CN111593318A - Diamond nanocrystalline/nitrogen-doped silicon carbide interface phase n-type semiconductor composite film and preparation method thereof - Google Patents

Diamond nanocrystalline/nitrogen-doped silicon carbide interface phase n-type semiconductor composite film and preparation method thereof Download PDF

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CN111593318A
CN111593318A CN202010667428.7A CN202010667428A CN111593318A CN 111593318 A CN111593318 A CN 111593318A CN 202010667428 A CN202010667428 A CN 202010667428A CN 111593318 A CN111593318 A CN 111593318A
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diamond
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hydrogen
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刘学杰
诸葛晨昱
孙士阳
谭心
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Inner Mongolia University of Science and Technology
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    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
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    • C23C16/50—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using electric discharges
    • C23C16/511—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using electric discharges using microwave discharges
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/56—After-treatment
    • H—ELECTRICITY
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/0405—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising semiconducting carbon, e.g. diamond, diamond-like carbon
    • H01L21/041—Making n- or p-doped regions
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    • H01L21/0445—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising crystalline silicon carbide
    • H01L21/0455—Making n or p doped regions or layers, e.g. using diffusion

Abstract

The invention discloses an n-type semiconductor composite film of a diamond nanocrystal/nitrogen-doped silicon carbide interface phase and a preparation method thereof, belonging to the field of composite film materials; the composite film prepared by the method consists of two parts, namely a crystal grain phase and an inter-crystal grain phase, wherein the crystal grain phase is a nano or superfine nano diamond crystal grain; the intergranular phase (interface phase) is a silicon carbide crystalline granular phase or an amorphous phase in which nitrogen atoms replace carbon atoms; intergranular phases (interphase) form a separation layer between the diamond grains; the composite film has n-type semiconductor performance; the preparation of the composite film comprises the steps of implanting high-density distributed seed crystals on the surface of a substrate, forming diamond crystal nuclei by utilizing microwave plasma gas phase deposition, co-depositing a diamond crystal grain phase and a nitrogen-doped silicon carbide interface phase, growing the nano-diamond composite film, and carrying out heat treatment to eliminate film stress and homogenize the grain size.

Description

Diamond nanocrystalline/nitrogen-doped silicon carbide interface phase n-type semiconductor composite film and preparation method thereof
Technical Field
The invention belongs to the field of composite film materials, and particularly relates to an n-type semiconductor composite film of a diamond nanocrystal/nitrogen-doped silicon carbide interface phase and a preparation method thereof.
Background
Diamond is a material with special performance, has the highest hardness (about 90 GPa) and the highest Young modulus (1100 GPa) in nature, has the fastest sound transmission speed (18.2 km/s), wide light transmission frequency width (from 200nm ultraviolet light to microwave), large forbidden bandwidth (5.4 eV) and large hole mobility; based on these characteristics, natural diamond, synthetic diamond particles, and diamond films have a wide range of applications.
In the prior art, the synthetic method of diamond comprises a static pressure method and a chemical vapor deposition method; chemical Vapor Deposition (CVD) diamond films can be made to a larger area in size compared to diamond single crystals synthesized by static pressure; this provides a basis for the application of diamond films in the fields of thermal, optical and electronics; the conventional CVD diamond film is composed of micron-sized columnar polycrystal, and the surface is rough; the grain size of the nano-diamond film is several to dozens of nanometers, the surface of the nano-diamond film is smooth, and the friction coefficient is small; therefore, the nano-diamond film has outstanding superiority in the aspects of friction and abrasion, optical coating, field emission, MEMS (micro electro mechanical systems), electrochemical application and the like;
CVD diamond film has good semiconductor properties such as high thermal conductivity (> 2000W/m · K), high breakdown electric field (10 MV/cm) and high carrier mobility (3000 cm2/V · s), and is therefore considered to be a good wide bandgap semiconductor material; research has found that p-type diamond semiconductor materials with good performance can be obtained by boron doping, but the construction of diamond n-type semiconductor materials has met with great challenges.
