JPH0620083B2 - Method for manufacturing semiconductor device - Google Patents

Description

Detailed Description of the Invention TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for manufacturing a semiconductor element in which one surface of a semiconductor substrate is fixed to a metal substrate having good thermal conductivity via an electrode plate made of metal having a thermal expansion coefficient close to that of a semiconductor material.

[Prior art and its problems]

The electrode plate inserted between the semiconductor substrate and the metal substrate has a thermal expansion coefficient close to that of the semiconductor substrate in order to prevent thermal stress from being applied to the semiconductor substrate, and to reduce the thermal resistance of the brazed portion with the semiconductor substrate. Good brazing properties of the surface are desired. As the electrode plate in the semiconductor element shown in FIG.
A silicon plate 1 having a thermal expansion coefficient close to that of a Mo plate 4 clad with a Ni layer 3 is used.
After being fixed by soldering, the silicon plate 1 is brazed to the surface of the Ni layer 3 by the solder 2. However, in such an electrode plate, since the side surface of the Mo plate 4 is not wet by the solder, the solder 2
Becomes thicker, air bubbles tend to form inside, and the thermal resistance increases. In the semiconductor device shown in FIG. 3, Mo
The composite electrode, in which the plate 4 is previously fixed to the Cu substrate 5 using the braze 6, is first coated with the electric Cu plating layer 7 to a thickness of 1 to 2 μm, and then the electric Ni plating layer 8 having a thickness of 2 to 5 μm, An electroless Ni plating layer 9 for improving the solderability is laminated on. In this case, the plating work must be repeated three times, and there are many control items to maintain constant quality.
It has the drawback of requiring time. In FIG. 4, the Cu plating layer 7 is directly electrolessly processed by the sendizing activator treatment.
The Ni plating layer 9 is covered. But this way,
Since the adhesion of the Ni plating layer is low and heat treatment must be applied, the wettability of the solder is impaired.

[Object of the Invention]

An object of the present invention is to solve the above problems and to provide a method for manufacturing a semiconductor element in which the thermal resistance between a semiconductor substrate and an electrode plate is small, and moreover, the surface treatment of the electrode plate does not require a lot of time. To do.

[Points of the Invention]

According to the present invention, an electrode plate made of only molybdenum or tungsten having a coefficient of thermal expansion close to that of a semiconductor material is fixed to a metal substrate made of copper having good thermal conductivity in advance, and the fixed electrode plate and metal substrate are fixed. Was immersed in an electroless nickel plating solution, the electrode plate and the metal substrate were used as cathodes, and a current of 6 to 24 V, 0.5 A or less was lengthened to coat the surfaces of the electrode plate and the metal substrate with a nickel layer. After that, by soldering one surface of the semiconductor substrate onto the electrode plate with solder, the plating work is completed only once, and the side surface of the electrode plate is also Ni.
Since it is covered with a layer, excess solder flows out to the side surface of the electrode plate along with the contained gas at the time of brazing, air bubbles in the solder film disappear, a uniform thin solder film is formed, and the thermal resistance decreases, thus achieving the above object. be able to.

