JPH10209124A - Dry etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a through hole superior in anisotropic form without etching a titanium nitride film formed below an interlayer oxide film. SOLUTION: In a first stage, the mixed gas of C4 F8 /O2 with the ratio of 1:1 is used and pressure 1mTorr, RF substrate bias power 700W and microwave power 1500W are applied, plasma by electron resonance is generated, the interlayer oxide film 3 about 80% thick is etched and the through hole 51 is formed. In a second stage, the mixed gas of C4 F8 /O2 with the ratio of 4:3 is used, pressure 1mTorr, RF substrate bias power 700W and microwave power 1500W are applied, a plasma is generated, the interlayer oxide film 3 remaining about 20% thick is etched and a through hole 52 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method, and more particularly to a dry etching method for forming a through hole for electrically connecting metal wirings having a multilayer structure.

[0002]

2. Description of the Related Art FIGS. 5 and 6 are sectional views sequentially showing an example of a dry etching method for forming a through hole as a conventional technique. First, a titanium nitride film 2 is formed on an aluminum wiring 1 and, for example, a silicon oxide film is deposited on the titanium nitride film 2 to form an interlayer oxide film 3. Here, the titanium nitride film 2 is formed to improve the electromigration characteristics of the aluminum wiring.

Next, a photoresist 4 having an opening above a region where a through hole is to be formed is formed on the interlayer oxide film 3 (FIG. 5), and anisotropic oxide film dry etching is performed using the photoresist 4 as a mask. As a result, a through hole 53 is formed (FIG. 6).

[0004]

With the recent increase in the degree of integration and performance of semiconductor devices, the technical problems required for the dry etching method for forming through holes have become more and more severe. For example, in a semiconductor device having a metal wiring having a multilayer structure as shown in FIG. 7, a certain bottom diameter is required at a desired position of an interlayer oxide film and in order to securely connect an upper aluminum wiring and a lower aluminum wiring. It is necessary to form a through hole having the same. Furthermore, in order to improve the reliability of the through-hole resistance, only the interlayer oxide film is etched,
It is necessary to leave the underlying titanium nitride film and aluminum wiring without etching.

However, if a conventional dry etching method is used to form a through hole having an excellent anisotropic shape in order to secure a constant bottom diameter, it is inevitable to select an interlayer oxide film / titanium nitride film by etching. The dry etching is performed under the condition that the ratio is low. Therefore, as shown in FIG. 6, the titanium nitride film 2 formed under the interlayer oxide film 3 and the titanium nitride film 2 Is etched down to the aluminum wiring 1 thereunder.

On the other hand, in order to prevent the underlying titanium nitride film from being etched, dry etching is initially performed under conditions where the etching selectivity between the interlayer oxide film and the titanium nitride film is high, as shown in FIG. In addition, since the anisotropic shape of the through hole 54 is deteriorated and the bottom diameter is reduced, there may be adverse effects such as a poor contact between the metal wirings and an extremely large through hole resistance.

Therefore, without etching the underlying titanium nitride film using the conventional dry etching method,
Further, in order to form a through hole having a constant bottom diameter, it is necessary to increase the top diameter of the through hole. However, when the through holes are close to each other as shown in FIG. However, there is a problem that a through hole cannot be formed.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and does not require etching of a titanium nitride film formed under an interlayer oxide film, and is excellent in anisotropic shape. An object is to obtain a dry etching method for forming a hole.

[0009]

Means for Solving the Problems Claim 1 of the present invention
The dry etching method according to the above, in a semiconductor device in which a silicon oxide film is deposited on a titanium nitride film,
(A) using a mixed gas of C ₄ F ₈ and O ₂ to selectively etch while leaving the silicon oxide film in a range where the titanium nitride film is not exposed, and (b) step (a) Etching the remaining silicon oxide film using a mixed gas of C ₄ F ₈ and O ₂ having a higher gas ratio of C ₄ F ₈ than the mixed gas used. is there.

According to a second aspect of the present invention, there is provided a dry etching method according to the second aspect, wherein (a) a mixed gas of C ₄ F ₈ and O _{2 in} a semiconductor device having a silicon oxide film deposited on a titanium nitride film. Generating a plasma by applying a predetermined microwave power to the silicon oxide film and selectively etching the silicon oxide film while leaving the titanium nitride film unexposed; (b) C ₄ F Generating a plasma by applying a microwave power higher than the microwave power applied in the step (a) using a mixed gas of ₈ and O ₂ to etch the remaining silicon oxide film; It is characterized by having.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 to 4 are sectional views sequentially showing a dry etching method according to the first embodiment of the present invention. First, a titanium nitride film 2 is formed on an aluminum wiring 1,
For example, a silicon oxide film is deposited on the titanium nitride film 2 to form an interlayer oxide film 3 (FIG. 1). Here, the titanium nitride film 2 is formed to improve the electromigration characteristics of the aluminum wiring.

Next, a photoresist 4 having an opening above a region where a through hole is to be formed is formed on the interlayer oxide film 3 (FIG. 2).

Next, through-holes are formed by performing dry etching through the following steps using an ECR etching apparatus. First, as a first step, through-holes 51 are formed by etching about 80% of the interlayer oxide film 3 under the condition of low interlayer oxide film / titanium nitride film etching selectivity but strong anisotropy (FIG. 3). .

The reason why "80%" is set here is that it is better to etch the interlayer oxide film 3 as thickly as possible in this first step in order to form a through hole having an excellent anisotropic shape. Interlayer oxide film 3 deposited on titanium film 2
The titanium nitride film 2 formed under the interlayer oxide film 3 is etched in consideration of the fact that the thickness variation of the film is about ± 10% of the target thickness and that the etching rate varies. In order to avoid this, the etching is limited to about 80%.

Next, as a second step, the remaining about 20% of the interlayer oxide film 3 is formed under the condition that the etching selectivity of the interlayer oxide film / titanium nitride film is strong although the anisotropy is weak (tapered).
Is etched to form a through hole 52. That is,
In this second stage, the interlayer oxide film 3 is entirely etched under the opening to expose the titanium nitride film 2 (FIG. 4).

As specific conditions, for example, the following conditions are used. First, in the first stage, a 1: 1 ratio of C ₄ F ₈
Using a / O ₂ mixed gas, a pressure of 1 mTorr, an RF substrate bias power of 700 W, and a microwave power of 1500 W are applied to generate plasma by electron resonance. Under this condition, etching with strong anisotropy can be performed.

[0017] Next, in the second stage, 4: a ratio of 3 C ₄ F ₈ /
Using an O ₂ mixed gas, a pressure of 1 mTorr, an RF substrate bias power of 700 W, and a microwave power of 1500 W are applied to generate plasma. As described above, when the gas ratio of C ₄ F ₈ is 4: 3 or more with respect to O ₂ , C ^* F ^* -based deposition is deposited on the titanium nitride film 2 and the etching rate of the titanium nitride film 2 is reduced. Can be suppressed. Therefore, the amount of etching in the second stage can be controlled with high precision, so that the through holes 52 can be formed without etching the titanium nitride film 2.
Can be formed.

As described above, in the dry etching method according to the first embodiment, about 80% of the interlayer oxide film 3 is etched in the first stage to form the through hole 51 having an excellent anisotropic shape. Then, in the second step, the remaining approximately 20% of the interlayer oxide film 3 is etched without etching the titanium nitride film 2 to form a through hole 52. At this time, the contact hole formed in the second stage has a tapered shape, but the film thickness etched in the second stage is the interlayer oxide film 3.
Since this is only about 20% of the whole, a through hole excellent in anisotropic shape is formed as a whole.

Embodiment 2 As another specific condition,
The following conditions can also be used. First, in the first stage, using 1: 1 of C ₄ F ₈ / O ₂ mixed gas ratio, pressure 1
mTorr, an RF substrate bias power of 700 W, and a microwave power of 1500 W are applied to generate plasma by electron resonance. This condition is the same as the condition used in the first embodiment.

Next, in the second stage, a 1: 1 ratio of C ₄ F ₈ /
Using an O ₂ mixed gas, a pressure of 1 mTorr, an RF substrate bias power of 700 W and a microwave power of 1700 W are applied to generate plasma. Thus, if the microwave power is 1700 W or more, C ₄ in the plasma
The dissociation of F ₈ gas is promoted, and C ^* F ^{* is formed} on the titanium nitride film 2 ^.
Since the deposition of the system adheres, the etching rate of the titanium nitride film 2 can be kept low. Therefore, the amount of etching in the second stage can be controlled with high precision, so that the through holes 52 can be formed without etching the titanium nitride film 2.
Can be formed.

As described above, the same effect as in the first embodiment can be obtained also in the dry etching method according to the second embodiment.

Embodiment 3 FIG. As another specific condition,
The following conditions can also be used. First, in the first stage, a 1: 1 ratio of C ₄ F ₈ / O ₂ mixed gas was used,
mTorr, an RF substrate bias power of 700 W, and a microwave power of 1500 W are applied to generate plasma by electron resonance. This condition is the same as the condition used in the first embodiment.

Next, in the second stage, a 1: 1 ratio of C ₄ F ₈ /
Plasma is generated by applying a pressure of 1 mTorr, an RF substrate bias power of 600 W, and a microwave power of 1500 W using an O ₂ mixed gas. By reducing the RF substrate bias power in this manner, the etching rate of the titanium nitride film 2 is also reduced, and particularly, as shown in this embodiment, R
If the F-substrate bias power is 600 W or less, the amount of etching in the second stage can be accurately controlled, so that the through hole 52 can be formed without etching the titanium nitride film 2.

As described above, in the dry etching method according to the third embodiment, the interlayer oxide film 3
Is etched to form a through hole 51 having an excellent anisotropic shape, and then the remaining 20% of the interlayer oxide film 3 is etched without etching the titanium nitride film 2 in the second stage. A through hole 52 is formed. In addition, since the contact holes formed in the second step also have anisotropic shapes, through holes having more anisotropic shapes can be formed than the methods described in the first and second embodiments.

[0025]

According to the dry etching method according to the first aspect of the present invention, in the step (a), since the silicon oxide film is etched under the condition of strong anisotropy, the through-hole having excellent anisotropic shape is obtained. Holes can be formed. In step (b), since the gas ratio of C ₄ F ₈ is high, C ^* F ^* -based deposition is deposited on the titanium nitride film, and the etching rate of the titanium nitride film is reduced. Therefore, the etching amount of the silicon oxide film in the step (b) can be accurately controlled, and a through hole can be formed without etching the titanium nitride film.

Accordingly, by etching the silicon oxide film as thick as possible within the range where the titanium nitride film is not exposed in the step (a), a through hole excellent in anisotropic shape is formed without etching the titanium nitride film. can do.

According to the dry etching method of the present invention, the silicon oxide film is etched under the condition of strong anisotropy in the step (a). Holes can be formed.
Further, in the step (b), the dissociation of the C ₄ F ₈ gas in the plasma is promoted with the increase in the microwave power, and C ^* F ^* -based deposition adheres to the titanium nitride film. As a result, the etching rate of the titanium nitride film decreases,
The etching amount of the silicon oxide film in the step (b) can be accurately controlled, and a through hole can be formed without etching the titanium nitride film.

Accordingly, by etching the silicon oxide film as thick as possible within the range where the titanium nitride film is not exposed in the step (a), a through hole excellent in anisotropic shape is formed without etching the titanium nitride film. can do.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a dry etching method according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a dry etching method according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing a dry etching method according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a dry etching method according to the first embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a conventional dry etching method.

FIG. 6 is a cross-sectional view showing a conventional dry etching method.

FIG. 7 is a cross-sectional view illustrating an example of a metal wiring having a multilayer structure.

FIG. 8 is a cross-sectional view showing a conventional dry etching method.

FIG. 9 is a cross-sectional view showing a conventional dry etching method.

[Explanation of symbols]

1 aluminum wiring, 2 titanium nitride films, 3 interlayer oxide films, 51, 52 through holes.

Claims (2)

[Claims] 1. A semiconductor device having a silicon oxide film deposited on a titanium nitride film, comprising: (a) using a mixed gas of C ₄ F ₈ and O ₂ to convert the silicon oxide film to a titanium nitride film; (B) selectively etching while leaving it in a range that is not exposed; and (b) C ₄ than the mixed gas used in the step (a).
Gas ratio of F ₈ by using a mixed gas of high C ₄ F ₈ and O _2,
Etching the remaining silicon oxide film. 2. A semiconductor device having a silicon oxide film deposited on a titanium nitride film, comprising: (a) applying a predetermined microwave power using a mixed gas of C ₄ F ₈ and O ₂ ; Generating plasma, and selectively etching the silicon oxide film while leaving the silicon oxide film in a range where the titanium nitride film is not exposed; and (b) using a mixed gas of C ₄ F ₈ and O ₂ , Generating a plasma by applying a microwave power higher than the microwave power applied in the step (a),
Etching the remaining silicon oxide film.