Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
1999-12-17
2002-10-22
Talbot, Brian K. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S532000, C427S553000, C427S165000
Reexamination Certificate
active
06468599
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of removing an organic polymer film, particularly, to a simple and convenient method of completely removing a polyimide film as an alignment film in the manufacture of a color filter substrate used in a liquid crystal display device. It is absolutely necessary to remove completely the polyimide film for the rework of a color filter substrate. And also, the present invention relates to a method of removing an organic polymer film on an array substrate.
2. Description of the Related Art
The manufacturing process of a cell of a liquid crystal display device includes the step of forming an organic polymer film serving to orient liquid crystal molecules followed by forming a color filter structure or an array structure on a substrate. The organic polymer film includes a film of, for example, polyimide resin (PI) and polyvinyl alcohol (PVA), and is formed on the entire surface of the substrate by a printing method or a spin coating method. Then, the film is baked, followed by applying an aligning process such as rubbing to the baked film so as to form an alignment film. However, where a defect is included in the organic polymer film thus formed, the entire substrate was discarded as a defective substrate. Since the substrate including a color filter structure or an array structure is prepared by employing a manufacturing technology of a very high level in order to achieve a high density and a high precision in a display device, the discarding of the entire substrate, which is defective, leads to an increased manufacturing cost.
In order to improve the situation, it is attempted to once remove the defective film of the organic polymer, followed by newly forming a satisfactory film. As the technique to remove the organic polymer film, some methods now in use for removing a photoresist film in the manufacturing process of a semiconductor device and the like, are applicable. For example, a wet etching is one of the well-known method for removing an organic polymer film in which the organic polymer film is dissolved in an appropriate solvent. In the case of a polyimide film, -butyrolactone, N-methyl pyrrolidone (NMP), etc. are used as the solvent. Even in the case of using such a solvent, it is impossible to remove completely the residual polyimide, with the result that a polyimide film having a thickness of about 10 to 100 is left unremoved on the substrate. Also known is a dry etching method such as a plasma etching method or an ozone ashing method. It may be possible to achieve the complete removal of the residual polyimide film by employing these dry etching methods. However, the dry etching method requires a vacuum apparatus and an exclusive ozone generator. In other words, a relatively costly and complex apparatus and manufacturing step is required in the dry etching method, compared with the other method. Such being the situation, the dry etching method has not yet been put to practical use. The dry etching method gives rise to an additional difficulty. Specifically, it is necessary to rotate or rock the substrate, making it difficult to deal with substrates of various sizes, particularly, a large substrate sized at 600×720 mm.
Japanese Patent Disclosure (Kokai) No. 6-202111 discloses a method of removing a polyimide liquid crystal alignment film. It is disclosed that the film is exposed to ultraviolet radiation having a wavelength of 230 to 300 nm, followed by dipping the film in a polar solvent or an alkaline solvent. However, it has been found that the ultraviolet radiation having a wavelength of 230 to 300 nm is transmitted through the underlying transparent conductive film of ITO (Indium-Tin-Oxide), though the transmission is only several percent, so as to do damage to the pigment contained in the color filter positioned below the ITO film. For example, discoloring is brought about in the pigment.
Also, it has been found that it is impossible to remove completely the polyimide film by only exposure to ultraviolet radiation having a wavelength of 230 to 300 nm.
As described above, it is unavoidable for an organic polymer film on a substrate for a cell of a liquid crystal display device to bear a defect caused by a defective printing or by a damage done during the aligning process such as rubbing. However, it was impossible to remove completely the organic polymer film for reworking the substrate. It is of high importance to develop a cheap and simple method for removing completely the organic polymer film such as a polyimide film attached to the substrate in order to improve the manufacturing yield and to reduce the manufacturing cost of the liquid crystal display device.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a simple and convenient method of completely removing an organic polymer film on a substrate.
Another object of the present invention is to provide a simple and convenient method of completely removing a polyimide film used as an alignment film but being defective in the manufacture of a color filter substrate and an array substrate for a liquid crystal display device. The complete removal of the defective polyimide film is absolutely necessary for the reworking of the substrate. It follows that an additional object of the present invention is to provide a method which permits improving the manufacturing yield of a cell of a liquid crystal display device.
Still another object of the present invention is to provide a simple and convenient apparatus for completely removing an organic polymer film on a substrate.
According to the present invention, an organic polymer film, which is to be removed from a substrate surface, is exposed to ultraviolet radiation having a wavelength of 180 nm or less so as to decompose and remove the organic polymer film. This particular removing method is useful for removing an alignment film comprising an organic polymer such as polyimide to rework the substrate.
The principle of the removing method is shown in FIG.
1
. To be more specific, the film is considered to be removed by a breaking function, that is, each bond of organic polymer in the film is broken by the energy of the irradiated ultraviolet radiation, and by an oxidizing function performed by oxygen within the air atmosphere, which is excited by the energy of the ultraviolet radiation. In general, the coupling energy (eV/molecule) between adjacent atoms contained in an organic molecule is mainly: C—N bond (3.02); C—C bond (3.60); C—H bond (4.29); and C═C bond (6.29). The energy (E) of the ultraviolet radiation is determined by:
E=hc/e&lgr;
where h represents the Planck's constant (6.626×10
−34
[J·sec]), c represents the speed of light (2.998×10
8
[m/sec]), e represents the energy of a single electron (1.602×10
−19
[J/eV]), and &lgr; represents the wavelength of the light [m]. The energy of the ultraviolet radiation emitted from a conventional low pressure mercury lamp having an output wavelength of 254 nm is 4.88 eV, which is smaller than the coupling energy of the C═C bond noted above. In other words, it is impossible for the ultraviolet radiation having a wavelength of 254 nm to break the C═C bond. It follows that the pyromellitic acid portion and the condensed ring portion of the polyimide structure given below are not decomposed but remain on the substrate:
On the other hand, ultraviolet radiation having a wavelength of 180 nm is capable of imparting an energy of 6.89 eV that is large enough to break the C═C bond. Therefore, the interatomic bonds included in almost all the organic polymer or molecule can be broken and thus the organic polymer or molecule can be decomposed.
Also, the oxygen molecules within the atmosphere generate excited oxygen atoms O* when exposed to ultraviolet radiation as shown below:
The excited oxygen atom O* readily reacts with each of the atoms and atomic groups broken by irradiation of the ultraviolet radiation
Scully Scott Murphy & Presser
Talbot Brian K.
Underweiser, Esq. Marian
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