Film thickness measuring method and optical measuring system

Abstract

The embodiment of the invention provides a film thickness measurement method and an optical measurement system, which are used for improving the accuracy of thickness measurement of a to-be-measured film. The method provided by the embodiment of the invention comprises the following steps: when the second position forwards deviates from the first position by a target distance, obtaining a first measurement signal by using the detection assembly and the processor; when the second position reversely deviates from the first position by the target distance, a second measurement signal is obtained through the detection assembly and the processor; performing differential processing on the first measurement signal and the second measurement signal by using the processor to obtain a sound wave echo signal transmitted between the to-be-measured films; and determining the thickness of the film layer of the to-be-measured film according to the acoustic echo signal.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technology, and in particular to a film thickness measurement method and an optical measurement system. Background Art

[0002] In the field of semiconductor chips, the thickness of the functional layer is a key parameter that affects chip performance. Femtosecond photoacoustic detection technology is widely used to measure key parameters such as film thickness and Young's modulus of metal film and dielectric film chips.

[0003] When measuring the film thickness, the pump light is emitted to the film to be measured. The pump light generates transient thermal expansion on the surface of the film to be measured and emits ultrashort sound waves. The sound waves are transmitted in the film along the film layer direction and reflected at the interface of the film layer to form sound wave echoes. Since sound waves are mechanical waves, they will not only cause the reflectivity of the film to be measured to change, but also cause the surface of the film to deform. At this time, another ultrashort pulse laser as the detection light will irradiate the excitation position of the film to be measured to detect the reflectivity change and surface morphology change of the film caused by the sound wave echo. By obtaining the time interval between the two sound wave echoes reaching the sample surface and substituting it into the film thickness calculation formula, the film thickness value of the film to be measured can be obtained.

[0004] According to the difference in the detection principle of acoustic wave echo, the measurement can be divided into two modes: ultrafast reflectivity measurement and position sensitive detection (PSD). Among them, the PSD mode detects the change of the reflection angle of the detection light caused by the acoustic wave echo by balanced detection. Its measurement principle is as follows Figure 1 When the probe light is directly irradiated to the sample surface (no acoustic wave echo), the probe light is directly reflected on the material surface as shown in Figure 1 As shown in the figure, when the acoustic wave echo reaches the sample surface, the detection light is reflected on the material surface as shown in Figure 1 This is because the acoustic wave echo causes a slight deformation on the sample surface. By detecting the difference between the reflected light M and N, the time it takes for the acoustic wave echo to reach the sample surface can be indirectly measured. The structural diagram of the PSD mode optical detection system is shown in Figure 1. Figure 2 As shown, the detection system mainly consists of four parts: the film 200 to be tested, the spectroscopic component 110, the detection components 121 and 122, and the information processing component 130. The main function of the spectroscopic component is to separate the detection light reflected by the film to be tested into the first path light and the second path light. The detection components 121 and 122 are used to respectively realize the conversion of the first path light and the second path light from optical signals to electrical signals. The information processing component 130 is used to perform differential processing on the electrical signal of the first path light signal and the electrical signal of the second path light signal to realize the measurement of the acoustic wave echo signal and the detection of the film thickness.

[0005] Since the industry cannot produce two identical photodetectors and cannot achieve completely even distribution of the two paths during the spectroscopic process, there are still large electron ultrafast dynamics signals and thermal substrate signals in the PSD mode measurement results. Since these two signals are much larger than the echo signals generated by the acoustic echo, it brings difficulties and calculation errors to the subsequent identification of the acoustic echo signal and the calculation of the film thickness. Summary of the invention

[0006] An embodiment of the present invention provides a method for measuring the thickness of a thin film and an optical measurement system, which are used to eliminate the electron ultrafast dynamics signal, the thermal base signal, and the thermal noise, shot noise or low-frequency noise in the first detector and the second detector in the measurement of the acoustic wave echo signal, so as to improve the accuracy of the acoustic wave echo signal measurement.

[0007] A first aspect of an embodiment of the present application provides a method for measuring film thickness, which is applied to an optical measurement system, wherein the optical measurement system comprises: a light source component, a film to be measured, a spectroscopic component, a detection component and a processor, wherein the light source component comprises a pump light emitting device and a detection light emitting device, wherein the pump light emitting device is used to emit a pump light beam to a first position of the film to be measured, and the detection light emitting device is used to emit a detection light beam to a second position of the film to be measured, and the method comprises:

[0008] When the second position deviates positively from the first position by a target distance, obtaining a first measurement signal using the detection component and the processor;

[0009] When the second position deviates from the first position by the target distance in the reverse direction, obtaining a second measurement signal by using the detection component and the processor;

[0010] Using the processor to perform differential processing on the first measurement signal and the second measurement signal to obtain an acoustic wave echo signal transmitted between the thin films to be measured;

[0011] The film thickness of the film to be measured is determined according to the acoustic wave echo signal.

