U.S. patent application number 10/237316 was filed with the patent office on 2003-01-09 for method for melting and evaporating a solid in a vapor deposition coating system.
Invention is credited to Ehrich, Horst, Plester, George.
Application Number | 20030007786 10/237316 |
Document ID | / |
Family ID | 22435473 |
Filed Date | 2003-01-09 |
United States Patent
Application |
20030007786 |
Kind Code |
A1 |
Plester, George ; et
al. |
January 9, 2003 |
Method for melting and evaporating a solid in a vapor deposition
coating system
Abstract
Apparatuses and methods for use in vacuum vapor deposition
coating provide for simpler, economical and continuous operation. A
system and method for continuously melting and evaporating a solid
material for forming a coating vapor includes the use of a separate
melting crucible and evaporating crucible. A system and method for
energizing the evaporative solids to form a plasma which includes
first and second electrodes and a device for selectively switching
polarity between the first and second electrodes to avoid coating
vapor deposition on the electrodes. Another a system and method for
energizing the evaporative solids to form a plasma which includes
an electric arc discharge apparatus with a cathodic and an anodic
part. A continuously fed electrode is disclosed for continuous
vaporization of electrode members in an electric arc discharge. An
apparatus and method provides for measurement of the rate of
evaporation from an evaporator and the degree of ionization in a
vapor deposition coating system. Lastly, a system is disclosed for
in-situ cleaning of vaporizable deposits for cleaning of the
enclosure of the vacuum vapor deposition system.
Inventors: |
Plester, George; (Brussels,
BE) ; Ehrich, Horst; (Dorsten, DE) |
Correspondence
Address: |
Peter G. Pappas
SUTHERLAND ASBILL & BRENNAN LLP
999 Peachtree Street, NE
Atlanta
GA
30309-3996
US
|
Family ID: |
22435473 |
Appl. No.: |
10/237316 |
Filed: |
September 9, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10237316 |
Sep 9, 2002 |
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09845885 |
Apr 30, 2001 |
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6447837 |
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09845885 |
Apr 30, 2001 |
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09128456 |
Aug 3, 1998 |
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6251233 |
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Current U.S.
Class: |
392/389 ;
118/726; 392/390 |
Current CPC
Class: |
C23C 14/564 20130101;
C23C 14/325 20130101; C23C 14/243 20130101; C23C 14/246
20130101 |
Class at
Publication: |
392/389 ;
118/726; 392/390 |
International
Class: |
C23C 016/00; C23C
014/26 |
Claims
1. A system for continuously melting and evaporating a solid
material comprising: a melting crucible for receiving and melting
the solid material to form molten material; and an evaporating
crucible for evaporating the molten material, the evaporating
crucible connected to the melting crucible in flow communication
with the melting crucible for receiving the molten material from
the melting crucible and having an opening for releasing vapor as
the molten material evaporates.
2. A melting and evaporating system as in claim 1 wherein the
melting crucible has an opening for receiving the solid material
and the melting and evaporating system further comprises a feeder
for feeding the solid material into the melting crucible as the
molten material evaporates.
3. A melting and evaporating system as in claim 2 wherein the
feeder automatically feeds the solid material into the melting
crucible as the molten material evaporates.
4. A melting and evaporating system as in claim 3 wherein the
feeder feeds the solid material into the melting crucible so as to
maintain the molten material in the evaporating crucible at a
substantially constant level during evaporation of the molten
material.
5. A melting and evaporating system as in claim 1 further
comprising: a melting crucible heater for heating the melting
crucible to a first temperature and melting the solid material in
the melting crucible; and an evaporating crucible heater for
heating the evaporating crucible and the molten material in the
evaporating crucible to a second temperature different then the
first temperature for evaporating the molten material.
6. A melting and evaporating system as in claim 5 wherein the
evaporating crucible heater is controllable independently of the
melting crucible heater.
7. A melting and evaporating system as in claim 1 wherein the
evaporating crucible is arranged so that the molten material is
maintained at a substantially constant level in the evaporating
crucible during evaporation of the molten material.
8. A melting and evaporating system as in claim 1 wherein the
evaporating crucible is a conduit which is arranged so that the
molten material flows from the melting crucible through the conduit
to the vapor releasing opening in the evaporating crucible.
9. A melting and evaporating system as in claim 1 wherein the
melting crucible and evaporating crucible are arranged so that the
melting crucible holds the molten material at a first hydraulic
level and the evaporating crucible holds molten material at a
second hydraulic level which is the same as the first hydraulic
level.
10. A melting and evaporating system as in claim 9 wherein the
melting crucible and evaporating crucible are arranged side-by-side
and the evaporating crucible is a conduit which is arranged so that
the molten material flows from the melting crucible through the
conduit to the vapor releasing opening in the evaporating
crucible.
11. A melting and evaporating system as in claim 9 further
comprising a level monitor for monitoring the level of solid
material and molten material in the melting crucible.
12. A melting and evaporating system as in claim 1 wherein the
melting crucible and evaporating crucible are arranged so that the
melting crucible holds the molten material at a first level and the
evaporating crucible holds molten material at a second level which
is above the first level and the evaporating crucible draws the
molten material from the melting crucible, through the evaporating
crucible, to the vapor releasing opening via capillary action.
13. A melting and evaporating system as in claim 11 wherein the
evaporating crucible is a conduit which is at least partially
disposed in the melting crucible so that the molten material flows
from the melting crucible through the conduit to the vapor
releasing opening in the evaporating crucible.
14. A melting and evaporating system as in claim 1 wherein the
melting crucible and evaporating crucible are arranged so that the
melting crucible holds the molten material at a first level and the
evaporating crucible holds molten material at a second level which
is above the first level and the evaporating crucible draws the
molten material from the melting crucible, through the evaporating
crucible, to the vapor releasing opening via thermal syphonic
force.
15. A melting and evaporating system as in claim 14 wherein: the
evaporating crucible is a conduit which is at least partially
disposed in the melting crucible, has an upper portion extending
above the level of solid and molten material in the melting
crucible to the vapor releasing opening, so that the molten
material flows from the melting crucible through the conduit to the
vapor releasing opening in the evaporating crucible; and the
melting and evaporating system further comprises: a melting
crucible heater for heating the melting crucible to a first
temperature and melting the solid material in the melting crucible;
and an evaporating crucible heater for heating the evaporating
crucible and the molten material in the evaporating crucible
proximate the vapor releasing opening to a second temperature
different then the first temperature for evaporating the molten
material.
16. A melting and evaporating system as in claim 1 wherein the
melting crucible is larger than the evaporating crucible.
17. A melting and evaporating system as in claim 1 further
comprising a heat shield covering at least a portion of the melting
crucible.
18. A melting and evaporating system as in claim 1 further
comprising a plurality of evaporating crucibles for evaporating the
molten material, the evaporating crucibles each connected to the
melting crucible in flow communication with the melting crucible
for receiving the molten material from the melting crucible and
each having an opening for releasing vapor as the molten material
evaporates.
19. A vacuum vapor deposition coating system comprising: a vacuum
cell capable of maintaining a vacuum within the vacuum cell; and
the melting and evaporating system of claim 1 disposed within the
vacuum cell.
20. A method for melting and evaporating a solid material
comprising the steps of: melting the solid material in a melting
crucible to form molten material; flowing the molten material from
the melting crucible into an evaporating crucible connected to the
melting crucible; evaporating the molten material in the
evaporating crucible to form a vapor; and releasing the vapor from
the evaporating crucible.
21. A method as in claim 20 further comprising feeding the solid
material into the evaporating crucible as the molten material
evaporates.
22. A method as in claim 21 wherein the feeding step comprises
automatically feeding the solid material into the melting crucible
as the molten material evaporates.
23. A method as in claim 22 wherein the feeding step further
comprises feeding the solid material into the melting crucible so
as to maintain the molten material in the evaporating crucible at a
substantially constant level during evaporation of the molten
material.
24. A method as in claim 1 further comprising the steps of: heating
the melting crucible to a first temperature to melt the solid
material in the melting crucible; and heating the evaporating
crucible and the molten material in the evaporating crucible to a
second temperature different then the first temperature to
evaporate the molten material.
25. A method as in claim 20 further comprising maintaining the
molten material at a substantially constant level in the
evaporating crucible during evaporation of the molten material.
26. A method as in claim 20 further comprising holding the molten
material at a first hydraulic level in the melting crucible and
holding the molten material at a second hydraulic level in the
evaporating crucible, the first hydraulic level being the same as
the second hydraulic level.
27. A method as in claim 26 further comprising monitoring the level
of solid material and molten material in the melting crucible.
28. A method as in claim 20 wherein the flowing step comprises
drawing the molten material from the melting crucible, through the
evaporating crucible, to a vapor releasing opening in the
evaporating crucible via capillary action.
29. A method as in claim 1 wherein the flowing step comprises
drawing the molten material from the melting crucible, through the
evaporating crucible, to a vapor releasing opening in the
evaporating crucible via thermal syphonic force.
30. A system for continuously melting and evaporating a solid
material comprising: a pivotable melting crucible for receiving and
melting the solid material to form molten material; and an
evaporating crucible, positioned below the melting crucible, for
evaporating the molten material, wherein the melting crucible is
selectively pivotable between an upright position in which the
melting crucible receives and melts the solid material, and
alternatively, a tilted position in which the melting crucible
pours the molten material in the evaporating crucible.
31. A melting and evaporating system as in claim 30 further
comprising a conduit for receiving the molten material from the
melting crucible in the tilted position and delivering the molten
material to the evaporating crucible.
32. A melting-and evaporating system as in claim 30 wherein the
melting crucible has an opening for receiving the solid material
and the melting and evaporating system further comprises a feeder
for feeding the solid material into the melting crucible as the
molten material evaporates.
33. A melting and evaporating system as in claim 32 wherein the
feeder automatically feeds the solid material into the melting
crucible as the molten material evaporates.
34. A melting and evaporating system as in claim 30 wherein the
melting crucible includes a spout for pouring the molten material
into the evaporating crucible.
35. A melting and evaporating system as in claim 34 wherein the
melting crucible further includes a pouring sieve to prevent solid
material from passing into the evaporating crucible with the molten
material.
36. A method for continuously melting and evaporating a solid
material comprising: (a) melting the solid material in a melting
crucible in an upright position to form molten material; and (b)
pivoting the melting crucible from the upright position to a tilted
position and pouring the molten material in an evaporating crucible
positioned below the melting crucible; (c) evaporating the molten
material from the evaporating crucible; (d) pivoting the melting
crucible from the tilted position to the upright position; and (e)
repeating steps a-d.
37. A method as in claim 36 wherein the melting crucible has an
opening for receiving the solid material and the method further
comprises feeding the solid material into the melting crucible as
the molten material evaporates.
38. A method as in claim 37 wherein the feeder automatically feeds
the solid material into the melting crucible as the molten material
evaporates.
39. A system for continuously melting and evaporating a solid
material comprising: a melting crucible for receiving and melting
the solid material to form molten material; an electrically
conductive evaporating member disposed in the melting crucible for
evaporating the molten material; and an electric power supply for
supplying electric power to the evaporating member such that the
power supply, the evaporating member, the molten material and the
melting crucible form an electric circuit, the power supply
supplying sufficient power to heat the evaporating member and
evaporate at least a portion of the molten material which contacts
the evaporating member.
40. A melting and evaporating system as in claim 39 further
comprising a heater for initially melting at least a portion of the
solid material so that the molten portion of the solid material can
complete the electric circuit and the evaporating member becomes
capable of heating, melting and evaporating the solid material.
41. A melting and evaporating system as in claim 39 wherein the
evaporating member is disposed in the melting crucible so that at
least a portion of the evaporating member extends above the molten
material in the melting crucible, and the molten material is drawn
up the portion of the evaporating member by electromagnetic forces
generated by the electric circuit and evaporated by heat from the
portion of the evaporating member.
