JPH07201821A - Aluminum alloy wiring formation method - Google Patents

Abstract

(57) [Abstract] [Purpose] Aluminum alloy wiring is formed using a clean dry etching that has a high selection ratio with an etching mask, can protect the wiring sidewall during etching, does not cause after-corrosion, and has few particles generated. Provide a way. [Structure] An aluminum alloy film 3 and a silicon oxide film 4 are laminated on a BPSG 2. The resist pattern 5 is used to pattern the silicon oxide film 4 to remove the resist. Next, using the silicon oxide film 4 as a mask, the aluminum alloy is dry-etched in plasma of a mixed gas containing chlorine-based gas and oxygen gas. As a result, the selection ratio with the mask is high,
Since chemically inert alumina is formed and etched on the aluminum surface, the side wall of the wiring can be protected, anisotropic etching can be performed, and after-corrosion can be prevented. Further, since the chlorine-based gas containing no carbon is used and the resist is not required, it is possible to perform a carbon-less clean etching with few particles.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the manufacture of semiconductors.
In particular, it relates to a method for forming aluminum alloy wiring.

[0002]

2. Description of the Related Art At present, as an aluminum wiring technique, aluminum (AlSiCu: hereinafter referred to as an aluminum alloy) containing a small amount of silicon and copper having various migration suppressing effects is widely used as a wiring material. In the future, as the integration of semiconductor devices becomes higher, it is necessary to reduce the wiring width and the width between wirings in the plane direction, and in the vertical direction, the aspect ratio will be reduced due to the three-dimensional structure of the device as represented by two-layer or three-layer wiring. A wiring forming technique having a high ratio and a wiring forming technique having a high step are required. The aspect ratio described here depends on the width between the wirings, the thickness of the aluminum alloy, and the thickness of the resist as shown in FIG. 6A, and the step is the aluminum alloy as shown in FIG. 6B. This is due to the step shape of the base.

Now, a wiring processing technique using a conventional aluminum alloy film as a wiring material of a semiconductor device will be described with reference to process sectional views outlined in FIG.

First, as shown in FIG. 7A, a thickness of 500 to 1000 n is formed as an interlayer insulating film on the surface of the semiconductor substrate 1.
m BPSG film 2 is deposited. Next, an aluminum alloy film 3 having a thickness of about 1 μm is deposited on the BPSG film 2 by a sputter deposition method, and a thickness of 1 is formed on the BPSG film 2 by a photolithography process.
A resist pattern 5 having a thickness of 2 μm is formed.

Next, as shown in FIG. 7B, the resist pattern 5 is used as a mask to dry-etch the aluminum alloy film 3 by a reactive ion etching method (hereinafter referred to as RIE method) to form wiring. Form a pattern. Generally, for dry etching of an aluminum alloy film, chlorine-based gas (CCl ₄ , SiCl ₄ , BCl ₃ , Cl _2, etc.) and carbon-based gas (CHCl ₃ , CHCl ₃ for preventing side etching) are used.
A mixed gas with F ₄ or the like) is used.

Then, as shown in FIG. 7C, the resist on the aluminum alloy is removed by oxygen plasma treatment using an ashing device to form wiring.

Here, a method of dry etching an aluminum alloy, especially R. I. E. The method will be described in more detail. The mixed gas used and its flow rate are chlorine 10-30s
ccm, silicon tetrachloride 70-150 sccm, chloroform 10-30 sccm. 13. For the cathode electrode
A high frequency of 56 MHz and 200 to 500 W is supplied from a high frequency power supply. The degree of vacuum during etching is 10 to 50 Pa.

When a wafer having an aluminum alloy film of 1 μm and a resist as a mask having a thickness of 1 μm is dry-etched under these conditions, the selectivity ratio of the resist and the aluminum alloy film is small. The resist, which is a mask, is etched to reduce the width of the aluminum alloy wiring, and the aluminum alloy film to be the wiring is also etched. Therefore, the resist does not function sufficiently as a mask for etching.

If the wafer is exposed to the atmosphere after the dry etching is finished, the aluminum alloy wiring is corroded in the wiring pattern in several hours (called after-corrosion).
Is observed.

Further, when the semiconductor substrate is processed under the above conditions, the amount of reaction products containing carbon, aluminum and chlorine attached to the electrodes of the etching chamber, the gas introduction plate, the chamber wall, etc. increases with the number of processed substrates. It is observed that the number of particles attached to the semiconductor substrate increases with the number of processed wafers due to these deposits.

[0011]

The conventional method of forming an aluminum alloy wiring as described above has the following problems regarding dry etching of an aluminum alloy wiring having a fine line width.

The first point is that since the selection ratio between the aluminum alloy which is the wiring material and the resist which is the mask material is small, the resist is not removed in the dry etching of the aluminum alloy wiring having a high aspect ratio and a high step. The problem is that it disappears during etching and it does not function as a mask. On the other hand, there is a method of increasing the resist film thickness or thinning the aluminum alloy film, but the former has a problem that the resolution is deteriorated when a fine resist pattern is formed, and the latter is a desired wiring. These means are impractical because the film thickness is limited to obtain resistance.

The second point is that aluminum is chemically very active, and R. I. E. The anisotropy cannot be sufficiently ensured even if the method is performed, and the side wall of the wiring is etched (called a side etching phenomenon). As shown in FIG. 8, a desired wiring width cannot be obtained, or the wiring has a reverse tapered cross-sectional shape. When the wiring shape is inversely tapered, there is a problem that a void is generated when the insulating interlayer film is deposited on the wiring. Therefore, the side etching phenomenon is suppressed by adding a carbon-based gas (for example, CHCl ₃ , CF ₄ ) to the etching gas for the purpose of protecting the sidewall of the wiring while the etching is in progress. However, after the etching is completed, chlorine-based products and chlorine gas are attached or adsorbed to the surface of the aluminum alloy and the carbon-based deposits attached to the surface. When this wafer is exposed to the atmosphere, there is a problem that a chlorine-based substance reacts with water to form hydrogen chloride, and an electrochemical reaction causes corrosion of aluminum alloy wiring (called after-corrosion).

The third point is that, as described above, the carbon-based gas is added to the etching gas for controlling the cross-sectional shape of the aluminum alloy wiring, and the resist is used as an etching mask. A large number of carbon-containing deposits are deposited inside the chamber. This deposit increases as the etching process is repeated, and the etching rate, uniformity, and the like change with the number of processed wafers due to a slight change in the shape of the reaction chamber. In addition, this deposit also serves as a source of particles in the processing chamber, resulting in a decrease in device yield.

In view of the above problems, the present invention does not use a carbon-based gas for protecting the side wall of the wiring, generates few particles during etching, and uses aluminum having a high selection ratio with respect to the mask material. A method for forming an alloy wiring is provided.

[0016]

In order to solve the above problems, an aluminum alloy wiring forming method of the present invention is a method of forming an aluminum alloy on a semiconductor substrate and then patterning the wiring to form a wiring. Dry etching the aluminum alloy film with a gas containing chlorine-based gas and oxygen gas, using the silicon oxide film or the silicon nitride film as an etching mask, and second, using the silicon oxide film or the silicon nitride film as an etching mask, Alternating dry etching with a gas containing a chlorine-based gas and dry etching with a gas containing an oxygen gas to dry-etch the aluminum alloy film. Thirdly, etching the first or second amount of oxygen gas described above. Continuously or stepwise with the progress of the fourth step, and fourth, carbon as the first or second chlorine-based gas. Characterized by using a gas containing no child.

[0017]

According to the present invention, when a resist is used as an etching mask for a conventional aluminum alloy, the selection ratio with respect to the aluminum alloy is about 1.5 to 3, but the silicon oxide film or the silicon nitride film is used as an etching mask. When used, the selection ratio becomes 10 or more, and an aluminum alloy wiring pattern having a high level difference and a high aspect ratio can be formed.

Further, since the surface of the aluminum alloy is etched by chlorine plasma while being oxidized in oxygen plasma, the selection ratio to the aluminum alloy is 10 as compared with the conventional sidewall protection of the aluminum alloy wiring by the carbon gas. Since the side wall is protected by alumina (Al ₂ O ₃ ) as described above, more anisotropic etching can be performed. Here, the resist mask cannot be used due to the use of oxygen gas, and it is necessary to use a silicon oxide film or a silicon nitride film as an etching mask. At the end of etching, the surface of the aluminum alloy wiring is sufficiently oxidized to form chemically inert and stable Al ₂ O ₃ , so chlorine gas and chlorine-based products adhere to the surface of the aluminum alloy. Alternatively, after adsorption, no after-corrosion occurs even if left in the atmosphere.

Further, since a gas containing no carbon is used as an etching gas and a resist is not used as an etching mask, it is possible to carry out the conventional etching without using a carbon substance which is the main cause of deposits in the reaction chamber. Therefore, there is little deposition of carbonaceous material into the reaction chamber, and it is possible to perform clean etching without carbon and with few particles generated.

[0020]

EXAMPLE A wiring processing technique of the present invention using an aluminum alloy film as a wiring material of a semiconductor device will be described with reference to process sectional views outlined in FIG.

First, as shown in FIG. 1A, a BPSG film 2 having a thickness of 500 to 1000 nm is deposited as an interlayer insulating film on the surface of the semiconductor substrate 1 on which a predetermined diffusion layer is formed. Next, an aluminum alloy film 3 having a thickness of about 1 μm is deposited on the BPSG film 2 by a sputter deposition method, and a silicon oxide film 4 having a thickness of 300 to 500 nm is laminated on the aluminum alloy film 3 by a CVD method. Here, as the CVD, an atmospheric pressure CVD method is used and the film is formed at a substrate temperature of 400 degrees.

Next, as shown in FIG. 1B, a resist 5 having a thickness of about 1 μm is deposited on the oxide film 4. Then, the resist pattern 5 is formed by a photolithography process.
To form.

Then, as shown in FIG. 1C, the silicon oxide film 4 is subjected to R.O. I. E. Fine processing by the method. The gas used and its flow rate are carbon tetrafluoride 3
0-100sccm, 13.56MH for cathode electrode
A high frequency power of z, 200 to 500 W is supplied from a high frequency power supply. The degree of vacuum during etching is 3 to 10 Pa. Next, the semiconductor substrate 1 is exposed to an atmosphere of oxygen plasma to remove the resist pattern 5 used as the etching mask for the silicon oxide film 4. The ashing device used is a down-flow type plasma ashing device, with an oxygen flow rate of 100 to 500 sccm and a vacuum degree of 40 to 100 Pa.
Then, a high frequency of 13.56 MHz and 200 to 500 W is supplied from a high frequency power source. When the processing shown above is performed,
A silicon oxide film pattern 4 can be formed on the aluminum alloy film 3.

Next, as shown in FIG. 1 (d), the aluminum alloy film 3 is formed into a red film by using the silicon oxide film pattern as a mask.
I. E. Dry etching is performed by the method to form a wiring pattern. Here, the mixed gas used and its flow rate are 50 to 100 sccm of carbon tetrachloride and 30 to 50 sc of chlorine.
cm, oxygen 20 to 50 sccm, chloroform 3 to 5 s
It is ccm. 13.56MHz for the cathode electrode, 2
A high frequency of 0 to 500 W is supplied from a high frequency power source. The degree of vacuum during etching is 5 to 50 Pa.

When a wafer having an aluminum alloy film 3 having a thickness of 1 μm and a silicon oxide film 4 as a mask having a thickness of 300 nm is dry-etched under these conditions, the aluminum alloy film 3 is etched, and even if it is sufficiently over-etched, it is oxidized. The film is etched only about 100 nm, aluminum alloy 3
And acts as a mask having a selection ratio of 10 or more. Also,
Even at a place having a high aspect ratio and a high step, the silicon oxide film as the mask remains and it is observed that the wiring pattern is formed.

Then, observing the cross section of the wiring with a scanning electron microscope (SEM), a vertical wiring without side etching and without dimensional shift can be obtained. This indicates that the surface of the wiring of the aluminum alloy 3 was formed with alumina having a selectivity of 10 or more by the oxygen plasma during etching, and the side wall was sufficiently protected.

Further, after the dry etching is completed, even if this semiconductor substrate is exposed to the atmosphere for 24 hours or more, aftercorrosion is not observed in the wiring pattern. This is because the surface of the wiring pattern is oxidized and chemically stable and stable alumina is formed.

The oxide film 4 used as the mask is
Considering that the insulating film is deposited after the aluminum alloy wiring is formed, it is not necessary to remove it.

In the above method for forming aluminum alloy wiring,
By using a silicon oxide film as an etching mask and using a mixed gas containing a chlorine-based gas and an oxygen gas as an etching gas for an aluminum alloy film, an aluminum alloy wiring having a vertical shape with no dimension shift is formed.

In the second embodiment, in the process of the first embodiment, in the etching of the aluminum alloy film, the flow rate of oxygen gas is changed with the progress of etching.

This will be specifically described. As shown in FIG. 1D, the surface area exposed to the plasma of the aluminum alloy when the semiconductor substrate 1 having the oxide film pattern 4 formed on the aluminum alloy film 3 is dry-etched with a mixed gas containing a chlorine-based gas. The change of is shown in FIG. This surface area change is 3
Area, area (a) increasing with etching time,
It is divided into a region (b) where the aluminum alloy is just etched and a region (c) where it is over-etched. The flow rate of oxygen gas is changed continuously or stepwise with the change of the surface area of the aluminum alloy to be etched. An example of continuous change is shown in FIG. 3, and an example of stepwise change is shown in FIG.

A wafer having an aluminum alloy of 1 μm and a silicon oxide film 4 as a mask having a thickness of 300 nm is dry-etched. The mixed gas and flow rate used here are carbon tetrachloride 50 to 100 sccm, chlorine 30 to 50 sccm, chloroform 3 to 5 sccm, and oxygen. The flow rate of oxygen is 40 sccm to 50 sccm in the region (a), 30 sccm in the region (b), and 15 sccm in the region (c).
Change stepwise. 13.56M for the cathode electrode
A high frequency of 200 to 500 W of Hz is supplied from a high frequency power source. The degree of vacuum during etching is 5 to 50 Pa. When dry etching is performed under these conditions, the aluminum alloy is
It is observed that the silicon oxide film, which is the etching mask, is highly selectively etched in the same manner as in Example 1 and that a wiring pattern is formed. Then, observing the cross section of the wiring with a scanning electron microscope (SEM), a vertical wiring without side etching is obtained.
Further, after completion of the dry etching, even after exposing this semiconductor substrate to the atmosphere for 24 hours or more, the occurrence of after-corrosion is not observed in the wiring pattern.

In the above method for forming aluminum alloy wiring,
In addition to the first embodiment, the flow rate of oxygen gas can be reduced by changing the flow rate of oxygen gas as the etching of the aluminum alloy film progresses. Therefore, the aluminum alloy wiring can be economically formed.

The third embodiment uses a chlorine-based gas containing no carbon atoms as a chlorine-based gas in the etching of the aluminum alloy film in the steps of the first embodiment.

This will be specifically described. 1 (a)-
As shown in (c), a silicon oxide film pattern 4 is formed on the aluminum alloy film 3. Next, as shown in FIG. 1D, the aluminum alloy film 3 is subjected to R.O. I. E. Dry etching by the method,
A wiring pattern is formed. Here, the mixed gas used and its flow rate are 50 to 100 sccm of boron trichloride, 30 to 50 sccm of chlorine, and 20 to 50 sccm of oxygen. 13.56 MHz, 200-50 for cathode electrode
A high frequency power of 0 W is supplied from a high frequency power source. The degree of vacuum during etching is 5 to 50 Pa.

When a wafer having an aluminum alloy of 1 μm and a silicon oxide film 4 serving as a mask having a thickness of 300 nm is dry-etched under these conditions, a selection ratio with respect to the silicon oxide film of 10 or more is obtained as in the first embodiment. A vertical wiring cross section without side etching is obtained. After the dry etching is finished, the semiconductor substrate is exposed to the atmosphere 2
After exposure for 4 hours or more, the occurrence of after-corrosion is not observed in the wiring pattern.

When a resist mask, which is a conventional method, is used and a gas containing carbon atoms is used as an etching gas, a large amount of deposits such as reaction products containing carbon are deposited inside the chamber. According to the method of the third embodiment, even if the number of processed semiconductor substrates is increased,
Almost no deposits adhere to the chamber. Therefore,
Even if the number of particles adhering to the semiconductor substrate is measured and the number of processed particles is increased, a very low particle level can be maintained. Moreover, since deposits do not adhere to the inside of the chamber, etching can always be performed at the same etching rate and uniformity. This is because the silicon oxide film is used as a mask instead of the conventional resist mask, and the conventional carbon-based sidewall protection gas is not used.
This is because etching can be performed without using a substance containing carbon atoms, which is the main cause of deposits.

In the above-mentioned method for forming aluminum alloy wiring,
In addition to the first embodiment, by using a gas containing no carbon atoms as an etching gas for the aluminum alloy film,
It is possible to prevent deposits from adhering to the inside of the processing chamber, and aluminum alloy wiring can be formed in a clean environment with few particles generated.

In the first to third embodiments, a similar effect can be obtained by using a silicon nitride film formed by the CVD method instead of the silicon oxide film used as the etching mask for the aluminum alloy film. The same effect can be obtained by using a sputtering method instead of the CVD method of forming.

Further, in Examples 1 to 3, instead of using a mixed gas containing a chlorine-based gas and an oxygen gas, FIG. 5 shows an example of the relationship between the elapsed etching time and the gas flow rate.
The same effect can be obtained by alternately repeating dry etching with a gas containing chlorine gas and dry etching with a gas containing oxygen gas a plurality of times.

Further, in Examples 1 to 3, the same effect can be obtained by using an aluminum single layer film instead of the aluminum alloy film.

In Examples 1 and 2, instead of carbon tetrachloride and chlorine, chlorine, carbon tetrachloride, boron trichloride,
The same effect can be obtained by using at least one gas selected from silicon tetrachloride, hydrogen chloride and chloroform.
Similar effects can be obtained by using at least one gas selected from chlorine, boron trichloride, silicon tetrachloride and hydrogen chloride in place of boron trichloride and chlorine in Example 3.

[0043]

As described above, according to the present invention, when a resist is used as an etching mask for an aluminum alloy, the selection ratio with respect to the aluminum alloy is about 1.5 to 3, but a silicon oxide film or a silicon nitride film is used as an etching mask. When used as, the selection ratio becomes 10 or more, and an aluminum alloy wiring pattern having a high aspect ratio and a high step can be formed.

The surface of the aluminum alloy is exposed to oxygen plasma.
While oxidizing with chlorine plasma etching
Protects the side walls of aluminum alloy wiring with conventional carbon
Compared with, the selection ratio for aluminum alloy is 10 or more.
Alumina (Al₂O₃) Protects the side wall, so
Anisotropic etching is possible. Also, etching ends
At times, the surface of aluminum alloy wiring is sufficiently oxidized and chemical
Inactive and stable Al ₂O₃Form a
Chlorine gas and chlorine-based products may adhere to the surface of the alloy.
After adsorption, even after being left in the atmosphere, after-corrosion
Does not occur. And etching the flow rate of oxygen gas
Economically by changing with the progress of
An alloy wiring pattern can be formed.

Further, since a gas containing no carbon is used as an etching gas and a resist is not used as an etching mask, there is little deposition in the chamber, and it is possible to perform clean etching without carbon and with few particles generated. Therefore, the device yield can be improved, and the throughput can be improved by reducing the maintenance time of the apparatus.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor substrate according to a method for forming aluminum alloy wiring in a first embodiment of the present invention.

FIG. 2 is a diagram showing changes in the surface area of the aluminum alloy film during etching of the aluminum alloy film in the second embodiment of the present invention.

FIG. 3 is a diagram showing a continuous change in oxygen gas flow rate during etching of an aluminum alloy film in the second embodiment of the present invention.

FIG. 4 is a diagram showing a stepwise change in oxygen gas flow rate during etching of an aluminum alloy film in a second embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between an etching elapsed time and a gas flow rate when etching an aluminum alloy film in an example of the present invention.

[Fig. 6] Aspect ratio for forming aluminum alloy wiring
Diagram showing steps

FIG. 7 is a sectional view of a semiconductor substrate in a conventional aluminum alloy wiring forming method.

FIG. 8 is a diagram of a cross-sectional shape of the wiring in the conventional aluminum alloy wiring forming method.

[Explanation of symbols]

 1 semiconductor substrate 2 BPSG film 3 aluminum alloy film 4 silicon oxide film 5 resist

Claims (6)

[Claims] 1. A method of forming an aluminum alloy wiring, which comprises dry-etching an aluminum alloy film with a gas containing a chlorine-based gas and an oxygen gas using a silicon oxide film or a silicon nitride film as an etching mask. 2. An aluminum alloy film is dry-etched by alternately performing dry etching with a gas containing a chlorine-based gas and dry etching with a gas containing an oxygen gas using a silicon oxide film or a silicon nitride film as an etching mask. A method for forming an aluminum alloy wiring characterized by the above. 3. The method for forming an aluminum alloy wiring according to claim 1, wherein the amount of oxygen gas is changed continuously or stepwise with the progress of etching. 4. The method for forming an aluminum alloy wiring according to claim 1, wherein the chlorine-based gas is a gas containing no carbon atoms. 5. A chlorine-based gas is Cl ₂ , CCl ₄ , or BC.
_{3. At} least one kind selected from l ₃ , SiCl ₄ , HCl, and CHCl ₃ is included.
A method for forming an aluminum alloy wiring as described. 6. A chlorine-based gas containing no carbon atoms is C
5. The method for forming an aluminum alloy wiring according to claim 4, wherein at least one kind selected from l ₂ , BCl ₃ , SiCl ₄ , and HCl is used.