A method and system for measuring the thermal conductivity of a single layer of thin film material

Abstract

This invention provides a method and system for measuring the thermal conductivity of a single-layer thin film material. The method includes: a calibration step in which a metal thin film is prepared on the surface of a standard sample with known thermal conductivity; a first proportional relationship is obtained between the change in the amplitude of the thermal reflection signal of the surface under periodic heating and the change in the modulated heating laser power; and a proportionality coefficient of the measurement system is calculated based on the first proportional relationship and the heat transfer analytical model corresponding to the standard sample. The measurement step involves preparing a metal thin film on the surface of the single-layer thin film sample to be tested; obtaining a second proportional relationship between the change in the amplitude of the thermal reflection signal of the surface under periodic heating and the change in the modulated heating laser power under the same measurement conditions; and inverting the calculation to obtain the thermal conductivity of the single-layer thin film sample to be tested. This method obtains the proportionality coefficient of the measurement system through the calibration step and detects the thermal conductivity of the sample through the measurement step.

Description

Technical Field

[0001] This invention relates to the field of material thermal property measurement technology, and in particular to a method and system for measuring the thermal conductivity of single-layer thin film materials. Background Technology

[0002] With the rapid development of advanced integrated circuits, flexible electronic devices, thermoelectric conversion materials, and other fields, the thermal conductivity of single-layer thin film materials has a crucial impact on device thermal management, reliability design, and performance optimization. Accurately measuring the thermal conductivity of such materials is essential for thermal management design and materials research.

[0003] However, traditional methods for measuring thermal conductivity (such as the steady-state heat flow method, The methods (such as those used in the steady-state method) have obvious limitations: steady-state methods require contact temperature measurement and have long measurement times, making them difficult to apply to submicron thickness films. While the method can achieve high precision, it requires the fabrication of metal electrodes, which may introduce contact thermal resistance and damage the thin film. Especially in the measurement of two-dimensional materials (such as graphene, transition metal sulfides, etc.) and ultrathin dielectric films (such as silicon nitride, alumina, etc.), the measurement accuracy and spatial resolution of traditional methods often fail to meet the requirements.

[0004] Existing non-contact measurement techniques mainly include time-domain thermal reflection (TDTR) and frequency-domain thermal reflection (FDTR). However, these methods still have certain limitations, such as:

[0005] While the time-domain thermal reflectance method offers high accuracy, it requires complex ultrafast laser systems and data processing algorithms, resulting in high equipment costs. Conversely, the frequency-domain thermal reflectance method, while offering faster measurement speeds, is sensitive to interface thermal resistance and requires complex model fitting.

[0006] To meet the need for rapid, low-cost, high spatial resolution, and non-destructive thermal conductivity measurement of single-layer thin film materials, a new measurement scheme is urgently needed. Summary of the Invention

[0007] Based on this, the present invention provides a method and system for measuring the thermal conductivity of monolayer thin film materials. This method combines low-frequency modulated heating laser with continuous-wave probe laser, and inverses the thermal conductivity of the thin film by measuring the changes in the thermal reflection signal caused by periodic heating. The aim is to achieve low-cost, high spatial resolution, non-contact, and wide-range applicable accurate measurement of thin film thermal conductivity.

[0008] In a first aspect, embodiments of this application provide a method for measuring the thermal conductivity of a single-layer thin film material, comprising:

[0009] Calibration steps: Prepare a metal thin film on the surface of a standard sample with known thermal conductivity; control the continuous wave probe laser and the modulated heating laser to be coaxial and focused on the same test surface of the metal thin film; obtain the first proportional relationship between the change in the amplitude of the thermal reflection signal of the test surface under periodic heating conditions and the change in the power of the modulated heating laser; wherein, the metal thin film is a metal film with a stable thermal reflectivity coefficient for the wavelength of the continuous wave probe laser;

[0010] Based on the first proportional relationship and the heat transfer analytical model corresponding to the standard sample, the proportional coefficient of the measurement system is calculated.

[0011] Measurement steps: Prepare a metal thin film on the surface of the monolayer thin film sample to be tested;

[0012] Under the same measurement conditions, the continuous wave probe laser and the modulated heating laser are controlled to be coaxial and focused on the same test surface of the metal thin film; the second proportional relationship between the change in the amplitude of the thermal reflection signal of the test surface under periodic heating conditions and the change in the power of the modulated heating laser is obtained;

[0013] The thermal conductivity of the single-layer thin film sample to be tested is obtained by inversion calculation based on the second proportional relationship, the proportional coefficient, and the heat transfer analytical model including the thermal conductivity of the single-layer thin film sample.

