5 minutes in an atmosphere. Although the adhesive strength between the obtained ceramic substrate and the copper foil was 5 kg/vi'' or more, the occurrence of blisters was observed.

Comparative Example 2 In the same process as in Example 2, the surface of an alumina substrate was roughened. Next, in the same process as Comparative Example I, a copper foil was heat bonded to the roughened surface of the ceramic substrate. However, the adhesion between the obtained ceramic substrate and copper foil was 1 to 2 kg.
/n+"L, and sufficient bonding force could not be exerted.

- Comparative Example 3 - The ceramic substrate and the copper layer were bonded through the same steps as in Example 1, except that the step of forming the bonded body using Si (QCs H%)4 was not performed.

As a result, the adhesion between the ceramic substrate and the copper layer was 3 to 4 kg.
/n+"L, and sufficient bonding force could not be exerted.

〔Effect of the invention〕

According to the above-described method for joining a ceramic substrate and copper according to the present invention, a bonded body containing a specific element is formed on the surface of the ceramic substrate before heating and joining the ceramic substrate and copper. This improves the wettability of the ceramic substrate surface, making it possible to firmly bond copper.

As a result, blisters and cracks do not occur during the heat bonding process. Unlike conventional methods, there is no need to increase the heating temperature or take a long time to increase the bonding strength, and it is possible to achieve sufficient bonding with a short heat bonding process at a relatively low temperature. Even if it is thin, there is no need to worry about it melting or deforming, and it can be bonded to the ceramic substrate while maintaining its precise shape.

In particular, even if the surface of the ceramic substrate is roughened and the flux component is removed, the bonded material instead of the flux component improves the bonding strength between the ceramic substrate and copper.
It becomes possible to improve the bondability of copper to roughened surfaces, which has been a problem in the past.

[Brief explanation of drawings]

The figures are schematic sectional views showing an example of the present invention in the order of steps.

Claims (1)

[Claims] 1 Be, Mg, Ca, Sr on the surface of the ceramic substrate
, Ba, B, Al, Y, Si, Ti, Zr, Cu. Copper joining method.