Upper electrode assembly three-dimensional

Abstract

To provide a lift bar-based upper electrode assembly that improves workability and maintains a constant fastening force when fastening and dismantling a plasma electrode plate to and from equipment.SOLUTION: A plasma electrode plate includes a bushing assembly fastened to the insertion hole of a plasma electrode plate, and a lift bar received in the receiving space of the electrode support plate to detachably connect the plasma electrode plate to the electrode support plate. The bushing assembly includes a bushing configured to be connected to the lift bar, and the lift bar includes a connecting portion configured to be connected to the bushing, the connecting portion including a bushing insertion groove into which the bushing is inserted, a first path configured to move the lift bar axially with the bushing inserted, and a second path configured to rotate the lift bar with the bushing positioned beyond the first path.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an upper electrode assembly, and more particularly, to an upper electrode assembly configured to improve the bonding force when coupling a plasma electrode plate to an electrode support plate using a lift bar and enable quick and convenient fastening.

Background Art

[0002] Semiconductor devices can be manufactured through various processes. For example, semiconductor devices are manufactured through processes such as photolithography, etching, and deposition on wafers such as silicon. Plasma-like substances are used in each process for manufacturing semiconductor devices. In a process using plasma, electrodes for generating and controlling plasma are used inside semiconductor manufacturing equipment. Electrodes for plasma are located at the lower and upper parts of the chamber, respectively. Electrodes for plasma are formed by combining a plurality of components.

[0003] Conventionally, a fixing structure combining an electrode plate with an insertion groove formed for coupling a plasma electrode plate to equipment, a bush, a fastening member (bolt), etc. has been generally used. However, such a fastening structure may have problems in that workability deteriorates when fastening and disassembling the plasma electrode plate, and the flatness and adhesion of the electrode plate may decrease due to uneven fastening force.

Prior Art Documents

[0006] An upper electrode assembly according to the concept of the present invention may include a bushing assembly fastened to an insertion hole in a plasma electrode plate, and a lift bar housed in a housing space of an electrode support plate, which detachably connects the plasma electrode plate to the electrode support plate. The bushing assembly includes a bush configured to be coupled to the lift bar, and the lift bar includes a coupling portion configured to be coupled to the bush, the coupling portion may include a bushing insertion groove into which the bush is inserted, a first path configured to move the lift bar axially with the bush inserted, and a second path configured to rotate the lift bar with the bush positioned at the end of the first path. [Effects of the Invention]

[0007] The upper electrode assembly according to an embodiment of the present invention is equipped with a lift bar that has a lift-up function that allows it to rotate after moving in the axial direction, thereby enabling quick and stable assembly and disassembly of the plasma electrode plate to be attached to and detached from the electrode support plate without the need for separate tools. Furthermore, by fastening the plasma electrode plate to the electrode support plate using the lift bar, uniformity of the fastening force can be ensured, and the degree of adhesion and flatness of the plasma electrode plate can be maintained.

[0008] In the upper electrode assembly according to the embodiment of the present invention, assembly errors in the equipment can be minimized by fastening the bush assembly and the lift bar along their respective unique insertion grooves and paths. Furthermore, the configuration of the fixing part between the bush assembly and the lift bar can improve mechanical stability by preventing movement of the lift bar after fastening. If a lift bar guide part is included, the insertion direction and alignment position of the lift bar can be guided more precisely. [Brief explanation of the drawing]

