KR19980036674A - Method of forming field oxide film - Google Patents

Abstract

The present invention relates to a method of forming a field oxide film, comprising: depositing a first pad oxide film and a nitride film on a semiconductor substrate and selectively patterning the semiconductor substrate to expose the semiconductor substrate; and forming a second pad oxide film on an exposed portion of the semiconductor substrate. Forming a sidewall on the side of the nitride film, oxidizing an exposed portion of the second pad oxide film to form a field oxide film, and removing the nitride film, the sidewall, and the first and second pad oxide films. Process. Therefore, since the formation of the field oxide film prevents the formation of grooves around the process, a separate process for filling the grooves is not required, and thus, the process can be reduced, and since the field oxide film forms a positive slope, the volume expansion is reduced to the semiconductor. The increase in stress between the substrate and the field oxide film can be prevented.

Description

Method of forming field oxide film

1 (A) to (D) are process drawings showing a method of forming a field oxide film according to the prior art.

2A to 2D are process charts showing a method for forming a field oxide film according to the present invention.

3 is a sectional view of an important part after the field oxide film is formed

4 is a graph showing the length L of the buzz beak according to the thickness of the second pad oxide film.

5 is a graph showing the inclination angle θ of the field oxide film according to the thickness of the second pad oxide film.

Explanation of symbols on the main parts of the drawings

31 semiconductor substrate 33 first pad oxide film

35 nitride film 37 trench

39 second pad oxide film 41 side wall

43: field oxide film

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a field oxide film of a semiconductor device, and more particularly, to a method of forming a field oxide film that can be applied to a highly integrated device having a small area.

As the integration of semiconductor devices continues, technology development for reducing device isolation regions occupying a large area in semiconductor devices has been actively progressed.

1A to 1D are process charts showing a method of forming a field oxide film according to the prior art.

Referring to FIG. 1A, a pad oxide film 13 is formed on a surface of a semiconductor substrate 11 by a thermal oxidation method, and chemical vapor deposition is performed on the pad oxide film 13. The nitride film 15 is formed by a CVD method.

Referring to FIG. 1B, the isolation layer and the active region are defined by selectively removing the nitride layer 15 and the pad oxide layer 13 to expose the semiconductor substrate 11 by photolithography. . Then, a thick nitride film is deposited on the semiconductor substrate 11 and the nitride film 15 by a CVD method, and the sidewall 17 is formed on the side surface of the nitride film 15 by etching back to expose the semiconductor substrate 11. Form.

Referring to FIG. 1C, the exposed portion of the semiconductor substrate 11 is oxidized for a long time at a high temperature to form a field oxide film 19 defining an active region of the device.

At this time, since the oxygen penetrates the lower part of the sidewall 17, the field oxide film 19 is grown to the active region and has a negative slope. The nitride layer 15, the pad oxide layer 13, and the sidewalls 17 are removed by wet etching to expose the active region of the device of the semiconductor substrate 11. At this time, the groove 21 is formed around the field oxide film 19 by the side wall 17.

Referring to FIG. 1D, the oxide film 23 is deposited on the surface of the semiconductor substrate 11 including the field oxide film 19 by CVD and then etched back to fill the groove 21.

However, the conventional method of forming the field oxide film described above requires a separate process for filling the grooves, which causes a complicated process. In addition, since the field oxide film has a negative inclination, there is a problem in that the stress increases with the semiconductor substrate due to the volume expansion.

Accordingly, it is an object of the present invention to provide a method of forming a field oxide film which can reduce the process since the formation of grooves around the field oxide film is prevented.

Another object of the present invention is to provide a method of forming a field oxide film which can prevent an increase in stress between a semiconductor substrate and the semiconductor substrate.

A method of forming a field oxide film according to the present invention for achieving the above object comprises the steps of depositing a first pad oxide film and a nitride film on a semiconductor substrate and selectively patterning the semiconductor substrate to expose the semiconductor substrate; Forming a second pad oxide film and forming sidewalls on the side surfaces of the nitride film, oxidizing an exposed portion of the second pad oxide film to form a field oxide film, the nitride film and the sidewall, and the first and second A step of removing the pad oxide film is provided.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2A to 2D are process charts showing a method for forming a field oxide film according to the present invention.

Referring to FIG. 2A, a first pad oxide film 33 and a nitride film 35 are formed on the surface of the semiconductor substrate 31. The first pad oxide film 33 is formed by growing to a thickness of about 100 to about 200 kPa by the thermal oxidation method, and the nitride film 35 is formed by depositing the thickness of about 1000 to about 2000 kPa by the CVD method.

Referring to FIG. 2B, predetermined portions of the nitride film 35 and the first pad oxide film 33 are removed by photolithography. At this time, the first pad oxide film 33 and the nitride film 35 are excessively etched so that the semiconductor substrate 31 is also etched to form a trench 37 having a depth of about 100 to 250 kPa.

