US 3666648 A
Master pattern silver emulsion images of microelectronic artwork are altered in situ so that they can be used as master patterns to provide photocopies of the reverse images. The silver is dissolved out and the remaining gelatin relief is dyed to a threshold level of opaqueness by an absorbed dye to produce the reversed master pattern image. Results of unusually fine detail resolution and contrast quality are achieved with substantial cost savings. Costs and risk of damage, due to excessive handling of the hard-to-replace masters in the alteration process, are reduced with undiminished quality of results by employing electrical means to control agitation of the silver dissolving agent. In a preferred exemplification, handling is further reduced by combining dissolution and dyeing phases of the process into one operation. Images on the reversed masters have better edge contrast quality than the original masters. This effect is used to advantage to improve masters which originally have poor edge definition.
Claims available in
Description (OCR text may contain errors)
United States Patent Lasky et a].
[541 IN-SITU RECLAMATION OF MASTER PATTERNS FOR PRINTING MICROCIRCUIT IMAGES ON REVERSELY SENSITIZED MATERIAL  Inventors: Daniel J. Lasky, Wappingers Falls; Harold C. Weisel, Pawling, both of N.Y.
 Assignee: International Business Machines Corporation, Armonk, N.Y.
22 Filed: Nov. 5, 1969 211 Appl.No.: 874,178
 US. Cl. ..204/180 R, 204/149, 96/59  Int. Cl ..B0lk 5/02  Field of Search ..204/180, 181, 149, 300, 299;
 References Cited UNITED STATES PATENTS 1,245,152 11/1917 dit Deval ..L ..96/59 1,525,766 2/1925 Capstaff.. .96/59 X 1,564,753 12/ l 925 Capstaff... ..96/59 2,193,023 3/1940 Evans et al.. .....95/88 2,939,787 6/1960 Giaimo 96/59 X 2,068,879 l/1937 Troland ..95/5.6 1,632,740 7/1927 Miller ..96/59 X 1,857,089 5/1932 Sease .....96/59 1,962,348 6/1934 .lelley ..96/59 1,970,869 8/1934 Schloemann ..95/88 [4 1 May 30,1972
3,471,387 10/1969 Lennon et a1. ..204/180 Primary Examiner-John H. Mack Assistant ExaminerA. C. Prescott Attorney-Hanifin and Jancin and Robert Lieber [5 7] ABSTRACT Master pattern silver emulsion images of microelectronic artwork are altered in situ so that they can be used as master patterns to provide photocopies of the reverse images. The silver is dissolved out and the remaining gelatin relief is dyed to a threshold level of opaqueness by an absorbed dye to produce the reversed master pattern image. Results of unusually fine detail resolution and contrast quality are achieved with substantial cost savings. Costs and risk of damage, due to excessive handling of the hard-to-replace masters in the alteration process, are reduced with undiminished quality of results by employing electrical means to control agitation of the silver dissolving agent. In a preferred exemplification, handling is further reduced by combining dissolution and dyeing phases of the process into one operation. images on the reversed masters have better edge contrast quality than the original masters. This effect is used to advantage to improve masters which originally have poor edge definition.
12 Claims, 9 Drawing Figures Patented May 30, 1972 3,666,648
z Shun-Sh. 1
FIG.1 m FIG. 2
ExPosE MIGRIIGIRGuIT IMAGE l IIEvELoP, FIX HARDEN MAsTER j MEGATIvE DEVELOP USE To PRIIIT COPIES OF MAsTER IMAGE IN RESIST MATERIAL 0F 1 PosITIvE SENSITIVITY T I,
REMOVE w m\\ T-5 CHANGE To REsIsT MATERIAL 0E AT TI TY ETCH, BLEACH MASTER NEGATIVE 50 6 To DESOLVE SILVER GRAIN AREAS DY E gnaw-Sm 2 OF IMAGE IA COLD r WATER RINSE GEMTLII IM sLow FLOWING R'NSET GooL WATER 5 FIG. 3 4
DYE GELATIM RELIEF ON I CLEAR/GELATN sILvER GRAINS MASTER I GRIGIIIAL T 24. l I RINSE GEMTLY IM sLow TLGIIIIMG MAsTER WQTER DIFFERENTIALLY NEGATWE 53 52 T'" USE REVERSED MAsTERTo PRINT 2 coPIEs OFREVERSED MAsTER IMAGE F IM MEGATIvE sEMsITIvITY REsIsT MATERIAL FUZZY OPAQUE LEvEL I' lmum TRAMsMITTAIIcE SILVER AcRoss SILVER LIME TRANSPARENL, DENSITY IMAGE LEVEL L APPARENT LIME wIIITII 9 DYED LIGIIT TRANSMITTANCE oPAouE LEvEL AGRoss DYED GELATIM DYE DYE REVERSED IMAGE sAME 'NVENTORS NTENSHY LINE DANIEL J. LASKY 'NTENS'TY HAROLD G. wEIsEL TRANSPARENT RAE Mfi A Wm FUZZY ATTORNEY IN-SITU RECLAMATION OF MASTER PATTERNS FOR PRINTING MICROCIRCUIT IMAGES ON REVERSELY SENSITIZED MATERIAL BACKGROUND OF THE INVENTION 1. Field of the Invention The invention pertains to handling of silver emulsion master patterns. I
As used herein the term master pattern," occasionally also referred to simply as master refers to a photographic plate, film or other transparent support on which there is an image of microelectronic artwork reproduced with high accuracy from an original master drawing or specification. It shall be understood that masters are used as copying instruments to produce printed circuit devices or the like by photocopying processes. The form of the image, i.e. negative or positive, is not implied in the use of this term. Hence there-can be negative" masters and positive" masters corresponding to one originally specified master image. Only the quality of the image as suitable for precision photocopying is implied in the use of the term.
In particular the invention concerns treatment of master patterns, which are formed in gelatin emulsions by suspended silver grains, .to effect in situ reversal of images thereon without loss of master quality. In situ reversal of masters is useful either as a reclamation expedient adaptive to an unscheduled substitution of reversely sensitizedresist material as the object medium in which photocopies of the master image are being made, or as an extension of an automated light tracing process for constructing masters.
2. Description of the Prior Art Until now in the microelectronic construction arts master patterns of artwork formed in silver emulsions have been treated generally as inviolable articles subject to utmost care in handling and storage. Presently artwork masters are produced at considerable expense by automated light tracing processes which utilize a computer program to control the shape and position of the light beam. Due to tolerance considerations such masters are generally not used to produce other masters. Hence the tracing process must be repeated to produce as many masters as are needed to fulfill printing (i.e. device productionlrequirements. To make other than minor changes in a master the automated tracing process is modified to produce new masters incorporating the changes and old masters are discarded if no longer useful.
' One type of change which is not infrequently made is reversal of the master artwork image to render opaque image elements transparent and transparent image elements opaque. Typically the purpose of such a change would be to adapt the master to print reverse artwork images after an unscheduled substitution of reversely sensitized material on the objects receiving the print exposures. The need to use object material I of reverse sensitivity may arise when shipments of a particular photosensitive resist material originally used as the photocopying medium begin to deteriorate in quality and fortuitously only one other resist material of reverse photosensitivity is available as a substitute object medium fulfilling resolution and contrast quality requirements.
Naturally, it would be quite difficult and costly to adapt to such object medium changes by modifying the program of the automated tracing process to provide new masters with reversed images. The alternative of forming new masters from the old masters by photocopying would be unacceptable as it would impose unnecessarily severe restrictions on dimensional tolerances to be held in the first instance while forming the original masters.
We have found surprisingly that with moderate care, and applying novel techniques disclosed herein to control the extent and severity of handling, artwork images of fully developed and fixed master patterns can be consistently reversed in situ. Naturally for our purposes an inconsistent process would not be acceptable since retention of master quality is absolutely essential.
In reversing the master image in situ fine grain silver forming the opaque image areas is removed by dissolution of the immediately surrounding gelatin in a weak etch-bleach solution. This leaves a transparent gelatin relief image pattern which we dye by an absorption process to a threshold level of opaqueness in relation to the actinic light required to expose the reversed image in the modified photocopying process.
By threshold level of opaqueness we mean a level of opaqueness which can be increased or darkened (i.e. up to a saturation level) by further exposure of the gelatin to the dye solution. At threshold level we obtain a beneficial darkening effect at image edges which results in improved detail resolution without loss of dimensional accuracy.
Electrodes in the etch-bleach vessel are excited by applied d.c. potentials to produce gaseous bubbles, which deftly dislodge dissolving charged waste products from the image surface of the processed master and to collect such products by electrophoretic attraction so that they do not interfere with the continuation of the dissolution process. The electrode placement, geometry and excitation are designed to provide a uniform agitation of the dissolving agent at the opaque surface areas of the master image defined by the presence of suspended silver grains and less turbulent agitation of the agent at the transparent image areas. Thus risk of dissolution or detachment of the clear gelatin forming the transparent relief image is minimized.
The dye substance applied to the relief gelatin is absorbed from a solution by imbibition. In the exemplary application of reversal to adapt to an unscheduled substitution of print materials of reverse sensitivity the dye color is selected to match (i.e. block) the actinic frequency of radiation to which the new substitute print receiving material is sensitive.
It is to be understood that removal of silver and dyeing of background gelatin'are well known procedures as practiced hitherto in other arts; particularly in the synthesizing of color photographs. In color photograph synthesis, as represented in U. 5. Pat. No. 1,315,464 (1959) to Capstaff and in Photography, Its Materials and Processes, Page 444 (D. Van Nostrand, 1962) by Neblette, it has been known for many years that continuous tone low resolution photograph images developed in wash-off" silver halide emulsions can be reversed in situ with occasional uncertainty of results. The finely divided silver grains forming the image are removed by differentially softening the gelatin immediately adjacent the silver grains and then removing the softened gelatin with hot water. The action of the hot water is somewhat harsh and would not be suitable for reversing delicate micro-circuit patterns where for example thin line images in the background gelatin could be separated from the main support substrate or even removed by the hot water.
We have modified and improved upon these in situ reversal techniques to adapt them for consistent reversal of high resolution high contrast master pattern images while preserving the master qualities of resolution and contrast.
SUMMARY We have invented certain new and useful processes and adaptations of earlier processes by which we can reverse master pattern images of microcircuit artwork when the images are formed by silver grains suspended in gelatin. The process provides consistent results wherein the reversed images retain master quality. Hence there is minimal risk of image deformation or destruction.
Some but by no means all of the novel aspects of our contribution are:
the aspect of salvaging or reclamation of master patterns after unscheduled substitution of reversely sensitive printing material as discussed;
the dyeing of the gelatin relief image to less than a saturation level of opaqueness as discussed;
the use of subject reversal technique in conjunction with programmed artwork generation apparatus to produce novel artwork effects;
the compatible blending together of etch-bleach. and dye preparations to effect simultaneous removal of the silver grains which constitute the opaque elements of the master image and dyeing of the remaining background gelatin to threshold level opopaqueness, thereby lessening exposure of the master to potentially destructive handling;
enhancement and improvement of the quality of the in situ reversal process by use of electrified electrode means to provide: (a) controlled agitation of the agent which is used to attack the silvered image areas on the master, by projection of gaseous bubbles in planar formation across the image surface during the attack process; and (b) prompt removal of the attack waste products from the image surface; further refinement of the process by quenching the attacking and dyeing operations with a water rinse of the master in gently flowing circulating water warmed to room temperature;
the discovery and utilization of synergistic edge definition enhancement effects resulting from the absorption of less 7 than a saturation level of coloring dye into the gelatin forming the reversed image; a
the development of a technique for difierentially reversing discrete area portions of a master image either as a means of producing novel artwork effects or as a means of providing visual inspection or alignment marks on the master which will not transfer in subsequent photocopying operations.
The foregoing and other objectives, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiment of the invention as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAMNGS- FIG. 1 illustrates the subject image reversal process in schematic sectional views of a master taken in progressive stages of reversal;
FIG. 2 is a flow diagram more completely characterizing the sequence of development, use reversal and continued use of reversed patterns as master patterns according to the invention;
FIG. 3 contains before and after schematic views of a master plate handled according to the invention in which a thin layer of clear gelatin underlies the opaque areas of the artwork image defined by the presence of suspended silver grains in the overlying gelatin;
FIG. 4 is an enlarged vertical sectional view of apparatus for carrying out the etch-bleach operation by which the suspended silver is dissolved out of the opaque area portions of the master image;
FIG. 5 is a schematic front elevational view of a representative master image which could be reversed in accordance with the present invention; FIG. 6 is an enlarged view of a portion of the master image shown in FIG. 5 illustrating line width and line spacing dimensional tolerances which can be preserved when reversing a master image by the method of the present invention; v
FIG. 7 indicates in a series of section views the reversal of a master in one combined etch and dye operation;
F IG. 8 indicates before and after elevational views of a portion of a master image in the process of being reversed and dyed by a touch-up applicator in accordance with the subject invention; and
FIG. 9 contains schematic light transmittance profiles of a transversely scanned line image element in a master photograph before and after reversal of the image element by subject technique. These are used to explain the edge sharpening phenomenon which we have observed.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS This invention concerns the handling of master patterns from which photocopies of intricate microcircuit artwork patterns are produced in printed circuits and the like. Masters of the type presently contemplated can be formed by a programmed light tracing process of the type performed by the well-known program controlled Gerber Model 532 Artwork Generator."
Referring to FIG. 1 a master such as I typically comprises a transparent substrate 2, in the exemplification an Ortho Type "I glass plate, which is covered by a layer 3 of silver halide emulsion useful to develop high resolution high contrast images. Results of desired quality are obtained from plates coated with Kodalith Ortho Type 3 or High Resolution type emulsions.
When exposed to a pattern of light and processed the layer 3 is transformed into contrasting opaque and transparent image areas 4 and 5 respectively contained in the master image la. The opaque image areas are formed by finely divided grains of metallic silver suspended in the clear gelatin which also covers the transparent areas.
Apparatus and method for developing master plates of this kind are fully disclosed in the co-pending United States patent application of D. J. Lasky Ser. No. 744,405 filed July 12, 1968. The master plates as formed are utilized as masks for photo-copying the master microelectronic artwork image pattern by transfer from the master to sensitive object materials in which it is desired to form such image copies; particularly to photosensitive resist materials.
Occasionally, a resist material of one working type, say positive type (i.e. unexposed areas develop into relief image), is found to be unsuited to a particular printing application; for example because of non-uniform properties in different shipments, or other defective conditions. When this occurs a new resist material is substituted as the object medium of printing. It is not always possible however to substitute a resist material of the same working type, and when a resist material of reverse working type is substituted it becomes necessary to provide a photographically reversed master image to obtain the correct image copies in the reversely sensitive substitute material. The problem of consistently reversing master images in situ without loss of master quality in subsequent photocopying usage is addressed by the present invention.
We have found that with the improved method described herein old master plates can be treated in situ to reverse the images thereon consistently without intolerable loss of fidelity in the reversed image and in most instances with improvement in quality of image copies transferred to the substitute material. Referring again to FIG. 1 the finished master plate la which carries the original fully developed silver grain in gelatin image is reversed in situ by removing the gelatin adjacent the silver grains, thereby also removing the silver grains, and dyeing the remaining gelatin. The gelatin surrounding the silver in areas 4 is attacked by a weak etchbleach solution as described herein to form the remaining gelatin 5 into a relief image having the interim form 1b. The master plate is also immersed in a dye 6 which is imbibed preferentially into the relief gelatin 5 and does not color the exposed substrate 2 thereby forming reversed master image lc.
Stages of the foregoing procedure are indicated more specifically in the flow chart of FIG. 2. It will be noted that one or more stages of rinsing in slow flowing circulating water at room temperature are used in the image reversal procedure to quench or terminate the etching and dyeing activities.
Apparatus which is used to reverse the master image is indicated in FIG. 4. This apparatus is similar, save for materials used, to apparatus described in the above-mentioned co-pending United States patent application of D. J. Lasky.
Mounted in tank 10 is a stainless steel electrode 11, having an upraised pointed ridge 12 extending its full length of approximately inches. Electrode 11 when excited by an applied negative d.c. potential undergoes an electrolysis reaction with the image attacking solution 14 which is especially intense along the lengthwise ridge 12. This reaction projects a continuous stream of gaseous bubbles 16 upward in a generally planar formation across the gelatinous image bearing surface 17 of master plate 1a, said surface being situated adjacent and parallel to the plane of the bubbles.
As gelatin in the image bearing surface is attacked by the solution 14 in silver-bearing image areas such as 18, waste products 19 forming at the surface 17 are dislodged by the traveling bubbles 16. By electrophoretic attraction the negatively charged dislodged particles 19 are collected at positive electrode 20 which preferably is a platinum plated fine mesh titanium screen receiving a positive d.c. potential. Electrodes 20 and 11 are adapted to be connected through not shown connection means to respective positive and negative terminals of a not shown supply of voltage.
When all of the silver grains in the master image have been extracted (after approximately 5 minutes of reaction) the master image assumes the interim form lb of a transparent gelatin relief of the reverse master image shown in FIG. 1. Since the interaction of bubbles l6, waste matter 19 and etching fluid 14 is concentrated most intensely at the image areas 18 it will be seen that the fluid motion is most intense at these areas. Hence the attack is intensified uniformly in the dissolving areas 18 while the fluid adjacent the transparent gelatin areas such as 21 remains comparatively less turbulent. Thus the likelihood of dislocation or distortion of areas 21 is lessened.
When all of the silver has been removed the action of the solution 14 must be stopped so that the gelatin in the clear image areas 21 will not be weakened. For thispurpose-the interim relief image 1b is rinsed carefully in a slow flow of circulating water. We have found it desirable for this purpose to immerse the plate with interim image lb in a basin of cool circulating tap water which is replenished and drained continuously at a very slow rate. It is important to avoid direct contact with turbulent water either at the influent stream from the tap or at the effluent stream approaching the drain, in order to avoid placing unnecessary stress upon the more delicate elements of the relief gelatin image.
Next, plate 1 in interim form 112 is immersed in a dye solution wherein a sufficient amount of dye substance is imbibed into the reliefed gelatin to produce a threshold level of opaqueness in image areas 21 to the actinic light associated with the object resist medium of reversed sensitivity as required to form the final reversed master image 10. If for example such actinic light is in the visible blue wavelength a red dye which transmits red light and absorbs blue light could be used. The action to quench the dyeing process consists of gentle rinsing in slow flowing water as described previously.
By not permitting the dye to fully saturate the gelatin in areas 21 we restrict the amounts of dye absorbed into the tapering gelatin in areas 18 so that the latter areas are not colored to an opaque level and we achieve desirable edge sharpening effects discussed later.
We have found also that the etch-bleach solution 14 and above-mentioned dye solution can be codispersed in the tank 10 and in effect simultaneously remove the silver bearing areas and dye the background clear gelatin to form the reversed master image 1c from the original master image 1a with less handling. This sequence is illustrated in FIG. 7. The stop action mentioned above, consisting of gentle rinsing in cool slowly circulating water then follows immediately after the combined etch and dye operation. The time required to simultaneously etch and dye is about the same as the time required previously to perform the etching operation.
ETCH-BLEACH EXAMPLES D.C. volts Immersion 2 and 3% H O, solution (Z= water-600 cc at F., cupric chloride- 10 gm,
citric acid-l50 gm, ureagm., water to make-l liter) DYE EXAMPLES Immerse plate 5 minutes in solution of 25 gms of dye material (D) per liter of water and rinse gently as above. D is selected according to desired spectral characteristic, solvency, and absorption properties of the gelatin. Excellent results in coloring relief gelatin red, to operate as barrier to actinic light in the blue or ultra violet range, have been obtained with each of the following: Dl-Pontacyl (DuPont), D2-Rubine Red (Du- Pont), D3-Crocein Scarlet (Kodak).
COMBINED ETCH-BLEACH-DYE EXAMPLES D.C. volts Immersion Solution (at 70F.) across electrodes Time 45% any one of the 4 volts at 5 min. then solutions X, Y, or Z 1 amp. rinse gently above; 45% solution of and dry as 3% H 0 10% solution above of one of the dye materials D1, D2 or D3 above (25 gm/liter of H 0) It is important that line elements such as 31,32 (FIG. 6) in the master image In, which may have precise thicknesses and spacings specified to tolerances of the order of 10.0005 inches, be reproduced in reversed image 1c without distortion so that the latter image remains useful as a master pattern for photographiccopying upon the substitute resist material. Accordingly the effects obtained from the electrodes 11,20, the rinsing procedure to stop the etching and dyeing processes, the amount of dye imbibed and the environmental parameters of temperatureand time given above are all important and to an extent critical to the practice of the present invention.
The spacing of the electrodes 11 and 20 is also material. In practice we employ approximately a 1-inch spacing between the image surface of the master plate and electrode 20 and we prefer to position the image surface parallel to and slightly displaced from the vertical plane intersecting ridge 12 on electrode 11. In practice the approximate dimensions of tank 10 used in processing 16 by 20 inch rectangular plates are: 18 inches by 21 inches by 2 inches.
It may be useful to employ two different color dyes, for example one opaque to actinic light and another transparent to the same light, in order to obtain specific visual effects incidental to the printing process; e.g. to provide reference marks for positioning the master image for copying. For this we prefer to use a swab-type applicator 41 (FIG. 8) to manually apply the dye to select image areas such as 42. We have found also that local application of the exemplary etchbleach solutions above can be used to reverse select portions of the master image; for example a border pattern defining isolated terminal areas of a microelectronic device We have observed certain advantageous effects in respect to the reversed image and particularly sharpening of edges such as 50 in the dyed relief image 1c (FIGS. 1,7). These are reflected in the comparative densitometric traces of HG. 9 and are attributed to increased absorption of dye at edges due to vertical and horizontal penetration of the dye at the edges. In the silver image light transmittance is a function of silver density which varies gradually at edges. Thus edges have an uncertain or fuzzy" quality due to density gradient which can vary considerably in extent relative to exemplary-line width dimensions and tolerances (FIG. 6). By contrast when we limit the dye absorption stage so that the dye does not completely saturate the gelatin relief we obtain a differential dyeing effect at image edges, due to horizontal penetration of dye at edges, which effectively reduces. the fuzzy or uncertain light transmittance profile as indicated in FIG. 9.
Microscopic edge irregularities in the oi'iginal image accrue as a result of many factors including the integrity of the original artwork and the intensity and depth of exposure of the silver halide layer 3 (FIG. 1 If the silver halide layer is not exposed to its full depth, as occurs in actual practice using automated tracing apparatus such as the Gerber apparatus mentioned reviously, after the silver removal step a layer of gelatin 52 (FIG. 3) will remain in the formerly opaque image areas. This thinner layer will absorb some dye but with proper timing not enough dye to render it opaque to the wavelength of actinic light for which the dye has been selected.
In actual practice the edges 53 (FIG. 3) of the relief are not absolutely vertical but have gradual slope relative to the image and substrate planes. This would tend to increase the width of fuzziness in the light transmittance profile at image edges.
Nevertheless this effect is counter-acted in the reversal process by the differential edge absorption effect so that reversed artwork is more sharply delineated than the original master.
We have also used the foregoing in situ reversal technique as a means of adapting the automated artwork tracing; process to trace patterns which have large areas of opaqueness. The tracing apparatus is operated most efficiently when it is programmed to trace out image patterns which develop in the silver emulsion master into small silver areas in comparatively large background areas of clear gelatin. Accordingly, by the present reversal method it is possible to produce images with broad opaque elements of design and narrow transparent elements of design which would be produced otherwise only by cumbersome reprogramming and inefficient usage of the automated tracing apparatus.
Details of the operation of the apparatus in FIG. 4 are as follows: Fresh solution of etch-bleach material, with or without codispersed dye material, is introduced into tank 10. The plate is immersed and positioned in the tank and voltage is applied to the electrodes. When processed for the appropriate time the plate is removed and rinsed as previously explained. If not already dyed the plate is immersed in the dye solution in any appropriate vessel, not necessarily the processing tank, and dyed. With a separate dyeing phase a second rinse is required. In each instance the dyed and rinsed plates are dried.
We have shown and described above the fundamental novel features of the invention as applied to several preferred embodiments. It will be understood that various omissions, substitutions and changes in form and detail of the invention as described herein may be made by those skilled in the art without departing from the true spirit and scope of the invention. It is the intention therefore to be limited only by the scope of the following claims.
What is claimed is:
1. To adapt a master photocopying pattern consisting of a gelatin emulsion photograph, in which there is formed by suspended silver grains a high resolution high contrast master image of microelectric artwork, so that said photograph can be used as a master pattern in photocopying said master image in reverse, the method comprising:
reversing said image in situ by etching said suspended silver grains out of said emulsion and contacting the relief gelatin remaining in said photograph with a quantity of an absorptive dye which is only sufficient to color said gelatin to a threshold level of opaqueness to radiant energy in a given spectral range; the fidelity of resolution of details in the processed image being enhanced by:
5 collecting the waste particles formed in said silver grain dissolving operation at an electrified electrode positioned to attract said particles as they become separated from the photograph surface. 7
2. The method according to claim 1 wherein said resolution 10 fidelity is further enhanced by:
uniformly agitating the said photograph surface with a stream of electrolytically formed bubbles during the dissolution of said silver grains in order to expedite the separation of said waste particles from said surface.
3. The method according to claim 2 wherein said bubbles are formed by providing another electrified electrode positioned to interact electrolytically with the medium which causes said silver grains to dissolve and to project the bubbles forming by the electrolytic action upward in a planar stream formation, which is generally parallel and adjacent to the surface of the photograph, while the dissolving operation is in process.
4. In a photographic process for producing master patterns as photocopying masks for use in constructing intricate subminiature printed circuit devices photographically, said masks being formed originally by rapid image-wise scanning of a programmed beam of actinic radiation over a surface of a trans parent support plate covered by a film layer of high contrast high resolution silver halide emulsion followed by processing of said emulsion layer to form therein a fixed master pattern image consisting of areas of clear gelatin contrasting with areas of gelatin containing opaque grains of suspended silver, which master pattern is useful then for photocopying said master pattern image upon photosensitive resist material of one sensitivity, the improvement to adapt said process and pattern to print said image copies upon photosensitive resist material of reverse sensitivity, comprising:
subjecting the image on said master pattern to attack in situ by a dilute agent only until all traces of silver grains forming the opaque elements of the image have been fully dissolved;
simultaneously, while subjecting said image to said attack,
contacting the image surface with an electrolytically formed stream of gaseous bubbles projected adjacent and generally parallel to said surface;
simultaneously, during said attack, removing by electrophoretic attraction dissolved particles of gelatin and silver grains loosed by said attack and dislodged by said bubbles;
rinsing said attacked surface, in order to terminate the dissolving action of said solution, by gently immersing said master pattern in gently circulating clean water warmed to room temperature while avoiding contact with turbulent influent and efiluent currents of the same water; and contacting said master pattern with a solution of an absorptive dye substance until the gelatin remaining in relief upon said pattern after said attack becomes colored to a threshold level of opaqueness relative to actinic radiation which activates said resist material of reverse sensitivity.
5. The process of claim 4 wherein the exposure of said image-wise scanned beam produces an unsaturated silver grain image with a thin layer of clear gelatin underlying the silver grains which form the opaque image elements, said dye solution concentration and said contacting step being controlled to produce reverse image of high contrast with sharply defined edges.
6. The process of claim 4 wherein said dye contacting step is combined with said attacking step, in order to reduce handling of the master pattern, by codispersing said dye substance in said attacking solution.
7. The processof claim 4 wherein said attacking solution is:
equal parts solution X and 3 percent H 0 solution (X= copper sulfate-453.6 gms, citric acid-567.0 gms, potassium bromide-28.3 gms, water to make-3,785 cc).
8. The process of claim 4 wherein said attacking solution is:
equal parts solution Y and 3 percent H solution (Y= water-750 cc at 125 F, cupric chloride-l0 gm, citric acid-l0 gm, water to make-l liter).
9. The process of claim 4 wherein said attacking solution is:
equal parts solution 2 and 3 percent H 0 solution (Z= water-600 cc at 125 F, cupric chloride-l0 gm, citric acid-150 gm, urea-150 gm, water to make-l liter).
10. The process of claim 4 wherein said resist material of reverse sensitivity is actinically sensitive to light in a particular spectral region and said dye is selected to absorb said light.
11. The process of claim wherein a plurality of differently colored dye substances each opaque to the said reverse material actinic light are applied in stages to the said gelatin remaining in said pattern after removal of said silver grains in order to produce visual imaging effects useful for inspection or positional registration of said master pattern.
12. in a process for in situ reversal of a photomask having the form of a free silver opaque image in a transparent gelatin layer, which is used as a photocopying master in a microelectronic photofabrication process, said reversal process including the step of dissolving said gelatin selectively at sites of free silver and not elsewhere by immersion of said layer in a bath containing an etch-bleach solution the improvement comprising:
providing electrochemical efiects in said bath to promote movement of said dissolving gelatin and silver away from said free silver sites of said layer during said dissolving step, thereby promoting more effective circulation of said solution relative to said layer sites.
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