Monocrystal diamond layer of high thickness, method of production of such layer and precious stones made from this layer

FIELD: production of diamond layers.

SUBSTANCE: diamond layer at thickness more than 2 mm is obtained through chemical deposition from gaseous phase. Method includes homo-epitaxial growth of diamond layer on surface of backing at low level of defects in atmosphere containing nitrogen at concentration lesser than 300 billion parts of nitrogen.

EFFECT: improved quality of diamond layers.

36 cl, 10 dwg, 1 tbl, 4 ex

 

The invention relates to a diamond, and more particularly to a diamond obtained by the method of chemical vapor deposition (hereinafter CVD-diamonds).

The method of deposition of diamond on a substrate typically includes a step of preparing a gas mixture of a source that can form in the dissociation of the hydrogen or halogen (F, Cl) in atomic form, the carbon or carbon-containing radicals and other reactive particles, that is, CHx, CFxwhere x may designate from 1 to 4. Moreover, the gas mixture may further comprise a source of oxygen, nitrogen or boron. In many processes using inert gases such as helium, neon or argon. Normally, therefore, the gas mixture source contains hydrocarbons WithxHywhere each of x and y takes values from 1 to 10; halogenated hydrocarbons, CxHyHalz(Hal denotes a halogen), where x and z each can mean from 1 to 10, and may indicate from 0 to 10; and optionally one or more of the following components: COxwhere x can mean from 0.5 to 2, O2N2N2, NH3In2H6and inert gas. The composition of each gas isotopic ratio can be natural or artificially regulated: for example, hydrogen can be used as deuterium or tritium, carbon - in the form of isotopes12With or13C. Dissociate the gas mixture source to cause the impact of such energy sources, as microwave radiation, energy EHF, flame, filament or flame jets. The result is the formation of reactive gaseous particles, which are deposited from the gas phase on a substrate and forming a diamond.

Perhaps getting CVD-diamond on a variety of substrates. Depending on the nature of the substrate and features of the chemistry of the process get a polycrystalline or single-crystal CVD-diamond. In the literature reported receiving homoepitaxial CVD-diamond layers.

The prior art relates primarily to the study of thermal, optical and mechanical properties of CVD-diamond.

The present invention features a layer of single crystal CVD diamond of high quality, having a thickness of at least 2 mm, preferably more than 2.5 mm, most preferably more than 3 mm, and having one or more of the following characteristics:

- high distance value accumulation charge, measured at field strength of 1 V/μm and at 300 K of at least 100 microns;

- high value of the product of the average mobility of charge carriers and the time of life, μτthat at 300 K exceed 1.0×10-6cm2/In;

the electron mobility (μe), the value of which, measured at 300 K, is more than 2400 cm2In-1with-1;

<> the hole mobility (μd), the value of which, measured at 300 K, is more than 2100 cm2In-1with-1; and

- specific resistance in the closed state, the value of which, measured at 300 K and the application field strength of 50 V/μm, is more than 1012Ohm·see

These characteristics are observed in almost the entire volume of the layer or sector growth of {100} in case of its presence and visibility.

The distance of the accumulation of charge is preferably at least 150 μm, and more preferably at least 400 μm, most preferably at least 600 μm, provided that all distance values of the accumulation of charge measured at field strength of 1 V/μm and 300 K; earlier it was reported that the distance values of the accumulation of charge in the high-quality natural diamond type II significantly less than 100 microns and are usually about 40 microns at a tension of 1 V/μm.

The product of the average mobility of charge carriers and the time of life μτpreferably greater than 1.5×10-6cm2/, Most preferably 4×10-6cm2/, Provided that all values measured at a temperature of 300 K.

The resistivity in the closed position is preferably more than 2×1013Ohm·cm, most preferably more than 5×1014Ohm on; cm at field strength of 50 V/μm and a temperature of 300 K.

In the device with a wide gap, made of diamond, the number of free charge carriers in conditions close to equilibrium, is extremely small and is determined mainly by the contribution of lattice defects and inclusions. In this case, it is considered that the device is in the so-called closed state (also called "off"). It can be translated into an open state (respectively, the "on"state) additional excitation of charge carriers: the photoexcitation (primarily the use of light energy that is close to or greater than the forbidden energy zone) or excitation by charged particles (such as alpha and beta particles). In the open state, the density of free charge carriers exceeds the equilibrium level, and when the excitation source is removed, the device returns to the closed state.

The value of electron mobility (μe), measured at 300 K, is preferably more than 3000 cm2In-1with-1most preferably more than 4000 cm2In-1with-1; earlier it was reported that the value of electron mobility in high-quality natural diamond type II, measured at 300 K, is usually 1800 cm2In-1with-1in eliminate the lnyh cases reaches 2200 cm 2In-1with-1.

The value of hole mobility (μd), measured at 300 K, is preferably more than 2500 cm2In-1with-1most preferably more than 3000 cm2In-1with-1; earlier it was reported that the value of hole mobility in high-quality natural diamond type II, measured at 300 K, is usually 1200 cm2In-1with-1in exceptional cases reaches 1900 cm2In-1with-1.

It should be noted that, in the invention, the diamond has a significantly higher electronic characteristics than the highest quality natural diamonds.

It suddenly gives the diamond properties, which can be used in electronics, where the layers of great thickness, and cost-effective production of more thin layers of other electronic devices. The production of one layer of a large thickness and its processing with the aim of obtaining many more thin layers advantageous from the point of view of reducing costs in the preparation of substrates and synthesis.

Proposed in the invention of the diamond is suitable for use as a diamond plates in experiments with high pressure and the products in which low density of defects in diamond makes them more durable than that made of natural diamond, and allows use is to them in a more extreme (in terms of temperature and pressure) conditions.

Proposed in the invention, single crystal diamond has a thickness suitable for the manufacture of him one or more precious stones, for example, by way of hraneniya.

In addition to the above characteristics proposed in the invention, the diamond layer may have one or more of the following characteristics:

1) the Level of any single impurity is not more than 5 frequent. per million, and the total amount of impurities is not more than 10 frequent. in million Amount of each impurity is preferably not more than 0.5-1 hour. per million, the total amount of impurities is preferably not more than 2-5 frequent. per million Concentration of the impurities can be measured by mass spectroscopy secondary ion (SIMS), mass spectroscopy glow discharge (♦), mass spectroscopy of combustion (MCC)(combustion mass spectroscopy), electron paramagnetic resonance (EPR), IR spectroscopy, and, in addition, to determine the single substituted nitrogen atoms measured value of the optical absorption at 270 nm (calibrated with respect to standard values obtained destructive analysis of samples by combustion). For the above to the notion of "impurities" are not hydrogen and its isotopes.

2) Missing or weak signal cathodoluminescence (CL) emission at 575 nm and the corresponding line in the spectrum of photoluminescence (PL) at 77 K and who is ojdenie argon laser 514 nm (the power of the incident beam 300 mW) peak height less than 1/25, preferably less than 1/300, and most preferably less than 1/1000 of the peak in the Raman spectrum of diamond at 1332 cm-1. The presence of these bands indicates the presence of defects in the film - the replacement of the nitrogen atoms and vacancies. Because of the possibility of the presence of the competing mechanisms of damping, the normalized intensity of the line at 575 nm is not a method of quantitative determination of nitrogen, as well as its absence does not indicate the absence in the film of nitrogen. Luminescence CL is due to excitation under the influence of the incident beam of electrons with a typical energy of electrons from 10 to 40 Kev, penetrating into the surface at a distance of approximately 10 microns. In the case of photoluminescence excitation usually occurs throughout the sample volume.

3) (i) and the High emission of free exciton (SE) in cathodoluminescence spectrum recorded at 77 K.

The emission of free excitons caused by the presence of point defects and structural defects such as dislocations. The presence cathodoluminescence emission spectrum of the free exciton indicates the almost complete absence of offsets and inclusions. The relationship between low density of vacancies and impurities and high SE peak was previously shown for individual crystals in the synthesis of polycrystalline CVD-diamond.

(ii) the High value of the emission svobodnokonvektivnye (SE) in the UV-excited photoluminescence spectrum at room temperature.

The emission of free excitons can be caused by radiation with energy above the bandgap, for example, by radiation of 193 nm ArF-excimer laser. The presence of an intense peak of the free exciton emission in the photoluminescence spectrum with the same excitation source indicates the almost complete absence of offsets and inclusions. The intensity of the free exciton emission, excited by 193 nm Ar-F excimer laser at room temperature such that the quantum yield of emission of the solar cell is not less than 10-5.

4) In the spectrum of electron paramagnetic resonance (EPR) single centres of substitution of nitrogen atoms [N-C]0at concentrations of <100 frequent. on bn, usually <40 frequent. at billion, more typically <20 frequent. on bn, indicate low levels of implementation of nitrogen.

5) In the EPR spectrum of the spin density less than 1×1017cm-3more typically 5×1016cm-3when g is equal to 2,0028. In the single-crystal diamond line at g=2,0028 indicates the concentration of lattice defects and is usually high in natural diamond type IIa, CVD-diamond is subjected to plastic deformation by indentation, and low-quality homoepitaxially diamonds.

6) Excellent optical properties, transparency in the UV-visible and IR (infrared) regions close to theoretical maximum for the diamond, the more con is specific, the value or lack of absorption lines of nitrogen from inclusions at 270 nm in the UV region, low intensity or lack of stretching vibrations of C-H bonds in the range of wave numbers from 2500 to 3400 cm-1in the infrared region.

Properties of diamond, outlined above, are observed in almost the entire volume of the diamond layer or stone. There may be areas, mostly less than 10% by volume, where these properties do not appear.

The objects of the invention are also synthetic diamond in the shape of a precious stone, made from a layer of single-crystal diamond of the above described type and a method of obtaining a layer of single-crystal CVD-diamond, including the use of the diamond substrate surface, virtually no defects in the crystal lattice, and the gas source, the decomposition gas source and homoepitaxially growing diamond on a specified surface of the substrate in the atmosphere containing nitrogen at a concentration of less than 300 frequent. on bn, it Was found that high-quality single-crystal CVD-diamond layers of great thickness can be produced using a substrate of diamond, containing no lattice defects, and when conducting stage homoepitaxial growth in an atmosphere containing molecular nitrogen in a concentration of less than 300 frequent. on billion

Manufacturer the substrate surface, practically free of surface defects, it is necessary for the synthesis of thin layers, since such defects are the cause of displacement and associated defects in the growing diamond on the substrate layer. Appearing, these shifts cannot end within a layer, and multiply and expand, resulting in decreasing the thickness of the layer appear stress, job openings and cracks. The presence of nitrogen even at low concentrations plays a role in the formation of the surface morphology of growth, leading to speed growth, which, in turn, causes growth defects and dislocations when reducing the thickness of the layer.

Further in accordance with the present invention offers a CVD-diamond, obtained from the above-described single-crystal CVD-diamond layer polished in the form of a precious stone, characterized by the presence of three orthogonal directions (or measurements) of length greater than 2 mm, preferably 2.5 mm, most preferably 3.0 mm, where at least one axis is located in the crystallographic direction <100> or along the main axis of symmetry of the stone. The diamond is of high quality and may have one or more of the characteristics described above.

