JPH0437132A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form an element isolation oxide film design specifications by depositing a 1st oxide film and a 2nd nitride film one after another after etching a 1st nitride film in an element isolation region and then, forming a sidewall consisting of the 2nd nitride film at the pattern side face of the 1st nitride film after performing anisotropic etching in the 2nd nitride film and further, taking the like measures for forming the element isolation oxide film. CONSTITUTION:In forming an element isolation region through oxidation of a silicon substrate 1, the manufacture of this device requires respective processes, i.e., a process for depositing a 1st nitride film 2 on the silicon substrate 1; a process for depositing a 1st oxide film 3 and a 2nd nitride film 4 one after another on the 1st nitride film 2 after etching the 1st nitride film 2 in the element isolation region; a process for forming a sidewall 4' consisting of the 2nd nitride film 4 at the pattern side face of the 1st nitride film 2 after performing anisotropic etching in the 2nd nitride film 4; a process for forming a 2nd oxide film 5 after performing oxidation by making the 1st and 2nd nitride films 2 and 4' act as masks. In this way, the length of element isolation is not larger than the size of each mask and further, the dispersion of the sidewall is reduced by the 1st oxide film and the element isolation region is formed as designed a mask.

Description

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

BACKGROUND OF THE INVENTION A conventional method of forming the above element isolation region is shown in FIGS.
The explanation will be given in order according to the cross-sectional view of the semiconductor device of el).

First, an oxide film 22 is formed on the silicon substrate 21 shown in FIG. 3(8) (FIG. 3(b)). Next, a nitride film 23 is formed, a resist element isolation pattern is formed using a photolithography technique, and only the nitride film 23 is etched using a dry etching technique (FIG. 3(C)).
). Thereafter, the resist is removed and oxidized to form an oxide film 24 for element isolation.

Since the nitride film 23 is difficult to be oxidized, the portions without the nitride film 23 are oxidized to form an oxide film 24 structure as shown in FIG. 3(d), and the oxide film 24 performs device isolation. Finally, the nitride film 23 is removed (FIG. 3(e)). Such an element isolation formation method is called the LOCO8 method.

Problems to be Solved by the Invention However, when oxidation for element isolation is performed using the LOCO3 method, the oxidation occurs isotropically, so that the bottom of the nitride film 23 is also oxidized. The penetration of the oxide film 24 at this time is called a bird's beak. Due to this bird's beak, as the device becomes finer, it becomes impossible to obtain the designed dimensions, resulting in the problem of deterioration of device characteristics or an increase in chip size to avoid this.

Furthermore, since the oxide film 24 is exposed above the surface of the silicon substrate 2, unevenness occurs on the surface of the silicon substrate 210, causing a problem of deterioration of step coverage in subsequent wiring formation.

The present invention solves the above problems, and aims to provide a method for forming an element isolation oxide film according to design dimensions and a method for manufacturing a semiconductor device in which the element isolation oxide film can be planarized. That is.

Means for Solving the Problems In order to solve the above problems, the method for manufacturing a semiconductor device of the present invention includes depositing a first nitride film on a silicon substrate in the step of forming an element isolation region by oxidizing the silicon substrate. a step of depositing a first oxide film and a second nitride film in order on the first nitride film after etching the first nitride film in the element isolation region; forming a side wall made of the second nitride film on the side surface of the pattern of the first nitride film by anisotropically etching the nitride film; and oxidizing using the first and second nitride films as masks. and forming a second oxide film.

Furthermore, the method for manufacturing a semiconductor device according to the second invention includes the method for manufacturing a semiconductor device according to the first invention.
The process of the invention further includes a step of etching the second oxide film using the first and second nitride films as a mask, and a step of sequentially depositing a third oxide film and a third nitride film, forming a third nitride film sidewall on the side surface of the second oxide film by anisotropically etching the third nitride film;
The present invention is characterized by adding a step of performing oxidation using the first, second, and third nitride films as masks to form a fourth oxide film.

