JPH1087368A - Ceramic substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic substrate for the production of a high strength aluminum nitride(AIlN) circuit board which is stable and has enough joining strength by controlling the weight ratio of O to Y in the ceramic material, the bending strength of a ceramic substrate, the amt. of boron nitride remaining on the surface and the surface roughness. SOLUTION: This substrate essentially composed of AlN and has >=30kg/mm<2> bending strength, >=0.71 weight ratio of O to Y included in the substrate, <=11×10<-2> ratio of surface roughness to the average grain diameter, and <=6×10<-2> ratio of X-ray diffraction intensity of boron nitride remaining on the surface layer to the X-ray diffraction intensity of AlN. The figure shows an example of the high strength AlN circuit board and it is composed of an AlN ceramic substrate 1, copper parts 2, brazing material 3, and measuring area 4 for peeling strength. The brazing material 3 is prepared by adding various kinds of additives to a mixture powder of titanium, silver and copper into a paste and then applied by printing on specified positions on both principal surfaces of the AlN ceramic substrate. Then copper parts 2 are disposed on the brazing material and heated in vacuum so as to join the copper parts 2 with the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a ceramic substrate and a method of manufacturing the same, and more particularly, to an aluminum nitride ceramic substrate having high thermal conductivity and high strength suitable for mounting an integrated circuit or a semiconductor component, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, ceramic circuit boards having conductive circuits have been widely used as mounting boards for electronic components such as hybrid ICs and high power power modules that generate a large amount of heat. Attention has been focused on the application of AlN ceramic circuit boards with
In order to manufacture a high-quality AlN ceramic circuit board, various devices have been devised for manufacturing a ceramic substrate, forming a conductive circuit, and the like.

In AlN, Al ₂ O ₃ is converted to Al ₂ O ₃ = 2Al + with the formation of aluminum vacancy V _Al.
It is known to exist in the form 3O + V _Al . Also,
At a high temperature, Y ₂ O ₃ reacts with Al ₂ O _{3 in} AlN to form a liquid of a composite oxide of aluminum and yttrium to promote sintering. Al ₂ Y ₄ O ₉ (YAM), AlYO ₃ (Y
It is known that a composite oxide of aluminum and yttrium such as AL) and Al ₅ Y ₃ O ₁₂ (YAG) exists.

[0004] Therefore, in the production of an AlN ceramic substrate, in order to obtain a dense substrate, generally, a few percent of rare earth oxides represented by yttria (Y ₂ O ₃ ) and alkaline earth oxides represented by calcia are used. An additive is added as a sintering aid. For example, currently commercially available AlN ceramic substrates having high thermal conductivity generally have a
About 8 wt% of Y ₂ O ₃ is added.

[0005] When mass-producing AlN ceramic substrates, several or several tens of substrates are stacked and sintered at a time. In this case, separation is required to prevent adhesion between the substrates. Boron nitride (BN) and the like have been widely used as agents.

On the other hand, in the formation of a conductive circuit on the surface of a ceramic substrate, a conductive paste is printed on the surface of the substrate and the conductive circuit is formed by firing at a high temperature. 2-258686) In advance, the AlN ceramic substrate is treated in air at a temperature of about 1000 ° C. to generate alumina on the surface of the substrate, and then heated in an inert atmosphere using a copper plate containing oxygen. Alternatively, by heating in an oxidizing atmosphere using oxygen-free copper, an eutectic solution of Cu ₂ O and Cu is generated at the interface, and an AlN ceramic substrate and a copper plate having alumina formed on the surface are used. And a direct joining method for forming a conductive circuit (Japanese Patent Laid-Open No. 3-93687), a brazing material is applied to the substrate surface in a circuit shape, and a copper part is placed on the brazing material and heated. Possibly In general, a method such as a brazing method for joining a substrate and a copper part to form a conductive circuit has been used. In particular, in the case of forming a conductive circuit at the time of manufacturing a large power circuit board, a direct bonding method or a brazing method has been mainly used.

