JPH07193348A - Ceramic circuit board - Google Patents

Abstract

PURPOSE:To provide a highly reliable ceramic circuit board for high-density mounting. CONSTITUTION:A ceramic circuit board comprises a silicon nitride film on a ceramic board. A film consisting of either of more than one kind of inorganic substances and more than one king of organic substances may be provided on the silicon nitride film and a film consisting of either of more than one kind of metallic substances and more than one kind of inorganic substances or more than one kind of organic substances may be provided between the ceramic board and the silicon nitride film. A metal film having one or more than two metal layers, which consist of at least one kind of a metallic substance, may be provided on the surface of the silicon nitride film or in the case where the film consisting of either of the inorganic substances and the organic substances is provided on the silicon nitride film, on the surface of the film. Accordingly, the formation of a wiring pattern, which has a wiring width of 10 to 30mum or thereabouts and consists of a metal conductor, is possible and the ceramic circuit board is high also in reliability and is suitable as a circuit board for high-density mounting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic circuit board used as a mounting board for electronic parts, and more particularly to a ceramic circuit board suitable for high density mounting of electronic parts.

[0002]

2. Description of the Related Art In recent years, due to various excellent characteristics, a ceramic circuit board which has attracted attention as a circuit board for high-density mounting of electronic components (in this specification, a ceramic circuit board is a ceramic mounting of electronic components). Means the board,
It is distinguished from a simple ceramic substrate. ) Is formed by depositing a metal conductor (wiring) having a desired wiring pattern on a ceramic substrate made of a sintered body such as alumina, aluminum nitride, mullite, beryllia. As a method of forming the metal conductor, a method of adhering a copper foil to a ceramic substrate at high temperature (DBC), a metallizing method (thick film method) of printing and firing a refractory metal or a metal paste, etc. are generally known. There is. However, the width of the metal conductor, that is, the minimum value of the wiring width is about several hundreds μm by any method,
This is unsuitable for high-density packaging that requires a wiring width of several tens of μm or less.

Further, a method (thin film method) of forming a metal thin film on a ceramic substrate by a thin film forming technique such as vapor deposition or sputtering and forming the metal thin film into a desired wiring pattern by a photolithography technique and etching has been studied. There is. However, the surface of the sintered ceramic circuit board has irregularities with a size of several μm, and since each crystal grain boundary is extremely acute, there is a risk of disconnection if the wiring width is narrow. Especially when the wiring width is several tens of μm, the thickness is 1 μm.
The risk of wire breakage is extremely high because of the degree. Therefore, even with this thin film method, it is difficult to form a wiring pattern made of a metal conductor having a wiring width of 100 μm or less.

That is, in the thin film method, the wiring width is several tens μ
In order to form a metal conductor of m or less, it is necessary to flatten the surface of the ceramic substrate before forming the metal thin film by vapor deposition or the like. As an effective means for flattening the surface, there is a surface polishing method for a ceramic substrate.

[0005]

However, when the surface of the ceramic substrate is polished, particles are dropped from the crystal grain boundaries, and holes (falling traces) having a size of 2 μm or more and a depth of 1 μm or more are generated. As a result, a smooth surface cannot be obtained. Therefore, even if a metal conductor having a thickness of about 1 μm and a wiring width of several tens of μm is formed on the surface where the drop trace is generated, the risk of disconnection becomes extremely high. It has not been possible to provide a ceramic circuit board for high-density mounting with high reliability of μm.

The dropout of particles during polishing as described above is excellent in thermal conductivity and has a thermal expansion coefficient close to that of silicon which is a semiconductor material (that is, a silicon semiconductor chip can be directly mounted on a mounting substrate. ) And non-toxic properties such as aluminum nitride are essential problems and cannot be avoided. Since such a problem is included, it is extremely difficult to form a fine wiring pattern on an aluminum nitride substrate to obtain a circuit board for high-density mounting.

Further, aluminum nitride has a problem in that it has poor wettability with metals such as gold, copper and titanium used as metal conductors, and has low adhesion with them. Further, aluminum nitride reacts with water in the atmosphere to cause hydrolysis and generate ammonia. There is also a problem that the ammonia corrodes the metal conductor. In addition, there is a problem that the electrical resistance of the surface portion of the aluminum nitride substrate is lowered by the hydrolysis, and the insulating property is deteriorated.

On the other hand, in oxide-based ceramics such as alumina, the coefficient of thermal expansion generally differs greatly from the coefficient of thermal expansion of the metal used as the metal conductor described above. In a cycle test (for example, −40 ° C. to 150 ° C.), the metal conductor peels off from the ceramic substrate, is disconnected,
Alternatively, there is a problem that cracks are generated in the ceramic substrate due to thermal stress.

