Process and composition for generation of acid

Organic compounds -- part of the class 532-570 series – Organic compounds – Phosphorus esters

Reexamination Certificate

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C558S194000

Reexamination Certificate

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06307085

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a process for generation of acid, and to a medium for use in this process. Preferred forms of the present process are useful for generating images.
Images can be generated by exposing a photosensitive medium to light in an imagewise fashion. Some conventional non-silver halide photosensitive compositions contain molecules which are inherently photosensitive, so that absorption of electromagnetic radiation brings about decomposition of, at most, as many molecules as photons absorbed. However, a dramatic increase in the sensitivity of such photosensitive compositions can be achieved if the absorption of each photon generates a catalyst for a secondary reaction which is not radiation-dependent and which effects conversion of a plurality of molecules for each photon absorbed. For example, systems are known in which the primary photochemical reaction produces an acid (which will hereinafter be called the “primary acid” or “first acid”), and this acid is employed catalytically to eliminate acid-labile groups in a secondary, radiation-independent reaction. Such systems may be used as photo-resists: see, for example, U.S. Pat. Nos. 3,932,514 and 3,915,706; and Ito et al., “Chemical Amplification in the Design of Dry Developing Resist Materials”, Polym. Sci. Eng., 23(18), 1012 (1983).
Among the known acid-generating materials for use in this type of process employing secondary, non-radiation dependent reactions are certain diazonium, phosphonium, sulfonium and iodonium salts. These salts, hereinafter referred to as superacid precursors, decompose to produce superacids, i.e., acids with a pKa less than about 0, upon exposure to electromagnetic radiation. Other materials decompose to produce superacids in a similar manner. However, in the absence of a spectral sensitizer, the known superacid precursors decompose to produce superacid only upon exposure to wavelengths which the precursors absorb, which are typically in the short ultraviolet region (below about 280 nm). The use of such wavelengths is often inconvenient, not least because special optical systems must be used.
It is known that various dyes can sensitize the decomposition of superacid precursors upon absorption by the dye of radiation which is not significantly absorbed by the superacid precursor; see, for example, European Patent Application Publication No. 120,601. Unfortunately, however, due to the very low pKa of the superacid, many such dyes are protonated by the superacid, so that no unbuffered superacid is produced (i.e., the sensitizing dye buffers any superacid produced). Since no unbuffered superacid is released into the medium, decomposition of superacid precursors sensitized by these dyes cannot be used to trigger any secondary reaction which requires the presence of unbuffered superacid.
(The term “unbuffered superacid” is used herein to refer to superacid which is not buffered by the sensitizing dye, and which thus provides an acidic species stronger than that provided by the protonated sensitizing dye. Because of the extreme acidity of superacids and their consequent tendency to protonate even species which are not normally regarded as basic, it is possible, and indeed likely, that “unbuffered superacid” will in fact be present as a species buffered by some component of the imaging medium less basic than the sensitizing dye. However, such buffering by other species may be ignored for the present purposes, so long as superacid is present as an acidic species stronger than that provided by superacid buffered by the sensitizing dye.)
Crivello and Lam, “Dye-Sensitized Photoinitiated Cationic Polymerization”, J. Polymer Sci., 16, 2441 (1978) and Ohe and Ichimura, “Positive-Working Photoresists Sensitive to Visible Light III, Poly(tetrahydropyranyl methacrylates) Activated by Dye-Sensitized Decomposition of Diphenyliodonium Salt”, J. Imag. Sci., Technol., 37(3), 250 (1993) describe small sub-groups of sensitizing dyes which are sufficiently non-basic that the buffered superacids produced can effect certain acid-catalyzed reactions. However, the need to restrict the choice both of sensitizers and of acid-catalyzed reactions may make it difficult to design an efficient imaging system at a specific desired wavelength.
A variety of non-basic, polycyclic aromatic compounds sensitize decomposition of superacid precursors to produce unbuffered superacid upon exposure to longer wavelengths than the superacid precursors absorb themselves. Such materials are discussed in, for example, DeVoe et al., “Electron Transfer Sensitized Photolysis of 'Onium salts”, Can. J. Chem., 66, 319 (1988); Saeva, U.S. Pat. No. 5,055,376; and Wallraff et al., “A Chemically Amplified Photoresist for Visible Laser Imaging”, J. Imag. Sci. Technol., 36(5), 468-476 (1992).
U.S. Pat. Nos. 5,286,612 and 5,453,345 describe a process by which a wider variety of dyes than those discussed above may be used together with a superacid precursor to generate free (unbuffered) superacid in a medium. In this process, acid is generated by exposing a mixture of a superacid precursor and a dye to actinic radiation of a first wavelength which does not, in the absence of the dye, cause decomposition of the superacid precursor to form the corresponding superacid, thereby causing absorption of the actinic radiation and decomposition of part of the superacid precursor, with formation of a protonated product derived from the dye; then irradiating the mixture with actinic radiation of a second wavelength, thereby causing decomposition of part of the remaining superacid precursor, with formation of unbuffered superacid. Generation of superacid by exposure to the second wavelength may be sensitized by one of the non-basic, polycyclic aromatic sensitizers mentioned above. (For convenience, the type of process disclosed in this patent will hereinafter be called the '612 process.)
U.S. Pat. Nos. 5,334,489 and 5,395,736 describe processes for the photochemical generation of acid and for imaging using conventional ultra-violet sensitizers; these processes will hereinafter collectively be called the '489 process.
U.S. Pat. No. 5,441,850 and its continuation-in-part, copending application Ser. No. 08/430,420, filed Apr. 29, 1995, now U.S. Pat. No. 5,631,118 (and the corresponding International Application No. PCT/US95/05130, Publication No. WO 95/29068) all describe a variation of the aforementioned '612 process which uses an imaging medium comprising a sensitizing dye having a first form and a second form, the first form having substantially greater absorption in a first wavelength range than the second form. The medium is exposed to actinic radiation in this first wavelength range while at least part of the sensitizing dye is in its first form so that the sensitizing dye decomposes at least part of a superacid precursor, with formation of unbuffered superacid. The medium is then heated to cause, in the exposed areas, acid-catalyzed thermal decomposition of a secondary acid generator and formation of a secondary acid. This secondary acid brings about a change in absorption of an image dye and thereby forms an image. Finally, in the non-exposed areas of the medium, the sensitizing dye is converted to its second form, thus removing the absorption in the first wavelength range caused by the first form of the sensitizing dye, and lowering the minimum optical density (D
min
) in this wavelength range. (For convenience, the type of process disclosed in this patent and these applications will hereinafter be called the '850 process.)
The entire disclosures of the aforementioned U.S. Pat. Nos. 5,286,612; 5,453,345; 5,334,489; 5,395,736 and 5,441,850 and copending application Ser. No. 08/430,420 are herein incorporated by reference.
The aforementioned '612, '489 and '850 processes all make use of a secondary acid generator, the thermal decomposition of which is catalyzed by the unbuffered superacid produced in the primary, radiation-dependent reaction. In effect, the secondary acid generator acts as

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