US 3651781 A
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iliiited @tates Patent M111 et a1. 14 1 Mar. 28, W72
54] METALLIC VAPOR DEPOSITION 3,419,718 12/1968 Hammond et a1. ..2s0/49.5 7 2,866,065 12/1958 Hirsh .219/19 ARRANGEMENT 2,930,879 3/1960 Scatchard ...2l9/19  Inventors: Klaus Brill, Stuttgart-W; Wolfgang 3,373,273 15/1968 Cily 50/49.5 Grothe, Stuttgart-Vaihingen, both of Ger- 2,630,780 3/1953 Falck ..1 18/7 many Primary Examiner-Mervin Stein [73} Asslgneet Robert Bosch GmbH, Stuttgart, Germany Assistant Examiner Leo Millstein Mar. 27, Att0rney-Michael Striker  Appl. No.: 23,340  ABSTRACT An arrangement for the vapor deposition of metallic layers  Foreign Application Priority Data upon moving bands of insulating material. The metal is vaporized in a crucible through an electron beam generated 28, 1969 Germany 19 15 9332 by an electron gun. The electron beam serves to both vaporize the metal and ionize the vapor stream emerging from the  US. Cl ..ll8/7, 1 18/6, 250/49.5 crucible The vapor tream is directed upon a predetermined  Int. Cl. ..H0lj 37/26 surface of the moving band of insulating material. Within the  Field of Search ..l18/4, 6, 7, 48; 219/420; vapor stream is located a probe which transmits current to a 324/71 CP; 250/49.5 regulator for the purpose of monitoring and regulating the thickness of the deposited metallic layer.  References Cited sktasedessLL 1 Ge kewin Fig r PAIENTEUmza m2 v V 3,651,781
sum 2 BF 2 IN VENTORS r Klaus BRILL Wolfgang GROTHE rhe/r ATTORNEY METALLIC VAPOR DEPOSITION ARRANGEMENT BACKGROUND OF THE INVENTION The present invention resides in an arrangement for vapor deposition of a metallic layers upon moving isolation or insulation bands in a vacuum. The bands are past over at least one crucible containing metal to be vaporized.
In the vaporization or vapor deposition of a band moving past continuously a crucible, the vapor deposited layer thickness depends primarily on the band velocity and the vapor stream density. For constant band velocity, fluctuations in the vapor stream density lead to layer thickness variations which, in turn, cause electrical, optical and mechanical properties of the vapor deposited metallic layer to be influenced or changed.
In the use of metallic vapor deposited insulation bands for registration purposes, surface heating or for other applications, in which the electrical, optical or mechanical properties of the vapor deposited layer are of importance, such variations in the layer thickness are disadvantageous and produce disturbing effects. In registration processes, for example, such disadvantages reside in non-uniform impressions or recording tracks, and in surface heating, non-uniform heating or even over-heating of individual locations may result. In order to avoid these problems, narrow fabrication tolerances for the layer thickness must be maintained.
In vacuum deposition, it is known to maintain the vapor deposited metallic layer upon insulation bands within a predetermined region. The layer thickness itself or a parameter associated therewith, such as the electrical resistance or optical transmissibility of the layer, become measured after the vapor deposition, and the heating power for the vaporizer becomes adjusted manually in accordance with the measured value. In such a known measuring method, the band to be vapor deposited with metal becomes past over two reels arranged one after the other, after leaving the vaporization zone with the metallic deposited side. A definite voltage is applied to one of the reels. The current flowing between the reels through the metallic layer on the band, is dependent upon the layer resistance and is, in fact, proportional to the layer thickness. This value becomes indicated through a measuring instrument, and upon fluctuations of the current magnitude, the heating power becomes adjusted manually.
Aside from the condition that at such measuring only an average value is realized on the section of the band between the reels, this method has a definite disadvantage. This resides in the condition that the measurement first takes place when the band section in question leaves the vaporization zone. The same situation also applies to regulating methods based upon optical transmissibility measurement. Between the vaporization stream fluctuations and its measuring technique as well as follow-up regulation, a considerable time delay takes place afterward. The arrangement is such that the section of the band between the vaporization zone and the measuring location is not affected from such follow-up regulation. As a result, considerable layer thickness variations or fluctuations of -20 percent are realized over corresponding band lengths. The magnitude of the deviation of the vapor stream density from the desired value, as well as the frequency of variations or fluctuations, depend thereby substantially upon the material to be vapor deposited, the apparatus used, and the magnitude of the vacuum.
It is an object of the present invention to provide a regulating or control arrangement which has a least amount of delay, and which is designed to maintain the layer thickness variations within narrow limits. For continuously moving band, the layer thickness is proportional to the vapor stream density, and with regulation or control not affected by delay, the vapor deposited layer thickness is determined through precise technological achievement of vapor stream density.
The object of the present invention is achieved by providing a crucible with metal to be vaporized, and to generate a vapor stream from the vaporized metal. The vapor stream is directed upon a predetermined portion of the band upon which the metal is to be vapor deposited. In the region of the vapor stream, a probe projects, which has a constant DC voltage applied to it. The probe conducts current which is directly dependent upon the vapor stream density. The current is, in turn, used to control or regulate the thickness of the metallic layer. The intensity or magnitude of the current in the probe is dependent upon the density of the charge carriers in the vapor stream, as well as upon the magnitude and polarity of the probe potential. For the purpose of realizing a large number of charge carriers, it is advantageous to arrange the probe in a vapor stream which has been ionized through an electron beam. Particularly adapted for this purpose, are electron beam heated band vapor deposition arrangements, since the electron beam produced by an electron gun and used for vaporizing the metal, can be used simultaneously for the purpose of ionizing the vapor stream. If the probe has applied to it the negative potential relative to the metal to be vaporized, then the ions in the vapor stream are received by the probe, and thereby only substantially little disturbing effects appear. With positive probe potential, the low-quantity electrons received by the probe, result in more severe disturbing effects, but these may be removed through a magnetic field. The advantage of regulating with positive probe potential resides in the condition that an essentially higher probe current results in the comparison with negative probe potential itself upon reduced voltage. The essentially higher probe current is substantially proportional to the vapor stream density within the regulating region.
SUMMARY OF THE INVENTION An arrangement for the vapor deposition of metallic layers upon bands of insulating material, within a vacuum. A crucible containing the metal to be vaporized and deposited upon the insulating bands, is subjected to an electron beam generated by an electron gun. The electron beam impinges upon the surface of the metal within the crucible and heats the metal thereby. At the same time, the resulting vapor stream of the metal from the crucible becomes ionized through the electron beam. The bands of insulating material upon which the metal is to be vapor deposited is moved past the vapor stream which is directed onto the band surface. A probe is situated in the vapor stream between the crucible and the band surface upon which the metal is deposited, and the current generated by the probe is applied to a regulator used to regulate the thickness of the deposited metallic layer. The regulator is an on-off type of regulator, and regulates the energy density of the electrons in the beam at the surface of impact.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic arrangement of a vaporization apparatus using an electron gun for vaporizing the metal within a crucible, and a regulator in conjunction with a probe for regulating the vapor stream density incident upon the deposited surface, in accordance with the present invention;
FIG. 2 is a schematic arrangement of a vapor deposition apparatus with an on-off regulator for maintaining constant the vapor stream density;
FIG. 3 is a graphical representation of the probe current and heater power of the electron gun, as a function of time, when used in the apparatus of FIGS. 1 and 2;
FIG. 4 is an isometric view for the construction of the probe used in FIGS. 1 and 2; and
FIG. 5 is a schematic arrangement of a vapor deposition device for controlling the speed of the insulation band when used in conjunction with the apparatuses of FIGS. 1 and 2, in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, and in particular to FIG. 1, a band is to be deposited with a metallic vapor through a vacuum vapor deposition arrangement. The band runs in the direction of the arrow upon a rotating roll 11, and through the vapor zone 12. At the lower portion of the arrangement, is a source 13 which contains the metal 14 to be vaporized. The source 13 has ground potential applied to it. The metal 14 is heated through an electron beam 15 which is emitted from an electron gun. The beam is deflected through a magnetic field and directed onto the metal 14 which is to be vaporized.
The magnetic field is directed vertically to the electronic beam 15, and between two poles of electromagnet 17. Only the rear pole 18 of this electromagnet is shown for purposes of clarity. The electron gun 16 consists of an electrically heated cathode 19, a focusing electrode 20, and an anode 21 which is connected to ground potential. In operation of the arrangement, the cathode 19 has applied to it a negative potential of approximately 10 kv. The electrons which are emitted through thermal emission from the cathode 19, become intensely accelerated through the high potential difference with respect to the anode 21. As a result, the electrons shoot past the anode 21, through the magnetic field of the electromagnet 17, and onto the upper surface of the source or crucible 13 filled with metal 14.
Upon impact, the kinetic energy of the electrons is converted into heat, and the metal at the impact area 22 of the electron beam 15, becomes instantaneously vaporized. In this manner, a vapor stream 23 is directed onto the roll 11. The density of this vapor stream or vapor beam 23 depends upon the concentration of the electron beam 15 and upon the energy of the electrons. Thus, the density of the vapor stream depends upon the energy density at the point of incidence or impact 22. The electron beam 15 thereby passes through the vapor stream 23 on the last portion of its path, and ionizes the vapor stream, thereby, more or less.
Two apertures or diaphragms 24 are located beneath the roll or drum 11. The apertures 24 assure that when the band to be vapor deposited passes through the vapor zone 12, it is exposed to the vapor stream only in the region confined to between the apertures 24.
A probe 25 is arranged between the crucible 13 containing the metal 14 to be vaporized, and the section of the band 10 upon which the vapor is to be vacuum deposited. The probe 25, furthermore, is situated within the region of the vapor stream 23. The probe 25 has applied to it a DC voltage relative to the crucible 13. The probe current results from the charge carriers impinging upon the probe from the ionized vapor stream 23. The probe current is applied to a regulator 26, and the magnitude of the current is taken directly for the purpose of regulating the vapor stream density, since the current magnitude or current density is dependent upon the vapor stream density directly. Through such regulation of the vapor stream density, the thickness of the deposited layer upon the band 10 in the form of a vapor deposited metallic layer, is regulated.
In accordance with the arrangement of FIG. 1, the electron beam 15 is regulated in energy density through which electrons impinge upon the area 22. The regulating arrangement is such that the heating power for the electron gun of the beam 15 is taken from a converter 28 connected to a power supply line. An adjusting element 27 connected to the converter, is also influenced by the regulator 26. As a result of this interconnected arrangement, the regulation of the heating power can be continuously or intermittently regulated in different ways through, for example, electrical or mechanically effected current or voltage variations.
The probe 25 is situated above the magnetic field of the electromagnet 16, and is within reach of essentially only the ions resulting from the electron beam 15 which, in turn,
produces the vapor stream 23. The electrons which are freed at the area of incidence or impact 22 of the electron beam 15, through thermal emission, become deflected through the magnetic field and maintained distant from the probe 25. This same situation applies to the electrons of the electron beam 15 reflected from the upper surface of the metallic band 22, as Well as the secondary electrons which are tossed out of the metal band 22 through the impact of the electron beam 15. The probe 25 which is mounted above the pole 18, extends transversely to the transport direction of a band 10, and into the metallic vapor stream 23. Through this arrangement, the formation of a vapor shadow onto the moving band 10 is avoided. In an arrangement of this type with a probe 25 made of wire one millimeter in diameter and millimeters in length, an average current of 2 ma. appears at the probe when a negative voltage of volts relative to the crucible 13 is applied. With the application of a positive voltage of only 10 volts, an average current of ma. is realized. These results show that for the purpose of regulating the vapor stream density, the probe current is substantially higher for positive probe potentials, then for negative probe potentials. Since even minute variations in the vapor stream density are sensed or detected at high probe currents, the regulation with positive probe potential becomes particularly advantageous when the magnetic field shown in FIG. 1 for deflecting the electron beam 15, is also used simultaneously for deflecting or suppressing disturbing electrons.
FIG. 2 shows in schematic form a two-point regulator for regulating the vapor stream density. In the arrangement of FIG. 2, the band vapor deposition arrangement of FIG. 1 is only in representative form. The crucible 13 is heated through an electron gun 16 which has its cathode connected to the secondary winding of an isolation transformer 30. The secondary winding has a center tap 31 to which a DC voltage of-lO kv. is applied. The DC voltage is derived from a three-phase rectifying circuit 32 connected to an alternating current supply source. The primary winding of the isolation transformer 30 is connected, through a resistor 33 and a variable transformer 34, to an alternating current supply of 220 volts, and 50 Hz. The resistor 33 is of 5 ohms and 30 watts. The resistor 33 is bridged by a switching contact 36 associated with a relay 35 in a two-point regulator 41.
The relay 35 has an operating coil 37 designed to accept a voltage of 2 volts. An adjustable resistor 38 having a maximum resistance of 1,000 ohms, is connected in parallel with the coil 37. One junction of the adjustable resistor 38 and coil 37 is connected to ground potential, whereas the other terminal junction of the coil 37 and resistor 38 is connected to the terminal ofa l2-volt battery 39. This positive terminal of the battery 39 is, furthermore, connected through a current measuring instrument 40, to the probe 25. As a result, the probe 25 acquires a positive potential of 10 volts in relation to the crucible 13 which is at ground potential.
In operation of the band vapor deposition arrangement, the band 10 which is to be vapor deposited is first set into motion upon the roller 11, in the direction of the arrow shown in the drawing. The vacuum is then generated, and the metal in the crucible 13 is heated through the electron beam 15 of the gun 16, so that a vapor stream 23 is produced. The density of the vapor stream is influenced through the heater power of the electron gun 16. The initial setting of the heater power is accomplished manually through the setting of the 10 kv. DC voltage and the SO-cycle alternating voltage applied to the secondary winding of the isolation transformer 30. The 50- cycle alternating voltage is adjustable through the adjustable transformer 34, within the range of zero to 30 volts.
Fine regulation of the heater power and thereby the energy density at the impact area of the electron beam 15 upon the upper surface of the metal within the crucible 13, results through the two-point regulator 41. Such regulation takes place within the probe current region of 20 to 400 ma., with respect to a desired input value which may be set for the vapor stream density. Through the adjustable resistor 38, the desired nun-m A...
input value as well as the probe current and hence the vapor stream density may be set or adjusted. This also applies for the setting of the permissible deviation from the desired input value and thereby the sensitivity and regulating frequency of the regulator. After the initial or basic setting, the resistor 33 becomes bridged through the relay 35 to which the probe current is applied with the fluctuations or variations of the vapor stream density. This bridging of the resistor 33 takes place in the primary circuit of the isolation transformer 30. The circuitry is scaled or dimensioned so that through such setting and bridging of the resistor 33, the power of the electron gun is varied by approximately 20 percent, and this results in a corresponding variation in the vapor stream density.
In FIG. 3, the probe current magnitude I, and the heating power N are diagrammatically illustrated as a function of time. The heater power N is that of the electron gun, and the periodic function realized through the two-point regulator 41 is readily apparent from FIG. 3. The functional waveform in FIG. 3 is represented in ideal form, since the actual function deviates from this ideal function through different feedback effects and other influences or effects. The direct relationship between the heater power and the probe current would thereby be less clear if these other feedback effects and influences would be taken into account. The two-point regulator 41 is set so that the desired input value of the probe current is to be 100 ma. corresponding, for example, to a vapor stream density at the band upper surface of 200 pg./cm. sec., in aluminum deposition. The regulator, thereby, switches in and out the resistor 33 upon a deviation of i ma. of the desired input value. The graphical representation shows that when the resistor 33 is switched into the circuit, a heating power reduction of approximately percent from the output value takes place. The heating power results in a corresponding return of the probe current, when the vapor stream density decreases, since the probe current is substantially proportional to the vapor stream density within the regulating region. When the lower limit of the regulator 41 is reached at point A, the relay becomes released or drops out, and thereby closes the switching contact 36. As a result, the resistor 33 becomes bridged or short circuited. The heater power becomes thereby again brought to the higher value, and an increase in the vapor stream density results through the corresponding increase in energy of the electron beam 23. The probe current now rises again until point B of the upper limit of the regulator 41 has been attained. The relay 35 then becomes again energized and opens the switching contact 36 so that the resistor 33 is again switched into the primary circuit of the isolation transformer 30. The heater power becomes, thereby, reduced to a lower value.
Through this operational mode of the regulator 41, periodic switching in and out of the resistor 33 takes place. When the vapor stream density varies through the appearance of disturbing parameters as, for example, voltage variations in the power supply network, or worsening of the vacuum, then the regulator 41 becomes compensated. The compensation is such that as a result of the curve of the probe current which is more or less steep, the duration for switching the resistor 33 in or out of the circuit varies by approximately 10 Hz., for constant regulating frequency. This may be seen from the righthand portion of the graphical representation. Depending upon the scaling or dimensioning of the regulator 41 and the resistor 33, it is possible that for occasional appearances of severe disturbing parameters, the fine regulation is not adequate. In such cases, therefore, it is possible without a large amount of equipment, to provide delay-type of contacts on the relay 35 for switching on a driving motor for the adjustable transformer 34. In this manner, a coarse regulation may be realized.
The velocity of the band 10 to be vapor deposited, and the regulating frequency of the two-point regulator 41, or relay servo 41, are established relative to each other for producing as uniform as possible the thickness of the metallic deposition on the band 10. The surface portion to be vapor deposited on the band 10 is exposed for at least a regulating period T of the vapor stream 23. In this manner, the periodic fluctuations of the vapor stream density caused by the regulator 41, have no influence upon the layer thickness of the metallic deposition.
The probe 50 shown in FIG. 4, is provided with three rods 51 situated in parallel and spaced 20 mm. from each other. The probe 50 is to be arranged within the vaporization zone of FIG. 1, so that all rods 51 project into the vapor stream 23 at the same level. Since the probe current with this arrangement is substantially two to three times as large as in the case of a simple probe design as shown in FIG. 1, this probe is particularly adapted for measuring small vapor stream densities and density variations. The probe 50 makes possible high band velocities, particularly when vaporizing very thin metallic layers of the order of 0.01 pm. Furthermore, the probe 50 permits good regulation of the vapor stream density.
FIG. 5 shows another embodiment of the present invention in which a band vaporization arrangement 61) is illustrated. In this arrangement, a uniformly thick metallic deposition through the control of the vaporization time of the surface portions of the band 61 which are to be deposited, are achieved. The band 61 runs from a storage roll 62 and reaches, through a deflecting roller 63, a vapor deposition drum 64. The band section between two apertures or diaphragms 65,654 becomes deposited with metal from a vapor stream 66. The vapor deposited band 61a runs thereby off the vaporization drum 64, over a deflection roller 63a, and then becomes wound upon a storage roll or reel 67. The vapor stream 66 originates from a crucible 68 to which ground potential is applied. An electron beam 69 is directed onto the metal in the crucible, and vaporizes the latter at the area of in cidence. The vapor stream density becomes set through the heater power of an electron gun 71 connected to a high voltage apparatus 70. The vapor stream density is measured through a probe 72 which is connected to a control unit 73. The output of the control unit 73 is connected with a driving motor 74 for the band 10. The arrangement provides a control path in which the probe current is applied as a control parameter for influencing the band velocity of the control unit 73. A change or variation in the vapor stream density leads, thereby, immediately to a variation in the band velocity, so that a longer or shorter vaporization time of the vapor stream 66 onto the surface portions of the band 61 are achieved. Through the surface portions of the band 61, variations in the vapor stream density are compensated.
A variable vaporization time can also be achieved by providing that a diaphragm or aperture in front of the band and in the vaporization zone, be adjusted or set, so that the section of the band subjected to the vaporization stream 66 becomes varied. This is shown in FIG. 5 through an adjustable or positioning motor 75 represented through dashed lines. The motor is shown to be connected to the control unit 73 through a dashed interconnecting line. In case of need, the vaporization time can be controlled through the drive motor 74 of the storage reel 67 and/or the motor 75 of the aperture 65a, as a function of the vapor stream density.
The present invention is not restricted to the embodiments shown, but instead encompasses all vaporization or vapor deposition arrangements in which the probe current is used for regulating or controlling the layer thickness of metal as a function of the vapor stream density, with the metal being vapor deposited upon bands. The regulating arrangements, furthermore, are not limited to the use of two-point regulators or on-off regulators. Thus, it is possible, for example, that with band vapor deposition arrangements at very high band velocities, the regulating frequency of the regulator 41 shown in FIG. 2, is not adequate as a result of the switching delay of the relay 35. At the same time, it is possible that the regulating power of the cathode beam gun, the regulating frequency is limited to the response time or the inertia of the cathode. The probe is then connected to a delayless regulator as, for example, any electronic regulator which influences a control voltage at a focusing electrode or Wehnelt cylinder. The entire quantity of metal vapor deposited upon the surface of the band stems directly from the incidence of the electron beam, and from corresponding focusing of the beam. Only a very small volume of metal must be influenced in order to achieve rapid and adequately large variations of the vapor stream density. When using an electronic regulator, therefore, and when influencing the energy density of the electron beam through focusing of the beam, substantially no limitation of the regulating frequency takes place within the border of the vapor stream density variations and band velocities which are of technical interest.
It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.
While the invention has been illustrated and described as embodied in vapor deposition apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
What is claimed as new and desired to be protected by Letters Patent is:
1. An arrangement for vapor deposition of a metallic layer upon insulating means in vacuum comprising, in combination, crucible means containing metal to be evaporated; transport means for moving said insulating means past said crucible means, said insulating means being spaced from said crucible means; vaporization means for vaporizing said metal in said crucible means and ionizing the vaporized metal, the vaporized metal forming an ionized vapor stream between said crucible means and said insulating means for deposition on a predetermined surface of said insulating means; unenclosed probe means substantially immersed in the cross section of said vapor stream between said crucible means and said insulating means; a source of DC voltage applying a predetermined constant voltage to said probe means for attracting charged carriers in said ionized vapor stream from a substantially large region of said vapor stream to said probe means, said probe means transmitting substantial electrical current dependent upon the vapor stream density; and regulating means connected to said probe means for regulating with substantial sensitivity the thickness of said metallic layer deposited onto said insulating means.
2. The arrangement as defined in claim 1 wherein said vaporization means comprises an electron gun emitting an electron beam, said electron beam also ionizing said vapor stream.
3. The arrangement as defined in claim 1 wherein said source of DC voltage applies negative potential to said probe relative to the metal to be vaporized, said probe accepting positive charge carriers.
4. The arrangement as claimed in 1 wherein said source of DC voltage applies positive potential to said probe relative to said metal to be vaporized, said probe accepting negative charge carriers.
5. The arrangement as defined in claim 2 including means for generating a magnetic field transverse to the direction of motion of said insulating means said magnetic field projecting into said electron beam above said crucible means at a substantially perpendicular angle to said electron beam for deflecting said electron beam onto the metal to be vaporized in said crucible, said magnetic field also deflecting the electrons in said vapor stream not generated by said electron beam.
6. The arrangement as defined in claim 1 wherein said vaporization means comprises an electron un for generating an electron beam impinging upon said meta within said crucible means, said regulating means regulating the energy density of the electrons in said electron beam at the surface of incidence of said electrons upon said metal to be vaporized, said regulating means regulating said energy density as a function of said probe current.
7. The arrangement as defined in claim 6 including means for adjusting manually the power of said electron gun; and means for applying fine regulation of said energy density by said regulating means.
8. The arrangement as defined in claim 6 wherein said regulating means comprises a two-point, on-off, regulator for regulating the energy density of said electron beam to an adjustable desired input value of the vapor stream density within a predetermined current region of said probe means.
9. The arrangement as defined in claim 8 wherein the speed of said moving insulating means and the regulating frequency of said regulator are adjusted relative to each other so that said predetermined surface of said insulating means to be vapor deposited is exposed for at least one regulating period of said vapor stream.
10. The arrangement as defined in claim 1 including control means connected to said probe means for adjusting the velocity of said moving insulating means.
11. An arrangement for vapor deposition of a metallic layer upon insulating means in vacuum comprising, in combination, crucible means containing metal to be evaporated; transport means for moving said insulating means past said crucible means, said insulating means being spaced from said crucible means; vaporization means for vaporizing said metal in said crucible means, the vaporized metal forming a vapor stream between said crucible means and said insulating means for deposition on a predetermined surface of said insulating means; probe means in said vapor stream between said crucible means and said insulating means; a source of DC voltage applying a predetermined constant voltage to said probe means, said probe means transmitting current dependent upon the vapor stream density; regulating means connected to said probe means for regulating the thickness of said metallic layer deposited onto said insulating means; aperture means in the path of said vapor stream for adjusting the opening on the surface of said insulating means upon which said metallic layer is vapor deposited; and control means connected to said probe means and controlling said aperture means as a function of the current of said probe means.