FR2564865A1 - PROCESS FOR THE COATING OF QUARTZ AND CERAMIC CRUCIBLES WITH A MATERIAL ELECTRICALLY TRANSFORMED INTO THE VAPOR PHASE. - Google Patents

Abstract

THIS PROCESS INCLUDES THE STEPS OF JUXTAPOSITION OF A PAIR OF ELECTRODES 701, 702, COMPOSED OF AT LEAST ONE COMPONENT OF THE MATERIAL INTENDED FOR COVERING SUCH A CRUCIBLE AND OF THE INTERNAL SURFACE OF SAID CRUCIBLE, OF VACUUM CREATION IN THE SPACE IN WHICH THE SAID ELECTRODES ARE JUXTAPOSED AT NOT MORE THAN 1.33 10 PA AND MAINTAINING IN SUCH A SPACE OF A VACUUM THAT DOES NOT EXCEED 1.33 10 PA DURING THE OPERATION OF DEPOSITION AND IGNITION OF AN ELECTRIC ARC BETWEEN THE SAID ELECTRODES ONE OF THE END OF EACH OF THEM HAS A VOLTAGE OF 30 TO 60 VOLTS AND AN INTENSITY OF 59 TO 90 AMPERES, BRINGING THE ELECTRODES INTERMITTENTLY INTO CONTACT WITH ONE OF THE OTHER THEN BY SEPARATING THEM TO DEPOSIT THE MATERIAL WHICH VAPORIZES THESE ELECTRODES IN A UNIFORM WAY ON THE SAME INTERIOR SURFACE OF THE SAID CREUSET710.

Description

PROCESS FOR COATING QUARTZ CRUCIBLES

  AND CERAMIC WITH AN ELECTRICALLY TRANSFORMED MATERIAL

IN STEAM

  The invention relates to a method for coating quartz and ceramic crucibles with a transparent material.

  electrically formed in vapor phase.

  The deposition of a material in the vapor phase on a substrate is a well-known technique in the field of coating and in that of the surface transformation of a substrate. In general, an element of the material is heated which must be transferred to the substrate near it by first passing it to the molten state and then

  in the vapor state. Matter thus undergoes two transforma-

  phase states: that leading from the solid phase to the liquid phase and then that leading from the liquid phase to

the vapor phase.

  Previous systems use heating

  by induction to effect these phase transformations.

  Special problems have arisen in this respect.

  which concerns the quartz crucibles used in the production

  tion of silicon supports for application in semi-

  conductors. These crucibles intended for the fusion of elementary silicon generally consist of quartz and are housed in a carbon support envelope containing an inductor coil which is used to melt the elementary silicon. A primer in monocrystalline silicon can then be lowered into the silicon fusion of the crucible and then slowly reassembled to draw a silicon rod which is cooled under control so that the monocrystalline product can then be cut into supports. These crucibles intended for the fusion of elementary silicon are

  worn and maintained for many hours during the process

  over draft at a high temperature near their softening point, at which temperature they can be

  attacked by molten silicon. This leads to deterioration

  ration of the crucible and risks of impurity introduction-

tees in the supports.

  The field of semiconductors has therefore long sought a method of protecting these crucibles,

increasing their lifespan.

  Another problem arises in the application of

  metals to ceramics. Many metals can be applied

  only on coated ceramics, but refractory metals such as tungsten and titanium have been applied less satisfactorily and adhesion problems have been encountered in almost all cases.

  during the processes of the prior art.

  The invention firstly relates to a method

  of vapor phase material deposition on pre-

  feeling a large surface and / or a complex configuration, at a relatively low energy cost and with

improved uniformity.

  Another object of the invention is to provide a method for coating surfaces at high speed.

complex and / or important.

  The invention also relates to a method of

  protection of quartz crucibles of the type used in the

  semiconductor industry to increase their duration

of life.

  The invention finally relates to an improved process for applying metallic coatings to ceramics

  which avoids the problems of poor adhesion which characterizes

  feels the systems of the prior art.

  These and many other objects will emerge well from

  the following description of an enphaseva deposition process

  fear which is based on the discovery where it is possible to form especially large surface deposits by juxtaposing laterally an elongated electrode of the material to be deposited and the surface of the substrate to be coated over a significant part of the length of the electrode, under vacuum, and by striking an arc between one end of this electrode and a counter-electrode so that the intensity of the current of the arc is between 50 and 90 amps, with a voltage

from 30 to 60 volts.

  It is surprisingly found that once the arc is struck when the two electrodes are separated, the arc, a part of it or a thermal effect generated by the arc forms a spiral around the long electrode and causes the vaporization of the electrode material in a generally helical or spiral shape

  gradually moving away from the counter electrode.

  It is quite surprising that the arc does not remain

  not confined to the space between the two electrodes but com-

  rather carries a component or an effect which goes away in

  spiral of the counter electrode towards a part of the length

  of the elongated electrode which is then moved away from the counterelectrode despite the fact that it would seem that the most important conductivity is located directly between the two electrodes where the part appears to be confined

main arc.

  This effect is manifest in that the elongated electrode, that is to say the deposition electrode, from

  uniform cross-section, forms a cone towards the counter

  electrode and that the coating coming from the deposition electrode and going on the substrate can be observed at considerable distances from the initiating face of the arc

the deposition electrode.