Attached to the description of the drawings shows:

figure 1 - spectrum of Raman scattering/total is minescence faceted synthetic CVD-diamond (1A), recorded at 77 K upon excitation of the argon ion laser 514 nm;

figure 2 is a Raman spectrum of a faceted synthetic CVD-diamond (1A), recorded at room temperature (excitation argon ion laser 514 nm), showing the width of the Raman peak (pulse duration at half amplitude) of 1.52 cm-1;

figure 3 spectra of cathodoluminescence recorded at 77 K, for the two areas faceted synthetic CVD-stone (1A), demonstrating the intense emission of free excitons at 235 nm;

figure 4 - spectrum UV absorption optical plate (1b);

figure 5 - EPR spectra faceted synthetic CVD-diamond (1A), recorded at room temperature on the instrument Bruker x-band (9,5 GHz) demonstrating the absence of P1 and low-intensity broadened line, close to g=2,0028 observed at high energies. It is important to note that the scale of the spectrum of the investigated sample 10,000 times more scale reference sample;

figure 6 - range Raman/photoluminescence faceted synthetic CVD-stone (2A)recorded at 77 K and the excitation of the argon ion laser 514 nm;

figure 7 - spectrum of Raman scattering faceted synthetic CVD-stone (2A), recorded at room temperature (excitation argon ion laser 514 nm), showing the width of the Raman peak (on the Naya width at half maximum) of 1.54 cm -1;

on Fig - emission spectrum of the free exciton CL, recorded at 77 K, faceted synthetic stone (2A);

figure 9 - spectrum UV absorption optical plate (2b);

figure 10 - EPR spectra faceted synthetic CVD-stone (2A), recorded at room temperature on the instrument Bruker X-band (9,5 GHz), demonstrating the absence of P1 and low-intensity broadened line, close to g=2,0028 observed at high energies. It is important to note that the scale of the spectrum of the investigated sample 10,000 times more scale reference sample.

Proposed in the invention of single-crystal CVD-diamond layer has a thickness of at least 2 mm and is of high quality, more specifically, has the lattice high degree of perfection and purity. This is evidenced by the presence of diamond has one or more characteristics described above.

The prior art is the nature of distance accumulation and methods of its determination. Distances accumulation of charge in this case is determined as follows.

Ohmic point contacts placed on both sides of the test plate. The plate thickness is typically 300-700 μm, and an area of 5-10 mm, allowing for point contacts with a diameter of 2-6 mm, the Formation of ohmic contacts (not principally showing a diode of nature) is important for the precision PR is produced measurements. This can be achieved in several ways, the most common is the following method.

Saturate the surface of the diamond atoms of oxygen using, for example, firing an oxygen plasma, minimize surface conductivity (reducing the "dark current" of the device).

Spend metallization deposition on diamond first carbidopa element (for example, Ti, Cr) and then a thicker layer of protective material, usually gold (which can be done wired connection), using the method of sputtering, evaporation, or other similar methods. The contact is usually annealed at a temperature of 400-600°within hours.

Contact attach a wired connection and include a diamond in the circuit with the bias voltage, typically comprising 2-10 kV/see Register "dark current", or leakage current, in good pattern, this value should be less than 5, preferably less than 100 PA at 2.5 kV/cm, while the diameter of point contacts 3 mm

Measure the distance accumulation by irradiation of a sample of beta-particles using silicon trigger detector on the output surface for (a) indication of the fact of irradiation and b) to ensure that beta particles were not detained diamond layer, since this would increase the number of generated carriers saradaga from a sample read, highly electrometric amplifier and on the basis of data about the intensity of formation of charge carriers in about 36 electron-hole pairs in a linear micrometer, passed a beta particle, calculate the distance of accumulation based on the value of measured charge, using the following relationship:

RNZ=ANS·t,

where t denotes the thickness of the sample,

ANS indicates the efficiency of accumulation of charge (accumulated charge/total generated charge),

RNZ denotes the distance of the accumulation of charge.

It is obvious that the measured distance accumulation is limited by the thickness of the sample. This is expressed in the equation above Hecht.

For completeness, the distance of the accumulation of charge is measured at various applied voltages offset, direct and inverse. Characteristic consider the distance values of the accumulation of charge at a bias voltage of 10 kV/cm only for those samples that showed a linear dependence of voltage offsets to the value of 10 kV/see In addition the measurement procedure entirely repeat several times to display the results, as the values measured on bad samples may be reduced depending on time and change order processing.

5) Next, in the process of distance measurement of the accumulation of charge find out whether the material in "inflated" or "nanochannel" state. "Pumping up" (also called "dressing") material consists in its exposure to certain types of radiation (beta, gamma and so on) within the access is part of a large period of time, thus the value of the distance savings can grow, usually 1.6 times in the case of polycrystalline CVD-diamond, but there are possible options. The effect of filling is less pronounced in the case of high-purity single-crystal samples, usually the filling factor is equal to 1,05-1,2, for some samples the factor is not detected. "Discharge", back filling, carry out irradiation with white light of sufficient power or light of certain wavelengths, and the process is completely reversible. Distances accumulation of charge given in this description, measured in "nanochannel" condition, regardless of what area you plan to reuse the material. In some cases (for example, for experiments in the physics of high energy particles) increased distance accumulation of charge at the "pumping" can be successfully used to improve the detection of individual acts by protecting the detector from any "discharge" of radiation. In other cases, the instability in the circuit of the device that occurs when the pumping, is extremely harmful.

Proposed in the invention of single-crystal CVD-diamond in one variation of the embodiment of the invention may have, in the closed state high resistivity at high field-strength values, in particular the specific resistance R1constituting the m ore than 1× 1012Ohm·cm, preferably more than 2×1013Ohm·cm, most preferably more than 5×1014Ohm·cm, provided that all values measured at a field strength of 50 V/μm and a temperature of 300 K. These values of resistivity with such a large field strengths indicate the high purity of the diamond and the almost complete absence of impurities and lattice defects. The material is less pure or containing more defects in the crystal lattice may have a high value of resistivity at lower (i.e. less than 30 V/µm) field strengths, but when the strength values of more than 30 V/μm (typically about 45 V/µm) there is a breakdown and rapidly increases the value of the leakage current. The resistivity can be determined by measurement of leakage (dark current) is known from the technology methods. The test sample is prepared in the form of plates of constant thickness, they are cleaned using standard methods for diamonds to grow the necessary contacts are evaporated, sputtered or planted diamond), which can be summed up external voltage, then the plate is subjected to partial or complete sealing to prevent fire. It is important to ensure that the seal does not have a significant influence on the measured value of the dark current. Tipin the e sample sizes: thickness is from 0.01 to 0.5 mm and an area of 3× 3 to 50×50 mm, however, you can use samples with blimi and smaller sizes.

