Photoacoustic measurement system

Abstract

The present invention provides a photoacoustic measurement system. The photoacoustic measurement system generates sound waves by irradiating the surface of the object to be measured with excitation light. The sound waves cause the surface of the object to be measured to deform. At the same time, the reflected light of the detection light, i.e., signal light, is obtained by irradiating the surface of the object to be measured with detection light. Since the sound waves move within the object to be measured and rebound to the surface of the object to be measured to form a deformation area, they will affect the signal light, causing the signal collected by the detector to change, and then the film thickness can be calculated based on the collected signal. The time of the signal light is fed back by collecting the position of the displacement stage of the delay device, and the optical power data collected by the detector and the position data of the displacement stage are processed by the control module. Then, the movement duration of the sound wave is determined according to the position of the displacement stage, and the film thickness of the object to be measured is calculated. A highly accurate result can be obtained, effectively avoiding the influence of various errors on the calculation accuracy in the existing technology.

Description

Technical Field

[0001] The present invention relates to the technical field of thickness measurement, and in particular to a photoacoustic measurement system. Background Art

[0002] The photoacoustic effect (PAE) is a phenomenon in which, when a medium is illuminated by a periodically intensity-modulated light source, changes in internal temperature cause changes in regional structure and volume, generating acoustic signals. Measurement techniques based on the PAE combine the high resolution of optical measurements with the high penetration of acoustic measurements. They have been widely used in fields such as biomedicine, military aerospace, and the semiconductor industry. The key to successful application of this technology lies in accurate feature recognition and extraction of the measurement signals.

[0003] Photoacoustic measurement technology for non-transparent solid materials is an effective way to achieve rapid and non-destructive defect detection, film thickness measurement, and physical property characterization.

[0004] Nondestructive testing and film thickness measurement techniques based on the solid-state photoacoustic effect typically utilize a pulsed laser to generate an acoustic pulse near the sample's surface. The propagation of this acoustic pulse within the sample is monitored using ultrasonic transducers and optical detection methods to obtain a one-dimensional time-series photoacoustic measurement signal. A zero-point signal is generated at the instant the acoustic pulse is generated. During its propagation, it is partially reflected at the sample interface and returns to the sample surface, forming an echo signal. By identifying and extracting the features of the zero-point signal and echo signal in the time-series measurement signal, information such as the sample's film thickness can be inverted and calculated.

[0005] In the prior art, the position signal obtained by the zero-point signal and the echo signal is used as a time domain signal to calculate information such as the film thickness. However, when the position is used as a time domain signal, there are often errors in the principle, manufacturing, and operation, which easily leads to low measurement accuracy. Summary of the Invention

[0006] The object of the present invention is to provide a photoacoustic measurement system to solve the problem of low measurement accuracy when position signals are used as time domain signals in the prior art.

[0007] The present invention provides a photoacoustic measurement system, which includes a light source, a delay device, a displacement sensor, a detector and a control module; the light source is used to generate detection light and excitation light, the excitation light is used to form an acoustic wave in the object to be measured, the acoustic wave is transmitted back to the surface of the object to be measured through the interface in the object to be measured to generate a deformation area, and the detection light is used to irradiate the deformation area on the surface of the object to be measured to form a signal light; the delay device includes a displacement stage and a plurality of reflection components, the plurality of reflection components are used to reflect the detection light multiple times, and the displacement stage is used to drive the reflection components to move linearly to adjust the total optical path of the detection light. The total optical path of the detection light includes the variable optical path controlled by the delay device and the fixed optical path in the detection light path; the detector collects the optical power of the signal light at a first frequency; the displacement sensor collects the position of the displacement stage in real time at a second frequency; the control module processes the collected optical power of the signal light and / or the position of the displacement stage so that the ratio of the data volume of the optical power of the signal light to the data volume of the position of the displacement stage in the same time period is 0.9 to 1.1, and obtains the film thickness of the object to be measured based on the optical power data of the signal light and the position data of the displacement stage after the data processing.

