JP2024072527A - Gas flow control pipe for plasma generating device - Google Patents

Abstract

To provide a gas flow rate adjusting pipe as gas flow rate adjusting means for a plasma generating device capable of introducing gas at a stable flow rate for a long period of time.SOLUTION: A gas flow control pipe for a plasma generating device 10 is installed in a path connecting a gas supply source and a vacuum chamber where plasma is generated, and adjusts the flow rate of gas introduced from the gas supply source to the vacuum chamber. The flow inside is a viscous flow at the end 10d close to the gas supply source, and a molecular flow at the end 10e close to the vacuum chamber.SELECTED DRAWING: Figure 2

Description

The present invention relates to a gas flow rate adjustment pipe for a plasma generating device.

Plasma is used to remove contamination from sample chambers in electron microscopes and in processes to strip photoresist (ashing). For example, electron microscopes are cleaned using a plasma generating device called a plasma cleaner (see Patent Document 1). A plasma generating device such as that shown in Patent Document 1 is configured to generate plasma by applying a high-frequency voltage to a vacuum chamber with a low-pressure atmosphere to which oxygen has been introduced.

As a configuration for introducing a gas (process gas) that is a raw material for plasma into the vacuum chamber of a conventional plasma generating device, a configuration is known in which a needle valve 99 with a variable gas flow rate is interposed between a gas supply source 90 and a vacuum chamber 30, as shown in FIG. 6. When introducing a process gas into the vacuum chamber 30 using a manual needle valve 99, it is possible to control the pressure at that time to an arbitrary value by first adjusting the opening of the needle valve 99. However, it is known that the flow rate of the process gas of the needle valve 99 decreases continuously over time (see Patent Document 2). If the flow rate of the gas introduced into the vacuum chamber 30 gradually decreases while the exhaust speed from the vacuum chamber 30 by the vacuum pump 40 is constant, the pressure in the vacuum chamber 30 decreases continuously. In order to keep the pressure in the vacuum chamber 30 constant, a method of controlling the exhaust speed of the vacuum pump 40 to decrease over time is also considered, but this method does not ensure the flow rate of the process gas.

This phenomenon will be explained with an actual example. Figure 7 shows the correlation between the pressure and reflected output and the time elapsed after the gas flow rate is controlled and adjusted to a specified pressure using a variable flow rate needle valve in a conventional plasma generating device. The pressure indication value inside the vacuum chamber fluctuates continuously over time, and in this measurement example, after the pressure is adjusted to the initial value, the indication value drops by about 20% after about 1 hour, and after about 2 hours it drops by about 30% compared to the initial value.

The cause of the pressure fluctuations in the vacuum chamber is thought to be the sealing mechanism of the needle valve. The needle valve has a structure where the seal part comes into contact with metal, which is so-called metal touch structure. In other words, when gas is not flowing, the metals come into contact with each other under a certain amount of pressure, and when gas is flowing, a very small gap is formed where the metals do not come into contact. The width of this gap adjusts the gas flow rate, which in turn adjusts the conductance. When the pressure generated at the contact point disappears, such as when the needle valve is slightly opened from a fully closed state, the elastic deformation of the contacting metal is relaxed, and the metals take time to restore their original shape before contact. In other words, as the gap between the contacting metal surfaces gradually narrows, the gas flow rate also decreases, which causes a decrease in pressure inside the vacuum chamber.

In the process of generating plasma in a vacuum chamber, the pressure fluctuations cause changes in the impedance of the RF circuit consisting of the high-frequency coil that supplies energy to the plasma, the high-frequency power supply that applies high-frequency waves to the coil, and the generated plasma, which causes the plasma to disappear. The disappearance of the plasma causes a further change in the impedance of the RF circuit, and the output supplied to the plasma from the high-frequency coil is no longer fully consumed, leading to an increase in the reflection of the high-frequency input. According to FIG. 7, after the plasma is ignited, the pressure in the vacuum chamber continues to decrease, and the plasma disappears after about four hours, at which point the reflected waves increase sharply. Thus, when a needle valve is used as a means for adjusting the gas flow rate, the gas flow rate cannot be stably introduced for a long period of time, causing the pressure in the vacuum chamber to decrease, and the impedance of the generated plasma to fluctuate, resulting in the problem of being unable to generate plasma efficiently.

