JPH06318573A - Etching of high melting point metal - Google Patents

Abstract

PURPOSE:To provide a plasma etching method by which a stacked film of an adhesive layer and a high melting point metal layer is anisotropically processed in one step. CONSTITUTION:A W film 14 anal a TiN film 13 are plasma-etched with mixed gas of Cl2+HBr. The requirements for the plasma etching include Cl2/HBr=75/25SCCM, a microwave output 300W, an RF output LOW, a stage temperature 70 deg.C, and pressure 0.4Pa. In this etching, an etch rate of the W film 14 was 250nm/min. and that of the TiN film 13 150nm/min. A selection ratio of the TiN film 13 to a silicon oxide film 12 was 50 to 1. Thus, the W film and the TiN film could be anisotropically processed in one step.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching refractory metal. In particular, the present invention relates to anisotropic etching of a refractory metal having an adhesion layer such as titanium nitride and can be used in the field of manufacturing semiconductor devices.

[0002]

2. Description of the Related Art Recently, demands for miniaturization, high integration, and high speed of semiconductor devices have been increasing. Therefore, it is important to reduce the resistance of the internal wiring material, improve the flatness of the surface step, and perform highly selective etching with the underlying material. For this reason, tungsten (W), which is a metal having a high melting point and a low resistance, is drawing attention as the next wiring material.

Conventionally, the following two methods are known as methods for plasma-etching tungsten using a photoresist as a mask.

(1) A fluorine-based gas such as SF ₆ is used as an etching gas and the temperature of the substrate to be etched is set to -20.
Etching by keeping at -30 ° C (Proceedings of Spring Meeting of Japan Society of Applied Physics 1991 28p-ZC-14, 1992)
Proceedings of the Spring Conference of the same year 28p-NC-1, 1992 Proceedings of the Autumn Lecture of the Society 16a-SK-8).

(2) Using Cl ₂ gas or HBr gas as an etching gas, the substrate to be etched is 75 to 1
Method of etching while keeping at 00 ° C. (JP-A-4-2199)
No. 29).

[0006]

However, in the above etching method (1), the tungsten film can be anisotropically etched, but the titanium nitride film as the adhesion layer cannot be etched. Therefore, when etching titanium nitride, it is necessary to use a bromine-based gas such as HBr and to keep the substrate to be etched at a high temperature of 80 ° C. or higher.
That is, in the above method (1), it is necessary to separately perform the two-step etching for the tungsten film and the titanium nitride film. Performing the two-step etching in this manner has a problem that the production capacity is reduced (30% is reduced) and further the cost is increased.

In the etching method (2), the tungsten film and the titanium nitride film can be etched in one step using Cl ₂ or HBr. However, when HBr is used, the tungsten film The etching was low and not suitable for practical use. When etching the titanium nitride film, it is necessary to increase the RF bias applied to the substrate to be etched. Further, when the RF bias is increased in this way, the base film (S
A large selection ratio with iO ₂ ) cannot be obtained. Therefore, when etching the titanium nitride film after etching tungsten with Cl ₂ , bromine-based gas such as HBr must be used, resulting in two-step etching, which is the same as the method (1) above. There's a problem.

The problem to be solved by the present invention is what kind of means should be taken to carry out dry etching capable of etching the refractory metal layer and its adhesion layer in one step. It is in.

[0009]

The invention according to claim 1 of this application provides a structure in which an adhesion layer and a refractory metal layer are sequentially stacked on a semiconductor substrate, and the refractory metal layer and the adhesion layer are adhered to each other. In the refractory metal etching method of plasma-etching a layer, using a mixed gas of a plurality of kinds as an etching gas used for the plasma etching is a solution.

The invention according to claim 2 is characterized in that the mixed gas comprises a chlorine-based gas and a bromine-based gas.

The invention according to claim 3 is characterized in that the refractory metal is made of tungsten and the adhesion layer is made of titanium nitride.

According to a fourth aspect of the present invention, the plasma etching is performed at a substrate temperature of 70 to 150 ° C. under a pressure of 1 Pa or less.

