Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-07-30
2001-07-03
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S277100, C430S278100, C430S271100, C430S909000, C430S905000, C430S944000, C525S056000, C525S060000, C525S061000, C522S153000, C522S154000
Reexamination Certificate
active
06255033
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of imaging, particularly resist imaging, more particularly to thermal resist imaging, and still more particularly laser direct imaging. The invention describes novel positive-acting thermal resist compositions, thermal resist structures, thermal resist processes, and thermal resist systems, as well as novel synthetic procedures for the formation of the resist materials.
2. Background of the Art
The merits of Laser Direct Imaging (LDI) have been recognized for a long time in the printing industry for production of offset printing plates, and also in printed circuit board (PCB) production. LDI offers the potential benefits of better line quality, just in-time processing, improved manufacturing yields, elimination of film costs, and other recognized advantages. In direct imaging methods, the exposure of only the selected areas of the heat-sensitive coating by a suitably focused source of energy effects required changes in the coating composition. See, e.g. U.S. Pat. No. 4,724,465, U.S. Pat. No. 5,641,608 (McDermid), U.S. Pat. No. 5,713,287 (Gelbart), the teachings of which are incorporated herein by reference.
Thermally-sensitive imaging elements are classified as compositions that undergo chemical transformation(s) in response to exposure to, and absorption of, suitable amounts of heat energy. The nature of thermally-induced chemical transformation may be to ablate the composition, or to change the solubility of the composition in a particular developer, or to change tackiness of the surface, or to change the hydrophilicity or the hydrophobicity of the surface of the thermally-sensitive layer. As such, selective heat exposure of predetermined areas (image-wise distribution of heat energy) of a film or layer formed of a thermally sensitive composition has the capability of directly or indirectly producing a suitably imaged pattern of composition which can serve as a resist pattern in PCB fabrication, or in production of lithographic printing plates.
In a manner similar to that with photoresists, heat-sensitive compositions can be positive-working or negative-working. With a positive-working heat-sensitive composition, the selective exposure of the film to an appropriately focused beam that can generate the requisite thermal energy will either (a) ablate the so-exposed composition, in which case the desired graphic pattern is directly produced, and the pattern is represented by the remaining film portions not exposed to the focused heat energy and thus not ablated, or (b) cause the so-exposed composition to become differentially more soluble in a suitable solvent, in which case what is essentially a latent image is produced in the film. This latent image enables the film to be dissolved in the heat-exposed areas and remain insoluble and left behind in the non-heat-exposed areas, providing the desired pattern. With a negative-acting heat-sensitive composition, selective exposure of the film to the appropriately focused beam of the requisite thermal energy causes the so-exposed areas to become differentially less soluble in a suitable developer, such that contact with the developer dissolves away the areas that are not heat-exposed and leaves behind the heat-exposed areas as the desired pattern.
Through use of the heat-sensitive imaging elements, the ability to produce a pattern on a substrate surface by direct imaging without use of a phototool is greatly enhanced because the imaging beam need only be a suitably focused source of required thermal energy, such as can be formed from low-cost solid state lasers, as opposed to the focused source of narrow-band radiation of a particular wavelength required for direct imaging of photoresists. Focused thermal energy sources, such as an infrared laser beam, are inherently better suited for use in commercial-scale operations in terms of expense, life and reliability than the UV beams needed for direct imaging of many photo-sensitive compositions. Moreover, the heat-sensitive compositions, which need undergo only thermally-induced composition change rather than a photo-induced change in components or compositions, should be inherently less complicated than photo-sensitive compositions in direct imaging processes. As such, not only can thermally-sensitive compositions be formulated in the cost-effective manner needed for industrial uses such as PCB fabrication, but their simpler mechanism of operation enables operation in room light or day light and tends to provide or enable generally better shelf stability.
Positive working photosensitive compositions based on novolak-diazoquinone resins are the main imaging material of the computer chip industry (see, e.g. R. R. Dammel, “Diazonaphthoquinone-based Resists”, Tutorial text No. 11, SPIE Press, Bellingham. Wash., 1993).
Compositions of light sensitive novolak-diazoquinone resins are also widely used in the printing plate fabrication. The light sensitive diazonaphthoquinone derivatives (DNQ) added to novolak resins (a phenol-formaldehyde condensation polymer) slows down the dissolution of the resin, and the exposed films (with the photoinduced decomposition product of the DNQ) dissolves even somewhat faster than the pure novolak films. A revised molecular mechanism of novolak-DNQ imaging materials was recently published (A. Reiser,
Journal of Imaging Science and Technology
, Volume 42, Number 1, January/February 1998, p.p. 15-22) and teaches that the basic features of the imaging phenomena in novolak-diazonaphthoquinone compositions is the observed inhibition of dissolution (of the resin), which inhibition is based on the formation of phenolic strings by the interaction of the strong hydrogen acceptor which acts as a solubility inhibitor with the OH groups of the resin. On exposure, the phenolic strings are severed from their anchor by a thermal effect: the Wolff rearrangement, which follows photolysis of the diazoquinone moiety of the inhibitor molecule. This rearrangement is not only very fast, but also highly exothermic (delta H° is at least −66 kcal/mol). The sudden appearance at the location of the solubility inhibitor of a heat pulse of that magnitude causes a temperature spike of not less than about 220° C. At the high temperature that is produced, the phenolic string is severed from its anchor at the DNQ and becomes inactive (dispersed), because it is no longer held together by the inductive effect of the solubility inhibitor.
This model may explain the fact that a wide range of heat sensitive compositions based on novolak resins where different types of inhibitors were incorporated have appeared in patent literature and in commercial announcements. For example, positive working direct laser addressable printing form precursors based on phenolic resins sensitive to UV, visible and/or infra-red radiation were described (see, e.g. U.S. Pat. No. 4,708,925 (Newman, 3M); U.S. Pat. No. 5,372,907 (Haley et. al., Kodak); U.S. Pat. No. 5,491,046 (DeBoer et. al., Kodak)). In U.S. Pat. No. 4,708,925, the phenolic resin dissolution in alkaline solution was decreased by a radiation sensitive onium salt instead of DNQ, with the native solubility of the resin being restored upon photolytic decomposition of the onium salt. The onium salt composition is intrinsically sensitive to UV radiation and can be additionally sensitized to infra-red radiation. U.S. Pat. Nos. 5,372,907 and 5,491,064 utilize direct positive working systems based on a radiation induced decomposition of a latent Bronsted acid to increase the solubility of the resin matrix on imagewise exposure. All three described compositions can be additionally utilized as a negative working system with additional processing after imaging and predevelopment.
WO 97/39894 (Horsell) describes a heat sensitive composition and a process for making lithographic printing plates by laser direct imaging (LDI). The composition is based on a complex of a phenolic resin and a range of inhibitors containing strong hydrogen acceptors, examples of which are nit
Levanon Moshe
Lurie Emmanuel
Malikov Sergei
Naigertsik Oleg
Postel Larisa
Creo Ltd.
Le Hoa Van
Lee Sin J.
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