JPH10189571A - Method for manufacturing semiconductor device - Google Patents

Abstract

(57) Abstract: Provided is a method of manufacturing a semiconductor device capable of suppressing growth of bird's beak in a selective oxidation method. A mask step of forming an oxidation mask on the surface of a silicon substrate in a pattern having an opening where a device isolation formation region is to be opened. Oxidation rate region 1
The LOCOS is formed by a passivation step of forming the element 1, and after the passivation step, an oxidation step of oxidizing the surface of the silicon substrate 10 in a region where a device isolation is to be formed to form a device isolation oxide film 24.

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 device in which a bird's beak of an element isolation oxide film (LOCOS) is shortened.

[0002]

2. Description of the Related Art In general, for element isolation of a semiconductor device,
A selective oxidation method (LOCOS) using a nitride film as an oxidation mask is mainly used. This method has the advantage that the steps are simpler than in the case of trench isolation, and element isolation can be stably formed.

On the other hand, bird's beak inevitably appears in the active region in the LOCOS method. With the miniaturization of the device, a sufficient active region cannot be secured due to bird's beak intrusion, and there is a problem that a narrow channel effect appears remarkably.

FIG. 4 shows the steps of a conventional selective oxidation method. In the selective oxidation method, as shown in FIG.
In general, a pad oxide film 21 for relaxing the stress of the nitride film on the zero plane and a silicon nitride film 22 functioning as an oxygen impermeable oxidation mask are formed on the pad oxide film 21.
After two layers of the pad oxide film 21 and the silicon nitride film 22 are formed, as shown in FIG. 4A, the silicon nitride film 22 is subjected to patterning for forming an opening 30 of a pattern of an element isolation oxide film. Next, the substrate surface not covered with the silicon nitride film 22 is thermally oxidized to form an element isolation oxide film 23 as shown in FIG. At this time, the oxidation proceeds below the edge of the silicon nitride film 22 and raises the edge of the silicon nitride film 22 to generate a bird's beak 23a.

In order to suppress the bird's beak 23a,
It is possible to some extent by increasing the thickness ratio of the silicon nitride film 22 to the pad oxide film 21 by reducing the thickness of the pad oxide film 21 and increasing the thickness of the silicon nitride film 22.

[0006]

However, in this case, the LO
Since a large stress concentration occurs to hold down the bird's beak 23a at the COS edge portion, problems such as an increase in junction leakage occur. Further, there is a bird's beak suppression method such as forming a sidewall on the side wall of the oxidation mask. However, there is a problem that the number of steps is greatly increased and a TAT (Turn Around Time) is also long.

The present invention has been made in view of the above circumstances, and has as its object to provide a method of manufacturing a semiconductor device capable of suppressing the growth of bird's beak in a selective oxidation method.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a masking step of forming an oxidation mask on a silicon substrate surface in a pattern in which a region for forming an element isolation is to be formed, A passivation step of forming a low oxidation rate region in the vicinity of the surface of the substrate covered with the oxidation mask, and after the passivation step, oxidizing the silicon substrate surface in the region where the device isolation is to be formed, thereby forming a device. An oxidation step of forming an isolation oxide film.

According to the present invention, there is provided a method for manufacturing a semiconductor device, comprising:
In other words, a low oxidation rate region is formed near the substrate surface below the opening edge of the oxidation mask. for that reason,
When oxidizing the substrate surface in the region where the element isolation is to be formed, the oxidation progresses in the lateral direction of the substrate due to the low oxidation rate region surrounding the region where the element isolation is to be formed and proceeds in the thickness direction. As a result, the oxidation is suppressed from penetrating under the oxidation mask, and the growth of bird's beak is suppressed.

The low oxidation rate region can be formed by, for example, obliquely implanting inert gas ions and implanting the inert gas into the substrate below the opening edge of the oxidation mask.