[0008] The beneficial effect of the photoacoustic measurement system of the present invention is that: the excitation light and the detection light are generated by a light source, the excitation light is irradiated on the surface of the object to be measured to form an acoustic wave, the acoustic wave is transmitted back to the surface of the object to be measured through the interface in the object to be measured to generate a deformation area, and at the same time, the reflected light of the detection light, i.e., the signal light, is obtained by irradiating the surface of the object to be measured with the detection light. Since the acoustic wave moves in the object to be measured and rebounds to the surface of the object to be measured to form a deformation area, it will affect the signal light, causing the signal collected by the detector to change, and then the film thickness can be calculated based on the collected signal. The delay device is arranged on the movement path of the detection light to adjust the optical path of the detection light. Since the collected signal light is related to the delay caused by the delay device on the detection light, the time of the signal light can be fed back by collecting the position of the displacement stage of the delay device. Since the frequency requirement of the collected signal light is very high, and the collection frequency of the position data (second frequency) is often not equal to the collection frequency of the signal light (first frequency), the control module processes the optical power data collected by the detector and the position data of the displacement stage to make the two match to a certain extent. Thereafter, the movement duration of the sound wave is determined according to the position of the displacement stage, and the film thickness of the object to be measured is calculated. This can obtain a result with a high accuracy, effectively avoiding the influence of various errors on the calculation accuracy in the existing technology.

[0009] In a feasible solution, the displacement sensor is a grating ruler, which has the beneficial effect of obtaining position data by collecting an image of the grating ruler, which is convenient to use.

[0010] In one feasible solution, the data processing of the collected optical power of the signal light and / or the position of the translation stage includes: interpolating the collected data obtained at the lower of the first and second frequencies and / or compressing the collected data obtained at the higher of the first and second frequencies. The beneficial effects are: by interpolating the data with the lower value of the first and second frequencies, the two frequencies can be matched or the data volume ratio between the two frequencies can be brought into a range of 0.9 to 1.1; or by compressing the data with the higher value of the first and second frequencies, the two frequencies can be matched or the data volume ratio between the two frequencies can be brought into a range of 0.9 to 1.1; or, by simultaneously compressing the higher data and interpolating the lower data, the two frequencies can be matched or the data volume ratio between the two frequencies can be brought into a range of 0.9 to 1.1.

[0011] In a feasible solution, the interpolation process includes linear interpolation or spline interpolation.

[0012] In one feasible solution, the compression process includes: obtaining a proportional coefficient Q between the higher of the first and second frequencies and the lower of the first and second frequencies; selecting k points in the data obtained from the higher frequency that are closest to the data acquisition timing points obtained from the lower frequency as target points for compression, calculating the average of the acquired data values ​​corresponding to the target points, and using the average as the acquired data corresponding to the higher frequency after data processing, where 0.9≤k / Q≤1.1. This advantageous effect is that such a setting can compress the higher of the first and second frequencies by a ratio k, so that the compressed frequency is within a range of 0.9 to 1.1 of the lower of the first and second frequencies.

[0013] In a feasible solution, the data collection timing points corresponding to the k target points are symmetrically distributed. The beneficial effect is that such a setting can improve the accuracy of the compression result during data compression.

[0014] In one feasible solution, after the data processing, the data volume of the optical power of the signal light and the data volume of the position of the translation stage within the same time period are equal. This advantageously enables the film thickness of the object to be measured to be calculated using the position data when the data volumes are equal, thereby obtaining the most accurate calculation result.

[0015] In a feasible solution, the method of obtaining the film thickness of the object to be measured based on the optical power data of the signal light and the position data of the displacement stage after the data processing includes: establishing a correspondence between the optical power data of the signal light and the position data of the displacement stage and their respective data acquisition timing points at the same time; obtaining the peak position of the optical power data of the signal light and the optical power data acquisition timing point corresponding to the peak position; and obtaining a data matching point of the displacement stage that matches the peak position in the position data of the displacement stage. F , and the data matching points F The corresponding position value of the displacement stage P F , the data matching point F The position data collection timing point closest to the optical power data collection timing point corresponding to the peak position; based on the data matching point F The corresponding position value of the displacement stage P F , obtain the position of the displacement stage at the data matching point F The optical path difference between the detection light and the excitation light when they reach the surface of the object to be measured is OPD F Based on the optical path difference OPD F ， Obtain the film thickness of the object to be measured.

