JPH07254594A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To shorten the length of a bird's beak which is extending under an oxidation-resistant film when forming an element-isolation oxide film by selective oxidation. CONSTITUTION:1) An oxide film 2 and a nitride film 3 are deposited in this order on an Si substrate 1 and these films are patterned. Then, the substrate is dipped in a chemical liquid to be wet-treated and thereby a natural oxide film 4 is formed on an exposed part of the substrate. After that, a polysilicon film 5 is formed and then is anisotropically etched to form a polysilicon side wall 5A on a side face of the nitrode film. Then, the substrate is thermal- oxidized. 2) A thin silicon nitrode film is formed instead of the chemical oxide film 4. 3) An oxide film 2 and a nitrode film 3 are deposited in this order on a substrate 1 and these films are patterned. Then, a silicon side wall 5A is formed on a side face of the nitrode film by selective epitaxial growth and after that, the substrate is thermal-oxidized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming an element isolation oxide film by a selective oxidation (LOCOS) method.

In recent years, with the high integration of silicon (Si) semiconductor devices, miniaturization of circuit patterns has progressed, element regions have been secured, and element isolation silicon oxide films (SiO ₂ films, hereinafter simply referred to as oxide films) have been formed. Thinning is required. In particular, when element isolation is performed by the selective oxidation method, it is necessary to shorten the oxide film (bird's beak) extending like a bird's beak below the oxidation resistant film formed in the element region in order to secure the element region.

[0003]

2. Description of the Related Art FIGS. 2A to 2C are sectional views of a conventional example. Conventional Example 1: In FIG. 2 (A), in forming a conventional element isolation oxide film by the conventional selective oxidation method, a thin buffer oxide film 2 is deposited on a semiconductor substrate 1 and then an oxidation resistant film 3 is formed thereon. A silicon nitride film (Si ₃ N ₄ film, hereinafter simply referred to as an oxide film) is formed, and an element isolation oxide film 7 is formed by thermal oxidation.

Conventional Example 2: In FIG. 2B, since the bird's beak 9 extends long during the thermal oxidation in the above-mentioned ordinary method, after the nitride film 3 is patterned, a polysilicon film is deposited on the substrate. There is a method in which the side wall 5A made of a polysilicon film is formed on the side surface of the nitride film by anisotropic etching, and thereby the element isolation oxidation is performed so as to prevent the progress of the oxidation under the nitride film.

Here, a thermal oxide film 4'is formed on the substrate as an etching stopper so that the substrate 1 is not etched during anisotropic etching for forming the sidewall 5A made of a polysilicon film. .

Conventional Example 3: In FIG. 2 (C), a method of forming a polysilicon side wall 5A without forming a thermal oxide film as an etching stopper. When the nitride film 3 is thin, it is difficult to form the side wall. In some cases, an oxide film 9 is formed on the nitride film 3 by vapor phase epitaxy (CVD) to increase its thickness, and then a polysilicon film is formed and anisotropically etched.

[0007]

According to the conventional method of Conventional Example 1, it is difficult to reduce the bird's beak length because the oxidizing species infiltrate along the buffer oxide film.

Further, in the method of forming the sidewall of the polysilicon on the side surface of the nitride film of the conventional example 2, the bird's beak is caused by the presence of the thermal oxide film used as the etching stopper during the anisotropic etching for forming the sidewall of the polysilicon. The reduction in length is insufficient.

Further, in Conventional Example 3, a sidewall of polysilicon is formed on the side surface of the nitride film, and a thermal oxide film of an etching stopper is not formed under the sidewall of the polysilicon. When the vapor growth oxide film is formed on the nitride film, the nitride film is formed. Before the removal, it is necessary to remove this vapor-grown oxide film, which reduces the thickness of the device isolation oxide film, or causes a step or slope on the surface of the exposed silicon substrate near the device isolation edge. There are drawbacks.

The present invention reduces the bird's beak length extending below the oxidation resistant film when a polysilicon side wall is formed on the side surface of the oxidation resistant film and an element isolation oxide film is formed by the selective oxidation method.
In addition, it is intended to facilitate formation of a silicon side wall attached to the side surface of the oxidation resistant film in order to suppress bird's beak.