In the prior art, n-type diamond is generally prepared by a method of doping V group and VI group elements as electron donors, and a semiconductor material with good performance is attempted to be obtained; among them, nitrogen has received much attention from scientists as an impurity having the largest content in natural and synthetic diamonds; however, since nitrogen atoms have strong electronegativity, when nitrogen is substitutionally doped into diamond to form 4C-N configuration with four surrounding carbon atoms, unpaired electrons are bound near the nitrogen atoms, thus causing nitrogen as a donor defect, N-type diamond has a 1.7eV (E) lower than the conduction bandC-1.7eV) very deep defect levels; this seriously affects the conductivity at room temperature, which results in failure to serve as a semiconductor material with good performance; in addition, researchers have discovered many n-type doping elements such as P (E) with shallow defect levelsC-0.6eV)，S(EC-0.38eV)，As(EC-0.50eV)，Sb(EC-0.48eV)，Li(EC-0.1 eV). However, even if the donor level is shallow, the dopant still has low doping concentration, and the defect complex formed causes lattice distortion, which causes the carrier concentration, electron movement and conductivity of diamond to be low.
In view of the above problems of single element doping, researchers have proposed a method of using two-element co-doping; segev et al used first-nature principles to calculate Si as 20034The N tetrahedron doped diamond can greatly lighten the defect energy level of the nitrogen doped diamond to 0.09 eV; further elaboration of Si by Goss et al from 2006 to 20074N-doped diamond; as a result, Si was found4The donor level of the N combination is deeper than that of phosphorus (P) (0.5-0.6 eV), and Si is present in the range of 0.1eV4The formation energy of N doped diamond grains is large (16 eV); therefore, Goss believes that co-doping of silicon nitrogen (Si-N) is unlikely to be from Si4N-type conductivity results in the formation of N complexes.
Disclosure of Invention
The above reports are related to the research of diamond n-type semiconductor materials at present; the inventors also made a related study. The inventors' first principle computational studies have shown that silicon doped diamond results in a two phase diamond/silicon carbide composite structure. And the silicon nitrogen codoped diamond is easy to enter silicon carbide to form the nitrogen-doped silicon carbide. The donor level of nitrogen doped silicon carbide is very shallow (0.026-0.054 eV). Therefore, the chemical vapor deposition process is adopted to prepare the silicon-nitrogen co-doped diamond film, and a diamond/nitrogen doped silicon carbide composite structure can be formed. The structure has shallow donor level n-type semiconductor properties. The inventor adopts a chemical vapor deposition process to prepare the n-type semiconductor composite film of the diamond nanocrystal/nitrogen-doped silicon carbide interface phase.
The technical scheme adopted by the invention is as follows: an n-type semiconductor composite film of diamond nanocrystalline/nitrogen-doped silicon carbide interface phase, which consists of two parts of a crystal grain phase and an inter-crystal grain phase, wherein the crystal grain phase is nano or superfine nano diamond crystal grains; the intergranular phase (interface phase) is a silicon carbide crystalline granular phase or an amorphous phase in which nitrogen atoms replace carbon atoms; the intergranular phase (interface phase) forms a separation layer between the diamond grains.
Further, the grain phase separated by the intergranular phase is a diamond grain of a nano size of 1 to 100 nm.
