Vacuum charge removal device

Abstract

To provide a vacuum static eliminator capable of eliminating static electricity without supplying gas from the outside in a high vacuum area.SOLUTION: A vacuum chamber 1 includes a mesh electrode 6 to which a positive voltage is applied, a ground electrode 2 that forms an electric field with the mesh electrode 6, and a filament 10 that is provided near the mesh electrode 6 and emits thermoelectrons, and residual gas molecules in the vacuum chamber 1 are ionized by motion of thermal electrons emitted from the filament 10 and receiving force from the electric field formed by the mesh electrode 6.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vacuum static eliminator for eliminating charged objects in a vacuum area.

Background Art

[0002] Conventionally, a thin film has been formed on the surface of a resin film by vapor deposition. Since the resin film on which vapor deposition is performed is insulating, it has a property of being easily electrostatically charged. Further, since the atmosphere of the vapor deposition process is a high vacuum, it is electrically insulating. Once the surface of the film or the like is charged under high vacuum, the charge is difficult to escape. Therefore, the charged state is maintained.

[0003] When charged, the films easily adhere to each other, causing conveyance failures or wrinkles and scratches. Also, if the film surface is charged before the vapor deposition process, the vapor deposition may become non-uniform. In addition, in the manufacturing process of devices such as LSI (Large Scale Integration), processing under high vacuum is required. And LSI and the like are electrostatically sensitive devices that can be damaged by electrostatic charging and discharge caused thereby.

[0004] Thus, there is an application for static elimination in a high vacuum area. However, in a high vacuum area, a general static eliminator that neutralizes the surface charge of a film with ions generated by corona discharge cannot be used as it is. This is because ions cannot be generated by corona discharge under the high vacuum in which the vacuum film forming process or the manufacturing of electrostatically sensitive devices is performed.

[0005] As a device capable of eliminating charged objects under such high vacuum, the device shown in Patent Document 1 was known. In this conventional device, a mesh electrode for applying a voltage and a ground electrode are provided in a chamber maintained at a high vacuum. A high voltage is applied to the mesh electrode to form an electric field, and gas is supplied pulsatively into this electric field to instantaneously and locally lower the degree of vacuum and generate a discharge. Plasma is generated by this discharge, and the surface charge of the charged object flows to the ground side through this plasma to be discharged. In addition, since the supply of the above gas is pulsative, that is, instantaneous, the degree of vacuum immediately recovers, and a high degree of vacuum can be maintained.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the above conventional static eliminator, the pulsative supply of gas into the electric field formed by the mesh electrode is to prevent the degree of vacuum in the entire chamber from decreasing more than necessary. For example, while maintaining the pressure of the gas supply source at a predetermined pressure, the opening time of the valve is controlled to a short time of about 100 [μs]. If the opening time of the valve becomes longer, the supply amount of gas increases and the degree of vacuum in the chamber decreases. On the other hand, if the opening time of the valve is too short and the supply amount of gas is small, the generated plasma is insufficient and the static elimination becomes insufficient.

[0008] As described above, in the above-described conventional vacuum static eliminator, accurate control of the gas supply amount into the vacuum chamber is required. Therefore, there is a problem that it is difficult to control the opening and closing of the valve and an expensive valve capable of high-precision control is required. An object of the present invention is to provide a vacuum static eliminator that can stably eliminate static electricity without requiring precise control of the gas supply amount and without reducing the degree of vacuum.

Means for Solving the Problems

[0009] The first invention includes a mesh electrode to which a positive voltage is applied, a ground electrode that forms an electric field with the mesh electrode, and a filament that is provided near the mesh electrode and emits thermoelectrons, within a vacuum area. The configuration is such that residual gas molecules within the vacuum area are ionized by the movement of thermoelectrons emitted from the filament and receiving a force from the electric field formed by the mesh electrode.

[0010] The second invention provides a thermoelectron emission area by providing the filament between the ground electrode and the mesh electrode, and a holding means for the object to be static-eliminated is provided on the side opposite to the thermoelectron emission area with the mesh electrode as a boundary.

[0011] The third invention includes a filament holding member made of an electrically insulating body that holds the filament. The filament holding member is attached to the ground electrode while maintaining a slit between the filament holding member and the ground electrode on the protruding side of the filament.

Effects of the Invention

[0012] According to the present invention, thermoelectrons emitted from the filament move due to the electric field formed by the mesh electrode at a positive potential, collide with residual gas molecules in the chamber, and can ionize the residual gas molecules. Ions and electrons generated by the ionization of gas molecules can neutralize the surface charges of the object to be static-eliminated and eliminate static electricity. Since thermoelectrons ionize residual gas molecules, there is no need to supply gas from the outside. Therefore, there is no need for opening and closing control of a valve considering a decrease in the degree of vacuum, and an expensive valve is not required.

[0013] According to the second invention, since the holding means for the object to be neutralized is not provided in the thermoelectron emission area, the distance between the mesh electrode and the ground electrode can be reduced, and thermoelectrons can be emitted into the strong electric field formed by the mesh electrode and the ground electrode, increasing the kinetic energy of the thermoelectrons. Also, since the object to be neutralized can be held near the mesh electrode, ions and electrons generated by the ionization collision with the thermoelectrons with momentum passing through the mesh electrode can effectively contribute to neutralization.

[0014] According to the third invention, the conduction between the filament and the ground electrode can be prevented by the vapor of the filament, and thermoelectron emission can be stably maintained.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0016] [Embodiment] An embodiment of this invention will be described with reference to FIGS. 1 to 4. FIG. 1 is a conceptual diagram near the thermoelectron emission area in the vacuum neutralization device of the embodiment. FIG. 2 is a plan view of the ring member which is the filament holding member of the embodiment. FIG. 3 is a graph showing the relationship between the filament current I F and the thermoelectron current I E when the filament of the embodiment is energized. FIG. 4 is a table showing the results of the neutralization experiment using the vacuum neutralization device of the embodiment.

[0017] As shown in FIG. 1, the vacuum charge eliminator of this embodiment maintains the ground potential, and the vacuum chamber 1 that constitutes the vacuum area is kept at a high vacuum by a vacuum pump (not shown). The high vacuum in this embodiment means a pressure of 10×10 ―1 [Pa] or less. The vacuum chamber 1 has a circular opening 1a, and a ground electrode 2 is provided so as to cover the opening 1a from the atmospheric side. The ground electrode 2 has a seal member (not shown) interposed between it and the outer peripheral surface of the vacuum chamber 1, and is fixed to the vacuum chamber 1 by a plurality of bolts 3. The vacuum chamber 1 and the ground electrode 2 are formed of a metal that is a conductor, and the ground electrode 2 and the vacuum chamber 1 maintain the same ground potential.

[0018] As described above, since the opening 1a of the vacuum chamber 1 is blocked from the atmospheric side by the ground electrode 2, the higher the degree of vacuum in the vacuum chamber 1, the greater the differential pressure acting on the ground electrode 2, and the force in the direction of blocking the opening 1a is exerted. Therefore, the vacuum chamber 1 maintains almost perfect airtightness. In addition, a circular recess 2a that coincides with the opening 1a is formed on the surface of the ground electrode 2 on the vacuum chamber 1 side. A ring member 4, which is a filament holding member made of an electrical insulator, is installed in the recess 2a, and the ring member 4 is fixed to the ground electrode 2 by a plurality of bolts 5. Furthermore, a mesh electrode 6 is fixed to the ring member 4 by a plurality of bolts 7 so as to cover the opening portion thereof. A DC power supply 8 is connected to the mesh electrode 6, and a positive voltage is applied.

[0019] Furthermore, a pair of holders 9, 9 are provided on the ring member 4 so as to project into the opening 1a (see FIG. 2), and these holders 9, 9 support both ends of a tungsten filament 10 bent in a U shape. In other words, the holders 9, 9 and the filament 10 are formed into a substantially U shape as a whole in combination, and the bent portion of the filament 10 faces the center of the concave portion 2a. The filament 10 formed in this way is connected to a variable DC power supply 11 via the holders 9, 9, and emits thermoelectrons when energized. The space surrounded by the opposing ground electrode 2, mesh electrode 6, and ring member 4 as described above is the thermoelectron emission area 12. Note that FIG. 2 is a plan view seen from the surface side fixed to the ground electrode 2, and the insertion holes of the bolts 5, 7 are omitted in this FIG. 2.

[0020] Note that the position of the filament 10 attached to the ring member 4 is near the mesh electrode 6. The vicinity of the mesh electrode 6 means a position where the thermoelectrons emitted from the filament 10 are affected by the electric field formed by the mesh electrode 6. Thus, if the filament 10 is positioned near the mesh electrode 6, the thermoelectrons can move sufficiently, and the probability of ionization collision with residual gas molecules can be increased.

[0021] The closer the position of the filament 10 is to the mesh electrode 6, the greater the movement speed of the thermoelectrons, the higher the probability of ionization collision with residual gas molecules, and it is considered that the function of ionizing gas molecules is enhanced. However, the probability of ionization collision with residual gas molecules depends not only on the distance between the mesh electrode 6 and the filament 10, but also on the filament current I supplied to the filament 10 F and the applied voltage of the mesh electrode 6 and their relative relationship with the above distance. Note that the position of the filament 10 may be on the same side as the ground electrode 2 or on the opposite side with the mesh electrode 6 as the boundary.

[0022] Further, on the bottom surface of the ring member 4 on the side that contacts the grounding electrode 2, a ring-shaped recess 4a is formed along the concentric circle of the opening 1a. The recess 4a has a depth of about 3 to 4 [mm] from the bottom surface that contacts the grounding electrode 2, and a slit is formed between the ring member 4 and the grounding electrode 2 on the side of the thermoelectron emission area 12, that is, the protruding side of the filament 10.

[0023] Also, in the vacuum chamber 1, holding means 13 for holding the object to be neutralized is provided. This holding means 13 has a configuration according to the form of the object to be processed, such as a table for placing the object to be neutralized or a transport roller for transporting a strip-shaped film. In this embodiment, the holding means 13 is provided on the side opposite to the thermoelectron emission area 12 where the filament 10 is provided, with the mesh electrode 6 as a boundary.

[0024] [Function, effect, etc.] The function of the neutralization device of this embodiment will be described below. First, while operating a vacuum pump (not shown) to maintain the inside of the vacuum chamber 1 at about 1×10 -4 [Pa], the filament 10 is energized to emit thermoelectrons from the filament 10. 1×10 -4 [Pa] inside the vacuum chamber 1 is a so-called high vacuum. At this degree of vacuum, various types of gases remain, such as gases adsorbed on the inner peripheral surface of the vacuum chamber 1 and gases dissolved in the chamber material.

[0025] Note that the amount of thermoelectrons emitted from the filament 10 depends on the filament current I F flowing through the filament 10. Therefore, in order to confirm the filament current I F required for the emission of thermoelectrons, the filament current I F is changed by the variable DC power supply 11 shown in FIG. 2, and the current flowing through the mesh electrode 6 is measured as the thermoelectron current I E .

[0026] At this time, a voltage of +500 [V] was applied to the mesh electrode 6 so that the mesh electrode 6 captured thermoelectrons. The measurement results are shown in FIG. 3. From FIG. 3, the filament current I supplied to the filament 10 F when it becomes 1.4 [A] or more, the thermoelectron current I E rapidly increases, and it was found that when the filament current I F exceeds 1.7 [A], the amount of increase becomes small.

[0027] The above thermoelectron current I E indicates the amount of thermoelectrons emitted from the filament 10 that flowed through the mesh electrode 6. Therefore, in this embodiment, in order to emit thermoelectrons from the filament 10, it was found that a filament current I of 1.4 [A] or more must be supplied to the filament 10. F It was found that it must be supplied.

[0028] When the filament current I F is supplied to the above filament 10, a positive voltage is applied to the mesh electrode 6. When a positive voltage is applied to the mesh electrode 6, the thermoelectrons emitted from the filament 10 move under the force from the electric field formed by the positive potential of the mesh electrode 6. Specifically, the thermoelectrons move so as to be attracted to the positive mesh electrode 6, but the thermoelectrons are not immediately absorbed by the mesh electrode 6. Instead, the thermoelectrons once pass through the mesh electrode 6 and move to the opposite side.

[0029] A force acting in the opposite direction to the previous one, toward the mesh electrode 6, acts on the thermoelectrons that have passed through the mesh electrode 6. Therefore, the moving direction of the thermoelectrons changes, and they pass through the mesh electrode 6 again and receive a force in the opposite direction. In this way, the thermoelectrons will perform a reciprocating motion with the mesh electrode 6 as the boundary.

[0030] The thermoelectrons performing the reciprocating motion as described above collide with the residual gas molecules in the vacuum chamber 1 and ionize the gas molecules. Due to this ionization, ions and electrons are generated. Note that the electrons generated by ionization also contribute to the ionization collision of gas molecules while performing the same reciprocating motion as the above-mentioned hot electrons, generating ions and electrons. The generated ions or electrons neutralize the surface charges of the object to be discharged held by the holding means 13, and the discharge is performed. For example, electrons and negative ions are attracted to the object to be discharged charged positively, and positive ions are attracted to the object to be discharged charged negatively, neutralizing the surface charges of the object to be discharged.

[0031] Next, the discharging experiment using the above-described discharging device will be described. As the object to be discharged, a metal plate PL held by the holding means 13 was charged and used. A charge plate monitor (Hugel Electronics 700A type) was connected to this plate PL outside the vacuum chamber 1. This charge plate monitor has a function of charging the plate PL and measuring the change in its surface potential. In the discharging experiment, the plate PL is charged to +1000 [V] or -1000 [V] by the charge plate monitor and used. Note that the plate PL used in the experiment is a square with a side length of 45 [mm].

[0032] The experimental conditions are as follows. The vacuum chamber 1 is a rectangular prism with a vertical, horizontal, and height of 750 [mm], 750 [mm], and 1250 [mm], respectively, and the upper bottom surface constitutes the ground electrode 2. The plate PL is held by the holding means 13 at a position approximately 1000 [mm] from the mesh electrode 6. Also, the inside of the vacuum chamber 1 is maintained at 5×10 -4 [Pa] by a vacuum pump (not shown), and the vacuum pump is kept operating constantly.

[0033] The following experiment is performed for each of the plates PL charged to +1000 [V] or -1000 [V] by the charge plate monitor. After the plate PL is charged to +1000 [V] or -1000 [V], a voltage of +500 [V] is applied to the mesh electrode 6 and the filament current IF Supply 1.7 [A] and measure the change in the surface potential of the plate PL using a charge plate monitor.

[0034] The results of the static elimination experiment are shown in Fig. 4. Fig. 4 is a graph showing time on the horizontal axis and the surface potential of the plate PL on the vertical axis. The solid line graph (1) shows the change in the surface potential of the plate PL charged to +1000 [V], and the dotted line graph (2) shows the change in the surface potential of the plate PL charged to -1000 [V]. In both cases, at the 0 time point on the horizontal axis, a voltage of +500 [V] is applied to the mesh electrode 6 and a filament current I F is supplied at 1.7 [A].

[0035] As shown in Fig. 4, it was found that the plate PL charged to +1000 [V] was instantaneously discharged by applying a voltage to the mesh electrode 6 and supplying a current to the filament 10. Specifically, after supplying the filament current I F at 1.7 [A] to the filament 10, the surface potential decreased to several tens [V] in about 0.1 [sec]. Thus, the reason for the instantaneous decrease in the positive surface potential is that the electrons generated by the ionization of the residual gas molecules and the thermoelectrons efficiently neutralized the positive surface charges of the plate PL.

[0036] Note that it has also been confirmed that almost the same results as in Fig. 4 can be obtained by simply supplying the filament current I F at 1.7 [A] without applying a voltage to the mesh electrode 6. From this, it was found that under the above conditions, a sufficient amount of thermoelectrons are emitted from the filament 10 to neutralize the surface charges of the 45 [mm] square plate PL charged to +1000 [V].

[0037] On the other hand, as shown in the dotted line graph (2), for the plate PL charged to -1000 [V], a voltage is applied to the mesh electrode 6 and the filament current I FAfter supplying, the surface potential decreased to several tens of [V] in about 10 [sec]. This is because the thermoelectrons emitted from the filament 10 collided ionizingly with the residual gas molecules, and the generated positive ions neutralized the negative charge of the plate PL.

[0038] As described above, in this embodiment, if the filament current I F and the voltage applied to the mesh electrode 6 are appropriately set, the thermoelectrons emitted from the filament 10 can be reciprocated and made to collide ionizingly with the residual gas molecules. Since the thermoelectrons collide ionizingly with the residual gas, electrons and ions necessary for static elimination can be generated without supplying gas into the vacuum chamber 1 from the outside. Therefore, in this embodiment, there is no need to precisely control the gas supply amount as in the conventional vacuum static elimination device that supplies gas for plasma generation from the outside.

[0039] Therefore, in the vacuum static elimination device of the embodiment, there is no worry that the static elimination effect becomes unstable according to the gas supply amount, or that the gas supply amount is too large and the degree of vacuum in the vacuum chamber 1 decreases. Also, equipment such as a gas supply source, a high-precision valve, and valve control means becomes unnecessary, the device configuration can be simplified, and the equipment cost can be reduced.

[0040] Furthermore, in this embodiment, a concave portion 4a is formed in the ring member 4 made of an insulator that holds the filament 10. By providing a slit between the ring member 4 and the ground electrode 2 by means of the concave portion 4a in this way, and increasing the distance between the filament 10 and the ground electrode 2, it is possible to prevent the tungsten constituting the filament 10 from depositing on the surfaces of the holder 9 and the ring member 4 and causing the filament 10 and the ground electrode 2 to conduct.

[0041] In the process of emitting thermoelectrons by energizing the filament 10, tungsten vapor is also emitted. When the surfaces of the holder 9, the ring member 4, and the ground electrode 2 are continuously vapor-deposited by this tungsten vapor, the filament 10 becomes conductive to the ground electrode 2 and is grounded, and thermoelectrons cannot be emitted. However, in this embodiment, the concave portion 4a is formed, and the surfaces of the ring member 4 and the ground electrode 2 are prevented from being continuously vapor-deposited by the slit formed by this concave portion 4a, so as to maintain the cut-off state between the filament 10 and the ground electrode 2. Therefore, it is possible to prevent the filament 10 from being conductive to the ground electrode 2, that is, to prevent the filament 10 from being grounded, and to continue thermoelectron emission. However, if tungsten enters the slit, conduction may occur, so appropriate cleaning and replacement of the ring member 4 are necessary. Also, if the vapor-deposited surface of tungsten is cleaned at an appropriate timing, thermoelectron emission can be maintained even without the concave portion 4a.

[0042] In this embodiment, the thermoelectron emission area 12 where the filament 10 is installed and the holding means 13 for the object to be neutralized are provided on opposite sides with the mesh electrode 6 as a boundary. By providing the thermoelectron emission area 12 and the holding means 13 on opposite sides, the distance between the mesh electrode 6 and the ground electrode 2 can be reduced, and thermoelectrons can be emitted into the strong electric field formed by the mesh electrode 6 and the ground electrode 2, increasing the kinetic energy of the thermoelectrons. As a result, the probability of ionization collision of thermoelectrons with gas molecules increases.

[0043] In addition, the holding means 13 for the object to be neutralized can be installed near the mesh electrode 6 by being provided on the side opposite to the filament 10 with the mesh electrode 6 as a boundary. Therefore, ions and electrons generated by ionization collision with high-speed thermoelectrons that have passed through the mesh electrode 6 can contribute more effectively to neutralization. However, the relative positions of the filament 10, the mesh electrode 6, and the ground electrode 2 are not limited to the above embodiment. Also, the material of the filament 10 is not limited to tungsten as long as it can withstand high temperatures that emit thermoelectrons. Also, the shape and attachment method of the filament are not limited to the above-described embodiment.

Industrial Applicability

[0044] It is useful for the charge removal treatment of charged objects in an area maintaining a high vacuum degree.

Explanation of Signs

[0045] 1 Vacuum chamber 2 Ground electrode 4 (Filament holding member) Ring member 4a (Forming a slit) Recess 6 Mesh electrode 8 (+) DC power supply 10 Filament 11 (Of the filament) Variable DC power supply 12 Thermoelectron emission area 13 (Holding means for the object to be discharged)

Claims

1. Inside a vacuum area, a mesh electrode to which a positive voltage is applied, a ground electrode that forms an electric field with this mesh electrode, a filament provided near the above mesh electrode and emitting thermoelectrons are provided, A vacuum degassing device that ionizes residual gas molecules in the above vacuum area by the movement of thermoelectrons emitted from the above filament and receiving force from the electric field formed by the above mesh electrode.

2. The above filament is provided between the above ground electrode and the above mesh electrode to form a thermoelectron emission area, The vacuum degassing device according to claim 1, wherein holding means for the object to be degassed is provided on the side opposite to the thermoelectron emission area with the above mesh electrode as a boundary.

3. A filament holding member made of an electrical insulator for holding the above filament is provided, The above filament holding member, On the protruding side of the above filament, a slit is maintained between the filament holding member and the above ground electrode and it is attached to the above ground electrode The vacuum degassing device according to claim 1 or 2.

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