A new thin film transistor structure and its processing method for liquid crystal displays

This paper describes a new thin film transistor (TFT) structure for applications in liquid crystal displays. The processing steps are discussed in detail. This new TFT is similar to the traditional tri4ayer, inverted, staggered TFT in the cross-section view, but different in the top view. It has a self-aligned semiconductor island and source/drain contact vias. The process is composed of one mask alignment step (with two masks), one backlight exposure step, and four etching steps. Compared with the conventional, complicated process, its process time is shorter, its process window is wider, and there is less consumption of chemicals. Important factors of the backlight exposure lithography, such as the light source, intensity profile along the path, exposure energy, and photoresist profile, are examined. Other alternative processing methods for preparing the same kind of TFT are also presented. Issues regarding the application of this TFT to liquid crystal displays are discussed.