Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-12-31
2003-07-29
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S170000, C528S026000, C528S125000, C528S126000, C528S128000, C528S171000, C528S172000, C528S173000, C528S174000, C528S176000, C528S183000, C528S185000, C528S220000, C528S229000, C528S272000, C430S270100, C525S436000
Reexamination Certificate
active
06600006
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a positive-type photosensitive polyimide precursor and a composition comprising the same. More specifically, the present invention relates to a polyamic ester having one or more reactive end-capping groups at either or both terminals of its molecular chain, wherein the ester structure of the polyamic ester degrades to yield carboxylic acid upon generation of acid by exposure; a mixture of at least one polyamic ester and at least one polyamic acid, the polyamic acid also having one or more reactive end-capping groups at either or both terminals of its molecular chain; and a composition comprising the mixture for use as a photosensitive polyimide precursor material.
2. Description of Background Art
In the field of semiconductor devices, and especially in the areas of semiconductor memory devices and liquid crystal display (LCD) devices, much effort has been made to date to improve the level of integration, densification, integrity, reliability and speed of semiconductor devices. In this connection, many advantages of organic materials, such as facility of processing and purification, are noteworthy. However, only those organic materials that are thermally stable at a temperature of 200° C. or higher may be used in this field.
Polyimide resins were approved suitable for the purposes as described above because of the following reasons: Polyimide resins exhibit excellent thermal resistance and mechanical strength while possessing excellent electrical properties by virtue of having a low dielectric constant and a high insulation capacity. Polyimide resins also provide coating films that exhibit excellent planation properties. The low level of impurities in polyimide resins also helps to increase the integrity and reliability of final semiconductor devices. From an application perspective, polyimide resins are easy to process in forming fine patterns.
Generally, polyimide resins are produced by a two-step condensation polymerization method. First, diamine and dianhydride are subjected to polymerization in a polar solvent such as NMP, DMAc or DMF to provide a polyimide precursor solution. Second, the polyimide precursor solution is coated onto a silicon wafer or a glass substrate and then cured through heat treatment. Commercial polyimide products for use in electronic industry are supplied as a polyimide precursor solution or as a polyimide film. In the field of semiconductor devices, polyimide precursor solutions are commonly used.
FIG. 1
shows a sectional structure of a semiconductor device, wherein a polyimide resin is applied in a buffer coating film of the device. Plastic packages of large scale integration (LSI) are subject to various physical forces, including contraction after a packaging process as well as thermal stress due to differences in coefficients of thermal expansion between a chip and the resin. These physical forces result in either cracks in a passivation film or damage to metal lines or both. In order to alleviate these types of problems, a buffer layer is formed between the chip and the package using a polyimide film. In order to obtain a buffer effect, the thickness of the polyimide film buffer layer should be at least 10 &mgr;m. Generally, thicker polyimide films result in increased buffer effects and helps to increase final production yield of semiconductor products. As shown in
FIG. 1
, fine patterns should be formed in the polyimide film, such as interconnection of electrodes and wire bonding pads. Typically, via holes in a polyimide film are formed by coating a conventional photoresist onto the polyimide film and etching the photoresist film. Recently, several photosensitive polyimides have been proposed, which were prepared by modifying polyimides to have inherent photosensitivity.
When conventional non-photosensitive polyimides are used in the buffer coating film, a separate etching process is required, and via holes for wire bonding and connections between metal lines are formed by using a photoresist. When photosensitive polyimides are employed, the use of a photoresist can be omitted. The elimination of the need for the photoresist reduces the overall buffer coating process by about 50% and results in higher productivity and lower production costs. Additionally, the final steps in the assembling process is reduced, which in turn further contributes to enhancing final production yield. Based on these advantages, research on photosensitive polyimides has been actively pursued.
The first practical photosensitive polyimide was developed by Rubner et al. on behalf of Siemens AG, Germany (U.S. Pat. No. 3,957,512), wherein photosensitive groups are attached to a polyimide precursor, i.e., polyamic acid via ester bonds. According to this U.S. patent, a polyimide precursor solution is coated onto a substrate to form a film, and the film is exposed to UV light so that photopolymerization can occur in the exposed region and form cross-linkages between the precursor molecules. The film is then subjected to development using an organic solvent to remove unexposed regions, followed by thermal treatment. During the thermal treatment, an imidization reaction occurs, and the ester-bonded photosensitive groups degrade to provide a desired pattern made of polyimide.
U.S. Pat. No. 4,243,743 assigned to Toray Co., Ltd., Japan, proposes a photosensitive polyimide, wherein photosensitive groups and compounds with an amino group are attached to a polyamic acid via ion bonds. Such a photosensitive polyimide is advantageous over conventional photosensitive polyimides from the standpoint of ease in preparation and relatively fewer toxic side products.
Currently, photosensitive polyimides are preferred over negative-type photosensitive polyimides, because positive-type photosensitive polyimides exhibit superior resolution. Moreover, positive-type photosensitive polyimides have a relatively small area of exposure and, consequently, are associated with a lower frequency of inferior products. Additionally, alkaline solutions are used as a developer for positive-type photosensitive polyimides, and since alkaline solutions to not generate environmental pollution issues, they enable reduction of processing costs. Negative-type photosensitive polyimides, on the other hand, use toxic organic solvents such as NMP and DMAc as developers and are problematic considering the cost factor and the environmental pollution caused by the liquid waste products. Production of positive-type photosensitive polyimides, however, has not been truly commercialized to date because of a large difficulty that must be overcome.
In prior art teachings relative to positive-type photosensitive polyimides, Japanese Laid-Open Publication Nos. 52-13315 and 62-135824 disclose a patterning method whereby a pattern is formed by virtue of the different dissolution rate of exposed and unexposed regions while using a mixture of polyamic acid as a polyimide precursor and naphthoquinonediazide as a dissolution inhibitor. Japanese Laid-Open Publication No. 64-60630 discloses a method for patterning using a mixture of soluble polyimide having hydroxyl groups and naphthoquinonediazide. Japanese Laid-Open Publication No. 60-37550 discloses a method for patterning by using a photosensitive polyimide, wherein the photosensitive polyimide was prepared through connecting an o-nitrobenzylester group as a photosensitive group to a polyimide precursor via an ester bond. These prior art teachings, however, are not satisfactory because of the following disadvantages. Firstly, the difference in dissolution rate between exposed regions and unexposed regions is not sufficient to form a pattern having high resolution (See: Japanese Laid-Open Publication Nos. 52-13315 and 62-135824). Secondly, the prior polyimide precursors are limited in structure and are poor in transparency and other physical properties (See: Japanese Laid-Open Publication No. 60-37550). Thirdly, the relatively low sensitivity makes an increase of film thickness difficult (See: Jap
Jung Myung Sup
Jung Sung Kyung
Kim Bong Kyu
Moon Bong Seok
Park Yong Young
Hampton-Hightower P.
Lee & Sterba, P.C.
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