JPH05226326A - Forming method of thermal oxide film - Google Patents

Abstract

PURPOSE:To prevent deterioration of dielectric strength and electric characteristics, and improve long term reliability, by forming a thermal oxide film uniformly and with reduced stress in a trench part. CONSTITUTION:In the manufacturing method of a thermal oxide film after a silicon trench is formed in a silicon semiconductor manufacturing process, a thermal oxide film is uniformly formed in the trench part by the following; a process wherein, after a trench is formed on a silicon wafer 1, a thermal oxide film 2 is formed by low temperature thermal oxidation at 900 deg.C or lower in an oxidizing gas atmosphere, a process for eliminating said thermal oxide film 2 by etching, and a process for forming again a thermal oxide film 2' by high temperature thermal oxidation at 1050 deg.C or higher in an oxidizing atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon semiconductor manufacturing process, and more particularly to improvement of a method for forming a thermal oxide film after processing a silicon groove.

[0002]

2. Description of the Related Art A manufacturing process of a silicon semiconductor includes a step of forming a thermal oxide film after processing a groove on a silicon wafer such as a vertical MOSFET or a capacitor cell of a memory. In the normal thermal oxidation process, 11
Thermal oxidation is performed at about 00 ° C. to form a SiO ₂ film (thermal oxide film), but the film thickness of the thermal oxide film becomes uneven at the corners of the convex portion and the concave portion of the groove. In particular, at the corners of the recesses, the thermal oxide film becomes thin, and compressive stress is applied to the film, which causes a problem in terms of long-term reliability due to deterioration of dielectric strength and electrical characteristics.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. By forming a thermal oxide film uniformly in the groove portion while reducing the film stress, the dielectric strength is improved. It is an object of the present invention to provide a method for forming a thermal oxide film capable of improving long-term reliability by preventing deterioration of electrical characteristics.

[0004]

The structure of the present invention for solving the above-mentioned problems is a method for forming a thermal oxide film after silicon groove processing in a silicon semiconductor manufacturing process, wherein the groove processing is performed on a silicon wafer. After that, a step of forming a thermal oxide film by low-temperature thermal oxidation at 900 ° C. or lower in an oxidizing gas atmosphere, a step of removing the thermal oxide film by etching, and a step of 1050 in an oxidizing gas atmosphere again. A thermal oxide film is formed uniformly in the groove by a step of forming a thermal oxide film by high-temperature thermal oxidation at a temperature of not less than ° C.

[0005]

According to the present invention, the thermally-oxidized film thickness can be formed uniformly regardless of the corners of the convex portions of the grooves and the corners of the concave portions, so that the dielectric strength voltage can be improved.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a process diagram showing a method for forming a thermal oxide film of the present invention.
In FIG. 1, as shown in FIG. 1A, a mask pattern is formed on the silicon wafer 1 and a groove is formed by dry etching. The groove has a depth of several μm to several tens of μm. After that, the low temperature thermal oxidation step shown in FIG.
SiO ₂ film 2 (thickness of several hundred angstroms to several μ) is formed by performing low-temperature thermal oxidation at 900 ° C. or lower in an oxidizing gas atmosphere.
m) is formed. This SiO ₂ film is etched and removed as shown in FIG. At this time, the edges of the protrusions and the curvature of the recesses, which are characteristic of the low temperature thermal oxidation, are formed at the corners of the protrusions and the recesses of the groove of the silicon wafer 1. Here, if necessary, as shown in (d), the edges of the convex corners of the groove are lightly etched by dry etching. Next, a high temperature thermal oxidation step shown in (e): High temperature thermal oxidation at 1100 ° C. or higher is performed in an oxidizing gas atmosphere to form a SiO ₂ film 2 ′ having a desired thickness. Through the above steps,
A thermal oxide film having a desired film thickness can be uniformly formed in the groove portion formed on the silicon wafer regardless of the corners of the concave portion or the corners of the convex portion.

Here, FIG. 2 shows the relationship between the radius of curvature of the concave and convex corners and the thermal oxide film thickness when a thermal oxide film is formed in the silicon groove, at high temperature (about 1100 ° C.) and at low temperature (900).
(° C) is used as a parameter. Generally, a groove formed on a silicon wafer is heated to a high temperature,
When thermal oxidation is performed at each low temperature, the thermal oxide film thickness at low temperature is smaller at the corners of the groove recesses than at the flat portion.
Compared to the other silicon portions, the degree of oxidation of silicon is less, and the corners of the recess have a curved structure in which the boundary between Si and SiO ₂ has a large radius of curvature. This cross-sectional shape appears as a difference between high temperature and low temperature, and the curve is larger at low temperature. Furthermore, when the groove shape is formed by thermal oxidation at low temperature and then thermal oxidation is performed at high temperature, the radius of curvature of the corner of the recess becomes large, so that the oxide film moves closer to the origin of the x-axis in FIG. The thickness becomes more uniform.

As described above, according to the present invention, the thermal oxide film can be uniformly formed in the groove of silicon, so that the breakdown voltage can be prevented from being deteriorated and the long-term reliability can be improved.

[0009]

As described above in detail with reference to the embodiments, according to the present invention, the thermal oxide film thickness can be uniformly formed irrespective of the corners of the convex portions or the concave portions of the groove. ,
Since the film stress can be reduced, the withstand voltage can be improved. Further, the pre-oxidation process used when forming a normal gate oxide film may be performed by low temperature thermal oxidation, and a desired oxide film uniform structure can be formed by a simple method without adding a new process. A method of forming a thermal oxide film having an effect can be realized.

[Brief description of drawings]

FIG. 1 is a process drawing showing a method for forming a thermal oxide film of the present invention.

FIG. 2 is a diagram showing the relationship between the radius of curvature and the thermal oxide film thickness, using high temperature and low temperature as parameters.

[Explanation of symbols]

1 Silicon wafer 2, 2'thermal oxide film (SiO ₂ film)

Claims (1)

[Claims] 1. A method of forming a thermal oxide film after processing a silicon groove in a silicon semiconductor manufacturing process, which comprises performing the groove processing on a silicon wafer and then performing low temperature thermal oxidation at 900 ° C. or lower in an oxidizing gas atmosphere. Then, a step of forming a thermal oxide film, a step of removing this thermal oxide film by etching, and a step of forming a thermal oxide film by performing high temperature thermal oxidation again at 1050 ° C. or higher in an oxidizing gas atmosphere. According to the method, a thermal oxide film is uniformly formed in the groove portion.