Apparatus and method for producing a doped diamond layer

Abstract

The invention relates to an apparatus (1) and a process for applying a doped diamond layer to a substrate (2, 2a) by chemical vapor deposition. The apparatus (1) comprises a deposition chamber for holding the substrate (2, 2a), a gas active element (7) in the form of a hollow body with a passage (7b) for a process gas, in particular hydrogen, an outlet opening (16) leading from the passage (7b) to the deposition chamber (3), a heating device (8) for heating the wall (7a) of the gas active element (7) surrounding the passage (7b) and a solid precursor other than carbon in the passage (7b).

Description

Technical Field

[0001] The present invention relates to an apparatus and a method for applying a doped diamond layer to a substrate by chemical vapor deposition.

Background Art

[0002] The chemical vapor deposition (CVD) process enables coating of surfaces with complex three-dimensional shapes because it can uniformly coat the interior even in the smallest recesses and hollow bodies. Various CVD diamond coating techniques mainly differ between a gas activation method and a gas dissociation method. The main characteristics are the growth rate, the coating area, and the quality of the diamond layer. Usually, a high growth rate is limited to very small coating areas. The "hot filament" process (HFCVD process) has been established for coating three-dimensional complex substrates. This is because this process can also be used to coat three-dimensional substrates on larger surfaces. Plasma processes are mainly used for two-dimensional substrates (e.g., Si wafers) because the enhancement of the local electric field and the higher density of plasma occur on three-dimensional surfaces, making it impossible to deposit layers homogeneously.

[0003] WO 2018 / 064694 A1 describes a CVD apparatus and a CVD process for applying a carbon layer, particularly a diamond layer, to a substrate. A process gas, hydrogen, or a mixed gas of hydrogen and a carbon-containing gas is introduced into the gas inlet and the flow path of the gas activation element. The process gas is activated by a combination of thermal excitation and shock excitation and then flows in a locally controlled manner through an outlet opening into the deposition chamber where the substrate is placed. This combination of thermal excitation and shock excitation of the process gas results in a significantly high excitation rate of atomic hydrogen, a higher growth rate, a uniform deposition of the carbon layer (diamond layer) on the substrate, and better control of the coating process, which is particularly advantageous for large coating areas and / or substrates with complex shapes.

[0004] Single crystal diamond is highly electrically insulating, 10 -18It has the lowest specific conductivity among all substances known in S / m. To adjust its electrical, optical, and structural properties, the diamond layer can be doped using a CVD process. By appropriate doping (e.g., using elements from the IVth, Vth, and VIth main groups; using transition metals; using elements from the IVth, Vth, and VIth subgroups), diamond can be made into a semiconductor (p-type or n-type). The conductive diamond layer is used, for example, as a semiconductor material, as an electrode material in electrochemistry, such as a material for a transducer for sensors, or in microsystem technology (MEMS), or, for example, as a coating layer for detecting wear or for contact vias in printed circuit boards.

[0005] Impurity atoms can replace both C atoms at regular lattice sites and thus have purely extrinsic properties. Impurity atoms such as H, Li, B, N, O, Ne, P, Si, As, Ti, Cr, Ni, Co, Zn, Zr, Ag, W, Xe, and Tl are known to form optically active centers in diamond (A.M. Zaitsev, Optical Properties of Diamond: Data Handbook, 1st Edition, Springer, 2001). In polycrystalline diamond layers, grain boundaries play an even more important role in doping. Generally, the aim is to "incorporate" impurity atoms into the diamond lattice. The smaller the deposited diamond crystals, the higher the number of intercrystalline grain boundaries associated with a certain region. These particle boundaries contain, in particular, non-diamond-like carbon (e.g., trans-polyacetylene; Frederik Klauser, Doris Steinmuller-Nethl et al.: Raman Studies of Nano- Ultra-nanocrystalline Diamond Films Grown by Hot-Filament CVD, Chemical Vapour Deposition, Vol. 16, Issue 4-6, pp. 127-135, 2010). Therefore, preferably in nanocrystalline diamond films (crystallites in the range of 2 - 100 nm), boron can be incorporated not only into the diamond lattice but also into the amorphous grain boundaries.

