Wafer film thickness measuring method and device based on same wavelength and different light intensities

Abstract

The invention provides a wafer film thickness measuring method and device based on the same wavelength and different light intensities. The method comprises the steps that a current signal # imgabs0 # and a current signal # imgabs1 # corresponding to reflected light signals of the surface of a wafer film under light sources with the same wavelength and different light intensities are obtained; the current signal # imgabs2 # and the current signal # imgabs3 # are converted into a voltage signal # imgabs4 # and a voltage signal # imgabs5 #; subtracting the voltage signal # imgabs6 # and the voltage signal # imgabs7 # to obtain an output voltage # imgabs8 # so as to reduce the interference of the noise signal; and determining the thickness of the wafer film according to the output voltage # imgabs9 #.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor parameter measurement, and particularly to a wafer thin film thickness measurement method and device based on different light intensities at the same wavelength. Background Art

[0002] In the semiconductor process flow, with the booming development of chip technology, the requirements for semiconductor processes are getting higher and higher. Chemical Mechanical Polishing (CMP) is a very important process, that is, a process of removing excess material from a semiconductor silicon wafer by the combined action of chemistry and mechanics and obtaining a flat surface. And in the CMP polishing process, the detection of the polishing end point is very important to prevent under-polishing and over-polishing.

[0003] In CMP polishing technology, the optical thin film thickness measurement method is widely applicable to the polishing process. The principle of the optical thin film method is to judge the polishing end point by the different reflection intensities of the light beam after passing through thin films of different thicknesses. Generally, a spectrometer and an ellipsometer are used for polishing end point detection. Although the above-mentioned instruments have high precision in the process of detecting the optical thin film thickness, there are also problems such as high cost and complex principle. It is a difficult problem in the field of thin film thickness measurement to measure the wafer thickness on the premise of taking into account the economic cost and measurement accuracy. To reduce the manufacturing cost, the polishing end point detection method based on single-beam or multi-beam lasers is widely used.

[0004] Currently, the schematic diagram of the polishing end point detection principle based on a single-beam laser is as Figure 2 shown. The light source is expanded by a lens and emits light through a reflector. The light passes through the transparent window opened on the polishing pad and irradiates the wafer for reflection. The reflected light passes through the window and irradiates into the photodetector. The photodetector converts the light intensity signal into a current signal, and the system can obtain the polishing end point film thickness information by processing the current signal.

[0005] The problem of the prior art is that in the signal received by the photodetector, in addition to the useful signal, there are also ambient light and electrical noise signals. These signals are very difficult to eliminate in the subsequent data processing, so they affect the final film thickness measurement result. Summary of the Invention

[0006] In view of this, the present application provides a wafer thin film thickness measurement method based on different light intensities at the same wavelength, including: Obtaining the current signals corresponding to the reflected light signals on the surface of the wafer thin film under light sources with the same wavelength and different light intensities and the current signal ; Taking the current signal and the current signal Convert to a voltage signal and the voltage signal ; Subtract the voltage signal from the voltage signal to obtain an output voltage so as to reduce the interference of the noise signal; Determine the thickness of the wafer film according to the output voltage .

[0007] Optionally, one of the different light intensities is 0, so that only the noise signal exists in the corresponding current signal, while both the thickness signal and the noise signal exist in the current signal corresponding to the other light intensity.

[0008] Optionally, the different light intensities are all not equal to 0, and the current signal and the current signal respectively include the thickness signal and the noise signal.

[0009] Optionally, the light sources with the same wavelength and different light intensities are two states corresponding to the change of the light intensity of the same modulated light source.

[0010] Optionally, the voltage signal is the mean value of the voltage signals corresponding to the current signals acquired under one light intensity; the voltage signal is the mean value of the voltage signals corresponding to the current signals acquired under another light intensity.

[0011] Optionally, the current signal and the current signal are acquired and converted into the voltage signal and the voltage signal as follows: As the light intensity changes periodically in an alternating manner, the current signal and the current signal are converted into voltage signals by using a transimpedance amplification method, and the mean values of the voltage signals are taken to obtain the voltage signal and the voltage signal .

[0012] Optionally, the voltage signal is the result obtained by accumulating the sampling results of the current signals in multiple cycles under one light intensity, and the voltage signal is the result obtained by accumulating the sampling results of the current signals in multiple cycles under another light intensity.