A preparation method of the composite film adopts a microwave plasma chemical vapor deposition process; the method specifically comprises the following steps:
step one, substrate surface treatment: carrying out ultrasonic cleaning on the monocrystalline silicon substrate by sequentially using acetone, absolute ethyl alcohol and deionized water to remove impurities on the surface;
step two, planting nano diamond seeds on the surface of the substrate cleaned in the step one:
(2.1) preparing the nano-diamond seed solution into a diluent with the concentration of 1% by using deionized water;
(2.2) putting the monocrystalline silicon substrate cleaned in the step one into the prepared diluent in the step (2.1) for ultrasonic crystal implantation to enable the nucleation density of diamond on the surface of the substrate to reach 1012/cm2；
Step three, cleaning the substrate: putting the monocrystalline silicon substrate subjected to the crystal implantation in the step (2.2) into absolute ethyl alcohol for ultrasonic cleaning; then drying by a fan;
step four, putting the monocrystalline silicon substrate processed in the step three into a vacuum chamber of microwave plasma chemical vapor deposition equipment, and vacuumizing until the pressure is less than or equal to 1 × 10-4Pa；
Step five, growing diamond crystal nucleuses: setting the diamond nucleation parameters as follows, setting the microwave power in a range of 1200-1500W and the substrate temperature in a range of 850-1000 ℃; simultaneously introducing methane and hydrogen; the working air pressure is 3.5-4.5kPa, and the nucleation process is 10-20 minutes;
step six, growing the composite film: according to the requirements of the size of the nano diamond crystal particles and the performance of the n-type semiconductor, four gases are introduced in proper proportion: co-depositing methane, hydrogen, tetramethylsilane and ammonia gas under a proper environmental condition to form a nano-diamond composite film;
step seven, surface treatment: and (5) after the growth stage of the film prepared in the sixth step is finished, performing surface etching treatment: etching redundant C-sp on the surface of the film by using hydrogen only2Phase (1);
step eight, annealing treatment is carried out after the step seven, wherein the annealing treatment is carried out in a hydrogen atmosphere, and the working pressure is 3.5-4 kPa; finally, the n-type semiconductor composite film of the diamond nanocrystalline/nitrogen-doped silicon carbide interface phase is prepared.
Further, the preparation method comprises the following steps:
in the sixth step, the specific growth conditions are set as follows:
(6.1) gas flow rate and gas ratio: in the four introduced gas sources, hydrogen is the environment atmosphere formed by the diamond film and accounts for the main component of the gas; methane is carbon source atmosphere formed by the diamond film, and the volume ratio of methane to hydrogen is about 1% when the film is stably grown; the using amount of tetramethylsilane is used for controlling the grain size of the diamond film, and specifically, when the grain size of the diamond is controlled to be below 20 nanometers, tetramethylsilane accounts for 0.5 per mill of the total gas amount; the ammonia amount is used for controlling the performance of the n-type semiconductor, and the ammonia accounts for 0.05-0.5 per mill of the total gas amount according to the proportion of nitrogen atoms in the interface phase to replace carbon atoms in the silicon carbide;
(6.2) reaction conditions: controlling the temperature to be more than 1000 ℃, controlling the pressure intensity range in the reaction chamber to be 3.9-5kPa, controlling the microwave power to be 1200W, and determining the deposition time according to the required deposition thickness;
in the seventh step, etching is carried out by using hydrogen under the experimental environments of the previous steps (6.1) and (6.2), wherein the flow rate of the hydrogen gas is 250sccm, and the working pressure is 3.5-4 kPa;
in the eighth step, the annealing treatment specifically requires the following: cooling to 500 ℃ from the substrate temperature of 1000 ℃, and cooling to 5 ℃ per minute; and naturally cooling to 500 ℃ until the temperature reaches the room temperature.
