JPS6387741A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To enable integration to be upgraded, by forming the second thick oxidation-proof film on the first thin oxidation-proof film through the second oxidizing film and thereafter patterning these films to form a mask and forming a field oxidizing film on the surface of a semiconductor substrate. CONSTITUTION:The second thick silicon nitride film 4 is formed on the first thin silicon nitride film 2 through the second silicon oxide film 3. The second thick silicon nitride film 4 is etched irrespective of a selection ratio of reactive ion etching. Even if irregularity of etching occurs when this first silicon nitride film 2 is etched, the etching stays in the first silicon oxide film 1 and it does not advance to the surface of a semiconductor substrate 5 because the first silicon nitride film 2 is formed thin. Therefore, this etching does not have effects on elements formed in the later process and so integration can be upgraded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming an oxidation-resistant film that serves as a mask in a selective oxidation method.

[Conventional technology]

A conventional method for forming a field region of a semiconductor device will be described with reference to FIGS. 2(a) to 2(c).

First, as shown in FIG. 2(a), a thin silicon oxide film 3A is formed on the semiconductor substrate 5 by thermal oxidation, and then an oxidation-resistant film 4A of silicon nitride or the like is formed by vapor phase growth or the like.

Next, as shown in FIG. 2(b), after forming a mask 6 made of photoresist, the oxidation-resistant film 4A is patterned using photolithography.

Next, as shown in FIG. 2(c), the mask 6 is removed, ions are implanted to form a channel stopper layer, and then a field oxide film 7 is formed by thermal oxidation.

[Problem that the invention seeks to solve]

In the conventional selective oxidation technique for forming the field oxide film 7 described above, oxidation progresses laterally during thermal oxidation, and silicon oxide sinks under the oxidation-resistant film 4A.
However, with the miniaturization of elements, the penetration of the silicon oxide described above poses a major problem in device design.

In order to suppress this penetration of silicon oxide, it is necessary to keep the thickness of the silicon oxide film 3A of the underlying semiconductor substrate small and to increase the thickness of the oxidation-resistant film 4A thereon.

However, when this oxidation-resistant film 4A is made thicker, the selective ratio of reactive ion etching for etching this oxidation-resistant film 4A cannot be made large, so that the semiconductor substrate 5 is etched during patterning, resulting in the device being damaged. If formed, there is a problem in that leakage current increases and the manufacturing yield and reliability of semiconductor devices are reduced.

The purpose of the present invention is to eliminate the above problems, achieve a high degree of integration,
Another object of the present invention is to provide a semiconductor device with improved manufacturing yield and reliability.

[Means for Solving the Problems] The method for manufacturing a semiconductor device of the present invention includes forming a first oxide film on the surface of a semiconductor substrate, and then forming a thin first oxidation-resistant film on the first oxide film. forming a thick second oxidation resistant film on the first oxidation resistant film via a second oxide film; and forming a photoresist layer on the second oxidation resistant film. After that, patterning is performed, and a step of forming a mask on the area where the element is to be formed, and using the mask, the second oxidation resistant film, the second oxide film, and the first oxidation resistant film are sequentially etched and removed. and a step of removing the mask and then oxidizing the surface of the semiconductor substrate using the first and second oxidation-resistant films as masks to form a field oxide film.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1(a) to 1(d) are cross-sectional views of a semiconductor chip shown in the order of steps for explaining one embodiment of the present invention.

First, as shown in FIG. 1(a), a first silicon oxide film 1 with a thickness of approximately 100 layers is formed on a semiconductor substrate 5 by thermal oxidation, and then CVD is applied to the first silicon oxide film 1.
A first silicon nitride film 2 having a thickness of about 200 wafers is formed by the method. Subsequently, the entire surface is coated with a thickness of 500~1 by CVD method.
000 second silicon oxide film 2 and thickness 1000~2
000 second silicon nitride [4] is sequentially formed.

Next, as shown in FIG. 1(b), a photoresist layer is formed on the entire surface and then patterned to form a mask 6 made of photoresist on the area where the element is to be formed. Subsequently, using this mask 6, the second silicon nitride film 4 is etched and removed by a reactive ion etching method. At this time, the second silicon oxide film 3 may be etched with variations in the etching rate.

Next, as shown in Figure 1(c), a second solution was prepared using buffered hydrofluoric acid solution.
The first silicon oxide film 3 is etched by reactive ion etching.
After sequentially etching the silicon nitride film 2 of
remove.

Next, as shown in FIG. 1(d), thermal oxidation is performed using the first and second silicon nitride films 2 and 4 as masks to form a field oxide film 7 on the surface of the semiconductor substrate.

As described above, in this embodiment, a thick second silicon oxide film is formed on a thin first silicon nitride film 2 via a second silicon oxide film 3.
By providing the silicon nitride film 4, the thick second silicon nitride film 4 can be etched without being affected by the selectivity of reactive ion etching. Since the first silicon nitride film 2 is formed thinly, this first silicon nitride film 2
When etching the silicon nitride film 2, even if there are variations in etching, the etching stops at the first silicon oxide film 1 and does not reach the surface of the semiconductor substrate 5. Therefore, this etching does not affect elements formed in subsequent steps.

[Effects of the Invention] As explained above, the present invention provides a method for forming a thick second oxidation-resistant film on a thin first oxidation-resistant film on a semiconductor substrate on which a first oxide film is formed, via a second oxide film. After forming the oxidation-resistant film, the second oxidation-resistant film, the second oxide film, and the first oxidation-resistant film are patterned to form a mask to form a field oxide film on the surface of the semiconductor substrate. As a result, a field oxide film can be formed with less digging into the lower part of the mask.

Therefore, a semiconductor device with a high degree of integration and improved manufacturing yield and reliability can be obtained.

[Brief explanation of the drawing]

1(a) to 1(d) are cross-sectional views of a semiconductor chip shown in the order of steps for explaining one embodiment of the present invention, and FIG. 2(a)
) to (c) are cross-sectional views of a semiconductor chip shown in order of steps for explaining a conventional method of manufacturing a semiconductor device. DESCRIPTION OF SYMBOLS 1... First oxide/silicon film, 2... First silicon nitride film, 3... Second silicon oxide film, 3A...
-Silicon oxide film, 4...Second silicon nitride film, 4
A... Oxidation-resistant film, 5... Semiconductor substrate, 6...
Mask, 7...Field oxide film. 1. -7 Agent Patent Attorney Uchihara Otoni l. ku・・〜SFigure 1

Claims (1)

[Claims] After forming a first oxide film on the surface of the semiconductor substrate, the first oxide film is formed on the surface of the semiconductor substrate.
forming a thin first oxidation-resistant film on the oxide film;
forming a thick second oxidation resistant film on the first oxidation resistant film via a second oxide film; forming a photoresist layer on the second oxidation resistant film and then patterning it; ,
a step of forming a mask on a region where an element is to be formed; a step of sequentially etching and removing the second oxidation-resistant film, the second oxide film, and the first oxidation-resistant film using the mask;
A method of manufacturing a semiconductor device, comprising the step of removing the mask and then oxidizing the surface of the semiconductor substrate using first and second oxidation-resistant films as masks to form a field oxide film.