JPH10284477A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a thick field oxide film for isolating elements. SOLUTION: The method comprises forming a pad oxide film 14 on an Si substrate 10, forming a nitride film 16 having openings 16B on this film 14, forming a prim. field oxide film 20A at the openings 16B of the film 16, forming openings 22 through this oxide film 20A, and forming a sec. field oxide film 20B at the openings 22, thereby forming a field oxide film 20. This forms the oxide film 20 deep in the substrate 10 and hence makes this film thick.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to LOCOS (Loca).
The present invention relates to a semiconductor device in which a field oxide film for element isolation is formed by an Oxidation of Silicon method and a method of manufacturing the same.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional device isolation process for forming a field oxide film for device isolation by the LOCOS method.
(A) to (c). This inter-element separation step is performed as a part of the semiconductor device manufacturing step. After the inter-element separation step, the semiconductor device manufacturing step is completed through an element forming step, a wiring step, and the like. The LOCOS method shown in FIG. 4 is a method for selectively forming a thick field oxide film 18 for element isolation by using the nitride film 16 as a mask.

More specifically, as can be seen from FIG. 4A, first, a pad oxide film (SiO ₂ film) 14 is formed on a silicon substrate 10 by thermal oxidation. Next, a CVD (Chemical Vapor Depositio) is formed on the pad oxide film 14.
A nitride film (Si ₃ N ₄ film) 16A is formed by n). On this nitride film 16A, a photoresist PR having an opening window W is formed by photolithography. That is, a photoresist is applied on the nitride film 16A, and after patterning by light exposure, the photoresist corresponding to the opening window W is removed. Thereby, the photoresist PR having the opening window W is formed. Next, RIE (Reactive I
An opening 16B is formed in the nitride film 16A by etching the nitride film 16A with an on-etching apparatus. Thereby, nitride film 16 as a mask having opening 16B is obtained. After the opening 16B is formed, P + ions (phosphorus ions) are implanted into the surface of the silicon substrate 10 with an ion implanter. By this ion implantation, a channel stopper 17A is formed. After the formation of the channel stopper 17A, the above-mentioned photoresist PR is removed.
Through the above steps, the intermediate semiconductor device shown in FIG.

Next, as can be seen from FIG. 4B, a field oxide film 18 for element isolation is formed in the opening 16B of the silicon substrate 10 by thermal oxidation. During this thermal oxidation treatment, the P + ions implanted into the silicon substrate 10 by the above-described ion implantation are also diffused, and the channel stopper 17 in which the crystal is restored to the original state is formed. Through the above steps, the intermediate semiconductor device shown in FIG. 4B is obtained.

Next, as can be seen from FIG. 4C, the nitride film 16 as a mask is peeled off by CDE or RIE. Through the above steps, the intermediate semiconductor device shown in FIG. 4C is obtained. This completes the element separation step, and thereafter, the semiconductor device is completed through an element formation step, a wiring step, and the like.

[0006]

In the semiconductor device formed in the element isolation step shown in FIG. 4, if the distance between the elements is reduced in order to miniaturize the semiconductor device, the field oxide film 18 Becomes thinner.
When the thickness of the field oxide film 18 is reduced, the isolation between the devices becomes insufficient, and there is a possibility that mutual interference between the devices, a decrease in the breakdown voltage, a current leak, and the like may occur. For this reason,
In the future, insufficient thickness of the field oxide film 18 may hinder miniaturization of the semiconductor device. On the other hand, if the thick field oxide film 18 is to be formed by the LOCOS method shown in FIG. 4, the bird's beak will inevitably increase, and the distance between the elements cannot be reduced. For this reason, the distance between the elements and the thickness of the field oxide film 18 may be restricted by bird's beak in the future.
That is, bird's beaks may limit these.

Accordingly, the present invention provides a method for forming a field oxide film 18 deeper in a silicon substrate 10 even if the distance between the elements is shortened in order to miniaturize a semiconductor device. The purpose is to increase the thickness. In other words, while suppressing the occurrence of bird's beak,
By forming the field oxide film 18 thickly, the elements are reliably separated from each other, so that mutual interference between the elements, reduction in breakdown voltage,
An object of the present invention is to prevent current leakage and the like. That is,
It is an object of the present invention to make it possible to reduce the distance between elements and to miniaturize a semiconductor device.

