CA1189199A - Process for making solid-state color imaging device - Google Patents

Abstract

Process for Making Solid-State Colour image device Abstract Processes for making an electronic color imaging device comprising a planar array of charge-handling semiconductive photosensors and a multicolor filter means comprising a planar array of color filter elements superimposed in precise registration over the sensing area of the photosensors. In general, the processes comprise the steps of: (1) successively coating on a planar array of semiconductive photosensors a plurality of photoresponsive layers; (2) subjecting each photoresponsive layer in succession to radiation to provide an exposed area of said layer; (3) removing unexposed photoresponsive coating from each layer in succession; and, (4) dyeing exposed areas of each layer of said coating in succession to obtain a series of chromatic filter elements.
Color filter elements having dimensions of approximately 6µ x 6µ may be produced by the processes.

Description

Descr~ption Process fox Making Solid-State Color Ima~e Devlce Field o~ the Invention The invention relates to processes for making electronic color imaging deviaes ~ particularly to a solid-state photosensitive device that has a planar array of charge~handlirlg semiconductive photosellsors in precise registration with a multi-color planar array of filter elements. The color imaging devices are particularly useful, for example, as solid-state video cameras.

Description o the Prior Art Color photosensitive devices using charge~-handling solid~state image sensors of various types, for example, charge-coupling devices, known as CCDs, and charge-coupling imagers known as CCIs~ have been used in video cameras. Tompsett et al, Electronics, vol. 46, pp. 162-169 (January 18, 1973). To avoid optical complexity and problems with image registration, it is highly desirable that color image sensing occur at a single imaging site~ e.g. at a single planar photosensitive array.
As recognizea in U.S. Pat. No. 4,081,277 and 4,168,44~, it is desirable for each element in the filter array to be as close as possible to the surface of the underlying photosensor element or elements in the array. This result is accomplished by producing a relatively thin, 3~
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single layer multicolor filter array superimposed on the surface of the image sensor. A single layer multicolor Eilter array substantially reduces the possibility o~ light xays which pass through a 5 filter element at an angle to the optical axis striking a photosensor element benea-th an adjacent fil~er element. In the pre~erred embodiment of the p~tents, each color filter element is rectaslgular in shape and has dimensions of 30~ x 40~.
The patents disclose a photoresist method for making a color imaging device using a transparent, polyester dye-receiving layer ~or receiving heat-transferable dyes. The heat-transferable dye is diffused into the polyester 15 layer at an elevated temperature through wi.ndow areas in a photoresist layer.
U.S. Patent No. 3,284,208 discloses a process for preparing photographic multicolor screen elements exhibiting a hic~h degree of 20 opkical acuity which are particularly adapted Eor use in additive multicolor photographic processes, both conventional and di~fusion transfer types, by successively coa-ting on the smooth or flat surface of a lenticular ~ilm a plurality of 25 photoresponsive layers. Each photoresponsive layer is subjected to exposure radiation incident on the lenticular film at angles adapted to provide exposed areas of the coating contiguous each lenticular. The unexposed areas of the coating 30 are then removed and the exposed axeas dyed ~o provide a series of chromatic filter elements.
The in~ident radiation employed to effect exposure o~ successive photoresponsive layers is directed so as to provide formation of each series of 35 chromatic filter element in substantial side-by-side ....

or screen relationship on the smooth surface of the lenticular film.
An ar-ticle by Edwin H. Land entitl.ed `'An Introduction to Polavision" published in Photogra~ Science and Engineering, vol. 21, pages 225-236 (1977), and United States Paten-t No.
3,734,737 describe and illustrate how the process o:E the ahove patent may be used to produce microscopically fine, regular multi-color stripes with great precision by the following steps: (1) em-bossing a film base to form fine lenticules; (2) exposing a ]ight-sensitive layer of dichromated gelatin on the opposite side of the base through the lenticules to form line images; (3) washing away the unexposed gelatin; and, (4) dyeing the lines t.hat remain.
The process is repeated to complete an ul-trafine array of alter nating col.or stripes in a repeating pattern of red, green, blue.
After -the lenticules have been used to form lines, they are removed The presen-t invention provides processes for making a color imaging device having an integral planar array of very small color filter elements superimposed on an array of solid-state photosensors. The processes of the present invention are suited for producing color filter elements having dimensions of approximately 6~ x 6~.
In general, the processes comprise the steps oE: (1) suc-cessively coating on an array of semiconductive photosensors a plurality of photoresponsive layers; (2) subjecting each photo-responsive layer in succession to active radia-tion whereby to provide an exposed area of that particular layer; (3) removing unexposed photoresponsive coating of each layer in succession;

