JPH06108272A - Plasma etching method - Google Patents

Abstract

PURPOSE:To uniformly execute plasma etching treatment to a metallic film having an Al alloy layer, a W layer or a W allay layer with good reproductivity. CONSTITUTION:Plasma etching treatment for an Al allay layer 14 using a mixed gas of a chlorine gas and a nitrogen gas and plasma etching treatment for a W layer 13 using a mixed gas of chlorine gas and oxygen gas are continuously executed in the same chamber with a patterned photoresist 15 as a mask.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for plasma etching a metal film, and more particularly to an Al alloy layer and a W layer or W layer.
And a plasma etching method for a metal film including an alloy layer.

[0002]

2. Description of the Related Art Al alloys are mainly used as wiring materials for semiconductor integrated circuits such as LSIs. 16M integration
In a highly integrated LSI with more than one bit, the wiring density increases with the miniaturization of the pattern size. When the wiring density increases, electromigration occurs in the wiring made of Al alloy, which causes element failure such as disconnection of the wiring. To prevent this electromigration, A
A multilayer film structure in which a metal layer made of a W alloy such as W or TiW is inserted between the 1-alloy layer and the underlayer is adopted.

When plasma etching a metal film composed of such an Al alloy layer and a W layer or a W alloy layer in a predetermined pattern, another mixed gas suitable for each metal layer is used. A chlorine-based mixed gas of chlorine gas and BCl ₃ gas is used for plasma etching of the Al alloy layer, and S is used for plasma etching of the W layer or W alloy layer.
A mixed gas containing a fluorine-based gas such as F ₆ gas or CF ₄ gas or a chlorine-based mixed gas of chlorine gas and oxygen gas is used.

[0004]

However, the plasma etching of the Al alloy layer with the chlorine-based mixed gas and the plasma etching of the W layer or the W alloy layer with the fluorine-based mixed gas are alternately performed in a single chamber. If so, the reproducibility of etching decreases.

If the Al alloy layer is plasma-etched with a mixed gas of chlorine gas and BCl ₃ gas and then the W layer or the W alloy layer is plasma-etched with a mixed gas of chlorine gas and oxygen gas, The residual B and the introduced O react with each other to generate a product (B _m O _n ). Therefore, when a large number of samples are subjected to plasma etching treatment, these products are deposited on the wall surface of the chamber and cause particles, and debris from the wall adheres to the surface of the sample to be etched, and the etching rate Deterioration or poor etching occurs.

In order to avoid such a situation, Al
It is necessary to plasma etch the alloy layer and the W layer or W alloy layer in separate chambers or to clean the walls of the reaction chamber before many products are deposited. However, in such a method, there are problems that it takes a long time to manufacture an LSI, the operation rate of the device is lowered, and the like.

The present invention has been made in view of the above circumstances, and for a large number of samples in which a metal multilayer film including an Al alloy layer and a W layer or a W alloy layer is formed, each of these metals is used. An object of the present invention is to provide a plasma etching method capable of performing plasma etching on a layer continuously and in a short time with good reproducibility in a single chamber.

[0008]

A plasma etching method according to the present invention is a method of plasma etching a metal film having an Al alloy layer and a W layer or a W alloy layer in a single chamber, wherein the Al alloy layer is formed. The mixed gas containing chlorine gas and nitrogen gas is used for the plasma etching, and the mixed gas containing chlorine gas and oxygen gas is used for the plasma etching of the W layer or the W alloy layer.

[0009]

In the plasma etching method of the present invention, the Al alloy layer is plasma-etched by using the mixed gas of chlorine gas and nitrogen gas, and the W layer or the W alloy layer is formed by using the mixed gas of chlorine gas and oxygen gas. Plasma etching. Even if the Al alloy layer is plasma-etched using a mixed gas of chlorine gas and nitrogen gas, an etching shape almost similar to that obtained by etching using a mixed gas of chlorine gas and BCl ₃ gas is obtained. After plasma etching the Al alloy layer with a mixed gas of chlorine gas and nitrogen gas, continuously plasma etching the W layer or the W alloy layer with a mixed gas of chlorine gas and oxygen gas in the same chamber. The residual nitrogen gas does not react with the oxygen gas, and even if it reacts, it only becomes a nitrogen oxide gas, no product is deposited on the wall surface of the chamber, and an etching shape with good reproducibility can be obtained.

[0010]

EXAMPLES The present invention will be specifically described below with reference to its examples.

