JPH09194254A - Substrate for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an insulating substrate for a power semiconductor module having increased strength and increased heat conductivity. SOLUTION: Silicon carbide is added to alumina by 5-30mass% and a sintering aid such as yttria is further added by 0-10% of the total, amt. of the alumina and silicon carbide to produce the objective ceramic substrate having mechanical strength increased by 10-56% and heat conductivity increased by 15-180%. When the ceramic substrate is made thin, the electric resistance is considerably increased, e.g., by 4 times in the case of 30mass% added silicon carbide.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating substrate for a semiconductor device in which a semiconductor chip is mounted in a power transistor module or the like by soldering, and more particularly, a CBC substrate (C) in which a foil-shaped copper plate is directly bonded to a ceramic substrate.
eramic Bonding Copper Substrate).

2. Description of the Related Art First, FIG. 3 shows a cross section of an example of a power transistor module using a CBC substrate in which a copper plate is directly bonded to a ceramics substrate. In FIG. 3, the power transistor module includes a CBC substrate 2 fixed on a heat-dissipating metal base 1 with solder or the like, and an I mounted on the CBC substrate 2.
A semiconductor chip 3 such as a GBT, an external lead-out terminal 4 whose bent tip portion is solder-connected to a circuit pattern of the surface copper plate 2c of the CBC substrate 2, a terminal block 7 for mutually fixing the plurality of external lead-out terminals 4, and a semiconductor chip 3 and the bonding wire 5 for connecting the circuit pattern to which the bent tip portion of the external lead-out terminal 4 is fixed, the heat radiating metal base 1 and the resin case 6 are fixed by an adhesive agent, and the gel-like resin filled in the internal space thereof. 9 and a sealing resin 8 that closes the resin case 6. Here, the CBC substrate 2 is made of alumina (Al ₂ O ₃ )
Alternatively, with respect to a ceramic substrate (insulating core plate) 2a such as aluminum nitride (AlN), thin copper plates 2b and 2c in a foil shape are formed on both front and back surfaces thereof by a Cu-O eutectic liquid phase which is generated by a reaction between copper and a slight amount of oxygen. Is used as a bonding agent and is directly bonded. A circuit pattern (thick film circuit pattern) is formed on the copper plate 2c on the main surface side (front surface side), and the semiconductor chip 3 is die-bonded thereto.

However, when the above-mentioned CBC substrate is used as a thick-film circuit board on which a power semiconductor chip such as a power transistor module is mounted, there are the following problems. That is, in a semiconductor chip such as a power transistor, a large amount of heat is generated in accordance with an energizing operation, and the heat is conducted to the heat-dissipating metal base 1 via the CBC substrate 2 and then dissipated outside from the heat-dissipating metal base 1. Therefore, the quality of the thermal conductivity of the CBC substrate 2 is an important factor influencing the current capacity of the semiconductor device itself. However, since the CBC substrate 2 has a laminated structure in which the ceramic substrate 2a is used as an insulating base material (core material) and the copper plates 2b and 2c are bonded to it,
Thermal conductivity is relatively low. Here, the ceramic substrate 2a
The thermal conductivity of the alumina and the aluminum nitride used as the material of the is as follows. Alumina: 21 W / (K · m) Aluminum nitride: 180 W / (K · m) Although aluminum nitride has much higher thermal conductivity than alumina, aluminum nitride has a higher material cost than alumina. There are drawbacks. In such a situation, the present inventor tried to suppress the heat transfer resistance to a ceramic substrate made of alumina, which has a low material cost, by reducing the thickness of the substrate as much as possible in order to improve heat dissipation. . However, when the thickness of the ceramic substrate made of alumina raw material is reduced to, for example, about 0.3 mm, the actual strength (resistance to impact) of the substrate decreases,
Based on this, it is clear that when the semiconductor chip (silicon) 3 and the copper plate 2c are bonded and fixed to each other, defects such as cracks and cracks are caused in the thinned ceramic substrate 2a due to the thermal stress caused by the difference in the thermal expansion coefficient of each material. Became. The thermal expansion coefficients of the above materials are listed below. Silicon (semiconductor chip): 4.0 × 10 ⁻⁶ / K Alumina: 7.5 × 10 ⁻⁶ / K Copper: 18.0 × 10 ⁻⁶ / K The present invention has been made in view of the above problems. Therefore, regarding the ceramic substrate mainly made of alumina powder whose raw material cost is low, by improving the material composition, the thermal conductivity and mechanical strength of the raw material are increased, which enables the thinning of the substrate itself. It is an object of the present invention to provide a substrate for a semiconductor device in which heat dissipation can be improved.