When ions are implanted by such an oblique ion implantation method, an inert gas is also implanted into an element isolation region which should be oxidized thickly, thereby lowering the oxidation rate and reducing the thickness of the element isolation oxide film. As a result, there is a possibility that the element isolation capability is reduced. Therefore, after the inert gas ions are implanted, oxygen is ion-implanted into the element isolation formation region, thereby leaving a low oxidation rate region on the substrate near the edge of the oxidation mask around the element isolation formation region. Can be activated, and as a result, a thick element isolation oxide film can be formed, and at the same time, bird's beak can be suppressed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited to the following embodiments.

According to the method of manufacturing a semiconductor device of the present invention, a low oxidation rate region is formed near the surface of a substrate covered with an oxidation mask in a region around an element isolation formation planned region which is an opening of an oxidation mask to suppress bird's beak. Things.

As an oxidation mask, a silicon nitride film can be usually employed, and can be formed by an LP-CVD method. The thickness is usually about 50 to 200 nm.
Before forming the silicon nitride film, it is preferable to interpose a pad oxide film between the substrate and the silicon nitride film in order to alleviate the stress between the silicon nitride film and the substrate surface. The thickness of the pad oxide film is about 5 to 50 nm. In a device isolation method called polybuffer locos, a polycrystalline silicon layer is interposed between a pad oxide film and a silicon nitride film.
LOCOS can be formed using the layer as an antioxidant film. In this case, the thickness of the polycrystalline silicon is about 40 nm.

After the formation of the oxidation mask, patterning is performed by photolithography to form an opening as a region where an element isolation is to be formed in the oxidation mask by film formation of a photoresist, exposure, development, and etching such as RIE.

Next, a low oxidation rate region is formed on the substrate below the edge of the opening of the oxidation mask. Such a low oxidation rate region can be formed by implanting ions of an inert gas into a silicon substrate. Other than the inert gas, the rate of silicon oxidation can be reduced. However, since this ion implantation irradiates the active region, the inert gas is an element that does not affect the characteristics of the transistor and the like. Is preferably used.

Examples of the inert gas include rare gases such as nitrogen and argon. For example, when nitrogen is ion-implanted into a silicon substrate at a dose of 1 × 10 ¹⁵ / cm ² , the oxidation rate is 0.5 times that when no ion is implanted, and when the dose is 1 × 10 ¹⁶ / cm ² , the oxidation rate is It becomes 0.2 times of normal. Therefore, the dose of the inert gas ion is suitably about 5 × 10 ^{15 to} 5 × 10 ¹⁶ / cm ² .

The energy of the ion implantation of the inert gas is determined from the relationship with the depth at which the inert gas is implanted.
For example, in the case of nitrogen, about 15 to 40 keV is preferable,
As a result, the inert gas is driven to a depth of about 0.03 to 0.09 μm.

In order to form the low oxidation rate region around the region where the element isolation is to be formed and near the surface of the substrate covered with the oxidation mask, as shown in the first embodiment, ions of an inert gas are formed. Oblique ion implantation is performed near the edge of the oxidation mask, and the region around the region where the element isolation is to be formed is set as a low oxidation rate region. In addition, there is a method in which a low oxidation rate region in which oxygen is not implanted is left while increasing the oxygen concentration.

Alternatively, as shown in the second embodiment, after the inert gas ions are vertically injected into the silicon substrate, sidewalls are formed at the opening ends of the oxidation mask.
There is a method of activating the silicon in the region where the element isolation is to be formed by implanting oxygen ions to increase the oxidation rate, but the method is not limited thereto.

The ion implantation amount of oxygen for activating the substrate is an amount for converting a low oxidation rate region by an inert gas into a normal oxidation rate or a higher oxidation rate. For example, if the dose is 5 × 10 ^{15 to} 5 × 1
0 ¹⁶ / cm ² and energy of about 10 to 30 keV.
It is driven down to about 6 μm.