First, an apparatus used for carrying out the plasma etching method of the present invention will be described. FIG. 1 is a vertical cross-sectional view of an ECR plasma etching apparatus using electron cyclotron resonance as an example of the plasma etching apparatus. In the figure, 1 is a plasma chamber, 2 is a waveguide, 3 is a reaction chamber, and 4 is an exciting coil.

The plasma chamber 1 has a hollow cylindrical shape having a double wall structure and a cooling water flow passage chamber 1a, and is formed to form a cavity resonator for microwaves. A cooling water supply system 1f and a drainage system 1g are in communication with the flow chamber 1a. A microwave introduction port 1c closed by a quartz glass plate 1b is provided at the center of the upper wall of the plasma chamber 1, and a plasma extraction window 1d is provided at a position facing the microwave introduction port 1c at the center of the lower wall thereof. . Plasma chamber 1
A gas introduction pipe 1e for introducing an etching gas from the reaction chamber 3 side toward the inside of the plasma chamber 1 is provided so as to penetrate the lower wall.

One end of the waveguide 2 is connected to the microwave introduction port 1c, and the reaction chamber 3 is arranged facing the plasma extraction window 1d. An exciting coil 4 is arranged around the plasma chamber 1 and one end of the waveguide 2 connected to the plasma chamber 1. The other end of the waveguide 2 is connected to a microwave oscillator (not shown) (frequency: 2.45 GHz), and the generated microwave is introduced into the plasma chamber 1. Excitation coil 4 is a DC power supply (not shown)
And a magnetic field is generated by the flow of a DC power source, and a microwave is introduced into the plasma chamber 1 to generate plasma. Further, the exciting coil 4 generates a divergent magnetic field having a lower magnetic flux density toward the reaction chamber 3, and the divergent magnetic field causes the plasma generated in the plasma chamber 1 to be projected into the reaction chamber 3. ing.

In the reaction chamber 3, an exhaust port 3a connected to an exhaust device (not shown) is opened on the bottom wall facing the plasma extraction window 1d. Further, inside the reaction chamber 3, a sample table 5 is disposed immediately below the plasma extraction window 1d so as to face the plasma extraction window 1d.
A sample S to be etched is placed on the sample table 5 so as to face the plasma extraction window 1d. The sample table 5 has a high frequency power source 6 (frequency: 1
3.56 MHz). A gas supply system 3b communicating with the reaction chamber 3 penetrates the side wall of the reaction chamber 3.

In the plasma etching apparatus having such a structure, the plasma chamber 1 and the reaction chamber 3 are set to a predetermined vacuum degree, and then the etching gas is introduced into the plasma chamber 1 through the gas introducing pipe 1e, so that the sample stage A high frequency voltage is applied to 5 by a high frequency power source 6, a magnetic field is formed by an exciting coil 4, and a microwave is introduced into the plasma chamber 1 through the microwave introduction port 1c. The plasma chamber 1 is used as a cavity resonator to etch gas. Resonance excitation is performed to generate plasma. The generated plasma is a divergent magnetic field whose magnetic flux density decreases toward the reaction chamber 3 formed by the exciting coil 4,
The sample S is projected around the sample S on the sample table 5, and the etching process is performed on the sample S.

Next, specific examples of the present invention will be described. FIG. 2A is a sectional view showing the structure of the sample S to be etched, which is placed on the sample table 5 in FIG. This sample S is a SiO ₂ layer 12 as a base on a silicon substrate 11.
(Film thickness: 0.3 μm), W layer 13 (film thickness: 0.2 μm), Al
An Al alloy layer 14 (film thickness: 1.0 μm) made of a —Si—Cu alloy (Si: 1%, Cu: 0.5%) is laminated in this order,
Furthermore, a photoresist 15 (film thickness: 1.5 μm, line width: 0.
5 μm) is formed.

The sample S having such a structure is placed on the sample table 5, and a mixed gas of chlorine gas and nitrogen gas is introduced from the gas introduction pipe 1e to plasma-etch the Al alloy layer 14 of the sample S. To do. The plasma generation conditions at this time are that the gas pressure is 5 mTorr and the microwave power is 1000 W. The flow rate of the mixed gas to be introduced is 75 sccm of chlorine gas,
Nitrogen gas is 25 sccm and total gas flow rate is 100
sccm. A preferable example of the mixing ratio of chlorine gas and nitrogen gas is N ₂ / (Cl ₂ + N ₂ ) = 2 to 40%
Is.

When the etching of the Al alloy layer 14 is completed,
The gas introduced from the gas introduction pipe 1e is switched from the mixed gas of chlorine gas and nitrogen gas to the mixed gas of chlorine gas and oxygen gas. Here, the intensity of the emission wavelength of AlCl is monitored by an optical method, and the time when the intensity decreases and does not change is determined to be the time when the etching of the Al alloy layer 14 ends. Then, after confirming the completion of the etching of the Al alloy layer 14, the etching gas is switched. This etching gas switching method includes a method of stopping introduction of microwaves and application of high-frequency voltage, then stopping nitrogen gas and introducing oxygen gas, and restarting introduction of microwaves and application of high-frequency voltage. There are two methods, that is, the introduction of microwaves and the application of high-frequency voltage are left as they are, and only nitrogen gas is stopped and oxygen gas is introduced.

The W layer 13 is plasma-etched using a mixed gas of chlorine gas and oxygen gas. The plasma generation conditions at this time are that the gas pressure is 5 mTorr and the microwave power is 1000 W. The flow rate of the mixed gas to be introduced is 60 sccm of chlorine gas and 40 sccm of oxygen gas,
The total gas flow rate is 100 sccm. A preferable example of the mixing ratio of chlorine gas and oxygen gas is O ₂ /
(Cl ₂ + O ₂₎ = 20 to 60%.

According to such etching, as shown in FIG.
As shown in (b), the photoresist 15 is also etched to some extent to reduce its film thickness, but the Al alloy layer 14 and W
Layer 13 is patterned and etched so that its etched sides are vertical.

FIG. 3 shows changes in the etching rate when a large number (1000 sheets) of samples having the structure shown in FIG. 2 are subjected to the plasma etching process by using the plasma etching method of the present invention. -●) is shown. In Figure 3,
The results are shown in which the etching rate of the first sample is set to 1 and the etching rate of the Al alloy layer 14 in each sample is normalized. Further, in FIG. 3, for the same sample, a mixed gas of chlorine gas and BCl ₃ was used for plasma etching of the Al alloy layer 14, and chlorine gas and oxygen gas were used for plasma etching of the W layer 13. The change in etching rate (○-○ in the figure) in the conventional example in which the plasma etching process is performed using the mixed gas is also shown.

In the case of the conventional example, the etching rate of the Al alloy layer 14 significantly decreases as the number of processed sheets increases (10
However, in the plasma etching method of the present invention, the etching rate after processing 1000 sheets is only a few percent lower than that at the beginning of etching.

In the present embodiment, the case of using the ECR plasma etching apparatus utilizing electron / cyclotron resonance has been described, but another parallel plate type plasma etching apparatus utilizing high frequency voltage may be used. Of course. Of course, gases such as He and Ar may be added to stabilize the plasma and improve the etching rate.

[0024]

As described above, in the plasma etching method of the present invention, the mixed gas of chlorine gas and nitrogen gas is used for the plasma etching of the Al alloy layer, and the chlorine gas is used for the plasma etching of the W layer or the W alloy layer. Since a mixed gas of oxygen gas and oxygen gas is used, even when the Al alloy layer and the W layer or the W alloy layer are continuously plasma-etched in a single chamber, the reaction does not occur on the wall surface in the chamber. It is possible to perform plasma etching on a large number of samples uniformly and with good reproducibility without depositing products.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the configuration of an ECR plasma etching apparatus for carrying out a plasma etching method of the present invention.

FIG. 2 is a cross-sectional view showing a shape of a sample to be subjected to the plasma etching method of the present invention before and after etching treatment.

FIG. 3 is a graph showing changes in etching rate when a plurality of samples are subjected to plasma etching etching treatment.

[Explanation of symbols]

1 Plasma chamber 1e Gas introduction tube 2 Waveguide 3 Reaction chamber 4 Excitation coil 5 Specimen stage 6 High frequency power supply 11 Si substrate 12 SiO ₂ layer 13 W layer 14 Al alloy layer 15 Photoresist S sample

Claims (1)

[Claims] 1. A method of plasma etching a metal film having an Al alloy layer and a W layer or a W alloy layer in a single chamber, wherein the plasma etching of the Al alloy layer includes chlorine gas and nitrogen gas. A plasma etching method using a mixed gas, wherein a mixed gas containing chlorine gas and oxygen gas is used for plasma etching the W layer or the W alloy layer.