Photoacoustic measurement method and device

Abstract

The invention provides a photoacoustic measurement method and device, and the method comprises the steps: carrying out the photoacoustic measurement of a to-be-measured object through a photoacoustic measurement device, and extracting a reference value of a physical parameter of each film material according to an obtained reflectivity change signal; further acquiring a reflectivity change simulation signal based on the reference value of the physical parameter of the material so as to acquire a simulation value of the physical parameter of each film material; and performing weighted correction on the reference value by the simulation value to obtain a fitting value of the physical parameter of each film layer material. The fitting value of the physical parameter of each film layer material obtained by the technical scheme of the invention can reflect the change of the physical parameter of the material in the actual film layer growth process of the object to be measured, has higher accuracy as the initial value of the physical parameter of the simulation model, and is beneficial to optimizing the efficiency and precision of photoacoustic measurement of the thickness of the film layer.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of optical measurement, in particular, to a photoacoustic measurement method and device. BACKGROUND

[0002] In the process of semiconductor device manufacturing, one or more material layers with thickness ranging from several nanometers to several microns are formed on the substrate to achieve different functional designs. The implementation of the above process is referred to as film coating. For the film coating process, the film thickness is a critical dimension, and process deviations or other possible system factors will affect the film thickness obtained after the film coating process, thereby affecting the overall performance of the semiconductor device. Therefore, after the film coating process, the film thickness needs to be measured at selected points to verify the stability of the film coating process and ensure the yield of semiconductor device manufacturing.

[0003] It can be understood that in the film coating process, the formed film layer can be a dielectric film layer or a metal film layer. Compared with the dielectric film layer, the metal film layer has a relatively strong absorption of light. When measuring a relatively thick metal film layer (here, "relatively thick" refers to a metal film layer with a thickness greater than the material absorption depth, i.e., an opaque film layer or a semi-transparent film layer) based on the traditional ellipsometry principle, the measurement result of the film thickness will be inaccurate due to the absorption of light by the metal material. The photoacoustic film thickness measurement is based on the principle of photoacoustic effect. A short pulse laser is irradiated on the surface of the sample to make the sample absorb photons to produce thermal-elastic deformation and induce sound wave transmission. The film thickness signal is obtained by detecting the time difference of the echo signal reaching the surface film layer. Since the generated sound wave signal can penetrate multiple transparent or opaque film layers, it can be used to accurately measure the film thickness of the metal film layer.

[0004] However, in the actual measurement process, when multiple film layers appear in the object to be measured, the echo signals corresponding to different film layers may be overlapped, making it difficult to detect and distinguish the echo signals returned by each film layer. It is necessary to further establish a theoretical simulation model to obtain a simulation signal, and to fit the simulation signal with the actual measurement signal to obtain an accurate film thickness. It can be understood that in the process of establishing the theoretical simulation model, the material physical parameters of each film layer are needed. For the dielectric film layer and the metal film layer deposited, the growth process will not only affect the film thickness, but also cause the material physical parameters of the film layer to change. In order to improve the simulation effect of the theoretical simulation model, the material physical parameters of these film layers need to be accurately measured and obtained. SUMMARY

[0005] In view of the problems in the prior art, the purpose of the present disclosure is to provide a photoacoustic measurement method and device, which can accurately obtain various material physical parameters of a to-be-measured object. Specifically, the first aspect of the present disclosure provides a photoacoustic measurement method, which can specifically include the following steps:

[0006] Performing photoacoustic measurement on the to-be-measured object by using a photoacoustic measurement device to obtain a measured signal of the reflectivity of the to-be-measured object changing with time;

[0007] Obtaining reference values of a plurality of key parameters of the to-be-measured object according to the measured signal;

[0008] Determining a plurality of target parameters required for establishing a simulation signal of the reflectivity of the to-be-measured object changing with time, the target parameters including all the key parameters;

[0009] Obtaining a value range corresponding to each target parameter, and generating a plurality of different target parameter combinations by randomly selecting values in each value range;

[0010] Respectively obtaining simulation signals of the reflectivity changing with time when photoacoustic measurement is performed under the condition of each target parameter combination, and respectively obtaining first error values of each target parameter combination corresponding to the simulation signal and the measured signal;

[0011] Based on the plurality of first error values, iteratively adjusting the target parameter combinations by using a genetic algorithm until a second error value between the simulation signal and the measured signal corresponding to the target parameter combination after iteration is less than a first preset threshold value or reaches a minimum extreme value, and taking the value of the key parameter in the target parameter combination obtained when the iteration is stopped as a simulation value of the key parameter;

[0012] Weightedly correcting the reference value of each key parameter and the simulation value of the corresponding key parameter to obtain a representation value of each key parameter of the to-be-measured object.

[0013] The second aspect of the present disclosure provides a photoacoustic measurement device, which can specifically include:

[0014] A measurement module, configured to perform photoacoustic measurement on the to-be-measured object to obtain a measured signal of the reflectivity of the to-be-measured object changing with time;

[0015] A key parameter obtaining module, configured to obtain reference values of a plurality of key parameters of the to-be-measured object according to the measured signal;

[0016] A target parameter determining module, configured to determine a plurality of target parameters required for establishing a simulation signal of the reflectivity of the to-be-measured object changing with time, the target parameters including all the key parameters;

[0017] The parameter combination obtaining module is configured to obtain a value range corresponding to each target parameter, and generate a plurality of different target parameter combinations by randomly selecting values in each value range.

[0018] The signal simulation module is configured to obtain a simulation signal of reflectivity change over time corresponding to each target parameter combination under the condition of photoacoustic measurement, and obtain a first error value of each target parameter combination between the simulation signal and the measured signal.

[0019] The iterative fitting module is configured to iteratively fit the target parameter combination based on the plurality of first error values by using a genetic algorithm until a second error value between the simulation signal and the measured signal corresponding to the iterated target parameter combination is less than a first preset threshold or reaches a minimum extreme value, and take the value of the key parameter in the target parameter combination obtained when the iteration is stopped as the simulation value of the key parameter.

[0020] The weighted correction module is configured to perform weighted correction on the reference value of each key parameter and the simulation value of the corresponding key parameter to obtain a characterization value of each key parameter of the object to be measured.

