JPH03138936A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form an element isolating oxide film in compliance with the designed dimensions and to make it possible to flatten the element isolating oxide film by forming the side wall formed of a second nitride film on the side surface of the pattern of a first nitride film, performing the first oxidation with the first and second nitride films as masks, and forming a first oxide film. CONSTITUTION:A side wall with a second nitride film 6 is formed at an opening part in a first nitride film 3 by etching. Thereafter, the first oxidation for element isolation is performed, and a first oxide film 8 is formed. When the nitride films 3 and 7 are removed with hot phosphoric acid, an oxide film shape is obtained. When selective oxidation is performed, the oxidation occurs in an isotropic mode. Therefore, a part beneath the nitride film is also oxidized. Since the size is decreased by the side wall 7 of the second nitride film, the element isolating region in conformity with the size of the mask can be formed by optimizing the size of the side wall 7. In this way, the manufacturing method by which the elements can be isolated in compliance with the dimensions of the mask and the element isolation and the flattening of the oxide film can be achieved is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a semiconductor device for forming isolation between elements such as transistors.Prior art Fig. 5 shows a structure of a process for forming element isolation by a conventional method. As shown in the cross-sectional view, an oxide film 2 is formed on a silicon substrate 1, and then a nitride film 3 is formed (FIG. 5(a)). Element isolation pattern 4 of resist using photolithography technology
Then, only the nitride film 3 is etched using a dry etching technique (FIG. 5(b)). Then resist 4
is removed and oxidized for element isolation. Since the nitride film 3 is difficult to oxidize, the parts without the nitride film 3 are oxidized to form the structure of the oxide film 5 as shown in FIG. 5(C). Device isolation is performed using this oxide film 5. The film 3 is removed (FIG. 5(d)). Such an element isolation formation method is LOCO8.
When oxidation for device isolation is performed using the LOCO3 method, the oxidation occurs isotropically, so even if the area under the nitride film 3 is oxidized, the oxide film will not penetrate into the oxide film at that time. This bird's beak is called a bird's beak, and this bird's beak causes the device to become smaller (and the dimensions as designed cannot be obtained), resulting in problems such as deterioration of device characteristics or an increase in chip size to avoid this. As the oxide film expands, the oxide film comes out from the surface of the silicon substrate, creating unevenness on the substrate.The problem of deterioration of step coverage occurs during subsequent wiring formation.Although the same effect can be obtained by directly etching the silicon substrate, etching Although there are still problems with the uniformity of the semiconductor device, the present invention takes into consideration the above-mentioned problems. In view of this, there is provided a method for manufacturing a semiconductor device that can form an element isolation oxide film according to the designed dimensions and planarize the element isolation oxide film. A Means for Solving the Problems The present invention (1) l;L In the step of forming an element isolation region by oxidizing a silicon substrate, a first nitride film is deposited on the silicon substrate. and the first step in the element isolation region.
A step of depositing a second nitride film on the first nitride film, and anisotropically etching the second nitride film to form a pattern side surface of the first nitride film. The method includes the steps of forming a sidewall made of the second nitride film, and performing a first oxidation using the first and second nitride films as masks to form a first oxide film. A method for manufacturing a semiconductor device, characterized in that the present invention (20; t), in the step of forming an element isolation region by oxidizing the silicon substrate, the step of depositing a first nitride film on the silicon substrate; Etching the first nitride film in the element isolation region First oxidation is performed using the first nitride film as a mask (X).

a step of forming a first oxide film; a step of etching the first oxide film using the first nitride film as a mask;
depositing a second nitride film over the first nitride film; and anisotropically etching the second nitride film to remove the first nitride film.
forming a sidewall made of the second nitride film on the side surface of the pattern of the first nitride film; The present invention (1), ( 2) g! By forming the second nitride film sidewall, even if a bird's beak is formed when the element isolation oxide film is formed, the element isolation length will be larger than the mask size because the sidewall reduces the dimension. Inventor 2)
By etching this oxide film after the first oxidation, it is possible to dig into the silicon substrate in the element isolation region. Embodiment (Example 1) in which protrusion above the substrate surface can be prevented (Example 1) FIG. 1 is a process cross-sectional view showing a method for manufacturing a semiconductor device according to a first example of the present invention. In FIG. 1, a silicon substrate 1 is oxidized to a thickness of about 50 nm to form an oxide film 2, and then a first nitride film 3 is formed to a thickness of about 200 nm by low pressure CVD.
(Fig. 1(a)). A resist pattern 4 is formed using a photolithography technique, and only the first nitride film 3 is etched using a dry etching technique (FIG. 1(b)). Thereafter, the resist 4 is removed by ashing. Further, a second nitride film 6 is deposited to a thickness of about 400 nm on it by low pressure CVD (FIG. 1(C)), and the second nitride film 6 is etched by anisotropic dry etching. This etching process removes the first nitride film 3.
A side wall of the second nitride film 6 is formed in the opening (FIG. 1(d)). After that, the first oxidation for element isolation is performed to 600 nm.1. X.

