U.S. patent number 3,637,381 [Application Number 04/839,038] was granted by the patent office on 1972-01-25 for radiation-sensitive self-revealing elements and methods of making and utilizing the same.
This patent grant is currently assigned to Teeg Research, Inc.. Invention is credited to Robert W. Hallman, Gary W. Kurtz.
United States Patent |
3,637,381 |
Hallman , et al. |
January 25, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
RADIATION-SENSITIVE SELF-REVEALING ELEMENTS AND METHODS OF MAKING
AND UTILIZING THE SAME
Abstract
Electromagnetic radiation-sensitive elements made essentially of
a metallic layer and of an overlayer of an inorganic material
capable of interreacting with the metal of the metallic layer, when
exposed to electromagnetic actinic radiation, so as to cause a
selective etching of the metallic layer surface at the boundary
between the metallic layer and the overlayer which is proportional
in depth to the amount of exposure to the electromagnetic actinic
radiation. The overlayer may be in a solid form as a thin coating
adhering to the metallic layer, or it may be in a liquid or a vapor
form. Electromagnetic radiation sensitive elements, consisting of a
plurality of strata, each made of a pair of layers of dissimilar
materials, one of which is metallic and the other is a layer of
actinically reactive inorganic material are provided for particular
applications. Exposure to actinic electromagnetic radiation of the
elements of the invention causes physical and chemical changes in
the materials of the two layers resulting in selective removal,
after exposure, of some of the materials of predetermined layers
for obtaining particular finished articles.
Inventors: |
Hallman; Robert W. (Utica,
MI), Kurtz; Gary W. (Southfield, MI) |
Assignee: |
Teeg Research, Inc. (Detroit,
MI)
|
Family
ID: |
25656480 |
Appl.
No.: |
04/839,038 |
Filed: |
July 3, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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591711 |
Nov 3, 1966 |
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Current U.S.
Class: |
430/297;
204/157.4; 204/157.48; 430/306; 430/323; 430/326; 204/157.45;
204/157.49; 430/310; 430/330; 216/87; 216/100; 216/53 |
Current CPC
Class: |
G03F
7/0044 (20130101); G03C 1/705 (20130101); G03F
7/0042 (20130101); C23F 4/00 (20130101); C23F
1/02 (20130101) |
Current International
Class: |
C23F
1/02 (20060101); C23F 4/00 (20060101); G03C
1/705 (20060101); G03F 7/004 (20060101); G03c
005/00 (); G03c 001/72 () |
Field of
Search: |
;96/1.5,27,35,36,36.2,36.3,88 ;252/501 ;117/93.3,217
;156/4,17,18,3,14 ;29/195 ;204/157.1 ;250/65,65.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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344,354 |
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Mar 1931 |
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GB |
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968,141 |
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Aug 1964 |
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GB |
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1,151,310 |
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Sep 1969 |
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GB |
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Other References
Remy, "Treatise on Inorganic Chemistry," 1956, Elsevier Publ. Co.,
pp. 782-785 .
Kostyship et al., "Photographic-Sensitivity Effect in Thin
Semiconducting Films on Metal Substrates," Soviet Physics-Solid
State, Vol. 8, No. 2, Feb. 1966, pp. 451-452.
|
Primary Examiner: Lesmes; George F.
Assistant Examiner: Martin; R. E.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a continuation-in-part of application
Ser. No. 591,711, filed Nov. 3, 1966, now abandoned, and it further
includes the subject matter disclosed in copending application Ser.
No. 636,864, filed May 8, 1967 now abandoned, and Ser. No. 641,202,
filed May 25, 1967, now abandoned.
Claims
Having thus described the invention by way of illustrative examples
thereof, what is sought to be protected by United States Letters
Patent is:
1. A method for making a plate element provided with a relief image
on a layer of a first inorganic material disposed on a support
backing, said method comprising: projecting an electromagnetic
actinic radiation image upon an electromagnetic radiation-sensitive
element having said support backing provided with said layer
adhering thereto and an overlayer on said first layer of an
inorganic second material different from that of said first layer
and capable when exposed to said electromagnetic actinic radiation
image to form an interreaction product therewith, wherein said
first layer comprises at least one element selected from the group
consisting of silver, copper, lead, cadmium, zinc, iron, tin,
arsenic, bismuth, cobalt, germanium, indium, manganese, mercury,
nickel, selenium, silicon, tellurium, thallium and vanadium, and
said inorganic second material is selected from the group
consisting of sulfur, selenium, M--X compounds and mixtures and
M--X--Y compounds and mixtures wherein M is a metal selected from
the group consisting of arsenic, antimony, bismuth, selenium,
tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium,
indium, thallium, germanium, tin, iron, cobalt, nickel and silver,
and X and Y are selected from the group consisting of halogen,
sulfur, selenium and tellurium, maintaining said plate element
substantially at room temperature while projecting said
electromagnetic actinic radiation image thereon, and removing said
interreaction product thus leaving said relief image formed by
portions of said first layer remaining adherent to said support
backing.
2. The method of claim 1, wherein the formation of said
interreaction product causes a selective etching of the metallic
layer which extends in depth all the way through said metallic
layer.
3. The method of claim 1, wherein said interreaction product is
mechanically removed.
4. The method of claim 1, wherein said interreaction product is
chemically removed.
5. The method of claim 1, wherein said interreaction product is
removed by subsequent heat sublimation.
6. The method of claim 3, wherein the portions of said material
which have not interreacted with the metal of said metallic layer
are also mechanically removed.
7. The method of claim 4, wherein the portions of said material
which have not interreacted with the metal of said metallic layer
are also chemically removed.
8. The method of claim 5, wherein the portions of said material
which have not interreacted with the metal of said metallic layer
are also removed by heat sublimation.
9. The method of claim 1, comprising the additional step of
disposing said element in an enclosure nontransmissive of said
electromagnetic radiation.
10. A method for obtaining a relief image on a surface comprising:
selectively and discretely impinging electromagnetic actinic
radiation upon said surface in the presence of a vapor of an
inorganic material different from that of said surface and capable
of forming a radiation provoked interreaction product with said
surface, wherein said surface comprises at least one element
selected from the group consisting of silver, copper, lead,
cadmium, zinc, iron, tin, arsenic, bismuth, cobalt, germanium,
indium, manganese, mercury, nickel, selenium, silicon, tellurium,
thallium and vanadium, and said inorganic material is selected from
the group consisting of sulfur, selenium, M--X compounds and
mixtures and M--X--Y compounds and mixtures wherein M is a metal
selected from the group consisting of arsenic, antimony, bismuth,
selenium, tellurium, copper, zinc, cadmium, mercury, lead,
chromium, gallium, indium, thallium, germanium, tin, iron, cobalt,
nickel and silver, and X and Y are selected from the group
consisting of halogen, sulfur, selenium and tellurium, and removing
said interreaction product thus leaving said relief image formed by
the unreacted portions of said surface.
11. The method of claim 10, wherein the formation of said
interreaction product causes a selective etching of the metallic
layer which extends in depth all the way through said metallic
layer.
12. The method of claim 10, wherein said interreaction product is
removed by chemical action.
13. The method of claim 12, wherein said interreaction product is
dissolved in an aqueous solution of a base.
14. The method of claim 12, wherein said interreaction product is
dissolved in an acid.
15. The method of claim 10, wherein said interreaction product is
removed by mechanical action.
16. The method of claim 10, wherein said interreaction product is
removed by heat sublimation.
17. A method for obtaining a relief image on a surface comprising:
selectively and discretely impinging electromagnetic actinic
radiation upon said surface in presence of an inorganic material
different from that of said surface, said inorganic material being
in a liquid phase and capable of forming a radiation-provoked
interreaction product with said surface, wherein said surface
comprises at least one element selected from the group consisting
of silver, copper, lead, cadmium, zinc, iron, tin, arsenic,
bismuth, cobalt, germanium, indium, manganese, mercury, nickel,
selenium, silicon, tellurium, thallium and vanadium, and said
inorganic material is selected from the group consisting of sulfur,
selenium, M--X compounds and mixtures and M--X--Y compounds and
mixtures wherein M is a metal selected from the group consisting of
arsenic, antimony, bismuth, selenium, tellurium, copper, zinc,
cadmium, mercury, lead, chromium, gallium, indium, thallium,
germanium, tin, iron, cobalt, nickel and silver, and X and Y are
selected from the group consisting of halogen, sulfur, selenium and
tellurium, and removing said interreaction product thus leaving
said relief image formed by the unreacted portions of said
surface.
18. The method of claim 17, wherein the formation of said
interreaction product causes a selective etching of the metallic
layer which extends in depth all the way through said metallic
layer.
19. The method of claim 17, wherein said interreaction product is
removed by chemical action.
20. The method of claim 19, wherein said interreaction product is
dissolved in an aqueous solution of a base.
21. The method of claim 19, wherein said interreaction product is
dissolved in an acid.
22. The method of claim 17, wherein said interreaction product is
removed by mechanical action.
23. The method of claim 17, wherein said interreaction product is
removed by heat sublimation.
24. A method for making a relief image by means of a multilayer
electromagnetic radiation-sensitive element comprising essentially
a plurality of superimposed adhering strata substantially
transmissive of said radiation, each one of said strata consisting
of a pair of adhering layers made of dissimilar materials capable
when exposed to actinic radiation to react with each other so as to
form an interreaction product having a chemical composition and
physical characteristics different from those of said layers prior
to exposure to actinic radiation wherein one of said layers
comprises at least one element selected from the group consisting
of silver, copper, lead, cadmium, zinc iron, tin, arsenic, bismuth,
cobalt, germanium, indium, manganese, mercury, nickel, selenium,
silicon, tellurium, thallium and vanadium, and the second of said
layer is an inorganic material selected from the group consisting
of sulfur, selenium, M--X compounds and mixtures and M--X--Y
compounds and mixtures, wherein M is a metal selected from the
group consisting of arsenic, antimony, bismuth, selenium,
tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium,
indium, thallium, germanium, tin, iron, cobalt, nickel and silver,
and X and Y are selected from the group consisting of halogen,
sulfur, selenium, and tellurium, said method comprising the steps
of: impinging an actinic radiation defined image upon the first of
said strata such that said radiation partially penetrates
selectively and discretely beyond the first of said strata to a
depth proportional to the intensity of said radiation thus forming
areas wherein said interreaction product is formed to a depth
locally dependent from the intensity of said radiation; and
removing said interreaction product.
25. The method of claim 24, wherein said radiation-defined image
consists of an outline of the relief image to be obtained and
comprising the additional step of:
removing at least one of said strata within the perimeter of said
outline whereby a recessed surface is defined which corresponds to
said outline.
26. The method of claim 24, wherein said radiation-defined image
consists of an outline of the relief image to be obtained and
comprising the additional step of:
removing at least one of said strata without the perimeter of said
outline whereby a raised surface is defined which corresponds to
said outline.
27. The method of claim 24, wherein said interreaction product is
removed by selective chemical action.
28. The method of claim 24, wherein said interreaction product is
removed by mechanical action.
29. The method of claim 24, wherein said interreaction product is
removed by heat sublimation.
30. The method of claim 24, wherein the formation of said
interreaction product causes a selective etching of the metallic
layer which extends in depth all the way through at least one of
said metallic layers.
31. A method for making a plate element provided with a relief
image comprising: projecting an electromagnetic actinic radiation
image upon an electromagnetic actinic radiation image upon an
electromagnetic radiation-sensitive element consisting essentially
of a pair of substantially adhering layers made of different
inorganic materials capable when exposed to actinic radiation to
form an interreaction product with each other, wherein one of said
layers comprises at least one element selected from the group
consisting of silver, copper, lead, cadmium, zinc, iron, tin,
arsenic, bismuth, cobalt, germanium, indium, manganese, mercury,
nickel, selenium, silicon, tellurium, thallium and vanadium, and
the second of said layers is an inorganic material selected from
the group consisting of sulfur, selenium, M--X compounds and
mixtures and M--X--Y compounds and mixtures, wherein M is a metal
selected from the group consisting of arsenic, antimony, bismuth,
selenium, tellurium, copper, zinc, cadmium, mercury, lead,
chromium, gallium, indium, thallium, germanium, tin, iron, cobalt,
nickel and silver, and X and Y are selected from the group
consisting of halogen, sulfur, selenium and tellurium, maintaining
said electromagnetic radiation element substantially at room
temperature while projecting said electromagnetic actinic radiation
image thereon, and removing said interreaction product and the
unreacted portion of said second layer thus forming said relief
image on said first layer.
32. The method of claim 31, wherein the formation of said
interreaction product causes a selective etching of the metallic
layer which extends in depth all the way through said metallic
layer.
33. The method of claim 31, wherein said interreaction product and
the unreacted portions of said overlayer are mechanically
removed.
34. The method of claim 31, wherein said interreaction product and
the unreacted portions of said overlayer are chemically
removed.
35. The method of claim 31, wherein said interreaction product and
the unreacted portions of said overlayer are removed by subsequent
heat sublimation.
36. The method of claim 31, comprising the additional step of
disposing said element in an enclosure nontransmissive of said
electromagnetic radiation.
Description
BACKGROUND OF THE INVENTION
As reported in the Soviet Physics-- Solid State, Vol. 8, No. 2,
Feb., 1966, pages 451-452, it is already known that films of some
metal halides, and sulfides, such as arsenic selenide and zinc
telluride, among others, when deposited on a metal substrate, such
as silver, copper, zinc, lead, etc., are capable of giving a
visible image, in other words, of exhibiting photosensitivity,
under the action of intense incident light. The image becomes
visible during the exposure, and there is generally no need of
additional processing for revealing the image. Once formed, the
image may be preserved for a considerable period of time without
fading. For certain materials, the application of heat to the
photosensitive elements is necessary in order to reveal or develop
the latent image.
The present invention, as will become evident from reading the
hereinafter detailed description thereof, constitutes a
considerable improvement upon the state of the art as reported by
the article hereinabove mentioned. In effect, the present invention
provides more particularly new methods for obtaining many useful
finished articles, such finished articles being obtainable in a
much simpler manner than by conventional methods. Utilizing
electromagnetic sensitive elements according to the present
invention by way of the methods of the present invention, for
example lithographic plates, metal engravings of all types,
electrical printed circuits, etc., may be obtained.
Briefly stated, the present invention contemplates projecting an
image upon an electromagnetic radiation-sensitive element
consisting of a layer of silicon or a metallic layer hereinafter
designated under the expression "metallic layer," disposed or not
upon a support backing, the metallic layer being provided with an
overlayer of a material or materials exhibiting an affinity for
interreacting with the metallic layer when exposed to
electromagnetic actinic radiation such as visible light, preferably
of a high intensity. The image formed upon the electromagnetic
radiation-sensitive element results from interface reactions under
the influence of actinic radiation which cause an etching effect
upon the surface of the metallic layer in contact with the
overlayer, and the interreaction products are subsequently removed
chemically or mechanically. If so desired, the unreacted portions
of the overlayer may also be removed. The finished article,
consequently, consists of the metallic layer presenting at least
one surface having selectively etched portions corresponding to the
exposed portions and of depths substantially proportional to the
amount of illumination or actinic radiation exposure, the unexposed
portions remaining intact. The relief image is thus a faithful
reproduction of the image projected upon the electromagnetic
radiation sensitive element.
If the image projected upon the sensitive element is a
high-contrast image, as is the case when the projected image is
caused by transparency projection of a model or mask consisting of
portions which are capable of transmitting all or almost all of the
incident actinic radiation, and other portions which are
substantially nontransmissive of such radiation, with appropriate
thickness of the metallic layer a complete radiation-induced
etching of the metallic layer can be obtained wherever the actinic
radiation impinges upon the surface of the element. Thus, clean
edge contoured perforations are obtained through the metallic layer
which may, for some applications, be used as such. A potential
application, for example, is the manufacture of color registration
masks for color kinescopes. In other applications the etched
metallic layer may be cemented or bonded, subsequently, to a
support backing. If the metallic layer is originally disposed upon
a support backing, such as glass, plastic, etc., to which it
normally adheres, the finished article has thus an integral support
backing without any further processing.
The present invention also contemplates that the materials forming
the overlayer of the radiation sensitive elements need not be in a
solid phase and are capable of interreacting with the metallic
layer when disposed in contact therewith in a liquid phase or in a
vapor phase, such interreaction being proportional in effect to the
amount of radiation impinging upon the metallic surface. By
utilizing such an arrangement, the present invention presents
definite advantages for obtaining finished articles in view of the
simplicity of the raw materials used in the process and in view of
the simple steps in the process. All that is required to practice
the method of the present invention is to project an actinic image
upon the surface of a metallic plate, foil, or thin-film, in the
presence of an inorganic material in a liquid or gaseous form
capable of interreacting with the material of the metallic plate,
foil or thin-film under the influence of electromagnetic actinic
radiation. This aspect of the present invention greatly simplifies
the preparation of radiation sensitive elements, and, in many cases
greatly simplifies the steps to be accomplished in order to obtain
a usable finished article. The material capable of reacting with
the metallic surface being in a liquid or vapor phase does not
remain, in most applications, adhering to the metallic surface, the
interreaction product may be easily removed by simple mechanical,
physical or chemical means, including vaporization or dissolution
in the liquid phase during the illumination by actinic radiation
and the radiation-sensitive element can be preserved indefinitely
without any precautions before exposure as well as after
exposure.
The present invention further contemplates providing a multilayer
radiation sensitive element, made of a plurality of strata each
made of a pair of layers of dissimilar materials capable of
actinically reacting with each other, which permits obtaining a
relief image corresponding to an original image projected upon the
surface of the element and having a substantially greater relief
depth than available by means of an element consisting only of two
layers of interreacting materials. Every layer is substantially
transmissive of the electromagnetic actinic radiation such that the
exposure of the element to electromagnetic radiation extends in
depth proportionally to the intensity of the actinic radiation.
Depending upon the method utilized, according to the present
invention, for processing the exposed electromagnetic radiation
sensitive multilayer element, the finished article presents a
two-level relief image corresponding to and being a reproduction of
the original image projected upon the element, or, alternately, the
finished article presents a variable depth relief image
corresponding to the shape of the image projected on the
radiation-sensitive element and varying in depth according to the
varied radiation intensity impinged upon the element.
SUMMARY OF THE INVENTION
The present invention thus relates to radiation-sensitive elements
consisting principally of a pair of separate adhering layers of
inorganic materials capable of discretely and selectively
interreacting when exposed to discrete and selective exposure to
actinic radiation, to methods of preparing such radiation-sensitive
element, to diverse structures in which the principle of the
invention may be incorporated, and to processes for utilizing the
radiation-sensitive elements of the invention for obtaining useful
finished articles.
It will be immediately apparent to those skilled in the art that
articles obtained by the methods of the present invention have
unlimited uses in applications such as, to enumerate a few,
photographic two- and three-dimensional reproductions,
transparencies, halftone plates, lithographic plates, masks, grids,
gratings, diffraction and interference slits, printing plates,
printed circuits, pseudosilk-screen, etc.
The objects and advantages of the present invention will become
apparent when the accompanying description of a few illustrative
examples is read in conjunction with the annexed drawings
wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates in sectional view an example of
structural embodiment of a radiation-sensitive element according to
the present invention;
FIG. 2 schematically illustrates in sectional view a modification
of the radiation-sensitive element of FIG. 1;
FIGS. 3-5 schematically illustrate steps in obtaining a finished
article according to a method of the present invention;
FIG. 6 schematically illustrates a modification of a finished
article obtained according to a modification of the methods of
FIGS. 3-5;
FIG. 7-12 schematically illustrate steps in further modifications
of the method illustrated in FIGS. 3-5;
FIG. 13 is a schematic perspective view of a multilayer
radiation-sensitive element according to a modification of the
present invention, shown in a grossly exaggerated manner with
respect to the thickness thereof, in the process of being exposed
to electromagnetic radiation through an appropriate mask or
screen;
FIG. 14 is a schematic representation in section of the arrangement
of FIG. 13;
FIG. 15 is a view similar to FIG. 14, but showing the
radiation-sensitive element after exposure to incident
electromagnetic radiation;
FIG. 16 is a perspective schematic view of an example of finished
article obtained from the radiation-sensitive element of FIG. 13
after exposure to electromagnetic radiation and removal of the
radiation provoked interreaction product, according to an aspect of
the present invention;
FIG. 17 is a sectional view of the article of FIG. 16;
FIG. 18 is a perspective schematic representation of another
example of finished article obtained from the article of FIG. 16 by
way of a further step in the process, according to another aspect
of the present invention;
FIG. 19 is a sectional view of the article of FIG. 18;
FIG. 20 is a perspective schematic view of an example of an
alternate resulting finished article;
FIG. 21 is a schematic sectional view illustrating a further aspect
of the present invention;
FIG. 22 is a schematic sectional view of an article resulting from
the method of FIG. 21;
FIG. 23 is a schematic representation of an arrangement according
to the present invention for exposing a metallic surface to
incident actinic radiation in the presence of a reacting material
in a nonsolid form;
FIG. 24 is a schematic representation of an example of a finished
article obtained by means of the method illustrated in FIG. 23;
FIG. 25 is a sectional view of a portion of the arrangement of FIG.
23 during exposure to incident electromagnetic radiation;
FIG. 26 is a view similar to FIG. 25 but showing a metallic plate,
foil or thin-film after exposure to incident radiation;
FIG. 27 is a view similar to FIG. 26 but showing the finished
article;
FIG. 28 is a view similar to FIG. 27 but showing a further variety
of finished article;
FIG. 29 is a schematic view similar to FIG. 25 but showing another
aspect of the methods of the present invention;
FIG. 30 is a schematic representation of the metallic plate, foil
or thin-film after exposure to incident radiation according to the
method of FIG. 29;
FIG. 31 is a schematic representation of an example of finished
article obtained by the method of FIG. 29; and
FIG. 32 is a schematic representation of a modified finished
article obtained according to the methods of a further aspect of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to an aspect of the present invention, a self-revealing
radiation-sensitive element as generally shown at 10 in FIG. 1 is
made by coating a metallic layer consisting of silicon, metal,
metal alloy or a compound containing silicon or a metal as one of
its constituents, and shown at 12, with an overlayer 14 of an
inorganic material capable, when exposed to actinic electromagnetic
radiation, of interreacting with the metallic layer 12 at the
boundary 16 therebetween such as to cause a selective etching of
the metallic layer which is, in depth, substantially proportional
to the amount of actinic electromagnetic radiation impinging upon
the sensitive element 10. By amount of actinic electromagnetic
radiation is meant both the intensity of the radiating energy
impinging upon the element and the duration of exposure of such
element to the radiation. The in-depth etching effect upon the
metallic layer 12 results from a radiation provoked interreaction
between the material of the overlayer 14 and the metallic layer 12,
with the formation of an interreaction product, or products,
different in chemistry as well as in physical characteristics from
either constituents.
Consequently, when an image is projected upon the surface of the
radiation-sensitive element 10 by way, for example, of an
arrangement as schematically illustrated in FIG. 3, a screen 18
being disposed in the path of the incident radiation 20, the amount
or intensity of the passing radiation 20' impinging upon the
surface of the sensitive element, thus depends from the
transmittance of the screen 18 to the incident radiation. If the
screen 18 has portions, such as shown at 22, which are fully
transmissive with respect to the incident radiation, full intensity
passing radiation impinges upon the sensitive element 10 on
portions corresponding to the fully transmissive portions 22 of the
screen. Portions of the screen such as shown at 24, which are
opaque to the incident radiation, prevent any radiation from
reaching the sensitive element. Other portions, such as shown at
26, which have only partial transmissivity, substantially reduce
the energy of the incident radiation passing therethrough, while
other portions of the screen 18 may be such as, as shown at 28, to
present more or less progressive transmissivity, such as to provide
the full range of the so-called "grey scale" or any portion
thereof.
While the sensitive element 10 is being exposed to the effect of
incident radiation through screen 18, there is a radiation provoked
interreaction taking place between the inorganic material of the
overlayer 14 and the material of the metallic layer 12 at the
borderline or interface 16 therebetween, such that, as shown in
FIG. 4, there is formed at the interface a radiation provoked
interreaction product, or products, generally designated at 30,
such product or products including the constituents of both layers
12 and 14, causing a selective in-depth etching of the metallic
layer 12, the depth of the etched portions being substantially
proportional to the incident radiation energy impinging upon the
sensitive element. Consequently, corresponding to the portions of
screen 18 which are fully transmissive of the incident radiation,
the in-depth etching of the metallic layer 12 is at its maximum,
for a given time of exposure, as shown at 32. The in-depth etching
of the metallic layer 12 is substantially reduced in areas
corresponding to the portions of the screen 18 having reduced
transmissivity, as shown at 34, and the in-depth etching of the
metallic layer 12, as shown at 36, varies proportionally, although
not linearly, to the transmissivity of the screen 18 where its
transmissivity varies from full transmissivity to full
absorption.
It has been discovered that the interreaction product 30, and, when
so desired, both the interreaction product and the nonreacted
portions of the overlayer 14, may be removed by dissolution in an
appropriate basic solution such as, for example, a 0.5 normal
solution of sodium hydroxide, or alternately, an aqueous solution
of sodium sulfide, preferably a saturated solution at 20.degree. C.
It has also been found that the unreacted portions of the overlayer
14, together with the interreaction product 30, may be mechanically
removed from the metallic layer 12 such as by wiping with a rag or,
preferably, removal by means of a sheet of flexible material coated
on one face with a pressure-sensitive adhesive which is applied
against the surface of the overlayer 14 and which is thus used to
remove the unreacted portions together with the interreaction
product 30 by simply peeling off. Alternately, the interreaction
product and the nonreacted portions of the overlayer 14 may be
removed by heat sublimation.
Whatever method is used for removing the nonreacted portions of the
overlayer 14, together with the interreaction product 30, the
finished article, as shown in FIG. 5, consists of the metallic
layer 12 presenting on its surface which, before processing,
constituted part of the boundary interface 16 between the metallic
layer 12 and the overlayer 14, various in-depth depressions as
shown at 32, 34 and 36, defining a relief image with the
depressions being of a depth corresponding to the amount of
exposure of the sensitive element to radiation. It is evident that
when the screen 18, shown in FIG. 3, is provided with only high
contrast portions, and the radiation-sensitive element comprises a
thin metallic layer 12 of the order of a few atom layers to a few
mils in thickness, if the time of exposure of the sensitive element
to the incident radiation is long enough, the interreaction between
the overlayer 14 and the metallic layer 12 becomes such as to
completely exhaust all the metal in the metallic layer 12
corresponding to the portions where the radiation provoked
interreaction takes place, such that the finished article, as shown
at FIG. 6, consists of the metallic layer 12 provided with
perforations or through apertures, as shown at 38. In some
applications the finished article of FIG. 6 may be used as such, or
if it is desired to provide a support backing therefore, the
metallic layer 12 may be cemented or bonded to any appropriate
backing material.
A list of elements particularly suitable for the metallic layer 12
includes, among others, silver, copper, lead, cadmium, zinc, iron,
tin, arsenic, bismuth, cobalt, germanium, indium, manganese,
mercury, nickel, selenium, silicon, tellurium, thallium, and
vanadium. In other words, silicon and practically every metal has
been found to be suitable, with the exception of substantially
unactive metals, such as gold, rhodium, palladium and platinum.
Aluminum and magnesium have also been found to be relatively
unactive when used in the structure of the invention with an
overlayer 14 of inorganic material of the type hereinafter
disclosed. The metallic layer 12 is in the form of a thin foil of a
thickness that may vary, according to the purpose to be
accomplished and according to the proposed use of the sensitive
element, from a few atom layers to a fraction of a mil or even to
several mils. When using a very thin metallic layer which is
substantially "transparent," i.e., which has substantially good
transmissivity to the actinic radiation, the sensitive element may
be exposed by having incident radiation impinge upon the surface of
the metallic layer 12 (FIG. 1) as well as having the radiation
impinging upon the surface of the overlayer 14.
By "metallic layer" is meant herein a layer containing silicon or
any one of the common metals hereinbefore mentioned, either alone,
or alloyed to another common metal, or in the form of a metallic
mixture. Consequently, the term "metallic layer" as used herein
means a layer of a material containing silicon or at least one
metal in the form hereinbefore indicated.
The overlayer 14 is also substantially thin, of the order of a few
atom layers to several microns, or even a few mils, and it may
consist of any one of a variety of ternary and binary materials and
compounds and any one of a few elements. An example of ternary
material, which has been found to be particularly suitable, is a
glassy material consisting of arsenic, sulfur and iodine for
example in the following proportions: arsenic-- 40 percent by
weight, sulfur-- 50 percent by weight and iodine-- 10 percent by
weight, although the proportion of iodine may be within the range
of 1 to 30 percent by weight. Appropriate examples of such ternary
materials are given in U.S. Pat. No. 3,024,119, issued Mar. 6,
1962. In such ternary materials, iodine may be replaced by
chlorine, bromine, selenium, thallium or tellurium.
A multitude of binary compounds and mixtures have been found to be
useful for the inorganic material of the overlayer 14. Examples of
such binary compounds or mixtures comprise halides of metals, such
as copper, antimony, arsenic, sulfur, thallium, lead, cadmium and
silver, sulfides, arsenides, selenides, and tellurides of such
metals. The most suitable materials, presenting substantial
sensitivity when deposited on a metallic layer of copper, silver,
lead, zinc, etc., for example, are arsenic-sulfur mixtures and
compounds, antimony-sulfur compounds and mixtures, silver-sulfur
compounds and mixtures, bismuth-sulfur compounds and mixtures,
chromium-sulfur compounds and mixtures, lead iodide, copper
chloride, stannous chloride, mercury chloride, arsenic selenides,
selenium-sulfur compounds and mixtures, chromium selenides, and
indium-sulfur compounds. It seems that the property of reacting
with a metallic layer under the influence of actinic
electromagnetic radiation is shared by a variety of mixtures and
compounds, having such property to varying but generally useful
degrees. Such binary compounds and mixtures may be generally
cataloged as consisting of a metal halide, or a mixture of a metal
with a halogen, metal selenide, or a mixture of metal with
selenium, metal sulfide, or a mixture of metal with sulfur, and
metal telluride, or a mixture of a metal with tellurium.
Stoichiometric proportions are not critical, but it is preferable
that the resulting material be substantially transparent to
electromagnetic actinic radiation of an appropriate wavelength,
specially when the overlayer is substantially thick.
Single elements, such as halogens, selenium or sulfur, are also
capable of reacting with a metallic layer when exposed to
electromagnetic actinic radiation. Consequently, a general grouping
of inorganic materials suitable as the material forming an
actinically reactive overlayer when disposed on a metallic layer
consists of halogens, sulfur, selenium, M-X compounds and mixtures
and M-X-Y compounds and mixtures, wherein M is a metal and X and Y
are selected from the group consisting of a halogen, sulfur
selenium, and tellurium. The metal M is preferably selected from
the group consisting of arsenic, antimony, bismuth, selenium,
tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium,
indium, thallium, germanium, tin, iron, cobalt, nickel and
silver.
A particularly suitable binary material presenting substantial
sensitivity when deposited on an appropriate metallic layer such as
of silver or other metal is an arsenic-sulfur compound or mixture.
For example, by using an overlayer 14 of arsenic-sulfur deposited
upon a metallic layer 12 of silver, the quality of the relief image
obtained in the finished article is remarkable in its resolution.
This is a very important quality when the finished article must
present a high resolution as will be the case, for example, if the
finished article is a diffraction grid or grating, or the like. The
proportions of arsenic and sulfur may be varied broadly, such
proportions preferably ranging from about 20 percent arsenic--80
percent sulfur by weight to 80 percent arsenic--20 percent sulfur
by weight.
Structures of electromagnetic radiation-sensitive elements
according to the present invention therefore consist principally of
a metallic layer as defined herein provided with an overlayer of
inorganic material capable of interreacting with the metallic layer
when exposed to electromagnetic actinic radiation. The choice of
the appropriate components for the diverse layers is a matter of
judgment depending upon economic considerations relative to the
cost of the components, the facility or difficulty of manufacturing
the element, and the type and particular characteristics of the
finished article to be obtained by the methods of the invention. As
previously mentioned, silicon or any one of the metals hereinbefore
listed as suitable for the metallic layer may be employed in
combination with any one of the inorganic materials suitable for
the overlayer.
The exact theory underlying the actinicly provoked interreaction
between the material of the overlayer and the metallic layer is not
entirely known at the present, but it may be postulated that the
inorganic materials suitable for forming the overlayer are
dissociable when impinged upon by electromagnetic actinic radiation
in such a way that one or more of the elements in the inorganic
materials, upon actinic activation, are capable of chemically
reacting with the adjacent metallic layer. It has been observed
that the appropriate group of inorganic materials suitable for
making the overlayer in cooperation with silicon or an appropriate
metal suitable for the metallic layer may be selected according to
certain physical and chemical parameters which seem to be useful in
choosing appropriate structures. As example of such parameters,
disassociation energy, heat of formation, and competitive oxidation
reactions for silicon and metals seem to be involved either
individually or collectively. The following table is a table of the
respective heat of formation, expressed in kilo cal. per mol of the
metallic compounds listed in the first vertical column with the
diverse metals listed in the upper horizontal column. It has been
observed, as a result of the numerous tests resulting in the
discovery of the invention, that the preferable metals for forming
the metallic layer in cooperation with the inorganic materials of
the overlayer of the invention are those having a heat of formation
below about 60 of the different sulfides, chlorides, iodides,
selenides, bromides and tellurides of the metal. The table seems to
confirm the observed strong reactivity of silver and copper as
compared to the relatively weak reactivity of aluminum and
magnesium. ##SPC1##
EXAMPLE I
A radiation-sensitive element was made by first dipping a silver
foil into a dilute nitric acid solution for about 4 seconds
followed by rinsing in water. The surface of the silver foil was
observed to turn to a frosted whitish coloration. The foil was then
dipped for a few seconds in a liquid arsenic-sulfur-iodine mixture
heated to 50.degree.-60.degree. C. and containing 40 percent
arsenic, 50 percent of sulfur, and 10 percent of iodine, by weight.
The foil was removed from the mixture and stood vertically to allow
the excess arsenic-sulfur-iodine mixture to drip off, thus leaving
a thin layer of arsenic-sulfur-iodine material upon the foil. The
sensitive element thus obtained was then exposed to a high
intensity light image being projected on one face thereof, the
light source for the image consisting of a 35-watt tungsten lamp
whose filament image was focused on the surface of the element.
After about 1 minute of exposure time, a stable self-revealed image
of the filament appeared on the sensitive element. The exposed
areas became dark brown while the unexposed areas of the element
remained yellow in color. The sensitive element was then rinsed in
a 0.5 normal solution of sodium hydroxide in order to remove or
eliminate remnants of the arsenic-sulfur-iodine film and byproducts
resulting from the interreaction between the arsenic-sulfur-iodine
film and the metal of the foil at the exposed areas, such as to
obtain a relief etched image of the filament upon the surface of
the foil. Mild aqueous solutions of sodium sulfide, ammonium
hydroxide or potassium hydroxide may be used instead of the sodium
hydroxide solution.
EXAMPLE II
A mixture consisting of 35 percent arsenic, 40 percent sulfur and
25 percent iodine, by weight, was heated to slightly above the
temperature at which it becomes very liquid or fluidic,
approximately 60.degree. C. A sheet of silver, about 3 inches by 4
inches, was immersed in the fluidic mixture, removed and stood in a
vertical position to allow the excess arsenic-sulfur-iodine mixture
to flow off the silver while allowing the plate to cool down to
room temperature. After the coating of arsenic-silver-iodine had
solidified, the sample was exposed to a high-intensity light image
in the same manner as explained with respect to example I, and the
same results were achieved.
EXAMPLE III
In order to study the influence of varying ratios of constituents
in arsenic-sulfur-iodine mixtures, several samples of silver
coating on a glass substrate where prepared. The samples were
prepared by conventional vacuum deposition techniques by placing
the glass substrates in a bell jar evacuated at about 0.5 microns
pressure. Silver metal was evaporated from tungsten electrical
resistance heaters brought to about 1,100.degree. C. by the passage
of electrical current therethrough. By evaporating silver for about
3 seconds, a silver layer on the substrate of about 4,000 A. was
obtained. Longer evaporation time provided proportionally thicker
silver layers. For example, 15- to 20 -second evaporation time
provided silver layers on the glass substrate of approximately 1
micron. The thickness of the thin film of silver deposited on the
glass substrate was continuously monitored by a thin-film thickness
monitor such as manufactured by Edwards High Vacuum Company.
Several samples of radiation-sensitive element were prepared by
dipping the glass plates with a silver coating thus obtained in
various arsenic-sulfur-iodine mixtures to study the effect of
various proportions of the constituents. It was found that wide
ranges of constituents permitted to obtain highly reactive
radiation sensitive elements when exposed to incident
electromagnetic radiation. Various ratio mixtures were used, from
mixtures containing as little as 25 percent per weight of arsenic
and as much as 40 percent of iodine, the balance being sulfur, to
mixtures containing as much as 60 percent of arsenic and 50 percent
of iodine, the balance being sulfur.
EXAMPLE IV
Several samples were prepared by utilizing an arsenic-sulfur-iodine
mixture containing 35 percent of arsenic, 40 percent of sulfur and
25 percent of iodine, by weight. Diverse metals were evaporated and
condensed on glass substrates according to the process of example
III, substituting for the silver of example III other common metals
such as copper, cadmium, zinc, iron, lead, etc.
When exposed to electromagnetic actinic radiation such as ordinary
light, as previously explained, all of the samples showed
sensitivity to exposure to diverse degrees with pronounced etching
of the metallic layer in depth all of the way to the glass
substrate, for sufficient exposure time and light intensity. Full
etching all the way to the substrate was observed as a result of
time exposures as short as three to 4 minutes for some metals such
as silver, copper and iron, while less active metals required
longer exposure time.
EXAMPLE V
A silver foil was placed in a bell jar evacuated at about 0.1
micron pressure. A quartz crucible located in an electrical
resistance heater disposed in the bell jar was loaded with pieces
of arsenic trisulfide, As.sub.2 S.sub.3, the silver foil being
located at about 6 inches from the quartz crucible. The arsenic
trisulfide was heated in the crucible to about 350.degree. to
400.degree. C., and a thin-film thereof was deposited on a surface
of the silver foil by evaporating the arsenic trisulfide from the
quartz crucible for about 30-40 seconds. Several samples were thus
prepared, nd after removal from the bell jar, were handled in
normal ambient light without any appearance of deterioration over a
short period of time. Some of the samples were exposed to an
intense white light pattern, utilizing a 35 -watt incandescent
lamp. After exposure for a few minutes, of the order to 3 to 4
minutes, an image of the lamp filament was obtained, after which
the samples were subsequently washed in a 0.5 normal solution of
sodium hydroxide in order to remove from the silver foil the
unreacted portions of the arsenic trisulfide coating and the
interreaction product. An etched image of the lamp filament was
thus obtained on the silver foil.
Other samples were exposed through photographic negatives, which
resulted in visible positive reproductions of the negative mask.
After washing of the exposed samples in a 0.5 normal solution of
sodium hydroxide, the images were found to be three-dimensional
etch reproductions of the originals.
EXAMPLE VI
A copper foil was coated with a thin-film of cuprous chloride by
vapor deposition according to the same technique as disclosed with
a respect to example V. The radiation-sensitive element thus
obtained was exposed in the same manner as disclosed with respect
to example V, although longer exposure times were required to
obtain a visible image, such exposure times being of the order of
10 minutes. The samples were washed in a 0.5 normal solution of
sodium hydroxide for removing the coating of cuprous chloride and
the interreaction product at the exposed areas, the resulting
product being a copper foil having an etched three-dimensional
image on the surface thereof.
EXAMPLE VII
Several samples were prepared of a thin metallic coating on a glass
substrate, such samples being made of many common metals such as
lead, zinc, iron, nickel, etc., in addition to silver and copper.
The metallic coatings were vacuum deposited on a glass substrate by
means of the techniques hereinbefore explained, the metals being
obtained from a tungsten filament in contact with a small quantity
of the metal, vaporized when the tungsten filament was connected
across a source of electrical power. The samples were thin coated
with a thin film of arsenic trisulfide vapor deposited also
according to the techniques hereinbefore explained. Silicon and all
the metals listed, when coated with a thin film of arsenic
trisulfide, exhibited sensitivity to diverse degrees when exposed
to actinic electromagnetic radiation such as intense light. For
sufficient exposure times, the thin films of silicon or metal, of
the order of 2,000 to 4,000 A. on the glass substrates, were etched
in depth all the way to the glass substrates when the samples were
washed in the 0.5 solution of sodium hydroxide. Some metals, such
as aluminum and gold, were found to be relatively unaffected by
exposure to incident light when coated with a thin film of arsenic
trisulfide and further experiments using other coatings on such
metals revealed that they remain unaffected by exposure to
light.
EXAMPLE VIII
Several samples were prepared of an evaporated thin film silver
coating on glass substrates according to the vacuum deposition
technique hereinbefore explained. A mixture consisting of 60
percent arsenic and 40 percent sulfur, by weight, was placed in a
quartz crucible in an electric resistance heater in a bell jar
evacuated to about 0.1 micron pressure. The silver on glass
substrate samples were located about 6 inches from the quartz
crucible and the arsenic-sulfur mixture was heated to about
350.degree. C., thus evaporating the mixture. Film thicknesses of
about 2 microns were obtained by evaporation of the mixture for
about 40 seconds, and the samples were removed from the bell jar
and stored in a darkened area. Prior to storage, the samples were
examined under normal room-lighting conditions and they were found
to be gold in color on the coated silver surface.
The samples were then subjected to an intense white light pattern
from a 35 -watt illumination lamp having its filament focused on
the sample for successive short periods of time with periodic
inspections. The periodic inspections disclosed that the silver
layer was being consumed in the areas impinged upon by the intense
illumination, while those areas not subjected to illumination
remained undisturbed. For total illumination periods of 3 to 4
minutes, the silver layer, where exposed to illumination, was
entirely consumed in depth all the way to the glass substrate. Many
samples were exposed through photographic transparencies and masks.
It was found that the interreaction product of the exposed areas
could be removed by simply wiping or brushing the surface of the
samples, or, alternately, by applying to the surface of the
arsenic-sulfur coating a conventional adhesive tape and lifting the
tape, the interreaction product at the exposed areas remaining
adhering to the adhesive tape, while the portions of the overlayer
corresponding to the unexposed areas remained strongly adhering to
the metal overlayer when the tape was pulled. Some samples were
prepared with the surface of the arsenic-sulfur coating or
overlayer covered with transparent tape. The samples were exposed,
and by lifting the adhesive tape in the interreaction product at
the exposed areas was removed without damaging the unexposed areas.
