JPS6254441A - Etching device - Google Patents

Abstract

PURPOSE:To assure excellent operation of etching device regardless of corrosive etching gas by a method wherein liquid nitrogen traps connecting to a vacuum vessel are provided to adsorb and exhaust etching gas. CONSTITUTION:A high-frequency electrode 2 is impressed with high-frequency voltage from a high-frequency power supply 21 to produce glow discharge plasma for etching aluminium by active chemical species such as chlorine ion etc. contained in the plasma. After finishing the etching process, a valve 12 is closed and purge line 14 is opened to flow inert gas such as argon, nitrogen etc. for heating a heater 17 so that boron trichloride or carbon tetrachloride adsorbed to a liquid nitrogen trap 10 may be exhausted therefrom. Finally boron trichloride or carbon tetrachloride in etching process is exhausted from another liquid nitrogen trap 11 alternately using these two liquid nitrogen traps 10, 11 to operate the etching device continuously. Through these procedures, excellent operation can be assured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an etching apparatus, and more particularly to an etching apparatus equipped with a liquid nitrogen trap for adsorbing and exhausting etching gas.

[Conventional technology]

In order to form fine aluminum wiring in semiconductor integrated circuits, a dry etching method using boron trichloride or carbon tetrachloride gas plasma is used. Since this method can normally etch a photoresist mask pattern without causing an undercut phenomenon, it is possible to form a highly accurate and fine aluminum wiring pattern by accurately transferring the mask pattern. However, since there is no undercut phenomenon and the wall surface of the etched aluminum wiring is perpendicular to the substrate surface, the insulation such as silicon dioxide or phosphosilicate glass that should be deposited on the aluminum or RAM wiring The coverage of objects is extremely poor. In order to improve the coverage of the insulator, it is necessary to create a controlled undercut phenomenon to the extent that microfabrication is not impaired, and to give the aluminum wall surface a desired slope after etching.

When aluminum is etched using plasma of a mixed gas of boron trichloride with a small amount of chlorine or hydrogen chloride added, an undercut phenomenon in which the lower part of the resist mask is etched has been found. The degree of this undercut is related to the addition ratio of chlorine or hydrogen chloride. In the example of adding chlorine to boron trichloride, as shown in Figure 1, as the addition ratio of chlorine increases, the aluminum wall surface The inclination angle of decreases. The experimental results shown in Figure 1 show that the gas pressure during etching is Q, 2 Torr, and the high frequency power density is 0.
．． It was obtained under conditions of 25 W/cm''.

As mentioned above, etching aluminum with plasma of boron trichloride gas to which a small amount of chlorine is added has the advantage that the etching rate is higher than etching with gas plasma of boron trichloride alone. FIG. 2 shows the relationship between the etching rate of aluminum and the addition ratio of chlorine. Addition ratio of chlorine is 10
%, the etching rate of aluminum is 5000λ/
min, which is extremely large, making it difficult to control the end of etching. For this reason, it is desirable that the addition ratio of chlorine be 10% or less. Further, even if a very small amount of chlorine is added, some undercut phenomenon is observed. However, in order to sufficiently improve the coverage of the insulator, it is desirable to add chlorine in an amount of about Q, 1 vol, % or more. When performing such etching, the vacuum pump used in connection with the vacuum chamber may deteriorate if the etching gas is a corrosive gas containing halogen or the like.

SUMMARY OF THE INVENTION An object of the present invention is to provide an etching apparatus that can operate satisfactorily even when the etching gas is corrosive.

[Means for solving problems]

In order to achieve the above object, according to the present invention, in an etching apparatus that etches an object to be etched by introducing an etching gas into a vacuum chamber, a liquid nitrogen trap is provided which is connected to the vacuum chamber and adsorbs and exhausts the etching gas. .

More preferably, a plurality of liquid nitrogen traps are provided so that the liquid nitrogen traps can be switched and used.

[Effect]

By installing a liquid nitrogen trap, the etching gas is adsorbed and exhausted by the liquid nitrogen trap, so the pressure inside the vacuum chamber can be maintained at a predetermined value.Since there is no vacuum pump installed, the etching gas will not corrode the rotating parts. There is no problem that the vacuum pump deteriorates due to

In addition, in the case where multiple liquid nitrogen traps are provided, while one liquid nitrogen trap is being regenerated, other liquid nitrogen traps can adsorb etching gas.
It becomes possible to operate the etching device continuously.

〔Example〕

The present invention will be described in detail below with reference to Examples.0 The following procedure was used to etch a sample in which a 4fLjfB pattern of photoresist was formed on an aluminum film deposited to a thickness of 1 μm on a silicon wafer. I obeyed.

The above sample was placed on one of a pair of parallel plate electrodes, and boron trichloride gas containing 2 vog,% chlorine was introduced at 100 mg per minute into the vacuum chamber containing these electrodes, which was connected to one end of the vacuum chamber. The gas was adsorbed and exhausted by a liquid nitrogen trap, and the pressure inside the vacuum chamber was set to Q, 2 Torr.

13. Place the sample on the electrode. A high frequency electric field of 6 MHz was applied to generate a high frequency glow discharge between both electrodes.

The power used was 0.25 W/cm2.

Under these conditions, the etching rate of aluminum is approximately 23
00λ/min, and etching progresses with an undercut phenomenon. In the case of this sample, etching of aluminum with a thickness of 1 μm was completed in about 5 minutes.

When the cross-sectional shape of the aluminum was observed after etching was completed, the aluminum wall surface showed an inclination of about 60°.

In addition, boron trichloride may be mixed with oxygen or a Freon gas such as CF4. Exactly the same effect can be obtained when a small amount of C2F6 or the like is added. These are intended to promote the decomposition of boron trichloride according to formulas (1) and (2) and liberate chlorine gas, thereby obtaining the same effect as chlorine addition. In addition, good results can be obtained by setting the total pressure of the introduced gas to 0.05 to 0.5 Torr0 BCn3+O□→B2O3+Cg2 (1) B
Cg +CF4-+BF3+CCn2F'2+Cg2 Next, the plasma etching apparatus will be described in detail.

In FIG. 3, an etching chamber 1 is equipped with a high-frequency electrode 2 and a counter electrode 3, and a first exhaust port 4 is equipped with a liquid nitrogen tank.
It is connected via a valve 8 to a vacuum pump consisting of a vacuum pump 5, an oil diffusion pump 6, and an oil rotary pump 7, and a second exhaust port 9.
In this case, two liquid nitrogen traps 10.11 are connected to valve 12.
．． 13 in parallel. liquid nitrogen trap 1
0.11 are each provided with a purge line 14.15 via a valve 16.17, and have a built-in heater 8.19.

When etching aluminum, the sample 20 is placed on the high-frequency electrode 2 or the counter electrode 3, and the etching chamber 1 is evacuated by the vacuum pumps 5, 6.7, and then the valve 8 is closed and boron trichloride or carbon tetrachloride gas is used. A mixed gas with chlorine or the like is introduced with a current of about 10 Or+ll/min, and is exhausted by a liquid nitrogen trap 10. Boron trichloride, carbon tetrachloride, chlorine gas, etc. are rapidly adsorbed on the inner wall of the liquid nitrogen trap, so while introducing these gases into the etching chamber 1, the pressure inside the etching chamber can be adjusted by adjusting the conductance of the valve 12. 0.02~ITorr
The pressure can be adjusted to . Thereafter, a high frequency voltage is applied to the high frequency electrode 2 by the high frequency power supply 21 to generate glow discharge plasma, and the aluminum is etched by activated chemical species such as chlorine ions in the plasma. After etching, close the valve 12, open the purge line 14,
The heater 17 is heated through an inert gas such as argon or nitrogen.
is heated to degas (regenerate) boron trichloride, carbon tetrachloride, etc. adsorbed in the liquid nitrogen trap 10.

During the next etching process, the exhaust of boron trichloride or carbon tetrachloride gas is performed by another liquid nitrogen trap 11, and by using the following two liquid nitrogen traps 10 and 11 alternately, the etching apparatus is continuously operated. It can be operated.

In this etching apparatus, corrosive gas such as boron trichloride containing chlorine does not flow into the vacuum pump such as the oil rotary pump at all, so problems such as deterioration of vacuum pump function and deterioration of pump oil do not occur. By employing a plurality of liquid nitrogen traps, there are advantages such as continuous operation of the device. In addition, in order to save etching gas, the etching gas such as boron trichloride adsorbed in the liquid nitrogen trap 10 is heated and evaporated and reintroduced into the etching chamber 1, while being adsorbed and evacuated by the other liquid nitrogen trap 11. It is also possible to etch the sample.

It goes without saying that this device can also be applied to cases where boron trichloride or carbon tetrachloride gas is used without mixing chlorine gas or hydrogen chloride gas.

〔Effect of the invention〕

Since the present invention is configured as described above, it is possible to provide an etching apparatus that can be operated satisfactorily without causing the problem of deterioration of the vacuum pump.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the amount of chlorine gas added and the inclination angle of the aluminum wall surface to be processed. Figure 2 is a diagram showing the relationship between the amount of chlorine gas added and the etching rate of aluminum. 1 is a diagram showing the structure of a plasma etching apparatus used in an embodiment of the invention. 1... Etching chamber, 10.11... Liquid nitrogen trap, 12.13... Valve, 18.19... Heater, 20... Sample. , Pa'-\, Agent Patent Attorney Katsuo Ogawa ψ 11!1 13d! afqt+ ctz';J:ytv)hi9(2
') Scale Z Ward

Claims (1)

[Claims] 1. An etching apparatus for etching an object to be etched by introducing an etching gas into a vacuum chamber, characterized in that a liquid nitrogen trap is provided which is connected to the vacuum chamber and adsorbs and exhausts the etching gas. Etching equipment. 2. The etching apparatus according to claim 1, wherein a plurality of the liquid nitrogen traps are provided, and the plurality of liquid nitrogen traps are configured to be switchable and usable.