1. Field of the Invention
The present invention relates to an electrode of a plasma display panel (PDP). More particularly, the present invention relates to a technology for improving exposure latitude and imparting improved PDP quality by modifying a photo-patternable paste.
2. Technical Background
In PDP's, 1000 or more electrodes measuring 80 to 100 μm in width by 0.5 to 1.5 m in length are formed. These electrodes are preferred to be free of defects and have superior linearity. Silver is typically used for the conductive metal particles contained in the electrodes.
Photolithography has recently become widely used to form the electrodes in PDP. In this method, a photo-patternable paste is first coated. A pattern is then formed by exposing and developing a film composed of the photo-patternable paste. Accompanying the increased size of glass substrates in recent years, proximity exposure has come to be used during exposure. Proximity exposure refers to a system whereby exposure is carried out while providing a gap of several hundred micrometers between a photomask and the coated film to be exposed.
In the case of pattern formation using a photo-patternable paste, it is desirable to increase the process latitude. It is desirable to increase the degree of freedom of the exposure conditions. In the case of low process latitude, the pattern shape may change easily depending on the exposure conditions, or the width of the electrodes may become uneven. Photosensitivity to changes in the pattern shape depending on exposure conditions signifies a low degree of freedom, and may even lead to restrictions on the production process. When carrying out proximity exposure, in particular, the width of the electrode formed tends to be greater than the designed electrode width, resulting in the decrease of sharpness of image. Measures to avoid this decrease in sharpness are needed.
Japanese Patent Application Laid-open No. 2003-195487 discloses a technology in which an ultraviolet absorber is added for the purpose of forming a fine, sharp transparent electrode. According to this publication, addition of the ultraviolet absorber makes it possible to diminish scattering of exposure light within the paste. Examples of ultraviolet absorbers include azo-based dyes, amino ketone-based dyes, xanthene-based dyes, quinoline-based dyes, anthraquinone-based dyes, benzophenone-based dyes, diphenylcyanoacrylate-based dyes, triazine-based dyes and p-aminobenzoic acid-based dyes.
However, if a dye-based ultraviolet absorber like that disclosed in Japanese Patent Application Laid-open No. 2003-195487 is used, since the ultraviolet absorber itself absorbs light, the paste that is produced is also colored. In a process for producing a PDP using a conductive paste, defect inspections are frequently carried out using visible light to confirm the coated state of the paste. At this time, if a dye which absorbs visible light is contained in the paste, there is the possibility of locations where defects are not present being detected. In addition, if the absorbance of visible light changes as a result of adding an ultraviolet absorber, there is the risk of having a detrimental effect on the efficiency of the photoinitiator. For example, since some photoinitiators have an absorbance range in the vicinity of up to 450 nm, in the case of using such a photoinitiator, a change in the absorbance in that range also ends up having an effect on the reflection efficiency of the photoinitiator.