JPH09260356A - Dry etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable improving the etching rate of a high melting point metal and sufficiently setting the etching selection ratio of the high melting point metal and SiO2 , by using reactive gas which contains fluorine containing compound gas and chlorine gas, or contains chloride material gas and oxygen gas. SOLUTION: Reactive gas is introduced in a discharge tube 12 as a pumping mechanism, the reactive gas is pumped and made a plasma state, and active species are generated. The active species in the discharge tube 12 is introduced in a treatment container 14, and a high melting point metal thin film on the surface of a board 19 mounted in the treatment container 14 is etched by using a resist pattern as a mask. In the case that dry etching is performed in the above processes, gas which contains fluorine containing compound gas and chlorine gas, or gas which contains chloride gas and oxygen gas is used as the reactive gas. For example, Mo, W, MoW alloy, etc., are used as the high melting point metal, CF3 , SF6 , CF2 H2 , etc., are used as the fluorine containing compound, and BCl3 , etc., are used as the chloride.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method for etching a refractory metal thin film used for a gate electrode or the like by utilizing active species generated by exciting a reactive gas into plasma. It is about.

[0002]

2. Description of the Related Art For example, a gate electrode of a thin film transistor is formed on a glass substrate by using the following downflow type etching apparatus. This dry etching apparatus includes a discharge tube made of a dielectric material having a gas introduction part, a waveguide connected to the discharge tube for irradiating the discharge tube with microwaves, and the discharge tube and the transport tube. A processing container connected to the processing container, a diffusion plate arranged in the processing container near the outlet of the transport pipe, an exhaust pipe connected to the processing container, and a holding table arranged in the processing container. To have.

First, a glass substrate, the surface of which is coated with a refractory metal thin film such as molybdenum-tungsten alloy (MoW), and a resist pattern is formed on the thin film, is placed on the holding table. Subsequently, the gas in the processing container, the transport pipe, and the discharge pipe is exhausted through the exhaust pipe, so that a predetermined degree of vacuum is obtained. Subsequently, a reactive gas is introduced into the discharge tube through a gas introducing part, and microwaves are applied to the discharge tube from the waveguide to excite the reactive gas to generate a plasma state, which is necessary for etching. Generates active species and ions. These active species and ions are transported into the processing container through the transport pipe. During this transportation, ions that damage the substrate and the like are extinguished, only the active species are introduced into the processing container through the diffusion plate, and the refractory metal thin film exposed from the resist pattern on the holder is selectively etched. As a result, a desired gate electrode is formed.

By the way, the reactive gas has conventionally been CF.
A mixed gas of ₄ and O ₂ is used. However,
When the MoW thin film on the surface of the glass substrate is etched by using the above-described downflow type etching apparatus using the reactive gas having the above composition with the resist pattern as a mask, there is a problem that MoW cannot be etched at a high speed. It was

That is, in the above-described downflow type etching apparatus in which the reactive gas having the above composition is introduced into the discharge tube through the gas introduction part, the microwave output is 700
W, the pressure was 40 Pa, the flow rate of CF ₄ gas + O ₂ gas was 400 sccm, and the flow rate ratio of these gases [CF
₄ / (CF ₄ + O ₂ )] was changed, and the etching rates of MoW and the resist were measured. The result is shown in FIG.

As is clear from FIG. 5, in the conventional dry etching method using a mixed gas of CF ₄ and O ₂ as a reactive gas, the maximum etching rate of MoW is 440 n.
High-speed etching was difficult because the flow rate ratio of m / min {[CF ₄ / (CF ₄ + O ₂ )] was about 0.3}.

