CN107419329B - Preparation method of in-situ n-type semiconducting all-carbon structure on the surface of single crystal diamond - Google Patents

Abstract

The invention discloses a method for preparing an in-situ n-type semiconducting all-carbon structure on the surface of a single crystal diamond, which belongs to the field of preparing base materials for semiconductor basic circuits. The process steps are: a. using mechanical polishing to polish the single crystal diamond until the surface roughness is lower than 1nm; b. pickling and using _H2 plasma in-situ etching to form microscopic nucleation points on the surface of the seed crystal; c. The single crystal diamond substrate is placed in the microgroove of the molybdenum support, and the ratio between the height of the sample surface to the groove and the gap between the sample and the microgroove is kept between 0.5-0.7; d. Using single crystal diamond as the seed crystal, the carbon-containing matrix is suppressed by controlling the deposition process The spatial transmission and surface diffusion of clusters suppress the extraction reaction under the sp ³ structure on the surface of single crystal diamond, relying on the steps and defect areas of single crystal diamond to realize the nucleation and growth of ultra-nano-diamond; at the same time, nitrogen doping realizes the n-type of ultra-nano-diamond Doping, and finally realize the preparation of in-situ n-type conductive ultra-nano-diamond thin layer on the surface without changing the original conditions of the single crystal diamond seed crystal, forming a diamond semiconductor with an all-carbon structure.

Description

Preparation method of in-situ n-type semiconducting all-carbon structure on the surface of single crystal diamond

Technical field:

The invention relates to the field of base material preparation for semiconductor basic circuits; in particular, plasma etching and vapor deposition are used on the surface of single crystal diamond to directly in-situ semiconductorize the surface of the diamond to form an n-type ultra-nano-diamond thin layer to obtain an all-carbon structure diamond semiconductor.

technical background

Diamond has a wider band gap (5.5eV), high carrier mobility (especially hole mobility is much higher than single crystal Si and GaAs), low dielectric constant (5.7), extremely high Johnson index and Keyse indicators (all ten times higher than Si and GaAs), etc., are known as the ultimate wide bandgap semiconductor in the field of high frequency, high power and high temperature withstand voltage, also known as the fourth generation semiconductor. And because of its excellent stability, semiconductor devices can work normally in extreme environments. However, the radius and lattice constant of carbon atoms in diamond are small, and the band gap is large. Therefore, the solubility of many impurity atoms in diamond is very low, and the high ionization energy of impurities restricts the development of diamond semiconductors. The n-type impurities doped into the diamond film have a deep energy level, resulting in low carrier concentration, low mobility, and high resistivity. At present, ion doping still faces many problems. The preparation methods of n-type diamond mostly adopt CVD method and ion implantation method, and the relevant research has made some progress, but the effect is still not ideal, and the crystal integrity of diamond itself is destroyed. For this reason, scholars have begun to explore and study the way of nitrogen-doped ultra-nanodiamond to realize n-type conduction (Phys. )).Because there are a large number of grain boundaries in the ultra-nanodiamond, and the nitrogen causes the percolation pathway in the grain boundary area to improve the n-type conduction, and the carrier mobility and the broadened energy band are improved with the increase of the nitrogen content The absolute value of the conductivity is increased. Neda et al. used nitrogen-doped ultra-nanodiamond to realize n-type conductivity and prepared a piezoresistive sensor (DiamondRelat.Mater.70, 145150 (2016); Abdelrahman et al. used nitrogen-doped n-type ultra-nano Diamond has made an ultraviolet detector (Appl.Phys.A.123,167 (2017)). It can be seen that nitrogen-doped n-type ultra-nanodiamond has become an effective method for diamond n-type semiconductorization, and its performance has reached that of boron-doped diamond. However, the current preparation of nitrogen-doped n-type ultra-nano-diamond films all use heterogeneous substrates, such as Si, etc., often due to the low thermal conductivity and low pressure resistance of the substrate, it is difficult to exert the excellent electrical properties of diamond. Limiting the full application of the excellent properties of ultra-nano-diamond. At the same time, growing nano-diamond or even ultra-nano-diamond on heterogeneous substrates often requires mechanical grinding or biasing to increase the nucleation rate, making the growth process complicated. And it is easy to cause stress and deformation of the substrate.

