JPH05347300A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing a semiconductor device, where a silicon oxide nitride film is restrained from increasing in thickness, a field oxide film is lessened in forming time, and bird's beaks are prevented from occurring. CONSTITUTION:A nitride film, used as a mask when a field oxide film 5 is formed on a semiconductor substrate 1 for isolating elements from each other, is formed of material gas composed of ammonia, dichlorosilane, and nitrogen gas or material gas composed of ammonia, silane, and nitrogen. By this setup, a nitride film excellent in density and acid resistance can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device in which an element isolation oxide film is formed by selective oxidation.

[0002]

2. Description of the Related Art Conventionally, as a semiconductor element isolation method,
LOC that selectively oxidizes only the portion to be the element isolation region
The OS (Local Oxidation of Silicon) method is widely used. In this LOCOS method, since an oxide film for element isolation (hereinafter referred to as “field oxide film”) is selectively formed only in the element isolation region, a pad is formed on the element region before the field oxide film is formed. A silicon nitride film having excellent oxidation resistance is formed through the oxide film to protect the element region. Then, the silicon oxide film is used as a mask to perform thermal oxidation on the semiconductor substrate to form a field oxide film in the element isolation region. Here, during this thermal oxidation, the silicon nitride film is also oxidized, and a silicon oxynitride film (SiON) is formed on the silicon nitride film. Next, the silicon oxynitride film, the silicon nitride film, and the pad oxide film are removed by etching to separate the elements of the semiconductor substrate.

The LOCOS method can improve the planarization because the field oxide film is formed in the semiconductor substrate so that it is submerged in the semiconductor substrate. There was a problem of causing. Therefore, a conventional example has been introduced in which the generation of bird's beak is suppressed by reducing the thickness of the field oxide film.

[0004]

However, when the thickness of the field oxide film is reduced as in the prior art example,
There has been a problem that the parasitic threshold of the element isolation region is lowered and the capacitance of the gate substrate is increased. In recent years,
As the element region becomes smaller due to the miniaturization of semiconductor devices, the area of the silicon nitride film formed in the element region also becomes smaller. Here, when forming a field oxide film by the LOCOS method, it is known that the field oxide film cannot be formed thicker as the area of the silicon nitride film becomes smaller, even if the semiconductor substrate is oxidized at the same time. Has been. Therefore, if the oxidation time is extended and the field oxide film is formed to be thick to some extent, there is also a problem that the bird's beak extends.

Further, if the oxidation time is lengthened, the film thickness of the silicon oxynitride film formed on the silicon nitride film also increases. In the LOCOS method, the silicon oxynitride film, the silicon nitride film and the pad oxide film are removed by etching to separate the elements of the semiconductor substrate. At this time, the field oxide film is also etched. Therefore, the field oxide film is formed thicker in consideration of the amount of film thickness reduction due to the etching. However, when the film thickness of the silicon oxynitride film becomes thicker, the amount of film thickness reduction increases, so that the field oxide film is increased accordingly. There is a problem that it is necessary to increase the thickness of the film, which causes an increase in bird's beak.

An object of the present invention is to solve such a problem and to suppress the increase in the film thickness of the silicon oxynitride film to reduce the formation time of the field oxide film.
An object of the present invention is to provide a method for manufacturing a semiconductor device in which the occurrence of bird's beaks is suppressed.

[0007]

In order to achieve this object, the present invention forms an oxide film and a nitride film on a device region of a semiconductor substrate in order from the substrate side, and uses this as a mask for selective oxidation. In the method for manufacturing a semiconductor device, the nitride film is formed by using a source gas containing ammonia, dichlorosilane and nitrogen gas, or a source gas containing ammonia, silane and nitrogen. It provides a method.

[0008]

The nitride film is usually made of SiN, SiN ₂ , Si
₃ N ₄ is used as a raw material gas containing ammonia, dichlorosilane and nitrogen gas, or ammonia,
By forming the nitride film using the source gas containing silane and nitrogen, the content of Si ₃ N ₄ existing in the nitride film can be increased. This Si ₃ N ₄ has a very high density, is extremely excellent in oxidation resistance, and has stable properties. Therefore, by including a large amount of Si ₃ N ₄ in the nitride film, Oxidation resistance can be improved.

When the field oxide film is formed, if the selective oxidation is performed by using the nitride film having excellent oxidation resistance as a mask, the silicon oxynitride film formed on the nitride film is selectively oxidized at the time of the selective oxidation. An increase in film thickness can be suppressed. Therefore, since the time of the subsequent etching process can be shortened, the reduction amount of the field oxide film in the etching can be reduced, and the film thickness of the field oxide film can be thinned accordingly. Therefore, it is possible to suppress the occurrence of bird's beak.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. 1 to 4 are partial cross-sectional views showing an element isolation process of a semiconductor device according to an embodiment of the present invention. In the step shown in FIG. 1, the pad oxide film 2 having a film thickness of about 25 nm is formed on the semiconductor substrate 1 in an oxidizing atmosphere. Next, on the semiconductor substrate 1 on which the pad oxide film 2 is formed, the temperature is 760 ° C., the raw material gas is ammonia (NH ₃ ) gas = 875 cc / min, and dichlorosilane (SiH ₂ Cl ₂ ) gas is 175 cc / min. , LPCV using nitrogen (N ₂ ) gas = 1050 cc / min
A D (Low Pressure Chemical Vapor Deposition) method is performed to form a silicon nitride film 3 having a film thickness of about 100 nm. Here, the silicon nitride film 3 formed by using the source gas has an increased Si ₃ N ₄ content.