[0016] Its beneficial effect is that: through the correspondence between the optical power data and the position data and their respective data collection points, the position data matching point corresponding to the optical power at the peak value can be obtained. F , and obtain the value corresponding to the position data at the peak P F , according to the value P F As well as the corresponding position data and value when the excitation light reaches the surface of the object to be measured, the optical path difference between the detection light and the excitation light when the signal light bounces back to the surface of the object to be measured can be calculated. OPD F , through the optical path difference OPD F The film thickness of the object to be measured can be calculated.

[0017] In a feasible solution, the translation stage is located at the data matching point F The optical path difference between the detection light and the excitation light when they reach the surface of the object to be measured is OPD F ， Including: obtaining the position of the displacement stage at the data matching pointF The total optical path length of the detection light is : , ; Get the position of the displacement stage at the data matching point F When the optical path difference between the detection light and the excitation light OPD F : ;in, is a fixed optical path in the detection light path, The displacement stage in the detection optical path is located at the data matching point F The optical path length of the variable optical path length segment of the detection light achieved when is the optical path of the excitation light, is the number of times the reflection component reflects the detection light. The sum of the fixed optical path and the optical path generated by the displacement stage is calculated by counting the optical path generated by the displacement stage during a single reflection, that is, the value corresponding to the position data when the optical power is at its peak. P F , and the optical path length during a single reflection P F Multiplying by the number of reflections n gives the total optical path length of the variable optical path segment. , the total optical path length through the variable optical path length segment and fixed optical path The total optical path length of the detection light can be obtained , through the total optical path Subtract the optical path length of the excitation light The optical path difference can be obtained OPD F , and then the film thickness can be calculated.

[0018] In a feasible solution, the optical path difference OPD F ， Obtaining the film thickness of the object to be measured, including: based on the optical path difference OPD F Obtain the time interval between two adjacent echoes formed by the sound wave returning to the surface of the object to be tested , ; Obtaining the film thickness of the object to be measured based on the time interval d , ;in, is the speed of light, is the propagation speed of the sound wave in the object to be measured. Its beneficial effect is that: the optical path difference OPD FThat is, when the signal light bounces back to the surface of the object to be measured, the optical path difference between the detection light and the excitation light is calculated by the optical path difference. OPD F Calculate the time interval between the moment when the detection light reaches the surface of the object to be measured, i.e., when the sound wave is generated, and the moment when the sound wave moves inside the object to be measured and rebounds to the surface of the object to be measured. , or by the optical path difference OPD F The time interval between two adjacent times when the sound waves move in the object to be tested and rebound to the surface of the object to be tested can be calculated. , and then the speed of the sound wave in the object to be tested is The film thickness can be calculated d . BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the photoacoustic measurement system in the first embodiment of the present invention;

[0020] Figure 2 Schematic diagram of the optical path of the detection light and the excitation light in the first embodiment of the present invention;

[0021] Figure 3 Schematic diagram of comparison between position data and optical power data in the second embodiment of the present invention;

[0022] Figure 4 for Figure 3 Schematic diagram of the comparison between the difference of the position data and the optical power data;

[0023] Figure 5 Schematic diagram showing the comparison of position data before and after compression in the third embodiment of the present invention;

[0024] Figure 6 for Figure 5 Schematic diagram comparing the position data before and after compression and the optical power data. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs. The words "including" and similar words used in this article mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0026] In response to the problems existing in the prior art, an embodiment of the present invention provides a photoacoustic measurement system.

[0027] Figure 1 Schematic diagram of the structure of the photoacoustic measurement system in the first embodiment of the present invention.

