JPH0521596A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To easily manufacture a high reliability semiconductor device whose operating speed is high. CONSTITUTION:An SiO2 film 14 having a central thin film part 14a and thick film parts 14b on both sides of the thin film part 14a is formed as a field oxide film. Photoresist 15 is so patterned that the end edge of an aperture 15a is positioned above the vicinity of the central part of the thick film part 14b. From above the SiO2 film 14 in an aperture 15a, impurities 16 are ion-implanted at an energy, e.g. that the thickness of the thin film part 14a becomes nearly equal to a projection range. Thereby a P<+> diffusion layer 17, as a channel stopper, is formed only under the central part of the SiO2 layer 14, in a self- alignment manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device in which element isolation is performed by a field oxide film and a channel stopper.

[0002]

2. Description of the Related Art In a monolithic IC, it is necessary to electrically separate a large number of elements arranged on one semiconductor chip. One of such element isolation techniques is dielectric isolation, and a typical technique of dielectric isolation is a method of performing element isolation by a field oxide film by the LOCOS method.

Further, the threshold voltage of the parasitic MOS transistor whose channel region is below the field oxide film is set higher than the potential of the wiring on the field oxide film, and the parasitic MOS transistor is completely operated within the operating voltage range of the IC. In order to cut off and thereby complete element isolation, a channel stopper, which is a high-concentration impurity diffusion layer of the same conductivity type as the semiconductor substrate, is formed under the field oxide film.

By the way, one of the methods of forming such a channel stopper is a method of ion-implanting an impurity for forming a channel stopper into a semiconductor substrate before forming a field oxide film. In this method, impurities are ion-implanted by using the oxidation resistant film when forming the field oxide film as a mask, and the impurities are diffused by the heat at the time of thermal oxidation, so that the channel stopper is formed simultaneously with the formation of the field oxide film. Form.

However, in this method, when the channel stopper spreads to the active region and an impurity diffusion layer having a conductivity type opposite to that of the channel stopper is formed in the active region, the impurity diffusion layer and the channel stopper are in contact with each other. For this reason,
The junction capacitance between the impurity diffusion layer and the channel stopper increases or the junction breakdown voltage decreases. As a result, the operating speed of the element formed in the active region is reduced and the reliability is also reduced.

Therefore, as another method of forming the channel stopper, a method of ion-implanting impurities after forming the field oxide film is considered. In this method, so-called field ion implantation is performed in which the active region is covered with a photoresist after the field oxide film is formed, and impurities are ion-implanted from above the field oxide film using the photoresist as a mask.

[0007]

However, even in this method, when the photoresist is misaligned with respect to the field oxide film due to misalignment of the mask in the lithography process, the impurity diffusion layer in the active region and the channel stopper are not formed. Will still come into contact. Therefore, it has not been possible to easily manufacture a semiconductor device having a high operating speed and high reliability by any of the conventional methods.

Therefore, an object of the present invention is to provide a method of manufacturing a semiconductor device which can easily manufacture a semiconductor device having a high operation speed and high reliability.

[0009]

According to the method of manufacturing a semiconductor device according to the present invention, a thin film portion having a relatively thin film thickness is formed at a central portion of a region sandwiched between active regions, and a thin film portion is formed on both sides of the thin film portion. A field oxide film having a thick film portion having a relatively thick film thickness is formed on the surface of the semiconductor substrate, and has a portion corresponding to the thin film portion of the thick film portion and an opening corresponding to the thin film portion. A mask is formed on the semiconductor substrate, and an impurity for forming a channel stopper is ion-implanted into the semiconductor substrate through the opening.

[0010]

In the method of manufacturing a semiconductor device according to the present invention, the impurity for forming the channel stopper is ion-implanted on the semiconductor substrate so that the film thickness of the thin film portion of the field oxide film becomes approximately the projection range. The thick film portion of the field oxide film as well as the mask formed in step 2 serves as a mask during ion implantation. Moreover, the opening of the mask corresponds not to the entire thick film portion but to only a part connected to the thin film portion and the thin film portion.