[0014] Optionally, in the calibration step and the measurement step, obtaining the proportional relationship between the change in the amplitude of the thermal reflection signal of the surface under test under periodic heating conditions and the change in the modulated heating laser power includes:

[0015] The laser power of the modulated heating laser is modulated, and the reflected light signal of the continuous wave probe laser reflected from the measurement area is collected simultaneously. The change in the amplitude of the thermal reflection signal of the reflected light signal is extracted. A positive correlation function relationship is established between the change in the amplitude of the thermal reflection signal and the change in the laser power.

[0016] Optionally, in the calibration step and the measurement step,

[0017] The calculation formula for the heat transfer analytical model is as follows:

[0018] ;

[0019] in, This refers to the change in the amplitude of the thermal reflection signal; The change in laser power for modulated heating laser; This is the scaling factor for the test system; The thermal conductivity of the sample; For heat flux density, The solution is determined by the analytical solution of the near-steady-state heat transfer problem of multilayer structures based on Fourier's law.

[0020] Optionally, in the calibration step and the measurement step, the control method further includes:

[0021] The spot radius of the continuous wave probe laser in the measurement area is controlled to be less than 5 micrometers, and the spot radius of the modulated heating laser in the measurement area is controlled to be greater than the spot radius of the continuous wave probe laser.

[0022] Optionally, in the calibration step and the measurement step, the modulation frequency of the modulated heating laser is... The frequency range is set to ensure that the heat conduction process in the measurement area is in a near-steady or quasi-steady state.

[0023] Optionally, the modulation frequency range of the heating laser is 0 Hz to 1 kHz.

[0024] Based on the same inventive concept, this application provides a measurement system for the thermal conductivity of a single-layer thin film material, used to implement the measurement method for the thermal conductivity of a single-layer thin film material provided in the first aspect, comprising:

[0025] A laser unit is provided for providing a continuous wave probe laser and a modulated heating laser; the laser power and frequency of the modulated heating laser are adjustable.

[0026] A beam combining and focusing unit is used to coaxially focus the continuous wave probe laser and the modulated heating laser onto the same measurement area on the sample surface;

[0027] The detection unit is used to receive the reflected light signal of the continuous wave detection laser reflected from the measurement area and convert it into an electrical signal;

[0028] The signal processing unit is configured as follows:

[0029] Control the power of the continuous wave probe laser and the modulation frequency and laser power of the modulated heating laser;

[0030] The electrical signal output by the detection unit is collected and processed, and the amplitude change of the heat reflection signal corresponding to the heating modulation frequency is extracted;

[0031] In the calibration step, the first proportional relationship between the change in the amplitude of the thermal reflection signal of the standard sample surface with known thermal conductivity under periodic heating conditions and the change in modulated heating laser power is obtained. Combined with the known thermal conductivity and the heat transfer analytical model corresponding to the standard sample, the proportional coefficient of the measurement system is calculated.

[0032] In the measurement step, a second proportional relationship is obtained between the change in the amplitude of the thermal reflection signal on the surface of the monolayer thin film sample under periodic heating conditions and the change in the modulated heating laser power. Combined with the proportional coefficient and a heat transfer analytical model that includes the thermal conductivity of the monolayer thin film sample, the thermal conductivity of the monolayer thin film sample under test is calculated by inversion.

[0033] Optionally, the beam combining and focusing unit includes a polarizing beam splitter, a quarter-wave plate, a dichroic mirror, and an objective lens arranged sequentially.

[0034] Optionally, the detection unit is a photodiode, which is disposed in the transmission optical path of the polarizing beam splitter; the signal processing unit includes a lock-in amplifier or a digital oscilloscope with spectrum analysis function.

[0035] Optionally, the output end of the modulated heating laser in the laser unit is provided with a beam expander to adjust the spot size of the heating laser in the measurement area.

[0036] In summary, the method for measuring the thermal conductivity of monolayer thin film materials provided in this application uses a low-frequency modulated laser to periodically heat the sample surface, and then relies on another continuous-wave laser to detect changes in the thermal reflectivity of the monolayer thin film material under test to measure its thermal conductivity. The proportionality coefficient of the measurement system is obtained through a calibration step. The thermal conductivity of the sample (single-layer thin film sample) is detected by measurement step S2. .