In the proposed invention, single crystal CVD-diamond work μτ over 1.5×10-6cm2/In, preferably greater than 4.0×10-6cm2/In, and most preferably more than 6.0×10-6cm2/, Provided that all values measured at a temperature of 300 K. the Work μτ due to the distance of the accumulation of charge carriers (RNZ) in the following proportions:

μτF=RNZ

(cm2/·×(C)×(In/cm)=cm

where E denotes the electric field strength.

Proposed in the invention of single-crystal CVD-diamond, particularly preferred variant of embodiment of the invention, has a high value works μτto the distance value of the accumulation of charge carriers.

When an electric field is applied to the sample with electrodes can be separated electron-hole pairs generated during irradiation of the sample with photons. The holes drift to the cathode and electrons to the anode. Light of low wavelength (ultraviolet or UV light with photon energy greater than the forbidden for diamond energy zone, has a very small penetration depth into the diamond. The use of this light allows you to identify the treasure of charge carrier, depending on which electrodes were subjected to photobleaching.

The above-mentioned work μτ for the purposes of this description is measured as follows.

Sample diamond is prepared in the form of a plate thickness of more than ≈100 microns.

Translucent titanium contacts sprayed on both sides of the diamond plate, and form a pattern, using standard photolithographic methods. This process formed the necessary contacts.

For excitation of charge carriers use monochromatic xenon lamp (wavelength of 218 nm) with pulse width 10 µs, measured in the external circuit generated photo libraries using circuit external load. The pulse duration of 10 μs is far superior to the duration of other ongoing processes, such as the transition time and the lifetime of the charge carrier, so that the system can be considered to be in equilibrium at any point in time within the impact pulse. The magnitude of the penetration depth of light in the diamond at this wavelength is only a few microns. The used light intensity is relatively small (about 0.1 W/cm2), so the value of N0relatively low, and the internal stress field satisfactorily approximated to external applications. The field strength of support just below the threshold, after which the CSO mobility depends on the tension. In addition, the field strength is supported below the value at which the majority charge carriers reaches the opposite side of the sample diamond and total accumulated charge reaches saturation (with locking pins, nenapirali contacts can show in this case, the gain).

Work μτ calculated as the ratio of the magnitude of the accumulated charge to the field strength using equation Hecht:

Q=N0eμτE/D[1-exp{-D/(μτE)}].

In this equation, Q denotes the accumulated charge in the unexposed contact, N0indicates the total number of electron-hole pairs generated by the light pulse, E denotes the electric field, D denotes the thickness of the sample, and μτ denotes the desired mobility and the lifetime of the sample.

For example, if the irradiated electrode is the anode (cathode), the charge carriers are generated within a few micrometers of the surface layer and the charge displacement of electrons (holes) to the nearest electrode can be neglected. On the contrary, the displacement of the charge holes (electrons) to the opposite contact significantly, and is limited μτ sample, where values μ and τ depend on the nature of the charge carriers moving to publicenemy electrode.

Proposed in the invention, the CVD-diamond can the t to be fixed on the diamond substrate (regardless of if the substrate is made of synthetic, natural or CVD-diamond). The advantage of this approach is the ability to obtain a greater total thickness of the layer when the thickness limits the use of, or increase the thickness of the diamond when it is reduced in the process. In addition, the proposed invention in CVD-diamond may form one layer in a multilayer material in which the other layers of diamond, for example, napisany to obtain electrical contact or electronic connections, or simply play the role of substrate for CVD diamond layer.

To obtain high-quality CVD diamond is important that the process of layer growth occurred on the surface of the diamond, are practically free from defects. In this case, the defects in the first place, mean bias, and microcracks. In addition, under the defects may be implied boundaries of twinning, point defects, small-angle interconnect borders and other violations of the crystal lattice. As the substrate, it is preferable to use natural diamond type Ia or IIb diamond with small birefringence, synthetic diamond type Ib or II obtained at high pressure/high temperature (WDT) or synthetic single-crystal CVD-diamond.

The density of defects easily determine the optical evaluation after plasma or chemical what about etching, optimized for the detection of defects (showing a plasma etching), for example, using the method of short-term plasma etching described below. Thus, there can be identified two types of defects:

1) Defects, natural for the studied material. In the sorted natural diamonds, the density of such defects can reach low values 50/mm2with a more typical value of 102/mm2whereas in other types of density can be up to 106/mm2and more.

2) Defects occurring after polishing, such as patterns of displacement, microcracks in the form of "vibrating traces" ("chatter tracks") along the direction of polishing. The density of these defects varies greatly from sample to sample, usually its values are in the range from 102/mm2to more than 104/mm2in a poorly polished areas or samples.

The preferred low density of defects is less than 5×103/mm2preferably less than 102/mm2and corresponds to the density of defects on the exposed etched surface, which are relevant to the above defects.

The number of defects on the surface of the substrate on which is grown by the CVD layer, or inside it, can be minimized by careful preparation of the substrate. This is the best preparation includes any process, through which material from the mine (in the case of natural diamonds) or synthesis (synthetic materials), as each stage can affect the density of defects in the material plane, which ultimately forms the surface of the substrate after the process of forming the substrate. The process may include traditional diamond production stage, such as mechanical sawing, grinding, polishing, and less traditional methods, such as laser machining, ion implementation, removable technology (lift off techniques), chemical mechanical polishing, liquid or plasma chemical processing. In addition, the function of the surface RA(arithmetic average absolute deviation of surface profile from the main line, measured needle profilometer, preferably a length of more than 0.08 mm) should be minimized, typical values of this function should be no more than a few nanometers, or less than 10 nm, for any plasma etching.