The present invention has been made to solve the above problems, and an object thereof is to provide a fine wiring pattern made of a metal conductor on a flattened surface of a ceramic substrate made of a sintered body. It is to provide a formed ceramic circuit board for high-density packaging with high reliability.

[0010]

In order to achieve the above object, the present inventor should develop a method for flattening the surface of a ceramic substrate before forming a metal conductor, instead of the conventional polishing method. As a result of intensive studies, it was found that a flat surface can be obtained by forming a silicon nitride film on the surface of a ceramic substrate.

In addition, the coefficient of thermal expansion of the silicon nitride film is not only close to the coefficient of thermal expansion of the ceramic substrate, but also close to that of silicon (semiconductor material). Further, the silicon nitride film is not only excellent in water resistance because it does not combine with water, but also has good adhesiveness to a ceramic substrate, and a metal substance, an inorganic substance or an organic substance which comes into contact with the silicon nitride film in the present invention. It has the property of excellent adhesion to substances. Therefore, it was found that forming a silicon nitride film on a ceramic substrate is extremely effective in providing a ceramic circuit substrate for high-density mounting, and completed the present invention.

That is, the ceramic circuit board according to the present invention comprises a silicon nitride film, for example, a silicon nitride film such as a compound represented by the chemical formula SiN or a compound represented by the chemical formula SiNH, on the ceramic substrate. Characterize.

A film made of one or more kinds of inorganic substances or one or more kinds of organic substances may be provided on the silicon nitride film, and between the ceramic substrate and the silicon nitride film. In addition, a film made of any one or more kinds of metal substances, one or more kinds of inorganic substances, or one or more kinds of organic substances may be provided. Then, on the surface of the silicon nitride film, or on the surface of the film made of an inorganic material or an organic material when the film is provided thereon,
A metal film having one or more metal layers made of at least one kind of metal substance may be provided.

[0014]

According to the above-mentioned ceramic circuit board, since a silicon nitride film, for example, a silicon nitride film such as a compound represented by SiN or SiNH, is formed on the ceramic substrate, a generally available ceramic substrate (sinter finished As it is, unevenness existing on the surface of the substrate (not polished) is covered with a silicon nitride film to obtain a flat surface, and the metal conductor has a wiring width of 30 μm and a thickness of 0.3 μm to 5 μm. It is possible to form a wiring pattern made of At that time, as for the thickness of the silicon nitride film, the average roughness Ra of a generally available ceramic substrate is 0.4 μm, and the maximum roughness Rmax is 4 μm.
Since it is m, a thickness of 4 μm or more is sufficient.

In the case of using a ceramic substrate whose substrate surface has been polished and flattened in advance, the traces of particle dropouts produced on the substrate surface by polishing are filled with the silicon nitride film, so that the wiring width is 10 μm. It is possible to form a wiring pattern made of a metal conductor having a thickness of 0.3 μm to 5 μm. In this case, since the surface of the substrate is already flat when the silicon nitride film or the like is formed on the ceramic substrate, the thickness of the silicon nitride film or the like to be formed can be reduced, and the characteristics of the ceramic substrate can be effectively used. Can be used for.

If a film of an inorganic material or an organic material is provided on the silicon nitride film, the surface of the ceramic circuit board is smoothed by the film of the inorganic material or the organic material, so that the wiring width is reduced. Is 10 μm and the thickness is 0.3 μm to 5
It is possible to form a wiring pattern made of a metal conductor of μm.

Alternatively, if a film made of a metal substance, an inorganic substance or an organic substance is provided between the ceramic substrate and the silicon nitride film, the film made of the metal substance, the inorganic substance or an organic substance is formed. When formed on a ceramic substrate,
The substrate surface is flat and smooth. Therefore, by further forming a silicon nitride film on it, the wiring width becomes 10 μm.
It is possible to form a wiring pattern made of a metal conductor having a thickness of m and a thickness of 0.3 μm to 5 μm.

In addition, when a wiring pattern made of a metal conductor is directly formed on a silicon nitride film provided through a film made of the above-mentioned metal substance, the coefficient of thermal expansion of silicon is substantially the same and the water resistance is high. In addition to being able to effectively utilize the excellent properties of the silicon nitride film such as (non-water permeability), prevention of alkali metal contamination, and good adhesion to a metal conductor, the film material made of a metal substance or the like can be used. By selecting such that the coefficient of thermal expansion is appropriate, it is expected that the thermal stress that can occur in the silicon nitride film due to the difference in coefficient of thermal expansion between the ceramic substrate and the silicon nitride film is relaxed.

