JPH09321024A - Method for manufacturing semiconductor device - Google Patents

Abstract

(57) Abstract: The main object of the present invention is to prevent an underlying silicon nitride film from being excessively etched when forming a contact hole such as a bit line contact in a DRAM. It is a characteristic. For example, a gate electrode is formed on a surface of a silicon substrate via a gate insulating film, and the surface and sidewalls of the gate electrode are covered with a silicon nitride film. Then, the silicon oxide film 1 is formed on the silicon nitride film 14.
After 6 is formed, it is etched using the resist pattern 17 as a mask to form a contact hole 18 in self-alignment with the gate electrode 13. At that time, first C ₄
After etching is performed using a mixed gas of F ₈ / Ar and the silicon nitride film 14 is exposed to plasma, C
Etching is performed by switching to a mixed gas of HF ₃ / CO.

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 the surface of a semiconductor substrate is processed by reactive ion etching using a fluorocarbon gas, for example, a SAC (Self Alignment) method.
ed Contact hole) DR using etching process
It is used when forming a contact hole such as a bit line contact in AM.

[0002]

2. Description of the Related Art As is well known, when an attempt is made to etch a silicon oxide film on a silicon nitride film as a base stopper by reactive ion etching (RIE) using a fluorocarbon gas, the base silicon nitride film is used. A high etching selection ratio is required for the film.

By the way, in the above-mentioned RIE, for example, fluorocarbon type C which has been generally used conventionally has been used.
In the plasma discharge of the mixed gas of HF ₃ and CO, the etching selection ratio of the silicon oxide film to the silicon nitride film is about 0.8. Similarly, when the C ₄ F ₈ / CO / Ar mixed gas is used, The etching selection ratio was about 1.2.

Therefore, the amount of abrasion of the underlying silicon nitride film is apt to be excessive during so-called over-etching, which is required from the in-plane non-uniformity of the wafer, which is a problem in the process.

FIG. 4 shows a process for forming a contact hole such as a bit line contact in a DRAM by RIE using a conventional fluorocarbon type gas.

That is, a silicon nitride film 4 is formed on the surface and side walls of a gate electrode 3 made of a polycrystalline silicon film formed on the surface of a silicon substrate 1 with a gate insulating film 2 interposed therebetween, and an upper layer of this silicon nitride film 4 is formed. After forming the silicon oxide film 5 as an interlayer insulating film on the silicon oxide film 5, when the contact hole 7 connected to the diffusion layer 6 is to be formed in self-alignment with the gate electrode 3, the silicon oxide film 5 is formed according to the resist pattern 8. Etching is performed.

At this time, by using the silicon nitride film 4 as an etching stopper layer (base stopper), some over-etching is performed to compensate for variations in the film thickness of the silicon oxide film 5 and etching rate.

However, if the etching selection ratio of the silicon oxide film 5 to the silicon nitride film 4 is insufficient, even the underlying silicon nitride film 4 is excessively etched,
In some cases, the reliability of the DRAM may be impaired.

In order to prevent excessive etching of the underlying silicon nitride film 4, for example, as shown in FIG.
As shown in (b), once the etching reaches the silicon nitride film 4, the formation of the contact hole 7 is interrupted, the resist pattern 9 is formed again, and then the silicon oxide film 5 is etched again. Is also proposed.

However, in this method, it is difficult to completely prevent the mask displacement when the resist pattern 9 is re-formed, so that the contact hole 7 is formed in the gate electrode 3.
Cannot be formed in a self-aligned manner.

[0011]

As described above, in the prior art, since the etching selection ratio of the silicon oxide film to the silicon nitride film is insufficient, there is a problem that the amount of abrasion of the underlying silicon nitride film is likely to be excessive. there were.

Therefore, according to the present invention, the etching selection ratio of the silicon oxide film to the silicon nitride film can be greatly improved, and the underlying silicon nitride film can be prevented from being excessively etched. Is intended to provide.

[0013]

In order to achieve the above object, in the method of manufacturing a semiconductor device of the present invention, in the case where the surface of a semiconductor substrate is treated by reactive ion etching, A first step of selectively etching a silicon oxide film with respect to a silicon nitride film using a first processing gas containing a fluorocarbon-based gas having no hydrogen bond, and a fluorocarbon-based gas having a hydrogen bond and CO gas Using a second process gas containing
The second step is to etch the silicon oxide film selectively with respect to the silicon nitride film.

Further, in the method of manufacturing a semiconductor device of the present invention, a silicon nitride film is formed on the surface and the side wall of the gate electrode formed on the surface of the silicon substrate via the gate insulating film, and the silicon nitride film is formed. In the case of forming a contact hole in the silicon oxide film in a self-aligned manner with respect to the gate electrode after forming a silicon oxide film in the upper layer, in a mixed gas plasma of C ₄ F ₈ / Ar,
After the silicon oxide film is selectively etched with respect to the silicon nitride film and the silicon nitride film is exposed to plasma, the silicon nitride film is exposed to the CHF ₃ / CO mixed gas plasma. The silicon oxide film is selectively etched.

According to the method of manufacturing a semiconductor device of the present invention, the etching rate of the silicon nitride film can be suppressed. This makes it possible to sufficiently secure the etching selection ratio of the silicon oxide film to the silicon nitride film.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an RIE using a fluorocarbon gas according to an embodiment of the present invention.
3 shows a process for forming a contact hole such as a bit line contact in a DRAM.

For example, as shown in FIG. 1A, a gate electrode 13 made of a polycrystalline silicon film is formed on the surface of a silicon substrate 11 via a gate insulating film 12, and a silicon nitride film 14 is formed on the surface and sidewalls of the gate electrode 13. After coating, diffusion is performed using the gate electrode 13 as a mask to form a diffusion layer 15 to be source / drain regions.

Then, after forming a silicon oxide film 16 as an interlayer insulating film on the silicon nitride film 14,
Etching processing (RIE) is performed using the resist pattern 17 as a mask.

For example, in the RIE here, first, the flow rate of a mixed gas (first processing gas) of C ₄ F ₈ gas having no hydrogen (CH) bond and Ar gas is set to 5/205 sccm, Pressure of 40 mTorr, RF. It is performed under the condition that the output is 850W.

Then, the silicon nitride film 14 is used as an etching stop layer (base stopper) to etch the silicon oxide film 16. Further, after the etching is performed under the above conditions, and further, after the surface of the underlying silicon nitride film 14 is exposed to the plasma or is etched for a short time, for example, as shown in FIG. , The flow rate of a mixed gas (second processing gas) of CHF ₃ gas having a C—H bond and CO gas is 45/15.
5 sccm, pressure 40 mTorr, RF. Output is 800W
Etching is performed by switching to the conditions described below.

The timing of this switching is, for example,
By monitoring the change of CO, which is reduced by exposing the surface of the silicon nitride film 14 to the plasma, as an end point by the emission spectroscopy or the like, it is possible to detect relatively accurately.

Thus, by changing the conditions during the etching, for example, as shown in FIG.
The silicon oxide film 16 is patterned with high selectivity, that is, the contact hole 18 can be formed in a self-aligned manner with respect to the gate electrode 13 while suppressing the scraping amount (etching rate) of the underlying silicon nitride film 14. .

As a result, since the SAC etching process can be surely executed, the cell size can be greatly reduced, and a compact and highly reliable DRAM can be obtained.

Here, in the above-mentioned present invention, C ₄ F
_While etching with a mixed gas of ₈ / Ar, CHF ₃
The reason why the patterning of the silicon oxide film 16 can be performed with high selectivity by switching to etching with a mixed gas of / CO will be considered.

FIG. 2 shows the etching selectivity with respect to the silicon nitride film in comparison between the present invention and the prior art. Under the plasma conditions of the gas system of the present invention, the etching rate for the silicon nitride film 14 is extremely reduced, while the etching rate for the silicon oxide film 16 is hardly reduced. Therefore, the silicon nitride film 1
It is possible to remarkably improve the etching selection ratio with respect to 4 as compared with the prior art.

FIG. 3 shows the results of ESCA analysis of the composition of the reaction product film on the silicon nitride film 14 under the plasma conditions of the respective gas systems.
In the result of this analysis, the fact that the value of Si or N is large means that the underlying silicon nitride film 14 is easily visible, and the film thickness of the reaction product film deposited on the silicon nitride film 14 is thin.

Further, the fact that the C / F ratio is large means that the degree of bonding as an organic substance film is high and that it is also strong as a reaction product film. From this, under the plasma condition of C ₄ F ₈ / Ar gas system, the silicon nitride film 1
It can be seen that the reaction product film grown on No. 4 is thick, but the film is weak, and under the plasma condition of the CHF ₃ / CO gas system, the reaction product film is thin but strong.

Therefore, under the plasma conditions of the gas system of the present invention, etching is performed using a mixed gas of C ₄ F ₈ / Ar and then etching is performed using a mixed gas of CHF ₃ / CO. In addition, a thick but weak (small C / F ratio) reaction product film and a thin but strong (large C / F ratio) reaction product film are successively formed on the silicon nitride film 14.

This is equivalent to forming a fairly thick and strong reaction product film on the silicon nitride film 14, and as a result, the silicon oxide film 14 can be sufficiently protected from ion bombardment, resulting in silicon nitride film. It is considered that the etching rate for the film 14 is lowered.

That is, under the plasma conditions of the gas system of the present invention, first, etching is performed using a mixed gas of C ₄ F ₈ / Ar to form a thick reaction product film on the silicon nitride film 14, Further, etching is performed while growing a strong reaction product film using a mixed gas of CHF ₃ / CO to relax the impact of ions on the silicon nitride film 14, and thereby the silicon nitride film 14 is formed.
The etching rate can be suppressed and the silicon nitride film 14 can be prevented from being excessively etched.

Moreover, since the etching selectivity with respect to the silicon nitride film 14 is improved, the silicon oxide film 16 can be patterned with high selectivity, so that the contact hole 18 is self-aligned with the gate electrode 13. Can be formed.

As described above, the etching rate of the silicon nitride film can be suppressed. That is, first, etching is performed using a mixed gas of C ₄ F ₈ / Ar to form a thick reaction product film on the silicon nitride film, and then,
Further, etching is performed while growing a strong reaction product film using a mixed gas of CHF ₃ / CO. As a result, the impact of ions on the silicon nitride film can be relaxed, so that it is possible to sufficiently secure the etching selection ratio of the silicon oxide film to the silicon nitride film. Therefore, the etching selection ratio of the silicon oxide film to the silicon nitride film can be significantly improved,
It is possible to prevent the underlying silicon nitride film from being excessively etched.

Moreover, since it becomes possible to prevent the amount of abrasion of the underlying silicon nitride film from being excessive, the SAC etching process can be carried out with high accuracy. In addition, in the above-described embodiment of the present invention, the case where the mixed gas of CHF ₃ / CO is used as the second processing gas has been described, but the present invention is not limited to this, and for example, CH ₃ F
The same effect can be expected by using a mixed gas of / CO.

The present invention can be applied not only to DRAM but also to various semiconductor devices. Of course, various modifications can be made without departing from the scope of the present invention.

[0035]

As described above in detail, according to the present invention, the etching selection ratio of the silicon oxide film to the silicon nitride film can be greatly improved, and the underlying silicon nitride film can be prevented from being excessively etched. It is possible to provide a method of manufacturing a semiconductor device capable of manufacturing the semiconductor device.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a step of forming a bit line contact hole in a DRAM according to an embodiment of the present invention.

FIG. 2 is a schematic view showing an etching selection ratio with respect to a silicon nitride film, comparing the present invention with a conventional technique.

FIG. 3 is a schematic view showing the result of ESCA analysis of the composition of the reaction product film on the silicon nitride film.

FIG. 4 is shown to explain the prior art and its problems;
FIG. 6 is a schematic cross-sectional view of a process of forming a contact hole in a DRAM.

FIG. 5 is a schematic cross-sectional view showing another step of forming a contact hole in the conventional DRAM.

[Explanation of symbols]

 11 ... Silicon substrate 12 ... Gate insulating film 13 ... Gate electrode 14 ... Silicon nitride film 15 ... Diffusion layer 16 ... Silicon oxide film 17 ... Resist pattern 18 ... Contact hole

Claims (11)

[Claims] 1. A method for manufacturing a semiconductor device, wherein a surface of a semiconductor substrate is processed by reactive ion etching, wherein a silicon nitride film is formed by using a first processing gas containing a fluorocarbon-based gas having no hydrogen bond. Using a first step of selectively etching the silicon oxide film with respect to the silicon oxide film and a second process gas containing a fluorocarbon-based gas having a hydrogen bond and a CO gas; And a second step of etching the oxide film. 2. The method for manufacturing a semiconductor device according to claim 1, wherein the fluorocarbon-based gas having no hydrogen bond can generate a large amount of CF ₂ ⁺ ions in plasma. 3. The method for manufacturing a semiconductor device according to claim 2, wherein the fluorocarbon-based gas capable of generating a large amount of CF ₂ ⁺ ions in the plasma is C ₄ F ₈ . 4. The first processing gas is C ₄ F ₈ and Ar.
2. The method for manufacturing a semiconductor device according to claim 1, wherein the mixed gas is 5. The method of manufacturing a semiconductor device according to claim 1, wherein the fluorocarbon-based gas having a hydrogen bond is CHF ₃ . 6. The method of manufacturing a semiconductor device according to claim 1, wherein the fluorocarbon-based gas having a hydrogen bond is CH ₃ F. 7. The silicon nitride film functions as an etching stop layer.
A method of manufacturing a semiconductor device according to item 1. 8. The manufacturing of a semiconductor device according to claim 1, wherein after the surface of the silicon nitride film is etched for a short time, the first step is switched to and the second step is executed. Method. 9. The semiconductor device according to claim 1, wherein when the surface of the silicon nitride film is exposed to plasma, the second step is performed by switching to the first step. Manufacturing method. 10. The method of manufacturing a semiconductor device according to claim 9, wherein the endpoint monitor confirms that the surface of the silicon nitride film is exposed to plasma. 11. A silicon nitride film is formed on a surface and a side wall of a gate electrode formed on a surface of a silicon substrate via a gate insulating film, a silicon oxide film is formed on an upper layer of the silicon nitride film, and then the silicon is formed. In a method of manufacturing a semiconductor device in which a contact hole is formed in an oxide film in a self-aligned manner with respect to the gate electrode, the silicon nitride film is selectively etched with respect to the silicon nitride film in a mixed gas plasma of C ₄ F ₈ / Ar. After etching the silicon oxide film and exposing the silicon nitride film to plasma, CH
A method of manufacturing a semiconductor device, wherein the silicon oxide film is selectively etched with respect to the silicon nitride film in a mixed gas plasma of F ₃ / CO.