U.S. patent number 3,649,339 [Application Number 04/855,517] was granted by the patent office on 1972-03-14 for apparatus and method for securing a high vacuum for particle coating process.
Invention is credited to Eugene C. Smith.
United States Patent |
3,649,339 |
Smith |
March 14, 1972 |
APPARATUS AND METHOD FOR SECURING A HIGH VACUUM FOR PARTICLE
COATING PROCESS
Abstract
A vacuum coating apparatus is provided with valves wherein the
volumes containing the coating material emitter and high-vacuum
pump can be isolated from the substrate table to preserve the high
vacuum of the system. A wide-throated valve between the coating
material emitter and the substrate table permits vacuum sealing of
the coating material emitter and high-vacuum pump when the
substrate is replaced, throttling of the gases within the volume of
the system containing the substrate table to reduce the roughing
cycle required to attain the requisite high vacuum, and complete
opening between the coating emitter apparatus and substrate table
to provide an unobstructed particle path for efficient high-vacuum
coating.
Inventors: |
Smith; Eugene C. (Los Altos
Hills, CA) |
Family
ID: |
25321451 |
Appl.
No.: |
04/855,517 |
Filed: |
September 5, 1969 |
Current U.S.
Class: |
417/152;
118/733 |
Current CPC
Class: |
C23C
14/56 (20130101) |
Current International
Class: |
C23C
14/56 (20060101); C23c 013/00 () |
Field of
Search: |
;118/47-50.1
;117/93-93.44,106-107.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kaplan; Morris
Claims
What is claimed is:
1. A vacuum coating apparatus comprising: a chamber; a valve seat
intermediate two ends of said chamber defining a valve aperture
substantially coextensive with the cross section of said chamber
and dividing said chamber into first and second portions; a valve
disc for engagement with said seat; a sealed housing adjoining said
seat, communicated to said chamber, and extending outwardly of said
chamber for receiving said disc clear of said seat; molecular pump
means communicated to one of said portions of said chamber; first
disc moving means for moving said disc between a first position
overlying said seat and a second position within said housing clear
of said seat; and, second means for moving said disc when overlying
said seat towards and away from said seat between a first overlying
position where said disc seals said seat closing said valve between
said first and second portions and a position where said disc
permits throttled molecular conductance between said first and
second portions.
2. The invention of claim 1 and wherein, said chamber, valve seat,
and disc are of circular section.
3. The invention of claim 1 and including valve means between said
molecular pump means and said chamber for sealing said molecular
pump means from said emitter portion.
4. The invention of claim 1 and wherein said first moving means
includes: an arm connected to said disc at one end and to said
housing at said opposite end; and, means for pivotally moving said
arm with respect to said housing to move said disc between said
first and second positions.
5. A process for evacuating a first portion of a vacuum coating
chamber by a molecular pump communicated to a second portion of
said vacuum coating chamber, said molecular pump operable only
below a predetermined gas pressure limit maintained within said
second portion, said processing comprising the steps of: providing
a valve disc and seat intermediate said chamber ends, said seat
defining an opening substantially coextensive with the intermediate
section of said chamber; seating said disc on said seat to seal
said substrate portion of said chamber from said molecular pump;
evacuating said substrate portion of said chamber to a pressure in
the range between said predetermined pressure limit and twice said
predetermined pressure limit; lifting said disc overlying said seat
to permit throttling molecular conductance of gas within said
substrate portion to said pump portion at a rate wherein said
molecular pump is not swamped; and, moving disc clear of said seat
after said throttling has substantially equilibrated gas within
said chamber portions.
6. The process of claim 5 and wherein, said molecular pump is an
ion pump and said evacuating step evacuates said chamber to a
pressure limit between 50 and 100 microns of mercury gas
pressure.
7. The process of claim 5 and wherein, said molecular pump is a
diffusion pump and said evacuating step evacuates said chamber to a
pressure range between 100 and 200 microns of mercury gas
pressure.
8. In a vacuum coating chamber having a first portion for mounting
a substrate and a second portion for mounting a coating material
emitter and molecular pump, and means for vacuum sealing said
substrate mounting from said coating emitter and molecular pump
therebetween, the improvement in said vacuum sealing means
comprising: a valve seat attached to the sidewalls of said chamber
intermediate said substrate portion and coating material emitter
portion, said seat defining aperture substantially coextensive with
the section of said chamber; a valve disc configured for engagement
with said seat; a sealed housing adjoining said seat, communicated
with said chamber and extending outwardly of said chamber for
receiving said disc clear of said seat; first disc moving means for
moving said disc between a first position overlying said seat and a
second position within said housing clear of said seat; and, second
disc moving means for moving said disc when overlying said seat
towards and away from said seat between a first position where said
disc on said seat seals said emitter portion from said substrate
portion and a second position where disc provides throttled
molecular conductance between substrate portion and said emitter
portion.
9. Apparatus according to claim 8 and wherein, said second disc
moving means includes first biasing means for continuously biasing
said disc away from said seat to said throttling position and
second biasing means for overcoming said first biasing means to
seat said disc.
Description
This invention relates to an apparatus and method for securing a
high vacuum for a molecular coating process. More particularly, an
improved valve construction is illustrated for isolating the
volumes between the substrate on one hand and coating material and
high-vacuum pump on the other hand. Moreover, use of the improved
valve construction permits an improved process for evacuating the
volume surrounding the substrate table.
Modern molecular coating machines contain high-vacuum ambients.
Typically, a substrate to be coated is placed within this
high-vacuum ambient and bombarded with high-velocity molecular
particles discharged from a coating material emitter. As the
presence of any appreciable amount of gas between the emitter and
substrate retards the passage of the high-velocity molecular
particles through intermolecular collisions, all such machines have
elaborate vacuum pumps for maintaining the required near-perfect
high vacuums.
To place substrates within the apparatus for coating and to remove
the substrates after coating, the vacuum interior of such coating
machines must be broken. Heretofore, the vast majority of coating
systems have required interruption of the vacuum around both the
coating material emitter, the substrate table area and the
molecular pump used to attain the high vacuum. This interruption
results in loss of vacuum within comparatively large volumes of the
entire system. Before coating can occur, these large volumes must
be evacuated. Moreover, the surfaces interior of such coating
machines when exposed to the atmosphere, adsorbs molecules of
atmospheric gas, moisture, and other contaminants. These adsorbed
molecules must be purged from the system before efficient coating
can occur.
In addition to the interruption of the vacuum necessitated by the
replacement of the substrate, the high-vacuum molecular pumping
systems conjoined to such apparatus must be protected from exposure
to appreciable amounts of gas. Typically, these pumps, either of
the diffusion or ion variety, cannot tolerate the presence of gases
in vapor pressures above 100 microns of mercury in the case of
diffusion pumps and 50 microns of mercury in the case of ion pumps.
When these pumps are subjected to gas in pressures above these
limits, they are "shocked" or "swamped" and their pumping
efficiency wholly lost, often with resultant damage to their
pumping media.
Heretofore when substrates have been replaced, the volumes
containing these substrates typically have been evacuated by
mechanical pumps to a gas pressure range wherein the high-molecular
pumps can efficiently operate. Unfortunately, the use of mechanical
pumps alone to reach the low-pressure limits where the molecular
pumps operate is highly inefficient; as the molecular density
within the chamber approaches a perfect vacuum, the mechanical
pumps become increasingly more inefficient.
To eliminate the inefficient use of mechanical or "roughing" pumps
to reach the vacuums required for the operation of the molecular
pumps, separate piping and valve systems have been provided to
throttle gases to the high-vacuum molecular pumping systems at a
pressure where the molecular pumps can operate. While this
throttling can take advantage of the improved efficiency of the
molecular pumps, it has the disadvantage of incorporating elaborate
piping, valving, and controls into the vacuum coating systems.
Moreover, the piping associated with these systems provides an
inefficient channel for the desired molecular conductance to the
high-vacuum pump.
It is an object of this invention to provide a vacuum coating
apparatus wherein the high-vacuum molecular pump alone or the
coating material emitter and high-vacuum pump can be maintained in
a vacuum during changing of the substrate. Accordingly, the coating
apparatus of this invention is confined within an enclosed cylinder
having the substrate table located at one end thereof and the
coating material emitter at the opposite end thereof. A valve with
a pivoted disc having a diameter substantially coextensive with the
cylinder cross section is positioned to isolate the coating
material emitter and high-vacuum pump from the substrate in the
closed position and permitted to pivot clear of the cylinder to
provide an unobstructed coating material path in the open
position.
A further object of this invention is to disclose a chamber
configuration wherein the high-vacuum molecular pump can be
isolated from both the substrate table and coating material emitter
to permit changes to be made to the emitter apparatus without
interrupting the high-vacuum state of the molecular pump or
damaging its molecule-entraining materials.
An advantage of the valve construction between the substrate table
and coating material emitter is that the volume about the substrate
table is reduced to an absolute minimum; consequently, pumping time
and energy necessary to achieve a high-vacuum state is
conserved.
A further object of this invention is to disclose a valve assembly
for insertion between the substrate table and high-vacuum molecular
pump, which valve has three operative positions; these operative
positions include a seated position for sealing the molecular pump
to preserve its high-vacuum state, a throttling position for
throttling gases from the substrate table to the high-vacuum pump
and a fully open position to permit the unrestricted passage of
coating materials when the coating is commenced.
An advantage of the throttling position of this valve is that a
substantial reduction in the time necessary to evacuate the volume
containing the substrate table is attained.
Yet another advantage of the throttling position of this valve is
that the substrate chamber need only be evacuated to a pressure
range exceeding by a factor of two that pressure range at which the
molecular pump is swamped. In the case of a diffusion pump the
pressure of evacuation can be as high as 200 microns of mercury; in
the case of an ion pump the pressure range can be as high as 100
microns of mercury.
A further advantage is that the throttling function of the valve
eliminates the need for complex and expensive auxiliary throttling
piping, valves and controls.
An additional advantage is that the throttling valve provides an
improved path for molecular conductance between the volume
containing the substrate table and the high-vacuum pump. This path
is effectively free of recesses and occluded areas where molecules
which might otherwise spoil the high-vacuum can accumulate.
A still further advantage of this invention is that the wide throat
of the valve permits an essentially unrestricted molecular flow
path for evacuating the area around the substrate table and permits
emitted coating materials to pass through the valve seat and onto
the substrate table.
Other objects, features and advantages will be more apparent after
referring to the following specification and attached drawings in
which:
FIG. 1 is a side elevation section schematically illustrating the
chambers containing the substrate table, the coating material
emitter and the high-vacuum pump;
FIG. 2 is a side elevation section illustrating the improved valve
construction between the substrate table on one hand and the
coating material emitter and high-vacuum pump on the other
hand;
FIG. 3 is a plan view of the improved valve construction of this
invention along lines 3--3 of FIG. 2; and
FIG. 4 is an expanded side elevation section illustrating the valve
in a view similar to that shown in FIG. 2 with the disc of the
valve in its throttling position.
With reference to FIG. 1, substrate chamber A is illustrated
overlying an emitter chamber C with a throttling gate valve B
therebetween. Emitter chamber C is in turn communicated through
poppit valve D into cold trap E and molecular pump F. Both the
molecular pump F and the substrate chamber A are shown communicated
by piping to a roughing pump G.
In operation, substrate 22 is typically inserted within substrate
chamber A. Thereafter, the chamber is sealed and roughing pump G,
through connected piping, evacuates the chamber to a range
approaching a perfect vacuum, typically in the order of 100-150
microns of mercury pressure. Thereafter, disc 14 of valve B is
actuated to move to the throttling position shown in FIG. 4. The
atmosphere remaining in the partially evacuated substrate volume A
is throttled around the periphery of disc 14 of valve D into
emitter chamber C and to molecular pump F. Typically, the throttled
rate of molecular flow or conductance is maintained between the
disc 14 and valve seat 16 at a flow rate wherein molecular pump F
is now "swamped" or "shocked." When the molecular densities in
chambers A and C has substantially equilibrated, disc 14 is pivoted
on arm 18 to a position out of registry with seat 16 (see FIG. 2).
In this position, emitter 20 is provided with an unobstructed path
to discharge coating material onto substrate 22 within substrate
chamber A.
When the coating of substrate 22 is completed, typically disc 14 of
valve B will be pivoted to the closed position, then sealed by
pressurizing bellows 42. Thereafter, the chamber A will be flooded
with atmospheric gas by piping (not shown), substrate chamber A
opened, and the coated substrate 22 removed and replaced with
uncoated substrate material.
Substrate chamber A and emitter chamber C are formed in the shape
of a cylindrical vessel 25, which vessel is closed at the top and
bottom thereof by circular walls 26 and 27. Chamber 25 above valve
B is cut into two separate sections at annular flanges 30 and 31,
flange 30 being attached to the top portion of chamber A and flange
31 being attached to the bottom portion of chamber A. As here
shown, the top and removable portion of cylindrical 25 is pivotal
about a hinge 32 towards and away from a sealed position between
flanges 30 and 31. When the chamber is opened, substrate 22 can be
removed and replaced; when the chamber is closed, its interior can
be evacuated and coating commenced.
Intermediate of chambers A and C, valve B is disposed. Valve B can
be best illustrated with reference to FIGS. 2, 3 and 4.
Valve B is contained within a hollow cardiod or heart-shaped
housing 34. Housing 34 is attached integrally to chamber C at the
top and bottom housing walls overlying seat 16. These connections
in cooperation with seat 16 define through housing 34 an aperture
which is effectively a continuation of the cross section of
cylinder 25. Housing 34 is hollow and extends beyond seat 16
transversely outward of cylinder 25. Disc 14 pivotally moves into
this concavity when valve B is in the open position.
Within the interior of housing 34 at the pointed portion of its
heart-shaped plan profile, disc 14 is pivotally mounted about a
shaft 36 on arm 18. Arm 18, at its end opposite from shaft 36, has
attached thereto disc 14.
With reference to FIG. 3, rotation of shaft 36 is actuated by a
pneumatic cylinder 37 to pivot valve disc 14 towards and away from
its position of registry with seat 16. As is shown in broken lines
in FIGS. 2 and 3, disc 14 pivoted on arm 18, can move from a
position overlying valve seat 16 to a position where seat 16 is
completely unobstructed. Vacuum is maintained interior of valve
housing 34 by a seal (not shown) where shaft 36 penetrates the
bottom housing wall.
In addition to the pivotal movement of disc 14 on arm 18, this disc
is movable towards and away from a position of sealing engagement
with seat 16. Such movement is provided by leaf spring 40 and
bellows 42 and guided by pins 43 of disc 14 passing through
apertures 44 in pivoted arm 18.
Arm 18 has drilled therein two apertures 44. Typically, disc 14 of
valve B has protruding upwardly therefrom and into registry with
apertures 43 of arm 18 two pins 44. These pins 44 simultaneously
locate disc 14 radially from the pivot point of arm 18 provided by
shaft 36 and additionally maintain disc 14 in a horizontal plane as
it moves towards and away from seat 16.
Leaf spring 40 functions to bias disc 14 away from seat 16. This
leaf spring fastens to disc 14 at its medial portion and extends
transversely of arm 18 fastening to disc 14 at its two outer
ends.
Bellows 42 are located between the lower surface of arm 18 and the
upper surface of a bellows aperture 46 configured within disc 14.
Inflation of the bellows through connected tubing 47 overcomes the
bias of leaf spring 40 moving disc 14 downwardly in sealing
relation onto seat 16. Conversely, release of the pressure within
bellows 42 permits the bias of spring 40 to move disc 14 upwardly
from sealing engagement with seat 16. Typically, bellows 42 overlie
only a relatively small area of the total area of disc 14. This
relatively small size is operable as only relatively small motive
forces are required to effect movement of the disc.
Typically, actuation of bellows 42 and the compression of disc 14
downwardly onto seat 16 will cause the end of arm 18 remote from
shaft 36 to flex upwardly and away from seat 16. To arrest such
movement, an angle bar 50 is provided. This bar has its vertically
extending surface limiting the pivotal movement of the end of arm
18 remote from shaft 36 and its horizontally extending surface
preventing the upward flexure of the end of arm 18.
It will be noted that valve disc 14 is movable upwardly from seat
16 by only a relatively small spatial interval. This spatial
interval is chosen to provide a desired throttling of pressure
between substrate chamber A and emitter chamber C. As is apparent,
such movement can be adjusted by the insertion of shims between
disc 14 and arm 18, the shims being placed typically about pins
43.
Referring again to FIG. 1, emitter apparatus 20 is located on the
bottom surface 27 of chamber C. As here shown, emitter apparatus 20
is adapted for the thermal coating of substrate 22. Typically, pot
53 defines a concavity 54 in which the coating material 55 is
placed. Thermal energy supplied to the material 55 causes its
molecular particles to be discharged upwardly and in the direction
of substrate 22. Typically, the pot is surrounded by a cylindrical
shield 56, which shield confines the emitted particles of coating
material 55 to an emitted pattern wherein they will impact the
substrate 22 without coating or contaminating other surfaces within
the chamber.
