Mono-crystal diamond produced by chemical deposition method from gas phase and method of production of such diamond

FIELD: production of diamonds for electronics.

SUBSTANCE: diamond is produced from gas phase by chemical deposition on diamond substrate whose surface is practically free from any defects in crystal lattice in flow of carrier gas in atmosphere containing nitrogen at concentration lesser than 300 part/109. Diamond thus produced is chemically pure with no defects in crystal lattice at enhanced electronic characteristics as compared with purest natural diamonds.

EFFECT: enhanced purity and improved electronic characteristics.

32 cl, 8 dwg, 1 tbl, 4 ex

 

The present invention relates to a diamond, in particular the diamond obtained by the method of chemical vapor deposition (hereinafter CVD-diamonds), as well as to a method for producing such a diamond.

Currently in the patent and other literature developed and described a number of ways CVD-deposition on substrate materials such as diamond. The method of deposition of diamond on a substrate typically includes a step of preparing a gas mixture capable of forming 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, O2H2N2, NH3In2H6and inert gas. The composition of each gas, the ratio of the isotope which can be natural or artificially regulated, for example, the hydrogen can be used as deuterium or tritium, carbon - in the form of isotopes12With or13C. Dissociation of the gas mixture source to cause the influence of such sources of energy such 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.

In EP 0582397 describes a method for polycrystalline CVD-diamond films with an average grain size of not less than 7 μm, resistivity, mobility of charge carriers and their time of life, which is the distance of the accumulation of charge is not less than 10 μm when the electric field strength of 10 kV/see Such characteristics of diamond films can also be used as a detector of radiation. However, when a film with such a low value (7 µm) distance accumulation of charge is extremely limited.

In EP 0635584 describes a method for polycrystalline CVD-diamond films using technology Duhov the process with low methane content (<0.07%) in the presence of an oxidant. Received the diamond material is characterized by a narrow Raman peak, a relatively large lattice constant and the distance of the accumulation of charge carriers more than 25 μm. However, on the performance of polycrystalline diamond films in electronics may be adversely affected by the presence of grain boundaries.

Not previously reported control process of the formation of single-crystal CVD-diamond order to obtain a high-performance detector material. In natural single-crystal diamond is measured distances accumulation was 28 microns at 10 kV/cm and 60 μm at a bias voltage of 26 kV/see high-quality natural monocrystalline diamond type IIa the value of the distance accumulation varies almost linearly with the bias voltages up to 25 kV/cm, in contrast to the polycrystalline material in which the distance accumulation usually reaches saturation at approximately 10 kV/see

The presence of impurities and lattice defects, which reduces the mobility of the free media and the time of recombination, has an adverse impact on the distance of the accumulation of charge carriers.

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

In accordance with the present invention offers nanocrystallites the rd diamond obtained by the method of chemical vapor deposition (CVD) and having at least one of the following characteristics:

(a) specific resistance (R1in the closed state (off state), measured at a field strength of 50 V/μm and at 300 K (or 20°With that in the framework of the present invention is considered to be equivalent)is more than 1×10 Ohm·cm, preferably more than 2×1013Ohm·cm, most preferably more than 5×1014Ohm·sm;

(b) the work μτwhere μ - mobility and τ the lifetime of the charge carriers. measured at 300 K, is more than 1.5×10-6cm2In-1preferably more than 4.0×10-6cm2/In, and most preferably more than 6.0×10-6cm2/In this work represents a contribution to the charge carrier in the total value of the offset charge, that is, in the current;

(b) electron mobility (μe), the value of which, measured at 300 K, is more than 2400 cm2In-1with-1preferably 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 IIa, measured at 300 K, usually leaves 1800 cm2In-1with-1in excluding the significant cases reaches 2200 cm 2In-1with-1;

(g) hole mobility (μd), the value of which, measured at 300 K, is more than 2100 cm2In-1with-1preferably 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 IIa, measured at 300 K, is usually 1200 cm2In-1with-1in exceptional cases reaches 1900 cm2In-1with-1;

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

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 closed state (off state). The device can be turned into an open state is s ("on") additional excitation of charge carriers: the photoexcitation (primarily the use of light energy, close to or above 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.

It should be noted that proposed in accordance with the present invention, the diamond has a value of electronic characteristics, significantly more than the highest-quality natural diamonds. This allows you to use them, for example, in electronic applications or detectors.

Proposed in accordance with the present invention, single crystal diamond is chemically pure and contains almost no lattice defects.

a) resistivity.

Proposed in accordance with the present invention, single crystal CVD diamond may in one variation of the embodiment of the invention possess in the closed state high resistivity at high field-strength values, in particular the specific resistance R1constituting more than 1×1012Ohm·cm, preferably more than 2×1013Ohm·cm, most preferably more than 5×1014Ohm·cm, provided that all the values measured by the ri field strength of 50 V/μm and a temperature of 300 K. Such values of resistivity with such a large field strength 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) values of the field strength, but 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 in 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. Typical dimensions of the samples following: the thickness is 0.01-0.5 mm and the area is from 3×3 to 50×50 mm, but you can use the sample with the larger or smaller sizes.

b) the Work μτ.

as proposed in accordance with the present invention, single crystal CVD-diamond work μ τ is more than 1.5×10-6cm2/In, preferably greater than 4.0×10-6cm2/V 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 accordance with the present invention, 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, which is higher than the values of all previously received single-crystal CVD-diamond.

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 depth of penetration of the diamond. The use of this light makes it possible to identify the contribution of the charge carrier, depending on how the th of the electrodes were subjected to photobleaching.

The above-mentioned work μτ for the purposes of this description were measured as follows:

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

II) semi-transparent titanium contacts deposited on both sides of the diamond plate and formed figure, using standard photolithographic methods. This process formed the necessary contacts.

III) For excitation of charge carriers used 30 monochromatic xenon lamp (wavelength of 218 nm) with pulse width 10 µs, measured in the external circuit, the generated photocurrent with a circuit external load. The pulse duration of 10 μs is far superior to the duration of other processes, for example, 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 is maintained below a threshold, after which the mobility depends on the tension. In addition, the voltage is held field is maintained below the value a large fraction of charge carriers reaches the opposite side of the sample diamond and total accumulated charge reaches saturation (with locking pins, not the locking pins can show in this case, the gain).

IV) 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 means desired mobility and the lifetime of the sample.

V) 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 and significantly limited μτ sample, where values μ and τ depend on the nature of the charge carriers moving to publicenemy electrode.

in) long distance accumulation charge (charge carriers).

Proposed in accordance with the present which m invention, single crystal CVD diamond has a large distance to the accumulation of charge, usually more than 150 μm, more preferably 400 μm, most preferably more than 600 μm, measured at a field strength of 1 V/μm and a temperature of 300 K.

The prior art is the nature of distance accumulation charge and methods of its determination. Falling on the diamond UV, x - ray and gamma radiation generates electron-hole pairs that drift between the electrodes under the influence of the field. As a rule, for penetrating radiation (beta and gamma particles) electrodes disposed on opposite surfaces of the diamond layer, the thickness of which is typically 200-700 μm, but may vary from less than 100 to more than 1000 μm, and the charge carriers migrate through the thickness of the layer. For paleogeodetic radiation penetrates only a few micrometers in depth of the diamond surface, for example, alpha radiation or UV radiation, whose energy is close to the forbidden energy band of diamond or above, can be used to bound (inter-digitated) system of electrodes within one surface of the diamond layer. Electrodes are placed on a flat surface in accordance with surface structures such as grooves.

However, electrons and holes have a finite mobility and lifetime, and move a certain distance to recombination. When an event occurs (for example, a collision with a beta particle), p is evodiamine to the formation of charge carriers, the total signal detector in the first place depends on the average distance traveled by the charge carriers. This displacement of charge is the product of the mobility of charge carrier and electric field strength (which gives the rate of migration of charge) and the lifetime of carriers before capture or recombination stops the migration. This is called the distance of the accumulation of charge that can be interpreted and how the volume of space around a charged electrode. The purer the diamond (or below level not compensated traps) or the lower the number of crystal defects, the higher mobility of carriers and/or their time of life. The measured distance of the accumulation of charge is limited by the thickness of the test specimen: if the distance accumulation exceeds about 80% of the thickness of the sample, the measured value is probably a lower limit than the real value.

The distance values of accumulation, defined above, was measured by the following method:

1) 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 accuracy of measurements That can be achieved in several ways, the most common is the following method:

I) 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).

II) Conducting 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.

2) To 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, is recorded; a good sample, 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

3) 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 charge carriers. The signal from the sample scity which indicate highly electrometric amplifier and based on known 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=EN·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.

4) 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 in the depleted 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) for a long period of time, while the value of the distance savings can grow, usually 1.6 times in case imported from Germany the ski CVD-diamond, however, the 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 to the 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.

d) the electron Mobility.

Proposed in accordance with the present invention, single crystal CVD diamond has a high value of electron mobility (μe). For example, the value of electron mobility at a temperature of 300 K is more than 2400 cm2In-1with-1preferably more than 3000 cm2In-1with-1most preferably more than 400 cm 2In-1with-1. High-quality natural diamond type IIa is the mobility of electrons at a temperature of 300 K is usually 1800 cm2In-1with-1in exceptional cases reaches 2200 cm2B-1c-1.

d) hole Mobility.

Proposed in accordance with the present invention, single crystal CVD diamond has a high value of hole mobility (μd). For example, the value of hole mobility at a temperature of 300 K is more than 2100 cm2In-1with-1preferably more than 2500 cm2In-1with-1most preferably more than 3000 cm2In-1with-1. High-quality natural diamond type IIa value of hole mobility at a temperature of 300 K is usually 1200 cm2In-1with-1in exceptional cases reaches 1900 cm2In-1with-1.

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

Proposed in accordance with the present invention, single crystal CVD-diamond finds use in electronics, in particular, as an element of the detector or switching element. The high value of the breakdown voltage in the closed state in the diamond which allows you to use it as a component for optoelectronic switches. The use of diamond in these areas is a separate aspect of the invention.

Proposed in accordance with the present invention a new single-crystal CVD diamond produced by the method, which is also the object of the present invention. Proposed in the invention is a method of obtaining single-crystal diamond includes the use of the diamond substrate surface, virtually no defects in the crystal lattice, and the gas source, the decomposition gas source and controlled homoepitaxially growing diamond on a specified surface of the substrate in the atmosphere containing nitrogen at a concentration of less than 300 parts per billion (frequent. on the billion).

Attached to the description of the drawings shows:

figure 1 - spectrum of cathodoluminescence issue of the free exciton sample HDS-1 at 77 K with a strong emission at 235 nm (transverse optical wave) (transverse optic mode)

figure 2 - spectrum of cathodoluminescence sample HDS-1 with a weak broadening of the line centered at 420 mm, very weak lines 533 nm and 575 nm and a very intense emission of free excitons (shown as a line of second order at 470 nm),

figure 3 - EPR spectra (room temperature) homoepitaxial CVD-diamond (1), containing approximately 0.6 frequent. on billion single inclusions of nitrogen and sample HDS-1 (2); spectra were recorded under identical conditions for Bristow approximately the same size,

figure 4 - EPR spectra at 4.2 K of high-purity homoepitaxial CVD-diamond (I), grown together with the HDS-1, plastically deformed after rising to demonstrate the effect of structural defects, resulting from the processing, on the EPR spectrum, and HDS-1 (II); spectra were recorded under identical conditions

figure 5 - EPR spectra of natural diamond type IIa and HDS-1, recorded at room temperature, under the same conditions, for samples of the same size,

figure 6 - absorption spectrum in the ultraviolet region (room temperature) sample HDS-1, with the edge of self-absorption and lack of absorption bands with center 270 nm, related to single inclusions of nitrogen.

