JPS6316903B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an integrated circuit device, and more particularly to a method for isolating elements of an integrated circuit.

In recent years, there has been a strong demand for higher density in integrated circuit devices, and the areas of elements incorporated therein have become smaller.

As the area of elements becomes smaller in this way, it has become clear that the area occupied by the area separating the elements in the integrated circuit device becomes a major obstacle to improving the degree of integration.

Conventionally, isolation between elements in integrated circuit devices has been achieved using selectively grown silicon oxide films. In order to selectively grow this silicon oxide film, a method is usually adopted in which a silicon substrate is thermally oxidized to form a selectively buried oxide film.
In this method, 500 ~
Thin thermally oxidized silicon oxide film of about 1000 Å and 1000 Å
A 2000 Å thick vapor-phase silicon nitride film was selectively formed, and these two-layer films were used as an oxidation mask during thermal oxidation to form a thermal oxide film approximately 1.0 μm thick on the silicon substrate. The role of the thin silicon oxide film in this two-layer film is to relieve the stress between the silicon substrate and the vapor-phase grown silicon nitride film during thermal oxidation. Defects caused by stress are prevented from forming on the substrate surface. On the other hand, in this thin silicon oxide film, oxidizing factors such as oxygen and hydroxyl groups easily diffuse, so when forming a thick oxide film of about 1.0 μm, the thin silicon oxide film also thickens at the edge of the nitride film. There was a phenomenon in which the thick oxide film penetrated beneath the vapor-phase grown nitride film that served as the acid mask. For this reason, the element isolation region has expanded and the active element area has decreased, posing a major obstacle to improving the degree of integration.

In order to eliminate these drawbacks of conventional element isolation methods, various methods have been proposed, such as etching the isolation region in advance into a groove shape and then forming a thick oxide film. The new separation method often involves extremely complicated processes, which poses practical difficulties.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a device isolation method that eliminates the above-mentioned drawbacks.

In the present invention, if silicon oxide with a thickness of several hundred Å is thermally nitrided in advance and used under a vapor-phase grown nitride film that serves as an oxidation mask, it is possible to form a thick oxide film without causing strain on the silicon substrate. This method is also based on the knowledge that a thick oxide film for isolation between elements can be formed without the lateral spread of the thick oxide.

The device isolation method of the present invention includes a step of thermally oxidizing a silicon substrate, a step of thermally nitriding the silicon oxide film in a gas containing, for example, ammonia, and selective vapor phase growth on the silicon oxide film. The method includes a step of forming a silicon nitride film, and a step of selectively oxidizing a silicon substrate using the silicon nitride film as a mask.

Next, in order to better understand the present invention, the present invention will be explained using the drawings. FIG. 1 is a cross-sectional view for explaining a conventional element isolation method. In this conventional method, first, as shown in FIG.
A silicon oxide film 102 with a thickness of several hundred angstroms is formed on 01 by thermal oxidation, and then a silicon nitride film 103 is grown by vapor phase growth as shown in FIG. 1b.
As shown in FIG. 1c, the silicon oxide film 102 and the silicon nitride film 103 are etched away from the element isolation region to selectively serve as a mask for later oxidation. The silicon oxide film 102 and the silicon oxide film 103 are left behind, and finally, as shown in FIG. Then, it is oxidized to form an inter-element isolation oxide film 104 having a thickness of about 1.0 μm.

In this conventional device isolation method, the thick oxide film 104 serves as a mask. It spreads laterally from the end of the silicon nitride film 103 and enters under the silicon nitride film 103 by a length L _B . The value of L _B ranges from 70% to 100% of the thickness of the thick silicon oxide film 104. For this reason, the area of the element isolation region increases, and therefore the area where active elements such as transistors are later formed becomes narrower, resulting in a major drawback in that an improvement in the degree of integration is hindered.

FIG. 2 is a sectional view for explaining the device isolation method of the present invention. The inter-element isolation method of the present invention begins with the second
As shown in Figure a, a silicon oxide film 202 with a thickness of several hundred angstroms is formed on a silicon substrate 201 by thermal oxidation, and then as shown in Figure 2 b, a silicon oxide film 202 is formed by heat treatment in an atmosphere containing ammonia gas. Oxide film 20
2 is replaced with a thermally nitrided silicon oxide film 203. Next, by growing the silicon nitride film in a vapor phase and selectively etching it, the thermal nitride silicon oxide film 20 is selectively left as shown in FIG. 2c.
3 and a silicon nitride film 204 is formed, and finally, as shown in FIG.
As shown in the figure, the thermal nitride silicon oxide film 203
Then, a thick insulating film 205 for isolation between elements is formed using the silicon nitride film 204 as an oxidation mask.

In the device isolation method of the present invention, the thin silicon oxide film under the silicon nitride film 204 is a thermally nitrided silicon oxide film 203. Since this thermally nitrided silicon oxide film 204 has barrier properties against oxidation, the thick oxide film 204
When forming the oxide film 205, the lateral spread of the oxide film 205 is very small. For this purpose, silicon nitride film 20
This has the advantage that the area of the region below 4, where (active) elements will be formed later, is prevented from becoming narrower, and the degree of integration is greatly improved. Furthermore, the thermally nitrided silicon oxide film 203 has the function of relieving stress between the silicon nitride film 204 and the silicon substrate 201, similar to a normal silicon oxide film, and since no strain is introduced into the silicon substrate 201, later There is no deterioration in the characteristics of the element formed by the method.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional method for manufacturing a semiconductor device, and FIG. 2 is a sectional view showing an embodiment of the present invention. In the figure, 101, 201... silicon substrate, 102, 202... silicon oxide film, 10
3,204...Silicon nitride film by vapor phase growth,
104, 205... Thick oxide film for isolation between elements, 2
03...A silicon oxide film that has been thermally nitrided.

Claims (1)

[Claims] 1. A step of thermally oxidizing a silicon substrate to form a silicon oxide film, a step of thermally nitriding the silicon oxide film, a step of vapor phase growing a silicon nitride film on the thermally nitrided silicon oxide film, and a step of thermally nitriding the silicon oxide film. The method includes a step of selectively etching away the silicon nitride film and the thermally nitrided silicon oxide film, and a step of thermally oxidizing the silicon substrate using the remaining silicon nitride film and the thermally nitrided silicon oxide film as masks. A method for manufacturing a featured semiconductor device.