JPS60208843A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To suppress the yield of bird beaks in separating elements and to make the width of the element separation small, by preliminarily forming a silicon nitride film on the element forming region of a silicon semiconductor and the side wall of a U-groove before burying the U-groove by a selective epitaxial growing method. CONSTITUTION:A U-groove 6 is formed in a silicon semiconductor base layer 1. Then the surfaces of the element forming region of the silicon semiconductor base layer 1 and the inside of the U-groove are coated by a silicon nitride film 8. Thereafter, the bottom part of the silicon nitride film 8 in the U-groove is selectively removed, and the silicon semiconductor base layer 1 is exposed. Then, a silicon semiconductor 10 is epitaxially grown in the U-groove selectively, and the U-groove 6 is buried. The surface of the silicon semiconductor 10 in the U-groove is oxidized 11. Even though the groove is buried by the selective epitaxial growing method and the surface is oxidized, the growth of the oxide film is stopped there owing to the presence of the nitride film.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for forming element isolation on a silicon semiconductor substrate.

Conventional technology and problems In semiconductor integrated circuits, it is often necessary to insulate between multiple confections. Conventionally, isolation using a PN junction, isolation using a selective oxide film,
Separation using U-shaped grooves or 7-shaped grooves is used. The selective oxidation method is widely used because of its complete insulation, high breakdown voltage, and simple process. However, since the oxide film grows in the same direction, oxidation progresses laterally in proportion to the required thickness of the oxide film, and the bird's beak is also large.
There are difficulties in increasing the degree of integration. In this respect, isolation by trench embedding, particularly U-shaped isolation, has excellent insulation and voltage resistance, and the width of the trench can be narrowed independently of the depth of the trench.

However, even in the U-shaped trench isolation, bird's beaks due to oxidation still exist, and there is a problem that the degree of integration cannot be increased any further. That is, a U-shaped groove is formed in the silicon base layer,
After oxidizing the trench surface, the inside of the trench is filled with polycrystalline silicon, but the top of the polycrystalline silicon that filled the trench needs to be oxidized again, so during this surface oxidation, the oxide film does not extend to the top of the element formation area. This forms a so-called bird's beak.

Furthermore, an element isolation method has been proposed in which the U-shaped groove is filled by a selective epitaxial method, but similarly, bird's beaks occur because the surface is oxidized at the end.

OBJECTS OF THE INVENTION In view of the above-mentioned prior art, an object of the present invention is to suppress the occurrence of bird's beak in element isolation, reduce the width of element isolation, and contribute to an increase in the degree of integration of integrated circuits.

Structure of the Invention In order to achieve the above object, in the present invention, before filling the U-shaped groove by selective epitaxial growth, a silicon nitride film is formed in advance on the element formation region of the silicon semiconductor base layer and on the side walls of the U-shaped groove. . By doing so, even if the surface is oxidized after filling the trench by selective epitaxial growth, the growth of the oxide film will stop there because of the presence of the nitride film. As a result, the occurrence of bird's beak is prevented.

Further, in the present invention, since (all) regions where epitaxial growth should not occur are covered with a silicon nitride film, selective epitaxial growth is superior even when silicon oxide is used.

Embodiments of the invention will be described with reference to the drawings. Referring to FIG. 1, ions are implanted into a p-type silicon substrate 1 to form an n++ doped layer 2, and an n''' type epitaxial layer 3 is grown to form a silicon semiconductor body. In order to form a groove, a 5in2 film 4 and a SiSl'J4 film 5 are formed on the surface of the epitaxial layer 3, and patterned.The silicon semiconductor body is formed using the patterned Si3N film 5 as a mask. Anisotropic etching is performed.This etching results in a width of 2 to 3 μm and a depth of 4 to 5 μm.
A U-shaped groove 6 of m is formed. This U-shaped groove 6 is formed deeper than the n+ type buried layer 2.

