JPH0249732Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of semiconductor pellets forming high voltage diodes.

A conventional high voltage diode generally has a structure as shown in FIG. That is, as shown in FIG. 1, a plurality of diode pellets 1, in this case three, each having a reverse withstand voltage of about 1000 to 1000s of hundreds of volts are connected in series, so that the reverse withstand voltage of the diode is also about 3. It is said to be over 1,000V. Further, 5a and 5b are heat sinks having external leads, and are made of tungsten or molybdenum, etc., which have a coefficient of thermal expansion similar to that of the diode pellet, and 6 is for electrically and mechanically protecting the diode pellet from the outside. 2 is silicon dioxide formed on the diode pellet, and 3 is the sealing glass formed on the diode pellet. 4 is a passivation glass that protects the PN junction end of the plate, and 4 is a connecting metal for connecting the diode pellets and the heat sink.

Next, the assembly process will be explained.

First, a number of diode pellets 1 that satisfy the desired reverse voltage are stacked, heat sinks 5a and 5b are placed above and below, and the temperature is raised to a temperature higher than the eutectic temperature of the connecting metal and the silicon of the diode pellets 1. This process consists of a mounting process in which a heat sink is connected between the diode pellets and at their ends, and a second sealing process in which the diode pellets are sealed with a sealing glass 6 to electrically and mechanically protect them from the outside.

As shown in FIG. 1, a conventional diode pellet 1 had silicon dioxide on one main surface. Since the connection metal does not adhere to silicon dioxide, the film must be thicker than the silicon dioxide for connection to occur. Also, as will be explained in detail in the manufacturing process of the pellets, the packaging glass 3
When forming silicon dioxide, passivation glass may be formed locally on this silicon dioxide due to formation nuclei such as pinholes and dust in the oxide film, and in this case, passivation glass may be formed locally on this silicon dioxide. As a result, the parallelism of the connecting surfaces deteriorates, creating gaps, resulting in problems such as a decrease in the adhesive strength of the connecting metals and thermal fatigue.

The present invention relates to a diode pellet structure for eliminating such defects and obtaining a highly reliable high voltage diode.

According to the present invention, in a high-voltage diode in which a plurality of mesa-shaped semiconductor pellets are stacked, the semiconductor pellets include a semiconductor substrate of one conductivity type, and a semiconductor pellet provided on the central portion of one principal surface of the semiconductor substrate. a first semiconductor layer of one conductivity type; a second semiconductor layer of another conductivity type provided on the first semiconductor layer;
the third semiconductor layer of the other conductivity type provided on the center of the surface of the second semiconductor layer;
The third semiconductor layer is provided to cover a peripheral portion of the front surface of the semiconductor layer, a side surface of the second semiconductor layer, a side surface of the first semiconductor layer, and a peripheral portion of the one principal surface of the semiconductor substrate. A passivation film having a thickness thinner than that of the third semiconductor layer, and a connection metal provided on the entire surface of the third semiconductor layer in direct contact with the third semiconductor layer. A high voltage diode is obtained.

A detailed explanation will be given below with reference to the drawings.

FIG. 25 shows a conventional diode pellet, which is manufactured by the steps a to e in FIG. 2. FIG. 2a shows a wafer with silicon dioxide formed on both sides, on which PN junctions have been formed, after which the silicon dioxide film in the groove-forming portions for separating each chip into chips has been removed by photolithography.

Next, as shown in FIG. 2b, a trench 7 is formed deeper than the depth of the PN junction in order to separate the PN junction using a silicon dioxide film as a mask using a mixed silicon etching solution of nitric acid and hydrofluoric acid.

Next, as shown in Figure 2c, the wafer is immersed in a solution in which passivation glass powder is suspended in a solvent, an electric field is applied, and the passivation glass powder is separated by electrophoresis using silicon dioxide as a mask. A passivation glass film 3 is formed only on the exposed silicon part of the groove and melted the powdered glass in an electric furnace.
form.

