JPH04290471A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce capacitance between an element region and a substrate and provide a method for fabricating a semiconductor device having good characteristic MOS transistor structure by forming a thin oxide film at an end of a field oxide film and further providing a layer whose impurity concentration is lower than that of a channel stop layer immediately under the field oxide film between the channel stop layer and the element region. CONSTITUTION:A thin oxide film 21 of predetermined width is provided between a field oxide film 22 surrounding an element region of a MOS transistor and the element region, while a layer 51 of low impurity concentration is formed between a p<+>-type channel stop layer 52 and an element region diffusion layer. Thus impurities in the p<+>-type channel stop layer will not diffuse directly into the element region, thereby preventing reduction in effective channel width.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to MOS (Metel
The present invention relates to a method of manufacturing a semiconductor device having a transistor structure (Oxide Semiconductor).

0002

[Prior art] LOCOS (Loc) is an element isolation technology.
The al oxidation of silicon method is widely known. In such devices, LOCOS
A channel stop layer is formed under the thick field oxide film formed by the method.

FIG. 4 is a cross-sectional view of each step of forming an NMOS transistor structure using the LOCOS method. When forming the field oxide film 2 surrounding the NMOS transistor structure, the surface of the active region 4 of the p-Si substrate 1 is coated with silicon nitride (Si3 N4).
It is covered with a film 3 (as shown in FIG. 3(a)). This Si3N
4 By using the film 3 as a mask, it is possible to selectively diffuse ions for forming the p-type channel stop layer 5, and at the same time prevent the formation of an oxide film in the active region (see FIG. b) As shown). Furthermore, after forming the field oxide film 2, the Si3N4 thin film 3 is removed and the gate electrode (G) etc. are formed.
A semiconductor device having the NMOS transistor structure shown in ) can be obtained.

0004

However, when the above manufacturing method is used, the impurity of the p-type channel stop layer 5 tends to diffuse into the active region 4 of the NMOS transistor, and as shown in FIG.
The effective channel width t shown in (b) is reduced, leading to deterioration of frequency characteristics. Furthermore, the drain electrode (
The capacitance between the n+ type diffusion layers 8 and 9 where the source electrode (S) and the source electrode (S) are formed and the p type channel stop layer 5 in the p-Si substrate 1 increases, resulting in deterioration of frequency characteristics and breakdown voltage. causing a decline.

[0005] Furthermore, the bird's beak of the field oxide film 2 formed thickly by the LOCOS method invades the device region, resulting in the problem that the device cannot be formed according to the designed value, and stress occurs at the boundary between the device region and the field oxide film 2. crystal defects may occur, or the field oxide film 2 may
Aluminum (Al)
There was a problem in that wires using wires such as wires were disconnected.

[0006] The above-mentioned disadvantage becomes a particularly serious drawback when preventing the generation of a parasitic MOS transistor in which the wiring on the field oxide film is used as a gate electrode and the field oxide film is used as the gate oxide film. This is because, in order to prevent parasitic transistors, it is necessary to make the channel stop layer highly doped or to make the field oxide film thicker. If this is done, the frequency characteristics will deteriorate as described above, or the substrate This is because the level difference on the surface becomes large.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a semiconductor device that solves the above problems.

[0008]

[Means for Solving the Problems] The present invention provides a method for manufacturing a semiconductor device in which a MOS transistor structure is formed using the LOCOS method. A second step of forming a first oxidation resistant film, a third step of selectively removing the first oxidation resistant film in the field region, and a second step of forming a silicon substrate using the first oxidation resistant film as a mask. a fourth step of implanting ions at a low concentration; a fifth step of selectively oxidizing the silicon substrate using the first oxidation-resistant film as a mask to form an oxide film; and removing the first oxidation-resistant film. a sixth step of depositing a second oxidation-resistant film over the entire surface; and a seventh step of selectively removing the second oxidation-resistant film, leaving the device region and a predetermined width region at its end.
an eighth step of implanting impurity ions of the same conductivity type as the ions into the silicon substrate at a high concentration using the second oxidation-resistant film as a mask, and selectively oxidizing the silicon substrate using the second oxidation-resistant film as a mask. and a ninth step of forming a thick field oxide film.

[0009]

According to the present invention, after a thin oxide film is formed in the region surrounding the element region of an NMOS transistor, a field oxide film is provided in the field region except for the region oversized than the element region. Therefore, when forming a field oxide film using the LOCOS method, the previously formed thin oxide film of a predetermined width can block the bird's beak from entering directly under the mask covering the element region.

Further, since a low concentration impurity layer is provided directly under the above-mentioned thin oxide film having a predetermined width, the channel stop layer directly under the field oxide film does not directly reach and contact the element region.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The content of the present invention will be described below with reference to FIGS. 1 and 2, taking an NMOS transistor structure as an example.

First, a p-Si substrate 1 is prepared, and a SiO2 film 2 is formed on its upper surface. Next, using the CVD method, the first Si3 N4 film 31, which is an oxidation-resistant film, is made of SiO2
A resist material 4a is deposited on the film 2, and a resist material 4a is spin-coated on the upper surface thereof (as shown in FIG. 1(a)).

Next, the resist material 4a is patterned by photolithography to form a first resist mask 4.
form 1. At this time, a pattern is formed so as to have an opening in the field oxide film formation region surrounding the element region of the NMOS transistor formed on the p-Si substrate 1. Through this first resist mask 41, the first Si3
The N4 film 31 is etched to selectively expose the SiO2 film 2. Thereafter, boron ions are implanted from above at a low concentration to form a layer 51 with a low impurity concentration on the p-Si substrate 1 (as shown in FIG. 2B).

After that, the first resist mask 41 is removed by ashing or the like, and the first Si3 N4 film 3 is removed.
Field oxidize the surface with 1 remaining. As a result, only the exposed portion of the SiO2 film 2 on the substrate is oxidized, resulting in a thin oxide film 21 (as shown in FIG. 3(c)).

Next, the first Si3 N4 film 31 is removed, and a second Si3 N4 film 32 is newly formed on its surface. Thereafter, a resist material 4b is spin-coated on the second Si3 N4 film 32 (as shown in FIG. 2(a)).

Next, the resist material 4b is patterned by photolithography, and a second resist mask 42 is formed.
form. At this time, a second resist mask 42 is formed so as to have an opening in a region other than the element formation region of the p-Si substrate 1 and a predetermined width region at the end of the thin oxide film 21 surrounding it. The second Si3 N4 film 32 is etched through this second resist mask 42 to selectively expose the thin oxide film 21. Thereafter, boron ions are implanted from above at a high concentration to form a p+ type channel stop layer 52 on the p-Si substrate 1 (FIG. 1(b)).
(Illustrated).

Next, the second resist mask 42 is removed, and the surface is field oxidized with the second Si3 N4 film 32 remaining. As a result, only the exposed portion of the thin oxide film 21 of the substrate is oxidized, resulting in a thick field oxide film 22 (as shown in FIG. 2(c)).

After that, the second Si3N4 film 32 is removed and a gate electrode (G), a source electrode (S), and a drain electrode (D) are formed to obtain the intended semiconductor device. can.

According to the above manufacturing method, a thin oxide film 21 is formed in advance in a region surrounding the element region of the NMOS transistor, and field oxidation is performed in a region narrower than this oxide film 21. For this reason, when forming a thick field oxide film 22 using the LOCOS method, the oxide film 22 of a predetermined width prevents the bird's beak from entering directly under the mask covering the element region.
1 can be prevented. Furthermore, the difference in level between the element forming surface and the field oxide film 22 can be reduced.

FIG. 3 is a diagram showing a semiconductor device obtained through the above-described manufacturing process. FIG. 3(a) is a top view, FIG. 3(b) is a cross-sectional view along B1-B2, and FIG. ) is C1
-C2 sectional view. A thin oxide film 21 having a predetermined width is provided in the boundary region between the element region of the p-Si substrate 1 and the field region where the field oxide film is formed. Further, a p+ type channel stop layer 52 is provided directly below this field oxide film 22, and a low concentration impurity layer 51 is formed directly below the oxide film 21 having a predetermined width.

Therefore, the p+ type channel stop layer 52
Since there is no risk of directly reaching and contacting the n+ type diffusion layers 8 and 9 in the element region, the withstand voltage will not decrease. Further, as shown in FIG. 2B, the effective channel width t is not narrowed by the p+ type channel stop layer 52. Further, since the oxide film 21 with a predetermined width is provided, the difference in level between the element region and the field region can be alleviated, and stress can be prevented from occurring.

[0022] In this embodiment, a method for manufacturing a semiconductor device having an NMOS transistor structure has been described.
It is fully possible to apply the present invention to semiconductor devices having other structures such as a PMOS transistor structure.

[0023]

As explained above, according to the present invention, by forming a thin oxide film with a predetermined width, it is possible to prevent the bird's beak of the field oxide film from entering the device region. can be formed. Furthermore, since the difference in level between the element region and the field oxide film surrounding the element area is alleviated, stress is less likely to occur in the substrate, preventing the occurrence of crystal defects, which may lead to disconnection of wiring at the step part. Nor.

Furthermore, in order to form a layer containing a low concentration of impurities of the same type as the channel stop layer between the element region diffusion layer and the channel stop layer surrounding it, the element region diffusion layer and the channel stop layer surrounding it are formed. It is possible to prevent deterioration of the withstand voltage at the junction with the layer. Furthermore, the effective channel width is not reduced, the capacitance between the element region diffusion layer and the channel stop layer is reduced, and deterioration of the frequency characteristics of the MOS transistor can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of each step of a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of each step of a semiconductor device according to an embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of a semiconductor device manufactured through a process according to the present invention.

FIG. 4 is a cross-sectional view of each step of a semiconductor device according to a conventional manufacturing method.

[Explanation of symbols]

1...p-Si substrate 21...Thin oxide film 22...Field oxide film 31...First Si3N4 film 32...Second Si3N4 film 41...First resist mask 42...Second resist mask 51...Low concentration impurity layer 52...p+ type channel stop layer 8...Drain region 9...Source area 10...Gate oxide film

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor device in which a MOS transistor structure is formed using a LOCOS method, comprising: a first step of forming an oxide film on a surface of a silicon substrate;
a second step of forming a first oxidation resistant film on the entire surface; a third step of selectively removing the first oxidation resistant film in the field region; and a masking of the first oxidation resistant film. As,
a fourth step of implanting low concentration ions into the silicon substrate; a fifth step of selectively oxidizing the silicon substrate using the first oxidation-resistant film as a mask to form an oxide film;
a sixth step of removing the first oxidation resistant film and depositing a second oxidation resistant film on the entire surface; a seventh step of selectively removing the oxidation-resistant film; an eighth step of implanting impurity ions of the same conductivity type as the ions into the silicon substrate at a high concentration using the second oxidation-resistant film as a mask; Said second
a ninth step of selectively oxidizing the silicon substrate using the oxidation-resistant film as a mask to form a thick field oxide film.