JPH02215129A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To eliminate the dependence of bird's beak length upon patterns by a method wherein the selective oxidation process from the nitride film pattern formation to the selective oxidation is divided into two time processes while O2 is fed in only one direction. CONSTITUTION:Si3N4 film pattern 5A, 5B are provided on a thermal oxide film 2 of an Si substrate. The film 5A is striped in the perpendicular direction to a region 1A while the film 5B is striped including an element isolating region 1B in parallel with the film 5A. When an isolating oxide film 61 is formed hy wet oxidation, O2 is fed in only one direction so that the bird's beak lengths may be shortened in almost the same length. In the second time oxidation, the region 1A, the isolating oxide film 61 and the region 1B are covered using an Si3N4 7A as a mask. The remaining isolating films 62, 63 are also formed by the wet oxidation to be formed into one body with the film 61. The bird's beaks 62A, 63B are shortened in almost the same length since O2 is also fed in only one direction. The Si3N4 7A is removed by hot phosphoric acid to complete the element isolation. Through these procedures, the dependence of the bird's beak length upon patterns is eliminated so that the beaks as a whole may be shortened thereby enabling this manufacturing process to contribute to the higher integration of the title semiconductor device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method of manufacturing a semiconductor device, and relates to a method of forming an element isolation oxide film.

The purpose of this method is to reduce the pattern dependence of the length of the bird's beak that invades the device formation region, shorten the bird's beak as a whole, and achieve higher integration of the device.

When forming an element isolation oxide film (6) on a semiconductor substrate (1) that defines a striped element formation region (1B) whose end portions are in contact with the isolation region in at least two directions.

forming a first oxidation-resistant mask (5B) on a region extending in the stripe width direction including the element formation region (1B);
The device isolation oxide film (6) in a part of the region where the device isolation oxide film (6) is to be formed by selectively oxidizing the substrate.
1) is formed in contact with the end of the element formation region (1B),
The step of removing the first oxidation-resistant mask (5B) and the step of removing the second oxidation-resistant mask (7A) on the element isolation oxide film (61) in the partial region of the substrate and the element formation region (1B) are performed. ) is formed, and the substrate is selectively oxidized to form element isolation oxide films (62) and (63) in the remaining regions.

and a step of removing the second oxidation-resistant mask (7A).

[Industrial application field]

The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming an element isolation oxide film.

In recent years, as semiconductor devices have become more highly integrated, there has been a demand for smaller element isolation regions.

One of the element isolation methods is to cover the element formation area on the semiconductor substrate with a nitride film, and use this as an oxidation-resistant mask to thermally oxidize the area other than the element formation area to form a thick element isolation oxide film (field oxide film). According to this method, the element isolation oxide film erodes into the element formation region in a bird's beak shape, hindering high integration.

[Prior Art] FIGS. 2(1) and 2(2) are a plan view and a cross-sectional view illustrating the formation of an element isolation oxide film according to a conventional example.

In the figure, a thin thermal oxide film 2 is formed on a St substrate 1, a nitride film 3 is grown on it, and the nitride film 11!3 is patterned to leave nitride films 3A and 3B on the element isolation region to provide oxidation resistance. Use as a mask.

The nitride film 3A is formed in vertical stripes.

The nitride film 3B is formed perpendicularly to the stripes of nitride 11i3A across the element isolation region.

Next, the substrate is wet oxidized to form an element isolation oxide film 4.

In this case, a thin thermal oxide film 2 is laid to alleviate the influence between the hard nitride film and the substrate, but since oxygen diffuses through this oxide film 2, oxidation occurs near the edges of the nitride film even under the nitride film. The film grows and bird's beaks 4A and 4B are formed.

This phenomenon occurs especially at the end of the nitride film 3B, where oxygen is supplied from three directions, so the bird's beak 4B in this region
is even larger than the bird's beak 4A on the nitride film 3A side.

Furthermore, the growth of the bird's beak 4A cannot be ignored due to the fact that the end corner of the nitride film 3B is rounded due to the rounding of the resist.

[Problem to be solved by the invention]

As described above, the conventional method has the disadvantage that the bird's beak becomes long depending on the pattern of the oxidation-resistant film.

An object of the present invention is to eliminate pattern dependence of the bird's beak length and to shorten the bird's beak as a whole.

[Means to solve the problem]

The solution to the above problem is to form an element isolation oxide film (6) on a semiconductor substrate (1) that defines a striped element formation region (1B) whose end portions are in contact with the isolation region in at least two directions. A first oxidation-resistant mask (5
B) and selectively oxidize the substrate to remove the element isolation oxide film (61) in a part of the region where the element isolation oxide film (6) is to be formed in the element formation region (1B). A step of removing the first oxidation-resistant mask (5B) formed in contact with the end portion, and a step of removing the element isolation oxide film (6B) in the partial region of the substrate.
1) and a second oxidation-resistant mask (7A) is formed over the element formation region (1B).

