JPH0338733B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for manufacturing a semiconductor device, and is particularly used in an element isolation method.

(Prior Art) Conventionally, a selective oxidation method has been used for element isolation of semiconductor integrated circuits. This selective oxidation method will be explained using FIGS. 4 to 6.

First, as shown in FIG. 4, a silicon substrate 11 is thermally oxidized to grow a pad oxide film 12 of, for example, 900 Å. After that, the silicon oxide film 13 is formed to a thickness of, for example, 3000 Å.
accumulate. Next, as shown in FIG. 5, the silicon nitride film 13 is patterned by photolithography to form openings. Next, as shown in FIG. 6, selective oxidation is performed using the silicon nitride film 13 as an oxidation-resistant film to grow an oxide film 14 of, for example, 8000 Å, and then the silicon nitride film 13 is removed by RIE (reactive ion etching). A field oxide film for device isolation was completed.

(Problems to be Solved by the Invention) The LOCOS method, which is a conventional technique, is widely used in semiconductor technology as an element isolation technique. However, the so-called "bird's beak" is an obstacle to miniaturization of element isolation regions. Therefore, bird's beak can be suppressed by increasing the thickness of the nitride film, which is an oxidation-resistant film, but the nitride film is very hard and if it becomes too thick, the edges of the nitride film openings may form on the silicon substrate. The problem arises that the stress increases and crystal defects are introduced into the silicon substrate 11. Furthermore, as the openings in the nitride film become finer, a problem arises in which the field oxide film is reduced due to the lack of oxidizing agent in the openings of the nitride film due to the formation of bird's beaks.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a method for manufacturing a semiconductor device using a selective oxidation method that suppresses bird's beak and allows miniaturization without crystal defects in a semiconductor substrate.

[Structure of the Invention] (Means and Effects for Solving the Problems) The present invention minimizes the stress applied to the semiconductor substrate by thinning only the edge portion of the oxidation-resistant film pattern and thickening the other regions. to prevent crystal defects and suppress bird's beak. For this purpose, on the first thin oxidation-resistant film (nitride film, etc.) on the semiconductor substrate,
A thick second oxidation resistant film is deposited through a material film that is difficult to remove when removing the oxidation resistant film, and after patterning this film, the first oxidation resistant film is patterned with an opening narrower than the opening of the first oxidation resistant film. It oxidizes.

(Example) Examples of the first and second inventions of the present application will be described below with reference to the drawings. FIG. 1 shows an example before the present invention, in which a silicon substrate 21 as shown in FIG.
is oxidized to grow a padded oxide film 22 of, for example, 500 Å, on which a first nitride film 23 of 1000 Å is deposited, and then a CVD SiO ₂ film (SiO ₂ film by CVD) is formed.
24 to a thickness of 500 Å. Next, as shown in FIG. 1b, a second nitride film 25 is deposited, a resist film 26 is provided thereon, and after patterning, the second nitride film 25 is isotropically etched using CDE (isotropic dry etching). The nitride film 25 is patterned by etching. At this time, the nitride film 25 is etched down to the vicinity of the opening edge of the resist 26, but the nitride film 25 is protected by the film 25 and is not affected in any way. Next, as shown in _FIG .
4 and the first nitride film 23 are etched and patterned. As a result, the opening 25 of the second nitride film 25
An opening 23 ₁ narrower than ₁ can be made in the first nitride film 23 . Thereafter, as shown in FIG. 1d, the resist film 26 is removed by etching and selective oxidation is performed.
The field oxide film 27 is grown to a thickness of, for example, 8000 Å to complete the element isolation region.

FIG. 2 shows an embodiment of the first invention of the present application. That is, as in the case of FIG. 1, after depositing the second nitride film 25, it is patterned by photolithography or the like.
After depositing a material much softer than the second nitride film 25, such as CVD SiO ₂ to a thickness of, for example, 2000 Å,
By etching back the CVD SiO ₂ by RIE, a side wall 28 made of the CVD SiO ₂ film is formed on the inner surface of the opening of the second nitride film 25. After that, the side wall 28,
If the first nitride film 23 is patterned by RIE using the nitride film 25 as a mask, field oxidation can be performed with the opening edges of the nitride film 23 being thin, as in the case of FIG.