In order to solve the above problems, a ceramic substrate for a semiconductor device according to the present invention is
It is characterized by being made of a ceramics sintered body produced by adding silicon carbide to alumina as a main component. Such a substrate for a semiconductor device has an improved thermal conductivity as compared with a ceramic substrate made of a simple substance of alumina, and the mechanical strength, especially the bending strength is significantly increased. Here, it is desirable that the mass ratio of alumina be 70% or more and 95% or less, and the mass ratio of silicon carbide be 5% or more and 30% or less. With such a range, not only the thermal conductivity and mechanical strength, but also the volume resistivity can be kept large.
Further, 0.5 to 10% of at least one of yttria, calcia, magnesia, ceria, manganese oxide, and silica is contained. With these additives in this range, the sintering of silicon carbide dispersed in alumina is promoted, so that the firing temperature of the ceramics substrate can be kept low and an alumina substrate having excellent strength can be obtained. A substrate for a semiconductor device, which is formed by bonding foil-shaped copper plates to the front and back surfaces, and in particular, is formed by directly bonding circuit-configured foil-shaped copper plates. By doing so, by thinning the substrate itself, it becomes a CBC substrate excellent in heat dissipation as a substrate of a semiconductor device.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. Note that the mixing ratios shown below are expressed in mass%, but the same applies to weight%. First, a method for manufacturing a ceramic substrate will be described. First, alumina (Al ₂ O ₃ ) [eg Sumitomo Chemical Al-M43] with silicon carbide (SiC) having an average particle size of 0.4 to 0.5 μm [eg Showa Denko] and yttria (Y) as a sintering aid. ₂ O
₃ ) [For example, 99.9% manufactured by Shin-Etsu Chemical] and the like are added and pulverized and mixed, and further 8% polyvinyl butyral (hereinafter PVB) as a binder, toluene as a solvent,
After adding 50% xylene mixed solution and 2% dioctyl phthalate (DOP) as a plasticizer and kneading for about 20 hours,
A green sheet is obtained by forming a sheet by the doctor blade method. Next, after pressing the green sheet into a predetermined shape by pressing, the green sheet is subjected to 70% in an oxidizing atmosphere.
The binder was removed from the molded body by heating to 0 ° C. and heating.
Furthermore, the molded body is heated in an inert atmosphere of nitrogen or argon containing nitrogen at a temperature of 1550 ° C. to 1750 ° C.
Is fired to obtain a ceramic substrate sintered body having a plate thickness of about 0.3 mm. [Experiment 1] In order to evaluate the mechanical properties of the ceramic substrate produced by adding silicon carbide to alumina as described above, a test piece was prepared by the method described above with the addition amount of silicon carbide being in the range of 0 to 50%. (Plate thickness 0.3 mm, width 26 mm, length 50 mm) was prepared, and a bending strength test was performed on this test piece. In each composition, yttria was added as a sintering aid in an amount of 5% with respect to the total amount of alumina and silicon carbide. FIG. 1 shows the result of this strength test. The horizontal axis represents the amount of silicon carbide added [= silicon carbide / (alumina + silicon carbide)], and the vertical axis represents the bending strength. As can be seen from the figure, as the amount of silicon carbide added increases, the mechanical strength increases more than that of a ceramic substrate (strength about 320 MPa) of alumina alone (the amount of silicon carbide added = 0%), and the maximum is about 510M.
It was confirmed that the value also improved to Pa. The maximum strength composition is about 40%. With respect to 5 to 30% of the amount of silicon carbide added, the increase in mechanical strength is about 10 to 56%. Moreover, when the maximum deflection amount of the test piece of the ceramic substrate with the added amount of silicon carbide of 30% and the test piece of the same size made of alumina alone was examined during the bending test at the distance between fulcrums of 40 mm, the alumina alone was found. The amount of deflection of the test piece of No. 3 was 0.35 mm, while that of the test piece containing silicon carbide was 0.5 mm. Therefore, it can be seen that the addition of silicon carbide not only improves the strength but also makes it a tough ceramic substrate having elasticity. In the range where the amount of silicon carbide added exceeds 40%, the strength sharply decreases. This is because the amount of silicon carbide added is 40%
This is because if it exceeds the above range, the sinterability will be reduced and a dense sintered body will not be obtained. When the amount of silicon carbide added is 40% or more, a decrease in density is recognized in the measurement of bulk density, and insufficient sintering is confirmed. On the other hand, the results of examining the thermal conductivity of these test pieces are shown in FIG. Similarly, the horizontal axis represents the amount of silicon carbide added, and the vertical axis represents the thermal conductivity. From the figure, it can be seen that the thermal conductivity improves as the amount of silicon carbide added increases. The highest thermal conductivity was 40% silicon carbide, and the thermal conductivity was 73 W / (K · m). For 5 to 30% of the amount of silicon carbide added, the increase in thermal conductivity is about 1
