Process for production of glass substrate coated with finely patterned Nesa glass membrane

Abstract: A process for production of a glass substrate coated with a patterned Nesa glass membrane which comprises, in sequence: the first step of coating a photoresist on a glass substrate to form a photoresist membrane, exposing the membrane to electromagnetic waves through a mask and then developing the photoresist to form a patterned photoresist membrane on the glass substrate; the second step of forming a Nesa glass membrane on the eitire surface of the glass substrate thus provided with the patterned photoresist membrane; and the third step of removing the patterned photoresist membrane together with the Nesa glass membrane thereon from the glass substrate to leave a patterned Nesa glass membrane on the glass substrate.

Description: This invention relates to a process for production of a glass substrate coated with a patterned Nesa glass membrane (a transparent and electroconductive inorganic tin oxide film) on a glass substrate. The glass substrate coated with a patterned Nesa glass membrane is especially suitable for use as a flat panel in liquid crystal displays or plasma displays. Various processes are already known for the production of a glass substrate coated with a finely patterned Nesa glass membrane, among which is an etching process wherein a Nesa glass membrane is formed on the entire surface of a glass substrate by, for example, a spraying method, a metal mask or a photoresist mask is formed on the Nesa glass membrane, and then a pattern is formed by etching and removing the membrane according to the pattern, as is disclosed in Japanese Patent Application Laid-open No. 56-94542, No. 63-65090 or No. 63-171886. According to this process, a pattern can be formed with high accuracy of about 30 µm in line width or line separation; however, nascent hydrogen is needed to effect the etching, and hence a concentrated mineral acid such as concentrated hydrochloric acid is required and the method is not suitable for practical use. There is also known a lift-off process wherein a glass substrate is masked with a masking paste by screen printing; a Nesa glass membrane is formed thereon; and then the masking paste is washed and removed to leave a patterned Nesa glass membrane on the glass substrate. This process is simple and convenient; however, based on limited fineness of the screen used and the viscosity of the paste, the process has had an accuracy limit of about 80 µm in line width or line separation. JP-A-63310513 and JP-A-61236634 disclose processes for the production of a glass substrate coated with a patterned Nesa glass membrane, in which a Nesa glass membrane is formed over the glass substrate carrying a patterned photoresist membrane by a chemical vapour deposition procedure using a liquid spray of stannic chloride or an air or nitrogen stream containing stannic chloride vapour. The present invention provides a process for production of a glass substrate coated with a patterned Nesa glass membrane which comprises coating a photoresist on a glass substrate to form a photoresist membrane, exposing the membrane to electromagnetic waves through a mask and then developing the photoresist to form a patterned photoresist membrane on the glass substrate; forming a Nesa glass membrane on the entire surface of the glass substrate thus provided with the patterned photoresist membrane; and removing the patterned photoresist membrane together with the Nesa glass membrane thereon from the glass substrate to leave a patterned Nesa glass membrane on the glass substrate; characterised in that the Nesa glass membrane is formed by a chemical vapour deposition process wherein (a) a solution of dimethyltin dichloride or monomethyltin trichloride in water containing trifluoroacetic acid or (b) a solution of dimethyltin dichloride or monomethyltin trichloride in a mixture of water and hydrochloric acid containing antimony trichloride is vaporized and the resultant vapour is blown onto the heated glass substrate to form the Nesa glass membrane on the glass substrate. The process of the present invention can provide a glass substrate coated with a finely patterned Nesa glass membrane with improved accuracy in line width or line separation of not more than 30 µm in a simple and inexpensive manner by a lift-off process wherein a photoresist is used, making use of the merits of both the etching process and the lift-off process. In the first step of the process of the invention, a photoresist is coated on a glass substrate to form a photoresist membrane thereon, the photoresist membrane is exposed to electromagnetic waves such as ultraviolet rays, electron rays or X-rays through a patterned mask, and then the photoresist membrane is developed to form a patterned photoresist membrane on the glass substrate. It is preferred that a silica-coated glass substrate is used, to prevent alkalis from separating from the glass substrate. The photoresists are divided into two types, positive and negative. Either type may be used in the invention; however, an o-quinonediazide type positive photoresist is in particular preferred. The photoresists inclusive of the o-quinoneadizide type positive photoresist are already well known in the art, as set forth in Nagamatsu et al., "Photosensitive Polymers", Kodansha (1977). The o-quinonediazide type positive photoresist is usually composed of o-naphthoquinonediazide dissolved in an alkali-soluble resin such as a novolak resin. As well known, o-naphthoquinonediazide generates a carboxyl group in the molecule when it is exposed to electromagnetic waves such as ultraviolet rays. Accordingly, when the photoresist is exposed to ultraviolet rays, the exposed portion has a larger solubility in alkaline solution, so that the exposed portion is removed by alkaline solution. That is, the photoresist is developed with an alkaline solution. The o-quinonediazide type positive photoresist is on the market, e.g.as OFPR 800 available from Tokyo Ohka Kogyo K.K. or ZPP 1700 available from Nippon Zeon K.K. The photoresist may be coated on a glass substrate by any known method such as by spin coating or roll coating. The latter method is advantageous for mass production. The Nesa glass membrane is formed on the entire surface of the glass substrate by a chemical vapor deposition (CVD) process preferably under normal pressure. During the normal pressure CVD process, the temperature of the glass substrate usually reaches as high as about 500°C, hence it is preferred that the photoresist membrane is formed to have a thickness of not less than about two microns, more preferably not less than about three microns, so that the photoresist membrane is not carbonized or burnt out during the CVD process. The glass substrate having the patterned photoresist membrane thereon may be placed in a CVD furnace in which vaporized solution (a) or (b) of tin compound and dopant is blown upon the glass substrate through a slit nozzle, thereby forming the Nesa glass membrane on the entire surface of the glass substrate. The solution (a) or (b) of tin compound and dopant may be prepared and heated in a heating pot provided with a normal pressure CVD apparatus to produce a vapour of the tin compound and the dopant, and the vapour is then introduced into the CVD apparatus where it is blown onto the heated glass substrate where the tin compound and the dopant are thermally decomposed to form a transparent and electroconductive tin oxide membrane doped with the dopant on the glass substrate. The normal pressure CVD process is a known process for the preparation of Nesa glass membranes. In the process of the invention, a continuous CVD process is preferably employed. A preferred process is carried out as follows. A patterned photoresist membrane is formed on the glass substrate, and then the glass substrate is fed into a CVD apparatus by a belt while the running speed of the belt and the temperature of the glass substrate are appropriately arranged so that the patterned photoresist membrane is not carbonized or burnt out during the CVD operation. Preferably the glass substrate is heated to a temperature usually of not less than 400°C, e.g. to a temperature of 480-520°C, i.e. a temperature a little below . the temperature at which the photoresist is carbonized or burnt out. The materials for the preparation of Nesa glass membranes are a tin compound and a dopant. The tin compounds usable according to the invention are dimethyltin dichloride and monomethyltin trichloride and the dopants usable are antimony trichloride and trifluoroacetic acid. In particular, the use of a tin compound selected from dimethyltin dichloride and monomethyltin trichloride together with trifluoroacetic acid as a dopant is preferred since these materials provide solutions which are readily usable in the continuous normal pressure CVD process and provide a Nesa glass membrane which is highly electroconductive and transparent. It is preferred that the Nesa glass membrane is formed on the glass substrate by a continuous normal pressure CVD process as above set forth. However, the Nesa glass membrane may be formed by other CVD processes, for example by a CVD process under reduced pressure or a plasma CVD process. In the third step of the process of the invention, the patterned photoresist membrane is removed from the glass substrate together with the Nesa glass membrane formed on the patterned photoresist membrane. The patterned photoresist membrane can be removed by immersing the glass substrate in an aqueous solution of an alkali, for example, in a 3-5% by weight aqueous solution of sodium hydroxide or potassium hydroxide, if necessary under heating at 30-100°C, preferably 40-80°C. The o-quinonediazide type photoresist membrane can be particularly readily removed from the glass substrate by the above mentioned immersion method,thereby to form a Nesa glass membrane finely patterned with high accuracy. Thus the Nesa glass membrane is left on the glass substrate where the photoresist has been exposed to electromagnetic waves and removed by development with an aqueous alkaline solution in the first step, thereby forming a pattern on the glass substrate. The results are the same as the photomechanical process wherein a negative photoresist is used. The invention will now be described in more detail below using an o-quinonediazide positive type photoresist which was available from Tokyo Ohka Kogyo K.K. as OFPR 800 or available from Nippon Zeon K.K. as ZPP 1700. Example 1 A glass substrate having a silica coating on the surface was cleaned and then a positive type photoresist was coated thereon to form an even membrane about two to three microns thick. The photoresist membrane was exposed to ultraviolet rays through a patterned mask and the photo-resist was developed with an aqueous alkaline solution thereby to form a patterned photoresist membrane on the glass substrate. A CVD apparatus was arranged so that the glass substrate was heated to a temperature in the range of 480-520°C under a slit nozzle from which vapor of a tin compound and a dopant was blown out. An amount of 100 parts by weight of antimony trichloride was dissolved in an aqueous solution composed of 850 parts by weight of concentrated hydrochloric acid and 250 parts by weight of water. Varying amounts (30-150 parts by weight) of the thus prepared solution were added to an aqueous solution