Effect In the first and second inventions described above, by forming the first nitride film and forming the sidewall of the second nitride film, even if a bird's beak is formed when the element isolation oxide film is formed, the side wall can be avoided. The dimensions are shortened by the wall, and since the first nitride film is formed directly on the silicon substrate, the device isolation length will not be larger than the mask size. Furthermore, the first oxide film in the middle is nitrided. This acts as an etching stopper for the film, reduces variations in film thickness and sidewall variations due to non-uniformity of etching, stabilizes sidewall formation, and forms element isolation regions as per the mask.

Furthermore, in the second invention, by etching this oxide film after forming the second oxide film, the silicon substrate in the element isolation region is dug down, so that the oxide film in the element isolation region 4 is formed by subsequent oxidation. This also prevents the element isolation oxide film from rising above the silicon substrate surface.

Example Hereinafter, one embodiment of the present invention will be briefly described with reference to the drawings.

FIGS. 1(1) to 1(h) are cross-sectional views of a semiconductor device sequentially showing a method for manufacturing a semiconductor device in an embodiment of the first invention.

First, a low pressure CVD film was applied onto the silicon substrate 1 shown in FIG. 1(1).
A nitride film 2 of approximately 150 nm is formed using method D, a resist pattern is formed using photolithography, only the nitride film 2 is etched using dry etching, and then the resist is removed by ashing (see Fig. 1). b)). Approximately 50% of the oxide film 3 is formed on top of it by low pressure CVD method.
Further, a nitride film 4 of about 20 hm is deposited thereon by a low pressure CVD method (FIG. 1(d)), and the nitride film 4 is etched by anisotropic dry etching. By this etching, a sidewall 4' of the nitride film 4 is formed in the opening of the nitride film 2, as shown in FIG. 1(e). At this time, since the oxide film 3 serves as an etching stopper, even if there is variation in film thickness or variation in etching, the variation can be suppressed by performing a large amount of overetching. After removing the oxide film 3 by wet etching (first
Figure 1 (f)), oxidation is performed using the nitride film 2°4' as a mask, and an oxide film 5 for element isolation is formed to a thickness of 600 nm.
g)) When the nitride film 2.4' is removed with hot phosphoric acid, an oxide film shape as shown in FIG. 1(h) is obtained.

When oxidation is performed, the oxidation occurs isotropically, so the bottom of the sidewall 4' of the nitride film is also oxidized, but since the dimension is reduced by the sidewall 4' of the nitride film, the sidewall 4' is By optimizing the size, element isolation regions can be formed according to the mask dimensions. Further, since the nitride film 2 is directly deposited on the silicon substrate 1, oxidation can be prevented from extending below the nitride film due to the stress of the nitride film. However, due to the stress of this nitride film 2, defects are likely to occur in the silicon substrate 1, but the sidewall 4, which is prone to defects, is
Since the oxide film 3 is formed under ', the stress can be relaxed and no defects will occur. Furthermore, since the shape of the sidewall 4' increases gradually, the stress applied to the oxide film 3 formed under the sidewall 4' can also be reduced.

Next, an embodiment of the second invention will be described in order according to the cross-sectional views of the semiconductor device shown in FIGS.

First, the silicon substrate 11 shown in FIG. 2(1) is coated with a low pressure CV
A nitride film 12 of approximately 150 nm is formed using method D, a resist pattern is formed using photolithography, only the nitride film 12 is etched using dry etching, and then the resist is removed by ashing (see Fig. 2). b)). On top of that, an oxide film 13 is formed by low pressure CVD method.
A nitride film 14 of about 200 nm is deposited thereon to a thickness of about 50 nm (FIG. 2(c)), and then a nitride film 14 of about 200 nm is deposited thereon by a low-pressure CVD method (FIG. 2(d)), and the nitride film 14 is etched by anisotropic dry etching. do. By this etching, a sidewall 14' of the nitride film 14 is formed in the opening of the nitride film 12, as shown in FIG. 2(e). After removing the oxide film 13 by wet etching (second
Figure (1)), oxidation is performed using the nitride films 12 and 14' as masks, and the oxide film 5 is formed to a thickness of about 40 on (Figure 2 (g)).
) Then, using the nitride films 12 and 14' as a mask, the oxide film 15 is dry-etched (FIG. 2(h)). Next, an oxide film 16 of about 50 nm is deposited (Fig. 2(i)).
, on which a nitride film 17 of about 200 nm is deposited (second
Figure (j)). Next, when only the nitride film 17 is etched by anisotropic etching, the shape shown in FIG. 2(k) is obtained, and a sidewall 17' of the nitride film 17 is formed. The oxide film 16 is removed by wet etching (FIG. 2(I)), and the oxide film 16 is removed by oxidation for element isolation (FIG. 2(I)).
), an oxide film 18 is formed, and a nitride film 12,14' is formed.
When all 17' are removed, the final shape shown in FIG. 2(n) is obtained.

