U.S. patent number 3,853,093 [Application Number 05/221,363] was granted by the patent office on 1974-12-10 for optical thickness rate monitor.
This patent grant is currently assigned to Optical Coating Laboratory, Inc.. Invention is credited to Martin L. Baker, Eugene A. Eufusia.
United States Patent |
3,853,093 |
Baker , et al. |
December 10, 1974 |
OPTICAL THICKNESS RATE MONITOR
Abstract
Optical thickness rate monitor for use with a vacuum chamber
having an evaporation source. Means is provided for forming an
aperture which is exposed to the vapors from the source. An
elongate element is provided and means is also provided for
progressively advancing the elongate element past the aperture so
that it is exposed to the vapor stream from the evaporation source
so that any coating material is deposited on the elongate element.
Means is provided for supplying a beam of radiation to the element
so that the radiation is affected by any coating deposited on the
element. Means is then provided for determining the manner in which
the radiation is affected by changes in the coating which is being
deposited on the element. Automatic means is provided for
controlling the rate of evaporation from the evaporation source and
monitoring the optical thickness to which the coating is deposited
on the element.
Inventors: |
Baker; Martin L. (Santa Rosa,
CA), Eufusia; Eugene A. (Santa Rosa, CA) |
Assignee: |
Optical Coating Laboratory,
Inc. (Santa Rosa, CA)
|
Family
ID: |
26670872 |
Appl.
No.: |
05/221,363 |
Filed: |
January 27, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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2789 |
Jan 14, 1970 |
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Current U.S.
Class: |
118/664; 118/715;
356/433; 356/437 |
Current CPC
Class: |
C23C
14/547 (20130101) |
Current International
Class: |
C23C
14/54 (20060101); C23c 013/12 () |
Field of
Search: |
;117/106,107.1,94
;118/7,8,48,49,49.1,49.5,9 ;356/204 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Van Horn; Charles E.
Assistant Examiner: Massie; J.
Attorney, Agent or Firm: Flehr, Hohbach, Test, Albritton
& Herbert
Parent Case Text
This is a X Division of application Ser. No. 2,789, filed Jan. 14,
1970, now abandoned
Claims
We claim:
1. In an optical thickness rate monitor for use with a vaccuum
chamber having an evaporation source therein providing a vapor
stream for measuring the rate of deposition of material on an
article while in the vacuum chamber, means forming an aperture
having one side exposed to the vapor stream from said evaporation
source, an elongate transparent element spaced from the article
disposed on one side of the aperture opposite the side exposed to
the evaporation source, means for progressively advancing the
elongate element past the aperture so that successive portions of
the elongate element are coated with material from said vapor
stream at the same time that material is being deposited on the
article, means for supplying a beam of radiation to the element so
that the radiation is affected by the material deposited on the
element from the vapor stream and means for determining the manner
in which the radiation is affected by the material deposited on the
element to determine the rate of deposition of the coating material
solely by determination of optical properties of the coating
material.
2. A monitor as in claim 1 together with means connected to said
means for determining any changes in the material and adapted to be
connected to the evaporation source for controlling the rate of
evaporation from the evaporation source.
3. A monitor as in claim 1 together with means for causing the beam
of radiation to sweep in a direction parallel to the direction of
movement of the element.
4. A monitor as in claim 1 wherein one side of the elongate element
is exposed to the vapor stream from the evaporation source and
wherein the beam of radiation is directed to the other side of the
elongate element.
5. A monitor as in claim 4 together with means for preventing
coating material from being deposited on the elongate element
during the time that the beam of radiation is being directed onto
the elongate element.
6. A monitor as in claim 1 together with a supply reel and a
take-up reel, said elongate element being wound on said supply reel
and take-up reels, capstan means for continuously advancing the
elongate element, and means for driving said supply reel and said
take-up reels so that said elongate element is continuously
maintained under tension.
7. A monitor as in claim 6 together with means for driving said
capstan at a predetermined rate of speed.
8. In an optical thickness rate monitor for use with a vacuum
chamber having an evaporation source therein providing a vapor
stream, means forming an aperture having one side exposed to the
vapor stream from said evaporation source, an elongate element
disposed on one side of the aperture opposite the side exposed to
the evaporation source, means for progressively advancing the
elongate element past the aperture so that progressive portions of
the elongate element are coated with material from said vapor
streams, first source for supplying a beam of radiation to the
element so that the radiation is affected by the material deposited
on the element from the vapor stream, means for determining the
manner in which the radiation is affected by the material deposited
on the element, means for chopping said beam of radiation at a
predetermined frequency, means for forming said beam of radiation
into spaced parallel sample and reference beams, means for
directing the sample and reference beams onto the elongate element,
means for receiving the sample and reference beams after they have
been affected by the coating material on the elongate element and
for combining the same into a single beam, means for comparing the
sample and reference beams for supplying an error signal, and means
utilizing the error signal to control the rate of evaporation from
said source.
9. A monitor as in claim 8 together with means mounted in said
sample and reference beams to cause said sample and reference beams
to sweep said elongate element in the direction of movement of the
elongate element.
10. A monitor as in claim 9 wherein said means in said sample and
reference beams includes a prism assembly having first and second
prisms, each of the prisms having a plurality of faces and means
for rotating said prisms in said sample and reference beams.
11. A monitor as in claim 10 wherein said prism assembly consists
of a housing with said first and second prisms mounted in said
housing, said housing having spaced slots formed therein in two
separate rows with said rows being in alignment with said first and
second prisms, said slots in each of said rows being positioned so
that when one of the beams is passing through one of said prisms,
the other of said beams cannot pass through the oher of said
prisms.
12. A monitor as in claim 10 together with first and second chopper
discs, one of said chopper discs being disposed on one side of said
aperture and the other of said chopper discs being disposed on the
other side of said aperture, said chopper discs being positioned so
that one chopper disc operates out of phase with the other chopper
disc, said chopper discs having the same number of openings as the
number of faces on said prisms, and means for rotating said chopper
discs in unison with the rotation of said prisms.
13. A monitor as in claim 12 wherein said means for rotating said
prisms and said means for rotating said first and second chopper
discs includes servo means.
