JP2940433B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming an element isolation structure by selectively oxidizing a silicon substrate.

[0002]

2. Description of the Related Art As a conventional representative method for forming an element isolation structure in a semiconductor device, as shown in FIG. 3, a selective oxidation method (Local Oxidation Of S
ilicon; referred to as the "LOCOS method"). FIG.
The conventional LOCOS method will be described below with reference to FIGS.

[0003] First, as shown in FIG. 3A, a thin silicon oxide film 22 and a silicon nitride film 23 are formed on a silicon substrate 21.

Next, an opening 24 is formed in the silicon oxide film 22 and the silicon nitride film 23 as shown in FIG. 3B by using a photolithography technique and an etching technique.

By performing a thermal oxidation step in this state,
As shown in FIG. 3C, a silicon oxide film 25 for element isolation is selectively grown in the opening 24, which becomes an element isolation region, and a region other than the element isolation region becomes an element region.

In the LOCOS method, in a selective oxidation step of forming a silicon oxide film 25 for element isolation,
Since the oxidant diffuses laterally through the silicon oxide film 22 below the silicon nitride film 23, which is an oxidation-resistant film, the silicon oxide film is called a bird's beak.
This has been a major problem that limits the miniaturization of elements.

In the LOCOS method, a step is formed between the surface of the element region and the surface of the element isolation region, which causes problems such as a decrease in accuracy of photolithography thereafter.

Further, at the time of selective oxidation, the oxide film expands toward the element region, and in addition, the silicon substrate 21 and the silicon nitride film 2
3 has a large difference in thermal expansion coefficient, so that a strong stress is applied to the element region, which adversely affects the element characteristics.

[0009] As a conventional example of trying to solve the above problem,
For example, JP-A-61-294839 and JP-A-61-294839
Various improved LOCOS methods have been proposed in JP-A-44442, JP-A-61-100945, and the like.

First, the improved LOCOS method disclosed in Japanese Patent Application Laid-Open No. 61-294839 will be described with reference to FIGS. 4 (A) to 5 (F).

[0011] As shown in FIG.
After the silicon nitride film 33 is selectively formed on the silicon oxide film 32 on the substrate 1, the first selective oxidation is performed as shown in FIG. A silicon oxide film 34 is formed.

Next, as shown in FIG. 4C, the first selective silicon oxide film 34 is removed by etching with a dilute hydrofluoric acid solution or the like, and then the first selective silicon oxide film 34 is removed by chemical vapor deposition (CVD). 2 is deposited on the entire surface of the silicon nitride film 35 as shown in FIG.
The structure shown in (D) is formed.

Here, by performing anisotropic etching on the second silicon nitride film 35, as shown in FIG. Only the second silicon nitride film 35 is left.

Thereafter, by performing a second selective oxidation, an element isolation structure composed of a silicon oxide film 36 for element isolation is formed as shown in FIG.

In the improved LOCOS method, since the second silicon nitride film 35 has oxidation resistance, the diffusion of the oxidizing agent into the element region during the second selective oxidation is reduced.
Bird's beak elongation is suppressed.

At the same time, the first selective silicon oxide film 34 formed by the first selective oxidation is removed, and the surface of the element isolation region of the silicon substrate 31 is depressed as shown in FIG. Then, the second selective oxidation is performed, so that a step between the surface of the element region and the surface of the element isolation region can be reduced.

Next, Japanese Patent Application Laid-Open No. 61-44442 discloses an improved LOCOS method whose steps are shown in FIGS.

First, as shown in FIG. 6A, after a silicon oxide film 42 and a first silicon nitride film 43 are selectively formed on a silicon substrate 41, side etching of the silicon oxide film 42 is performed. The structure shown in FIG. 6B is formed.

After that, as shown in FIG. 6C, a second silicon nitride film 44 is deposited on the whole, and the second silicon nitride film 44 is formed only on the portion where the silicon oxide film 42 is side-etched by anisotropic etching. The silicon nitride film 44 is left.

In this state, selective oxidation is performed, and FIG.
As shown in (D), a silicon oxide film 45 for element isolation is formed. Here, since the silicon nitride film 44 suppresses the diffusion of the oxidizing agent in the lateral direction, the elongation of the bird's beak is suppressed.

