JPH07211774A - Method for manufacturing semiconductor device - Google Patents

Abstract

(57) [Abstract] [Purpose] The bird's beak generated when the element isolation silicon oxide film is formed by selective oxidation is small and the MOS
Provided is a method for manufacturing a semiconductor device having a small narrow channel effect that appears in a transistor. [Structure] The silicon nitride film 3 serving as a mask for selective oxidation is formed into an inverse taper shape, and the silicon nitride film is used as a mask to introduce a channel stopper 6 for selective oxidation. [Effect] Since the silicon nitride film has a reverse taper shape,
It is possible to suppress the formation of bird's beaks in which the silicon oxide film bites under the silicon nitride film and grows as compared with the case of the vertically-shaped silicon nitride film. Also, since the channel stopper is inside the position where the silicon nitride film and the pad oxide film are in contact with each other, the MO
It is difficult for the narrow channel effect such as the protrusion to be reduced in the region serving as the channel of the S transistor and the increase in Vth of the MOS transistor.

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, and more particularly to a method for manufacturing an element isolation region by selective oxidation.

[0002]

2. Description of the Related Art A conventional method of manufacturing a semiconductor device having an element isolation region formed by selective oxidation on a semiconductor substrate will be described with reference to FIGS. 2 (a) to 2 (c).

A pad silicon oxide film 2 is formed on a semiconductor substrate 1.
And the silicon nitride film 3 is formed. Next, leave the photoresist on the active area by photolithography,
Using this as a mask, the silicon nitride film on the element isolation region is removed. Then, using the silicon nitride film as a mask, impurities serving as channel stoppers 5 are introduced.
Then, the photoresist is peeled off. FIG. 2A is a diagram showing this state.

Then, the element isolation region is selectively oxidized using the silicon nitride film as a mask to form a field oxide film 4. FIG. 2B shows this state.

Finally, a semiconductor device having an element isolation region formed by selective oxidation on a semiconductor substrate by removing the silicon nitride film was manufactured. Note that FIG. 2C shows this state.

[0006]

In the prior art, when the element isolation field oxide film is formed by selective oxidation, the silicon oxide film for element isolation bites under the silicon nitride film and grows. Will be formed. This bird's beak is a major obstacle to LSI integration.

Further, when the element isolation field oxide film is formed, the impurities introduced as the channel stoppers are extruded into the region serving as the channel of the MOS transistor of the transistor, so that the narrow channel effect such as the increase of Vth of the MOS transistor is produced. Appears and hinders miniaturization.

Therefore, the present invention is intended to solve these problems, and an object of the present invention is to provide a MOS.
An object of the present invention is to provide a method for manufacturing a semiconductor device having an element isolation oxide film having a small bird's beak and a small narrow channel effect of a transistor.

[0009]

A method of manufacturing a semiconductor device according to the present invention is a method of manufacturing a semiconductor device having an element isolation region formed on a semiconductor substrate by selective oxidation, wherein a pad silicon oxide film is formed on the semiconductor substrate. Forming step, forming a silicon nitride film on the silicon oxide film, removing the silicon nitride film on the element isolation region of the semiconductor substrate, and forming the silicon nitride film in an inverse tapered shape on the active region. A step of leaving, a step of introducing impurities serving as a channel stopper using the silicon nitride film as a mask, a step of forming a field oxide film by selectively oxidizing the element isolation region of the semiconductor substrate, and a step of removing the silicon nitride film It is characterized by comprising a step of

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a method of manufacturing a semiconductor device of the present invention will be described with reference to FIGS. 1 (a) to 1 (c).

First, a pad silicon oxide film 2 having a thickness of 100 Å to 500 Å is formed on a semiconductor substrate 1 in wet oxygen at 800 ° C. to 900 ° C. for about 10 minutes.
Formed by thermal oxidation for 1 to 40 minutes, and further 1
A silicon nitride film 3 having a thickness of 000 angstroms to 2000 angstroms is formed by a chemical vapor deposition method using a gas of SiH ₂ Cl ₂ and NH ₃ .

Then, the photoresist is left on the active region by photolithography, the silicon nitride film in the field region is removed by dry etching using a plasma etching device so as to have an inverse taper shape, and the photoresist is peeled off. .