Referring to FIG. 2C, the inner surface of the trench 37 is thermally oxidized to form a second pad oxide film 39 having a thickness of about 150 to about 200 kHz. After the nitride film is deposited on the entire surface of the above-described structure, the second pad oxide film 39 is etched back to expose the sidewalls 41 having a thickness of about 150 to 250 에 on the side surfaces of the trench 37 and the nitride film 35. Form.

Referring to FIG. 2D, the exposed portion of the second pad oxide film 39 is oxidized to form a field oxide film 43. In this case, the second pad oxide film 38 not only buffers stress but also suppresses growth of the field oxide film 43 into the active region under the nitride film 35. Therefore, the growth of the bird's beak is reduced and the field oxide film 43 has a positive slope, thereby reducing the stress of the contact portion of the semiconductor substrate 31. The nitride film 35, the sidewalls 41, and the first and second pad oxide films 33 and 39 are removed.

3 is a cross-sectional view of an important part after the field oxide film 43 is formed, and FIGS. 4 and 5 show the length L of the buzz beak and the field oxide film 43 depending on the thickness of the second pad oxide film 39. It is a graph which shows the inclination angle (theta), respectively.

As shown in FIG. 3, when the field oxide film 43 is formed, a portion of the sidewall 41 and the nitride film 35 that extends underneath generates a buzz beak and is in contact with the semiconductor substrate 31 of the field oxide film 43. It has a positive or negative inclination angle. The length L of the burj beak and the inclination angle θ of the field oxide film 43 are defined according to the thickness of the second pad oxide film 39.

As shown in FIG. 4, the length L of the buzz beak is formed to a thickness of about 50 to about 200 kPa when the second pad oxide film 39 is formed to a thickness of about 68 kPa. When the second pad oxide film 38 is formed to have a thickness of about 150 mW, 200 mW and 300 mW, the length L of the buzz beak is formed to have a thickness of about 100 mW, 150 mW and 300 mW, respectively. Therefore, the thinner the thickness of the second pad oxide film 38, the shorter the length L of the buzz beak.

In addition, the inclination angle θ of the field oxide film 43 has an inclination angle of -5 °, that is, a negative inclination angle when the second pad oxide film 39 is formed to a thickness of about 68 占 as shown in FIG. When the second pad oxide film 38 is formed to have a thickness of about 150 kPa, 200 kPa and 300 kPa, respectively, the field oxide film 43 has an inclination angle of 0 °, + 2 ° and + 5 °, that is, a positive inclination angle, respectively. Therefore, the thinner the field oxide film 43 has a negative inclination angle, and the thicker the field oxide film 43 has a positive inclination angle.

In the above, when the thickness of the second pad oxide film 39 is thin, the length L of the buzz beak is reduced, but the inclination angle θ of the field oxide film 43 has a negative inclination angle. However, if the thickness of the second pad oxide film 39 is thick, the inclination angle θ of the field oxide film 43 has a positive inclination angle when the length L of the buzz beak is increased. Therefore, the thickness of the second pad oxide film 39 is about 150 to 200 Å so that the length L of the buzz beak is not large and the inclination angle θ of the field oxide film 43 has a positive inclination angle.

As described above, in the method of forming the field oxide film of the semiconductor device according to the present invention, when the nitride film and the first pad oxide film are patterned, the trench is over-etched so as to etch the semiconductor substrate. A second pad oxide film is formed on the inner surface of the trench, and nitrided sidewalls are formed on the side surfaces of the trench and the nitride film, and then a field oxide film is formed.

Therefore, since the present invention prevents the formation of grooves around the field oxide film formation, a separate process for filling the grooves is not required, and thus the process can be reduced, and since the field oxide film has a positive inclination, volume expansion can be achieved. There is an advantage in that it is possible to prevent the stress from increasing between the semiconductor substrate and the field oxide film by reducing it.

Claims (5)

Depositing a first pad oxide film and a nitride film on the semiconductor substrate and selectively patterning the semiconductor substrate to expose the semiconductor substrate; Forming a second pad oxide film on the exposed portion of the semiconductor substrate and forming sidewalls on a side surface of the nitride film; Performing an oxidation process to form a field oxide film, And removing the nitride film, the sidewall, and the first and second pad oxide films. The method of claim 1, And forming a trench by etching the semiconductor substrate when patterning the first pad oxide film and the nitride film. The method of claim 2, A method of forming a field oxide film for forming the trench to a depth of 100 ~ 250Å. The method of claim 1, A method of forming a field oxide film, wherein the first pad oxide film is formed to a thickness of 150 to 200 GPa. The method of claim 1, A method of forming a field oxide film, wherein the sidewall is formed of a nitride film having a thickness of 150 to 250 Å.