JPH0744213B2 - Method for manufacturing semiconductor device - Google Patents

Description

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 such as a trench capacitor having a groove region in a semiconductor substrate.

2. Description of the Related Art Conventionally, when forming a trench capacitor on the surface of a semiconductor substrate, CVD is used when forming a groove on the substrate by etching.
It is common to use a silicon oxide film formed by the method as a mask. However, after the trench etching is completed, it is necessary to remove the silicon oxide film used as the mask. At that time, since the hydrofluoric acid solution is used, the LOCOS oxide film in the element isolation region formed in the previous step is also etched, and the film thickness is reduced. The isolation width is reduced, and the element isolation characteristics are deteriorated. As a countermeasure against this, a silicon nitride film is formed under the CVD silicon oxide film, which is used when etching with hydrofluoric acid solution.
It has been proposed to use it as a protective film for the LOCOS oxide film. A method of forming the groove will be described with reference to process step sectional views shown in FIGS. As shown in FIG. 2 (a),
Substrate 2 on which LOCOS oxide film 1 is formed is 10 nm to 70 nm
After forming the thin silicon oxide film 3 as a protective film, the silicon nitride film 4 is formed to a thickness of 20 nm to 100 nm by the CVD method, and then used as a mask for groove etching.
After the silicon oxide film 5 is formed by the CVD method, the CVD silicon oxide film 5, the silicon nitride film 4, and the thin silicon oxide film 3 are selectively etched by the photoetching method to form the opening 6 for groove etching. The resist for photo etching is removed. In FIG. 2B, the silicon substrate 2 is selectively etched using the CVD silicon oxide film 5 as a mask to form a groove.

The CVD silicon oxide film used as the etching mask in FIG. 2C is removed by etching with a hydrofluoric acid solution. At this time, the thin silicon oxide film 3 below the silicon nitride film 4
Fluoric acid solution permeates from the end facing the groove, and LOCOS
The oxide film 1 is etched up to a part thereof. Next, in order to remove the silicon nitride film 4, the exposed portion of the silicon substrate 2 is thermally oxidized to a thickness of 10 nm to 100 nm to form a thin silicon oxide film 8 for protecting the silicon substrate 2 from phosphoric acid. And then in phosphoric acid at about 150 ° C
The silicon nitride film is removed to obtain the shape shown in FIG. 2 (d), and the groove forming process is completed.

However, in the above-described process, when the distance between the LOCOS oxide film 1 and the groove becomes 1 μm or less as shown in FIG. CVD silicon oxide film 5
During the etching of, the silicon oxide film 3 is also etched from the end facing the groove and progresses to a part of the LOCOS oxide film 1,
There is a problem that even the LOCOS oxide film 1 for element isolation is etched. LOCOS for miniaturization of device dimensions
When the region and the groove are in contact with each other, the width of the infiltrating portion of the hydrofluoric acid solution is further increased, so that the etching amount of the LOCOS oxide film 1 is further expanded and the element isolation characteristic is deteriorated.

Means for Solving the Problems In the present invention, a silicon nitride film is formed on a side wall of a groove, and a portion of the end of the thin silicon oxide film exposed in the groove is covered to form a protective film for the thin silicon oxide film. Is.

Action The thin silicon oxide film is not exposed due to the protective effect of the silicon nitride film formed on the side wall of the groove, and the thin silicon oxide film and the LO film are not removed when the CVD silicon oxide film is etched by hydrofluoric acid.
COS oxide film is not etched at all.

Example FIGS. 1A to 1F show sectional views in order of steps from the step (a) of opening a window for forming a groove to the removal (f) of a silicon nitride film.

First, as shown in FIG. 1A, a first silicon oxide film 3 having a thickness of 10 nm to 100 nm and a first silicon nitride film having a thickness of 10 nm to 100 nm are formed on the surface of a silicon substrate 2 on which a LOCOS oxide film 1 is formed. A film 4, a CVD oxide film 5 having a thickness of 500 nm to 1500 nm is formed, and a groove opening 6 is formed by photoetching. Next, as shown in FIG. 2B, a groove 7 is formed using the CVD oxide film 5 as a mask. Then, as shown in FIG. 2 (c), a second silicon oxide film 8 having a thickness of 10 nm to 150 nm is formed inside the groove 7 as a silicon substrate protective film, and a second silicon film having a thickness of 30 nm to 150 nm is further formed. The nitride film 9 is formed on the entire surface. Next, as shown in FIG. 2D, the second silicon nitride film 9 is anisotropically etched by reactive ion etching, and the second silicon nitride film 9 is formed on the sidewall of the groove 7.
Leave. Then, as shown in FIG. 2 (e), the CVD oxide film 5 and the second silicon oxide film 8 at the bottom of the groove 7 are formed using a hydrofluoric acid solution.
To etch. At this time, the LOCOS oxide film 1 is not etched at all because the end portion of the first silicon oxide film 3 is protected by the silicon nitride film 9. Finally, as shown in FIG. 2 (f), the silicon substrate exposed at the bottom of the groove 7 is removed.
Thermal oxidation is performed at a thickness of 20 nm to 100 nm, and the protective film for the silicon substrate is formed by boiling phosphoric acid in the next step.
The first silicon nitride film 4 and the second silicon nitride film 9 are removed in the phosphoric acid of.

EFFECTS OF THE INVENTION According to the present invention, the thick silicon oxide film formed by the LOCOS method remains in the initial film thickness and shape even after the groove forming step, so that the element isolation characteristics are significantly improved.

[Brief description of drawings]

1 (a) to 1 (f) are cross-sectional views in order of the steps for explaining the manufacturing process of the groove forming step according to the present invention, and FIGS. 2 (a) to 2 (f).
(D) is a process order cross-sectional view showing a conventional manufacturing process. 1 ... LOCOS oxide film, 2 ... silicon substrate, 3 ... first
Silicon oxide film, 4 …… First silicon nitride film, 5 …… CV
D oxide film, 6 ... groove opening, 7 ... groove, 8 ... second silicon oxide film, 9 ... second silicon nitride film.

Claims (1)

[Claims] 1. A step of sequentially forming a first silicon oxide film, a first silicon nitride film, and a second silicon oxide film on a semiconductor substrate, the second silicon oxide film, and the first silicon nitride film. And a step of selectively etching the first silicon oxide film to form openings therein, a step of selectively etching the semiconductor substrate through the openings to form a groove, and a step of forming the groove by a thermal oxidation method. Forming a third silicon oxide film on the surface of the substrate, forming a second silicon nitride film on the entire surface including the groove, and leaving the second silicon nitride film on the side surface of the groove by anisotropic etching. A step of removing the second silicon oxide film and the third silicon oxide film at the bottom of the groove, and oxidizing the semiconductor substrate exposed at the bottom of the groove by a thermal oxidation method. The method of manufacturing a semiconductor device according to symptoms.