Further, the specific operation requirements of the composite film which is prepared by the method and has the grain size below 20nm and only a few nanometers of interface phase are as follows;
in the first step, the crystal orientation of the monocrystalline silicon substrate is (100); the ultrasonic power of the ultrasonic cleaning is 700W;
in the step (2.1), 1mL of 2.5% kg/L nano-diamond seed solution with the nano-diamond grain size of 3nm and 100mL of deionized water are mixed to prepare a diluent;
in the step (2.2), the ultrasonic power is 700W, the crystal planting temperature is room temperature, and the crystal planting time is 30-40 minutes;
in the third step, ultrasonic cleaning is carried out for 2 minutes;
in step four, vacuum is applied until the pressure is equal to 1 × 10-4Pa；
In the fifth step, the microwave power is 1200W, and the volume ratio of methane to hydrogen is 4.16%; specifically, the method for controlling the volume ratio of methane to hydrogen gas comprises the following steps: the flow rate of methane is 10sccm, the flow rate of hydrogen is 240sccm, the working pressure is 4kPa, and the nucleation process is 12 minutes;
in the step (6.1), the total flow rate of the gas is 250sccm, wherein the flow rate of methane is 2.5sccm, the flow rate of tetramethylsilane is 0.125sccm, the flow rate of ammonia is 0.125sccm, and the flow rate of hydrogen is 247.25 sccm;
in the step (6.2), the temperature is 1000 ℃, and the pressure in the reaction chamber is 4.5 kPa;
in the seventh step, the working pressure is 3.9kPa, and the etching time is 10 minutes;
in the eighth step, the hydrogen flow is 250 sccm; the working pressure was 3.9 kPa.
The invention has the beneficial effects that: the invention provides a method for preparing an n-type semiconductor composite film of a diamond nanocrystalline/nitrogen-doped silicon carbide interface phase by adopting a chemical vapor deposition process; the composite film prepared by the method consists of two parts, namely a crystal grain phase and an inter-crystal grain phase, wherein the crystal grain phase is a nano or superfine nano diamond crystal grain; the intergranular phase (interface phase) is a silicon carbide crystalline granular phase or an amorphous phase in which nitrogen atoms replace carbon atoms; intergranular phases (interphase) form a separation layer between the diamond grains; the composite film has n-type semiconductor properties.
Drawings
FIG. 1 is an SEM image of a composite film prepared according to an embodiment of the present invention.
Fig. 2 is a schematic view of the microstructure of the silicon nitrogen co-doped diamond composite film drawn on the basis of fig. 1.
Fig. 3 is a band contrast diagram of silicon carbide and nitrogen doped silicon carbide according to embodiments of the present invention.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the present invention will be further described in detail with reference to the following embodiments, which are only used for illustrating the technical solution of the present invention and are not limited.
Example 1
The preparation method of the n-type semiconductor composite film of the diamond nanocrystal/nitrogen-doped silicon carbide interface phase specifically comprises the following steps:
step one, substrate surface treatment: putting a monocrystalline silicon substrate with a crystal orientation (100) into a weighing bottle, and sequentially carrying out ultrasonic cleaning for 5-10 minutes by using acetone, absolute ethyl alcohol and deionized water to remove impurities on the surface, wherein specifically, the acetone is used for removing polar organic stains, the absolute ethyl alcohol is used for removing particle impurities, and the deionized water is used for removing surface charges; the ultrasonic power was 700W.
Step two, planting nano diamond seeds on the surface of the substrate cleaned in the step one:
(2.1) uniformly mixing the nano-diamond seed solution with deionized water in a weighing bottle to prepare a diluent with the concentration of 1%; in this example, the concentration of the nano-diamond seed solution used was 2.5% kg/L, the size of the nano-diamond grains was 3nm, and the nano-diamond seed solution was purchased from NanoAmando corporation, and 1mL of the nano-diamond seed solution was taken and prepared into a diluent with 100mL of deionized water;
(2.2) placing the monocrystalline silicon substrate cleaned in the step one into the prepared diluent in the step (2.1) for ultrasonic crystal implantation, wherein the ultrasonic power is 700W, the crystal implantation temperature is room temperature, and the crystal implantation time is 30-40 minutes; the diamond nucleation density of the surface of the substrate reaches 1012/cm2。
Step three, cleaning the substrate: putting the monocrystalline silicon substrate subjected to the crystal implantation in the step (2.2) into absolute ethyl alcohol, and ultrasonically cleaning for 2 minutes; and then blowing the substrate by using a fan, wherein the operation of the step is to prevent the trace of the redundant nano-diamond seed solution on the surface of the monocrystalline silicon substrate from influencing the uniform nucleation of the diamond.
Step four, putting the monocrystalline silicon substrate processed in the step three into a vacuum chamber of Microwave Plasma Chemical Vapor Deposition (MPCVD) equipment, and vacuumizing until the pressure is less than or equal to 1 × 10-4Pa, in this example a vacuum is applied to a pressure equal to 1 × 10- 4Pa。
Step five, growing diamond crystal nucleuses: setting diamond nucleation parameters as follows, setting the microwave power at the interval of 1200-1500W (specifically 1200W in the embodiment), and setting the substrate temperature at 1000 ℃; simultaneously introducing methane and hydrogen to prevent the diamond seeds implanted on the substrate from being etched by the hydrogen introduced alone; and controlling methane and hydrogen (CH)4:H2) The volume ratio of the gas is 4.16%; in this embodiment, the method for controlling the volume ratio of methane to hydrogen gas includes: the flow rate of methane is 10sccm, the flow rate of hydrogen is 240sccm, the working gas pressure is in the range of 3.5-4.5kPa (specifically 4kPa in this embodiment), and the nucleation process is about 10-20 minutes, which is specifically 12 minutes in this embodiment.
Step six, growing the composite film: according to the requirements of the size of the nano diamond crystal particles and the performance of the n-type semiconductor, introducing four gases of methane, hydrogen, tetramethylsilane and ammonia in proper proportion, and carrying out co-deposition under proper environmental conditions to form a nano diamond composite film; the growth conditions in this example were set as follows:
(6.1) gas flow rate and gas ratio: the four gas sources are methane, hydrogen, ammonia and Tetramethylsilane (TMS); wherein, hydrogen is the environment atmosphere formed by the diamond film and accounts for the main component of the gas; methane is carbon source atmosphere formed by the diamond film, and the volume ratio of methane to hydrogen is about 1% when the film is stably grown; the using amount of tetramethylsilane is used for controlling the grain size of the diamond film, and specifically, when the grain size of the diamond is controlled to be below 20 nanometers, tetramethylsilane accounts for 0.5 per mill of the total gas amount; the ammonia amount is used for controlling the performance of the n-type semiconductor, and the ammonia accounts for 0.05-0.5 per mill of the total gas amount according to the proportion of nitrogen atoms in the interface phase to replace carbon atoms in the silicon carbide;
in this embodiment, the total flow rate of the gas is 250sccm, wherein the flow rate of methane is 2.5sccm, the flow rate of tetramethylsilane is 0.125sccm (to realize a small flow rate of tetramethylsilane, in this embodiment, a mixed gas of tetramethylsilane and hydrogen is used, wherein the concentration of tetramethylsilane is 1%, and the flow rate of the mixed gas is 12.5 sccm), the flow rate of ammonia is 0.125sccm or less (in this embodiment, 0.125sccm is used, a mixing manner of ammonia and hydrogen is used, wherein the concentration of ammonia is 1%, and the flow rate of the mixed gas is 12.5 sccm), the total flow rate of the hydrogen is 247.25sccm, and the crystal grain of the composite film prepared under this condition is less than 20 nm;
(6.2) reaction conditions: the temperature is controlled to be above 1000 ℃ (the temperature is 1000 ℃ in the embodiment), the pressure range in the reaction chamber is 3.9-5kPa (4.5 kPa in the embodiment), the microwave power is 1200W, the deposition time is determined according to the required deposition thickness, the thickness and the deposition time approximately present a linear relation, and the thickness of the 4-hour deposited film in the embodiment is 1.2 μm.
Step seven, surface treatment: after the film growth stage is finished, surface etching treatment is required: in the previous experimental environment (6.1-6.2 conditions), only hydrogen (other gases are closed) is used for etching redundant C-sp on the surface of the film2Phase, reduction film watchA defect of the facet. In this embodiment, the microwave power is 1200KW, the flow rate of the hydrogen gas is 250sccm, the working pressure is 3.5-4kPa (3.9 kPa in this embodiment), and the etching time is 10 minutes.
Step eight, reducing and eliminating stress in the film by adopting heat treatment, and specifically operating as follows: the final stage of film deposition needs annealing treatment, wherein the temperature is reduced to 500 ℃ from the substrate temperature of 1000 ℃, and the temperature is reduced by 5 ℃ per minute; naturally cooling to 500 deg.C to room temperature to homogenize crystal size; the annealing treatment is carried out in a hydrogen atmosphere at a flow rate of 250sccm under a working pressure of 3.5 to 4kPa (3.9 kPa in the present example).
The SEM image of the composite film prepared in this example is shown in FIG. 1.
To illustrate the above composite film structure, the inventors have used the first principles software package VASP based on the density functional theory to create C64Diamond supercell model and C32Si32The superlattice model of silicon carbide crystal was calculated from the formation energy of silicon and nitrogen atoms substituting for carbon atoms in diamond crystal and silicon carbide crystal, and the results are shown in table 1.
TABLE 1 formation energies of silicon and nitrogen in diamond and silicon carbide
Figure DEST_PATH_IMAGE002
The results in table 1 show that both silicon and nitrogen atoms are difficult to enter the diamond crystal; silicon atoms are easy to gather in an interface phase, and the effect of refining crystal grains is achieved; nitrogen atoms readily enter the silicon carbide at the interface phase by displacing carbon atoms in the silicon carbide. Referring to fig. 1, the grain size of the composite film of the present embodiment is below 20nm, the interface phase is only a few nanometers, and we draw a schematic view of the microstructure of the silicon nitrogen co-doped diamond composite film based on the grain size, as shown in fig. 2; in fig. 2, diamond grains are subjected to silicon nitrogen co-doping to form nano-grains with the grain size of less than 20 nm; and the nitrogen-doped silicon carbide is filled in the middle of the diamond grains as an interface phase. The diamond/nitrogen-doped silicon carbide composite film with the structure can improve the hardness and modulus of the composite film through the nano diamond grains, and meanwhile, the interface phase of the nitrogen-doped silicon carbide can also enable the n-type semiconductor performance of the composite film, and more rarely, the donor level of the nitrogen-doped silicon carbide is only 0.026eV, so that great possibility is provided for application of the shallow donor level n-type diamond semiconductor material.
To demonstrate the semiconductor properties of the thin film produced in this example, the inventors compared the band diagrams of nitrogen-doped silicon carbide and silicon carbide using first principles of calculation, as shown in fig. 3, and as a result, it was shown that nitrogen doping changes the band structure of silicon carbide such that the donor level is closer to the conduction band bottom, showing n-type semiconductor properties, and that both the conduction band bottom and the doping band minimum are shifted to the Gamma point such that the indirect band gap becomes a direct band gap, and the forbidden band width is also narrowed from 1.42eV to 1.24 eV.
Further description of the composite film of the present invention is as follows.
The nano diamond composite structure film provided by the invention belongs to a nano composite structure, and the performance of the nano diamond composite structure film can be adjusted through the size, the shape and the distribution of the nano structure; by changing the size of crystal grain in the film, the thickness and distribution of interface phase, the mechanical, thermal, electrical, optical and magnetic properties of the whole composite film can be changed. The diamond composite film has a nano composite hardening mechanism and is expected to become the development direction of the superhard diamond film. In addition, due to the quantum effect of the nano structure, the energy band structure of the composite film can be adjusted by changing the size and the shape of the nano diamond or changing the thickness and the distribution of the interface phase, so that the electrical property, the optical property and the magnetic property of the nano diamond composite film can be controlled, and the nano diamond composite film has better application in the fields of microelectronics, optics, magnetics and the like.
The current research results show that the semiconductor performance, the optical performance and the magnetic performance of the composite film are mainly determined by the following factors:
the size, shape and distribution of diamond grains, the thickness and distribution of inter-grain phases (interface phases) of nitrogen-doped silicon carbide and the proportion of the diamond phase to the nitrogen-doped silicon carbide phase;
doping rate of nitrogen into silicon carbide;
the number of defects in diamond grains, in nitrogen-doped silicon carbide and at the contact position of the two phases;
the three factors cause the electronic structure (charge distribution, state density and energy band structure) and the dielectric coefficient of the film to change, and the n-type semiconductor performance, the optical performance and the magnetic performance of the whole film are changed due to the nano-structure effect and the quantum effect, and particularly in research experiments.
The present invention shows that the mechanical property of the composite film is improved by the following four factors:
the grain size is as small as nanometer, thereby realizing grain refinement, enhancement and hardening;
secondly, the interface phase separates crystal grains, prevents the crystal grains from growing and can prevent the crystal grains from growing and softening;
the structure of the interface separated nano diamond grains can change the deformation mode of the single diamond after being loaded, and realize composite enhancement and hardening;
and fourthly, in the process of forming the composite surface, the interface phase particles can promote the migration of the carbon (C) particles, so that the defects in the nano diamond grains are reduced, the grains are more compact, and the enhancement and hardening are realized.
It should be noted that the present application is only a preliminary research result, and the above description needs further intensive research and demonstration.
Although the present invention has been described in detail with reference to the foregoing examples, it will be apparent to one skilled in the art that various changes in the embodiments and/or modifications of the embodiments and/or portions thereof may be made, and all changes, equivalents, and modifications that fall within the spirit and scope of the invention are therefore intended to be embraced by the appended claims.

Claims (5)

1. An n-type semiconductor composite film of diamond nanocrystalline/nitrogen-doped silicon carbide interface phase is composed of a crystal grain phase and an intergranular phase, and is characterized in that the crystal grain phase is nano or superfine nano diamond crystal grains; the intergranular phase (interface phase) is a silicon carbide crystalline granular phase or an amorphous phase in which nitrogen atoms replace carbon atoms; the intergranular phase (interface phase) forms a separation layer between the diamond grains.
2. The n-type semiconductor composite film of diamond nanocrystal/nitrogen doped silicon carbide interface phase as claimed in claim 1, wherein the crystal grain phase separated by the inter-crystal grain phase is a diamond crystal grain of nano-scale 1-100 nm.
3. A preparation method of the composite film adopts a microwave plasma chemical vapor deposition process; the method is characterized by comprising the following steps:
step one, substrate surface treatment: carrying out ultrasonic cleaning on the monocrystalline silicon substrate by sequentially using acetone, absolute ethyl alcohol and deionized water to remove impurities on the surface;
step two, planting nano diamond seeds on the surface of the substrate cleaned in the step one:
(2.1) preparing the nano-diamond seed solution into a diluent with the concentration of 1% by using deionized water;
(2.2) putting the monocrystalline silicon substrate cleaned in the step one into the prepared diluent in the step (2.1) for ultrasonic crystal implantation to enable the nucleation density of diamond on the surface of the substrate to reach 1012/cm2；
Step three, cleaning the substrate: putting the monocrystalline silicon substrate subjected to the crystal implantation in the step (2.2) into absolute ethyl alcohol for ultrasonic cleaning; then drying by a fan;
step four, putting the monocrystalline silicon substrate processed in the step three into a vacuum chamber of microwave plasma chemical vapor deposition equipment, and vacuumizing until the pressure is less than or equal to 1 × 10-4Pa；
Step five, growing diamond crystal nucleuses: setting the diamond nucleation parameters as follows, setting the microwave power in a range of 1200-1500W and the substrate temperature in a range of 850-1000 ℃; simultaneously introducing methane and hydrogen; the working air pressure is 3.5-4.5kPa, and the nucleation process is 10-20 minutes;
step six, growing the composite film: according to the requirements of the size of the nano diamond crystal particles and the performance of the n-type semiconductor, four gases are introduced in proper proportion: co-depositing methane, hydrogen, tetramethylsilane and ammonia gas under a proper environmental condition to form a nano-diamond composite film;
step seven, surface treatment: and (5) after the growth stage of the film prepared in the sixth step is finished, performing surface etching treatment: etching redundant C-sp on the surface of the film by using hydrogen only2Phase (1);
step eight, annealing treatment is carried out after the step seven, wherein the annealing treatment is carried out in a hydrogen atmosphere, and the working pressure is 3.5-4 kPa; finally, the n-type semiconductor composite film of the diamond nanocrystalline/nitrogen-doped silicon carbide interface phase is prepared.