[0028] In some embodiments of the present invention, referring to Figure 1 The photoacoustic measurement system includes a light source, a delay device, a displacement sensor, a detector and a control module; the light source is used to generate detection light and excitation light, the excitation light is used to form an acoustic wave in the object to be measured, the acoustic wave is transmitted back to the surface of the object to be measured through the interface in the object to be measured to generate a deformation area, the detection light is used to irradiate the deformation area on the surface of the object to be measured to form a signal light; the delay device includes a displacement stage and a plurality of reflection components, the plurality of reflection components are used to reflect the detection light multiple times, the displacement stage is used to drive the reflection component to move linearly to adjust the total optical path of the detection light, the detection light The total optical path includes the variable optical path controlled by the delay device and the fixed optical path in the detection optical path; the detector collects the optical power of the signal light at a first frequency; the displacement sensor collects the position of the displacement stage in real time at a second frequency; the control module processes the collected optical power of the signal light and / or the position of the displacement stage so that the ratio of the data volume of the optical power of the signal light to the data volume of the position of the displacement stage in the same time is 0.9 to 1.1, and obtains the film thickness of the object to be measured based on the optical power data of the signal light and the position data of the displacement stage after the data processing.

[0029] In some specific embodiments of the present invention, the light source is divided into two beams of light by a beam splitter, namely, the detection light and the excitation light. The excitation light is directly irradiated onto the surface of the object to be measured to form an acoustic wave. The acoustic wave is transmitted back to the surface of the object to be measured through the interface in the object to be measured, causing a deformation area on the surface of the object to be measured. The detection light is irradiated onto the deformation area through the delay device and generates signal light. The detector collects optical power data of the signal light at the first frequency, and the displacement sensor collects position data of the displacement stage in real time at the second frequency. The control module obtains the first frequency and the second frequency information, and interpolates or compresses the information of the first frequency and the second frequency, so that the ratio of the data volume of the optical power information of the signal light to the position information of the displacement stage is in the range of 0.9 to 1.1, and then the film thickness is calculated based on the processed data.

[0030] In some embodiments, the detection light and the excitation light are initially made to reach the surface of the object to be measured at the same time, that is, the optical path of the excitation light is equal to the optical path of the detection light at the beginning. As the delay device acts, the optical path of the detection light changes. When the sound wave reaches the surface of the object to be measured, the time when the optical path of the detection light is equal is equal to the optical path time of the excitation light plus the time when the sound wave moves in the object to be measured. Similarly, the optical path time point of the excitation light is the time point when the excitation light reaches the surface of the object to be measured. In other words, the optical path difference OPD F The time is the time interval between when the excitation light reaches the surface of the object to be tested and generates the sound wave and when the sound wave moves inside the object to be tested and rebounds to the surface of the object to be tested. , then you can use the time interval Calculate the film thickness of the object to be measured.

[0031] In some embodiments, part of the plurality of reflective components is disposed on the translation stage, and the position of the reflective components of the part is adjusted when the translation stage moves.

[0032] In some embodiments, the plurality of reflective components are entirely disposed on the translation stage.

[0033] In some embodiments, when the detector collects the optical power, the translation stage drives the reflective assembly to reciprocate, thereby adjusting the total optical path length of the detection light. When the acoustic wave propagates back to the surface of the object under test, the optical power signal collected by the detector changes significantly, indicating that a sudden change in optical power indicates that the acoustic wave has reached the upper surface of the object under test.

[0034] In some embodiments, hardware performance differences often lead to sampling frequency mismatches between the acquisition device, specifically, mismatches between the first and second frequencies. This makes it impossible to directly match the appropriate numerical value of the stage position data when calculating the stage position based on the peak value of the acoustic wave. Directly obtaining the closest value will increase the error to a certain extent. Therefore, the control module acquires the optical power data of the signal light and the stage position data, and processes both data to ensure that the data volumes are within a ratio range of 0.9 to 1.1. This allows for error control within a certain range, resulting in a higher accuracy in the calculated film thickness.

[0035] In some embodiments, the position data of the translation stage is obtained through a displacement sensor, not through parameter control of the translation stage itself, but through the displacement sensor. This can avoid errors caused by the principle, manufacturing and operation of the translation stage, and avoid the impact of the position tolerance of the translation stage.

