Film layer measuring method and device

Abstract

The invention relates to the technical field of semiconductor measurement, in particular to a film layer measuring method and device, and the method comprises the steps: employing pump light to irradiate a measurement position of a to-be-measured sample; the probe light is split into first probe light and second probe light, the first probe light is adopted to irradiate the measurement position, the second probe light is adopted to irradiate the adjacent position of the to-be-measured sample, and the adjacent position and the measurement position are not overlapped; the first detection light is reflected by a measurement position to form first signal light, and the second detection light is reflected by an adjacent position to form second signal light; performing photoelectric conversion on the first signal light to obtain a first signal, and performing photoelectric conversion on the second signal light to obtain a second signal; demodulating the first signal to obtain an initial echo signal, demodulating the second signal to obtain a noise signal, obtaining an echo signal according to the initial echo signal and the noise signal, and obtaining the film property of the sample to be detected based on the echo signal. The invention is at least beneficial to improving the measurement precision of the film property.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor measurement technology, and particularly relates to a method and apparatus for film measurement. Background Technology

[0002] When measuring film thickness using photoacoustic film thickness measurement, the pump light needs to irradiate the sample surface to excite the sample to generate heat, which in turn produces thermoelastic deformation. The thermoelastic deformation generates ultrasonic waves within the sample. The generated ultrasonic waves propagate longitudinally back and forth in the film. When they propagate to the upper surface of the sample, they cause a change in the reflectivity of the upper surface and a slight deformation. The change in reflectivity or deformation of the upper surface can be detected by the probe light. Therefore, an echo signal can be generated by irradiating the position of the pump light by a beam of probe light passing through a time delay line to measure the properties of the film layer.

[0003] However, when photoacoustic film thickness measurement is used to measure films of different thicknesses or with low damage resistance thresholds, the continuous laser irradiation can cause the accumulation of thermal effects on the sample surface. Therefore, thermal noise is introduced when the probe light detects the echo signal. At the same time, due to the influence of the transmission optical path, the probe light itself also has problems such as spot jitter and power fluctuation, which also introduce measurement noise during the measurement process. In summary, there is an urgent need for a method to eliminate noise to improve the signal-to-noise ratio of the measured echo signal, thereby improving the measurement accuracy. Summary of the Invention

[0004] In view of this, the present invention aims to provide a film measurement method and apparatus that at least helps to improve the signal-to-noise ratio of the echo signal, thereby improving the measurement accuracy of film properties.

[0005] To achieve the above objectives, the technical solution created by this invention is implemented as follows: This invention provides a film measurement method, comprising: illuminating a measurement position of a sample under test with pump light; splitting a probe light into a first probe light and a second probe light, illuminating the measurement position with the first probe light and illuminating an adjacent position of the sample under test with the second probe light, wherein the adjacent position and the measurement position do not overlap; the first probe light being reflected by the measurement position to form a first signal light, and the second probe light being reflected by the adjacent position to form a second signal light; performing photoelectric conversion on the first signal light to obtain a first signal, and performing photoelectric conversion on the second signal light to obtain a second signal; demodulating the first signal to obtain an initial echo signal, demodulating the second signal to obtain a noise signal, obtaining an echo signal based on the initial echo signal and the noise signal, and obtaining the film properties of the sample under test based on the echo signal.

[0006] Furthermore, demodulating the first signal to obtain the initial echo signal includes: demodulating the first signal at the frequency of the pump light to obtain the initial echo signal; demodulating the second signal to obtain the noise signal includes: demodulating the second signal at the frequency of the probe light to obtain the noise signal.

[0007] Furthermore, the film properties of the sample to be tested include the film thickness of the sample to be tested.

[0008] Furthermore, obtaining the film thickness of the sample under test based on the echo signal includes obtaining the film thickness based on the time interval between two adjacent light intensity peaks of the echo signal.

[0009] Furthermore, the distance between adjacent positions and the measurement position is not greater than a preset value, which is equal to the diameter of the spot formed by the first probe light at the measurement position, or the preset value is equal to the diameter of the spot formed by the second probe light at the adjacent position.