Next, the improved LOCOS method proposed in Japanese Patent Application Laid-Open No. 61-100945 is as follows. That is, by replacing the silicon oxide film 22 in the conventional LOCOS method shown in FIG. 3 with a silicon oxynitride film, the bird's beak can be extended and the device can be selectively oxidized when forming the silicon oxide film for device isolation. It is said that the application of stress to the region can be reduced.

[0022]

However, the above-mentioned various improved LOCOS methods have various problems as described below.

First, in the improved LOCOS method disclosed in Japanese Patent Application Laid-Open No. 61-294839, first selective oxidation is performed on the structure shown in FIG. Inevitably, a bird's beak 37 is generated. Therefore, even in the final device isolation structure shown in FIG. 5F, the silicon substrate is formed at the end of the device region by reflecting the shape of the bird's beak 37. The surface deformation 38 occurs.

The degree of this deformation is the same as that of the prior art shown in FIG.
Although it is suppressed as compared with that caused by the occurrence of bird's beak in the LOCOS method, it becomes a serious problem when the element is further miniaturized. Further, in the improved LOCOS method, formation of a first selective silicon oxide film 34, etching of the silicon oxide film 34, deposition of a second silicon nitride film 35, anisotropic etching of the silicon nitride film 35, and the like are performed. Such a large increase in the number of steps and the increase in complexity are problematic from the viewpoint of reduction in manufacturing cost.

In the improved LOCOS method disclosed in Japanese Patent Application Laid-Open No. 61-44442, side etching is performed on the silicon oxide film 42 shown in FIG.
Although the structure as shown in FIG. 1B is formed, it is difficult to control the degree of side etching accurately, and the influence of the bite 46 below the silicon nitride film 43 is also reflected in the final device isolation structure. 7, deformation 47 near the surface of the silicon substrate occurs at the end of the element region (FIG. 7).
(E)).

Further, a silicon oxide film 4 for element isolation
As shown in FIG. 7D, in the step of performing selective oxidation at the time of forming 5, the silicon nitride film 44, which is an oxidation-resistant film that suppresses diffusion of an oxidizing agent into the element region, becomes a surface of the silicon substrate 41 as shown in FIG. Since it is formed only in the upper part and the oxidation resistant film does not exist in the part deeper from the silicon substrate surface, it is difficult to prevent the infiltration of the oxidizing agent through the part deeper than the silicon substrate surface.

Therefore, according to the improved LOCOS method, although the occurrence of bird's beak is suppressed as compared with the conventional LOCOS method shown in FIG. 3, the suppression degree is small.

Further, since the silicon nitride film is used as the oxidation-resistant film, a large area is left in the element region during selective oxidation when forming the silicon oxide film 45 for element isolation, as in the conventional LOCOS method. It is still a problem that stress is applied and adversely affects device characteristics. In addition, conventional LO
As in the case of the COS method, there is a problem that a step is formed between the surface of the element region and the surface of the element isolation region.

The present invention has been made to solve the above-mentioned problems in the conventional LOCOS method or the improved LOCOS method. A slight change in the conventional LOCOS method greatly increases the number of steps and the complexity. And simultaneously suppressing the occurrence of bird's beak, the step between the element region surface and the element isolation region, and the stress applied to the silicon substrate during selective oxidation when forming a silicon oxide film for element isolation. It is an object of the present invention to provide a completely novel method of manufacturing a semiconductor device which enables the following.

[0030]

According to the present invention, there is provided a method of manufacturing a semiconductor device in which an element isolation structure is formed by selectively oxidizing a surface of a silicon substrate. Selectively forming an oxidation resistant film on the first silicon oxide film formed on the surface; and (b) oxidizing and nitriding the first silicon oxide film using the oxidation resistant film as a mask. Forming a silicon oxynitride film in an element isolation region not covered by (c)
Performing anisotropic etching on the silicon oxynitride film using the oxidation resistant film as a mask to expose the silicon substrate in an element isolation region; and (d) etching the silicon substrate in the element isolation region using the oxidation resistant film as a mask. Selectively oxidizes
Forming a silicon oxide film for element isolation.

