JPH06163531A - Formation of element isolation region in semiconductor - Google Patents

Abstract

PURPOSE:To provide a method for forming isolation region of semiconductor device in which growth of bird's beak is retarded while relaxing stress in LO COS process. CONSTITUTION:In place of a conventional pad oxide, a thin nitride film (about 200Angstrom ) is formed on a substrate 1 and then patterned to form field oxide 3. Since the nitride film 2 is oxidized substantially completely, stress is relaxed and growth of bird's beak is retarded because no pad oxide is employed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an element isolation region in a semiconductor device.

[0002]

2. Description of the Related Art As is well known, the formation of an element isolation region for insulating and isolating adjacent elements formed on a semiconductor substrate is conventionally performed by, for example, J. Electrochem. Soc. SOLID-ST.
ATE SCIENCE AND TECHNOLOGY, 130 [7] (1983) (US) p.156
As disclosed in 3-1566, many LOCOS (Local Oxid
ation of Silicon) method. The forming method is shown in FIG. 4 and described below.

First, as shown in FIG. 4A, a thin pad oxide film 11 having a thickness of about 300 Å is formed on a semiconductor substrate (generally a Si substrate) 1 by thermal oxidation.

Next, as shown in FIG. 4B, a silicon nitride film (Si ₃ N ₄ film) 2 is formed on the pad oxide film 11 by LPCVD (Low Pressure Chemical Vapor Deposition) method, and element isolation is performed. Although not shown, the Si ₃ N ₄ film 2 to be a region is removed by photolithography (photolithography) using a resist pattern or an etching technique (so-called patterning).

Thereafter, as shown in FIG. 4 (c), when it is oxidized by thermal oxidation, a so-called field oxide film 3 is formed in the element isolation region with a thickness of about 6000Å.

However, at this time, as shown in the same figure and as described in the above-mentioned document, a shape called "bird's beak" that bites into the element formation region by oxidation occurs. The larger the bite beak bites, the more difficult it is to secure a sufficient element formation region. Therefore, it is necessary to reduce this bird's beak as much as possible, and as a countermeasure against it, conventionally, a method of making the pad oxide film 11 thinner, a method of making the nitride film 2 thicker, a method of making the field oxide film 3 thinner, etc. have been taken. Has been.

[0007]

However, a sufficient solution has not been obtained by any of the methods described above. Both the method of thinning the pad oxide film and the method of thickening the nitride film increase the stress induced in the peripheral portion of the bird's beak, so that a crystal defect occurs in the Si substrate. This defect has a fatal effect on the electrical characteristics of the device. On the other hand, under the condition that no defect occurs, the bird's beak digs into the entire element region, which makes it difficult to secure the element region. Further, even in the method of thinning the field oxide film, there is a limit to thinning it in order to secure sufficient insulation characteristics, and the effect for reducing bird's beak is small.

According to the present invention, in order to suppress the growth of the bird's beak described above and to alleviate the stress, the pad oxide film is not formed, and the thickness of the silicon nitride film is set so that the film is almost oxidized. The purpose is to form a field oxide film with less stress and less bird's beak growth.

[0009]

For the above-mentioned purpose, the present invention provides a method of forming an element isolation region in which a pad oxide film which has been conventionally formed is not formed and most of the silicon nitride film is oxidized by thermal oxidation. The thickness is set to the extent that

[0010]

As described above, according to the present invention, since the pad oxide film is not formed, the growth of bird's beaks can be suppressed, and the silicon nitride film is thinly formed. The film is almost oxidized, and the stress caused by the difference in the coefficient of thermal expansion when the temperature is lowered is relieved.

[0011]

1 shows a first embodiment of the present invention, which will be described below.

First, as shown in FIG. 1A, a silicon nitride film (hereinafter simply referred to as a nitride film) 2 is formed on a silicon substrate (hereinafter simply referred to as a substrate) 1 by LPCVD or RTN.
It is formed by the (Rapid Thermal Nitrization) method. At this time, the thickness of the nitride film 2 is set to about 200Å, which is the thickness at which most of it is oxidized by the thermal oxidation described later. As is well known, when such a nitride film is thermally oxidized at about 1500 ° C., it is oxidized to a thickness of about 200Å.

Then, as shown in FIG. 1B, patterning is performed by photolithography and etching techniques so that the nitride film 2 is left only in the element formation region.

