JP2000086368A - Nitride ceramic substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a nitride ceramic substrate with high reliability by strongly connecting a nitride ceramic board with a copper sheet while suppressing the residual stress by the connection to the utmost. SOLUTION: (1) An active brazing material layer 4 is formed on an AlN board 1 and a copper sheet 2 is connected by a solder layer 3 thereon. (2) A thin ground copper sheet 5 is connected on the AlN board 1 by the active brazing material layer 4, and the copper sheet 2 is connected on the ground copper sheet 5 by the solder layer 3. (3) The thin ground copper sheet 5 is connected on the AlN board 1 by a direct connecting method, and the copper sheet 5 is connected on the ground copper sheet 5 by the solder layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic substrate which is mainly used for a semiconductor device such as a power transistor module and the like, in which a ceramic plate and a copper plate are joined together. The present invention relates to a ceramic substrate.

[0002]

2. Description of the Related Art Large-capacity power transistors and insulating gates
Bipolar transistor (hereinafter referred to as IGBT)
The modularized power module has insulation and heat dissipation
Ceramic substrates are used as substrates with
You. As a ceramic, it has good insulation and heat conduction
Rate is relatively large and the strength is high.
Luminium (hereinafter Al_TwoO_ThreeIs widely used
Came. In recent years, power modules have become smaller and more sophisticated.
Insulation material with even higher thermal conductivity to improve heat dissipation
Aluminum nitride (hereinafter referred to as AlN) or nitriding
Silicon (Si _ThreeN_FourNitride) ceramics such as
Boxes have been used.

When a ceramic plate is used as a substrate for a semiconductor, it is necessary to bond a circuit conductor or a metal plate as a cooling body to the ceramic plate. Copper is generally used as the metal material to be joined in view of electric conductivity, heat conductivity, and price. As a method of joining the AlN plate and the metal plate,
An active metal method that joins copper plates using silver-copper brazing material containing active metals such as titanium, zirconium, and hafnium, and directly joins copper plates by oxidizing the AlN surface in advance and using the eutectic reaction between copper and oxygen Direct bonding, silver,
Thick film method of printing and heating paste containing powder of silver-palladium, silver-platinum, copper, etc., simultaneous sintering method of simultaneously sintering and joining AlN with tungsten or molybdenum, which is a high melting point metal, etc. It has been known.

In general, when joining a nitride ceramic plate and a copper plate, a direct joining method using an active metal method is often used. In the active metal method, nitrogen atoms near the AlN surface react with the active metal such as titanium, zirconium, and hafnium of the brazing material by heat treatment to form titanium nitride, zirconium nitride, and hafnium nitride at the interface. Therefore, the AlN plate and the copper plate are firmly joined.

FIG. 4 shows a copper-clad A prepared by an activated metal method.
It is sectional drawing of an 1N board | substrate. The copper plate 2 is joined on the AlN plate 1 with an active brazing material layer 4. In the direct bonding method, an AlN plate whose surface has been thermally oxidized in advance is used. Then, a molten layer of a eutectic phase of copper and cuprous oxide is formed at the interface with the copper plate, and the AlN plate and the copper plate are firmly joined.

FIG. 5 is a sectional view of an AlN substrate manufactured by a direct bonding method. The copper plate 2 is directly joined to the AlN plate 1 by the eutectic layer 6.

[0007]

However, each of the above-mentioned conventional joining methods for joining a nitride ceramic plate and a copper plate has disadvantages. Originally, the coefficient of thermal expansion of copper was 17 × 10 ⁻⁶ / K, whereas AlN and S
4 × 10 ^-6 / K for nitride ceramics such as i ₃ N ₄
There is a big difference between the two. The bonding temperature of the active metal method is 780 ° C. or higher, and 10
A high temperature of 50 ° C. or higher is required. When a nitride ceramic plate and a copper plate are joined at such a high temperature, a large joining stress is generated due to a difference in thermal expansion between them, and a large residual strain or residual stress remains when used near room temperature.

