JPS641066B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method of manufacturing a semiconductor substrate for power use. In a semiconductor device in which a collector electrode is taken out from the back surface, a highly concentrated impurity layer of the same conductivity type as the collector is required on the back surface in order to reduce the saturation resistance of the collector. A method for manufacturing a semiconductor substrate for such a semiconductor device is to diffuse impurities of the same conductivity type as the collector (N ⁺ layer in an NPN semiconductor element) onto both sides of the semiconductor substrate, and then scrape off the diffusion layer on one side by wrapping. Furthermore, a method is known in which the crushed layer is removed by mirror wrapping and the surface is mirror-finished. Semiconductor substrates manufactured in this manner are generally referred to as one-side wrapping finished wafers (OSL wafers). Hereinafter, a conventional method for manufacturing a semiconductor substrate will be explained with reference to FIGS. 1A to 1E. First, as shown in FIG. 1A, for example, an N-type semiconductor substrate 1 having a thickness of 500 μm and a #1000 lap finish is prepared. Next, as shown in FIG. B, on both sides of this semiconductor substrate 1,
N ⁺ type impurities such as phosphorus oxychloride ( _POCl3 )
The high concentration ^impurity layer 2 (sheet resistance
2.3 to 0.5 Ω/, N ⁺ depth 15 μm).
Next, as shown in Figure C, this was heated to a temperature of 1270℃.
The highly concentrated impurity layer 2 is placed in a diffusion furnace for 270 hours and slumped to obtain a highly concentrated impurity layer 3 having a diffusion depth of 190 μm. Next, as shown in figure D,
Remove the high concentration impurity layer 3 on one side by scraping up to 220 μm from the surface using #1000 lap. Furthermore, mirror wrapping is performed to remove the crushed layer on the surface of the high concentration impurity layer 3 and give the surface a ^mirror finish, and as shown in Fig. A semiconductor substrate 5 having a mirror finish on the surface of 250 μm is obtained. However, the conventional semiconductor substrate manufacturing method has the following drawbacks. In order to manufacture a semiconductor substrate 5 with a finished thickness of 250 μm, a thick semiconductor substrate 1 having an inner thickness of 500 μm is required, and a large amount of the semiconductor substrate 1 is lost. The amount of scraping on one side must be at least 200μm,
Since mirror lap finishing and mechanical finishing are required after polishing with #1000 lap, the lifetime of the substrate will be shortened when making power semiconductor devices. The present invention has been made in view of this point, and has discovered a method for manufacturing a semiconductor substrate that can easily manufacture a semiconductor substrate with a long lifetime using a thin semiconductor. An embodiment of the present invention will be described above with reference to the drawings. First, as shown in Figure 2A, the thickness
An N conductivity type semiconductor substrate 10 with a 270 μm #1000 wrap finish is prepared. Next, as _shown in ^FIG .
The film is deposited in an oxidizing atmosphere at a temperature of 3 hours to form a highly concentrated impurity layer 11 (sheet resistance 0.3 to 0.5 Ω/□ diffusion depth 15 μm). Next, as shown in FIG. 3C, oxidation is performed at a temperature of 1000° C. for 2 minutes while flowing steam to form a first oxide film 12 on the surface of the high concentration impurity layer 11. This first oxide film 12 is
High concentration impurity layer 1 in the next N ⁺ slumping diffusion
The film thickness is preferably set to 8000 Å to 10000 Å. Next, after protecting the back surface with wax or the like, the first oxide film 12 on one surface is removed using a hydrofluoric acid solution. Furthermore, chemical etching is applied to the removed surface. In this case, the etched finished surface needs to be a mirror finished surface because there is an oxide film etching step using a photonist in the semiconductor device manufacturing process. In addition, the semiconductor substrate 10
This is done so that the inside is uniform and the high concentration impurity layer 11 on one side can be removed reliably. For example, using a mixed acid etching solution with a volume ratio of hydrofluoric acid: nitric acid: acetic acid = 1:2:1, etching is performed for 200 seconds at a solution temperature of 15° C. to obtain an etching amount of 30 μm. Thereafter, as shown in Figure D, the protective wax on the back surface is removed by triclean treatment. Next, as shown in Figure E, a second oxide film 13 is formed on the mirror-etched surface. The second oxide film 13 is, for example,
The film is formed by oxidation in a steam atmosphere at 1000° C. for 4 hours, and the film thickness is 10000 to 11000 Å. Next, as shown in FIG. 3, the first oxide film 12,
A large number of semiconductor substrates 10 each having a high concentration impurity layer 11 and a second oxide film 13 formed thereon are prepared.
The stack 15 is assembled by abutting the oxide films 12 and the second oxide films 13 back to back so that they overlap and fixing them together while applying pressure with the guide plate 14 so that no gaps are left. 50 between guide plates 14
~100 semiconductor substrates 10 are provided back to back. Next, this stack 15 was placed in an oxidizing atmosphere at 1270°C for 270 hours to form a highly concentrated impurity layer 1.
Stack diffusion is performed until the diffusion depth of 1 reaches 190 μm. After the stack diffusion, the semiconductor substrates 10 that are stuck together in a back-to-back state are immersed in a hydrofluoric acid solution.
The first oxide film 12 and the second oxide film 13 are dissolved and removed to obtain a semiconductor substrate 16 whose surface is finished by mirror etching, as shown in FIG. 2F. As described above, according to this semiconductor substrate manufacturing method, it is possible to easily obtain the semiconductor substrate 16 whose surface is finished by chemical mirror etching using the thin semiconductor substrate 10. Further, the first oxide film 12 was attached to the surface of the high concentration impurity layer 11 before etching one side, the second oxide film 13 was attached to the exposed surface after etching one side, and the number of semiconductor substrates 10 The first oxide film 1
By stacking the high concentration impurity layer 11 and the second oxide film 13 back to back and bringing them into close contact with each other while applying pressure with the guide plate 14, the high concentration impurity layer 11 is stacked and diffused as shown in FIG. The impurities in the concentrated impurity layer 11 are diffused to the outside to form the semiconductor substrate 10.
Formation of high concentration impurity region 16a therein can be prevented. Furthermore, the high concentration impurity layer 11
Because there is no need to scrape off more than 200μm on one side after the stack is diffused, 30μm can be removed without wrapping.
A mirror surface can be formed by single-sided chemical etching of about m. Also, since a mirror surface can be formed by chemical etching, fracture and strain layers can be reduced compared to conventional mechanical surface finishing methods. As a result, as shown in FIG. 5, it is possible to manufacture a semiconductor device 18 in which an impurity region 17 forming a PN junction with a planar structure is formed at a depth of 30 to 40 μm from the surface and an electrode is provided. The lifetime distribution of this semiconductor substrate 16 is as shown in FIG. 6B, which is much longer than the lifetime distribution diagram of a semiconductor substrate manufactured by the conventional method shown in FIG. 6A. Although the embodiments have been described with reference to an NPN type semiconductor substrate, the present invention can of course be similarly applied to a PNP type semiconductor substrate. As explained above, according to the method for manufacturing a semiconductor substrate according to the present invention, a semiconductor substrate with a long lifetime can be easily manufactured using a thin semiconductor substrate.

[Brief explanation of drawings]

1A to 1E are explanatory diagrams showing conventional semiconductor substrate manufacturing process diagrams, and FIGS. 2A to 2F are
An explanatory diagram showing a manufacturing process diagram of the semiconductor substrate of the present invention,
Fig. 3 is an explanatory diagram showing the state of stack diffusion, Fig. 4 is an explanatory diagram showing abnormal diffusion on the N ^- plane due to the jumping out of the N ⁺ impurity from the back surface during N ⁺ diffusion, and Fig. 5 is an explanatory diagram showing the state of stack diffusion.
The figure is a cross-sectional view of a semiconductor device using a semiconductor substrate manufactured by the present invention, Figure 6A is a lifetime distribution diagram of a semiconductor substrate manufactured by a conventional method, and Figure 6B is a diagram of a semiconductor device manufactured by the present invention The lifetime distribution diagram of semiconductor substrates manufactured in 10... Semiconductor base, 11... High concentration impurity layer, 12... First oxide film, 13... Second oxide film,
14...Guide plate, 16...Semiconductor substrate.

Claims (1)

[Claims] 1. A step of forming a high concentration impurity layer of the same conductivity type on both surfaces of each of at least two semiconductor substrates of one conductivity type, a step of forming a first oxide film on the surface of the high concentration impurity layer, and a step of forming a first oxide film on the surface of the high concentration impurity layer; a step of removing the high concentration impurity layer and the first oxide film by chemical etching and applying a mirror etching finish to the exposed surface; a step of forming a second oxide film on the mirror etching finished surface; the first oxide film of the semiconductor substrate and the first oxide film of the other semiconductor substrate, or the second oxide film of one of the semiconductor substrates and the first oxide film of the other semiconductor substrate. a step of forming a slumping layer in the semiconductor by introducing an impurity of the same conductivity type as the semiconductor substrate under heating in an oxygen atmosphere with the two oxide films butted against each other; and removing the first oxide film on the other side. A method for manufacturing a semiconductor substrate, comprising the steps of: