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
2000-06-26
2003-09-30
Ashton, Rosemary (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
C430S326000, C430S905000
Reexamination Certificate
active
06627377
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a positive photosensitive polyimide composition, insulation film formed therefrom and to a method for forming insulation film pattern using the same.
BACKGROUND ART
Photosensitive resin compositions are classified into A) polarity-changing type wherein the polarity of the exposed regions is changed so that the solubility thereof is changed, B) cutting type wherein chemical bonds are cut by exposure and the exposed regions are solubilized, and C) cross-linking type wherein cross-linking reaction proceeds so that exposed regions are insolubilized. The polarity-changing type may be used as either positive working or negative working composition depending on the composition of the developing solution. The cutting type may be used as positive working composition, and the cross-linking type may be used as negative working composition in theory. The cross-linking type photosensitive materials have a disadvantage in carrying out microscopic processing with high resolution that the exposed regions are swollen by the developing with an organic solvent.
In recent years, the molding materials used for overcoating flexible printed circuits, interlayer insulation films of multilayer substrates, insulation films and passivation films of solid elements in semiconductor industry, as well as the interlayer insulation materials of semiconductor integrated circuits and multilayer printed circuit boards are demanded to have good heat resistance. Further, the need to attain higher densification and higher integration demands photosensitive heat-resisting materials.
The semiconductor substrates which are used as semiconductor integrated parts in microelectronic industry are covered with photoresists. Photoresist relief structures are formed by forming images and subsequent development of the photoresist layers. The relief structures are used as the masks for preparing circuit patterns on the semiconductor substrates. By this processing cycle, the relief structure of a microchip can be transferred to a substrate.
Photoresists include two different types, that is, positive working photoresist and negative working photoresist. These are different in that the exposed regions of the positive working photoresist is removed by development so that the non-developed regions are left on the substrate, while the exposed regions of the negative working photoresist are left as the relief structure. The positive working photoresists have intrinsically high image resolutions so that they are suited for production of VLSIs (large scale integrated circuits).
Conventional positive working photoresists contain a type of novolak resin which is soluble in aqueous alkali and a photosensitive quinone diazide which decreases the solubility of the resin in alkali. When the photoresist layer is irradiated, the quinone diazide is photoexcited so as to be converted to carboxylic acid, so that the solubility in alkali of the exposed regions is increased. Thus, by developing the photoresist with an aqueous alkali, a positive working photoresist relief structure is obtained (U.S. Pat. No. 36,664,735 etc).
The characteristics of the photoresist compositions used in industries are the solubility of the photoresist in the solvent to be applied, the photosensitization rate of the photoresist, the developing contrast, the solubility of the developing solution acceptable from the view point of environment, adhesiveness of the photoresist, dimensional stability at high temperatures, and abrasion resistance.
The photoresist relief structures obtained by the exposure and development are usually subjected to heat treatment (postbake) at a temperature of 120° C. to 180° C. The purpose of this treatment is to promote the adhesiveness of the photoresist with the substrate, curing of the photoresist structure, and removal of all of the remaining volatile components to decrease the erosion in the subsequent etching step.
However, in plasma etching, the substrates are subjected to a temperature higher than 200° C. The photoresists containing as the base a novolak resin and a stabilizing improver cannot be thermally stabilized at a temperature of not lower than 180° C.
Polyimide resins are resistant to high temperature of about 400° C. and are stable to chemicals. Therefore, they are useful in forming heat-resisting photoresist layers,
Conventional polyimide photoresists are negative-type photoresists. The system of the negative-type photoresists is based on polyamic acid polymer having photoreactive side chains. However, this basic material has problems in that it has a poor storage stability, a very slow sensitizing rate, and an excess structural shrinkage after development and curing (the rate of shrinkage after baking is about 60%). With this composition, to attain a high resolution, exposure of about 10 minutes is necessary. Further, high concentration solutions thereof for forming thick films have especially poor storage stabilities.
With positive-type photoresists, high resolution is attained, exposure time is short and developing properties with alkali are excellent. Positive working high temperature type photoresist having phenol group was developed. A polyoxazole precursor was synthesized by the reaction between 3,3′-dihydroxy-4,4′-diaminobiphenyl and isophthalic acid dichloride. This composition is mixed with o-quinone diazide or naphthoquinone diazide to form a high sensitive positive working photosensitive polyoxazole precursor, and polyoxazole having a heat resistance and mechanical properties comparable to those of polyimide membrane is formed after processing (U.S. Pat. No. 4,339,521 and U.S. Pat. No. 4,395,482).
A solvent-soluble polyimide was synthesized by the reaction of hexafluoro-2,2-bis(hydroxyaminophenol)propane with hexafluoro-2,2-bis-(dicarboxyphenyl)propane dianhydride (6FDA) or with 3,4,3′,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) or with 5,5′-oxy-bis-1,3-isobenzofurandione (4,4′-oxydiphthalic acid dianhydride), and positive working photosensitive polyimides were prepared by mixing the polyimides and o-naphthoquinone diazide, respectively. In this method (Japanese Laid-open Patent Application (Kokai) No. 64-60630 and U.S. Pat. No. 4,927,736), the fluorine atom-containing polyimides are soluble in polar solvents. A novel method in which polyimide solutions are directly formed by heating the polyimide at 140 to 160° C. in the presence of p-toluene sulfonic acid as a catalyst was employed. However, to separate the catalyst and the polyimide, a method in which the polyimide solution is poured into methanol to recover the polyimide resin as precipitates and the precipitates are re-dissolved, is employed, which method is unsuitable for industrial application.
Phenol group or carboxyl group is protected with tetrahydro-2H-pyranyl group to vanish the solubility in alkali. By adding a photoacid generator to the resultant and by irradiating the resulting composition with light, an acid is generated. By this acid, the block of the hydroxyl group or carboxyl group is decomposed so that the material is converted to soluble in alkali. By carrying out heat treatment after exposure, a plurality of blocks are catalytically removed by the acid, so that an amplification effect is obtained, thereby the composition is highly sensitized (T. Omote et al.; Macromol., 23, 4788 (1990), K. Naitoh et al.; Polym. Adv. Technol. 4, 294 (1993), K. Naitoh et al.; J. Photopolym. Sci. Technol. 4, 294 (1993), T. Yamaoka et al.; Photosensitive Polyimides Fundamental & Application, 177-211, Technomic Publish Company Inc. USA(1995)).
A positive-type photosensitive polyamic acid was reported, wherein the carboxyl group of polyamic acid is converted to ester of 2-nitrobenzyl alcohol to prevent dissolution in alkali, and upon irradiation with light, the ester of the 2-nitrobenzyl group is decomposed to generate a carboxylic acid so that the compound is converted to soluble in alkali (S. Kubota et al.; J. Macromol. Sci. Chem. A24 (10) 1407 (1987), Ao Yamaoka et a
Itatani Hiroshi
Matsumoto Shunichi
Ashton Rosemary
Birch & Stewart Kolasch & Birch, LLP
PI R&D Co., Ltd.
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