U.S. patent number 3,710,072 [Application Number 05/141,791] was granted by the patent office on 1973-01-09 for vapor source assembly.
This patent grant is currently assigned to Airco, Inc.. Invention is credited to Robert L. Shrader, Kazumi N. Tsujimoto.
United States Patent |
3,710,072 |
Shrader , et al. |
January 9, 1973 |
VAPOR SOURCE ASSEMBLY
Abstract
A vapor source assembly is described in which an electron beam
is deflected in an arcuate path by a main magnetic field from an
electron beam gun positioned below the level of the crucible to
impinge upon the top surface of material in the crucible. A second
magnetic field is produced within the first magnetic field and has
lines of force of variable orientation to provide a controllable
variation in beam deflection so that the beam may be swept upon the
surface of the material contained in the crucible.
Inventors: |
Shrader; Robert L. (Castro
Valley, CA), Tsujimoto; Kazumi N. (El Cerrito, CA) |
Assignee: |
Airco, Inc. (New York,
NY)
|
Family
ID: |
22497272 |
Appl.
No.: |
05/141,791 |
Filed: |
May 10, 1971 |
Current U.S.
Class: |
219/121.15;
219/121.21; 313/156; 118/726; 219/121.28; 335/210 |
Current CPC
Class: |
C23C
14/30 (20130101); H01J 37/3053 (20130101) |
Current International
Class: |
C23C
14/30 (20060101); C23C 14/28 (20060101); H01J
37/305 (20060101); B23k 015/00 () |
Field of
Search: |
;219/121EB,121EM
;313/49.5R,156 ;13/31 ;335/210,213 ;336/184 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Truhe; J. V.
Assistant Examiner: Peterson; Gale R.
Claims
What is claimed is:
1. A vapor source assembly comprising, means forming a crucible for
containing material to be vaporized, an electron beam gun
positioned below the level of said crucible for producing an
electron beam directed, initially, in a direction away from the
material to be vaporized, deflecting means for producing a main
magnetic field having lines of force extending generally
transversely of the initial electron beam direction to deflect the
electron beam produced by said electron beam gun through an arcuate
path from said electron beam gun to said crucible, said deflecting
means including a pair of pole plates arranged substantially
parallel with each other on opposite sides of said crucible, said
pole plates being of a configuration such that said main magnetic
field is of generally uniform strength in the region of said
electron beam gun and in the region of said crucible, and sweeping
means including a plurality of coils positioned on coplanar axes
between said pole plates and oriented for producing a sweeping
magnetic field when said coils are energized with variable
currents, said sweeping field being substantially smaller than said
main magnetic field and having lines of force of variable
orientation within said main magnetic field to provide a
controllable variation in beam deflection, said sweeping means
being positioned closer to said electron beam gun than to said
crucible with respect to the total amount of deflection of the
electron beam produced by said electron beam gun.
2. A vapor source assembly according to claim 1 wherein said
deflecting means include a permanent magnet.
3. A vapor source assembly according to claim 1 wherein said
deflecting means include a permanent magnet extending between said
pole plates and positioned adjacent the side of said crucible
opposite the electron beam path such that leakage flux from said
permanent magnet intercepts secondary electrons emitted from the
surface of the material in said crucible.
4. A vapor source assembly comprising, means forming a crucible for
containing material to be vaporized, an electron beam gun
positioned below the level of said crucible for producing an
electron beam directed, initially, in a direction away from the
material in said crucible, a pair of pole plates positioned on
opposite sides of said crucible and said electron beam gun in
substantially parallel relationship with each other, means for
polarizing said pole plates to produce a main magnetic field
therebetween, said pole plates extending a sufficient distance in a
direction away from said crucible such that the main magnetic field
produces deflection of the electron beam produced by said electron
beam gun through an arcuate path from said electron beam gun to
said crucible, sweeping means for producing a sweeping magnetic
field in the path of the electron beam in a region wherein said
electron beam has undergone a deflection from the initial path of
between 70.degree. and 130.degree., said sweeping means comprising
at least three solenoidal coils arranged with coplanar axes and
means for energizing said coils with variable currents to produce
variation in the orientation of the lines of force of said sweeping
magnetic field.
5. A vapor source assembly comprising, means forming a crucible for
containing material to be vaporized, an electron beam gun
positioned below the level of said crucible for producing an
electron beam directed, initially, in a direction away from the
material to be vaporized, deflecting means for producing a main
magnetic field having lines of force extending generally
transversely of the initial electron beam direction to deflect the
electron beam produced by said electron beam gun through an arcuate
path from said electron beam gun to said crucible, said deflecting
means being of a configuration such that said main magnetic field
is of generally uniform strength in the region of said electron
beam gun and in the region of said crucible, and sweeping means
producing a sweeping magnetic field substantially smaller than said
main magnetic field and having lines of force of variable
orientation within said main magnetic field to provide a
controllable variation in beam deflection, said sweeping means
being positioned closer to said electron beam gun than to said
crucible with respect to the total amount of deflection of the
electron beam produced by said electron beam gun, said sweeping
means including at least three solenoidal coils arranged with
coplanar axes, and means for energizing said coils with variable
currents to produce variation in the orientation of the lines of
force of said sweeping magnetic field.
6. A vapor source assembly according to claim 5 wherein two of said
solenoidal coils are arranged with their axes substantially
parallel with each other in spaced relationship on opposite sides
of the electron beam path, and wherein the third of said solenoidal
coils is arranged with its axis substantially perpendicular to the
axes of the other of said solenoidal coils, forming a generally
U-shaped assembly therewith.
7. A vapor source assembly according to claim 6 wherein said two
parallel solenoidal coils are connected in series.
8. A vapor source assembly according to claim 6 wherein said
crucible forming means include socket means for receiving said
U-shaped coil assembly and supporting same in an operative
position.
Description
This invention relates to the evaporation of materials under high
vacuum and, more particularly, to a vapor source assembly for use
in a vacuum deposition system.
High vacuum deposition systems often employ electron beams for
heating the material to be vaporized. Typically, the material is
contained within a crucible or equivalent structure and is
bombarded by one or more electron beams to heat the material in the
crucible to a sufficiently high temperature to vaporize. The vapor
then moves from the crucible to a substrate positioned at an
appropriate location, upon which the vapor condenses to form a
desired coating.
Vapor source assemblies are often used in high vacuum evaporation
and deposition systems as replaceable units. A vapor source
assembly typically comprises a crucible for containing evaporant,
an electron beam gun for heating the material in the crucible, and
suitable supporting structure. One or more vapor source assemblies
may be employed in a single high vacuum deposition system,
depending upon the composition of the desired coating or coatings.
For example, several vapor source assemblies may be employed to
produce a coating of a composite material or such assemblies may be
selectively operated to produce successive layers of different
materials on the substrates.
Electron beam guns for use in vapor source assemblies generally
comprise an electron emissive filament or other element for
emitting electrons, and suitable means for focusing the electrons
into a beam. The beam of electrons is accelerated along an initial
path by a suitable accelerating anode. Magnetic fields may be
provided to direct the electron beam through a desired path onto
the surface of the material in the crucible and to focus the beam
to a desired concentration and thereby control the size of the
impact area on the surface of the target.
One type of vapor source assembly of particular advantage utilizes
an electron beam gun positioned beneath the level of the crucible
and such that the initial path of the electron beam is directed
away from the material in the crucible (i.e., not directly at the
target). A magnetic field or magnetic fields having lines of force
extending transversely to the direction of travel of the electrons
in the electron beam is used to deflect the beam of electrons
through a curving path onto the target. Deflection of the beam by
such so-called transverse fields enables the electron emissive
filament to be positioned out of a line of sight of the target.
Thus the filament is not directly exposed to materials vaporized
from the target, and evolved condensible materials do not readily
contact the surfaces of the filament. A substantial decrease in
erosion of the electron emissive filament and a resulting longer
life of the filament is achieved. Moreover, the tendency for
negative ions and secondary electrons to be trapped in the electron
beam is substantially reduced by the use of transverse fields. This
reduces space charge build up which can detrimentally affect
focusing and deflection. A successful electron beam gun assembly of
this type is shown and described in U. S. Pat. No. 3,177,535.
As shown in the cited patent, vapor source assemblies often employ
an upright crucible. Under some circumstances, spalling of
condensed materials from cooled surfaces of the vacuum enclosure,
and splashing and splattering of molten material from the upright
crucible, constitute a potential impairment to satisfactory
operation of an electron beam gun as described in the cited patent.
Where these factors are a problem, they may be alleviated by
positioning the electron emissive filament underneath the crucible
and by deflecting the electron beam through a curving path of
approximately 270.degree.. In such a case, the electron emissive
filament is protected from splashing, splattering and spalling.
In order to provide uniform heating of the surface of the evaporant
in the crucible while at the same time providing efficient heat
transfer to the material in the crucible, it is typically desirable
to provide a system for sweeping the beam across the surface of the
crucible in a predetermined pattern. Moreover it is sometimes
desirable that such sweeping be at a very high frequency to enhance
the uniformity of the heating of the material in the crucible.
Although known prior art systems have proved highly satisfactory in
many instances, further improvements in efficiency of heating,
while at the same time enhancing reliability of the equipment and
minimizing its cost, are desirable.
It is an object of the present invention to provide an improved
vapor source assembly for use in a vacuum deposition system.
Another object of the invention is to provide a vapor source
assembly of improved heating efficiency.
It is another object of the invention to provide a vapor source
assembly of high heating efficiency which is low in cost and
reliable of operation.
Another object of the invention is to provide a vapor source
assembly which provides for very high frequency sweep of an
electron beam over the surface of material in a crucible while
maintaining a substantially uniform focus of the beam.
Other objects of the invention will become apparent to those
skilled in the art from the following description, taken in
connection with the accompanying drawings wherein:
FIG. 1 is a full sectional view of a vapor source assembly
constructed in accordance with the invention; and
FIG. 2 is an exploded perspective view of the vapor source assembly
of FIG. 1.
Very generally, the vapor source assembly of the invention
comprises means 11 forming a crucible 12 for containing material 13
to be vaporized. An electron beam gun 14 is positioned below the
level of the crucible for producing an electron beam 15 directed
initially in a direction away from the material in the crucible.
Deflecting means 16 and 17 produce a main magnetic field having
lines of force extending generally transversely of the initial
electron beam direction to deflect the electron beam produced by
the electron beam gun through an arcuate path from the electron
beam gun to the crucible. The deflecting means are of a
configuration such that the main magnetic field is of generally
uniform strength in the region of the electron beam gun and in the
region of the crucible. Sweeping means 18 are provided for
producing a sweeping magnetic field having lines of force of
variable orientation within the first magnetic field to provide a
controllable variation in beam deflection. The sweeping means are
positioned closer to the electron beam gun than to the crucible
with respect to the total amount of deflection of the electron beam
produced by the electron beam gun.
Referring now more particularly to the drawings, the crucible
forming means 11 comprise a copper block. A recess 21 is formed in
the block on the underside at one end thereof extending across the
entire width of the block. Two recesses 23 and 25 are formed on the
underside of the block and at the opposite end thereof from the
recess 21 and are contiguous with each other to form a step. The
crucible 12 is formed with frustoconical walls in the region of the
block between the recess 21 and the recess 23. A second
frustoconical section 27 extends from the upper rim 29 of the
crucible 12 to the upper surface of the block 11 and forms an upper
cone or hopper for the crucible. This aids in focusing the vapor
flow, protects the pole pieces 16 and 17 from condensation of vapor
thereon, and provides a hopper for melting loosely compacted
material. The block 11 is cooled by coolant passages 31 bored
therein and suitable coolant conduits 33 communicate with the
passages 31 for conducting flowing coolant, such as water, to and
from the passages. Suitable coolant connections 35 are provided for
the conduits 33.
A generally horizontal U-shaped recess 37 is formed in the block 11
just below the upper surface thereof to leave two generally
horizontal shelves 39 and 41 extending therefrom above the recess
25. An opening 43 is formed in the block 11 extending from the
upper surface thereof to the lower surface of the lower shelf 41 in
the recess 25. The opening 43 also partially intercepts the
frustoconical surface 27, extending downwardly about half way from
the upper surface of the block 11 to the upper rim 29 of the
crucible 12. The opening 43 and the recess 37 thus leave a vertical
wall 45 separating the opening 43 from the recess 37 and extending
between the shelves 39 and 41.
Support for the vapor source assembly includes a generally
rectangular base plate 47 of non-magnetic material having a pair of
support blocks 49 and 51 supported thereon and secured thereto by
any suitable means, such as by welding. A permanent magnet 53 in
rectangular block form is supported between the base plate 47 and
the block 11 by suitable bolts 55 which extend through the magnet
and into the block. The crucible forming means or block 11 rests
upon the blocks 49 and 51 and upon the magnet 53, with the magnet
53 fitting within the recess 21 in the block 11.
The deflecting means 16 and 17 comprise a pair of parallel pole
plates which are polarized by the magnet 53. The pole plates 16 and
17 are generally rectangular in shape except for chamfers 57 and
59, respectively, formed in the lower edges toward one end. This
provides the plates with a slight taper. The lower edge of each of
the plates 16 and 17 rests upon the upper surface of the base plate
47 and the facing sides of the plates 16 and 17 abut the adjacent
sides of the blocks 49 and 51. The same faces of the plates 16 and
17 also abut opposite sides of the crucible forming block 11.
Suitable screws, not shown, are provided for attaching the plates
16 and 17 to the base plate 47 and the block 11 to form a rigid
assembly.
The permanent magnet 53 thus polarizes the pole plates 16 and 17 so
that the main magnetic field is established between the pole
plates. The main magnetic field will, of course, have some
variation in its strength with distance from the magnet. The taper
prevents the strength from falling off excessively, and for all
practical purposes, the main magnetic field is of substantially
uniform strength, the variation in strength being negligible.
The electron beam gun 14 is mounted to the blocks 49 and 51 just
above the base plate 47 and in the region between the pole plates
16 and 17. The electron beam gun 14 may be of any suitable
construction. In the illustrated embodiment, however, the electron
beam gun includes an electron emitting filament 61 formed generally
in the shape of an inverted U. The filament may have the transverse
section of the U formed in a coil, as is known in the art, to
provide a large emissive area. The filament is formed of tungsten
or other suitable emissive material.
The filament is clamped in an upright position at each of its
parallel legs by clamping blocks 63. The clamping blocks 63 are
held by bolts 65 and clamp the filament against one of two cathode
blocks 67 and 69. The clamping blocks are formed with a suitable
notch, not shown, for accommodating the filament legs. The cathode
blocks are made out of molybdenum and are mounted adjacent each
other and formed with a central beam forming opening 71 therein
which the transverse portion of the filament 61 spans. The blocks
are separated by a gap 73 so that a suitable heating current can be
passed through the filament superimposed on the high voltage,
described below, for heating the filament to an emissive
temperature.
Each of the cathode blocks is provided with a recess 75 in the back
side in which the clamping blocks 63 seat. Filament current and
high negative voltage are supplied to the cathode blocks 67 and 69
by means of high voltage straps 77 and 79, suitably bolted to the
cathode blocks 67 and 69, respectively. Bolts 83 and 85 secure the
high voltage straps 77 and 79 respectively to the cathode blocks,
passing into a non-magnetic steel bar 86 on the opposite side of
the cathode blocks. A beam former plate 81 extends up the back of
and over the top of the cathode blocks 67 and 69. The plate 81
engages and is secured to the block 67 but the block 69 is made
smaller than the block 67 so the plate 81 is in spaced relationship
to the block 69. The bolts 85 and the bar 86 are insulated from the
block 69 so as to prevent electrical shorting of the filament
current. The beam former plate 81 closes the top of the opening 71
defined by the cathode blocks 67 and 69, and forms a back for the
opening. Thus, in effect, the filament is disposed in a recess in a
beam forming block maintained at a very high negative
potential.
An anode plate 91 is provided folded over the top of the beam
former plate 81 and spaced a distance therefrom. The anode plate is
supported on a suitably shaped support bracket 93 spaced from the
bar 86 by cylindrical alumina insulators 97, and mechanically
supported from the insulators by bolts 95. Thus, electrical
separation is maintained between the bar 86 and the anode plate 91,
the latter being at ground potential during the operation of the
electron beam gun 14. Pins 98 extend through the support bracket 93
from the insulators 97 and are secured in suitable openings 99 in
the blocks 49 and 51 on the base plate 47 by set screws 101. Thus,
the electron beam gun 14 is supported below the level of the
crucible in a simple plug-in type of support, and may be removed
simply by loosening the set screws 100 through clearance holes 103
in the pole pieces 16 and 17.
When properly energized, the electron beam gun 14 produces a stream
of electrons in the form of the electron beam 15 which initially
issues from the opening 71 in a direction generally away from the
target. This initial direction is substantially horizontal and to
the right in FIG. 1. Because of the transverse magnetic fields set
up between the pole plates 16 and 17, and because the direction of
the lines of force in such fields is appropriately selected in
accordance with the right hand rule, the electrons of the electron
beam are deflected upwardly and then around through an arcuate path
for a change in direction of approximately 270.degree. to the top
surface of the material in the crucible 12.
The sweeping means 18 comprise three solenoidally wound coils 101,
103 and 105. The coils 101 and 105 have generally parallel axes and
the coil 103 is supported extending transversely of the coils 101
and 105 at one end thereof to form a generally U-shaped structure.
The coils are suitably supported within a U-shaped housing 107 of
generally square cross sectional configuration. Electrical
connection is provided on the housing for the coils and comprises a
pair of terminals 109 and a pair of terminals 111. The coils 101
and 105 are connected in series with each other and to the
terminals 109, and the coil 103 is connected to the terminals
111.
By applying currents of variable strength and direction to the
terminals 109 and 111, a magnetic field may be established within
the region bounded by the coils. This magnetic field has lines of
force of variable or controllable orientation. As the beam passes
through this region, it may be deflected according to the
orientation of the lines of force therein. By appropriate control
of the direction and strength of the lines of force, the beam may
be moved or swept across the surface of the target material within
the crucible 12.
The housing 107 mates in the recess 37 in the block 11 to form a
plug-in arrangement and support the steering means at the
appropriate position. This position is preferably between
70.degree. and 130.degree. of deflection of the beam by the main
field, and not more than one half the total amount of deflection in
any case. The opening 43 is provided such that the beam may pass up
through the block and into the crucible 12 as shown in FIG. 1, due
to the deflection force provided by the main magnetic field. The
shelves 39 and 41 help to prevent vapor in the region above the
crucible 12 from reaching the electron beam gun 14 and the filament
61 thereof such as to cause erosion of the filament.
In operating the device, suitable attachment is made to the straps
77 and 79 to provide a high voltage negative potential on the
cathode blocks 67 and 79 to provide a high voltage negative
potential on the cathode blocks 67 and 69 and on the beam former
plate 81, and also to provide a heating current for the filament
61. The beam thus formed is deflected around through the main
magnetic field, passing through the region defined by the sweep
means 18. By suitably controlling the sweep means, a repetitive
impact pattern may be produced on the surface of the melt at a very
high frequency. Vapor thus produced moves to the substrate, not
shown, to thereby coat the substrate.
The leakage flux from the permanent magnet 53 extends into the
region above the crucible 12 at the side thereof opposite the side
from which the electron beam arrives. As is known to those skilled
in the art, bombardment of metallic material by electron beams
produces secondary electrons due to emission thereof by the molten
material. Such secondary electrons can form space charges and
deleteriously affect the operation of the device. By placing the
permanent magnet 53 as is shown in the drawings, the leakage flux
therefrom captures many of the secondary electrons thus emitted,
substantially reducing the problems caused thereby and enhancing
operation of the device.
The vapor source assembly of the invention is particularly well
suited to the evaporation of aluminum, and provides very high
evaporation rates with virtually no crucible erosion. Steering or
sweep of the beam is accomplished without serious variation in the
focusing of the beam because of the high uniformity of the main
magnetic field. By using a permanent magnet, rather than an
electromagnet, less heat is generated by the system and a more
simple electrical system may be utilized. Moreover, there is no
possibility for the main magnetic field to suddenly fail, causing
the electron beam to be projected elsewhere within the vacuum
enclosure to possibly damage other components. The plug-in type
steering mechanism greatly facilitates assembly of the device and
the general arrangement protects the cathode or emitter of the
electron beam gun from impingement of ions thereon which would
cause erosion.
The invention also provides a substantial improvement with respect
to electron beam focusing. More particularly, the precise amount of
focus on the electron beam may be closely controlled by controlling
the relative amounts of deflection produced by the main magnetic
field and the deflection provided by the steering means. The beam
may be swept over a relatively wide variation without deterioration
of focus. By placing the steering means relatively close to the
emitter, that is, where less than 120.degree. of total beam
deflection has taken place, a favorable lever arm relationship is
established. This reduces the total energy necessary for sweeping
the beam. As a result, a very high frequency sweep may be achieved
by using laminated cores in the solenoidal coils 101, 103 and
105.
Some other advantages exist in the mechanical construction of the
invention. The large funnel-shaped upper cone 27 above the crucible
12 can be used as a hopper for loosely compacted charge material so
that a nearly full crucible of molten metal can be made from a
charge of relatively low bulk density. Replacement of the emitter
assembly or electron beam gun 14 may be accomplished relatively
quickly because of the plug-in type arrangement with the pins 99
passing into the blocks 49 and 51. The fact that the housing 107 of
the sweeping means 18 is in contact on three sides with the block
11 shields the housing 107 from radiant heat and provides heat
conduction to the cooled block 11 for cooling the coils 101, 103
and 105.
Under some circumstances, evaporation of certain materials (e.g.
aluminum) is carried out more efficiently with a diffuse beam
rather than a narrow, highly focused beam. To this end, small
plates 113 and 115 may be attached to the edges of the pole plates
16 and 17 by bolts 117. The plates 113 and 115 extend inwardly from
the pole plates 16 and 17. The wider the plates, the greater the
beam diffusion which results. The plates are of sufficient length
to exceed the width of the central section of the housing 107 (as
seen in FIG. 1).
It may therefore be seen that the invention provides an improved
vapor source assembly for use in a high vacuum evaporation system.
The vapor source assembly of the invention is of simple
construction, is low in cost, and provides superior operation than
prior art devices.
Various modifications of the invention in addition to those shown
and described herein will become apparent to those skilled in the
art from the foregoing description and accompanying drawings. Such
modifications are intended to fall within the scope of the appended
claims.
* * * * *