APPARATUS AND METHOD FOR PRODUCING DOPED DIAMOND LAYERS

Abstract

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

Claims

1. A device for applying a doped diamond layer to a substrate by chemical vapour deposition, comprising: a deposition chamber for receiving the substrate, a gas activation element in the form of a hollow body with a flow channel for a process gas, an outlet opening leading from the flow channel into the deposition chamber, a heating device for heating a wall of the gas activation element, said wall surrounding the flow channel, and a solid, precursor other than carbon within the flow channel.

2. The device according to claim 1, wherein the solid precursor is selected from the group comprising boron, silicon, lithium, sodium, phosphorus, nitrogen, sulphur, arsenic or a combination thereof.

3. The device according to claim 2, wherein boron-containing particles, a boron-containing wire or a combination thereof is or are provided as a solid precursor.

4. The device according to claim 3, wherein the boron-containing wire is arranged in the longitudinal direction of the flow channel.

5. The device according to claim 3, wherein the boron-containing wire has a diameter in the range from 0.05 to 2.2 mm.

6. The device according to claim 3, wherein several boron-containing wires are provided as the solid precursor.

7. The device according to claim 1, wherein a plurality of gas activation elements are provided in the deposition chamber.

8. A process for applying a doped diamond layer to a substrate by chemical vapour deposition comprising the steps of: (a) providing the substrate and a gas activation element in the form of a hollow body with a flow channel in a deposition chamber, (b) providing a precursor other than carbon in the solid state inside the flow channel, (c) heating a wall of the gas activation element with a heating device, said wall surrounding the flow channel. (d) introducing a process gas, into the flow channel of the gas activation element, (e) activation of the process gas by impact excitation and thermal excitation, and activation of the precursor by thermal excitation, (f) introducing the activated process gas and the activated precursor through an outlet opening of the gas activation element into the deposition chamber, and (g) deposition of a doped diamond layer on the substrate.

9. The process according to claim 8, wherein the solid precursor is selected from the group comprising boron, silicon, lithium, sodium, phosphorus, nitrogen, sulphur, arsenic or a combination thereof.

10. The process according to claim 8, wherein boron-containing particles, a boron-containing wire or a combination thereof is or are provided as a solid precursor.

11. The process according to claim 8, wherein a gas inlet element for introducing a further process gas, is arranged in the deposition chamber in such a way that the further process gas flows over the heated wall of the gas activation element.

12. A method for thermal excitation and impact excitation of a process gas and for the thermal excitation of a solid precursor other than carbon for applying a doped diamond layer to a substrate by chemical vapour deposition, said method comprising utilizing the device of claim 1 for the thermal excitation and impact excitation of the process gas and for the thermal excitation of the solid precursor.

13. The device according to claim 1, wherein the process gas is hydrogen.

14. The device according to claim 3, wherein the solid precursor is the boron-containing wire.

15. The device according to claim 3, wherein the boron-containing wire is arranged in the longitudinal direction of the flow channel along the entire length of the flow channel.

16. The device according to claim 3, wherein the boron-containing wire has a diameter in the range from 0.1 to 1 mm.

17. The device according to claim 3, wherein two or three boron-containing wires are provided as the solid precursor.

18. The process according to claim 10, wherein the solid precursor is the boron-containing particles.

19. The process according to claim 11, wherein the process gas is a carbon-containing process gas.

20. The process according to claim 8, wherein the process gas is hydrogen.

Description

[0052] The invention is further explained below with reference to preferred embodiments and descriptions of figures, to which, however, it is not intended to be limited.

[0053] FIG. 1 shows a device according to the invention for applying a doped diamond layer to substrates by chemical vapour deposition.

[0054] FIG. 2-4 shows a gas activation element with different numbers of wires, which are provided as a solid precursor other than carbon.

[0055] FIG. 5 shows SEM images of a boron-doped diamond layer.

[0056] FIG. 1 shows a device 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 the substrate 2 on the one hand and on the inside of the substrate 2a on the other. The device 1 has a deposition chamber 3 for holding the substrates 2, 2a. A gas and electricity supply element 4 is also provided. The gas and electricity supply element 4 has an inner element 5a for supplying a process gas (preferably hydrogen) and an outer element 5b made of an electrically conductive material for supplying an electric current.

[0057] As can also be seen from FIG. 1, the gas and electricity supply element 4 inside the deposition chamber 3 is connected via a clamping screw connection 6 to a gas activation element 7 arranged horizontally in the arrangement shown in such a way that the process gas can be fed into the gas activation element 7 via the inner element 5a of the gas and electricity supply element 4. Inside the gas activation element there is a solid precursor other than carbon, which is provided in the form of a wire 11. Furthermore, a heating device 8 is shown (only schematically), with which a wall 7a of the gas activation element 7 is heated.

[0058] In the embodiment shown in FIG. 1, the heating device 8 has a power supply 8a (only symbolically illustrated), with which an electric current can be conducted to the gas activation element 7 via the outer element 5b of the gas and electricity supply element 4. The electrical current is converted into heat due to the resistance of the material of the gas activation element 7, which causes the gas activation element 7 to heat up. The wall 7a of the gas activation element 7 is heated so that a flow channel 7b in the gas activation element is heated to at least 2000 C. As a result, the process gas is activated by thermal excitation and impact 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. Electrical insulation 9, for example made of a ceramic material, is also provided between the outer element 5b of the gas and current supply element 4 and a housing of the deposition chamber 3.

[0059] FIG. 1 also shows a gas inlet element 10 arranged vertically at the top of the deposition chamber 3 in the version shown, 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 over the heated wall 7a of the gas activation element 7, so that carbon-containing radicals (for example methyl radicals) are generated. Alternatively, the carbon-containing process gas can also be introduced into the deposition chamber 3 together with hydrogen in a defined mixing ratio through the heated gas activation element 7 and thereby activated. Other process gases, for instance nitrogen, oxygen or argon, can also be fed in via other gas inlet elements (not shown). A substrate holder 13, on which the substrates 2, 2a are arranged, is located 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).

[0060] FIGS. 2a, 3a and 4a show an embodiment of the gas activation element 7, in whose flow channel 7b a solid precursor other than carbon in the form of a wire 11 is provided in the longitudinal direction. FIGS. 2b, 3b and 4b each show a section through the gas activation element 7. It can be seen that FIGS. 2-4 differ in the number of wires 11 provided in the flow channel 7b. In FIG. 2, one wire 11 is provided in the flow channel 7b, in FIG. 3 two wires 11 are provided and in FIG. 4 three wires 11 are provided.

[0061] As further shown in FIGS. 2-4, the gas activation element 7 has an inlet opening 15 in each of the two end regions, through which the process gas (preferably hydrogen) is fed into the flow channel 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 channelled through these outlet openings 16 in the direction of the substrates 2 and 2a; the direction of flow is illustrated by arrows 17. Furthermore, end bodies 18 for closing the flow channel 7b at the ends of the gas activation element 7 can be seen schematically.

[0062] FIG. 5a-d show SEM images of a boron-doped, microcrystalline diamond layer on a tungsten carbide-cobalt hard metal tool (WCCo hard metal tool) with a layer thickness of 10 m. Boron wires of type B 005915, Goodfellow Cambridge Ltd, England, were used in the flow channel of the gas activation element. Hydrogen and methane were used as process gases 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 a solid precursor (type B 005915, Goodfellow Cambridge Ltd., England). FIGS. 5b-d show a doped diamond layer, for the production of which two boron wires (type B 005915) were used as a solid precursor, at different magnifications.

EXAMPLES

[0063] The following examples are intended to further illustrate the invention as described in this application, without limiting the scope of the invention.

[0064] A WCCo hard metal tool was coated with diamond coatings with different boron concentrations. One to three boron-containing wires (type B 005915, Goodfellow Cambridge Ltd., England) were used as a solid precursor in the flow channel of the gas activation element. These are continuous single filaments with a tungsten core (core diameter of 5 m), a wire diameter of 0.2 mm and a wire length of 140 mm. The process parameters were kept constant for all coatings. Hydrogen and methane were used as process gases 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.

[0065] The concentration of boron atoms in the boron-doped diamond layers produced according to the invention was determined using secondary ion mass spectrometry (SIMS). This measurement revealed a boron concentration in the range of 10.sup.20 to 10.sup.21 boron atoms/cm.sup.3, whereby the boron concentration varies depending on the penetration depth (up to 1.5 m). As shown in Table 1, the sheet resistance and the specific resistance of the boron-doped diamond layers decrease significantly with an increasing number of boron-containing wires (which were used for the production of the boron-doped diamond layers according to the invention) and accordingly with an increasing boron concentration, which leads to a significant increase in the electrical conductivity.

TABLE-US-00001 TABLE 1 Resistance measurement (2-point method, length: 10 mm) of a diamond coating produced with different numbers of boron wires (microcrystalline diamond coating, coating thickness: 10 m, substrate: WCCo hard metal) Layer on Sheet Specific Electrical WCCo hard metal resistance resistance conductivity substrate () ( m) (S/m) uncoated 0.3 Undoped diamond >Detection limit Boron-doped diamond 100-489 110 9.1 .Math. 10.sup.3 (1 boron-containing wire) Boron-doped diamond 13.2 2.9 0.35 (2 boron-containing wires) Boron-doped diamond 2.05 0.4 2.5 (3 boron-containing wires)