Ultra-high speed ellipsometer based on single-beam optical modulation self-feedback

Abstract

The application belongs to the technical field of ellipsometric accurate measuring device and method, and particularly relates to an ultrahigh-speed ellipsometric accurate measuring device and method based on single photoelasticity modulation self-feedback, wherein a polarizer, a quarter-wave plate and a measured sample are sequentially arranged in the light path direction of a light source, a photoelasticity modulator, a polarizer and a detector are sequentially arranged in the reflection light path of the measured sample, and the photoelasticity modulator is electrically connected with a photoelasticity modulator driving control and a multi-channel digital lock-in amplification circuit. The application carries out multi-frequency signal lock-in amplification on the photoelectric signal modulated by a single photoelasticity modulator, takes the photoelasticity modulator driving frequency as a reference, obtains the signal amplitude of one frequency multiplication, two frequency multiplications, three frequency multiplications and four frequency multiplications, combines theoretical calculation to obtain the modulation phase amplitude caused by the long-term working temperature influence and environmental influence of the two photoelasticity modulators, and further realizes the accurate measurement of the ellipsometric parameters Δ and Ψ of the measured sample.

Description

Technical Field

[0001] This invention belongs to the technical field of ellipticity precision measurement devices and methods, specifically relating to an ultra-high-speed ellipticity precision measurement device and method based on single-elastic optical modulation self-feedback. Background Technology

[0002] With the development of microelectronics, optical coating, semiconductor, and flat panel display technologies in my country, high-precision ellipsometry 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 ellipsometry methods mostly employ mechanical rotation, resulting in low time resolution (on the order of seconds), which cannot meet the measurement requirements of high-speed online in-situ detection.

[0003] Photoelastic modulators (PEMs) are high-speed phase modulation devices based on the photoelastic effect of optically birefringent crystal materials. Due to their advantages such as no mechanical vibration influence, large incident angle, high modulation frequency, low loss, and wide wavelength range (from vacuum ultraviolet to far-infrared), they have played a positive role in promoting the field of optical polarization measurement and show great potential for application in ultra-high-speed ellipsometrics. However, traditional photoelastic modulator ellipsometric measurements suffer from poor long-term stability of phase delay amplitude, leading to decreased ellipsometric measurement accuracy and rendering them unusable in high-speed online detection. Therefore, a precise ultra-high-speed ellipsometric measurement method based on single photoelastic modulation self-feedback is proposed. Summary of the Invention

[0004] To address the technical problem of decreased ellipticity measurement accuracy due to the inability to precisely control the phase delay amplitude in existing elastic-optical modulation ellipticity measurements, this invention provides an ultra-high-speed ellipticity measurement device and method based on single elastic-optical modulation self-feedback. This method employs single elastic-optical modulation combined with different frequency signals of the optical signal after phase-locked loop modulation to obtain the phase delay amplitude of the elastic-optical modulator in real time, achieving self-feedback of the phase delay amplitude of the elastic-optical modulator, and then accurately obtaining the ellipticity parameters through calculation.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] The ultra-high-speed ellipsometry precision measurement device based on single-elastic-optical modulation self-feedback includes a light source, a polarizer, a quarter-wave plate, a sample under test, an elastic-optical modulator, an analyzer, a detector, an elastic-optical modulator drive control and multi-channel digital lock-in amplifier circuit, and a computer. The polarizer, quarter-wave plate, and sample under test are arranged sequentially in the optical path of the light source. The elastic-optical modulator, analyzer, and detector are arranged sequentially in the reflected optical path of the sample under test. The elastic-optical modulator is electrically connected to the elastic-optical modulator drive control and multi-channel digital lock-in amplifier circuit. The detector is electrically connected to the computer. The elastic-optical modulator drive control and multi-channel digital lock-in amplifier circuit is electrically connected to the computer.

[0007] The polarizer is a 0° polarizer, the quarter-wave plate is a 45° quarter-wave plate, the elastic modulator is a 0° elastic modulator, and the analyzer is a 45° analyzer.

[0008] The measurement method based on a high-speed ellipticity measurement device with single-elastic optical modulation self-feedback includes the following steps:

[0009] S1. The light source passes sequentially through a polarizer, a quarter-wave plate, the sample under test, an optical modulator, an analyzer, and a detector to form the measurement optical path.

[0010] S2. Using the frequency of the elastic-optical modulation drive signal provided by the elastic-optical modulation drive control and multi-channel digital lock-in amplifier circuit as a reference, the digital lock-in amplifier performs phase-locked amplification on the modulation signal obtained by the detector.

[0011] 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.

[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, quarter-wave plate, sample under test, optical modulator and analyzer;

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

[0016] S3.4 Calculate the amplitude of the modulation phase delay of the elastic-optical 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] Stokes parameter S of the light source in Stokes parameter S after the entire measurement optical path out for:

[0019] S out =M A M PEM M X M W M P S in (1)

[0020] Among them, S in=[I in Q in U in V in ] T ,S out =[I out Q out U out V out ] T ;

[0021] In S3.2, the Miller matrices corresponding to the polarizer, quarter-wave plate, sample under test, elastic modulator, and analyzer are M, respectively. P M W M X M PEM and M A :

[0022]

[0023] Where δ=δ0sin(2πft) is the modulation phase delay of the photoelastic modulator, δ0 is the amplitude of the modulation phase delay of the photoelastic modulator, and ω is the modulation drive angular frequency of the photoelastic modulator.

[0024] The method for calculating the Bessel function of the detector's light intensity in S3.3 is as follows:

[0025] 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:

[0026]

[0027] Where m is an odd number and n is an even number, J x (y) is the x-th Bessel function corresponding to y.

[0028] The method for calculating the amplitude of the modulation phase delay of the elastic modulator at any time in S3.4 is as follows:

[0029] According to formula (3), combined with lock-in amplification, and taking the drive frequency of the optical modulator as a reference, the amplitudes of different harmonic signals are obtained as follows:

[0030]

[0031] Among them, I ω I 2ω I 3ω I 4ω The frequencies of the signals obtained by the detector after phase-locked amplification are ω, 2ω, 3ω, and 4ω, respectively.

[0032] According to equation (4), the real-time measured amplitude of the elastic-optical modulation phase delay δ0 is:

[0033]

[0034] in, for The inverse function of .

[0035] The method for obtaining the ellipticity parameters Δ and Ψ of the sample under test in S3 is as follows:

[0036] Based on equations (4) and (5), the ellipticity parameters Δ and Ψ of the tested sample are obtained as follows:

[0037]

[0038]

[0039] Based on the above derivation, as long as the amplitudes of the detector signals with frequencies of ω, 2ω, 3ω, and 4ω are obtained, the amplitudes of the modulation phase delay δ0 of the photoelectric modulator at any time, the ellipsometric parameters Δ and Ψ of the sample under test can be accurately obtained by combining them with the light intensity of the light source.

[0040] Compared with the prior art, the beneficial effects of this invention are:

[0041] This invention amplifies the photoelectric signal modulated by a single photoelectro-optic modulator through multi-frequency signal lock-in amplification, using the driving frequency of the photoelectro-optic modulator as a reference to obtain the signal amplitudes of the first, second, third, and fourth harmonics. Combined with theoretical calculations, the modulation phase amplitude caused by the long-term operating temperature and environmental influences of the two photoelectro-optic modulators is obtained in real time. This solves the problem of unstable phase delay amplitude of the photoelectro-optic modulator caused by long-term operation and environmental influences, thereby achieving accurate measurement of the ellipticity parameters Δ and Ψ of the sample under test. 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 light source, 2 is the polarizer, 3 is the quarter-wave plate, 4 is the sample under test, 5 is the photoelectric modulator, 6 is the analyzer, 7 is the detector, 8 is the photoelectric modulator drive control and multi-channel digital lock-in amplifier circuit, and 9 is the 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] 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.

[0049] In this embodiment, as Figure 1As shown, the test system consists of a light source 1, a polarizer 2, a quarter-wave plate 3, a sample under test 4, a photoelectric modulator 5, an analyzer 6, a detector 7, a photoelectric modulator drive control and multi-channel digital lock-in amplifier circuit 8, and a computer 9. The light source 1 sequentially forms the measurement optical path through the polarizer 2, quarter-wave plate 3, sample under test 4, photoelectric modulator 5, analyzer 6, and detector 7. Using the photoelectric modulation drive signal frequency provided by the photoelectric modulation drive control and multi-channel digital lock-in amplifier circuit 8 as a reference, the digital lock-in amplifier amplifies the modulation signal obtained from the detector 7. Finally, the computer 9 processes the data to obtain the phase delay amplitude of the photoelectric modulator 5 in real time, thereby accurately obtaining the ellipsometric parameters Δ and Ψ of the sample under test. Preferably, the polarizer 2 is a 0° polarizer, the quarter-wave plate 3 is a 45° quarter-wave plate, the photoelectric modulator 5 is a 0° photoelectric modulator, and the analyzer 6 is a 45° analyzer. The specific scheme is as follows:

[0050] Stokes parameter S of light source 1 in Stokes parameter S after the entire measurement optical path out for:

[0051] S out =M A M PEM M X M W M P S in (1)

[0052] Among them, S in =[I in Q in U in V in ] T ,S out =[I out Q out U out V out ] T M P M W M X M PEM and M A The Miller matrices for polarizer 2, quarter-wave plate 3, sample under test 4, optical modulator 5, and analyzer 6 are as follows:

[0053]

[0054] Where δ=δ0sin(2πft) is the modulation phase delay of the photoelastic modulator 5, δ0 is the amplitude of the modulation phase delay of the photoelastic modulator 5, and ω is the modulation drive angular frequency of the photoelastic modulator 5.

[0055] Since the detector can only obtain the Stokes parameter S out I in out Therefore, the detector detects the light intensity and expands the Bessel function as follows:

[0056]

[0057] Where m is an odd number and n is an even number, J x (y) is the x-th Bessel function corresponding to y.

[0058] Traditional elliptic modulation methods assume that the modulation phase delay amplitude δ0 is constant; however, in practical applications, the elliptic modulator suffers from problems such as ambient temperature and long-term temperature changes leading to resonant frequency drift, resulting in an unstable modulation phase delay amplitude δ0.

[0059] In order to accurately obtain the ellipsometric parameters Δ and Ψ of the sample under test, the instability of the amplitude of the phase delay δ0 of the elastic-optical modulation needs to be considered, that is, δ0 needs to be obtained at all times. Therefore, in addition to the ellipsometric parameters Δ and Ψ of the sample under test, the amplitude of the phase delay δ0 of the elastic-optical modulation also needs to be measured in real time. According to formula (3), combined with lock-in amplification, with the driving frequency of the elastic-optical modulator 5 as a reference, the amplitudes of different harmonic signals can be obtained as follows:

[0060]

[0061] Among them, I ω I 2ω I 3ω I 4ω The frequencies of the signals obtained by the detector after phase-locked amplification are ω, 2ω, 3ω, and 4ω, respectively.

[0062] According to equation (4), the amplitude of the phase delay δ0 of the photoelastic modulation can be measured in real time as follows:

[0063]

[0064] in, for The inverse function of .

[0065] Furthermore, based on equations (4) and (5), the ellipticity parameters Δ and Ψ of the tested sample can be measured as follows:

[0066]

[0067]

[0068] As can be seen from the above derivation, as long as the signal amplitudes of the detector signals with frequencies of ω, 2ω, 3ω, and 4ω are obtained, and combined with the light intensity of the light source, the amplitude of the modulation phase delay δ0 of the photoelectric modulator at any time, and the ellipsometric parameters Δ and Ψ of the sample under test can be accurately obtained. This solves the problem of decreased ellipsometric measurement accuracy caused by the instability of the modulation phase amplitude due to environmental influences and the temperature effect of the photoelectric modulator itself during long-term operation.

[0069] 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. An ultra-high speed ellipsometry apparatus based on single-shot optical modulation self-feedback, characterized in that: The application relates to a single photoelastic modulation self-feedback based high-speed ellipsometry device, which comprises a light source (1), a polarizer (2), a quarter-wave plate (3), a measured sample (4), a photoelastic modulator (5), a polarimeter (6), a detector (7), a photoelastic modulator driving control and multi-channel digital lock-in amplifier circuit (8) and a computer (9), the light path direction of the light source (1) is sequentially provided with the polarizer (2), the quarter-wave plate (3) and the measured sample (4), the reflected light path of the measured sample (4) is sequentially provided with the photoelastic modulator (5), the polarimeter (6) and the detector (7), the photoelastic modulator (5) is electrically connected with the photoelastic modulator driving control and multi-channel digital lock-in amplifier circuit (8), the detector (7) is electrically connected with the computer (9), and the photoelastic modulator driving control and multi-channel digital lock-in amplifier circuit (8) is electrically connected with the computer (9). The measurement method of the single photoelastic modulation self-feedback based high-speed ellipsometry device comprises the following steps: S1, the light source sequentially passes through the polarizer, the quarter-wave plate, the measured sample, the photoelastic modulator, the polarimeter and the detector to form a measurement light path; S2, according to the photoelastic modulation driving signal frequency provided by the photoelastic modulation driving control and multi-channel digital lock-in amplifier circuit, the digital lock-in is used to perform lock-in amplification on the modulation signal obtained by the detector; S3, the phase delay amplitude of the photoelastic modulator is obtained in real time through computer data processing, and then the ellipsometric parameters Delta and Psi of the measured sample 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 quarter-wave plate, the measured sample, the photoelastic modulator and the polarimeter is obtained; S3.3, the Bessel function of the light intensity detected by the detector is calculated; Since the detector can only obtain the Stokes parameter S out , I out , the Bessel function expansion of the light intensity detected by the detector is: (3) wherein, wherein m is an odd number, n is an even number, J x (y) is the xth order Bessel function of argument y; S3.4, the modulation phase delay amplitude of the photoelastic modulator at any moment is calculated; According to formula (3), combined with lock-in amplification, the different frequency signal amplitudes are obtained as follows by taking the photoelastic modulator driving frequency as a reference: (4) wherein I ω , I 2ω , I 3ω , I 4ω are the signal amplitudes at the frequencies ω, 2ω, 3ω, 4ω, respectively, obtained by the detector via lock-in amplification. According to formula (4), the real-time measured photoelastic modulation phase delay amplitude delta0 is: (5) wherein is the inverse function of 2. The single-pulse optical modulation self-feedback based ultrafast ellipsometry apparatus of claim 1, wherein: The polarizer (2) is a 0-degree polarizer, the quarter-wave plate (3) is a 45-degree quarter-wave plate, the photoelastic modulator (5) is a 0-degree photoelastic modulator, and the polarimeter (6) is a 45-degree polarimeter.

3. The single-pulse optical modulation self-feedback based ultrafast ellipsometry apparatus of claim 1, wherein: The method of S3.1 calculates the Stokes parameters S of the measured light out is: Stokes parameter S of the light source in Stokes parameter S after the entire measurement light path out is: (1) where S in = [I in , Q in , U in , V in ] T , S out = [I out , Q out , U out , V out ] T .

4. The single-pulse optical modulation self-feedback based ultrafast ellipsometry apparatus of claim 1, wherein: The Miller matrices corresponding to the polarizer, quarter-wave plate, sample under test, photoelastic modulator, and analyzer in S3.2 are M P , W , X , PEM , and M A , respectively. ， , , (2) wherein, is the modulation phase delay of the photoelastic modulator, δ0is the modulation phase delay amplitude of the photoelastic modulator, and ω is the modulation drive angular frequency of the photoelastic modulator.

5. The single-pulse photomodulation self-feedback based ultrafast ellipsometry apparatus of claim 1, wherein: The method for obtaining the ellipsometric parameters Delta and Psi of the measured sample in S3 is: According to formula (4) and formula (5), the ellipsometric parameters Delta and Psi of the measured sample are respectively: (6) (7) As long as the signal amplitudes of the frequencies omega, 2omega, 3omega and 4omega in the detector signal are obtained, the photoelastic modulator modulation phase delay amplitude delta0 and the ellipsometric parameters Delta and Psi of the measured sample can be accurately obtained by combining the light intensity of the light source.

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