On the surface of the AlN ceramic substrate,
There is a surface layer with a high grain boundary component phase component formed by exudation of the grain boundary component phase component, and impurities such as a mold release agent remain on the surface of the surface layer to inhibit the bonding between the aluminum nitride and the conductive circuit. For this reason, Japanese Patent Application Laid-Open No. H2-258686 discloses an invention in which, when a conductive circuit is formed by a metallization method, it is necessary to remove a grain boundary constituent phase component by a method such as lapping and honing.

Further, Japanese Patent Application Laid-Open No. 2-149485 discloses that a grain boundary constituent phase component precipitated on the surface of an AlN ceramic substrate roughens the bonding surface, lowers the bonding strength between the ceramic substrate and the conductor, and reduces the thermal conductivity. A method for removing a component of a grain boundary constituent phase on a surface by using a liquid solvent in order to impair the surface roughness is disclosed.

Further, Japanese Patent Application Laid-Open No. 3-93687 discloses an AlN
Grain boundary constituent phase components precipitated on the surface of the ceramic substrate remain on the surface of the AlN ceramic substrate almost unaffected by the oxidation treatment, and adhere to the surface coating layer (the aluminum oxide layer in the direct bonding method) and the ceramic substrate. It discloses a method for forming a surface coating layer after removing a grain boundary constituent phase component by performing a chemical surface treatment using an acidic solution in order to cause a decrease in force.

[0010]

In a ceramic circuit board for a high power power module, coarse electrodes are connected to the substrate in addition to a semiconductor and an integrated circuit, and a large force is applied to the ceramic circuit board. Further, in integrated circuit substrates, miniaturization of conductive circuit patterns has been promoted. Therefore, in spite of the recent demand for high-strength bonding between the conductive circuit and the ceramic substrate, when a circuit board is manufactured by the above-described conventional direct bonding method, the circuit between the conductive circuit portion of the substrate and the ceramic substrate is Peel strength is 10kg /
I could only get around cm. Further, when the circuit board is manufactured by the brazing method, although the average value of the joining strength is high, the dispersion is large and the peel strength may be 10 kg / cm or less.

Therefore, when such a low bonding strength substrate is used as a circuit board for a power module, there has been a problem that peeling is likely to occur at a bonding portion between the conductive circuit and the ceramic substrate.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ceramic substrate for a high-strength aluminum nitride circuit board having a stable and sufficient bonding strength and a method of manufacturing the same, which solves the above-mentioned problems of the prior art. .

[0013]

Means for Solving the Problems The present invention has been intensively studied to solve the above problems, and as a result, the bending strength of the ceramic substrate, the weight ratio of oxygen to yttrium in the ceramic substrate, the surface roughness of the ceramic substrate, The inventors have found that the amount of boron nitride remaining on the surface of the ceramic substrate and the joining temperature have a strong influence on the joining strength, and have provided the present invention.

That is, the present invention has a flexural strength of 30 kg / mm
² or more, the ratio of the weight of oxygen (Owt) to the weight of yttrium (Ywt) (Owt / Ywt) is 0.71 or more, and the ratio of the surface roughness (Ra) to the average grain size (D) (Ra / D) Is 11
× 10 ^-2 or less, and the ratio of the X-ray diffraction intensity (IBN) of boron nitride remaining on the surface layer to the X-ray diffraction intensity (IAN) of aluminum nitride (IBN / IAN) is 6 × 10 ^-2 or less And a method of manufacturing the same.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When a circuit board is manufactured by the brazing method, a sound bonded body can be obtained by controlling brazing conditions such as the composition of the brazing material, the temperature, the time, and the atmosphere. In a circuit board manufactured by controlling the soldering conditions in this way, the joining strength between the metal and the brazing material and between the brazing material and the ceramic is greater than the strength of the ceramic itself.

[0016] Therefore, physical stress is applied to the substrate by applying mechanical stress to the substrate to separate the metal and the ceramic, or by repeatedly heating and cooling the substrate by utilizing the difference in thermal expansion coefficient between the ceramic and the metal. When a stress is generated at the interface of the substrate and the separation of the metal and the ceramic is attempted, the separation is caused by the destruction of the ceramic substrate itself. Therefore, in order to obtain high bonding strength, it is better that the strength of the substrate is large.

According to the study of the present inventors, AlN
A correlation was observed between the bending strength and the peel strength of the ceramic substrate up to a bending strength of 30 kg / mm ^2, and it was confirmed that the peel strength increased as the bending strength increased.
Therefore, the bending strength of the AlN ceramic substrate is 30
It is necessary to be at least kg / mm ² .

The breaking mode when the bending strength exceeds 30 kg / mm ² is mainly classified into two types shown in FIGS. 3 and 4 depending on the state of crack propagation. That is, in the AlN ceramic substrate 1 having the copper parts 2 formed on both main surfaces, a crack having a high peel strength penetrates deeply into the AlN ceramic substrate 1 and peels off (FIG. 3), and the peel strength is low. The peeling occurs at the surface layer (about 10 μm from the surface) of the AlN ceramic substrate 1 (FIG. 4).

When the average crystal grain size and the grain size distribution in the AlN ceramic substrate are kept constant, the rougher the surface of the ceramic substrate, the smaller the peel strength and the more often the ceramic layer peels off at the surface layer. This is because the rougher the surface, the smaller the contact area between the crystal particles on the substrate surface and the surrounding and internal particles, and the more easily the crystal particles on the substrate surface are peeled off.

Further, as shown in FIG. 2, since the brazing material 3 cannot always sufficiently wet the surface of the AlN ceramic substrate, the brazing material cannot penetrate into the concave portions on the surface of the ceramic substrate, and only the convex portions are formed. It joins with a metal conductor, and the non-contact part 7 arises between the brazing material 3 and a board | substrate. Therefore, in order to obtain sufficient bonding strength, it is necessary to smooth the substrate surface. Specifically, the ratio (Ra) between the surface roughness Ra measured according to the JIS standard and the average crystal grain size D of the ceramic substrate is considered. / D) is preferably 11 × 10 ⁻² or less.

Further, as shown in FIG. 2, boron nitride 6 used as a separating agent when firing the AlN ceramic substrate often remains at the grain boundaries of AlN crystal grains 5 in the surface layer of the AlN ceramic substrate. On the other hand, if the residual amount of boron nitride is large, sufficient bonding strength cannot be obtained even if the above conditions of surface roughness are satisfied.

This is because aluminum nitride and boron nitride have low reactivity, so that the bonding strength between the particles is low, and furthermore, boron nitride itself is a substance having a high cleavage property, and the strength of boron nitride itself is low. Therefore, in order to obtain high bonding strength, it is better to reduce the residual amount of boron nitride on the substrate surface. The specific residual amount of boron nitride is determined by using a Rigaku Corporation X-ray diffraction apparatus. Is Cu, the accelerating voltage and the accelerating current are 50 kV and
When the surface of the ceramic substrate is diffracted under the condition of 30 mA, the diffraction intensity IBN of the (002) plane of boron nitride and the average diffraction intensity IAlN of the (100), (002), and (101) planes of aluminum nitride are as follows. Ratio (IBN / IAlN) is 6 × 10 ^-2
It must be:

The surface roughness of the ceramic substrate and the residual amount of boron nitride differ depending on the manufacturing process of the substrate. If the above conditions are satisfied at the time of sintering, the surface roughness is further increased. There is no need to perform any processing, and if the above conditions are not met, honing,
The surface treatment may be performed by a mechanical or chemical method such as lapping, grinding, and etching with a chemical.

When Y ₂ O ₃ is used as a sintering aid, Al ₂ Y ₄ O ₉ (YA)
M), AlYO ₃ (YAL), Al ₅ Y ₃ O ₁₂ (YA
Although a composite oxide of aluminum and yttrium as in G) exists, it has been confirmed that the bonding strength of an AlN ceramic substrate having a YAG phase at a grain boundary is higher than that of a substrate having a grain boundary phase of YAL and YAM. ing. That is, the grain boundary phase of the AlN ceramic substrate varies depending on the amount of oxygen in the AlN raw material powder, the amount of Y ₂ O ₃ added, the amount of residual carbon in the compact before sintering, the atmosphere, and the like.
Since the weight ratios O / Y of oxygen and yttrium in YAM are 0.71, 0.54 and 0.41, respectively, if the O / Y of the AlN ceramic substrate is 0.71 or more, the grain boundary phase YAG can be formed.

However, when the grain boundary phase contains a large amount of YAG, sufficient thermal conductivity cannot be achieved, so that the amount of YAG must be appropriately controlled. Therefore, in the present invention, the amount of the YAG phase in the AlN ceramic substrate is X
Diffraction strength of (640) crystal plane of YAG by X-ray diffraction
The ratio of 1N to the diffraction intensity of the (100) crystal plane (IYAG / I
AlN) in the range of 0.001 to 0.030, preferably 0.005 to
0.025 was set. By setting IYAG / IAlN within the above range, it is possible to provide an AlN ceramic substrate having a peel strength of 30 kg / cm or more and a thermal conductivity of 150 W / m · k or more.

It has also been confirmed that the bonding temperature affects the quality of the circuit board. If the bonding temperature is low, the reaction at the bonding interface becomes insufficient, and high bonding strength cannot be obtained. Conversely, when the joining temperature is high, the brazing material reacts violently with the metal conductor, so that the brazing material wraps around the metal conductor surface,
Color unevenness occurs. Therefore, it is necessary to join at a joining temperature suitable for the brazing material. For example, when using an Ag-Cu-Ti-based brazing material, the joining temperature is 780 to 900 ° C for 1 minute or more, preferably 790 to 850 ° C. By maintaining the bonding temperature for 5 to 60 minutes, a circuit board having high bonding strength and no color unevenness can be manufactured.

Incidentally, Japanese Patent Laid-Open Publication No.
According to the inventions disclosed in Japanese Patent No. 8686, JP-A-2-149485 and JP-A-3-93687, the grain boundary constituent phase component precipitated on the surface of the AlN ceramic substrate contains a metallizing paste and Cu ₂ generated at the grain boundary. It is said that it hardly reacts with the O-Cu eutectic liquid (in the case of the direct bonding method), so that it adversely affects the bonding strength between the conductive circuit and the ceramic substrate.

However, for a high-purity AlN ceramic substrate having a high thermal conductivity of 200 W / mK or more, the effect of the grain boundary constituent phase component deposited on the surface is particularly strong, but the present invention is not so effective. As described above, in the case of a substrate having a thermal conductivity of 200 W / mK or less, the influence of the component of the grain boundary constituent phase that exudes to the surface of the sintered body is small, and the effect is extremely small. In addition, since the brazing material containing an active metal used for forming a conductive circuit by the brazing method can react with the constituent components of the grain boundaries, the constituent components of the grain boundaries deposited on the surface do not adversely affect the bonding. Has been confirmed.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited by the following examples.

[0030]

Examples 1 to 5 The method of using the separating agent boron nitride (BN) as shown in Table 1 and the honing conditions
Five types of substrates were prepared in which / IAIN was not more than 6 × 10 ^-2 and Ra / D was not more than 11 × 10 ^-2 . These substrates have a weight ratio O / Y of oxygen to yttrium of 1.29,
The grain boundary phase is composed of YAG.

[0031]

[Table 1] First, a brazing material 3 made by adding various additives to a mixed powder of titanium, silver and copper is printed by a printing method at a predetermined position on both main surfaces of the prepared AlN ceramic substrate 1 by a printing method. Put copper part 2 on the
^The circuit was heated at 810 ° C. for 20 minutes in a vacuum of ^-5 torr to join the copper parts and the ceramic substrate to produce a circuit board as shown in FIG.

Next, the peel strength of each circuit board obtained as described above was measured (the peel strength was measured at the peel strength measuring point 4 in FIG. 1), and the results are shown in Table 1. Was. As can be seen from Table 1, the peel strength was 30 kg / cm or more in each of the circuit boards.

