JP7246802B1 - Gas flow adjustment pipe for plasma generator - Google Patents

Abstract

A gas flow regulating pipe as a gas flow regulating means for a plasma generating apparatus is provided, which can introduce a gas at a stable flow rate over a long period of time. SOLUTION: A gas flow rate adjusting pipe 10 for a plasma generating apparatus 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 the internal flow is viscous flow at the end 10d close to the gas supply source and molecular flow at the end 10e close to the vacuum chamber. [Selection drawing] Fig. 2

Description

TECHNICAL FIELD The present invention relates to a gas flow control pipe for a plasma generator.

Plasma is used for the removal of contamination in the sample chamber of an electron microscope, the process of removing photoresist (ashing), and the like. For example, electron microscopes are cleaned using a plasma generator called a plasma cleaner (see Patent Document 1). A plasma generation apparatus as disclosed in Patent Document 1 is configured to generate plasma by applying a high-frequency voltage to a vacuum chamber having a low-pressure atmosphere into which oxygen is introduced.

As a configuration for introducing a gas (process gas) as a material of plasma into a vacuum chamber of a conventional plasma generation apparatus, a needle with a variable gas flow rate is placed between a gas supply source 90 and a vacuum chamber 30 as shown in FIG. A configuration in which a valve 99 is interposed for connection is known. When the process gas is introduced into the vacuum chamber 30 using the manual needle valve 99, the pressure at that time can be controlled to an arbitrary value by adjusting the opening of the needle valve 99 first. It is possible. However, it is known that the needle valve 99 continuously decreases the flow rate of the process gas over time (see Patent Document 2). While the flow rate of the gas introduced into the vacuum chamber 30 gradually decreases, the pressure in the vacuum chamber 30 continuously decreases if the exhaust speed from the vacuum chamber 30 by the vacuum pump 40 is constant. In order to keep the pressure in the vacuum chamber 30 constant, it is conceivable to control the pumping speed of the vacuum pump 40 to decrease over time, but this method cannot ensure the flow rate of the process gas.

This phenomenon will be explained with an example. FIG. 7 shows the correlation between elapsed time, pressure, and reflected output after adjusting the gas flow rate to a predetermined pressure by controlling the gas flow rate with a flow-variable needle valve in a conventional plasma generator. The indicated value of the pressure inside the vacuum chamber fluctuates continuously with the passage of time. In this measurement example, after the pressure was adjusted to the initial value, the indicated value decreased by about 20% after about 1 hour, and about 2 hours passed. Afterwards, it drops by about 30% compared to the initial value.

The cause of the pressure fluctuation in the vacuum chamber is thought to be the sealing mechanism of the needle valve. The needle valve has a structure in which the sealing portion is in contact with metal, and is derived from the adoption of a so-called metal touch structure. That is, when the gas is not flowed, the metals come into contact with each other under a certain amount of pressing pressure, and when the gas is flowed, a very small gap is formed at a position where the metals do not contact each other. The width of this gap adjusts the gas flow rate, that is, adjusts the conductance. When the pressing pressure generated in the contact part disappears, as in the case when the needle valve is slightly opened from the fully closed state, the elastic deformation of the metal in contact is alleviated, and the metal returns to its pre-contact state. It will return to its original shape over time. That is, the gap between the contacting metal surfaces gradually narrows, and the flow rate of gas decreases, which causes a decrease in the pressure inside the vacuum chamber.

In the process of generating plasma in a vacuum chamber, pressure fluctuations affect the impedance of the RF circuit consisting of the high frequency coil supplying energy to the plasma, the high frequency power source applying high frequency to the coil, and the generated plasma. It causes a change so that the plasma disappears. Extinguishing the plasma further changes the impedance of the RF circuit, the power supplied from the RF coil to the plasma is not sufficiently consumed, and the reflection of the RF input also increases. According to FIG. 7, after plasma ignition, the pressure in the vacuum chamber continued to drop, and after about 4 hours the plasma disappeared, whereupon the reflected wave increased rapidly. As described above, when a needle valve is used as a means of adjusting the gas flow rate, the gas flow rate cannot be stably introduced for a long period of time, and the pressure in the vacuum chamber decreases, causing fluctuations in the impedance of the generated plasma. There is a problem that plasma cannot be generated efficiently.