[0006] The use of boron-doped diamond layers in particular is widespread because boron atoms have an atomic radius similar to that of carbon atoms, meaning that the lattice strain when incorporating boron atoms into the carbon lattice is relatively low. Boron has three outer electrons, one less than carbon, so boron acts as an electron acceptor in the carbon lattice and boron-doped diamond is p-conductive. The ionization energy of boron is very low at 0.37 eV, which means that boron-doped diamond achieves good conductivity even at room temperature.

[0007] As described in US 2013 / 0234165 A1, solid, liquid or gaseous boron sources can be used in the CVD process to deposit boron-doped diamond layers. The use of liquid or gaseous (usually toxic) boron sources is particularly widespread. In US 10,487,396 B2, CN 108396309 A, CN 111778506 A and CN 111304690 A, gaseous boron-containing precursors are used, while in CN 108565124 B, trimethyl borate is used as a liquid boron-containing precursor. In CN 104862663 A, for example, acetone is used as a carbon source and trimethyl borate is used as a liquid boron source, whereby a boron-doped nanodiamond film with a layer thickness of 1 to 10 μm is deposited on a single-crystalline silicon substrate.

[0008] The large-scale use of liquid or gaseous precursors other than carbon in the CVD process is often associated with health risks. For example, boron or boron compounds such as diborane (also called borane ethane) or trimethyl borate are highly toxic, and absorption into the human body can lead to chronic poisoning or damage to the central nervous system and skin. In addition, diborane is highly self-igniting and explosive and can cause severe burns, and trimethyl borate is highly corrosive, which can damage the equipment used in the CVD process and shorten its service life if used for a long time.

[0009] Using solid non-carbon precursors (instead of liquid or gaseous ones) in the CVD process has very significant advantages in terms of safety and health. Methods for producing diamond coatings doped with solid non-carbon precursors in the CVD process have been disclosed in several documents.

[0010] In the methods described in CN 111945131 A and CN 112063996 A, solid boron carbide particles are evenly distributed around the substrate. Hydrogen, argon, and methane are used as process gases. Boron and carbon radicals are generated from boron carbide particles by radiation using microwave plasma, and a boron-doped diamond layer is deposited on the substrate surface. In CN 110527973 A, a carbon source (graphite powder) and a boron source (boron powder or boron oxide powder) are mixed and pressed into a bulk material for wafer formation. In the CVD process, some of these wafers are evenly arranged around the substrate, and a gas is supplied, which is either hydrogen or a mixed gas of hydrogen, methane, and an inert gas. The gas is activated by microwave radiation to generate plasma.

[0011] In summary, the CVD processes known in the prior art for manufacturing doped diamond coatings typically use gaseous or liquid precursors different from carbon, which involve health and safety risks. In the few known CVD processes that use solid precursors other than carbon, the process gas is solely activated by plasma. However, plasma activation can damage the crystal structure of the substrate material, and it is very difficult to achieve a homogeneous coating on three-dimensional objects.

Summary of the Invention

[0012] Therefore, an object of the present invention is to generate a doped diamond layer by a CVD process that does not use plasma using a solid precursor different from carbon, thus avoiding the drawbacks of the CVD processes known in the prior art.

[0013] This problem is solved by the device according to claim 1 and the method according to claim 8. Preferred embodiments are described in the dependent claims.

[0014] The present invention relates to an apparatus for applying a diamond layer doped by chemical deposition to a substrate, the apparatus comprising a deposition chamber for receiving the substrate, a gas activation element in the form of a hollow body having a flow path for a process gas, in particular hydrogen, an outlet opening leading from the flow path to the deposition chamber, a heating device for heating the wall of the gas activation element surrounding the flow path, and a solid precursor other than carbon in the flow path.

[0015] Furthermore, the present invention relates to a method for applying a diamond layer doped by chemical vapor deposition to a substrate, the method comprising the following steps. (a) Providing a substrate and a gas activation element in the form of a hollow body having a flow path in a deposition chamber, (b) Providing a precursor other than solid carbon in the flow path, (c) Heating the wall surrounding the flow path of the gas activation element with a heating device, (d) Introducing a process gas, in particular hydrogen, into the flow path of the gas activation element, (e) Activating the process gas by shock excitation and thermal excitation, and activating the precursor by thermal excitation, (f) Introducing the activated process gas and the activated precursor into the deposition chamber via the outlet port of the gas activation element, (g) Depositing a doped diamond layer on the substrate.

[0016] The present invention also relates to the use of an apparatus for thermal excitation and shock excitation of a process gas and thermal excitation of a solid precursor other than carbon for depositing a diamond layer doped by chemical vapor deposition on a substrate.

[0017] Surprisingly, it has been found that by providing a solid non-carbon precursor in the flow path of the gas activation element of the CVD apparatus according to the present invention, it is possible to deposit a uniformly doped diamond layer on a substrate. By using a solid, non-carbon precursor for doping, it is possible to completely avoid the negative effects on health and / or process safety that occur with liquid or gaseous, non-carbon precursors. The use of combined activation by thermal activation and shock excitation enables the deposition of a uniform doped diamond layer even on a three-dimensional substrate.

[0018] A process gas, preferably hydrogen or a mixture with another gas such as a carbon-containing gas, is supplied via a gas supply element to a gas activation element preferably arranged perpendicular thereto. The gas activation element is a formation of a hollow body having a lateral surface, and has a flow path for the process gas and a wall surrounding the flow path heated by a heating device. The process gas is preferably introduced into the flow path of the gas activation element via two gas supply elements arranged at two end regions of the lateral surface of the gas activation element. Thereby, a uniform distribution of the process gas in the flow path of the gas activation element is ensured.

[0019] The wall of the gas activation element is preferably heated over its entire length by a heating device to ensure a uniform temperature distribution. For this purpose, the wall of the gas activation element is connected to a heating device that heats the wall of the gas activation element. The wall of the gas activation element is preferably heated by a resistance heater. Thereby, simple and accurate control of the heating process becomes possible.

[0020] The process gas and solid precursors other than carbon arranged in the flow path of the gas activation element are preferably heated to at least 2000 °C, preferably at least 2200 °C, particularly preferably at least 2400 °C, to achieve good thermal excitation of the process gas. The process gas, particularly preferably hydrogen, is activated by shock excitation and thermal excitation, while solid precursors different from carbon are activated by thermal excitation. Then, the activated process gas and the activated solid precursors are transported through at least one outlet opening of the gas activation element to a substrate arranged in a deposition chamber.

[0021] The cross-sectional area of the flow path is preferably in the range of 0.1 - 50 mm 2 and preferably 5 - 30 mm 2The range is particularly preferred. This increases the impact excitation with the wall surface. The flow path of the gas activation element is preferably closed at both ends by, for example, end bodies so that the gas activation element does not have other openings away from the inlet opening and the outlet opening. The ratio between the area of exactly one outlet opening and the cross-sectional area of the gas activation element is preferably 1:5 to 1:20, particularly 1:10, which further increases the excitation rate of the process gas. Since the number of openings is small and the flow path is closed at both ends, the partial pressure of the flow path of the gas activation element increases significantly, which is several times higher than the pressure in the deposition chamber. In addition to thermal excitation, this high partial pressure also enables impact excitation (i.e., collision-induced dissociation) of the process gas, which is preferably hydrogen, resulting in a very high yield of atomic hydrogen. This combined activity consisting of thermal excitation and impact excitation can achieve an excitation rate of 80% or more of atomic hydrogen, while only thermal excitation results in an excitation rate of up to 30%. This high excitation rate combining thermal excitation and impact excitation enables the acceleration of the growth of a highly pure doped diamond layer and energy-efficient deposition at a high growth rate.

[0022] Due to the high excitation rate by the combination of thermal excitation and impact excitation, the mean free path length of the hydrogen radicals can increase up to several centimeters. This makes it possible to increase the distance between the gas activation element and the substrate, and significantly improves the homogeneity of the deposited doped diamond layer.

[0023] In a preferred embodiment of the present invention, the solid precursor other than carbon is preferably selected from the group consisting of boron, silicon, lithium, sodium, phosphorus, nitrogen, sulfur, arsenic or combinations thereof. These elements are particularly suitable for doping the diamond layer, for example, for incorporation into the diamond lattice, and make it possible to impart specific properties such as conductivity to the diamond layer. The solid precursor can be provided in various forms, for example, in the form of particles (e.g., chips, powders), or in the form of wires. Since the boron-doped diamond layer has very good conductivity, the solid precursor different from carbon is preferably a boron-containing precursor. For ease of handling, boron-containing particles, boron-containing wires or combinations thereof are particularly preferred or preferred as the solid precursor.

[0024] In the present invention, when a boron-containing wire is used as the solid precursor, its diameter is preferably in the range of 0.05 to 2.2 mm, and particularly preferably in the range of 0.1 to 0.5 mm. This makes it possible to vary and very precisely adjust the degree of doping in order to customize the properties of the deposited doped diamond layer. Furthermore, this range of diameters ensures that the reservoir of the solid precursor in the flow path can be used for a long time and enables the production of a doped diamond layer with a greater layer thickness.

[0025] In a preferred embodiment, the boron-containing wire is basically arranged along the entire length of the flow path of the gas active element. This results in a particularly uniform and homogeneous doping of the entire diamond layer. Furthermore, several, preferably two or three, boron-containing wires are preferably provided as the solid precursor in the flow path of the gas active element. This not only ensures very good process control, but also the deposited doped diamond layer is very homogeneous.

[0026] In order to adjust the doping concentration accordingly, the structure or chemical composition of the solid precursor can be changed. For example, in the case of a boron-containing wire, the core of the wire can be composed of a chemical element or compound other than boron, such as tungsten or tantalum. This not only ensures stable process control but also achieves the best results regarding the homogeneity and conductivity of the boron-doped diamond layer.

[0027] Depending on the desired doping concentration, a corresponding amount of the solid precursor is provided in the flow path and can be evaporated in a controlled manner using process parameters. The doping concentration in the diamond layer can be affected in a controlled manner by various parameters. On the one hand, the doping concentration can be controlled in both the process parameters, such as the flow rate, temperature, and pressure of the process gas, the flow path, and the deposition chamber. On the other hand, the doping concentration can be affected by the geometric shape of the device according to the invention, such as the number and / or geometric shape of the outlet openings, the distance of the substrate from the gas activation element, and the amount of the solid precursor.

[0028] Due to the preferably horizontal arrangement of the gas activation element in the deposition chamber, the solid precursor can be arranged in the flow path so as to rest on the outside / lateral surface inside of the gas activation element at the bottom. If the ends of the flow path are closed, for example, by end bodies, the solid precursor can also be alternatively attached to these closed ends and thus can be arranged at any possible position in the flow path.

[0029] In a preferred embodiment of the present invention, a gas inlet element for introducing an additional process gas, in particular a carbon-containing process gas, is arranged in the deposition chamber in such a way that the additional process gas flows over the heated wall of the gas activation element. Other, preferably carbon-containing process gases can be used, preferably methane, but also other carbon-containing process gases such as ethylene or acetylene. This additional process gas is thermally activated by flowing over the heated wall of the gas inlet element, so that carbon-containing radicals such as methyl radicals are formed by homolytic fission. The effectiveness of the excitation is further increased by the collision of the activated hydrogen with the carbon-containing process gas. The highest possible excitation rate of hydrogen achieved in the device according to the invention by combining thermal excitation and shock excitation is very important for achieving a high excitation rate of the carbon-containing process gas. The formed carbon-containing radicals can be deposited on the substrate surface not only in the form of sp 3 -hybrid carbon (diamond), but also as spand / or sp 2 -hybrid carbon. However, the activated hydrogen atoms prevent or remove these unwanted sp and sp 2 hybridization forms, so that sp 3 hybridization, and thus the formation of a pure doped diamond structure, is promoted. The greater the amount of activated hydrogen, the more efficient the suppression or removal of unwanted hybrid formation. This enables the deposition of high-purity doped diamond crystals in the micrometer and / or nanometer range on the substrate.