Examples of the invention

FIG. 1 shows the structure of a semiconductor device manufactured according to an embodiment of the present invention, in which Cu is formed on a composite electrode composed of a Mo plate 4 and a Cu substrate 5.
The Ni layer 10 is directly coated without plating. When the silicon plate 1 is brazed to such a composite electrode, the solder 2 also wets the Ni layer 10 on the side surface of the Mo plate 4, so the amount other than the amount necessary for adhesion with the silicon plate 1 is excluded. Of the solder flows out to the side surface of the Mo plate 4 to form a uniform and thin solder film 2, or the gas contained in the solder flows out together, so that the bubbles disappear. Direct Ni plating on the Mo plate 4 and the Cu substrate 5 can be formed as in the following example. Example 1: Composite electrodes 4,5 in an acidic electroless nickel-phosphorus plating bath
Then, a composite electrode was used as a cathode, and a current of 6 V and 0.5 A was applied to form a Ni-P plating film having a thickness of 5 μm. Acidic Ni
The composition of the -P plating bath is as follows. Nickel sulfate 30 g / sodium hypophosphite 10 g / sodium acetate 10 g / pH 4-6 temperature 90 ° C. Example 2: A current of 12 V, 0.3 A was applied to an alkaline electroless Ni-P plating bath to give a thickness of 3 μm. A Ni-P plating film was formed on the composite electrodes 4 and 5. The composition of the plating bath is as follows. Nickel chloride 45 g / sodium hypophosphite 11 g / sodium citrate 100 g / ammonium chloride 50 g / pH 8.5 to 9.5 temperature 90 to 100 ° C. Example 3: An electric current of 24 V and 0.5 A is applied to an electroless nickel boron bath, Ni-B plating film with a thickness of 2.5 μm is used for composite electrodes 4, 5
Formed on. The composition of the plating bath is as follows. Nickel sulfate 20 g / potassium sodium tartrate 40 g / sodium borohydride 2.3 g / pH 12.5 temperature 40 to 50 ° C. For comparison, semiconductor devices of Comparative Examples 1 to 3 were prepared as samples. Comparative Example 1: As shown in FIG. 2, a Ni layer 3 having a thickness of 1 to 2 μm 3, a clad Mo plate 4 were punched out, and a Cu substrate 5 was adhered to the composite electrode to bond Si.
Plate 1 was brazed. Comparative Example 2: As shown in FIG. 3, an electric Cu plating layer 7 having a thickness of 1 to 2 μm was formed on a composite electrode composed of a Mo plate 4 and a Cu substrate 5.
Then, the electric Ni plating layer 8 was laminated to a thickness of 1 to 2 μm, and the electroless Ni plating layer 9 was laminated to a thickness of 5 to 8 μm, and the Si plate 1 was brazed. The composition of the electric Cu plating bath is as follows. Copper cyanide 65-90g / Sodium cyanide 80-155g / Roccal salt 40-70g / Rhodan sodium 10-15g / pH 10.5-11.0 Temperature 50-70 ° C Current density 1-3A / dm ² The composition of electric Ni plating bath is It is as follows. Nickel sulfate 240 g / nickel chloride 45 g / boric acid 30 g / pH 4.0 to 5.5 Temperature 40 to 55 ° C. Current density 1 to 6 A / dm ² The composition of the electroless Ni plating bath is as follows. Nickel chloride 10 g / sodium hypophosphite 24 g / sodium succinate 16 g / malic acid 18 g / pH 5.6 Temperature 100 ° C. Comparative Example 3: The structure shown in FIG. 4 is used, but the Cu substrate 4 and the Mo plate 5 are replaced. Under the same conditions as in Comparative Example 2, an electric Cu plating layer 7 having a thickness of 1 to 2 μm and an electroless nickel layer 9 having a thickness of 5 μm were formed on the composite electrode made of a W plate, and then the silicon plate 1 was formed.
Brazed First, the thermal resistance evaluation and the electrode manufacturing cost comparison of the semiconductor devices prepared in Examples 1 to 3 and Comparative Examples 1 to 3 are compared.
Shown in the table. The thermal resistance value is expressed as the voltage value required to pass a current of 10A. As can be seen from Table 1, in the device according to the present invention, the thermal resistance between the silicon plate 1 and the Cu substrate 5 is significantly improved, and the manufacturing cost is also significantly reduced in the electrode manufacturing. Similar effects were obtained when a W electrode plate was used instead of the Mo electrode plate described in the examples.

【The invention's effect】

The present invention covers the surfaces of an electrode plate and a metal substrate to be brazed with a semiconductor substrate to a side surface by a Ni layer having good adhesion directly without passing through a Cu plating layer by passing a current through an electroless nickel plating bath. It does not require much time for the surface treatment of the electrode plate because the plating work is done only once, and extra solder and the gas in the solder are pulled to the Ni layer on the side surface of the electrode plate when brazing the semiconductor substrate. Therefore, a thin, uniform and sound solder film is interposed between the semiconductor substrate and the electrode plate, the thermal resistance is lowered, and a highly reliable semiconductor element can be manufactured at a low cost.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a semiconductor device according to an embodiment of the present invention,
2 is a cross-sectional view of an essential part of an element of Comparative Example 1, FIG. 3 is a cross-sectional view of an essential part of an element of Comparative Example 2, and FIG. 4 is a cross-sectional view of an essential part of an element similar to Comparative Example 3. 1: Silicon plate, 2: Solder, 4: Mo plate, 5: Cu substrate,
10: Ni plating layer.

Claims (1)

[Claims] 1. An electrode plate made of only molybdenum or tungsten having a coefficient of thermal expansion close to that of a semiconductor material is fixed to a metal substrate made of copper having good thermal conductivity in advance, and the fixed electrode plate and the metal substrate are bonded together. Is immersed in an electroless nickel plating solution, and the electrode plate and the metal substrate are used as a cathode for 6 to 2
Manufacturing a semiconductor device characterized in that a current of 4 V or less and 0.5 A or less is applied, the surfaces of the outer electrode plate and the metal substrate are covered with a nickel layer, and then one surface of the semiconductor substrate is brazed onto the electrode plate by soldering. Method.