Next, in the step shown in FIG. 2, a resist film 4 is applied on the silicon nitride film 3 obtained in the step shown in FIG. 1 and patterned to form an element isolation region on the semiconductor substrate 1. The formed resist film 4, silicon nitride film 3, and pad oxide film 2 are selectively removed. Then, using the remaining resist film 4, silicon nitride film 3, and pad oxide film 2 as a mask, for example, B ⁺ (boron) is ion-implanted into the semiconductor substrate 1 to form a channel stop.

Next, in the step shown in FIG. 3, after removing the resist film 4 obtained in the step shown in FIG. 2, thermal oxidation is carried out at 950 ° C. in an oxidizing and wet atmosphere to form an element isolation region of the semiconductor substrate 1. A field oxide film 5 having a film thickness of about 600 nm is formed. At this time, the silicon nitride film 3 was also oxidized, and the silicon oxynitride film 6 having a film thickness of about 40 nm was formed on the silicon nitride film 3. FIG. 6 shows an enlarged cross-sectional view near the field oxide film 5. Here, since the silicon oxide film 3 is extremely excellent in oxidation resistance, it is difficult to form the silicon oxynitride film 6 on the silicon oxide film 3.

Next, in the step shown in FIG. 4, the silicon oxynitride film 6, the silicon nitride film 3 and the pad oxide film 2 formed on the element region of the semiconductor substrate 1 are removed by etching. At this time, since the silicon oxynitride film 6 is thin, etching can be performed in a short time. Therefore, the amount of reduction in the thickness of the field oxide film 5 in the etching can be reduced. Therefore, as shown in FIG.
In the step shown in (1), the film thickness of the field oxide film 5 can be thinned, and the occurrence of bird's beak can be suppressed.

In this way, the elements of the semiconductor substrate 1 were separated. Next, for comparison, on the semiconductor substrate 1 on which the pad oxide film 2 obtained in the step shown in FIG. 1 is formed, the temperature is 760 ° C., the raw material gas is ammonia (NH ₃ ) gas = 875 cc / min, dichloride Silane (SiH ₂
LPCVD using Cl ₂ ) gas = 175 cc / min
Then, a silicon nitride film having a film thickness of about 100 nm was formed.

Then, the silicon oxynitride film 3 formed by the method according to the present invention (invention product) and the silicon nitride film formed by the conventional method (conventional product) are thermally oxidized under the same conditions. The film thickness of the film was investigated. This result is shown in FIG.
Shown in. It can be seen from FIG. 5 that the silicon oxynitride film of the invention product is thinner than that of the conventional product. From this, it was proved that the invention product is superior in oxidation resistance to the conventional product.

Next, using the silicon nitride film formed by the conventional method as a mask, the same steps as described above were performed to isolate the semiconductor substrate 1 from elements. In this step, as shown in FIG.
A diagram corresponding to is shown in FIG. Then, the shape of the bird's beak (bird's beak of the invention) generated when the element isolation is performed by the method according to the present invention, and the bird's beak (conventional bird's beak) generated when the element isolation is performed by the conventional method As a result of comparison with the above-mentioned shape, as shown in FIGS. 6 and 7, it was confirmed that the bird's beak of the present invention was smaller than the conventional bird's beak.

In the present embodiment, ammonia gas, dichlorosilane gas and nitrogen gas were used as the raw material gas when forming the silicon nitride film, but the present invention is not limited to this.
Ammonia, silane and nitrogen gas may be used, and the nitrogen gas may be mixed with another substance as long as it does not hinder the formation of the silicon nitride film.

[0018]

As described above, according to the present invention,
By forming a nitride film using a source gas containing ammonia, dichlorosilane and nitrogen gas, or a source gas containing ammonia, silane and nitrogen, the nitride film has a very high density and is extremely resistant to oxidation. Excellent Si ₃ N ₄
Can be contained in a large amount. Therefore, the oxidation resistance of the nitride film can be improved.

When the field oxide film is formed, selective oxidation is performed using the nitride film having excellent oxidation resistance as a mask, and the silicon oxynitride film formed on the nitride film is selectively oxidized at the time of the selective oxidation. An increase in film thickness can be suppressed. Therefore, since the time of the subsequent etching process can be shortened, the reduction amount of the field oxide film in the etching can be reduced, and the film thickness of the field oxide film can be thinned accordingly. As a result, it is possible to suppress the occurrence of bird's beaks, the element region can be made relatively large, and miniaturization of the semiconductor device can be achieved.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing an element isolation process of a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing an element isolation process of a semiconductor device according to an example of the present invention.

FIG. 3 is a partial cross-sectional view showing an element isolation process of a semiconductor device according to an example of the present invention.

FIG. 4 is a partial cross-sectional view showing an element isolation process of a semiconductor device according to an example of the present invention.

FIG. 5 is a diagram showing film thicknesses of a silicon oxynitride film formed when a silicon nitride film formed by a method according to the present invention and a silicon nitride film formed by a conventional method are thermally oxidized under the same conditions.

FIG. 6 is an enlarged partial sectional view of FIG.

FIG. 7 is a view corresponding to FIG. 6 when the element isolation of the semiconductor substrate is performed by the conventional method.

[Explanation of symbols]

 1 semiconductor substrate 2 pad oxide film 3 silicon nitride film 4 resist film 5 field oxide film 6 silicon oxynitride film

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor device, wherein an oxide film and a nitride film are sequentially formed on a device region of a semiconductor substrate from the substrate side, and selective oxidation is performed using the oxide film and the nitride film as a mask. A method for manufacturing a semiconductor device, which is formed by using a source gas containing dichlorosilane and nitrogen gas or a source gas containing ammonia, silane and nitrogen.