JPS60217634A - Method for plasma etching - Google Patents

Abstract

PURPOSE:To obtain the state wherein an anisotropic etching is easily accomplished and to have the state suited for employment of microscopic working technique by a method wherein a mixed gas, in which hydrogen gas is added besides chlorine reaction gas, is used as the reaction gas to be used when a plasma etching is performed on aluminum or an aluminum alloy. CONSTITUTION:A mixed gas in which hydrogen gas is added besides carbon tetrachloride and trichloroboron is used as the reaction gas to be used when a plasma etching is performed on aluminum. When said plasma etching is going to be performed, a hydrocarbon polymer is grown on the side wall part of an aluminum film, and an anisotropic etching can be accomplished. This hydrocarbon polymer can be removed easily by performing an oxygen plasma treatment. The content of hydrogen gas of approximately 10-50vol% is considered practicable. When hydrogen gas is mixed, cathode dropping voltage is boosted, an anisotropic etching can be accomplished even when making power density is low, and the ratio of selectivity can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plasma etching method, and particularly to an etching gas used in plasma etching aluminum or an aluminum alloy.

[Prior art and its problems]

Conventionally, etching processing of aluminum or aluminum alloy (hereinafter simply referred to as aluminum) during microfabrication of semiconductor devices, for example, has been carried out using a parallel plate type glue actuator.
1' 3.56 MHz
This is done by generating plasma using high frequency power and realizing anisotropic etching (etching with an etching surface perpendicular to the film surface).

That is, as shown in the outline of plasma etching in FIG. 1, the aluminum film 1 is etched by chlorine radicals in the plasma using the resist film 2 as a mask. It is highly desirable that a protective film 3 be formed on the sidewalls of the aluminum film 1 during etching to protect the sidewall portions of the aluminum film 1 from attack by chlorine radicals.

In addition, the etching rate for the aluminum film is high, that is, when the etching rates for the aluminum film and the resist film are compared, the etching rate for the aluminum film is high (high selectivity), and furthermore, the etching rate for the aluminum film is high (selectivity is high).

It is also required that no etching residue or the like remains on the underlying layer 4 of the substrate.

It is also required that after-corrosion (a phenomenon in which the aluminum film is corroded when it is taken out into the atmosphere after etching), which is a phenomenon unique to plasma etching of aluminum films, does not easily occur.

It has been found that the etching characteristics mentioned above are greatly affected by the type of reaction gas, and recently it has been said that a mixed gas of carbon tetrachloride, which has a high etching rate, and boron trichloride, which has a high selectivity, is good. There is.

However, when a mixed gas of carbon tetrachloride and boron trichloride is used as an etching gas, the etching characteristics vary greatly depending on the mixing ratio of carbon tetrachloride and boron trichloride. In the plasma, chlorocarbon (CnCtm)-based polymers are easily generated, and although these polymers play the role of the above-mentioned protective film, they are difficult to remove and remain as a residue after plasma etching is completed. On the other hand, when the proportion of boron trichloride increases, it becomes difficult to form a polymer as a protective film, and it becomes difficult to realize anisotropic etching.
The disadvantage is that it is not suitable for microfabrication.

Therefore, taking the above points into consideration, it is said that a mixed gas with a boron trichloride ratio of 80 is good.

However, even if the condition that the proportion of boron trichloride is approximately 80% is satisfied, anisotropic etching is not achieved if the input power density during plasma etching is about 0.2 W/cr& or less. In other words, anisotropic etching will not be performed unless power is supplied at approximately 0.3 W/ff1 or more.

However, as the input power density increases, the etching speed for the resist film increases, which means that the etching selectivity decreases. For example, when the input power density is about 0.3 W/cr&, the aluminum/resist etching selectivity is about 2. However, as the input power density increases, the selectivity decreases rapidly, resulting in fatal drawbacks such as the resist film used as a mask disappearing before etching of the aluminum film is completed. .

In addition, when a binary gas mixture of carbon tetrachloride and boron trichloride is used, after the plasma etching is completed, the chlorocarbon-based polymer remains, so the after-color
There are also problems such as John being intense.

[Disclosure of the invention]

The present inventor has proposed that a mixed gas such as carbon tetrachloride and boron trichloride, or a mixed gas containing hydrogen in addition to a chlorine-based reactive gas such as dichlorodifluoromethane, be used as a reactive gas during plasma etching of aluminum or aluminum alloy. It has been found that extremely desirable plasma etching can be achieved using the following methods.

In other words, when hydrogen gas is contained in the reaction gas, a hydrocarbon (CnHm)-based polymer is generated in the plasma, and this polymer acts as a protective film instead of the chlorocarbon-based polymer. Become. This hydrocarbon-based polymer is easily formed even when the amount of boron trichloride is large, and therefore anisotropic etching is easily performed.

Furthermore, unlike chlorocarbon polymers, hydrocarbon polymers can be easily decomposed by oxygen plasma treatment after etching, and do not remain as residues that may cause adverse effects.

In addition, if hydrogen gas is included, the cathode drop voltage (when plasma is generated with parallel plate electrodes, the electrode potential on the sample side and the high-frequency power input side of the tweezers always decreases, and this high-frequency power input side (potential difference when the potential of Etching characteristics similar to those obtained with electric power can be obtained, which means that anisotropic etching can be achieved with a small input power density, and etching with a high selectivity to the resist can be achieved.

Furthermore, after-corrosion is less likely to occur. In other words, the cause of after-corrosion is that hydrogen chloride, which is generated by the reaction between chlorine remaining on the wafer after etching and moisture in the atmosphere, corrodes aluminum. After-corrosion can be prevented by removing chlorine before it is released into the atmosphere.

In other words, if excess chlorine is reacted with hydrogen after etching and this reactant is removed in a vacuum, after-coloring can be achieved.
John will be prevented.

〔Example〕

A mixed gas of carbon tetrachloride, boron trichloride, and hydrogen is used as a reactive gas during plasma etching of aluminum films used in semiconductor devices, for example.

In addition, the reaction gas used in the plasma etching of aluminum is hydrogen gas in addition to the conventional carbon tetrachloride and boron trichloride, and the other steps are substantially the same as in the conventional case.

During this plasma etching, a hydrocarbon polymer is generated on the side wall portion of the aluminum film, realizing anisotropic etching.

This hydrocarbon polymer could be easily removed by oxygen plasma treatment (plasma ashing) after etching.

In addition, the input power density is approximately 0; 2 W/c++t, and BCt30vct4 +H2 (flow rate ratio 16:4:5)
When examining the change in cathode fall voltage with respect to gas pressure, it is as shown in FIG. In the same figure, the solid line shows the characteristics using the etching gas of the present invention, and the dotted line shows the characteristics using the etching gas of BClN + CCt4 (flow rate ratio 4:1).
) shows the characteristics using gas.・In other words, when hydrogen gas is mixed, the cathode drop voltage increases, which means that anisotropic etching can be achieved even if the input power density is low, and the selectivity is high. are doing.

Further, when examining how the selectivity, which is the etching rate of the aluminum film/the etching rate of the resist film, changes depending on the amount of hydrogen gas added, the results are shown in FIG. The test was carried out by setting BCt3:CC24=4:1 and adding hydrogen gas to this. That is, when hydrogen gas is included, for example, 20 volumes of candy, the selectivity is improved by about 2.5 times compared to when no hydrogen gas is included, and the hydrogen gas content is about 10 to 50%. In the volume-related case, anisotropic etching is carried out with a desirable selectivity for practical use. It was something.

Further, even when the wafer was taken out after plasma etching was completed, after-corrosion was unlikely to occur.

[Effect] Anisotropic etching is easy to perform and is therefore suitable for microfabrication technology.

In addition, the protective film for realizing anisotropic etching can be easily removed after etching is completed, so that no inconveniences such as scratches occur during implementation.

In addition, plasma anisotropic etching can be achieved at low power density, making it economical, and because it can be performed at low power density and contains hydrogen gas, the etching selectivity is high.

In addition, it is resistant to after-corrosion and is suitable for microfabrication of semiconductor devices and the like.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of plasma etching of an aluminum film, and FIGS. 2 and 3 are graphs showing the effects of implementing the plasma etching method of the present invention. Patent applicant: Victor Company of Japan.゛＼−2,／ ”−N ← Torture 3 Shikyo Explosion

Claims (1)

[Claims] ■ A plasma etching method characterized by plasma etching aluminum or an aluminum alloy with a mixed gas containing a chlorine-based reactive gas and hydrogen gas. (2) A plasma etching method according to claim 1, wherein the hydrogen gas content is about 10 to 50 vol.