7 - biaxial profile lines of the x-ray spectrum of the sample HDS-1.

on Fig - Raman spectrum HDS-1, recorded at 300 K using the 488 nm line of Ar ion laser.

In addition to the above properties is proposed in accordance with the present invention, single crystal CVD diamond may have one or more of the following properties:

1. The level of any single impurity is not more than 5 frequent. at billion, and the total amount of impurities is not more than 10 frequent. in billion Amount of each impurity is preferably not more than 0.5-1 hour. at billion, the total amount of impurities is preferably the leaves not more than 2-5 frequent. on billion Concentrations of impurities can be measured by mass spectroscopy secondary ion (SIMS), mass spectroscopy glow discharge (♦), mass spectroscopy of combustion (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 using a quality control standard values obtained destructive analysis of samples by combustion). For the above to the term "impurities" are not hydrogen and isotopy.

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 the excitation argon laser 514 nm (the power of the incident beam 300 mW) peak height less than 1/1000 of the peak in the Raman spectrum of diamond at 1332 cm-1. The presence of these bands is associated with defects nitrogen/vacancy, the presence of which indicates the presence in the film of nitrogen. Because of the possibility of the presence of competing mechanisms damping normalized intensity of the line at 575 nm is not a quantitative measure for 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 is typical electron energy of 10 to 40 Kev, penetrating into the surface at a distance of from 10 nm to 30 μm. In the case of photoluminescence excitation usually occurs throughout the sample volume.

I) Uniform intense peak of the free exciton (SE) at 235 nm in the CL spectrum recorded at 77 K. the Presence of a peak indicates the almost complete absence of defects, such as bias and inclusion. The relationship between the small number of inclusions and high SE peak was previously shown for individual crystals in the synthesis of polycrystalline CVD-diamond.

II) High free exciton emission (SE) in the UV-excited photoluminescence spectrum at room temperature.

Free exciton emission can be caused by radiation with energy above the bandgap, for example, radiation ArF-excimer laser 193 nm. 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 is 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]Oat concentrations of <40 frequent. on bn, typically <10 frequent. on the MLR is, indicate low levels of implementation of nitrogen.

5) In the EPR spectrum of the spin density less than 1×1017cm-3more typically less than 5×1016cm-3when g is equal to 2,0028. In the single-crystal diamond line 10 if 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, more specifically, 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.

Proposed in accordance with the present invention, the CVD-diamond can be deposited on a substrate of the diamond (the substrate may be a 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 diminished in the process. In addition, proposed in accordance with the present invention, the CVD-diamond can form Tinsley in multilayer material in which 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.

For the production of high quality CVD diamond is important that the process of growing a layer 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. Preferably, the substrate is a natural diamond type Ia or IIb with a small birefringence obtained at high pressure/high temperature (WDT) synthetic diamond type Ib or IIa, or synthetic single-crystal CVD-diamond.

The density of defects easily determine the optical evaluation after plasma or chemical 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 may be low, so it is 50/mm 2usually 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 about 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 CVD diamond, or inside it, can be minimized by careful preparation of the substrate. In this case, the 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 VK is ucati 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 etched surface in situ, which is then precipitated homoepitaxially diamond. In principle not necessary to carry out etching in situ or immediately before the deposition process, however, the best result is achieved by etching in situ, because 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 ri best control at the stage of etching is achieved at a slightly lower temperature. For example, the composition may be next.

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: pressure 50-450×102PA, the oxygen content in the etching gas from 1 to 4 vol.%, the amount of argon in the etching gas from 0 to 30 vol.%, the rest is hydrogen, at a temperature of the substrate 600-1100°With (preferably 800°C)the normal duration of the etching 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 hydrogen etching, and 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. dislocations)that intersect the surface, since this brings about is osowaniu deep depressions. 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 and on the surface of the substrate. Hydrogen etching, following oxygen, less specific to crystalline defects, 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, 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, since it greatly reduces the reproducibility.

It is important that proposed in accordance with the present 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. on bn, which is the fraction of several molecules on the whole the volume of gas) 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 at a concentration 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. on bn, and 300 part. on billion or less. For measuring the amount of nitrogen in such low concentrations require complex methods such as gas chromatography. An example of such method is shown below:

1) 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 the sample with a small diameter, optimized for maximum flow rate and minimum dead volume, and passed through GC loop to the input of the sample before the output is m on reset. Loop for 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, and without saturation of the column is complete separation of the target gas (N2). This procedure is called 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 individuality determine the largest retention time of the gas, calibrated 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 billion 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 serial dilution.

2) This well-known technology 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 and adversely affect the 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, the volume of the loop with the sample is m increase by approximately 5 see Depending on the design of the tube to enter the sample, this technique allows you 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 mixture source can be any known in the art and contains carbonaceous material dissociate with the formation of radicals or other reactive particles. In addition, the gas mixture typically contains gases that can form a hydrogen or halogen in atomic form.

Dissociation of the gas mixture source preferably occurs under the influence of microwave radiation in the reactor, the design examples 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 the Udet to happen, 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 nm) for gas under high pressure (50-100×102PA, preferably 100-450×102PA).

The compliance of the conditions listed above allows to obtain high-quality single-crystal layers of CVD-diamond, piece mobility during the life of the media, exceeding 1,5×10-6cm2/In, for example, 320×10-6cm2/For electrons and 390×10-6cm2/For holes.

The invention is illustrated by the following examples.

Example 1

Substrates suitable for the synthesis proposed in accordance with the present invention, single crystal CVD-diamond, is prepared as follows.

I) the Process of selecting material (natural stone type Ia or stones WDT type Ib) optimize using electron microscopic studies and method birefringence to identify substrates that do not contain stresses and defects in the lattice.

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

III) 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 (high temperature/high pressure) 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 with an area of 5×5 mm and a thickness of 500 μm, with all faces {100}. The surface roughness at this stage was less than 1 nm, RA. The substrate is applied on the tungsten base suitable 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, given the nogo above.

2) Oxygen plasma etching in situ, make use of a mixture of About2/Ar/N2supplied with intensity 30/150/1200 Art. cm3/sec (standard cubic centimeters per second) at a pressure of 333×102PA and the temperature of the substrate 800°C.

3) Without a stop process of the hydrogen plasma etching, removing oxygen from the gas stream.

4) Then start the growth process by adding a carbon source, in this case methane, with an intensity of 30 Art. cm3/C. the growth Temperature at this stage was 980°C.

5) the above-Described modified GC method was determined 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, the substrate is removed from the reactor and a layer of CVD diamond is removed from the substrate.

7) This layer is flat and polished to a thickness of 410 μm, cleaned and subjected to oxygen annealing to obtain a surface layer with oxygen atoms, then measure it length accumulation of charge. When the value of the field strength of 1 V/μm determine the distance of 380 μm (the value is limited by the thickness of the sample), corresponding to the lower value works μτ 3,8×10-6.

8) For resistivity diamond layer in the closed state was found is 6�D7; 1014Ohm·see, the parameter was measured at 20°and the magnitude of the field strength of 50 V/μm.

9) Layer, identified as the HDS-1, was then characterized by the following parameters, shown below and on the attached figure 1-8:

I) the Spectrum of CL with low emission in the blue region, low emission at 575 nm and high SV-emission (figure 1 and 2).

II) EPR Spectrum, indicating a low content of nitrogen substitution, the weak g-factor 2,0028 (Fig.3-5)

III) Spectra in the visible region, demonstrating the value of bandwidth is close to theoretical (Fig.6).

IV) Map of profile lines of the x-ray spectrum in which the range of angles in the sample is less than 10 arc sec (Fig.7).

V) Raman spectrum with line width (pulse duration at half amplitude) of about 2 cm-1(Fig).

Example 2

The procedure set forth in example 1 is repeated with the following variations of conditions:

Ar - 75 STS3/s H2- 600 LSM3/s, CH4- 30 STS3/s, 820°s, 7.2 kW, the nitrogen content measured above by the modified method of HCG, less than 200 frequent. on billion

The resulting layer of CVD-diamond for testing process to a thickness of 390 μm. For option works μτ values were found 320×10-6cm2/For electrons and 390×10-6cm2/For holes (measured at 300 K), pending the average value 355× 10-6cm2/C.

Example 3

The procedure set forth in example 1 is repeated with the following variations of conditions:

Ar - 150 stem3/s H2- 1200 LSM3/s, CH4- 30 STS3/s, pressure 237×102PA, the temperature of the substrate 822°C, the nitrogen content measured above by the modified method of HCG, less than 100 frequent. on billion

The resulting layer of CVD-diamond for testing process to a thickness of 420 μm. The measured distance is the accumulation of charge is larger than 400 μm. The resistivity of the layer for a field strength of 50 V/μm exceeded 1×1014Ohm·see

Example 4

The procedure set forth in example 1 was repeated with the following variations of conditions:

Conditions of the oxygen plasma etching: the flow rate of O2/Ar/N2was 15/75/600 LSM3/C. this is followed by hydrogen plasma etching filing Ar/N2when 75/600 LSM3/s Growth initiate the addition of a carbon source, in this case, methane, at a speed of 30 STM3/C. the growth Temperature at this stage was 780°C.

Received CVD-diamond layer thickness of 1500 μm for test process to a thickness of 500 μm.

1) the distance Value of the accumulation charge amounted to 480 μm at field strength of 1 V/μm and 300 K (the value is limited by the thickness of the sample), which corresponds to lower the he limit values work mobility at the time of life, μτ, 4,8×10-6cm2/C.

2) Measured using the above ratio Hecht at 300 To work μτ 1.7×10-3cm2/In and 7.2×10-4cm2/For electrons and holes, respectively.

3) the Value of electron mobility μemeasured using time-of-flight method, amounted to 4400 cm2/·s at the sample temperature of 300 K.

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

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

6) the resistivity measured for the field strength of 100 V/μm at 300 K, exceeded 5×1014Ohm·see

7) In the spectrum of the fluorescence was observed low-intensity absorption in the blue region and low-intensity peak at 575 nm (<1 / 1000th of a Raman peak). Line width (pulse duration at half amplitude) Raman peak was 1.5 cm-1. In the spectrum of CHL a strong peak ST In the EPR spectrum is not detected (less than 7 frequent. in billion) replacement of nitrogen and lines with g=2,0028 (less than 10 frequent. on the billion).

Additional examples

Using the procedure outlined in example 4, was able to get the offline high is kachestvennye high-purity single-crystal CVD-diamond layers with a thickness from 50 to 3200 μm. The results of measurements of the values of the various characteristics of diamonds (at 300 K) are shown in table. The voltage values of the dielectric breakdown of the samples exceeded 100 V/μm.

No. sample No. sample)Plate thickness (µm)RNZ (µm)μeτe(cm2/In)
1 (HDS-1)410>380*
23903,2×10-4
3420>400*
4500>480*1,7×10-3
5700>650*1,7×10-3
610003,3×10-3

No. sample No. sample)μdτd(cm2/In)μe(cm2/·)μd(cm2/·)Resistivity (Ohm·cm) at 50 V/µm
1 (HDS-1)6×1014
23,9×10-4
3>1×1014
47,2×10-444003800>5×1014
56,5×10-439003800>1×1014
61,4×10-340003800>5×1012
* the minimum value limited by the thickness of the sample.

1. Single-crystal diamond obtained by the method of chemical vapor deposition (CVD), with at least one of the following characteristics:

(a) specific resistance (R1in the closed state, measured at field strength of 50 V/μm and at 300 K, which accounts for more than 1×1012Ohm·sm;

b) the work μτwhere μ - mobility and τ the lifetime of the charge carriers, measured at 300 K in excess of 1.5×10-6cm2In-1;

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

(g) hole mobility (μd), the value of which, ismaren the e at 300 K, is more than 2100 cm2In-1with-1;

(d) high distance value accumulation charge, measured at field strength of 1 V/μm and 300 K and in excess of 150 microns.

2. Single-crystal diamond according to claim 1, the specific resistance (R1) is measured at a field strength of 50 V/μm and at 300 K, is more than 2×1013Ohm·see

3. Single-crystal diamond according to claim 2, the specific resistance (R1) is measured at a field strength of 50 V/μm and at 300 K, is more than 5×1014Ohm·see

4. Single-crystal diamond according to any one of the preceding paragraphs, the work μτ of which, measured at 300 K, is greater than 4.0×10-6cm2In-1.

5. Single-crystal diamond according to claim 4, work μτ of which, measured at 300 K, is more than 6.0×106cm2In-1.

6. Single-crystal diamond according to any one of the preceding paragraphs, the mobility of electrons (μe), measured at 300 K, is more than 3000 cm2In-1with-1.

7. Single-crystal diamond according to claim 6, the electron mobility (μe), measured at 300 K, is more than 4000 cm2In-1with-1.

8. Single-crystal diamond according to any one of the preceding paragraphs, the hole mobility (μd) is otorongo, measured at 300 K, is more than 2500 cm2B-1c-1.

9. Single-crystal diamond of claim 8, the hole mobility (μd), measured at 300 K, is more than 3000 cm2In-1with-1.

10. Single-crystal diamond according to any one of the preceding paragraphs, the distance of the accumulation of charge which, measured at 300 K, is more than 400 μm.

11. Single-crystal diamond of claim 10, the distance of the accumulation of charge which, measured at 300 K, is more than 600 microns.

12. Single-crystal diamond according to any one of the preceding paragraphs, having all of the following characteristics (a), (b), (C), (d) and (e).

13. The method of obtaining single-crystal diamond according to any one of the preceding paragraphs, 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 billion

14. The method according to item 13, 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.

15. The method according to item 13, in which the substrate is monocrystalline diamond received what Ecodom chemical vapor deposition (CVD).

16. The method according to any of PP-15, 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.

17. The method according to any of PP-15, 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.

18. The method according to any of PP-17, in which the surface on which the growth of the diamond, before growing diamond is subjected to plasma etching to minimize surface damage.

19. The method according to p, in which plasma etching is produced in situ.

20. The method according to p or 19, in which plasma etching is an oxygen etching using etching gas containing hydrogen and oxygen.

21. The method according to claim 20, in which the oxygen etching is carried out in the following conditions: a pressure of from 50 to 450×102The PA content in the etching gas of oxygen from 1 to 4 vol.%, argon - up to 30 vol.%, the rest of the hydrogen, the temperature of the substrate 600 to 1100°C, the duration of etching from 3 to 60 minutes

22. The method according to p or 19, in which plasma etching is a hydrogen etching.

23. The method according to item 22, in which the hydrogen etching is carried out in SL is blowing 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

24. The method according to any of PP-23, in which the surface on which the growth of the diamond, before growing diamond expose and oxygen, and hydrogen etching to minimize surface damage.

25. The method according to paragraph 24, in which, after oxygen etching spend hydrogen etching.

26. The method according to any of PP-25, 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.

27. The method according to any of p-26, in which the growth of diamond is carried out in an atmosphere containing nitrogen at a concentration of less than 100 frequent. on billion

28. The method according to any of PP-27, in which the surface on which the growth of the diamond represents the surface{100}, {110}, {113} or {111}.

29. The method according to any of PP-28, in which the Stripping gas source is performed under the action of energy of microwave radiation.

30. Switching element, containing a single crystal diamond according to any one of claims 1 to 12.

31. Component optoelectrical switch containing a single crystal diamond according to any one of claims 1 to 12.

32. The detector element containing mo is kristallicheskii diamond according to any one of claims 1 to 12.

Priorities:

15.06.2000 - claim 1(a), (b), (d), 2-5, 10, 11, 13, 14 (except for the sign of "natural type IIb diamond"), 15-25, 27-32;

20.03.2001 - claim 1 (b), 6, 7;

14.06.2001 - claim 1(g), 8, 9, 12, 14, (the sign of the "natural type IIb diamond"), 26.



 

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