[0036] In some embodiments, the displacement sensor is a grating ruler. In some specific embodiments, the position information of the displacement stage can be directly read out by collecting image information of the grating ruler.

[0037] In some embodiments, the position data of the translation stage changes linearly within a certain range.

[0038] In some embodiments, the ratio of the data amount of the optical power of the signal light to the data amount of the position of the translation stage is 0.8, 0.9, 1.0, 1.1 or 1.2.

[0039] In some embodiments, a modulator is further included; the modulator is arranged corresponding to the transmission path of the excitation light, and the modulator is used to perform amplitude modulation or polarization modulation on the excitation light.

[0040] In some embodiments, a lock-in amplifier is further included; the lock-in amplifier is electrically connected to the detector, and the lock-in amplifier is used to analyze the optical power signal.

[0041] In some embodiments, it also includes a signal generator and a signal processor; the signal generator is electrically connected to the modulator, the signal generator is used to transmit a first modulation signal to the modulator, and the modulator is used to output modulated excitation light according to the modulation signal; the signal generator is electrically connected to the phase-locked amplifier, the signal generator is used to send a second modulation signal to the phase-locked amplifier, and the phase-locked amplifier is used to parse the optical power signal according to the second modulation signal; the signal processor is electrically connected to the phase-locked amplifier, and the signal processor is used to obtain information in the parsed optical power signal.

[0042] In some embodiments of the present invention, referring to Figure 1 , the data processing of the collected optical power of the signal light and / or the position of the translation stage includes: interpolating the collected data obtained by the lower of the first frequency and the second frequency and / or compressing the collected data obtained by the higher of the first frequency and the second frequency.

[0043] In some embodiments, the first frequency is greater than the second frequency, and compression processing is performed on the optical power data of the signal light, or interpolation processing is performed on the position data of the translation stage.

[0044] In some embodiments, the first frequency is smaller than the second frequency, and interpolation processing is performed on the optical power data of the signal light, or compression processing is performed on the position data of the translation stage.

[0045] In some embodiments, the first frequency is greater than the second frequency, the optical power data of the signal light is compressed within a certain range, and the position data of the displacement stage is interpolated within a certain range, so that the amount of the compressed optical power data and the amount of the interpolated position data are within the range of 0.9 to 1.1.

[0046] In some embodiments of the present invention, referring to Figure 1 , the interpolation processing includes linear interpolation or spline interpolation.

[0047] In some specific embodiments of the present invention, since the position data of the displacement stage approaches a linear distribution, the position data is usually interpolated by linear interpolation; since the optical power data approaches a Gaussian distribution, the optical power data is usually interpolated by spline interpolation.

[0048] In some embodiments of the present invention, referring to Figure 1 The compression processing includes: obtaining a proportional coefficient Q between the higher and lower of the first and second frequencies; selecting k points closest to the data acquisition timing points of the lower data acquired from the higher frequency as target points for compression, calculating the average value of the acquired data values ​​corresponding to the target points, and using the average value as the acquired data corresponding to the higher frequency after the data processing, wherein 0.9≤k / Q≤1.1.

[0049] In some embodiments, the data acquisition timing points corresponding to the k target points are symmetrically distributed.

[0050] In some specific embodiments of the present invention, the proportional coefficient Q is obtained by the ratio of the larger (higher) to the smaller (lower) of the first frequency and the second frequency, and the target point position of the higher frequency is summed up for a total of k points before and after the timing sequence to obtain the average value P(I).

[0051] In some embodiments, the average value P(I) is calculated as:

[0052]

[0053] I is the time series corresponding to the data point after compression, i is the time series corresponding to the data point before compression, and P(i) is the data value corresponding to the time series of the target point before compression. to It is the data value corresponding to each time point before and after the target point.

[0054] In some embodiments of the present invention, referring to Figure 1 After the data processing, the data amount of the optical power of the signal light and the data amount of the position of the displacement stage within the same time period are equal.

[0055] In some specific embodiments of the present invention, the data in the lower one is subjected to a difference of the proportional coefficient Q or the data in the higher one is subjected to compression of the proportional coefficient Q so that the data amounts of the two processed data are equal.

