JPS5832421A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To electrodeposit fine glass powder uniformly on a mesa grooves among pellets on a wafer by applying cataphoresis, using electrodes that have a larger porosity rate at the peripheral section. CONSTITUTION:Stainless steel rings 11 are supported by radially extending rods 12 around the circumference of a central circular plate made of stainless steel, and the distance between the rings 11 is larger towards the circumference. An electrode 18 is formed by making the electric field intensity at the circumference equal to that of the central position. The electrode 18 is immersed into an electrodeposition solution 7. The electrode 18 is made positive and the wafer 1 negative and voltage is applied to both to make the fine glass powder in the solution electrodeposited on an exposed mesa groove. With this constitution the thickness of the glass electrodeposition on the mesa groove becomes uniform on the whole wafer area with the result of improved ratio of good products.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device including a step of forming a glass protective film in a mesa groove carved between pellet regions of a semiconductor wafer.

In general, me? Semiconductor devices such as type transistors and Nyristors are manufactured through the process of forming multiple semiconductor pellet regions (hereinafter simply referred to as pellets) on a single semiconductor wafer by selective diffusion, etc., and the process of forming mesa grooves between the pellets of the wafer by etching. The semiconductor wafer is manufactured through the steps of applying a protective film to the mesa groove, forming electrodes on both the front and back surfaces of the semiconductor wafer, and dividing the semiconductor wafer into finely divided semiconductor pellets.

Incidentally, the protective film for protecting the mesa grooves is sometimes made of rubber, but usually glass is used, and the process of forming this glass protective film is called glazing. There are precipitation methods, electrophoresis methods, printing methods, and coating methods as methods for graphigraphy, and the present invention relates to electrophoresis methods. □For example, to explain the conventional method of the glassy pinning process using 8CR as a semiconductor device, Figures 1 and 2 show a wafer that has completed the mesa groove forming process and is undergoing the glassy baking process. In the figure, P-type impurities are diffused from both the front and back surfaces of an N-type wafer 1 to form a P-type region 2, and a plurality of N-type impurities are formed in the P-type region on the front side.
A mold region is formed by selective diffusion of an N-type cotton material to form a plurality of pellet regions 3 including the N-type region, and then an oxide film 4 is formed on the entire front and back surfaces of the wafer, and then on this oxide film. For example, wax 5 is applied to the wafer except on the circumference of the pellets, and the oxide film and the wafer are etched from the areas where the wax 5 is not applied to form mesa grooves 6 between the pellets of the wafer.

At this time, the PN junction of each pellet area is exposed in the mesa groove 6, and if foreign substances such as heavy metals, moisture, and goo are attached thereto, it will cause leakage and voltage resistance deterioration, so it is necessary to protect the mesa groove 6. .

That is, first, the Quaeno-9 is immersed in an electrodeposition solution as shown in FIG. This electrodeposition solution is made by suspending fine glass powder in an electrolytic solution. Next, an electrode plate 8 is placed near both the front and back surfaces of the wafer l, and a positive voltage and an i-minus voltage are applied to the electrode plate and the wafer. Then, as shown in FIG. 4, the glass fine powder 9 in the electrodeposition liquid 7 is electrodeposited on the mesa #I6 which has a negative potential. After that, the wafer 1 is baked with electrodeposition liquids 7 to 9 to form a glass protective film.

By the way, there are the following problems with this conventional gracipaging process. That is, the wafer has a high probability of forming a pellet on the periphery and being defective, and therefore, the pellet is formed only on the portion of the wafer other than the periphery. Gracipation of this wafer was carried out by insulating and protecting the entire surface of the wafer except for the mesa groove with wax or an oxide film. When voltage is applied in the state shown in Figure 3, only the mesa grooves are exposed in the electrodeposition solution and electrodeposited, but the strength of the electric field is not uniform at the periphery and center of the wafer, especially at the outermost periphery of the wafer. The difference in strength from the electric field at the center is greatest near the center. Therefore, the layer of fine glass powder tends to be significantly thicker near the periphery than in the center. This is the biggest cause of variations in glass thickness after firing.

An object of the present invention is to provide a method for manufacturing semiconductor devices with high yield while suppressing the above-mentioned variations in glass thickness.

Next, the present invention will be explained with reference to the drawings. For example, when the wafer shown in Figures 1 and 2 is to be wrapped around the wafer, one example of weakening the electric field strength at the periphery of the wafer is to wrap it in concentric circles as shown in Figure 5 (-), Φ)K. A divided electrode 18 may be used. The electrode 18 has a structure in which several rings 11 of stainless steel strips with different diameters are supported by support rods 12 arranged radially around a central disc made of stainless steel.
The spacing of 1 becomes gradually sparser towards the periphery,
K to make the electric field strength at the periphery equal to that at the center.
It is.

As shown in FIG. 6, the entire structure is immersed in an electrodeposition liquid 7. Then, a positive voltage and a negative voltage of the wafer IK are applied to the electrode 18. Then, the fine glass powder in the electrodeposition liquid 7 is exposed and electrodeposited in the nine mesa grooves.

Conventional flat plate electrodes have a strong electric field at the periphery and the fine glass powder is electrodeposited significantly thicker, but with the electrode 18 described above,
It is possible to achieve uniform electrodeposition in the peripheral area, which is equal to that in the central area.

As explained above, according to the present invention, when a flat plate electrode is used during glass electrodeposition, the electric field is concentrated in the peripheral area and the glass thickness is not uniform. 2) The thickness of the glass electrodeposited layer in the mesa groove is made uniform over the entire area, making it possible to always achieve good glass basing and improving the yield rate of products.

[Brief explanation of the drawing]

Fig. 1 is a plan view of a semiconductor wafer, Fig. 2 is a partially enlarged sectional view of Fig. 1, Fig. 3 is a schematic sectional view of a glass electrodeposition apparatus explaining the conventional glassy basin process, and Fig. 4 is a partially enlarged cross-sectional view of FIG. 3, FIG. 1 is a schematic cross-sectional view of a glass electrodeposition apparatus using parts. l・−・−・Semiconductor wafer, 2=, −p type region, 3・
...--Bellet region, 4... Oxide film, 5.
−・−Wax, 6・−・・・・Mesa groove, 7−・・・・
Electrodeposition liquid, 8, 18--electrode, 9--glass powder, 10--center disk, 11--circular body, 12--... support rod. 3rd Figure 6

Claims (1)

[Claims] In order to suppress electric field concentration at the periphery of the wafer, a camellia slanting layer is formed between the pellet areas of the conductive conductor in which a large number of pellet regions are formed except for the periphery of the wafer. 9. A method of manufacturing a semiconductor device, characterized in that glass powder is electrodeposited in the mesa groove using an electrophoresis method using an electrode having a large void ratio in the peripheral portion.