[0008] Therefore, the joint is largely warped or broken at a low strength, and there is a problem in its reliability. For details, refer to the comparative experiment described in the embodiment of the invention. When the thick film method is used for bonding, the bonding strength between the nitride ceramic plate and the thick film conductor is weak, and when the semiconductor is soldered to the thick film conductor, the nitride ceramic and the thick film conductor are separated from each other. There was a problem.

In the simultaneous sintering method, the residual stress due to the difference in thermal expansion coefficient between the nitride ceramic and the high melting point metal,
As a result, there are cracks in the ceramics and warpage of the joined body,
There was a problem with its reliability. In view of such a situation, the present invention strongly bonds a nitride ceramic plate and a copper plate,
Moreover, it is an object of the present invention to provide a highly reliable nitride ceramic substrate by minimizing residual stress due to bonding.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a nitride ceramics substrate in which a nitride ceramics plate and a copper plate are joined, wherein a solder layer is provided between the nitride ceramics plate and the copper plate. Shall be. Specifically, a copper-based, silver-based, or copper-silver-based brazing material layer containing an active metal is formed on a nitride ceramic plate, and the brazing material layer and the copper plate are joined by soldering.

A nitride ceramic plate and a base copper plate are joined by a copper-based, silver-based, or copper-silver-based brazing material layer containing an active metal, and the base copper plate and a copper plate thicker than the base copper plate are joined by soldering. May be. When a nitride ceramic plate and a copper plate were joined with a copper-based, silver-based, or copper-silver-based brazing filler metal containing active metal, a large residual stress was generated due to the difference in thermal expansion between the two. It is considered that the stress was alleviated by sandwiching the solder with a thin copper base plate. Copper of a thickness required as a circuit conductor is joined by solder at a low temperature of, for example, 350 ° C. or less.
The difference due to thermal expansion is small, and the generated stress is small.

In particular, the thickness of the base copper plate is 0.03 to 0.1
It is important to be in the range of 5 mm. In such a range, no crack was observed. It is also assumed that the active metal in the brazing material layer is any of titanium, zirconium, and hafnium.

If such a metal is used, it reacts with the nitride ceramic to produce titanium nitride, zirconium nitride, and hafnium nitride, and a strong bond can be obtained. The nitride ceramic plate and the underlying copper plate are joined by a direct joining method,
The base copper plate and the copper plate thicker than the base copper plate may be joined by soldering. Also in this case, the stress is reduced by sandwiching the thin base copper plate.

In particular, the thickness of the base copper plate is 0.03-0.1.
When it is within the range of 5 mm, the occurrence of cracks can be suppressed.
It is assumed that the nitride ceramic plate is a sintered body containing aluminum nitride or silicon nitride as a main component. A sintered body containing aluminum nitride or silicon nitride as a main component has a high thermal conductivity, is easily available, and is suitable as a material for a nitride ceramic substrate.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the experiments and results up to the present invention, and the progress and results of experiments by a conventional method for comparison will be described in detail. [Experiment 1] FIG. 1 is a sectional view of an AlN substrate in which a copper plate is joined to an AlN plate according to the first method of the present invention.

An active brazing material layer 4 is provided on an AlN plate 1, and a copper plate 2 is joined thereon with a solder layer 3. The AlN substrate of FIG. 1 was manufactured by the following steps. First,
Al with dimensions of 30mm x 60mm and thickness of 0.635mm
A silver-copper-titanium-based brazing material paste containing 2% by weight of titanium, 70% by weight of silver, and 28% by weight of copper was coated on the surface of the N plate 1 in a size of 28 mm × 58 excluding 1 mm around the AlN plate 1.
A thickness of 30 μm was applied to the range of mm by screen printing. Dry it in air at 120 ° C for 10 minutes,
10 ^-2 30 min heating and degreasing at 450 ° C. in a low pressure vacuum from Pa, and heat treated further as 1 × 10 ^-2 10 minutes at 850 ° C. than in the low pressure vacuum Pa. Thus, a brazing material layer 4 firmly joined to the AlN plate 1 was formed. In addition,
At this time, the thickness of the brazing material layer 4 is about 10 μm, and the warpage is 10 μm.
μm or less.

