CN113340818A - Self-consistent verification differential spectrometer and measurement method - Google Patents
Self-consistent verification differential spectrometer and measurement method Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
- G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
- G01B11/0625—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating with measurement of absorption or reflection
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
Abstract
The invention discloses a self-consistent verification differential spectrometer and a measurement method, wherein a non-polarization beam splitter is arranged, one beam of light realizes oblique incidence reflection differential module test, the other beam of light is used for realizing oblique incidence differential reflection module test, the method can realize simultaneous measurement of second-level wide spectrum differential reflection signals and reflection differential signals, corresponding models are established based on two measurement signals, film thickness parameters are obtained through respective iterative inversion, self-consistent verification is carried out by utilizing the actual property that the film thickness parameters at the same moment are necessarily unique, the measurement precision is improved, and the method can be widely applied to online monitoring application of different processes such as chemical vapor deposition, molecular beam epitaxy, spin coating and the like in the industrial growth field of nano films.
Description
Technical Field
The invention relates to the technical field of testing of a growth process of a nano film material, relates to the technical field of in-situ, real-time and on-line optical detection of growth (including epitaxial growth, vapor deposition and spin coating processes) processes of a semiconductor nano film, a two-dimensional material, a perovskite material and a metal organic framework material, and particularly relates to a self-consistent verified differential spectrometer and a measurement method.
Background
The reflection differential spectroscopy and the differential reflection method are two common thin film on-line growth monitoring technologies, and the reflection differential spectroscopy realizes measurement of crystalline physical properties of a thin film by measuring the change of the polarization state of incident linearly polarized light by the thin film, such as the arrangement of anisotropic molecules, the direction of a crystal axis and the like. In the case of near normal incidence, the reflected differential signal Δ R/R has the formula: Δ R/R ═ 2 (R)s-Rp)/(Rs+Rp) Wherein R ispAnd RsThe reflected light p-polarized component and s-polarized component, respectively, are only suitable for the measurement of anisotropic films. In the case of oblique incidence, the mathematical expression for the reflected differential signal is: Δ R/R ═ Δp-Δs＝(Rp-Rp0)/Rp0-(Rs-Rs0)/Rs0Wherein R isp0And Rs0The p-polarized and s-polarized components of the light reflected by the bare substrate before the film growth is started, respectively. The advantage of the oblique incidence reflective differential system is that it works with both anisotropic and isotropic films. According to the definition, the reflection differential spectroscopy technology greatly suppresses the signal contribution of the substrate by using a differential algorithm, such as R of an isotropic substrate under the condition of approximately vertical incidencep＝RsAnd the reflected differential signal delta R/R of the substrate is 0. Under oblique incidence, the R is enabled to pass through the phase modulation device before starting to generatep0＝Rs0That is, when the reflected differential signal Δ R/R is 0. Therefore, the reflection differential spectroscopy has the greatest advantage of being highly sensitive to the physical properties of the surface/interface and is very suitable for the measurement of the nanometer thickness film.
The differential reflection spectroscopy realizes the evolution rule of the measurement of the optical reflection/absorption physical property of the film along with the change of the growth time by comparing the difference between the reflection light of the bare substrate and the reflection light of the film in the growth process at different moments, and the mathematical expression of the differential reflection spectroscopy is as follows:
ΔR(t)/R(t)＝(R(t)sample-R(t0)substrate)/R(t0)substrate (1)
wherein, R (t)sampleIs a film at time tReflectivity of R (t)0)substrateIs at t0The reflectivity of the bare substrate at the moment.
The reflected differential signal generally needs to use a polarized light modulation technology, and has higher sensitivity and signal-to-noise ratio, but in order to obtain a wide spectrum signal, a wavelength scanning mode needs to be used, the acquisition speed is slower, and the single acquisition time is in the order of minutes. The differential reflection spectrum is relatively simple and has high time resolution. Particularly, when a wide-spectrum light source is used, the time resolution of the differential reflection signal is only limited by the acquisition rate of the spectrometer, high-speed acquisition in a wide-band range can be realized, and the time resolution can reach millisecond magnitude at most. The two measurement methods are based on inversion of a physical model to obtain the thickness of the film, and the measurement accuracy depends on fitting of the physical model. However, in the practical application process, the ideal physical model cannot truly reflect the measurement error caused by the specific experimental conditions, such as the stress influence of the experimental observation window is difficult to calibrate, and the neglect processing is usually performed in the physical model. In addition, the periodicity of the optical interference results in non-unique fitting results, requiring additional conditions for limitation. A novel optical path system is designed, a broadband differential reflection signal and a single-wavelength reflection differential signal are simultaneously realized, respective advantages can be inherited, and the measurement of crystalline physical properties and broad-spectrum reflection/absorption physical properties of the film can be simultaneously realized under the high-speed time resolution. And respectively establishing corresponding physical models aiming at the two signals, respectively obtaining film thickness parameters by using an inversion algorithm, then comparing and self-consistent verifying the thickness parameters obtained respectively, and stopping respective fitting processes until the two signals obtain the thickness parameters. The online self-consistent verification method can greatly improve the measurement precision of the film thickness.
Disclosure of Invention
The invention provides a self-consistent verification differential spectrometer and a measurement method, which simultaneously realize the optical technology of rapid measurement of reflection differential signals and differential reflection spectra, the reflection differential signals of a single wavelength channel carry out high-sensitivity detection on the thickness of a film, the measurement resolution of a monoatomic layer and a submonolayer is realized, the absorption characteristics, the nucleation state and the appearance of a growing film are monitored in real time and on line by wide-spectrum differential reflection signals, and the self-consistent verification is carried out by utilizing the thickness respectively fitted by the two signals, so that the measurement accuracy is improved. The invention can record the growth process on line in real time under the time resolution of second level, directly reveal the mechanism of the film growth process, and is described in detail as follows:
in a first aspect, a self-consistent validating differential spectrometer, the spectrometer comprising: an incident arm assembly, a differential reflective module assembly, a reflective differential module assembly,
the incident arm assembly includes: the wide-spectrum white light source emits light beams with a large divergence angle, the light beams are converged into parallel light beams after passing through the collimating lens group, then the parallel light beams are changed into linear polarized light through the polarizer, and the linear polarized light and the elliptical polarized light are changed into linear polarized light through the half-wave plate arranged on the precision rotating platform;
the differential reflection module assembly sequentially comprises: the reflected light beam passes through a chopper to realize the periodic blocking and passing of a light path, then passes through a second converging lens group, is changed into a converging light beam from a parallel light beam, and then is converted into an electric signal by a spectrometer detector;
the reflective differential module assembly includes: the reflected light beam is converted into single-wavelength light beam through the filter plate, then the single-wavelength light beam sequentially passes through the photoelastic modulator and the analyzer to be subjected to optical polarization modulation, then passes through the first converging lens group, is converted into converging light beam by parallel light, and then is converted into an electric signal by the high-frequency photoelectric detector.
In a second aspect, a self-consistent verification differential spectrum measurement method, which enables simultaneous measurement of a oblique-incidence reflected differential signal and a oblique-incidence differential reflected signal, includes the following steps:
the reflected light reflected by the sample passes through the non-polarization beam splitter, wherein the light with the 90-degree turning direction passes through the chopper and the second converging lens group and enters a spectrometer detector for acquiring a differential reflection signal;
the light beams with unchanged propagation directions sequentially pass through the filter, the photoelastic modulator, the analyzer and the first converging lens group, are collected by the photomultiplier detector and are used for acquiring reflection differential signals;
and respectively establishing corresponding physical models aiming at the reflection differential signals and the differential reflection signals, respectively obtaining film thickness parameters through iterative inversion, comparing the 2 thickness parameters, and performing self-consistent verification.
The technical scheme provided by the invention has the beneficial effects that:
1) simultaneous measurement of differential reflectance spectra and reflected differential signals: the light beam reflected from the surface of the sample is divided into two beams of light by introducing a non-polarization beam splitter, and the two beams of light are respectively used for measuring a differential reflection signal and a reflection differential signal;
2) in terms of film thickness measurement: self-consistent verification is carried out on the film thickness obtained by inverting the broadband differential reflection signal and the film thickness obtained by inverting the reflection differential signal, and the iteration process, the limiting condition and the optimization algorithm of the physical model are automatically changed, so that the accuracy of the online measurement of the film thickness based on the physical model is greatly improved;
3) in terms of measurement speed, the single acquisition time is as fast as milliseconds: the wide-spectrum white light is used as a light source, the acquisition time of the differential reflection spectrum depends on the acquisition time of an adopted wide-spectrum spectrometer, meanwhile, the reflection differential signal works in a single wavelength mode, and the acquisition time is only limited by the working frequency of a detector; the collection of the differential reflection spectrum and the collection of the reflection differential signals are mutually independent and parallel, so that the time for collecting the primary differential reflection spectrum and the reflection differential signals can reach millisecond level as soon as possible;
4) in terms of measurement function: the method has the advantages that the physical model is corrected by utilizing the self-consistent verification of the unique film thickness, and the accuracy of physical interpretation of the absorption characteristic, the nucleation state and the morphology of the growing film obtained by utilizing the broadband differential reflection signal is improved.
Drawings
FIG. 1 is a schematic structural diagram of a self-consistent verification differential spectrometer;
FIG. 2 is a flow chart of calibration before growth begins;
FIG. 3 is a flow chart of a self-consistent verification step based on thickness parameters;
FIG. 4 is a schematic diagram of the variation rule of the reflection differential signal with the thickness in the process of growing molybdenum disulfide on a sapphire (0001) substrate by simulation calculation;
fig. 5 is a schematic diagram of the differential spectrum evolution of a single layer of molybdenum disulfide grown on a sapphire (0001) substrate through simulation calculation.
In the drawings, the components represented by the respective reference numerals are listed below:
1: a broad spectrum light source; 2: a collimating lens group;
3: a polarizer; 4: a precision rotating table;
5: a half-wave plate; 6: an incident observation window;
7: a growth chamber support mechanism; 8: a growth reaction chamber;
9: a sample; 10: a mechanical support mechanism of the growth chamber;
11: a reflective viewing window; 12: a non-polarizing beam splitter;
13: a filter plate; 14: a photoelastic modulator;
15: an analyzer; 16: a first converging lens group;
17: a high frequency photodetector; 18: a reflective differential module measurement arm assembly;
19: a chopper; 20: a second converging lens group;
21: a spectrometer detector; 22: a differential reflection module measurement arm assembly;
23: an incident arm assembly.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below.
A self-consistent validated differential spectrometer, see fig. 1, the spectrometer comprising: incident arm assembly 23, differential reflection module measurement arm assembly 22, reflection differential module measurement arm assembly 18,
the incident arm assembly 23 includes, in order: the device comprises a broad spectrum white light source 1, a collimating lens group 2, a polaroid 3 and a half-wave plate 5;
the differential reflection module measurement arm assembly 22 includes in order: a chopper 19, a second converging lens group 20 and a spectrometer detector 21;
the reflective differential module measurement arm assembly 18 comprises in sequence: the device comprises a filter 13, a photoelastic modulator 14, an analyzer 15, a first converging lens group 16 and a high-frequency photoelectric detector 17.
Wherein, self-consistent verifies that the difference spectrum appearance includes:
the chopper 19 that half cycle passed through is set up to the measuring light path of the module of difference reflection, through the frequency of control chopper 19, realizes the interdiction and the passing of light path, realizes the measurement respectively of environmental background noise and measuring signal.
The chopper 19 can be used for testing the stray light spectrum of the environment in real time, environmental noise and photon noise of a spectrometer detector are eliminated by utilizing an algorithm, and the environment anti-interference capability of a differential reflection signal is enhanced.
The chopper 19 is arranged only for improving the signal-to-noise ratio and the anti-interference capability of the differential reflection signal, the main test function is not affected, and the chopper 19 can be omitted in the application with low requirement on the signal-to-noise ratio.
Features of the incident arm assembly 23 include: the half-wave plate 5 is arranged on the precision rotary table 4 and controls the precision rotary table 4 to obtain a high-precision zero-reflection differential signal. The azimuth angle of the polarizer 3 is 0 degree, the azimuth angle of the photoelastic modulator 14 is 45 degrees, the azimuth angle of the analyzer 15 is 0 degree, the azimuth angles of the polarizer 3, the photoelastic modulator 14 and the analyzer 15 are not strict values, and the azimuth angle errors of the three devices are guaranteed to be 0 degree, 45 degrees and 0 degree relatively.
A self-consistent verification differential spectral measurement method, see fig. 2-4, comprising the steps of:
1) after the collimated light beam vertically enters the polarizer 3, the light beam passes through a half-wave plate 5 arranged on a precise rotating seat 4, passes through an entrance observation window 6 of a growth device, and obliquely enters a sample 9, and the sample is placed in a closed environment formed by growth cavity supporting mechanisms 7 and 10 and a growth cavity 8, and can be a positive air pressure environment or a negative air pressure environment;
2) reflected light is obtained after being reflected by a sample 9, passes through a reflection observation window 11 and a non-polarization beam splitter 12, wherein light rays with 90-degree turning in the transmission direction pass through a first converging lens group 16 and enter a spectrometer detector 21 to obtain a differential reflection signal;
3) the light beam with unchanged propagation direction passes through the filter 13, the photoelastic modulator 14, the analyzer 15 and the second converging lens group 20 in sequence, and is collected by the high-frequency photoelectric detector 17 to obtain a reflection differential signal.
The oblique incidence type reflection differential signal and the oblique incidence type differential reflection signal can be measured simultaneously.
In specific implementation, the testing step of the differential reflection spectrum comprises the following steps:
1) before the film starts to grow, controlling the chopper 19 to realize the conduction and the blockage of the light path of the measuring arm of the differential reflection module, and respectively collecting the substrate reflection spectrum Rsubstrate(t0) And system noise spectrum Rb(t0)；
2) After the growth is started, the reflection spectrum R of the sample is respectively collected within one rotation of the chopper 19sample(t) and System noise Spectrum Rb(t)；
3) In the growth process, the formula for calculating the differential reflectance spectrum at any time t is as follows:
in a specific implementation, the step of testing the reflected differential signal includes:
1) selecting a test wavelength by using the filter 13;
2) the phase retardation value of the measuring wavelength is pi through the arrangement of the half-wave plate 5;
3) high frequency photovoltaic is caused by rotating the azimuth angle of the half-wave plate 5 before starting growthDetermining the azimuth angle H of the half-wave plate by setting the coefficient of the frequency component of the twofold fundamental of the detector to zero0At this time:
|rp0|2cos2(2H0)＝|rs0|2cos2(2H0) (3)
wherein r isp0Is the p-polarization of the reflected light, rs0Is the s-polarized component of the reflected light.
After the growth is started, the reflected differential signal is obtained by the formula:
wherein S is2fIs a coefficient of a 100kHz component of the detector frequency, IincThe light intensity of the detector when no modulation is applied to the photoelastic modulator, J2For a second order Bessel function expansion, deltamIs the phase retardation value of the photoelastic modulator.
Example 1
The embodiment of the invention provides a self-consistent verification differential spectrometer, which is used for monitoring the growth thickness and the form of a thin film in the growth process of the thin film, and is shown in figure 1, and comprises:
the wide-spectrum light source 1 is used for providing a non-polarized wide-spectrum light beam and can be selected as a xenon lamp or a white light LED and the like; the collimating lens group 2 is used for processing light beams emitted by a light source transmitted by an optical fiber to generate parallel incident light beams, and an infinite optical system consisting of an off-axis parabolic mirror or a convex lens group can be selected; a polarizer 3 for applying a linear polarization characteristic to non-polarized incident light; a precision rotation stage 4 for performing in-plane high-precision rotation on the half-wave plate; a half-wave plate 5 for modulating a pi phase retardation to incident light; sample 9, a substrate supporting the growth of the nano-film; a non-polarizing beam splitter 12 that splits the light reflected from the sample into two beams, one beam being used for differential reflection measurement and the other beam being used for differential reflection measurement; a filter 13 for selecting a measurement wavelength of the reflected differential signal; a photoelastic modulator 14 for modulating the reflected differential signal measurement beam at a high frequency of 50 kHz; an analyzer 15 for analyzing the reflected differential measurement beam carrying the sample signal; the first converging lens group 16 converges the measuring beam of the differential reflection module measuring arm, and can select a concave lens group or an off-axis parabolic mirror; a high-frequency photodetector 17 for receiving the reflected differential measurement optical signal and converting it into an electrical signal, optionally a photomultiplier tube; the chopper 19 controls the periodic passing and blocking of the reflected light path; the second converging lens group 20 converges the measuring beam of the differential reflection module, and can select a concave lens group or an off-axis parabolic mirror; a spectrometer detector 21 for receiving optical path signals of the measuring arm of the differential reflection module
In the specific embodiment, the wide-spectrum light source 1, the collimating lens group 2, the polarizer 3, the precision rotating platform 4 and the half-wave plate 5 sequentially form an incident arm assembly 23;
in the specific embodiment, the filter 13, the photoelastic modulator 14, the analyzer 15, the first focusing lens group 16, and the high-frequency photodetector 17 sequentially form a reflection difference module measurement arm assembly 18.
In a particular embodiment, chopper 19, second focusing lens group 20 and spectrometer detector 21 form a differential reflection module receiving arm assembly 22.
Example 2
The embodiment of the invention provides a self-consistent verification differential spectrum measurement method, which is used for in-situ real-time monitoring in a film growth process, and comprises the following measurement steps:
for the reflected differential signal, before starting to grow, the device is calibrated, that is, the process of obtaining the zero-reflection differential signal, the steps are as shown in fig. 2, and the specific principle is as follows:
1) selecting a test wavelength by using the filter 13;
2) rotating the azimuth angle of the half-wave plate 5 by controlling the precision rotary table 4 on which the half-wave plate 5 is mounted;
3) after the reflected light passing through the sample 9 passes through the photoelastic modulator 14, phase modulation with the frequency of 50kHz is obtained;
4) detecting the light intensity of the reflected light received in real time by using a high-frequency photoelectric detector; and obtaining a double frequency component in the high-frequency photoelectric detector by using a fast Fourier transform algorithm, and keeping the azimuth angle data of the half-wave plate 5 when the coefficient of the double frequency component is closest to a zero signal, so as to finish the calibration process of the instrument.
In the specific embodiment, after the film growth is started for the reflected differential signal, the electrical signal detected by the detector is subjected to fast Fourier transform to obtain the coefficient S of the frequency-doubled signal2f；
In a specific implementation, the reflected differential signal Δ R/R is obtained using equation (4) above.
In specific implementation, the method for measuring the differential reflection signal comprises the following steps:
before the film starts to grow, controlling a chopper 19 of the differential reflection module to realize the conduction and the blockage of a light path in a measurement arm of the differential reflection module, and respectively collecting substrate reflection spectrums Rsubstrate(t0) And system noise spectrum Rb(t0)；
After the growth is started, the reflection spectrum R of the sample is respectively collected within one rotation of the chopper 19sample(t) and System noise Spectrum Rb(t)。
The formula for calculating the differential reflectance spectrum at any time t in the growth process is as follows:
after the reflection differential signal and the differential reflection signal are respectively obtained by using a formula (4) and a formula (5), physical models are respectively established, iterative fitting and inversion are carried out to obtain the film thickness and the film thickness is compared, if the film thickness results obtained by the two measurement methods are not unique, the respective physical models are continuously corrected, wherein the initial values, the boundary conditions, the dielectric constants, the limiting conditions, the optimization algorithm and the like of the film and the substrate are included. By utilizing the self-consistent verification function, the accuracy of the physical model is improved, and the measurement of other physical properties is realized. The specific steps are shown in fig. 3.
Example 3
Taking the example of growing the molybdenum disulfide thin film by using the chemical vapor deposition method, using sapphire as the substrate, and the oblique incidence angle is 83 °, when the test wavelength is 632 nm, the change rule of the reflection differential signal along with the number of layers of the molybdenum disulfide thin film is shown in fig. 4, and the evolution rule of the broadband differential reflection spectrum of the single-layer molybdenum disulfide in the growth process is shown in fig. 5.
In the embodiment of the present invention, except for the specific description of the model of each device, the model of other devices is not limited, as long as the device can perform the above functions.
Those skilled in the art will appreciate that the drawings are only schematic illustrations of preferred embodiments, and the above-described embodiments of the present invention are merely provided for description and do not represent the merits of the embodiments.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (7)
1. A self-consistent validating differential spectrometer, the spectrometer comprising: an incident arm assembly, a differential reflective module assembly, a reflective differential module assembly,
the incident arm assembly includes: the wide-spectrum white light source emits light beams with a large divergence angle, the light beams are converged into parallel light beams after passing through the collimating lens group, then the parallel light beams are changed into linear polarized light through the polarizer, and the linear polarized light and the elliptical polarized light are changed into linear polarized light through the half-wave plate arranged on the precision rotating platform;
the differential reflection module assembly sequentially comprises: the reflected light beam passes through a chopper to realize the periodic blocking and passing of a light path, then passes through a second converging lens group, is changed into a converging light beam from a parallel light beam, and then is converted into an electric signal by a spectrometer detector;
the reflective differential module assembly includes: the reflected light beam is converted into single-wavelength light beam through the filter plate, then the single-wavelength light beam sequentially passes through the photoelastic modulator and the analyzer to be subjected to optical polarization modulation, then passes through the first converging lens group, is converted into converging light beam by parallel light, and then is converted into an electric signal by the high-frequency photoelectric detector.
2. The self-consistent validating differential spectrometer of claim 1, wherein the differential reflection module assembly further comprises: and setting a half-period passing chopper, and controlling the frequency of the chopper to realize the blocking and passing of a light path so as to realize the measurement of environmental background noise and a measurement signal.
3. A self-consistent verifying differential spectrometer according to claim 1, wherein the half-wave plate is mounted on a rotary stage, and the rotary stage is controlled to obtain a high precision zero reflection differential signal.
4. A self-consistent verifying differential spectrometer according to claim 1, wherein the polarizer has an azimuth angle of 0 °, the photoelastic modulator has an azimuth angle of 45 °, and the analyzer has an azimuth angle of 0 °.
5. A self-consistent verification differential spectrum measurement method is characterized in that a non-polarization beam splitter is arranged, so that simultaneous measurement of oblique incidence type reflection differential signals and oblique incidence type differential reflection signals is achieved, and the method comprises the following steps:
the reflected light reflected by the sample passes through the non-polarizing beam splitter, wherein the light rays with 90-degree turning in the propagation direction enter a spectrometer detector through a second converging lens group for obtaining a differential reflection signal;
the light beams with unchanged propagation directions sequentially pass through a filter, a photoelastic modulator, an analyzer and a first converging lens group, are collected by a photomultiplier detector and are used for acquiring reflection differential signals;
and respectively establishing corresponding physical models aiming at the reflection differential signals and the differential reflection signals, respectively obtaining film thickness parameters through iterative inversion, comparing the 2 thickness parameters, and performing self-consistent verification.
6. A self-consistent verification differential spectral measurement method according to claim 5, wherein the step of obtaining differential reflection signals is specifically:
before the film starts to grow, the chopper controls the conduction and the blockage of the differential reflection module assembly, and the substrate reflection spectrum R is respectively collectedsubstrate(t0) Sum noise spectrum Rb(t0)；
After the growth is started, the reflection spectrums R of the samples are respectively collected within one circle of the choppersample(t) and noise spectrum Rb(t)；
At any time t in the growth process, the formula for calculating the differential reflection spectrum is as follows:
7. the method according to claim 5, wherein the obtaining of the reflected differential signal specifically comprises:
selecting a test wavelength by using a filter plate; setting a half-wave plate to enable the phase retardation value of the measuring wavelength to be pi;
before growth, the azimuth angle H of the half-wave plate is rotated to make the coefficient of the twofold fundamental frequency component of the detector be zero0Comprises the following steps: | rp0|2cos2(2H0)＝|rs0|2cos2(2H0)；
In the growing process, the obtaining formula of the reflection differential signal is as follows:
wherein S is2fIs a coefficient of a 100kHz component of the detector frequency, rp0Is the p-polarization of the reflected light, rs0Is the s-polarized component of the reflected light, IincThe light intensity of the detector when no modulation is applied to the photoelastic modulator, J2For a second order Bessel function expansion, deltamIs the phase retardation value of the photoelastic modulator.
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