JPH11186253A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a semiconductor device in quality, by a method wherein an isolator which is excellent in reproducibility, uniform in thickness, and capable of preventing bird'beaks from being formed in a LOCOS method is formed by keeping the surface nearly flat, and stress and diffusion of a nitrogen component which occur when the isolator is formed are markedly restrained. SOLUTION: An opening 23 is provided to a mask layer composed of a thin oxide film 21 and a silicon oxide film 22 formed on a semiconductor substrate 20 by selective etching, a part of the substrate 20 where an inter-element isolator is required to be formed is exposed through the opening 23. Oxygen ions are obliquely implanted in the exposed surface of the substrate 20 in the opening 23 to form an ion-implanted region 24 which reaches below the edge of the mask layer. Furthermore, a field oxide film serving as an inter-element isolator is formed on the exposed part of the semiconductor substrate 20 through a thermal oxidation growth method. Furthermore, the mask layer is removed, and thus the formation of an inter-element isolator is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor integrated circuit, for example, and more particularly to a method for manufacturing a semiconductor device using an element isolation method in a semiconductor device.

[0002]

2. Description of the Related Art In recent years, with the development of semiconductor integrated circuit manufacturing technology, the number of semiconductor elements mounted on one wafer has been steadily increasing. As such high integration advances, semiconductor elements themselves continue to be miniaturized, and wiring widths used in production lines are already in the submicron order. However, no matter how fine the semiconductor elements are, as described above, high quality semiconductor elements cannot be manufactured unless the semiconductor elements on the wafer are appropriately separated. This technology is generally known as device isolation technology (De-
vice Isolation Technology)
It is necessary to form an opening between the semiconductor elements and form an opening by minimizing the area of the isolation as much as possible while maintaining the element separation effect by the separating element, and to mount as many semiconductor elements as possible. The main purpose is.

At present, a selective oxidation method (hereinafter referred to as a LOCOS method) is widely used as a technique for separating a semiconductor element. The reason is that by forming an insulating layer made of a thick oxide film between the semiconductor elements by the LOCOS method, the semiconductor elements can be effectively separated. As an example, L is described with reference to the longitudinal sectional views of FIGS. 4A and 4B.
A general semiconductor device isolation process by the OCOS method will be described in detail below.

[0004] First, a thin oxide film 11 and a silicon nitride film 12 are sequentially formed as a mask layer on a semiconductor substrate 10 such as a silicon wafer. Subsequently, as shown in FIG. 4A, the openings 1 are formed in the oxide film 11 and the silicon nitride film 12 by performing light exposure and etching.
By forming the silicon nitride film 3, the silicon nitride film 12 and the thin oxide film 11 are patterned, and a portion of the semiconductor substrate 10 where an element isolation is to be formed is exposed from the opening 13.

Subsequently, a thermal oxidation growth method is performed as shown in FIG. For example, a substrate device provided with a mask layer (silicon nitride film 12 + oxide film 11) as shown in FIG.
By setting the temperature to 100 ° C. and flowing a gas containing oxygen into the high-temperature furnace, an oxidation reaction is promoted on the silicon wafer exposed through the opening 13 to form a thick field oxide film 14. An active region of the semiconductor device is formed between the portions where the field oxide film 14 is formed. When the field oxide film 14 is formed, the silicon nitride film 1
2 plays the role of a mask because its oxidation rate is much lower than that of the silicon wafer of the semiconductor substrate 10,
Therefore, the field oxide film 14 is formed on the portion of the semiconductor substrate 10 that is not covered with the silicon nitride film 12 (the portion of the semiconductor substrate 10 exposed through the opening 13). Finally, the silicon nitride film 12 and the thin oxide film 11
The element layer is completed by removing the mask layer formed by the field oxide film 14.

[0006]

The above-described conventional LOCOS method has been widely and generally employed because the manufacturing process is simple and the effect of separating semiconductor elements is excellent.

However, when the size of the semiconductor element is reduced and a process for handling a size on the order of submicrons is performed, the above-described conventional LOCOS method has many disadvantages.