Thereafter, as shown in FIG. 1C, a field oxide film 3 is formed by thermal oxidation. At this time, since there is no pad oxide film that serves as a diffusion passage for the oxidizing species unlike in the conventional case, lateral diffusion of the oxidizing species is strongly suppressed and the growth of the bird's beak becomes extremely small. Further, since the nitride film 2 is completely or almost completely oxidized by the thermal oxidation as described above, the stress caused by the elastic deformation of the nitride film can be largely relieved, and the pattern edge may be changed due to the difference in the thermal expansion coefficient of the material when the temperature is lowered. Almost no stress is induced. That is, conventionally, there are three layers of a substrate, a pad oxide film, and a nitride film, and the stress is large due to the difference in the coefficient of thermal expansion of the three kinds of materials, but in this embodiment, the nitride film 2 is oxidized. Therefore, so to speak, only the difference in the coefficient of thermal expansion between the substrate 1 and the oxidized nitride film 2 results in less stress.

FIG. 2 shows a second embodiment of the present invention, which will be described below.

First, as shown in FIG. 2, a nitride film 2 is formed on a substrate 1.
Is thinly formed as in the first embodiment, and is patterned by photolithography and etching to remove the element isolation region portion.

Next, as shown in FIG. 2B, an oxide film 4 is formed on the patterned element isolation region by thermal oxidation. At this time, the oxidation also oxidizes the upper portion of the substrate 1 in the region. Therefore, when the oxide film is removed by etching in the process described later, the oxidized portion of the substrate 1 is also removed and a recess is formed.

Next, as shown in FIG.
Patterning the element isolation region with etching technology,
When the oxide film 4 is removed by HF (hydrofluoric acid) treatment,
As described above, the recess is formed in the substrate 1.

Thereafter, as shown in FIG. 2D, thermal oxidation is performed again to form a field oxide film 3 in the element isolation region. Also in this case, since the nitride film 2 is almost oxidized as in the first embodiment, the stress is relieved as described in the first embodiment. Also, as in the first embodiment, since there is no pad oxide film, the growth of bird's beak is also suppressed.

FIG. 3 shows a third embodiment of the present invention, which will be described below.

First, as shown in FIG. 3A, the nitride film 2 is thinly formed on the substrate 1 as in the first and second embodiments. Then
As shown in FIG. 3B, patterning is performed by photolithography or an etching technique until a recess is formed in the substrate 1 in the element isolation region.

Next, as shown in FIG. 3C, the field oxide film 3 is formed in the element isolation region by thermal oxidation. At this time, the nitride film 2 is almost oxidized as in the first and second embodiments, and contributes to stress relaxation. After this, for example, SOG
An oxide film type insulating film 5 such as (Spin on Glass) is deposited on the entire surface and the surface is made as flat as possible.

Then, as shown in FIG. 3D, the SOG
5 and the oxidized nitride film 2 are removed by etching by HF treatment to form an element formation region (that is, other than the element isolation region).
When exposed, the field oxide film 3 having almost no bird's beak is formed.

[0024]

As described above, according to the present invention,
Since the pad oxide film is not formed when the element isolation region is formed by the LOCOS method, the bird's beak can be prevented from entering. Further, since the thickness of the silicon nitride film is formed so thin that it is almost oxidized by thermal oxidation, the stress caused by the elasticity of the nitride film and the stress caused by the difference in the coefficient of thermal expansion during temperature reduction can be relaxed. The effect of suppressing the generation of defects in the silicon substrate can be expected.

That is, a very good element isolation region with a small bird's beak can be formed.

[Brief description of drawings]

FIG. 1 is a first embodiment of the present invention.

FIG. 2 is a second embodiment of the present invention.

FIG. 3 is a third embodiment of the present invention.

FIG. 4 Conventional example

[Explanation of symbols]

 1 silicon substrate 2 silicon nitride film 3 field oxide film 4 oxide film 5 SOG

Claims (3)

[Claims] 1. A step of: (a) forming a nitride film having a thickness such that it is completely or almost completely oxidized in an oxidation step on a semiconductor substrate; and (b) leaving the nitride film in an element formation region portion. A method of forming an element isolation region in a semiconductor device, comprising: a step of patterning into a shape; and (c) a step of forming a field oxide film in the element isolation region by oxidation and oxidizing the nitride film. 2. A step of: (a) forming a nitride film having a thickness such that it is completely or almost completely oxidized in the oxidation step on a semiconductor substrate, and patterning it into a shape in which an element formation region is left; A step of oxidizing part of the element isolation region on the substrate to form an oxide film; and (c) patterning the element isolation region and removing the oxide film to form a recess in the element isolation region part of the substrate. And (d) forming a field oxide film in the element isolation region by oxidation, and oxidizing the nitride film, the method for forming an element isolation region in a semiconductor device. 3. A step of: (a) forming a nitride film having a thickness such that it is completely or almost completely oxidized in an oxidation step on a semiconductor substrate; Patterning until the recess is removed to form a recess, (c) a field oxide film is formed in the recess and the nitride film is oxidized, and (d) an insulating film is formed on the entire surface of the surface. After flattening
A method of forming an element isolation region in a semiconductor device, comprising the step of removing the insulating film and at least the oxidized nitride film.