FIG. 3 shows an embodiment of the second invention of the present application. That is, after depositing the second nitride film 25, a polycrystalline silicon film 29 is deposited to a thickness of, for example, 4000 Å, and the polycrystalline silicon film 29 and the second nitride film 25 are patterned by photolithography (FIG. 3a). Silicon film 29
is thermally oxidized with its surface and opening side surfaces exposed (this causes the thermal oxide film 30 to expand), and the material film 24 and first nitride film 23 are patterned using the oxide film 30 as a mask (the third As shown in Figure b, field oxidation is then performed.As shown in the above embodiments, the first nitride film 23 is thin at the edge of the nitride film opening, and the first nitride film 23 is thin in other regions.
3 and the second nitride film 25, the stress at the edge of the nitride film opening is alleviated, thereby preventing crystal defects in the Si substrate 21 and suppressing bird's beak. Further, as shown in FIGS. 2 and 3, after patterning the second nitride film 25, the first
Since the opening that serves as a mask for forming the nitride film opening 23 ₁ is narrowed by the sidewall 28 and the bulge of the oxide film 30, it can be made finer than a resist pattern, resulting in finer element isolation. can be realized. Moreover, without the pad oxide film 22, bird's beak can be further suppressed. Further, as shown in FIGS. 2 and 3, an opening for forming an opening in the oxidation-resistant film 23 is formed on the side wall 2.
8. By narrowing it with a thermal oxide film 30 of polycrystalline silicon, by increasing the thickness of the side wall 28 when using it, or by oxidizing it while leaving the surface and opening side surface exposed when using an oxide film 30. By forming and protruding the opening, the opening can be significantly reduced in a short time.

[Effects of the Invention] As explained above, according to the present invention, it is possible to manufacture a semiconductor device using a selective oxidation method that suppresses bird's beak, has no crystal defects in the semiconductor substrate, and allows miniaturization in a relatively simple and short time. method can be provided.

[Brief explanation of drawings]

FIG. 1 is a process explanatory diagram of element isolation formation before reaching the present invention, FIGS. 2 and 3 are process explanatory diagrams of each embodiment of the first and second inventions of the present application, and FIGS. 4 to 6 The figure is a process explanatory diagram of a conventional example. 21...Silicon substrate, 22...Padded oxide film, 23...First nitride film (first oxidation-resistant film),
23 ₁ , 25 ₂ ... opening, 24, 28 ... CVD
SiO ₂ film, 26... resist film, 27... field oxide film, 29... polycrystalline silicon, 30...
Oxide film.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a semiconductor device in which an oxidation-resistant film pattern is formed on a surface of a semiconductor substrate and then the semiconductor substrate is selectively oxidized to perform element isolation, wherein a first oxidation-resistant film pattern is formed on the semiconductor substrate. a step of depositing a film, a step of forming a first material film for protecting the film on the first oxidation resistant film, and a step of depositing a film thicker than the first oxidation resistant film on the first material film. After depositing a second oxidation resistant film and patterning the second oxidation resistant film, the exposed surface of the second oxidation resistant film and the first oxidation resistant film are deposited.
By forming a second material softer than the first oxidation-resistant film on the exposed surface of the material film, and etching back the second material film by directional etching,
In order to narrow the opening of the second oxidation resistant film, which is a mask for forming the opening of the first oxidation resistant film, a second material film is formed on the inner surface of the opening of the second oxidation resistant film. a step of forming remaining sidewalls consisting of the second oxidation-resistant film and the sidewalls;
and a step of forming an opening in a first oxidation-resistant film, wherein the first material film is selective with respect to etching with respect to a second oxidation-resistant film. A method for manufacturing a semiconductor device. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the first and second oxidation-resistant films are nitride films, and the first material film is a CVD SiO ₂ film. 3. A method for manufacturing a semiconductor device in which an oxidation-resistant film pattern is formed on a surface of a semiconductor substrate, and then the semiconductor substrate is selectively oxidized to perform element isolation, including the step of depositing a first oxidation-resistant film on the semiconductor substrate. , forming a first material film on the first oxidation resistant film for protecting the film; and a second oxidation resistant film thicker than the first oxidation resistant film on the first material film. a step of depositing a polycrystalline silicon layer for a mask on the second oxidation-resistant film; and a step of forming a second oxidation-resistant film using the polycrystalline silicon layer for a mask on the second oxidation-resistant film. After patterning, a step of narrowing the first oxidation-resistant film patterning opening of the polycrystalline silicon layer by oxidation while leaving the surface of the polycrystalline silicon layer and the side surfaces of the opening exposed; forming an opening in the first material film and the first oxidation resistant film by directional etching using the second oxidation resistant film having the first oxidation resistant film patterning opening as a mask; A method for manufacturing a semiconductor device, characterized in that: