JPH0366127A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To manufacture a semiconductor device capable of forming an element isolation region whose pattern accuracy is high by executing a thermal oxidation operation after a mask for thermal oxidation use of a four-layer structure which is composed of a first silicon oxide film, a first silicon nitride film, a second silicon oxide film and a second silicon nitride film has been formed on an element formation region of a semiconductor substrate. CONSTITUTION:In order to increase a width of sidewall parts 7, a third silicon oxide film 6 by a CVD method and by a patterning operation is formed additionally on a second silicon nitride film 5. After the sidewall parts 7 have been formed in this manner, a first silicon nitride film 3 in regions other than lower parts of the sidewall parts 7 is removed by executing an RIE method using a fluorine-based gas; then, a first silicon oxide film 2 and said sidewall parts 7 are removed by a wet etching operation to obtain a mask for thermal oxidation use of a four-layer structure. By this manufacturing method, a semiconductor device provided with an element isolation region which reduces a bird's beak remarkably and whose pattern accuracy is excellent is obtained without exerting an adverse influence by a mechanical stress on a semiconductor substrate.

Description

[Detailed description of the invention] (b) Industrial application fields The present invention relates to a method for manufacturing a semiconductor device.

More specifically, the present invention relates to a method of manufacturing a semiconductor device having an element isolation region.

(B) Conventional Technology Conventionally, as a method for separating elements of semiconductor integrated circuits, a method is used in which a silicon nitride film patterned on a semiconductor substrate via an oxide film is subjected to selective thermal oxidation using as a mask for thermal oxidation.
The so-called Locos method has been used. Figure 2 shows a process diagram of the Locos method. In the figure, 1 is a silicon semiconductor substrate, 9 is a silicon oxide film, and IO is a patterned silicon nitride film.

After the state shown in FIG. 2, by performing selective scorching oxidation,
A thick silicon oxide layer 8 is grown on the silicon semiconductor substrate in the portion not covered by the silicon nitride film, and an element isolation region is secured. Note that the silicon nitride film IO is usually removed thereafter. The thickness of the silicon oxide film 9 is usually 2
The thickness of the silicon nitride film IO is usually about 1,500 to 2,500.

(c) Problems to be Solved by the Invention With the recent increase in the integration and density of semiconductor integrated circuits, it is desired to form element isolation regions with higher precision. In order to form the silicon nitride film with high precision, it is basically necessary to wrap around from the side edges of the silicon nitride film during thermal oxidation.
The width of the silicon oxide layer formed under the silicon nitride film (
Length of the so-called bird's beak; Fig. 4 12. ) should be minimized as much as possible.

As a method for reducing the length of the bird's beak in the conventional LOCOS method, the thickness of the silicon oxide film 9 serving as the underlying layer is made thin (usually about 100 to 200 layers), and the silicon nitride film 1 is made thinner.
Thickness of 0 to thickness < shi (usually around 2000 to 3000 people),
Furthermore, a method of increasing the thermal oxidation temperature has been adopted.

However, this method of increasing the thickness of the silicon nitride film IO is
Basically, by adopting a thickness that is difficult to bend or deform, it prevents silicon oxide from forming around the edges.
A large mechanical stress is applied to the semiconductor substrate under this film, and as a result, crystal defects are generated in the semiconductor substrate, which causes problems such as current leakage when used as a semiconductor device.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for manufacturing a semiconductor device that can reduce bird's beak and form element isolation regions with high pattern accuracy without applying mechanical stress to the semiconductor substrate. It is something.

(d) Means for solving problems/problems Thus, according to the present invention, on a silicon semiconductor substrate,
A thin first silicon nitride film is formed through the first silicon oxide film, and a thick second silicon nitride film is formed thereon through the second silicon oxide film. The silicon nitride film is patterned together with the second silicon oxide film into a shape corresponding to the element formation region, and the first silicon nitride film is patterned into a shape wider than the above shape, and then this semiconductor substrate is thermally oxidized. There is provided a method for manufacturing a semiconductor device, characterized in that a silicon oxide layer for element isolation is formed on a portion of the semiconductor substrate not covered with a silicon nitride film by subjecting the semiconductor substrate to certain conditions.

