Frame assembly for mounting pellicle on photomask

Abstract

To provide a frame assembly for mounting a pellicle on a photomask.SOLUTION: The frame assembly includes a frame to which the pellicle is attached, a stud attached to the photomask, and a fixture that is inserted into the lower side of the frame. The stud and the fixture are magnetically bonded to each other, and when bonded, the stud positioned beneath the fixture creates a gap of a certain height between the photomask and the frame. This eliminates the need for precise alignment of the frame during the mounting process on the photomask, and facilitates the separation of the frame from the photomask for reuse. The formation of the gap eliminates the need for a separate process to create vent holes in the frame.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a Frame Assembly, and more particularly to a frame assembly for attaching a pellicle to a photomask used in a photolithography process.

Background Art

[0002] EUV (Extreme Ultra-Violet) lithography technology using 13.5 nm wavelength exposure light to implement fine patterns has been developed. In the lithography process, a photomask is used as a master for patterning. However, if impurities such as particles and foreign substances adhere to the photomask, the exposure light may be absorbed or reflected by these impurities, and the transferred pattern may be damaged. Therefore, in order to prevent impurities from adhering to the surface of the photomask, a method of attaching a pellicle on the photomask surface is used. In recent years, with the miniaturization of circuit line widths, the size of impurities that can affect pattern damage has also decreased, so the role of the pellicle for protecting the photomask is becoming more important.

[0003] FIG. 1 is a diagram showing a conventional structure to which a pellicle is attached.

[0004] The pellicle 30 includes a rectangular membrane 20 that transmits exposure light, and a border 10 that supports the membrane 20 in the outer region of the membrane 20. Generally, after forming the membrane 20 on a silicon substrate, the lower surface of the substrate is etched to form the border 10, thereby producing a pellicle 30 having a structure as shown in FIG. 1.

[0005] In order to attach the pellicle 30 to the photomask 60, a frame 50 is installed on the upper part of the photomask 60. By attaching the structure with the pellicle 30 attached onto the frame 50, the pellicle 30 is attached to the upper part of the photomask 60. For the adhesion between the frame 50 and the photomask 60, an adhesive is applied to the lower surface of the frame 50.

[0006] As the exposure process using the photomask 60 is repeated, the life of the pellicle 30 is exhausted and it becomes necessary to replace the pellicle 30. Since it is uneconomical to replace the frame 50 as well, which is more durable than the pellicle 30 and can be reused, a technique is required to replace only the pellicle 30 and reuse the frame 50. To replace the pellicle 30, first, it is necessary to separate the frame 50 from the photomask 60. For this purpose, it is necessary to separate the frame 30 and the photomask 60 at the adhesion surface between the lower surface of the frame 30 and the upper surface of the photomask 60, using another tool or manually. Therefore, the process for separation is complicated and there is a risk of damage to the photomask 60 or the frame 50 during the separation operation.

[0007] Also, in the conventional configuration, in order to attach the frame 50 at an exact position on the photomask 60 during the coupling process between the frame 50 and the photomask 60, very precise alignment is required.

[0008] In addition, since the EUV exposure process is carried out in an environment of high vacuum and high vibration force, the membrane 20 must not be damaged due to the pressure change from atmospheric pressure to vacuum. To cope with such a pressure change, usually, a large number of vent holes (not shown) penetrating horizontally are formed in the frame 50. These vent holes function to buffer the pressure change by communicating the internal space S of the frame 50 formed between the membrane 20 and the photomask 60 with the external space. Conventionally, the formation of vent holes in the frame 50 has been essentially required, increasing the manufacturing cost of the frame 50 due to the high-precision vent hole processing process.

[0009] Moreover, in the conventional configuration as described above, the adhesive applied between the frame 50 and the photomask 60 acts as particles in the EUV exposure process, which may lead to a decrease in exposure precision. Summary of the Invention Problems to be Solved by the Invention

[0010] The present invention was devised to solve the above problems, and an object of the present invention is to provide a frame assembly in which high-precision frame alignment is unnecessary in the process of coupling a photomask and a frame, and the operation of separating the frame from the photomask is very easy.

[0011] Another object of the present invention is to provide a frame assembly that does not require a process of forming another vent hole in the frame.

