JPH07321103A - Fine element isolation formation method - Google Patents

Abstract

(57) [Summary] [Purpose] A thick field oxide film is formed only in the element isolation region without increasing the size conversion difference. [Structure] After forming the first polycrystalline silicon film 3 on the entire surface by a low pressure CVD method, the first polycrystalline silicon film 3 is patterned so as to remain only in the element isolation region 4. Then, after forming the silicon nitride film 5, the silicon nitride film 5 is patterned to form the opening 6 on the first polycrystalline silicon film 3. After that, the second polycrystalline silicon film 7 is selectively formed only in the opening 6 by the low temperature ECR plasma CVD method, and the thermal oxidation process is performed to form the field oxide film 8 in the region to be the element isolation region 4.
To form.

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 a fine element isolation of a semiconductor device, and relates to a selective oxidation method (hereinafter referred to as "LOCOS").
It is suitable for application in the case of forming an element isolation region of a semiconductor device by a “method”).

[0002]

2. Description of the Related Art In recent years, the degree of integration of semiconductor integrated circuits has been remarkably high, and along with the miniaturization of elements of semiconductor integrated circuits, miniaturization of element isolation regions has become an important technical issue.

As a conventional element isolation method, Japanese Patent Publication No. 49-3
As described in Japanese Patent No. 9308, etc., LOCOS capable of obtaining sufficient element isolation characteristics in a simple process.
The law is widespread. However, with the miniaturization of elements of semiconductor integrated circuits, bird's beaks that cannot be avoided by the LOCOS method have come to be noticed as a factor that hinders the miniaturization of element isolation regions.

Therefore, as a method of shortening the bird's beak length, JP-A-61-74350 and JP-A-56-7.
As described in Japanese Patent No. 0644, a silicon nitride film is formed on a silicon oxide film on a silicon semiconductor substrate via a polycrystalline silicon layer, and then silicon nitride is formed to have a desired element isolation region size. A method has been devised in which the film is patterned and the polycrystalline silicon layer and the silicon semiconductor substrate are selectively oxidized using the silicon nitride film as a mask. The improved LOCOS method has a structure in which a polycrystalline silicon layer is sandwiched between a pad oxide film and a silicon nitride film which serves as an oxidation resistant mask in the conventional LOCOS method. , LOPOS
It is called (Local Oxidation of Poly Silicon).

The conventional improved LOCOS method will be described below.
This will be described with reference to FIG.

2A to 2D show a conventional improved LO.
It is a schematic sectional drawing which shows the manufacturing method of the element isolation by COS method in order of a process.

First, as shown in FIG. 2A, after a pad oxide film 2 is formed on the surface of a silicon semiconductor substrate 1 by a thermal oxidation method, a polycrystalline silicon film 3 and a silicon nitride film 5 are formed by a thermal CVD method. Form on the entire surface.

Next, as shown in FIG. 2B, after removing the silicon nitride film 5 in the element isolation region by etching, channel ion implantation (not shown) is performed.

Next, as shown in FIG. 2C, the polycrystalline silicon film 3 and the silicon semiconductor substrate 1 are thermally oxidized to form a field oxide film 7.

Next, as shown in FIG. 2D, the silicon nitride film 5 which is an oxidation resistant mask is removed by a wet etching method, and then the polycrystalline silicon film 3 is removed by a dry etching method. A device isolation region is formed.

As described above, the conventional improved LOC
The OS method partially oxidizes the polycrystalline silicon film 3 between the pad oxide film 2 and the silicon nitride film 5. And
Part of the polycrystalline silicon film 3 from which the silicon nitride film 5 has been removed
Is completely oxidized, the silicon semiconductor substrate 1 is partially thermally oxidized through the pad oxide film 2.

Therefore, the amount of oxidizing the silicon semiconductor substrate 1 can be reduced as compared with the conventional LOCOS method by the amount of oxidizing the polycrystalline silicon film 3. Therefore, lateral oxidation in the silicon semiconductor substrate 1 is reduced, and the bird's beak length is shortened.

