RU2395620C1 - Procedure for fabrication of coating and facility for implementation of this procedure - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to procedure and facility for fabrication of coating. Coating is produced by ion sedimentation on a preliminary cleaned substrate. Sedimentation is performed from axial zone of flow of jet diaphragm discharge with power of E ions corresponding to condition: E_bond<E<E_sputter, where E_bond is power of atoms bond of synthesised substance of coating layer, keV, E_sputter, is power of sputtering substance in the synthesised layer of coating, keV, of specified duration. When coating is settled, an item is annealed during an interval sufficient for re-combination of between-nodular atoms and vacancies, for saturation of not filled chemical bonds in the layer of coating and for creation of stable chemical compounds upon completion of chemical absorption on surface of coating. A separating chamber and a sedimentation chamber of the facility are pressure tight connected to the discharge chamber. The separating chamber is arranged before the sedimentation chamber and has an inlet window in kind of a screen with a mould and an orifice of diametre equal to diametre of the axial zone of discharge jet, it also has an outlet window in form of a geometric nozzle, dimensions and shape of which facilitate super sound acceleration of plasma flow. High voltage pulse source of electric current ensures specified amplitude of discharge current.

EFFECT: invention facilitates stable fabrication of high qualitative coating out of wide range of materials of high adhesion to substrates out of metals, dielectrics and transistors.

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Description

The invention relates to a technology for producing coatings and can be used in the synthesis of thin films of a wide class of materials on substrates of metals, dielectrics and semiconductors.

In modern materials science, coatings are used to change the surface properties, the application of which is carried out, in particular, during the condensation of a plasma stream in vacuum conditions during an electric discharge.

The modern technology for applying high-quality coatings is developing towards the creation of methods that provide a high flow rate of the applied material through the use of detonation devices, various types of combustion chambers and electromagnetic accelerators. Studies show that for the formation of a dense coating that adheres well to the surface of the product, it is necessary to have a particle velocity of about 1-10 km / s.

A known method of producing coatings [Pogrebnyak AD and others // ZhTF. 2001. V.71, b.7. P.111], where a high-speed jet of combustion products is formed in rocket combustion chambers. Moreover, the maximum speed of particles with a diameter of 45 μm reaches 600-650 m / s. To form a high-speed flow of combustion products in the combustion chambers, 30-150 m ³ / h of combustible mixture is burned, at least 10 m ^{3 of} gas is consumed for applying 1 kg of tungsten carbide coatings.

The disadvantage of this method is that the performance of the coating and its quality are not proportional to the increase in thermal power, and a large volume of components of the combustible gas mixture is necessary only to create a high-speed jet of combustion products. In addition, the problem of uniform distribution of the powder material over the jet cross section has not been solved, and as a result, the problem of the useful use of energy has not been solved.

A device for pulsed coating [Z.Yu. Gotra. Technology of microelectronic devices. Directory. M., "Radio and Communications." 1991. P.274-278, Fig. 7.14, d], containing a plasma-forming tube, central and external electrodes, a capacitive source of pulsed electrical power, a substrate, where the flow of erosive plasma (a pair of destroyed materials) directed to the product, hereinafter referred to as the substrate, acts on its surface and forms a thin layer of substance from the erosion products of the tube. This device allows, removing temperature restrictions during the evaporation of a sample of a condensed body (plasma-forming substance), using ionization and plasma acceleration, to increase the instantaneous deposition rate by several orders of magnitude.

The disadvantage of using such a device to obtain layers of a wide class of materials is a large number of physical factors that degrade the stability of the properties of the obtained layers.

A known method of producing coatings, selected by us as a prototype [US Pat. RU No. 2180160, IPC Н05Н 1/42, prior. 07/05/2000], which describes a method for producing fractal-like structures from high-temperature erosion products of a plasma-forming material with the possibility of their deposition on a substrate surface, which was previously cleaned prior to deposition of a diaphragm discharge jet in vacuum by vacuum at the current phase of the discharge. The disadvantages of this method for producing coatings include the low growth rate of the coating thickness, the unevenness in the thickness of the coating layer, the heterogeneity of the chemical composition of the coating over the coating area, as well as the low adhesive strength of the coating.