In the present invention, it is preferable that the first silicon oxide film is formed to have a predetermined film thickness to limit the growth of a bird's beak of the silicon oxynitride film below the oxidation-resistant film during oxynitriding. It is characterized by the following.

In the present invention, preferably, the silicon oxynitride film left by the anisotropic etching is resistant to acid against selective oxidation at the time of forming the silicon oxide film for element isolation in the step (d). Characterized by acting as an oxide film.

In the present invention, preferably, a recess is formed in the silicon substrate in the element isolation region by the anisotropic etching, and selective oxidation for element isolation is performed on the surface of the recess. I do.

Further, the present invention provides a method of manufacturing a semiconductor device for forming an element isolation structure by selectively oxidizing the silicon substrate surface, the (a) the silicon substrate surface
Oxidation-resistant film is selectively formed on the formed silicon oxide film
Then, the silicon oxide film is formed using the oxidation resistant film as a mask.
Forming a silicon oxynitride film in a region corresponding to the element isolation region not covered with the oxidation-resistant film by oxynitriding, wherein the silicon oxynitride film is at an interface of the silicon substrate and / or near the surface of the silicon oxynitride film; nitrogen has a region rich in, (b) prior to the silicon oxynitride film is anisotropically etching the oxidation resistant film as a mask the isolation region
Exposing the silicon substrate , and (c) suppressing the growth of bird's beaks in the nitrogen-rich region remaining at the side of the device isolation region when selectively forming an oxide film for device isolation. A method for manufacturing a semiconductor device, characterized in that:

[0035]

According to the present invention, first, the first silicon oxide film is oxynitrided using the oxidation resistant film as a mask to form a silicon oxynitride film in the element isolation region. By this oxynitridation process,
The bird's beak of the silicon oxynitride film containing a large amount of nitrogen bites into a lower portion of the oxidation-resistant film which will later be an element region.

The bird's beak digging of the silicon oxynitride film is self-suppressed due to a large amount of nitrogen existing near the interface with the oxidation-resistant film or the silicon substrate.
Biting below the oxidation-resistant film can be extremely small.

Next, the silicon oxynitride film is anisotropically etched using the oxidation resistant film as a mask, thereby leaving only a small bird's beak under the oxide resistant film in the silicon oxynitride film.

In this state, selective oxidation is performed to form a silicon oxide film for element isolation. The bird's beak of the silicon oxynitride film, which has been minimized, has oxidation resistance. Furthermore, since the oxidation-resistant bird's beak is also present in a portion deeper than the silicon substrate surface, the diffusion of the oxidizing agent to the lower portion of the oxidation-resistant film during selective oxidation is effectively suppressed, and the final Bird's beak and deformation of the element region can be reduced.

Further, in the manufacturing method of the present invention, the silicon oxynitride film in the element isolation region is etched to perform selective oxidation for element isolation from a state where the substrate is depressed from the surface. Between the substrate and the surface of the element isolation region can be reduced.

At the same time, the oxidation resistant film against selective oxidation when forming a silicon oxide film for element isolation is not a silicon nitride film but a silicon oxynitride film. Since the thermal expansion coefficient has a value close to the thermal expansion coefficients of silicon and silicon oxide, the stress applied to the silicon substrate during oxidation is small, and it is possible to minimize adverse effects on device characteristics.

[0041]

Next, embodiments of the present invention will be described with reference to the drawings. FIGS. 1A to 2E are diagrams for explaining a manufacturing method of an embodiment of the present invention in the order of steps.

First, the silicon nitride film 13 on the silicon oxide film 12 deposited on the silicon substrate 11 is left only in a portion to be an element region later by photolithography and etching, as shown in FIG. Form a shape.

In this state, heat treatment is performed in a gas atmosphere such as dinitrogen monoxide or nitrogen monoxide at a temperature of 800 ° C. to 1050 ° C. for 1 minute to 5 minutes to oxynitrid the silicon oxide film 12. As shown in FIG. 1B, a silicon oxynitride film 14 is formed in an element isolation region.

In the silicon oxide film 12 before this oxynitriding step, an incomplete silicon oxide layer is remarkably present near the interface between the surface thereof and the silicon substrate 11 or the silicon nitride film 13. By oxynitriding the film 12, nitrogen is preferentially introduced into the incomplete silicon oxide layer. Due to this effect, the portion 1 near the interface or surface of the silicon oxynitride film 14 in FIG.
5 will contain a large amount of nitrogen.

