In-situ reclamation of master patterns for printing microcircuit images on reversely sensitized material

Claim 2

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.

Claim 3

In a photographic process for producing master patterns as photocopying masks for use in constructing intricate sub-miniature 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 transparent 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 effluent 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.

Claim 4

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.

Claim 5

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.

Claim 6

The process of claim 4 wherein said attacking solution is: equal parts solution X and 3 percent H2O2 solution (X copper sulfate-453.6 gms, citric acid-567.0 gms, potassium bromide-28.3 gms, water to make-3,785 cc).

Claim 7

The process of claim 4 wherein said attacking solution is: equal parts solution Y and 3 percent H2O2 solution (Y water-750 cc at 125* F, cupric chloride-10 gm, citric acid-10 gm, water to make-1 liter).

Claim 8

The process of claim 4 wherein said attacking solution is: equal parts solution Z and 3 percent H2O2 solution (Z water-600 cc at 125* F, cupric chloride-10 gm, citric acid-150 gm, urea-150 gm, water to make-1 liter).

Claim 9

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.

Claim 10

The process of claim 10 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.

Claim 11

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 effects 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.