[0010] Furthermore, the probe light and pump light have a time delay, which gradually increases or decreases over time.

[0011] Furthermore, the polarization state of the first probe light is the same as that of the second probe light.

[0012] Furthermore, obtaining the echo signal based on the initial echo signal and the noise signal includes obtaining the echo signal based on the differential signal between the initial echo signal and the noise signal.

[0013] In another aspect, this invention provides a film measurement device for implementing the aforementioned film measurement method. The film measurement device includes: a light source emitting pump light and probe light, the pump light illuminating the measurement position of the sample under test; a beam splitter splitting the probe light into a first probe light and a second probe light, the first probe light illuminating the measurement position, and the second probe light illuminating an adjacent position of the sample under test, the adjacent position not overlapping with the measurement position; a signal receiver receiving a first signal light formed by reflection of the first probe light from the measurement position and generating a first signal, and receiving a second signal light formed by reflection of the second probe light from an adjacent position and generating a second signal; and a signal processing module configured to at least: demodulate the first signal to obtain an initial echo signal, demodulate the second signal to obtain a noise signal, obtain an echo signal based on the initial echo signal and the noise signal, and then obtain the film properties of the sample under test based on the echo signal.

[0014] Furthermore, the film measurement device also includes a retroreflector, which is located in the transmission optical path of the probe light or in the transmission optical path of the pump light. The retroreflector moves back and forth in a preset direction to delay the probe light or pump light, and the time delay gradually increases or decreases over time.

[0015] Furthermore, the film measurement device also includes a first half-wave plate, which converts the polarization state of the first probe light or the polarization state of the second probe light so that the polarization state of the first probe light and the polarization state of the second probe light are the same.

[0016] Furthermore, the signal receiver includes a first detector and a second detector, the first detector being used to receive the first signal light and generate a first signal, and the second detector being used to receive the second signal light and generate a second signal.

[0017] Furthermore, the signal processing module includes a signal generator, a lock-in amplifier, and a data processing unit. The lock-in amplifier receives a first signal, a second signal, and a reference signal output by the signal generator. Based on the reference signal, the lock-in amplifier demodulates the first signal at the frequency of the pump light to obtain an initial echo signal, and demodulates the second signal at the frequency of the probe light to obtain a noise signal. The data processing unit receives the initial echo signal and the noise signal and performs differential processing to obtain an echo signal, and then obtains the film properties of the sample under test based on the echo signal.

[0018] Compared with existing technologies, the present invention achieves the following beneficial effects: The film thickness measurement method provided by the present invention is a photoacoustic film thickness measurement method based on dual-probe optical paths. Compared with traditional photoacoustic film thickness measurement methods, the present invention splits the probe light into a first probe light and a second probe light. The first probe light is used to illuminate the measurement position illuminated by the pump light, and the second probe light is used to illuminate the adjacent position adjacent to the measurement position. In this way, the first signal light formed by the reflection of the first probe light at the measurement position can be obtained by photoelectric conversion and signal demodulation of the first signal light, and an initial echo signal containing probe light noise can be obtained. The second signal light formed by the reflection of the second probe light at the adjacent position can be obtained by photoelectric conversion and signal demodulation of the second signal light, and a noise signal can be obtained. The noise signal is the probe light noise. Thus, the initial echo signal minus the noise signal can obtain an echo signal with probe light noise eliminated. Based on the echo signal, more accurate film properties can be measured, the influence of thermal effect noise introduced by the long-term laser irradiation of the sample under test during the measurement process can be alleviated, the probe light noise in the echo signal is greatly reduced, and the signal-to-noise ratio of the echo signal is effectively improved. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram illustrating the positional relationship between the measurement position and adjacent positions as described in the embodiments of the present invention. Figure 2This is a schematic diagram of the structure of the film measurement device described in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0022] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] This invention provides a film measurement method, comprising: illuminating a measurement position of a sample under test with pump light; splitting a probe light into a first probe light and a second probe light, illuminating the measurement position with the first probe light and illuminating an adjacent position of the sample under test with the second probe light, wherein the adjacent position and the measurement position do not overlap; the first probe light being reflected by the measurement position to form a first signal light, and the second probe light being reflected by the adjacent position to form a second signal light; performing photoelectric conversion on the first signal light to obtain a first signal, and performing photoelectric conversion on the second signal light to obtain a second signal; demodulating the first signal to obtain an initial echo signal, demodulating the second signal to obtain a noise signal, obtaining an echo signal based on the initial echo signal and the noise signal, and obtaining the film properties of the sample under test based on the echo signal.

[0026] The first and second probe lights have the same wavelength and frequency.

[0027] In some embodiments, the probe beam needs to be split into a first probe beam and a second probe beam that are parallel to each other.

[0028] In some embodiments, the sample to be tested can be a wafer.

[0029] In some embodiments, obtaining the echo signal based on the initial echo signal and the noise signal includes obtaining the echo signal based on the differential signal between the initial echo signal and the noise signal.

[0030] In some embodiments, demodulating the first signal to obtain an initial echo signal includes: demodulating the first signal at the frequency of the pump light to obtain the initial echo signal; demodulating the second signal to obtain a noise signal includes: demodulating the second signal at the frequency of the probe light to obtain the noise signal. It should be noted that the illumination position of the first probe light coincides with the illumination position of the pump light, and the initial echo signal obtained by demodulating the first signal at the frequency of the pump light is an echo signal carrying probe light noise, which includes echo information reflecting the film properties and probe light noise information; while the illumination position of the second probe light does not coincide with the illumination position of the pump light at all. Therefore, the second signal demodulated at the frequency of the probe light only contains the same probe light noise information as the first signal, and does not contain echo information reflecting the film properties. This signal can be used as a noise signal reflecting the probe light noise.

[0031] In some embodiments, the film properties of the sample to be tested include the film thickness of the sample to be tested.

[0032] In some embodiments, obtaining the film thickness of the sample under test based on the echo signal includes obtaining the film thickness based on the time interval between two adjacent light intensity peaks of the echo signal.

[0033] The echo signal exists in spectral form. In some cases, the time interval between two adjacent light intensity peaks of the echo signal can be calculated using a peak-finding algorithm. Then, the film thickness can be calculated based on the following film thickness calculation formula: Where Δt represents the time interval, The speed at which ultrasound propagates within the membrane layer. This represents the thickness of the film layer.

[0034] In some embodiments, the distance between adjacent positions and the measurement position is no greater than a preset value, which is equal to the spot diameter formed by the first probe light at the measurement position, or the preset value is equal to the spot diameter formed by the second probe light at the adjacent position. It should be noted that when the surface roughness of the sample to be tested is poorly uniform, if the distance between adjacent positions and the measurement position is too large, it may lead to a significant difference between the measurement position and the adjacent positions. This would result in a significant difference between the acquired noise signal and the probe light noise in the initial echo signal, thus introducing additional noise during the denoising process or failing to effectively remove the probe light noise in the initial echo signal. Therefore, setting the distance between adjacent positions and the measurement position to a preset value or less than the preset value helps to ensure effective removal of probe light noise in the initial echo signal and avoids introducing additional noise.

[0035] It should be noted that there is no minimum requirement for the distance between adjacent positions and the measurement position, as long as the adjacent positions and the measurement position do not overlap at all.

[0036] In some embodiments, reference Figure 1 The adjacent positions can be the first adjacent position 3 above the measurement position 1, the second adjacent position 5 below the measurement position, the third adjacent position 2 to the left of the measurement position, or the fourth adjacent position 4 to the right of the measurement position.

[0037] In some embodiments, the probe light and the pump light have a time delay, which gradually increases or decreases over time.

[0038] In some embodiments, the polarization state of the first probe light and the polarization state of the second probe light are the same. It should be noted that the polarization state of the first probe light is different from that of the pump light. Therefore, during detection, the pump light can be polarized before the detector to filter out stray light from the pump light, thereby preventing stray light from interfering with the first signal light. Similarly, to prevent stray light from the pump light from interfering with the second signal light, the second probe light and the pump light also need to be designed with different polarization states. Therefore, the polarization states of the first probe light and the second probe light are the same.