[0019]

EXAMPLES The features of the present invention will be clarified below with reference to Examples 1 to 3 and conventional examples.

In each of the examples and comparative examples, a commercially available alumina substrate (alumina purity: 95%), an aluminum nitride substrate, and a mullite substrate were used as the ceramic substrate. Each board has a size of 2 inches square and a thickness of 0.6.
It was 35 mm. In addition, two types were prepared, one for polishing the surface of each substrate and one for not polishing.

Example 1 A 5 μm thick silicon nitride film made of a compound represented by the chemical formula SiNH was formed on the alumina substrate by a CVD method (chemical vapor deposition method) using a laser. At that time, monosilane (SiH ₄ ) gas and ammonia gas were used as source gases, and the substrate holding temperature was 300 ° C. Then, a metal layer of aluminum (Al) having a thickness of 5 μm was vapor-deposited on the substrate with the silicon nitride film by a sputtering method. A resist is applied on the metal layer, and unnecessary portions of the metal layer are removed by a photolithography technique and a wet etching method (a dry etching method may be used).
Wiring width 200μm, 150μm, 100μm, 50μ
m, 30 μm, and 10 μm each of the metal conductors were formed in a comb shape. Similarly, a metal conductor made of chromium (Cr), titanium (Ti), and copper (Cu) having the same shape and size as the aluminum metal conductor was also formed.

The electrical resistance of each metal conductor in the alumina-ceramic circuit board obtained as described above was measured to check for the presence or absence of disconnection. Then, in the metal conductor group of each wiring width of each metal type (the number of samples of each group is 10), the minimum width of the wiring widths of the group in which no disconnection occurred in all 10 conductor samples. Is the minimum wiring width that can be formed in the ceramic circuit board according to the present invention. In addition, after performing a temperature cycle test (temperature range: −40 ° C. to 150 ° C., the number of cycles: 50) on the metal conductor group having the minimum wiring width, the electrical resistance was measured again and the presence or absence of disconnection was examined. Table 1 shows the value of the minimum wiring width and the number of non-defective products in which no disconnection occurred in the temperature cycle test.

[Table 1]

As for the aluminum nitride substrate and the mullite substrate, similarly to the above-mentioned alumina substrate, a metal conductor group of each wiring width made of each metal type is formed on each substrate, and the presence or absence of disconnection of each metal conductor is checked to determine the minimum. While obtaining the wiring width,
The number of non-defective products after the temperature cycle test of the metal conductor group having the minimum wiring width was obtained. The results are also shown in Table 1.

Example 2 A lead metal film having a thickness of 3 μm was formed on each of the alumina substrate, the aluminum nitride substrate, and the mullite substrate, and the chemical formula S was formed on the lead metal film.
A 2 μm thick silicon nitride film made of a compound represented by iN was formed by a high frequency sputtering method. When forming the lead metal film, the substrate holding temperature is 50 ° C. and the power is 30.
The temperature was set to 0 W, and when forming the silicon nitride film, the substrate holding temperature was set to 50 ° C. and the power was set to 500 W.

Then, in the same procedure as in Example 1, a metal conductor group of each wiring width made of each metal of aluminum, chromium, titanium, and copper was formed on the silicon nitride film, and before and after the temperature cycle test. Check the presence of disconnection and check the minimum wiring width,
And the number of non-defective products of the metal conductor group having the minimum wiring width after the temperature cycle test. The results are shown in Table 2. However, in this example, the thickness of each metal conductor was 1 μm. In addition, the shape, length, wiring width, and the like of each metal conductor were the same as in Example 1 above.

[Table 2]

Example 3 A 2 μm thick silicon nitride film made of a compound represented by the chemical formula SiN was formed on each of the alumina substrate, the aluminum nitride substrate and the mullite substrate by a high frequency sputtering method. At that time, the substrate holding temperature was 200 ° C. and the power was 500 W. further,
On the silicon nitride film, silanol (generally the chemical formula H _n
It is represented by Si (OH) _4-n (n is 0, 1, 2, 3). ) Was dissolved in ethyl cellosolve by a spin coating method, dried and heated to a thickness of 1 μm.
A silicon oxide film was formed. On the other hand, instead of the silicon oxide film, a commercially available solution (made by Hitachi Chemical Co., Ltd.) in which an imide resin is dissolved in a solvent is applied on the silicon nitride film by a spin coating method, dried and heat-treated to form an imide having a thickness of 2 μm. A substrate on which a resin film was formed was also prepared.

