CN115218796A - DEABC method for detecting parameters of multilayer film based on in-situ common-angle SPR - Google Patents
DEABC method for detecting parameters of multilayer film based on in-situ common-angle SPR Download PDFInfo
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- 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
- 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
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
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- G01N2021/8438—Mutilayers
Abstract
The invention discloses a DEABC method for detecting parameters of a multilayer film based on in-situ common-angle SPR, which comprises the following steps: measuring interference fringe information of incident light of a multilayer film sample in a continuous wavelength lambda range and a reflection spectrum of TM polarized wave by using an SPR measuring device in an in-situ co-angle mode, processing to obtain incident wavelength-reflectivity and incident wavelength-phase difference relation curves, then selecting data from the relation curves for preprocessing, using the data as input values of a difference bee colony algorithm, setting resolving termination conditions, finally performing inversion calculation by using the difference bee colony algorithm based on a target function, wherein the target function takes a parameter to be measured as a function parameter, reflects the similarity between the inversion calculation value and an experimental measurement value, and solves corresponding parameter vectors by taking the minimum value of the target function as an optimization direction, so that parameters such as refractive index, extinction coefficient, thickness and the like of all metal film layers under each wavelength are obtained. The invention has the advantages of convenient detection, high solving efficiency and high precision.
Description
Technical Field
The invention belongs to the technical field of material analysis and measurement, relates to measurement of optical constants and thickness parameters of a metal film material, and particularly relates to a DEABC method for characterizing multilayer film parameters based on an in-situ common-angle SPR phase and a reflectance spectrum.
Background
With the wide application of nanoscale thin films in the fields of microelectronics, optoelectronics, aerospace, medical instruments and high polymer materials, thin film technology has become a research hotspot in the fields of current scientific and technological research and industrial production. The continuous improvement and rapid development of thin film technology also put more demands on various parameters of the thin film, for example, the optical constant of the thin film changes with the change of wavelength, and the optical constant of the thin film is influenced by the difference of thickness, thereby playing a decisive role in the optical, mechanical and electromagnetic properties of the thin film. Moreover, with the continuous development of micro-nano technology, devices plated with single-layer films cannot meet the requirements of the prior art, and at present, in order to further improve the performance of photoelectric devices, devices plated with multi-layer films are generally selected in various fields to replace traditional single-layer film devices. Therefore, it has become an urgent problem to simultaneously and precisely detect the thickness and optical constants of the multi-layered nanoscale thin film at multiple wavelengths.
At present, the prior art generally adopts a fixed incident wavelength to change an incident angle to collect reflected light intensity or phase variation to realize the detection of the optical constant and thickness of the metal film under the excitation SPR effect. For example, patent document CN108844474a discloses an IAGA method for SPR phase measurement of metal film thickness and optical constants, that is, measurement using such a concept. On one hand, the method needs to change the incident angle continuously, so that the incident point of the incident light on the film surface changes, but is limited by the preparation process, the thickness and the optical property of each part of the film surface cannot be guaranteed to be absolutely uniform, and further the in-situ measurement cannot be realized, and meanwhile, the change of the incident angle can cause the continuous change of the position of the reflectivity or the phase acquisition device, so that the measurement error is easily introduced into the experimental process, and the accuracy of the measurement result is further influenced. On the other hand, the method can solve the optical constants and thickness at one wavelength at a time. For solving the optical parameters of the metal film under multiple wavelengths, a common SPR spectroscopy introduces a large imaginary part error of an optical constant when analyzing or fitting the optical constant of the film, so that the problem of low solving precision is caused. Therefore, under the condition of in-situ angle sharing, the phase difference and reflection spectrum information of the multilayer metal film under multiple wavelengths are collected simultaneously, the differential evolution idea is introduced into the bee colony algorithm, so that the hybrid optimization algorithm is more favorable for solving the multi-parameter problem, the multilayer film optical constant and thickness of the fixed film sample measuring point under the continuous spectrum can be obtained by simultaneously calculating the incident wavelength-phase difference and incident wavelength-reflection light intensity curve of the multilayer metal film, and the problem of one-time rapid solving of the multilayer film parameters corresponding to each wavelength under continuous multiple wavelengths is effectively solved.
Disclosure of Invention
In view of the above, the present invention is directed to a DEABC method for detecting parameters of a multilayer thin film based on in-situ common-angle SPR.
