Photoelastic modulation type wide-spectrum micro-area reflection differential signal measuring device and photoelastic modulation type wide-spectrum micro-area reflection differential signal measuring method

Abstract

The invention belongs to the technical field of optical measurement, and relates to an optical measurement technology of semiconductor nano-films and anisotropic film materials, in particular to a photoelastic modulation type wide-spectrum micro-area reflection differential signal measurement device and method. Based on the photoelastic modulation type broadband spectrum micro-area reflection differential signal measuring device, the photoelastic modulation type broadband spectrum micro-area reflection differential signal measuring method comprises the following steps: S1, calibrating azimuth angles of a polarizer, an analyzer and a photoelastic modulator and a control voltage of the photoelastic modulator; s2, placing a thin film material sample on the six-axis displacement table; and S3, performing measurement to obtain a reflection differential signal of the thin film material. When polarized light is used for measurement, the transverse resolution reaches the micron level, and a depolarization effect can be brought by using a high-power objective lens, so that the size of a light spot incident on a sample is reduced to about 30 microns by designing a light path and combining a pinhole with a low-power objective lens, and micro-area measurement is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical measurement, and relates to the optical measurement technology of semiconductor nanofilms and anisotropic thin film materials. In particular, it relates to a photoelastic modulation type wide-spectrum micro-region reflection differential signal measurement device and method. Background Art

[0002] With the continuous progress of semiconductor technology and the development of Moore's law, the chip manufacturing process technology is also continuously evolving, and the microscopic structure of devices is further reduced, which puts forward higher requirements for the lateral resolution of measurement. At present, there are various testing methods for microscopic structures, such as scanning probe method, electron beam method, and optical measurement method, etc. Among them, the optical measurement method is widely used because of its non-contact and non-destructive characteristics. As an important part of optical measurement, polarization light measurement has a wide range of applications in the fields of lithography and optical communication because of its high sensitivity and high resolution. In polarization light measurement, the accurate measurement of the polarization state depends on the relative configuration between the polarization direction of the incident light and the optical element (such as a polarizer). A larger convergence angle will cause the directivity of the incident light in space to become more dispersed, that is, the light rays are incident on the sample surface at multiple different angles. At this time, the amplitude and direction of the polarized light will change significantly with the change of the incident angle, resulting in different polarization states of the transmitted or reflected light, so that the measurement result of the polarized light becomes unstable and difficult to accurately control and predict. However, in order to focus the light beam into a micron-sized spot, a high numerical aperture (NA) objective lens is usually used, and this objective lens will introduce a larger convergence angle when focusing the light beam, thus destroying the basic principle of polarization light measurement. Therefore, there are great challenges in using polarized light for micro-region measurement. In addition, the local structure of the sample may be uneven, resulting in complex changes in the polarization state, further increasing the measurement difficulty. At the same time, the micro-region signal is usually weak and the noise interference is large, which will also lead to the instability and unreliability of the measurement result.

[0003] A typical representative of polarization light measurement is ellipsometry, including oblique-incidence ellipsometers and normal-incidence reflection difference spectrometers. In a micro-area ellipsometer, due to its oblique-incidence characteristic, the light spot is elliptical. Taking the RC2 model ellipsometer of J.A.Woollam as an example, its resolution in the x direction can reach 60 μm, while in the y direction it is about 100 μm. This characteristic limits its application in high-precision micro-area measurement, especially in scenarios that require higher resolution. In a rotating device reflection difference spectrometer, the rotation of the device may cause a slight shift in the position of the light spot, thereby affecting the relative position between the light beam and the sample, and affecting the optical path stability and measurement accuracy. Therefore, when this instrument is applied to micro-area measurement, the installation position and alignment accuracy of each component of the instrument are required to be very strict. Taking the RC2 ellipsometer as an example, it realizes micro-area measurement with a light spot size of about 60 μm × 100 μm through the modulation method of rotating the glass slide. At present, liquid crystal imaging reflection difference spectrometry has been able to achieve small light spot measurement of 3 μm per pixel, with relatively high spatial resolution. However, due to the characteristics of liquid crystal materials themselves, it is impossible to effectively obtain the spectral information of the sample in the ultraviolet band, which limits its application in ultraviolet spectral measurement. In contrast, a photoelastic modulation reflection difference spectrometer (PEM-RDS) covers the ultraviolet to near-infrared band and can perform a wider range of spectral measurements. The photoelastic modulation technology modulates polarized light, improves the extraction efficiency of polarization signals, reduces the interference of the external environment on the measurement results, and significantly enhances the stability and reliability of the measurement. Although PEM-RDS has significant advantages in polarization light measurement, its application in micro-area measurement remains to be developed. Therefore, there is an urgent need for a new type of reflection difference spectrometer that needs to have a wide spectral range, high measurement accuracy, and be able to achieve precise measurement of small light spots under non-large incident angle conditions to meet the high-resolution and high-sensitivity requirements in micro-area measurement. Summary of the Invention

[0004] In the research of L.F. Lastras-Martínez et al., a mode combining a PEM and a CCD camera was adopted to achieve the measurement of reflection differential signals at a single wavelength. The researchers obtained the values of two reflectance spectra by controlling the on and off states of the PEM, and calculated the reflectance difference through numerical subtraction. Specifically, the reflectance when the light is polarized in a certain direction is measured when the PEM is off, while the reflectance of unpolarized light is measured when the PEM is on. In the liquid crystal modulated reflection differential spectrometer reported by W.Shen et al., the researchers phase-modulated linearly polarized light by applying different voltages to the liquid crystal. This instrument also uses a CCD camera as a detector to obtain different light intensity data varying with the liquid crystal voltage, thereby resolving the reflection differential signal. However, since the PEM is a high-frequency modulation device and there is currently no CCD camera with a frequency matching it, therefore, this invention patent is significantly different from the method of L.F. Lastras-Martínez et al. and the liquid crystal modulated reflection differential spectrometer. In this invention, the data acquisition method does not rely on a CCD camera, but uses a photomultiplier tube that can adapt to the high-frequency signal of the PEM for data acquisition, and is not limited to single-wavelength measurement. In addition, this invention also has the advantages of a wide spectral measurement range from ultraviolet to near-infrared, high measurement accuracy, and can achieve micro-region measurement with a spot size of about 30 μm for anisotropic thin film materials at an approximately normal incidence angle.

[0005] The present invention provides an optoelastic modulation type wide-spectrum micro-region reflection differential signal measurement device and method. The present invention uses a monochromator to control wavelength scanning to obtain wide-spectrum reflection differential signals, realizing the micro-region characterization of the anisotropy of thin film materials, and can be widely applied to the industrial characterization field of microstructures.

[0006] To achieve the above object, the technical solution adopted by the present invention is: an optoelastic modulation type wide-spectrum micro-region reflection differential signal measurement device, including an optical path collimation module, an optical path modulation module, a focusing module, and an acquisition module;

[0007] The optical path collimation module sequentially includes: a wide-spectrum light source, an off-axis parabolic mirror;

[0008] The optical path modulation module sequentially includes: a first reflector, a first rotary servo, a polarizer, a second reflector, a pinhole, a D-shaped reflector, an optoelastic modulator, an analyzer, a second rotary servo, a third reflector;

[0009] The focusing module sequentially includes: a microscope system, a six-axis displacement stage;

[0010] The acquisition module sequentially includes: a converging lens group, a monochromator, and a photomultiplier tube;

[0011] The off-axis parabolic mirror collimates the light beam emitted by the broadband light source to generate a parallel incident beam. The polarizer imparts a linear polarization characteristic to the incident unpolarized light. The reflector transmits the incident light into the microscopic system, and the microscopic system focuses the incident light onto the sample. The six-axis displacement stage is used to carry the sample and drive the sample to translate and rotate in the horizontal and vertical planes. The photoelastic modulator performs high-frequency modulation at 50 kHz on the light reflected from the sample. The analyzer analyzes the light emitted by the photoelastic modulator. The converging lens group converges the reflected light into the monochromator, and the light output by the monochromator enters the photomultiplier tube for photoelectric conversion to output an electrical signal.

[0012] The photoelastic modulation-based broadband spectral micro-region reflection differential signal measurement method, based on the photoelastic modulation-based broadband spectral micro-region reflection differential signal measurement device, includes the following steps:

[0013] S1. Calibrate the azimuth angles of the polarizer, analyzer, and photoelastic modulator and the control voltage of the photoelastic modulator;

[0014] S2. Place the thin film material sample on the six-axis displacement stage;

[0015] S3. Conduct measurements to obtain the single-wavelength angle-resolved reflection differential signal of the anisotropic thin film material.

[0016] By controlling the voltage of the photoelastic modulator, the phase delay value of the measurement wavelength is made 137.8°;

[0017] During the measurement process, by controlling the voltage of the photoelastic modulator, selecting the wavelength of the monochromator, and rotating the six-axis displacement stage, the single-wavelength angle-resolved reflection differential signal test of the thin film material is completed; by controlling the voltage of the photoelastic modulator and the wavelength scanning of the monochromator, the broadband spectral reflection differential signal test of the thin film material is completed.

[0018] Before the measurement starts, the calibration step is executed to obtain the phase delay amount of the photoelastic modulator;

[0019] Among them, the specific steps for calibrating the azimuth angles of the polarizer, analyzer, and photoelastic modulator and the control voltage of the photoelastic modulator in the above calibration step S1 are as follows:

[0020] S11. Use the monochromator to select the test wavelength, and make the fast axes of the polarizer and analyzer coincide through the first rotary servo and the second rotary servo;

[0021] S12. Rotate the polarizer and analyzer through the first rotary servo and the second rotary servo until, by changing the control voltage of the photoelastic modulator, the DC voltage collected by the photomultiplier tube remains unchanged. At this time, the fast axes of the polarizer, analyzer, and photoelastic modulator coincide;

[0022] S13. Rotate the polarizer and analyzer by 45° through the first rotary servo and the second rotary servo. At this time, it is considered that the fast axes of the polarizer and analyzer form an angle of 45° with the instrument coordinate reference axis, and the fast axis of the photoelastic modulator is parallel to the instrument coordinate reference axis.

[0023] S14. Obtain the signal received by the photomultiplier tube.

[0024] I = I0(1 + J0(A) - 2J2(A)cos(2ωt) +......)

[0025] The coefficient of the DC component is;

[0026] S DC = I0(1 + J0(A0))

[0027] When no voltage is applied to the photoelastic modulator, J0(A0) is 1 and the DC component is 2I0; when a voltage is applied to the photoelastic modulator to make A0 137.8°, J0(A0) is 0 and the DC component is I0. That is, by adjusting the voltage of the photoelastic modulator, the DC component at this time reaches half of the DC component when no voltage is applied to the photoelastic modulator, so as to obtain the control voltage of the photoelastic modulator at the corresponding wavelength.

[0028] S15. Use the monochromator to select the test wavelength and obtain the voltage of the photoelastic modulator for each wavelength channel to complete the calibration process.

[0029] The specific steps to obtain the anisotropic signal of the thin film material in step S3 are as follows:

[0030] S31. Set the azimuth angle of the polarizer to 0° through the first rotary servo, set the azimuth angle of the analyzer to 45° through the second rotary servo. At this time, the azimuth angle of the photoelastic modulator is 0°. Use the monochromator to select the test wavelength and set the voltage of the photoelastic modulator at the corresponding wavelength according to the calibration data, so that the phase delay value of this test wavelength is 137.8°.

[0031] S32. According to the Jones matrix, calculate the S of the component with twice the frequency of the photoelastic modulator 2f The coefficient is:

[0032]

[0033] Among them, J2(A0) represents the Bessel function, A0 represents the phase delay amount, represents the real part of the reflection differential signal;

[0034] Calculate the S of the component with the frequency of the photoelastic modulator f The coefficient:

[0035]

[0036] Among them, represents the imaginary part of the reflected differential signal;

[0037] Calculate the S of the DC component of the photoelastic modulator DC Coefficient:

[0038]

[0039] Among them, the reflected differential signal Δr / r is:

[0040]

[0041] Among them, r p is the p-polarization component of the reflected light at this time; r s is the s-polarization component of the reflected light at this time

[0042] The real part of the reflected differential signal is:

[0043]

[0044] S33, finally solve the reflected differential signal

[0045] Due to the adoption of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0046] 1. When the present invention uses polarized light measurement, the lateral resolution reaches the micron level: Since using a high-power objective lens will bring a depolarization effect, in the present invention, the spot size incident on the sample is reduced to about 30 um by designing an optical path using a pinhole combined with a low-magnification objective lens to achieve micro-area measurement.

[0047] 2. It can realize micro-area measurement of single-wavelength angle-resolved reflected differential signals: The anisotropy measurement of anisotropic thin film materials at different crystal axis angles is realized by rotating the sample. In the present invention, a monochromator is used to select the test wavelength, and the phase delay amount is adjusted by controlling the voltage of the photoelastic modulator to ensure that the phase delay value of the test wavelength is fixed at 137.8° with high precision. Then, combined with the precision rotation control console in the six-axis displacement stage to control the azimuth angle of the sample stage, the anisotropy values of the thin film material at different azimuth angles at a specific wavelength are obtained.

[0048] 3. It can realize wide-spectrum reflected differential micro-area measurement: Wide-spectrum measurement is realized by wavelength scanning. In the present invention, a monochromator is used to select the test wavelength, and the phase delay amount is adjusted by controlling the voltage of the photoelastic modulator to ensure that the phase delay value for each test wavelength is fixed at 137.8° with high precision, and the anisotropy measurement of the thin film material in a wide spectral range is obtained; at the same time, in order to obtain a faster response, this design can also realize the measurement of single-wavelength or limited-wavelength signals. Description of the Drawings

[0049] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0050] Figure 1 It is a schematic structural diagram of a photoelastic modulation type wide-spectrum micro-region reflection differential signal measurement device;

[0051] Figure 2 It is a calibration flowchart before testing;

[0052] Figure 3 It is a single-wavelength angular resolution reflection differential signal test flowchart;

[0053] Figure 4 It is a wide-spectrum reflection differential signal test flowchart;

[0054] Figure 5 It is a micrograph of spot size;

[0055] The component names represented by the reference numerals in the above figures are as follows:

[0056] 1. Wide-spectrum light source; 2. Off-axis parabolic mirror; 3. First reflector; 4. First rotary servo; 5. Polarizer; 6. Second reflector; 7. Pinhole; 8. D-shaped reflector; 9. Microscope system; 10. Six-axis displacement stage; 11. Photoelastic modulator; 12. Analyzer; 13. Second rotary servo; 14. Third reflector; 15. Converging lens group; 16. Monochromator; 17. Photomultiplier tube. Specific Embodiments

[0057] In order to be able to more clearly understand the above-mentioned objects, features, and advantages of the present invention, the following further describes the present invention in conjunction with the drawings and embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0058] In the following description, many specific details are set forth to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the present invention is not limited by the specific embodiments disclosed in the following specification.

[0059] As Figures 1 to 5 shown, a photoelastic modulation type wide-spectrum micro-region reflection differential signal measurement device includes an optical path collimation module, an optical path modulation module, a focusing module, and an acquisition module;

[0060] The optical path collimation module successively includes: a wide-spectrum light source 1 and an off-axis parabolic mirror 2;

[0061] The optical path modulation module sequentially includes: a first reflecting mirror 3, a first rotary servo 4; a polarizer 5, a second reflecting mirror 6, a pinhole 7, a D-shaped reflecting mirror 8, an acousto-optic modulator 11, an analyzer 12, a second rotary servo 13; a third reflecting mirror 14;

[0062] The focusing module sequentially includes: a microscope system 9, a six-axis displacement stage 10;

[0063] The acquisition module sequentially includes: a converging lens group 15, a monochromator 16, and a photomultiplier tube 17;

[0064] The off-axis parabolic mirror 2 collimates the beam emitted by the broadband light source 1 to generate a parallel incident beam. The polarizer 5 imparts a linear polarization characteristic to the incident unpolarized light. The reflecting mirror transmits the incident light into the microscopic system, and the microscopic system focuses the incident light onto the sample. The six-axis displacement stage 10 is used to carry the sample and drive the sample to translate and rotate in the horizontal and vertical planes. The acousto-optic modulator 10 performs high-frequency modulation at 50 kHz on the light reflected from the sample. The analyzer 12 analyzes the polarization of the light modulated by the acousto-optic modulator 11. The converging lens group 15 converges the reflected light into the monochromator 16, and the light output by the monochromator 16 enters the photomultiplier tube 17 for photoelectric conversion to output an electrical signal.

[0065] An acousto-optic modulation type broadband micro-region reflection differential signal measurement method, and this measurement method is for the characterization of the anisotropy of microscopic structures. Usually, the sample is placed on the six-axis displacement stage 10 under the microscope system 9 to complete the characterization of the anisotropy of the microscopic structure. This method includes the following steps:

[0066] S1. Calibrate the azimuth angles of the polarizer 5, the analyzer 12, and the acousto-optic modulator 11 and the control voltage of the acousto-optic modulator 11;

[0067] S2. Place the thin film material sample on the six-axis displacement stage 10;

[0068] S3. Perform measurement to obtain the anisotropy signal of the thin film material.

[0069] The specific steps for calibrating the azimuth angles of the polarizer 5, the analyzer 12, and the acousto-optic modulator 11 and the control voltage of the acousto-optic modulator 11 in step S1 include the following:

[0070] S11. Use the monochromator 14 to select the test wavelength, and make the fast axes of the polarizer 5 and the analyzer 12 coincide through the first rotary servo 4 and the second rotary servo 13;

[0071] S12. Rotate the polarizer 5 and the analyzer 12 through the first rotary servo 4 and the second rotary servo 13 until the control voltage of the photoelastic modulator 11 is changed, and keep the DC voltage collected by the photomultiplier 17 unchanged. At this time, the fast axes of the polarizer 5, the analyzer 12, and the photoelastic modulator 11 coincide;

[0072] S13. Rotate the polarizer 5 and the analyzer 12 by 45° through the first rotary servo 4 and the second rotary servo 13. At this time, it is considered that the fast axes of the polarizer 5 and the analyzer 12 form an angle of 45° with the instrument coordinate reference axis, and the fast axis of the photoelastic modulator 11 is parallel to the instrument coordinate reference axis;

[0073] S14. Obtain the signal received by the photomultiplier 17;

[0074] I = I0(1 + J0(A) - 2J2(A)cos(2ωt) +......)

[0075] The coefficient of the DC component is;

[0076] S DC = I0(1 + J0(A0))

[0077] When no voltage is applied to the photoelastic modulator 11, J0(A0) is 1 and the DC component is 2I0; when a voltage is applied to the photoelastic modulator 11 to make A0 137.8°, J0(A0) is 0 and the DC component is I0. That is, by adjusting the voltage of the photoelastic modulator 11, the DC component at this time reaches half of the DC component when no voltage is applied to the photoelastic modulator 11, so as to obtain the control voltage of the photoelastic modulator 11 at the corresponding wavelength;

[0078] S15. Use the monochromator 16 to select the test wavelength and obtain the voltage of the photoelastic modulator 11 in each wavelength channel to complete the calibration process.

[0079] Among them, the azimuth angle of the polarizer 5 is 0°, the azimuth angle of the photoelastic modulator 11 is 45°, and the azimuth angle of the analyzer 12 is 0°.

[0080] Before the measurement starts, perform the above calibration steps. The calibration process is to obtain the control voltage when the phase delay value of the photoelastic modulator 11 is 137.8° under a wide spectrum.

[0081] The test for obtaining the reflection differential spectral signal of the micro-area anisotropic thin film material includes the following steps:

[0082] S31. Set the azimuth angle of the polarizer 5 to 0° through the first rotary servo 4, and set the azimuth angle of the analyzer 12 to 45° through the second rotary servo 13. At this time, the azimuth angle of the photoelastic modulator 11 is 0°. Select the test wavelength using the monochromator 17, and set the voltage of the photoelastic modulator 11 at the corresponding wavelength according to the calibration data, so that the phase delay value at this test wavelength is 137.8°;

[0083] S32. According to the Jones matrix, calculate the S coefficient of the component with a frequency twice that of the photoelastic modulator: 2f where:

[0084]

[0085] J2(A0) represents the Bessel function, and A0 represents the phase delay amount, represents the real part of the reflected differential signal; calculate the S coefficient of the component with a frequency once that of the photoelastic modulator: f where:

[0086]

[0087] where, represents the imaginary part of the reflected differential signal;

[0088] Calculate the S coefficient of the DC component of the photoelastic modulator: DC where:

[0089]

[0090] where the reflected differential signal Δr / r is:

[0091]

[0092] where r p is the p-polarized component of the reflected light at this time; r s is the s-polarized component of the reflected light at this time

[0093] The real part of the reflected differential signal is:

[0094]

[0095] S33. Finally, resolve the reflected differential signal

[0096] The test to obtain the single-wavelength angular resolution reflected differential spectroscopy signal of the micro-area anisotropic thin film material includes the following steps:

[0097] (1) Select the test wavelength using the monochromator 17;

[0098] (2) Use the data in the above calibration steps to set the voltage of the photoelastic modulator 11 at the corresponding wavelength, so that after the polarized light reflected from the sample passes through the photoelastic modulator 11, a phase delay of 137.8° is obtained;

[0099] (3) Use the rotary displacement stage in the six-axis displacement stage to select the sample test azimuth angle;

[0100] (4) After the reflected light passing through the sample passes through the photoelastic modulator 11, a modulation with a frequency of 50 kHz is obtained;

[0101] (5) Use the photomultiplier tube 17 to detect the light intensity of the reflected light received in real time; use the Fourier transform algorithm to obtain the coefficients of the second harmonic component, the fundamental frequency component, and the DC component in the light intensity of the photomultiplier tube 17;

[0102] (6) Repeat the above steps (3) to (5), and the micro-region angle-resolved reflection difference spectrum signal can be obtained.

[0103] The test for obtaining the wide-spectrum reflection difference spectrum signal of the micro-region anisotropic thin film material includes the following steps:

[0104] (1) Based on the detected sample angle-resolved reflection difference signal, use the six-axis displacement stage 10 to set the azimuth angle of the sample;

[0105] (2) Use the monochromator 17 to select the test wavelength;

[0106] (3) Use the data in the above calibration steps to set the voltage of the photoelastic modulator 11 at the corresponding wavelength, so that after the polarized light reflected from the sample passes through the photoelastic modulator 11, a phase delay of 137.8° is obtained;

[0107] (4) After the reflected light passing through the sample passes through the photoelastic modulator 11, a modulation with a frequency of 50 kHz is obtained;

[0108] (5) Use the photomultiplier tube 17 to detect the light intensity of the reflected light received in real time; use the Fourier transform algorithm to obtain the coefficients of the second harmonic component, the fundamental frequency component, and the DC component in the light intensity of the photomultiplier tube 17;

[0109] (6) Repeat the above steps (2) to (5), and the micro-region wide-spectrum reflection difference spectrum signal can be obtained.

[0110] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the relevant art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes and apply them to other fields. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A photoelastic modulation wide spectrum micro-area reflection differential signal measurement device, characterized in that: It includes an optical path collimation module, an optical path modulation module, a focusing module, and a collection module; The optical path collimation module includes: a wide spectrum light source, an off-axis parabolic mirror; The optical path modulation module includes in sequence: a first reflector, a first rotating servo, a polarizer, a second reflector, a pinhole, a D-type reflector, a photoelastic modulator, an analyzer, a second rotating servo, and a third reflector; The focusing module includes: a microscope system, a six-axis translation stage; The acquisition module includes: a converging lens group, a monochromator and a photomultiplier tube.

2. A method for measuring a differential signal of a micro-area reflection using a photoelastic modulation wide spectrum, based on the device for measuring a differential signal of a micro-area reflection using a photoelastic modulation wide spectrum, according to claim 1, characterized in that: The following steps are involved: S1, calibrating the azimuth angles of the polarizer, analyzer and photoelastic modulator and the control voltage of the photoelastic modulator; S2, placing a thin film material sample on a six-axis translation stage; S3. Perform measurement to obtain a wide-spectrum reflectance differential signal of the anisotropic thin film material.

3. The method for measuring the differential signal of the photoelastic modulation wide spectrum micro-area reflection according to claim 2, characterized in that: The step S1 of calibrating the azimuth angles of the polarizer, the analyzer and the photoelastic modulator and the control voltage of the photoelastic modulator includes the following specific steps: S11, using a monochromator to select a test wavelength, and using a first rotating servo and a second rotating servo to make the fast axes of the polarizer and the analyzer coincide with each other; S12, rotating the polarizer and the analyzer by the first rotary servo and the second rotary servo until the control voltage of the photoelastic modulator is changed, keeping the DC voltage collected by the photomultiplier tube unchanged, and at this time, the fast axes of the polarizer, the analyzer and the photoelastic modulator coincide; S13, rotating the polarizer and the analyzer by 45° through the first rotary servo and the second rotary servo, at which time it is considered that the fast axes of the polarizer and the analyzer are 45° to the instrument coordinate reference axis, and the fast axis of the photoelastic modulator is parallel to the instrument coordinate reference axis; S14, obtaining a signal received by a photomultiplier tube; I=I0(1+J0(A)-2J2(A)cos(2ωt)+......) The coefficient of the DC component is; S DC =I0(1+J0(A0)) S15. Use a monochromator to select a test wavelength, obtain the photoelastic modulator voltage in each wavelength channel, and complete the calibration process.

4. The method for measuring the differential signal of the photoelastic modulation wide spectrum micro-area reflection according to claim 3, characterized in that: The specific steps of obtaining the anisotropy signal of the thin film material in step S3 are: S31, setting the azimuth angle of the polarizer to 0° through the first rotary servo, setting the azimuth angle of the analyzer to 45° through the second rotary servo, at which time the azimuth angle of the photoelastic modulator is 0°, selecting a test wavelength using a monochromator, and setting the voltage of the photoelastic modulator at the corresponding wavelength according to the calibration data, so that the phase delay value of this test wavelength is 137.8°; S32, according to the Jones matrix, calculate S which is twice the frequency component of the photoelastic modulator 2f The coefficients are: Among them, J2(A0) represents the Bessel function, A0 represents the phase delay, represents the real part of the reflected differential signal; S is calculated to be twice the frequency component of the photoelastic modulator f coefficient: in, represents the imaginary part of the reflected differential signal; The DC component S of the photoelastic modulator is calculated DC coefficient: Wherein, the reflected differential signal Δr / r is: Among them, r p This is the p-polarization component of the reflected light; r s This is the s-polarization component of the reflected light The real part of the reflected differential signal is: S33, finally solve the reflected differential signal

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