JP2775772B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for forming an insulating isolation film in an element formation region.

[Conventional technology]

In a semiconductor integrated circuit, it is necessary to form many circuit elements on a common substrate and electrically insulate them. One of the methods is an insulation separation method using an oxide film. In this method, an oxidation-resistant film is partially left on a semiconductor substrate, and so-called selective oxidation is performed using the difference in oxidation rate with the semiconductor substrate to form a buried oxide film in the substrate to form an insulating isolation film. It is. This will be described below with reference to the drawings.

3 (a) to 3 (d) are cross-sectional views of a semiconductor chip shown in the order of steps for explaining a conventional method of manufacturing a buried oxide film.

First, as shown in FIG. 3 (a), a Si substrate 1 is thermally oxidized to form a thin first pad SiO ₂ film 2 having a thickness of about 500 °, and a first silicon film having a thickness of about 1000 ° is formed thereon. Nitride film (Si
₃ N ₄ film) 3 is deposited by a CVD method or the like, and then the first Si
The ₃ N ₄ film 3 is patterned by photolithography. Next, using this first Si ₃ N ₄ film 3 as a mask,
Selectively oxidize the surface of the substrate 1 to obtain a thick SiO
_Two films are formed. The thick SiO ₂ film is removed by buffered hydrofluoric acid or the like, and the second pad SiO ₂ having a thickness of about 500 mm is again formed.
After forming the film 4, a second Si ₃ N ₄ film 5 having a thickness of about 500 ° is deposited.

Next, as shown in FIG. 3B, when the entire surface of the Si substrate 1 is anisotropically etched until the second Si ₃ N ₄ film 5 is removed, the bird's beak portions of the Si ₃ N ₄ films 5A and 5B are formed. Remains.

Next, as shown in FIG. 3 (c), these Si ₃ N ₄ films 5A,
When the second selective oxidation is performed using 5B as a mask, a thick SiO ₂ film 6 having a thickness of about 12000 ° for insulation separation is formed. 7 in FIG. 3 (c) is the Si ₃ N formed by the second selective oxidation.
₄ SiO ₂ on the film.

Next, as shown in FIG. 3 (d), the SiO ₂ on the Si ₃ N ₄ film
After removing the film 7 with buffered hydrofluoric acid, the Si ₃ N ₄ film is removed with hot phosphoric acid or the like.

[Problems to be solved by the invention]

However, as the method of oxide film isolation prior described above shown in FIG. 3 (c), after the second selective oxidation, Si ₃ N ₄ film on the SiO
There is a problem that the second Si ₂ N ₄ films 5A and 5B stick together with the _two films 7 sandwiched therebetween.

When the Si ₃ N ₄ film adheres, as shown in FIG. 3 (d), the second Si ₃ N ₄ film is wet-etched with hot phosphoric acid.
₃ N ₄ film 5B part will remain, this will be a later process and appear in a whisker-like form, causing waste in the production line,
There is a disadvantage that the yield and quality of the semiconductor device are reduced.

[Means for solving the problem]

According to the method of manufacturing a semiconductor device of the present invention, a first pad oxide film and a first oxidation resistant film are sequentially formed on a silicon substrate, and the first oxidation resistant film is patterned to form an opening in an element isolation region. Forming a thick first oxide film having a bird's beak in the opening after forming the portion, and forming a second pad oxide film and a second oxidation-resistant film after removing the first oxide film. Forming a polysilicon film over the entire surface after removing the second oxidation-resistant film except for a bird's beak portion of the first oxide film by anisotropic etching, and selectively oxidizing the film. Oxidizing the polysilicon film in the opening and the silicon substrate in the opening to form a thick second oxide film.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIGS. 1A to 1E are sectional views of a semiconductor chip shown in the order of steps for explaining a first embodiment of the present invention.

First, as shown in FIGS. 1 (a) and 1 (b), processing is performed in the same manner as in a conventional manufacturing process. That is, after forming the first pad SiO ₂ film 2 and the first Si ₃ N ₄ film 3 on the Si substrate 1, the first Si ₃ N ₄ film 3 is patterned. Next in this first
Thick SiO ₂ by selective oxidation using the Si ₃ N ₄ film 3 as a mask
After forming the film, the thick SiO ₂ film is removed by buffered hydrofluoric acid. Next, after a second pad SiO ₂ film 4 is formed, a second Si ₃ N ₄ film 5 is deposited. Next, the second Si ₃ N ₄ film 5 is etched by anisotropic etching to form the Si ₃ N ₄ films 5A and 5B only in the bird's beak portion.

Next, as shown in FIG. 1C, a polysilicon film 18 having a thickness of about 1000 ° is deposited. Of course, a polysilicon film is also deposited between the Si ₃ N ₄ films 5A and 5B.