[0012] Preferably, the detection component includes a first detector and a second detector, and when the second position deviates positively from the first position target distance, obtaining a first measurement signal by using the detection component and the processor includes:

[0013] When the second position deviates positively from the first position by the target distance and no acoustic wave signal exists, the reflected light of the detection beam is divided into a first reflected light and a second reflected light by using a light splitting component in a target adjustment state;

[0014] When the second position deviates positively from the first position by the target distance and the acoustic wave signal exists, the reflected light of the detection beam is divided into a third reflected light and a fourth reflected light by using the light splitting component in the target adjustment state;

[0015] Using the first detector to convert the third reflected light into a first electrical signal, and using the second detector to convert the fourth reflected light into a second electrical signal;

[0016] The processor is used to perform differential processing on the first electrical signal and the second electrical signal to obtain the first measurement signal.

[0017] Preferably, the first electrical signal and the second electrical signal respectively include:

[0018] An acoustic wave echo signal in a first phase, an electron ultrafast dynamics signal, a thermal background signal, and at least one of thermal noise, shot noise, and low-frequency noise of the first detector and the second detector.

[0019] Preferably, when the second position deviates in the reverse direction from the first position by the target distance, obtaining the second measurement signal by using the detection component and the processor includes:

[0020] When the second position deviates from the first position by the target distance in the reverse direction and the acoustic wave signal does not exist, the reflected light of the detection beam is divided into a fifth reflected light and a sixth reflected light by using the light splitting component in the target adjustment state;

[0021] When the second position deviates from the first position by the target distance in the reverse direction and the acoustic wave signal exists, the reflected light of the detection beam is divided into a seventh reflected light and an eighth reflected light by using the light splitting component in the target adjustment state;

[0022] using the first detector to convert the seventh reflected light into a third electrical signal, and using the second detector to convert the eighth reflected light into a fourth electrical signal;

[0023] The processor is used to perform differential processing on the third electrical signal and the fourth electrical signal to obtain the second measurement signal.

[0024] Preferably, the third electrical signal and the fourth electrical signal respectively include:

[0025] The acoustic wave echo signal, the electron ultrafast dynamics signal, the thermal background signal in the second phase, and at least one of the thermal noise, shot noise and low frequency noise of the first detector and the second detector.

[0026] Preferably, the first electrical signal and the second electrical signal respectively include acoustic wave echo signals in a first phase, the third electrical signal and the fourth electrical signal respectively include acoustic wave echo signals in a second phase, and the phase difference between the acoustic wave echo signal in the first phase and the acoustic wave echo signal in the second phase is 180 degrees.

[0027] Preferably, the distance between the first position and the second position is the target distance, the distance range of the target distance is [1 / 4*d1, 1 / 2*d1], and the size d2 of the detection beam spot and the size d1 of the pump beam spot satisfy the first relationship d1=2*d2.

[0028] Preferably, when the light splitting component is in the target adjustment state, the light splitting ratio between the first reflected light and the second reflected light in the light splitting component is different from the light splitting ratio between the third reflected light and the fourth reflected light in the light splitting component; the light splitting ratio between the fifth reflected light and the sixth reflected light in the light splitting component is also different from the light splitting ratio between the seventh reflected light and the eighth reflected light in the light splitting component;

[0029] When the spectroscopic component is in the target adjustment state, the splitting ratio of the first reflected light and the second reflected light between the spectroscopic component is the same as the splitting ratio of the fifth reflected light and the sixth reflected light between the spectroscopic component; the splitting ratio of the third reflected light and the fourth reflected light between the spectroscopic component is the same as the splitting ratio of the seventh reflected light and the eighth reflected light between the spectroscopic component.

[0030] Preferably, the measuring the thickness of the film to be measured according to the acoustic wave echo signal comprises:

[0031] Determining a plurality of peak positions in the acoustic echo signal;

[0032] Calculating the time difference between adjacent peaks according to the adjacent peaks at the plurality of peak positions;

[0033] The thickness of the film to be measured is calculated according to the time difference and the propagation speed of the sound wave between the film to be measured.

[0034] Preferably, the determining of multiple peak positions in the acoustic wave echo signal comprises:

[0035] Preliminarily determining the time t corresponding to the target peak position in the acoustic echo signal;

[0036] Taking t as the center and Δt as the variation value, determine the time interval [t-Δt, t+Δt];

[0037] Within the time interval [t-Δt, t+Δt], determining again the time t′ corresponding to the target peak position;

[0038] Performing Gaussian fitting on the target peak corresponding to the t′ to filter out the noise of the target peak;

[0039] The target peak after Gaussian fitting is determined as the final peak position.

[0040] Preferably, the beam splitter assembly comprises a stereo beam splitter or a plane beam splitter;

[0041] The first detector and the second detector each include:

[0042] Photodetector, photoenhanced detector or avalanche photodiode.

[0043] A second aspect of the embodiment of the present application provides an optical measurement system, including: a light source component, a film to be measured, a spectroscopic component, a detection component and a processor;

[0044] The light source assembly includes a pump light emitting device and a detection light emitting device, wherein the pump light emitting device is used to emit a pump light beam to a first position of the film to be measured, and the detection light emitting device is used to emit a detection light beam to a second position of the film to be measured;

[0045] The detection component is used to obtain a first measurement signal using the detection component when the second position deviates positively from the first position by a target distance;

[0046] The detection component is further used to obtain a second measurement signal using the detection component when the second position deviates from the first position by the target distance in the reverse direction;

[0047] The processor is used to perform differential processing on the first measurement signal and the second measurement signal to obtain an acoustic wave echo signal transmitted between the thin films to be measured;

[0048] The film thickness of the film to be measured is determined according to the acoustic wave echo signal.

[0049] Optionally, the detection assembly includes a first detector and a second detector;

[0050] The light splitting component is used to split the reflected light of the detection beam into a first reflected light and a second reflected light when the target adjustment state is in place and the second position is positively deviated from the first position by the target distance and there is no acoustic wave signal;

[0051] The light splitting component is further used to split the reflected light of the detection beam into a third reflected light and a fourth reflected light when the second position is in the target adjustment state and deviates positively from the first position by the target distance and the acoustic wave signal exists;

[0052] The first detector is used to convert the third reflected light into a first electrical signal;

[0053] The second detector is used to convert the fourth reflected light into a second electrical signal;

[0054] The processor is used to obtain a first measurement signal between the first electrical signal and the second electrical signal.

[0055] Optionally, the first electrical signal and the second electrical signal respectively include:

[0056] An acoustic wave echo signal in a first phase, an electron ultrafast dynamics signal, a thermal background signal, and at least one of thermal noise, shot noise, and low-frequency noise of the first detector and the second detector.

[0057] Optionally, the light splitting component is used to split the reflected light of the detection beam into a fifth reflected light and a sixth reflected light when the second position is in a target adjustment state and the second position deviates from the first position by the target distance in the reverse direction and the acoustic wave signal does not exist;

[0058] The light splitting component is further used for, when the target adjustment state is in place and the second position deviates from the first position by the target distance in the opposite direction and the acoustic wave signal exists, splitting the reflected light of the detection light beam into a seventh reflected light and an eighth reflected light;

[0059] The first detector is used to convert the seventh reflected light into a third electrical signal;

[0060] The second detector is used to convert the eighth reflected light into a fourth electrical signal;

[0061] The processor is used to obtain a second measurement signal between the third electrical signal and the fourth electrical signal.

[0062] Optionally, the third electrical signal and the fourth electrical signal respectively include:

[0063] The acoustic wave echo signal, the electron ultrafast dynamics signal, the thermal background signal in the second phase, and at least one of the thermal noise, shot noise and low frequency noise of the first detector and the second detector.

[0064] Optionally, the first electrical signal and the second electrical signal respectively include acoustic wave echo signals in a first phase, the third electrical signal and the fourth electrical signal respectively include acoustic wave echo signals in a second phase, and the phase difference between the acoustic wave echo signal in the first phase and the acoustic wave echo signal in the second phase is 180 degrees.

[0065] Optionally, the size d2 of the detection beam spot and the size d1 of the pump beam spot satisfy a first relationship d1=2*d2, and the distance range of the target distance is [1 / 4*d1, 1 / 2*d1].

[0066] Optionally, when the light splitting component is in the target adjustment state, the light splitting ratio between the first reflected light and the second reflected light in the light splitting component is different from the light splitting ratio between the third reflected light and the fourth reflected light in the light splitting component; the light splitting ratio between the fifth reflected light and the sixth reflected light in the light splitting component is also different from the light splitting ratio between the seventh reflected light and the eighth reflected light in the light splitting component;

[0067] When the spectroscopic component is in the target adjustment state, the splitting ratio of the first reflected light and the second reflected light between the spectroscopic component is the same as the splitting ratio of the fifth reflected light and the sixth reflected light between the spectroscopic component; the splitting ratio of the third reflected light and the fourth reflected light between the spectroscopic component is the same as the splitting ratio of the seventh reflected light and the eighth reflected light between the spectroscopic component.

[0068] Optionally, the processor is specifically configured to:

[0069] Determining a plurality of peak positions in the acoustic echo signal;

[0070] Calculating the time difference between adjacent peaks according to the adjacent peaks at the plurality of peak positions;

[0071] The thickness of the film to be measured is calculated according to the time difference and the propagation speed of the sound wave between the film to be measured.

[0072] Optionally, the processor is specifically configured to:

[0073] Preliminarily determining the time t corresponding to the target peak position in the acoustic echo signal;

[0074] Taking t as the center and Δt as the variation value, determine the time interval [t-Δt, t+Δt];

[0075] Within the time interval [t-Δt, t+Δt], determining again the time t′ corresponding to the target peak position;

[0076] Performing Gaussian fitting on the target peak corresponding to the t′ to filter out the noise of the target peak;

[0077] The target peak after Gaussian fitting is determined as the final peak position.

[0078] Optionally, the beam splitting component includes a stereo beam splitter or a plane beam splitter;

[0079] The first detector and the second detector each include:

[0080] Photodetector, photoenhanced detector or avalanche photodiode.