Then, in the same procedure as in the above-mentioned first embodiment,
On the silicon oxide film or the imide resin film, a metal conductor group made of aluminum, chromium, titanium, and copper with each wiring width is formed, and the presence or absence of disconnection is checked before and after the temperature cycle test to determine the minimum wiring. The width and the number of non-defective products after the temperature cycle test of the metal conductor group having the minimum wiring width were obtained. The results are shown in Table 3. However, in this example, the thickness of each metal conductor was 1 μm. In addition, the shape, length, wiring width, and the like of each metal conductor were the same as in Example 1 above.

[Table 3]

(Prior art example) For comparison, on the alumina substrate, the aluminum nitride substrate, and the mullite substrate, as in the case of the first embodiment, a metal of each wiring width made of aluminum, chromium, titanium, and copper is used. After forming a conductor group, the minimum wiring width that can be formed and the number of non-defective products after the temperature cycle test of the metal conductor group having the minimum wiring width were obtained. The results are shown in Table 4.

[Table 4]

In each of Examples 1 to 3, the minimum wiring width that can be formed is 10 μm or 30 μm, which is suitable as a circuit board for high-density mounting, and no disconnection is observed even after the temperature cycle test. , Found to be reliable. On the other hand, in the conventional example, the minimum wiring width exceeds 100 μm in the case where the substrate surface is not polished, and is 50 μm even in the case where the substrate surface is polished. Moreover, disconnection occurs after the temperature cycle test. Not suitable as a mounting circuit board.

The present invention is not limited to the above embodiments. For example, in any of the embodiments, the silicon nitride film may be a compound represented by the chemical formula SiN, a compound represented by the chemical formula SiNH, or a silicon nitride film represented by any other chemical formula. that time,
The composition ratio of silicon and nitrogen or the composition ratio of silicon, nitrogen and other elements is not particularly limited.

Further, the thickness of the silicon nitride film can be arbitrarily changed according to the surface roughness of the ceramic substrate by selecting various forming conditions in the CVD method, the sputtering method and other thin film forming methods.

Further, in the second embodiment, the lead metal film is interposed between the ceramic substrate and the metal conductor, but not limited to lead, other metal substances, inorganic substances or organic substances may be used. The thickness of the film is also not limited. And, the metal substance, the inorganic substance, and the organic substance may be two or more kinds.

Further, although the silicon oxide film or the imide resin film is formed on the silicon nitride film in the third embodiment, a film made of various inorganic or organic substances other than silicon oxide or imide resin may be formed. The thickness of the film is not limited either. And, these inorganic substances and organic substances may be two or more kinds.

Further, even if a film of a metal substance, an inorganic substance or an organic substance is provided between the ceramic substrate and the silicon nitride film, and an inorganic substance or an organic substance film is provided on the silicon nitride film, It goes without saying that the effects of the above-described embodiments can be obtained.

Further, the metal species of the metal conductor may be other metals such as gold, silver and palladium, in addition to aluminum, chromium, titanium and copper, or may be a metal conductor formed by laminating a plurality of these metal layers. Good. The ceramic substrate is also alumina,
Not limited to aluminum nitride and mullite.

[0036]

According to the ceramic circuit board of the present invention, a silicon nitride film, for example, a silicon nitride film of a compound represented by SiN or SiNH is formed on the ceramic substrate, and the surface is flattened by the silicon nitride film. Therefore, it is possible to form a wiring pattern made of a metal conductor having a wiring width of about 10 μm to 30 μm. In addition, there is no risk of breaking of the metal conductor due to cracks or peeling of the metal conductor, which is suitable as a circuit board for high-density mounting.

Further, by polishing the surface of the ceramic substrate,
By reducing the thickness of the silicon nitride film or the like, the characteristics of the ceramic substrate can be effectively utilized. Further, the silicon semiconductor chip can be directly mounted on the ceramic circuit board. Furthermore, the substrate itself can be protected from moisture. Further, depending on the combination of the silicon nitride film and the silicon oxide film, the effect of lowering the dielectric constant of the ceramic substrate can be expected. Furthermore, when α-rays are generated from the ceramic substrate, the α-rays are shielded by the silicon nitride film, so the material of the ceramic substrate is not specified in particular, and there is no restriction when selecting the material. Complete.

Claims (4)

[Claims] 1. A ceramic circuit substrate comprising a silicon nitride film on a ceramic substrate. 2. The ceramic circuit board according to claim 1, further comprising a film made of one or more kinds of inorganic substances or one or more kinds of organic substances on the silicon nitride film. 3. A film made of any one or more kinds of metal substances, one or more kinds of inorganic substances, or one or more kinds of organic substances is provided between the ceramic substrate and the silicon nitride film. The ceramic circuit board according to claim 1 or 2, which is characterized in that. 4. The ceramic circuit board according to claim 1, wherein the upper surface is provided with a metal film having one or more metal layers made of at least one kind of metal substance.