Thereafter, in a normal oxidation step, the surface of the silicon substrate at the opening not covered with the oxidation mask is oxidized to form an element isolation oxide film. During this oxidation, the surface of the silicon substrate below the edge of the opening covered by the oxidation mask is a low oxidation rate region, so oxidation proceeds in the thickness direction in the region not covered by the oxidation mask. Lateral oxidation of the substrate is slowed down due to the low oxidation rate region surrounding the isolation region. As a result, the oxidation hardly proceeds under the oxidation mask, and the growth of bird's beaks penetrating the edge of the oxidation mask is suppressed.

Thereafter, a channel stopper is formed by, for example, ion implantation, and further, a transistor, a memory transistor, a wiring layer, an insulating layer, and the like are formed to finally obtain a semiconductor device. The method for manufacturing a semiconductor device according to the present invention includes:
The present invention can be applied to any semiconductor device having element isolation using LOCOS as described above.

[First Embodiment] A first embodiment of the present invention will be described with reference to FIGS. First, FIG.
The steps leading to (a) will be described. A pad oxide film 21 having a thickness of about 10 nm is formed on the silicon substrate 10 by, for example, a dry oxidation method at 950 ° C. Next, for example, a silicon nitride film is formed by LP-CVD (low pressure CVD) under the following conditions.
Deposit about 0 nm.

[0025] Next, as shown in FIG. 1B, a photoresist R1 is formed by spin coating or the like, and patterning is performed to expose a region where an element isolation oxide film is to be formed by exposure and development.
Thereafter, the opening 30 is formed by etching the silicon nitride film in the opening of the photoresist R1 by, for example, dry etching under the following conditions.

[0026] Then, an inert gas which is a feature of the present invention is obliquely ion-implanted under the following conditions, for example, as shown in FIG.

Type of ion: nitrogen Injection angle: 45 ° Energy: 15 keV Dose amount: 1 × 10 ¹⁶ / cm ² By ion implantation obliquely as shown in FIG.
As shown in (c), nitrogen gas is also effectively injected into the vicinity of the silicon substrate surface below the end of the silicon nitride film 21 where the bird's beak enters. The ion implantation angle is not particularly limited, but is preferably about 70 to 20 ° so that ions can be effectively implanted into the substrate below the silicon nitride film. The silicon substrate into which an inert gas ion such as nitrogen is implanted has a low oxidation rate, and becomes a low oxidation rate region 11. However, since nitrogen gas is also injected into the silicon substrate in the opening region serving as the element isolation region, the oxidation rate is reduced, the element isolation oxide film becomes thinner, and there is a concern that the element isolation capability may be reduced. Therefore, the next oxygen ion implantation is performed to activate the region where the element isolation is to be formed. This oxygen ion implantation is performed as shown in FIG.
As shown in (2), for example, the silicon substrate is irradiated vertically under the following conditions.

Implantation angle: 0 ° Energy: 15 keV Dose: 1 × 10 ¹⁶ / cm ² By performing such oxygen ion implantation vertically, as shown in FIG. The oxygen implantation region 12 is formed in the silicon substrate 10, and the region where the element isolation is to be formed is activated to increase the oxidation rate. on the other hand,
The low oxidation rate region 11 into which oxygen has not been implanted, that is, the low oxidation rate region 11 of the silicon substrate below the opening edge of the silicon nitride film 21 remains. Therefore, the silicon substrate below the edge of the silicon nitride film, into which the bird's beak enters, is hardly oxidized, and the bird's beak does not easily enter.

After removing the photoresist R1, FIG.
As shown in (e), for example, selective oxidation is performed under the following conditions to form an element isolation oxide film having a thickness of, for example, 300 to 400 nm.

Gas: Pyro 1.8 Temperature: 1000 ° C. In this thermal oxidation, oxidation usually proceeds to the silicon substrate under the silicon nitride film 21 and bird's beak proceeds. In the present embodiment, the edge of the silicon nitride film 22 is formed. Since the low oxidation rate region 11 is located near the surface of the silicon substrate below the portion, oxidation in the lateral direction from the opening edge of the silicon nitride film 22 is suppressed, and bird's beak expansion is suppressed.

