An apparatus and method for efficient realization of silicon doping in diamond

Abstract

An effective device for realizing silicon doping in diamond, using an MPCVD system, including a gas control module, a microwave module and a reaction deposition module including a reaction chamber; the reaction deposition module includes a quartz window, a reaction chamber, a sample table and a sample holder, the microwave enters the reaction chamber through the quartz window, and the sample holder is placed on the sample table in the reaction chamber; the sample holder is in the shape of a cylinder, there is a gas inlet ring around the sample holder for gas to enter from below, the center of the sample holder with a hole has a through hole with a diameter of 2mm for gas to enter from below, there is an inclined surface around the through hole of the sample holder, the inclined surface has different angles with the horizontal surface of 0-90°, the angle of the substrate is changed, and different angle deposition growth is carried out; methane and nitrogen are introduced into the chamber from below through the through hole of the sample holder, the temperature is between 760-780℃, and a nitrogen-silicon doped diamond film with gradient distribution is prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to an apparatus and method for effectively realizing silicon doping in diamond, in particular to an apparatus and method for preparing silicon-doped diamond material by changing the substrate tilt angle, reaction gas flow direction, reaction material type, reaction temperature, reaction pressure and other processes using a microwave plasma chemical vapor deposition (MPCVD) system. BACKGROUND

[0002] Diamond has excellent optical, electrical, chemical and mechanical properties, and is known as the ultimate semiconductor material and the next generation of quantum device material. Doped diamond is the key to the application of diamond as a semiconductor material and quantum device material. Doped diamond material has wide application prospects as a single photon emitting device in high-power semiconductor devices, quantum communication and quantum sensing, and as a detection material in high-sensitivity temperature and magnetic field sensors. The preparation of doped diamond material mainly uses chemical vapor deposition (CVD), high temperature and high pressure (HTHP), and ion implantation. The microwave plasma chemical vapor deposition (MPCVD) method in the CVD method uses electromagnetic wave energy to excite the reaction gas. In the reaction process, the electrode is not evaporated at high temperature, which avoids pollution, and the microwave power can be continuously and smoothly adjusted to deposit stable diamond film, which is beneficial to large-area uniform deposition of high-quality diamond film. It is considered to be the most promising method for preparing doped diamond. However, in the MPCVD system, the plasma distribution is complex, and the preparation of silicon-doped diamond usually uses silane as the doping gas. When silane is used as the doping gas, the concentration of the substance and the concentration of silicon doping have a strong nonlinear change, which has limitations for controllable doping of silicon. In the absence of additional silicon, the quartz window of the MPCVD system also causes the incorporation of silicon. In this case, the doping efficiency of silicon is low, and the doping position and concentration are random and uncontrollable. Therefore, how to change the doping efficiency, especially the silicon doping efficiency, during the growth of doped diamond in the MPCVD system is a difficult problem in the growth of diamond silicon doping.

[0003] CN2021106076292 proposes a laser-assisted MPCVD method for enhancing SiV color centers of single crystal diamond and single crystal diamond with SiV color centers. The formation of SiV color centers is achieved by growing silicon-doped single crystal diamond on a single crystal diamond substrate using a laser-assisted MPCVD method. The method uses a laser-assisted MPCVD method to prepare single crystal diamond. Si elements enter the diamond crystal grains through plasma assistance during the preparation process, forming SiV luminescent centers, so that the single crystal diamond has strong SiV luminescent properties.

[0004] However, silicon and silicon-nitrogen-doped diamond are also important functional materials for diamond. SUMMARY

[0005] The present application aims at changing the doping efficiency of silicon-doped diamond in the MPCVD system, and proposes an effective device and method for doping silicon in diamond, and a device and method for silicon-nitrogen doping.

[0006] The present application provides an effective device for doping diamond, which is based on the MPCVD system.

[0007] The gas module is composed of a flow controller and a vacuum pump.

[0008] Further, the reaction chamber is provided with an upper gas inlet and a lower gas inlet structure: the upper gas inlet is located at the top of the reaction chamber, and the lower gas inlet is located at the center of the sample table in the reaction chamber.

[0009] The microwave module is composed of a microwave source, a waveguide, and a mode conversion antenna.

[0010] Further, the microwave power and the substrate temperature can be controlled by adjusting the voltage of the microwave source, and the chamber pressure can be controlled by adjusting the amount of gas through the angle valve.

[0011] The reaction deposition module includes a quartz window, a reaction chamber, a sample table, and a sample holder.

[0012] Further, the sample holder is made of molybdenum, but is not limited to molybdenum.

[0013] The present application provides a method for effectively doping silicon in diamond, which is carried out in a microwave plasma chemical vapor deposition system.

[0014] 1) First, the diamond single crystal is pretreated, the pretreatment conditions are as follows: first, the diamond substrate is placed in a mixed solution of concentrated nitric acid and concentrated sulfuric acid, the ratio of concentrated sulfuric acid to concentrated nitric acid is 1:1, then it is placed on a heating table and heated at 290°C for 30 minutes to remove impurities on the surface of the diamond single crystal substrate, after heating, it is taken out and soaked in acetone solution for ultrasonic treatment for 15 minutes to remove acidic substances on the surface of the substrate, then it is soaked in ethanol solution for ultrasonic treatment for 15 minutes to remove acetone on the surface of the substrate, finally it is ultrasonically treated in deionized water for 15 minutes to remove residual ethanol solution on the surface of the substrate, and then it is taken out and dried with nitrogen.

[0015] 2) The diamond single crystal is subjected to plasma etching treatment: the diamond substrate pretreated according to the conditions of step 1) is placed on a specially designed cylindrical sample holder in the cavity, there is a gas inlet ring around the sample holder for gas to enter from below, the center of the sample holder with holes has a 2mm diameter through hole for gas to enter from below, and the surface of the sample holder has an inclined surface with different angles of 0-90° with the horizontal plane, especially the sample holder has an inclined surface of 20-90°; the inclined surface is used to place the substrate for deposition growth, and then the sample holder is placed on the sample table in the reaction cavity for plasma etching treatment, wherein the specific conditions of plasma etching are as follows: hydrogen flow rate 500±100sccm, microwave power between 1800-2200W, etching temperature between 550-600℃, reaction gas pressure between 10000-12000Pa, etching time 10-30 minutes, at this time the diamond surface will be etched and cleaned by hydrogen plasma and form etching pits, which is beneficial to deposition growth.

[0016] 3) Preparation of doped diamond film: grow doped diamond film on the diamond substrate obtained by plasma etching in step 2), the deposition growth conditions are as follows: on the basis of step 2), continue to increase the microwave power to 2400W, the etching temperature reaches 600-650℃, the reaction gas pressure is between 13000-15000Pa, at this time the hydrogen flow rate is kept unchanged, methane and nitrogen are introduced, the methane flow rate is 10±3sccm, and the nitrogen flow rate is between 0.1-2sccm, at this time the substrate temperature is between 650℃ to 750℃, after maintaining stability, deposition growth is carried out for at least 1 hour, and the obtained doped diamond film thickness is between 2μm to 30μm.

[0017] The preparation of the doped diamond film growth conditions: after the end of the plasma etching treatment, the hydrogen flow is kept unchanged, the microwave power is increased to 2400±200W, the temperature is 700-800℃, the pressure is 13000-14000Pa, the sample holder is a 20-90° inclined surface, at this time 10±3sccm of methane and 1-3sccm of nitrogen are introduced from the lower part of the chamber through the through hole of the sample holder, the angle valve is adjusted to maintain the pressure at 13000-14000Pa, the temperature is between 760-780℃, the deposition time is more than 30 minutes, and finally a nitrogen-silicon doped diamond film with gradient distribution is prepared.

[0018] The silicon doping of the present application is derived from the quartz window of the MPCVD system. When growing diamond in MPCVD, microwaves enter the reaction chamber system through the quartz (pure silicon dioxide) window of the MPCVD system, thereby introducing SiO2 silicon source and doping silicon.

