Plasma ignition device and plasma ignition method

Abstract

To provide a plasma ignition device and a plasma ignition method in which a voltage to be applied is suppressed low with a simple configuration.SOLUTION: A plasma ignition device 1 includes: a vacuum tank 10 that applies a voltage to a gas at the inside to make it into plasma; a gas source 20 that supplies the gas into the vacuum tank 10; a flow path 30 that connects the gas source 20 and the vacuum tank 10 and through which the gas flows; throttling means 40 that is provided in the flow path 30 for throttling a flow rate of the gas which flows from the gas source 20 to the vacuum tank 10; a switching valve 50 that is provided in the flow path 30 between the throttling means 40 and the vacuum tank 10 for opening and closing the flow path 30; and a gas storage part 60 that is provided in the flow path 30 between the throttling means 40 and the switching valve 50 for storing a predetermined amount of the gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a plasma ignition device and a plasma ignition method. [Background technology]

[0002] Plasma is used to remove contamination from sample chambers in electron microscopes, in processes for stripping photoresist (ashing), and the like. 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 into which oxygen has been introduced.

[0003] Among the electron microscopes to which plasma cleaners are applied, CD-SEM (Critical Dimension-Scanning Electron Microscope) is a device used for measuring the dimensions of fine patterns formed on semiconductor wafers. When measuring the wiring width of semiconductor devices using a CD-SEM, if hydrocarbon contaminants are present in the vacuum chamber, measurement errors will occur. For this reason, plasma cleaners are used to remove hydrocarbons from within the vacuum chamber of the CD-SEM.

[0004] Incidentally, the structure of transistors, which are semiconductor elements, has been miniaturized in recent years, and complex three-dimensional structures called Fin-FET and GAA-FET structures have appeared. In order to measure such complex semiconductor structures, CD-SEM is generally insufficient, and a FIB-SEM (Focused Ion Beam-Scanning Electron Microscope) is required.

[0005] In FIB-SEM, it is necessary to clean a wider area than in CD-SEM. Therefore, high vacuum and high density plasma are required. However, according to Paschen's law, the voltage required to ignite plasma in a high vacuum increases rapidly. Therefore, a large capacity power supply is required to handle the high voltage required only when igniting plasma.

[0006] On the other hand, a method for igniting plasma is known in which the applied voltage is suppressed by adjusting the pressure of the raw material gas (see Patent Document 2). The method disclosed in Patent Document 2 is configured to ignite plasma by adjusting the pressure of the raw material gas while keeping the applied voltage constant (see paragraphs 0036 to 0038 of Patent Document 2). In this method, the pressure of the raw material gas is adjusted by detecting the pressure inside the vacuum chamber and then controlling a pressure adjustment unit (such as a mass flow controller) from time to time with a pressure control unit. In other words, this method requires a device such as a mass flow controller and a device to control it, and there is a problem in that the entire device for igniting plasma becomes complicated. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2016-54136 A [Patent Document 2] JP 2017-174730 A Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above problems, an object of the present invention is to provide a plasma ignition device and a plasma ignition method that have a simple configuration and are capable of keeping the applied voltage low. [Means for solving the problem]

[0009] The plasma ignition device according to the present invention is characterized in comprising: a vacuum chamber in which a voltage is applied to a gas inside to generate plasma; a gas source that supplies a gas to the vacuum chamber; a flow path connecting the gas source and the vacuum chamber through which the gas flows; a throttle means that is provided in the flow path and throttles a flow rate of the gas that flows from the gas source toward the vacuum chamber; an opening / closing valve that is provided in the flow path between the throttle means and the vacuum chamber and opens and closes the flow path; and a gas storage section that is provided in the flow path between the throttle means and the opening / closing valve and stores a predetermined amount of gas.

[0010] According to the present invention, it is possible to provide a plasma ignition device that can suppress the applied voltage to a low level and ensure reliable ignition.

[0011] Another plasma ignition device according to the present invention is characterized in that the gas storage portion is composed of the flow path itself between the throttling means and the on-off valve.

[0012] According to the present invention, it is possible to provide a plasma ignition device that is capable of reliable ignition with a simple configuration.

