A system using dual wavelength characteristics of light passing through a film being deposited was described to generate an output signal that changes rapidly at the point when the deposition process should stop or change. Photodetectors are used to sense the light intensity changes at the two wavelengths, and the monitored signal represents the ratio of their sums and difference signal strengths

Zurasky, J. L.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.C. 20546
ATTN OF:
<NASA-Case-HFS-20675) MONITORING
DEPOSITION OF FI1MS Patent (NASA) 5 p
N73-26751 .
CSCL 20L
Unclas
00/26 06467
TOt
PROM:
FSI/Scientific & Technical Information Division
Attention: Miss Winnie M. Morgan
GP/Office of Assistant General Counsel for
Patent Matters
SUBJECT} Announcement of NASA-Owned U.S. patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No. ;
Government or
Corporate Employee
Supplementary Corporate
Source (if applicable)
NASA Patent Case No.
NOTE - If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
Yes / / No / ?*/
Pursuant to Section 305(a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of the patent; however, the name of the actual
inventor (author) appears at the heading of column No. 1 of
the Specification, following the words "... with respect to
an invention of . . ."
Elizabeth A. Carter
Enclosure
Copy of patent cited above
NASA-HQ
https://ntrs.nasa.gov/search.jsp?R=19730018024 2020-03-17T08:33:21+00:00Z
United States Patent 09]
Zurasky
in] 3,737,237
[45] June 5,1973
154] MONITORING DEPOSITION OF FILMS
[75] Inventor: James L. Zurasky, Hunstville, Ala.
[73] Assignee: The United States of America as
represented by the Secretary of the
Administrator of the National
Aeronautics and Space Administra-
tion, Washington, D.C.
[22] Filed: Nov. 18,1971
[21] Appl. No.: 200,085
[52] U.S. Cl 356/161, 356/108, 356/202,
250/219 TH
[51] Int. Cl GOlb 11/00
[58] Field of Search 356/161, 108;
250/219 TH
3,238,839 3/1966
3,322,962 5/1967
3,439,175 4/1969
Day, Jr 250/219 TH
Muller.: 356/161
Kammuller 356/161
OTHER PUBLICATIONS
"Alternating Wavelength Vampo" By Pliskin et al.
IBM Tech, Bltn. Vol. 13 No. 3 Aug. 1970
Primary Examiner—Ronald L. Wibert
Assistant Examiner—Paul K. Godwin
Attorney— L. D. WofFord, Jr., W. H. Riggins and J. R.
Manning
[57] ABSTRACT
[56]
2,973,686
3,017,512
References Cited
UNITED STATES PATENTS
3/1961 Dreyfus et al 250/219 TH
1/1962 Wolbert 356/161
A system using dual wavelength characteristics of light
passing through a film being deposited to generate an
output signal that changes rapidly at the point when
the deposition process should stop or change.
Photodetectors are used to sense the light intensity
changes at the two wavelengths and the monitored
signal represents the ratio of their sums and difference
signal strengths.
3 Claims, 3 Drawing Figures
SUM 8 DIFF.
AMPLIFIER
DIGITAL READOUT
*
PATENTEDJUN 51973
SHEET 1 CF 2
3.737.237
SUM a DIFF.
AMPLIFIER
DIGITAL READOUT
V 4,
FIG.
SUM a DIFF.
AMPLIFIER
DIGITAL READOUT
F I G . 2
PATENTED JUN 51973 3,737.237
o
CO
V)
CO
<
tr
lOO-r
80 4-
60 4-
40 +
20 4-
SHEET 2 OF 2
-r 100
+ 80
20
UJ
r>
<
UJ
»-
-3
_i
o
CO
m
<
a:
FILM NUMBER
INCREASING THICKNESS
FIG. 3
3,737,237
1 2
MONITORING DEPOSITION OF FILMS This will become apparent upon reference to the fol-
ORIG.N OF THE INVENTION '°wing drawingS a"d descriPtion'
The invention described herein was made by an em- BRIEF DESCRIPTION OF THE DRAWING
ployee of the United States Government and may be 5 FIG. 1 illustrates the monitoring system of the pres-
manufactured and used by or for the Government for ent invention for light transmitted through the film
governmental purposes without the payment of any being deposited
royalties thereon or therefor. FIG. 2 illustrates the similar monitoring system for
BACKGROUND OF THE INVENTION ,
 n
 HSht reflected throu8h the fllm bejng ^posited.10 FIG. 3 is a graph of a ratio readout curve for a five
Field of the Invention layer filter.
The invention relates to the art of monitoring the DESCRIPTION OF THE PREFERRED
thickness of thin films for optics so as to obtain a de- EMBODIMENT
sired optical characteristic.
'5 Referring now to FIG. 1 wherein is illustrated a sys-
Description of the Prior Art
 tem for monitoring the film deposition in an evapora-
A thin film on a substrate changes the character of tion chamber. A light source 11 with focusing lens proj-
the light reflected or transmitted by the substrate. Of- ects a collimated light beam 13, that is modulated by
ten, to achieve desired optical properties, it is neces- a chopper 15, through a lower tube 17 leading into the
sary to have multilayers of thin layers on a substrate to evaporation chamber 19. The modulated light beam 13
act on the transmitted or reflected light. The thickness passes through a substrate and film 21 being deposited
of the film layer is critical and the film deposition pro- thereon and into an upper tube 23 which contains a
cess must be stopped or changed at a very precise point mirror 25 that reflects the light beam 13 toward a di-
to achieve the proper thickness which results in the de- chroic filter 27 that reflects light having a wavelength
sired optical property. ' greater than a certain wavelength toward a first select
One of the better methods of monitoring the deposi- filter 31 and photodetector 32 arrangement and passes
tion process of films on a substrate uses a photodetec- light having a wavelength less than a certain wave-
tor to measure the intensity of the light transmitted or length toward a second select filter 33 and photodetec-
reflected through the film. The thickness of the film
 tor 34 arrangement. While a beam splitter could be
having been correlated by previous techniques to the
 used rather than a dichroic filter 27, the dichroic filter
intensity of such light reflected or transmitted. The dif- js preferred because it assures an adequate light beam
ficulty with the method is that an error is most often in-
 win be directed to a specific filter and photodetector
troduced by having a stopping point which not only arrangement
necessarily requires an overshoot to determine that a
 35 The flrst filter 31 is seiected to pass the light of a
stopping point has been reached but having a changing
 waveiength slightly greater than the filter being made
light intensity at the desired film thickness which is so
 in the evaporation chamber 19 toward the first photo-
slight that it is difficult to know when the stopping point
 detector 32. The second filter 33 is selected to pass the
has occurred.
 u ht of a waveiength slightly less than the filter being
Accordingly, it is an object of the present invention
 4Q made toward the second photodetector 34. For exam.
to prov.de a very prec.se momtor.ng system for thin
 p,e jf a fiye ,ayer fi,ter for Hght transmissions having a
film deposition. , , _ , . , _ wavelength of 5893 angstroms (A) is being made, theAnother object .s to prov.de a dual wavelength light
 first ^ M cou,d fee £iected tQ ^ ^ * ht hayi
monitonng system wh.ch produces a very rap.d chang-
 transmission wave,ength of 6600 (A) and the seconding signal near the desired stopping point in the deposi- ., _. _, ... . e. .
. " °. . . , . . , . 45 filter 33 could be selected to have a transmission wave-tion of the film layer. , . -,.,. . ... .. ,. . . . „_
Other objects and advantages of the present inven- l6"^ °,f 5,46' *' W±* ? T T™' ^
tion will become more apparent as the description pro- in8'he h8ht, a'the 60°° * wavelength.
ds
 rr
 r r
 The S1gnais from the photodetectors 32, 34 repre-
sents the light intensity received at the select wave-
SUMMARY OF THE INVENTION 50 lengths of the filters 31,33 and the signals are amplified
A dual-wavelength system for monitoring the fabrica- and flltered to have *"* noise Amoved by tuned ampli-
tion of high-quality optical filters and other highly pre- flers 37' 39 associated with each photodetector. The
cise film deposition operations. A light beam is passed modulation of the light by the beam chopper 15 assures
or reflected through a thin film being deposited and the „ that the correct light is being identified and amplified
resulting light beam is divided into two separated bV the tuned amplifiers 37, 39.
beams. Each of the divided branches of the light beam The outPut of the tuned amplifiers 37, 39 are both
is passed through an independent system having a filter inputed into a sum and difference amplifier and digital
to pass a certain wavelength light to a photodetector to readout device 41 which gives a ratio readout of the
measure the light intensity at that wavelength. Both sig-
 6Q sum
 of the signal strength from both amplifiers 37, 39
nals from the photodetector are inputed into a sum and and the difference in signal strength from both amplifi-
difference amplifier to provide a ratio signal that is rap- ers 37,39. As indicated by FIG. 3 the light transmission
idly changing at the point where the film deposition of the select wavelengths changes very little as the de-
must be stopped or changed. If a filter is being manu- sired film thickness is obtained which would normally
factured, the light filters selected for the system are
 65 make it difficult to determine the desired stopping
such that one passes light having a wavelength slightly point. As the ratio readout of the sum and difference
less than the designed wavelength and the other passes between the signals is very large and changes very rap-
light having a wavelength slightly greater. idly the desired stopping point can readily be identified.
3,737,237
The graph is plotted for five layers using the first filter
of 6600 A and the second filter of 5461 A.
Obviously, many modifications and variations of the
present invention are possible in light of the above
teachings. As indicated by FIG. 2 in which the primed 5
numbers corresponds to the numbers of FIG. 1, the
same arrangement may be made to monitor the re-
flected light from the substrate in which the reflected
light passes through the film being deposited and is di-
rected into the output tube 23' by the addition of a 10
beam splitter 43. It is to be understood that within the
scope of the appended claims the invention may be
practiced other than as specifically claimed.
What is claimed is:
1. A monitor for determining the thickness of a thin 15
film being deposited, comprising:
a light source which directs a light beam so it will be
incident on the film being deposited,
a dichroic filter to split the resulting light beam acted
upon by said film so that said resulting light beam 20
is divided into two branch light beams of differing
wavelengths,
a first filter of a known light transmission wavelength
acting upon one of said branch light beams,
a second filter of a known light transmission wave- 25
length acting upon the other of said branch light
beams,
a first means for producing an electrical signal repre-
sentative of the intensity of light transmitted by
said first filter, 30
a second means for producing an electrical signal
representative of the intensity of light transmitted
by said second filter,
a readout device which receives said electrical signals
35
of said first and second means and gives a ratio
readout of the sum and difference of said electrical
signals which readout changes rapidly at the point
where film deposition must be stopped or changed.
2. A monitor according to claim 1 wherein:
said light source projects a collimated modulated
light beam.
3. A monitor for deposition of thin films in an evapo-
ration chamber, comprising:
a light source which directs a collimated light beam
into said evaporation chamber so said light beam
will be incident on the thin film being deposited,
a mirrow device for reflecting the resulting light
beam acted upon by said film into a dichroic filter
so that said resulting beam is divided into two
branch light beams,
one of the branch light beams being directed through
a first filter of a known transmission wavelength,
and the other of said branch light beams being di-
rected through a second filter of a slightly different
transmission wavelength,
a first photodetector means for producing an electri-
cal signal representative of the light transmitted by
said first filter,
a second photodector means for producing an elec-
trical signal representative of the light transmitted
by said second filter, and
an amplifier and readout device for receiving said
electrical signals from said first and second photo-
detectors for giving a ratio readout of the sum and
difference between said two electrical signals
which readout rapidly changes at the point where
film deposition must be stopped or changed.
40
45
50
55
60
65


Monitoring deposition of films

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server