[0019] In the above technical solution, in order to change the material concentration distribution on the surface of the substrate, the material concentration distribution on the surface of the substrate can be changed by controlling the gas flow direction in step 3), thereby affecting the doping concentration. The gas flow direction is divided into two kinds of up gas and up and down gas. The up gas means that all the growth gas is introduced from the upper part of the reaction chamber. The up and down gas means that part of the growth gas is introduced from the upper part of the reaction chamber and part of the growth gas is introduced from the lower part of the reaction chamber through the center hole of the sample holder. Since the content of the doping gas is less, the doping growth gas is introduced from the lower part of the chamber, which can change the distribution of the doping material on the surface of the substrate. The specific changing method is that in step 3), hydrogen is introduced from the upper part of the reaction chamber, and methane and nitrogen or other doping gases are introduced from the through hole in the lower part of the reaction chamber.

[0020] The introduction of nitrogen is beneficial to the introduction of silicon. When nitrogen is not introduced, the introduction of silicon is difficult. However, there is a competition mechanism between nitrogen vacancies and silicon vacancies during the growth of diamond. The plasma concentration, temperature, gas concentration and other parameters will affect the result of the competition. Therefore, the distribution of related substances is affected by the angle of the substrate inclination, thereby affecting the doping of silicon and nitrogen.

[0021] The concentration of nitrogen and the concentration of silicon can be judged by the luminescence intensity of NV- and SiV- in the spectrum.

[0022] Beneficial effects: in the above technical scheme, the substrate includes a diamond single crystal substrate, a diamond polycrystal substrate, a silicon wafer substrate, but is not limited to the above substrates, further, in order to change the doping efficiency of the dopant on the surface of the substrate and change the doping area, the angle of the substrate on the sample holder inclined surface can be changed in step 2), so that the surface plasma concentration distribution and temperature distribution of the substrate are changed. The present application is to change the doping efficiency of the silicon-doped diamond deposited in the MPCVD system, change the substrate angle by using the sample holder with different angles, perform plasma etching treatment, change the substrate surface material distribution by different gas inlet modes, and then perform doping deposition growth to obtain a doped diamond thin film material.

[0023] Advantages of the present application: (1) the present application adds a doping gas and an up-and-down gas inlet mode during the deposition of the diamond thin film in the MPCVD system, so that the dopant is effectively doped. (2) the present application adjusts the deposition angle of the substrate by using a specially-made metal molybdenum sample holder with an inclined surface with different inclination angles of 0-90°, changes the distribution of the plasma concentration and temperature on the surface of the substrate, changes the doping area of the dopant, and thus changes the doping efficiency. (3) in addition, the doped diamond thin film deposited by the method provided by the present application has good quality and good surface flatness, high silicon doping efficiency, and different concentration doping distributions of silicon and nitrogen.

[0024] The equipment and method of the present application have low cost and high flexibility, can change the doping efficiency of silicon in the diamond thin film, and can obtain a diamond thin film with different nitrogen and silicon concentration doping distributions, which has wide significance in the application of doped diamond. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The microwave plasma chemical vapor deposition system of the present application;

[0026] Figure 2 The sample holder schematic diagram of the present application;

[0027] Figure 3 The PL spectrum diagram of the 0° horizontal doped diamond thin film center of the present application;

[0028] Figure 4 The PL spectrum distribution diagram of the 30° inclination angle doped diamond thin film center axis of the present application with position;

[0029] Figure 5 The PL spectrum distribution diagram of the 45° inclination angle doped diamond thin film center axis of the present application with position;

[0030] Figure 6 The PL spectrum distribution diagram of the 90° vertical doped diamond thin film center axis of the present application with position;

[0031] Figure 7 The silicon vacancy intensity distribution along the position of the 30°, 45°, 90° doped diamond film central axis of the present application is shown in the following figure. DETAILED DESCRIPTION

[0032] Figure 1 The reference signs are as follows: microwave source 1, rectangular waveguide 2, impedance screw 3, mode conversion antenna 4, quartz window 5, upper gas inlet 6, upper gas inlet 7, deposition reaction chamber 8, gas outlet 9, lower gas inlet 10, sample holder 11.

[0033] Figure 2 The reference signs are as follows: sample 1, inclined surface at a certain angle with the horizontal plane 2, through hole of the sample holder with through hole 3, gas inlet ring 4.

[0034] Figure 3 Since the points on the surface of the film are uniformly distributed, only the PL spectrum at the center is given.

[0035] The present application will be described in detail below with reference to the accompanying drawings and specific examples, wherein the illustrative examples are only used to explain the present application, but not as improper limitation to the present application.

[0036] Example 1

[0037] Reference Figure 1 The method of the present application will be described in detail by the following specific steps.

[0038] 1. First, the diamond substrate is pretreated, a diamond single crystal substrate is used, the diamond single crystal substrate is placed in a mixed solution of concentrated nitric acid and concentrated sulfuric acid, the ratio of concentrated sulfuric acid to concentrated nitric acid is 1:1, then it is placed on a heating table and heated at 290℃ for 30 minutes, after heating, it is soaked in acetone solution for ultrasonic treatment for 15 minutes, then it is soaked in ethanol solution for ultrasonic treatment for 15 minutes, and finally it is soaked in deionized water for ultrasonic treatment for 15 minutes, and then it is taken out and dried with nitrogen;

[0039] 2. After pretreatment, the diamond single crystal substrate is placed on a 0° horizontal metal molybdenum sample holder, the sample holder is referred to Figure 2 (a), and is placed in a deposition reaction chamber; then plasma etching treatment is carried out, the plasma etching treatment conditions are as follows: hydrogen gas flow rate is 500sccm, microwave power is 2000W, temperature is 550-600℃, pressure is 10000-11000Pa, and time is 20 minutes; in particular, the above plasma etching treatment conditions are not very strict, the purpose is to clean the surface of the substrate and form an etched surface to facilitate doping growth;

[0040] 3. Preparation of doped diamond film 1, growth conditions: after the end of the plasma etching process, the hydrogen flow is maintained, the microwave power is increased to 2400W (typical frequency 2.4GHz, the volume of the reaction chamber is 1.5 liters, the power is adjustable when the gas volume of the reaction chamber changes, the appropriate process for the reaction), the temperature is 700-800℃, the pressure is 13000-14000Pa, at this time 10sccm of methane and 2sccm of nitrogen are introduced from the hole of the sample holder below the chamber, the angle valve is adjusted to maintain the pressure at 13000-14000Pa, the temperature is between 760-780℃, the deposition time is 60 minutes, and finally a nitrogen-doped diamond film 1 material with a thickness of 20μm is prepared. The microwave frequency can also be 2.4-6GHz. The area of the quartz window is about 100cm 2 around, and the thickness is about 1 centimeter.

[0041] The photoluminescence spectrum of the nitrogen-doped diamond film prepared in this embodiment under 514nm laser excitation is shown in Figure 2. Figure 4 The nitrogen-doped diamond film has obvious nitrogen vacancy luminescence, the nitrogen vacancy luminescence spectrum peak position is 575nm and 637nm, and there is no silicon vacancy luminescence, and the nitrogen vacancy distribution on the surface of the film is uniform.

[0042] Example 2

[0043] Reference Figure 1 The method of the present application is described in detail by the following specific steps.

[0044] 1. The diamond substrate is pretreated, and the pretreatment conditions are the same as those of Example 1;

[0045] 2. After pretreatment, the diamond single crystal substrate is placed on a 30° inclined surface of a metal molybdenum sample holder, the sample holder is placed in the deposition reaction chamber according to Figure 2 (b), then the plasma etching process is carried out, and the plasma etching process conditions are the same as those of Example 1;

[0046] 3. Preparation of doped diamond film 2, growth conditions are the same as those of Example 1, and finally a nitrogen-silicon-doped diamond film with a gradient distribution of thickness is prepared.

[0047] The photoluminescence distribution of the nitrogen-silicon-doped diamond film prepared in this embodiment is shown in Figure 4. Figure 4 The nitrogen vacancy luminescence of the nitrogen-silicon-doped diamond film gradually weakens from the bottom to the top (the substrate is placed in an inclined position during deposition, and the bottom and top of the inclined surface are described, the same below. The distance from the bottom is: 100μm-3000μm), and the silicon vacancy corresponding to the 738nm luminescence gradually increases, indicating that the silicon doping gradually increases from the bottom to the top of the film, as shown in Figure 4. Figure 7The silicon doping region at a 30° tilt angle is approximately 1300 μm, which improves the doping efficiency of silicon compared to the 0° horizontal growth method.

[0048] Example 3

[0049] refer to Figure 1 The method of the present invention will be described in detail through the following specific steps.

[0050] 1. The diamond substrate was first pretreated under the same conditions as in Example 1;

[0051] 2. After pretreatment, the diamond single crystal substrate is placed on a 45° inclined molybdenum support, with the sample support as a reference. Figure 2 (c) Place it into the deposition reaction chamber; then perform plasma etching treatment under the same conditions as in Example 1.

[0052] 3. Prepare doped diamond film 3. The growth conditions are the same as in Example 1. Finally, a nitrogen-silicon doped diamond film with a thickness gradient distribution is prepared.

[0053] The surface PL distribution map of the nitrogen-silicon-doped diamond film prepared in this embodiment is shown in the appendix. Figure 5 The nitrogen-silicon-doped diamond film exhibits a gradual decrease in luminescence from nitrogen vacancies to silicon vacancies and a gradual increase in luminescence from bottom to top. (See attached image.) Figure 7 The silicon vacancy doping area at a 45° tilt angle is approximately 2100 μm. Compared to the horizontal and 30° growth methods, the increased doping area indicates a further improvement in doping efficiency.

[0054] Example 4

[0055] refer to Figure 1 The method of the present invention will be described in detail through the following specific steps.

[0056] 1. The diamond substrate was first pretreated under the same conditions as in Example 1;

[0057] 2. After pretreatment, the diamond single crystal substrate is placed vertically on a horizontal molybdenum metal support, with the sample support as a reference. Figure 2 (a) The sample is placed in the deposition reaction chamber; then plasma etching is performed under the same conditions as in Example 1.

[0058] 3. Prepare doped diamond film 4. The growth conditions are the same as in Example 1. Finally, a nitrogen-silicon doped diamond film with a thickness gradient distribution is prepared.

[0059] The photoluminescence distribution pattern on the surface of the nitrogen-silicon-doped diamond film prepared in this embodiment is shown in the appendix. Figure 6 The nitrogen-silicon-doped diamond film exhibits a gradual decrease in luminescence from nitrogen vacancies to silicon vacancies and a gradual increase in luminescence from bottom to top. (See attached image.) Figure 7, 90° tilt angle silicon vacancy doped region is about 1000 μm, the doping area is reduced compared to 45°, indicating that the doping efficiency is reduced.

[0060] The results of these examples demonstrate that effective unintentional silicon doping can be achieved using the apparatus and growth method of the present application, suitable for use in MPCVD systems.

[0061] In particular, the gas and plasma distribution in an MPCVD system is complex, and by using the top and bottom gas inlet method, the distribution of gas and plasma on the substrate surface in the system can be changed, thereby affecting the incorporation of silicon. As can be seen from the results of the examples, by changing the angle of the substrate, the doping position and doping intensity of silicon and nitrogen can be changed, which shows that the present application can effectively achieve controllable doping of unintentional silicon.

[0062] In existing technologies, for example, when using silane as a silicon source for doping, the influence of unintentional silicon is also superimposed. The nonlinear superposition of the concentration of silane itself and the silicon doping concentration with the influence of unintentional silicon makes the silicon doping more uncontrollable, and the silane gas used has the characteristics of high risk level, which is not conducive to safe production. The apparatus and method provided by the present application can effectively solve such problems.