A known device for producing coatings, selected by us as a prototype [US Pat. RU No. 2180160, IPC Н05Н 1/42, prior. 07/05/2000], including a sealed vacuum chamber with a high-voltage generator of current pulses of adjustable amplitude and duration, a gas-vacuum system, ring electrodes, the inner holes of which are made in the form of truncated cones with their vertices facing each other, and made of a dielectric plasma-forming material and mounted on an axis a circular electrode with a diaphragm with a round hole with a ratio of radius r ₀ and length 1 ₀ holes

0.5 <2r ₀ / l ₀ <2.0,

and a substrate placed at a distance from the electrodes. However, at this installation it is not possible to carry out the process of ion deposition of the material and create a coating from a wide class of materials of a given composition with high adhesive strength of the coating.

The present invention allows to stably obtain high-quality coatings from a wide class of materials with high adhesion to substrates of metals, dielectrics, semiconductors.

This technical result was obtained by us when

- in a method for producing a coating comprising ionic deposition on a pre-cleaned substrate of products of high-temperature erosion of a plasma-forming material by forming a high-speed plasma stream of a jet diaphragm discharge between ring electrodes through a plasma-forming diaphragm with gas-dynamic and electromagnetic acceleration, the deposition of ions from the substrate is carried out from the axial zone of the stream of jet diaphragm discharge with an energy of E ions, corresponding to the condition:

E _sv <E <E _rasp ,

where E _sv is the binding energy of atoms of the synthesized substance of the layer, keV;

E _rasp is the atomization energy of the substance in the synthesized layer, keV;

and with duration τ = h / V, s,

where h is the specified thickness of the coating layer, mm;

V is the layer growth rate, mm / s,

and after coating formation on the substrate, the obtained layer is annealed for a period of time sufficient for recombination of interstitial atoms and vacancies, saturation of unfilled chemical bonds in the coating layer, and formation of stable chemical compounds after the end of the chemisorption process on the coating surface;

- in a device for producing a coating containing a high-voltage switching power supply, a gas-vacuum system and a sealed vacuum discharge chamber with a substrate, ring electrodes, the internal openings of which are made in the form of truncated cones with their vertices facing each other, with an ignition electrode placed between them and installed coaxially with electrodes a diaphragm made of a dielectric plasma-forming material with an aperture of radius r ₀ and a length l ₀ that satisfy the condition

0.5 <2r ₀ / l ₀ <2.0,

new is that it is equipped with a separating chamber and a deposition chamber sealed to the discharge chamber, and a temperature-controlled base for the substrate, which is placed in the deposition chamber at a distance A from the annular cathode, which meets the condition

50R <A <100R,

where R is the radius of the inner hole of the electrodes, mm,

wherein the separating chamber is placed in front of the deposition chamber and is made with an input window in the form of a screen with a shape and a hole with a diameter equal to the diameter of the axial zone of the discharge jet, which ensure the elimination of the ejector effect at the entrance to the separating chamber, and with the exit window in the form of a geometric nozzle, the size and shape of which provide supersonic acceleration of the plasma flow, and the high-voltage switching power supply is configured to obtain the amplitude of the discharge current I ₀ corresponding to the condition

2.5 · 10 ⁴ · l ₀ ^1.4 / r ₀ ^1.4 (1 + r ₀ / l ₀ ) <I ₀ <7.1 · 10 ⁴ · l ₀ ^1.4 / r ₀ ^1.4 ( 1 + r ₀ / l ₀ ),

where r ₀ is the radius of the hole in the plasma-forming diaphragm, mm;

l ₀ is the length of the hole in the plasma-forming diaphragm, mm

Methods for cleaning the surface of a substrate are known.

Methods for producing a jet diaphragm discharge in the gas-dynamic regime of a plasma flow in a discharge gap are known.

Methods of electromagnetic and gas-dynamic acceleration of the flow of charged particles and plasma flows are known.

Approaches to solving the problem of ion selection by energy and elemental composition are known.

Approaches to solving the problem of coating annealing, which ensures the recombination of interstitial atoms and vacancies, the saturation of unfilled chemical bonds in the layer, and the formation of stable chemical compounds after the end of the chemisorption process on the coating surface are known.