[0081] It can be seen from the above technical solutions that the embodiments of the present invention have the following advantages:

[0082] In an embodiment of the present application, when the second position deviates from the first position by a positive distance and deviates from the first position by a negative distance, the phase difference between the acoustic wave echo signals in the first measurement signal and the second measurement signal is 180 degrees. However, the first measurement signal and the second measurement signal respectively include an electronic ultrafast dynamics signal, a thermal base signal, and thermal noise, shot noise or low-frequency noise of the detection component, and the phases of the electronic ultrafast dynamics signal, thermal base signal, thermal noise, shot noise and low-frequency noise in the first measurement signal and the second measurement signal are independent of the target distance by which the detection beam deviates from the detection beam. That is, the electronic ultrafast dynamics signal, thermal base signal, thermal noise, shot noise or low-frequency noise in the first measurement signal and the second measurement signal are exactly the same, but the phase difference between the acoustic wave echo signals in the first measurement signal and the second measurement signal is 180°. Therefore, by performing differential processing on the first measurement signal and the second measurement signal, the electronic ultrafast dynamics signal, thermal base signal, thermal noise, shot noise and low-frequency noise can be eliminated to obtain an accurate acoustic wave echo signal, thereby improving the accuracy of calculating the thickness of the film to be measured based on the acoustic wave echo signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 It is a schematic diagram of the reflected light beam M of the probe light directly on the material surface when the probe light is directly irradiated to the surface of the film to be tested (no acoustic wave echo), and a schematic diagram of the reflected light beam N of the probe light on the material surface when the acoustic wave echo reaches the sample surface;

[0084] Figure 2 A schematic diagram of the structure of an optical measurement system in a position sensitive detection mode;

[0085] Figure 3 A schematic diagram of an optical measurement system in an embodiment of the present application;

[0086] Figure 4A schematic diagram of the detection beam spot deviating in the positive direction from the pump beam spot by a target distance Δx, the reflected light M of the detection beam when there is no acoustic wave signal, and the reflected light N of the detection beam when there is an acoustic wave signal, and a schematic diagram of the third differential signal;

[0087] Figure 5 A schematic diagram of the detection beam spot deviating in the reverse direction from the pump beam spot by a target distance Δx, a reflected light M of the detection beam when there is no acoustic wave signal, and a schematic diagram of the reflected light N of the detection beam when there is an acoustic wave signal, and a schematic diagram of the sixth differential signal;

[0088] Figure 6 is a schematic diagram of a seventh differential signal;

[0089] Figure 7 The invention is a refinement step to measure the thickness of the film to be measured according to the acoustic wave echo signal. DETAILED DESCRIPTION

[0090] An embodiment of the present invention provides a method for measuring film thickness and an optical measurement system, which are used to eliminate electron ultrafast dynamics signals, thermal base signals, and thermal noise, shot noise or low-frequency noise in a first detector and a second detector in the measurement of an acoustic wave echo signal, thereby improving the accuracy of measuring film thickness based on an acoustic wave echo signal.

[0091] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only 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 creative work should fall within the scope of protection of the present invention.

[0092] The terms "first", "second", "third", "fourth", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0093] For ease of understanding, the following is a description of the method for measuring the film thickness in the present application. An embodiment of the method for measuring the film thickness in the embodiment of the present application includes:

[0094] Specifically, the method for measuring the film thickness in the embodiment of the present application is applied to Figure 3 The optical measurement system includes: a light source component 301, a film to be measured 302, a spectroscopic component 303, a detection component 304, and a processor 305, wherein the light source component 301 includes a pump light emitting device 3011 and a detection light emitting device 3012, wherein the pump light emitting device 3011 is used to emit a pump light beam to a first position of the film to be measured to excite an acoustic wave, and the detection light emitting device 3012 is used to emit a detection light beam to a second position of the film to be measured, wherein the distance between the first position and the second position is a target distance Δx, and the method includes:

[0095] When the second position deviates from the first position by a target distance Δx in the positive direction, the detection component 304 and the processor 305 are used to obtain a first measurement signal. When the second position deviates from the first position by a target distance Δx in the negative direction, the detection component 304 and the processor 305 are used to obtain a second measurement signal. The processor 305 then performs differential processing on the first measurement signal and the second measurement signal to obtain an acoustic wave echo signal transmitted between the film to be measured, and further determines the film thickness of the film to be measured based on the acoustic wave echo signal.

[0096] Because in the embodiment of the present application, when the second position deviates from the first position target distance Δx in the positive direction, the first measurement signal obtained, and when the second position deviates from the first position target distance Δx in the reverse direction, the acoustic wave echo signal in the second measurement signal obtained has a phase difference of 180°, but the first measurement signal and the second measurement signal respectively include the electron ultrafast dynamics signal, the thermal base signal, and the thermal noise, shot noise or low-frequency noise of the detection component, and the phases of the electron ultrafast dynamics signal, the thermal base signal, the thermal noise, the shot noise and the low-frequency noise in the first measurement signal and the second measurement signal, It has nothing to do with the target distance at which the detection beam deviates from the detection beam, that is, the electron ultrafast dynamics signal, thermal base signal, thermal noise, shot noise or low-frequency noise in the first measurement signal and the second measurement signal are exactly the same, but the phase difference between the acoustic wave echo signals in the first measurement signal and the second measurement signal is 180°. Therefore, by performing differential processing on the first measurement signal and the second measurement signal, the electron ultrafast dynamics signal, thermal base signal, thermal noise, shot noise and low-frequency noise can be eliminated to obtain an accurate acoustic wave echo signal, thereby improving the accuracy of calculating the thickness of the film to be measured based on the acoustic wave echo signal.

[0097] based on Figure 3 The optical measurement system of FIG. 1 is a process for how the detection component 304 and the processor 305 obtain the first measurement signal and the second measurement signal.

[0098] Specifically, the detection component 304 in the embodiment of the present application includes a first detector 3041 and a second detector 3042. When the second position deviates positively from the first position by a target distance Δx and there is no acoustic signal (i.e., there is no pump light), the spectroscopic component 303 is used to receive the reflected light of the detection beam, and the reflected light is divided into a first reflected light and a second reflected light, so that the spectroscopic component 303 is in a target adjustment state. When the second position deviates positively from the first position by a target distance Δx, but there is an acoustic signal (i.e., there is pump light), the spectroscopic component 303 in the target adjustment state is used to receive the reflected light of the detection beam, and the reflected light is divided into a third reflected light and a fourth reflected light.

[0099] It should be noted here that, for the convenience of operation, the reflected light of the detection light is generally divided into a first reflected light and a second reflected light by using a spectroscopic component 303, so that the spectroscopic component 303 is in a target adjustment state, that is, the state in which the spectroscopic component divides the first reflected light and the second reflected light equally is determined as the target adjustment state.

[0100] The third reflected light is converted into a first electrical signal using the first detector 3041, and the fourth reflected light is converted into a second electrical signal using the second detector 3042, wherein the first electrical signal and the second electrical signal respectively include: an acoustic wave echo signal in a first phase, an electron ultrafast dynamics signal, a thermal base signal, and at least one of thermal noise, shot noise and low-frequency noise of the first detector 3041 and the second detector 3042, and the first phase here is any phase in the acoustic wave echo signal.

[0101] The processor 305 performs differential processing on the first electrical signal and the second electrical signal to obtain a first measurement signal. For ease of understanding, Figure 4 A schematic diagram of the reflected light M of the detection beam when there is no acoustic signal and the reflected light N of the detection beam when there is an acoustic signal, as well as a schematic diagram of the first measurement signal, is given when the detection beam spot deviates from the pump beam spot in the positive direction by a target distance Δx.

[0102] Further, when the second position deviates from the first position by a target distance Δx in the reverse direction, and there is no acoustic wave signal (that is, there is no pump light), the reflected light of the detection beam is divided into a fifth reflected light and a sixth reflected light by using the beam splitter component 303, so that the beam splitter component 303 is in a target adjustment state (the target adjustment state of the beam splitter component for dividing the fifth reflected light and the sixth reflected light is the same as the target adjustment state of the beam splitter component for dividing the first reflected light and the second reflected light); when the second position deviates from the first position by a target distance Δx in the reverse direction, and there is an acoustic wave signal, the reflected light of the detection beam is divided into a seventh reflected light and an eighth reflected light by using the beam splitter component 303 in the target adjustment state;

[0103] The seventh reflected light is converted into a third electrical signal by using the first detector 3041, and the eighth reflected light is converted into a fourth electrical signal by using the second detector 3042, wherein the third electrical signal and the fourth electrical signal respectively include: an acoustic wave echo signal in the second phase, an electron ultrafast dynamics signal, a thermal background signal, and at least one of thermal noise, shot noise and low-frequency noise of the first detector and the second detector, but the phase difference between the acoustic wave echo signal of the second phase and the acoustic wave echo signal of the first phase is 180°.

[0104] The processor 305 performs differential processing on the third electrical signal and the fourth electrical signal to obtain a second measurement signal. For ease of understanding, Figure 5 A schematic diagram of the second position deviating in the opposite direction from the first position by a target distance Δx, the reflected light M of the detection beam when there is no acoustic wave signal, and the reflected light N of the detection beam when there is an acoustic wave signal, as well as a schematic diagram of the second measurement signal are given.