[0056] In some embodiments of the present invention, referring to Figure 1 The method of obtaining the film thickness of the object to be measured based on the optical power data of the signal light and the position data of the displacement stage after the data processing includes: establishing a corresponding relationship between the optical power data of the signal light and the position data of the displacement stage and their respective data acquisition timing points at the same time; obtaining the peak position of the optical power data of the signal light and the optical power data acquisition timing point corresponding to the peak position; obtaining the data matching point of the displacement stage that matches the peak position in the position data of the displacement stage. F , and the data matching points F The corresponding position value of the displacement stage P F , the data matching point F The position data collection timing point closest to the optical power data collection timing point corresponding to the peak position; based on the data matching point F The corresponding position value of the displacement stage P F , obtain the position of the displacement stage at the data matching point F The optical path difference between the detection light and the excitation light when they reach the surface of the object to be measured is OPDF Based on the optical path difference OPD F ， Obtain the film thickness of the object to be measured.

[0057] In some specific embodiments of the present invention, a correspondence between the data and the respective timing points is established based on the optical power data and the position data, or a corresponding chart between the data and the respective timing points is established. Since the optical power data is Gaussian distributed (spline curve distribution), the timing corresponding to the optical power peak can be calculated based on the optical power data, and the corresponding translation stage data matching point F and position value under the calculated timing are obtained based on the calculated timing. P F , based on the position data corresponding to the peak P F The optical path difference can be calculated OPD F , and according to the optical path difference OPD F Calculate the film thickness.

[0058] In some embodiments, when the optical power data is calculated using a linear distribution, the data matching point F of the translation stage in the time sequence corresponding to the maximum value of the optical power data can be directly obtained.

[0059] In some embodiments, since the first frequency and the second frequency are often not equal, there is no equal timing stage data at the timing corresponding to the peak of the optical power, and the position data closest to the timing corresponding to the peak is obtained as the data matching point. F In some other embodiments, since the position data is linearly distributed within a certain range, when there is no displacement stage data with the same timing at the timing corresponding to the optical power peak, the position data corresponding to the timing at the peak can be calculated using the linear equation of the position data.

[0060] In some embodiments, the difference in position data corresponding to two adjacent peaks can be used as the optical path difference. OPD F In some specific embodiments, the position data corresponding to two adjacent peaks may be the position data corresponding to the two moments when the sound wave occurs and when the sound wave rebounds to the surface of the object to be measured for the first time, or the position data corresponding to the two moments when the sound wave rebounds to the surface of the object to be measured for the first time and when the sound wave rebounds to the surface of the object to be measured for the second time.

[0061] Figure 2 Schematic diagram of the optical path of the detection light and the excitation light in the first embodiment of the present invention.

[0062] In some embodiments of the present invention, referring to Figure 1 and Figure 2 , the translation stage is located at the data matching point F The optical path difference between the detection light and the excitation light when they reach the surface of the object to be measured is OPD F ， Including: obtaining the position of the displacement stage at the data matching point F The total optical path length of the detection light is : , ; Get the position of the displacement stage at the data matching point F When the optical path difference between the detection light and the excitation light OPD F : ;in, is a fixed optical path in the detection light path, The displacement stage in the detection optical path is located at the data matching point F The optical path length of the variable optical path length segment of the detection light achieved when is the optical path of the excitation light, is the number of times the reflection component reflects the detection light.

[0063] In some specific embodiments of the present invention, initially, the detection light and the excitation light reach the surface of the object to be detected at the same time. At this time, the optical path length of the excitation light is Equal to the optical path of the detection light, with the effect of the delay device, the position value of the displacement stage P F When the optical power reaches its maximum value, the position value of the displacement stage is recorded. P F , and calculate the optical path length of the variable optical path length segment of the detection light accordingly , and then calculate the total optical path of the detection light , minus the optical path length of the excitation light Get the optical path difference OPD F .

