JPH0697130A - Plasma cleaning method - Google Patents

Abstract

(57) [Abstract] [Purpose] An axially symmetric vacuum container that has a microwave transparent window on the axis and that makes the introduced gas into a plasma state, and a microwave that is arranged coaxially with the vacuum container. And a plasma cleaning method capable of cleaning the inside of the vacuum container of the ECR type microwave plasma processing apparatus at a high speed and uniformly, which comprises a solenoid coil forming a magnetic field region (ECR region) in which the electron cyclotron resonance occurs. [Structure] High-density radicals are generated in a vacuum container, and cleaning is performed so that a region to be cleaned exists in a spatial region until the density is reduced to half. Specifically, the cleaning gas pressure is set to 50 mTorr or more, and E
The CR area is moved within the vacuum container, and the stage on which the object to be processed is placed is cleaned so that the position is within 130 mm from the ECR area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma cleaning method for removing a film deposited inside a vacuum container by using microwave plasma, and more particularly, it has a microwave transmitting window on an axis and is introduced. An axisymmetric vacuum container for making a gas into a plasma state, and a solenoid coil arranged coaxially with the vacuum container and forming a planar magnetic field region in the vacuum container where electron cyclotron resonance with microwaves occur, In the microwave plasma processing apparatus for performing a surface treatment such as thin film formation or etching treatment on the surface of the object to be processed by plasma irradiation of the object to be processed placed on the stage facing the wave transmission window, the vacuum Inside the container,
The present invention relates to a cleaning method in which a cleaning gas is introduced into the vacuum container and a microwave electric field and a magnetic field generated by a solenoid coil are superposed on the gas to perform cleaning.

[0002]

2. Description of the Related Art FIG. 1 shows a microwave plasma processing apparatus disclosed in Japanese Patent Application No. 2-253730 as an example of a microwave plasma processing apparatus targeted by the present invention. Microwaves oscillated by a microwave source (not shown) pass through the waveguide 1 and the microwave transmission window 2, and are introduced into the plasma generation chamber 3 kept in vacuum by a vacuum exhaust device (not shown). A plasma generation gas is supplied to the plasma generation chamber 3 through a gas introduction pipe 4, and the microwave and a solenoid coil 5 arranged coaxially to surround the axially symmetrical plasma generation chamber 3 are formed in the plasma generation chamber 3. Microwave plasma is generated by the action with the magnetic field.

For example, if a region of magnetic flux density of 875 Gauss is formed in the plasma generation chamber by using 2.45 GHz which is usually industrially used as a frequency of microwave, it is also referred to as Electron Cyclotron Resonance (hereinafter referred to as ECR). ) The effect efficiently ionizes the plasma-producing gas, generating high-density plasma. The plasma moves downward along the divergent magnetic field formed by the solenoid coil 5 and is applied to the wafer 9 placed on the stage 8 in the plasma generation chamber 3. In such an apparatus, when oxygen as a plasma generating gas and silane as a reaction gas are supplied into the plasma generating chamber 3 through the gas introducing pipes 4 and 10, respectively, a silicon oxide film is formed on the wafer 9. During film formation, the film is deposited not only on the wafer but also on the inner wall surface of the plasma generation chamber 3, the surface of the microwave transmission window, and the surface of the stage (hereinafter collectively referred to as the inside of the vacuum container). This film is sputtered by the collision of plasma or is peeled off due to the stress of the film itself, which causes the contamination of the wafer surface. Therefore, it is common practice to clean the inside of the vacuum container when the film thickness reaches a certain level.

[0004]

As a cleaning method, for example, there is a method of removing NF ₃ plasma by generating NF ₃ plasma and chemically reacting with the deposited film. It is very simple because it does not need to break the vacuum or reconfigure the device, because it only needs to change the plasma generation gas to the cleaning gas, but it has a drawback that the cleaning speed is slow and it is difficult to uniformly clean the inside of the vacuum container. .

An object of the present invention is to provide a plasma cleaning method which can uniformly clean the interior of a vacuum container at high speed.

[0006]

In order to solve the above problems, in the present invention, as a plasma cleaning method for the inside of a vacuum container in a microwave plasma processing apparatus having the structure described at the beginning, a high-density radical in the vacuum container is used. Is generated, and the cleaning method is performed so that the cleaning target area exists in the spatial area until the density is reduced to half.

In order to realize this method concretely, in the present invention, the gas pressure in the vacuum container is set to 50 mTorr or more in order to generate high density radicals. Further, in order to perform cleaning so that the region to be cleaned exists within the spatial region until the radical density is halved, the electron cyclotron resonance magnetic field region (hereinafter, also referred to as electron cyclotron resonance region or simply resonance region) is set in the vacuum container. It is assumed that the cleaning is performed while moving the inside of the entire region to be cleaned so as to be within the radical density half region.

Further, the cleaning is performed so that the position of the stage is within 130 mm at the shortest distance from the electron cyclotron resonance magnetic field region. The pressure control when the gas pressure in the vacuum container is set to 50 mTorr or more is provided with an auxiliary exhaust passage in parallel with the main exhaust passage of the vacuum container,
The conductance valve with variable opening is provided in the auxiliary exhaust passage to change the opening, or gas is supplied from the vacuum container side of the turbo molecular pump for exhausting the inside of the vacuum container into the exhaust passage. To do so.

Further, the electron cyclotron resonance magnetic field region is moved by increasing / decreasing the solenoid coil current or by moving the solenoid coil.

[0010]

The principle of plasma cleaning is a reaction in which radicals forming the cleaning gas combine with atoms forming the film to be cleaned and are extracted. Therefore, the higher the number of radicals and the higher the activity, the faster cleaning is possible. When the gas pressure is increased, the number of gas molecules increases, so the probability of collision between electrons and gas molecules also increases. However, since the electron energy is high in the pressure range of a few millitorr, most gas molecules are decomposed into ions. Unlike radicals, ions do not contribute to surface reactions, so the cleaning rate does not increase. When the gas pressure increases, multiple scattering of electrons and gas molecules occurs, and the electron energy decreases, so more radicals are generated than ions. In the experiment in the course of reaching the present invention, the cleaning rate drastically increases at 40 mTorr or more and reaches the maximum value at about 100 mTorr, so it is estimated that the radical generation amount also increases.

The collision between the gas molecule and the electron is mainly performed in the electron cyclotron resonance magnetic field region, and the generated radical returns to the gas molecule again after a certain life. Therefore, the cleaning speed is increased by setting the distance between the resonance region and the region to be cleaned so that the radicals reach the region to be cleaned within the half life of the radical life. In addition, among the above-mentioned means, the operation of each means described after the set value of the gas pressure in the vacuum container will be described using specific examples in the section of Examples.

[0012]

EXAMPLE FIG. 2 shows the result of cleaning using the apparatus shown in FIG. An 8-inch wafer 9 with a silicon oxide film is placed on the stage 8, NF ₃ gas is introduced into the plasma generation chamber 3 as a cleaning gas, and a microwave electric field and a magnetic field generated by the solenoid coil 5 are superposed on the NF ₃ gas. The cleaning rate was calculated from the decrease in the film thickness by irradiating the wafer 9 with so-called NF ₃ plasma for a certain period of time. At this time, the gas flow rate was kept constant, and the opening angle of a conductance valve (not shown) provided in the exhaust pipe 13 was adjusted to change the pressure to 5 to 800 mTorr.

In the range of 5-40 mTorr, the cleaning rate is almost constant regardless of the pressure. In this pressure region, NF ₃ is mostly decomposed into ions and the ratio of radicals is small, so that sputter etching by ions is predominant. In the region of 40 to 100 mTorr, the cleaning speed rapidly increases. This is because the electrons are multiply scattered as the gas pressure increases, so the ionization efficiency gradually decreases,
This is because the radical generation efficiency increases instead.

In the range of 100 to 800 mTorr, the cleaning rate gradually decreases. This is because the gas pressure has become too high, the electron energy decreases, and the radical density also decreases. From the above, the lower limit of the pressure is preferably 40 mTorr, but it is certain to set it to 50 mTorr with a margin. The upper limit is 100 millitorr or more and 80
Up to 0 mTorr is a monotonic decrease, so there is no need to specify it. As a practical matter, the pumping speed of the turbo molecular pump decreases sharply when it exceeds 2 Torr, so it is advisable to hold it down at around 1 Torr.