4. The method of claim 3, wherein:
in the sixth step, the specific growth conditions are set as follows:
(6.1) gas flow rate and gas ratio: in the four introduced gas sources, hydrogen is the environment atmosphere formed by the diamond film and accounts for the main component of the gas; methane is carbon source atmosphere formed by the diamond film, and the volume ratio of methane to hydrogen is about 1% when the film is stably grown; the using amount of tetramethylsilane is used for controlling the grain size of the diamond film, and specifically, when the grain size of the diamond is controlled to be below 20 nanometers, tetramethylsilane accounts for 0.5 per mill of the total gas amount; the ammonia amount is used for controlling the performance of the n-type semiconductor, and the ammonia accounts for 0.05-0.5 per mill of the total gas amount according to the proportion of nitrogen atoms in the interface phase to replace carbon atoms in the silicon carbide;
(6.2) reaction conditions: controlling the temperature to be more than 1000 ℃, controlling the pressure intensity range in the reaction chamber to be 3.9-5kPa, controlling the microwave power to be 1200W, and determining the deposition time according to the required deposition thickness;
in the seventh step, etching is carried out by using hydrogen under the experimental environments of the previous steps (6.1) and (6.2), wherein the flow rate of the hydrogen gas is 250sccm, and the working pressure is 3.5-4 kPa;
in the eighth step, the annealing treatment specifically requires the following: cooling to 500 ℃ from the substrate temperature of 1000 ℃, and cooling to 5 ℃ per minute; and naturally cooling to 500 ℃ until the temperature reaches the room temperature.
5. The method according to claim 4, wherein:
in the first step, the crystal orientation of the monocrystalline silicon substrate is (100); the ultrasonic power of the ultrasonic cleaning is 700W;
in the step (2.1), 1mL of 2.5% kg/L nano-diamond seed solution with the nano-diamond grain size of 3nm and 100mL of deionized water are mixed to prepare a diluent;
in the step (2.2), the ultrasonic power is 700W, the crystal planting temperature is room temperature, and the crystal planting time is 30-40 minutes;
in the third step, ultrasonic cleaning is carried out for 2 minutes;
in step four, vacuum is applied until the pressure is equal to 1 × 10-4Pa；
In the fifth step, the microwave power is 1200W, and the volume ratio of methane to hydrogen is 4.16%; specifically, the method for controlling the volume ratio of methane to hydrogen gas comprises the following steps: the flow rate of methane is 10sccm, the flow rate of hydrogen is 240sccm, the working pressure is 4kPa, and the nucleation process is 12 minutes;
in the step (6.1), the total flow rate of the gas is 250sccm, wherein the flow rate of methane is 2.5sccm, the flow rate of tetramethylsilane is 0.125sccm, the flow rate of ammonia is 0.125sccm, and the flow rate of hydrogen is 247.25 sccm;
in the step (6.2), the temperature is 1000 ℃, and the pressure in the reaction chamber is 4.5 kPa;
in the seventh step, the working pressure is 3.9kPa, and the etching time is 10 minutes;
in the eighth step, the hydrogen flow is 250 sccm; the working pressure was 3.9 kPa.
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