[0105] It should be noted that, in the embodiment of the present application, when the second position deviates from the first position by a target distance Δx in the positive direction and deviates from the first position by a target distance Δx in the reverse direction, the phase difference of the acoustic wave echo signal is 180 degrees, and the first measurement signal contains an acoustic wave echo signal in the first phase, as well as at least one of an electronic ultrafast dynamics signal, a thermal base signal, thermal noise, shot noise and low-frequency noise, and the second measurement signal contains an acoustic wave echo signal in the second phase, as well as at least one of an electronic ultrafast dynamics signal, a thermal base signal, thermal noise, shot noise and low-frequency noise, and the first measurement signal and the second measurement signal are The phases of the electron ultrafast dynamics signal, thermal base signal, thermal noise, shot noise and low-frequency noise in the measurement signal are independent of the target distance and deviation direction of the second position from the first position, that is, the electron ultrafast dynamics signal, thermal base signal, thermal noise, shot noise or low-frequency noise in the first measurement signal and the second measurement signal are exactly the same, but the phase difference of the acoustic wave echo signal in the first measurement signal and the second measurement signal is 180°. Therefore, by calculating the differential signal between the first measurement signal and the second measurement signal, the electron ultrafast dynamics signal, thermal base signal, thermal noise, shot noise and low-frequency noise can be eliminated, and the result is Figure 6 The accurate acoustic echo signal shown improves the accuracy of calculating the thickness of the film to be measured based on the acoustic echo signal.

[0106] Because the embodiment of the present application eliminates the electron ultrafast dynamics signal, thermal base signal, thermal noise, shot noise and low-frequency noise when measuring the film thickness using the differential signal between the first measurement signal and the second measurement signal, thereby obtaining an accurate acoustic wave echo signal, the accuracy of measuring the film thickness based on the acoustic wave echo signal can be improved.

[0107] Based on the above-mentioned method for measuring the thickness of a thin film, as an optional embodiment, in order to better allow the pump light to excite an acoustic wave signal, the size of the pump light spot d1 and the size of the detection light spot are generally set to satisfy a first relationship, wherein the first relationship includes: d1 = 2*d2, and in order to increase Figure 4 and Figure 5 The angle between the M light and the N light, and the distance Δx between the detection beam spot and the pump beam spot are set to satisfy:

[0108] Furthermore, based on the above-mentioned method for measuring the thickness of a thin film, when there is an acoustic wave signal, the reflected light of the detection light deviates by a certain angle (such as Figure 4 The N light deviates from the M light by a certain angle), so in the above method for measuring the thickness of the thin film, when the spectroscopic component is in the target adjustment state, the splitting ratio between the first reflected light and the second reflected light is different from the splitting ratio between the third reflected light and the fourth reflected light, and the splitting ratio between the fifth reflected light and the sixth reflected light is different from the splitting ratio between the seventh reflected light and the eighth reflected light. However, when the spectroscopic component is in the target adjustment state, the splitting ratio between the first reflected light and the second reflected light is the same as the splitting ratio between the fifth reflected light and the sixth reflected light, and the splitting ratio between the third reflected light and the fourth reflected light is the same as the splitting ratio between the seventh reflected light and the eighth reflected light.

[0109] It is precisely because the splitting ratio between the third reflected light and the fourth reflected light is the same as the splitting ratio between the seventh reflected light and the eighth reflected light, so the first measurement signal obtained by the difference between the first electric signal and the second electric signal and the second measurement signal obtained by the difference between the third electric signal and the fourth electric signal are exactly the same in terms of the electron ultrafast dynamics signal, thermal background signal, thermal noise, shot noise and low-frequency noise.

[0110] Further, based on the above-mentioned method for measuring film thickness, as an optional embodiment, the spectroscopic component 303 includes a stereoscopic spectrometer or a plane spectrometer, wherein the stereoscopic spectrometer is such as a prism, and in order to ensure that the thermal noise, shot noise and low-frequency noise in the detector are the same, the first detector 3041 and the second detector 3042 use the same type of detector, and the detector can be a photodetector, a photoelectric enhanced detector or an avalanche photodiode.

[0111] Next, the process of measuring the thickness of the film to be measured according to the acoustic echo signal in the above-mentioned method for measuring the film is described. Figure 7 , Figure 7 The detailed steps of the process for measuring the thickness of the film to be tested are:

[0112] 701. Determine multiple peak positions in the acoustic wave echo signal;

[0113] Get as Figure 6 After obtaining the acoustic wave echo signal, multiple peak positions in the acoustic wave echo signal can be further obtained, because the time interval t1 between adjacent peak positions and the propagation speed v of the acoustic wave echo in the film to be measured satisfy the following relationship: 2d=t1*v, where d is the thickness of the film to be measured.

[0114] Further, when determining the position of each peak in the acoustic wave echo signal, the following steps may be adopted:

[0115] (1) Preliminarily confirm the time t corresponding to the target peak, wherein this step may be to accept the time t confirmed manually

[0116] (2) Taking t as the center and Δt as the variation value, determine the time interval [t-Δt, t+Δt], and again determine the time t′ corresponding to the target peak position within the time interval [t-Δt, t+Δt];

[0117] In order to ensure the accuracy of the target peak, the time interval [t-Δt, t+Δt] can be determined with t as the center and Δt as the variation value, and the time t′ corresponding to the target peak position can be reconfirmed through the peak finding algorithm within the time interval [t-Δt, t+Δt]. The peak finding algorithm here is similar to that described in the prior art and will not be repeated here.

[0118] (3) performing Gaussian fitting on the target peak corresponding to t′ to filter out the noise of the target peak;

[0119] In order to further eliminate the noise around the target peak signal, Gaussian fitting can be further performed on the target peak to filter out the noise of the target peak.

[0120] (4) Determine the target peak after Gaussian fitting as the final peak position.

[0121] After filtering out the noise signal of the target peak, the target peak after Gaussian fitting is used as the final peak position.

[0122] Because the embodiment of the present application uses multiple peak searches and Gaussian fitting methods to filter the peak position, the accuracy of the peak position is improved.

[0123] 702. Calculate the time difference between adjacent peaks according to adjacent peaks at multiple peak positions;

[0124] After obtaining multiple peaks in the acoustic wave echo signal, the time difference between adjacent peaks is further calculated according to adjacent peaks at the multiple peak positions, and step 703 is performed according to the time difference between adjacent peaks.

[0125] 703. Calculate the thickness of the film to be measured according to the time difference and the propagation speed of the sound wave between the film to be measured.

[0126] Furthermore, after obtaining the time difference between adjacent peaks and the propagation speed v of sound waves in the film to be tested, it can be based on: 2d=t1*v, where d is the thickness of the film to be tested, t1 is the time interval between adjacent peak positions, and v is the propagation speed of sound waves in the film to be tested.

[0127] In the embodiment of the present application, the process of measuring the thickness of the film to be measured based on the acoustic wave echo signal is described in detail, and when determining each peak position, the embodiment of the present application adopts multiple peak searching and Gaussian fitting methods to further improve the accuracy of peak position determination.

[0128] Furthermore, an optical measurement system is also provided in an embodiment of the present application. Figure 3 As shown, the optical measurement system includes a light source component 301 (including a pump light emitting device 3011 and a detection light emitting device 3012), a film to be measured 302, a spectroscopic component 303, a detection component 304 (including a first detector 3041 and a second detector 3042), and a processor 305, wherein the function of each component is the same as the function of each component in the above-mentioned method for measuring film thickness, and will not be repeated here.

[0129] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring film thickness, It is characterized in that Applied to an optical measurement system, the optical measurement system comprises: a light source component, a film to be measured, a spectroscopic component, a detection component and a processor, wherein the light source component comprises a pump light emitting device and a detection light emitting device, the pump light emitting device is used to emit a pump light beam to a first position of the film to be measured, and the detection light emitting device is used to emit a detection light beam to a second position of the film to be measured, and the method comprises: When the second position deviates positively from the first position by a target distance, obtaining a first measurement signal using the detection component and the processor; When the second position deviates from the first position by the target distance in the reverse direction, obtaining a second measurement signal by using the detection component and the processor; Using the processor to perform differential processing on the first measurement signal and the second measurement signal to obtain an acoustic wave echo signal transmitted between the thin films to be measured; The film thickness of the film to be measured is determined according to the acoustic wave echo signal.

2. The method according to claim 1, It is characterized in that The detection assembly includes a first detector and a second detector. When the second position deviates positively from the first position by a target distance, obtaining a first measurement signal by using the detection assembly and the processor includes: When the second position deviates positively from the first position by the target distance and no acoustic wave signal exists, the reflected light of the detection beam is divided into a first reflected light and a second reflected light by using a light splitting component in a target adjustment state; When the second position deviates positively from the first position by the target distance and the acoustic wave signal exists, the reflected light of the detection beam is divided into a third reflected light and a fourth reflected light by using the light splitting component in the target adjustment state; Using the first detector to convert the third reflected light into a first electrical signal, and using the second detector to convert the fourth reflected light into a second electrical signal; The processor is used to perform differential processing on the first electrical signal and the second electrical signal to obtain the first measurement signal.

3. The method according to claim 2, It is characterized in that The first electrical signal and the second electrical signal respectively include: An acoustic wave echo signal in a first phase, an electron ultrafast dynamics signal, a thermal background signal, and at least one of thermal noise, shot noise, and low-frequency noise of the first detector and the second detector.

4. The method according to claim 2, It is characterized in that When the second position deviates from the first position by the target distance in the reverse direction, obtaining a second measurement signal by using the detection component and the processor includes: When the second position deviates from the first position by the target distance in the reverse direction and the acoustic wave signal does not exist, the reflected light of the detection beam is divided into a fifth reflected light and a sixth reflected light by using the light splitting component in the target adjustment state; When the second position deviates from the first position by the target distance in the reverse direction and the acoustic wave signal exists, the reflected light of the detection beam is divided into a seventh reflected light and an eighth reflected light by using the light splitting component in the target adjustment state; using the first detector to convert the seventh reflected light into a third electrical signal, and using the second detector to convert the eighth reflected light into a fourth electrical signal; The processor is used to perform differential processing on the third electrical signal and the fourth electrical signal to obtain the second measurement signal.

5. The method according to claim 4, It is characterized in that The third electrical signal and the fourth electrical signal respectively include: The acoustic wave echo signal, the electron ultrafast dynamics signal, the thermal background signal in the second phase, and at least one of the thermal noise, shot noise and low frequency noise of the first detector and the second detector.