Further, there is a problem that the etching selection ratio between MoW and the oxide film (SiO ₂ film) cannot be sufficiently obtained in the etching by the down-flow type etching apparatus using the reactive gas having the above composition. That is,
The etching rate of SiO _{2 under} the above etching conditions is also shown in FIG. 5 described above. From FIG. 5, the above [CF ₄ /
_{(CF 4 + O 2)]} MoW of SiO ₂ by the ratio of
Since the etching rate of the MoW thin film is about 1/2 to 1/3, the MoW thin film is deposited on the SiO ₂ film (particularly the thermal oxide film), and the MoW thin film is masked with the resist pattern using the reactive gas of the above composition There is a problem that the SiO ₂ film is also punched out by the selective etching.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a dry etching method capable of improving the etching rate of refractory metal such as MoW and having a sufficient etching selection ratio between the refractory metal and SiO _2. It is intended to provide a method.

[0009]

In the dry etching method according to the present invention, a step of introducing a reactive gas into an excitation mechanism and exciting the reactive gas to generate plasma to generate active species In the dry etching method, which comprises a step of introducing active species in the excitation mechanism into a processing container, and etching the refractory metal thin film on the surface of the substrate arranged in the processing container using a resist pattern as a mask, The reactive gas contains a fluorine-containing compound gas and chlorine gas or a chloride gas and oxygen gas.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The dry etching method of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a schematic diagram showing the downflow type etching apparatus of FIG. 1. The discharge tube 12 made of a dielectric material having the gas introduction part 11 is connected to the processing container 14 via a transport tube 13 made of polytetrafluoroethylene, for example. The waveguide 15 for irradiating the discharge tube 12 with microwaves is
It is connected to. The discharge tube 12 having the gas introduction part 11 and the waveguide 15 constitute an excitation mechanism. The diffusion plate 16 is arranged in the processing container 14 near the outlet of the transport pipe 13. The exhaust pipe 17 is connected to the bottom of the processing container 14. Substrate support 18
Are arranged in the processing container 14.

Next, the dry etching method of the present invention will be described using the downflow type etching apparatus described above. First, a substrate 19 whose surface is coated with a refractory metal thin film and a resist pattern is formed on the thin film is placed on a support base 18. Then, the gas in the processing container 14, the transport tube 13 and the discharge tube 12 is exhausted through the exhaust pipe 17 to obtain a predetermined degree of vacuum. Subsequently, a reactive gas containing a fluorine-containing compound gas and a chlorine gas or a chloride gas and an oxygen gas is introduced into the discharge tube 12 through the gas introduction part 11, and a microwave is guided from the waveguide 15 to the discharge tube 12. By irradiating and exciting the reactive gas into a plasma state, active species and ions necessary for etching are generated. These active species and ions are transported into the processing container 12 through the transport pipe 13. During this transportation, the ions are extinguished, only the active species are introduced into the processing container 14 through the diffusion plate 16, and the refractory metal thin film on the surface of the substrate 19 on the support 18 is dry-etched.

As the substrate 19, for example, a semiconductor substrate, a glass substrate or the like can be used. As the refractory metal, for example, molybdenum, tungsten, tantalum, molybdenum-tungsten alloy, molybdenum-tantalum alloy, or the like can be used.

The degree of vacuum in the processing container 14, the transport tube 13 and the discharge tube 12 is preferably 30 to 40 Pa. As the fluorine-containing compound that is a component of the reactive gas, for example, CF ₄ , SF ₆ , CF ₂ H _{2 and the} like can be used.

As the chloride which is another component of the reactive gas, for example, BCl ₃ or the like can be used. The mixing volume ratio of the reactive gas fluorine-containing compound gas constitutes the and (F _G) and chlorine gas or chloride gas (C _{G) is, F G: C G = 0.9~0.3} : 0.1 ~ 0.7,
In addition, the mixing volume ratio of the mixed gas of F _G and C _G and the oxygen gas (O _G ) is preferably mixed gas: O _G = 1: 3 to 6. By using the reactive gas having such a mixing ratio, the etching rate of the refractory metal thin film can be increased and the etching selection ratio between the refractory metal and the oxide film can be further increased.

