JPH03101251A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To enable formation of an isolation region having a high breakdown strength by forming a P-type impurity diffusion layer only around the middle of a semiconductor substrate of the isolation region. CONSTITUTION:An oxide film 2 is formed on a surface of a semiconductor substrate 1, and a nitride film 3 and a photoresist film 4 are formed thereon. An opening part is formed selectively in a photoresist film 4 and a nitride film 3. The photoresist film 4 is baked to form a photoresist film 4' which creeps in from an end of the nitride film 3. Then, boron implantation is carried out using the photoresist film 4' as a mask to form a P-type impurity diffusion layer 5 selectively on a surface of the semiconductor substrate 1. Since the P-type impurity diffusion layer 5 of high concentration is thereby formed only around the middle of the P-type semiconductor substrate 1 of the isolation region, a P-N junction is formed by an N-type impurity diffusion layer and the P-type semiconductor substrate 1. Accordingly, it is possible to relax the electric field inside a depletion layer which extends from the P-N junction and to form an isolation region having high breakdown strength.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a semiconductor device in which an element isolation region is formed by a LOGO3 oxidation process.

(Prior Art) In recent years, with the increasing integration and density of semiconductor devices, isolation between circuit elements has become increasingly important.

Conventionally, when forming isolation regions between MOS transistor elements by oxide film isolation method (LOGO8), isolation between elements is achieved by selectively implanting boron ions into the entire isolation region using nitride and photoresist as a mask. There are known methods to increase

A conventional method for manufacturing a semiconductor device will be described below.

FIG. 2 is a cross-sectional view of an element isolation region at the main process stage of a conventional semiconductor device, in which 1 is a semiconductor substrate made of P-type silicon, 2 is an oxide film formed on the surface of the semiconductor substrate 1, and 3 is a nitride film selectively formed on the surface of the oxide film 2, 4 is a photoresist film selectively formed on the surface of the nitride film 3, 5 is a P-type impurity diffusion layer, and 6 is a LO
A GO8 oxide film 7 indicates an N-type impurity diffusion layer selectively formed on the surface of the semiconductor substrate 1.

That is, in the conventional method of manufacturing a semiconductor device, as shown in FIG.
), an oxide film 2 is formed on the surface of a semiconductor substrate 1, and a nitride film 3 and a photoresist film 4 are formed thereon.
form. Next, after selectively forming openings 8 in the photoresist film 4 and nitride film 3 by photolithography and etching, boron ions are implanted.
Next, as shown in FIG. 2(b), the photoresist film 4 is removed and oxidized to form a LOGO8 oxide film 6, which will become the source/drain region. The N-type impurity diffusion layer 7 was selectively formed.

(Problems to be Solved by the Invention) However, the above method does not allow for high integration and
With the increase in density, a high concentration P-type impurity diffusion layer 5 is required in a region with a short separation width, which causes a problem in that the breakdown voltage of the device becomes low.

(Purpose of the invention) The present invention solves the above-mentioned conventional problems.

An object of the present invention is to provide a method for manufacturing a semiconductor device that enables formation of an element isolation region with high breakdown voltage.

(Means for Solving the Problems) In order to achieve this object, the method for manufacturing a semiconductor device of the present invention includes a step of selectively forming a P-type impurity diffusion layer only in the vicinity of the center of the semiconductor substrate in the element isolation region. Let's do it.

(Function) In the method for forming an element isolation region according to the present invention, ions are selectively implanted only in the center of the semiconductor substrate in the element isolation region, so that the formed high concentration P-type impurity diffusion layer becomes an N-type impurity diffusion layer of the element. Since it does not spread to the impurity diffusion layer, an element isolation region with high breakdown voltage can be formed.

(Example) An example of the present invention will be described below with reference to the drawings.

FIGS. 1A to 1C show cross-sectional views of an element isolation region at main process steps in an embodiment of the present invention. 1st
In Figure Ca), 1 is a semiconductor substrate made of P-type silicon, 2 is an oxide film formed on the surface of the semiconductor substrate 1,
Reference numeral 3 indicates a nitride film selectively formed on the surface of the oxide film 2, and reference numeral 4 indicates a photoresist film selectively formed on the surface of the nitride film 3.

In FIG. 1(b), 4' indicates a photoresist film after baking the photoresist film 4, and 5 indicates a P-type impurity diffusion layer selectively formed using the photoresist film 4' as a mask.

In FIG. 1(c), 6 indicates an LOC:O8 oxide film, and 7 indicates an N-type impurity diffusion layer selectively formed on the surface of the semiconductor substrate 1. In FIG.

First, as shown in FIG. 1(a), a semiconductor substrate 1
An oxide film 2 is formed on the surface of the oxide film 2, and a nitride film 3 is formed on it.
and a photoresist film 4 is formed.

Next, openings 8 are selectively formed in the photoresist film 4 and the nitride film 3 by photolithography and etching.Next, the photoresist film 4 is heated to 180° C. as shown in FIG. 1(b). After forming a photoresist film 4' that penetrates about 0.3 microns from the edge of the nitride film 3 by baking at a temperature of about 100 mL, boron is implanted using the photoresist film 4' as a mask to form a semiconductor substrate. A P-type impurity diffusion layer 5 is selectively formed on the surface of 1. As a result, a high concentration P-type impurity diffusion layer 5 is formed only near the center of the P-type semiconductor substrate 1 in the element isolation region.
Since the PN junction is formed between the N type impurity diffusion layer and the P
type semiconductor substrate 1. Therefore, P
The electric field in the depletion layer extending from the N junction is relaxed, and an element isolation region with high breakdown voltage can be formed.

(Effects of the Invention) As explained above, the present invention forms an element isolation region with a high breakdown voltage by selectively forming a P-type impurity diffusion layer only near the center of a semiconductor substrate in an element isolation region. This makes it possible to realize an excellent method for manufacturing semiconductor devices.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor device at a main process step in a method for manufacturing a semiconductor device according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of a semiconductor device at a main process step in a conventional method for manufacturing a semiconductor device. . 1... P-type silicon semiconductor substrate, 2... Oxide film, 3... Nitride film, 4°4'...
Photoresist film, 5... P-type impurity diffusion layer,
6... LOGO8 oxide film, 7... N-type impurity diffusion layer, 8... Opening part.

Claims (1)

[Claims] A method for manufacturing a semiconductor device, which comprises selectively forming a P-type impurity diffusion layer only in the vicinity of the center of the semiconductor substrate in the element isolation region when forming the element isolation region on the semiconductor surface by a LOCOS oxidation process.