JPH09199494A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a fine semiconductor device with high yield by reducing a step while suppressing the generation of bird's beak on an element isolating SiO2 film. SOLUTION: At the time of forming an element isolating SiO2 film 15, the polycrystal Si film 13 formed on a SiO2 film 12 on a Si substrate 11 is removed by the film thickness of 25%-65%, and an SiO2 film 15 is formed by selectively oxidizing the Si substrate 11 using an SiN film 14 as a mask. As a result, a step is reduced while suppressing the generation of bird's beak on the SiO2 film 15.

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 in which a SiO ₂ film for element isolation is formed on a Si substrate by the LOCOS method.

[0002]

2. Description of the Related Art As an element isolation structure in a semiconductor device, Si for element isolation is formed on a Si substrate by the LOCOS method.
The structure for forming an O ₂ film is most commonly used, but in a semiconductor device whose minimum line width is miniaturized to about 0.35 μm, in order to suppress bird's beak generation and promote miniaturization, A modified LOCOS method, PPL (Pad Po
lyLOCOS) method is used.

In this PPL method, as shown in FIG. 1A, a SiO ₂ film 12 for a pad and an O ₂ film are formed on a Si substrate 11.
A polycrystalline Si film 13 having a diffusion coefficient smaller than that of the SiO ₂ film 12 and a SiN film 14 which is an antioxidant film are sequentially formed.

Then, in the region to be the element isolation region, a part of the polycrystalline Si film 13 in the film thickness direction and the SiO ₂ film 12 are left and the other SiN film 14 and the polycrystalline Si film 13 are removed. , SiN film 1 left in the region to be the device active region
4 is used as a mask to selectively oxidize the Si substrate 11 to form a SiO ₂ film 15 for element isolation. In the conventional example of the invention of the present application, 30 nm is formed in the region which should be the element isolation region.
The polycrystalline Si film 13 having the film thickness of 1 is left.

[0005]

By the way, FIG. 1 (b)
In (C), in the PPL method, the film thickness of the polycrystalline Si film 13 at the initial formation is set to 40 nm, the film thickness of the polycrystalline Si film 13 left in a region to be an element isolation region, and the Si substrate in the SiO ₂ film 15. 11 shows the relationship between the depth a from the surface of No. 11, the height b of the convex portion, and the length c of the bird's beak. Therefore, in the conventional example in which the polycrystalline Si film 13 having a film thickness of 30 nm was left in the region to be the element isolation region, the height b of the convex portion was high and the step difference in the SiO ₂ film 15 was large.

On the other hand, if the numerical aperture of the optical system in the exposure apparatus used in lithography is increased to increase the resolution in order to miniaturize the pattern of the element isolation region and the like, the depth of focus margin of the optical system is conversely increased. It decreases in inverse proportion to the square of. Therefore, if the step difference in the SiO ₂ film 15 is large as in the conventional example, the first step formed on the Si substrate 11
Since the depth of focus margin d when patterning the wiring of the layer is further reduced, it is difficult to manufacture a fine semiconductor device with a high yield in the conventional example.

[0007]

According to a first aspect of the present invention, there is provided a method of manufacturing a semiconductor device, wherein a step of sequentially forming a SiO ₂ film, a polycrystalline Si film and an antioxidant film on a Si substrate, and an element isolation region are formed. And the polycrystalline S in the region to be
A step of removing 25 to 65% of the i film and a step of selectively oxidizing the Si substrate by using the removed anti-oxidation film as a mask to remove SiO ₂ for element isolation.
And a step of forming a film.

A method of manufacturing a semiconductor device according to a second aspect is the method of manufacturing a semiconductor device according to the first aspect, characterized in that the film thickness of the polycrystalline Si film after the removal is set to 10 to 25 nm.

According to a third aspect of the present invention, there is provided a method of manufacturing a semiconductor device according to the first aspect, wherein the polycrystalline Si is used.
It is characterized in that after the SiO ₂ film is formed on the surface of the film, the antioxidant film is formed on the SiO ₂ film.

In the method of manufacturing a semiconductor device according to the first and _second aspects, when the SiO ₂ film for element isolation is formed, 25 to 25 of the polycrystalline Si films formed on the SiO ₂ film on the Si substrate are formed.
Since 65% of the film thickness is removed, Si for element isolation
The step can be reduced while suppressing the occurrence of bird's beaks in the O ₂ film.

In the method of manufacturing a semiconductor device according to the third aspect, since the SiO ₂ film is formed on the surface of the polycrystalline Si film and then the antioxidant film is formed, the oxidation is performed after the SiO ₂ film for element isolation is formed. When the protective film is removed, the SiO ₂ film on the surface of the polycrystalline Si film serves as a stopper to prevent digging of the Si substrate.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. In this embodiment, as shown in FIG. 2A, the Si substrate 21 is oxidized to
A pad SiO ₂ film 22 having a film thickness of about 10 nm is formed on the surface of the Si substrate 21. And the film thickness is 50n
A polycrystalline Si film 23 having a thickness of about m is deposited on the SiO ₂ film 22 by the CVD method.