Extending transversely outwardly of emitter chamber C underlying
housing 34 of valve B there is a duct 60. Duct 60 provides a
passage between emitter chamber C on one hand and cold trap E and
molecular pump F on the other hand.
Duct 60 is communicated to cold trap E and molecular pump F through
poppet valve D. Poppet valve D includes a disc 62 movable towards
and away from a seat 63 by means of the pneumatic cylinder 64.
Typically, cylinder 64 attaches to disc 62 at rod 65. When
communication between duct 60 and cold trap E and molecular pump F
is desired, disc 62 is actuated to the position shown in FIG. 1.
Conversely, when cold trap E and molecular pump F are to be
isolated from duct D, disc 62 is seated on seat 63. Actuation of
pneumatic cylinder 64 through tubing (not shown).
Cold trap E and molecular pump F are apparatuses well known in the
art. Typically, cold trap E functions to immediately freeze all
water vapor within the system and to prevent the oil from molecular
pump F from backing into the high-vacuum maintained within
substrate chamber A and emitter chamber C. Molecular pump F can be
of any known variety; as here illustrated, pump F is of the
diffusion variety wherein a stream of oil entraps and entrains the
molecules and causes the molecules to be discharged. Alternatively,
molecular pump F can be of the ion variety.
Roughing pump G is a mechanical pump. Typically, this pump operates
to mechanically displace the atmosphere interior of the coating
system. Inlet 73 of roughing pump G is connected to the outlet of
molecular pump F through valve 75 and piping 74. Additionally,
inlet 73 of pump G is connected to substrate chamber A through
valve 76 and piping inlet 77.
Assuming that the entire apparatus herein illustrated is at
atmospheric pressure, the operating cycle of the coating apparatus
will be as follows: Initially, valve B will be moved with disc 14
into registry with seat 16. With valve 76 closed and valve 65 open,
roughing pump G will be actuated to evacuate the entire system to a
level wherein the molecular pump F can be actuated. When this state
of evacuation is attained, molecular pump F is activated and
emitter chamber C, duct 60, cold trap E and molecular pump F placed
in an essentially atmosphere-free environment.
Assuming that substrate 22 has been placed within substrate chamber
A and the substrate chamber closed by the sealing of flanges 30 and
31, the system will be "roughed." This will occur by closure of
valve 75 and opening of valve 76 to the inlet 73 of roughing pump
G. Pump G will typically evacuate the interior of roughing chamber
A and valve housing 34 until a pressure sufficient for the
operation of the molecular pump is attained. This pressure will be
approximately 100-200 microns of mercury in the case of the
illustrated diffusion pump F or 50-75 microns of mercury of an ion
pump.
When such pressure is attained, valve B is moved from its seated
position to its throttling position. Such movement is actuated by
releasing pressure on bellows 42 and allowing leaf spring 40 to
bias disc 14 upwardly relative to seat 16.
In the throttling position, the periphery of disc 14 of valve B
overlying seat 16 will define a channel through which molecular
conductance or throttling will occur.
Typically, the spatial separation of disc 14 relative to seat 16 as
well as the length of overlap between the outside periphery of the
disc and the inside periphery of the seat will determine the flow
desired. In the case of a sixteen inch valve provided with a
three-eighth of an inch overlap between the outside periphery of
the disc and the inside periphery of the seat a valve clearance of
three-sixteenth inches has been found sufficient. Dependent upon
the pump used and atmospheric content desired, the position of disc
14 relative to seat 16 can be varied to move in the range of
four-thousandths of an inch to 1 inch.
With disc 14 in the throttling position, substrate chamber A will
typically equilibrate with emitter chamber C, molecular pump F
effecting the desired evacuation. Thereafter, when complete
equilibration has occurred, disc 14 will be pivoted on arm 18 out
of registry and clear of seat 16 and coating commenced.
Generally all materials used for the construction of the chamber
are either of stainless steel or other vacuum compatible materials.
That is to say, all surfaces interior of the coating apparatus have
no substantial vapor pressure which will interfere with the near
perfect vacuum within the chamber.
It should be apparent that the throttling function provided by
valve B could be used between a single chamber in which the entire
coating apparatus was confined and a cold trap E and molecular pump
F. Likewise, other modifications of my invention may be practiced,
it being understood that the form of my invention as described
above is to be taken as a preferred example of the same. Such
description has been by way of illustration and example for
purposes of clarity and understanding. Changes and modifications
may be made without departing from the spirit of my invention.
* * * * *