42. A melting and evaporating system as in claim 39 wherein the
evaporating member is a rod.
43. A melting and evaporating system as in claim 39 wherein the
melting crucible has an opening for receiving the solid material
and the melting and evaporating system further comprises a feeder
for feeding the solid material into the melting crucible as the
molten material evaporates.
44. A melting and evaporating system as in claim 43 wherein the
feeder automatically feeds the solid material into the melting
crucible as the molten material evaporates.
45. A melting and evaporating system as in claim 39 wherein the
heater is an electric arc discharge apparatus.
46. A method for continuously melting and evaporating a solid
material comprising: filling a melting crucible with the solid
material; placing an electrically conductive evaporating member in
the melting crucible; melting at least a portion of the solid
material to form molten material; and supplying electric power
supply to the evaporating member such that the power supply, the
evaporating member, the molten material and the melting crucible
form an electric circuit, the power supply supplying sufficient
power to heat the evaporating member and evaporate at least a
portion of the molten material which contacts the evaporating
member.
47. A method as in claim 46 wherein the evaporating member is
placed in the melting crucible so that at least a portion of the
evaporating member extends above the molten material in the melting
crucible, and the molten material is drawn up the portion of the
evaporating member by electromagnetic forces generated by the
electric circuit and evaporated by heat from the portion of the
evaporating member extending above the molten material.
48. A method as in claim 46 wherein the evaporating member is a
rod.
49. A method as in claim 46 wherein the melting crucible has an
opening for receiving the solid material and the method further
comprises feeding the solid material into the melting crucible as
the molten material evaporates.
50. A method as in claim 49 wherein the feeder automatically feeds
the solid material into the melting crucible as the molten material
evaporates.
51. A method as in claim 46 wherein the heater is an electric arc
discharge apparatus.
52. A vapor deposition coating system comprising: a vacuum cell
capable of maintaining a vacuum within the vacuum cell; a source of
coating vapor disposed in the vacuum cell; a first electrode
disposed in the vacuum cell; a second electrode disposed in the
vacuum cell so that there is a gap between the first and second
electrodes and coating vapor passes through the gap when the source
of coating vapor produces coating vapor; an electric power supply
for supplying electric power to the first and second electrodes so
that the first and second electrodes become oppositely charged and
create an electric arc discharge between the first and second
electrodes; and a switch connecting the power supply to the first
and second electrodes for selectively switching polarity between
the first and second electrodes.
53. A coating system as in claim 52 wherein: the switch is a first
switch; the first and second electrodes form a first pair of
electrodes; the coating system further comprises a second pair of
electrodes including a third electrode and a fourth electrode
spaced from one another so that there is a gap between the third
and fourth electrodes and coating vapor passes through the gap when
the source of coating vapor produces coating vapor; the electric
power supply supplies electric power to the third and fourth
electrodes so that the third and fourth electrodes become
oppositely charged and create an electric arc discharge between the
third and fourth electrodes; and a second switch connecting the
power supply to the third and fourth electrodes for selectively
switching polarity between the third and fourth electrodes, wherein
the first and second switches are phased so that whenever one of
the first and second pairs of electrodes is switching polarity,
another of the first and second pairs of electrodes has an electric
arc discharge therebetween.
54. A coating system as in claim 52 wherein the switch is capable
of automatically and repeatedly switching the polarity between the
first and second electrodes.
55. A coating system as in claim 52 wherein the electric arc
discharge is capable of ionizing the coating vapor in the gap and
forming a plasma.
56. A coating system as in claim 52 wherein the source of coating
vapor is an evaporator for melting and vaporizing a solid
material.
57. A coating system as in claim 52 wherein the source of coating
vapor comprises a plurality of evaporators for melting and
vaporizing a plurality of different solid materials.
58. A coating system as in claim 52 wherein the first and second
electrodes comprise an electrode material which significantly
erodes during the electric arc discharge when negatively
charged.
59. A coating system as in claim 58 wherein the electrode material
of the first electrode is different from the electrode material of
the second electrode.
60. A coating system as in claim 52 wherein the switch is capable
of switching the polarity of the first and second electrodes with
sufficient frequency to prevent insulating deposits on the
electrodes from interrupting the electric arc discharge between the
first and second electrodes.
61. A coating system as in claim 52 wherein the power supply for
the first and second electrodes is controllable independently from
power supplied to the coating vapor source.
62. A method for ionizing a coating vapor in a vapor deposition
coating system comprising the steps of: forming a vacuum within a
vacuum cell; supplying a coating vapor in the vacuum cell; passing
the coating vapor through a gap between a first electrode disposed
in the vacuum cell and a second electrode disposed in the vacuum
cell; supplying electric power to the first and second electrodes
so that the first and second electrodes become oppositely charged
and create an electric arc discharge between the first and second
electrodes; and switching polarity between the first and second
electrodes while the electric power is supplied to the first and
second electrodes.
63. A method as in claim 62 wherein the switching step comprises
automatically and repeatedly switching the polarity between the
first and second electrodes.
64. A method as in claim 62 wherein the electric power supply is a
DC power supply.
65. A method as in claim 62 wherein the electric arc discharge
ionizes the coating vapor in the gap and forms a plasma.
66. A method as in claim 62 wherein the step of forming the coating
vapor comprises melting and vaporizing a solid material.
67. A method as in claim 62 wherein the step of forming the coating
vapor comprises melting and vaporizing a plurality of different
solid materials.
68. A method as in claim 62 wherein the first and second electrodes
comprise an electrode material which, when negatively charged,
vaporizes during the electric arc discharge.
69. A method as in claim 68 wherein the electrode material of the
first electrode is different from the electrode material of the
second electrode.
70. A method as in claim 62 wherein the switching step comprises
switching the polarity of the first and second electrodes with
sufficient frequency to prevent insulating deposits on the
electrodes from interrupting the electric arc discharge between the
first and second electrodes.
71. A vapor deposition coating system comprising: a vacuum cell
capable of maintaining a vacuum within the vacuum cell; a source of
coating vapor disposed in the vacuum cell; an electric arc
discharge apparatus disposed in the vacuum cell, the electric arc
discharge apparatus comprising a cathode, an anodic hood at least
partially covering the cathode, and an electrical insulating
material connecting the cathode to the anodic hood, the cathode and
the anodic hood arranged to form an ionization chamber and the
anodic hood having a plasma discharge opening for discharging
plasma from the electric arc discharge apparatus; and an electric
power supply for supplying electric power to the electric arc
discharge apparatus so that when the electric power supply supplies
electric power to the electric arc discharge apparatus, the cathode
becomes negatively charged and the anodic hood becomes positively
charged so that (a) an electric arc discharge is created between
the cathode and the anodic hood in the ionization chamber, (b) the
cathode emits electrons and ionizes the coating vapor in the vacuum
cell by the source of coating vapor, (c) the cathode vaporizes and
forms an ionized cathode vapor within the ionization chamber, and
(d) the ionized cathode vapor is emitted from the discharge opening
of the anodic hood and mixes with the coating vapor.
72. A coating system as in claim; 71 further comprising an ignitor
for igniting the electric arc discharge in the ionization
chamber.
73. A coating system as in claim 72 wherein the ignitor includes a
electrically conductive element connected to the anodic hood and
the power supply and a mechanism for selectively connecting the
electrically conductive element to the cathode to ignite the
electric arc discharge apparatus, and alternatively, disconnecting
the electrically conductive element from the cathode.
74. A coating system as in claim 71 wherein the insulating material
comprises a sleeve, the cathode comprises a metallic disk disposed
in the sleeve, the insulating material comprises a sleeve and the
anodic hood tapers from the sleeve to the discharge opening.
75. A coating system as in claim 71 wherein the electric power
supply is a DC power supply.
76. A coating system as in claim 71 wherein the source of coating
vapor is an evaporator for melting and vaporizing a solid
material.
77. A coating system as in claim 71 wherein the source of coating
vapor comprises a plurality of evaporators for melting and
vaporizing a plurality of different solid materials.
78. A coating system as in claim 71 wherein the cathode comprises
an electrode material which vaporizes during the electric arc
discharge.
79. A coating system as in claim 78 wherein the electrode material
of the cathode has a composition different from the coating vapor
composition.
80. A coating system as in claim 71 wherein the power supply for
the electric arc discharge apparatus is controllable independently
from power supplied to the coating vapor source.
81. A coating system as in claim 71 wherein the anodic hood has an
interior surface and shields the interior surface and the cathode
from the coating vapor.
82. A method for ionizing a coating vapor in a vapor deposition
coating system comprising the steps of: forming a vacuum within a
vacuum cell; supplying a coating vapor in the vacuum cell; passing
the coating vapor adjacent an electric arc discharge apparatus
disposed in the vacuum cell, the electric arc discharge apparatus
comprising a cathode, an anodic hood at least partially covering
the cathode, and an electrical insulating material connecting the
cathode to the anodic hood, the cathode and the anodic hood
arranged to form an ionization chamber and the anodic hood having a
plasma discharge opening; and supplying electric power to the
electric arc discharge apparatus so that the cathode becomes
negatively charged and the anodic hood becomes positively charged
so that (a) an electric arc discharge is created between the
cathode and the anodic hood in the ionization chamber, (b) the
cathode emits electrons and ionizes the coating vapor in the vacuum
cell by the source of coating vapor, (c) the cathode vaporizes and
forms an ionized cathode vapor within the ionization chamber, and
(d) the ionized cathode vapor is emitted from the discharge opening
of the anodic hood and mixes with the coating vapor.
83. A method as in claim 82 further comprising the step of igniting
the electric arc discharge in the ionization chamber.
84. A method as in claim 82 wherein the insulating material
comprises a cylindrical sleeve, the cathode comprises a metallic
disk disposed in the cylindrical sleeve, the insulating material
comprises a cylindrical sleeve and the anodic hood comprises a
frustoconical shell extending from the cylindrical sleeve to the
discharge opening.
85. A method as in claim 82 wherein the electric power supplied is
DC power.
86. A method as in claim 82 wherein the coating vapor is supplied
by melting and vaporizing a solid material.
87. A method as in claim 82 wherein the coating vapor is supplied
by melting and vaporizing a plurality of different solid
materials.
88. A method as in claim 82 wherein the coating vapor has a
composition and the cathode vaporizes to form a composition
different from the coating vapor composition.
89. A method as in claim 82 further comprising controlling the
power supply for the electric arc discharge apparatus independently
from power supplied to the coating vapor source.
90. A continuously fed electrode comprising: a plurality of
electrode members which vaporize when discharged in an electric arc
discharge; a housing defining a loading chamber for receiving the
electrode members in series; and an electrode member feeder for
continuously feeding the plurality of electrode members, in series,
through the housing to an electric arc discharge position so that
one of the plurality of electrode members is in the electric arc
discharge position at a time.
91. An electrode as in claim 90 further comprising a hood for at
least partially covering the one electrode member in the electric
arc discharge position, the hood including a discharge opening.
92. An electrode as in claim 90 wherein the electrode functions as
a cathode in an electric arc discharge apparatus.
93. An electrode as in claim 90 further comprising a magazine for
feeding the plurality of electrode members, in series, into the
housing.
94. An electrode as in claim 93 wherein the magazine automatically
feeds the electrode members into the housing so that the electrode
member feeder can continuously feed the plurality of electrode
members, in series, through the housing to the electric arc
discharge position.
95. An electrode as in claim 90 wherein the electrode members each
have a cavity in one end and a protrusion in an opposite end so
that the protrusions and cavities of the plurality of electrode
members mate when the electrode members are fed through and out of
the housing.
96. An electrode as in claim 90 further comprising a cooler for
cooling the one electrode member in the electric arc discharge
position.
97. An electric arc discharge apparatus comprising the continuously
fed electrode of claim 68, an anode, and an electric power supply
for supplying electric power to the one electrode member and the
anode so that the one electrode member and the anode become
oppositely charged with the one electrode having a cathodic charge
and the anode having an anodic charge, and create an electric arc
discharge between the one electrode member and the anode, so that
the plurality of electrode members are vaporized, in series, at the
electric arc discharge position.
98. An electric arc discharge apparatus comprising the continuously
fed electrode of claim 91 and an electric power supply, wherein:
the continuously fed electrode further comprises an electrical
insulating material insulating the one electrode member from the
hood in the electric arc discharge position; the hood is arranged
to form an ionization chamber into which the electrode members are
fed from the housing; and when the electric power supply supplies
electric power to the electric arc discharge apparatus, the one
electrode member in the electric arc discharge position in the
ionization chamber becomes negatively charged and the hood becomes
positively charged so that an electric arc discharge is created
between the one electrode member and the hood in the ionization
chamber, the one electrode member emits electrons, vaporizes and
forms an ionized cathode vapor within the ionization chamber, and
the ionized cathode vapor is emitted from the discharge opening of
the hood.
99. A vapor deposition coating system comprising: a vacuum cell
capable of maintaining a vacuum within the vacuum cell; a source of
coating vapor disposed in the vacuum cell; the continuously fed
electrode of claim 90 disposed in the vacuum cell; a second
electrode disposed in the vacuum cell; an electric power supply for
supplying electric power to the one electrode member and the second
electrode so that the one electrode member and the second electrode
become oppositely charged, create an electric arc discharge, and
ionize the coating vapor.
100. A vapor deposition coating system as in claim 99 further
comprising an evacuation cell for feeding electrode members into
the vacuum cell while the vacuum cell maintains a vacuum, the
evacuation cell being capable of receiving electrode members from
outside the vacuum cell, evacuating air from the evacuation cell
under vacuum, and feeding the electrode members into the vacuum
cell without disrupting the vacuum within the vacuum cell.
101. A method for producing an electric arc discharge comprising
the steps of: continuously feeding a plurality of electrode
members, in series, through an electrode housing to an electric arc
discharge position so that one of the plurality of electrode
members is in the electric arc discharge position at a time; and
supplying electric power to the one electrode member as the one
electrode member is fed to the electric arc discharge position and
to a second electrode proximate the one electrode member, so that
the one electrode member and the anode become oppositely charged
with the one electrode having a cathodic charge and the anode
having an anodic charge, and create an electric arc discharge
between the one electrode member and the anode, so that the
plurality of electrode members are vaporized, in series, at the
electric arc discharge position.
102. A method as in claim 101 further comprising cooling the
electrode members in the electric arc discharge position.
103. A method for vacuum vapor deposition coating comprising the
steps of: forming a vacuum within a vacuum cell; supplying a
coating vapor in the vacuum cell; producing an electric arc
discharge in the vacuum cell in accordance with the method as in
claim 101; and passing the coating vapor adjacent the electric arc
discharge.
104. A vapor deposition coating system comprising: an ionized vapor
enclosure; an evaporator for producing coating vapor in the ionized
vapor enclosure at a rate of evaporation; an ionizing source for
ionizing the coating vapor to a degree of ionization; and an
apparatus for measuring the rate of evaporation from the evaporator
and the degree of ionization of the coating vapor comprising: an
electrically conductive element; an ammeter connected to the
electrically conductive element for measuring electric current
through the electrically conductive element; an electric power
supply for supplying electric current to the electrically
conductive element through the ammeter; and a switch for
selectively connecting the electric power supply to the
electrically conductive element, closing the electric circuit, and
causing the power supply to heat the electrically conductive
element, and, alternatively, disconnecting the electric power
supply from the electrically conductive element, opening the
electric circuit, and allowing the electrically conductive element
to cool, wherein, when the switch is open and electric power is
supplied to the electrically conductive element, a first circuit is
formed and electric current flows from the electric power source,
through the electrically conductive element, ammeter, and the
ionizing vapor to a ground, and when the switch is closed and
electric power is supplied to the electrically conductive element,
a second circuit is formed and electric current flows from the
power supply, through the electrically conductive element, the
ammeter, and the switch.
105. A measuring apparatus as in claim 104 further comprising a
timer for controlling the opening and closing of the switch.
106. A measuring apparatus as in claim 104 wherein the electrically
conductive element is positioned in the ionized vapor enclosure
such that, when the switch is open and electric power is supplied
to the electrically conductive element, the electric current flows
from the electrically conductive element to the ionized vapor
enclosure and to ground.
107. A measuring apparatus as in claim 104 wherein the electrically
conductive element is a wire.
108. A measuring apparatus as in claim 104 wherein the electrically
conductive element is a first electrically conductive element and
the measuring apparatus further comprises a second electrically
conductive element positioned in the ionized vapor enclosure such
that, when the switch is open and electric power is supplied to the
first electrically conductive element, the electric current flows
from the first electrically conductive element to the second
electrically conductive element and to ground.
109. A method for measuring the degree of ionization in a vapor
deposition coating system which comprises an ionized vapor
enclosure, an evaporator for producing coating vapor in the ionized
vapor enclosure, and an ionizing source for ionizing the coating
vapor to a degree of ionization, the method comprising the steps
of: exposing an electrically conductive element to the ionized
coating vapor in the ionized vapor enclosure; supplying electric
current to the electrically conductive element so that the electric
current flows through the electrically conductive element and the
ionized vapor to ground; and measuring electric current through the
electrically conductive element with an ammeter.
110. A method as in claim 108 wherein the electric power is
supplied to the electrically conductive element flows from the
electrically conductive element to the ionized vapor enclosure and
to ground.
111. A method as in claim 108 wherein the electrically conductive
element is a wire.
112. A method for measuring the rate of evaporation from an
evaporator in a vapor deposition coating system which comprises an
ionized vapor enclosure, the evaporator for producing coating vapor
in the ionized vapor enclosure at a rate of evaporation, and an
ionizing source for ionizing the coating vapor, the method
comprising the steps of: exposing an electrically conductive
element to the ionized coating vapor; supplying electric current to
the electrically conductive element and closing a first circuit
including the electrically conductive element to heat the
electrically conductive element; opening the first circuit; and
thereafter while still supplying electric current to the
electrically conductive element, measuring the rate of change of
the electric current through the electrically conductive element
and the ionized coating vapor to ground with an ammeter.
113. A method as in claim 112 wherein the electric power supply is
a DC power supply.
114. A method as in claim 112 wherein the electric power is
supplied to the electrically conductive element flows from the
electrically conductive element to the ionized vapor enclosure and
to ground.
115. A method as in claim 112 wherein the electrically conductive
element is a wire.
116. A vapor deposition coating system comprising: a vacuum cell
having an interior and capable of maintaining a vacuum within the
vacuum cell; a source of ionized coating vapor disposed in the
vacuum cell; an electrode disposed in the vacuum cell; and an
ionizing power supply connected to the electrode for supplying
sufficient power to the electrode to ionize gas in the vacuum cell
so that the ionized gas removes deposited volatile material from
the interior of the vacuum cell.
117. A vapor deposition coating system as in claim 116 wherein the
ionizing power supply is selected from high frequency, radio
frequency, or DC power.
118. A vapor deposition coating system as in claim 116 further
comprising a plurality of electrodes disposed in the vacuum cell
and wherein the power supply is connected to the plurality
electrodes for supplying sufficient power to the electrode to
ionize gas in the vacuum cell so that the ionized gas removes
deposited coating vapor from the interior of the vacuum cell
119. A vapor deposition coating system as in claim 116 wherein the
ionized gas removes volatile or oxidizable particles deposited from
the coating vapor on the interior of the vacuum cell.
120. A method for removing material deposited in a vacuum cell from
a coating vapor in a vapor deposition coating system comprising the
step of supplying sufficient ionizing power to an electrode
disposed in the vacuum cell to ionize gas in the vacuum cell so
that the ionized gas removes the deposited coating vapor from the
interior of the vacuum cell.
121. A method as in claim 120 further comprising supplying
sufficient power to a plurality of electrodes to ionize gas in the
vacuum cell so that the ionized gas removes the deposited coating
vapor from the interior of the vacuum cell.
122. A method as in claim 120 wherein the ionizing power is
selected from high frequency, radio frequency, or DC power.
123. A method as in claim 120 wherein the ionized gas removes
volatile or oxidizable particles deposited from the coating vapor
on the interior of the vacuum cell.
Description
TECHNICAL FIELD
[0001] This invention generally relates to vacuum vapor deposition
coating of substrates and methods and systems involved in vacuum
vapor deposition. More particularly, this invention relates to the
production of a highly-active and energized plasma-enhanced vapor
from a solid source, such as silicon, and to the application of the
plasma within a continuously-operating high-speed coating
system.
BACKGROUND OF THE INVENTION
[0002] The plasma-enhanced vapor may be used for deposition onto
plastic articles, particularly for depositing a glass-like coating
onto plastic bottles. The coating provides an enhanced gas-barrier
and better adhesion compared with prior art coatings, and is
suitable for pressurized containers, whose surface flexes and
stretches, and whose internal pressure acts against an external
coating. The primary component of the vapor is produced by
evaporating, in an evaporative source, one or more solids and the
deposition of the coating may be applied in conjunction with a
reactive gas, or gases, to provide desired coating clarity or
colorization. Further, it may be produced by using more than one
evaporation source and solids of different boiling points.
[0003] Commercial applications of plastic articles have experienced
a growth, because of the properties of these articles such as
low-cost, light weight, flexibility, resistance to breakage, and
ease of manufacture and shaping. However, plastics also have the
disadvantage of relatively low abrasion-resistance and poor barrier
properties against the permeation of vapors such as water, oxygen,
and carbon dioxide. In food packaging applications, limitations in
barrier properties have limited the use of plastics. For example,
in the case of beverage bottles, inadequate barrier properties have
restricted the use of smaller bottles required in some markets.
Solutions to this problem, including the use of high-barrier
plastics and coatings of various types, have been either
uneconomical or have provided inadequate barrier-improvement or add
expense to the known recycling processes.
[0004] A number of processes have been developed for the
application of coatings on plastic, but these have been mainly for
plastic films. Relatively few processes have been developed which
allow the economic application of a glass-like coating onto
preformed plastic containers such as PET bottles, where the demands
on the coating's barrier performance are increased by the flexing
of the walls of the bottle, the stretching of said walls under
pressure, and the delaminating force due to the in-bottle pressure.
Also, most processes are on the batch-production principle, and
very few processes exist which can be applied to a
continuously-running process.
[0005] U.S. patent application Ser. No. 08/818,342 filed by Plester
et al on Mar. 14, 1997, and PCT International Application
PCT/US98/05293 filed on Mar. 13, 1998 describe the use of an anodic
arc for externally-coating beverage bottles and their disclosures
are incorporated by reference herein in their entirety. Anodic arc
systems are also described by Ehrich et al in U.S. Pat. Nos.
4,917,786; 5,096,558; and 5,662,741, the disclosures of which are
also incorporated herein by reference.
[0006] The basic anodic system, as described by the prior art, has
the following disadvantages:
[0007] a) The crucibles evaporative material content, such as
silicon, cannot be replenished continuously when this evaporative
material is in powder or pellet/chip form.
[0008] b) The quantity of vapor evolved from the crucible depends
partly on the degree of filling of the crucible with evaporative
material. Since the degree of crucible-filling is a variable which
constantly changes, this could present a control problem.
[0009] c) The distribution, at various angular displacements, of
the quantity of vapor evolved from the crucible, also depends
partly on the degree of filling of the crucible with evaporative
material. This makes it difficult to use the vapor from the
crucible for the purpose of coating several articles
simultaneously, without the risk that these will all receive
different amounts of coating.
[0010] d) The lips of the crucible are eroded by the anodic arc.
This not only presents a maintenance problem, but it also means
that the material of the crucible may thus be included in the
coating composition and thereby reduce the performance of the
coating. For example, crucibles for holding silicon are normally
constructed of carbon, which is eroded and vaporized by the anodic
arc and the carbon vapor is free to form a contaminant in the
desired silicon or silicon dioxide coating.
[0011] e) The said crucible lip erosion further affects the
quantity of vapor evolved and the distribution of this vapor at
various angular displacements around the crucible.
[0012] f) Even where the crucible is independently heated (rather
than intentionally heated by the anodic arc), the anodic arc
represents a second and uncontrolled source of heating. This second
source of heating partly affects the quantity of vapor evolved,
irrespective of any control device for the crucible's independent
heating system. This makes process control of evaporation rate
difficult, whilst evaporation rate is an important parameter.
[0013] g) The anodic arc energizes the plasma, but since an
uncontrolled and unknown portion of this arc's energy is dissipated
by evaporation of the material in the crucible, this makes the
process control of the critical parameter of plasma-enhancement
difficult.
[0014] h) Since part of the energy of the anodic arc inadvertently
causes evaporation, even in anodic arc systems with independent
crucible heating, this limits the amount of energy available for
plasma enhancement.
[0015] i) Anodic arc systems employing independent crucible heating
have complicated designs around the crucible in view of the
conflicting needs, on the one hand to heat the crucible and on the
other hand to provide a cooled anodic connection. This can result
in additional cost and complication, oversized heating systems, and
energy waste, as well as lead to crucible-damage on shut-down due
to the cooling-effect of the anodic connection.
[0016] j) Many applications, particularly those involving colored
coatings, require the simultaneous evaporation of more than one
solid substance. For barrier enhancement, it can also be desirable
to add other substances to the base coating. Since such substances
differ in boiling point, they cannot be combined in a single
evaporating crucible, because evaporative fractionation within the
crucible would lead to poor coating composition control. Therefore,
multi-component coatings using the anodic arc system must be
produced by a multi-series of anode-cathode couples, since one
separate anodic arc source for each crucible is needed for
process-control purposes. This not only makes a multi-component
coating systems complicated and expensive, but also risks
interference between the closely positioned array of anodic
arcs.
[0017] k) The cathode's evaporative material cannot be replenished
continuously and it is therefore desirable in practice to use
materials which erode slowly. This acts contrary to the desire to
use the cathode for optimum plasma enhancement and ionization,
since materials which achieve this often have a high erosion rate.
The use of Zn, Cu, Al, noble metals, alkaline earths, and
particularly Mg, has been found to be highly desirable, and in most
cases continuous cathode replenishment is needed for economic
operation.
[0018] Prior art exists (German Patent DE 4440521C1, Hinz et al)
where the crucible is independently heated by electrical resistance
or by thermal radiation, and where the anodic arc
plasma-enhancement is provided separately by means of a cathode and
a separate anode. However, the anode of such systems quickly
becomes coated with the evaporated material from the crucible, or
with plasma particles, or with the reaction product when a reactive
gas is used. Such systems are therefore only usable where the
coating is electrically conducting, since the anode would otherwise
quickly become inoperative and the system would shut down. Since
the barrier coating of plastic articles often requires the use of
coatings with materials such as silicon, which are electrically
non-conducting, such prior art cannot be used for many barrier
coating systems.
[0019] It is important to control accurately the coating thickness
on a plastic article and therefore highly desirable to be able to
measure continuously, and in situ, the rate of deposition from an
evaporative source, so that adjustments to the controls of the said
evaporator source can be made as needed throughout the coating
operation. Prior art provides means for measuring the rate of
deposition by measuring the change of the oscillation frequency of
a crystalline substance as the evaporated solids deposit on said
crystalline substance. However, the crystalline substance quickly
becomes coated and can no longer function, so the system is not
usable for normal process control in continuous operating coating
systems. A self-regenerating system for rate-of-deposition
measurement is needed to enhance process control.
[0020] The quality of a coating on plastic articles, particularly
the quality of the barrier property of coatings on plastic bottles,
is dependent on the control of the degree of ionization and thus on
the energy-level of the plasma. A suitably high-energy plasma
enables the substrate surface to be cleared of dirt and inert
molecules, promoting coating adhesion and coating purity, and
further enables coating particles to become embedded in the
substrate or to react with the substrate, additionally promoting
adhesion. High-energy plasma also promotes the chemical reaction of
coating particles with each other, thus forming a dense matrix on
the substrate surface, which further enhances adhesion and barrier
properties. Finally, high-energy plasma induces coating particles
to be deposited in a flat, dense physical structure due to the
impingement of high-energy collisions, enhancing coating continuity
and denseness. On the other hand, over-energized plasma may
overheat the substrate, or cause excessive decomposition or
degassing from the substrate, or damage the coating. The evolution
of gases from the substrate surface during its degassing mixes with
the coating particles and reduces coating quality. It is thus
important to measure and control plasma energy and degree of
ionization. Prior art does not teach how this can be achieved.
[0021] An example of the need for controlled use of high-energy
plasma is presented by barrier coating of plastic bottles for
carbonated beverages. A barrier coating on a plastic bottle for
carbonated beverages must desirably be able to flex, stretch, have
adhesion capable of withstanding the pressure migration of the
carbon dioxide from the inside of the bottle, and be robust and
abrasion resistant in use. It is also desirably dense, preferably
amorphous and continuous over the bottle surface. These properties
rely on applying controlled. high-energy plasma.
[0022] All evaporator systems deposit particles within their
enclosure, the latter being normally a high vacuum enclosure.
Operation under vacuum is necessary so as to avoid heat damage of
heat sensitive substrates such as plastic, and also to avoid gas
phase reactions, which in turn would reduce the barrier and other
qualities of the coating, since many of these desired properties
rely on the on-surface interaction of the coating particles.
Particles deposited within the vacuum enclosure tend to disturb the
mechanical operation of the coating system and in particular tend
to absorb volatiles and make vacuum pump-down more difficult. As a
result, the walls of such vacuum enclosures must be cleaned
regularly, and this involves production loss and shut-down. An
in-situ cleaning system which enables regular and rapid cleaning of
the enclosure internals without releasing vacuum and opening the
enclosure is desirable for continuous operation and would improve
economic operation by reducing downtime.
SUMMARY OF THE INVENTION
[0023] Accordingly, it is an object of this invention to provide a
system for plasma-enhanced evaporation of one or more solid
materials, normally inorganic solid material(s), and for use of
such an evaporation system in vapor deposition coating of a plastic
substrate such as a plastic beverage container, with or without
reactive gases, in a manner which enables continuous operation and
the provision of a well controlled, high energy plasma. The
following are further objects of this invention:
[0024] a) To enable replenishment, within the evaporator-crucible
system, of the solid material to be evaporated and used for coating
without interrupting the evaporator operation;
[0025] b) To enable the said evaporator crucible to remain at
substantially the same degree of filling during its operation;
[0026] c) To provide a vapor particle distribution around the said
crucible, which continuously remains constant and well
directed;
[0027] d) To provide an evaporation system where both the
evaporator-energy supply to the crucible and the control of this
energy are substantially independent of the energy supplied for
plasma-enhancement;
[0028] e) To provide an evaporation system with electric arc
discharge plasma enhancement which has improved control of each
system function, substantially avoids erosion or damage of the
evaporator crucible, whose crucible can have a simpler design,
which can operate with vapors whose deposited solids are
non-conducting electrically, which enables several materials to be
evaporated separately but enhanced by the same single arc;
[0029] f) To enable continuous replenishment of the cathode's
evaporative material;
[0030] g) To enable high energy plasma through use of rapidly
eroding materials at the cathode, particularly Mg, other alkali
metals, and metals of relatively low boiling point;
[0031] h) To enable materials produced by the erosion of the
cathode (e.g. Mg, alkaline metals, low boiling point metals. etc.)
to be incorporated as dopants in the coating;
[0032] i) To enable substantially uninterrupted measurement and
control in a continuously running coating process, of evaporation
rate and degree of ionization; and
[0033] j) To enable in-situ cleaning of vacuum enclosures without
need to release vacuum, thereby enhancing the operation of
continuously running coating processes.
[0034] The foregoing and other objects of this invention are
fulfilled by providing a system and method for continuously melting
and evaporating a solid material for use in a vapor deposition
coating system, a vapor deposition coating system including said
continuous melting and evaporating system, a vapor deposition
coating system including an electric arc discharge system which
switches polarity between electrodes during operation, a vapor
deposition coating system comprising an electric arc discharge
system including an electrode with combined anodic and cathodic
parts for ionization, a continuously fed electrode for producing an
electric arc discharge and a coating vapor, a system for measuring
the rate of evaporation from an evaporator and the degree of
ionization in a vapor deposition coating system, and a
self-cleaning vapor deposition coating system. Each of these
aspects of the present invention are summarized below.
[0035] The system of this invention for continuously melting and
evaporating a solid material comprises a melting crucible for
receiving and melting a solid material to form molten material and
an evaporating crucible for evaporating the molten material. The
evaporating crucible is connected to the melting crucible in flow
communication with the melting crucible for receiving the molten
material from the melting crucible and releasing vapor through an
opening in the evaporating crucible as the molten material
evaporates. This arrangement allows for additional evaporative
solid material to be continuously added to the melting crucible
without interfering with evaporation of the molten solid in the
evaporating crucible. Accordingly, solid evaporative material can
be continuously added to the evaporator during operation of the
evaporator so that a coating system incorporating this melting and
evaporating system can continue uninterrupted for an extended
period. Furthermore, because the evaporating crucible is separate
from the melting crucible, the melting crucible and the evaporating
crucible can be heated separately and maintained at different
temperatures and the evaporating crucible can be made much smaller
than the melting crucible. In addition, the evaporating crucible
and the melting crucible can be arranged so that the level of
molten evaporative material in the evaporating crucible remains
substantially constant to provide constant and well directed
coating vapor.
[0036] The corresponding method of this invention for continuously
melting and evaporating a solid material therefore comprises the
steps of melting the solid material in a melting crucible to form
molten material, flowing the molten material from the melting
crucible into an evaporating crucible connected to the melting
crucible, evaporating the molten material in the evaporating
crucible to form a vapor, and releasing the vapor from the
evaporating crucible. This system and method of the present
invention desirably includes continuously and automatically feeding
the solid evaporative material into the melting crucible as the
molten material evaporates so as to maintain the molten material in
the evaporating crucible at a substantially constant level during
evaporation of the molten material. Various embodiments of this
continuous melting and evaporating system include an arrangement
wherein the melting crucible and evaporating crucible are arranged
so that the melting crucible and the evaporating crucible hold
molten material at the same hydraulic level, an arrangement wherein
the evaporating crucible draws the molten evaporative solid from
the melting crucible via capillary action, and an arrangement
wherein the evaporating crucible draws the molten evaporative
material from the melting crucible via thermal syphonic force.
Other embodiments include an arrangement wherein a pivoting melting
crucible melts solid evaporative material and periodically pours
molten evaporative material into an evaporation chamber and an
arrangement wherein an electrically heated element melts and
evaporates solid evaporative material in a melting crucible. Such
embodiments do not require energy from an electric arc discharge
for evaporation of the solid material and are simple, relatively
inexpensive, and resistant to heat damage.
[0037] The foregoing system for continuously melting and
evaporating a solid evaporative material is particularly useful in
a vacuum vapor deposition coating system wherein the continuous
melting and evaporating system is disposed within a vacuum cell
capable of maintaining a vacuum within the vacuum cell.
[0038] The vapor deposition coating system and method of the
present invention involving switching polarity between electrodes
includes forming a vacuum within a vacuum cell, supplying a coating
vapor in the vacuum cell, passing the coating vapor through a gap
between a first electrode disposed in the vacuum cell and a second
electrode disposed in the vacuum cell, supplying electric power to
the first and second electrodes so that the first and second
electrodes become oppositely charged and create an electric arc
discharge between the first and second electrodes, and switching
polarity between the first and second electrodes while the electric
power is supplied to the first and second electrodes. The switch is
desirably operated automatically and repeatedly switches the
polarity between the first and second electrodes and the electric
power supply is a DC power supply. By switching the polarity
between the first and second electrodes, each electrode alternates
between anodic and cathodic function, so that coating vapor, which
deposits on the first and second electrodes when the electrodes are
in the anodic function, is evaporated when the electrodes are in
the cathodic function. Eventually, the coating vapor, when
non-electrically conductive, can disrupt the operation of an
electrode in a vapor deposition coating system. By switching the
polarity between first and second electrodes, the first and second
electrodes remain substantially free of deposited coating.
[0039] According to another vapor deposition coating system and
method of the present invention, a vacuum is formed within a vacuum
cell, coating vapor is supplied in the vacuum cell, the coating
vapor is passed adjacent an electric arc discharge apparatus, and
electric power is supplied to the electric arc discharge apparatus
so that a cathode portion of the electric arc discharge apparatus
becomes negatively charged and an anodic hood, at least partially
covering the cathode becomes positively charged, so that an
electric arc discharge is created between the cathode and the
anodic hood. The electric arc discharge apparatus includes an
electrically insulating material connecting the cathode to the
anodic hood, and the cathode and the anodic hood are arranged to
form an ionization chamber with the anodic hood having a plasma
discharge opening. When electric power is supplied to the electric
arc discharge apparatus, an electric arc discharge is created
between the cathode and the anodic hood in the ionization chamber,
the cathode emits electrons and ionizes the coating vapor disposed
in the vacuum cell by the source of coating vapor, the cathode
vaporizes and forms an ionized cathode vapor within the ionization
chamber and the ionized cathode vapor is emitted from the discharge
opening of the anodic hood and mixes with the coating vapor from
the evaporation source and the reactive gas, if any, in the vacuum
cell to form a coating plasma. The foregoing method and system are
relatively simple and economical for producing a plasma enhanced
coating vapor in a vapor deposition coating system.
[0040] The continuously fed electrode of this invention comprises a
plurality of electrode members which vaporize when connected
electrically to provide an electric arc discharge, a housing
defining a loading chamber for receiving the electrode members in
series and including an electrically insulating sleeve, and an
electrode member feeder for continuously feeding the plurality of
electrode members, in series, through the insulating sleeve in the
housing to an electric arc discharge position so that one of the
plurality of electrode members is being fed to the electric arc
discharge position at a time. This system enables continuous
replenishment of the electrodes evaporative material and enables
the use of rapidly eroding materials at the cathode of a high
energy plasma coating system, enables materials produced by the
vaporization of the electrode members to be incorporated as dopants
in a vapor deposition coating system, and enables substantially
uninterrupted production of ionized vapor in an electric arc
discharge vapor deposition coating system.
[0041] Desirably, the continuously fed electrode functions as a
cathode in an electric arc discharge apparatus. The electrode
members are desirably elongate rods or cylinders and are
automatically fed from a magazine into the loading housing so that
the electrode member feeder can continuously feed the plurality of
electrode members, in series, to the electric arc discharge
position. In addition, the continuously fed electrode includes a
cooling system for cooling the one electrode member, which is in
the electric arc discharge position.
[0042] The present invention also encompasses an electric arc
discharge apparatus comprising the continuously fed electrode
described above, an anode, and an electric power supply for
supplying electric power to the one electrode member and the anode.
The electric power is supplied so that the one electrode member and
the anode become oppositely charged with the one electrode having a
cathodic charge and the anode having an anodic charge. This creates
an electric arc discharge between the one electrode member and the
anode so that the plurality of electrode members are vaporized, in
series, as each of the plurality of electrode members are fed into
the electric arc discharge position within the electrode
housing.
[0043] Alternatively, the present invention encompasses electric
arc discharge apparatus comprising the continuously fed electrode
described above and an electric power supply. The continuously fed
electrode includes a hood for at least partially covering the one
electrode member in the electric arc discharge position. An
electrically insulating material insulates the one electrode member
in the electric arc discharge position from the hood and the hood
is arranged to form an ionization chamber into which the electrode
members are fed from the housing. When the electric power supply
supplies electric-power to the electric arc discharge apparatus,
the one electrode member being fed to the electric arc discharge
position and into the ionization chamber becomes negatively charged
and the hood becomes positively charged so that an electric arc
discharge is created between the one electrode member and the hood
in the ionization chamber, the one electrode member vaporizes and
forms an ionized vapor within the plasma chamber, and the ionized
vapor is emitted from the discharge opening of the hood to mix with
the vapor from the evaporation source and form a plasma.
[0044] The present invention also encompasses a vapor deposition
coating system comprising the continuously fed electrode described
above and a vacuum cell in which the continuously fed electrode is
disposed. This vapor deposition coating system also includes a
source of coating vapor disposed in the vacuum cell, a second
electrode disposed in the vacuum cell, and an electric power supply
for supplying electric power to the one electrode member and the
second electrode so that the one electrode member and the second
electrode become oppositely charged, create an electric arc
discharge and ionize the coating vapor. Desirably, this vapor
deposition coating system further includes an evacuation cell for
feeding electrode members into the vacuum cell while the vacuum
cell maintains a vacuum. The evacuation cell is capable of
receiving electrode members from outside the vacuum cell,
evacuating air from the evacuation cell, and feeding the electrode
members into the vacuum cell under vacuum without disrupting the
vacuum within the vacuum cell.
[0045] The present invention further encompasses an apparatus for
measuring the rate of evaporation from evaporator and the degree of
ionization in a vapor deposition coating system comprising two
electrical circuits connected to a wire. The first electrical
circuit includes a wire, an ammeter connected to the wire for
measuring electric current through the wire and a variable DC-power
source. When the wire is exposed to an ionized gas, a current flows
from the said DC-power source, through the ammeter and through the
ionized gas to the walls of the ionized gas enclosure or vacuum
cell and to ground. The current flow, measured by the ammeter,
bears a relationship to the degree of ionization in the ionized gas
and increases as the degree of ionization increases.
[0046] The second electrical circuit includes the said wire, a DC
or AC supply and a switch. The apparatus desirably includes a timer
for controlling the opening and closing of the switch. Particles
from the ionized gas deposit on the said wire when the wire is cold
and the electrical resistance of theses particles reduces the
current flow in the first electrical circuit. When the switch is
closed, a current flows within the second electrical circuit and
heats up the said wire, thus causing the deposited particles to
re-evaporate, which prevents these particles from insulating the
wire and affecting the electrical current flow. The electrical
current flow measured in the first electrical circuit therefore
retains a constant relationship to the degree of ionization, so
long as the wire is heated. The measurement of degree of ionization
which this relationship provides, can be used to control the degree
of ionization, by means of adjusting the current flow from the
power supply to the electric arc by conventional means.
[0047] When the switch is opened, the wire cools and particles from
the ionized gas begin to deposit on the wire. The electrical
resistance of these particles reduces the current flow in the first
electrical circuit and the rate of reduction bears a relationship
to the rate of deposition of particles, which in turn bears a
relationship to the rate of production of coating particles by the
evaporator and electric arc means. The rate of evaporation can thus
be controlled by adjusting the current flow from the power supply
to the evaporator by conventional means.
[0048] The vapor deposition system itself is as described above and
includes an enclosure or cell, which must normally be maintained
under vacuum, and a source of ionized coating vapor which is
disposed within the said cell. The self-cleaning means includes one
electrode, or a plurality of electrodes, disposed within the cell.
The electrodes are connected to a power supply and are arranged so
that the entire gas space within the cell can be subjected to an
ionizing discharge. Suitable forms of power supply include HF, RF
and DC. As the coating of substrate proceeds within the cell, it is
inevitable that the coating particles deposit also on the interior
of the cell and on its internal parts. Such deposits include
volatile components which can re-evaporate and impair the function
of the coating system. The volatile components of the deposits
within the interior of the cell and its internal parts are removed
by supplying sufficient ionizing power to the electrode or
electrodes disposed in the vacuum cell to ionize gas in the vacuum
cell so that the ionized gas removes the deposited coating vapor.
This could be done during the operation of the coating system or
while the coating system is inoperative.
[0049] Other objects, features, and advantages of this invention
will become apparent from the follow detailed description,
drawings, and claims.
BRIEF DESCRIPTION OF DRAWINGS
[0050] FIG. 1 is a schematic diagram of an evaporator system, made
according to an embodiment of this invention, including a
continuously-fed melting crucible connected to an evaporating
crucible.
[0051] FIGS. 1A, 1B, 1C, 1D and 1E are schematic diagrams of
optional arrangements of a continuously-fed dual crucible system,
according particular embodiments of the present invention.
[0052] FIG. 2 is a schematic diagram of an evaporator system, made
according to an embodiment of this invention, wherein vapor is
energized to a plasma state by means of the arc generated by a pair
of DC electrodes, whose relative polarity periodically
alternates.
[0053] FIG. 2A is a schematic diagram of an evaporator system
similar to that shown in FIG. 2, except with two pairs of
electrodes whose relative polarity periodically alternates.
[0054] FIG. 3 is a schematic diagram of an evaporator system, made
according to an embodiment of this invention, wherein vapor is
energized to a plasma state by means of the discharge from a
cathode/anode combination.
[0055] FIG. 4 is a side elevation view of a continuously fed
electrode made according to an embodiment of this invention.
[0056] FIG. 4A is a sectional end view of the electrode illustrated
in FIG. 4.
[0057] FIG. 4B is a schematic diagram of an electrode member feeder
for the continuously fed electrode illustrated in FIG. 4.
[0058] FIG. 5 is a schematic diagram of a system for measuring the
rate of evaporation and degree of ionization within a vacuum vapor
deposition coating system, in accordance with an embodiment of this
invention.
[0059] FIG. 5A is an example graph of current versus voltage when
measuring degree of ionization with the electric circuit
illustrated in FIG. 5.
[0060] FIG. 5B is a schematic diagram illustrating an alternative
system for measuring the rate of evaporation and degree of
ionization within a vacuum vapor deposition coating system, in
accordance with an embodiment of this invention.
[0061] FIG. 6 is a schematic diagram of a vacuum chamber with
several DC-discharge probes (or alternatively RF or HF antennas)
mounted within it, enabling discharge within the interior of the
vacuum chamber, in accordance with an embodiment of this
invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0062] Overview
[0063] As summarized above, this invention encompasses vacuum vapor
deposition systems and methods, and systems and methods for use in
vacuum vapor deposition onto substrates. The following includes a
detailed description of embodiments of this invention including
evaporator systems and methods, electric arc discharge systems and
methods with polarity switching electrodes, electric arc discharge
systems and methods with a combination cathodic/anodic electrode,
electric arc discharge systems and methods with a continuously fed
electrode, a system and method for measuring rate of evaporation
and degree of ionization in a vapor deposition coating system, and
a self-cleaning vacuum vapor deposition coating system. In the
detailed description, like reference numerals are used to refer to
like parts throughout the Figures.
