JPH0794578A - Fabrication of semiconductor device - Google Patents

Abstract

PURPOSE:To restrain a thick field oxide from biting, in bird's beak, into an element forming region from the end part of an antioxidant mask, i.e., silicon nitride, when the isolation of an integrated circuit is effected by forming the field oxide selectively. CONSTITUTION:After deposition of silicon oxide 2 on a semiconductor substrate 1, silicon nitride 3 is deposited on the silicon oxide 2 in an element forming region 8. Subsequently, a field antireversion layer 4 is formed in an isolation region 7 through ion implantation followed by ion implantation 32 for rendering the silicon amorphous in the isolation region 7 using the silicon nitride 3 as a mask. In this regard, the field oxide 6 is restrained from biting, in bird's beak, into the element forming region 8 because the amorphous silicon has higher oxidation rate than single crystal silicon and the oxidation is proceeds selectively in the vertical direction.

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 forming an element isolation layer of a MOS transistor.

[0002]

2. Description of the Related Art Conventionally, a selective oxidation (LOCOS) method for forming a thick insulating film in a field region between elements, which is a transistor, has been known as a manufacturing method for a semiconductor device, particularly a MOS type transistor. There is. Hereinafter, this selective oxidation method will be described with reference to FIGS.

As shown in FIG. 2A, for example, p-type (1
00) A silicon oxide film 12 having a thickness of about 80 nm is formed on the silicon substrate 11 by, for example, thermal oxidation at 1000 ° C., and then an oxidation resistant film, for example, a silicon nitride film 13 is formed by a chemical vapor deposition (CVD) method. It is formed to a thickness of about 100 nm.

Next, as shown in FIG. 2B, the silicon nitride film 13 in the field region 21 between the elements is removed, and field ion implantation 30 of, for example, boron is performed in self alignment with the field region 21. The inversion prevention layer 14 is formed.

Thereafter, as shown in FIG. 2 (c), the field oxide film 15 is oxidized in an oxidizing atmosphere containing water vapor at 1000 ° C. for about 4 hours to form the field oxide film 15 in the field region 21.
Only selectively formed.

Next, as shown in FIG. 2D, the silicon oxide film 12 and the silicon nitride film 13 in the element forming region 22 are formed.
Are removed to expose the silicon substrate 11 in the element formation region 22.

[0007]

According to the conventional selective oxidation method, the thick field oxide film 15 is selectively formed in the element isolation of the integrated circuit which has been miniaturized and highly densified as described above. 2C, the oxidation proceeds to the element formation region 22 as well, so that the thick field oxide film 15 is formed on the element formation region 22 from the end of the silicon nitride film 13 which is an oxidation resistant mask. A problem has emerged in which the bird's beak-like bite (the so-called bird's beak) interferes with high integration.

Therefore, an object of the present invention is to suppress the bird's beak-like bite of the field oxide film in the element formation region when the field oxide film is formed in the field region.

[0009]

In order to achieve the above object, a method of manufacturing a semiconductor device according to the present invention comprises a step of forming an oxide film on a semiconductor substrate and an oxidation resistance on the oxide film in an element formation region. A step of forming a substance, a step of forming a field inversion prevention layer in the element isolation region, a step of implanting ions into the semiconductor substrate of the element isolation region using the oxidation resistant material as a mask, and a step of thermally oxidizing the element isolation region. It comprises a step of forming a field oxide film and a step of removing the oxidation resistant material.

In the step of implanting ions into the semiconductor substrate in the element isolation region using the oxidation resistant material as a mask, silicon, oxygen, nitrogen, neon, argon, krypton,
It is preferable to ion-implant any element of xenon.

Further, in the step of implanting ions into the semiconductor substrate in the element isolation region using the oxidation resistant material as a mask, the dose amount of ion implantation is preferably 1 × 10 ¹⁴ cm ^-2 or more.

[0012]

FUNCTION For example, silicon becomes amorphous when ion implantation is performed with a dose amount of 1 × 10 ¹⁴ cm ^-2 or more. Since the diffusion coefficient of the oxidizing species in the amorphous silicon is larger than that in the single crystal, when compared with the same oxidation time, the oxidation reaction proceeds more efficiently in the amorphous silicon. Therefore, in order to obtain LOCOS having the same film thickness, amorphous silicon can reduce the oxidation time more than single crystal silicon. That is, before the field oxide film is formed in the element isolation region, ion implantation into the semiconductor substrate in the element isolation region to make it amorphous makes the beak-like bite of the bird into the element formation region small.

[0013]

Embodiment An embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a cross-sectional view showing the selective oxidation method according to the embodiment in the order of steps.

