JPS5917973B2 - semiconductor equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, particularly an electrode extraction structure for a high power semiconductor device.

As is well known, in semiconductor devices for high power, the diameter of the wafer becomes large, and when metal electrodes are soldered on both sides of the wafer, as in semiconductor devices for medium to low power,
Due to the difference in thermal expansion coefficient between the wafer and the metal electrode, there is a risk that the wafer itself may be damaged. For this reason, in this type of high-power semiconductor device, metal electrodes are generally pressure-bonded to both or one side of the wafer to compensate for misalignment due to differences in thermal expansion coefficients. FIG. 1 shows a conventional example of this type of flat high-power semiconductor device.

In FIG. 1, each main surface of the silicon wafer 1 has
Aluminum layer 2 to make ohmic contact
.
The locks 5, 5 form a press-contact structure. In the above configuration, when the semiconductor device is energized, it becomes in the same state as when a thermal cycle is applied. D) When the coefficient of thermal expansion of each component metal is 1 for silicon, the coefficient of thermal expansion for molybdenum is approximately twice that.
Copper is about 6 times more expensive, so the upper aluminum layer 2
At the pressure contact surface between the molybdenum plate 4 and the molybdenum plate 4, a slat-like movement occurs as shown in an enlarged view in FIG. That is,
The surface roughness of the molybdenum plate 4 is at most 3 to 5μ, and the surface roughness of the molybdenum plate 45 and the aluminum layer 2 are
Due to the distortion of the silicon wafer 1 and the molybdenum plate 4 themselves, the surface is not in uniform contact with the surface of More and more current is concentrated, and aluminum!
0 Alloying of Ni and molybdenum progresses as shown by code 6, and the forward voltage drop of the device fluctuates from its initial value.
Cracks occur in silicon in highly alloyed areas.

In fact, according to the experience of the inventors, the forward voltage drop fluctuates by about 0.5V after 50 hours of energization, and it has been observed that cracks occur in the silicon. The causes of this have not yet been well investigated, but as mentioned above, the cracks and distortion of the silicon wafer, the surface roughness of the molybdenum plate, the fact that molybdenum and aluminum are metals that easily alloy, and the release of distortion 30. It is presumed that the dispute was due to insufficiency. In order to eliminate such drawbacks of the conventional method, the present invention has developed a silver plated film in which a copper flash plating layer and then a rhodium plating layer are formed between the aluminum layer on the main surface of the semiconductor substrate and the aluminum layer of the molybdenum plate on both sides. A plate is interposed between the layers, and this structure makes it easier to absorb stress and distortion caused by thermal cycles. Hereinafter, one embodiment of a semiconductor device according to the present invention will be described in detail with reference to FIG.

In FIG. 3, a silver plate 7 is used in this embodiment.
After forming a copper flash layer 8 of about μ, using this copper flash layer 8 as a base, plating is performed in the same manner as V)0,3.
A layer 9 of about 0.8 μm is formed. According to experiments conducted by the inventors, without the base copper flash layer 8, the adhesion of the rhodium layer 9 is poor, and the rhodium layer 9 is
It has been confirmed that cracks occur in this dianium when it is formed more than μ. Similarly to the aluminum layer 2 formed on the main surface of the silicon wafer 1 by vapor deposition of about 10 to 20 μm, an aluminum layer 10 of about 5 to 10 μm is also formed on the surface of the molybdenum plate 4. The silver plate 7 treated as described above is placed between these aluminum layers 2 and 10, and these are brought into pressure contact. The reason why the aluminum layer 2 is formed on the molybdenum plate 4 is that if the molybdenum plate 4 was in direct contact with the aluminum layer 9, it would not be possible to crack the aluminum layer 9 by the slicing motion. Moreover, if the thickness of the silver plate 7 is less than 100 μm, it cannot absorb the warping of the silicon wafer or the distortion of the molybdenum plate, and if the thickness is more than 300 μm, its coefficient of thermal expansion is about 10 times that of silicon. Therefore, the outside is affected by thermal expansion, which is undesirable. As described in detail above, according to the present invention, a silver plate having a zinc plating layer formed on both sides is laid between the aluminum layer on the main surface of the semiconductor substrate and the aluminum layer of the molybdenum plate with a copper flashing layer interposed therebetween. Because it has a press-contact structure, it has the advantage of effectively absorbing stress, distortion, etc. caused by thermal cycles during energization, and in practice, in a semiconductor device to which this invention is applied, it is possible to effectively absorb stress and strain caused by thermal cycles during energization. It was also confirmed that there was no change in the forward voltage drop and that no cracks occurred in the silicon wafer.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the main part configuration of a conventional flat high-power semiconductor device, FIG. 2 is an enlarged explanatory view of the same main part, and FIG.
The figure is a sectional view showing the main part configuration of a flat high power semiconductor device to which an embodiment of the present invention is applied. 1... Silicon wafer, 2... Aluminum layer, 3
4... Molybdenum plate, 5... Copper block, 7...
Silver plate, 8...Copper flash layer, 9...Dinium layer.

Claims (1)

[Claims] 1. A first layer of copper and a second layer of rhodium were formed on both sides between the aluminum layer formed on at least one main surface of the semiconductor substrate and the aluminum layer of the molybdenum plate opposed thereto. A semiconductor device characterized in that the electrodes on the main surface are taken out by interposing a silver plate having a thickness in the range of 100 to 300 μm and applying weight to the molybdenum plate.