[0011]

[Means for Solving the Problems] To solve the above problems, 1) stack a silicon oxide film 2 and a silicon nitride film 3 on a silicon substrate 1 in this order, and pattern the silicon oxide film 2 and the silicon nitride film 3. And then,
A step of immersing the semiconductor substrate 1 in a chemical solution to perform a wet treatment to form a native oxide film 4 formed by the wet treatment on the semiconductor substrate 1 exposed by the patterning; and then, on the semiconductor substrate 1. On the polysilicon film
5 is formed, and the polysilicon film 5 is anisotropically etched to form a sidewall made of polysilicon on the side surface of the silicon nitride film.
5A, a method of manufacturing a semiconductor device including a step of thermally oxidizing the semiconductor substrate 1, or 2) forming a silicon nitride film in place of the chemical oxide film 4, 3. The method for manufacturing a semiconductor device according to 1 above, wherein the film thickness is less than or equal to the film thickness that is oxidized in the step of thermally oxidizing the semiconductor substrate 1 and is larger than the film thickness that disappears by the anisotropic etching. ) A step of laminating a silicon oxide film 2 and a silicon nitride film 3 in this order on a silicon substrate 1 and patterning the silicon oxide film 2 and the silicon nitride film 3, and then performing selective epitaxial growth on the side surface of the silicon nitride film 3. The step of growing the side wall 5A made of silicon, and then,
It is achieved by a method for manufacturing a semiconductor device including a step of thermally oxidizing the semiconductor substrate 1.

[0012]

The features of the present invention are summarized as follows. (1) After patterning the nitride film, an oxide film is formed on the substrate by a wet process, and polysilicon is vapor-deposited and anisotropic etching is used to form a polysilicon side wall on the side surface of the nitride film. An element isolation oxide film is formed. At this time, a chemical oxide film formed by wet pretreatment of the silicon substrate is used as an etching stopper for anisotropic etching for forming the polysilicon side wall. (2) A thin nitride film is used as an etching stopper for anisotropic etching for forming polysilicon sidewalls. The thickness of this nitride film is sufficiently thin so that it is oxidized during element isolation oxidation, and is formed after patterning of the nitride film used as an oxidation resistant mask. (3) Alternatively, after patterning the nitride film, the element isolation oxide film is formed after growing the silicon sidewall only on the side surface of the nitride film by selective epitaxial growth.

With the above structure, (1) since the chemical oxide film under the polysilicon sidewall is a sufficiently thin natural oxide film, lateral diffusion of oxidizing species can be prevented during element isolation oxidation, and the bird's beak length can be reduced. Is possible. (2) In contrast to Conventional Example 3, since the present invention does not form a vapor growth oxide film on the nitride film, the film thickness of the element isolation oxide film is reduced, or a step is formed on the surface of the silicon substrate at the edge of the element isolation oxide film. Does not occur. (3) When a nitride film is used as an etching stopper on the side wall of polysilicon, there is no oxide film under the polysilicon, so lateral diffusion of oxidizing species can be sufficiently suppressed. (4) In the case of silicon sidewalls formed by selective epitaxial growth, it is not necessary to perform anisotropic etching.
It is not necessary to provide an etching stopper. Moreover, since the silicon sidewall is directly adhered to the substrate, the occurrence of bird's beak can be suppressed.

[0014]

1A to 1D are sectional views of a first embodiment of the present invention. In Fig. 1 (A), the thickness of 50
A thermal oxide film 2 with a thickness of ~ 200Å is formed, and a nitride film 3 with a thickness of 1000 ~ 2000Å is grown on it by vapor phase epitaxy. Then,
Nitride film 4 and thermal oxide film
Pattern 2 to leave the element isolation region.

In FIG. 1 (B), the thickness of the substrate is wet-processed as an etching stopper film 4 on the substrate.
Form a chemical oxide film of about 5-10Å. Alternatively,
A nitride film with a thickness of 10 to 50 Å is formed by vapor phase epitaxy.

