Method for measuring growth thickness precision of diamond epitaxial layer based on weighing method

Abstract

The invention discloses a method for measuring the growth thickness precision of a diamond epitaxial layer based on a weighing method, and aims to solve the problem that the thickness and the growth rate of a diamond epitaxial thin layer are difficult to accurately evaluate by an existing method for measuring a thin drift layer of a diamond thin layer. The measuring method comprises the following steps: 1, polishing the diamond substrate; 2, the polished diamond substrate is placed in strong oxidation mixed acid to form an oxygen terminal, and then ultrasonic cleaning is carried out; 3, measuring the weight of the diamond substrate by using a high-precision balance, and measuring the surface area of the diamond substrate by using a vernier caliper; 4, cleaning the surface again; 5, epitaxially growing a single crystal diamond layer on the surface of the diamond substrate; sixthly, surface cleaning is conducted for the third time; and 7, calculating to obtain the thickness of the epitaxial growth monocrystal diamond layer. According to the method, the thickness of the diamond epitaxial growth layer is subjected to characterization measurement by adopting the high-precision balance, the measurement and control of the ultrathin layer diamond can be realized, and the measurement of the ultrathin layer diamond can be simply realized without damage by adopting the high-precision balance.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor power devices, and in particular relates to a method for measuring the thickness accuracy of a diamond epitaxial layer growth based on a weighing method. Background Art

[0002] Diamond has excellent electrical properties. The bandgap width of diamond (5.47eV) is 5 times that of silicon (Si), and is also higher than other wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN). It has a low intrinsic carrier concentration (~10 -27 cm -3 ) and high breakdown field strength (10MV / cm); in addition, diamond has extremely high thermal conductivity (22W / cm·K), which is the semiconductor material with the highest thermal conductivity known so far. It has great application prospects in high temperature, high power and ultra-high voltage environments; diamond also has high carrier mobility and hole mobility (3800cm 2 / Vs) and electron mobility (4500cm 2 / Vs) is also much higher than other semiconductor materials, so diamond is also known as the "ultimate semiconductor". With the rapid development of artificial diamond, especially the rapid development of diamond growth technology using microwave plasma chemical vapor deposition system (MPCVD), its application in the field of electronic devices has been promoted. Before diamond is used to prepare electronic devices, a high-quality functional layer needs to be epitaxially grown on its surface. The thickness of the drift layer formed by the diamond epitaxial layer is a key factor affecting the performance of diamond semiconductor electronic devices. The thickness of the drift layer is usually between tens of nanometers and tens of microns. It is particularly important to measure the growth thickness and growth rate of diamond in a timely and accurate manner. Through investigation, it is found that in current device research, diamond thin drift layers are usually grown according to long-term growth parameters in the literature, and the drift layer thickness is estimated based on the growth rate of known growth parameters. However, the drift layer growth is concentrated in the initial growth period of 10min-120min. It is obviously impossible to accurately obtain the drift layer thickness by estimating the long-term growth parameters. The drift layer thickness is mainly measured using a spiral micrometer or a vernier caliper. Such methods have large errors and are difficult to measure drift layer thicknesses below 1μm. Alternatively, a Kelvin probe force microscope (KPFM) is used to test the potential distribution of the diamond longitudinal section and the sample surface, and to determine the diamond epitaxial layer thickness based on the potential mutation point. This method is complex and costly, and can only measure diamond heavily phosphorus (P)-doped epitaxial layers. Currently known measurement methods are difficult to accurately evaluate the diamond epitaxial thin layer thickness and growth rate, so the growth thickness of diamond is difficult to accurately control, and the electrical properties of diamond devices are difficult to stabilize and regulate. Summary of the invention

[0003] The purpose of the present invention is to solve the problem that the existing diamond thin layer drift layer measurement method is difficult to accurately evaluate the diamond epitaxial thin layer thickness and growth rate, and the use of a spiral micrometer is difficult to measure the drift layer thickness below 1μm, and to provide a simple, easy, non-destructive testing method to measure the thickness of the diamond thin layer epitaxial layer by a high-precision balance weighing method.

