RU2644216C2 - Microwave plasma reactor for obtaining a homogeneous nanocrystalline diamond film - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: invention relates to a microwave plasma reactor with volume-cavity energy transfer to an area above substrate limited by the shape of a plasma formation in the form of half-ellipse, which creates indirect heating when the coating is deposited on a low-aspect substrate or simultaneously on a group of substrates. Microwave plasma reactor for obtaining a homogeneous nanocrystalline diamond film contains a hermetically sealed axisymmetric chamber, the central part of which is a microwave resonator and is a radial wave guide with microwave field, and a cooled substrate holder installed therein, and is noted for the fact that the plasma-forming cassette with an external diameter proportional to the microwave field length is installed axially in the microwave resonator, this cassette has at least one inner opening, where the base of said cassette facing the substrate holder, and the axes of holes are oriented perpendicular to it, while the height H of the cassette is 1.75h ≤ H > 0.75h, where h is the height of the substrate for placement in the inner hole of the cassette.

EFFECT: it is possible to create a microwave plasma reactor with a high temperature field homogeneity on the surface of the substrates to obtain a homogeneous nanocrystalline diamond film.

1 cl, 3 dwg, 1 ex, 1 tbl

Description

The present invention relates to microwave reactors for plasma-chemical synthesis of materials from the gas phase, using the cavity-resonator method of transferring microwave energy to the region above the substrate with the limitation of the shape of the plasma formation in the hemisphere. One of the technological problems is the deposition of a carbon-containing film on a low-aspect substrate or on a group of such substrates with a high degree of adhesion and uniformity of the crystal structure. When a diamond film is formed in a radial waveguide, the nonuniformity of the field distribution and, accordingly, the local energy input into the plasma increases with a decrease in the aspect number of the substrate, the number of substrates, and the lateral asymmetry of the input microwave power. For uniform film growth over the entire surface of a low-aspect substrate, it is necessary to eliminate the temperature inhomogeneity arising due to the edge effect of the microwave electric field both on a separate substrate and on a group in the case of simultaneous group growth.

Known substrate holder with temperature control and control (PCT application WO 9737375), in which the substrate holder contains many thermoelectric modules that are in thermal contact with the surface of the substrate holder. A disadvantage of the known method is that it is technologically complicated and incurs additional energy and material costs due to the need for external control to maintain a critical surface temperature of a low aspect ratio substrate or a group of such substrates; constant external control not only complicates the system and reduces its reliability, but becomes ineffective. In addition, thermoelectric modules can affect the microwave field of the discharge, creating interference.

A substrate holder is known (Application EP 0867538 (A1)), in which, for uniform heat distribution, the substrate holder located between the heating source and the semiconductor substrate is made of a material with a conductivity higher than that of graphite. A disadvantage of the known method is that it is technologically complicated and incurs additional energy and material costs due to the need to efficiently remove excess heat to maintain optimal temperature from local overheating zones due to the edge effect caused by the perturbation of the microwave field when a low-aspect substrate or group is introduced into it such substrates.

A microwave plasma reactor is known that contains a sealed axisymmetric chamber with gas channels and a radial waveguide installed in it, the central part of which is a microwave resonator, and a substrate holder (patent RU 2403318 C2), which, thanks to the heat exchange system, controls how to remove excess heat from the substrate holder , and its additional heating, which makes it possible to further equalize the temperature field during growth on high-aspect substrates. A disadvantage of the known method is that it is technologically complicated and incurs additional energy and material costs in the case of the growth of a diamond coating on smaller substrates, for example with a low aspect shape, the uniformity of the temperature field is violated, overheating zones form on the periphery of the substrate as a result of the edge effect. In this case, the removal of excess heat due to the thermal conductivity of the substrate in the cooled holder becomes ineffective, and local overheating of the growth surface leads to a violation of the crystal structure, the uniformity of the grain composition and the quality of the diamond film, as well as the diamond coating.

A new achievable technical result of the claimed invention is the creation of a microwave plasma reactor with high temperature field uniformity on the surface of substrates with low aspect geometry of the form to obtain a homogeneous nanocrystalline diamond film.

A new technical result is achieved in that a microwave plasma reactor for producing a homogeneous nanocrystalline diamond film containing a sealed axisymmetric chamber, the central part of which is a microwave resonator and is a radial waveguide with a microwave field, and a cooled substrate holder installed in it, characterized in that A plasma-forming cartridge with an external diameter proportional to the wavelength of the microwave field having at least one internal ERSTU, wherein said tape base facing the substrate holder, and the axes of the holes are oriented perpendicular thereto, wherein the height H of the cassette is 1,75h ≤ H> 0,75h, where h - height of the substrate for placing in the inner hole of the cassette.

A new result of the proposed technical solution is the creation of a microwave plasma reactor with a uniform temperature maintenance system for the deposition of homogeneous nanocrystalline coatings on a group of substrates with a low aspect shape geometry.

In FIG. 1 is a schematic cross-sectional view of a microwave plasma reactor for group growth of coatings on low aspect substrates. The plasma-forming cartridge 1 is placed in an axially axisymmetric reactor chamber with a resonator 2, forming a plasma circuit 3 in the standing wave generation section, the substrate 4 is mounted in the hole of the cartridge 1 and the lower base lies on the cooled substrate holder 5. The substrate holder 5 is made of molybdenum and is cooled by heat transfer to the underlying heat exchanger which is in close contact with. The air is pumped out in the reactor by a vacuum system 6. The plasma power is supported by microwave energy 7. Cassette 1 consists of a housing with holes and has dimensions: height H, diameter D and the number of holes n according to the number of substrates. The height of the cassette H and the height of the substrate h installed in the hole of the cassette are related by a relationship determining the relative position of the plasma forming surface of the cassette and the deposition surface of the coating on the substrates in the form 1.75h ≤ H> 0.75h. The diameter of the plasma-forming cassette is taken as a multiple of the wavelength λ, D = n⋅λ, where n is the multiplicity coefficient for a given frequency of the microwave field.

, т.е.When the system is turned on, gas and microwave energy are supplied to the reactor. In the central part of the reactor 2, the microwave wave propagates along the substrate holder 5 and the plasma forming surface of the cartridge 1, forming a plasma 3, which is a heating source for the synthesis of material on the growth surface of the substrates 4 located in the holes of the cartridge. The spherical plasma contour is formed by a microwave field that flows around the perimeter of the cartridge at a height λ. The cross-sectional shape of a contour with a diameter of D = n⋅λ can be described by the canonical equation of an ellipse with large (a = 2) and small (b = 1) semi-axes, characterized by a compression ratio and focal perimeter equal to

, i.e.

x ^{2/2 2} + y ^{2/1 2} = 1.

In this case, the growth surfaces of all substrates lying in the plane of the semimajor axis of the ellipse are equidistant from the plasma contour, which serves as a source of indirect heating for them. Indirect heating eliminates local overheating from the edge effect, which makes it possible to simultaneously deposit coatings both on single substrates and on groups of substrates with equal or different aspect numbers. A massive substrate holder 5 made of molybdenum equalizes the temperature on the surface of the cartridge directed toward the substrate holder and on the base of the substrates 4 installed in the holes of the cartridge due to the thermal conductivity of the material of the cartridge and the substrate. Thus, the temperature on the growth surface of the substrate is stabilized to the optimum value necessary for the growth of the film of the desired lateral size. The temperature in the film growth plane on the substrate 4 becomes uniform. Indirect heating allows you to adjust the heating temperature of the growth surface of the substrate while maintaining the uniformity of the temperature field within the critical range of heights and to obtain uniform films with specified structural characteristics of polycrystalline grains. The size of polycrystalline grains without sacrificing quality can be controlled within the critical range of 1.75h ≤ H> 0.75h, determined by the ratio of the height of the cassette and the substrate, by controlling the temperature of the growth surface of the substrate. Going out of this range to a smaller side leads to overheating of the growth surface due to penetration into the region of direct heating of microwave plasma; going up leads to a temperature drop below critical, at which cracking is possible in the coating.

The proposed technical solution makes it possible to obtain high-quality homogeneous films on low-aspect substrates of various shapes in a microwave plasma reactor with indirect heating and to realize the group growth method in a cassette comparable in diameter with the microwave wavelength.

An example of the implementation of a technical solution.

A comparative experiment was performed on growth on low-aspect substrates in a microwave plasma reactor using and without a plasma-forming cassette. The plasma chemical reactor ARDIS-100 (Optosystems LLC, 5 kW, 2.45 GHz) was used. A plasma-forming cassette was introduced with an outer diameter of 60 mm, a multiple of the wavelength at a frequency of 2.45 GHz, a height of 3.5 mm with 4 inner holes with a diameter of 10.5 mm. Four substrates of VK 6 carbide with a diameter of 10 mm and a height of 4.5 mm were installed in the holes of the cartridge. The synthesis of diamond films was carried out under the following conditions: microwave power 2.5-2.9 kW, pressure in the chamber 9.3-10.6 kPa, gas mixture H ₂ / CH ₄ = 96/4 (%), gas consumption 1 , 0 dm ³ / min, the duration of the deposition process is 5 hours. The temperature of the growth surface of the substrate was controlled by a Mikron M770 double-beam pyrometer. The dependence of the temperature of the growth surface of the substrate on the type of heating in a microwave plasma reactor is shown in FIG. 2.

. Сформированная плазма распространяется на всю группу подложек и не зависит от размера подложек и зазора между ними. Латеральная неравномерность нагрева как отдельной низкоаспектной подложки, так и всей группы подложек отсутствует. При использовании технического решения прототипа (фиг. 3, в, г) основание контура плазмы замыкается вблизи ростовой поверхности подложки, при этом плазма формируется индивидуально на каждой из группы подложек, затем сливается в единое облако, имеет не симметричную форму и зависит от размера подложек и зазора между ними. Стрелкой на фиг. 3, в выделена зона неравномерного нагрева отдельной подложки, что характерно и для всей группы подложек. Зона перегрева связана с неоднородностью СВЧ-поля при внесении в него низкоаспектных подложек. Экспериментально установлено, что при горении плазмы на подложках с малым аспектным числом эффект выравнивания температуры с помощью подложкодержателя, описанного в данном прототипе, неэффективен из-за высокого градиента температуры в зоне прямого нагрева плазменным разрядом, локально горящим на кромках подложек. Как следует из Таблицы 1, рост в СВЧ плазменном реакторе без использования нового технического решения вызывает локальный рост температуры в плоскости осаждения подложки до 200°С, с дальнейшим частичным отслоением покрытия по завершении процесса и чрезмерного роста зерна в зонах перегрева от 05, до 3 мкм.As can be seen from Table 1, the proposed technical solution ensured a temperature deviation in the deposition plane of the diamond film by 7.5 ° C at an average heating temperature of T = 725 ° C. This facilitated the production of a uniform diamond coating on samples with an aspect number of 2.2. The grain size of the formed nanocrystalline diamond film was 100 ± 20 nm. Thus, it was found that indirect heating of substrates located inside a hemispherical plasma contour with a diameter multiple of λ / 4 at a microwave frequency of 2.45 GHz (61 mm) eliminates the edge effect at the edges of low-aspect substrates and ensures uniform coating temperature in the lateral plane growth. The photographs (Fig. 3, a, b, c, d) show a typical heating of a group of low-aspect substrates in and without a cassette. View through the upper (a, c) and side (b, d) window of the microwave plasma reactor. The numbers indicate the temperature control points of the growth surface. When using the new technical solution (Fig. 3, a, b), a single plasma contour is formed with the base on the plasma forming surface of the cartridge, the plasma contour has the form of a semi-ellipse with large (a = 2) and small (c = 1) half-axes, compression ratio of the ellipse and focal perimeter equal to

. Formed plasma spreads over the entire group of substrates and does not depend on the size of the substrates and the gap between them. There is no lateral unevenness in heating of both a single low-aspect substrate and the entire group of substrates. When using the technical solution of the prototype (Fig. 3, c, d), the base of the plasma circuit is closed near the growth surface of the substrate, while the plasma is formed individually on each of the groups of substrates, then merges into a single cloud, has an asymmetric shape and depends on the size of the substrates and the gap between them. The arrow in FIG. 3, a zone of uneven heating of a single substrate is highlighted, which is also characteristic of the entire group of substrates. The overheating zone is associated with the inhomogeneity of the microwave field when low-aspect substrates are introduced into it. It was experimentally established that when plasma is burned on substrates with a small aspect number, the effect of temperature equalization using the substrate holder described in this prototype is ineffective due to the high temperature gradient in the direct heating zone by a plasma discharge that locally burns on the edges of the substrates. As follows from Table 1, growth in a microwave plasma reactor without using a new technical solution causes a local increase in temperature in the plane of substrate deposition to 200 ° C, with further partial delamination of the coating at the end of the process and excessive grain growth in overheating zones from 05 to 3 μm .

Based on the foregoing, a new achieved technical result of the claimed invention provides the following technical advantages (compared with the prototype).

1. The edge effect is eliminated when substrates with a low aspect shape geometry are introduced into the microwave field, causing a local temperature increase in the overheating zone (up to 200 ° C), leading to rejection or excessive grain growth in the overheating zones from 500 to 3000 nm.

2. The temperature uniformity in the plane of deposition of the diamond film is of the order of 7.5 ° C at an average heating temperature of T = 725 ° C, obtaining a homogeneous nanocrystalline diamond film of 100 ± 20 nm in size, high adhesion on samples of carbide with an aspect number of 2.2 .

Microwave plasma reactor to obtain a homogeneous nanocrystalline diamond film

The results of measuring the heating temperature of the substrate in a microwave plasma reactor according to the prototype (without cassette) and the proposed solution in the cassette

Claims (1)

Microwave plasma reactor for producing a homogeneous nanocrystalline diamond film containing a sealed axisymmetric chamber, the central part of which is a microwave resonator and is a radial waveguide with a microwave field, and a cooled substrate holder installed in it, characterized in that the microwave axial reactor a plasma-forming cassette is installed with an outer diameter proportional to the wavelength of the microwave field having at least one inner hole, the base of the cassette being about facing the holder of the substrate, and the axis of the holes are oriented perpendicular to it, while the height H of the cartridge is 1.75h ≤ H> 0.75h, where h is the height of the substrate for placement in the inner hole of the cartridge.

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