Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1998-03-11
2001-01-30
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S325000, C430S326000, C430S331000
Reexamination Certificate
active
06180319
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for developing and/or stripping aqueous-developable photosensitive compositions in which less residue, or sludge, is produced. More specifically, it is related to such processes in which the photosensitive composition includes a hexaarylbiimidazole photoinitiator.
BACKGROUND OF THE INVENTION
Photosensitive compositions are well known and are useful as photoresists in the formation of printed circuit materials, in the formation of lithographic printing plates, and in proofing applications. In such systems, actinic radiation impinges on a material containing photoactive components to induce a physical or chemical change in that material. The latent image thereby produced can then be processed to form a patterned mask or an image. The photosensitive systems can be positive-working or negative-working. In positive-working systems, the areas exposed to actinic radiation are removed in the post-exposure processing step; in negative-working systems, the areas not exposed to actinic radiation are removed. Particularly useful compositions are negative-working photopolymerizable and/or photocrosslinkable compositions, hereinafter referred to collectively as “photopolymerizable.” In such systems, exposure to actinic radiation initiates polymerization and/or crosslinking reactions, resulting in insolubilization of the material in suitable developer solvents. The latent image is developed by treating with the developer solvent. The photopolymerizable compositions generally contain a binder, a monomeric or oligomeric material capable of polymerizing and/or cross-linking, and a photoinitiator.
In recent years there has been increased emphasis on aqueous-developable, or aqueous-processable, compositions. Such compositions have significant advantages in terms of lower costs and environmental safeguards. Aqueous-developable systems frequently use binders having acid groups which are removable in aqueous alkaline solution. In continuous processes for the production of printed circuit materials, lithographic printing plates and proofing materials, the developer solution is recycled and used repeatedly in the development step. A problem has been the accumulation of residues, known collectively as “sludge,” in the recycled developer. This sludge reduces the amount of time the developer can be used without clean up and thus reduces efficiency. Furthermore, the sludge can be intractable and difficult to remove.
Frequently, after the photoresist has served its purpose, it is removed from the substrate in what is known as a stripping step. There can also be an accumulation of sludge in the stripping solution.
It would be desirable to have a process for processing aqueous-processable photopolymerizable compositions which results in lower sludge accumulation.
SUMMARY OF THE INVENTION
This invention relates to a process for producing a pattern on a substrate, said process producing less sludge. The process comprises the steps:
(a) applying an aqueous-developable photoresist to a surface of a first substrate, said photoresist comprising a photoinitiator;
(b) imagewise exposing to actinic radiation to produce exposed and non-exposed areas in the photoresist;
(c) treating the imagewise exposed photoresist with a sample of aqueous alkaline solution, resulting in removal of either the exposed or the non-exposed areas of the photoresist; and
(d) repeating steps (a) to (c) at least 5 times, wherein each repetition uses a new sample of photoresist and a new substrate and essentially the same sample of aqueous alkaline solution;
wherein the photoinitiator comprises at least one hexaarylbiimidazole compound having at least one hydrophilic group, and wherein treatment of 3 grams of unexposed photoresist with 100 grams of the aqueous alkaline solution produces less than 0.05 grams precipitate.
In a second embodiment, this invention relates to a process for removing a pattern of processed photoresist from a substrate, said process comprising the steps:
(a) treating the processed photoresist with a sample of a stripper solution, resulting in removal of the photoresist mask; and
(b) repeating step (a) at least 5 times, wherein each repetition uses a new substrate and processed photoresist and essentially the same sample of stripper solution;
wherein the photoresist comprises at least one hexaarylbiimidazole compound having at least one hydrophilic group, and wherein treatment of 3 grams of processed photoresist with 100 grams of the stripper solution produces less than 0.05 grams precipitate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process of the invention is a continuous process for the development of aqueous-developable photoresists in which less sludge is produced. By “aqueous-developable” is meant a material in which either exposed or non-exposed areas can be preferentially removed by a developer solution which is water-based and contains less than 10% by weight of organic material. By “photoresist” is meant a photosensitive composition which can be used to form a printed circuit material, a lithographic printing plate or a proofing product. By “sludge” is meant material which accumulates in the developer solution which is insoluble in the developer solution and decreases the efficiency of the developer solution by permitting redeposition of material on the already developed substrate.
The first step in the process of the invention is: (a) applying an aqueous-developable photoresist to a surface of a first substrate, said photoresist comprising a photoinitiator; wherein the photoinitiator comprises a hexaarylbiimidazole compound having at least one hydrophilic group.
Hexaarylbiimidazoles, abbreviated as “HABI”, are generally 2,4,5-triphenylimidazolyl dimers, and are well known photoinitiators. HABIs and photosensitive systems using HABIs have been disclosed in, for example, Chambers, U.S. Pat. No. 3,479,185; Chang et al., U.S. Pat. No. 3,549,367; Cescon, U.S. Pat. No. 3,684,557; Dessauer, U.S. Pat. Nos. 4,252,887 and 4,311,783; Chambers et al., U.S. Pat. No. 4,264,708; Wada et al., U.S. Pat. No. 4,410,621; Tanaka et al., U.S. Pat. No. 4,459,349; and Sheets, U.S. Pat. No. 4,622,286.
A HABI that is frequently used in photopolymerizable systems, including photoresists, is 2,2′,-bis(
o
-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-biimidazole, commonly known as “ortho-chloro HABI” (o-Cl-HABI). Alternative nomenclature for o-Cl-HABI is 2,2′-bis(2-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-bi-1H-imidazole. Surprisingly and unexpectedly, it has been found that the amount of sludge in a recycled developer solution can be significantly reduced by using a HABI which has at least one hydrophilic substituent, even though the HABI with the hydrophilic substituent is generally substantially insoluble in water.
Any hydrophilic substituent can be used as long as it does not significantly interfere with the photosensitivity of the HABI or adversely impact any other properties of the photoresist. By “hydrophilic” is meant a substituent which readily associates with water. Examples of suitable hydrophilic substituents include alkoxy groups, such as methoxy and ethoxy; hydroxy; dialkyl amino groups such as diethylamino and dipropylamino; carboxylic acid groups and their alkyl esters, amides and salts. More than one type of hydrophilic substituent can also be used. Alkoxy substituents are preferred, with methoxy being particularly preferred.
It is preferred that the HABI also have at least one chloro substituent. Without any chloro substituent the HABIs are generally less photosensitive and the resulting photoresists require longer exposure times. It is more preferred, that the HABI have at least two chloro substituents.
Examples of suitable photoinitiators include 2,2′,5-tris-(
o
-chlorophenyl)-4-(3,4-dimethoxyphenyl)-4′,5′-diphenyl-1,1′-biimidazole, abbreviated as “TCDM-HABI”; 2,2′4,4′-tetra-(
o
-chlorophenyl)-5,5′-bis-(3,4-dimethoxyphenyl)-1,1′-biimidazole, abbreviated as “TCTM-HAB
E. I. Du Pont de Nemours and Company
Young Christopher G.
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