[0063] The apparatus and method and the idea provided in the present application can also be extended to the doping growth of other doping substances in diamond. By changing the doping substance, the gas inlet method, the angle of the substrate, and other conditions can be changed to change the doping position and doping concentration.

[0064] Of course, the present application can have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application. However, these corresponding changes and modifications should all belong to the protection scope of the claims attached to the present application.

Claims

1. A method for effectively achieving silicon doping in diamond, characterized in that, The MPCVD system is based on the following equipment, including a gas control module, a microwave module, and a reaction deposition module including a reaction chamber; The gas control module consists of a flow controller and a vacuum pump. The flow controller controls the inlet flow rate and the type of gas introduced. There are two types of gas introduction: top inlet and top and bottom inlet structures. The vacuum pump is used to maintain a high vacuum state in the reaction chamber. The above-inlet and below-inlet structures are as follows: there are inlets at the top and bottom of the chamber. The upper inlet is located at the top of the reaction chamber, and the lower inlet is located at the center of the sample stage inside the reaction chamber. In the upper-inlet state, all gas is introduced from the top. In the lower-inlet state, some gas is introduced from the upper inlet and some gas is introduced from the lower inlet. The microwave module consists of a microwave source, a waveguide, and a mode conversion antenna. The microwave source is used to generate the microwaves required for the reaction, the waveguide is used to conduct the microwaves and introduce them into the reaction chamber, and the mode conversion antenna is used to convert the TM mode microwaves generated by the microwave source into the TE mode microwaves required for the deposition reaction. The aforementioned reactive deposition module includes a quartz window, a reaction chamber, a sample stage, and a sample holder. Microwaves enter the reaction chamber through the quartz window, and the sample holder is placed on the sample stage within the reaction chamber. The sample holder is cylindrical with an air intake ring around it for gas to enter from below. The perforated sample holder has a 2mm diameter through hole in the center for air intake from below. The sample holder has an inclined surface around the through hole, with different angles (0-90°) between the inclined surface and the horizontal plane, allowing for different angle deposition and growth by changing the substrate angle. The microwave power and substrate temperature are controlled by adjusting the voltage of the microwave source, and the air intake is controlled by an angle valve to control the chamber pressure. And it is done through the following steps: 1) First, the diamond substrate is pretreated. Pretreatment conditions: First, the diamond substrate is placed in a mixed solution of concentrated nitric acid and concentrated sulfuric acid, with a ratio of 1:

1. Then, it is placed on a heating table and heated at 290°C for 30 minutes. After that, it is removed and immersed in acetone solution and sonicated for 15 minutes. Then, it is immersed in ethanol solution and sonicated for 15 minutes. Finally, it is sonicated in deionized water for 15 minutes. After that, it is removed and dried with nitrogen. 2) Plasma etching treatment of diamond substrate: After the diamond substrate is pretreated according to the conditions in step 1), it is placed on the sample holder, and then the sample holder is placed on the sample stage in the reaction chamber for plasma etching treatment. The specific conditions for plasma etching are: hydrogen flow rate 500±100sccm, microwave power between 1800-2200W, etching temperature between 550-600℃, reaction pressure between 10000-12000Pa, and etching time 10-30 minutes. 3) Preparation of doped diamond film growth conditions: After plasma etching, the hydrogen flow rate is kept constant, the microwave power is increased to 2400W±200W, the temperature is 700-800℃, the pressure is 13000-14000Pa, and the sample holder is inclined at 20-90°. At this time, 10±3sccm of methane and 1-3sccm of nitrogen are introduced through the sample holder through the bottom of the chamber. The angle valve is adjusted to maintain the pressure at 13000-14000Pa and the temperature at 760-780℃. The deposition time is more than 30 minutes. Finally, a nitrogen-silicon doped diamond film with gradient distribution is prepared.

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