[0039] In some embodiments, the power of the first probe light and the power of the second probe light may be the same or different.

[0040] It should be noted that when measuring the film thickness of films made of different materials, since the reflectivity of different material surfaces is different, the splitting ratio of the first probe light and the second probe light can be adjusted according to the material of the film layer to balance the power of the first probe light and the second probe light, so that the signal ratio of the first signal and the second signal is balanced, thereby outputting an echo signal with a better signal-to-noise ratio. The splitting ratio of the first probe light and the second probe light needs to be determined according to the actual material, type and thickness of the film layer. This invention does not limit the splitting ratio of the first probe light and the second probe light.

[0041] In another aspect, the present invention provides a film measurement device for implementing the above-described film measurement method. The same or similar parts as those described above can be referred to the foregoing embodiments, and will not be repeated here.

[0042] refer to Figure 2 The film measurement device includes: a light source emitting pump light and probe light, the pump light illuminating the measurement position of the sample 18 under test; a beam splitter splitting the probe light into a first probe light and a second probe light, the first probe light illuminating the measurement position and the second probe light illuminating an adjacent position of the sample 18 under test, the adjacent position and the measurement position not overlapping; a signal receiver receiving a first signal light formed by the reflection of the first probe light from the measurement position and generating a first signal, and receiving a second signal light formed by the reflection of the second probe light from an adjacent position and generating a second signal; and a signal processing module configured to at least: demodulate the first signal to obtain an initial echo signal, demodulate the second signal to obtain a noise signal, obtain an echo signal based on the initial echo signal and the noise signal, and then obtain the film properties of the sample 18 under test based on the echo signal.

[0043] In some embodiments, the film measurement device further includes a first mirror group and a second mirror group. A first probe light illuminates the measurement position after passing through the first mirror group, and a second probe light illuminates an adjacent position after passing through the second mirror group. In some examples, the first probe light passing through the first mirror group and the second probe light passing through the second mirror group can be parallel to each other.

[0044] In some embodiments, the light source includes an ultrashort pulse laser source 10, a second half-wave plate 11, and a first polarization beam splitter 12. The beam emitted by the ultrashort pulse laser source 10 is split into probe light and pump light after passing through the second half-wave plate 11 and the first polarization beam splitter 12.

[0045] In some embodiments, the pump light passes through the modulation device 13, the second reflector 14, the third reflector 15, the fourth reflector 16, and the third scanning mirror 17 before entering the measurement position. It is understood that this embodiment is merely an example, and the number and arrangement of reflectors in the pump light transmission path can be designed according to actual needs, as long as the pump light can be guided to the measurement position of the sample 18 under test.

[0046] In some embodiments, the beam-splitting element includes a third half-wave plate 26 and a second polarization beam splitter 27 arranged sequentially along the transmission direction of the probe light.

[0047] In some embodiments, the film measurement device further includes a retroreflector 25, which is located in the transmission optical path of the probe light or in the transmission optical path of the pump light. The retroreflector 25 moves back and forth in a preset direction to delay the probe light or the pump light, and the time delay gradually increases or decreases over time.

[0048] In some embodiments, a high-precision linear electric displacement stage can be used to drive the retroreflector 25 to move back and forth along a preset direction. The present invention does not limit the preset direction, as long as the retroreflector 25 can perform a time delay on the probe light or pump light. In some embodiments, the retroreflector 25 may not be used, and the delay can be achieved by frequency modulation of the probe light and pump light.

[0049] In some embodiments, the film measurement device further includes a first half-wave plate 29, which converts the polarization state of the first probe light or the polarization state of the second probe light so that the polarization state of the first probe light and the polarization state of the second probe light are the same.

[0050] It should be noted that the beam emitted by the ultrashort pulse laser source 10 is linearly polarized light. After passing through the second half-wave plate 11, the linearly polarized light is converted into elliptically polarized light. After passing through the first polarization beam splitter 12, the probe light and pump light formed by the elliptically polarized light are both linearly polarized light. The probe light is converted into elliptically polarized light after passing through the third half-wave plate 26, and then passes through the second polarization beam splitter 27 to obtain two beams of linearly polarized light with mutually perpendicular deflection directions. Among them, one linearly polarized light passes through the first half-wave plate 29 to obtain two beams with the same polarization direction, namely the first probe light and the second probe light.

[0051] In some embodiments, the first mirror group includes a first scanning mirror 30, and the first probe light emitted from the beam splitter is guided by the first scanning mirror 30 to illuminate the measurement position; the second mirror group includes a first reflecting mirror 28 and a second scanning mirror 31, and the second probe light emitted from the beam splitter is guided by the first reflecting mirror 28 and the second scanning mirror 31 in sequence to illuminate adjacent positions.

[0052] In some implementations, the first half-wave plate 29 can be located in the transmission optical path of the second probe light. Specifically, the first half-wave plate 29 can be located between the first reflector 28 and the second scanning mirror 31.

[0053] When measuring the sample 18, the pump light and the first probe light can be simultaneously incident on the same measurement point (i.e., measurement position) on the surface of the sample 18 by adjusting the deflection angle of the first scanning mirror 30, the deflection angle of the second scanning mirror 31, and the deflection angle of the third scanning mirror 17, and the second probe light can be irradiated on the adjacent position adjacent to the measurement position.

[0054] In some embodiments, the first signal light formed by the reflection of the first probe light at the measurement position and the second signal light formed by the reflection of the second probe light at an adjacent position are both reflected by the fifth reflector 19 and then incident on the signal receiver.

[0055] In some embodiments, the signal receiver includes a first detector 21 and a second detector 20, wherein the first detector 21 is used to receive a first signal light and generate a first signal, and the second detector 20 is used to receive a second signal light and generate a second signal.

[0056] In some embodiments, the signal processing module includes a signal generator 23, a lock-in amplifier 22, and a data processing unit 24. The lock-in amplifier 22 receives a first signal, a second signal, and a reference signal output by the signal generator 23. Based on the reference signal, the lock-in amplifier 22 demodulates the first signal at the frequency of the pump light to obtain an initial echo signal, and demodulates the second signal at the frequency of the probe light to obtain a noise signal. The data processing unit 24 receives the initial echo signal and the noise signal and performs differential processing to obtain an echo signal, and then obtains the film properties of the sample 18 under test based on the echo signal.

[0057] In some embodiments, the signal generator 23 also sends a second reference signal to the modulator 13 to modulate the pump light.

[0058] The film measurement method and apparatus provided by this invention obtain a first probe light and a second probe light with the same transmission direction by beam splitting, realizing simultaneous measurement of the measurement position and adjacent positions. Two detectors receive the first signal light and the second signal light to obtain a first signal and a second signal. The first and second signals are demodulated by a lock-in amplifier to obtain a noise signal and an initial echo signal containing the noise signal. Subtracting the noise signal from the initial echo signal yields an echo signal with a high signal-to-noise ratio, effectively mitigating the influence of probe light thermal effect noise and measurement noise, and improving the signal-to-noise ratio of the echo signal. Furthermore, the power ratio of the first probe light to the second probe light is adjustable, as are the deflection angle of the first probe light and the polarization angle of the second probe light, making it applicable to film measurements of different materials and thicknesses. The adjustable deflection angle and polarization angle of the first probe light are achieved by synchronously adjusting the deflection angle and polarization angle of the second probe light, based on the condition that "the polarization directions of the pump light and the probe light are perpendicular, and the polarization directions of the first and second probe lights are the same."