In this way, the oxidation process is complicated twice, but as shown in Figure 2 (
As shown in (n), the amount of the oxide film 18 raised above the silicon substrate 1 can be reduced. This can reduce unevenness on the surface of the silicon substrate 11, and can reduce disconnections in the wiring formed thereon. A similar effect can be obtained by directly etching the silicon substrate 11, but there are also problems with etching uniformity.

As described in detail of the invention, according to the first and second inventions, the mask size can be changed in the self-line, element isolation can be performed according to the mask dimensions without worrying about bird's beak, and the practical effects thereof are achieved. is big. Furthermore, by forming an oxide film between the first and second nitride films, the etching uniformity of the nitride film is improved, and furthermore, by omitting the oxide film between the nitride film and the silicon substrate, which was conventionally used. It is possible to suppress the bird's beak from entering, and stable element isolation can be formed, which has a great practical effect.

Furthermore, according to the second invention, by etching the second oxide film and digging into the silicon substrate, it is possible to reduce the bulge caused by the next oxidation, and therefore, it is possible to reduce unevenness on the surface of the silicon substrate, thereby reducing wiring defects. can be reduced, and its practical effects are significant.

[Brief explanation of drawings]

1(a) to (h) are cross-sectional views of a semiconductor device sequentially showing a method for manufacturing a semiconductor device in an embodiment of the first invention,
FIGS. 2(1) to (n) are cross-sectional views of a semiconductor device sequentially showing a method for manufacturing a semiconductor device in an embodiment of the second invention;
FIGS. 3(1) to 3(e) are cross-sectional views of a semiconductor device sequentially showing a conventional method of manufacturing a semiconductor device. 1.11... Silicon substrate, 2.12... (first) nitride film, 3.13... (first) oxide film, 4, 14
...(Second) nitride film, 4', 14'...Side wall, 5°15...(Second) oxide film, 16
...(third) oxide film, F...(third) nitride film, 17'...side wall, 18...(fourth)
Oxide film. Agent Morimoto Yoshihiroki (-7 bu υ Δ' 5- ($2#)j-sleeping L1' (Fig. 2 (buki) 14' I162)! ) - Figure 2 (7bsa) 18...C approx. 4 o'clock) #I4 and position Figure 3

Claims (1)

[Claims] 1. In the step of forming an element isolation region by oxidizing a silicon substrate, the step of depositing a first nitride film on the silicon substrate and etching the first nitride film in the element isolation region are performed. After that, a first oxide film and a second oxide film are formed on the first nitride film.
a step of sequentially depositing nitride films, and a step of anisotropically etching the second nitride film to form a sidewall made of the second nitride film on a side surface of the pattern of the first nitride film; A method for manufacturing a semiconductor device, comprising the step of performing oxidation using the first and second nitride films as masks to form a second oxide film. 2. In the step of forming an element isolation region by oxidizing the silicon substrate, a step of depositing a first nitride film on the silicon substrate, and after etching the first nitride film in the element isolation region, a step of depositing the first nitride film on the silicon substrate; A first oxide film and a second oxide film are formed on the nitride film.
a step of sequentially depositing a nitride film, and a step of anisotropically etching the second nitride film to form a sidewall made of the second nitride film on a side surface of the pattern of the first nitride film; A step of performing oxidation using the first and second nitride films as masks to form a second oxide film; and a step of etching the second oxide film using the first and second nitride films as masks. a step of sequentially depositing a third oxide film and a third nitride film on the first and second nitride films; and anisotropically etching the third nitride film to form the second oxide film. A step of forming a sidewall made of the third nitride film on the side surface of the film pattern, and a step of performing oxidation using the first, second, and third nitride films as masks to form a fourth oxide film. A method for manufacturing a semiconductor device, comprising: