JPH09270498A - Manufacture of semiconductor memory device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a silicon nitride film from being locally broken by a method wherein the surface of a first polycrystalline silicon film is thermally oxidized for the formation of a first silicon oxide film, the oxide film is removed, a silicon nitride film is formed, and a second silicon oxide and a second polycrystalline silicon are laminated thereon. SOLUTION: A first ground polysilicon film 2 is formed on a semiconductor substrate 1 through the intermediary of a silicon oxide film 11, and the surface of the ground polysilicon film is thermally oxidized for the formation of a first silicon oxide film 6. Then, the first silicon oxide film 6 is removed, when the pattern edge of the first ground polysilicon film 2 is rounded by trimming. A silicon nitride film 3 is formed on the first ground polysilicon film 2, and a second silicon oxide film 4 is formed thereon. Furthermore, a second polysilicon film 5 is formed on the second silicon oxide film 4. By this setup, the silicon nitride film 3 can be prevented from being locally broken, and a semiconductor memory device of this constitution can be ensured of a high capacity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor memory device, and is particularly suitable for application to, for example, a method of manufacturing a capacitive element included in a DRAM.

[0002]

2. Description of the Related Art Generally, a capacitive element in a DRAM is
Poly-Si is used for the lower and upper electrodes, and S is used for the dielectric film.
An iN film and a film converted to SiO ₂ by oxidizing the surface thereof are used. To increase the capacity,
It is advantageous to use only SiN having a higher dielectric constant than SiO ₂ as the dielectric film, but the SiN film alone has a high leak current and a low electric breakdown voltage. Therefore, by oxidizing the SiN film surface, It prevents this.

A conventional method of manufacturing such a capacitive element will be described with reference to FIG.

First, as shown in FIG. 2A, a Poly-Si film 2 to be a lower electrode of a capacitor is patterned on a base insulating film 11 formed on a substrate (not shown).

Next, as shown in FIG. 2 (b), the SiN film 3 is usually formed by a chemical vapor deposition method (CVD method) to a thickness of 50 to 50 nm.
It is formed to a film thickness of 100Å.

Next, as shown in FIG. 2C, the surface of the SiN film 3 is changed to the SiO ₂ film 4 with a film thickness of usually about 20Å by performing thermal oxidation.

Next, as shown in FIG. 2 (d), a Poly-Si film 5 to be an upper electrode of the capacitive element is formed.

[0008]

Conventionally, when the SiN film 3 is thinned, when the surface of the SiN film 3 is oxidized, as shown in FIG.
As shown in FIG. 5, the SiN film 3 is locally broken, so that a thick SiO ₂ film 36 is locally formed, and as a result, there is a problem that the capacitance value does not reach a desired value.
The portion where the SiN film 3 is locally broken is, as shown in the figure,
It is known that this is the pattern edge of the lower electrode Poly-Si film 2. It is estimated that this is because stress concentrates on the edge portion.

Therefore, the present invention is further improved by preventing local breakage of the SiN film at the time of oxidation of the surface of the SiN film at the pattern edge of the lower electrode Poly-Si film even if the SiN film is thinned. An object of the present invention is to provide a method for manufacturing a semiconductor device including a capacitance element having a capacitance value.

[0010]

According to a method of manufacturing a semiconductor device of the present invention, a first polycrystalline silicon film is formed on a semiconductor substrate, and the first polycrystalline silicon film is processed into a lower electrode pattern of a capacitor. And a second step of thermally oxidizing the surface of the first polycrystalline silicon film to form a first silicon oxide film on the first polycrystalline silicon film, A third step of removing the silicon oxide film, a fourth step of forming a silicon nitride film on the first polycrystalline silicon film, and a second step of forming a second silicon oxide film on the silicon nitride film. 5 and a sixth step of forming a second polycrystalline silicon film on the second silicon oxide film.

In one aspect of the present invention, in the third step, the first silicon oxide film is removed using hydrofluoric acid.

In one aspect of the present invention, in the third step, the first silicon oxide film is removed by using fluorine plasma.

[0013]

In the present invention, for example, the surface of the Poly-Si film is oxidized once between the step of forming the pattern of the Poly-Si film as the lower electrode of the capacitor and the step of forming the SiN film, and then the surface of the Poly-Si film is oxidized. The SiO ₂ film formed on the substrate is removed.