[0009] [Figure 1] This is a partially exploded view of the upper electrode assembly according to an embodiment of the present invention. [Figure 2] This is an assembly diagram showing the upper electrode assembly assembled according to an embodiment of the present invention. [Figure 3a] This is a cross-sectional view of the assembled upper electrode assembly according to an embodiment of the present invention. [Figure 3b] This is a cross-sectional view of an assembled upper electrode assembly according to another embodiment of the present invention. [Figure 4a] These are perspective and enlarged views of a lift bar according to an embodiment of the present invention. [Figure 4b] This is a left-side perspective view of a lift bar according to an embodiment of the present invention. [Figure 4c] This is a lower perspective view of a lift bar according to an embodiment of the present invention. [Figure 4d] This is a bottom view of a lift bar according to an embodiment of the present invention. [Figure 4e] This is a right side view of a lift bar according to an embodiment of the present invention. [Figure 4f] This is a top view of a lift bar according to an embodiment of the present invention. [Figure 4g] This is a left side view of a lift bar according to an embodiment of the present invention. [Figure 4h] This is a front view of a lift bar according to an embodiment of the present invention. [Figure 5a] This is an assembly diagram showing a bush assembly according to an embodiment of the present invention in an assembled state. [Figure 5b] This is a cross-sectional view of a bush assembly according to an embodiment of the present invention in an assembled state. [Figure 5c] This is an exploded view of a bush assembly according to an embodiment of the present invention. [Figure 5d] This is an assembly diagram showing a bush assembly according to an embodiment of the present invention in an assembled state. [Figure 6] This is a perspective view of an electrode support plate further including rib insertion holes according to an embodiment of the present invention. [Figure 7] An assembled view of an upper electrode assembly including a lift bar guide portion according to an embodiment of the present invention. [Figure 8] A cross-sectional view of an upper electrode assembly including a lift bar guide portion according to an embodiment of the present invention in an assembled state. [Figure 9a] A perspective view of a lift bar guide portion according to an embodiment of the present invention. [Figure 9b] A bottom view of a lift bar guide portion according to an embodiment of the present invention. [Figure 10a] A perspective view of a part of an upper electrode assembly according to an embodiment of the present invention disassembled. [Figure 10b] A perspective view sequentially showing a fastening process according to an embodiment of the present invention. [Figure 10c] A perspective view sequentially showing a fastening process according to an embodiment of the present invention. [Figure 10d] A perspective view sequentially showing a fastening process according to an embodiment of the present invention. [Figure 10e] A perspective view sequentially showing a fastening process according to an embodiment of the present invention. [Figure 10f] A front view sequentially showing a fastening process according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0010] In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention can be implemented in various forms and can be subjected to various modifications, not limited to the embodiments disclosed below. However, this description of the embodiments is provided to make the disclosure of the present invention complete and to fully inform those having ordinary knowledge in the technical field to which the present invention pertains of the scope of the invention.

[0011] In this specification, where one component is referred to as being on top of another, it means that it can be formed directly on top of the other component, or that a third component may be interposed between them. Furthermore, in the drawings, the thickness of components is exaggerated for the sake of effective illustration of the technical content. Throughout the specification, parts indicated by the same reference numeral indicate the same component.

[0012] The embodiments described herein are explained with reference to cross-sectional views, plan views, and / or perspective views, which are ideal illustrative representations of the present invention. In the various embodiments herein, terms such as first, second, third, etc., are used to describe various components, but these components are not limited to such terms. These terms are used merely to distinguish one component from another. The embodiments described and illustrated herein also include complementary embodiments.

[0013] The terms used herein are for illustrative purposes only and do not limit the invention. In this specification, the singular form includes the plural form unless otherwise specified in the statement. As used in the specification, “comprises” and / or “comprising” does not imply that the components mentioned are not limited to the presence or addition of one or more other components.

[0014] Referring to Figures 1 and 2, the upper electrode assembly 10 according to an embodiment of the present invention may be composed of an electrode support plate 100, a plasma electrode plate 200, a lift bar 300, and a bushing assembly 400.

[0015] The upper electrode assembly 10 may be installed in a chamber for a plasma-utilizing process. For example, the upper electrode assembly 10 may be installed in a chamber for etching a semiconductor. More specifically, the upper electrode assembly 10 may be an electrode installed in an etching chamber, spaced above the lower electrode (not shown).

[0016] The electrode support plate 100 is an upper end structure of the equipment and can be formed in the shape of a disc. The electrode support plate 100 has an opening 110 on its side for inserting a lift bar 300, and a through groove 120 may be formed at the bottom into which a bush assembly 400, which is inserted into and fastened to the plasma electrode plate 200, can be inserted. A housing space 130 formed inside the electrode support plate 100 may be formed in which the lift bar 300 and the bush assembly 400 can be housed. The housing space 130 may have a three-dimensional shape such as a hexahedron or a cylinder, but is not limited to these.

[0017] The plasma electrode plate 200 may contain ceramic materials such as silicon, silicon carbide, alumina, or quartz. The plasma electrode plate 200 may be formed in a disc-like structure. The upper surface of the plasma electrode plate 200 may be formed flat to ensure close contact with the electrode support plate 100.