Figure 1 presents a diagram of a device that implements the claimed method for producing coatings, where the discharge vacuum chamber 1, power supply 2, gas-vacuum system 3, ring electrodes 4, plasma-forming diaphragm 5, substrate on a temperature-controlled base 6, separation chamber 7, deposition chamber 8;

A is the distance from the annular cathode 4 to the substrate on a temperature-controlled base 6;

D is the distance from the annular cathode 4 to the input window E of the separation chamber 7;

R is the radius of the inner hole of the ring electrodes 4;

R ₁ is the radius of the window e;

L is the interelectrode distance;

r ₀ is the radius of the hole in the plasma-forming diaphragm;

l ₀ is the length of the hole in the plasma-forming diaphragm;

E - input window of the separating chamber 7;

C - nozzle of the separating chamber 7;

F - quadrupole mass filter of the separating chamber 7.

Figure 2 shows a panoramic x-ray spectrum of the chemical composition of the surface layer on a substrate of single-crystal germanium hydroelectric power station 0.3 / 02, deposited using the claimed group of inventions with a plasma-forming diaphragm made of polytetrafluoroethylene (fluoroplastic grade F4), where the binding energy of atoms in eV, and along the ordinate axis the number of atoms in relative units.

Figure 3 shows a panoramic x-ray spectrum of the chemical composition at a depth of 0.64 μm of the same layer obtained using the claimed group of inventions.

A device that implements the proposed group of inventions works as follows.

In the vacuum chamber between the ring electrodes 4 through the plasma-forming diaphragm 5 form a jet diaphragm discharge. To do this, using the synchronization circuit, a start signal is supplied to the ignition device, which opens the switch (for example, an ignitron) of the power supply, which is a high-current discharge circuit with a high-voltage capacitive energy storage C ₀ . Then a high voltage is applied to the ignition electrode, the ring electrodes 4 and the capacitor bank С _{0 is} discharged at the load, the interelectrode gap (anode-cathode). The current impulse of the jet diaphragm discharge of a given shape, duration and amplitude is obtained by choosing the parameters of the discharge circuit based on the electrical calculation - choosing the interelectrode gap L, the thickness of the diaphragm l _{0 of the} hole diameter 2r ₀ in it, the charging voltage U _{0 of the} batteries, the loop inductance L _to , the resistance contour R _to , and the composition of the plasma-forming material. This gives a certain spatio-temporal structure of the flow of the erosion products of the plasma-forming material of the diaphragm with the zone of receipt of the erosion products in the hole of the diaphragm; with an axial zone of blowing the discharge gap with erosion products; with the axial zone of the flow of erosion products, slightly compressed by the magnetic field of the discharge’s own current; the sheath zone and the zone of the outflow into the vacuum behind the ring electrodes. Approaches to solving these problems are known.

Depending on the rate of ablation of the mass of the plasma-forming material, an erosion plasma is obtained in the aperture opening with high specific parameters (temperature from 2000K to 70,000K at pressures from 0.1 to 100 MPa) by choosing a current density from 1 kA / cm ² to 1 MA / cm ² .

Thus, by creating SDRs, we met the essential condition necessary for subsequent ion deposition on the substrate: we obtained ions of a given composition from high-temperature erosion products for any selected material.

Electromagnetic acceleration of erosion products is carried out in the area of the diaphragm-ring electrode due to the difference in the magnetic pressure of the conductive fluid (plasma stream) in the section at the section of the hole in the diaphragm and in the plane of the hole of the ring electrode, and additional gas-dynamic acceleration due to the effect of outflow into the vacuum in the supersonic outflow mode axisymmetric underexpanded jet in the area of the ring electrode-input window E of the separation chamber 7.

When forming a coating, two processes occur on the surface of the substrate:

- ionic stimulation of the substrate, sufficient for the formation of an optimal stationary concentration of point defects n ^J _td (here, a point defect is a defect the size of the order of the atomic) on the surface of the substrate to create active condensation centers of the deposited particles;

- ion deposition,

which can be performed by producing ions with the required energy after accelerating the plasma flow from the erosion products of the diaphragm material.

