JPH05304143A - Formation of isolation region - Google Patents

Abstract

PURPOSE:To grow a LOCOS oxide sufficiently by etching a silicon substrate, removing side wall, and then performing oxidation to expose a polysilicon film thereby suppressing bird's beak. CONSTITUTION:A silicon substrate 1 is sequentially deposited with a silicon oxide 2, a polysilicon 3, and a silicon nitride 4, and then subjected to isolation patterning. Silicon nitride is then removed from an isolation region to expose the surface of the polysilicon 3 thus forming an opening. A pattern 8 is then removed and a silicon oxide 5 is deposited on the entire surface by CCD method and subsequently etched back to form a side wall 6 at the opening. The polysilicon 3 and silicon oxide 2 are then removed through etching with the silicon nitride 4 and the side wall 6 as a mask. Thereafter, the side wall 6 is removed by means of diluted HF solution and oxidation is performed in wet atmosphere thus forming an isolation region 7.

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.

[0002]

2. Description of the Related Art In order to develop a large-capacity VLSI, it is necessary to develop an integrated circuit having a high degree of integration within a limited chip area, which requires miniaturization of transistors and element isolation regions. Required.

Generally, a method called selective oxidation method is used for forming the element isolation region. This method involves forming a silicon nitride film on a silicon substrate, patterning it by a photolithography process, removing the silicon nitride film in the area that will become the element isolation region, and selectively oxidizing the exposed silicon substrate surface to isolate the element. This is a method of forming a region.

[0004]

However, in the case of using the conventional technique, the following points are problems regarding the reduction of the element isolation region.

First, at the time of selective oxidation, the silicon substrate at the interface with the silicon nitride film around the opening is oxidized, the silicon oxide film called bird's beak spreads, the element region becomes narrower than the mask size, and the integrated circuit is miniaturized. It will be difficult.

As a technique for suppressing bird's beak, a method of forming a sidewall beside a silicon nitride film, a silicon oxide film, a polysilicon film and a silicon nitride film are sequentially formed on a substrate, and a silicon nitride film is opened. , There is a polylocos method for performing selective oxidation.

In the method of forming the sidewall, there is a problem that the opening width of the selective oxide film becomes smaller as the pattern becomes finer, and the locos film thickness becomes thinner than that in the case of a wide opening portion. Problems such as a decrease in the threshold voltage occur. In the Polylocos method,
Although the Locos film thickness is ensured even in a fine pattern, since the substrate is oxidized after the polysilicon film on the upper surface is oxidized, the oxidation in the substrate is reduced and the effective separation distance is shortened, so that the separation There is a problem that the breakdown voltage is lowered.

An object of the present invention is to provide a method of forming an element isolation region in which a sufficient amount of locos oxide film has been grown.

[0009]

A method of forming an element isolation region according to the present invention comprises a step of sequentially forming a first oxide film, a polysilicon film and a nitride film on a silicon substrate, and patterning and etching. A step of removing the nitride film in a portion to be formed, exposing the surface of the polysilicon film and forming an opening, and forming a second oxide film on the entire surface,
Forming a side wall on the side wall of the opening by etching back; and using the side wall as a mask to remove the polysilicon film and the first oxide film and etch the silicon substrate to a predetermined depth. After removing the sidewall, oxidation is performed to form an element isolation region.

[0010]

By using the above-described invention, a silicon oxide film is formed to a sufficient depth from the surface of a silicon substrate, and an element isolation region in which bird's beak is suppressed as compared with the conventional case is formed.

[0011]

EXAMPLES The present invention will be described in detail below based on examples. FIG. 1 is a manufacturing process diagram of an embodiment of the present invention.

First, on the silicon substrate 1, a silicon oxide film 2 as an antioxidant film having a film thickness of about 100 Å, a polysilicon film 3 having a film thickness of 300 to 900 Å, and a silicon nitride film 4 having a film thickness of 1200 to 1600 Å. The layers are sequentially formed, and then a portion to be an element isolation region is patterned by a photolithography process (FIG. 1A).

Next, by plasma etching or the like, the silicon nitride film 4 in the portion which becomes the element isolation region is removed, the surface of the polysilicon film 3 is exposed, and an opening is formed. Next, after removing the pattern 8 formed by the lithography process, the silicon oxide film 5 is formed on the entire surface by the CVD method (FIG. 1B), and the etch-back is performed by the RIE method to form the opening. A side wall 6 having a film thickness of about 1000Å is formed on the side surface (FIG. 1C).

Next, the polysilicon film 3 and the silicon oxide film 2 are removed using the silicon nitride film 4 and the sidewall 6 as a mask, and the depth 700 from the surface of the silicon substrate 1 is removed.
Etching is performed up to 800 Å (Fig. 1 (d)).

Next, the side wall 6 is removed with a dilute HF solution (FIG. 1E), and oxidation is performed in a wet atmosphere.
The element isolation region 7 is formed (FIG. 1F).

Next, the silicon nitride film 4 is removed by using boiling phosphoric acid, and the polysilicon film 3 is removed by using the RIE method.
A semiconductor integrated circuit is formed by forming a semiconductor element such as a transistor according to a normal process.

[0017]

As described above in detail, since the silicon substrate is previously etched by using the present invention, effective element isolation in the depth direction of the substrate, which is a problem in the polylocos method, is obtained. The distance can be secured. Further, since the oxidation is performed after removing the sidewalls, the polysilicon film is exposed more than in the conventional case, bird's beak can be suppressed, and the locos oxide film can be sufficiently grown.

[Brief description of drawings]

FIG. 1 is a process drawing of an embodiment of the present invention.

[Explanation of symbols]

 1 Silicon Substrate 2 Silicon Oxide Film 3 Polysilicon 4 Silicon Nitride Film 5 Silicon Oxide Film 6 Sidewall 7 Element Isolation Area 8 Pattern

Claims (1)

[Claims] 1. A step of sequentially forming a first oxide film, a polysilicon film and a nitride film on a silicon substrate, and a step of patterning and etching to remove the nitride film in a portion to be an element isolation region, and the polysilicon film Exposing the surface to form an opening; forming a second oxide film on the entire surface and forming a sidewall on the sidewall of the opening by etching back; and using the sidewall as a mask A step of removing the silicon film and the first oxide film and etching the substrate to a predetermined depth; and a step of removing the side wall and then oxidizing the substrate to form an element isolation region. A method for forming an element isolation region.