and (~) dyeing exposed areas of each layer of said coating in succession to obtain a series of chromatic filter e:l.emen-ts.
The inven-tion will now be clescribed in greater detail wi-th reference to the accompanying draw:ings~ in which:
Figure 1 is a schematic drawing oE a planar mul-ticolor planar Eil-ter array made in acco:rdance wi-th -the invention.
Figure 2 is a diagrammatic cross-sectional vi.ew illus--trating the fLrst preferred process o:E the invention.
Figure 3 is a partial cross-sectional view of a row of sensing elements of a color imaging device haviny a multicolor planar Eilter array made in accordance with the invention.
Figure 4 is a perspective view in partial. cross-section illustrating the lenticular film layer consisting of offset rows of lenticules employed in the second preferred process of the invention.
Figure 5 is a diagrammatic cross-sectional view illus-trating the second preferred process of the invention.
In accordance with the present invention, methods are provided for making a color imaging device having an integral planar array of very small color filter elements superimposed on an array of solid-state photosensors. The solid-state photo-sensors used in the processes of this invention are charge-hand-ling image sensors, which include, for instance, charge-coupled devices (also known as charge-coupled imagers, charge--transfer devices, charge-transfer imagers, etc.), charge injection devices, bucket brigate \ devices, diode arrays, combinations of these, and the like.
The color filter elements are in micro~
5 registration with the radial;ion sensing area o the underlying photosensor or photosensors. ~s used herein, the term "micrQ-registration"
means that the color filter elements and the underlying sensing areas are alic~ned so that, on lO a mic~ometer scale, ~he filter element and the underlying sensing area are substantially coex-tensive with each other and the boundaries of such areas are substantially superimposed.
The color filter means consists of kriplets 15 or sets of three dyed fil~er elements. In each set like elements having common light absorption and transmission characteristics are made by applying a dye to a transparent dye absorbing layer. Advantageously, the individual filter 20 elements in each set of light intercepting means contain a dye having radiation absorption and transmission in a different region of the spectrum from the other two elements in the set.
The very small color ~ilter elements made 25 by the present invention have extremely sharp edges. Therefore, the dyes in two adjacent filter elements have no overlap. This allows maximum transmission of ligh-t having the desired wavelength to the sensing area o~ the photosensor 30 lying in micro-registration beneath the color ilter element.
The importance of edge sharpness for the filter elements and the ability to make arrays of filter elements with the respective dyed 35 areas being confined to desired dimensions is readily apparent when one considers the very small size of the sensing areas of the photosensors in a useful color imaging device and thus the correspond-ingly small size of the superimposed color filter ele 5 ments. ~seful color imaging devic:es made by this in-vention consist of an array of inclividual color fil-ter elements each having dimensions of approximately 30~ x 30~ superimposed over an array of photosensors each having a corresponding sensing area with dimen-sions of approximately 30~ x 30~v The invention issuch that color filter elements with dimensions of approximately 6~ x 6~ may be produced.
Thus, important advantages achieved by this invention are the potential for greatly reduced size of the individual color filter elements, the sharp edge definition of the individual colsr filter ele-ments, and the micro-registration of each filter element with the underlying photosensor.
An example of a three color filter array 10 having a planar array of color filter elemPnts arranged in sequential triplets made in accord with the invention is illustrated in Fig. 1 wherein R repxesents xed, G represents green, and B represents blue. The sequential kriplets of filker elements form an interlaid pattern to provide the three-color filter array. ~ach color ilter element has a common light absorp~ion and transmission characteristic which is different from each other color~ In a color imaging device made by khe invention, the filter array 10 is superimposed on an array of photosensors so that each individual ilter element is in micro-registration with a photosensor. As a result of this arrangement, an image can be sampled for all three color veckors by selecting appropriate 3~
dyes to make the three sets oE color filter elements of ~he filter array 10.
The :Eilter array 10 consists of a transparent photoresponsive polymeric layer which has been 5 exposed to electromagnetic :radiation actinic to the layer and then treated with dyes to form the individual color filter elements~ The photo responsive polymeric layer is, for example, photohardenable gelatin sensitized with potassium 10 dichromate, sodium dichromate or ammonium dichromate, or photosensitized album.in, casein gum arabic, polyvinyl alcohol or any other radiation-sensitive polymer. The photoresponsive layer is, preferably, approximately 4~ thick when 15 dry.
Referring to Fig. 2, there is shown, in stages, the first preferred process for the production of a solid-state color imaging device in accordance with the present invention. As 20 specifically illustra~ed in stage 1, a semi-conductive photosensox substrate 11 is coated with a transparent selectively photoresponsive polymeric layer 12, such as dichromated yelatin r which is exposed at portions 13 to radiation 14, 25 pre~erably ultraviolet radiation, ~rom an exposure source 15 through windows 16 in photomask 17 which is in micro-registration with the substrate 11. Photomask 17 may be, for example, a piece of glass with a chrome layer mask. When using ~he 30 dichromated gelatin,. approximately 0.08 joule/cm2 (0.5 joule/sq. in.) is adequate to harden the selected expo~ed portions 13 of such material.
The open area o~ each window 16 and consequently the area of each exposed portion 13have 35dimensions, for example, of approximately 30~ x 30~.

Subs~.quent to pho-~oexposure, in stage 2, the photomask 17 is removed ancl the photoresponsive layer 12 is contacted with water or oth~r su.itable solvent for the unexposed photoresponsive layer, 5 preEerably within the range of ~25 to 60C, or a t.ime interval of about 3 ko 60 seconds, to remove the unexposed porti.ons o:f pho~oresponsive layer 12 in accordance with the selected exposure pattern, and to leave standing exposed portions 18.
10In stage 3, the exposed portions 18 are contacted with a dye solution, containi.ng a dye substantive to the hardened dichromated gelatin, generally a primary red color acid dye such as described in U.S. Patent No. 3r284,208 in order 15 to impart the desired coloration thereto and, as a result, to form optical filter elements 19.
: In addition to the dye, the dye solution may contain suitable wetting agen~s and dispersing agents, etc~ Subsequent to forming optical 20 ~ilter elements 19, the workpiece may be contacted with cold water or other suitable solvent to remove any residual or excess dye.
In sta~e 4, the workpiece is dried and khe first optical filter elements 19 and the 25 remaining semiconductive photosensor substrate 11 are coated with an adhesive lacquer layer 20.
Subsequent to the drying of lacquer coaking 20, a second photoresponsive layer 21, such as the stated dichromated gelatin, is then overcoated 30 on adhesive layer 20.
In stage 5, the photoresponsi-ve layex 21 is exposed at portions 22 to radiation 14, preferably ultraviolet radiation, frQm an exposure source 15 through windows 23 in a second photomask 24 35 which is in micro-registration with the semiconductive photosensor substrate ll.
The open area of each window 23 and consequently the area of each exposed portion 22 have dimensions of approximately 30~1 x 3()~.
5 Subsequent to photoexposure, in stage 6, ` photomask 24 is removed and the photoresponslve layer 21 is contacted wit:h water ox other suitable solvent for the unexposecl photoresponsive layer, to remove the unexposed portions o~ photoresponsive lO layer 21, in accordance with the selected exposure pattern, and to leave standing exposed portions 25.
The workpiece is, in stage 7, contacted with a second dye solution containing a dye subskantive to the hardened dichromated gelatin, generally an 15 acid dye of green coloration such as described in U.S. Patent ~o. 3,284,208, to provide second optical filter elements 26.
I~ stage 8, the workpiece, now containing a : first and second series of optical color filter 20 elements, has the external surface thereo~
coated with a third adhesive lacquer layer 27 which, subsequent to drying, is overcoated with a third photoresponsive layer 28 which is exposed at por~ions 29 to radiation l4 from an :25 exposure source 15 through windows 30 in a third photomask 31 which is in micro-registration wlth the semiconductive substrate ll.
The open area of each window 30 and consequently the area of each exposed portion 29 have dimensions 30 of approximately 30~ x 30~.
Subsequent to photoexposure, the workpiece is contacted with water in stage 9, as previously described, whe;reby to e~fect removal of unexposed photoresponsive layer, in accordance with the 35 exposure pattern, and to leave standing exposed portions 32.
In stage 10, the workpiece is contacted with a dye solution ccntaining a dye substantive to the hardened dichromated gelatin, generally an acid 5 dye of blue coloration such as described in U.S.
Patent No. 3,284,20~, to provide third optical fil~er elements 33.
Optionally, the multicolor filter array may be overcoated with a transparent protective 10 pol~m~ric composition 34, illustrated in staye 11, such as nitrocellulose, cellulose acetate, e~c.
As illustrated by Fig. 3~ a color imaging device made by the foregoing process has a solid-state imaginy array 35 consisting of individual 15 charge-coupled photosensors (e.g., the individual photos~nsor extendiny between the dashed lines of Fig. 3). The multicolor ~ilter array, consisting of individual red filter elements 19, green filter elements 26 and blue filter elements 20 33, is superimposed over the imaginy array 35.
The individual filter elements 19, 26, and 33 are aligned in one-to-one micro-registration with the individual photosensors of the imaging array 35 to form individual color imaging elements.
25 Individual elements of the filter array are of the selectively transmitting type. The color imaging device consists of an array of color imaging elements, each consisting of an individual color filter element combined with an individual 30 photosensor, each being sensitive to a particular region of the spactrum.
A second preerred process of the invention may be employed to make the three-color filter array 10 illustrated in Fig. 1. Referriny to Fig.
35 4, the second preferred process uses a separate 4.;3 transpa.rent polymeric lenticular film layer 42 having individual lenticul.es 45 and 46 which are arran~ed in rows. Each row of lenticules is offset from the preceding row ~y a distance 5 equal to one-third the length of a lenticule.
For example, one lenticule may be. 90~ .in length and 30~ in width. The lenticules in the next adjacent row are oE~se~ Erom the lenticules in the preceding row by one-third the length of 10 o~e lenticule or 30~. In this process lenticules may be used which are approximately 18~ in length and 6~ in width, thereby producing color filter elements which havs dirnensions of approximately 6~l ~ 6~.
The fine lenticules in lenticular ilm layer 42 are formed in the surface of the film layer by contacting the film with a rotating embossing roller under appropriate conditions of temperature, pressure and/or solvents to pxovide lenticules of 20 the shaps and size desired.
Lenticular layer 42 is micro-registered over a photorespons.ive polymeric layer 41 which is coated on a semiconductive photosensor substrate 40. The photoresponsive polymeric layer is, 25 for example, photohaxdenable gelatin sensitized with potassium dichromate, sodium dichromate, or ammonium dich.romate, or photosensitized albumin, casein, gum arabic, polyvinyl alcohol or any other radiation sensitive polymer. The photoresponsive 30 layer is, pre~erably, approximately 4~ thick when dry.
Fig. 5 shows the stages in the second preferred process~ As illustrated in stage 1, semiconductive photosensor substrate 40 is coated with transparent 35 selective:Ly photoresponsive polymeric layer 41, such as dichromated gelatin, whi.ch is exposed to radi.ation 46, preferably ult:raviolet radiation, from exposure source 43.
The lines of radiation 46 are directed so as S to impinge on lenticule 45, of lenticular film layer 42, whereby the radialion traversiny each lenticule is Eocused in an area 44 o~ photo-responsive layer 41 immediately conti~uous each lenticule 45. The area of exposure 44 comprises lQ approximately one third o~ the photoresponsive area immediately contiguous each lenticule 45 and, as a result thereof, approximately one third of the photoresponsive area 41 immediately contiguous each lenticule 45 is subjecked to 15 ~xposure radiation. For example, exposed area 44 may have dimensions of approximately 30~ x 30~.
Subse~uent to photoexposure, in stage 2, the lenticular film layer 42 is removed and the photoresponsi~e layer 41 is contacted with water 20 or other suitable solvent for the unexposed photore~ponsive layer, preferably within the range of ~25 to 60C, for a -time interval of about 3 to 60 seconds, to remove the unexposed portions of photoresponsive layer 41 in accordance with 25 the selected exposure pattern, and to leave standing exposed portions 47.
In stage 3, the exposed portions 47 are contacted with a dye solution, containing a dye substantiue to the hardened dichroma~ed gelatin, 30 generally a primary red color acid dye such as described in U.S. Paten~ No. 3,284,208, in order to impart the desired coloration there-to and, as a result, to form optical filter elements 48.
In addition to the dye, the dye solution may 35 contain suitable wetting agents and dispersing agents, etc. Subsequent to forming optical filter elemsnts 48, the workpiece may be contacted with cold water or other suitable solvent to remove any residual or exc~ss dye.
In ~tage 4, the workpiece is drie~ and the first optical filter elements 48 and the remainillg semiconductive photosensor substrate 40 ar~ coated with an adhesive lac~uer la.yer ~9. Subsequent to the drying of lac~uer la.yer 49, a second 10 photorespo.nsive layer 50, such as the stated dichromated ~elatin, is then overcoated on adhesive layer 49.
In stage 5, lenticular :Eilm layer 42 is again superimposed over photoresponsive layer 15 50 so as to be in micro-regist.rat.ion with photo-sensor sub~trate 40. Photoresponsive layer 50 is then exposed to radiation 46 from exposure source 43, the lines o~ radiation 46 being di.rected so as to impinge on lenticule 45, of 20 lenticular film layer 42, at such angles as to provide radiation traversing Pach lenticul.e 45 and focusin~ in area 51 of photoresponsive layer 50, contiguous each lenticule.45. Area 51 is preferably equal to one-third of the surface ; 25 area of the re.spective lenticular 45 immediately adjacent photoresponsive layer 50 and, as a result thereo, pro~ides an exposed area 51 approximately equal in dimensions to that o~
preceding optical filter element 48, for example, 30 approximately 30~ x 30~.
Subsequent to photoexposure, in stage 6, lenticular film layer 42 is removed and photo-responsive layer 50 is contacted with water or other suitable solvent for the unexpo~ed photo-35 responsive layer, to xemove the unexposed portions 3~of photoresponsive layer 50 in accordance with the selected exposure pattern, and to leave standing exposed portions 51.
The workpiece is, in stage 7, contacted 5 with a second dye solu~ion contai.ning a dye substantive to the haxdened dichromated gelatin, generally acid dye of green colora~ion as described in U.S. Patent NoO 3,284,208, to provide second optical filter elements 52.
In stage 8~ the workpiece, now containing a first and second series of optical filter elements, has the external surface thereof coated with a third adhesive lacquer layer 53 which, subsequent to drying, is overcoated with 15 a third photo.responsive layer 54.
The workpiec0 is then exposed, in stage 9, to diffuse radiation 56l deri.ved from exposure source 57, whereby to effect impingement of dif~use radiation on the surface of lenticule 20 45 so as expose area 55 of photoresponsive layer 54, contiguous lenticule 45, which is not occupied by first and second op~ical Eilter elements 48 and 52, respectively.
Subsequent to photoexposure, lenticular 25 ~ilm lay~r 42 is removed and the workpiece is contacted with water in stage 10, as previously described, whereby to remove the unexposed portions of photoresponsive layer 54 in accordance with the selected exposure pattern, and to leave 30 standing exposed portions 55.
In stage 11, the workpiece is contacted with a dye solution contain.ing a dye substantive to hardened dichromated gelatin 55, generally an acid dye of blue coloration as described in U.S.
35 Patent No. 3,284,208, to provide third optical filter elements 56.
Optionally, the multicolor filter arra~ may be overcoated with a transparent protective polymeric comp~sition 57, illustrated in stage 12, 5 such as nitrocellulose, c~llulose acetate, ekc.
The color imaging dev.ice, as made by the foregoing process, is illustrated in Fig. 3, described above.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for making a color imaging device, said color imaging device comprising an array of charge-handling semi--conductive photosensors with an array of color filter elements superimposed in microregistration with the sensing area of said photosensors, the process comprising the steps of: (1) succes-sively coating on an array of semiconductive photosensors a plur-ality of photoresponsive layers; (2) subjecting each photorespon-sive layer in succession to active radiation whereby to provide an exposed area of that particular layer; (3) removing unexposed photoresponsive coating of each layer in succession; and (4) dye-ing exposed areas of each layer of said coating in succession to obtain a series of chromatic filter elements.

2. In a process for making a color imaging device, said color imaging device comprising an array of charge-handling semi-conductive photosensors with an array of color filter elements superimposed in microregistration with the sensing area of said photosensors, the process comprising the steps of: (1) applying a first coating of photoresponsive material on said array of semiconductive photosensors, said photoresponsive material being adapted to be hardened as a result of photoexposure to radiation incident on said material; (2) exposing said first photorespon-sive coating to active radiation incident in a pattern represen-ting a first set of filter elements to provide selectively exposed areas of said first coating; (3) removing unexposed photoresponsive coating; (4) dyeing the remaining areas of said first coating with a first color to obtain a first series of chromatic filter elements; (5) applying a second coating of photoresponsive mate-rial on said array of semiconductive photosensors; (6) exposing said second photoresponsive coating to active radiation incident in a pattern representing a second set of filter elements to provide selectively exposed areas of said second coating; (7) re-moving unexposed photoresponsive coating; (8) dyeing the remin-ing areas of said second coating with a second color to obtain a second series of chromatic filter elements; (9) applying a third coating of photoresponsive material on said array of semi-conductive photosensors; (10) exposing said third photoresponsive coating to active radiation incident in a pattern representing a third set of filter elements to provide selectively exposed areas of said third coating; (11) removing unexposed photorespon-sive coating; and (12) dyeing the remaining areas of said third coating with a third color to obtain a third series of chromatic filter elements.

3. A process as defined in claim 2, including the step of coating a protective polymeric layer on the external surface of said optical filter elements.

4. A process as defined in claim 2, wherein one of said colors comprises red, one of said colors comprises green, and one of said colors comprises blue.

5. A process as defined in claim 2, wherein at least one of said photoresponsive coatings comprises a polymer selected from the group consisting of potassium, sodium and ammonium di-chromate sensitized gelatin.

6. A process as defined in claim 2, wherein an adhesive lacquer is interposed between each of said photoresponsive coatings and the immediately preceding coating.

7. The process of claim 2 wherein said exposing steps com-prise exposing the successive photosensitive coatings through different photomasks representing said first, second and third sets of said filter elements respectively.

8. The process of claim 2 wherein said exposing steps com-prise exposing the successive photosensitive coatings at differ-ent angles through a lenticular array to respectively provide exposed areas representing said first, second and third sets of filter elements.

9. A color imaging device comprising an array of charge-handling semiconductive photosensors having an array of color filter elements superimposed in microregistration with the sen-sing area of said photosensors, constructed by the steps of:
(1) applying a first coating of photoresponsive material on said array of semiconductive photosensors, said photoresponsive mat-erial being adapted to be hardened as a result of selective photo-exposure to radiation incident on said material;(2) exposing said first photoresponsive coating to active radiation in a pat-tern representing a first set of filter elements to provide selec-tively exposed areas of said first coating; (3) removing unex-posed photoresponsive coating; (4) dyeing the remaining areas of said first coating with a first color to obtain a first series of chromatic filter elements; (5) applying a second coating of photoresponsive material on said array of semiconductive photo-sensors; (6) exposing said second photoresponsive coating to active radiation in a pattern representing a second set of filter elements to provide selectively exposed areas of said second coating; (7) removing unexposed photoresponsive coating; (8) dye-ing the remaining areas of said second coating with a second color to obtain a second series of chromatic filter elements;
(9) applying a third coating of photoresponsive material on said array of semiconductive photosensors; (10) exposing said third photoresponsive coating to active radiation in a pattern represen-ting a third set of filter elements to provide selectively exposed areas of said third coating; (11) removing unexposed photorespon-sive coating; and (12) dyeing the remaining areas of said third coating with a third color to obtain a third series of chroma-tic filter elements an adhesive layer between each of said photo-responsive coatings.

10. The product as defined in claim 9, including the step of coating a protective polymeric layer on the external surface of said optical filter elements.