JPH1074752A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a non-alloy type semiconductor device stable in withstand voltage by a method in which air bubbles are restrained from being left in a passivation film. SOLUTION: A silicon wafer 1 is set in a passivation potting mold 4, the potting mold 4 is made to stand upright, liquid passivation material 7 (e.g. silicone rubber or the like) is infected into the potting mold 4 through an inlet opening 5 with normal pressure, and a gap between the potting mold 4 and the silicon wafer 1 is filled up with liquid passivation material 7 from below. The liquid passivation material 7 fully filled into the mold 4 is discharged from the mold 4 through an outlet opening 6, air bubbles in the liquid passivation material 7 are moved opposite to the direction of gravitation shown by an arrow and also discharged from the potting mold 4, the liquid passivation material 7 is hardened after the potting mold 4 is fully filled up with the passivation material 7, and the mold 4 is dismounted, thereby the peripheral edge of the silicone wafer 1 is covered with an air bubble-free passivation film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a power semiconductor device such as a diode, a thyristor and a GTO thyristor.

[0002]

2. Description of the Related Art In order to maintain a high withstand voltage, a power semiconductor device such as a diode, a thyristor or a GTO thyristor, which is a one-wafer or one-device, has a peripheral portion of a silicon wafer covered with a passivation film such as silicone rubber. FIG. 2 is a configuration diagram showing a conventional method for coating a non-alloy type semiconductor device with a passivation film. In a typical alloy type semiconductor device, a silicon wafer having a pn junction formed thereon is alloyed with a molybdenum plate serving as a support plate, and thereafter, a passivation film is coated on a peripheral portion and housed in a package.
On the other hand, in a non-alloy type semiconductor device, the silicon wafer 1 is stored in a package (not shown) without alloying the silicon wafer 1 with a molybdenum plate as a support plate. A method for coating the passivation film of the non-alloy type semiconductor device will be described. A metal film (not shown) such as an aluminum film is selectively deposited on both surfaces of the silicon wafer 1 on which the pn junction is formed to form electrodes. After that, the circumferential end 3 of the silicon wafer 1 is beveled and chemically treated so as to ensure a withstand voltage. The silicon wafer 1 is set in an injection mold 4 for passivation, the injection mold 4 is placed horizontally, a liquid passivation material 7 is injected from an injection port 5, and a filled liquid passivation material 7 is taken out from an outlet 6. These operations are performed in the decompression chamber 9, and the air in the liquid passivation material 7 is deaerated from the inlet 5 and the outlet 6 by reducing the pressure in the decompression chamber 9. Thereafter, the liquid passivation material 7 is cured, and the peripheral portion 2 of the silicon wafer 1 is covered with a passivation film. Thereafter, both surfaces of the silicon wafer 1 are sandwiched between metals such as molybdenum and stored in a flat package.

[0003]

However, in this method using reduced pressure, it is difficult to completely deaerate the air bubbles accumulated on the upper part of the injection mold, and air bubbles often remain in the passivation film. If a bubble remains in the passivation film, when a voltage is applied to the semiconductor device, electric field concentration occurs at a location where the bubble is present, and the withstand voltage of the semiconductor device decreases.

An object of the present invention is to provide a non-alloy type semiconductor device capable of ensuring a stable breakdown voltage by preventing bubbles from remaining in a passivation film.

[0005]

In order to achieve the above object, a disk-shaped silicon wafer on which at least one pn junction is formed is covered with a passivation film and housed in a package. In a method for manufacturing a semiconductor device, a peripheral portion of a silicon wafer is surrounded by an injection mold for passivation, the injection mold is placed upright, an injection port for injecting a liquid passivation material into the injection mold, and a liquid injection port. An outlet for taking out the passivation material is provided, the injection port is disposed below, the outlet is disposed above, the liquid passivation material is injected from the injection port, and the liquid passivation material is filled upward from the bottom of the injection mold. After the bubbles mixed in the liquid passivation material are taken out from the outlet, the peripheral edge of the silicon wafer is covered with the liquid passivation material. Curing the passivation material liquid, to have a step of coating the periphery of the silicon wafer with a passivation film. This passivation material is preferably silicone rubber. Further, it is preferable that the inclination angle of the injection mold is 0 to 45 ° with respect to the direction of gravity.

