JPH10150020A - Method and device for plasma treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a plasma treatment at a high speed which is stable for a long time by retarding corrosion and preventing break of a microwave introducing window. SOLUTION: A plasma treatment device produces a plasma by introducing a microwave in a plasma producing space (an inner space comprising an inner tube 16 and a second microwave introducing window 13b) in a reaction receptacle (a plasma forming chamber 10 and a reaction chamber 11) through microwave introducing windows 13a and 13b. The microwave introducing window 13b which comes into a direct contact with plasma is formed by aluminum nitride. With the aid of the device, plasma of fluorine base gas such as C4 F8 is produced for etching a silicon oxide film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a plasma processing apparatus and a plasma processing method used for manufacturing semiconductors and liquid crystal displays, and more particularly to a plasma processing apparatus and a plasma processing method used for etching a silicon oxide film. .

[0002]

2. Description of the Related Art A plasma processing apparatus for generating plasma using microwaves and processing a sample is widely used in the manufacture of semiconductors, liquid crystal displays, and the like.

In these apparatuses, microwaves are transmitted from a microwave oscillator to a reaction vessel by a waveguide, and are introduced into the reaction vessel through a microwave introduction window. Since the inside of the reaction vessel is almost in a vacuum and the inside of the waveguide is at atmospheric pressure, a microwave introduction window is required for the purpose of sealing the inside of the reaction vessel to a vacuum and transmitting microwaves. The space between the microwave introduction window and the reaction vessel wall is vacuum-sealed by a method of providing an O-ring or the like.

[0004] The microwave introduction window is required to have microwave permeability for transmitting microwaves, heat resistance for heating microwaves and plasma, and corrosion resistance for etching by plasma.

Conventionally, quartz or alumina (Al ₂ O ₃ ) has been used as a material for the microwave introduction window.

However, quartz has low corrosion resistance to, for example, fluorine-based plasma. Therefore, when plasma of a fluorine-based gas is used, since the microwave introduction window is etched, the supply of reactive species to the sample is reduced, and there is a problem that the etching rate of the sample is reduced.

In addition, alumina has a problem that, when used for a long time, it is easily damaged by microwave dielectric heating or heating by plasma. Breakage of the microwave introduction window hinders stable operation of the device and reduces the throughput of the device.

Therefore, in order to solve these problems, silicon nitride (Si ₃ N ₄ ) has been used for a microwave introduction window. For example, a microwave introduction window of silicon nitride is provided on a plasma generation side of a microwave introduction window of quartz.

The etching rate of silicon nitride by plasma of a fluorine-based gas is much lower than that of quartz. Therefore, according to this method, the problem of the quartz microwave introduction window that the microwave introduction window is etched by the plasma and the etching rate of the sample is reduced can be solved. In addition, there is not much problem with the microwave introduction window made of alumina that the microwave introduction window is easily broken by microwave heating or plasma heating.

However, it has been found that the microwave introduction window of silicon nitride causes a phenomenon that the etching rate of the sample is gradually changed. This phenomenon occurs as follows.

Silicon nitride is not etched at all by plasma of a fluorine-based gas, but is etched a little. Normally, silicon nitride contains a lot of impurities. Therefore, when the sample is etched by the plasma of the fluorine-based gas, impurities that are not etched deposit on the surface of the silicon nitride microwave introduction window with the passage of time. As a result, the exposed area of the silicon nitride to be etched decreases with time, and the reactive species consumed for etching the microwave introduction window decreases. And gradually increase the etch rate of the sample.

The change over time of the etching rate of this sample is as follows:
It is not preferable from the viewpoint of process stability. This is because if the etching rate of the sample changes with time, it is necessary to change the etching time and the like in accordance with the change in the etching rate of the sample.

[0013] Further, there is also a problem of contamination that the precipitated impurities fall off and adhere to the sample with the passage of time.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and provides a plasma processing apparatus and a plasma processing method capable of performing high-speed and stable plasma processing for a long time. It is intended to be.

[0015]

A plasma processing apparatus according to the present invention is a plasma processing apparatus for generating a plasma by introducing a microwave into a plasma generator in a reaction vessel through a microwave introduction window, The microwave introduction window which is in direct contact with the plasma is characterized in that aluminum nitride (AlN) is formed.

Further, the plasma processing method of the present invention is characterized in that the silicon oxide film is etched by generating plasma of a fluorine-based gas using the above-described plasma processing apparatus.

The microwave introduction window referred to here is
The microwave is transmitted and introduced into the plasma generation unit.

The present inventors have investigated materials for microwave introduction windows which have excellent corrosion resistance to fluorine gas plasma and are not easily damaged by heating by microwaves or plasma.

As a result, it was confirmed that the aluminum nitride was hardly etched by the plasma of the fluorine-based gas and had excellent heat resistance against microwaves and plasma heating.

The present invention has been made based on this finding.

That is, the plasma processing apparatus of the present invention comprises:
A microwave introduction window that is in direct contact with the plasma is formed of aluminum nitride. For this reason, even if a fluorine-based gas plasma is used, the reactive species hardly react with the microwave introduction window, so that the reactive species are mainly used for the reaction with the sample and the active species used for the reaction with the sample. Is hardly changed with time. As a result, stable plasma processing at high speed for a long time can be performed. Also, since aluminum nitride is hardly etched, there is no problem of contamination that the precipitated impurities fall off and adhere to the sample. Furthermore, because the microwave introduction window is hard to break,
The device can be operated stably, and the throughput of the device can be improved.

According to the plasma processing method of the present invention, a silicon oxide film is etched by generating plasma of a fluorine-based gas using the above-described apparatus. Therefore, the silicon oxide film can be etched stably at high speed for a long time.

The above-mentioned fluorine-based gas includes, for example, C
_{2 F 6, C 3 F 8} , is C ₄ F _8, CHF _3, fluorocarbons such as CH ₂ F ₂ (fluorocarbon) based gas.

[0024]

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

FIG. 1 is a schematic longitudinal sectional view showing one example of the plasma processing apparatus of the present invention. This device uses electron cyclotron resonance (E) by the interaction of microwave and magnetic field.
This is an apparatus that generates plasma using CR (Electron Cyclotron Resonance) and etches a silicon oxide film.

The reaction vessel has a plasma generation chamber 10 and a reaction chamber 11.

In the upper part of the plasma generation chamber 10, a first microwave introduction window 13a is provided. A second microwave introduction window 13b is provided above the inner tube 16 in the plasma generation chamber 10 which will be described later. The first microwave introduction window 13a is formed of quartz or the like. The second microwave introduction window 13b is formed of aluminum nitride. The microwave is supplied from a microwave oscillator (not shown) via the waveguide 12 and is introduced into the plasma generation chamber 10 through the microwave introduction window 13. Around the plasma generation chamber 10, a magnetic field generating coil 14 is concentrically arranged.
Are arranged.

On the side wall of the reaction chamber 11, a gas introduction pipe 15 is provided, and an exhaust port 19 is provided. Reaction chamber 1
A sample table 20 is provided at the center of the sample table 1. Sample table 2
Reference numeral 0 includes an electrostatic chuck mechanism, a cooling mechanism, and a high-frequency electrode. The electrostatic chuck mechanism holds the sample S on the sample table 20 by electrostatic force, cools the sample S by a cooling mechanism, and applies high frequency to the high frequency electrode from the high frequency power supply 21 to thereby ionize the sample S. Energy can be controlled.

An inner tube 16 and an inner tube 17 are provided so as to cover the inner side walls of the plasma generation chamber 10 and the reaction chamber 11, respectively. By preventing the inner walls of the plasma generation chamber 10 and the reaction chamber 11 from being directly exposed to plasma, these inner pipes prevent contamination caused by spattering of the inner wall and adhesion of reaction deposits to the inner wall. To prevent. The inner tube 16 is made of a material having a low reactivity with the plasma of the fluorine-based gas, for example, aluminum (Al) because the inner tube 16 is in the vicinity of the plasma generating portion and strongly receives the plasma irradiation. Since the inner tube 17 is provided in a region of the reaction chamber 11 that is not much exposed to plasma irradiation, the inner tube 17 is made of a conventionally used material such as quartz. The inner tube 17 may not be used in some cases. Further, since plasma is generated in the internal space defined by the inner tube 16 and the second microwave introduction window 13b, the first microwave introduction window 13a is not exposed to plasma.

A method for etching a silicon oxide film using this plasma processing apparatus will be described. Sample S
Is a silicon wafer on which a silicon oxide film is formed.

The sample S is placed on the sample table 20 and held by suction.

The plasma generation chamber 10 and the reaction chamber 11 are evacuated to a predetermined pressure.

From the gas introduction pipe 15 to the plasma generation chamber 10
And, for example, C ₄ F _{8 is used} as an etching gas in the reaction chamber 11.
And O ₂ are each introduced at a predetermined flow rate to a predetermined pressure.

A direct current is passed through the magnetic field generating coil 14 to generate a magnetic field required for ECR excitation in the plasma generation chamber 10. Microwaves are introduced from a microwave oscillator (not shown) into the plasma generation chamber 10 via the waveguide 12. The etching gas is turned into plasma by ECR excitation due to the interaction between the microwave and the magnetic field. After the plasma is generated, high frequency power is applied to the sample table 20 by the high frequency power supply 21. Active species such as ions and radicals in the plasma are guided onto the sample S, and the silicon oxide film on the sample S is etched.

As an etching gas for the silicon oxide film, for example, C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₈ , CHF ₃ , CH ₂ F
Or the like may be used fluorocarbon gas and a mixed gas of O _2, such as _2. Note that an inert gas such as Ar may be added.

This device includes a second microwave introduction window 13
b is made of aluminum nitride. Therefore, even if the fluorine-based gas plasma is used, the reactive species hardly reacts with the microwave introduction window 13b. As a result, stable plasma processing at high speed for a long time can be performed.
In addition, the second microwave introduction window 13b is hardly damaged by microwave heating and plasma heating, and the first microwave introduction window 13a is hardly damaged by microwave heating. It can be operated, and the throughput of the device can be improved.

In this example, the first microwave introduction window 13a is made of quartz or the like, but it goes without saying that it may be made of aluminum nitride. Also,
The inner tube 16 and the inner tube 17 may also be made of aluminum nitride.

FIG. 2 is a schematic vertical sectional view showing another example of the plasma processing apparatus of the present invention. This apparatus is also an ECR plasma processing apparatus like the apparatus of the previous example, but has a relatively simple apparatus configuration. That is, the apparatus has a configuration in which microwaves are introduced into the plasma generation chamber 10 from the microwave introduction window 13 to generate plasma in the plasma generation chamber 10. The microwave introduction window 13 is made of aluminum nitride.

Also in this apparatus, the reactive species of the plasma of the fluorine-based gas hardly react with the microwave introduction window 13, so that high-speed and long-time stable plasma processing can be performed as in the above-described example. Further, since the microwave introduction window 13 is not easily damaged by microwave heating and plasma heating, the apparatus can be operated stably, and the throughput of the apparatus can be improved.

The plasma generation chamber 10 and the reaction chamber 1
In 1, an inner wall may be exposed, or an inner tube 16 or 17 made of aluminum nitride, aluminum, quartz, alumina or the like may be provided as necessary.

The aluminum nitride used for the microwave introduction window in the plasma processing apparatus of the present invention is Y
It goes without saying that a sintering aid component such as ₂ O ₃ may be included.

As described in the previous example, the silicon oxide film was etched as an example. However, the plasma processing apparatus of the present invention is effective for plasma processing using fluorine-based gas plasma. In addition to the etching of the silicon oxide film, the present invention can be applied to the etching of a polysilicon film or the etching of a metal oxide film such as TaO ₂ . However, it is needless to say that the method is suitable for etching a silicon oxide film using plasma of a fluorine-based gas such as a fluorocarbon-based gas.

Although the example of the ECR plasma processing apparatus has been described, the present invention can be applied to a plasma processing apparatus that generates a plasma by introducing a microwave into a plasma generation unit in a reaction vessel through a microwave introduction window. . However, since the ECR plasma processing apparatus has a feature of generating high-density and highly active plasma below the microwave introduction window, the plasma processing apparatus of the present invention is suitable for the ECR plasma processing apparatus.

[0044]

An embodiment of the present invention will be described. The apparatus used in this embodiment is the plasma processing apparatus shown in FIG. The first microwave introduction window 13a is made of quartz, and the second microwave introduction window 13a is made of quartz.
The microwave introduction window 13b was made of aluminum nitride.
The inner tube 16 was made of aluminum, and the inner tube 17 was made of quartz. The frequency of the microwave is 2.45 GHz, and the frequency of the high frequency applied to the high frequency electrode of the sample stage 20 is 400.
kHz.

Using this apparatus, the silicon oxide film was etched and the etching rate was measured. The etching conditions are as follows. The flow rate of the etching gas is C
₄ F ₈ : 19 sccm, O ₂ : 15 sccm, pressure was ₁ mTorr, microwave power was 1600 W, and high frequency power was 700 W. In addition, as a comparative example, the second microwave introduction window 1
The same evaluation was performed for an apparatus in which 3b was made of conventional silicon nitride.

The result of the etching rate is 400 nm / min in the example of the present invention in which the second microwave introduction window 13b is made of aluminum nitride, and is 400 nm / min in the comparative example in which the second microwave introduction window 13b is made of silicon nitride. 410 nm / m
was in. That is, the second microwave introduction window 13
It was confirmed that the etching rate was not substantially changed even if b was made of aluminum nitride.

Further, using the apparatus of the present invention, the silicon oxide film was etched on the 25 silicon wafers on which the silicon oxide film was formed under the above conditions.
It was confirmed that there was almost no change in the etching rate. On the other hand, the silicon oxide film was similarly etched using the apparatus of the comparative example, but the etching rate of the final silicon wafer was changed to 390 nm / min compared to the initial etching rate.

In the above test, the first microwave introduction window 13a of the apparatus of the present invention and the apparatus of the comparative example
No break such as a crack was observed in any of the second microwave introduction window 13b and the second microwave introduction window 13b.

[0049]

According to the plasma processing apparatus and the plasma processing method of the present invention, it is possible to suppress the occurrence of corrosion and cracks in the microwave introduction window, and to perform stable plasma processing at high speed for a long time.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing one example of a plasma processing apparatus of the present invention.

FIG. 2 is a schematic longitudinal sectional view showing another example of the plasma processing apparatus of the present invention.

[Explanation of symbols]

 Reference Signs List 10 Plasma generation chamber 11 Sample chamber 12 Waveguide 13, 13a, 13b Microwave introduction window 14 Magnetic field generation coil 15 Gas introduction pipe 16 Inner tube 17 Inner tube 19 Exhaust port 20 Sample table 21 High frequency power supply S Sample (silicon wafer) )

Claims (2)

[Claims] 1. A plasma processing apparatus for generating a plasma by introducing a microwave into a plasma generator in a reaction vessel through a microwave introduction window, wherein the microwave introduction window directly in contact with the plasma is made of aluminum nitride. A plasma processing apparatus characterized by being formed. 2. A plasma processing method comprising generating plasma of a fluorine-based gas using the plasma processing apparatus according to claim 1 and etching a silicon oxide film.