[0008]

In order to solve the above-mentioned problems, a semiconductor device according to the present invention is a semiconductor device having a field insulating film for element isolation formed on a semiconductor substrate. The film is composed of a primary field insulating film disposed on a peripheral portion thereof and a secondary field insulating film disposed on a central portion thereof.

That is, a field oxide film including a primary field oxide film having an opening formed at the center and a secondary field oxide film formed at an opening of the primary field oxide film is provided on a semiconductor substrate. It is characterized by the following.

That is, a field oxide film formed by performing a plurality of oxidations is provided on a semiconductor substrate.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) A first embodiment of the present invention will be described with reference to the process sectional views shown in FIGS. FIG. 1 is a view showing an element isolation step of forming a field oxide film for element isolation by the manufacturing method according to the present invention. In the first embodiment, the primary field oxide film 2 is formed even if the distance between the elements is shortened in order to miniaturize the semiconductor device.
After the formation of 0A, an opening 22 is formed in the primary field oxide film 20A, and a secondary field oxide film 20B is formed in the opening 22, thereby suppressing the occurrence of bird's beak and increasing the thickness of the field oxide film 20. It is possible to form them and to secure the isolation between the elements.

1 (a) and 1 (b) of FIG.
The processes up to the intermediate semiconductor device shown in FIG. That is, as can be seen from FIG. 1A, first, a pad oxide film (SiO ₂ film) 14 is formed on a silicon substrate 10 by thermal oxidation. Next, a CVD (Chemical Vapor Deposit) is formed on the pad oxide film 14.
ion) to form a nitride film (Si ₃ N ₄ film) 16A.
Prior to forming the nitride film 16A, the pad oxide film 14 is formed directly on the silicon substrate 10 by the nitride film 1A.
This is because a defect occurs in the silicon substrate 10 when 6A is brought into contact. That is, the silicon substrate 10 is protected by the thin pad oxide film 14. Next, the aforementioned nitride film 1
A photoresist PR having an opening window W is formed on 6A by photolithography. That is, a photoresist is applied on the nitride film 16A, and after patterning by light exposure, the photoresist corresponding to the opening window W is removed. Thereby, the photoresist P having the opening window W
R is formed. Next, RIE (Reactive Ion Ecthin
g) The opening is formed in the nitride film 16A by etching the nitride film 16A with an apparatus. Thereby, the opening 16
A nitride film 16 as a mask having B is obtained. After the opening 16B is formed, P + ions (phosphorus ions) are formed on the surface of the silicon substrate 10 in the field oxide film forming region.
Is implanted with an ion implanter. By this ion implantation, a channel stopper 17A is formed in the field oxide film formation planned region. The ions implanted into the silicon substrate 10 may be B + ions (boron ions) or the like instead of P + ions. After the formation of the channel stopper 17A, the above-described photoresist PR
Is removed. Through the above steps, the intermediate semiconductor device shown in FIG. 1A is obtained.

Next, as can be seen from FIG. 1B, a primary field oxide film 20A for element isolation is formed in the opening 16B of the silicon substrate 10 by thermal oxidation. During this thermal oxidation treatment, the P + ions implanted into the silicon substrate 10 by the above-described ion implantation are also diffused, and the channel stopper 17 in which the crystal is restored to the original state is formed. The steps up to the above are the same steps as those of the above-described conventional technique, whereby the intermediate semiconductor device shown in FIG. 1B is obtained.

Next, as can be seen from FIG. 1C, the nitride film 16 is used as a mask without being stripped, and
Next, anisotropic selective etching is performed on the field oxide film 20A by RIE. The opening 2 is formed by this selective etching.
2 is formed, and the channel stopper 17 of the silicon substrate 10 is exposed again. That is, the opening 22 penetrating the primary field oxide film 20A is formed. Through the above steps, the intermediate semiconductor device shown in FIG. 1C is obtained.

Next, as can be seen from FIG. 1D, thermal oxidation is again performed using the nitride film 16 as a mask to oxidize the opening 22 portion of the silicon substrate 10 again to form the secondary field oxide film 20B. Form. By forming this secondary field oxide film 20B, a field oxide film 20 for element isolation is completed. By the above steps, FIG.
An intermediate semiconductor device shown in (d) is obtained.

Next, as can be seen from FIG.
The nitride film 16 as a mask is removed by E or RIE. Through the above steps, the intermediate semiconductor device shown in FIG. 1E is obtained. This completes the inter-element separation step. Thereafter, the semiconductor device is completed through an element forming step, a wiring step, and the like.