[0059] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0060] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for measuring film layers, characterized in that, include: The measurement location of the sample is illuminated by a pump light; The probe light is split into a first probe light and a second probe light. The first probe light is used to illuminate the measurement position, and the second probe light is used to illuminate the adjacent positions of the sample to be tested. The adjacent positions do not overlap with the measurement position. The first probe light is reflected at the measurement position to form a first signal light, and the second probe light is reflected at the adjacent position to form a second signal light; The first signal light is photoelectrically converted to obtain a first signal, and the second signal light is photoelectrically converted to obtain a second signal; The first signal is demodulated to obtain an initial echo signal, the second signal is demodulated to obtain a noise signal, an echo signal is obtained based on the initial echo signal and the noise signal, and the film properties of the sample under test are obtained based on the echo signal.

2. The film measurement method according to claim 1, characterized in that, Demodulating the first signal to obtain the initial echo signal includes: demodulating the first signal at the frequency of the pump light to obtain the initial echo signal; Demodulating the second signal to obtain a noise signal includes: demodulating the second signal at the frequency of the probe light to obtain a noise signal.

3. The film measurement method according to claim 1, characterized in that, The film properties of the sample to be tested include the film thickness of the sample to be tested.

4. The film measurement method according to claim 3, characterized in that, Obtaining the film thickness of the sample under test based on the echo signal includes: obtaining the film thickness based on the time interval between two adjacent light intensity peaks of the echo signal.

5. The film measurement method according to claim 1, characterized in that, The distance between the adjacent position and the measurement position is not greater than a preset value, the preset value being equal to the diameter of the spot formed by the first probe light at the measurement position, or the preset value being equal to the diameter of the spot formed by the second probe light at the adjacent position.

6. The film measurement method according to claim 1, characterized in that, The probe light and the pump light have a time delay, which gradually increases or decreases over time.

7. The film measurement method according to claim 1, characterized in that, The polarization state of the first probe light is the same as that of the second probe light.

8. The film measurement method according to claim 1, characterized in that, Obtaining the echo signal based on the initial echo signal and the noise signal includes: obtaining the echo signal based on the differential signal between the initial echo signal and the noise signal.

9. A film layer measuring device, characterized in that, The film measurement device is used to implement the film measurement method according to any one of claims 1 to 8, and the film measurement device comprises: A light source that emits pump light and probe light, wherein the pump light illuminates the measurement position of the sample to be tested; A beam splitter element splits the probe light into a first probe light and a second probe light. The first probe light illuminates the measurement position, and the second probe light illuminates an adjacent position of the sample to be tested. The adjacent position does not overlap with the measurement position. A signal receiver, wherein the signal receiver receives a first signal light formed by the reflection of the first probe light at the measurement position and generates a first signal, and receives a second signal light formed by the reflection of the second probe light at the adjacent position and generates a second signal; The signal processing module is configured to at least: demodulate the first signal to obtain an initial echo signal, and demodulate the second signal to obtain a noise signal, obtain an echo signal based on the initial echo signal and the noise signal, and then obtain the film properties of the sample under test based on the echo signal.

10. The film layer measuring device according to claim 9, characterized in that, The film measurement device further includes a retroreflector, which is located in the transmission optical path of the probe light or the transmission optical path of the pump light. The retroreflector moves back and forth in a preset direction to delay the probe light or the pump light, and the time delay gradually increases or decreases over time.

11. The film layer measuring device according to claim 9, characterized in that, The film measurement device further includes a first half-wave plate, which converts the polarization state of the first probe light or the polarization state of the second probe light so that the polarization state of the first probe light and the polarization state of the second probe light are the same.

12. The film layer measuring device according to claim 9, characterized in that, The signal receiver includes a first detector and a second detector. The first detector is used to receive the first signal light and generate a first signal, and the second detector is used to receive the second signal light and generate a second signal.

13. The film layer measuring device according to claim 9, characterized in that, The signal processing module includes a signal generator, a lock-in amplifier, and a data processing unit. The lock-in amplifier receives the first signal, the second signal, and a reference signal output by the signal generator. Based on the reference signal, the lock-in amplifier demodulates the first signal at the frequency of the pump light to obtain an initial echo signal, and demodulates the second signal at the frequency of the probe light to obtain a noise signal. The data processing unit receives the initial echo signal and the noise signal and performs differential processing to obtain the echo signal, and then obtains the film properties of the sample under test based on the echo signal.

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