That is, for example, after the lower electrode pattern is formed of the Poly-Si film, the surface of the Poly-Si film is thermally oxidized.
At this time, in the edge portion of the Poly-Si film pattern, Po
Oxidation proceeds from the upper surface and the side surfaces of the ly-Si film, so that the unoxidized Poly-Si portion changes from a sharp angle of about 90 ° to a rounded shape. Therefore, after this, Poly−
Si formed after the SiO ₂ film on the surface of the Si film is removed
There is no sharp corner of the Poly-Si film under the N film.

As a result, stress concentration of the SiN film at the edge of the poly-Si film pattern is relaxed in the subsequent step of oxidizing the surface of the SiN film, so that local SiN film breakage is less likely to occur.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The first embodiment of the present invention will be described below with reference to FIG.
A method of forming the capacitive element of the DRAM according to the embodiment will be described.

First, as shown in FIG. 1A, a first film is formed on the SiO ₂ film 11 formed on the silicon semiconductor substrate 1.
A Poly-Si film 2 is formed by a CVD method to a film thickness of about 5000 Å, and is further patterned into a desired lower electrode pattern of a capacitor.

Then, as shown in FIG. 1B, a heat treatment is performed at 900 ° C. in an oxidizing atmosphere to give Poly-S.
Oxide a portion of the thickness of about 500Å from the surface of the i film 2
The iO ₂ film 6 is formed.

Next, as shown in FIG. 1C, the SiO ₂ film 6 on the surface of the Poly-Si film 2 is removed using an HF solution. At this time, the pattern edge of the Poly-Si film 2 has a rounded shape compared to the initial state, that is, a so-called edged shape.

Then, as shown in FIG. 1D, CVD
The SiN film 3 is formed to a film thickness of about 50Å by the method.

Then, as shown in FIG. 1 (e), a heat treatment at 900 ° C. is performed in an oxygen atmosphere to oxidize a portion of the SiN film 3 having a thickness of about 20 Å from the surface thereof, and SiO ₂
The film 4 is formed.

Next, as shown in FIG. 1F, a second Poly-Si film 5 which will be the upper electrode of the capacitor is formed.

In the first embodiment, as shown in FIG.
As a result of going through the step (c), local breakage of the SiN film 3 at the pattern edge portion of the first Poly-Si film 2 is eliminated,
No decrease in the capacitance value of the capacitive element was observed.

Next, a second embodiment of the present invention will be described.

The process sectional view of the second embodiment is substantially the same as that of the above-described first embodiment, and therefore the illustration thereof is omitted, but in the second embodiment, As a method of removing the SiO ₂ film 6 formed on the surface of the first Poly-Si film 2 shown in FIG. 1C, dry etching using plasma using F-based gas is used. That is, a parallel plate type etcher (not shown) is used as an etching device, and a mixed gas of CF ₄ and O ₂ is used as an F-based gas.

[0026]

According to the present invention, due to the local breakage of the SiN film in the oxidation process of the surface of the SiN film as a measure against the leak current and the withstand voltage deterioration of the SiN film used as a part of the dielectric film of the capacitive element. It is possible to prevent the resulting decrease in the capacitance value and realize a method for manufacturing a semiconductor device with a high yield.

[Brief description of drawings]

FIG. 1 is a process cross-sectional view showing a method of manufacturing a capacitive element according to an embodiment of the present invention.

2A to 2D are process cross-sectional views showing a conventional method of manufacturing a capacitive element.

FIG. 3 is a schematic cross-sectional view showing a conventional problem.

[Explanation of symbols]

1 Silicon Semiconductor Substrate 2 Poly-Si Film (Lower Electrode) 3 SiN Film 4 SiO ₂ Film 5 Poly-Si Film (Upper Electrode) 6 SiO ₂ Film 11 SiO ₂ Film

Claims (3)

[Claims] 1. A first step of forming a first polycrystalline silicon film on a semiconductor substrate and processing the first polycrystalline silicon film into a lower electrode pattern of a capacitor, the first polycrystalline silicon film. The first surface is formed by thermally oxidizing the film surface.
A second step of forming a first silicon oxide film on the polycrystalline silicon film, a third step of removing the first silicon oxide film, and a silicon nitride film on the first polycrystalline silicon film. A fourth step of forming a film, a fifth step of forming a second silicon oxide film on the silicon nitride film, and a second polycrystalline silicon film on the second silicon oxide film And a sixth step, which is a method for manufacturing a semiconductor memory device. 2. The method of manufacturing a semiconductor memory device according to claim 1, wherein in the third step, the first silicon oxide film is removed using hydrofluoric acid. 3. The method of manufacturing a semiconductor memory device according to claim 1, wherein in the third step, the first silicon oxide film is removed using a fluorine-based plasma.