[0013]

However, in the conventional improved LOCOS method, when the field oxide film 7 is formed by thermal oxidation, the polycrystalline silicon film 3 is thermally oxidized in the lateral direction to form the silicon nitride film 5. There is a problem in that the width w ₂ of the field oxide film 7 becomes larger than the width w ₁ of the pattern dimension, resulting in a dimension conversion difference. This hinders miniaturization of the element isolation region, and has been a serious problem particularly when the field oxide film 7 is to be formed thick.

Therefore, an object of the present invention is to provide a fine element isolation forming method capable of forming a thick field oxide film only in the element isolation region without increasing the size conversion difference.

[0015]

In order to solve the above-mentioned problems, according to the present invention, a step of depositing a first polycrystalline silicon film on a semiconductor substrate by a thermal CVD method,
Of the first polycrystalline silicon film other than the element isolation region by selectively etching the polycrystalline silicon film of 1), a step of forming an oxidation resistant film on the entire surface, and remaining in the element isolation region. Removing the oxidation resistant film on the first polycrystalline silicon film to form an opening in the oxidation resistant film; and forming a second polysilicon film on the first polycrystalline silicon film in the opening. The method includes the steps of selectively growing a crystalline silicon film and thermally oxidizing the first polycrystalline silicon film and the second polycrystalline silicon film through the opening.

Further, according to one aspect of the present invention, the opening is formed so that a part of the oxidation resistant film overlaps the first polycrystalline silicon film.

[0017]

According to the present invention, the second polycrystalline silicon film is selectively grown on the first polycrystalline silicon film formed only in the element isolation region. By thermally oxidizing the second polycrystalline silicon film, a thick field oxide film can be formed only in the element isolation region.

Further, since the first and second polycrystalline silicon films are present only in the element isolation regions, the lateral oxidation of the first and second polycrystalline silicon films during selective oxidation is prevented. The width is limited by the widths of the first and second polycrystalline silicon films, and the dimensional conversion difference can be reduced as compared with the conventional improved LOCOS method.

[0019]

Embodiments of the present invention will be described below with reference to FIG.

FIG. 1 is a schematic sectional view showing a method of manufacturing an element isolation according to an embodiment of the present invention in the order of steps.

First, as shown in FIG. 1A, a silicon oxide film 2 having a thickness of 10 nm to 50 nm is formed on one main surface of a silicon semiconductor substrate 1 by a thermal oxidation method, and then a reduced pressure CV is applied.
A first polycrystalline silicon film 3 is formed as a semiconductor layer on the entire surface by D method to a thickness of 50 nm to 200 nm. The substrate temperature when forming the first polycrystalline silicon film 3 is 620 ° C.
˜650 ° C. and the deposition rate is about 10 nm / min. Further, since the low pressure CVD method is used, batch processing is also possible and throughput during production is improved.

Next, a resist (not shown) for patterning the first polycrystalline silicon film 3 is applied by a method such as spin coating. Then, as shown in FIG.
Patterning is performed by a method such as photolithography so that the resist remains only in the element isolation regions 4, and then anisotropic dry etching is performed using the resist as a mask to remove the first regions other than the element isolation regions 4.
Then, the polycrystalline silicon film 3 is removed.

Next, after removing the resist, low pressure CVD is performed.
A silicon nitride film 5 is formed on the entire surface by a method to a thickness of 50 nm to 300 nm. Then, as shown in FIG. 1C, a resist (not shown) for patterning the silicon nitride film 5 is applied by a method such as spin coating, and then the resist is patterned by a method such as photolithography. Then, anisotropic dry etching is performed using the resist as a mask to selectively remove the silicon nitride film 5 to form an opening 6 for oxidizing the first polycrystalline silicon film 3. .

At this time, the resist is patterned so that the silicon nitride film 5 and the first polycrystalline silicon film 3 after patterning overlap each other by about 0.1 μm to 0.3 μm. This is performed so that the opening 6 is formed on the film 3.

In this embodiment, the silicon nitride film 5 after patterning and the first polycrystalline silicon film 3 are overlapped by about 0.1 μm to 0.3 μm. The first polycrystalline silicon film 3 may not be overlapped with the first polycrystalline silicon film 3.

