JPH05129596A - Method of forming gate oxide film - Google Patents

Abstract

PURPOSE:To obtain a method of forming a gate oxide film in which an insulation breakdown strength is enhanced. CONSTITUTION:A method for forming a gate oxide film on a silicon wafer comprises the steps of oxidizing it in a dry atmosphere and then oxidizing it in a steam atmosphere. When a gate insulating film of a MOS transistor is formed, its gate oxide film is formed by footing a part having a thickness of 20-99% of the thickness of the gate oxide film by a dry oxidizing method and then forming a residual part by a wet oxidizing method. As a result, an insulation breakdown strength of the gate oxide film is enhanced.

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 a gate oxide film formed by thermally oxidizing a silicon wafer,
For example, the present invention relates to improvement of a method of forming a thermal oxide film used as a gate insulating film of a MOS structure.

[0002]

2. Description of the Related Art Conventionally, MO formed on a silicon wafer
The thermal oxide film for the gate insulating film in the S transistor may be formed by the dry O ₂ oxidation method or the wet O ₂ oxidation method. The former can remove the water in oxygen used to the extent that the dew point becomes −80 ° C. or lower to obtain a very dense thermal oxide film (SiO ₂ ). In the latter case, since steam is used as the oxidant, the oxidization rate becomes faster than that in the dry oxidization.

[0003]

However, the conventional thermal oxide film formed only by dry oxidation has a problem that when it is used as a gate insulating film, dielectric breakdown occurs at a low electric field. In the case of a thermal oxide film formed only by wet oxidation, when this is used as a gate oxide film, the breakdown electric field in C mode (called intrinsic breakdown) tends to be slightly low.

Therefore, an object of the present invention is to provide a method for forming a gate oxide film having a high dielectric strength voltage.

[0005]

The present invention provides a method for forming a gate oxide film on a surface of a silicon wafer, wherein the gate oxide film is oxidized in a dry oxygen atmosphere and then in an atmosphere containing water vapor. This is a method of forming a gate oxide film for oxidation.

[0006]

In forming the gate insulating film of the MOS transistor, the target gate insulating film is formed by, for example, dry-oxidizing a portion having a thickness of 20 to 99%, and then wet-oxidizing (steam) the remaining portion. (Including oxidation)
To form. As a result, the breakdown voltage of the gate insulating film of the MOS transistor can be increased. The interface is flattened by dry oxidation to avoid concentration of an electric field, and defects are stabilized by wet oxidation to increase dielectric breakdown voltage.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. 1A to 1E are graphs showing an embodiment of a method for forming a gate oxide film according to the present invention. In this graph, the horizontal axis is the breakdown electric field (megavolts / cm),
The vertical axis represents the frequency (%). In this example, 30 silicon mirror wafers (diameter 5 inches, P-type (100), resistance value 10 Ωcm, CZ wafer) were placed in an oxidation furnace and subjected to 9 atmospheres in the atmosphere shown in Table 1 and graphs.
A gate oxide film having a thickness of about 25 nm was formed by heat treatment at 00 ° C. Then, an aluminum electrode was formed and deposited on the gate oxide film of this silicon wafer, and the dielectric breakdown electric field was measured according to a conventional method.

[0008]

[Table 1]

Further, this result is shown by a histogram in FIG. In the figure, (A) shows a dry oxidation of 85.
When the thickness of the gate oxide film is set to 25.3 nm, the dry oxidation of (B) is performed for 80 minutes, and the wet oxidation is performed for 1 minute, and the film thickness is set to 26.3 nm. Dry oxidation for 20 minutes, wet oxidation 1
When the film thickness is 5 minutes and the film thickness is 24.0 nm, (D) performs the dry oxidation for 5 minutes and the wet oxidation for 18 minutes. When the film thickness is 22.9 nm, (E) is the wet oxidation for 20 minutes. This shows the case where the film is formed to a film thickness of 23.3 nm.

FIG. 2 is a graph showing the relationship between the method of oxidizing the gate oxide film and the dielectric breakdown electric field according to one embodiment. In this figure, the horizontal axis shows the oxidation method when the combined time (minutes) of dry oxidation and wet oxidation is changed, and the vertical axis shows the dielectric breakdown electric field. D60W5 means a case where dry oxidation is performed for 60 minutes and then wet oxidation is performed for 5 minutes. Therefore, D85 shows the result only after 85 minutes of dry oxidation, and W24 shows the result only after 24 minutes of wet oxidation. In the graph, ○ indicates the average value of the measured values of the experimental results.

As a result of the above, by performing the wet oxidation subsequent to the dry oxidation, the dielectric breakdown electric field of the gate oxide film can be increased.

Further, FIG. 3 is a graph showing the relationship between the dielectric breakdown electric field and the oxidation method in another embodiment of the present invention as in FIG. In this embodiment, a polysilicon electrode that is often used in an actual device is used as a gate electrode, and FIG. 3 shows the result of measurement of a gate insulating film which is dry-oxidized and then wet-oxidized as in the above-described embodiment. Shows. As can be seen from this graph, the effect of increasing the dielectric breakdown electric field is more significantly shown.

[0013]

As described above, in the method of forming a gate oxide film according to the present invention, the breakdown voltage of the gate oxide film can be increased, and a semiconductor device using this gate oxide film can be increased. Can be improved in quality, and the manufacturing yield thereof can be increased.

[Brief description of drawings]

FIG. 1 is a graph showing a distribution of dielectric breakdown voltage by an oxidation method according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an oxidation method and a dielectric breakdown electric field according to an example of the present invention.

FIG. 3 is a graph showing a relationship between an oxidation method and a dielectric breakdown electric field according to another embodiment of the present invention.

Claims (1)

[Claims] 1. A method for forming a gate oxide film on a surface of a silicon wafer by a thermal oxidation method, wherein the gate oxide film is oxidized in a dry oxygen atmosphere and then oxidized in an atmosphere containing water vapor. A characteristic method of forming a gate oxide film.