[0021] Compared with the prior art, the present disclosure has the following beneficial effects:

[0022] According to the technical solution provided by the present disclosure, the object to be measured can be measured by the traditional photoacoustic measurement method, the reference value of the material physical parameter required by each film layer can be extracted according to the obtained reflectivity change measured signal, the parameter combination can be determined based on the obtained reference value and the simulation model can be established, the reflectivity change simulation signal can be obtained through the simulation model, the simulation value of the material physical parameter of each film layer can be obtained by iterative fitting according to the simulation signal and the measured signal of the reflectivity change, and finally the characterization value of the material physical parameter of each film layer can be obtained by weighted correction of the simulation value on the reference value. The characterization value obtained based on the above technical solution can accurately reflect the actual situation of the physical parameters of each film layer in the object to be measured, has high accuracy, can improve the precision of the initial value of the material physical parameter used by the simulation model, and thus reduces the required time of the subsequent simulation fitting process, and improves the accuracy and time efficiency of the photoacoustic measurement. BRIEF DESCRIPTION OF DRAWINGS

[0023] Other features, objects and advantages of the present disclosure will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0024] Figure 1 According to the prior art, a schematic diagram of the principle of photoacoustic film thickness measurement of an object to be measured is provided.

[0025] Figure 2 According to the prior art, a schematic diagram of the echo of the sound wave propagating along the film thickness direction in a single-layer film object to be measured is provided.

[0026] Figure 3 According to the prior art, a schematic diagram of echo of acoustic wave propagating along the film thickness direction in a multi-layer film object is provided.

[0027] Figure 4 According to the embodiment of the present disclosure, a flowchart of a photoacoustic measurement method is provided.

[0028] Figure 5 According to the embodiment of the present disclosure, a flowchart of obtaining reference values of a plurality of key parameters of an object to be measured from measured signals is provided.

[0029] Figure 6a According to the embodiment of the present disclosure, a schematic diagram of a measured signal curve of reflectivity changing with time is provided.

[0030] Figure 6b According to the embodiment of the present disclosure, a schematic diagram of a background signal curve changing with time is provided.

[0031] Figure 6c According to the embodiment of the present disclosure, a schematic diagram of an echo signal curve changing with time is provided.

[0032] Figure 7 According to the embodiment of the present disclosure, a flowchart of obtaining acoustic impedance and density of a thin film is provided.

[0033] Figure 8a According to the embodiment of the present disclosure, a local enlarged schematic diagram of an echo signal curve is provided.

[0034] Figure 8b According to the embodiment of the present disclosure, another local enlarged schematic diagram of an echo signal curve is provided.

[0035] Figure 9 According to the embodiment of the present disclosure, a flowchart of obtaining refractive index coefficient of a thin film is provided.

[0036] Figure 10 According to the embodiment of the present disclosure, a flowchart of iterating a target parameter combination by using a genetic algorithm is provided.

[0037] Figure 11 According to the embodiment of the present disclosure, a flowchart of weighting and correcting reference values of each key parameter and corresponding simulation values of the key parameter to obtain a characterization value of each key parameter of an object to be measured is provided.

[0038] Figure 12 According to the embodiment of the present disclosure, a structural schematic diagram of a photoacoustic measurement device is provided. DETAILED DESCRIPTION

[0039] The present disclosure is described in greater detail by way of specific preferred embodiments as follows. Other advantages and benefits of the present disclosure will become apparent to those of ordinary skill in the art upon implementation of the disclosure, the advantages and benefits being derived from the various drawings, detailed description and from the appended claims.

[0040] The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. The present disclosure can be embodied in many different forms, and is not limited to the embodiments described herein.

[0041] In the description of the present disclosure, the expressions "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" indicate that the specific feature, structure, material or characteristic accompanying the embodiment or example is included in at least one embodiment or example of the present disclosure. In addition, the accompanying expressions of the specific feature, structure, material or characteristic can be used in any one or more embodiments or examples in a suitable manner. Also, the different embodiments or examples of the present disclosure and the features of the different embodiments or examples can be combined and combined with each other, without contradiction.

[0042] In addition, the terms "first", "second", etc. are used only to indicate a purpose, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present disclosure, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0043] In order to clearly explain the present disclosure, devices irrelevant to the description are omitted, and the same or similar constituent elements are given the same reference numerals throughout the specification.

[0044] Throughout the specification, when it is said that a device is "connected" to another device, it includes not only the case of "direct connection", but also the case of "indirect connection" in which other elements are interposed therebetween. In addition, when it is said that a device "includes" a certain constituent element, unless otherwise specifically stated, other constituent elements are not excluded, but it means that other constituent elements can also be included.

[0045] When a device is said to be "on" another device, it may be directly on the other device, but there may also be other devices between it. In contrast, when a device is said to be "directly on" another device, there are no other devices between it.

[0046] Although the terms first, second, etc. are used in some instances herein to represent various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, the first interface and the second interface, etc. are represented. Furthermore, as used in this article, the singular forms "one," "an," and "the" are intended to also include the plural forms, unless there is a contrary indication in the context. It should be further understood that the terms "comprise," "include," and "include" indicate the presence of features, steps, operations, elements, components, items, types, and / or groups, but do not exclude the presence, occurrence, or addition of one or more other features, steps, operations, elements, components, items, types, and / or groups. The terms "or" and "and / or" used herein are interpreted as inclusive, or mean any one or any combination. Therefore, "A, B, or C" or "A, B, and / or C" means "any of the following: A; B; C; A and B; A and C; B and C; A, B, and C." Exceptions to this definition only occur when the combination of elements, functions, steps, or operations is inherently mutually exclusive in some way.

[0047] The technical terms used herein are intended only to refer to specific embodiments and are not intended to limit the present disclosure. The singular form used herein also includes the plural form, unless the statement explicitly indicates otherwise. The term "comprising" as used in this specification specifies specific features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0048] Although not defined differently, all terms used herein, including technical and scientific terms, have the same meanings as those generally understood by those skilled in the art to which this disclosure belongs. Terms defined in commonly used dictionaries are supplementally interpreted as having meanings consistent with the relevant technical literature and the current disclosure, and unless otherwise defined, they should not be overly interpreted as ideal or highly formal meanings.