[0018] An insertion hole 210 may be formed on the plasma electrode plate 200, penetrating the upper surface of the plasma electrode plate 200. A bushing assembly 400 may be inserted into the insertion hole 210. By inserting the bushing assembly 400 into the insertion hole 210, the plasma electrode plate 200 can be mechanically connected to the upper electrode support plate 100. Multiple insertion holes 210 may be provided. Multiple insertion holes 210 may be spaced circumferentially apart from each other. Multiple bushing assemblies 400 may be provided. For example, as many bushing assemblies 400 may be provided as there are insertion holes 210. Multiple bushing assemblies 400 may be inserted into each of the multiple insertion holes 210.

[0019] The plasma electrode plate 200 may include a plurality of nozzles provided on its surface. The nozzles may be configured to supply process gases. As an example, the plasma electrode plate 200 may be a showerhead. Furthermore, the plasma electrode plate 200 may include micropores (not shown). These micropores may, but are not limited to, holes through which process gases pass. Multiple micropores may be provided.

[0020] Figure 3a is a cross-sectional view showing a section of the upper electrode assembly 10 in its assembled state according to the embodiment of the present invention shown in Figure 2, cut along the line A-A'. Figure 3b is a cross-sectional view showing a section of the upper electrode assembly 10 in its assembled state according to another embodiment of the present invention, cut along the line A-A'. Figures 4a to 4h are perspective views and plan views of the lift bar 300 from various directions. Figures 5a to 5d show the assembled and disassembled states of the bush assembly 400. Referring to these drawings, the structural shape and interrelationship of the lift bar 300 and the bush assembly 400 can be understood in more detail.

[0021] Referring to Figures 3a and 5a to 5c, the bush assembly 400 according to an embodiment of the present invention may include a bush 410, a washer 420, and a bush fastening member 430. The bush 410 may include a bush body 412, a bush head 411, and a fastening portion 413.

[0022] The fastening portion 413 may be formed on the lower part of the bush body 412. The fastening portion 413 may be positioned in the insertion hole 210 of the plasma electrode plate 200. The fastening portion 413 may be fastened within the insertion hole 210 by the bush fastening member 430. When fastening the bush 410 and the plasma electrode plate 200, a washer 420 may be interposed between the fastening portion 413 and the bush fastening member 430. The washer 420, interposed between the fastening portion 413 and the bush fastening member 430, may play a role in maintaining the fastening height and fastening force, and absorbing vibrations. Multiple washers 420 may be provided.

[0023] The bush body 412 may be formed as an extension upward from the fastening portion 413. The bush body 412 may be inserted into the housing space 130 by passing through the through groove 120 of the electrode support plate 100. The bush body 412 may be cylindrical or the like, and may be inserted into the bush insertion hole 311 of the joint portion 310 of the lift bar 300.

[0024] A bush head 411 having a curved or disc-shaped form may be formed on the upper part of the bush body 412, but is not limited to this. The bush head 411 may have a larger diameter than the bush body 412 and may be inserted into the housing space 130 by passing through the through groove 120 of the electrode support plate 100. Alternatively, it may be inserted into the bush insertion groove 311 of the coupling portion 310 of the lift bar 300. When fastening the plasma electrode plate 200 to the electrode support plate 100, the bush head 411 may be located at the upper end of the bush fixing portion 340 of the lift bar 300.

[0025] Referring to Figures 3b and 5d, the bush 410 may further include a projection 415 that protrudes from the bush body 412. The fastening portion 413 may further include a support piece 414. The support piece 414 may be formed at the lowest end of the fastening portion 414 and may be in a form that is in close contact with the bottom surface of the insertion hole 210. The projection 415 may be in the form of a disc or a sphere, but is not limited thereto. The projection 415 may have a larger diameter than the bush head 411 and a smaller diameter than the support piece 414 located at the lowest end of the fastening portion 413. The projection 415 may be formed at the lower part of the bush body 412. The projection 415 may interfere with other components of the upper electrode assembly 10, such as the lift bar 300. Further details regarding the projection 415 will be described later.

[0026] Referring to Figure 3, the lift bar 300 according to an embodiment of the present invention is inserted through the opening 110 of the electrode support plate 100 and housed in the housing space 130, and can serve to detachably connect the plasma electrode plate 200 to the electrode support plate 100. The lift bar 300 can be positioned to provide a uniform fastening force and to ensure the adhesion and flatness of the plasma electrode plate 200 by contacting the lower upper surface of the housing space 130. The lift bar 300 can be formed in a cylindrical shape or the like.

[0027] Referring to Figures 3 and 4, the lift bar 300 may include a coupling portion 310, an operating portion 320, a main body portion 330, a bush fixing portion 340, and a lift portion 350. The operating portion 320 may be positioned adjacent to the opening 110 of the electrode support plate 100. The lift bar 300 can be moved and rotated axially within the housing space 130 by the operating portion 320. The axial direction may mean the direction in which the lift bar 300 moves from the opening 110 of the electrode support plate 100 toward the center of the electrode support plate 100, and such an axial direction may be exemplary represented as the A-A' direction shown in Figure 2. The main body portion 330 may be formed in the shape of a bar extending axially from the lift bar 300. The main body portion 330 may serve as a structural center supporting the axial movement and rotation of the lift bar 300. The main body portion 330 may be in the form of a cylinder or the like. Multiple main body portions 330 may be provided.

[0028] The connecting portion 310 is the part to which the lift bar 300 and the bush assembly 400 are connected, and may include a bush insertion groove 311, a first path 312, and a second path 313. The connecting portion 310 may be in the form of a cylinder or the like, but is not limited thereto. Multiple connecting portions 310 may be provided. The main body portion 330 may be arranged between multiple connecting portions 310.

[0029] Referring to Figures 3a and 4, the lift portion 350 according to the embodiment of the present invention may be formed protruding from the side surface of the joint portion 310, but is not limited thereto. The lift portion 350 may be in the form of a semicircle, but is not limited thereto. The lift portion 350 may come into contact with the lower part of the electrode support plate 100 when the lift bar 300 rotates. The lift portion 350 may come into contact with the lower part of the electrode support plate 100, thereby lifting the lift bar 300 from the lower part of the electrode support plate 100.

[0030] Figure 4h is a front view of the lift bar 300 showing the state in which the lift portion 350 is formed to protrude from the connecting portion 310. The diameter L2 of the connecting portion 310 including the lift portion 350 may be formed to be larger than the diameter L1 of the main body portion 330, so that when the lift bar 300 rotates, the lift portion 350 comes into contact with the lower part of the electrode support plate 100, and the lift bar 300 can be lifted upward. At this time, the height to which the lift bar 300 rises may be the difference L2-L1 between the diameter L2 of the connecting portion 310 including the lift portion 350 and the diameter L1 of the main body portion 330. As the lift bar 300 is lifted upward, the plasma electrode plate 200 can be fastened to be in close contact with the lower surface of the electrode support plate 100.

[0031] Referring to Figure 3b, in another embodiment of the present invention, the lift portion 350 may be formed protruding from the side surface of the main body portion 330. In this case, the height to which the lift bar 300 rises may be the difference L1-L2 between the diameter L1 of the main body portion 330 including the lift portion 350 and the diameter L2 of the connecting portion 310. The protrusion 415 may be formed on the lower surface of the electrode support plate 100 or on the lower part of the bush body 412 at a height equal to or less than the height L1-L2 to which the lift bar 300 rises. Thereafter, the protrusion 415 may limit the height to which the lift portion 350 rises via the lift portion 350.

[0032] A bush 410 of the bush assembly 400 can be inserted into the bush insertion groove 311. For example, the bush body 412 and bush head 411 of the bush 410 can be inserted into the bush insertion groove 311.

[0033] The first path 312 may serve to allow the lift bar 300 to move axially while the bush 410 is inserted into the bush insertion groove 311. The first path 312 formed in the joint 310 may also be structured to allow passage through the bush body 412. The first path 312 may be an open or through-type structure that extends axially from the lift bar 300.

[0034] The second path 313 may be formed continuously from the end of the first path 312 and may have a structure such as a sector or a curve. The second path 313 may also be formed in a structure that allows it to pass through the bush body 412. The second path 313 may serve to allow the lift bar 300 to rotate with the bush 410 positioned at the end of the first path 312 and to guide the bush head 411 so that it is positioned above the bush fixing portion 340 when the lift bar 300 rotates.

[0035] The bush fixing portion 340 can be configured to stably maintain the fastened state between the lift bar 300 and the bush assembly 40 by supporting the lower surface of the bush head 411 when the lift bar 300 is rotated. The bush fixing portion 340 can maintain a fixed state so that the lift bar 300 does not rotate in the reverse direction.

[0036] Referring to Figures 6 to 9b, the upper electrode assembly 10 according to an embodiment of the present invention may further include a lift bar guide portion 500. The lift bar guide portion 500 may be located within the housing space 130 of the electrode support plate 100. The lift bar guide portion 500 can guide the lift bar 300 so that it can be inserted into a predetermined position.

[0037] The lift bar guide section 500 may include a lift bar guide 510, a bush head insertion section 520, and a bush head fixing section 530. The lift bar guide 510 may provide an insertion space that guides the lift bar 300 to be inserted into a predetermined position.

[0038] The lift bar guide 510 can guide the axial movement and rotational position of the lift bar 300 within the housing space 130 of the electrode support plate 100 so that they are precisely aligned. The lift bar guide 510 may be formed in the shape of a hexagonal housing with an open bottom, but is not limited to this. The lift bar guide 510 may further include ribs 540 protruding from its outer side surface, and the ribs 540 may be inserted into rib insertion grooves 140 formed on the side surface of the housing space 130 of the electrode support plate 100 so that the entire lift bar guide portion 500 is maintained in a precisely fixed state within the equipment.

[0039] The bush head insertion portion 520 and the bush head fixing portion 530 may be positioned on the upper surface of the lift bar guide 510. The bush head insertion portion 520 and the bush head fixing portion 530 may be formed in a circular shape or other shapes, but are not limited to these. If the upper electrode assembly 10 further includes a lift bar guide portion 500, the bush head 411 may be located at the upper ends of the bush head insertion portion 520 and the bush head fixing portion 530.

[0040] Referring to Figures 10a to 10f, the fastening process of the upper electrode assembly 10 according to an embodiment of the present invention can be understood in more detail. Figure 10a is an exploded perspective view of a part of the upper electrode assembly 10 according to an embodiment of the present invention. Figures 10b to 10f sequentially show the process of fastening the plasma electrode plate 200, into which the bush assembly 400 is inserted, to the electrode support plate 100 by axial movement and rotation of the lift bar 300.

[0041] Referring to Figure 10a, in the embodiment of the present invention, the upper electrode assembly 10, with the lift bar 300 inserted into the opening 110 of the electrode support plate 100 and housed in the housing space 130, allows the bush assembly 400 inserted into the plasma electrode plate 200 to be inserted into the through groove 120 of the electrode support plate 100 and then into the bush insertion groove 311 of the lift bar 300.

[0042] Referring to Figure 10b, with the bush assembly 400 inserted into the bush insertion groove 311 of the lift bar 300, the lift bar 300 can be moved axially by operating the operating unit 320. The first path 312 formed in the joint 310 of the lift bar 300 may be configured as an open structure that allows the bush 410 to pass through, and can guide the lift bar 300 to move axially.

[0043] Referring to Figures 10c to 10f, with the lift bar 300 moving axially and the bush 410 positioned at the end of the first path 312, the lift bar 300 can be rotated by operating the operating unit 320. As the lift bar 300 rotates, the second path 313 can pass over the bush 410 and guide the bush 410 so that it can be positioned on the bush fixing part 340. It can also guide the bush head 411 so that it is positioned on the upper part of the bush fixing part 340.

[0044] As the lift bar 300 rotates, a lift portion 350 is formed protruding from the joint portion 310, which comes into contact with the lower part of the electrode support plate 100, thereby lifting the lift bar 300 from the lower part of the electrode support plate 100. The lift bar 300 can be lifted up by the difference L2-L1 between the diameter L2 of the joint portion 310 including the lift portion 350 and the diameter L1 of the main body portion 330. As the lift bar 300 is lifted upward, the bush 410 can be positioned on the bush fixing portion 340, and once the rotation is complete, the bush fixing portion 340 is positioned below the bush head 411 and supports the bush head 411, so that the plasma electrode plate 200 can be fastened in close contact with the lower part of the electrode support plate 100.

[0045] The upper electrode assembly according to the embodiment of the present invention, with the configuration described above, can improve the functionality when joining and separating the plasma electrode plate and the electrode support plate. Furthermore, it can ensure uniform fastening force and maintain the degree of adhesion and flatness of the plasma electrode plate. In other words, by increasing the ease of replacing the plasma electrode plate in the upper electrode assembly and improving the structural stability of the upper electrode assembly, product quality and economic efficiency can be ensured.

[0046] Although embodiments of the present invention have been described above with reference to the attached drawings, the present invention may be implemented in other specific forms without changing its technical idea or essential features. Therefore, the embodiments described above should be understood to be illustrative in all respects and not limiting. [Explanation of Symbols]

[0047] 10 Upper electrode assembly 100 Electrode support plate 110 Aperture 120 Through groove 130 Containment space 140 Rib insertion grooves 200 Plasma electrode plate 210 Insertion hole 300 Lift Bar 310 Joint 311 Bush insertion groove 312 Route 1 313 Second Route 320 Control unit 330 Main body 340 Bush fixing part 350 Lift section 400 Bush Assembly 410 Bush 411 Bushhead 412 Bush body 413 Fastening section 414 Protrusion 415 Support piece 420 Washer 430 Bush fastening member 500 Lift bar guide section 510 Lift Bar Guide 520 Bush head insertion part 530 Bush head fixing part 540 Rib L1 Main body diameter L2 Diameter of the joint

Claims

1. A bushing assembly fastened to the insertion hole of the plasma electrode plate, It includes a lift bar housed in the housing space of an electrode support plate, which detachably connects the plasma electrode plate to the electrode support plate, The bushing assembly includes a bushing configured to be coupled to the lift bar, The lift bar includes a coupling portion configured to connect with the bush, The aforementioned joint is A bush insertion groove into which the bush is inserted, A first path configured to move the lift bar axially with the bush inserted, An upper electrode assembly characterized by including a second path configured such that the lift bar rotates with the bush located at the end of the first path.

2. The aforementioned bush assembly is A bush fastening member for fastening the bush to the insertion hole of the plasma electrode plate, The present invention further includes a washer interposed between the bush fastening member and the bush, The aforementioned bush, A fastening portion is placed in the insertion hole of the plasma electrode plate, A bush body is configured to protrude from the fastening portion and pass through the lift bar, The upper electrode assembly according to claim 1, characterized in that it includes a bush head formed on the upper part of the bush body and configured to be fixed to the lift bar.

3. The bush further includes a protruding portion that is formed to protrude from the bush body, The fastening portion further includes a support piece formed at the lowest end, The upper electrode assembly according to claim 2, characterized in that the protruding portion has a larger diameter than the bush head and a smaller diameter than the support piece.

4. The electrode support plate is An opening is formed on the side surface of the electrode support plate into which the lift bar is inserted, The upper electrode assembly according to claim 2, characterized in that it includes a through groove formed in the lower part of the electrode support plate into which the bush body and the bush head are inserted.

5. The aforementioned lift bar is An operating unit for controlling the axial movement and rotation of the lift bar, The upper electrode assembly according to claim 1, further comprising a bar-shaped main body portion that extends in the axial direction.

6. The operating section is located at the tip of the lift bar adjacent to the opening. The aforementioned joint includes a plurality of joints, The upper electrode assembly according to claim 5, characterized in that the main body is positioned between the plurality of connecting parts.

7. The lift bar further includes a lift portion formed on either the connecting portion or the main body portion, The upper electrode assembly according to claim 5, characterized in that the lift section lifts the lift bar from below the electrode support plate by the rotation of the lift bar.

8. The lift bar further includes a bush fixing portion that fixes the bush head and the lift bar when the lift bar is rotated, The upper electrode assembly according to claim 2, characterized in that the bush fixing portion is positioned below the bush head and supports the bush head.

9. The electrode support plate further includes a lift bar guide portion disposed within the housing space, The upper electrode assembly according to claim 2, characterized in that the lift bar guide portion includes a lift bar guide configured to allow the lift bar to be inserted.

10. The aforementioned lift bar guide section is The bush head insertion portion into which the bush head is inserted, The upper electrode assembly according to claim 9, further comprising a bush head fixing portion to which the bush head is fixed.

11. The lift bar guide further includes ribs that protrude from its side surface, The upper electrode assembly according to claim 10, characterized in that the housing space of the electrode support plate further includes a rib insertion groove into which the rib is inserted.

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