JPH0529509A - Board for semiconductor - Google Patents

Abstract

PURPOSE:To obtain a board for semiconductor of high reliability wherein heat dissipation plates excellent in thermal conductivity are provided and generation of cracks and warps is little. CONSTITUTION:In a board for semiconductor provided with a multilayered board 1 formed of aluminum nitride sintered body, and heat dissipation plates 2a, 2b transmitting the heat generated from a semiconductor element 4 arranged on the multilayered board 1, the heat dissipation plates 2a, 2b are bonded to the multilayered board 1 to be in a unified body, via stress buffering material 3 having a thermal expansion coefficient being intermediate between the heat dissipation plates 2a, 2b and the multilayered board 1. The heat dissipation plates 2a, 2b are made of copper, and the thermal expansion coefficient of the stress buffering material 3 is preferably set to be 7X10<-6>-11X10<-6>/ deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate which constitutes an electronic device or the like, and in particular, it has a heat dissipation plate, so that it has excellent heat dissipation characteristics. The present invention relates to a highly reliable semiconductor substrate capable of preventing peeling.

[0002]

2. Description of the Related Art Conventionally generally used semiconductor substrates are formed by laminating a plurality of sheets of alumina (Al ₂ O ₃ ) green sheet as an insulating material on which desired circuit patterns and the like are printed. It further comprises a fired multilayer substrate and a heat radiating plate for rapidly transmitting heat generated from the semiconductor IC chips arranged on the multilayer substrate to a cooling unit such as a heat sink. As the heat dissipation plate, a Cu / W alloy obtained by alloying 10% to 20% Cu (copper) in tungsten (W) is used, and the thermal expansion coefficient of this Cu / W alloy is almost equal to that of alumina (Al ₂ O ₃ ) is set equal to. Therefore, even when a Cu / W alloy heat dissipation plate is integrally joined to the multilayer substrate by brazing or when the semiconductor chip generates heat during the operation of the electronic device, the multilayer substrate is cracked or peeled due to thermal stress. There are few things.

By the way, in recent years, there has been a strong demand for higher speed, smaller size, and higher integration and performance of electronic devices and power devices using semiconductors. For example, a high speed (ECL) ceramic multilayer substrate having an operating speed of about 50 to 100 ns has been developed. For semiconductor substrates that are becoming mainstream and are used in bipolar devices that consume a large amount of power and generate a large amount of heat, there is a demand for a thermal design that allows the heat generated from the semiconductor chips to be more efficiently discharged to the outside of the system. .

[0004]

However, although alumina (Al ₂ O ₃ ) generally used as a conventional ceramic material for multilayer substrates has excellent electrical and mechanical properties, it has a high thermal conductivity. (K) is 17W /
Since it has a low difficulty of about m · k, it is not suitable for a device that consumes a large amount of heat and has a high power consumption at a high speed. Therefore, there is a case where beryllia (BeO) or aluminum nitride (AlN), which has an extremely high thermal conductivity as compared with alumina and is excellent in heat dissipation, is used.

However, beryllia has a problem because it emits a toxic gas in the raw material preparation process, and as an alternative material, it has a thermal conductivity almost equal to that of BeO, and an aluminum nitride sintered body having a particularly excellent thermal conductivity. Is attracting attention.

However, when a conventional heat dissipation plate made of a Cu / W alloy is brazed to this aluminum nitride sintered body, the aluminum nitride multilayer substrate tends to crack or the heat dissipation plate is largely warped. There is. That is, the conventional Cu / W alloy heat dissipation plate is set to have the same thermal expansion coefficient as that of alumina, and when bonded to an aluminum nitride multilayer substrate, the thermal expansion coefficients of both members are greatly different. However, thermal stress is generated, which causes cracks and warpage.

When the content of Cu is set to about 8% or less in order to reduce the difference in thermal expansion, bonding can be performed without cracking, but the thermal conductivity is sharply reduced. There is a point.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a highly reliable semiconductor substrate provided with a heat dissipation plate having excellent thermal conductivity and having few cracks and warps. To aim.

[0009]

In order to achieve the above object, the present invention provides a multilayer substrate formed of an aluminum nitride sintered body and a heat dissipation plate for transmitting heat generated from a semiconductor element arranged on the multilayer substrate. In the provided semiconductor substrate,
The heat dissipation plate is integrally joined to the multilayer substrate via a stress buffering material having a thermal expansion coefficient intermediate between the heat dissipation plate and the multilayer substrate.

Further, it is preferable that the heat dissipation plate is made of copper and the thermal expansion coefficient of the stress buffer material is set to 7 × 10 ^{−6 to} 11 × 10 ⁻⁶ / ° C.

In the present invention, the multilayer substrate is formed by alternately stacking a plurality of aluminum nitride sintered bodies as an insulating layer and a metallized layer, and has a thermal conductivity K of 170 W / m.multidot.
k or more, and the coefficient of thermal expansion in the temperature range from room temperature to 500 ° C. is 5 to 6 × 10 ⁻⁶ / ° C. A metal heat dissipation plate is integrally bonded to the multilayer substrate via a stress buffering material to manufacture a semiconductor substrate.