[0049] According to the relevant explanations and descriptions in the prior art, it can be understood that a photoacoustic film thickness measurement scheme can be used to measure the film thickness of a coating structure including a metal film layer. The following will first briefly describe the implementation of the photoacoustic film thickness measurement scheme:

[0050] Specifically, Figure 1 The figure shows a schematic diagram of the principle of photoacoustic film thickness measurement of an object to be measured. Figure 1As shown, the pump light 101 is irradiated on the surface of the object 100 as an excitation light beam, so that the object 100 absorbs photons to generate a thermoelastic deformation, i.e. Figure 1 As shown in the middle 102, the thermoelastic deformation 102 will form a propagating acoustic wave on the surface and inside of the sample: when the acoustic wave propagating along the film thickness direction first propagates to the film layer junction, the first echo signal is generated, and when the first echo signal returns to the surface of the object 100, the reflectivity of the surface of the object 100 changes, and the change of the reflectivity of the incident probe light 103a is detected by the detection module 103. Figure 1 The first echo signal bounces off the surface of the object 100, and after the bounce, it continues to propagate along the film thickness direction to the film layer junction to generate a second echo signal, and the second echo signal also changes the reflectivity when it returns to the surface of the object 100. The time difference between the two reflectivity changes obtained by detection can be used to obtain the corresponding surface film thickness, i.e.

[0051]

[0052] Where d is the surface film thickness, Δt is the time difference between the two reflectivity changes, and v is the propagation speed of the acoustic wave in the surface film layer. Correspondingly, Figure 2 A schematic diagram of an acoustic echo along the film thickness direction in a single-layer film object is shown, and those skilled in the art can directly obtain the film thickness according to the above method.

[0053] For a multi-layer film object, the situation becomes more complex: when the acoustic wave propagating along the film thickness direction first propagates to the junction of the first layer film and the second layer film, part of the acoustic signal is reflected to form the first echo signal, and the other part continues to propagate along the film thickness direction towards the inside of the multi-layer film object; when it propagates to the junction of the second layer film and the third layer film, part of the acoustic signal is reflected to form the echo signal, and the other part continues to propagate to the inside of the object……With the increase of the number of film layers, it is easy for the echo signal returned to the sample surface to be overlapped. Correspondingly, Figure 3 A schematic diagram of an acoustic echo along the film thickness direction in a multi-layer film object is shown, as Figure 3 As shown, the echo signals of different film layers are easily overlapped, and it is difficult to distinguish the echo signals returned by each film layer only by the measured signals of the surface reflectivity, and thus the thickness of each film layer cannot be determined.

[0054] It can be understood that based on the prior art and the foregoing related description, it can be seen that the difficulty of film thickness measurement of the multi-layer film to be measured object is mainly due to the aliasing of the echo signals corresponding to different film layers, and needs to be assisted by establishing a simulation model for fitting. In the process of establishing the theoretical simulation model, the material physical parameters of each film layer need to be relied on; and for the deposition formed dielectric film layer and metal film layer, the growth process will not only affect the film thickness, but also cause the material physical parameters of the film layer to change. In order to improve the simulation effect of the simulation model and accurately measure and obtain the material physical parameters of each film layer of the to-be-measured object, the present disclosure provides a photoacoustic measurement method and device, which can accurately obtain the required material physical parameters of the to-be-measured object based on the traditional photoacoustic measurement method without introducing a new measurement process. The specific implementation of the simulation model establishment and data fitting will be explained and described as follows:

[0055] It can be understood that the establishment of the simulation model is a basic and difficult part in the film thickness measurement of the multi-layer film to be measured object, and whether the initial value selection of the material physical parameters of each film layer is accurate plays a crucial role in the establishment of the simulation model. In some embodiments provided by the present disclosure, Figure 4 A flowchart of a simulation method for photoacoustic measurement is provided. As Figure 4 shown, the specific steps can include the following steps:

[0056] Step 401: Using a photoacoustic measurement device to perform photoacoustic measurement on the to-be-measured object to obtain a measured signal of the reflectivity change of the to-be-measured object with time. It can be understood that the photoacoustic signal measurement on the to-be-measured object can refer to the prior art scheme, and the person skilled in the art can also make adaptive adjustment to the specific implementation steps according to the actual needs, which is not limited here.

[0057] Step 402: According to the measured signal, obtaining reference values of a plurality of key parameters of the to-be-measured object. It can be understood that the to-be-measured object includes a multi-layer film to be measured object and a single-layer film to be measured object, that is, the technical solution provided by the present disclosure aims to obtain the selected material physical parameters of each film layer in the multi-layer film to be measured object, and the related technical solution can also be applied to the material physical parameters of the single-layer film to be measured object, which is not described here. The key parameters can include at least one of the heat capacity of the surface film layer of the to-be-measured object, the thermal conductivity of the surface film layer, the acoustic impedance of each thin film, the density of each thin film, the Young's modulus of each thin film, the refractive index of each thin film and the film thickness of each thin film. These key parameters will change due to the growth process. How to obtain the reference values of the above key parameters according to the reflectivity change diagram as Figure 6a shown will be described in detail below.

[0058] Step 403: Determine a plurality of target parameters required for establishing the simulation signal of the reflectivity of the to-be-tested object changing over time. The target parameters include all key parameters. It can be understood that in the process of establishing the simulation model, not only the key parameters of the to-be-tested object are required, but also other parameters such as system parameters of the photoacoustic measurement device, material physical parameters that are not affected by the growth process, and the like, which are not limited herein.

[0059] Step 404: Obtain the value range corresponding to each target parameter, and generate a plurality of different target parameter combinations by randomly selecting values in each value range. It can be understood that for the key parameters in the target parameters, the initial values can be the reference values obtained in the foregoing step 402; and for other non-key parameters in the target parameters, the initial values can be selected as experience values. For example, the value range of each target parameter can be configured as an initial value ± 20%, and other suitable value ranges can also be selected by those skilled in the art according to actual needs, which are not limited herein.

[0060] Step 405: Obtain the simulation signal of the reflectivity changing over time corresponding to each target parameter combination when photoacoustic measurement is performed under the condition of each target parameter combination, and obtain the first error value of each target parameter combination between the simulation signal and the measured signal. The first error value can be the standard deviation between the simulation signal and the measured signal, or the mean square error or the root mean square error between the simulation signal and the measured signal, which is not limited herein.