First, as a first drawback, when the field oxide film 14 as described above is formed, the range in which an oxidation reaction occurs due to the diffusion action of oxygen from the opening 13 is shown in FIG.
Expand in both lateral directions as shown. For this reason, the field oxide film 14 is also formed below the ends of the silicon nitride film 12 and the thin oxide film 11, and the field oxide film 14 has a bird-like structure at its ends. This is called Bird's beak.

As a second drawback, a component containing nitrogen in a portion where a compressive stress acts on the surface of the silicon nitride film 12 due to a pressure from the bird's beak during the formation of the bird's beak is reduced to a thin oxide film immediately below. 11 and semiconductor substrate 10
Is diffused to the portion where the tensile force acts on the interface with the silicon wafer, and acts on the silicon nitride film 1 through the action of silicon.
5 is formed. This is because the silicon nitride film 15 acts as a mask when the gate oxide film of the semiconductor element is grown later, so that the gate oxide film at that location becomes thin. When observed with an optical microscope, the silicon oxide film 15 has a white band shape at the end of the active region of the semiconductor element.
bbon). The white ribbon effect affects the quality of the semiconductor device.

Further, as a third disadvantage, when the field oxide film 14 is formed, the volume of the silicon oxide is increased to about 2.2 times when silicon is oxidized to silicon dioxide. Non-recessed surface protruding from the surface side of the surface
To form This goes against the flattening conditions.

Further, as a fourth disadvantage, when the field oxide film 14 is formed, the volume of silicon also expands in the horizontal direction, so that a large stress also acts on the active region of the semiconductor element to cause lattice defects near the bird's beak. Many occur. In this case, the leakage of current at the interface increases, and the reliability of the semiconductor element decreases.

Further, as a fifth disadvantage, in the thermal oxidation growth method, the flow rate of the gas containing oxygen into the silicon wafer varies depending on the size of the opening 13, so that the processing by the thermal oxidation growth method is performed for the same time. The opening 13
The smaller the opening is, the thinner the formed field oxide film 14 is. Such poor reproducibility is also one of the disadvantages affecting the element isolation effect.

In view of the above, a number of methods for separating semiconductor elements have been developed and proposed for the purpose of improving the drawbacks of the conventional LOCOS method as mentioned in the first to fifth. For example, U.S. Pat. No. 4,211,582 discloses that
An element isolation method in which a two-stage oxidation process is performed using a multi-order mask technique is described. U.S. Pat. No. 4,868,136 also describes a device isolation method by Ravaglia et al. That combines a LOCOS method and a trenching technique. However, even when such improved element isolation methods are used, disadvantages such as a low production rate, poor reproducibility, a complicated manufacturing process, and an uneven surface are still unresolved.

The present invention solves the above-mentioned conventional problems. By improving the element isolation process in a semiconductor device, it is possible to prevent the formation of bird's beaks, which is a drawback of the conventional LOCOS method, and to provide excellent reproducibility. To form a segregated product, and at the same time, while maintaining a substantially flat surface even when the segregated product is formed, significantly reduce the stress and the diffusion of nitrogen components generated when the separated product is formed. It is an object of the present invention to provide a method of manufacturing a semiconductor device which can improve the quality of a semiconductor element.

[0015]

According to a method of manufacturing a semiconductor device of the present invention, a mask layer is formed on a surface of a semiconductor substrate in a method of manufacturing a semiconductor device using a LOCOS method used for separating a semiconductor element. Forming an opening in the mask layer by selectively etching the mask layer;
A step of obliquely implanting oxygen ions into the semiconductor substrate below the opening to form an ion-implanted region whose area reaches below the end of the mask layer, and exposing the semiconductor substrate through the opening using a thermal oxidation growth method; Forming a field oxide film on the formed semiconductor substrate.