In samples where it was desired to remove the remaining
arsenic-sulfur coating so as to physically expose the metallic
underlayer, mild alkaline solutions such as solutions of 10 percent
of NH.sub.4 OH were used.
EXAMPLE IX
A plurality of samples were prepared each consisting of a thin film
of a different metal, deposited on a glass substrate according to
the vacuum-deposition technique hereinbefore explained or
consisting of a foil of the appropriate metal. The samples of
diverse metal layers were coated with a vapor-deposited
arsenic-sulfur mixture evaporated from a crucible containing 60
percent of arsenic and 40 percent of sulfur, by weight, in the same
manner and by the same methods as explained hereinbefore. The
diverse metals were found to react with the material of the
overlayer when exposed to electromagnetic actinic radiation such as
intense white light, the samples being exposed as hereinbefore
explained. Silicon and the diverse metals hereinbefore listed were
found to be reactive in various degrees, the most reactive ones, in
addition to silver and copper, being cadmium, lead, zinc and
iron.
EXAMPLE X
Samples consisting of an evaporated thin film of silver on a glass
substrate were coated by the vacuum technique hereinbefore
explained with arsenic-sulfur compounds and mixtures obtained from
a boat disposed in a heater, a plurality of samples being prepared
with various ratios of arsenic and sulfur placed in the evaporation
boat, from mixtures containing as little as 20 percent of arsenic
and as much as 80 percent of sulfur, by weight, to 90 percent of
arsenic and 10 percent of sulfur, by weight. All of the samples
were found to be remarkably sensitive to exposure to
electromagnetic actinic radiation such as light, the variations in
sensitivity being practically insignificant over the ratio range of
the constituents.
EXAMPLE XI
A plurality of silver-coated glass plates were prepared according
to the techniques hereinbefore explained. The silver layer was in
turn coated, by way of the vacuum-deposition technique hereinbefore
explained, with thin films of diverse inorganic materials
comprising metal sulfides, metal iodides, metal chlorides, metal
selenides, metal tellurides, arsenic-sulfur-halogen mixtures and
other inorganic materials, such diverse inorganic materials being
those listed hereinbefore. The samples exhibited reaction as a
result of exposure to electromagnetic actinic reaction.
EXAMPLE XII
A substrate of paper or cardboard was coated with a thin layer of
silver about 1,500 A thick The vacuum-deposition technique
hereinbefore explained was used for coating the paper with silver,
although any known commercial process used for making metallized
paper for the electronics industry, as well as the decorative paper
industry, may be used. Following the coating of the paper with
silver, a thin layer of cuprous chloride was evaporated upon the
silver surface, using also the techniques hereinbefore explained,
such overlayer of cuprous chloride being about 3,000 A thick
Some samples were prepared by using lead iodide instead of cuprous
chloride as a coating over the silver.
These samples were used as ordinary photographic contact paper and
were exposed for periods of several minutes through photographic
negatives, the duration of exposure depending on the density of the
negative and the source of light utilized. In the areas where light
was transmitted to the photosensitive surface, a light induced
photoreaction took place resulting in darkening of the surface to
the point of turning black for sufficient exposure. After exposure,
the samples were rinsed in warm tapwater. Alternately, a slight
ammoniacal solution may be used instead of water. The immersing of
the element in the water removed the unreacted overlayer material,
thus "fixing" the image. The dark interreaction product remained
attached to the silver coating forming a contrasting visual
impression relatively to the silver background of the unreacted
areas, resulting in photographic prints of high quality presenting
all the conventional graduations in diverse degrees of the grey
scale in the partly exposed areas.
Electromagnetic radiation-sensitive elements according to the
present invention and provided with a substrate have a structure as
schematically shown in cross section at FIG. 2. The
radiation-sensitive element, generally designated at 11, and
obtained according to any one of the processes hereinbefore
explained in detail, comprises a substrate 40 which may be made of
any one of many convenient materials such as glass, an epoxy resin,
a fiberboard, a plastic, etc., on a face of which is disposed an
adhering metallic layer 12, placed on a surface of the substrate 40
by any convenient means such as being vapor deposited thereon as
hereinbefore explained or cemented or bonded thereon, as shown at
42. Upon the metallic layer 12 is disposed another layer 14 of an
inorganic material belonging to the class of materials mentioned
hereinbefore. The sensitive element 11 of FIG. 2 is, for all
purposes, similar in structure, operation and applications to the
sensitive element 10 of FIG. 1, the only difference being that the
metallic layer 12 is generally much thinner than the metallic foil
12 of FIG. 1 and physical strength and rigidity are provided by the
substrate or support backing 40 on which is disposed the metallic
layer in adhesion therewith. When an image is projected, preferably
upon the side provided with the overlayer 14, and when such image
is of a variable density having a full range of "grey scale,"
corresponding self-revealing images are obtained, as precedently
explained in detail, in all points similar to the relief image
shown in FIG. 5, with the addition of a substrate or support
backing being provided for the revealed metallic layer.
FIG. 7 represents an exploded view of an arrangement for exposing
the radiation-sensitive element 11 through a mask or screen 18
having portions as shown at 22 substantially transmissive of the
incident actinic radiation 20 and having other portions, as shown
generally at 24, capable of absorbing such incident radiation. In
order to obtain a sharp image upon the surface of the sensitive
element 11, it is best to have the screen 18 actually in contact
with the surface of the overlayer 14, as diagrammatically
illustrated in the cross-sectional view of FIG. 9, or, a lens
system, not shown, may be used to project a sharp focused image
upon the surface of the sensitive element, the lens system being
such as to project either an enlarged or a reduced image, or, when
so required, an image of the same size as provided on the screen
18. The incident radiation 20 passing through the transmissive
portions 22 of the screen 18 impinges, as shown by arrows 20', upon
the surface of the sensitive element 11. A shadow of the
nontransmitting portions 24 of the screen is projected upon the
surface of the sensitive element 11, as shown at 24' in FIG. 7. For
illustrative purpose only, the shadow has been shown in the drawing
as capital letters A and B of the alphabet. As previously explained
hereinbefore and as illustrated in FIGS. 7 and 9, the transmitting
portions 22 of the screen 18 permit the incident radiation to cause
an interreaction between the inorganic material of the overlayer 14
and the silicon or metal of the metallic layer 12 which in turn
causes a radiation-provoked etchlike action upon the metallic layer
12, with formation of an interreaction product as shown at 30 in
FIG. 10, such that the radiation-provoked etching of the metallic
layer 12 may be deep enough to reach the surface 42 of the support
backing 40. By heat sublimation, or washing in water or in a mild
alkaline solution, or by mechanical wiping, or, as previously
explained also, by utilizing a flexible sheet of material, not
shown, having on one surface thereof a pressure-sensitive adhesive,
the interreaction product 30 can be removed, thus obtaining a
finished article schematically represented in cross section at FIG.
11 wherein the support backing 40 is provided with an adhering
etched metallic layer 12 still coated with an etched overlayer 14.
Because the adherence of the overlayer 14 upon the metallic layer
12 at the interlayer boundary 16 thereof is generally less than the
adherence of the metallic layer 12 to the support backing 40 at the
interlayer boundary 42 therebetween, it is also quite feasible to
remove, by washing in water or in a mild alkaline solution, or by
mechanical means, both the interreaction product and the
superficial overlayer 14 thus obtaining the finished article
illustrated in FIG. 12 in schematic cross section and in FIG. 8 in
perspective view. Such finished article consists of the support
backing 40 and of the portions of the metallic layer 12 which have
not been exposed to the influence of the incident radiation.
It is readily apparent that the invention permits relief
reproduction of an image or engraving and is particularly useful
for many applications, one of which constitutes a method of
obtaining printed circuits by pseudophotographic means in a simple
and low-cost manner. For so doing, the screen 18 of FIGS. 7 and 9
is simply an opaque drawing on a transparent support of the printed
circuit to be reproduced, the support backing 40 of the sensitive
element 11 consists of nonconductive material such as glass,
fiberboard or a resin, and the finished article, similar to the
article shown in FIG. 8, consists of a support backing 40 having
strongly adhering thereon a metallic printed circuit of any
thickness desired, depending upon the thickness of the metallic
layer 12 of the sensitive element. It is evident that the screen 18
may consist of a transparent support for an opaque printed circuit
drawing designed at any practical size and that the circuit board,
the finished article, may be of any convenient size as obtained by
means of a size-reducing projection lens system. Such a process
leads naturally to any amount of miniaturization that may be
desired.
Preparing printed circuits according to the methods of the
invention compares favorably with any printed circuit board
manufacturing processes, whether they are chemical processes such
as the etched foil process, the screening processes, the photo
methods and the like, that all require the use of resist
compositions for coating the foil and the use of acid etchants, or
whether they are the mechanical processes for making printed
circuits such as the stamp wiring methods, the embossed wiring
methods, the sprayed wiring methods, the molded wiring methods, the
universal grid-wiring methods, which not only require a
considerable amount of equipment to be practiced, but which also
lead to many rejects.
In some printed circuit applications of the invention, it has been
found desirable not to remove the interreaction product nor the
nonreacted portions of the overlayer which form good electrical
insulation. The printed circuits thus prepared are simply
encapsulated in a material which is not light radiation
transmissive or they are placed in a light-shielding enclosure.
It can thus be seen that the methods of the inventions lead to
finished articles having many applications, as will be obvious to
those skilled in the art, which compare very favorably with any
conventional methods for obtaining such articles, and which are
even simpler than ordinary photographic processes by requiring no
complicated chemicals or conditions for processing of the plates,
the finished article being actually the residue of the original
materials which remains after exposure to appropriate radiation,
the interreaction products resulting from the exposure being
eliminated, contrary to other photographic processes where the
residue is generally eliminated and the interreaction products are
utilized in the finished article.
A multilayer radiation element can be made, according to the
present invention, by superimposing a plurality of bilayer members,
each comprising a metallic layer as herein defined and an overlayer
of inorganic material capable of reacting with silicon or the metal
of the metallic layer when exposed to appropriate electromagnetic
actinic radiation. For example, referring more particularly to
FIGS. 13-14 of the drawings, a multilayer radiation-sensitive
element 10' according to the present invention comprises a
plurality of strata each consisting of a pair of substantially
adhering layers 12 and 14 made of dissimilar materials. The
multilayer radiation-sensitive element 10' may be disposed upon a
support backing or substrate 40, although such support backing or
substrate may be omitted in some applications.
In the example of the invention, illustrated at FIGS. 13-14, a
radiation-sensitive element 10 is shown as consisting of three
strata, each including a pair of layers 12 and 14 made of
dissimilar materials capable of interreacting when exposed to
electromagnetic radiation with the formation of a resulting
interreaction product having chemical and physical characteristics
different from the original constituents. As described in detail
hereinbefore, each stratum comprises a metallic layer 12, as
defined herein, containing silicon or at least one metal, either
alone, alloyed with another metal or with other metals, or combined
or mixed with another element or other elements. Each metallic
layer 12 may thus include silicon or any one of common metals such
as silver, lead, nickel, copper, iron, etc., mentioned
hereinbefore. The material of each layer 14 may be any one of the
groups of ternary, binary or other materials, or any one of a
plurality of single elements, as mentioned hereinbefore.
Each layer 12 or 14 is substantially thin, and may have a thickness
comprised between a few atom layers to several thousand Angstroms.
As many strata or layer pairs as practical may be used in a
radiation-sensitive element according to the present invention, the
only condition being that each stratum be substantially
transmissive of the actinic electromagnetic radiation used for
exposure, such electromagnetic radiation being in many cases simply
ordinary intense white light, such that the impinging radiation may
reach substantially deeply to an appropriate stratum during
exposure. Because there is a certain amount of absorption of the
electromagnetic radiation at each layer, the depth of penetration
of the electromagnetic radiation is substantially proportional to
the irradiation intensity.
Exposure to electromagnetic radiation of a multilayer
radiation-sensitive element according to the invention may be
effected by projection of an appropriate image upon the surface of
the element, such exposure being represented at FIGS. 13 and 14 as
being effected through a mask 18 having areas, such as shown at 22,
which are substantially transmissive of the incident
electromagnetic radiation arbitrarily represented by arrows 20, and
other areas such as shown at 24, which are substantially
nontransmissive of the electromagnetic radiation. Consequently, the
electromagnetic radiation 20 is allowed to impinge selectively and
discretely upon the radiation-sensitive element at appropriate
areas 44 corresponding to the transmissive portions 22 of the mask
or screen 18, while other areas 46 are shielded by the
nontransmissive portions 24 of the screen and are not impinged upon
by the radiation. At the areas 44 irradiated by the electromagnetic
radiation 20, for sufficient intensity of the radiation energy,
there is caused an in-depth penetration of the radiation as
arbitrarily shown by arrows 20' with the result that the materials
of the layers 12 and the layers 14 at the areas thus irradiated and
penetrated interreact so as to form an interreaction product as
shown at 30 in FIG. 15. The formation of such interreaction product
causes a local decrease in the interlayer adhesion which permits
mechanical removal of the radiation exposed portions of the element
10, according to the methods hereinbefore explained. Alternately,
the interreaction product 30 is capable of selective removal by
chemical means or by heat sublimation, as also explained
hereinbefore.
A typical example of a multilayer radiation-sensitive element 10'
according to the invention comprises a first metallic layer 12
made, for example, of silver vacuum deposited according to the
techniques hereinbefore explained on a substrate 40 made of any
appropriate convenient material such as paper, glass, plastic,
metallic foil, or the like. The thickness of the metallic layer 12
is typically of a few atom layers to several Angstroms. On top of
the first metallic layer 12 is deposited, for example, also
according to the vacuum-deposited technique hereinbefore explained,
a thin coating 14 of an inorganic material which when exposed to
electromagnetic radiation interreacts with the silver of the
metallic layer 12. For example, the coating or overlayer 14
consists of an arsenic-sulfur mixture or compound, preferably of
the type which is substantially transmissive of the actinic
electromagnetic radiation. Arsenic disulfide, trisulfide and
pentasulfide are convenient materials in view of their glassy
structure substantially transmissive of ordinary light, infrared
radiation and the like. Typically, the thickness of the overlayer
14 is also of the order of a few atom layers to several microns.
The first overlayer 14 is in turn provided with an adhering layer
of a second metallic layer 12, in turn provided with an overlayer
14 of an appropriate inorganic material such as arsenic trisulfide
or arsenic pentasulfide. As many strata, as desired, each
consisting of a metallic layer 12 with an appropriate overlayer of
inorganic material 14 are thus superimposed on top of each other by
successive deposition operations. The resulting radiation sensitive
element 10', FIGS. 13-14, consists of a plurality of alternating
thin metallic layers and inorganic layers, each thin enough to be
substantially transmissive of electromagnetic radiation such as
ordinary intense white light, such that, for appropriate radiation,
the formation of interreaction product 30 is caused to extend in
depth all the way through the whole thickness of the
radiation-sensitive element 10', for appropriate exposure, such
that, in the example shown herein which is provided with a support
backing or substrate 40, for appropriate exposure, interreaction
product is formed at the irradiated areas all the way to such
support backing or substrate. The interreaction product 30 thus
formed is also substantially transmissive of the electromagnetic
radiation. Consequently, the formation of the interreaction product
does not substantially impede the formation of further
interreaction product at lower levels of the structure for adequate
illumination. If so desired, the substrate 40 may be omitted and
the diverse metallic layers 12 may be made of different metals,
while the diverse layers 14 of inorganic materials may be made of
different materials.
After removal of the interreaction product 30, there results a
finished article 11, as shown in FIGS. 16 and 17, comprising voids
48 corresponding to the irradiated areas thereof, and portions such
as shown at 50 and 52 corresponding to the areas having not been
struck by the electromagnetic radiation.
If it is desired to obtain a finished article provided with a
recessed representation of the contour of the image originally
projected upon the radiation-sensitive element, the portions of the
finished article 11 of FIGS. 16 and 17 included within the
perimeter of such contour are removed by conventional mechanical
means or by way of a subsequent exposure to electromagnetic
radiation through an appropriate mask permitting the
electromagnetic radiation to impinge upon appropriate areas, such
as 50, in order to provoke the formation of interreaction product
weakening the bond between layers thereof for facilitating
mechanical removal thereof, or, alternately, permitting such
interreaction product to be removed chemically or by heat
sublimation. The resulting article 11' is as shown at FIGS. 18 and
19, and includes raised portions 52 corresponding to the unexposed
areas and recessed portions such as shown at 54 defining a recessed
representation of the original image.
If an opposite result is desired, the portions 52 of the article 11
of FIGS. 16 and 17 are removed, thus leaving, as shown at FIG. 20,
an article 11" presenting a relief image 56 of the original
image.
In view of the progressive absorption of the radiation transmitted
in depth through the multiple layers of a multilayer
radiation-sensitive element according to the present invention, a
finished article provided with a relief image presenting a contour
in depth substantially representative of the intensity of the
electromagnetic radiation impinged thereupon may be obtained with
an arrangement as schematically represented at FIG. 21. A
radiation-sensitive element comprising several strata each
including a pair of layers 12 and 14 of dissimilar materials
capable of interreacting, as precedently explained, when
irradiated, is exposed through a mask 18 presenting portions 24
nontransmissive of the incident electromagnetic radiation 20,
portions 22 fully transmissive of the electromagnetic radiation and
portions 28 partially transmissive of the electromagnetic
radiation. Such portions 28 of the mask 18 are arbitrarily shown as
having a gradual progressive increase of transmissivity of the
radiation from the leftmost edge thereof, as seen in FIG. 21, to
the rightmost edge, such that the radiation-provoked interreaction
extends in depth within the radiation-sensitive element to a varied
level, as shown at 36, substantially corresponding to the diverse
boundaries between two consecutive layers at which enough radiation
causes sufficient formation of interreaction product 30 to
accomplish an effective result such as for example weakening the
interlayer bond sufficiently to facilitate mechanical removal of
the irradiated portions of the sensitive element.
The resulting article, as represented at FIG. 22, presents
contoured recesses, such as shown at 36, extending in depth to the
appropriate boundary between the diverse layers 12 and 14 reached
by the electromagnetic radiation with sufficient intensity to
provoke appropriate formation of the interreaction product.
Radiation-sensitive elements according to the present invention
need not include the layer of interreacting inorganic material in a
solid form as heretofore disclosed. For some applications it has
been found preferable to utilize a plate of silicon or a metallic
plate, foil or thin-film without an overlayer of inorganic material
in a solid form, the inorganic material being disposed in contact
with the metallic layer in a liquid or vapor phase during exposure
of the metallic layer to actinic radiation.
According to the invention, a useful article in the form of a
relief image on, and integral with a silicon or a metallic surface,
as shown at FIG. 24, can be obtained by disposing, as shown at
FIGS. 23 and 25, a silicon or metallic element in the form of a
plate, foil, or thin-film 12 in contact with an inorganic material,
as shown at 14, which is in a liquid or vapor phase, such as to
provide substantial mobility to the material and intimate contact
between the material and the metal or metals of the plate, foil or
thin-film.
An image is projected upon the surface of the silicon or metallic
element 12 by way, for example, of the arrangement of FIGS. 23 and
25, a screen 18 being disposed in the path of actinic incident
radiation 20. The screen 18 has portions, as shown at 22, which are
transparent to or transmissive of the incident radiation and
portions, such as shown at 24, which are nontransmissive of the
incident radiation. It is obvious that means may be utilized to
project an image upon the surface of the silicon or metallic
element 12 other than the one represented in the drawing, such as
will provide optical enlargement or reduction of an appropriate
image which is sought to be reproduced in relief on the metallic
element 12.
At the surface areas of the silicon or metallic element 12 which
are impinged upon, discretely and selectively, by the
electromagnetic radiation transmitted by the transmissive portions
22 of the mask 18, there is caused an interreaction between the
inorganic material 14 and the silicon or metal or metals of the
element 12. After exposure, the surface of the element 12 is thus
discretely and selectively etched as a result of the formation
thereon, at the areas impacted by the electromagnetic radiation, of
recesses, as shown at 34 in FIG. 26 resulting from the formation of
interreaction product 30 at such areas. The formation of the
interreaction product causes a selective etching of the silicon or
metallic surface corresponding in depth to the intensity and
duration of exposure to the actinic electromagnetic radiation. Once
the interreaction product 30 is removed from the silicon or
metallic surface, the finished article, as shown in FIGS. 24 and
27, consists of the element 12, provided with a surface having a
relief image 58 consisting of the portions, or areas, of the
surface of the element left undisturbed as a result of having not
been impinged upon by the electromagnetic radiation in the presence
of the inorganic material 14 in a vapor of liquid phase. Such
portions 58 project, from as little as a few atom layers to several
thousand Angstroms, from the recessed surfaces 34 of the element
12, the recessed surfaces corresponding to the portions of the
element which have been partially etched as a result of the
interreaction between the silicon or metal or metals of the element
12 and the inorganic material 14 causing a superficial etching of
such recessed surfaces. If such superficial etching is allowed to
continue, with sufficient exposure to electromagnetic radiation
with enough intensity and duration to consume all of the silicon or
metals or metal of the metallic element 12, these results a
complete etching in depth of the element with surface to surface
voids being formed, as a result of removing the interreaction
product 30, such as shown at 38 on FIG. 6, leaving a silicon or
metallic pattern, as shown at 60, consisting of the portions of the
element 12 having not entered into a reaction with the material 14
under the influence of the impinging actinic electromagnetic
radiation.
If instead of the mask, precedently described, comprising portions
entirely nontransmissive of the incident electromagnetic radiation
and portions fully transmissive of the electromagnetic radiation, a
mask, substantially as shown at 18 at FIG. 29, is utilized, such
mask being provided with portions 22 substantially fully
transmissive of the incident radiation 20, portions 24
substantially nontransmissive of such radiation and portions 28
providing diverse degree of transmissivity to the electromagnetic
radiation, and portions, such as shown at 26, which are partly
transmissive of the electromagnetic radiation, there is formed on
the element 12 after exposure a discrete and selective in-depth
etching of the surface thereof, the depth of the etched portions
being substantially proportional to the incident actinic radiation
energy 20' impinging upon the element 12. There results a
three-dimensional etching of the element 12 defining on the surface
thereof etched depression resulting from the formation of the
interreaction product 30. As shown at FIG. 31, the element 12 is
thus provided, after removal of the interreaction product 30, with
portions etched in depth so as to correspond to the electromagnetic
radiation energy having impinged upon the surface of element.
Consequently, the element 12 is provided with substantially deeply
etched portions 32 corresponding to the areas having been impinged
upon by the greatest amount of radiation energy, with moderately
etched areas 34, corresponding to the portions having received
moderate irradiation, and with portions, as shown at 36, of varied
depth representing a three-dimensional "grey scale" rendition of
the degree of irradiation of the surface.
As shown at FIG. 32, if the element 12 is provided with a substrate
or support backing 40, for adequate exposure of portions of the
element 12 to the incident radiation in the presence of an
inorganic material 14 which is sufficient to etch all the way
through such irradiated portions, the resulting finished article
represents a structure having a relief pattern 60 adhering to the
substrate or support backing 40.
As mentioned hereinbefore, the element 12 may include silicon or
any one of the common metals, either alone, or as alloys, or as
intermetallic compounds or in mixture.
The inorganic material 14 may be any one of the groups mentioned
hereinbefore.
As an example of typical application of the method of the present
invention, a silicon or metallic plate, foil, or thin-film is
etched in a predetermined pattern according to the method
hereinbefore described by disposing the plate, foil or thin-film in
a vessel containing vapors of arsenic trisulfide, at a temperature
of about 250.degree. C. at atmospheric pressure. After exposure to
an image projected thereon with ordinary white light for a duration
of a fraction of a second to a few seconds, a slightly recessed
planar reproduction of the image is obtained on the surface of the
plate without further processing, as the interreaction product
formed at the boundary between the surface of the plate and the
arsenic trisulfide vapor is vaporized as soon as formed, as long as
the surface temperature of the plate remains of the same order. A
finished article can thus be obtained without further processing,
and the relief image thus obtained can be preserved for an
indefinite time without further precaution by simple removal from
the atmosphere vapor-laden in arsenic trisulfide. Instead of
arsenic trisulfide, any of the other inorganic materials
hereinbefore mentioned may be used.
Operating at a lower temperature results in the surface of the
plate being wetted with the reactant material such as arsenic
trisulfide or the like being in a liquid phase, or alternately, the
plate may be placed in a molten bath of the reactant material such
as arsenic trisulfide or the like. With proper agitation and
circulation of the bath, the interreaction product formed at the
surface of the plate at the areas subjected to illumination, under
appropriate conditions of proper flow, are carried away and remain
in suspension or solution in the bath. The finished article
emerging from the bath thus presents a relief image coated with a
thin crystallized or glassy film of the reactant material adhering
thereto which may be removed by appropriate mechanical means or
which may be dissolved in a mild basic solution. Furthermore, any
interreaction product that may remain adhering to the surface of
the plate may also be soluble in such basic solutions. Alternately,
also, if the temperature of the plate, when removed from the bath,
is high enough to maintain the reactant material adhering to the
surface thereof in a liquid phase, simple wiping cleans the plate
dry and removes any interreaction product that may adhere thereto.
It is evident that by heating the plate, the interreaction product
and any reactant material adhering thereto may thus be removed by
sublimation.
In some applications, it may be advantageous to leave the
interreaction product adhering to the plate surface so as, for
example, to provide variable wettability of the surface or
resistivity thereof for wet or electrostatic printing purposes, or
for electronic purpose and in these cases precautions are taken so
as to prevent the removal thereof.
* * * * *