The etching condition at this time is about 50.
using cc / min flow rate CF ₄ gas, usually about 300W
The RF power of about 100 W is set to a low RF power of about 100 W, and about 0.2 Tarr is usually processed at a pressure of about 0.1 Tarr. At this time, it should be remembered that the processing temperature is kept at 20 to 60 degrees. By etching the silicon nitride film under such conditions, it is possible to obtain an etching shape of the silicon nitride film having an inverse taper where the etching shape is vertical.

Then, using the silicon nitride film as a mask, impurities to serve as the channel stopper 6 are introduced by ion implantation. When forming an N-type MOS transistor, 1 × 10 ¹⁴ to 1 × 10 ¹⁵ ions are implanted with B or BF ₂ at an acceleration energy of 20 keV to 40 keV. At this time, since the nitride film has a reverse taper shape, the channel stopper is inside the position where the silicon nitride film and the pad oxide film are in contact with each other. A diagram showing this state is shown in FIG.

Then, by performing thermal oxidation in wet oxygen at about 1000 ° C. for about 2 hours, the element isolation field oxide film 4 of about 5000 Å to 7000 Å is selectively formed. FIG. 1B is a diagram showing this state.

The length of the bird's beak generated during the selective oxidation decreases as the silicon nitride film becomes thicker. This is because if the silicon nitride film is thickened, the stress in the vicinity of the edge of the silicon nitride film, in other words, at the place where the bird's beak is generated is increased, and the progress of oxidation to the lower side of the silicon nitride film is suppressed. In the case of the present invention, the silicon nitride film serving as a mask at the time of selective oxidation has an inverse taper shape. Therefore, at the initial stage of selective oxidation (when the oxidation time is short), the stress at the edge of the silicon nitride film is increased by the amount of the inverse taper shape. This is because the reverse taper-shaped silicon nitride film has the same effect as the thickened silicon nitride film at the edge of the silicon nitride film. Therefore, it is possible to suppress the formation of bird's beaks in which the silicon oxide film bites under the silicon nitride film to grow, rather than the vertical silicon nitride film. As the selective oxidation progresses (bird's beak digs under the silicon nitride film),
Since the center of stress moves to the inside of the nitride film edge, the stress at the nitride film edge decreases.

Therefore, when the silicon nitride film is formed into an inverse taper shape, bird's beak 5 generated by selective oxidation
However, it is needless to say that the silicon nitride film is smaller than that in the vertical shape because it is suppressed in the initial stage of selective oxidation. Moreover, since the bird's beak is not reduced by increasing the silicon nitride film thickness, the occurrence of crystal defects is small.

Further, the channel stopper spreads during this selective oxidation, but since the channel stopper is inside the position where the silicon nitride film and the pad oxide film are in contact with each other, the region which becomes the channel of the MOS transistor of the transistor is formed. The narrow channel effect such that the amount of protrusion is reduced and the Vth of the MOS transistor is increased becomes difficult to appear.

Then, as shown in FIG. 1C, an element isolation silicon oxide film is formed by stripping the silicon nitride film with hot phosphoric acid.

[0020]

As described above, according to the present invention, since the silicon nitride film serving as a mask at the time of selective oxidation has an inverse taper shape, the force of the silicon nitride film for suppressing the pad oxide film is At the edge of the film, the reverse taper shape makes it stronger. Therefore, it is possible to suppress the formation of bird's beaks which the silicon oxide film tries to dig under the silicon nitride film to grow, as compared with the case of the vertically-shaped silicon nitride film.

Further, according to the present invention, since the channel stopper is located inside the position where the silicon nitride film and the pad oxide film are in contact with each other, the protrusion in the channel region of the MOS transistor of the transistor is reduced. , M
A narrow channel effect such as an increase in Vth of the OS transistor is less likely to appear.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a method for manufacturing a semiconductor device of the present invention.

FIG. 2 is a diagram showing a conventional method for manufacturing a semiconductor device.

[Explanation of symbols]

 1 semiconductor substrate 2 pad oxide film 3 silicon oxide film 4 field oxide film 5 bird's beak 6 channel stopper

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 27/08 A 9170-4M

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor device comprising an element isolation region formed by selective oxidation on a semiconductor substrate, the step of forming a pad silicon oxide film on the semiconductor substrate, and a silicon nitride film on the silicon oxide film. And a step of removing the silicon nitride film on the element isolation region of the semiconductor substrate and leaving the silicon nitride film in an inverse taper shape on the active region, and a channel stopper using the silicon nitride film as a mask. A step of introducing an impurity, a step of forming a field oxide film by selectively oxidizing the element isolation region of the semiconductor substrate, and a step of removing the silicon nitride film. Method.