The substrate is selectively oxidized to form an element isolation oxide film (62
), (63), and the second oxidation-resistant mask (7A
) is achieved by a method for manufacturing a semiconductor device.

[Effect]

The present invention divides the process from nitride film pattern formation to selective oxidation in the selective oxidation process into two steps, and supplies oxygen, which causes bird's beak formation, from only one direction in both the first and second oxidation, thereby eliminating bird's beak formation. This eliminates the pattern dependence of length.

〔Example〕

FIGS. 1(1) to 1(5) are a plan view and a cross-sectional view illustrating the formation of an element isolation oxide film according to an embodiment of the present invention.

This example uses the same pattern as the conventional example shown in FIG. 2 for comparison.

The regions corresponding to the nitride films 3^ and 3B in FIG. 2 are here referred to as the first element formation area IA and the second element formation area 1B.
shall be.

■ First selective oxidation In Figures 1 (1) and (2), a thin thermal oxide film 2 with a thickness of 300 mm is formed on the Si substrate 1, and a nitride film 5 is grown on it. 5 is patterned to leave the nitride films 5^ and 5B as a first oxidation-resistant mask.

The nitride film 5A is formed in vertical stripes on the element formation region IA, and the nitride film 5B is formed in a stripe shape parallel to the nitride film 5A, including the element formation region 1B with the element isolation region in between.

Next, the substrate is wet-oxidized to form an element isolation oxide film 61 on a partial region of the element isolation oxide film 6.

In this case, bird's beaks 61A and 61B are formed, but since oxygen is supplied only from one direction, the bird's beak lengths are approximately the same and short.

Next, oxidation-resistant masks 5A and 5B are removed using hot phosphoric acid.

■ Second selective oxidation In Figures 1 (3) to (5), a nitride film 7 is grown on the entire surface of the substrate, and the nitride film 7 is patterned to leave the nitride film 7 as a second oxidation-resistant mask. shall be.

The nitride film 7A covers the element formation region 1^ and the element isolation oxide film 61.
and is formed to cover the element formation region 1B.

Next, wet oxidize the substrate to remove the remaining element isolation oxide film 6.
2.63 is formed and integrated with the element isolation oxide film 61 to obtain the entire element isolation oxide film 6.

In this case, bird's beaks 62^ and 63B are formed, but since oxygen is supplied from only one direction in both cases, the bird's beak lengths are similar and short.

Next, the nitride film 7A is removed using hot phosphoric acid to complete the element isolation process.

The above element isolation oxide film was formed for 900 minutes in a water vapor atmosphere.
A film thickness of 500 layers can be obtained in 320 minutes at ℃.

Furthermore, for this film thickness, the bird's beak length was conventionally long at about 0.4 μm, but in the examples it was all 0.15 μm.
It was possible to form a film with a size of approximately μm.

In addition, all nitride films for oxidation-resistant masks are grown by vapor phase growth (C
The film was grown to a thickness of 1500 using the VD) method.

Thereafter, elements are formed in the element formation region through normal steps to complete the semiconductor device.

〔Effect of the invention〕

As described above, according to the present invention, pattern dependence of the length of a bird's beak can be eliminated in the element isolation oxide film forming step in manufacturing a semiconductor device. As a result, the overall bird's beak can be shortened, contributing to higher integration of devices.

[Brief explanation of the drawing]

FIG. 1 (υ to (5)) is a plan view and a cross-sectional view illustrating the formation of an element isolation oxide film according to an embodiment of the present invention. FIGS. 2 (1) and (2) are element isolation oxide films according to a conventional example. 1 is a plan view and a cross-sectional view illustrating the formation of. 1 is a St substrate. IA is a first element formation region. 1B is a second element formation region. 2 is a thin thermal oxide film. 5 is a nitride film. 5A, 5B is a nitride film and is the first oxidation-resistant mask. 6 (61, 62, 63) is an element isolation oxide film. 7 is a nitride film. 7A is a nitride film and is the second oxidation-resistant mask. -8 Figures explaining the new and conventional examples

Claims (1)

[Claims] When forming an element isolation oxide film (6) on a semiconductor substrate (1) that defines a striped element formation region (1B) whose end portions are in contact with the isolation region in at least two directions, forming a first oxidation-resistant mask (5B) on a region extending in the stripe width direction including the element formation region (1B);
The device isolation oxide film (6) in a part of the region where the device isolation oxide film (6) is to be formed by selectively oxidizing the substrate.
1) is formed in contact with the end of the element formation region (1B),
removing the first oxidation-resistant mask (5B); and removing a second oxidation-resistant mask (7A) over the element isolation oxide film (61) in the partial region of the substrate and the element formation region (1B).
forming the substrate, selectively oxidizing the substrate to form element isolation oxide films (62) and (63) in the remaining regions, and removing the second oxidation-resistant mask (7A). A method for manufacturing a semiconductor device.