Method of fabricating a liquid crystal panel

Abstract: In fabricating a liquid crystal panel, preparing a substrate sized larger than the same at a finished state, following to bonding the prepared substrate, an excess peripheral portion of the substrate is cut off. A dummy seal (4) having an opening portion (5) at least in part thereof is formed on the excess portion of the substrate. And, the opening portion (5) of the dummy seal (4) is sealed off to make the dicing (7) after bonding of upper (2) and lower (1) substrates and curing of the seal.

Description: The present invention relates to a method of fabricating a liquid crystal panel according to the preamble of claim 1. A method comprising the measures of the preamble of claim 1 is known from JP-A-63 298 219. In particular the present invention relates, to a method of fabricating a liquid crystal panel which is produced by using a substrate larger in size than a completed panel substrate, and cutting off excess peripheral portions by dicing, after bonding of substrates. Conventional liquid crystal panels of the simple matrix type have been fabricated with a slab chocolate method in which a plurality of panel patterns are formed on a large substrate, and such substrates are then bonded and scribed to divide into individual panels. When using a quartz glass or Si wafer for a TFT substrate of the liquid crystal panel, because the scribe is difficult, a dicing method is adopted in which a disk-like grinding stone is rotated for cutting. However, the dicing method had a problem that because the liquid crystal inlets of the liquid crystal panels were not yet closed at the time of dicing, the cooling water which was necessary to be flowed therethrough in the dicing process might enter the liquid crystal panels. Means for resolving such a problem has been disclosed in Japanese Patent Application Laid-open No. 63-298219, in which the invasion of the cooling water into the liquid crystal panels is prevented in such a way that a larger substrate than a completed panel substrate is used to form a dummy seal in the excess peripheral portion of the substrate, and the dicing is performed after curing of the seal. However, the above-described conventional method had a problem that since in bonding two substrates, the internal air might be enclosed by the dummy seal which was formed in a thickness of two to three times a desired cell gap thickness, the air compressed to half or one-third of its volume by a bonding pressure would expand due to heating for curing the seal, thereby enlarging the cell gap, so that a desired cell gap could not be obtained. SUMMARY OF THE INVENTION To resolve the above-mentioned conventional problems, it is an object of the present invention to provide a method of fabricating a liquid crystal panel in which the invasion of the cooling water into the liquid crystal panel at the time of dicing is prevented, and the enlargement of the cell gap at the time of heat curing the seal is prevented. It is another object of the present invention to provide a method of fabricating a liquid crystal panel in which a desired cell gap can be stably obtained, whereby an excellent display can be realized. It is a further object of the present invention to provide a method of fabricating a reliable liquid crystal panel without restrictions on the temperature condition for the heat curing. It is still another object of the present invention to provide a method of fabricating a liquid crystal panel in which a larger substrate than a finished panel substrate is cut off excess peripheral portions thereof by dicing after bonding of the substrates, characterized in that a dummy seal having an opening portion at least in part thereof is formed on the excess portion of the substrate, and the opening portion of the dummy seal is sealed off to make the dicing after bonding of upper and lower substrates and curing of the seal. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing the state of a substrate before bonding of substrates in the present invention. Fig. 2 is a schematic view showing one example of a liquid crystal panel after dicing. Fig. 3 is a schematic view of a substrate before bonding of substrates in the present invention. Fig. 4 is a schematic view showing the state of a substrate before bonding of substrates in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, the above objects are achieved by a method of fabricating a liquid crystal panel comprising the steps of forming a seal on a first substrate, bonding said first substrate to a second substrate, curing said seal, carrying out dicing to provide a panel and excess peripheral portions, said panel thereby comprising finished substrates smaller than the initial sizes of said first and second substrates, and said excess peripheral portions including said seal, wherein said seal is formed such that it has an opening portion, and said opening portion is sealed after said curing step but before said dicing step. The preferred embodiments are specified in the dependent claims. Since the seal is provided with an opening portion in this invention, a desired gap can be obtained without enclosing the air between substrates, whereby a liquid crystal panel which can make excellent display can be fabricated. Further, the variation in the cell gap owing to expansion of the air on heat curing of the sealing material can be prevented. Accordingly, it is possible to fabricate a reliable liquid crystal panel without restrictions on the temperature condition of the heat curing. And since the opening portion of the seal is sealed off before dicing, the invasion of the cooling water into the liquid crystal panel can be prevented. In the present invention, the material for the seal may be a thermosetting epoxy resin or ultraviolet setting epoxy resin, for example. Specific examples of the thermosetting epoxy resin include XN-21 (trade name) and XN-5A (trade name) made by Mitsui Toatsu Chemical. The thickness of seal is typically in a range from 4 µm to 20 µm, and preferably in a range from 4 µm to 7 µm to be equivalent to a gap thickness of liquid crystal layer. The width of seal is typically in a range from 0.1 mm to 1.5 mm, and preferably in a range from 0.1 mm to 0.5 mm. The seal is formed in the following way, for example. That is, a seal is printed in a thickness (e.g., about 10 µm to 30 µm) of approximately two to three times the thickness of final seal, and in a print width of about 0.1 mm to 1.5 mm, by seal printing, and then is pressurized and treated with the heat curing to form a seal. In the present invention, the opening portion of the seal is sealed off by an adhesive or epoxy resin. The present invention will be described below with reference to the drawings. (Embodiment 1) Fig. 1 is an upper view showing a state before bonding of substrates in this embodiment, and Fig. 2 is a cross-sectional view of a liquid crystal panel after dicing. A TFT substrate 1 composed of Si wafer on which the electrodes for driving the liquid crystal are formed and the thin film transistors are fabricated and an opposite substrate 2 composed of a low alkali glass of low thermal expansion (AL made by Asahi Glass) were treated for orientation. On one substrate, seals 3 constituting liquid crystal panels 8 and a seal 4 on peripheral excess portion of the substrate, as shown in Fig. 1, were formed using a sealing material having a spacer mixed for forming a cell gap at good precision. Two substrates were bonded in a predetermined alignment, pressurized, and heated to cure the seals 3 and the seal 4. Since an opening portion 5 for the outlet of the air was provided on the seal 4, it was possible to prevent the variation in the gap width due to thermal expansion of the air on the heat curing. Then, the opening portion 5 of outer peripheral seal was sealed off by instantaneous adhesive 6, and diced (half-cut 7) in which the substrate was not completely cut. The provision of the seal 4 can prevent the invasion of the cooling water into the liquid crystal panels 8 at the time of dicing. After the dicing, the substrate was dried in a drying process to remove water contents therefrom, and divided into individual panels by applying a shearing force. After dividing, liquid crystal was poured into respective panels, and the inlet of the liquid crystal was sealed by sealant. The processes involving this liquid crystal relied on any of the well-known fabrication techniques for liquid crystal display. The surface opposite to that as formed with TFT of Si substrate is covered with hydrofluoric acid resistant rubber except for immediately below the liquid crystal pixel portion, and Si wafer was partially removed down to insulation layer, using a mixture solution of hydrofluoric acid, acetic acid and nitric acid, whereby light transmission-type liquid crystal image displays could be completed. Note that Si wafer for use with the TFT substrate 1 was fabricated by the following method. Anodization was conducted on a P-type (100) monocrystalline Si substrate having a thickness of 300 µm in an HF solution to form a porous Si substrate. Anodization was performed under the following conditions: Applied voltage 2.6 (V) Current density 30 (mA·cm -2 ) Anodizing solution HF:H 2 O:C 2 H 5 OH=1:1:1 Time 2.4 (hours) Thickness of porous Si 300 (µm) Porosity 56 (%) An Si epitaxial layer with a thickness of 1.0 µm was grown on the P-type (100) porous Si substrate by low-pressure CVD. Deposition was conducted under the following conditions. Source gas SiH 4 Carrier gas H 2 Temperature 850°C Pressure 1,33 Pa (1 x 10 -2 Torr) Growth rate 3.3 nm/sec Then, a 100 nm (1,000 Å) oxide layer was formed on the surface of this epitaxial layer, and on this oxide surface, another Si substrate having formed a 500 nm (5,000 Å) oxide layer, a 100 nm (1,000 Å) oxide layer and a 100 nm (1,000 Å) nitride layer on its surface was superposed. The whole structure was heated at 800°C in a nitrogen atmosphere for 0.5 hour to firmly join the two substrates to each other. Thereafter, selective etching was conducted on the bonded substrates in a mixed solution of 49% hydrofluoric acid, alcohol and 30% hydrogen peroxide solution (10:6:50) without stirring. In sixty five minutes, the porous Si substrate was completely removed by selective etching with the monocrystalline Si layer acting as an etch stopper, only the non-porous Si layer being left behind without etching. The etching rate of the non-porous monocrystalline Si in such etching solution was so low that the etching layer reached only a maximum of 5 nm (50 Å) in sixty five minutes, with the selection ratio of the etching rate of the non-porous monocrystalline Si to that of the porous layer being 1:10 5 or more, so that the amount of non-porous layer which was etched (several nanometers (tens angstroms)) could be ignored in the practical operation. Thus, the 200-micron thick porous Si substrate was removed, with a result that the 1.0 µm thick monocrystalline Si layer was formed on SiO 2 . When SiH 2 Cl 2 was used as the source gas, the growth temperature had to be higher by several tens of degrees. However, high-speed etching characteristic to the porous substrate was maintained. A field effect transistor was fabricated on the above-mentioned monocrystalline Si thin film and connected to creat complementary elements and its integrated circuit, thereby forming pixel switching elements and a drive circuit necessary for the liquid crystal image display. Note that the method of fabricating each transistor relied on one of the well-known MOS integrated circuit fabrication techniques. Also, the opposite substrate 2 was fabricated in the following way. A chromium dioxide film was formed as the black matrix on a low alkali glass substrate of low thermal expansion by sputtering, and shaped into a predetermined pattern by photo-etching. Then, each filter of red, blue and green was formed by pigment dispersing, a top coat layer was provided thereon, and further an ITO layer was formed by sputtering. (Embodiment 2) A liquid crystal panel was fabricated in the same way as in the embodiment 1, except that a bank 9 was provided on the opening portion 5 of the seal 4 as shown in Fig. 3. Because a sealant for the opening portion 5, even though being low viscous, can be dammed by the bank 9, according to this embodiment, the sealant can be prevented from flowing within the dummy seal 4 owing to surface tension to seal off liquid crystal inlets 10 of individual panels 3. Accordingly, using a seal 4 of this shape, the usable range of viscosity of sealant for the seal 4 can be extended. Note that the shape of bank is not limited to that as shown in Fig. 3, but a variety of shapes such as "⊐" may be used. (Embodiment 3) A polycrystalline silicon was formed on a quartz glass as the TFT substrate, and a field effect transistor was created on the polycrystalline silicon thin film, and connected to creat complementary elements and its integrated circuit, thereby forming pixel switching elements and a drive circuit necessary for the liquid crystal image display. A chromium dioxide film was first formed as the black matrix on a quartz glass substrate as the opposite substrate by sputtering, and shaped into a predetermined pattern by photo-etching. Then, each filter of red, blue and green was formed by a dyeing method, a top coat layer was provided thereon, and further an ITO layer was formed by sputtering. Fig. 4 shows schematically a shape of the seal in this embodiment. While the quartz glass was of a square shape in this embodiment, it may be formed in the same shape as the wafer. As above described, since the seal is provided with an opening portion according to the present invention, a desired cell gap can be obtained without enclosing the air between substrates, whereby a liquid crystal panel which can make excellent display can be fabricated. Further, the variation in the cell gap due to expansion of the air on heat curing of the sealant can be prevented. Accordingly, a reliable liquid crystal panel can be fabricated without restrictions on the temperature condition for the heat curing. And since the opening portion of dummy seal is sealed off before dicing, the invasion of the cooling water into the liquid crystal panel can be prevented.

Claims: A method of fabricating a liquid crystal panel comprising the steps of: forming a seal (4) on a first substrate (1); bonding said first substrate (1) to a second substrate (2); curing said seal (4); carrying out dicing to provide a panel and excess peripheral portions, said panel thereby comprising finished substrates smaller than the initial sizes of said first and second substrates (1, 2), and said excess peripheral portions including said seal (4); characterized in that said seal (4) is formed such that it has an opening portion (5); and said opening portion (5) is sealed after said curing step but before said dicing step. The method of fabricating a liquid crystal panel according to claim 1, characterized in that one of said substrates (1, 2) employs an Si wafer. The method of fabricating a liquid crystal panel according to claim 1, characterized in that an adhesive is used as a sealant of said opening portion (5). The method of fabricating a liquid crystal panel according to claim 1, characterized in that said dicing is made in half-cut in which the substrate (1, 2) is not completely cut. The method of fabricating a liquid crystal panel according to claim 4, characterized in that after said dicing, said substrate (1, 2) is divided by applying a shearing force on said substrate (1, 2). The method of fabricating a liquid crystal panel according to claim 2, characterized in that said Si wafer is obtained through a process in which after a monocrystalline Si substrate is made porous, an epitaxial layer is formed on said porous substrate.

Inventors: FURUSHIMA TERUHIKO, GENCHI YUTAKA, KAMIO MASARU, OKAMURA MORIYUKI, FURUSHIMA, TERUHIKO, GENCHI, YUTAKA, KAMIO, MASARU, OKAMURA, MORIYUKI, Furushima, Teruhiko, c/o Canon Kabushiki Kaisha, GENCHI, YUTAKA, C/O CANON KABUSHIKI KAISHA, KAMIO, MASARU, C/O CANON KABUSHIKI KAISHA, Okamura, Moriyuki, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: G02F1
IPC codes: G02F1, B26D1