Next, as shown in Figure 2 d, the connecting metal is formed at 2.
The silicon oxide is removed by photolithography, and a connecting metal is formed on this portion and the entire back surface by vapor deposition as shown in FIG. 2e.

Next, a notch was made in the center of the groove of the wafer using a laser or a dicer scribe, and the pellet was separated into individual pellets to obtain diode pellets 5.

As described above, in the conventional structure, since the connection metal and the silicon dioxide exist on the same surface, and in the process shown in FIG. The defect that passivation glass is formed locally on the silicon dioxide due to dust on the silicon oxide remains as it is in the final pellet, causing the above-mentioned defect in the diode assembly process.

The present invention will be explained with reference to FIGS. 4a to 4h. 4a is the same as the conventional process, and then, in FIG. 4b, the groove is made shallower than the desired depth (slightly thicker than the thickness of the passivation glass 3 formed in FIG. 4e). form. Next, as shown in FIG. 4c, unnecessary silicon dioxide is removed by photolithography to form silicon dioxide 2a smaller in surface area than the P diffusion layer under the silicon dioxide. Next, as shown in FIG. 4d, the groove is etched again to form a groove of a desired depth. A step 8 corresponding to the groove depth added at this time is formed. The depth of the step is larger than the thickness of the passivation film to be formed next for the reason mentioned above. Next, as shown in FIG. 4e, a passivation glass 3 is formed in the same manner as in the conventional method. At this time, the passivation glass 3 formed in the stepped portion is formed lower than the surface of the P diffusion layer for the reason described above. Next, as shown in Figure 4 f, all of the silicon dioxide and the passivation glass in the inner part from the center of the step are removed by photolithography, and vapor deposition is carried out on this area and the entire back surface as shown in Figure 4 g. The connecting metal is formed by the method.

Next, in the same manner as in the prior art, a notch is made in the center of the groove by a laser or diode scribe, and the pellets are separated into individual pellets to obtain the diode pellets shown in FIG. 4h.

As described above, by using the diode pellet of the present invention, silicon dioxide does not exist on the main surface of the diode pellet, that is, the adhesive surface, as shown in FIG. 3, and the adhesive surface is only the silicon substrate. Since the passivation glass is also lower than the silicon bonding surface, the above-mentioned problems that occur in conventional high-voltage diodes do not occur, and a highly reliable high-voltage diode can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional high voltage diode, and FIGS. 2a to 2f are sectional views showing the manufacturing process of the diode pellet. FIG. 3 is a sectional view of a high voltage diode according to the present invention, and FIGS. 4a to 4h are sectional views showing the manufacturing process of the diode pellet. In the figure, 1... diode pellet, 2a, 2b... silicon dioxide, 3... passivation glass film, 4... connection metal, 5
a, 5b...heat sink, 6...sealing glass,
7...PN junction separation groove, 8...PN junction separation groove step.

Claims (1)

[Scope of utility model registration request] In a high-voltage diode in which a plurality of mesa-shaped semiconductor pellets are stacked, the semiconductor pellets include a semiconductor substrate of one conductivity type, and a first semiconductor pellet of one conductivity type provided on the center of one principal surface of the semiconductor substrate. a second semiconductor layer of another conductivity type provided on the first semiconductor layer, and a second semiconductor layer of the other conductivity type provided on the center portion of the surface of the second semiconductor layer. a third semiconductor layer, a peripheral portion of the front surface of the second semiconductor layer, a side surface of the second semiconductor layer, a side surface of the first semiconductor layer, and a peripheral portion of the one principal surface of the semiconductor substrate; A passivation film is provided to cover the third semiconductor layer and has a thickness thinner than the third semiconductor layer, and a connection metal is provided on the entire surface of the third semiconductor layer in direct contact with the third semiconductor layer. A high voltage diode characterized by being formed as follows.