On this brazing material layer 4, a size of 28 mm ×
58 mm lead / tin (Pb 95%, Sn 0.1 mm thick)
5%) A solder sheet is placed at a predetermined position excluding the surrounding area of 1 mm, and the dimensions are 28 mm × 58 mm and the thickness is 0.2 mm.
A copper plate 2 5.0 mm was laminated thereon. Then, heat treatment was performed at 350 ° C. for 5 minutes in an atmosphere of nitrogen to hydrogen at a ratio of 1: 1 to perform bonding, thereby forming an AlN substrate.

The AlN substrate thus obtained was checked for color, and cracks and peeling were observed under a microscope.
Next, the surface warpage was measured by a contact-type warpage measuring device.
Furthermore, 2mm ×
A 2-mm pad was prepared, and a solder-plated copper wire having a diameter of 0.6 mm was soldered to each pad at 200 ° C., and a 90 ° peel test was performed. Table 1 shows the results.

[0019]

[Table 1]

No crack or peeling was observed in any of the samples obtained by soldering the copper plate 2 having a thickness of 0.2 to 5.0 mm. Also, the warpage is 12 μm as the thickness of the copper plate 2 increases from 0.2 mm to 5.0 mm.
To 40 μm, but did not become large enough to hinder semiconductor bonding. The peel strength of all samples was 40 N / mm ² or more, and peeled off at the joint of the solder-plated copper wire.

From the results in Table 1, it can be seen that the AlN substrate formed by bonding a copper plate with a nitride plate having a copper-silver brazing material layer containing an active metal formed on the AlN plate by solder has defects such as cracks and peeling. Therefore, it is considered that a nitride ceramic substrate having high bonding strength is obtained. In this case, the brazing material containing the active metal forms a strong bond with the nitride-based ceramic, but does not bond the copper plate 2, so that the stress generated even at a high temperature of 780 ° C. or more is small. On the other hand, the copper plate 2 required as a circuit conductor / cooling body is joined at a low temperature of 350 ° C. or less by soldering. For this reason, the difference due to thermal expansion is small and the generated stress is small. Therefore, the residual stress is reduced.

[Experiment 2] FIG. 2 is a partial sectional view of a nitride ceramics substrate according to the second method of the present invention. AlN
A base copper plate 5 is joined to the plate 1 with an active brazing material layer 4, and a copper plate 2 is joined to the base copper plate 5 with a solder layer 3.

The AlN substrate shown in FIG. 2 was manufactured by the following steps. In the same manner as in Experiment 1, a paste of a silver-copper-titanium brazing material was applied to the AlN plate 1 and dried at 120 ° C. for 10 minutes in the air.
The base copper plates 5 of × 58 mm and thicknesses of 0.05, 0.1 and 0.2 mm were stacked. Next, at 450 ° C. in a vacuum at a pressure lower than 1 × 10 ⁻² Pa,
The resultant was degreased by heating for 0 minutes, and then heat-treated at 850 ° C. for 10 minutes in a vacuum at a pressure lower than 1 × 10 ⁻² Pa. Thus, the thin copper base plate 5 was firmly joined onto the AlN plate 1.
The warpage at this time was 7 μm for a 0.05 mm thick base copper plate, 12 μm for a 0.1 mm thick plate, and 65 μm for a 0.2 mm thick plate.

A lead / tin solder sheet was placed at a predetermined position on the base copper plate 5 as in Experiment 1, and a copper plate 2 having a thickness of 0.2 to 5.0 mm was further stacked thereon. And 350 ° C. in an atmosphere of 1: 1 nitrogen to hydrogen.
For 5 minutes to produce a sample. Crack / peeling observation, warpage measurement, and peel strength measurement were performed on the thus obtained sample having the base copper plate 5 having a thickness of 0.05 mm and 0.1 mm in the same manner as in Experiment 1. Table 2 shows the results.

In the sample using the base copper plate 5 having a thickness of 0.2 mm, no crack was observed at the stage where the base copper plate 5 was brazed, but all the samples were soldered when the copper plate 2 was soldered. As a result, cracks occurred in the AlN plate 1 and joining was not possible.
Was not listed.