[0013] Optionally, the current signal and current signal and convert it into a voltage signal and voltage signal : With the periodic alternating change of the light intensity, using the current signals of multiple cycles under one light intensity charge the first capacitor, and discharge the first capacitor after reaching a predetermined number of cycles to obtain a voltage signal , and using the current signals of multiple cycles under another light intensity charge the second capacitor, and discharge the second capacitor after reaching a predetermined number of cycles to obtain a voltage signal .

[0014] Optionally, subtract the voltage signal and voltage signal to obtain an output voltage , including: subtract the voltage signal and voltage signal to obtain a differential signal; convert the differential signal into a digital signal to obtain an output voltage .

[0015] Optionally, subtract the voltage signal and voltage signal to obtain an output voltage , including: convert the voltage signal and voltage signal into digital signals respectively; subtract the digital signals to obtain an output voltage .

[0016] Correspondingly, the present application provides a wafer film thickness measuring device based on different light intensities at the same wavelength, including: an acquisition unit for acquiring the current signals corresponding to the reflected light signals on the surface of the wafer film under light sources with the same wavelength and different light intensities and current signal and convert it into a voltage signal and voltage signal ; a denoising unit for subtracting the voltage signal and voltage signal to obtain an output voltage to reduce the interference of noise signals; a calculation unit for determining the thickness of the wafer film according to the output voltage .

[0017] Optionally, one of the different light intensities is 0, such that only a noise signal is present in the corresponding current signal, while the current signal corresponding to the other light intensity includes both a thickness signal and a noise signal.

[0018] Optionally, the different light intensities are all not equal to 0, and the current signal and the current signal respectively include a thickness signal and a noise signal.

[0019] Optionally, the light sources with the same wavelength and different light intensities are two states corresponding to the change in the light intensity of the same modulation light source.

[0020] Optionally, the acquisition unit includes: a signal selection circuit module and a transimpedance amplifier circuit module; wherein the signal selection circuit module outputs the current signal and the current signal to the transimpedance amplifier circuit module along with the periodic alternating change of the light intensity; the transimpedance amplifier circuit module respectively converts the current signal and the current signal into voltage signals, and takes the average value of the voltage signals to obtain the voltage signal and the voltage signal .

[0021] Optionally, the acquisition unit includes: a signal selection circuit module and an integration circuit module; wherein the signal selection circuit module outputs the current signal and the current signal to the integration circuit module along with the periodic alternating change of the light intensity; the first integration circuit in the integration circuit module charges the first capacitor using the current signal for multiple periods, and controls the first capacitor to discharge after reaching a predetermined number of periods to output the voltage signal , and the second integration circuit in the integration circuit module charges the second capacitor using the current signal for multiple periods, and controls the second capacitor to discharge after reaching a predetermined number of periods to output the voltage signal .

[0022] Optionally, the denoising unit includes: a filtering module, a differential amplification module, and an AD conversion module; wherein the filtering module is used to filter the voltage signal and the voltage signal ; the differential amplification module is used to take the differential signal of the filtered voltage signal and the voltage signal ; The AD conversion module is used to convert the differential signal into a digital signal to obtain an output voltage .

[0023] Optionally, the denoising unit includes: a filtering module, a differential amplification module, and an AD conversion module; where The filtering module is used to filter the voltage signal and the voltage signal for filtering; The AD conversion module is used to convert the voltage signal and the voltage signal into digital signals respectively; The differential amplification module is used to subtract the digital signals to obtain an output voltage .

[0024] According to the wafer thin film thickness measurement method and device based on the same wavelength and different light intensities provided by the embodiments of the present invention, the reflected light signals of the wafer thin film surface under the same wavelength and different light intensities are collected respectively and converted into current signals. The current signals and the current signal are converted into voltage signals and the voltage signal , the voltage signals and the voltage signal are subtracted to obtain an output voltage to reduce the interference of noise signals, and the influence of ambient light in the measurement scene and noise in the circuit on the collected signals can be suppressed. Based on this processing result, the thickness of the wafer thin film is determined, and the accuracy of the calculation result can be improved.

