Compact and automatic refractive index characterization method and system suitable for photoetching system

Abstract

The invention discloses a compact and automatic refractive index characterization method and system suitable for a photoetching system, and the method comprises the following steps: after being collimated by a collimating lens, S light enters a polarization splitting prism; the electric 1 / 4 wave plate performs primary phase modulation on the S light, and the S light is reflected to the objective lens and focused to the surface of a substrate in the liquid to be measured; the S light is reflected back to the objective lens, one part of the S light is imaged by the industrial camera, and the other part of the S light is subjected to secondary phase modulation by the electric 1 / 4 wave plate; one part of the light enters a first small hole and a first photomultiplier, and the other part of the light enters a second small hole and a second photomultiplier; controlling the objective lens to move along the axial direction and recording the position; and solving the equation to obtain the refractive index of the liquid to be measured. The device can be used for automatically and accurately measuring the refractive index of the liquid to be measured in real time in a lossless manner, has no pollution to the environment, can be directly attached to an industrial photoetching system, and can be used for rapid focusing of a focal plane while playing a role in representing the refractive index.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor lithography technology, in particular to a compact and automatic refractive index characterization method and system suitable for a lithography system. BACKGROUND

[0002] In semiconductor lithography technology, the refractive index of photoresist is a core parameter affecting imaging quality and critical dimension control accuracy.

[0003] Traditionally, the characterization of photoresist refractive index mainly relies on offline measurement techniques such as Abbe refractometer or spectroscopic ellipsometer. Although Abbe refractometer is easy to operate, it needs to take samples separately and cannot reflect the actual state of the photoresist in the lithography machine, and there is a risk of sample contamination. Spectroscopic ellipsometer can provide high-precision data, but the equipment is large, the cost is high, and the measurement process is complex, and it is also difficult to integrate into the lithography system for real-time monitoring.

[0004] In recent years, although some research has tried to combine microfluidic technology with optical sensing to achieve in-situ measurement, these methods usually require complex independent systems and are difficult to integrate with existing lithography equipment in a compact manner.

[0005] Currently, the development bottleneck in this field is that existing characterization methods generally have three major problems: offline measurement, cumbersome operation, and difficulty in integration. Offline measurement cannot capture the dynamic changes in the refractive index of photoresist during the lithography process; cumbersome operation cannot meet the requirements of modern production lines for efficiency and automation; and difficulty in integration means that real-time, non-destructive online monitoring of photoresist cannot be achieved in a real production environment, which has become an implicit obstacle to improving the process window and control accuracy of advanced processes. SUMMARY

[0006] The present application aims to provide a compact and automatic refractive index characterization method and system suitable for a lithography system to solve the problems in the prior art. The method is simple and can accurately measure the refractive index of the liquid to be measured in real time, non-destructively and automatically, without polluting the environment. At the same time, through compact and modular design, it can be directly attached to an industrial lithography system, serving as a refractive index characterization while also being used for fast focusing of the focal plane.

[0007] To solve the above technical problems, the present application adopts the following technical solutions:

[0008] A compact and automatic refractive index characterization method suitable for a lithography system, characterized by comprising the following steps:

[0009] S1, the S light emitted by the laser is collimated by the collimating lens and then incident to the polarization beam splitter prism, which reflects the S light to the electric 1 / 4 wave plate;

[0010] S2. The electric quarter-wave plate modulates the phase of the S-beam once. The modulated S-beam is reflected by the beam splitter to the objective lens controlled by the piezoelectric displacement stage. The objective lens focuses the S-beam onto the substrate surface in the liquid to be tested. The piezoelectric displacement stage can control the objective lens to move at a response speed in milliseconds.

[0011] S3. The S-beam is reflected back to the objective lens by the substrate. A portion of the S-beam is reflected by the beam splitter to the motorized quarter-wave plate for secondary phase modulation. The modulated S-beam passes through the polarizing beam splitter to become the P-beam. The angle of the motorized quarter-wave plate is adjusted to control the component of the P-beam.

[0012] S4. The P-beam components pass through the polarizing beam splitter and reach the focusing lens. The P-beams, after being focused by the focusing lens, enter the depolarizing beam splitter. Part of the P-beams are reflected by the depolarizing beam splitter and enter the first small aperture and the first photomultiplier tube perpendicularly. The other part of the P-beams are reflected by the mirror through the depolarizing beam splitter and enter the second small aperture and the second photomultiplier tube perpendicularly.

[0013] S5. Control the piezoelectric displacement stage to move along the axial direction with the astroscope, and record the position of the piezoelectric displacement stage when the light signal of the first photomultiplier tube is at its maximum, when the light signal of the second photomultiplier tube is at its maximum, and when the light signals of the first photomultiplier tube and the second photomultiplier tube are equal.

[0014] S6. Based on the position of the piezoelectric displacement stage, the refractive index of the liquid to be tested is obtained by solving the equation.

[0015] This method is simple in procedure and can accurately measure the refractive index of the liquid under test in real time, without damage, and automatically. It is also environmentally friendly. Furthermore, through its compact and modular design, it can be directly attached to industrial lithography systems, serving as a refractive index characterizer and also enabling rapid focusing of the focal plane.

[0016] A refractive index characterization apparatus for implementing a compact, automated refractive index characterization method suitable for photolithography systems as described above, comprising:

[0017] A piezoelectric displacement stage, connected to the objective lens, is used to control the axial movement of the objective lens;

[0018] Objective lens, used to focus S-beams onto the substrate surface of the liquid to be tested;

[0019] Industrial cameras, used for imaging;

[0020] Its features are:

[0021] It also includes a laser for emitting S-beams;

[0022] A collimating lens, located in the output optical path of the laser, is used to collimate the S-beam;

[0023] A polarizing beam splitter, located on the collimating optical path, is used to reflect S-beams;

[0024] An electrically operated quarter-wave plate is located in the reflected light path of a polarizing beam splitter and is used to modulate the phase of the S-ray.

[0025] The beam splitter, located in the modulation path of the motorized quarter-wave plate, is used to reflect the S-ray to the objective lens;

[0026] A focusing lens, located in the projection path of a polarizing beam splitter, is used to focus P-beams;

[0027] A depolarizing beam splitter is located on the output light path of the focusing lens and is used to split the P-beam into a first light path and a second light path.

[0028] The first small aperture and the first photomultiplier tube are located on the first optical path;

[0029] The second small aperture and the second photomultiplier tube are located on the second optical path;

[0030] The reflector, located in the second optical path, is used to reflect P-beams to the second pinhole.

[0031] This refractive index characterization device, with its compact and modular design, can be directly attached to industrial lithography systems, meeting the requirements for offline measurement. It is also easy to operate and can effectively improve the process window and control accuracy of advanced manufacturing processes.

[0032] The present invention, by adopting the above-described technical solution, has the following beneficial effects:

[0033] 1. The method of the present invention has simple steps and can not only measure the refractive index of the liquid under test in real time, without damage and automatically, but also has no pollution to the environment. While playing the role of refractive index characterization, it can also be used for rapid focusing of the focal plane.

[0034] 2. The refractive index characterization device of the present invention, through its compact and modular design, can be directly attached to an industrial lithography system, meeting the requirements of offline measurement. At the same time, it is easy to operate and can effectively improve the process window and control accuracy of advanced manufacturing processes. Attached Figure Description

[0035] The present invention will be further described below with reference to the accompanying drawings:

[0036] Figure 1 This invention provides a compact and automated method for characterizing refractive index in a photolithography system, along with a flowchart of the characterization method within the system.

[0037] Figure 2 This is a structural block diagram of the system in this invention;

[0038] Figure 3 This is a graph showing the change of refractive index over time in this invention.

[0039] Wherein: 1-Laser; 2-Collimating lens; 3-Polarizing beam splitter; 4-Electrified quarter-wave plate; 5-Beam splitter; 6-Piezoelectric displacement stage; 7-Objective lens; 8-Liquid to be tested; 9-Substrate; 10-Industrial camera; 11-Focusing lens; 12-Depolarizing beam splitter; 13-First pinhole; 14-First photomultiplier tube; 15-Reflector; 16-Second pinhole; 17-Second photomultiplier tube. Detailed Implementation

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0042] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0043] like Figure 1 As shown, this invention provides a compact and automated method for refractive index characterization suitable for photolithography systems, comprising the following steps:

[0044] S1. The S-beam emitted from laser 1 (which is the laser beam with the vertical polarization direction) is collimated by collimating lens 2 and then incident directly onto polarizing beam splitter 3. Polarizing beam splitter 3 reflects the S-beam onto motorized quarter-wave plate 4. Due to the characteristics of polarizing beam splitter 3, most of the S-beam is reflected into motorized quarter-wave plate 4.

[0045] Define the fast axis direction of the electro-driven quarter-wave plate 4 as the X-axis and the slow axis direction as the Y-axis. Assume the angle between the S-beam and the fast axis of the electro-driven quarter-wave plate 4 is θ. Therefore, the Jones vector of the S-beam incident on the electro-driven quarter-wave plate 4 is:

[0046] (1)

[0047] The Jones matrix of the electrically driven quarter-wave plate 4 for normally incident light is:

[0048] (2)

[0049] S2 and the electric quarter-wave plate 4 perform phase modulation on the S-light once. The modulated S-light is reflected by the beam splitter 5 to the entrance pupil of the objective lens 7 controlled by the piezoelectric displacement stage 6. The objective lens 7 focuses the S-light onto the surface of the substrate 9 in the liquid to be tested 8. The piezoelectric displacement stage 6 can control the objective lens 7 to move at a response speed in milliseconds.

[0050] In this invention, the liquid to be tested 8 is preferably a photoresist, and the substrate 9 is preferably a silicon wafer.

[0051] The process also includes a focusing step: when observing a silicon wafer coated with the refractive index to be measured, the piezoelectric displacement stage 6 can be moved to find the position of the piezoelectric displacement stage 6 when the light signals of the first photomultiplier tube 14 and the second photomultiplier tube 17 are equal, thus achieving rapid positioning of the focal plane of the substrate 9. When the substrate 9 of the liquid to be measured 8 is not a silicon wafer, the light signal intensity of the first photomultiplier tube 14 and the second photomultiplier tube 17 can be controlled in real time by an electrically driven quarter-wave plate 4.

[0052] S3 and S-beams are reflected back to objective lens 7 by substrate 9. Part of the S-beams are reflected by beam splitter 5 to industrial camera 10 for imaging, and another part of the S-beams are reflected by beam splitter 5 to motorized quarter-wave plate 4 for secondary phase modulation. The modulated S-beams are then passed through polarizing beam splitter prism 3 to become P-beams (which are parallel polarized light).

[0053] Since reflection does not change the polarization state of the incident light, its Jones matrix can be considered as the identity matrix:

[0054] (3)

[0055] In summary, after the S-beam passes through the electrodynamic quarter-wave plate 4 and is reflected back to the electrodynamic quarter-wave plate 4 by the silicon wafer, the overall Jones matrix is:

[0056] (4)

[0057] The Jones vector of the S-beam transmitted through the electrodynamic quarter-wave plate 4 is:

[0058] (5)

[0059] Therefore, it can be concluded that the modulated S-light becomes P-light after passing through polarizing beam splitter 3, and the intensity ratio of the P-light is:

[0060] (6)

[0061] (7)

[0062] Among them, P rate E represents the intensity ratio of P light. pThe P-component of the laser light that passes through the electrically driven quarter-wave plate 4 twice. Let be the unit vector in the direction of P-beam.

[0063] By adjusting the angle of the motorized quarter-wave plate 4, the component of the P-light that is transmitted twice through the motorized quarter-wave plate 4 can be controlled.

[0064] The components of S4 and P light pass through the polarizing beam splitter 3 and reach the focusing lens 11. The P light, after being focused by the focusing lens 11, enters the depolarizing beam splitter 12. Part of the P light is reflected by the depolarizing beam splitter 12 and enters the first small hole 13 perpendicularly, and then enters the first photomultiplier tube 14. The other part of the P light is reflected by the mirror 15 through the depolarizing beam splitter 12 and enters the second small hole 16 perpendicularly, and then enters the second photomultiplier tube 17.

[0065] When objective lens 7 is in a standard refractive index matching solution (n=1.518), its effective focal length is 3mm. When the silicon wafer is located at the focal plane of objective lens 7, the P-light reflected by the silicon wafer is parallel light when it reaches focusing lens 11. Therefore, when the P-light passes through focusing lens 11, it will be focused at the rear focal plane of focusing lens 11. The axial position of the first pinhole 13 is located 20mm in front of the rear focal plane of focusing lens 11, and the axial position of the second pinhole 16 is located 20mm behind the rear focal plane of focusing lens 11.

[0066] Since the silicon wafer behind objective lens 7 can be considered as a plane mirror, if the working distance of objective lens 7 changes by u, the reflected light from the silicon wafer can be equivalent to a virtual light source that has moved 2u from the focal point, and objective lens 7 then images this virtual light source.

[0067] When objective lens 7 is in a medium with different refractive indices, it is equivalent to an ideal lens with a fixed focal length, which is: The expression is:

[0068] (8)

[0069] (9)

[0070] in, n is the equivalent focal length of objective lens 7 in air, n1 is the refractive index of the liquid 8 to be tested, and n0 is the refractive index of the known liquid. Let be the equivalent focal length in a liquid with a known refractive index.

[0071] When the piezoelectric displacement stage 6 moves the objective lens 7 axially, if the working distance of the objective lens 7 increases by u, the axial distance from the objective lens 7 to the focusing lens 11 will correspondingly decrease by u. Since the reflected light from the silicon wafer can be equivalent to a virtual light source that has moved 2u from the focal point, the image point position of this virtual light source after passing through the objective lens 7 and the focusing lens 11 can be calculated using the Gaussian formula:

[0072] (10)

[0073] (11)

[0074] (12)

[0075] (13)

[0076] in, The object distance of the virtual light source. d is the image distance of the virtual light source after being imaged by objective lens 7, and d is the distance from objective lens 7 to focusing lens 11 when objective lens 7 is at the focal plane. The object distance is the distance between the image point of the virtual light source after imaging through objective lens 7 and the object point of focusing lens 11. This represents the image distance of the corresponding image point after imaging by focusing lens 11. This is the focal length of the focusing lens 11.

[0077] By calculating equations (8) to (13), the focal position of light behind the focusing lens 11 after the working distance of objective lens 7 changes can be obtained:

[0078] (14)

[0079] It also includes a calibration step: when the objective lens 7 is located at the focal plane, the focusing lens 11 is moved axially to make the light signal reading of the first photomultiplier tube 14 equal to the light signal reading of the second photomultiplier tube 17, thereby calibrating the installation error of the first small hole 13 and the second small hole 16.

[0080] When the focal point of the P-beam is located at the first aperture 13 and the second aperture 16, the light signals received by the first photomultiplier tube 14 and the second photomultiplier tube 17 are the strongest, which correspond to the increase in the working distance of the unique objective lens 7, denoted as u1 and u2, respectively, and can be directly read by the piezoelectric displacement stage 6.

[0081] When objective lens 7 is located at the focal plane, the initial number of piezoelectric displacement stage 6 is recorded as p0.

[0082] S5. During the process of controlling the piezoelectric displacement stage 6 to move along the axial direction with the objective lens 7, the reading of the piezoelectric displacement stage 6 is recorded as the first position p1 when the light signal of the first photomultiplier tube 14 is at its maximum, the reading of the piezoelectric displacement stage 6 is recorded as the second position p2 when the light signal of the second photomultiplier tube 17 is at its maximum, and the reading of the piezoelectric displacement stage 6 is recorded as the third position p3 when the light signals of the first photomultiplier tube 14 and the second photomultiplier tube 17 are equal.

[0083] Since the axial position of the first small hole 13 is located in front of the rear focal plane of the focusing lens 11, and the axial position of the second small hole 16 is located behind the rear focal plane of the focusing lens 11, the following relationship exists:

[0084] (15)

[0085] (16)

[0086] The positions of the first small hole 13 and the second small hole 16 can be calculated by simultaneously solving equations (8) to (14). and :

[0087] (17)

[0088] (18)

[0089] Among them, equations (17) and (18) are equivalent to Regarding u, n1 , The expression for d, and u1, u2, , , d are both known numbers.

[0090] S6. Based on the first position p1, the second position p2 and the third position p3, the refractive index of the liquid to be tested 8 is obtained by solving the equation.

[0091] Since the relative distance between the first small hole 13 and the second small hole 16 is 40mm, equations (17) and (18) can be combined to obtain the following equation:

[0092] (19)

[0093] Where u1 and u2 are the changes in the working distance of objective lens 7, and n1 is the refractive index. The equivalent focal length of objective lens 7 in air, Let d be the focal length of focusing lens 11, and d be the distance from objective lens 7 to focusing lens 11. This is the image distance of the corresponding image point after imaging by the focusing lens 11.

[0094] Let u1 be an equation with respect to n1, and u1 > 0, u2 < 0. Since equations (17) and (18) are rational functions with respect to n1, when n1 > 0... continuous.

[0095] In addition, through calculation The partial derivative with respect to n1 can be used to prove that when n1 > 0 Since it is monotonic, n1 can be solved to obtain the refractive index value of the liquid 8 being tested. Given u1, u2, and n1, , After obtaining the value of d, a unique value of n1 (n1 > 0) can be calculated.

[0096] Specifically, when u1 > 0 and u2 < 0, let u1 = a and u2 = b. According to equations (8) to (19), we can rearrange them to obtain the following equation:

[0097] (20)

[0098] Where n1 > 0, the refractive index n1 of the liquid 8 to be tested can be calculated from the values ​​of u1 and u2.

[0099] In particular, since the positions of the first small hole 13 and the second small hole 16 are symmetrical about the back focal plane of the focusing lens 11, we can approximate u1 = -u2, that is, b = -a. According to equations (8) to (19), we can obtain the following equation:

[0100] (twenty one)

[0101] Therefore, the refractive index n1 of the liquid 8 under test can be calculated from the value of u1. When the piezoelectric displacement stage 6 increases by u1 and u2, the light signal values ​​of the first photomultiplier tube 14 and the second photomultiplier tube 17 reach their maximum values, respectively. The peak-to-peak distance is recorded as u1-u2. The relationship curve between u1-u2 and the refractive index n1 of the liquid 8 under test is calculated as follows: Figure 3 As shown.

[0102] This method is simple in procedure and can accurately measure the refractive index of the liquid 8 under test in real time, without damage, and automatically. It is also environmentally friendly. Furthermore, through its compact and modular design, it can be directly attached to industrial lithography systems, serving as a refractive index characterizer and also enabling rapid focusing of the focal plane.

[0103] like Figure 2 As shown, this invention provides a refractive index characterization apparatus for implementing a compact, automated refractive index characterization method suitable for photolithography systems, comprising:

[0104] Laser 1 is used to emit S-beams. Laser 1 is preferably a probe laser 1, and the laser emitted by the probe laser 1 is deflected in a vertical polarization direction.

[0105] Collimating lens 2 is located in the output optical path of the laser 1 and is used to collimate the S-beam;

[0106] The polarizing beam splitter 3 is located on the collimating optical path and is used to reflect the S-ray;

[0107] An electrically driven quarter-wave plate 4 is located on the reflected light path of the polarizing beam splitter 3 and is used to modulate the phase of the S-beam.

[0108] Beam splitter 5, located on the modulation optical path of motorized quarter-wave plate 4, is used to reflect S-rays to objective lens 7. The transmission / reflection ratio of beam splitter 5 is 1:99.

[0109] The piezoelectric displacement stage 6 is connected to the objective lens 7 and is used to control the axial movement of the objective lens 7.

[0110] Objective 7 is used to focus the S-beam onto the surface of the substrate 9 of the liquid to be tested 8. Objective 7 is an Olympus oil-immersion objective 7 with a focal length of 3mm and a numerical aperture of 1.42 (the oil refractive index of objective 7 is 1.518). The substrate 9 needs to be a smooth and flat solid, and silicon wafers can generally be selected.

[0111] The industrial camera 10 is located on the reflected light path of the beam splitter 5 and is used for imaging. The industrial camera 10 has a built-in focusing lens 11, which can directly image the image.

[0112] The focusing lens 11 is located on the projection light path of the polarizing beam splitter 3 and is used to focus the P-beam. The focal length of the focusing lens 11 is 200mm and it can be electrically controlled to move axially.

[0113] The depolarization beam splitter 12 is located on the outgoing light path of the focusing lens 11 and is used to split the P-light into a first light path and a second light path. The transmission / reflection ratio of the depolarization beam splitter 12 is 1:1.

[0114] The first small aperture 13 and the first photomultiplier tube 14 are located on the first optical path;

[0115] The second aperture 16 and the second photomultiplier tube 17 are located on the second optical path; the aperture diameter of the first aperture 13 and the second aperture 16 is 50µm.

[0116] The reflector 15 is located in the second optical path and is used to reflect P light to the second pinhole 16.

[0117] The optical components within the dashed box constitute the main structure of this invention.

[0118] This refractive index characterization device, with its compact and modular design, can be directly attached to industrial lithography systems, meeting the requirements for offline measurement. It is also easy to operate and can effectively improve the process window and control accuracy of advanced manufacturing processes.

[0119] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to achieve substantially the same technical effect are all covered within the protection scope of the present invention.

Claims

1. A compact and automated method for refractive index characterization suitable for photolithography systems, characterized in that: Includes the following steps: S1. The S-beam emitted from the laser is collimated by a collimating lens and then incident on a polarizing beam splitter, which reflects the S-beam onto an electric quarter-wave plate. S2. The electric quarter-wave plate performs phase modulation on the S-beam once. The modulated S-beam is reflected by a beam splitter to an objective lens controlled by a piezoelectric displacement stage. The objective lens focuses the S-beam onto the substrate surface in the liquid to be tested. S3. The S-beam is reflected back to the objective lens by the substrate. A portion of the S-beam is reflected by the beam splitter to the motorized quarter-wave plate for secondary phase modulation. The modulated S-beam passes through the polarizing beam splitter to become the P-beam. The angle of the motorized quarter-wave plate is adjusted to control the component of the P-beam. S4. The component of the P-light passes through the polarizing beam splitter and reaches the focusing lens. After focusing, it enters the depolarizing beam splitter. Part of the P-light is reflected by the depolarizing beam splitter and enters the first small hole and the first photomultiplier tube perpendicularly. The other part of the P-light is reflected by the mirror through the depolarizing beam splitter and enters the second small hole and the second photomultiplier tube perpendicularly. S5. Control the piezoelectric displacement stage to move the objective lens along the axial direction, and record the position of the piezoelectric displacement stage when the light signal of the first photomultiplier tube is at its maximum, when the light signal of the second photomultiplier tube is at its maximum, and when the light signals of the first photomultiplier tube and the second photomultiplier tube are equal. S6. Based on the position of the piezoelectric displacement stage, the refractive index of the liquid to be tested is obtained by solving the equation.

2. The compact and automated refractive index characterization method for photolithography systems according to claim 1, characterized in that: The liquid to be tested in step S2 is photoresist, and the substrate is a silicon wafer.

3. The compact and automated refractive index characterization method for photolithography systems according to claim 1, characterized in that: The modulated S-beam from step S3 passes through the polarizing beam splitter to become P-beam, and the intensity ratio of the P-beam is: ； Among them, P rate E represents the intensity ratio of P light. p This refers to the P-component of the laser light that passes through the electrodynamic quarter-wave plate twice. Let be the unit vector in the direction of P-beam.

4. The compact and automated refractive index characterization method for photolithography systems according to claim 1, characterized in that: Another portion of the S-light in step S3 is reflected by the beam splitter to the industrial camera for imaging.

5. The compact and automated refractive index characterization method for photolithography systems according to claim 1, characterized in that: In step S4, the axial position of the first small hole is located 20 mm in front of the rear focal plane of the focusing lens, and the axial position of the second small hole is located 20 mm behind the rear focal plane of the focusing lens.

6. The compact and automated refractive index characterization method for photolithography systems according to claim 1, characterized in that: When the objective lens is in a medium environment with different refractive indices, it is equivalent to an ideal lens with a fixed focal length, which is: The expression is: ； ； in, Let n be the equivalent focal length of the objective lens in air, n1 be the refractive index of the liquid to be measured, and n0 be the refractive index of the known liquid. Let be the equivalent focal length in a liquid with a known refractive index.

7. The compact and automated refractive index characterization method for photolithography systems according to claim 1, characterized in that: Between steps S4 and S5, there is also a calibration step: when the objective lens is located at the focal plane, the focusing lens is moved axially to make the light signal reading of the first photomultiplier tube equal to the light signal reading of the second photomultiplier tube, thereby calibrating the installation error of the first and second pinholes.

8. The compact and automated refractive index characterization method for photolithography systems according to claim 1, characterized in that: Step S2 also includes a focusing step: by moving the piezoelectric displacement stage, the light signals of the first photomultiplier tube and the second photomultiplier tube are made equal, thereby achieving rapid positioning of the focal plane of the substrate.

9. The compact and automated refractive index characterization method for photolithography systems according to claim 1, characterized in that: The equation in step S6 is: ； Where u1 and u2 are the changes in the objective lens working distance, and n1 is the refractive index. The equivalent focal length of the objective lens in air, Let be the focal length of the focusing lens, and d be the distance from the objective lens to the focusing lens. This is the image distance of the corresponding image point after imaging by the focusing lens.

10. A refractive index characterization apparatus for implementing a compact, automated refractive index characterization method suitable for photolithography systems as described in any one of claims 1 to 9, comprising: A piezoelectric displacement stage, connected to the objective lens, is used to control the axial movement of the objective lens; Objective lens, used to focus S-beams onto the substrate surface of the liquid to be tested; Industrial cameras, used for imaging; Its features are: It also includes a laser for emitting S-beams; A collimating lens, located in the output optical path of the laser, is used to collimate the S-beam; A polarizing beam splitter, located on the collimating optical path, is used to reflect the S-ray; An electrically operated quarter-wave plate is located on the reflected light path of the polarizing beam splitter and is used to perform phase modulation on the S-beam. A beam splitter, located in the modulation optical path of the motorized quarter-wave plate, is used to reflect the S-ray to the objective lens; A focusing lens, located in the projection optical path of the polarizing beam splitter, is used to focus P-beams; A depolarizing beam splitter is located on the outgoing light path of the focusing lens and is used to split the P-beam into a first light path and a second light path. The first small aperture and the first photomultiplier tube are located on the first optical path; The second small aperture and the second photomultiplier tube are located on the second optical path; A reflector, located in the second optical path, is used to reflect the P-light to the second small aperture.

11. A compact, automated refractive index characterization device for photolithography systems according to claim 10, characterized in that: The diameter of both the first and second small holes is 50µm.

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