A method for measuring the thickness of a nanoscale oxidation-resistant film

Abstract

The application discloses a kind of measurement methods of nanoscale oxidation-preventing film film thickness, it is related to nanoscale film film thickness measurement technical field, including the following operating steps: the metal foil containing nanoscale oxidation-preventing film is placed in hydrochloric acid solution and soaked, remaining liquid is recorded as extract liquid, record extract liquid volume V1;Extract liquid is diluted, and record dilution ratio a;After dilution, extract liquid is ultrasonic treated, liquid is taken, titration is on polished silicon chip, and record liquid volume V2;It is heated and treated under protective atmosphere, the area of wet spreading is measured, and record wet area S2;The film thickness of the obtained sample is measured by atomic force microscope and the average film thickness is calculated, which is the minimum fragment film thickness h2;The measurement picture is analyzed by pixel point, and the proportion of black points in the picture is recorded, and the black point proportion b is recorded;Substitute formula h1=a×S2×V1×b×h2 / (V2×S1) to calculate the film thickness h1 of nanoscale oxidation-preventing film.

Description

Technical Field

[0001] This invention relates to the field of nanoscale film thickness measurement technology, specifically a method for measuring the thickness of a nanoscale anti-oxidation film. Background Technology

[0002] Anti-oxidation film is a surface treatment technology used to protect metal surfaces from oxidation and corrosion. It is an organic film formed on the metal surface through chemical methods. This film is usually composed of organic compounds and forms a dense and stable protective layer on the metal surface, designed to prevent the metal from oxidizing and discoloring due to exposure to air. This film also has the effects of anti-oxidation and moisture resistance. Moreover, in the subsequent high temperature of soldering, the protective film can be easily removed, allowing the copper surface to immediately bond with the molten solder to form a strong solder joint. However, if the film thickness is too small, the required anti-oxidation effect cannot be achieved.

[0003] Conventional micron-level anti-oxidation films can be obtained by extracting the surface of the anti-oxidation treated product with hydrochloric acid and calculating the film thickness by measuring the absorbance. However, this method is not suitable for nano-level anti-oxidation films because the measurement method itself has a certain bias. Furthermore, since nano-level anti-oxidation films are relatively thin, the extraction amount is small, resulting in a larger measurement error. Therefore, the measurement results are unreliable when testing the thickness of nano-level anti-oxidation films. The accuracy of film thickness measuring instruments is also insufficient for measuring the thickness of nano-level films. If a more precise (optical) method is used, diffuse reflection caused by the excessive roughness of the underlying metal (Ra≈1000nm) will also result in unreliable measurement results.

[0004] This paper proposes a method for measuring the thickness of nanoscale anti-oxidation films, which can accurately measure the thickness of nanoscale anti-oxidation films. Summary of the Invention

[0005] The purpose of this invention is to provide a method for measuring the thickness of nanoscale anti-oxidation films, so as to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] Step 1: Sample preparation: Use metal foil containing a nanoscale anti-oxidation film (metal foil containing an OSP film) as the sample;

[0008] Step 2: Immerse the sample in hydrochloric acid solution; remove the sample, and record the remaining liquid as the extract, and record the volume of the extract as V1;

[0009] Step 3: Dilute the extract and record the dilution ratio as 'a';

[0010] Step 4: The diluted extract obtained in Step 3 is subjected to ultrasonic treatment, the liquid is collected, and it is titrated onto a polished silicon wafer, allowed to freely wet and spread, and the volume of the liquid collected is recorded as V2.

[0011] Step 5: Heat the sample obtained in Step 4 under a protective atmosphere, measure the area of ​​wetting and spreading, and record the wetting area as S2;

[0012] Step 6: Measure the film thickness of the sample obtained in Step 5 at multiple points using an atomic force microscope and calculate the average film thickness, which is the minimum fragment thickness. Record the minimum fragment thickness as h2.

[0013] Step 7: Simultaneously analyze the proportion of black dots in the measured image from Step 6 by pixel point analysis, and record the proportion of black dots as b.

[0014] Step 8: Calculate the thickness h1 of the nanoscale anti-oxidation film of the sample in Step 1 using the formula h1=a×S2×V1×b×h2 / (V2×S1).