[0025] This solution can perform on-line detection during the wafer grinding process. It can not only detect the thickness of the wafer thin film in real time during the grinding process, but also be used for grinding end point detection. When the detected thickness of the wafer thin film reaches the predetermined thickness, the grinding is stopped, thereby improving the accuracy and efficiency of the wafer grinding process. Description of the Drawings

[0026] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 is the flowchart of the wafer thin film thickness detection method in the embodiments of the present invention; Figure 2 is the optical signal acquisition scenario in the embodiments of the present invention; Figure 3 Waveform diagram of the acquisition signal in the embodiment of the present invention; Figure 4 Voltage output circuit diagram in the embodiment of the present invention; Figure 5 Circuit structure diagram of the wafer thin film thickness measuring device in the embodiment of the present invention. Specific implementation manner

[0028] Next, the technical solution of the present invention will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The embodiment of the present invention provides a wafer thin film thickness measuring method based on different light intensities at the same wavelength. This method can be executed by electronic devices such as computers or servers, such as Figure 1 shown, including the following operations: S1. Obtain the current signals corresponding to the reflected light signals on the surface of the wafer thin film under light sources with the same wavelength and different light intensities and the current signal .

[0031] Figure 2 shows an exemplary acquisition scenario of the optical thin film method. The light emitted by the laser 11 (light source) passes through the lens 12 and the mirror 13 and is incident on the wafer thin film 01. The photodetector 21 collects the reflected light of the wafer thin film 01 and converts the light intensity into a photocurrent. At this time, the collected photocurrent signal includes the current signal s(t) generated by the reflected light reflected to the photodetector and the noise signals generated by factors such as ambient light and circuit dark current.

[0032] This solution uses two light sources with different light intensities but the same wavelength, namely a bright light source and a dim light source, which are incident on the wafer film 01 at the same incident angle. As a preferred embodiment, the light sources with the same wavelength but different light intensities can be two states corresponding to the change in the light intensity of the same modulated light source. Specifically, it can be a Super Luminescent Diode (SLD) light source. The SLD realizes the switching between the bright light source and the dim light source by controlling the change in the output light intensity by the MCU. Further, the output light intensity can alternately change at a certain frequency, so that the wafer film surface alternately reflects the light signals in the corresponding states. Therefore, ideally, the current signal output by the photodetector is a high and low level signal that changes at a certain frequency. (It can be understood that the SLD light source changes every 50 ms, that is, the bright light source is output in the first 50 ms, the dim light source is output in the second 50 ms, the bright light source is output in the third 50 ms... Therefore, the signal collected at this time is a periodic signal.) In other embodiments, two light sources can also be used as the bright light source and the dim light source respectively.

[0033] In one embodiment, one of the different light intensities can be 0, that is, the dim light source means that the light source does not emit light, so that only the noise signal exists in the corresponding current signal, while the bright light source has a fixed light intensity, and the current signal corresponding to this light intensity includes both the thickness signal and the noise signal.

[0034] In one embodiment, neither of the different light intensities is equal to 0, and the current signal and the current signal respectively include the thickness signal and the noise signal.

[0035] S2. Convert the current signal and the current signal into the voltage signal and the voltage signal .

[0036] S3. Subtract the voltage signal and the voltage signal to obtain the output voltage to reduce the interference of the noise signal.

[0037] Let the light intensity of the ambient light be , the reflected light intensity in the bright state of the light source be , the reflected light intensity in the dark state be , the noise current in the bright state of the light source be , the noise current in the dark state of the light source be , is the conversion coefficient between the light intensity and the photocurrent, then there is the following relationship: ; ; The purpose of this step is to reduce , and the influence on the thickness of the wafer film. Specifically, by integrating the current signal and the current signal or performing transimpedance amplification, the voltages and are obtained. By taking the difference between the two analog signals or subtracting them after converting the two analog signals into digital signals, the interference of , and is reduced.

[0038] S4. Determine the thickness of the wafer film according to the digital measurement output voltage . The method adopted in this solution is a single-beam laser (light beam with a single wavelength) thickness detection method based on the optical thin film method. The thickness detection principle of the single-beam laser is that the light source irradiates the wafer and is reflected, and the reflected light irradiates into the photodetector. The photodetector converts the light intensity signal into an electrical signal, and the film thickness of the wafer film is determined by the electrical signal.

[0039] Before measurement, a correspondence library (database) of reflectance R and thickness D needs to be established for the wafer film to be measured. This database can be calculated based on a theoretical mathematical model or obtained by measuring wafer films with different thicknesses in a laboratory environment. When this database is used for actual measurement, the measured value is the reflectance of the wafer film (the output voltage is directly measured and then converted into reflectance), and then the thickness corresponding to the reflectance can be determined through this database.