[0061] Step 406: Based on a plurality of first error values, the target parameter combination is iterated by using a genetic algorithm until the second error value between the simulation signal and the measured signal corresponding to the target parameter combination after iteration is less than a first preset threshold or reaches a minimum extreme value, and the value of the key parameter in the target parameter combination obtained when the iteration is stopped is taken as the simulation value of the key parameter. The second error value reaching the minimum extreme value means the minimum second error value that cannot be further reduced through iteration. The specific implementation of the genetic algorithm will be described below.

[0062] Step 407: Weighted correction is performed on the reference value of each key parameter and the simulation value of the corresponding key parameter to obtain the representation value of each key parameter of the to-be-tested object.

[0063] It can be understood that through the above steps 401 to 407, the reference values of the material physical parameters required by each film layer can be extracted from the reflectivity change measured signal obtained by photoacoustic measurement; further based on the obtained reference values, the parameter combination is determined and the simulation model is established, the reflectivity change simulation signal is obtained through the simulation model, and the simulation value of the material physical parameters of each film layer is obtained through iterative fitting of the simulation signal and the measured signal. Finally, the characterization value of the material physical parameters of each film layer is obtained by weighting correction of the simulation value to the reference value, so as to accurately obtain the required material physical parameters of the measured object. The implementation of the above steps 401 to 407 will be further described through specific embodiments:

[0064] In the specific implementation of the foregoing step 402, Figure 5 According to the embodiments of the present disclosure, a flowchart for obtaining the reference values of several key parameters of the measured object from the measured signal is shown, as shown in Figure 5 The specific steps can include the following steps:

[0065] Step 501: Based on the measured signal of the reflectivity change of the measured object with time, a background signal curve changing with time is generated based on a filtering algorithm, and an echo signal curve changing with time is generated. Exemplarily, Figure 6a A schematic diagram of a measured signal curve of reflectivity change with time is shown, Figure 6b A schematic diagram of a background signal curve changing with time is shown, Figure 6c A schematic diagram of an echo signal curve changing with time is shown. Specifically, as shown in Figure 6a The vertical axis in the measured signal curve schematic diagram is Where ΔR represents the measured reflectivity change value, R represents the initial reflectivity of the measured object only under the irradiation of the measurement beam, That is, the change rate of the normalized reflectivity; the horizontal axis is time, in picoseconds. In order to display more intuitively and better explain, in the above Figure 6a and the signal curve schematic diagrams provided in the subsequent embodiments, the vertical axis of all signal curve schematic diagrams represents the normalized reflectivity change, and the horizontal axis represents time, in picoseconds, which will not be described in detail.

[0066] As Figure 6aAs shown, the overall trend of the measured signal curve for the reflectivity of the object under test over time is an initial rise followed by a fall, with significant periodic fluctuations along the falling edge. This is due to the presence of a background signal in the reflectivity change signal detected by the photoacoustic measurement device, in addition to the echo signals generated by reflections from the various film layers. Those skilled in the art will understand that when the temperature change of the object under test is less than 10 Kelvin, the reflectivity of the object under test is linearly related to the current temperature. This indicates that the background signal represents the thermal effect caused by the pump light provided by the photoacoustic measurement device heating the surface film layer.

[0067] Step 502: Based on the background signal curve, obtain the heat capacity and / or thermal conductivity of the surface film layer of the object to be measured. The specific method of obtaining the heat capacity and thermal conductivity of the surface film layer will be described in detail later.

[0068] Step 503: Based on the echo signal curve, obtain at least one of the acoustic impedance, density, Young's modulus and refractive index of each thin film in the object to be measured. Figure 6c As shown, the echo signal curve includes at least one echo pattern, each echo pattern corresponding to each thin film layer of the object to be measured. The specific method for obtaining the acoustic impedance, density, Young's modulus, and refractive index of each thin film layer will be described in detail later. It is understood that the above steps 502 and 503 can be performed synchronously or asynchronously, and this is not limited here.

[0069] In some embodiments of the present disclosure, for a multi-layer object to be measured, it can include both a metal film layer and a dielectric film layer. If a transparent film layer exists in the dielectric film layer, that is, a film layer that absorbs less light, then periodic oscillations will be observed in the measured signal of the reflectivity change obtained during the photoacoustic measurement. Such oscillations are called Brillouin oscillations. It will be understood by those skilled in the art that Brillouin oscillations refer to the interference between the reflected light of the incident light at the surface film layer and the reflected light at the acoustic wave in the transparent film layer. When the acoustic wave moves in the object to be measured, the two will periodically change between interference enhancement and interference reduction, which is then reflected in the measured signal of the reflectivity change. Since the performance of Brillouin oscillations in the measured signal will affect the acquisition of the reference value of the key parameter, before executing the aforementioned step 501, it is necessary to first determine whether the object to be measured includes a transparent film layer: if so, the measured signal is subjected to a fast Fourier transform to obtain the Brillouin oscillation frequency corresponding to the transparent film layer; if not, the aforementioned step 501 and its subsequent steps can be directly executed.

[0070] In the above embodiments, it can be understood that for the object to be measured including a transparent film layer, which is often used in an oscillator, the propagation speed of the transparent film layer is an important indicator reflecting its performance and is one of the key parameters required in the subsequent photoacoustic measurement process. In the case where the object to be measured includes a transparent film layer, a reference value of the propagation speed of the transparent film layer can be directly obtained by using the Brillouin oscillation frequency. Specifically, the propagation speed of the transparent film layer can satisfy the following formula:

[0071]

[0072] Among them, f B is the Brillouin oscillation frequency, n is the refractive index of the transparent film, v L is the propagation sound velocity in the thickness direction of the transparent film layer, cosθ is the incident angle of the incident light provided by the photoacoustic measurement equipment, and λ is the wavelength of the incident light provided by the photoacoustic measurement equipment.

[0073] In the above embodiment, based on the case where the object to be measured includes a transparent film layer, the influence of Brillouin oscillation in the measured signal can be removed according to the Brillouin oscillation frequency corresponding to the transparent film layer to obtain a corrected signal, and then the first curve and the second curve mentioned above can be generated based on the filtering algorithm according to the corrected signal after removing the Brillouin oscillation, which will not be elaborated here.