This invention provides a thermal oxidation mask having a four-layer structure consisting of a first silicon oxide film, a first silicon nitride film, a second silicon oxide film, and a second silicon nitride film on an element formation region of a semiconductor substrate. One of the features is that thermal oxidation is carried out by forming . Furthermore, the first silicon nitride film is thin and wider than the element formation area, and the second silicon nitride film is thick and has a pattern corresponding to the element formation area. The points used here are additional features.

In the present invention, the first silicon oxide film can be formed by, for example, a thermal oxidation method or a CVD method, and a thickness of about 50 to 200 is usually sufficient.

This first silicon oxide film is formed to prevent the first silicon nitride film from having an adverse effect on the semiconductor substrate and to improve etching removability.

The first silicon nitride film can be formed, for example, by a CVD method, and its thickness is usually suitably about 500-1500, and is thinner than the second silicon nitride film.

On the other hand, the second silicon oxide film can be formed by, for example, a CVD method, and a thickness of about 100 to 300 people is usually sufficient. Further, the second silicon nitride film can also be formed by, for example, the CVD method, and the thickness is made thicker than the first silicon nitride film, and the thickness is usually suitable for 2,000 to 3,000 people.

Such a four-layer thermal oxidation mask is formed by laminating a first silicon oxide film, a first silicon nitride film, a second silicon oxide film, and a second silicon nitride film in this order on a semiconductor substrate, and then patterning the film. It can be formed by More specifically, after forming the four-layer stack, (a) patterning the uppermost second silicon nitride film into a shape with approximately the same dimensions as the device shape tc@ region, (b) patterning the silicon oxide layer by CVD. Forming a sidewall part on the side of the pattern of the second silicon nitride film by deposition and anisotropic etching, and removing the second silicon nitride film and the second silicon oxide film other than the lower part of the sidewall part. (c) etching the exposed first silicon nitride film to pattern it into a shape wider than the second silicon nitride film by the amount of the sidewall, and removing the sidewall portion; It can be formed by a process.

Note that the patterning in the above step (a) is performed using, for example, RrE.
The process can be carried out under selective etching conditions for silicon nitride. The anisotropic etching in step (b) is performed by, for example,
This can be carried out under selective etching conditions for silicon oxide using the RIE method. Note that the removal of the second silicon oxide film is performed using C.
Although it may be performed before forming the silicon oxide layer by VD, C
This can be done simultaneously with the progress of etching of the silicon oxide layer after deposition of the silicon oxide layer by VD. Process (c
) can be carried out under the same silicon nitride etching conditions as described above. At this time, the surface of the first silicon nitride film is also slightly etched, but since the film thickness is large, no particular inconvenience occurs. Note that there is no particular need to remove the first silicon oxide film in the area exposed in step (c), but since it is a thin film as described above, it is necessary to remove the sidewall portion by isotropic etching such as wet etching and remove the first silicon oxide film in step (c). ) are removed during the process.

As described above, the wide pattern of the first silicon nitride film is determined by the width of the sidewall portion. Here, since the sidewall portion is determined by the thickness of the second silicon nitride film, it can be controlled by adjusting the film thickness. However, when forming a sidewall portion that is wider than the thickness of the second silicon nitride film, a third silicon oxide film is formed on this silicon nitride film after forming the second silicon nitride film. This is patterned into a shape corresponding to the element formation area, and then a second silicon nitride film is patterned in the same shape to form a two-layer structure pattern corresponding to the element formation area. The sidewall portion may be formed using the following steps.

In any case, the width of such sidewall section is usually 2
A range of approximately 500 to 3,500 people is suitable.

In the present invention, the thermal oxidation of the semiconductor substrate can be carried out under known conditions, and it is usually suitable to carry out heat treatment at about 950 to 1100 DEG C. in a 10 DEG gas atmosphere of H and O.

(e) Operation Under thermal oxidation conditions, silicon oxide wraps around and forms at the edges of the first silicon nitride film, especially below the wide portion, or the presence of the wide portion causes a thick film to form. The second silicon nitride film significantly suppresses or prevents the formation of silicon oxide that wraps around below the ends of the pattern. As a result, it is possible to significantly reduce the mechanical stress on the semiconductor substrate and to reduce the bird's beak caused by the thick second silicon nitride film pattern.

(f) Example A first silicon oxide film of about 100 layers was formed on a silicon semiconductor substrate (150 mmφ) by thermal oxidation, and a first silicon nitride film of about 1,000 layers was formed on this by low pressure CVD, and a first silicon nitride film of about 280 layers A second silicon oxide film of about 3,000 people and a second silicon nitride film of about 3,000 people were formed in this order. Next, the second silicon nitride film, which is the uppermost layer, is patterned by RIE (using fluorine-based gas) in a shape corresponding to the core formation region in the semiconductor substrate, and then the second silicon oxide film is patterned in the same shape by RIE (using fluorine-based gas). (using fluorine gas).

A silicon oxide layer with a thickness of approximately 2,500 to 3,500 layers is formed by low-pressure CVD to cover the pattern formation area, and is subjected to anisotropic etching with fluorine gas to form a sidewall portion (width of approximately 0.26 μm). ) was formed.

This state is shown in FIG. 1A. In the figure, ■ is a silicon semiconductor substrate, 2 is a first silicon oxide film, 3 is a first silicon nitride film, 4 is a patterned second silicon oxide film, 5 is a patterned second silicon nitride film, and 7 is an oxide film. This is a sidewall part made of silicon.

Note that FIG. 1B shows a state in which a third silicon oxide film 6 is further formed by CVD and patterning on the second silicon nitride film 5 in order to increase the width of the sidewall portion 7. be.

After forming the sidewall part 7 in this way, the first silicon nitride film 3 in the area other than the lower part of the sidewall part 7 is removed by subjecting it to the RrE method using fluorine gas, and then the first silicon oxide film 3 is removed from the area other than the lower part of the sidewall part 7. The film 2 and the sidewall portion 7 were removed by wet etching to obtain a thermal oxidation mask having a four-layer structure according to the present invention. This state is shown in FIG. 1C.

9-G- After this, the semiconductor substrate was heated with HtO10! By subjecting the semiconductor substrate to thermal oxidation conditions in a gas atmosphere at a temperature of 1050 DEG C., an element isolation region made of a silicon oxide layer 8 having a thickness of approximately eooo was formed in the exposed portion of the semiconductor substrate, as shown in the first diagram.

FIG. 3 shows an enlarged view of the element isolation region and the edge of the mask.

As described above, according to the method of this embodiment, the bird's beak length Q is approximately 0.18 μm, which is reduced by more than half of Q1 of approximately 0.44 μm in the conventional method (Locos method) shown in FIG. It turns out that it is done. Note that the arrows in FIGS. 3 and 4 indicate the magnitude of mechanical stress generated in each film,
In the conventional LOCO8 method, the stress was concentrated on the semiconductor substrate below the bird's beak, but the embodiment shown in FIG. 3 shows that stress is dispersed.

(G) Effects of the Invention According to the manufacturing method of the present invention, it is possible to obtain a semiconductor device having an element isolation region with significantly reduced bird's beak and excellent pattern accuracy without adversely affecting the semiconductor substrate due to mechanical stress. .

Therefore, its usefulness and usefulness are extremely great in the field of manufacturing semiconductor devices having miniaturized and highly integrated elements within a semiconductor substrate.

[Brief explanation of drawings]

1A to 1D are process explanatory diagrams of the manufacturing method of the present invention, FIGS. 2A and B are process explanatory diagrams of the conventional method, and FIG. 3 is an element isolation region and mask edge formed by the present invention. FIG. 4 is an enlarged cross-sectional view showing the relationship with FIG. 4, and is a diagram corresponding to FIG. 3 according to the conventional method. 1... Silicon semiconductor substrate, 2... First silicon oxide film, 3... First silicon nitride film, 4... Second silicon oxide film, 5. ...Second silicon nitride film, 6...Third silicon oxide film 7...Side wall portion, 8...Silicon oxide layer. Figure 1 A Figure B Figure 2 A 0 Figure 1 C Figure 2 B

Claims (1)

[Claims] 1. A thin first silicon nitride film is formed on a silicon semiconductor substrate via a first silicon oxide film. A thick second silicon nitride film is formed on the bracket via a second silicon oxide film. This second silicon nitride film is patterned together with a second silicon oxide film into a shape corresponding to the element formation region, and the first silicon nitride film is patterned into a shape wider than the above shape, and then . A method of manufacturing a semiconductor device, comprising: forming a silicon oxide layer for element isolation on a portion of the semiconductor substrate not covered with a silicon nitride film by subjecting the semiconductor substrate to thermal oxidation conditions.