[0037] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0038] First, it has the advantages of low cost. It uses continuous wave lasers and low-frequency modulation technology, eliminating the need for expensive ultrafast laser systems and high-frequency lock-in amplifiers, thus significantly reducing hardware costs.

[0039] Secondly, it features simple operation, strong anti-interference, low-frequency measurement is less affected by environmental noise and vibration, stable signal, and easy system setup and operation.

[0040] Third, it has high spatial resolution. By controlling the probe laser spot to the micrometer level, this application can realize the measurement of local thermal properties in micro-regions.

[0041] Fourth, it features non-contact and non-destructive, fully optical measurement, requiring no electrode preparation or mechanical contact with the sample, thus avoiding damage to fragile thin film samples and the introduction of contact thermal resistance.

[0042] Fifth, it has a wide range of applicability and measurement range. The measurement method provided in this application is based on the universal thermal reflection effect and heat transfer model, and is applicable to a variety of single-layer thin film materials such as metals, semiconductors, and insulators. Theoretically, it can measure a wide range of thermal conductivity (e.g., 0.1-1000 W / (m·K)).

[0043] Sixth, it features simplified models and rapid analysis. By employing low-frequency (near steady-state) heating, the heat transfer analytical model is simplified, reducing complex fitting parameters and improving the efficiency and reliability of data analysis. Attached Figure Description

[0044] Figure 1 A schematic diagram of the optical path for measuring the thermal conductivity of a single-layer thin film material provided by the present invention;

[0045] Figure 2 A schematic diagram illustrating a method for measuring the thermal conductivity of a single-layer thin film material provided by the present invention;

[0046] Figure 3 This is a schematic diagram of the optical path and structure of the standard sample irradiated by laser in the measurement method provided by the present invention.

[0047] Figure 4 This is a schematic diagram of the optical path and structure of the laser irradiation of the sample under test in the measurement method provided by the present invention.

[0048] Explanation of reference numerals in the attached figures:

[0049] 1. Laser unit; 11. Continuous wave detection light source; 12. Modulated heating light source;

[0050] S1, continuous wave detection laser; S2, modulated heating laser;

[0051] 2. Beam combining and focusing unit; 3. Detection unit; 4. Signal processing unit;

[0052] 21. Polarizing beam splitter; 22. Quarter-wave plate; 23. Dichroic mirror; 24. Objective lens; 25. Beam expander;

[0053] M1, metal thin film; M2, standard sample; M3, single-layer thin film sample to be tested (single-layer thin film); 26, substrate. Detailed Implementation

[0054] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the present application and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the present application are shown in the drawings, not the entire structure. Various modifications and variations can be made to the present application without departing from its spirit or scope, which will be apparent to those skilled in the art. Therefore, the present application is intended to cover modifications and variations of the present application that fall within the scope of the technical solutions claimed in the corresponding claims and their equivalents. It should be noted that the implementation methods provided in the embodiments of the present application can be combined with each other without contradiction.

[0055] Figure 1 This is a schematic diagram of the optical path of a system for measuring the thermal conductivity of a single-layer thin film material according to the present invention. This application provides a system for measuring the thermal conductivity of a single-layer thin film material, used to implement the method for measuring the thermal conductivity of a single-layer thin film material described below. (Reference) Figure 1 The system for measuring the thermal conductivity of single-layer thin film materials includes a laser unit 1, a beam combining and focusing unit 2, a detection unit 3, and a signal processing unit 4.

[0056] Specifically, the laser unit 1 includes a continuous wave detection light source 11 and a modulated heating light source 12. The continuous wave detection light source 11 provides a continuous wave detection laser S1, and the modulated heating light source 12 provides a modulated heating laser S2. The laser power and frequency of the modulated heating laser S2 are adjustable. For example, the continuous wave detection light source 11 uses a laser with a wavelength of 785 nm, and the modulated heating light source 12 uses a laser with a wavelength of 457 nm. The power and frequency of the heating laser can be modulated by an external signal.

[0057] The beam combining and focusing unit 2 is used to coaxially focus the continuous wave probe laser S1 and the modulated heating laser S2 onto the same measurement area on the sample surface. Specifically, the beam combining and focusing unit 2 precisely coaxially focuses the two laser beams onto the same point on the sample surface. The specific optical path is as follows: after being reflected by the polarizing beam splitter 21, the continuous wave probe laser 10 and the modulated heating laser 11 pass sequentially through the quarter-wave plate 22, the dichroic mirror 23, and the objective lens 24, and are finally focused onto the predetermined detection area on the sample surface. At the same time, a beam expander 25 can be provided on the output optical path of the modulated heating laser S2 to adjust the spot size of the modulated heating laser S2.

