CS248397B1 - A method of forming a cathode contact of power semiconductor devices - Google Patents

Abstract

The solution concerns a method of creating a cathode contact of power semiconductor components based on silicon, e.g. diodes, thyristors or transistors. The silicon wafer is, after conventional cleaning, evaporated in vacuum with a silver layer of a maximum thickness of 1 <u»f, further with an aluminum layer of a maximum thickness of i /ns, with subsequent reinforcement with a silver or aluminum layer of a maximum thickness of 10 fm.

Description

The invention relates to a method of making a cathode contact of silicon-based power semiconductor devices such as diodes, thyristors or transistors.

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In the manufacture of these components, the silicon wafer and the PN junction formed are usually first soldered with aluminum-lead alloys to a molybdenum or tungsten diode electrode. This is followed by metallization of the other side of the silicon plate, the so-called cathode or emitter, which is most often carried out by vacuum vapor deposition of aluminum, gold, nickel and the like.

For technological reasons, it would be preferable to perform this plating prior to soldering the silicon wafer to the molybdenum (tungsten) electrode. However, this would mean providing a cathodic (emitter) contact with a structural resistance to the temperature of soldering the silicon wafer to the diode electrode, which in the case of an aluminum-lead solder is about 700 ° C. Commonly used contact materials do not have this resistance due to low melting temperatures (aluminum, gold) or due to the formation of intermetallic phases with silicon (nickel).

This problem is solved by the method of cathodic contact of the power semiconductor components according to the invention, which consists in that after cleaning the silicon wafer vaporizes in vacuum with a layer of silver of maximum 1 µm, Thickness maximum 10 pm.

Preferably, up to 95% of the thickness of the third silver layer is eliminated electrochemically. _t

The benefit of the application of the invention in mass production of power semiconductor devices is the saving of labor and materials, especially of precious metals.

While the soldering temperature of the silicon to the diode electrode 700 ° C melts the contact metals, but only in a very narrow area on the side of the silicon wafer. The external contact area remains structurally unchanged. If the temperature resistance of the contact is only up to 550 ° C, the third silver layer can be replaced by aluminum. The cathode contacts thus formed are distinguished by very good ohmicness and reliability.

Exemplary embodiment No. 1

The 28 mm silicon wafer for the power diode is vacuum cleaned with 0.2 µm silver, 0.5 µm aluminum and 0.2 µm silver again after vacuum cleaning. After the vaporization process is completed, the third layer is silver plated to a total contact thickness of 4 µm.

Embodiment No. 2

The 40 mm medium-frequency thyristor silicon plate is vacuum cleaned after vacuum cleaning with a 0.2 µm silver layer and a 0.2 µm aluminum layer which is then thickened to a total contact thickness of 8 µm.

Claims (2)

OBJECT IN ΪΗ (LIS U Method for making a cathode contact of power semiconductor components, characterized in that the silicon wafer, after normal cleaning, is vaporized by vacuum with a silver layer of max. 2. The method of forming a cathode contact according to claim 1, characterized in that up to 95% of the thickness of the silver layer is precipitated electrochemically.