According to the present invention described above, the surface of the substrate is processed by the down-flow type etching apparatus shown in FIG. 1 using the reactive gas containing the fluorine-containing compound gas and the chlorine gas or the chloride gas and the oxygen gas. By etching the refractory metal thin film with the resist pattern thereon as a mask, the refractory metal thin film can be etched at a high speed, and a sufficient etching selection ratio between the refractory metal and the resist can be obtained. .

That is, in the above-described downflow type etching apparatus in which the reactive gas having the above composition is introduced into the discharge tube 12 through the gas introduction section 11 shown in FIG. 1, the microwave output is 700 W, the pressure is 40 Pa, and O ₂ The gas flow rate is 380 sccm, the CF ₄ gas + Cl ₂ gas flow rate is 70 sccm, and the flow rate ratio [Cl ₂
/ (Cl ₂ + CF ₄ )] was changed, and the etching rates of MoW and the resist were measured. The result is shown in FIG.

As is apparent from FIG. 2, in the dry etching method of the present invention in which a mixed gas of CF ₄ , Cl ₂ and O ₂ is used as a reactive gas, the above [Cl ₂ / (Cl ₂ + CF _2
4)] ratio is 0.5 before and after, that is CF _4: Cl _2/1
The maximum MoW etching rate before and after is about 700 nm
/ Min, which shows that high-speed etching is possible. Further, the etching selection ratio between MoW and the resist can be increased to about 3.5 times.

Under the above conditions, a gate electrode is formed on a glass substrate by selective etching of a MoW thin film using a resist pattern as a mask, and the taper angle (Θ) at the end of the gate electrode is determined. As shown in FIG. Cl ₂ / (Cl ₂ +
CF ₄ )] is changed, the taper angle at the end of the gate electrode becomes 42 ° to 65 °, and the allowable taper angle (25 to 70 ° for improving the step coverage at the end of the gate electrode). ) Is within the range.

Furthermore, in the etching by the downflow type etching apparatus shown in FIG. 1 using the reactive gas having the above composition, MoW and an oxide film (SiO ₂ film) are formed.
It is possible to obtain a sufficient etching selection ratio with respect to.
That is, the Si under the etching conditions shown in FIG.
The etching rate of O ₂ is also shown. From FIG. 2, if the ratio of [Cl ₂ / (Cl ₂ + CF ₄ )] is set to about 0.5, the etching rate of MoW with respect to SiO ₂ can be about 10. Therefore, even if a MoW thin film is deposited on a SiO ₂ film (particularly a thermal oxide film) and the MoW thin film is selectively etched by using a reactive gas having the above composition with a resist pattern as a mask, the SiO ₂ film is etched. Can be sufficiently suppressed, and an oxide film can be present around the formed MoW gate electrode.

In the dry etching described above, the etching end point can be detected by measuring the pressure fluctuation in the processing container 14 of the dry etching apparatus. That is, when the etching of the refractory metal thin film on the surface of the substrate 19 progresses in the processing container 14, the pressure inside the processing container 14 increases due to the generation of etching products. When the etching of the refractory metal thin film is stopped, the pressure increase factor due to the etching products disappears, and the pressure in the processing container 14 decreases. The end point of etching can be detected by detecting this pressure change.

[0021]

An embodiment of the present invention will be described below in detail with reference to FIG. Example 1 First, as shown in FIG. 4A, a MoW thin film 22 having a thickness of 300 nm was deposited on the surface of a glass substrate 21 by sputtering, and then a 1200 nm thick film was formed on the MoW thin film 22 by a photo-etching technique. Resist pattern 23 was formed.

Next, the glass substrate was placed on the support base 18 shown in FIG. Subsequently, the gas in the processing container 14, the transport tube 13 and the discharge tube 12 was exhausted through the exhaust pipe 17 to obtain a vacuum degree of 40 Pa. Continuously, the flow rate of the reactive gas composed of CF ₄ gas, Cl ₂ gas and O ₂ gas in the discharge tube 12 is set to 35 sccc for CF ₄ gas, Cl ₂ gas and O ₂ gas respectively.
m, 35 sccm and 380 sccm, and then introduced through the gas introduction part 11 and then the waveguides 15 to 70
By irradiating the discharge tube 12 with a microwave of 0 W to excite the reactive gas into a plasma state, active species and ions necessary for etching were generated. These active species and ions were transported into the processing container 14 through the transport pipe 13, the ions were extinguished during the transportation, and only the active species were introduced into the processing container 14 through the diffusion plate 16. The MoW thin film on the surface of the glass substrate on the support 18 was selectively dry-etched with the active species using the resist pattern as a mask. By such selective dry etching, as shown in FIG. 4B, the gate electrode 2 made of MoW is formed on the surface of the glass substrate 21.
4 was formed.

The taper angle of the end portion of the obtained gate electrode 24 was measured and found to be 60 °. In addition, after removing the resist pattern, CVD-
When a SiO2 film and an amorphous silicon film as an active layer were deposited, no step breakage was found at the end of the gate electrode.

[0024]

As described above in detail, according to the present invention, M
To provide a dry etching method which can improve the etching rate of refractory metal such as oW and can sufficiently obtain the etching selection ratio of the refractory metal and SiO ₂ and is useful for forming a gate electrode and the like. You can

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a downflow type dry etching apparatus used in a dry etching method of the present invention.

[Figure 2] of the present invention CF _4, Cl ₂ and a reactive gas comprising a mixed gas of O ₂ is introduced into the etching apparatus downflow type shown in Figure 1 at the time of etching [Cl ₂ / (Cl
₂ + CF ₄ )] ratio and MoW, resist and SiO
FIG. 3 is a characteristic diagram showing the relationship with the etching rate of ₂ .

[Figure 3] of the present invention CF _4, Cl ₂ and a reactive gas comprising a mixed gas of O ₂ is introduced into the etching apparatus downflow type shown in Figure 1 at the time of etching [Cl ₂ / (Cl
₂ + CF ₄ )] ratio and the taper angle of the end portion of the gate electrode.

FIG. 4 is a cross-sectional view showing a step of forming a gate electrode in Example 1 of the present invention.

FIG. 5 shows a ratio [CF ₄ / (CF ₄ + O ₂ )] and MoW when a conventional reactive gas composed of a mixed gas of CF ₄ and O ₂ is introduced into a down-flow type etching apparatus for etching. FIG. 6 is a characteristic diagram showing the relationship between the resist and the etching rate of SiO ₂ .

[Explanation of symbols]

 12 ... Discharge tube, 13 ... Waveguide, 14 ... Processing container, 18 ... Support stand, 19 ... Substrate, 21 ... Gasra substrate, 22 ... MoW thin film, 23 ... Resist pattern, 24 ... Gate electrode.

Claims (2)

[Claims] 1. A step of introducing a reactive gas into an excitation mechanism, and exciting the reactive gas here to generate plasma, thereby generating active species, and the active species in the excitation mechanism being introduced into a processing container. Introduced, in a dry etching method comprising a step of etching the refractory metal thin film of the substrate surface placed in this processing container using a resist pattern as a mask, the reactive gas, fluorine-containing compound gas and chlorine gas or A dry etching method comprising a chloride gas and an oxygen gas. Wherein the fluorine-containing compound gas constitutes the reactive gas (F _G) and chlorine gas or chloride gas (C
_G ) is mixed in a volume ratio of F _G : C _G = 0.9-0.
3: 0.1 to 0.7, and the volume mixing ratio of the fluorine-containing compound gas and chlorine gas or a mixed gas and oxygen gas and chloride gas (O _G) is mixed gas: O _G = 1: 3 ~
6. The dry etching method according to claim 1, wherein the dry etching method is 6.