JPS6341228B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing mesa semiconductor pellets, and more particularly to a mesa etching process for mesa semiconductor chips.

When forming a mesa groove in the manufacturing process of a so-called mesa-type semiconductor device in which a mesa groove is provided from one side (or both sides) of a silicon semiconductor substrate, conventionally, a silicon oxide film is formed on the surface of the silicon substrate at high temperature and a known optical method is used. The oxide film was selectively removed from the portion that would become the mesa groove using a etchant, and then mesa etching was performed using a hydrofluoric acid etching solution using the silicon oxide film as a mask to form the mesa groove.

In this case, when the silicon oxide film is selectively removed using an optical method, minute pinholes are created in the oxide film that is supposed to be a mask due to pinholes in the photoresist film or defects in the silicon oxide film. This has disadvantages such as forming holes during mesa etching, impairing the electrical properties of the pellet and causing poor appearance. Alternatively, instead of using an oxide film as a mask, there is a method of using a metal film as a mask by vapor deposition or the like and selectively removing it using a photoresist, but this also has the same effect on defects in the metal film due to pinholes in the photoresist. Both have the same drawbacks. There is also a method of selectively applying wax or the like and using this as a mask, but since the wax flows around the pellet, it becomes uneven instead of straight, which deteriorates the withstand voltage characteristics, which is not preferable.

The object of the present invention is to provide a manufacturing method that eliminates such drawbacks and improves the pressure resistance and appearance yield by suppressing the formation of holes on the pellet surface.

According to the present invention, in order to eliminate such drawbacks, the first mask is structured using an optical method such as a photoresist in order to obtain linearity in the peripheral part of the pellet,
On top of that, a second mask is formed using a screen printing method or the like so that the wax is etched from the first mask, and then the silicon substrate is etched inward by approximately the same amount as the side etching in the lateral direction.Then, the grooves are etched. When this is done, the peripheral part of the pellet is maintained in a straight line by the first mask formed by an optical method, and defects such as pinholes on the first mask are covered by the second mask, so that holes do not occur. Mesa-shaped semiconductor pellets can be manufactured with high yield without any problems. Also, in this case, placing the second mask inward from the first mask by approximately the same amount as the amount of lateral etching (side etching) of the silicon substrate that occurs in the mesa etching process will maximize the effect in terms of mask accuracy. I found out. In other words, the alignment accuracy when alignment printing is performed using a screen printing method for wax such as Apiezon wax and the amount of side etching of the silicon substrate are approximately the same, so the second mask is the same as the first mask. If the amount that goes further inside is smaller than the side etching amount, the printing mask will shift during screen printing, and the second mask will be printed extending beyond the first mask. For this reason, the wax flows around the pellet after mesa-etching, so that it is not straight but uneven, and the withstand voltage characteristics deteriorate.

On the other hand, if the amount of the second mask that goes inside the first mask is greater than the side etching amount, the second mask will not be printed protruding from the first mask, but the first mask will be The area not covered by the second mask increases, and holes are formed in the silicon substrate due to the effects of pinholes and the like generated in the first mask, resulting in poor characteristics.

On the other hand, if the amount of the second mask that goes inside the first mask is approximately equal to the side etching amount, the second mask will not be printed protruding from the first mask, and the second mask will not be printed outside the first mask. Since it also covers most of the pinholes that occur in the mask, the rate of good products after Mesa etching is maximized.

Next, an embodiment of the present invention will be described with reference to the drawings. P-N-P using gallium and phosphorus
The silicon substrate 1 (FIG. 1) on which the -N junctions 3, 1, 2, and 4 have been formed is oxidized at high temperature to form a silicon oxide film 5, and an opening 6 is formed using photoresist.
At this time, oxide film holes 7 may be formed where the oxide film is partially removed due to pinholes in the photoresist. If this is etched as is in the conventional manner, the hole 7 will be eroded after etching, resulting in the formation of a silicon hole 8, as shown in FIG. Accordingly, in the present invention, alignment printing is performed using a screen printing machine using, for example, Apiezon wax, the mask 9 is provided from the front and back, and post-etching is performed. In this way, the hole 7 etc. on the oxide film will not be etched. Furthermore, when the glass 10 was attached using electrophoresis, the bonding was completely bonded and the yield was very good.

[Brief explanation of drawings]

Figure 1 shows a silicon substrate with a selective mask provided on the silicon oxide film using a conventional optical method;
The figure shows a silicon substrate coated with glass after etching, Figure 3 shows a silicon substrate with a double mask of silicon oxide film and Apiezon wax according to an embodiment of the present invention, and Figure 4 shows a silicon substrate after etching it. FIG. 3 is a cross-sectional view showing a silicon substrate coated with glass after the above-mentioned steps. In the figure, 1...N-type silicon substrate, 2
... P-type base diffusion layer, 3 ... Anode P-type diffusion layer, 4 ... Cathode N-type diffusion layer, 5 ... Silicon oxide film mask, 6 ... Oxide film opening, 7 ... Pinhole on oxide film , 8... Silicon pinhole, 9
...Apiezon Wax Mask, 10...Glass.

Claims (1)

[Claims] 1. When producing a mesa-shaped semiconductor pellet by forming a groove in a semiconductor substrate, a screen printing method is further used to form a mesa-shaped semiconductor pellet on top of the first mask formed using an optical method, and after mesa etching, the first mask is A second mask made of wax is formed inward from the first mask by a length approximately equal to the amount by which the semiconductor substrate is side-etched in the lateral direction from the periphery, and then the semiconductor substrate is etched to form a groove. 1. A method for producing a mesa-shaped semiconductor pellet, the method comprising: providing a mesa-shaped semiconductor pellet;