JPS60196955A - Manufacture of dielectric isolation plate - Google Patents

Abstract

PURPOSE:To improve the crystallizability of a polycrystalline silicon layer which is formed on the surface, and facilitate oxidation to form an insulating layer, by a method wherein the surface is made to a porous silicon layer having small hole diameter, and the inner part of a base plate is made to a porous silicon layer having large hole diameter. CONSTITUTION:Single crystal silicon of 5mum is made porous in a 50% hydrogen fluoride solution. On this occasion, a 0.5mum part of the surface is anode formation treated at the current density of 5mA/cm<2>, and a remaining 4.5mum part is anode formation treated at the current density of 100mA/cm<2>. The qualities of the two porous silicon which were produced on this consequence are different, and at the part which was anode formation treated at the condition current density of the surface is small, the hole diameter is small, and at the part which was anode formation-treated under the condition current density of the inner part is large, the hole diameter is large. Hereby, the crystallizability of epitaxial silicon layer becomes excellent, and easy to be oxidized the hole diameter becoming large at the inner part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention provides a method for manufacturing a dielectric isolation substrate for a semiconductor integrated circuit in which the side and bottom surfaces of a plurality of single-crystal silicon islands are surrounded by an insulating layer of silicon dioxide. It is related to.

[Technical background of the invention]

The use of dielectric isolation technology is being considered for the purpose of increasing the degree of integration and improving the characteristics of semiconductor integrated circuit devices.

This is intended to completely isolate the periphery and bottom of a single-crystal silicon island by surrounding it with a silicon dioxide layer.

There are various types of dielectric isolation, but one that has recently attracted attention is a method in which a dielectric isolation region of silicon dioxide is formed by oxidizing porous silicon. Porous silicon is formed by anodizing a single crystal silicon substrate in a hydrogen fluoride solution.

The present invention relates to a method of manufacturing a dielectric isolation substrate as described above, and is characterized by a method of forming a porous silicon layer by anodization treatment.

[Prior art and its problems]

A general example of a method for manufacturing a dielectric isolation substrate by oxidizing porous silicon, which is the premise of the present invention, will be described with reference to FIG. FIG. 1 is a front sectional view showing a method of manufacturing a dielectric isolation substrate.

A P-type pre-crystalline silicon substrate 10 is prepared (A).

This single crystal silicon differential plate 10 is anodized in a hydrogen fluoride solution to form porous silicon Nll on the surface (
B). A Nm single crystal silicon layer 12 is epitaxially grown on the surface of this porous silicon layer 110 (C). A P-type region 13 is formed in a part of the single crystal silicon layer 12 by diffusion or ion implantation (D). This P-type region 13 is anodized to form a porous silicon 14.
(E). CF) in which a porous silicon layer 11 formed in a single crystal silicon substrate 10 and a porous silicon region 14 formed in an epitaxial layer 12 are silicon oxide 15. In this way, a dielectric isolation substrate is obtained in which islands 16 of single crystal silicon surrounded by silicon dioxide 15 are formed.

In the method for manufacturing a dielectric isolation substrate as described above, a single crystal silicon layer is epitaxially grown on a porous silicon layer. Porous silicon literally has many pores formed within its crystal.

This can be schematically represented as shown in Figure 2. That is, the structure is such that a hole 21 is formed within the substrate 20.

If the diameter of the pores is too large or the density is too high, the crystallinity of the single crystal silicon layer formed on the porous silicon layer will deteriorate. Therefore, if the thickness of the epitaxial layer is small, the crystallinity will be significantly degraded, so in order to improve the crystallinity, the thickness of the epitaxial layer must be increased.

[Purpose of the invention]

An object of the present invention is to provide a method for manufacturing a dielectric isolation substrate that can solve the above problems and epitaxially grow a single crystal silicon layer with good crystallinity on a porous silicon layer. do.

Another object of the present invention is to form a porous silicon layer that not only improves crystallinity but also facilitates oxidation so that a silicon dioxide region can be formed in a short time.

