Measurement system and measurement method based on wide-field picosecond ultrasound imaging

Abstract

The application provides a measurement system and a measurement method based on wide-field picosecond ultrasonic imaging, comprising: a light source assembly for forming pulsed pump light and pulsed probe light with a time delay; a light guide assembly for combining and guiding the pulsed pump light and the pulsed probe light to the surface of a sample to be measured; a first image sensor for converting first feedback light formed by the pulsed probe light on the surface of the sample to be measured into a first electrical signal; a first optical filter for blocking second feedback light formed by the pulsed pump light on the surface of the sample to be measured from entering the first image sensor; and a processor for obtaining an optoacoustic signal ΔR / R corresponding to a feature time delay of the first pattern layer according to the first electrical signal, wherein ΔR represents the intensity difference between the first feedback light when the pulsed pump light is excited and when the pulsed pump light is not excited, and R represents the intensity of the first feedback light when the pulsed pump light is not excited. The position of the first pattern layer under the light shielding layer can be tested, and the testing efficiency and the testing accuracy are improved.

Description

Technical Field

[0001] This application relates to the field of testing technology, and in particular to a measurement system and method based on wide-field picosecond ultrasound imaging. Background Technology

[0002] Semiconductor manufacturing involves hundreds or even thousands of processes, and process control directly affects the yield, reliability, and performance of the finished product. Semiconductor devices are manufactured through multiple manufacturing processes to sequentially form the desired circuit structure at specific locations. These manufacturing processes involve sequentially creating patterned layers on a semiconductor substrate. Each patterned layer needs to be aligned within the allowable range of the manufacturing process to avoid problems with the electrical performance and reliability of the semiconductor device. For example, in industrial inspection, it is often necessary to check the alignment accuracy of multilayer structures in semiconductor devices. During the manufacturing process, overlay marks are formed on the upper and lower patterned layers. By detecting the position of these overlay marks, the alignment accuracy of the upper and lower patterned layers can be determined.

[0003] As the feature size of semiconductor devices shrinks and their integration density increases, overlay tolerance is a crucial indicator for detecting alignment errors at different heights within semiconductor devices. In photolithography, the lateral alignment accuracy of upper and lower layer patterns, i.e., overlay error, is a critical process control parameter. Online monitoring and measurement of overlay error are typically achieved using optical methods. At designated locations on the wafer, upper and lower layer patterns combine to form specific overlay marks. Measurement equipment obtains the overlay error between upper and lower layer patterns by performing microscopic imaging of these marks; this is called image-based overlay measurement (IBO). Measurement equipment also obtains the overlay error between upper and lower layer patterns by measuring the optical diffraction signals of the upper and lower layer patterns; this is called diffraction-based overlay measurement (DBO).

[0004] However, in some process stages, there are opaque film layers between the upper and lower patterns, such as hard metal masks, which makes it impossible to detect the information of the lower pattern layer by optical methods. Summary of the Invention

[0005] This application provides a measurement system and method based on wide-field picosecond ultrasound imaging, which can detect the position of the first pattern layer under the light-shielding layer and improves the testing efficiency and accuracy.

[0006] This application provides a measurement system based on wide-field picosecond ultrasound imaging, comprising: a light source assembly for generating a pulsed pump light and a pulsed probe light with a delay; a light guide assembly for combining the pulsed pump light and the pulsed probe light and guiding them to the surface of the sample under test; a first image sensor for converting a first feedback light formed by the pulsed probe light on the surface of the sample under test into a first electrical signal; a first filter for blocking a second feedback light formed by the pulsed pump light on the surface of the sample under test from entering the first image sensor; and a processor for acquiring a photoacoustic signal ΔR / R corresponding to a characteristic delay of the first pattern layer based on the first electrical signal, wherein ΔR characterizes the intensity difference of the first feedback light when excited by pulsed pump light and when not excited by pulsed pump light, and R characterizes the intensity of the first feedback light when not excited by pulsed pump light.

[0007] Optionally, the light source assembly includes: a light source; a first optical parametric amplifier; a second optical parametric amplifier; a first beam splitter located between the first optical parametric amplifier and the light source, and between the second optical parametric amplifier and the light source; wherein the first beam splitter is used to split the light beam emitted by the light source into a first light path and a second light path, the first optical parametric amplifier is used to receive the first light path and output a pulse probe light, the second optical parametric amplifier is used to receive the second light path and output a pulse pump light; and a delay component is used to adjust the delay of the pulse probe light relative to the pulse pump light.

[0008] Optionally, it further includes: a first modulator for modulating the pulsed probe light output by the light source assembly, wherein the probe pulses in the modulated pulsed probe light are set within multiple consecutive characteristic periods, the characteristic periods including a first sub-stage, a second sub-stage, a third sub-stage, and a fourth sub-stage with the same duration, the modulated pulsed probe light includes multiple probe pulses with a first pulse interval in each of the first, second, and third sub-stages, and the modulated pulsed probe light includes a first probe pulse group and a second probe pulse group in the fourth sub-stage, wherein there is a first pulse interval between adjacent probe pulses in the first probe pulse group, a first pulse interval between adjacent probe pulses in the second probe pulse group, and a second pulse interval between the first probe pulse group and the second probe pulse group, the second pulse interval being greater than the first pulse interval; and a second modulator for modulating the pulsed pump light, wherein the pump pulses in the modulated pulsed pump light are set within multiple consecutive characteristic periods, the modulated pulsed pump light includes multiple pump pulses with a first pulse interval in the first sub-stage, and has no pump pulses in the second, third, and fourth sub-stages.

[0009] Optionally, the first modulator includes an acousto-optic modulator, an electro-optic modulator, or an optical chopper, and the second modulator includes an acousto-optic modulator, an electro-optic modulator, or an optical chopper.

[0010] Optionally, the light guide assembly includes: a second beam splitter, a third beam splitter, and a lens group; wherein the second beam splitter is located between the first modulator and the lens group and between the second modulator and the lens group; the third beam splitter is used to reflect the light output from the lens group toward the sample under test and to transmit the first feedback light and the second feedback light from the sample under test.

[0011] Optionally, the first image sensor and the processor are integrated into a phase-locked camera; wherein the processor includes: a modulation signal generation unit for outputting a first modulation signal u1(t) and a second modulation signal u2(t), both of which have a characteristic period T;

[0012]

[0013] The first generation unit is used to multiply the first electrical signal and the first modulation signal u1(t) to obtain the first modulation electrical signal; the second generation unit is used to multiply the first electrical signal and the second modulation signal u2(t) to obtain the second modulation electrical signal; the third generation unit is used to add the first modulation electrical signal of the first sub-stage and the first modulation electrical signal of the third sub-stage to obtain ΔR; the fourth generation unit is used to add the second modulation electrical signal of the second sub-stage and the second modulation electrical signal of the fourth sub-stage to obtain R; where t5-t1=T; the first sub-stage is (t1+kT,t2+kT], the second sub-stage is (t2+kT,t3+kT], the third sub-stage is (t3+kT,t4+kT], and the fourth sub-stage is (t4+kT,t5+kT]; k is an integer greater than or equal to 0.