[0058] The detection unit 3 is used to receive the reflected light signal of the continuous wave probe laser S1 reflected from the measurement area and convert it into an electrical signal. The detection unit 3 can be a photodiode. The reflected light from the sample surface (mainly the continuous wave probe laser S1) returns along the original path, passes through the objective lens 24, the dichroic mirror 23, and the quarter-wave plate 22. Due to the change in its polarization direction, it passes through the polarizing beam splitter 21 and is received by the detection unit 3 (photodiode) behind it and converted into an electrical signal.

[0059] The signal processing unit 4 is configured to control the power of the continuous wave probe laser S1 and the modulation frequency and laser power of the modulated heating laser S2; acquire and process the electrical signal output by the probe unit 3, and extract the amplitude change of the thermal reflection signal corresponding to the heating modulation frequency. Specifically, the signal processing unit 4 receives the electrical signal from the probe unit 3 (photodiode), and the signal processing unit 4 can be a digital oscilloscope or a lock-in amplifier with spectrum analysis capabilities. It controls the modulation of the modulated heating laser to acquire the reflected light signal in the electrical signal of the probe unit 3 (photodiode) and extract the amplitude change of the thermal reflection signal at the modulation frequency. Then, perform the subsequent calibration and calculation process.

[0060] In calibration step S1 described below, the first proportional relationship between the change in the amplitude of the thermal reflection signal of a standard sample surface with known thermal conductivity under periodic heating conditions and the change in the power of the modulated heating laser S2 is obtained. Combined with the known thermal conductivity and the heat transfer analytical model corresponding to the standard sample, the proportionality coefficient of the measurement system is calculated. .

[0061] In measurement step 2 described below, a second proportional relationship is obtained between the change in the amplitude of the thermal reflection signal on the surface of the monolayer thin film sample under periodic heating conditions and the change in the power of the modulated heating laser S2, and combined with the proportionality coefficient. And the thermal conductivity of samples containing monolayer thin films The thermal conductivity of the single-layer thin film sample under test is obtained by inversion calculation using the heat transfer analytical model. .

[0062] Based on the same inventive concept, embodiments of this application also provide a method for measuring the thermal conductivity of a single-layer thin film material. Figure 2 This is a schematic diagram illustrating a method for measuring the thermal conductivity of a single-layer thin film material provided by the present invention. Figure 3 This is a schematic diagram of the optical path and structure of the standard sample irradiated by laser in the measurement method provided by the present invention. Figure 4 This is a schematic diagram of the optical path and structure of the laser irradiation of the sample under test in the measurement method provided by the present invention, for reference. Figures 1-4The method for measuring the thermal conductivity of a single-layer thin film material provided in this application includes a calibration step S1 and a measurement step S2. This method uses a low-frequency modulated laser to periodically heat the sample surface, and then relies on another continuous-wave laser to detect changes in the thermal reflectivity of the single-layer thin film material under test to measure its thermal conductivity. The proportionality coefficient of the measurement system is obtained through the calibration step S1. The thermal conductivity of the sample (single-layer thin film sample) is further detected by measurement step S2. The testing methods provided in the embodiments of this application will be explained in detail below.

[0063] The calibration step S1 in the method for measuring the thermal conductivity of a single-layer thin film material provided in this application embodiment specifically includes:

[0064] S11. Prepare a metal thin film on the surface of a standard sample with a known thermal conductivity.

[0065] For example, combined Figure 3 A thin metal film M1 (such as an aluminum film) is prepared on the surface of a standard sample 33 (such as sapphire) with known thermal conductivity, wherein the standard sample M2 serves as the substrate 26. It should be noted that the metal film M1 is a metal film with a stable thermal reflectivity coefficient (dR / dT) for the continuous wave detection laser wavelength, so as to realize the subsequent detection of thermal reflection signals.

[0066] S12, control the continuous wave probe laser and the modulated heating laser to be coaxial and focused on the same test surface of the metal thin film.

[0067] Specifically, a standard sample is placed at the measurement position, and the continuous wave probe laser S1 and the modulated heating laser S3 are adjusted to be coaxial and precisely focused on the same test surface of the metal thin film M1.

[0068] Optionally, the modulation frequency of the modulated heating laser S2 can be set. In the low-frequency range (e.g., between 10Hz and 1kHz), the sample is brought to near steady-state conditions. The modulated heating laser S1 is activated to periodically heat the standard sample at a low frequency, while the continuous-wave detection laser S1 reflects light from the surface of the standard sample. This reflected light is detected by the detection unit 3 (photodiode) and generates an electrical signal. Because the reflectivity of the metal thin film M1 deposited on the sample surface changes due to heating, the detected reflected light signal is a thermal reflection signal. The wavelengths of the continuous-wave detection laser S1 and the modulated heating laser S2 are determined based on the deposited metal thin film M1. For example, the metal thin film M1 is an aluminum film, and the corresponding wavelength of the continuous-wave detection laser S1 can be selected as 785nm, and the wavelength of the modulated heating laser S2 can be selected as 457nm.

[0069] S13. Obtain the first proportional relationship between the change in the amplitude of the thermal reflection signal of the surface under test under periodic heating conditions and the change in the modulated heating laser power. Based on the first proportional relationship and the heat transfer analytical model corresponding to the standard sample, calculate the proportionality coefficient of the measurement system. .

[0070] The specific modulation steps of the modulated heating laser are as follows:

[0071] The laser power of the modulated heating laser is modulated, and the reflected light signal of the continuous wave probe laser reflected from the measurement area is simultaneously acquired. The amplitude change of the thermal reflection signal of the reflected light signal is extracted; the amplitude change of the thermal reflection signal is established. ) and the change in laser power ( The positive correlation function between them.

[0072] Specifically, the laser power of the modulated heating laser S1 is changed, and the change in laser power is recorded. Simultaneously, the signal processing unit 4 (oscilloscope) acquires the electrical signal detected by the detection unit 3 (photodiode) and extracts the corresponding thermal reflection signal amplitude change. The signal processing unit 4 (oscilloscope) records the changes in the amplitude of the thermal reflection signal. A model for the amplitude change of the thermal reflection signal is established. With the change in laser power A database of proportional relationships between them.

[0073] The calculation formula for the near-steady-state heat transfer analytical model between the metal thin film and the sample structure is as follows:

[0074] (1.1)

[0075] in, This refers to the change in the amplitude of the thermal reflection signal; The change in laser power for modulated heating laser; This is the scaling factor for the test system; The thermal conductivity of the sample; For heat flux density, The solution is determined by the analytical solution of the near-steady-state heat transfer problem of multilayer structures based on Fourier's law. It can also be understood as the temperature rise response per unit heat flux density calculated by using a heat transfer analytical model based on the known thermal conductivity and structural parameters of a standard sample.

[0076] in, Satisfying Relationship: (1.2)

[0077] It is related to the radius of the modulated heating laser and the continuous wave probe laser, as well as the thermal conductivity and interfacial thermal resistance of each layer of the thin film under test. The radius of modulated heating lasers and continuous wave probe lasers is related to the frequency of the modulated heating laser. The time is approximately a constant; The frequency of the modulated heating laser.

[0078] For example, using an aluminum-plated sapphire wafer (standard sample) as the standard, the change in the amplitude of the obtained thermal reflection signal is analyzed. With laser power Based on the direct proportional relationship between the two and the calculation formula of the heat transfer analytical model of the sapphire sheet (standard sample), the proportionality coefficient of the test system is determined. .

[0079] The calculation formula for the heat transfer analytical model based on the metal thin film (aluminum film) M1 and the standard sample M2 / 26 (sapphire sheet) is as follows:

[0080] (1.3)

[0081] in, The change in the amplitude of the thermal reflection signal between the coating and the sapphire wafer; The change in laser power for modulated heating laser; This is the scaling factor for the test system; The thermal conductivity of the sapphire crystal is denoted as φ. The heat flux density of the sapphire wafer. The solution is determined by the analytical solution of the near-steady-state heat transfer problem of multilayer structures based on Fourier's law.

[0082] It should be explained that the metal thin film (aluminum) is a metal film with a stable thermal reflectivity coefficient (dR / dT) for the continuous wave probe laser wavelength, and the thermal conductivity of the standard sample is known. When the laser power of the modulated heating laser S1 increases, the amplitude of the thermal reflection signal changes. The proportionality coefficient increases with increasing power. Combining this with formulas (1.1)-(1.3) above, the proportionality coefficient of the entire test system... To approximate a constant value, it can be seen that the above calibration steps in this application can obtain an accurate proportional coefficient for the test system. .

[0083] It should be noted that the proportional coefficient of the measurement system It is related to the thermal reflectivity of continuous wave probe lasers, modulated heating lasers, and metal thin films, but not to the substrate material.