The specific method of minimizing damage to the surface of the substrate is plasma etching in situ surface then spend homoepitaxially growing diamond. In principle not necessary to carry out etching in situ or immediately before the deposition process, t is m is not less than the best result is achieved by etching in situ, since there is no risk of further damage or chemical contamination. Etching in situ convenient when the deposition process is also used plasma. Conditions in the method of plasma etching can be similar to the conditions of deposition and growth of diamond, however, is unacceptable presence of carbon-containing gas mixtures. The best control at the stage of etching is achieved at a slightly lower temperature. For example, the composition may be as follows:

I) In an oxygen etching, as a rule, the main component is hydrogen, optionally a small amount of argon and always a small amount Of2. Typical conditions for oxygen etching of the following: a pressure of from 50 to 450×102The PA content in the etching gas of oxygen from 1 to 4 vol.%, argon - from 0 to 30 vol.%, the rest of the hydrogen, at a temperature of the substrate 600-1100°With (preferably 800°C)normal exposure time from 3 to 60 minutes.

II) Hydrogen etching as in (I), but is carried out in the absence of oxygen.

III) Alternative methods of etching can be based not only on the use of argon, hydrogen and oxygen, but also on the use of, for example, Halogens, other inert gases or nitrogen.

Typically, the etch process comprises an oxygen etching, followed by bodoro the Noah etching, then the process goes directly into the stage of synthesis by entering a carbon-containing gas mixture. The temperature and pressure during etching choose the best for any traces of surface treatment, but do not allow the formation of a rough surface and a strong etching along extended defects (e.g., offsets)that intersect the surface, as this leads to the formation of deep trenches. The etching is aggressive, so it is very important to ensure that the design of the chamber and to choose the material for its manufacture so that at this stage no matter from the camera couldn under the influence of the plasma to pass into the gas phase or on the surface of the substrate. Hydrogen etching, following oxygen, less specific to the crystalline defects and softens uncouthness, created by oxygen etching (which aggressive attacks similar defects), softens and improves the surface for subsequent crystal growth.

One or more surfaces of the substrate of the diamond, which produces CVD-diamond, preferred are surface{100}, {110}, {113} or {111}. Due to the limited processing capabilities of the real orientation of the sample surface may differ from the ideal orientation angle of up to 5°in some cases up to 10°but this is less desirable item is because greatly reduces the reproducibility.

It is important that proposed in the invention method provides a thorough control of impurities in the growth medium CVD-diamond. More specifically, the growth of the diamond must occur in an atmosphere containing no nitrogen, that is, its content should be less than 300 parts per billion (frequent. at billion), which is the fraction of several molecules on the entire gas volume) and preferably less than 100 frequent. on billion In the literature discussed the role of nitrogen in the synthesis of CVD-diamond, mainly polycrystalline CVD-diamond. For example, it was shown that the content in the gas phase of nitrogen in the amount of 10 frequent. per million and above affects the relative growth rate on the surface {100} and {111} and leads to an overall increase in the rate of growth, and in some cases to improve the quality of crystals. In addition, it has been suggested that some of the processes of synthesis of CVD-diamond, you can use the nitrogen content of less than several parts per million. However, none of the described in the literature processes not mentioned analytical methods for the determination of nitrogen, are sensitive enough to detect its contents in quantities significantly smaller 1 frequent. per million, and 300 ppb or less. For measuring the amount of nitrogen in such low concentrations require complex methods, such as gas chromatograph who I am. An example of such method is shown below.

The standard method of gas chromatography (GC) consists of the following stages. The sample gas stream is selected in the desired time using the tube to enter sample of small diameter, optimized for maximum flow rate and minimum dead volume, passed through GC-loop before a reset. GC-loop input sample is a round tube fixed volume (usually 1 cm3for injection at atmospheric pressure), which can be disconnected from the tube to the input of the sample and to include in the flow of carrier gas (high-purity), a leading columns for gas chromatography. Thus, the gas sample with a known volume gets into the gas stream, leading to column. The described procedure in technology called input sample.

Put a sample together with the carrier gas passes through the first GC column (filled with molecular sieves, optimized for simple removal of inorganic gases), while there is a partial separation. However, large concentrations of primary gases (i.e. H2, Ar) is called the saturation column, which makes the final division. The relevant portion of effluent served in the second column, and remain where most other gases included in the second column, is without saturation of the column is complete separation of the target gas (N 2). This procedure is called by collecting the main fraction ("heart-cutting").

Emerging from the second column stream is passed through the detector ionization discharge DEERE, registering an increase in the value of the dark current in the stream of carrier gas due to the presence of the sample. Chemical identity is determined by the value of the retention time of the gas, calibrated against a standard gas mixtures. The response of the detector CONDUCTOR is linear over 5 orders of magnitude and is calibrated using a special calibration gas mixtures, usually in the range from 10 to 100 frequent. on million the Calibration interval is carried out by gravimetry and checked by the manufacturer. The linearity of the detector response can be tested experimentally by the method of successive dilutions.

This known method of gas chromatography was later modified and refined to analyze the processes occurring at pressures 50-500×102PA. Conventional GC method involves the use of excessive compared to atmospheric pressure by passing the carrier gas through the tube to enter the sample. In this case, the input sample is carried out at reduced pressure by attaching a vacuum pump at the outlet. However, caused by passing gas resistance in the system can create strong pressure drops and the negative the positive affect calibration and sensitivity. To avoid this, between the loop input and a vacuum pump is placed a valve that opens for a short time before entering the sample to stabilize the pressure in the loop with the sample and to measure the pressure gauge. In order to ensure the introduction of the main mass of the sample volume loop with the sample increase by approximately 5 cm3. Depending on the design of the tube to enter the sample, this method allows to work effectively with pressures up to 70×102PA. Calibration of GC depends on the mass of the injected sample, and the highest accuracy is achieved when the calibration sample under the same pressure, and that the analyzed source samples. For correct measurement requires the use of high vacuum and a carrier gas of high quality.

The sampling point may be located in front of the camera synthesis for the analysis of incoming gases inside the chamber for environmental analysis in it, and behind the camera for the analysis with the highest concentration of nitrogen in the chamber.

Used gas source can be any known in the art and contains carbonaceous material dissociate with the formation of radicals and other reactive particles. In addition, the gas mixture typically contains gases that can form a hydrogen or halogen in atomic form.

The decomposition gas source preferably occurs under near the action of microwave radiation in the reactor, examples of structures are known in the technology. However, it is necessary to minimize the removal of impurities from the reactor. Microwave radiation is used to ensure isolation of plasma from contact with all surfaces except the surface of the substrate, on which will be the growth of the diamond layer and the substrate.

Examples of preferred materials for the base include molybdenum, tungsten, silicon and silicon carbide. Examples of preferred materials for the cameras reactor are stainless steel, aluminum, copper, gold, platinum.

Used plasma high power density obtained by exposure to microwaves of high energy (typically 3-60 kW for substrates with a diameter of 50-100 mm) gas under high pressure (50-500×102PA, preferably 100-450×102PA).

The compliance of the conditions listed above allows to obtain high-quality CVD-diamond layers with a thickness more than 2 mm (e.g., 3.4 mm), and to develop these high-quality CVD-diamond layers of faceted gems form, in which there are three orthogonal directions with a length of more than 2 mm (i.e. round diamond weight at 0.31 carat, height 2.6 mm, the diameter of the girdle 4.3 mm).

The invention is illustrated by the following examples.

Example 1

Substrates suitable for the synthesis proposed in the invention, single crystal X Is G-diamond prepared as follows.

The process of selecting material (natural stone type Ia and stones type Ib, obtained by synthesis at VDWT) optimize using electron microscopic studies and method birefringence to identify substrates that do not contain stresses and defects in the lattice.

To minimize subsurface defects using methods of laser cutting, grinding and polishing. The method of showing the plasma etching determine the levels of defects introduced during processing.

Perhaps the routine preparation of substrates, in which the defect density measured after treatment showing the plasma is primarily dependent on the quality of the material is less than 5×103/mm2usually less than 102/mm2. Thus prepared substrate used in the subsequent synthesis.

Synthetic diamond type Ib (obtained by VDT), grown in media of high pressure, and to minimize defects made him a substrate as described above. In a final embodiment, the substrate is a plate 5.8 mm × 4.9 mm thickness 1.6 mm, with all surfaces such as {100}. The surface roughness at this stage is less than 1 nm, RA. This substrate (Ia) is fixed together with similarly prepared second substrate (Ib) titanium is a suitable basis for diamond using high-temperature quenching. Then it is introduced into the reactor and begin cycles of etching and growth of diamond in accordance with the above procedure, as follows:

1) At the entrance to the reactor establish cleaners, reducing the content of nitrogen in the incoming gas stream to below 80 frequent. at billion, the contents of the stream is determined using a modified method of GC, above.

2) Oxygen plasma etching in situ produced using a mixture of O2/Ar/H2supplied with intensity 30/150/1200 LSM3/sec (standard cubic centimeters per second) at a pressure of 237×102PA and the temperature of the substrate 849°C.

3) Without a stop process of the hydrogen plasma etching, excluding O2from the gas stream.

4) Then start the growth process by adding a carbon source, in this case methane supplied at an intensity of 30 STM3/C. the growth Temperature at this stage is 822°C.

5) the above-Described modified method GC determines that the atmosphere of the reactor, in which the growth of the diamond contains nitrogen at a concentration of less than 100 frequent. on billion

6) At the end of the growth process two substrates is removed from the reactor. A layer of CVD diamond with a thickness of 3.4 mm is removed from the substrate (1a) and for experimental purposes it is produced in the form of faceted CVD-synthetic brillian is as round shape, using standard methods for the manufacture of precious stones. Faceted synthetic stone had the height (from classy to the ice diamond) 2,62 mm and weight at 0.31 carats. A layer of CVD-diamond from the substrate (1b) used for the preparation of CVD-plate to measure characteristics that are difficult to measure in stone round shape.

7) Synthesized by CVD-layers were then characterized by the data shown in Fig. 1 through 5 (CVD layers on the numbers correspond to the substrates on which they were grown):

I) the distance Measured accumulation in the plate (1b) was >400 microns.

II) the resistivity of the plate (1b) at field strength of 50 V/mm exceeded 1×1014Ohm·see

III) In the spectrum of the Raman/photoluminescence cut CVD synthetic diamond (1a)recorded at 77 K and the excitation 514 nm argon ion laser, is dominated by the Raman peak (figure 1). Line zero phonon very low intensity and the ratio of the intensity of its peak intensity of the Raman peak at approximately 1:7800.

IV) the Width of the Raman lines (full width at half maximum) in the diamond at 1332 cm-1to cut CVD synthetic stone (1a) made of 1.53 cm-1(measured at excitation laser 514 nm) (figure 2).

V) In CL spectrum recorded at 77 K for a faceted synthetic CVD-diamond is dominated by line emission freely what about the exciton very high intensity (figure 3).

VI) In the spectrum of the optical absorption of the optical plate (1b) does not show signs of internal absorption, and measured the absorbance at 240 nm is limited only by the return loss characteristic of the diamond (figure 4).

VII) the EPR spectrum of a faceted synthetic CVD-diamond (1a) was recorded on spectrometer Bruker x-band (9,5 GHz) at room temperature. Not been a single of atoms substitution of nitrogen (P1 EPR center) when the value of the detection limit of 0.014 frequent. on million At high energies can be observed weak broadened line, close to g=2,0028 that sets an upper limit on the spin density of 1.6×1015cm-3(figure 5).

Example 2

The procedure described in Example 1 is repeated with the following variations of conditions.

Two substrate manufactured by the method described in Example 1, to minimize subsurface defects. The substrate (2A) for faceted synthetic CVD diamond has dimensions of 6.8 mm × 6.65 mm × 0.71 mm with all surfaces of type {100}. Again for making the optical plate 2b has been used for more similar substrate.

Oxygen etching with a useful capacity of 7.8 kW carried out at 780°C for 30 minutes.

Hydrogen etching is carried out at 795°C for 30 minutes,

Growing produce by the addition of CH4supplied with intensity 32 with cm 3/s at a temperature of 840°C.

The atmosphere in which growth occurs, contains nitrogen at a concentration of less than 100 frequent. on billion

After the growth process, the thickness of the CVD-diamond layer from the substrate (2A) is 2,75 mm Layer process in cut CVD synthetic diamond round shape for experimental purposes, using a convenient method of processing precious stones. Finally faceted synthetic CVD diamond had a weight of 0.3 carat and color and quality characteristics corresponding to the types of F and VS1 standard diamond dial.

Faceted synthetic CVD-diamond (2A) and an optical plate (2b) described below, the data and the accompanying drawings.

(I) the distance Measured accumulation in the plate (2b) is more than 400 μm.

(II) the resistivity of the plate (2b) at field strength of 50 V/mm exceeds 1×1014Ohm·see

(III) In the spectrum of the Raman/photoluminescence cut CVD synthetic stone (2A)recorded at 77 K, the excitation of the argon ion laser 514 nm is dominated by the Raman peak (6). Line zero phonon low-intensity and the ratio of the intensity of its peak intensity of the Raman peak at approximately 1:28. The width of the Raman lines (full width at half maximum) in the diamond at 1332 cm-1for faceted CVD-si is Tethyan stone (2A) is 1,54 cm -1(measured at excitation laser 514 nm) (Fig.7).

(IV) In the CL spectrum recorded at 77 K for a faceted synthetic CVD-diamond (2A), is dominated by line emission of the free exciton very high intensity (Fig).

(V) In the spectrum of the optical absorption of the optical plate (2b) there are no signs of internal absorption, and measured the absorbance at 240 nm is limited only by the return loss characteristic of the diamond (Fig.9).

(VI) the EPR spectrum of a faceted synthetic CVD-diamond (2A) was recorded on spectrometer Bruker x-band (9,5 GHz) at room temperature. Not been a single of atoms substitution of nitrogen (P1 EPR center) when the value of the detection limit of 0.014 frequent. on million At high energies can be observed weak broadened line, close to g=2,0028 that sets an upper limit on the spin density of 1.6×1015cm-3(figure 10).

Example 3

Diamond synthetic type 1b high pressure/high temperature grown in media of high pressure and is prepared according to the procedure described in example 1 to form a polished plate with low content of subsurface defects. The surface roughness at this stage is less than 1 nm, RA. Then it is introduced into the reactor and begin cycles of etching and growth of diamond in accordance with the above procedure, the following is the Braz.

1) At the inlet of the reactor was set purifiers, reducing the content of nitrogen in the incoming gas stream to below 80 frequent. at billion, the contents of the stream was determined using a modified method of GC, above.

2) Oxygen plasma etching in situ produced using a mixture of O2/Ar/H2supplied with intensity 15/75/600 LSM3/s at a pressure of 333×102PA. Followed by hydrogen etching using Ar/N2supplied with intensity 75/600 LSM3/s Then the addition of a carbon source, in this case methane supplied at an intensity of 30 STM3/to start the growth process. The growth temperature at this stage is 780°C.

3) the above-Described modified method GC determines that the atmosphere of the reactor, in which the growth of the diamond contains nitrogen at a concentration of less than 100 frequent. on billion

4) At the end of the growth process, the substrate is removed from the reactor and a layer of CVD-diamond thickness of 3.2 mm is removed from the substrate.

5) Measured using the above equation Hecht at 300 To work μτ is 3.3×10-3cm2/And 1.4×10-3cm2/For electrons and holes, respectively, with a mean of works μτ about 2.3×10-3cm2/C.

6) the Value of agility. the electrons μ emeasured using time-of-flight method is 4000 cm2/·s at the sample temperature of 300 K.

7) the Value of hole mobility μdmeasured using time-of-flight method, 3800 cm2/·s at the sample temperature of 300 K.

8) Measurement of SIMS showed the absence of single defects at concentrations above 5×1016cm-3(excluding H and its isotopes).

The measured value of resistivity exceeded 2×1013Ohm·cm at a field strength of 50 V/cm and a temperature of 300 K. the Value of the breakdown voltage exceeded 100 V/μm.

Example 4

The procedure described in Example 3 is repeated for the preparation of the next diamond layer. Various characteristics of the layer (measured at 300 K), is given in the table.

The number of the sample (sample number)The thickness of the grown wafer (μm)Plate thickness (µm)RNZ (µm)
13400420>400*
22750435>400*
33200 500>480*
42100280
The number of the sample (sample number)μeτe(cm2/In)μdτd(cm2/In)μe(cm2/·)μd(cm2/·)Resistivity (Ohm·cm) at 50 V/µm
1>1×1014
2>1×1014
33,3×10-31,4×10-340003800>2×1013
41,7×10-30,72×10-3
* the minimum value limited by the thickness of the sample

1. A layer of monocrystalline al the Aza high quality, obtained by the method of chemical vapor deposition (CVD diamond), having a thickness not less than 2 mm and with one or more of the following characteristics:

a) high distance value accumulation charge, measured at field strength of 1 V/μm and at 300 K of at least 100 microns;

b) high value of the product of the average mobility of charge carriers and the time of life μτthat at 300 K exceed 1.0·10-6cm2/In;

C) electron mobility (μe), the value of which, measured at 300 K, is more than 2400 cm2In-1c-1;

g) hole mobility (μd), the value of which, measured at 300 K, is more than 2100 cm2In-1c-1; and

d) specific resistance in the closed state, the value of which, measured at 300 K and the application field strength of 50 V/μm, is more than 1012Ohm·see

2. A layer of single crystal CVD diamond according to claim 1, having a thickness of more than 2.5 mm

3. A layer of single crystal CVD diamond according to claim 1, having a thickness more than 3 mm

4. A layer of single crystal CVD diamond according to any one of claims 1 to 3, in which the distance of the accumulation of charge at 300 K is at least 150 microns.