Referring to FIG. 2, the previously formed 5t3N4 film 5 and 5i02 film 4 are removed, and a SiO□ film 7, a Si3N film 8, and a film 8 are formed on the entire surface again by low pressure CVD to a thickness of about 0.3 μm and 0.2 μm, respectively. Form. This SiO
The Si3N4 film 7 and the Si3N4 film 8 cover not only the surface of the element formation region, that is, the n-type epitaxial layer 3, but also the inner wall of the U-shaped groove (
In particular, it is essential to form it also on the side walls.

Referring to FIG. 3, 5t3N at the bottom of the U-shaped groove 6,
Film 8 and 5in2 film 7 are selectively removed by anisotropic controlled etching to expose silicon substrate 1. Next, for example, arsenic ions are implanted into the silicon substrate 1 at the bottom of the U-shaped groove to form a p+ type region (channel stopper).
form 9.

Referring to FIG. 4, the reaction gas, pressure, temperature, etc. are controlled by utilizing the difference in surface condition between the silicon substrate 1 exposed at the bottom of the U-shaped groove and the Si3N4 film 8 covering the surface other than the bottom of the U-shaped groove. Then, selective epitaxial growth is performed only on the exposed silicon surface. Selective epitaxial growth itself is already a commonly used technique. If this selective epitaxial growth method is used, silicon will be deposited (grown) only within the U-shaped groove, and will not be deposited (adhered) at all on the Si3N film. Therefore, unlike the conventional polycrystalline silicon burying method, there is no need for a step of removing the polycrystalline silicon deposited on the element formation region after burying in the U-shaped trench. Furthermore,
The material filled in the U-shaped groove can also be uniform by selective epitaxial growth, and is not non-uniform as in the case of filling with polycrystalline silicon. Selective growth within the U-shaped groove (
The silicon 10 (non-doped or p-type) is stopped just before the trench is completely filled to allow for volume expansion due to surface oxidation in the next step.

Referring to FIG. 5, the surface of the silicon 10 selectively grown in the U-shaped groove is oxidized to form a 5io2 layer with a thickness of about 0, l-pm.
A film 11 is formed. At this time, silicon 10 inside the U-shaped groove
Since the Si3N4 film 8 exists between the wafer and the silicon in the element forming region 3, the oxidation of the silicon 10 in the U-shaped groove reverses only in the vertical direction and does not proceed in the horizontal direction. In other words, bird's beak does not occur.

Conventionally, when polycrystalline silicon was buried in a U-shaped groove and the surface was oxidized, a bird's beak with a width of about 0.3 μm on one side was generated, so the present invention achieves a size reduction of about 0.6 μm on both sides. has been done.

Effects of the Invention The general rule that is clear from the above explanation is that according to the present invention, the width of element isolation of an integrated circuit can be reduced, thereby contributing to an increase in the degree of integration.

[Brief explanation of the drawing]

1 to 5 are cross-sectional views of a semiconductor device in order of steps for explaining the present invention in detail. 1... Silicon substrate, 3... Epitaxial layer, 6
...U-shaped groove, 7...SiO□ film, 8...Si3N
, film, 9... Channel stopper, 10... Selectively grown epitaxial silicon, 11... Surface oxide film. Patent applicant Fujitsu Limited Patent agent Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Yukio Uchida Akira Yamaguchi

Claims (1)

[Claims] a step of forming a U-shaped groove in a silicon semiconductor base layer, a step of scattering a silicon nitride film over the element formation region of the silicon semiconductor base layer and the surface inside the U-shaped groove, and a step of covering the bottom portion of the U-shaped groove in the silicon nitride film. selectively removing to expose the silicon semiconductor base layer; selectively epitaxially growing silicon semiconductor within the U-shaped groove to fill the U-shaped groove;
A method for manufacturing a semiconductor device, comprising the step of oxidizing the surface of the silicon semiconductor within the U-shaped groove.