1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly to a method of forming transparent electrode and fabricating an array substrate for an LCD device being capable of preventing a problem in a patterning process resulted from reflection of light by a chuck.
2. Discussion of the Related Art
The LCD device, which uses an optical anisotropy and a polarization property to display an image, is widely used for notebook computers, monitors, TV, and so on, because of their high contrast ratio and characteristics adequate to display moving images.
The LCD device includes a liquid crystal panel having a first substrate, a second substrate and a liquid crystal layer. The first and second substrates face each other, and the liquid crystal layer is interposed therebetween. An arrangement of the liquid crystal molecules in the liquid crystal layer is changed by an electric field induced in the liquid crystal panel to control light transmissivity.
In twisted nematic (NT) mode LCD device, the liquid crystal molecules are driven by a vertical electric field between the pixel electrode and the common electrode, has excellent properties of transmittance and aperture ratio. Unfortunately, since the LCD device uses the vertical electric field, the device has a bad viewing angle.
An in-plane switching (IPS) mode LCD device may be used to resolve the above-mentioned limitations. FIG. 1 is a schematic cross-sectional view of a liquid crystal panel for the related art IPS mode LCD device. Referring to FIG. 1, the liquid crystal panel includes first and second substrates 1 and 3 facing each other and a liquid crystal layer 5 therebetween.
On the first substrate 1, both of a pixel electrode 21 and a common electrode 25 are formed. The liquid crystal molecules of the liquid crystal layer 5 are driven by a horizontal electric field L generated between the pixel and common electrodes 21 and 25. Since the liquid crystal molecules are driven by the horizontal electric field L between the pixel and common electrodes 21 and 25 on the first substrate 1, the IPS mode LCD device has a wide viewing angle.
The LCD devices are fabricated using a photolithography process including a step of forming a photosensitive material layer, a step of exposing, a step of developing, and a step of etching. The photolithography process may be referred to as a mask process. In the exposing step, an exposing mask having the portions for transmitting light and the other portions for blocking light and an exposing apparatus irradiating the light are used.
In the photolithograph process, an objective material layer is formed on a substrate, and a photoresist (PR) layer as the photosensitive material layer is formed on the objective material layer. The substrate, on which the objective material layer and the PR layer are formed, is transferred into the exposing apparatus. In the exposing apparatus, the exposing mask is disposed over the substrate and aligned. Then, the PR layer is exposed to the light through the exposing mask. In this case, to prevent a mis-align problem between the substrate and the mask during the exposing step, the substrate is positioned on and fixed by a chuck.
On the other hand, some problems are caused in the photolithography process for a transparent conductive material. For example, when the transparent conductive material is patterned by the photolithography process, there is a deviation in a critical dimension. Namely, a width of the pixel electrode obtained by the photolithography process is smaller than a desired width of the pixel electrode such that a width of the pixel electrodes or the common electrodes is not uniform. An electric field between the pixel and common electrodes is to be different such that a problem, which looks like a stain on the images, is generated.