[0013]

In the invention described in claim 1 of this application, since the mixed gas of plural kinds is used for the plasma etching, the etching of the refractory metal layer and the adhesion layer can be performed in one step. The invention according to claim 2 uses chlorine-based gas and bromine-based gas as the mixed gas, whereby the chlorine-based gas mainly etches the refractory metal and the bromine-based gas mainly etches the adhesion layer. To do. Therefore, the mixed gas enables one-step etching and improves the production capacity. In the invention according to claim 3, the tungsten layer is mainly etched by the chlorine-based gas in the mixed gas, and the titanium nitride layer is mainly etched by the bromine-based gas. Further, in the plasma etching, the temperature of the semiconductor substrate is maintained at 70 to 150 ° C. and the pressure is set to 1 Pa or less in the plasma etching, so that the reaction products (WClx, WBrx, etc.) are redeposited. This has the effect of preventing the generation of residues due to. For this reason, reaction products attached to the etching side wall are not increased along with the etching, and the etching surface is prevented from being tapered and anisotropic etching is enabled.

[0014]

EXAMPLES By applying the present invention, a laminated film of a titanium nitride film and a tungsten film having an HBr of 25 to 75 can be obtained.
% HBr + Cl ₂ mixed gas is used to keep the pressure at 1 Pa or less, and the substrate to be etched is kept at 70 to 150 ° C.
By keeping the etching selectivity of the underlying oxide film (S _i O ₂ film) can be obtained more than 50, yet can be anisotropic processing in one step.

An embodiment in which the high melting point metal etching method according to the present invention is applied to a laminated film composed of a tungsten film and a titanium nitride film will be described below with reference to the drawings.

First, in this embodiment, E as shown in FIG.
A CR plasma etching device is used. This ECR plasma etching system uses a quartz bell jar 1 and a wafer 1
Is provided with a wafer stage 3 and a quartz waveguide 4 is provided with a waveguide 4 for guiding microwaves. A magnetic field generating coil 5 is arranged on the outer periphery of the quartz bell jar 1.

Next, an etching process using such an ECR plasma etching apparatus will be described with reference to FIGS.

First, as shown in FIG. 1, a silicon substrate 1
A silicon oxide film 12 is deposited on the substrate 1 by the CVD method so as to have a film thickness of 300 nm. Next, a TiN film 13 as an adhesion layer is deposited on the silicon oxide film 12 by a sputtering method so as to have a film thickness of 100 nm. Then
A W film 14 having a film thickness of 30 is formed on the TiN film 13 by the CVD method.
It is deposited to have a thickness of 0 nm. Then, a resist is applied on the entire surface, and a resist pattern 15 serving as an etching mask is formed by a lithography technique.

Next, the wafer was carried in and mounted on the wafer stage 3 of the ECR plasma etching apparatus shown in FIG. 9, and plasma etching was performed under the following conditions.

(Plasma etching conditions) ・ Etching gas and its flow rate Cl ₂ ...... 75 _sccM HBr ...... 25 _sccM・ Magnetic field ・ ・ ・ 875 Gauss ・ Microwave output ・ ・ ・ 300 W (2.46 GHz) ・ RF output ・ ・ ・ 10 W ( 2MHz) ・ Wafer stage temperature 70 ℃ ・ Pressure 0.4Pa (3mTorr) High density plasma can be generated under the above conditions, and by applying 2MHz RF, ion energy and ion I was able to control the acceleration.

The above temperature was controlled by pure water circulated on the wafer stage 3.

By plasma etching under these conditions,
The etching of the W film 14 shown in FIG. 2 provided an etching rate of 250 nm / min. Further, the sidewall protection film 16 shown in FIG. 2 is mainly made of a chlorine compound-based reaction product, but since the wafer stage temperature is relatively high at 70 ° C. and the pressure is low at 0.4 Pa, it is excessive on the etching sidewall. Will not adhere to. Therefore, as the etching progressed, the side wall protective film 16 was not gradually thickened, and the isomer processing was performed. Further, even in the etching of the TiN film 13 shown in FIG. 3, the sidewall protection film 16 does not become thick under the same conditions, so that anisotropic processing can be performed. This TiN film 1
The etching rate of 3 was 150 nm / min.
This etching rate is lower than that of the W film 14, but the TiN film 13 is usually thinner than the W film 14, and thus has a sufficiently good etching rate.

The graph shown in FIG. 5 shows the ratio of HBr to the mixed gas of Cl ₂ and HBr, the W film 14 and the TiN film 1.
3 shows an outline of the relationship with the etching rate of No. 3. In this embodiment, the proportion of HBr is set to 25%, but as can be seen from the graph, good one-step etching is possible even if the proportion is increased to about 50%. As described above, in this embodiment, since the W and Ti laminated film is etched in one step, the underlying silicon oxide film (SiO ₂ ) is used.
It is also important that the etching selection ratio with respect to 12 be large.

The graph shown in FIG. 6 shows that the value of the etching selection ratio (TiN: SiO ₂ ) is 50 or more at a ratio of 25 to 75% HBr. In this embodiment, as described above, HBr is 25%, the selection ratio is 50, and a sufficient margin at the end point of the undercoat overetch can be secured.

Further, as shown in the graph of FIG.
The temperature of the wafer stage 3 is 70 at r25% (in this embodiment).
It can be seen that a high etching rate (both W and TiN) can be obtained if the temperature is at least ° C. However, in this embodiment, since a photoresist is used as the etching mask, it is appropriate to set the temperature to about 70 ° C to 150 ° C in consideration of its heat resistance.

FIG. 8 is a graph showing the relationship between the wafer stage temperature and the inclination angle (θ) of the etching side wall. From this graph, it can be seen that it is appropriate to perform plasma etching at a temperature of 70 ° C. or higher. That is, since the film thickness of the reaction product (side wall protection film 16) attached to the side walls of the W film 14 and the TiN film 13 which are being etched becomes thin at 70 ° C. or higher, it is possible to prevent the film from being gradually thickened as the etching progresses. . In addition to this, if the pressure is 1.0 Pa or less, the vapor pressure of the reaction product becomes high, and the sidewall protection film 16 adhering to the etching sidewall does not have an excessive film thickness and contributes to anisotropic processing. . In this example, a sidewall angle θ of 87 to 90 ° C., which is almost vertical, was obtained.

Further, the sidewall angle θ can be brought close to 90 ° C. by increasing the mixing ratio (flow ratio) of HBr.

Although the embodiment has been described above, the present invention is not limited to this, and various changes accompanying the gist of the configuration can be made.

For example, although W is used as the refractory metal layer in the above embodiments, refractory metals such as Cu, Mo and Ta can be applied. In this case, depending on each refractory metal. The material of the adhesion layer may be selected appropriately.

Further, the adhesion layer in the above embodiment may have a laminated structure with Ti in addition to the TiN single layer.

Further, the etching conditions in the above-mentioned embodiment are appropriately changed within the scope of claims.

[0032]

As is apparent from the above description, according to the invention described in claims 1 to 4, there is an effect that the laminated film of the refractory metal layer and the adhesion layer can be anisotropically processed in one step. Therefore, the production capacity is improved.

According to the invention of claim 4, in particular,
By setting the pressure and the substrate temperature, it is possible to prevent the generation of residues due to the re-adhesion of reaction products (WClx, WBrx, etc.) and to prevent the side wall protective film made of reaction products from becoming excessively thick, which is good. There is an effect that various anisotropic processing can be achieved.

[Brief description of drawings]

FIG. 1 is a process sectional view showing an embodiment of the present invention.

FIG. 2 is a process sectional view showing an embodiment of the present invention.

FIG. 3 is a process sectional view showing an embodiment of the present invention.

FIG. 4 is a process sectional view showing an embodiment of the present invention.

FIG. 5 is a graph showing the relationship between the mixing ratio of HBr and the etching rate.

FIG. 6 is a mixture ratio of HBr and an etching selection ratio (Ti
N: graph showing the relationship between SiO _2).

FIG. 7 is a graph showing the relationship between the wafer stage temperature and the etching rate.

FIG. 8 is a graph showing the relationship between the wafer stage and the angle (θ).

FIG. 9 is a schematic explanatory diagram of an ECR plasma etching apparatus used in an example of the present invention.

[Explanation of symbols]

 11 ... Silicon substrate 12 ... Silicon oxide film 13 ... TiN film 14 ... W film 15 ... Resist pattern 16 ... Side wall protective film

Claims (4)

[Claims] 1. A method of etching a refractory metal, which comprises plasma-etching the refractory metal layer and the adhesion layer to a structure in which an adhesion layer and a refractory metal layer are sequentially stacked on a semiconductor substrate. A method of etching a refractory metal, wherein a mixed gas of a plurality of types is used as an etching gas used for etching. 2. The method for etching a refractory metal according to claim 1, wherein the mixed gas is a chlorine-based gas and a bromine-based gas. 3. The refractory metal layer is tungsten (W)
3. The method for etching a refractory metal according to claim 1, wherein the adhesion layer is made of titanium nitride (TiN). 4. The method of etching a refractory metal according to claim 1, wherein the plasma etching is performed under a pressure of 1 Pa or less while keeping the semiconductor substrate at a temperature of 70 to 150 ° C.