JPS59191351A - Method for formation of interelement isolation oxide film in semiconductor device - Google Patents

Abstract

PURPOSE:To form a flat silicon oxide layer by a method wherein a recessed part is formed on an interelement isolation region by performing an etching, and a low temperature oxide film deposition and a thermal oxidation are performed thereon. CONSTITUTION:An SiO2 film 2a and an Si3N4 film 3a are formed on a silicon substrate 1, a recessed part 7 reaching the substrate 1 is formed on an interelement isolation region A by performing an etching, and the SiO2 film 2a and the Si3N4 film 3a are left on an active region B. Then, an isolation SiO2 film 8 is formed. Subsequently, a resist 9 for positive electron beam (EB) is applied, an electron beam is made to irradiate, a developing process is performed, and the EB resist layer 9a is left. Then, an etching is performed on the film 8 using the layer 9a as a mask. An SiO2 film 10 is then formed by performing thermal oxidation. As a result, a flat SiO2 isolation film having no bird's beak can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method of forming an isolation oxide film between elements in a semiconductor device.

[Prior art]

FIGS. 1(a) to 1(c) are cross-sectional views showing the main stages of a conventional method for forming an element isolation oxide film. First, as shown in FIG. 1(a), a silicon oxide film (2) is formed on a silicon semiconductor substrate ft1O, and a silicon nitride film (3) is further formed on the silicon oxide film (3). A resist mask (4) having an opening and covering the silicon nitride film (3) in the active region B is formed. Then, as shown in FIG. 1(b), the silicon nitride film (3) is etched through the resist mask (4) to form a silicon nitride film (3) in the element isolation region A.
is removed, leaving the silicon nitride film (3a) in the active region B. Next, the resist mask (4) is removed and selective oxidation is performed using the silicon nitride film (3a) as a mask.
As shown in FIG. 1(c), a thick isolation silicon oxide layer (6) is formed in the element isolation region A. The reason why the silicon oxide film (2) is used is to alleviate the stress caused by the difference in thermal expansion coefficient between the silicon substrate (1) and the silicon nitride film (3). The oxidation at the stage shown in FIG. 1 (0) takes place for a long time in a high-temperature oxygen atmosphere, for example, in the active region B where the silicon nitride film (3a) is present, where there is little oxygen diffusion. Silicon substrate (
In the inter-element isolation (7e iv) region A which does not react with silicon nitride film (3a) and does not react with silicon nitride film (3a), the silicon 7 substrate [1
) reacts with oxygen to form an isolated silicon oxide layer (5), and this isolated silicon oxide layer (5) extends from the upper surface of the silicon substrate fi+ (in activated region B) to the isolated silicon oxide layer (6). ) to a thickness of about A.

At the same time, the isolation oxide film (6) sinks under the edge of the silicon nitride film (3a), forming a bird's beak-shaped region of the oxide film called a "bird beak" (
6) is formed.

When an isolated silicon oxide layer with a film thickness of, for example, iμm is formed by the penetration of the silicon oxide film (5) as described above, that is, the bird's beak (6), the penetration of about 0.5μm occurs on both sides of the active region B. It arises from the edges. This hinders device integration.

[Summary of the invention]

This invention was made in view of the above points, and by forming recesses in the element isolation region by etching and combining low-temperature oxide film deposition and thermal oxidation, it is possible to reduce the penetration of the silicon oxide layer. In addition, the present invention provides a method that can form an isolated silicon oxide layer that is planar compared to the conventional method.

[Embodiments of the invention]

FIGS. 2(a) to 2(f) are cross-sectional views showing the main stages of an embodiment of the present invention.

Components equivalent to those of the conventional example shown in FIG. 1 are designated by the same reference numerals.

First, as shown in FIG. 2(a), a silicon substrate (tl
An underlying silicon oxide (Sin2) film (2) and silicon nitride (Eli3N4) film (3) are sequentially formed thereon, and the inter-element isolation region A is etched.
1, and a 5in2 film (2a) and a 5t3N4 film (3) are formed in the active region B.
Leave a). Next, as shown in FIG. 2(b), 813
The recess (7) on the N4 film (3a) and in the element isolation region A
) was plasma OVD applied to the separated 5io2 film (8) covering the inner surface of the
Formed by law etc. Next, as shown in FIG. 2(C), for example, a positive electron beam (gB) resist (9) is applied.
is applied onto the 5in2 film (8) so as to fill the concave portion (7), and the entire upper surface thereof is irradiated with an electron beam as shown by the arrow. When this was developed, the part near the bottom of the recess (7) was not exposed to the electron beam, so
As shown in FIG. 2(d), the EB resist layer (9a) remains only in this portion.

Next, the 5in2 film (8) is etched using this EB resist Nt (9a) yi: mask. For example, this etching is performed using carbon 47thride (C!F4) and hydrogen (H2).
). In order to completely remove the SiO□ film (8) in each activated region B, the etching is carried out slightly overly. As shown, the 51o2 film at both ends of the element isolation region A was also removed, and the E film used as a mask was removed.
The SiO□ film (8a) remains under the B resist layer (9a).

However, the width of the groove formed at both ends of this inter-element isolation region A is /J%. It also depends, but it is 0.2 to 0.37 an
It will be about. Subsequently, as shown in FIG. 2(f), a 5in2 film (10) is formed in this groove by thermal oxidation.

If the width of the groove is 0.2 μm, it is sufficient to oxidize for about 5 minutes in a wet oxygen (WetO2) atmosphere at a temperature of 1100°C. With this level of oxidation, almost no bird's beak is formed, and a flat separation of 5in2 is required. A film is formed.

〔Effect of the invention〕

As explained above, in the present invention, a recess is formed in the element isolation region by etching, an oxide film is formed on the inner surface of the recess at a low temperature, and the recess formed in the oxide film corresponding to the recess is filled with a resist material. Using this as a mask, the above oxide film is removed to form narrow exposed parts of the silicon substrate at both ends of the element isolation region, which are then thermally oxidized for a short time and filled with an oxide film to form an element isolation oxide film. As a result, a flat isolation oxide film without bird's beaks can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the state at the main stages to explain a conventional method of forming an element isolation oxide film, and FIG. 2 shows the state at the main stages to explain an embodiment of the present invention. FIG. In the figure, (1) is a silicon substrate, (7) is a recess, (
8). (8a) is S10□ film (first oxide film), (9),
(9a) is EB resist material, (10) is 5in2 film (
second oxide film). Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Masuo Oiwa Figure 1 A A 〆 f

Claims (1)

[Claims] fi+ A first step of forming a recess by etching in an element isolation region of a silicon substrate; a second step of forming a first oxide film on the silicon substrate including the inner surface of the recess at a low temperature; a third step of applying a positive resist material onto the oxide film of the first oxide film to substantially fill in the recesses of the first oxide film corresponding to the recesses with the resist material; Irradiating the entire surface with an electron beam or ion beam and performing a development process, leaving only the resist material in the portions buried in the recesses of the first oxide film and not irradiated with the electron beam or ion beam, and leaving other portions. a fourth step of removing the resist material; using the remaining resist material as a mask, the first oxide film on the inner surface of the recess in the element isolation region is removed by etching, and the first oxide film is removed only directly under the mask; The fifth step of leaving a film,
A second oxide film is formed by thermal oxidation on the surface of the silicon substrate exposed in the recess of the element isolation region by the etching in the fifth step, and this second oxide film is formed in the fifth step. A method for forming an element isolation oxide film in a semiconductor device, comprising a sixth step of forming an element isolation oxide film with the remaining first oxide film.