JP2907314B2 - Method for manufacturing semiconductor device - Google Patents

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, and more particularly to a method of dry etching a composite film of a polycrystalline silicon film and a metal silicide film, that is, a so-called polycide film.

[0002]

2. Description of the Related Art In a semiconductor device, as a material of a gate electrode and a wiring thereof, polycrystalline silicon capable of forming a transistor having stable characteristics by utilizing a self-alignment technique has been used. In order to meet this demand, it is necessary to form a transistor having a sheet resistance one digit lower than that of polycrystalline silicon and having characteristics similar to those of a polycrystalline silicon gate. Polycide films that can be used have been adopted. In recent years, the semiconductor integrated circuit device has been further miniaturized, and accordingly, the polycide film has also become thinner, and its patterning has also been required to have higher precision.

As a conventional technique for etching a polycide film, there is a method described in Japanese Patent Publication No. 61-168228. As shown in FIG. 10A, a polysilicon film 403 and a tungsten silicide film 404 are laminated on a silicon oxide film 402 on a silicon substrate 401, and a patterned photoresist film 4 is formed thereon.
After the formation of the film 05, the tungsten silicide film 404 is etched using a gas containing fluorine such as SF ₆ , and then the polycrystalline silicon film 403 is etched with a gas containing Cl ₂ to pattern the polycide film. This is a two-stage etching method.

However, in etching with a gas containing fluorine such as SF ₆ , the etching rate of the polycrystalline silicon film is more than twice the etching rate of the metal silicide film. Before switching to film etching, the polycrystalline silicon film may be etched. At this time, as shown in FIG. 10B, side etching occurs in the polycrystalline silicon film. Further, in the etching using a gas containing fluorine, the selectivity between the metal silicide film and the silicon oxide film is also reduced to 1-2. The gate oxide film is also etched because it is low. This problem becomes more serious when the polycide film is made thinner due to higher integration and miniaturization of devices.

To solve this problem, Japanese Patent Laid-Open No.
There is a method proposed in -105321.
Hereinafter, this will be described with reference to FIG. First,
As shown in FIG. 11A, a silicon oxide film 502 is formed on a silicon substrate 501 by thermal oxidation, a polycrystalline silicon film 503 is formed at a thickness of 2000 °, and a tungsten silicide film 504 is formed at a thickness of 2000 °. A pattern of the photoresist film 505 is formed.

This semiconductor substrate is mounted in a parallel plate type RIE apparatus, and the substrate temperature is set to 60 ° C. or more and 150 ° C. or less (80 ° C. in the embodiment). First, the tungsten silicide film 504 is formed by Cl ₂ : 89 sccm. , O ₂ : 11 sccm, pressure: 0.05 Torr, RF power density: 1.1 W / cm ² [FIG. 11B]. After the etching of the tungsten silicide film 504 is completed, the polycrystalline silicon film 503 is subsequently formed with HBr: 100 sccm, pressure: 0.
Etching is performed under the conditions of ² Torr and RF power density: 1.1 W / cm ² [FIG. 11C].

In this method, the metal silicide film Cl ₂ /
In the etching using O ₂ , the uniformity of the etching of the metal silicide film is improved by setting the substrate temperature to 60 ° C. or higher, and the etching rate of the polycrystalline silicon film is equal to or higher than the etching rate of the metal silicide film. Less than that,
At the end of the etching of the metal silicide film, the polycrystalline silicon film can be made to sufficiently exist, and as a result, as shown in FIG. Good polycide etching becomes possible.

[0008]

In the above-mentioned first conventional example using an etchant containing fluorine such as SF ₆ , since the etching speed of polycrystalline silicon is higher than that of metal silicide, the etching of the metal silicide film is performed. At the end of the process, the polycrystalline silicon disappears, and the polycrystalline silicon film is largely side-etched. This technique is not suitable for fine processing of a thinned polycide.

In the second conventional example in which Cl ₂ / O ₂ is used as an etchant for a metal silicide film and the substrate temperature is set to 60 ° C. or higher, when the substrate temperature is set to 80 ° C., the etching of the tungsten silicide film is performed. The speed can be about 5000 ° / min and the etching rate of the polycrystalline silicon film can be about 5500 ° / min, but the etching uniformity of the tungsten silicide film has been improved only to about ± 15%. Therefore, the etching amount of the tungsten silicide film varies about ± 300 °, that is, 600 ° within the silicon substrate surface.

In the case of such a degree of variation, Japanese Patent Laid-Open No.
In the case of the tungsten silicide film 2000 # and the polycide film thickness of about 2000 # of the polycrystalline silicon film shown in Japanese Patent No. 05321, when the etching of the tungsten silicide film is completed, the remaining film of the polycrystalline silicon film is about 1400-2000 #. And good etching is possible. However, in the case where the thickness of the polycide film is reduced to, for example, a tungsten silicide film 1000 # and a polycrystalline silicon film 500 # as the device becomes highly integrated and miniaturized, the etching disclosed in Japanese Patent Application Laid-Open No. 4-105321 is disclosed. In performance, when switching from tungsten silicide film to etching of polycrystalline silicon film,
The remaining film of the polycrystalline silicon film is 200 to 500 °.

However, in an actual device manufacturing process, for example, since a step such as a field region is present, it is necessary to completely remove the tungsten silicide film.
Since further etching is required, there arises a problem that the polycrystalline silicon film is partially removed completely and the silicon oxide film which is the underlying film of the polycide film is also etched.

Accordingly, it is an object of the present invention to improve the etching selectivity between the metal silicide film and the polycrystalline silicon film and to improve the in-plane etching uniformity of the metal silicide film. The purpose is to enable the processed polycide film to be processed with high precision.

[0013]

According to the present invention, there is provided a method for forming a polycide film comprising a polycrystalline silicon film and a metal silicide film on a semiconductor substrate. selectively forming a mask material, Cl _2, O _2, a mixed gas containing He to the metal silicide film is a polycrystalline silicon film remains
Selectively etching the said metal silicide
Under conditions different from the etching conditions when etching the film
Selectively etching the polycrystalline silicon film
And a method for manufacturing a semiconductor device comprising: Preferably, the gas flow ratio of the mixed gas is Cl
₂ : O ₂ : He = 10: 2 to 4: 6 to 8 and the pressure of this mixed gas is made 0.02 Torr or less.

[0014]

According to the present invention, by having the above structure, the etching uniformity of the metal silicide film is improved, and the etching selectivity of the metal silicide film to polycrystalline silicon is improved. Therefore, in the patterning of the polycide film, it is possible to perform etching with excellent controllability at the interface between the metal silicide film and the polycrystalline silicon film, and it is possible to perform good etching even for thinning the polycide film. It becomes possible.

FIG. 4 shows the He flow rate dependency when the tungsten silicide film is etched with Cl ₂ / O ₂ / He gas. As can be seen from the figure, good etching uniformity of ± 6 to 7% is obtained when the He flow rate is in the range of 12 to 16 sccm. From this result, it can be seen that good etching uniformity can be obtained by adding He in a specific amount.

FIG. 5 shows the pressure dependence of the etching rate for each material to be etched when etching is performed with Cl ₂ / O ₂ / He gas. From this result, it can be seen that, by lowering the pressure, the etching rates of the tungsten silicide film and the polycrystalline silicon film tend to approach each other.

FIG. 6 shows the Cl ₂ flow rate dependence of the etching rate for each material to be etched when etching is performed with Cl ₂ / O ₂ / He gas. From this result, it can be seen that the etching rate between the tungsten silicide film and the polycrystalline silicon film tends to approach by decreasing the Cl ₂ flow rate.

In order to favorably etch the thinned polycide film, the selectivity between the tungsten silicide film and the polycrystalline silicon film, that is, the etching rate of the tungsten silicide film / the etching rate of the polycrystalline silicon film must be reduced. 5 and 6 that the object of the present invention can be achieved by reducing the pressure of the processing gas and decreasing the flow rate of Cl ₂ .

On the basis of the above findings, in order to find the optimum conditions for the gas flow ratio, experiments were conducted in which the gas pressure was reduced and the Cl ₂ flow rate was reduced, and the etching conditions were changed. FIG. 7 shows that the gas flow ratio is expressed as Cl ₂ : O ₂ : He =
10: 3: 7, and the pressure of the mixed gas is 0.02 Torr.
The graph shows the RF power density dependence of the etching rate of each material to be etched and the uniformity of the etching rate when the pressure is reduced. 8 and 9 show the O ₂ flow rate dependency and the He flow rate dependency of the etching rate and the uniformity of the etching rate of each material to be etched, respectively. From these results, when the RF power density is 1.1 W / cm ² ,
The gas flow ratio is set to Cl ₂ : O ₂ : He = 10: 2 to 4: 6.
When set to ８8, the etching rates of the tungsten silicide film and the polycrystalline silicon film are each about 2000.
Å / min, and the etching uniformity of the tungsten silicide film of about ± 6.5% can be obtained.

Therefore, by setting the etching conditions in this manner, for example, when the tungsten silicide film is etched at 1000 ° and the polycrystalline silicon film is etched at 500 °, the variation in the etching of the tungsten silicide film is reduced. About 65 °, that is, about 130 °, and the remaining polycrystalline silicon film at the time when the etching of the tungsten silicide film is completed is reduced to 370-500 °.
Therefore, the remaining film can sufficiently cope with a reduction in the thickness of the polycide film and an in-plane step.

[0021]

Next, embodiments of the present invention will be described with reference to the drawings. [First Embodiment] FIG. 1 is a schematic sectional view of a semiconductor substrate showing a method for dry-etching a polycide film according to a first embodiment of the present invention. First, as shown in FIG.
Forming a silicon oxide film 102 on a silicon substrate 101, followed by a polycrystalline silicon film 103 having a thickness of 500 °;
A tungsten silicide film 104 having a thickness of 1000 Å was formed, and a pattern of a photoresist film 105 was formed thereon. Subsequently, this silicon substrate is shown in FIG.
Two electrodes opposing the inside of a chamber 201 having a gas supply mechanism in the upper part and a gas exhaust port in the lower part, an upper electrode 2
02, a lower electrode 203 is mounted on a lower electrode 203 of a cathode-coupled RIE device in which an RF power supply 205 is connected to the lower electrode 202 via a matching box 204, and etching is performed.

First, the tungsten silicide film 104
Is Cl ₂ : 20 sccm, O ₂ : 6 sccm, He: 14 sccc
m, pressure: 0.02 Torr, RF power density: 1.1 W / c
Etching is performed under the condition of m ² [FIG. 1 (b)]. Then
The polycrystalline silicon film 103 is formed of Cl ₂ : 45 sccm, HB
r: 45 sccm, O ₂ : 1.2 sccm, He: 2.8 sccm,
Pressure: 0.1 Torr, RF power density: 0.82 W / cm ²
[FIG. 1 (c)].

In the etching of the tungsten silicide film under the above conditions, the in-plane etching uniformity is as high as ± 6.5%, the etching rate is almost equal to that of the polycrystalline silicon film, and the end point can be easily detected as described later. Therefore, as shown in FIG.
The etching of the tungsten silicide film 104 can be completed in a state where is not so etched. In addition, in the etching of the polycrystalline silicon film under the above conditions, the selectivity to the underlying silicon oxide film can be set to about 40, and as a result, as shown in FIG.
There is no side etching in the polycrystalline silicon film 103, and the polycide film with good residual silicon oxide film 102 can be etched.

The end point of the etching is detected by monitoring the emission wavelength of 440 nm at the interface between the tungsten silicide film and the polycrystalline silicon film, and monitoring the emission wavelength of 307.3 nm at the interface between the polycrystalline silicon film and the silicon oxide film. In this embodiment, the emission wavelength 4
The etching of the tungsten silicide film was terminated at the point where the emission intensity of 40 nm increased and became flat, as the end point. At that time, observation was performed using a scanning electron microscope. As a result, the tungsten silicide film was completely removed, and the etching amount of the polycrystalline silicon film was 100%.
Å It was below.

[Second Embodiment] FIG. 3 is a schematic sectional view of a semiconductor substrate showing a method for dry-etching a tungsten silicide film according to a second embodiment of the present invention. First, as shown in FIG. 3A, a silicon oxide film 302 is formed on a silicon substrate 301, followed by a polycrystalline silicon film 303 having a thickness of 500 °, a tungsten silicide film 304 having a thickness of 1000 °, and a silicon oxide film. 306 were sequentially formed, and a pattern of a photoresist film 305 was formed thereon. Subsequently, this silicon substrate was replaced with the RI shown in FIG.
Etching is performed by placing the device on the lower electrode of the E apparatus.

First, the silicon oxide film 306 is coated with CF ₄ :
100 sccm, pressure: 0.1 Torr, RF power density: 2.
Etching is performed under the condition of 75 W / cm ² , and then the tungsten silicide film 304 is formed by Cl ₂ : 20 sccm, O ₂ : 6.
Etching is performed under the conditions of sccm, He: 14 sccm, pressure: 0.02 Torr, and RF power density: 1.1 W / cm ² [FIG.
(B)]. Next, the photoresist film 305 is removed by, for example, O ₂ plasma or the like. Next, the polycrystalline silicon film 303 is formed by changing Cl ₂ : 45 sccm, HBr: 45 sccm,
₂ : 1.2 sccm, He: 2.8 sccm, pressure: 0.1 Torr
r, Etching is performed under the condition of RF power density: 0.82 W / cm ² . As a result, as shown in FIG. 3 (c), good polycide etching with a small etching amount of the silicon oxide film 302 without side etching of the polycrystalline silicon film 303 was performed.