[0084] Determining the proportional coefficient of the measurement system Then, according to the calibration step S1 provided in the above embodiment, the thermal conductivity of the sample to be tested (single-layer thin film sample) is determined using the same measurement method. .

[0085] Furthermore, the measurement step S2 in the method for measuring the thermal conductivity of a single-layer thin film material provided in this application embodiment specifically includes:

[0086] S21. Prepare a metal thin film on the surface of the single-layer thin film sample to be tested.

[0087] For example, combined Figure 4 A thin metal film M1 (such as an aluminum film) is prepared on the surface of the monolayer thin film sample M3 to be tested. The monolayer thin film sample M3 is placed on a substrate 26. The substrate 26 can be a sapphire wafer or other chemically stable substrate materials, such as silicon nitride thin film / silicon substrate.

[0088] S22. Under the same measurement conditions, control the continuous wave probe laser and the modulated heating laser to be coaxial and focused on the same surface of the metal thin film.

[0089] Specifically, refer to Figure 1 The single-layer thin film sample to be tested is placed in the measurement position, and the continuous wave probe laser S1 and the modulated heating laser S2 are adjusted to be coaxial and precisely focused on the test surface corresponding to the metal thin film M1 on the single-layer thin film sample to be tested.

[0090] Under the same measurement conditions as in calibration step S1, set the modulation frequency of the modulated heating laser S2. In the low-frequency range (e.g., between 10Hz and 1kHz), the sample is brought to near steady-state conditions. The modulated heating laser S1 is activated to periodically heat the monolayer thin film sample at a low frequency, while the continuous-wave probe laser S1 reflects light from the surface of the sample. The reflected light is detected by the detection unit 3 (photodiode) and generates an electrical signal. Because the reflectivity of the metal thin film M1 deposited on the sample surface changes due to heating, the detected reflected light signal is a thermal reflection signal. The metal thin film M1 is an aluminum film, and the corresponding wavelength of the continuous-wave probe laser S1 can be selected as 785nm, while the wavelength of the modulated heating laser S2 can be selected as 457nm.

[0091] S23. Obtain the second proportional relationship between the change in the amplitude of the thermal reflection signal of the surface under test under periodic heating conditions and the change in the modulated heating laser power. Based on the second proportional relationship and the proportionality coefficient... And the thermal conductivity of samples containing monolayer thin films The thermal conductivity of the single-layer thin film sample under test is obtained by inversion calculation using the heat transfer analytical model. .

[0092] The specific modulation steps of the modulated heating laser are as follows: change the laser power of the modulated heating laser S1 and record the change in laser power. Simultaneously, the signal processing unit 4 (oscilloscope) acquires the electrical signal detected by the detection unit 3 (photodiode) and extracts the corresponding thermal reflection signal amplitude change. The signal processing unit 4 (oscilloscope) records the changes in the amplitude of the thermal reflection signal. A model for the amplitude change of the thermal reflection signal is established. With the change in laser power A database of proportional relationships between them.

[0093] Furthermore, the proportional coefficient of the measurement system is obtained according to calibration step S1. Changes in the amplitude of thermal reflection signal With the change in laser power The proportional relationship between them and the thermal conductivity of the monolayer thin film sample to be tested. The thermal conductivity of the single-layer thin film sample under test is obtained by inversion calculation using the heat transfer analytical model. .

[0094] Specifically, based on the thermal conductivity of the metal thin film (aluminum film) and the single-layer thin film sample to be tested. The calculation formula for the heat transfer analytical model is:

[0095] (1.4)

[0096] in, The change in the amplitude of the thermal reflection signal of the single-layer thin film sample to be tested; The change in laser power for modulated heating laser; This is the scaling factor for the test system; The thermal conductivity of the single-layer thin film sample to be tested; The heat flux density of the single-layer thin film sample to be tested; The solution is determined by the analytical solution of the near-steady-state heat transfer problem of multilayer structures based on Fourier's law.

[0097] Specifically, combining formula (1.4) and the various parameters obtained from the test... , , , as well as The database was used to inversely calculate the thermal conductivity of the monolayer thin film sample to be tested. .

[0098] Optionally, in the calibration and measurement steps, the control method further includes optical path alignment, specifically including:

[0099] The spot radius of the continuous wave probe laser in the measurement area is controlled to be less than 5 micrometers, while the spot radius of the modulated heating laser in the measurement area is controlled to be greater than that of the continuous wave probe laser. Combined with... Figure 1 and Figure 2 This application improves the utilization rate of beam heating and reflection recovery, and enhances detection accuracy by adjusting the positions of various components in the optical path to ensure that the centers of the two laser beams overlap in the detection area on the sample surface.