[0026]

[Table 2]

No crack or peeling was observed in any of the samples in which the copper plate 2 having a thickness of 0.2 to 5.0 mm was soldered. In addition, the warpage is increased by increasing the thickness from 0.2 mm to 5.0 mm,
The thickness increased from 14 μm to 44 μm in the case of 5 mm and from 16 μm to 45 μm in the case of the base copper plate of 0.1 mm, but did not become large enough to support the bonding of the semiconductor.

The peel strength of each sample was 40 N / mm ² or more, and peeled off at the joint of the solder-plated copper wire. Although the brazing filler metal containing the active metal forms a strong bond with the nitride ceramics, the thickness of the base copper plate 5 is small, so that the stress generated even when bonded at a high temperature of 780 ° C. or more is small, and is absorbed by the base copper plate 5. Is done. On the other hand, the copper plate 2 required as a circuit conductor / cooling body is joined at a low temperature of 350 ° C. or less by soldering. For this reason, the difference due to thermal expansion is small and the generated stress is small. Therefore, the residual stress is reduced.

When a base copper plate 5 having a thickness of 0.2 mm is used,
It is considered that the stress at the time of joining at a high temperature of 780 ° C. or more is so large that it cannot be absorbed by the base copper plate 5 and cracks occur in the AlN plate 1. [Experiment 3] FIG. 3 is a partial cross-sectional view of a semiconductor device in which a copper plate is soldered to a copper-clad nitride ceramic substrate according to the third method of the present invention.

An underlying copper plate 5 is directly bonded on the AlN plate 1, and a copper plate 2 is bonded thereon with a solder layer 3. 6
Is a eutectic layer of copper and cuprous oxide. The AlN substrate of FIG. 3 was manufactured by the following steps. Dimension is 30mm x 60
AlN plate 1 having a thickness of 0.635 mm and a thickness of
Heat treatment was performed at 00 ° C. for 10 minutes. Thereby, the AlN plate 1
An oxide layer having a thickness of about 5 μm was formed on the surface of.

Except for 1 mm around the AlN plate 1 whose surface has been oxidized, 200 to 300 mm of dimensions 28 mm × 58 mm and thickness 0.05, 0.1, 0.2 mm
The base copper plate 5 made of tough pitch copper containing ppm of oxygen was laminated and heat-treated at 1070 ° C. for 10 minutes in a nitrogen atmosphere. Thus, the thin copper base plate 5 was joined onto the AlN plate 1. The warpage at this time was 5 μm for a 0.05-thick underlying copper plate, 10 μm for a 0.1-mm-thick plate, and 60 μm for a 0.2-mm-thick plate.

On this thin base copper plate 5, a lead / tin solder sheet was used in a thickness of 0.2 to
A copper plate 2 having a thickness of 5.0 mm was laminated and heat-treated at 350 ° C. for 5 minutes in an atmosphere in which the flow ratio of nitrogen to hydrogen was 1: 1.
Was prepared. For the sample thus obtained, crack / peel observation, warpage measurement,
Peel strength was measured. Thickness 0.05mm and 0.1
Table 3 shows the results of the samples having the base copper plate of mm.

In this experiment 3, the thickness was 0.2 m.
Table 3 does not describe the samples having the m base copper plate, since cracks occurred in the AlN plate in all the samples after soldering and could not be joined.

[0034]

[Table 3]

No crack or peeling was observed in any of the samples obtained by soldering the copper plate 2 having a thickness of 0.2 to 5.0 mm. In addition, the warpage is increased by increasing the thickness from 0.2 mm to 5.0 mm,
The thickness increased from 10 μm to 42 μm in the case of 5 mm and from 15 μm to 42 μm in the case of the base copper plate of 0.1 mm, but did not become large enough to support the bonding of the semiconductor.

The peel strength of each sample was 40 N / mm ² or more, and peeled off at the joint of the solder-plated copper wire. In the direct joining method, the AlN plate 1 and the base copper plate 5 are firmly joined. Also, since the base copper plate 5 is thin,
Even when joining is performed at a high temperature of 1050 ° C. or more by the direct joining method, the generated stress is small and is absorbed by the base copper plate 5. Then, the thick copper plate 2 serving as a circuit conductor / cooling body is joined to the base copper plate 5 at a low temperature by soldering. For this reason, the difference due to thermal expansion is small and the generated stress is small. Therefore, the residual stress is reduced by the method of the present invention.