[0030] The activated process gas, preferably hydrogen, and the activated precursor are introduced from the gas activation element into the deposition chamber through an outlet opening preferably located on the outer / lateral surface of the gas activation element. The outlet opening is preferably oriented laterally rather than vertically downward to prevent the precursor from flowing out in a molten state. Also, several outlet openings can be provided at defined (regular or irregular) distances from each other, which are preferably arranged alternately at an angle to each other and cover a larger volume range for coating. This is particularly advantageous when coating a three-dimensional substrate. The shape and arrangement of the outlet openings depend on the required activity and flow rate. By having a large number (preferably small) of outlet openings, the process gas is evenly distributed in the deposition chamber, and as a result, the deposited doped diamond layer has a very uniform thickness and a very high degree of homogeneity. The advantageous arrangement and geometry of the outflow openings can be determined by flow simulations for each CVD apparatus. Accordingly, by arranging several outlet openings, the process gas can be introduced into the deposition chamber in a spatially evenly distributed manner, and as a result, a homogeneous deposition is ensured over the entire substrate surface. The flow of the process gas together with the precursor through the outlet openings is not hindered due to the small particle size. Depending on the position of the substrate, the gas activation element can be arranged above or on the side of the substrate.

[0031] Hydrogen and a carbon-containing process gas can be introduced separately into the deposition chamber. Hydrogen is supplied to the deposition chamber through a gas activation element, and the carbon-containing process gas is supplied through a gas inlet element through a high-temperature gas activation element. This provides greater flexibility with respect to process parameters. For example, separate introduction allows for spatially and / or temporally separated gas inlets. As a result, the temperature, the gas inlet velocity into the deposition chamber, the time sequence and / or concentration of these components of the process gas can be adjusted individually. These parameters can be optimized for coating processes with different requirements, and can be adapted, for example, to the thickness of the doped diamond layer, its purity, grain size, doping concentration, the duration of the coating process, the substrate material and / or the substrate shape.

[0032] Alternatively, the carbon-containing process gas can also be introduced into the deposition chamber together with hydrogen through a gas activation element and can be activated by thermal excitation. This simplifies process control and the design of the apparatus since no gas inlet element for introducing the carbon-containing process gas into the deposition chamber is required.

[0033] The weight ratio of hydrogen to the carbon-containing process gas is preferably in the range of 95:5 to 99.99:0.01, depending on the desired form. To accelerate diamond growth, additional process gases, such as nitrogen, oxygen and / or argon, can be used as required, and these can be supplied by one or more gas injection / injection elements.

[0034] In order to preferably form a diamond layer on the surface of the substrate, the deposition chamber is preferably operated under reduced pressure. This ensures a high degree of purity and homogeneity of the deposited doped diamond layer. For this purpose, the deposition chamber is evacuated before and during the deposition process. For this purpose, it is preferably arranged outside the device a vacuum pump, which generates the vacuum necessary for the deposition process in the deposition chamber. The pressure in the deposition chamber is preferably in the range of 0.5 to 50 mbar, particularly 1 to 10 mbar. The partial pressure of the gas active element flow path is preferably a multiple of the pressure of the deposition chamber.

[0035] In the known HFCVD process, due to the low excitation rate of the process gas, a small distance (usually in the range of 5 to 10 mm) between the gas active element and the substrate must be selected, which results in a highly non-uniform temperature distribution on the substrate surface, high temperature, generation of local concentration of atomic hydrogen, and as a result, non-uniform coating. In the process according to the invention, the relatively high excitation rate of the process gas makes it possible to provide a greater distance between the gas active element and the substrate surface, which is preferably in the range of 20 to 100 mm, particularly preferably in the range of 40 to 60 mm. In the process according to the invention, this greater distance between the gas active element and the substrate ensures a uniform temperature distribution on the substrate surface.

[0036] Usable substrate materials include hard metals, silicon wafers, titanium implants, electrode materials (e.g., silicon, titanium, tantalum, tungsten, molybdenum, copper, niobium), graphite, sapphire, high melting point glass and / or quartz. In order to further improve the adhesion of the coating, the surface of the base material can also be pretreated, if necessary, for example, to increase the roughness and thus increase the mechanical anchor / adhesion.

[0037] The substrate temperature ranges from 500 to 950 °C depending on the parameters of the substrate and the coating. Preferably, a substrate temperature in the range of 750 to 850 °C is used, whereby a very homogeneous and doped diamond layer is deposited. It should be noted that at lower temperatures (lower than the preferred temperature range, for example, 600 °C or lower), the growth rate is correspondingly lower. This may require adjustment of the process parameters. The substrate to be coated can be placed inside the deposition chamber on a substrate holder that is preferably positioned below or laterally to the gas activation element in the operating state of the deposition chamber. Depending on the temperature resistance / stability of the substrate, the substrate holder can be connected to a cooling device. Due to the possibility of cooling the substrate and the relatively large distance between the substrate and the gas activation element, more temperature-sensitive substrates such as glass can also be coated, whereby the substrate temperature for more temperature-sensitive substrates is preferably in the range of 500 to 700 °C. This enables the deposition of a uniformly doped diamond layer, thereby simultaneously avoiding damage to more temperature-sensitive substrates.

[0038] The orientation of the gas activation element can preferably be adapted to the shape of the substrate. The gas activation element is preferably arranged horizontally in the deposition chamber and thus parallel to the substrate surface. This ensures a uniform distance between the gas activation element and the substrate and, in particular, in the case of two-dimensional substrates, enables the doped diamond layer to have a uniform thickness across the entire substrate surface. The gas activation element can also be arranged inside the hollow substrate to be coated (e.g., inside a forming tool or a stretching die) or on the side surface of a complex 3D substrate. By arranging several outlet openings on the corresponding side surface of the gas activation element, a uniform coating inside the hollow substrate or the 3D structure can then be achieved.

[0039] In a preferred embodiment of the present invention, several gas activation elements are provided in the deposition chamber. This is advantageous, for example, for coating large-area substrates such as silicon wafers or for coating three-dimensional substrates. It is also possible to coat several substrates simultaneously. The heating device can be designed in such a way that the gas activation elements can be heated separately, together, or in several groups. Also, the various gas activation elements can be connected to separate gas supply lines, and various process gases can be supplied to the deposition chamber of the individual gas activation elements. In this way, the properties of the coating can be adjusted locally, for example, the doping concentration in a doped diamond layer and the resulting properties such as conductivity.

[0040] The gas activation elements or the shape and arrangement of the gas activation elements can be of any design, and preferably, they are oriented to the shape of the substrate to be coated. When several gas activation elements are used, they are preferably arranged parallel to each other. This enables the entire substrate surface to be coated uniformly. When coating a two-dimensional substrate, all the gas activation elements are preferably arranged parallel and at the same distance from the substrate. By selecting the respective distances accordingly, a uniform temperature distribution and, accordingly, a uniform coating of the substrate are ensured.

[0041] The substrate located on the substrate holder below the gas activation system is preferably moved in a horizontal plane. The substrate arranged on the side of the gas activation element can be moved by rotation. Naturally, the speed at which the substrate moves is adapted to the process parameters.

[0042] All embodiments of the present invention are interrelated, and any disclosed embodiment and / or feature can be combined with each other, or can also be in any combination of two or more embodiments and / or features.

[0043] For the purposes of the present disclosure, terms such as "top", "upper part", "bottom", "lower part", "above", "upper", "below", "lower" refer to the intended operating state of the CVD apparatus.

[0044] In the present application, the term "process gas" refers to both a single gas (such as hydrogen) and a gas mixture (composed of another gas such as a hydrogen and a carbon-containing gas), unless explicitly disclosed otherwise.

[0045] The present invention will be further described below with reference to the preferred embodiments and descriptions of the drawings, but is not limited thereto.

Brief Description of the Drawings

[0046]

Figure 1

Figure 2a

Figure 2b

Figure 3a

Figure 3b

Figure 4a

Figure 4b

Figure 5a

Figure 5b

Figure 5c

Figure 5d

DETAILED DESCRIPTION OF THE INVENTION

[0047] Figure 1 shows an apparatus 1 for applying a doped diamond layer to substrates 2, 2a. In the design shown, the doped diamond layer is deposited on the outside of substrate 2 on one hand and on the inside of substrate 2a on the other hand. This apparatus 1 has a deposition chamber 3 for holding the substrates 2, 2a. Also provided is a gas and electrical supply element 4. The gas and electrical supply element 4 has an inner element 5a for supplying a process gas (preferably hydrogen) and an outer element 5b made of a conductive material for supplying an electric current.

[0048] As can also be seen from Figure 1, the gas and electrical supply element 4 inside the deposition chamber 3 is connected to a gas activation element 7 arranged horizontally in an arrangement shown such that the process gas can be supplied to the gas activation element 7 via the inner element 5a of the gas and electrical supply element 4 through a clamp screw connection 6. Inside the gas activation element is a solid precursor other than carbon, which is provided in the formation of wire 11. Further, a heating device 8 is shown (only schematically), by which the wall 7a of the gas activation element 7 is heated.

[0049] In the embodiment shown in FIG. 1, the heating device 8 has a power source 8a (shown symbolically only), and can conduct current to the gas activation element 7 through the outer element 5b of the gas and electrical supply element 4. The current is converted into heat by the resistance of the material of the gas activation element 7, whereby the gas activation element 7 is heated. The wall 7a of the gas activation element 7 is heated such that the flow path 7b of the gas activation element is heated to at least 2000 °C. As a result, the process gas is activated by thermal excitation and shock excitation, and the solid precursor is activated by thermal excitation. For this purpose, the wall 7a of the gas activation element 7 is made of a high-temperature resistant material. The electrical insulator 9 is made of, for example, a ceramic material, and is also provided between the outer element 5b of the gas and current supply element 4 and the housing of the deposition chamber 3.

[0050] FIG. 1 also shows a gas inlet element 10 vertically arranged at the top of the deposition chamber 3 in the version shown in the figure, through which a carbon-containing process gas (preferably methane) can be introduced into the deposition chamber 3. The carbon-containing process gas is thermally excited by flowing through the heated wall 7a of the gas activation element 7, and as a result, carbon-containing radicals (e.g., methyl radicals) are generated. Alternatively, the carbon-containing process gas can be introduced into the deposition chamber 3 together with hydrogen at a specified mixing ratio through the heated gas activation element 7 and thereby activated. Other process gases, such as nitrogen, oxygen or argon, can also be supplied through other gas inlet elements (not shown). A substrate holder 13 on which the substrates 2, 2a are arranged is disposed inside the deposition chamber 3 and below the gas activation element 7. The substrate holder 13 can be heated or cooled via a temperature control element 14 (shown schematically).

[0051] FIGS. 2a, 3a and 4a show embodiments of the gas activation element 7, in the flow path 7b of which a solid precursor other than carbon is provided longitudinally in the form of a wire 11. FIGS. 2b, 3b and 4b each show a section through the gas activation element 7. It can be seen from FIGS. 2 to 4 that the number of wires 11 provided in the flow path 7b is different. In FIG. 2, one wire 11 is provided in the flow path 7b, in FIG. 3, two wires 11 are provided, and in FIG. 4, three wires 11 are provided.

[0052] Furthermore, as shown in FIGS. 2a to 4b, the gas activation element 7 has an inlet opening 15 in each of the two end regions, through which a process gas (preferably hydrogen) is supplied to the flow path 7b of the gas activation element 7. In addition, the gas activation element 7 has a plurality of outlet openings 16 arranged in the longitudinal direction of the gas activation element 7 laterally on its lateral surface. The activated process gas and the activated precursor are channeled through these outlet openings 16 in the direction of the substrates 2 and 2a, and the direction of the flow is indicated by the arrow 17. Furthermore, an end body 18 for closing the flow path 7b at the end of the gas activation element 7 can be seen schematically.

[0053] FIGS. 5a to 5d show SEM images of a boron-doped, microcrystalline diamond layer on a tungsten carbide-cobalt hard metal tool (WC-Co hard metal tool) with a layer thickness of 10 μm. A boron wire of type B 005915 from Goodfellow Cambridge, UK was used in the flow path of the gas ionization element. Hydrogen and methane were used as the process gas in a weight ratio of 99.8:0.2. The pressure in the deposition chamber was 1 mbar and the substrate temperature was 850°C. In FIG. 5a, a boron wire was used as the solid precursor (type B 005915, Goodfellow Cambridge Ltd., UK). FIGS. 5b to 5d show the doped diamond layer, for the production of which two boron wires (type B 005915) were used as the solid precursor, with different magnifications.

[0054] (Example) The following examples are intended to further illustrate the invention as described in this application without limiting the scope of the invention.

[0055] WC-Co cemented carbide tools were coated with diamond coatings of different boron concentrations. One to three boron-containing wires (type B 005915, Goodfellow Cambridge Ltd., UK) were used as solid precursors in the gas activation element flow path. These are continuous single fibers with a tungsten core (core diameter 5 μm), wire diameter 0.2 mm, and wire length 140 mm. The process parameters were kept constant for all coatings. Hydrogen and methane were used as process gases at a weight ratio of 99.8:0.2. The pressure in the deposition chamber was 1 mbar and the substrate temperature was 850 °C.

[0056] The concentration of boron atoms in the boron-doped diamond layer produced according to the present invention was determined using secondary ion mass spectrometry (SIMS). Boron atoms 10 20 ~10 21 / cm 3 As a result of measuring the boron concentration, the boron concentration changed depending on the penetration depth (maximum 1.5 μm). As shown in Table 1, the sheet resistance and specific resistance of the boron-doped diamond layer decreased significantly with an increase in the number of boron-containing wires (used for the production of the boron-doped diamond layer according to the present invention) and accordingly with an increase in the boron concentration, resulting in a significant increase in conductivity.

[0057] Table 1 shows the resistance measurement (two-point method, length 10 mm) of diamond films prepared by changing the number of boron wires (microcrystalline diamond film, film thickness 10 μm, substrate: WC-Co cemented carbide).

Table 1

Claims

1. An apparatus (1) for applying a doped diamond layer to a substrate (2, 2a) by chemical vapor deposition, a deposition chamber for accommodating the substrate (2, 2a), a gas activation element (7) in the form of a hollow body having a flow path (7b) for a process gas, an outlet opening (16) leading from the flow path (7b) to the deposition chamber (3), a heating device (8) for heating a wall (7a) of the gas activation element (7) surrounding the flow path (7b), a solid precursor other than carbon inside the flow path (7b), and the apparatus (1) comprising the same.

2. The apparatus (1) according to claim 1, characterized in that the solid precursor is selected from the group consisting of boron, silicon, lithium, sodium, phosphorus, nitrogen, sulfur, arsenic, and combinations thereof.

3. The apparatus (1) according to claim 2, characterized in that at least one of boron-containing particles, boron-containing wires, and combinations thereof is provided as the solid precursor.

4. The apparatus (1) according to claim 3, characterized in that the boron-containing wire is arranged in the longitudinal direction of the flow path (7b).

5. The apparatus (1) according to claim 3 or 4, characterized in that the boron-containing wire has a diameter in the range of 0.05 to 2.2 mm.

6. The apparatus (1) according to claim 3 or 4, characterized in that several of the boron-containing wires are provided as the solid precursor.

7. The apparatus (1) according to any one of claims 1 to 4, characterized in that a plurality of the gas activation elements (7) are provided in the deposition chamber (3).

8. A method for applying a doped diamond layer to a substrate (2, 2a) by chemical vapor deposition, comprising: (a) providing in a deposition chamber (3) the substrate (2, 2a) and a gas activation element (7) in the form of a hollow body having a flow path (7b); (b) providing a solid precursor other than carbon inside the flow path (7b); (c) heating a wall (7a) of the gas activation element (7) surrounding the flow path (7b) with a heating device (8); (d) introducing a process gas into the flow path (7b) of the gas activation element (7); (e) activating the process gas by impact excitation and thermal excitation, and activating the precursor by thermal excitation; (f) introducing the activated process gas and the activated precursor into the deposition chamber (3) through an outlet opening (16) of the gas activation element (7); (g) depositing the doped diamond layer on the substrate (2, 2a). A method comprising the above steps.

9. The method according to claim 8, wherein the solid precursor is selected from the group consisting of boron, silicon, lithium, sodium, phosphorus, nitrogen, sulfur, arsenic, and combinations thereof.

10. The method according to claim 8 or 9, wherein at least one of boron-containing particles, boron-containing wires, and combinations thereof is provided as the solid precursor.

11. The method according to claim 8 or 9, wherein a gas inlet element (10) for introducing an additional process gas is arranged in the deposition chamber (3) such that the additional process gas flows over a heated wall (7a) of the gas activation element (7).

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