5. A layer of single crystal CVD diamond according to any one of claims 1 to 3, in which the distance is their accumulation of charge at 300 K is at least 400 microns.

6. A layer of single crystal CVD diamond according to any one of claims 1 to 5, the resistivity of which at 300 K is more than 2·1013Ohm·see

7. A layer of single crystal CVD diamond according to any one of paragraphs 1-5, the resistivity of which at 300 K is more than 5·1014Ohm·see

8. A layer of single crystal CVD diamond according to any one of claims 1 to 7, in which the electron mobility at 300 K is more than 3000 cm2In-1with-1.

9. A layer of single crystal CVD diamond according to any one of claims 1 to 7, in which the electron mobility at 300 K is more than 4000 cm2In-1with-1.

10. A layer of single crystal CVD diamond according to any one of claims 1 to 9, in which the hole mobility at 300 K is more than 2500 cm2In-1with-1.

11. A layer of single crystal CVD diamond according to any one of claims 1 to 9, in which the hole mobility at 300 K, is more than 3000 cm2In-1with-1.

12. A layer of single crystal CVD diamond according to any one of claims 1 to 11, in which the work (μτ) at 300 K greater than 1.5·10-6cm2/C.

13. A layer of single crystal CVD diamond according to any one of claims 1 to 11, in which the work (μτ) at 300 K greater than 4·10-6cm2/C.

14. A layer of single crystal CVD diamond according to any of the preceding paragraphs, fixed, hence, is her least partially on the substrate.

15. A layer of single crystal CVD diamond according to any one of claims 1 to 13, mounted at least partially on the diamond substrate.

16. Diamond in the shape of a precious stone, made from a layer of single-crystal CVD diamond according to any one of claims 1 to 15.

17. Diamond in the shape of a precious stone, made from a layer of single-crystal diamond according to any one of claims 1 to 15 obtained by the method of chemical vapor deposition (CVD diamond), characterized by the presence of three orthogonal directions of length greater than 2 mm, where at least one axis is located in the crystallographic direction <100> or along the main axis of symmetry of the stone.

18. The diamond 17, characterized by the presence of three orthogonal directions of a length exceeding 2.5 mm, where at least one axis is located in the crystallographic direction <100> or along the main axis of symmetry of the stone.

19. Diamond on 17 having three orthogonal directions of a length exceeding 3 mm, where at least one axis is located in the crystallographic direction <100> or along the main axis of symmetry of the stone.

20. A method of obtaining a layer of single crystal CVD diamond according to any one of claims 1 to 13, including the use of the diamond substrate surface, virtually no defects in the crystal lattice, and the gas source, according to the provision of a gas-source and homoepitaxially growing diamond on a specified surface of the substrate in the atmosphere, containing nitrogen at a concentration of less than 300 billion hours of nitrogen.

21. The method according to claim 20, in which the substrate is a natural diamond type Ia or IIb with a small birefringence or obtained at high pressure/high temperature synthetic diamond type Ib or IIa.

22. The method according to claim 20, in which the substrate is single-crystal diamond obtained by the CVD method.

23. The method according to any of PP-22, in which the surface on which the growth of diamond has a density of defects encountered during the processing of this surface by etching, constituting less than 5·103/mm2.

24. The method according to any of PP-22, in which the surface on which the growth of diamond has a density of defects encountered during the processing of this surface by etching, constituting less than 102/mm2.

25. The method according to any of PP-24, in which the surface on which the growth of the diamond, before growing diamond is subjected to plasma etching to minimize surface damage.

26. The method according A.25, in which plasma etching is produced in situ.

27. The method according to p. 25 or 26, in which plasma etching is an oxygen etching using etching gas containing hydrogen and oxygen.

28. The method according to item 27, in which the oxygen etching is carried out in the following conditions: a pressure of from 5 to 450· 102The PA content in the etching gas of oxygen from 1 to 4 vol.%, argon - up to 30 vol.%, the rest is hydrogen, the temperature of the substrate 600 to 1100°C, the duration of etching from 3 to 60 minutes

29. The method according to p. 25 or 26, in which plasma etching is a hydrogen etching.

30. The method according to clause 29, in which the hydrogen etching is carried out in the following conditions: a pressure of from 50 to 450·102PA, the etching gas contains hydrogen and up to 30% vol. argon, the temperature of the substrate 600 to 1100°C, the duration of etching from 3 to 60 minutes

31. The method according to any of A.25-30, in which the surface on which the growth of the diamond, before growing diamond expose and oxygen, and hydrogen etching to minimize surface damage.

32. The method according to p, in which, after oxygen etching spend hydrogen etching.

33. The method according to any of p-32, in which before carrying out the plasma etching of the surface is a function of the surface RAfor the surface on which the growth of the diamond is less than 10 nm.

34. The method according to any of PP-33, in which the growth of diamond is carried out in an atmosphere containing nitrogen at a concentration of less than 100 frequent. on billion

35. The method according to any of PP-34, in which the surface on which the growth of the diamond represents the surface {10}, {110}, {113} or {111}.

36. The method according to any of PP-35, in which the Stripping gas source is performed under the action of energy of microwave radiation.

Priorities:

15.06.2000 - claim 1(a), (b), (d), 2-7, 12, 13, 16-20, 21 (except for the sign of "natural type IIb diamond"), 22-32, 34-36;

20.03.2001 - claim 1(C), 8, 9;

14.06.2001 - claim 1(g), 10, 11, 14, 15, 21 (the sign of the "natural type IIb diamond"), 33.



 

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