CS269214B1 - A method of etching aluminum contact A power semiconductor devices - Google Patents

Abstract

The method of etching a contact of power semiconductor components formed by an aluminum layer or an aluminum layer and at least one silver layer consists in selectively etching the surface of the semiconductor system provided with the contact through a photoresist mask in a solution of orthophosphoric, nitric and acetic acids in a ratio of 15 to 1 to 4 to 8 at a temperature of 30 to 90 °C.

Description

The invention relates to a method of etching an aluminum contact A1 of power semiconductor components, optionally provided with at least one layer of silver Ag.

The following fundamental requirements are placed on the contact layer:

Adhesion and good electrical parameters of the metal-semiconductor interface, such as contact ohmicity, low contact resistance, etc., precise geometry of the surface division of the contact into a cathode-emitter contact and a control structure-base contact.

Good contact parameters are usually achieved by a suitable evaporation regime, especially heat treatment of the evaporated layer, which is usually performed during plating or after the evaporation itself without interrupting the vacuum. Contact segmentation is most often performed in two ways, during plating using a mechanical mask, or photolithography - by selective etching of the metal contact layer through a photoresist mask.

The disadvantage of the first method is its considerable inaccuracy and it is practically impossible to use it in the case of a complexly structured structure. In the second method, the geometric accuracy depends on the temperature of the previous processing of the contact layer, the choice of etching agent and the etching technology.

The use of alkaline etching agents based on an aqueous solution of potassium hydroxide and ferrous ferricyanide results in significant etching of the photoresist layer, thereby reducing the contact cross-section, reducing its electrical conductivity and increasing the switching losses of the component.

Furthermore, etching agents based on phosphoric acid and nitric acid are used in a ratio of 15:1 to 33:1, at temperatures of 60 to 110 °C. The disadvantage of the method is that unetched areas remain on the etched motif, so-called aluminum bridges, or entire parts of the motif are not etched, which must be removed mechanically, otherwise they lead to short circuits on the contacted structure.

The above disadvantages are eliminated by the method of etching the aluminum contact A1 of power semiconductor components according to the invention, the essence of which lies in the fact that the surface of the semiconductor system provided with an aluminum contact layer is selectively etched through a photoresist mask in a mixture of orthophosphoric, nitric and acetic acids in a ratio of 15:1:1 to 4:1:8 at a temperature of 30 to 90 °C.

The advantages of the contact etching method for power semiconductor components are ensuring high accuracy of reproduction of the segmented motif, flawless etching of the motif, good adhesion of the unetched contact and low contact resistance. The use of acetic acid affects the quality and speed of the etching process, in addition, this etchant component prevents the formation of spots on the free collector side of the silicon wafer. The entire etching process can be accelerated if etching is performed in an ultrasonic field.

Example

Before the alloy connection with the expansion electrode, the silicon plate is covered with a contact consisting of a 0.3 µm thick layer of aluminum A1 and subsequently a layer of silver.

Ag with a thickness of 3.5 -0.5 by vacuum evaporation method.

guarantees the stability of its parameters during subsequent temperature changes

The composition of this contact alloy. On a silicon plate with a contact layer ee, a photoresist mask SCR 7.1 is photolithographically processed and a silver-aluminum contact is etched in a mixture of acids with the composition: orthophosphoric acid, nitric acid, acetic acid in a ratio of 8:1:1 at an etching temperature of 55 °C for 35 to 50 seconds. After etching 50 to 100 pieces of silicon plates, the acid mixture is revived by adding one part of acetic acid. The etched structure is subsequently ignited during alloying - at a temperature of 700 °C, with a time delay of 20 minutes.

The invention will find application in the segmentation of the aluminum-silver or aluminum contact layer in the production of power semiconductor components with a vertically planar or planar metal contact with high demands on the accuracy of the geometric shape of the contact and its good mechanical and electrical properties.

Claims (1)

SUBJECT OF THE INVENTION Method for etching an aluminum contact Al of power semiconductor components, optionally provided with at least one layer of silver Ag, characterized in that the surface of the semiconductor system provided with an aluminum contact layer is selectively etched through a photoresist mask in a mixture of orthophosphoric, nitric and acetic acids in a ratio of 15 to 1:1 to 4:1:8 at a temperature of 30 to 90 °C.