[0015] In the scheme, the formula h1=a×S2×V1×b×h2 / (V2×S1) is derived from S1×h1 / V1=a×S2×b×h2 / V2; h2 is obtained by multi-point measurement of the sample obtained in step 5 using an atomic force microscope.

[0016] In the procedure, the sample is immersed in hydrochloric acid solution to completely dissolve the OSP film. During immersion, the OSP film will break into fragments. Subsequent dilution prevents the fragments from stacking. The fragments are then dropped onto a silicon wafer, dried, and measured at multiple points. The average value of the multi-point measurements is recorded as the minimum fragment thickness h2. The thermal decomposition temperature of the OSP film is around 150℃, and heating at 40-60℃ has no effect on the OSP film.

[0017] For optimal results, the dilution factor is a = 5 to 50; and the liquid volume is V2 = 0.1 μL to 10 μL.

[0018] More optimally, the concentration of the hydrochloric acid solution is 3wt% to 7wt%; the ratio of sample to hydrochloric acid solution in step 1 is (30mm×50mm):(25-100mL).

[0019] A more optimized heat treatment condition is: under vacuum / nitrogen conditions, at a temperature of 40–60°C for 30–60 minutes.

[0020] In a more optimized configuration, the vibration frequency of the ultrasonic treatment is ≥28KHz, and the ultrasonic treatment time is ≥5 minutes.

[0021] In a more optimized manner, the roughness of the polished silicon wafer is ≤1nm; the immersion treatment time is 1 to 5 minutes.

[0022] More preferably, the metal foil includes one of copper foil, aluminum foil, and nickel foil.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. It can measure nanoscale anti-oxidation films (OSP films); 2. The measurement error is small. Attached Figure Description

[0025] Figure 1 The copper foil containing a nanoscale anti-oxidation film prepared in step 1 of Example 1;

[0026] Figure 2 In step 2 of Example 1, the sample is immersed in hydrochloric acid solution;

[0027] Figure 3 The diluted extract solution from step 4 of Example 1 is used to wet and spread on a polished silicon wafer;

[0028] Figure 4 In step 6 of Example 1, the thickness of the sample obtained in step 5 is measured at multiple points.

[0029] Figure 5 The image is a measurement image from step 6 of step 7 in Example 1. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1: A method for measuring the thickness of a nanoscale anti-oxidation film, comprising the following steps;

[0032] Step 1: Prepare the sample: such as Figure 1 As shown, copper foil containing a nano-scale anti-oxidation film (S1 = 30 × 50 mm) 2 ) as a sample;

[0033] Step 2: As Figure 2 As shown, the sample was immersed in a 3wt% hydrochloric acid solution (V1 = 50 mL) for 1 minute (extraction time); the sample was removed, and the remaining liquid was recorded as the extract, with the volume of the extract recorded as V1.

[0034] Step 3: Dilute the extract 10 times and record the dilution factor as a;

[0035] Step 4: The diluted extract obtained in Step 3 is ultrasonically treated at a vibration frequency of 28 kHz for 5 minutes. 0.1 μL of the solution is then titrated onto a polished silicon wafer, allowing it to freely wet and spread. Figure 3As shown; record the volume of liquid taken as V2;

[0036] Step 5: Heat the sample obtained in Step 4 at 50°C for 45 minutes under a protective atmosphere, measure the area of ​​wetting and spreading, and record the wetting area as S2;

[0037] Step 6: Measure the film thickness of the sample obtained in Step 5 at multiple points (5 points) using an atomic force microscope, and calculate the average film thickness at the 5 points. Figure 4 As shown, it is the minimum fragment film thickness. The minimum fragment thickness h2 is recorded in Table 2.

[0038] Step 7: Simultaneously transfer the measurement images from Step 6, such as... Figure 5 As shown in Table 2, the proportion of black dots in the image is analyzed by pixel points, and the proportion of black dots is recorded as b.

[0039] Step 8: Calculate the thickness h1 of the nanoscale anti-oxidation film of the sample in Step 1 using the formula h1=a×S2×V1×b×h2 / (V2×S1).

[0040] Example 2 is based on Example 1, except that the sample is extracted in hydrochloric acid solution for 3 minutes and the liquid volume V2 = 0.5 μL;

[0041] Step 1: Sample preparation: Using copper foil containing a nano-scale anti-oxidation film (S1 = 30 × 50 mm) 2 ) as a sample;

[0042] Step 2: Immerse the sample in 3wt% hydrochloric acid solution (V1 = 50 mL) for 3 minutes (extraction time); remove the sample, and record the remaining liquid as the extract, and record the volume of the extract as V1;

[0043] Step 3: Dilute the extract 10 times and record the dilution factor as a;

[0044] Step 4: The diluted extract obtained in Step 3 is sonicated at a vibration frequency of 28 kHz for 5 minutes. Take 0.5 μL of the extract and titrate it onto the polished silicon wafer, allowing it to freely wet and spread. Record the volume of the extract as V2.

[0045] Step 5: Heat the sample obtained in Step 4 at 50°C for 45 minutes under a protective atmosphere, measure the area of ​​wetting and spreading, and record the wetting area as S2;

[0046] Step 6: Measure the film thickness of the sample obtained in Step 5 at multiple points (5 points) using an atomic force microscope, and calculate the average film thickness at the 5 points, which is the minimum fragment film thickness. Record the minimum fragment thickness h2.

[0047] Step 7: Simultaneously analyze the proportion of black dots in the measured image from Step 6 by pixel point analysis, and record the proportion of black dots as b.

[0048] Step 8: Calculate the thickness h1 of the nanoscale anti-oxidation film of the sample in Step 1 using the formula h1=a×S2×V1×b×h2 / (V2×S1).

[0049] Example 3 is based on Example 1, except that the sample is extracted in hydrochloric acid solution for 5 minutes and the liquid volume V2 = 1.0 μL;

[0050] Step 1: Sample preparation: Using copper foil containing a nano-scale anti-oxidation film (S1 = 30 × 50 mm) 2 ) as a sample;

[0051] Step 2: Immerse the sample in 3wt% hydrochloric acid solution (V1 = 50 mL) for 5 minutes (extraction time); remove the sample, and record the remaining liquid as the extract, and record the volume of the extract as V1;

[0052] Step 3: Dilute the extract 10 times and record the dilution factor as a;

[0053] Step 4: The diluted extract obtained in Step 3 is sonicated at a vibration frequency of 28 kHz for 5 minutes. Take 1.0 μL of the extract and titrate it onto the polished silicon wafer, allowing it to freely wet and spread. Record the volume of the extract as V2.

[0054] Step 5: Heat the sample obtained in Step 4 at 50°C for 45 minutes under a protective atmosphere, measure the area of ​​wetting and spreading, and record the wetting area as S2;

[0055] Step 6: Measure the film thickness of the sample obtained in Step 5 at multiple points (5 points) using an atomic force microscope, and calculate the average film thickness at the 5 points, which is the minimum fragment film thickness. Record the minimum fragment thickness h2.

[0056] Step 7: Simultaneously analyze the proportion of black dots in the measured image from Step 6 by pixel point analysis, and record the proportion of black dots as b.

[0057] Step 8: Calculate the thickness h1 of the nanoscale anti-oxidation film of the sample in Step 1 using the formula h1=a×S2×V1×b×h2 / (V2×S1).

[0058] Example 4 is based on Example 1, except that the hydrochloric acid solution is 5 wt%;

[0059] Step 1: Sample preparation: Using copper foil containing a nano-scale anti-oxidation film (S1 = 30 × 50 mm) 2 ) as a sample;

[0060] Step 2: Immerse the sample in 5wt% hydrochloric acid solution (V1 = 50mL) for 1 minute (extraction time); remove the sample, and record the remaining liquid as the extract, and record the volume of the extract as V1;

[0061] Step 3: Dilute the extract 10 times and record the dilution factor as a;

[0062] Step 4: The diluted extract obtained in Step 3 is sonicated at a vibration frequency of 28 kHz for 5 minutes. Take 0.1 μL of the extract and titrate it onto the polished silicon wafer, allowing it to freely wet and spread. Record the volume of the extract as V2.

[0063] Step 5: Heat the sample obtained in Step 4 at 50°C for 45 minutes under a protective atmosphere, measure the area of ​​wetting and spreading, and record the wetting area as S2;

[0064] Step 6: Measure the film thickness of the sample obtained in Step 5 at multiple points (5 points) using an atomic force microscope, and calculate the average film thickness at the 5 points, which is the minimum fragment film thickness. Record the minimum fragment thickness h2.

[0065] Step 7: Simultaneously analyze the proportion of black dots in the measured image from Step 6 by pixel point analysis, and record the proportion of black dots as b.

[0066] Step 8: Calculate the thickness h1 of the nanoscale anti-oxidation film of the sample in Step 1 using the formula h1=a×S2×V1×b×h2 / (V2×S1).

[0067] Example 5 is based on Example 4, except that the sample is extracted in hydrochloric acid solution for 3 minutes; the liquid volume V2 = 0.5 μL.

[0068] Step 1: Sample preparation: Using copper foil containing a nano-scale anti-oxidation film (S1 = 30 × 50 mm) 2 ) as a sample;

[0069] Step 2: Immerse the sample in 5wt% hydrochloric acid solution (V1 = 50 mL) for 3 minutes (extraction time); remove the sample, and record the remaining liquid as the extract, and record the volume of the extract as V1;

[0070] Step 3: Dilute the extract 10 times and record the dilution factor as a;

[0071] Step 4: The diluted extract obtained in Step 3 is sonicated at a vibration frequency of 28 kHz for 5 minutes. Take 0.5 μL of the extract and titrate it onto the polished silicon wafer, allowing it to freely wet and spread. Record the volume of the extract as V2.

[0072] Step 5: Heat the sample obtained in Step 4 at 50°C for 45 minutes under a protective atmosphere, measure the area of ​​wetting and spreading, and record the wetting area as S2;

[0073] Step 6: Measure the film thickness of the sample obtained in Step 5 at multiple points (5 points) using an atomic force microscope, and calculate the average film thickness at the 5 points, which is the minimum fragment film thickness. Record the minimum fragment thickness h2.

[0074] Step 7: Simultaneously analyze the proportion of black dots in the measured image from Step 6 by pixel point analysis, and record the proportion of black dots as b.

[0075] Step 8: Calculate the thickness h1 of the nanoscale anti-oxidation film of the sample in Step 1 using the formula h1=a×S2×V1×b×h2 / (V2×S1).

[0076] Example 6 is based on Example 5, except that the sample is extracted in hydrochloric acid solution for 5 minutes; the liquid volume V2 = 1.0 μL;

[0077] Step 1: Sample preparation: Using copper foil containing a nano-scale anti-oxidation film (S1 = 30 × 50 mm) 2 ) as a sample;

[0078] Step 2: Immerse the sample in 5wt% hydrochloric acid solution (V1 = 50mL) for 5 minutes (extraction time); remove the sample, and record the remaining liquid as the extract, and record the volume of the extract as V1;

[0079] Step 3: Dilute the extract 10 times and record the dilution factor as a;

[0080] Step 4: The diluted extract obtained in Step 3 is sonicated at a vibration frequency of 28 kHz for 5 minutes. Take 1.0 μL of the extract and titrate it onto the polished silicon wafer, allowing it to freely wet and spread. Record the volume of the extract as V2.

[0081] Step 5: Heat the sample obtained in Step 4 at 50°C for 45 minutes under a protective atmosphere, measure the area of ​​wetting and spreading, and record the wetting area as S2;

[0082] Step 6: Measure the film thickness of the sample obtained in Step 5 at multiple points (5 points) using an atomic force microscope, and calculate the average film thickness at the 5 points, which is the minimum fragment film thickness. Record the minimum fragment thickness h2.

[0083] Step 7: Simultaneously analyze the proportion of black dots in the measured image from Step 6 by pixel point analysis, and record the proportion of black dots as b.

[0084] Step 8: Calculate the thickness h1 of the nanoscale anti-oxidation film of the sample in Step 1 using the formula h1=a×S2×V1×b×h2 / (V2×S1).

[0085] Example 7 is based on Example 1, except that the concentration of the hydrochloric acid solution is 7 wt%.

[0086] Step 1: Sample preparation: Using copper foil containing a nano-scale anti-oxidation film (S1 = 30 × 50 mm) 2 ) as a sample;

[0087] Step 2: Immerse the sample in 7wt% hydrochloric acid solution (V1 = 50 mL) for 1 minute (extraction time); remove the sample, and record the remaining liquid as the extract, and record the volume of the extract as V1;

[0088] Step 3: Dilute the extract 10 times and record the dilution factor as a;

[0089] Step 4: The diluted extract obtained in Step 3 is sonicated at a vibration frequency of 28 kHz for 5 minutes. Take 0.1 μL of the extract and titrate it onto the polished silicon wafer, allowing it to freely wet and spread. Record the volume of the extract as V2.

[0090] Step 5: Heat the sample obtained in Step 4 at 50°C for 45 minutes under a protective atmosphere, measure the area of ​​wetting and spreading, and record the wetting area as S2;

[0091] Step 6: Measure the film thickness of the sample obtained in Step 5 at multiple points (5 points) using an atomic force microscope, and calculate the average film thickness at the 5 points, which is the minimum fragment film thickness. Record the minimum fragment thickness h2.

[0092] Step 7: Simultaneously analyze the proportion of black dots in the measured image from Step 6 by pixel point analysis, and record the proportion of black dots as b.

[0093] Step 8: Calculate the thickness h1 of the nanoscale anti-oxidation film of the sample in Step 1 using the formula h1=a×S2×V1×b×h2 / (V2×S1).

[0094] Example 8 is based on Example 7, except that the sample is extracted in hydrochloric acid solution for 3 minutes; the liquid volume V2 = 0.5 μL;

[0095] Step 1: Sample preparation: Using copper foil containing a nano-scale anti-oxidation film (S1 = 30 × 50 mm) 2 ) as a sample;

[0096] Step 2: Immerse the sample in 7wt% hydrochloric acid solution (V1 = 50 mL) for 3 minutes (extraction time); remove the sample, and record the remaining liquid as the extract, and record the volume of the extract as V1;

[0097] Step 3: Dilute the extract 10 times and record the dilution factor as a;

[0098] Step 4: The diluted extract obtained in Step 3 is sonicated at a vibration frequency of 28 kHz for 5 minutes. Take 0.5 μL of the extract and titrate it onto the polished silicon wafer, allowing it to freely wet and spread. Record the volume of the extract as V2.

[0099] Step 5: Heat the sample obtained in Step 4 at 50°C for 45 minutes under a protective atmosphere, measure the area of ​​wetting and spreading, and record the wetting area as S2;

[0100] Step 6: Measure the film thickness of the sample obtained in Step 5 at multiple points (5 points) using an atomic force microscope, and calculate the average film thickness at the 5 points, which is the minimum fragment film thickness. Record the minimum fragment thickness h2.

[0101] Step 7: Simultaneously analyze the proportion of black dots in the measured image from Step 6 by pixel point analysis, and record the proportion of black dots as b.

[0102] Step 8: Calculate the thickness h1 of the nanoscale anti-oxidation film of the sample in Step 1 using the formula h1=a×S2×V1×b×h2 / (V2×S1).

[0103] Example 9 is based on Example 7, except that the sample is extracted in hydrochloric acid solution for 5 minutes; the liquid volume V2 = 1.0 μL;

[0104] Step 1: Sample preparation: Using copper foil containing a nano-scale anti-oxidation film (S1 = 30 × 50 mm) 2 ) as a sample;

[0105] Step 2: Immerse the sample in 7wt% hydrochloric acid solution (V1 = 50mL) for 5 minutes (extraction time); remove the sample, and record the remaining liquid as the extract, and record the volume of the extract as V1;

[0106] Step 3: Dilute the extract 10 times and record the dilution factor as a;

[0107] Step 4: The diluted extract obtained in Step 3 is sonicated at a vibration frequency of 28 kHz for 5 minutes. Take 1.0 μL of the extract and titrate it onto the polished silicon wafer, allowing it to freely wet and spread. Record the volume of the extract as V2.

[0108] Step 5: Heat the sample obtained in Step 4 at 50°C for 45 minutes under a protective atmosphere, measure the area of ​​wetting and spreading, and record the wetting area as S2;

[0109] Step 6: Measure the film thickness of the sample obtained in Step 5 at multiple points (5 points) using an atomic force microscope, and calculate the average film thickness at the 5 points, which is the minimum fragment film thickness. Record the minimum fragment thickness h2.

[0110] Step 7: Simultaneously analyze the proportion of black dots in the measured image from Step 6 by pixel point analysis, and record the proportion of black dots as b.

[0111] Step 8: Calculate the thickness h1 of the nanoscale anti-oxidation film of the sample in Step 1 using the formula h1=a×S2×V1×b×h2 / (V2×S1).

[0112] Calculate the thickness h1 of the nanoscale OSP film;

[0113] Based on the concentration of the extract and the concentration of the diluted extract, this invention yields S1×h1 / V1=a×S2×b×h2 / V2, and the film thickness calculation formula is h1=a×S2×V1×b×h2 / (V2×S1).

[0114] The liquid volume V2 in Table 1 corresponds to the minimum fragment thickness h2, wetting area S2, and black spot percentage b in Table 2, where S1 = 1500 mm. 2 Given a = 10 and V1 = 50 mL, substituting these values ​​into the formula h1 = a × S2 × V1 × b × h2 / (V2 × S1), the thickness h1 of the nanoscale OSP membrane is calculated, as shown in Table 2.

[0115]

[0116]

[0117] Table 1

[0118]

[0119] Table 2

[0120] Conclusion: As can be seen from the data in Table 2, the error in the calculated OSP membrane thickness is small.

[0121] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method of measuring the thickness of a nanoscale oxidation resistant film, characterized by: The method comprises the following steps: Step 1: preparing a sample: taking a copper foil with a nanoscale anti-oxidation film as the sample; Step 2: immersing the sample in a hydrochloric acid solution for treatment; Taking out the sample, and recording the volume of the remaining liquid as V1; Step 3: diluting the liquid, and recording the dilution multiple as a; Step 4: treating the diluted liquid obtained in step 3 by ultrasonic treatment, taking the liquid, titrating it on a polished silicon wafer, and recording the volume of the taken liquid as V2; Step 5: heating the sample obtained in step 4 in a protective atmosphere, measuring the wet-spreading area, and recording the wet-spreading area as S2; Step 6: measuring the film thickness of the sample obtained in step 5 by atomic force microscopy, and calculating the average film thickness, which is the minimum fragment film thickness, and recording the minimum fragment thickness as h2; Step 7: synchronously taking the measurement picture in step 6, analyzing the black point proportion in the picture by pixel points, and recording the black point proportion as b; Step 8: calculating the film thickness h1 of the nanoscale anti-oxidation film of the sample in step 1 by the formula h1 = a x S2 x V1 x b x h2 / (V2 x S1).

2. The method of claim 1, wherein the thickness of the nano-oxidation film is measured by using a scanning electron microscope. The dilution multiple is a = 5-50; and the volume of the taken liquid is V2 = 0.1-10 μL.

3. The method of claim 1, wherein the thickness of the nano-oxidation film is measured by using a scanning electron microscope. The concentration of the hydrochloric acid solution is 3-7 wt%; and the ratio of the sample in step 1 to the hydrochloric acid solution is (30 mm x 50 mm):(25-100 mL).

4. The method of claim 1, wherein the thickness of the nano-oxidation film is measured by using a scanning electron microscope. The heating treatment conditions are: under vacuum / nitrogen conditions, the temperature is 40-60 ℃, and the time is 30-60 minutes.

5. The method of claim 1, wherein the thickness of the nano-oxidation film is measured by using a scanning electron microscope. The ultrasonic treatment has a vibration frequency of ≥28 KHz, and the ultrasonic treatment time is ≥5 minutes.

6. The method of claim 1, wherein the thickness of the nano-oxidation film is measured by using a scanning electron microscope. The polished silicon wafer has a roughness of ≤1 nm; and the immersion treatment time is 1-5 minutes.

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