JPS61174634A - Method of dry etching - Google Patents

Abstract

PURPOSE:To enable to control the quantity of etching by chlorine radicals or chlorine molecules and to enable to improve the uniformity of etching in a material to be etched by a method wherein the exhaust velocity to exhaust gas for etching in the etching chamber is quickened. CONSTITUTION:Chlorine gas or gas containing at least chlorine is introduced in an etching chamber 11, and at the same time, discharge is made to generate between a pair of electrodes disposed in opposition to each other in the etching chamber 11 and an etching is performed on an aluminum material or a material containing at least aluminum. The exhaust velocity to exhaust gas in the etching chamber 11 is set at a velocity, at which gas equivalent to 1/2 or more of the capacity of the etching chamber 11 in the duration of one second can be exhausted. For performing actually an exhaust of gas in the etching chamber 11, firstly valves 21b and 21d are opened and valves 21c and 21e are shut and gas in the vacuum chamber 11 is exhausted by a DP24 and an RP26. After gas in the container 11 is once exhausted to the prescribed pressure (the pressure at the time of etching to perform on the foregoing aluminum material), the valves 21b and 21d are shut and the valves 21c and 21e are opened, and gas in the container 11 is exhausted by an MBP25 and the RP26.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for dry etching an aluminum film, and more particularly to a method for etching an aluminum film with good uniformity.

[Technical background of the invention and its problems]

Currently, the metal most commonly used as an interconnection material for ICs and LSIs is aluminum, and this aluminum is used as interconnections by etching its vapor-deposited film using a photoresist as a mask.

As with other etching methods, methods for etching aluminum films include a wet processing method using a phosphoric acid etching solution and a dry processing method using plasma. However, in the wet processing method.

■ Air bubbles adhere during etching and aluminum remains locally.

■ Large undercuts make it difficult to form high-precision patterns.

■ Constriction is likely to occur due to differences in level.

Due to these problems, it is extremely difficult to form fine patterns with high precision and good reproducibility.

On the other hand, plasma etching of an aluminum film as a dry processing method uses Cff12. This can be carried out using a gas containing 0° C. in plasma such as CC4,8Ca3.

Although this etching is also possible using a cylindrical plasma apparatus, in this case, the temperature of the sample increases during etching due to reaction heat, and the chlorine component in the plasma causes significant thermal deterioration of the photoresist.

On the other hand, a parallel plate type plasma apparatus, which can cool the substrate and easily remove the aluminum oxide film that is thought to exist on the surface of the aluminum film, is more advantageous in forming aluminum interconnections.

However, even in the parallel plate type plasma apparatus, there is a problem of non-uniformity in the start of etching due to the removal of the oxide film (AQ203) on the aluminum surface. That is, sufficiently A
If CCλ3'', BCλ2+, etc. are not present in an amount capable of reducing Q203, aluminum will not be exposed uniformly, and a difference will occur in the start of subsequent etching of aluminum, promoting non-uniformity. This is because Al2203 is not a radical. This is due to the fact that it is etched only by ions.

Conventionally, to solve this problem, the exhaust pressure was lowered to reduce H2O, which is the main component of residual gas, and CC
Uniform removal of AQ20s has been achieved by reducing the consumption of j23+ and BCβ2'', increasing high frequency output, and strengthening the ion bombardment effect.

However, it is difficult to etch aluminum with good uniformity using only this method, and in fact, it is difficult to etch aluminum with good uniformity.
Only values of 0 to 30% were obtained. The reason for the poor uniformity of aluminum is thought to be that the aluminum after the A4203 layer is removed is etched by chlorine radicals or chlorine molecules, as has been reported recently. That is, the plasma etching apparatus has a structure in which the etching gas is introduced from the electrode side opposite to the electrode on which the object to be etched is placed, and is exhausted from the periphery of the electrode on which the object to be etched is placed. However, this is because the amount etched by chlorine radicals and chlorine molecules unrelated to the electric field differs between the center and the periphery of the object due to the difference in gas residence time. Furthermore, the amount etched by these chlorine molecules and radicals is a non-negligible value in the overall etching rate, and as a result, as shown in Figure 5, the periphery of the electrode, that is, the periphery of the material to be etched, becomes abnormal. It is thought that it is etched quickly, which deteriorates the overall uniformity.

[Purpose of the invention]

An object of the present invention is to provide a method for dry etching aluminum that can suppress the amount of etching caused by chlorine radicals or chlorine molecules, which are factors that impair etching uniformity, and that can improve etching uniformity within an object to be etched. Our goal is to provide the following.

[Summary of the invention]

The gist of the present invention is to increase the exhaust speed of the etching gas in the etching chamber in order to eliminate as much as possible the non-uniformity of etching caused by chlorine radicals or chlorine.

That is, the present invention provides a dry etching method in which chlorine or at least a gas containing chlorine is introduced into an etching chamber, and a discharge is generated between a pair of electrodes disposed opposite each other in the etching chamber, thereby etching aluminum or at least a material containing aluminum. In this method, the exhaust speed for exhausting the gas in the etching chamber is set to a rate at which more than half of the volume of the etching chamber can be exhausted in one second.

Here, the above pumping speed is set to 1 of the etching chamber capacity per second.
The reason why the speed was set to allow evacuation of /2 or more is to keep the etching uniformity within ±0.5%, and experiments by the inventors have shown that the above etching speed is necessary for this purpose. This is because it has been confirmed.

〔Effect of the invention〕

According to the present invention, by setting the exhaust speed within the above-mentioned range, the residence time of chlorine radicals and chlorine molecules that stay on the surface of the material to be etched such as aluminum can be shortened, and the difference in these residence times can be reduced. can be reduced. Therefore, the nonuniformity of etching within the object to be etched caused by chlorine radicals or molecules is eliminated, and the uniformity of etching within the object to be etched is dramatically improved.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic diagram showing the general structure of a dry etching apparatus used in an embodiment of the method of the present invention.

In the figure, reference numeral 11 denotes a vacuum container forming an etching chamber, and inside this container 11 a pair of parallel plate electrodes 12 and 13 are arranged facing each other. The upper electrode 12 is grounded together with the container 11, and high frequency power from a high frequency power source 14 is applied to the lower electrode 13.

A sample 15 to be etched, on which a material to be etched such as an aluminum film is deposited, is placed on the lower electrode 13.

On the other hand, inside the container 11 is a valve 21a and a gas introduction pipe 22.
An etching gas, for example, 0° C. 2 gas, is introduced through the wafer. The gas introduced into the container 11 passes through an exhaust pipe 23 and valves 21b and 21G to a diffusion pump (hereinafter abbreviated as DP) 24 and a mechanical booster pump (hereinafter M
(abbreviated as BP) 25. In addition, a rotary pump (
(hereinafter abbreviated as RP) 26 is connected.

Here, in order to actually perform the exhaust, first the valves 21b and 2
Open 1d, close valves 21G and 21ei, and open DP24.
And the inside of the vacuum container 11 is evacuated by RP26. container 1
Once the inside of 1 is evacuated to a predetermined pressure (the pressure during aluminum etching), close the valves 21b and 21d,
Open valves 21c and 21e, MBP25 and RP26
The inside of the container 11 is evacuated.

As shown in FIGS. 2(a) and 2(b), the upper electrode 12 is made up of an electrode body 31 having a recessed portion at the center of the lower part, and a plate 32 attached to the lower surface of the electrode 31. A plurality of small holes (gas exhaust ports) 32a are provided in the plate 32 so that the etching species flows uniformly over the sample 15 to be etched. For example, φ1.5[
am] small holes 32a are provided at equal intervals.

On the other hand, the lower electrode 13 is placed on a plate-shaped insulator 33 closely fixed to the inner wall surface of the vacuum vessel 11, as shown in FIG. A ventilation hole 33a is provided around the insulator 33.
A plurality of are provided on concentric circles. The etching gas introduced into the vacuum chamber 11 from the gas outlet hole 32a of the upper electrode 12 flows from the upper part of the etching chamber to the lower part through the vent hole 33a, and is exhausted from the exhaust pipe 23. There is. Note that 35 and 36 in FIG. 3 indicate water cooling pipes for cooling the lower electrode 13.

Next, an etching method using the above apparatus will be explained.

First, an aluminum film was used as the material to be etched, and chlorine (12) and boron trichloride (BCffi3) were used as the etching gas. Further, the exhaust capacity of MBP25 was set to 4000 [n/sin], and the exhaust capacity of RP26 was set to 1200 [ff110+in]. The high frequency power is 100 [W], the pressure during etching is Q, 1 [
torr] and the evacuation speed was varied to examine the etching uniformity of the aluminum film.

FIG. 4 is a characteristic diagram showing the results. Note that the effective pumping speed was determined from the total area of the ventilation holes 33a provided in the insulator 33. The value of etching uniformity within the etched material improves as the effective pumping speed increases, and it is clear from this result that pumping speed and uniformity are closely related. Here, the reason why etching uniformity improves as the pumping speed increases is that the residence time of chlorine radicals and chlorine molecules on the material to be etched becomes shorter, and as a result, the chlorine radicals and chlorine molecules on the surface of the material to be etched are This is thought to be because the difference in residence time of molecules is reduced.

On the other hand, the volume of the vacuum vessel 11 used at this time was 80β, and the effective pumping speed calculated from the total area of the vent hole 33a when the etching uniformity was ±5E% was approximately 40β.
j2/sec ]. In other words, in order to suppress the etching uniformity of aluminum oxide to less than ±5%, it is clear that the ratio of the total volume of the etching chamber to the effective pumping speed (the pumping volume per second) needs to be 1/2 or more. .

The inventors of the present invention also found that the above relationship (the effective pumping speed relative to the maximum etching volume in order to achieve etching uniformity of ±5% or less is 2 or more) holds true, and it has also been confirmed that the same holds true even when the pressure during etching is changed.

As described above, according to the method of this embodiment, the exhaust speed of the etching gas in the vacuum container 11 is set to 1/of the total volume of the container 11.
By setting the speed at which the exhaust gas can be evacuated by 2 or more, the etching uniformity of aluminum can be suppressed to within ±5%. Therefore, great effects can be obtained when applied to the formation of wiring patterns, etc.

Note that the present invention is not limited to the embodiments described above. For example, the vacuum pump used to evacuate the etching chamber is not limited to a diffusion pump or a mechanical booster pump. Any pump that has the ability to do this will suffice. Further, the present invention can be applied to etching not only aluminum but also materials containing at least aluminum. Further, the etching gas is not limited to chlorine, and any gas containing at least chlorine may be used. Further, the structure of the dry etching apparatus used in the method of the present invention is not limited to the structure shown in FIGS. 1 to 3, but can be changed as appropriate according to the specifications. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the general structure of a dry etching apparatus used in a method according to an embodiment of the present invention, FIG. 2 is a cross-sectional view and a plan view showing the specific structure of the upper electrode, and FIG. Its installation is a cross-sectional view showing the specific structure of the insulator, which is a component, Figure 4 is a characteristic diagram showing the relationship between effective pumping speed and etching uniformity, and Figure 5 is a characteristic diagram to explain the problems of the conventional method. It is a diagram. 11... Vacuum container (etching, 12... Upper electrode, 13... Lower N pole, 14... High frequency power supply, 15
... Sample to be etched, 21a, -, 21e... Valve, 22... Gas inlet pipe, 23... Gas exhaust pipe,
24... Diffusion pump, 25... Mechanical booster pump, 26... Rotary pump, 31... Electrode body, 32... Plate body, 32a... Gas introduction hole, 33
...Insulator, 33a...Vent hole, 35.36...
Cooling water piping. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 3 Figure 4

Claims (3)

[Claims] (1) In a dry etching method in which chlorine or at least a gas containing chlorine is introduced into an etching chamber and a discharge is generated between a pair of electrodes placed oppositely in the etching chamber to etch aluminum or at least a material containing aluminum, A dry etching method, characterized in that an exhaust speed for exhausting the gas in the etching chamber is set at a rate at which 1/2 or more of the volume of the etching chamber can be exhausted in one second. (2) The dry etching method according to claim 1, wherein the electrode is a parallel plate electrode. (3) The dry etching method according to claim 2, wherein the aluminum or at least a material containing aluminum is placed on the electrode on the high-frequency power application side of the parallel plate electrodes.