In this embodiment, the photoresist film 305 is removed before the etching of the polycrystalline silicon film, and the etching of the silicon oxide film 302 which is the underlying film of the polycide film is performed when the photoresist is present. Since etching can be suppressed in comparison with the above, etching with excellent selectivity can be performed.

The preferred embodiment has been described above.
The present invention is not limited to these embodiments, and various changes can be made without departing from the spirit of the present invention. For example, although a tungsten silicide film has been described in the embodiments, similar results can be obtained by using another refractory metal silicide film such as a molybdenum silicide film or a titanium silicide film instead of the tungsten silicide film.

[0029]

As described above, according to the present invention, when dry etching a polycide film, the metal silicide film is etched using a mixed gas of Cl ₂ / O ₂ / He. Etching can be performed with high in-plane uniformity and a selectivity of about 1 with the underlying polycrystalline silicon. Therefore, according to the present invention, even if the polycide film is thinned, the etching of the metal silicide film can be completed by reducing the etching amount of the underlying polycrystalline silicon film, and the polycrystalline silicon film This makes it possible to pattern the polycide film with high precision by reducing the side etching. Further, according to the present invention, since the silicon oxide film is not exposed at the time of etching the metal silicide film, it is possible to prevent loss or loss of the underlying silicon oxide film and to manufacture a highly reliable semiconductor device. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a process sectional view showing a method for etching a polycide film according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a dry etching apparatus used in an embodiment of the present invention.

FIG. 3 is a process sectional view showing a method for etching a polycide film according to a second embodiment of the present invention.

FIG. 4 is an etching characteristic diagram for explaining the operation of the present invention.

FIG. 5 is an etching characteristic diagram for explaining the operation of the present invention.

FIG. 6 is an etching characteristic diagram for explaining the operation of the present invention.

FIG. 7 is an etching characteristic diagram for explaining the operation of the present invention.

FIG. 8 is an etching characteristic diagram for explaining the operation of the present invention.

FIG. 9 is an etching characteristic diagram for explaining the operation of the present invention.

FIG. 10 is a process sectional view for explaining the first conventional example.

FIG. 11 is a process sectional view for describing a second conventional example.

[Explanation of symbols]

101, 301, 401, 501 Silicon substrate 102, 302, 306, 402, 502 Silicon oxide film 103, 303, 403, 503 Polycrystalline silicon film 104, 304, 404, 504 Tungsten silicide film 105, 305, 405, 505 Photo Resist film 201 chamber 202 upper electrode 203 lower electrode 204 matching box 205 RF power supply

Claims (9)

(57) [Claims] 1. A on a semiconductor substrate, forming a polycide film of a polycrystalline silicon film and a metal silicide film, and forming a selectively mask material on the polycide film, Cl _2, O _2, Selectively etching the metal silicide film with a gas mixture containing He so that the polycrystalline silicon film remains ; and
Under the conditions different from the etching conditions at the time of etching
Selectively etching a polycrystalline silicon film . 2. A gas flow ratio of the mixed gas used for etching the metal silicide film is Cl ₂ : O ₂ :
2. The method according to claim 1, wherein He = 10: 2 to 4: 6 to 8. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the pressure of the mixed gas when etching the metal silicide film is 0.02 Torr or less. 4. The method according to claim 1, wherein an RF power density when etching the metal silicide film is 1.1 W / cm ² or more. 5. The method according to claim 1, wherein after the etching of the metal silicide film is completed, the polycrystalline silicon film is etched with a gas containing HBr and O ₂ . 6. The method according to claim 1, wherein after the etching of the metal silicide film is completed, the polycrystalline silicon film is etched with a gas containing Cl ₂ , HBr, O ₂ , and He. Method. 7. The method according to claim 1, wherein the mask material is a photoresist film. 8. The method according to claim 1, wherein the mask material is a composite film of a photoresist film and a silicon oxide film.
The manufacturing method of the semiconductor device described in the above. 9. The method according to claim 8, wherein the photoresist film is removed after the etching of the metal silicide film, and thereafter the polycrystalline silicon film is etched.