[0040] The digital measurement output voltage has a linear correspondence with the reflectance R. The correspondence between the output voltage and the thickness of the wafer film can be simplified to a quasi-sine function relationship. The value of a voltage corresponds to periodic thickness values. For example: ; where represents the voltage value, t represents the thickness value, represents the calibration coefficient, and a and b are constants.

[0041] Based on the above correspondence, after obtaining the digital measurement output voltage Periodic thickness values can be obtained, which can be used at least in the wafer polishing process to determine the relative change in thickness over a period of time; alternatively, technical means can be further adopted to determine one of the thickness values as the absolute thickness value of the wafer thin film based on the periodic thickness values.

[0042] As Figure 3 shown, the light source adjustment drive signal is used to control the light intensity, and one bright-dark change of the light source is regarded as a cycle. Figure 3 A total of cycles are shown, and the measured optical signal (current signal) fluctuates as an alternating high-low level signal at different light intensities.

[0043] In one embodiment, the voltage signal in step S2 is the mean value of the voltage signals corresponding to the current signals collected at one light intensity; the voltage signal is the mean value of the voltage signals corresponding to the current signals collected at another light intensity. Specifically, as the light intensity changes periodically and alternately, the current signals and the current signals are converted into voltage signals by means of transimpedance amplification, and the mean values of the voltage signals are taken to obtain the voltage signal and the voltage signal and the voltage signal and the voltage signal .

[0044] As Figure 3 in the first cycle, the measured optical signal (current signal) in the bright light source state and the measured optical signal in the dark light source state are respectively converted into voltage signals, and then the mean value of the voltage signals in this cycle is taken. Taking the mean value of the voltage signals over a period of time as the result in this embodiment can improve the reliability of the measurement result. Specifically, the measured current signal has large fluctuations, and the current signals collected at different time points under the same light intensity may vary greatly. The method of taking the mean value can reduce the influence caused by the current fluctuations, and the average voltages under different light intensities can reflect sufficient differences, thereby improving the accuracy of the denoised signal.

[0045] In another embodiment, considering that the fluctuations of the measured optical signal may cause the voltage signal of any cycle to be unstable, the voltage signal in this embodiment is the result obtained by accumulating the sampling results of the current signals of multiple cycles at one light intensity, and the voltage signal is the result obtained by accumulating the sampling results of the current signals of multiple cycles at another light intensity.

[0046] Specifically, the current signal can be collected in the following manner and current signal and convert it into a voltage signal and voltage signal : As the light intensity periodically alternates, use the current signals of multiple cycles at one light intensity to charge the first capacitor, and discharge through the first capacitor after reaching a predetermined number of cycles to obtain a voltage signal , and use the current signals of multiple cycles at another light intensity to charge the second capacitor, and discharge through the second capacitor after reaching a predetermined number of cycles to obtain a voltage signal .

[0047] As Figure 3 shown, the measured optical signals in the bright and dark states in each cycle can be integrated respectively, that is, for the signals of multiple cycles are accumulated to obtain a bright integration signal and a dark integration signal . At the th cycle, a voltage signal is sampled and voltage signal . The number of integration cycles and the cycle length can be set as needed

[0048] Then use the sampling result of each cycle to charge the storage capacitor; the sampling results of multiple cycles increase the charge of the storage capacitor C to obtain a signal integration value. Use the sampling integrator to integrate the measured signals corresponding to the bright and dark light sources respectively, and the bright integration signal and dark integration signal can be obtained

[0049] The present invention requires a selector and two sampling integrators. When the light source drive signal outputs a high level, the selector triggers the first sampling integrator to work at this time. The first sampling integrator accumulates the charge of the storage capacitor C to obtain a signal at the high level; when the light source drive signal outputs a low level, the selector triggers the second sampling integrator to work at this time. The second sampling integrator accumulates the charge of the storage capacitor C to obtain a signal at the low level; when this level signal passes through multiple cycles, the storage capacitors of the two sampling integrators continuously accumulate charge, and the bright integration signal and dark integration signal can be obtained

[0050] After obtaining the voltage signal and voltage signal , step S3 may include: Take the difference signal of the voltage signal and voltage signal ; Convert the differential signal into a digital signal to obtain the output voltage In this embodiment, the analog signal is differentiated and then converted into a digital signal.

[0051] Step S3 may further include: Convert the voltage signals and the voltage signals into digital signals respectively; Subtract the digital signals to obtain the output voltage . As Figure 4 shown, in this embodiment, the voltage signals obtained by integration and the voltage signals are respectively subjected to AD conversion to obtain the corresponding digital signals M 1 and M 2 , and then the difference is taken based on the digital signals to obtain the result U = M 1 - M 2 .