On the other hand, gas flow controllers (mass flow controllers) are known as devices that control the flow rate of gas introduced into the vacuum chamber of a plasma generation device to an arbitrary value. The gas flow controller adjusts the flow control valve via a solenoid or piezoelectric actuator using the signal from a gas flow sensor installed midway through the piping, making it possible to always introduce a constant amount of gas into the vacuum chamber of the plasma generation device. However, when a gas flow controller is used to introduce process gas, the device becomes complicated, and there is a problem in that power must be constantly supplied to the gas flow sensor, solenoid, or piezoelectric actuator used for flow control.

JP 2016-54136 A Japanese Patent Application Laid-Open No. 11-82787

In view of the above problems, the present invention aims to provide a gas flow rate adjustment means for a plasma generating device that can introduce gas at a stable flow rate for a long period of time.

The gas flow rate adjustment pipe for a plasma generating device according to the present invention is a gas flow rate adjustment pipe for a plasma generating device that is provided in a path connecting a gas supply source and a vacuum chamber in which plasma is generated, and adjusts the flow rate of gas introduced from the gas supply source to the vacuum chamber, and is characterized in that the flow inside the pipe is a viscous flow at the end close to the gas supply source and a molecular flow at the end close to the vacuum chamber.

This invention provides a gas flow rate adjustment means for a plasma generating device that allows gas to be introduced at a stable flow rate for a long period of time.

A gas flow control pipe for a plasma generating device according to another aspect of the present invention is characterized by an inner diameter of 0.3 mm or less and a length of 3 mm or more.

This invention provides a gas flow rate adjustment means for a plasma generating device that can introduce gas at a stable flow rate while maintaining the pressure in the vacuum chamber.

A gas flow rate adjustment pipe for a plasma generating device according to another aspect of the present invention is characterized in that it is made of metal and has an outer diameter of 1.5 mm or more.

This invention provides a gas flow rate adjustment means for a plasma generating device that does not deform the shape of the flow path over time and maintains a constant flow rate of the introduced gas.

A gas flow rate adjustment pipe for a plasma generating device according to another aspect of the present invention is characterized in that the gas supply source is the atmosphere.

This invention provides a gas flow rate adjustment means for a plasma generating device that can introduce gas from the atmosphere at a stable flow rate even when the gas supply source is the atmosphere and there is a large pressure difference with the vacuum chamber.

The gas flow rate control tube for a plasma generating device according to the present invention is provided in a path connecting a gas supply source and a vacuum chamber in which plasma is generated, and controls the flow rate of gas introduced from the gas supply source into the vacuum chamber. The gas flow rate control tube for a plasma generating device comprises a hollow tube and a gas flow rate control pipe for the plasma generating device housed inside the tube, and is characterized in that the inner surface of the tube and the outer surface of the gas flow rate control pipe for the plasma generating device are in close contact with each other.

This invention provides a gas flow rate adjustment means for a plasma generating device that can introduce gas at a stable flow rate for a long period of time and can easily adjust the gas flow rate by changing the number of gas flow rate adjustment pipes inside the tube.

The plasma generating device according to the present invention is characterized by having a gas flow rate adjustment pipe for the plasma generating device.

The present invention provides a plasma generating device that can introduce gas at a stable flow rate for a long period of time, which prevents fluctuations in the impedance of the plasma generated in the vacuum chamber and allows for efficient plasma generation.

The present invention provides a gas flow rate adjustment means for a plasma generating device that allows gas to be introduced at a stable flow rate for a long period of time.

1 is a schematic perspective view showing a plasma generation device according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a gas flow rate adjusting pipe for a plasma generating apparatus according to an embodiment of the present invention. 11 is a graph showing the relationship between the length of the gas flow rate adjusting pipe and the pressure of the vacuum chamber in the plasma generating apparatus according to the embodiment of the present invention. 11 is a graph showing changes in pressure in a vacuum chamber and reflected output over time after plasma is ignited in a plasma generating device according to an embodiment of the present invention. 1 is a perspective schematic view showing a gas flow rate adjusting tube for a plasma generating apparatus according to an embodiment of the present invention, with a part cut away; FIG. 1 is a schematic diagram showing a conventional plasma generating device. 11 is a graph showing the change in pressure in a vacuum chamber and the change in reflected output over time from when plasma is ignited after the opening of a needle valve is adjusted to a predetermined pressure in a conventional plasma generating device.

Next, an embodiment of a plasma generating device and a gas flow rate adjusting means to which the present invention is applied will be described with reference to the drawings. Note that the embodiment described below is a preferred embodiment of the present invention, and therefore includes various technically preferable limitations. However, the scope of the present invention is not limited to these aspects unless otherwise specified in the following description to the effect that the present invention is limited.

[Embodiment]
A plasma generation device and a gas flow rate adjusting means according to an embodiment of the present invention will be described with reference to Figures 1 to 5. Figure 1 is a schematic diagram showing a plasma generation device according to an embodiment of the present invention, and Figure 2 is a schematic diagram showing a gas flow rate adjusting pipe for a plasma generation device according to an embodiment of the present invention. Figure 3 is a graph showing the relationship between the length of the gas flow rate adjusting pipe and the pressure of a vacuum chamber in a plasma generation device according to an embodiment of the present invention, and Figure 4 is a graph showing the change in the pressure of a vacuum chamber and the reflected output depending on the time after plasma is ignited in a plasma generation device according to an embodiment of the present invention. Figure 5 is a schematic diagram showing a gas flow rate adjusting tube for a plasma generation device according to an embodiment of the present invention.

The plasma generating device 1 according to this embodiment is equipped with a vacuum chamber 30 in which gas is turned into plasma, a vacuum pump 40 that reduces the pressure in the vacuum chamber 30 to an almost vacuum state, a high-frequency coil 50 arranged around the vacuum chamber 30, and a high-frequency power supply 60 that applies a high-frequency voltage to the high-frequency coil, and is configured to generate plasma within the vacuum chamber 30. A vacuum gauge 70 that measures pressure is also connected to the vacuum chamber 30.

The gas to be converted into plasma in the vacuum chamber 30 is supplied from a gas supply source 90. A gas flow rate adjustment means 100 is provided in the path connecting the gas supply source 90 and the vacuum chamber 30 to adjust the flow rate of the gas flowing through the path. A stop valve 80 that switches between fully open and fully closed is provided upstream of the gas flow rate adjustment means 100. By providing the gas flow rate adjustment means 100 in the plasma generation device 1 according to this embodiment, plasma can be generated stably and efficiently.

[Example 1]
Next, an embodiment in which a gas flow rate adjustment pipe 10 is used as the gas flow rate adjustment means 100 will be described with reference to Fig. 2. In this embodiment, the gas flow rate adjustment means 100 is composed only of the gas flow rate adjustment pipe 10. As shown in Fig. 2, the gas flow rate adjustment pipe 10 has an overall cylindrical shape, and a thin flow path 10a is provided at the center thereof, penetrating in the longitudinal direction. When gas flows through this flow path 10a, resistance is exerted, and the flow rate is adjusted.

Of the gas flow rate adjustment pipe 10, end 10d is on the gas supply source 90 side, and end 10e is on the vacuum chamber 30 side. That is, end 10d side is at high pressure close to atmospheric pressure, and end 10e side is at low pressure close to vacuum. Therefore, the nature of the gas flow in flow path 10a varies depending on the location, with viscous flow near end 10d and molecular flow near end 10e. Therefore, the conductance of the gas flow rate adjustment pipe 10 is determined by the distribution of viscous flow regions and molecular flow regions formed in flow path 10a.

Figure 3 is a graph showing the relationship between the length of the gas flow control pipe 10 and the pressure in the vacuum chamber 30 in the plasma generating device 1. In this graph, the horizontal axis is the length of the gas flow control pipe 10, and the vertical axis is the pressure in the vacuum chamber 30 when the vacuum pump 40 is operated and a steady state is reached. The inner diameter d1 (see Figure 2) of the gas flow control pipes 10 used was 0.08 mm, 0.09 mm, 0.1 mm, and 0.21 mm, and Figure 3 was plotted using gas flow control pipes 10 with various overall lengths L for each.

According to this graph, if the length of the gas flow control pipe 10 is sufficiently short, the pressure drops significantly even if the total length is increased slightly, but if the total length exceeds about 15 mm, the rate of pressure drop becomes smaller. In other words, it is thought that if the total length exceeds a certain length, the molecular flow area with low resistance increases in the flow path 10a. Note that, to determine what dimensions of the gas flow control pipe 10 should be adopted in the plasma generating device 1, the required total length L can be obtained by reading this graph based on the required pressure of the vacuum chamber 30. Note that, according to the graph in FIG. 3, if the length of the gas flow control pipe 10 is 3 mm or more, the pressure of the vacuum chamber can be kept sufficiently low. In addition, if the inner diameter d1 of the gas flow control pipe 10 is 0.08 mm, if the length is 3 mm or more, the pressure of the vacuum chamber will be 0.1 Pa or less, so it can be used suitably for applications such as plasma cleaners.

Next, the gas flow rate adjustment pipe 10 will be described in detail with reference to FIG. 2. The gas flow rate adjustment pipe 10 is made of metal, preferably nickel. The outer diameter d2 is preferably 1.5 mm or more, and d1 is preferably 0.3 mm or less. These dimensions ensure that the gas flow rate adjustment pipe 10 has a sufficient thickness, so that the dimensions of the flow path 10a do not change due to pressure, and a stable flow rate can be maintained over time.

Next, the change in pressure and reflected output over time when plasma is generated in the vacuum chamber 30 by introducing gas using this gas flow rate adjustment pipe 10 will be described with reference to FIG. 4. As shown in FIG. 4, when the gas flow rate adjustment pipe 10 is used, the pressure fluctuation in the vacuum chamber 30 is small and is maintained almost constant. The flow rate of the supplied gas is stable, and the impedance of the plasma does not fluctuate. Therefore, the matching situation with the high-frequency circuit does not change. The reflected output shown in FIG. 4 is stable at a low level, which also shows that the impedance matching is good and plasma can be generated efficiently.

[Example 2]
Next, an embodiment in which a gas flow rate adjustment tube 20 is used as the gas flow rate adjustment means 100 will be described with reference to FIG. 5. In this embodiment, the gas flow rate adjustment means 100 is configured by the gas flow rate adjustment tube 20 having a gas flow rate adjustment pipe 10. As shown in FIG. 5, the gas flow rate adjustment tube 20 has a hollow tube 11 and the above-mentioned gas flow rate adjustment pipe 10, and the gas flow rate adjustment pipe 10 is accommodated inside the tube 11, and the inner peripheral surface 11a of the tube 11 and the outer peripheral surface 10c of the gas flow rate adjustment pipe 10 are in close contact with each other. Also, as shown in FIG. 5, a plurality of gas flow rate adjustment pipes 10 arranged in series are accommodated inside the tube 11. When this gas flow rate adjustment tube 20 is used as the gas flow rate adjustment means 100, the gas flow rate can be adjusted by changing the number of gas flow rate adjustment pipes 10.

The tube 11 is preferably made of a soft resin, and more specifically, a silicone tube is preferable. The gas flow control tube 20 is formed by inserting the required number of gas flow control pipes 10 from the end of the tube 11. Because the pressure inside the gas flow control tube 20 is low, the external pressure strengthens the adhesion between the inner surface 11a of the tube 11 and the outer surface 10c of the gas flow control pipe 10.

[Other Modifications]
1, a stop valve 80 is provided between the gas supply source 90 and the gas flow rate adjusting means 100, but it is also possible to omit the stop valve 80. In addition, the plasma generating device 1 shown in FIG. 1 is configured to introduce the gas to be turned into plasma from the gas supply source 90, but it is also possible to configure the gas supply source 90 as the atmosphere.

The plasma generating device according to the present invention can be used as an asher for ashing photoresist or as a plasma cleaner for electron microscopes, etc. In this case, the pressure set in the vacuum chamber can be from about 1 Torr to about 0.1 Pa, but in either case, a stable and efficient plasma can be generated by employing the gas flow rate adjustment means according to the present invention.

1 Plasma generating device 9 Plasma generating device 10 Gas flow rate control pipe 10a Flow path 10b Inner peripheral surface 10c Outer peripheral surface 10d End 10e End 11 Tube 11a Inner peripheral surface 20 Gas flow rate control tube 30 Vacuum chamber 40 Vacuum pump 50 High frequency coil 60 High frequency power source 70 Vacuum gauge 80 Stop valve 90 Gas supply source 99 Needle valve 100 Gas flow rate control means

The gas flow control pipe for a plasma generation apparatus according to the present invention is a gas flow control pipe for a plasma generation apparatus that is provided in a path connecting a gas supply source and a vacuum chamber in which plasma is generated, and adjusts the flow rate of gas introduced from the gas supply source into the vacuum chamber to be turned into plasma , and is characterized in that the flow inside the pipe is a viscous flow at the end close to the gas supply source and a molecular flow at the end close to the vacuum chamber, the gas supply source is the atmosphere, the end close to the gas supply source is connected to the atmosphere, and the flow rate of gas introduced from the gas supply source into the vacuum chamber is adjusted only by the gas flow control pipe for the plasma generation apparatus .

The gas flow control tube for a plasma generation apparatus according to the present invention is provided in a path connecting a gas supply source and a vacuum chamber in which plasma is generated, and adjusts the flow rate of gas introduced from the gas supply source into the vacuum chamber, and is characterized in that it comprises a hollow tube made of a soft resin and a gas flow control pipe for the plasma generation apparatus housed inside the tube, and the inner surface of the tube and the outer surface of the gas flow control pipe for the plasma generation apparatus are in close contact with each other.

Claims (6)

A gas flow rate adjusting pipe for a plasma generating apparatus, which is provided in a path connecting a gas supply source and a vacuum chamber in which plasma is generated, and adjusts a flow rate of a gas introduced from the gas supply source into the vacuum chamber,
1. A gas flow rate adjusting pipe for a plasma generating apparatus, wherein an internal flow is a viscous flow at an end portion closer to the gas supply source, and a molecular flow at an end portion closer to the vacuum chamber. 2. The gas flow rate adjusting pipe for a plasma generating device according to claim 1, wherein the pipe has an inner diameter of 0.3 mm or less and a length of 3 mm or more. 3. The gas flow rate adjusting pipe for a plasma generating device according to claim 2, characterized in that the pipe is made of a metal and has an outer diameter of 1.5 mm or more. 4. The gas flow rate adjusting pipe for a plasma generating apparatus according to claim 3, wherein the gas supply source is the atmosphere. A gas flow rate adjusting tube for a plasma generating apparatus, which is provided in a path connecting a gas supply source and a vacuum chamber in which plasma is generated, and adjusts a flow rate of a gas introduced from the gas supply source to the vacuum chamber,
A hollow tube;
and a gas flow rate control pipe for the plasma generating apparatus according to any one of claims 1 to 4, which is housed inside the tube;
A gas flow control tube for a plasma generating apparatus, characterized in that an inner peripheral surface of the tube and an outer peripheral surface of the gas flow control pipe for the plasma generating apparatus are in close contact with each other. A plasma generating device comprising the gas flow rate adjusting pipe for a plasma generating device according to any one of claims 1 to 4.

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