As shown in FIG. 1A, p-type (100)
After forming a silicon oxide film 2 having a thickness of about 80 nm on the silicon substrate 1 by thermal oxidation at 1000 ° C., an oxidation resistant film, for example, a silicon nitride film 3 having a thickness of about 100 nm is formed by a chemical vapor deposition (CVD) method. Form to thickness.

Next, as shown in FIG. 1B, the silicon nitride film 3 in the field region 7 is removed and self-aligned with the field region 7, for example, a boron field having a dose amount of 3 × 10 ¹¹ cm ^-2. Ion implantation 31 is performed, and the inversion prevention layer 4 is formed.
To form.

Thereafter, as shown in FIG. 1C, ion implantation 32 for amorphization is performed under the conditions of oxygen as an ion species, a dose amount of 3 × 10 ¹⁵ cm ^-2 , and an acceleration voltage of 150 keV. Form layer 5. Here, it is known that the oxidation rate of amorphous silicon is higher than that of single crystal silicon. Ion implantation 3 for amorphization into the element isolation region 7 as in the present embodiment
When the step 2 is performed, the substrate becomes amorphous only in the element isolation region 7 due to the straightness of the ion beam, and the lower portion of the silicon nitride film 3 serving as a mask is not made amorphous.

Next, as shown in FIG. 1D, the field oxide film 6 is formed by performing oxidation at 1000 ° C. for 3 hours in an oxidizing atmosphere containing water vapor. As described above, when the field oxidation is performed, the oxidation rate of the amorphous layer 5 is higher than the oxidation rate of the single crystal silicon, so that the vertical oxidation selectively progresses. Therefore, the oxidation time can be shortened as compared with the conventional method of oxidizing single crystal silicon, so that the bird's beak-like bite in the lateral direction of the element formation region 8 is suppressed.

Next, as shown in FIG. 1E, the silicon oxide film 2 and the silicon nitride film 3 in the element forming region 8 are removed to expose the silicon substrate 1 in the element forming region 8.

The dose amount in the impurity ion implantation 31 for preventing inversion which is usually performed before field oxidation is about 10 ¹¹ to 10 ¹² cm ^−2, which is an amount enough to change the crystallinity of the semiconductor substrate 1. Since it does not exist, the above effect does not occur.

It is widely known that the ion implantation causes the crystallinity of the ion-implanted material to be lost at a dose amount higher than a certain value. For example, in silicon, the dose amount value is about 10 at room temperature. ^{It is 14} cm ^-2 .

In this embodiment, the ion implantation 31 for preventing inversion precedes the ion implantation 32 for amorphization, but the ion implantation 32 for amorphization precedes the ion implantation 31 for prevention of inversion. You may let me.

Although oxygen is used as the ion species in this embodiment, the same effect can be obtained by making the silicon substrate 1 in the field region 7 amorphous. Therefore, in addition to oxygen, silicon, nitrogen, neon, argon, and krypton are used. Alternatively, xenon may be used.

[0023]

As described above, according to the present invention,
The bird's beak-shaped bite into the element formation region caused by the selective oxidation method can be effectively suppressed, and the yield and design margin of the semiconductor device can be improved.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view showing, in the order of steps, a selective oxidation method for an element isolation region according to a conventional method.

[Explanation of symbols]

 1 p-type silicon substrate 2 silicon oxide film 3 silicon nitride film 4 inversion prevention layer 5 amorphous layer 6 field oxide film 7 field region 8 element formation region 31 ion implantation for inversion prevention 32 ion implantation for amorphization

Claims (3)

[Claims] 1. A step of forming an oxide film on a semiconductor substrate, a step of forming an oxidation resistant material on the oxide film in an element formation region, and a step of forming a field inversion prevention layer in an element isolation region, A step of implanting ions into the semiconductor substrate of the element isolation region using the oxidation resistant material as a mask; a step of forming a field oxide film in the element isolation area by thermal oxidation; and a step of removing the oxidation resistant material. A method for manufacturing a semiconductor device, comprising: 2. The step of ion-implanting into the semiconductor substrate of the element isolation region using the oxidation resistant material as a mask, ion-implanting any element of silicon, oxygen, nitrogen, neon, argon, krypton, and xenon. The method for manufacturing a semiconductor device according to claim 1, wherein 3. The step of implanting ions into the semiconductor substrate in the element isolation region using the oxidation resistant material as a mask has a dose amount of ion implantation of 1 × 10 ¹⁴ cm ⁻² or more. 1. The method for manufacturing a semiconductor device according to 1.