Contents of the invention

In order to solve the above problems, the object of the present invention is to propose a method of nucleation and growth of supernano n-type diamond based on high thermal conductivity single crystal diamond, thereby forming an all-diamond carbon structure semiconductor with good thermal conductivity and electrical conductivity. After the single crystal diamond is polished to a very low roughness by mechanical polishing, it is placed in the molybdenum support microgroove by pickling to ensure that the sample and the groove maintain a certain geometric relationship, and the seed crystal is etched by _H2 plasma in situ The surface forms microscopic nucleation sites. Then, by controlling the deposition process and relying on the steps and defect regions after etching of the single crystal diamond without changing the original conditions of the diamond seed crystal, the nucleation of ultra-nanodiamonds can be achieved while doping nitrogen to achieve n-type doping growth, satisfying the in-situ n on the surface. The preparation of a type conductive ultra-nano-diamond thin layer forms a diamond semiconductor with an all-carbon structure.

Technical scheme of the present invention is:

A preparation method for in-situ n-type semiconducting on the surface of single crystal diamond. It is characterized in that an n-type conductive ultra-nano-diamond thin layer is directly generated on the surface of single crystal diamond by microwave plasma etching and vapor deposition technology, and the process steps are as follows:

(1) Grinding and polishing of single crystal diamond seed crystal

In order to ensure that the surface after growing ultra-nanometer diamond meets the requirements of electronic devices, the surface of single crystal diamond growth is firstly polished precisely. Pre-polish with diamond micropowder with a particle size of 40, 20, 10 and 2.5; then place it on a precision diamond polishing disc for fine polishing. After polishing, the surface roughness is less than 1nm.

(2) Single crystal diamond seed crystal pickling treatment

In order to ensure the smooth surface of single crystal diamond, remove possible metal inclusions, hydrocarbons, graphite, etc. After polishing, the seed crystal samples were boiled in a mixture of HCl:H ₂ SO ₄ and rinsed with deionized water; then ultrasonically cleaned and dried in acetone solution and absolute ethanol in turn.

(3) Establishment of single crystal diamond deposition environment

Place the single crystal diamond substrate in the square microgroove of the molybdenum holder, the height from the surface of the sample to the surface of the groove and the distance between the edge of the sample and the distance between the microgroove are kept between 0.5-0.7, the thickness of the molybdenum holder is 5-15mm, and the depth of the microgroove is 500 Between microns and 1500 microns. And place the molybdenum bracket on the copper heat conduction base to ensure heat dissipation. The method is able to maintain a suitable local and immediate environment for diamond substrate deposition. Because if the diamond single crystal is in the plasma field, the temperature and the cavity pressure will affect each other and cannot reach the appropriate conditions, and the process of depositing ultra-nano diamond on the surface is prone to the appearance of microcrystals and the edge temperature of the seed crystal surface is too high in the plasma. The uneven temperature distribution on the surface of the seed crystal affects the flatness of the deposited layer, so as to avoid the rapid growth of nano-clusters and make the deposited layer on the diamond surface smooth. Moreover, the grain size depends on the average degree of freedom of chemical reactions and the thickness of the boundary layer. The designed groove depth can increase the thickness of the stable flow layer on the diamond surface, and the grain size decreases with the increase of the boundary layer thickness, which is beneficial to the two Secondary nucleation; at the same time, it can ensure the concentration of active groups and ensure the rapid nucleation and growth of ultra-nanocrystals. At the same time, the thickness of the molybdenum support is controlled so that its surface is at the edge of the plasma sphere, while reducing the erosion of the flow field on the diamond surface, while ensuring the concentration of the groups required for growth, and stabilizing the nucleation and growth of ultra-nano diamond.

(4) Plasma surface etching of single crystal diamond seed crystal

H2 plasma etching is used to remove the possible distortion regions or dislocation outcrops on the diamond surface, and at the same time produce steps and defect regions of single crystal diamond. This process is completed in situ during the process of starting the plasma and adjusting the process parameters to reach a steady state, specifically: the hydrogen flux is 200-300sccm, and the methane flow rate is 5-25sccm. Since the introduction of methane will increase the temperature by about 30-50°C, after the introduction of H ₂ , the power is 2000-3000W, the chamber pressure is adjusted to control the temperature at about 700-740°C, and the etching is performed for 10-15 minutes. The steps and defect areas of single crystal diamond are produced while removing the distortion area or dislocation outcrop that may exist on the diamond surface. In the actual etching process, the etching rate of hydrogen plasma on the surface distortion and dislocation expansion area is much higher than that on the intact area. While removing the possible distortion areas or dislocation outcrops on the diamond surface, steps and defect areas of single crystal diamond are generated, relying on this to realize the direct nucleation and growth of nano-diamonds. At the same time, the H2 plasma in-situ etching of the single crystal diamond seed crystal causes a large number of H terminations to be formed on the surface, and the atoms H on the dangling bonds are constantly removed and replaced by C-containing components to maintain the diamond growth. The ideal interface is conducive to the nucleation and growth of ultra-nanocrystals. The dangling bond is the replacement of carbon source C provided by methane, which is realized by controlling the flow of methane, adjusting the pressure of the power chamber, and ensuring the temperature.

