JPS6360531B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device in which glass packaging is performed by electrophoresis.

Generally, in a mesa-type semiconductor device, the PN junction surface is exposed when the semiconductor substrate is cut and disassembled into individual devices. If this exposed PN junction surface is contaminated from the outside, the electrical characteristics of the semiconductor device will be impaired and the value as a product will be lost. Therefore, the exposed part of the PN junction surface is protected by covering it with silicone resin or glass, for example. The so-called passivation is being carried out.

Silicone resin or glass is generally used as a protective material to protect the PN bonding surface, but when comparing the electrical characteristics of semiconductor devices of the same type that are bonded with silicone resin and those that are bonded with glass, glass The passivation semiconductor device is excellent and has extremely high reliability especially in high temperature bias tests. Examples of methods for depositing glass on the exposed PN junction surface of a semiconductor device include vacuum evaporation, doctor blade method, printing, and electrophoresis. It is necessary that the coating be applied to a uniform thickness. Particularly when electrophoresis is used, uniformity of the glass layer to be deposited is strongly required due to process considerations. That is, to explain the process of applying glass powder to a mesa-type semiconductor device by electrophoresis and passivation, for example, in the case of a transistor, a P-type base layer and an N-type emitter layer are sequentially diffused and formed on an N-type silicon substrate. Thereafter, a silicon oxide film of 1 μm or more is formed on the surface of this semiconductor element substrate by thermal oxidation or the like.
Next, a blade machine or the like is used to form mesa grooves in the area where glass paving is to be performed in a lattice pattern, and the crushed layer is removed by etching. This state is shown in FIGS. 1a and 1b. A large number of unit elements transistors a ₁₁ , a ₁₂ . Next, holes are made in the thermal oxide film on the back surface of the semiconductor substrate for taking out electrodeposited electrodes using photolithography or the like.

When the glass powder is ready to be deposited on the semiconductor element substrate 1, the semiconductor element substrate 1 is lightly treated with dilute hydrofluoric acid, the back side is fixed with a vacuum chuck, and the glass powder is coated on the semiconductor element substrate 1 as shown in FIG. Electrodeposition liquid tank 4
Inside, the anode 5 and the semiconductor element 1 are placed at a predetermined position so that their surfaces face each other. When a positive DC voltage is applied to the anode 5 and a negative voltage is applied to the semiconductor element substrate 1 in this manner, a glass layer is deposited on the mesa groove where silicon on the semiconductor element substrate is exposed. The glass adhered to the mesa groove is a solidified powder that has weak mechanical strength and does not satisfy the electrical properties of a passivation film, so it is melted and fired at about 700°C for about 10 minutes. Therefore, if steps such as forming an Al electrode are not performed after this glass firing step, it is expected that Al will diffuse into the silicon and deteriorate the characteristics of the semiconductor device.

For the reasons mentioned above, a process such as photolithography for forming Al electrodes must be performed after glass firing, so the glass layer rises above the surface of the semiconductor element substrate, and the height of the rise increases. If they are uneven, when a pattern is exposed on the photosensitive resin on the Al using a mask when forming the Al electrode, there will be variations in the gap between the mask and the photosensitive resin, the Al electrode pattern will collapse, and the Al electrode disconnection or short-circuit accidents occur.

Therefore, it is desired that the raised height of the glass layer after firing is uniform, and for this purpose, it is important to make the height of the glass layer after electrodeposition uniform. It is possible to melt the glass in the firing process and raise the firing temperature to a temperature where the thickness of the glass is uniform due to fluidity and surface tension, but this would impair the electrical characteristics of the semiconductor device and is not practical. Can not.

In view of the above points, the present invention makes the thickness of the deposited glass layer uniform within the semiconductor element substrate when electrodepositing the glass layer in the mesa groove by electrophoresis, and improves the thickness of the electrode wiring formed thereafter. The present invention provides a method for manufacturing a semiconductor device that reliably prevents wire breakage and short circuit accidents.

In order to uniformly deposit the glass, the inventors tried various methods such as stirring the liquid in the electrodeposition liquid tank and applying ultrasonic vibration from outside the tank. As a result of numerous measurements of the height of the deposited glass layer,
It was discovered that there is a regularity in the variation. In other words, when the horizontal grooves 3 and vertical grooves 2 of the mesa grooves in the lattice pattern are fixed in the liquid during electrodeposition so as to be horizontal and vertical as shown in FIG. The amount of glass deposited on the vertical grooves is significantly different, and the height of the glass layer deposited on the vertical grooves is smaller than that on the horizontal grooves. adjacent two of the second adjacent unit elements
Looking at the horizontal grooves of a book, the glass layer is higher in the bottom groove than in the upper groove. These regularities are considered to be due to the precipitation effect of glass powder in the electrodeposition solution.

Therefore, the present invention aims at keeping the surface of a semiconductor element substrate within a vertical plane and facing the anode in the electrodeposition solution, and also so that the vertical and horizontal grooves of the mesa grooves on the surface are symmetrically inclined with respect to the vertical line. It is characterized in that the above-mentioned variations in the height of the glass layer are eliminated by electrodepositing the glass layer.

FIG. 4 shows vertical lines (arrows) on the semiconductor element substrate 1 in the glass electrodeposition solution in one embodiment of the present invention.
The figure shows the inclination relative to the Unlike FIG. 3, both the vertical grooves 2 and the horizontal grooves 3 of the mesa grooves formed in a lattice pattern on the substrate 1 are maintained at an angle of 45 degrees with respect to the vertical line. As a result of performing glass electrodeposition while maintaining such a state, the variation in the height of the glass layer within the surface of the substrate 1 was kept within 5%. According to this embodiment, as a result of the glass layer being deposited with good uniformity, the patterning of the Al electrode to be formed thereafter is carried out with high accuracy, and breakage and short-circuit accidents of the Al electrode are reliably prevented.

In the above embodiments, the semiconductor element substrate was kept stationary in the electrodeposition solution, but the substrate may be electrodeposited while keeping its surface within the vertical plane and rotating within the vertical plane. Even in this case, if the relationship between the electrodeposition time and the rotational speed is appropriately set, the inclinations of the horizontal grooves and vertical grooves of the mesa groove with respect to the vertical line can be made substantially symmetrical, and the same as in the above embodiment can be achieved. You can expect good results.
In this case, the substrate may be rotated continuously in one direction or reciprocated within a predetermined angular range.

As described above, according to the present invention, glass passivation of a mesa-type semiconductor device by electrophoresis can be performed with good uniformity, and therefore, the process of forming electrode wiring after passivation can also be made highly reliable. , it is possible to improve the yield and characteristics of mesa-type semiconductor devices.

[Brief explanation of drawings]

Figures 1a and 1b are a plan view of the glass packaging of the mesa-type semiconductor element substrate and its A-A' cross-sectional view;
Fig. 2 is a diagram schematically showing the glass layer electrodeposition process using the electrophoresis method, Fig. 3 is a diagram showing the state of a semiconductor element substrate in a glass electrodeposition liquid bath according to the conventional method, and Fig. 4 is a diagram showing the state of the semiconductor element substrate in the glass electrodeposition liquid bath according to the conventional method. FIG. 2 is a diagram showing the state of a semiconductor element substrate in a glass electrodeposition liquid bath in one example. DESCRIPTION OF SYMBOLS 1...Semiconductor element substrate, 2...Vertical groove, 3...Horizontal groove, 4...Glass electrodeposition liquid tank, 5...Anode.

Claims (1)

[Claims] 1. A semiconductor device substrate having a mesa groove formed in a lattice pattern on the surface in which a PN junction of a unit device is exposed,
A method for manufacturing a semiconductor device comprising the step of electrodepositing a glass layer in the mesa groove in a glass electrodeposition solution with its surface facing the anode, A method for manufacturing a semiconductor device, characterized in that the glass layer is electrodeposited by arranging the longitudinal grooves and the lateral grooves of the mesa groove in the electrodeposition liquid so that their inclinations with respect to the vertical line are symmetrical. 2. The semiconductor element substrate in the glass electrodeposition liquid is placed so that the vertical and horizontal grooves of the mesa grooves on the surface thereof are 45 mm with respect to the vertical line.
A method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device is held in a tilted state. 3. By rotating the semiconductor element substrate in the glass electrodeposition liquid within the vertical plane while keeping its surface within the vertical plane, the inclinations of the longitudinal grooves and the lateral grooves of the mesa grooves on the surface with respect to the vertical line are substantially reduced. A method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device is symmetrical.