JPH1117066A - Substrate for mounting semiconductor chip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the strain at the junction interface to hold good radiation characteristics, by adding ceramics or metal grains having a less thermal expansion to Cu. SOLUTION: A substrate is composed of at least two plates having different thermal expansion coefficients i.e., a sintered plate composed of Cu or Cu alloy grains 20-70 vol.% and at least one kind of grains selected among ceramics and metals having smaller thermal expansion coefficients than that of Cu and ceramic plate. The metal is selected among Mo, W and Si. This reduces the thermal expansion coefficient difference between the ceramics and the metal for the metal substrate, and hence reduces the strain at the junction interface to hold good radiation characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a substrate for mounting a semiconductor chip, and more particularly to a heat sink.

[0002]

2. Description of the Related Art As a package structure in a power semiconductor device, an Al ₂ O ₃ ceramic plate, Mo
A structure in which a layer and a silicon semiconductor are joined by brazing is known. In these package structures, it is required to improve the heat radiation characteristics of the substrate material in order to cope with the increase in the amount of heat generated by the increase in the density, speed, and output of the semiconductor device. Bonding structures are also known.

The coefficients of thermal expansion and thermal conductivity of copper, AlN, and Al ₂ O ₃ are as follows. Coefficient of thermal expansion (10 ⁻⁶ / K) Thermal conductivity (W / mK) Cu 16.5 398 AlN 5.1 200 Al ₂ O ₃ 7.2 20

[0004]

In a joined body of a ceramic and a metal-based substrate subjected to repeated thermal loads, strain and stress are generated near the interface due to the difference in the thermal expansion coefficients of the respective materials. Damage occurs. Therefore, a metal-based substrate needs to have a small difference in thermal expansion from ceramics and high thermal conductivity in order to improve heat radiation characteristics. Therefore, an object of the present invention is to provide a metal-based substrate that can meet such a demand.

[0005]

In order to achieve the above object, the present invention provides a semiconductor chip mounting board comprising at least two boards having different thermal expansion coefficients joined to each other, wherein the at least two boards have different thermal expansion coefficients. , Copper or copper alloy and 20-70
A substrate for mounting a semiconductor chip, comprising: a volume% of a sintered material plate comprising at least one kind of particles selected from the group consisting of ceramics and metals having a smaller coefficient of thermal expansion than Cu; and a ceramic plate. I will provide a. The metal-based substrate of the present invention is obtained by adding ceramics and metal particles having low thermal expansion to copper as an additive in order to reduce the difference in thermal expansion between ceramics and metal (radiator plate).

[0006] Explaining the case where the ceramic particles in the composite material are the additive, the copper particles have a coefficient of thermal expansion α _cu , while the ceramics have a coefficient of thermal expansion α _cer.
(Α _cer <α _cu ). In this case, when the composite material satisfies the following premise, its thermal expansion coefficient is expressed as α _comp = α _cu · v _cu + α _cer · v _cer (where v _cu is the volume of copper) Rate, v _cer is the volume fraction of the ceramic). Therefore, α _comp <α _cu . However, it is necessary that the ceramics and the copper particles are sufficiently fine and form a sintered material having extremely small pores, which are sufficiently uniformly dispersed in each other. In a sintered material that does not satisfy this requirement, if the ceramic and copper particles are locally segregated or the particles are coarse, distortion occurs between the copper particles and the ceramic particles and uniform expansion of the entire composite material occurs. Not shown. Also, if the pores are very large or large, the material will exhibit significantly less thermal expansion than the above equation since the thermal expansion of each material will be spent on pore reduction.

The copper or copper alloy preferably has a particle size of 1 to 100 μm. As a copper alloy, P, which is a deoxidizing element and generates a liquid phase during sintering with ceramic to promote sintering, can be added. In addition, Sn, Pb,
Zn and the like can also be added. These additional elements can be appropriately added in the range of 1 to 20% by weight. These Sn, Pb, and Zn also have an effect of not generating vacancies, especially when mixed with copper powder in a metal form.

As ceramics composited with copper (alloy), in addition to the above-mentioned AlN and Al ₂ O ₃ , ceramics having a thermal expansion coefficient of 3.7 × 10 ^-6 and a thermal conductivity of 270 W / mK are used.
iC can also be used. As shown in these examples, the ceramic has a coefficient of thermal expansion of 1/2 or less of Cu and 10 ^-6 and a thermal conductivity of 20 W / mK.
The above compounds or intermetallic compound-based substances can be used. Next, as a metal, the coefficient of thermal expansion is 4.2 ×
10 ⁻⁶ and a thermal conductivity of 115.50 W / mK
i, the coefficient of thermal expansion is 5.1 × 10 ^-6 and the thermal conductivity is 1
Mo of 50 W / mK, a thermal expansion coefficient of 4.3 × 10 ⁻⁶ , and a thermal conductivity of 163 W / mK can be used. However, since Si easily forms an alloy with copper during sintering, it is necessary to increase the particle size so that the particle form is maintained after sintering. The proportion of these metals or ceramics must be 20 to 70% by volume. If this ratio is less than 20%, the effect of lowering the thermal expansion coefficient is small, and if it exceeds 70%, the thermal conductivity is reduced. A preferred ratio is 30 to 60% by volume. Ceramics and metals preferably have a particle size of 1 to 100 μm.

Next, a method for producing a sintered material will be described. First, a metal powder and a ceramic powder are mixed. When a copper alloy powder is used, the method of preparing the copper powder is as follows: (a) a method of preparing a powder having a final alloy composition; How to
(C) a method of preparing a copper powder, a pre-alloyed copper powder (Cu-Sn alloy powder having a higher Sn content than the final composition), a metal powder such as Sn, and alloying during sintering; A method of preparing electroless-plated copper alloy powder or the like can be adopted. The degree of uniform dispersion of copper (alloy) particles and particles of ceramics and the like can be determined by mixing copper (alloy) particles and particles of ceramics and the like having substantially the same particle size in a V-type blender for 30 minutes or more and in a ball mill for 10 minutes or more. Can be realized.

The sintering can be carried out by a usual sintering method in which the compacting and the sintering are performed separately. However, it is preferable to repeat the compacting and the sintering. The compacting pressure is 4 to 8 ton /
cm ^2, after sintering is carried out at a pressure of 1~10ton / cm ^2, to enhance the sintering times together with pressure, prior to final sintering 6-1
Preferably, it is 0 ton / cm ² . Although a desired high density can be obtained by a sintering method in a broad sense such as a hot press method or a hot extrusion method, a sufficiently high density can be obtained by a normal sintering method. However, when the metal plate is placed on the upper and lower surfaces or on one surface and sintering is performed integrally, temporary sintering is performed before compacting, so that the metal plate is less likely to peel off. Sintering temperature is 800
~ 950 ° C is preferred. Here, the above (b) to (d)
Adopting has the effect of promoting the sintering by generating a liquid phase at a temperature lower than the sintering temperature. The generated liquid phase is almost alloyed with the copper particles at the sintering temperature, and a part thereof remains at the particle interface.
The compacting performed after sintering reduces the sintering pores to increase the density, and also increases the bonding surface between the copper alloy particles and the ceramic particles to enhance the reaction between these particles in the next sintering, and the copper alloy particles Enhance the role of binding ceramic particles. By such a method, a sintered body having a density of 95% or more of the theoretical density can be obtained.

The difference in thermal expansion between the two plates can be further reduced by increasing the ceramic content ratio v _cer on the side where the sintered plate contacts the ceramic plate. In order to change the ceramic content ratio v _cer in the thickness direction, powders having different v _cers are sequentially filled at the time of powder filling, or the ceramic content ratio V _{cer is obtained by} pre-sintering.
However, it is possible to adopt a method in which a plurality of plates are prepared from different plates, these are pressed or hot pressed, and then sintered.

Next, the method of using the sintered material according to the present invention will be described. The sintered material of the present invention is made of Al
It is used by being bonded to a ceramic plate such as N, Al ₂ O _3, etc., and it can be preferably used by exposing one side as a heat sink instead of a conventional copper plate. The use of a metal plate such as pure copper integrally sintered on the surface of the sintered plate further improves the heat radiation of the heat radiation surface. Further, there is no chipping of the sintered material and the material strength is improved. It is desirable that the thickness of the sintered material be in the range of 1 to 10 mm. When the metal plate is fixed to one or both surfaces of the sintered material, the thickness of the metal plate is 10% or less of the total thickness when the amount of the ceramic contained in the sintered material is 20% by volume. 50% of the total thickness in the case of volume%
The following is desirable. Hereinafter, the present invention will be described in more detail with reference to examples.

[0013]

EXAMPLES Copper powder (average particle size 30 μm), copper-phosphorus alloy powder (average particle size 10 μm), tin powder (average particle size 15 μm)
m), lead powder (average particle size 20 μm), zinc dust powder (average particle size 15 μm), SiC powder (average particle size 20 μm), A
1N powder (average particle diameter 10 μm), Al ₂ O ₃ powder (average particle diameter 20 μm), W powder (average particle diameter 20 μm), Mo powder (average particle diameter 20 μm), Si powder (average particle diameter 30 μm)
m) was blended to have the composition shown in Table 1 and mixed for 30 minutes in a V-type blender. The ratio (V _f ) of the ceramic particles was calculated based on the apparent density of each powder measured at the tap density. The mixed powder is packed into a stainless steel bottomed concave portion, and the surface is coated with a copper plate (0.03-
0.3 mm). Then 800 ° C in a hydrogen stream
800 at 6t / cm followed powder in ² pressure hydrogen stream; in presintering; 1~2t / cm intermediate sintered at 800 ° C. in a hydrogen stream in following the intermediate powder in ^second pressure Final sintering at <RTIgt; The obtained sintered plate had a thickness of 2 mm and a density ratio of 96%. The coefficient of thermal expansion of the sintered material is 20-30.
Table 1 shows the results measured at 0 ° C. The coefficient of thermal expansion was measured using a sample obtained by cutting and removing the upper and lower copper plates. FIG. 2 shows the results of measuring the bending strength of each of the sample with the copper plate attached (B) and the sample with the copper plate removed (A). .

[0014]

[Table 1] Copper (alloy) particles Ceramic particles Thermal expansion coefficient Kind Ratio (V _f )% (× 10 ⁻⁶ / K) Pure copper SiC 30 12.7 Pure copper SiC 50 10.4 Pure copper SiC 64 8.7 Cu-5% Sn SiC 50 10.8 Cu-10% Sn SiC 50 11.5 Cu-5% Pb SiC 50 10.9 Cu-10% Pb SiC 50 11.6 Cu-20% Zn SiC 50 11.7 Cu-5% Zn SiC 50 10.7 Cu-0.1% P SiC 50 10.7 Pure copper AlN 50 11.0 Pure copper Al ₂ O ₃ 50 11.8 Pure copper W 50 10.5 Pure copper Mo 50 11.1 Pure copper Si 50 10.7

As shown in Table 1, a value lower than the thermal expansion coefficient of pure copper of 16.5 × 10 ⁻⁶ is obtained.

FIG. 1 shows the calculated values of the thermal expansion coefficient of the SiC composite copper according to the formulas and the measured values, which show that they are in good agreement. In addition, the measured value is slightly higher than the calculated value, and the difference increases as the SiC volume ratio (V _f ) increases. This is because the SiC / Cu joint interface has a defect and becomes an incomplete interface. It is thought that it is.

The bending strength of a sintered body of pure copper-50% SiC and a plate obtained by integrally sintering pure copper-50% SiC powder into pure copper were measured. Figure 2 shows the result.
It was shown to. It became clear that the bending strength was improved in the sintered body having the copper plate. Also, no defects such as chipping of SiC were observed.

[0018]

When the copper (alloy) -ceramic sintered material provided by the present invention is used as a substrate for bonding with ceramics, the distortion generated at the bonding interface can be reduced, and good heat conduction of copper can be achieved. The heat radiation characteristics can also be kept good depending on the rate.

[Brief description of the drawings]

FIG. 1 is a diagram in which measured values are added to a calculated value graph of a SiC volume ratio (V _f ) and a thermal expansion coefficient of a Cu—SiC sintered body.

FIG. 2 is a diagram in which a cross section of a sintered plate is added to a graph showing the bending strength of the material of the present invention.

Claims (9)

[Claims] 1. A semiconductor chip mounting substrate formed by joining at least two plates having different coefficients of thermal expansion, wherein said at least two plates are made of copper or copper alloy particles and 20 to
A semiconductor chip comprising 70% by volume of a sintered material plate made of at least one kind of particles selected from the group consisting of a metal and a ceramic having a lower coefficient of thermal expansion than Cu, and a ceramic plate. Mounting substrate. 2. The semiconductor chip mounting substrate according to claim 1, wherein said metal is a metal selected from the group consisting of Mo, W and Si. 3. The ceramic material contained in the sintered material is at least one selected from the group consisting of SiC, AlN and Al ₂ O _3.
Or the substrate for mounting a semiconductor chip according to 2. 4. The method according to claim 1, wherein the plate of the sintered material is manufactured by a sintering method in which pressing and heating are performed separately.
The substrate for mounting a semiconductor chip according to the above item. 5. The substrate for mounting a semiconductor chip according to claim 1, wherein the plate of the sintered material is a heat sink having one surface exposed. 6. The method according to claim 1, wherein said copper alloy contains 1 to 20% by weight of P, P
The substrate for mounting a semiconductor chip according to claim 1, further comprising at least one of b, Zn, and Sn. 7. The sintered material plate is made of copper powder, P, Pb,
7. The substrate for mounting a semiconductor chip according to claim 1, wherein a powder comprising at least one of Zn and Sn and a ceramic powder are sintered. 8. The method according to claim 1, wherein the ceramic plate is made of AlN or Al.
A semiconductor chip mounting board according to any one of claims 1 consisting of ₂ O ₃ to 7. 9. The semiconductor chip mounting substrate according to claim 1, wherein the sintered material has a metal plate fixed to one or both surfaces thereof.