FR2850116A1 - Reactor for diamond synthesis assisted by microwave plasma has system for forcing and depositing diamond germination species on inner walls of holes in wire drawing dies - Google Patents

Abstract

The reactor for diamond synthesis assisted by microwave plasma for depositing a diamond layer on a surface incorporates a system for forcing the species responsible for diamond germination through holes in one or more wire drawing dies so that they deposit the diamond material on the holes' inner walls. The species enter the reactor through an upper inlet (5) in a chamber where a plasma ball is formed over a substrate (3) of nuclear quality graphite supporting a wire drawing die (8). The reactor has a copper tube (4) passing vertically through the center of its sole plate (2) to allow gases to be pumped just under the substrate.

Description

The present invention relates to a reactor for diamond synthesis

  assisted by microwave plasma and the dies for the drawing of metallic wires obtained by treatment in such a reactor.

  The invention sees its primary application in the reinforcement of the orifices of the dies for the drawing of metals.

  It is already known to produce the orifices of the dies in diamond inserts obtained by diamond crystallization in the vapor phase, generally by a process called chemical vapor deposition (abbreviation C.V. D.), said inserts being mounted on a support.

  One of the most used CVD processes is the microwave plasma assisted synthesis process, which is carried out in two types of reactor, the "surfaguide" reactor not shown or the "bell" type reactor shown in FIG. 1 (detailed more far) and constituting the state of the art for the present invention.

  The main drawbacks of this process are: - currently known application limited to flat substrates - difficulty in locating the plasma Inserts of the aforementioned type are for example described in patents EP O 494 799 or EP O 652 057, they are obtained by deposition CVD on a flat substrate which is then cut and perforated and then mounted on a support.

  The main disadvantages of the inserts are their costs, their irregular wear.

  The invention overcomes all the drawbacks of the prior art by proposing a reactor for implementing a diamond synthesis technique assisted by microwave microwave for the deposition of a layer of diamond on a wall, characterized in that 'It includes means for forcing the species responsible for the germination of the diamond to penetrate and deposit on the internal wall of the hole of one or more dies for the drawing of metal wires.

  Preferably, the reactor is a bell type reactor in which the species enter the reactor via a high inlet, are led into a chamber where the plasma ball is formed above a substrate carrier, the gas pumping being positioned in below the substrate holder, characterized in that the gas pumping is positioned in the center of the bottom of the reactor, in the central axis of the substrate holder, one or more dies being installed on the substrate holder so that the axis of the hole emerging from each die is parallel to that of the substrate holder 35.

  For this purpose, a copper tube is provided which crosses the hearth in its center and vertically to allow the pumping of the gases just below the substrate carrier.

  Preferably, the substrate holder is mounted on a rotary assembly, comprising a motor and a pumping means in the axis of the substrate holder.

  In addition, the rotary assembly comprises: - in the upper part a circular plate comprising a plurality of through-cut lamella holes for receiving the dies, - an interface plating a tuning disc by screwing on a rotary plug.

  The interface comprises a hollow cylindrical upper part on which the plate carrying the dies is positioned, a circular flange resting on the tuning disc, a tube with external thread for screwing into the internal thread of the rotary plug.

  In addition, the cylindrical rotary plug has a peripheral shoulder to rest on the copper tube which constitutes the pumping tunnel and which also contains the rotation shaft connecting the substrate carrier to the motor.

  The pumping outlet is then provided laterally in the copper tube.

  Ball bearings are used to center the shaft for the lower 20 ball bearings, and to support the mass of the axle for the upper bearing.

  In addition, the substrate holder consisting of two coaxial cylindrical parts crossed by a hole of coaxial diameter with the pumping axis, with an upper part of larger diameter than d, in which the die is placed, a lower part dipping to the inside the copper tube.

  In this case, provision is made to close the space between the copper tube and the substrate holder with an intermediate graphite disc pierced in its center, the lower part of the substrate holder is then adjusted to the orifice.

  A die according to the invention and comprising a through hole is characterized in that the internal wall of the through hole is completely or at least partially coated with a layer of diamond deposited directly on the tungsten carbide surface by a synthetic technique of diamond in vapor phase assisted by microwave plasma.

  The invention will be better understood using the description below made with reference to the following appended figures: - Figure 1: diagram of a reactor of the state of the art.

  - Figure 2: diagram of the reactor of Figure 1 modified for the implementation of the invention.

  - Figure 3: diagram of a modified substrate holder given by way of non-limiting example.

  - Figure 4: diagram showing the modification of pumping, in accordance with a substrate holder according to Figure 3 - Figure 5: Diagram of an optional rotary assembly for the implementation of the invention.

  Reference is first made to FIG. 1 of the state of the art. The mixture of 10 gases enters the reactor (a) via a high inlet (b), is led into a chamber (c) where a plasma ball (d) is formed above a flat substrate (e) placed on a fixed copper support (f) forming a susceptor carried by a quartz tube (k) and surrounded by a cooled screen (g).

  The microwave wave ensuring the wave / gas interaction is generated by a generator (h) and conducted by a waveguide opening directly onto the top of the chamber (c) near an antenna (i).

  The pumping (j) of the gases is positioned on the bottom of the reactor between the wall of the chamber and the quartz tube (k).

  The processing of the dies requires numerous modifications to a microwave plasma-assisted chemical vapor deposition reactor, initially designed to treat flat substrates. In fact, the surfaces to be treated are those of a deeper than wide cavity and are difficult to immerse in the microwave plasma. It is then necessary to force the species responsible for the germination of the diamond to penetrate and deposit on the walls of the die. The inventors have moved the pumping system so that convection in the reactor is favorable to this configuration. The substrate holder too must be modified, not only to promote deposition on the internal walls but also to avoid hot spots, which degrade the adhesion of deposits.

  The size of the dies makes it possible to envisage processing several dies 30 simultaneously, for example four. To increase the uniformity of the deposits on each of them, the inventors installed an optional rotating substrate holder incorporating the first modifications above (pumping and substrate holder).

  The dies treated according to the invention have a through hole, the internal wall of which is completely or at least partially coated with a layer of diamond deposited directly on the tungsten carbide surface. This layer covers at least the height of the most stressed part during the drawing.

  We now detail each of the modifications by referring to Figures 2 to 5: - The pumping means (see Figure 2): To force the species responsible for diamond growth to pass 5 inside the cavity of the hollow body , the evacuation (1) of the gases is moved inside the reactor. Formerly located on the floor of the reactor but on the wall side (Figure 1), the gas outlet is positioned in the center of the floor (2). To force the "flow" of the species at the level of the substrate holder (3) a copper tube (4) is provided crossing the hearth (2) in its center and vertically, this arrangement 10 allows the pumping of the gases just below of the substrate holder (3).

  This configuration makes it possible to have a vertical flow of the species in the reactor: these enter via a high inlet (5) of the reactor, at the level of the microwave antenna (6), and are evacuated by the tube in central copper (4).

  - The substrate holder (see Figures 3 and 4): Centered pumping can be optimized by modifying the substrate holder (3). The latter must meet two characteristics: the first is not to cause hot spots on the die during treatment. The second is to best promote the penetration of the deposit into the pressurization corridor of the die.

  A first possibility consists in placing a die with its horizontal working axis on a substrate holder (3) intended for the treatment of flat products. This particular position of the die on the substrate carrier allows it to have its inlet and outlet in contact with the microwave plasma. The penetration of the deposit into the cavity is made favorable. Note however the formation of a hot micro plasma 25 caused by a significant antenna effect on the blank of the die. This micro plasma generates a significant thermal gradient in the sector. After cooling, the thermal stresses then generated by this type of heterogeneous heating cause the diamond film to loosen.

  To eliminate this drawback and the effects of spikes on the dies, a new substrate holder (7) is provided, the diagram of which is shown in FIG. (3). It consists of two coaxial cylindrical parts, crossed by a hole of diameter (d). The upper part (7a) of the substrate holder has a larger diameter (dl) than d, for example 22 mm, a counterbore with a predetermined depth (h), for example 4.5 mm, and a diameter (A) capable of receiving a die with its vertical axis. This must be deep enough not to cause hot spots and not too far from the microwave discharge to promote the establishment of the coating. The lower part of the substrate holder, narrower and longer, for example with a length I = 20 mm, must plunge inside the copper tube of the pumping system, to force the flow of gases in said tube copper (4). By way of example, two types of substrate holder have been designed to receive two types of die with A = 11 mm and A = approximately 7 mm.

  The substrate holders (3 or 7) are made of nuclear grade graphite.

  This material has, in fact, a high density and thus makes it possible to limit the pumping losses by the porosities. On the other hand, it has a good purity which gives it a low ash rate. To promote pumping through the die hole (8) placed on a tuning disc (9), it is planned to close the space between the copper tube (4) and the substrate holder (7) with an intermediate graphite disc (10) pierced in its center (Figure 4). The lower part (7b) of the substrate holder is then fitted into the orifice (10).

  The gas inlet (5) is always carried out in the upper part near the microwave antenna (6).

  - The rotating assembly (see FIG. 5): It is optional to install a substrate holder capable of rotating during diamond syntheses. This rotational movement makes it possible to obtain a homogenization of the heating by the microwave plasma. Indeed, the microwave plasma is never perfectly symmetrical on the substrate holder because it is sensitive to the antenna effects operated by the walls of the reactor. A rotational movement of the substrate holder makes it possible to reduce these heterogeneities. This arrangement 25 is particularly suitable for the treatment of small dies which can then be treated in groups of four (for example).

  The rotary assembly must comply with the previous modifications (centered pumping, vertical gas flow). Therefore, the substrate holder as the lower part of the reactor must undergo further modifications. It must be possible to tune in the positioning of an engine with central pumping.

  The modifications made in order to install a rotating substrate holder (11) are described in FIG. 5. The upper part of the rotating substrate holder (11) is a circular plate (diameter 22 and thickness 8 for example) in nuclear grade graphite. This plate (12) has several through holes (15) 35 through (for example four) to receive dies (8). The die (8) and plate (12) assembly is supported by a graphite interface (13). The latter plates the copper tuning disc (9) by screwing onto a rotating plug (14) also made of graphite. To do this, the interface (13) comprises a hollow cylindrical upper part (13a) on which is positioned the plate (12) carrying the dies (8), a circular flange (13b) resting on the tuning disc. (9), a tube (13c) 5 with external thread for screwing into the internal thread of the rotary plug (14). Said cylindrical rotary plug (14) has a peripheral shoulder (14a) to rest on the copper tube (4) which constitutes the pumping tunnel and which also contains the rotation shaft (16) connecting the substrate holder (11) to the engine (1 7).

  The installation of the motor (17) and of the pumping in the axis of the dies was made possible by the installation of a pumping tube in T. The pumping outlet (1) is then provided laterally in the tube in copper (4). As for the motor (17), it is in the axis of the rotating substrate holder (11) and of the dies (8). It operates on rectified direct current and is imperatively located outside the deposit enclosure to avoid degradations due to the synthesis atmosphere.

  An electrical assembly gives it an adjustable speed using a potentiometer. The motor is crowned by a reduction gear (18) which drives the shaft (16) in the copper tube (4). The seal between the shaft and the deposit enclosure is produced by an appropriate "seal" (21). Ball bearings (19.20) are used to center the shaft for the lower ball bearings (19), and to support the mass of the shaft for the upper bearing (20).

  The rotation shaft (16) is made of copper to avoid parasitic graphite deposits. It communicates the rotational movement to the rotating plug by two rods (21). The rotating assembly has been designed so that its axis does not support the weight of the substrate holder (11) and the tuning disc (9). Indeed, the substrate holder assembly and disc agreement on the copper tube (4) which confines the pumping of gases. In addition, the weight of the drive shaft is supported by ball bearings (20) located near the motor. In this way, the motor provides only the rotational movement to the drive shaft.

  The microwave plasma is not disturbed by the rotation of the substrate holder (11). Experimentation has not found any unusual detachment of the plasma during the deposition phases.

  In the reactor described above, the forces causing the species responsible for the germination of the diamond to enter the die hole have a constant sense, it is however possible to improve the quality of the deposit to provide for forces acting alternately in both directions from the same direction.

  The reactor is then modified accordingly.

Claims (14)

  1. Reactor for implementing a diamond synthesis technique assisted by microwave plasma for depositing a layer of diamond on a wall, characterized in that it includes means for forcing the species responsible for germination diamond to be penetrated and deposited on the internal wall of the hole of one or more dies for the drawing of metal wires.   2. Reactor according to claim 1, bell-type reactor in which the species enter the reactor via a high inlet, are led into a chamber where the plasma ball is formed above a substrate holder, the pumping of gases being positioned below the substrate holder, characterized in that the gas pumping is positioned in the center of the bottom of the reactor, in the central axis 15 of the substrate holder, one or more channels being installed on the substrate holder so that the axis of the through hole of each die is parallel to that of the substrate holder.   3. Reactor according to claim 2 characterized in that there is provided a copper tube (4) passing through the hearth (2) in its center and vertically to allow the pumping of gases just below the substrate carrier (3).   4. Reactor according to one of claims 1 to 3, characterized in that the substrate holder is mounted on a rotary assembly.   5. Reactor according to claim 4 characterized in that the rotary assembly comprises a motor (17) and a pumping means in the axis of the substrate holder.   6. Reactor according to claim 5, characterized in that the rotary assembly further comprises: - in the upper part a circular plate (12) comprising a plurality of through-hole holes (15) for receiving the dies, - an interface (13) plating a tuning disc (9) by screwing on a rotating plug (14).   7. Reactor according to claim 6 characterized in that the interface 35 (13) comprises a hollow cylindrical upper part (13a) on which is positioned the plate (12) carrying the dies (8), a circular flange (13b) based on the tuning disc (9), a tube (1 3c) with external thread for screwing into the internal thread of the rotating plug (14).   8. Reactor according to one of claims 6 to 7 characterized in that 5 the cylindrical rotary plug (14) has a peripheral shoulder (14a) to rest on the copper tube (4) which constitutes the pumping tunnel and which contains also the rotation shaft (16) connecting the substrate holder (11) to the motor (17).   9. Reactor according to one of claims 5 to 8 characterized in that the pumping outlet (1) is then provided laterally in the copper tube (4).   10. Reactor according to one of claims 5 to 9 characterized in that ball bearings (19.20) allow to center the shaft for the lower ball bearings (19), and to support the mass of the axis 15 for the upper bearing (20).   11. Reactor according to one of claims 5 to 10 characterized in that the substrate holder consisting of two coaxial cylindrical parts traversed by a hole of diameter (d) coaxial with the pumping axis, with an upper part (7a) of larger diameter (d1) than d, in which the die is placed, a lower part plunging inside the copper tube (4). 12. Reactor according to claim 11 characterized in that provision is made to close the space between the copper tube (4) and the substrate holder (7) with an intermediate graphite disc (10) pierced at its center, the 25 lower part (7b) of the substrate holder is then adjusted in the orifice (10).   13. Tungsten carbide wire drawing die for wire drawing of metal wires having a through hole characterized in that the internal wall of the through hole is totally or at least partially coated with a layer of diamond deposited directly on the carbide surface of tungsten by a diamond synthesis technique in the vapor phase assisted by microwave plasma. 14. Wire drawing die according to claim 13 characterized in that the diamond coating is deposited by means of a reactor according to one of claims 1 to 12.