A first oxide film 8 is formed (FIG. 1(e)). If nitride films 3 and 7 are removed with hot phosphoric acid, an oxide film shape as shown in Figure 1(f) can be obtained, but when selective oxidation is performed, oxidation occurs isotropically, so the bottom of the nitride film is also oxidized. Although the dimensions are reduced by the sidewalls 7 made of the second nitride film, by optimizing the size of the sidewalls 7 it is possible to form an element isolation region according to the mask dimensions. However, it is also possible to reduce the stress applied to the oxide film formed under the sidewalls due to the increase in stress (Example 2). Embodiment 2 is a process cross-sectional diagram showing Embodiment 1.
Since the steps in FIGS. 1(a) to (b) are the same, their explanation will be omitted.a After the step in FIG. 1(b), resist 4
are removed by ashing (Fig. 2(a)). After that, using the first nitride film 3 as a mask, the first oxidation process is performed for about 400 nm.
A first oxide film 9 is formed in m rows (FIG. 2(b)).

Furthermore, the first oxide film 9 is dry etched using the nitride film 3 as a mask (FIG. 2(C)). Next, 50 nm of oxidation is performed to form an oxide film 10, and a second nitride film 1 is formed on it.
1 with a thickness of about 400 nm (FIG. 2(d)). When only the second nitride film 11 is etched by anisotropic etching, a shape as shown in FIG. 2(e) is obtained, and a sidewall 12 of the second nitride film is formed (FIG. 2(e)). When the second oxidation for element isolation is performed, a second oxide film 13 is obtained.
The shape is as shown in FIG. 2(f), and when the nitride film 3.12 is completely removed, the final shape as shown in FIG. 2(g) is obtained. By etching the first oxide film 9, the silicon substrate in the element isolation region can be dug down, and even if the second oxide film 13 is then formed by the second oxidation, this oxide film 13 will not rise above the silicon substrate surface. (Example 3) FIG.
Wet etching using hydrofluoric acid was used to etch the first oxide film 9 (Fig. 3(C)) (all other steps were the same).
Because the oxide film 9 is etched isotropically and the first nitride film 3 is also etched, its final shape is similar to that of the third nitride film 3.
Even though it is different from the case of dry etching as shown in FIG. Even if it is a process cross-sectional diagram showing the manufacturing method of the device, Example 4 is similar to Example 1.
Since the steps are the same as those shown in FIGS. 1(a) to (e) in FIG. do(
Figure 4(a)). After that, oxidation is performed to a thickness of about 50 nm to form an oxide film 10, and then a third nitride film 14 is formed by low pressure CVD.
When the third nitride M14 is deposited to a thickness of about 400 nm using the anisotropic etching method (FIG. 4(b)), the fourth
The second sidewall 15 has a shape as shown in Figure (C).
However, when a second oxide film 16 is formed by performing a second oxidation for element isolation, the shape becomes as shown in FIG. 4(d). Figure (e
) is obtained.

In the second, third, and fourth embodiments, the oxidation process is performed twice (the amount that rises above the silicon substrate as in the final shape can be reduced), and this reduces the unevenness of the silicon substrate surface. According to the present invention, mask size can be changed with self-line without worrying about bird's beak. By etching the oxide film and digging into the silicon substrate, it is possible to reduce the bulge caused by the next oxidation, and the practical effect is large. tree(~

[Brief explanation of the drawing]

FIG. 1 is a cross-section of the manufacturing process of a semiconductor device in Example 1 of the present invention. FIG. 2 is a cross-section of the manufacturing process of a semiconductor device of Example 2. FIG. 3 is a cross-section of the manufacturing process of a semiconductor device of Example 3. The figure is a sectional view of the manufacturing process of the semiconductor device of Example 4. Figure 5 is the sectional view of the manufacturing process of the conventional semiconductor device.
7.12.15...Sidewartz t, 8.9...
First oxidation WX, 13...Second oxidation [14...Third nitriding wind 16...Third oxidation wind

Claims (2)

[Claims] (1) In the step of forming an element isolation region by oxidizing a silicon substrate, a step of depositing a first nitride film on the silicon substrate, etching the first nitride film in the element isolation region, and then etching the first nitride film on the silicon substrate; depositing a second nitride film on the nitride film; and anisotropically etching the second nitride film to form a side surface of the second nitride film on the side surface of the pattern of the first nitride film. a step of forming a wall;
A method for manufacturing a semiconductor device, comprising the step of performing first oxidation using the second nitride film as a mask to form a first oxide film. (2) In the step of forming an element isolation region by oxidizing a silicon substrate, a step of depositing a first nitride film on the silicon substrate, and a step of etching the first nitride film in the element isolation region; performing a first oxidation using the nitride film as a mask to form a first oxide film; etching the first oxide film using the first nitride film as a mask; and etching the first oxide film using the first nitride film as a mask. a step of depositing a second nitride film from above the nitride film; and anisotropic etching of the second nitride film to form a side surface of the second nitride film on the patterned side surface of the first nitride film. a step of forming a wall;
A method for manufacturing a semiconductor device comprising the step of performing a second oxidation using a second nitride film as a mask to form a second oxide film (3) forming an element isolation region by oxidizing a silicon substrate; In the forming process, a first
a step of depositing a second nitride film on the first nitride film after etching the first nitride film in the element isolation region; and a step of depositing a second nitride film on the first nitride film; forming a sidewall made of the second nitride film on the side surface of the pattern of the first nitride film by anisotropic etching; a step of performing oxidation to form a first oxide film; a step of etching the first oxide film using the first and second nitride films as a mask; and a step of etching the first oxide film using the first and second nitride films as masks. Depositing a third nitride film from above, and anisotropically etching the third nitride film to form a sidewall made of the third nitride film on the side surface of the pattern of the first oxide film. process and
A method of manufacturing a semiconductor device, comprising the step of performing a second oxidation using the first, second, and third nitride films as masks to form a second oxide film.