[0074] In the specific implementation of the aforementioned step 502, the reference Figure 6b It can be seen that the background signal curve diagram includes a monotonically increasing area on the left and a monotonically decreasing area on the right. The monotonically increasing area can be considered as a scene where the surface film layer of the object to be measured receives the energy of the incident light and generates heat but has no time to propagate outward. At this time, the slope k of the rising edge can be used to calculate the heat generated by the surface film layer. p To obtain the reference value of the heat capacity of the surface film layer, the slope k p It can be calculated from the coordinates corresponding to the minimum and maximum points in the monotonically increasing region. The mathematical fitting of the corresponding monotonically increasing region can specifically satisfy the following formula:

[0075]

[0076]

[0077] Where P is the average power of the pulsed laser provided by the photoacoustic measurement equipment, f p is the frequency of the pulsed laser provided by the photoacoustic measurement equipment, Q is the energy of a single laser pulse, ζ is the absorption depth of the object to be measured for the energy of a single laser pulse, S p is the spot area on the surface of the object to be measured, c is the heat capacity of the surface film layer, A l is the rate of change of the reflectivity of the object to be measured with respect to temperature.

[0078] Similarly, as shown in Figure 6b the monotonically decreasing region in the background signal curve schematic diagram can be considered as the scenario that the photoacoustic measurement device stops providing incident light and the surface film layer stops being heated and starts to spread heat outward, at this time, the thermal conductivity reference value of the surface film layer can be obtained according to the falling rate of the falling edge, and the following formula can be satisfied:

[0079]

[0080] wherein R(t) is the reflectivity of the object to be measured at time t, A l is the rate of change of the reflectivity of the object to be measured with respect to temperature, k is the thermal conductivity of the surface film layer, S p is the spot area of the surface of the object to be measured.

[0081] In the specific implementation of the foregoing step 503, Figure 7 According to the embodiments of the present disclosure, a flowchart for obtaining the acoustic impedance and density of the film is shown, as shown in Figure 7 which can specifically include:

[0082] Step 701: According to the amplitude change of any two adjacent echo patterns, the ratio of the reflected sound wave intensity to the transmitted sound wave intensity at each film interface of the object to be measured is obtained. Among them, the maximum amplitude of the echo pattern occurring earlier in the adjacent two echo patterns represents the reflected sound wave intensity at the film interface, and the maximum amplitude of the echo pattern occurring later represents the transmitted sound wave intensity at the film interface. It can be understood that in the process of photoacoustic measurement, when the sound wave is transmitted to the interface of the film prepared by two layers of different materials, part of the sound wave is transmitted into the next layer, and the other part is reflected, which is reflected in the amplitude change of the echo signal in the second curve schematic diagram. Exemplarily, Figure 8a a local enlarged schematic diagram of an echo signal curve is shown, as shown in Figure 8a , wherein A1 is the reflected sound wave intensity at the interface of the adjacent two films, A2 is the transmitted sound wave intensity at the interface of the adjacent two films, and the ratio between the two represents the acoustic reflection coefficient at the interface of the adjacent two films, which can be specifically represented as:

[0083]

[0084] wherein r is the acoustic reflection coefficient at the interface of the adjacent two films, which is the ratio of the reflected sound wave intensity and the transmitted sound wave intensity, and its sign determines whether the polarity of the reflected sound pulse is reversed, in the schematic diagram as shown in Figure 8a , the polarity of the reflected sound pulse is not reversed. Exemplarily, Figure 8b a local enlarged schematic diagram of another second curve representing an echo signal is shown, as shown in Figure 8bAs shown, the reflected acoustic pulse polarity at the interface of the two adjacent films is reversed.

[0085] Step 702: Based on the acoustic impedance of the substrate layer in the object to be measured, the acoustic impedance of each film layer is obtained in sequence according to the ratio. Specifically, the acoustic impedance of the two adjacent film layers satisfies the following formula:

[0086]

[0087] Wherein, in the process of the acoustic wave generated in the photoacoustic measurement process from the upper film into the lower film, Z upper is the acoustic impedance of the upper film in the two adjacent film layers, Z lower is the acoustic impedance of the lower film in the two adjacent film layers, A1 is the reflected acoustic wave intensity at the interface of the two adjacent film layers, and A2 is the transmitted acoustic wave intensity at the interface of the two adjacent film layers. It can be understood that in the case where the acoustic impedance of the bottom film of the object to be measured is known, the acoustic impedance reference value of each film layer can be obtained from the bottom to the top according to the above formula.

[0088] Step 703: Based on the propagation speed and acoustic impedance of each film layer, the density of each film layer is obtained. Specifically, the density of each film layer satisfies the following formula:

[0089]

[0090] Wherein, p is the density of the film, Z is the acoustic impedance of the film, v L is the propagation speed of the film. It can be understood that in the case where the propagation speed of each film layer of the object to be measured is known, the density reference value of each film layer can be obtained in sequence according to the acoustic impedance reference value.

[0091] Further, on the basis of obtaining the film density reference value based on the foregoing embodiment, the reference value of the Young's modulus can be further obtained. The Young's modulus is a very important parameter for measuring the mechanical properties of materials, which can satisfy the following formula:

[0092]

[0093] Wherein, E is the Young's modulus of the film, and υ is the material Poisson's ratio of the film. Since the Poisson's ratio of the material is generally fixed, the Young's modulus reference value of each film layer can be obtained in the case where the density reference value of each film layer is known.

[0094] In the specific implementation of the foregoing step 503, Figure 9 According to the embodiment of the present disclosure, a flowchart for obtaining the refractive index coefficient of the film is shown, as Figure 9 shown, specifically can include:

[0095] Step 901: According to the change of each echo pattern, the oscillation period of the echo signal of each layer of film and the attenuation trend of the echo signal are obtained. Among them, the time interval between two adjacent wave peaks or troughs in the echo pattern represents the oscillation period, and the amplitude decreasing trend of the wave peak or trough in the echo pattern represents the attenuation trend. It can be understood that in the photoacoustic measurement process, the temperature gradient is generated due to the different lattice temperature rising speeds of different positions of the measured object, and then the strain propagation is triggered, and the strain changes with time, causing the reflectivity to change accordingly. Specifically, there is a mathematical relationship between the strain η(z) of the material at any position z in the thickness direction of the film and the change δR(t) of the reflectivity with time as follows:

[0096]

[0097] Where f(z) is the sensitivity function, which represents the sensitivity of the change of reflectivity with time to strain, and its expression is as follows:

[0098]

[0099] In the above formula, f0 satisfies:

[0100] In the above formula, ψ satisfies:

[0101] In the above formula, ζ satisfies:

[0102] Where n is the material refractive index, κ is the material extinction coefficient, λ is the pump light wavelength, ζ is the pump light absorption depth, c is the speed of light, and ω is the pump light angular frequency. It can be seen that the sensitivity function can be simplified to a product of a sinusoidal oscillation and an e exponential decay, and the oscillation period is The attenuation trend can be expressed as

[0103] Step 902: According to the oscillation period of the echo signal, the material refractive index coefficient of each layer of film is obtained; and according to the attenuation trend of the echo signal, the material extinction coefficient of each layer of film is obtained. Wherein the oscillation period of the echo signal satisfies the following formula:

[0104]

[0105] Where f is the oscillation period of the echo signal, n is the material refractive index coefficient of the film at any position z, and λ is the pump light wavelength; correspondingly, the attenuation trend of the echo signal satisfies the following formula:

[0106]

[0107] Wherein, ω is the pump light angular frequency, κ is the material extinction coefficient of the film at any position z, c is the speed of light.

[0108] In the specific implementation of the foregoing step 405, in the process of obtaining the simulation signal, in combination with the mathematical relationship between the strain η(z) and the reflectivity change δR(t) of the material at any position z in the film thickness direction over time, the displacement u(z, t) of the material at time t at any position z in the film thickness direction can be obtained by establishing a partial differential equation, and the strain η(z, t) of the material at time t at any position z can be obtained by further deriving the displacement u(z, t) in the film thickness direction. Specifically, the expression of the partial differential equation can be as follows:

[0109]

[0110] Wherein, ρ(z) is the density of the material at any position z, F z is the force acting on the material at any position z. It can be understood that the temperature gradient will generate strains of different amplitudes at different positions. The difference in strain size will generate forces between materials at different positions. The relationship between the force and the strain will be propagated in the form of a sound wave. Further, the expression of F z can be as follows:

[0111]

[0112] Wherein, ρ(z) is the density of the material at any position z, v(z) is the sound speed of the material at any position z, α(z) is the thermal expansion coefficient of the material at any position z, E(z) is the Young's modulus of the material at any position z, γ(z) is the Poisson's ratio of the material at any position z, is the lattice temperature gradient, that is, the lattice temperature T l (z, t) in the film thickness direction. It can be found that the physical parameters of the material used in the establishment of the above partial differential equation can be obtained by referring to the reference values of the key parameters obtained in the foregoing steps 501 to 503.

[0113] In the specific implementation of the foregoing step 406, Figure 10 According to the embodiments of the present disclosure, a flowchart of iterating the target parameter combination based on a plurality of first error values using a genetic algorithm until the second error value between the simulation signal corresponding to the iterated target parameter combination and the measured signal is less than a first preset threshold or reaches a minimum extreme value is shown, as Figure 10 shown, which can specifically include:

[0114] Step 1001: comparing the first error value with a deviation threshold value, discarding the target parameter combination corresponding to the first error value greater than the deviation threshold value, and retaining the remaining target parameter combinations. The first error value between the simulated signal of the change of reflectivity over time and the measured signal includes one of the standard deviation of the measured signal and the simulated signal, the mean square error of the measured signal and the simulated signal, and the root mean square of the measured signal, which is not limited here.

[0115] It can be understood that the setting of the deviation threshold value in the above step 1001 will affect the genetic iteration speed and fitting accuracy, and those skilled in the art can select a suitable deviation threshold value according to the actual situation, which will not be repeated here.

[0116] Step 1002: performing parameter exchange operation and / or parameter mutation operation on the remaining target parameter combinations to generate several generation target parameter combinations. The generation target parameter combination is not the same as the remaining target parameter combination. In the above step 1002, the parameter exchange operation refers to the exchange of the value of each physical parameter between different target parameter combinations at a certain probability (for example, 1%); the parameter mutation operation refers to the change of the value of each physical parameter in any target parameter combination at a certain probability (for example, 1%).

[0117] Step 1003: obtaining the second error value of the simulated signal and the measured signal corresponding to each generation target parameter combination.

[0118] Step 1004: if the second error value is less than the first preset threshold value or the minimum value is obtained, the iteration ends; if the second error value is not less than the preset threshold value and the minimum value is not obtained, comparing the second error value with the deviation threshold value, discarding the target parameter combination corresponding to the second error value greater than the deviation threshold value, retaining the remaining target parameter combinations, repeating the above steps 1002 to 1004, until the second error value is less than the preset threshold value or the minimum extreme value is obtained, and the iteration ends.

[0119] In the specific implementation of the foregoing step 407, Figure 11 According to the embodiments of the present disclosure, a flowchart for weighting and correcting the reference value of each key parameter and the simulation value of the corresponding key parameter to obtain the characteristic value of each key parameter of the object to be measured is shown, as shown in Figure 11 As shown in the figure, the specific steps can include the following steps:

[0120] Step 1101: obtaining the second error value corresponding to each simulation value.

[0121] Step 1102: In the case that the second error value corresponding to the simulation value is less than the second preset threshold, a weight value corresponding to the simulation value is obtained. In a specific implementation of the above embodiment, the root mean square error can be taken as the second error value and as the basis for calculating the weight value; if the second error value is greater than the second preset threshold, it indicates that the fitting result has no confidence, and the reference value does not need to be additionally weighted and corrected. The weight value satisfies the following formula:

[0122]

[0123] Step 1103: The reference value is weighted and corrected according to the weight value and the simulation value to obtain a characteristic value. The characteristic value satisfies the following formula:

[0124] J r =(1-q)*J1+q*J2.

[0125] Wherein, J r , J1, J2 are the characteristic value, the reference value and the simulation value of the same key parameter; q, D are the weight value and the second error value of the simulation value J2 of the corresponding key parameter, and Y is the second preset threshold.

[0126] In some embodiments of the present disclosure, the characteristic value of the key parameter obtained based on the foregoing embodiment can not only improve the modeling initial value precision of the theoretical simulation model, but also be used to evaluate the coating uniformity of the to-be-tested object, so as to further monitor the production process level of the to-be-tested object, which will not be repeated here.

[0127] In some embodiments of the present disclosure, Figure 12 A structural schematic diagram of a photoacoustic measurement device is shown, as Figure 12 shown, specifically can include:

[0128] The measurement module 1201 is configured to perform photoacoustic measurement on the to-be-tested object to obtain a measured signal of the reflectivity of the to-be-tested object changing with time.

[0129] The key parameter acquisition module 1202 is configured to acquire reference values of a plurality of key parameters of the to-be-tested object according to the measured signal.

[0130] The target parameter determination module 1203 is configured to determine a plurality of target parameters required to establish a simulation signal of the reflectivity of the to-be-tested object changing with time, and the target parameters include all the key parameters.

[0131] The parameter combination acquisition module 1204 is configured to acquire a value range corresponding to each target parameter, and generate a plurality of different target parameter combinations by randomly taking values in each value range.

[0132] The signal simulation module 1205 is configured to obtain a simulated signal of reflectivity change over time corresponding to the photoacoustic measurement under the condition of each target parameter combination, and obtain a first error value of the simulated signal of each target parameter combination and the measured signal.

[0133] The iterative fitting module 1206 is configured to iteratively fit the target parameter combination by using a genetic algorithm based on the first error values until a second error value between the simulated signal and the measured signal corresponding to the target parameter combination after iteration is less than a first preset threshold or reaches a minimum extreme value, and take the value of the key parameter in the target parameter combination obtained when the iteration is stopped as the simulated value of the key parameter.

[0134] The weighted correction module 1207 is configured to perform weighted correction on the reference value of each key parameter and the simulated value of the corresponding key parameter to obtain a characterization value of each key parameter of the object to be measured.

[0135] It can be understood that the functions performed by the measurement module 1201 to the weighted correction module 1207 are consistent with the aforementioned steps 401 to 407, and will not be repeated here.

[0136] In summary, the technical solution provided by the present disclosure can be used to perform photoacoustic measurement on an object to be measured based on a conventional photoacoustic measurement method, extract reference values of material physical parameters required by each film layer according to the obtained reflectivity change measured signal, further determine a parameter combination based on the obtained reference values and establish a simulation model, obtain a reflectivity change simulated signal through the simulation model, and perform iterative fitting according to the reflectivity change simulated signal and the measured signal to obtain simulated values of the material physical parameters of each film layer. Finally, the characterization values of the material physical parameters of each film layer are obtained by weighted correction of the simulated values on the reference values. The characterization values obtained based on the above technical solution can accurately reflect the actual situation of the physical parameters of each film layer in the object to be measured, have high accuracy, can improve the precision of the initial values of the material physical parameters used by the simulation model, and thus reduce the required time of the subsequent simulation fitting process, improve the accuracy and time efficiency of photoacoustic measurement. In addition, the high-precision material physical parameters can also be used to evaluate the film uniformity of the object to be measured, to further monitor the production process level of the object to be measured, and have promotional value.

[0137] The above is a further detailed description of the present disclosure in combination with specific preferred embodiments, and the specific implementation of the present disclosure cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present disclosure belongs, some simple deductions or substitutions can be made without departing from the concept of the present disclosure, and all of them should be regarded as falling within the protection scope of the present disclosure.

Claims

1. A photoacoustic measurement method, characterized by, The method comprises the following steps: performing photoacoustic measurement on the object to be measured by using a photoacoustic measurement device to obtain a measured signal of reflectivity of the object to be measured changing with time; obtaining reference values of a plurality of key parameters of the object to be measured according to the measured signal; determining a plurality of target parameters required for establishing a simulation signal of reflectivity of the object to be measured changing with time, wherein the target parameters include all the key parameters; obtaining a value range corresponding to each of the target parameters, and generating a plurality of different target parameter combinations by randomly selecting values within each of the value ranges; obtaining a simulation signal of reflectivity changing with time when photoacoustic measurement is performed under the condition of each of the target parameter combinations respectively, and obtaining a first error value of each of the simulation signals corresponding to the target parameter combinations and the measured signal respectively; iterating the target parameter combinations by using a genetic algorithm based on a plurality of the first error values until a second error value between the simulation signal corresponding to the target parameter combinations after iteration and the measured signal is less than a first preset threshold value or reaches a minimum extreme value, and taking values of the key parameters in the target parameter combinations obtained at the time of iteration as simulation values of the key parameters; performing weighted correction on the reference values of each of the key parameters and the simulation values of the corresponding key parameters to obtain representation values of each of the key parameters of the object to be measured.

2. The photoacoustic measurement method according to claim 1, wherein The object to be measured comprises a substrate layer and one or more film layers. The key parameters include at least one of thermal capacity of a surface film layer of the object to be measured, thermal conductivity of the surface film layer, acoustic impedance of each of the film layers, density of each of the film layers, Young's modulus of each of the film layers, and refractive index of each of the film layers.

3. The photoacoustic measurement method according to claim 2, wherein The method of obtaining reference values of a plurality of key parameters of the object to be measured according to the measured signal comprises the following steps: generating a background signal curve changing with time and a return signal curve changing with time based on a filtering algorithm according to the measured signal of reflectivity of the object to be measured changing with time, wherein the return signal curve comprises at least one return pattern, and each of the return patterns corresponds to each of the film layers of the object to be measured one by one; obtaining thermal capacity and / or thermal conductivity of a surface film layer of the object to be measured based on the background signal curve; obtaining at least one of acoustic impedance, density, Young's modulus, and refractive index of each of the film layers of the object to be measured based on the return signal curve.

4. The photoacoustic measurement method according to claim 3, wherein Before generating the background signal curve and the return signal curve based on the filtering algorithm, the method further comprises the following steps: judging whether the object to be measured comprises a transparent film layer: if yes, performing fast Fourier transform on the measured signal to obtain a Brillouin oscillation frequency corresponding to the transparent film layer; According to the Brillouin oscillation frequency, the propagation sound speed v of the transparent film layer is obtained T , the propagation sound speed v of the transparent film layer T , satisfies the following formula: where f B is the Brillouin oscillation frequency, n is the refractive index of the transparent film layer, θ is the angle of incidence of the measurement beam provided by the photoacoustic measurement device, and λ is the wavelength of the measurement beam provided by the photoacoustic measurement device.

5. The photoacoustic measurement method according to claim 4, wherein generating the background signal curve and the return signal curve based on the filtering algorithm comprises: obtaining a modified signal by removing the influence of Brillouin oscillation in the measured signal according to the Brillouin oscillation frequency; generating the background signal curve and the return signal curve based on the filtering algorithm according to the modified signal.