[0004] The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method of the present invention is implemented according to the following steps:

[0005] Step 1: Surface flattening:

[0006] Polishing the surface of the diamond substrate to obtain a polished diamond substrate;

[0007] Step 2: Surface cleaning:

[0008] The polished diamond substrate is placed in a strong oxidizing mixed acid, heated at 200-250°C for 0.4-0.6h, then heated to 330-370°C and continued to be heated for 1.4-1.8h to form oxygen terminals on the surface of the diamond substrate, and then placed in plasma water at 70-85°C for heating treatment to remove the residual mixed acid on the diamond surface, and after ultrasonic cleaning, a diamond substrate with oxygen terminals is obtained;

[0009] Step 3: Sample measurement:

[0010] First, the weight of the diamond substrate with oxygen terminals is measured using a high-precision balance, and then the length and width of the diamond substrate with oxygen terminals are measured using a vernier caliper, thereby obtaining the surface area S of the diamond substrate;

[0011] Step 4: Clean the surface again:

[0012] The diamond substrate with oxygen terminals is ultrasonically cleaned again using plasma water, anhydrous ethanol, and acetone in sequence to obtain a diamond substrate after secondary cleaning;

[0013] Step 5: Epitaxial growth:

[0014] Placing the diamond substrate after the secondary cleaning on a molybdenum tray and on a sample stage of a microwave plasma chemical vapor deposition device (MPCVD), introducing a mixed gas of hydrogen and methane, and performing deposition under the conditions of a hydrogen flow rate of 100 sccm to 500 sccm, a methane flow rate of 1 sccm to 20 sccm, a diamond substrate temperature of 700° C. to 1100° C., a pressure of 50 mbar to 300 mbar, and a microwave power of 1000 W to 4000 W, epitaxially growing a single crystal diamond layer on the surface of the diamond substrate to obtain a grown diamond substrate;

[0015] Step 6. Three-time surface cleaning:

[0016] The grown diamond substrate is placed in a strong oxidizing mixed acid, heated at 200-250° C. for 0.4-0.6 h, then heated to 330-370° C. and continued to be heated for 1.4-1.8 h to form oxygen terminals on the surface of the diamond substrate, and then placed in plasma water at 70-85° C. for heating treatment to remove the residual mixed acid on the diamond surface, and after ultrasonic cleaning, a diamond substrate after three cleanings is obtained;

[0017] Step 7: Sample measurement:

[0018] The weight of the diamond substrate after three cleanings was measured using a high-precision balance. The weight difference between the diamond substrate after three cleanings and the diamond substrate with oxygen termination was Δm. The standard average density of diamond is ρ ava , calculated by the following formula,

[0019]

[0020] Thereby, the thickness Δh of the epitaxially grown single crystal diamond layer is obtained.

[0021] The present invention provides a method for measuring the weight of clean diamond before growth based on a high-precision balance (one hundred thousandth or more), and using a vernier caliper and a micrometer to measure the length, width and thickness of the diamond respectively. After the diamond substrate sample is cleaned, a microwave plasma chemical vapor deposition system (MPCVD) is used to grow diamond. After growth, the sample is cleaned and measured again. The growth thickness and growth rate of the diamond can be obtained based on the weight difference before and after growth. The method is simple and easy to implement, and has high accuracy. According to this method, an accurate diamond growth rate can also be obtained, which is of great significance to the controllable growth of the diamond epitaxial layer.