14. A monitor as in claim 12 wherein said means connected to said
error signal includes a source of power supply connected to the
evaporation source, an evaporation rate controller connected to
said power supply, an adjustable reference for said evaporation
rate controller and means connecting said error signal into said
evaporation rate controller.
15. A monitor as in claim 14 wherein said means responsive to said
error signal includes a power supply for said first source of
radiation, an adjustable reference for said power supply and means
connecting said error signal to said power supply.
16. A monitor as in claim 12 together with an additional source of
radiation, a chopper mounted on said prisms and rotatble with said
prisms, said chopper having a number of openings therein
corresponding to the number of faces on each of said prisms, means
for detecting radiation from said additional source of radiation
and means connected to said detector means for supplying an error
signal to control the intensity of radiation from said first source
of radiation.
Description
BACKGROUND OF THE INVENTION
Apparatus has heretofore been provided for measuring evaporation
rates from evaporation sources. For example, coating materials have
been depositied on quartz crystals which causes the frequency of
the crystal to change. Ion gauge evaporation rate monitors have
been provided. Another type of rate monitor looks at the plasma
surrounding an electron gun evaporation source and utilizes the
intensity of the plasma to indicate the rate of evaporation.
However, none of such rate monitors monitor the optical thickness
of the coating. There is, therefore, a need for a rate monitor
which will monitor the optical thickness evaporation rate.
SUMMARY OF THE INVENTION AND OBJECTS
The optical thickness rate monitor is adapted for use with a vacuum
chamber having an evaporation source. Means is provided for forming
an aperture which is exposed to the vapors from said source. An
elongate element is disposed over said aperture on the side
opposite said source. Means is provided for progressively advancing
the elongate element past the aperture so that successive portions
of the elongate element are exposed to the vapors from the source.
Means is provided for supplying a beam of radiation to the element
so that it is affected by the coating which is deposited on the
element. Means is then provided for determining a characteristic of
the radiation after it has been affected by the coating deposited
on the element. Automatic means is provided for controllng the rate
of evaporation from the evaporation source so that the coating
material is applied at a predetermined rate.
In general, it is an object of the present invention to provide an
optical thickness rate monitor which monitors the optical thickness
evaporation rate.
Another object of the invention is to provide a monitor and method
of the above character in which the optical thickness rate can be
monitored over long periods of time.
Another object of the invention is to provide a monitor and method
of the above character in which a dual beam is utilized.
Another object of the invention is to provide a monitor and method
of the above character in which the monitoring is carried out by
depositing the coating on one side of the element and viewing the
element from the other side.
Another object of the invention is to provide a monitor and method
of the above character in which the film is not monitored during
the time that coating material is being placed on the film.
Another object of the invention is to provide a monitor and method
of the above character which can be set for a predetermined rate of
evaporation from the evaporation source and which thereafter will
be controlled automatically.
Additional objects and features of the invention will appear from
the following description in which the preferred embodiment is set
forth in detail in conjunction with the accompanying drawing,
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a side elevational view of an optical thickness rate
monitor incorporating the present invention.
FIG. 2 is an enlarged top plan view of the atmosphere side of the
monitor shown in FIG. 1.
FIG. 3 is a front elevational view of the monitor looking along the
line 3--3 of FIG. 1.
FIG. 4 is a rear elevational view of the monitor shown in FIG. 1
looking along the line 4--4 of FIG. 1.
FIG. 5 is an enlarged side elevational view, partially in
cross-section, of a portion of the monitor shown in FIG. 1 and
particularly showing the chopper assembly and a beam splitter
assembly.
FIG. 6 is a side elevational view in cross-section of the octagon
prism assembly.
FIG. 7 is a cross-sectional view taken along the line 7--7 of FIG.
6.
FIG. 8 is an enlarged cross-sectional view showing additional
portions of the monitor.
FIG. 9 is an enlarged view of a portion of the structure shown in
FIG. 8.
FIG. 10 is a schematic illustration of the monitor together with
the necessary associated circuitry.
FIG. 11 is a block diagram of the monitor system amplifier and the
evaporation rate controller shown in FIG. 10.
FIG. 12 is an enlarged isometric view showing the chopper
assembly.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The optical thickness rate monitor consists of the main housing 11
which also may be called a thimble. The main housing 11 is provided
with a main wall 12 which has a vacuum assembly 13 mounted on one
side and an atmosphere assembly 14 mounted on the other side. The
main housing 11 is generally rectangular in cross-section and is
provided with spaced parallel walls 16 which are secured to the
main wall 12 at right angles thereto and additional spaced parallel
walls 17 secured at right angles to the main wall 12 and to the
walls 16.
The main housing 11 of the rate monitor is adapted to be mounted on
a large vacuum chamber. Thus, as shown in FIG. 1, the main housing
or thimble 11 is adapted to extend through a large opening 18
provided in the chamber wall 19 of the vacuum chamber. A cover 21
is provided with an opening 22 through which the housing 11
extends. An O-ring 23 is disposed between the cover 21 and the
chamber wall 19. A spacer 26 is provided and engages the cover 21.
An O-ring 27 is disposed between the spacer 26 and the cover 21.
The main housing 11 is provided with a flange 28 which is secured
thereto by suitable means such as welding and which has its outer
extremity engaging the spacer 26. An O-ring 29 is disposed between
the flange 28 and the spacer 26.
The atmosphere assembly 14 includes a chopper assembly 31 which is
mounted upon a large base plate 32 secured to the main wall 12 of
the housing 11. The chopper assembly 31 consists of a pedestal 33
secured to the base plate 32. A lamp socket 34 is mounted in the
upper part of the pedestal 33 which is split as shown in FIG. 2 and
is clamped therein by a screw 36. A lamp 37 is mounted in the lamp
socket 34. A lamp housing 38 extends over the lamp and is secured
to the pedestal 33 by suitable means such as screws 39. A slip ring
41 is mounted on the outer extremity of the lamp housing 38 and
also has mounted therein a lens mount housing 42. As can be seen,
the lamp housing 38 and the slip ring 41 as well as the lens mount
housing 42 are provided with axially aligned passages 43, 44 and
46, respectively. A sleeve 47 is slidably mounted within the lens
mount housing 42 and carries a lens 48. The lens 48 is held in
place by a nut 49. The sleeve 47 is also provided with a passage 51
which is axially aligned with the passages 43, 44 and 46 and
similarly the nut 49 is provided with an axially aligned passage
52. The sleeve 47 can be held in the proper axial position so as to
focus the image projected by the lens 48 and consists of a screw 53
which is threaded into the sleeve 47 and which extends through an
elongate slot 54 provided in the lens mount housing 42
The lens mount housing 42 is secured to a cover plate 56 by
suitable means such as screws 57. The cover plate 56 forms a part
of a chopper housing 58 which is formed in two parts, one of which
is the cover plate 56 and the other of which is a cup-like member
59. The chopper housing 58 is light-tight and has a chopper disc or
plate 61 disposed therein. The chopper disc 61 is provided with a
hub 62 which is secured to a shaft 63 by suitable means such as a
set screw 64. The shaft 63 is driven by an electric motor 66. The
motor 66 is of a suitable type such as an 3600 RPM synchronous
direct drive motor. The chopper disc 61 is provided with a
plurality of holes 67 spaced equally adjacent to the outer margin
of the discc By way of example, with a chopper disc of 4 inches in
diameter, approximately 200 such holes can be provided which are
approximately 0.226 inch in diameter.
An aperture plate 71 is mounted in one end of a sleeve 72 and is
provided with an aperture 73. The sleeve 72 is mounted in a hole 74
provided in the cup-like member 59 of the chopper housing 58 and is
postioned in such a manner that the aperture 73 carried by the
aperture plate 71 is immediately opposite the holes 67 in the
chopper disc 61 as it is rotated. The aperture 73 is relatively
small to ensure that only one hole at a time in the chopper disc
will be exposed by the aperture. The cover plate 56 is provided
with a hole 76 which is in axial alignment with the hole 74. The
sleeve 72 extends into a mounting member 77 which is secured to the
cup-like member 59 by screws 78. The mounting member 77 is provided
with a passage 79 in axial alignment with the aperture 73 so that
any image passing through the aperture 73 can pass through a lens
81 carried by a lens housing 82. The lens housing 82 is slidably
mounted on the mounting member 77 so that the image from the lens
81 can be focused. The lens 81 is held in place by a nut 83.
The light from the chopper assembly 31 impinges upon a beam
splitter assembly 86. The beam splitter assembly 86 consists of a
support block 87 which is secured to the base plate 32 by screws 88
and by dowel pins (not shown). The support block 87 is provided
with a passage 91 which is in the upper portion of the support
block 87 and extends in a generally horizontal direction. The
support block is also provided with a slot 92 which extends through
the support block 87 in such a manner that it opens into the
passage 91 and extends at an angle with respect to the passage 91.
A beam splitter 93 is mounted within the slot 92 as shown and
engages a pin 94 provided in the slot 92. The beam splitter 93 is
held in place by a spring member 96 which is secured to the support
block 87 by screws 97. The beam splitter 93 is held against the pin
94 by the force of gravity. An iris diaphragm 98 is rotatably
mounted on the support block 87 on the forward end of the passage
91. Suitable means is provided for mounting the iris diaphragm 98
and consists of a pair of shoulder members 99 which are secured to
the support block 87 by screws 101. The iris diaphragm 98 is
provided with a handle 102 to facilitate rotation of the same. A
cover plate 103 (see FIG. 2) is mounted upon the support block 87
and serves to close the open sides of the passages 91 and 92. The
cover plate is held in place by screws 104.
The beam splitter 93 is provided with spaced, parallel surfaces 106
and 107 on opposite sides of the beam splitter. These surfaces 106
and 107 are provided with coatings as hereinafter described.
Thus, the beam splitter 93 is provided with an antireflection
coating for optimum transmittance on surface 107 in the area where
the light beam first strikes surface 107. As can be seen from the
arrows shown in FIG. 5, a portion of the light beam which is
received by the beam splitter is transmitted by a beam splitter
coating on surface 106 of the beam splitter, whereas another
portion of the light beam is reflected downwardly to an area of
surface 107 which is provided with a mirror coating which fully
reflects the light through the beam splitter and through another
anti-reflection coating provided on an area of surface 106 for
maximum transmittance. The result is that the beam splitter
provides a pair of spaced parallel beams from a single beam.
The light beam from the beam splitter 86 is supplied to an octagon
prism assembly 111. The octagon prism assembly 111 consists of a
cylindrical cup-shaped housing 112 which is provided with a
centrally disposed hub portion 112a which receives the upper end of
a shaft 113. The housing 112 is secured to the shaft 113 by a set
screw 114. The shaft 113 is rotatably mounted in a pair of spaced
ball bearing assemblies 116 mounted within a flanged bearing
housing 117. The flanged bearing housing 117 is secured to the base
plate 32 by cap screws 118.
A pulley 121 is mounted on the lower extremity of the shaft 113
(see FIG. 4) and is driven by a timing belt 122. The timing belt
122 is driven by a pulley 123 mounted on the output shaft 124 of a
synchronous motor 126. The motor 126 is mounted in a split bracket
127 secured to the base plate 32 by cap screws 138 which extend
through slots 129 provided in the base plate 32 and are threaded
into the split bracket 127. A cap screw 131 is mounted in the
bracket 127 for securing the motor 126 in the desired position in
the bracket.
The timing belt 122 also drives another pulley 132 mounted on a
shaft 133 of a synchro-transmitter 134. The synchro-transmitter 134
is secured to the base plate 32 by a split bracket 136 secured to
the base plate 32 by cap screws 137. Cap screw 138 is provided for
fastening the synchro-transmitter 134 in the desired position
within the bracket 136.
The cylindrical housing 112 is provided with two spaced rows of
elongated slots 141 which are equally spaced around the
circumference of the cylindrical housing. Thus, there are provided
8 of these slots in each row with the slots in one row being skewed
with respect to the slots in the other row by a suitable angle such
as 22.50.
A pair of octagonal prisms 142 and 143 formed of a suitable
material such as flint glass are mounted within the cylindrical
housing 112. As can be seen particularly in FIG. 7, the two
octagonal prisms 142 and 143 are each provided with 8 flat surfaces
144. The prisms 142 and 143 are arranged in such a manner that the
surface 144 of each of the prisms are immediately opposite the
slotted openings as shown particularly in FIG. 7. Thus, since the
slots 141 in the two rows are skewed by 22.5.degree. with respect
to each other, the surfaces 144 of the octagonal prisms 142 and 143
are also skewed 22.5.degree. with respect to each other.
Means is provided for retaining the prisms 142 and 143 within the
housing 112 and consists of suitable means such as a plastic
cement. A cover plate 146 is mounted on the cylindrical housing 112
by suitable means such as screws 147. A synchronizing wheel 148 is
secured to the cover plate 146 by screws 149 (see FIG. 7). The
synchronizing wheel 148 is provided with a cylindrical upstanding
wall 151 which has a plurality of openings 152 evenly spaced along
the circumference of the wall 151 with the number of openings 152
corresponding to the number of sides provided on the prisms 142 and
143 and the number of slots 141 in each row of slots.
From the foregoing construction, it can be seen that the
synchronous motor 126 will drive the octagon prism assembly 111,
the synchronous detector wheel 148 and the synchro-transmitter 143
so that all are driven synchronously. In other words, they are
locked together and rotate at a predetermined speed as, for
example, 600 RPM.
Means is provided for sensing rotation of the synchronous detector
wheel 148 and consists of a housing 154 secured to an L-shaped
bracket 156. The bracket 156 is mounted upon the base plate 32 by
screws 157 extending through slots 158 provided in the bracket 156.
The housing 154 is provided with a slot 159 extending upwardly from
the bottom side intermediate the ends of the housing so that the
wall 151 of the synchronous detector wheel 148 can rotate through
the slot 159 as shown in FIG. 2. A lamp 161 is mounted in the
housing 154 on one side of the slot 159, as can be seen in FIG. 2
and FIG. 10. Light from the lamp 161 can travel through the
openings 152 provided in the wall 151 of the wheel 148 and be
received by a photosensitive detector 162 which is mounted in the
housing 154 on the opposite side of the slot 159 and outside the
wheel 148.
It should be noted that the spacing between the two rows of slots
141 and the size of the slots 141 is such so that there is some
space between each pair of slots from each of the two rows so that
there is a finite period of time in which no light is being
transmitted through the octagon prism assembly 111. Thus, there is
provided a dwell time which is utilized for a purpose hereinafter
described.
After the two light beams leave the octagon prism assembly 111,
they impinge upon the film frame projection assembly 166 which is
mounted on the vacuum side of the main wall 12. This film frame
projection assembly 166 consists of a generally U-shaped base plate
167 which is secured to but spaced from the wall 12 by spacers 168
and cap screws 169. The main wall 12 is provided with an opening
171 (see FIG. 8) in which there is mounted a window 172. Suitable
means is provided for establishing sealing engagement between the
window 172 and the main wall 12 and includes an O-ring 173. The
window 172 is positioned in such a manner that the light from the
octagon prism assembly 111 can pass through the window 172 and the
opening 171 and then through an opening 176 provided in the base
plate 167.
The light beams impinge upon a beam spliter 177 which is of a
conventional type. For example, it can be formed of a thin piece of
glass with a conventional beam splitter coating provided on it so
that approximately 50 percent of the light coming from the
octagonal prism assembly is reflected downwardly as indicated by
the arrows in FIG. 8 and then reflected back through the beam
splitter 177. Beam splitter 177 is carried at a 45.degree. angle as
shown in FIG. 8 and is mounted in a beam splitter housing 178. The
beam splitter housing 178 is secured to the base plate 167 by cap
screws 179.
A film head housing 181 is also mounted on the base plate 167 below
the beam splitter housing 178 and is secured to the base plate 167
by cap screws 182. The housing 181 is provided with a
rectangulary-shaped window 183 which faces outwardly in the forward
direction. The window 183 is bounded by an inclined side wall 184
so that the vapor stream can be properly monitored as hereinafter
described. The film head housing 181 is generally box-shaped in
configuration and is provided with a top wall 186, the outer side
margins of which are curved as shown in FIG. 3 so that it can serve
as a film guide shoe. The top wall 186 is provided with a circular
aperture 187 (see FIGS. 9 and 10). The top wall 186 is also
provided with downwardly and outwardly inclined side walls 188
which form the aperture 187. The aperture 187 and the window 183
are positioned so that the coating stream can pass therethrough as
hereinafter described. The housing 181 is formed in such a manner
so as to keep out as much stray light as possible. The housing 181
is provided with a slot 189 immediately below the top wall 186
which extends across the housing for a purpose hereinafter
described.
A chopper assembly 191 is mounted below the beam splitter housing
178 and consists of a shaft 192 which is rotatably mounted in a
bearing housing 193 secured to the beam splitter housing 178 by cap
screws 195. A hub 190 is mounted on the shaft 192 and carries upper
and lower chopper wheels or discs 194 and 196. The upper chopper
wheel or disc 194 rotates in a plane which is immediately above the
top of the top wall 186 of the film head housing 181 and the lower
chopper wheel or disc 196 rotates in the slot 189 immediately below
the top wall 186 in such a manner that both chopper wheels extend
over the aperture 187 which is provided in the top wall 186. As can
be seen from FIG. 12, both of the wheels or discs 194 and 196 are
provided with eight blades 197 and the necessary openings 198
between the blades. The spacing between the openings 198 and the
blades 197 is such that the top or upper wheel 194 exposes the
aperture 187 40 percent of the time and closes the aperture 60
percent of the time, whereas the lower wheel 196 exposes the
aperture 187 40 percent of the time and closes it 60 percent of the
time. It should also be noted that the the upper and lower blades
are 180 electrical .degree. out of phase so that the upper blade
blocks the aperture when the lower blade exposes it and vise-versa.
It can be seen in this arrangement that there is total overlap
between the two wheels with repect to the aperture and so no light
can pass through the aperture 187 and through both blades 196 and
194 at the same instant in time.
The shaft 192 for the chopper assembly 191 is driven by a flexible
coupling 201 connected to a shaft 202. Shaft 202 is connected to
another flexible coupling 203 which is connected to the output
shaft 204 of a synchro-receiver 206. The synchro-receiver 206 is
carried by a large split mounting block 207 which is secured to the
main wall 12 by cap screws 208. The synchro-receiver 206 is clamped
within the mounting block 207 by a screw 209 threaded into the
mounting block as shown particularly in FIG. 3.
A substantially transparent length of flexible elongate element 211
in the form of a thin strip of film, such as 35 mm. film, is
positioned so that it is adapted to travel over the top of the film
shoe or top wall 186 of the film head housing so that one side of
the same will be exposed through the aperture 187 as it is advanced
past the aperture.
A film drive system 212 is provided for advancing the film 211 past
the aperture. This film drive system 212 consists of a supply reel
assembly 213, a take-up reel assembly 214, an idler wheel assembly
216 and a capstan drive assembly 217. The supply reel assembly 213
consists of a conventional reel 221 which is mounted upon and keyed
to a shaft 222. The reel 221 is held on the shaft 222 by a cotter
pin 223.
The take-up reel assembly 214 also consists of a conventional reel
224 is mounted upon and keyed to a shaft 226 so that it will rotate
with a shaft 226. It is retained on the shaft 226 by cotter pin
227. A length of the film 211 is carried by the supply reel 221 and
is taken up by the take-up reel 224. The film, after it leaves the
supply reel 221, passes under the idler wheel assembly 216 which
consists of a flanged idler wheel 228. The idler wheel 228 is
provided with a hub 229, the central portion of which has been
relieved or, in other words, provided with an annular recess as
indicated by the broken line 230 so that only the side margins of
the film are engaged by the idler wheel as the film passes over the
same. This prevents a portion of the film between the side margins
of the same from being contacted by any mechanical parts for a
purpose hereinafter described. The idler wheel 228 is retained on a
shaft 231 by a retaining ring 232. The shaft 231 is mounted upon a
mounting plate 233 which is secured to the base plate 167 by cap
screws 234.
The film 211, after passing from the idler assembly, passes over
the top wall or film guide shoe 186 and then passes under the
capstan drive assembly 217. The capstan drive assembly 217 consists
of a capstan 236 which is mounted upon and keyed to a shaft 237.
The capstan 236 is retained on the shaft 237 by a retaining ring
238. The length of film 211 is preferably provided with
perforations along at least one edge of the same which are adapted
to be engaged by pins 239 carried by the capstan so that the film
will be positively advanced by the capstan. The film 211 is held in
engagement with the capstan by suitable means such as a
rubber-covered roller 241. The rubber-covered roller 241 is
rotatably mounted upon a shaft 242 mounted in a yoke 243. The yoke
243 is secured to a shaft 244 that is slidably mounted in a bracket
246 mounted upon a block 247 secured to the main wall 12 by cap
screws 248. A lever arm 249 is pivotally mounted on a bracket 251
secured to the mounting block 247 by cap screws 252. A toggle link
(not shown) is connected to the lever arm 249 and to the shaft 244
whereby the roller 241 may be moved into and out of engagement with
the capstan 236 merely by shifting the lever arm 249 between open
and closed positions.
The capstan drive shaft 237 extends through the main wall 12 and
through a vacuum feed-through 254 for a rotary shaft mounted on the
main wall 12. The shaft 237 is connected to a flexible coupling 256
which is connected to the output shaft 257 of a gear reducer or
speed reducer 258. The input shaft 259 of the speed reducer is
connected to a coupling 261. The coupling 261 is connected to the
output shaft 252 of a variable speed drive motor 263. As can be
seen particularly from FIG. 2, the parts hereinbefore described are
carried by a plurality of plates 264 which are held apart in a
spaced relationship by spacers 266 and cap screws 267 in such a
manner that the entire assembly is supported by the main wall
12.
The motor 263 is provided with an additional output shaft 268. A
hub 269 is mounted upon the shaft 268 and carries therewith a
chopper disc or wheel 271 and is provided with a plurality of
blades 272 formed by placing openings 273 in the outer periphery of
the disc 271. The chopper disc 271 travels in a slot 274 provided
in a housing 276. The housing 276 is mounted in a clamp 277 secured
to one end of the variable speed drive motor 263. This housing 276
is substantially identical to the housing 154 and carries a lamp
(not shown) which is disposed on one side of the chopper disc 271
and a photosensitive detector (not shown) which is disposed on the
other side of the chopper disc. As hereinafter described, the
photosensitive detector will give an indication of the speed of
rotation of the output shaft 268 of the variable speed drive motor
263 so that the variable speed drive motor 263 can be controlled as
a d.c. servo motor generator.
The shafts 222 and 226 for the take-up and supply reels are driven
so that the length of film 211 is continuously under tension. Each
shaft is provided with a vacuum feed-through 281 for a rotary shaft
which is mounted upon the main wall 12. The shafs 222 and 226 are
each connected to a flexible coupling 282. The flexible coupling
282 is connected to the output shaft 283 of a conventional magnetic
clutch assembly 284. The input shaft 286 of the magnetic clutch
assembly is connected to a coupling 287. The coupling 287 is
connected to the output shaft 288 of a gear motor 289 of a suitable
type such as an a.c. hysteresis motor. Thus, it can be seen that
various parts of the apparatus for driving the shafts 222 and 226
are supported by the space plates 264 of the type hereinbefore
described.
The motors 289 are reversed in direction and it is their sole
purpose through the magnetic clutch assemblies 284 to continuously
maintain tension on the length of film. The length of film 211 is
actually driven by the capstan drive assembly 217 which controls
the speed of movement of the film.
The two light beams which are reflected upwardly through the beam
splitter 177 through a multi-element lens assembly 291 mounted
within a lens housing 292. Another housing 293 is mounted above the
housing 292 and is clamped to the housing 292 by a split clamp 294
which is provided with a screw 296 for tightening the same. A
mirror 297 which is provided with a first surface reflective
coating is mounted within the housing 293 so that it is disposed at
an angle of 45.degree. with respect to the two beams passing
through the lens assembly 291. A double element lens 298 is also
mounted within the housing 293 and receives the beams after they
have been reflected by the mirror 297. The lens 298 is mounted in
front of an opening 299 provided in the housing 293 so that the
light beams passing through the lens 298 can pass through the
opening and thence into an opening 301 provided in the main wall
12. A window 302 is mounted in the wall 12 and closes the opening
301. An O-ring 303 is provided for establishing a sealing
engagement between the window 302 and the wall 12. The two light
beams then pass through a filter 306 mounted in a filter housing
307. The filter housing 307 is secured to the main wall 12 by cap
screws 308. An O-ring 309 is provided for establishing sealing
relationship between the filter housing 307 and the window 302.
The light beams, after passing through the filter 306, pass through
a multi-element lens assembly 311 mounted in a lens housing 312
which is threaded into the support housing 314. Spacers 313 are
mounted upon the filter housing 307. A support housing 314 is
mounted upon the spacers 313 by cap screws 316. A photomultiplier
tube housing 317 is slidably mounted in the support housing 314. A
split clamp 318 encircles the support housing 314 and is provided
with a screw 319 for fastening the housing 317 within the housing
314. The socket housing 321 is provided which is secured to a
fitting 322 by cap screws 323. The fitting 322 is threaded into the
housing 317. A photomultiplier tube 326 is mounted within the
housing 317 and has its cathode 327 (see FIG. 10) mounted at a
point where the two light beams converge to a point.
An electronic feed-through assembly 329 is mounted in the wall 12
for supplying power to the synchro-receiver 206.
A large water-cooled shield 331 is provided as a part of the vacuum
assembly 313 and enclose the same. The shield 331 is provided with
an opening 332 through which vapors from an evaporation source 33
can enter the film head housing 181.
The optical thickness rate monitor also includes electrical and
electronic systems which are schematically illustrated in FIGS. 10
and 11. Thus, there is shown in FIG. 10 a power supply 341 for the
lamp 37. A power supply 342 is provided for supplying power to the
source 333. A power supply 343 is provided for supplying power to
the photomultiplier tube 326. Also, there is provided a monitor
system amplifier 344 and an evaporation rate controller 346.
The evaporation rate controller 346 consists of an error amplifier
348 which supplies its output to a differentiator compensator 349.
The output of the differentiator compensator 349 is supplied to a
non-linear amplifier 351, the output of which is supplied to
another differentiator compensator 352. The output of the
differentiator compensator 352 is supplied to a level detector 353
and the output of the level detector 353 is supplied to a motor
drive integrator 354. The output of the motor drive integrator 354
is supplied to an error amplifier 356 whose output is supplied to
the evaporation source power supplies 342. Three outputs 342 from
the evaporation source power supplies 342 are supplied to a summing
amplifier 357 and the output of the summing amplifier is supplied
to the error amplifier 356.
The monitor system amplifier 344 consists of a 12 kc tuned
amplifier 361 which receives its input from the photo-multiplier
tube 326. The output of the amplfier 361 is supplied to a linear
full wave low level detector 362. The output of the level detector
362 is supplied to a demodulator 363. The demodulator 363 receives
its signal from the photocell 162. The demodulator is schematically
illustrated as consisting of an amplifier which operates a switch
so that the signal from the level detector 362 is supplied to
either an amplifier 366 or an amplifier 367. The amplifier 366 is a
suitable type such as a loow pass amplifier which has a cutoff
response of 40 db. The amplifier 367 is a wide band amplifier. The
monitor system amplifier 344 also includes a voltage source 368 for
the light 161.
Operation and use of the optical thickness rate monitor in
performing the present method may now be briefly described as
follows. Let it be assumed that the optical thickness rate monitor
has been mounted in the side wall of a vacuum chamber in such a
position so that it is adapted to receive the vapor stream from an
evaporation source such as source 333 and that it is desired to
continuously monitor the evaporation from this source and to
control the rate of evaporation from the source.
Light is supplied from the lamp 37 and passes through the lens 48
which images the light from the filament of the light source onto
the holes 67 provided in the chopper disc or blade 61. The aperture
73 in the sleeve 72 prevents light from passing through any more
than one hole 67 in the chopper disc 61. The lens 81 re-focuses the
light which passes through the chopper blade. The light then
strikes the beam splitter 93 and forms the beam from the lens 81
into two separate spaced parallel sample and reference beams which
are spaced in such a manner so that one of the light beams will
pass through the prism 142 and the other light beam will pass
through the prism 143. The two light beams are thus chopped out of
phase with each other because of the spacing between the openings
141 permitting light to enter and leave the octagonal prisms 142
and 143. As pointed out previously, the spacing between pairs of
openings 141 is such that there are periods of time in which no
light passes from either of the octagonal prisms 142 and 143.
The portions of the light beams which pass from the octagonal
prisms 142 and 143 strike the beam splitter 177 and are deflected
downwardly onto the back side of and through the length of film 211
in the region in which the film is exposed by the aperture 187 to
the vapor stream passing from the source 333. Depending upon the
quantity of coating material which is deposited upon the other side
of the length of film 211, a certain portion of the one beam which
sees the coating material is reflected upwardly and passes through
the beam splitter 177. A constant percentage (depending only on the
properites of the uncoated film) of the other beam which does not
see the coating material is reflected upwardly and passes through
the beam splitter 177. The beams continue to pass upwardly as shown
in FIG. 10 through the lens assembly 211 which serves to cause
partial convergence of the image carried by the beams. The beams
then pass upwardly and are reflected through 90.degree. by the
mirror 297. Both light beams then pass through the lens 298 and
then through a band pass filter 306 which selects the desired
wavelength and excludes the undesired wavelengths. The light beams
then pass through a lens assembly 311 which causes the two light
beams to converge at a point which generally lies in a plane in
which the cathode 327 of the photomultiplier tube 326 lies.
The combination of the lens assembly 291, the plane mirror 297, the
lens 298, the band pass filter 206 and the lens assembly 311 can be
adjusted to form an image of the film 211 onto the photomultiplier
tube 327. Alternatively, it is possible to focus an image of the
iris diaphragm 88 onto the photomultiplier tube 327. The second or
alternative method is preferred over the first method because the
gain of the photomultiplier for the cathode varies as a function of
beam position on the cathode of the photomultiplier. Since the
second method places all the light from both beams in one spot on
the photomultiplier tube, the gain for both reference and sample
beams is the same at all times independent of beam position on the
photomultiplier tube. By way of example, using the system of the
type hereinbefore described, it was found to be possible to focus
all the light from both beams reflected from the film 211 into a
spot smaller than 1/8 of an inch in diameter onto the
photomultiplier tube 326.
The reference beam can be identified as the beam which passes
through the upper octagon prism 142, whereas the sample beam can be
considered as the beam passing through the octagon prism 143.
In one embodiment of the present invention, the chopper disc 61
chopped the light from the lamp 37 at the rate of 12,000 cycles per
second.
As pointed out previously, the octagon prisms 142 and 143, the
synchronous detector wheel 148 and the synchro-transmitter 134 are
all tied together by the timing belt 122 and are driven by a common
motor 126 which has a speed of 1,800 RPM. The pulley 132 on the
synchro 134 and the pulley 121 on the octagon prisms 142 and 143
are both three times the diameter of the pulley 123 on the motor.
Thus it can be seen that the synchro and octagon prisms rotate at
600 RPM.
The octagon prisms 142 and 143 cause the light beams which are
approximately 1/8 inch in diameter at the plane where they strike
the film 211 to linearly traverse the film in the direction of
travel of the film for approximately .sup.3/8 inch. By linearly
scanning the film in this manner, it is possible to reduce the
variations in signal level due to imperfections in the film by an
averaging process and also to eliminate the need for precise
positioning of the sample beam over the aperture 187.
The synchronous detector wheel 148 in conjunction with the light
source 161 and the photocell 162 provide a reference signal for the
synchronous demodulator 363 of the monitor system amplifier 344.
Since the synchronous detector wheel 148 is provided with eight
holes or openings 152 and both of the octagon prisms 142 and 143
have eight faces, the chopping frequency and the scanning frequency
is 80 cycles per second. The synchro-transmitter 134 which is
driven by the motor 126 sends an electrical signal to the
synchro-receiver 206. As is well known to those skilled in the art,
the shaft position of the synchro-receiver 206 will follow the
shaft position of the synchro-transmitter 134.
The chopper wheels 194 and 196 are mechanically linked to the shaft
204 of the synchro-receiver as hereinbefore described. The chopper
discs 194 and 196 are each provided with eight openings and are
phased in such a manner so that when light from the sample beam can
travel through the chopper disc 194, coating material is blocked
from striking the film 211 through the chopper disc 196 and when
coating material can travel through the chopper disc 196 to strike
the bottom side of the film 211, light from the sample beam cannot
travel through the chopper disc 194 to the back side of the film
211. In this manner, the two chopper discs 194 and 196 in
combination serve to prevent light from the coating source from
entering the system and being transmitted to the photomultiplier
tube 326 and possibly saturating the photomultiplier tube 326
because the coating source may be extremely bright.
The anti-reflection coating provided on the beam splitter 93 serves
to reduce to a minimum the reflection from the first surface of the
beam splitter 93, thus transmitting maximum light through the beam
splitter to the beam splitting coating provided on the surface 106.
By way of example, such a beam splitting coating typically
transmits approximately 50 percent of the light to the octagon
prism 142 and reflects approximately the other 50 percent to the
mirror coating carried by the surface 107. The mirror coating
reflects approximately 90 percent of the light which is incident on
it to the anti-reflection coating carried on the surface 106 which
transmits substantially all of that light to the lower octagon
prism 143.
As pointed out previously, the openings or windows 141 provided for
the octagon prisms 142 and 143 have a size so that light can only
pass through the octagon prism 142 only when there is no light
passing through the octagon prism 143, and conversely, light can
only pass through the octagon prism 143 when there is no light
pasing through the octagon prism 142. The phase relationship
between the chopper discs 193 and 194 and the octagon prisms 142
and 143 must be such that light passing through octagon prism 143
will never strike the chopper disc 194. This phasing can be readily
accomplished by shifting the synchro-receiver 206 within its
mounting block 207 and then securing it in the desired
position.
The output from the photomultiplier tube 326 is supplied to the
monitor system amplifier 344 which processes the signal and
compensates it so that when the loop is closed through the
evaporation source power supply 342 and the evaporation source 333,
oscillations will not occur. A reference 36 is supplied for the
evaporation rate controller 346 and is used to set the desired
evaporation rate. The reference level for the power supply 341 is
used to set the evaporation rate signal level.
From the schematic diagram which is shown in FIG. 10, it can be
seen that several feedback loops are provided in the system. There
is a loop which takes the reference light beam signal from the
monitor system amplifier 344 and feeds it to the power supply 341.
This input is compared with the reference level supplied to the
power supply 341 and then a determination made to ascertain whether
or not the intensity of the light source 37 should be changed so
that the end result is that the reference signal from the monitor
system amplifier 342 will be held at a constant level equal to the
reference level supplied to the power supply 341.
The reference level for the power supply 341 is adjustable so that
compensation can be made for various types of thin film materials
that are utilized during the coating process. For example, if the
high index material being utilized for the coating process has an
index of refraction which is higher than the index of refraction
for the film 211 which is being utilized, then the reflection level
or signal level must be set at a low value or low percent of full
scale so that when the coating material is applied to the film 211
and the reflection increases, the signal level can increase without
saturating the photomultiplier tube 326. On the other hand, if a
low index material is being utilized in the coating operation, that
is, the coating material has an index of refraction which is less
than the index of refraction of the film 211, then the reference
level for the power supply 341 must be adjusted to a high percent
of its maximum value so that when the coating material is applied
to the film 211 and the signal level decreases, the signal will not
go into the cut-off region for the photomultiplier tube.