According to this structure, in the step of implanting oxygen ions, oxygen ions are obliquely implanted into the semiconductor substrate.
Oxygen ions are also distributed below the end of the mask layer. Subsequently, an isolate is formed in the oxygen ion implantation region by the LOCOS method. At this time, oxygen ions in the lower portion of the end portion of the mask layer implanted in the previous stage interact with silicon of the semiconductor substrate, so that the reaction speed of the lower portion of the end portion of the mask layer also increases, thereby increasing the thickness of the separated material. Evenly, the formation of a bird's beak as in the related art is prevented. By preventing the formation of the bird's beak, the stress and the diffusion of the nitrogen component generated during the formation of the bird's beak can be significantly suppressed, and the quality of the semiconductor element can be improved. Further, since oxygen ions are implanted in advance, the oxidation reaction time is shortened, and the field oxide film is formed deeper, so that the flatness of the surface of the semiconductor substrate can be further improved. Since oxygen ions have been implanted in advance, it is possible to increase the oxidation rate when performing the thermal oxidation growth method, and the thickness of the field oxide film changes with a slight change in the size of the opening 23. The degree of separation is suppressed, the reproducibility is excellent, and the thickness of the separated material becomes uniform. In this way, many disadvantages of the conventional LOCOS method can be improved.

In the method of manufacturing a semiconductor device according to the present invention, the mask layer has at least an oxide film and a silicon nitride film. In this case, this mask layer preferably has a two-layer structure of an oxide film and a silicon nitride film, or a three-layer structure of a thin oxide film, a polysilicon film, and a silicon nitride film. In this manner, when a polysilicon film is provided between the thin oxide film and the silicon nitride film to form a three-layer structure, the stress acting on the isolation can be reduced more effectively.

Further, in the method of manufacturing a semiconductor device according to the present invention, the thin oxide film has a thickness of 50 to 200 °, the silicon nitride film has a thickness of 500 to 2000 °, and the polysilicon film has a thickness of 200 to 1000 °. Preferably, there is.

Further, in the method of manufacturing a semiconductor device according to the present invention, the step of implanting oxygen ions is performed at an implantation energy of 50 to 150 KeV and an implantation amount of 1 × 10 ^15.
It is preferably set to 1 × 10 ¹⁷ atoms / cm ² . In the method of manufacturing a semiconductor device according to the present invention, it is preferable that the temperature at which the thermal oxidation growth method is performed is set to 800 to 1100 ° C.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a method for manufacturing a semiconductor device according to the present invention will be described in detail with reference to the drawings.

FIG. 1A, FIG. 1B, FIG. 2A and FIG. 2B show a schematic configuration of each manufacturing process of a semiconductor device according to an embodiment of the present invention. 2A is a longitudinal sectional view in a mask layer forming step, FIG. 1B is a longitudinal sectional view in an oxygen ion implantation step, FIG. 2A is a longitudinal sectional view in a field oxide film forming step, and FIG. () Is a longitudinal sectional view in a mask layer removing step.

As shown in FIG. 1A, a semiconductor substrate 20
A mask layer having a two-layer structure of a thin oxide film (pad oxide layer) 21 and a silicon nitride film 22 is formed thereon. continue,
The mask layer is selectively etched to form openings 23 in the mask layer so that the mask layer has a predetermined pattern.

For example, a thin oxide film 21 having a thickness of 50 to 200 ° is formed on the surface of the silicon wafer of the semiconductor substrate 20 by using a chemical vapor method (CVD method) or a thermal oxidation growth method. On the surface of the thin oxide film 21, a silicon nitride film 22 having a thickness of 500 to 2000 ° is deposited by using the CVD method. Subsequently, openings 23 are formed in the thin oxide film 21 and the silicon nitride film 22 by performing light exposure and etching, and the silicon nitride film 22 and the thin oxide film 21 are patterned. In this manner, the portion of the semiconductor substrate 20 where the later-described field oxide film 25 as an isolator between semiconductor elements is to be formed is exposed through the opening 23.

Next, as shown in FIG. 1B, oxygen ions (O ⁺ ) are obliquely implanted through the opening 23 of the semiconductor substrate 20 to form an oxygen ion implanted region 24. At this time, it is preferable that the implantation energy and the implantation amount of the oxygen ions are adjusted to meet the demand of each manufacturing process. For example, in the present embodiment, the oxygen ion implantation energy is 50
１５０150 KeV and the injection amount is 1 × 10 ¹⁵ -1
× 10 ¹⁷ atom / cm ² . At this time, since oxygen ions are obliquely implanted, the distribution range of the mask layer is expanded from a portion where the silicon wafer is exposed through the opening 23 to, for example, both lateral directions in FIG. It has reached the lower position of the end.

