Metal film thickness measuring method, device and system

Abstract

The embodiment of the invention discloses a method, a device and a system for measuring the thickness of a metal film. The method for measuring the thickness of the metal film comprises the following steps of: performing frequency modulation on pump light according to a first reference signal with a first frequency to obtain modulated pump light; performing frequency modulation on the probe light according to a second reference signal with a second frequency to obtain modulated probe light, wherein the second frequency is different from the first frequency; performing frequency mixing processing on the first reference signal and the second reference signal to obtain a frequency-mixed reference signal; receiving reflected probe light in reflected light obtained by reflecting the modulated pump light and the modulated probe light on the surface of the metal film to be detected; performing conversion demodulation processing on the reflected detection light according to the frequency-mixed reference signal to obtain a demodulated detection signal; and determining the thickness of the metal film to be detected according to the demodulated detection signal. According to the embodiment of the invention, the signal-to-noise ratio of the detection signal is improved through the pump light and the detection light with different frequencies.

Description

Technical Field

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

[0002] At present, the thickness of metal films on semiconductor wafers is usually measured by laser ultrasonic detection and pump detection. The principle is to generate ultrasound on the metal film to be measured by pump light, and use the image of the laser reflectivity caused by the tiny morphological changes when ultrasound is transmitted and reflected on the surface of the metal film. The detection light is used to detect and scan the change of its reflectivity over time, and the time corresponding to the signal peak can be converted into the thickness of the metal film. Among them, the signal-to-noise ratio of the demodulated detection signal is usually used to measure the quality of the detection result, as well as to determine the key indicators such as the stability and repeatability of the metal film thickness measurement equipment. Conventional metal film thickness measurement equipment usually adopts the pump detection method, adjusts the pump light and the detection light to the same specific frequency, and the pump light and the detection light interact for detection, converts the optical signal formed by the reflection into an electrical signal, and demodulates the electrical signal according to the same frequency through a phase-locked amplifier to obtain the final signal. However, in the actual detection process, due to the roughness of the metal film surface and the influence of diffuse reflection in the spatial structure, the pump light will introduce stray light into the photodetector. Since the stray light has the same frequency, it is difficult to be isolated, resulting in a decrease in the signal-to-noise ratio of the final signal. Summary of the invention

[0003] Therefore, in view of at least some of the shortcomings and defects in the prior art, the embodiments of the present invention provide a metal film thickness measurement method, a metal film thickness measurement device, and a metal film thickness measurement system.

[0004] Specifically, an embodiment of the present invention proposes a method for measuring the thickness of a metal film, comprising: frequency modulating a pump light according to a first reference signal having a first frequency to obtain a modulated pump light; frequency modulating a detection light according to a second reference signal having a second frequency to obtain a modulated detection light, wherein the second frequency is different from the first frequency; mixing the first reference signal and the second reference signal to obtain a mixed reference signal; receiving a reflected detection light in the reflected light obtained by reflecting the modulated pump light and the modulated detection light from the surface of the metal film to be measured; converting and demodulating the reflected detection light according to the mixed reference signal to obtain a demodulated detection signal; and determining the thickness of the metal film to be measured according to the demodulated detection signal.

[0005] In one embodiment of the present invention, the frequency of the mixed reference signal is the sum or difference of the first frequency and the second frequency.

[0006] In one embodiment of the present invention, the first frequency is greater than the second frequency, and the ratio of the first frequency to the second frequency is in the range of (10:1) to (1000:1).

[0007] In one embodiment of the present invention, the reflected light also includes post-reflection pump light; before receiving the post-reflection detection light in the reflected light obtained after the modulated pump light and the modulated detection light are reflected on the surface of the metal film to be measured, the metal film thickness measurement method also includes: blocking the post-reflection pump light in the reflected light.