FIG. 3 shows the relationship between the position of the electron cyclotron resonance region and the cleaning speed. The wafer with the silicon oxide film was cut into small pieces, fixed on the inner wall of the plasma chamber, and cleaned with NF ₃ plasma. At this time, the resonance region was formed flat, and the cleaning speed was compared between the position where this region intersects the inner wall of the plasma generation chamber and the position away from this position. The cleaning speed is the highest in the vicinity of the resonance region and decreases as the distance increases. This is because the radical density is the highest in the resonance region, and as the distance increases due to thermal diffusion, the life increases and the density decreases. Therefore, by moving the resonance region during cleaning, the entire interior of the vacuum container can be cleaned.

FIG. 4 shows the relationship between the stage position and the cleaning speed. The cleaning rate decreases with distance from the resonance region. This is because the life of the radicals generated in the resonance region reaches the end while reaching the stage.
By arranging it within 0 mm, it is possible to prevent a sharp decrease and remove the film attached on the stage. FIG. 5A is a vacuum exhaust system diagram for controlling the gas pressure in the vacuum container. An auxiliary exhaust system is added in parallel with the main exhaust system whose exhaust passage passes through the main valve, and a conductance valve is installed. The main valve is closed and exhaust is performed by the auxiliary exhaust system, and the opening angle of the conductance valve is adjusted to obtain the desired pressure. Although not shown, the valve angle can be automatically adjusted by feeding back the pressure.

FIG. 5 (b) is another system of vacuum exhaust system for controlling the gas pressure in the vacuum container. Gas from the vacuum container side of the pump (for example, turbo molecular pump) into the exhaust path
When (for example, nitrogen) is supplied, the gas occupies a part of the exhaust volume, and the exhaust capacity for the vacuum container decreases.
Adjust the gas flow rate to obtain the desired pressure. Figure 6
(a) shows a method for moving the electron cyclotron resonance region. In the case of a solenoid coil, the resonance region normally has a dome shape, but when the coil current value increases, the height of the dome decreases and the resonance region moves to the lower end side of the coil. Therefore, if the coil position is fixed so that the microwave transmission window is within the length range of the coil and the current value is increased, the resonance region intersects the entire surface of the microwave transmission window, so that the microwave transmission window surface can be moved at high speed. It can be uniformly cleaned.

FIG. 6 (b) shows another method for moving the electron cyclotron resonance region. By fixing the coil current so that a flat resonance region is formed and moving the entire coil in the axial direction, the resonance region moves along the inner wall of the plasma generation chamber, so that the inside of the plasma generation chamber is cleaned rapidly and uniformly. be able to.

[0019]

According to the present invention, the cleaning method for plasma cleaning the inside of the vacuum container of the microwave plasma processing apparatus according to the present invention, which is the object of the present invention, has a radical cleaning action, that is, the radical is a magnetic field or an electric field. Focusing on the cleaning action by uniformly diffusing in the thermal motion and chemically reacting with the substance to be cleaned without restraining the movement to generate high-density radicals in the vacuum container until the density is halved. Since the cleaning method is performed so that the area to be cleaned is present in the spatial area, the cleaning can be performed at high speed and uniformly.

The density of the high-density radicals is determined based on the experimental result that the cleaning rate dramatically increases when the pressure of the cleaning gas in the vacuum container is 40 to 50 mTorr or more. Since it was set to 50 mTorr or more, high-speed cleaning which has never been possible has been possible. Then, the pressure control when the gas pressure in the vacuum container is maintained at 50 mTorr or more is performed by adjusting the opening degree of the flow rate adjusting conductance valve in the conventional main exhaust passage by arranging the auxiliary exhaust passage in parallel. Alternatively, since it is performed by supplying a relatively inexpensive gas such as nitrogen gas into the exhaust passage on the vacuum container side of a turbo molecular pump used as an ultrahigh vacuum vacuum pump, it is particularly large compared to the device. It has become possible to generate high density radicals without requiring additional cost.

Further, as a method for making the area to be cleaned exist in the spatial area until the density of radicals is reduced to half, the electron cyclotron resonance magnetic field area which is a source of radicals is moved in the vacuum container. Therefore, high-speed and uniform cleaning of the microwave transmission window and the inner wall surface of the vacuum container can be reliably achieved. Since the electron cyclotron resonance magnetic field region is moved by increasing / decreasing the solenoid current, or by moving the solenoid coil itself, the microwave plasma processing apparatus normally uses a solenoid coil current adjusting means or a solenoid. Since the coil moving means is provided, the above effect can be obtained without any additional cost.

Further, in cleaning the stage, the stage is positioned so that it is located within 130 mm at the shortest distance from the electron cyclotron resonance magnetic field region. Therefore, when the electron cyclotron resonance magnetic field region has a dome shape, , The average radical density in a plane parallel to the stage that passes through the shortest distance point from the stage on this dome surface is the source of radicals, the area of the dome surface on the back side of this plane is large Therefore, although there is a decay of the radical density until reaching this plane, it becomes equivalent to the radical density when the electron cyclotron resonance magnetic field region is formed flat, and the stage position exists within the radical density half region. And it is cleaned at high speed.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an example of the structure of a microwave plasma processing apparatus targeted for plasma cleaning according to the present invention.

FIG. 2 is a diagram showing a relationship between a cleaning gas pressure in a vacuum container and a cleaning rate, which is obtained in an experimental process of the present invention.

FIG. 3 is a diagram showing the relationship between the position in the vacuum container of the flat electron cyclotron resonance magnetic field region and the cleaning speed obtained in the experimental process of the present invention.

FIG. 4 is a diagram showing the relationship between the distance from the flat electron cyclotron resonance magnetic field region to the stage surface and the cleaning speed obtained in the experimental process of the present invention.

5A and 5B are diagrams showing a method of controlling gas pressure in a vacuum container according to the present invention, wherein FIG. 5A is a diagram showing a method of using a conductance valve with a variable opening, and FIG. 5B is a vacuum pump. A diagram showing a method for controlling pressure by supplying gas into the exhaust passage on the vacuum container side of a turbo molecular pump

6A and 6B are diagrams showing a method of moving an electron cyclotron resonance magnetic field region according to the present invention, wherein FIG. 6A shows a principle of movement by increasing / decreasing a solenoid coil current, and FIG. 6B shows a solenoid coil itself. Diagram showing the method by moving

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Waveguide 2 Microwave transmission window 3 Plasma generation chamber (vacuum container) 4 Plasma generation gas introduction pipe 5 Solenoid coil 7 Coil drive mechanism 8 Stage 9 Wafer (processing target) 12 Electron cyclotron resonance magnetic field region

Claims (8)

[Claims] 1. An electron cyclotron having an axially symmetric vacuum container having a microwave transmitting window on the axis thereof to bring an introduced gas into a plasma state, and an electron cyclotron arranged coaxially with the vacuum container and having a microwave therein. A solenoid coil that forms a planar magnetic field region where resonance occurs, and a thin film is formed on the surface of the object to be processed by irradiating the object mounted on the stage facing the microwave transmission window with plasma. Alternatively, in a microwave plasma processing apparatus that performs a surface treatment such as an etching treatment, a cleaning gas is introduced into the vacuum container and a microwave electric field and a magnetic field generated by a solenoid coil are superposed on the gas. A cleaning method for cleaning, in which a high-density radical is generated in the vacuum container and the cleaning target is generated in a spatial region until the density is reduced to half. Plasma cleaning method characterized in that for cleaning such region is present. 2. The cleaning method according to claim 1, wherein the gas pressure in the vacuum container is set to 50 mTorr or more. 3. The cleaning method according to claim 1, wherein cleaning is performed while moving the electron cyclotron resonance magnetic field region such that the entire region to be cleaned inside the vacuum container is within the radical density half region. A characteristic plasma cleaning method. 4. The plasma cleaning method according to claim 1, wherein the stage is positioned within a distance of 130 mm at the shortest distance from the electron cyclotron resonance magnetic field region. 5. The cleaning method according to claim 2, wherein the pressure control when the gas pressure in the vacuum container is set to 50 mTorr or more is provided with an auxiliary exhaust passage in parallel with the main exhaust passage of the vacuum container, A plasma cleaning method, characterized in that a conductance valve having a variable opening is provided in the auxiliary exhaust passage to change the opening. 6. The cleaning method according to claim 2, wherein the pressure control when the gas pressure in the vacuum container is set to 50 mTorr or more is performed by exhausting from the vacuum container side of a turbo molecular pump that exhausts the inside of the vacuum container. A plasma cleaning method, characterized in that gas is supplied into the passage. 7. The plasma cleaning method according to claim 3, wherein the electron cyclotron resonance magnetic field region is moved by increasing or decreasing a solenoid coil current. 8. The plasma cleaning method according to claim 3, wherein the electron cyclotron resonance magnetic field region is moved by moving a solenoid coil.