6. The method according to claim 4, It is characterized in that The first electrical signal and the second electrical signal each include an acoustic wave echo signal in a first phase, the third electrical signal and the fourth electrical signal each include an acoustic wave echo signal in a second phase, and a phase difference between the acoustic wave echo signal in the first phase and the acoustic wave echo signal in the second phase is 180 degrees.

7. The method according to claim 1, It is characterized in that The distance between the first position and the second position is the target distance, the distance range of the target distance is [1 / 4*d1, 1 / 2*d1], and the size d2 of the detection beam spot and the size d1 of the pump beam spot satisfy the first relationship d1=2*d2.

8. The method according to claim 4, It is characterized in that When the light splitting component is in a target adjustment state, the light splitting ratio between the first reflected light and the second reflected light in the light splitting component is different from the light splitting ratio between the third reflected light and the fourth reflected light in the light splitting component; The splitting ratio between the fifth reflected light and the sixth reflected light in the beam splitting component is also different from the splitting ratio between the seventh reflected light and the eighth reflected light in the beam splitting component; When the spectroscopic component is in the target adjustment state, the splitting ratio of the first reflected light and the second reflected light between the spectroscopic component is the same as the splitting ratio of the fifth reflected light and the sixth reflected light between the spectroscopic component; the splitting ratio of the third reflected light and the fourth reflected light between the spectroscopic component is the same as the splitting ratio of the seventh reflected light and the eighth reflected light between the spectroscopic component.

9. The method according to claim 1, It is characterized in that The step of measuring the thickness of the film to be measured according to the acoustic wave echo signal comprises: Determining a plurality of peak positions in the acoustic echo signal; Calculating the time difference between adjacent peaks according to the adjacent peaks at the plurality of peak positions; The thickness of the film to be measured is calculated according to the time difference and the propagation speed of the sound wave between the film to be measured.

10. The method according to claim 9, It is characterized in that The determining of a plurality of peak positions in the acoustic wave echo signal comprises: Preliminarily determining the time t corresponding to the target peak position in the acoustic echo signal; Taking t as the center and Δt as the variation value, determine the time interval [t-Δt, t+Δt]; Within the time interval [t-Δt, t+Δt], determining again the time t′ corresponding to the target peak position; Performing Gaussian fitting on the target peak corresponding to the t′ to filter out the noise of the target peak; The target peak after Gaussian fitting is determined as the final peak position.

11. The optical measurement system according to claim 1, It is characterized in that The light splitting component includes a stereoscopic light splitter or a plane light splitter; The first detector and the second detector each include: Photodetector, photoenhanced detector or avalanche photodiode.

12. An optical measurement system, It is characterized in that It includes: light source component, film to be tested, spectroscopic component, detection component and processor; The light source assembly includes a pump light emitting device and a detection light emitting device, wherein the pump light emitting device is used to emit a pump light beam to a first position of the film to be measured, and the detection light emitting device is used to emit a detection light beam to a second position of the film to be measured; The detection component is used to obtain a first measurement signal using the detection component when the second position deviates positively from the first position by a target distance; The detection component is further used to obtain a second measurement signal using the detection component when the second position deviates from the first position by the target distance in the reverse direction; The processor is used to perform differential processing on the first measurement signal and the second measurement signal to obtain an acoustic wave echo signal transmitted between the thin films to be measured; The film thickness of the film to be measured is determined according to the acoustic wave echo signal.

13. The optical measurement system according to claim 12, It is characterized in that The detection assembly includes a first detector and a second detector; The light splitting component is used to split the reflected light of the detection beam into a first reflected light and a second reflected light when the target adjustment state is in place and the second position is positively deviated from the first position by the target distance and there is no acoustic wave signal; The light splitting component is further used to split the reflected light of the detection beam into a third reflected light and a fourth reflected light when the second position is in the target adjustment state and deviates positively from the first position by the target distance and the acoustic wave signal exists; The first detector is used to convert the third reflected light into a first electrical signal; The second detector is used to convert the fourth reflected light into a second electrical signal; The processor is used to perform differential processing on the first electrical signal and the second electrical signal to obtain the first measurement signal.

14. The optical measurement system according to claim 12, It is characterized in that The detection assembly includes a first detector and a second detector; The light splitting component is used to split the reflected light of the detection beam into a fifth reflected light and a sixth reflected light when the second position is in a target adjustment state and the second position deviates from the first position by the target distance in the reverse direction and the acoustic wave signal does not exist; The light splitting component is further used for, when the target adjustment state is in place and the second position deviates from the first position by the target distance in the opposite direction and the acoustic wave signal exists, splitting the reflected light of the detection light beam into a seventh reflected light and an eighth reflected light; The first detector is used to convert the seventh reflected light into a third electrical signal; The second detector is used to convert the eighth reflected light into a fourth electrical signal; The processor is used to perform differential processing on the third electrical signal and the fourth electrical signal to obtain the second measurement signal.

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