Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With provision for cooling the housing or its contents
Reexamination Certificate
2000-02-04
2003-01-14
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With provision for cooling the housing or its contents
C257S706000
Reexamination Certificate
active
06507105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a member for semiconductor devices comprising an aluminum-silicon carbide-based composite alloy, to a method for producing it, and to a semiconductor device comprising the member.
2. Description of the Prior Art
The recent market demand for high-speed operation, large-scale integration semiconductor devices is greatly increasing. Therefore, the market has required much more increase in the thermal conductivity of heat-radiating substrates to be mounted with semiconductor chips, for the purpose of more efficiently removing the heat as generated by semiconductor chips. The market has further required the heat-radiating substrates to have a thermal expansion coefficient that is much nearer to that of the other members to be disposed adjacent to them, for the purpose of minimizing the thermal strain between the substrates and the adjacent members. The thermal expansion coefficient of silicon (hereinafter referred to as Si) and gallium arsenide (hereinafter referred to GaAs) that are generally used for semiconductor chips is 4.2×10
−6
/°C. and 6.5×10
−6
/°C., respectively. The thermal expansion coefficient of alumina ceramics that are generally used for outer frame members for semiconductor devices is around 6.5×10
−6
/°C. Therefore, it is desired that the thermal expansion coefficient of the substrates is near to those values.
With the recent increasing expansion of the application area of electronic appliances, the application area of semiconductor devices is being much more diversified. Above all, the same shall apply to the field of semiconductor power devices such as high-power AC conversion devices and frequency conversion devices. The quantity of heat from the semiconductor chips of those devices is from a few times to tens times that from semiconductor memories and microprocessors (in general, the former is, for example, tens W). Therefore, the requirements noted above for the heat-radiating substrates for those devices are extremely severe. Accordingly, the basic structure of the substrates may be, for example, as follows: First, Si semiconductor chips are mounted on a first heat-radiating substrate of an electricity-insulating aluminum nitride (hereinafter referred to as AlN in a simple manner) ceramic substrate with high thermal conductivity. Next, a second heat-radiating substrate with higher thermal conductivity of, for example, copper is disposed below the first heat-radiating substrate. Then, this is fitted to a water-cooling or air-cooling heat-radiating system. In that manner, therefore, the structure of the heat-radiating substrates is complicated. In this case, where an AlN ceramic having a thermal conductivity of around 170 W/m·K is used for the first heat-radiating substrate, the second heat-radiating substrate shall have a thermal conductivity of at least 200 W/m·K or more at room temperature, for efficient heat removal from the first substrate. In addition, in that case, the second heat-radiating substrate shall have a low thermal expansion coefficient of at most 10×10
−6
/°C., especially at most 8×10
−6
/°C., in order that its thermal expansion coefficient could be near to that of the AlN ceramic.
Especially in those of the power devices that generate a large quantity of heat in practical operation, the heat-radiating substrates themselves will often be heated at temperatures of 100° C. or higher. As the case may be, therefore, the heat-radiating substrates in them are often required to still have a high thermal conductivity of at least 150 W/m·K at such high temperatures. In addition, the increase in the operation capacity of power devices requires much more efficient heat radiation from them. In that case, the size of the heat-radiating substrates on which semiconductor chips are mounted shall be inevitably enlarged. In this connection, the size of the heat-radiating surface of substrates for personal computers is at most from 20 to 40 mm square or so. As compared with those, for example, the size of the same for some high-power devices with large operation capacity is often over 200 mm square. In such large-sized substrates, it is necessary that the dimension change to be caused by temperature elevation during packaging and practical operation is small. For instance, warp or deformation of substrates, if occurred, gives some gaps between the warped or deformed substrates and radiators or fins, thereby lowering the heat radiativity of the substrates. As the case may be, semiconductor chips mounted on the warped or deformed substrates will be broken. For these reasons, ensuring good thermal conductivity at high temperatures of heat-radiating substrates is one of important themes in the art.
For such substrates, for example, Cu—W-based or Cu—Mo-based composite alloys have heretofore been used. However, the cost of the substrates of those composite alloys is high, since the materials for them are expensive, and, in addition, they are heavy. Recently, therefore, various aluminum (hereinafter referred to as Al in a simple manner) composite alloys have been used for inexpensive and lightweight substrate materials. For example, as one type of those alloys, mentioned are Al—SiC-based composite alloys comprising Al and silicon carbide (hereinafter referred to as SiC in a simple manner) as main components. The materials for the composite alloys are relatively inexpensive, and the composite alloys themselves are lightweight and have high thermal conductivity. In this connection, the density of Al and SiC alone is around 2.7 g/cm
3
and around 3.2 g/cm
3
, respectively, and the thermal conductivity thereof is around 240 W/m·k and around 270 W/m·K, respectively. The thermal expansion coefficient of SiC alone is around 3.5×10
−6
/°C., and that of aluminum alone is 24×10
−6
/°C. Therefore, the thermal expansion coefficient of the composite alloys comprising them could be controlled within a broad range, and the composite alloys are specifically noticed in the art.
Such Al—SiC-based composite alloys and methods for producing them are disclosed in (1) JP-W-1-501489, (2) JP-A-2-243729, (3) JP-A-61-222668, and (4) JP-A-9-157773. The method in (1) comprises melting Al in a mixture of SiC and Al followed by solidifying the mixture through casting. The method in (2) and (3) comprises infiltrating Al melt into the pores of porous SiC. Of those, the method in (3) is a so-called pressure infiltration method, in which the Al melt is infiltrated into the porous SiC under pressure. The method in (4) comprises disposing a compact or a hot-pressed body of SiC and Al in a mold followed by heating it in vacuum therein at a temperature not lower than the melting point of Al for sintering it in liquid phase.
We, the present inventors have previously proposed an Al—SiC-based composite alloy in JP-A-10-335538. This has a thermal conductivity of at least 100 W/m·K, and a thermal expansion coefficient of at most 20×10
−6
/°C., and contains from 10 to 70% by weight of granular silicon carbide. This alloy is obtained according to a sintering method (which comprises preparing a mixed powder originally having the intended compositional ratio of Al—SiC, followed by sintering it). In one preferred embodiment of the alloy, aluminum carbide (hereinafter referred to as Al
4
C
3
in a simple manner) is dispersed in the interface between Al and SiC. For producing the alloy, powdery materials of Al and SiC are mixed in the ratio noted above, and the resulting mixture is compacted, and then sintered in a non-oxidizing atmosphere (in general, in an atmosphere which contains at least 99% by volume of nitrogen gas and has an oxygen concentration of at most 200 ppm, and which has a dew point of not higher than −20° C.) at a temperature falling between 600 and 750° C. According to this method, obtained is the intended composite alloy having a thermal conductivity of at least 180 W/m·K. When the compact is sintered to give th
Fukui Akira
Kawai Chihiro
Suwata Osamu
Takeda Yoshinobu
Yamagata Shin-ichi
Chaudhuri Olik
Louie Wai-Sing
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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