Subsequently, as shown in FIG. 2A, a field oxide film 25 is formed on the silicon wafer exposed through the opening 23 by using a thermal oxidation growth method. For example, the substrate device after the oxygen ion implantation step as shown in FIG.
° C and flowing a gas containing oxygen into the high-temperature furnace, thereby promoting the oxidation reaction of the silicon wafer exposed through the opening 23, and causing the exposed portion of the semiconductor substrate 20 to have a thick field oxidation. Forming a film 25,
The range of the active region of the semiconductor device is set. At this time, in the formation of the field oxide film 25, in addition to the gas containing oxygen flowing by diffusion, oxygen ions implanted into the semiconductor substrate 20 through the opening 23 also participate in the oxidation reaction. Can be increased. Thus, the thickness of the formed field oxide film 25 becomes uniform in the plane direction of the semiconductor substrate 20. Therefore, the field oxide film 25 formed at the lower end portion of the mask layer also has approximately the same thickness as the middle portion.
No bird's beak as in (B) is formed.

Finally, the silicon nitride film 22 having a two-layer structure and the thin oxide film 21 serving as a mask layer are sequentially removed, so that only the substantially planarized field oxide film 25 can be left. For example, a silicon nitride film 22 is first heated with a heated phosphoric acid solution.
Is removed, and then the thin oxide film 21 is removed with a solution containing hydrofluoric acid, thereby forming an isolation between semiconductor elements composed of the field oxide film 25 as shown in FIG. Is completed.

Therefore, as compared with the prior art, the process of forming the device isolation according to the present invention has many advantages as follows. A first advantage of the present invention is that oxygen ions are implanted into the semiconductor substrate 20 at a portion where a device isolation is to be formed (a portion of the silicon wafer exposed through the opening 23) to form an oxygen ion implanted region 24. Therefore, the oxidation rate when performing the thermal oxidation growth method can be increased. In addition, since oxygen ions are obliquely implanted, the end of the oxygen ion implanted region 24 reaches a position below the mask layer, and the thickness of the formed element isolation becomes uniform in the plane direction of the substrate. The formation of bird's beak can be prevented. By preventing the formation of the bird's beak, the stress and the diffusion of the nitrogen component generated during the formation of the bird's beak can be largely suppressed, and the quality of the semiconductor element can be improved.

Also, as a second advantage of the present invention, since oxygen ions are implanted in advance in the exposed portion of the semiconductor substrate 20 through the opening 23, the time of the oxidation reaction can be reduced, and The field oxide film 15 can be formed deeper than the field oxide film 20. Therefore, the flatness of the surface of the semiconductor substrate 20 can be further improved, which is advantageous for application of a multi-layering process.

Further, as a third advantage of the present invention, since the oxygen ion implanted region 24 is formed in advance, the oxidation rate at the time of performing the thermal oxidation growth method can be increased.
The degree to which the thickness of the field oxide film 25 changes due to a slight change in the size of the opening of the opening 23 can be suppressed, and the reproducibility is excellent, so that the thickness of the isolation is uniform.

Further, as a fourth advantage of the present invention, the improved device isolation method of the present invention is completely compatible with the current device isolation method, and the above-mentioned known technology can be obtained simply by adding a step of obliquely implanting oxygen ions. Various disadvantages can be improved. Therefore, the steps of forming the inter-element isolation are not complicated, the production efficiency is not affected, and a large increase in manufacturing cost can be avoided.

Although the present invention has been described with reference to the preferred embodiments, the contents of the present embodiments are not intended to limit the scope of the present invention only thereto.
This embodiment has been selected in order to explain the basic principles and examples of the present invention in an optimal manner, and those skilled in the art may modify the present invention without departing from the spirit and scope of the present invention. And can add hydration. Therefore, the protection scope of the present invention is based on the claims.

