JPS5950089B2 - Manufacturing method of semiconductor rectifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor rectifier, and particularly to a method for manufacturing a semiconductor rectifier using Ni plating.

Electroless Ni plating is performed to form an electrode film on the silicon after the PN junction has been formed, but currently, nitric acid or hydrofluoric acid is used as a pre-treatment for Ni plating to obtain ohmic contact between the silicon and the Ni plating film. Etching is performed using a mixed acid of , acetic acid, and iodine.

According to this pretreatment method, since the etching speed is high, countless pinhole-shaped recesses (hereinafter abbreviated as etching pits) are observed on the silicon surface after etching. When Ni plating is performed in this state and heat treatment is performed in an H2 atmosphere to obtain more ohmic contact between the silicon and the Ni plating film, the Ni plating film peels off from the N surface.

By etching as a pretreatment for Ni plating, countless etch pits are generated on the silicon, and the etch pit portions have a larger surface area than other surfaces and the Ni plating precipitation speed is faster. On the other hand, in electroless Ni plating, hydrogen gas is generated at the same time as Ni is deposited. Particularly, a large amount of hydrogen gas is generated in the etch pit area and a Ni plating film is formed, but the hydrogen gas remains in the etch pit area, and the hydrogen gas remaining in the etch pit area during heat treatment of the Ni plating film thermally expands due to the heat treatment and the Ni plating film is formed. It destroys the membrane and comes to the surface. Due to the hydrogen gas present in the Ni plating film, the Ni plating film frequently peels off, and ohmic contact between silicon and the Ni plating film cannot be achieved. An object of the manufacturing method of the present invention is to provide a method for manufacturing a semiconductor rectifier that eliminates the above-mentioned drawbacks and can provide better ohmic contact and plating quality.

The manufacturing method of the present invention is characterized by the weight ratio of hydrofluoric acid:
By etching with a mixed acid of 1:70 nitric acid, the occurrence of etch pits can be reduced, and ohmic contact can be obtained between both sides of the silicone to eliminate defects in plating film peeling. Hereinafter, the manufacturing method of the present invention will be explained based on Examples.

First, the silicon on which the PN junction has been formed is etched using a mixed acid having a weight ratio of hydrofluoric acid and nitric acid of 1:70. At this weight ratio, the etch speed of a mixed acid of hydrofluoric acid: nitric acid = 1:70 is 0.04 μ per second, and the etch speed of the conventional etching solution mentioned above is 0.16 μ per second, which is a gentle etch speed of 1/4. The etch pits formed on the silicon surface are shallow and have a gentle slope, and the etch pits that are steep and deep and cause poor peeling of the Ni plating film do not appear and are not oxidized. Next, when electroless Ni plating is applied to the silicon obtained in this way, a uniform Ni plating film is obtained on both sides of the silicon, and at the same time, a stable Ni plating film is obtained evenly on the same surface.
An i-plated film is formed.

Next, even if heat treatment (700°C) is applied, there are no etch pits that would cause the Ni plating film to peel off, so there is no hydrogen gas, and the Ni plating film is not destroyed.
An i-sinter layer is formed to provide better ohmic contact.

When we measured the number of pinholes per unit area, we found that with conventional pretreatment liquid, there were 500 to 2000 pinholes/unit area on the P-type surface of silicon.
1. On the N-type surface, there were 9000 to 25,000 particles per unit, but in the pretreatment liquid of the present invention, there were 500 to 1700 on the P-type surface.
There were 4000 to 10000 pieces/1 on the N-type surface.

On the other hand, the relationship between the number of etching pits and the defect rate due to Ni plating film peeling is 0% when the number of etching pits is up to 10,000 pieces/piece, 10% when it is 30,000 pieces/piece, and about 25% when the number of etching pits is 50,000 pieces/piece.
%, as mentioned above, according to the present invention, the N-type surface is 10,000
The Ni plating film peeling defect rate was 0% because the etch pit itself was shaped so that the Ni plating film did not easily peel off.

The manufacturing method of the present invention has reduced the defective rate of 5-6% to almost 0.
I was able to keep it down to %.

Claims (1)

[Claims] 1 When performing electroless Ni plating to form an electrode film on the silicon on which the PN junction has been formed, a mixed acid with a weight ratio of hydrofluoric acid: nitric acid = 1:70 is used as a pretreatment for the Ni plating. A method for manufacturing a semiconductor rectifier characterized by etching the surface.