JPH08306677A - Formation of element isolation film - Google Patents

Abstract

PURPOSE: To inhibit the formation of a white ribbon by a method wherein an oxide film is formed on a surface part of a substrate with a silicon nitride oxidation preventive film on its upper part by a dry oxidation and the oxide film is grown by a moistening oxidation and is formed into an element isolation film. CONSTITUTION: An oxidation preventive film 14 consisting of a silicon nitride film 13 is formed on a pad oxide film 12. Then, high-purity oxygen gas is introduced in a heat-treating furnace formed with a substrate 11 and the air in the interior of the furnace is turned into a dried oxygen atmosphere. After that, the temperature in the interior of the furnace is made to heat-up to 1050 deg.C or thereabouts and an oxide film 15 of a film thickness of several nm or thereabouts is formed on the surface part, which is exposed through the film 14, of the substrate 11. Then, oxygen gas and high-purity hydrogen gas are introduced in this furnace to react both of the oxygen gas and the high-purity hydrogen gas with each other to generate water vapor and the film 15 is grown in a film thickness of 400nm in a moistening atmosphere. Thereby, an element isolation film 15a consisting of the film 15 of a thick film thickness is formed on the surface part of the substrate 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an element isolation film on the surface of a substrate in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing process, an element isolation film made of an oxide film is formed between a plurality of elements formed on a substrate surface by, for example, the selective oxidation method described below.
First, an oxidation prevention mask made of silicon nitride is formed on the surface of a substrate made of silicon via a pad oxide film. Next, by wet oxidation such as pyrogenic oxidation, the surface portion of the substrate exposed from the oxidation prevention mask is selectively oxidized to form an element isolation film made of silicon oxide.

In the above-described method for forming the element isolation film, the oxidation prevention mask is made of silicon nitride, so that stress is applied to the substrate during the oxidation process so that the oxidation film on the substrate portion below the end of the oxidation prevention mask is formed. Is suppressed, and the bird's beak of the element isolation film is suppressed to be small. Further, the element isolation film having a large film thickness is formed by oxidizing the surface portion of the substrate by wet oxidation.

[0004]

However, the above-mentioned method for forming an element isolation film has the following problems. That is, as shown in FIG. 2A, at the time of performing wet oxidation, the surface of the anti-oxidation mask 23 formed on the substrate 21 via the pad oxide film 22 constitutes the anti-oxidation mask 23. Ammonia is produced by the reaction between silicon and water contained in the oxidizing atmosphere. This ammonia reacts with the silicon forming the substrate 21 to generate a silicon nitride on the surface of the substrate 21. As a result,
As shown in (2), a so-called white ribbon 24 made of the nitride is formed on the substrate 21. The white ribbon 24 is formed by forming the element isolation film 25 on the surface of the substrate 21 by the above-mentioned humid oxidation, and then forming the oxidation prevention mask 23.
Even if the pad oxide film 22 is removed, it remains on the substrate 21. Therefore, for example, when a gate oxide film is formed on the substrate, there arises a problem that the thickness and film quality of the gate oxide film become non-uniform and the insulating property deteriorates.

In order to remove the white ribbon, a sacrificial oxide film having a certain thickness is formed on the surface of the substrate before the gate oxide film is formed, and the sacrificial oxide film is removed to remove the sacrificial oxide film. There is a way to remove the white ribbon with the film. However, this method has a problem that the element isolation film is simultaneously etched and the element isolation film thickness is reduced.

Therefore, an object of the present invention is to provide a method for forming an element isolation film which can suppress the formation of white ribbons.

[0007]

According to the method of forming an element isolation film of the present invention for achieving the above object, an oxide film is formed on a surface portion of a substrate on which an antioxidation mask made of silicon nitride is formed by dry oxidation. Then, the above oxide film is grown by wet oxidation, and the grown oxide film is used as an element isolation film.

[0008]

In the method for forming the element isolation film, the oxide film is formed on the surface portion of the substrate by dry oxidation using silicon nitride as an oxidation prevention mask, and then the oxide film is grown by wet oxidation. The above humid oxidation is performed without directly exposing the surface portion of the above to the humid atmosphere. Further, the oxide film prevents ammonia generated by the reaction between the moisture in the humidified atmosphere and the silicon nitride forming the antioxidation mask from directly acting on the surface portion of the substrate.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. First, in a first step shown in FIG. 1A, a surface of a silicon substrate (hereinafter referred to as a substrate) 11 on which an element isolation film is formed is oxidized by a thermal oxidation process, and a pad oxide film made of silicon oxide is formed on the surface. 12 is formed into a film. The pad oxide film 12 is formed to have a film thickness of about 10 nm.

Next, on the pad oxide film 12, vapor phase growth (Chemical Vapor Deposition) in a low pressure atmosphere (Low Pressure) is performed.
position) method The so-called LP-CVD method is used to form the silicon nitride film 13. This silicon nitride film 13 is
The film is formed to a film thickness of about 100 nm.

