A full-range ellipsometer based on dual-pulse optical level cascade frequency modulation

Abstract

The application belongs to the technical field of full-range ellipsometry devices, and particularly relates to a full-range ellipsometry device based on double photoelasticity cascade difference frequency modulation, which comprises a detection light source, a polarizer, a first photoelasticity modulator, a sample, a second photoelasticity modulator, a detection polarizer and a photodetector, the light path direction of the detection light source is sequentially provided with the polarizer, the first photoelasticity modulator and the sample, and the reflected light path of the sample is sequentially provided with the second photoelasticity modulator, the detection polarizer and the photodetector. The application utilizes the advantages of high modulation frequency, large modulation purity, wide light spectrum range and large field of view angle of the photoelasticity modulator, selects two photoelasticity modulators with inconsistent modulation frequencies for joint use, constructs double photoelasticity cascade difference frequency modulation, and based on the modulation technology, can realize the measurement of all four Stokes vectors of the outgoing light, and further can realize the full-range measurement of ellipsometric parameters.

Description

Technical Field

[0001] This invention belongs to the technical field of full-range ellipticity measurement devices, specifically relating to a full-range ellipticity measurement device based on dual-elastic-optical cascaded difference frequency modulation. Background Technology

[0002] When incident light is reflected or transmitted through a thin film layer, the polarization state of the outgoing light changes. Specifically, the amplitudes and phases of the two polarization components (p-component and s-component) of the outgoing light, which are parallel to and perpendicular to the incident plane, change. This is quantitatively described using two ellipticity parameters: the amplitude ratio of the p-component and the phase difference Δ between the s-component and the p-component. By combining Fresnel thin film theory with the measured ellipsometric parameters, physical parameters such as film thickness, refractive index, and extinction coefficient can be further analyzed. Therefore, ellipsometric parameter measurement has important applications in optical coating, determination of physical constants of new materials, biomembrane determination, and molecular self-assembly film research, and is of great significance to the development of information technology, new material development, biomedicine, integrated circuits, and other fields.

[0003] Currently, based on their working principles, two main types of ellipsometric measurement methods and instruments have been developed: those using rotating polarization elements and those using phase modulation. Rotating polarization element ellipsometric measurement technology mainly utilizes rotating polarizers or compensators, offering advantages such as simple instrument structure, low cost, and easy data processing. It has been extensively studied since the development of ellipsometric technology and was quickly commercialized; currently, the ellipsometers sold on the market are still predominantly of the rotating polarization element type. However, this type of ellipsometer can only measure the first three Stokes vectors of the emitted light, limiting the measurement range of the ellipsometric parameter Δ to -180° to 0° or 0° to 180°. It cannot perform full-range measurement of Δ, and the measurement accuracy of Δ near 0° or 180° is relatively low. Compared to ellipsometers with rotating polarizers, ellipsometers with rotating compensators incorporate a quarter-wave plate or compensator into their instrument structure. The azimuth angles of the transmission axes of the polarizer and analyzer remain constant, and the rotating compensator enables the measurement of all Stokes vectors, thus achieving full-range measurement of the amplitude ratio Ψ and phase difference Δ, two ellipsometric parameters. However, ellipsometers with rotating polarizers use stepper motors to mechanically rotate the element, and the time resolution of ellipsometric measurements has never exceeded the millisecond level. This limits the application of this type of ellipsometric measurement technology and instrument in rapid physical film detection, such as molecular self-assembly, online film monitoring, chemical process monitoring, and material phase transitions. Furthermore, the mechanical rotation of the polarizer element causes translation of the detection beam on the sample, compromising the accuracy and repeatability of the ellipsometric measurement.

[0004] Phase-modulated ellipsometers employ electrically controlled phase modulation elements such as liquid crystal variable phase delayers, electro-optic modulators, Faraday rotators, and photoelastic modulators to achieve in-situ, online ellipsometric measurements. However, compared to other phase modulation elements, photoelastic modulators offer higher modulation frequencies, wider spectral ranges, greater modulation purity, and larger field of view, making ultra-high-speed ellipsometric measurements with microsecond-level time resolution possible. However, current phase-modulated ellipsometric measurement techniques based on photoelastic modulation mostly use a single photoelastic modulator, with data processing relying on lock-in amplifiers. This results in limited ellipsometric measurement range and high data processing costs. Furthermore, photoelastic modulators are high-quality, heat-dissipating resonant opto-electromechanical devices; their resonant heating and changes in ambient temperature both affect their resonant operating state. This problem has become a critical obstacle to the development and engineering application of photoelastic modulation-based phase-modulated ellipsometric measurement technology, requiring urgent solutions. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a full-range ellipsometric measurement device based on dual-elastic-optical cascaded difference frequency modulation. It employs dual-elastic-optical cascaded difference frequency modulation technology to obtain full-range ellipsometric parameter measurements, and combines multi-channel digital signal processing technology to simultaneously achieve real-time calibration and stable control of the phase modulation amplitude of the elastic-optical modulator, thus completing ultra-high-speed, online, in-situ, high-precision, full-range ellipsometric parameter measurements with microsecond-level time resolution.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A full-range ellipsometric measurement device based on dual-elastic cascaded difference frequency modulation includes a detection light source, a polarizer, a first elastic modulator, a sample, a second elastic modulator, an analyzer, and a photodetector. The polarizer, the first elastic modulator, and the sample are arranged sequentially in the optical path of the detection light source, and the second elastic modulator, the analyzer, and the photodetector are arranged sequentially in the reflected optical path of the sample.

[0008] The first light-sensitive modulator is electrically connected to the driving circuit of the first light-sensitive modulator, the second light-sensitive modulator is electrically connected to the driving circuit of the second light-sensitive modulator, the photodetector is electrically connected to the control computer, the driving circuits of the first light-sensitive modulator and the second light-sensitive modulator are both electrically connected to the data processing and control module, and the data processing and control module is electrically connected to the control computer.

[0009] The data processing and control module includes a core FPGA unit, a first data acquisition unit, a second data acquisition unit, and a third data acquisition unit. The first, second, and third data acquisition units are all electrically connected to the core FPGA unit. The driving circuit of the first photosensitive modulator is electrically connected to the core FPGA unit and the first data acquisition unit, respectively. The driving circuit of the second photosensitive modulator is electrically connected to the core FPGA unit and the second data acquisition unit, respectively. The photodetector is electrically connected to the third data acquisition unit, and the control computer is electrically connected to the core FPGA unit.

[0010] The detection light source is a laser or a monochromator quasi-monochromatic light source. The polarizer and analyzer both use dichroic thin-film polarizers in the visible light measurement band. The polarizer and analyzer both use GranTale calcite polarizers in the near-infrared measurement band. The polarizer and analyzer both use magnesium fluoride Rohung prisms in the short-wave infrared measurement band. The polarizer and analyzer both use metal wire grid polarizers in the mid-infrared measurement band.

[0011] Both the first and second elastic optical modulators are two-dimensional octagonal symmetrical elastic optical modulators with large aperture and large field of view. The light-transmitting crystals of the first and second elastic optical modulators are made of fused silica, calcium fluoride or zinc selenide.

[0012] The polarizer, the first photosensitive modulator, and the second photosensitive modulator have axial directions that differ by 45°. The first photosensitive modulator and the second photosensitive modulator are cascaded. The modulation frequencies of the first photosensitive modulator and the second photosensitive modulator are not equal. The frequency of the first photosensitive modulator is set to 47kHz, and the frequency of the second photosensitive modulator is set to 54kHz.

[0013] The photodetector uses a silicon photodetector in the visible light measurement band, a mercury cadmium telluride photodetector in the near-infrared measurement band, an indium telluride photodetector in the short-wave infrared measurement band, and an indium gallium arsenide photodetector in the mid-infrared measurement band.

[0014] A data demodulation method for a full-range ellipsometric measurement device based on dual-elastic optical cascaded difference frequency modulation includes the following steps:

[0015] S1. The optical signal is described using Stokes vectors, and the polarization transmission characteristics of the components and the sample under test are described using Muller matrices. The description is as follows:

[0016] S out =M A M PEM2 M S M PEM1M P S in

[0017] Among them, S in The Stokes vector representing the incident light is described as S in =I0[1 0 0 0] T Where I0 is the total intensity of the incident light, and the Muller matrices of the first and second light-sensitive modulators are respectively M PEM1 and M PEM2 express;

[0018] S2. Calculate the Stokes vector of the emitted light based on the polarization transmission characteristics. The first component of the Stokes vector of the emitted light represents the light intensity, i.e., the light intensity that the photodetector can measure and obtain, described as follows:

[0019]

[0020] Where δ1 and δ2 are the phase modulations of the first and second photoelectric modulators, δ 10 and δ 20 These represent the phase modulation amplitudes of the first and second optical modulators, respectively, δ1 = δ 10 sinω1t and δ2=δ 20 sinω2t, where ω1 and ω2 represent the frequencies of the first and second photoelectric modulators, respectively, and ω2 is the amplitude ratio of the p and s polarized light components of the detected light after reflection or transmission from the sample, with a value range of (0-90°); Δ is the phase difference between the p and s polarized light, with a value range of (-180°-180°).

[0021] S3, the modulation term sinδ of the two cascaded photoelastic modulators i =sin(δ) i0 sinω i t) and cosδ i =cos(δ i0 sinω i t) Using the first kind of Bessel function expansion:

[0022]

[0023] Among them, J0, J 2k-1 and J 2k These represent the 0th, 2k-1th, and 2kth order Bessel series, respectively, with the first and second light-sensitive modulators corresponding to i = 1 and 2, respectively.

[0024] S4. The output light intensity of the analysis device, after being modulated by the cascaded difference frequency modulation of the first and second light modulators, is loaded with the sample ellipticity parameter into the difference frequency modulated light signal. The modulated light signal is detected by the photodetector and converted by the third data acquisition unit and input into the core FPGA unit. Digital phase-locked loop data processing is used to simultaneously extract the amplitude of multiple channel signals.

[0025]

[0026] S5. By using the ratio of the difference frequency signal and the sum frequency signal, combined with the Bessel series, the phase amplitude calibration of the first and second optical modulators is completed in real time.

[0027]

[0028] S6. Define the ratio r using the frequency signal amplitude loaded by the correlation term of the thin film sample ellipticity parameter. I and r II for

[0029]

[0030] The ratio r is obtained by solving the frequency signal amplitude loaded by the correlation term of the sample ellipsometric parameters. I and r II It can solve for the elliptic parameters Ψ and Δ.

[0031]

[0032] By simultaneously measuring the three elliptic parameters sin(2Ψ)sinΔ, sin(2Ψ)cosΔ, and cos(2Ψ), the full range of elliptic parameter Ψ can be measured from 0 to 90°, and the full range of elliptic parameter Δ can be measured from -180° to 180°.

[0033] The Muller matrices of the first and second optical modulators in S1 are respectively:

[0034] and

[0035] The sample to be tested in S1 uses a Muller matrix, and its polarization characteristics are described as follows:

[0036]

[0037] The related terms sin(2Ψ)sinΔ in S3 and the sample ellipticity parameter are included in the frequency signals ω2, 3ω2, 2ω1+ω2, 2ω1-ω2, 2ω1+3ω2, 2ω1-3ω2, etc., the related term sin(2Ψ)cosΔ is included in the frequency signals ω1+ω2, ω2-ω1, ω1+3ω2, ω2-3ω1, 3ω1+ω2 and 3ω2-ω1, and the related term cos(2Ψ) is included in the frequency signal 2ω2.

[0038] Compared with the prior art, the beneficial effects of this invention are:

[0039] 1. This invention utilizes the advantages of elastic-optic modulators, such as high modulation frequency, high modulation purity, wide transmission spectrum range and large field of view. It selects two elastic-optic modulators with different modulation frequencies to be used together to construct a dual elastic-optic cascaded difference frequency modulation. Based on this modulation technology, it is possible to measure all four Stokes vectors of the emitted light, and thus achieve full-range measurement of ellipsometric parameters.

[0040] 2. The ellipticity parameter measurement data processing method of the present invention involves inputting the modulated optical signal emitted by the system into the FPGA control module after analog-to-digital conversion. In the FPGA control module, digital phase-locked loop technology is used to extract the amplitude of multiple frequency signals, which can both ensure the real-time performance of data processing and reduce data processing costs.

[0041] 3. The data processing described in this invention uses digital phase-locked loop technology to simultaneously extract the amplitude of multiple frequency signals. The invention patent uses the frequency signals associated with the phase modulation amplitude of the elastic-optical modulator to calculate the ratio, and combines it with Bessel series to realize the real-time calibration of the phase amplitude of the elastic-optical modulator, which is then applied to the solution of ellipticity parameters, thus ensuring the accuracy of data measurement. Attached Figure Description

[0042] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0043] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0044] Figure 1 This is a schematic diagram of the structure of the present invention.

[0045] Wherein: 1 is the detection light source, 2 is the polarizer, 3 is the first light-sensitive modulator, 4 is the sample, 5 is the second light-sensitive modulator, 6 is the analyzer, 7 is the photodetector, 8 is the driving circuit of the first light-sensitive modulator, 9 is the driving circuit of the second light-sensitive modulator, 10 is the data processing and control module, 101 is the core FPGA unit, 102 is the first data acquisition unit, 103 is the second data acquisition unit, 104 is the third data acquisition unit, and 11 is the control computer. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. These descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the claims of the present invention. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0047] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0048] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0049] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0050] like Figure 1As shown, the device in this embodiment includes a detection light source 1, a polarizer 2, a first light-sensitive modulator 3, a sample 4, a second light-sensitive modulator 5, an analyzer 6, a photodetector 7, a driving circuit 8 for the first light-sensitive modulator, a driving circuit 9 for the second light-sensitive modulator, a data processing and control module 10, and a control computer 11.

[0051] The detection light source 1 can be a laser, a monochromator, or a quasi-monochromatic light source, depending on the application requirements. The polarizer 2 and analyzer 6, based on the application spectral range, can use a dichroic thin-film polarizer for the visible light measurement band, and a GranTale calcite polarizer, a magnesium fluoride Rohung prism, and a metal wire grid polarizer for the near-infrared, short-wave infrared, and mid-infrared bands, respectively. The first and second light modulators 3 and 5 are two-dimensional octagonal symmetrical light modulators with large apertures and wide field of view. The light-transmitting crystal can be selected from isotropic crystals such as fused silica, calcium fluoride, and zinc selenide. The photodetector 7, based on the application spectral range, can be a silicon photodetector, a mercury cadmium telluride photodetector, an indium telluride photodetector, or an indium gallium arsenide photodetector for the visible, near-infrared, short-wave infrared, and mid-infrared bands, respectively.

[0052] The inductors L in the driving circuit 8 of the first and second light-sensitive modulators both contain secondary coils. These secondary coils act as feedback units, providing real-time feedback to the driving circuit and the light-sensitive modulator resonant network that match the light-sensitive modulator's resonant operation. The data processing and control module 10 includes a core FPGA unit 101, a first data acquisition unit 102, a second data acquisition unit 103, and a third data acquisition unit 104. The core FPGA unit 101 provides the driving source signals for the two light-sensitive modulators, which are amplified by the LC driving circuit to drive the light-sensitive modulators. The feedback voltage signals from the secondary coils of the two driving circuits are acquired by the first and second data acquisition units 102 and input into the core FPGA unit 101, respectively. The photodetector converts the detected light signal into a voltage signal, which is then acquired by the third data acquisition unit 104 and input into the core FPGA unit 101. Simultaneously, while providing the driving source signals for the light-sensitive modulators, the core FPGA unit 101 performs digital signal processing. The signals converted by the multi-channel ADC are then synchronously processed in the core FPGA unit 101 to extract useful frequency components.

[0053] In this embodiment, the full-range ellipsometric measurement device has polarizer 2, first optical modulator 3, second optical modulator 5, and analyzer 6 arranged with their axes 45° apart. Two optical modulators are cascaded to form a polarization analysis device structure capable of performing all Stokes vector measurements. First, the detection light source 1 is converted into linearly polarized light with equal p and s polarization component amplitudes by polarizer 2 (with its transmission axis set at 45°). This light is then modulated by the first optical modulator 3 (with its fast modulation axis set at 0°) and incident on the sample to be measured. The polarization information of the sample 4 is loaded into the modulated light signal, which is further modulated by the second optical modulator 5 (with its fast modulation axis set at 45°). Finally, the light exits through analyzer 6 (with its transmission axis set at 0°) and is detected by photodetector 7. This embodiment uses Stokes vectors to describe the light signal and Muller matrices to describe the polarization transmission characteristics of the components and the sample to be measured.

[0054] S out =M A M PEM2 M S M PEM1 M P S in (1)

[0055] Among them, S in The Stokes vector representing the incident light is described as S in =I0[1 0 0 0] T Where I0 is the total intensity of the incident light. Depending on the axis arrangement of the polarization elements, their Muller matrices can be described as...

[0056] and

[0057] Among them, the Muller matrix of the first light-sensitive modulator 3 and the second light-sensitive modulator 5 adopts M PEM1 and M PEM2 This indicates that δ1 and δ2 are the phase modulations of the first optical modulator 3 and the second optical modulator 5, δ 10 and δ 20 These represent the phase modulation amplitudes of the first optical modulator 3 and the second optical modulator 5, respectively, δ1 = δ 10 sinω1t and δ2=δ 20 sinω2t, where ω1 and ω2 represent the frequencies of the first photosensitive modulator 3 and the second photosensitive modulator 5, respectively. The key to the device in this embodiment is the two photosensitive modulators, whose modulation frequencies are not equal (ω1≠ω2), forming a dual photosensitive cascaded difference frequency modulation. The typical frequency of the first photosensitive modulator 3 is generally set to 47kHz, and the frequency of the second photosensitive modulator 5 is generally set to 54kHz, forming a difference frequency modulation with non-repetitive frequencies.

[0058] The polarization characteristics of the thin film sample 4 under test were described using the Muller matrix.

[0059]

[0060] Where Ψ is the amplitude ratio of the p and s polarized light components of the detected light after reflection or transmission from sample 4, and its value ranges from 0 to 90°; Δ is the phase difference between the p and s polarized light, and its value ranges from -180° to 180°. The Muller matrix describing the polarization transmission characteristics of the polarization element and sample as described in equations (2) and (3), combined with the Stokes vector of the incident light, is substituted into equation (1) to complete the polarization transmission characteristic analysis and calculate the Stokes vector of the outgoing light. The first component of the Stokes vector of the outgoing light represents the total light intensity of the outgoing light, that is, the light intensity that the photodetector 7 can measure and obtain, which can be described as...

[0061]

[0062] In the above formula, the modulation term sinδ of the first optical modulator 3 and the second optical modulator 5 i =sin(δ) i0 sinω i t) and cosδ i =cos(δ i0 sinω i t) can be expanded using the first kind of Bessel function to obtain:

[0063] and J0 and J are positive integers. 2k-1 and J 2k These represent the 0th, 2k-1th, and 2kth order Bessel series, respectively. The first optical-elastic modulator 3 and the second optical-elastic modulator 5 correspond to i = 1 and 2, respectively. The delay of the optical-elastic modulator generally does not exceed one modulation wavelength, and the phase modulation amplitude generally does not exceed 2π. The Bessel series can take corresponding low-order values. The values ​​described in this patent are J0, J1, J2, and J3. Therefore, equation (4) can be rewritten as follows:

[0064]

[0065] Analysis of equation (5) shows that the related terms sin(2Ψ)sinΔ of the ellipticity parameter of sample 4 are contained in the frequency signals of ω2, 3ω2, 2ω1+ω2, 2ω1-ω2, 2ω1+3ω2, and 2ω1-3ω2, while the related term sin(2Ψ)cosΔ is contained in the frequency signals of ω1+ω2, ω2-ω1, ω1+3ω2, ω2-3ω1, 3ω1+ω2, and 3ω2-ω1, and the related term cos(2Ψ) is contained in the frequency signal of 2ω2. From the above analysis, it can be seen that this embodiment uses a dual-elastic cascaded difference frequency modulation method to achieve simultaneous measurement of the three related terms of the ellipticity parameter sin(2Ψ)sinΔ, sin(2Ψ)cosΔ, and cos(2Ψ), thus enabling full-range measurement of the ellipticity parameter Ψ from 0-90° and the ellipticity parameter Δ from -180° to 180°.

[0066] In the device described in this patent, the output light intensity of the analysis device, which is cascaded with dual-elastic light and frequency modulation, is loaded with the ellipsometric parameters of the thin film sample into the frequency modulation optical signal. The modulated optical signal is detected by the photodetector 7 and converted by the third data acquisition unit 104 and input into the core FPGA unit 101. Digital phase-locked loop data processing is used to simultaneously extract the amplitude of multiple channel signals.

[0067]

[0068] Meanwhile, in order to quickly and accurately solve and calibrate the phase modulation amplitude of the photoelectric modulator in real time, the inductors of the driving circuits of the two photoelectric modulators are equipped with secondary coils. The first acquisition unit 102 acquires the voltage signal of the secondary coil of the driving circuit 8 of the first photoelectric modulator and inputs it into the core FPGA unit 101. At the same time, it completes the digital phase-locked loop processing of the feedback voltage signal, and completes the resonance matching of the photoelectric modulator and the driving circuit network. When the photoelectric modulator heats up due to its own heat dissipation, the phase of the feedback voltage signal decreases. The core FPGA unit 101 increases the frequency of the driving signal source signal of the driving circuit 8 of the first photoelectric modulator, and decreases the frequency, so as to always keep the first photoelectric modulator working in the resonant working state and keep the phase modulation amplitude within a controllable range. The second acquisition unit 103 similarly implements the resonant driving control of the second photoelectric modulator 5. From the extracted signal, three frequency components, namely the sum frequency signal ω1+ω2, the difference frequency signal ω2-3ω1, and 3ω2-ω1, are selected and combined with Bessel series to complete the real-time calibration of the two photoelectric modulators. To simultaneously achieve large signal amplitudes for multiple frequency components and improve the signal-to-signal ratio in signal processing, the typical phase amplitude values ​​of the two elastic-optical modulators in this embodiment are set near half the delay amplitude λ / 2, and the phase modulation amplitude is set near π. Real-time calibration of the phase modulation amplitudes of the two elastic-optical modulators is achieved by using the ratio of the difference frequency signal and the sum frequency signal.

[0069]

[0070] Based on the ratio of the difference frequency signal and the sum frequency signal in equation (7), the phase amplitude calibration of the two photoelastic modulators is completed in real time using Bessel series. The ratio r is defined using the frequency signal amplitude loaded by the correlation term of the thin film sample ellipticity parameter. I and r II for

[0071]

[0072] The ratio r is obtained by solving the frequency signal amplitude loaded with the correlation term of the thin film sample ellipsometric parameters. I and r II It can solve for the elliptic parameters Ψ and Δ.

[0073]

[0074] By simultaneously measuring the three ellipticity parameters sin(2Ψ)sinΔ, sin(2Ψ)cosΔ, and cos(2Ψ), the full-range measurement of ellipticity parameter Ψ (0-90°) and ellipticity parameter Δ (-180°-180°) can be achieved. Simultaneously, the drive control circuit of the photoelliptic modulator is introduced into the feedback sub-coil to maintain the photoelliptic modulator's resonant operation, and the phase delay amplitude of the photoelliptic modulator is calibrated in real time. Digital phase-locked loop (PLL) digital data processing is employed, simultaneously demodulating multiple channels of digital signals, improving data processing accuracy and reducing signal demodulation costs. The single-data measurement time can be set to the microsecond range, providing advanced technical means and instrumentation for full-range, high-speed, and high-precision phase-modulated ellipticity measurement.

[0075] The above description only illustrates the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A data demodulation method of a full-range ellipsometry device based on dual-pump optical level cascade difference frequency modulation, characterized in that , comprising the following steps: S1, the Stokes vector is used to describe the optical signal, and the Muller matrix is used to describe the polarization transmission characteristics of the components and the sample to be measured in the device, which is described as: wherein, represents the Stokes vector of the incident light, described as , wherein is the total light intensity of the incident light, the Muller matrices of the first and second Pockels cells are represented by M PEM1 and M PEM2 respectively; S2, the first component of the Stokes vector of the outgoing light represents the light intensity, that is, the light intensity that can be tested by the photodetector, which is described as: wherein and are phase modulations of the first and second photoelastic modulators, and represent the phase modulation amplitudes of the first and second photoelastic modulators, respectively, and , wherein and represent the frequencies of the first and second photoelastic modulators, respectively; and Ψ and Δ represent the ellipticity parameters, Ψ is the amplitude ratio of the p and s polarized light components of the detected light after reflection or transmission by the sample, and has a range of 0-90°; Δ is the phase difference of the p and s polarized light, and has a range of -180°-180°. S3, modulation term of two cascaded photoelastic modulators and with the first kind Bessel function expansion; S4, the outgoing light intensity of the analysis device is modulated by the first and second photoelastic modulators, the sample ellipsometric parameters are loaded into the difference frequency modulation light signal, the modulated light signal is detected by the photodetector, and the third data acquisition unit is converted and input into the core FPGA unit, the digital lock phase data processing is used, and the amplitude extraction of multiple channel signals is completed synchronously; S5, the ratio of the difference frequency signal and the sum frequency signal is used to complete the phase amplitude scaling of the first and second photoelastic modulators in real time. S6. Defining a ratio using the frequency signal amplitude of the thin film sample ellipsometric parameter correlation term and ; The ratio is obtained by using the frequency signal amplitude loaded by the sample ellipsometric parameter correlation term and , ellipsometric parameters Ψ and Δ can be solved Utilizing , and three ellipsometric parameter related items are measured simultaneously, so as to realize full range measurement of ellipsometric parameter Ψ in 0-90° and ellipsometric parameter Δ in -180°-180°. The device for measuring the full range of ellipsometry based on the cascade difference frequency modulation of the double photoelastic modulators comprises a detection light source (1), a polarizer (2), a first photoelastic modulator (3), a sample (4), a second photoelastic modulator (5), a polarizer (6), and a photodetector (7). The light path direction of the detection light source (1) is sequentially provided with the polarizer (2), the first photoelastic modulator (3), and the sample (4). The reflected light path of the sample (4) is sequentially provided with the second photoelastic modulator (5), the polarizer (6), and the photodetector (7).

2. The data demodulation method of a full-range ellipsometry device based on dual-pulse optical cascade difference frequency modulation according to claim 1, characterized in that The first photoelastic modulator (3) is electrically connected with a first photoelastic modulator driving circuit (8), the second photoelastic modulator (5) is electrically connected with a second photoelastic modulator driving circuit (9), and the photodetector (7) is electrically connected with a control computer (11). The first photoelastic modulator driving circuit (8) and the second photoelastic modulator driving circuit (9) are both electrically connected to a data processing and control module (10), and the data processing and control module (10) is electrically connected to the control computer (11).

3. The data demodulation method of a full-range ellipsometry device based on dual-pulse optical cascade difference frequency modulation according to claim 2, characterized in that The data processing and control module (10) comprises a core FPGA unit (101), a first data acquisition unit (102), a second data acquisition unit (103), and a third data acquisition unit (104). The first data acquisition unit (102), the second data acquisition unit (103), and the third data acquisition unit (104) are all electrically connected to the core FPGA unit (101). The first photoelastic modulator driving circuit (8) is respectively electrically connected to the core FPGA unit (101) and the first data acquisition unit (102). The second photoelastic modulator driving circuit (9) is respectively electrically connected to the core FPGA unit (101) and the second data acquisition unit (103). The photodetector (7) is electrically connected to the third data acquisition unit (104), and the control computer (11) is electrically connected to the core FPGA unit (101).

4. The data demodulation method of a full-range ellipsometry device based on dual-pulse optical cascade difference frequency modulation according to claim 1, characterized in that The detection light source (1) adopts a laser or a monochromatic light source, the polarizer (2) and the analyzer (6) adopt bichromatic film polarizers in the visible light measurement waveband, the polarizer (2) and the analyzer (6) adopt Glan-Taylor calcite polarizers in the near-infrared measurement waveband, the polarizer (2) and the analyzer (6) adopt magnesium fluoride Lohaus prisms in the short-wave infrared measurement waveband, and the polarizer (2) and the analyzer (6) adopt metal wire grid polarizers in the mid-infrared measurement waveband.

5. The data demodulation method of a full-range ellipsometry device based on dual-pulse optical cascade difference frequency modulation according to claim 1, characterized in that The first photoelastic modulator (3) and the second photoelastic modulator (5) adopt two-dimensional octagonal symmetric structure photoelastic modulators with large light apertures and large field angles, and the light transmission crystals of the first photoelastic modulator (3) and the second photoelastic modulator (5) are fused quartz, calcium fluoride or zinc selenide.

6. The data demodulation method of a full-range ellipsometry apparatus based on dual-pulse optical cascade difference frequency modulation according to claim 1, characterized in that The axis directions of the polarizer (2), the first photoelastic modulator (3) and the second photoelastic modulator (5) are sequentially different by 45°, the first photoelastic modulator (3) and the second photoelastic modulator (5) are cascaded, the modulation frequencies of the first photoelastic modulator (3) and the second photoelastic modulator (5) are set to be different, the frequency of the first photoelastic modulator (3) is set to be 47 kHz, and the frequency of the second photoelastic modulator (5) is set to be 54 kHz.

7. The data demodulation method of a full-range ellipsometry apparatus based on dual-pulse optical cascade difference frequency modulation according to claim 1, characterized in that The photodetector (7) adopts a silicon photodetector in the visible light measurement waveband, a mercury cadmium tellurium photodetector in the near-infrared measurement waveband, an indium arsenide photodetector in the short-wave infrared measurement waveband, and an indium gallium arsenide photodetector in the mid-infrared measurement waveband.

8. The data demodulation method of a full-range ellipsometry apparatus based on dual-pulse optical cascade difference frequency modulation according to claim 1, characterized in that The Muller matrices of the first photoelastic modulator and the second photoelastic modulator in S1 are respectively: and The polarization characteristics of the sample to be measured in S1 are described by using the Muller matrix. 。 9. The data demodulation method of a full-range ellipsometry apparatus based on dual-pulse optical cascade difference frequency modulation according to claim 1, characterized in that : the S3 neutralizing sample ellipsometric parameter correlation term contained in , , , , , correlation term in the frequency signal contained in , , , , and correlation term in the frequency signal contained in the frequency signal.

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