6. The photoacoustic measurement method according to claim 3, wherein Obtaining the heat capacity of the surface film layer of the object to be measured based on the background signal curve includes the following steps: According to the slope k of the monotonically increasing region in the background signal curve p Mathematical fitting is performed to obtain the heat capacity of the surface film layer; The mathematical fitting of the monotonically increasing region in the background signal curve satisfies the following formula: wherein P is the average power of the pulsed laser provided by the photoacoustic measurement device, f p is the frequency of the pulsed laser provided by the photoacoustic measurement device, Q is the energy of a single pulsed laser, ζ is the absorption depth of the single pulsed laser energy by the object under test, S p is the spot area on the surface of the object under test, c is the heat capacity of the surface film layer, A l is the rate of change of reflectivity with temperature of the object under test.

7. The photoacoustic measurement method according to claim 3, wherein Obtaining the thermal conductivity of the surface film layer of the object to be measured based on the background signal curve includes the following steps: Performing mathematical fitting based on the curve change in the monotonically decreasing region of the background signal curve to obtain the thermal conductivity of the surface film layer; The mathematical fitting of the monotonically decreasing region in the background signal curve satisfies the following formula: Wherein, R(t) is the reflectivity of the object to be measured at time t, A l is the rate of change of the reflectivity of the object to be measured with temperature, k is the thermal conductivity of the surface film layer, S p is the spot area of the surface of the object to be measured.

8. The photoacoustic measurement method according to claim 3, wherein Obtaining the density of each thin film layer in the object to be measured based on the echo signal curve includes the following steps: According to the amplitude changes of any two adjacent echo patterns, respectively obtaining the ratio of the reflected sound wave intensity to the transmitted sound wave intensity at each thin film junction of the object to be measured, wherein, of the two adjacent echo patterns, the maximum amplitude of the echo pattern occurring earlier represents the reflected sound wave intensity, and the maximum amplitude of the echo pattern occurring later represents the transmitted sound wave intensity; Based on the acoustic impedance of the base layer in the object to be measured, sequentially obtaining the acoustic impedance of each layer of the film according to the ratio; Obtaining the density of each layer of the film based on the propagation sound velocity and the acoustic impedance of each layer of the film; The acoustic impedance of two adjacent layers of the film satisfies the following formula: wherein Z upper is the acoustic impedance of the upper film of the two adjacent films, Z lower is the acoustic impedance of the lower film of the two adjacent films, A1 is the reflected acoustic wave intensity at the interface of the two adjacent films, and A2 is the transmitted acoustic wave intensity at the interface of the two adjacent films. The density of each layer of the film satisfies the following formula: wherein p, Z, v L are the density, acoustic impedance, and propagation speed of the film, respectively.

9. The photoacoustic measurement method according to claim 8, wherein Acquiring the Young's modulus of each thin film in the object to be measured based on the echo signal curve includes the following steps: Obtaining the Young's modulus of the film of each layer according to the density of the film; The Young's modulus of the film satisfies the following formula: Where E is the Young's modulus of the film, and υ is the Poisson's ratio of the film material.

10. The photoacoustic measurement method according to claim 3, wherein Obtaining the refractive index of each thin film in the object to be measured based on the echo signal curve includes the following steps: Obtaining the oscillation period and attenuation trend of the echo signal of each layer of the film according to the change of each echo pattern, wherein the time interval between two adjacent peaks or troughs in the echo pattern represents the oscillation period, and the decreasing trend of the amplitude of the peaks or troughs in the echo pattern represents the attenuation trend; The material refractive index coefficient of each layer of the film is obtained according to the oscillation period of the echo signal, and the oscillation period of the echo signal satisfies the following formula: Wherein, f is the oscillation period of the echo signal, n is the refractive index coefficient of the material of the thin film at any position z, and λ is the wavelength of the pump light; According to the attenuation trend of the echo signal, the material extinction coefficient of each layer of the film is obtained. The mathematical fitting of the attenuation trend of the echo signal satisfies the following formula: Wherein, ω is the angular frequency of the pump light, κ is the extinction coefficient of the material of the film at any position z, and c is the speed of light.

11. The photoacoustic measurement method according to claim 1, wherein The step of performing weighted correction on the reference value of each key parameter and the simulation value of the corresponding key parameter to obtain a characterization value of each key parameter of the object to be measured comprises the following steps: Obtaining the second error value corresponding to each of the simulation values; In a case where the second error value corresponding to the simulation value is less than a second preset threshold, a weight value corresponding to the simulation value is obtained, and the weight value satisfies the following formula: According to the weight value, the reference value and the simulation value of the corresponding key parameter are weighted and corrected to obtain the representation value of the corresponding key parameter, and the representation value satisfies the following formula: J r = (1 - q) * J1+ q * J2; wherein J r J1, J2 are the characteristic value, reference value, the simulation value of the same key parameter, respectively, and q, D are the weight value, the second error value of the simulation value J2 of the corresponding key parameter, respectively, and Y is the second preset threshold value.

12. A photoacoustic measuring apparatus, characterized by Comprise: A measurement module configured to perform photoacoustic measurement on a to-be-measured object to obtain a measured signal of reflectivity of the to-be-measured object changing over time; A key parameter acquisition module configured to acquire reference values of a plurality of key parameters of the to-be-measured object according to the measured signal; A target parameter determination module configured to determine a plurality of target parameters required for establishing a simulation signal of reflectivity of the to-be-measured object changing over time, wherein the target parameters include all the key parameters; A parameter combination acquisition module configured to acquire a value range corresponding to each of the target parameters, and generate a plurality of different target parameter combinations by randomly selecting values in each of the value ranges; A signal simulation module configured to respectively acquire simulation signals of reflectivity changing over time when photoacoustic measurement is performed under the condition of each of the target parameter combinations, and respectively acquire first error values of each of the target parameter combinations between the simulation signal and the measured signal; An iterative fitting module configured to perform iteration on the target parameter combinations by using a genetic algorithm based on the plurality of first error values until a second error value between the simulation signal and the measured signal corresponding to the target parameter combination after iteration is less than a first preset threshold or reaches a minimum extreme value, and take values of the key parameters in the target parameter combination obtained at the time of iteration as simulation values of the key parameters; A weighted correction module configured to perform weighted correction on the reference value of each of the key parameters and the simulation value of the corresponding key parameter to obtain a representation value of each of the key parameters of the to-be-measured object.

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