[0014] Optionally, the light source assembly includes a first light source and a second light source, wherein the first light source is used to emit pulsed probe light having a first repetition frequency, and the second light source is used to emit pulsed pump light having a second repetition frequency.

[0015] Optionally, the light guide assembly includes: a second beam splitter, a third beam splitter, and a lens group; wherein the second beam splitter is located between the first light source and the lens group and between the second light source and the lens group; the third beam splitter is used to reflect the light output from the lens group toward the sample under test and to transmit the first feedback light and the second feedback light from the sample under test.

[0016] Optionally, the measurement system based on wide-field picosecond ultrasound imaging also includes: a photodetector; and a second filter located between the second beam splitter and the photodetector, the second filter being used to filter pulse pump light.

[0017] Optionally, the first image sensor is also used to generate a first test image of the first pattern layer based on the photoacoustic signal ΔR / R.

[0018] Optionally, the measurement system based on wide-field picosecond ultrasound imaging also includes: a second image sensor for acquiring a second test image of the second patterned layer located above the light-shielding layer in the sample to be tested.

[0019] This application also provides a measurement method based on wide-field picosecond ultrasound imaging, comprising: forming a pulsed probe light and a pulsed pump light with delay; combining the pulsed probe light and the pulsed pump light and guiding them to the surface of the sample to be measured, respectively forming a first feedback light and a second feedback light; filtering the second feedback light using a first filter; converting the first feedback light transmitted through the first filter into a first electrical signal using a first image sensor; and obtaining a photoacoustic signal ΔR / R corresponding to the characteristic delay of the first pattern layer based on the first electrical signal, wherein ΔR characterizes the intensity difference of the first feedback light when excited by pulsed pump light and when not excited by pulsed pump light, and R characterizes the intensity of the first feedback light when not excited by pulsed pump light.

[0020] Optionally, it further includes: after adjusting the delay of the pulse probe light and the pulse pump light, modulating the pulse probe light, wherein the probe pulses in the modulated pulse probe light are set within multiple consecutive characteristic periods, the characteristic periods including a first sub-stage, a second sub-stage, a third sub-stage, and a fourth sub-stage with the same duration, the modulated pulse probe light includes multiple probe pulses with a first pulse interval in each of the first, second, and third sub-stages, and the modulated pulse probe light includes a first probe pulse group and a second probe pulse group in the fourth sub-stage, wherein adjacent probe pulses in the first probe pulse group are separated by a first pulse interval, and adjacent probe pulses in the second probe pulse group are separated by a first pulse interval. A second pulse interval exists between the probe pulse group and the second probe pulse group, and the second pulse interval is greater than the first pulse interval. The pulse pump light is modulated, and the pump pulses in the modulated pulse pump light are set within multiple consecutive characteristic periods. The modulated pulse pump light includes multiple pump pulses with a first pulse interval in the first sub-stage, and there are no pump pulses in the second, third, and fourth sub-stages. The photoacoustic signal ΔR / R corresponding to the characteristic delay of the first pattern layer is obtained according to the first electrical signal, including: generating a first modulation signal u1(t) and a second modulation signal u2(t), both of which have a characteristic period T.

[0021]

[0022] The first modulated electrical signal is obtained by multiplying the first electrical signal and the first modulated signal u1(t);

[0023] The second modulated electrical signal is obtained by multiplying the first electrical signal and the second modulated signal u2(t);

[0024] The first modulation signal of the first sub-stage and the first modulation signal of the third sub-stage are added together to obtain ΔR;

[0025] The second modulation signal of the second sub-stage and the second modulation signal of the fourth sub-stage are added together to obtain R;

[0026] Where t5-t1=T; the first sub-stage is (t1+kT,t2+kT], the second sub-stage is (t2+kT,t3+kT], the third sub-stage is (t3+kT,t4+kT], and the fourth sub-stage is (t4+kT,t5+kT]; k is an integer greater than or equal to 0.

[0027] Optionally, forming a pulse probe light and a pulse pump light with a delay includes: forming a pulse probe light with a first repetition frequency; and forming a pulse pump light with a second repetition frequency.

[0028] Optionally, it also includes: generating a first test image of the first pattern layer based on the photoacoustic signal ΔR / R; acquiring a second test image of the second pattern layer located above the light-shielding layer in the sample to be tested; and acquiring the overlay error of the first pattern layer and the second pattern layer based on the first test image and the second test image.

[0029] The technical solution of this application has the following beneficial effects:

[0030] The measurement system based on wide-field picosecond ultrasound imaging provided in this application can measure a first patterned layer beneath a light-shielding layer. A first image sensor converts the first feedback light formed by the pulsed probe light on the surface of the sample into a first electrical signal. A processor acquires a photoacoustic signal ΔR / R corresponding to the characteristic delay of the first patterned layer based on the first electrical signal. ΔR represents the intensity difference of the first feedback light when excited by pulsed pump light and when not excited by pulsed pump light, while R represents the intensity of the first feedback light when not excited by pulsed pump light. Increasing the sampling rate and measurement speed significantly improves both measurement accuracy and efficiency. Attached Figure Description

[0031] Figure 1 A schematic diagram of a measurement system based on wide-field picosecond ultrasound imaging provided in an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of a lock-in camera provided according to an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of a first pattern layer provided in an embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram of the second patterned layer provided in an embodiment of the present invention;

[0035] Figure 5 This is a schematic diagram of the orthographic projection of the first patterned layer and the second patterned layer onto the surface of the sample to be tested, according to an embodiment of the present invention.

[0036] Figure 6 A schematic diagram of a processor provided according to an embodiment of the present invention;

[0037] Figure 7 A timing diagram of the pulse probe light, pulse pump light, first modulation signal, second modulation signal, reference signal, and first feedback light intensity provided in an embodiment of the present invention;

[0038] Figure 8 A timing diagram of the intensity of pulse probe light, pulse pump light and first feedback light during the first characteristic period to the second characteristic period provided in an embodiment of the present invention;

[0039] Figure 9 A schematic diagram of a measurement system based on wide-field picosecond ultrasound imaging provided in another embodiment of the present invention;

[0040] Figure 10 A schematic diagram of pulse probe light and pulse pump light according to another embodiment;

[0041] Figure 11 This is a schematic diagram illustrating the change in the photoacoustic signal ΔR / R according to another embodiment;

[0042] Figure 12 This is a schematic diagram illustrating the variations of the pulse probe light, pulse pump light, I(t), and R'(t) in another embodiment. Detailed Implementation

[0043] To enable those skilled in the art to better understand the technical solutions of this disclosure, and to fully understand and implement the process of how this disclosure applies technical means to solve technical problems and achieve corresponding technical effects, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, not all embodiments. The embodiments of this disclosure and the various features within them can be combined with each other without conflict, and the resulting technical solutions are all within the protection scope of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort should fall within the protection scope of this disclosure.

[0044] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this disclosure described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0045] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0046] One embodiment of this application provides a measurement system based on wide-field picosecond ultrasound imaging, used to measure the position of the first pattern layer located below the light-shielding layer in a sample 170, in conjunction with a reference. Figure 1 and Figure 2 ,include:

[0047] The light source assembly 100 is used to generate pulsed pump light and pulsed probe light with delay;

[0048] The light guide assembly 150 is used to combine the pulsed pump light and the pulsed probe light and guide them to the surface of the sample to be tested 170.

[0049] The first image sensor 221 is used to convert the first feedback light formed by the pulse probe light on the surface of the sample to be tested into a first electrical signal.

[0050] The first filter 200 is used to block the second feedback light formed by the pulse pump light on the surface of the sample 170 from entering the first image sensor 221;

[0051] The processor 222 is configured to acquire a photoacoustic signal ΔR / R corresponding to the characteristic delay of the first pattern layer based on the first electrical signal. ΔR represents the intensity difference of the first feedback light when there is pulsed pump light excitation and when there is no pulsed pump light excitation, and R represents the intensity of the first feedback light when there is no pulsed pump light excitation.

[0052] In this embodiment, it is possible to measure the first pattern layer beneath the light-shielding layer. Increasing the sampling rate and measurement speed will significantly improve both measurement accuracy and efficiency.

[0053] In this embodiment, instead of performing point scanning on the sample 170 to be tested, the first image sensor 221 is used to perform wide-field imaging on the sample 170 to be tested. This allows the position of the first pattern layer to be obtained quickly with a higher spatial sampling rate, thus improving testing efficiency.

[0054] The pulse pump light is a femtosecond pulse pump light. The pulse probe light is a femtosecond pulse probe light.

[0055] In one embodiment, the area of ​​the light spot illuminating the surface of the sample 170 is larger than the area of ​​the outer contour of the first pattern layer. In one embodiment, the area of ​​the light spot illuminating the surface of the sample 170 is 25 μm. 2 ~1600μm 2 For example, 400μm 2 .

[0056] In one embodiment, the size of the light spot illuminating the surface of the sample 170 along the first direction is larger than the size of the outer contour of the first pattern layer along the first direction. The size of the light spot illuminating the surface of the sample 170 along the second direction is larger than the size of the outer contour of the first pattern layer along the second direction. The first and second directions intersect, for example, the first and second directions are perpendicular.

[0057] In this embodiment, the sample to be tested 170 can be a wafer, a chip, or a semiconductor semi-finished product.

[0058] refer to Figure 1 The light source assembly 100 includes: a light source 101; a first optical parametric amplifier 103; a second optical parametric amplifier 104; a first beam splitter 102 located between the first optical parametric amplifier 103 and the light source 101, and between the second optical parametric amplifier 104 and the light source 101; wherein, the first beam splitter 102 is used to split the light beam emitted by the light source 101 into a first light and a second light, the first optical parametric amplifier 103 is used to receive the first light and output a pulse probe light, the second optical parametric amplifier 104 is used to receive the second light and output a pulse pump light; and a delay assembly 110 is used to adjust the delay of the pulse probe light relative to the pulse pump light.

[0059] The light source 101 includes a femtosecond laser.

[0060] The first optical parametric amplifier 103 is used to adjust the center wavelength of the probe pulse in the pulse probe light, and the second optical parametric amplifier 104 is used to adjust the center wavelength of the pump pulse in the pulse pump light.

[0061] In this embodiment, the center wavelength of each probe pulse in the pulse probe light is a first wavelength, and the center wavelength of each pump pulse in the pulse pump light is a second wavelength, which is different from the first wavelength. In other embodiments, the polarization directions of the pulse probe light and the pulse pump light are different.

[0062] refer to Figure 1 The delay assembly 110 includes a retroreflector 112, a first reflector 111, a second reflector 114, and a first driving stage 113. The first driving stage 113 drives the retroreflector 112 to move, thereby changing the distance between the retroreflector 112 and the first reflector 111, and the distance between the retroreflector 112 and the second reflector 114. After the pulse probe light passes through the delay assembly 110, the optical path difference between the pulse probe light and the pulse pump light changes, thus changing the delay of the pulse probe light and the pulse pump light.

[0063] In one embodiment, the first drive stage 113 is a voice coil motor.

[0064] The first reflector 111 is used to reflect the pulse probe light output from the first optical parametric amplifier 103 to the retroreflector 112. The second reflector 114 is used to reflect the pulse probe light output from the retroreflector 112.

[0065] refer to Figure 1 The measurement system based on wide-field picosecond ultrasound imaging also includes a first modulator 141, used to modulate the pulsed probe light output by the light source assembly 100, wherein the probe pulse in the modulated pulsed probe light is set within multiple consecutive characteristic periods T. Specifically, the first modulator 141 is used to modulate the pulsed probe light output by the delay assembly 110.

[0066] refer to Figure 7 The characteristic period T includes a first sub-stage I1, a second sub-stage Q2, a third sub-stage I3, and a fourth sub-stage Q4. The modulated pulse probe light includes multiple probe pulses with a first pulse interval in each of the first sub-stage I1, the second sub-stage Q2, and the third sub-stage I3. The modulated pulse probe light includes a first probe pulse group and a second probe pulse group in the fourth sub-stage Q4. There is a first pulse interval between adjacent probe pulses in the first probe pulse group, a first pulse interval between adjacent probe pulses in the second probe pulse group, and a second pulse interval between the first probe pulse group and the second probe pulse group. The second pulse interval is greater than the first pulse interval.

[0067] In one embodiment, the second pulse interval is 10% to 90% of the characteristic period T.

[0068] In one embodiment, the first pulse interval is 1 / 10000 to 1 / 1000 of the characteristic period T.

[0069] In one embodiment, the first pulse interval is 8.30 ns to 100 ns, for example, 25 ns or 12.5 ns.

[0070] In this embodiment, the measurement system based on wide-field picosecond ultrasound imaging further includes a third reflecting mirror 120. The third reflecting mirror 120 is used to reflect the pulsed probe light reflected by the second reflecting mirror 114 to the first modulator 141.

[0071] In other embodiments, the third reflector 120 may be omitted. The pulsed probe light reflected by the second reflector 114 directly enters the first modulator 141.

[0072] refer to Figure 1 The measurement system based on wide-field picosecond ultrasound imaging also includes a second modulator 142, which is used to modulate the pulse pump light output by the light source assembly 100. Specifically, the second modulator 142 is used to modulate the pulse pump light output by the second optical parametric amplifier 104.

[0073] In this embodiment, the measurement system based on wide-field picosecond ultrasound imaging further includes a fourth reflecting mirror 130. The fourth reflecting mirror 130 is used to reflect the pulsed pump light output from the second optical parametric amplifier 104 to the second modulator 142. In other embodiments, the fourth reflecting mirror 130 may be omitted, and the pulsed pump light output from the second optical parametric amplifier 104 may directly enter the second modulator 142.

[0074] refer to Figure 7 The pump pulses in the pulsed pump light modulated by the second modulator 142 are set within multiple consecutive characteristic periods T. The modulated pulsed pump light includes multiple pump pulses with a first pulse interval in the first sub-stage I1. The modulated pulsed pump light has no pump pulses in the second sub-stage Q2, the third sub-stage I3 and the fourth sub-stage Q4.

[0075] In this embodiment, the first modulator 141 includes an acousto-optic modulator, an electro-optic modulator, or an optical chopper. The second modulator 142 includes an acousto-optic modulator, an electro-optic modulator, or an optical chopper.

[0076] In this embodiment, reference Figure 1 The light guide assembly 150 includes a second beam splitter 151, a third beam splitter 153, and a lens group 152; wherein the second beam splitter 151 is located between the first modulator 141 and the lens group 152 and between the second modulator 142 and the lens group 152; the third beam splitter 153 is used to reflect the light output from the lens group 152 toward the sample under test 170 and to transmit the first feedback light and the second feedback light from the sample under test 170.

[0077] The second beam splitter 151 is used to combine the pulse probe light from the first modulator 141 and the pulse pump light from the second modulator 142 and transmit them to the lens group 152.

[0078] Lens group 152 includes one or more lenses. The lenses are, for example, convex lenses.

[0079] In this embodiment, reference Figure 1 The measurement system based on wide-field picosecond ultrasound imaging also includes: a second drive stage 180, which is used to carry the sample 170 to be tested, and the bearing surface of the second drive stage 180 carries the sample 170 to be tested. The second drive stage 180 is also used for movement, for example, the second drive stage 180 is used to move in a direction parallel to the bearing surface and in a direction perpendicular to the bearing surface.

[0080] In this embodiment, reference Figure 1 The measurement system based on wide-field picosecond ultrasound imaging also includes an objective lens 160, located between the third beam splitter 153 and the second drive stage 180.

[0081] In one embodiment, the second beam splitter 151, lens group 152, the third beam splitter 153, and the objective lens 160 constitute the Köhler illumination optical path.

[0082] The first and second feedback beams are combined together between the third beam splitter 153 and the sample 170 under test.

[0083] In this embodiment, reference Figure 1 and Figure 2 The first image sensor 221 and processor 222 are integrated into a phase-locked camera 220. The phase-locked camera 220 is, for example, a multi-element phase-locked detector array. The multi-element phase-locked detector array is, for example, a CMOS area array phase-locked camera.

[0084] In this embodiment, reference Figure 1 The measurement system based on wide-field picosecond ultrasound imaging also includes a fourth beam splitter 190. Specifically, a first filter 200 is located between the fourth beam splitter 190 and the phase-locked camera 220; more specifically, the first filter 200 is located between the fourth beam splitter 190 and the first image sensor 221.

[0085] The fourth beam splitter 190 is used to transmit the first and second feedback beams from the combined beams of the third beam splitter 153 to the first filter 200.

[0086] In this embodiment, the second wavelength is different from the first wavelength, and the first filter 200 is a filter. In other embodiments, the pulse probe light and the pulse pump light have different polarization directions, and the first filter 200 is a polarization modulator.

[0087] In this embodiment, reference Figure 1 The measurement system based on wide-field picosecond ultrasound imaging also includes: a first focusing lens 210, which is located between the first filter 200 and the phase-locked camera 220, and between the first filter 200 and the first image sensor 221.

[0088] In this embodiment, reference Figure 6 The processor 222 includes a modulation signal generation unit 2221, which outputs a first modulation signal u1(t) and a second modulation signal u2(t), both of which have a characteristic period T.

[0089]

[0090] Where t1 is the first time point, t2 is the second time point, t3 is the third time point, t4 is the fourth time point, and t5 is the fifth time point. Here, t is the independent variable of the first modulation signal u1(t) and the second modulation signal u2(t), and k is an integer greater than or equal to 0. Where t5 - t1 = T.

[0091] The first sub-stage is (t1+kT, t2+kT], the second sub-stage is (t2+kT, t3+kT], the third sub-stage is (t3+kT, t4+kT], and the fourth sub-stage is (t4+kT, t5+kT). Where t2-t1=t3-t2=t4-t3=t5-t4. The durations of the first, second, third, and fourth sub-stages are equal.

[0092] The first modulation signal u1(t) and the second modulation signal u2(t) have the same characteristic period T. The phase of the first modulation signal u1(t) and the phase of the second modulation signal u2(t) are 90 degrees apart.

[0093] refer to Figure 8 Multiple consecutive characteristic periods T include the first characteristic period T1 to the nth characteristic period T. n n is an integer greater than or equal to 2. The first pulse interval is the same for different characteristic periods T, but the delay between the probe pulse and the pump pulse is different in the first sub-stage I1 of different characteristic periods T.

[0094] In this embodiment, reference Figure 6The processor 222 further includes: a first generation unit 2222, configured to multiply the first electrical signal and the first modulation signal u1(t) to obtain a first modulation electrical signal; a second generation unit 2223, configured to multiply the first electrical signal and the second modulation signal u2(t) to obtain a second modulation electrical signal; a third generation unit 2226, configured to add the first modulation electrical signal of the first sub-stage and the first modulation electrical signal of the third sub-stage to obtain ΔR; and a fourth generation unit 2227, configured to add the second modulation electrical signal of the second sub-stage and the second modulation electrical signal of the fourth sub-stage to obtain R.

[0095] In one embodiment, the third generation unit 2226 includes a first low-pass filter and a first adder. The first low-pass filter is used to filter out high-frequency components and noise components of the first modulated electrical signal, retaining the fundamental frequency component of the first modulated electrical signal, the frequency of which is equal to (the frequency of the reference signal - the modulation frequency of the first modulator 141). The first adder is used to add the first modulated electrical signal of the first sub-stage and the first modulated electrical signal of the third sub-stage. The frequency of the reference signal = 1 / characteristic period T.

[0096] The frequency of the reference signal and the modulation frequency of the first modulator 141 may differ slightly. Preferably, the frequency of the reference signal and the modulation frequency of the first modulator 141 are the same.

[0097] In one embodiment, the fourth generation unit 2227 includes a second low-pass filter and a second adder. The second low-pass filter is used to filter out high-frequency and noise components of the second modulated electrical signal, retaining the fundamental frequency component of the second modulated electrical signal, the frequency of which is equal to (the frequency of the reference signal - the modulation frequency of the second modulator 142). The second adder is used to add the second modulated electrical signal of the second sub-stage and the second modulated electrical signal of the fourth sub-stage.

[0098] The frequency of the reference signal and the modulation frequency of the second modulator 142 may differ slightly. Preferably, the frequency of the reference signal and the modulation frequency of the second modulator 142 are the same.

[0099] In another embodiment, the third generation unit 2226 includes a first switched capacitor integrator, which can filter the high-frequency components and noise components of the first modulated electrical signal and retain the fundamental frequency component of the first modulated electrical signal. The first switched capacitor integrator can also add the first modulated electrical signal of the first sub-stage and the first modulated electrical signal of the third sub-stage.

[0100] In another embodiment, the third generation unit 2226 includes a second switched-capacitor integrator. The second switched-capacitor integrator is used to filter high-frequency and noise components of the second modulated electrical signal, retaining the fundamental frequency component of the second modulated electrical signal. The second switched-capacitor integrator can also add the second modulated electrical signal of the second sub-stage and the second modulated electrical signal of the fourth sub-stage.

[0101] In this embodiment, the first image sensor 221 is also used to generate a first test image of the first pattern layer 51 based on the photoacoustic signal ΔR / R.

[0102] In this embodiment, reference Figure 1 The measurement system based on wide-field picosecond ultrasound imaging also includes a second image sensor 240 for acquiring a second test image of the second pattern layer 52 located above the light-shielding layer in the sample 170 to be tested.

[0103] The second image sensor 240 is also used to acquire the overlap between the pulsed pump light and the probe light on the surface of the sample under test.

[0104] In this embodiment, reference Figure 1 The measurement system based on wide-field picosecond ultrasound imaging also includes a second focusing lens 230, which is located between the fourth beam splitter 190 and the second image sensor 240.

[0105] In this embodiment, the overlay error of the second pattern layer 52 and the first pattern layer 51 is obtained based on the deviation between the center of the second test image and the center of the first test image.

[0106] The second pattern layer 52 and the first pattern layer 51 have different heights in the sample 170 under test. The projections of the second pattern layer 52 and the first pattern layer 51 onto the surface of the sample 170 under test do not overlap. For example, refer to... Figure 3 , Figure 4 and Figure 5 The sample to be tested 170 has a first pattern layer 51 and a second pattern layer 52 located at different heights. The projections of the second pattern layer 52 and the first pattern layer 51 on the surface of the sample to be tested 170 do not overlap. For example, the projection of the second pattern layer 52 on the surface of the sample to be tested 170 surrounds the projection of the first pattern layer 51 on the surface of the sample to be tested 50.

[0107] It should be noted that the projection pattern of the first pattern layer 51 onto the surface of the sample 170 under test includes any one of the following: square, annular, strip, and grating shapes. The projection pattern of the second pattern layer 52 onto the surface of the sample 170 under test includes any one of the following: square, annular, strip, and grating shapes.

[0108] In this embodiment, the first pattern layer 51 is the first set of engraving marks. The second pattern layer 52 is the second set of engraving marks.

[0109] In this embodiment, reference Figure 1 The measurement system based on wide-field picosecond ultrasound imaging also includes: a synchronous control circuit 250.

[0110] Synchronization control circuit 250 is used to generate reference signal Ref (reference Figure 7 The reference signal Ref is input to the modulation signal generation unit 2221, which is used to generate a first modulation signal u1(t) and a second modulation signal u2(t) based on the reference signal Ref.

[0111] Reference signal

[0112] The synchronization control circuit 250 also generates a third modulation signal and transmits the third modulation signal to a first modulator, which modulates the pulse probe light output by the light source assembly 100 according to the third modulation signal.

[0113] The synchronization control circuit 250 also generates a fourth modulation signal and transmits the fourth modulation signal to a second modulator, which modulates the pulse pump light output by the light source assembly 100 according to the fourth modulation signal.

[0114] The first modulation signal u1(t), the second modulation signal u2(t), the third modulation signal, and the fourth modulation signal have the same period, that is, the periods of the first modulation signal u1(t), the second modulation signal u2(t), the third modulation signal, and the fourth modulation signal are all equal to the characteristic period T.

[0115] The first modulation signal u1(t), the second modulation signal u2(t), the third modulation signal, and the fourth modulation signal have the same phase.

[0116] refer to Figure 7 The diagram illustrates the variation in the intensity D of the first feedback light. In the first sub-stage, due to the excitation of the pulsed pump light, the intensity of the first feedback light formed by the pulsed probe light illuminating the surface of the sample under test is relatively high. In the second, third, and fourth sub-stages, due to the absence of pulsed pump light excitation, the intensity of the first feedback light formed by the pulsed probe light illuminating the surface of the sample under test is relatively low.

[0117] Pulsed pump light illuminates a light-shielding layer, which absorbs the energy of the pulsed pump light and generates acoustic waves. For example, the light-shielding layer absorbs the energy of ultrafast pulsed pump light and generates high-frequency ultrasound waves, which are picosecond ultrasound waves. The guided wave in the acoustic wave is reflected by the first patterned layer, "transferring" the first patterned layer onto the light-shielding layer and above it, changing the reflectivity of the sample surface at the corresponding position of the first patterned layer, thereby modulating the first feedback light and changing its intensity. The intensity change of the first feedback light occurs on a picosecond timescale and is in phase with the fourth modulation signal used to modulate the pulsed pump light. The photoacoustic signal formed by the first patterned layer can be extracted from the background using phase-locked detection technology. Through imaging relationships, the first image sensor can achieve sampling at hundreds of nanometers or higher. The image of the first patterned layer can be extracted from the differential signals of the photoacoustic signals of adjacent pixels, or it can be formed by analyzing the time-domain and frequency-domain characteristics of the photoacoustic signal of each pixel individually.

[0118] Another embodiment of this application provides a measurement system based on wide-field picosecond ultrasound imaging for measuring the position of a first pattern layer located below a light-shielding layer in a sample under test, with reference to... Figure 9 The system includes: a light source assembly 340 for forming a pulsed pump light and a pulsed probe light with a delay; a light guide assembly 150 for combining the pulsed pump light and the pulsed probe light and guiding them to the surface of the sample 170 under test; a first image sensor 321 for converting the first feedback light formed by the pulsed probe light on the surface of the sample under test into a first electrical signal; a first filter 300 for blocking the second feedback light formed by the pulsed pump light on the surface of the sample under test from entering the first image sensor 321; and a processor 322 for acquiring a photoacoustic signal ΔR / R corresponding to the characteristic delay of the first pattern layer based on the first electrical signal, where ΔR represents the intensity difference of the first feedback light when excited by pulsed pump light and when not excited by pulsed pump light, and R represents the intensity of the first feedback light when not excited by pulsed pump light.

[0119] refer to Figure 9 The light source assembly 340 includes a first light source 341 and a second light source 342. The first light source 341 is used to emit pulse probe light with a first repetition frequency, and the second light source 342 is used to emit pulse pump light with a second repetition frequency.

[0120] The first repetition frequency is f1 = f0 + Δf. The second repetition frequency is f2 = f0. The constraints are that (1 / f2 - 1 / f1) is greater than the pulse width of the pulse pump light, and Δf is less than 1 / 9 of f2.

[0121] The center wavelength of each probe pulse in the pulse probe light is the first wavelength, and the center wavelength of each pump pulse in the pulse pump light is the second wavelength, which is different from the first wavelength. Alternatively, the polarization directions of the pulse probe light and the pulse pump light are different.

[0122] The pulse pump light is a femtosecond pulse pump light. The pulse probe light is a femtosecond pulse probe light.

[0123] The first light source 341 is a femtosecond laser. The second light source 342 is a femtosecond laser.

[0124] In one embodiment, the area of ​​the light spot illuminating the surface of the sample 170 is larger than the area of ​​the outer contour of the first pattern layer. In one embodiment, the area of ​​the light spot illuminating the surface of the sample 170 is 25 μm. 2 ~1600μm 2 For example, 400μm 2 .

[0125] In one embodiment, the size of the light spot illuminating the surface of the sample 170 along the first direction is larger than the size of the outer contour of the first pattern layer along the first direction. The size of the light spot illuminating the surface of the sample 170 along the second direction is larger than the size of the outer contour of the first pattern layer along the second direction. The first and second directions intersect, for example, the first and second directions are perpendicular.

[0126] In this embodiment, the sample to be tested 170 can be a wafer, a chip, or a semiconductor semi-finished product.

[0127] refer to Figure 9 The light guide assembly 150 includes: a second beam splitter 151, a third beam splitter 153, and a lens group 152; wherein, the second beam splitter 151 is located between the first light source 341 and the lens group 152, and between the second light source 342 and the lens group 152; the third beam splitter 153 is used to reflect the light output from the lens group 152 toward the sample under test 170 and to transmit the first feedback light and the second feedback light from the sample under test 170.

[0128] The second beam splitter 151 is used to combine the pulsed probe light from the first light source 341 and the pulsed pump light from the second light source 342 and transmit them to the lens group 152.

[0129] Lens group 152 includes one or more lenses. The lenses are, for example, convex lenses.

[0130] In this embodiment, reference Figure 9 The measurement system based on wide-field picosecond ultrasound imaging also includes: a second drive stage 180, which is used to carry the sample 170 to be tested, and the bearing surface of the second drive stage 180 carries the sample 170 to be tested. The second drive stage 180 is also used for movement, for example, the second drive stage 180 is used to move in a direction parallel to the bearing surface and in a direction perpendicular to the bearing surface.

[0131] In this embodiment, reference Figure 9The measurement system based on wide-field picosecond ultrasound imaging also includes an objective lens 160, located between the third beam splitter 153 and the second drive stage 180.

[0132] The first and second feedback beams are combined together between the third beam splitter 153 and the sample 170 under test.

[0133] In this embodiment, the second wavelength is different from the first wavelength, and the first filter 300 is a filter. In other embodiments, the pulse probe light and the pulse pump light have different polarization directions, and the first filter 300 is a polarization modulator.

[0134] In this embodiment, reference Figure 9 The measurement system based on wide-field picosecond ultrasound imaging also includes a first focusing lens 310, which is located between the first filter 300 and the first image sensor 321.

[0135] The measurement system based on wide-field picosecond ultrasound imaging also includes: a photodetector 323; and a second filter 320 located between the second beam splitter 151 and the photodetector 323, the second filter 320 being used to filter pulse pump light.

[0136] In this embodiment, the second wavelength is different from the first wavelength, and the second filter 320 is a filter. In other embodiments, the pulse probe light and the pulse pump light have different polarization directions, and the second filter 320 is a polarization modulator.

[0137] The processor 322 is connected to the first image sensor 321, and the processor 322 is also connected to the photodetector 323.

[0138] In this embodiment, reference Figure 1 The measurement system based on wide-field picosecond ultrasound imaging also includes a synchronization control circuit 330. The synchronization control circuit 330 is connected to the first light source 341 and the second light source 342. The synchronization control circuit 330 is used to control the pulse pump light and pulse probe light to be output in phase-locked mode with a certain frequency difference Δf.

[0139] In this embodiment, the pulsed pump light and the pulsed probe light are phase-locked out with a certain frequency difference Δf, which is equivalent to the pulsed probe light being output at a frequency difference Δf. 2The frequency of / Δf)+f0 is sampled every Δt = Δf / [f0(f0+Δf)] for the transient process of pulse pump light excitation. For example, if the repetition frequency of the pulse pump light is 2.01MHz and the repetition frequency of the pulse probe light is 2MHz, then for each pump pulse irradiating the surface of the sample under test, different probe pulses will arrive at the sample surface within time intervals of 0, 2.5ns, 5ns, ... 100μs, respectively, thus obtaining the intensity of the first feedback light excited by the pulse pump light at 0, 2.5ns, 5ns, ... 100μs. The first feedback light transmitted through the first filter is converted into a first electrical signal using a first image sensor. Based on the first electrical signal, the photoacoustic signal ΔR / R corresponding to the characteristic delay of the first pattern layer is obtained. ΔR characterizes the intensity difference of the first feedback light when there is pulse pump light excitation and when there is no pulse pump light excitation, and R characterizes the intensity of the first feedback light when there is no pulse pump light excitation.

[0140] The first image sensor is also used to generate a first test image of the first pattern layer based on the photoacoustic signal ΔR / R.

[0141] In this embodiment, reference Figure 9 The measurement system based on wide-field picosecond ultrasound imaging also includes a second image sensor (not shown) for acquiring a second test image of the second pattern layer 52 located above the light-shielding layer in the sample 170 to be tested.

[0142] The second image sensor is also used to acquire the overlap between the pulsed pump light and the probe light on the surface of the sample under test.

[0143] In this embodiment, the overlay error of the second pattern layer 52 and the first pattern layer 51 is obtained based on the deviation between the center of the second test image and the center of the first test image.

[0144] The second pattern layer 52 and the first pattern layer 51 have different heights in the sample 170 to be tested.

[0145] The projections of the second pattern layer 52 and the first pattern layer 51 onto the surface of the sample 170 do not overlap.

[0146] The specific descriptions of the second pattern layer 52 and the first pattern layer 51 refer to the descriptions of the foregoing embodiments.

[0147] Another embodiment of this application also provides a measurement method based on wide-field picosecond ultrasound imaging, including:

[0148] Step S1: Form a pulsed probe light and a pulsed pump light with a time delay;

[0149] Step S2: Combine the pulse probe light and the pulse pump light and guide them to the surface of the sample to be tested, so as to form the first feedback light and the second feedback light respectively;

[0150] Step S3: Filter the second feedback light using the first filter;

[0151] Step S4: The first feedback light transmitted through the first filter is converted into a first electrical signal using the first image sensor;

[0152] Step S5: Obtain the photoacoustic signal ΔR / R corresponding to the characteristic delay of the first pattern layer based on the first electrical signal. ΔR represents the intensity difference of the first feedback light when there is pulse pump light excitation and when there is no pulse pump light excitation, and R represents the intensity of the first feedback light when there is no pulse pump light excitation.

[0153] The measurement method based on wide-field picosecond ultrasound imaging further includes: adjusting the delay of the pulse probe light and the pulse pump light, and then modulating the pulse probe light. The probe pulses in the modulated pulse probe light are set within multiple consecutive characteristic periods. The characteristic periods include a first sub-stage, a second sub-stage, a third sub-stage, and a fourth sub-stage with the same duration. Within the first, second, and third sub-stages, the modulated pulse probe light includes multiple probe pulses with a first pulse interval. Within the fourth sub-stage, the modulated pulse probe light includes a first probe pulse group and a second probe pulse group. Adjacent probe pulses in the first probe pulse group and adjacent probe pulses in the second probe pulse group have a first pulse interval. A second pulse interval, greater than the first pulse interval, exists between the detection pulse group and the second probe pulse group. The pulse pump light is modulated, and the pump pulses in the modulated pulse pump light are set within multiple consecutive characteristic periods. The modulated pulse pump light includes multiple pump pulses with the first pulse interval in the first sub-stage. The modulated pulse pump light has no pump pulses in the second, third, and fourth sub-stages.

[0154] The measurement method based on wide-field picosecond ultrasound imaging further includes: obtaining the photoacoustic signal ΔR / R under the characteristic delay corresponding to the first pattern layer according to the first electrical signal, including: generating a first modulation signal u1(t) and a second modulation signal u2(t), both of which have a characteristic period T;

[0155]

[0156] The first modulated electrical signal is obtained by multiplying the first electrical signal and the first modulated signal u1(t);

[0157] Multiply the first electrical signal and the second modulation signal u2(t) to obtain a second modulated electrical signal;

[0158] Add the first modulated electrical signal in the first sub-stage and the first modulated electrical signal in the third sub-stage to obtain ΔR;

[0159] Add the second modulated electrical signal in the second sub-stage and the second modulated electrical signal in the fourth sub-stage to obtain R;

[0160] Where, t5 - t1 = T; the first sub-stage is [t1 + kT, t2 + kT], the second sub-stage is [t2 + kT < t ≤ t3 + kT], the third sub-stage is [t3 + kT < t ≤ t4 + kT], and the fourth sub-stage is [t4 + kT < t ≤ t5 + kT]; k is an integer greater than or equal to 0.

[0161] In this embodiment, adjusting the delay between the pulsed probe light and the pulsed pump light includes: using the delay component 110 to adjust the delay between the pulsed probe light and the pulsed pump light. The delay component 110 includes a retroreflector 112, a first reflector 111, a second reflector 114, and a first driving stage 113. Specifically, the first driving stage 113 drives the retroreflector 112 to move, so as to change the distance between the retroreflector 112 and the first reflector 111 and the distance between the retroreflector 112 and the second reflector 114. After the pulsed probe light passes through the delay component 110, the optical path difference between the pulsed probe light and the pulsed pump light changes, thereby changing the delay between the pulsed probe light and the pulsed pump light.

[0162] The measurement method based on wide-field picosecond ultrasonic imaging further includes: generating a first test image of the first pattern layer according to the photoacoustic signal ΔR / R; obtaining a second test image of the second pattern layer located above the light shielding layer in the待测样品; obtaining the overlay error between the first pattern layer and the second pattern layer according to the first test image and the second test image.

[0163] Another embodiment of the present application further provides a measurement method based on wide-field picosecond ultrasonic imaging. The difference between the present application and the measurement method based on wide-field picosecond ultrasonic imaging in the foregoing embodiment is that adjusting the delay between the pulsed probe light and the pulsed pump light includes: adjusting the delay of the pulsed probe light relative to the pulsed pump light by adjusting the repetition frequencies of the pulsed probe light and the pulsed pump light to be different.

[0164] The pulsed probe light has a first repetition frequency, and the pulsed pump light has a second repetition frequency.

[0165] The first repetition frequency f1 = f0 + Δf. The second repetition frequency f2 = f0. The constraint condition is that (1 / f2 - 1 / f1) is greater than the pulse width of the pulsed pump light, and Δf is less than 1 / 9 of f2.

[0166] The center wavelength of each probe pulse in the pulse probe light is the first wavelength, and the center wavelength of each pump pulse in the pulse pump light is the second wavelength, which is different from the first wavelength. Alternatively, the polarization directions of the pulse probe light and the pulse pump light are different.

[0167] The pulse pump light is a femtosecond pulse pump light. The pulse probe light is a femtosecond pulse probe light.

[0168] In one embodiment, the area of ​​the light spot illuminating the surface of the sample 170 is larger than the area of ​​the outer contour of the first pattern layer. In one embodiment, the area of ​​the light spot illuminating the surface of the sample 170 is 25 μm. 2 ~1600μm 2 For example, 400μm 2 .

[0169] In t x The delay of the pulse probe light and pulse pump light at time t is x*Δt, where x is an integer greater than or equal to 1. x Let x be the time when the x-th probe pulse reaches the surface of the sample under test; (t x -x*Δt) represents the moment when the x-th pump pulse reaches the surface of the sample under test.

[0170] In another embodiment, the photoacoustic signal formed by the xth probe pulse m is an integer greater than or equal to 2;

[0171] When m equals 2

[0172] R'(t) is the first electrical signal at time t. x ) is t = t x The first electrical signal at that moment.

[0173] R'(t n+1 ) is t = t n+1 The first electrical signal at time t. R'(t) n+2 ) is t = t n+2 The first electrical signal at time t. R'(t) n-1 ) is t = t n-1 The first electrical signal at time t. R'(t) n+m ) is t = t n+m The first electrical signal at time n. Where n is an integer greater than or equal to 2.

[0174] When t = t n+1 At that time, the delay of the pulse probe light and the pulse pump light is (n+1)*Δt. When t=t n+2 At that time, the delay of the pulse probe light and the pulse pump light is (n+2)*Δt. When t=tn+m At that time, the delay between the pulse probe light and the pulse pump light is (n+m)*Δt. R'(t) n+1 )=R'(t n+2 )=R'(t n )=R'(t n+m R'(t) n ) and R'(t n-1 The sizes are different.

[0175] The measurement method based on wide-field picosecond ultrasound imaging also includes: acquiring the light intensity signal I(t) of the pulse probe light reflected by the second beam splitter 151.

[0176] In another embodiment,

[0177]

[0178] I(t x ) is t = t x The light intensity signal I(t) at time t. n+1 ) is t = t n+1 The light intensity signal I(t) at time t.

[0179] In one embodiment, after obtaining photoacoustic signals formed by different probe pulses, the maximum value among the photoacoustic signals formed by different probe pulses is obtained, and the maximum value among the photoacoustic signals formed by different probe pulses corresponds to the photoacoustic signal of the first pattern layer.

[0180] While the embodiments disclosed herein are as described above, the foregoing content is merely for the purpose of facilitating understanding of this disclosure and is not intended to limit this disclosure. Any person skilled in the art to which this disclosure pertains may make any modifications and changes in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection of this disclosure shall still be determined by the scope defined in the appended claims.

Claims

1. A measurement system based on wide-field picosecond ultrasound imaging, used to measure the position of a first pattern layer located below a light-shielding layer in a sample under test, characterized in that, include: A light source assembly for generating pulsed pump light and pulsed probe light with delay; A light guide assembly is used to combine and guide the pulsed pump light and pulsed probe light to the surface of the sample to be tested. The first image sensor is used to convert the first feedback light formed by the pulsed probe light on the surface of the sample under test into a first electrical signal. The first filter is used to block the second feedback light formed by the pulse pump light on the surface of the sample from entering the first image sensor; The processor is configured to acquire a photoacoustic signal ΔR / R corresponding to the characteristic delay of the first pattern layer based on the first electrical signal. ΔR represents the intensity difference of the first feedback light when there is pulsed pump light excitation and when there is no pulsed pump light excitation, and R represents the intensity of the first feedback light when there is no pulsed pump light excitation.

2. The measurement system based on wide-field picosecond ultrasound imaging according to claim 1, characterized in that, The light source assembly includes: A light source; a first optical parametric amplifier; a second optical parametric amplifier; a first beam splitter located between the first optical parametric amplifier and the light source, and between the second optical parametric amplifier and the light source; wherein the first beam splitter is used to split the light beam emitted by the light source into a first light path and a second light path, the first optical parametric amplifier is used to receive the first light path and output a pulse probe light, and the second optical parametric amplifier is used to receive the second light path and output a pulse pump light; a delay component is used to adjust the delay of the pulse probe light relative to the pulse pump light.