[0012] Still another object of the present invention is to provide a frame assembly that can minimize the phenomenon in which the adhesive acts as particles between the frame and the photomask. Means for Solving the Problems

[0013] The present invention presents a frame assembly for attaching a pellicle to a photomask used in a photolithography process. The frame assembly of the present invention includes a frame that is mounted on the upper surface of the photomask and to which a pellicle adheres at its upper part, a stud that is attached to the upper surface of the photomask between the photomask and the frame, and a fixture that is fitted and installed on the lower surface of the frame at a position corresponding to the stud between the photomask and the frame. The stud and the fixture are mutually bound by magnetic force, and a gap of a certain height is formed between the photomask and the frame by the stud placed at the lower part of the fixture in the bound state.

[0014] Either the stud or the fixture may be formed of a magnetic material, and the other may be formed of a material that is magnetically coupled to the magnetic material.

[0015] The magnetic material may be formed of a rare earth material that loses its magnetic force at a temperature exceeding a predetermined magnetic force disappearance temperature.

[0016] A fitting groove into which the fixture is fitted is formed on the lower surface of the frame.

[0017] The constant height is preferably 0.05 to 0.5 mm.

[0018] At least one of the stud and the fixture is preferably coated on its surface with a metal or non-metal material.

[0019] The fixture includes a fixture body extending in the longitudinal direction of the frame, and support portions formed to protrude downward at both ends of the fixture body, respectively, and forming mounting grooves in which the studs are mounted. The stud includes a stud body that is fitted and mounted in the mounting groove to prevent movement in the longitudinal direction.

[0020] The fixture has a coupling groove formed on the bottom surface of the mounting groove, and the stud has a protruding portion that is fitted and coupled to the coupling groove.

[0021] The fixture body and the stud body have a flat cross-section having one of a circular, elliptical, triangular, quadrangular, and polygonal shape.

[0022] The fixture body has a length of 5 to 150 mm, a width of 1 to 6 mm, and a thickness of 0.5 to 2 mm in the longitudinal direction.

[0023] The support portion has a length of 0.5 to 10 mm in the longitudinal direction and a height of 0.1 to 1 mm based on the bottom surface of the installation groove.

[0024] The stud body has a length of 4 to 130 mm, a width of 1 to 10 mm, and a thickness of 0.15 to 1.5 mm in the longitudinal direction.

[0025] The stud body has a width greater than or equal to that of the fixture body.

[0026] The protruding portion has a height of 0.1 to 1.5 mm.

[0027] The protruding portion has a cylindrical or conical shape whose cross-section has one or more of the shapes of a circle, a triangle, a quadrilateral, and a polygon.

[0028] It is preferable that at least one of the stud and the fixture has a shape formed by protruding or recessing from the surface, and a magnetic force strengthening portion for strengthening the magnetic force is formed.

[0029] As a modification of the present invention, the fixture includes a coupling groove formed in the bottom surface of the installation groove, the stud includes a protruding portion that couples to the coupling groove, the coupling groove has a size larger than that of the protruding portion, and the protruding portion may include an elastic portion on the outside that is fitted into the coupling groove together with the protruding portion.

[0030] The elastic portion may be formed of one or more of metal, plastic, resin, and silicon.

Effects of the Invention

[0031] According to the present invention, the frame and the photomask are bonded by fitting the protruding portion of the stud and the coupling groove of the fixture by the magnetic force between the fixture and the stud. Thereby, accurate alignment of the frame is not required in the process of attaching the frame to the photomask, and separation from the photomask for reuse of the frame is also easy.

[0032] In addition, since the vent holes are formed by the gap between the frame formed by the studs and the photomask, there is no need for a process to form separate vent holes in the frame.

[0033] Also, the use of the adhesive is very small and the adhesive is not exposed to the outside, so the generation of particles and out-gasing induced by the adhesive is minimized.

Brief Description of the Drawings

[0034]

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Modes for Carrying Out the Invention

[0035] Hereinafter, the present invention will be specifically described with reference to the accompanying drawings. In the description of the present invention, detailed description of the general structures of the pellicle 30 and the frame 50 will be omitted, and the contents described with reference to FIG. 1 in the description of the prior art will be incorporated by reference. In the description of the present invention, the same reference numerals are assigned to the same components as those shown in FIG. 1 and incorporated by reference.

[0036] FIG. 2 is a perspective view of a frame assembly according to a first embodiment of the present invention, and FIG. 3 is an exploded perspective view of FIG. 2.

[0037] The frame assembly according to the present invention is applicable to a photomask 60 used in a photolithography process for manufacturing semiconductors and flat panel displays (FPDs), and in particular, is suitable for use in the photomask 60 of an extreme ultraviolet (EUV) photolithography process.

[0038] The frame assembly of the present invention is mounted on the photomask 60 with the pellicle 30 attached to its upper part, thereby providing means for attaching the pellicle 30 on the photomask 60. The frame assembly of the present invention includes the frame 50, and also includes a fixture 70 and a stud 80.

[0039] The photomask 60 has a fine circuit pattern (not shown) formed on its upper surface so that a transfer process using EUV exposure light is performed. The photomask 60 is formed on a glass substrate (Qz) used in a general EUV exposure process, and any photomask 60 according to the present invention is applicable without being limited by the size and shape of the glass substrate.

[0040] The frame 50 is formed in the form of frames of various shapes such as circular, triangular, quadrangular, and polygonal, and generally has the form of a quadrangular frame, particularly a rectangular frame. The frame 50 has a general shape and size applicable to the EUV exposure process, and its size and shape can be variously changed corresponding to the photomask 60. The frame 50 is made of any one of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Pt, Au, SUS, Si, carbon steel, tool steel, ceramic, metal-ceramic composite material, and resin, or an alloy thereof. A pellicle 30 adheres to the upper surface of the frame 50, but the illustration of the pellicle 30 is omitted in FIG. 2.

[0041] The stud 80 is attached to the upper surface of the photomask 60 between the photomask and the frame 50. The fixture 70 is attached to the lower surface of the frame 30 and is disposed at a position corresponding to the stud 80 between the photomask 60 and the frame 50. The stud 80 and the fixture 70 are mutually bonded by magnetic force. Thus, one stud 80 and one fixture 70 form a pair and are mutually bonded.

[0042] Both the stud 80 and the fixture 70 may be formed of a magnetic material (magnet), or only one of them may be formed of a magnetic material. A magnetic material means a material made of a substance magnetized by a magnetic field, including any of ferromagnetic, paramagnetic, and diamagnetic materials, and including any common magnet such as an alnico magnet, a ferrite magnet, a samarium cobalt (SmCo) magnet, a neodymium magnet, a rubber magnet, a plastic magnet, or a magnet using rare earth metals. When only one of the stud 80 and the fixture 70 is made of a magnetic material, the other is made of a metallic substance, and in addition to the metal, it may be formed of any substance that can be attached to the magnetic material by magnetic force.

[0043] Preferably, as the magnetic material, a magnetic material made including rare earth metals is used. Generally, a rare earth substance becomes a magnet through a magnetization process of applying a magnetic force after mixing raw materials and processing them into a certain shape using mechanical tools. The magnetization process is a process of applying a strong magnetic field so that the raw materials of the magnet are magnetized while being arranged in a certain direction. Rare earth magnets, such as neodymium magnets, can set the intensity of the magnetic force and the temperature at which they are destroyed by the mixing of their raw materials. When heat is applied to a rare earth magnet at the magnetic force disappearance temperature, which is a temperature exceeding the working temperature, the magnetic force disappears, and when the magnetization process is performed again, the disappeared magnetic force is restored. Using such a principle, if the stud 80 or the fixture 70, particularly the fixture 70, is made of a rare earth magnet having a predetermined magnetic force disappearance temperature, they are strongly magnetically bonded to each other by the magnetic material during the exposure process, but when heat is applied from the outside at a temperature exceeding the magnetic force disappearance temperature, the magnetic force of the magnetic material disappears, and thereby, the stud 80 and the fixture 70 can be easily separated.

[0044] For the reuse of the frame 50, for example, the fixture 70 whose magnetic force has disappeared is separated from the frame 50, a magnetic force is applied by the magnetization process, and thereby, the fixture 70 that has become a magnetic material again is attached to the frame 50.

[0045] The stud 80 and the fixture 70 preferably have a coating film formed of a metal or non-metal material on their surfaces to prevent out-gassing. At this time, due to the strong adhesive force by the mutual magnetic force, the coating film may be formed of a metal material.

[0046] At least one of the stud 80 and the fixture 70 is attached, and preferably, in correspondence with the shape of the frame 50, they are arranged at positions and in numbers that can stably fix the frame 50 against the force (vibratory force) caused by the moving direction of the stage that reciprocates in the exposure process.

[0047] Figs. 4 to 12 are diagrams showing the configurations of the respective parts of the stud 80 and the fixture 70 according to the first embodiment of the present invention and their combined states.

[0048] A fitting groove 55 is formed on the lower surface of the frame 50, and the fixture 70 is installed by being fitted into the fitting groove 55. It is preferable that the fixture 70 does not move in a state where it is fitted into the fitting groove 55. For this purpose, the fitting groove 50 has the same shape as the fixture 70 so that the fixture 70 fits and couples. The fixture 70 may be adhered by applying an adhesive in the fitting groove 55, and preferably, it may be coupled by press-fitting so that the fixture 70 is firmly coupled without being separated without another adhesive. The depth of the fitting groove 55 is preferably configured to be the same as the thickness of the fixture 70, specifically, the thickness at the portions of the support portions 72 formed at both ends of the fixture 70. Thereby, the fixture 70 fitted into the fitting groove 55 is arranged to be flush with the lower surface of the frame 50 without protruding downward from the lower surface of the frame 50 or being filled inside the fitting groove 55.

[0049] The fixture 70 includes a fixture body 71 extending in the longitudinal direction of the frame 50, and support portions 72 protruding downward from both ends of the fixture body 71 respectively, forming mounting grooves 73 in which the studs 80 are installed. A coupling groove 75 is formed on the bottom surface of the mounting groove 73. Thereby, a two-stage recessed shape is configured in which the mounting groove 73 of the fixture 70 is recessed, and the coupling groove 75 is recessed inside the mounting groove 73.

[0050] The stud 80 includes a stud body 81. The length of the stud body 81 is configured to match the length of the mounting groove 73. Thereby, the stud body 81 is fitted and installed in the mounting groove 73, and the movement of the stud 80 in the longitudinal direction is blocked. The stud 80 includes a protruding portion 85 that fits and couples with the coupling groove 75. With such a configuration, the entire longitudinal region of the stud body 81 of the stud 80 is fitted into the mounting groove 73 of the fixture 70 and is position-fixed by the support portions 72 on both sides. In this state, the protruding portion 85 is inserted into the coupling groove 75, fitted, and coupled, thereby being doubly position-fixed. With such a structure, the fixture 70 and the stud 80 are not separated from each other even by the strong force associated with the rapid reciprocating movement of the stage during the exposure process.

[0051] The fixture body 71 and the stud body 81 may have a flat cross-section in one of the shapes of circular, elliptical, triangular, quadrangular, and polygonal.

[0052] The protruding portion 85 may have a cylindrical or conical shape having one or more cross-sectional shapes among circular, triangular, quadrangular, and polygonal. Since the coupling groove 75 fits and couples with the protruding portion 85, it has a shape corresponding to the protruding portion 85.

[0053] Referring to FIGS. 6 to 9, the sizes of each part of the fixture 70 and the stud 80 are described.

[0054] The fixture body 71 has a length L1 of 5 to 150 mm in the longitudinal direction, a width W1 of 1 to 6 mm, and a thickness T1 of 0.5 to 2 mm. The support portion 72 has a length d11 of 0.5 to 10 mm in the longitudinal direction and a height d12 of 0.1 to 1 mm with respect to the bottom surface of the mounting groove 73. The coupling groove 75 has a depth d13 of 0.1 to 1.5 mm.

[0055] The stud body 81 has a length L2 of 4 to 130 mm in the longitudinal direction, a width W2 of 1 to 10 mm, and a thickness T2 of 0.15 to 1.5 mm.

[0056] When both the stud body 81 and the fixture body 71 are made of a magnetic material, the stud body 81 has a width greater than or equal to that of the fixture body 71. When the fixture body 71 is a magnetic material and the stud body 81 is made of a material that adheres to the magnetic material by magnetic force, since the maximum magnetic field is formed in the boundary region having a shape including the edge portion of the fixture body 71, the stud body 81 preferably has a width greater than that of the fixture body 71.

[0057] The protruding portion 85 of the stud 80 has a height d23 of 0.1 to 1.5 mm, which is the same as the depth d13 of the coupling groove 75. For the workability and structural stability of the fixture 70 and the stud 80, preferably, the coupling groove 75 and the protruding portion 81 have a depth d13 and a height d23 of 0.3 to 1 mm.

[0058] As shown in FIG. 12, a gap of a constant height is formed between the lower surface of the frame 50 and the upper surface of the photomask 60. In a state where the stud 80 and the fixture 70 are coupled, a part of the thickness section of the stud body 81 is not fitted into the installation groove 73 and protrudes outside the installation groove 73, that is, downward. Thereby, a gap is formed between the lower surface of the frame 50 and the upper surface of the photomask 60 by the lower part of the thickness section of the stud body 81. At this time, the gap is preferably formed to have a height of 0.05 to 0.5 mm. This gap functions as a vent hole that allows the internal space S formed by the pellicle 30 and the frame 50 to communicate with the external space.

[0059] An adhesive groove 87 is recessed and formed on the lower surface of the stud body 81. An adhesive C is applied in the adhesive groove 87, and this adhesive C has a function of adhering the stud body 81 to the photomask 60. Since the adhesive C is accommodated in the recessed adhesive groove 87, the adhesive C does not leak to the outside in the coupled state as shown in FIG. 12, and the generation of particles due to the adhesive C is minimized.

[0060] FIGS. 13 to 18 are diagrams showing a second embodiment of the present invention.

[0061] In this embodiment, the stud 180 includes two protrusions 185, and correspondingly, the fixture 170 includes two coupling grooves 175. The configuration in which the stud 180 includes a stud body 181 and the fixture 170 includes a fixture body 171, a support portion 172, and a mounting groove 173 is the same as that of the first embodiment described above. The stud 180 and the fixture 170 of this embodiment are configured to have a longer length in the longitudinal direction than that of the first embodiment. This embodiment provides a stronger coupling between the frame 50 and the photomask 60 when the photomask 60 moves in the longitudinal direction of the frame 50 during the exposure process. Thus, the lengths of the fixture 170 and the stud 180 and the coupling grooves 175 and protrusions 185 provided thereon are not limited in number and can be set to various numbers in consideration of the force of the reciprocating motion generated during the exposure process and the fastening strength between the fixture 170 and the stud 180.

[0062] Figs. 19 to 21 are views showing a third embodiment of the present invention.

[0063] In this embodiment, the fixture 270 is basically the same as the second embodiment described above, except that a magnetic force strengthening portion 279 is further provided. The magnetic force strengthening portion 279 is formed in the form of one or more, preferably a plurality of grooves 279 recessed in the outer surface of the fixture 270. When the fixture 270 is made of a magnetic material, a magnetic field with the maximum intensity is formed in the boundary region having a shape including the edge portion of the fixture body 71. Therefore, by forming a plurality of magnetic force strengthening portions 279, the coupling between the fixture 70 and the stud 80 can be strengthened. The magnetic force strengthening portion 279 is not limited in length, depth, width, etc.

[0064] Note that the magnetic force strengthening portion 279 may be configured in the form of a rib protruding from the fixture body 71 instead of in the form of a groove as shown in the figure.

[0065] Further, the magnetic force strengthening portion 279 may be configured in various shapes other than the groove 279 or the rib-like stripe shape, for example, in the shape of protrusions or grooves formed to protrude or recess from the surface of the fixture 270.

[0066] In this embodiment, an example in which the magnetic force strengthening portion 279 is formed on the fixture 270 is illustrated. However, the magnetic force strengthening portion 279 may be formed on the stud, or may be formed in independent shapes or corresponding shapes that can be mutually coupled on both the fixture 270 and the stud.

[0067] FIG. 22 is a diagram showing a modified example of the stud according to the first embodiment.

[0068] In this embodiment, the coupling groove 75 of the fixture 70 has a size larger than the protruding portion 85 of the stud 80. Specifically, when the protruding portion 85 and the coupling groove 75 have a circular cross-sectional shape, the diameter R1 of the coupling groove 75 is larger than the diameter R2 of the protruding portion 85. The protruding portion 85 is provided with an elastic portion 88 on its outer side. The elastic portion 88 is formed of one or more of metal, plastic, resin, and silicon, and is attached in a manner of fitting and coupling to the outer surface of the protruding portion 85, or is formed in a coated form. The thickness r1 of the elastic portion 88 is set such that the size of the entire protruding portion 85 including the elastic portion 88, that is, R2 + 2r1, is the same as or slightly larger than the size of the coupling groove 75, that is, R1. Therefore, when the protruding portion 85 and the elastic portion 88 are both fitted into the coupling groove 75, they are fitted in a form similar to the coupling by press-fitting, thereby making the coupling between the fixture 70 and the stud 80 stronger. This modified example may also be applied to the second and third embodiments described above.

[0069] In the above, the present invention has been specifically described with reference to the drawings according to embodiments of the present invention. However, these embodiments are merely given for the purpose of exemplifying and explaining the present invention, and are not given for the purpose of meaning limitation or for limiting the scope of the present invention described in the claims. Therefore, those having ordinary knowledge in the technical field of the present invention should be able to understand that various modifications and equivalent other embodiments are possible from the embodiments. Therefore, the true technical protection scope of the present invention should be determined by the technical matters of the claims.

Explanation of Reference Numerals

[0070] 10: Border 20: Membrane 30: Pericle 50: Frame 55: Fitting Groove 60: Photomask 70: Fixture 71: Fixture Body 72: Support Portion 73: Installation Groove 75: Coupling Groove 80: Stud 81: Stud Body 85: Protrusion 87: Adhesive Groove 88: Elastic Portion 279: Magnetic Force Strengthening Portion

Claims

1. A frame assembly for attaching a pellicle to a photomask used in a photolithography process, comprising: a frame mounted on the upper surface of the photomask, to which the pellicle is attached at the upper part; studs attached to the upper surface of the photomask between the photomask and the frame; fixtures installed by being fitted into the lower surface of the frame at positions corresponding to the studs between the photomask and the frame; wherein the studs and the fixtures are mutually bonded by magnetic force, and a gap of a certain height is formed between the photomask and the frame by the studs placed at the lower part of the fixtures in the bonded state. The frame assembly is characterized by this.

2. The frame assembly according to claim 1, wherein either one of the studs and the fixtures is formed of a magnetic material, and the other is formed of a material that is magnetically bonded to the magnetic material.

3. The frame assembly according to claim 1, wherein the magnetic material is formed of a rare earth material that loses magnetic force at a temperature exceeding a predetermined magnetic force disappearance temperature.

4. The frame assembly according to claim 1, wherein a fitting groove into which the fixture is fitted is formed on the lower surface of the frame.

5. The frame assembly according to claim 1, wherein the certain height is 0.05 to 0.5 mm.

6. The frame assembly according to claim 1, wherein at least one of the studs and the fixtures has a surface coated with a metal or non-metal material.

7. The fixture includes a fixture body extending in the longitudinal direction of the frame, and support portions formed by protruding downward at both ends of the fixture body, and forming mounting grooves in which the studs are mounted. The frame assembly according to claim 1, wherein the stud includes a stud body that is prevented from moving in the longitudinal direction by being fitted and mounted in the mounting grooves.

8. The fixture is provided with a coupling groove formed on the bottom surface of the mounting groove. The frame assembly according to claim 7, wherein the stud includes a protruding portion that fits into and engages with the coupling groove.

9. The fixture body has a length of 5 to 150 mm, a width of 1 to 6 mm, and a thickness of 0.5 to 2 mm in the longitudinal direction. The support portion has a length of 0.5 to 10 mm in the longitudinal direction and a height of 0.1 to 1 mm based on the bottom surface of the mounting groove. The stud body has a length of 4 to 130 mm, a width of 1 to 10 mm, and a thickness of 0.15 to 1.5 mm in the longitudinal direction. The frame assembly according to claim 7, wherein the protruding portion has a height of 0.1 to 1.5 mm.

10. The frame assembly according to claim 7, wherein the stud body has a width that is greater than or equal to that of the fixture body.

11. The frame assembly according to claim 1, wherein at least one of the stud and the fixture has a shape formed by protruding or recessing from the surface, and a magnetic force strengthening portion for strengthening the magnetic force is formed.

12. The fixture includes a coupling groove formed in the bottom surface of the mounting groove. The stud includes a protruding portion that engages with the coupling groove. The coupling groove has a size larger than that of the protruding portion. The frame assembly according to claim 7, wherein the protruding portion is provided with an elastic portion that is fitted into the coupling groove together with the protruding portion on the outside.

13. The frame assembly according to claim 12, wherein the elastic portion is formed of one or more of metal, plastic, resin, and silicon.

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