Next, as shown in FIG. 1 (d), a second selective oxidation is performed so that the total SiO ₂ film in the groove is about 14000 °. At this time, the SiO ₂ film 19 having a surface thickness of about 2000 ° is made of the polysilicon film 18. Here Si ₃ N ₄ SiO ₂ film 19 is formed of polysilicon having a thickness of about about 2000Å also on the membrane of course the Si ₃ N ₄ film 5A, that the SiO ₂ film 19 in between 5B is formed This prevents the Si ₃ N ₄ films 5, 5B from sticking to each other.

Next, as shown in FIG. 1 (e), the SiO ₂ film 19 having a thickness of 2000 ° on the Si ₃ N ₄ films 5A and 5B is wet-etched with buffered hydrofluoric acid or the like, and furthermore, the Si ₃ N ₄ film 5A , 5B are removed by hot phosphoric acid.

By this operation, insulation separation by an ideal buried oxide film having no remaining Si ₃ N ₄ film becomes possible. Further, according to the first embodiment, it is not necessary to consider the thickness of SiO _{2 in} the _second selective oxidation and the thickness of SiO ₂ in the first selective oxidation. Can be set to

2 (a) to 2 (e) are sectional views of a semiconductor chip shown in the order of steps for explaining a second embodiment of the present invention.

First, as shown in FIG. 2 (a), a _second pad SiO ₂ film 2 and a first Si ₃ N ₄ film 4 are formed on a Si substrate 1 by the same operation as in the prior art, patterned, and then selectively oxidized. Next, after removing the thick SiO ₂ film formed by selective oxidation,
A thin second pad SiO ₂ film 3 having a thickness of about 500 ° and a second Si ₃ N ₄ film having a thickness of about 1000 ° are deposited.

Next, as shown in FIG. 2B, a polysilicon film 28 having a thickness of about 1000 ° is deposited.

Next, as shown in FIG. 2C, the polysilicon film 28 and the second Si ₃ N ₄ film 5 are anisotropically etched.

Next, as shown in FIG. 2D, a second selective oxidation is performed to form a SiO ₂ film 26 having a thickness of about 14000 °. Also at this time, Si ₃ N ₄
Since the SiO ₂ film 29 made of polysilicon having a thickness of about 2000 mm is formed between the films 5A and 5B, the Si ₃ N ₄ films do not stick together.

Next, as shown in FIG. 2 (e), the SiO ₂ film 29 is etched with buffered hydrofluoric acid and then the Si ₃ N ₄ film is etched with hot phosphoric acid to form an element isolation film with a thick SiO ₂ film 26. Is done.

In the second embodiment, as compared with the first embodiment, since there is no polysilicon on the pad SiO ₂ film before the second selective oxidation, an insulating oxide film can be formed in a deep direction, and the parasitic capacitance can be reduced. There is an advantage that it can be reduced. Also, polysilicon film, Si
₃ N ₄ when the membrane was ion etching, the film thickness of the polysilicon fraction only the Si ₃ N ₄ film 5B is increased, there is also an advantage of reducing the bite amount after the second selective oxidation.

〔The invention's effect〕

The present invention described above, compared with the conventional manufacturing method, Si ₃ by the second anti-oxidation film is grown polysilicon film after growth, replacing the oxide film this during the second selective oxidation Since the N ₄ films can be prevented from sticking to each other, an insulating separation film having no remaining Si ₃ N ₄ film can be formed. Accordingly, since the generation of dust due to the Si ₃ N ₄ film is eliminated, a semiconductor device having high yield and high reliability can be manufactured.

[Brief description of the drawings]

FIGS. 1 (a) to 1 (e) and 2 (a) to 2 (e) are sectional views of a semiconductor chip shown in the order of steps for explaining the first and second embodiments of the present invention. 1A to 1D are cross-sectional views of a semiconductor chip shown in the order of steps for explaining a conventional method of manufacturing a semiconductor device. 1... Si substrate, 2... First pad SiO ₂ film, 3.
The Si ₃ N ₄ film of 4 ...... second pad SiO ₂ film, 5 ...... second S
i ₃ N ₄ film, 5A, 5B …… Si ₃ N ₄ film, 6,16,26 …… SiO ₂ film, 7,27
…… SiO ₂ film, 18,28 …… Polysilicon film, 19,29 …… SiO ₂
film.

Claims (1)

(57) [Claims] A step of sequentially forming a first pad oxide film and a first oxidation-resistant film on a silicon substrate; and forming an opening in an element isolation region by patterning the first oxidation-resistant film. Forming a thick first oxide film having a bird's beak in the opening by performing selective oxidation, and sequentially forming a second pad oxide film and a second oxidation-resistant film after removing the first oxide film Forming a polysilicon film over the entire surface after removing the second oxidation-resistant film except for a bird's beak portion of the first oxide film by anisotropic etching, and forming a polysilicon film in the opening by selective oxidation. Oxidizing the polysilicon film and the silicon substrate to form a thick second oxide film.