[0100] The core principle of the calibration and testing steps in this application is based on the thermal reflection effect of a metal thin film: when a modulated heating laser periodically heats the metal film on the sample surface, its temperature changes periodically, causing a corresponding change in its reflectivity to the probe laser (dR / dT effect). The change in reflected light intensity (i.e., the thermal reflection signal) is detected and extracted. Under low-frequency (near steady-state) heating conditions, the temperature field distribution inside the sample is directly related to the thermal conductivity and interface characteristics of each layer of material (metal film, test film, substrate). Calibration eliminates inherent system parameters ( After the influence of heat, the ratio of the amplitude of the thermal reflection signal to the heating power is uniquely determined by the thermal conductivity of the film under test. The heat transfer analytical model determines the result, which can then be obtained through inversion calculations. .

[0101] An ideal method should have a wide thermal conductivity measurement range, be non-contact, have micron-level spatial resolution, be widely applicable to materials, have low hardware costs, and be highly resistant to environmental interference.

[0102] The following is a specific embodiment to further explain the testing method provided in the embodiments of this application.

[0103] Example

[0104] The first step is to prepare the sample: an aluminum film of about 50 nm thickness is deposited on the surface of the silicon nitride thin film / silicon substrate sample to be tested by electron beam evaporation.

[0105] The second step is to calibrate the standard sample: a sapphire wafer with the same aluminum film coating is selected as the standard sample. It is placed on the sample stage, and the laser is focused. The laser power of the modulated heating laser is gradually changed, and the changes in laser power are recorded. Record the amplitude changes of the corresponding thermal reflection signal on the oscilloscope. and DC level The change in the amplitude of the thermal reflection signal was obtained. ,draw and The slope of the relationship curve is... .

[0106] The third step is to develop a near-steady-state analytical model of heat transfer based on a metal thin film and sapphire structure:

[0107] (1.3) Calculate the temperature rise per unit heat flux. Calculate the proportionality coefficient of the measurement system. .

[0108] Step 4: Measure the sample to be tested: Replace the standard sample with the "aluminum film / silicon nitride thin film / silicon substrate" sample to be tested. Under the same test conditions, measure the change in the amplitude of the thermal reflection signal of the silicon nitride thin film to be tested. With changes in laser power The slope of the relationship curve is... .

[0109] Step 5: Near-steady-state analytical heat transfer model based on aluminum / silicon nitride film:

[0110] (1.4) Calculate the temperature rise per unit heat flux. Inversion calculation of the thermal conductivity of silicon nitride thin film .

[0111] In this heat transfer analytical model, the thermal conductivity of the aluminum film and the silicon substrate is known, the interfacial thermal resistance can be estimated or used as a secondary parameter, and the thermal conductivity of the silicon nitride film is... Let this be the variable to be determined. The measured values... and calibration coefficients Substitute into formula (1.4) and adjust... The value makes the model calculate Matching the measurement results, the corresponding The value is the thermal conductivity of the silicon nitride thin film.

[0112] The results verify that the measurement method provided in this application is used to measure the reference thin film with known thermal conductivity. The results are in good agreement with the literature values, proving the accuracy of this method.

[0113] In summary, the embodiments of this application provide a method and system for measuring the thermal conductivity of monolayer thin film materials. It uses conventional continuous lasers and optical components, and its cost is significantly lower than that of TDTR and FDTR systems. Moreover, the low-frequency measurement makes the signal very stable and insensitive to environmental vibrations, and it has high measurement accuracy for the thermal conductivity of monolayer thin film materials.

[0114] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein. Features of various embodiments of the present invention can be partially or wholly coupled or combined with each other, and can cooperate and be technically driven in various ways. Various obvious changes, readjustments, combinations, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments. Many other equivalent embodiments may be included without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for measuring the thermal conductivity of a single-layer thin film material, characterized in that, include: Calibration steps: Prepare a metal thin film on the surface of a standard sample with known thermal conductivity; control the continuous wave probe laser and the modulated heating laser to be coaxial and focused on the same test surface of the metal thin film; obtain the first proportional relationship between the change in the amplitude of the thermal reflection signal of the test surface under periodic heating conditions and the change in the power of the modulated heating laser; wherein, the metal thin film is a metal film with a stable thermal reflectivity coefficient for the wavelength of the continuous wave probe laser; Based on the first proportional relationship and the heat transfer analytical model corresponding to the standard sample, the proportional coefficient of the measurement system is calculated. Measurement steps: Prepare a metal thin film on the surface of the monolayer thin film sample to be tested; Under the same measurement conditions, the continuous wave probe laser and the modulated heating laser are controlled to be coaxial and focused on the same test surface of the metal thin film; the second proportional relationship between the change in the amplitude of the thermal reflection signal of the test surface under periodic heating conditions and the change in the power of the modulated heating laser is obtained; The thermal conductivity of the single-layer thin film sample to be tested is obtained by inversion calculation based on the second proportional relationship, the proportional coefficient, and the heat transfer analytical model including the thermal conductivity of the single-layer thin film sample.