Here, the conditions of the wet treatment are as follows. For example, it is dipped in an aqueous solution of hydrogen peroxide and hydrochloric acid. The natural oxide film formed on the silicon surface after the chemical treatment is called a chemical oxide film in distinction from the natural oxide film formed by leaving it in the atmosphere. From the experimental results of the present inventor, it was found that this film can be used as an etching stopper.

In FIG. 1C, a polysilicon film 5 having a thickness of 200 to 500 Å is grown on the substrate by the vapor phase growth method.
In FIG. 1 (D), the polysilicon film 5 on the substrate surface is anisotropically etched to form polysilicon sidewalls 5A.

The anisotropic etching of the polysilicon film 5 is performed by reactive ion etching (RIE). An example of the condition is shown below. Reaction gas: Cl ₂ 100 to 200 SCCM RF Power: 150 to 200 W Gas pressure: 0.05 to 0.1 Torr Substrate temperature: 20 ° C After that, an element isolation oxide film is formed by the conventional method. At this time, the polysilicon side wall 5A is oxidized. Then,
The nitride film 3 is removed by hot phosphoric acid or the like.

Example 2 After FIG. 1 (A), a polysilicon side wall 5A is formed by growing polysilicon to about 500 Å by a selective epitaxial method. Next, element isolation oxidation is performed.

Next, an example of conditions for selective epitaxial growth of polysilicon will be shown. Reaction gas: Si ₂ H ₆ 50 SCCM H ₂ 30 SLM HCl 100 SCCM Gas pressure: 50 Torr Substrate temperature: 900 ℃ When epitaxially grown under these conditions, only the sides of the nitride film grow to _a thickness of 700 Å.

In this embodiment, since there is no oxide film or the like under the polysilicon side wall, bird's beak is suppressed. In this case, the etching stopper is not required because the anisotropic etching is not required for forming the side wall.

[0022]

According to the present invention, the bird's beak length extending below the oxidation resistant film can be reduced when the polysilicon side wall is formed on the side surface of the oxidation resistant film and the element isolation oxide film is formed by the selective oxidation method. This can contribute to miniaturization of the device.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a conventional example.

[Explanation of symbols]

1 Silicon substrate 2 Thermal oxide film as buffer oxide film 3 Oxide resistant film as nitride film 4 Chemical oxide film or thin nitride film as etching stopper 5 Polysilicon film 5A Silicon sidewall 7 Element isolation oxide film 8 Bird's beak 9 Vapor grown oxide film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/76

Claims (3)

[Claims] 1. A silicon oxide film on a silicon substrate (1)
(2) and the silicon nitride film (3) are laminated in this order, and the silicon oxide film (2) and the silicon nitride film (3) are patterned, and then the semiconductor substrate (1) is immersed in a chemical solution. Wet process is performed to form a native oxide film (4) formed by the wet process on the semiconductor substrate (1) exposed by the patterning, and then polysilicon is formed on the semiconductor substrate (1). A step of forming a film (5) and anisotropically etching the polysilicon film (5) to form a side wall (5A) made of polysilicon on the side surface of the silicon nitride film; 1) The method of manufacturing a semiconductor device, comprising the step of thermally oxidizing 2. A silicon nitride film is formed instead of the chemical oxide film (4), and the film thickness of the silicon nitride film is a film thickness that is oxidized in the step of thermally oxidizing the semiconductor substrate (1). The method of manufacturing a semiconductor device according to claim 1, wherein the thickness is equal to or less than the thickness and is larger than the film thickness that disappears by the anisotropic etching. 3. A silicon oxide film on a silicon substrate (1)
(2) and the silicon nitride film (3) are laminated in this order, and the silicon oxide film (2) and the silicon nitride film (3) are patterned, and then the side surface of the silicon nitride film (3) is formed by selective epitaxial growth. Side wall made of silicon (5A)
1. A method of manufacturing a semiconductor device, comprising: a step of growing a semiconductor substrate; and a step of thermally oxidizing the semiconductor substrate (1).