The technical scheme is as follows:
a DEABC method for detecting parameters of a multilayer film based on in-situ common-angle SPR is characterized by comprising the following steps:
s1, measuring interference fringe information of incident light of a multilayer film sample in a continuous wavelength lambda range and a reflection spectrum of TM polarized wave by using an SPR measuring device, and keeping an incident angle and an incident point unchanged in the measuring process, wherein the incident angle is an angle capable of exciting an SPR effect;
s2, processing the reflection spectrum and the interference fringe information obtained in the step S1 to obtain incident wavelength-reflectivity and incident wavelength-phase difference relation curves;
s3, selecting reflection spectrum and phase difference data from the relation curve, carrying out normalization processing to obtain a reflectance value and phase difference value data set in the same magnitude, using the reflectance value and phase difference value data set as input values of a difference bee colony algorithm, and setting a resolving termination condition;
s4, performing inversion calculation based on the target function by adopting a differential bee colony algorithm, wherein the inversion calculation is performed on the basis of the target functionThe size of the target function reflects the similarity between the reflectivity values and the phase difference values measured by inversion calculation and experiments, the target function takes the parameter vector a to be measured of the multilayer thin film sample as a function parameter, and the parameter vector a, a = (n =) is solved by searching the minimum value of the target function 1 ，k 1 ，d 1 …n m ，k m ，d m ) Wherein m is the number of layers of the multilayer film sample, m is more than or equal to 2, and n x 、k x 、d x Respectively the refractive index, extinction coefficient and thickness of the x-th layer of film, x belongs to [1,m ]]。
Preferably, in step S4, the solution space { n ] is initialized by substituting the reflectance value and the phase difference value data set obtained in step S3 into the objective function 1 ，k 1 ，d 1 …n m ，k m ，d m Performing inversion calculation based on the target function by adopting a differential bee colony algorithm, and judging the accuracy of the solution according to the size of the target function to obtain the parameters of the multilayer film sample when the target function is minimum;
the objective function formula is as follows (1):
where Q is the total number of wavelengths involved,
Δφ cal (i, a) represents the phase difference value of the TE polarized wave and the TM polarized wave under the SPR effect calculated by the algorithm inversion,
Δφ exp (i) Showing the phase difference value of the TE polarized wave and the TM polarized wave under the SPR effect of the ith reference point extracted from the incident wavelength-phase difference curve measured by experiments,
a represents a vector containing the parameters to be determined, a = (n) 1 ，k 1 ，d 1 …n m ，k m ，d m )。
Preferably, the SPR reflectance values in the objective function
And a phase difference of delta phi cal (i, a) is obtained by multiplication of multiple matrices based on a transmission matrix method, calculated according to equations (2) to (6),
wherein eta is h Is the admittance, η, of the h-th layer of the structural layer of the multilayer film sample 0 Is admittance of incident interface, eta N Is the admittance of the exit interface;
B. c is the electric field intensity and the magnetic field intensity of the emergent interface of the multilayer film respectively;
δ h is the phase difference of the h layer;
θ h is the h-th layer incident angle;
ε represents the dielectric constant and ε is the real part of the dielectric constant real ＝n 2 -k 2 Dielectric constant imaginary part ε imag =2nk, n, k denote refractive index and extinction coefficient, respectively.
Preferably, the step S4 specifically comprises the steps of,
s41, initializing each parameter: setting the maximum iteration number and initializing the swarm number of the differential swarm algorithm, and initializing the solution space { n 1 ，k 1 ，d 1 …n m ，k m ，d m Setting the maximum times limit for searching optimization around the solution vector;
s42, randomly placing M (M is more than 0 and is a natural number) bee groups in a solution space, and calculating the objective function value of each solution vector;
s43, for M bee colonies
Each solution vector X i Employing bees to generate a new solution vector X using differential evolution operations i ', while ensuring the new solution vector X i ' in the initialized solution space n 1 ，k 1 ，d 1 …n m ，k m ，d m And calculating an objective function value f (X ') of the new solution vector' i )；
S44, comparing the new position vector X' i And the original vector X i If f (X' i ) Greater than f (X) i ) Then is prepared from X' i Updating X i Updating the bee colony position, otherwise X i Keeping the process unchanged, and performing the process according to the formula (9);
s45, calculating a solution vector X i The objective function value f (X) i ) Then, the probability value p corresponding to each solution vector is calculated according to the formula (10) i ，
S46, selecting a solution vector according to the probability value of the follower bee, searching in the neighborhood of the solution vector, and generating a new solution vector V i While ensuring that the newly generated solution vector is in the initialized solution space n 1 ，k 1 ，d 1 …n m ，k m ，d m Within the range of f, and calculates the objective function value f (V) of the new solution vector i )；
S47, adopting greedy selection to compare V i And X i Corresponding objective function value, if f (V) i ) Greater than f (X) i ) Then use V i Updating X i Otherwise X i Keeping the population unchanged, and recording the optimal objective function value f _ best reached after the population is finally updated and the corresponding solution vector;
s48, if limit times of search are carried out around the solution vector and no more optimal position is found, the detection bee updates the solution vector;
and S49, judging whether the termination condition is met, if so, stopping searching and outputting the optimal solution a, otherwise, returning to the steps S42-S48 to continue iterative computation until termination.
