U.S. patent number 3,667,424 [Application Number 04/815,814] was granted by the patent office on 1972-06-06 for multi-station vacuum apparatus.
This patent grant is currently assigned to Stanford Research Institute. Invention is credited to William L. Cornelius, John G. Martner.
United States Patent |
3,667,424 |
Cornelius , et al. |
June 6, 1972 |
MULTI-STATION VACUUM APPARATUS
Abstract
A high-current vacuum system suitable for on-vacuum deposition
of multiple layers onto a substrate. A vacuum chamber encloses a
stationary substrate holder disposed above a plurality of vapor
sources utilizing diverse heating elements. The vapor sources are
arranged on a rotatable support for sequential movement to a
deposition station for the vaporization and deposit of low and high
temperature metals and dielectrics. Manipulators for making and
breaking electrical contact to the station and for rotation of the
support are positioned without the chamber and are externally
operated to change sources without breaking vacuum. A liquid
nitrogen cooled cold cam is situated between the station and the
substrate support to funnel the vapor stream toward the stationary
substrate target.
Inventors: |
Cornelius; William L. (Mountain
View, CA), Martner; John G. (Atherton, CA) |
Assignee: |
Stanford Research Institute
(Menlo Park, CA)
|
Family
ID: |
25218907 |
Appl.
No.: |
04/815,814 |
Filed: |
April 14, 1969 |
Current U.S.
Class: |
118/720; 118/725;
118/727; 200/11R; 219/437; 118/726; 118/730; 219/422; 392/389 |
Current CPC
Class: |
C23C
14/56 (20130101); C23C 14/24 (20130101) |
Current International
Class: |
C23C
14/56 (20060101); C23C 14/24 (20060101); C23c
013/12 () |
Field of
Search: |
;118/5,48-49.1,620,9
;219/422,437,271-276 ;200/11,18 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Kaplan; Morris
Claims
What is claimed is:
1. A multi-source vacuum deposition system comprising in
combination:
a vacuum chamber containing:
a rotatable support;
a plurality of vapor sources mounted on said support, at least one
of said sources comprises a reservoir receptacle for containing a
source of vaporizable material; a first electrical heating element
for heating the receptacle and an electrical wick heating element
extending into the receptacle for vaporizing the body of
vaporizable material;
electrical connecting studs connected to said heating elements and
extending through said rotatable support and terminating in a first
electrical contact;
a second electrical contact, a shaft connected to said second
contact, a portion of said shaft extending without said chamber and
a portion extending within said chamber adjacent said connecting
studs and means connected to said shaft without said chamber for
making and breaking connection between said contacts;
substrate holder means disposed above said sources; and
means extending without said chamber for rotating said support to
dispose each of said sources below said holder means.
2. A system according to claim 1 further including vapor funneling
means disposed between said holder and said support comprising a
tubular member disposed axially below said holder and means to cool
the walls of said tubular member comprising a coolant coil
surrounding said tubular member for receiving a flow of liquid
coolant.
3. A system according to claim 1 further including heat exchange
means associated with said holder for controlling the temperature
of the substrate.
4. A system according to claim 3 wherein said heat exchange means
comprises an electrical heating element surrounding at least a
portion of said holder.
5. A system according to claim 4 further including shutter means
disposed between said holder and said funnel means, means without
said chamber for positioning said shutter and linkage means within
said chamber associating said shutter means with said positioning
means.
6. A vacuum deposition system comprising:
a base housing;
a removable cover for said housing defining a vacuum chamber, said
chamber containing:
stationary substrate holder means;
a rotatable support below said holder;
a plurality of reservoirs for receiving vaporizable material
mounted on said support;
a first electrical heating element in contact with the exterior of
at least one reservoir;
a second wick electrical heating element extending into the
interior of at least one reservoir;
a first fixed electrical contact connected to each said heating
element;
a second translatable contact disposed adjacent said first contact;
and
means extending through said housing into said chamber for moving
said second contact into engagement with said first contact.
7. A system according to claim 6 wherein said moving means
comprises an axial rod supporting said second contact and bearing
means engaging said rod.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a vacuum system for multi-layer
deposition and more particularly to an apparatus for continuously
and sequentially depositing a plurality of diverse layers onto a
substrate without breaking vacuum.
2. Description of the Prior Art:
Thin film multi-layered structures are becoming common place in the
fields of optics and microwave acoustics, i.e., where wavelengths
of the order of microns are used. These thin film structures can be
utilized either as narrow band pass or band elimination filters
depending on the combination of 1/2 and 1/4 wavelength thick layers
that are used. In the manufacture of ultrasonic multi-layered
filters for operation at frequencies of several hundred megahertz,
forty or more metal and dielectric layers in the region of 100
angstroms to 10 microns thick are consecutively deposited to form a
stack. When the acoustic impedances of the layers are properly
controlled, such stacks form bandstop or band-pass filters that
operate in a manner similar to those used in thin film
monochromatic or narrow-band optical filters. Furthermore, the
layers must deposit in a manner to form very good bonding and the
physical properties such as grain compaction and orientation must
be carefully controlled.
The available vacuum systems are not capable of efficiently or
effectively forming such multi-layered deposits.
The deposition of such thin films in such critically controlled
thicknesses requires that the source be turned ON and turned OFF
quickly. Many of the dielectrics and metals have high melting
points which require high electric power and therefore, equipment
that can safely and effectively accomodate the necessary power
level. Moreover, available multi-source vacuum systems are very
wasteful, in that the vapor clouds deposit throughout the apparatus
involving a loss in material and cleanup time and risk of
contamination between layers. Though contamination is lessened by
operating in continuous vacuum, such systems do not have the
capability of accurately starting and stopping the film depositions
over short time periods as well as the capability of carefully
controlling the rate and amount of deposition with the required
precision.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a
multi-source vacuum deposition apparatus having provision for in
vacuum exchange of sources.
Another object of the invention is to provide for efficient and
effective deposition of diverse layers of films onto a substrate
within a single vacuum chamber.
Yet another object of the invention is to accurately control the
rate, thickness and character of diverse metal and dielectric
layers sequentially deposited in vacuum.
A still further object of the invention is to minimize
contamination and spread of vapor in the vacuum deposition of
plural layers onto a substrate.
These and other objects and many attendant advantages of the
invention will become apparent as the description proceeds.
The multi-source vacuum deposition system in accordance with the
invention comprises a vacuum chamber containing a rotatable support
on which is mounted a plurality of deposition vapor sources, and a
substrate holder mounted above said sources. Means extending
without said chamber are provided for rotating said support to
dispose each of said sources below said substrate holder. The
system may further include a vapor funnel means disposed between
the substrate holder and the vapor sources.
In accordance with the invention a substrate is coated with a
plurality of thin layers by positioning the substrate within the
chamber over an energizable station and disposing a plurality of
vapor sources with the chamber. The chamber is evacuated to low
vacuum and maintained at low vacuum throughout operation. A first
source of vaporizable material is positioned at the station and the
station is energized to create vapor. The vapor is transported
through a vapor funnel having cool walls to the substrate. The
station is deenergized and a second source is positioned at said
station and the station energized and vapor transported to the
substrate.
The invention will now become better understood by reference to the
following detailed description when considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front sectional view of one embodiment of a vacuum
system according to the invention;
FIG. 2 is a sectional view taken along the line 2--2 of FIG. 1;
FIG. 3 is a partial enlarged perspective view of the contact
closure mechanism;
FIG. 4 is a cross-sectional view of a standard coil heater-crucible
evaporator assembly;
FIG. 5 is an enlarged view of the substrate holder assembly taken
along the line 5--5 of FIG. 1;
FIG. 6 is a cross-sectional view taken along the line 6--6 of FIG.
5;
FIG. 7 is a schematic illustration of a design of a narrow band
multi-layer microwave acoustical transmission filter; and
FIG. 8 is a view of a series of masks to be used in fabricating the
filter of FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIGS. 1 and 2 the multi-source vacuum deposition
system comprises generally a vacuum chamber 10, a rotatable support
12, a plurality of vapor sources 14 mounted on the support and a
substrate holder assembly 16 supported above a vapor station
17.
Chamber 10 may also include according to the invention, a vapor
funnel 28 axially supported over vapor station 17 between substrate
holder assembly 16 and sources 14 and at least one shutter 91
positioned between the substrate holder 16 and the vapor funnel 28.
External to chamber 10, the system further includes control means
18 for rotating the support 12 and externally operated energizing
means 20 for activating one of the sources 14 when positioned over
the vapor station 17.
The chamber 10 is enclosed by a removable cover member 22 which is
supported on a base housing 24. The cover is preferably arcuate in
shape and is formed of a high strength transparent material such as
quartz. The base housing 24 is usually round and in the case of the
present invention has a depth sufficient to receive the controls
and connecting linkages for operating and manipulating the various
equipment contained within the chamber 10.
Referring now, more particularly, to FIG. 2, eight vapor sources 14
are arranged spaced around the rotatable support 12. Support 12 is
in the form of a flat turntable to which is attached a central
bearing collar 13. The collar 13 is rotatably mounted on a
stationary shaft 15. A bracket 21 secures the shaft 15 to the
bottom plate 19 of the housing 24 forming a stand for the shaft
15.
The external control means 18 includes a rod 23 attached outside
the housing 24 to a turn knob 25 and extending into housing 24
through a vacuum sealed feed-through. A vertical bevel gear 27 is
attached to the inner end of the rod 23. The rod 23 is supported
along its middle portion by means of an L-shaped bracket 29
attached to the bottom wall 19 of the housing having an aperture
provided in the vertical arm of the bracket. The bevel gear 27
engages a horizontal annular bevel gear 31 secured to bearing
collar 13. Positioning of the particular source unit 14 over the
vapor station 17 is effected by turning knob 25 which rotates
turntable 12 to position the source over station 12 and under
funnel 28 and substrate support 16.
Each vapor source is associated with a set of outer electrical
input posts 50 and 52 disposed a fixed distance from each other and
extending downwardly from turntable 12. The leading posts 50 of
each source and the trailing posts 52 of the sources are
respectively positioned on substantially the same radial distance
from the shaft 15. In the present embodiment all the input posts 50
and 52 are disposed the same radial distance from the shaft 15. An
inner ground post 54 is also provided to each source 14.
The posts 50 and 52 extend upwardly through the turntable 12 into
the vapor source 14 and are secured to the turntable by means of a
nut 53. The posts 50 and 52 are electrically insulated from
turntable 12 and source 14 by means of ceramic insulators 49 which
extend through the post receiving apertures in the turntable 12 and
extend past the upper and lower edges of the apertures. In
contrast, the inner ground contact post 54 extends upwardly into
source 14 but terminates just below turntable 12 and is in
electrical contact therewith. The post 54 is also secured to
turntable 12 by means of nuts 53.
Each input post 50 and 52 contains a wedge-shaped contact groove 60
and 62, respectively, which outwardly face toward housing wall 36.
A circle through the center of the posts 50 and 52 would be tangent
to each line formed by the intersection of the faces forming wedges
60 and 62. Each set of adjacent posts 50 and 52 for each source 14
are in a fixed relation to the housing wall 36 and are adapted to
be rotated sequentially to the vapor station 17 and to be energized
at that location.
Referring now to FIGS. 1 to 3 station 17 is disposed directly below
vapor funnel 28 and substrate holder 16 and includes a plurality of
translatable electrical contact heads 30 and 32 supported
upstandingly on flexible copper plates 40 and 42. The lower end of
each plate 40 and 42 is connected to a shaft 34 and 35 which
extends through the side wall 36 of the base housing 24 below
rotatable support 12. Control knobs 38 and 39 are connected to the
outer ends of shafts 34 and 35. The portion of the shafts extending
through wall 36 is sealed and each shaft contains totally insulated
section 37 to isolate the housing and the control knob from the
high current source. High current is introduced by means of high
current feed-throughs 41 which are in the form of female insulator
plug members connected to a conductive stud 47 extending through
insulated feed-throughs provided in the wall 14 of the housing 34.
The studs are each connected to a connector strap 43 which is
attached to the upper end of plates 40 and 42 by inserting the
strap 43 between the plate and wedge-shaped contact head 30 and 32
and securing them together with a screw 45. More details of the
contact assembly will be discussed in reference to FIG. 3.
Referring more particularly to FIG. 3, axial motion feed-through
manipulators 46 and 48 for the contacts are shown. Each manipulator
is adapted to cause the contact heads 30 and 32 to move inwardly or
outwardly and to close or open and make contact with the opposed
wedge recess contacts 60 and 62 provided on the power input posts
50 and 52 extending downwardly from rotatable platform 12. The
shafts 34 and 35 are slidingly received in bearing housings 51 and
53 which are attached to the vacuum chamber housing wall 36 by
means of nuts 55. A set screw 57 is mounted on each bearing housing
55 for securing the shafts 34 and 35 to maintain contact heads 32
or 30 in either closed or open position.
Each source 14 includes a circular base plate 56 separated from
turntable 12 by means of electrical insulators 49. The input posts
50 and 52 are provided to power the inner and outer heating coils
associated with the vapor source crucibles. Since the level of
power input to the different types of coils are usually in
different ranges it is desirable for purposes of convenience and
safety to consistently utilize the same post to power the same
coil. Therefore, in a counterclockwise direction of rotation, the
leading post 50 of each source will always power the outer coil
heater and in turn will be powered by righthand manipulator 46. The
trailing post 52 will power the inner coils and will in turn always
be powered by means of lefthand manipulator 48.
The coils are each powered by a high current, 300 amp 50 volt
source which can be set at a selected level by means of a
variac-controlled heavy duty transformer, not shown. The power is
fed to the apparatus through the standard high current
feed-throughs 41.
In FIG. 3 the righthand set of contacts 30 and 60 are shown open
while the lefthand set of contacts 32 and 62 are shown almost
closed. The wedge-shaped contact heads 32 and 30 are manipulated
from the outside by axial motion of the feed-through manipulators
46 and 48. When the chamber 10 is evacuated, the suction provided
by the inner vacuum on the manipulator shafts further causes the
contacts to be pushed together and maintained in contact. Breaking
of the contact is provided by a reverse axial motion of the
manipulator shaft. The mating surfaces of the wedge-shaped grooves
60 and 62 on the stainless steel posts 50 and 52 into which the
wedge-shaped heads 32 and 30 fit are ground smooth and fit suitably
have an angle of slant of about 25 percent.
The fabrication of acoustical and optical filters requires that
materials of diverse vaporization temperatures and conductivities
be deposited. Furthermore, these materials will not always be
deposited in the same order.
The multiple electrical inputs to each source 14 provide great
flexibility in the types of materials that may be consecutively
evaporated from the eight separate sources as well as permitting
sensitive control of the rate of evaporation. For example, three
different types of evaporation units may be provided.
Referring now to the righthand vapor station 14 shown in FIG. 1 the
station consists of the base plate 56 enclosed by a cylindrical
cover 59. A standard refractory crucible 61 such as one made out of
alumina is surrounded by a filamentary heating coil 63 and is
housed within the cover 59. The input lead to filament 63 is
connected to post 50 as discussed. A double twisted wick wire 67
such as one formed of 15 ml diameter tungsten wire is introduced
into the molten material 65 contained within the crucible 61. One
end of this wick wire is connected to electric contact post 52 the
other end as discussed is introduced into the melt deeply enough to
make electrical contact with the molten material at all levels. The
ground contact from the wick is provided by a second tungsten wire
69 also immersed into the melt 65 near the wall of the crucible 61
and is connected to ground post 54. The ground wire 72 from the
heater coil 63 is also connected to ground post 54. Inside the melt
the wires are disposed parallel to each other to near the bottom of
the crucible. However, it is not necessary that they touch since
electric contact is made through the molten charge 65. Of course,
this type of crucible should only be utilized with conductive
charges such as gold.
Capillary action causes the molten gold to wet the wick. The wick
temperature is kept high enough to produce gold evaporation from
its small area rather than from the entire top surface of the
crucible. This permits very accurate and sudden control of the
evaporating rate and quick ON-OFF manipulation. For a rate of
evaporation of 1 micron in 20 minutes at the substrate, this
requires 35 amp through the wick circuit. A current of 150 amps is
required through the heater circuit to produce this melt and the
crucible can be maintained at melting temperature at current of
about 80 amps, typically.
To evaporate non-conductive dielectrics that remain poor conductors
in the molten state, another arrangement can be utilized. This
arrangement is shown in the lefthand side of FIG. 1 and comprises a
standard alumina crucible 71 surrounded again by an external
heating filament 73 connected on its input side to post 50 and on
its output side to ground post 54. Inside crucible 71 a second
heating filament 75 is incorporated connected on its input side to
post 52 and on its output side to ground post 54. The inner heating
coil can be made of standard 15 mil tungsten wire.
In the operation of this evaporator unit the operation is initiated
by heating the crucible 71 to a dull red (approximately 750.degree.
C) with the external crucible filament 73. When this temperature is
reached the inner heating coil 75 is energized to produce an
evaporating melt whose final temperature depends on the dielectric
material utilized. Evaporation proceeds from the surface of the
melt. With this double heating arrangement careful control of the
evaporation rate is possible. In film deposition where the
acoustical or optical properties of the film depend, among others,
on the density or orientation of the crystallites of the film, it
becomes necessary to control the rate of deposition as well as the
evaporating temperatures. Dielectrics such as SiO.sub.X (M.P.
970.degree. C), MgFz (M.P. 1,690.degree. C) and ZnS (M.P.
1,900.degree. C) have been deposited at varying rates with the
double coil arrangement according to the invention.
With high-melting point metals a commercially available cone-type
filament unit may be utilized. This unit is shown in FIG. 4. This
unit comprises a crucible 80 in which is inserted a cone-type
filament coil heater 82. The input side of the coil is connected to
post 52 and the output side is connected to ground post 54.
Secondary post 50 is not utilized with this unit. The heater coil
is wetted by the molten charge 84 and evaporating temperature is
achieved with the same coil. Metals such as titanium (M.P.
1,800.degree. C), aluminum (M.P. 600.degree. C), silver (M.P.
957.degree. C) and tin (M.P. 232.degree. C) have been deposited
using a standard cone filament evaporator.
The vapor rises from the heated crucible and leaves the vapor
sources 14 through the aperture 88 in the top 90 of the removable
cover 59. To prevent excessive metal and dielectric spillage over
the exposed surfaces of the apparatus it is preferred to situate
vapor funnel 28 over the vapor station 17 below the substrate
holder. The vapor funnel is a thin walled cylinder having its
surface maintained at low temperature by means of an external coil
92 which receives a flow of refrigerant, preferably at cryogenic
temperatures, through inlet 94 and outlet 96. Inlet 94 and outlet
96 pipes extend through sealed feed-throughs to an external source
of cryogenic liquid, not shown, such as liquid nitrogen. The vapor
funnel 28 cold can arrangement substantially eliminates
contamination and prevents the vapor from spreading by containing
the vapor cloud within the cold can. The vapor funnel 28 at
cryogenic temperatures acts to scavenge excess vapor and to remove
impurities from the system. The vapor funnel 28 may suitably be
maintained in position by means of an upper flange 100 through
which bolts 102 are inserted to suspend the funnel 28 directly
below the substrate holder assembly 16.
The deposition apparatus of the invention may further include at
least one shutter plate 91 and linkages associating plate 91 with
external positioning controls. The shutter 91 may be utilized to
shield the substrate after the desired thickness has been deposited
or to maintain the substrate covered until the vapor source has
reached temperature and is delivering a steady cloud of vapor at
constant rate. The linkage may take many forms. In FIG. 1 the
shutter plate 91 is fixed to a post 106 which extends through an
aperture in upper bracket 108 and is connected to a bevel gear 110.
A horizontal shaft 112 rotatably mounted in a bearing attached to
shaft 15 carries a pulley 116 and a bevel gear 114 meshing with
gear 110.
A control rod 118 extends outside housing 24 where it is connected
to a control knob 120 and extends through a guide 122 inside the
housing. The rod carries a second pulley 124 and a cable 126 joins
pulleys 116 and 124. Rotation of control knob 120 in a first
direction will remove shutter plate 91 from shielding the substrate
and rotation of the knob 120 in the opposite direction will return
the shutter plate 91 to its closed position. The positioning
mechanism for shutter plate 93 is not illustrated. The mechanism
described with respect to shutter plate 91 or other equivalent
arrangements may be utilized to move shutter plate 93 from without
chamber 10.
In some of the depositions steps involved in filter manufacturing
it becomes necessary to maintain the substrate at an elevated
temperature to achieve the desired physical properties in the
deposited films. For this purpose, a substrate heating oven and a
thermocouple temperature monitor may be incorporated. A substrate
holder assembly incorporating these components as well as a
thickness monitor sensitive in the desired range is illustrated in
FIGS. 5 and 6.
Referring now to FIGS. 5 and 6 the substrate holder assembly is
adjustably supported on a threaded section 150 of the shaft 15. The
height of the holder assembly may be raised or lowered depending on
the size of the particular substrate. The holder assembly is
supported by means of an upper annular bracket 108 attached to a
threaded support member 130 riding on the threaded section 150 of
the shaft 15.
The upper bracket 108 acts as a suspending support for the flange
100 of the funnel 28, as a rotatable support for the shutters 91
and 93 and to support brackets suspending the thickness gages,
temperature sensors as well as the substrate holder 132.
The substrate 134 with the face intended to be deposited facing
down is supported between clamping screws 136 insertable through
the walls 138 of the substrate holder 132. A thermocouple 139 is in
mechanical contact with the substrate during a run. The substrate
holder may further include masks for depositing particular
configurations of metals or dielectrics onto the substrate. For
this purpose clips may be provided at the lower end of the holder
for holding the masks in place during the run. The holder 132 rests
on an annular plate 140 suspended in the control opening of annular
bracket 108 by means of bolts 142. The holder 132 is in turn
surrounded by a metal can 144 the outer surface of which contains a
heating element 146 in the form of a coil of ceramic coated wire.
The can 144 rests on annular plate 140 and the top face 149 of the
can is attached to a bracket 148 suspended from upper bracket plate
108. The lead wires 152 to the heating element 146 are attached to
a clip 154.
A pair of piezoelectric crystals 160 and 162 are disposed on each
side of the substrate 134 above separately operable shutter plates
91 and 93 but axially within the opening 164 of the cold can vapor
funnel 28. The crystals 160 and 162 are housed in cold cans 166
suspended from bracket 108 by means of angles 168. Water inlets and
outlets 170 and 172 and electrical leads 174 are supported by means
of various brackets and clamps, not shown, and are connected to
external sources of water and electrical monitoring equipment by
means of high vacuum feed-throughs, not shown.
Commercially available 5-MHz quartz oscillator wafers may be
utilized as the film thickness monitor. Since the vibrating
crystals are calibrated for only one type of depositing material at
a time, it is necessary to utilize a separate crystal for each
material being deposited. Superimposed layers of different metals
would render the crystal useless for further monitoring during the
run. In accordance with the invention, a plurality of separately
controlled shutter plates can be utilized so that one plate may be
maintained in position to isolate one crystal during the run while
the other plate is fully opened to expose the substrate and the
active monitoring crystal. The thickness monitors are carefully
precalibrated with a well-known multiple beam interferometer
technique. The commercial piezoelectric thickness monitors utilized
were of the beat frequency type and the output can also be
connected to a frequency counter. A variation of 1 kHz in 5 MHz may
be readily detected and identified to the interferometer
thickness.
The substrate heater oven surrounds the holding mechanism and in
this embodiment takes the form of a stainless steel cylinder having
a ceramic insulated heater wire wound on its outer surface. The
substrate temperature is monitored by the thermocouple situated at
the rim of the surface being evaporated on and in mechanical
contact with the substrate. With this arrangement substrate
temperatures of up to 900.degree. C can be maintained during
deposition of layers. Generally these high substrate temperatures
are utilized when depositing dense acoustical or optical layers.
One of the reasons for high temperature is the necessity to achieve
high compaction in the deposited film.
A generalized operating procedure comprises filling the crucibles
in counterclockwise order with the desired vaporizable materials to
be consecutively deposited as layers on the substrate. The
substrate is placed in the holder mechanism and the thermocouple
attached to it. Clean precalibrated quartz crystals are placed in
cold cans of the thickness monitor and the clear cover is then
placed over the assembly and onto the base housing. The chamber is
then evacuated to low vacuum and the first chamber rotated into
position in the vapor station.
The cooling water is flowed into and through the thickness gage
cold cans and liquid nitrogen is flowed through the coil
surrounding the vapor funnel. The axial feed-through manipulators
are operated to close the contacts and power is turned ON to feed
power to the first crucible. The shutter isolating the crystal
calibrated for the material being deposited is opened and vapor is
continuously deposited as a first layer until the thickness gage
indicates the desired amount of material has been deposited. The
shutter over the thickness crystal that has been utilized is then
closed and the opposite shutter is opened to expose a fresh
thickness gage. The second crucible is rotated into position in the
vapor station and the contacts are again closed and energized to
create a flow of vapor that rises through the cold can and onto the
substrate.
The chamber is brought to vacuum by means of a standard pumping
unit attached to a vacuum feed-through and includes a mechanical
roughing pump to bring the system to 10 microns or less and a
sublimation pump with a capacity of 3,600 liters per second to
evacuate the chamber to 10.sup.-.sup.4 torr and finally two 25
liters per second ion pumps are utilized to bring the system to
10.sup.-.sup.8 torr. Flowing liquid nitrogen through the cold can
of the vapor funnel 28 during pumping helps to scavenge residual
ions from the system and with the cold can in operation about 30
minutes is required to bring the system to the desired low vacuum.
During operation the vacuum outside the cold can may rise
temporarily to 2 to 4 .times. 10.sup.-.sup.7 torr but recovers
within 2 to 3 minutes after deposition is terminated.
Prior to assembling the components into the system, a very careful
standard cleaning and degreasing procedure should be followed.
After assembling, several dry runs are made with the purpose of
further cleaning and degassing. The system is always brought to
atmospheric pressure by introducing purified N.sub.2 to partially
prevent the absorption of oxygen and other gases by the components.
The parts that operate at high temperature within the system are
degassed prior to and during the evacuating cycle. Any parts
handling is done by using lint-free gloves and the entire system is
constantly kept in a clean room (free of organic matter and dust).
The system is constantly kept under vacuum and is brought to room
pressure only for as long as it takes to introduce substrates and
to charge the evaporators. Cleaning of the system is minimal since
the use of a cold can as vapor funnel as well as trap, considerably
reduces the spreading of metal or dielectric vapors onto the rest
of the system.
As an example, the apparatus of the invention was utilized to
prepare a microwave acoustic filter consisting of a stack of gold
and aluminum film layers terminated with cadmium sulphide input and
output transducers. The input transducer generates a compressional
acoustic wave that travels through the multi-layer metal stack.
This acoustic wave is then converted back to an electromagnetic
signal by the output transducer. One possible design for this type
of filter is shown schematically in FIG. 7. This filter is designed
to exhibit a narrowband transmission response having minimum
insertion loss at a frequency f.sub.0. The acoustic Q's of
evaporated aluminum and gold films have been measured at 575 MHz
and were found to be large enough to provide an expected one
percent bandwidth with this configuration. The filter was deposited
on the end face a 0.685 inch diameter fused quartz substrate. Four
large metal pads were provided to electrically connect the filter
to a test circuit. The active area of the device was 0.016 inch
.times. 0.020 inch and the acoustic filter was designed to operate
at 1,000 MHz. The steps required in the fabrication of this filter
are illustrated in the following Table and the open configuration
of the mask for the corresponding step is shown in FIG. 8.
TABLE I
---------------------------------------------------------------------------
Fabrication Steps
Step Film Thickness 1 Ti 300 A Au 0.76.mu. 2 CdS 1.12.mu. 3 SiO 100
A Ti 300 A Au 0.76.mu. Al 3.35.mu. filter Au 0.76.mu. 4 Ti 300 A Au
2.mu. 5 CdS 2.14.mu. 6 SiO 1000 A Ti 300 A Au 1000 A 7 Ti 300 A Au
2.mu.
__________________________________________________________________________
Steps 1, 3, 4, 6, and 7 were carried out in the multi-source system
described herein. The CdS depositions were carried out in a
separate vacuum system, but in principle, provisions for making
this deposition could also have been incorporated in the
multi-source system. Step 3 is the critical step in the fabrication
of the filter and was accomplished without breaking vacuum. A thin
layer of SiO.sub.X was deposited on top of the CdS in order to
prevent pinhole shorts across the CdS layers. Next, a thin layer of
Ti was deposited to promote adhesion between the SiO.sub.X and the
Au. Finally, the multilayer filter section of Au-Al-Au was
deposited. In order to deposit the rather large thickness of Al
that was required (i.e., 3.35.mu.), it was necessary to use five of
the eight evaporation stations.
It is to be realized that only preferred embodiments of the
invention have been disclosed and that numerous substitutions,
alterations and modifications are all permissible without departing
from the scope of the invention as defined in the following
claims.
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