Therefore, even if the mask is slightly displaced from the field oxide film, the channel stopper can be formed in a self-aligning manner only under the central portion of the field oxide film. Therefore, when an impurity diffusion layer having a conductivity type opposite to that of the channel stopper is formed in the active region, the impurity diffusion layer and the channel stopper are separated from each other, and the junction capacitance between them is small and the junction breakdown voltage is high.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

In this embodiment, as shown in FIG.
Type SiO ₂ film 12 for pad on the surface of Si wafer 11
And a Si ₃ N ₄ film 13 is deposited on the SiO ₂ film 12. Then, the Si ₃ N ₄ film 13 is patterned to form a Si ₃ N ₄ film 13a having a pattern in the active region and a Si ₃ N ₄ film 13b having a pattern along the central portion of the element isolation region sandwiched between the active regions. To form.

Next, thermal oxidation is performed in this state. Then,
As shown in FIG. 1B, the Si ₃ N ₄ film 13 becomes an oxidation resistant film, and a portion of the Si wafer 11 which is not covered with the Si ₃ N ₄ film 13 is selectively oxidized, resulting in a field. A SiO ₂ film 14 which is an oxide film is formed on the surface of the Si wafer 11.

However, such selective oxidation (LOCOS)
In the method, the SiO ₂ film 14 bites laterally in the end portion of the Si ₃ N ₄ film 13 to generate bird's beak. Therefore, bird's beaks also bite into the bottom of the Si ₃ N ₄ film 13b from both sides, and the thin SiO ₂ film 14 is formed also in this portion.

Therefore, the thin film portion 14a located under the Si ₃ N ₄ film 13b, the thick film portions 14b located on both sides of the thin film portion 14a, and the bird's beak 14c connected to these thick film portions 14b, SiO with a hollow center
_{The 2} film 14 is formed as a field oxide film.

If the width of the Si ₃ N ₄ film 13b is narrowed, the bird's beaks that bite from both sides below the Si ₃ N ₄ film 13b will be overlapped with each other, and the thin film portion 14a.
Becomes thicker. On the contrary, when the width of the Si ₃ N ₄ film 13b is widened, the above-mentioned overlap is reduced and the thin film portion 1
The film thickness of 4a becomes thin. Therefore, the film thickness of the thin film portion 14a can be adjusted by the width of the Si ₃ N ₄ film 13b.

Next, as shown in FIG. 1C, Si ₃ N ₄
After removing the film 13, a photoresist 15 is applied, and the photoresist 15 is patterned so that the edge of the opening 15a of the photoresist 15 is located above the central portion of the thick film portion 14b.

Next, as shown in FIG. 1D, with the photoresist 15 as a mask, the SiO ₂ film 1 in the opening 15a is formed.
4 from above, for example, the thin film portion 14 of the SiO ₂ film 14
P-type impurities 16 such as boron are ion-implanted into the Si wafer 11 with such energy that the film thickness of “a” becomes approximately the projection range.

As a result, the P ⁺ diffusion layer 17 serving as a channel stopper is formed below the thin film portion 14a, that is, below the central portion of the SiO ₂ film 14. Then, the photoresist 15 and the SiO ₂ film 12 are removed, and an element such as a MOS transistor is formed in the active region surrounded by the SiO ₂ film 14.

[0021]

According to the method of manufacturing the semiconductor device of the present invention, even if the mask for ion-implanting the impurity for forming the channel stopper is displaced with respect to the field oxide film, the impurity of the conductivity type opposite to that of the channel stopper is used. When the diffusion layer is formed in the active region, the impurity diffusion layer and the channel stopper are separated from each other, and the junction capacitance between them is small and the junction breakdown voltage is high. Therefore, a semiconductor device having a high operating speed and high reliability can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a side sectional view sequentially showing an embodiment of the present invention.

[Explanation of symbols]

11 Si Wafer 14 SiO ₂ Film 14a Thin Film Part 14b Thick Film Part 15 Photoresist 15a Opening 16 Impurity 17 P ⁺ Diffusion Layer

Claims (1)

Claim: What is claimed is: 1. A thin film portion, which is located in the central portion of the region sandwiched by the active regions and has a relatively thin film thickness, and a thin film portion, which is located on both sides of this thin film portion, and is relatively thick A field oxide film having a thick film portion is formed on a surface of a semiconductor substrate, and a mask having an opening corresponding to a portion of the thick film portion connected to the thin film portion and the thin film portion is formed on the semiconductor substrate. Then, a method of manufacturing a semiconductor device in which an impurity for forming a channel stopper is ion-implanted into the semiconductor substrate from the opening.