After that, a resist pattern not shown here is formed on the upper surface of the silicon nitride film 13 by the lithography method. This resist pattern is patterned into a shape that covers the element formation region of the substrate 11 and exposes the element isolation film formation region. Then, the silicon nitride film 1 is etched by etching using the resist pattern as a mask.
3 and the pad oxide film 12 are etched to form an oxidation prevention mask 14 made of a silicon nitride film 13 on the pad oxide film 12.

Next, in the second step shown in FIG. 1B, the substrate 1 exposed from the oxidation preventing mask 14 by dry oxidation.
An oxide film 15 is formed on the surface portion of 1. In this dry oxidation, high-purity oxygen gas is introduced into the heat treatment furnace containing the substrate 11 to create a dry oxygen atmosphere in the heat treatment furnace. After that, by raising the temperature inside the heat treatment furnace to about 1050 ° C., the substrate 11 exposed from the antioxidant mask 14 is exposed.
An oxide film 15 having a film thickness of several nm is formed on the surface of the.

Next, in the third step shown in FIG. 1C, the oxide film 1 formed on the surface portion of the substrate 11 by wet oxidation.
Grow 5 This humid oxidation is performed by so-called pyrogenic oxidation, and high-purity hydrogen gas is introduced into the heat treatment furnace heated to 1050 ° C. together with the oxygen gas. As a result, oxygen gas and hydrogen gas are reacted in the heat treatment furnace to generate water vapor, and the oxide film 15 is grown to a film thickness of 400 nm in a humidified atmosphere.

In the method of forming the element isolation film 15a, the oxide film 15 is grown by wet oxidation, so that the element isolation film 15a made of the thick oxide film 15 is formed on the surface portion of the substrate 11. Further, during the dry oxidation and the humid oxidation, stress is applied to the substrate 11 by the anti-oxidation mask 14 made of the silicon nitride film 13, and the growth of the oxide film on the substrate portion below the end of the anti-oxidation mask 14 is caused. The element isolation film 15a that is suppressed and has a small bird's beak is formed.

Further, since the humidification oxidation is performed with the surface portion of the substrate 11 covered with the oxide film 15 formed by the dry oxidation, the oxide film 15 is formed and grown without exposing the surface portion of the substrate 11 to the humidified atmosphere. Can be made. Therefore, the moisture in the humidified atmosphere and the antioxidant mask 1
Ammonia generated by the reaction with the silicon nitride forming 4 is prevented from directly acting on the substrate 11. Therefore, it is possible to prevent the formation of silicon nitride, a so-called white ribbon, which is formed by the ammonia acting on the substrate 11.

When a gate oxide film is formed on the portion of the substrate 11 separated by the element isolation film 15a formed while preventing the formation of the white ribbon as described above, the gate oxide film has a film thickness and film quality. Becomes uniform. Therefore, it is possible to obtain a stable gate withstand voltage.

Since the generation of the white ribbon can be suppressed, it is not necessary to remove the white ribbon by removing the thick sacrificial oxide film, so that the sacrificial oxide film thickness before the gate oxidation can be thinned. Therefore, it is possible to prevent the element isolation film thickness from being significantly reduced by removing the sacrificial oxide film.

Further, since the dry oxidation and the humid oxidation are carried out by introducing oxygen gas or oxygen gas and hydrogen gas into the same heat treatment furnace, there is a conventional process of forming an element isolation film only by humid oxidation. The process is not particularly complicated in comparison.

[0019]

As described above, according to the method of forming an element isolation film of the present invention, an oxide film is formed on the surface portion of the substrate exposed from the oxidation prevention mask by dry oxidation, and then the above oxidation is performed by wet oxidation. By growing the film, it becomes possible to generate and grow the oxide film without directly exposing the substrate surface to a humidified atmosphere. Therefore, when the element isolation film is formed by wet oxidation using silicon nitride as an antioxidation mask, the oxide film formed by dry oxidation produces nitrogen on the surface of the antioxidation mask and moisture in the humid atmosphere. Ammonia can be prevented from directly acting on the substrate surface. Therefore, it is possible to suppress the formation of a nitride of a material forming the substrate, that is, a white ribbon, on the surface of the substrate.

[Brief description of drawings]

FIG. 1 is a sectional process diagram illustrating an example.

FIG. 2 is a sectional process diagram illustrating a problem.

[Explanation of symbols]

 11 substrate 13 silicon nitride film 14 oxidation prevention mask 15 oxide film 15a element isolation film

Claims (1)

[Claims] 1. A step of patterning a silicon nitride film formed on a substrate to form an anti-oxidation mask made of the silicon nitride film on the substrate, and a step of exposing the substrate from the anti-oxidation mask by dry oxidation. A method for forming an element isolation film, comprising: a step of forming an oxide film on a surface portion; and a step of growing the oxide film by wet oxidation to form an element isolation film.