Preferably, in S43, the following formula (7) is adopted for the differential evolution operation:
in the formula, j is in the range of {1,2,. D }, D is the dimension of a solution vector, and D =3m;
CR is cross probability, and the value of CR is set to be between 0 and 1;
sn is a randomly generated dimension;
wherein the content of the first and second substances,
in the formula，X r1 、X r2 、X r3 To remove X i With 3 solution vectors chosen randomly outside,
f is the scaling factor, and F is the [0,1].
Preferably, the above-mentioned solution termination condition is satisfied with an experimental value
And inverse solution value
And the experimental value of delta phi exp (i) And the inverse solution value delta phi cal And (e) the minimum approximation error between (i, a) or the total iteration number is larger than the initially set maximum iteration number, and the iteration calculation is terminated when one of the minimum approximation error and the total iteration number meets the initially set maximum iteration number.
Preferably, in step S1, the wavelength λ of the incident light is a continuous wavelength band,
the unit is nm.
Preferably, the multilayer thin film sample is at least two metal film layers plated on a substrate, and in the step S1, when the SPR measuring apparatus is used for measurement, the substrate-the multilayer metal film layer-the dielectric layer is used as a multiphase thin film structure for detection.
Compared with the prior art, the invention has the beneficial effects that:
(1) The in-situ common-angle SPR measurement mode with a fixed incident angle and an incident point is adopted, so that the measurement is convenient and quick, the measurement error caused by the fact that the incident angle and the incident point are continuously changed in the single-wavelength measurement mode in the prior art is avoided, and the influence of the measurement method on the accuracy of the measurement result is reduced;
(2) The method adopts incident light of continuous wave bands for measurement, selects an SPR phase and reflectance spectrum combined representation mode, synchronously realizes the solution of the optical constants and the thickness of the multilayer metal film under multiple wavelengths, avoids the defect that the large imaginary part error of the optical constants is introduced when the optical constants of the film are analyzed and fitted through the reflectivity calculation under the multiple wavelengths in the SPR spectroscopy in the prior art, and improves the solution precision;
(3) The global convergence capability of the differential evolution algorithm and the quick convergence capability of the bee colony algorithm are fully utilized, the low valley region jumping is prevented, the optimal solution can be accurately found, the convergence speed in the iterative computation process is high, and the optimization precision is high;
(4) The measurement method is improved from two aspects of SPR measurement operation and algorithm calculation, meanwhile, the measurement efficiency and accuracy are improved, and the applicability is strong.
Drawings
FIG. 1 is a flow chart of a DEABC method for measuring parameters of a single-layer thin film based on in-situ co-angle SPR phase and reflectance spectroscopy in accordance with the present invention;
FIG. 2 is a schematic representation of a prismatic metal film multilayer structure for use in the present invention;
FIG. 3 is an iterative comparison graph of the difference swarm algorithm DEABC and the swarm algorithm ABC target functions obtained under multiple wavelengths in the invention;
FIG. 4 is a graph of the measured multi-wavelength optical constants of the dual-layer metal film according to the embodiment of the present invention;
FIG. 5 is a graph showing the thickness of gold (a) and silver (b) films at multiple wavelengths measured according to an embodiment of the present invention;
FIG. 6 is a graph comparing the incident wavelength-reflectance and incident wavelength-phase difference curves obtained by the example of the present invention with the calculated curves.
Detailed Description
The present invention will be further described with reference to the following examples and the accompanying drawings.
A DEABC method for detecting parameters of a multilayer film based on in-situ common-angle SPR is carried out according to the following steps:
s1, measuring interference fringe information of incident light of a multilayer film sample in a continuous wavelength lambda range and a reflection spectrum of TM polarized wave by using an SPR measuring device, and keeping an incident angle and an incident point unchanged in the measuring process to form an in-situ co-angle measuring mode. The angle of incidence is the angle at which the SPR effect may be excited. The interference fringe information and the reflection spectrum of the TM polarized wave contain information on the refractive index n, extinction coefficient k, and thickness d of the multilayer metal thin film at multiple wavelengths. The multilayer film sample is at least two metal film layers plated on a substrate, and in the step S1, when the SPR measuring device is used for measuring, the substrate-the multilayer metal film layers-the dielectric layer are used as a multiphase film structure for detection.
And S2, processing the reflection spectrum and the interference fringe information obtained in the step S1 to obtain incident wavelength-reflectivity and incident wavelength-phase difference relation curves.
And S3, selecting the reflection spectrum and the phase difference data from the relation curve, carrying out normalization processing to obtain a data set of the reflection rate value and the phase difference value which are in the same magnitude, using the data set as an input value of the difference bee colony algorithm, and setting a resolving termination condition.
Resolving the termination condition to satisfy the experimental value
And inverse solution value
And the experimental value of delta phi exp (i) And the inverse solution value delta phi cal And (e) the minimum approximation error between (i, a) or the total iteration number is larger than the initially set maximum iteration number, and the iteration calculation is terminated when one of the minimum approximation error and the total iteration number meets the initially set maximum iteration number.
S4, performing inversion calculation based on an objective function by adopting a differential bee colony algorithm, wherein the size of the objective function reflects the similarity between the inversion calculation and a reflectivity value and between phase difference values measured in an experiment, the objective function takes a parameter a to be measured of the multilayer thin film sample as a function parameter, and a parameter vector a, a = (n) is solved by searching the minimum value of the objective function 1 ，k 1 ，d 1 …n m ，k m ，d m ) Wherein m is the number of layers of the multilayer film sample, and m is not less than 2,n x 、k x 、d x Respectively the refractive index, extinction coefficient and thickness of the x-th layer of film, x belongs to [1,m ]]。
In step S4, the reflectance value and the phase difference value data set obtained in step S3 are substituted into the objective function to initialize a solution space { n } 1 ，k 1 ，d 1 …n m ，k m ，d m The search range of the method adopts a differential bee colony algorithmPerforming inversion calculation based on the target function, and judging the accuracy of a solution according to the size of the target function to obtain the parameters of the multilayer film sample when the target function is minimum;
the objective function formula is as follows (1):
where Q is the total number of wavelengths involved,
Δφ cal (i, a) represents the phase difference value of the TE polarized wave and the TM polarized wave under the SPR effect calculated by the algorithm inversion,
Δφ exp (i) Showing the phase difference value of the TE polarized wave and the TM polarized wave under the SPR effect of the ith reference point extracted from the incident wavelength-phase difference curve measured by experiments,
a represents a vector containing the parameters to be determined, a = (n) 1 ，k 1 ，d 1 …n m ，k m ，d m )。
SPR reflectance values in the target function
And a phase difference of delta phi cal (i, a) is obtained by multiplication of multiple matrices based on a transmission matrix method, and calculated according to equations (2) to (6),
wherein eta is h Is the admittance, η, of the h-th layer of the structural layer of the multilayer film sample 0 Is admittance of incident interface, eta N Is the admittance of the exit interface; eta. For the multiphase thin film structure of substrate-multilayer metal film layer-dielectric layer in this embodiment 0 I.e. the admittance, eta, of the base layer N I.e. the admittance of air;
B. c is the electric field intensity and the magnetic field intensity of the emergent interface of the multilayer film respectively;
δ h is the phase difference of the h layer;
θ h is the h-th layer incident angle;
from the above equation, it can be seen that the reflectivity and phase are related to the thickness d of the metal film, the incident wavelength λ and the dielectric constant of the metal film, ε represents the dielectric constant, and ε is the real part of the dielectric constant real ＝n 2 -k 2 Dielectric constant imaginary part ε imag =2nk, n, k denote refractive index and extinction coefficient, respectively.
In this example, the substrate was BK7 glass. The substrate is plated with a gold film and a silver film, so that a glass-gold film-silver film-air four-phase structure is used as a detection model during SPR measurement, and air is selected as a medium. Refractive index n of BK7 glass p =1.5151, refractive index of airn a And =1. Accordingly, the number of metal film layers m =2, and the solution a = (n) of the film parameter to be solved 1 ，k 1 ，d 1 ，n 2 ，k 2 ，d 2 )。
In this embodiment, the wavelength λ of the incident light is in the range of 400nm to 1000nm. One skilled in the art will readily appreciate that any continuous band within this range may be selected depending on the actual measurement needs.
The differential bee colony algorithm is to fuse a differential evolution algorithm with a bee colony algorithm, and specifically, the step S4 includes:
s41, initializing each parameter: setting the maximum iteration number and initializing the colony number of the differential colony algorithm. In this embodiment, the maximum iteration count =200 and the minimum approximation error are set<0.01, the number of swarms initializing the differential swarms algorithm =100. At the same time, the solution space n is initialized 1 ，k 1 ，d 1 ，n 2 ，k 2 ，d 2 }, setting n 1 Delocalization of [0,0.5]，k 1 Delocalization of [2,6]，d 1 Delocalization of [0,50]，n 2 Delocalization of [0,0.5]，k 2 Delocalization of [2,7]，d 2 Delocalization of [0,50]. Further, the maximum number limit of seek optimization searches around the solution vector is set.
S42, since each solution vector is composed of the refractive index n, the extinction coefficient k and the thickness d of the multilayer thin film and corresponds to an objective function, M (M is greater than 0 and is a natural number) bee colonies are randomly placed in a solution space, and the objective function value of each solution vector is calculated. This embodiment M =100.
S43, for 100 bee colonies
Each solution vector X i Employing bee to generate a new solution vector X 'with differential evolution operation' i While ensuring the new solution vector X' i In the initialized solution space n 1 ，k 1 ，d 1 ，n 2 ，k 2 ，d 2 And calculating objective function values f (X ') of the new solution vector' i )；
The differential evolution operation employs the following equation (7):
wherein j ∈ {1,2,. D }, D being the dimension of the solution vector, D =6 in this embodiment;
CR is cross probability, and is taken as 0.6;
sn is a randomly generated dimension;
wherein the content of the first and second substances,
in the formula, X r1 、X r2 、X r3 To remove X i With 3 solution vectors chosen randomly outside,
f is the scaling factor, and F ∈ [0,1], which is 0.5 in this example.
S44, comparing the new position vector X' i And the original vector X i If f (X' i ) Greater than f (X) i ) Then is prepared from X' i Updating X i Updating the bee colony position, otherwise X i Keeping the process unchanged, and performing the process according to the formula (9);
s45, calculating a solution vector X i The objective function value f (X) i ) Then, the probability value p corresponding to each solution vector is calculated according to the formula (10) i ，
S46, selecting a solution vector according to the probability value of the follower bee, searching in the neighborhood of the solution vector, and generating a new solution vector V i While ensuring that the newly generated solution vector is initially nulledM { n } 1 ，k 1 ，d 1 ，n 2 ，k 2 ，d 2 Within the range of f, and calculates the objective function value f (V) of the new solution vector i )；
S47, adopting greedy selection to compare V i And X i Corresponding objective function value, if f (V) i ) Greater than f (X) i ) Then use V i Updating X i Otherwise X i Keeping the population unchanged, and recording the optimal objective function value f _ best reached after the population is finally updated and the corresponding solution vector;
s48, if limit =100 searches are performed around the solution vector and no more optimal position is found yet, the scout updates the solution vector;
and S49, judging whether the termination condition is met, if so, stopping searching and outputting the optimal solution a, otherwise, returning to the steps S42-S48 to continue iterative computation until termination.
In this embodiment, the optical constants and thicknesses of the thin film at the target multi-wavelength are calculated by a differential bee colony algorithm, and meanwhile, the optical constants and thicknesses are calculated by a conventional bee colony algorithm ABC, and the optical constants and the thicknesses are compared.
The method of the present invention operates 50 times, the program iterates 200 times each time, and an iteration curve graph is obtained as shown in fig. 3, and it can be seen from fig. 3 that the method provided by the present invention can converge to an optimal solution in about 60 generations, and an objective function value can reach 0.23, whereas the traditional bee colony algorithm can converge to an optimal solution in about 100 generations, and the minimum value of the objective function is 0.35. The difference bee colony algorithm provided by the invention has the characteristics of high convergence speed, high optimization precision and the like.
FIG. 4 is the optical constant of the multi-wavelength metal film calculated by the method, and FIG. 5 is the calculated thickness of each wavelength under multi-wavelength, the mean thickness d of the gold film 1 =30.526 ± 0.325nm, silver film thickness d 2 ＝25.425±0.179nm。
Fig. 6 is a phase difference and reflectivity curve obtained by the inversion of the difference bee colony algorithm and measured by an experiment, and it can be seen from the graph that the phase difference and reflectivity curve obtained by the inversion of the difference bee colony algorithm almost completely coincides with the curve obtained by the experiment, which shows that the structural parameter precision of the double-layer film obtained by the inversion method of the present invention is high.
In summary, the method simultaneously collects the phase difference and reflection spectrum information of the multilayer metal film under multiple wavelengths under the SPR measurement condition based on in-situ common angle, and can calculate and obtain the optical parameters and the thickness of each layer of the multilayer metal film of the fixed film sample measurement point under the continuous spectrum by simultaneously inputting the incident wavelength-phase difference and incident wavelength-reflectivity curve of the multilayer metal film based on the difference bee colony algorithm, thereby realizing one-time rapid measurement and calculation of the parameters of each layer of the film corresponding to each wavelength under continuous multiple wavelengths, and having the advantages of high efficiency and high accuracy.
Finally, it should be noted that the above-mentioned description is only a preferred embodiment of the present invention, and those skilled in the art can make various similar representations without departing from the spirit and scope of the present invention.
Claims (8)
1. A DEABC method for detecting parameters of a multilayer film based on in-situ common-angle SPR is characterized by comprising the following steps:
s1, measuring interference fringe information of incident light of a multilayer film sample in a continuous wavelength lambda range and a reflection spectrum of TM polarized wave by using an SPR measuring device, and keeping an incident angle and an incident point unchanged in the measuring process, wherein the incident angle is an angle capable of exciting an SPR effect;
s2, processing the reflection spectrum and the interference fringe information obtained in the step S1 to obtain incident wavelength-reflectivity and incident wavelength-phase difference relation curves;
s3, selecting reflection spectrum and phase difference data from the relation curve, carrying out normalization processing to obtain a data set of a reflectivity value and a phase difference value which are in the same magnitude, using the data set as an input value of a difference bee colony algorithm, and setting a resolving termination condition;
s4, performing inversion calculation based on a target function by adopting a difference bee colony algorithm, wherein the size of the target function reflects the similarity between the inversion calculation and a reflectivity value and between phase difference values measured by experiments, and the target function is used for solving the problem that the target function is not suitable for the target functionThe target function takes the parameter vector a to be measured of the multilayer film sample as a function parameter, and the parameter vector a, a = (n) is solved by searching the minimum value of the target function 1 ，k 1 ，d 1 …n m ，k m ，d m ) Wherein m is the number of layers of the multilayer film sample, and m is not less than 2,n x 、k x 、d x Respectively the refractive index, extinction coefficient and thickness of the x-th layer of film, x belongs to [1,m ]]。
2. The DEABC method for detecting parameters of multilayer thin films based on in-situ co-angular SPR as claimed in claim 1, wherein: in step S4, the reflectance value and the phase difference value data set obtained in step S3 are substituted into the objective function to initialize a solution space { n } 1 ，k 1 ，d 1 …n m ，k m ，d m Performing inversion calculation based on the target function by adopting a differential bee colony algorithm, and judging the accuracy of the solution according to the size of the target function to obtain the parameters of the multilayer film sample when the target function is minimum;
the objective function formula is as follows (1):
where Q is the total number of wavelengths involved,
Δφ cal (i, a) stands for inverse meter by algorithmCalculating the phase difference value of the TE polarized wave and the TM polarized wave under the SPR effect,
Δφ exp (i) Showing the phase difference value of the TE polarized wave and the TM polarized wave under the SPR effect of the ith reference point extracted from the incident wavelength-phase difference curve measured by experiments,
a represents a vector containing the parameters to be determined, a = (n) 1 ，k 1 ，d 1 …n m ，k m ，d m )。
3. The DEABC method for detecting parameters of multilayer thin films based on in-situ co-angular SPR as claimed in claim 2, wherein: SPR reflectance values in the target function
And a phase difference of delta phi cal (i, a) is obtained by multiplication of multiple matrices based on a transmission matrix method, calculated according to equations (2) to (6),
wherein eta is h Is the multilayerAdmittance, eta, of the h-th layer of the structural layer of the film sample 0 Is admittance of incident interface, eta N Is the admittance of the exit interface;
B. c is the electric field intensity and the magnetic field intensity of the emergent interface of the multilayer film respectively;
δ h is the phase difference of the h layer;
θ h is the h-th layer incident angle;
ε represents the dielectric constant and ε is the real part of the dielectric constant real ＝n 2 -k 2 Dielectric constant imaginary part ε imag =2nk, n, k denote refractive index and extinction coefficient, respectively.
4. The DEABC method for detecting parameters of multilayer thin films based on in-situ co-angular SPR as claimed in claim 2, wherein: the step S4 specifically includes the steps of,
s41, initializing each parameter: setting the maximum iteration number and initializing the swarm number of the differential swarm algorithm, and initializing the solution space { n 1 ，k 1 ，d 1 …n m ，k m ，d m Setting the maximum times limit for searching optimization around the solution vector;
s42, randomly placing M (M is more than 0 and is a natural number) bee groups in a solution space, and calculating the objective function value of each solution vector;
s43, for M bee colonies
Each solution vector X i Employing bee to generate a new solution vector X 'with differential evolution operation' i While ensuring the new solution vector X' i In the initialized solution space n 1 ，k 1 ，d 1 …n m ，k m ，d m And calculating an objective function value f (X ') of the new solution vector' i )；
S44, comparing the new position vector X' i And the original vector X i If f (X' i ) Greater than f (X) i ) Then is prepared from X' i Updating X i Updating the bee colony position, otherwiseX i Keeping the process unchanged, and performing the process according to the formula (9);
s45, calculating a solution vector X i The objective function value f (X) i ) Then, the probability value p corresponding to each solution vector is calculated according to the formula (10) i ，
S46, selecting a solution vector according to the probability value of the follower bee, searching in the neighborhood of the solution vector, and generating a new solution vector V i While ensuring that the newly generated solution vector is in the initialized solution space n 1 ，k 1 ，d 1 …n m ，k m ，d m Within the range of f, and calculates the objective function value f (V) of the new solution vector i )；
S47, greedy selection is adopted, and V is compared i And X i Corresponding objective function value, if f (V) i ) Greater than f (X) i ) Then use V i Updating X i Otherwise X i Keeping the population unchanged, and recording the optimal objective function value f _ best reached after the population is finally updated and the corresponding solution vector;
s48, if limit searching is carried out around the solution vector and no more optimal position is found, the solution vector is updated by the scout;
and S49, judging whether the termination condition is met, if so, stopping searching and outputting the optimal solution a, otherwise, returning to the steps S42-S48 to continue iterative computation until termination.
5. The DEABC method for detecting parameters of multilayer thin films based on in-situ co-angular SPR as claimed in claim 4, wherein: in S43, the following formula (7) is adopted for the differential evolution operation:
in the formula, j is in the range of {1,2,. D }, D is the dimension of a solution vector, and D =3m;
CR is cross probability, and the value of CR is set to be between 0 and 1;
sn is a randomly generated dimension;
wherein the content of the first and second substances,
in the formula, X r1 、X r2 、X r3 To remove X i With 3 solution vectors chosen randomly outside,
f is the scaling factor, and F is the [0,1].
6. The DEABC method for detecting parameters of multilayer thin film based on in-situ co-angular SPR as claimed in claim 4, wherein: the solution termination condition is to satisfy the experimental value
And inverse solution value
And the experimental value of delta phi exp (i) And the inverse solution value delta phi cal And (e) the minimum approximation error between (i, a) or the total iteration number is larger than the initially set maximum iteration number, and the iteration calculation is terminated when one of the minimum approximation error and the total iteration number meets the initially set maximum iteration number.
7. The DEABC method for detecting parameters of multilayer thin film based on in-situ co-angular SPR according to any one of claims 1 to 6, wherein: in step S1, the wavelength λ of the incident light is a continuous band,
the units are nm.
8. The DEABC method for detecting parameters of multilayer thin films based on in-situ co-angular SPR according to any one of claims 1 to 6, wherein: the multilayer film sample is at least two metal film layers plated on a substrate, and in the step S1, when the SPR measuring device is used for measuring, the substrate-the multilayer metal film layers-the dielectric layer are used as a multiphase film structure for detection.
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