Even when the base copper plate 5 having a thickness of 0.2 mm is used by the direct bonding method, the stress at the time of bonding at a high temperature of 1050 ° C. is too large to be absorbed by the base copper plate 5 and the copper plate 2
It is considered that cracks occurred in the AlN plate 1 at the time of soldering. Comparative Experiment 1 As Comparative Experiment 1, a copper plate was joined to an AlN plate by a conventional activated metal method.

The size was 30 mm × 60 in the same manner as in Experiment 1.
mm, the surface of an AlN plate 1 having a thickness of 0.635 mm
A paste of a copper-titanium brazing material was applied by screen printing to a thickness of 30 μm and dried in air. A copper plate 2 having a size of 28 mm × 58 mm and a thickness of 0.2 to 5.0 mm was laminated thereon. Then, under the same conditions as in Experiment 1,
Degreasing by heating under vacuum, and 850 ° C 10 in vacuum as it is
The AlN plate 1 and the copper plate 2 were joined by heat treatment for one minute. The cross section of the joined AlN substrate is as shown in FIG.

The thus obtained comparative test samples were subjected to crack / peel observation, warpage measurement, and peel strength measurement in the same manner as the samples of Experiments 1 to 3. Table 4 shows the results.

[0040]

[Table 4]

In the case of the copper plates having a thickness of 0.2 mm and 0.5 mm, neither cracking nor peeling was recognized, but the thickness was 0.1 mm.
70 mm for 2 mm and 2 mm for 0.5 mm
It was difficult to bond a silicon chip or the like. Also in the peel strength test, 20 N / mm ² for 0.2 mm and ¹ N for 0.5 mm copper plate.
At 0 N / mm ² , cracks occur in the AlN plate 1
It cannot be used as a substrate. This is considered to be due to residual stress at the time of joining.

In the case of a copper plate having a thickness of 1 mm, cracks occurred after joining, and in the case of a copper plate having a thickness of 2 mm, cracks and peeling were observed. Therefore, in these, the peel strength test could not be performed. The warpage was as large as 250 μm or more. [Comparative experiment 2] As comparative experiment 2, A
The copper plate 2 was joined to the 1N plate 1.

The dimensions were 30 mm × 60 as in Experiment 3.
An AlN plate 1 having a thickness of 0.635 mm and a thickness of 0.635 mm is subjected to a heat treatment in the air, and the size is 28 mm on the AlN plate 1 whose surface has been oxidized.
× 58 mm, thickness of 0.2 to 5.0 mm, 200 to 3
A tough pitch copper plate 2 containing 00 ppm of oxygen was laminated and heat-treated at 1070 ° C. for 10 minutes in a nitrogen atmosphere to directly join. The cross section of the joined AlN substrate is as shown in FIG.

The samples thus obtained were subjected to crack / peel observation, warpage measurement, and peel strength measurement in the same manner as the samples of Experiments 1 to 3. Table 5 shows the results.

[0045]

[Table 5]

In the case of the copper plates having a thickness of 0.2 mm and 0.5 mm, neither cracking nor peeling was observed, but the warpage was 60 μm for the one having a thickness of 0.2 mm and 170 μm for the one having a thickness of 0.5 mm. It was difficult to join chips and the like. Also in peel strength test, intended for 0.2 mm 20 N / mm ^2, is intended 0.5mm copper plate cracks occur in AlN plate 1 with 10 N / mm ^2, can not be used as a semiconductor substrate. This is considered to be due to residual stress at the time of joining.

In the case of a copper plate having a thickness of 1 mm, cracks occurred after bonding, and in the case of a copper plate having a thickness of 2 mm, cracks and peeling were observed. Therefore, in these, the peel strength test could not be performed. The warpage was as large as 250 μm or more. When the above experiments were combined, in any of the examples of the present invention, an AlN plate joined with a thick copper plate was free of cracks and had no peeling of the copper plate. The amount of warpage was as small as 45 μm or less, and did not hinder the mounting of the semiconductor chip. These are considered to be because the stress was alleviated by the solder layer or the underlying copper plate, and the residual stress due to bonding was reduced. Further, the peel strength is 40 N /
mm ² or more, which is high, and suitable as a substrate for a semiconductor device, believed could reliable ceramic substrate.

In particular, it is surprising that the reliability is high even for a copper plate as thick as 5 mm, and the warpage tends to be almost saturated. It is expected to be a very promising substrate for power devices for use. In the above experiment, AlN was exemplified as the nitride ceramic, but the same effect was obtained with nitride ceramic such as silicon nitride or a mixture of AlN and boron nitride without being limited to AlN.
Also, the silver-copper-titanium brazing material containing 2% by weight of titanium, 70% by weight of silver, and 28% by weight of copper has been exemplified as the active metal brazing material, but instead of titanium, an active metal such as zirconium or hafnium is used. The weight ratio is not limited to this, and if titanium is used, the same effect can be obtained at 0.5 to 5% by mass. Although only the example in which the copper plate 2 is joined to only one side of the AlN plate 1 is shown, the copper plate 2 may be joined to both sides.

[0049]

As described above, according to the present invention, a brazing material layer containing an active metal is formed on a nitride ceramic plate, and the brazing material layer and the copper plate are joined by soldering. Conventionally, the board and the thin underlying copper sheet are joined by a copper-based, silver-based, or copper-silver-based brazing filler metal layer containing an active metal, and the underlying copper sheet and the copper sheet thicker than the underlying copper sheet are joined by soldering. The problem of the nitride ceramics substrate using nitride ceramics, which was difficult to join with the copper plate, was solved, and a highly reliable substrate was realized. The nitride ceramic plate and the thin base copper plate may be joined by a direct joining method, and the base copper plate and a copper plate thicker than the base copper plate may be joined by solder.

Accordingly, it is possible to realize a semiconductor device such as a transistor module having high thermal resistance and excellent durability against thermal shock and thermal history, with low thermal resistance using aluminum nitride, silicon nitride, or the like having high conductivity. Because it can be applied to thick copper plates, it contributes to the spread and development of power modules, especially for electric power.
The economic effect is great.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an AlN substrate bonded to a copper plate according to the method of Experiment 1.

FIG. 2 is a cross-sectional view of an AlN substrate bonded to a copper plate according to the method of Experiment 2.

FIG. 3 is a cross-sectional view of an AlN substrate to which a copper plate has been bonded by the method of Experiment 3.

FIG. 4 is a cross-sectional view of an AlN substrate bonded to a copper plate by an active metal method.

FIG. 5 is a cross-sectional view of an AlN substrate bonded to a copper plate by a direct bonding method.

[Explanation of symbols]

 Reference Signs List 1 AlN plate 2 Copper plate 3 Solder layer 4 Brazing material layer 5 Base copper plate 6 Eutectic layer

Claims (8)

[Claims] 1. A nitride ceramic substrate comprising a nitride ceramic plate and a copper plate joined to each other, wherein the nitride ceramic substrate has a solder layer between the nitride ceramic plate and the copper plate. 2. A nitriding method comprising forming a copper-based, silver-based, or copper-silver-based brazing material layer containing an active metal on a nitride ceramic plate, and joining the brazing material layer and the copper plate by soldering. Object ceramic substrate. 3. A nitride ceramic plate and a base copper plate are joined by a copper-based, silver-based, or copper-silver-based brazing material layer containing an active metal, and the base copper plate and a copper plate thicker than the base copper plate are soldered. A nitride ceramics substrate, characterized by being joined by: 4. The thickness of a base copper plate is 0.03 to 0.15 mm.
4. The nitride ceramic substrate according to claim 3, wherein 5. The nitride ceramic substrate according to claim 2, wherein the active metal in the brazing material layer is any one of titanium, zirconium and hafnium. 6. A nitride ceramics substrate, wherein a nitride ceramics plate and a base copper plate are bonded by a direct bonding method, and the base copper plate and a copper plate thicker than the base copper plate are bonded by soldering. 7. The base copper plate has a thickness of 0.03 to 0.15 mm.
7. The nitride ceramics substrate according to claim 6, wherein: 8. The nitride ceramic substrate according to claim 1, wherein the nitride ceramic plate is a sintered body containing aluminum nitride or silicon nitride as a main component.