(5) Deposition and growth of super-nanolayer on the surface

The state of the diamond is not changed after etching, and the n-type doped ultra-nano-diamond is formed in the process of rapid nucleation and growth only by controlling the power, temperature, chamber pressure and gas flow. By controlling the concentration of carbon-containing groups in the plasma, inhibiting the spatial transmission and surface diffusion of carbon-containing groups, suppressing the extraction reaction under the sp ³ structure on the surface of single crystal diamond, and relying on the steps and defect areas of single crystal diamond, the direct Nucleation and growth, the methane flow rate is 5-25 sccm, which makes the realization of high CH ₄ flux, under the condition of suitable temperature and relatively low pressure, CH ₃ and CH ₂ matrix are formed in the environment, and the dimer C ₂ is in the form of nano-diamond Substances required for nuclear growth. Nitrogen addition also increases the growth rate. By controlling the ratio of nitrogen doping, the incorporation of nitrogen atoms into the CC lattice is realized at the same time as the nucleation of nanodiamonds. Compared with CH ₄ /H ₂ plasma, the addition of N ₂ provides many additional reaction pathways and new intermediate reactants including N leading to different N ₂ can induce the formation of nanocrystals in the product.

Further, the pre-polishing time in step (1) is 24-48 hours.

Further, the fine polishing step in step (1) is: on the precision diamond polishing disc, the control speed is 40 rpm, 80 rpm, and 120 rpm, respectively, for 20-30 hours, 40-60 hours and 80-100 hours for polishing.

The pickling treatment in the further step (2) is that after polishing, the seed crystal sample is placed in a mixture of HCl:H ₂ SO ₄ =1:5 and boiled for 45 minutes to 1 hour, and then rinsed with deionized water; and then sequentially Place in acetone solution and absolute ethanol for ultrasonic cleaning for 10-15 minutes, and dry.

Further, the specific process conditions for forming n-type doped ultra-nano-diamond in step (5) are: power 800w-3000w, temperature 400-750°C, chamber pressure maintained at 5-15.5kPa, flow rate of 100 - 500 sccm of hydrogen and 5-25 sccm of methane are fed with N ₂ at a flow rate of 1-60 sccm.

The key of the present invention's implementation process is:

(1) In the process of surface treatment of single crystal diamond seed crystal, the growth surface of seed crystal is precisely polished with diamond powder of different particle sizes and moderate polishing time to achieve extreme smoothness, eliminate graphite phase, and avoid abnormal grain growth or form nanoclusters.

(2) In the process of surface polishing, in addition to mechanical polishing, mechanochemical polishing, plasma-assisted or composite polishing are also used to precisely planarize the surface of the diamond substrate to achieve a surface roughness of less than 1nm .

(3) The establishment of the single crystal diamond deposition environment is to design the geometric structure of the deposition table based on the size of the diamond single crystal seed crystal. The height from the sample surface to the groove surface is kept between 0.5-0.7 between the sample edge and the distance between the micro grooves. The molybdenum support is so thick that its surface is at the edge of the plasma sphere. Establish and stabilize a suitable environment for the nucleation and growth of ultra-nanometer diamonds.

(4) Pure _H2 plasma surface etching of single crystal diamond seed crystal. The step and defect area of single crystal diamond can be produced while removing the distortion area or dislocation outcrop that may exist on the diamond surface. Simultaneously a large number of hydrogen terminations are formed. Maintaining the ideal interface required for diamond growth contributes to the nucleation and growth of ultra-nanocrystals.

(5) In the pure _H2 environment, by controlling the concentration of carbon-containing groups in the plasma, the methane flow rate is 8-15 sccm, so that high _CH4 flux can be realized, and at a suitable temperature and relatively low pressure, _CH3 and The C ₂ H matrix and the dimer C ₂ are the substances required for the nucleation and growth of ultra-nano diamond.

(6) The set power is 800-3000W, the temperature is 400-750°C, and the cavity pressure is kept at 5-15.5kPa. The added high-concentration nitrogen source 1-60sccm _N2 can accelerate the growth of diamond, so as to ensure the rapid nucleation and growth of ultra-nano diamond. At the same time, nitrogen doping can be realized while super-nano-diamond can be formed on the surface of single-crystal diamond to form an n-type conductive super-nano-diamond layer.