[0022] The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method of the present invention has the following beneficial effects:

[0023] The thickness of the diamond epitaxial growth layer is characterized and measured by a high-precision balance, which can achieve the measurement and control of ultra-thin layers (<1μm) of diamond. The high-precision balance can achieve the measurement of ultra-thin layers of diamond without damage and simply, and at the same time provides a simple and easy measurement and characterization method for the control and design of ultra-thin functional epitaxial layers of diamond semiconductor devices. Finally, the relationship between the test accuracy of the high-precision balance and the size of the diamond sample is studied. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of realizing epitaxial growth of single crystal diamond on a diamond substrate in an embodiment;

[0025] Figure 2This is a physical picture of using a high-precision balance to measure the weight of diamond in the embodiment;

[0026] Figure 3 Graph showing the relationship between the accuracy of the high-precision balance (one hundred thousandth) and the size of the diamond sample in the embodiment. DETAILED DESCRIPTION

[0027] Specific implementation method 1: The method for measuring the thickness accuracy of the diamond epitaxial layer growth based on the weighing method in this implementation method is implemented according to the following steps:

[0028] Step 1: Surface flattening:

[0029] Polishing the surface of the diamond substrate to obtain a polished diamond substrate;

[0030] Step 2: Surface cleaning:

[0031] The polished diamond substrate is placed in a strong oxidizing mixed acid, heated at 200-250°C for 0.4-0.6h, then heated to 330-370°C and continued to be heated for 1.4-1.8h to form oxygen terminals on the surface of the diamond substrate, and then placed in plasma water at 70-85°C for heating treatment to remove the residual mixed acid on the diamond surface, and after ultrasonic cleaning, a diamond substrate with oxygen terminals is obtained;

[0032] Step 3: Sample measurement:

[0033] First, the weight of the diamond substrate with oxygen terminals is measured using a high-precision balance, and then the length and width of the diamond substrate with oxygen terminals are measured using a vernier caliper, thereby obtaining the surface area S of the diamond substrate;

[0034] Step 4: Clean the surface again:

[0035] The diamond substrate with oxygen terminals is ultrasonically cleaned again using plasma water, anhydrous ethanol, and acetone in sequence to obtain a diamond substrate after secondary cleaning;

[0036] Step 5: Epitaxial growth:

[0037] Placing the diamond substrate after the secondary cleaning on a molybdenum tray and on a sample stage of a microwave plasma chemical vapor deposition device (MPCVD), introducing a mixed gas of hydrogen and methane, and performing deposition under the conditions of a hydrogen flow rate of 100 sccm to 500 sccm, a methane flow rate of 1 sccm to 20 sccm, a diamond substrate temperature of 700° C. to 1100° C., a pressure of 50 mbar to 300 mbar, and a microwave power of 1000 W to 4000 W, epitaxially growing a single crystal diamond layer on the surface of the diamond substrate to obtain a grown diamond substrate;

[0038] Step 6. Three-time surface cleaning:

[0039] The grown diamond substrate is placed in a strong oxidizing mixed acid, heated at 200-250° C. for 0.4-0.6 h, then heated to 330-370° C. and continued to be heated for 1.4-1.8 h to form oxygen terminals on the surface of the diamond substrate, and then placed in plasma water at 70-85° C. for heating treatment to remove the residual mixed acid on the diamond surface, and after ultrasonic cleaning, a diamond substrate after three cleanings is obtained;

[0040] Step 7: Sample measurement:

[0041] The weight of the diamond substrate after three cleanings was measured using a high-precision balance. The weight difference between the diamond substrate after three cleanings and the diamond substrate with oxygen termination was Δm. The standard average density of diamond is ρ ava , calculated by the following formula,

[0042]

[0043] Thereby, the thickness Δh of the epitaxially grown single crystal diamond layer is obtained.

[0044] This embodiment grows diamond through a microwave plasma chemical vapor deposition system (MPCVD), uses a high-precision balance to weigh the sample weight, uses a vernier caliper and a micrometer to measure the size of the sample, and obtains the growth thickness and growth rate based on the weight change before and after growth.

[0045] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that the strong oxidizing mixed acid in step 2 is a mixture of 98.3% by mass concentrated sulfuric acid and 65% by mass concentrated nitric acid in a volume ratio of 3:1.

[0046] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that in step two, the polished diamond substrate is placed in a strong oxidizing mixed acid, heated at 230°C for 0.5h, and then heated to 350°C and continued to be heated for 1.5h to form oxygen terminals on the surface of the diamond substrate.

[0047] Specific implementation method 4: The difference between this implementation method and specific implementation methods 1 to 3 is that the ultrasonic cleaning described in step 2 is to use plasma water, anhydrous ethanol and acetone for ultrasonic cleaning for 15 to 20 minutes respectively.

[0048] Specific implementation method five: The difference between this implementation method and specific implementation methods one to four is that the accuracy of the high-precision balance described in step three is one in one hundred thousand.

[0049] Specific implementation example 6: This implementation example is different from specific implementation examples 1 to 5 in that a high-precision balance is used in step 3 to measure the weight of the diamond substrate with oxygen terminals, and the weight is measured three times in total to obtain an average value.

[0050] Specific embodiment 7: This embodiment differs from any one of specific embodiments 1 to 6 in that in step 5, the diamond substrate after secondary cleaning is etched pre-treated with hydrogen plasma for 5 min to 30 min before epitaxial growth, and the hydrogen flow rate is controlled to be 100 sccm to 500 sccm during etching.

[0051] Specific embodiment eight: The difference between this embodiment and any of specific embodiments one to seven is that a mixed gas of hydrogen and methane is introduced in step five, and deposition is performed under the conditions of a hydrogen flow rate of 180 sccm to 240 sccm, a methane flow rate of 1 sccm to 6 sccm, a diamond substrate temperature of 800°C to 1000°C, a pressure of 100 mbar to 180 mbar, and a microwave power of 3200W to 3600W.

[0052] Specific embodiment 9: This embodiment is different from any one of specific embodiments 1 to 8 in that in step 6, the mixture is placed in plasma water and heated at 80-85° C. for 0.5 h.

[0053] Specific implementation method ten: The difference between this implementation method and specific implementation method six is ​​that in step seven, a high-precision balance is used to measure the weight of the diamond substrate after three cleanings, and a total of three measurements are taken as an average.

[0054] Embodiment 1: The method for measuring the thickness accuracy of the diamond epitaxial layer growth based on the weighing method in this embodiment is implemented according to the following steps:

[0055] Step 1: Surface flattening:

[0056] Polishing the surface of the diamond substrate to obtain a polished diamond substrate;

[0057] Step 2: Surface cleaning:

[0058] The polished diamond substrate is placed in a strong oxidizing mixed acid, which is a mixture of 98.3% concentrated sulfuric acid and 65% concentrated nitric acid in a volume ratio of 3:1, heated at 230°C for 0.5h, and then heated to 350°C for 1.5h to form oxygen terminals on the surface of the diamond substrate, and then placed in plasma water and heated at 85°C for 30min to remove the residual mixed acid on the diamond surface, and then ultrasonically cleaned with plasma water, anhydrous ethanol, and acetone for 15min respectively to obtain a diamond substrate with oxygen terminals;

[0059] Step 3: Sample measurement:

[0060] First, a high-precision balance was used to measure the weight of the diamond substrate with oxygen terminals, and the average value was taken after three measurements. Then, a vernier caliper was used to measure the length and width of the diamond substrate with oxygen terminals, and a micrometer was used to measure the initial thickness of the diamond substrate with oxygen terminals. The initial size of the diamond substrate was 5.04 mm*5.04 mm*0.5616 mm, and the initial weight was 0.04912 g.

[0061] Step 4: Clean the surface again:

[0062] The diamond substrate with oxygen terminals was ultrasonically cleaned again using plasma water, anhydrous ethanol, and acetone in sequence, each cleaning for 15 minutes to obtain a diamond substrate after secondary cleaning;

[0063] Step 5: Epitaxial growth:

[0064] The diamond substrate after secondary cleaning was placed on a molybdenum tray and placed together on a sample stage of a microwave plasma chemical vapor deposition device (MPCVD), and first 200 sccm of hydrogen was introduced for etching for 10 minutes, and then a mixed gas of hydrogen and methane was introduced, and deposition was performed for 1.5 hours (t) under the conditions of a hydrogen flow rate of 196 sccm, a methane flow rate of 4 sccm, a diamond substrate temperature of 830°C, a pressure of 108 mbar, and a microwave power of 2600 W, and a single crystal diamond layer was epitaxially grown on the surface of the diamond substrate to obtain a grown diamond substrate;

[0065] Step 6. Three-time surface cleaning:

[0066] The grown diamond substrate was placed in a strong oxidizing mixed acid, heated at 230°C for 0.5h, then heated to 350°C for 1.5h to form oxygen terminals on the surface of the diamond substrate, and then placed in plasma water for heating at 85°C for 0.5h to remove the residual mixed acid on the diamond surface, and then ultrasonically cleaned with plasma water, anhydrous ethanol, and acetone for 15min respectively to obtain a diamond substrate after three cleanings;

[0067] Step 7: Sample measurement:

[0068] The weight of the diamond substrate after three cleanings was measured using a high-precision balance. The average value was taken for the three measurements. The weight difference between the diamond substrate after three cleanings and the diamond substrate with oxygen terminals was Δm. The density of diamond is known to be max =3.51554g / cm 3 , min =3.51447g / cm 3 , ava =3.51539g / cm 3 , calculated by the following formula,

[0069]

[0070] The thickness of the epitaxially grown single-crystal diamond layer is Δh, and the growth rate is Formula calculation.

[0071] In this embodiment, steps 2 to 7 are repeated for six rounds of growth. After each growth is completed, the weight of the diamond is measured using a high-precision balance, and the average value is taken for three measurements. The weight difference before and after the growth of the diamond is obtained, and the statistical data of each epitaxial growth is shown in Table 1 below.

[0072] Table 1

[0073] Growth batch Growth time (h) Growth weight (g) Growth rate (μm / h) Growth thickness (μm) 1 1.5 0.00024 1.7918 2.6877 2 1.5 0.000256 1.9112 2.8668 3 1 0.00030 3.5496 3.5496 4 2 0.000524 2.9340 5.8680 5 2 0.000527 2.9508 5.9016 6 3 0.001144 4.2704 12.8112

[0074] In order to compare the credibility of the test data, the sixth round of growth experiment was compared with the results of the micrometer test. The thickness of the diamond obtained by the high-precision balance weighing method was 33.495μm, and the thickness tested by the micrometer was 33.7μm. This shows that this method is feasible as a thin layer thickness measurement method.

[0075] Embodiment 2: The method for measuring the thickness accuracy of the diamond epitaxial layer growth based on the weighing method in this embodiment is implemented according to the following steps:

[0076] Step 1: Surface flattening:

[0077] Polishing the surface of the diamond substrate to obtain a polished diamond substrate;

[0078] Step 2: Surface cleaning:

[0079] The polished diamond substrate is placed in a strong oxidizing mixed acid, which is a mixture of 98.3% concentrated sulfuric acid and 65% concentrated nitric acid in a volume ratio of 3:1, heated at 230°C for 0.5h, and then heated to 350°C for 1.5h to form oxygen terminals on the surface of the diamond substrate, and then placed in plasma water and heated at 85°C for 30min to remove the residual mixed acid on the diamond surface, and then ultrasonically cleaned with plasma water, anhydrous ethanol, and acetone for 15min respectively to obtain a diamond substrate with oxygen terminals;

[0080] Step 3: Sample measurement:

[0081] First, a high-precision balance was used to measure the weight of the diamond substrate with oxygen terminals, and the average value was taken after three measurements. Then, a vernier caliper was used to measure the length and width of the diamond substrate with oxygen terminals, and a micrometer was used to measure the initial thickness of the diamond substrate with oxygen terminals. The initial size of the diamond substrate was 4.12 mm*4.13 mm*0.549 mm, and the initial weight was 0.03220 g.

[0082] Step 4: Clean the surface again:

[0083] The diamond substrate with oxygen terminals was ultrasonically cleaned again using plasma water, anhydrous ethanol, and acetone in sequence, each cleaning for 15 minutes to obtain a diamond substrate after secondary cleaning;

[0084] Step 5: Epitaxial growth:

[0085] The diamond substrate after secondary cleaning was placed on a molybdenum tray and placed together on a sample stage of a microwave plasma chemical vapor deposition device (MPCVD), and first 200 sccm of hydrogen was introduced for etching for 10 minutes, and then a mixed gas of hydrogen and methane was introduced, and deposition was performed for 1.5 hours under the conditions of a hydrogen flow rate of 196 sccm, a methane flow rate of 4 sccm, a diamond substrate temperature of 830°C, a pressure of 110 mbar, and a microwave power of 2700 W, and a single crystal diamond layer was epitaxially grown on the surface of the diamond substrate to obtain a grown diamond substrate;

[0086] Step 6. Three-time surface cleaning:

[0087] The grown diamond substrate was placed in a strong oxidizing mixed acid, heated at 230°C for 0.5h, then heated to 350°C for 1.5h to form oxygen terminals on the surface of the diamond substrate, and then placed in plasma water for heating at 85°C for 0.5h to remove the residual mixed acid on the diamond surface, and then ultrasonically cleaned with plasma water, anhydrous ethanol, and acetone for 15min respectively to obtain a diamond substrate after three cleanings;

[0088] Step 7: Sample measurement:

[0089] The weight of the diamond substrate after three cleanings was measured using a high-precision balance. The average value was taken for the three measurements. The weight difference between the diamond substrate after three cleanings and the diamond substrate with oxygen terminals was Δm. The density of diamond is known to be max =3.51554g / cm 3 , min =3.51447g / cm 3 , ava =3.51539g / cm 3 , calculated by the following formula,

[0090]

[0091] Thereby, the thickness Δh of the epitaxially grown single crystal diamond layer is obtained.

[0092] In this embodiment, steps 2 to 7 are repeated for six rounds of growth. After each growth is completed, a high-precision balance is used to measure the weight of the diamond, and the average value is taken for three measurements. The weight difference before and after the growth of the diamond is obtained, and the statistical data of each epitaxial growth is shown in Table 2 below.

[0093] Table 2

[0094] Growth batch Growth time (h) Growth weight (g) Growth rate (μm / h) Growth thickness (μm) 1 0.5 0.00011 3.6779 1.8389 2 1 0.000227 3.7949 3.7949 3 2 0.000487 4.0708 8.1416 4 3 0.000836 4.6587 13.9761 5 1.5 0.000434 4.8370 7.3095 6 1.5 0.000473 5.2717 7.9075

[0095] In order to compare the credibility of the test data, the sixth round of growth experiment was compared with the results of the micrometer test. The thickness of the diamond obtained by the high-precision balance weighing method was 42.914μm, and the thickness tested by the micrometer was 42.75μm. This shows that this method is feasible as a thin layer thickness measurement method.

[0096] According to the formula It can be seen that the measurement accuracy of diamond thickness by a high-precision balance is related to the area of ​​the diamond sample, and the relationship is as follows: Figure 3 As shown, the sample area is negatively correlated with the measurement accuracy, and the test accuracy of Example 1 and Example 2 are 114nm and 178nm respectively. The difference between Example 2 and Example 1 is that the sample area is different. The results of the examples show that the present invention is feasible for testing different areas.