[0064] Evaporator Systems and Methods
[0065] FIG. 1 shows an evaporator system suitable for a solid, such
as silicon, and principally comprising a melting crucible 1, a
molten evaporative material 2, a short conduit 3, and an
evaporating crucible 4 connected in fluid flow communication to the
melting crucible by the short conduit, the evaporating crucible
being in the form of a straight-through, relatively narrow bore
pipe. In this arrangement, the melting crucible 1 and the
evaporating crucible are side-by-side. The melting crucible 1 is
heated by a melting crucible heater 5, which is a suitable,
conventional device, and normally consists either of a radiant
heater, or a contact heater, or a resistance heater. For example,
for melting silicon, a radiant heater complete with an external
heat insulating mantle is an effective solution. The melting
crucible heater 5 is provided with an adjustable AC or DC
power-supply 6 and this power supply incorporates the necessary
conventional means for controlling the energy output of the melting
crucible heater 5 so as to provide temperature control.
[0066] The solid evaporative material 7 to be melted is fed through
an opening in the melting crucible 1 in the form of powder or chips
or pellets or the like by means of a feeder such as a chute 8.
Suitable solid evaporative materials for vacuum vapor deposition
coating include silicon and are listed in PCT International
Application PCT/US98/05923, already incorporated herein by
reference. The design of the feed-system, connected to chute 8 is
not shown, and will depend on the material and its form, and employ
conventional material feed means. For example, in the case when
silicon is used as the solid evaporative material, the material
would preferably be in form of pellets, and the feed system would
include a silo or bin to hold the said pellets, and a valving
system at base of the silo/bin to enable a controlled amount of
pellets to flow down chute 8 whenever the melting crucible 1
requires material make-up. Said material make-up is necessary
whenever the level 9 of molten evaporative material in the melting
crucible 1 drops by a predetermined amount. The level 9 of molten
evaporative material can be monitored by a level-monitor 10, using
conventional non-contact methods such as X-rays, ultrasound, or by
weighing the melting crucible 1, together with any components
rigidly attached to it.
[0067] The molten evaporative material 2 flows from the melting
crucible 1 through the conduit 3 to the evaporating crucible 4. The
evaporating crucible 4 is heated by the evaporating crucible heater
11 and a separate, adjustable, evaporating crucible power supply
12, employing similar conventional means as already described for
the heating of melting crucible 1. The evaporating crucible 4 is
heated to a temperature suitable for evaporating the molten
evaporative material 2 in the evaporating crucible and the coating
vapor produced is released from the evaporating crucible through an
opening 13 in the top of the evaporating crucible. The power supply
12 for the evaporating crucible 4 is independently controlled from
the power supply 5 for the melting crucible 1 so that the
temperature of the melting crucible, which is desirable larger than
the evaporating crucible, can be maintained at a lower level than
the temperature of the evaporating crucible.
[0068] The hydraulic level 9 of material 2 in the melting crucible
1 equates to the hydraulic level in the evaporating crucible 4 due
to natural hydraulic forces. As the evaporative material 2 is
automatically fed into the melting crucible 1 to maintain level 9,
this automatically maintains a substantially constant and correct
level in the evaporating crucible 4 as the molten evaporative
material evaporates, and thus the conditions for constant vapor
evolution rate and constant particle distribution from the
evaporating crucible are achieved.
[0069] The rate of evaporation from the evaporating crucible 4 is
controlled by regulating the energy input to the evaporating
crucible power supply 12, using conventional heater power
regulation means. The rate of evaporation from the evaporating
crucible 4 is adjusted to give the desired rate for the coating
process by means described hereinafter.
[0070] The melting crucible 1 is provided with a lid 15 to reduce
migration of vapor. Excessive vapor in this melting crucible 1 can
adversely affect the material feed system to chute 8 and the
heaters 5 and 11. Ideally, the melting crucible 1 should be
maintained at a temperature which is sufficient to melt the
evaporative material 2 while producing minimal vapor. Control of
the temperature of the evaporative material 2 in the melting
crucible 1 is through the energy input from power supply 6 and this
energy input is regulated by conventional means. The energy
regulator can be controlled according to the rate of in-flow of
pellets 7, which in-flow will normally be constant, or, optionally,
according to the temperature measurement 16 of the evaporative
material 2 by conventional non-contact means such as
IR-measurement. Optionally, temperature measurement 16 can be by an
electric resistance thermometer or a bimetallic thermocouple
embedded in the walls of the melting crucible 1.
[0071] For coating heat-sensitive articles, such as PET beverage
bottles, it is important to reduce the heat radiated from the
evaporator system. A heat shield 17 constructed of reflective
material of suitable heat and corrosion resistance, such as
stainless steel, covers the melting crucible 1 and the connecting
conduit 3. The system illustrated in FIG. 1 is particularly
advantageous with respect to avoiding heat damage of coated
articles, since the only part able to radiate heat directly onto
the coated articles is the evaporating crucible 4, whose dimensions
are small because the evaporating crucible has little capacity due
to its continuous feed.
[0072] Although not illustrated in FIG. 1, the melting crucible 1
can be linked to more than one evaporating crucible 4 by means of
multiple conduits 3 where this is needed by a specific system. Such
an arrangement reduces the cost and/or complication of multiple
solid feed systems to the chute 8.
[0073] Construction materials for the evaporator system described
will depend on the material 2 to be evaporated. Generally, suitable
construction materials for the evaporator system can withstand the
high temperature necessary to melt and evaporate the solid
evaporative material 2 without deteriorating or melting and must be
inert to the evaporative material 2. For the evaporation of
silicon, system components 1, 3 and 4 are preferably constructed of
a heat conductive grade of carbon.
[0074] FIG. 1A, 1B and 1C show versions of the system illustrated
in FIG. 1 not requiring the short connecting conduit 3, since this
feature can lead to leaks with molten evaporative materials 2 of
certain substances. In FIG. 1A, a melting crucible 1a is heated by
a melting crucible heater 5a and an adjustable power-supply 6a. A
tubular evaporating crucible 4a is mounted within the melting
crucible la so that the melting crucible holds the molten material
2 at a first level and the evaporating crucible holds the molten
material at a second level which is above the first level and the
evaporating crucible, at least partially submerged in the molten
material, draws the molten material from the melting crucible,
through the evaporating crucible, to a vapor releasing opening 13a
via capillary action. The top of the tubular evaporating crucible
4a extends through an opening in the melting crucible lid 15a and
is heated by the evaporating crucible heater 11a and the associated
adjustable power-supply 12a, and thus the temperature of the molten
evaporative material is brought from melting temperature level to
evaporation temperature level.
[0075] An overflow cavity 18 is positioned to allow excess molten
material 2 to drip back into the melting crucible 1a. This overflow
cavity 18 enables the outside of the top of the tubular evaporating
crucible 4a to remain essentially free of molten evaporative
material 2 and thus the top of tubular evaporating crucible 4a may
be heated by conventional radiant or resistance heating. A heat
shield 17a is positioned above the melting crucible 1a for the same
purpose, and with same basic construction, as already described
with regard to FIG. 1. Vapor is emitted from the release opening
13a at the top of the tubular evaporating crucible 4a in same
manner as described under FIG. 1. Control of the temperature of the
evaporative material 2 and of the evaporative material level 9 are
also as described under FIG. 1.
[0076] In FIG. 1B, a melting crucible 1b has a well 19 extending
below the bottom of the melting crucible and an adjustable power
supply 6b. The foot of the tubular evaporating crucible 4b fits
tightly into the well 19 and can be fed with molten evaporative
material 2 from the melting crucible 1b by a small channel 20 and
the upper portion of the evaporating crucible extends out of the
melting crucible through an opening in the lid 15b of the melting
crucible. The tubular evaporating crucible 4b is mounted within the
melting crucible 1b so that the melting crucible 1b holds the
molten material 2 at a first level and the evaporating crucible
holds the molten material at a second level which is above the
first level and the evaporating crucible, at least partially
submerged in the molten material, draws the molten material from
the melting crucible, through the evaporating crucible, to a vapor
releasing opening 13a via thermal syphonic forces. The well 19 is
externally heated by the evaporating crucible heater 11b and
associated adjustable power supply 12b to evaporating temperature,
as is the upper portion of the evaporating crucible 4b proximate a
vapor releasing opening 13b. By the action of the thermal-syphon
forces, molten evaporative material 2 rises up the tubular
evaporating crucible 4b and excess molten evaporative material 2
continuously overflows back down to the melting crucible 1b via a
series of cavities 18a. A heat shield 17b is provided for the same
purpose and with same basic construction as already described
above. Vapor is emitted from the vapor release opening 13b in the
top of the tubular evaporating crucible 4b in the same manner as
already described under FIG. 1. Control of the temperature of the
evaporative material 2 and of the evaporative material level 9 are
also as described under FIG. 1.
[0077] In FIG. 1C, a tubular evaporating crucible 4c is an integral
part of a melting crucible 1c and its spout-like extension 1'c.
This arrangement can be beneficial where it is difficult to seal
vapor evolution from molten evaporative material 2 through
component joints, since such joints are completely avoided in FIG.
1C. The flow of pellets 7 now flows into the spout-like extension
1'c so as to the maintain the level 9 of the evaporative material
substantially constant. The melting crucible 1c incorporates a
loose-baffle 1"c which is introduced through the opening of
spout-like extension 1'c and this loose-baffle 1"c prevents
unmolten pellets 7 from flowing to the tubular evaporating crucible
4c. The evaporator system in FIG. 1C functions similarly to the
systems already described with regard to FIGS. 1, 1A, and 1B, and
incorporates a melting crucible heater 5c, an evaporating crucible
heater 11c, associated adjustable power supplies 6c and 12c, and a
heat shield 17c.
[0078] FIG. 1D shows a method of melting the evaporative material 2
in a batchwise-operating melting crucible 1d which is heated, in
the manner already described, by crucible heater 5d and power
supply 6d. The melting crucible 1d receives a fixed batch of solid
pellets 7 via chute 8d when in its upright position (shown in solid
line). When the batch of solid pellets 7 has melted, the melting
crucible 1d can be tilted to a pouring position (shown in
chain-clothed line) and in this position releases a required amount
of molten material 2, which flows down conduit 3 to evaporating
crucible 4d. The released amount of material 2 is controlled by a
level-monitor 10a such as to maintain an hydraulic level 9. As
material 2 is evaporated in evaporating crucible 4d, level 9d falls
and the filling operation, by means of tilting melting crucible 1d,
is repeated. Melting crucible 1d can be fitted with a pouring spout
1'd and a pouring sieve 1"d to avoid drips and to avoid passage of
relatively large solid pieces of material 2 to the evaporating
crucible 4d. The evaporating crucible 4d is heated by the
evaporating crucible power supply 12d, using conventional heater
power regulation means. The tilting of melting crucible 1d is by
conventional means (not shown).
[0079] FIG. 1E shows a means of avoiding the need for an
evaporating crucible, particularly where the evaporative material 2
is nearly electrically non-conducting in the cold solid state, but
gradually increases its conductivity as the solid is heated and
further increases its conductivity in the molten state as in the
case of silicon. Solid pellets 7 are fed to melting crucible 1e via
chute 8e so as to maintain an approximate pellet level 9e. An
electrical circuit is formed between an adjustable power supply 6e,
via a switch 81 and via an electrically conductive evaporative
element or rod 4e, which is in contact with the base of crucible
1e. The rod 4e is heated by the current in the said electrical
circuit and can therefore melt the solid pellets 7 of material 2 in
contact with it. The rod 4e therefore maintains a pool of molten
material 2 in its immediate vicinity and near its base (as
indicated in FIG. 1E) and this pool is surrounded by solid pellets
7.
[0080] Suitable material for making the conductive rod 4e depends
on the composition of the evaporative material 2 to be melted.
Generally, material which is suitable for making the melting
crucible 1e is suitable for making the conductive rod 4e. Desirably
therefore, the conductive rod 4e is made of material which is
substantially inert to the evaporative material 2 at the conditions
under which the evaporative material is melted and evaporated. When
the evaporative material 2 is silicon, the conductive rod 4e is
desirably carbon.
[0081] Depending on the characteristics of the evaporative material
2, it may at start-up be necessary to produce an initial melt of
material 2 by means of an external heating source. When this
start-up need for melting arises, the solid pellets 7 can initially
be melted either by means of an arc which can be generated by a
cathode 35e which is connected via a power supply 26e to the
melting crucible 1e, or by the heater and power supply means
already described under FIG. 1a to 1d. Where an arc is to be used
this can be achieved by switching the electrode 35e, which is
similar to electrode 35 as shown and described with FIG. 3
hereunder, to a negative polarity by means of closing switch 82 and
forming an arc by discharging to the positive polarity of melting
crucible 1e, by closing switch 81, and maintaining this arc until
the solid pellets 7 have melted sufficiently to produce an initial
pool of molten material 2. This pool of molten material 2 can then
conduct sufficient heat to the mass of solid pellets 7 to ensure
that the melting process can continue simply by the heat generated
in rod 4e, and without the further need of an external heating
source. From that point on, the electrode 35e can revert to its
normal function and be used to produce a plasma in the manner
described hereunder, since it is only needed for producing molten
material 2 in the start-up phase. Electrode 20 as described
hereunder with FIG. 2 can also be temporarily switched in the
start-up phase to produce molten material 2 by connecting one of
the electrodes 20 via a switch so as to conform to the circuit
shown for this purpose in FIG. 1e. The rod 4e can take the form of
various other electrically conductive elements such as a plate or
the like. Also, a plurality of rods 4e may be applied.
[0082] In the particular case of silicon, (or materials like
silicon which exhibit a negatice temperature coefficient), the
electrode system 35e may be used by means of switches 81 and 82 to
heat or melt the solid pellets 7 whenever the electrical connection
of rod 4e with the base of crucible 1e becomes inadequate. The
heating using electrode 35e is maintained by means of switches 81
and 82 until the current flow through rod 4e restarts due to the
electrical conduction of the silicon in the base of crucible
1e.
[0083] Depending on characteristics of material 2 and particularly
in case of silicon, the electrical current flowing in rod 4e forces
some molten material 2 to flow to its rod ends 4'e and 4"e, due to
electromagnetic forces whereby 4"e is above level 9e. A thin film
of molten material 2 flows up to rod-end 4"e, where it meets the
hottest part of rod 4e, because this part must conduct the whole
electrical current from power supply 6e in contrast to the parts of
rod 4e which are in full contact with electrically-conducting
molten material 2, such as in the case of rod-end 4'e, since the
molten material 2 helps to augment the circuit. When the
evaporative material 2 comes in contact with the hottest part of
rod 4e (i.e. rod-end 4"e), it evaporates and the vapor is emitted
from vapor releasing opening 13e. The power supply 6e to rod 4e is
adjusted to give the required evaporation rate of material 2 and
this maintains a quantity of molten material 2 in contact with rod
4e, which in turn maintains the electrical circuit and enables the
evaporation to continue.
[0084] Electric Arc Discharge System With Polarity Switching
Electrodes
[0085] FIG. 2 illustrates an electric arc discharge apparatus
including two identical electrodes 20 comprising a disc 21 of a
suitable, coating process specific material to which a DC-potential
is connected, an electrical insulating sleeve 22, a hood 23, and a
cooling system 24, which comprises water-cooled chambers in good
thermal contact with the disc 21.
[0086] The discs 21 of the electrodes 20 are connected to a
switching system 25 which in turn is connected to an adjustable
DC-power supply 26 whose energy output is regulated by conventional
means. The switching system 25 enables the polarity (+ or -) of the
two electrodes to change, so that when one electrode A becomes
negatively charged, i.e. cathodic, electrode B simultaneously
becomes positively charged, i.e. anodic, and vice-versa.
[0087] In the cathodic (i.e. negative polarity state), a stream of
electrons emerges from disc 21 and ionizes the vapor from
evaporator system 27 to form a plasma. The discs 21 erode during
the electric arc process and the rate of erosion is dependent on
the material chosen. Since the eroded material passes to the gas
phase, and is ionized to form a plasma within the space defined by
hood 23 and disc 21, it mixes with the plasma formed from the
vaporized particles from evaporation system 27. It is often
desirable to choose the material of disc 21 such that its erosion
particles can form a property-enhancing dopant within the coating.
The compositions of the disks 21 of the two electrodes A and B can
even be different so as to add multiple components to the coating
vapor.
[0088] For example, in the case of deposition of a silicon oxide by
evaporating silicon (or a silicon oxide) in evaporator system 27,
it is often desirable to add dopants to the main coating supplied
by evaporator system 27 through the addition of the erosion
particles from disc 21. In case of mainly silicon or silicon oxide
coatings, useful dopants are disclosed in PCT International
Application PCT/US98/05293, and these can either be alloyed within
the basic material of disc 21 or disc 21 can be entirely composed
of them. Common basic materials for disc 21 are brass and
magnesium.
[0089] The material of the hood 23 should remain essentially inert
to the electric arc discharge process and thus resist erosion and
corrosion. For example, stainless steel is appropriate for many
applications.
[0090] The electrodes A and B and an evaporator system 27 are
disposed in a vacuum cell (such as in FIG. 6) which is capable of
maintaining a vacuum. The evaporator system 27 produces a vapor
from a solid either by a method as described by FIG. 1, or by any
other means, such as the simple means of a conventional, heated
crucible. The evaporator system 27 is positioned so that the vapor
emerging from the evaporator system mainly passes through the gap
between electrodes A and B. Since the electrodes A and B are
oppositely charged, an electrical discharge occurs between them,
and a plasma is formed consisting of the ions and electrons
discharged from the discs 21, ionized material produced from vapor
from evaporator system 27, and ionized reactive gases, if used.
Reactive gas or gases (not shown) are fed into the space between
electrodes A and B, when reactive gases are a necessary component
of the coating. An example of the use of reactive gas is the
application of oxygen as reactive gas with a silicon vapor in a
vacuum cell to produce a transparent silicon dioxide coating and is
described in U.S. patent application Ser. No. 08/818,342 filed by
Plester et al and PCT International Application PCT/US98/05293,
already incorporated by reference.
[0091] The detailed operation of electrodes A and B is as follows.
When electrode A is to be the cathode and B is to be the anode,
electrode A is switched to the negative polarity by switch 25 and
electrode B to positive polarity. An electric discharge arc is
formed between the two electrodes and disc 21 of electrode B
gradually becomes coated with particles from the evaporator system
27 and disc 21. Meanwhile, disc 21 of electrode A begins to
vaporize and erode due to the discharge of particles. The coating
of disc 21 of electrode B with particles would lead to the
disruption of the arc between the two electrodes if, as in case of
silicon dioxide or silicon, the coating particles are electrically
non-conducting. By switching polarity after a time, so that
electrode B becomes cathodic and electrode A becomes anodic, disc
21 of electrode B commences to erode, and thus naturally cleans any
deposits collected during its period as anode, whilst disc 21 of
electrode A begins to receive a coating. The electrodes A and B are
thus maintained free of insulating deposits by the switching of
polarity, and the frequency of switching is adjusted to the
particular process and to the requirement of maintaining a viable
discharge arc.
[0092] The arc intensity, set up between electrodes A and B, and
the degree of ionization of the vapor from the evaporator system 27
are regulated by the energy input of the electrode power-supply 26,
which is independent of the power supply for the evaporator system.
During the instant of polarity switching by switch 25, the arc set
up between electrodes A and B may die out depending on the rapidity
of switching. Each electrode A and B is fitted with an ignition
system 28 which conventionally consists of a mechanically operated
metal finger or electrically conductive element, which is connected
by connection 29 to the anode of the DC power supply, and is made
momentarily to touch disc 21 of the cathodic electrode at the
instant of ignition, so as to recommence ignition and restart the
discharge arc between the electrodes. Connection 29 can incorporate
an electrical resistor 29a and a switch 29b, as required to control
the ignition system.
[0093] Although only one evaporator 27 is shown in FIG. 2, it
should be understood that the arrangement of electrodes A and B can
be used to ionize vapors from a plurality of evaporators producing
an ionized gas mixture from a variety of vapors of different
composition.
[0094] FIG. 2a shows an alternative arrangement to that of FIG. 2,
which avoids the need for re-ignition when the electrodes 20 in the
A and B positions of FIG. 2 switch polarity. On FIG. 2a, two sets
of electrodes, denoted 20A, 20B and 20C, 20D, are employed and each
set has a separate DC-power supply 26 and switching system 25. The
switching of the two sets of electrodes is phased so that only one
set is switching polarity at any instant, leaving the other set to
maintain a plasma. By ensuring that the switching is rapid and that
the electrodes are positioned close to the plasma cloud generated
by evaporator system 27 and the electrodes 20 themselves, this
plasma acts as re-ignition means for the electrodes.
[0095] It should be understood that although two pairs of
electrodes are illustrated in FIG. 2a, more than two sets of
electrodes could be used simultaneously provided that at least one
pair of electrodes is generating an electric arc discharge at any
time during operation.
[0096] Electric Arc Discharge System With Combined Anode/Cathode
Electrode
[0097] An alternative to the electric arc discharge apparatus
described by FIG. 2 is shown in FIG. 3, which shows an electrode 35
comprising a disc 21, to which the cathodic terminal of a DC-power
supply 26 is connected, an electrical insulating sleeve 22 for the
disc 21, an anodic hood 23 in the shape of a tapered shell at least
partially covering the disc, and a cooling system 24 for cooling
the disk 21. The anodic terminal of the adjustable DC power supply
26 is connected via a fixed resistor 36 and a switch 37 to the
anodic hood 23. The electrode 35 in FIG. 3 can be constructed
identically to electrode 20 in FIG. 2 and the only difference in
principle is the connection of the anodic hood 23 to the anodic
terminal of power supply 26. Vapor is generated by an evaporator
system 27 adjacent the electrode 35 in a vacuum cell (not shown).
The function and embodiment of the evaporator system 27 follows the
description already given for FIG. 2. In this embodiment, the
anodic hood 23 has the function of shielding its own interior
surface and the cathodic disk 21 from coating vapor emitted by the
evaporator 27.
[0098] A cathodic discharge arc is established in an ionization
chamber within the combined anode/cathode electrode 35 between the
in-built cathode disc 21 and the integral, anodic hood 23. This
discharge is emitted from the hood 23 through a plasma discharge
opening 23a into the vapor rising from evaporator system 27,
energizing this vapor, and forming a plasma which consists of
ionized particles from disc 21, electrons from disc 21 and ionized
particles within the vapor emitted by evaporator system 27. The
degree of plasma enhancement can be regulated by the energy input
of the power supply 26, which in turn is regulated by conventional
means and is independent of the power supply for the evaporator
27.
[0099] Ignition can be by means of the ignition system 28, as
already described under FIG. 2. However, the discharge from disc 21
forms a plasma which condenses and deposits within the anodic hood
23 when the combined electrode 35 is shut down. This deposit
consists of electrically conducting particles, which bridge across
the gap between disc 21 and hood 23, causing a short-circuit
whenever the electrode 35 ceases to be energized. When the
energizing switch 37 is closed and energy is reapplied to electrode
35, there is a momentary short-circuit between the cathodic disc 21
and the anodic hood 23 enabling ignition. The short-circuit does
not persist because the deposit bridging the cathodic disc 21 with
the anodic hood 23 re-evaporates immediately after ignition, and
this permits electrode 35 to ignite and commence normal
operation.
[0100] Although only one evaporator 27 is shown in FIG. 3, it
should be understood that the combined anode/cathode electrodes 35
can be used to ionize vapors from a plurality of evaporators
producing a variety of vapors of different composition. The
temperature increase in the ionization chamber formed by the disk
21 and the anodic hood 23 can rise to a point where the anodic hood
erodes significantly. The erosion of the anodic hood 23 can be
reduced or prevented by cooling the outside of the anodic hood, for
example, by means of a water jacket 38 and inlet and outlet water
flows 39' and 39".