When expanding the plasma jet behind the ring electrode, the axial zone and the zone of the jet shell are cut off at the input window E of the separation chamber, due to the choice of the hole diameter of the input window equal to the diameter of the axial zone of the discharge jet and its shape to eliminate the ejector effect at the entrance to the separation chamber. For this, the input window E is made in the form of a truncated cone directed by a truncated vertex towards the flow (towards the ring electrode). The high-speed axial zone of the plasma flow with a diameter of 2R ₁ passes through an opening in the inlet window E and enters the separation chamber 7, where it is then accelerated in the geometric supersonic nozzle C, which is the exit window of the separation chamber 7.

If you want to get a monokinetic ion flow, which gives, in turn, a high degree of uniformity of the coating in chemical composition, you can place the mass filter F coaxially with the inlet window E. in the separation chamber 7. The mass filter F for separating ions of a certain mass is for example, a quadrupole Paul mass filter [1], which consists, in particular, of four rods, to which a certain combination of direct and radio frequency alternating voltages is applied in pairs in opposite polarity. Ions flying parallel to the axis of these rods fall into a hyperbolic field, and they, depending on the ratio of their mass and frequency, are passed through this field or not passed further.

After the separation chamber 7, the effluent flow of erosion products in the form of ions enters the deposition chamber 8 with a substrate on a temperature-controlled base 6. The substrate is placed in the deposition chamber at a distance A from the ring cathode, found from the condition

50R <A <100R;

where R is the radius of the inner hole of the electrodes, mm, selected from the condition

ln R / r <1.6πLω / µµ _o I ₀ ² t _n ,

where L is the interelectrode distance, m;

ω is the average rate of ablation of the mass of the plasma-forming substance from the inner wall of the opening of the diaphragm, kg / s;

µ is the magnetic permeability of the plasma of the discharge jet;

µ _o = 1.257 · 10 ^-6 GN / m;

I ₀ is the amplitude of the discharge current, A;

t _n = (0.2-1.1) · 10 ^-6 s is the development time of the magnetogasdynamic instabilities in the discharge gap of the jet diaphragm discharge.

This choice of distance A provides the necessary amount of ion energy and their flux density when forming a high-quality coating with high adhesion, uniformity in area and layer thickness. In the zone of inhibition of a high-speed flow of erosion products on the surface of a substrate located on a temperature-controlled base, the coating formation process directly goes through.

Approximating expressions for calculating the specific plasma parameters (thermodynamic, gasdynamic characteristics of the flow, its component and ionization composition) were obtained by us earlier [2] when solving the system of equations of radiation magnetic gasdynamics, supplemented by the radiation transfer equation, which plays a decisive role in the energy balance of the jet diaphragm discharge . This makes it possible to determine the energy values of particles E incident on the surface of the substrate, taking into account the geometry of the placement of the substrate and gas-dynamic (ejector) effects in the stream during transportation of particles through the window system of the separation chamber between the slice of the ring SDR electrode and the substrate.

The values of the binding energy of the atoms of the synthesized substance of the layer E _sv , the sputtering coefficients and the energy of spraying E _{ra of} substances are taken from the corresponding literature [3]. The speed V of the coating layer growth process during deposition with simultaneous ion-stimulation with a current density j ions determined from the condition optimal steady-state concentration of point defects n ^j _etc. on the substrate surface. Point defects are formed by pairs (Frenkel pairs) - an interstitial atom (an atom knocked out of its node in the internode) and the vacancy remaining in its place. The formation of such defects is proportional to the flux density of incident ions on the substrate surface j.

Moreover, on the surface with defects, the energy barrier of nucleation decreases. The adatom – vacancy complex is so stable that it can be considered as a supercritical nucleus of a new phase. Vacancies become directly condensation centers (on an ideal surface, condensation centers were critical nuclei). Obtaining the optimal value of the stationary concentration of point defects n ^J _td on the surface under the conditions of ion irradiation leads to the fact that the layer simultaneously grows with a large number of islands, the graininess of the layer decreases, uniformity and continuity at a small layer thickness increase, and the coating structure is improved.

