Semiconductor process equipment

Abstract

The utility model provides semiconductor process equipment. According to the semiconductor process equipment, a supporting bulge with a curved surface is adopted to bear a wafer. Compared with a planar support structure, the curved surface support can limit the displacement of the wafer under the condition that the wafer vibrates, and ensures that the edge of the wafer can automatically slide to a target bearing position through the curved surface when the wafer stops vibrating, so that the condition that the wafer deviates from the bearing position due to vibration is effectively avoided, and the service life of the wafer is prolonged. Therefore, the wafer bearing position is limited, the wafer taking success rate of the mechanical arm is improved, and the waste of process cost is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of semiconductor manufacturing, and particularly relates to a semiconductor process equipment. Background Art

[0002] Insulated Gate Bipolar Transistor (IGBT) combines the advantages of Power Transistor (GTR) and Power Metal Oxide Semiconductor Field Effect Transistor (Power MOSFET), has good electrical characteristics, and is widely used. In the manufacturing process of IGBT, backside grinding (BG) and backside metallization (BM) of wafers are extremely important process steps. Among them, the backside grinding process has the functions of improving the chip thermal diffusion efficiency, reducing the chip packaging volume, and lowering the packaging mounting height, etc.; while the backside metallization process usually forms a multi-layer metallization structure with four metals, namely aluminum (Al), titanium (Ti), nickel vanadium (NiV), and silver (Ag). It can not only reduce the thermo-mechanical stress of the chip, improve its thermal characteristics, but also obtain a lower ohmic contact resistance and optimize the electrical contact performance.

[0003] However, during the backside metallization process, especially in the aluminum chamber, the problem of wafer picking failure is likely to occur. The reason is that the polyimide (PI) layer on the front side of the IGBT has strong water absorption, so a certain amount of water vapor will be absorbed before the wafer enters the aluminum chamber. As Figure 1 and Figure 2 shown, when the wafer W enters the aluminum chamber with a high-temperature environment, the PI layer on the wafer W will release water vapor, and the thickness of the thinned wafer W is low, so it is easy to cause the wafer W to vibrate, resulting in the position of the wafer W on the carrier 10 to shift. Therefore, when the robotic arm 20 picks up the wafer, it is very easy to collide with the wafer W, resulting in the wafer W being damaged. Moreover, the thinner the thickness and / or the higher the proportion of the PI layer of the wafer W, the greater the probability of fragmentation. This not only causes waste of manufacturing cost, but also seriously affects the process progress.

[0004] Therefore, there is an urgent need for a new semiconductor process equipment to solve the above technical problems. Summary of the Utility Model

[0005] The purpose of the utility model is to provide a semiconductor process equipment to solve at least one of the problems of how to limit the wafer carrying position, reduce the wafer picking failure rate of the robotic arm, and how to reduce the waste of process cost.

[0006] To solve the above technical problems, the present utility model provides a semiconductor process equipment, including a reaction chamber; a carrier table is arranged in the reaction chamber; the top surface of the carrier table has a plurality of support protrusions, and the plurality of support protrusions are spaced apart along the edge of the top surface to carry a wafer; wherein, one side of the support protrusion facing the central region of the top surface is a curved surface, so that the edge of the wafer slides down to the target carrying position through the curved surface.

[0007] Optionally, in the semiconductor process equipment, the curved surface includes an adjacent first surface and a second surface; the first surface is a horizontal plane, and the second surface is an inclined plane; wherein,

[0008] The first surface is arranged close to the top surface of the carrier table and extends a set distance towards the central region of the top surface of the carrier table;

[0009] The second surface is arranged on one side of the first surface close to the edge of the top surface of the carrier table, and along the direction towards the edge of the top surface of the carrier table, the height of the second surface increases relative to the first surface.

[0010] Optionally, in the semiconductor process equipment, the curved surface includes an upward concave arc surface; and one side of the upward concave arc surface is close to the top surface of the carrier table and extends a set distance towards the central region of the top surface of the carrier table.

[0011] Optionally, in the semiconductor process equipment, the plurality of support protrusions are annularly distributed, and the maximum inner diameter of the ring formed by the plurality of support protrusions is greater than the diameter of the wafer, and the minimum inner diameter of the ring formed by the plurality of support protrusions is less than the diameter of the wafer, so that the target carrying position is located on the curved surfaces of the plurality of support protrusions.

[0012] Optionally, in the semiconductor process equipment, the semiconductor process equipment further includes a robotic arm; the robotic arm is arranged on one side of the reaction chamber, and the robotic arm has a gripper, and the gripper can extend into and out of the reaction chamber to pick up and place the wafer;

[0013] Wherein, a plurality of limit members are arranged on the top surface of the gripper to limit the position of the wafer when the gripper carries the wafer.

[0014] Optionally, in the semiconductor process equipment, the gripper has a plurality of grooves, and the plurality of limit members are respectively arranged in the plurality of grooves; and, the limit member includes a stud and a driving motor; one end of the stud is connected to the driving motor, and under the drive of the driving motor, the stud extends out of or retracts into the groove.

[0015] Optionally, in the semiconductor processing equipment, the position limiting member includes a telescopic tube and a driving motor; one end of the telescopic tube is connected to the driving motor, and under the drive of the driving motor, the telescopic tube extends or contracts in a direction perpendicular to the top surface of the gripper.

[0016] Optionally, in the semiconductor processing equipment, the robotic arm further includes a detector, the detector is arranged on the gripper, and the detector is connected to the driving motor, at least for exciting the driving motor when the gripper carries the wafer, so that the position limiting member limits the position of the wafer.

[0017] Optionally, in the semiconductor processing equipment, the gripper has a connecting arm and at least two arc-shaped arms; one end of the at least two arc-shaped arms is connected to the connecting arm, and along the extending direction of the connecting arm, the at least two arc-shaped arms are arranged in parallel; wherein, the outer chord length of the arc-shaped arm is greater than the diameter of the wafer.

[0018] Optionally, in the semiconductor processing equipment, the plurality of position limiting members are arranged at intervals on the top surface of the at least two arc-shaped arms and are distributed in a ring shape; wherein,

[0019] the diameter of the ring formed by the plurality of position limiting members is greater than the diameter of the wafer; and the difference between the radius of the ring formed by the plurality of position limiting members and the radius of the wafer is less than or equal to 1 mm.

[0020] In summary, the present invention provides a semiconductor processing equipment. Compared with the prior art, the semiconductor processing equipment uses a support convex with a curved surface to carry the wafer. Compared with the planar support structure, the curved surface support can limit the displacement of the wafer under the condition of wafer vibration, and ensure that when the wafer stops vibrating, its edge can automatically slide down to the target carrying position through the curved surface, effectively avoiding the situation that the wafer deviates from the carrying position due to vibration, realizing the limitation of the carrying position of the wafer, which is beneficial to improving the wafer picking success rate of the robotic arm, and further reducing the waste of process costs.

[0021] In a further solution, a plurality of position limiting members are further arranged on the gripper of the robotic arm adopted by the semiconductor processing equipment, so as to be able to limit the position of the wafer when the gripper carries the wafer, and further improve the wafer picking success rate of the robotic arm. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Those of ordinary skill in the art will understand that the provided drawings are used to better understand the present invention and do not constitute any limitation to the scope of the present invention.

[0023] Figure 1 is a schematic diagram of a wafer deviating from the carrying position on a carrier table in the prior art.

[0024] Figure 2 It is a schematic diagram of a wafer falling off a support structure in the prior art.

[0025] Figure 3 It is a schematic structural diagram of a semiconductor process equipment in an embodiment of the present invention.

[0026] Figure 4 It is a top view of a first bearing part in an embodiment of the present invention.

[0027] Figure 5 It is a schematic structural diagram of a support protrusion carrying a wafer in an embodiment of the present invention.

[0028] Figure 6 It is a schematic structural diagram of a support protrusion in an embodiment of the present invention.

[0029] Figure 7 It is a schematic structural diagram of another support protrusion in an embodiment of the present invention.

[0030] Figure 8 It is a schematic structural diagram of a gripper in an embodiment of the present invention.

[0031] Figure 9 It is a schematic structural diagram of a limiting member protruding from an arc-shaped arm in an embodiment of the present invention.

[0032] Figure 10 It is a schematic structural diagram of a limiting member in an embodiment of the present invention.

[0033] Figure 11 It is a schematic structural diagram of another limiting member in an embodiment of the present invention.

[0034] And, in the drawings:

[0035] 10 - Carrying platform; 20 - Robot arm;

[0036] 30 - Carrying platform; 301 - Support protrusion; 302 - First bearing part; 303 - Second bearing part; 304 - Support pin;

[0037] 40 - Gripper; 401 - Limiting member; 402 - Arc-shaped arm; 403 - Connecting arm; 41 - Connecting shaft; 42 - Driving component;

[0038] W - Wafer; S - Curved surface; a1 - First surface; a2 - Second surface; D - Maximum inner diameter of the ring formed by multiple support protrusions; d - Minimum inner diameter of the ring formed by multiple support protrusions; H - Difference between the radius of the ring formed by multiple limiting members and the radius of the wafer; L1 - Outer chord length of the arc-shaped arm; L2 - Diameter of the ring formed by multiple limiting members; T - Groove. Detailed implementation manners

[0039] To make the objectives, advantages and features of the present utility model clearer, the following further describes the present utility model in detail with reference to the accompanying drawings and specific embodiments. It should be noted that the accompanying drawings are all in a very simplified form and are not drawn to scale, only for conveniently and clearly assisting in explaining the objectives of the embodiments of the present utility model. In addition, the structures shown in the accompanying drawings are often part of the actual structures. In particular, the focuses to be shown in each accompanying drawing are different, and sometimes different scales are adopted. It should also be understood that unless otherwise specifically stated or indicated, the terms "first", "second", "third", etc. in the specification are only used to distinguish each component, element, step, etc. in the specification, rather than to represent the logical relationship or sequential relationship, etc. between each component, element, step. And, the X-axis direction, Y-axis direction and Z-axis direction referred to in the specification of the present application are three mutually perpendicular directions in a three-dimensional space.

[0040] Please refer to Figure 3 , this embodiment provides a semiconductor processing device, including a reaction chamber; a carrier table 30 is arranged in the reaction chamber; the top surface of the carrier table 30 has a plurality of support protrusions 301, and the plurality of support protrusions 301 are spaced apart along the edge of the top surface to carry a wafer W; wherein, one side of the support protrusion 301 facing the central area of the top surface is a curved surface, so that the edge of the wafer W slides down to the target carrying position through the curved surface.

[0041] It can be understood that in the semiconductor processing device provided in this embodiment, the support protrusion 301 with a curved surface is used to carry the wafer W. Compared with a flat support structure, the curved surface support can limit the displacement amount of the wafer W when the wafer W vibrates, and ensure that when the wafer W stops vibrating, its edge can automatically slide down to the target carrying position through the curved surface, effectively avoiding the situation that the wafer W deviates from the carrying position due to vibration, realizing the limitation of the carrying position of the wafer W, and further reducing the probability of the robotic arm breaking the wafer W when positioning and picking up the wafer.

[0042] The following specifically describes the semiconductor processing device provided in this embodiment with reference to the attached Figures 3 to 11 drawings.

[0043] Please continue to refer to Figure 3, the semiconductor process equipment provided in this embodiment includes the reaction chamber and the robotic arm. Among them, the reaction chamber is used to accommodate the wafer W and perform semiconductor processes on the wafer W. The semiconductor processes include but are not limited to backside metallization process, ion implantation process, epitaxial layer growth process, etc. The robotic arm is used to pick up and place the wafer W and realize the transportation of the wafer W. Optionally, the robotic arm is arranged on one side of the reaction chamber. For example, it is located at the top of the reaction chamber or at the side of the reaction chamber.

[0044] Please refer to Figure 3 and Figure 4 , according to different semiconductor processes, the types of modules arranged in the reaction chamber are different, and the module distributions are also different. However, regardless of the type of semiconductor process, a carrier stage 30 is arranged in the reaction chamber for carrying the wafer W. Further, the carrier stage 30 includes a first carrier portion 302 and a second carrier portion 303. The first carrier portion 302 and the second carrier portion 303 are connected, and the first carrier portion 302 is arranged on the top surface of the second carrier portion 303 for carrying the wafer W.

[0045] Further, the first carrier portion 302 has a flat top surface to serve as the top surface of the carrier stage 30. And a plurality of support protrusions 301 and a plurality of support pins 304 are arranged on the top surface. The support protrusions 301 are used to carry the wafer W during the execution of semiconductor processes. The support pins 304 have an automatic lifting function. When the wafer W enters and exits the reaction chamber, the support pins 304 rise to lift the wafer W from the support protrusions 301, so as to facilitate the gripper 40 of the robotic arm to pick up and place the wafer W; when the gripper 40 finishes placing the wafer W, the support pins 304 slowly lower to make the wafer W located on the support protrusions 301; and when the wafer W is placed on the support protrusions 301 or the wafer W is taken away, the support pins 304 remain in the lowered state. Preferably, each of the support protrusions 301 and each of the support pins 304 are annularly distributed along the edge of the first carrier portion 302 and are spaced from each other; and each of the support protrusions 301 and each of the support pins 304 are also symmetrically distributed relative to the central axis of the first carrier portion 302 to stably support the wafer W. It should be noted that the specific numbers of the support protrusions 301 and the support pins 304 are not specifically limited in this embodiment.

[0046] Please refer to Figure 3 , Figure 5 , Figure 6 and Figure 7, on one side of the supporting protrusion 301 provided in this embodiment facing the central region of the top surface of the first bearing portion 302 is a curved surface S, so that the edge of the wafer W slides down to the target bearing position through the curved surface S. In one example, as Figure 5 and Figure 6 shown, the curved surface S includes an adjacent first surface a1 and second surface a2. The first surface a1 is a horizontal plane; that is, the plane where the X-axis - Y-axis is located. The second surface a2 is an inclined plane; that is, a plane having a certain inclination angle relative to the plane where the X-axis - Y-axis is located. Among them, the first surface a1 is parallel to the top surface of the first bearing portion 302 and is disposed close to the top surface of the first bearing portion 302; and, the first surface a1 extends a set distance towards the central region of the top surface of the first bearing portion 302, for avoiding directly abutting against the top surface of the first bearing portion 302 in the case where the wafer W vibrates severely, and realizing the protection of the wafer W and the first bearing portion 302. The second surface a2 is disposed on one side of the first surface a1 close to the edge of the top surface of the first bearing portion 302, and along the direction towards the edge of the top surface of the first bearing portion 302, the height of the second surface a2 increases relative to the first surface a1. That is, in the X-axis - Z-axis section plane, the angle formed by the first surface a1 and the second surface a2 is an obtuse angle, and the opening of the obtuse angle is upward and towards the central region of the top surface of the first bearing portion 302. Based on this, the curved surfaces S of the plurality of supporting protrusions 301 can enclose an inverted frustum-shaped groove. In another example, as Figure 3 and Figure 7 shown, the curved surface S includes an upwardly concave arc surface. And one side of the upwardly concave arc surface is close to the top surface of the first bearing portion 302 and extends a set distance towards the central region of the top surface of the first bearing portion 302, which can also play a role in protecting the wafer W and the first bearing portion 302.

[0047] Further, the specific morphology of the curved surface S is not limited in this embodiment. However, based on the above two examples of the curved surface S, a plurality of the support protrusions 301 are distributed in a ring shape, and the annular region surrounded by their respective curved surfaces S resembles a trumpet-shaped groove. Therefore, when the wafer W vibrates due to factors such as placement or water vapor release, the support walls with the curved surface S can effectively restrict the displacement amount of the wafer W, and when the wafer W stops vibrating, its edge can automatically slide down along the curved surface S to the target bearing position, ensuring the stable position of the wafer W, and further reducing the probability of the manipulator breaking the wafer W when positioning and picking up the wafer. Preferably, to ensure effective control of the position change of the wafer W, the maximum inner diameter D of the ring formed by the plurality of support protrusions 301 is greater than the diameter of the wafer W, and the minimum inner diameter d of the ring formed by the plurality of support protrusions 301 is less than the diameter of the wafer W, so that the target bearing position is located on the curved surface S of the plurality of support protrusions 301.

[0048] Please refer to Figure 3 and Figure 8 , the manipulator includes the gripper 40, the connecting shaft 41, and the driving assembly 42. Among them, the driving assembly 42, the connecting shaft 41, and the gripper 40 are connected in sequence, and under the drive of the driving assembly 42, the connecting shaft 41 drives the gripper 40 to move in multiple degrees of freedom. Preferably, the driving assembly 42 includes a plurality of driving motors to achieve multi-degree-of-freedom movement in combination. Further, the gripper 40 can extend into and out of the reaction chamber to pick up and place the wafer W. And the gripper 40 has at least two arc-shaped arms 402 and a connecting arm 403. One end of each arc-shaped arm 402 is connected to the connecting arm 403, and along the extending direction of the connecting arm 403, that is, the Y-axis direction, the arc-shaped arms 402 are arranged side by side at intervals. That is, the gripper 40 is located on the plane where the X-axis and the Y-axis are located to facilitate picking up, placing, and transporting the wafer W. It should be noted that the arc-shaped arms 402 are used to carry the wafer W when picking up, placing, and transporting the wafer W. The connecting arm 403 is connected to one end of the connecting shaft 41 to transmit the driving force provided by the driving assembly 42, thereby driving the wafer W to move.

[0049] Further, the outer chord length L1 of the arc-shaped arm 402 is greater than the diameter of the wafer W, so as to expand the bearing contact area between the arc-shaped arm 402 and the wafer W, adapt to the topography of the wafer W, and improve the bearing stability of the wafer W. Further, in order to prevent the wafer W from being displaced on the arc-shaped arm 402 during the process of moving the wafer W, which may cause the wafer W to fall, etc., a plurality of limiting members 401 are provided on each of the arc-shaped arms 402 to limit the position of the wafer W when the gripper 40 carries the wafer W. Preferably, the plurality of limiting members 401 are annularly distributed, and the diameter L2 of the enclosed ring is greater than the diameter of the wafer W, and the difference H between the radius of the ring formed by the plurality of limiting members 401 and the radius of the wafer W is less than or equal to 1 mm. That is, 0 mm < H ≤ 1 mm. Based on this, each of the limiting members 401 can ensure the position limitation of the wafer W without squeezing or damaging the wafer W. It should be noted that the state of carrying the wafer W referred to in this embodiment includes the state of contacting the wafer W and the state of completely carrying the wafer W.

[0050] Preferably, the limiting member 401 has an automatic lifting function, so as to rise after carrying the wafer W to realize the limitation of the wafer W; and when not carrying the wafer W, it is in a lowered or contracted state. Wherein, the specific lifting structure of the limiting member 401 is not limited in this embodiment. And in one example, as Figure 9 and Figure 10 shown, the arc-shaped arm 402 has a plurality of grooves T, and the plurality of limiting members 401 are respectively arranged in the plurality of grooves T. And, the limiting member 401 includes a pin 4011 and a driving motor 4012. One end of the pin 4011 is connected to the driving motor 4012, and under the drive of the driving motor 4012, the pin 4011 can extend or retract into the groove T, so as to limit the carried wafer W when extending; when retracting, it does not affect the movement of the gripper 40 or the execution of other operations. In another example, as Figure 9 and Figure 11 shown, the limiting member 401 includes a telescopic tube 4013 and a driving motor 4012. One end of the telescopic tube 4013 is connected to the driving motor 4012, and under the drive of the driving motor 4012, the telescopic tube 4013 extends or contracts in a direction perpendicular to the top surface of the gripper 40. Similarly, when the telescopic tube 4013 is in an extended state, it can limit the carried wafer W; when the telescopic tube 4013 is in a contracted state, it does not affect the movement of the gripper 40 or the execution of other operations.

[0051] Further, the robotic arm further includes a detector for detecting whether the gripper 40 holds the wafer W. Exemplarily, the detector is disposed on the gripper 40 and is connected to the drive motor 4012 to activate the drive motor 4012 when the gripper 40 holds the wafer W, so that the limiting member 401 can limit the position of the wafer W; and when the gripper 40 does not hold the wafer W, the detector provides a signal to the drive motor 4012 to make the limiting member 401 in a lowered or contracted state. Optionally, the detector is a pressure sensor and / or an optoelectronic position sensor, etc.

[0052] In summary, the semiconductor processing equipment provided in this embodiment uses the support protrusion 301 with the curved surface S to carry the wafer W. Compared with the planar support structure, the curved surface support can limit the displacement of the wafer W in the case of vibration of the wafer W, and ensure that when the wafer W stops vibrating, its edge can automatically slide down to the target carrying position through the curved surface S, effectively avoiding the situation that the wafer W deviates from the carrying position due to vibration, realizing the limitation of the wafer carrying position, and further reducing the wafer picking failure rate of the robotic arm. In addition, the shape of the gripper 40 of the robotic arm used in the semiconductor processing equipment is adapted to the shape of the wafer W, and a plurality of limiting members 401 with automatic lifting functions are further provided on the gripper 40 to limit the position of the wafer W when the gripper 40 holds the wafer W, further improving the success rate of wafer picking by the robotic arm and facilitating the reduction of waste of process costs.

[0053] In addition, it should also be recognized that although the present invention has been disclosed above with preferred embodiments, the above embodiments are not intended to limit the present invention. For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the protection of the technical solution of the present invention.

Claims

1. A semiconductor process equipment, characterized in that, It includes a reaction chamber and a robotic arm; A carrier stage is provided in the reaction chamber; the top surface of the carrier stage has a plurality of support protrusions, and the plurality of support protrusions are spaced apart along the edge of the top surface to carry a wafer; wherein, one side of the support protrusion facing the central region of the top surface is a curved surface, so that the edge of the wafer slides down to the target carrying position through the curved surface; The robotic arm is provided on one side of the reaction chamber, and the robotic arm has a gripper, and the gripper can extend into and out of the reaction chamber to pick up and place the wafer; and, The gripper has a connecting arm and at least two arc-shaped arms; one end of the at least two arc-shaped arms is connected to the connecting arm, and along the extending direction of the connecting arm, the at least two arc-shaped arms are arranged in parallel; wherein, the outer chord length of the arc-shaped arm is greater than the diameter of the wafer.

2. The semiconductor processing equipment according to claim 1, characterized in that, The curved surface includes a first surface and a second surface that are connected; the first surface is a horizontal surface, and the second surface is an inclined surface; wherein, The first surface is arranged close to the top surface of the carrier stage and extends a set distance towards the central region of the top surface of the carrier stage; The second surface is arranged on one side of the first surface close to the edge of the top surface of the carrier stage, and along the direction towards the edge of the top surface of the carrier stage, the height of the second surface increases relative to the first surface.

3. The semiconductor process equipment according to claim 1, characterized in that, The curved surface includes a concave arc surface; and one side of the concave arc surface is close to the top surface of the carrier stage and extends a set distance towards the central region of the top surface of the carrier stage.

4. The semiconductor processing equipment according to any one of claims 1 to 3, characterized in that The plurality of support protrusions are distributed in a ring shape, and the maximum inner diameter of the ring formed by the plurality of support protrusions is greater than the diameter of the wafer, and the minimum inner diameter of the ring formed by the plurality of support protrusions is less than the diameter of the wafer, so that the target carrying position is located on the curved surface of the plurality of support protrusions.

5. The semiconductor processing equipment according to claim 1, characterized in that, A plurality of limit members are provided on the top surface of the gripper to limit the position of the wafer when the gripper carries the wafer.

6. The semiconductor processing equipment according to claim 5, characterized in that, The gripper has a plurality of grooves, and the plurality of limit members are respectively arranged in the plurality of grooves; and, the limit member includes a pin and a driving motor; one end of the pin is connected to the driving motor, and under the drive of the driving motor, the pin extends out of or retracts into the groove.

7. The semiconductor processing equipment according to claim 5, characterized in that, The limit member includes a telescopic tube and a driving motor; one end of the telescopic tube is connected to the driving motor, and under the drive of the driving motor, the telescopic tube extends or contracts in a direction perpendicular to the top surface of the gripper.

8. The semiconductor process equipment according to claim 6 or 7, characterized in that, The robotic arm further includes a detector, the detector is provided on the gripper, and the detector is connected to the driving motor, and is at least used to activate the driving motor when the gripper carries the wafer, so that the limit member limits the position of the wafer.

9. The semiconductor processing equipment according to claim 5, wherein, The plurality of limit members are spaced apart and arranged in a ring shape on the top surface of the at least two arc-shaped arms; wherein, The diameter of the ring formed by the plurality of limit members is greater than the diameter of the wafer; and the difference between the radius of the ring formed by the plurality of limit members and the radius of the wafer is less than or equal to 1 mm.

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