[0006]

FIG. 1 is a view showing a method of coating a passivation film of a non-alloy type semiconductor device according to a first embodiment of the present invention. A metal electrode film (not shown) is selectively formed on both surfaces of the disc-shaped silicon wafer 1 on which at least one pn junction is formed, and the circumferential end 3 of the silicon wafer 1 is subjected to bevel processing and chemical treatment. Then, the silicon wafer 1 is set on the injection mold 4 for passivation. The injection mold 4 is configured such that the liquid passivation material 7 is coated only on the peripheral edge 2 of the silicon wafer 1. The injection mold 4 is set up, and a liquid passivation material 7 (for example, silicone rubber is effective) is injected under normal pressure from an injection port 5 provided below the injection mold 4, and a gap between the injection mold 5 and the silicon wafer 1 is formed. Fill with liquid passivation material 7 from below. The filled liquid passivation material 7 flows out of the injection mold 4 from the outlet 6. The bubbles 8 in the liquid passivation material 7 move in the direction opposite to the direction of gravity indicated by the arrow, and escape through the outlet 6 to the outside of the injection mold 4.
After the liquid passivation material 7 is filled up to the upper part of the injection mold 4, the liquid passivation material 7 is cured and the injection mold 4 is removed. When the liquid passivation material 7 is silicone rubber, the curing temperature is about 150 ° C. In this manner, a passivation film without bubbles can be formed on the peripheral edge of the silicon wafer. Thereafter, the silicon wafer is sandwiched on both sides by a molybdenum plate and stored in a flat package. By using this method, bubbles in the passivation film can be eliminated, partial discharge caused by the bubbles can be prevented, and the breakdown voltage of the non-alloy type semiconductor device can be maintained with high reliability. Further, unlike the conventional case, it is not necessary to reduce the pressure in the decompression chamber so that the processing time can be reduced.

[0007] The injection mold 4 may be inclined by a certain angle with respect to the direction of gravity. The angle is related to the viscosity of the liquid passivation material. When the viscosity is high, the angle can be reduced, and when the viscosity is low, the angle can be increased. This is because it is related to the force with which bubbles can move upward in the liquid passivation material against gravity. This angle is practically 0 ° to 45 °.

[0008]

According to the present invention, by injecting the liquid passivation material from the injection port into the injection mold for passivation set on the peripheral edge of the silicon wafer that has been set up, the bubbles are repelled by gravity and the liquid is removed. Is moved above the passivation material and escaped from the outlet to form a passivation film without bubbles. Since there are no air bubbles, the breakdown voltage of the semiconductor device can be stabilized. Further, since it is not necessary to depressurize and deaerate as in the conventional case, the process can be shortened.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for coating a passivation film of a non-alloy type semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a view showing a conventional method for coating a non-alloy type semiconductor device with a passivation film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon wafer 2 Peripheral part 3 Circular end part 4 Injection type 5 Injection port 6 Outlet 7 Liquid passivation material 8 Bubbles 9 Decompression chamber

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor device in which a peripheral portion of a disk-shaped silicon wafer on which at least one pn junction is formed is covered with a passivation film and is housed in a package, the peripheral portion of the silicon wafer is provided. Is surrounded by an injection mold for passivation, the injection mold is placed upright, an injection port for injecting the liquid passivation material into the injection mold, and an outlet for taking out the liquid passivation material are provided. Then, the outlet is placed on the upper side, the liquid passivation material is injected from the injection port, the liquid passivation material is filled upward from the bottom of the injection mold, and bubbles mixed in the liquid passivation material are taken out from the outlet, After the peripheral edge of the silicon wafer is covered with the liquid passivation material, the liquid The method of manufacturing a semiconductor device comprising coating the peripheral portion of the wafer with a passivation film. 2. The method according to claim 1, wherein the passivation material is silicone rubber. 3. The angle of inclination of the injection mold is 0 to the direction of gravity.
2. The method according to claim 1, wherein the angle is 45 [deg.].