Precise grating immersion measurement system and method based on liquid medium layer regulation

Abstract

This invention discloses a precision grating immersion measurement system and method based on liquid medium layer control, belonging to the field of optical measurement and photoelectric detection technology. The system includes an immersion grating ruler, a liquid medium layer, a packaging plate, and a reading head. A special liquid is used to construct a stable spatial diffraction light interference liquid medium layer environment between the reading head and the grating ruler. By utilizing liquid medium layers with different refractive indices, the position, depth, shape, and intensity of the spatial interference surface of the diffracted light are controlled, thereby adjusting the installation distance and tolerance between the reading head and the grating ruler, reducing the high-precision assembly requirements between the reading head and the grating ruler caused by the reduction in grating pitch. Simultaneously, by utilizing the differences in the influence of the flow field in the near-wall region and bulk region of different thin-film liquids on the diffraction light interference, different liquid medium layers are selected to effectively reduce the impact of vibration disturbances, environmental fluctuations, background noise, and light source heat dissipation on the measurement light field during precision grating measurement, ensuring long-term stable and high-precision measurement of the precision grating.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement and photoelectric detection technology, specifically relating to a precision grating immersion measurement system and method based on liquid medium layer control, which helps to improve the robustness of precision measurement under environmental disturbances, and is particularly suitable for technical fields such as ultra-precision machining, semiconductor manufacturing, and nano-positioning that require high-precision and high-stability displacement measurement. Background Technology

[0002] With the continuous evolution of ultra-precision machining technology and semiconductor manufacturing processes, increasingly higher requirements are being placed on the accuracy and stability of displacement measurement systems. Grating measurement systems, due to their advantages such as high measurement accuracy, strong anti-interference capability, and good environmental adaptability, have been widely used in CNC machine tools, coordinate measuring machines, semiconductor lithography equipment, and other fields.

[0003] In reflective grating measurement systems based on the Talbot imaging principle, traditional methods use air as the medium for optical diffraction interference. The Talbot effect (also known as the "Talbot effect"), first observed by Henry Fox-Talbot in 1836, refers to the phenomenon where, when a plane wave is incident on a periodic diffraction grating, the grating image repeats at a specific periodic distance away from the grating plane. This effect has been widely applied in interferometry and optical detection. Specifically, the Talbot image of the grating appears at a distance of [missing information - likely a distance in the original text]. z m = 2 mnd 2 / λ In the position ( z m for m Distance of the next Talbot image m It is a positive integer. n Let be the refractive index of the light propagation medium. d For the grating period, λThese special distances (where the incident light wavelength is 160 nm) are called Talbot distances. The Talbot effect of gratings is widely used in interferometry, laser array illumination, and laser phase locking. However, existing air-medium grating measurement systems face the following technical problems in practical applications: (i) Fluctuations in the air medium lead to decreased measurement accuracy. Air, as a diffraction interference medium, is highly susceptible to disturbances from ambient airflow, temperature gradients, and local pressure changes. These disturbances cause random fluctuations in the spatial diffraction interference field, directly coupling into noise in the measurement signal, severely limiting the system's repeatability and stability at the sub-micron and even nanometer scale. (ii) The contradiction between reducing the grating pitch and assembly tolerance is prominent. According to the Talbot effect, the Talbot distance (self-imaging distance) of the grating is proportional to the square of the grating pitch. To improve measurement resolution, a smaller grating pitch must be used, but this leads to a sharp reduction in the Talbot distance. This makes the installation tolerance between the reading head and the scale grating extremely stringent, significantly increasing the difficulty and cost of system integration and on-site debugging, becoming a key technical bottleneck restricting the miniaturization and practical application of high-precision grating measurement systems. (iii) Limited environmental adaptability. In industrial production environments, factors such as vibration disturbances, temperature changes, and background noise can be transmitted to the measurement optical field through the air medium, causing a decrease in measurement accuracy. Existing technologies lack effective means to isolate these environmental factors. (iv) Poor adjustability of measurement parameters. In traditional grating measurement systems, key parameters such as the position, depth, shape, and intensity of the spatial interference surface of diffracted light are fixed by the system structure, making it difficult to flexibly adjust according to actual measurement needs, thus limiting the system's adaptability to different operating conditions.

[0004] To address the aforementioned issues, some technological explorations have been undertaken in related fields. For example, in immersion lithography, filling the space between the last projection lens and the silicon wafer with a high-refractive-index liquid increases the numerical aperture (NA) of the projection lens, thereby improving the resolution and depth of focus of the lithography equipment. Simultaneously, research has proposed a reflective all-dielectric two-dimensional planar metrological grating suitable for planar grating measurement systems under immersion exposure conditions. Furthermore, in the field of grating interferometers, due to their better measurement stability under environmental disturbances compared to laser interferometers, grating interferometers have become the preferred solution for six-degree-of-freedom displacement measurement sensors on the silicon wafer stage in immersion lithography machines. However, the aforementioned technical solutions have not yet resolved the issue of adjusting the installation distance and tolerance between the reading head and the grating ruler.

[0005] Therefore, developing a new precision grating measurement system and method that can fundamentally overcome the defects of air medium and achieve flexible control of measurement parameters, while ensuring measurement accuracy, and improving the system's environmental adaptability, assembly tolerance, and parameter adjustability, will be of great significance to the technical field of high-precision displacement measurement. Summary of the Invention

[0006] This invention addresses the technical problems of existing Talbot imaging-based reflective grating measurement systems, such as susceptibility to disturbances in the air medium, small assembly tolerance, limited environmental adaptability, and non-adjustable measurement parameters. It provides a precision grating immersion measurement system and method based on liquid medium layer control.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a precision grating immersion measurement system based on liquid medium layer control, comprising: an immersion grating ruler and a reading head, wherein the immersion grating ruler is encapsulated with a liquid medium layer, the two ends of the liquid medium layer are respectively encapsulated by two encapsulation plates, and the lower part of the reading head is immersed in the liquid medium layer; The immersion grating ruler includes a grating ruler substrate and a grating line structure. The grating ruler substrate has a groove, and the grating line structure is a rectangular stripe array with equal periods etched on the bottom of the groove. The reading head includes a housing, a light source, an indicator grating, and a photodetector. The light source is encapsulated in the housing, and the indicator grating and photodetector are mounted on the bottom surface of the housing.

[0008] Furthermore, the photodetector is a photodiode, photomultiplier tube, or CMOS photoelectric unit, used to detect the light field information at a preset position in the liquid medium layer.

[0009] Furthermore, a liquid medium layer injection device is installed at one end of the reading head, which is used to inject a liquid medium layer into the groove.

[0010] Furthermore, the liquid medium layer injection device has a cavity structure for storing, guiding, and draining the liquid medium layer.

[0011] Furthermore, the immersion grating ruler is mounted on the workpiece stage, and the upper end of the reading head is mounted on the displacement stage.

[0012] Secondly, the present invention provides a precision grating immersion measurement method based on liquid medium layer modulation, comprising the following steps: S1. The light emitted by the light source is diffracted by the indicator grating to form diffracted light, which then enters the liquid medium layer. The diffracted light overlaps in the liquid medium layer to form interference fringes, and the position of the interference fringes is the preset position. S2. Adjust the vertical distance between the indicator grating and the grating structure so that the grating structure is placed at the preset position; S3. At the preset position, the interference fringes and the grating structure form moiré fringes in the liquid medium layer; S4. The reading head and the immersion grating ruler move relative to each other along the direction of the grating structure, causing the moiré fringes to move and forming an optical signal of changing moiré fringes. S5. The optical signal of the changing moiré fringes is acquired and output by a photodetector.

[0013] Furthermore, in step S1, the liquid medium layer is injected by the liquid medium layer injection device.

[0014] Furthermore, in step S1, different preset positions are obtained by injecting liquid medium layers with different refractive indices.

[0015] Furthermore, in step S1, the preset position satisfies the following formula:

[0016] Where Δ is the distance from the preset position in the liquid medium layer to the indicator grating. m It is a positive integer. n The refractive index of the liquid medium layer, d To indicate the period of the grating, λ λ is the wavelength of the light source.

[0017] Furthermore, in step S2, the vertical distance between the indicator grating and the grating line structure is adjusted by adjusting the displacement stage.

[0018] Compared with the prior art, the present invention has at least the following beneficial technical effects: The measurement system provided by this invention significantly reduces assembly requirements and improves the practicality of the measurement system. Since the refractive index of liquids is greater than that of air, by filling the space between the reading head and the grating structure of the immersion grating ruler as a liquid medium layer, the Talbot distance can be effectively "stretched." This allows for a larger installation distance and tolerance between the reading head and the grating ruler while maintaining high resolution (small grating pitch). This directly solves the high-precision assembly problem caused by the reduction of grating pitch and reduces the manufacturing and maintenance costs of the system.

[0019] The measurement system provided by this invention has a compact structure and combines heat dissipation and cleaning functions. By using a liquid medium layer injection device and encapsulation plate installed on the right side of the reading head, a stable spatial diffraction light interference liquid medium layer environment can be constructed and maintained without significantly increasing the system volume. Simultaneously, the flowing liquid medium layer can efficiently dissipate heat generated by the internal light source and circuitry of the reading head, and wash away tiny particulate contaminants, thus achieving a dual function of active heat dissipation and self-cleaning.

[0020] Furthermore, the present invention provides a liquid guide on one side of the reading head. The cavity structure of the liquid guide is beneficial to guiding the flow direction and stabilizing the flow state during the injection of the liquid medium layer, reducing the interference of the liquid medium layer on the measurement optical field during injection, and can be used to adjust the liquid medium layer in real time during dynamic measurement.

[0021] The measurement method provided by this invention achieves a methodological innovation by transforming measurement parameters from "passively fixed" to "actively adjustable," fundamentally solving the problem of the difficulty in adjusting the diffraction interference surface. In traditional grating measurement methods, key optical parameters such as the Talbot distance and the position of the interference surface are uniquely determined by the grating pitch and wavelength, and are difficult to change once the system is assembled. This invention introduces a dynamic control step of "selection-injection-adjustment" of the liquid medium layer, treating the liquid refractive index as a new, real-time adjustable degree of freedom. Operators can flexibly select and inject special liquids with corresponding refractive indices according to different measurement accuracy requirements, environmental conditions, or installation conditions, achieving on-demand setting of the position, depth, shape, and intensity of the spatial interference surface. This methodological innovation allows the same hardware system to adapt to various measurement tasks, greatly improving the versatility and engineering applicability of the measurement method.

[0022] This invention provides an active environmental disturbance suppression method based on "liquid-stabilized field," significantly improving measurement robustness in harsh service environments. Unlike traditional methods that passively accept fluctuations in the air medium, this invention utilizes the flow field distribution in the near-wall and bulk regions within the liquid medium layer to provide a stable environment for optical interference. The liquid in the near-wall region, strongly constrained by the wall, exhibits high viscosity, incompressibility, shear layer effect, and damping characteristics against disturbances, significantly reducing the transmission of external vibrations and impacts to the measurement optical field. Simultaneously, the uniform flow in the bulk region actively mitigates refractive index inhomogeneities caused by temperature gradients. This active control method of "liquid-stabilized field" provides a novel dynamic stabilization approach for precision grating measurements, distinct from traditional passive vibration isolation. Compared to the air medium, the liquid medium layer provides a "quiet" and stable environment for the diffraction interference process, ensuring long-term, stable, and high-precision measurements of precision gratings even under harsh conditions such as industrial environments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the measurement system provided by the present invention; Figure 2 This is a structural diagram of an immersion grating ruler; Figure 3 Here is a structural diagram of the reading head; Figure 4a This is a structural diagram of the upper shell; Figure 4b This is a structural diagram of the lower shell; Figure 5a A structural diagram of a liquid medium layer injection device; Figure 5b This is a structural diagram of a liquid drainage device; Figure 6 A schematic diagram showing the change of a preset position in a liquid medium layer with different refractive indices; Figure 7 Simulation diagram of the interference variation of diffracted light in liquid media layers with different refractive indices; Figure 8 This is a simulation diagram of the flow field distribution in the liquid medium layer; Figure 9 A schematic diagram showing the formation of moiré fringes by interference fringes and grating structures in a liquid medium layer, and the movement of moiré fringes; Figure 10 A schematic diagram of the electrical signal output by a photodetector showing changing moiré fringes; Figure 11 Simulation diagram of density fluctuations in air and liquid media layers.

[0024] In the attached figures: 1-Immersion grating ruler; 11-Gramming ruler substrate; 12-Gramming line structure; 2-Liquid medium layer; 3-Encapsulation board; 4-Reading head; 41-Upper housing; 42-Lower housing; 43-Light source; 44-Indicating grating; 45-Photodetector; 46-Cable; 5-Liquid medium layer injection device; 51-Liquid drainer; 511-Cavity structure; 512-Outlet tube; 52-Fluid hose. Detailed Implementation

[0025] To more clearly explain the technical solution and purpose of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0026] The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0027] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not 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 the invention. 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 indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] Reference Figure 1A precision grating immersion measurement system based on liquid medium layer control includes an immersion grating ruler 1, a liquid medium layer 2, encapsulation plates 3, a reading head 4, and a liquid medium layer injection device 5. The liquid medium layer 2 is located within the immersion grating ruler 1, with the lower end of the reading head 4 immersed in it to a depth of 0.1 mm to 0.5 mm. The refractive index of the liquid medium layer 2 is greater than that of air, preferably a liquid with a refractive index greater than 1.3. The liquid medium layer injection device 5 is installed at the right end of the reading head 4 and is used to inject the liquid medium layer 2 into the immersion grating ruler 1. The liquid medium layer 2 is encapsulated at both ends of the immersion grating ruler along the x-axis by two encapsulation plates 3 installed at the left and right ends of the immersion grating ruler 1, respectively, to prevent the liquid medium layer 2 from flowing out. The lower end of the immersion grating ruler 1 is mounted on the workpiece stage, and the upper end of the reading head 4 is mounted on the displacement stage (the displacement stage is a three-axis displacement stage, which can drive the reading head 4 to move in three directions). The reading head 4 is parallel to the immersion grating ruler 1, and the two can make horizontal reciprocating movements along the x-axis. The thickness of the encapsulation plate 3 is 1.0 cm to 1.5 cm. The left and right encapsulation plates are exactly the same, only their installation positions are different.

[0030] Reference Figure 2 The immersion grating ruler 1 includes a grating ruler substrate 11 and a grating line structure 12. The grating ruler substrate 11 is a steel plate with grooves, and the grating line structure 12 is a rectangular stripe array arranged at equal periods along the x-axis direction. The bottom surface of the grooves on the grating ruler substrate 11 is etched at equal periods and uniformly by an etching method.

[0031] Reference Figure 3 , Figure 4a and Figure 4b The reading head 4 includes an upper housing 41, a lower housing 42, a light source 43, an indicator grating 44, a photodetector 45, and a cable 46. The reading head 4 is parallel to the grating structure 12 of the immersion grating ruler.

[0032] The lower end of the upper housing 41 and the upper end of the lower housing 42 are assembled and connected, encapsulating the light source 43, the indicator grating 44, and the photodetector 45 within the housing. The lower housing 42 has mounting holes for the indicator grating and the photodetector. The indicator grating 44 and the photodetector 45 are mounted and positioned within the lower housing through the mounting holes, and the connection is sealed with sealant. After installation, the lower surface of the indicator grating 44 is flush with the bottom surface of the lower housing 42. The light source 43 is connected and fixed by a cable 46, providing incident light to the indicator grating 44. The mounting holes for the indicator grating and the photodetector are manufactured according to the dimensions of the indicator grating 44 and the photodetector 45. The power supply and the light source 43 are connected via the cable 46, as are the photodetector 45 and the signal processing module. The power supply provides power to the light source 43, and the signal processing module receives the electrical signals converted by the photodetector 45.

[0033] The photodetector 45 is a photodiode, photomultiplier tube, or CMOS photoelectric unit, used to detect the light field information at a preset position in the liquid medium layer 2.

[0034] Reference Figure 5a and Figure 5b The liquid medium layer injection device 5 includes a liquid drainer 51 and a fluid hose 52. The outlet end of the fluid hose 52 is connected to the inlet end of the liquid drainer 51, and the inlet end is connected to a liquid injection pump, which can inject the liquid medium layer 2 into the liquid drainer 51. Meanwhile, the liquid drainer 51 includes a cavity structure 511 and an outlet tube 512. The outlet of the fluid hose 52 is connected to the inlet of the cavity structure 511, and the outlet of the cavity structure 511 is connected to the inlet end of the outlet tube 512. The outlet end of the outlet tube 512 is at the same level as the bottom surface of the lower housing 42 of the reading head. The liquid medium layer injection device 5 can store, guide, and drain the liquid medium layer 2 to the area below the reading head 4 and fill the immersion grating ruler 1.

[0035] A precision grating immersion measurement method based on liquid medium layer modulation includes the following steps: S1. The light emitted by the light source 43 is diffracted by the indicator grating 44 and then enters the liquid medium layer 2 to propagate. The propagated diffracted light overlaps in the liquid medium layer 2 to form stable interference fringes. The interference fringes are a set of periodic rectangular fringes with alternating bright and dark colors, located at a horizontal position at a certain distance from the indicator grating 44 in the liquid medium layer 2.

[0036] S2. Adjust the height of the indicator grating 44 by using a displacement stage so that the interference fringes overlap with the grating line structure 12 of the immersion grating ruler 1 at the same horizontal position. At this horizontal position, the superposition of the interference fringes and the grating line structure forms a moiré fringe.

[0037] S3, photodetector 45 receives the light intensity signal in the moiré fringes and converts it into an electrical signal for output.

[0038] S4. Moving the reading head 4 along the x-axis will change the moiré fringes in the liquid medium layer 2. Correspondingly, the electrical signal output by the photodetector 45 will change. The displacement and direction of movement of the reading head 4 can be determined by the subsequent signal processing module.

[0039] Reference Figure 6 After the liquid medium layer is injected into the groove of the immersion grating ruler, it forms a thin liquid film. The reading head is immersed in the liquid film to a very small depth, between 0.1 mm and 0.5 mm. For ease of demonstration, the upper housing 41, lower housing 42, and photodetector 45 are omitted here; only the diffracted light emitted from the light source 43 is shown after being diffracted by the indicator grating 44 and then propagating and interfering in the liquid medium layer 2. When the refractive index of the injected liquid medium layer 2 is different, the location of the interference fringes (i.e., the preset position) formed after the incident light is diffracted by the indicator grating is different. Therefore, various preset positions can be obtained by injecting different liquid medium layers 2. For example, when the refractive index of the liquid medium layer 2 is different... n 1< n 2< n 3< n At time 4, the distance Δ from the preset position in the liquid medium layer 2 to the indicator grating 44 increases sequentially. That is, by using the liquid medium layer 2 with a larger refractive index, the installation distance and installation tolerance between the indicator grating 44 and the immersion grating ruler 1 can be effectively increased.

[0040] The preset position is a horizontal position at a certain distance from the distance indicator grating 4 in the liquid medium layer 2, and it is also the position of the grating line structure 12 of the immersion grating ruler 1.

[0041] Reference Figure 6 In the calculation, the vertical distance Δ from the preset position to the indicator grating is:

[0042] Where Δ is the vertical distance from the location of the interference fringes in the liquid medium layer (preset position) to the indicator grating. m It is a positive integer. n The refractive index of the liquid medium layer, d To indicate the period of the grating, λ λ is the wavelength of the light source.

[0043] Reference Figure 7The method for adjusting the interference variation of diffracted light in liquid medium layer 2 is as follows: liquid medium layers 2 with different refractive indices are injected into the immersion grating ruler 1, thus changing the light field intensity of the interference fringes at the preset position. It can be seen that the light field intensity of the interference fringes in water is greater than that in glycerol. The higher light field intensity results in higher contrast in the moiré fringes, which is beneficial for improving measurement accuracy.

[0044] Reference Figure 8 In this invention, the immersion grating ruler 1 remains stationary, while the reading head 4 moves horizontally along the x-axis at a certain speed. The flow field distribution in the near-wall region and the bulk region of the liquid medium layer 2 differs. The near-wall region is a thin liquid layer (typically on the order of micrometers) adjacent to the grating line structure 12 and the lower surface of the indicator grating 44 of the immersion grating ruler 1. In this region, the liquid is subjected to strong viscous shear force from the wall, resulting in a very large velocity gradient and highly laminar flow. External high-frequency vibrations and pressure fluctuations are rapidly attenuated when penetrating this highly damped near-wall region. The bulk region, far from the wall, exhibits relatively uniform liquid flow, with refractive index and temperature uniformity primarily controlled through overall circulation.

[0045] Meanwhile, the heat generated by the light source 43 is first transferred to the liquid medium layer 2 and carried out of the measurement area through circulating flow, avoiding thermal deformation. The flowing liquid can also carry away tiny particles, achieving self-cleaning. Therefore, by selecting liquid medium layers 2 with different properties and actively controlling their flow field, this invention effectively reduces the impact of vibration disturbance, environmental fluctuations, background noise, and light source heat dissipation, ensuring long-term stable and high-precision measurement of the precision grating in harsh service environments and significantly improving the measurement robustness of the system.

[0046] Reference Figure 9 and Figure 10 When the reading head 4 moves horizontally along the x-axis, the interference fringes in the liquid medium layer 2 also move horizontally along the x-axis. The interference fringes and the moiré fringes formed by the grating structure change, and the moiré fringe electrical signal collected by the photodetector 45 changes. The displacement and direction of movement of the reading head can be determined by the subsequent signal processing module.

[0047] Reference Figure 11 When the reading head 4 moves horizontally along the x-axis, the density fluctuation in the liquid medium layer 2 is smaller than that in the air. Therefore, the optical diffraction interference environment in the liquid medium layer is more stable and the measurement accuracy is higher.

[0048] The relationship between the optical refractive index and the liquid density in liquid medium layer 2 satisfies the following formula:

[0049] in, n Let be the refractive index of liquid medium layer 2. NA Let Avogadro's constant be 1. α The molecular polarizability of liquid medium layer 2. ρ The density of liquid medium layer 2, ε 0 is the vacuum permittivity. M The molar mass of liquid medium layer 2 is given. This indicates that for a given liquid medium layer 2, the change in its optical refractive index is directly proportional to the change in density. This means that for liquid medium layer 2 with small density fluctuations, the change in light refractive index is small, the light field is more stable, and a good optical interference environment is provided, enhancing the anti-interference capability and robustness of precision measurement of the grating. This measurement system and method are particularly suitable for scenarios with extremely high requirements for accuracy and stability, such as silicon wafer stage displacement measurement in immersion lithography machines. The immersion grating ruler 1 of this invention is integrated into the silicon wafer stage motion platform, and the reading head 4 is fixed to the reference frame. A special liquid with matching refractive index and high thermal stability is injected between the reading head 4 and the grating ruler 1 through the liquid medium layer injection device 5. This system not only utilizes the inherent advantage of small environmental disturbances of the grating interferometer, but also further isolates the complex vibrations and thermal effects inside the lithography machine through the liquid medium layer, providing real-time position feedback at the nanometer or even sub-nanometer level for the silicon wafer stage, and possessing extremely high long-term stability.

[0050] This invention features a compact system structure, suitable for fields requiring high-precision and high-stability displacement measurement, such as ultra-precision machining, semiconductor manufacturing, and nano-positioning, and possesses excellent integration potential. By utilizing liquid media layers with different refractive indices, the position, depth, shape, and intensity of the spatial interference surface of diffracted light can be controlled, thereby adjusting the installation distance and tolerance between the reading head and the grating ruler, reducing the high-precision assembly requirements between the reading head and the grating ruler caused by the reduction in grating pitch. Simultaneously, within the confined liquid space between the reading head and the grating ruler, the differences in the influence of the flow fields in the near-wall and bulk regions of different thin-film liquids on the interference of diffracted light are utilized to select different liquid media layers. This effectively reduces the impact of vibration disturbances, environmental fluctuations, background noise, and light source heat dissipation on the measurement light field in precision grating measurements, ensuring long-term stable and high-precision measurement of precision gratings. This system reduces the impact of spatial light interference medium fluctuations on measurement accuracy in traditional grating measurements and improves the robustness of precision grating measurements in harsh service environments.

[0051] Finally, it should be noted that the above descriptions are merely examples of the present invention and are not intended to limit the invention. The liquid medium layer encapsulation method that can be used with respect to the present invention is not limited to the one described above. Although the present invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A precision grating immersion measurement system based on liquid medium layer regulation, characterized in that, It includes an immersion grating ruler (1) and a reading head (4). The immersion grating ruler (1) is encapsulated with a liquid medium layer (2). The two ends of the liquid medium layer (2) are respectively encapsulated by two encapsulation plates (3). The lower part of the reading head (4) is immersed in the liquid medium layer (2). The immersion grating ruler (1) includes a grating ruler substrate (11) and a grating line structure (12). The grating ruler substrate (11) has a groove, and the grating line structure (12) is a rectangular stripe array etched at the bottom of the groove with equal periodicity. The reading head (4) includes a housing, a light source (43), an indicator grating (44), and a photodetector (45). The light source (43) is encapsulated in the housing, and the indicator grating (44) and the photodetector (45) are mounted on the bottom surface of the housing.

2. The precision grating immersion measurement system based on liquid medium layer regulation according to claim 1, characterized in that, The photodetector (45) is a photodiode, photomultiplier tube or CMOS photoelectric unit, used to detect the light field information at a preset position in the liquid medium layer (2).

3. The precision grating immersion measurement system based on liquid medium layer regulation according to claim 1, characterized in that, One end of the reading head (4) is equipped with a liquid medium layer injection device (5), which is used to inject a liquid medium layer (2) into the groove.

4. The precision grating immersion measurement system based on liquid medium layer control according to claim 3, characterized in that, The liquid medium layer injection device (5) has a cavity structure (511) for storing, guiding and draining the liquid medium layer (2).

5. The precision grating immersion measurement system based on liquid medium layer control according to claim 1, characterized in that, The immersion grating ruler (1) is mounted on the workpiece stage, and the upper end of the reading head (4) is mounted on the displacement stage.

6. A precision grating immersion measurement method based on liquid medium layer control, based on the measurement system according to any one of claims 1 to 5, characterized in that, The measurement method includes the following steps: S1. The light emitted by the light source (43) is diffracted by the indicator grating (44) to form diffracted light, and enters the liquid medium layer (2); the diffracted light overlaps in the liquid medium layer (2) to form interference fringes, and the position of the interference fringes is the preset position; S2. Adjust the vertical distance between the indicator grating (44) and the grating structure (12) so that the grating structure (12) is placed at the preset position; S3. At the preset position, the interference fringes and the grating structure (12) form moiré fringes in the liquid medium layer (2); S4, the reading head (4) and the immersion grating ruler (1) make relative translational movements along the arrangement direction of the grating structure (12), causing the moiré fringes to move and forming optical signals of changing moiré fringes; S5. The optical signal of the changing moiré fringes is acquired and output by a photodetector (45).

7. The precision grating immersion measurement method based on liquid medium layer control according to claim 6, characterized in that, In step S1, the liquid medium layer (2) is injected by the liquid medium layer injection device (5).

8. The precision grating immersion measurement method based on liquid medium layer control according to claim 6, characterized in that, In step S1, different preset positions are obtained by injecting liquid medium layers (2) with different refractive indices.

9. The precision grating immersion measurement method based on liquid medium layer control according to claim 6, characterized in that, In step S1, the preset position satisfies the following formula: Where Δ is the distance from the preset position in the liquid medium layer (2) to the indicator grating (44), m It is a positive integer. n Let be the refractive index of the liquid medium layer (2). d To indicate the period of the grating (44), λ The wavelength of the light source (43) is denoted as .

10. The precision grating immersion measurement method based on liquid medium layer control according to claim 6, characterized in that, In step S2, the vertical distance between the indicator grating (44) and the grating structure (12) is adjusted by adjusting the displacement stage.

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