5 to 180%. Further, when the content of silicon carbide is 40% or more, the thermal conductivity sharply decreases. This is because, as with the above-mentioned strength, when the content of silicon carbide is 40% or more, the sinterability is deteriorated and a dense sintered body cannot be obtained. Therefore, it was found that, by adding silicon carbide to alumina as the material composition of the ceramic substrate, not only the mechanical strength is improved as compared with the ceramic substrate made of only alumina, but also high thermal conductivity can be obtained in terms of heat conductivity. .
Further, a volume resistivity of the ceramic substrate was measured using a test piece (plate thickness: 0.3 mm) of a ceramic substrate prepared by adding 0 to 50% of silicon carbide to alumina to evaluate mechanical properties. As a result, the volume resistivity decreased as the amount of silicon carbide added increased, but was 10 ¹⁴ Ω · m or more at an amount of 30% or less, which was a practically no problem. From these results of mechanical strength, thermal conductivity and insulating property, it was found that it is generally desirable that the amount of silicon carbide added be 5 to 30% for the alumina ceramic substrate to which silicon carbide is added. It was The 5% yttria added in the above material composition was added as a sintering aid for alumina and silicon carbide, but as a result of experiments, the range of addition amount was 0.5-10.
It turns out that it is better to set it in the range of%. That is,
If the amount of yttria added is less than 0.5%, it becomes difficult for sintering to proceed, and a heating temperature of 1750 ° C. or higher is required for sintering the substrate, which makes it difficult to manufacture the substrate. Also, if the addition amount exceeds 10%, the shrinkage rate of the ceramic substrate,
Large variations in strength will occur. It has been confirmed that, in addition to yttria, one or more kinds of calcia, magnesia, ceria, manganese oxide, and silica can be added to obtain the same effect as sintering. Example 1 A ceramic substrate (plate thickness 0.3 m
m) was prepared, and tough pitch electrolytic copper having a plate thickness of 0.3 mm was superposed on both front and back surfaces of the silicon carbide-added ceramics substrate, and the temperature was 1050 to 1070 ° C.
The ceramic substrate and the copper plate were directly bonded by heating for 0 minutes to produce a CBC substrate. A transistor module having a cross section shown in FIG. 3 was assembled using the obtained CBC substrate. As a comparative example, a plate thickness of 0.63 mm,
C prepared on an alumina substrate of 0.3 mm alumina alone
Similar transistor modules were assembled using the BC substrate, and a mechanical deformation resistance test and an intermittent current test were performed on these. First, in the deformation resistance test, an external force was applied to the heat-dissipating metal base to forcibly deform it, and the amount of deformation until the insulation failure of the substrate was examined. As a result, a ceramic substrate (plate thickness 0.3 m
m) and an alumina substrate with a plate thickness of 0.63 mm having almost the same resistance as alumina, but an alumina substrate with a plate thickness of 0.3 mm was found to have poor insulation with a deformation amount of about half. That is, it was proved that the plate thickness of the ceramic substrate can be practically reduced to about 1/2 by adding an appropriate amount of silicon carbide to alumina. Further, in the intermittent current test, the silicon carbide-added ceramics substrate (plate thickness 0.3 mm) was bonded to the semiconductor plate when the same collector loss was given, as compared with the alumina substrate having a plate thickness 0.63 mm ( It was confirmed that the temperature rise ΔTj in the portion 2c) was reduced by about 40% and the intermittent current resistance was improved four times. As you can see from this,
The ceramic substrate with silicon carbide added to alumina is
It has superior mechanical properties compared to a substrate made of alumina alone,
By improving the thermal conductivity of the substrate itself and making it thinner, it has been found that it can be used as a substrate for semiconductor devices with high heat dissipation. Although the ceramic substrate has a plate thickness of 0.3 mm in the above-described examples, the sheet forming method can form a substrate having a plate thickness of 0.05 to 1 mm. A binder having a thickness of 1 mm or more is formed by adding a binder such as polyvinyl alcohol PVA to the raw material powder, wet-mixing, and dry granulating with a spray dryer, and press-molding using the granulated powder. It is also possible.

As described above, according to the present invention,
By using a ceramic substrate obtained by adding silicon carbide to alumina and firing it at a high temperature as the ceramic substrate of the CBC substrate, mechanical strength can be significantly enhanced as compared with the conventional alumina substrate of simple alumina, and further high thermal conductivity can be obtained. can get. Therefore, it is possible to make the ceramic substrate thinner in practical use. Further, by controlling the content of silicon carbide with respect to alumina, it is possible to form a ceramic substrate having excellent insulating properties. In particular, the mass ratio of alumina is in the range of 70 to 95%, and the mass ratio of silicon carbide is 5 to 3
In the range of 0%, one or more of yttria, calcia, magnesia, ceria, manganese oxide, and silica added in an amount of 0.5 to 10% with respect to the total amount of alumina and silicon carbide has a practically excellent mechanical property. A ceramic substrate having high strength and high thermal conductivity can be obtained, and it is excellent as a substrate for a semiconductor device in terms of strength, thermal conductivity, insulation and low cost. As a result, a CBC substrate having a high heat dissipation property can be obtained as a substrate for a semiconductor device, and particularly when applied to a substrate such as a power transistor module, miniaturization of the semiconductor device,
The cost can be reduced and the current capacity can be increased. Since this ceramic substrate has excellent mechanical properties as a single substrate, it has the same effect when applied to a hybrid IC circuit substrate, an IC package, or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of silicon carbide added and the bending strength of a substrate.

FIG. 2 is a diagram showing the relationship between the amount of silicon carbide added and the thermal conductivity of the substrate.

FIG. 3 is a sectional view of a transistor module using a CBC substrate.

[Explanation of symbols]

 1 Heat Dissipation Metal Base 2 CBC Substrate 2a Ceramics Substrate 2b, 2c Copper Plate 3 Semiconductor Chip 4 External Lead-out Terminal 5 Bonding Wire 6 Resin Case 7 Terminal Block 8 Sealing Resin 9 Gel Filling Material

Claims (4)

[Claims] 1. A substrate for a semiconductor device, comprising a ceramics sintered body produced by adding silicon carbide to alumina as a main component. 2. The substrate for a semiconductor device according to claim 1, wherein the material composition ratio of the ceramics sintered body is in the range of alumina (mass) 70 to 95% and silicon carbide 5 to 30%. . 3. At least one of yttria, calcia, magnesia, ceria, manganese oxide or silica is used in an amount of 0.5 to 10 with respect to the total amount of alumina and silicon carbide.
%, The semiconductor device substrate according to claim 1 or 2. 4. The substrate for a semiconductor device according to claim 1, wherein a foil-shaped copper plate is bonded to the front and back surfaces of the ceramic sintered body.