JPH08250476A - Reactive ion etching method - Google Patents

Abstract

PURPOSE: To form electric wiring having an excellent fine cross section which has less thinned-off part by controlling the ratio of a chlorine gas to the sum total of a fluorine gas and the chlorine gas to a prescribed value at the time of etching a silicon thin film in plasma. CONSTITUTION: After an aluminum thin film 21 and silicon thin film 22 are successively formed on the surface of a glass substrate 20, a photoresist pattern 23 is formed on the thin film 22. Then the substrate 20 is set on an RIE device and the thin films 22 and 21 are successively etched by using the pattern 23 as a mask. In the final process, the mask 23 is removed and required electric wiring is formed on the unetched part of the thin film 22 by forming an insulating film 24 composed of SiO2 , etc., on the thin film 22. At the time of etching the silicon thin film 22, fluorine gas and chlorine gas are used as etching gases by controlling the ratio of the chlorine gas to the sum total of the fluorine gas and chlorine gas to 40-60%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactive ion etching method, and more particularly to a method for etching a silicon-based thin film or an alloy thin film with silicon placed on an aluminum thin film.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor device, pure aluminum (Al) or a metal obtained by mixing at least one of silicon (Si) and copper (Cu) with aluminum is used as an electric wiring material.

It is known that when the temperature of the electric wiring exceeds a certain temperature, a projection called a hillock is generated on the surface of the wiring due to the diffusion of aluminum element. Due to the presence of these protrusions, when the wiring is covered with an insulating film typified by an oxide film (SiO ₂ ) to electrically insulate, the protrusions break the insulating film and are placed on the insulating film. There is a problem that the thin film is electrically short-circuited and cannot be used as electric wiring.

As a countermeasure against this, a method has been proposed in which a metal having a higher hardness and a higher heat resistance temperature than other thin films, particularly aluminum, is arranged on the aluminum thin film to suppress the occurrence of the unevenness. As a typical metal thin film, a simple metal film such as titanium or an alloy of silicon and tungsten is often used.

However, when the electric wiring has a two-layer structure as a countermeasure against hillocks, it is necessary to form the wiring by etching each. Conventionally, there is a technique for etching aluminum, but when a silicon-based thin film is formed on aluminum, there is no method for appropriately etching a two-layer thin film.

[0006]

A chemical etching (CDE) method is usually used for etching a silicon-based thin film single layer. However, since the CDE method is not suitable for fine etching and the angle of the etching cross section becomes gradual, the film becomes thin at the wiring end face, and the effect of reducing aluminum hillock in the base is weakened. In the case of a film, it cannot be used for silicon-based thin film etching, and an appropriate etching means is required.

Further, since the base aluminum cannot be etched by the CDE method, when etching a silicon-based thin film with a CDE device, it is necessary to perform the aluminum etching as a separate step, which leads to an increase in the number of etching steps. There is a problem that it is not preferable because it increases the chances of adhesion of dust and impurities.

The present invention provides an etching method which solves such inconveniences and problems.

[0009]

According to the present invention, a thin film composed of two layers of a silicon thin film and an aluminum thin film is etched in a plasma by using a mixed gas containing fluorine and chlorine. In the reactive ion etching method of performing, for the total amount of fluorine-based gas and chlorine-based gas,
A reactive ion etching method is characterized in that the proportion of chlorine-based gas is 40 to 60%.

Further, there is obtained a reactive ion etching method in which the mixed gas of fluorine-based gas and chlorine-based gas is a mixed gas of sulfur hexafluoride (SF ₆ ) and chlorine (Cl ₂ ).

[0011]

The present invention uses, for example, a reactive ion etching apparatus (RIE) to use a mixed gas of a fluorine-based gas and a chlorine-based gas as an etching gas. The mixing ratio is such that the mixing ratio of the chlorine-based gas is 40 to 60% with respect to the total amount of the fluorine-based gas and the chlorine-based gas. This allows fine processing of the electric wiring. When a thin film is processed by an RIE apparatus, not only the thin film to be etched but also the underlying thin film may be etched. However, the gas conditions of the present invention enable etching with a sufficiently high etching ratio to the underlying layer.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an RIE apparatus for carrying out the present invention, and FIG. 2 is a sectional view of a semiconductor device for explaining the steps of this embodiment. In FIG. 1, a pair of electrodes 2 and 3 facing each other in parallel are grounded in a vacuum chamber 1 in a vertical relationship. The upper electrode 2 has a box shape, and a gas ejection port 2 a is opened on the surface facing the lower electrode 3 on which the substrate 12 to be etched is placed, and is connected to the gas introduction pipe 4. C as an etching gas is introduced into the gas introduction pipe 4.
The l ₂ source 5 and the SF ₆ source 6 are connected. The gases are mixed, but the flow rate can be freely set by mass flow. The upper electrode 2 is grounded.

A substrate 12 is provided on the upper surface of the lower electrode 3, a cooling water inlet 3a for introducing cooling water for cooling the substrate is provided, and a matching network 7 is provided.
And the high frequency power source 8 are connected. When a high frequency is input between the pair of electrodes 2 and 3 from the high frequency power source 8, a self-bias voltage is generated in the vicinity of the lower electrode 3 due to the mobility difference between the ions and the electrons, and the accelerated ions are generated on the lower electrode. Collide with the etching target 12. An exhaust pipe 9 is connected to a lower portion of the vacuum chamber 1 so that the inside of the vacuum chamber can be exhausted via a vacuum pump 10 of the exhaust pipe 9, and a heater 1 is provided on the outer circumference of the chamber.
1 is provided. This RIE apparatus is capable of anisotropic etching due to the generation of the self-bias described above, and is therefore suitable for realizing fine processing as compared with the isotropic etching characteristics of the CDE apparatus.

FIG. 2 illustrates a process of etching an etching target composed of a two-layer thin film of an aluminum layer and a silicon layer formed on a glass support base material by using the RIE apparatus shown in FIG.

First, as shown in (a), the glass substrate 20.
On the surface of the aluminum thin film 21 and the silicon-based thin film 22 on it
Are laminated. The silicon-based thin film 22 is silicon or a silicon alloy, that is, titanium silicide, molybdenum silicide, tungsten silicide, or the like.

Next, as shown in (b), the silicon-based thin film 22
A pattern 23 of photoresist is formed on top.

In the next step (c), the substrate is placed in the apparatus of FIG. 1 and the silicon-based thin film 22 is etched by using the pattern 23 as a mask. Then, in the step (d), the aluminum thin film 21 is etched.
Is etched. In step (e) which is the final step, the resist mask 23 is removed, and an insulating film 24 such as SiO ₂ is deposited on the remaining laminated thin film after etching to form necessary electric wiring.

In the present embodiment, chlorine gas (Cl ₂ ) and boron hexafluoride (SF) are used for etching the silicon-based thin film 22.
₆ ) is used. By introducing this gas into the RIE apparatus shown in FIG. 1 to generate plasma discharge and exposing the etching target to the plasma, etching becomes possible.

FIG. 3 shows changes in the etching rate when the chlorine gas mixing ratio is changed with respect to the total gas flow rate of the etching gas. It was confirmed that the etching rate decreased as the mixing ratio of chlorine gas increased.

Further, FIG. 4 shows the etching rate ratio (selection ratio) of the films other than the silicon-based thin film to the silicon-based thin film with the mixing ratio of Cl ₂ and SF ₆ as a variable. From the figure, it can be seen that the selection ratio with respect to the underlying aluminum film is almost constant. However, the selection ratio with the patterned resist is the largest when the mixing ratio of chlorine is 50%, and the selection ratio is high even if the chlorine gas Cl ₂ increases or the boron hexafluoride gas SF ₆ increases. It was confirmed that it would be smaller.

[0022] This is the case of increasing the mixing ratio of Cl _2, it is believed to be caused by the reaction of chlorine and resist proceeds resist becomes thinner as the gas flow rate of Cl ₂ is increased.

The reason why the selection ratio decreases with an increase in the gas flow rate of SF ₆ is considered to be that the resist is etched due to the sputtering effect caused by the collision of the gas body with the resist rather than the reaction by the gas.

The selection ratio with respect to the etching rate with respect to aluminum is hardly affected by the gas mixing ratio.

FIG. 5 shows an etching cross section at a typical mixing ratio. (A) is an etching cross-sectional shape when the chlorine gas mixture ratio is 40%. The cross section 22a of the silicon-based thin film 22 is vertical, but the cross section 2a of the aluminum thin film 21 is
It is inside 1a. Reference numeral 20 indicates a glass substrate.

(B) is a cross-sectional shape when the mixing ratio of chlorine gas is 50%. The cross-section 22a of the silicon-based thin film 22 is 7
There is an inclination of about 0 °, and the cross section of the aluminum thin film 21, that is, the edge portion 21a and the cross section of the silicon-based thin film 22, that is, the edge portion 22a, coincide.

(C) is a cross-sectional shape when the mixing ratio of chlorine gas is 60%. The cross section 22a of the silicon-based thin film 22 is 3
There is a slope of around 0 °.

From the above, the etching rate and the selection ratio of the underlying aluminum thin film and the resist thin film for patterning,
From the etching cross-sectional shape, it is understood that the chlorine gas selection ratio is the best at 50% and the range of 40% to 60% is practical.

The present invention has been described with reference to the embodiments.
In the present invention, not only the gas obtained by mixing the chlorine gas and the sulfur hexafluoride gas, but the same effect can be obtained when an inert gas or the like is mixed and introduced for the purpose other than etching. Similar effects can be obtained even when the etching target is installed on the ground side electrode (upper electrode) like the device.

[0030]

As described above, according to the present invention, it is possible to form an electric wiring which is fine and has a good cross-sectional shape with a small amount of thinning, and the electric wiring is formed without damaging the underlying aluminum thin film. can do.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an RIE device for carrying out an embodiment of the present invention.

FIG. 2 illustrates steps of one embodiment of the present invention.
(A) thru | or (e) is the schematic which shows the cross-sectional shape of a process order.

FIG. 3 is a graph illustrating a gas mixture rate (%) and an etching rate.

FIG. 4 is a graph illustrating a gas mixture ratio (%) and etching selectivity with respect to resist and aluminum.

FIG. 5 is a cross-sectional view illustrating a state of etching a two-layer thin film at various gas mixture ratios.

[Explanation of symbols]

1 ... Vacuum chamber 5 ... Cl ₂ source 6 ... SF ₆ source 20 ... Glass substrate 21 ... Aluminum thin film 22 ... Silicon thin film

Claims (2)

[Claims] 1. A reactive ion etching method in which a thin film composed of two layers of a silicon thin film and an aluminum thin film is etched in plasma by using a mixed gas containing fluorine and chlorine. A reactive ion etching method characterized in that the ratio of chlorine gas is 40 to 60% with respect to the total amount of fluorine gas and chlorine gas. 2. The reactive ion etching method according to claim 1, wherein the mixed gas of the fluorine-based gas and the chlorine-based gas is a mixed gas of sulfur hexafluoride (SF ₆ ) and chlorine (Cl ₂ ).