2. The method according to claim 1, characterized in that, In the calibration step and the measurement step, obtaining the proportional relationship between the change in the amplitude of the thermal reflection signal of the surface under test under periodic heating conditions and the change in the modulated heating laser power includes: The laser power of the modulated heating laser is modulated, and the reflected light signal of the continuous wave probe laser reflected from the measurement area is collected simultaneously. The change in the amplitude of the thermal reflection signal of the reflected light signal is extracted. A positive correlation function relationship is established between the change in the amplitude of the thermal reflection signal and the change in the laser power.

3. The method according to claim 1, characterized in that, In the calibration step and the measurement step, The calculation formula for the heat transfer analytical model is as follows: ； in, This refers to the change in the amplitude of the thermal reflection signal; The change in laser power of the modulated heating laser; The proportionality coefficient of the system; The thermal conductivity of the sample; For heat flux density, The solution is determined by the analytical solution of the near-steady-state heat transfer problem of multilayer structures based on Fourier's law.

4. The method according to claim 1, characterized in that, In the calibration step and the measurement step, the control method further includes: The spot radius of the continuous wave probe laser in the measurement area is controlled to be less than 5 micrometers, and the spot radius of the modulated heating laser in the measurement area is controlled to be greater than the spot radius of the continuous wave probe laser.

5. The method according to claim 1, characterized in that, In the calibration step and the measurement step, the modulation frequency of the modulated heating laser is set to a frequency range that keeps the heat conduction process in the measurement area in a near-steady or quasi-steady state.

6. The method according to claim 5, characterized in that, The modulation frequency range of the heating laser is 0 Hz to 1 kHz.

7. A system for measuring the thermal conductivity of a single-layer thin film material, used to implement the method for measuring the thermal conductivity of a single-layer thin film material as described in any one of claims 1-6, characterized in that, include: A laser unit is provided for providing a continuous wave probe laser and a modulated heating laser; the laser power and frequency of the modulated heating laser are adjustable. A beam combining and focusing unit is used to coaxially focus the continuous wave probe laser and the modulated heating laser onto the same measurement area on the sample surface; The detection unit is used to receive the reflected light signal of the continuous wave detection laser reflected from the measurement area and convert it into an electrical signal; The signal processing unit is configured as follows: Control the power of the continuous wave probe laser and the modulation frequency and laser power of the modulated heating laser; The electrical signal output by the detection unit is collected and processed, and the amplitude change of the heat reflection signal corresponding to the heating modulation frequency is extracted; In the calibration step, the first proportional relationship between the change in the amplitude of the thermal reflection signal of the standard sample surface with known thermal conductivity under periodic heating conditions and the change in modulated heating laser power is obtained. Combined with the known thermal conductivity and the heat transfer analytical model corresponding to the standard sample, the proportional coefficient of the measurement system is calculated. In the measurement step, a second proportional relationship is obtained between the change in the amplitude of the thermal reflection signal on the surface of the monolayer thin film sample under periodic heating conditions and the change in the modulated heating laser power. Combined with the proportional coefficient and a heat transfer analytical model that includes the thermal conductivity of the monolayer thin film sample, the thermal conductivity of the monolayer thin film sample under test is calculated by inversion.

8. The system according to claim 7, characterized in that, The beam combining and focusing unit includes a polarizing beam splitter, a quarter-wave plate, a dichroic mirror, and an objective lens arranged in sequence.

9. The system according to claim 8, characterized in that, The detection unit is a photodiode, which is disposed in the transmission optical path of the polarizing beam splitter; the signal processing unit includes a lock-in amplifier or a digital oscilloscope with spectrum analysis function.

10. The system according to claim 7, characterized in that, The output end of the modulated heating laser in the laser unit is equipped with a beam expander to adjust the spot size of the heating laser in the measurement area.

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