Thereafter, as shown in FIG. 2F, the silicon nitride film 22 is removed by hot phosphoric acid, and the pad oxide film 21 is removed by dilute hydrofluoric acid to form an element isolation oxide film 23.

The bird's beak 23a of the obtained element isolation oxide film 23 is shorter than the conventional one, and the length of the bird's beak of the conventional element isolation oxide film depends on the thickness of the pad oxide film.
The bird's beak length of the element isolation oxide film according to the present embodiment is about 0.05 μm, whereas the length is about 0.2 μm.
It can be suppressed to about 0.1 μm. As a result, variation in transistor dimensions and short channel effect can be suppressed, which can contribute to improvement in the degree of integration.

[Second Embodiment] This embodiment will be described with reference to FIG. The process leading to FIG.
(B) is substantially the same as that of FIG.
0 is formed to be slightly larger than the element isolation formation region by the sidewall to be formed later. Then, using the silicon nitride film 22 as a mask, the substrate is irradiated with nitrogen gas as an inert gas vertically, for example, under the above conditions.

As a result, a low oxidation rate region 11 into which nitrogen has been implanted is formed in the silicon substrate at the opening. Next, after removing the photoresist, as shown in FIG. 3C, a silicon nitride film is deposited by CVD and then etched back to form a silicon nitride film 22 as an oxidation-resistant film at the opening end. Side wall 2 composed of silicon nitride on the side
2a is formed. Thereafter, oxygen is vertically ion-implanted, thereby implanting oxygen into the substrate not covered with the silicon nitride films 22 and 22a, forming an oxygen implanted region 12 in a region where element isolation is to be formed, and activating the low oxidation rate region. To a region having a normal oxidation rate. On the other hand, since oxygen is not injected into the portion covered with the sidewall 22a, the substrate below the sidewall 22a remains as the low oxidation rate region 11.

Thereafter, oxidation is performed as in the first embodiment to form an element isolation oxide film. Also in this case, the oxidation in the lateral direction is difficult to progress due to the low oxidation rate region 11 existing in the substrate below the sidewall 22a, and thus the progress of the bird's beak is suppressed.

The method using this sidewall is the first method.
Although the number of steps increases as compared with the oblique ion implantation method of the embodiment, for example, when the isolation width is small and oblique ion implantation is difficult because of the height of the silicon nitride film, or the width of the low oxidation rate region is controlled. It is effective when you want to.

[0037]

According to the method of manufacturing a semiconductor device of the present invention, bird's beak can be suppressed as much as possible, which is effective for improving the degree of integration.

[Brief description of the drawings]

FIGS. 1A to 1C are cross-sectional views illustrating steps of a first embodiment of the present invention.

FIGS. 2D to 2F are cross-sectional views illustrating steps of the first embodiment following FIG. 1;

FIGS. 3A to 3C are cross-sectional views illustrating steps of a second embodiment of the present invention.

FIGS. 4A and 4B are cross-sectional views illustrating a conventional process for forming an isolation oxide film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Silicon substrate, 11 ... Low oxidation rate area, 12 ... Oxygen implantation area, 21 ... Pad oxide film, 22 ... Silicon nitride film (oxidation mask), 22a ... Side wall

Claims (4)

[Claims] 1. A masking step of forming an oxidation mask on a silicon substrate surface in a pattern having an opening where a device isolation formation region is to be opened, and in a region around the device isolation formation region and near a surface of the substrate covered with the oxidation mask. A deactivation step of forming a low oxidation rate region; and an oxidation step of oxidizing a silicon substrate surface of the element isolation formation scheduled area to form an element isolation oxide film after the inactivation step. Semiconductor device manufacturing method. 2. The method according to claim 1, wherein the inactivating step obliquely implants ions of an inert gas into the silicon substrate.
The manufacturing method of the semiconductor device described in the above. 3. The method according to claim 2, wherein the inert gas is nitrogen. 4. The method of manufacturing a semiconductor device according to claim 2, further comprising an activation step of implanting oxygen ions into a region where element isolation is to be formed after the inactivation step.