[Summary of the invention]

The present invention achieves the above object by forming a porous silicon layer formed in a single crystal silicon substrate in two layers hL, with a porous silicon layer with a small pore diameter on the surface and a porous silicon layer with a large pore diameter inside the substrate. The goal is to achieve the following.

As a result, the epitaxial silicon layer formed on the surface has good crystallinity, but the inside has a large pore diameter and is easily oxidized.

As a means of changing the pore diameter of the porous silicon layer, the current density applied to the porous silicon layer during anodization is changed. The change can be made multiple times, but for practical purposes, two layers are sufficient, and a small current density is applied at first, and a slightly larger current density is applied later.

[Example of the present invention]

Hereinafter, embodiments of the present invention will be described with a focus on the method of forming a porous silicon layer.

As described above, the anodization treatment is performed in a hydrogen fluoride solution by applying a current between the electrode on the back surface of the substrate and the electrode in the hydrogen fluoride solution. This anodizing treatment is generally performed for 30~
It has been carried out in a 50% solution at a current density of 5-100 rnA/cm'.

The present invention was made by focusing on the fact that the current density under the conditions of anodizing treatment influences the properties of porous silicon, and it forms a two-layer porous silicon layer by changing the current density. be.

In an embodiment of the invention, in a 50% hydrogen fluoride solution, 5
Single crystal silicon of μm size was made porous.

In this case, Id 5 mA/C at a 0.5 μm portion of the surface.
W? The remaining 4.5 μm was anodized at a current density of 100 mA/c-. The two resulting porous silicones have different properties.

The pore diameter was small in the part anodized with a low current density on the surface, and large in the part anodized with a high internal current density. 3 and 4 are diagrams schematically showing this.

Note that the two porous silicon layers formed as described above were oxidized later or in the process.

It was confirmed that the properties of the oxide films were slightly different.

〔Effect of the invention〕

In the present invention, since a porous silicon layer with a small pore diameter and a porous silicon layer with a large pore diameter are formed as described above, the crystallinity of the single crystal silicon layer formed on one surface is improved, and the insulating layer It becomes easier to oxidize to form.

It was also confirmed that the warpage after oxidation was reduced. The substrate obtained by oxidation at 950° C. for 1 hour in the above-mentioned series (
20×20 am) was 32 μm, which was smaller than that of the one subjected to anodization treatment at the same current density.

[Brief explanation of drawings]

Figure 1 shows a front view showing the manufacturing method of a dielectric isolation substrate Patent applicant: Toko Co., Ltd. Figure 1 Figure 2 Figure 21 Figure 3 Figure 4 Procedural amendment May 4, 1981 Mr. Kazuo Wakasugi, Commissioner of the Patent Office Display of case 1982 Patent Application No. 53278 2 Name of invention Method for manufacturing dielectric isolation substrate 3 Person making amendment Relationship to case Patent applicant Main lawsuit (8145) 2-1-17 Higashiyukidani, Ota-ku, Tokyo
No. 4゜5, Number of inventions increased by amendment O Contents of the amendment to the detailed description of the invention in the specification subject to amendment 1) In the 6th line of page 4 of the specification, ``above'' has been replaced with ``. (3) On page 4, line 8, correct "crystallinity is significant" to "crystallinity throughout the entire layer."

Claims (1)

[Claims] °One surface of a single-crystal silicon substrate is anodized in a 7-hydrogen fluoride solution to form a porous silicon layer, and a single-crystal silicon layer is epitaxy on the surface of the porous silicon layer. A dielectric isolation substrate which forms a silicon dioxide region around and on the bottom surface of the single crystal silicon island by growing a part of the single crystal silicon layer into silicon dioxide and oxidizing the porous silicon layer. In the manufacturing method. Anodization treatment is performed to reduce the pore size near the surface of the porous silicon layer and increase the internal pore size, and a single crystal 7 licon layer is epitaxially grown on the surface of the porous silicon layer with the small pore size. A method for manufacturing a dielectric isolation substrate featuring features.