On the other hand, a gas flow controller (mass flow controller) is known as a device for controlling the flow rate of gas introduced into the vacuum chamber of the plasma generation apparatus to an arbitrary value. The gas flow controller adjusts the flow control valve via a solenoid or piezo actuator based on the signal from the gas flow sensor installed in the middle of the pipe, making it possible to always introduce a constant amount of gas into the vacuum chamber of the plasma generator. and However, when a gas flow rate controller is used to introduce process gas, the device becomes complicated, and there is a problem that power must always be supplied to the gas flow rate sensor, solenoid or piezo actuator used for flow rate control.

JP 2016-54136 A JP-A-11-82787

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a gas flow rate adjusting means for a plasma generating apparatus that can introduce a gas at a stable flow rate over a long period of time.

A gas flow rate adjusting pipe 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. A gas flow regulating pipe for a plasma generator for regulating gas flow, wherein the internal flow is viscous flow at the end near the gas supply source and molecular flow at the end near the vacuum chamber. wherein the gas supply source is the atmosphere, the end portion close to the gas supply source is connected to the atmosphere, and the gas is introduced from the gas supply source into the vacuum chamber only by a gas flow rate adjusting pipe for the plasma generation device. characterized in that the flow rate of the gas to be supplied is adjusted .

According to the present invention, it is possible to provide a gas flow rate adjusting means for a plasma generation apparatus that can introduce gas at a stable flow rate over a long period of time.

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

According to the present invention, it is possible to provide a gas flow rate adjusting means for a plasma generation apparatus capable of introducing gas at a stable flow rate while maintaining the pressure of the vacuum chamber.

Another gas flow control pipe for a plasma generating apparatus according to the present invention is characterized by being made of metal and having an outer diameter of 1.5 mm or more.

According to the present invention, it is possible to provide a gas flow rate adjusting means for a plasma generation apparatus, in which the flow rate of introduced gas is kept constant without the shape of the flow channel deforming over time.

A gas flow rate adjusting 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. A gas flow rate adjustment tube for a plasma generation device to be adjusted, comprising a hollow tube made of soft resin and a gas flow rate adjustment pipe for the plasma generation device housed inside the tube, It is characterized in that the inner peripheral surface and the outer peripheral surface of the gas flow rate adjusting pipe for the plasma generation device are in close contact with each other.

According to the present invention, the gas can be introduced at a stable flow rate for a long period of time, and the gas flow rate can be easily adjusted by changing the number of gas flow rate adjustment pipes inside the tube. of gas flow rate adjustment means can be provided.

A plasma generator according to the present invention is characterized by comprising a gas flow rate adjusting pipe for the plasma generator.

According to the present invention, there is provided a plasma generator capable of introducing gas at a stable flow rate for a long period of time, thereby preventing fluctuations in the impedance of the plasma generated in the vacuum chamber and efficiently generating plasma. can do.

According to the present invention, it is possible to provide a gas flow rate adjusting means for a plasma generator that can introduce a gas at a stable flow rate over a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS It is a perspective schematic diagram which shows the plasma generation apparatus which concerns on embodiment of this invention. It is a schematic diagram which shows the gas flow control pipe for the plasma generator which concerns on embodiment of this invention. 4 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 generator according to the embodiment of the present invention. 4 is a graph showing changes in vacuum chamber pressure and reflected output with time after plasma is ignited in the plasma generator according to the embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a perspective schematic diagram which fractures|ruptures one part and shows the gas flow regulating tube for the plasma generator which concerns on embodiment of this invention. It is a schematic diagram which shows the conventional plasma generation apparatus. 5 is a graph showing changes in vacuum chamber pressure and reflected output with time after plasma is ignited after adjusting the opening of the needle valve to a predetermined pressure in a conventional plasma generator.

Next, an embodiment of a plasma generator and gas flow rate adjusting means to which the present invention is applied will be described with reference to the drawings. In addition, since the embodiments described below are preferred embodiments of the present invention, various technically preferable limitations are applied, but the scope of the present invention is particularly limited in the following description. Unless otherwise stated, the present invention is not limited to these modes.