[0101] Continuously Fed Electrode
[0102] FIG. 4 shows an embodiment of an electric arc discharge
apparatus, as already described in the case of electrodes 20 and
35, where the erodable component can be continuously replaced and
comprises an electrode member 21a in the form of a bar or rod which
can be continuously replaced by a plurality of electrode members
21a and which is identical in operating principle to the disc 21 in
FIGS. 2 and 3. This continuously fed electrode is particularly
advantageous when the electrode members 21a are composed of a
material which quickly vaporizes during electric arc discharge.
Materials for the electrode members 21a which quickly vaporize or
erode are often beneficial because they help energize, ionize, and
enhance the plasma. Particularly, for plasma enhancement of silicon
vapor mixed with a reactive gas such as oxygen, the use of rapidly
eroding materials, such as zinc, brass and magnesium have been
found to be very beneficial to the barrier properties of a coating
on PET-bottles, as reported in PCT International Application
PCT/US98/05293.
[0103] Each electrode member 21a is continuously fed, in series,
from a housing 59 defining a loading chamber so that one of the
plurality of electrode members is fed to an electric arc discharge
position E at a time. As each one of the electrode members is fed
to the electric arc discharge position E, the one electrode member
being fed is gripped between two water-cooled, semi-circular cold
segments 40a and 40b. The cold segments 40a and 40b are served by
flexible cooling water pipes 41, and are mounted on two arms 42a,
42b which are held by a hinge 43 and forced together or apart, when
desired, by conventional mechanical means 44 (not shown in detail)
which could involve a conventional electrically activated piston,
or similar mechanism. The two cold segments 40a, 40b and the two
arms 42a, 42b are in electrical contact with the cathodic terminal
of a DC power supply 26, as already described. Hinge 43 is
connected to a support bracket (not shown), which itself is mounted
in an electrically insulated manner.
[0104] The hood 23, already described in conjunction with FIGS. 2
and 3, is split into 2 halves, forming a split-hood 45 and the two
halves of split-hood 45 are mounted via electrically insulating
mountings on arms 42a, 42b, so that one half of the split-hood 45
is mounted on each arm 42a and 42b and the two halves of the
split-hood come together to form a complete hood when the arms 42a,
42b are forced together by mechanical means 44. The split hood 45
is arranged to form an ionization chamber into which the electrode
members 21a are fed. For the sake of clarity, split-hood 45 is
shown in broken lines in FIG. 4. to avoid over-complicating the
presentation.
[0105] Each electrode member 21a, as it is fed to the discharge
position E, is held in an insulating sleeve 46, which is
constructed of an inert, insulating, high temperature tolerant
material, such as glass or ceramic, and is supported, along with
the housing 59 by a bracket 47. The rearward end of the electrode
member 21a being fed to the discharge position E is pressed against
a piston 48 which can be moved by a drive means 49. As the
electrode member 21a erodes, arms 42a, 42b open periodically at
fixed time intervals, determined by the process and the rate of
erosion of the electrode member, and drive means 49 pushes the
electrode member 21a in direction B by an amount which compensates
for the erosion. Erosion rates of the electrode member 21a can be
accurately determined by proper control of current from power
supply 26 and of material purity of the electrode member 21.
[0106] A magazine 50 holds numerous unused electrode members 21a.
Stops 51 hold the stack of unused discs 21 and allow one unused
electrode member 21 to enter position C when a positioner 52 on
drive means 49 determines that drive means 49 has advanced to a
point where position C is clear and therefore can accommodate a
replacement electrode member 21a. At that point, stops 51 are
opened by activators 53 and allow just one replacement electrode
member 21 to drop into position C. Stops 51 and activators 53
together form a conventional feed escapement, and will not be
described further.
[0107] The electrode members 21a have a protrusion 54 on the
rearward end and a matching cavity 55 on the forward end, as marked
by direction B, such that the protrusion and cavity fit and grip
together when pushed by piston 48. When position C is free to
receive a replacement electrode member 21a, as detected by
positioner 52, the drive means 49 withdraws in direction D to make
space for the replacement electrode member 21a which is then
allowed by stops 51 to fall into position C. Drive means 49 then
advances to push replacement disc 21a till the cavity 55 on its
front end engages and locks with the protrusion 54 on the rearward
end of the particular electrode member 21a which is in actual use
at that time in the discharge position E. Thereafter, the drive
means 40 continues periodically to advance the electrode member 21a
to keep pace with erosion, in the manner already described.
[0108] The system described by FIG. 4 is intended to be mounted
within a high vacuum enclosure and the magazine 50 can be refilled
during maintenance shutdowns. As shown in FIG. 4B, the magazine 50
can also be fed from outside the vacuum enclosure by providing an
evacuation cell 50a located in communication with the vacuum
enclosure and consisting of a separate chamber which can be sealed
by two doors 56a, 56b. During refilling of the magazine 50, the
separate evacuation cell 50a is brought to atmospheric pressure by
closing door 56b and opening door 56a. The evacuation cell 50a is
then filled with electrode members 21. Door 56a of the second
compartment 50a is then closed and the second compartment 50a
evacuated by operating valve 57. When the second compartment 50a
has been evacuated, door 56b is opened and electrode members 21 are
allowed to roll in a controlled manner down a chute from
compartment 50a to compartment 50. This procedure can be repeated
indefinitely, without the main vacuum enclosure being vented.
[0109] The system described in FIG. 4, 4A, and 4B, can be used as a
continuously fed means instead of electrode 20 in FIG. 2, or
electrode 35 in FIG. 3, when a continuous feed is required.
[0110] System and Apparatus for Measuring Rate of Evaporation and
Degree of Ionization
[0111] FIG. 5 shows a means of continuously measuring the rate of
evaporation from an evaporator system 27, whether evaporator system
27 is a simple, electrically heated crucible or a continuously fed
system as described by FIG. 1, or a cathodic-arc-heated crucible as
in PCT International Application PCT/US98/05293. FIG. 5 also shows
a means of measuring the degree of ionization within the plasma.
For the function of the evaporation rate and ionization degree
measuring device in FIG. 5, the plasma can be generated by an
electric arc discharge apparatus such as illustrated in FIGS. 2, 3,
or 4, or by other means. In the example shown in FIG. 5, the plasma
making means actually shown is the combined anode/cathode electrode
35 by way of example only. As well as measuring the two said
operating factors, rate of evaporation and degree of ionization,
these said factors can be regulated, using the measurement data,
either automatically or manually. In principle, the rate of
evaporation can be regulated by the conventionally adjustable
energy input of power supply of the evaporator system 27 and the
degree of ionization can be regulated by the conventionally
adjustable energy input of the power supply 26 of the electrode
35.
[0112] The measuring device in FIG. 5 includes an electrically
conductive element which is a wire 60, supported in an appropriate
position within a vacuum vapor deposition coating chamber by an
electrically insulated support 61. The electrically conductive
element 60 could be another type of conductive member such as a
plate or rod. The wire 60 is connected to a power supply 62 via a
switch 63. When the switch 63 is closed, the wire 60 is heated, and
when the switch 63 is open, the wire 60 cools. The switch 63 is
opened/closed by a timer 64 which controls the open/close sequence
appropriately. The wire 60 is placed within and exposed to the
plasma to be measured and controlled. When the wire 60 is heated,
deposited particles from source 27 are evaporated and removed from
the surface of wire 60 and when wire 60 is not heated, deposited
particles build up on its surface. A DC-power source 65 is
connected via an ammeter 66 to the wire 60 and forms a circuit via
the ionized particles from source 27 and via the inside of the
walls of the vacuum cell 70 to ground, whereby the current
generated in this circuit is related to the electrical resistance
of the plasma and thus to the degree of ionization.
[0113] The I/U (current/voltage) diagram (see FIG. 5A) shows that
the degree of ionization is proportional to the current (I)
generated. As the wire 60 is coated with solid particles from the
plasma, if these are non-electrically conducting, as for example in
case of a silica coating process, the I/U curve is displaced (see
chain-dotted curve in FIG. 5A). When the wire 60 is heated,
deposits evaporate and/or are sputtered away, and within a fixed
time period, the current reverts to being a measure of the degree
of ionization (see solid-line curve in FIG. 5A). The fixed time
period and the relationship between current and degree of
ionization must be determined experimentally for the specific
process. When a measurement of degree of ionization has been made,
the heater circuit 67 is switched off by opening switch 63. This
allows coating particles to build up on wire 60 and an evaporation
rate measurement can begin. The rate of change of the current
measured by ammeter 66 is related to the rate of deposition of
non-electrically conducting particles onto wire 60, and this gives
a measure of rate of evaporation. By alternating, therefore, from
heating the wire 60 to not heating it, measurements of both rate of
evaporation and degree of ionization can be made.
[0114] In cases when the inside of the walls of the vacuum cell is
quickly coated with non-electrically conducting material during the
specific coating process, the measurement of current flow between
wire 60 and the walls of the vacuum cell to ground via the ionized
particles from source 27 is disrupted. A means of avoiding this
disruption of the measurement circuit is shown in FIG. 5b. This
includes a reference wire 60a with its own means of heating/cooling
which are provided, as already described for wire 60 under FIG. 5,
through power supply 62a, switch 63a and timer 64a. The measurement
circuit now runs from AC or DC power source 65' to wire 60, via the
ionized particles to wire 60a and back to power source 65' (the
symmetrical use of similarly-sized wires 60a and 60 enables chice
of AC or DC power supply). Wire 60a receives coating particles in
the same way as the inner walls of the vacuum cell, but remains
unaffected because these particles are removed during the heating
cycle of wire 60a.
[0115] Self-Cleaning Vacuum Vapor Deposition System
[0116] FIG. 6 shows a vacuum cell 70 for coating articles by the
processes described above, and illustrates, in schematic form, an
evaporator source 76, such as illustrated in FIG. 1, or another
source of coating vapor, an article to be coated, i.e. coating
substrate 77, plasma making electrodes 78 such as those disclosed
in FIGS. 2-4, and a device 80 for measuring process parameters as
illustrated in FIG. 5, all disposed in the vacuum cell. It is well
known that the internals of vacuum coating enclosures gradually
become coated with misdirected coating particles and that such
unwanted coating of equipment can severely affect coating
performance, particularly the performance of the vacuum system,
because the misdirected particles which coat the equipment surfaces
trap water vapor and other volatiles. This necessitates frequent
shut-down for maintenance cleaning.
[0117] Several probes 71 are located within the vacuum enclosure
70, mounted in insulating-sleeves 72 and connected to an ionizing
power supply 73. Depending on the process and the type of coating
being applied, the power supply 73 can be HF, or RF, or DC.
Sufficient power must be supplied by the power supply 73 to cause
the gas in the vacuum enclosure 70 to ionize. The process of
ionizing the gas in enclosure 70 quickly vaporizes deposits within
the enclosure 70 and burns these up when they are combustible (as
for example, organic deposits due to condensation of vapor
emanating from plastic substrates). This reduces the frequency of
the need to undertake more time consuming and labor intensive
cleaning. This cleaning process, using strategically mounted probes
71 throughout the vacuum enclosure 70, can be ignited periodically,
normally without interrupting the coating process. Alternatively,
it can be applied during brief shut-downs of the coating process,
particularly where the cleaning of the inside of vacuum enclosure
70 can be enhanced by increasing pressure, typically in the range
from 1 to 10.sup.-2 mbar. The material of probes 71 must be
suitable for the chosen form of power supply (HF or RF or DC) and
resist corrosion under the process conditions in enclosure 70.
Examples of suitable materials are stainless steel, copper and
titanium.
[0118] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *