JPH02205340A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent the leaving of strain in a semiconductor substrate by forming a polycrystalline silicon film and a nitride film onto the semiconductor substrate in an element region, conducting the thermal oxidation of a silicon layer and the formation of an element isolation oxide film and removing the nitride film and the polycrystalline silicon film when the silicon layer buried in a trench is thermally oxidized and the element isolation oxide film is shaped. CONSTITUTION:A first oxide film 2, a first polycrystalline silicon film 3, a nitride film 4 and a second polycrystalline silicon film 5 are shaped successively onto a semiconductor substrate 1, and a trench is shaped. A polycrystalline silicon film 9 for burying and the second polycrystalline silicon film 5 are etched back, the silicon layer 9 is left only in the trench, and an element isolation oxide film 10 is formed through thermal oxidation while using the nitride film 4 as a mask. Stress generated in the process is applied to the first oxide film 2, the first polycrystalline silicon film 3 and the nitride film 4, but it hardly has an effect on the substrate 1. Accordingly, strain 11 is generated in the first polycrystalline silicon film 3, but it is not generated in the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for manufacturing a semiconductor device provided with an element isolation oxide film.

[Prior Art] A conventional method for manufacturing this type of semiconductor device is shown in FIGS. 4(a) to 4(a).
This will be explained with reference to (f). First, as shown in FIG. 4(a), after sequentially forming a first oxide WA2 and a first nitride M4 on a semiconductor substrate 1, a first nitride film 4 and a first nitride film 4 are formed using a selectively formed photoresist 6 as a mask. The oxide film 2 and the semiconductor substrate 1 are sequentially etched to form a groove. Subsequently, as shown in FIG. 4(b), a second oxidation layer M! is applied to the inner wall of the groove by a thermal oxidation method. 4 (C
), a polycrystalline silicon layer 9 for embedding is formed on the entire surface.
Then, as shown in FIG. 4(d), the polycrystalline silicon layer 9 for embedding is etched back to leave it only in the trench.Subsequently, as shown in FIG. 4(e), As shown, the buried polycrystalline silicon layer 9 is thermally oxidized using the nitride film 4 as a mask, and an element isolation oxide film 1 is formed on its upper surface.
After forming 0, the nitride film 4 is removed as shown in FIG. 4(f).

[Problems to be Solved by the Invention] In the conventional semiconductor device manufacturing method described above, when an element isolation oxide film is formed by thermally oxidizing the buried polycrystalline silicon, the semiconductor substrate in the element region is Since there are only oxide and nitride films, the stress generated by thermal oxidation of the polycrystalline silicon buried in the trench is reduced to 1gI of nitride around the element isolation oxide film.
4. It is directly applied to the oxide film 2 and the semiconductor substrate 1, causing distortion 11 in the semiconductor substrate 1. As a result, phenomena such as an increase in leakage current that inhibit the normal operation of the device occur.

Further, since the polycrystalline silicon buried in the trench is insulated from the semiconductor substrate by an oxide film, it is electrically floating and its potential is not fixed, which causes malfunction of the device.

[Means for Solving the Problems] A method for manufacturing a semiconductor device according to the present invention includes a step of sequentially forming a polycrystalline silicon film and a nitride film on a semiconductor substrate of one conductivity type, A step of sequentially etching away the polycrystalline silicon film and the one conductivity type semiconductor substrate to form a trench, a step of forming an oxide film on at least the inner wall portion of the trench, and a step of exposing the oxide film to an anisotropic etching atmosphere. a step of leaving the oxide film only on the side walls of the trench; a step of forming a buried silicon layer in the trench; and a step of forming an element isolation oxide film by oxidizing the exposed portion of the buried silicon layer using the nitride film as a mask. a step of forming;
and a step of sequentially etching and removing the nitride film and the polycrystalline silicon film.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIGS. 1(a) to 1(h) are cross-sectional views showing the order of steps in an embodiment of the present invention. First, as shown in Figure 1 (a),
On a semiconductor substrate 1, a first oxide film 2 (for example, an oxide film with a thickness of 200 to 1,000 oxides formed by thermal oxidation) and a first polycrystalline silicon film 3 (for example, a 50-millimeter thick oxide film formed by chemical vapor deposition)
0 to 5,000 polycrystalline silicon), a nitride film 4 (for example, a nitride film with a thickness of 500 to 5,000 by chemical vapor deposition), and a second polycrystalline silicon film 5 (for example, by chemical vapor deposition) After sequentially forming polycrystalline silicon films with a thickness of 500 to 5,000 times using a photoresist 6, a second polycrystalline silicon film 5, a nitride film 4, and a first polycrystalline silicon film 3 are selectively formed using a photoresist 6. , the first oxide M2 and the semiconductor substrate 1 are sequentially etched away to form a groove.