[0013] Another plasma ignition device according to the present invention is characterized in that the throttling means comprises a pipe having a hole penetrating in the longitudinal direction, and resistance is generated when the gas flows through the hole.

[0014] According to the present invention, it is possible to provide a plasma ignition device that is capable of generating plasma from a stable flow rate of gas with a simple configuration.

[0015] Another plasma ignition device according to the present invention is characterized in that the cross-sectional area of ​​the hole of the pipe is smaller than the cross-sectional area of ​​the flow passage between the throttling means and the on-off valve.

[0016] According to the present invention, it is possible to provide a plasma ignition device that can throttle the flow rate of gas with a simple configuration.

[0017] Another plasma ignition device according to the present invention is characterized in that the throttle means is a valve whose opening is adjustable.

[0018] According to the present invention, it is possible to provide a plasma ignition device capable of adjusting the manner in which the pressure inside the vacuum chamber changes.

[0019] Another plasma ignition device according to the present invention is characterized in that the gas source is the atmosphere.

[0020] According to the present invention, it is possible to provide a plasma ignition device that is capable of reliable ignition with a simple configuration.

[0021] The plasma ignition method of the present invention is a plasma ignition method for converting gas supplied from a gas source into plasma inside a vacuum chamber, and is characterized in that it includes the steps of closing an on-off valve provided in a flow path connecting the upstream gas source and the downstream vacuum chamber, storing a predetermined amount of gas in a gas storage section provided upstream of the on-off valve, reducing the pressure inside the vacuum chamber to a low pressure, applying a predetermined voltage to the vacuum chamber, and opening the on-off valve to introduce the gas in the gas storage section into the vacuum chamber.

[0022] According to the present invention, it is possible to provide a plasma ignition method that can suppress the applied voltage to a low level and ensure reliable ignition. Effect of the Invention

[0023] According to the present invention, it is possible to provide a plasma ignition device and a plasma ignition method that can suppress the applied voltage to a low level and ensure ignition. [Brief description of the drawings]

[0024] [Figure 1] 1 is a schematic diagram showing a plasma ignition device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic perspective view showing an example of a throttle means of the plasma ignition device according to the embodiment of the present invention. [Diagram 3] FIG. 2 is a schematic perspective view showing an example of a gas storage section of a plasma ignition device according to an embodiment of the present invention. [Figure 4]FIG. 2 is a diagram showing a Paschen curve, the pressure in a vacuum chamber, and the applied voltage, superimposed on each other, in a plasma ignition device according to an embodiment of the present invention. [Diagram 5] FIG. 4 is a diagram showing a schematic diagram of a change in pressure in a vacuum chamber after an on-off valve is opened in a plasma ignition device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Next, an embodiment of a plasma ignition device and a plasma ignition method 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 various technically preferable limitations are attached, but 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.

[0026] A plasma ignition device and a plasma ignition method according to an embodiment of the present invention will be described with reference to Figs. 1 to 5. Fig. 1 is a schematic diagram showing a plasma ignition device according to an embodiment of the present invention. Fig. 2 is a schematic perspective view showing an example of a throttling means of a plasma ignition device according to an embodiment of the present invention. Fig. 3 is a schematic perspective view showing an example of a gas storage section of a plasma ignition device according to an embodiment of the present invention. Fig. 4 is a diagram showing a Paschen curve, a pressure in a vacuum chamber, and an applied voltage superimposed thereon in a plasma ignition device according to an embodiment of the present invention. Fig. 5 is a diagram showing a schematic diagram of a change in pressure in a vacuum chamber after an opening / closing valve is opened in a plasma ignition device according to an embodiment of the present invention.

[0027] <Plasma ignition device> As shown in FIG. 1, the plasma ignition device 1 according to this embodiment has as its main components a vacuum chamber 10 in which the gas inside is converted into plasma, a gas source 20 which supplies gas to the vacuum chamber 10, and a flow path 30 which connects the gas source 20 and the vacuum chamber 10 and through which gas flows.

[0028] A vacuum pump 70 is connected to the vacuum chamber 10, which reduces the pressure inside the chamber to a near vacuum. A high-frequency coil 81 is arranged around the vacuum chamber 10, and a high-frequency power supply 82 is connected to the coil to apply a high-frequency voltage. The high-frequency coil 81 and the high-frequency power supply 82 constitute a voltage application means 80 that applies a voltage to the gas in the vacuum chamber 10. The gas supplied from the gas source 20 to the vacuum chamber 10 is turned into plasma by the energy of the applied voltage. A vacuum gauge (not shown) that measures the pressure is connected to the vacuum chamber 10. The vacuum chamber 10 is not limited to a single container, and can be configured by connecting multiple containers. For example, the plasma generated in one container of the vacuum chamber 10 that is configured with multiple containers can be transferred to another container and used (for cleaning, etc.).

[0029] The gas source 20 can be composed of a gas cylinder or the like that contains a gas to be turned into plasma in the vacuum chamber 10. When composed of a gas cylinder, the gas can be supplied via a regulator (not shown) that adjusts the pressure. The gas source 20 can also be the atmosphere.

[0030] The flow path 30 is provided with, in order from the upstream, a throttle means 40, a gas storage section 60, and an on-off valve 50. The throttle means 40 is configured to throttle the flow rate of the gas flowing from the gas source 20 toward the vacuum chamber 10. In this embodiment, a pipe 41 (see FIG. 2) is used as the throttle means 40. As shown in FIG. 2, the pipe 41 has a hole 41a penetrating in the longitudinal direction, and the diameter d1 of the hole 41a is sufficiently small. Therefore, resistance acts when the gas flows through the hole 41a, thereby throttling the flow rate of the gas. The conductance of the pipe 41 is determined by the diameter d1 and length L1 of the hole 41a. That is, the smaller d1 is, the smaller the conductance is, and the longer L1 is, the smaller the conductance is. The flow rate of the gas flowing through the flow path 30 is configured to be throttled by the pipe 41, which is the throttle means 40. That is, the conductance of the pipe 41 is set to be sufficiently smaller than the conductance of the flow path 30.

[0031] In addition, since the end of pipe 41 close to gas source 20 is at high pressure, the flow in hole 41a is a viscous flow near this end. In contrast, when vacuum chamber 10 is at a low pressure close to a vacuum and on-off valve 50 is open, the end of pipe 41 close to vacuum chamber 10 is at a low pressure close to a vacuum, so the flow in hole 41a is a molecular flow near this end. Pipe 41 has sufficient strength to withstand the pressure difference.

[0032] Next, the on-off valve 50 will be described. The on-off valve 50 is provided in the flow path 30 between the throttle means 40 and the vacuum chamber 10, and is configured to open and close the flow path 30, i.e., to switch between a fully open state and a fully closed state. As the on-off valve 50, a solenoid valve can be preferably used, but other appropriate valves can also be used.

[0033] A gas storage section 60 that stores a predetermined amount of gas is provided in the flow path 30 between the throttling means 40 and the on-off valve 50. The gas storage section 60 can be configured as appropriate, but the gas storage section 60 in this embodiment is configured by the portion 30b itself between the throttling means 40 and the on-off valve 50 in the flow path 30. Specifically, a pipe 61 shown in FIG. 3 is provided between the throttling means 40 and the on-off valve 50, and a hole 61a of the pipe 61 configures the portion 30b of the flow path 30. The hole 61a of the pipe 61 stores a predetermined amount of gas, and the amount is determined by the diameter d2 and length L2 of the hole 61a.

[0034] In this embodiment, a tube 61 serving as a gas storage section 60 is connected to the downstream side of a pipe 41 serving as a throttle means 40. The tube 61 constitutes the portion 30b of the flow path 30, and is set to have a larger conductance than the pipe 41. That is, a diameter d2 of a hole 61a of the tube 61 is sufficiently larger than a diameter d1 of a hole 41a of the pipe 41. That is, a cross-sectional area of ​​the hole 41a of the pipe 41 is smaller than a cross-sectional area of ​​the portion 30b of the flow path 30.

[0035] <Plasma ignition method> Next, a method for igniting plasma using the plasma ignition device 1 will be described.

[0036] First, the on-off valve 50 provided in the flow passage 30 is closed.

[0037] At this time, the pressure in the flow passage 30 from the portion 30a communicating with the gas source 20 to the throttle means 40 and the portion 30b (gas storage section 60) of the flow passage 30 becomes the same as that of the gas source 20 and is filled with gas. That is, a predetermined amount of gas is stored in the gas storage section 60 upstream of the on-off valve 50.

[0038] Next, the vacuum pump 70 is operated to create a low pressure inside the vacuum chamber 10 that is almost a vacuum. Then, the portion 30c of the flow path 30 downstream of the on-off valve 50 also becomes low pressure close to a vacuum, just like the vacuum chamber 10. The pressure inside the vacuum chamber 10 at this time is p1 as shown in FIG.

[0039] Of course, it is also possible to store a predetermined amount of gas in the gas storage section 60 before closing the on-off valve 50. Also, it is also possible to close the on-off valve 50 during the step of operating the vacuum pump 70 to reduce the pressure inside the vacuum chamber 10, and then store a predetermined amount of gas in the gas storage section 60.

[0040] Next, the high frequency power supply 82 of the voltage application means 80 is operated to apply a voltage to the vacuum chamber 10 via the high frequency coil 81. The voltage applied at this time is Vs shown in Fig. 4. From the relationship between the Paschen curve shown in Fig. 4 and the plot of the pressure in the vacuum chamber 10 and the applied voltage, plasma is not ignited at the pressure and voltage at this stage.

[0041] Here, the Paschen curve in FIG. 4 will be explained. Discharge occurs when electrons accelerated by external energy collide with gas molecules and ionize the gas. Here, if there is little gas (i.e., pressure is low), collisions are less likely to occur. Also, if there is a lot of gas (i.e., pressure is high), electrons are not accelerated enough to collide with gas molecules. That is, if the pressure is too high or too low, the external energy required for discharge becomes large, and at an intermediate pressure, the external energy required for discharge becomes minimum (Paschen's law). The Paschen curve in FIG. 4 shows the relationship between pressure and external energy required for discharge. The shape of the Paschen curve differs depending on the type of gas. Note that the external energy in this embodiment is a high-frequency voltage. Therefore, the vertical axis in FIG. 4 is the applied voltage. Also, the axis in FIG. 4 is in a logarithmic scale.

[0042] Next, the on-off valve 50 is opened. Here, the change in pressure in the vacuum chamber 10 after the on-off valve 50 is opened will be described with reference to FIG. 5. The pressure before the on-off valve 50 is opened is p1. When the on-off valve 50 is opened, the gas in the gas storage section 60 is introduced into the vacuum chamber 10 all at once. As a result, the pressure in the vacuum chamber 10 rises temporarily and reaches p2. Although the pressure in the vacuum chamber 10 rises temporarily, the pressure in the vacuum chamber 10 drops because the vacuum pump 70 is operating and the flow rate of the gas flowing in from the gas source 20 is throttled by the throttle means 40. After that, the pressure in the vacuum chamber 10 is maintained almost constant at pressure p3 at which the flow rate of the gas flowing in via the throttle means 40 is equal to the flow rate of the gas discharged by the vacuum pump 70. In one embodiment, the pressure reaches a maximum of about 1.2 Pa about 0.3 seconds after the on-off valve 50 is opened, and then the pressure drops and becomes constant at about 0.1 Pa about 0.7 seconds after the on-off valve 50 is opened.

[0043] Next, plasma ignition in the vacuum chamber 10 will be described with reference to Figure 4. As mentioned above, the pressure inside the vacuum chamber 10 before the on-off valve 50 is opened is p1 and the applied voltage is Vs. Since this point is below the Paschen curve, no discharge occurs and the plasma does not ignite. After the on-off valve 50 is opened, the pressure inside the vacuum chamber 10 temporarily rises to p2. At this time, the applied voltage remains at Vs. Since this point is above the Paschen curve, a discharge occurs, i.e., the plasma ignites.

[0044] After this, the pressure inside the vacuum chamber 10 drops again to p3 (see FIG. 5), but the plasma that was once ignited does not disappear, and the gas supplied from the gas source 20 continues to be turned into plasma.

[0045] Thus, in the plasma ignition method according to this embodiment, plasma can be ignited simply by opening the on-off valve 50, and the generation of plasma can be maintained thereafter. During this time, the voltage applied to the vacuum chamber 10 remains constant. Furthermore, the pressure inside the vacuum chamber 10 changes due to the action of the gas storage section 60 and the on-off valve 50, and there is no need for a device that detects the pressure and controls the pressure from moment to moment.

[0046] The pressure inside the vacuum chamber 10 changes as shown in Fig. 5, and the manner in which this changes can be set by changing the amount of gas stored in the gas storage section 60, the volume of the vacuum chamber 10, the conductance of the throttling means 40, etc. Of course, the applied voltage can also be set appropriately. By setting these amounts appropriately, it is possible to set the pressure inside the vacuum chamber 10 to temporarily exceed the Paschen curve after the on-off valve 50 is opened.

[0047] <Modification> In the above-described embodiment, a high-frequency voltage is applied to the gas in the vacuum chamber 10 via the high-frequency coil 81, but instead of the high-frequency coil, it is also possible to configure the configuration so that the high-frequency voltage is applied to a pair of electrodes. The voltage to be applied is not limited to high-frequency voltage and can be selected appropriately. It is also possible to apply a direct current voltage. When electrodes are used, the horizontal axis of the graph corresponding to FIG. 4 is the product of the pressure in the vacuum chamber and the distance between the electrodes, but the shape of the Paschen curve will be the same as that shown in FIG. 4.

[0048] In the above embodiment, the entire portion 30b of the flow path 30 from the throttle means 40 to the on-off valve 50 is the gas storage section 60. Alternatively, the portion 30b may be locally expanded at any position to store the gas. The shape and structure of the flow path 30, including the portion 30b, may be appropriately set. In the above embodiment, the pipe 41 is used as the throttle means 40. Alternatively, a valve with an adjustable opening, such as a leak valve, may be used. This allows the flow rate of gas flowing from the gas source 20 to the vacuum chamber 10 to be changed. In addition, by adjusting the opening of this valve, the manner in which the pressure in the vacuum chamber 10 changes after the on-off valve 50 is opened in the process of igniting the plasma (see FIG. 5) can be changed. [Explanation of symbols]

[0049] 1 Plasma ignition device 10 Vacuum chamber 20 Gas Source 30 Flow Path 30a,30b,30c part 40 Squeezing means 41 Pipe 41a hole 50 On-off valve 60 Gas storage section 61 tube 61a hole 70 Vacuum Pump 80 Voltage application means 81 High Frequency Coil 82 High frequency power supply

Claims

1. A vacuum chamber in which a voltage is applied to the gas inside to create plasma; a gas source for supplying gas to the vacuum chamber; a flow path connecting the gas source and the vacuum chamber through which a gas flows; a throttle means provided in the flow path for throttling a flow rate of gas flowing from the gas source toward the vacuum chamber; an on-off valve provided in the flow path between the throttle means and the vacuum chamber for opening and closing the flow path; a gas storage section that is provided in the flow path between the throttle means and the on-off valve and that stores a predetermined amount of gas. A plasma ignition device characterized by:

2. The gas storage portion is formed of the flow path itself between the throttle means and the on-off valve.

2. The plasma ignition device according to claim 1.

3. The throttle means is a pipe having a hole penetrating in the longitudinal direction, and resistance is applied when the gas flows through the hole.

3. The plasma ignition device according to claim 2.

4. The cross-sectional area of ​​the hole of the pipe is smaller than the cross-sectional area of ​​the flow path between the throttle means and the on-off valve.

4. The plasma ignition device according to claim 3.

5. The throttle means is a valve whose opening is adjustable.

3. The plasma ignition device according to claim 1 or 2.

6. The gas source is the atmosphere.

5. The plasma ignition device according to claim 1, wherein the plasma ignition device is a plasma ignition device.

7. A plasma ignition method for generating plasma from a gas supplied from a gas source inside a vacuum chamber, comprising the steps of: closing an on-off valve provided in a flow path connecting the upstream gas source and the downstream vacuum chamber; storing a predetermined amount of gas in a gas storage section provided upstream of the on-off valve; creating a low pressure inside the vacuum chamber; applying a predetermined voltage to the vacuum chamber; and opening the on-off valve to introduce the gas from the gas storage section into the vacuum chamber. A plasma ignition method comprising:

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