(7) In addition to nitrogen doping, different gas sources can also be introduced to realize S and P doping to form n-type conduction, or B and other doping to form p-type conduction.

(8) The diamond substrate seed crystal can be high temperature and high pressure seed crystal or homoepitaxial single crystal diamond. Similarly, polycrystalline diamond and composite structures of silicon, GaN, SiC, etc. and diamond can also be used.

Compared with the prior art, the present invention has the beneficial effects of:

(1) Single crystal diamond has the highest thermal conductivity in nature, and n-type conductive nano/ultra-nano diamond is formed on the surface of high thermal conductivity single crystal diamond, which can realize efficient heat dissipation of devices while forming good n-type conductivity.

(2) Deposit ultra-nano-diamond on the surface of single-crystal diamond, without grinding, adding nano-diamond powder, biasing and other nucleation pretreatment methods on the surface, and using the steps and defects of single-crystal diamond itself after etching, Nano-diamond grains and grain boundaries can be quickly formed to realize nucleation, which greatly reduces the complexity of the preparation process.

(3) The present invention realizes the deposition of ultra-nanometer diamond on the surface of single crystal diamond, avoiding the problem that the performance is affected by the interface mismatch between different substances. At the same time, it also avoids the phase damage of diamond caused by ion implantation and CVD growth doping, the impurity atoms are difficult to ionize, and the problems of easy graphitization under high temperature environment are avoided. The all-diamond structure has better thermal stability.

(4) A nano-diamond composite structure is formed on the surface of the diamond single crystal, which becomes an all-diamond structure, or an all-carbon structure. In addition to having good thermal conductivity and electrical conductivity, due to the chemical inertia of the diamond carbon material, the all-carbon structure will also have It has a series of excellent properties such as good acid and alkali corrosion resistance and radiation resistance, and can provide a substrate for the development of harsh environment electronic devices, further expanding the application field of the diamond electronic device.

Description of drawings

Fig. 1 is the front and back Raman spectrograms of a sample with a high nitrogen-containing ultra-nano-diamond thin layer deposited on the surface of the single crystal diamond of the present invention.

Fig. 2 is the scanning (SEM) photograph of the high nitrogen-containing ultra-nano-diamond thin layer deposited on the surface of single crystal diamond of the present invention

Detailed ways

Specific implementation mode one

(1) The ratio of the surface of the high temperature and high pressure single crystal diamond seed crystal to the height H of the molybdenum bracket and the distance L between the seed crystal and the groove wall is 0.57, the thickness of the molybdenum bracket is 5mm, and the depth of the microgroove is 700 μm; (2) According to N ₂ : (H ₂ + CH ₄ ) = 1:312 flow ratio: N ₂ is 1 sccm, H ₂ is 12 sccm, CH ₄ is 300 sccm, the chamber pressure is 10.6-10.65kPa, and the power is slowly increased and maintained at 1600-1650W; (3) The surface temperature of the seed crystal is 640°C-645°C, the deposition time is 1 hour, and then slowly cooled to room temperature. The Raman spectrum of the obtained sediment layer is shown in the accompanying drawing, and the main Raman shift peaks are located at 1140, 1332, 1340, 1470 and 1580 cm ⁻¹ . Among them, what appears at 1332cm ^-1 is the characteristic peak of diamond, and the half-maximum width of this peak is very large, which is a typical Raman spectrum of ultra-nano diamond. The surface topography is shown in Fig. 2.

Specific implementation mode two

(1) The ratio of the surface of the high temperature and high pressure single crystal diamond seed crystal to the height H of the molybdenum bracket and the distance L between the seed crystal and the groove wall is 0.62, the thickness of the molybdenum bracket is 8mm, and the depth of the microgroove is 800 μm; (2) According to N ₂ : (H ₂ + CH ₄ ) = 30:312 flow ratio: N ₂ is 30 sccm, H ₂ is 12 sccm, CH ₄ is 300 sccm, the chamber pressure is 12.7-12.75kPa, and the power is slowly increased and maintained at 1800-1850W; (3) The surface temperature of the seed crystal is 680°C-685°C, the deposition time is 1 hour, and then slowly cooled to room temperature. The obtained deposition layer pull spectrum is the same as that of Embodiment 1.