[Embodiment]
A plasma generator and gas flow rate adjusting means according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG. FIG. 1 is a schematic diagram showing a plasma generator according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing a gas flow rate adjusting pipe for the plasma generator according to an embodiment of the present invention. FIG. 3 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 generation device according to the embodiment of the present invention, and FIG. 3 is a graph showing changes in vacuum chamber pressure and reflected output with time after plasma ignition. FIG. 5 is a schematic diagram showing a gas flow rate adjusting tube for a plasma generator according to an embodiment of the invention.

The plasma generation apparatus 1 according to the present embodiment includes a vacuum chamber 30 in which gas is turned into plasma, a vacuum pump 40 that decompresses the vacuum chamber 30 to a substantially vacuum state, a high frequency coil 50 arranged around the vacuum chamber 30, and a high frequency coil. A high-frequency power source 60 for applying a high-frequency voltage is provided, and plasma is generated within the vacuum chamber 30 . A vacuum gauge 70 for measuring pressure is connected to the vacuum chamber 30 .

A gas to be plasmatized in the vacuum chamber 30 is supplied from a gas supply source 90 . A path connecting the gas supply source 90 and the vacuum chamber 30 is provided with a gas flow rate adjusting means 100 for adjusting the flow rate of the gas flowing through the path. A stop valve 80 for switching between fully open/fully closed is provided upstream of the gas flow rate adjusting means 100 . Plasma can be generated stably and efficiently by including the gas flow rate adjusting means 100 in the plasma generation apparatus 1 according to the present embodiment.

[Example 1]
Next, an embodiment using the gas flow rate adjusting pipe 10 as the gas flow rate adjusting means 100 will be described with reference to FIG. In this embodiment, the gas flow rate adjusting means 100 is composed only of the gas flow rate adjusting pipe 10 . As shown in FIG. 2, the gas flow regulating pipe 10 has a cylindrical shape as a whole, and a thin flow path 10a is provided in the center thereof in the longitudinal direction. Since resistance acts when the gas flows through this flow path 10a, the flow rate is adjusted.

The end portion 10d of the gas flow rate adjusting pipe 10 is on the gas supply source 90 side, and the end portion 10e is on the vacuum chamber 30 side. That is, the end portion 10d side has a high pressure close to atmospheric pressure, and the end portion 10e side has a low pressure close to vacuum. Therefore, the properties of the gas flow in the flow path 10a differ depending on the location, being a viscous flow near the end 10d and a molecular flow near the end 10e. Therefore, the conductance of the gas flow control pipe 10 is determined by the distribution of the viscous flow area and the molecular flow area formed within the flow path 10a.

FIG. 3 is a graph showing the relationship between the length of the gas flow control pipe 10 and the pressure of the vacuum chamber 30 in the plasma generator 1. As shown in FIG. In this graph, the horizontal axis is the length of the gas flow rate adjusting pipe 10, and the vertical axis is the pressure in the vacuum chamber 30 when the vacuum pump 40 is actuated and the steady state is reached. The inner diameter d1 (see FIG. 2) of the gas flow rate adjusting pipe 10 used was four types of 0.08 mm, 0.09 mm, 0.1 mm, and 0.21 mm, and various gas flow rate adjusting pipes with various total lengths L were used for each of them. 10 was used to plot FIG.

According to this graph, if the length of the gas flow rate adjusting pipe 10 is sufficiently short, the pressure will drop significantly even if the overall length is slightly longer, but if the overall length exceeds about 15 mm, the rate of pressure drop will be small. That is, it is considered that when the total length exceeds a certain level, the molecular flow region with low resistance increases in the channel 10a. In addition, in the plasma generation apparatus 1, the size of the gas flow rate adjustment pipe 10 to be adopted can be determined by reading this graph based on the required pressure of the vacuum chamber 30, and the required total length L can be obtained. be done. According to the graph of FIG. 3, the pressure in the vacuum chamber can be kept sufficiently low if the length of the gas flow rate adjusting pipe 10 is 3 mm or more. In addition, when the inner diameter d1 of the gas flow rate adjusting pipe 10 is 0.08 mm, the pressure in the vacuum chamber becomes 0.1 Pa or less if the length is 3 mm or more, so that it can be suitably used for applications such as plasma cleaners. can.