As pointed out previously, at no time does any of the coating
material coat the side of the film upon which the reference beam is
incident. For this reason, the reference level for the power supply
341 is set at some fixed point. Thus if any component or light
source, or the photomultiplier should vary its transmission
intensity or gain within the reference signal closed loop, the
light power supply 341 will cause the light level to increase or
decrease to automatically compensate for that change and hold the
signal level constant and equal to the reference level. It is for
this reason that a dual beam system is utilized, i.e., a system
with sample and reference beams.
As pointed out previously, the octagon prisms 142 and 143 cause the
light beam to scan the film 211 in the direction of movement of the
film for a distance which is greater than the size of the coating
aperture 187. This prevents variations in signal level that would
be seen if the sample and reference beams were not scanning the
film and the beams were to move within the aperture 187. The
scanning has an additional advantage in that it prevents signal
variation due to imperfections in the film.
It should be pointed out that it is possible to utilize the
principles of the present invention by scanning the front surface
of the film. However, this does have the disadvantage in that it is
necessary to frost or sandblast the back side of the film to
prevent the sample and reference beams from seeing the back surface
of the film.
The monitor system amplifier operation is as follows. The reference
signals and the rate signal are time shared by the photomultiplier
326. These signals are both fed into the monitor system amplifier
344. The information from the photomultiplier tube 326 is supplied
to a 12 kc tuned amplifier 361 which has a bandwidth of 1200 cycles
per second. This amplifier amplifies the signal level and is tuned
to the frequency of the incoming signal. The output of this
amplifier is detected by a linear full wave low level detector 362.
The signal from the detector 362 is fed into the demodulator 363
which is controlled by a signal from the photocell 162. This
demodulator 363 is synchronously switched in the proper phase and
supplies a signal alternately to the rate amplifier 366 and the
reference amplifier 367. The rate amplifier has a roll-off of 40 db
per decade. The reference amplifier 366 is a wide band amplifier
and provides the necessary compensation for the light power supply
341 to prevent the internal loop from oscillating.
The voltage source 368 for the light 161 is unregulated and is
sufficient to keep the light at approximately 80 percent of its
full brilliance. The light 161 supplies more than enough light to
operate the photocell 162 fully on when light is incident upon the
photocell 162 and when the synchronous chopper 148 prevents light
from becoming incident on photocell 162, the photocell 162 is fully
off.
The reference for the evaporation rate controller is set for the
desired evaporation rate level to be obtained. The rate signal
which is supplied from the amplifier 366 is compared with the
reference by the error amplifier 348. A signal from the error
amplifier 348 is supplied to a first differentiator compensator 349
of a conventional type. This compensator 349 feeds a signal into a
non-linear amplifier 351. The non-linear amplifier feeds its signal
to a second differentiator compensator 352. The first
differentiator compensator serves to compensate for the time lag in
the evaporation source, the crucible and the time constant of the
coating material. The non-linear amplifier serves to compensate for
the non-linear gain of the evaporation source. In other words, the
evaporation rate of the evaporation source is not linearly related
to the power level on the evaporation source. The scond
differentiator compensator serves to compensate for the time
constant obtained with the optical thickness rate monitor
itself.
Both differentiator compensators 349 and 352 are adjustable and the
non-linear amplifier 351 is also adjustable.
The differentiator compensator 352 supplies a signal to the level
detector 353 which operates a motor drive integrator 354. The level
detector 353 causes the motor drive integrator to operate in one
direction or the other. If the signal level from the second
differentiator compensator is below plus or minus some preset
voltage, which is adjustable, the level indicator does not drive
the motor in either direction. If the signal is above this
predetermined plus or minus voltage level, the level detector will
drive the motor drive integrator in one direction for a positive
voltage above the predetermined voltage level and in an opposite
direction for a negative voltage below the predetermined voltage
level. The motor drive integrator 354 supplies the signal to the
error amplifier 356. This signal level from the motor drive
integrator varies only during the time the motor is running and
when the motor stops, the signal level is held constant at the
value it had when the motor stopped. This signal level requires
that the beam emission current signal from the evaporation source
power supplies 342 be constant because of the action of the summing
amplifier 357 supplying a signal to the error amplifier 356. A
motor drive integrator 354 is utilized because of the long
integrating time constants involved. By way of example, a time
constant of 5 minutes may be present in the system. The motor drive
integrator 354 is a motor driving a potentiometer.
The error amplifier 356 compares the signal from the motor drive
integrator to a signal which is proportional to the sum of the
three electron beam currents for the evaporation sources from the
three electron guns as supplied by the summing amplifier 357. The
error amplifier 356 supplies the signal the signal to all of the
power supplies and forces the current from the power supplies to be
proportional to the signal received from the motor drive integrator
354. This has a distinct advantage because in the event any of the
evaporation sources should fail, the other evaporation sources will
assume the current which previously had been supplied to the
malfunctioning power supply. By way of example, if three
evaporation sources are utilized, it is possible with the present
system that two of the power supplies can malfunction and the
system would still operate satisfactorily because the one remaining
power supply would assume the total power for all three of the
evaporation to evaporate the necessary material for the coating
operation.
During the time that the foregoing operations are taking place, the
film 211 is being continuously advanced by the capstan assembly
217. By utilizing the large tape reels 221 and 224, it is possible
to store hundreds of feet of the film within the vacuum chamber in
which the coating operation is taking place and to thereby
continuously monitor the coating operations taking place for long
periods of time. Thus, by way of example, it is possible to
continuously monitor the operations in the vacuum chamber for a
period as long as a week without shutting down the vacuum
chamber.
The monitor measures the rate of evaporation because the thickness
of the coating deposited on the film 211 is wedged or, in other
words, is tapered in thickness along a direction which is parallel
to the direction of movement of the film.
The rate monitor also has the unique advantage in that it does its
monitoring from the back side of the film so that the field of view
for the film is always clean. There is no problem of the coating
material and the like obscuring the field of view of the film. In
addition, the film itself is always clean and unmarred in the
regions of interest.
* * * * *