Next, after removing the resist, FIG.
As shown in, by the low temperature ECR plasma CVD method,
A second polycrystalline silicon film 7 is selectively formed in the opening 6 on the first polycrystalline silicon film 3.

In the low temperature ECR plasma CVD method, when the second polycrystalline silicon film 7 is grown on the first polycrystalline silicon film 3, the second polycrystalline silicon film 7 does not grow on the silicon nitride film 5. The second polycrystalline silicon film 7 can be selectively formed only in the opening 6 on the first polycrystalline silicon film 3. The growth at this time was carried out at a substrate temperature of 300.
This is carried out by single-wafer processing which is kept at a low temperature of around ℃, and the deposition rate of the polycrystalline silicon film is set to about 1 to 10 nm / min.

Next, as shown in FIG. 1E, an oxidation process is performed by a method such as pyrogenic oxidation in a water vapor atmosphere using the silicon nitride film 5 as a mask to form a field in the region to be the element isolation region 4. The oxide film 8 is formed.

By the oxidation treatment at this time, the first polycrystalline silicon film 3 and the second polycrystalline silicon film 7 are oxidized to become a silicon oxide film, and this silicon oxide film constitutes a main part of the field oxide film 8. Therefore, the field oxide film 8 can be easily formed thick by forming the first polycrystalline silicon film 3 and the second polycrystalline silicon film 7 thick.

Further, in this embodiment, the first polycrystalline silicon film 3 and the second polycrystalline silicon film 7 are present only in the element isolation region, and the silicon nitride film 5 is the first.
Are also formed on the side walls of the polycrystalline silicon film 3 and the second polycrystalline silicon film 7, the oxides of the first polycrystalline silicon film 3 and the second polycrystalline silicon film 7 form element isolation regions. The bird's beak length can be shortened without laterally expanding.

Further, since the first polycrystalline silicon film 3 is formed immediately below the opening end of the silicon nitride film 5, the first polycrystalline silicon film 3 is silicon nitrided when the field oxide film 8 is formed. Since the film 5 relaxes the stress, it is possible to suppress the occurrence of crystal defects due to the stress near the end of the element isolation region of the silicon semiconductor substrate 1.

[0032]

According to the present invention, the second polycrystalline silicon film is selectively grown on the first polycrystalline silicon film formed only in the element isolation region.
And by thermally oxidizing the second polycrystalline silicon film,
A thick field oxide film can be formed only in the element isolation region.

Further, since the first and second polycrystalline silicon films are present only in the element isolation regions, the lateral oxidation of the first and second polycrystalline silicon films at the time of performing selective oxidation is prevented. The width is limited by the widths of the first and second polycrystalline silicon films, and the dimensional conversion difference can be reduced as compared with the conventional improved LOCOS method.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a method of manufacturing an element isolation according to an embodiment of the present invention in the order of steps.

FIG. 2 is a schematic cross-sectional view showing, in the order of steps, a method for manufacturing element isolation by a conventional improved LOCOS method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon semiconductor substrate 2 Pad oxide film 3 First polycrystalline silicon film 4 Element isolation region 5 Silicon nitride film 6 Opening 7 Second polycrystalline silicon film 8 Field oxide film

Claims (2)

[Claims] 1. A first semiconductor device is formed on a semiconductor substrate by a thermal CVD method.
A step of depositing a polycrystalline silicon film, and a step of selectively etching the first polycrystalline silicon film to remove the first polycrystalline silicon film other than the element isolation region; A step of forming the entire surface, a step of removing the oxidation resistant film on the first polycrystalline silicon film remaining in the element isolation region, and forming an opening in the oxidation resistant film; Selectively growing a second polycrystalline silicon film on the first polycrystalline silicon film; and thermally oxidizing the first polycrystalline silicon film and the second polycrystalline silicon film through the opening. A method for forming a fine element isolation, comprising: 2. The fine element isolation according to claim 1, wherein the opening is formed so that a part of the oxidation resistant film overlaps the first polycrystalline silicon film. Forming method.