The stress buffering material is provided to relieve stress caused by the difference in thermal expansion amount between the multilayer substrate and the heat sink, and is made of a material having a coefficient of thermal expansion intermediate between the multilayer substrate and the heat sink. To be done.

On the other hand, the heat dissipation plate has a thermal conductivity of 200.
~ 280 W / m · K and high heat dissipation with a thickness of 0.5 ~
It is advisable to use a product formed by punching out an oxygen-free copper (OFC) plate of about 3 mm. Then, a heat dissipation plate made of copper (coefficient of thermal expansion α ₁ = 16.7 × 10 ^{−6 to} 20 × 10 ⁻⁶ / ° C.) and a multilayer substrate made of aluminum nitride (coefficient of thermal expansion α ₃ = 5 × 1)
0 ^{-6 to} 6 x 10 ^-6 / ° C), the thermal expansion coefficient α ₂ of the stress buffer material is 7 x 1 which is an intermediate value between the _two.
It is recommended to set it in the range of 0 ^{-6 to} 11 x 10 ^-6 / ° C.

As a concrete material of the stress buffer, for example, iron 53%, nickel 28%, cobalt 18% are contained,
Kovar alloy with the same coefficient of thermal expansion as glass (coefficient of thermal expansion 4-5 × 10 ^-6 / ° C), nickel steel containing 42% of nickel (coefficient of thermal expansion 7.9 × 10 ^-6 / ° C) or Cu-W , A Cu-Mo clad material may be used. In particular, by using a clad material having a three-layer structure in which a Cu plate having the same coefficient of thermal expansion is laminated on both surfaces of a W or Mo plate as a core material as a joining material as a stress buffer material, the stress buffer material itself warps due to temperature change. Can be prevented.

[0015]

According to the semiconductor substrate having the above structure, since the heat sink is integrally bonded to the multilayer substrate through the stress buffer material having a coefficient of thermal expansion that is intermediate between the heat sink and the multilayer substrate, the temperature change is prevented. The accompanying displacement of the heat sink and the multilayer substrate due to thermal expansion is restrained by the stress buffer material, and the stress of the heat sink acting on the multilayer substrate can be relieved significantly.
Therefore, when joining the heat sink to the multi-layer substrate, cracks and warpage are less likely to occur in the multi-layer substrate,
A semiconductor substrate having high reliability can be obtained.

Particularly, it becomes possible to solder-bond a heat dissipation plate having excellent heat dissipation characteristics to a multi-layer substrate without damaging the characteristics of the aluminum nitride substrate having a high thermal conductivity and without causing cracks or the like. It becomes possible to deal with a bipolar element which is faster and generates a large amount of heat.

[0017]

Embodiments of the present invention will now be described with reference to the accompanying drawings. 1 and 2 are a sectional view and a plan view, respectively, showing an embodiment of a semiconductor substrate according to the present invention, and FIG. 3 is a plan view showing an example of the shape of a stress buffer material used in each embodiment.

Example 1 100 aluminum nitride multilayer substrates 1 used in the semiconductor substrates of the examples shown in FIGS. 1 and 2 were manufactured in the following steps.

That is, a powder containing AIN raw material powder and 3% by weight of yttrium oxide (Y ₂ O ₃ ) as a normal pressure sintering aid was slurried to obtain a slurry. Next, after molding the obtained slurry into a green sheet (GS) with a thickness of 0.7 mm by the doctor blade method, a large number of blanks are punched out so that one side is 53 mm and a square shape is formed, and further a wiring pattern is printed. Wiring parts such as electrode pads and wire bonding pads were printed with a conductive paste mainly composed of tungsten (W).

Then, a plurality of green sheets are integrally laminated by thermocompression bonding to form a laminated body having a thickness of 3 mm, and after degreasing,
Sintering was carried out by heating in an N ₂ gas atmosphere at a temperature of 1800 ° C. for 6 hours to obtain a sintered body having a square shape with a side of 42 mm and a thickness of 2 mm.

On the other hand, oxygen-free copper (OFC) having a thickness of 3 mm was punched out to prepare a square heat radiating plate 2a having one side of 23 mm, containing 42% nickel and having a coefficient of thermal expansion of 7.9 × 10 ^{−. A} 2.5 mm thick Ni steel having a thickness of ⁶ / ° C. was punched out to prepare a large number of square frame-shaped stress buffer materials 3 having a width W of 5 mm and one side of 23 mm as shown in FIG.

Here, the width W of the stress buffer material 32 is preferably about 3 to 5 mm. If the width W is less than 3 mm, the stress buffering effect is insufficient, while if the width W exceeds 5 mm, cracks and warpage are likely to occur. Further, as shown in FIG. 3, a haunch h and a chamfer c may be formed at the inner and outer peripheral corners of the stress buffer material 3. The haunch h and the chamfer c can prevent the generation of radial cracks starting from the portion.