[0052] An embodiment of the present invention provides a wafer thin film thickness measuring device based on different light intensities at the same wavelength, including: An acquisition unit for acquiring current signals corresponding to reflected light signals on the surface of the wafer thin film under light sources with the same wavelength and different light intensities and current signals and converting them into voltage signals and voltage signals . The acquisition unit may include one or more light sources. Regarding the light sources and their light intensities, reference may be made to the embodiments of the above wafer thin film thickness measuring method, which will not be elaborated here.

[0053] A denoising unit for subtracting the voltage signals and the voltage signals to obtain the output voltage to reduce the interference of noise signals; A calculation unit for determining the thickness of the wafer thin film according to the output voltage .

[0054] In one embodiment, the acquisition unit includes: a signal selection circuit module and an integration circuit module; wherein the signal selection circuit module outputs the current signals and the current signals to the integration circuit module as the light intensity periodically alternates; the first integration circuit in the integration circuit module charges the first capacitor with the current signals of multiple cycles and controls the first capacitor to discharge after reaching a predetermined number of cycles to output the voltage signal , and the second integration circuit in the integration circuit module uses the current signals of multiple cycles The second capacitor is charged, and after reaching a predetermined number of cycles, the second capacitor is controlled to discharge so as to output a voltage signal. .

[0055] Figure 5 A more specific circuit structure is shown, and an exemplary signal acquisition process is as follows: first, the MCU module outputs high and low level drive signals to drive the light source module to generate light signals that alternate between bright and dark. The photodiode converts the reflected light signal received from the wafer film into a current signal and outputs it to the signal selection circuit. The signal selection circuit module is controlled by the high and low levels generated by the MCU module. When the photodiode outputs a large current signal (a current signal under a strong light intensity), the signal selection circuit module outputs a high level and transmits the current signal to the first integration circuit; otherwise, it is output to the second integration circuit. The integration circuit is also controlled by the MCU module. It collects the current signal in the current cycle and stores the current through the capacitor. The integration circuit collects current signals under multiple cycles. If 10 cycles are set, at the end of the 10th cycle, the MCU module drives the capacitor in the integration circuit to discharge by controlling the level switch. At this time, the two integration circuits simultaneously output voltage signals and To the denoising unit.

[0056] Furthermore, the denoising unit includes: a filtering module, a differential amplification module and an AD conversion module; wherein The filter module is used to filter the voltage signal and voltage signal Perform filtering; The differential amplifier module is used to filter the voltage signal. and voltage signal Take the differential signal; The AD conversion module is used to convert the differential signal into a digital signal to obtain the output voltage .

[0057] The filter module outputs the signal after removing high-frequency noise to the differential amplifier circuit for processing, and the differential amplifier module outputs the differential signal The signal is sent to the AD conversion module for processing. The MCU module can verify the current film thickness value through the obtained voltage signal, and output the film thickness information to the host computer for display.

[0058] Another way to obtain the difference is to use a filter module to filter the voltage signal. and voltage signal Filtering; AD conversion module is used to convert voltage signal and voltage signal Converted into a digital signal; the differential amplifier module is used to obtain an output voltage by performing a differential operation on the digital signal The MCU module can be used as a differential amplification module to perform subtraction on digital signals.

[0059] In another embodiment, the acquisition unit includes: a signal selection circuit module and a transimpedance amplification circuit module; where The signal selection circuit module outputs the current signal and the current signal to the transimpedance amplification circuit module along with the periodic alternating change of the light intensity; the transimpedance amplification circuit module respectively converts the current signal and the current signal into voltage signals, and takes the average of the voltage signals to obtain the voltage signal and the voltage signal .

[0060] In this embodiment, the transimpedance amplification circuit module amplifies the current signal and the current signal respectively and outputs the voltage signal and the voltage signal . There is no need to accumulate the current signals under multiple light intensity change cycles, and only the electrical signals in a single cycle need to be amplified and sampled to obtain the corresponding voltage signals.

[0061] Those skilled in the art should understand that the embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0062] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the processes and / or blocks in the flowchart and / or block diagram can also be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the specified functions in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0063] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to operate in a particular manner, such that the instructions stored in the computer-readable memory produce a manufacture including an instruction device that implements the functions specified in one or more of the processes and / or blocks Figure 1 one or more of the processes and / or blocks Figure 1 specified in the block or blocks.

[0064] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable apparatus provide steps for implementing the functions specified in one or more of the processes and / or blocks Figure 1 one or more of the processes and / or blocks Figure 1 specified in the block or blocks.

[0065] Obviously, the above-described embodiments are merely examples for clear illustration and are not limitations on the implementation. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A wafer film thickness measurement method based on the same wavelength and different light intensities, characterized in that: include: Obtain the current signal corresponding to the reflected light signal of the wafer film surface under the same wavelength and different light intensity light sources and Current signal ; The current signal and current signal Convert to voltage signal and voltage signal ; For voltage signal and voltage signal Subtract the output voltage To reduce the interference of noise signals; According to the output voltage The thickness of the wafer film is determined.

2. The method according to claim 1, characterized in that One of the different light intensities is 0, so that the corresponding current signal contains only a noise signal, while the current signal corresponding to the other light intensity contains both a thickness signal and a noise signal.

3. The method according to claim 1, characterized in that The different light intensities are not equal to 0, the current signal and current signal The thickness signal and the noise signal are included in them respectively.

4. The method according to claim 1, characterized in that: The light sources with the same wavelength but different light intensities are two states corresponding to the light intensity changes of the same modulated light source.

5. The method according to claim 1, characterized in that Voltage signal It is the current signal collected under a certain light intensity. The mean value of the corresponding voltage signal; voltage signal is the current signal collected under another light intensity The corresponding voltage signal.

6. The method according to claim 5, characterized in that The current signal is collected as follows and current signal And converted into a voltage signal and voltage signal : As the light intensity changes periodically, the current signal is amplified by transimpedance amplification. and current signal Convert to voltage signal and average the voltage signal to get voltage signal and voltage signal .

7. The method according to claim 1, characterized in that Voltage signal It is the current signal of multiple cycles under one light intensity. The sampling results are accumulated to obtain the voltage signal is the current signal of multiple cycles under another light intensity The result obtained by adding up the sampling results.

8. The method according to claim 7, characterized in that The current signal is collected as follows and current signal And converted into a voltage signal and voltage signal : As the light intensity changes periodically, the current signal of multiple cycles under one light intensity is used The first capacitor is charged and discharged through the first capacitor when a predetermined number of cycles is reached to obtain a voltage signal , and using the current signal of multiple cycles under another light intensity The second capacitor is charged and discharged after a predetermined number of cycles to obtain a voltage signal. .

9. A wafer film thickness measurement device based on the same wavelength and different light intensities, characterized in that: include: The acquisition unit is used to obtain the current signal corresponding to the reflected light signal of the wafer film surface under the same wavelength and different light intensity light sources and current signal And converted into a voltage signal and voltage signal ; De-noising unit for voltage signals and voltage signal Subtract the output voltage To reduce the interference of noise signals; A calculation unit is used to calculate the output voltage according to the The thickness of the wafer film is determined.

10. The device according to claim 9, characterized in that One of the different light intensities is 0, so that the corresponding current signal contains only a noise signal, while the current signal corresponding to the other light intensity contains both a thickness signal and a noise signal.

11. The device according to claim 9, characterized in that The different light intensities are not equal to 0, the current signal and current signal The thickness signal and the noise signal are included in them respectively.

12. The device according to claim 9, characterized in that The light sources with the same wavelength but different light intensities are two states corresponding to the light intensity changes of the same modulated light source.

13. The device according to claim 9, characterized in that The acquisition unit includes: a signal selection circuit module and a transimpedance amplifier circuit module; wherein The signal selection circuit module converts the current signal into and current signal Output to the transimpedance amplifier circuit module; The transimpedance amplifier circuit module converts the current signal and current signal Convert to voltage signal and average the voltage signal to get voltage signal and voltage signal .

14. The device according to claim 9, characterized in that The acquisition unit includes: a signal selection circuit module and an integration circuit module; wherein The signal selection circuit module converts the current signal into and current signal Output to the integration circuit module; The first integration circuit in the integration circuit module uses a current signal of multiple cycles The first capacitor is charged, and after reaching a predetermined number of cycles, the first capacitor is controlled to discharge so as to output a voltage signal. The second integration circuit in the integration circuit module uses a current signal of multiple cycles The second capacitor is charged, and after reaching a predetermined number of cycles, the second capacitor is controlled to discharge so as to output a voltage signal. .

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