Spectroscopic ellipsometry device and method based on a single-shot optical modulator

Abstract

The application belongs to the technical field of spectral ellipsometry devices and methods, and particularly relates to a spectral ellipsometry accurate measurement device and method based on a single photoelastic modulator, wherein a polarizer, a photoelastic modulator and a measured sample are sequentially arranged in the light path direction of the monochromator, and a polarizer and a detector are sequentially arranged in the reflection light path of the measured sample. By scanning the single photoelastic modulator and the wide-band monochromatic light of the monochromator, and by combining the phase-locked amplification of the multiple frequency signals of the modulated photoelectric signals, the signal noise ratio is improved, the fluctuation of the modulation phase amplitude of the photoelastic modulator is obtained in real time by combining the theoretical calculation of the amplitude of the multiple frequency signals, the problem of the unstable phase delay amplitude of the photoelastic modulator caused by long-time work and environmental influence is solved, and the driving voltage of the photoelastic modulator can be adjusted in real time according to the different output wavelengths of the monochromator, so as to ensure the optimal modulation efficiency.

Description

Technical Field

[0001] This invention belongs to the technical field of spectral ellipticity measurement devices and methods, specifically relating to a precise spectral ellipticity measurement device and method based on a single-elastic optical modulator. Background Technology

[0002] With the development of microelectronics, optical coating, semiconductors, and flat panel displays, high-precision spectral ellipsometric thin-film technology has become an important means of detection in this field, offering advantages such as non-contact, non-destructive testing, and high precision. However, existing spectral ellipsometric methods rely on mechanically rotating polarization devices, resulting in slow speeds that cannot meet the requirements of high-speed online spectral ellipsometric detection. Photoelastic modulators (PEMs) offer advantages such as high modulation frequencies and wide spectral ranges (from vacuum ultraviolet to far-infrared), while traditional phase modulation devices cannot achieve wide-band phase modulation. While reports have described the use of PEMs for high-speed ellipsometric measurements, traditional PEM-based ellipsometric measurements suffer from poor long-term stability of phase delay amplitude, leading to decreased ellipsometric measurement accuracy and rendering them unsuitable for high-speed online detection. Furthermore, they cannot achieve high-precision spectral ellipsometric measurements. Therefore, this paper proposes a precise spectral ellipsometric measurement method based on single-photoelastic modulation. Summary of the Invention

[0003] To address the aforementioned problems of slow spectral ellipticity measurement speed and inaccurate control of phase delay amplitude in elastic-optical modulation ellipticity measurement, which lead to slow measurement speed and decreased accuracy, this invention provides a precise spectral ellipticity measurement device and method based on a single elastic-optical modulator. The method employs a spectral ellipticity measurement method using a single elastic-optical modulation widened-band monochromator, combined with different frequency signals of the phase-locked-mode modulated optical signal, to obtain the delay amplitude of the elastic-optical modulator in real time, achieving real-time monitoring of the phase delay amplitude of the elastic-optical modulator. This is simpler than monitoring systems using external optical paths. Finally, precise spectral ellipticity analysis is obtained through monochromator and calculation.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A precise spectral ellipsometric measurement device based on a single elastic optical modulator includes a monochromator, a polarizer, an elastic optical modulator, a sample to be measured, an analyzer, a detector, an elastic optical modulator drive controller, a multi-channel digital lock-in amplifier circuit, and a computer. The polarizer, elastic optical modulator, and sample to be measured are sequentially arranged along the optical path of the monochromator. The analyzer and detector are sequentially arranged along the reflected optical path of the sample to be measured. The elastic optical modulator is electrically connected to the elastic optical modulator drive controller, which is electrically connected to the multi-channel digital lock-in amplifier circuit. The detector is electrically connected to the multi-channel digital lock-in amplifier circuit, which is electrically connected to the computer. The computer is electrically connected to the monochromator.

[0006] The polarizer is a 0° polarizer, the optical modulator is a 45° optical modulator, and the analyzer is a 45° analyzer.

[0007] A measurement method for a precise spectral ellipsometric measurement device based on a single-elastic optical modulator includes the following steps:

[0008] S1. The monochromatic light emitted by the monochromator passes sequentially through the polarizer, the light modulator, the sample under test, the analyzer, and the detector to form the measurement optical path.

[0009] S2. The modulation signal obtained by the multi-channel digital lock-in amplifier circuit is amplified by using the drive frequency of the elastic-optical modulation drive control as a reference signal.

[0010] S3. The phase delay amplitude of the photoelastic modulator is obtained in real time through computer data processing, thereby accurately obtaining the ellipticity parameters Δ and Ψ of the sample under test at this wavelength;

[0011] S4. By controlling the monochromator to pass different output wavelengths of light through the test system, and adjusting the driving voltage of the photoelectric modulator according to the output wavelength so that its phase delay amplitude meets the test requirements, the above measurement is repeated to achieve spectral ellipsometric measurement.

[0012] The method for obtaining the phase delay amplitude of the optical modulator in real time through computer data processing in S3 includes the following steps:

[0013] S3.1 Calculate the Stokes parameter S of the measured light. out ;

[0014] S3.2 Calculate the Miller matrix corresponding to the polarizer, the elastic modulator, the sample under test, and the analyzer;

[0015] S3.3 Calculate the Bessel function for the intensity of the detected light by the detector;

[0016] S3.4. Using the drive signal of the elastic-optic modulator drive controller as a reference, the multi-channel digital lock-in amplifier circuit obtains the amplitude of the first, second, third, and fourth harmonic signals, and calculates the modulation phase delay amplitude of the elastic-optic modulator at any time.

[0017] In step S3.1, the Stokes parameter S of the measured light is calculated. out The method is as follows:

[0018] The monochromator emits monochromatic light with wavelength λ. Stokes parameter S in Stokes parameter S after the entire measurement optical path out for:

[0019] Sout (λ)=M A M X (λ)M PEM (λ)M P S in (λ) (1)

[0020] Among them, S in (λ)=[I in (λ),Q in (λ),U in (λ),V in (λ)] T ,S out (λ)=[I out (λ),Q out (λ),U out (λ),V out (λ)] T .

[0021] In S3.2, the Miller matrices corresponding to the polarizer, the elastic modulator, the sample under test, and the analyzer are M, respectively. P M PEM (λ), M X (λ) and M A :

[0022]

[0023]

[0024] Where, Δ λ and Ψ λ Let Δ be the ellipticity parameter of the sample being tested. λ Ψ represents the phase difference between the p-polarized and s-polarized reflected light of the sample with wavelength λ. λ The amplitude ratio of the reflected p-polarized light and the s-polarized light of the sample with wavelength λ is given. The modulation phase delay corresponds to the wavelength λ of the photoelastic modulator. λ is the modulation phase delay amplitude corresponding to the wavelength λ of the photoelastic modulator, and ω is the modulation drive angular frequency of the photoelastic modulator.

[0025] The method for calculating the Bessel function of the detector's light intensity in S3.3 is as follows:

[0026] Since the detector can only obtain the Stokes parameter S out I in out Therefore, the Bessel function expansion of the light intensity detected by the detector is:

[0027]

[0028] Where n = 1, 2, 3..., J x (y) is the x-th Bessel function corresponding to y.

[0029] The method for calculating the amplitude of the modulation phase delay of the elastic-optic modulator at any time in S3.4 is as follows:

[0030] According to equation (3), with the drive signal of the elastic modulator drive controller as a reference, the amplitudes of the first, second, third, and fourth harmonic signals obtained by the multi-channel digital lock-in amplifier circuit are as follows:

[0031]

[0032] Among them, I ω (λ), I 2ω (λ), I 3ω (λ), I 4ω (λ) represents the signal amplitudes of the detector at frequencies of ω, 2ω, 3ω, and 4ω, obtained by phase-locked amplification.

[0033] The amplitude of the elastic-optical modulation phase delay is measured in real time according to equation (4). for:

[0034]

[0035] in, for The inverse function of .

[0036] The method for obtaining the ellipticity parameters Δ and Ψ of the sample under test at this wavelength in S3 is as follows:

[0037] Substituting equation (5) into equation (4) yields the spectral ellipticity parameter Ψ of the sample. λ for:

[0038]

[0039] Substituting equations (5) and (6) into equation (4), the spectral ellipticity Δ of the sample is measured. λ for:

[0040]

[0041] Based on the above derivation, it can be seen that as long as the amplitudes of the detector signals with frequencies of ω, 2ω, 3ω, and 4ω are obtained, and combined with the light intensity of each wavelength of the monochromator, the amplitude of the modulation phase delay of the photoelectric modulator at any wavelength λ at any given time can be accurately obtained. The ellipticity Ψ of the sample under test at this wavelength λ λ and Δ λ By combining the wide-band scanning of the monochromator with the above process, the wide-band spectral ellipsometric measurement can be achieved.

[0042] Compared with the prior art, the beneficial effects of this invention are:

[0043] This invention improves the signal-to-noise ratio by combining a single photoelectro-optic modulator with a wide-band monochromator scan, and amplifying the modulated photoelectric signal using multi-frequency harmonic amplification. It also addresses the problem of unstable phase delay amplitude caused by prolonged operation and environmental influences by obtaining the real-time amplitude fluctuation of the photoelectro-optic modulator's own modulation phase through theoretical calculation of the multi-frequency harmonic signal amplitude. Furthermore, the driving voltage of the photoelectro-optic modulator can be adjusted in real-time according to the different output wavelengths of the monochromator to ensure optimal modulation efficiency. Finally, by combining different monochromator scans, it enables precise measurement of the spectral ellipsometric parameters Δ and Ψ of the sample under test. Attached Figure Description

[0044] 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.

[0045] 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.

[0046] Figure 1 This is a schematic diagram of the structure of the present invention.

[0047] Wherein: 1 is a monochromator, 2 is a polarizer, 3 is a photoelectric modulator, 4 is the sample under test, 5 is a polarizer, 6 is a detector, 7 is a photoelectric modulator drive controller, 8 is a multi-channel digital lock-in amplifier circuit, and 9 is a computer. Detailed Implementation

[0048] 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.

[0049] 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.

[0050] 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.

[0051] In this embodiment, as Figure 1 As shown, the test system consists of a monochromator 1, a polarizer 2, a photosensitive modulator 3, a sample under test 4, an analyzer 5, a detector 6, a photosensitive modulator drive controller 7, a multi-channel digital lock-in amplifier circuit 8, and a computer 9. Monochromatic light emitted by the monochromator 1 passes sequentially through the polarizer 2, photosensitive modulator 3, sample under test 4, analyzer 5, and detector 6 to form the measurement optical path. Using the drive frequency of the photosensitive modulator drive controller 7 as a reference signal, the modulation signal obtained by the multi-channel digital lock-in amplifier circuit 8 is amplified. Finally, the phase delay amplitude of the photosensitive modulator 3 is obtained in real time through data processing by the computer 9, thereby accurately obtaining the ellipticity parameters Δ and Ψ of the sample under test at that wavelength. The computer 9 then controls different output wavelengths of light from the monochromator to pass through the test system, while simultaneously adjusting the drive voltage of the photosensitive modulator 3 according to the output wavelength to ensure that its phase delay amplitude meets the test requirements. This measurement is repeated to achieve spectral ellipticity measurement. Preferably, polarizer 2 is a 0° polarizer, optical modulator 3 is a 45° optical modulator, and analyzer 5 is a 45° analyzer. The specific scheme is as follows:

[0052] Monochromator 1 emits monochromatic light with wavelength λ. Stokes parameter S in Stokes parameter S after the entire measurement optical path out for:

[0053] S out (λ)=M A M X (λ)M PEM (λ)M P S in (λ) (1)

[0054] Among them, S in (λ)=[I in (λ),Q in (λ),U in (λ),Vin (λ)] T ,S out (λ)=[I out (λ),Q out (λ),U out (λ),V out (λ)] T M P M PEM (λ), M X (λ) and M A The Miller matrices for polarizer 2, optical modulator 3, sample under test 4, and analyzer 5 are as follows:

[0055]

[0056]

[0057] Where, Δ λ and Ψ λ Let Δ be the ellipticity parameter of the sample being tested. λ Ψ represents the phase difference between the p-polarized and s-polarized reflected light of the sample with wavelength λ. λ The amplitude ratio of the reflected p-polarized light and s-polarized light of the sample at wavelength λ is given. The modulation phase delay corresponding to wavelength λ of the photoelastic modulator. ω is the modulation phase delay amplitude corresponding to wavelength λ of the photoelastic modulator 3, and ω is the modulation drive angular frequency of the photoelastic modulator 3.

[0058] Since the detector can only obtain the Stokes parameter S out I in out Therefore, detector 6 detects the light intensity and expands it using the Bessel function as follows:

[0059]

[0060] Where n = 1, 2, 3..., J x (y) is the x-th Bessel function corresponding to y.

[0061] According to equation (3), with the drive signal of the light-sensitive modulator drive controller 7 as a reference, the amplitudes of the first, second, third, and fourth harmonic signals obtained by the multi-channel digital lock-in amplifier circuit 8 are as follows:

[0062]

[0063] Among them, I ω (λ), I 2ω (λ), I 3ω (λ), I 4ω(λ) represents the signal amplitudes of detector 6 at frequencies of ω, 2ω, 3ω, and 4ω, obtained by phase-locked amplification.

[0064] The amplitude of the elastic-optical modulation phase delay can be measured in real time according to equation (4). for:

[0065]

[0066] in, for The inverse function of .

[0067] Substituting equation (5) into equation (4) yields the spectral ellipticity parameter Ψ of the sample. λ for:

[0068]

[0069] Substituting equations (5) and (6) into equation (4) yields the spectral ellipsometry parameter Δ of the sample 4. λ for:

[0070]

[0071] Based on the above derivation, it can be seen that as long as the amplitudes of the signals with frequencies of ω, 2ω, 3ω, and 4ω in detector 6 are obtained, and combined with the light intensity of each wavelength in monochromator 1, the modulation phase delay amplitude of the light modulator 3 at any wavelength λ at any time can be accurately obtained. The ellipsometric parameter Ψ of the tested sample 4 at this wavelength λ λ and Δ λ By combining the monochromator with wide-band scanning and repeating the above process, wide-band spectral ellipsometric measurement can be achieved. This solves the problem of decreased spectral ellipsometric measurement accuracy caused by environmental influences and the temperature effect of the elastic modulator itself during long-term operation, which leads to instability of the modulation phase amplitude. Furthermore, the driving voltage of the elastic modulator can be adjusted according to different wavelengths, ensuring that the elastic modulator phase amplitude operates at the optimal position in real time, thus solving the problem of decreased ellipsometric measurement accuracy caused by dispersion in traditional phase waveplates.

[0072] 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 measuring method of a single-pulse optical modulator-based spectroscopic ellipsometry apparatus, characterized by, It comprises the following steps: S1, monochromatic light emitted by the monochromator passes through the polarizer, the photoelastic modulator, the measured sample, the analyzer and the detector in turn to form a measurement light path; S2, the modulation signal obtained by the multi-channel digital lock-in amplifier is phase-locked according to the drive frequency of the photoelastic modulation drive control as a reference signal; S3, the phase delay amplitude of the photoelastic modulator is obtained in real time through computer data processing, and then the ellipsometric parameters Δ and Ψ of the measured sample at the measured wavelength are accurately obtained; S3.1, calculating the Stokes parameters S of the measured light out ; S3.2, the Miller matrix corresponding to the polarizer, the photoelastic modulator, the measured sample and the analyzer is obtained; S3.3, the Bessel function of the light intensity detected by the detector is calculated; S3.4, the amplitude of the one-fold frequency, two-fold frequency, three-fold frequency and four-fold frequency signals obtained by the multi-channel digital lock-in amplifier is calculated with the drive signal of the photoelastic modulator drive controller as a reference, and the modulation phase delay amplitude of the photoelastic modulator at any time is calculated; According to the Bessel function of the light intensity detected by the detector, the amplitude of the one-fold frequency, two-fold frequency, three-fold frequency and four-fold frequency signals obtained by the multi-channel digital lock-in amplifier is calculated with the drive signal of the photoelastic modulator drive controller as a reference, and the modulation phase delay amplitude of the photoelastic modulator at any time is calculated; (4) wherein, I ω (λ), I 2ω (λ), I 3ω (λ), I 4ω (λ) are the signal amplitudes obtained by the detector through lock-in amplification with the frequencies of ω, 2ω, 3ω, 4ω respectively; Δ λ and Ψ λ are the ellipsometric parameters of the measured sample, Δ λ is the phase difference between the p-polarized light and s-polarized light of the reflected light of the measured sample with the wavelength of λ, Ψ λ is the amplitude ratio between the p-polarized light and s-polarized light of the reflected light of the measured sample with the wavelength of λ, is the modulation phase delay corresponding to the wavelength λ of the photoelastic modulator, is the modulation phase delay amplitude corresponding to the wavelength λ of the photoelastic modulator, and ω is the modulation driving angular frequency of the photoelastic modulator; J x (y) is the xth Bessel function corresponding to y; The real-time measured elastic light modulation phase delay amplitude according to the formula (4) is: (5) wherein is the inverse function of S4, the different output wavelengths of the monochromator are controlled by the computer to pass through the test system, and the drive voltage of the photoelastic modulator is adjusted according to the output wavelength to make its phase delay amplitude meet the test requirements, and the above measurement is repeated to realize the spectral ellipsometric measurement; The spectral ellipsometric accurate measurement device based on a single photoelastic modulator comprises a monochromator (1), a polarizer (2), a photoelastic modulator (3), a measured sample (4), an analyzer (5), a detector (6), a photoelastic modulator drive controller (7), a multi-channel digital lock-in amplifier circuit (8) and a computer (9). The light path direction of the monochromator (1) is sequentially provided with the polarizer (2), the photoelastic modulator (3) and the measured sample (4). The reflected light path of the measured sample (4) is sequentially provided with the analyzer (5) and the detector (6). The photoelastic modulator (3) is electrically connected to the photoelastic modulator drive controller (7). The photoelastic modulator drive controller (7) is electrically connected to the multi-channel digital lock-in amplifier circuit (8). The detector (6) is electrically connected to the multi-channel digital lock-in amplifier circuit (8). The multi-channel digital lock-in amplifier circuit (8) is electrically connected to the computer (9). The computer (9) is electrically connected to the monochromator (1).

2. The method according to claim 1, wherein the method is characterized by: The polarizer (2) is a 0° polarizer. The photoelastic modulator (3) is a 45° photoelastic modulator. The analyzer (5) is a 45° analyzer.

3. The method according to claim 1, wherein the method is characterized by: The method of S3.1 calculates the Stokes parameters S of the measured light out is: The monochromator emits monochromatic light of wavelength λ Stokes parameter S in Stokes parameter S after passing through the entire measurement light path out is: (1) where S in (λ) = [I in (λ), Q in (λ), U in (λ), V in (λ)] T , S out (λ) = [I out (λ), Q out (λ), U out (λ), V out (λ)] T , M P , M PEM (λ), M X (λ), and M A are the Mueller matrices corresponding to the polarizer, the photoelastic modulator, the sample under test, and the analyzer, respectively.

4. The method according to claim 1, wherein the method is characterized by: The Miller matrices corresponding to the polarizer, the electro-optic modulator, the sample under test and the analyzer in S3.2 are M P (λ), M PEM (λ), M X (λ) and M A (λ), respectively. , , , (2) wherein Δ λ and Ψ λ are ellipsometric parameters of the sample under test, Δ λ is the phase difference between the p- and s-polarized light reflected by the sample under test at a wavelength λ, and Ψ λ is the amplitude ratio of the p- and s-polarized light reflected by the sample under test at a wavelength λ, is the modulation phase delay corresponding to the wavelength λ of the photoelastic modulator, is the amplitude of the modulation phase delay corresponding to the wavelength λ of the photoelastic modulator, and ω is the modulation drive angular frequency of the photoelastic modulator.

5. The method according to claim 1, wherein the method is characterized by: measuring the light intensity of the light beam outputted from the single-shot optical modulator; and calculating the ellipsometric parameters based on the measured light intensity of the light beam outputted from the single-shot optical modulator. The method for obtaining the ellipsometric parameters Δ and Ψ of the measured sample at the wavelength in S3 is: Substituting (5) into (4) gives the measured sample's spectral ellipsometric parameter Ψ λ is: (6) The measured sample's spectral ellipsometric parameters Δ and Ψ of formula (4) are measured by putting formula (5) and (6) into formula (4) λ are: (7) As long as the signal amplitude of the frequency ω, 2ω, 3ω, 4ω in the detector signal is obtained, the modulation phase delay amplitude of the photoelastic modulator at any moment at the wavelength λ is accurately obtained in combination with the light intensity of each wavelength of the monochromator , the ellipsometric parameter Ψ of the measured sample at the wavelength λ λ and Δ λ , in combination with the wide band scanning of the monochromator, repeating steps S1-S3, that is, the wide band spectral ellipsometric measurement is realized.

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