Wave plate ellipsometer with variable azimuth angle and measuring method thereof

Abstract

The invention relates to the technical field of ellipsometers, and discloses a variable azimuth angle wave plate ellipsometer and a measuring method thereof, the wave plate ellipsometer comprises: a polarizing arm modulation unit comprising a light source and a polarizer, and the polarizer is located at the right side of the light source; the sample table is used for placing a to-be-tested sample; the polarization detection arm modulation unit comprises a compensator and a polarization analyzer; and the image sensor is used for sampling the emergent light beam of the polarization analyzer to obtain a light intensity modulation image. According to the variable azimuth angle wave plate ellipsometer, the structure is simple and stable, rapid measurement can be achieved, in-situ detection can be achieved, the wave plate unit is adopted in the polarization detection arm modulation unit, the flexibility and adaptability of measurement are improved, the wave plate azimuth angle can be flexibly adjusted according to different sample characteristics, light modulation of various samples is more effective, and various measurement requirements are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ellipsometry, in particular to a variable azimuth angle wave plate ellipsometer and a measurement method thereof. BACKGROUND

[0002] In the field of optical measurement, ellipsometry as an important measuring instrument plays a key role in analyzing the optical properties of samples, especially the polarization characteristics. Among them, the Chinese patent CN115060658B discloses a double-vortex wave plate Mueller matrix ellipsometer and a measurement method thereof. The double-vortex wave plate Mueller matrix ellipsometer includes a polarization modulation unit, the polarization modulation unit includes a light source, a polarizer and a first vortex quarter wave plate, a detection modulation unit includes a second vortex quarter wave plate and a detector; the light intensity modulation image alternately changes in brightness with the azimuth angle of the light intensity modulation image; a first analysis unit, a second analysis unit and a third analysis unit, the first analysis unit is adapted to obtain a light intensity modulation function according to the light intensity modulation image; the second analysis unit is adapted to perform Fourier analysis on the light intensity modulation function to obtain a Fourier expression; the third analysis unit is adapted to obtain the Mueller matrix of the sample to be measured according to the coefficients in the Fourier expression. The double-vortex wave plate Mueller matrix ellipsometer has the advantages of simple structure, good stability, fast measurement speed and simple solving process.

[0003] However, although the double-vortex wave plate Mueller matrix ellipsometer has the above advantages, there is still a key technical problem that has not been solved in practical application: the structural characteristics of the double-vortex wave plate used limit the measurement flexibility and adaptability of the instrument. The first vortex quarter wave plate and the second vortex quarter wave plate used by the instrument have specific vortex characteristics, and the order of the vortex wave plate is clearly defined. The fixed requirement for the order of the wave plate makes it difficult to flexibly adjust the performance parameters of the wave plate according to the specific characteristics of the sample when measuring samples with different optical characteristics (such as different refractive indices, birefringence characteristics, different thicknesses, etc.), thereby limiting the applicability of the ellipsometer in different measurement scenarios (such as different refractive indices, birefringence characteristics, different thicknesses, etc.).

[0004] For example, when some samples with special polarization state change requirements need to be measured, due to the inability to flexibly adjust the order of the wave plate, the light may not be effectively modulated, which in turn affects the formation of the subsequent light intensity modulation image and the accurate analysis of the optical characteristics of the sample by the analysis unit, ultimately affecting the accuracy and reliability of the measurement results. In many practical measurement scenarios, it may be necessary to dynamically adjust the relevant parameters of the wave plate according to the different characteristics of the sample to achieve more accurate and more extensive measurement, but the double-vortex wave plate Mueller matrix ellipsometer cannot meet this demand due to the limitation of the wave plate structure, which becomes a significant technical bottleneck in the application of optical measurement. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a variable azimuth wave plate ellipsometer and a measuring method thereof, and solves the problem that the measuring flexibility and adaptability of the existing double-vortex wave plate Mueller matrix ellipsometer are limited due to the fixed order of the double-vortex wave plate, and it is difficult to flexibly adjust the wave plate performance parameters according to different sample characteristics.

[0006] To achieve the above object, the present application is implemented by the following technical solutions: a variable azimuth wave plate ellipsometer, comprising:

[0007] A polarizing arm modulation unit comprises a light source and a polarizer, and the polarizer is located on the right side of the light source.

[0008] A sample stage is used for placing a sample to be measured.

[0009] A polarized light modulation unit comprises a compensator and an analyzer.

[0010] An image sensor is used for sampling the outgoing light beam of the analyzer to obtain a light intensity modulation image, and the light intensity of the light intensity modulation image alternately changes in brightness and darkness with the azimuth angle.

[0011] A first analysis unit obtains a light intensity modulation function with the azimuth angle of the light intensity modulation image as the independent variable and the light intensity value as the dependent variable according to the light intensity modulation image.

[0012] A second analysis unit performs Fourier analysis on the light intensity modulation function to obtain a Fourier expression.

[0013] A third analysis unit calculates the Mueller matrix of the sample to be measured according to the coefficients in the Fourier expression.

[0014] Preferably, the sample stage has a table center axis perpendicular to its surface, and the arrangement direction of the light source and the polarizer in the polarizing arm modulation unit is symmetrical to the arrangement direction of the variable azimuth wave plate and the analyzer in the polarized light arm modulation unit relative to the table center axis.

[0015] Preferably, the compensator is composed of multiple independent or continuous wave plate units with different azimuth angles on the same plane, and its function is that when the light wave propagates through different units on the wave plate, the polarization state of the light wave is modulated differently at different units; the above wave plate is a vortex wave plate manufactured by mask method, or a wave plate mechanically spliced by several independent small wave plates, wherein the small wave plates are liquid crystal wave plates controlled by light field modulation, or true zero-order, multi-order and achromatic wave plates processed by birefringent crystals.

[0016] Preferably, it further comprises a first position adjusting unit for adjusting the arrangement direction of the light source and the polarizer in the polarizing arm modulation unit.

[0017] Preferably, a second position adjusting unit is further included for adjusting the arrangement direction of the variable azimuth angle wave plate and the analyzer in the analyzer arm modulation unit.

[0018] Preferably, a third position adjusting unit is further included for switching between the horizontal placement position and the vertical placement position of the sample to be measured on the sample table.

[0019] Preferably, when the sample to be measured is a transmissive sample, the thickness direction of the sample to be measured is parallel to the surface of the sample table, and the arrangement direction of the light source, the polarizer, the variable azimuth angle wave plate and the analyzer is parallel to the surface of the sample table.

[0020] Preferably, when the sample to be measured is a reflective sample, the thickness direction of the sample to be measured is perpendicular to the surface of the sample table, and the arrangement direction of the light source and the polarizer forms an angle greater than zero with the surface of the sample table, and the arrangement direction of the variable azimuth angle wave plate and the analyzer also forms an angle greater than zero with the surface of the sample table.

[0021] Preferably, the compensator can be placed spatially after the polarizer to form a PCSA configuration, or placed after the sample table to form a PSCA configuration.

[0022] Preferably, a measurement method of the variable azimuth angle wave plate ellipsometer is provided for the variable azimuth angle wave plate ellipsometer, and the method comprises the following steps:

[0023] Placing the sample to be measured on the sample table;

[0024] Turning on the light source, and adjusting the arrangement direction of the light source and the polarizer in the polarizer arm modulation unit and the arrangement direction of the variable azimuth angle wave plate and the analyzer in the analyzer arm modulation unit according to the transmittance and reflectance of the sample to be measured;

[0025] Sampling the emergent light beam of the analyzer by the image sensor to obtain a light intensity modulation image;

[0026] Analyzing the light intensity modulation image to obtain a light intensity modulation function;

[0027] Performing Fourier analysis on the light intensity modulation function to obtain a Fourier expression;

[0028] Calculating the Mueller matrix of the sample to be measured according to the coefficients in the Fourier expression.

[0029] Preferably, the analysis of the light intensity modulation function is performed by mathematically processing the azimuth angle and the light intensity value of the light intensity modulation image, and establishing a functional relationship with the azimuth angle as the independent variable and the light intensity value as the dependent variable.

[0030] Preferably, in the Fourier analysis process, an efficient Fourier transform algorithm is used to process the light intensity modulation function to obtain an accurate Fourier expression.

[0031] The light intensity modulation function is processed by using a Fourier transform algorithm, an accurate Fourier expression is obtained, and then the Fourier coefficient is used to calculate the parameters of the sample;

[0032] For the PSCA type ellipsometer: the light wave before the detector is derived from the Mueller matrix: ;

[0033] Wherein,

[0034] Si: the polarization state of the incident light wave;

[0035] R(x): rotation matrix, x is the angle of counterclockwise rotation;

[0036] M P , M S , M C , M A : Mueller matrix of polarizer, sample, compensator and analyzer;

[0037] The direct current and alternating current components are obtained by using Fourier analysis method;

[0038] At the same time, the light intensity of the detector can also be expressed as

[0039] ;

[0040] Wherein, the direct current and alternating current components are:

[0041] ;

[0042] According to the above formula, the expression of the ellipsometric parameter is calculated as

[0043] ;

[0044] ;

[0045] For the PCSA type ellipsometer, only the parameter values of P and A in the above formula are exchanged to calculate the ellipsometric angle of the sample.

[0046] In addition, other similar methods can also be used to calculate the ellipsometric angle of the sample.

[0047] The application provides a variable azimuth angle wave plate ellipsometer and a measurement method thereof.

[0048] 1、The variable azimuth angle wave plate ellipsometer in the application has simple structure, no moving device, good stability, and can quickly measure and realize in-situ detection. In the application, a wave plate unit is used in the detection arm modulation unit, the flexibility and adaptability of measurement are improved, the wave plate azimuth angle can be flexibly adjusted according to different sample characteristics, the light modulation of various samples is more effective, and the demand of various measurement is met.

[0049] 2、The sample alignment system with microscope and telescope system can assist in adjusting the height and pitch of the sample table, accurately adjust the position and angle of the sample, ensure that the sample is in the best state during measurement, and improve the accuracy and reliability of measurement.

[0050] 3、The image sensor is used to capture the outgoing light beam of the analyzer, generate a light intensity modulation image, and intuitively reflect the light intensity information, which provides high-quality data for subsequent analysis and is beneficial to the extraction and analysis of the light intensity modulation function.

[0051] 4、The first, second and third analysis units can extract the function from the light intensity modulation image, obtain the accurate expression through Fourier analysis, and accurately calculate the Mueller matrix according to the key coefficient, so as to accurately characterize the optical properties of the sample and provide strong support for accurate measurement and calculation.

[0052] 5、The present application has reflection and transmission measurement modes, and is equipped with first, second and third position adjusting units, which can adjust the position according to the properties and requirements of the sample, realize various measurement modes, flexibly adjust the position of the components, improve the universality and practicability of the instrument, and meet the requirements of in-situ detection and rapid measurement.

[0053] 6、The overall structure is simple and stable, easy to operate and maintain, can ensure the stability of measurement, reduce the manufacturing and maintenance cost, and ensure the stable performance of the instrument, which provides a guarantee for long-term stable measurement. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 An embodiment of a variable azimuth wave plate ellipsometer according to the present application is shown in the figure;

[0055] Figure 2 Another embodiment of a variable azimuth wave plate ellipsometer according to the present application is shown in the figure;

[0056] Figure 3 A flowchart of a measurement method of a variable azimuth wave plate ellipsometer according to the present application is shown in the figure;

[0057] Figure 4 One of the implementation methods of the variable azimuth wave plate is that ten hole positions are evenly distributed in the circumferential direction on the circular base disc, each hole position can place a broadband quarter wave plate with only different azimuth angles, and the fast axis azimuth of each position wave plate is arranged in the radial direction.

[0058] Wherein, 1, polarizing arm modulation unit; 101, light source; 102, polarizer; 2, sample table; 201, sample to be measured; 3, detection arm modulation unit; 301, wave plate unit; 302, analyzer; 4, analysis processing system; 401, image sensor; 402, computer; 5, sample alignment system. DETAILED DESCRIPTION

[0059] The technical solutions of the present application will be described clearly and completely below in combination with the drawings of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0060] Technical concept: the variable azimuth wave plate ellipsometer and the measuring method thereof, the light of a specific polarization state is generated by the polarizing arm modulation unit 1, after reflection or transmission of the sample, the light is further modulated by the wave plate unit 301 and the analyzer 302 in the detection arm modulation unit 3, the light intensity modulation image is collected by the image sensor 401, and finally the Mueller matrix of the sample to be measured is obtained through the processing of multiple analysis units. The whole process involves the placement of the sample, the adjustment of the sample table 2, the arrangement adjustment of the light source and related components, and the collection and analysis of the light intensity modulation image, which can effectively overcome the shortcomings of the prior art, and provide accurate, flexible and efficient measurement scheme for samples with different characteristics.

[0061] The specific embodiments will be described below:

[0062] Please refer to the drawings Figure 1 - the drawings Figure 4 The embodiment of the present application provides a variable azimuth wave plate ellipsometer, which comprises:

[0063] The polarizing arm modulation unit 1 comprises a light source 101 and a polarizer 102, and the polarizer 102 is located on the right side of the light source 101.

[0064] The sample table 2 is used for placing the sample to be measured 201.

[0065] The detection arm modulation unit 3 comprises a compensator and an analyzer 302.

[0066] The sample alignment system 5 comprises a microscope and a telescope system, which is used for adjusting the height and pitch of the sample table 2.

[0067] The analysis processing system 4 comprises a computer 402 and an image sensor 401.

[0068] Among them, the image sensor 401 is used to sample the emitted beam of the analyzer 302 to obtain a light intensity modulated image, wherein the light intensity of the light intensity modulated image changes alternately with the azimuth angle.

[0069] Computer 402 includes a first analysis unit, a second analysis unit, and a third analysis unit;

[0070] The first analysis unit obtains a light intensity modulation function with the azimuth angle of the light intensity modulation image as the independent variable and the light intensity value as the dependent variable based on the light intensity modulation image; the second analysis unit performs Fourier analysis on the light intensity modulation function to obtain a Fourier expression; and the third analysis unit calculates the Mueller matrix of the sample to be tested based on the coefficients in the Fourier expression.

[0071] Specifically, Figure 1 For reflection measurement, Figure 2 For through-beam measurements, the light source 101 in the polarizer modulation unit 1 can be a high-power, high-stability laser source, emitting light with high energy and good stability, providing reliable light input for subsequent measurements. The polarizer 102 utilizes the polarization characteristics of light, selectively transmitting or blocking certain vibration directions of light to convert the unpolarized light emitted by the light source 101 into linearly polarized light. Its principle is based on the transverse wave characteristics of light, using physical mechanisms such as birefringence of materials to ensure that only polarized light in specific directions is allowed to pass through after passing through the polarizer 102. The polarizer 102 is located to the right of the light source 101, effectively receiving the light emitted by the light source 101 and performing polarization state conversion.

[0072] The sample stage 2 is a platform with a high-precision plane. Its surface flatness is precisely machined to ensure that when the sample 201 is placed on it, no additional measurement errors such as optical path difference will be introduced due to surface unevenness. It provides a stable bearing surface for the sample 201 to be tested, allowing the sample 201 to be in a precisely controllable measurement environment.

[0073] The microscopic system in sample alignment system 5 utilizes a high-magnification optical microscope, providing a clear microscopic field of view and facilitating precise placement of the tiny sample 201 in the ideal position. The telescope system offers a broader perspective, aiding in the overall observation of the relative position of sample 201 to the instrument, ensuring alignment of sample 201 with the entire optical path system. Through the combined use of these two systems, the operator can precisely control the height and pitch of the sample stage 2 via manual or electric adjustment knobs. For example, adjusting the knobs changes the height of the precision screw beneath the sample stage 2, raising and lowering it; the rotation mechanism adjusts the pitch, ensuring that sample 201 is positioned optimally on the optical axis during measurement, allowing light to enter and exit at the best angle, reducing measurement errors caused by sample 201 positional deviations.

[0074] The compensator is composed of multiple independent or continuous wave plate units 301 with different azimuth angles on the same plane. The function is that when the light wave propagates through different units of the wave plate, the polarization state of the light wave is modulated differently at different units. The wave plate is a vortex wave plate manufactured by mask method, or a wave plate composed of multiple independent small wave plates mechanically spliced together. The small wave plates are liquid crystal wave plates controlled by optical field, or zero-order, multi-order and achromatic wave plates processed by birefringent crystals. The variable azimuth angle characteristics of the wave plate unit 301 enable the azimuth angle gradient or continuous change of the wave plate within a certain range, thereby changing the polarization state of the light to adapt to different measurement requirements.

[0075] In an embodiment, by stepping the azimuth angle of the wave plate between 0° and 360°, a continuously variable wave plate can be placed on the spatial plane to achieve the compensation effect. The polarization state of the light after passing through the wave plate unit 301 is changed. The function of the polarizer 302 is to further screen the polarization state of the light modulated by the wave plate unit 301, and only allow light with a specific polarization state to pass through, providing different polarized light inputs for subsequent light intensity modulation image acquisition.

[0076] The image sensor 401 can be a high-resolution CCD or CMOS image sensor. The principle is to use the photoelectric effect of a semiconductor to convert the received light signal into an electrical signal, and through the arrayed pixels to convert the light intensity information into quantifiable digital signals. When receiving the light beam emitted by the polarizer 302, due to the influence of the sample 201 and the wave plate unit 301 in the previous modulation process, the light intensity modulation phenomenon will occur. The image sensor 401 will collect light intensity modulation images with alternating light and dark changes. This image can directly reflect the changes of light intensity at different azimuth angles, providing a rich data basis for subsequent data analysis.

[0077] The first analysis unit processes the light intensity modulation image collected by the image sensor 401, and according to the position information and corresponding light intensity value of each pixel point in the image, uses a special image processing algorithm and mathematical model to establish a light intensity modulation function with the azimuth angle of the light intensity modulation image as the independent variable and the light intensity value as the dependent variable.

[0078] The second analysis unit performs Fourier analysis on the light intensity modulation function obtained by the first analysis unit, and uses the fast Fourier transform (FFT) algorithm to convert the light intensity modulation function from the spatial domain (azimuth angle domain) to the frequency domain. This conversion can reveal the periodic components in the light intensity modulation function. The principle is to decompose a complex periodic function into the superposition of sine and cosine functions of different frequencies.

[0079] The third analysis unit calculates the Mueller matrix of the sample 201 according to the coefficients in the Fourier expression, in combination with the theory of polarization state of light and optical matrix operation. The Mueller matrix can completely describe the polarization state transformation of light after passing through the sample 201, and the calculation of the elements thereof involves complex optical theory and matrix operation.

[0080] In an embodiment, the sample stage 2 has a stage center axis perpendicular to its surface, and the arrangement directions of the light source 101 and the polarizer 102 in the polarizing arm modulation unit 1 and the arrangement directions of the wave plate unit 301 and the analyzer 302 are symmetrical with respect to the stage center axis.

[0081] The embodiment of the application further comprises a first position adjusting unit for adjusting the arrangement directions of the light source 101 and the polarizer 102 in the polarizing arm modulation unit 1.

[0082] The embodiment of the application further comprises a second position adjusting unit for adjusting the arrangement directions of the wave plate unit 301 and the analyzer 302 in the analyzing arm modulation unit 3.

[0083] The embodiment of the application further comprises a third position adjusting unit for switching between the horizontal placement position and the vertical placement position of the sample 201 on the sample stage 2.

[0084] Specifically, the stage center axis of the sample stage 2 serves as the symmetry reference of the entire system, and the polarizing arm modulation unit 1 and the analyzing arm modulation unit 3 are symmetrical in relative position, which helps to simplify the layout and adjustment process of the optical path, and improve the stability of the instrument and the accuracy of the measurement. When calibrating and adjusting the optical path, the propagation path of the light in the entire system can be more conveniently ensured to meet the design requirements by taking the stage center axis as the reference.

[0085] The first position adjusting unit adopts high-precision motorized translation stages and rotation stages, which can accurately adjust the positions and angles of the light source 101 and the polarizer 102 in the polarizing arm modulation unit 1 through motor driving and precise transmission mechanisms. The operator can input the required position and angle parameters through the computer control interface, and the motorized translation stages and rotation stages will adjust the light source 101 and the polarizer 102 to the precise positions. In an embodiment, the translation accuracy can reach the micron level, and the angle adjustment accuracy can reach 0.1°, so as to realize the accurate adjustment of the polarization state of light under different samples 201 and measurement scenarios.

[0086] The working principle of the second position adjusting unit is similar to that of the first position adjusting unit 601, and is used for fine adjustment of the wave plate unit 301 and the polarizer 302 in the polarizing arm modulation unit 3. During the placing process, it is necessary to ensure that the fast axis directions of the two wave plates are in the incident plane at the same azimuth angle, so as to ensure normal Fourier analysis. Through rotation and translation adjustment, the azimuth angle and position of the wave plate unit 301 and the polarizer 302 can be changed, so as to optimize the polarization state modulation effect of light and improve the flexibility and accuracy of measurement.

[0087] The compensator can be placed spatially after the polarizer to form a PCSA configuration, or can be placed after the sample table to form a PSCA configuration.

[0088] The third position adjuster adopts a reversible or slidable mechanism, which can conveniently switch the sample 201 between the horizontal position and the vertical position when the sample 201 of different shapes or different placement requirements needs to be measured. For some sheet-shaped measured samples 201, the sample 201 can be placed horizontally to measure the in-plane optical properties, or can be placed vertically to measure the optical properties in the vertical direction. Through simple operations such as pressing an operation button or using software control, the position conversion of the measured sample 201 can be realized, and diversified measurement requirements can be met.

[0089] When the measured sample 201 is a transmissive sample, the thickness direction of the measured sample 201 is parallel to the surface of the sample table 2, and the arrangement directions of the light source 101, the polarizer 102, the wave plate unit 301 and the polarizer 302 are all parallel to the surface of the sample table 2. When the measured sample 201 is a reflective sample, the thickness direction of the measured sample 201 is perpendicular to the surface of the sample table 2, and the arrangement direction of the light source 101 and the polarizer 102 forms an angle greater than zero with the surface of the sample table 2, and the arrangement directions of the wave plate unit 301 and the polarizer 302 also form an angle greater than zero with the surface of the sample table 2.

[0090] Reference Figure 3 The embodiment of the present application provides a measurement method of a variable-azimuth-angle wave plate ellipsometer, which is used for the variable-azimuth-angle wave plate ellipsometer and includes the following steps: placing a measured sample 201 on a sample table 2; adjusting the height and pitch of the sample table 2 by using a sample alignment system 5; turning on a light source 101, and adjusting the arrangement directions of the light source 101 and a polarizer 102 in a polarizing arm modulation unit 1 and the arrangement directions of a wave plate unit 301 and the polarizer 302 in a polarizing arm modulation unit 3 according to the transmittance and reflectance of the measured sample 201; sampling an outgoing light beam of the polarizer 302 by using an image sensor 401 to obtain a light intensity modulation image; analyzing the light intensity modulation image to obtain a light intensity modulation function; performing Fourier analysis on the light intensity modulation image to obtain a Fourier expression; and calculating a Mueller matrix of the measured sample 201 according to the coefficients in the Fourier expression.

[0091] The analysis of the light intensity modulation function is performed by mathematically processing the azimuth angle and the light intensity value of the light intensity modulation image, taking the azimuth angle as the independent variable and the light intensity value as the dependent variable to establish a functional relationship. In the Fourier analysis process, a high-efficiency Fourier transform algorithm is used to process the light intensity modulation function to obtain an accurate Fourier expression.

[0092] Specifically, for the transmissive sample 201, its thickness direction is parallel to the surface of the sample stage 2, ensuring that the light can pass through the sample 201 vertically or nearly vertically, thereby reducing the additional effects such as reflection and scattering of light. At the same time, the arrangement directions of the light source 101, the polarizer 102, the wave plate unit 301, and the analyzer 302 are all parallel to the surface of the sample stage 2, which can make the propagation path of light in the entire system simple and easy to analyze, reducing the loss of light and the complex change of polarization state. When measuring a transmissive sample 201 such as a transparent film, this parallel arrangement is beneficial to accurately measuring the optical parameters such as refractive index and transmittance. During the measurement, according to the actual transmittance of the sample 201, the positions and angles of the light source 101 and the polarizer 102, as well as the wave plate 301 and the analyzer 302, are fine-tuned by the first position adjustment unit 601 and the second position adjustment unit 602 to achieve the best measurement state.

[0093] For the reflective sample 201, its thickness direction is perpendicular to the surface of the sample stage 2, at this time the included angle between the arrangement direction of the light source 101 and the polarizer 102 and the surface of the sample stage 2 and the included angle between the arrangement direction of the wave plate unit 301 and the analyzer 302 and the surface of the sample stage 2 are set to be greater than zero, to ensure that the light is effectively reflected on the surface of the sample 201. By adjusting these angles, according to the law of reflection, the change of the polarization state of the reflected light can be accurately measured and analyzed. For example, when measuring the reflection characteristics of a metal surface, by adjusting the angles, the changes of light of different polarization states after reflection can be observed, providing a basis for accurately calculating the reflection characteristics of the sample 201.

[0094] In the specific measurement method steps: first, the sample to be measured 201 is carefully placed on the sample table 2, ensuring that its position is stable and meets the measurement requirements. Using the sample alignment system 5, the operator adjusts the height and pitch of the sample table 2 according to the observation results of the microscope and telescope system, ensuring that the sample 201 is in the best measurement position. After turning on the light source 101, according to the transmittance and reflectance of the sample 201, the first position adjustment unit 601 and the second position adjustment unit 602 are used to optimize the position and angle of the components of the polarizing arm modulation unit 1 and the analyzing arm modulation unit 3 through computer program or manual adjustment knob, so that the light path of the whole system adapts to the characteristics of the sample 201. When the image sensor 401 samples the outgoing light beam of the analyzer 302, it converts the light intensity information into digital signals and stores them in the computer memory, forming a light intensity modulation image. Through special image analysis software, the light intensity alternately changes with the azimuth angle image can be clearly seen, providing intuitive data for subsequent analysis. The analysis of the light intensity modulation image is carried out by special data analysis software, according to the method of establishing a functional relationship between the azimuth angle and the light intensity value mentioned above, and the light intensity modulation function is accurately calculated. When performing Fourier analysis on the light intensity modulation image, the efficient fast Fourier transform algorithm is used to convert the light intensity modulation function into a Fourier expression, and the software will automatically calculate the Fourier coefficients, which reflect the periodicity information of the light intensity modulation. Finally, the third analysis unit substitutes the coefficients in the Fourier expression into the optical formula and matrix operation formula, and accurately calculates the Mueller matrix.

[0095] Where, for the ellipsometer with P (polarizer) -S (sample) -rC (rotating compensator) -A (analyzer) structure, the light wave before the detector is derived from the Mueller matrix:

[0096]

[0097] Where,

[0098] Si: the polarization state of the incident light wave;

[0099] R （x） : rotation matrix, x is the angle of counterclockwise rotation;

[0100] M P , M S , M C , M A : Mueller matrix of polarizer, sample, compensator, and analyzer;

[0101] From the experimental point of view, the direct current and alternating current components can be obtained by Fourier analysis method.

[0102] The light intensity of the detector is represented as

[0103]

[0104] wherein the direct current and alternating current components

[0105]

[0106] Therefore, according to the above formula, the expression of the ellipsometric parameter can be calculated as

[0107] ss

[0108] .

[0109] The application provides a variable azimuth wave plate ellipsometer and a measurement method thereof, which has the following advantages:

[0110] 1. The variable azimuth wave plate ellipsometer of the application has simple structure, good stability and fast measurement capability, and can realize in-situ detection. A wave plate unit is used in the analyzer arm modulation unit, which achieves the technical effect of improving measurement flexibility and adaptability. Compared with the technical solution of using a fixed characteristic vortex wave plate in the prior art, the limitation of the wave plate characteristics on measurement adjustment is solved, so that when facing different sample characteristics and measurement requirements, the azimuth angle of the wave plate can be adjusted flexibly to avoid the limitation of the adjustment range and precision caused by the characteristics of the wave plate itself in the prior art, thereby more effectively modulating light for different types of samples and better meeting diversified measurement requirements.

[0111] 2. The application is equipped with a sample alignment system including a microscope and a telescope system, which is used to assist in adjusting the height and pitch of the sample stage, so as to accurately adjust the position and angle of the sample to adapt to different measurement scenes. Compared with some prior art, the prior art is not accurate enough in sample position adjustment or can only be adjusted simply. The design of the application can realize more precise control of the sample position, ensure that the sample is in the best measurement state during the measurement process, solve the problem that the prior art is difficult to accurately adjust the height and pitch of the sample during the measurement process, and improve the accuracy and reliability of the measurement.

[0112] 3. The application captures the light beam output by the analyzer through the image sensor and generates a light intensity modulation image, which presents a unique pattern of light and dark interlaced with the change of the azimuth angle, which achieves the technical effect of intuitively and effectively reflecting the light intensity information, and can more clearly present the light modulation condition, providing a better data basis for the subsequent analysis unit, solving the problem of inaccurate or non-intuitive light intensity information collection in the prior art, and providing a reliable data source for the subsequent light intensity modulation function extraction and analysis.

[0113] 4. The present application comprises a first analysis unit, a second analysis unit and a third analysis unit, realizes the extraction of the light intensity modulation function from the light intensity modulation image, carries out the Fourier analysis to obtain the accurate Fourier expression, and accurately calculates the Mueller matrix of the sample to be measured by using the key coefficient in the Fourier expression, so as to achieve the technical effect of accurately measuring and calculating the Mueller matrix of the sample; compared with some prior art which may not be able to accurately calculate the Mueller matrix due to the limitation of the analysis means, or the calculation process is complex and the accuracy is not high, the analysis unit system of the present application can accurately obtain the Mueller matrix through a series of logical processing and calculation, solves the problems of low accuracy and complex process in the measurement and calculation of the optical properties of the sample, and provides strong technical support for accurately characterizing the optical properties of the sample.

[0114] 5. The present application has a reflection measurement mode and a transmission measurement mode, and is equipped with a first position adjusting unit, a second position adjusting unit and a third position adjusting unit, which can adjust the position according to the different properties of the sample and the measurement requirements, so as to realize the technical effect of realizing multiple measurement modes and flexibly adjusting the position of the instrument parts. Compared with some prior art which has a single measurement mode or is not flexible in adjustment, the overall design of the present application makes the instrument better adapt to different measurement scenes, including different types of samples (transmission and reflection) and different placement positions (horizontal or vertical), solves the problems of single measurement mode and inflexible position adjustment in the prior art, improves the versatility and practicality of the instrument, and at the same time meets the demand of in-situ detection and realizes rapid measurement.

[0115] 6. The present application has the characteristics of simple structure design and good stability, and achieves the technical effect of easy operation and maintenance and stable measurement. Compared with some prior art which may have a complex structure or poor stability, the simple and stable structure design of the present application can reduce the manufacturing and maintenance cost of the instrument, and at the same time ensure the stable performance of the instrument during measurement, solve the problems of complex structure, difficult maintenance and low measurement stability in the prior art, and provide protection for long-term stable measurement.

[0116] Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A waveplate ellipsometer with variable azimuth angle, characterized in that, include: The polarization modulation unit includes a light source and a polarizer, with the polarizer located to the right of the light source; The sample stage is used to place the sample to be tested. The polarization modulation unit includes a compensator and a polarization analyzer; An image sensor is used to sample the emitted beam from the analyzer to obtain a light intensity modulated image, wherein the light intensity of the light intensity modulated image changes alternately with the azimuth angle; The first analysis unit obtains a light intensity modulation function based on the light intensity modulation image, with the azimuth angle of the light intensity modulation image as the independent variable and the light intensity value as the dependent variable. The second analysis unit performs Fourier analysis on the intensity modulation function to obtain the Fourier expression; The third analysis unit calculates the Mueller matrix of the sample to be tested based on the coefficients in the Fourier expression.

2. The waveplate ellipsometer with variable azimuth angle according to claim 1, characterized in that, The compensator is composed of multiple independent or continuous waveplate units with different azimuth angles on the same plane. Its function is that when light waves propagate through different units on the waveplate, the polarization state of the light waves is modulated differently at different units. The waveplates are vortex waveplates manufactured by the mask method, or waveplates formed by mechanically splicing several independent small waveplates. The small waveplates are liquid crystal waveplates made by light field modulation, or true zero-order, multi-order and achromatic waveplates processed by birefringent crystals.

3. A waveplate ellipsometer with variable azimuth angle according to claim 1, characterized in that, It also includes a first position adjustment unit, used to adjust the arrangement direction of the light source and polarizer in the polarizing arm modulation unit; The sample stage has a central axis perpendicular to its surface, and the arrangement of the light source and polarizer in the polarization modulation unit is symmetrical with respect to the central axis of the stage to the arrangement of the variable azimuth waveplate and analyzer in the polarization modulation unit.

4. A waveplate ellipsometer with variable azimuth angle according to claim 1, characterized in that, It also includes a second position adjustment unit, used to adjust the arrangement direction of the waveplates with variable azimuth angles and the analyzer in the polarization arm modulation unit.

5. A waveplate ellipsometer with variable azimuth angle according to claim 1, characterized in that, The compensator can be placed behind the polarizer to form a PCSA configuration, or behind the sample stage to form a PSCA configuration.

6. A waveplate ellipsometer with variable azimuth angle according to claim 1, characterized in that, It also includes a third position adjuster for switching between horizontal and vertical placement of the sample on the sample stage.

7. A waveplate ellipsometer with variable azimuth angle according to claim 1, characterized in that, When the sample to be tested is a transmissive sample, the thickness direction of the sample is parallel to the surface of the sample stage, and the arrangement directions of the light source, polarizer, variable azimuth waveplate and analyzer are all parallel to the surface of the sample stage.

8. A waveplate ellipsometer with variable azimuth angle according to claim 1, characterized in that, When the sample to be tested is a reflective sample, the thickness direction of the sample to be tested is perpendicular to the surface of the sample stage, and the angle between the arrangement direction of the light source and polarizer and the surface of the sample stage is greater than zero. The angle between the arrangement direction of the variable azimuth waveplate and the analyzer and the surface of the sample stage is also greater than zero.

9. A measurement method for a waveplate ellipsometer with variable azimuth angle, used in the waveplate ellipsometer with variable azimuth angle as described in any one of claims 1-8, characterized in that, Includes the following steps: Place the sample to be tested on the sample stage; Turn on the light source and adjust the arrangement of the light source and polarizer in the polarization modulation unit and the variable azimuth waveplate and analyzer in the polarization modulation unit according to the transmittance and reflectance of the sample to be tested. An intensity-modulated image is obtained by sampling the emitted beam from the analyzer using an image sensor. The intensity modulation image is analyzed to obtain the intensity modulation function; Fourier analysis was performed on the intensity modulation function to obtain its Fourier expression; Calculate the Mueller matrix of the sample to be tested based on the coefficients in the Fourier expression.

10. The measurement method of a waveplate ellipsometer with variable azimuth angle according to claim 9, characterized in that, The analysis of the light intensity modulation function is achieved by mathematically processing the azimuth angle and light intensity value of the light intensity modulation image, and establishing a functional relationship with the azimuth angle as the independent variable and the light intensity value as the dependent variable. The light intensity modulation function is processed using the Fourier transform algorithm to obtain an accurate Fourier expression, and then the parameters of the sample are calculated using the Fourier coefficients. For a PSCA-type ellipsometer: the light wave in front of the detector is derived from the Mueller matrix: ; in, Si: Polarization state of the incident light wave; R(x): Rotation matrix, where x is the angle of counterclockwise rotation; M P M S M C M A Mueller matrix of polarizer, sample, compensator, analyzer; The DC and AC components were obtained using Fourier analysis. At the same time, the light intensity of the detector can also be expressed as ； The DC and AC components are: ； Based on the above formula, the expression for the ellipticity parameter is calculated as follows: ； ； For PCSA type ellipsometer, the ellipticity angle of the sample can be calculated by simply changing the parameter values ​​of P and A in the above formula; In addition, other similar methods can be used to calculate the ellipticity of the sample.

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