of 550 parts by weight of dimethyltin dichloride in 500 parts by weight of water to prepare solutions for for CVD process. The solution was fed into a container heated at about 300°C with a pump to evaporate the solution instantaneously, and the resultant vapor was blown out of the slit nozzle upon the glass substrate to form a Nesa glass membrane on the entire surface of the glass substrate inclusive of the patterned photoresist membrane. The glass substrate was then immersed in a 5 % by weight aqueous solution of sodium hydroxide at 50°C for 5 minutes to remove the patterned photoresist membrane together with the Nesa glass membrane thereon to leave a patterned Nesa glass membrane on the glass substrate. Except that a photoresist membrane was not formed on the glass substrate, a Nesa glass membrane was formed directly on the entire surface of the silica-coated glass substrate in the same manner as above described. Table 1 shows surface resistivity and light transmittance at a wavelength of 550 nm of the thus prepared Nesa glass membrane on the glass substrate in relation to the amount of the antimony trichloride in the solution for the CVD process. The surface resistivity is the resistance between two opposing electrodes on a unit surface area (1 m 2 ) of an insulating material ("Revised Electric Terms Dictionary", Corona K.K. (1975)). In other words, the surface resistivity is the resistance between the opposing sides of a sheet resistor in the form of regular square. When the resistance distribution is uniform, the surface resistivity is not related to the size of the sheet. The surface resistivity and transmittance change not only according to the composition of the solution for CVD process but also according to the amount of the vapor fed into the CVD apparatus. The relation of the composition of the solution for the CVD process and the amount of the vapor of the solution fed into the CVD apparatus to the resultant surface resistivity of the Nesa glass membrane can be determined empirically. Thus a Nesa glass membrane having a desired surface resistivity can be prepared based on the empirical results thus obtained. The Nesa glass memrane prepared according to the process of the invention has a surface resistivity usually in the range of several tens to several hundred Ω/square and has a fine pattern of accuracy of about 25 µm in line width or line separation. Amount of SbCl 3 (parts by weight) Surface Resistivity (Ω/square) Transmittance (%) 49 280 74 74 150 76 92 110 82 Example 2 An amount of 500 parts by weight of dimethyltin dichloride was dissolved in 500 parts by weight of water, and then varying amounts (20-100 parts by weight) of trifluoroacetic acid according to required surface resistivity of the resultant Nesa glass membrane. A patterned Nesa glass membrane was prepared in the same manner as in Example 1. Table 2 shows surface resistivity and transmittance at a wavelength of 550 nm of the thus prepared patterned Nesa glass membranes on the glass substrate in relation to the amount of the trifluoroacetic acid in the solution for the CVD process. Amount of CF 3 COOH (parts by weight) Surface Resistivity (Ω/square) Transmittance (%) 43 310 85 54 290 84 76 180 82 98 150 80 In common with Example 1, the relation of the composition of the solution for the CVD process and the amount of the vapor of the solution for the CVD process fed into the CVD apparatus to the resultant surface resistivity of the Nesa glass membrane can be determined empirically, so that a Nesa glass membrane having a desired surface resistivity can be prepared based on the empirical results. Thus, a Nesa glass membrane can be prepared according to the invention which has a surface resistivity in the range of several tens to several hundred Ω/square and has a fine pattern of the same accuracy as Example 1.

Claims: A process for production of a glass substrate coated with a patterned Nesa glass membrane which comprises coating a photoresist on a glass substrate to form a photoresist membrane, exposing the membrane to electromagnetic waves through a mask and then developing the photoresist to form a patterned photoresist membrane on the glass substrate; forming a Nesa glass membrane on the entire surface of the glass substrate thus provided with the patterned photoresist membrane; and removing the patterned photoresist membrane together with the Nesa glass membrane thereon from the glass substrate to leave a patterned Nesa glass membrane on the glass substrate; characterised in that the Nesa glass membrane is formed by a chemical vapour deposition process wherein (a) a solution of dimethyltin dichloride or monomethyltin trichloride in water containing trifluoroacetic acid or (b) a solution of dimethyltin dichloride or monomethyltin trichloride in a mixture of water and hydrochloric acid containing antimony trichloride is vaporized and the resultant vapour is blown onto the heated glass substrate to form the Nesa glass membrane on the glass substrate. A process according to claim 1 wherein the photoresist is a positive one and is developed with aqueous alkaline solution. A process according to claim 2 wherein the aqueous alkaline solution is a 3-5% by weight aqueous solution of sodium hydroxide or potassium hydroxide. A process according to any preceding claim wherein the electromagnetic waves are ultraviolet rays. A process according to any preceding claim wherein the glass substrate has a coating of silica on the surface.

Inventors: MATSUMURA JOHJI, MINAMIGAWA TOSHIO, YOSHIDA GOHEI, MATSUMURA, JOHJI, MINAMIGAWA, TOSHIO, YOSHIDA, GOHEI
Applicants: HONJO SOREX CO LTD, HONJO SOREX CO. LTD.
Application year: 1995
Main classification: C03C17
IPC codes: C03C17, C03C15