Therefore, when the oxynitridation of the silicon oxide film 12 proceeds to a certain extent during the oxynitridation of the silicon oxide film 12, a large amount of nitrogen near the interface between the silicon nitride film 13 and the silicon oxynitride film 14 is formed below the end of the silicon nitride film 13. The region containing nitrogen and the region containing a large amount of nitrogen near the interface between the silicon substrate 11 and the silicon oxynitride film 14 come into contact with each other, and the diffusion of the oxidizing agent introduced during the oxynitridation into the lower part of the silicon nitride film 13 is reduced Since the silicon oxide film 12 to be oxynitrided is, for example, 15 nm in thickness, the bird's beak 16 at the time of oxynitridation is formed below the silicon nitride film 13 because the silicon oxide film 12 to be oxynitrided is hindered by the region containing a large amount of nitrogen. Biting can be minimized.

Next, anisotropic etching of the silicon oxynitride film 14 is performed on the structure of FIG. 1B using the silicon nitride film 13 as a mask, as shown in FIG. A shape is formed in which a small bird's beak 16 of the silicon oxynitride film 14 existing below the end of the silicon film 13 is left alone.

Thereafter, an oxidation step is performed in an oxidation atmosphere to form a silicon oxide film 17 for element isolation (see FIG. 2D).

In the above series of steps, the bird's beak in FIG. 1B can be suppressed by the oxynitridation of the silicon oxide film 12, and a large amount of nitrogen formed in a portion deeper than the surface of the silicon substrate 11 is contained. The small bird's beak 16 of the silicon oxynitride film 15 effectively suppresses the diffusion of the oxidizing agent into the silicon substrate below the silicon nitride film 13 during the selective oxidation for forming the silicon oxide film 17 for element isolation. By doing so, the penetration 18 of the final bird's beak into the element region is
Compared to the COS method or the improved LOCOS method, it can be significantly reduced.

At the same time, the silicon oxynitride film 14 in the device isolation region in FIG. 1B is removed by anisotropic etching, and the device isolation region is depressed as shown in FIG. Since selective oxidation for isolation is performed, a step between the surface of the element region and the surface of the element isolation region can be reduced as shown in FIG.

Further, since a silicon oxynitride film is used to suppress a bird's beak during the formation of a silicon oxide film for element isolation, the stress applied to the silicon substrate during selective oxidation can be reduced.

In the above embodiment, only the oxynitridation step and the etching step of the formed silicon oxynitride film are added to the conventional LOCOS method. This is an effective method from the viewpoint of solving the problems of the conventional example and reducing the production cost.

In the actual manufacture of a semiconductor device, the silicon nitride film 13 is removed by etching after the above selective oxidation for element isolation to form a structure as shown in FIG. The process may be shifted to a normal transistor manufacturing process.

In the above embodiment, the silicon oxide film 12 shown in FIG. 1A is oxynitrided in an atmosphere of dinitrogen monoxide or nitrogen monoxide, so that the silicon oxide film 12 shown in FIG. Although the silicon nitride film 14 is formed, the silicon oxynitride film 14 may be formed by nitriding the silicon oxide film 12 in an ammonia atmosphere and then performing oxidation in an oxygen atmosphere.

Although the present invention has been described with reference to the above embodiment, the present invention is not limited to the above embodiment, but includes various embodiments according to the principle of the present invention.

[0055]

As described above, according to the method of manufacturing a semiconductor device of the present invention, in the formation of an element isolation structure by selectively oxidizing the surface of a silicon substrate, an element of an insulating film for element isolation is formed. Biting into a region and a surface step between an element region and an element isolation region can be effectively reduced, and miniaturization of a semiconductor device can be facilitated.

At the same time, according to the present invention, it is possible to reduce the stress applied to the silicon substrate at the time of selective oxidation when forming a silicon oxide film for element isolation, thereby suppressing adverse effects on semiconductor element characteristics. And improve the yield.