[0008] In one embodiment of the present invention, the converting and demodulating the reflected detection light according to the mixed reference signal to obtain the demodulated detection signal includes: converting the reflected detection light into a photoelectric signal to obtain the converted detection signal; and demodulating the converted detection signal according to the mixed reference signal to obtain the demodulated detection signal.

[0009] In one embodiment of the present invention, determining the thickness of the metal film to be measured based on the demodulated detection signal includes: obtaining the signal peak time of the demodulated detection signal; and determining the thickness of the metal film to be measured based on the propagation speed and peak time of the ultrasound generated by the modulated pump light irradiating the metal film to be measured.

[0010] In addition, a metal film thickness measuring device proposed in an embodiment of the present invention includes: a first modulation module, used to frequency modulate the pump light according to a first reference signal with a first frequency to obtain a modulated pump light; a second modulation module, used to frequency modulate the detection light according to a second reference signal with a second frequency to obtain a modulated detection light, wherein the second frequency is different from the first frequency; a signal control module, used to mix the first reference signal and the second reference signal to obtain a mixed reference signal; a detection module, used to receive the reflected detection light in the reflected light obtained by reflecting the modulated pump light and the modulated detection light on the surface of the metal film to be measured; a demodulation module, used to convert and demodulate the reflected detection light according to the mixed reference signal to obtain a demodulated detection signal; and a data processing module, used to determine the thickness of the metal film to be measured according to the demodulated detection signal.

[0011] In one embodiment of the present invention, the reflected light further includes post-reflection pump light; and the metal film thickness measurement device further includes: a blocking module for blocking the post-reflection pump light in the reflected light.

[0012] In one embodiment of the present invention, the demodulation module includes: a photoelectric conversion unit, which is used to perform photoelectric signal conversion processing on the reflected detection light to obtain a converted detection signal; and a signal demodulation unit, which is used to demodulate the converted detection signal according to the mixed reference signal to obtain the demodulated detection signal.

[0013] In addition, a metal film thickness measurement system proposed in an embodiment of the present invention includes: a laser for emitting laser; a spectroscopic component for performing spectroscopic processing on the laser to obtain pump light and detection light; a first modulator for frequency-modulating the pump light according to a first reference signal having a first frequency to obtain modulated pump light; a second modulator for frequency-modulating the detection light according to a second reference signal having a second frequency to obtain modulated detection light, wherein the second frequency is different from the first frequency; a function generator for mixing the first reference signal and the second reference signal to obtain a mixed reference signal; a detection component for receiving reflected detection light in the reflected light obtained by reflecting the modulated pump light and the modulated detection light from the surface of the metal film to be measured; a phase-locked amplifier for converting and demodulating the reflected detection light according to the mixed reference signal to obtain a demodulated detection signal; and a data processing device for determining the thickness of the metal film to be measured according to the demodulated detection signal.

[0014] It can be seen from the above that the above technical features of the present invention can have one or more of the following beneficial effects: a metal film thickness measurement method, device and system proposed in an embodiment of the present invention, by frequency-modulating the pump light and the detection light respectively according to reference signals of different frequencies, irradiating the modulated pump light and the modulated detection light onto the surface of the metal film to be measured for detection, and obtaining the reflected detection light in the reflected light; since the frequencies of the modulated pump light and the modulated detection light are different, the stray light introduced by the reflected pump light is different from the frequency of the reflected detection light; when the reflected detection light is demodulated according to the mixed reference signal, the influence of the stray light on the detection signal can be effectively reduced, and the signal-to-noise ratio of the detection signal can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0016] Figure 1 A schematic flow chart of a method for measuring the thickness of a metal film provided in accordance with the first embodiment of the present invention.

[0017] Figure 2 A schematic flow chart of another method for measuring the thickness of a metal film provided in the first embodiment of the present invention.

[0018] Figure 3 for Figure 1 A detailed flowchart of step S19 is shown in FIG.

[0019] Figure 4 for Figure 1 Detailed flowchart of step S21 is shown in FIG.

[0020] Figure 5 A schematic structural diagram of components of a metal film thickness measurement system provided by an embodiment of the present invention.

[0021] Figure 6 for Figure 5 Schematic diagram of the working process of the metal film thickness measurement system shown in FIG.

[0022] Figure 7a It is a waveform diagram of the demodulated detection signal without irradiating the metal film to be tested.

[0023] Figure 7b Schematic diagram of the waveform of the demodulated detection signal irradiated to the metal film to be tested.

[0024] Figure 8a A schematic diagram of a metal film thickness measuring device according to a second embodiment of the present invention

[0025] Figure 8b FIG. 4 is a schematic structural diagram of another metal film thickness measuring device according to the second embodiment of the present invention.

[0026] Fig. 9 for Figure 8a A structural schematic diagram of the demodulation module is shown in FIG. DETAILED DESCRIPTION

[0027] The technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiment of the present invention. The specific structural and functional details disclosed here are only representative and are for the purpose of describing the exemplary embodiments of the present invention. However, the present invention can be specifically implemented in many alternative forms and should not be interpreted as being limited to the embodiments described here. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0028] [First embodiment]

[0029] like Figure 1As shown, a method for measuring the thickness of a metal film provided by a first embodiment of the present invention includes, for example, the following steps:

[0030] S11: frequency modulating the pump light according to a first reference signal having a first frequency to obtain modulated pump light;

[0031] S13: frequency modulating the detection light according to a second reference signal having a second frequency to obtain modulated detection light, wherein the second frequency is different from the first frequency;

[0032] S15: Mixing the first reference signal and the second reference signal to obtain a mixed reference signal;

[0033] S17: receiving reflected detection light from among the reflected lights obtained by reflecting the modulated pump light and the modulated detection light from the surface of the metal film to be tested;

[0034] S19: converting and demodulating the reflected detection light according to the mixed reference signal to obtain a demodulated detection signal;

[0035] S21: Determine the thickness of the metal film to be measured according to the demodulated detection signal.

[0036] Specifically, the frequency of the mixed reference signal is the sum or difference of the first frequency and the second frequency.

[0037] In addition, the first frequency is greater than the first frequency, and a ratio of the first frequency to the first frequency is in a range of (10:1) to (1000:1).

[0038] Furthermore, the reflected light also includes reflected pump light. Figure 2 As shown, before receiving the reflected detection light in the reflected light obtained after the modulated pump light and the modulated detection light are reflected by the surface of the metal film to be measured, the metal film thickness measurement method of this embodiment further includes the steps of:

[0039] S16: Blocking the post-reflection pump light in the reflected light.

[0040] Furthermore, if Figure 3 As shown, in the metal film thickness measurement method of this embodiment, step S19 includes, for example:

[0041] S191: performing photoelectric signal conversion processing on the reflected detection light to obtain a converted detection signal;

[0042] S193: Demodulate the converted detection signal according to the mixed reference signal to obtain the demodulated detection signal.

[0043] Furthermore, if Figure 4 As shown, step S21 specifically includes, for example:

[0044] S211: Acquire the signal peak time of the demodulated detection signal;

[0045] S213: Determine the thickness of the metal film to be measured according to the propagation speed of ultrasound generated by the modulated pump light irradiating the metal film to be measured and the peak time.

[0046] To facilitate a clearer understanding of the metal film thickness measurement method of this embodiment, the following will be combined with Figure 5-7b Provide detailed explanation with examples.

[0047] The metal film thickness measurement method provided in the embodiment of the present invention can be applied to a metal film thickness measurement system, for example. The metal film thickness measurement system can be used to measure the thickness of a metal film on a semiconductor wafer. Specifically, Figure 5 As shown, the metal film thickness measurement system involved in the first embodiment of the present invention includes, for example, a laser 110, a spectrometer component 120, a first modulator 130, a second modulator 140, a function generator 150, a detection component 160, a phase-locked amplifier 170 and a data processing device 180.

[0048] Among them, Figure 5 , Figure 6 As shown, the laser 110 is used to emit laser light to the spectroscopic component 120. The spectroscopic component 120, for example, includes a spectroscope for splitting the laser light, and the laser light is split by the spectroscopic component 120 to obtain pump light and detection light. The first modulator 130 and the second modulator 140 are, for example, signal modulators such as a chopper, an acousto-optic modulator or an electro-optic modulator, and are used to modulate the optical signal according to the reference signal. The first modulator 130 and the second modulator 140 are, for example, electrically connected to the function generator 150. The function generator 150 is, for example, a multi-waveform signal source, and is used to generate the first reference signal and the second reference signal, and the user can, for example, adjust and output the first reference signal and the second reference signal through the function generator 150. The function generator 150, for example, transmits the first reference signal to the first modulator 130, and transmits the second reference signal to the second modulator 140. The first reference signal is, for example, a carrier signal with a first frequency ω1, and the second reference signal is, for example, a carrier signal with a second frequency ω2. Further, the first modulator 130 is used to frequency modulate the pump light according to the first reference signal to obtain modulated pump light, and the frequency of the modulated pump light is the first frequency ω1; the second modulator 140 is used to frequency modulate the detection light according to the second reference signal to obtain the detection light of the second frequency, and the frequency of the detection light of the second frequency is the second frequency ω2, wherein the second frequency ω2 is different from the first frequency ω1.

[0049] In other embodiments of the present invention, Figure 5 , Figure 6 As shown, the metal film thickness measurement system also includes a delay component 121 and a focusing collimation component 190. The detection light after the laser is split by the splitter component 120 enters the delay component 121, so that a time difference is formed between the detection light and the pump light, and the detection light is delayed relative to the pump light. The metal film thickness measurement system is provided with a pump light transmission component 131 and a detection light transmission component 141, and the pump light and the detection light are modulated by the first modulator 130 and the second modulator 140 respectively, and the modulated pump light is transmitted to the focusing collimation component 190 through the pump light transmission component 131, and the modulated detection light is transmitted to the focusing collimation component 190 through the detection light transmission component 141.

[0050] Further, the modulated pump light and the modulated detection light are focused by the focusing and collimating component 190 and then sequentially irradiated onto the surface of the metal film 100 to be tested. The metal film 100 to be tested is, for example, disposed on the surface of a substrate 200 of a semiconductor wafer. The modulated pump light is used to excite ultrasound in the metal film 100 to be tested, and the ultrasound is transmitted and reflected in the metal film 100 to be tested, so that the surface of the substrate 200 undergoes morphological changes. The modulated detection light is irradiated onto the surface of the metal film 100 to be tested with a delay relative to the modulated pump light, and the reflectivity of the light changes. The modulated detection light is used to detect the surface of the metal film 100 to be tested after the modulated pump light excites ultrasound. Afterwards, the modulated pump light and the modulated detection light are reflected by the surface of the metal film 100 to be tested to form reflected light, and the reflected light is received by the detection component 160 after, for example, passing through another focusing and collimating component 190. The reflected light, for example, includes reflected pump light and reflected detection light, wherein the reflected detection light is affected by stray light, which is generated by the modulated pump light being affected by the roughness of the surface of the metal film 200 to be tested and the diffuse reflection in the spatial structure, and the frequency of the stray light is, for example, the first frequency ω1.

[0051] Wherein, the first frequency is greater than the second frequency, and the ratio of the first frequency to the second frequency is in the range of (10:1) to (1000:1). The function generator 150 is also used, for example, to perform mixing processing on the first reference signal and the second reference signal to obtain a mixed reference signal. Since the frequency of the first reference signal is the first frequency ω1, and the frequency of the second reference signal is the second frequency ω2, according to the principle of signal mixing, the first reference signal is multiplied by the second mixing signal to obtain a high-frequency or low-frequency mixed reference signal, and the frequency of the mixed reference signal obtained after the mixing processing is the sum ω1+ω2 of the first frequency ω1 and the second frequency ω2, or the difference ω1-ω2 between the first frequency ω1 and the second frequency ω2.

[0052] Furthermore, if Figure 5 , Figure 6As shown, the metal film thickness measurement system further includes, for example, a blocking component 210 and an optoelectronic signal converter 171. The blocking component 210 is, for example, a polarizer component, and the blocking component 210 is used to limit the reflected light. The blocking component 210 is used to isolate the post-reflection pump light in the reflected light. The detection component 160 receives the reflected light reflected from the surface of the metal film 100 to be measured and then projects the reflected light toward the blocking component 210. The blocking component 210 blocks the post-reflection pump light in the reflected light, and the post-reflection detection light passes through the blocking component 210 and projects toward the optoelectronic signal converter 171. The optoelectronic signal converter 171 is used to perform optoelectronic signal conversion processing on the post-reflection detection light to obtain a converted detection signal, and the converted detection signal is an electrical signal. The phase-locked amplifier 170 is, for example, electrically connected to the photoelectric signal converter 171, the function generator 150 and the data processing device 180. The phase-locked amplifier 170 receives the converted detection signal, demodulates the converted detection signal according to the mixed reference signal to obtain the demodulated detection signal, and transmits the demodulated detection signal to the data processing device 180. The data processing device 180 is used to determine the thickness of the metal film to be measured based on the demodulated detection signal. Among them, the reflected detection light is affected by stray light, and the frequency of the stray light is the first frequency ω1. According to the frequency superposition principle, the reflected detection light will produce reflected detection light with frequencies ω1+ω2 and ω1-ω2 after being affected by the stray light. There are also interferences with frequencies ω1+ω2 and ω1-ω2 in the converted detection signal, and the high-frequency interference noise with a frequency of ω1+ω2 is more obvious. Therefore, the function generator 150 transmits the mixed reference signal with a frequency of ω1+ω2 to the phase-locked amplifier 150, thereby reducing the influence of stray light on the demodulated detection signal, improving the signal-to-noise ratio of the demodulated detection information, and thus improving the accuracy of the calculated thickness of the metal film to be measured. In other embodiments of the present invention, the function generator 150 can also transmit the mixed reference signal with a frequency of ω1-ω2 to the phase-locked amplifier 150 for demodulation, and the embodiments of the present invention are not limited to this.

[0053] In one embodiment of the present invention, Figure 5 , Figure 7a , Figure 7bAs shown, the data processing device 180 is, for example, a host computer such as a PC or other electronic device with data processing function, which, for example, runs a metal film thickness measurement software that can process the acquired demodulated detection signal and obtain the thickness of the metal film 100 to be measured. The data processing device 180 is electrically connected to the phase-locked amplifier 170. The phase-locked amplifier 170, for example, transmits the demodulated detection signal obtained by demodulation to the data processing device 180. The demodulated detection signal is, for example, the change of the light reflectivity of the surface of the metal film 100 to be measured detected by the modulated detection light over time, wherein the change of the light reflectivity of the surface of the metal film 100 to be measured is caused by the ultrasound generated by the modulated pump light on the metal film 100 to be measured. As shown in FIG. Figure 7a and Figure 7b As shown, the data processing device 180 obtains the peak time T according to the relative time between the first peak time T0 of the transient state generated by the substrate 200 in the demodulated detection signal and the time T1 of the characteristic peak generated by the ultrasonic wave in the metal film 100 to be tested. peak The characteristic peak is affected by the thickness of the metal film, and the time T1 corresponding to the characteristic peak is the corresponding time point when the characteristic peak of the metal film 100 to be tested is most obvious due to the influence of ultrasound. Further, the data processing device calculates the characteristic peak according to the sound velocity V and the peak time T in the metal film 100 to be tested. peak The metal film thickness THK is calculated, for example:

[0054]

[0055] In summary, a metal film thickness measurement method and system proposed in an embodiment of the present invention performs frequency modulation on the pump light and the detection light respectively according to reference signals of different frequencies, irradiates the modulated pump light and the modulated detection light onto the surface of the metal film to be measured for detection, and obtains the reflected detection light in the reflected light. Since the frequencies of the modulated pump light and the modulated detection light are different, the stray light introduced by the reflected pump light is different from the frequency of the reflected detection light. When the reflected detection light is demodulated according to the mixed reference signal, the influence of the stray light on the detection signal can be effectively reduced, and the signal-to-noise ratio of the detection signal can be improved.

[0056] [Second embodiment]

[0057] like Figure 8a As shown, a metal film thickness measuring device provided by the second embodiment of the present invention includes, for example: a first modulation module 310 , a second modulation module 320 , a signal control module 330 , a detection module 340 , a demodulation module 350 and a data processing module 360 ​​.

[0058] Among them, Figure 8aAs shown, the first modulation module 310 is used to frequency modulate the pump light according to the first reference signal with the first frequency ω1 to obtain the modulated pump light; the second modulation module 320 is used to frequency modulate the detection light according to the second reference signal with the second frequency ω2 to obtain the modulated detection light, wherein the second frequency ω2 is different from the first frequency ω1, and the first frequency ω1 is greater than the second frequency ω2. The signal control module 330 is used to mix the first reference signal and the second reference signal to obtain the mixed reference signal, and the frequency of the mixed reference signal is the sum of the first frequency ω1 and the second frequency ω2 ω1+ω2 or the difference ω1-ω2 between the first frequency ω1 and the second frequency ω2. The detection module 340 is used to receive the reflected detection light in the reflected light obtained by the modulated pump light and the modulated detection light reflected from the surface of the metal film to be measured. The demodulation module 350 is used to convert and demodulate the reflected detection light according to the mixed reference signal to obtain the demodulated detection signal. The data processing module 360 ​​is used to determine the thickness of the metal film to be measured according to the demodulated detection signal.

[0059] The first frequency ω2 is greater than the first frequency ω1, and a ratio of the first frequency ω2 to the first frequency ω1 is in a range of (10:1) to (1000:1).

[0060] In addition, the reflected light may also include the reflected pump light. Figure 8b As shown, the metal film thickness measuring device provided in the second embodiment of the present invention may further include a blocking module 370. Specifically, the blocking module 370 is used to block the post-reflection pump light in the reflected light.

[0061] like Fig. 9 As shown, in a specific implementation, the demodulation module 350 of this embodiment includes:

[0062] The photoelectric conversion unit 351 is used to convert the reflected detection light into a photoelectric signal to obtain a converted detection signal;

[0063] The signal demodulation unit 352 is used to demodulate the converted detection signal according to the mixed reference signal to obtain a demodulated detection signal.

[0064] The specific functions and beneficial effects of the metal film thickness measuring device in the embodiment of the present invention can be referred to the description of the first embodiment above, which will not be repeated here.

[0065] In addition, it can be understood that the aforementioned embodiments are only exemplary descriptions of the present invention. Under the premise that there is no conflict in technical features, no structural contradiction, and no violation of the purpose of the present invention, the technical solutions of the various embodiments can be arbitrarily combined and used in combination.

[0066] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0067] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0068] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of hardware plus software functional units.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring the thickness of a metal film, characterized in that: include: Frequency modulating the pump light according to a first reference signal having a first frequency to obtain modulated pump light; Frequency modulating the detection light according to a second reference signal having a second frequency to obtain modulated detection light, wherein the second frequency is different from the first frequency; Mixing the first reference signal and the second reference signal to obtain a mixed reference signal; Receiving the reflected detection light among the reflected lights obtained by reflecting the modulated pump light and the modulated detection light from the surface of the metal film to be measured; Performing conversion and demodulation processing on the reflected detection light according to the mixed reference signal to obtain a demodulated detection signal; as well as The thickness of the metal film to be measured is determined according to the demodulated detection signal.

