FR2650841A1 - DEVICE FOR DEPOSITING A MATERIAL ON A THERMALLY CONDUCTIVE SUPPORT - Google Patents

Abstract

The invention relates to a device for depositing a material in accordance with a controlled design on a substrate (1) to be treated which is heat-conductive and electrically insulating. The material to be deposited originates from the vapour-phase decomposition of a body. A winding through which flows a high-frequency current surrounds a component (2) and heats it by induction. The substrate (1) is placed near the component (2) and is heated by thermal radiation. At least the substrate (1) and the induction-heated component (2) are placed in a low-pressure vessel (4) containing the body to be decomposed in the vapour phase. The invention is applicable in particular to the manufacture of hyperfrequency tubes.

Description

DEVICE FOR DEPOSITING A MATERIAL
ON A TIIEBMIQUENT CONDUCTIVE SUPPORT
The present invention relates to a device for depositing a material, according to a controlled profile, on a thermally conductive support.

In certain techniques, it may be necessary to deposit a material, sometimes electrically conductive, on a thermally conductive but electrically insulating support and the deposit must have a predetermined profile.
In the microwave tube technique, it may be necessary to deposit a material whose role is to attenuate in certain areas, microwave waves. For example, to prevent the traveling wave tubes from oscillating, a layer of attenuating material can be deposited on a portion of the rods which support the delay line. The rods or supports are generally made of a dielectric material but good conductor of heat. For example, aluminum nitride, beryllium oxide, boron nitride, etc. are used.

 In a fairly old technique, deposits are obtained by one or more layers of paint followed by annealing.

Unfortunately, this method is sensitive to parameters that are difficult to control, linked inter alia to the nature of the paint and the support. It is really not possible to obtain a deposit according to a given profile, in a reliable manner.

 Another more recent technique consists in carrying out the deposition by vapor decomposition of a body containing the material to be deposited. It is a cracking reaction. It suffices to place the support to be covered and the body in a resistance oven and to heat. This reaction takes place at low pressure, of the order of a few hectopascals. The bodies used are very often organic or organometallic compounds.

 One can thus deposit carbon from benzene, the decomposition taking place around 1zoo0 C.

 This technique gives relatively satisfactory results as long as the support is not too thermally conductive. If this is not the case, in areas fairly distant from the area to be covered, deposits of parasitic and unstable products are obtained. In fact, these zones are brought to intermediate temperatures between the optimum temperature for obtaining cracking and the temperature outside the oven. The reactions that occur at these intermediate temperatures are incomplete. These unstable products can be modified during possible subsequent treatments and we will then obtain completely harmful new deposits, located around the area to be treated.

 Furthermore, the resistances of the furnace can be polluted by these unstable products, which causes their characteristics to vary over time.

 This technique does not allow repositioning of sufficiently reproducible deposits from one manipulation to another and it cannot be reliably used for mass productions.

 However, experience has shown the superiority of the vapor deposition technique over paint.

However, this technique is conditioned by the temperature at which the reaction takes place and this is highly dependent on the material constituting the furnace and on the nature of the support to be treated.

 The invention aims to remedy these drawbacks and proposes a device for depositing a material on a thermally conductive support, this device making it possible to control the temperature of the zone to be covered, of the adjacent zones and to obtain a deposit according to a determined profile.

 The present invention provides a device for depositing a material according to a controlled profile, on the surface of at least one support to be treated, thermally conductive and electrically insulating, the material coming from the decomposition of a body in vapor phase, characterized in that it comprises - a winding traversed by a high frequency current, - a part heated by induction thanks to the winding, placed near the support to be treated so as to heat it by athermal radiation, - a low pressure enclosure containing the body to decompose in the vapor phase, at least the - support to be treated and the part heated by induction.

 The winding is placed inside the enclosure or outside if it is electrically insulating. It surrounds the room heated by induction.

 The induction heated part is a block pierced with at least one hole so as to introduce a support to be treated therein.

 The block is made of an electrically conductive material which can be heated by induction.

 The dimensions of the hole vary along the support and the external dimensions - of the block vary - along the winding so as to adjust the temperature profile of each support to be treated.

 The room heated by Induction can consist of a stack of electrically conductive elements, heated by induction separated by insulating spacers. It comprises at least one hole so as to introduce therein a support to be treated.

 The external dimensions of the conductive elements and spacers, their thicknesses and the dimensions of the holes are adjusted so as to obtain a predetermined profile deposit on the support.

 The position of the support can vary inside the enclosure during deposition.

 The material to be deposited is carbon or a metal.

 The decomposing body is an organic or organometallic body.

 the material of the induction heated part is graphite or a refractory metal such as molybdenum, tungsten, titanium, tantalum.

 The support to be treated is an electrical insulator such as beryllium oxide, boron nitride, aluminum nitride.

 The present invention will be explained by the following description. This description will be made with reference to the accompanying drawings, in which - FIG. 1 represents a cross-sectional view of a device for depositing, in accordance with the invention, a material of controlled profile that is substantially constant on a thermally conductive support - the FIG. 2 represents a cross-sectional view of a variant of the device of FIG. 1 - FIG. 3 represents a cross-sectional view of a device for depositing, according to the invention, a material of variable controlled profile, on a thermally conductive support; - Figure 4 shows a cross-sectional view of a variant of the device of Figure 3 - Figure 5 shows a cross-sectional view of a device for depositing on several supports simultaneously.

 There is shown in Figure 1, a support 1 of thermally conductive and electrically insulating material. Its outer surface 9 must be covered with a material according to a controlled profile.

 This material can be either electrically conductive or electrically insulating.

 This support 1 is close to a room 2 heated by induction.

The part 2 is placed near a coil 3 traversed by a high frequency current and is thus heated by induction.

The support 1 is then heated by thermal radiation.

 In Figure 1, the heated part 2 is a cylindrical tube, the support 1 is placed inside. It is central. The coil 3 surrounds the part 2. This construction is only an example. The winding 3 will have contiguous turns or spaced from each other.

 The support 1 and the part 2 heated by induction are placed inside a closed enclosure 4, at low pressure, containing a body intended to be decomposed in the vapor phase in order to supply the material to be deposited. The body's vapor decomposition reaction is a cracking reaction. Preferably choose a body having a sufficient vapor pressure at room temperature so that the reaction takes place fairly quickly at working temperature.

 The material to be deposited can be either carbon or a metal and the body to be decomposed will preferably be chosen from organic or organometallic bodies.

 The induction heated part can be graphite or a refractory metal such as molybdenum, tungsten, titanium, tantalum, etc.

 The enclosure 4 comprises a tube 5 which communicates with the outside. This tubing 5 is connected to a vacuum pump (not shown) which makes it possible to obtain a very low pressure inside the enclosure 4.

 After emptying the enclosure 4, the body to be decomposed is introduced through this tube 5. Its vapor pressure at room temperature is sufficient to produce in the enclosure the pressure necessary for the reaction.

 If we want to deposit carbon, during tests, we noticed that stable gases such as the first elements of the cyclic or fatty series made it possible to obtain particularly stable and pure deposits. Benzene gives very good results with a part 2 heated in graphite. We can also use methane, ethane etc.

It is from 9500 C that the cracking reaction occurs and the carbon is deposited on the areas of the support 18 at this temperature.
The internal pressure of the enclosure 4 is of the order of a fraction of a hectopascal.

 In Figure 1, there is shown an enclosure 4 in the form of a vacuum bell resting on a base 8. It can be made of glass for example. It is the base 8 which comprises the tubing 5.

 Was placed at the base of the bell, all around its periphery a groove It containing an O-ring 7. I1 ensures the seal between the inside and the outside of the enclosure 4.

Gasket. 7 is in contact with the base 8.

 The part 2 heated by induction has in Figure 1 the shape of a cylindrical tube of constant thickness.

 The support 1 to be covered is here entirely contained inside the part 2 heated by induction. The heated part 2 and the support 1 each rest on an electrically insulating element 6.

 One could have envisaged that the support 1 to be covered is longer than the heated part 2 and that it protrudes on each side. Only part of the support 1 will be treated, this part is then located inside the heated part 2.

 The material is deposited on the outer surface 9 of the support 1 in areas brought to a sufficient temperature.

In FIG. 1, the deposition of the material will be carried out substantially over the entire outer surface of the support 1 facing the heated part 2. The thickness of the material will be - substantially constant because the heated part 2 is here a tube whose outside and inside diameters are constant. The distance between the outer surface 12 of the heated part 2 and the coil 3 is constant over the entire height of the tube. I1 is the same for the distance between the internal surface 10 of the heated part 2 and the external surface 9 of the support 1.

 2 shows a variant of the device shown in Figure 1. The elements of this figure, identical to those of Figure 1 have the same references.

The difference between the two figures is at the level of the winding 20 which is now outside the enclosure 4, in the open air. I1 surrounds the enclosure 4 which is a vacuum bell placed on a base 8. The material of the enclosure 4 will be an electrically insulating material such as glass, for example.

 This variant makes it possible to make a deposit on larger supports 1 because the interior volume of the enclosure 4 can be used more completely.

 It is often preferable to place the winding 20 outside of. enclosure 4 because the risk of electric arcs between turns increases considerably at reduced pressure according to Paschen's law.

 The device shown in Figure 3 allows a deposition of a material according to a controlled profile on a support 33. The elements of this figure identical to those of Figure 1 have the same references. This device makes it possible to obtain a deposit whose profile is predetermined in advance and is not constant.

 the coil 3 surrounds the part 30 heated by induction.

 To obtain the desired result, the thermal profile of the support 33 was adjusted by adjusting the internal and external dimensions of the heated room 30. This heated room 30 is then more or less close to the support 33 to be treated and the high frequency winding 3 .

 To make the part 30 heated by induction, we started with a block of conductive material. We drilled a hole 36, preferably right through the block, and this hole is a little larger than the support 33. Here this hole is central and in a vertical direction.

 We could have located hole 36 in another direction and we could have shifted it. The hole could also not have gone right through the block. One could also consider drilling several holes so as to simultaneously treat several supports.

 The outer surface 37 of the block opposite has been machined with the coil 3 so as to vary the distance between the coil 3 and the block.

 The inner surface 38 of the block has also been machined along the hole 36 so as to vary the distance between the support 33 and the heated part 30.

 In fact, the smaller the distance between the support 33 and the heated part 30, the higher the temperature of the support 33. Likewise, the smaller the distance between the winding 3 and the heated part 30, the higher the temperature of the heated part 30. The thickness of the deposited material increases proportionally with the temperature of the support 33. The temperature of the heated part 30 varies in the same direction as its thickness.

 There are shown at two places 31, 32 of the heated room 30 reliefs with cut sides directed towards the support 33. These reliefs make it possible to concentrate the heat on the areas of the support 33 facing each other and therefore to increase the thickness of the material. deposited on these areas.

 The shapes which are given to the heated part 30 are determined solely as a function of the profile of the deposit which it is desired to achieve.

In FIG. 3, the support 33 no longer rests on an insulating element. I1 is now hanged at the end of a rod 34 which crosses the upper wall of the enclosure 4, for example
A seal 35 was placed at the place where the rod 34 passes through the wall of the enclosure.

 It is thus possible to move - the support 33 in the enclosure during deposition. We can, for example, drive the rod 34 in a vertical movement from bottom to top and from top to bottom or in a rotational movement.

 FIG. 4 represents a variant of a device for depositing controlled thickness along the support 1. Now the part 40 heated by induction consists of a stack of conductive elements 41 separated by insulating spacers 42. It is only the conductive elements 41 which will heat by induction. The conductive elements 41 and the spacers 42 are shown in the form of rings. Support 1 is central.

We could have used plates of various shapes and sizes, drilled with a hole so as to introduce the support
The outside and inside diameters of the conductive rings 41 as well as their thickness can vary from one ring to another. It is the same for the dimensions of the spacers 42.

 The choice of dimensions and profiles of the conductive elements 41 and of the spacers 42 is guided by the profile of the deposit which it is desired to produce on the support 1.

 In order to precisely position the stack of conductive elements 41 and spacers 42 relative to the support 1, at least two conduits 43 have been drilled through the stack. These conduits will preferably be placed on the periphery of the stack. In Figure 4 there are shown two conduits 43 which are diametrically opposed on the rings. An insulating rod 44 will be placed in each conduit 43.

 FIG. 5 represents a deposition device allowing workers to work simultaneously on several supports 50. There is no longer any central support as in FIG. 1.

 In Figure 5 there is a room 51 heated by induction consisting of a stack of conductive elements 52 separated by insulating spacers 53. The heated part 51 has the shape of a cylinder; the conductive elements 52 and the spacers 53 are discs, of variable thickness and diameter. This construction is only one example, one could consider others.

 The stack is pierced over its entire height with at least two conduits 54 each intended to receive a support 50 to be treated. The conduits 54 have been shown at the periphery of the stack and they are diametrically opposite, but they could be arranged otherwise.

 The conduits 54 do not necessarily have constant dimensions, they can be varied from one conductive element 52 to another, from a spacer 53 to another. One could even vary the dimensions of a conduit 54 along the same conductive element 52. The dimensional variations make it possible to adjust the profiles of the deposits which it is desired to obtain on the supports 50.

 This deposition device according to the invention makes it possible in particular to cover with a layer of an attenuation material, rods which support the delay line of a traveling wave tube.

 The invention is not limited to the examples described; it is possible to modify the shapes and positions of the parts heated by induction, of the supports without departing from the scope of the invention.

Claims (14)

 1 - Device for depositing a material according to a controlled profile, on the surface of at least one support (1) to be treated, thermally conductive and electrically insulating, the material originating from the decomposition of a body in vapor phase characterized in what it comprises - a coil (3) traversed by a high frequency current, - a part (2) heated by induction thanks to the coil (3), placed near the support (1) to be treated so as to heat it by athermal radiation, - a low pressure enclosure (4) containing the body to be decomposed in the vapor phase, at least the support (I) to be treated and the part (2) heated by induction.  2 - Depositing device according to claim 1, characterized in that the coil (3) surrounds the part (2) heated by induction.  3 - Depositing device according to one of claims 1 or 2 characterized in that the coil (3) is placed inside the enclosure (4).  4 - Depositing device according to one of claims 1 or 2 characterized in that the coil (3) is placed outside the enclosure (4) when it is electrically insulating.  5 - Device dept- according to one of claims 1 to 4 characterized in that the part (30) heated by Induction is a block of a conductive material comprising at least one hole (36) so as to introduce a support (33) to be treated  6 - depositing device according to claim 5 characterized in that - the dimensions of the hole (36) vary along the support (33), - the external dimensions of the block vary along the winding (3) so as to adjust the profile temperature of the support (33) to be treated.  7 - Depositing device according to one of claims 1 å 4 characterized in that the part (40) heated by induction consists of a stack of elements (41) conductors heated by induction separated by spacers (42) insulating , this stack comprising at least one hole so as to introduce therein at least one support (1) to be treated.  8 - deposition device - according to claim 7 characterized in that - the thicknesses of the elements (41) conductors and the thicknesses of the spacers (42) vary from one element to another or spacer to the other, - the dimensions of the hole vary along the support (1) to be treated, - the external dimensions of the conductive elements (41) vary along the winding (3), so as to adjust the temperature profile of the support (1) to be treated.  9 - Depositing device according to one of claims 1 to 8 characterized in that the support (1) to be treated moves relative to the part (2) heated by induction, during deposition.  10 - Depositing device according to one of claims 1 å 9 characterized in that the material to be deposited is carbon or a metal.  11 - Depositing device according to one of claims 1 to 10 characterized in that the body to decompose in the vapor phase is an organic or organometallic body.  12 - Depositing device according to one of claims 1 å 11 characterized in that the part heated by induction is made of graphite or a refractory metal such as molybdenum, tungsten, titanium, tantalum.  13 - Depositing device according to one of claims 1 å 12 characterized in that the support to be treated is an electrical insulator such as aluminum nitride, beryllium oxide, boron nitride.  14 - Depositing device according to one of claims 1 to 13 characterized in that the support to be treated is a stick intended to support the delay line of a traveling wave tube.