Specific implementation mode three

(1) The ratio of the surface of the high temperature and high pressure single crystal diamond seed crystal to the height H of the molybdenum bracket and the distance L between the seed crystal and the groove wall is 0.63, the thickness of the molybdenum bracket is 10mm, and the depth of the microgroove is 900 μm; (2) According to N ₂ : (H ₂ +CH ₄ )=30:312 flow ratio: N ₂ is 30sccm, H ₂ is 12sccm, CH ₄ is 300sccm, the chamber pressure is 14.1-14.5kPa, slowly increase the power and keep it at about 2350-2400W; (3 ) The surface temperature of the seed crystal is 745° C. to 755° C., the deposition time is 1 hour, and then slowly cooled to room temperature. The obtained deposition layer pull spectrum is the same as that of Embodiment 1.

Specific implementation mode four

(1) The ratio of the surface of the high temperature and high pressure single crystal diamond seed crystal to the height H of the molybdenum bracket and the distance L between the seed crystal and the groove wall is 0.60, the thickness of the molybdenum bracket is 15mm, and the depth of the microgroove is 1500 μm; (2) According to N ₂ : (H ₂ + CH ₄ ) = 60:312 flow ratio: N ₂ is 60 sccm, H ₂ is 12 sccm, CH ₄ is 300 sccm, the chamber pressure is 14.5-15kPa, and the power is slowly increased and maintained at about 2350-2400W; (3) The surface temperature of the seed crystal is 745°C-755°C, the deposition time is 1 hour, and then slowly cooled to room temperature. The obtained deposition layer pull spectrum is the same as that of Embodiment 1.

Claims (4)

1. a kind of preparation method of single-crystal diamond surface in situ n-type semiconductor, it is characterised in that pass through microwave plasma Etching and gas phase deposition technology on single-crystal diamond surface directly generate the super Nano diamond thin layer of N-shaped conduction, and processing step is It is as follows:

(1) grinding and polishing of single crystal diamond seed crystal

The diadust for being 40,20,10 and 2.5 with granularity carries out pre-polish(ing)；It is enterprising to be placed on precision diamond polishing disk Row finishing polish realizes that surface roughness is lower than 1nm after polishing；

(2) single crystal diamond seed crystal pickling processes

(3) foundation of single-crystal diamond depositional environment

Single crystal diamond substrate is placed in the rectangular microflute of molybdenum support, sample surfaces to rooved face height and sample side edge and microflute Spacing ratio is maintained between 0.5-0.7, and molybdenum support thickness is in 5-15mm, and depth of mini longitudinal channels is between 500 microns -1500 microns；And Molybdenum support is placed on the thermally conductive base station of copper and guarantees heat loss；

(4) the plasma surface etching of single crystal diamond seed crystal

Using H₂Plasma etching, so that being produced while removing diamond surface distortion area that may be present or end of dislocation The step and defect area of single-crystal diamond are given birth to；

(5) deposition growing of the super nanometer layer in surface

Do not change diamond state after etching, is only grown by control power, temperature, chamber pressure and gas flow in quick forming core The super Nano diamond of n-type doping is formed in the process；

The pre-polish(ing) time described in step (1) is 24-48 hours；

Step (1) the finishing polish step is: on precision diamond polishing disk, control revolving speed is 40 revs/min, 80 revs/min Clock is carried out 20-30 hours respectively in the case of 120 revs/min, 40-60 hours and is processed by shot blasting for 80-100 hours.

2. a kind of preparation method of single-crystal diamond surface in situ n-type semiconductor as described in claim 1, it is characterised in that step Suddenly (2) described pickling processes are that seed crystal sample is placed in HCl:H after polishing₂SO₄It is boiled in the mixed liquor of=1:5 45 minutes small to 1 When, after rinsed with deionized water；It is sequentially placed into acetone soln and dehydrated alcohol and is respectively cleaned by ultrasonic 10-15 minutes again, dry up.

3. a kind of preparation method of single-crystal diamond surface in situ n-type semiconductor as described in claim 1, it is characterised in that step Suddenly (4) are described uses H₂Plasma etch process is: hydrogen 200-300sccm is being passed through H₂Afterwards, power is set 2000-3000W, the voltage-controlled temperature processed of adjusting cavity etch 10-15 minutes at 700-740 DEG C or so.

4. a kind of preparation method of single-crystal diamond surface in situ n-type semiconductor as described in claim 1, it is characterised in that step Suddenly the concrete technology condition of (5) described super Nano diamond for forming n-type doping is: power 800w-3000w, temperature 400-750 DEG C, chamber pressure is maintained in the case of 5~15.5kPa, is passed through in the methane of hydrogen and 5-25sccm that flow is 100-500sccm The N of 1-60sccm flow₂。