JPS5854651A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To suppress the oxidation of a silicon substrate under a silicon nitrided film at the selectively oxidizing time and to prevent the distortion of the substrate by forming a silicon etching groove and then forming a polycrystalline silicon film layer on the side surface of the groove. CONSTITUTION:A silicon oxidized film 12 is formed by a thermal oxidation method on the surface of an N type silicon substrate 11, and a silicon nitrided film 13 is covered by a vapor growth method on the film 12. Then, the films 13, 12 are selectively etched and removed by a photoprocess method, and the surface of the exposed substrate 11 is etched bya plasma etching, thereby forming a groove 14. Subsequently, a polycrystalline silicon film 16 is formed by a vapor growth method, and the film 16 is then etched to remove the film 16 except the side surface of the groove 14. Thereafter, a buried silicon oxidized film 15 is formed by a thermal oxidation method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a trenched silicon oxide film for element isolation.

In the manufacturing method of semiconductor devices such as integrated circuits, dielectric isolation using a buried oxide film and self-alignment (8elf-allgnment) technology using the buried oxide film are used to improve the degree of integration and simplify the manufacturing process. Element formation using this method is being actively carried out. As a method for forming this buried oxide film, a selective oxidation method using thermal oxidation using a silicon nitride film as an oxidation-resistant film, which is the easiest to use, is mainly used.

An example of a conventional selective oxidation method will be explained with reference to FIGS. 1 to 3. First, a silicon oxide film 12 and a silicon nitride film 13t- are formed on the surface of an n-type silicon substrate 11.

Form them sequentially (Fig. 1). Next, using a photo process method, selective etching is performed to etch the silicon nitride film 13 on the element isolation region. The silicon oxide film 12'e is removed and the exposed silicon substrate surface is etched to form a groove 14f (FIG. 2). After etching, a buried silicon/oxide film 15 is formed using a thermal oxidation method to form the groove. Fill in 14.

Element isolation is thus performed, and desired elements are formed in each isolated island region.

However, according to this manufacturing method, when forming a buried silicon oxide film, oxygen (Os) diffuses into the oxide film and under the silicon nitride film, resulting in lateral oxidation and The silicon substrate is also slightly oxidized, so-called '
A bird beak''l is formed. Therefore, the pattern width is reduced.For example, silicon oxide film is approximately 20 OA, silicon nitride film is approximately 100 OA, silicon etching groove depth is approximately α6fi* buried silicon oxide film thickness is approximately If L2Jm is used, the pattern width will be reduced by about 2 μm, and such a large pattern width reduction will be a big problem in improving the degree of integration.Furthermore, the silicon oxide film under the nitride film will partially When formed, a large strain is applied to the silicon substrate, resulting in the generation of crystal defects, which is a major drawback in device formation.

In view of the above points, the present invention suppresses lateral oxidation when forming a buried silicon oxide film layer, prevents strain from occurring within the substrate, and improves the degree of integration by reducing the area occupied by the element isolation region. The present invention provides a method for manufacturing a semiconductor device that makes it possible to perform the following steps.

The main feature of the present invention is that by adding a step of forming a polycrystalline silicon film layer on the sides of the trench after forming the silicon etching trench, the silicon substrate under the silicon/nitride film is oxidized during selective oxidation. The goal is to prevent

Next, the present invention will be explained in detail according to examples.

4 to 8 are main cross-sectional views of the manufacturing process of a buried oxide film buried in a silicon substrate to a depth of about 1.1 μm.

In the ts4 diagram, a silicon oxide film with a thickness of about 200^ is formed on the surface of an n-type silicon substrate 11 by a thermal oxidation method, and a silicon nitride film 13t'' is formed on it by vapor phase growth (C0V, D
)ffiK! It is coated with a film thickness of 100 OA. Next, using a photo process method, the silicon nitride film 13. Silicon oxide film 1
2 was removed by etching, and the exposed silicon substrate surface was
A groove 14t-10.6 .mu.m deep is formed by etching using plasma etching using CCJ14 i3 system (FIG. 5).

Thereafter, a polycrystalline silicon film 16t is formed by vapor phase growth (FIG. 6). The film thickness at this time varies depending on the desired thickness of the buried silicon oxide film, and if the film thickness of the buried silicon oxide film is about t2 μm, the appropriate thickness of the polycrystalline silicon film is α5 μm 11 degrees. .

Next, polycrystalline silicon film 16 is etched.

At this time, as the etching method, anisotropic plasma etching using CCJ24 gas is used, and the phagocytic bacteria on the substrate surface are exposed to the etching gas. Then, since the etching is directional and etching is performed only from the direction that is perpendicular to the substrate surface, the polycrystalline silicon/film other than the side surfaces of the silicon etching groove 14 must be removed (FIG. 7). At this time, after etching the polycrystalline silicon film, the exposed silicon substrate may be etched again. Thereafter, a buried silicon oxide film 15 is formed using a thermal oxidation method (FIG. 8). Then, during selective oxidation, the bottom surface of the groove 14 is oxidized as in the conventional manner, but on the side surface, the polycrystalline silicon film 16 is oxidized and the silicon substrate 11 itself is not oxidized.

Therefore, under the silicon nitride film 16, during selective oxidation,
No silicon oxide film is formed.

As a result, it is possible to prevent a reduction in the turn width and generation of crystal distortion due to selective oxidation.

As described in detail above, according to the present invention, when forming a buried silicon oxide film by selective oxidation, after forming a silicon etching groove, a polycrystalline silicon film layer is formed only on the side surfaces of the groove. This prevents lateral oxidation during thermal oxidation. This makes it possible to prevent thinning of the pattern width and generation of crystal distortion during selective oxidation, and is therefore expected to improve the degree of integration and yield.

[Brief explanation of drawings]

FIGS. 1 to 3 are cross-sectional views showing the conventional manufacturing method in the order of steps, and FIGS. 4 to 8 are cross-sectional views showing the main process St of the manufacturing method of the embodiment of the present invention. Please note that the symbols in the diagram correspond to the following items.

Claims (1)

[Claims] In a method for manufacturing a semiconductor device in which a buried silicon oxide film is formed using an oxidation-resistant film on both surfaces of a semiconductor substrate, etching a surface of the semiconductor substrate on which an oxidation-resistant film pattern is not provided,
A method for manufacturing a semiconductor device, comprising the steps of forming a trench, forming a polycrystalline silicon film layer in the trench, and then forming a buried silicon oxide film.