As described above, according to the first embodiment of the present invention, after the formation of the primary field oxide film 20A, the opening 22 is formed and oxidized again to perform the secondary field oxide film 20B.
To form a field oxide film 20 for element isolation. Therefore, field oxide film 20 can be grown deep in silicon substrate 10. That is, the field oxide film 20 can be formed thick. The thickness of the field oxide film 20 is as shown in FIG.
This can be clearly understood by comparing FIG. 1C with FIG. That is, the thickness of the field oxide film 18 shown in FIG.
In contrast, the field oxide film 2 shown in FIG.
A thickness of 0 is a greater I. Therefore, even if the width M of the field oxide film 20 is reduced, the so-called element separation distance can be increased, and sufficient isolation between elements can be ensured. That is, even if the distance between the elements is shortened, mutual interference between the elements, reduction in the withstand voltage, current leakage, and the like can be prevented, and the semiconductor device can be miniaturized.

Moreover, after the opening 22 is formed in the primary field oxide film 20A, that is, after the silicon substrate 10 is dug, the oxidation is performed again, so that the step of the field oxide film 20 on the front surface side of the semiconductor device is reduced. It becomes smaller and flatness can be improved. Furthermore, the conventional LO
When the field oxide film 20 having the same thickness I as that of the present embodiment is formed by the COS method, the bird's beak becomes too large. However, in the present embodiment, when forming the secondary field oxide film 20B, the bird's beak is formed on the periphery of the opening. Since the primary field oxide film 20A has already been provided and the silicon substrate 10 is dug and oxidized again from the state of being selectively exposed, the bird's beak does not increase so much. That is, the growth of bird's beak can be suppressed as compared with the related art.

Furthermore, since the nitride film 16 is commonly used as a mask, an increase in the number of manufacturing steps can be minimized. That is, the primary field oxide film 2
Formation of 0A, primary field oxide film 20A by RIE
Of opening 22 in field, secondary field oxide film 20B
Formation of the nitride film 16 having the opening 16B.
Are used as a common mask. For this reason, despite the fact that the field oxide film 20 is oxidized twice in forming it, an increase in the number of manufacturing steps can be minimized.

(Second Embodiment) FIG. 2 is a process sectional view showing a second embodiment of the present invention. In the second embodiment,
The opening 24 is formed by RIE to the middle of the primary field oxide film 20A, and the remaining film 20C is left. Is also controllable.

As can be seen from FIGS. 2A and 2B of FIG. 2, the steps leading to the intermediate semiconductor device shown in FIGS. 2A and 2B are the same as those in the first embodiment described above. The same is true. Therefore, detailed description is omitted here.

Next, as can be seen from FIG. 2C, the primary field oxide film 20A is selectively etched by RIE using the nitride film 16 as a mask. By this selective etching, an opening 24 is formed halfway in the primary field oxide film 20A. That is, the difference from the first embodiment is that the opening 24 is not penetrated. The thickness of the remaining film 20C of the primary field oxide film 20A remaining at the time of this selective etching is an arbitrary thickness of about 800 nm or less. This primary field oxide film 20A
The channel stopper 17 of the silicon substrate 10 is covered and not exposed by the remaining film 20C. Through the above steps, the intermediate semiconductor device shown in FIG. 2C is obtained.

Next, as can be seen from FIG. 2D, the silicon substrate 10 is oxidized again by performing thermal oxidation again using the nitride film 16 as a mask to form a secondary field oxide film 20B. The field oxide film 20 is completed by forming the secondary field oxide film 20B.
Through the above steps, the intermediate semiconductor device shown in FIG. 2D is obtained.

Next, as can be seen from FIG.
The nitride film 16 as a mask is removed by E or RIE. Through the above steps, the intermediate semiconductor device shown in FIG. 2E is obtained. This completes the inter-element separation step. Thereafter, the semiconductor device is completed through an element forming step, a wiring step, and the like.

As described above, according to the second embodiment, the field oxide film 20 can be grown deep in the silicon substrate 10 as in the first embodiment. For this reason, the field oxide film 20 can be formed thick, so that the semiconductor device can be miniaturized and the field oxide film 20 can be flattened.

Moreover, the depth of the opening 24, that is, the remaining film 2
By controlling the thickness of Oc, the depth of field oxide film 20 that enters silicon substrate 10 can also be controlled. Therefore, a field oxide film 20 having a desired thickness can be formed. In addition, since the silicon substrate 10 can be protected by the remaining film 20C of the primary field oxide film 20A, damage to the silicon substrate 10 due to the formation of the opening 24 in the primary field oxide film 20A by RIE is reduced. Can be reduced.

The present invention is not limited to the above embodiment, but can be variously modified. For example, the channel stopper 17 need not always be provided. FIG. 3 is FIG.
FIG. 4E is a diagram corresponding to FIG. 3E, but it is also possible to omit the channel stopper as in the intermediate semiconductor device shown in FIG. That is, the channel stopper is formed to prevent an inversion layer from being formed at the interface between the field oxide film 20 and the silicon substrate 10.
By controlling the doping concentration of the silicon substrate 10, the formation of an inversion layer can be avoided. Further, by forming an opening in the secondary field oxide film 20B, a tertiary, quaternary,... Field oxide film can be formed.

[0028]

According to the present invention, after a primary field oxide film is formed, an opening is formed in the primary field oxide film, and a secondary field oxide film is formed in the opening portion, whereby a field oxide film is formed. A film was formed. Therefore, the field oxide film can be formed deep in the silicon substrate, and the semiconductor device can be miniaturized.

[Brief description of the drawings]

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

FIG. 2 is a process sectional view in a second embodiment of the present invention.

FIG. 3 is a diagram showing a modification in which a channel stopper is omitted.

FIG. 4 is a process cross-sectional view of a conventional semiconductor device.

[Explanation of symbols]

 Reference Signs List 10 silicon substrate 14 pad oxide film 16 nitride film (thin film) 16B opening (first opening) 17 channel stopper 20 field oxide film (field insulating film) 20A primary field oxide film 20B secondary field oxide film 22 opening (second Opening) 24 opening (second opening)

Claims (11)

[Claims] 1. A semiconductor device comprising a semiconductor substrate and a field insulating film for element isolation formed on a semiconductor substrate, wherein the field insulating film is provided at a central portion with a primary field insulating film disposed at a peripheral portion thereof. A semiconductor device comprising a secondary field insulating film disposed. 2. A semiconductor device comprising a field oxide film comprising a primary field oxide film having an opening formed at a central portion thereof and a secondary field oxide film formed at an opening of the primary field oxide film. A semiconductor device characterized by the above-mentioned. 3. The semiconductor device according to claim 2, wherein said opening of said primary field oxide film penetrates said primary field oxide film so that a semiconductor substrate is exposed. 4. The primary field oxide film according to claim 2, wherein the opening of the primary field oxide film does not penetrate the primary field oxide film and is formed halfway through the primary field oxide film.
3. The semiconductor device according to claim 1. 5. The semiconductor device according to claim 2, wherein a channel stopper is formed immediately below said field oxide film. 6. A semiconductor device comprising a field oxide film formed by performing a plurality of oxidations on a semiconductor substrate. 7. A step of forming an oxide film on a semiconductor substrate, a step of forming a nitride film on the oxide film, a step of forming a first opening in the nitride film, and a surface side of the semiconductor substrate. The first of the nitride films in
Forming a primary field oxide film in the opening portion of the semiconductor device; forming a second opening in the primary field oxide film; and forming a secondary field in the second opening portion on the front surface side of the semiconductor substrate. A method for manufacturing a semiconductor device, comprising: forming an oxide film. 8. The step of forming a second opening in the primary field oxide film includes forming a second opening penetrating the primary field oxide film to expose the semiconductor substrate. A method for manufacturing a semiconductor device according to claim 7. 9. The semiconductor according to claim 7, wherein in the step of forming the second opening in the primary field oxide film, the second opening is formed halfway through the primary field oxide film. Device manufacturing method. 10. The semiconductor device according to claim 7, wherein a channel stopper is formed in a field oxide film forming region of the semiconductor substrate before the step of forming the primary field oxide film. 13. The method for manufacturing a semiconductor device according to item 5. 11. A step of forming a thin film on a semiconductor substrate, a step of forming a first opening in the thin film, and oxidizing the first opening on the front side of the semiconductor substrate using the thin film as a mask. Forming a second opening by etching the primary field oxide film using the thin film as a mask; forming a second opening in the semiconductor substrate; Forming a secondary field oxide film by oxidizing the opening portion with the thin film used as a mask.