[0064] In some embodiments, in order to make the detection light and the excitation light reach the surface of the object at the same time, the initial optical path of the detection light is adjusted by the delay device at the beginning. The total optical path length of the probe light Equal; on the contrary, the optical path of the excitation light The fixed optical path length of the probe light equal.

[0065] In some embodiments of the present invention, referring to Figure 1 and Figure 2 , the optical path difference based on OPD F ， Obtaining the film thickness of the object to be measured, including: based on the optical path difference OPD F Obtain the time interval between two adjacent echoes formed by the sound wave returning to the surface of the object to be tested , ; Obtaining the film thickness of the object to be measured based on the time interval d , ;in, is the speed of light, is the propagation speed of the sound wave in the object to be measured.

[0066] In some specific embodiments of the present invention, when performing two adjacent measurements, the sound wave moves from the surface of the object to be measured to the bottom surface and then bounces back to the surface, so the optical path difference OPD F The corresponding wavelength divided by the speed of light The time interval obtained is the time it takes for the sound wave to travel back and forth within the object to be tested, and the time interval is calculated accordingly. The propagation speed of the sound wave in the object to be measured Divide by 2 to get the film thickness of the object to be measured d .

[0067] Figure 3 Schematic diagram of comparison between position data and optical power data in the second embodiment of the present invention. Figure 4 for Figure 3 Schematic diagram of the comparison between the position data difference and the optical power data.

[0068] In some embodiments, reference Figure 3 and Figure 4 The sampling frequency of the position data is less than that of the optical power data, and the amount of position data per unit time C odl The data volume C is less than the optical power data lia , linear interpolation is performed on the position data. Linear interpolation is an interpolation method for one-dimensional data. It estimates the value based on the two data points on the left and right of the point to be interpolated in the one-dimensional data sequence. The interpolated data can make C odl =C lia , the interpolated position data and optical power data can be matched one by one, that is, several data points are added to the original position data interval, which improves the resolution of the position data.

[0069] Figure 5FIG. 1 is a schematic diagram showing the comparison of position data before and after compression in the third embodiment of the present invention. Figure 6 for Figure 5 Schematic diagram comparing the position data before and after compression and the optical power data.

[0070] In some embodiments, reference Figure 5 and Figure 6 The sampling frequency of the position data is greater than that of the optical power data, and the amount of position data per unit time C odl The amount of data C greater than the optical power data lia , compress the position data, take the target point as the center, select k data around it for compression, and calculate the average value of k data as the value of the compressed point. The compressed data can make C odl =C lia , the compressed position data and optical power data can be matched one by one, that is, several data points are cancelled or changed at intervals in the original position data, which reduces the resolution of the position data.

[0071] While the embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations of these embodiments are possible. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as set forth in the claims. Furthermore, the invention described herein is susceptible to other embodiments and may be practiced or implemented in a variety of ways.

Claims

1. A photoacoustic measurement system, characterized in that: It includes a light source, a delay device, a displacement sensor, a detector and a control module; The light source is used to generate detection light and excitation light. The excitation light is used to form an acoustic wave in the object to be measured. The acoustic wave is transmitted back to the surface of the object to be measured through the interface in the object to be measured to generate a deformation area. The detection light is used to irradiate the deformation area on the surface of the object to be measured to form a signal light. The delay device includes a translation stage and a plurality of reflective components, wherein the plurality of reflective components are used to reflect the detection light multiple times, and the translation stage is used to drive the reflective components to move linearly to adjust the total optical path of the detection light, wherein the total optical path of the detection light includes the variable optical path controlled by the delay device and the fixed optical path in the detection light path; The detector collects the optical power of the signal light at a first frequency; The displacement sensor collects the position of the displacement stage in real time at a second frequency; The control module processes the collected optical power of the signal light and / or the position of the translation stage so that the ratio of the amount of data on the optical power of the signal light to the amount of data on the position of the translation stage within the same period of time is 0.9 to 1.1, and obtains the film thickness of the object to be measured based on the processed optical power data of the signal light and the position data of the translation stage; The obtaining of the film thickness of the object to be measured based on the optical power data of the signal light and the position data of the displacement stage after the data processing comprises: obtaining the film thickness of the object to be measured based on the optical power data of the signal light and the position data of the displacement stage after the data processing; Acquire the peak position of the optical power data of the signal light and the optical power data collection timing point corresponding to the peak position; In the position data of the displacement stage, obtain the data matching point F and position value of the displacement stage corresponding to the timing point of the peak position P F ; Get the data matching point where the translation stage is located F The optical path difference between the detection light and the excitation light when they reach the surface of the object to be measured is OPD F ; Based on the optical path difference OPD F ， Obtain the film thickness of the object to be measured.

2. The photoacoustic measurement system according to claim 1, wherein The displacement sensor is a grating ruler.

3. The photoacoustic measurement system according to claim 2, characterized in that The data processing of the collected optical power of the signal light and / or the position of the translation stage includes: interpolating the collected data obtained at the lower of the first frequency and the second frequency and / or compressing the collected data obtained at the higher of the first frequency and the second frequency.

4. The photoacoustic measurement system according to claim 3, wherein: The interpolation process includes linear interpolation or spline interpolation.

5. The photoacoustic measurement system according to claim 3, wherein: The compression process includes: Obtaining a proportional coefficient Q of a higher frequency to a lower frequency of the first frequency and the second frequency; In the data obtained by the higher one, k points closest to the data acquisition timing points obtained by the lower one are selected as target points for compression, and the average value of the acquired data values ​​corresponding to the target points is calculated, and the average value is used as the acquired data corresponding to the higher one after the data processing, where 0.9≤k / Q≤1.

1.

6. The photoacoustic measurement system according to claim 5, characterized in that The data collection timing points corresponding to the k target points are symmetrically distributed.

7. The photoacoustic measurement system according to claim 3, wherein: After the data processing, the data amount of the optical power of the signal light and the data amount of the position of the translation stage within the same time period are equal.

8. The photoacoustic measurement system according to any one of claims 1 to 7, characterized in that: The obtaining of the film thickness of the object to be measured based on the optical power data of the signal light and the position data of the displacement stage after the data processing comprises: obtaining the film thickness of the object to be measured based on the optical power data of the signal light and the position data of the displacement stage after the data processing; Establishing corresponding relationships between the optical power data of the signal light and the position data of the translation stage and their respective data acquisition timing points at the same time; Based on the corresponding relationship, a peak position of the optical power data of the signal light and an optical power data collection timing point corresponding to the peak position are obtained; In the position data of the displacement stage, a data matching point of the displacement stage that matches the peak position is obtained. F , and the data matching points F The corresponding position value of the displacement stage P F , the data matching point F The position data collection timing point closest to the optical power data collection timing point corresponding to the peak position; Matching points based on the data F The corresponding position value of the displacement stage P F , obtain the position of the displacement stage at the data matching point F The optical path difference between the detection light and the excitation light when they reach the surface of the object to be measured is OPD F ; Based on the optical path difference OPD F ， Obtain the film thickness of the object to be measured.

9. The photoacoustic measurement system according to claim 8, characterized in that The translation stage is located at the data matching point F The optical path difference between the detection light and the excitation light when they reach the surface of the object to be measured is OPD F ， include: Obtain the position of the displacement stage at the data matching point F The total optical path length of the detection light is : ， ； Obtain the position of the displacement stage at the data matching point F When the optical path difference between the detection light and the excitation light OPD F : ； in, is a fixed optical path in the detection light path, The displacement stage in the detection optical path is located at the data matching point F The optical path length of the variable optical path length segment of the detection light achieved when is the optical path of the excitation light, is the number of times the reflection component reflects the detection light.

10. The photoacoustic measurement system according to claim 9, characterized in that The optical path difference OPD F ， Obtaining the film thickness of the object to be measured, comprising: Based on the optical path difference OPD F Obtain the time interval between two adjacent echoes formed by the sound wave returning to the surface of the object to be tested , ; Obtaining the film thickness of the object to be measured based on the time interval d , ; in, is the speed of light, is the propagation speed of the sound wave in the object to be measured.

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