2. The method for measuring the thickness of a metal film according to claim 1, characterized in that: The frequency of the mixed reference signal is the sum or difference of the first frequency and the second frequency.

3. The method for measuring the thickness of a metal film according to claim 1, characterized in that: The first frequency is greater than the second frequency, and a ratio of the first frequency to the second frequency ranges from (10:1) to (1000:1).

4. The method for measuring the thickness of a metal film according to claim 1, characterized in that: The reflected light also includes reflected pump light; before receiving the reflected detection light in the reflected light obtained after the modulated pump light and the modulated detection light are reflected on the surface of the metal film to be measured, the metal film thickness measurement method also includes: The reflected pump light in the reflected light is blocked.

5. The method for measuring the thickness of a metal film according to claim 1, characterized in that: The converting and demodulating the reflected detection light according to the mixed reference signal to obtain a demodulated detection signal includes: Performing photoelectric signal conversion processing on the reflected detection light to obtain a converted detection signal; and The converted detection signal is demodulated according to the mixed reference signal to obtain the demodulated detection signal.

6. The method for measuring the thickness of a metal film according to claim 1, characterized in that: The step of determining the thickness of the metal film to be measured according to the demodulated detection signal comprises: Obtaining the signal peak time of the demodulated detection signal; The thickness of the metal film to be measured is determined according to the propagation speed of ultrasound generated by the modulated pump light irradiating the metal film to be measured and the peak time.

7. A metal film thickness measuring device, characterized in that: include: A first modulation module, configured to frequency modulate the pump light according to a first reference signal having a first frequency to obtain modulated pump light; A second modulation module, configured to frequency modulate the detection light according to a second reference signal having a second frequency to obtain modulated detection light, wherein the second frequency is different from the first frequency; A signal control module, configured to perform mixing processing on the first reference signal and the second reference signal to obtain a mixed reference signal; A detection module, used for receiving the reflected detection light among the reflected lights obtained by reflecting the modulated pump light and the modulated detection light from the surface of the metal film to be tested; A demodulation module, used for converting and demodulating the reflected detection light according to the mixed reference signal to obtain a demodulated detection signal; A data processing module is used to determine the thickness of the metal film to be measured according to the demodulated detection signal.

8. The metal film thickness measuring device according to claim 7, characterized in that: The reflected light also includes reflected pump light; The metal film thickness measuring device further comprises: The blocking module is used to block the post-reflection pump light in the reflected light.

9. The metal film thickness measuring device according to claim 7, characterized in that: The demodulation module comprises: A photoelectric conversion unit, used for performing photoelectric signal conversion processing on the reflected detection light to obtain a converted detection signal; A signal demodulation unit is used to demodulate the converted detection signal according to the mixed reference signal to obtain the demodulated detection signal.

10. A metal film thickness measurement system, characterized in that: include: Laser, used for emitting laser light; A light splitting component, used for performing light splitting processing on the laser to obtain pump light and detection light; A first modulator, configured to frequency modulate the pump light according to a first reference signal having a first frequency to obtain a modulated pump light; A second modulator, configured to frequency modulate the detection light according to a second reference signal having a second frequency to obtain modulated detection light, wherein the second frequency is different from the first frequency; a function generator, configured to perform mixing processing on the first reference signal and the second reference signal to obtain a mixed reference signal; A detection component, used for receiving the reflected detection light among the reflected lights obtained by reflecting the modulated pump light and the modulated detection light from the surface of the metal film to be tested; A lock-in amplifier, used for converting and demodulating the reflected detection light according to the mixed reference signal to obtain a demodulated detection signal; A data processing device is used to determine the thickness of the metal film to be measured according to the demodulated detection signal.

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