Subsequently, as shown in FIG. 1(b), a third polycrystalline silicon film 7 (for example, a film with a thickness of 5 cm by chemical vapor deposition) is deposited on the entire surface.
00λ~2000 polycrystalline silicon), and then, as shown in FIG. 1(c), the entire surface is thermally oxidized to form a second layer.
An oxide film 8 (for example, an oxide film with a thickness of 1,000 to 6,000 thick) is formed. Next, as shown in Figure 1(d),
The entire surface is exposed to an anisotropic etching atmosphere and the second oxide JII 8 is left only on the side walls of the groove.This etching is such that the second oxide film 8 is exposed to the second polycrystalline silicon film 5 and the first oxide film 8. It should be made so that it does not remain on the side walls of the nitride film 4.

Next, as shown in FIG. 1(e), a semiconductor substrate 1 is placed over the entire surface.
A buried polycrystalline silicon layer 9 (for example, polycrystalline silicon with a thickness of 1 μm to 3 μm formed by chemical vapor deposition) containing an impurity of the same conductivity type (e.g., boron) as shown in FIG. As shown in f), the buried polycrystalline silicon layer 9 and the second polycrystalline silicon film 5 are etched back, leaving the buried polycrystalline silicon layer 9 only in the trench.

Next, as shown in FIG. 1(g), thermal oxidation is performed using the nitride film 4 as a mask, and the element isolation oxide film 10 (for example, a film thickness of 2
000 to 8,000 oxide film). The stress generated in this step is applied to the first oxide fi2, the first polycrystalline silicon film 3, and the nitride film 4, but has almost no effect on the semiconductor substrate 1. Strain 11 occurs in film 3, but not in semiconductor substrate 1.Finally, as shown in FIG. 1(h), nitride film 4 and first polycrystalline silicon film 3 are removed by etching.

Next, another embodiment of the present invention will be described with reference to FIGS.
＞, after forming a groove in which the second polycrystalline silicon film 5 used in the previous example is not formed, a groove is formed only on the inner wall of the groove using the same means as in the previous example. 2
An oxide film 8 is formed. Next, as shown in FIG. 2(b), a single crystal silicon layer 9a having the same conductivity type as the substrate is grown in the trench by selective epitaxial method. The subsequent steps are the same as in the previous embodiment.

Next, still another embodiment of the present invention will be described with reference to FIGS. 3(a) to 3(c). In this embodiment, as in the previous embodiment, the second polycrystalline silicon film 5 used in the first embodiment is omitted. After forming the grooves, as shown in FIG. 3(a), a second oxide film 8 is formed using a vapor phase growth method. The oxide film 8 is anisotropically etched to leave it only on the inner wall of the trench. Next, a non-doped buried polycrystalline silicon layer 9 is formed over the entire surface. Next, Figure 3 (
As shown in c), the polycrystalline silicon layer 9 is etched back leaving it only in the trench.

In this case, the surface of the polycrystalline silicon layer 9 is etched back so that it is somewhat lower than the surface of the nitride film.

The subsequent steps are the same as in the other examples.

The second oxide film 8 may be formed by thermally oxidizing the polycrystalline silicon layer or by chemical vapor deposition, or by thermally oxidizing the substrate surface.

[Effects of the Invention] As explained above, the present invention provides a method for forming a polycrystalline silicon film and a nitride film on a semiconductor substrate in an element region when thermally oxidizing a silicon layer embedded in a trench to form an element isolation oxide film. This is done by providing a nitride film and then removing the polycrystalline silicon film. Therefore, according to the present invention, the silicon buried in the trench is thermally oxidized to form an element isolation oxide film. This stress is applied to the nitride film and polycrystalline silicon film surrounding the element isolation oxide film, but can be prevented from being applied to the semiconductor substrate. Therefore, although strain occurs in the polycrystalline silicon film, it can be prevented from occurring on the semiconductor substrate side. According to the present invention, the polycrystalline silicon film around the element isolation oxide film is removed later, so that no strain remains in the semiconductor substrate after all.

Further, since the silicon layer embedded in 1 is formed so as to be connected to the semiconductor substrate at the bottom of the groove, it can be fixed at the same potential as the semiconductor substrate, and the operation of the device can be stabilized.

DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... First oxide film, 3...
・First polycrystalline silicon film, 4... Nitride film, 5...
・Second polycrystalline silicon film, 6... Photoresist, 7... Third polycrystalline silicon film, 8... Second oxide film, 9... Polycrystalline silicon layer for embedding, 9
a... Single crystal silicon layer for embedding, 10... Element isolation oxide film, 11... Strain.

Claims (1)

[Claims] A step of sequentially forming a polycrystalline silicon film and a nitride film on a semiconductor substrate of one conductivity type, and forming a groove by sequentially etching away the nitride film, the polycrystalline silicon film, and the semiconductor substrate of one conductivity type in a predetermined region. a step of forming an oxide film on at least the inner wall portion of the trench; a step of exposing the oxide film to an anisotropic etching atmosphere to leave the oxide film only on the side walls of the trench; a step of forming a silicon layer; a step of oxidizing the exposed portion of the buried silicon layer using the nitride film as a mask to form an element isolation oxide film; and a step of sequentially removing the nitride film and the polycrystalline silicon film. A method for manufacturing a semiconductor device, comprising: