Integrated air floatation main shaft suitable for high-frequency adjustment in Z-axis direction

Abstract

The invention discloses an integrated air floating main shaft which is provided with a bearing outer ring and a bearing inner ring which are nested inside and outside and are in clearance fit, the top of the bearing inner ring is connected with an objective table and is driven to rotate, the bottom of the air floating main shaft is provided with an adjusting unit for driving the objective table to move in the Z-axis direction, and the bearing outer ring is fixedly connected. The adjusting unit is sealed in a counter bore formed in the bottom of the bearing inner ring through the lower end cover, the linear motor stator is fixedly connected to the lower end cover, the linear motor rotor is coaxially connected to the linear motor stator in a sleeved mode, and the linear motor rotor supports the bearing inner ring to conduct Z-axis direction adjustment. A cavity communicated with an air passage in the air floating main shaft is formed between the bottoms of the bearing inner ring and the bearing outer ring and the lower end cover, and the air pressure in the cavity is increased to balance the self weight of the bearing inner ring and the attachment thereof. According to the integrated air floating main shaft, the frequency of adjustment in the Z-axis direction can be greatly improved, and the volume duty and the energy efficiency of the air floating main shaft are optimized on the basis that the production efficiency and the product quality are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wafer processing and detection, and in particular to an integrated air-floating spindle suitable for high-frequency adjustment in a Z-axis direction. Background Art

[0002] Air bearings (also called air bearings) are sliding bearings that use gas (usually air, but it can also be other gases) as lubricant. Air is less viscous than oil, is resistant to high temperatures, and is pollution-free, so it can be used in high-speed machines used in semiconductor manufacturing or special instruments and radioactive devices.

[0003] In the semiconductor manufacturing industry, wafers are the basic raw materials for chip production, and they need to meet a number of very demanding technical parameters such as shape and thickness. Therefore, in order to meet the efficiency and high-performance yield of large-scale chip production, comprehensive and high-precision inspections are required after the wafers are produced. The air-floating spindle is one of the preferred and widely used auxiliary machines, which can carry the wafers to be inspected and rotate at high speed in a controllable manner, and adjust and position them at high frequency in the Z-axis direction, so as to cooperate with high-definition cameras to realize quality inspection operations.

[0004] like Figure 1 As shown in the figure, it is a schematic diagram of the cross-sectional structure of a commonly used spindle system. It mainly includes a lifting unit B arranged at the bottom and an air-floating spindle unit A with a shell on it. As can be seen from the figure, the upper part is a conventional principle setting of the air-floating spindle, which is mainly used to apply high-pressure air to the inside to make the inner ring A2 of the air-floating bearing suspended, and driven to drive the wafer 9 loaded on the top to rotate at high speed; therefore, this part is simply illustrated and not detailed. The lower part is controlled by a servo motor to operate and drive the upper part to adjust the position along the Z axis at a certain frequency. The lifting unit B includes a servo motor B1, a reducer B2, a coupling B3, a ball screw B4, a horizontal guide rail B5, a first wedge block B6, a second wedge block B7, a guide rail B8 and a Z-axis direction guide bearing B9. The servo motor B1 outputs power through the reducer B2 and the coupling B3 to rotate the ball screw B4, and the first wedge block B6 is sleeved on the horizontal guide rail B5 and connected to the ball screw B4 to be driven to move horizontally. The second wedge block B7 is invertedly mounted on the bottom of the housing A3 and slides with the inclined surface of the first wedge block B6 through the guide rail B8. When the two wedge blocks are close to each other, the second wedge block is lifted up, and when the two wedge blocks are separated from each other, the second wedge block slides down, and the housing is controlled by the distributed guide bearings to drive the upper half of the housing to adjust its position along the Z axis.

[0005] However, such a spindle system objectively has several obvious shortcomings: 1) the upper part of the air-floating spindle unit (including the air-floating bearing outer ring and housing, Figure 11) The weight of the lifting unit (shown in the dotted box M) is relatively large, so it is impossible to achieve high-frequency lifting and lowering adjustment along the Z-axis direction. 2) The Z-axis direction adjustment needs to be achieved through continuous transmission of servo motors, reducers, couplings, ball screws and multi-track guide mechanisms, and strict guidance assistance is also required. Therefore, the components cannot respond quickly. Taking the reciprocating motion within the range of 10μm in the Z-axis direction as an example, the maximum frequency of the Z-axis direction adjustment can only reach 20Hz, and no further breakthrough can be made. 3) Due to the complex mechanical composition and transmission of the lifting unit, its own volume is difficult to simplify, resulting in an overall overload and high power consumption; and with so many mechanical rigid contact connections, frequent friction during the Z-axis direction adjustment causes very serious wear, and the accuracy deteriorates significantly after long-term operation. Summary of the invention

[0006] The purpose of the present invention is to provide an integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction, so as to improve the high-frequency response of the adjustment in the Z-axis direction without affecting the original radial rotation performance of the air-floating spindle.

[0007] The technical solution for achieving the above-mentioned purpose of the present invention is an integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction, which has an outer ring and an inner ring of a bearing that are nested and clearance-matched inside and outside, and a torque motor rotor and a torque motor coil mounted between the two, a loading platform is mounted on the top of the inner ring of the bearing, and an adjustment unit for driving the loading platform to move along the Z-axis direction is provided at the bottom of the air-floating spindle. In particular, the outer ring of the bearing is fixedly mounted, and the inner ring of the bearing is driven by the torque motor to coaxially rotate relative to the outer ring of the bearing; the adjustment unit is closed in the countersunk hole provided at the bottom of the inner ring of the bearing through the lower end cover, and the adjustment unit is mainly composed of a linear motor mover and a linear motor stator, wherein the linear motor mover is coaxially sleeved on the linear motor stator and supports the inner ring of the bearing to mainly adjust the Z-axis direction, the linear motor stator is fixed to the lower end cover, and a cavity connected to the airway in the air-floating spindle is formed between the bottom of the inner ring of the bearing and the outer ring of the bearing and the lower end cover, and the air pressure in the cavity is increased to balance the deadweight of the inner ring of the bearing and its mounting accessories.

[0008] Furthermore, the lower end cover is provided with a pressure regulating valve, and when the air pressure in the cavity exceeds the state of maintaining deadweight balance, the pressure regulating valve immediately responds to exhaust air to the outside, thereby releasing the excess pressure in the cavity.

[0009] Furthermore, a displacement sensor for external signal connection is embedded in the middle of the lower end cover, and a sensing sheet opposite to the displacement sensor is installed in the middle of the counterbore.

[0010] Furthermore, the bearing outer ring includes an upper outer ring and a lower outer ring that are separately formed and assembled as one body, and the upper outer ring is provided with a plurality of upper air flotation air channels in a radial surface area close to the top of the bearing inner ring, and all the upper air flotation air channels are equally distributed in the circumferential direction; the lower outer ring is provided with a plurality of lower air flotation air channels in a radial surface area close to the bottom of the bearing inner ring, and all the lower air flotation air channels are equally distributed in the circumferential direction.

[0011] Furthermore, the outer ring of the bearing is provided with an expanded diameter cavity between the two groups of air flotation air channels, and the torque motor coil is fixedly connected to the inner wall of the upper outer ring and externally connected to the lead wire, and the torque motor rotor is sleeved and fixed on the surface of the inner ring of the bearing. When the torque motor coil is energized, the torque motor rotor drives the inner ring of the bearing to rotate.

[0012] Furthermore, the inner hole straight wall of the upper outer ring is coaxially arranged with the inner hole straight wall of the lower outer ring, and the axial positioning tolerance is less than 1 μm, and the docking planes of the upper outer ring and the lower outer ring are perpendicularly arranged relative to their respective inner hole straight walls.

[0013] Furthermore, a Z-axis limiting ring integrally locked with the bottom of the bearing inner ring is provided in the cavity, and the outer diameter of the Z-axis limiting ring is larger than the inner diameter of the bottom side of the bearing outer ring.

[0014] Furthermore, an adapter plate is provided between the top of the bearing inner ring and the stage, and a circular grating is provided on the radial outer side of the adapter plate; a circular grating reading head facing the axis is provided on the top of the bearing outer ring, and the signal feeds back the real-time circumferential position of the stage.

[0015] The integrated air-floating spindle of the present invention has outstanding substantial characteristics, and its application is significantly progressive. The technical effects or advantages it brings include: 1) A motor for driving the Z-axis direction adjustment is directly integrated at the bottom of the inner ring of the bearing, and a cavity is set at the corresponding position, so that the original air film of the air-floating spindle can be connected and expanded downward; most of the load is removed by separating the static assembly of the outer ring of the bearing and the dynamic assembly of the inner ring of the bearing, so that the optimized load mainly based on the inner ring of the bearing can be supported by the air pressure in the cavity to balance the dead weight, creating conditions for the maximum frequency of the Z-axis direction adjustment to exceed 150Hz, which is conducive to greatly improving production efficiency; 2) On the basis of mechanical processing, displacement sensor accuracy and linear motor performance, the linear motor directly outputs driving force to the optimized load, which can make the accuracy of Z-axis movement reach 20nm, compared with Figure 1The traditional spindle system shown in the figure can improve the accuracy in this aspect by more than 10 times without the support of additional guiding mechanisms; 3) The motor composed of a linear motor stator and a linear motor mover directly drives the inner ring of the bearing to achieve high-frequency adjustment in the Z-axis direction without an intermediate transmission link, thereby improving the transmission efficiency and helping to reduce the volume occupancy; 4) It also avoids mechanical friction and pollution caused by frequent addition of lubricating oil, thereby achieving very high equipment accuracy retention and improving product quality; 5) At the same time, it reduces power loss and optimizes energy efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a schematic diagram of the axial cross-section structure of an air-floating spindle with Z-axis adjustment capability in the prior art.

[0017] Figure 2 It is a schematic diagram of the axial section structure of the integrated air-floating main shaft of the present invention.

[0018] Figure 3 yes Figure 2 Schematic diagram of the enlarged structure of the middle Q part. DETAILED DESCRIPTION

[0019] The specific implementation modes of the present invention will be further described below in conjunction with the accompanying drawings of the embodiments, so that the technical solution of the present invention is easier to understand and grasp, thereby making a clearer definition of the protection scope of the present invention.

[0020] In view of the many deficiencies exposed by the existing air-floating spindles used in semiconductor processing, the present invention innovatively proposes an integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction to meet the demand for high-frequency adjustment in the Z-axis direction in wafer inspection operations.

[0021] like Figure 2 and Figure 3As shown, the one-piece air-floating spindle suitable for high-frequency adjustment in the Z-axis direction of the present invention has the basic structure and assembly characteristics of a conventional air-floating spindle, namely, the outer ring 1 and the inner ring 2 of the bearing are nested inside and outside and have clearance fit, and the torque motor rotor 31 and the torque motor coil 32 are installed between the two. The lead wire of the torque motor coil 32 passes through the outer ring 1 of the bearing and is externally connected to the power supply lead wire, and the top of the inner ring 2 of the bearing is equipped with a stage 4 for fixing the wafer and other detection objects in position. The bottom of the air-floating spindle is provided with an adjustment unit for driving the stage to move along the Z-axis direction. As an overview of the key points of the technical transformation of the present invention: the outer ring 1 of the bearing is fixedly installed, that is, it is fixedly installed with the external equipment in the actual application state and remains stationary during the entire operation of the spindle. The inner ring 2 of the bearing is driven by the torque motor to rotate coaxially relative to the outer ring 1 of the bearing. The adjustment unit is enclosed in the countersunk hole 21 provided at the bottom of the bearing inner ring 2 through the lower end cover 13. The adjustment unit is mainly composed of a linear motor mover 51 and a linear motor stator 52, wherein the linear motor mover 51 is coaxially sleeved on the linear motor stator 52 and supports the bearing inner ring 2 to adjust the Z-axis direction. The linear motor stator 52 is fixed to the lower end cover 13 and the external lead wires through the lower end cover need to be sealed. A cavity 6 connected to the airway in the air-floating spindle is formed between the bottom of the bearing inner ring 2 and the bearing outer ring 1 and the lower end cover 13. When the air-floating spindle is running, the air pressure in the cavity increases to balance the deadweight of the bearing inner ring and its attached accessories.

[0022] In order to make it easier to understand the structural optimization and functional realization of the above-mentioned air-floating spindle, the principle is further explained as follows: On the one hand, the outer ring of the bearing is fixedly installed and does not participate in the high-frequency adjustment of the inner ring of the bearing in the Z-axis direction. That is, by separating the static installation of the outer ring of the bearing and the dynamic installation of the inner ring of the bearing, most of the load (usually the deadweight of the outer ring of the bearing is relatively high) can be stripped off, which can reduce the output energy consumption of the adjustment unit. On the other hand, a linear motor for driving the adjustment in the Z-axis direction is directly integrated at the bottom of the inner ring of the bearing, and a cavity is set at the corresponding position, so that the original air film of the air-floating spindle can be connected and expanded downward, and the pressure is increased in the cavity to provide a suspension support force F for this part of the load mainly based on the inner ring of the bearing, so as to achieve the purpose of balancing the deadweight; see Figure 2 The thick lines and Figure 3 As shown by the continuous arrows in the lower right corner, the control action output by the linear motor can be transmitted to the stage with high security and move in the Z-axis direction, that is, the full air-floating mode of the spindle driven by dual motors is realized. Taking the reciprocating motion in the Z-axis direction within a range of 10μm as an example, the conditions are created so that the maximum frequency of the Z-axis adjustment can exceed 150Hz.

[0023] In the preferred embodiment shown in the figure, the lower end cover 13 is also provided with a pressure regulating valve 7, which can be a manual bolt-adjustable pressure relief valve or a digital pressure regulating valve. The pressure regulating valve 7 is used to maintain the air pressure in the cavity required to achieve self-weight balance. When the air pressure in the cavity is too high and affects the reciprocating motion of the inner ring of the bearing along the Z-axis direction, the pressure regulating valve can respond quickly with high sensitivity to exhaust air to the outside, so that the cavity can quickly release excess pressure.

[0024] A displacement sensor 101 for external signal connection is embedded in the middle of the lower end cover 13, and a sensing piece 102 opposite to the displacement sensor is installed in the middle of the counterbore 21, so that the signal feedback is used to determine the real-time axial position (micrometer-level reciprocating motion stroke) of the stage or wafer.

[0025] From a further refinement and optimization point of view, the cavity 6 is provided with a Z-axis limit ring 14 integrally locked with the bottom of the bearing inner ring 2, and the outer diameter of the Z-axis limit ring 14 is larger than the inner diameter of the bottom side of the bearing outer ring 1. That is, the up and down distances of the bearing inner ring driven by the linear motor are limited to prevent it from being suddenly ejected from the bearing outer ring or directly hitting the lower end cover. Figure 2 and Figure 3 Detailed illustration, the Z-axis limit ring occupies most of the cavity space, and a directional gas path is formed on the outer surface of the Z-axis limit ring I , especially forming a gas diaphragm on its top and bottom surfaces that does not touch the bearing outer ring and the lower end cover.

[0026] Due to the principle and assembly structure of the torque motor in the air-floating spindle to drive in the circumferential direction, if the outer ring of the bearing is formed by one-piece processing and even if the processing accuracy is met, it is impossible to realize the assembly of the torque motor and the inner ring of the bearing. Therefore, in this embodiment, the outer ring 1 of the spindle includes an upper outer ring 11 and a lower outer ring 12 that are formed separately and assembled as one, and the upper outer ring 11 is provided with a plurality of upper air-floating airways 111 in a radial surface area near the top of the inner ring of the bearing, and all the upper air-floating airways are equally distributed in the circumferential direction. The lower outer ring 12 is provided with a plurality of lower air-floating airways 121 in a radial surface area near the bottom of the inner ring of the bearing, and all the lower air-floating airways are also equally distributed in the circumferential direction. Since the principle of radial rotation air-floating is relatively well known to those skilled in the art, it is omitted for further description, and the so-called radial surface area refers to a collection of radial planes (or cylindrical areas) at the height of each air-floating airway. In order to meet the requirements of installing the torque motor, the outer ring 1 of the bearing is provided with an expanded diameter cavity 1112 between two groups of air-floating air channels, and the torque motor coil 32 is fixed to the inner wall of the upper outer ring 11 and connected to the external lead wire, and the torque motor rotor 31 is sleeved and fixed on the surface of the bearing inner ring 2. When the torque motor coil is energized, the torque motor rotor can drive the bearing inner ring to rotate. However, since the spindle outer ring is formed by separate molding and integrated assembly, in order to keep the bearing inner ring rotating stably in the circumferential direction in the formed air film, the bearing outer ring also has higher surface molding requirements, specifically including the coaxial arrangement of the inner hole straight wall 112 of the upper outer ring and the inner hole straight wall 122 of the lower outer ring, and the axial positioning tolerance is strictly controlled to be less than 1μm; and the docking plane 1211 of the upper outer ring and the lower outer ring needs to be vertically arranged relative to their respective inner hole straight walls, so as to ensure the coaxial accuracy after integrated assembly.

[0027] In addition, an adapter plate 41 is provided between the top of the bearing inner ring 2 and the stage 4, and a circular grating 81 is provided on the radial outer side of the adapter plate; a circular grating reading head 82 facing the axis is provided on the top of the bearing outer ring 1, and the real-time circumferential position of the stage is fed back through this signal.

[0028] From the above introduction to the integrated air-floating spindle solution suitable for high-frequency adjustment in the Z-axis direction and the detailed description of the embodiments of the present invention, it can be seen that its application is significantly progressive, and the technical effects or advantages it brings include: 1) A motor for driving the Z-axis adjustment is directly integrated at the bottom of the inner ring of the bearing, and a cavity is set at the corresponding position, so that the original air film of the air-floating spindle can be connected and expanded downward; most of the load is removed by separating the static assembly of the outer ring of the bearing and the dynamic assembly of the inner ring of the bearing, so that the optimized load mainly based on the inner ring of the bearing can be supported by the air pressure in the cavity to balance its own weight, creating conditions for the maximum frequency of the Z-axis adjustment to exceed 150Hz, which is conducive to greatly improving production efficiency; 2) On the basis of mechanical processing, displacement sensor accuracy and linear motor performance, the linear motor directly outputs driving force to the optimized load, which can make the accuracy of Z-axis movement reach 20nm, compared with Figure 1 The traditional spindle system shown in the figure can improve the accuracy in this aspect by more than 10 times without the support of additional guiding mechanisms; 3) The motor composed of a linear motor stator and a linear motor mover directly drives the inner ring of the bearing to achieve high-frequency adjustment in the Z-axis direction without an intermediate transmission link, thereby improving the transmission efficiency and helping to reduce the volume occupancy; 4) It also avoids mechanical friction and pollution caused by frequent addition of lubricating oil, thereby achieving very high equipment accuracy retention and improving product quality; 5) At the same time, it reduces power loss and optimizes energy efficiency.

[0029] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the scope of protection required by the present invention.

Claims

1. An integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction, comprising an outer bearing ring and an inner bearing ring which are nested and clearance-matched, and a torque motor rotor and a torque motor coil mounted therebetween, a stage mounted on the top of the inner bearing ring, and an adjustment unit for driving the stage to move along the Z-axis direction is provided at the bottom of the air-floating spindle, characterized in that: The outer ring of the bearing is fixedly mounted, and the inner ring of the bearing is driven by the torque motor to rotate coaxially relative to the outer ring of the bearing; the adjustment unit is closed in the countersunk hole provided at the bottom of the inner ring of the bearing through the lower end cover, and the adjustment unit is mainly composed of a linear motor mover and a linear motor stator, wherein the linear motor mover is coaxially sleeved on the linear motor stator and supports the inner ring of the bearing to mainly adjust the Z-axis direction, the linear motor stator is fixed to the lower end cover, and a cavity connected to the airway in the air-floating main shaft is formed between the bottom of the inner ring of the bearing and the outer ring of the bearing and the lower end cover, and the air pressure in the cavity is increased to balance the deadweight of the inner ring of the bearing and its mounted accessories.

2. The integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction according to claim 1, characterized in that: The lower end cover is provided with a pressure regulating valve, and when the air pressure in the cavity exceeds the state of maintaining deadweight balance, the pressure regulating valve immediately responds to exhaust air to the outside.

3. The integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction according to claim 1, characterized in that: A displacement sensor for external signal connection is embedded in the middle of the lower end cover, and a sensing sheet opposite to the displacement sensor is installed in the middle of the counterbore.

4. The integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction according to claim 1, characterized in that: The bearing outer ring includes an upper outer ring and a lower outer ring which are formed separately and assembled as one body, and the upper outer ring is provided with a plurality of upper air flotation air channels in a radial surface area close to the top of the bearing inner ring, and all the upper air flotation air channels are equally distributed in the circumferential direction; the lower outer ring is provided with a plurality of lower air flotation air channels in a radial surface area close to the bottom of the bearing inner ring, and all the lower air flotation air channels are equally distributed in the circumferential direction.

5. The integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction according to claim 4, characterized in that: The outer ring of the bearing is provided with an expanded diameter cavity between the two groups of air-floating air passages, and the torque motor coil is fixedly connected to the inner wall of the upper outer ring and externally connected to the lead wire, and the torque motor rotor is sleeved and fixed on the surface of the inner ring of the bearing. When the torque motor coil is energized, the torque motor rotor drives the inner ring of the bearing to rotate.

6. The integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction according to claim 4, characterized in that: The inner hole straight wall of the upper outer ring is coaxially arranged with the inner hole straight wall of the lower outer ring, and the axial positioning tolerance is less than 1 μm. The butt joint planes of the upper outer ring and the lower outer ring are perpendicularly arranged relative to their respective inner hole straight walls.

7. The integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction according to claim 1, characterized in that: A Z-axis limiting ring is provided in the cavity and is integrally locked with the bottom of the inner ring of the bearing, and the outer diameter of the Z-axis limiting ring is larger than the inner diameter of the bottom side of the outer ring of the bearing.

8. The integrated air-floating spindle suitable for high-frequency adjustment in the Z-axis direction according to claim 1, characterized in that: An adapter plate is provided between the top of the bearing inner ring and the stage, and a circular grating is provided on the radial outer side of the adapter plate; a circular grating reading head facing the axis is provided on the top of the bearing outer ring, and the signal feeds back the real-time circumferential position of the stage.

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