Nondestructive pump-probe thermal reflection testing method based on thin film transfer

Abstract

This invention discloses a nondestructive pump-probe thermal reflectance testing method based on thin film transfer. This method ensures that no metal or organic material remains on the surface after testing. While the quality, thickness, and interface of metal films vary from batch to batch during film coating, transfer ensures consistent quality, thickness, and interface conditions for metal films. This method is versatile, fast, low-cost, highly reproducible, and reliable, and can also enable metal recycling.

Description

Technical Field

[0001] The present invention relates to the fields of transfer technology and thermal reflection testing, and in particular to a non-destructive pump-probe thermal reflection testing method based on thin film transfer. Background Art

[0002] Pump-probe thermoreflectance techniques include time-domain thermoreflectance (TDTR), frequency-domain thermoreflectance (FDTR), transient thermoreflectance (TTR), and steady-state thermoreflectance (SSTR). These techniques are commonly used to characterize the thermophysical properties of electronic device materials (metals, ceramics, semiconductors, etc.). A pump light source heats the sample surface, causing a temperature change. A probe laser detects changes in surface reflectivity. Based on the principle of thermoreflectance (reflectivity changes proportional to temperature), the probe laser indirectly detects changes in surface temperature. This temperature change contains information about the material's thermophysical properties, and combined with a heat conduction model, the thermophysical properties of multilayer materials (thermal conductivity, interfacial thermal resistance) are fitted. To achieve a linear relationship between reflectivity and temperature changes, metal plating is usually required on the material surface, as most metals, such as Au and Al, satisfy good linearity. Furthermore, the surface metal ensures that the heating laser light is fully absorbed and converted into heat. Common coating methods include thermal evaporation, electron beam evaporation, magnetron sputtering, etc. They can all form a good bonding force between the material and the metal film. However, during the testing process, the metal will diffuse into the material to form a mixed layer that destroys the material, so it cannot be applied to fast production lines. Summary of the Invention

[0003] Traditional heat reflection technology is destructive to materials when using metal films. In the prior art, the metal film of the transition substrate is transferred to the sample to be tested using a polydimethylsiloxane (PDMS)-assisted transfer method. The main purpose of the present invention is to provide a non-destructive testing technology based on thin film transfer and realize the recycling of metal films. It is a more universal, fast and low-cost non-destructive pump-probe heat reflection testing method, which realizes the recycling of metal on the material surface.

[0004] To achieve the above objectives, the present invention provides a non-destructive pump-probe thermal reflection testing method based on thin film transfer, which is characterized by the following steps:

[0005] S1: A metal film is deposited on a transition substrate and the film thickness needs to be calibrated;

[0006] S2: Covering the metal film with PDMS, and controlling the temperature within a range from room temperature to 200°C; the PDMS is formed by mixing a main agent, namely glue A, and a hardener, namely glue B, and then curing the mixture;

[0007] S3: After the glass slide is brought into contact with the PDMS, the glass slide is squeezed;

[0008] S4: PDMS peels off the metal film;

[0009] S5: Place the sample to be tested; fully contact the metal film with the sample to be tested, and squeeze the glass slide at room temperature to 200°C;

[0010] S6: The metal film is separated from PDMS and transferred to the sample;

[0011] S7: Measure the thickness, roughness and wrinkles of the metal film and determine the area for testing after transfer;

[0012] S8: Using the transferred metal film to perform pump-probe thermal reflection testing on the sample to be tested;

[0013] S9: After the test, repeat steps S2-S4 on the metal film to remove the metal on the sample to be tested; thereafter, clean the sample surface;

[0014] S10: Analyze the sample surface to verify whether there is any residue.

[0015] The specific steps are:

[0016] Step S1: A metal film is deposited on a transition substrate. The substrate can be a flat substrate such as silicon (Si), sapphire, or silicon dioxide / silicon (SiO2 / Si). The metal film can be a single layer of metal such as gold (Au), aluminum (Al), copper (Cu), or platinum (Pt). The film thickness needs to be calibrated. Common coating methods include thermal evaporation, electron beam evaporation, and magnetron sputtering.

[0017] Step S2: Covering the metal film with PDMS, controlling the temperature within the range of room temperature to 200°C, preferably 150°C; the PDMS is made by mixing a main agent (glue A) and a hardener (glue B) and then curing; preferably, covering the metal film with PDMS at a temperature of 150°C; the mass ratio of glue A to glue B is 10:1.

[0018] Step S3: Using a micro-motion platform, adhere the glass slide to the bottom of the platform, slowly lower it until it is in full contact with the PDMS, and squeeze the glass slide for 0-20 minutes; preferably, the squeezing time is 5-10 minutes.

[0019] Step S4: The platform is rapidly raised, and the PDMS and the glass sheet are raised together, while the PDMS peels off the metal film.

[0020] The second solution of step S4: In step S1, SiO2 / Si is selected as the substrate, and the entire PDMS / gold film / SiO2 / Si structure obtained through steps S2-S3 is placed in a strong acid or strong base solution, where the strong acid or strong base is no more than 1% hydrofluoric acid (HF) or sodium hydroxide solution (NaOH). The strong acid or strong base solution will etch the sacrificial layer SiO2, and the PDMS will adhere to the metal and separate from the Si. The key to selecting a strong acid or strong base in the present invention is that the strong acid or strong base reacts chemically with SiO2, but does not react with PDMS or metal; it can etch away SiO2, so that the PDMS / metal is separated from the Si substrate.

[0021] For metals Au and Pt with poor adhesion, steps S1-S4 are used to prepare PDMS / metal films.

[0022] For metals with good adhesion, such as Al and Ni, a layer of a metal with poor adhesion (Au, Pt) approximately 1nm (1nm-5nm) can be plated between the metal and the transition substrate. Steps S1-S4 can then be used to create a PDMS / multilayer metal film. This method uses the poorly adhesive metal to peel off the well-adhesive metal. Furthermore, any metal can be fabricated using the second method of steps S1-S4.

[0023] Step S5: Place the sample to be tested, which can be a single-layer material or a multi-layer thin film. Slowly lower the platform, bringing the PDMS / metal film close to the sample until the metal film is in full contact with the sample. Press the glass slide at room temperature to 200°C for 0-20 minutes; preferably, press the glass slide at room temperature to 200°C for 5-10 minutes.

[0024] Step S6: Slowly raise the platform, and the PDMS and glass rise together. At the same time, the metal film will separate from the PDMS and transfer to the sample.

[0025] Step S7: Using an atomic force microscope (AFM) to measure the thickness, roughness, and wrinkles of the metal film, and determine the area that can be used for testing after transfer.

[0026] Step S8: using the transferred metal film to perform a pump-probe thermal reflection test on the sample to be tested.

[0027] Step S9: After the test, repeat steps S2-S4 on the metal film to remove the metal from the sample. Then, clean the sample surface with acetone. Preferably, the cleaning steps include ultrasonic cleaning followed by drying; after the acetone cleaning, repeat the same cleaning steps with isopropyl alcohol.

[0028] Step S10: Analyze the sample surface using high-power microscopy, Raman spectroscopy, fluorescence spectroscopy, AFM, and other tests to verify whether there is any residue. Raman spectroscopy and fluorescence spectroscopy can reveal signals of different materials through peaks, while high-power microscopy and AFM can directly observe the surface structure.

[0029] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0030] The outstanding advantages of the method of the present invention are repeatability, that is, the same result can be obtained after multiple transfers; and reliability, that is, the samples obtained by this method can successfully complete the subsequent thermal reflection test. Specifically:

[0031] 1. Compared with the traditional coating method, this method can achieve no metal material or organic material residue on the surface after testing.

[0032] 2. In the coating method, the quality, thickness and interface of each batch of metal film will be different. Transfer hair can ensure the consistency of the quality, thickness and interface of the metal film.

[0033] 3. This method is universal, fast, low-cost, highly repeatable and reliable, and can achieve the recycling of metals on materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the process from steps S1 to S2 in Example 1 of the present invention;

[0035] Figure 2 Schematic diagram of the process from steps S3 to S4 in Example 1 of the present invention;

[0036] Figure 3 Schematic diagram of the process of steps S5 to S6 in Example 1 of the present invention;

[0037] Figure 4 Schematic diagram of the material structure of a layer of Au (about 1 nm, or 1 nm to 5 nm) plated between the metal and the transition substrate provided in Example 2 of the present invention;

[0038] Figure 5 Schematic diagram of the process from steps S2 to S3 in Example 3 of the present invention. DETAILED DESCRIPTION

[0039] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0040] Example 1

[0041] A non-destructive pump-probe thermal reflection test method, see Figure 1 and Figure 2 , including the following steps:

[0042] Step S1: depositing a layer of Au thin film 20 on the transition substrate 10. Specifically, the thickness of the Au thin film is 80 nm.

[0043] Step S2: Polydimethylsiloxane (PDMS) 30 is placed over the Au film 20 and placed on a heating platform 40. Specifically, PDMS 30 is made by curing a mixture of a base (glue A) and a hardener (glue B) in a ratio of 10:1. The area should be smaller than that of the Au film 20. The heating platform temperature is controlled at 150°C.

[0044] Step S3: The glass sheet 50 is attached to the bottom of the micro-motion platform 60 and slowly lowered until it is in full contact with the PDMS 30, and the glass sheet is pressed for a certain time. Specifically, the temperature is controlled at 150° C. and the pressing time is 5 minutes.

[0045] Step S4: The fine motion platform 60 is rapidly raised, and the PDMS 30 and the glass sheet 50 are raised together. At the same time, the PDMS 30 peels off the Au film 20 .

[0046] Step S5: Place the sample 70 to be tested, slowly lower the micro-motion platform 60, and bring the PDMS 30 / Au film 20 close to the sample 70 until the Au film 20 is in full contact with the sample 70. The glass sheet 50 is then pressed. Specifically, the sample 70 to be tested can be any material, such as a single layer or a multilayer film. This step is performed at 150°C for 5 minutes.

[0047] Step S6: slowly raising the fine motion platform 60 , the PDMS 30 and the glass sheet 50 rise together, and at the same time the Au film 20 is separated from the PDMS 30 and transferred to the sample 70 to be tested.

[0048] Step S7: Using an atomic force microscope (AFM) to measure the thickness, roughness and wrinkles of the Au film 20 to determine the area that can be used for testing after transfer.

[0049] Step S8: using the transferred Au film 20 to perform a pump-probe thermal reflection test on the sample 70 to be tested.

[0050] Step S9: After the test, repeat steps S2-S4 on the Au film 20 to remove the Au from the sample 70. The sample surface is then cleaned with acetone. The cleaning steps include ultrasonic cleaning followed by drying. After the acetone cleaning, the sample surface is then cleaned again using isopropyl alcohol, following the same cleaning steps.

[0051] Step S10: Analyze the sample surface using high-power microscopy, Raman spectroscopy, fluorescence spectroscopy, AFM, and other tests to verify whether there is any residue. Raman spectroscopy and fluorescence spectroscopy can reveal signals of different materials through peaks, while high-power microscopy and AFM can directly observe the surface structure.

[0052] Example 2

[0053] Example 2 provides another non-destructive pump-probe thermal reflection test method. The difference between Example 2 and Example 1 is that the metal film used in Example 2 is an Al structure. Al has a strong bonding force with the transition substrate, so the transfer is assisted by the Au layer with weak bonding force. Figure 2 、 Figure 3 and Figure 4 , including the following steps:

[0054] Step S1: depositing an Al / Au thin film 20 on the transition substrate 10. Specifically, the thickness of the Al thin film 21 in the Al / Au thin film 20 is 80 nm, and the thickness of the Au thin film 22 is 1 nm.

[0055] Step S2: Polydimethylsiloxane (PDMS) 30 is placed over the Al film 21 and placed on a heating platform 40. Specifically, PDMS 30 is made by curing a mixture of a base (glue A) and a hardener (glue B) in a ratio of 10:1. The area should be smaller than that of the Al / Au film 20. The heating platform temperature is controlled at 150°C.

[0056] Step S3: The glass sheet 50 is attached to the bottom of the micro-motion platform 60 and slowly lowered until it is in full contact with the PDMS 30, and the glass sheet is pressed for a certain time. Specifically, the temperature is controlled at 150° C. and the pressing time is 5 minutes.

[0057] Step S4: The fine motion platform 60 is rapidly raised, and the PDMS 30 and the glass sheet 50 are raised together. At the same time, the PDMS 30 peels off the Al / Au film 20 .

[0058] The following steps are basically the same as steps S5-S10 in Example 1, but the difference is that the film to be peeled and transferred is an Al / Au film, and the Al film is smoothly transferred by taking advantage of the relatively low bonding strength of the Au film.

[0059] Example 3

[0060] Example 3 provides another non-destructive pump-probe thermal reflection test method. The difference between Example 3 and the previous two examples is that Example 3 uses a dry-wet hybrid method to transfer the metal film and uses an acid-base solution to etch the sacrificial layer, thereby separating the PDMS, metal film and transition substrate. Figure 5 , including the following steps:

[0061] Step S1: depositing an Al film 20 on a SiO2 / Si substrate 10. Specifically, the thickness of the Al film is 80 nm.

[0062] Step S2: Polydimethylsiloxane (PDMS) 30 is placed over the Al film 20 and placed in a 1% HF solution 40. Specifically, PDMS 30 is made by curing a mixture of a base (glue A) and a hardener (glue B) in a ratio of 10:1. The area of ​​the PDMS 30 should be smaller than that of the Al film 20.

[0063] Step S3: After soaking for a period of time, SiO2 is etched, and the composite structure consisting of PDMS30 and Al film 20 is peeled off from Si substrate 10. The composite structure floats in solution 40.

[0064] Step S4: taking out the above-mentioned combined structure and cleaning and drying it.

[0065] The following steps are essentially the same as steps S5-S10 in Example 1, except that the film being stripped and transferred is an Al film. The bond between the transferred Al film and the sample to be tested is much weaker than the bond between the Al film obtained by direct coating and the transition sample. Therefore, the transfer step does not require the use of an acid or base solution and can be directly transferred using PDMS.

[0066] In summary, the embodiments of the present invention are not limited to the above 1-3. The same and reliable results have been obtained through multiple experiments, which proves that the method of the present invention has high repeatability and reliability.

Claims

1. A non-destructive pump-probe thermal reflection test method based on thin film transfer, characterized by: The steps include: S1: A metal film is deposited on a transition substrate and the film thickness needs to be calibrated; S2: Covering the metal film with PDMS, and controlling the temperature within a range from room temperature to 200°C; the PDMS is formed by mixing a main agent, namely glue A, and a hardener, namely glue B, and then curing the mixture; S3: After the glass slide is brought into contact with the PDMS, the glass slide is squeezed; S4: PDMS peels off the metal film; S5: Place the sample to be tested; fully contact the metal film with the sample to be tested, and squeeze the glass slide at room temperature to 200°C; S6: The metal film is separated from PDMS and transferred to the sample; S7: Measure the thickness, roughness and wrinkles of the metal film and determine the area for testing after transfer; S8: Using the transferred metal film to perform pump-probe thermal reflection testing on the sample to be tested; S9: After the test is completed, steps S2-S4 are repeated on the metal film to transfer the metal on the sample to be tested; Afterwards, the sample surface was cleaned; S10: Analyze the sample surface to verify whether there is any residue.

2. The non-destructive pump-probe thermal reflection testing method based on thin film transfer according to claim 1, characterized in that: The specific steps are: Step S1: depositing a metal film on a transition substrate, wherein the substrate is silicon, sapphire or silicon dioxide / silicon, and the metal film is a single layer of gold, aluminum, copper or platinum, and the film thickness needs to be calibrated; Step S2: Covering the metal film with PDMS, and controlling the temperature within a range from room temperature to 200° C.; the PDMS is formed by mixing a main agent, namely glue A, and a hardener, namely glue B, and then curing the mixture; Step S3: Using a micro-motion platform, adhere the glass slide to the bottom of the platform, slowly lower it until it is in full contact with the PDMS, and squeeze the glass slide for 0-20 minutes; Step S4: rapidly raising the platform, raising the PDMS and the glass sheet together, while the PDMS peels off the metal film; Step S5: placing a sample to be tested, wherein the sample to be tested includes a single-layer material or a multi-layer film material; Slowly lower the platform to bring the PDMS / metal film close to the sample until the metal film is fully in contact with the sample to be tested, and squeeze the glass slide at room temperature to 200°C for 0-20 minutes; Step S6: slowly raising the platform, the PDMS and the glass rise together, and the metal film separates from the PDMS and transfers to the sample; Step S7: using an atomic force microscope (AFM) to measure the thickness, roughness, and wrinkles of the metal film to determine the area to be used for testing after transfer; Step S8: performing a pump-probe thermal reflection test on the sample to be tested using the transferred metal film; Step S9: After the test is completed, repeat steps S2-S4 on the metal film to transfer the metal on the sample to be tested; Afterwards, the sample surface was cleaned with acetone; Step S10: Analyze the sample surface using a high-power microscope, Raman spectroscopy, fluorescence spectroscopy or AFM test to verify whether there is any residue; Raman spectroscopy and fluorescence spectroscopy see signals of different materials through peaks, and high-power microscope and AFM directly observe the surface structure.

3. The non-destructive pump-probe thermal reflection testing method based on thin film transfer according to claim 2, characterized in that: In the step S2: PDMS is covered on the metal film at a temperature of 150° C.; the mass ratio of the A glue to the B glue is 10:

1.

4. The non-destructive pump-probe thermal reflection testing method based on thin film transfer according to claim 3, characterized in that: In step S3, the slide is squeezed for 5-10 minutes.

5. The non-destructive pump-probe thermal reflection testing method based on thin film transfer according to claim 4, characterized in that: In step S4: SiO2 / Si is selected as the substrate in step S1, and the entire PDMS / gold film / SiO2 / Si structure obtained through steps S2-S3 is placed in a strong acid or strong base solution, where the strong acid or strong base is no more than 1% hydrofluoric acid or sodium hydroxide solution; the strong acid or strong base solution will etch the sacrificial layer SiO2, and the PDMS will adhere to the metal and separate from the Si substrate.

6. The non-destructive pump-probe thermal reflection testing method based on thin film transfer according to claim 5, characterized in that: In the step S5: the glass slide is pressed at room temperature to 200° C. for 5-10 minutes.

7. The non-destructive pump-probe thermal reflection testing method based on thin film transfer according to claim 6, characterized in that: In step S9, the cleaning step is: ultrasonic cleaning followed by drying; after cleaning with acetone, the same cleaning steps are repeated with isopropyl alcohol.

8. The non-destructive pump-probe thermal reflection testing method based on thin film transfer according to any one of claims 1 to 7, characterized in that: For metals Au and Pt with poor adhesion, steps S1-S4 are used to prepare PDMS / metal thin films.

9. The non-destructive pump-probe thermal reflection testing method based on thin film transfer according to any one of claims 1 to 7, characterized in that: For metals Al and Ni with good adhesion, a layer of 1nm-5nm of metals Au and Pt with poor adhesion is plated between the metal and the transition substrate, and then steps S1-S4 are used to prepare the PDMS / multilayer metal film to peel off the metal with good adhesion with the help of the metal with poor adhesion.

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