Next, after the LSI circuit element (semiconductor element) 4 is directly bonded to the heat sink 2a, the heat sink 2a and the stress buffer 3a are further formed on the peripheral edge of the hollow portion of the multilayer substrate 1 to form a metallized layer. (Metalized layer) 5 Silver brazing material 6 on top
Was joined using. The temperature at the time of joining was set to 800 to 850 ° C. Then, when the heat dissipation plate 2a is joined, the multilayer substrate 1
Each semiconductor substrate was observed with a metallographic microscope with a magnification of 300 times and a scanning electron microscope (SEM) with a magnification of 2000 times in order to measure the rate of occurrence of cracks and warpage.

A thermal shock test (TCT) of 500 cycles was performed on each semiconductor substrate. The test condition is -5
The operation of holding each of the three temperatures of 5 ° C., room temperature (RT) and 150 ° C. for 10 minutes was set as one cycle. In addition, a thermal shock test for one cycle was performed in which the temperature was raised from room temperature (RT) to 450 ° C. and held for 10 minutes, and then returned to room temperature (RT). The rate of warpage of the heat sink 2a was counted and the results shown in Table 1 were obtained.

[0025] Except for setting Example 2 Example thickness 1.5mm oxygen-free copper as a 2 (OFC) that was prepared radiating plate 2b by punching a plate, and the temperature at the time of bonding to from 400 to 460 ° C., A semiconductor substrate was manufactured under the same conditions and processes as in Example 1. Then, in the same manner as in Example 1, the occurrence rates of cracking and warpage were measured during joining and after each thermal shock test, and the results shown in Table 1 were obtained.

Comparative Examples 1-2 As Comparative Examples 1-2, Examples were carried out except that the heat dissipation plates 2a and 2b were directly brazed to the metallized layer 5 of the multilayer substrate 1 without interposing the stress buffering material 3. A large number of semiconductor substrates having exactly the same dimensions as those of Example 1 and Example 2 were prepared, and the occurrence ratio of cracks and warpage was investigated, and the results shown in Table 1 below were obtained.

[0027]

[Table 1]

As is clear from the results shown in Table 1, in the semiconductor substrates according to Examples 1 and 2, the multi-layer substrate was cracked without damaging the characteristics of the aluminum nitride substrate having high thermal conductivity. It has become clear that the heat sink can be joined to the heat sink without warping or the like, and the heat sink can be mounted on an electronic device or the like that generates a larger amount of heat.

On the other hand, in Comparative Examples 1 and 2, since the difference in thermal expansion between the multilayer substrate and the heat sink is significant, cracks and warps are likely to occur at the time of joining the heat sinks and due to thermal shock, resulting in a decrease in both product yield and reliability. However, it turned out that it could not be put to practical use.

[0030]

As described above, according to the semiconductor substrate of the present invention, the heat sink is integrally bonded to the multilayer substrate through the stress buffer material having a thermal expansion coefficient intermediate between the heat sink and the multilayer substrate. Therefore, the displacement due to the thermal expansion of the heat dissipation plate and the multilayer substrate due to the temperature change is restrained by the stress buffer material, and the stress of the heat dissipation plate acting on the multilayer substrate can be relieved significantly. Therefore, when the heat dissipation plate is bonded to the multilayer substrate, the multilayer substrate is less likely to be cracked or warped, and a highly reliable semiconductor substrate can be obtained.

It is possible to braze a heat dissipation plate having excellent heat dissipation characteristics to a multi-layer substrate without damaging the characteristics of the aluminum nitride substrate having particularly high thermal conductivity, and thus a bipolar device which is faster and has a large heat generation amount. It becomes possible to correspond to.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a semiconductor substrate according to the present invention.

FIG. 2 is a plan view of the semiconductor substrate shown in FIG.

FIG. 3 is a plan view showing an example of the shape of a stress buffer material used in each example.

[Explanation of symbols]

1 Multi-layer board 2a, 2b heat sink 3 stress buffer 4 LSI circuit element (semiconductor element) 5 Metallized layer (metallized layer) 6 silver brazing material

Claims (2)

[Claims] 1. A semiconductor substrate comprising a multilayer substrate formed of an aluminum nitride sintered body and a radiator plate for transmitting heat generated from a semiconductor element arranged on the multilayer substrate, wherein the radiator plate and the multilayer substrate are included. A substrate for semiconductors, wherein the heat dissipation plate is integrally bonded to the multilayer substrate through a stress buffering material having an intermediate coefficient of thermal expansion. 2. The semiconductor substrate according to claim 1, wherein the heat dissipation plate is made of copper, and the thermal expansion coefficient of the stress buffer material is set to 7 × 10 ^{−6 to} 11 × 10 ⁻⁶ / ° C. .