Next, details of the gas flow rate adjusting pipe 10 will be described with reference to FIG. The gas flow control 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. With this dimension, the wall thickness of the gas flow rate adjusting pipe 10 is sufficiently secured, so that the dimension of the flow path 10a does not change due to pressure, and a stable flow rate can be maintained over time.

Next, changes in pressure and reflected output over time when gas is introduced using this gas flow rate adjusting pipe 10 to generate plasma in the vacuum chamber 30 will be described with reference to FIG. As shown in FIG. 4, when the gas flow rate adjusting pipe 10 is used, the pressure in the vacuum chamber 30 fluctuates little and is maintained substantially constant. The flow rate of the supplied gas is stable and the plasma impedance does not fluctuate. Therefore, the state of matching with the high frequency circuit does not change. The reflected power shown in FIG. 4 is stable at a low level, which also indicates that impedance matching is good and plasma can be efficiently generated.

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

The tube 11 is preferably made of a soft resin, and specifically a silicon tube is suitable. A gas flow rate adjusting tube 20 is constructed by inserting a required number of gas flow rate adjusting pipes 10 from the end of the tube 11 . Since the pressure inside the gas flow rate adjusting tube 20 is low, the tight contact between the inner peripheral surface 11a of the tube 11 and the outer peripheral surface 10c of the gas flow rate adjusting pipe 10 is strengthened by the external pressure.

[Other Modifications]
Although the plasma generation apparatus 1 shown in FIG. 1 is provided with a stop valve 80 between the gas supply source 90 and the gas flow rate adjusting means 100, the stop valve 80 can be omitted. Further, the plasma generation apparatus 1 shown in FIG. 1 is configured to introduce a plasma-forming gas from the gas supply source 90, but the gas supply source 90 can be configured as the atmosphere.

The plasma generation apparatus according to the present invention can be used as an asher for ashing a photoresist or a plasma cleaner for an electron microscope or the like. At this time, the set pressure in the vacuum chamber can range from about 1 Torr to about 0.1 Pa. In either case, the gas flow rate adjusting means according to the present invention should be employed to generate stable and efficient plasma. can be done.

1 plasma generator 9 plasma generator 10 gas flow rate adjusting 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 adjusting tube 30 vacuum tank 40 vacuum pump 50 high frequency coil 60 High-frequency power supply 70 Vacuum gauge 80 Stop valve 90 Gas supply source 99 Needle valve 100 Gas flow rate adjusting means

Claims (5)

A gas flow rate adjustment pipe for a plasma generation device, which is provided in a path connecting a gas supply source and a vacuum chamber where plasma is generated, and adjusts the flow rate of the gas introduced from the gas supply source into the vacuum chamber and turned into plasma. and
the flow therein is viscous at the end close to the gas source and molecular flow at the end close to the vacuum chamber ;
wherein the gas supply source is the atmosphere, and the end portion closer to the gas supply source is connected to the atmosphere;
The flow rate of the gas introduced from the gas supply source into the vacuum chamber is adjusted only by the gas flow rate adjustment pipe for the plasma generator.
A gas flow rate adjusting pipe for a plasma generator, characterized by: The gas flow control pipe for a plasma generator according to claim 1, wherein the inner diameter is 0.3 mm or less and the length is 3 mm or more. The gas flow control pipe for a plasma generator according to claim 2, wherein the material is metal and the outer diameter is 1.5 mm or more. A gas flow rate adjusting tube for a plasma generation device, which is provided 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 into the vacuum chamber,
a hollow tube made of soft resin ;
and a gas flow rate adjusting pipe for a plasma generator according to any one of claims 1 to 3 , which is housed inside the tube,
A gas flow control tube for a plasma generation device, wherein an inner peripheral surface of the tube and an outer peripheral surface of the gas flow control pipe for the plasma generation device are in close contact with each other. A plasma generator comprising the gas flow rate adjusting pipe for the plasma generator according to any one of claims 1 to 3 .

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