JPH08167602A - Method of manufacturing semiconductor device - Google Patents

Abstract

PURPOSE: To suppress generation of a bird's beak in an element isolation region when making a semiconductor device. CONSTITUTION: In a step of forming an element isolation region for a semiconductor device, a first silicon nitride film 3a is selectively formed in an element isolation non-formation region on a silicon substrate 1, and an oxidizing species diffusion prevention film composed of a silicon oxide film 6 is formed on the silicon substrate 1 containing the first silicon nitride film 3a. Further, a second silicon nitride film 3b is selectively formed on the first silicon nitride film 3a thereon, and with the user of a film comprising the first silicon nitride film 3a, the oxidizing species diffusion prevention film 6 and the second silicon nitride film 3b as a mask, the silicon substrate is oxidized. Next, the mask is etched and removed, whereby the element isolation region is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device having an element isolation region of LOCOS structure. More specifically, the present invention relates to a method of manufacturing a semiconductor device in which an element isolation region having a LOCOS structure is formed so as to suppress bird's beak.

[0002]

2. Description of the Related Art In a semiconductor device, many circuit elements such as transistors and diodes are formed on one silicon substrate, and therefore element isolation regions are formed to isolate each circuit element.

The LOCOS structure is an element isolation region widely used in LSI. As a basic formation method of this LOCOS structure, as shown in FIG. 3, after a silicon oxide film 2 called a pad silicon oxide film is formed on the surface of a silicon substrate 1, it is formed in a region where element isolation is not formed. A silicon nitride film (Si ₃ N ₄ ) 3 is selectively formed ((a) in the same figure), and then the silicon nitride film 3 is used as a mask in a diffusion furnace to oxidize oxygen, ozone, etc., to 1000 to 1200.
The silicon nitride film 3 is formed by diffusing and reacting at a high temperature of about ℃ to oxidize the silicon substrate 1 (LOCOS oxidation).
A thick silicon oxide film 4 is formed in the non-forming region (FIG. 3B). After that, the silicon nitride film 3 and the silicon oxide film 2 thereunder are removed by etching, and the thick silicon oxide film 4 is left on the silicon substrate 1 (FIG. 7C). The thick silicon oxide film 4 thus formed serves as an element isolation region.

However, according to this forming method, L
Since the oxidation of the silicon substrate 1 during the OCOS oxidation proceeds not only in the thickness direction of the silicon substrate 1 but also in the horizontal direction, L
About half of the film thickness of the thick silicon oxide film 4 having the OCOS structure is embedded in the silicon substrate, and so-called bird's beak 4a is formed at the end of the thick silicon oxide film 4. The bird's beak 4a limits the minimum distance between the circuit elements formed on the silicon substrate 1, and thus poses a problem in improving the degree of integration of the semiconductor device.

On the other hand, as a method of forming a LOCOS structure so as to suppress bird's beak, PPL is used.
Method (Poly Pad LOCOS) has been proposed. In the PPL method, a polysilicon layer is formed between the silicon oxide film 2 and the silicon nitride film 3, whereby diffusion of oxidizing species is suppressed and bird's beak generation is suppressed.

[0006]

However, the PPL
The method cannot significantly suppress the generation of bird's beaks, and it has been desired to suppress the generation of bird's beaks for higher integration of semiconductor devices.

The present invention is intended to solve the above-mentioned problems of the prior art, and it is an object of the present invention to significantly suppress the generation of bird's beaks in element isolation regions during the manufacture of semiconductor devices.

[0008]

The present inventor has found that the LOCOS
It has been found that the above object can be achieved by doubling the silicon nitride film used as an oxidation mask, and sandwiching an oxidizing species diffusion preventing layer made of a silicon oxide film or the like between the double silicon nitride films, and the present invention It came to completion.

That is, according to the present invention, the first silicon nitride film is selectively formed in the element isolation non-formation region on the silicon substrate, and the oxidation species diffusion preventing film is formed on the silicon substrate including the first silicon nitride film. And further forming a second silicon nitride film on the first silicon nitride film selectively.
The method includes a step of oxidizing the silicon substrate using the laminated film of the first silicon nitride film, the oxide species diffusion preventing film and the second silicon nitride film as a mask, and then etching and removing the mask to form an element isolation region. A method for manufacturing a semiconductor device is provided.

In particular, as a preferred embodiment of the present invention, there is provided a method of sequentially forming a pad silicon oxide film and a pad polysilicon film on a silicon substrate in advance, and then forming the first silicon nitride film thereon as described above. To do. In a further preferred embodiment, a method of forming a silicon oxide film as an oxide species diffusion prevention film is provided.

[0011]

According to the present invention, a silicon nitride film serving as a mask for LOCOS oxidation is made a double layer of a first silicon nitride film and a second silicon nitride film, and a silicon layer is formed between the double silicon nitride film. Since the oxide species diffusion preventing layer such as an oxide film is sandwiched, it is possible to prevent the oxide species from diffusing in a direction other than the vertical direction of the silicon substrate during LOCOS oxidation.
Therefore, the generation of bird's beaks is greatly suppressed.

Further, according to the present invention, as a LOCOS oxidation mask, first, a first silicon nitride film is first selectively formed on a silicon substrate, and then an oxidizing species diffusion preventing layer such as a silicon oxide film is entirely formed on the first silicon nitride film. And the second silicon nitride film is selectively formed on the first silicon nitride film, so that the oxidation species diffusion preventing layer is not patterned into a mask pattern. Therefore, as compared with the case where the oxide species diffusion prevention layer is also patterned into a mask pattern by sequentially stacking the first silicon nitride film, the oxidation species diffusion prevention layer and the second silicon nitride film, and then patterning them, There is an advantage that the LOCOS oxide film can be formed thick.

In particular, applying the method of the present invention to the PPL method,
By sequentially forming a pad silicon oxide film and a pad polysilicon film on a silicon substrate prior to formation of the first silicon nitride film, an element isolation region in which bird's beak is suppressed while mitigating thermal stress due to LOCOS oxidation is formed. Can be formed.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 and 2 are explanatory views of a manufacturing process according to a preferred embodiment of the present invention.

First, as shown in FIG. 1A, the pad silicon oxide film 2 is formed by thermally oxidizing the surface of the silicon substrate 1. The thickness of the pad silicon oxide film 2 is preferably 5 to 15 nm, particularly about 10 nm.

Next, a pad polysilicon film 5 is formed by the CVD method. This pad polysilicon film 5 is
Relieves thermal stress during COS oxidation and suppresses bird's beak. The thickness of the pad polysilicon film 5 is preferably 45 to 75 nm, particularly about 60 nm.

Next, as shown in FIG. 1B, the first silicon nitride film 3a is selectively formed in the element isolation non-formation region on the silicon substrate 1. That is, the first silicon nitride film 3a is formed by the CVD method, and the silicon nitride film 3a is patterned into a LOCOS oxidation mask pattern by using the photolithography technique. The thickness of the first silicon nitride film 3a is 80 to 120 nm, especially 10
About 0 nm is preferable.

Next, as shown in FIG. 3C, a silicon oxide film 6 is formed as an oxide species diffusion preventing film on the silicon substrate 1 including the first silicon nitride film 3a. In this case, as a method of forming the silicon oxide film 6, TEOS (Tetraeth
A low pressure CVD method using yoxysilane or Tetraethylorthosilicate is preferred. The thickness of the silicon oxide film 6 is preferably 80 to 120 nm, particularly about 100 nm. In the present invention, the oxidation species diffusion preventing film is not limited to the silicon oxide film, and various films can be formed as long as the diffusion of the oxidation species in the horizontal direction of the silicon substrate can be suppressed. For example, a polysilicon film or the like can be formed as the oxidation species diffusion prevention film.