[0033]

Examples 6 to 12 A circuit board was manufactured and the peel strength was measured in the same manner as in Example 2 except that the bonding temperature was changed within the range of 780 to 910 ° C., and the results were shown in Tables 1 and 2. 2 is shown.

[0034]

[Table 2] As can be seen from Tables 1 and 2, the peel strength was 30 kg / cm or more in each of the circuit boards.

[0035]

EXAMPLE 13 The weight ratio of oxygen to yttrium (O /
Y) is 0.77, and the grain boundary phase is composed of YAG and YAL;
The surface IBN / IAN is 0.7 × 10 ⁻² or less and Ra /
Production of a circuit board was performed in the same manner as in Examples 1 to 5, except that an AlN ceramic substrate having D of 8.4 × 10 ⁻² was used.
And the peel strength were measured, and the results are shown in Table 2. As can be seen from Table 2, the peel strength is 40 kg / cm.
That was all.

[0036]

Comparative Examples 1-2 The weight ratio of oxygen to yttrium (O /
Y) were 0.59 and 0.52, and a circuit board was manufactured and the peel strength was measured in the same manner as in Example 13 except that an AlN ceramic substrate having a grain boundary phase of YAL and YAM was used. Also shown in Table 2. As can be seen from Table 2, the peel strength was less than 30 kg / cm for any of the circuit boards.

[0037]

Comparative Examples 3 to 5 Production of a circuit board and peeling were carried out in the same manner as in Examples 1 to 5 except that the method of using the separating agent (BN) was liquid coating, and a ceramic substrate manufactured with a small honing pressure was used. The strength was measured, and the results are shown in Table 2. As can be seen from Table 2, the peel strength was 20 kg / cm or less in each of the circuit boards.

From these results, it was found that IBN / IAN was 6
× 10 ^-2 or more, of course if Ra / D of 11 × 10 ^-2 or more, even if either of the IBN / IAlN and Ra / D is the value, sufficient bonding strength Could not get.

[0039]

As described above, by controlling the weight ratio of oxygen to yttrium in the ceramic, the flexural strength of the ceramic substrate, the amount of boron nitride remaining on the surface of the ceramic substrate, and the surface roughness, brazing is achieved. A high-strength aluminum nitride circuit board can be manufactured by the method. Therefore, a high-strength circuit board having a peel strength of 30 kg / cm or more can be provided to the market. Further, the present invention can be widely applied not only to the manufacture of a high-strength aluminum nitride circuit board but also to the manufacture of a composite of AlN ceramics and a metal that requires high bonding strength.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a high-strength aluminum nitride circuit board manufactured using a ceramic substrate of the present invention.

FIG. 2 is a schematic cross-sectional view showing a state of a surface layer of an AlN ceramic substrate and a bonding interface between a brazing material and the AlN ceramic substrate.

FIG. 3 is a diagram showing an example of a schematic destruction of a peel strength measurement sample, and is a cross-sectional view of a broken ceramic circuit board.

FIG. 4 is a view showing another example of a destruction pattern of a peel strength measurement sample, and is a cross-sectional view of a ceramic circuit board in which destruction has occurred.

[Description of Signs] 1 AlN ceramic substrate 2 Copper parts 3 Brazing material 4 Peel strength measurement point 5 AlN crystal grain 6 Boron nitride 7 Not yet Contact

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yu Namura 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Masami Kimura 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd.

Claims (1)

[Claims] (1) The transverse rupture strength is 30 kg / mm ² or more, and the ratio (O wt) between the contained oxygen weight (O wt) and the contained yttrium weight (Y wt) is
wt / Ywt) is 0.71 or more, the ratio of surface roughness (Ra) to average crystal grain size (D) (Ra / D) is 11 × 10 ^-2 or less, and the X-ray diffraction of boron nitride remaining on the surface layer A ceramic substrate containing aluminum nitride as a main component and having a ratio (IBN / IAIN) of diffraction intensity (IBN) to X-ray diffraction intensity (IAN) of aluminum nitride of 6 × 10 ⁻² or less.