3. The measurement system based on wide-field picosecond ultrasound imaging according to claim 1 or 2, characterized in that, Also includes: A first modulator is used to modulate the pulsed probe light output by the light source assembly. The probe pulses in the modulated pulsed probe light are set within multiple consecutive characteristic periods. The characteristic periods include a first sub-stage, a second sub-stage, a third sub-stage, and a fourth sub-stage with the same duration. The modulated pulsed probe light includes multiple probe pulses with a first pulse interval in the first sub-stage, the second sub-stage, and the third sub-stage. The modulated pulsed probe light includes a first probe pulse group and a second probe pulse group in the fourth sub-stage. There is a first pulse interval between adjacent probe pulses in the first probe pulse group, a first pulse interval between adjacent probe pulses in the second probe pulse group, and a second pulse interval between the first probe pulse group and the second probe pulse group. The second pulse interval is greater than the first pulse interval. The second modulator is used to modulate the pulsed pump light. The pump pulses in the modulated pulsed pump light are set in multiple consecutive characteristic periods. The modulated pulsed pump light includes multiple pump pulses with a first pulse interval in the first sub-stage. The modulated pulsed pump light has no pump pulses in the second, third and fourth sub-stages. Preferably, the first modulator includes an acousto-optic modulator, an electro-optic modulator, or an optical chopper, and the second modulator includes an acousto-optic modulator, an electro-optic modulator, or an optical chopper. Preferably, the light guide assembly includes: a second beam splitter, a third beam splitter, and a lens group; wherein the second beam splitter is located between the first modulator and the lens group and between the second modulator and the lens group; the third beam splitter is used to reflect the light output from the lens group toward the sample under test and to transmit the first feedback light and the second feedback light from the sample under test.

4. The measurement system based on wide-field picosecond ultrasound imaging according to claim 3, characterized in that, The first image sensor and the processor are integrated into a phase-locked camera; The processor includes: The modulation signal generation unit is used to output a first modulation signal u1(t) and a second modulation signal u2(t), both of which have a characteristic period T. The first generation unit is used to multiply the first electrical signal and the first modulation signal u1(t) to obtain the first modulation electrical signal; The second generation unit is used to multiply the first electrical signal and the second modulation signal u2(t) to obtain the second modulation electrical signal; The third generation unit is used to add the first modulation signal of the first sub-stage and the first modulation signal of the third sub-stage to obtain ΔR; The fourth generation unit is used to add the second modulation signal of the second sub-stage and the second modulation signal of the fourth sub-stage to obtain R; Where t5-t1=T; the first sub-stage is (t1+kT,t2+kT], the second sub-stage is (t2+kT,t3+kT], the third sub-stage is (t3+kT,t4+kT], and the fourth sub-stage is (t4+kT,t5+kT]; k is an integer greater than or equal to 0.

5. The measurement system based on wide-field picosecond ultrasound imaging according to claim 1, characterized in that, The light source assembly includes a first light source and a second light source, wherein the first light source is used to emit pulsed probe light with a first repetition frequency, and the second light source is used to emit pulsed pump light with a second repetition frequency. Preferably, the light guide assembly includes: a second beam splitter, a third beam splitter, and a lens group; wherein, the second beam splitter is located between the first light source and the lens group and between the second light source and the lens group; the third beam splitter is used to reflect the light output from the lens group toward the sample under test and to transmit the first feedback light and the second feedback light from the sample under test. Preferably, the measurement system based on wide-field picosecond ultrasound imaging further includes: a photodetector; and a second filter located between the second beam splitter and the photodetector, the second filter being used to filter pulse pump light.

6. The measurement system based on wide-field picosecond ultrasound imaging according to claim 1, characterized in that, The first image sensor is also used to generate a first test image of the first pattern layer based on the photoacoustic signal ΔR / R; Preferably, the measurement system based on wide-field picosecond ultrasound imaging further includes: a second image sensor for acquiring a second test image of the second patterned layer located above the light-shielding layer in the sample to be tested.

7. A measurement method based on wide-field picosecond ultrasound imaging, characterized in that, include: This generates delayed pulse probe light and pulse pump light; The pulsed probe light and pulsed pump light are combined and guided to the surface of the sample to be tested, respectively forming the first feedback light and the second feedback light. The second feedback light is filtered using a first filter; A first image sensor is used to convert the first feedback light transmitted through the first filter into a first electrical signal; The photoacoustic signal ΔR / R corresponding to the characteristic delay of the first pattern layer is obtained based on the first electrical signal. ΔR represents the intensity difference of the first feedback light when there is pulsed pump light excitation and when there is no pulsed pump light excitation, and R represents the intensity of the first feedback light when there is no pulsed pump light excitation.

8. The measurement method based on wide-field picosecond ultrasound imaging according to claim 7, characterized in that, Also includes: After adjusting the delay of the pulse probe light and the pulse pump light, the pulse probe light is modulated. The probe pulses in the modulated pulse probe light are set in multiple consecutive characteristic periods. The characteristic periods include a first sub-stage, a second sub-stage, a third sub-stage, and a fourth sub-stage with the same duration. The modulated pulse probe light includes multiple probe pulses with a first pulse interval in the first sub-stage, the second sub-stage, and the third sub-stage. The modulated pulse probe light includes a first probe pulse group and a second probe pulse group in the fourth sub-stage. There is a first pulse interval between adjacent probe pulses in the first probe pulse group, a first pulse interval between adjacent probe pulses in the second probe pulse group, and a second pulse interval between the first probe pulse group and the second probe pulse group. The second pulse interval is greater than the first pulse interval. The pulsed pump light is modulated, and the pump pulse in the modulated pulsed pump light is set in multiple consecutive characteristic periods. The modulated pulsed pump light includes multiple pump pulses with a first pulse interval in the first sub-stage, and there are no pump pulses in the second, third and fourth sub-stages. The process of obtaining the photoacoustic signal ΔR / R corresponding to the characteristic delay of the first pattern layer based on the first electrical signal includes: generating a first modulation signal u1(t) and a second modulation signal u2(t), both of which have a characteristic period T; The first modulated electrical signal is obtained by multiplying the first electrical signal and the first modulated signal u1(t); The second modulated electrical signal is obtained by multiplying the first electrical signal and the second modulated signal u2(t); The first modulation signal of the first sub-stage and the first modulation signal of the third sub-stage are added together to obtain ΔR; The second modulation signal of the second sub-stage and the second modulation signal of the fourth sub-stage are added together to obtain R; Where t5-t1=T; the first sub-stage is (t1+kT,t2+kT], the second sub-stage is (t2+kT,t3+kT], the third sub-stage is (t3+kT,t4+kT], and the fourth sub-stage is (t4+kT,t5+kT]; k is an integer greater than or equal to 0.

9. The measurement method based on wide-field picosecond ultrasound imaging according to claim 7, characterized in that, Forming a pulsed probe light and a pulsed pump light with a time delay includes: forming a pulsed probe light with a first repetition frequency; and forming a pulsed pump light with a second repetition frequency.

10. The measurement method based on wide-field picosecond ultrasound imaging according to claim 7, characterized in that, Also includes: A first test image of the first pattern layer is generated based on the photoacoustic signal ΔR / R; Acquire a second test image of the second patterned layer located above the light-shielding layer in the sample to be tested; The overlay error of the first pattern layer and the second pattern layer is obtained based on the first test image and the second test image.

Images