Then, the surface of the polycrystalline Si film 23 is oxidized to form a SiO ₂ film 24 having a thickness of about 10 nm.
Is formed on the surface of the polycrystalline Si film 23, and
The film thickness of the film 23 is set to about 40 nm. And the film thickness is 1
A SiN film 25 having a thickness of about 00 nm is deposited on the SiO ₂ film 24.

Next, as shown in FIG. 2B, the SiN film 2
5, the resist 26 is processed into a pattern of the element active region, and the resist 26 is used as a mask to anisotropically etch the SiN film 25, the SiO ₂ film 24 and the polycrystalline Si film 23 having a film thickness of about 20 nm. After that, the resist 26 is removed. Therefore, the film thickness of the polycrystalline Si film 23 left in the region to be the element isolation region is also about 20 nm.

Next, as shown in FIG. 2C, the SiN film 2
5 as an antioxidation mask and Si substrate 21 and polycrystalline Si
By oxidizing the film 23, a SiO ₂ film 27 for element isolation having a film thickness of about 300 nm is selectively formed on the surface of the Si substrate 21. Then, as shown in FIG. 2D, the SiN film 25 is removed by etching. At this time,
The SiO ₂ film 24 serves as an etching stopper to prevent the polycrystalline Si film 23 and the Si substrate 21 from being etched.

After that, the SiO ₂ film 24 and the polycrystalline Si film 2
3. Polycrystalline Si film 2 at the edge of SiO ₂ film 27
Remove the rest of 3 and the roughness at this edge,
The formation of the element isolation region is completed. Then, the conventionally known process is further executed to complete the semiconductor device.

In the above embodiment, about 20 nm of the film thickness of about 40 nm of the polycrystalline Si film 23 is anisotropically etched to leave about 20 nm in the step of FIG. 2B. As is clear from FIG. 1 (c), 30 to 15
The thickness of about 10 nm is anisotropically etched to 10 to 25n
Even if a film thickness of about m is left, the step difference can be reduced while suppressing the occurrence of bird's beaks in the SiO ₂ film 27.

Further, in the above embodiment, polycrystalline Si at the time of etching the SiN film 25 in the step of FIG. 2B.
Although the film thickness of the film 23 is set to about 40 nm, the film thickness of the polycrystalline Si film 23 at this time may be other than 40 nm, and even in this case, the film thickness of the polycrystalline Si film 23 at this time is 25 to 65.
%, The step difference can be reduced while suppressing the occurrence of bird's beaks in the SiO ₂ film 27.

[0019]

According to the method of manufacturing a semiconductor device of the first and _second aspects, since it is possible to suppress the occurrence of bird's beaks in the SiO ₂ film for element isolation, miniaturization of the semiconductor device can be promoted, and moreover, Since the step difference in the SiO ₂ film for element isolation can be reduced, the depth of focus margin in lithography for patterning the wiring can be increased. Therefore, a fine semiconductor device can be manufactured with a high yield.

In the method of manufacturing a semiconductor device according to the present invention, since the Si substrate can be prevented from being dug when the antioxidant film is removed after the SiO ₂ film for element isolation is formed, the Si substrate is damaged. It is possible to manufacture a highly reliable semiconductor device without such problems.

[Brief description of drawings]

FIG. 1A is a side sectional view for explaining a PPL method,
(B) is a schematic side view of the element isolation SiO ₂ film formed by the PPL method, and (c) is the remaining film thickness of the polycrystalline Si film and the depth, height and bird's beak of the element isolation SiO ₂ film in the PPL method. 2 is a graph showing the relationship between the length of the line and the depth of focus margin in lithography of the first layer wiring on the Si substrate.

FIG. 2 is a side sectional view sequentially showing an embodiment of the present invention.

[Explanation of symbols]

11 Si substrate 12 SiO ₂ film 13 Polycrystalline Si film 14 SiN film 15 SiO ₂ film 21 Si substrate 22 SiO ₂ film 23 Polycrystalline Si film 24 SiO ₂ film 25 SiN film 27 SiO ₂ film

Claims (3)

[Claims] 1. A step of sequentially forming a SiO ₂ film, a polycrystalline Si film, and an antioxidant film on a Si substrate, and a step of forming the SiO ₂ film and the polycrystalline Si film in a region where an element isolation region is to be formed. A step of removing 25 to 65% of the film thickness, and a step of selectively oxidizing the Si substrate using the removed anti-oxidation film as a mask.
And a step of forming an O ₂ film. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the film thickness of the polycrystalline Si film after the removal is set to 10 to 25 nm. 3. The method of manufacturing a semiconductor device according to claim 1, wherein after forming a SiO ₂ film on the surface of the polycrystalline Si film, the antioxidant film is formed on the SiO ₂ film.