  In fact, the effect seems to be prolonged for a brief period following the extinction of the original arc and it is preferred according to the invention to put in contact and separate

  periodically the electrodes to form the arc and allow

be its extinction.

  According to one embodiment of the invention, means are provided at one end of the electrode of material which it is desired to deposit, remote from the electrode initiating the arc, to control the temperature of the electrode providing the material, generally to keep it in the range from 800 F to 1000 F (427 to 538 C). In conditions of low voltage and current and temperature

  according to the invention, the speed at which the material vaporizes

  rise from the electrode can be 1.5 to 2 times greater than the vaporization rate of previous systems. Virtually all metals, alloys, car-

  bures and silicides for the electrode providing the material.

  In addition to metals and alloys, one can deposit on the sub-

  carburet, gilding, silicides and nitrides.

  Although we have not been able to fully understand

  why the vaporization rate of the material

  to deposit increases with the use of lower energy

  In accordance with the invention, it is possible that the migration of the arc may extend the molten surface by

  puddle on a larger surface of the electrode four-

  thinning the material to allow the metal to vaporize

melted as a thin film.

  According to another characteristic of the invention, the principles set out above are put into practice in

  the application of metallic coatings to syn-

  in the form of boxes or housings for components

  electronic health. We discovered, surprisingly,

  that since the support is not affected by the coatings

  on large areas, which can be applied

  quées according to the invention, it is extremely interesting--

  health for coating the interior parts of the cof-

  freight or accommodation for electronic components,

  the coating constituting an electromagnetic shield.

  It has also been discovered, quite surprisingly, that the invention is very advantageous for the application of coatings of pure silicon or other protective coatings, for example, of silicon carbide,

  silicon nitride or boron nitride, with internal surfaces

  of quartz crucibles used by the fusion of silicon during the manufacture of monocrystalline bars to be extracted by drawing from a bath of molten silicon in the

semiconductor field.

  The invention can, moreover, be used for the application of metallic coatings to ceramic products, with improved adhesion, even when the metals applied are refractory metals such as nickel, tungsten, titanium, tantalum or similar that has been difficult to apply to ceramic substrates so far. Any ceramic substrate can practically be used according to the invention; in the case of quartz crucibles and ceramic substrates,

  prefer to submit the surface provided to receive the coating

  sandblasting or similar treatment making the

  rough surface by blowing. The term "sandblasting" is used

  read here to describe entrainment of abrasive particles

  against the surface, the abrasive particles being generally-

  metal particles, silicon carbide, silicon nitride, diamond dust, oxide

  iron, silicon dioxide or any other material

  likely to roughen the surface. Central gas

  it may be air or any other gas. In all cases, the substrate can, moreover, be preheated in the vacuum chamber, or before its introduction into this chamber, to

  a temperature below the melting point of the metal.

  The preheating temperature will however be at least

several hundred degrees.

  According to the invention, the coating is carried out by juxtaposition of two electrodes of two different metals, preferably a highly conductive metal and a metal

  highly refractory and a substrate which is preferably

  rence, a ceramic body and striking of an arc between these electrodes in a chamber where a vacuum has been created

  and which contains the electrodes and the substrate. According to the-

  First of all, a relative polarity is communicated to the electrodes, that is to say that one is positively polarized while the other is negatively polarized in order to selectively deposit the metal of. one of these electrodes while simultaneously depositing a

  small amount of the latter metal on the second electrode.

  When the polarity is reversed, the metal preferably vaporizes from the second electrode, including at the beginning the small metal part of the first electrode which has been deposited on the latter, so that it forms at the interface between the two layers, a composition

mixed metals.

  We can overcome the disadvantages that we have

  hitherto countered with metals of high conductivity, more particularly with copper but also with gold and silver, when they are applied on ceramic substrates (more particularly with regard to adhesion after or during the welding of the conductive elements) if, before applying the highly conductive metal,

  the ceramic of a refractory metal, over a thickness

  laterally weak and if this intermediate layer is, at

  in turn, coated with conductive metal.

  It has been discovered, more particularly, that it is possible to deposit a coating, for example from 5 to 10 microns thick, of tungsten, molybdenum, titanium or zirconium (as a refractory metal). on the substrate then apply a thicker coating, for example from 0.254 to 5.08 mm of copper or an alloy of copper, gold, silver or other non-refractory metal i.e. -say

  of a metal with a significantly lower boiling point

  lower than that of the refractory metal used.

  It has been discovered that when the two-electrode method according to the invention is used, it is possible to make one electrode of refractory metal and the other of non-refractory metal, the regulation of the polarity of the electrodes during deposition making it possible to control

metal deposition.

  It has been found that the present invention allows

  was to multiply the adhesion, expressed in terms of force required to separate the coating from the substrate, by 100 or more, all other things being equal, if the thin coating of refractory metal is applied between the coating

  of copper and the ceramic substrate.

  A ceramic substrate can be used according to the present invention and masking techniques can be used so that the deposition takes place according to any desired design. According to an important characteristic of the invention, one of the two electrodes juxtaposed to the substrate can be misaligned from the other electrode and replaced by another electrode, and the process can be repeated to deposit in addition at least one layer of the metal of the third electrode

on the second layer.

  All of the above as well as other features

  ticks and advantages of the present invention will be ex-

  plicated more clearly using the description which

  follows, with reference to the attached schematic drawing in which: - Figure 1 is a sectional view of an apparatus

  to carry out vapor deposition according to a mode of exe

  cution of the invention; - Figure 2 is a similar view showing another device in which the material deposited in the vapor phase is collected on another vertical electrode;

  - Figure 3 is a vertical section of a device-

  lage for the deposition of material on a substrate disposed en-

below the metal puddle;

  - Figure 4 is a view similar to Figure 3 illus-

  trant another embodiment of the invention; - Figure 5 is a longitudinal section of another apparatus for depositing material on a substrate according to the invention;

  - Figure 6 is a longitudinal section of an apparatus

  portable, very compact reillage for implementing the method according to the invention; - Figure 7 is a schematic section of another

  apparatus for implementing the process according to the invention

tion;

  - Figure 8 is a schematic sectional view, illus-

  trant the application of the invention to the coating of a hollow

  quartz set used for the manufacture of semiconductor supports; - Figure 9 is a schematic view of another apparatus for the application of large area coatings on ceramic substrates according to the invention; - Figure 10 is a diagram of an apparatus for implementing the method according to the invention; - Figure 11 is a sectional view on a large scale of a product obtained by implementation of the invention; - Figure 12 is a view similar to Figure 10 of another apparatus for implementing the method according to the invention; Figure 13 is a diagram illustrating an effect obtained during the dep8t of the metal of the first layer before the start of the second layer;

  - Figure 14 is a sectional view of the product obtained -

naked according to figure 13.

  Figure 1 shows a system using a

  simple arc method according to the present invention for obtaining

  hold protective coatings of the mirror type on substrates or to vaporize various metals or alloys, including heat resistant and refractory metals,

  and to apply these coatings to the substrate.

  As shown in Figure 1, the basic apparatus may include a vacuum chamber (not shown) which may be similar to the vacuum chamber of Figure 6 and in which a metal electrode (1) can be

  brought by an electrode charger (7) to an electic body

  trode (2) to form the puddle (3) of molten metal with

which the arc (4) is struck.

  The electrode body (2) is held on a support

  port (5) and the direct current source applies the

  rant of arc through the electrode (1) and the body (2) by a conventional circuit stabilizing the arc shown in (8). It has been found advantageous to provide the electrode (1) of relatively small cross section with a thermal regulator (6) tending to prevent overheating of this electrode. Since the cross section of the body (2) is significantly larger than that of the electrode (1), the

  puddle (3) is in a concave recess formed in

located in the body (2).

Example 1

  The apparatus of FIG. 1, using the elect

  trodes (1) and (2) made of titanium, aluminum, tungsten, tantalum or copper strike an arc at a temperature of 5,000 to 7,000 F (2,742 to 3,835 C) to generate metal vapors from the puddle ( 3), which cross the distance of 10 to 15 cm to the substrate (10) and form a metal coating on this substrate. The puddle (3) can be formed by a mixture of metal coming from the electrodes (1) and (2) thus depositing on the substrate an alloy of the metals of the two electrodes. Preferably, the electrode is made of titanium while the molten metal is predominantly of

  aluminum, tungsten, tantalum or copper.

  The apparatus of FIG. 1 can be used, without significant modification, in a crucible-free process for generating protective carbide coatings, for making silicide coatings on the substrate or for forming, on the substrate, layers of carbide or

  of silicide or even silicon carbide.

  If we lay layers of silicon carbide-carbide

  tungsten on the substrate, the electrode (2) is in gra-

  phite and the tungsten silicide electrode (1). The vacuum is at the beginning of 1.33 x 10-4 Pa then it is maintained at 1.33 x 10-3 Pa or lower. Direct current voltage

  arc generator is 100 volts and the intensity of 150 am-

  fathers. The deposit forms at a rate of about 0.2 grams

per minute.

  In this case, the apparatus of FIG. 1 is used, still in the usual vacuum chamber, although the electrode (1) may be made of silicon or carbon while the electrode (2) is made of metal, of which wishes to form silicide or carbide; in the case of a deposit

  silicon on the substrate, it can also be silicon

  cium. For example, when it is desired to deposit a silicon carbide on the substrate (10), the electrode (1) can be made of silicon while the electrode (2) is a block of carbon which receives a puddle (3) silicon

and solubilized carbon.

  The vapors are transferred to the substrate and there

  are deposited as a layer of silicon carbide. The subs-

  trat can be made of titanium and the deposit formed on the substrate can be a mixture of titanium silicide and carbide

titanium.

  Alternatively, when the electrode (1) is made of silicon or carbon and the electrode body (2) is made of titanium, it is possible to deposit carbide or silicide of

  titanium on a substrate of different composition.

  When the vacuum chamber receives a slightly oxidizing atmosphere, deposits of silicon dioxide

form with the substrate.

  It is obvious to the apparatus of Figure 1

  is particularly effective for the production of semi

  conductors. The thermoregulator (6) can be split on the

  length of the electrode (1) and thermo

  additional regulators for the electrode body (2)

to prevent overheating.

  When one or the other of the electrode (1) or of the body (2) is made of silicon and the other is made of carbon, the reaction generates silicon carbide which is deposited with an improved purity compared to silica and at

original carbon.

  When the two electrodes are made of silicon, it is possible to obtain deposits of silicon and high density silica which is particularly desirable for the

coating of semiconductors.

l1

  The apparatus of Figure 2 is, in essence

  tiel, similar to that of figure 1 but it works se-

  lon a somewhat different principle, the vaporization being carried out at least in part from the upper humidified electrode (101). In this figure, the elements that correspond

  to those of FIG. 1 bear the same references assigned

tees of the coefficient 100.

  In Figure 2, the electrode charger (107) is coupled to a vertical double-acting device (112) which communicates back and forth to the electrode (101) in the direction of the arrow (114 ) so that the end of the electrode (101) periodically plunges into the pool (103) of molten metal formed in the body

electrode (102).

  By rising from this puddle to re-strike the arc (104), the coating (113) of molten metal on the electrode (101) vaporizes and the deposit is formed on the substrate.

(110).

  The electrode body (102) is presented in the support (105) and the arc current supply is made by the direct current source (109) and the stabilizer (108) as described, the electrode (101) being equipped

of the thermo-regulator (106).

  This system has proven to be particularly effective

  in a modification of the previous example, when the elect

  trode (101) is made of titanium and the puddle (103) is made of aluminum. Figure 3 shows another embodiment

  of the invention in which the vapor is deposited on a subs-

  trat (210) arranged below a crucible (217) in the form of an upwardly open ring containing the molten metal (203), the crucible being mounted in a support or

frame (205).

  The upper electrode (201) here has the shape of a spherical segment which functions as a reflector so that when an arc (204) is struck between the electrode

  (201) and the melted part in the crucible (217), the

  fears rise as shown by the arrows (219) and are redirected downwards to gather on the substrate (210) as shown by the arrows (218). The direct current source (209) is here connected to the electrode (201) and to the crucible (217) by the arc stabilizer (208) and the upper electrode (201), mounted on the bar (216), is positioned vertically by the loader (207) and positioned horizontally by an auxiliary mechanism (215) which adjusts the position of

  the electrode (201) above the metal which vaporizes.

  In this embodiment, the electrode (201) can be made of titanium, molybdenum or tungsten while the molten metal can be aluminum or copper and the crucible

(217) in graphite.

  FIG. 4 represents another embodiment.

  tion of the apparatus according to the invention in which the

  vapors descend to deposit on the substrate (310).

  In this case, the upwardly open crucible (317) containing the molten metal (303) can be supplied with additional molten metal from a pocket or any other source represented in (322), or with molten solid metal in the crucible (317). The latter can be heated by

  auxiliary means such as an induction heater

  tion (323) and is held by a support (305).

  The bottom of the crucible (317) is provided with openings (321) where droplets of molten metal appear, these droplets being vaporized by the arc (304) struck between

  the electrode (301) and the bottom of the crucible (317).

  The temperature in the arc region can be

  regulated by additional inductive means (324) and electro-

  of (301) can be cooled, as shown, by the element

cooling (306).

  The electrode (301) is directed towards the crucible (317) by the electrode holder (307) and the arc is maintained by an arc stabilizer (308) connected to the current source

continuous (309).

  In this embodiment, the molten metal can

to be copper.

  Instead of the auxiliary device (324), a substrate to be coated can be placed, for example, in the form of a ring of titanium which can collect the vapor under

the shape of a coating.

  The embodiment shown in Figure 5 vaporizes the molten metal as it forms in an enclosed space, the vapors being discharged through the openings

(425) on the substrate (410).

  In this case, the puddle of liquid is formed by fusion and the electrode (402) held by the support (405)

  by introduction of the counter-electrode (401) by the char-

  electrode electrode (407) through a central bore (426) in the electrode (402), the electrode (401) passing through an insulating sleeve (427) forming a guide. A temperature regulator (406) is provided coaxially around the two electrodes adjacent to the arc (404) to prevent overheating in the region before the openings (425). The

  deposit is formed on the substrate (410).

  The current is supplied between the electrodes by

  the arc stabilizer (408) and the current source

  tinu (409) as previously described.

  Figure 6 shows a volt arc device

  portable pad for depositing carbide coatings and

  silicide reflectors, anticorrosive, protective and semi

  metal type conductors according to the principles described above

cedent.

  This apparatus includes a vacuum chamber (500)

  the upper end of which has a handle (530) for

* putting an easy transport of the portable unit.

  Inside this chamber is placed a hollow sphere (517), the lower part of which forms a crucible for the molten metal (503) and which is internally

  coated with a high temperature resistant (refractory) material

  temperature, such as aluminum oxide.

  The upper part of this sphere is coated, at (531) with a reflective layer concentrating the heat which is reflected from the bath. An arc (504) is struck between an electrode (501) and the bath (503), the electrode being brought by the unit (507) to the bath when the material of the electrode is consumed. The bath is supplied with additional metal, by

  example, in solid form, in bar form (532) also

  Lely connected to the loading device (533 ') so that, as the bath is consumed, there

add additional metal.

  The electrode (501) and the bath (503) are connected to opposite terminals of an arc stabilizer and to a

  direct current source as previously described.

  A tubular electrode (502) surrounds the bar

(532).

  The lower part of the chamber (500) is equipped with an air pump, shown in (533), the latter creating a vacuum in the chamber containing the hollow sphere (517) and, by a vacuum pipe (534) , by a valve (535) of an adapter (536) of divergent profile towards the outside which can be connected to a lateral opening

(525) of the hollow sphere (517).

  The adapter (536) may include a heating coil (537) to prevent non-condensing

desired steam.

  Between the opening (525) and the adapter (536)

  there is a vacuum valve (538) and a mounting device

  ge (539) to support a variety of adapters

of different shapes and sizes. The adapter (536) thus comprises a vacuum seal (540) which means that

the adapter can rest against the

substrate to be coated (510).

  The portable unit shown in Figure 6 is transported to where the substrate (510) to be coated is located; the adapted adapter (536) is mounted on the connector (539) and

  press the seal (540) against the surface (510) to be coated.

  The arc current is supplied and the system evacuated by the air pump (533) thereby melting the metal and

  forming the bath (503) inside the hollow sphere.

  We then open the door (538) and let the

  fears on the substrate (510) at least in part by a

  pressure difference, controlled by the valve (535),

  be inside the sphere (517) and the adapter (536).

  You can practically coat any product at any

  location and use of a variety of different adapters

  rentes shapes and sizes allows to cover even complicated bodies without moving them from the place where they are to be used. The device can be dismantled so as to be used to apply coatings inside

of pipes or the like.

  The device shown in the drawing, without adapter

  (536), can be used as a propellant for individuals

due or as space equipment.

  When generating the arc, simply open the door (538) to let flow

  through the opening (525) and carry out the direct propulsion

  opposite tion. The vacuum of space provides a natural vacuum

  to the device and the air pump (533) is not required.

  Almost any waste encountered in space applications can be used in the container (517)

  to generate such propulsion.

  FIG. 7 represents another embodiment of the apparatus which combines certain characteristics

previously described.

  In this system that can be used for deposition

  ser a coating (610 ') on the inner surface (610a) of a tube (610) forming a substrate, of complex shape, we

  mounted centrally with respect to the tube an elect

  trode providing the material (602), of corresponding shape,

  on a support (602a), and we mount a heating coil

  induction fage (606a) of a temperature regulator

  (606) which may include a thermocouple (606b) or a test

  similar temperature sensor, sensitive to the temperature of the electrode supplying the material (602) to maintain the temperature of the latter constant in the range of 800 to 1000 F (427 to 538 C) by a conventional capacitive circuit. As in the previous embodiment, the substrate and the material force to be deposited on the latter are placed in a vacuum chamber (600) in which a vacuum of 1.33 x 104 Pa can be made so that the deposit of steam can be carried out at a pressure of

1.33 x 10-3 Pa.

  The end of the material-supplying electrode (602) is equipped with an arc-striking electrode (601) which can be reciprocated by an electrically controlled reciprocating control (607) . The latter can be started by reaction to a zero current detector (607a) so that, when the arc current declines completely, the electrode (601) moves to the left in contact with the end (602a ) from the electrode (602) and is then removed to restore an arc. The stream

  of arc is supplied by a direct current source at im-

  pulse (609) by an arc stabilizer (608) which regulates the parameters of intensity and voltage of the arc between

  50 and 90 amps and between 30 and 60 volts.

  In practice, using the system illustrated, a

  once the arc is struck, the arc itself, a va-

  porization or some other electromagnetic phenomenon

  seems to progress generally helically and spi-

  as shown by the arrow A, so that the initiation of the arc and the deposition of vapor occurs over the entire length of the electrode supplying the material (602) which is subjected to this phenomenon, it is that is, the length at which this phenomenon is effective up to

what the arc declines.

  Due to the lost material, the electrode (602) gradually takes the conical shape represented by the

  dashed lines (602b) of figure 7.

  The distance between the electrode and the sub-

  trat caused by cone formation does not cause a problem, since the largest deposit is in the region of the greatest distance; as a result, the finished coating, progressing along the substrate,

is very uniform.

  The system according to the invention is specially

  used in the coating of temperature sensitive materials

  tures with very thin coatings since the coating operation is especially fast and it

  deposition is possible without significant heating

tif of the substrate.

  Example 2 A copper electrode (602) of the indicated shape is installed in a substrate tube, the initial spacing between the electrode (602) and the substrate is approximately 10 cm, The electrode is maintained at a temperature of 9009F (4823C) and an arc is struck at one of its ends as previously described. The intensity of the arc current is approximately 70 amperes and the applied voltage, once

  the electrode (601) is removed to form the arc, is of

  about 40 volts. The vaporization speed of the electrode

  (602) exceeds in these conditions the vaporization rate

tion of example 1.

  FIG. 8 represents a device allowing the application of a silicon coating (710 ′) on a quartz crucible (710) of the type used for the fusion of silicon; it is from this fusion that we can draw a monocrystalline silicon bar intended to be

  then cut into silicon supports used in the

  semiconductor industry. According to the invention, the surface

  this interior of the crucible is sandblasted and the crucible preheated

  fairy, for example at a temperature of 200 to 600 ° C before the crucible is placed in the vacuum chamber. Two silicon electrodes (701) and (702) are juxtaposed to one another inside the crucible, then using

  the reciprocating means of the electrode of the type shown

  tee in (607), the electrodes are joined and then separated as indicated by the arrows (707a) and (707b) so that they touch and then move apart to strike the arc. The energy source, which can also be of the type described, is shown in (709). The intensity of the arc current can be between 50 and 90 amps and the voltage between 30 and 60 volts. Uniform and highly adherent silicon coatings can be obtained, especially when the silicon is previously heated, for example by means similar to those used in the

realization of figure 7.

  If there is an atmosphere of nitrogen in the

  region of the arc, silicon nitride Si3N4 is deposited.

  If one of the electrodes is made of carbon, a deposit of silicon carbide is formed. The same system can be used to coat any substrate with pure silicon or one of the other coatings mentioned. Once the initial arc

  product, the electrodes can be cooled.

  FIG. 9 represents a system for coating a large surface of a ceramic substrate (801) which, before its introduction into the vacuum chamber, can be preheated, once the surface which is to receive the coating has been sandblasted, by moving a burner

  (820) along the underside of the substrate. Electro-

  (801) may be of refractory metal or nickel; via the control mechanism (807), it is brought into contact and then withdrawn from the counter-electrode (802)

  which can also be made from the same metal.

  The energy source has been represented in (809).

  The electrodes are here mounted on a slide (821) and are moved along the substrate so that when the arc is repeatedly struck and that it flows along the electrode (801) in the receiving vacuum chamber the entire device, the entire surface of the substrate

  is coated according to the principles described for figure 7.

Example 3

  Using equipment working according to

  the principles described for figure 9, one covers a

  than tungsten aluminum oxide over a thickness

  from 0.0254 to 0.0508 mm using tungsten electrodes

  stene. The intensity of the arc current is 50 amps and

  the voltage of 40 volts for a maximum electric gap

  trode of about 4 mm. The diameter of the electrode is approx.

  about 1 cm. The tungsten coating adheres very well to

the alumina plate.

  FIG. 10 very schematically represents an apparatus for implementing the method according to the invention. This apparatus comprises a chamber (1010) in which, by means of a pump (1011), it is possible to make

  a vacuum which is, in general, from 1.33 x 10 -3Pa to 1.33 x10 -4Pa.

  Means (not shown) make it possible to have in this chamber a ceramic substrate (1012) which can be protected by a mask shown diagrammatically in (1013) so that only the defined parts are coated

  through the windows (1014) formed in the mask.

  The part of the substrate to be coated is juxtaposed in the vacuum chamber and a pair of electrodes, namely a copper electrode (1015) and a tungsten electrode (1016), the electrodes being equipped with means such as electromagnetic motors (solenoids ) (1017) and (1018) to bring them into contact for a short time in order to strike the arc and then to separate them. The generator

  of pulses intended to periodically initiate the arrangements

  tifs (1017) and (1018) is represented in (1019).

  The power supply includes the alternating current source (1010) connected to a rectifier (1021), the latter being equipped with an inverter (1022) which can reverse the polarity of the electrodes (1015) and (1016)

  under the control of a timer (1023).

  When we walk with a positive polarity for the copper electrode (1015) and a negative polarity for the tungsten electrode (1016) we can strike an arc by passing an electric current from 30 to 100

  amps at a voltage of 40 to 100 volts across the inter-

  valle, after brief contact with the electrodes in order to preferentially vaporize the tungsten and thereby deposit tungsten, through the window (1014) in the mask (1013) on the substrate. The duration of the coating is controlled by the timer (1023) which, after applying a coating of the order of a few microns, reverses the polarity to

  negatively charge the copper electrode (1015) and charge

  positively manage the tungsten electrode (1016), which causes the copper to vaporize from the electrode (1015) and

settles on the substrate.

  As shown in Figure 11, the article ob-

  held comprises a substrate (1030), for example of aluminum oxide, protecting a copper coating (1032) and separated from the latter by the thin coating

  made of refractory metal (tungsten) (1031).

Example 4

  Always according to the same principles, with an in-

  voltage of approximately 70 amperes, a voltage of 80 volts and a vacuum of approximately 1.33 x 10-3 Pa, a plate is coated

  of tungsten aluminum oxide over a thickness of

  about 8 microns and copper to a thickness of about 0.508 mm. We measure the adhesion and the necessary force

  to remove the coating is between 500 and 700 li-

  vres / square inch (35 to 49 kg / cm2). If a copper coating of the same thickness is applied under the same conditions to the same substrate, the adhesion is only 6 to 8 pounds / square inch (0.42 to 0.656 kg / cm2). It was found that the direct copper-ceramic bond was sensitive to both mechanical and thermal effects when a connection was made there by trimming whereas, with the copper-tungsten contact according to the invention,

don't have this problem.

  Virtually identifiable results can be obtained

  ques by replacing tungsten with molybdenum, titanium

  and zirconium, as well as by combinations of these

  refractory rates with another metal, and with tungsten as an intermediate layer. Likewise, high adhesions can be obtained with nickel, gold, silver and alloys of these metals with another metal and with copper. FIG. 12 represents a modification of the apparatus of FIG. 10 in which the chamber (1110) evacuated by the pump (1111) contains a ceramic substrate (1112) which it is desired to coat with a plurality of

metals.

  In this case, in addition to the electrode,

  mune (1116) and its actuator (1118) driven by the general-

  pulse counter / rhythm (1119) a pair of counter

  electrodes (1115) and (1115a), respectively of copper and

  in gold, each being provided with an actuator (1117) (1117a).

  The set of counter-electrodes is put on a rail (1124), the line of which allows the offset of the two electrodes

  to the left as illustrated in the figure by the representation

  feeling of the dashed electrode (1115) in its posi-

  shifted tion. Naturally, in this position, the elect

  trode (1115a) is aligned with the common electrode (1116).

  An inverter (1122), as described for figure..10, is also provided and the apparatus is supplied by alternating current coming from (1120) by the rectifier

(1121).

  In this operating mode, once the vacuum is created in the chamber, the actuators (1117) and (1118) are operated to move the electrodes (1115) and (1116) together and separately to strike an arc, the electrode of tungsten (1116) being positively polarized while

  that the copper electrode (1115) is negatively polarized.

  Continue as indicated until

  the initial tungsten coating has been thickened

desired sister.

  As can be seen in Figure 13, this process

  not only leads to erosion of the tungs electrode-

  tene (1116) but it also gives rise to a small deposit

  (1125) of tungsten on the copper electrode (1115).

  When the polarity is reversed, i.e. when the copper electrode (1115) becomes positive and the tungsten electrode negative, the arc is struck and vaporization occurs from the copper electrode, the deposit of tungsten (1125) whose thickness has been exaggerated in FIG. 13 vaporizes at the same time as the copper

  and we have a mixed tungsten / copper deposit at the interface.

  It can be seen, for example, in FIG. 14, that the substrate (1112) has been covered at (1131) with a layer of tungsten. The mixed layer or the tungsten layer

  (1126) is then applied before, the vaporization

  t inuant- by arcing between the electrodes (1115)

  and (1116), the copper coating (1132) is applied.

  When the copper coating has reached the thick-

  seur desired, the electrode assembly (1115) (1117) is shifted to the left and replaced by the assembly (1115a) (1117a) and the arc is struck between the electrodes (1115a)

  (1116) to deposit a layer of gold (1133) on the coating

copper.

  A controller (1127) can be provided for the

  positive electrode displacement (1124), the pulse / rhythm generator Jr (1119) and the inverter (1122), and we

  can use a preprogrammed microprocessor to perform

  kill reverse polarity and switch electors

  trodes when the desired layer thicknesses have been obtained.

Example 5

  The procedure of Example 4 is repeated, but below

  placing the copper electrode and replacing it with a gold electrode. With the same vacuum and striking a similar arc, a rapid coating of gold, of the order of 5 microns, is deposited on the copper coating in the

  conditions mentioned for the deposit of copper.

  The adhesion is not lowered and it has been found that the gold layer thus obtained constitutes an ideal contact for microelectronic applications. The study of the interface between copper and tungsten revealed the existence of a mixed transition zone (1126) coming

  of the vaporization of a minor tungsten deposit of the elect

copper trode.

Claims (24)

- CLAIMS -   1- A method of coating a quartz crucible intended for melting silicon, characterized in that it comprises the following stages: juxtaposition of a pair of electrodes,   of at least one component of the material intended to coat   firing said crucible, and from the interior surface of said crucible; creation of a vacuum in the space in which the said electrodes are juxtaposed at a maximum of 1.33 x 10 Pa and maintenance in said space of a vacuum which does not exceed 1.33 x 10-3 Pa during the operation deposit, and, - initiation of an electric arc between said electrodes, at one of the ends of each of them at a voltage of 30 to 60 volts and at an intensity of 50 to 90   amperes, by intermittently bringing said electro-   in contact with each other and then separating them to deposit the material which vaporizes from these electrodes   uniformly over said interior surface of said crucible.   2- A method according to claim 1, characterized in that at least one of said electrodes is made of silicon and in that it further comprises a step of controlling   the temperature of this electrode to maintain this tem- between 427 and 538 C.   3- Method according to claim 1, characterized in that it includes a step of sanding said surface to make it rough.   4- A method according to claim 3, characterized in that it comprises a step of preheating said crucible before striking the arc.   5- A method of coating a ceramic with a metal, characterized in that it comprises the following steps: - sandblasting of the surface of a ceramic substrate; - Preheating said substrate to a temperature of at least 200 C but lower than the melting point of the metal to be applied; - juxtaposition of said surface of said substrate and an electrode of said metal; - evacuating the space in which said electrode is juxtaposed to said substrate at a maximum of 1.33 x 10-4Pa and maintaining, in said space, a vacuum which does not exceed 1.33 x 10 -3Pa, and, - striking an arc with said electrode by striking it with another electrode while applying to said electrodes a current of a voltage of 50 to   volts with an intensity of 50 to 90 amps for vapo-   riser the electrode composed of said metal and deposit said metal on said surface.   6- A method according to claim 5, characterized in that said metal is nickel, copper, tungsten, titanium or tantalum.   7- Method according to claim 5, characterized   in that said ceramic is alumina.   8- A method of joining a material to a ceramic, characterized in that it comprises the following stages: - application to a ceramic of a thin layer of refractory metal;   - joining of said material to said layer.   9- Method according to claim 8, characterized   in that said material is a highly conductive metal.   - Method according to claim 9, characterized in that said highly conductive metal is copper,   gold, silver or an alloy of these metals.   11- Method according to claim 10, characterized   in that said refractory metal is tungsten, molyb-   dene, titanium, zirconium or an alloy or a combination sound of these metals.   12- The method of claim 11, characterized in that said refractory metal is applied to said substrate over a thickness of the order of a few microns and said metal is applied to a thickness of about 0.254 to 5.08 mm.   13- The method of claim 12, characterized in that said highly conductive metal is applied to a thickness of about 0.254 to 5.08 mm and said metal   refractory is applied on a thickness of 5 to 10 mi-   crons. 14-A method according to claim 13, characterized in that said highly conductive metal is copper and   said refractory metal is tungsten.   - Method according to claim 13, character-   se in that each of said metals is applied by striking an arc between a pair of electrodes to vaporize the metal respectively from one of said electrodes in an empty chamber.   16- The method of claim 15, character-   dried in that an electrode of said refractory metal is jux-   tapped to an electrode of said highly conductive metal, said electrodes are brought into contact and separated to strike said arc and said electrodes are initially given positive and negative polarity   in one direction to deposit said refractory metal first   shut up on said substrate then the polarity is reversed to   depositing said highly conductive metal on said substrate.   17- Ceramic body, characterized in that it comprises a ceramic substrate to which is secured a first thin layer of refractory metal, a second relatively thick layer of a highly conductive metal   being secured to the first layer.   18- Method for obtaining multilayer metallic coatings on a substrate, characterized in that it comprises the following steps: juxtaposition of a first electrode of a first metal to a second electrode of a second metal to another and placement of a substrate, in a vaporization reception relationship with said electrodes in a chamber; - placing said chamber under vacuum; - striking of an arc between said electrodes   in said vacuum chamber while applying a pola-   electrical rity at said first electrode and another   electrical polarity at said second electrode for vapo-   selectively risking the metal from said first electrode and depositing it on said substrate; - reversing the polarities of said electrodes, then striking an arc between them to selectively deposit the metal of said second electrode on the metal of said first electrode previously deposited on said substrate; - juxtaposition to one of said electrodes of a substitution electrode and striking of an arc between said substitution electrode and said electrode in said chamber to vaporize the metal of said substitution electrode and deposit it on said layer of metal   of said second electrode on said substrate.   19- The method of claim 18, character-   se in that said substrate is a ceramic.   - Method according to claim 18, character-   se in that said first electrode is a refractory metal to hush up.   21- The method of claim 20, character-   laughed in that said refractory metal is chosen from the group which comprises tungsten, molybdenum, titanium zirconium as well as alloys and combinations of these metals.   22- The method of claim 18, character-   risé in that at least one of said second electrode and substitution electrode is a metal chosen from the group which comprises nickel, copper, gold, silver and any alloy of these metals.   23- The method of claim 18, characterized in that the metal layer of said first electrode   is applied over a thickness of the order of a few half   crons and the layer formed by one of the second electrode and of the substitution electrode has a thickness lying between 0.254 and 5.08 mm.   24- Method of coating a substrate, characteristic   laughed in that it comprises the following stages: - juxtaposition of a pair of electrodes of different metals and a substrate in a chamber; - creation of vacuum in said chamber; - Application of an electrical polarity to one of said electrodes and of an electrical polarity opposite to la1treo of said electrodes and striking of an arc between said electrodes by bringing them into contact then by separating them, in order to vaporize the material one of said electrodes and depositing the vaporized material on said   substrate in a first layer - while simul-   temporarily a part of said material on the other of said electrodes and, - changing the electrical polarity of said electrodes and striking an arc between them to vaporize   the material of said other electrode comprising said part   tie and deposit a mixed layer of the material of the two said   electrodes on said first layer as a traning layer   sition then deposit the material of said second electrode on said transition layer.   - Method according to claim 24, characterized   in that said substrate is a ceramic.   26- A method according to claim 24, characterized in that the material of one of said electrodes is a refractory metal.   - 27- Method according to claim 26, characterized   in that said refractory metal is tungsten, molyb-   dene, zirconium or an alloy or a combination of these metals. 28.The method as claimed in claim 24, characterized in that said other electrode is made of nickel copper, gold,   silver or an alloy of these metals.   29- Method according to claim 24, characterized   in that one of said electrodes is made of tungsten.   - Method according to claim 24, characterized in that said other electrode is moved relative to one of the electrodes and replaced by a substitution electrode with which an arc is struck in said chamber to deposit another material on said material of said other electrode ..   31- Apparatus for multilayer coating   a substrate according to any one of claims   above, characterized in that it comprises: - a chamber (1110) - means (1111) for creating a vacuum in said chamber; - a substrate (1112) to be coated placed in said chamber; - a pair of first electrodes (1115, 1115a)   juxtaposed with another in said room.   - means (1120) for applying an electrical potential to said electrodes, one of said electrodes having an electrical polarity and the other of said electrodes having an opposite electrical polarity; - means (1117-1118) for bringing said electrodes together and separating them, in order to strike an arc between them   by selectively spraying the material of one of the   said electrodes for depositing on said substrate in a first layer; - means (1122) for reversing the polarities of said electrodes, said electrodes striking an arc to selectively deposit the material of the other of said electrodes on said first layer and, means (1124) in said chamber for the automatic replacement of one of the first electrodes mentioned by a substitution electrode and the priming   of an arc between the remaining electrode of the first electro-   of the mentioned and said substitution electrode for selectively depositing the material of said electrode substitution on said substrate.   32- Compound obtained by implementing the process   according to any one of claims 9 to 30.