Further, the method of manufacturing a semiconductor device according to the present invention
With only minor changes to the conventional LOCOS method, it is possible to solve the problems in the conventional element isolation method,
Since the increase in the number of steps is not accompanied by complication, this is an extremely effective manufacturing method from the viewpoint of reduction in manufacturing cost, and its practical value is extremely high.

[Brief description of the drawings]

FIGS. 1A to 1C are diagrams illustrating a manufacturing method according to an embodiment of the present invention in the order of steps.

FIGS. 2D to 2E are diagrams for explaining a manufacturing method according to an embodiment of the present invention in the order of steps.

FIGS. 3A to 3C are diagrams showing an example of a conventional element isolation method in the order of steps.

FIGS. 4A to 4C are views showing an example of a conventional element isolation method in the order of steps.

FIGS. 5D to 5F are views showing an example of a conventional element isolation method in the order of steps.

FIGS. 6A to 6C are diagrams showing another conventional element isolation method in the order of steps.

FIGS. 7D to 7E are views showing another conventional element isolation method in the order of steps.

[Explanation of symbols]

 Reference Signs List 11 silicon substrate 12 silicon oxide film (first silicon oxide film) 13 silicon nitride film 14 silicon oxynitride film 15 silicon oxynitride film containing much nitrogen 16 bird's beak of oxynitride film 17 silicon oxide film for element isolation 18 bird's beak Reference Signs List 21 silicon substrate 22 silicon oxide film 23 silicon nitride film 24 opening 25 silicon oxide film for element isolation 26 bird's beak 31 silicon substrate 32 silicon oxide film 33 first silicon nitride film 34 first selective silicon oxide film 35 second Silicon nitride film 36 Silicon oxide film for device isolation 37 Bird's beak 38 Deformation of device region 41 Silicon substrate 42 Silicon oxide film 43 First silicon nitride film 44 Second silicon nitride film 45 Silicon oxide film for device isolation 46 bite 47 Deformation of the child area

Claims (5)

(57) [Claims] 1. A method of manufacturing a semiconductor device in which an element isolation structure is formed by selectively oxidizing a surface of a silicon substrate, wherein: (a) an oxidation-resistant film is formed on a first silicon oxide film formed on the surface of the silicon substrate; (B) oxynitriding the first silicon oxide film using the oxidation resistant film as a mask to form a silicon oxynitride film in an element isolation region not covered by the oxidation resistant film (C) performing anisotropic etching on the silicon oxynitride film using the oxidation-resistant film as a mask to expose the silicon substrate in an element isolation region; and (d) using the oxidation-resistant film as a mask. Selectively oxidizing the silicon substrate in an element isolation region to form a silicon oxide film for element isolation. 2. The method according to claim 1, wherein the first silicon oxide film is formed to have a predetermined thickness, and growth of a bird's beak of the silicon oxynitride film below the oxidation-resistant film during oxynitridation is limited. 2. The method of manufacturing a semiconductor device according to claim 1, wherein 3. The silicon oxynitride film left by the anisotropic etching acts as an oxidation-resistant film against selective oxidation in forming the silicon oxide film for element isolation in the step (d). 2. The method for manufacturing a semiconductor device according to claim 1, wherein: 4. A method according to claim 1, wherein a recess is formed in said silicon substrate in said device isolation region by said anisotropic etching, and selective oxidation for device isolation is performed on said surface of said recess. Of manufacturing a semiconductor device. 5. A method of manufacturing a semiconductor device in which an element isolation structure is formed by selectively oxidizing a surface of a silicon substrate, comprising: (a) forming a silicon oxide film on the surface of the silicon substrate ;
An oxidation resistant film is selectively formed on the substrate, and the oxidation resistant film is used as a mask.
Oxynitriding the silicon oxide film to cover the oxidation resistant film
A silicon oxynitride film is formed in a region corresponding to an unisolated element isolation region, and the silicon oxynitride film has a region rich in nitrogen near an interface of the silicon substrate and / or near the surface of the silicon oxynitride film. and the silicone of the isolation region is anisotropically etched as a mask said oxidation resistant film; (b) a silicon oxynitride film
Exposing the emission substrate, when selectively forming an oxide film for the (c) element isolation,
A method of manufacturing a semiconductor device, wherein growth of a bird's beak is suppressed in a region containing abundant nitrogen left at an end of the element isolation region.