A method for preparing diamond films with high NV color center strength by MPCVD

Abstract

A method for preparing a diamond film with high NV color center intensity using MPCVD is described. The method involves depositing a nitrogen-doped micronized diamond film on a substrate using MPCVD, performing surface modification on the diamond film using reactive ion etching (RIE) to enhance the structural conditions for high NV color center intensity, and performing high-temperature annealing to fully diffuse vacancies, thereby producing a diamond film with high NV color center intensity. This method addresses the issues of low color center intensity and poor optical properties associated with MPCVD-prepared diamond films with NV color centers, thereby improving the fluorescence intensity of NV color centers and the application value of the color centers in MPCVD diamond films.

Description

Technical Field

[0001] This invention belongs to the field of NV color center diamond film materials, and in particular relates to a surface modification technology for diamond films that can significantly enhance the NV color center strength of diamonds produced by MPCVD. Specifically, this method involves preparing a diamond film with high NV color center strength using MPCVD. The method involves surface modification of a nitrogen-doped micronized diamond film produced by MPCVD using reactive ion etching, followed by high-temperature vacuum annealing to form a diamond film with high NV color center strength. Background Art

[0002] In recent years, with the continuous deepening of related research, diamond NV color centers have been widely used in high-precision imaging, microscopic physical field detection and other fields due to their excellent mechanical and optical properties and unique quantum properties, playing an important role. How to use MPCVD to produce high-strength NV color center diamond films has become a difficult problem that researchers need to overcome.

[0003] MPCVD uses microwave energy to ionize a gas mixture into active radicals, which react on the substrate surface to deposit a diamond film. The advantages of this method are ease of operation, fast deposition rates, and the resulting diamond films are low in impurities and high in quality. However, its disadvantages are the inability to precisely control the location of nitrogen vacancies, and the relatively small number of diamond vacancies formed during deposition makes it difficult for them to combine with nitrogen atoms to form color centers. This results in an extremely low color center yield, necessitating subsequent processes such as irradiation or ion implantation followed by annealing to achieve high NV color center strength. Summary of the Invention

[0004] The purpose of the present invention is to address the defects of the existing MPCVD method for preparing NV color center diamond films, such as low color center intensity and poor optical properties. Based on the existing preparation process, an MPCVD method for preparing diamond films with high NV color center intensity is invented. It combines reactive ion etching technology to form an MPCVD diamond film with high color center intensity and excellent color center optical properties.

[0005] The technical solution of the present invention is:

[0006] A method for preparing a diamond film with high NV color center strength by MPCVD is characterized in that it comprises the following steps:

[0007] Step 1: polishing the substrate with a silica sol solution for at least 30 minutes to remove the oxide layer on the substrate surface;

[0008] Step 2: Place the substrate in a diamond powder acetone suspension and perform ultrasonic vibration treatment. The scraping action between the substrate and the diamond powder causes a large number of microscopic defects on the substrate surface, while simultaneously growing the crystal. The substrate is then ultrasonically cleaned in anhydrous ethanol for 5 to 10 minutes.

[0009] Step 3: placing the processed substrate in an MPCVD device to grow a nitrogen-doped micronized diamond film;

[0010] Step 4: Using MPCVD equipment, the prepared nitrogen-doped micron diamond film is surface modified by reactive ion etching (RIE) to provide structural conditions for improving the strength of NV color centers. After etching is completed, it is ultrasonically cleaned in anhydrous ethanol for 5 to 10 minutes.

[0011] Step 5: Place the sample obtained in the above step in a muffle furnace for high-temperature vacuum annealing for 2 h±15 min to allow the vacancies to fully diffuse and obtain a diamond film material with high NV color center strength.

[0012] The silica sol solution has a particle size of 100 nm and a concentration of 40%, and the polishing cloth used is a metallographic velvet polishing cloth.

[0013] The diamond powder used in the ultrasonic crystal planting of the substrate has a particle size of 0.2 to 1 μm, a ratio concentration of 3 to 6 g diamond powder / 100 ml acetone, and a crystal planting time of 30 to 60 minutes; the ultrasonic cleaning time of anhydrous ethanol is 10 to 15 minutes; and compressed nitrogen is used to blow dry the substrate surface for subsequent use.

[0014] The deposition parameters of the nitrogen-doped micron diamond film prepared by MPCVD are as follows: the background vacuum degree in the vacuum reaction chamber reaches below 1 Pa to ensure the purity of the reaction gas, CH4 / H2 / N2 gas is introduced, the total gas flux is 200 sccm, the CH4 flux accounts for 5%, the H2 flux accounts for 94.5% to 93%, and the N2 flux accounts for 0.5% to 2%. The deposition temperature is 850 to 900°C, the reaction gas pressure is 12 kPa, the microwave power is 15 kW, the deposition time is 2 h±15 min, and the substrate bias is turned on at -120 to -200 V in the initial stage of deposition. The bias is turned on for no less than 30 min to increase the nucleation rate.

[0015] The MPCVD equipment performs reactive ion etching surface modification on nitrogen-doped micron diamond films: the background vacuum in the vacuum reaction chamber is evacuated to below 1 Pa; the microwave source power is 800 W; the reaction gases are H2 and Ar, the H2 gas flow rate is 20-40 sccm, the Ar gas flow rate is 10-30 sccm, the reaction gas pressure is 1.2-1.8 kPa, the substrate bias voltage is -120--200 V, and the etching time is 1h±5min.

[0016] The high temperature vacuum annealing parameters in the muffle furnace are as follows: the substrate is placed in the crucible, the crucible is placed in the muffle furnace, and the vacuum is pumped to 5×10 -3Pa, heating temperature to 600 ~ 700 ℃, high temperature annealing for 2 h ± 15 min.

[0017] The substrate is a silicon wafer.

[0018] The beneficial effects of the present invention are:

[0019] The present invention combines reactive ion etching technology to improve the color center yield of color center diamond film prepared by MPCVD method, modifies the surface of diamond film by reactive ion etching, and then performs high temperature vacuum annealing to prepare diamond film with high NV color center strength.

[0020] The diamond surface modification of the present invention has the following benefits for the color center diamond film: (1) the diamond surface micro-nano structure can effectively limit the position of the color center, prevent the color center from agglomerating, and affect the color center's optical function; (2) the diamond surface micro-nano structure can be used as an optical cavity to effectively increase the fluorescence intensity of the color center and improve the application value of the color center; (3) the diamond surface micro-nano structure can actively penetrate the sample and realize its application in the field of biological imaging; (4) by increasing the contact area between the film and the surrounding environment, the effect of annealing on improving the color center yield is more significant. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a process flow chart of reactive ion etching of the present invention.

[0022] Figure 2 This is a surface morphology diagram of the nitrogen-doped micron diamond film of the present invention.

[0023] Figure 3 This is a surface morphology diagram of the surface-modified diamond film of the present invention.

[0024] Figure 4 This is the PL spectrum of the diamond film before and after surface modification of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0026] like Figures 1-4 shown.

[0027] A method for preparing a diamond film with high NV color center strength by MPCVD, such as Figure 1 As shown, it includes the following steps:

[0028] Step 1: Polish the silicon wafer substrate using a metallographic silk velvet polishing cloth and a silica sol solution with a particle size of 100 nm and a molar concentration of 40% ± 5% for at least 30 minutes.

[0029] Step 2: Place the silicon wafer in an acetone suspension of 0.2-1 μm diamond powder (3-6 g diamond powder / 100 ml acetone) and ultrasonically vibrate the wafer for 30-60 minutes. Then, ultrasonically clean the wafer in anhydrous ethanol for 5-10 minutes, and blow dry the silicon wafer surface with compressed nitrogen.

[0030] Step 3: Place the processed silicon wafer in the MPCVD equipment to grow nitrogen-doped micron diamond film. The specific parameters are: the background vacuum degree in the vacuum reaction chamber reaches below 1 Pa to ensure the purity of the reaction gas, and the gas CH4 / H2 / N2 is introduced. The total gas flux is 200 sccm, the CH4 flux accounts for 5%, the H2 flux accounts for 94.5% to 93%, and the N2 flux accounts for 0.5% to 2%. The deposition temperature is 850 to 900 ° C, the reaction gas pressure is 12 kPa, the microwave power is 15 kW, the deposition time is 2 h ± 15 min, and the substrate bias is turned on at the initial stage of deposition. -120 to -200 V, the bias is applied for at least 30 min; Figure 2 Surface morphology of nitrogen-doped micronized diamond film shown;

[0031] Step 4: Use MPCVD equipment to modify the surface of the prepared nitrogen-doped micron diamond film using reactive ion etching technology (RIE). The specific parameters are: the background vacuum in the vacuum reaction chamber is evacuated to below 1 Pa; the microwave source power is 800 W; the reaction gases are H2 and Ar, the H2 gas flow rate is 20-40 sccm, the Ar gas flow rate is 10-30 sccm, the reaction gas pressure is 1.2-1.8 kPa, the substrate bias is -120--200 V, the etching time is 1h±5min, and after the etching is completed, it is placed in anhydrous ethanol for ultrasonic cleaning for 5-10 min; the following is obtained: Figure 3 The surface modified diamond film shown;

[0032] Step 5: Place the sample obtained in the above step in a muffle furnace for high temperature vacuum annealing. The specific annealing parameters are: vacuum to 5×10 -3 Pa, heating temperature to 600 ~ 700 ℃, high temperature annealing for 2 h ± 15 min.

[0033] The PL spectra of the diamond film before and after surface modification prepared by the above steps are shown in Figure 2. Figure 4 shown.

[0034] Example 1.

[0035] 1. Use a 0.5 mm thick silicon wafer and an automatic grinding and polishing machine, a metallographic velvet polishing cloth, and a silica sol solution with a particle size of 100 nm (concentration 40%) to grind and polish the silicon wafer for 30 minutes at a grinding and polishing speed of 180 r / min, and then rinse it with deionized water.

[0036] 2. Prepare a suspension of 0.5 μm diamond powder and acetone at a ratio of 3 g of diamond powder per 100 ml of acetone (30 ml). Place the silicon wafer in the suspension and ultrasonically vibrate the wafer for 40 minutes at 50°C. Then, ultrasonically clean the wafer in anhydrous ethanol for 5–10 minutes, and blow dry the wafer surface with compressed nitrogen.

[0037] 3. Place the processed silicon wafer on the MPCVD sample stage. Raise the sample stage, evacuate to below 1 Pa, close the roughing valve, and open the automatic pressure regulating valve. Introduce 50 sccm of H₂. When the pressure reaches 0.8 kPa, turn on the microwave power with an initial power of 600 W. After ignition, gradually increase the H₂ flux and microwave power. When the microwave power reaches 15 kW, the pressure reaches 12 kPa, and the temperature reaches 860°C, introduce CH₂ and N₂ at a ratio of 10 sccm / 189 sccm / 1 sccm, respectively. Turn on the bias power supply and set a -150 V bias for 30 minutes. Turn off the bias power and continue deposition for 90 minutes. After deposition is complete, close the CH₂ and N₂ gas lines and gradually reduce the pressure and microwave power to room temperature.

[0038] 4. After the temperature drops to room temperature, turn off the microwave power and gas line, and evacuate to below 1 Pa. Restart the H2 and microwave power. Adjust the microwave power to 800 W and the pressure to 1.6 kPa. Flow Ar with H2 and Ar fluxes set to 30 sccm and 20 sccm, respectively. Set the substrate bias to -180 V and perform surface modification for 1 hour. After modification, remove the silicon wafer and ultrasonically clean it in anhydrous ethanol for 5-10 minutes.

[0039] 5. Place the diamond film sample in a crucible, place the crucible in a muffle furnace, and evacuate to 5×10 -3 Pa, heated to 700 °C, and vacuum high temperature annealed for 2 h.

[0040] Example 2.

[0041] 1. Use a 0.5 mm thick silicon wafer and an automatic grinding and polishing machine, a metallographic velvet polishing cloth, and a silica sol solution with a particle size of 100 nm (concentration 40%) to grind and polish the silicon wafer for 30 minutes at a grinding and polishing speed of 180 r / min, and then rinse it with deionized water.

[0042] 2. Prepare a suspension of 0.5 μm diamond powder and acetone at a ratio of 5 g of diamond powder per 100 ml of acetone (30 ml). Place the silicon wafer in the suspension and ultrasonically vibrate the wafer for 30 minutes at 50°C. Then, ultrasonically clean the wafer in anhydrous ethanol for 5–10 minutes, and blow dry the wafer surface with compressed nitrogen.

[0043] 3. Place the processed silicon wafer on the MPCVD sample stage. Raise the sample stage, evacuate to below 1 Pa, close the roughing valve, and open the automatic pressure regulating valve. Introduce 50 sccm of H₂. When the pressure reaches 0.8 kPa, turn on the microwave power with an initial power of 600 W. After ignition, gradually increase the H₂ flux and microwave power. When the microwave power reaches 15 kW, the pressure reaches 12 kPa, and the temperature reaches 850°C, introduce CH₂ and N₂ at a ratio of 10 sccm / 186 sccm / 4 sccm, respectively. Turn on the bias power supply and set a -120 V bias for 30 minutes. Turn off the bias power and continue deposition for 90 minutes. After deposition is complete, close the CH₂ and N₂ gas lines and gradually reduce the pressure and microwave power to room temperature.

[0044] 4. After the temperature drops to room temperature, turn off the microwave power supply and gas line, and evacuate to below 1 Pa. Restart the H2 and microwave power supply. Adjust the microwave power to 800 W and the pressure to 1.8 kPa. Flow Ar with H2 and Ar fluxes set to 40 sccm and 30 sccm, respectively. Set the substrate bias voltage to -200 V, and allow the surface to be modified for 1 hour. Upon completion, remove the silicon wafer and ultrasonically clean it in anhydrous ethanol for 5–10 minutes.

[0045] 5. Place the diamond film sample in a crucible, place the crucible in a muffle furnace, and evacuate to 5×10 -3 Pa, heating temperature to 650 ℃, vacuum high temperature annealing for 2h.

[0046] Example 3.

[0047] 1. Use a 0.5 mm thick silicon wafer and an automatic grinding and polishing machine, a metallographic velvet polishing cloth, and a silica sol solution with a particle size of 100 nm (concentration 40%) to grind and polish the silicon wafer for 30 minutes at a grinding and polishing speed of 180 r / min, and then rinse it with deionized water.

[0048] 2. Prepare a suspension of 0.5 μm diamond powder and acetone at a ratio of 6 g of diamond powder per 100 ml of acetone (30 ml). Place the silicon wafer in the suspension and ultrasonically vibrate the wafer at 50°C for 60 minutes. Then, ultrasonically clean the wafer in anhydrous ethanol for 5–10 minutes, and blow dry the wafer surface with compressed nitrogen.

[0049] 3. Place the processed silicon wafer on the MPCVD sample stage. Raise the sample stage, evacuate to below 1 Pa, close the roughing valve, and open the automatic pressure regulating valve. Introduce 50 sccm of H₂. When the pressure reaches 0.8 kPa, turn on the microwave power with an initial power of 600 W. After ignition, gradually increase the H₂ flux and microwave power. When the microwave power reaches 15 kW, the pressure reaches 12 kPa, and the temperature reaches 900°C, introduce CH₂ and N₂ at a ratio of 10 sccm / 187 sccm / 3 sccm, respectively. Turn on the bias power supply and set a -200 V bias for 30 minutes. Turn off the bias power and continue deposition for 90 minutes. After deposition is complete, close the CH₂ and N₂ gas lines and gradually reduce the pressure and microwave power to room temperature.

[0050] 4. After the temperature drops to room temperature, turn off the microwave power and gas line, and evacuate to below 1 Pa. Restart the H2 and microwave power. Adjust the microwave power to 800 W and the pressure to 1.2 kPa. Flow Ar with H2 and Ar fluxes set to 20 sccm and 10 sccm, respectively. Set the substrate bias voltage to -120 V, and perform surface modification for 1 hour. Upon completion, remove the silicon wafer and ultrasonically clean it in anhydrous ethanol for 5-10 minutes.

[0051] 5. Place the diamond film sample in a crucible, place the crucible in a muffle furnace, and evacuate to 5×10 -3 Pa, heated to 600 °C, and vacuum high temperature annealed for 2 h.

[0052] The parts not involved in the present invention are the same as the existing technology or can be implemented by using the existing technology.

Claims

1. A method for preparing a diamond film with high NV color center strength by MPCVD, characterized by: It includes the following steps: Step 1: polishing the substrate with a silica sol solution for at least 30 minutes to remove the oxide layer on the substrate surface; Step 2: Place the substrate in a diamond powder acetone suspension and perform ultrasonic vibration treatment. The scraping action between the substrate and the diamond powder causes a large number of microscopic defects on the substrate surface, while simultaneously growing the crystal. The substrate is then ultrasonically cleaned in anhydrous ethanol for 5 to 10 minutes. Step 3: placing the processed substrate in an MPCVD device to grow a nitrogen-doped micronized diamond film; Step 4: Using MPCVD equipment, the prepared nitrogen-doped micron diamond film is surface modified by reactive ion etching (RIE) to provide structural conditions for improving the strength of NV color centers. After etching is completed, it is ultrasonically cleaned in anhydrous ethanol for 5 to 10 minutes. Step 5: Place the sample obtained in the above step in a muffle furnace for high-temperature vacuum annealing for 2 h ± 15 min to allow the vacancies to fully diffuse and obtain a diamond film material with high NV color center strength; The diamond powder used in the ultrasonic crystal planting of the substrate has a particle size of 0.2 to 1 μm, a ratio concentration of 3 to 6 g of diamond powder per 100 ml of acetone, and a crystal planting time of 30 to 60 minutes; compressed nitrogen is used to blow dry the substrate surface for subsequent use; The deposition parameters of the nitrogen-doped micronized diamond film prepared by MPCVD are as follows: the background vacuum in the vacuum reaction chamber reaches below 1 Pa to ensure the purity of the reaction gas, CH4 / H2 / N2 gas is introduced, the total gas flux is 200 sccm, the CH4 flux accounts for 5%, the H2 flux accounts for 94.5% to 93%, and the N2 flux accounts for 0.5% to 2%. The deposition temperature is 850-900°C, the reaction gas pressure is 12 kPa, the microwave power is 15 kW, and the substrate bias voltage is turned on at -120 to -200 V in the initial stage of deposition. The bias voltage is turned on for no less than 30 minutes to increase the nucleation rate. The MPCVD equipment was used to perform reactive ion etching surface modification on nitrogen-doped micron diamond films: the background vacuum in the vacuum reaction chamber was evacuated to below 1 Pa; the microwave source power was 800 W; the reaction gases were H2 and Ar, the H2 gas flow rate was 20 to 40 sccm, the Ar gas flow rate was 10 to 30 sccm, the reaction gas pressure was 1.2 to 1.8 kPa, the substrate bias voltage was -120 to -200 V, and the etching time was 1 h ± 5 min; The high temperature vacuum annealing parameters in the muffle furnace are as follows: the substrate is placed in the crucible, the crucible is placed in the muffle furnace, and the vacuum is pumped to 5×10 -3 Pa, heating temperature to 600 ~ 700 ℃.

2. The method according to claim 1, wherein: The silica sol solution has a particle size of 100 nm and a concentration of 40%, and the polishing cloth used is a metallographic velvet polishing cloth.

3. The method according to claim 1, wherein: The substrate is a silicon wafer.

Images