On the other hand, when the ion current density increases under conditions of surface stimulation by slow ions above a certain value (j> j _pre ), the role of point defects on the substrate surface decreases on the rate of condensation of erosion products on the substrate surface and the growth rate of the coating layer V. This can be explained by the fact that most of the ion energy under these conditions of ion irradiation goes to the excitation of phonons. Thus, it is possible to control the process of condensate nucleation on the substrate, and thereby the structure and properties of the coating, by changing equally the ion current density or ion energy E.

To clarify the found dependence, we obtained the experimental characteristics V (j, E) during the deposition of products of high-temperature erosion of a plasma-forming material on the substrate under ion irradiation using a diaphragm jet discharge in vacuum.

After the coating is formed on the substrate, the resulting layer is annealed - to anneal point defects, when the interstitial atom occupies a vacancy and the surface is restored. Annealing is carried out under controlled environmental conditions for a time period τ _annealing sufficient to recombine interstitial atoms and vacancies, saturate unfilled chemical bonds in the layer and form stable chemical compounds after the end of the chemisorption process on the coating surface. To achieve this goal, the temperature-controlled base with the substrate is first heated to a temperature T _anne and the resulting layer is held for a time τ _anne, followed by cooling to room temperature. Approaches to solving these problems are known [4].

Concrete example

The use of the proposed method for producing thin layers on substrates from an erosive discharge plasma can be illustrated by a specific example of obtaining a layer on a substrate with a diameter of 50 mm from single-crystal germanium grade HES 0.3 / 02 from erosive plasma of a diaphragm discharge in vacuum (p _beg = 10 ^-2 Pa) where polytetrafluoroethylene (F4 grade fluoroplast) was used as the material of the plasma-forming diaphragm.

To deposit on the surface of the substrate products of high temperature erosion of a plasma-forming material with simultaneous ionic stimulation of the substrate surface by slow ions with energy (E _ion <1 keV) from a high-speed stream of a relaxing plasma jet diaphragm discharge (SDR), a gas-dynamic plasma flow regime on an interelectrode gap of adjustable duration τ was chosen.

When the reference mode of power supply from a capacitive storage device is C = 2.8 mF, L = 5.6 μG, Rk = 1.9 mOhm at a charging voltage of U ₀ = 4.5 kV, discharge through a cylindrical hole in the diaphragm with a thickness of 5 mm and a diameter of 4 , 0 mm had a high-current stage with a current amplitude of 65 kA per 90 μs from the beginning of the discharge with a duration of 350 μs, corresponding to light cleaning with irradiation of 0.1 J / cm ² in the VUV spectral region (Δλ = 0.1 ... 0.2 μm) , and low-current with a current of 500 A at 600 μs from the beginning of the discharge with a duration of 5 ms, corresponding to ion stimulation of the substrate and simultaneously to the ion deposition process s and carbon and fluorine atoms on a substrate located on a thermostatic base at a distance of 2000 mm from the slice of the diaphragm when its surface was perpendicular to the plane passing through the axis of the discharge gap; with a duration sufficient to obtain a layer with a thickness of 840 nm. The temperature-controlled base is equipped with a fuel element and a temperature sensor (thermocouple). The element is heated by the release of Joule heat when current is passed through it from a power source. After the discharge in the vacuum chamber, the substrate with the layer deposited on it was kept in vacuum at a temperature of T = 400 ° C and a pressure in the chamber of 10 ^-2 Pa for 50 minutes.

The coating was dark blue in daylight, uniform throughout the area. The appearance of the coating is without visible damage, even, without peeling, swelling, cracks and peeling.

We investigated using optical and electron microscopes the quality of the coating obtained on a substrate of single-crystal germanium grade HES 0.3 / 02. It was found that the coating obtained by this method has a structural density and reduced porosity.

The coating was tested at the Central Research Institute of Materials (St. Petersburg) for resistance to external influences, carried out using the methods reflected in the documents for testing for wear resistance (clause 4.5.10 MIL-C675C and clause 6.4 ARSM 01071/00001), adhesion test (adhesion to the substrate surface) (clause 4.5.12 of MIL-C675C and clause 6.3 of APCM 01071/00001), check for resistance to precipitation (MIL-STD - 810, method 506/4 and clause 6.8 of APCM 01071.00001). The results obtained led to the conclusion about the high adhesion and cohesion of the applied layer and its uniformity.

Similar results were obtained when coating substrates made of single-crystal silicon, quartz glass of the K8 brand, magnesium fluoride, titanium, and PMMA.

Thus, the use of the proposed technology for producing thin layers on various materials from erosive plasma discharge provides coatings with the following advantages:

- coatings have high physicochemical properties;

- the possibility of applying layers of hardly volatile plasma-forming substances;

- coatings are characterized by density of the structure and reduced porosity and, as a consequence, increased corrosion resistance;

- coatings have a finely divided structure;

- ionic coatings have high adhesion to the substrate and cohesion.

The advantages of the proposed method:

- allows you to process parts of various shapes with high uniformity of coatings;

- high speed coating (up to 2 mm / s);

- high controllability and reproducibility;

- simplicity of protection methods for non-machined surfaces.

Literature

1. V. Paul. Electromagnetic traps for charged and neutral particles. // Usp. 1990.V. 160, issue 12. C.109-127.

2. E.V. Kalashnikov, T.G. Kostitsyna. Thermodynamic properties of erosive plasma diaphragm discharge on jets in a vacuum. // TWT. 2000. Vol. 38, No. 2. S.194-199.

3. V.I. Nefedov, V.T. Cherepits. Physical methods for studying the surface of solids. M .: Science. 1983.

4. Z.Yu. Gotra. Technology of microelectronic devices. Directory. M., "Radio and Communications." 1991. S.241-244.

Claims (2)

1. A method of producing a coating, comprising ionic deposition of high-temperature erosion products of a plasma-forming material onto a pre-cleaned substrate by forming a high-speed plasma stream of jet diaphragm discharge between the ring electrodes through a plasma-forming diaphragm with gas-dynamic and electromagnetic acceleration, characterized in that the deposition of ions on the substrate is carried out from axial zone flow jet diaphragm discharge with an energy of E ions corresponding to the condition:
E _sv <E <E _rasp ,
wherein E _binding - binding energy of the atoms of the synthesized substance coating layer keV E _dis - sputtering energy substance in a synthesized coating layer keV and with a duration
τ = h / V, s, where h is the specified thickness of the coating layer, mm, V is the growth rate of the layer, mm / s, and after coating formation on the substrate, the resulting layer is annealed for a period of time sufficient for the recombination of interstitial atoms and vacancies saturation of unfilled chemical bonds in the coating layer and the formation of stable chemical compounds after the end of the chemisorption process on the coating surface. 2. A device for producing a coating containing a high-voltage switching power supply, a gas-vacuum system and a sealed vacuum discharge chamber with a substrate, with ring electrodes, the internal openings of which are made in the form of truncated cones with their vertices facing each other, with an igniting electrode placed between them and installed coaxially with electrodes a diaphragm made of a dielectric plasma-forming material, with an aperture of radius r ₀ and length l ₀ that correspond to the condition
0.5 <2r ₀ / l ₀ <2.0,
characterized in that it is equipped with a separation chamber and a deposition chamber sealed to the discharge chamber, and a temperature-controlled base for the substrate, which is placed in the deposition chamber at a distance A from the annular cathode, which corresponds to the condition
50R <A <100R,
where R is the radius of the inner hole of the electrodes, mm, while the separating chamber is placed in front of the deposition chamber and is made with an input window in the form of a screen with a shape and a hole with a diameter equal to the diameter of the axial zone of the discharge jet, which ensure the elimination of the ejector effect at the entrance to the separating chamber, and with the exit window in the form of a geometric nozzle, the size and shape of which provide supersonic acceleration of the plasma flow, and the high-voltage switching power supply is configured to obtain an amplitude discharge current I ₀ corresponding to the condition
2.5 · 10 ⁴ · l ₀ ^1.4 / r ₀ ^1.4 (1 + r ₀ / l ₀ ) <I ₀ <7.1 · 10 ⁴ · l ₀ ^1.4 / r ₀ ^1.4 ( 1 + r ₀ / l ₀ ),
where r ₀ is the radius of the hole in the plasma forming diaphragm, mm, l ₀ is the length of the hole in the plasma forming diaphragm, mm

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