JP2707901B2 - Method for manufacturing semiconductor device - Google Patents

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 oxide film by a selective oxidation method.

[0002]

2. Description of the Related Art A method for forming an element isolation oxide film in a conventional semiconductor device manufacturing process will be described with reference to FIG.

First, as shown in FIG. 4A, a pad oxide film (SiO ₂ ) 2A and a silicon nitride film (Si ₃ N ₄ ) 3A are formed on a silicon substrate 1, and then the silicon nitride film is patterned. An opening is provided in the separation region. Next, thermal oxidation is performed using the silicon nitride film 3A as a mask to form an element isolation oxide film 7B.

Next, as shown in FIG. 4B, the silicon nitride film 3A and the pad oxide film 2A other than the element isolation region are removed.

[0005]

As the degree of integration of the device increases, it is required to reduce the element isolation region, that is, to reduce the lateral spread (bird's beak) of the element isolation oxide film 7B by the selective oxidation method. I have. Therefore, in the conventional method of forming an element isolation oxide film by selective oxidation, it is necessary to increase the thickness of the silicon nitride film and reduce the thickness of the pad oxide film in order to reduce the bird's beak. By reducing the thickness of the pad oxide film and increasing the thickness of the silicon nitride film, the bird's beak is reduced, but the stress caused by the silicon nitride film cannot be reduced by the pad oxide film.
There is a disadvantage that defects are generated in the silicon substrate and device characteristics deteriorate.

In addition, when a desired impurity is ion-implanted as a channel stopper, a silicon oxide is implanted through a pad oxide film to suppress the occurrence of defects. However, when the pad oxide film becomes thinner, the silicon nitride film is removed. In this case, the pad oxide film is removed at the same time, resulting in a bare implantation, which has a disadvantage that a large number of defects are generated on the substrate.

[0007]

According to a method of manufacturing a semiconductor device of the present invention, a thin silicon oxide film and a silicon nitride film are sequentially formed on a silicon substrate, and then at least the silicon nitride film in an element isolation region is selectively formed. Removing, forming a sidewall made of an insulating film on the side wall of the silicon nitride film, and then forming a polysilicon film on the entire surface, and ion-implanting a desired impurity from above the polysilicon film as a channel stopper. Selectively oxidizing the element isolation region to form an element isolation oxide film.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. 1A and 1B are sectional views of a semiconductor chip for explaining a first embodiment of the present invention.

First, as shown in FIG. 1A, a pad oxide film 2 and a silicon nitride film 3 are formed on a silicon substrate 1 having a low-concentration p-type plane orientation (100) at 45 nm and a silicon nitride film 3 at 300 nm.
Formed to a thickness of Next, after the silicon nitride film 3 on the element isolation region is patterned to provide an opening, a silicon nitride film is formed as a sidewall 4 on a side wall of the silicon nitride film 3. The sidewalls 4 suppress the lateral oxidation process and reduce the lateral spread of the element isolation region. Further, an element isolation region smaller than the actual mask design dimension is formed. Thereafter, a polysilicon film 5 having a thickness of about 100 nm is formed on the sidewalls 4 as a cover film and an ion implantation protection film. Thereafter, the polysilicon film 5 is formed as a channel stopper under the condition of boron ions 6 of 50 keV and a dose of 1.5 × 10 ¹³ cm ^−2.
Is injected into the silicon substrate 1. At this time, the polysilicon film 5 becomes a protective film for alleviating implantation damage.

Next, as shown in FIG.
At 2 ° C., wet oxidation is performed for 2 hours to obtain an element isolation oxide film 7.
To form Thereafter, as shown in FIG. 1C, the silicon nitride film 3 and the like are removed by a wet etching method or the like to complete an element isolation region composed of the oxide film 7.

FIG. 3 shows the dependence of the lateral expansion of the isolation region on the thickness of the isolation oxide film for comparison with the prior art.
Compared to the lateral expansion of the element isolation region according to the prior art,
In this embodiment, since the bird's beak of the element isolation oxide film 7 is suppressed, the lateral expansion of the element isolation region is small, and the superiority of this embodiment is recognized.

FIGS. 2A to 2C are sectional views of a semiconductor chip for explaining a second embodiment of the present invention.

First, as shown in FIG. 2A, on a silicon substrate 1 having a low-concentration P-type plane orientation (100), a pad oxide film 2 and a silicon nitride film 3 are formed to a thickness of 20 nm and 300 nm, respectively.
Formed to a thickness of Next, after patterning the silicon nitride film 3 on the element isolation region, a silicon nitride film is formed as a sidewall 4 on the side wall. Thereafter, a groove 10 is formed to a depth of 100 nm in the silicon substrate 1 using the silicon nitride films 3 and 4 as a mask. At this time, the anisotropy of dry etching is weakened, and the side wall of the groove 10 is inclined. Then, as a cover film and an ion implantation protection film,
A polysilicon film 5A is deposited to a thickness of 100 nm.
After that, boron ions 6 are implanted into the silicon substrate 1 via the polysilicon film 5A.

Next, as shown in FIG. 2B, after an element isolation oxide film 7A is formed by wet oxidation,
As shown in (c), the silicon nitride film 3 and the like are removed by a wet etching method.

As described above, according to the second embodiment, the groove 10
Since the element isolation oxide film 7A is formed deeper by the formation of the gate electrode, the bird's beak can be further reduced as compared with the first embodiment.

[0016]

As described above, according to the present invention, a side wall is formed on a side wall of an insulating film on a silicon substrate, and a polysilicon film is formed thereon as a cover film and an ion implantation protection film. By oxidizing the element isolation region after ion implantation of a desired impurity as a stopper, there is an effect that the lateral spread of the element isolation region made of an oxide film can be reduced. Further, there is an effect that generation of defects due to ion implantation can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor chip for explaining a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a semiconductor chip for explaining a second embodiment of the present invention.

FIG. 3 is a view showing the dependence of the lateral expansion of the element isolation region on the oxide film thickness for explaining the effect of the embodiment.

FIG. 4 is a sectional view of a semiconductor chip for explaining a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2, 2A Pad oxide film 3, 3A Silicon nitride film 4 Side wall 5, 5A Polysilicon film 6 Boron ion 7, 7A, 7B Element isolation oxide film 10 Groove

Claims (2)

(57) [Claims] A step of sequentially forming a thin silicon oxide film and a silicon nitride film on a silicon substrate and then selectively removing at least the silicon nitride film in an element isolation region; and forming an insulating film on a side wall of the silicon nitride film. Forming a polysilicon film over the entire surface after forming a sidewall made of a silicon oxide film, and selectively oxidizing the device isolation region after ion implantation of a desired impurity from above the polysilicon film as a channel stopper. Forming a semiconductor device. 2. The method according to claim 1, wherein a polysilicon film is formed after forming a shallow groove in the silicon substrate between the side walls.