In this embodiment, as shown in FIG. 1A, the mask layer is made of a thin oxide film 21 and a silicon nitride film 2.
2, but the mask layer was formed as shown in FIG.
A three-layer structure of a thin oxide film 21, a polysilicon film 26, and a silicon nitride film 22 may be employed. in this way,
When a polysilicon film 26 having a thickness of about 200 to 1000 ° is formed between the silicon nitride film 22 of the mask layer and the thin oxide film 21, if the field oxide film 25 is formed in a subsequent step, the field oxide film 25 is formed. It is possible to more effectively reduce the stress applied to the constituent element isolation material.

[0033]

As described above, according to the present invention, in the step of implanting oxygen ions, after the oxygen ions are implanted obliquely into the semiconductor substrate, the isolation is formed in the oxygen ion implanted region by the LOCOS method. By increasing the reaction rate in the lower portion of the end portion of the mask layer, the thickness of the separated material becomes uniform, and the formation of a bird's beak as in the related art can be prevented.

Further, by preventing the formation of the bird's beak, it is possible to greatly suppress the stress and the diffusion of the nitrogen component which are conventionally generated during the formation of the bird's beak, thereby improving the quality of the semiconductor element.

Further, since the oxygen ions are previously implanted, the oxidation reaction time can be reduced and the field oxide film can be formed deeper, so that the flatness of the surface of the semiconductor substrate can be further improved. it can. Also,
Oxygen ions are implanted in advance, so that the oxidation rate when performing the thermal oxidation growth method can be increased, and the degree to which the thickness of the field oxide film changes due to a slight change in the size of the opening. Can be suppressed, and the thickness of the separated material can be made uniform with excellent reproducibility.

[Brief description of the drawings]

FIG. 1 shows a schematic configuration of each manufacturing process of a semiconductor device according to an embodiment of the present invention, in which (A) is a longitudinal sectional view in a mask layer forming process, and (B) is a longitudinal sectional view in an oxygen ion implantation process. FIG.

FIGS. 2A and 2B are schematic cross-sectional views of a manufacturing process of a semiconductor device according to an embodiment of the present invention, in which FIG. 2A is a longitudinal sectional view in a field oxide film forming process, and FIG. It is a longitudinal cross-sectional view.

FIG. 3 is a longitudinal sectional view illustrating a schematic configuration of a process of forming a mask layer of a semiconductor device according to another embodiment of the present invention.

FIG. 4 is a vertical cross-sectional view of each step in forming a device isolation using a conventional LOCOS method.

[Explanation of symbols]

 Reference Signs List 20 semiconductor substrate 21 oxide film 22 silicon nitride film 23 opening 24 oxygen ion implantation region 25 field oxide film 26 polysilicon film

Claims (7)

[Claims] 1. A method for manufacturing a semiconductor device using a selective oxidation method used for separating a semiconductor element, comprising: forming a mask layer on a surface of a semiconductor substrate; and selectively etching the mask layer. Forming an opening in the mask layer; obliquely implanting oxygen ions into the semiconductor substrate below the opening to form an ion-implanted region whose area extends below the end of the mask layer; Forming a field oxide film on the semiconductor substrate exposed through the opening using a growth method. 2. The method according to claim 1, wherein the mask layer has at least an oxide film and a silicon nitride film. 3. The method according to claim 2, wherein the thickness of the oxide film is 50 ° to 200 °. 4. The method according to claim 1, wherein said silicon nitride film has a thickness of 500Å or more.
4. The method for manufacturing a semiconductor device according to claim 2, wherein the angle is 2,000. 5. The mask layer further includes a polysilicon film, wherein the thickness of the polysilicon film is 200Å to 1000１０００.
5. The method of manufacturing a semiconductor device according to claim 2, wherein Å is satisfied. 6. The oxygen ion implantation step is performed at an implantation energy of 50 to 150 KeV and an implantation amount of 1 × 10 ¹⁵ to 1 × 10 ¹⁷ atoms / cm ^2. Item 6. A method for manufacturing a semiconductor device according to any one of Items 1 to 5. 7. The thermal oxidation growth method is performed at 800 to 1100 ° C.
7. The method for manufacturing a semiconductor device according to claim 1, wherein the method is performed at a temperature.