Laser interference measurement system comprising suspension type workpiece table

Abstract

The invention discloses a laser interference measurement system comprising a suspension type workpiece table, a vacuum cavity comprises a cavity body and a cavity cover, the top of a suspension cavity is connected with the inner side of the cavity cover, so that the suspension cavity is suspended in the vacuum cavity, and the workpiece table is arranged in the suspension cavity; the laser is located outside the vacuum cavity and installed below one side of the cavity cover, and a light conversion mirror is installed in the light emitting direction and used for steering laser to be emitted into the cavity. A vacuum window is arranged on the side wall of the cavity, the spectroscope and the interference mirror are both located in the cavity and installed on one side of the upper portion of the suspension cavity, and the reflective mirror is located in the suspension cavity and installed on the workpiece table. The laser passes through the vacuum window, reaches the spectroscope, passes through the interference mirror and then is emitted to the reflective mirror on the workpiece table. According to the invention, the outer-layer cavity is used for providing a vacuum environment, the inner-layer cavity is used for providing a supporting effect, and the workpiece table and the measuring lens group are designed on the inner-layer cavity, so that the influence of vacuum deformation on a measuring light path is greatly eliminated.

Description

Technical Field

[0001] This invention relates to the field of workpiece stages and laser measurement systems, and more specifically to a laser interferometry system including a suspended workpiece stage. Background Technology

[0002] A workpiece stage is a device that provides loading, fixing, and moving functions. While workpiece stages may vary between different devices, they are generally composed of panel-type structural components, moving parts, and loading components, making them one of the most common components in various types of equipment. A laser workpiece stage refers to a workpiece stage system equipped with a laser measuring device, also often called a laser interferometer. This device consists of a laser, interferometer, reflector, and measuring board, and is a high-precision measuring instrument capable of nanometer-level measurements. It is widely used in micro-nano fabrication fields such as lithography machines and electron beam lithography machines, where high-precision operations are required.

[0003] As a high-precision measurement system, the accuracy and stability of laser measurements are the two most important factors for laser stages. For stage systems requiring vacuum conditions, the system also includes a vacuum cavity that provides and maintains the vacuum environment. This type of laser stage operating in a vacuum is typical of electron beam equipment. Under these conditions, the laser stage faces the problem of vacuum deformation affecting the measurement optical path. Since the installation and adjustment of the optical path are done manually under atmospheric conditions, while the actual operating environment is vacuum, the originally adjusted measurement optical path will be deformed due to the vacuum deformation of the cavity, thus affecting the measurement accuracy. The most significant factor is the measurement optical path from the interferometer to the reflector, followed by measurement errors caused by the tilt of the optical path angle between the laser beam and the interferometer. In conclusion, when using laser stages in a vacuum environment, considering the impact of vacuum cavity deformation is a crucial benchmark for ensuring the accuracy of laser measurements. Summary of the Invention

[0004] The technical problem this invention aims to solve is how to achieve more stable and reliable engineering applications of laser workpiece stages in a vacuum environment. It provides a compact, easy-to-operate, and highly reliable laser interferometry system including a suspended workpiece stage, focusing on achieving more accurate and stable laser interferometry measurements of the workpiece stage under vacuum conditions. Therefore, this invention does not limit the specific structure of the moving stage, but rather focuses on the installation scheme of the workpiece stage and the arrangement scheme of the related mirror groups of the laser interferometry device.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A laser interferometry system including a suspended workpiece stage includes: a vacuum cavity, a suspended cavity, a workpiece stage, and a laser interferometry assembly; the vacuum cavity includes a cavity body and a cavity cover, and the top of the suspended cavity is connected to the inner side of the cavity cover to suspend the suspended cavity body within the vacuum cavity; the workpiece stage is disposed within the suspended cavity body. The laser interferometry assembly includes a laser, a vacuum window, a beam-splitter, a beam splitter, an interferometer, and a reflector. The laser is located outside the vacuum cavity and installed below one side of the cavity cover. A beam-splitter is installed along the light output direction to redirect the laser beam into the cavity. A vacuum window is provided on the side wall of the cavity, through which the laser beam enters the cavity. The beam splitter and interferometer are both located inside the cavity and installed on one side of the upper part of the suspended cavity. The reflector is located inside the suspended cavity and installed on the workpiece stage. After passing through the vacuum window, the laser beam splitter reaches the beam splitter and, after passing through the interferometer, is directed towards the reflector on the workpiece stage. As a further improvement of the present invention, the suspension cavity includes a suspension cavity top plate, the suspension cavity top plate is provided with a boss, the inner side of the boss is provided with a circular hole channel, the circular hole channel is aligned with the flange hole of the cavity cover, a fastener is provided between the boss and the cavity cover, and the upper surface of the boss contacts the inner wall surface of the cavity cover, so as to realize the connection and fixation between the suspension cavity and the suspension cavity top plate.

[0006] As a further improvement of the present invention, the beam splitter and the interference mirror are mounted on one side of the cavity cover below.

[0007] As a further improvement of the present invention, the suspension cavity also includes a fixed side plate, a movable side plate and a bottom plate; when the movable side plate is removed, it facilitates the loading and unloading or maintenance of the workpiece stage in the suspension cavity.

[0008] As a further improvement of the present invention, the cavity cover is provided with a water cooling assembly, the water cooling assembly including a Z-shaped groove and a rectangular panel, the rectangular panel covering the Z-shaped groove, the Z-shaped groove being fixed to the side of the cavity cover and located above the laser, so as to achieve cooling of the laser mounting area.

[0009] As a further improvement of the present invention, the water cooling assembly further includes an annular groove and an annular panel. The annular groove is disposed on the inner side of the cavity cover, and the flange hole of the cavity cover is located inside the annular groove. The annular panel covers the annular groove.

[0010] As a further improvement of the present invention, the annular groove is a two-layer annular cooling channel connected in series.

[0011] As a further improvement of the present invention, the Z-shaped groove and the annular groove are each provided with a corresponding water inlet and water outlet, and the water inlet and water outlet are both connected to an external constant temperature controller.

[0012] As a further improvement of the present invention, the interference mirror includes a single-output interference mirror and a three-output interference mirror; the beam splitter divides the laser beam into two parts in the vertical direction, which respectively enter the single-output interference mirror and the three-output interference mirror, and then are projected onto the reflector on the workpiece table; the single-output interference mirror is used to measure the distance in the Y direction of the laser at a single point; the three-output interference mirror is used to measure the distance in the X direction of the laser at the first point, the second point and the third point distributed in a "pin" shape.

[0013] As a further improvement of the present invention, a height adjustment support foot is provided in the suspension cavity, and the height adjustment support foot is arranged at the bottom of the workpiece table to adjust the height of the workpiece table.

[0014] Compared with the prior art, the advantages of the present invention are as follows: 1. The laser interference measurement system including the suspended workpiece table of the present invention suspends the suspension cavity in the vacuum cavity, sets both the workpiece table and the measurement mirror group on the suspension cavity, and uses a double-layer cavity to form the system. The outer vacuum cavity provides a vacuum environment, and the inner suspension cavity provides a supporting function, greatly eliminating the influence of vacuum deformation on the measurement optical path, well meeting the requirements of the equipment for a high-precision laser workpiece table under vacuum conditions, and significantly improving the operation stability of the laser workpiece table in a vacuum environment.

[0015] 2. The laser interference measurement system including the suspended workpiece table of the present invention considers that the influence of vacuum deformation cannot be completely eliminated, uses an interference mirror with three-axis light output to measure the attitude of the workpiece table, and reduces the influence of optical path deformation on the measurement accuracy through correction. At the same time, in the design of the cavity cover, a cooling flow channel with a specific structure is used to reduce the influence of heat sources and eliminate the interference risk caused by cavity deformation, better meeting the operation stability of the laser workpiece table in a vacuum environment, and is particularly suitable for equipment such as electron beam exposure machines that require a vacuum working condition and are extremely sensitive to measurement accuracy. Brief Description of the Drawings

[0016] Figure 1 It is a schematic structural principle diagram of the laser interference measurement system including the suspended workpiece table in a specific embodiment of the present invention; Figure 2 It is an exploded structural principle diagram of the laser interference measurement system in a specific embodiment of the present invention Figure 3 It is a schematic optical path diagram in a specific embodiment of the present invention; Figure 4 It is a schematic structural principle diagram of the water cooling channel in a specific embodiment of the present invention; Legend: 1. Vacuum cavity; 101. Cavity; 102. Cavity cover; 1020. Flange hole; 1021. Z-shaped groove arrangement; 1022. Rectangular panel; 1023. First water inlet; 1024. First water outlet; 1025. Annular groove; 1026. Annular panel; 1027. Second water inlet; 1028. Second water outlet; 2. Suspended cavity; 201. Suspended cavity top plate; 2011. Boss; 20 12. Circular hole channel; 202. First fixed side plate; 203. Second fixed side plate; 204. Third fixed side plate; 205. Movable side plate; 206. Base plate; 3. Height-adjustable support leg; 4. Laser; 5. Vacuum window; 6. Beam-splitter; 7. Beam splitter; 7011. Single-path point; 7021. First point; 7022. Second point; 7023. Third point; 8. Interferometer; 801. Single-path beam-emitting interferometer; 802. Three-path beam-emitting interferometer; 9. Reflector; 10. Workpiece stage. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0018] In the description of this invention, it should be understood that the terms "side", "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0019] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more unless otherwise explicitly specified.

[0020] Example This study addresses the issue of measurement accuracy being affected by optical path deformation caused by cavity deformation when transitioning from atmospheric pressure to a vacuum state in laser interferometry systems. It also prioritizes system stability, particularly the adverse effects of external temperature variations. Figure 1As shown, this invention provides a laser interferometry system including a suspended workpiece stage, comprising: a vacuum chamber 1, a suspended chamber 2, a workpiece stage 10, and a laser interferometry assembly. The vacuum chamber 1 includes a cavity 101 and a cavity cover 102; the cavity 101 adopts a welded structure, providing good sealing performance. The top of the suspended chamber 2 is connected to the inner side of the cavity cover 102, so that the suspended chamber 2 is suspended within the vacuum chamber 1; the workpiece stage 10 is disposed within the suspended chamber 2. The laser interferometry assembly consists of a laser 4, a vacuum window 5, a beam splitter 6, a beam splitter 7, an interferometer 8, a reflector 9, a signal receiver (installed in conjunction with the interferometer 8), and a fiber optic feedthrough flange. The laser 4 is located outside the vacuum cavity 1 and mounted below one side of the cavity cover 102. A beam splitter 6 is mounted along the light output direction to redirect the laser beam into the cavity 101. A vacuum window 5 is located on the side wall of the cavity 101, through which the laser beam enters the cavity 101. The beam splitter 7 and interferometer 8 are both located inside the cavity 101 and mounted on one side of the upper part of the suspended cavity 2. The reflector 9 is located inside the suspended cavity 2 and mounted on the workpiece stage 10. After passing through the vacuum window 5, the laser beam reaches the beam splitter 7, passes through the interferometer 8, and then strikes the reflector 9 on the workpiece stage 10.

[0021] In this embodiment, by suspending the suspension cavity 2 inside the vacuum cavity 1, and setting the workpiece stage 10 and the measuring mirror assembly on the suspension cavity 2, a double-layer cavity system is adopted. The outer vacuum cavity 1 provides a vacuum environment, and the inner suspension cavity 2 provides support. This greatly eliminates the influence of vacuum deformation on the measuring optical path, well meets the equipment's requirements for a high-precision laser workpiece stage under vacuum conditions, and significantly improves the operational stability of the laser workpiece stage under vacuum conditions. like Figure 1 As shown, the suspension cavity 2 is equipped with height adjustment feet 3, which are located at the bottom of the workpiece stage 10 for adjusting the height of the workpiece stage 10. The suspension cavity 2 is suspended inside the vacuum cavity 1 as an independent rigid body component. Since it is not a sealed cavity, it will not generate pressure difference deformation. Therefore, the relative positional relationship of the mirror assembly installed on the suspension cavity 2 will not change, ensuring the stability of the measurement optical path and reducing the thickness requirements of the cavity.

[0022] like Figure 1 and Figure 2As shown, the suspension cavity 2 includes a suspension top plate 201, on which a boss 2011 is provided. A circular hole channel 2012 is provided inside the boss 2011, aligning with the flange hole of the cavity cover 102. Fasteners are provided between the boss 2011 and the cavity cover 102, and the upper surface of the boss 2011 is in close contact with the inner wall of the cavity cover 102 to achieve a connection and fixation between the suspension cavity 2 and the cavity cover 102. The suspension cavity 2 is suspended entirely below the cavity cover 102. Except for the area where the boss 2011 is located, there is a gap of several millimeters between the top of the suspension top plate 201 and the inner wall of the cavity cover 102. Compared to large-area surface contact, this significantly reduces the parallelism requirement between the two contact surfaces, avoiding the tilting of the suspension cavity 2 caused by the inevitable deformation of the vacuum cavity 1 after the system is evacuated, which would affect the accuracy of the measurement optical path.

[0023] like Figure 1 As shown, the beam splitter 7 and the interference mirror 8 are installed on one side of the cavity cover 102 below.

[0024] like Figure 1 and Figure 2 As shown, the suspension cavity 2 also includes a first fixed side plate 202, a second fixed side plate 203, a third fixed side plate 204, a movable side plate 205, and a base plate 206. Except for the movable side plate 205, which serves as a maintenance window, the other plates are all fixed by strong connections such as welding and pin riveting. When maintenance of the workpiece stage 10 is required, the cavity cover 102 is lifted and removed from the suspension cavity 2, and then the movable side plate 205 is removed, allowing for the insertion and removal of the workpiece stage 10 or other maintenance operations within the cavity.

[0025] The deformation of the cavity caused by vacuum is unavoidable, and the adverse effects of temperature changes on the measurement optical path after vacuum deformation are even greater. However, the temperature changes during system operation can be controlled by certain means, which is an important guarantee for improving measurement accuracy. In this invention, temperature control is implemented to address the problem of temperature deformation of the vacuum cavity 1 causing changes in the measurement optical path and thus affecting measurement accuracy. Research has found that the part most affected by temperature deformation is the cavity cover 102. Therefore, a water-cooling component is designed for the cavity cover 102, using constant-temperature water to reduce its deformation due to temperature.

[0026] like Figure 1 and Figure 4As shown, a water-cooling assembly is provided on the cavity cover 102. The water-cooling assembly is mainly distributed in areas where heat sources may have an impact, primarily at the laser 4 mounting location and the connection points between the cavity cover 102 and other subsystems (such as the lens barrel in an electron beam exposure machine). The former is used to reduce the impact of heat generated by the laser 4, while the latter is used to reduce the impact from other subsystems and the overall environmental temperature changes. Specifically, the water-cooling assembly includes a Z-shaped groove 1021 and a rectangular panel 1022. The rectangular panel 1022 is welded onto the Z-shaped groove 1021, which is fixed to the side of the cavity cover 102 and located above the laser 4 to achieve cooling of the laser 4 mounting area.

[0027] like Figure 4 As shown, the water-cooling assembly also includes an annular groove 1025 and an annular panel 1026. The annular groove 1025 is disposed on the inner side of the cavity cover 102, and the flange hole 1020 of the cavity cover 102 is located inside the annular groove 1025. The annular panel 1026 covers the annular groove 1025. Further, the annular groove 1025 is a two-layer annular series cooling channel.

[0028] In this embodiment, the Z-shaped groove 1021 is provided with a first water inlet 1023 and a first water outlet 1024, and the annular groove 1025 is provided with a corresponding second water inlet 1027 and a second water outlet 1028. Each water inlet and each water outlet is connected to an external thermostat. The deformation of the cavity cover 101 is controlled by high-precision thermostat water control, thereby achieving stable measurement function.

[0029] like Figure 2 and Figure 3 As shown, the interferometer 8 includes a single-path interferometer 801 and a three-path interferometer 802. The beam splitter 7 divides the laser beam vertically into two, one reaching the X-axis measurement area and the other the Y-axis measurement area. The two laser beams enter the single-path interferometer 801 and the three-path interferometer 802 respectively, and then are directed towards the reflector 9 on the workpiece stage 10. The single-path interferometer 801 is used to measure the Y-axis distance of the laser at a single point 7011; the three-path interferometer 802 is used to measure the X-axis distance of the lasers at the first point 7021, the second point 7022, and the third point 7023, which are arranged in a triangular pattern. It is understandable that, in addition to the basic X-direction distance measurement, the spatial measurement of the torsional (Ry) angle and tilt (Rz) angle can also be achieved by calculating the difference between the three points 7021, 7022 and 7023, thereby detecting the changes in position and orientation of the workpiece stage 10 caused by the vacuum deformation of the cavity, and improving the accuracy of the measurement by correcting it with software.

[0030] In this embodiment, based on the influence of vacuum deformation on the laser optical path, a triangular interferometer 8 is used to detect the spatial attitude of the workpiece stage along one of the directional axes. The optical path offset angle and direction under atmospheric and vacuum conditions can be calculated and derived by measuring the changes in the three optical outputs, thereby enabling better correction and improving measurement accuracy. Furthermore, since the optical path mirror assembly is mounted through the suspension cavity 2, the influence of vacuum deformation on the positional relationship between the mirror assemblies can be ignored, thus achieving a greater measurement effect.

[0031] After the interferometers 8 in the X-axis and Y-axis measurement areas complete their measurements, the laser signal is received by a signal receiver mounted on the interferometer. The signal is then transmitted along an optical fiber (not shown in the accompanying drawings, not the focus of this invention) through a fiber optic feedthrough flange on the cavity (not shown in the accompanying drawings, not the focus of this invention), to an external measurement board. The control software then calculates and performs the measurement function. Compared to traditional XY-axis measurement schemes, the laser measurement scheme of this invention has more comprehensive measurement capabilities, especially in vacuum applications, where it can better leverage the high precision of laser interferometry.

[0032] In this embodiment, based on the suspension scheme, a series of structural designs are used to improve the system's stability. Firstly, the protrusion 2011 structure on the top plate 201 of the suspension cavity reduces unnecessary contact surfaces, lowering the parallelism requirements between the top plate 201 and the cavity cover 102. This significantly avoids the impact of deformation of the vacuum cavity 1 on the measurement optical path, while also reducing the heat source propagation path, greatly minimizing the adverse effects of heat transfer on the internal workpiece stage 10 and ensuring system stability. Secondly, the design of a constant-temperature cooling channel allows for constant-temperature control of the two locations most likely to generate heat sources without occupying space or affecting strength, further improving stability and anti-interference capabilities.

[0033] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A laser interferometric measurement system comprising a suspended workpiece stage, characterized in that, include: Vacuum cavity (1), suspension cavity (2), workpiece stage (10), and laser interferometry assembly; the vacuum cavity (1) includes a cavity (101) and a cavity cover (102), the top of the suspension cavity (2) is connected to the inside of the cavity cover (102) so that the suspension cavity (2) is suspended in the vacuum cavity (1); the workpiece stage (10) is disposed in the suspension cavity (2); The laser interferometry assembly includes a laser (4), a vacuum window (5), a beam-splitter (6), a beam splitter (7), an interferometer (8), and a reflector (9). The laser (4) is located outside the vacuum cavity (1) and installed below one side of the cavity cover (102). A beam-splitter (6) is installed along the light output direction to redirect the laser into the cavity (101). A vacuum window (5) is provided on the side wall of the cavity (101). The laser passes through the vacuum window (5) and enters the cavity (101). The beam splitter (7) and the interferometer (8) are both located inside the cavity (101) and installed on one side of the upper part of the suspended cavity (2). The reflector (9) is located inside the suspended cavity (2) and installed on the workpiece stage (10). After passing through the vacuum window (5), the laser reaches the beam splitter (7) and then, after passing through the interferometer (8), is directed towards the reflector (9) on the workpiece stage (10).

2. The laser interferometry system including a suspended workpiece stage according to claim 1, characterized in that, The suspension cavity (2) includes a suspension cavity top plate (201), on which a boss (2011) is provided. A circular hole channel (2012) is provided on the inner side of the boss (2011). The circular hole channel (2012) is aligned with the flange hole (1020) of the cavity cover (102). Fasteners are provided between the boss (2011) and the cavity cover (102), and the upper surface of the boss (2011) is in contact with the inner wall surface of the cavity cover (102) to realize the connection and fixation between the suspension cavity (2) and the suspension cavity top plate (201).

3. The laser interferometry system including a suspended workpiece stage according to claim 2, characterized in that, The beam splitter (7) and the interference mirror (8) are installed on one side of the cavity cover (102) below.

4. The laser interferometry system including a suspended workpiece stage according to claim 2, characterized in that, The suspension cavity (2) also includes a fixed side plate, a movable side plate (205) and a bottom plate (206); when the movable side plate (205) is removed, it is convenient to load or unload the workpiece table (10) in the suspension cavity (2) or to perform maintenance operations.

5. The laser interferometry system comprising a suspended workpiece stage according to any one of claims 1 to 4, characterized in that, The cavity cover (102) is provided with a water cooling assembly, which includes a Z-shaped groove (1021) and a rectangular panel (1022). The rectangular panel (1022) covers the Z-shaped groove (1021), which is fixed to the side of the cavity cover (102) and located above the laser (4) to achieve cooling of the laser (4) mounting area.

6. The laser interferometry system including a suspended workpiece stage according to claim 5, characterized in that, The water-cooling assembly also includes an annular groove (1025) and an annular panel (1026). The annular groove (1025) is disposed on the inner side of the cavity cover (102), and the flange hole (1020) of the cavity cover (102) is located inside the annular groove (1025). The annular panel (1026) covers the annular groove (1025).

7. The laser interferometry system including a suspended workpiece stage according to claim 6, characterized in that, The annular groove (1025) is a two-layer annular cooling channel connected in series.

8. The laser interferometry system including a suspended workpiece stage according to claim 6, characterized in that, The corresponding water inlets and water outlets are provided on the Z-shaped arranged groove (1021) and the annular groove (1025), and the water inlets and water outlets are both connected to an external constant temperature controller.

9. The laser interferometric measurement system comprising a suspended workpiece stage according to any one of claims 6 to 8, characterized in that, The interferometer (8) includes a single-output interferometer (801) and a triple-output interferometer (802); the beam splitter (7) divides the laser beam into two parts in the vertical direction, which respectively enter the single-output interferometer (801) and the triple-output interferometer (802), and then are projected onto the reflector (9) on the workpiece table (10); the single-output interferometer (801) is used for measuring the distance in the Y direction of the laser at the single-point position (7011); the triple-output interferometer (802) is used for measuring the distance in the X direction of the laser at the first position (7021), the second position (7022) and the third position (7023) distributed in a "pin" shape.

10. The laser interferometry system comprising a suspended workpiece stage according to any one of claims 6 to 8, characterized in that, The height-adjusting support feet (3) are arranged in the suspension cavity (2), and the height-adjusting support feet (3) are arranged at the bottom of the workpiece table (10) for adjusting the height of the workpiece table (10).

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