Next, as shown in FIG. 3D, a second silicon nitride film 3b is formed by a CVD method, and a photolithography technique is used so that the pattern thereof overlaps the first silicon nitride film 3a. Pattern. The thickness of the second silicon nitride film 3b is 80 to 120 nm,
Particularly, about 100 nm is preferable.

Then, LOCOS oxidation is carried out by oxidizing the silicon substrate 1 by applying an oxidizing species such as oxygen and ozone in a diffusion furnace at 1000 to 1200 ° C., as shown in FIG.
A thick silicon oxide film 4 is formed as shown in FIG. In this case, the thickness of the silicon oxide film 4 is 320 to 420n.
m, especially about 370 nm at the thickest part. According to such LOCOS oxidation, the double silicon nitride films 3a and 3b and the silicon oxide film 6 sandwiched between them prevent the oxidizing species from diffusing in the horizontal direction of the silicon substrate 1 and the first silicon. Oxidation of the silicon substrate 1 immediately below the nitride film 3a is suppressed.

After the LOCOS oxidation, the second silicon nitride film 3b, the silicon oxide film 6 and the first silicon nitride film 3a are formed.
Are sequentially removed by etching as follows.

First, the second silicon nitride film 3b is removed by wet etching using hot phosphoric acid as shown in FIG. 2 (f), and then the silicon oxide film 6 is removed by using HF (FIG. 2 (g)). As shown in FIG. 6H, the first silicon nitride film 3a is removed by wet etching using hot phosphoric acid. After that, reactive ion etching (RIE)
Then, the pad polysilicon film 5 is removed by HF, and the pad silicon oxide film 2 is removed by using HF. As a result, as shown in FIG. 1I, the thick silicon oxide film 4 can be left on the silicon substrate 1, and the remaining silicon oxide film 4 becomes the element isolation region.

The element isolation region thus obtained is
For the element isolation region formed by the conventional PPL method,
The bird's beak will be greatly reduced.

Although the embodiments of the present invention have been specifically described above, the present invention can have various embodiments other than the embodiments described above. For example, when forming a channel stopper having an increased impurity concentration under the element isolation region, in the above-described embodiment, the first silicon nitride film 3a is formed.
After patterning and before forming the silicon oxide film 6,
Ion implantation for forming a channel stopper can be performed.

[0025]

According to the present invention, it is possible to significantly suppress the generation of bird's beaks in the element isolation region when manufacturing a semiconductor device.

[Brief description of drawings]

FIG. 1 is a process explanatory view of a manufacturing method of the present invention.

FIG. 2 is a process explanatory view of the manufacturing method of the present invention.

FIG. 3 is an explanatory diagram of a conventional method for forming an element isolation region.

[Explanation of symbols]

 1 silicon substrate 2 pad silicon oxide film 3 silicon nitride film 3a first silicon nitride film 3b second silicon nitride film 4 silicon oxide film 5 pad polysilicon film 6 silicon oxide film

Claims (3)

[Claims] 1. A first silicon nitride film is selectively formed in a device isolation non-formation region on a silicon substrate, and an oxidation species diffusion preventing film is formed on the silicon substrate including the first silicon nitride film. Further, a second silicon nitride film is selectively formed on the first silicon nitride film, and the laminated film of the first silicon nitride film, the oxide seed diffusion preventing film and the second silicon nitride film is used as a mask. A method of manufacturing a semiconductor device, comprising the steps of oxidizing a silicon substrate and then removing the mask by etching to form an element isolation region. 2. The manufacturing method according to claim 1, wherein the oxidation species diffusion preventing film comprises a silicon oxide film or a polysilicon film. 3. The manufacturing method according to claim 1, wherein a pad silicon oxide film and a pad polysilicon film are sequentially formed in advance on a silicon substrate, and a first silicon nitride film is selectively formed on the pad silicon oxide film.