Claims

1. A method for measuring the thickness accuracy of diamond epitaxial layer growth based on weighing method, characterized in that The method for measuring the thickness accuracy of the diamond epitaxial layer growth is implemented according to the following steps: Step 1: Surface flattening: Polishing the surface of the diamond substrate to obtain a polished diamond substrate; Step 2: Surface cleaning: The polished diamond substrate is placed in a strong oxidizing mixed acid, heated at 200-250°C for 0.4-0.6h, then heated to 330-370°C and continued to be heated for 1.4-1.8h to form oxygen terminals on the surface of the diamond substrate, and then placed in plasma water at 70-85°C for heating treatment to remove the residual mixed acid on the diamond surface, and after ultrasonic cleaning, a diamond substrate with oxygen terminals is obtained; Step 3: Sample measurement: First, the weight of the diamond substrate with oxygen terminals is measured using a high-precision balance, and then the length and width of the diamond substrate with oxygen terminals are measured using a vernier caliper, thereby obtaining the surface area S of the diamond substrate; Step 4: Clean the surface again: The diamond substrate with oxygen terminals is ultrasonically cleaned again using plasma water, anhydrous ethanol, and acetone in sequence to obtain a diamond substrate after secondary cleaning; Step 5: Epitaxial growth: Placing the diamond substrate after the secondary cleaning on a molybdenum tray and on a sample stage of a microwave plasma chemical vapor deposition device, introducing a mixed gas of hydrogen and methane, and performing deposition under the conditions of a hydrogen flow rate of 100 sccm to 500 sccm, a methane flow rate of 1 sccm to 20 sccm, a diamond substrate temperature of 700° C. to 1100° C., a pressure of 50 mbar to 300 mbar, and a microwave power of 1000 W to 4000 W, epitaxially growing a single crystal diamond layer on the surface of the diamond substrate to obtain a grown diamond substrate; Step 6. Three-time surface cleaning: The grown diamond substrate is placed in a strong oxidizing mixed acid, heated at 200-250° C. for 0.4-0.6 h, then heated to 330-370° C. and continued to be heated for 1.4-1.8 h to form oxygen terminals on the surface of the diamond substrate, and then placed in plasma water at 70-85° C. for heating treatment to remove the residual mixed acid on the diamond surface, and after ultrasonic cleaning, a diamond substrate after three cleanings is obtained; Step 7: Sample measurement: The weight of the diamond substrate after three cleanings was measured using a high-precision balance. The weight difference between the diamond substrate after three cleanings and the diamond substrate with oxygen termination was Δm. The standard average density of diamond is ρ ava , calculated by the following formula, Thereby, the thickness Δh of the epitaxially grown single crystal diamond layer is obtained.

2. The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method according to claim 1, characterized in that The strong oxidizing mixed acid in step 2 is a mixture of 98.3% by mass concentrated sulfuric acid and 65% by mass concentrated nitric acid in a volume ratio of 3:

1.

3. The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method according to claim 1, characterized in that In step 2, the polished diamond substrate is placed in a strong oxidizing mixed acid, heated at 230° C. for 0.5 h, and then heated to 350° C. for a further 1.5 h to form oxygen terminals on the surface of the diamond substrate.

4. The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method according to claim 1, characterized in that The ultrasonic cleaning described in step 2 is to use plasma water, anhydrous ethanol and acetone to ultrasonically clean for 15 to 20 minutes respectively.

5. The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method according to claim 1, characterized in that The accuracy of the high-precision balance described in step 3 is one in one hundred thousand.

6. The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method according to claim 1, characterized in that In step 3, a high-precision balance is used to measure the weight of the diamond substrate with oxygen terminals, and the weight is measured three times in total and the average value is taken.

7. The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method according to claim 1, characterized in that In step 5, before epitaxial growth, the diamond substrate after secondary cleaning is etched and pre-treated with hydrogen plasma for 5 minutes to 30 minutes, and the hydrogen flow rate is controlled to be 100 sccm to 500 sccm during etching.

8. The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method according to claim 1, characterized in that In step five, a mixed gas of hydrogen and methane is introduced, and deposition is performed under the conditions of a hydrogen flow rate of 180 sccm to 240 sccm, a methane flow rate of 1 sccm to 6 sccm, a diamond substrate temperature of 800° C. to 1000° C., a pressure of 100 mbar to 180 mbar, and a microwave power of 3200 W to 3600 W.

9. The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method according to claim 1, characterized in that In step six, the sample is placed in plasma water and heated at 80-85° C. for 0.5 h.

10. The method for measuring the thickness accuracy of diamond epitaxial layer growth based on the weighing method according to claim 6, characterized in that In step seven, a high-precision balance is used to measure the weight of the diamond substrate after three cleanings, and the average value is taken after a total of three measurements.

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